Shoe lift construction

Abstract

 This disclosure comprises a replaceable lift 3 for attachment to the heel of a shoe. The lift is molded from two resin layers, an upper layer and lower layer, and one of these two resin layers is preferably molded from a hard resin, and the other layer is preferably molded from a relatively soft resin. Furthermore, connecting holes are formed in one of the layers and connecting projections are formed in the other layer in order to form the upper and lower resin layers into a single piece. For example, a nylon resin layer is used for the upper layer and a urethane resin layer is used for the lower layer.

Description

[0001] This invention relates to a lift or sole construction for a shoe, in which the lift attached to the bottom of the heel of either a man's shoe or woman's shoe is molded into a single piece from two resin layers and which displays excellent advantages with regard to both health and wearing comfort.

[0002] Accompanying the trends of recent years toward more diversified consumer needs and greater health awareness, there have also been changes made in the constructions used for shoe heels. The lifts or soles attached to the bottom of shoe heels have always been easily subject to wear, and the replaceability of those lifts has been an important problem. Iron ring lifts, hard rubber, and other constructions were originally used for the lifts on women's shoes, but there were problems with such matters as wear resistance, and recently the most common material used for lifts has come to be urethane resin, which features excellent wear resistance. However, the change to this material did not eliminate the need for replaceability. Especially on high-heeled shoes, the largest proportion of the weight of the wearer is exerted upon the lifts attached to the bottom of the heel, and because of the small surface area, these lifts are subject to severe wear and thus require replacement frequently. In the past, because it has been difficult to replace lifts other than at a shop specializing in shoe repair, the result was a shortening of the life of the product. For this reason, heel devices have been proposed for which it is possible for the lift to be replaced relatively easily without requiring any special skill, such as that described in laid open in Japanese Utility Model Publication Sho. 63-4407.

[0003] Incidentally, even if the lifts of the prior art differ as to whether or not replacement is easy, the entire lift is still molded into a solid piece from urethane resin or a similar substance.

[0004] The following problems occurred as a result of the lifts of the prior art being molded into a solid piece from a single layer of resin:

(1) If the lift was molded into a solid piece from hard urethane resin, the impact shock from walking on a hard floor surface would reverberate to the head of the wearer, thus presenting problems with regard to both health and wearing comfort.

(2) In addition, the lifts were often colored black (colored with carbon black) in order to present a slim appearance from a design aspect, and this could result in marks being made on the floor surface while walking.

(3) Furthermore, If the entire lift was molded into a solid piece from soft resin in consideration of the health aspect, the manner in which the weight of the wearer was applied while walking could cause the lift to tilt sideways, thus presenting the danger of the wearer twisting an ankle.

[0005] In consideration of the factors described above, it is a general object of this invention is to provide a lift construction which increases the product value of the shoe, by molding a replaceable lift into a single piece from two resin layers, upper and lower, and, moreover, by selecting resins having properties which are suitably matched to the various needs.

[0006] A shoe lift constructed in accordance with this invention comprises a replaceable lift attached to the bottom of the heel of the shoe. The lift is molded from two resin layers, upper and lower, and, in addition to one of these two resin layers being molded from a hard resin and the other being molded from a relatively soft resin, in order to mold the upper and lower resin layers into a single piece, connecting holes are formed in one of the layers and connecting projections are formed in the other layer. In addition, in this composition, the upper layer is a nylon resin layer and the lower layer is a urethane resin layer.

[0007] With the composition described above, by molding the lift into two layers, upper and lower, it is possible to mold the upper and lower layers from resin layers having properties which are suitably matched to the various needs. In other words, if one of the upper and lower layers is molded from a hard resin layer and the other from a relatively soft resin layer, the shock-absorbing action of the soft resin layer prevents the impact force from the floor from reverberating to the head of the wearer, thus both improving the health aspect and also providing good wearing comfort. In addition, the hard resin layer makes it possible to ensure sufficient rigidity for the entire lift, thus eliminating the danger of the wearer twisting an ankle as a result of the manner in which the weight of the wearer is applied while walking which might cause the lift to tilt sideways. Furthermore, it is possible to select different coloring for the upper and lower layers, and in particular, if the lower layer is a urethane resin layer, a bright, natural color can be easily used, thus making it possible to prevent marking of a floor surface.

[0008] The following is a description of an embodiment of the invention, given with reference to the figures of the accompanying drawings, wherein:

Fig. 1 is a perspective view of the heel part of a shoe incorporating the present invention;

Fig. 2 is an enlarged side view of the heel part with some parts in section;

Fig. 3 shows four diagrams (a), (b), (c) and (d) in schematic form, of steps in molding a shoe lift;

Figs. 4(a) and 4(b) are a plan view and a perspective view of the lower layer of the lift showing an example of the connecting projections;

Figs. 5(a) through 5(c) are plan views of the lower layer of the lift showing various styles of connecting projections; and

Figs. 6(a) and 6(b) show additional embodiments of the lift construction.

[0009] Although the shoe in the embodiment shown in Figs. 1 and 2 is a type of a woman's shoe, the invention is also equally applicable to a man's shoe. The shoe comprises a shoe body 1, a heel body 2 made of, in this specific example, rigid plastic which projects from the bottom rear of the shoe body 1, and a two-layer molded lift 3 which is attached to the bottom of this heel body 2 and which will be described later. The heel body 2 may also be molded into two separate layers, upper and lower.

[0010] The heel body 2 described above is attached as a continuous single piece to the bottom of the shoe body 1, and a wedge-shaped notch 4 (see Fig. 2) which tapers in the inward and downward direction is formed at the bottom of the heel body 2. In addition, an insertion hole 5 is formed in the center part of the bottom of the heel body 2. The hole 5 is substantially perpendicular to the bottom surface 2a of the body 2. A metal mounting fixture 6 which projects upwardly from the top of the horseshoe-shaped lift 3 extends into this insertion hole 5, so that, as shown in Fig. 2, the heel body 2 and the lift 3 are connected together as a single piece. The mounting fixture 6 has a head or flange 6a at its bottom, and this flange 6a is embedded into the lift 3 so that the mounting fixture is secured to the lift 3 as a single piece. In addition, multiple vertical grooves are formed into the circumference of a shank or insertion part 6b of the mounting fixture 6 for the purpose of increasing the adhesion and also preventing the lift 3 from turning. The hole 5 and the insertion part 6b have mating cross-sectional shapes and the part 6b is sized to fit tightly in the hole 5. The notch 4 is used when removing a worn lift 3 from the heel body 2 in order to replace it. In other words, by inserting the tip of a screwdriver or similar tool D into the notch 4 as indicated by the imaginary lines in Fig. 2, the lift 3 can be pried loose and removed from the heel body 2 by the principle of leverage. It should be noted that, because the notch 4 is provided on the inward-facing side of the bottom of the heel body 2, even if, for example, there is no outer covering (wrapping) around the heel, it is not especially visible from the outside, and thus there is no impairment to the appearance of the shoe.

[0011] The following is a detailed explanation of the lift construction of this invention.

[0012] As shown in Fig. 2, the lift 3 is molded from two resin layers, an upper layer 3A and a lower layer 3B. In other words, the lift 3 is not a solid piece made entirely of a single resin, as in the prior art, but is comprised of two resin layers, the upper layer 3A and the lower layer 3B, which divide it vertically into two approximately equal halves. For example, of the upper and lower layers, one layer is molded from hard nylon resin, and the other layer is molded from relatively softer urethane resin. Rather than using two different resins for the upper and lower layers, it is also possible to mold both the upper and the lower layers from the same resin, for example, urethane. If different resins are used for the upper and lower layers, it becomes easy to provide each layer with the mechanical properties which meet the corresponding needs required of that layer. Of course, even if both layers are molded from the same resin, it is also possible to allot different hardnesses or other properties to the upper and lower layers. The reason why a relatively soft resin layer is used for one of the two layers is that, by providing that layer with a shock-absorbing function, the impact shock generated while walking on a hard surface does not reverberate to the head of the wearer, thus improving the health aspect, wearing comfort, etc.

[0013] In addition, the reason for specifically using a urethane resin layer for the lower layer 3B is that, because the black coloring (colored with carbon black) used in order to present a slim appearance could result in marks being made on the floor surface while walking, this is prevented by allotting urethane resin for the lower layer and utilizing its bright, natural color.

[0014] Furthermore, the reason for composing either the upper layer or the lower layer from a hard resin is that, if the upper layer 3A and the lower layer 3B were both molded into a single piece from the same soft resin, the entire lift 3 would lack rigidity, and the manner in which the weight of the wearer is applied while walking could cause the lift to tilt sideways, thus presenting the danger that the wearer may twist an ankle; however, by composing a layer which comprises one-half of the lift from a hard resin layer, it is possible to provide the rigidity required for the entire lift, thus eliminating such danger.

[0015] By molding the lift into two layers, upper and lower, in this way, it becomes possible to appropriately select resins having properties which are suitably matched to the various needs and to allot them to the upper and lower layers, and, in particular, because it is possible to mold the two layers from different resins, it thus becomes possible to achieve a lift which has multiple composite functions.

[0016] The upper and lower resin layers which comprise the lift construction of this invention are not connected together into one piece by adhesive, but are composed so as to form a single piece by a male-female dovetail type of connection in the molding stage, as will be described later. In other words, as shown in Fig. 2, multiple connecting projections 3b are formed so that they project from the top of the resin layer of the lower layer 3B and fit into connecting holes 3a formed in the resin layer of the upper layer 3A in order to connect the two layers together into one piece. The reason for using this type of connection is that, although connection by adhesive might be considered in order to utilize the good adhesion of the two layers if urethane resin layers are used for both the upper and lower layers, if this method were used, adhesive material could protrude from the adhesion surfaces, thus impairing the external appearance. In addition, another reason is to make it possible to also use nylon resins or the like having poor adhesion properties as one of the resins which compose the material of the lift.

[0017] With the lift construction of this invention as described above, it is possible to manufacture it by injection molding. The following is a description of the lift molding method based on the schematic diagrams shown in Fig. 3.

[0018] In step (a) of Fig. 3, the mounting fixture 6 described earlier is first placed and secured in the prescribed location in a die (female die) 7 having projections 7a of trapezoidal cross-sections inside it. A male die or cover 8 is set in place on the die 7, forming a cavity 3A' which forms the upper layer of the lift inside the dies. Then, after the dies 7 and 8 are secured, the prescribed molten resin (for example, urethane resin) is injected in through an injection port 8a. The flange 6a is exposed on its top and bottom sides. When this resin is injected, the molten resin also flows into the space between the flange 6a of the mounting fixture 6 and the die 7, thus embedding and securing the mounting fixture 6 in the resin.

[0019] After the resin has been injected and solidified, the dies are opened and a molded piece which corresponds to the upper layer of the lift plus the fixture 6 is released from the dies.

[0020] Due to the trapezoidal shape of the projections 7a, parts of this molded piece are thus formed into trapezoidal cavities 3a having a reverse taper, i.e. the connecting holes 3a.

[0021] In step (b), the molded piece which corresponds to the upper layer 3A of the lift is then placed inside a different female die 9 and a cover die 8 is placed in position in the same way as just described, as shown in step (c).

[0022] With reference to step (c), the inside of this die is formed with a cavity 3B' for the purpose of molding the lower layer 3B of the lift. The layer 3A is placed on a flat bottom surface 9a of the cavity 3B', and the shank of the mounting fixture 6 extends downwardly into a hole 9b in the die 9 at the bottom of the cavity 3B'. The side walls 9C of the cavity 3B' fit snugly against the outer sides of the layer 3A. After the dies 8 and 9 are secured, molten resin (for example, nylon resin) is injected in through the injection port 8a. This nylon resin also fills the connecting holes 3a having a trapezoidal cross-section with a reverse taper which were formed in the resin of the upper layer 3A. After the injected resin solidifies, the dies are opened, the molded piece is released and removed from the dies, and thus the molded lift of this invention shown in step (d) is obtained.

[0023] Because the connecting holes 3a mentioned above are formed with a reverse-taper trapezoidal cross-section, when they become filled by the lower layer resin, reverse-taper connecting projections 3b are formed. Thus a dovetail type of connection between the layers is formed, thereby forming or connecting the resin layer of the lower layer 3B into essentially one piece with the resin layer of the upper layer 3A in such a manner that it is almost impossible for them to become separated. In this lift construction, the connecting holes 3a are formed as through holes in order to make it possible to open the dies. For the shape or positioning of the connecting projections 3b which fit into the connecting holes 3a, for example, as shown in Fig. 4, conically shaped or mushroom-shaped connecting projections 3b are formed on the surface of the horseshoe-shaped lower layer 3B in approximately three or four locations according to the amount of surface area. In addition, as shown in Fig. 5, avoiding the space occupied by the flange 6a of the mounting fixture 6, it is also possible to form a continuous U-shaped connecting projection 3b (Fig. 5(a)) or to form two longitudinal or lateral elongated connecting projections 3b (Figs. 5(b) and 5(c)).

[0024] In Fig. 6, if insert dies are used in order to make it possible to open the dies, it then becomes possible to connect the lift into one piece without using through-holes for the connecting holes as is the case in the embodiment explained above. Fig. 6(a) shows an example of screwhead-shaped connecting projections 3b, and Fig. 6(b) shows an example of knob-shaped connecting projections 3b. In either case, in the same way as in the embodiment described above, the upper and lower layers are composed in such a manner that it is impossible for them to become separated.

[0025] A shoe lift according to this invention has numerous advantages as follows:

(1) By molding the lift in two layers, upper and lower, it is possible to select resin materials having properties which are suitably matched to the various needs and to allot them to the upper and lower layers. In other words, if one of the upper and lower layers is molded from a hard resin and the other layer from a relatively soft resin, it is possible to obtain a lift construction which has advantages with regard to both health and wearing comfort, with none of the impact shock from the floor reverberating to the head of the wearer, while at the same time ensuring sufficient rigidity for the entire lift.

(2) It is possible to use different coloring for the upper and lower layers, and, in particular, if the lower layer is molded from urethane resin and a bright, natural color is used, it is possible to prevent marking of the floor surface.

(3) Because it is possible to mold the two-layer lift construction of this invention into one piece as an injection-molded product, it is possible to obtain a lift having a beautiful finish and a high product value at a reasonable cost.

Claims

1. A shoe lift for a shoe having a heel, said lift comprising an upper resin layer and a lower resin layer, one of said resin layers comprising a hard resin and the other of said layers comprising a relatively soft resin, at least one connecting hole being formed in one of said layers and at least one connecting projection being formed on the other of said layers, said projection being anchored in said hole and thereby securing said layers together.

2. A shoe lift as described in Claim 1, wherein said layers comprise an upper layer and lower layer, said upper layer being molded from nylon resin and said lower layer being molded from urethane resin.

3. A shoe lift as described in Claim 1, wherein said projection and said hole form a dovetail connection.

4. A shoe lift as described in Claim 1, wherein one of said layers is a molded part and the other of said layers is molded on said part.

Drawing