GOLF CLUB HEAD

Abstract

 A head includes a face portion including a striking face. The face portion includes a face main portion that includes: a central section including a face center, a transition section located outside the central section, and a peripheral section located outside the transition section. The peripheral section includes: a first peripheral subsection located in toe and heel side parts; and a second peripheral subsection located in crown and sole side parts. The transition section includes a first transition subsection located between the central section and the first peripheral subsection, and a second transition subsection located between the central section and the second peripheral subsection. The central section has a central section uniform wall thickness tc and a surface area of 100 mm² or more. The first peripheral subsection has a wall thickness greater than the thickness tc. The second peripheral subsection has a wall thickness smaller than the thickness tc.

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority to Japanese Patent Application No. 2023-218687 filed on December 25, 2023. The entire contents of this Japanese Patent Application are hereby incorporated by reference.

BACKGROUND

Technical Field

[0002] The present disclosure relates to golf club heads.

Description of the Related Art

[0003] Various golf club heads have been proposed for improvement in rebound performance as shown in, for example, JP2021-132995A (US2021/0268346A1), JP2022-108598A (US2022/0219050A1), and JP2022-120289A (US2022/0249921A1) .

SUMMARY

[0004] There has been known a golf club head having a high forgiveness for reducing missed shots. Such a golf club head has, for example, a wall thickness distribution of its face designed to suppress reduction of ball flight distance even when a golfer hits a ball at a point apart from an ideal hit point (The ideal hit point means the face center, for example. The same applies below).

[0005] On the other hand, regarding an increase in ball flight distance, such a golf club head having a high forgiveness is less advantageous for professional golfers and advanced golfers who have a high probability of hitting a ball at the ideal hit point. In addition, professional golfers and advanced golfers usually adjust the hit point in an up-down direction of the head to achieve an adjusted spin rate and desired ball trajectory when they hit a teed-up ball at a first shot of each hole. From this viewpoint, the inventors of the present disclosure have found that a technique of enlarging a high rebound area in the up-down direction to increase the flight distance of the hit ball is preferable for golfers who can hit a ball at the ideal hit point and adjust the hit point in the up-down direction.

[0006] One of the objects of the present disclosure is to provide a golf club head having an enlarged high rebound area in the up-down direction and being capable of increasing the flight distance of the hit ball.

[0007] In one aspect, a golf club head includes a hollow interior inside thereof. The head includes a face portion including a striking face, a crown portion, and a sole portion. The face portion includes a face main portion including a face center. The face main portion includes a central section including the face center, a transition section located outside the central section, and a peripheral section located outside the transition section. The peripheral section includes a first peripheral subsection located in a toe side part and a heel side part of the face main portion, and a second peripheral subsection located in a crown side part and a sole side part of the face main portion. The transition section includes a first transition subsection located between the central section and the first peripheral subsection, and a second transition subsection located between the central section and the second peripheral subsection. The central section has a central section uniform wall thickness and a surface area of greater than or equal to 100 mm². The first peripheral subsection has a first peripheral subsection uniform wall thickness, and the first peripheral subsection uniform wall thickness is greater than the central section uniform wall thickness. The second peripheral subsection has a second peripheral subsection uniform wall thickness, and the second peripheral subsection uniform wall thickness is smaller than the central section uniform wall thickness. The first transition subsection has a wall thickness that increases from the central section uniform wall thickness to the first peripheral subsection uniform wall thickness. The second transition subsection has a wall thickness that decreases from the central section uniform wall thickness to the second peripheral subsection uniform wall thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] 

FIG. 1 shows a golf club that includes a head according to a first embodiment;

FIG. 2A is a front view of the head of the first embodiment, and FIG. 2B shows a cross section taken along line E1 in FIG. 2A, FIG. 2B showing only a part of a cross-sectional contour line of the head outer surface;

FIG. 3 is the same front view as FIG. 2A;

FIG. 4 is the same front view as FIG. 2A, FIG. 4 showing contour lines of parts/sections/subsections of a face portion with dashed lines;

FIG. 5 is a cross-sectional view showing a part of a vertical cross section of the head of the first embodiment, the vertical cross section passing through a face center;

FIG. 6 is a cross-sectional view showing a part of a horizontal cross section of the head of the first embodiment, the horizontal cross section passing through the face center;

FIG. 7 is a front view of a head according to a second embodiment;

FIG. 8 is the same front view as FIG. 7, FIG. 8 showing contour lines of parts/sections/subsections of a face portion with dashed lines;

FIG. 9 is a cross-sectional view showing a part of a vertical cross section of the head of the second embodiment, the vertical cross section passing through a face center;

FIG. 10 is a cross-sectional view showing a part of a horizontal cross section of the head of the second embodiment, the horizontal cross section passing through the face center;

FIG. 11 is a front view of a head according to a third embodiment;

FIG. 12 is the same front view as FIG. 11, FIG. 12 showing contour lines of
parts/sections/subsections of a face portion with dashed lines;

FIG. 13 is a cross-sectional view showing a part of a vertical cross section of the head of the third embodiment, the vertical cross section passing through a face center;

FIG. 14 is a cross-sectional view showing a part of a horizontal cross section of the head of the third embodiment, the horizontal cross section passing through the face center;

FIG. 15 is a front view of a head according to a fourth embodiment;

FIG. 16 is the same front view as FIG. 15, FIG. 16 showing contour lines of parts/sections/subsections of a face portion with dashed lines;

FIG. 17 is a cross-sectional view showing a part of a vertical cross section of the head of the fourth embodiment, the vertical cross section passing through a face center;

FIG. 18 is a cross-sectional view showing a part of a horizontal cross section of the head of the fourth embodiment, the horizontal cross section passing through the face center;

FIG. 19 is a cross-sectional view showing a part of the vertical cross section of the outer surface of each of the heads of the third and fourth embodiments;

FIG. 20 is a cross-sectional view showing a part of the horizontal cross section of the outer surface of each of the heads of the third and fourth embodiments;

FIG. 21 is a front view of a head of Comparative Example;

FIG. 22 is the same front view as FIG. 21, FIG. 22 showing contour lines of sections of a face portion with dashed lines; and

FIG. 23 is a conceptual diagram for illustrating a reference state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the present disclosure will be described in detail based on preferred embodiments with appropriate references to the accompanying drawings. In the following embodiments, the same or common elements are denoted by the same reference symbols, and duplicated explanations will be omitted as appropriate.

[0010] In the present disclosure, a reference state, a reference perpendicular plane, a toe-heel direction, a face-back direction, an up-down direction, a face center, a vertical cross section, a horizontal cross section, and a head front elevation view are defined as follows.

[0011] The reference state is defined as a state where a head is placed at a predetermined lie angle on a ground plane HP. As shown in FIG. 23, in the reference state, a shaft axis line Z lies on (is contained in) a plane VP that is perpendicular to the ground plane HP. The shaft axis line Z is the center line of a shaft. The shaft axis line Z normally coincides with the center line of a hosel hole (shaft hole). The plane VP is referred to as the reference perpendicular plane. The predetermined lie angle is shown in a product catalog, for example.

[0012] There has been known a club that allows adjustment of its loft angle, lie angle and face angle by, for example, changing the rotational position of a sleeve provided at the tip portion of a shaft. In such a club, the sleeve can be detachably fixed to the head with a fixing means such as a screw. For this reason, in this club, the shaft is attachable to and detachable from the head. In a club having such an attachable/detachable mechanism, all adjustable items are set to be neutral when the club is in the reference state. The term "neutral" means the center of the range of adjustment. Clubs of the present disclosure may include such an attachable/detachable mechanism.

[0013] In the reference state, a face angle is 0°. That is, in a planar view of a head as viewed from above, a line normal to its striking face at the face center is set to be perpendicular to the toe-heel direction. The definitions of the face center and the toe-heel direction are explained below.

[0014] In the present disclosure, the toe-heel direction is defined as the direction of an intersection line NL between the reference perpendicular plane VP and the ground plane HP (see FIG. 23). However, the toe-heel direction in the head front elevation view (front view) is a direction obtained by projecting the toe-heel direction onto the front view. A toe side in the toe-heel direction is also simply referred to as "toe side". A heel side in the toe-heel direction is also simply referred to as "heel side".

[0015] In the present disclosure, the face-back direction is defined as a direction that is perpendicular to the toe-heel direction and is parallel to the ground plane HP. A face side in the face-back direction is also simply referred to as "face side" or "front side". A back side in the face-back direction is also simply referred to as "back side" or "rear side".

[0016] In the present disclosure, the up-down direction is defined as a direction that is perpendicular to the toe-heel direction and is perpendicular to the face-back direction. In other words, the up-down direction in the present disclosure is a direction perpendicular to the ground plane HP. However, the up-down direction in the head front elevation view (front view) is a direction obtained by projecting the up-down direction onto the front view.

[0017] In the present disclosure, the face center is determined in the following manner. First, a point Pr is selected roughly at the center of a striking face in the up-down direction and the toe-heel direction. Next, a plane that passes through the point Pr, extends in the direction of a line normal to the striking face at the point Pr, and is parallel to the toe-heel direction is determined. An intersection line between this plane and the striking face is drawn, and a midpoint Px of this intersection line is determined. Next, a plane that passes through the midpoint Px, extends in the direction of a line normal to the striking face at the midpoint Px, and is parallel to the up-down direction is determined. An intersection line between this plane and the striking face is drawn, and a midpoint Py of this intersection line is determined. Next, a plane that passes through the midpoint Py, extends in the direction of a line normal to the striking face at the midpoint Py, and is parallel to the toe-heel direction is determined. An intersection line between this plane and the striking face is drawn, and a midpoint Px of this intersection line is newly determined. Next, a plane that passes through this newly-determined midpoint Px, extends in the direction of a line normal to the striking face at this midpoint Px, and is parallel to the up-down direction is determined. An intersection line between this plane and the striking face is drawn, and a midpoint Py of this intersection line is newly determined. By repeating the above-described steps, points Px and Py are sequentially determined. In the course of repeating these steps, when the distance between a newly-determined midpoint Py and a midpoint Py determined in the immediately preceding step first becomes less than or equal to 0.5 mm, the newly-determined midpoint Py (the midpoint Py determined last) is defined as the face center.

[0018] In the present disclosure, the vertical cross section is defined as each of cross sections taken along respective planes perpendicular to the toe-heel direction. A vertical cross section that passes through the face center is also referred to as a center vertical cross section. In the present disclosure, the horizontal cross section is defined as each of cross sections taken along respective planes perpendicular to the up-down direction. In other words, the horizontal cross section in the present disclosure means each of cross sections taken along respective planes parallel to the ground plane HP. A horizontal cross section that passes through the face center is also referred to as a center horizontal cross section.

[0019] In the present disclosure, the head front elevation view means an orthogonal projection of a head obtained by projecting the head in a projecting direction that is a direction of a line normal to its striking face at the face center. Unless otherwise described, shapes, areas, dimensions and other characteristics of respective portions/parts/sections/subsections of a face portion are determined in the head front elevation view. The head front elevation view is also simply referred to as a front view in the present disclosure.

[First embodiment]

[0020] FIG. 1 is an overall view of a golf club 2 that includes a head 4 according to a first embodiment of the present disclosure. FIG. 2A is a front view of the head 4, and FIG. 2B is a cross-sectional view taken along line E1 in FIG. 2A. FIG. 2B shows only a part of a cross-sectional contour line of the head outer surface. FIG. 3 and FIG. 4 are the same front views as FIG. 2A. FIG. 4 shows contour lines of parts/sections/subsections of a face portion 10 with dashed lines. FIG. 5 is a cross-sectional view showing a part of a vertical cross section of the head 4. FIG. 5 shows a part of the center vertical cross section. FIG.6 is a cross-sectional view showing a part of a horizontal cross section of the head 4. FIG. 6 shows a part of the center horizontal cross section.

[0021] As shown in FIG. 1, the golf club 2 includes the golf club head 4, a shaft 6, and a grip 8. The shaft 6 has a tip end Tp and a butt end Bt. The head 4 is attached to a tip end portion of the shaft 6. The grip 8 is attached to a butt end portion of the shaft 6.

[0022] The golf club 2 is a driver (No.1 wood). The head 4 is a head used for drivers. Typically, the club as a driver has a length of greater than or equal to 43 inches and less than or equal to 48 inches. Preferably, the golf club 2 is a wood-type golf club or a hybrid-type golf club.

[0023] The shaft 6 is in a tubular form. The shaft 6 is hollow. The material of the shaft 6 is a carbon fiber reinforced resin. From the viewpoint of weight reduction, a carbon fiber reinforced resin is preferable as the material for the shaft 6. The shaft 6 is a so-called carbon shaft. Preferably, the shaft 6 is formed with a cured prepreg sheet. In the prepreg sheet, fibers are substantially oriented in one direction. Such a prepreg in which fibers are substantially oriented in one direction is also referred to as UD prepreg. The term "UD" stands for unidirectional. A prepreg other than the UD prepreg may be used. For example, fibers contained in the prepreg sheet may be woven. The shaft 6 may include a metal wire. The material of the shaft 6 is not limited, and may be a metal, for example.

[0024] The grip 8 is a part that a golfer grips during a swing. Examples of the material of the grip 8 include rubber compositions and resin compositions. The rubber composition for the grip 8 may contain air bubbles.

[0025] The head 4 is hollow. In the present embodiment, the head 4 is a wood type head. The head 4 may be a hybrid type head. The head 4 may be an iron type head. The head 4 is preferably a wood type head or a hybrid type head, and more preferably a wood type head.

[0026] The main portion of the head 4 may be made of a metal material, for example. In the embodiments described below, a head body may be made of a metal material, and/or a face member may be made of a metal material. The metal material is not particularly limited. Examples of the metal material include pure titanium, a titanium alloy, stainless steel, maraging steel, an aluminum alloy, a magnesium alloy, and a tungsten-nickel alloy. A part of the head 4 (for example, a crown portion 12) may be made of a non-metal material such as a fiber reinforced resin. Examples of the fiber reinforced resin include a carbon fiber reinforced resin. The head 4 may be a composite head including a portion made of a metal and a portion made of a fiber reinforced resin. In the head 4 described later, the head body is made of a titanium alloy. In the head 4 described later, the face member is made of a titanium alloy.

[0027] The head 4 includes the face portion 10, the crown portion 12, a sole portion 14, and a hosel portion 16. The face portion 10 includes a striking face 10a and a face inner surface 10b. The striking face 10a constitutes the outer surface of the face portion 10. The striking face 10a includes a face center Fc as defined above. The hosel portion 16 has a shaft hole 16a.

[0028] The striking face 10a has a contour edge k1 that can be defined as follows (hereinafter, the contour edge k1 of the striking face 10a is also referred to as "striking face contour edge k1"). As shown in FIG. 2A and FIG. 2B, there are cross sections each of which contains a straight line that connects a center of gravity of the head 4 and a sweet spot SS, for example, cross sections E1, E2, and E3 in FIG. 2A. In each of the cross sections, when a curvature radius r of the cross-sectional contour line of the head outer surface is sequentially observed from the sweet spot SS toward the outside of the striking face 10a, a point at which the curvature radius r becomes 200 mm for the first time is defined as a position Pe. A set of the positions Pe can be the contour edge k1 of the striking face 10a. Note that the sweet spot SS means a foot of a perpendicular drawn from the center of gravity of the head 4 to the striking face 10a.

[0029] From the viewpoint of members constituting the head 4, the head 4 includes a head body 4a and a face member 4b. As shown in FIG. 5 and FIG. 6, in the head 4, the head body 4a and the face member 4b are joined to each other at a boundary k2 between the two. The boundary k2 coincides with a contour edge k3 of the face member 4b. The head body 4a and the face member 4b are welded to each other. The face member 4b constitutes a part (a part including the face center Fc) of the striking face 10a. The entirety of the outer surface of the face member 4b is the striking face 10a. The head body 4a is a plate-shaped member. Note that a weld bead can cause a localized increase in a face wall thickness t at the boundary k2. Such a weld bead is not shown in FIG. 5 or FIG. 6. Note that, alternatively, the head 4 does not have to include a face member 4b, and may include a head body that is integrally formed as a single-piece member including the face portion. Further alternatively, the face member may be a cup-shaped member including a portion constituting the face portion and a rising portion that extends backward from the portion.

[0030] The face portion 10 has a wall thickness. The wall thickness of the face portion 10 is a distance between the striking face 10a and the face inner surface 10b. The wall thickness of the face portion 10 is measured in the direction of a line normal to the striking face 10a. The face portion 10 has a distribution of wall thickness. When comparing the wall thicknesses of different sections or subsections in the present disclosure, if the wall thickness of a section or subsection varies, the average wall thickness of that section or subsection can be used as its wall thickness. The average wall thickness means a uniform wall thickness obtained by adjusting the varying wall thickness to be uniform throughout the section or subsection while maintaining the same volume.

[0031] As shown in FIG. 4, the face portion 10 includes a face main portion 20. The face main portion 20 includes the face center Fc. The face main portion 20 has a surface area of preferably greater than or equal to 50% of the surface area of the striking face 10a, more preferably greater than or equal to 55% of the surface area of the striking face 10a, and still more preferably greater than or equal to 60% of the surface area of the striking face 10a. The surface area is measured on the outer surface of the head 4, that is, on the striking face 10a. When face lines are formed on the striking face 10a, the surface area is measured in a state where the face lines are filled to be a smooth striking face.

[0032] The face main portion 20 includes a central section 22, a transition section 24 located outside the central section 22, and a peripheral section 26 located outside the transition section 24. In the present embodiment, a contour edge k4 of the face main portion 20 coincides with the contour edge k3 of the face member 4b. Alternatively, the contour edge k4 of the face main portion 20 does not have to coincide with the contour edge k3 of the face member 4b.

[0033] The central section 22 includes the face center Fc. The central section 22 has a surface area of greater than or equal to 100 mm². When face lines are formed on the striking face 10a, the surface area is measured in a state where the face lines are filled to be a smooth striking face. The surface area of the central section 22 is preferably greater than or equal to 140 mm², more preferably greater than or equal to 150 mm², and still more preferably greater than or equal to 250 mm². Increasing the surface area of the central section 22 causes a greater local deformation at and in the vicinity of the face center Fc, which can further increase the flight distance of the hit ball.

[0034] On the other hand, from the viewpoint of having a sufficient durability at the face center Fc, the surface area of the central section 22 is preferably less than or equal to 400 mm², more preferably less than or equal to 350 mm², and still more preferably less than or equal to 300 mm².

[0035] From another viewpoint, the ratio of the surface area of the central section 22 to the area of the striking face 10a is preferably greater than or equal to 5% and less than or equal to 15%. When the ratio of the surface area of the central section 22 to the area of the striking face 10a is greater than or equal to 5%, the local deformation at and in the vicinity of the face center Fc upon impact with a golf ball can be further increased, which can further increase the flight distance of the hit ball. From this viewpoint, the ratio of the surface area of the central section 22 to the area of the striking face 10a is more preferably greater than or equal to 60, and still more preferably greater than or equal to 7%. In addition, when the ratio of the surface area of the central section 22 to the area of the striking face 10a is less than or equal to 15%, the face portion 10 can be prevented from deterioration in the durability. From this viewpoint, the ratio of the surface area of the central section 22 to the area of the striking face 10a is more preferably less than or equal to 14%, and still more preferably less than or equal to 13%. Note that the striking face contour edge k1 as defined above may be a line having two ends, not a line having a closed shape (such as annular shape) with no ends. In this case, the striking face contour edge k1 can be a line having a closed shape with no ends by connecting the two ends with a line segment, and then the area of the striking face 10a can be defined.

[0036] The central section 22 has a uniform wall thickness tc (see FIG. 5 and FIG. 6). In the present disclosure, the uniform wall thickness of the central section 22 means not only a completely unchanging wall thickness throughout the central section 22 extending along the striking face 10a, but also a wall thickness varying within the range of manufacturing and measurement tolerances that may occur unavoidably. The wall thickness of a part of the central section 22 is considered uniform with the wall thickness of the face portion 10 at the face center Fc, when the variation of the wall thickness of the part is in the range of -0.05 mm to +0.05 mm relative to the wall thickness of the face portion 10 at the face center Fc. When face lines are formed on the striking face 10a, the wall thickness of each part/portion/section/subsection of the face portion 10 is measured in a state where the face lines are filled to be a smooth striking face. To distinguish this wall thickness from other wall thicknesses, the wall thickness tc of the central section 22 is also referred to as a central section uniform wall thickness in the present disclosure.

[0037] The wall thickness tc of the central section 22 is preferably greater than or equal to 2.5 mm, more preferably greater than or equal to 2.6 mm, and still more preferably greater than or equal to 2.7 mm. This can effectively prevent deterioration in the durability of the face portion 10. On the other hand, the wall thickness tc of the central section 22 at the face center Fc is preferably less than or equal to 3.0 mm, more preferably less than or equal to 2.9 mm, and still more preferably less than or equal to 2.8 mm. This can increase the local deformation at and in the vicinity of the face center Fc upon impact with a golf ball, which can further increase the flight distance of the hit ball. In the present embodiment, the wall thickness tc of the central section 22 at the face center Fc is 2.75 mm.

[0038] As shown in FIG. 4, the contour of the central section 22 (contour of the central section 22 represented by contour line k5) is shaped such that the length in the toe-heel direction is longer than the length in the up-down direction. The contour line k5 of the central section 22 has a shape similar to an ellipse. This shape is a closed shape. This shape may be, for example, an elliptical shape or an oval shape. The striking face 10a has a contour shaped such that the length in the toe-heel direction is longer than the length in the up-down direction. When the contour shape of the central section 22 corresponds to the contour shape of the striking face 10a, it is possible to effectively bring about a great local deformation at and in the vicinity of the face center Fc upon impact with a golf ball. Although not particularly limited, the maximum length in the toe-heel direction of the central section 22 is preferably greater than or equal to 10 mm, more preferably greater than or equal to 15 mm, and still more preferably greater than or equal to 20 mm. Similarly, although not particularly limited, the maximum length in the up-down direction of the central section 22 is preferably greater than or equal to 10 mm, and more preferably greater than or equal to 15 mm.

[0039] The peripheral section 26 is located outside the transition section 24. The peripheral section 26 includes a first peripheral subsection 261 located in a toe side part and a heel side part of the face main portion 20, and a second peripheral subsection 262 located in a crown side part and a sole side part of the face main portion 20. The first peripheral subsection 261 is in contact with the contour edge k4 of the face main portion 20. The second peripheral subsection 262 is in contact with the contour edge k4 of the face main portion 20.

[0040] The first peripheral subsection 261 includes a toe-side first peripheral subsection 26t located on the toe side relative to the central section 22. The first peripheral subsection 261 also includes a heel-side first peripheral subsection 26h located on the heel side relative to the central section 22. The second peripheral subsection 262 includes a crown-side second peripheral subsection 26c located on the crown side relative to the central section 22. The second peripheral subsection 262 also includes a sole-side second peripheral subsection 26s located on the sole side relative to central section 22.

[0041] The first peripheral subsection 261 has a uniform wall thickness t1 (see FIG. 6). In the present disclosure, the uniform wall thickness of the first peripheral subsection 261 means not only a completely unchanging wall thickness throughout the first peripheral subsection 261 along the striking face 10a but also a wall thickness varying within the range of manufacturing and measurement tolerances that may occur unavoidably. The first peripheral subsection 261 is considered to have a uniform wall thickness when the variation of the wall thickness of the first peripheral subsection 261 is in the range of -0.05 mm to +0.05 mm. To distinguish this wall thickness from other wall thicknesses, the wall thickness t1 of the first peripheral subsection 261 is also referred to as a first peripheral subsection uniform wall thickness in the present disclosure.

[0042] The first peripheral subsection uniform wall thickness t1 is greater than the central section uniform wall thickness tc. The first peripheral subsection uniform wall thickness t1 is preferably greater than or equal to 2.8 mm, more preferably greater than or equal to 2.9 mm, and still more preferably greater than or equal to 3.0 mm. This can effectively prevent deterioration in the durability of the face portion 10. On the other hand, the first peripheral subsection uniform wall thickness t1 is preferably less than or equal to 3.4 mm, more preferably less than or equal to 3.3 mm, and still more preferably less than or equal to 3.2 mm. This can increase the local deformation at and in the vicinity of the face center Fc upon impact with a golf ball, which can increase the flight distance of the hit ball. In the present embodiment, the first peripheral subsection uniform wall thickness t1 is 3.1 mm. Such an increased first peripheral subsection uniform wall thickness t1 can enhance the durability of the face portion 10 while improving rebound performance at and in the vicinity of the face center Fc.

[0043] The second peripheral subsection 262 has a uniform wall thickness t2 (see FIG. 5). In the present disclosure, the uniform wall thickness of the second peripheral subsection 262 means not only a completely unchanging wall thickness throughout the second peripheral subsection 262 along the striking face 10a but also a wall thickness varying within the range of manufacturing and measurement tolerances that may occur unavoidably. The second peripheral subsection 262 is considered to have a uniform wall thickness when the variation of the wall thickness of the second peripheral subsection 262 is in the range of -0.05 mm to +0.05 mm. To distinguish this wall thickness from other wall thicknesses, the wall thickness t2 of the second peripheral subsection 262 is also referred to as a second peripheral subsection uniform wall thickness in the present disclosure.

[0044] The second peripheral subsection uniform wall thickness t2 is smaller than the central section uniform wall thickness tc. The second peripheral subsection uniform wall thickness t2 is preferably greater than or equal to 1.8 mm, more preferably greater than or equal to 1.9 mm, and still more preferably greater than or equal to 2.0 mm. This can effectively prevent deterioration in the durability of the face portion 10. On the other hand, the second peripheral subsection uniform wall thickness t2 is preferably less than or equal to 2.4 mm, more preferably less than or equal to 2.3 mm, and still more preferably less than or equal to 2.2 mm. This can enlarge a local high rebound area in the up-down direction to improve the flight distance of the hit ball, when a golfer adjusts a hit point on the striking face 10a in the up-down direction for achieving a desired ball trajectory. In the present embodiment, the second peripheral subsection uniform wall thickness t2 is 2.1 mm. Such a reduced second peripheral subsection uniform wall thickness t2 can enlarge the local high rebound area in the up-down direction.

[0045] The ratio of the surface area of the toe-side first peripheral subsection 26t to the area of the striking face 10a is preferably greater than or equal to 1% and less than or equal to 9%. By setting the ratio of the surface area of the toe-side first peripheral subsection 26t to the area of the striking face 10a to be greater than or equal to 1%, the durability of the face portion 10 can be enhanced while improving rebound performance at and in the vicinity of the face center Fc. From this viewpoint, the ratio of the surface area of the toe-side first peripheral subsection 26t to the area of the striking face 10a is more preferably greater than or equal to 20, and still more preferably greater than or equal to 3%. From the viewpoint of rebound performance, the ratio of the surface area of the toe-side first peripheral subsection 26t to the area of the striking face 10a is preferably less than or equal to 90, more preferably less than or equal to 80, and still more preferably less than or equal to 7%.

[0046] The ratio of the surface area of the heel-side first peripheral subsection 26h to the area of the striking face 10a is preferably greater than or equal to 1% and less than or equal to 9%. By setting the ratio of the surface area of the heel-side first peripheral subsection 26h to the area of the striking face 10a to be greater than or equal to 1%, the durability of the face portion 10 can be enhanced while improving rebound performance at and in the vicinity of the face center Fc. From this viewpoint, the ratio of the surface area of the heel-side first peripheral subsection 26h to the area of the striking face 10a is more preferably greater than or equal to 20, and still more preferably greater than or equal to 3%. From the viewpoint of rebound performance, the ratio of the surface area of the heel-side first peripheral subsection 26h to the area of the striking face 10a is preferably less than or equal to 90, more preferably less than or equal to 80, and still more preferably less than or equal to 7%.

[0047] The ratio of the surface area of the crown-side second peripheral subsection 26c to the area of the striking face 10a is preferably greater than or equal to 1% and less than or equal to 7%. From the viewpoint of enlarging the high rebound area in the up-down direction, the ratio of the surface area of the crown-side second peripheral subsection 26c to the area of the striking face 10a is preferably greater than or equal to 1%, more preferably greater than or equal to 20, and still more preferably greater than or equal to 3%. From the viewpoint of the durability, the ratio of the surface area of the crown-side second peripheral subsection 26c to the area of the striking face 10a is preferably less than or equal to 70, more preferably less than or equal to 60, and still more preferably less than or equal to 5%.

[0048] The ratio of the surface area of the sole-side second peripheral subsection 26s to the area of the striking face 10a is preferably greater than or equal to 1% and less than or equal to 7%. From the viewpoint of enlarging the high rebound area in the up-down direction, the ratio of the surface area of the sole-side second peripheral subsection 26s to the area of the striking face 10a is preferably greater than or equal to 1%, more preferably greater than or equal to 20, and still more preferably greater than or equal to 3%. From the viewpoint of the durability, the ratio of the surface area of the sole-side second peripheral subsection 26s to the area of the striking face 10a is preferably less than or equal to 70, more preferably less than or equal to 60, and still more preferably less than or equal to 5%.

[0049] As shown in FIG. 4, the second peripheral subsection 262 has a width B1. The width B1 is measured in a direction perpendicular to a boundary line between a third peripheral section 28 and the second peripheral subsection 262. In the present embodiment, the boundary line between the second peripheral subsection 262 and the third peripheral section 28 coincides with the boundary k2.

[0050] From the viewpoint of enlarging the high rebound area in the up-down direction, the width B1 of the second peripheral subsection 262 is preferably greater than or equal to 1 mm, more preferably greater than or equal to 2 mm, and still more preferably greater than or equal to 3 mm. From the viewpoint of the durability, the width B1 of the second peripheral subsection 262 is preferably less than or equal to 7 mm, more preferably less than or equal to 6 mm, and still more preferably less than or equal to 5 mm. The width B1 of the second peripheral subsection 262 may be uniform (unchanging) or does not have to be uniform. In the present embodiment, the width B1 is uniform. In the present embodiment, the width B1 is 3 mm.

[0051] A double-pointed arrow B3 in FIG. 3 shows an up-down directional width of the striking face 10a at the position of the face center Fc. The up-down directional width B3 is measured along a perpendicular axis Z2.

[0052] The ratio of the width B1 of the second peripheral subsection 262 to the up-down directional width B3 is denoted by B1/B3. From the viewpoint of enlarging the high rebound area in the up-down direction, B1/B3 is preferably greater than or equal to 0.02, more preferably greater than or equal to 0.04, and still more preferably greater than or equal to 0.06. From the viewpoint of the durability, B1/B3 is preferably less than or equal to 0.20, more preferably less than or equal to 0.18, and still more preferably less than or equal to 0.16.

[0053] The transition section 24 is located outside the central section 22. The transition section 24 is contiguous to the outer contour of the central section 22. In other words, the transition section 24 is continuous with the outer contour of the central section 22.

[0054] The transition section 24 includes a first transition subsection 241 located between the central section 22 and the first peripheral subsection 261. The transition section 24 also includes a second transition subsection 242 located between the central section 22 and the second peripheral subsection 262. The first peripheral subsection 261 is continuous with the outer contour of the first transition subsection 241. The second peripheral subsection 262 is continuous with the outer contour of the second transition subsection 242.

[0055] The first transition subsection 241 includes a toe-side first transition subsection 24t that is continuous with the toe side contour of the central section 22. The first transition subsection 241 also includes a heel-side first transition subsection 24h that is continuous with the heel side contour of the central section 22. The second transition subsection 242 includes a crown-side second transition subsection 24c that is continuous with the crown side contour of the central section 22. The second transition subsection 242 also includes a sole-side second transition subsection 24s that is continuous with the sole side contour of the central section 22.

[0056] A wall thickness t3 of the first transition subsection 241 is greater than or equal to the central section uniform wall thickness tc. The wall thickness t3 of the first transition subsection 241 is less than or equal to the first peripheral subsection uniform wall thickness t1. The wall thickness t3 of the first transition subsection 241 continuously increases from the central section uniform wall thickness tc to the first peripheral subsection uniform wall thickness t1. Increasing the wall thickness t3 of the first transition subsection 241 can enhance the durability while enlarging the local high rebound area in the up-down direction. In addition, continuously varying the wall thickness t3 can prevent stress concentration and enhance the durability.

[0057] A wall thickness t4 of the second transition subsection 242 is greater than or equal to the second peripheral subsection uniform wall thickness t2. The wall thickness t4 of the second transition subsection 242 is less than or equal to the central section uniform wall thickness tc. The wall thickness t4 of the second transition subsection 242 continuously decreases from the central section uniform wall thickness tc to the second peripheral subsection uniform wall thickness t2. Decreasing the wall thickness t4 of the second transition subsection 242 can enlarge the high rebound area in the up-down direction. In addition, continuously varying the wall thickness t4 can prevent stress concentration and enhance the durability.

[0058] The face portion 10 further includes the third peripheral section 28. The third peripheral section 28 is located outside the face main portion 20. An inner contour line of the third peripheral section 28 coincides with the contour edge k4 of the face main portion 20. An outer contour line of the third peripheral section 28 coincides with the contour edge k1 of the striking face 10a. The third peripheral section 28 surrounds the face main portion 20 either continuously or discontinuously. When the third peripheral section 28 surrounds the face main portion 20 "discontinuously", the third peripheral section 28 may have gaps at a plurality of positions in the entire circumference (360-degree circumference) of the face main portion 20. In this case, the third peripheral section 28 preferably surrounds greater than or equal to 700 of the entire circumference (360-degree circumference) of the face main portion 20, more preferably surrounds greater than or equal to 80% of the entire circumference (360-degree circumference) of the face main portion 20, and still more preferably surrounds greater than or equal to 90% of the entire circumference (360-degree circumference) of the face main portion 20. When the third peripheral section 28 surrounds the face main portion 20 "continuously", the third peripheral section 28 may surround the entire circumference (360-degree circumference) of the face main portion 20, or may have a gap at a single position in the entire circumference (360-degree circumference) of the face main portion 20.

[0059] The third peripheral section 28 has a wall thickness t5. In the present embodiment, the wall thickness t5 of the third peripheral section 28 is smaller than the central section uniform wall thickness tc. Reducing the wall thickness t5 of the third peripheral section 28 can further enhance rebound performance. When the wall thickness t5 of the third peripheral section 28 is smaller than the central section uniform wall thickness tc, the wall thickness t5 can be less than or equal to 2.7 mm, further can be less than or equal to 2.6 mm, and still further can be less than or equal to 2.5 mm. From the viewpoint of the durability, the wall thickness t5 can be greater than or equal to 2.1 mm, further can be greater than or equal to 2.2 mm, and still further can be greater than or equal to 2.3 mm.

[0060] The third peripheral section 28 includes a crown-side third peripheral subsection 28c that is located in a crown side part of the face portion 10, and a sole-side third peripheral subsection 28s that is located in a sole side part of the face portion 10. The third peripheral section 28 also includes a toe-side third peripheral subsection 28t that is located in a toe side part of the face portion 10, and a heel-side third peripheral subsection 28h that is located in a heel side part of the face portion 10.

[0061] As shown in FIG. 3, the following two axes are defined: a parallel axis Z1 that extends in the toe-heel direction and passes through the face center Fc; and the perpendicular axis Z2 that passes through the face center Fc and extends in a direction perpendicular to the parallel axis Z1. In addition, the following two straight lines are defined: a straight line L1 that passes through the face center Fc, has an angle of 30 degrees relative to the parallel axis Z1, and extends from the toe lower side toward the heel upper side; and a straight line L2 that passes through the face center Fc, has an angle of 30 degrees relative to the parallel axis Z1, and extends from the toe upper side toward the heel lower side.

[0062] The straight line L1 and the straight line L2 can be demarcation lines that divide the third peripheral section 28 into the following four subsections: the crown-side third peripheral subsection 28c, the sole-side third peripheral subsection 28s, the toe-side third peripheral subsection 28t and the heel-side third peripheral subsection 28h. A region located on the toe side relative to the straight line L1 and on the heel side relative to the straight line L2 can be defined as a crown region Rc. A region located on the heel side relative to the straight line L1 and on the toe side relative to the straight line L2 can be defined as a sole region Rs. A region located on the upper side relative to the straight line L1 and on the lower side relative to the straight line L2 can be defined as a toe region Rt. A region located on the lower side relative to the straight line L1 and on the upper side relative to the straight line L2 can be defined as a heel region Rh. Of the third peripheral section 28, a part located in the crown region Rc can be defined as the crown-side third peripheral subsection 28c. Of the third peripheral section 28, a part located in the sole region Rs can be defined as the sole-side third peripheral subsection 28s. Of the third peripheral section 28, a part located in the toe region Rt can be defined as the toe-side third peripheral subsection 28t. Of the third peripheral section 28, a part located in the heel region Rh can be defined as the heel-side third peripheral subsection 28h.

[0063] The crown-side third peripheral subsection 28c is continuous with the crown side contour of at least one selected from the group consisting of the first peripheral subsection 261, the second peripheral subsection 262, the first transition subsection 241, and the second transition subsection 242. In the present embodiment, the crown-side third peripheral subsection 28c is continuous with the crown side contours of the first transition subsection 241, the first peripheral subsection 261, and the second peripheral subsection 262. More specifically, the crown-side third peripheral subsection 28c is continuous with the crown side contours of the heel-side first transition subsection 24h, the crown-side second peripheral subsection 26c, and the toe-side first peripheral subsection 26t.

[0064] The sole-side third peripheral subsection 28s is continuous with the sole side contour of at least one selected from the group consisting of the first peripheral subsection 261, the second peripheral subsection 262, the first transition subsection 241, and the second transition subsection 242. In the present embodiment, the sole-side third peripheral subsection 28s is continuous with the sole side contours of the first peripheral subsection 261, and the second peripheral subsection 262. More specifically, the sole-side third peripheral subsection 28s is continuous with the sole side contours of the heel-side first peripheral subsection 26h, the sole-side second peripheral subsection 26s, and the toe-side first peripheral subsection 26t.

[0065] The toe-side third peripheral subsection 28t is continuous with the toe side contour of at least one selected from the group consisting of the first peripheral subsection 261, the second peripheral subsection 262, the first transition subsection 241, and the second transition subsection 242. In the present embodiment, the toe-side third peripheral subsection 28t is continuous with the toe side contour of the first peripheral subsection 261. More specifically, the toe-side third peripheral subsection 28t is continuous with the toe side contour of the toe-side first peripheral subsection 26t.

[0066] The heel-side third peripheral subsection 28h is continuous with the heel side contour of at least one selected from the group consisting of the first peripheral subsection 261, the second peripheral subsection 262, the first transition subsection 241, and the second transition subsection 242. In the present embodiment, the heel-side third peripheral subsection 28h is continuous with the heel side contours of the first peripheral subsection 261 and the first transition subsection 241. More specifically, the heel-side third peripheral subsection 28h is continuous with the heel side contours of the heel-side first peripheral subsection 26h, and the heel-side first transition subsection 24h.

[0067] A wall thickness t51 of the sole-side third peripheral subsection 28s is smaller than a wall thickness t52 of the crown-side third peripheral subsection 28c (see FIG. 5).

[0068] A wall thickness t53 of the toe-side third peripheral subsection 28t is smaller than the wall thickness t52 of the crown-side third peripheral subsection 28c. A wall thickness t54 of the heel-side third peripheral subsection 28h is smaller than the wall thickness t52 of the crown-side third peripheral subsection 28c (see FIG. 5 and FIG. 6).

[0069] The third peripheral section 28 includes a transition subsection 29a located in both its toe side part and its heel side part. The transition subsection 29a located in the third peripheral section 28 is referred to as a peripheral transition subsection. The peripheral transition subsection 29a is constituted by a toe peripheral transition subsection 29t located in the toe side part and a heel peripheral transition subsection 29h located in the heel side part. The third peripheral section 28 is divided into a crown side zone 29c and a sole side zone 29s by the toe peripheral transition subsection 29t and the heel peripheral transition subsection 29h. These divisions (29t, 29h, 29c, 29s) of the third peripheral section 28 are different from the above-described divisions (28t, 28h, 28c, 28s) of the third peripheral section 28.

[0070] The crown side zone 29c is continuous with the crown side contours of the toe peripheral transition subsection 29t and the heel peripheral transition subsection 29h. The sole side zone 29s is continuous with the sole side contours of the toe peripheral transition subsection 29t and the heel peripheral transition subsection 29h. The wall thickness of each of the toe peripheral transition subsection 29t and the heel peripheral transition subsection 29h varies from the wall thickness of the sole side zone 29s to the wall thickness of the crown side zone 29c.

[0071] The crown side zone 29c is continuous with the crown side contour of at least one selected from the group consisting of the first peripheral subsection 261, the second peripheral subsection 262, the first transition subsection 241, and the second transition subsection 242. In the present embodiment, the crown side zone 29c is continuous with the crown side contours of the first transition subsection 241, the second peripheral subsection 262, and the first peripheral subsection 261. More specifically, the crown side zone 29c is continuous with the crown side contours of the heel-side first peripheral subsection 26h, the heel-side first transition subsection 24h, the crown-side second peripheral subsection 26c, and the toe-side first peripheral subsection 26t.

[0072] The sole side zone 29s is continuous with the sole side contour of at least one selected from the group consisting of the first peripheral subsection 261, the second peripheral subsection 262, the first transition subsection 241, and the second transition subsection 242. In the present embodiment, the sole side zone 29s is continuous with the sole side contours of the first peripheral subsection 261, and the second peripheral subsection 262. More specifically, the sole side zone 29s is continuous with the sole side contours of the heel-side first peripheral subsection 26h, the sole-side second peripheral subsection 26s, and the toe-side first peripheral subsection 26t.

[0073] The toe peripheral transition subsection 29t is continuous with the toe side contour of at least one selected from the group consisting of the first peripheral subsection 261, the second peripheral subsection 262, the first transition subsection 241, and the second transition subsection 242. In the present embodiment, the toe peripheral transition subsection 29t is continuous with the toe side contour of the first peripheral subsection 261. More specifically, the toe peripheral transition subsection 29t is continuous with the toe side contour of the toe-side first peripheral subsection 26t.

[0074] The heel peripheral transition subsection 29h is continuous with the heel side contour of at least one selected from the group consisting of the first peripheral subsection 261, the second peripheral subsection 262, the first transition subsection 241, and the second transition subsection 242. In the present embodiment, the heel peripheral transition subsection 29h is continuous with the heel side contour of the first peripheral subsection 261. More specifically, the heel peripheral transition subsection 29h is continuous with the heel side contour of the heel-side first peripheral subsection 26h.

[0075] The wall thickness of the crown side zone 29c is different from the wall thickness of the sole side zone 29s. The peripheral transition subsection 29a has a wall thickness that varies from the wall thickness of the crown side zone 29c to the wall thickness of the sole side zone 29s. In the present embodiment, the wall thickness of the crown side zone 29c is greater than the wall thickness of the sole side zone 29s. The wall thickness of the toe peripheral transition subsection 29t is smaller than the wall thickness of the crown side zone 29c. The wall thickness of the heel peripheral transition subsection 29h is smaller than the wall thickness of the crown side zone 29c. The wall thickness of the toe peripheral transition subsection 29t is greater than the wall thickness of the sole side zone 29s. The wall thickness of the heel peripheral transition subsection 29h is greater than the wall thickness of the sole side zone 29s.

[0076] The crown side zone 29c includes the entirety of the crown-side third peripheral subsection 28c. The crown side zone 29c also includes a part of the toe-side third peripheral subsection 28t. The crown side zone 29c also includes a part of the heel-side third peripheral subsection 28h. The sole side zone 29s includes the entirety of the sole-side third peripheral subsection 28s. The sole side zone 29s also includes a part of the toe-side third peripheral subsection 28t. The sole side zone 29s also includes a part of the heel-side third peripheral subsection 28h.

[0077] As shown in FIG. 4, the face portion 10 includes a third transition section 30. The third transition section 30 extends along a line inclined by either - 70° to -20° or 20° to 70° relative to the parallel axis Z1 (see FIG. 3) extending in the toe-heel direction and passing through the face center Fc. The shape of the line is not limited, and the line may be a straight line, a line having one or more vertices, or a curved line. A center line CL1 of the third transition section 30 is inclined by either -70° or more and -20° or less, or 20° or more and 70° or less relative to the parallel axis Z1. An angle θ shown in FIG. 4 is greater than or equal to -70° and less than or equal to -20°, or greater than or equal to 20° and less than or equal to 70°.

[0078] The third transition section 30 has a width B2. The width B2 is measured in a direction perpendicular to a toe-side contour line 30a of the third transition section 30. From the viewpoint of reserving sufficient areas for the remaining sections, the width B2 of the third transition section 30 is reduced. The width B2 is preferably less than or equal to 7 mm, more preferably less than or equal to 6 mm, and still more preferably less than or equal to 5 mm. From the viewpoint of gradually varying the face wall thickness for easy forming of the face portion, the width B2 of the third transition section 30 is preferably greater than or equal to 1 mm, more preferably greater than or equal to 2 mm, and still more preferably greater than or equal to 3 mm. The width B2 of the third transition section 30 may be uniform (unchanging) or does not have to be uniform. In the present embodiment, the width B2 is uniform. In the present embodiment, the width B2 is 3 mm.

[0079] The third transition section 30 is located in the face main portion 20. At least one third transition section 30 is formed. In the embodiment of FIG. 4, four third transition sections 30 are formed at different positions. The third transition sections 30 include: a toe upper third transition section 301 located on the toe side and crown side relative to the face center Fc; a heel upper third transition section 302 located on the heel side and crown side relative to the face center Fc; a heel lower third transition section 303 located on the heel side and sole side relative to the face center Fc; and a toe lower third transition section 304 located on the toe side and sole side relative to the face center Fc.

[0080] The toe upper third transition section 301 extends while inclining such that it goes toward the crown side as it goes to the toe side. The toe upper third transition section 301 extends from the central section 22 to the third peripheral section 28. The toe upper third transition section 301 extends from the contour line k5 of the central section 22 to the contour edge k4 of the face main portion 20.

[0081] The heel upper third transition section 302 extends while inclining such that it goes toward the crown side as it goes to the heel side. The heel upper third transition section 302 extends from the central section 22 to the third peripheral section 28. The heel upper third transition section 302 extends from the contour line k5 of the central section 22 to the contour edge k4 of the face main portion 20.

[0082] The heel lower third transition section 303 extends while inclining such that it goes toward the sole side as it goes to the heel side. The heel lower third transition section 303 extends from the central section 22 to the third peripheral section 28. The heel lower third transition section 303 extends from the contour line k5 of the central section 22 to the contour edge k4 of the face main portion 20.

[0083] The toe lower third transition section 304 extends while inclining such that it goes toward the sole side as it goes to the toe side. The toe lower third transition section 304 extends from the central section 22 to the third peripheral section 28. The toe lower third transition section 304 extends from the contour line k5 of the central section 22 to the contour edge k4 of the face main portion 20.

[0084] The third transition section 30 is located between the first peripheral subsection 261 and/or the first transition subsection 241, and the second peripheral subsection 262 and/or the second transition subsection 242.

[0085] The toe upper third transition section 301 is located between the first transition subsection 241 and the second transition subsection 242, as well as between the first transition subsection 241 and the second peripheral subsection 262. More specifically, the toe upper third transition section 301 is located between the toe-side first transition subsection 24t and the crown-side second transition subsection 24c. The toe upper third transition section 301 is contiguous to both the toe-side first transition subsection 24t and the crown-side second transition subsection 24c. The toe upper third transition section 301 is located also between the toe-side first transition subsection 24t and the crown-side second peripheral subsection 26c. The toe upper third transition section 301 is contiguous to both the toe-side first transition subsection 24t and the crown-side second peripheral subsection 26c.

[0086] The heel upper third transition section 302 is located between the first transition subsection 241 and the second transition subsection 242, as well as between the first transition subsection 241 and the second peripheral subsection 262. More specifically, the heel upper third transition section 302 is located between the heel-side first transition subsection 24h and the crown-side second transition subsection 24c. The heel upper third transition section 302 is contiguous to both the heel-side first transition subsection 24h and the crown-side second transition subsection 24c. The heel upper third transition section 302 is located also between the heel-side first transition subsection 24h and the crown-side second peripheral subsection 26c. The heel upper third transition section 302 is contiguous to both the heel-side first transition subsection 24h and the crown-side second peripheral subsection 26c.

[0087] The heel lower third transition section 303 is located between the first transition subsection 241 and the second transition subsection 242, as well as between the first transition subsection 241 and the second peripheral subsection 262. More specifically, the heel lower third transition section 303 is located between the heel-side first transition subsection 24h and the sole-side second transition subsection 24s. The heel lower third transition section 303 is contiguous to both the heel-side first transition subsection 24h and the sole-side second transition subsection 24s. The heel lower third transition section 303 is located also between the heel-side first transition subsection 24h and the sole-side second peripheral subsection 26s. The heel lower third transition section 303 is contiguous to both the heel-side first transition subsection 24h and the sole-side second peripheral subsection 26s.

[0088] The toe lower third transition section 304 is located between the first transition subsection 241 and the second transition subsection 242, as well as between the first transition subsection 241 and the second peripheral subsection 262. More specifically, the toe lower third transition section 304 is located between the toe-side first transition subsection 24t and the sole-side second transition subsection 24s. The toe lower third transition section 304 is contiguous to both the toe-side first transition subsection 24t and the sole-side second transition subsection 24s. The toe lower third transition section 304 is located also between the toe-side first transition subsection 24t and the sole-side second peripheral subsection 26s. The toe lower third transition section 304 is contiguous to both the toe-side first transition subsection 24t and the sole-side second peripheral subsection 26s.

[0089] Each of the third transition sections 30 has a continuously varying wall thickness, ensuring no step is formed due to a difference in wall thickness between subsections adjacent to each other with one of the third transition sections 30 interposed. As shown in FIG. 4, the face main portion 20 is divided into four regions, a first region R1 to a fourth region R4, by the central section 22 and the four third transition sections 30 which extend from the central section 22 toward the contour edge of the face portion 10. The crown-side second transition subsection 24c and the crown-side second peripheral subsection 26c are included in the first region R1 located on the crown side. The heel-side first transition subsection 24h and the heel-side first peripheral subsection 26h are included in the second region R2 located on the heel side. The sole-side second transition subsection 24s and the sole-side second peripheral subsection 26s are included in the third region R3 located on the sole side. The toe-side first transition subsection 24t and the toe-side first peripheral subsection 26t are included the fourth region R4 located on the toe side. The third transition sections 30 prevent stress concentration and contribute to improvement of the durability.

[Second embodiment]

[0090] FIG. 7 is a front view of a head 42 according to the second embodiment. FIG. 8 is a front view of the head 42, showing contour lines of parts/sections/subsections of a face portion 10 with dashed lines. FIG. 9 is a cross-sectional view showing a vertical cross section of the head 42. FIG. 10 is a cross-sectional view showing a horizontal cross section of the head 42. FIG. 9 shows the center vertical cross section. FIG. 10 shows the center horizontal cross section.

[0091] The head 42 includes the face portion 10, a crown portion 12, a sole portion 14, and a hosel portion 16. The face portion 10 includes a striking face 10a and a face inner surface 10b. The hosel portion 16 has a shaft hole 16a.

[0092] As shown in FIG. 8, the face portion 10 includes a face main portion 20. The face main portion 20 includes a central section 22, a transition section 24 located outside the central section 22, and a peripheral section 26 located outside the transition section 24. The central section 22 includes a face center Fc. The central section 22 has a surface area of greater than or equal to 100 mm². The central section 22 has a uniform wall thickness tc (hereinafter, this wall thickness is also referred to as central section uniform wall thickness tc).

[0093] The peripheral section 26 is located outside the transition section 24. The peripheral section 26 includes a first peripheral subsection 261 located in a toe side part and a heel side part of the face main portion 20, and a second peripheral subsection 262 located in a crown side part and a sole side part of the face main portion 20.

[0094] The first peripheral subsection 261 includes a toe-side first peripheral subsection 26t located on the toe side relative to the central section 22. The first peripheral subsection 261 also includes a heel-side first peripheral subsection 26h located on the heel side relative to the central section 22. The second peripheral subsection 262 includes a crown-side second peripheral subsection 26c located on the crown side relative to the central section 22. The second peripheral subsection 262 also includes a sole-side second peripheral subsection 26s located on the sole side relative to central section 22. The first peripheral subsection 261 has a uniform wall thickness t1 (hereinafter, also referred to as first peripheral subsection uniform wall thickness t1). The second peripheral subsection 262 has a uniform wall thickness t2 (hereinafter, also referred to as second peripheral subsection uniform wall thickness t2). The second peripheral subsection uniform wall thickness t2 is smaller than the central section uniform wall thickness tc.

[0095] The transition section 24 is located outside the central section 22. The transition section 24 is continuous with the outer contour of the central section 22. The transition section 24 includes a first transition subsection 241 located between the central section 22 and the first peripheral subsection 261. The transition section 24 also includes a second transition subsection 242 located between the central section 22 and the second peripheral subsection 262. The first peripheral subsection 261 is continuous with the outer contour of the first transition subsection 241. The second peripheral subsection 262 is continuous with the outer contour of the second transition subsection 242.

[0096] The first transition subsection 241 includes a toe-side first transition subsection 24t that is continuous with the toe side contour of the central section 22. The first transition subsection 241 also includes a heel-side first transition subsection 24h that is continuous with the heel side contour of the central section 22. The second transition subsection 242 includes a crown-side second transition subsection 24c that is continuous with the crown side contour of the central section 22. The second transition subsection 242 also includes a sole-side second transition subsection 24s that is continuous with the sole side contour of the central section 22.

[0097] A wall thickness t3 of the first transition subsection 241 is greater than or equal to the central section uniform wall thickness tc. The wall thickness t3 of the first transition subsection 241 is less than or equal to the first peripheral subsection uniform wall thickness t1. The wall thickness t3 of the first transition subsection 241 increases from the central section uniform wall thickness tc to the first peripheral subsection uniform wall thickness t1. The maximum wall thickness of the first transition subsection 241 (maximum value of the wall thickness t3) is greater than the central section uniform wall thickness tc.

[0098] A wall thickness t4 of the second transition subsection 242 is greater than or equal to the second peripheral subsection uniform wall thickness t2. The wall thickness t4 of the second transition subsection 242 is less than or equal to the central section uniform wall thickness tc. The wall thickness t4 of the second transition subsection 242 decreases from the central section uniform wall thickness tc to the second peripheral subsection uniform wall thickness t2. The minimum wall thickness of the second transition subsection 242 (minimum value of the wall thickness t4) is smaller than the central section uniform wall thickness tc.

[0099] The face portion 10 further includes a third peripheral section 28. The third peripheral section 28 is located outside the face main portion 20. The third peripheral section 28 continuously surrounds the face main portion 20. The third peripheral section 28 includes a crown-side third peripheral subsection 28c that is located in a crown side part of the face portion 10, and a sole-side third peripheral subsection 28s that is located in a sole side part of the face portion 10. The third peripheral section 28 also includes a toe-side third peripheral subsection 28t that is located in a toe side part of the face portion 10, and a heel-side third peripheral subsection 28h that is located in a heel side part of the face portion 10.

[0100] The third peripheral section 28 includes a peripheral transition subsection 29a located in both its toe side part and its heel side part. The peripheral transition subsection 29a is constituted by a toe peripheral transition subsection 29t and a heel peripheral transition subsection 29h. The third peripheral section 28 includes a crown side zone 29c and a sole side zone 29s separated by the peripheral transition subsection 29a. The wall thickness of the crown side zone 29c is different from the wall thickness of the sole side zone 29s. In the present embodiment, the wall thickness of the crown side zone 29c is greater than the wall thickness of the sole side zone 29s. The wall thickness of the toe peripheral transition subsection 29t is smaller than the wall thickness of the crown side zone 29c. The wall thickness of the heel peripheral transition subsection 29h is smaller than the wall thickness of the crown side zone 29c. The wall thickness of the toe peripheral transition subsection 29t is greater than the wall thickness of the sole side zone 29s. The wall thickness of the heel peripheral transition subsection 29h is greater than the wall thickness of the sole side zone 29s.

[0101] The face portion 10 includes a third transition section 30. The third transition section 30 is located in the face main portion 20. Four third transition sections 30 are formed at different positions. The third transition sections 30 include: a toe upper third transition section 301 located on the toe side and crown side relative to the face center Fc; a heel upper third transition section 302 located on the heel side and crown side relative to the face center Fc; a heel lower third transition section 303 located on the heel side and sole side relative to the face center Fc; and a toe lower third transition section 304 located on the toe side and sole side relative to the face center Fc.

[0102] The head 42 is different from the head 4 of the first embodiment in the wall thickness t5 of the third peripheral section 28. Except the wall thickness t5 of the third peripheral section 28, the head 42 of the second embodiment has the same configuration as the head 4.

[0103] In the head 42, the wall thickness t5 of the third peripheral section 28 is greater. The wall thickness t5 of the third peripheral section 28 is greater than the central section uniform wall thickness tc (see FIG. 9 and FIG. 10). Such a greater wall thickness t5 of the third peripheral section 28 can enhance the durability while maintaining a high rebound area extending upward and downward from the face center. When the wall thickness t5 of the third peripheral section 28 is greater than the central section uniform wall thickness tc, the wall thickness t5 can be greater than or equal to 2.7 mm, further can be greater than or equal to 2.8 mm, and still further can be greater than or equal to 2.9 mm. An excessively great wall thickness t5 reduces the flexibility of the wall thickness distribution in the face portion 10. From this viewpoint, the wall thickness t5 is preferably less than or equal to 3.3 mm, more preferably less than or equal to 3.2 mm, and still more preferably less than or equal to 3.1 mm.

[0104] A wall thickness t51 of the sole-side third peripheral subsection 28s is smaller than a wall thickness t52 of the crown-side third peripheral subsection 28c. A wall thickness t53 of the toe-side third peripheral subsection 28t is smaller than the wall thickness t52 of the crown-side third peripheral subsection 28c. A wall thickness t54 of the heel-side third peripheral subsection 28h is smaller than the wall thickness t52 of the crown-side third peripheral subsection 28c.

[Third embodiment]

[0105] FIG. 11 is a front view of a head 43 according to the third embodiment. FIG. 12 is a front view of the head 43, showing contour lines of parts/sections/subsections of a face portion 10 with dashed lines. FIG. 13 is a cross-sectional view showing a vertical cross section of the head 43. FIG. 14 is a cross-sectional view showing a horizontal cross section of the head 43. FIG. 13 shows the center vertical cross section. FIG. 14 shows the center horizontal cross section.

[0106] The head 43 includes the face portion 10, a crown portion 12, a sole portion 14, and a hosel portion 16. The face portion 10 includes a striking face 10a and a face inner surface 10b. The hosel portion 16 has a shaft hole 16a.

[0107] As shown in FIG. 12, the face portion 10 includes a face main portion 20. The face main portion 20 includes a central section 22, a transition section 24 located outside the central section 22, and a peripheral section 26 located outside the transition section 24. The central section 22 includes a face center Fc. The central section 22 has a surface area of greater than or equal to 100 mm². The central section 22 has a uniform wall thickness tc (hereinafter, this wall thickness is also referred to as central section uniform wall thickness tc).

[0108] The peripheral section 26 is located outside the transition section 24. The peripheral section 26 includes a first peripheral subsection 261 and a second peripheral subsection 262. The first peripheral subsection 261 includes a toe-side first peripheral subsection 26t located on the toe side relative to the central section 22, and a heel-side first peripheral subsection 26h located on the heel side relative to the central section 22. The second peripheral subsection 262 includes a crown-side second peripheral subsection 26c located on the crown side relative to the central section 22, and a sole-side second peripheral subsection 26s located on the sole side relative to central section 22. The first peripheral subsection 261 has a uniform wall thickness that is referred to as first peripheral subsection uniform wall thickness t1. The second peripheral subsection 262 has a uniform wall thickness that is referred to as second peripheral subsection uniform wall thickness t2. The second peripheral subsection uniform wall thickness t2 is smaller than the central section uniform wall thickness tc.

[0109] The transition section 24 includes: a first transition subsection 241 located between the central section 22 and the first peripheral subsection 261; and a second transition subsection 242 located between the central section 22 and the second peripheral subsection 262. The first peripheral subsection 261 is continuous with the outer contour of the first transition subsection 241. The second peripheral subsection 262 is continuous with the outer contour of the second transition subsection 242.

[0110] The first transition subsection 241 includes a toe-side first transition subsection 24t that is continuous with the toe side contour of the central section 22, and a heel-side first transition subsection 24h that is continuous with the heel side contour of the central section 22. The second transition subsection 242 includes a crown-side second transition subsection 24c that is continuous with the crown side contour of the central section 22, and a sole-side second transition subsection 24s that is continuous with the sole side contour of the central section 22.

[0111] A wall thickness t3 of the first transition subsection 241 is greater than or equal to the central section uniform wall thickness tc. The wall thickness t3 of the first transition subsection 241 is less than or equal to the first peripheral subsection uniform wall thickness t1. The wall thickness t3 of the first transition subsection 241 increases from the central section uniform wall thickness tc to the first peripheral subsection uniform wall thickness t1.

[0112] A wall thickness t4 of the second transition subsection 242 is greater than or equal to the second peripheral subsection uniform wall thickness t2. The wall thickness t4 of the second transition subsection 242 is less than or equal to the central section uniform wall thickness tc. The wall thickness t4 of the second transition subsection 242 decreases from the central section uniform wall thickness tc to the second peripheral subsection uniform wall thickness t2.

[0113] The face portion 10 further includes a third peripheral section 28. The third peripheral section 28 continuously surrounds the face main portion 20. The third peripheral section 28 includes a crown-side third peripheral subsection 28c that is located in a crown side part of the face portion 10, and a sole-side third peripheral subsection 28s that is located in a sole side part of the face portion 10. The third peripheral section 28 also includes a toe-side third peripheral subsection 28t that is located in a toe side part of the face portion 10, and a heel-side third peripheral subsection 28h that is located in a heel side part of the face portion 10.

[0114] The third peripheral section 28 includes a peripheral transition subsection 29a located in both its toe side part and its heel side part. The peripheral transition subsection 29a is constituted by a toe peripheral transition subsection 29t and a heel peripheral transition subsection 29h. The third peripheral section 28 includes a crown side zone 29c and a sole side zone 29s. The wall thickness of the crown side zone 29c is greater than the wall thickness of the sole side zone 29s. The wall thickness of the toe peripheral transition subsection 29t is smaller than the wall thickness of the crown side zone 29c. The wall thickness of the heel peripheral transition subsection 29h is smaller than the wall thickness of the crown side zone 29c. The wall thickness of the toe peripheral transition subsection 29t is greater than the wall thickness of the sole side zone 29s. The wall thickness of the heel peripheral transition subsection 29h is greater than the wall thickness of the sole side zone 29s.

[0115] The face portion 10 includes a third transition section 30. A plurality of third transition sections 30 are formed at positions spaced apart from each other. The third transition sections 30 include: a toe upper third transition section 301 located on the toe side and crown side relative to the face center Fc; a heel upper third transition section 302 located on the heel side and crown side relative to the face center Fc; a heel lower third transition section 303 located on the heel side and sole side relative to the face center Fc; and a toe lower third transition section 304 located on the toe side and sole side relative to the face center Fc.

[0116] The wall thickness t5 of the third peripheral section 28 is smaller than the central section uniform wall thickness tc (see FIG. 13 and FIG. 14). The wall thickness t51 of the sole-side third peripheral subsection 28s is smaller than the wall thickness t52 of the crown-side third peripheral subsection 28c. The wall thickness t53 of the toe-side third peripheral subsection 28t is smaller than the wall thickness t52 of the crown-side third peripheral subsection 28c. The wall thickness t54 of the heel-side third peripheral subsection 28h is smaller than the wall thickness t52 of the crown-side third peripheral subsection 28c.

[0117] The head 43 differs from the head 4 of the first embodiment in two aspects: the cross-sectional shape of a toe side part relative to the face portion 10; and the shapes of a bulge and a roll in the peripheral region of the striking face 10a (hereinafter, the peripheral region of the striking face 10a is also referred to as striking face peripheral region). Except for the two differences, the head 43 has the same configuration as the head 4 of the first embodiment.

[0118] As to the first difference (hereinafter also referred to as difference A), in the head 43, the shape of the horizontal cross section in a portion Pt (toe portion Pt) (see FIG. 14) located on the toe side relative to the face portion 10 is more rounded compared to the head 4. This shifts the position of the toe side portion of the contour edge k1 of the striking face 10a toward the heel side as compared to that of the head 4. As shown in FIG. 11, the head 43 has a toe point T1. In the head front elevation view, the toe point T1 is a point that is an intersection point between the parallel axis Z1 and the striking face contour edge k1 and that is located on the toe side. The head 43 also has a heel point H1. When the head 43 is in the reference state, an intersection line between the outer surface of the head 43 and a horizontal plane located 0.875 inches above the ground plane HP is determined. A heel-most point of the intersection line is the heel point H1. In the head front elevation view, a toe-heel directional distance between the face center Fc and the toe point T1 is denoted by W1, and a toe-heel directional distance between the face center Fc and the heel point H1 is denoted by W2. Since the toe portion Pt is rounded, the toe point T1 shifts toward the heel side, thereby reducing the ratio W1/W2. From the viewpoint of durability, W1/W2 can be less than or equal to 0.90, further can be less than or equal to 0.86, and still further can be less than or equal to 0.82. An excessively rounded toe portion Pt results in an excessively small area of the striking face 10a. From this viewpoint, W1/W2 can be greater than or equal to 0.70, further can be greater than or equal to 0.75, and still further can be greater than or equal to 0.80. The rounded shape of the toe side portion allows the extending direction of the horizontal cross section of the toe side portion located on the toe side relative to the face portion to align more closely with the direction of the normal line of the striking face. This alignment increases the rigidity of the face portion when hitting a ball at a toe-side hit point. The increased rigidity further improves the durability. From this viewpoint, a toe-heel directional distance W3 between the heel point H1 and the toe point T1 is preferably less than or equal to 98 mm, more preferably less than or equal to 96 mm, and still more preferably less than or equal to 94 mm. The head 43 is a driver head, and the head volume of the head 43 may be greater than or equal to 440 cm³, further may be greater than or equal to 450 cm³, and still further may be greater than or equal to 460 cm³ (the upper limit of the head volume may be less than or equal to 470 cm³). From this viewpoint, the distance W3 is preferably greater than or equal to 84 mm, more preferably greater than or equal to 86 mm, and still more preferably greater than or equal to 88 mm.

[0119] As to the second difference (hereinafter also referred to as difference B), the peripheral region of the striking face 10a of the head 43 is more rounded as compared to that of the head 4. In the head 43, the roll radii of upper and lower regions are smaller than the roll radius of an up-down directional center region. The upper and lower regions collectively refer to: a region that extends toward the upper side from a position spaced 7.5 mm apart from the parallel axis Z1 toward the upper side; and a region that extends toward the lower side from a position spaced 7.5 mm apart from the parallel axis Z1 toward the lower side. The up-down directional center region refers to a region that extends from the position spaced 7.5 mm apart from the parallel axis Z1 toward the upper side to the position spaced 7.5 mm apart from the parallel axis Z1 toward the lower side. In addition, the bulge radii of toe and heel regions are smaller than the bulge radius of a lateral center region. The toe and heel regions collectively refer to: a region that extends toward the toe side from a position spaced 20.0 mm apart from the perpendicular axis Z2 toward the toe side; and a region that extends toward the heel side from a position spaced 20.0 mm apart from the perpendicular axis Z2 toward the heel side. The lateral center region refers to a region that extends from the position spaced 20.0 mm apart from the perpendicular axis Z2 toward the toe side to the position spaced 20.0 mm apart from the perpendicular axis Z2 toward the heel side. Further details of the difference B are described later.

[Fourth embodiment]

[0120] FIG. 15 is a front view of a head 44 according to the fourth embodiment. FIG. 16 is a front view of the head 44, showing contour lines of parts/sections/subsections of a face portion 10 with dashed lines. FIG. 17 is a cross-sectional view showing a vertical cross section of the head 44. FIG. 18 is a cross-sectional view showing a horizontal cross section of the head 44. FIG. 17 and FIG. 18 show cross-sections passing through the face center Fc.

[0121] The head 44 includes the face portion 10, a crown portion 12, a sole portion 14, and a hosel portion 16. The face portion 10 includes a striking face 10a and a face inner surface 10b. The hosel portion 16 has a shaft hole 16a.

[0122] As shown in FIG. 16, the face portion 10 includes a face main portion 20. The face main portion 20 includes a central section 22, a transition section 24 located outside the central section 22, and a peripheral section 26 located outside the transition section 24. The central section 22 includes the face center Fc. The central section 22 has a surface area of greater than or equal to 100 mm². The central section 22 has a uniform wall thickness tc (hereinafter, this wall thickness is also referred to as central section uniform wall thickness tc).

[0123] The peripheral section 26 is located outside the transition section 24. The peripheral section 26 includes a first peripheral subsection 261 and a second peripheral subsection 262. The first peripheral subsection 261 includes a toe-side first peripheral subsection 26t and a heel-side first peripheral subsection 26h. The second peripheral subsection 262 includes a crown-side second peripheral subsection 26c and a sole-side second peripheral subsection 26s. The first peripheral subsection 261 has a uniform wall thickness that is referred to as first peripheral subsection uniform wall thickness t1. The second peripheral subsection 262 has a uniform wall thickness that is referred to as second peripheral subsection uniform wall thickness t2. The second peripheral subsection uniform wall thickness t2 is smaller than the central section uniform wall thickness tc.

[0124] The transition section 24 includes a first transition subsection 241 and a second transition subsection 242. The first peripheral subsection 261 is continuous with the outer contour of the first transition subsection 241. The second peripheral subsection 262 is continuous with the outer contour of the second transition subsection 242. The first transition subsection 241 includes a toe-side first transition subsection 24t and a heel-side first transition subsection 24h. The second transition subsection 242 includes a crown-side second transition subsection 24c and a sole-side second transition subsection 24s.

[0125] A wall thickness t3 of the first transition subsection 241 is greater than or equal to the central section uniform wall thickness tc. The wall thickness t3 of the first transition subsection 241 is less than or equal to the first peripheral subsection uniform wall thickness t1. The wall thickness t3 of the first transition subsection 241 increases from the central section uniform wall thickness tc to the first peripheral subsection uniform wall thickness t1.

[0126] A wall thickness t4 of the second transition subsection 242 is greater than or equal to the second peripheral subsection uniform wall thickness t2. The wall thickness t4 of the second transition subsection 242 is less than or equal to the central section uniform wall thickness tc. The wall thickness t4 of the second transition subsection 242 decreases from the central section uniform wall thickness tc to the second peripheral subsection uniform wall thickness t2.

[0127] The face portion 10 further includes a third peripheral section 28. The third peripheral section 28 is continuous with the outer contour of the face main portion 20. The third peripheral section 28 continuously surrounds the face main portion 20. The third peripheral section 28 includes a crown-side third peripheral subsection 28c and a sole-side third peripheral subsection 28s. The third peripheral section 28 also includes a toe-side third peripheral subsection 28t and a heel-side third peripheral subsection 28h.

[0128] The third peripheral section 28 includes a peripheral transition subsection 29a. The peripheral transition subsection 29a is constituted by a toe peripheral transition subsection 29t and a heel peripheral transition subsection 29h. The third peripheral section 28 includes a crown side zone 29c and a sole side zone 29s. The wall thickness of the crown side zone 29c is greater than the wall thickness of the sole side zone 29s. The wall thickness of the toe peripheral transition subsection 29t is smaller than the wall thickness of the crown side zone 29c. The wall thickness of the heel peripheral transition subsection 29h is smaller than the wall thickness of the crown side zone 29c. The wall thickness of the toe peripheral transition subsection 29t is greater than the wall thickness of the sole side zone 29s. The wall thickness of the heel peripheral transition subsection 29h is greater than the wall thickness of the sole side zone 29s.

[0129] The face portion 10 includes a third transition section 30. A plurality of third transition sections 30 are formed at positions spaced apart from each other. The third transition sections 30 include a toe upper third transition section 301, a heel upper third transition section 302, a heel lower third transition section 303, and a toe lower third transition section 304.

[0130] The wall thickness t5 of the third peripheral section 28 is smaller than the central section uniform wall thickness tc (see FIG. 17 and FIG. 18). The wall thickness t51 of the sole-side third peripheral subsection 28s is smaller than the wall thickness t52 of the crown-side third peripheral subsection 28c. The wall thickness t53 of the toe-side third peripheral subsection 28t is smaller than the wall thickness t52 of the crown-side third peripheral subsection 28c. The wall thickness t54 of the heel-side third peripheral subsection 28h is smaller than the wall thickness t52 of the crown-side third peripheral subsection 28c.

[0131] The head 44 differs from the head 43 of the third embodiment in the wall thickness of the crown portion. Except for this difference, the head 44 has the same configuration as the head 43 of the third embodiment. Similar to the head 43, the head 44 differs from the head 4 in the difference A and the difference B. In addition, the head 44 differs from the head 43 of the third embodiment in another aspect that is referred to as difference C.

[0132] The difference C (wall thickness of a crown front portion) of the head 44 is as follows. As shown in FIG. 17, the crown portion 12 of the head 44 includes a crown front portion 12a. In the vertical cross section of the head 44, a tangent line S1 that is a line tangent to the striking face 10a at the center point of the striking face 10a is determined. The center point is located on the parallel axis Z1 in the head front elevation view. When the vertical cross section includes the face center Fc as shown in FIG. 17, the center point is at the face center Fc. A distance D1 between a front end 46 of the crown front portion 12a and the tangent line S1, measured in a direction perpendicular to the tangent line S1, is greater than or equal to 9 mm and less than or equal to 13 mm. In the present embodiment, the distance D1 is 11 mm. A width D2 of the crown front portion 12a, measured in the direction perpendicular to the tangent line S1, can be greater than or equal to 4 mm and less than or equal to 8 mm. In the present embodiment, the width D2 is 6 mm. The crown front portion 12a is a thin-wall portion having a wall thickness t6 of greater than or equal to 0.3 mm and less than or equal to 0.6 mm, and more preferably greater than or equal to 0.4 mm and less than or equal to 0.5 mm. A transition portion 12b is formed between the face portion 10 and the crown front portion 12a. The wall thickness of the transition portion 12b continuously decreases from the face portion 10 to the crown front portion 12a. The crown front portion 12a having a thin wall thickness contributes to improved rebound performance.

[The rounded shape of the bulge and roll in the striking face peripheral region]

[0133] The head 43 and the head 44 each have the difference B (a rounded shape in the striking face peripheral region) as detailed below.

[0134] FIG. 19 is a vertical cross-sectional view of the outer surface of each of the heads 43 and 44. FIG. 20 is a horizontal cross-sectional view of the outer surface of each of the heads 43 and 44.

[0135] As described above, the present disclosure defines: the parallel axis Z1 which passes through the face center Fc and extends in the toe-heel direction; and the perpendicular axis Z2 which passes through the face center Fc and extends in the up-down direction. The parallel axis Z1 is indicated by a point in the vertical cross-sectional view shown in FIG. 19. The perpendicular axis Z2 is indicated by a point in the horizontal cross-sectional view shown in FIG. 20.

[0136] As shown in the vertical cross section of FIG. 19, the striking face 10a has a vertical cross section center point P1. The vertical cross section center point P1 is a point located on the parallel axis Z1 in the head front elevation view (see FIG. 3). Since FIG. 19 shows the center vertical cross section, the vertical cross section center point P1 is at the face center Fc.

[0137] In the vertical cross section, the striking face 10a has the tangent line S1 which is tangent to the striking face 10a at the vertical cross section center point P1. The tangent line S1 is indicated by a dash-dot-dot-dash line in FIG. 19.

[0138] The striking face 10a also has a point P2 that is spaced 7.5 mm apart from the vertical cross section center point P1 toward the upper side, and a point P3 that is spaced 7.5 mm apart from the vertical cross section center point P1 toward the lower side. These distances, 7.5 mm, are measured in the direction of the tangent line S1. The striking face 10a also has: a point P4 that is located on the upper side relative to the point P2 and located on the striking face contour edge k1; and a point P5 that is located on the lower side relative to the point P3 and located on the striking face contour edge k1. The striking face 10a also has a point P6 located between the point P2 and the point P4. The distance between the point P6 and the point P4 is equal to the distance between the point P6 and the point P2. These distances are measured in the direction of the tangent line S1. The striking face 10a also has a point P7 located between the point P3 and the point P5. The distance between the point P7 and the point P5 is equal to the distance between the point P7 and the point P3. These distances are measured in the direction of the tangent line S1.

[0139] A region that extends from the point P2 to the point P3 is defined as the up-down directional center region F1. A region that extends from the point P2 to the point P4 is defined as an upper region F2, and a region that extends from the point P3 to the point P5 is defined as a lower region F3. The upper region F2 and the lower region F3 are collectively referred to as upper and lower regions F4 .

[0140] The vertical cross section can be taken at each of different positions in the toe-heel direction. The up-down directional center region F1, the upper region F2, the lower region F3, and the upper and lower regions F4 can be defined at each position in the toe-heel direction. Accordingly, these regions F1, F2, F3, and F4 can each have a width in the toe-heel direction.

[0141] As shown in the horizontal cross section of FIG. 20, the striking face 10a has a horizontal cross section center point P10. The horizontal cross section center point P10 is a point located on the perpendicular axis Z2 in the head front elevation view (see FIG. 3). Since FIG. 20 shows the center horizontal cross section, the horizontal cross section center point P10 is at the face center Fc.

[0142] In the horizontal cross section, the striking face 10a has a tangent line S2 that is a line tangent to the striking face 10a at the horizontal cross section center point P10. The tangent line S2 is indicated by a dash-dot-dot-dash line in FIG. 20.

[0143] The striking face 10a also has a point P12 that is spaced 20.0 mm apart from the horizontal cross section center point P10 toward the toe side, and a point P13 that is spaced 20.0 mm apart from the horizontal cross section center point P10 toward the heel side. These distances, 20.0 mm, are measured in the direction of the tangent line S2. The striking face 10a also has: a point P14 that is located on the toe side relative to the point P12 and located on the striking face contour edge k1; and a point P15 that is located on the heel side relative to the point P13 and located on the striking face contour edge k1. The striking face 10a also has a point P16 located between the point P12 and the point P14. The distance between the point P16 and the point P14 is equal to the distance between the point P16 and the point P12. These distances are measured in the direction of the tangent line S2. The striking face 10a also has a point P17 located between the point P13 and the point P15. The distance between the point P17 and the point P15 is equal to the distance between the point P17 and the point P13. These distances are measured in the direction of the tangent line S2.

[0144] A region that extends from the point P12 to the point P13 is defined to as a lateral center region G1. A region that extends from the point P12 to the point P14 is defined as a toe side region G2, and a region that extends from the point P13 to the point P15 is defined as a heel side region G3. The toe side region G2 and the heel side region G3 are collectively referred to as toe and heel regions G4.

[0145] The horizontal cross section can be taken at each of different positions in the up-down direction. The lateral center region G1, the toe side region G2, the heel side region G3, and the toe and heel regions G4 can be defined at each position in the up-down direction. Accordingly, these regions G1, G2, G3, and G4 can each have a width in the up-down direction.

[0146] The roll radii of the respective regions are determined in each of vertical cross sections such as the vertical cross section shown in FIG. 19. A roll radius r1 of the up-down directional center region F1 is the radius of a circle that passes through three points: P1, P2, and P3. Roll radii r4 of the upper and lower regions F4 are: a radius r2 of a circle that passes through three points P2, P4 and P6; and a radius r3 of a circle that passes through three points P3, P5 and P7. The radius r2 is the roll radius of the upper region F2. The radius r3 is the roll radius of the lower region F3.

[0147] The bulge radii of the respective regions are determined in each of horizontal cross sections such as the horizontal cross section shown in FIG. 20. A bulge radius r5 of the lateral center region G1 is the radius of a circle that passes through three points: P10, P12, and P13. Bulge radii r8 of the toe and heel regions G4 are: a radius r6 of a circle that passes through three points P12, P14 and P16; and a radius r7 of a circle that passes through three points P13, P15 and P17. The radius r6 is the bulge radius of the toe side region G2. The radius r7 is the bulge radius of the heel side region G3.

[0148] As shown in FIG. 19, the roll radii r4 of the upper and lower regions F4 are smaller than the roll radius r1 of the up-down directional center region F1. That is, the roll radius r2 of the upper region F2 is smaller than the roll radius r1 of the up-down directional center region F1, and the roll radius r3 of the lower region F3 is smaller than the roll radius r1 of the up-down directional center region F1.

[0149] As shown in FIG. 20, the bulge radii r8 of the toe and heel regions G4 are smaller than the bulge radius r5 of the lateral center region G1. That is, the bulge radius r6 of the toe side region G2 is smaller than the bulge radius r5 of the lateral center region G1, and the bulge radius r7 of the heel side region G3 is smaller than the bulge radius r5 of the lateral center region G1.

[Shape of the head inner surface at and in the vicinity of the boundary of the face portion]

[0150] All of the embodiments described above each have the following structures at the boundary portion between the face portion 10 and the crown portion 12, and at the boundary portion between the face portion 10 and the sole portion 14. These structures are described below with reference to FIG. 5.

[0151] The center vertical cross section satisfies the following structures (a) and (b).

(a) When a boundary point between the inner surface of the crown portion 12 and the inner surface of the face portion 10 is referred to as a CF inner surface boundary point kc, the radius of curvature of the head inner surface at the CF inner surface boundary point kc is greater than or equal to 6.0 mm and less than or equal to 10.0 mm. The head wall thickness t9 at the CF inner surface boundary point kc is greater than or equal to 2.0 mm.

(b) When a point that is spaced 10 mm apart from the CF inner surface boundary point kc toward the crown side is referred to as a point C10, the head wall thickness gradually decreases from the CF inner surface boundary point kc to the point C10. The head wall thickness t10 at the point C10 is less than or equal to 1.0 mm.

[0152] The center vertical cross section further satisfies the following structure (a1).
(a1) When a region, of the head inner surface, that extends from a position spaced 5 mm apart from the CF inner surface boundary point kc toward the crown side (back side) to a position spaced 5 mm apart from the CF inner surface boundary point kc toward the sole side is referred to as a CF boundary region X1, the radius of curvature of the head inner surface in the CF boundary region X1 is greater than or equal to 6.0 mm and less than or equal to 10.0 mm.

[0153] The center vertical cross section further satisfies the following structures (c) and (d).

(c) When a boundary point between the inner surface of the sole portion 14 and the inner surface of the face portion 10 is referred to as an SF inner surface boundary point ks, the radius of curvature of the head inner surface at the SF inner surface boundary point ks is greater than or equal to 7.0 mm and less than or equal to 11.0 mm. The head wall thickness t11 at the SF inner surface boundary point ks is greater than or equal to 2.0 mm.

(d) When a point that is spaced 15 mm apart from the SF inner surface boundary point ks toward the sole side (back side) is referred to as a point S15, the head wall thickness gradually decreases from the SF inner surface boundary point ks to the point S15. The head wall thickness t12 at the point S15 is less than or equal to 1.0 mm.

[0154] The center vertical cross section further satisfies the following structure (c1).
(c1) When a region, of the head inner surface, that extends from a position spaced 5 mm apart from the SF inner surface boundary point ks toward the sole side (back side) to a position spaced 5 mm apart from the SF inner surface boundary point ks toward the crown side is referred to as an SF boundary region X2, the radius of curvature of the head inner surface in the SF boundary region X2 is greater than or equal to 7.0 mm and less than or equal to 11.0 mm.

[0155] In the structures (a) to (d), (a1) and (c1), each distance is a route distance measured along the route of the cross-sectional contour line of the head inner surface. In the structures (a) to (d), (a1) and (c1), the radius of curvature at a certain point is defined as the radius of a circle passing through three points: the certain point, a point spaced 1 mm apart from the certain point toward one side of the certain point, and a point spaced 1 mm apart from the certain point toward the other side of the certain point. The distance, 1 mm, is a route distance measured along the route of the cross-sectional contour line of the head inner surface. Each of the CF inner surface boundary point kc and the SF inner surface boundary point ks is an intersection point between the head inner surface and a normal line that is normal to the head outer surface at striking face contour edge k1. The structures (a) to (d), (a1) and (c1) may be satisfied not only in the center vertical cross section but also in other vertical cross sections taken at toe-heel directional positions different from that of the center vertical cross section. From the viewpoint of rebound performance, one or more selected from the group consisting of the structures (a) to (d), (a1) and (c1) are preferably satisfied in the center vertical cross section, more preferably satisfied in all vertical cross sections taken at positions in a region that extends from a position spaced 5 mm apart from the face center Fc toward the toe side to a position spaced 5 mm apart from the face center Fc toward the heel side, still more preferably satisfied in all vertical cross sections taken at positions in a region that extends from a position spaced 10 mm apart from the face center Fc toward the toe side to a position spaced 10 mm apart from the face center Fc toward the heel side, still more preferably satisfied in all vertical cross sections taken at positions in a region that extends from a position spaced 15 mm apart from the face center Fc toward the toe side to a position spaced 15 mm apart from the face center Fc toward the heel side, and yet more preferably satisfied in all vertical cross sections taken at positions in a region that extends from a position spaced 20 mm apart from the face center Fc toward the toe side to a position spaced 20 mm apart from the face center Fc toward the heel side.

[0156] In these structures, the boundary region between the face portion 10 and a body portion (crown portion 12 or sole portion 14) is rounded, and has an increased wall thickness. Accordingly, a bending point when the head hits a golf ball is not located in the boundary region, allowing the deformation of the face portion to be transmitted to the body portion. As a result, the starting point of bending can be shifted toward the body side, and the body portion can be efficiently bent. The bending of the body portion can increase the degree of bending of the face portion, which can enhance rebound performance.

[Advantageous effects]

[0157] The above-described embodiments can exhibit the following advantageous effects.

[0158] In all the embodiments, the local deformation that occurs at and in the vicinity of the face center can be enlarged in the up-down direction while enhancing durability because of the wall thickness distribution. This can enlarge the high rebound area in the up-down direction, and can improve the flight distance of the hit ball for golfers who adjust the hit point on the striking face in the up-down direction to achieve a desired ball trajectory. The structures (a) to (d) can increase the degree of bending of the face portion by facilitating the bending of the body portion, which can enhance rebound performance.

[0159] In the third and fourth embodiments, the toe side portion of the head has a rounded shape. The rounded shape of the toe side portion allows the extending direction of the horizontal cross section of the toe side portion located on the toe side relative to the face portion to align more closely with the direction of the normal line of the striking face. This alignment increases the rigidity of the face portion when hitting a ball at a toe-side hit point. The increased rigidity further improves the durability. In the third and fourth embodiments, the shapes of the bulge and the roll are more rounded in the striking face peripheral region. The rounded shapes allow the extending direction of the striking face peripheral region of the face portion to align more closely with the direction of the normal line of the striking face. This alignment increases the rigidity of the face portion when hitting a ball at a position in the striking face peripheral region. The increased rigidity further improves the durability. In the fourth embodiment, the crown front portion is a thin-wall portion having a thin wall thickness. The thin-wall portion improves rebound performance when hitting a ball at an upper-side hit point.

[0160] As described above, the vertical cross section can be taken at each of different positions in the toe-heel direction. When the rounded shape of the roll in the striking face peripheral region is enlarged in the toe-heel direction, durability can be further increased. From this viewpoint, the rounded shape of the roll is preferably satisfied in the center vertical cross section, more preferably satisfied in all vertical cross sections taken at positions in the region that extends from the position spaced 5 mm apart from the face center Fc toward the toe side to the position spaced 5 mm apart from the face center Fc toward the heel side, still more preferably satisfied in all vertical cross sections taken at positions in the region that extends from the position spaced 10 mm apart from the face center Fc toward the toe side to the position spaced 10 mm apart from the face center Fc toward the heel side, still more preferably satisfied in all vertical cross sections taken at positions in the region that extends from the position spaced 15 mm apart from the face center Fc toward the toe side to the position spaced 15 mm apart from the face center Fc toward the heel side, and yet more preferably satisfied in all vertical cross sections taken at positions in the region that extends from the position spaced 20 mm apart from the face center Fc toward the toe side to the position spaced 20 mm apart from the face center Fc toward the heel side.

[0161] As described above, the horizontal cross section can be taken at each of different positions in the up-down direction. When the rounded shape of the bulge in the striking face peripheral region is enlarged in the up-down direction, durability can be further increased. From this viewpoint, the rounded shape of the bulge is preferably satisfied in the center horizontal cross section, more preferably satisfied in all horizontal cross sections taken at positions in a region that extends from a position spaced 5 mm apart from the face center Fc toward the upper side to a position spaced 5 mm apart from the face center Fc toward the lower side, still more preferably satisfied in all horizontal cross sections taken at positions in a region that extends from a position spaced 10 mm apart from the face center Fc toward the upper side to a position spaced 10 mm apart from the face center Fc toward the lower side, and yet more preferably satisfied in all horizontal cross sections taken at positions in a region that extends from a position spaced 15 mm apart from the face center Fc toward the upper side to a position spaced 15 mm apart from the face center Fc toward the lower side.

[0162] As described above, the vertical cross section can be taken at each of different positions in the toe-heel direction. When the structure in which the crown front portion has a thin wall thickness is enlarged in the toe-heel direction, rebound performance when hitting a ball at an upper-side hit point can be further enhanced. From this viewpoint, the structure in which the crown front portion has a thin wall thickness is preferably satisfied in the center vertical cross section, more preferably satisfied in all vertical cross sections taken at positions in the region that extends from the position spaced 5 mm apart from the face center Fc toward the toe side to the position spaced 5 mm apart from the face center Fc toward the heel side, still more preferably satisfied in all vertical cross sections taken at positions in the region that extends from the position spaced 10 mm apart from the face center Fc toward the toe side to the position spaced 10 mm apart from the face center Fc toward the heel side, and still more preferably satisfied in all vertical cross sections taken at positions in the region that extends from the position spaced 15 mm apart from the face center Fc toward the toe side to the position spaced 15 mm apart from the face center Fc toward the heel side.

Examples

[0163] Hereinafter, Examples of the present disclosure are explained. However, the present disclosure should not be construed in a limited manner based on the specific Examples.

[Example 1]

[0164] A head having the same configuration as the head 4 of the first embodiment was produced. The volume of the head of Example 1 was 460 cm³. The central section uniform wall thickness tc was 2.75 mm. The first peripheral subsection uniform wall thickness t1 was 3.10 mm. The second peripheral subsection uniform wall thickness t2 was 2.10 mm. The wall thickness t3 of the first transition subsection continuously increased from 2.75 mm to 3.10 mm toward the face contour edge. The wall thickness t4 of the second transition subsection continuously decreased from 2.75 mm to 2.10 mm toward the face contour edge. The wall thickness t5 of the third peripheral section was 2.50 mm in the crown side zone 29c, and was 2.30 mm in the sole side zone 29s. The specifications of Example 1 are shown in Table 1 below.

[Example 2]

[0165] A head having the same configuration as the head 42 of the second embodiment was produced. That is, the head of Example 2 was obtained in the same manner as in Example 1 except that the wall thickness t5 of the third peripheral section was increased. The wall thickness t5 of the third peripheral section was 3.10 mm in the crown side zone 29c, and was 2.90 mm in the sole side zone 29s. The specifications of Example 2 are shown in Table 1 below.

[Example 3]

[0166] A head having the same configuration as the head 43 of the third embodiment was produced. That is, the head of Example 3 was obtained in the same manner as in Example 1 except that the head includes the toe side portion having a rounded shape, and includes the bulge and roll each having a rounded shape in the striking face peripheral region. The specifications of Example 3 are shown in Table 1 below.

[Example 4]

[0167] A head having the same configuration as the head 44 of the fourth embodiment was produced. That is, the head of Example 4 was obtained in the same manner as in Example 3 except that the crown front portion had a thinner wall thickness. The specifications of Example 4 are shown in Table 1 below.

[Comparative Example 1]

[0168] FIG. 21 is a front view of a head 50 of Comparative Example 1. FIG. 22 is the same front view as FIG. 21. FIG. 22 shows contour lines of sections of a face portion 10 with dashed lines. The face portion 10 of the head 50 includes a central section 52 including a face center Fc, a transition section 54 that continuously surrounds the outside of the central section 52, and a peripheral section 56 that continuously surrounds the outside of the transition section 54. The central section 52 has a contour line k5. An inner contour line k6 of the transition section 54 coincides with the contour line k5 of the central section 52. An outer contour line k7 of the transition section 54 has points 58 at which the outer contour line k7 intersects the contour edge k3 of the face member 4b. An inner contour line k8 of the peripheral section 56 coincides with the contour line k7. An outer contour line k9 of the peripheral section 56 coincides with the contour edge k1 of the striking face 10a. The central section 52 has a uniform wall thickness. The wall thickness of the central section 52 is 3.48 mm. The peripheral section 56 has a uniform wall thickness. The wall thickness of the peripheral section 56 is 2.23 mm. The wall thickness of the transition section 54 continuously decreases from 3.48 mm to 2.23 mm toward the face contour edge. A head of Comparative Example 1 was obtained in the same manner as in Example 1 except that the above-described wall thickness specifications were adopted. The specifications of Comparative Example 1 are shown in Table 1 below.

[0169] For each of Examples and Comparative Example, the ratio W1/W2, the distance W3, the roll radius r1 of the up-down directional center region F1, the roll radius r2 of the upper region F2, the roll radius r3 of the lower region F3, the bulge radius r5 of the lateral center region G1, the bulge radius r6 of the toe side region G2, and the bulge radius r7 of the heel side region G3 are shown in Table 1 below.

[Table 1]

Table 1 Specifications of Examples and Comparative Example
	Unit	Example 1	Example 2	Example 3	Example 4	Comparative Example. 1
Corresponding embodiment	--	First embodiment	Second embodiment	Third embodiment	Fourth embodiment
Corresponding drawing	--	FIG. 4	FIG. 8	FIG. 12	FIG. 16	FIG. 22
Thickened third transition sections	--	not applied	applied	not applied	not applied	not applied
Rounded shape of the toe side portion	--	not applied	not applied	applied	applied	not applied
Rounded shape of bulge and roll in the striking face peripheral region	--	not applied	not applied	applied	applied	not applied
Thinned crown front portion	--	not applied	not applied	not applied	applied	not applied
W1/W2	--	0.91	0.91	0.81	0.81	0.91
W3	mm	98.3	98.3	93.4	93.4	98.2
Roll radius r1 of the up-down directional center region	mm	238.4	238.4	212.2	212.2	238.4
Roll radius r2 of the upper region	mm	422.2	422.2	152.9	152.9	421.6
Roll radius r3 of the lower region	mm	131.2	131.2	88.2	88.2	116.4
Bulge radius r5 of the lateral center region	mm	304.8	304.8	303.0	303.0	304.8
Bulge radius r6 of the toe side region	mm	347.1	347.1	161.5	161.5	347.1
Bulge radius r7 of the heel side region	mm	498.4	498.4	264.7	264.7	497.0
Wall thickness of the crown front portion	mm	0.6	0.6	0.6	0.4	0.6

[0170] As shown in Table 1, the heads (Examples 3 and 4) in which the toe side portion had the rounded shape had a smaller W1/W2. In the heads (Examples 3 and 4) having the rounded shape of the striking face peripheral region, the roll radius r2 of the upper region and the roll radius r3 of the lower region were smaller than the roll radius r1 of the up-down directional center region, and the bulge radius r6 of the toe side region and the bulge radius r7 of the heel side region were smaller than the bulge radius r5 of the lateral center region.

[0171] The COR was evaluated for Examples 2 to 4 and Comparative Example 1. The evaluation method was as follows.

[COR]

[0172] The COR means the coefficient of restitution. The COR was measured according to "Interim Procedure for Measuring the Coefficient of Restitution of an Iron Clubhead Relative to a Baseline Plate Revision 1.3 January 1, 2006" specified by the USGA (United States Golf Association). Measurement points were set at the face center Fc, and also set at intervals of 5 mm in the up-down direction and at intervals of 5 mm in the toe-heel direction, from the face center Fc. Evaluation values at upper side points and lower side points relative to the face center Fc were calculated as average values of three measured COR values: a measured COR value at the hit point; a measured COR value at a point spaced 5 mm apart from the hit point toward the toe side; and a measured COR value at a point spaced 5 mm apart from the hit point toward the heel side. For example, for the evaluation value at the point spaced 5 mm apart from the face center Fc toward the upper side, the following three values were used: a first measured COR value at the point 5 mm apart from the face center Fc toward the upper side; a second measured COR value at the point 5 mm apart from the first measured COR value toward the toe side; and a third measured COR value at the point 5 mm apart from the first measured COR value toward the heel side, and the average value of the first to third measured COR values was adopted as the evaluation value. Evaluation values at toe side points and heel side points relative to the face center Fc were calculated as average values of three measured COR values: a measured COR value at the hit point; a measured COR value at a point spaced 5 mm apart from the hit point toward the upper side; and a measured COR value at a point spaced 5 mm apart from the hit point toward the lower side. For example, for the evaluation value at the point spaced 5 mm apart from the face center Fc toward the toe side, the following three values were used: a first measured COR value at the point 5 mm apart from the face center Fc toward the toe side; a second measured COR value at the point 5 mm apart from the first measured COR value toward the upper side; and a third measured COR value at the point 5 mm apart from the first measured COR value toward the lower side, and the average value of the first to third measured COR values was adopted as the evaluation value. The evaluation value at the face center Fc of Comparative Example 1 was set as 100, and the evaluation values at the other points were represented as indexes relative to the evaluation value at the face center Fc of Comparative Example 1. These indexes are shown in Table 2 below. The evaluation value (index) of each head at the face center Fc is shown in the column of "COR (face center Fc)". The evaluation value (index) of each head at the point spaced 5 mm apart from the face center Fc toward the upper side is shown in the column of "COR (5 mm above)". The evaluation value (index) of each head at the point spaced 5 mm apart from the face center Fc toward the lower side is shown in the column of "COR (5 mm below)". The evaluation value (index) of each head at the point spaced 10 mm apart from the face center Fc toward the upper side is shown in the column of "COR (10 mm above)". The evaluation value (index) of each head at the point spaced 10 mm apart from the face center Fc toward the lower side is shown in the column of "COR (10 mm below)". The evaluation value (index) of each head at the point spaced 5 mm apart from the face center Fc toward the toe side is shown in the column of "COR (5 mm toe)". The evaluation value (index) of each head at the point spaced 5 mm apart from the face center Fc toward the heel side is shown in the column of "COR (5 mm heel)". The evaluation value (index) of each head at the point spaced 10 mm apart from the face center Fc toward the toe side is shown in the column of "COR (10 mm toe)". The evaluation value (index) of each head at the point spaced 10 mm apart from the face center Fc toward the heel side is shown in the column of "COR (10 mm heel)".

[Table 2]

Specifications and evaluation results of Examples and Comparative Example
	unit	Example 2	Example 3	Example 4	Comparative Example 1
Corresponding embodiment	--	Second embodiment	Third embodiment	Fourth embodiment	--
Corresponding drawing	--	FIG. 8	FIG. 12	FIG. 16	FIG. 22
Thickened third transition sections	--	applied	not applied	not applied	not applied
Rounded shape of the toe side portion	--	not applied	applied	applied	not applied
Rounded shape of bulge and roll in the striking face peripheral region	--	not applied	applied	applied	not applied
Thinned crown front portion	--	not applied	not applied	applied	not applied
W1/W2	--	0.91	0.81	0.81	0.91
W3	mm	98.3	93.4	93.4	98.2
Wall thickness of the crown front portion	mm	0.6	0.6	0.4	0.6
COR (face center Fc)	index	101.2	101.7	101.8	100.0
COR (5 mm above)	index	101.6	102.6	102.4	100.6
COR (5 mm below)	index	99.3	99.3	100.1	97.6
COR (10 mm above)	index	100.2	101.2	101.4	99.6
COR (10 mm below)	index	95.7	97.0	96.3	94.9
COR (5 mm toe)	index	101.4	101.4	101.6	99.6
COR (5 mm heel)	index	100.8	100.8	101.1	99.3
COR (10 mm toe)	index	99.7	100.1	100.9	99.0
COR (10 mm heel)	index	98.2	99.7	99.3	97.8

[0173] The durability performance was evaluated for Examples 2 and 3, and Comparative Example 1. The evaluation method was as follows.

[Durability performance]

[0174] Each golf club was attached to a swing robot, and the swing robot hit two-piece balls with the club at a head speed of 54 m/s. The hit point was at the face center Fc. The striking face was elaborately examined after every 50 hits to determine whether damage such as a crack was found. When damage was found, the swing robot stopped hitting balls. When no damage occurred after 5000 hits, the swing robot stopped hitting balls at 5000 hits.

[0175] No damage occurred after 5000 hits in Example 2, Example 3, or Comparative Example 1. It was confirmed that Example 2 and Example 3 each have a durability performance equivalent to Comparative Example 1.

[0176] As shown in Tables 1 and 2, the advantages of the present disclosure are clear.

[0177] The following clauses are a part of invention included in the present disclosure.

[Clause 1] A golf club head including a hollow interior inside thereof, wherein:

the golf club head includes a face portion including a striking face, a crown portion, and a sole portion,

the face portion includes a face main portion including a face center,

the face main portion includes a central section including the face center, a transition section located outside the central section, and a peripheral section located outside the transition section,

the peripheral section includes a first peripheral subsection located in a toe side part and a heel side part of the face main portion, and a second peripheral subsection located in a crown side part and a sole side part of the face main portion,

the transition section includes a first transition subsection located between the central section and the first peripheral subsection, and a second transition subsection located between the central section and the second peripheral subsection,

the central section has a central section uniform wall thickness and a surface area of greater than or equal to 100 mm²,

the first peripheral subsection has a first peripheral subsection uniform wall thickness, and the first peripheral subsection uniform wall thickness is greater than the central section uniform wall thickness,

the second peripheral subsection has a second peripheral subsection uniform wall thickness, and the second peripheral subsection uniform wall thickness is smaller than the central section uniform wall thickness,

the first transition subsection has a wall thickness that increases from the central section uniform wall thickness to the first peripheral subsection uniform wall thickness, and

the second transition subsection has a wall thickness that decreases from the central section uniform wall thickness to the second peripheral subsection uniform wall thickness.

[Clause 2] The golf club head according to clause 1, wherein

the face portion further includes a third peripheral section located outside the face main portion,

the third peripheral section surrounds the face main portion either continuously or discontinuously, and

the third peripheral section has a wall thickness greater than the central section uniform wall thickness.

[Clause 3] The golf club head according to clause 1, wherein

the face portion further includes a third peripheral section located outside the face main portion,

the third peripheral section surrounds the face main portion either continuously or discontinuously, and

the third peripheral section has a wall thickness smaller than the central section uniform wall thickness.

[Clause 4] The golf club head according to clause 2 or 3, wherein
the third peripheral section surrounds the face main portion continuously.

[Clause 5] The golf club head according to any one of clauses 2 to 4, wherein

the third peripheral section includes:

a crown-side third peripheral subsection that is continuous with a crown side contour of at least one selected from the group consisting of the first peripheral subsection, the second peripheral subsection, the first transition subsection, and the second transition subsection; and

a sole-side third peripheral subsection that is continuous with a sole side contour of at least one selected from the group consisting of the first peripheral subsection, the second peripheral subsection, the first transition subsection, and the second transition subsection, and

the sole-side third peripheral subsection has a wall thickness smaller than a wall thickness of the crown-side third peripheral subsection.

[Clause 6] The golf club head according to any one of clauses 2 to 5, wherein

the third peripheral section includes:

a toe peripheral transition subsection that is continuous with a toe side contour of at least one selected from the group consisting of the first peripheral subsection, the second peripheral subsection, the first transition subsection, and the second transition subsection;

a heel peripheral transition subsection that is continuous with a heel side contour of at least one selected from the group consisting of the first peripheral subsection, the second peripheral subsection, the first transition subsection, and the second transition subsection;

a crown side zone that is continuous with crown side contours of the toe peripheral transition subsection and the heel peripheral transition subsection; and

a sole side zone that is continuous with sole side contours of the toe peripheral transition subsection and the heel peripheral transition subsection,

the toe peripheral transition subsection has a wall thickness smaller than a wall thickness of the crown side zone, and

the heel peripheral transition subsection has a wall thickness smaller than the wall thickness of the crown side zone.

[Clause 7] The golf club head according to any one of clauses 1 to 6, wherein

the face portion further includes a third transition section that extends along a line inclined by either -70° to -20°, or 20° to 70° relative to a parallel axis, the parallel axis extending in a toe-heel direction and passing through the face center, and

the third transition section is located between the first peripheral subsection and/or the first transition subsection, and the second peripheral subsection and/or the second transition subsection.

[Clause 8] The golf club head according to any one of clauses 2 to 6, wherein
the second peripheral subsection has a width of greater than or equal to 1.0 mm and less than or equal to 7.0 mm, the width being measured in a direction perpendicular to a boundary line between the third peripheral section and the second peripheral subsection.

[Clause 9] The golf club head according to clause 7, wherein the third transition section has a width of greater than or equal to 1.0 mm and less than or equal to 7.0 mm.

[Clause 10] The golf club head according to any one of clauses 1 to 9, wherein a ratio of the surface area of the central section to an area of the striking face is greater than or equal to 5% and less than or equal to 15%.

[Clause 11] The golf club head according to any one of clauses 1 to 10, wherein

the first peripheral subsection includes a toe-side first peripheral subsection and a heel-side first peripheral subsection,

a ratio of a surface area of the toe-side first peripheral subsection to an area of the striking face is greater than or equal to 1% and less than or equal to 9%, and

a ratio of a surface area of the heel-side first peripheral subsection to the area of the striking face is greater than or equal to 1% and less than or equal to 9%.

[Clause 12] The golf club head according to any one of clauses 1 to 11, wherein

the second peripheral subsection includes a crown-side second peripheral subsection and a sole-side second peripheral subsection,

a ratio of a surface area of the crown-side second peripheral subsection to an area of the striking face is greater than or equal to 1% and less than or equal to 70, and

a ratio of a surface area of the sole-side second peripheral subsection to the area of the striking face is greater than or equal to 1% and less than or equal to 7%.

[Clause 13] The golf club head according to any one of clauses 1 to 12, wherein
a contour of the central section is shaped such that a length in a toe-heel direction is longer than a length in an up-down direction.

[Clause 14] The golf club head according to any one of clauses 1 to 13, wherein the central section uniform wall thickness of the central section is greater than or equal to 2.5 mm and less than or equal to 3.0 mm.

[Clause 15] The golf club head according to any one of clauses 1 to 14, wherein the first peripheral subsection uniform wall thickness of the first peripheral subsection is greater than or equal to 2.8 mm and less than or equal to 3.4 mm.

[Clause 16] The golf club head according to any one of clauses 1 to 15, wherein the second peripheral subsection uniform wall thickness of the second peripheral subsection is greater than or equal to 1.8 mm and less than or equal to 2.4 mm.

[Clause 17] The golf club head according to any one of clauses 2 to 6, wherein the third peripheral section has a wall thickness of greater than or equal to 2.1 mm and less than or equal to 3.3 mm.

[Clause 18] The golf club head according to any one of clauses 1 to 17, wherein

when a parallel axis that extends in a toe-heel direction and passes through the face center, and a perpendicular axis that extends in an up-down direction and passes through the face center are defined,

in the face portion, roll radii of upper and lower regions are smaller than a roll radius of an up-down directional center region,

the upper and lower regions collectively referring to: a region that extends toward an upper side from a position spaced 7.5 mm apart from the parallel axis toward the upper side; and a region that extends toward a lower side from a position spaced 7.5 mm apart from the parallel axis toward the lower side, and

the up-down directional center region referring to a region that extends from the position spaced 7.5 mm apart from the parallel axis toward the upper side to the position spaced 7.5 mm apart from the parallel axis toward the lower side, and

in the face portion, bulge radii of toe and heel regions are smaller than a bulge radius of a lateral center region,

the toe and heel regions collectively referring to: a region that extends toward a toe side from a position spaced 20.0 mm apart from the perpendicular axis toward the toe side; and a region that extends toward a heel side from a position spaced 20.0 mm apart from the perpendicular axis toward the heel side,

the lateral center region referring to a region that extends from the position spaced 20.0 mm apart from the perpendicular axis toward the toe side to the position spaced 20.0 mm apart from the perpendicular axis toward the heel side.

List of Reference Symbols

[0178] 

2

Golf club

4, 42, 43, 44, 50

Head

10

Face portion

10a

Striking face

12

Crown portion

12a

Crown front portion

14

Sole portion

20

Face main portion

22

Central section

24

Transition section

241

First transition subsection

24t

Toe-side first transition subsection

24h

Heel-side first transition subsection

242

Second transition subsection

24c

Crown-side second transition subsection

24s

Sole-side second transition subsection

26

Peripheral section

261

First peripheral subsection

26t

Toe-side first peripheral subsection

26h

Heel-side first peripheral subsection

262

Second peripheral subsection

26c

Crown-side second peripheral subsection

26s

Sole-side second peripheral subsection

28

Third peripheral section

28t

Toe-side third peripheral subsection

28h

Heel-side third peripheral subsection

28c

Crown-side third peripheral subsection

28s

Sole-side third peripheral subsection

29a

Peripheral transition subsection

29t

Toe peripheral transition subsection

29h

Heel peripheral transition subsection

29c

Crown side zone

29s

Sole side zone

30

Third transition section

301

Toe upper third transition section

302

Heel upper third transition section

303

Heel lower third transition section

304

Toe lower third transition section

Fc

Face center

F1

Up-down directional center region

F2

Upper region

F3

Lower region

F4

Upper and lower regions

G1

Lateral center region

G2

Toe side region

G3

Heel side region

G4

Toe and heel regions

k1

Contour edge of the striking face

SS

Sweet spot

[0179] The above descriptions are merely illustrative and various modifications can be made without departing from the principles of the present disclosure.

[0180] The terminology used in the description of the various described embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The use of the terms "a", "an", "the", and similar referents in the context of throughout this disclosure (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. As used throughout this disclosure, the word "may" is used in a permissive sense (i.e., meaning "having the potential to"), rather than the mandatory sense (i.e., meaning "must"). Similarly, as used throughout this disclosure, the terms "comprising," "having," "including," and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted.

Claims

1. A golf club head comprising a hollow interior inside thereof, wherein:

the golf club head includes a face portion including a striking face, a crown portion, and a sole portion,

the face portion includes a face main portion including a face center,

the face main portion includes a central section including the face center, a transition section located outside the central section, and a peripheral section located outside the transition section,

the peripheral section includes a first peripheral subsection located in a toe side part and a heel side part of the face main portion, and a second peripheral subsection located in a crown side part and a sole side part of the face main portion,

the transition section includes a first transition subsection located between the central section and the first peripheral subsection, and a second transition subsection located between the central section and the second peripheral subsection,

the central section has a central section uniform wall thickness and a surface area of greater than or equal to 100 mm²,

the first peripheral subsection has a first peripheral subsection uniform wall thickness, and the first peripheral subsection uniform wall thickness is greater than the central section uniform wall thickness,

the second peripheral subsection has a second peripheral subsection uniform wall thickness, and the second peripheral subsection uniform wall thickness is smaller than the central section uniform wall thickness,

the first transition subsection has a wall thickness that increases from the central section uniform wall thickness to the first peripheral subsection uniform wall thickness, and

the second transition subsection has a wall thickness that decreases from the central section uniform wall thickness to the second peripheral subsection uniform wall thickness.

2. The golf club head according to claim 1, wherein

the face portion further includes a third peripheral section located outside the face main portion,

the third peripheral section surrounds the face main portion either continuously or discontinuously, and

the third peripheral section has a wall thickness greater than the central section uniform wall thickness.

3. The golf club head according to claim 1, wherein

the face portion further includes a third peripheral section located outside the face main portion,

the third peripheral section surrounds the face main portion either continuously or discontinuously, and

the third peripheral section has a wall thickness smaller than the central section uniform wall thickness.

4. The golf club head according to claim 2 or 3, wherein
the third peripheral section surrounds the face main portion continuously.

5. The golf club head according to any one of claim 2 to 4, wherein

the third peripheral section includes:

a crown-side third peripheral subsection that is continuous with a crown side contour of at least one selected from the group consisting of the first peripheral subsection, the second peripheral subsection, the first transition subsection, and the second transition subsection; and

a sole-side third peripheral subsection that is continuous with a sole side contour of at least one selected from the group consisting of the first peripheral subsection, the second peripheral subsection, the first transition subsection, and the second transition subsection, and

the sole-side third peripheral subsection has a wall thickness smaller than a wall thickness of the crown-side third peripheral subsection.

6. The golf club head according to any one of claim 2 to 5, wherein

the third peripheral section includes:

a toe peripheral transition subsection that is continuous with a toe side contour of at least one selected from the group consisting of the first peripheral subsection, the second peripheral subsection, the first transition subsection, and the second transition subsection;

a heel peripheral transition subsection that is continuous with a heel side contour of at least one selected from the group consisting of the first peripheral subsection, the second peripheral subsection, the first transition subsection, and the second transition subsection;

a crown side zone that is continuous with crown side contours of the toe peripheral transition subsection and the heel peripheral transition subsection; and

a sole side zone that is continuous with sole side contours of the toe peripheral transition subsection and the heel peripheral transition subsection,

the toe peripheral transition subsection has a wall thickness smaller than a wall thickness of the crown side zone, and

the heel peripheral transition subsection has a wall thickness smaller than the wall thickness of the crown side zone.

7. The golf club head according to any one of claim 2 to 6, wherein

the face portion further includes a third transition section that extends along a line inclined by either -70° to -20°, or 20° to 70° relative to a parallel axis, the parallel axis extending in a toe-heel direction and passing through the face center, and

the third transition section is located between the first peripheral subsection and/or the first transition subsection, and the second peripheral subsection and/or the second transition subsection.

8. The golf club head according to any one of claim 2 to 6, wherein
the second peripheral subsection has a width of greater than or equal to 1.0 mm and less than or equal to 7.0 mm, the width being measured in a direction perpendicular to a boundary line between the third peripheral section and the second peripheral subsection.

9. The golf club head according to claim 7, wherein the third transition section has a width of greater than or equal to 1.0 mm and less than or equal to 7.0 mm.

10. The golf club head according to any one of claim 2 to 9, wherein a ratio of the surface area of the central section to an area of the striking face is greater than or equal to 5% and less than or equal to 15%.

11. The golf club head according to any one of claim 1 to 10, wherein

the first peripheral subsection includes a toe-side first peripheral subsection and a heel-side first peripheral subsection,

a ratio of a surface area of the toe-side first peripheral subsection to an area of the striking face is greater than or equal to 1% and less than or equal to 9%, and

a ratio of a surface area of the heel-side first peripheral subsection to the area of the striking face is greater than or equal to 1% and less than or equal to 9%.

12. The golf club head according to any one of claim 1 to 11, wherein

the second peripheral subsection includes a crown-side second peripheral subsection and a sole-side second peripheral subsection,

a ratio of a surface area of the crown-side second peripheral subsection to an area of the striking face is greater than or equal to 1% and less than or equal to 70, and

a ratio of a surface area of the sole-side second peripheral subsection to the area of the striking face is greater than or equal to 1% and less than or equal to 7%.

13. The golf club head according to any one of claim 1 to 12, wherein
a contour of the central section is shaped such that a length in a toe-heel direction is longer than a length in an up-down direction.

14. The golf club head according to any one of claim 1 to 13, wherein the central section uniform wall thickness of the central section is greater than or equal to 2.5 mm and less than or equal to 3.0 mm.

15. The golf club head according to any one of claim 1 to 15, wherein the first peripheral subsection uniform wall thickness of the first peripheral subsection is greater than or equal to 2.8 mm and less than or equal to 3.4 mm.

16. The golf club head according to claim 1, wherein the second peripheral subsection uniform wall thickness of the second peripheral subsection is greater than or equal to 1.8 mm and less than or equal to 2.4 mm.

17. The golf club head according to any one of claim 2 to 6, wherein the third peripheral section has a wall thickness of greater than or equal to 2.1 mm and less than or equal to 3.3 mm.

18. The golf club head according to any one of claim 1 to 17, wherein

when a parallel axis that extends in a toe-heel direction and passes through the face center, and a perpendicular axis that extends in an up-down direction and passes through the face center are defined,

in the face portion, roll radii of upper and lower regions are smaller than a roll radius of an up-down directional center region,

the upper and lower regions collectively referring to: a region that extends toward an upper side from a position spaced 7.5 mm apart from the parallel axis toward the upper side; and a region that extends toward a lower side from a position spaced 7.5 mm apart from the parallel axis toward the lower side, and

the up-down directional center region referring to a region that extends from the position spaced 7.5 mm apart from the parallel axis toward the upper side to the position spaced 7.5 mm apart from the parallel axis toward the lower side, and

in the face portion, bulge radii of toe and heel regions are smaller than a bulge radius of a lateral center region,

the toe and heel regions collectively referring to: a region that extends toward a toe side from a position spaced 20.0 mm apart from the perpendicular axis toward the toe side; and a region that extends toward a heel side from a position spaced 20.0 mm apart from the perpendicular axis toward the heel side,

the lateral center region referring to a region that extends from the position spaced 20.0 mm apart from the perpendicular axis toward the toe side to the position spaced 20.0 mm apart from the perpendicular axis toward the heel side.

Drawing