golf balls

Abstract

SOLUTION: In a golf ball having a rubber core of at least one layer and a cover of at least one layer encasing the core, at least one layer of the cover is formed from a resin composition that includes (I) a polyurethane or a polyurea and (II) a (meth)acrylic block copolymer, the (meth)acrylic block copolymer as the component (II) being included in an amount of 20 pts.wt. or less relative to 100 pts.wt. of the component (I).EFFECT: A golf ball has excellent controllability on approach shots and is able to maintain good scuff resistance and moldability.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 increased flight distance, but other requirements include the ability to stop the ball well on approach shots and abrasion resistance. To date, many golf balls have been developed that fly well on driver shots and generate favorable backspin on approach shots. Recently, golf balls targeting professionals and advanced players have increasingly 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 in. The present inventor previously proposed, in JP 2019-107401 A (Patent Document 1), the use of an acrylic or methacrylic resin as the main material for the cover as a polymer blend of the urethane resin material. While this technology provides a golf ball that achieves high initial velocities on driver shots and low initial velocities on approach shots, acrylic or methacrylic resins are essentially hard resin materials, and therefore, approach controllability was not fully satisfactory. Approach controllability is one factor in the maneuverability of the club on the approach shot, and the quality of the club's maneuverability is influenced not only by the amount of spin on the ball but also by the length of contact time between the ball and the club face due to the club's low resilience. A longer contact time improves maneuverability, while a shorter contact time reduces maneuverability. In other words, there was a need for an improved golf ball with even better approach controllability than the golf ball described in Patent Document 1.

[0004] Furthermore, the resin material for the cover described in Patent Document 1 requires a higher molding temperature because the urethane resin material has an increased melt viscosity and poor flowability due to the addition of acrylic resin. This can result in defects such as burns on the entire surface of the cover after molding, leaving room for improvement in the moldability and abrasion resistance of the golf ball.

[0005] Additionally, Japanese Patent Laid-Open Publication No. 2019-88770 (Patent Document 2) discloses a golf ball resin material formed from a mixture containing a thermoplastic polymer and an acrylic copolymer (MMA copolymer). However, the acrylic copolymer described in Patent Document 2 is a polymer with a special core-shell chemical structure, and Patent Document 1 does not disclose that blending this acrylic copolymer with a urethane resin material results in sufficiently excellent approach controllability, abrasion resistance, and moldability. Therefore, it is difficult to say that this technology can solve the above-mentioned problems of the present invention. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-107401 [Patent Document 2] Japanese Patent Application Publication No. 2019-88770 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above circumstances, and its object is to provide a golf ball that has superior controllability on approach shots and is also fully satisfactory in abrasion resistance and moldability compared to golf balls with conventional urethane covers. [Means for solving the problem]

[0008] To achieve the above-mentioned object, the present inventors have fabricated a golf ball having a core and a cover. The cover is made of a polymer blend of a resin material primarily composed of polyurethane or polyurea, and a (meth)acrylic block copolymer is blended within a specified range to form a golf ball with a cover molded from a resin composition composed of these materials. They have found that this golf ball exhibits excellent controllability on approach shots, as well as good abrasion resistance and moldability, leading to the creation of the present invention. Specifically, the present invention provides a resin composition primarily composed of polyurethane or polyurea, and by using a (meth)acrylic block copolymer with a relatively low Shore D hardness and relatively low impact resilience as an additive resin, the controllability on approach shots is sufficiently high. Furthermore, blending the (meth)acrylic block copolymer with a base material such as polyurethane does not increase the melt viscosity during molding, thereby eliminating moldability (productivity) problems and enabling the production of a golf ball that is fully satisfactory in terms of abrasion resistance and moldability, thereby solving the problems of the present invention.

[0009] Accordingly, the present invention provides the following golf balls. 1. A golf ball having at least one rubber core layer and at least one cover layer covering the core, wherein at least one layer of the cover contains the following components (I) and (II): (I) Polyurethane or Polyurea (II) (Meth)acrylic block copolymer The resin composition is formed from a resin composition containing The block copolymer of component (II) has two or more blocks constituting hard segments and one or more blocks constituting soft segments, the hard segments being mainly composed of methyl methacrylate units, and the soft segments being mainly composed of n-butyl acrylate units, The amount of the (meth)acrylic block copolymer of the component (II) is 100 parts by mass of the component (I). 3~15 parts by mass A golf ball characterized by: 2 The material hardness of the component (II) is 35 or less in Shore D hardness. 1 The golf ball described herein. 3 The above component (II) has a rebound resilience of 40% or less as measured according to JIS-K 6255. 1 or 2 The golf ball described herein. 4 1. The cover has a Shore D hardness of 48 or less. 3 1. The golf ball according to claim 1, [Effects of the Invention]

[0010] The golf ball of the present invention has superior controllability on approach shots, maintains good abrasion resistance, and is easily moldable, compared to golf balls having conventional urethane covers. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in more detail below. In this specification, the term "(meth)acrylic block copolymer" is used to mean both acrylic block copolymers and methacrylic block copolymers.

[0012] The golf ball of the present invention is a golf ball in which a core made of at least one layer is covered with at least one cover layer, that is, a single-layer or multi-layer cover.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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) (Meth)acrylic block copolymer It is formed from a resin composition containing

[0019] (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:

[0020] (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.

[0021] As the polymer polyol, it is preferable to use a polyether polyol.

[0022] 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.

[0023] 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).

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] (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.

[0030] (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.

[0031] (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.

[0032] 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.

[0033] 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.

[0034] (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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] The polyurea can be produced by any known method, such as a prepolymer method or a one-shot method.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] In the present invention, by blending component (II), which will be described in detail below, with component (I) above, the controllability on approach shots, abrasion resistance and moldability are excellent.

[0043] (II) (Meth)acrylic block copolymer The (meth)acrylic block copolymer of component (II) is preferably a block copolymer having two or more blocks constituting hard segments and one or more blocks constituting soft segments. That is, the (meth)acrylic block copolymer used in the present invention is a polymer containing block polymers A and B, and can be represented by an AB or ABA chemical structure. Note that the (meth)acrylic block copolymer used in the present invention has a different chemical structure from general core-shell acrylic copolymers such as those described in Patent Document 2.

[0044] Block polymer A is a moiety that constitutes a hard segment, and specific examples of the monomer unit include methacrylate esters such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, phenyl methacrylate, and 2-hydroxyethyl methacrylate, with methyl methacrylate (MMA) being preferred as the main component. Block polymer A can be constructed using any one of the above monomer units or two or more of them in combination.

[0045] On the other hand, block polymer B is a moiety that constitutes a soft segment, and specific examples of monomer units include acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, pentadecyl acrylate, dodecyl acrylate, benzyl acrylate, phenoxyethyl acrylate, and 2-methoxyethyl acrylate, with n-butyl acrylate (nBA) being preferred as the main component. Block polymer B can be constructed using one or more of the above monomer units.

[0046] The glass transition temperature (Tg) of the block polymer A showing the hard segment is preferably 80 to 140°C, more preferably 100 to 120°C. On the other hand, the glass transition temperature (Tg) of the block polymer B showing the soft segment is preferably -80 to -20°C, more preferably -60 to -40°C, or 100 to 120°C.

[0047] In the (meth)acrylic block copolymer, the ratio of the hard segment to the soft segment, expressed as a mass ratio, is preferably 5:95 to 40:60, and more preferably 10:90 to 30:70. As the proportion of the soft segment increases, it is expected that the resin composition will be softened and the desired approach controllability will be obtained, but if the proportion of the hard segment is too low, compatibility with the base material, such as a polyurethane resin, will decrease, and moldability may deteriorate.

[0048] The (meth)acrylic block copolymer can be obtained by polymerizing the above-mentioned monomer units, and examples of the polymerization method include radical polymerization, living anionic polymerization, living radical polymerization, etc. Examples of the polymerization form include solution polymerization, emulsion polymerization, suspension polymerization, bulk polymerization, etc.

[0049] The weight-average molecular weight of the (meth)acrylic block copolymer is not particularly limited, but from the viewpoints of moldability, plasticity, etc., it is preferably in the range of 20,000 to 700,000, and more preferably in the range of 50,000 to 200,000. The weight-average molecular weight can be measured by gel permeation chromatography (GPC).

[0050] The (meth)acrylic block copolymer used in the present invention is preferably a polymer in which the hard segment is mainly composed of methyl methacrylate units and the soft segment is mainly composed of n-butyl acrylate units. Such a (meth)acrylic block copolymer can be a commercially available product, such as "CLARITY" manufactured by Kuraray Co., Ltd., specifically, products under the trade names "CLARITY LA2250" and "CLARITY LA2270".

[0051] With regard to the material hardness of the component (II), from the viewpoint of improving the approach spin rate, it is preferable that the Shore D hardness is 38 or less, more preferably 35 or less, and even more preferably 32 or less. The lower limit of the Shore D hardness is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more.

[0052] The rebound resilience of component (II) is preferably 40% or less, more preferably 35% or less, and even more preferably 30% or less, in order to maintain the approach spin rate and keep the rebound low on the approach shot to obtain controllability. The lower limit of the rebound resilience is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more. The rebound resilience is measured in accordance with JIS-K 6255:2013.

[0053] The blend amount of component (II) is 20 parts by mass or less, preferably 15 parts by mass or less, and more preferably 12 parts by mass, per 100 parts by mass of component (I). If this value is exceeded, abrasion resistance may decrease. The lower limit of the blend amount is 0.5 parts by mass or more, preferably 1 part by mass or more, and more preferably 2 parts by mass or more, per 100 parts by mass of component (I).

[0054] In addition to the resin components described above, the resin composition containing (I) and (II) may contain other resin materials in order to further improve the flowability of the golf ball resin composition and enhance its physical properties such as resilience and crack resistance.

[0055] Specific examples of the other resin materials include polyester elastomers, polyamide elastomers, ionomer resins, ethylene-ethylene-butylene-ethylene block copolymers or modified products thereof, polyacetal, polyethylene, nylon resins, styrene-based resins, polyvinyl chloride, polycarbonate, polyphenylene ether, polyarylate, polysulfone, polyethersulfone, polyetherimide, and polyamideimide, and one or more of these may be used.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] Furthermore, any additives can be appropriately blended into the resin composition depending on 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), short organic 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 amount of the additives blended is preferably at least 0.1 parts by weight, more preferably at least 0.5 parts by weight, and preferably no more than 10 parts by weight, more preferably no more than 4 parts by weight, per 100 parts by weight of the base resin.

[0060] In order to improve low resilience and approach spin rate, the resin composition needs to have a rebound resilience of 48% or more as measured in accordance with JIS-K 6255:2013, 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.

[0061] Furthermore, from the viewpoint of abrasion resistance and imparting an appropriate amount of spin on approach shots, 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] In the present invention, a coating film layer is formed on the surface of the cover. As the coating material for forming this coating film layer, a two-component curing urethane coating material is preferably used. Specifically, in this case, the two-component curing urethane coating material contains a base agent whose main component is a polyol resin and a curing agent whose main component is polyisocyanate.

[0068] The method for applying the above-mentioned paint to the cover surface to form a coating film layer is not particularly limited, and any known method can be used, such as air gun coating or electrostatic coating, as desired.

[0069] The thickness of the coating layer is not particularly limited, but is usually 8 to 22 μm, preferably 10 to 20 μm.

[0070] 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]

[0071] 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.

[0072] [Examples 1 to 8, Comparative Examples 1 to 4] Common Core A rubber composition for the core common to all examples was prepared using the formulation shown in Table 1, and a core having a diameter of 38.6 mm was fabricated by vulcanization molding.

[0073] [Table 1]

[0074] Details of the core material are as follows: "cis-1,4-Polybutadiene" manufactured by JSR Corporation, 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

[0075] A common middle class The 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 a blend of 50 parts by weight of a sodium-neutralized ethylene-unsaturated carboxylic acid copolymer with an acid content of 18% by weight and 50 parts by weight of a zinc-neutralized ethylene-unsaturated carboxylic acid copolymer with an acid content of 15% by weight, totaling 100 parts by weight.

[0076] Cover (outermost layer) Next, for Examples 2, 4, 6, and 8 and Comparative Example 1, the outermost layer cover material shown in Table 2 below was injection molded around the above-mentioned mid layer-covered sphere to produce three-piece golf balls with a diameter of 42.7 mm and an outermost layer thickness of 0.8 mm. In this process, common dimples were formed on the surface of the cover in each Example and Comparative Example, although not specifically shown. The resin composition of the cover was designed to contain the components in the amounts shown in Table 2 below, and was injection molded at a molding temperature of 200 to 250°C. Furthermore, for Examples 1, 3, 5, and 7 and Comparative Examples 2, 3, and 4, three-piece golf balls were prepared in the same manner as above.

[0077] Details of the components contained in the compositions shown in Table 2 below are as follows: "TPU (1)": DIC Covestro Polymers' trade name "Pandex", an ether-type thermoplastic polyurethane (Shore D hardness: 43, rebound resilience: 61%) "(Meth)acrylic block copolymer 1" Kuraray's product name "Clarity LA2250" acrylic block copolymer (hard segment PMMA / soft segment PBA), Shore D hardness "22", rebound resilience "28%" "(Meth)acrylic block copolymer 2" Kuraray's product name "Clarity LA2270" acrylic block copolymer (hard segment PMMA / soft segment PBA), Shore D hardness "31", rebound resilience "26%" "PMMA1" Kuraray's product name "Parapet Soft Acrylic SA-NW201" methacrylic resin (Shore D hardness "40", rebound resilience "23%) "PMMA2" Kuraray's product name "Parapet GF" methacrylic resin (Shore D hardness "87", rebound resilience "31%)

[0078] Physical properties of resin composition (1) Shore D hardness The resin material was molded into a 2 mm thick sheet and left at a temperature of 23 ± 2°C for two weeks. Three sheets were stacked together during measurement. The hardness of the resin material was measured using a Shore D hardness tester in accordance with 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 of the resin composition measured based on JIS-K 6255:2013 standard is shown in Table 2.

[0079] The spin performance, initial velocity performance, approach controllability, abrasion resistance, and moldability of each golf ball were evaluated by the following methods. The results are shown in Table 2.

[0080] Initial speed and spin performance during approach A sand wedge (SW) is attached to a golf hitting robot, and the initial velocity and backspin amount immediately after hitting the ball at a head speed (HS) of 20 m / s are measured using an initial condition measuring device.

[0081] Controllability In addition, a sensory evaluation of the controllability of the ball during approach was conducted using the following method. The club used was the same sand wedge (SW) as above, product name "Bridgestone Tour Stage TW-03 (loft angle 57°)", and golfers evaluated the actual shots using the following criteria. [Judgment evaluation] ◎ ··· Extremely easy to operate. 〇 ··· Excellent operability. △ ··· Slightly inferior in operability. × ··· Poor operability. In addition to the amount of spin on the ball, the length of contact time between the ball and the club face, which is caused by low resilience, also affects whether or not the controllability is excellent. A long contact time improves controllability, while a short contact time reduces controllability. Here, we evaluate controllability (controllability) including the amount of spin and the length of contact time.

[0082] Scratch resistance evaluation The balls are kept warm at 23°C, and using a swing robot machine, five balls of each type are hit at a head speed of 33 m / s using a pitching wedge (PW) club, and the damage caused by the impact is visually evaluated according to the following criteria. 〇 ··· Slightly damaged or barely noticeable damage. × The dimple has been completely removed.

[0083] Evaluation of moldability (removal) The balls of each example were evaluated for ease of release from the mold after the cover was injection molded, according to the following criteria. ○ ··· No external damage such as broken runners or pins being stuck occurs when demolding. △ ··· When demolding, external damage such as runner breakage or pin sticking may occur, and the molding temperature must be increased due to increased viscosity.

[0084] [Table 2]

[0085] As shown in the results in Table 2, the golf balls of Comparative Examples 1 to 4 are inferior to the products of the present invention (Examples) in the following respects. In Comparative Example 1, the component (II) was not blended into the resin composition, and the controllability during approach was poor. In Comparative Example 2, the amount of component (II) in the resin composition was large, and although the controllability at the time of approach was excellent, the abrasion resistance and moldability were poor. In Comparative Example 3, PMMA is blended into the resin composition, which increases the melt viscosity and reduces fluidity, necessitating an increase in molding temperature. As a result, defects such as burns occur on the entire cover surface, resulting in poor moldability. In Comparative Example 4, the resin composition contains PMMA, which increases the melt viscosity and reduces fluidity, necessitating a higher molding temperature, resulting in defects such as burns on the entire cover surface and poor moldability. Furthermore, the high hardness of PMMA reduces approach spin and reduces controllability on approach shots.

Claims

1. A golf ball having at least one rubber core layer 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) (Meth)acrylic block copolymer a resin composition containing the component (II), wherein the block copolymer of the component (II) has two or more blocks constituting hard segments and one or more blocks constituting soft segments, the hard segments being composed mainly of methyl methacrylate units, and the soft segments being composed mainly of n-butyl acrylate units; and the blending amount of the (meth)acrylic block copolymer of the component (II) is 3 to 15 parts by mass per 100 parts by mass of the component (I).

2. 2. The golf ball of claim 1, wherein the material hardness of component (II) is 35 or less in Shore D hardness.

3. 3. The golf ball of claim 1, wherein component (II) has a rebound resilience of 40% or less as measured according to JIS-K 6255.

4. 4. The golf ball according to claim 1, wherein the cover has a Shore D hardness of 48 or less.

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