JP4563321B2 - Mold for golf ball half shell - Google Patents

Description

  The present invention relates to a mold for a half shell. This half shell is used for molding a golf ball cover.

  The two-piece golf ball includes a core and a cover that covers the surface of the core. For forming the cover, a compression molding method or an injection molding method may be employed. In general, an injection molding method with excellent mass productivity is employed. Japanese Patent Application Laid-Open No. 2005-143610 discloses a mold suitable for an injection molding method.

  In the injection molding method, the core is first held at the center of the spherical cavity by a holding pin. Next, the molten thermoplastic resin composition is injected into the gap between the cavity surface and the core. In the final stage of injection, the holding pin moves backward, so that the core may move from the center as the resin composition flows. Due to the movement, the thickness of the cover becomes non-uniform. Due to deformation of the core due to the injection pressure, a cover having a non-uniform thickness may be formed. The non-uniform cover thickness leads to non-uniform physical properties of the golf ball. In particular, in a golf ball with a thin cover, the non-uniformity of the cover thickness has a serious adverse effect on the physical properties of the golf ball. From the viewpoint of golf ball uniformity, there is a limit to the injection molding method.

  In the compression molding method, first, a half shell made of a resin composition is molded. Next, the two half shells and the core covered with the half shells are put into a mold. By tightening the mold, the half shell is pressurized and heated, and the excess resin composition flows out of the spherical cavity. In the compression molding method, non-uniform cover thickness is unlikely to occur. A golf ball manufacturing method employing a compression molding method is disclosed in Japanese Patent Application Laid-Open No. 2004-113703.

The mold for the half shell includes an upper mold having a hemispherical convex portion and a lower mold having a hemispherical cavity surface. The lower mold has a through hole, and a vent pin is inserted into the through hole. The radius of the convex portion is slightly smaller than the radius of the cavity surface. When the mold is tightened, a cavity is formed between the convex portion and the cavity surface. A molten resin composition is injected into this cavity. As the resin composition flows in, the air present in the cavity is discharged to the outside through the clearance between the through hole and the vent pin. This resin composition is solidified to obtain a half shell.
JP 2005-143610 A JP 2004-113703 A

  If the air is not sufficiently discharged during the molding of the half shell, a bear is generated in the half shell. Half-shell bears invite cover bears. Half-shell bears further impair the durability of golf balls.

  A thin half shell is used for forming the thin cover. In a mold for a thin half shell, the cavity is narrow. When this mold is used, a half-shell bear is particularly likely to occur. In recent years, golf balls equipped with a cover made of a thermoplastic polyurethane elastomer have become widespread. In forming the cover, a half shell made of a thermoplastic polyurethane elastomer is used. The fluidity of this elastomer is low. When this elastomer is used, bears are particularly likely to occur.

  An object of the present invention is to provide a mold for half shell from which a high-quality golf ball can be obtained.

  The molding die according to the present invention includes an upper die, a lower die having a through hole, and a vent pin inserted into the through hole. The upper mold includes a substantially hemispherical convex portion. The lower mold includes a substantially hemispherical cavity surface that forms a cavity by fitting with the convex portion. The vent pin includes a slit. In this slit, the upper end is released to the cavity, and the outer end reaches the outer peripheral surface of the vent pin. With this mold, the half shell of the golf ball is formed. Preferably, the width of the slit is not less than 10 μm and not more than 200 μm, and the ratio of the depth of the slit to the diameter of the vent pin is not less than 3% and not more than 45%. Preferably, the vent pin is made of a porous material.

  Another molding die according to the present invention includes an upper die, a lower die having a through hole, and a vent pin inserted into the through hole. The upper mold includes a substantially hemispherical convex portion. The lower mold includes a substantially hemispherical cavity surface that forms a cavity by fitting with the convex portion. The lower mold further includes a slit. In this slit, the upper end is released to the cavity, and the inner end reaches the inner peripheral surface of the through hole. With this mold, the half shell of the golf ball is formed. Preferably, the width of the slit is 10 μm or more and 200 μm or less, and the ratio of the depth of the slit to the radius of the cavity surface is 3% or more and 90% or less. Preferably, the vent pin is made of a porous material.

A golf ball manufacturing method according to the present invention includes:
(1) An upper mold, a lower mold having a through hole, and a vent pin inserted into the through hole. The upper mold has a substantially hemispherical convex portion. A mold that has a substantially hemispherical cavity surface that fits together to form a cavity, and this vent pin has a slit whose upper end is released into the cavity and whose outer end reaches the outer peripheral surface of the vent pin. A step of discharging air in the cavity through the slit while the molten resin composition is injected,
(2) A step in which the molten resin composition is solidified to obtain a half shell; and (3) In another mold having a spherical core and two half shells covered with the core. Including the step of being compressed.

Other manufacturing methods according to the present invention include:
(1) An upper mold, a lower mold having a through hole, and a vent pin inserted into the through hole. The upper mold has a substantially hemispherical convex portion. It has a substantially hemispherical cavity surface that forms a cavity by fitting together, and this lower mold has a slit whose upper end is released into the cavity and whose inner end reaches the inner peripheral surface of the through hole A step of discharging the air in the cavity through the slit while the molten resin composition is injected into the mold,
(2) A step in which the molten resin composition is solidified to obtain a half shell; and (3) In another mold having a spherical core and two half shells covered with the core. Including the step of being compressed.

  In the mold according to the present invention, since air is discharged from the slit, the golf ball is less likely to be defective.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 is a partially cutaway sectional view showing a golf ball 2 obtained by a manufacturing method according to an embodiment of the present invention. The golf ball 2 includes a spherical core 4 and a cover 6 that covers the core 4. The core 4 includes a spherical center 8 and an intermediate layer 10 that covers the center 8. A large number of dimples 12 are formed on the surface of the cover 6. A portion of the surface of the cover 6 other than the dimples 12 is a land 14. The golf ball 2 includes a paint layer and a mark layer outside the cover 6, but these layers are not shown. The core may be composed of a single layer. The core may be composed of three or more layers.

  The golf ball 2 has a diameter of 40 mm to 45 mm. The diameter is preferably 42.67 mm or more from the viewpoint that the American Golf Association (USGA) standard is satisfied. In light of air resistance suppression, the diameter is preferably equal to or less than 44 mm, and more preferably equal to or less than 42.80 mm. The golf ball 2 has a mass of 40 g or more and 50 g or less. From the viewpoint of obtaining a large inertia, the mass is preferably 44 g or more, and more preferably 45.00 g or more. From the viewpoint that the USGA standard is satisfied, the mass is preferably equal to or less than 45.93 g.

  The center 8 is obtained by crosslinking the rubber composition. Examples of the base rubber of the rubber composition include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, and natural rubber. Two or more kinds of rubbers may be used in combination. From the viewpoint of resilience performance, polybutadiene is preferred, and high cis polybutadiene is particularly preferred.

  For crosslinking of the center 8, a co-crosslinking agent is usually used. From the viewpoint of resilience performance, preferred co-crosslinking agents are zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. It is preferable that an organic peroxide is blended with the co-crosslinking agent in the rubber composition. Suitable organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t- Butyl peroxy) hexane and di-t-butyl peroxide.

  In the rubber composition, various additives such as a filler, a sulfur compound, an anti-aging agent, a colorant, a plasticizer, and a dispersant are blended in appropriate amounts as necessary. Crosslinked rubber powder or synthetic resin powder may be blended with the rubber composition.

  The center 8 has a diameter of 30.0 mm or more, particularly 35.0 mm or more. The center 8 has a diameter of 41.5 mm or less, particularly 41.0 mm or less. The center 8 may be subjected to surface treatment such as polishing, brushing, framing, and plasma treatment. The center 8 may be composed of two or more layers. Another layer made of a thermoplastic resin composition may be provided between the center 8 and the intermediate layer 10.

  The mid layer 10 is made of a thermoplastic resin composition. Examples of the base polymer of the resin composition include ionomer resins, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, thermoplastic polyurethane elastomers, thermoplastic polyolefin elastomers, and thermoplastic polystyrene elastomers. In particular, an ionomer resin is preferable. The ionomer resin is highly elastic. As will be described later, the cover 6 of the golf ball 2 is extremely thin. When the golf ball 2 is hit with a driver, the mid layer 10 is greatly deformed. The intermediate layer 10 using the ionomer resin contributes to the flight performance in a shot with a driver. When the ionomer resin and another resin are used in combination, the ionomer resin is the main component of the base polymer from the viewpoint of flight performance. The proportion of the ionomer resin in the total base polymer is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 85% or more.

  A preferable ionomer resin includes a binary copolymer of an α-olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms. Other preferable ionomer resins include ternary α-olefin, α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and α, β-unsaturated carboxylic acid ester having 2 to 22 carbon atoms. A copolymer is mentioned. In the binary copolymer and ternary copolymer, preferred α-olefins are ethylene and propylene, and preferred α, β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. In the binary copolymer and ternary copolymer, some of the carboxyl groups are neutralized with metal ions. Examples of the metal ions for neutralization include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions. Neutralization may be performed with two or more metal ions. Particularly suitable metal ions from the viewpoint of resilience performance and durability of the golf ball 2 are sodium ion, zinc ion, lithium ion and magnesium ion.

  A preferable binary copolymer contains 80% by mass or more and 90% by mass or less α-olefin and 10% by mass or more and 20% by mass or less α, β-unsaturated carboxylic acid. This binary copolymer is excellent in resilience performance. Preferred terpolymers are 70% to 85% by weight α-olefin, 5% to 30% by weight α, β-unsaturated carboxylic acid, and 1% to 25% by weight. α, β-unsaturated carboxylic acid ester. This ternary copolymer is excellent in resilience performance. A particularly preferred ionomer resin is a copolymer of ethylene and acrylic acid or methacrylic acid.

  Specific examples of the ionomer resin include Mitsui Dupont Polychemical's trade names “HIMILAN 1555”, “HIMILAN 1557”, “HIMILAN 1605”, “HIMILAN 1706”, “HIMILAN 1707”, “HIMILAN AM7311”, “HIMILAN AM7315”. "High Milan AM 7317", "Hi Milan AM 7318" and "High Milan MK 7320"; DuPont's trade names "Surlin 7930", "Surlin 7940", "Surlin 8140", "Surlin 8940", "Surlin 8945", "Surlin 9120" , "Surlin 9910" and "Surlin 9945"; and Exxon's trade names "IOTEK 7010", "IOTEK 7030", "IOTEK 8000" and "IOTEK 8030". Two or more ionomer resins may be used in combination. An ionomer resin neutralized with a monovalent metal ion and an ionomer resin neutralized with a divalent metal ion may be used in combination.

  From the viewpoint of flight performance, the thickness of the intermediate layer 10 is preferably 0.3 mm or more, more preferably 0.5 mm or more, and particularly preferably 0.7 mm or more. In light of feel at impact, the thickness is preferably equal to or less than 2.5 mm, and more preferably equal to or less than 2.0 mm.

  From the viewpoint of the close contact between the intermediate layer 10 and the cover 6, it is preferable that the intermediate layer 10 is subjected to a surface treatment to increase its roughness. Specific examples of the surface treatment include brushing and polishing. A reinforcing layer may be provided between the intermediate layer 10 and the cover 6 in order to increase the adhesion between them.

  The cover 6 is made of a thermoplastic resin composition. Examples of the base polymer of the resin composition include thermoplastic polyurethane elastomers, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, thermoplastic polyolefin elastomers, thermoplastic polystyrene elastomers, and ionomer resins. A thermoplastic polyurethane elastomer is preferably used as the base polymer. The thermoplastic polyurethane elastomer is soft. When the golf ball 2 having the cover 6 made of a thermoplastic polyurethane elastomer is hit with a short iron, the spin rate is high. The cover 6 made of a thermoplastic polyurethane elastomer contributes to control performance in a shot with a short iron. The thermoplastic polyurethane elastomer also contributes to the scratch resistance performance of the cover 6.

  The thermoplastic polyurethane elastomer includes a polyurethane component as a hard segment and a polyester component or a polyether component as a soft segment. Examples of the curing agent for the polyurethane component include alicyclic diisocyanate, aromatic diisocyanate and aliphatic diisocyanate. In particular, alicyclic diisocyanates are preferred. Since the alicyclic diisocyanate does not have a double bond in the main chain, yellowing of the cover 6 is suppressed. In addition, since the alicyclic diisocyanate is excellent in strength, damage to the cover 6 is suppressed. Two or more diisocyanates may be used in combination.

Examples of alicyclic diisocyanates include 4,4′-dicyclohexylmethane diisocyanate (H ₁₂ MDI), 1,3-bis (isocyanatomethyl) cyclohexane (H ₆ XDI), isophorone diisocyanate (IPDI), and trans-1,4- Examples are cyclohexane diisocyanate (CHDI). From the viewpoint of versatility and workability, H ₁₂ MDI is preferable.

  Aromatic diisocyanates include 4,4'-diphenylmethane diisocyanate (MDI) and toluene diisocyanate (TDI). As the aliphatic diisocyanate, hexamethylene diisocyanate (HDI) is exemplified.

  Specific examples of thermoplastic polyurethane elastomers include BASF Japan's trade name “Elastolan XNY90A”, trade name “Elastolan XNY97A”, trade name “Elastolan XNY585”, and trade name “Elastolan XKP016N”; The trade name “Rezamin P4585LS” and the trade name “Rezamin PS62490” of the industrial company are listed.

  In the cover 6, when the thermoplastic polyurethane elastomer and another resin are used in combination, the thermoplastic polyurethane elastomer is a main component of the base polymer from the viewpoint of control performance. The ratio of the thermoplastic polyurethane elastomer in the total base polymer is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 85% by mass or more.

  If necessary, the cover 6 includes a colorant such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, a fluorescent whitening agent, and the like. Appropriate amount is blended. For the purpose of adjusting the specific gravity, the cover 6 may be mixed with powder of a high specific gravity metal such as tungsten or molybdenum.

  The hardness of the cover 6 measured with a JIS-A type hardness meter is preferably 98 or less. This cover 6 is soft. This cover 6 contributes to the feel at impact and control performance. From this viewpoint, the hardness is more preferably 97 or less. The hardness is preferably 70 or more. The cover 6 having a hardness of 70 or more does not significantly impair the resilience performance of the golf ball 2. In this respect, the hardness is more preferably 75 or more. For the measurement of hardness, a sheet made of the same material as that of the cover 6 and having a thickness of about 2 mm formed by hot pressing is used. Prior to measurement, the sheet is stored at a temperature of 23 ° C. for 2 weeks. At the time of measurement, three sheets are overlaid.

  The thickness of the cover 6 is preferably 0.8 mm or less. As described above, the cover 6 is soft. The soft cover 6 is disadvantageous in terms of the coefficient of restitution of the golf ball 2. In the shot with the driver, the mid layer 10 and the center 8 of the golf ball 2 are also greatly deformed. By setting the thickness of the cover 6 to 0.8 mm or less, even if the cover 6 is soft, the cover 6 does not have a significant adverse effect on the coefficient of restitution upon a shot with a driver. From the viewpoint of flight performance and ease of molding, the thickness of the cover 6 is more preferably 0.6 mm or less, and particularly preferably 0.5 mm or less. From the viewpoint of easy forming of the cover 6, the thickness is preferably 0.1 mm or more, and more preferably 0.2 mm or more.

  FIG. 2 is a sectional view showing a mold 16 used in the method for manufacturing the golf ball 2 of FIG. The mold 16 includes an upper mold 18, a lower mold 20, and a vent pin 22. The upper mold 18 is located above the lower mold 20. The upper and lower positions of the upper mold 18 and the lower mold 20 may be reversed.

  The upper mold 18 includes a convex portion 24 and a base 26. The convex part 24 protrudes downward from the base 26. The convex part 24 is substantially hemispherical. The base 26 includes a groove-like gate G. Although not shown, the cross section of the gate G is semicircular. One end of the gate G reaches the convex portion 24. The other end of the gate G reaches the outer peripheral surface of the base 26.

  The lower mold 20 includes a main body 28 and a cavity surface 30. A through hole 32 is formed in the center of the main body 28. The through hole 32 penetrates the main body 28 from the bottom surface 34 of the main body 28 toward the cavity surface 30. The cross section of the inner peripheral surface of the through hole 32 is circular. The vent pin 22 is inserted into the through hole 32. A minute clearance is formed between the through hole 32 and the vent pin 22. The main body 28 further includes a gate G. Although not shown, the cross section of the gate G is semicircular. One end of the gate G reaches the cavity surface 30. The other end of the gate G reaches the outer peripheral surface of the main body 28. The cavity surface 30 is recessed. The cavity surface 30 is substantially hemispherical. The radius of the cavity surface 30 is slightly larger than the radius of the convex portion 24. When the mold 16 is tightened, the convex portion 24 is fitted into the cavity surface 30. A cavity is formed between the cavity surface 30 and the convex portion 24.

  3A is a plan view showing the vent pin 22 of the mold 16 of FIG. 1, and FIG. 3B is a front view thereof. FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. The vent pin 22 has a circular cross section. The vent pin 22 includes a main part 36 and a flange 38. A recessed portion 40 is formed at the tip of the main portion 36. The curvature radius of the recessed portion 40 is substantially equal to the curvature radius of the cavity surface 30. As is apparent from FIG. 2B, the recessed portion 40 and the cavity surface 30 are located on the same spherical surface.

  The vent pin 22 includes four vertical grooves 42, a first annular groove 44, and a second annular groove 46. The vertical groove 42, the first annular groove 44 and the second annular groove 46 are formed by cutting the outer peripheral surface of the vent pin 22. The vent pin 22 further includes four slits 48. As apparent from FIG. 4, the outer end 50 of the slit 48 reaches the outer peripheral surface of the vent pin 22, and the upper end 52 of the slit 48 reaches the recessed portion 40. In other words, the upper end 52 is open to the cavity. The lower end 54 of the slit 48 is released toward the first annular groove 44. The first annular groove 44 is connected to the vertical groove 42. The lower end of the vertical groove 42 is released toward the atmosphere (see FIG. 3). In other words, the cavity is communicated with the outside air by the slit 48, the first annular groove 44, and the vertical groove 42. The lower end of the slit 48 may be directly released toward the atmosphere without passing through the groove.

  In order to obtain a half shell with the mold 16, the mold 16 is first tightened. Next, the molten resin composition is injected from the injection molding machine and injected into the cavity through the gate G. As the injection proceeds, the air present in the cavity is discharged through the clearance between the through hole 32 and the vent pin 22. Air is also discharged through the slit 48. When the vent pin 22 is made of a porous material, air is also discharged through the pores of the vent pin 22. Smooth discharge suppresses half-shell bears. After completion of the injection, the resin composition is cooled inside the mold 16. After the resin composition is solidified, the mold 16 is opened and the half shell is taken out. The half shell is bowl-shaped. Since the molten resin composition slightly flows into the slit 48, fins are formed at positions corresponding to the slit 48 on the outer peripheral surface of the half shell.

  This half shell is put on the core 4. The core 4 is covered with two half shells. The half shell and the core 4 are put into a final mold having a spherical cavity. In this mold, the half shell and the core 4 are heated while being pressurized. The resin composition melts and flows by pressurization and heating. Excess resin composition flows out of the spherical cavity by pressurization. Thereafter, the final mold temperature is gradually cooled. The resin composition is solidified by slow cooling, and the cover 6 is formed. When the temperature is sufficiently lowered, the final mold is opened and the golf ball 2 is taken out. Since the half shell has no bear, this golf ball 2 is of high quality.

  In FIG. 4, what is indicated by a double arrow D is the diameter of the vent pin 22. The diameter D is preferably 10 mm or more and 25 mm or less. By setting the diameter D to 10 mm or more, the air is sufficiently discharged. In this respect, the diameter D is more preferably 12 mm or more. The vent pin 22 having a diameter D of 25 mm or less does not hinder the appearance of the cover 6. From this viewpoint, the diameter D is more preferably 18 mm or less.

  In FIG. 4, what is indicated by a double arrow W is the width of the slit 48. The width W is preferably 10 μm or more and 200 μm or less. By setting the width W to 10 μm or more, air is sufficiently discharged. In this respect, the width W is more preferably 30 μm or more. By setting the width W to 200 μm or less, the size of the fin is suppressed. The small fins do not remain on the cover 6 and thus do not hinder the appearance of the golf ball 2. In this respect, the width W is more preferably 100 μm or less.

  A double arrow L in FIG. 4 indicates the depth of the slit 48. The ratio of the depth L to the diameter D is preferably 3% or more and 45% or less. By setting this ratio to 3% or more, air is sufficiently discharged. From this viewpoint, the ratio is more preferably 15% or more. By setting this ratio to 45% or less, the size of the fin is suppressed. In this respect, the ratio is more preferably equal to or less than 30%.

  The number of slits 48 is preferably 2 or more and 16 or less. By setting the number to two or more, air is sufficiently discharged. In this respect, the number is more preferably four or more. By setting the number to 16 or less, the strength of the vent pin 22 is maintained. In this respect, the number is more preferably eight or less.

  The vent pin 22 is preferably made of a porous material. As described above, the air is sufficiently discharged by the porous vent pin 22. From the viewpoint of achieving both the discharge of air and the strength of the vent pin 22, the porosity of the vent pin 22 is preferably 3% or more and 30% or less.

  As described above, the thickness of the cover 6 is 0.8 mm or less. This cover 6 is thin. The half shell for this cover 6 is also thin. In the formation of a thin half shell, a bear is likely to occur, but the bear is suppressed by the slit 48. This mold 16 is suitable for the golf ball 2 having a cover 6 thickness of 0.8 mm or less, further 0.6 mm or less, and particularly 0.5 mm or less. The mold 16 is further suitable for forming a half shell mainly composed of a thermoplastic polyurethane elastomer.

  FIG. 5 is a plan view showing a mold 60 according to another embodiment of the present invention. 6 is a cross-sectional view taken along line VI-VI in FIG. 5 and 6 show the lower mold 62 and the vent pin 64. FIG. Although not shown, the mold 60 also includes an upper mold. The shape of the upper mold is equivalent to that of the upper mold 18 shown in FIG.

  The lower mold 62 includes a main body 66, a cavity surface 68, a through hole 70, and a gate G, similarly to the lower mold 20 shown in FIG. A vent pin 64 is inserted into the through hole 70. The vent pin 64 is located at the center of the lower mold 62. The vent pin 64 includes a main portion 72 and a flange 74, like the vent pin 22 shown in FIG. A concave portion 76 is formed at the tip of the main portion 72. The vent pin 64 also includes a vertical groove 78, a first annular groove 80, and a second annular groove 82. The vent pin 64 does not include the slit 48 shown in FIG. The vent pin 64 may include a slit.

  The lower mold 62 includes four slits 83. As is clear from FIG. 6, the inner end 84 of the slit 83 reaches the inner peripheral surface of the through hole 70, and the upper end 86 of the slit 83 reaches the cavity surface 68. In other words, this upper end 86 is open to the cavity. A lower end 88 of the slit 83 is connected to the first annular groove 80. The first annular groove 80 is connected to the vertical groove 78. The lower end of the vertical groove 78 is released toward the atmosphere. In other words, the cavity is communicated with the outside air by the slit 83, the first annular groove 80 and the vertical groove 78. The lower end of the slit 83 may be directly released toward the atmosphere without passing through the groove.

  When the half shell is molded by the mold 60, the air present in the cavity is discharged through the clearance between the through hole 70 and the vent pin 64. Air is also discharged through the slit 83. When the vent pin 64 is made of a porous material, air is also discharged through the pores of the vent pin 64. Smooth discharge suppresses half-shell bears.

  In FIG. 6, the diameter of the vent pin 64 is indicated by a double arrow D. The diameter D is preferably 10 mm or more and 25 mm or less. By setting the diameter D to 10 mm or more, the air is sufficiently discharged. In this respect, the diameter D is more preferably 12 mm or more. The vent pin 64 having a diameter D of 25 mm or less does not hinder the appearance of the cover. From this viewpoint, the diameter D is more preferably 18 mm or less.

  The width of the slit 83 is indicated by a double arrow W in FIG. The width W is preferably 10 μm or more and 200 μm or less. By setting the width W to 10 μm or more, air is sufficiently discharged. In this respect, the width W is more preferably 30 μm or more. By setting the width W to 200 μm or less, the size of the fin is suppressed. Small fins do not remain on the cover 6 and therefore do not impair the appearance of the cover 4. In this respect, the width W is more preferably 100 μm or less.

  In FIG. 6, a double arrow L indicates the depth of the slit 83, and a double arrow R indicates the radius of the cavity surface 68. The ratio of the depth L to the radius R is preferably 3% or more and 90% or less. By setting this ratio to 3% or more, air is sufficiently discharged. From this viewpoint, the ratio is more preferably 15% or more. By setting this ratio to 90% or less, the size of the fin is suppressed. In this respect, the ratio is more preferably equal to or less than 60%.

  The number of slits 83 is preferably 2 or more and 16 or less. By setting the number to two or more, air is sufficiently discharged. In this respect, the number is more preferably four or more. By setting the number to 16 or less, the strength of the vent pin 64 is maintained. In this respect, the number is more preferably eight or less.

  The vent pin 64 is preferably made of a porous material. In the vent pin 64, the air is sufficiently discharged as described above. From the viewpoint of achieving both the discharge of air and the strength of the vent pin 64, the porosity of the vent pin 64 is preferably 3% or more and 30% or less.

  This mold 60 is suitable for the golf ball 2 in which the thickness of the cover 6 is 0.8 mm or less, further 0.6 mm or less, and particularly 0.5 mm or less. The mold 60 is further suitable for forming a half shell mainly composed of a thermoplastic polyurethane elastomer.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
A core composed of a center using polybutadiene as a base polymer and an intermediate layer using ionomer resin as a base polymer was prepared. The core diameter was 41.1 mm. On the other hand, 80 parts by mass of a polyurethane-based thermoplastic elastomer (trade name “Elastollan XNY97A” from BASF Japan), 20 parts by mass of thermoplastic polyamide elastomer (trade name “Pebax 5533” from Arkema), and 5 parts by mass of titanium dioxide The resin composition was obtained by kneading with a twin screw extruder. This resin composition was injected into the mold shown in FIG. 2 by an injection molding method. In this mold, the radius of the cavity surface is 21.54 mm, and the diameter of the vent pin is 14.98 mm. The vent pin is made of a porous material. This vent pin has four slits. The slit width W is 30 μm, and the slit depth L is 2.2 mm. This resin composition solidified to obtain a half shell. The thickness of this half shell was 0.9 mm. The core was covered with the two half shells and put into a final mold to obtain a golf ball. The golf ball cover had a thickness of 0.8 mm.

[Examples 4 and 5]
A golf ball was obtained in the same manner as in Example 1 except that the slit depth L was as shown in Table 1 below.

[Examples 3, 6 and 7]
A golf ball was obtained in the same manner as in Example 1 except that the slit width W was as shown in Table 1 below.

[Examples 2 and 8]
A golf ball was obtained in the same manner as in Example 1 except that the number of slits was as shown in Table 1 below.

[Examples 9 to 12]
A golf ball was obtained in the same manner as in Example 1 except that the specifications of the vent pin and slit were as shown in Table 2 below.

[Examples 13 and 14]
A golf ball was obtained in the same manner as in Example 1 except that a lower die was provided with a slit and a vent pin was not provided with a slit. The slit specifications are shown in Table 2 below.

[Comparative example]
A golf ball was obtained in the same manner as in Example 1 except that a mold having no slit was used.

[Visual observation]
500 golf balls were visually observed, and the number of golf balls in which air entered the cover was counted. Furthermore, the size of the fin resulting from the slit was evaluated. These results are shown in Tables 1 and 2 below.

[Evaluation of durability]
The golf ball was repeatedly collided with the metal plate at a speed of 45 m / s, and the number of times until the golf ball was destroyed was counted. Ten golf balls were measured and the average value was calculated. The results are shown in Tables 1 and 2 below as indices when Example 9 is set to 100.

  As shown in Tables 1 and 2, in the golf balls obtained from the molds of the examples, the infiltration of air into the cover is small and the fins are small. And the golf ball obtained from the shaping | molding die of the Example is excellent in durability. From this evaluation result, the superiority of the present invention is clear.

  The molding die according to the present invention is also suitable for molding a half shell for an inner cover of a golf ball having a two-layer cover. The mold according to the present invention is also suitable for molding a half shell made of a polymer composition (typically a rubber composition) other than the resin composition.

FIG. 1 is a partially cutaway sectional view showing a golf ball obtained by a manufacturing method according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a mold used in the golf ball manufacturing method of FIG. FIG. 3A is a plan view showing the vent pin of the mold of FIG. 1, and FIG. 3B is a front view thereof. FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. FIG. 5 is a plan view showing a mold according to another embodiment of the present invention. 6 is a cross-sectional view taken along line VI-VI in FIG.

Explanation of symbols

2 ... Golf ball 4 ... Core 6 ... Cover 16, 60 ... Mold 18 ... Upper mold 20, 62 ... Lower mold 22, 64 ... Bent pin 24 ... Convex Part 30, 68 ... cavity surface 32, 70 ... through hole 40, 76 ... recessed part 42, 78 ... vertical groove 44, 80 ... first annular groove 46, 82 ... first Double annular groove 48, 83 ... Slit G ... Gate

Claims (9)

An upper die, a lower die having a through hole, and a vent pin inserted into the through hole;
This upper mold has a substantially hemispherical convex part,
The lower mold has a substantially hemispherical cavity surface that forms a cavity by fitting with the convex part,
This vent pin has a slit whose upper end is released to the cavity and whose outer end reaches the outer peripheral surface of the vent pin ,
Mold for the half shell of the golf ball diameter of the vent pin is Ru der more than 25mm below 12mm.   2. The mold according to claim 1, wherein a width of the slit is 10 μm or more and 200 μm or less, and a ratio of a depth of the slit to a diameter of the vent pin is 3% or more and 45% or less.   The mold according to claim 1 or 2, wherein the vent pin is made of a porous material. The mold according to any one of claims 1 to 3, wherein the vent pin includes a recessed portion at a tip thereof. An upper die, a lower die having a through hole, and a vent pin inserted into the through hole;
This upper mold has a substantially hemispherical convex part,
The lower mold has a substantially hemispherical cavity surface that forms a cavity by fitting with the convex part,
A molding die for a half shell of a golf ball, wherein the lower die is provided with a slit whose upper end is released into the cavity and whose inner end reaches the inner peripheral surface of the through hole. The mold according to claim 5 , wherein the slit has a width of 10 µm or more and 200 µm or less, and a ratio of the depth of the slit to the radius of the cavity surface is 3% or more and 90% or less. The mold according to claim 5 or 6 , wherein the vent pin is made of a porous material. An upper die, a lower die having a through-hole, and a vent pin inserted into the through-hole are provided. The upper die has a substantially hemispherical convex portion, and the lower die is fitted to the convex portion. The vent pin has a substantially hemispherical cavity surface forming a cavity, and the vent pin has a slit whose upper end is released into the cavity and whose outer end reaches the outer peripheral surface of the vent pin, and the diameter of the vent pin is 12 mm. above 25mm in der Ru mold following the step of melting the resin composition being injected, air in the cavity through the slit is discharged,
A golf process comprising the step of solidifying the molten resin composition to obtain a half shell, and the step of compressing a spherical core and two half shells placed on the core in another mold having a spherical cavity Ball manufacturing method. An upper die, a lower die having a through-hole, and a vent pin inserted into the through-hole are provided. The upper die has a substantially hemispherical convex portion, and the lower die is fitted to the convex portion. The lower die has a substantially hemispherical cavity surface that forms a cavity with a lower die whose upper end is released into the cavity and whose inner end has a slit that reaches the inner peripheral surface of the through hole. A step of discharging air in the cavity through the slit while the molten resin composition is injected,
A golf process comprising the step of solidifying the molten resin composition to obtain a half shell, and the step of compressing a spherical core and two half shells placed on the core in another mold having a spherical cavity Ball manufacturing method.

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