Mold for golf ball and method of manufacturing golf ball

Abstract

To provide a mold that can reduce burr and reliably release gas during molding to outside and can produce a golf ball with a good surface state without decreasing the durability of the ball.SOLUTION: A vertically split mold for a golf ball includes: a spherical cavity; a plurality of support pins and pin holes therefor for disposing a core inside the spherical cavity; and a vent pin and a pin hole therefor. The pin holes for the support pins each include a clearance for releasing gas generated inside the spherical cavity to outside during injection molding. The vent pin is disposed on the inner side with respect to the position of the support pin provided outermost as seen from an edge of the spherical cavity. A minimum distance between the pin hole for the vent pin and the pin hole for the support pin is defined. A sum of a total area of the clearance between the vent pin and the pin hole therefor and a total area of the clearance between the support pin and the pin hole therefor is set within a particular range.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a golf ball mold and a method of manufacturing a golf ball that can be suitably used to mold a golf ball having a core covered with one or more cover layers, particularly the outermost layer of the cover, on whose surface numerous dimples are formed. [Background technology]

[0002] Golf balls are typically manufactured by injection molding or compression molding, but either method often results in defective products due to air remaining in the mold during molding, air entrapped in the molten resin, or gas generated by the resin.

[0003] When a golf ball is molded, gas is released from the molten resin, and if it is not properly released, it can cause a weld defect (a weld mark resembling a bird's foot forms on the surface of the golf ball, rendering it a defective product). It can also cause a defect known as "burn" due to adiabatic compression of the internal gas. For this reason, in the past, to prevent such defects, the gas release clearance (the gap between the pin and the hole) was widened to allow the gas to escape.

[0004] However, in this case, the large gas release clearance (the gap between the pin and its pin hole) creates relatively large burrs on the surface of the golf ball, necessitating the introduction of a full-scale burr removal process, which significantly increases manufacturing costs. In addition, in the above case, the durability of the ball (cracks) becomes poor and the ball is more likely to crack.

[0005] As prior art, the inventions disclosed in the following Patent Documents 1, 2, and 3 have been proposed, in which the shape and arrangement of support pins and vent pins have been improved for the purpose of venting gas. However, even the techniques described in these documents cannot be said to be capable of smoothly and reliably dissipating gas during molding to the outside, and to reliably and satisfactorily manufacture golf balls with good surface condition without reducing the durability of the ball. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-130670 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-212910 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-346 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above circumstances, and has as its object to provide a cavity (mold) for a golf ball that reduces the formation of burrs, allows gas to escape smoothly and reliably to the outside during molding, and ensures the production of golf balls with good surface condition without reducing the durability of the ball. [Means for solving the problem]

[0008] As a result of extensive research into achieving the above-mentioned object, the inventors discovered that, while injection molds for golf balls typically have support pins that hold the core (the contents of the golf ball) and pin holes in the cavity, by adding gas vent vent pins to increase the number of gas venting locations, it is possible to narrow the spacing (clearance) between the support pins and the pin holes in the vent pins, thereby solving the above-mentioned problems of the present invention, and have thus completed the present invention.

[0009] Accordingly, the present invention provides the following golf ball mold and golf ball manufacturing method. 1. A two-piece golf ball mold having a spherical cavity, a plurality of support pins and their pin holes for placing a core in the spherical cavity, and a vent pin and its pin hole, wherein the pin holes of the support pins have clearances for releasing gas generated in the spherical cavity during injection molding to the outside, and the vent pins are positioned inside the outermost support pins as viewed from the pole of the spherical cavity, and there is at least one vent pin with a shortest distance between the pin hole of the vent pin and the pin hole of the support pin of 0.20 mm or less, and the sum of the total area of ​​the clearance between the vent pin and its pin hole and the total area of ​​the clearance between the support pin and its pin hole is 1.00 mm. 2 A mold for a golf ball characterized by the above. 2. A golf ball mold according to claim 1, wherein the support pins are positioned so that the angle between the axis connecting the upper and lower poles of the mold and the normal line from the center of the axis toward the cavity wall from which the support pin exits is 15 to 30 degrees. 3. The golf ball mold according to 1 or 2 above, wherein the upper or lower mold has three or more support pins. 4. The mold for golf balls according to 1 or 2 above, wherein the upper or lower mold has three or more vent pins. 5. The golf ball mold according to claim 4, wherein at least one of the vent pins is disposed at a pole. 6. The golf ball mold according to 1 or 2 above, wherein the number of the vent pins is equal to or greater than the number of the support pins. 7. The golf ball mold according to 1 or 2 above, wherein the clearance between the support pin and its pin hole is 0.020 mm or less. 8. The golf ball mold according to 1 or 2 above, wherein the clearance between the vent pin and its pin hole is 0.020 mm or less. 9. The mold for a golf ball according to 1 or 2 above, wherein the support pin slides back and forth along the pin hole, while the vent pin does not slide. 10. A method for manufacturing a golf ball having a core and a single-layer or multi-layer cover, comprising the step of forming the outermost layer of the cover to a thickness of 1.5 mm or less using the golf ball mold described above. [Effects of the Invention]

[0010] The golf ball mold of the present invention and the method for manufacturing a golf ball using the mold can reduce the formation of burrs and allow gas to escape smoothly and reliably during molding, thereby reliably producing golf balls with good surface condition without reducing the durability of the ball. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic view showing a golf ball mold according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic view of the lower mold of the mold shown in FIG. 1 as viewed from directly above. [Figure 3] FIG. 10 is a schematic cross-sectional view showing the positions of support pins arranged in a mold. [Figure 4] FIG. 10 is a schematic diagram for explaining the distance between a support pin hole and a vent pin hole. [Figure 5] 1A and 1B are plan views showing examples of the shapes of support pins and vent pins, where FIG. 1A is a plan view showing a pin with a straight neck, and FIG. 1B is a plan view showing a pin with a tapered portion. [Figure 6] 1A and 1B are schematic diagrams showing an example of a mechanism in which all of the support pins and vent pins are slid, in which (A) is a schematic perspective view showing the mechanism and a mold body, and (B) is a schematic cross-sectional view of (A). [Figure 7] 10A and 10B are schematic diagrams showing another example of a mechanism in which all of the support pins and vent pins are slid, where FIG. 10A is a schematic perspective view showing the mechanism and the mold body, and FIG. 10B is a schematic cross-sectional view of FIG. 10A. [Figure 8]1A and 1B are schematic diagrams showing an example of a mechanism in which only the support pins slide and the vent pins are integrated and fixed, where (A) is a schematic perspective view showing the mechanism and the mold body, and (B) is a schematic cross-sectional view of (A). [Figure 9] 10A and 10B are schematic diagrams showing another example of a mechanism in which only the support pins slide and the vent pins are integrated and fixed, where (A) is a schematic perspective view showing the mechanism and the mold body, and (B) is a schematic cross-sectional view of (A). [Figure 10] FIG. 1A is a plan view of the mold (lower mold) of Example 1 as viewed from above, and FIG. 1B is a partially enlarged view showing the support pins and vent pins near the poles. [Figure 11] FIG. 1(A) is a plan view of the mold (lower mold) of Example 2 as viewed from above, and FIG. 1(B) is a partially enlarged view showing the support pins and vent pins near the poles. [Figure 12] FIG. 10(A) is a plan view of the mold (lower mold) of Example 3 as viewed from above, and FIG. 10(B) is a partially enlarged view showing the support pins and vent pins near the poles. [Figure 13] FIG. 1(A) is a plan view of the mold (lower mold) of Comparative Example 1 as viewed from above, and FIG. 1(B) is a partially enlarged view showing the support pins and vent pins near the poles. [Figure 14] FIG. 1A is a plan view of the mold (lower mold) of Comparative Example 2 as viewed from above, and FIG. 1B is a partially enlarged view showing the support pins and vent pins near the poles. [Figure 15] FIG. 1A is a plan view of the mold (lower mold) of Comparative Example 3 as viewed from above, and FIG. 1B is a partially enlarged view showing the support pins and vent pins near the poles. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in more detail below. The golf ball mold of the present invention has a spherical cavity, a gate for injecting a resin material for a cover into the spherical cavity, a vent pin for venting gas, and a support pin that is arranged so as to be able to advance and retreat in a direction perpendicular to the parting line of the mold. For example, Fig. 1 is a schematic diagram showing the state inside the mold before injection molding, showing an injection mold 10 equipped with a spherical cavity 1, a predetermined number of gates 2, a predetermined number of support pins 3, and a vent pin 4. The mold is used by injecting a molten resin material into the cavity through the gate 2 with a target sphere 20, such as an intermediate layer-coated sphere, supported by the support pins 3 within the spherical cavity 1.

[0013] Support pins, arranged to be retractable in a direction perpendicular to the mold parting line, are typically arranged at a predetermined interval along a circle drawn around the pole of the spherical cavity, preferably three or more (e.g., three at 120° intervals). The tip shape of the support pins may be circular or noncircular. Furthermore, because the tip surface of the support pin can form the inner wall surface of the cavity, the tip shape of the support pin may be convex to form a dimple, or may not form a dimple. The support pins are typically arranged to be retractable in their pin holes. As shown in FIG. 1 , when they enter the cavity, they hold the intermediate layer-coated sphere, fill the cavity with a cover resin material, and then retract to a position corresponding to the inner wall surface of the cavity. It is desirable to optimize the diameter and number of the support pins to suppress deformation of the intermediate layer-coated sphere set in the cavity during the process of filling the cavity with resin material and to stably position the core at the center of the cavity. The diameter of the tip of the support pin does not refer to the diameter of the cross section when the support pin is cut perpendicular to its axis, but refers to the diameter of the planar shape along the outline of the tip of the support pin.

[0014] The number of support pins on each side of the upper or lower mold is preferably 3 or more, more preferably 4 or more, and even more preferably 6 or more. The upper limit of this number is preferably 12 or less, more preferably 10 or less, and even more preferably 9 or less. If the number does not fall within the above range, it may be difficult to hold the intermediate layer-coated sphere at the center of the cavity, suppress deformation of the intermediate layer-coated sphere, and form the cover resin material to a uniform thickness throughout the space between the intermediate layer-coated sphere and the cavity wall.

[0015] As shown in Figure 3, the support pins 3 are preferably positioned so that the angle θ between the axis X connecting the upper and lower poles of the mold and the normal line from the center O on the axis toward the cavity wall 1a from which the support pins 3 exit is 15 to 30°. This angle is preferably 16° or more, and even more preferably 17° or more, with the upper limit being preferably 30° or less, more preferably 28° or less, and even more preferably 25° or less. If the angle does not fall within the above range, it may be difficult to hold the intermediate layer-coated sphere 20 at the center O of the cavity, suppress deformation of the intermediate layer-coated sphere 20, and form a cover resin material with a uniform thickness between the intermediate layer-coated sphere and the cavity.

[0016] The vent pin is arranged more inward (toward the pole) than the support pin with the largest angle θ among the support pins. It is preferable that the vent pin is arranged so that it is surrounded by multiple support pins. It is also preferable that at least one of the vent pins is arranged at the pole, i.e., a center pin is arranged. For example, FIG. 2 is a plan view of the lower mold of a mold, and six support pins 3 are arranged on the wall surface of a spherical cavity 1 at a predetermined distance around the pole, and five vent pins 4 are arranged inside these support pins 3 (toward the pole), with one vent pin (center pin) 4' being arranged at the pole.

[0017] The number of vent pins is not particularly limited, as long as one is provided in either the upper or lower mold, but it is preferable that there are three or more vent pins.More preferably, the number of vent pins is equal to or greater than the number of support pins.

[0018] The shape of the tip of the vent pin may be circular or non-circular, similar to the tip of the support pin. Furthermore, because the tip surface of the vent pin can form the inner wall surface of the cavity, the shape of the tip of the vent pin may be convex so as to form a dimple, or may not form a dimple.

[0019] It is desirable to narrow the clearance (the gap between the pin and the pin hole) of each of the support pins and the vent pins as much as possible. Specifically, as shown in Fig. 4, the gap (clearance) t between the support pin 3 and its pin hole 3a is preferably 0.020 mm or less, and more preferably 0.015 mm or less. Similarly, for the vent pin, the gap (clearance) t between the vent pin 4 and its pin hole 4a is preferably 0.020 mm or less, and more preferably 0.015 mm or less.

[0020] Furthermore, the distance between the support pin and the vent pin, i.e., the shortest distance between the pin holes of each pin (the shortest distance between the pin hole contours), must be narrow. Specifically, as shown in Figure 4, there must be at least one embodiment in which the shortest distance m between the pin hole 3a of the support pin and the pin hole 4a of the vent pin is 0.20 mm or less, preferably 0.15 mm or less. By making the shortest distance 0.2 mm or less, it becomes possible to efficiently exhaust generated gas to the outside of the mold.

[0021] Furthermore, the sum of the total area of ​​the clearance between the vent pin and its pin hole and the total area of ​​the clearance between the support pin and its pin hole is 1.00 mm 2 It is necessary that the thickness is equal to or greater than 1.05 mm, and preferably 1.05 mm. 2 If the total area of ​​the above clearances is 1.00 mm 2If the space is less than this, the absolute amount of space for discharging gas as a whole will be insufficient, causing gas to accumulate and increasing the occurrence of welds.

[0022] A plurality of gates are formed along the parting line of the mold. In the example shown in Fig. 2, six gates 2 are evenly spaced along the parting line PL. The gates 2 arranged along the parting line PL of the mold are preferably arranged at equal intervals around the parting line PL from the viewpoint of allowing the molten resin material to flow evenly into the spherical cavity 1 and form a cover of the desired thickness.

[0023] A composite plating film can be formed on the spherical cavity of the mold so as to cover the cavity surface. The base material (substrate) of the mold body is not particularly limited as long as it is a metal that can be plated, and for example, a mold formed from a common metal material such as carbon steel, beryllium-copper alloy, stainless steel, or copper can be used. Among these, it is preferable to use pre-hardened steel that has been heat-treated in advance. Pre-hardened steel has excellent workability and does not require subsequent heat treatment, so complex dimple shapes can be produced with high precision. The composite plating film is not particularly limited, and for example, a material in which fluororesin particles are dispersed in a nickel-based matrix can be used.

[0024] There are no particular restrictions on the materials for the support pins and vent pins, but for example, pre-hardened steel, stainless steel, and die steel can be mainly used.

[0025] The support pins can slide during injection molding, while the vent pins can be either sliding or fixed. Alternatively, the support pins and vent pins can be configured to slide together as a single unit.

[0026] The support pins and vent pins can both have a straight neck or a tapered shape where the neck thickness gradually changes to facilitate gas discharge. The center pin, which is placed at or near the pole of the golf ball during injection molding, is a type of vent pin. The center pin can also have a straight neck or a tapered shape.

[0027] For example, in Figure 5(A), the support pin (SP) 3, vent pin (VP) 4, and center pin (CP) 4' all have a straight neck shape without any tapered or other changes in shape. On the other hand, in Figure 5(B), in the support pin (SP) 3, the tip 30a of the support pin has a smaller outer diameter than the support pin body 30 due to the tapered portion 30b, and its shaft is long and protruding upward. In the vent pin (VP) 4, the tip 40a of the vent pin has a slightly smaller outer diameter than the vent pin body 40 due to the tapered portion 40b. In the center pin (CP) 4', the tip 41a of the center pin has a smaller outer diameter than the center pin body 41 due to the tapered portion 41b, and its shaft is slightly long and protruding upward.

[0028] 6 to 9 are schematic diagrams showing a specific example of a mechanism (configuration) in which support pins and vent pins having the above-mentioned shapes are combined and all pins are slidable, and a specific example of a mechanism (configuration) in which only the support pins are slidable while the vent pins are fixed.

[0029] Figure 6 shows a mechanism for sliding all of the support pins and vent pins, where (A) is a schematic perspective view showing the mechanism and the mold body, and (B) is a schematic cross-sectional view of (A). In Figure 6, all of the support pins 3 and vent pins 4 slide together through the operation of the support pin support body 30, the vent pin support body 40, and the center pin alone. Each of the support pins 3 and vent pins 4 has a tapered portion.

[0030] 7 shows a mechanism in which all of the support pins and vent pins slide, similar to that shown in FIG. 6, where (A) is a schematic perspective view showing the mechanism and the mold body, and (B) is a schematic cross-sectional view of (A). All of the support pins and vent pins slide together through the operation of the support pin support body 30, the vent pin support body 40, and the center pin alone. In FIG. 7, the support pins and vent pins do not have a tapered portion and have a straight neck shape.

[0031] Figure 8 shows a mechanism in which only the support pins slide, while the vent pins are integrated and fixed; (A) is a schematic perspective view showing the mechanism and the mold body, and (B) is a schematic cross-sectional view of (A). As shown in Figure 8(B), the vent pin mechanism is an integrated type in which multiple vent pins 4 are integrated on a vent pin support 40, which is fixed within the mold. The multiple support pins slide integrally due to the operation of the support pin support 30. In Figure 8, each of the support pins and vent pins has a tapered portion.

[0032] Similar to FIG. 8, FIG. 9 shows a mechanism in which only the support pins slide and the vent pins are integrated and fixed. (A) is a schematic perspective view showing the mechanism and the mold body, and (B) is a schematic cross-sectional view of (A). The vent pin mechanism is an integrated type in which multiple vent pins 4 are integrated on a vent pin support 40, which is fixed within the mold. Multiple support pins 3 slide integrally due to the movement of the support pin support. In FIG. 9, the support pins and vent pins do not have tapered portions and have a straight neck shape.

[0033] The spherical cavity wall of the golf ball mold of the present invention has numerous dimple-forming protrusions formed on it. That is, when the cover material is injection molded, numerous dimples are formed simultaneously with the cover by the numerous dimple-forming protrusions formed on the spherical cavity wall of the mold. It is preferable to use an arrangement of dimples that is polyhedral, such as an icosahedron, dodecahedron, or octahedron, or that has three-fold or five-fold symmetry, in order to spread the dimples evenly over the spherical surface.

[0034] When manufacturing the golf ball mold of the present invention, a method can be adopted in which the entire surface shape is directly cut in three dimensions on an inverted master mold using 3D CAD / CAM, or a method can be adopted in which the cavity portion of a molding mold is directly cut in three dimensions.

[0035] The present invention also provides a method for manufacturing a golf ball, including the step of manufacturing the cover using the golf ball mold. In this case, the golf ball manufactured has only to have a core and a single-layer or multi-layer cover, and there are no particular limitations on the type or structure of the golf ball. When molding a cover using the golf ball mold of the present invention, it is preferable to mold the outermost layer of the cover to a thickness of preferably 1.5 mm or less, more preferably 1.4 mm or less, in order to fully achieve the desired effects of the present invention. [Example]

[0036] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0037] [Examples 1 to 3, Comparative Examples 1 to 3] Using the molds of Examples 1 to 3 and Comparative Examples 1 to 3, a cover (outermost layer) was injection molded around a core or an intermediate layer-coated sphere, which was a core coated with an intermediate layer. The details are shown in Table 1. The core was formed from a rubber composition primarily containing polybutadiene, and the intermediate layer was formed from a resin material primarily containing ionomer resin.

[0038] The types of covers (outermost layers) are as follows: In the case of a two-piece golf ball, the cover material is a resin material (Shore D hardness "62") whose main component is an ionomer resin. In the case of a three-piece golf ball, the cover material is a resin material (Shore D hardness "43") whose main component is polyurethane.

[0039] The positions of the support pins and vent pins provided in the molds of each example are shown in Figure 10 (Example 1), Figure 11 (Example 2), Figure 12 (Example 3), Figure 13 (Comparative Example 1), Figure 14 (Comparative Example 2), and Figure 15 (Comparative Example 3). (A) in these figures is a plan view of the lower mold of the mold as seen from above, and (B) is a partially enlarged view showing the support pins and vent pins near the poles. Regarding the arrangement of these pins in each figure, the pole of the spherical cavity is set to latitude 0 degrees, and the seam surface is set to latitude 90 degrees, and the latitude and longitude are shown in Table 1.

[0040] Three types of dimples, TYPE 1 to TYPE 3, were used for each example, and the dimples were arranged on the cavity wall surface of the lower mold as shown in FIG. 10 (Example 1) to FIG. 15 (Comparative Example 3).

[0041] The clearance between the support pins and the vent pins and the pin holes is indicated by the symbol t in Fig. 4. The distance between the support pin hole and the vent pin hole is indicated by the symbol m.

[0042] The support pins gradually recede and slide as the molten resin material fills the spherical cavity, and stop moving when the molten resin material has completely filled the cavity. The tip surfaces of the support pins either coincide with the cavity wall surface or are convex relative to the cavity wall surface so as to form a dimple. On the other hand, like the support pins, the tip surfaces of the vent pins also either coincide with the cavity wall surface or are convex relative to the cavity wall surface so as to form a dimple. The vent pins can be designed to be fixed or to slide like the support pins, but in this embodiment, the vent pins are fixed and do not slide.

[0043] Covers were injection molded using the molds of each example to produce golf balls. The crack resistance of the resulting golf balls was evaluated as follows. The results are shown in Table 1.

[0044] Resistance to cracking due to repeated impacts Ball durability was evaluated using an ADC Ball COR Durability Tester manufactured by Automated Design Corporation in the United States. Golf balls were fired using air pressure and then collided continuously with two parallel metal plates. The average number of shots required for the ball to break was taken as the durability. In this case, the average value was calculated by averaging the number of shots required for each of the 10 balls to break after ten identical balls were fired. The tester was a horizontal COR, and the incident speed on the metal plates was 43 m / s. 〔Judgment criteria〕 ○ Average value: 150 times or more △ ··· Average value: 130 times or more, 149 times or less × Average value 129 times or less

[0045] [Table 1] [Explanation of symbols]

[0046] 10 Golf ball molds 1 spherical cavity 2 Gate 3 support pins 4 vent pins 3a Support pin hole 4a Vent pin hole 20 Target Sphere t Clearance between each pin and pin hole m Distance between support pin and vent pin

Claims

1. In a two-piece golf ball mold having a spherical cavity, a plurality of support pins and pin holes for placing a core in the spherical cavity, and a vent pin and pin hole, the pin holes of the support pins have clearances for releasing gas generated in the spherical cavity during injection molding to the outside, the vent pins are positioned inside the outermost support pins as viewed from the pole of the spherical cavity, there is at least one vent pin with a shortest distance between the pin hole of the vent pin and the pin hole of the support pin of 0.20 mm or less, and the sum of the total area of ​​the clearance between the vent pin and its pin hole and the total area of ​​the clearance between the support pin and its pin hole is 1.00 mm. 2 A mold for a golf ball characterized by the above.

2. 2. The golf ball mold according to claim 1, wherein the support pins are positioned so that the angle between an axis connecting the upper and lower poles of the mold and a normal line extending from the center of the axis toward the cavity wall from which the support pin exits is 15 to 30 degrees.

3. 3. The mold for a golf ball according to claim 1, wherein the upper or lower mold has three or more support pins.

4. 3. The mold for a golf ball according to claim 1, wherein the upper or lower mold has three or more vent pins.

5. 5. The golf ball mold of claim 4, wherein at least one of said vent pins is located at a pole.

6. 3. The golf ball mold according to claim 1, wherein the number of said vent pins is equal to or greater than the number of said support pins.

7. 3. The mold for a golf ball according to claim 1, wherein the clearance between the support pin and its pin hole is 0.020 mm or less.

8. 3. The mold for a golf ball according to claim 1, wherein the clearance between the vent pin and its pin hole is 0.020 mm or less.

9. 3. The mold for a golf ball according to claim 1, wherein the support pins slide back and forth along the pin holes, while the vent pins do not slide.

10. 10. A method for manufacturing a golf ball having a core and a single-layer or multi-layer cover, comprising the steps of: forming an outermost layer of the cover to a thickness of 1.5 mm or less using the golf ball mold of claim 1.

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