JP7119909B2 - Spherical core and golf ball manufacturing method - Google Patents

Description

The present invention relates to a spherical core and a method of manufacturing a golf ball.

A rubber composition containing a base rubber, a co-crosslinking agent, and a cross-linking initiator is widely used as a material for forming the core of a golf ball because of its good resilience.

For example, Patent Document 1 discloses a golf ball having a spherical core and at least one layer or more of a cover covering the spherical core, wherein the spherical core comprises (a) a base rubber and (b) a co-crosslinking agent. α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof, (c) a cross-linking initiator, (d) a petroleum resin, and (b) a co-crosslinking agent having 3 carbon atoms A golf ball is disclosed which is formed from a rubber composition which further contains (e) a metal compound if it contains only up to 8 α,β-unsaturated carboxylic acids.

Further, in Patent Document 2, a viscoelastic body having an impact resilience (according to JIS K 630) of 40% or less and a maximum internal loss factor tan δ of 0.3 or more in the range of 0° to 40°C is used. The inner core is vulcanized to butyl rubber, ethylene-propylene-diene terpolymer, high-styrene rubber, ethylene-propylene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber or norbornene polymer. A golf ball having an inner core made of a rubber composition containing conventional additives such as agents, vulcanization accelerators, lubricants, plasticizers, etc., as well as large amounts of fillers, softening agents, and resins such as petroleum resins and terpene resins. is disclosed.

Patent Document 3 discloses at least three core layers including a center, an inner core layer, and an outer core layer, at least one cover layer, and the cover layer between the outer core layer and at least the cover layer. at least one water vapor barrier layer that achieves a water vapor transmission rate greater than the water vapor transmission rate, and wherein the center, the inner core layer, and the outer core layer are provided with a hardness gradient. A ball is disclosed. It is described that a terpene resin, a terpene resin ester, or the like may be added to the water vapor barrier layer (Paragraph 0031).

Patent Document 4 includes a core, an intermediate layer, and a cover, wherein the intermediate layer is made from a composition containing an ionomer resin and a rosin material having a softening point of at least about 50°C. A golf ball is disclosed which features:

U.S. Pat. No. 5,400,003 discloses a golf ball having a core and a cover layer, at least one of the core or cover layer having a plasticized polyurethane formulation having at least one polyurethane and at least one plasticizer. .

Patent Document 6 describes the dynamic viscoelasticity of a golf ball consisting of a core and a cover in a tension mode measured under the conditions of a heating rate of 4° C./min, a frequency of 10 Hz, and an initial strain of 1.0 mm. There is disclosed a golf ball characterized by a loss tangent (tan δ) at −10° C. of 0.15 to 0.70 in a temperature dispersion curve. The cover composition comprises an ionomer resin alone or a mixture of an ionomer resin as a main component and one or more elastomers having a rubber component, and a terpene resin and/or a rosin ester resin as a tackifier. contains.

JP 2016-019620 A JP-A-63-54181 JP 2008-126062 A Japanese Patent Application Laid-Open No. 2006-320725 JP 2005-185836 A JP 2001-137386 A

A spherical core obtained by heating a core rubber composition at a temperature of about 150° C. to 170° C. for about 10 minutes to 30 minutes has a hardness difference between the surface hardness and the center hardness. It is believed that this is because a temperature distribution occurs inside the spherical core with the curing reaction of the rubber composition, causing a difference in the curing reaction between the surface portion of the core and the center portion of the core. A spherical core having a hardness difference between the surface hardness and the center hardness reduces the spin rate of the golf ball. A golf ball with a low spin rate travels a greater flight distance on driver shots.

On the other hand, a spherical core with a small difference between the surface hardness and the center hardness improves the durability of the golf ball. A spherical core with a small difference between surface hardness and center hardness needs to be molded by heating at a low temperature of about 120° C. to 130° C. for 60 to 90 minutes. That is, there is a problem that the production time is long in order to manufacture a spherical core having a small hardness difference between the surface hardness and the center hardness. The present invention has been made in view of the above circumstances, and an object of the present invention is to improve production efficiency of a method for manufacturing a spherical core having a small difference between surface hardness and central hardness.

The method for producing the spherical core of the present invention comprises (a) a base rubber, (b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof as a co-crosslinking agent, and (c) cross-linking. By pressing a core rubber composition containing an initiator and (d) a terpene resin under conditions of press temperature: 125° C. to 180° C., press pressure: 1 MPa to 25 MPa, press time: 15 minutes to 40 minutes. and forming a spherical core by cross-linking the core composition. The present inventors have found that by blending (d) a terpene-based resin into a core rubber composition, a spherical core having a small difference between surface hardness and center hardness can be produced in a short period of time, thereby completing the present invention. reached.

According to the present invention, a spherical core having a small difference between surface hardness and central hardness can be produced in a short period of time.

1 is a partially cutaway cross-sectional view showing a golf ball according to one embodiment of the present invention; FIG.

The method for producing the spherical core of the present invention comprises (a) a base rubber, (b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof as a co-crosslinking agent, and (c) cross-linking. By pressing a core rubber composition containing an initiator and (d) a terpene resin under conditions of press temperature: 125° C. to 180° C., press pressure: 1 MPa to 25 MPa, press time: 15 minutes to 40 minutes. and forming a spherical core by cross-linking the core rubber composition.

First, the core rubber composition used in the present invention will be described.

[(a) base rubber]
As the base rubber, natural rubber and/or synthetic rubber can be used, such as polybutadiene rubber, natural rubber, polyisoprene rubber, styrene polybutadiene rubber, ethylene-propylene-diene rubber (EPDM). These may be used independently and may use 2 or more types together. Among these, high-cis polybutadiene having 40% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more of cis-1,4-bonds that are advantageous for repulsion is particularly suitable.

The high-cis polybutadiene preferably has a 1,2-vinyl bond content of 2% by mass or less, more preferably 1.7% by mass or less, and even more preferably 1.5% by mass or less. If the 1,2-vinyl bond content is too high, the resilience may decrease.

The high-cis polybutadiene is preferably synthesized with a rare earth element-based catalyst, and in particular, the use of a neodymium-based catalyst using a neodymium compound, which is a lanthanum-series rare earth element compound, has a high content of 1,4-cis bonds. , 1,2-vinyl bonds are preferred because they yield low-content polybutadiene rubbers with excellent polymerization activity.

The high-cis polybutadiene preferably has a Mooney viscosity (ML ₁₊₄ (100° C.)) of 30 or more, more preferably 32 or more, still more preferably 35 or more, and preferably 140 or less, more preferably It is 120 or less, more preferably 100 or less, and most preferably 80 or less. The Mooney viscosity (ML ₁₊₄ (100° C.)) referred to in the present invention refers to conditions of 100° C., using an L rotor, preheating for 1 minute, rotating the rotor for 4 minutes, in accordance with JIS K6300. It is the value measured below.

The high-cis polybutadiene preferably has a molecular weight distribution Mw/Mn (Mw: weight average molecular weight, Mn: number average molecular weight) of 2.0 or more, more preferably 2.2 or more, still more preferably 2.2. It is 4 or more, most preferably 2.6 or more, preferably 6.0 or less, more preferably 5.0 or less, still more preferably 4.0 or less, and most preferably 3.4 or less. If the molecular weight distribution (Mw/Mn) of the high-cis polybutadiene is too small, the workability may deteriorate, and if it is too large, the resilience may deteriorate. The molecular weight distribution was measured by gel permeation chromatography (manufactured by Tosoh Corporation, "HLC-8120GPC") using a differential refractometer as a detector, column: GMHHXL (manufactured by Tosoh Corporation), column temperature: 40 ° C., mobile phase : Value measured under tetrahydrofuran conditions and calculated as a standard polystyrene conversion value.

In the present invention, it is preferable to use polybutadiene as (a) the base rubber, and high-cis polybutadiene containing 90% by mass or more of cis-1,4-bonds (hereinafter simply referred to as "high-cis polybutadiene"). It is more preferable to use

[(b) co-crosslinking agent]
The (b) α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or metal salt thereof used in the core rubber composition is blended into the rubber composition as a co-crosslinking agent. , have the effect of cross-linking rubber molecules by graft polymerization to the base rubber molecular chains.

Examples of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid and crotonic acid.

The metal constituting the metal salt of α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms includes monovalent metal ions such as sodium, potassium and lithium; magnesium, calcium, zinc, barium, cadmium and the like. trivalent metal ions such as aluminum; other ions such as tin and zirconium. The metal components may be used singly or as a mixture of two or more. Among these, divalent metals such as magnesium, calcium, zinc, barium, and cadmium are preferable as the metal component. This is because the use of a divalent metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms facilitates the formation of metal crosslinks between rubber molecules. In particular, zinc acrylate is suitable as the divalent metal salt because the resulting golf ball has a high resilience. The α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms and/or metal salts thereof may be used alone or in combination of two or more.

The content of the (b) α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof is preferably 15 parts by mass or more with respect to 100 parts by mass of the base rubber (a). , more preferably 20 parts by mass or more, more preferably 25 parts by mass or more, preferably 50 parts by mass or less, more preferably 45 parts by mass or less, and even more preferably 35 parts by mass or less. (b) When the content of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or the metal salt thereof is less than 15 parts by mass, the core formed from the core rubber composition has an appropriate hardness. In order to achieve this, the amount of (c) a crosslinking initiator, which will be described later, must be increased, which tends to reduce the resilience of the resulting golf ball. On the other hand, when the content of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or the metal salt thereof exceeds 50 parts by mass, the core formed from the core rubber composition becomes too hard. , the feel at impact of the resulting golf ball may deteriorate.

[(c) cross-linking initiator]
The (c) cross-linking initiator used in the core rubber composition is blended to cross-link the (a) base rubber component. (c) As the cross-linking initiator, an organic peroxide is suitable. Specific examples of the organic peroxide include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di Examples include organic peroxides such as (t-butylperoxy)hexane and di-t-butylperoxide. These organic peroxides may be used alone or in combination of two or more. Among these, dicumyl peroxide is preferably used.

The one-minute half-life temperature of the (c) crosslinking initiator is preferably 100° C. or higher, more preferably 130° C. or higher, preferably 200° C. or lower, and more preferably 180° C. or lower.

The content of the (c) cross-linking initiator is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, and 0.7 parts by mass or more relative to 100 parts by mass of the (a) base rubber. is more preferably 5.0 parts by mass or less, more preferably 2.5 parts by mass or less, and even more preferably 2.0 parts by mass or less. If the content of the cross-linking initiator is less than 0.2 parts by mass, the core formed from the core rubber composition tends to be too soft and the resilience of the resulting golf ball tends to decrease. above, it is necessary to reduce the amount of the above-mentioned (b) co-crosslinking agent in order to make the core formed from the core rubber composition have an appropriate hardness, and the resilience of the resulting golf ball is reduced. There is a possibility that it will be insufficient or the durability will be deteriorated.

[(d) Terpene-based resin]
The terpene-based resin used in the present invention is not particularly limited as long as it is a polymer having a terpene compound as a constituent component. The terpene-based resin is, for example, a terpene polymer, a terpene-phenol copolymer, a terpene-styrene copolymer, a terpene-phenol-styrene copolymer, a hydrogenated terpene-phenol copolymer, a hydrogenated terpene-styrene copolymer. It is preferably at least one selected from the group consisting of polymers and hydrogenated terpene/phenol/styrene copolymers.

The terpene polymer is a homopolymer obtained by polymerizing a terpene compound. Terpene compounds are hydrocarbons represented by the composition (C ₅ H ₈ ) _n and their oxygen-containing derivatives, such as monoterpene (C ₁₀ H ₁₆ ), sesquiterpene (C ₁₅ H ₂₄ ), diterpene (C ₂₀ H ₃₂ ) is a compound having a terpene as a basic skeleton. Examples of the terpene compounds include α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineol, 1,4 -cineol, α-terpineol, β-terpineol, γ-terpineol and the like. The terpene compounds can be used alone or in combination of two or more.

A terpene polymer is obtained, for example, by polymerizing the terpene compound. Examples of the terpene polymer include α-pinene polymer, β-pinene polymer, limonene polymer, dipentene polymer, and β-pinene/limonene polymer.

A terpene-phenol copolymer (sometimes referred to as a “terpene phenol resin”) is, for example, a copolymer of the terpene compound and a phenolic compound. Examples of the phenolic compound include phenol, cresol, xylenol, catechol, resorcinol, hydroquinone, bisphenol A and the like. As the terpene-phenol copolymer, a copolymer of a terpene compound and phenol is preferable.

The acid value of the terpene-phenol copolymer is preferably 10 mgKOH/g or more, more preferably 35 mgKOH/g or more, and even more preferably 60 mgKOH/g or more. The acid value of the terpene-phenol copolymer is preferably 300 mgKOH/g or less, more preferably 250 mgKOH/g or less, even more preferably 200 mgKOH/g or less, and 150 mgKOH/g or less. is particularly preferred, and 90 mgKOH/g or less is most preferred. In the present invention, the acid value of the terpene-phenol copolymer is the amount of potassium hydroxide required to neutralize the acid contained in 1 g of the terpene-phenol copolymer expressed in milligrams. It is a value measured by a potentiometric titration method (JIS K 0070:1992).

The hydroxyl value of the terpene-phenol copolymer is preferably 30 mgKOH/g or more, more preferably 50 mgKOH/g or more. The hydroxyl value of the terpene-phenol copolymer is preferably 150 mgKOH/g or less, more preferably 100 mgKOH/g or less. In the present specification, the hydroxyl value is the amount of potassium hydroxide required to neutralize the acetic acid bound to the hydroxyl group when 1 g of the resin is acetylated, expressed in milligrams, by potentiometric titration. It is a value measured according to (JIS K 0070:1992).

The terpene/styrene copolymer is, for example, a copolymer of the terpene compound and a styrene compound. Examples of the styrene compounds include styrene and α-methylstyrene. The terpene/styrene copolymer is preferably a copolymer of the terpene compound and α-methylstyrene.

The terpene-phenol-styrene copolymer is, for example, a copolymer of the terpene compound, the phenol compound, and the styrene compound. The terpene/phenol/styrene copolymer is preferably a copolymer of the terpene compound, phenol and α-methylstyrene.

The hydrogenated terpene-phenol copolymer is obtained by hydrogenating the terpene-phenol copolymer. The hydrogenated terpene-styrene copolymer is obtained by hydrogenating the terpene-styrene copolymer. The hydrogenated terpene-phenol-styrene copolymer is obtained by hydrogenating the terpene-phenol-styrene copolymer.

(d) The terpene-based resin is preferably at least one selected from compounds having structures represented by the following formulas (1) to (4).

［式（１）～（４）中、Ｒ^１およびＲ^２は、それぞれ独立して、フェノール系化合物および／またはスチレン系化合物の二価の残基を表す、ｍ^１～ｍ^４は、それぞれ独立に１～３０の自然数を表し、ｎ^１～ｎ^２は、それぞれ独立に１～２０の自然数を表す。］

[In formulas (1) to (4), R ¹ and R ² each independently represent a divalent residue of a phenolic compound and/or a styrenic compound, m ¹ to m ⁴ each independently represents a natural number of 1 to 30, and n ¹ to n ² each independently represents a natural number of 1 to 20. ]

All of the compounds having the structures represented by formulas (1) to (4) have a structure derived from pinene in the molecule.

A compound having a structure represented by formula (1) has a repeating unit consisting of a structural portion derived from α-pinene and R ¹ bonded to the structural portion derived from α-pinene. R ¹ is preferably a divalent residue obtained by removing two hydrogen atoms from the benzene ring of the phenolic compound and/or the styrenic compound. Examples of compounds having a structure represented by formula (1) include copolymers of α-pinene and phenolic compounds and/or styrene compounds.

Examples of the phenolic compound include phenol, cresol, xylenol, catechol, resorcinol, hydroquinone, bisphenol A and the like. Examples of the styrene compounds include styrene and α-methylstyrene.

In formula (1), m ¹ represents the degree of polymerization of structural units derived from α-pinene, and is preferably a natural number of 1-30. m ¹ is preferably 1 or more, more preferably 2 or more, still more preferably 3 or more, and preferably 30 or less, more preferably 25 or less, still more preferably 20 or less.

In formula (1), n ¹ represents the degree of polymerization of a repeating unit composed of a structural moiety derived from α-pinene and R ¹ bonded to the structural moiety derived from α-pinene, and is a natural number of 1 to 20. is preferably The n1 is preferably ¹ or more, more preferably 2 or more, still more preferably 3 or more, and preferably 20 or less, more preferably 18 or less, still more preferably 15 or less.

A compound having a structure represented by formula (2) has a repeating unit consisting of a structural portion derived from β-pinene and R ² bonded to this structural portion in the molecule. Examples of compounds having a structure represented by formula (2) include copolymers of β-pinene and phenolic compounds and/or styrene compounds. R ² is a divalent residue obtained by removing two hydrogen atoms from a benzene ring of a phenolic compound and/or a styrene compound.

Examples of the phenolic compound include phenol, cresol, xylenol, catechol, resorcinol, hydroquinone, bisphenol A and the like. Examples of the styrene compounds include styrene and α-methylstyrene.

In formula (2), m ² represents the degree of polymerization of structural units derived from β-pinene, and is preferably a natural number of 1-30. m ² is preferably 1 or more, more preferably 2 or more, still more preferably 3 or more, and preferably 30 or less, more preferably 25 or less, still more preferably 20 or less.

In formula ( ² ), n2 represents the degree of polymerization of a repeating unit consisting of a structural portion derived from β-pinene and ^R2 bonded to this structural portion, and is preferably a natural number of 1-20. The n2 is preferably 1 or more, more preferably ² or more, still more preferably 3 or more, and preferably 20 or less, more preferably 18 or less, and still more preferably 15 or less.

The compound having the structure represented by formula (3) is a polymer having structural units derived from α-pinene, and more preferably a polymer having only structural units derived from α-pinene.

In formula (3), m ³ represents the degree of polymerization of structural units derived from α-pinene, and is preferably a natural number of 1-30. m ³ is preferably 1 or more, more preferably 2 or more, still more preferably 3 or more, and preferably 30 or less, more preferably 25 or less, still more preferably 20 or less.

A compound having a structure represented by formula (4) is a β-pinene polymer having structural units derived from β-pinene in the molecule, and is a polymer having only structural units derived from β-pinene. is more preferable.

In formula (4), m ⁴ represents the degree of polymerization of structural units derived from β-pinene, and is preferably a natural number of 1-30. m ⁴ is preferably 1 or more, more preferably 2 or more, still more preferably 3 or more, and preferably 30 or less, more preferably 25 or less, still more preferably 20 or less.

The (d) terpene-based resin includes an α-pinene/phenol copolymer, an α-pinene/α-methylstyrene copolymer, an α-pinene/α-methylstyrene/phenol copolymer, and a β-pinene/phenol copolymer. It preferably contains at least one selected from the group consisting of polymers, β-pinene/α-methylstyrene copolymers, and β-pinene/α-methylstyrene/phenol copolymers. As the (d) terpene-based resin, these copolymers may be used alone, or two or more thereof may be used in combination.

The softening point of the terpene-based resin (d) is preferably 60° C. or higher, more preferably 80° C. or higher, even more preferably 100° C. or higher, preferably 150° C. or lower, and 130° C. or lower. and more preferably 120° C. or less. This is because use of the (d) terpene-based resin having a softening point within the above range improves resin dispersibility during rubber kneading. The softening point of the (d) terpene-based resin is the temperature at which the sphere descends when the softening point specified in JIS K 6220-1:2001 is measured with a ring and ball type softening point measuring device.

As the (d) terpene-based resin, a commercially available product can be used, and examples thereof include Sylvares TP2019, Sylvares TP7042, Sylvares TR7115, Sylvares TR7125, and Sylvatraxx6720 manufactured by KRATON; YS Resin PX1150 and YS Resin PX1250 manufactured by Yasuhara Chemical.

The content of the (d) terpene-based resin is preferably 3 parts by mass or more, more preferably 4 parts by mass or more, further preferably 5 parts by mass or more, and 20 parts by mass with respect to 100 parts by mass of the (a) base rubber. parts by mass or less is preferable, 18 parts by mass or less is more preferable, and 15 parts by mass or less is even more preferable. If the content of component (d) is less than 3 parts by mass, the effect of adding component (d) may be small, and the effect of improving the shot feel on driver shots may not be obtained. On the other hand, if the content of component (d) exceeds 20 parts by mass, the resulting core may become too soft overall, resulting in a decrease in resilience.

The blending ratio of the component (b) and the component (d) (component (b)/component (d)) is preferably 2.0 or more, more preferably 2.5 or more, and still more preferably 2.5 or more in mass ratio. It is 2.8 or more, preferably 15.0 or less, more preferably 12.0 or less, still more preferably 10.0 or less, and particularly preferably 8.0 or less. If the compounding ratio of component (b) and component (d) (component (b)/component (d)) is within the above range, the resulting golf ball will have a better shot feel on driver shots.

[(e) Organic sulfur compound]
The core rubber composition preferably further contains (e) an organic sulfur compound. (e) The inclusion of an organic sulfur compound improves the resilience of the resulting core.

The (e) organic sulfur compounds include thiols (thiophenols, thionaphthols), polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, and thiazoles. At least one compound selected from the group is preferred.

Thiols include, for example, thiophenols and thionaphthols. Examples of the thiophenols include thiophenol; 4-fluorothiophenol, 2,4-difluorothiophenol, 2,5-difluorothiophenol, 2,6-difluorothiophenol, 2,4,5-trifluoro Thiophenols substituted with a fluoro group such as thiophenol, 2,4,5,6-tetrafluorothiophenol, pentafluorothiophenol; 2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothio Chloro groups such as phenol, 2,5-dichlorothiophenol, 2,6-dichlorothiophenol, 2,4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol, and pentachlorothiophenol substituted thiophenols; 4-bromothiophenol, 2,4-dibromothiophenol, 2,5-dibromothiophenol, 2,6-dibromothiophenol, 2,4,5-tribromothiophenol, 2, Bromo-substituted thiophenols such as 4,5,6-tetrabromothiophenol and pentabromothiophenol; 4-iodothiophenol, 2,4-diiodothiophenol, 2,5-diiodothiophenol , 2,6-diiodothiophenol, 2,4,5-triiodothiophenol, 2,4,5,6-tetraiodothiophenol, pentaiodothiophenol, and other iodine-substituted thiophenols; Alternatively, metal salts thereof may be mentioned. A zinc salt is preferred as the metal salt.

The thionaphthols (naphthalenephthols) include 2-thionaphthol, 1-thionaphthol, 1-chloro-2-thionaphthol, 2-chloro-1-thionaphthol, 1-bromo-2-thionaphthol, 2 -bromo-1-thionaphthol, 1-fluoro-2-thionaphthol, 2-fluoro-1-thionaphthol, 1-cyano-2-thionaphthol, 2-cyano-1-thionaphthol, 1-acetyl-2- Thionaphthol, 2-acetyl-1-thionaphthol, or metal salts thereof may be mentioned, with 2-thionaphthol, 1-thionaphthol, or metal salts thereof being preferred. The metal salt is preferably a divalent metal salt, more preferably a zinc salt. Specific examples of metal salts include zinc salts of 1-thionaphthol and zinc salts of 2-thionaphthol.

Polysulfides are organic sulfur compounds having a polysulfide bond, and examples thereof include disulfides, trisulfides, and tetrasulfides. Diphenyl polysulfides are preferred as the polysulfides.

Diphenyl polysulfides include diphenyl disulfide, bis(4-fluorophenyl) disulfide, bis(2,5-difluorophenyl) disulfide, bis(2,6-difluorophenyl) disulfide, bis(2,4,5- trifluorophenyl)disulfide, bis(2,4,5,6-tetrafluorophenyl)disulfide, bis(pentafluorophenyl)disulfide, bis(4-chlorophenyl)disulfide, bis(2,5-dichlorophenyl)disulfide, bis( 2,6-dichlorophenyl)disulfide, bis(2,4,5-trichlorophenyl)disulfide, bis(2,4,5,6-tetrachlorophenyl)disulfide, bis(pentachlorophenyl)disulfide, bis(4-bromophenyl) Disulfide, bis(2,5-dibromophenyl)disulfide, bis(2,6-dibromophenyl)disulfide, bis(2,4,5-tribromophenyl)disulfide, bis(2,4,5,6-tetrabromo) phenyl)disulfide, bis(pentabromophenyl)disulfide, bis(4-iodophenyl)disulfide, bis(2,5-diiodophenyl)disulfide, bis(2,6-diiodophenyl)disulfide, bis(2,4 ,5-triiodophenyl)disulfide, bis(2,4,5,6-tetraiodophenyl)disulfide, bis(pentayodophenyl)disulfide and other halogen-substituted diphenyldisulfides; bis(4-methylphenyl) ) disulfide, bis(2,4,5-trimethylphenyl)disulfide, bis(pentamethylphenyl)disulfide, bis(4-t-butylphenyl)disulfide, bis(2,4,5-tri-t-butylphenyl) disulfides, diphenyl disulfides substituted with an alkyl group such as bis(penta-t-butylphenyl) disulfide; and the like.

Thiurams include, for example, thiuram monosulfides such as tetramethylthiuram monosulfide, thiuram disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetrabutylthiuram disulfide, and thiuram tetrasulfides such as dipentamethylenethiuram tetrasulfide. is mentioned. Thiocarboxylic acids include, for example, naphthalenethiocarboxylic acid. Examples of dithiocarboxylic acids include naphthalenedithiocarboxylic acid. Examples of sulfenamides include N-cyclohexyl-2-benzothiazolesulfenamide, N-oxydiethylene-2-benzothiazolesulfenamide, and Nt-butyl-2-benzothiazolesulfenamide. mentioned.

As the (e) organic sulfur compound, thiophenols and/or metal salts thereof, thionaphthols and/or metal salts thereof, diphenyl disulfides and thiuram disulfides are preferable, and 2,4-dichlorothiophenol is more preferable. , 2,6-difluorothiophenol, 2,6-dichlorothiophenol, 2,6-dibromothiophenol, 2,6-diiodothiophenol, 2,4,5-trichlorothiophenol, pentachlorothiophenol, 1 -thionaphthol, 2-thionaphthol, diphenyl disulfide, bis(2,6-difluorophenyl) disulfide, bis(2,6-dichlorophenyl) disulfide, bis(2,6-dibromophenyl) disulfide, bis(2,6- diiodophenyl)disulfide and bis(pentabromophenyl)disulfide.

The (e) organic sulfur compound can be used alone or in combination of two or more.

The content of the (e) organic sulfur compound is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and still more preferably 0.2 parts by mass with respect to 100 parts by mass of the (a) base rubber. It is at least 5.0 parts by mass, preferably 3.0 parts by mass or less, and even more preferably 2.0 parts by mass or less. If the content of the (e) organic sulfur compound is less than 0.05 parts by mass, the effect of adding the (e) organic sulfur compound cannot be obtained, and the resilience of the golf ball may not be improved. On the other hand, if the content of (e) the organic sulfur compound exceeds 5.0 parts by mass, the amount of compressive deformation of the resulting golf ball may increase and the resilience may decrease.

[(f) metal compound]
When the core rubber composition contains only an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent, it preferably further contains (f) a metal compound. By neutralizing an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms in the core rubber composition with a metal compound, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms is used as a co-crosslinking agent. This is because substantially the same effect as in the case of using a metal salt of saturated carboxylic acid can be obtained. When an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and a metal salt thereof are used together as a co-crosslinking agent, (f) a metal compound may be used as an optional component.

The metal compound (f) is not particularly limited as long as it can neutralize the (b) α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms in the core rubber composition. . Examples of the (f) metal compound include metal hydroxides such as magnesium hydroxide, zinc hydroxide, calcium hydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide and copper hydroxide; magnesium oxide and calcium oxide; , zinc oxide and copper oxide; and metal carbonates such as magnesium carbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithium carbonate and potassium carbonate. The (f) metal compound is preferably a divalent metal compound, more preferably a zinc compound. This is because the divalent metal compound reacts with an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms to form a metal bridge. Also, by using a zinc compound, a golf ball with high resilience can be obtained.

The (f) metal compound may be used alone or in combination of two or more. The content of the (f) metal compound may be appropriately adjusted according to the desired degree of neutralization of the (b) α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms.

The core rubber composition used in the present invention may optionally contain additives such as pigments, fillers for weight adjustment, anti-aging agents, peptizers and softeners.

The filler used in the core rubber composition is mainly used as a weight modifier for adjusting the weight of the golf ball obtained as the final product, and may be added as necessary. Examples of the filler include inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder. Zinc oxide is particularly preferred as the filler. Zinc oxide is believed to function as a vulcanization aid and increase the overall hardness of the core. The content of the filler is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 30 parts by mass or less, and 25 parts by mass with respect to 100 parts by mass of the (a) base rubber. Parts or less is more preferable, and 20 parts by mass or less is even more preferable. If the filler content is less than 0.5 parts by mass, it becomes difficult to adjust the weight.

The content of the anti-aging agent is preferably 0.1 parts by mass or more and 1 part by mass or less with respect to 100 parts by mass of the (a) base rubber. The content of the peptizer is preferably 0.1 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the (a) base rubber.

The core rubber composition is prepared by, for example, (a) base rubber, (b) α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof as a co-crosslinking agent, ( c) a cross-linking initiator and (d) a terpene-based resin are blended and kneaded. The core rubber composition may optionally contain (e) an organic sulfur compound and/or (f) a metal compound. The kneading method is not particularly limited, and may be performed using a kneading roll, Banbury mixer, kneader, or other known kneading machine.

The material temperature of the core rubber composition during kneading is preferably 80° C. or higher, more preferably 90° C. or higher, preferably 140° C. or lower, and more preferably 130° C. or lower. The kneading time is preferably 6 minutes or longer, more preferably 7 minutes or longer, preferably 12 minutes or shorter, and more preferably 10 minutes or shorter. By carrying out the kneading under the above conditions, the compounded materials are uniformly dispersed.

A core rubber composition obtained by kneading is extruded into a rod shape by an extruder and cut into a predetermined length to prepare a preform (also called a “plug”). Alternatively, the core rubber composition may be formed into a thick sheet and punched out to form a plug. The size of the plug may be appropriately changed according to the size of the compression mold. The obtained plugs are preferably immersed in an anti-adhesion agent liquid so as not to stick to each other, dried, and then aged for about 8 to 48 hours. Next, the plug is put into a mold for core molding and press-molded.

In the method for producing a spherical core of the present invention, a preform of the core rubber composition is pressed under the following conditions to crosslink the core rubber composition and form a spherical core.
(1) The press pressure is preferably 1 MPa or higher, more preferably 3 MPa or higher, preferably 25 MPa or lower, and more preferably 15 MPa or lower.
(2) The press temperature is preferably 125° C. or higher, more preferably 150° C. or higher, preferably 200° C. or lower, and more preferably 180° C. or lower.
(3) The pressing time is preferably 15 minutes or longer, preferably 20 minutes or longer, preferably 40 minutes or shorter, and more preferably 30 minutes or shorter.
Under the above molding conditions, the cross-linking reaction of the rubber composition forming the spherical core proceeds efficiently. That is, since a spherical core having a small difference between surface hardness and center hardness can be obtained in a short time, the production efficiency of spherical cores is increased.

Prior to the molding step, a preheating step may be performed in which a preform of the core rubber composition is put into a core molding die and the preform is formed into a spherical shape. In the preheating step, it is preferable to plastically change the shape of the preform into a spherical shape in advance while suppressing the cross-linking reaction of the core rubber composition. This is because if the cross-linking reaction proceeds too much, it becomes difficult to plastically change the shape of the preform into a spherical shape. From such a point of view, the preheating step is preferably performed under the following conditions.
(1) The press pressure is preferably 1 MPa or more and preferably 5 MPa or less.
(2) The press temperature is preferably less than 125°C, more preferably 120°C or less.
(3) The pressing time is preferably 3 minutes or longer, and more preferably 5 minutes or shorter.

The spherical core obtained by the production method of the present invention has a surface hardness (Hs) in Shore C hardness of preferably 60 or more, more preferably 62 or more, and even more preferably 65 or more. It is preferably 83 or less, more preferably 80 or less, and even more preferably 78 or less. If the surface hardness (Hs) is 60 or more in Shore C hardness, the resilience of the core will be better. Further, when the surface hardness (Hs) of the core is 83 or less in Shore C hardness, the feel at impact on driver shots is further improved.

The center hardness (Ho) of the spherical core is preferably 30 or more, more preferably 35 or more, and even more preferably 40 or more in Shore C hardness. If the center hardness (Ho) of the core is 30 or more in Shore C hardness, the resilience will be good without becoming too soft. The center hardness (Ho) of the core is preferably 70 or less, more preferably 68 or less, and even more preferably 67 or less in Shore C hardness. When the center hardness (Ho) is 70 or less in Shore C hardness, the ball does not become too hard and the feel at impact is good.

The hardness difference (Hs-Ho) between the surface hardness (Hs) and the center hardness (Ho) of the spherical core is preferably −20 or more, more preferably −10 or more, in terms of Shore C hardness. It is more preferably 0 or more, preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less. If the hardness difference (Hs-Ho) between the surface hardness (Hs) and center hardness (Ho) of the core is 0 or more in Shore C hardness, a golf ball with good resilience can be obtained. If the hardness difference (Hs-Ho) between the surface hardness (Hs) and center hardness (Ho) of the core is 20 or less in Shore C hardness, a golf ball with improved durability and feel at impact can be obtained.

The diameter of the spherical core obtained by the production method of the present invention is preferably 34.8 mm or more, more preferably 36.8 mm or more, even more preferably 38.8 mm or more, and 42.2 mm or less. is preferably 41.8 mm or less, more preferably 41.2 mm or less, and most preferably 40.8 mm or less. When the diameter of the spherical core is 34.8 mm or more, the thickness of the cover does not become too thick, and the resilience is improved. On the other hand, if the diameter of the spherical core is 42.2 mm or less, the cover does not become too thin, and the function of the cover is exhibited more effectively.

When the spherical core has a diameter of 34.8 mm to 42.2 mm, the amount of compressive deformation (the amount of shrinkage of the core in the compression direction) from the initial load of 98 N to the final load of 1275 N is 2.0 mm. is preferably 2.3 mm or more, more preferably 2.5 mm or more, preferably 5.0 mm or less, more preferably 4.3 mm or less, 4.5 mm More preferably: If the amount of compressive deformation is 2.0 mm or more, the feel at impact will be better, and if it is 5.0 mm or less, the resilience will be better.

The present invention includes a method of manufacturing a golf ball by forming a cover on the spherical core obtained by the manufacturing method of the present invention.

[cover]
In the golf ball manufacturing method of the present invention, the cover is formed from a cover composition containing a resin component. Examples of the resin component include an ionomer resin, a thermoplastic polyurethane elastomer commercially available from BASF Japan under the trade name "Elastollan (registered trademark)", and a trade name "Pebax (registered trademark)" from Arkema Co., Ltd. ”, a thermoplastic polyester elastomer commercially available under the trade name “Hytrel (registered trademark)” from Toray DuPont Co., Ltd., a trade name “Lavalon (registered trademark)” from Mitsubishi Chemical Corporation )” and commercially available thermoplastic styrene elastomers.

Examples of the ionomer resin include those obtained by neutralizing at least a part of the carboxyl groups in a binary copolymer of an olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms with a metal ion; and at least part of the carboxyl groups of a terpolymer of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α,β-unsaturated carboxylic acid ester are neutralized with metal ions, or , and mixtures thereof. As the olefin, olefins having 2 to 8 carbon atoms are preferable, and examples thereof include ethylene, propylene, butene, pentene, hexene, heptene and octene, and ethylene is particularly preferable. Examples of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, crotonic acid and the like, with acrylic acid and methacrylic acid being particularly preferred. Examples of α,β-unsaturated carboxylic acid esters include methyl, ethyl, propyl, n-butyl and isobutyl esters of acrylic acid, methacrylic acid, fumaric acid and maleic acid. Alternatively, a methacrylic acid ester is preferred. Among these, the ionomer resin includes an ethylene-(meth)acrylic acid binary copolymer neutralized metal ion, an ethylene-(meth)acrylic acid-(meth)acrylic acid ester terpolymer. Neutralized metal ions are preferred.

The cover composition used in the golf ball manufacturing method of the present invention preferably contains a thermoplastic polyurethane elastomer or an ionomer resin as a resin component. When using an ionomer resin, it is also preferable to use a thermoplastic styrene elastomer together. The content of the polyurethane or ionomer resin in the resin component of the cover composition is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

In addition to the resin component described above, the cover composition includes pigment components such as white pigment (e.g., titanium oxide), blue pigment, and red pigment, weight modifiers such as zinc oxide, calcium carbonate, and barium sulfate, dispersants, An anti-aging agent, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent whitening agent, or the like may be contained within a range that does not impair the performance of the cover.

The content of the white pigment (for example, titanium oxide) is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and 10 parts by mass with respect to 100 parts by mass of the resin component constituting the cover. The following is preferable, and 8 parts by mass or less is more preferable. By setting the content of the white pigment to 0.5 parts by mass or more, the cover can be provided with concealing properties. Also, if the content of the white pigment exceeds 10 parts by mass, the durability of the obtained cover may decrease.

The slab hardness of the cover composition is preferably set appropriately according to the desired performance of the golf ball. For example, in the case of a distance golf ball where flight distance is important, the slab hardness of the cover composition is preferably 50 or more, more preferably 55 or more, even more preferably 60 or more, and preferably 80 or less in terms of Shore D hardness. 70 or less is more preferable, and 68 or less is even more preferable. By adjusting the slab hardness of the cover composition to 50 or more, a golf ball with a high launch angle and a low spin rate on driver shots and iron shots can be obtained, and flight distance is improved. By setting the slab hardness of the cover composition to 80 or less, a golf ball with excellent durability can be obtained. In the case of a spin-type golf ball where controllability is important, the slab hardness of the cover composition is preferably less than 50, preferably 20 or more, more preferably 25 or more, and even more preferably 30 or more in Shore D hardness. . If the slab hardness of the cover composition is less than 50 in Shore D hardness, the spin rate on approach shots will be high, and a golf ball that will easily stop on the green will be obtained. Further, by setting the slab hardness to 20 or more, the scratch resistance is improved. In the case of a plurality of cover layers, the slab hardness of the cover composition constituting each layer may be the same or different.

In the method of manufacturing the golf ball of the present invention, the method of molding the cover includes, for example, a method of molding a hollow shell from the cover composition, covering the core with a plurality of shells, and compression molding (preferably, , a method of molding a hollow shell-like half shell from a cover composition, covering a core with two half shells and compression molding), or a method of directly injection molding a cover composition onto a core. be able to.

When molding the cover by compression molding, the half shells can be molded by either compression molding or injection molding, but compression molding is preferred. Conditions for compression molding the cover composition into half shells include, for example, a pressure of 1 MPa or more and 20 MPa or less and a temperature of -20°C or more and 70°C or less relative to the flow start temperature of the cover composition. Molding temperature can be mentioned. A half shell having a uniform thickness can be molded under the above molding conditions. As a method of molding the cover using half shells, for example, a method of covering a core with two half shells and compression molding can be given. The conditions for compression-molding the half shells into the cover include, for example, a molding pressure of 0.5 MPa or more and 25 MPa or less, and a temperature of −20° C. or more and 70° C. or less with respect to the flow initiation temperature of the cover composition. Molding temperature can be mentioned. Under the above molding conditions, a golf ball cover having a uniform cover thickness can be molded.

When the cover composition is injection-molded to form the cover, the pellet-like cover composition obtained by extrusion may be injection-molded, or the base resin component, the pigment, or the like for the cover may be injection-molded. The materials may be dry blended and directly injection molded. As the upper and lower molds for molding the cover, it is preferable to use those having hemispherical cavities and pimples, a part of which also serves as a retractable hold pin. Molding of the cover by injection molding can be performed by projecting a hold pin, inserting and holding a core, injecting a cover composition, and cooling to mold a cover. A cover composition heated to 200° C. to 250° C. is poured into a mold clamped with pressure over 0.5 to 5 seconds, cooled for 10 to 60 seconds, and opened.

When molding the cover, depressions called dimples are usually formed on the surface. The total number of dimples formed on the cover is preferably 200 or more and 500 or less. If the total number of dimples is less than 200, it is difficult to obtain the dimple effect. Moreover, if the total number of dimples exceeds 500, the size of each dimple becomes small, and it is difficult to obtain the effect of the dimples. The shape of the dimples to be formed (plan view shape) is not particularly limited, and circular; may be used, or two or more may be used in combination.

The thickness of the cover is preferably 4.0 mm or less, more preferably 3.0 mm or less, and even more preferably 2.0 mm or less. If the thickness of the cover is 4.0 mm or less, the resulting golf ball will have better resilience and feel at impact. The thickness of the cover is preferably 0.3 mm or more, more preferably 0.5 mm or more, still more preferably 0.8 mm or more, and particularly preferably 1.0 mm or more. If the thickness of the cover is less than 0.3 mm, the durability and abrasion resistance of the cover may deteriorate. In the case of multiple cover layers, the total thickness of the multiple cover layers is preferably within the above range.

It is preferable that the golf ball body having the cover formed thereon is removed from the mold and, if necessary, subjected to surface treatments such as deburring, cleaning, and sandblasting. Also, if desired, a coating film or a mark can be formed. The film thickness of the coating film is not particularly limited, but is preferably 5 µm or more, more preferably 7 µm or more, preferably 50 µm or less, more preferably 40 µm or less, and even more preferably 30 µm or less. If the film thickness is less than 5 μm, the coating film tends to wear away with continuous use.

[Golf ball]
The structure of the golf ball obtained by the manufacturing method of the present invention is not particularly limited as long as it has a spherical core and one or more layers of cover covering the spherical core. FIG. 1 is a partially cutaway cross-sectional view showing a golf ball 1 according to one embodiment of the present invention. A golf ball 1 has a spherical core 2 and a cover 3 covering the spherical core 2 . A large number of dimples 31 are formed on the surface of this cover. The portion of the surface of the golf ball 1 other than the dimples 31 is the land 32 . This golf ball 1 has a paint layer and a mark layer on the outside of the cover 3, but the illustration of these layers is omitted.

The shape of the core is preferably spherical. The structure of the core may be either a single-layer structure or a multi-layer structure, but the single-layer structure is preferred. This is because the single-layer core has no energy loss at the interface of the multi-layer structure and improves resilience. Moreover, the cover may have a structure of one layer or more, and may have a single layer structure or a multilayer structure of two or more layers. The golf ball of the present invention includes, for example, a two-piece golf ball consisting of a core and a single-layer cover covering the core; a core and two or more layers covering the core. multi-piece golf balls (including three-piece golf balls) having a cover of The present invention can be suitably applied to golf balls having any of the structures described above.

The diameter of the golf ball obtained by the manufacturing method of the present invention is preferably 40 mm to 45 mm. A diameter of 42.67 mm or more is particularly preferable from the viewpoint that the standards of the United States Golf Association (USGA) are satisfied. From the viewpoint of air resistance suppression, the diameter is more preferably 44 mm or less, and particularly preferably 42.80 mm or less. Further, the weight of the golf ball of the present invention is preferably 40 g or more and 50 g or less. From the viewpoint of obtaining a large inertia, the mass is more preferably 44 g or more, particularly preferably 45.00 g or more. From the viewpoint that the USGA standard is satisfied, the mass is particularly preferably 45.93 g or less.

When the golf ball obtained by the manufacturing method of the present invention has a diameter of 40 mm to 45 mm, the amount of compressive deformation (the amount of shrinkage in the compression direction) when the initial load of 98 N is applied and the final load of 1275 N is applied is 2.0 mm. is preferably 2.3 mm or more, more preferably 2.5 mm or more, and preferably 4.0 mm or less, more preferably 3.3 mm or less, further preferably 3.5 mm or less. is. A golf ball having a compressive deformation amount of 2.0 mm or more does not become too hard and provides a good feel at impact. On the other hand, by setting the amount of compressive deformation to 4.0 mm or less, the resilience increases.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples, and any modifications and embodiments that do not depart from the scope of the present invention can be made within the scope of the present invention. Included in scope.

[Evaluation method]
(1) Amount of compression deformation The amount of deformation in the direction of compression (the amount of shrinkage of the core or golf ball in the direction of compression) from when the core or golf ball was subjected to an initial load of 98 N to when a final load of 1275 N was applied was measured.

(2) Core hardness (Shore C hardness)
H. The Shore C hardness measured on the surface of the core using an automatic hardness meter Digitest II manufactured by Burleith Co., Ltd. was defined as the core surface hardness. In addition, the core was cut in a hemispherical shape, and the core was also cut in a hemispherical shape, and the hardness at the center of the cut surface was measured.

(3) Slab hardness (Shore D hardness)
Using the cover composition, a sheet having a thickness of about 2 mm was produced by injection molding and stored at 23° C. for 2 weeks. The hardness was measured using an automatic hardness tester (manufactured by H. Burleith, Digitest II) in a state in which three or more of these sheets were stacked so as not to be affected by the measurement substrate or the like. The detector used was "Shore D".

(4) Feeling at Impact Ten amateur golfers (advanced golfers) conducted a hitting test using a driver and asked each of them to evaluate the feel at impact according to the following criteria. The feel at impact of the golf ball was the most frequently evaluated among the 10 evaluations.
Evaluation Criteria ⊚: Good feeling with little impact.
◯: There is a shock, but the feeling is good.
△: Normal.
x: The impact is large and the feeling is poor.
(5) Durability A metal head W#1 driver (XXIO S loft 11° manufactured by Dunlop Sports) was attached to a swing robot M/C manufactured by Golf Laboratory, and a golf ball was hit repeatedly at a head speed of 45 m/sec. Then, the number of impacts until cracking occurred was measured. Twelve measurements were taken for each golf ball, and the average value was taken as the number of times the golf ball was hit. The number of hits for each golf ball is determined by golf ball No. Assuming that the number of hits of 1 is 100, the values were indexed.

[Production of Golf Ball]
(1) Preparation of core The rubber compositions shown in Tables 1 to 3 are kneaded by kneading rolls and hot-pressed under predetermined conditions in upper and lower molds having hemispherical cavities to form spherical cores with a diameter of 40.0 mm. got the core.

Materials used in Tables 1 to 3 are as follows.
BR730: High-cis polybutadiene rubber manufactured by JSR (cis-1,4-bond content = 95% by mass, 1,2-vinyl bond content = 1.3% by mass, Mooney viscosity (ML ₁₊₄ (100°C) ) = 55, molecular weight distribution (Mw / Mn) = 3)
ZN-DA90S: Nissho Techno Fine Chemical Co., Ltd. zinc acrylate Dicumyl peroxide: Tokyo Chemical Industry Co., Ltd. SylvaresTP2019 (pinene-phenol copolymer, softening point: 125 ° C.): KRATON Co. SylvaresTP7042 (terpene-phenol copolymer , softening point: 148 ° C.): KRATON Sylvares TR7115 (polyterpene, softening point: 116 ° C.): KRATON Sylvares TR7125 (polyterpene, softening point: 124 ° C.): KRATON YS Resin PX1150N (β-pinene polymer, softening Point: 115 ± 5 ° C.): YS Resin PX1250 (polyterpene, softening point: 125 ± 5 ° C.) manufactured by Yasuhara Chemical Co., Ltd. PBDS: manufactured by Kawaguchi Chemical Co., Ltd. Bis (pentabromophenyl) disulfide Zinc oxide: manufactured by Toho Zinc Co., Ltd. , "Ginrei R"
Barium sulfate: "Barium sulfate BD" manufactured by Sakai Chemical Co., Ltd.

(2) Production of cover and production of golf ball The cover material shown in Table 4 was extruded by a twin-screw kneading extruder to prepare a pelletized cover composition. The extrusion conditions for the cover composition were screw diameter 45 mm, screw rotation speed 200 rpm, screw L/D=35, and the formulation was heated to 160-230° C. at the die position of the extruder. The resulting cover composition was injection molded onto the spherical core obtained as described above to produce a golf ball having a spherical core and a cover covering the core. Tables 1 to 3 also show the evaluation results of the obtained golf balls.

The materials used in Table 4 are as follows.
Himilan 1555: Na-neutralized ionomer manufactured by DuPont Mitsui Polychemicals Himilan 1605: Na-neutralized ionomer manufactured by DuPont Mitsui Polychemicals Himilan AM7329: Zn-neutralized ionomer A-220 manufactured by DuPont Mitsui Polychemicals: Dioxide manufactured by Ishihara Sangyo Co., Ltd. Titanium JF-90: light stabilizer manufactured by Johoku Chemical Co., Ltd.

As shown in Tables 1 to 3, according to the present invention, the production efficiency of spherical cores having a small difference between surface hardness and central hardness can be increased.

Golf ball no. 1 is a production example in which a spherical core is formed by hot pressing at 170° C. for 20 minutes, but the feel at impact is poor and the durability is not good. Golf ball no. 2 is a production example in which a spherical core was molded by hot pressing at 125° C. for 100 minutes. A golf ball having excellent durability and feel at impact has been obtained, but the molding time is long and the production efficiency is low.

INDUSTRIAL APPLICABILITY The present invention is useful as a method of manufacturing a golf ball.

Claims (9)

(a) a base rubber, (b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof as a co-crosslinking agent, (c) a crosslinking initiator, and (d) a terpene resin The core rubber composition is crosslinked by pressing the core rubber composition containing A method for producing a spherical core, characterized by comprising a step of molding a spherical core. (d) The terpene-based resin is a terpene polymer, a terpene/phenol copolymer, a terpene/styrene copolymer, a terpene/phenol/styrene copolymer, a hydrogenated terpene/phenol copolymer, or a hydrogenated terpene/styrene 2. The method for producing a spherical core according to claim 1, wherein the polymer is at least one selected from the group consisting of copolymers and hydrogenated terpene-phenol-styrene copolymers. 3. The method for producing a spherical core according to claim 1, wherein the terpene-based resin is at least one compound selected from compounds having structures represented by the following formulas (1) to (4).

[In formulas (1) to (4), R ¹ and R ² each independently represent a divalent residue of a phenolic compound and/or a styrenic compound, m ¹ to m ⁴ each independently , represents a natural number of 1 to 30, and n ¹ to n ² each independently represents a natural number of 1 to 20. ] 4. The core rubber composition according to any one of claims 1 to 3, wherein (d) a terpene-based resin (d) contains 3 parts by mass to 20 parts by mass with respect to 100 parts by mass of (a) the base rubber. A method for producing a spherical core according to 1. The method for producing a spherical core according to any one of claims 1 to 4, wherein the (d) terpene-based resin has a softening point of 60°C to 150°C. 6. Any one of claims 1 to 5, wherein the blending ratio of the component (b) and the component (d) (component (b)/component (d)) is 2.0 to 15.0 in mass ratio. 3. A method for producing a spherical core according to item 1. The method for producing a spherical core according to any one of claims 1 to 6, wherein high-cis polybutadiene containing 90% by mass or more of cis-1,4-bonds is used as the base rubber. The hardness difference (Hs-Ho) between the center hardness (Ho) of the core and the surface hardness (Hs) of the core is 20 or less in Shore C hardness according to any one of claims 1 to 7. A method for manufacturing a spherical core. A method for manufacturing a golf ball, comprising forming a cover on a spherical core obtained by the method for manufacturing a spherical core according to any one of claims 1 to 8.

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