JP2023089494A - Golf ball - Google Patents

Abstract

SOLUTION: A golf ball provided by the present invention includes at least one layer of rubber core and at least one layer of cover covering the core, wherein at least one layer of the cover is formed by a resin composition containing the following (I) and (II) components, and HMa and HMb satisfy the following formula (1), here, the Martens hardness of the resin material of the component (I) is HMa[N/mm2], and that of the cover layer formed by the resin composition containing the components (I) and (II) is HMb[N/mm2]. (I) Polyurethane or polyurea. (II) (Meth)acrylic block copolymer. 1.020≤HMa/HMb≤1.500 (1).EFFECT: The golf balls of the present invention have excellent controllability during approach shots and maintain good abrasion resistance and moldability.SELECTED DRAWING: None

Description

The present invention relates to golf balls having at least one layer of core and at least one layer of cover.

A major requirement for golf balls is an increase in flight distance, but other than that, the ball needs to stop well on approach shots and is scratch resistant. That is, until now, many golf balls have been developed that fly well when hit with a driver and give favorable backspin on approach shots. Recently, urethane resin materials are increasingly used as substitutes for ionomer resin materials for professionals and advanced users.

Several polymer blend cover materials have been proposed in which a urethane resin material is used as a base resin and other resin materials are mixed. The inventor of the present invention has previously proposed in Japanese Patent Application Laid-Open No. 2019-107401 (Patent Document 1) that an acrylic resin or a methacrylic resin is adopted as a polymer blend of a urethane resin material and used as the main material of the cover. . This technology provides a golf ball that can achieve a high initial velocity on driver shots and a low initial velocity on approach shots. It cannot be said that the approach controllability is sufficiently satisfactory. Approach controllability is one of the factors in club operability during approach. The length of contact time has an effect. When the contact time is long, the operability is improved, and when it is short, the operability is deteriorated. That is, it has been desired to improve a golf ball that is even more excellent in approach controllability than the golf ball described in Patent Document 1.

Further, in the resin material for the cover described in Patent Document 1, the melt viscosity of the urethane resin material increases due to the mixing of the acrylic resin, and the flowability deteriorates, so the molding temperature must be raised. For this reason, after molding, the entire surface of the cover may suffer from defects such as burning, and there is room for improvement in terms of moldability and scratch resistance of the golf ball.

Japanese Patent Application Laid-Open 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 having a core-shell type special chemical structure, and when this acrylic copolymer is blended with a urethane resin material, the approach controllability is improved. Patent document 1 does not disclose that it is sufficiently excellent, and that it is excellent in scratch resistance and moldability, and it is difficult to say that it is a technology that can solve the above problems of the present invention.

JP 2019-107401 A JP 2019-88770 A

The present invention has been devised in view of the above circumstances, and provides a golf ball that is superior in controllability on approach shots, as well as sufficiently satisfactory in scuff resistance and moldability, as compared with conventional golf balls having a urethane cover. intended to provide

In order to achieve the above objects, the present inventors have found that a golf ball having a core and a cover uses a (meth)acrylic block copolymer as a polymer blend of a resin material containing polyurethane or polyurea as a main component, and HMa [N/mm ² ] is the Martens hardness of the polyurethane or polyurea resin material; When HMb [N/mm ² ], HMa and HMb are represented by the following formula (1)
1.020≦HMa/HMb≦1.500 (1)
A golf ball having a cover made of a molded product of the above resin composition was produced so as to satisfy the above condition. The present inventors have found that there is a problem, and have completed the present invention. That is, the present invention uses a (meth)acrylic block copolymer having a relatively low Shore D hardness and a relatively low impact resilience as a resin to be added to a resin composition using polyurethane or polyurea as a main component. By adopting it, the controllability at the time of approach is sufficiently high. In addition, even if the above (meth)acrylic block copolymer is mixed with the main material such as polyurethane, the melt viscosity does not increase during molding, so there is no problem with moldability (productivity), scratch resistance and moldability. A golf ball which is sufficiently satisfactory in terms of properties can be obtained, and the problems of the present invention can be solved.

Accordingly, the present invention provides the following golf balls.
1. In a golf ball comprising at least one layer of rubber core and at least one layer of cover covering said core, at least one layer of said cover comprises the following components (I) and (II): (I) polyurethane or polyurea ( II) Formed from a resin composition containing a (meth)acrylic block copolymer, the Martens hardness of the resin material of component (I) is HMa [N/mm ² ], (I) and (II) ), the Martens hardness of the cover layer formed of the resin composition containing the component is HMb [N/mm ² ], HMa and HMb are represented by the following formula (1):
1.020≦HMa/HMb≦1.500 (1)
A golf ball characterized by satisfying
2. 2. The golf ball of item 1, wherein component (II) is added in an amount of 15 parts by mass or less per 100 parts by mass of component (I).
3. 3. The golf ball of 1 or 2 above, wherein the material hardness of component (II) is 40 or less in Shore D hardness.
4. 4. The golf ball of any one of 1 to 3 above, wherein the rebound resilience of component (II) is 50% or less as measured according to JIS-K 6255 standards.
5. 5. The golf ball of any one of 1 to 4 above, wherein the weight average molecular weight of component (II) is 10,000 or more.
6. 6. The golf ball of any one of 1 to 5 above, wherein the block copolymer of component (II) has two or more blocks constituting the hard segment and one or more blocks constituting the soft segment.
7. 7. The golf ball of any one of 1 to 6, wherein in the block copolymer of component (II), the hard segment is mainly composed of methyl methacrylate units.
8. 8. The golf ball of any one of 1 to 7, wherein in the block copolymer of component (II), the soft segment is mainly composed of n-butyl acrylate units.
9. 9. The golf ball of any one of 1 to 8, wherein the cover has a Shore D hardness of 48 or less.
10. 10. The golf ball according to any one of 1 to 9, wherein the resin composition further contains (III) a thermoplastic polyester elastomer.
11. 11. The golf ball according to 10 above, wherein the material hardness of component (III) is 20 to 50 in Shore D hardness.
12. 12. The golf ball of item 10 or 11, wherein the rebound resilience of component (III) is 50 to 80% as measured according to JIS-K 6255 standard.
13. 13. Any one of 10 to 12 above, wherein the component (III) has a melt viscosity of 0.3×10 ⁴ to 1.5×10 ⁴ (dPa·s) at 200° C. and a shear rate of 243 (1/sec). golf ball.
14. When the elastic work recovery rate of the cover layer formed of the resin composition containing the above components (I) and (II) is ηItb [%], ηItb and HMb are expressed by the following formula (2).
5.00≦ηItb/HMb≦8.00 (2)
14. The golf ball according to any one of 1 to 13 above, which satisfies
15. When the elastic work recovery rate of the resin material of the component (I) is ηIta [%], the following formula (3)
0.97≤ηIta/ηItb≤1.12 (3)
15. The golf ball according to 14 above, which satisfies
16. Furthermore, the following formula (4)
0.70≦(ηIta·HMb)/(ηItb·HMa)≦1.06 (4)
16. The golf ball according to 15 above, which satisfies

The golf ball of the present invention has much better controllability on approach shots, maintains good scratch resistance, and has good moldability as compared to golf balls having conventional urethane covers.

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.

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

The core can be formed using a known rubber material as a base material. As the base rubber, known base rubbers such as natural rubber or synthetic rubber can be used. recommended to be used for Further, in the base rubber, natural rubber, polyisoprene rubber, styrene-butadiene rubber, etc. can be used in combination with the polybutadiene described above, if desired.

Moreover, polybutadiene can be synthesized using a metal catalyst such as a rare earth element-based catalyst such as an Nd catalyst, a cobalt catalyst, or a nickel catalyst.

Co-crosslinking agents such as unsaturated carboxylic acids and metal salts thereof, inorganic fillers such as zinc oxide, barium sulfate and calcium carbonate, dicumyl peroxide and 1,1-bis(t-butyl Organic peroxides such as peroxy)cyclohexane and the like can be blended. In addition, if necessary, a commercially available anti-aging agent or the like can be added as appropriate.

The core can be produced by vulcanizing and curing a rubber composition containing the above components. For example, it is kneaded using a kneader such as a Banbury mixer or a roll, compression molded or injection molded using a core mold, and the temperature is 100 to 100 as a temperature sufficient for the organic peroxide or co-crosslinking agent to act. By appropriately heating the molded article under conditions of 200° C., preferably 140 to 180° C., for 10 to 40 minutes, the molded article can be cured and produced.

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

In the present invention, at least one layer of the resin material of the cover is formed of a resin composition containing the following components (I) and (II): (I) polyurethane or polyurea (II) (meth)acrylic block copolymer be done.

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

(Ia) Polyurethane The structure of polyurethane is composed of a soft segment composed of a high-molecular-weight polyol (polymeric glycol), which is a long-chain polyol, and a chain extender and polyisocyanate constituting a hard segment. Here, as the polymer polyol used as a raw material, any of those conventionally used in techniques related to polyurethane materials can be used, and there is no particular limitation. 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-based polyols that can be used include adipate-based polyols such as polyethylene adipate glycol, polypropylene adipate glycol, polybutadiene adipate glycol, and polyhexamethylene adipate glycol, and lactone-based polyols such as polycaprolactone polyol. Polyether polyols include poly(ethylene glycol), poly(propylene glycol) and poly(tetramethylene glycol), poly(methyltetramethylene glycol) and the like. These may be used individually by 1 type, and may use 2 or more types together.

As the polymer polyol, it is preferable to use a polyether-based polyol.

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

The number average molecular weight mentioned above is the number average molecular weight calculated based on the hydroxyl value measured according to JIS-K1557 (hereinafter the same).

As the chain extender, those used in conventional polyurethane technology can be suitably used, and are not particularly limited. In the present invention, a low-molecular-weight compound having two or more active hydrogen atoms capable of reacting with an isocyanate group in the molecule and having a molecular weight of 2,000 or less can be used. Group diols can be preferably used. Specific examples include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, and the like. Among them, 1,4-butylene glycol can be preferably used.

As the polyisocyanate, those used in conventional polyurethane technology can be suitably used, and there is no particular limitation. Specifically, 4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethylxylene diisocyanate, hydrogenation 1 selected from the group consisting of xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, 1,4-bis(isocyanatomethyl)cyclohexane, dimer acid diisocyanate A species or two or more species can be used. However, with some isocyanate species, it is difficult to control the cross-linking reaction during injection molding.

Also, the compounding ratio of active hydrogen atoms to isocyanate groups in the polyurethane-forming reaction can be appropriately adjusted within a preferred range. Specifically, in producing a polyurethane by reacting the long-chain polyol, the polyisocyanate compound and the chain extender, the polyisocyanate compound is It is preferable to use each component in such a proportion that the isocyanate group contained in is 0.95 to 1.05 mol.

The method for producing polyurethane is not particularly limited, and a long-chain polyol, a chain extender, and a polyisocyanate compound can be used, and a known urethanization reaction can be used to produce the polyurethane by either the prepolymer method or the one-shot method. good. Among them, it is preferable to carry out melt polymerization in the absence of a solvent, and it is particularly preferable to carry out continuous melt polymerization using a multi-screw extruder.

A thermoplastic polyurethane material is preferably used as the polyurethane described above, and an ether-based thermoplastic polyurethane material is particularly preferable. As the thermoplastic polyurethane material, commercially available products can be suitably used. be able to.

(Ib) Polyurea Polyurea is a resin composition mainly composed of urea bonds produced by the reaction of (i) isocyanate and (ii) amine-terminated compounds. This resin composition will be described in detail below.

(i) Isocyanate As the isocyanate, those used in the conventional techniques related to polyurethane can be suitably used, and there is no particular limitation, and the same isocyanate as explained for the polyurethane material can be used.

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

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

On the other hand, an amine-based curing agent is an amine compound having two or more amino groups capable of reacting with an isocyanate group in its 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, more preferably less than 600. Specific examples of the amine 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, diethanolamine, 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, without limitation. These amine-based curing agents may be used singly or in combination of two or more.

(iii) Polyol Polyurea may contain a polyol in addition to the above components (i) and (ii), although it is not an essential component. As this polyol, those used in conventional polyurethane technology can be suitably used, and there is no particular limitation. Specific examples include the following long-chain polyols and/or polyol-based curing agents. can.

As the long-chain polyol, any one conventionally used in polyurethane technology can be used, and there is no particular limitation. Examples include polyester polyol, polyether polyol, polycarbonate polyol, polyester polycarbonate polyol, and polyolefin polyol. , conjugated diene polymer-based polyols, castor oil-based polyols, silicone-based polyols, vinyl polymer-based polyols, and the like. One of these long-chain polyols may be used alone, or two or more thereof may be used in combination.

The number average molecular weight of the long-chain polyol is preferably 1,000 to 5,000, more preferably 1,700 to 3,500. Within this number-average molecular weight range, the resilience, productivity and the like are further improved.

As the polyol-based curing agent, those used in conventional polyurethane technology can be suitably used, and are not particularly limited. In the present invention, a low-molecular-weight compound having two or more active hydrogen atoms capable of reacting with an isocyanate group in the molecule and having a molecular weight of less than 1000 can be used. can be preferably used. Specific examples include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, and the like. Among them, 1,4-butylene glycol can be preferably used. The number average molecular weight of the polyol-based curing agent is preferably less than 800, more preferably less than 600.

As for the method for producing the polyurea, a known method can be adopted, and a known method such as a prepolymer method or a one-shot method can be appropriately selected.

Regarding the material hardness of component (I), the Shore D hardness is preferably 52 or less, more preferably 50 or less, and even more preferably 50 or less in Shore D hardness, from the viewpoint of the spin characteristics and scratch resistance of the golf ball. is 48 or less. The lower limit thereof is preferably 38 or more in Shore D hardness, more preferably 40 or more in Shore D hardness, from the standpoint of moldability.

The impact resilience of component (I) is preferably 55% or more, more preferably 57% or more, and still more preferably 59% or more, from the viewpoint of improving the spin rate on approach. The rebound resilience is measured according to JIS-K 6255:2013 standard.

The above component (I) is the main component of the resin composition, and from the viewpoint of sufficiently imparting the scratch resistance of the urethane resin, it is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass of the resin composition. % by mass or more, more preferably 80% by mass or more, and most preferably 90% by mass or more.

In the present invention, by blending the component (II) described in detail below with the component (I), controllability, scratch resistance and moldability on approach shots are excellent.

(II) (Meth)acrylic block copolymer The (meth)acrylic block copolymer of component (II) has two or more blocks constituting hard segments and one or more blocks constituting soft segments. Block copolymers are preferred. 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 a chemical structure of AB or ABA. The (meth)acrylic block copolymer used in the present invention has a chemical structure different from that of a general core-shell type acrylic copolymer as described in Patent Document 2.

Block polymer A is a site constituting a hard segment, and specific monomer units include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, and methacrylic acid. Examples include methacrylic acid esters such as cyclohexyl acid, isobornyl methacrylate, phenyl methacrylate, and 2-hydroxyethyl methacrylate, and it is preferable to use methyl methacrylate (MMA) as the main component. The block polymer A can be composed of the above monomer units singly or in combination of two or more.

On the other hand, block polymer B is a site constituting a soft segment, and specific monomer units include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, and isobutyl acrylate. , sec-butyl acrylate, amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, pentadecyl acrylate, dodecyl acrylate, benzyl acrylate, phenoxyethyl acrylate, 2-methoxyethyl acrylate and the like, and it is preferable to use n-butyl acrylate (nBA) as a main component. The block polymer B can be composed of the above monomer units singly or in combination of two or more.

The glass transition temperature (Tg) of the block polymer A representing 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 above block polymer B representing the soft segment is preferably -80 to -20°C, more preferably -60 to -40°C.

In the (meth)acrylic block copolymer, the content ratio of the hard segment and the soft segment is preferably 5:95 to 40:60, more preferably 10:90 to 30, by mass. :70. As the proportion of the soft segment increases, it can be expected that the desired approach controllability can be obtained by softening the resin composition. It may decrease and the moldability may deteriorate.

The (meth)acrylic block copolymer can be obtained by polymerizing each of the monomer units described above, and examples of the polymerization method include radical polymerization, living anion polymerization, and living radical polymerization. Examples of the form of polymerization include a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, a bulk polymerization method, and the like.

The weight average molecular weight of the (meth)acrylic block copolymer is not particularly limited, but is preferably 10,000 or more, more preferably 30,000 or more, and still more preferably 45,000 or more. The upper limit is preferably 200,000 or less, more preferably 150,000 or less, even more preferably 100,000 or less. The higher the weight-average molecular weight, the lower the resilience effect, the higher the spin rate, and the better the controllability on approach shots. This weight average molecular weight can be measured by gel permeation chromatography (GPC).

The (meth)acrylic block copolymer used in the present invention is 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. It is preferable to have Such a (meth)acrylic block copolymer can be a commercially available product, for example, "Clarity" manufactured by Kuraray Co., Ltd. Specifically, the product name is "Clarity LA2140" Examples include Clarity LA2250, Clarity LA2270, and Clarity LA2330.

Regarding the material hardness of the component (II), from the viewpoint of improving the spin rate on approach, the Shore D hardness is preferably 38 or less, more preferably 35 or less, and even more preferably 32 or less. be. The lower limit thereof is preferably 4 or more, more preferably 5 or more, and even more preferably 6 or more in Shore D hardness.

The modulus of rebound resilience of component (II) is preferably 50% or less, more preferably 45% or less, and even more preferably 45% or less, in order to maintain the spin rate on approach and to obtain controllability by keeping the rebound on approach low. is 42% or less. Also, 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 according to JIS-K 6255:2013 standard.

The amount of component (II) is 20 parts by mass or less, preferably 15 parts by mass or less, more preferably 12 parts by mass or less per 100 parts by mass of component (I), and exceeds this value. , the scratch resistance may decrease. The lower limit of the above compounding 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). preferred.

The resin composition containing the above components (I) and (II) may further contain (III) a thermoplastic polyester elastomer. (III) A description of the thermoplastic polyester elastomer is as follows.

(III) Thermoplastic Polyester Elastomer A specific thermoplastic polyester elastomer can be blended into the resin composition in order to obtain the desired effect of the present invention and to further improve the feel on impact. That is, this specific thermoplastic polyester elastomer imparts a certain level of resilience to the resin composition, and together with this resilience, it is possible to maintain a high spin rate on approach. Moreover, by blending a specific thermoplastic polyester elastomer into the resin composition, the compatibility with component (I), which is the base resin, is good, and as a result, good scratch resistance can be imparted. Furthermore, by blending a specific thermoplastic polyester elastomer into the resin composition, the resin composition has a melt viscosity of a certain level or more, thereby imparting a solidification property after molding of the resin composition. The softness of the components prevents the overall viscosity of the resin composition from decreasing, preventing a decrease in moldability (productivity), preventing an increase in appearance defects of golf balls after molding, and suppressing high production costs due to an increase in cooling time. be able to. Such a thermoplastic polyester elastomer will be described below.

The thermoplastic polyester-based elastomer of component (III) is
A resin composition comprising (b-1) a polyester block copolymer and (b-2) a hard resin. Further, the component (b-1) is composed of (b-1-1) a high melting point crystalline polymer segment and (b-1-2) a low melting point polymer segment.

The (b-1-1) high melting point crystalline polymer segment constituting the polyester block copolymer of the component (b-1) is an aromatic dicarboxylic acid or an ester-forming derivative thereof, a diol or an ester-forming derivative thereof. It is a polyester formed of one or more selected from the group consisting of:

Specific examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, anthracenedicarboxylic acid, diphenyl-4,4′- dicarboxylic acids, diphenoxyethanedicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 5-sulfoisophthalic acid, and sodium 3-sulfoisophthalate. In the present invention, aromatic dicarboxylic acids are mainly used, and if necessary, some of these aromatic dicarboxylic acids may be 1,4-cyclohexanedicarboxylic acid, cyclopentanedicarboxylic acid, and 4,4′-dicyclohexyldicarboxylic acid. Aliphatic dicarboxylic acids such as acids and aliphatic dicarboxylic acids such as adipic acid, succinic acid, oxalic acid, sebacic acid, dodecanedioic acid, and dimer acid may be substituted. Specific examples of ester-forming derivatives of dicarboxylic acids include lower alkyl esters, aryl esters, carbonic acid esters and acid halides of the dicarboxylic acids described above.

As the diol, a diol having a molecular weight of 400 or less can be preferably used. Specifically, aliphatic diols such as 1,4-butanediol, ethylene glycol, trimethylene glycol, pentamethylene glycol, hexamethylene glycol, neopentyl glycol, and decamethylene glycol, 1,1-cyclohexanedimethanol, 1 , 4-dicyclohexanedimethanol and tricyclodecanedimethanol, 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- Aromatic diols such as p-terphenyl and 4,4'-dihydroxy-p-quarterphenyl can be exemplified. Further, specific examples of ester-forming derivatives of diols include the above-described acetyl derivatives of diols and alkali metal salts.

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

Examples of the component (b-1-1) include those composed of polybutylene terephthalate units derived from terephthalic acid and/or dimethyl terephthalate and 1,4-butadiol, isophthalic acid and/or dimethyl isophthalate and 1, A polybutylene terephthalate unit derived from 4-butanediol and a copolymer of both can be preferably used.

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

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, poly(propylene oxide) Examples include ethylene oxide addition polymers of glycols, copolymer glycols of ethylene oxide and tetrahydrofuran, and the like. Aliphatic polyesters include poly(ε-caprolactone), polyenantholactone, polycaprolactone, polybutylene adipate, polyethylene adipate and the like. In the present invention, from the viewpoint of elastic properties, poly(tetramethylene oxide) glycol, ethylene oxide adduct of poly(propylene oxide) glycol, copolymer glycol of ethylene oxide and tetrahydrofuran, poly(ε-caprolactone), polybutylene adipate, and Polyethylene adipate and the like can be preferably used. Furthermore, among these, it is particularly recommended to use poly(tetramethylene oxide) glycol, ethylene oxide adduct of poly(propylene oxide) glycol, and copolymer glycol of ethylene oxide and tetrahydrofuran. The number average molecular weight of these segments is preferably about 300 to 6000 in the copolymerized state.

The above component (b-1) can be produced by a known method. Specifically, a method of subjecting a lower alcohol diester of a dicarboxylic acid, an excessive amount of a low-molecular-weight glycol, and a low-melting-point polymer segment component to a transesterification reaction in the presence of a catalyst, and polycondensing the resulting reaction product; and an excess amount of glycol and the low-melting-point polymer segment component in the presence of a catalyst, and polycondensing the resulting reaction product.

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

The hard resin of component (b-2) is not particularly limited, but examples include polycarbonate, acrylic resin, ABS resin, styrene resin such as polystyrene, polyester resin, polyamide resin, polyvinyl chloride, and modified One or more selected from the group consisting of polyphenylene ethers can be used. In the present invention, a polyester resin can be preferably used from the viewpoint of compatibility, and more preferably, it is recommended to use polybutylene terephthalate and/or polybutylene naphthalate.

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

Commercially available products can be used as the (III) polyester-based elastomer, and a specific example thereof is "Hytrel" manufactured by DuPont-Toray.

Regarding the material hardness of the above component (III), the Shore D hardness is preferably 50 or less, more preferably 43 or less in Shore D hardness, from the viewpoint of improving the spin rate on approach. The lower limit thereof is preferably 20 or more in Shore D hardness, more preferably 30 or more in Shore D hardness.

The impact resilience of component (III) is preferably 50% or more, more preferably 60% or more, from the viewpoint of improving the spin rate on approach, and the upper limit is preferably 80% or less, more preferably 70% or less. The rebound resilience is measured according to JIS-K 6255:2013 standard.

The melt viscosity of component (III) is preferably 0.3×10 ⁴ dPa·s or more, more preferably 0.4×10 ⁴ dPa·s or more, and the upper limit is preferably 1.5. ×10 ⁴ dPa·s or less, more preferably 1.0 × 10 ⁴ dPa·s or less. By having this melt viscosity, solidification property can be imparted after molding of the resin composition, and deterioration of moldability (productivity) can be suppressed. This melt viscosity indicates the melt viscosity at a shear rate of 243 (1/sec) when measured with a capillograph at a temperature condition of 200° C. according to ISO 11443:1995.

The blending ratio of component (III) is 30 parts by mass or less, preferably 20 parts by mass or less, and more preferably 15 parts by mass or less with respect to 100 parts by mass of the resin composition. This lower limit is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and still more preferably 10 parts by mass. If this value is exceeded, there is a possibility that moldability and abrasion resistance may be deteriorated.

In addition to the resin components described above, other resin materials may be added to the resin composition containing the components (I), (II), and optionally (III). The purpose is to further improve the fluidity of the resin composition for golf balls and improve various physical properties such as resilience and resistance to cracking.

Specific examples of other resin materials include polyamide elastomers, ionomer resins, ethylene-ethylene/butylene-ethylene block copolymers or modified products thereof, polyacetal, polyethylene, nylon resins, styrene resins, polyvinyl chloride, and polycarbonate. , polyphenylene ether, polyarylate, polysulfone, polyethersulfone, polyetherimide and polyamideimide, and one or more of them can be used.

In addition, the resin composition can further contain an active isocyanate compound. This active isocyanate compound reacts with polyurethane or polyurea, which is the main component, to further improve the scratch resistance of the entire resin composition. can be improved.

As the above isocyanate compound, any isocyanate compound that is commonly used in polyurethane can be used without particular limitation. Mixtures of these two, 4,4-diphenylmethane diisocyanate, m-phenylene diisocyanate, 4,4'-biphenyl diisocyanate, etc., and hydrogenated products of these aromatic isocyanate compounds, such as dicyclohexylmethane diisocyanate, can also be used. Aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate (HDI) and octamethylene diisocyanate, and alicyclic diisocyanates such as xylene diisocyanate are also included. Furthermore, a blocked isocyanate compound obtained by reacting an isocyanate group of a compound having two or more isocyanate groups at its end with a compound having an active hydrogen, and a uretidione compound obtained by dimerization of isocyanate may be mentioned.

The amount of the above isocyanate compound is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the polyurethane or polyurea resin as component (I). The value is preferably 30 parts by mass or less, more preferably 20 parts by mass or less. If this amount is too small, a sufficient cross-linking reaction may not be obtained, and no improvement in physical properties may be observed. On the other hand, if the blending amount is too large, problems such as discoloration due to heat or ultraviolet rays over time, loss of thermoplasticity, and a decrease in resilience may occur.

Furthermore, any additive can be appropriately added to the resin composition according to the application. For example, when the golf ball material of the present invention is used as a cover material, the above ingredients include a filler (inorganic filler), organic staple fiber, reinforcing agent, cross-linking agent, pigment, dispersant, anti-aging agent, ultraviolet absorber, Various additives such as light stabilizers can be added. 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, with respect to 100 parts by mass of the base resin, and the upper limit is preferably 10 parts by mass. parts or less, more preferably 4 parts by mass or less.

The rebound resilience of the resin composition is required to be 48% or more, preferably 50% or more, as measured according to the JIS-K 6255:2013 standard in order to improve low resilience and approach spin rate. , More preferably 52% or more, the upper limit is 72% or less, preferably 70% or less, more preferably 68% or less.

Further, the material hardness of the resin composition is preferably 50 or less, more preferably 48 or less, more preferably 48 or less in terms of Shore D hardness from the viewpoint of imparting scratch resistance and an appropriate approach spin rate. Shore D hardness is 45 or less. From the standpoint of moldability, the lower limit of the Shore D hardness is preferably 30 or more, more preferably 35 or more, and still more preferably 37 or more.

Regarding the method of preparing each component of the resin composition, for example, it is possible to mix using various kneaders such as a kneading type (single-screw or) twin-screw extruder, Banbury, kneader, labo plastomill, or Each component may be mixed by dry blending during injection molding of the resin composition. Furthermore, when using the above-mentioned active isocyanate compound, it may be contained at the time of resin mixing using various kneaders, or a master batch containing the active isocyanate compound and other components is prepared separately in advance, and the resin composition The components may be mixed by dry blending during injection molding of the article.

For example, as a method of molding the cover with the above resin composition, for example, the above resin composition may be supplied to an injection molding machine, and the cover may be molded by injecting the melted resin composition around the core. can. In this case, the molding temperature is usually in the range of 150 to 270° C., depending on the type of the main component (I) polyurethane or polyurea.

In the present invention, the Martens hardness of the resin material of component (I) is HMa [N/mm ² ], and the Martens hardness of the cover layer formed of the resin composition containing components (I) and (II) is HMb. [N/mm ² ], it is necessary to satisfy the following formula (1) from the viewpoint of improving the control performance during approach while maintaining the scratch resistance.
1.020≦HMa/HMb≦1.500 (1)

The lower limit of the formula (1) is 1.020 or more, preferably 1.050 or more, more preferably 1.100 or more, and the lower limit is 1.500 or less, preferably 1.400. 1.300 or less, more preferably 1.300 or less. If the value of formula (1) is too large, the scratch resistance will be low, while if the value of formula (1) is too small, approach controllability may be low.

The lower limit of the Martens hardness HMa of the resin material of component (I) is preferably 10.00 N/mm ² or more, more preferably 11.00 N/mm ² or more. The upper limit is preferably 30.00 N/mm ² or less, more preferably 25.00 N/mm ² or less.

The lower limit of the Martens hardness HMb of the cover layer formed of the resin composition containing the components (I) and (II) is preferably 8.00 N/mm ² or more, more preferably 9.0 N/mm 2 . 00 N/mm ² or more. The upper limit is preferably 28.00 N/mm ² or less, more preferably 23.00 N/mm ² or less.

The above Martens hardness HMa and HMb can be measured with an ultra-micro hardness tester based on ISO 14577:2002 "Metallic materials - Instrumented indentation test for hardness and materials parameters". That is, it is a physical property value obtained by pushing the indenter into the object to be measured while applying a load, and is obtained by pressing force [N]/area of pressure receiving portion [mm ² ]. The measurement of Martens hardness can be performed using, for example, an ultra-micro hardness test system "Fischerscope HM2000" (manufactured by Fisher Instruments). For example, this measuring device can measure the hardness of the cover while continuously applying a load stepwise, and as a setting condition, the applied load can be set to 50 mN for 10 seconds at room temperature.

Also, when measuring the surface of the cover, it is difficult to identify if a coating film or the like is formed on the surface of the cover. Since it is affected by hardness, the Martens hardness inherent in the cover can be stably obtained at a point approximately 0.3 mm from the surface of the cover toward the center of the ball, so the Martens hardness is measured at the above position. is desirable.

Further, in the present invention, when the elastic work recovery rate of the cover layer formed of the resin composition containing the components (I) and (II) is ηItb [%], it is preferable that the following formula (2) is satisfied. is.
5.00≦ηItb/HMb≦8.00 (2)

The lower limit of the above formula (2) is preferably 5.00 or more, more preferably 5.30 or more, more preferably 5.80 or more, and the lower limit is preferably 8.00 or less. , more preferably 7.50 or less, and still more preferably 7.20 or less. If the value of formula (2) is too large or too small, the scratch resistance may deteriorate.

The lower limit of the elastic work recovery rate ηItb of the cover layer is preferably 50% or more, more preferably 55% or more. The upper limit is preferably 85% or less, more preferably 80% or less.

Further, when the elastic work recovery rate of the resin material of component (I) is ηIta [%], it is preferable that the following formula (3) is satisfied.
0.97≤ηIta/ηItb≤1.12 (3)

The lower limit of the above formula (2) is preferably 0.97 or more, more preferably 0.98 or more, more preferably 0.99 or more, and the lower limit is preferably 1.12 or less. , more preferably 1.05 or less, and still more preferably 1.03 or less. If the value of formula (3) is too large, the scratch resistance or durability may deteriorate. On the other hand, if the value of the above formula (3) is too small, there is a risk that the controllability in the approach will deteriorate.

The lower limit of the elastic work recovery rate ηIta of the resin material of component (I) is preferably 45% or more, more preferably 50% or more. The upper limit is preferably 80% or less, more preferably 75% or less.

The above elastic work recovery rates ηIta and ηItb are such that the cover formed on the surface of the golf ball maintains a certain level of hardness and elasticity while enhancing the self-healing recovery function, resulting in excellent durability and scratch resistance of the ball. can contribute to Even if the Martens hardness is low, if the elastic work recovery rate is too low, the spin performance on approach is good, but the scuff resistance is poor. A method for measuring the elastic work recovery rate will be described later.

The above elastic work recovery rate is an ultra-micro hardness test method that controls the indentation load on the order of micro Newtons (μN) and tracks the indenter depth during indentation with nanometer (nm) accuracy. is one parameter of the nanoindentation method for evaluating Conventional methods could only measure the size of the deformation mark (plastic deformation mark) corresponding to the maximum load, but the nanoindentation method automatically and continuously measures the relationship between the indentation load and the indentation depth. can be obtained. Therefore, it is believed that the physical properties of the cover can be evaluated reliably and with high precision without the individual differences that occur when visually measuring deformation marks with an optical microscope. For this reason, the cover of a golf ball is greatly affected by the impact of a driver or various clubs, and the impact of the cover on various physical properties of the golf ball is not small. Measuring with higher accuracy than before is a very effective evaluation method.

Further, from the viewpoint of enhancing the desired effect of the present invention, it is preferable to satisfy the following formula (4).
0.70≦(ηIta·HMb)/(ηItb·HMa)≦1.06 (4)

The lower limit of the above formula (4) is preferably 0.70 or more, more preferably 0.75 or more, more preferably 0.78 or more, and the lower limit is preferably 1.06 or less. , more preferably 1.00 or less, and still more preferably 0.90 or less. If the value of the formula (4) is too large, the approach spin rate may deteriorate, and if it is too small, the scratch resistance and durability may deteriorate.

The thickness of the cover is preferably 0.4 mm or more, more preferably 0.5 mm or more, still more preferably 0.6 mm or more, and the upper limit is preferably 3.0 mm or less, more preferably 2.0 mm or less. .

When at least one intermediate layer is interposed between the core and the above, the material of the intermediate layer is preferably selected from various thermoplastic resins used in golf ball cover materials, particularly ionomer resins. and a commercial product can be used as the ionomer resin. In this case, the thickness of the intermediate layer can be set within the same range as the thickness of the cover.

In terms of aerodynamic performance, the golf ball of the present invention is provided with a large number of dimples on the surface of the outermost layer. The number of dimples formed on the surface of the outermost layer is not particularly limited, but is preferably 250 or more, more preferably 270 or more, still more preferably 270 or more, from the viewpoint of enhancing aerodynamic performance and increasing flight distance. The number is 290 or more, most preferably 300 or more, and the upper limit is preferably 400 or less, more preferably 380 or less, still more preferably 360 or less.

In the present invention, a coating film layer is formed on the surface of the cover. As the paint for forming this coating layer, it is preferable to employ a two-liquid curable urethane paint. Specifically, in this case, the two-liquid curing type urethane paint contains a main component having a polyol resin as a main component and a curing agent having a polyisocyanate as a main component.

The method for forming the coating film layer by coating the above-mentioned paint on the surface of the cover is not particularly limited, and any known method can be used, and a desired method such as an air gun coating method or an electrostatic coating method can be used. can be done.

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

The golf ball of the present invention may conform to the Rules of Golf for use in competitions, and has an outer diameter of 42.672 mm or less, which does not pass through a ring with an inner diameter of 42.672 mm, and a weight of 45.0 mm or less. ˜45.93 g.

EXAMPLES Hereinafter, the present invention will be specifically described by showing examples and comparative examples, but the present invention is not limited to the following examples.

[Examples 1 to 12, Comparative Examples 1 to 5]
common core
A core having a diameter of 38.6 mm was produced by preparing and vulcanizing a core rubber composition common to all examples according to the formulation shown in Table 1.

Details of the core material are as follows.
・"cis-1,4-polybutadiene" manufactured by JSR, trade 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. )
・ “Organic peroxide (1)” dicumyl peroxide, trade name “Percumyl D” (manufactured by NOF Corporation)
・ “Organic peroxide (2)” 1,1-di(tert-butylperoxy)cyclohexane and silica mixture, trade name “Perhexa C-40” (manufactured by NOF Corporation)
・"Zinc stearate" manufactured by NOF Corporation

A resin material for the intermediate layer was injection-molded around a core having a common intermediate layer diameter of 38.6 mm to produce an intermediate layer-covered sphere having an intermediate layer with a thickness of 1.25 mm. The resin material for the intermediate layer has a resin formulation common to all examples, and includes 50 parts by mass of an ethylene-unsaturated carboxylic acid copolymer neutralized with sodium having an acid content of 18% by mass and 50 parts by mass of an acid content of 15% by mass. and 50 parts by weight of zinc-neutralized ethylene-unsaturated carboxylic acid copolymer to make a total of 100 parts by weight.

Cover (outermost layer)
Next, for Examples 1 to 4, 6 to 8, 10 to 12, and Comparative Example 1, the cover material for the outermost layer shown in Table 2 below was injection-molded around the above intermediate layer-covered spheres to a thickness of 0. A three-piece golf ball with a diameter of 42.7 mm having an outermost layer of 0.8 mm was made. At this time, common dimples were formed on the cover surface of each example and comparative example, although not shown. The resin composition of the cover was designed to have the blending amounts of the respective components shown in Tables 2 and 3 below, and was injection molded at a molding temperature of 200 to 250°C.
For Examples 5 and 9 and Comparative Examples 2 to 5, three-piece golf balls were produced in the same manner as described above by designing so as to have the blending amounts of the respective components shown in Tables 2 and 3.

The details of the ingredients in the composition in Table 2 below are as follows.
・"TPU (1)" Trade name "Pandex" manufactured by DIC Covestro Polymer Co., Ltd., ether type thermoplastic polyurethane (Shore D hardness "43")
・"(Meth)acrylic block copolymer 1"Kuraray's trade name "Clarity LA2250" acrylic block copolymer (hard segment PMMA/soft segment PBA), Shore D hardness "22"
- "(Meth)acrylic block copolymer 2"Kuraray's trade name "Clarity LA2270" acrylic block copolymer (hard segment PMMA/soft segment PBA), Shore D hardness "31"
- "(Meth)acrylic block copolymer 1"Kuraray's trade name "Clarity LA2140" acrylic block copolymer (hard segment PMMA/soft segment PBA), Shore D hardness "7"
- "(Meth)acrylic block copolymer 2"Kuraray's trade name "Clarity LA2330" acrylic block copolymer (hard segment PMMA/soft segment PBA), Shore D hardness "6"
・ “PMMA1” Kuraray Co., Ltd. trade name “Parapet Soft Acrylic SA-NW201” methacrylic resin (Shore D hardness “40”)
・ “PMMA2” Kuraray Co., Ltd. trade name “Parapet GF” methacrylic resin (Shore D hardness “87”)
・ “Hydrogenated styrene elastomer (1)” trade name “Tuftec H1051” manufactured by Asahi Kasei Corporation (Shore D hardness: 45)
・ “Hydrogenated styrene elastomer (2)” trade name “Tuftec H1517” manufactured by Asahi Kasei Corporation (Shore D hardness: 47)
- "Thermoplastic polyester elastomer" trade name "Hytrel 2401" manufactured by Toray DuPont, thermoplastic polyether ester elastomer (Shore D hardness "40")

Physical Properties of Cover Resin Composition (1) Shore D Hardness A resin material was formed into a sheet having a thickness of 2 mm and left at a temperature of 23±2° C. for 2 weeks. Three sheets are superimposed during the measurement. The material hardness of the resin was measured with a Shore D hardness tester conforming to the ASTM D2240 standard. For hardness measurement, an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd. equipped with a Shore D type hardness tester is used.
(2) Rebound resilience Tables 2 and 3 show the rebound resilience of the resin composition measured according to JIS-K 6255:2013.
(3) Melt Viscosity Tables 2 and 3 show melt viscosities at a shear rate of 243 (1/sec) when measured with a capillograph at a temperature of 200° C. according to ISO 11443:1995.

The Martens hardness (HMa) and elastic work recovery rate (ηIta) of the polyurethane "TPU1" resin used in each example and each comparative example were measured by the following methods. In addition, Martens hardness (HMb) and elastic work recovery rate (ηItb) were measured for the resin composition of the cover layer (outermost layer) used in each example and each comparative example. Next, the following three relational expressions (1) of these parameters: HMa/HMb,
Equation (2): ηItb/HMb,
Equation (3) ηIta/ηItb and Equation (4) (ηIta HMb)/(ηItb HMa)
was calculated. These calculated values are shown in Tables 2 and 3.

Martens hardness (HMb) of outermost layer (cover layer)
The golf ball of each example was cut in half, and a point of 0.3 mm from the surface of the cover toward the center of the ball was specified from the cross section of the ball ^. was measured using an ultra-micro hardness tester manufactured by Fisher Instruments under the trade name of "Fischerscope HM2000". The hardness measurement was performed at room temperature under an applied load of 50 mN/10 s.

Martens hardness (HMa) of resin material
The Martens hardness (HMa) of the polyurethane resin "TPU1" is as follows. The apparatus and conditions for measuring the Martens hardness of this resin are the same as those described above.
・ Martens hardness (HMa) of TPU1: 14.3 N/mm ²

Elastic Work Recovery Rate of Cover Layer (Outermost Layer) The elastic work recovery rate of the cover layer was measured using an ultra-micro hardness tester under the trade name "Fischerscope HM2000" manufactured by Fisher Instruments. The measurement conditions are as follows: under the applied load of 50 mN/10 s at room temperature, the elastic work is calculated by the following formula based on the indentation work W _elast (Nm) due to the return deformation of the cover and the mechanical indentation work W _total (Nm). A recovery rate is calculated.
Elastic work recovery rate = W _elast / W _total x 100 (%)

Elastic Work Recovery Rate of Resin Material The elastic work recovery rate (%) of the polyurethane resin "TPU1" is as follows. The apparatus and conditions for measuring the elastic work recovery rate of this resin are the same as those described above.
・ Elastic work recovery rate of TPU1: 72%

Spin performance, initial speed performance, approach controllability, scratch resistance and moldability of each golf ball are evaluated by the following methods. The results are shown in Tables 2 and 3.

Initial Velocity 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 at a head speed (HS) of 20 m/s are measured by an initial condition measuring device.

Controllability Sensory evaluation of controllability of the ball during approach was carried out by the following method. The club used was a sand wedge (SW) product name "Bridgestone Tour Stage TW-03 (loft angle 57°)" similar to the above.
[Judgment evaluation]
(double-circle) ... Very excellent in operability.
O: Excellent in operability.
Δ: Slightly inferior in operability.
x: Inferior in operability.
In addition to the spin rate of the ball, the length of contact time between the ball and the club face due to the low resilience affects the determination of whether or not the maneuverability is excellent. When the contact time is long, the operability is improved, and when it is short, the operability is deteriorated. Here, the controllability (operability) including the amount of spin and the length of contact time is determined.

Scratch resistance evaluation The balls were kept warm at 23°C, and a pitching wedge (PW) was used to hit each ball five times at a head speed of 33 m/s using a swing robot machine. is visually evaluated according to the following criteria.
◯: Slightly scratched or almost unnoticeable.
× . . . Dimples are completely scraped off.

Evaluation of moldability (demoldability) The ball of each example was evaluated for demoldability from the mold after injection molding of the cover according to the following criteria.
⊚: No damage such as broken runners or sticking of pins occurs during demolding.
◯: Damage such as broken runners and sticking of pins occurs during demolding, but there is no problem with molding.
Δ: Damage such as broken runners or sticking of pins occurs during demolding, and molding temperature must be raised due to increased viscosity.

As shown in Tables 2 and 3, the golf balls of Comparative Examples 1 to 5 are inferior to the products of the present invention (Examples) in the following points.
Comparative Example 1 does not contain the component (II) in the resin composition, and is inferior in controllability during approach.
In Comparative Example 2, component (II) was not blended in the resin composition, and instead PMMA was blended, but the melt viscosity increased and the fluidity deteriorated, so the molding temperature had to be raised. As a result, defects such as burning occur on the entire surface of the cover, resulting in poor formability.
In Comparative Example 3, since PMMA was blended into the resin composition, the melt viscosity increased and the flowability deteriorated, so the molding temperature had to be increased. Poor moldability. In addition, since PMMA has a high hardness, the spin rate on approach decreases, resulting in poor controllability during approach.
In Comparative Example 4, HMa/HMb is smaller than the lower limit of "1.020" of formula (1), and as a result, the controllability during approach is deteriorated.
In Comparative Example 5, HMa/HMb is smaller than the lower limit of "1.020" in formula (1), resulting in poor controllability during approach.

Claims (16)

In a golf ball comprising at least one layer of rubber core and at least one layer of cover covering said core, at least one layer of said cover comprises the following components (I) and (II): (I) polyurethane or polyurea ( II) Formed from a resin composition containing a (meth)acrylic block copolymer, the Martens hardness of the resin material of component (I) is HMa [N/mm ² ], (I) and (II) ), the Martens hardness of the cover layer formed of the resin composition containing the component is HMb [N/mm ² ], HMa and HMb are represented by the following formula (1):
1.020≦HMa/HMb≦1.500 (1)
A golf ball characterized by satisfying 2. The golf ball of claim 1, wherein component (II) is added in an amount of 15 parts by mass or less per 100 parts by mass of component (I). 3. The golf ball of claim 1, wherein the material hardness of component (II) is 40 or less in Shore D hardness. 4. The golf ball of claim 1, wherein component (II) has a modulus of impact resilience of 50% or less as measured according to JIS-K 6255 standards. 5. The golf ball of claim 1, wherein component (II) has a weight average molecular weight of 10,000 or more. The golf ball of any one of claims 1 to 5, wherein the block copolymer of component (II) has two or more blocks constituting hard segments and one or more blocks constituting soft segments. 7. The golf ball of claim 1, wherein in the block copolymer of component (II), the hard segment is mainly composed of methyl methacrylate units. 8. The golf ball of claim 1, wherein in the block copolymer of component (II), the soft segment is mainly composed of n-butyl acrylate units. 9. The golf ball of claim 1, wherein the cover has a Shore D hardness of 48 or less. The golf ball of any one of claims 1 to 9, wherein the resin composition further contains (III) a thermoplastic polyester elastomer. 11. The golf ball of claim 10, wherein the material hardness of component (III) is 20 to 50 in Shore D hardness. 12. The golf ball of claim 10, wherein component (III) has a rebound resilience of 50 to 80% as measured according to JIS-K 6255 standards. 13. Any one of claims 10 to 12, wherein the component (III) has a melt viscosity of 0.3×10 ⁴ to 1.5×10 ⁴ (dPa·s) at 200° C. and a shear rate of 243 (1/sec). A golf ball according to any one of claims 1 to 3. When the elastic work recovery rate of the cover layer formed of the resin composition containing the above components (I) and (II) is ηItb [%], ηItb and HMb are expressed by the following formula (2).
5.00≦ηItb/HMb≦8.00 (2)
14. The golf ball according to any one of claims 1 to 13, which satisfies: When the elastic work recovery rate of the resin material of the component (I) is ηIta [%], the following formula (3)
0.97≤ηIta/ηItb≤1.12 (3)
15. The golf ball of claim 14, wherein: Furthermore, the following formula (4)
0.70≦(ηIta·HMb)/(ηItb·HMa)≦1.06 (4)
16. The golf ball of claim 15, wherein: