Flexible rotary cutting die

Abstract

 A rotary cutting die (10) includes a durable, flexible rotary die plate (14) having an inner surface and an outer surface. A cutting rule (12) that defines a cutting design is supported by the die plate. The cutting rule incluees a cutting edge (16) which extends above the outer surface of the die plate, and a support edge (20) disposed within the die plate. The support edge includes a plurality of keyhole shaped notches (22). Preferably, a plurality of S-shaped hooks (24) are connected to the key-hole notches, and serve to reinforce the rotary die plate and to support the cutting rule in the rotary die plate. The rotary die plate is preferably formed from a durable and flexible urethane-based material that exhibits a low shrink factor during curing or hardening.

Description

[0001] The invention generally relates to the field of rotary cutting dies used in rotary cutting machines, and more particularly, to an improved method and apparatus for making and using such dies.

[0002] Rotary cutting machines are widely used in such industries as the printing or converting industry to cut, score and perforate paper and other web-products such as plastic, cardboard, non-wovens and the like. In general, these rotary cutting machines have two cooperating cylinders, one of which carries a rotary cutting die having a knife or cutting rule, and the other cylinder that acts as an anvil against which the knife bears as the paper is cut. The cutting edge of the knife and the surface of the anvil cylinder normally rotate at the same speed and the paper is cut as the cutting edge of the knife moves into and out of engagement with the anvil surface.

[0003] Rotary cutting dies have been manufactured and used for numerous years. Conventionally, rotary cutting dies are formed from a rigid, epoxy-based material supporting a metallic cutting rule. The cutting rule extends above the surface of the rigid die plate and defines a cutting design. The design created by the metallic cutting rule is employed to cut, score or perforate material, such as paper, cardboard or the like, through the rotary cutting process.

[0004] Conventional rotary cutting dies are mounted on discrete sections of a rotary cutting machine die cylinder or along the entire surface thereof. To accommodate either type of die, the die cylinder typically contains a number of receiving holes spaced at predetermined intervals. The receiving holes are positioned in an array along the die cylinder, and are configured to receive screws or other fasteners that extend through or along the side of the rigid die plate so as to affix the cutting die to the die cylinder. Mounting holes are bored into the die plate to align with the receiving holes in the die cylinder. The rotary cutting die is thus aligned and positioned on the die cylinder to reflect the predetermined pattern for the cutting, scoring or perforating process.

[0005] Conventional rotary cutting dies must be sized to fit on the die cylinder. In particular, each rotary cutting die must be manufactured with a mounting radius that precisely matches the radius of the die cylinder on which the cutting die is to be mounted. Precise matching of the rotary die plate to the die cylinder is necessary to insure accurate cutting of the material by the cutting rule. Precise matching of these components is also necessary to eliminate excessive wear on the cutting rule. Imprecise or inaccurate matching may lead to premature wear due to fretting corrosion, and may even lead to breakage or failure of the rotary cutting die.

[0006] Manufacturing a rotary cutting die to precisely match the die cylinder can be difficult. For example, it may be difficult to accurately measure the radius of the die cylinder by conventional means. Moreover, conventional rotary cutting dies are typically manufactured from a molding process. Consequently, any deviance between the radius of the die cylinder and the radius of the manufacturing mold will necessarily lead to inaccuracies in the radius of the rotary cutting die.

[0007] Another reason for the difficulty in matching the rotary cutting die to the die cylinder is because the die plate of a conventional rotary cutting die is typically manufactured from a rigid; epoxy-based material. Epoxy-based materials tend to shrink during the curing process, thereby altering the radius or distorting the shape of the rotary die plate. Moreover, the amount and degree of shrinkage will very depending on the configuration or layout of the cutting rule. It is therefore nearly impossible to predict the shrinkage of the die plate with any precision. Shrinkage of the die plate material may also create internal stresses that may compromise the integrity of the rotary cutting die.

[0008] The use of a rigid, epoxy based material for the die plates of conventional rotary cutting dies results in a number of additional problems. For example, if the radius of the rotary cutting die does not precisely match the radius of the die cylinder, then the die plate must be "flexed" to fit onto the die cylinder. In other words, the die plate must be "flexed" or bent so as to eliminate any gaps between the die plate and the die cylinder. The rigidity of the epoxy-based material, however, will prevent any appreciable "flexing" of the die plate. If the die plate cannot be "flexed" sufficiently to fit onto the die cylinder, then the rotary cutting die is typically discarded. On the other hand, even if the die plate can be "flexed" sufficiently to fit onto the die cylinder, the rotary cutting die will tend to wear faster and have a shorter life span.

[0009] In the event that the rigid die plate is "flexed" to fit onto the die cylinder, additional mounting fasteners or clamps will usually be required to secure and hold the die plate tightly against the die cylinder. These additional mounting fasteners will necessarily require the installation of additional receiving holes in the die cylinder.

[0010] "Flexing" of the die plate to fit the die cylinder may also cause adverse stresses in the die plate. These adverse stresses may lead to premature wearing or failure of the rotary cutting die. Moreover, a failure of the rotary cutting die can create a dangerous situation. This is because the rigid die plate of a conventional rotary cutting die can shatter, thereby propelling shattered pieces of the die plate and the cutting rule outwardly from the die cylinder.

[0011] Accordingly, it would be desirable to have a cutting die that overcomes the disadvantages and limitations described above.

[0012] In view of the above, the present invention provides a unique rotary cutting die that overcomes the disadvantages and limitations described above. In particular, the rotary cutting die of the present invention includes a durable, flexible rotary die plate having an inner surface and an outer surface. The die plate supports a cutting rule that defines a cutting design. The cutting rule includes a cutting edge, which extends above the outer surface of the die plate, and a support edge disposed within the die plate. The support edge includes a plurality of keyhole shaped notches. Preferably, a plurality of S-shaped hooks are connected to the key-hole notches, and serve to reinforce the rotary die plate and to support the cutting rule in the rotary die plate.

[0013] The rotary die plate of the present invention is preferably formed from a durable and flexible urethane-based material that exhibits a low shrink factor during curing or hardening. The urethane-based material of the preferred embodiment, when cured, is more flexible than the rigid epoxy-based materials used for conventional rotary cutting dies. This flexibility allows the die plate to be flexed or deformed as necessary to fit onto the surface of the die cylinder, thereby eliminating the need to manufacture the die plate with a radius precisely matching the radius of the die cylinder. This flexibility likewise permits a single die plate to be mounted onto die cylinders of different radiuses.

[0014] The urethane-based material of the preferred embodiment also improves the distribution of adverse stresses that are often incurred by the cutting rule during jam-ups. The flexibility of the die plate permits the cutting rule to flex slightly during such jam-ups, dissipating the adverse stresses throughout the die plate. The flexible die plate is also less likely to shatter during jam-ups.

[0015] The preferred embodiment of the invention includes features in addition to those listed above. Moreover, the advantages over the current art discussed above are directly applicable to the preferred embodiment. but are not exclusive. The other features and advantages of the present invention will be further understood and appreciated when considered in relation to the detailed description of the preferred embodiment which now follows with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a rotary cutting die of the invention having a cutting rule supported therein;

FIG. 2 is a side view of the rotary cutting die shown in FIG.1;

FIG. 3 is a side view of the cutting rule shown in FIGS. 1 and 2, including an end view thereof;

FIG. 4 is a front plan view of a rotary cutting machine including the rotary cutting die shown in FIGS. 1 and 2 mounted thereon;

FIG. 5 is a perspective view of the transfer plate material disposed along a cutting cylinder;

FIG. 6 is a side view of the transfer plate showing the cutting rule positioned therein;

FIG. 7 is an elevational view of a three-roll curver for curving the cutting rule shown in FIGS. 1-3;

FIG. 8 is a partially exploded perspective view of a rotary cutting die mold; and

FIG. 9 is a side view of the rotary cutting die and transfer plate after being removed from the rotary cutting die mold shown in FIG. 8.

[0016] Referring now to the drawings, FIGS. 1 and 2 show the preferred embodiment of the rotary cutting die 10 of the present invention. The rotary cutting die 10 includes a cutting rule 12 supported in a flexible rotary die plate 14. The cutting rule 12 has a cutting edge 16, which extends above the outer surface 18 of the rotary die plate 14, and a support edge 20 disposed within the rotary die plate 14. The cutting rule 12 forms a predetermined cutting design 21 on the rotary cutting die 10.

[0017] The cutting edge 16 of the cutting rule 12 is preferably sharp to enable it to cut, score or perforate the design 21 into a given cutting material (not shown). Preferably, the cutting edge 16 extends approximately 1/8 inch above the outer surface 18 of the rotary die plate 14. However, as those skilled in the art will appreciate, the cutting edge 16 can extend to any distance dictated by a specific application without departing from the spirit and scope of the invention.

[0018] As best shown in FIG. 3, the support edge 20 preferably includes a plurality of notches 22. As shown in FIGS. 1 and 2, the notches 22 are connected to a plurality of interlocking connectors 24 disposed throughout the rotary die plate 14. The interlocking connectors 24 serve both to reinforce the rotary die plate 14 and to secure the cutting rule 12 in the rotary die plate 14. Preferably, the notches 22 are keyhole shaped notches and the interlocking connectors 24 are S-shaped hooks. As those skilled in the art will appreciate, other shapes for the notches 22 and the interlocking connectors 24 can be employed and are contemplated. For example, the notches 22 can comprise circular holes through the cutting rule 12, and the interlocking connectors 24 can comprise metal pins or screws inserted through the circular holes.

[0019] The rotary die plate 14, as best shown in FIGS. 1 and 2, may be formed of any suitable material and to any suitable thickness to obtain the desired flexibility and durability. Preferably, the rotary die plate 14 is formed of a urethane-based material that exhibits a low shrink factor upon hardening. The low shrink factor is desired to ensure that the design 21 formed by the cutting rule 12 is not skewed when the die plate 14 is formed, and to ensure that the required shape of the die plate 14 is retained. The rotary die plate 14 preferably has a thickness of between 1/4 to 7/16 inches, although other thicknesses dictated by particular uses for the rotary cutting die 10 are contemplated. For example, rotary die plates 14 having a thickness in the range of 3/16 to 5/8 inches have been used with satisfactory results. A preferred urethane-based material is distributed by Ciba Geigy Corp., located in East Lansing, Michigan, and is referred to as RP 6444R/TDT 178-87H Polyurea Elastomer. This particular material is a wear resistant, semi-rigid, black, two component polyurea elastomer having a hardness of approximately 60 ± 5 (Shore D). An alternative urethane-based material that can be used for the rotary die plate 14 is referred to as TDT 178-88R/RP 6444H Polyurea Elastomer. This alternative material has properties similar to the preferred material, but is red in color. Of course, any material, and particularly urethane-based materials, having the required properties can be used for the rotary die plate 14.

[0020] The urethane-based material of the preferred embodiment can also be altered with additives, dyes or color pastes to change the color of the rotary die plate 14. Changing the color of the material may be advantageous for a number of reasons, such as increasing the visibility of the rotary cutting die 10 on the die cylinder 26, or of the cutting rule 12 on the die plate 14. Since the die cylinder 26 is typically rotated at a high rate of speed, increasing the visibility of these components could enhance the safety to the operator. For example, manufacturing the rotary die plate 14 from a urethane-based material that has been dyed a light color such as white, yellow or red would improve the operators ability to see the contrasting dark colored cutting rule 12, even when the die cylinder 26 is rotating. Different colorings could likewise improve the operator's ability to inspect the rotary cutting die 10 for wear or damage.

[0021] The urethane-based material of the preferred embodiment, when cured, is more flexible than the rigid epoxy-based materials used for conventional rotary cutting dies. The flexibility of the urethane-based material allows the die plate 14 to be flexed or deformed as necessary to fit onto the surface of the die cylinder 26. This eliminates the need to manufacture the die plate 14 with a radius precisely matching the radius of the die cylinder 26, thereby reducing manufacturing costs. Moreover, a single die plate 14 can be flexed to fit onto die cylinders 26 of different radiuses. This eliminates the need to manufacture individual rotary cutting dies 10 for each individual die cylinder 26.

[0022] The urethane-based material of the preferred embodiment permits the manufacture of a thinner rotary die plate 14 than the conventional epoxy-based die plate. The urethane-based material therefore allows a more free flowing injection molding process with fewer, if any, air voids in the finished product.

[0023] The rotary cutting die 10 of the present invention is also a more durable and safer product. In particular, a die plate 14 manufactured from the urethane-based material of the preferred embodiment will distribute any adverse stresses that may be incurred by the cutting rule 12. Such adverse stresses often occur during a jam-up, which typically places transverse loads on the cutting rule 12. With a conventional rotary cutting die, these loads are transferred directly to the die plate, occasionally causing the die plate to shatter. The die plate 14 of the preferred embodiment, however, has sufficient flexibility to permit the cutting rule 12 to flex slightly, thereby alleviating most of the adverse stresses. Moreover, the flexibility of die plate 14 of the preferred embodiment makes the die plate 14 unlikely to shatter during such a jam-up, thereby reducing or eliminating potentially dangerous situations. Of course, the urethane-based material of the preferred embodiment must have sufficient stiffness so that the cutting rule 12 is supported and securely held in position by the die plate 14.

[0024] Referring now to FIG. 4, the rotary cutting die 10 is preferably sized for use on a discrete section of a die cylinder 26 of a rotary cutting machine 28. Alternately, however, the rotary cutting die 10 may be sized to cover all, or a substantial portion, of the die cylinder 26, and numerous individual rotary cutting dies may be mounted on the die cylinder 26. To properly fit on the die cylinder 26, the radius of curvature of the rotary cutting die 10 should approximate that of the die cylinder 26. However, and as discussed above, the urethane-based material of the preferred embodiment permits some disparity between the radius of the rotary cutting die 10 and the die cylinder 26.

[0025] The preferred die cylinder 26 contains a plurality of receiving holes 30 positioned in a uniform matrix or array about its outer surface, as shown in FIG. 4. The rotary die 10 is mounted on the die cylinder 26 by means of a plurality of fasteners 32 disposed through mounting holes 34 located in the rotary die plate 14 of the die 10. The fasteners 32 are secured within the receiving holes 30 in the die cylinder 26 to mount the rotary die plate 14 of the rotary die 10 to the die cylinder 26. Any suitable form of fastener may be utilized to secure the rotary die 10 on the die cylinder 26. In one preferred embodiment of the invention, the fasteners 32 comprise screws, or the like, that turn into the preferably threaded receiving holes 30 in the die cylinder 26.

[0026] As shown in FIG. 4, the rotary cutting machine 28 also includes an opposing cylinder 36 positioned parallel to and in opposite rotary relationship with the die cylinder 26. When the rotary cutting machine 28 is in operation, the opposing cylinder 36 rotates counter to the die cylinder 26. During operation of the rotary cutting machine 28, cutting material, such as paper, cardboard, plastic, polyethylene, non-wovens or paperboard, is fed between the die cylinder 26 and the opposing cylinder 36. The cutting rule 12 in the rotary die plate 14, which is mounted on the die cylinder 26, and the opposing cylinder 36 cooperate to cut, score or perforate the cutting material in the pattern of the cutting design 21.

[0027] A method for forming the rotary cutting die 10 of the present invention is described below. As shown in FIGS. 5 and 6, a curved cutting rule transfer plate 38, preferably formed of phenolic material 56 and having an inner surface 40 and an outer surface 42, is provided. The phenolic material 56 from which the transfer plate 38 is formed is fixedly secured to a cutting cylinder 54 having approximately the same radius of curvature as the die cylinder 26 on the rotary cutting machine 28. Preferably, the phenolic material 56 is fastened to the cutting cylinder 54 by screws 58 or the like. Alternately, the phenolic material 56 may be adhered to the cutting cylinder 54 by the use of glue or spray mount.

[0028] A Computer Numeric Controlled (CNC) machine (not shown), which is operatively associated with the cutting cylinder 54 supporting the phenolic transfer plate material 56, cuts the phenolic material 56 to form the transfer plate 38, in a manner generally known in the art. In addition, the CNC machine forms a cutting rule channel 44 in the transfer plate 38 in the pattern of the cutting design 21.

[0029] As shown in FIG. 7, a three-roll curver 46 is use to bend and shape the cutting rule 12 into the cutting design 21 cut into the transfer plate 38. Because the transfer plate 38, and the resulting rotary die plate 14, are curved, the cutting rule 12 must be curved to the same radius of curvature.

[0030] Referring back to FIGS. 5 and 6, after the cutting rule 12 is curved in the three-roll curver 46, the cutting edge 16 of the cutting rule 12 is inserted into the inner surface 40 of the transfer plate 38, through the cutting rule channel 44, until the cutting edge 16 is substantially flush with the outer surface 42 of the transfer plate 38. At this point, the support edge 20 of the cutting rule 12 is exposed and extends beyond the inner surface 40 of the transfer plate 38.

[0031] As shown in FIG. 8, the curved transfer plate 38 is placed in the rotary cutting die mold 50 with its inner surface 40, and the support edge 20 of the cutting rule 12, exposed. The interlocking connectors 24 are connected to or through the notches 22 present in the support edge 20, as described above. Consequently, the interlocking connectors 24 are also exposed, as shown in FIG. 8.

[0032] After the mold cylinder 52 is lowered onto the inner surface 40 of the transfer plate 38 and the mold 50 is sealed, a urethane-based die plate material (preferably having a low shrink factor) is injected into the mold 50 at ambient temperature. The urethane-based material is cured at an elevated temperature until the urethane hardens and forms the durable, flexible rotary die plate 14 on the inner surface 40 of the transfer plate 38. Preferably, the die plate material is cured at 180°F, although it is contemplated that various other curing temperatures could be used depending on the particular urethane-based material and the specific application.

[0033] As shown in FIGS. 8 and 9, subsequent to the rotary die plate 14 being formed, the mold cylinder 52 is raised, and the rotary die plate 14 and the transfer plate 38 are removed from the mold 50. The transfer plate 38 is then physically removed from the rotary die plate 14, and the resultant rotary cutting die 10 is formed. The rotary cutting die 10 may now be mounted to the die cylinder 26 for use on the rotary cutting machine 28. As can be readily seen, it is contemplated that numerous individual rotary cutting dies may be mounted on a single die cylinder.

[0034] It should be appreciated that the present invention may be performed or configured as appropriate for the application. The embodiments described above are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is indicated by the claims rather than by the foregoing description. All changes, which come within the meaning and range of equivalency of the claims, are to be embraced within their scope.

Claims

1. A rotary cutting die comprising:

a urethane-base flexible rotary die plate comprising an inner surface and an outer surface, the rotary die plate being sized for use on a discrete section of a rotary cutting machine die cylinder;

a cutting rule defining a predetermined design and comprising a cutting edge and a support edge, the cutting edge extending above the outer surface of the rotary die plate, the support edge comprising a plurality of notches; and

a plurality of interlocking connectors connected through the notches in the cutting rule, the interlocking connectors operable to reinforce the rotary die plate and to secure the cutting rule in the rotary die plate.

2. A rotary cutting die as claimed in Claim 1, wherein the urethane-based flexible rotary die plate comprises a polyurea elastomer having a hardness of 60 ± 5 (Shore D).

3. A rotary cutting die as claimed in Claim 1 or Claim 2, wherein the urethane-based flexible rotary die plate plate comprises a thickness in the range of 3/16 to 5/8 inches thick.

4. A rotary cutting die as claimed in Claim 1 or claim 2, wherein the urethane-based flexible rotary die plate comprises a thickness in the range of 1/4 to 7/16 inches thick.

5. A rotary cutting die as claimed in any one of claims 1 to 4, wherein the urethane-based flexiblerotary die plate comprises a first colour and the cutting rule comprises a second colour, said first colour contrasting with said second colour.

6. A rotary cutting die of any of claims 1 to 5, wherein the urethane-based flexible rotary die plate comprises a yellow colour.

7. A rotary cutting die of any of claims 1 to 6, wherein the plurality of notches comprise circular holes through the cutting rule.

8. A rotary cutting die of any of claims 1 to 7, wherein the plurality of interlocking connectors comprise metal fasteners positioned through the circular holes in the cutting rule.

9. A rotary cutting die of Claim 8, wherein the plurality of interlocking connectors comprise metal S-hooks positioned through the circular holes in the cutting rule.

10. A rotary cutting die comprising:

a urethane-based flexible rotary die plate comprising a polyurea elastomer having a hardness of 60 ± 5 (Shore D), the rotary die plate further comprising an inner surface, an outer surface and being sized for use on a discrete section of a rotary cutting machine die cylinder;

a cutting rule defining a predetermined design and comprising a cutting edge and a support edge, the cutting edge extending above the outer surface of the rotary die plate and the support edge being disposed within the rotary die plate, the support edge comprising a plurality of notches; and

a plurality of interlocking connectors connected through the notches in the cutting rule, the interlocking connectors operable to reinforce the rotary die plate and to secure the cutting rule in the rotary die plate.

11. A rotary cutting die of Claim 10, wherein the urethane-based flexible rotary die plate comprises a thickness in the range of 3/16 to 5/8 inches thick.

12. A rotary cutting die of Claim 10 or Claim 11, wherein the urethane-based flexible rotary die plate comprises a yellow colour.

13. A rotary cutting die comprising:

a urethane-based flexible rotary die plate comprising a polyurea elastomer having a hardness of 60 ± 5 (Shore D), said flexible rotary die plate further comprising an inner surface, an outer surface and a thickness, said thickness being in the range of 1/4 to 7/16 inches thick, said flexible rotary die plate being sized for use on a discrete section of a rotary cutting machine die cylinder;

a cutting rule defining a predetermined design and comprising a cutting edge and a support edge, the cutting edge extending above the outer surface of the flexible rotary die plate and the support edge being disposed within the flexible rotary die plate, the cutting rule comprising a plurality of openings near the support edge of said cutting rule; and

a plurality of interlocking connectors connected through the openings in the cutting rule, the interlocking connectors operable to reinforce the flexible rotary die plate and to secure the cutting rule in the flexible rotary die plate.

14. A rotary cutting die of Claim 13, wherein the urethane-based flexible rotary die plate comprises a yellow colour.

Drawing