Golf Ball

Abstract

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 of a resin composition that includes (A) polyurethane or polyurea, and (B) a thermoplastic polyester elastomer. Component (B) is included in a ratio of not more than 45 wt % of the overall amount of the resin composition, and the resin composition has a Shore D hardness of 42 or less and a rebound resilience of from 60 to 72%. The golf ball has an excellent controllability on approach shots, is able to maintain a good feel at impact and a good scuff resistance, and also has a good moldability.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This non-provisional application claims priority under 35 U.S.C. .sctn. 119(a) on Patent Application No. 2020-096539 filed in Japan on Jun. 3, 2020, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

[0002] This invention relates to a golf ball which has a core of at least one layer and a cover of at least one layer.

BACKGROUND ART

[0003] The chief property desired in a golf ball is an increased distance, but other desirable properties include the ability for the ball to stop well on approach shots and a good scuff resistance. Many golf balls that exhibit a good flight performance on shots with a driver and are suitably receptive to backspin on approach shots have hitherto been developed. Recently, an increasing number of golf balls for professional golfers and skilled amateurs use urethane resin materials in place of ionomer resin materials. Thermoplastic urethane elastomers in particular are often used as the urethane resin material, and their properties are constantly being upgraded. A number of disclosures have been made that further improve the properties of cover resin compositions in which a thermoplastic urethane elastomer serves as the base resin by including other resins and additives.

[0004] However, there is a desire, when blending a thermoplastic urethane elastomer with another resin material, to keep the scuff resistance inherent to the thermoplastic urethane elastomer from decreasing by suitably adjusting the type and amount of that resin. In addition, there is also a desire, when blending a urethane resin material with another resin material for the purpose of lowering the hardness, to avoid as much as possible a change in the resilience and a worsening of the moldability.

[0005] For example, JP-A 2008-119461 describes the use of a low-hardness urethane resin as the cover material, although softening of the resin material is required to further enhance the spin rate on approach shots. In this case, further softening the urethane resin-based cover material itself worsens the moldability, making production difficult at this point in time. Hence, the notion of including additives so as to soften the cover material is also described.

[0006] In this connection, JP-A 2017-12737 and other art describes golf balls in which the resin composition is softened by including a plasticizer within a urethane-based resin composition. However, the resin composition in this case merely becomes softer and fails to adequately enhance the spin rate on approach shots.

SUMMARY OF THE INVENTION

[0007] It is therefore an object of the present invention to provide a golf ball which has an excellent controllability on approach shots and which also can maintain a good feel at impact and a good scuff resistance and moreover has a good moldability.

[0008] With this object in mind, in order to further improve a resin material composed primarily of polyurethane or polyurea as the cover material in a golf ball having a core and a cover, I began by weighing (i) the addition of a plasticizer versus (ii) the addition of a resin having softening properties. As a result, I learned that, with the first approach, i.e., (i) plasticizer addition, the resin composition merely becomes softer and, in the molded ball, is unable to increase the spin rate of the ball on approach shots. Also, I realized from the experimental results for (i) that, in order to achieve the object of this invention, the material that is added must have a certain resilience. I then selected a resin that has softening properties for the second approach (ii) and fabricated a golf ball using as the cover the molded form of a resin composition obtained by including a specific amount of a specific, relatively soft, thermoplastic polyester elastomer in a polyurethane or polyurea-based resin composition, whereupon I discovered that this golf ball has an excellent controllability on approach shots, is able to maintain a good feel at impact and a good scuff resistance, and moreover has a good moldability. This invention was thus arrived at based on the finding that, in a resin composition containing polyurethane or polyurea as the base resin ingredient, the specific thermoplastic polyester elastomer, when used as the added resin, has a good compatibility with the polyurethane or other base resin, gives the resin composition a low hardness, imparts at least a certain degree of resilience and has hardenability.

[0009] Accordingly, the present invention provides a golf ball having a rubber core of at least one layer and a cover of at least one layer encasing the core, wherein at least one layer of the cover is formed of a resin composition containing (A) polyurethane or polyurea and (B) a thermoplastic polyester elastomer, component (B) being included in a ratio of not more than 45 wt % of the overall amount of the resin composition and the resin composition having a Shore D hardness of 42 or less and a rebound resilience of from 60 to 72%.

[0010] In a preferred embodiment of the golf ball of the invention, the rebound resilience of the resin composition is from 62 to 70%.

[0011] In another preferred embodiment, the polyurethane or polyurea serving as component (A) has a Shore D hardness of 45 or less and a rebound resilience of at least 55%.

[0012] In yet another preferred embodiment, the thermoplastic polyester elastomer serving as component (B) has a Shore D hardness of not more than 35 and a rebound resilience of at least 65%.

[0013] In still another preferred embodiment, component (B) has a melt viscosity at 200.degree. C. and a shear rate of 243 sec.sup.-1 which is from 0.2.times.10.sup.4 to 1.0.times.10.sup.4 dPas.

Advantageous Effects of the Invention

[0014] The golf ball of the invention has an excellent controllability on approach shots, is able to maintain a good feel at impact and a good scuff resistance, and moreover has a good moldability.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The objects, features and advantages of the invention will become more apparent from the following detailed description.

[0016] The golf ball of the invention is a ball having a core of at least one layer, which core is encased by a cover of at least one layer; that is, a single-layer cover or a multilayer cover.

[0017] The core may be formed using a known rubber material as the base material. A known base rubber such as natural rubber or a synthetic rubber may be used as the base rubber. More specifically, it is recommended that polybutadiene, especially cis-1,4-polybutadiene having a cis structure content of at least 40%, be chiefly used. If desired, natural rubber, polyisoprene rubber, styrene-butadiene rubber or the like may be used together with the foregoing polybutadiene in the base rubber.

[0018] The polybutadiene may be synthesized with a metal catalyst, such as a neodymium or other rare-earth catalyst, a cobalt catalyst or a nickel catalyst.

[0019] Co-crosslinking agents such as unsaturated carboxylic acids and metal salts thereof, 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 may be included in the base rubber. If necessary, commercial antioxidants and the like may be suitably added.

[0020] The core may be produced by vulcanizing/curing the rubber composition containing the above ingredients. For example, production may be carried out by kneading the composition using a mixer such as a Banbury mixer or a roll mill, compression molding or injection molding the kneaded composition using a core mold, and curing the molded body by suitably heating it at a temperature sufficient for the organic peroxide and the co-crosslinking agent to act, i.e., from about 100.degree. C. to about 200.degree. C., and preferably from 140 to 180.degree. C., for a period of 10 to 40 minutes.

[0021] In the golf ball of the invention, the core is encased by a single-layer or multilayer cover. This golf ball may be in the form of, for example, a golf ball having a single-layer cover over a core, or a golf ball having a core, an intermediate layer encasing the core, and an outermost layer encasing the intermediate layer.

[0022] In this invention, at least one layer of the cover is formed of a resin composition containing components (A) and (B) below:

[0023] (A) polyurethane or polyurea

[0024] (B) a thermoplastic polyester elastomer.

(A) Polyurethane or Polyurea

[0025] The polyurethane (A-1) or polyurea (A-2) serving as this component is described in detail below.

(A-1) Polyurethane

[0026] The polyurethane has a structure which includes soft segments composed of a polymeric polyol (polymeric glycol) that is a long-chain polyol, and hard segments composed of a chain extender and a polyisocyanate. Here, the polymeric polyol serving as a starting material may be any that has hitherto been used in the art relating to polyurethane materials, and is not particularly limited. It is exemplified by polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymer-based polyols, castor oil-based polyols, silicone-based polyols and vinyl polymer-based polyols. Specific examples of polyester polyols that may be used include adipate-type polyols such as polyethylene adipate glycol, polypropylene adipate glycol, polybutadiene adipate glycol and polyhexamethylene adipate glycol; and lactone-type polyols such as polycaprolactone polyol. Examples of polyether polyols include poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol) and poly(methyltetramethylene glycol). These polyols may be used singly, or two or more may be used in combination.

[0027] It is preferable to use a polyether polyol as the above polymeric polyol.

[0028] The long-chain polyol has a number-average molecular weight that is preferably in the range of 1,000 to 5,000. By using a long-chain polyol having a number-average molecular weight in this range, golf balls made with a polyurethane composition that have excellent properties, including a good rebound and good productivity, can be reliably obtained. The number-average molecular weight of the long-chain polyol is more preferably in the range of 1,500 to 4,000, and even more preferably in the range of 1,700 to 3,500.

[0029] Here and below, "number-average molecular weight" refers to the number-average molecular weight calculated based on the hydroxyl value measured in accordance with JIS-K1557.

[0030] The chain extender is not particularly limited; any chain extender that has hitherto been employed in the art relating to polyurethanes may be suitably used. In this invention, low-molecular-weight compounds with a molecular weight of 2,000 or less which have on the molecule two or more active hydrogen atoms capable of reacting with isocyanate groups may be used. Of these, preferred use can be made of aliphatic diols having from 2 to 12 carbon atoms. Specific examples include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. Of these, the use of 1,4-butylene glycol is especially preferred.

[0031] Any polyisocyanate hitherto employed in the art relating to polyurethanes may be suitably used without particular limitation as the polyisocyanate. For example, use can be made of 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, 1,5-naphthylene 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. However, depending on the type of isocyanate, crosslinking reactions during injection molding may be difficult to control.

[0032] The ratio of active hydrogen atoms to isocyanate groups in the polyurethane-forming reaction may be suitably adjusted within a preferred range. Specifically, in preparing a polyurethane by reacting the above long-chain polyol, polyisocyanate and chain extender, it is preferable to use the respective components in proportions such that the amount of isocyanate groups included in the polyisocyanate per mole of active hydrogen atoms on the long-chain polyol and the chain extender is from 0.95 to 1.05 moles.

[0033] The method for preparing the polyurethane is not particularly limited. Preparation using the long-chain polyol, chain extender and polyisocyanate may be carried out by either a prepolymer process or a one-shot process via a known urethane-forming reaction. Of these, melt polymerization in the substantial absence of solvent is preferred. Production by continuous melt polymerization using a multiple screw extruder is especially preferred.

[0034] It is preferable to use a thermoplastic polyurethane material as the polyurethane, with an ether-based thermoplastic polyurethane material being especially preferred. The thermoplastic polyurethane material used may be a commercial product, illustrative examples of which include those available under the trade name PANDEX from DIC Covestro Polymer, Ltd., and those available under the trade name RESAMINE from Dainichiseika Color & Chemicals Mfg. Co., Ltd.

(A-2) Polyurea

[0035] The polyurea is a resin composition composed primarily of urea linkages formed by reacting (i) an isocyanate with (ii) an amine-terminated compound. This resin composition is described in detail below.

(i) Isocyanate

[0036] The isocyanate is not particularly limited. Any isocyanate used in the prior art relating to polyurethanes may be suitably used here. Use may be made of isocyanates similar to those mentioned above in connection with the polyurethane material.

(ii) Amine-Terminated Compound

[0037] An amine-terminated compound is a compound having an amino group at the end of the molecular chain. In this invention, the long-chain polyamines and/or amine curing agents shown below may be used.

[0038] A long-chain polyamine is an amine compound which has on the molecule at least two amino groups capable of reacting with isocyanate groups, and which has a number-average molecular weight of from 1,000 to 5,000. In this invention, the number-average molecular weight is more preferably from 1,500 to 4,000, and even more preferably from 1,900 to 3,000. Examples of such long-chain polyamines 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 singly, or two or more may be used in combination.

[0039] An amine curing agent is an amine compound which has on the molecule at least two amino groups capable of reacting with isocyanate groups and which has a number-average molecular weight of less than 1,000. In this invention, the number-average molecular weight is more preferably less than 800, and even more preferably less than 600. Specific examples of such amine curing agents include, but are not limited to, ethylenediamine, hexamethylenediamine, 1-methyl-2,6-cyclohexyldiamine, tetrahydroxypropylene ethylenediamine, 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, imidobis(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 derivatives thereof, 1,4-bis(sec-butylamino)benzene, 1,2-bis(sec-butylamino)benzene, N,N'-dialkylaminodiphenylmethane, 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 curing agents may be used singly or two or more may be used in combination.

(iii) Polyol

[0040] Although not an essential ingredient, in addition to above components (i) and (ii), a polyol may also be included in the polyurea. The polyol is not particularly limited, but is preferably one that has hitherto been used in the art relating to polyurethanes. Specific examples include the long-chain polyols and/or polyol curing agents mentioned below.

[0041] The long-chain polyol may be any that has hitherto been used in the art relating to polyurethanes. Examples include, but are not limited to, polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin-based polyols, conjugated diene polymer-based polyols, castor oil-based polyols, silicone-based polyols and vinyl polymer-based polyols. These long-chain polyols may be used singly or two or more may be used in combination.

[0042] The long-chain polyol has a number-average molecular weight of preferably from 1,000 to 5,000, and more preferably from 1,700 to 3,500. In this average molecular weight range, an even better resilience and productivity are obtained.

[0043] The polyol curing agent is preferably one that has hitherto been used in the art relating to polyurethanes, but is not subject to any particular limitation. In this invention, use may be made of a low-molecular-weight compound having on the molecule at least two active hydrogen atoms capable of reacting with isocyanate groups and having a molecular weight of less than 1,000. Of these, the use of aliphatic diols having from 2 to 12 carbon atoms is preferred. Specific examples include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. The use of 1,4-butylene glycol is especially preferred. The polyol curing agent has a number-average molecular weight of preferably less than 800, and more preferably less than 600.

[0044] A known method may be used to produce the polyurea. A prepolymer process, a one-shot process or some other known method may be suitably selected for this purpose.

[0045] Component (A) has a material hardness on the Shore D hardness scale which, to enhance the spin rate on approach shots, is preferably 45 or less, more preferably 44 or less, and even more preferably 43 or less. From the standpoint of the moldability, the lower limit in the material hardness on the Shore D scale is preferably at least 35, and more preferably at least 37.

[0046] Component (A) has a rebound resilience which, to enhance the spin rate on approach shots, is preferably at least 55%, more preferably at least 57%, and even more preferably at least 59%. The rebound resilience is measured in accordance with JIS-K 6255: 2013.

(B) Thermoplastic Polyester Elastomer

[0047] In this invention, to obtain the desired effects of the invention, a specific thermoplastic polyester elastomer is included as an essential ingredient in the resin composition. This specific thermoplastic polyester elastomer imparts at least a certain degree of resilience to the resin composition and, along with imparting such resilience, enables the ball to maintain an elevated spin rate at or above a certain level on approach shots. Also, because the specific thermoplastic polyester elastomer included as an essential ingredient in the resin composition has a good compatibility with component (A) serving as the base resin, it is able to impart the ball with a good scuff resistance. In addition, including the specific thermoplastic polyester elastomer as an essential ingredient in the resin composition provides the resin composition with at least a certain level of melt viscosity, thus imparting hardenability to the resin composition after it has been molded. That is, the thermoplastic polyester elastomer suppresses a decline in the viscosity of the overall resin composition due to the softness of component (A) serving as the base resin, thus preventing a decrease in moldability (productivity) and an increase in appearance defects in the molded golf balls and also holding down a rise in production costs due to an increased cooling time. This thermoplastic polyester elastomer is described below.

[0048] The thermoplastic polyester elastomer serving as component (B) is a resin composition made up of (b-1) a polyester block copolymer and (b-2) a rigid resin. In turn, component (b-1) is made up of (b-1-1) a high-melting crystalline polymer segment and (b-1-2) a low-melting polymer segment.

[0049] The high-melting crystalline polymer segment (b-1-1) within the polyester block copolymer serving as component (b-1) is a polyester formed from one or more compound selected from the group consisting of aromatic dicarboxylic acids and ester-forming derivatives thereof and diols and ester-forming derivatives thereof.

[0050] Illustrative examples of the aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, anthracenedicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, diphenoxyethanedicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sulfoisophthalic acid and sodium 3-sulfoisophthalate. In this invention, an aromatic dicarboxylic acid is primarily used. However, where necessary, some of this aromatic dicarboxylic acid may be replaced with an alicyclic dicarboxylic acid such as 1,4-cyclohexanedicarboxylic acid, cyclopentanedicarboxylic acid or 4,4'-dicyclohexyldicarboxylic acid or with an aliphatic dicarboxylic acid such as adipic acid, succinic acid, oxalic acid, sebacic acid, dodecanedioic acid or a dimer acid. Exemplary ester-forming derivatives of dicarboxylic acids include lower alkyl esters, aryl esters, carboxylic acid esters and acid halides of the above dicarboxylic acids.

[0051] Next, a diol having a molecular weight of 400 or less may be suitably used as the diol. Specific examples include aliphatic diols such as 1,4-butanediol, ethylene glycol, trimethylene glycol, pentamethylene glycol, hexamethylene glycol, neopentyl glycol and decamethylene glycol; alicyclic diols such as 1,1-cyclohexanedimethanol, 1,4-dicyclohexanedimethanol and tricyclodecanedimethanol; and aromatic diols such as xylylene glycol, bis(p-hydroxy)diphenyl, bis(p-hydroxy)diphenylpropane, 2,2'-bis[4-(2-hydroxyethoxy)phenyl]propane, bis[4-(2-hydroxyethoxy)phenyl]sulfone, 1,1-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane, 4,4'-dihydroxy-p-terphenyl and 4,4'-dihydroxy-p-quaterphenyl. Exemplary ester-forming derivatives of diols include acetylated forms and alkali metal salts of the above diols.

[0052] These aromatic dicarboxylic acids, diols and derivatives thereof may be used singly or two or more may be used together.

[0053] In particular, the following may be suitably used as component (b-1-1): high-melting crystalline polymer segments composed of polybutylene terephthalate units derived from terephthalic acid and/or dimethyl terephthalate together with 1,4-butanediol; high-melting crystalline polymer segments composed of polybutylene terephthalate units derived from isophthalic acid and/or dimethyl isophthalate together with 1,4-butanediol; and copolymers of both.

[0054] The low-melting polymer segment serving as component (b-1-2) is an aliphatic polyether and/or an aliphatic polyester.

[0055] Examples of the aliphatic polyether include poly(ethylene oxide) glycol, poly(propylene oxide) glycol, poly(tetramethylene oxide) glycol, poly(hexamethylene oxide) glycol, copolymers of ethylene oxide and propylene oxide, ethylene oxide addition polymers of poly(propylene oxide) glycol, and copolymer glycols of ethylene oxide and tetrahydrofuran. Examples of aliphatic polyesters include poly(s-caprolactone), polyenantholactone, polycaprolactone, polybutylene adipate and polyethylene adipate. In this invention, from the standpoint of the elastic properties, suitable use can be made of poly(tetramethylene oxide) glycol, ethylene oxide adducts of poly(propylene oxide) glycol, copolymer glycols of ethylene oxide and tetrahydrofuran, poly(.epsilon.-caprolactone), polybutylene adipate and polyethylene adipate. Of these, the use of, in particular, poly(tetramethylene oxide) glycol, ethylene oxide adducts of poly(propylene oxide) glycol and copolymer glycols of ethylene oxide and tetrahydrofuran is recommended. The number-average molecular weight of these segments in the copolymerized state is preferably from about 300 to about 6,000.

[0056] Component (b-1) can be produced by a known method. Specifically, use can be made of, for example, the method of carrying out a transesterification reaction on a lower alcohol diester of a dicarboxylic acid, an excess amount of a low-molecular-weight glycol and a low-melting polymer segment component in the presence of a catalyst and polycondensing the resulting reaction product, or the method of carrying out an esterification reaction on a dicarboxylic acid, an excess amount of glycol and a low-melting polymer segment component in the presence of a catalyst and polycondensing the resulting reaction product.

[0057] The proportion of component (b-1) accounted for by component (b-1-2) is from 30 to 60 wt %. The preferred lower limit in this case can be set to 35 wt % or more, and the preferred upper limit can be set to 55 wt % or less. When the proportion of component (b-1-2) is too low, the impact resistance (especially at low temperatures) and the compatibility may be inadequate. On the other hand, when the proportion of component (b-1-2) is too high, the rigidity of the resin composition (and the molded body) may be inadequate.

[0058] The rigid resin serving as component (b-2) is not particularly limited. For example, one or more selected from the group consisting of polycarbonates, acrylic resins, styrene resins such as ABS resins and polystyrenes, polyester resins, polyamide resins, polyvinyl chlorides and modified polyphenylene ethers may be used. In this invention, from the standpoint of compatibility, a polyester resin may be suitably used. More preferably, the use of polybutylene terephthalate and/or polybutylene naphthalate is recommended.

[0059] Component (b-1) and component (b-2) are blended in a ratio, expressed as (b-1):(b-2), which is not particularly limited, although this ratio by weight is preferably set to from 50:50 to 90:10, and more preferably from 55:45 to 80:20. When the proportion of component (b-1) is too low, the low-temperature impact resistance may be inadequate. On the other hand, when the proportion of (b-1) is too high, the rigidity of the composition (and the molded body), as well as the molding processability, may be inadequate.

[0060] A commercial product may be used as the polyester elastomer (B). Specific examples include those available as Hytrel.RTM. from DuPont-Toray Co. Ltd.

[0061] Component (B) has a material hardness on the Shore D hardness scale which, to enhance the spin rate on approach shots, is preferably 35 or less, more preferably 33 or less, and even more preferably 31 or less. The lower limit is a Shore D hardness of preferably at least 27, and more preferably at least 29.

[0062] Component (B) has a rebound resilience which, to enhance the spin rate on approach shots, is preferably at least 65%, more preferably at least 67%, and even more preferably at least 69%. The rebound resilience is measured according to JIS-K 6255: 2013.

[0063] Component (B) has a melt viscosity which is preferably from 0.2.times.10.sup.4 dPas to 1.0.times.10.sup.4 dPas. With this melt viscosity, hardenability after molding of the resin composition is imparted and a decrease in moldability (productivity) can be suppressed. This melt viscosity indicates the value measured with a capillary viscometer at a temperature of 200.degree. C. and a shear rate of 243 sec.sup.-1 in accordance with ISO 11443: 1995.

[0064] Component (B) is blended in a proportion which is not more than 45 wt %, preferably not more than 40 wt %, and more preferably not more than 30 wt %, of the resin composition. At above this value, decreases in the moldability and the scuff resistance may occur.

[0065] The blending ratio (A)/(B) of component (A) and component (B) is preferably from 90/10 to 60/40 by weight. When the content of component (B) is higher than this range, the moldability may worsen or the scuff resistance may decrease. On the other hand, when the component (B) content is lower than this range, an improvement in the spin rate on approach shots may not be achieved.

[0066] The resin composition containing components (A) and (B) may include other resin materials in addition to the above-described resin components. The purposes for doing so are, for example, to further improve the flowability of the golf ball resin composition and to increase such ball properties as the rebound and the scuff resistance.

[0067] Examples of other resin materials that may be used include polyester elastomers, polyamide elastomers, ionomer resins, ethylene-ethylene/butylene-ethylene block copolymers and modified forms thereof, polyacetals, polyethylenes, nylon resins, methacrylic resins, polyvinyl chlorides, polycarbonates, polyphenylene ethers, polyarylates, polysulfones, polyethersulfones, polyetherimides and polyamideimides. These may be used singly or two or more may be used together.

[0068] In addition, an active isocyanate compound may be included in the above resin composition. This active isocyanate compound reacts with the polyurethane or polyurea serving as the base resin, enabling the scuff resistance of the overall resin composition to be further increased. Moreover, the isocyanate has a plasticizing effect which increases the flowability of the resin composition, enabling the moldability to be improved.

[0069] Any isocyanate compound employed in conventional polyurethanes may be used without particular limitation as the above isocyanate compound. For example, aromatic isocyanate compounds that may be used include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate and mixtures of both, 4,4-diphenylmethane diisocyanate, m-phenylene diisocyanate and 4,4'-biphenyl diisocyanate. Use can also be made of the hydrogenated forms of these aromatic isocyanate compounds, such as dicyclohexylmethane diisocyanate. Other isocyanate compounds that may be used include aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate (HDI) and octamethylene diisocyanate, and alicyclic diisocyanates such as xylene diisocyanate. Further examples of isocyanate compounds that may be used include blocked isocyanate compounds obtained by reacting the isocyanate groups on a compound having two or more isocyanate groups on the ends with a compound having active hydrogens, and uretdiones obtained by the dimerization of isocyanate.

[0070] The amount of the above isocyanate compounds included per 100 parts by weight of the polyurethane or polyurea resin serving as component (A) is preferably at least 0.1 part by weight, and more preferably at least 0.5 part by weight. The upper limit is preferably not more than 30 parts by weight, and more preferably not more than 20 parts by weight. When too little is included, a sufficient crosslinking reaction may not be obtained and an increase in the properties may not be observable. On the other hand, when too much is included, discoloration over time due to heat and ultraviolet light may increase, or problems such as a loss of thermoplasticity or a decline in resilience may arise.

[0071] In addition, optional additives may be suitably included in the above resin composition according to the intended use thereof. For example, when the resin composition is to be used as a golf ball cover material, various additives, such as inorganic fillers, organic staple fibers, reinforcing agents, crosslinking agents, pigments, dispersants, antioxidants, ultraviolet absorbers and light stabilizers, may be added to the above ingredients. When such additives are included, the amount thereof per 100 parts by weight of the base resin is preferably at least 0.1 part by weight, and more preferably at least 0.5 part by weight, but preferably not more than 10 parts by weight, and more preferably not more than 4 parts by weight.

[0072] In order to enhance the spin rate on approach shots, the rebound resilience of the resin composition, as measured in accordance with JIS-K 6255: 2013, must be at least 60%, and is preferably at least 62%, and more preferably at least 64%. The upper limit must be not more than 72%, and is preferably not more than 70% and more preferably not more than 68%.

[0073] The resin composition has a material hardness on the Shore D hardness scale which, to enhance the spin rate on approach shots, must be 42 or less, and is preferably 41 or less, and more preferably 40 or less. From the standpoint of moldability, the lower limit in the Shore D hardness is preferably at least 30, and more preferably at least 35.

[0074] The resin composition may be prepared by mixing together the ingredients using any of various types of mixers, such as a kneading-type single-screw or twin-screw extruder, a Banbury mixer, a kneader or a Labo Plastomill. Alternatively, the ingredients may be mixed together by dry blending when the resin composition is injection-molded. In addition, in cases where an active isocyanate compound is used, it may be incorporated at the time of resin mixture using various types of mixers, or a resin masterbatch already containing the active isocyanate compound and other ingredients may be separately prepared and the various components mixed together by dry blending when the resin composition is injection-molded.

[0075] The method of molding the cover from the above resin composition may involve, for example, feeding the resin composition into an injection molding machine and molding the cover by injecting the molten resin composition over the ball core. In this case, the molding temperature differs according to the type of polyurethane or polyurea (A) serving as the base resin, but is typically in the range of 150 to 270.degree. C.

[0076] The cover has a thickness of preferably at least 0.4 mm, more preferably at least 0.5 mm, and even more preferably at least 0.6 mm. The upper limit is preferably not more than 3.0 mm, and more preferably not more than 2.0 mm.

[0077] When at least one intermediate layer is interposed between the above core and cover, various types of thermoplastic resins used as golf ball cover materials, particularly ionomer resins, may be suitably employed as the intermediate layer material. A commercial product may be used as the ionomer resin. In such a case, the thickness of the intermediate layer may be set within a similar range as the cover thickness.

[0078] Numerous dimples are provided on the surface of the outermost layer of the inventive golf ball for reasons having to do with the aerodynamic performance. The number of dimples formed on the surface of the outermost layer is not particularly limited. However, to enhance the aerodynamic performance and increase the distance traveled by the ball, this number is preferably at least 250, more preferably at least 270, even more preferably at least 290, and most preferably at least 300. The upper limit is preferably not more than 400, more preferably not more than 380, and even more preferably not more than 360.

[0079] In this invention, a coating layer is formed on the cover surface. A two-part curable urethane coating may be suitably used as the coating that forms this coating layer. Specifically, in this case, the two-part curable urethane coating is one that includes a base resin composed primarily of a polyol resin and a curing agent composed primarily of a polyisocyanate.

[0080] A known method may be used without particular limitation as the method for applying this coating onto the cover surface and forming a coating layer. Use can be made of a desired method such as air gun painting or electrostatic painting.

[0081] The thickness of the coating layer, although not particularly limited, is typically from 8 to 22 .mu.m, and preferably from 10 to 20 .mu.m.

[0082] The golf ball of the invention can be made to conform to the Rules of Golf for play. The inventive ball may be formed to a diameter which is such that the ball does not pass through a ring having an inner diameter of 42.672 mm and is not more than 42.80 mm, and to a weight which is preferably between 45.0 and 45.93 g.

[0083] The following Examples and Comparative Examples are provided to illustrate the invention, and are not intended to limit the scope thereof.

Examples 1 to 6, Comparative Examples 1 to 6

[0084] In Examples 1, 3 and 5 according to the invention and Comparative Examples 1, 2 and 5, a core-forming rubber composition formulated as shown in Table 1 and common to all of the Examples was prepared and then molded and vulcanized to produce a 38.6 mm diameter core. In Examples 2, 4 and 6 according to the invention and Comparative Examples 3, 4 and 6, the golf ball core is produced in the same way as in the foregoing Examples and Comparative Examples.

TABLE-US-00001 TABLE 1 Rubber composition parts by weight cis-1,4-Polybutadiene 100 Zinc acrylate 27 Zinc oxide 4.0 Barium sulfate 16.5 Antioxidant 0.2 Organic peroxide (1) 0.6 Organic peroxide (2) 1.2 Zinc salt of pentachlorothiophenol 0.3 Zinc stearate 1.0

[0085] Details on the above core materials are given below. [0086] cis-1,4-Polybutadiene: Available under the trade name "BR 01" from JSR Corporation [0087] Zinc acrylate: Available from Nippon Shokubai Co., Ltd. [0088] Zinc oxide: Available from Sakai Chemical Co., Ltd. [0089] Barium sulfate: Available from Sakai Chemical Co., Ltd. [0090] Antioxidant: Available under the trade name "Nocrac NS6" from Ouchi Shinko Chemical Industry Co., Ltd. [0091] Organic peroxide (1): Dicumyl peroxide, available under the trade name "Percumyl D" from NOF Corporation [0092] Organic peroxide (2): A mixture of 1,1-di(tert-butylperoxy)cyclohexane and silica, available under the trade name "Perhexa C-40" from NOF Corporation [0093] Zinc stearate: Available from NOF Corporation

[0094] Next, in Examples 1, 3 and 5 and Comparative Examples 1, 2 and 5, an intermediate layer-forming resin material was injection-molded over the 38.6 mm diameter core, thereby producing an intermediate layer-encased sphere having a 1.25 mm thick intermediate layer. In Examples 2, 4 and 6 and Comparative Examples 3, 4 and 6, an intermediate layer-encased sphere having an intermediate layer is produced in the same way as in the foregoing Examples and Comparative Examples. This intermediate layer-forming resin material, which is a resin blend common to all of the Examples, is composed of 50 parts by weight of the sodium neutralization product of an ethylene-unsaturated carboxylic acid copolymer having an acid content of 18 wt % and 50 parts by weight of the zinc neutralization product of an ethylene-unsaturated carboxylic acid copolymer having an acid content of 15 wt %, for a total of 100 parts by weight.

[0095] In Examples 1, 3 and 5 and Comparative Examples 1, 2 and 5, the outermost layer-forming cover material shown in Table 2 below was then injection-molded over the above intermediate layer-encased sphere, thereby producing a 42.7 mm diameter three-piece golf ball having a 0.8 mm thick outermost layer. At this time, dimples common to all of the Examples and Comparative Examples were formed on the surface of the cover. With regard to the cover-forming resin composition, the ingredients were mixed by blending in the amounts shown in Table 2, and the resulting composition was injection-molded at a molding temperature of between 200.degree. C. and 250.degree. C.

[0096] In Examples 2, 4 and 6 and Comparative Examples 3, 4 and 6, three-piece golf balls are produced in the same way as in the foregoing Examples and Comparative Examples.

[0097] Details on the ingredients included in the compositions in Tables 2 are given below. [0098] TPU (1): An ether-type thermoplastic polyurethane available from DIC Covestro Polymer. Ltd. under the trade name "Pandex" (Shore D hardness, 43; rebound resilience, 61%) [0099] TPU (2): An ether-type thermoplastic polyurethane available from DIC Covestro Polymer, Ltd. under the trade name "Pandex" (Shore D hardness, 47; rebound resilience, 54%) [0100] TPU (3): An ether-type thermoplastic polyurethane available from DIC Covestro Polymer, Ltd. under the trade name "Pandex" (Shore D hardness, 35; rebound resilience, 64%) [0101] Polyester Elastomer 1: A thermoplastic polyether-ester elastomer available from DuPont-Toray Co., Ltd. under the trade name "Hytrel 3001" (Shore D hardness, 31; rebound resilience, 79%) [0102] Polyester Elastomer 2: A thermoplastic polyether-ester elastomer available from DuPont-Toray Co., Ltd. under the trade name "Hytrel 4001" (Shore D hardness, 37: rebound resilience, 77%) [0103] Plasticizer: Methyl oleate

Properties of Resin Composition

(1) Rebound Resilience:

[0104] The rebound resiliences of the resin compositions measured in accordance with JIS-K 6255: 2013 are shown in Table 2.

(2) Melt Viscosity:

[0105] The melt viscosities measured with a capillary viscometer at a temperature of 200.degree. C. and a shear rate of 243 sec.sup.-1 in accordance with ISO 11443: 1995 are shown in Table 2.

[0106] The spin performance on approach shots, scuff resistance, feel at impact and moldability of each of the golf balls are evaluated by the following methods. The results are shown in Table 2.

Spin Performance on Approach Shots

[0107] A sand wedge (SW) is mounted on a golf swing robot and the backspin rate of the ball immediately after being struck at a head speed (HS) of 20 m/s is measured with an apparatus for measuring the initial conditions.

Scuff Resistance

[0108] The golf balls are held isothermally at 23.degree. C. and five balls of each type are hit at a head speed of 33 m/s using as the club a pitching wedge (PW) mounted on a swing robot machine. The damage to the ball from the impact is visually rated according to the following criteria.

[0109] Excellent (Exc): Slight scuffing or substantially no apparent scuffing.

[0110] Good: Slight fraying of surface or slight dimple damage.

[0111] NG: Dimples completely obliterated in places.

Feel at Impact

[0112] Sensory evaluations of the feel of the ball when struck with a sand wedge (SW) are carried out by ten skilled amateur golfers on approach shots at 30 to 40 yards, and the feel is rated according to the following criteria.

[0113] Rating Criteria: [0114] Good: Six or more of the ten golfers rate the feel as good [0115] Fair: Four or five of the ten golfers rate the feel as good [0116] NG: Three or fewer of the ten golfers rate the feel as good

Moldability (Mold Releasability)

[0117] Releasability of the ball from the mold following injection molding of the cover is rated according to the following criteria for the balls in each Example. [0118] Good: External defects such as runner stubs and ejector pin marks do not arise during demolding. [0119] Fair: External defects such as runner stubs and ejector pin marks arise during demolding, but molding proceeds without difficulty. [0120] NG: External defects such as runner stubs and ejector pin marks arise during demolding, and molding is impossible.

TABLE-US-00002 [0120] TABLE 2 Example 1 2 3 4 5 6 Cover (A) TPU (1) 100 100 100 100 100 100 Composition (A) TPU (2) (pbw) (A) TPU (3) (B) Polyester elastomer 1 5 10 15 20 30 40 (B) Polyester elastomer 2 Plasticizer Properties Melt viscosity of (B) 0.348 0.348 0.348 0.348 0.348 0.348 (.times.10.sup.4 dPa s) Resin Composition Hardness (Shore D) 42 42 42 41 40 38 Rebound resilience (%) 62 62 63 64 67 70 Evaluation results Spin rate on approach shots (rpm) 6,457 6,488 6,526 6,548 6,609 6,664 Scuff resistance good good good good good good Feel at impact good good good good good good Moldability good good good good good good Comparative Example 1 2 3 4 5 6 Cover (A) TPU (1) 100 100 100 100 Composition (A) TPU (2) 100 (pbw) (A) TPU (3) 100 (B) Polyester elastomer 1 50 10 (B) Polyester elastomer 2 15 Plasticizer 5 Properties Melt viscosity of (B) -- 0.285 0.348 0.348 -- -- (.times.10.sup.4 dPa s) Resin Composition Hardness (Shore D) 43 43 35 47 42 35 Rebound resilience (%) 61 61 74 56 61 64 Evaluation results Spin rate on approach shots (rpm) 6,384 6,367 6,730 6,146 6,370 6,608 Scuff resistance good good NG NG gooc good Feel at impact fair fair good NG fair good Moldability good good NG good good NG

[0121] As demonstrated by the results in Table 2, the golf balls of Comparative Examples 1 to 6 are inferior in the following respects to the golf balls obtained in Examples 1 to 6 according to the present invention.

[0122] In Comparative Example 1, the hardness of the resin composition is higher than the prescribed range, as a result of which the spin rate on approach shots is inadequate.

[0123] In Comparative Example 2, the hardness of the resin composition is higher than the prescribed range, as a result of which the spin rate on approach shots is inadequate.

[0124] In Comparative Example 3, the blending ratio of component (B) included in the resin composition is high, as a result of which a good scuff resistance and moldability are not obtained.

[0125] In Comparative Example 4, the hardness of the resin composition is higher than the prescribed range, as a result of which the spin rate on approach shots is inadequate.

[0126] In Comparative Example 5, the rebound resilience of the resin composition is lower than the prescribed range, as a result of which the spin rate on approach shots is inadequate.

[0127] In Comparative Example 6, component (B) is not included in the resin composition. As a result, although the spin rate is satisfactory, the hardenability is low and the moldability is inadequate.

[0128] Japanese Patent Application No. 2020-096539 is incorporated herein by reference.

[0129] Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.

Claims

1. A golf ball comprising a rubber core of at least one layer and a cover of at least one layer encasing the core, wherein at least one layer of the cover is formed of a resin composition comprised of (A) polyurethane or polyurea, and (B) a thermoplastic polyester elastomer, component (B) being included in a ratio of not more than 45 wt % of the overall amount of the resin composition and the resin composition having a Shore D hardness of 42 or less and a rebound resilience of from 60 to 72%.

2. The golf ball of claim 1, wherein the rebound resilience of the resin composition is from 62 to 70%.

3. The golf ball of claim 1, wherein the polyurethane or polyurea serving as component (A) has a Shore D hardness of 45 or less and a rebound resilience of at least 55%.

4. The golf ball of claim 1, wherein the thermoplastic polyester elastomer serving as component (B) has a Shore D hardness of not more than 35 and a rebound resilience of at least 65%.

5. The golf ball of claim 1, wherein component (B) has a melt viscosity at 200.degree. C. and a shear rate of 243 sec.sup.-1 which is from 0.2.times.10.sup.4 to 1.0.times.10.sup.4 dPas.