Golf ball and manufacturing method thereof

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a solid golf ball, particularly a solid golf ball having excellent uniformity, resilience performance and durability, and a method for manufacturing the same.

【0002】

[Conventional technology]

The core of a solid golf ball is made by heating a rubber composition in which a rubber component mainly composed of polybutadiene is mixed with an unsaturated carboxylic acid metal salt as a co-crosslinking agent and a free radical initiator to crosslink the main chain of rubber molecules. Manufactured by forming. Then, zinc acrylate is generally used as the unsaturated carboxylic acid metal salt, and graft polymerization is carried out on the polybutadiene main chain with a free radical initiator such as dicumyl peroxide to form a co-crosslink. Here, the dispersed state in the rubber composition such as an unsaturated carboxylic acid metal salt and the rate of the cross-linking reaction to the rubber molecule main chain largely depend on the basic physical properties of the rubber composition after cross-linking and the characteristics of the golf ball using the cross-linked. Affect.

【0003】

Therefore, conventionally, it has been proposed to coat the particle surface of zinc acrylate with a higher fatty acid or a higher fatty acid metal salt to improve the dispersibility of zinc acrylate in a rubber composition (Japanese Patent Laid-Open No. 59-141961). No., Japanese Patent Application Laid-Open No. 60-92781).

【0004】

Further, an unsaturated carboxylic acid metal salt having an average particle size of 5 μm or less and an unsaturated carboxylic acid salt having a particle size distribution of 0.1 to 5 μm and an average particle size of 1 to 4.5 μm are used as a co-crosslinking agent in the rubber composition. It has also been proposed to increase the dispersibility of unsaturated carboxylic acid metal salts (Japanese Patent Laid-Open Nos. 8-196661, 9-235413, 11-57068, 11-57069). ..

【0005】

These techniques are preferred methods for improving the dispersibility of the cocrosslinking agent in the rubber composition and increasing the hardness of the rubber composition. However, in this method, since the co-crosslinking agent is finely dispersed, the cross-linking density between the rubber molecule main chains, which contributes most to the repulsion performance, decreases, while the rubber molecule main chain and the co-crosslinking agent do not contribute much to the repulsion performance. The form of graft polymerization increases and the repulsion performance is not sufficiently exhibited.

【0006】

Therefore, the inventor has already proposed a method of improving the repulsion performance by adjusting the cross-linking rate between the rubber molecule main chains and the graft polymerization rate by using microcapsules in which the co-crosslinking agent is coated with a thermoplastic resin (special feature). Request 2000-281468).

【0007】

[Problems to be Solved by the Invention]

The present invention improves the uniform dispersibility of the co-crosslinking agent in the rubber composition of the rubber composition used for the solid core of a golf ball, and adjusts the cross-linking rate and the graft polymerization rate between the rubber molecule main chains. By doing so, a golf ball having further improved resilience performance and durability and a method for manufacturing the golf ball are provided.

【0008】

[Means for solving problems]

The present invention is a golf ball having a solid core and a cover covering the solid core. The solid core is blended with a co-crosslinking agent, and a part thereof is as a microcapsule coated with the co-crosslinking agent with a thermoplastic resin. It is a golf ball characterized by being a compounded rubber composition. Here, zinc acrylate and / or zinc methacrylate are preferably used as the co-crosslinking agent. The thermoplastic resin is preferably a material having a softening point in the range of 80 ° C to 250 ° C. Further, the co-crosslinking agent contained in the microcapsules is preferably 70 to 99% by weight of the total co-crosslinking agent.

【0009】

Next, another invention is a method for manufacturing a golf ball having a solid core and a cover that covers the circumference of the solid core. The solid core is manufactured by (1) using a cocrosslinking agent and a thermoplastic resin. It is characterized by including a step of mixing a microcapsule coated with a cross-linking agent with a rubber composition, and (2) a step of heating the rubber composition at a temperature higher than the softening point of the thermoplastic resin and cross-linking. This is a method for manufacturing a golf ball.

【0010】

BEST MODE FOR CARRYING OUT THE INVENTION

The golf ball according to the present invention is typically formed by coating a solid core with an ionomer resin or a thermoplastic resin such as trans 1,4-polyisoprene (TPI) as a cover material. For the solid core, microcapsules in which a co-crosslinking agent is blended in the rubber composition and a part thereof is coated with the co-crosslinking agent with a thermoplastic resin are used.

【0011】

In the present invention, an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metal salt thereof is used as the co-crosslinking agent. Examples of the α, β-unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid and the like, and acrylic acid is particularly preferable in order to enhance the resilience performance. Examples of the metal salt include metal salts such as zinc, sodium, magnesium, calcium and aluminum, and zinc salt is particularly preferable.

【0012】

As a co-crosslinking agent, a co-crosslinking agent microencapsulated with a thermoplastic resin that melts at a specific temperature and a co-crosslinking agent that is not microencapsulated are used in combination. By using the microencapsulated co-crosslinking agent, the graft polymerization rate of the rubber molecule main chain and the co-crosslinking agent can be controlled, the cross-linking density between the rubber molecule main chains can be optimized, and the repulsion performance is improved. On the other hand, by blending a small amount of a co-crosslinking agent that is not microencapsulated, the durability can be improved by performing graft polymerization to the extent that the resilience performance is not deteriorated.

【0013】

The microencapsulated co-crosslinking agent is in the range of 70-99% by weight, preferably 80-97% by weight, particularly 80-94% by weight of the total co-crosslinking agent. Here, if it is less than 70% by weight, the effect of improving the resilience performance by the microcapsules is small, while if it exceeds 99%, the improvement in durability cannot be expected sufficiently.

【0014】

The thermoplastic resin used for the membrane material of the microcapsules has a softening point of 80 to 250 ° C, preferably 100 to 200 ° C, particularly 120 to 160 ° C. If the softening point is lower than 80 ° C, the microcapsules may break during kneading of the rubber components. On the other hand, when the softening point exceeds 250 ° C., the thermoplastic resin which is the film material of the microcapsules does not melt and the co-crosslinking agent is not released from the microcapsules at the normal cross-linking temperature of the rubber composition. Therefore, the type of thermoplastic resin is preferably selected in relation to the vulcanization temperature.

【0015】

The thermoplastic resin used as the film material of the microcapsules in the present invention is, for example, polystyrene, polyethylene, polypropylene, polyurethane, nylon resin, acrylic resin, methacrylic resin, ethylene acrylic copolymer, ethylene vinyl acetate copolymer, vinyl chloride. It is possible to use resins, butadiene resins, butene resins, polycarbonates, ABS resins, AS resins and the like. When a chlorine-based resin such as vinyl chloride resin is used, it is preferable that the resin is soluble in an organic solvent and has a softening point near the intended temperature range.

【0016】

As a method for producing microcapsules by coating a co-crosslinking agent with a thermoplastic resin, a generally known microencapsulation method is adopted. For example, in the aerial suspension method, a core substance (powder) is fluidized and suspended by an air flow, and a thermoplastic resin film material is sprayed as an emulsified emulsion on the surface of suspended particles. Then, the suspended air can be heated to evaporate the solvent to form a capsule membrane. In the spray drying method, the core material is suspended in an emulsion obtained by emulsifying a thermoplastic resin membrane material, and the suspension is sprayed, made into fine particles, and instantly dried to form an encapsulated film. Can be done. Furthermore, a method of encapsulating powders by a dry method (a method of mixing core material particles and finer film material particles and then applying an impact by centrifugal force or the like to embed a film agent on the surface of the core material). Etc. can be adopted. From the viewpoint of the film strength of the microcapsules, a dry method of encapsulating the powders is preferable.

【0017】

The microcapsules obtained by the above method preferably contain 70 to 95% by weight of a cocrosslinking agent. If it is less than 70% by weight, the release of the co-crosslinking agent is insufficient, while if it exceeds 95% by weight, it becomes difficult to produce uniform microcapsules.

【0018】

In the present invention, the blending amount of the entire co-crosslinking agent in the rubber composition is in the range of 10 to 70 parts by weight, preferably 15 to 40 parts by weight, based on 100 parts by weight of the rubber component in terms of the co-crosslinking agent. .. If it is less than 10 parts by weight, a sufficient cross-linking density cannot be obtained, while if it exceeds 70 parts by weight, it becomes too hard and the density of graft polymerization of the co-crosslinking agent on the main chain of the rubber molecule is high, which is disadvantageous to the repulsion performance. At the same time, the feeling gets worse.

【0019】

The solid core rubber composition contains a microencapsulated co-crosslinking agent and a non-microencapsulated co-crosslinking agent, as well as a rubber component, an organic peroxide, a filler and the like. As the rubber component, either a natural rubber or a synthetic rubber diene rubber may be used, but it is preferable to use a high cis polybutadiene rubber containing 40% or more, particularly 90% or more of cis-1,4 bonds. .. If necessary, diene such as natural rubber (NR), polyisoprene rubber (IR), styrene-butadiene rubber (SBR), and ethylene / propylene / diene ternary copolymer (EPDM) may be added to the above high cis polybutadiene rubber. System rubber can be mixed.

【0020】

The organic peroxide is mainly blended as a cross-linking initiator to form a cross-link between the rubber molecule main chains. Since the crosslinked form of the organic peroxide mainly contributes to the repulsion performance, the blending amount of the organic peroxide is determined in consideration of the characteristics of the desired solid core. Organic peroxides include, for example, dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t-butylper). Oxy) hexane, di-t-butyl peroxide and the like are used, and among these, dicumyl peroxide is preferable. The blending amount of the organic peroxide is 0.1 to 5.0 parts by weight, preferably 0.3 to 3.0 parts by weight with respect to 100 parts by weight of the rubber component. If it is less than 0.1 parts by weight, the crosslink density is low and the hardness and resilience performance are low. On the other hand, if it exceeds 5.0 parts by weight, the crosslink density becomes high and it becomes too hard.

【0021】

Examples of the filler include metal salts such as zinc oxide, barium sulfate and calcium carbonate, which are mainly used for adjusting the specific gravity, and high specific gravity metal powders such as tungsten powder or molybdenum powder, and if necessary, an antiaging agent. Etc. may be blended.

【0022】

The outer diameter of the solid core is preferably 30 to 42 mm, particularly preferably 32 to 40 mm. When the outer diameter of the solid core is smaller than 30 mm, the cover becomes relatively thick, and as a result, the resilience performance tends to decrease. On the other hand, when the outer diameter of the solid core is larger than 42 mm, the cover becomes thin, and as a result, the molding of the golf ball becomes difficult and the durability deteriorates.

【0023】

Furthermore, the amount of deformation of the solid core when an initial load of 98 N to a final load of 1275 N is applied is adjusted to a range of 2.5 to 5.0 mm, preferably 2.8 to 4.0 mm. If it is less than 2.5 mm, the impact at the time of hitting is large and the shot feeling is not preferable. On the other hand, if it exceeds 5.0 mm, the hardness becomes low and the resilience performance deteriorates.

【0024】

In the present invention, as the solid core, either a solid core alone or a thread-wound core in which a thread rubber is wound around the solid core can be adopted. The solid core may be a core having a one-layer structure or a multi-layer core having two or more layers.

【0025】

The volume of the solid core of the present invention is preferably in the range of 30 to 90% of the entire golf ball, further in the range of 50 to 85%, and particularly preferably in the range of 60 to 80%. If it is less than 30%, the effect of the present invention is not sufficiently recognized. On the other hand, if it exceeds 90%, the cover becomes relatively thin and the durability of the golf ball is inferior.

【0026】

The solid core cross-linking reaction of the present invention is blended into the rubber composition as a co-crosslinking agent, partially as microcapsules coated with the co-crosslinking agent with a thermoplastic resin. Then, for example, the heating is carried out at a temperature of 120 to 230 ° C. for 10 to 50 minutes, preferably 130 to 200 ° C. for 10 to 40 minutes, and more preferably 140 to 180 ° C. for 10 to 40 minutes. The relationship between the heating temperature (A) and the softening point (B) of the thermoplastic resin that is the film material of the microcapsules is such that (AB) is in the range of 0 to 100 ° C, and further 10 to 90 ° C, especially 20 to 80. It is preferable to set it in the range of ° C.

【0027】

If it is not (A> B), the release of the co-crosslinking agent from the microcapsules will be delayed, the cross-linking time will be long, and the productivity will be reduced. On the other hand, when (AB) exceeds 100 ° C, the microcapsules are destroyed during kneading of the rubber composition, and the effect of the present invention cannot be achieved.

【0028】

For example, when the cross-linking reaction is carried out at 140 to 170 ° C, it is preferable to use a thermoplastic resin such as polystyrene or polyethylene whose softening point is in the vicinity of 100 to 120 ° C. Since the crosslinking reaction is an exothermic reaction, the crosslinking temperature is higher than the heating temperature for the mold. Therefore, it is preferable to control the cross-linking temperature by the measured value inside the solid core. In the present invention, since a co-crosslinking agent that is not microencapsulated is used in combination, the internal temperature of the rubber composition of the core rises above the heating temperature due to the exothermic reaction during cross-linking. Therefore, the co-crosslinking agent is released from the microcapsules even when (AB) is 0 ° C.

【0029】

When the heating temperature of the solid core rubber composition is below the softening point of the thermoplastic resin, the cross-linking reaction by the co-crosslinking agent in the rubber composition is unlikely to occur, so there is less time constraint from kneading to molding and process control. Becomes easier.

【0030】

The softening point of the thermoplastic resin is measured using the analyzer TMA. The specific method for measuring the softening point is to place a measuring needle loaded on a plate-shaped thermoplastic resin sample and raise the temperature at a predetermined heating rate such as 5 ° C / min. At ° C, measure whether the measuring needle penetrates into the sample.

【0031】

The golf ball of the present invention is configured by covering the solid core with a cover. Here, the cover composition contains trans 1,4-polyisoprene, ionomer resin, polyethylene resin, polypropylene resin, polyester-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polystyrene-based thermoplastic elastomer, and the like alone. Alternatively, they can be mixed and used.

【0032】

The trans 1,4-polyisoprene refers to a polymer molecule containing 60% or more of a trans structure. If the transformer structure is less than 60%, there are few crystal parts, and therefore the softening point is too low to satisfy the basic characteristics as a cover.

【0033】

Further, the ionomer resin is obtained, for example, by neutralizing at least a part of the carboxyl groups in the copolymer of α-olefin and α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms with metal ions. At least one of the carboxyl groups in the ternary copolymer of 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. Examples thereof include those obtained by neutralizing the part with metal ions. As the above-mentioned α-olefin, for example, ethylene, propylene, 1-butene, 1-pentene and the like are used, ethylene is particularly preferable, and as the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms, for example, Acrylic acid, methacrylic acid, fumaric acid, maleic acid, crotonic acid and the like are used, and acrylic acid and methacrylic acid are particularly preferable. As the unsaturated carboxylic acid ester having 2 to 22 carbon atoms, for example, methyl, ethyl, propyl, n-butyl, isobutyl ester such as acrylic acid, methacrylic acid, fumaric acid, and maleic acid are used, and particularly acrylic. Acid esters and methacrylic acid esters are preferred.

【0034】

Then, a copolymer of the above α-olefin and α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms or α-olefin and α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and 2 to 2 carbon atoms. Examples of metal ions that neutralize at least a part of the carboxyl groups in the ternary copolymer with 22 α, β-unsaturated carboxylic acid esters include sodium ion, lithium ion, zinc ion, magnesium ion, and potassium. Examples include ions.

【0035】

From the viewpoint of enhancing durability and resilience performance, it is preferable to use a polymer component mainly composed of a thermoplastic resin and / or a thermoplastic elastomer in the cover composition of the present invention. In particular, when ionomer resin is blended in the cover composition in an amount of 50% by weight or more, preferably 70% by weight or more, durability and resilience performance are improved.

【0036】

Here, the thickness of the cover is preferably 0.35 to 6.35 mm, more preferably 0.7 to 5.35 mm, particularly preferably 1.0 to 4.0 mm. This is because if it is less than 0.35 mm, the cover strength and durability are lowered, while if it exceeds 6.35 mm, the volume fraction of the cover component in the entire ball is increased and the repulsion performance of the ball is lowered.

【0037】

Fiber reinforced rubber, fiber reinforced resin, specific gravity adjusting agent, metal powder, metal oxide, colored powder, specific gravity adjusting agent, fluorescent whitening agent, lubricant and the like can be appropriately mixed in the cover.

【0038】

Next, in the method for producing a golf ball of the present invention, the cover composition is first kneaded with a roll or a kneader. Then, in order to coat the solid core with the cover composition, a half-shell-shaped half shell is prepared in advance, two of them are used to wrap the solid core, and pressure molding is performed at 130 to 170 ° C for 1 to 5 minutes. Alternatively, the cover composition is injection-molded directly onto the solid core to coat the solid core.

【0039】

[Example]

(1) Manufacture of microcapsules 5 g of polystyrene (softening point 100 ° C) was dissolved in 50 ml of methylene chloride, 100 g (concentration 20%) of an aqueous zinc acrylate solution was added to this solution as a cocrosslinking agent, and the mixture was stirred for 30 minutes for emulsification. The emulsified state was a (W / O) type emulsion. Next, 1 liter of a 4% PVA aqueous solution was prepared, and the above-mentioned (W / O) type emulsion was added while stirring to obtain a [(W / O) / W] type composite emulsion. The temperature of the system was gradually raised to 40 ° C. to evaporate methylene chloride, and then the mixture was stirred at 55 ° C. for 1 hour to cure the membrane material to obtain microcapsules. Zinc acrylate is contained in the microcapsules at 78% by weight.

【0040】

(2) Fabrication of solid core The rubber compositions shown in Table 1 were kneaded using a kneader and a roll, and heat-press molded at 160 ° C. for 30 minutes to prepare a solid core having an outer diameter of 38.4 mm and a weight of 34.6 g. During kneading, the temperature was controlled so that the temperature of the rubber composition did not exceed 100 ° C. Table 1 shows the amount of compressive deformation (mm) when the final load of 1275N is applied from the initial load of 98N of the solid core.

【0041】

(3) Manufacture of cover compositions and golf balls The cover composition shown in Table 1 was coated on the solid core to a thickness of 2.3 mm by injection molding, and a urethane clear paint was applied thereto. The obtained golf ball had a diameter of 42.7 mm and a weight of 45.4 g.

【0042】

[table 1]

<img file="JP2002159595A_D0001.tif" />【0043】

The contents of the polymer components and compounding agents used in the core composition and the cover composition in Table 1 are as follows. Note 1: BR01 manufactured by JSR was used as the polybutadiene. The cis-1,4 bond content is 96%. Note 2: The microcapsules used in the examples were used. Note 3: ZNDA-90S manufactured by Nippon Distillery Co., Ltd. was used as zinc acrylate. Note 4: Zinc oxide manufactured by Toho Zinc Co., Ltd. was used. Note 5: Park Mill D manufactured by NOF CORPORATION was used as the dicumyl peroxide. Note 6: For Hymilan 1605, a sodium-neutralized ionomer manufactured by Mitsui DuPont Polychemical Co., Ltd. was used. Note 7: For Hymilan 1706, a zinc-neutralized ionomer manufactured by Mitsui DuPont Polychemical Co., Ltd. was used. Note 8: A-220 manufactured by Ishihara Sangyo Co., Ltd. was used as titanium oxide.

【0044】

The physical characteristics of the obtained golf ball were measured by the following method. 1) Amount of compression deformation The amount of deformation of the solid core when the initial load of 98N to the final load of 1275N was measured was measured.

【0045】

2) Coefficient of restitution It was calculated from the speed of a golf ball when an aluminum cylinder weighing 198.4 g was launched at an initial speed of 45 m / s and hit the golf ball.

【0046】

3) Durability The number of times a golf ball is repeatedly hit with Wood No. 1 club at an initial velocity of 45 m / s until the golf ball is destroyed is shown as an index with Comparative Example 2 as 100.

【0047】

From Table 1, Examples 1 to 3 of the present invention were microencapsulated in a co-crosslinking agent, and a part of the microencapsulated material was used for a solid core rubber composition. It is recognized that the coefficient of restitution and durability are comprehensively superior to those of Comparative Example 2, which is a rubber composition that does not use microcapsules.

【0048】

It should be noted that the embodiments and examples disclosed this time are examples in all respects and are not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and it is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

【0049】

[Effect of the invention]

In the present invention, by encapsulating a part of the co-crosslinking agent blended in the solid core rubber composition in a capsule with a thermoplastic resin, most of the co-crosslinking agent is contained in the rubber composition in the state of microcapsules at the time of kneading. Can be evenly dispersed. During the cross-linking reaction, the rubber composition is heated above the softening point of the thermoplastic resin, so that the co-crosslinking agent trapped by melting the microcapsules is released and comes into contact with the cross-linking initiator to start the cross-linking reaction. Since the co-crosslinking agent starts the reaction immediately after the microcapsules are melted, the co-crosslinking agent performs a cross-linking reaction with the main chain of the rubber molecule as a certain amount of mass.

【0050】

Further, the reaction between the rubber molecule and the co-crosslinking agent is adjusted in its graft polymerization rate by the non-microencapsulated co-crosslinking agent and the microencapsulated co-crosslinking agent. Therefore, it is possible to reduce the number of graft bond points between the rubber molecule and the co-crosslinking agent, and it is possible to obtain a solid core that is soft and has excellent resilience performance. Further, since the size of the particles can be made uniform by the microcapsules, a solid core having uniform physical characteristics can be obtained. Furthermore, since cross-linking of the rubber molecule main chain is formed by a cross-linking initiator such as peroxide until the microcapsules are melted, a cross-linked form advantageous for repulsion performance can be formed, and repulsion performance and durability are improved. can do.