RUBBER COMPOSITION FOR GOLF BALL, AND GOLF BALL

Abstract

A rubber composition for golf balls includes (a) a base rubber, (b) a co-crosslinking agent which is an α,β-unsaturated carboxylic acid and/or a metal salt thereof, (c) a crosslinking initiator, (d) an alcohol and (e-1) an organosulfur, and the amount of component (d) is from 0.1 to 10 parts by weight per 100 parts by weight of the base rubber (a) and the organosulfur of component (e-1) is alkylphenoldisulfide polymers represented by the specific chemical formula. When the rubber composition is used in a golf ball having a core and a cover of one or more layers encasing the core, by setting the hardness difference in the core interior hardness profile to a large value while maintaining a desired core hardness, low spin properties can be manifested on golf ball shots, enabling the flight performance of the ball to be improved.

Claims

1. A rubber composition for golf balls, comprising: (a) a base rubber, (b) a co-crosslinking agent which is an α,β-unsaturated carboxylic acid or a metal salt thereof or both, (c) a crosslinking initiator, (d) an alcohol, (e-1) an organosulfur, wherein the amount of component (d) is from 0.1 to 10 parts by weight per 100 parts by weight of the base rubber (a) and the organosulfur of component (e-1) is alkylphenoldisulfide polymers represented by the following chemical formula: ##STR00002## wherein R is an alkyl group and n is degree of polymerization in a range of 2 to 20.

2. The rubber composition of claim 1, wherein the alkyl group of R in the chemical formula is an lower alkyl group of 1 to 6 carbon atoms selected from the group consisting of methyl, ethyl, n-propyl, iso-propyl, n-butyl, tert-butyl, n-amyl (pentyl), iso-amyl (pentyl), tert-amyl (pentyl), sec-isoamyl, neopentyl, n-hexyl, iso-hexyl, tert-hexyl groups.

3. The rubber composition of claim 1, wherein the organosulfur of component (e-1) is amylphenoldisulfide polymers.

4. The rubber composition of claim 1, wherein the amount of component (e-1) is from 0.05 to 5.0 parts by weight per 100 parts by weight of the base rubber (a).

5. The rubber composition of claim 1, wherein component (d) is a lower alcohol having a molecular weight of less than 500.

6. The rubber composition of claim 5, wherein component (d) is a lower alcohol having a molecular weight of less than 200.

7. The rubber composition of claim 1, wherein the amount of component (d) is from 0.5 to 5 parts by weight per 100 parts by weight of the base rubber (a).

8. The rubber composition of claim 1, wherein component (d) is a monohydric, dihydric or trihydric alcohol.

9. The rubber composition of claim 3, wherein component (d) is butanol, glycerol, ethylene glycol or propylene glycol.

10. The rubber composition of claim 1, further comprising (e) an organosulfur compound which is different from the organosulfur of component (e-1).

11. The rubber composition of claim 1, wherein the vulcanized form of the rubber composition is a golf ball core.

12. The rubber composition of claim 11, wherein the vulcanized rubber composition has a surface and a center with a hardness difference therebetween of at least 20 on the JIS-C hardness scale.

13. A golf ball comprising a core and a cover of one or more layers encasing the core, wherein the core is formed of the rubber composition of claim 1.

14. The golf ball of claim 13, wherein the core has a hardness profile in which a surface and a center of the core have a hardness difference therebetween of at least 20 on the JIS-C hardness scale.

15. The golf ball of claim 13, wherein the core has a center hardness of from 50 to 65 on the JIS-C hardness scale.

16. The golf ball of claim 13, wherein the core has a surface hardness of from 72 to 95 on the JIS-C hardness scale.

17. The golf ball of claim 13, wherein the core has an amount of deflection of from 2.0 to 5.0 mm when compressed under a find load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf).

Description

EXAMPLES

[0077] Examples of the invention and Comparative Examples are given below by way of illustration, although the invention is not limited by the following Examples.

Examples 1 to 5, Comparative Examples 1 to 3

[0078] Cores having a diameter of 38.6 mm were produced by using the core materials composed primarily of polybutadiene shown in Table 1 below to prepare core compositions formulated for Working Examples 1 to 5 and Comparative Examples 1 to 3, subsequently vulcanizing the compositions at 155° C. for 20 minutes, and then abrading the core surface.

TABLE-US-00001 TABLE 1 Rubber Comparative formulation Working Example Example (pbw) 1 2 3 4 5 1 2 3 Polybutadiene 100 100 100 100 100 100 100 100 rubber Zinc oxide 8.6 8.3 6.4 6.9 5.6 19.6 15.5 16.0 Antioxidant (1) 0.1 0.1 Antioxidant (2) 0.3 0.3 0.3 0.3 0.3 0.3 Zinc acrylate 49.4 50.4 54.4 53.3 54.7 29.0 39.0 34.8 Zinc methacrylate 5.0 5.0 5.0 5.0 5.0 1.0 Zinc salt of 1.0 1.0 1.0 1.0 1.0 0.5 0.5 0.6 pentachloro- thiophenol Alkylphenol- 0.5 0.5 1.0 1.0 1.0 disulfide polymers Propylene glycol 1.5 1.5 1.5 1.5 1.5 Water 0.4 Organic 0.5 0.8 0.5 0.8 1.0 1.0 1.0 peroxide (1) Organic 2.0 peroxide (2)

[0079] Details on the above formulations are given below. [0080] Polybutadiene: Available under the trade name “BR 01” from JSR Corporation [0081] Zinc oxide: Available as “Zinc Oxide Grade 3” from Sakai Chemical Co., Ltd. [0082] Antioxidant (1): A phenolic antioxidant available under the trade name “Nocrac NS-6” from Ouchi Shinko Chemical Industry Co., Ltd. [0083] Antioxidant (2): A benzimidazole antioxidant available under the trade name “Nocrac MB” from Ouchi Shinko Chemical Industry Co., Ltd. [0084] Zinc acrylate: Available under the trade name “ZN-DA85S” [0085] (85% zinc acrylate/15% zinc stearate) from Nippon Shokubai Co., Ltd. [0086] Zinc methacrylate: [0087] Available under the trade name “M-CP” [0088] (100% zinc methacrylate) from Asada Chemical Industry Co., Ltd. [0089] Zinc salt of pentachlorothiophenol: [0090] Available from Wako Pure Chemical Industries, Ltd. [0091] Amylphenoldisulfide polymers: [0092] Available the trade name “Sanceler AP” from Sanshin Chemical Industry Co., Ltd. [0093] Propylene glycol (a lower dihydric alcohol): [0094] molecular weight, 76.1 (from Hayashi Pure Chemical Ind., Inc.) [0095] Water: Pure water (from Seiki Chemical Industrial Co., Ltd.) [0096] Organic Peroxide (1) (Dicumyl peroxide): available under the trade name “Percumyl D” from NOF Corporation [0097] Organic Peroxide (2) (Peroxyketal peroxide):

[0098] available under the trade name “Perhexa C-40” from NOF Corporation

Cross-Sectional Hardnesses of Core

[0099] The cross-sectional hardnesses at various positions, including the surface and center, of the 38.6 mm diameter core in each of the above Working Examples and Comparative Examples were measured by the following methods.

(1) Surface Hardness of Core

[0100] At a temperature of 23+1° C., the indenter of a durometer was perpendicularly set against a surface portion of the spherical core and the JIS-C hardness was measured at four random points on the core surface. The average value of these measurements was treated as the measured value for one core, and the average value for three measured cores was determined. These results are presented in Table 3.

(2) Cross-Sectional Hardnesses of Core

[0101] The core was cut through the center to obtain a flat cross-sectional plane. At a temperature of 23±1° C., the indenter of a durometer was perpendicularly set against the cross-sectional plane and the JIS-C hardness was measured at the center of the hemispherical core and at 2 mm intervals from the center toward the surface, thereby collecting the measurements for one core. The average values for three measured cores were determined.

[0102] These results are presented in Table 3.

Core and Ball Deflection

[0103] The amount of deflection (mm) by each core and ball when compressed at a speed of 10 mm/s under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) was measured at a temperature of 23±1° C. In each case, the average value for 10 measured cores or balls was determined.

Formation of Cover (Intermediate Layer and Outermost Layer)

[0104] Using an injection mold, the intermediate layer material (ionomer resin material) shown in Table 2 was then injection-molded over the surface of the above core, thereby forming an intermediate layer having a thickness of 1.3 mm and a Shore D hardness of 64. Next, using a different injection mold, the outermost layer material (urethane resin material) shown in Table 2 was injection-molded over the intermediate layer-encased sphere, thereby forming an outermost layer having a thickness of 0.8 mm and a Shore D hardness of 40.

TABLE-US-00002 TABLE 2 Formulation Intermediate Outermost (pbw) layer layer Himilan 1706 35 Himilan 1557 15 Himilan 1605 50 TPU 100 Polyethylene wax 1.0 Isocyanate compound 6.3 Titanium oxide 3.3 Trimethylolpropane 1.1

[0105] Details on the compounding ingredients in the table are given below. [0106] Himilan 1706, Himilan 1557, Himilan 1605: [0107] Ionomer resins available from Dow-Mitsui Polychemicals Co., Ltd. [0108] TPU: An ether type-thermoplastic polyurethane available under the trade name “Pandex” from DIC Covestro Polymer, Ltd.; Shore D hardness, 40 [0109] Polyethylene wax: Available under the trade name “Sanwax 161P” from Sanyo Chemical Industries, Ltd. [0110] Isocyanate compound: 4,4′-Diphenylmethane diisocyanate

[0111] The spin rates of the resulting golf balls on shots with a driver were evaluated by the following method. The results are shown in Table 3.

Spin Rate on Shots with a Driver

[0112] A driver (W#1) was mounted on a golf swing robot and the spin rate of the ball immediately after being struck at a head speed of 45 m/s was measured using an apparatus for measuring the initial conditions. The club used was the TourB XD-3 Driver (2016 model; loft angle,)9.5° manufactured by Bridgestone Sports Co., Ltd.

TABLE-US-00003 TABLE 3 Working Example Comparative Example 1 2 3 4 5 1 2 3 Core Deflection (mm) 2.99 2.98 3.09 3.12 3.03 3.35 2.19 3.13 Hardness Center hardness 56.4 51.7 53.4 55.5 56.2 65.0 73.7 68.5 profile (B) (JIS-C) Hardness 2 mm 57.3 53.9 53.3 56.0 62.2 65.3 73.8 69.0 from center Hardness 4 mm 59.1 57.9 54.6 57.4 68.0 65.6 74.1 71.0 from center Hardness 6 mm 60.4 61.0 56.3 58.6 71.0 66.4 75.5 72.2 from center Hardness 8 mm 60.8 62.5 57.4 59.4 72.7 68.7 76.0 72.6 from center Hardness 10 mm 61.5 62.5 58.5 61.0 72.9 69.9 78.5 72.4 from center Hardness 12 mm 64.6 63.8 61.4 64.5 71.7 72.7 81.8 71.9 from center Hardness 14 mm 75.9 72.6 74.8 75.2 70.1 77.1 86.8 75.9 from center Hardness 16 mm 84.1 85.2 84.5 85.2 79.5 79.9 89.8 80.7 from center Hardness 18 mm 88.0 89.3 88.0 89.3 86.8 79.3 91.4 82.5 from center Surface hardness 89.6 92.2 89.1 91.3 90.5 81.9 93.1 87.5 (A) Hardness 33.2 40.5 35.7 35.8 34.3 16.9 19.4 19.0 difference (A − B) Ball Deflection (mm) 2.44 2.36 2.44 2.44 2.51 2.77 1.89 2.26 Spin rate on driver 2745 2735 2650 2634 2677 2878 3094 2988 shots (rpm)

[0113] As shown in Table 3, in each of Working Examples 1 to 5 in which a rubber composition containing both of an alcohol and alkylphenoldisulfide polymers was used as the core material, unlike in Comparative Examples 1 to 3, the hardness difference between the center and surface of the core was more than 20 on the JIS-C hardness scale, and so a sufficient hardness difference was obtained. As a result, the spin rate of the golf ball on shots with a driver was about 100 to 500 rpm lower than in the Comparative Examples in which the hardness difference was less than 20 and thus inadequate.

[0114] Japanese Patent Application No. 2018-111044 is incorporated herein by reference.

[0115] Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.