golf balls

Abstract

To provide a golf ball which, although the golf ball includes a silicone-based additive in an outer surface (a coating layer) of the golf ball, has a good spin performance on approach shots not only in a wet situation but also in a (normally) dry situation, and can exhibit both good water-repelling performance and good friction performance.SOLUTION: In a golf ball having a core, a cover, and a coating layer, the coating layer is formed of an urethane coating that includes an organic solvent having a boiling point of 80°C or less and a silicone-based additive, and the urethane coating includes a polyisocyanate as a curing agent. The polyisocyanate contains an adduct and an isocyanurate of hexamethylene diisocyanate (HMDI).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a golf ball having a core, a cover, and a paint layer, and more particularly to a golf ball having a cover formed from a polyurethane resin composition and a paint layer made from a urethane paint composition. [Background technology]

[0002] For the purpose of protecting the surface of a golf ball or maintaining a good aesthetic appearance, the surface of the ball is often coated with a paint composition. As a paint composition for such golf balls, a two-component curing polyurethane paint, in which a polyol and a polyisocyanate are mixed immediately before use, is preferably used because of its resistance to large deformation, impact, and friction.

[0003] JP 2014-524335 A (Patent Document 1) describes a golf ball incorporating a "low energy" composition in a soft surface coating, which reduces the coefficient of friction, making it easier to handle during manufacturing, reducing the tendency for mud to stick to the ball, etc. It also describes the use of a silicone-based additive in the low energy composition.

[0004] Furthermore, Japanese Patent Laid-Open Publication No. 2019-10190 (Patent Document 2) describes that imparting water repellency to the surface of a golf ball reduces the coefficient of friction of the surface of the golf ball and prevents a decrease in driver distance when playing in the rain. Examples of water repellent additives include silicone-based additives such as silicone resin, silicone oil, and silicone rubber.

[0005] Furthermore, Japanese Patent Application Laid-Open No. 2021-53367 (Patent Document 3) describes that by forming an outer surface layer using a material with a contact angle of 90° or more, the surface of the golf ball becomes water-repellent, the coefficient of friction of the surface of the golf ball decreases, and it is possible to prevent a decrease in driver distance when playing on rainy days. Examples of water-repellent additives include silicone-based additives such as silicone resin, silicone oil, and silicone rubber.

[0006] However, in the golf balls proposed above, the use of silicone-based additives provides water-repellent properties and improves spin performance in wet conditions, but tends to reduce approach spin performance in dry conditions (normal conditions).

[0007] For this reason, the above-mentioned Patent Document 3 proposes that the outer surface layer of a golf ball be formed from a material containing a water-repellent additive and hexamethylene diisocyanate (HMDI), and that the HMDI further contains an adduct and an isocyanurate. However, even this proposed golf ball does not provide fully satisfactory spin performance on approach shots. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2014-524335 [Patent Document 2] JP 2019-10190 A [Patent Document 3] Patent Publication No. 2021-53367 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide a golf ball that, even when the outer surface (paint layer) of the golf ball contains a silicone-based additive, exhibits good approach spin performance not only in wet conditions but also in dry conditions (normal conditions), and that is capable of achieving both water-repellent properties and frictional properties. [Means for solving the problem]

[0010]

[0006] The present inventors have conducted extensive research to achieve the above-mentioned object, and have found that, in a urethane coating composition typically used to form a coating layer corresponding to the outer surface of a golf ball, if the polyisocyanate contains a hexamethylene diisocyanate (HMDI) adduct and an isocyanurate, and if the organic solvent used in the base resin or curing agent has a relatively low boiling point, the organic solvent in the coating surface will volatilize before the silicone component rises to the outer surface during coating, thereby curing the coating composition. This finding led to the completion of the present invention. In particular, the use of a urethane resin composition with low rebound properties as a golf ball cover material further improves controllability during approach shots, thereby enabling the effects of the present invention to be fully realized.

[0011] Accordingly, the present invention provides the following golf balls. 1. A golf ball having a core, a cover, and a paint layer, At least one layer of the cover comprises the following components (I), (II), and (III): (I) Polyurethane or Polyurea (II) Aromatic vinyl elastomer (III) Thermoplastic polyester elastomer The aromatic vinyl elastomer of component (II) has a Shore D hardness of 30 or less and a rebound resilience of 30% or less, and the thermoplastic polyester elastomer of component (III) has a Shore D hardness of 45 or less and a rebound resilience of 74% or less, and a melt viscosity of 1.5 x 10 at 200°C and a shear rate of 243 (1 / sec). 4 (dPa·s) or less,The golf ball is characterized in that the paint layer is formed from a urethane paint containing an organic solvent having a boiling point of 80°C or less and a silicone-based additive, the urethane paint containing a polyisocyanate as a curing agent, and the polyisocyanate containing an adduct and an isocyanurate of hexamethylene diisocyanate (HMDI). 2. The golf ball according to 1 above, wherein the organic solvent having a boiling point of 80° C. or less is blended in an amount of 20% by mass or more based on the total amount of the coating composition. 3. The golf ball according to 1 or 2 above, wherein the mixing ratio (A) / (B) of the isocyanurate of hexamethylene diisocyanate to the adduct (B) is 85 / 15 to 15 / 85 by mass. 4 The blending amount of the component (II) is 5 to 20 parts by mass per 100 parts by mass of the component (I). 3 1. The golf ball according to claim 1, [Effects of the Invention]

[0012] According to the golf ball of the present invention, even if the outer surface (paint layer) of the golf ball contains a silicone-based additive, the approach spin performance is good not only in wet conditions but also in dry conditions (normal conditions), and water repellency and friction performance can be sufficiently achieved at the same time.

[0013] The present invention will be described in more detail below. The golf ball of the present invention is a golf ball having a core, a cover, and a paint layer.

[0014] The core can be formed using a known rubber material as a base material. Known natural or synthetic rubbers can be used as the base rubber. More specifically, polybutadiene, particularly cis-1,4-polybutadiene having at least 40% or more cis structures, is recommended as the primary base material. Furthermore, natural rubber, polyisoprene rubber, styrene-butadiene rubber, etc. can be used in combination with the polybutadiene in the base rubber, if desired.

[0015] Polybutadiene can also be synthesized using a metal catalyst such as a rare earth element catalyst such as a Nd catalyst, a cobalt catalyst, or a nickel catalyst.

[0016] The base rubber may contain co-crosslinking agents such as unsaturated carboxylic acids and their metal salts, inorganic fillers such as zinc oxide, barium sulfate, and calcium carbonate, and organic peroxides such as dicumyl peroxide and 1,1-bis(t-butylperoxy)cyclohexane. Commercially available antioxidants may also be added as needed.

[0017] The core can be produced by vulcanizing and curing a rubber composition containing the above components. For example, the core can be produced by kneading the rubber composition using a kneader such as a Banbury mixer or a roll, compression molding or injection molding using a core mold, and curing the molded product by appropriately heating the molded product at a temperature sufficient for the organic peroxide and co-crosslinking agent to act, 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes.

[0018] The golf ball of the present invention has a core surrounded by a single-layer or multi-layer cover. Examples of such golf balls include a golf ball having a core surrounded by a single-layer cover, and a golf ball having a core, an intermediate layer surrounding the core, and an outermost layer surrounding the intermediate layer.

[0019] In the present invention, the resin material for at least one layer of the cover comprises the following components (I) and (II): (I) Polyurethane or Polyurea (II) Aromatic vinyl elastomer It is preferable that the resin composition contains

[0020] (I) Polyurethane or Polyurea Polyurethane or polyurea can be the main or base resin of the cover material (resin composition). Details of this component, polyurethane (Ia) or polyurea (Ib), are as follows:

[0021] (Ia) Polyurethane The polyurethane structure consists of a soft segment made of a long-chain polyol (polymeric glycol), and a hard segment made of a chain extender and polyisocyanate. The polymeric polyol used as the raw material can be any of those conventionally used in polyurethane material technology, and is not particularly limited. Examples include polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymer polyols, castor oil polyols, silicone polyols, and vinyl polymer polyols. Specific examples of polyester polyols include adipate polyols such as polyethylene adipate glycol, polypropylene adipate glycol, polybutadiene adipate glycol, and polyhexamethylene adipate glycol, as well as lactone polyols such as polycaprolactone polyols. Examples of polyether polyols include poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol), and poly(methyltetramethylene glycol). These may be used alone or in combination of two or more.

[0022] As the polymer polyol, it is preferable to use a polyether polyol.

[0023] 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, golf balls made from polyurethane compositions having various excellent properties such as the above-mentioned resilience and productivity can be reliably obtained. 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.

[0024] The number average molecular weight mentioned above is a number average molecular weight calculated based on the hydroxyl value measured in accordance with JIS-K1557 (the same applies hereinafter).

[0025] The chain extender may be any of those used in conventional polyurethane-related technologies, 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 may be used, and among these, an aliphatic diol having 2 to 12 carbon atoms may be preferably used. Specific examples include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, and 2,2-dimethyl-1,3-propanediol, and among these, 1,4-butylene glycol may be particularly preferably used.

[0026] The polyisocyanate may be any of those used in conventional polyurethane-related technologies, 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, tetramethylxylene 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, depending on the isocyanate, it may be difficult to control the crosslinking reaction during injection molding.

[0027] The 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 the components in such a ratio that the amount of isocyanate groups contained in the polyisocyanate compound is 0.95 to 1.05 moles per mole of active hydrogen atoms contained in the long-chain polyol and chain extender.

[0028] The method for producing polyurethane is not particularly limited, and polyurethane may be produced by either a prepolymer method or a one-shot method using a long-chain polyol, a chain extender, and a polyisocyanate compound, utilizing a known urethane reaction. Among these methods, melt polymerization in the substantial absence of a solvent is preferred, and production by continuous melt polymerization using a multi-screw extruder is particularly preferred.

[0029] As the polyurethane, it is preferable to use a thermoplastic polyurethane material, and particularly an ether-based thermoplastic polyurethane material. As the thermoplastic polyurethane material, commercially available products can be suitably used, such as "Pandex" manufactured by DIC Covestropolymer Co., Ltd. and "Rezamin" manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.

[0030] (Ib) Polyurea Polyurea is a resin composition primarily composed of urea bonds formed by the reaction of (i) isocyanate with (ii) an amine-terminated compound. This resin composition is described in detail below.

[0031] (i) Isocyanate The isocyanate can be suitably any isocyanate used in conventional polyurethane-related techniques, and is not particularly limited, and the same isocyanates as those explained above for the polyurethane material can be used.

[0032] (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 long-chain polyamine and / or amine-based curing agent shown below can be used.

[0033] The long-chain polyamine is an amine compound having two or more amino groups in the molecule that can react with isocyanate groups and 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.

[0034] On the other hand, the amine curing agent is an amine compound having two or more amino groups capable of reacting with isocyanate groups 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.

[0035] (iii) Polyol Although not essential, polyurea can further contain a polyol in addition to the above-mentioned components (i) and (ii). As this polyol, those used in conventional polyurethane-related technologies can be suitably used without any particular limitation, but specific examples include the long-chain polyols and / or polyol-based curing agents shown below.

[0036] The long-chain polyol may be any of those conventionally used in polyurethane-related technologies, 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.

[0037] The number average molecular weight of the long chain polyol is preferably 1,000 to 5,000, and more preferably 1,700 to 3,500. If the number average molecular weight is within this range, the resilience, productivity, etc. will be even more excellent.

[0038] The polyol-based curing agent can be suitably one used in conventional polyurethane-related technologies, and is not particularly limited. In the present invention, a low-molecular-weight compound having two or more active hydrogen atoms in the molecule capable of reacting with an isocyanate group and a molecular weight of less than 1,000 can be used, and among these, aliphatic diols having 2 to 12 carbon atoms can be suitably used. Specific examples include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, and 2,2-dimethyl-1,3-propanediol, and among these, 1,4-butylene glycol is particularly suitable. Furthermore, the number-average molecular weight of the polyol-based curing agent is preferably less than 800, more preferably less than 600.

[0039] The polyurea can be produced by any known method, such as a prepolymer method or a one-shot method.

[0040] From the viewpoint of spin characteristics and abrasion resistance of the resulting golf ball, the material hardness of component (I) is preferably not more than 52 Shore D hardness, more preferably not more than 50 Shore D hardness, and even more preferably not more than 48. From the viewpoint of moldability, the lower limit is preferably not less than 38 Shore D hardness, more preferably not less than 40 Shore D hardness.

[0041] 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 viewpoint of improving the approach spin rate. The rebound resilience is measured in accordance with JIS-K 6255:2013.

[0042] The above component (I) is the main material of the resin composition, and in order to provide sufficient abrasion resistance that urethane resins possess, it accounts for 50% by mass or more of the resin composition, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and most preferably 90% by mass or more.

[0043] (II) Aromatic vinyl elastomer Next, (II) the aromatic vinyl elastomer will be described. As described below, the (II) aromatic vinyl elastomer, when blended in a small amount below a certain level, has good compatibility with the base resin, component (I), and also has good compatibility with the thermoplastic polyester elastomer, component (III), described below, allowing the golf ball and its manufacturing method to maintain good abrasion resistance and moldability.

[0044] Aromatic vinyl elastomers are polymers (elastomers) composed of polymer blocks primarily composed of aromatic vinyl compounds and random copolymer blocks of aromatic vinyl compounds and conjugated diene compounds. Aromatic vinyl elastomers, such as SEBS, typically have hard segments composed of aromatic vinyl compounds at both ends and soft segments composed of conjugated diene compounds in the middle. Recent research has also reported polymers in which aromatic vinyl compounds are randomly incorporated into the midblock in addition to conjugated diene compounds. The hardness of aromatic vinyl elastomers generally decreases as the aromatic vinyl content of the hard segments decreases, while the soft segment content increases, resulting in increased resilience. On the other hand, randomly incorporating aromatic vinyl compounds into the soft segments of the midblock results in a significant decrease in hardness but a decrease in resilience. Similar effects can also be achieved by using a conjugated diene compound with a high Tg instead of the aromatic vinyl compound randomly incorporated into the midblock. In particular, in the present invention, in order to fully exert the above-mentioned effects, it is preferable to use, as component (III), the above polymer (elastomer) that has been subjected to a hydrogenation treatment.

[0045] Examples of aromatic vinyl compounds in the polymer include styrene, α-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylethylene, N,N-dimethyl-p-aminoethylstyrene, and N,N-diethyl-p-aminoethylstyrene. These may be used alone or in combination of two or more. Among these, styrene is preferred.

[0046] Examples of the conjugated diene compound in the polymer include butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, and 1,3-hexadiene. These may be used alone or in combination of two or more. Among these compounds, butadiene and isoprene are preferred, and butadiene is more preferred.

[0047] Note that units derived from the above conjugated diene compounds, such as units derived from butadiene, become ethylene units or butylene units when subjected to hydrogenation treatment. For example, hydrogenation treatment of a styrene-butadiene-styrene block copolymer (SBS) turns it into a styrene-ethylene-butylene-styrene block copolymer (SEBS).

[0048] As mentioned above, it is preferable to use a hydrogenated aromatic vinyl elastomer, i.e., a hydrogenated aromatic vinyl elastomer, as the aromatic vinyl elastomer (component (II)). Preferred hydrogenated aromatic vinyl elastomers are elastomers obtained by hydrogenating a polymer consisting of a polymer block primarily composed of an aromatic vinyl compound and a random copolymer block of an aromatic vinyl compound and a conjugated diene compound. Elastomers obtained by hydrogenating a polymer consisting of a styrene-based polymer block and a styrene-butadiene random copolymer block are more preferred. Elastomers obtained by hydrogenating a polymer consisting of a styrene-based polymer block and a styrene-butadiene random copolymer block, particularly a polymer block primarily composed of styrene at both ends (especially a polymer block consisting only of styrene at both ends) and a random copolymer block in the middle, are particularly preferred. The use of a copolymer with this structure is believed to provide both low hardness and low resilience, and to have low tack due to rapid solidification after molding. It is also believed to have excellent compatibility with the main component (I), polyurethane or polyurea, thereby minimizing the deterioration of physical properties due to blending.

[0049] Specific examples of the hydrogenated aromatic vinyl elastomer include styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-isobutylene-styrene block copolymer (SIBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isobutylene block copolymer (SIB), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), styrene-butadiene-butylene-styrene block copolymer (SBBS), and styrene-ethylene-propylene block copolymer (SEP).

[0050] In the aromatic vinyl elastomer, the proportion of units derived from aromatic vinyl compounds in the copolymer (i.e., the aromatic vinyl compound content, preferably the styrene content) is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and most preferably 60% by mass or more. By setting the aromatic vinyl compound content, preferably the styrene content, to a high level, compatibility with polyurethane or polyurea, which is component (I), is improved, and deterioration of the desired hardness and moldability can be prevented. The content of units derived from aromatic vinyl compounds (preferably the styrene content) is measured by H 1 - It can be calculated by NMR measurement.

[0051] Furthermore, the aromatic vinyl elastomer preferably has a glass transition temperature (Tg) of −20 to 50° C., as indicated by the tan δ peak temperature obtained by dynamic mechanical analysis (DMA), and more preferably 0° C. or higher, and even more preferably 5° C. or higher. In other words, by having the tan δ peak temperature near the temperature range at which golf balls are normally used, it is believed that the impact resilience of the entire resin composition can be kept low in the temperature range at which golf balls are normally used, thereby enhancing the desired effects of the present invention.

[0052] The aromatic vinyl elastomer (II) may be commercially available, such as "SOE (trade name)," "TUFTECH," and "TUFPREN" manufactured by Asahi Kasei Corporation, or "DIC STYRENE" manufactured by DIC Corporation.

[0053] Regarding the material hardness of component (II), from the viewpoint of improving the approach spin rate, the Shore D hardness is preferably 30 or less, more preferably 28 or less, and even more preferably 26 or less. The lower limit of the Shore D hardness is preferably 18 or more, and more preferably 20 or more.

[0054] The rebound resilience of component (II) is preferably 30% or less, more preferably 25% or less, and even more preferably 22% or less, in order to maintain approach spin rate and maintain low resilience on approach shots to improve control. By maintaining the rebound resilience at such a low level, a small amount of component (II) can be added without adversely affecting the physical properties of the golf ball, thereby reducing the initial velocity of the ball on approach shots. However, the lower limit of the rebound resilience is preferably 15% or more, more preferably 20% or more, in order to minimize the impact of a decrease in rebound on driver shots and a reduction in flight distance. The above rebound resilience is measured in accordance with JIS-K 6255:2013.

[0055] The blend amount of component (II) is 30 parts by weight or less, preferably 20 parts by weight or less, and more preferably 15 parts by weight or less, per 100 parts by weight of component (I). The lower limit of the blend amount is preferably 5 parts by weight or more, more preferably 10 parts by weight or more. If the blend amount of component (II) is too high, abrasion resistance and moldability may deteriorate. On the other hand, if the blend amount of component (II) is too low, the cover resin material may not have the low hardness and desired impact resilience, and the effect of reducing the initial velocity of the ball on approach shots may also be reduced.

[0056] The resin composition containing the above components (I) and (II) may further contain a thermoplastic polyester elastomer (III), which will be described below.

[0057] (III) Thermoplastic polyester elastomer The thermoplastic polyester elastomer (III) imparts a certain level of resilience to the resin composition, which, combined with this resilience, helps maintain a certain level of spin rate during approach shots. The thermoplastic polyester elastomer (III) also has good compatibility with the base resin (I), particularly better compatibility than conventionally used thermoplastic polyester elastomers, thereby imparting good abrasion resistance. Furthermore, by incorporating the thermoplastic polyester elastomer into the resin composition as an essential component, the resin composition has a certain level of melt viscosity, which imparts solidification properties to the resin composition after molding. This prevents a decrease in the viscosity of the entire resin composition due to the softness of the base resin (I), thereby preventing a decrease in moldability (productivity), an increase in poor appearance of the molded golf ball, and suppresses increased production costs due to increased cooling time.

[0058] The thermoplastic polyester elastomer of component (III) is The resin composition comprises (b-1) a polyester block copolymer and (b-2) a hard resin. The (b-1) component further comprises (b-1-1) a high-melting-point crystalline polymer segment and (b-1-2) a low-melting-point polymer segment.

[0059] The (b-1-1) high-melting point crystalline polymer segment constituting the polyester block copolymer of the component (b-1) is a polyester formed from one or more members selected from the group consisting of aromatic dicarboxylic acids or their ester-forming derivatives, and diols or their ester-forming derivatives.

[0060] Specific examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, anthracene dicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, diphenoxyethane dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 5-sulfoisophthalic acid, and sodium 3-sulfoisophthalate. In the present invention, aromatic dicarboxylic acids are primarily used, but if necessary, a portion of these aromatic dicarboxylic acids may be substituted with aliphatic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, cyclopentanedicarboxylic acid, and 4,4'-dicyclohexyldicarboxylic acid, or adipic acid, succinic acid, oxalic acid, sebacic acid, dodecanedioic acid, and dimer acid. Specific examples of ester-forming derivatives of dicarboxylic acids include lower alkyl esters, aryl esters, carbonate esters, and acid halides of the above-mentioned dicarboxylic acids.

[0061] Next, as the diol, a diol having a molecular weight of 400 or less can be suitably used. Specific examples include aliphatic diols such as 1,4-butanediol, ethylene glycol, trimethylene glycol, pentamethylene glycol, hexamethylene glycol, neopentyl glycol, and decamethylene glycol, alicyclic diols such as 1,1-cyclohexanedimethanol, 1,4-dicyclohexanedimethanol, and tricyclodecanedimethanol, and aromatic diols such as xylylene glycol, bis(p-hydroxy)diphenyl, bis(p-hydroxy)diphenylpropane, 2,2′-bis[4-(2-hydroxyethoxy)phenyl]propane, bis[4-(2-hydroxyethoxy)phenyl]sulfone, 1,1-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane, 4,4′-dihydroxy-p-terphenyl, and 4,4′-dihydroxy-p-quaterphenyl. Specific examples of the ester-forming derivatives of diols include acetylated forms and alkali metal salts of the above-mentioned diols.

[0062] The above aromatic dicarboxylic acids, diols, and derivatives thereof may be used alone or in combination of two or more.

[0063] As the component (b-1-1), particularly, those comprising polybutylene terephthalate units derived from terephthalic acid and / or dimethyl terephthalate and 1,4-butanediol, those comprising polybutylene terephthalate units derived from isophthalic acid and / or dimethyl isophthalate and 1,4-butanediol, and further copolymers of these two can be suitably used.

[0064] The (b-1-2) low-melting point polymer segment is an aliphatic polyether and / or an aliphatic polyester.

[0065] Examples of aliphatic polyethers include poly(ethylene oxide) glycol, poly(propylene oxide) glycol, poly(tetramethylene oxide) glycol, poly(hexamethylene oxide) glycol, copolymers of ethylene oxide and propylene oxide, ethylene oxide addition polymers of poly(propylene oxide) glycol, and copolymer glycols of ethylene oxide and tetrahydrofuran. Examples of aliphatic polyesters include poly(ε-caprolactone), polyenantholactone, polycaprolactone, polybutylene adipate, and polyethylene adipate. In the present invention, from the viewpoint of elastic properties, poly(tetramethylene oxide) glycol, ethylene oxide addition products of poly(propylene oxide) glycol, copolymer glycols of ethylene oxide and tetrahydrofuran, poly(ε-caprolactone), polybutylene adipate, and polyethylene adipate can be preferably used. Among these, it is particularly recommended to use poly(tetramethylene oxide) glycol, an ethylene oxide adduct of poly(propylene oxide) glycol, and a copolymer glycol of ethylene oxide and tetrahydrofuran.The number average molecular weight of these segments in the copolymerized state is preferably about 300 to 6,000.

[0066] The component (b-1) can be produced by a known method, such as a method of transesterifying a lower alcohol diester of a dicarboxylic acid, an excess amount of a low-molecular-weight glycol, and a low-melting-point polymer segment component in the presence of a catalyst, followed by polycondensation of the resulting reaction product, or a method of esterifying a dicarboxylic acid, an excess amount of a glycol, and a low-melting-point polymer segment component in the presence of a catalyst, followed by polycondensation of the resulting reaction product.

[0067] The proportion of the (b-1) component accounted for by the (b-1-2) component is 30 to 60 mass%. In this case, the preferred lower limit can be 35 mass% or more, and the preferred upper limit can be 55 mass% or less. If the proportion of the (b-1-2) component is too low, impact resistance (especially at low temperatures) and compatibility may be insufficient. On the other hand, if the proportion of the (b-1-2) component is too high, the rigidity of the resin composition (and molded article) may be insufficient.

[0068] The hard resin of component (b-2) is not particularly limited, but may be, for example, one or more selected from the group consisting of polycarbonate, acrylic resin, styrene resin such as ABS resin or polystyrene, polyester resin, polyamide resin, polyvinyl chloride, and modified polyphenylene ether. In the present invention, polyester resin is preferably used from the viewpoint of compatibility, and it is more preferable to use polybutylene terephthalate and / or polybutylene naphthalate.

[0069] The blending ratio of the above-mentioned components (b-1) and (b-2) [(b-1):(b-2)] is not particularly limited, but is preferably 50:50 to 90:10 by mass, more preferably 55:45 to 80:20. If the proportion of component (b-1) is too low, impact resistance (at low temperatures) may be insufficient. On the other hand, if the proportion of component (b-1) is too high, the rigidity and moldability of the composition (and molded article) may be insufficient.

[0070] As such (III) thermoplastic polyester elastomer, commercially available products can be used, and a specific example is "Hytrel" manufactured by Toray DuPont Co., Ltd.

[0071] With regard to the material hardness of the component (III), from the viewpoint of improving the approach spin rate, the Shore D hardness is preferably 45 or less, more preferably 43 or less, and even more preferably 41 or less. The lower limit of the Shore D hardness is preferably 36 or more, and more preferably 38 or more.

[0072] The rebound resilience of component (III) is preferably 74% or less, more preferably 73% or less, and even more preferably 72% or less, from the viewpoint of reducing the initial approach velocity. The lower limit of the rebound resilience is preferably 50% or more, more preferably 52% or more, and even more preferably 60% or more. The rebound resilience is measured in accordance with JIS-K 6255:2013.

[0073] The melt viscosity of the thermoplastic polyester elastomer of component (III) is 1.5 x 10 4 (dPa·s) or less, preferably 1.45×10 4 (dPa·s) or less, more preferably 1.0×104 (dPa·s) or less, and even more preferably 0.8×10 4 (dPa·s) or less, and the lower limit is 0.4×10 4 (dPa·s) or more, and more preferably 0.5×10 4 (dPa·s) or more. This melt viscosity allows the resin composition to solidify after molding, maintaining good moldability (productivity). This melt viscosity is measured at a shear rate of 243 (1 / sec) using a capillograph at a temperature of 200°C in accordance with ISO 11443:1995.

[0074] The amount of component (III) to be blended is 20 parts by mass or less, and preferably 15 parts by mass or less, per 100 parts by mass of component (I). If this amount is exceeded, abrasion resistance may be reduced. The lower limit of the blending amount is preferably 3 parts by mass or more, and more preferably 5 parts by mass or more, per 100 parts by mass of component (I).

[0075] In addition to the resin components described above, the resin composition containing the above components (I) to (III) may contain other resin materials in order to further improve the flowability of the golf ball resin composition and enhance various physical properties such as resilience and crack resistance.

[0076] The other resin material may be selected from polyamide elastomer, ionomer resin, ethylene-ethylene-butylene-ethylene block copolymer or modified product thereof, polyacetal, polyethylene, nylon resin, methacrylic resin, polyvinyl chloride, polycarbonate, polyphenylene ether, polyarylate, polysulfone, polyethersulfone, polyetherimide, and polyamideimide, and one or more of these may be used.

[0077] The resin composition may further contain an active isocyanate compound, which reacts with the polyurethane or polyurea that 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.

[0078] The isocyanate compound can be any isocyanate compound commonly used in polyurethanes. Examples of aromatic isocyanate compounds include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, or a mixture of these, 4,4-diphenylmethane diisocyanate, m-phenylene diisocyanate, and 4,4'-biphenyl diisocyanate. Hydrogenated versions of these aromatic isocyanate compounds, such as dicyclohexylmethane diisocyanate, can also be used. Other examples include aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), and octamethylene diisocyanate, and alicyclic diisocyanates such as xylene diisocyanate. Other examples include blocked isocyanate compounds obtained by reacting the isocyanate groups of a compound having two or more terminal isocyanate groups with a compound having active hydrogen, and uretidione compounds obtained by dimerization of isocyanates.

[0079] The amount of the isocyanate compound is preferably at least 0.1 parts by mass, more preferably at least 0.5 parts by mass, per 100 parts by mass of the polyurethane or polyurea resin (component (I)). The upper limit is preferably no more than 30 parts by mass, more preferably no more than 20 parts by mass. If this amount is too small, a sufficient crosslinking reaction may not be achieved, and improvement in physical properties may not be observed. On the other hand, if this amount is too large, problems such as significant discoloration over time due to heat or ultraviolet rays, loss of thermoplasticity, or reduced resilience may occur.

[0080] Furthermore, optional additives can be appropriately blended into the resin composition depending on the application. Examples of optional additives include fillers (inorganic fillers), short organic fibers, reinforcing agents, crosslinking agents, pigments, dispersants, antioxidants, UV absorbers, and light stabilizers. 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 preferably 10 parts by mass or less, more preferably 4 parts by mass or less, per 100 parts by mass of the base resin.

[0081] In order to improve the approach spin rate, the rebound resilience of the resin composition needs to be 50% or more as measured according to JIS-K 6255:2013, preferably 52% or more, and more preferably 54% or more, with the upper limit being 72% or less, preferably 70% or less, and more preferably 68% or less.

[0082] Furthermore, from the viewpoint of improving the approach spin rate, the material hardness of the resin composition must be 49 or less in Shore D hardness, preferably 48 or less, and more preferably 47 or less in Shore D hardness. From the viewpoint of moldability, the lower limit is preferably 30 or more in Shore D hardness, and more preferably 35 or more in Shore D hardness.

[0083] The components of the resin composition can be prepared by mixing them using various kneaders such as a kneading type (single-screw or) twin-screw extruder, a Banbury mixer, a kneader, a Labo Plastomill, etc. Alternatively, the components may be mixed by dry blending during injection molding of the resin composition. Furthermore, when the active isocyanate compound is used, it may be added during resin mixing using various kneaders, or a masterbatch containing the active isocyanate compound and other components may be separately prepared and dry blended during injection molding of the resin composition to mix the components.

[0084] For example, the cover can be molded from the resin composition by feeding the resin composition into an injection molding machine and injecting the molten resin composition around the core to form the cover. In this case, the molding temperature varies depending on the type of main component (I), such as polyurethane or polyurea, but is usually in the range of 150 to 270°C.

[0085] The cover thickness is preferably at least 0.4 mm, more preferably at least 0.5 mm, and even more preferably at least 0.6 mm, and is preferably at most 3.0 mm, and more preferably at most 2.0 mm.

[0086] When at least one intermediate layer is interposed between the core and the core, the intermediate layer is preferably made of a thermoplastic resin, particularly an ionomer resin, used in golf ball cover materials. 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.

[0087] 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 are no particular restrictions on the number of dimples formed on the surface of the outermost layer, but from the viewpoint of improving aerodynamic performance and increasing flight distance, the number is preferably at least 250, more preferably at least 270, even more preferably at least 290, and most preferably at least 300, with the upper limit being preferably at most 400, more preferably at most 380, and even more preferably at most 360.

[0088] In the present invention, a paint layer is formed on the cover surface. This paint layer is formed from a urethane paint containing an organic solvent with a boiling point of 80°C or less and a silicone-based additive. As the urethane paint, a two-component curing urethane paint is preferably used, specifically one containing a base agent whose main component is a polyol resin and a curing agent whose main component is polyisocyanate.

[0089] The polyol is not particularly limited, but it is preferable to use one or more polyester polyols. For example, two types of polyester polyols, polyester polyol (A) and polyester polyol (B), can be used as the main component. These two types of polyester polyols have different weight average molecular weights (Mw), and it is preferable that the weight average molecular weight (Mw) of component (A) is 20,000 to 30,000 and the weight average molecular weight (Mw) of component (B) is 800 to 1,500. The weight average molecular weight (Mw) of component (A) is more preferably 22,000 to 29,000, and even more preferably 23,000 to 28,000. On the other hand, the weight average molecular weight (Mw) of component (B) is more preferably 900 to 1,200, and even more preferably 1,000 to 1,100.

[0090] The two types of polyester polyols mentioned above are obtained by polycondensation of a polyol with a polybasic acid, and examples of the polyol include diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, hexylene glycol, dimethylolheptane, polyethylene glycol, and polypropylene glycol, as well as triols, tetraols, and polyols having an alicyclic structure. Examples of polybasic acids include aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, azelaic acid, and dimer acid; aliphatic unsaturated dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid, and citraconic acid; aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, and pyromellitic acid; dicarboxylic acids having an alicyclic structure such as tetrahydrophthalic acid, hexahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and endomethylenetetrahydrophthalic acid; and tris-2-carboxyethyl isocyanurate. In particular, the polyester polyol of component (A) can be a polyester polyol having a cyclic structure introduced into the resin skeleton, such as a polyester polyol obtained by polycondensation of a polyol having an alicyclic structure such as cyclohexanedimethanol with a polybasic acid, or a polyol having an alicyclic structure with a diol or triol with a polybasic acid. On the other hand, as the polyester polyol of component (B), a polyester polyol having a multi-branched structure can be used, and examples thereof include polyester polyols having a branched structure such as "NIPPOLAN 800" manufactured by Tosoh Corporation.

[0091] The overall weight-average molecular weight (Mw) of the base material comprising the two polyester polyols is preferably 13,000 to 23,000, more preferably 15,000 to 22,000. The overall number-average molecular weight (Mw) of the base material comprising the two polyester polyols is preferably 1,100 to 2,000, more preferably 1,300 to 1,850. If these average molecular weights (Mw and Mn) fall outside the above ranges, the abrasion resistance of the coating film may be reduced. The weight-average molecular weight (Mw) and number-average molecular weight (Mn) are values (polystyrene equivalent) measured by gel permeation chromatography (hereinafter abbreviated as GPC) using a differential refractometer.

[0092] The blending amounts of the two polyester polyols (A) and (B) are not particularly limited, but it is preferable that the blending amount of component (A) is 20 to 30 mass % of the total amount of the base material, and the blending amount of component (B) is 2 to 18 mass % of the total amount of the base material.

[0093] When only one type of polyol is used, it is preferable to use the polyester polyol (A) described above.

[0094] On the other hand, polyisocyanates include two types: isocyanurates and adducts of hexamethylene diisocyanate. Isocyanate prepolymers are usually divided into three types of structures (adducts, biurets, and isocyanurates). Adducts are addition products of diisocyanates and trimethylolpropane. Isocyanurates are trimers of diisocyanates.

[0095] The above-mentioned hexamethylene diisocyanate also includes modified products thereof. Examples of modified products of hexamethylene diisocyanate include polyester modified products and urethane modified products of hexamethylene diisocyanate.

[0096] The mixing ratio (A) / (B) of the isocyanurate (A) of hexamethylene diisocyanate to the adduct (B) is preferably 85 / 15 to 15 / 85 by mass, more preferably 80 / 20 to 20 / 80, and even more preferably 75 / 25 to 25 / 75, in order to improve the amount of spin on approach.

[0097] Examples of nurate derivatives of hexamethylene diisocyanate (HMDI) include trade names "Coronate 2357" (manufactured by Tosoh Corporation), "Sumidur N3300" (manufactured by Sumika Covestro Urethane Co., Ltd.), "Duranate TPA-100" (manufactured by Asahi Kasei Corporation), "Takenate D170N" and "Takenate D177N" (both manufactured by Mitsui Chemicals, Inc.), and "Barnock DN-980" (manufactured by DIC Corporation). These may be used alone or in combination of two or more.

[0098] Examples of adducts of hexamethylene diisocyanate (HMDI) include products under the trade names "Coronate HL" (manufactured by Tosoh Corporation), "Takenate D160N" (manufactured by Mitsui Chemicals, Inc.), "Duranate E402-80B" and "Duranate E405-70B" (all manufactured by Asahi Kasei Corporation), and "Burnoc DN-955" and "Burnoc DN-955S" (all manufactured by DIC Corporation). These products can be used alone or in combination of two or more.

[0099] The molar ratio (NCO / OH) of the hydroxyl groups (OH) of the polyester polyol to the isocyanate groups (NCO) of the polyisocyanate is preferably 0.6 or greater, more preferably 0.65 or greater, with an upper limit of preferably 1.5 or less, more preferably 1.0 or less, and even more preferably 0.9 or less. If this molar ratio is less than 0.6, unreacted hydroxyl groups may remain, potentially deteriorating the performance and water resistance of the golf ball coating. On the other hand, if the molar ratio exceeds 1.5, the excess isocyanate groups may react with water to form urea groups (which are brittle), potentially deteriorating the performance of the golf ball coating.

[0100] As the curing catalyst (organometallic compound), an amine catalyst or an organometallic catalyst can be used, and as this organometallic compound, metal soaps such as aluminum, nickel, zinc, tin, etc., which have traditionally been compounded as curing agents in two-component curing urethane paints, can be suitably used.

[0101] In the present invention, the coating composition contains silicone-based additives such as silicone resin, silicone oil, and silicone rubber to reduce the coefficient of friction and impart water repellency to the golf ball surface. Silicone-modified acrylate can be used as the silicone resin. Silicone-modified acrylate is a surface conditioner that incorporates an acrylic structure and a silicone structure in one molecule. Unlike conventional polyrotaxane-based silicone resins, the polysiloxane chain attached to the acrylic skeleton makes it less slippery and improves water repellency even when a large amount of silicone-based additive is added. Examples of silicone-modified acrylates include those under the trade names "BYK3550" and "BYK3700" (both manufactured by BYK-Chemie). Examples of silicone oils include methyl hydrogen silicone oil and dimethyl silicone oil.

[0102] The silicone additive content relative to the total paint composition is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.03% by mass or more, to reduce the coefficient of friction on the surface of the golf ball and provide sufficient water repellency. The upper limit is 0.5% by mass or less. If the upper limit is exceeded, the desired control performance may not be achieved when approaching.

[0103] If necessary, known paint compounding components may be added to the paint composition. Specifically, appropriate amounts of thickeners, ultraviolet absorbers, fluorescent brighteners, slipping agents, pigments, etc. may be added.

[0104] When using a coating composition, the coating composition is prepared at the time of application, applied to the surface of the ball using a conventional coating process, and then dried to form a coating layer on the surface of the ball. In this case, the coating method can be suitably spray coating, electrostatic coating, dipping, or the like, and is not particularly limited.

[0105] The coating composition can be mixed with various organic solvents, such as aromatic solvents such as toluene, xylene, and ethylbenzene, ester solvents such as ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, and propylene glycol methyl ether propionate, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, ether solvents such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and dipropylene glycol dimethyl ether, alicyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, and ethylcyclohexane, and petroleum hydrocarbon solvents such as mineral spirits.

[0106] In the present invention, organic solvents with a boiling point of 80°C or less are included. This is to minimize the amount of silicone components that float to the surface during coating. Examples of organic solvents with a boiling point of 80°C or less include hydrocarbon solvents such as normal hexane (68°C), cyclohexane (80°C), and benzene (80°C), ester solvents such as methyl acetate (57°C) and ethyl acetate (77°C), and ketone solvents such as acetone (56°C) and methyl ethyl ketone (79°C). The numbers in parentheses indicate the boiling point. Of the organic solvents with a boiling point of 80°C or less, ester solvents and ketone solvents are preferred, considering their impact on the human body and the environment.

[0107] The blending ratio of the organic solvent with a boiling point of 80°C or less to the total amount of the coating composition is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, in order to fully reduce the silicone component floating to the surface during coating. The upper limit is 80% by mass or less. If this upper limit is exceeded, the leveling ability of the coating layer surface will not be improved, and the gloss of the coating surface may be reduced.

[0108] The drying process can be carried out in the same manner as for known two-component curing urethane paints, with the drying temperature being approximately 40°C or higher, particularly 40 to 60°C, and the drying time being 20 to 90 minutes, particularly 40 to 50 minutes.

[0109] There are no particular restrictions on the thickness of the paint layer, but it is preferably 3 to 50 μm, more preferably 5 to 20 μm.

[0110] In the golf ball of the present invention having the above-described paint layer, the deflection when the ball is subjected to an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is preferably 2.0 mm or more, more preferably 2.3 mm or more, and even more preferably 2.5 mm or more, with the upper limit being preferably 3.3 mm or less, more preferably 3.0 mm or less. If this value is too small, spin on driver shots may increase, potentially reducing distance. On the other hand, if this value is too large, approach spin may decrease, potentially reducing controllability.

[0111] Furthermore, when a golf ball of the present invention having the above-described paint layer is allowed to free fall from a height of 3 m onto an impact surface inclined at 58 degrees from the horizontal, the amount of vertical displacement of the golf ball from when it starts to slide on the impact surface until it stops is defined as the amount of slippage (Ds). Ds is preferably 2.0 mm or less, more preferably 1.5 mm or less, and even more preferably 1.2 mm or less. Within this range, the golf ball feels sufficiently "sticky" with the face, resulting in a good feel at impact. The "stickiness" of the golf ball with the face is presumably a state in which the golf ball does not slide significantly on the surface of the golf club face when the golfer hits the ball. This sensory evaluation uses the numerical value of the amount of slippage Ds as an evaluation index. Specifically, this is described in

[0043] and Figure 3 of Japanese Patent Application Laid-Open No. 2019-217078, which is the applicant's prior art.

[0112] Furthermore, for the above golf ball, the post-slip contact time (Tc) is defined as the time from when the golf ball stops sliding on the impact surface until it separates from the impact surface. It is preferable that Tc be 400 μs or greater, preferably 500 μs or greater, and more preferably 540 μs or greater. Within this range, the golf ball feels sufficiently "sticky" to the face, resulting in a good feel at impact. The "stickiness" of the golf ball to the face is presumably a phenomenon in which the golf ball remains in contact with the golf club face for a long period of time when the golfer hits the golf ball and the face of the golf club. This sensory evaluation uses the above-mentioned post-slip contact time (Tc) as an evaluation index. Specifically, this is explained in

[0048] and Figures 3 and 4 of JP 2019-217078 A, the applicant's prior art. The post-slip contact time (Tc) corresponds to the "second contact time" described in JP 2019-217078 A.

[0113] The golf ball of the present invention can be made to conform to the Rules of Golf for competitive use, and can be formed to have 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. [Example]

[0114] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0115] [Examples 1 to 8, Comparative Examples 1 to 6] A core with a diameter of 38.6 mm was prepared. The core formulation was the same for all examples and comparative examples. The base rubber consisted of 20 parts by weight of polybutadiene A (trade name "BR51" manufactured by JSR Corporation), 80 parts by weight of polybutadiene B (trade name "BR730" manufactured by JSR Corporation), 29.5 parts by weight of zinc acrylate (manufactured by Wako Pure Chemical Industries, Ltd.), 0.6 parts by weight of dicumyl peroxide (trade name "Percumyl D" manufactured by Nippon Oil & Fats Corporation) as an organic peroxide, 0.1 parts by weight of 2,2-methylenebis(4-methyl-6-butylphenol) (trade name "Nocrac NS-6" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) as an antioxidant, 19.3 parts by weight of zinc oxide (trade name "Triple Zinc Oxide" manufactured by Sakai Chemical Industry Co., Ltd.), and 0.3 parts by weight of pentachlorothiophenol zinc salt (manufactured by Wako Pure Chemical Industries, Ltd.) as an organic sulfur compound. The rubber composition was vulcanized at a temperature of 155°C for 15 minutes. The compound density is 1.138.

[0116] Formation of the intermediate layer Next, a resin material for the intermediate layer was injection molded around a 38.6 mm diameter core to produce an intermediate-layer-coated sphere with a 1.25 mm thick intermediate layer. The resin material for the intermediate layer was the same for all examples and comparative examples: Himilan 1605, Himilan 1557, and Himilan 1706 (all ionomer resins manufactured by Mitsui Dow Polychemicals) blended in a mass ratio of 50:12:38, respectively. 100 parts by mass of this ionomer resin was blended with 1.1 parts by mass of trimethylolpropane (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0117] Formation of the cover (outermost layer) Next, using another injection molding mold, the resin material for the cover (outermost layer) shown in Table 1 below is injection molded around the above-mentioned mid layer-coated sphere to produce a three-piece golf ball with a diameter of 42.7 mm and an outermost layer 0.8 mm thick.

[0118] Details of the components contained in the cover material in Table 1 are as follows. "TPU 1": DIC Covestro Polymers' trade name "Pandex", an ether-type thermoplastic polyurethane (Shore D hardness "43" and rebound resilience "61%)) "TPU 2": DIC Covestro Polymers, trade name "Pandex", ether-type thermoplastic polyurethane (Shore D hardness "47" and rebound resilience "54%) SOE S1611: Asahi Kasei hydrogenated aromatic vinyl elastomer (styrene content: 60 wt%, Shore D hardness: 23, and rebound resilience: 20%) Hytrel 2401: Thermoplastic polyetherester elastomer manufactured by Toray DuPont (Shore D hardness: 40, rebound resilience: 67%, melt viscosity: 5700 dPa·s)

[0119] Cover material hardness The resin material is molded into a 2mm thick sheet and left to stand for two weeks at a temperature of 23±2°C. Three sheets are stacked together when measuring. The Shore D hardness is 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, is used. The hardness value is read as the maximum value.

[0120] Formation of paint layer (paint film) Next, a paint composition consisting of the following base agent and curing agent was applied using an air spray gun to the surface of the outermost layer, on which numerous dimples had been formed, in the paint formulation shown in Table 1 below, to form a paint layer (coating film) 15 μm thick, thereby producing the golf balls of each example.

[0121] <Main ingredient> As the main polyol, a polyester polyol synthesized by the following method is used. A reaction apparatus equipped with a reflux condenser, a dropping funnel, a gas inlet tube, and a thermometer was charged with 140 parts by mass of trimethylolpropane, 95 parts by mass of ethylene glycol, 157 parts by mass of adipic acid, and 58 parts by mass of 1,4-cyclohexanedimethanol, and the mixture was heated to 200-240°C with stirring and heated (reacted) for 5 hours, yielding a polyester polyol with an acid value of 4, a hydroxyl value of 170, and a weight-average molecular weight (Mw) of 28,000.

[0122] As the organic solvent used in the base agent, ethyl acetate (boiling point 77°C) was used in the amount shown in Table 1 except for Comparative Examples 3, 5, and 6, and butyl acetate (boiling point 126°C) was used in the amount shown in Table 1 for Comparative Examples 3, 5, and 6. Furthermore, in Examples 1 to 8 and Comparative Examples 3, 5, and 6, the base agent contained silicone-modified acrylate (trade name "BYK3700" manufactured by BYK-Chemie) as a silicone-based additive in the amount shown in Table 1.

[0123] <Curing agent> The isocyanate used for curing agent A was a nurate (isocyanurate) of hexamethylene diisocyanate (HMDI) manufactured by Asahi Kasei Corporation under the trade name "Duranate TPA-100" (NCO content 23.1%, non-volatile content 100%).The isocyanate used for curing agent B was an adduct of hexamethylene diisocyanate (HMDI) manufactured by Asahi Kasei Corporation under the trade name "Duranate E402-80B" (NCO content 7.6%, non-volatile content 80%).

[0124] In all examples, butyl acetate (boiling point 126°C) is used in the amount shown in Table 1 as the organic solvent for the curing agent.

[0125] The golf balls of each example were evaluated for ball deformation, static friction coefficient, hitting feel, and approach controllability. The results are shown in Table 1.

[0126] Ball deformation amount The ball, which is the spherical object under test, is placed on a hard plate and the amount of deflection is measured when an initial load of 98N (10kgf) is applied and a final load of 1275N (130kgf) is applied. Note that the above deflection amount is measured after adjusting the temperature to 23.9°C.

[0127] Coefficient of static friction The golf ball is attached to a jig and pulled under the following conditions, and the static friction coefficient of the golf ball is recorded as a value. <Measurement conditions> Vertical force: 3.5N Face plate: Stainless steel Tensile speed: 50 mm / min Temperature: 23 degrees

[0128] Evaluation of feel A sand wedge (58 degrees, product name "X-WEDGE H8101" manufactured by Bridgestone Sports Co., Ltd.) was attached to the golf hitting robot, and the golf ball was hit at a head speed of 20 m / s. The amount of slippage Ds (mm) of the golf ball and the contact time after slippage Tc (μs) were used as indicators for evaluation. <Test Method> An evaluation system similar to that shown in Fig. 1 of JP 2019-217078 A is prepared. That is, as shown in Fig. 1 of the publication, the evaluation system includes a high-speed camera, an evaluation device, and a collision member. Step 1: Free-fall a golf ball from a height of 3m. Step 2: Collide the golf ball against a collision surface tilted at 58 degrees from the horizontal. Step 3: The state of the golf ball on the impact surface is observed with a high-speed camera, and the amount of slippage Ds (mm) and post-slip contact time Tc (μs) of the golf ball are analyzed and calculated.

[0129] <Evaluation of bite> [Judgment criteria] ◎ Slippage (Ds) 1.30 mm or less ○ Sliding amount (Ds) within the range of 1.31 to 2.00 mm × Slippage (Ds) 2.01 mm or more

[0130] <Evaluation of adhesiveness> [Judgment criteria] ◎ Post-slip contact time (Tc) 540 μs or more ○ ··· Contact time after sliding (Tc) is within the range of 500 to 539 μs × ··· Contact time after sliding (Tc) 499 μs or less

[0131] Approach controllability (DRY: normal) A sand wedge (Bridgestone Sports brand "X-WEDGE H8101" 58 degrees) was attached to the golf hitting robot, and the initial velocity (m / s) and backspin (rpm) were measured when hitting a golf ball at a head speed of 20 m / s. Controllability was determined by sensory evaluation. Each golfer used their own sand wedge (SW), and evaluated the club according to the following criteria when actually hitting the ball. [Judgment criteria] ◎ ··· Extremely easy to operate. 〇 ··· Excellent operability. × ··· Poor operability. Whether or not a club has excellent operability depends not only on the amount of spin on the ball, but also on the length of time the ball is in contact with the club face, which is caused by the initial velocity of the ball.

[0132] Approach controllability (wet conditions) Furthermore, to confirm the water-repellent effect, the amount of spin on wet approaches is also evaluated under the following conditions. A golf ball is submerged in a bucket of water, and the backspin rate (rpm) is measured when the ball is hit with water droplets attached, and is judged according to the following criteria. [Judgment criteria] ◎ 5750 rpm or more 〇 5000~5749rpm × 4999 rpm or less

[0133] [Table 1]

[0134] As shown in Table 1, Examples 1 to 4 contain a silicone additive in the paint and an HMDI adduct in the curing agent, and they show good controllability during approach (both normal and wet). Examples 5 to 7 also contain a cover containing urethane, polyester, and aromatic vinyl elastomer, and they show better controllability than Example 2.

[0135] In contrast, Comparative Example 1 does not contain a silicone additive in the coating material and does not contain an HMDI adduct in the curing agent, so the amount of spin in the wet state is low. In Comparative Example 2, the coating material does not contain a silicone-based additive, and therefore the amount of spin when wet is low. In Comparative Example 3, the coating material does not contain an organic solvent with a boiling point of 80° C. or less, and therefore the static friction coefficient is small and the spin rate is also small. In Comparative Example 4, the coating material does not contain a silicone-based additive, and therefore the amount of spin when wet is low. In Comparative Example 5, the coating material does not contain an organic solvent with a boiling point of 80° C. or less, and therefore the static friction coefficient is small and the spin rate is also small. In Comparative Example 6, the coating material does not contain an organic solvent with a boiling point of 80° C. or less, and therefore the static friction coefficient is small and the spin rate is also small.

Claims

1. A golf ball having a core, a cover, and a paint layer, wherein at least one layer of the cover contains the following components (I), (II), and (III): (I) Polyurethane or Polyurea (II) Aromatic vinyl elastomer (III) Thermoplastic polyester elastomer the aromatic vinyl elastomer of component (II) has a Shore D hardness of 30 or less and a rebound resilience of 30% or less, and the thermoplastic polyester elastomer of component (III) has a Shore D hardness of 45 or less and a rebound resilience of 74% or less, and a melt viscosity at 200°C and a shear rate of 243 (1 / sec) of 1.5 x 10 (dPa·s) or less, and the paint layer is formed from a urethane paint containing an organic solvent having a boiling point of 80°C or less and a silicone-based additive, the urethane paint containing a polyisocyanate as a curing agent, and the polyisocyanate contains an adduct and an isocyanurate of hexamethylene diisocyanate (HMDI).

2. 2. The golf ball of claim 1, wherein the organic solvent having a boiling point of 80[deg.] C. or less is blended in an amount of 20% by mass or more based on the total amount of the coating composition.

3. 3. The golf ball according to claim 1, wherein the mixing ratio (A) / (B) of the isocyanurate of hexamethylene diisocyanate to the adduct of hexamethylene diisocyanate is 85 / 15 to 15 / 85 by mass.

4. 4. The golf ball of claim 1, wherein the blending amount of component (II) is 5 to 20 parts by weight per 100 parts by weight of component (I).

Images