Golf ball

Abstract

SOLUTION: To provide a golf ball which includes a rubber core of at least one layer, and a cover of at least one layer covering the core, and in which at least the one layer of the cover is formed from a resin composition containing the following (I) and (II) components as (I) polyurethane or polyurea, and (II) a core shell type polymer having core comprising acrylic bridged rubber particles and shell comprising an acrylic polymer, and a CS1 value calculated by the following formula (1) is larger than -4.08×10-3: CS1=(CV50-CV12) / 38 ...(1) (in the formula, CV50 represents a restitution coefficient value at an injection speed of 50.0 m / s, and CV12 represents a restitution coefficient value at an injection speed of 12.0 m / s.)EFFECT: A golf ball has excellent controllability at approach shot, and excellent hitting feeling, and can excellently retain abrasion resistance.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a golf ball having at least one core layer and at least one cover layer. [Background technology]

[0002] The main characteristic required for a golf ball is the increased flight distance, but other characteristics include the ability to stop the ball well on approach shots and abrasion resistance. That is, up until now, many golf balls have been developed that fly well on driver shots and generate a good amount of backspin on approach shots. Recently, many golf balls that are suitable for professionals and advanced players have adopted urethane resin materials as an alternative to ionomer resin materials.

[0003] Several polymer blend cover materials have been proposed in which a urethane resin material is used as the base resin and other resin materials are mixed. The present inventor previously proposed in JP 2019-107401 A (Patent Document 1) to use acrylic resin or methacrylic resin as the main material of the cover as a polymer blend of urethane resin material. This technology provides a golf ball that can achieve a high initial velocity during a driver shot and a low initial velocity during an approach shot, but since acrylic resin or methacrylic resin is basically a hard resin material, it could not be said that the approach controllability is fully satisfactory. One of the factors in approach controllability is the operability of the club during an approach shot, and the quality of the operability of the club is affected by the length of contact time between the ball and the club face due to the low resilience in addition to the high or low spin amount of the ball. If the contact time is long, the operability is good, and if the contact time is short, the operability is poor. In other words, it was desired to improve a golf ball with even better approach controllability than the golf ball described in Patent Document 1.

[0004] In addition, the resin material of the cover described in Patent Document 1 requires a higher molding temperature because the urethane resin material has a higher melt viscosity and poorer fluidity due to the addition of acrylic resin, which means that after molding, the entire surface of the cover may be burned or otherwise defective, leaving room for improvement in terms of moldability and abrasion resistance of the golf ball.

[0005] In addition, JP 2019-97573 A (Patent Document 2) and JP 2020-191906 A (Patent Document 3) disclose cover resin compositions that contain a styrene-based resin and an aromatic vinyl-based elastomer as a polymer blend of a urethane resin material, but there is room for improvement in terms of the feel when approaching.

[0006] Furthermore, JP 2019-88770 A (Patent Document 4), US Patent No. 10,124,214 (Patent Document 5), and US Patent No. 10,150,008 (Patent Document 6) disclose a resin material for golf balls formed from a mixture having a thermoplastic polymer and an acrylic copolymer (MMA copolymer). However, these patent documents do not disclose that the approach controllability is sufficiently excellent, and that the abrasion resistance and moldability are also excellent, and it is difficult to say that the technology can solve the above-mentioned problems of the present invention. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2019-107401 A [Patent Document 2] JP 2019-97573 A [Patent Document 3] JP 2020-191906 A [Patent Document 4] JP 2019-88770 A [Patent Document 5] U.S. Patent No. 10,124,214 [Patent Document 6] U.S. Patent No. 10150008 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in consideration of the above circumstances, and has as its object to provide a golf ball which is superior in controllability on approach shots as well as in abrasion resistance and feel when hit, compared to golf balls having conventional urethane covers. [Means for solving the problem]

[0009] In order to achieve the above object, the present inventors have provided a golf ball having a core and a cover, the cover being made of a polymer blend of a resin material mainly composed of polyurethane or polyurea, the core being made of acrylic crosslinked rubber particles, the shell being made of an acrylic polymer, and the polymer blend being less than a specific amount of a core-shell type polymer, the core being made of acrylic crosslinked rubber particles, and the shell being made of an acrylic polymer, and CS1=(CV 50 -CV 12 ) / 38 ···(1) [In the above formula, CV 50 is the coefficient of restitution at an incident speed of 50.0 m / s, and CV 12 indicates the value of the restitution coefficient at an incident speed of 12.0 m / s. The CS1 value calculated is -4.08×10 -3 When a golf ball was produced with a cover made of a molded resin material to make the ball larger, it was found that the golf ball had excellent controllability on approach shots, a good feel on impact, and good abrasion resistance, which led to the creation of the present invention.

[0010] Furthermore, the present inventors have found that by including in the urethane resin material less than a specific amount of a core-shell type polymer, the core of which is made of acrylic crosslinked rubber particles and the shell of which is made of an acrylic polymer, the COR value decreases in the low initial velocity range but does not decrease in the high initial velocity range, which is effective in improving approach controllability. In particular, a urethane resin composition containing a core-shell type polymer, the core of which is made of acrylic crosslinked rubber particles and the shell of which is made of an acrylic polymer, has good compatibility with the urethane resin material and does not require a plasticizer, and therefore there is no volatilization of the plasticizer due to shear heat during molding, so that the physical properties such as hardness and rebound resilience of the golf ball are stable, and it is considered that there is almost no adverse effect on the spin performance during approach.

[0011] Accordingly, the present invention provides the following golf ball. 1. A golf ball having at least one rubber core and at least one cover layer covering the core, wherein at least one layer of the cover comprises the following components (I) and (II): (I) Polyurethane or polyurea (II) Core-shell polymer in which the core is an acrylic crosslinked rubber particle and the shell is an acrylic polymer The amount of the component (II) is less than 15 parts by mass relative to 100 parts by mass of the component (I), and the CS1 value calculated by the following formula (1) is -4.08 × 10 -3 A golf ball that is larger. CS1=(CV 50 -CV 12 ) / 38 ···(1) [In the above formula, CV 50 is the coefficient of restitution at an incident speed of 50.0 m / s, and CV 12 indicates the value of the restitution coefficient at an incident speed of 12.0 m / s. 2. The CS2 value calculated using the following formula (2) is -5.23 x 10 -3 2. A golf ball as defined in claim 1 above. CS2=(1.0-CV 12 / 45 ) / 33 ···(2) [In the above formula, CV 12 / 45 indicates the value of the restitution coefficient at an incident speed of 12.0 m / s when the restitution coefficient at an incident speed of 45.0 m / s is taken as 1.0.] 3. The golf ball according to 1 or 2 above, wherein component (II) does not contain a plasticizer. 4. The golf ball according to 1 or 2 above, wherein the melt flow rate (MFR) value of component (II) is 18 g / 10 min or less when measured under conditions (ISO1133) of 230° C. and a load of 2.16 kgf. 5. The golf ball according to 1 or 2 above, wherein the rebound resilience of component (II) is 22% or less. 6. The golf ball according to 1 or 2 above, wherein the Shore D hardness of component (II) is 22 to 40. Effect of the Invention

[0012] Compared with golf balls having conventional urethane covers, the golf ball of the present invention exhibits superior controllability on approach shots, provides a good feel on approach shots, and maintains good abrasion resistance. [Brief description of the drawings]

[0013] [Figure 1] 1 is a graph illustrating the relationship between the incidence velocity and the COR value for a golf ball of the present invention and a conventional product. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will now be described in further detail. The golf ball of the present invention has a CS1 value of −4.08×10 calculated by the following formula (1): -3 It requires something bigger. CS1=(CV 50 -CV 12 ) / 38 ···(1) [In the above formula, CV 50 is the coefficient of restitution at an incident speed of 50.0 m / s, and CV 12indicates the value of the restitution coefficient at an incident speed of 12.0 m / s.

[0015] As shown in FIG. 1, the golf ball of the present invention has a COR value that does not change much when the ball is hit at a high speed compared to a conventional ball product. However, as the ball is hit at a slower speed, the COR value decreases and the slope of the straight line graph becomes smaller. 50 -CV 12 ) / 38 means the slope of this straight line graph. In other words, the value of CS1 is -4.08×10 -3 If it is larger, the COR value decreases in the low initial velocity range, but does not decrease in the high initial velocity range, which is effective for approach controllability. 12 The reason why the head speed (HS) was set at 11 to 13 m / s was because it corresponds to the hitting condition for a 15-yard approach shot, and the CV 50 The incident velocity of 50.0 m / s was used because it corresponds to the conditions when a top professional or advanced player hits the ball with a driver (W#1).

[0016] In addition to the above requirements, the golf ball of the present invention has a CS2 value calculated by the following formula (2): -3 It is preferable that the axial length is larger than the axial length. CS2=(1.0-CV 12 / 45 ) / 33 ···(2) [In the above formula, CV 12 / 45 indicates the value of the restitution coefficient at an incident speed of 12.0 m / s when the restitution coefficient at an incident speed of 45.0 m / s is taken as 1.0.] In the above formula (2), CV 12 The reason why the head speed (HS) was set at 11 to 13 m / s was because it corresponds to the hitting condition for a 15-yard approach shot, and the CV 45 The reason why the standard was used (entrance velocity of 45.0 m / s) is that it corresponds to the condition when a typical male amateur golfer hits the ball with a driver (W#1).

[0017] The golf ball of the present invention has a ball structure in which a core made of at least one layer is covered with at least one cover layer, ie, a single-layer or multi-layer cover.

[0018] The core can be formed using a known rubber material as a base material. Known base rubbers such as natural rubber or synthetic rubber can be used as the base rubber, and more specifically, it is recommended to mainly use polybutadiene, particularly cis-1,4-polybutadiene having at least 40% or more of a cis structure. Furthermore, natural rubber, polyisoprene rubber, styrene butadiene rubber, etc. can be used in combination with the above-mentioned polybutadiene in the base rubber as desired.

[0019] Polybutadiene can also be synthesized using metal catalysts such as rare earth element catalysts such as Nd catalysts, cobalt catalysts, and nickel catalysts.

[0020] The above base rubber may be blended with co-crosslinking agents such as unsaturated carboxylic acids and their metal salts, inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, and organic peroxides such as dicumyl peroxide and 1,1-bis(t-butylperoxy)cyclohexane, etc. Also, commercially available antioxidants and the like may be added as necessary.

[0021] The core can be produced by vulcanizing and curing a rubber composition containing the above-mentioned components. For example, the rubber composition is kneaded using a kneading machine such as a Banbury mixer or a roll, compression molded or injection molded using a core mold, and the molded body is appropriately heated at a temperature sufficient for the organic peroxide and co-crosslinking agent to act, that is, 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes, to cure the molded body.

[0022] In the golf ball of the present invention, a core is covered with a single-layer or multi-layer cover. Examples of such golf balls include a golf ball having a core with a single-layer cover, and a golf ball having a core, an intermediate layer covering the core, and an outermost layer covering the intermediate layer.

[0023] In the present invention, the resin material for at least one layer of the cover contains the following components (I) and (II): (I) Polyurethane or polyurea (II) Core-shell polymer in which the core is an acrylic crosslinked rubber particle and the shell is an acrylic polymer It is formed from a resin composition containing

[0024] (I) Polyurethane or Polyurea Polyurethane or polyurea can be the main material or base resin of the cover material (resin composition). Details of this component, polyurethane (Ia) or polyurea (Ib), are as follows.

[0025] (Ia) Polyurethane The polyurethane structure is composed of a soft segment made of a polymer polyol (polymeric glycol) which is a long-chain polyol, and a chain extender and polyisocyanate which constitute a hard segment. Here, the polymer polyol used as the raw material can be any of those conventionally used in the technology related to polyurethane materials, and is not particularly limited. For example, polyester-based polyols, polyether-based polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin-based polyols, conjugated diene polymer-based polyols, castor oil-based polyols, silicone-based polyols, vinyl polymer-based polyols, etc. can be mentioned. As the polyester-based polyols, specifically, adipate-based polyols such as polyethylene adipate glycol, polypropylene adipate glycol, polybutadiene adipate glycol, polyhexamethylene adipate glycol, and lactone-based polyols such as polycaprolactone polyols can be used. As the polyether polyols, poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol), poly(methyltetramethylene glycol), etc. can be mentioned. These may be used alone or in combination of two or more.

[0026] As the polymer polyol, it is preferable to use a polyether polyol.

[0027] The number average molecular weight of the long-chain polyol is preferably within the range of 1,000 to 5,000. By using a long-chain polyol having such a number average molecular weight, it is possible to reliably obtain a golf ball made of a polyurethane composition having various excellent properties such as the above-mentioned resilience and productivity. The number average molecular weight of the long-chain polyol is more preferably within the range of 1,500 to 4,000, and even more preferably within the range of 1,700 to 3,500.

[0028] The number average molecular weight mentioned above is a number average molecular weight calculated based on a hydroxyl value measured in accordance with JIS-K1557 (the same applies hereinafter).

[0029] The chain extender can be suitably used in conventional polyurethane-related techniques, and is not particularly limited. In the present invention, a low molecular weight compound having two or more active hydrogen atoms in the molecule that can react with an isocyanate group and a molecular weight of 2,000 or less can be used, and among them, an aliphatic diol having 2 to 12 carbon atoms can be suitably used. Specifically, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, etc. can be mentioned, and among them, 1,4-butylene glycol can be suitably used.

[0030] The polyisocyanate may be suitably used in conventional polyurethane-related techniques, and is not particularly limited. Specifically, one or more selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethyl xylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, 1,4-bis(isocyanatomethyl)cyclohexane, and dimer acid diisocyanate may be used. However, some isocyanate species may be difficult to control the crosslinking reaction during injection molding.

[0031] In addition, the mixing ratio of active hydrogen atoms to isocyanate groups in the polyurethane-forming reaction can be adjusted within a suitable range. Specifically, when the long-chain polyol, polyisocyanate compound, and chain extender are reacted to produce polyurethane, it is preferable to use each component in a ratio such that the isocyanate groups contained in the polyisocyanate compound are 0.95 to 1.05 moles per mole of active hydrogen atoms possessed by the long-chain polyol and the chain extender.

[0032] The method for producing polyurethane is not particularly limited, and polyurethane may be produced by any of the prepolymer method and the one-shot method using a long-chain polyol, a chain extender and a polyisocyanate compound and utilizing a known urethane reaction. Among these, it is preferable to carry out melt polymerization substantially in the absence of a solvent, and it is particularly preferable to carry out the production by continuous melt polymerization using a multi-screw extruder.

[0033] As the above-mentioned polyurethane, it is preferable to use a thermoplastic polyurethane material, and in particular, it is preferable to use an ether-based thermoplastic polyurethane material. As the thermoplastic polyurethane material, a commercially available product can be preferably used, for example, "Pandex" (trade name) manufactured by DIC Covestropolymer Co., Ltd., or "Rezamin" (trade name) manufactured by Dainichiseika Chemicals Mfg. Co., Ltd.

[0034] (Ib) Polyurea Polyurea is a resin composition mainly composed of urea bonds formed by the reaction of (i) isocyanates and (ii) amine-terminated compounds, and is described in detail below.

[0035] (i) Isocyanate The isocyanate may be any of those used in conventional polyurethane-related techniques, and is not particularly limited. The same isocyanates as those described above for the polyurethane material may be used.

[0036] (ii) Amine-terminated compounds The amine-terminated compound is a compound having an amino group at the end of the molecular chain, and in the present invention, the following long-chain polyamines and / or amine-based curing agents can be used.

[0037] The long-chain polyamine is an amine compound having two or more amino groups in the molecule that can react with an isocyanate group and having a number average molecular weight of 1,000 to 5,000. In the present invention, the number average molecular weight is more preferably 1,500 to 4,000, and even more preferably 1,900 to 3,000. Specific examples of the long-chain polyamine include, but are not limited to, amine-terminated hydrocarbons, amine-terminated polyethers, amine-terminated polyesters, amine-terminated polycarbonates, amine-terminated polycaprolactones, and mixtures thereof. These long-chain polyamines may be used alone or in combination of two or more.

[0038] On the other hand, the amine-based curing agent is an amine compound having two or more amino groups capable of reacting with an isocyanate group in the molecule and having a number average molecular weight of less than 1,000. In the present invention, the number average molecular weight is more preferably less than 800, and even more preferably less than 600.Specific examples of the amine-based curing agent include ethylenediamine, hexamethylenediamine, 1-methyl-2,6-cyclohexyldiamine, tetrahydroxypropyleneethylenediamine, 2,2,4- and 2,4,4-trimethyl-1,6-hexanediamine, 4,4'-bis-(sec-butylamino)-dicyclohexylmethane, 1,4-bis-(sec-butylamino)-cyclohexane, 1,2-bis-(sec-butylamino)-cyclohexane, derivatives of 4,4'-bis-(sec-butylamino)-dicyclohexylmethane, 4,4'- Dicyclohexylmethanediamine, 1,4-cyclohexane-bis-(methylamine), 1,3-cyclohexane-bis-(methylamine), diethylene glycol di-(aminopropyl)ether, 2-methylpentamethylenediamine, diaminocyclohexane, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, propylenediamine, 1,3-diaminopropane, dimethylaminopropylamine, diethylaminopropylamine, dipropylenetriamine, imido-bis-propylamine, monoethanolamine, di Ethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, isophoronediamine, 4,4'-methylenebis-(2-chloroaniline), 3,5-dimethylthio-2,4-toluenediamine, 3,5-dimethylthio-2,6-toluenediamine, 3,5-diethylthio-2,4-toluenediamine, 3,5-diethylthio-2,6-toluenediamine, 4,4'-bis-(sec-butylamino)-diphenylmethane and its derivatives, 1,4-bis-(sec-butylamino)-benzene, 1,2-bis-( sec-butylamino)-benzene, N,N'-dialkylamino-diphenylmethane, N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine, trimethylene glycol-di-p-aminobenzoate, polytetramethylene oxide-di-p-aminobenzoate, 4,4'-methylenebis-(3-chloro-2,6-diethyleneaniline), 4,4'-methylenebis-(2,6-diethylaniline), m-phenylenediamine, p-phenylenediamine, and mixtures thereof.These amine-based curing agents may be used alone or in combination of two or more kinds.

[0039] (iii) Polyol Although not essential, polyol can be further blended in the polyurea in addition to the above-mentioned components (i) and (ii). As this polyol, those used in conventional polyurethane-related techniques can be suitably used, and there is no particular restriction, but specific examples include the long-chain polyols and / or polyol-based curing agents shown below.

[0040] The long-chain polyol may be any of those conventionally used in polyurethane-related techniques, and is not particularly limited, but examples thereof include polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymer polyols, castor oil polyols, silicone polyols, vinyl polymer polyols, etc. These long-chain polyols may be used alone or in combination of two or more.

[0041] The number average molecular weight of the long-chain polyol is preferably from 1,000 to 5,000, and more preferably from 1,700 to 3,500. If the number average molecular weight is within this range, the resilience, productivity, and the like will be further improved.

[0042] The polyol-based curing agent can be suitably used in the conventional polyurethane-related technology, and is not particularly limited. In the present invention, a low molecular weight compound having two or more active hydrogen atoms in the molecule that can react with an isocyanate group and a molecular weight of less than 1000 can be used, and among them, an aliphatic diol having 2 to 12 carbon atoms can be suitably used. Specifically, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, etc. can be mentioned, and among them, 1,4-butylene glycol can be suitably used. In addition, the number average molecular weight of the polyol-based curing agent is preferably less than 800, more preferably less than 600.

[0043] The polyurea may be produced by any known method, such as a prepolymer method or a one-shot method.

[0044] From the viewpoint of spin characteristics and abrasion resistance of the resulting golf ball, the material hardness of the above component (I) is preferably not more than 52 in Shore D hardness, more preferably not more than 50, and even more preferably not more than 48. From the viewpoint of moldability, the lower limit is preferably not less than 38 in Shore D hardness, and more preferably not less than 40 in Shore D hardness.

[0045] The rebound resilience of the component (I) is preferably 55% or more, more preferably 57% or more, and even more preferably 59% or more, from the overall viewpoint of a golf ball, such as initial velocity performance and spin performance upon impact. The rebound resilience is measured according to the JIS-K 6255:2013 standard.

[0046] The above component (I) is the main material of the resin composition, and in order to provide sufficient abrasion resistance that the urethane resin possesses, it accounts for 50 mass % or more of the resin composition, preferably 60 mass % or more, more preferably 70 mass % or more, even more preferably 80 mass % or more, and most preferably 90 mass % or more.

[0047] In the present invention, by blending component (II), which will be described in detail below, with component (I) above, excellent controllability and abrasion resistance are achieved on approach shots.

[0048] (II) Core-shell polymer in which the core is an acrylic crosslinked rubber particle and the shell is an acrylic polymer Next, the core-shell polymer of component (II) will be described. Core-shell polymers generally have a structure consisting of a core and an outer shell. By making the composition of the core and the outer shell different, it is possible to improve various physical properties, such as compatibility with matrix resins, due to differences in the glass transition point (Tg) and viscoelasticity.

[0049] The core is a core portion made of acrylic crosslinked rubber particles, and specifically, is a crosslinked rubber particle obtained by polymerizing a monomer mixture consisting of 30 to 99.9 mass% of at least one alkyl acrylate ester having an alkyl group with 1 to 12 carbon atoms, 0 to 70 mass% of at least one alkyl methacrylate ester having an alkyl group with 1 to 8 carbon atoms, 0 to 30 mass% of an unsaturated monomer copolymerizable therewith, and 0.1 to 10 mass% of a polyfunctional crosslinkable monomer and / or a polyfunctional graft monomer.

[0050] On the other hand, the shell is a polymer layer (outer shell) obtained by polymerizing a monomer mixture consisting of 30 to 99 mass % of at least one alkyl acrylate ester having an alkyl group with 1 to 12 carbon atoms, 1 to 70 mass % of at least one alkyl methacrylate ester having an alkyl group with 1 to 8 carbon atoms, and 0 to 30 mass % of an unsaturated monomer copolymerizable therewith.

[0051] Specifically, the acrylic acid alkyl ester used in the core-shell polymer may be methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, cyclohexyl acrylate, benzyl acrylate, etc., used alone or in combination of two or more. Particularly preferred are ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. As the methacrylic acid alkyl ester, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, etc., may be used alone or in combination of two or more. Particularly preferred is methyl methacrylate. Examples of unsaturated monomers copolymerizable with these include butadiene, isoprene, styrene, α-methylstyrene, vinyltoluene, acrylonitrile, methacrylonitrile, N-cyclohexylmaleimide, N-ethylmaleimide, Nt-butylmaleimide, N-phenylmaleimide, and N-orthochlorophenylmaleimide. Examples of multifunctional crosslinkable monomers include ethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and divinylbenzene. Examples of multifunctional graft monomers include allyl methacrylate, allyl acrylate, allyl maleate, allyl fumarate, diallyl fumarate, and triallyl cyanurate. Each of the above monomers can be used alone or in combination of two or more.

[0052] The core-shell polymer can be produced by a known emulsion polymerization method. For example, a monomer for obtaining a polymer constituting the core can be emulsion-polymerized to obtain a seed particle, and a monomer for obtaining a polymer constituting the shell can be seed-emulsion-polymerized in the presence of the seed particle. As the emulsifier used in the emulsion polymerization, a known emulsifier such as an anionic surfactant, a cationic surfactant, or a nonionic surfactant can be used, and an anionic surfactant is particularly preferred. There is no particular restriction on the polymerization initiator used in the emulsion polymerization, and a persulfate-based or redox-based initiator can be used. In addition, a chain transfer agent such as an alkyl mercaptan can be used as necessary.

[0053] The volume average particle size of the primary particles of the core-shell polymer is not particularly limited, but is preferably 0.05 to 0.5 μm.

[0054] The acrylic core-shell polymer and the resin composition containing the polymer generally have good moldability and can be used as an injection molding material or processed directly into sheets, films, tubes, etc. by an extruder. Processed products such as injection molded products, sheets, films, and tubes obtained from the resin composition have good flexibility and bending durability at room temperature, good transparency, and excellent weather resistance.

[0055] As the aromatic vinyl elastomer which is component (II), a commercially available product can be used, for example, the "Parapet" series manufactured by Kuraray Co., Ltd.

[0056] Regarding the material hardness of the component (II), from the viewpoint of improving the approach spin rate, the Shore D hardness is 40 or less, preferably 35 or less, more preferably 30 or less, and even more preferably 22 or less. The lower limit is preferably 5 or more in Shore D hardness.

[0057] The rebound resilience of the (II) component is preferably 40% or less, more preferably 38% or less, even more preferably 36% or less, and most preferably 30% or less, in order to maintain the approach spin amount and obtain controllability by suppressing the rebound at the approach to a low level. By suppressing the rebound resilience to a low level in this way, a small amount of the component can be added without adversely affecting the physical properties of the golf ball, and the initial velocity of the ball at the approach shot can be reduced. However, the lower limit of the rebound resilience is preferably 5% or more, more preferably 8% or more, even more preferably 10% or more, and most preferably 15% or more, in order to suppress the impact on the rebound reduction and the reduction in the flight distance at the driver shot as much as possible. The above rebound resilience is measured based on the JIS-K 6255:2013 standard.

[0058] The amount of component (II) is less than 15 parts by mass, and preferably 10 parts by mass or less, per 100 parts by mass of component (I). The lower limit of the amount is preferably 1 part by mass or more, and more preferably 2 parts by mass or more. If the amount of component (II) is too large, the abrasion resistance and moldability may deteriorate. On the other hand, if the amount of component (II) is too small, good control performance and good hitting feel may not be obtained when approaching.

[0059] The melt flow rate (MFR) of the (II) component is preferably 20 g / 10 min or less, more preferably 18 g / 10 min or less, with the lower limit being 1.0 g / 10 min or more. Such a low MFR (poor fluidity) allows the (II) component in the matrix to be kept in a relatively good dispersion state, and the golf ball cover is more likely to exhibit low resilience performance. The melt flow rate (MFR) value is measured in accordance with ISO 1133-1:2011 under the conditions of a test temperature of 230°C and a test load of 21.18 N (2.16 kgf).

[0060] It is preferable that component (II) does not contain a plasticizer, because if the cover resin composition contains a plasticizer, the plasticizer will volatilize due to shear heat during molding, resulting in molding defects such as air inclusions, and will also have an adverse effect on the hardness and rebound resilience of the molded cover, as well as the spin performance on approaches.

[0061] In addition to the resin components described above, the resin composition containing the above-mentioned (I) and (II) may contain other resin materials in order to further improve the flowability of the resin composition for golf balls and to enhance various physical properties such as resilience and durability.

[0062] The other resin material may be specifically selected from polyester elastomers, polyamide elastomers, ionomer resins, ethylene-ethylene-butylene-ethylene block copolymers or modified products thereof, polyacetal, polyethylene, nylon resins, methacrylic resins, polyvinyl chloride, polycarbonate, polyphenylene ether, polyarylate, polysulfone, polyethersulfone, polyetherimide, and polyamideimide, and one or more of these may be used.

[0063] The resin composition may further contain an active isocyanate compound, which reacts with the polyurethane or polyurea, which is the main component, to further improve the abrasion resistance of the entire resin composition, and also improves the flowability and moldability due to the plasticizing effect of the isocyanate.

[0064] The isocyanate compound may be any isocyanate compound used in ordinary polyurethanes without any particular limitations. For example, aromatic isocyanate compounds include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, or a mixture of these two, 4,4-diphenylmethane diisocyanate, m-phenylene diisocyanate, 4,4'-biphenyl diisocyanate, etc., and hydrogenated products of these aromatic isocyanate compounds, such as dicyclohexylmethane diisocyanate, etc., may also be used. In addition, aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), octamethylene diisocyanate, etc., and alicyclic diisocyanates such as xylene diisocyanate, etc. may also be used. In addition, blocked isocyanate compounds obtained by reacting an isocyanate group of a compound having two or more isocyanate groups at the terminal with a compound having active hydrogen, and uretidione bodies obtained by dimerization of isocyanates may also be used.

[0065] The amount of the isocyanate compound is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and the upper limit is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, based on 100 parts by mass of the polyurethane or polyurea resin (I) component. If the amount is too small, the crosslinking reaction may not be sufficient, and the improvement of physical properties may not be observed. On the other hand, if the amount is too large, discoloration due to heat or ultraviolet rays may increase over time, or thermoplasticity may be lost, or problems such as a decrease in resilience may occur.

[0066] Furthermore, any additives can be appropriately blended into the resin composition according to the application. For example, when the golf ball material of the present invention is used as a cover material, various additives such as fillers (inorganic fillers), organic short fibers, reinforcing agents, crosslinking agents, pigments, dispersants, antioxidants, UV absorbers, and light stabilizers can be added to the above components. When these additives are blended, the blending amount is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and the upper limit is preferably 10 parts by mass or less, more preferably 4 parts by mass or less, per 100 parts by mass of the base resin.

[0067] In order to obtain appropriate resilience and approach spin performance, the rebound resilience of the resin composition needs to be 48% or more as measured according to the JIS-K 6255:2013 standard, preferably 50% or more, and more preferably 52% or more, with the upper limit being 72% or less, preferably 70% or less, and more preferably 68% or less.

[0068] In addition, from the viewpoint of abrasion resistance and imparting an appropriate approach spin amount, the material hardness of the resin composition is preferably 50 or less in Shore D hardness, more preferably 48 or less, and even more preferably 45 or less in Shore D hardness. From the viewpoint of moldability, the lower limit is preferably 30 or more in Shore D hardness, more preferably 35 or more, and even more preferably 37 or more.

[0069] Regarding the method of preparing each component of the above resin composition, for example, they can be mixed using various kneading machines such as a kneading type (single screw or) twin screw extruder, a Banbury, a kneader, a lab plastomill, etc., or each component may be mixed by dry blending at the time of injection molding of the resin composition. Furthermore, when the above active isocyanate compound is used, it may be included at the time of resin mixing using various kneading machines, or a master batch containing the active isocyanate compound and other components may be separately prepared in advance, and each component may be mixed by dry blending at the time of injection molding of the resin composition.

[0070] For example, the method for molding the cover with the resin composition may be, for example, to supply the resin composition to an injection molding machine and inject the molten resin composition around the core to mold the cover. In this case, the molding temperature varies depending on the type of the main component (I), such as polyurethane or polyurea, but is usually in the range of 150 to 270°C.

[0071] The cover has a thickness of preferably 0.4 mm or more, more preferably 0.5 mm or more, and even more preferably 0.6 mm or more, and is preferably 3.0 mm or less, and more preferably 2.0 mm or less.

[0072] When at least one intermediate layer is interposed between the core and the cover, it is preferable to use, as the material of the intermediate layer, various thermoplastic resins used in the cover materials of golf balls, particularly ionomer resins, and commercially available ionomer resins can be used. In this case, the thickness of the intermediate layer can be set within the same range as the thickness of the cover.

[0073] The golf ball of the present invention has a large number of dimples on the surface of the outermost layer from the viewpoint of aerodynamic performance. There is no particular restriction on the number of dimples formed on the surface of the outermost layer, but from the viewpoint of improving aerodynamic performance and increasing the flight distance, the number is preferably 250 or more, more preferably 270 or more, even more preferably 290 or more, and most preferably 300 or more, with the upper limit being preferably 400 or less, more preferably 380 or less, and even more preferably 360 or less.

[0074] In the golf ball of the present invention, a coating layer can be formed on the surface of the cover. As the coating material for forming the coating layer, it is preferable to use a two-component curing urethane coating material. Specifically, in this case, the two-component curing urethane coating material contains a base material mainly composed of a polyol resin and a curing agent mainly composed of a polyisocyanate.

[0075] The method for applying the above-mentioned paint to the cover surface to form a coating layer is not particularly limited, and any known method can be used, such as an air gun coating method or an electrostatic coating method.

[0076] The thickness of the coating layer is not particularly limited, but is usually 8 to 22 μm, preferably 10 to 20 μm.

[0077] The golf ball of the present invention can be made for competitive use in accordance with the Rules of Golf, with an outer diameter of 42.80 mm or less so as not to pass through a ring with an inner diameter of 42.672 mm, and a mass of preferably 45.0 to 45.93 g. EXAMPLES

[0078] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0079] [Examples 1 to 4, Comparative Examples 1 to 4] Common Core A rubber composition for the core common to all the examples was prepared according to the formulation shown in Table 1, and a core having a diameter of 38.6 mm was produced by vulcanization molding.

[0080] [Table 1]

[0081] Details of the core material are as follows: "cis-1,4-polybutadiene" (manufactured by ENEOS Materials), product name "BR01" "Zinc acrylate" manufactured by Nippon Shokubai Co., Ltd. "Zinc oxide" manufactured by Sakai Chemical Industry Co., Ltd. "Barium sulfate" manufactured by Sakai Chemical Industry Co., Ltd. "Anti-aging agent" Product name: "Nocrac NS6" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) "Organic peroxide (1)" Dicumyl peroxide, trade name "Percumyl D" (manufactured by NOF Corporation) "Organic peroxide (2)" A mixture of 1,1-di(tert-butylperoxy)cyclohexane and silica, trade name "Perhexa C-40" (manufactured by NOF Corporation) "Zinc stearate" manufactured by NOF Corporation

[0082] A common middle class The resin material for the intermediate layer was injection molded around a core with a diameter of 38.6 mm to produce an intermediate layer-coated sphere with an intermediate layer of 1.25 mm thickness. The resin material for the intermediate layer was a resin composition common to all examples, a blend of 50 parts by mass of sodium neutralized ethylene-unsaturated carboxylic acid copolymer with an acid content of 18% by mass and 50 parts by mass of zinc neutralized ethylene-unsaturated carboxylic acid copolymer with an acid content of 15% by mass, totaling 100 parts by mass.

[0083] Resin composition of cover (outermost layer) The resin composition of the cover for each example was prepared by mixing component (I), which is the base resin, with component (II) or an equivalent resin component, appropriately blended with "TPU" (DIC Covestro Polymer Co., Ltd., product name "Pandex"), an aromatic ether type thermoplastic polyurethane (Shore D hardness "40"). Details of component (II) are shown in Table 2 below.

[0084] [Table 2]

[0085] Details of the resin components in Table 2 are as follows: "PARAPET SA-FW001" and "PARAPET SA-CW001" are both acrylic core-shell polymers in Kuraray's "PARAPET" series. "SOES1611" Hydrogenated aromatic vinyl elastomer manufactured by Asahi Kasei Corporation

[0086] Physical properties of resin composition (1) Shore D hardness Each of the above resins was molded into a sheet of 2 mm thickness and left at 23±2°C for two weeks, after which three sheets were stacked and the material hardness of the resin was measured using a Shore D hardness tester conforming to the ASTM D2240 standard. To measure the hardness, an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd., equipped with a Shore D hardness tester, was used. (2) Rebound elasticity The rebound resilience was measured based on the JIS-K 6255:2013 standard. (3) Liquidity (MFR) The MFR (g / 10 min) was measured under the measurement conditions (ISO1133) of 230°C and a load of 2.16 kgf.

[0087] Cover (outermost layer) Next, the above cover resin composition was injection molded around the intermediate layer-coated sphere to produce a three-piece golf ball having a diameter of 42.7 mm and an outermost layer having a thickness of 0.8 mm. In this process, common dimples were formed on the surface of the cover of each of the Examples and Comparative Examples, although not shown in the figures.

[0088] The restitution coefficient, spin rate on approach shots, approach controllability, hitting feel and abrasion resistance of the golf balls produced in each example were evaluated by the following methods. The results are shown in Table 3.

[0089] Ball's coefficient of restitution (COR value) The COR value of a golf ball was measured using an ADC Ball COR Durability Tester manufactured by Automated Design Corporation in the United States. A golf ball is launched with an initial velocity of 12 to 50 m / s using air pressure. A speed measurement sensor is placed at a distance of about 0.8 meters, and when the golf ball hits a metal plate placed about 1.2 meters away, the golf ball bounces back so that it passes through the speed measurement sensor. The COR value is the return velocity divided by the initial velocity.

[0090] Approach shot spin rate A sand wedge (SW) was attached to a golf hitting robot, and the initial velocity and backspin amount immediately after hitting with a head speed (HS) of 20 m / s were measured by an initial condition measuring device. In addition, the backspin amount at the approach shot of Comparative Example 1 was used as a standard to examine the difference in spin amount between each Example and Comparative Example 1.

[0091] Approach controllability In addition, a sensory evaluation of the controllability of the ball during approach shots was conducted using the following method. The club used was the same sand wedge (SW) as above, product name "Bridgestone TourStage TW-03 (loft angle 57°)", and golfers actually hit the ball and evaluated it according to the following criteria. [Judgment and Evaluation] ◎ Excellent operability. 〇 ··· Excellent operability. ×... Slightly inferior in operability. In addition, the judgment of whether or not the controllability is excellent is influenced not only by the amount of spin of the ball, but also by the length of contact time between the ball and the club face due to low resilience. If the contact time is long, the controllability is good, and if it is short, the controllability is poor. Here, the controllability (controllability) including the amount of spin and the length of contact time is judged.

[0092] Hitting Feel The sensory evaluation of the feel of the shot was carried out as follows. The club used was the same sand wedge (SW) as above. [Judgment and Evaluation] ○ There is no clicky sound and the feel is good. △ ··· There is a slightly clicky sound, which makes the feel of the impact slightly unpleasant. × There is a clicking sound and the impact feels unpleasant.

[0093] Evaluation of abrasion resistance The balls were kept warm at 23°C and five balls of each type were hit using a swing robot machine with a pitching wedge (PW) at a head speed of 33 m / s. The damage caused by the impact was then visually evaluated according to the following criteria. ○: No scratches, or some scratches but not very noticeable. △ ··· Slightly scratched.

[0094] [Table 3]

[0095] As shown in the results in Table 3, the golf balls of Comparative Examples 1 to 4 are inferior to the products of the present invention (Examples) in the following points. In Comparative Example 1, the resin composition does not contain the component (II) and has a small CS1 value, so that the approach controllability is poor. In Comparative Example 2, although the resin composition contains a hydrogenated aromatic vinyl elastomer, the spin rate at the time of approach is smaller than those in each of the Examples, and the hit feel is somewhat uncomfortable. In Comparative Example 3, although the resin composition contains a hydrogenated aromatic vinyl elastomer, the spin rate at the time of approach is smaller than in each of the Examples, and the hit feel is somewhat uncomfortable. In Comparative Example 4, the resin composition contains a hydrogenated aromatic vinyl elastomer in a large amount, resulting in a small spin rate on approach, a poor feel on impact, and poor abrasion resistance.

Claims

1. In a golf ball having at least one rubber core and at least one cover layer covering the core, at least one layer of the cover contains the following components (I) and (II): (I) Polyurethane or Polyurea (II) Core-shell polymer in which the core is an acrylic crosslinked rubber particle and the shell is an acrylic polymer The amount of the component (II) is less than 15 parts by mass relative to 100 parts by mass of the component (I), and the CS calculated by the following formula (1) is 1 The value is -4.08 x 10 -3 A golf ball that is larger. CS 1 =(CV 50 -CV 12 ) / 38 ・・・(1) [In the above formula, CV 50 indicates the value of the restitution coefficient at an incident speed of 50.0 m / s, and CV 12 indicates the value of the restitution coefficient at an incident speed of 12.0 m / s.

2. CS calculated by the following formula (2) 2 The value is -5.23 x 10 -3 The golf ball of claim 1 . CS 2 =(1.0-CV 12 / 45 ) / 33 ・・・(2) [In the above formula, CV 12 / 45 indicates the value of the restitution coefficient at an incident speed of 12.0 m / s when the restitution coefficient at an incident speed of 45.0 m / s is taken as 1.0.]

3. 3. The golf ball of claim 1, wherein component (II) does not contain a plasticizer.

4. 3. The golf ball according to claim 1, wherein component (II) has a melt flow rate (MFR) value of 18 g / 10 min or less measured under conditions (ISO 1133) of 230° C. and a load of 2.16 kgf.

5. 3. The golf ball of claim 1, wherein the rebound resilience of component (II) is 22% or less.

6. 3. The golf ball according to claim 1, wherein component (II) has a Shore D hardness of 22-40.

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