JP2000086816A - Rubber composition and golf ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition that has improved kneadability of a metal salt of an unsaturated carboxylic acid and has enhanced impact resistance and durability without reducing impact resilience by incorporating a base rubber containing a polybutadiene rubber having a cis-1,4 bond, a metal salt of an unsaturated carboxylic acid, an organic peroxide and a nitroxide radical compound into the composition. SOLUTION: Into 100 pts.wt. base rubber containing a polybutadiene rubber having a cis-1,4 bond of not less than 40%, 10-40 pts.wt., preferably 20-30 pts.wt. metal salt of an unsaturated carboxylic acid, 0.5-5.0 pts.wt., preferably 1-3 pts.wt. organic peroxide, 0.1-10 pts.wt., preferably 0.1-0.3 pts.wt. nitroxide radical compound of formula I-formula III are formulated. In the formulae, R is 1-30C alkylene or 6-30C aryl which each contains at least one selected from O, N or S; A is H, amino, isocyanate, hydroxyl, carboxyl, oxirane or thiirane; n is 1-6; and R1-4 are each H or 1-4C alkyl.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition and a golf ball, and more particularly to a golf ball core which can obtain a crosslinked product excellent in impact resistance and durability without lowering resilience. The present invention relates to a rubber composition suitable as a raw material for golf balls, and a golf ball comprising the rubber composition.

[0002]

2. Description of the Related Art Multi-piece solid golf balls such as two-piece golf balls and three-piece golf balls have a structure in which a core disposed at the center is covered with a cover material. The core of this golf ball is
Base rubber containing polybutadiene or the like as a main component, unsaturated carboxylic acid metal salt, zinc oxide, barium sulfate, manufactured by heating and pressure molding a rubber composition containing peroxide, etc.
It shows high strength and good resilience.

However, in this rubber composition, the polybutadiene rubber and the unsaturated metal carboxylate are inferior in kneading processability, so that it is difficult to prepare a composition in which the unsaturated metal carboxylate is sufficiently dispersed. In addition, there is a problem that the physical properties of the obtained rubber composition are deteriorated due to the heat of reaction of the unsaturated metal carboxylate during the heating and pressing.

[0004] Therefore, there has been proposed a method of improving the kneading processability by using a surface-treated unsaturated carboxylic acid metal salt or by using a solution mixture and a master batch (Japanese Patent Laid-Open No. 1-314465). . On the other hand, a method has been proposed in which a runaway reaction of a metal salt of an unsaturated carboxylic acid is suppressed by adding a chain transfer agent, an antioxidant, or the like as a polymerization reaction regulator. However, these methods are basically methods of inhibiting the crosslinking of the base rubber and adjusting the crosslinking efficiency. If the rebound resilience is to be increased, the durability is reduced, and if the durability is to be increased, the rebound is reduced. There is a disadvantage that the elasticity decreases,
Since it is difficult to obtain a rubber composition having both rebound resilience and durability, there is room for improvement in any of them.

[0005]

Therefore, the first aspect of the present invention
The purpose of the method is to improve the kneading processability of the unsaturated metal carboxylate during kneading of each component and to suppress the runaway reaction of the unsaturated metal carboxylate, so that the impact resistance can be reduced without lowering the resilience. Another object of the present invention is to provide a rubber composition capable of obtaining a crosslinked product having excellent durability.

A second object of the present invention is to provide a golf ball having excellent impact resistance and durability without a decrease in resilience, since it has a core made of the rubber composition.

[0007]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted intensive studies and as a result, by adding a nitroxide radical compound having a polar group to a base rubber, an unsaturated metal carboxylate is obtained. The kneading processability of the salt and the dispersibility in rubber are improved, and the reaction rate of peroxide crosslinking is slowed to suppress the runaway reaction of the unsaturated metal salt of carboxylic acid, thereby reducing the repulsion by crosslinking. And found that a rubber composition capable of forming a crosslinked product having excellent impact resistance and durability could be obtained, and further found that the rubber composition was suitable as a material for a golf ball core. The invention has been completed.

That is, in order to solve the above problems, the present invention provides a base rubber containing a polybutadiene rubber having at least 40% of cis-1,4 bonds, a metal salt of an unsaturated carboxylic acid and an organic peroxide, It is intended to provide a rubber composition containing a nitroxide radical compound.

It is preferable that the nitroxide radical compound is a compound containing a polar group. Further, when the nitroxide radical compound is 2,2,6,6-tetramethyl-1-piperidinyloxy free radical,
preferable.

Further, it is preferable that the nitroxide radical compound is a compound having at least one polar group selected from an amino group, an isocyanate group, a hydroxyl group, a carboxyl group, an oxirane group and a thiirane group.
preferable.

Further, it is preferable that the unsaturated carboxylic acid metal salt is at least one selected from zinc acrylate and zinc methacrylate.

Further, the present invention provides a golf ball having a core made of the above rubber composition.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the rubber composition and golf ball of the present invention will be described in detail.

The rubber composition of the present invention contains a base rubber, a metal salt of an unsaturated carboxylic acid, an organic peroxide and a nitroxide radical compound as essential components.

As the base rubber which is an essential component of the rubber composition of the present invention, polybutadiene rubber is preferably used. This polybutadiene rubber has a cis 1,4-structure of 4
0% or more, high rebound resilience, extrudability,
It is preferable from the viewpoint of increasing the strength of the crosslinked product, and in particular, cis 1,4
-Those having a structure of 90% or more are preferred.

As the base rubber, the above polybutadiene rubber can be used alone, but if necessary, another rubber component may be used in combination. Examples of other rubber components used include natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, EPDM, and the like.

As the metal salt of an unsaturated carboxylic acid which is an essential component of the rubber component of the present invention, various metal salts of a carboxylic acid having an unsaturated bond can be used. As the carboxylic acid, for example, acrylic acid, methacrylic acid,
Α, β-unsaturated carboxylic acids such as maleic acid and fumaric acid; Among these, acrylic acid and methacrylic acid are particularly preferred. The metal species of the metal salt includes a metal ion having a valence of 1 to 3, and examples thereof include zinc, sodium, magnesium, calcium, and aluminum, and zinc is particularly preferable.

The organic peroxide which is an essential component of the rubber composition of the present invention includes, for example, benzoyl oxide, t
-Butyl hydroperoxide, 2,4-dichlorobenzoyl peroxide, 2,5-dimethyldi (t-butylperoxy) hexane, 2,5-dimethylhexane-2,5-di (peroxylbenzoate), dicumylper Oxide and the like. Among these, dicumyl peroxide is particularly preferred.

The nitroxide radical compound, which is an essential component of the rubber composition of the present invention, is a compound containing at least one nitroxide radical in the molecule and stably existing at room temperature in the presence of oxygen. Examples of the nitroxide radical compound include those represented by the following formulas (a) and (b).

[0020]

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In the formulas (a) and (b), R is O, N
And at least one carbon selected from the group consisting of
A is an alkylene group or an aryl group having 6 to 30 carbon atoms, A is independently a hydrogen atom, an amino group, an isocyanate group, a hydroxyl group, a carboxyl group, an oxirane group or a thiirane group, and n is 1 to 6 It is an integer.
When n is 2 or more, a plurality of groups (RA) may be the same as or different from each other. Further, R and A may be a combination of any groups selected from the groups described above. Further, R ¹ , R ² , R ³ and R
⁴ may be the same or different and include a hydrogen atom, a methyl group,
It is an alkyl group having 1 to 4 carbon atoms such as an ethyl group.

The following are specific examples of the nitroxide radical compound represented by the formula (a).

[0023]

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[0024]

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The following are specific examples of the nitroxide radical compound represented by the formula (b) or (c).

[0026]

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[0027]

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[0028]

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Further, as the nitroxide radical compound used in the present invention, the following compounds can be exemplified.

[0030]

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[0031]

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Among these nitroxide radical compounds, a nitroxide radical compound containing a polar group is preferred in that it imparts polarity to the polybutadiene rubber and improves the kneading processability of the unsaturated carboxylic acid metal salt. In particular, a nitroxide radical compound having at least one polar group selected from an amino group, an isocyanate group, a hydroxyl group, a carboxyl group, an oxirane group and a thiirane group is preferred. In the present invention, among these nitroxide radical compound parts, 2,2,6,6-tetramethyl-1-piperidinyloxy free radical is preferable.

In the rubber composition of the present invention, a base rubber,
The mixing ratio of the unsaturated metal salt of carboxylic acid, organic peroxide and nitroxide radical compound is usually 10
0 to 100 parts by weight, metal unsaturated carboxylate 10 to 40
Parts by weight, 0.5 to 5.0 parts by weight of an organic peroxide, and 0.1 to 1.0 parts by weight of a nitroxide radical compound. 20 to 30 parts by weight of an acid metal salt, 1 to 3 parts by weight of an organic peroxide, and 0.1 parts of a nitroxide radical compound.
It is a ratio of 1 to 0.3 parts by weight.

Further, the rubber composition of the present invention comprises, in addition to the base rubber, unsaturated carboxylic acid metal salt, organic peroxide and nitroxide radical compound, other components commonly used in this rubber composition. As long as the purpose of the invention is not impaired,
It can be blended as needed. Other components include, for example, inorganic fillers, dispersants, softeners and the like. Specific examples of the inorganic filler include zinc oxide, barium sulfate, calcium carbonate and the like. Among these, zinc oxide is preferred. When zinc oxide is compounded, the compounding amount is 5 to 50 parts by weight based on 100 parts by weight of the base rubber.
In the range of parts by weight, the weight of the obtained golf ball is adjusted so as to have a prescribed weight.

Further, the present invention provides a golf ball having a core made of the rubber composition. This golf ball may have any cover material as long as it has a core made of the rubber composition. For example, a golf ball having a two-layer structure in which the outer periphery of a core is covered with a cover made of a single layer of a cover material, a so-called two-piece golf ball, and a golf ball having a three-layer structure in which the outer periphery of a core is covered with an intermediate layer. Any type of golf ball, such as a so-called three-piece ball, or a multilayer golf ball having a cover layer and a core layer may be used.

In the golf ball of the present invention, the cover material is not particularly limited, and any of those generally used as cover materials for golf balls can be used. For example, an ionomer resin alone, a blend of two or more ionomer resins, or a thermoplastic composition containing an ionomer resin and a diene rubber can be used as a material. Particularly preferred is a thermoplastic resin composition in which butadiene rubber is dispersed in an ionomer resin. Since the thermoplastic resin composition performs kneading of the ionomer resin and butadiene rubber in a temperature range of 150 ° C. or more and less than 260 ° C., the butadiene rubber can be cross-linked only by heat without using a cross-linking agent. It is possible to easily obtain a composition having an appropriate shot feeling, resilience and durability.

In the production of the golf ball of the present invention, the base rubber, the unsaturated metal salt of a carboxylic acid, the organic peroxide and the nitroxide radical compound, and other components to be blended if necessary are first mixed. Prepare a rubber composition,
After uniformly kneading this rubber composition according to a conventional method,
The core is formed by supplying the mixture to a predetermined mold, heat-crosslinking under pressure, and integrally forming the core. At this time, in the rubber composition of the present invention, the kneading processability of the unsaturated metal carboxylate is improved by the addition of the nitroxide radical compound, the runaway reaction of the unsaturated metal carboxylate is suppressed, and the metal is crosslinked to repel. A crosslinked product excellent in impact resistance and durability can be obtained without lowering the properties.

In the case where the golf ball of the present invention is a so-called two-piece ball comprising a core and a cover covering the outer periphery of the core, the components constituting the cover material are mixed with a twin-screw extruder or the like. Melt kneading in to prepare a kneaded material,
The golf ball of the present invention can be manufactured by coating the outer peripheral surface of the core obtained above with the kneaded material. The covering of the core with the cover material can be performed by arranging the core in a predetermined injection mold and injecting the molten cover material.

In the case where the golf ball of the present invention is a golf ball having another multilayer structure, ordinary methods and conditions can be adopted for the manufacturing method and conditions.

[0040]

The present invention will be described in more detail with reference to the following examples and comparative examples. In the following Examples and Comparative Examples, the evaluation of kneading processability and the measurement or evaluation of the core properties (strength, index) and the ball properties (durability index) of the golf ball were performed according to the following methods.

Evaluation of kneading processability Observing the uptake of the unsaturated carboxylic acid metal salt during the kneading process, and observing whether the unsaturated carboxylic acid metal salt adheres to the wall surface of the kneading machine, Evaluation was based on criteria. Evaluation criteria ◎ Very good uptake and no adhesion ○ Good uptake and no adhesion × Poor uptake and adhesion

Core Characteristics The force required for breaking when the molded core (diameter: 38.3 mm) was compressed at a compression speed of 10 mm / min using an autograph was measured. In Example 4, the relative value when the force required for destruction was 100 was determined as an index, and in Example 4, the relative value when the force required for destruction in Comparative Example 2 was 100 was determined as an index.

Ball characteristics 43 m with a driver (# 1) using a swing robot
/ Sec, the number of repetitions up to destruction when hitting the ball was measured. In Examples 1 to 3, the relative value when the number of repetitions in Comparative Example 1 was set to 100 was determined as an index. The relative value when the number of repetitions in Example 2 was set to 100 was determined as an index, and was set as a durability index.

(Examples 1-4, Comparative Examples 1-2) Polybutadiene rubber, zinc oxide, zinc acrylate or zinc methacrylate, an antioxidant and dicumyl peroxide,
Further, TEMPO is used as a nitroxide radical compound.
(2,2,6,6-tetramethyl-1-piperidinyloxy free radical), 4-hydroxy-TEMPO or 4-carboxy-TEMPO are kneaded according to the formulation shown in Table 1 to produce a kneaded product. did. At this time, the kneading processability was evaluated. Table 2 shows the results.

Next, the obtained kneaded materials were each added to 160
It was heated and pressed at 20 ° C. for 20 minutes to produce a core having a diameter of 38.3 mm, and the core characteristics were evaluated. Further, this solid core was coated with a cover composition shown in Table 1 to a thickness of 2.5 mm by injection molding to produce a two-layer two-piece golf ball, and the ball characteristics were evaluated. The ball characteristics were evaluated. Table 2 shows the results.

[0046] Note * 1: Polybutadiene rubber (cis-1,4 structure 97%), manufactured by Nippon Synthetic Rubber Co., Ltd. * 2: manufactured by Seiko Chemical Co., Ltd., Swanox BHT * 3: 2,2,6,6-tetramethyl-1 -Piperidinyloxy-free radical * 4: 4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy free radical * 5: 4-carboxy-2,2,6,6-tetramethyl-piperidinyl oxy free radical  * 6: Manufactured by Mitsui Dupont Polychemicals, sodium ionic ethylene-method  Tacrylic acid copolymer, Shore D hardness 67  * 7: Zinc ionic ethylene-methacrylate, manufactured by DuPont-Mitsui Polychemicals  Luic acid copolymer, Shore D hardness 66

[0047]

[0048]

The rubber composition of the present invention improves the kneading processability of the unsaturated metal carboxylate during the kneading of each component and suppresses the runaway reaction of the unsaturated metal carboxylate. A crosslinked product having excellent impact resistance and durability can be obtained without lowering the properties. Further, since the golf ball of the present invention has a core made of the rubber composition, the resilience is not reduced,
It is excellent in impact resistance and durability.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08K 5/32 C08K 5/32 F-term (Reference) 4J002 AC051 BB232 EG026 EG036 EG046 EG056 EK037 EK047 EU028 EU038 EU078 FD010 GC01

Claims (6)

[Claims] 1. A rubber composition comprising a base rubber containing a polybutadiene rubber having at least 40% of cis-1,4 bonds, a metal salt of an unsaturated carboxylic acid and an organic peroxide, and a nitroxide radical compound. 2. The rubber composition according to claim 1, wherein the nitroxide radical compound is a compound containing a polar group. 3. The method according to claim 1, wherein the nitroxide radical compound is 2,2.
The rubber composition according to claim 1 or 2, which is 2,6,6-tetramethyl-1-piperidinyloxy free radical. 4. The nitroxide radical compound is a compound having at least one polar group selected from an amino group, an isocyanate group, a hydroxyl group, a carboxyl group, an oxirane group and a thiirane group.
The rubber composition according to any one of the above. 5. The rubber composition according to claim 1, wherein the unsaturated metal salt of a carboxylic acid is at least one selected from zinc acrylate and zinc methacrylate. 6. A golf ball having a core comprising the rubber composition according to claim 1.