US20220401795A1

US20220401795A1 - Golf ball

Info

Publication number: US20220401795A1
Application number: US17/843,259
Authority: US
Inventors: Hirotaka Shinohara; Takuichi Shimizu; Masahiro Yamabe
Original assignee: Bridgestone Sports Co Ltd
Current assignee: Bridgestone Sports Co Ltd
Priority date: 2021-06-21
Filing date: 2022-06-17
Publication date: 2022-12-22
Also published as: JP7718114B2; JP2023001555A

Abstract

In a golf ball having a core, a cover and a coating layer, the coating layer is formed of a urethane coating that includes an organic solvent having a boiling point of 80° C. or less, a silicone-based additive and, as a curing agent, a polyisocyanate which contains an adduct and an isocyanurate of hexamethylene diisocyanate. Although the golf ball includes a silicone-based additive in the outer surface (coating layer) of the ball, it has a good spin performance on approach shots not only when wet but also when normally dry, and is capable of exhibiting both a good water-repelling performance and a good friction performance.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2021-102359 filed in Japan on Jun. 21, 2021, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to golf ball having a core, a cover and a coating layer. The invention relates more particularly to a golf ball in which the cover is formed of a polyurethane resin composition and the coating layer is made of a urethane coating composition.

BACKGROUND ART

A coating composition is often applied to the surface portion of a golf ball in order to protect the ball surface or maintain an attractive appearance. Such golf ball coating compositions are preferably two-part curable polyurethane coatings prepared by mixing together a polyol and a polyisocyanate just prior to use, in part because such coatings are able to withstand large deformation, impacts and friction.
JP-A 2014-524335 describes a golf ball which incorporates a “low-energy” composition as a soft surface coating. This low-energy composition, which lowers the coefficient of friction and is easy to handle during production, is applied in order to, for example, lower the tendency of mud to stick to the ball. A silicone-based additive is described as being used in the low-energy composition.
JP-A 2019-10190 discloses that imparting water repellency to the surface of a golf ball lowers the friction coefficient of the golf ball surface, preventing a drop in the distance traveled by the ball on driver shots when the ball is played in rainy weather. Examples of water-repelling additives mentioned therein include silicone-based additives such as silicone resins, silicone fluids and silicone rubbers.
In addition, JP-A 2021-53367 teaches that by forming the outer surface layer of a material having a contact angle of 90° or more, the surface of a golf ball becomes water-repelling and the friction coefficient of the golf ball surface decreases, making it possible to prevent a drop in the distance traveled by the ball on driver shots when played in rainy weather. Examples of water-repelling additives mentioned therein include silicone-based additives such as silicone resins, silicone fluids and silicone rubbers.
However, with the use of a silicone-based additive in these prior-art golf balls, although a water-repelling performance is obtained and the spin performance when the ball is wet rises, when the ball is dry as is normally the case, the spin rate on approach shots tends to decrease.
For this reason, JP-A 2021-53367 discloses that the outer surface layer of the golf ball is formed of a material which includes a water-repelling additive and hexamethylene diisocyanate (HMDI), and moreover that this HMDI includes an adduct and an isocyanurate thereof. However, even this golf ball is unable to provide a fully satisfactory spin performance on approach shots.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a golf ball which, although it includes a silicone-based additive in the outer surface (coating layer) of the ball, has a good spin performance on approach shots not only when wet but also when normally dry, and can exhibit both a good water-repelling performance and a good friction performance.
We have discovered that, in a urethane coating composition which forms the coating layer normally serving as the outer surface portion of a golf ball, certain desirable effects can be achieved by including as the curing agent a polyisocyanate which includes an adduct and an isocyanurate of hexamethylene diisocyanate (HMDI), and by also selecting, as an organic solvent that can be used in the base resin or the curing agent, a relatively low-boiling solvent. Namely, when the composition is prepared such that the organic solvent in the surface portion of the applied film (coat) evaporates before the silicone ingredient rises to the outer surface during application and curing of the coating composition takes place, achieving both a good water-repelling performance and a good friction performance is possible, giving the ball a good spin performance on approach shots not only when wet, but also when normally dry. In particular, by using a low-resilience urethane resin composition as the golf ball cover material, the controllability on approach shots is improved even more, enabling the object of the invention to be fully achieved.
Accordingly, the present invention provides a golf ball having a core, a cover and a coating layer, wherein the coating layer is formed of a urethane coating that includes an organic solvent having a boiling point of 80° C. or less, a silicone-based additive and, as a curing agent, a polyisocyanate which includes an adduct and an isocyanurate of hexamethylene diisocyanate (HMDI).
In a preferred embodiment of the golf ball of the invention, the organic solvent having a boiling point of 80° C. or less is included in a proportion, based on the overall amount of the coating composition, of at least 20 wt %.
In another preferred embodiment of the inventive golf ball, the mixing ratio by weight (A)/(B) between the isocyanurate (A) and the adduct (B) of hexamethylene diisocyanate is from 85/15 to 15/85.
In yet another preferred embodiment, at least one layer of the cover is formed of a resin composition composed of (I) a polyurethane or a polyurea and (II) aromatic vinyl elastomer, which aromatic vinyl elastomer has a Shore D hardness of 30 or less and a rebound resilience of 30% or less. In this embodiment, the content of component (II) may be from 5 to 20 parts by weight per 100 parts by weight of component (I). The resin composition in the same embodiment may further include (III) a thermoplastic polyester elastomer having a Shore D hardness of 45 or less, a rebound resilience of 74% or less, and a melt viscosity at 200° C. and a shear rate of 243 sec⁻¹of 1.5×10⁴dPa·s or less. In still another preferred embodiment, when the ball is allowed to fall freely onto an impact surface inclined 58° to the horizontal from a height position 3 m above the surface, the amount of sliding by the ball, designated as “Ds” and defined as the perpendicular displacement by the ball from where sliding of the ball on the impact surface begins to where sliding ends, is 2.0 mm or less, and the contact time of the ball after sliding, designated as “Tc” and defined as the time from when sliding of the ball on the impact surface ends until the ball separates from the impact surface, is at least 400 μs.

Advantageous Effects of the Invention

The golf ball of the invention, even when a silicone-based additive is included in the outer surface (coating layer) of the ball, has a good spin rate on approach shots not only when wet but also when normally dry, and is capable of exhibiting both a good water-repelling performance and a good friction performance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The objects, features and advantages of the invention will become more apparent from the following detailed description.
The golf ball of the invention is a golf ball having a core, a cover and a coating layer.
The core may be formed using a known rubber material as the base material. A known base rubber such as natural rubber or 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.
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.
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.
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., between 100° C. and 200° C., preferably between 140° C. and 180° C., for a period of 10 to 40 minutes.
In the golf ball of the invention, the core is encased with a cover of one layer or a plurality of layers. Such a golf ball is exemplified by golf balls having a core and a one-layer cover, and golf balls having a core, an intermediate layer encasing the core and an outermost layer encasing the intermediate layer.
In this invention, the resin material making up at least one layer of the cover is formed of a resin composition containing components (I) and (II) below:

- (I) a polyurethane or a polyurea, and
- (II) an aromatic vinyl elastomer.

(I) Polyurethane or Polyurea

The polyurethane or polyurea is a substance that is capable of serving as the base resin of the above cover material (resin composition). The polyurethane (I-a) and polyurea (I-b) which may be used as this component are described in detail below.

(I-a) Polyurethane

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.
It is preferable to use a polyether polyol as the polymeric polyol.
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.
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.
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. The use of 1,4-butylene glycol is especially preferred.
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.
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.
The method of 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.
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.

(I-b) Polyurea

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

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

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.
The 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.
The 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

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.
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.
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 number-average molecular weight range, an even better resilience and productivity are obtained.
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.
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.
Component (I) has a material hardness on the Shore D hardness scale which, from the standpoint of the spin properties and scuff resistance achieved by the golf ball, is preferably 52 or less, more preferably 50 or less, and even more preferably 48 or less. From the standpoint of the moldability, the lower limit in the material hardness on the Shore D scale is preferably at least 38, and more preferably at least 40.
Component (I) has a rebound resilience which, from the standpoint of enhancing 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.
Component (I) serves as the base resin of the resin composition. To fully impart the scuff resistance of the urethane resin, it accounts for at least 50 wt %, preferably at least 60 wt %, more preferably at least 70 wt %, even more preferably at least 80 wt %, and most preferably at least 90 wt %, of the resin composition.

(II) Aromatic Vinyl Elastomer

Next, the aromatic vinyl elastomer (II) is described.
By including the aromatic vinyl elastomer (II) in, as subsequently described, a small amount at or below a given level, the compatibility with above component (I) serving as the base resin is good, the compatibility with the subsequently described thermoplastic polyester elastomer serving as component (III) is good, and a good scuff resistance and moldability can be maintained in a golf ball and the method of manufacture thereof.
The aromatic vinyl elastomer is a polymer (elastomer) composed of polymer blocks made up primarily of an aromatic vinyl compound, and random copolymer blocks made up of an aromatic vinyl compound and a conjugated diene compound. That is, the aromatic vinyl elastomer generally has, as exemplified by SEBS, blocks made up of an aromatic vinyl compound component that are located at both ends of the polymer and serve as hard segments, and intermediate blocks made up of a conjugated diene compound component that are located between the ends and serve as soft segments. Polymers in which an aromatic vinyl-based component has been randomly introduced into the conjugated diene compound component that makes up the intermediate blocks have also been reported in recent research. The hardness of the aromatic vinyl elastomer generally becomes lower as the content of the aromatic vinyl that forms the hard segments decreases; at the same time, because the amount of the soft segment component increases, the rebound resilience rises. On the other hand, in cases where an aromatic vinyl component is randomly introduced into the soft segments serving as the intermediate blocks, the rebound resilience decreases with little if any rise in the hardness. A similar effect can be obtained by using a conjugated diene compound having a high glass transition temperature (Tg) in place of the aromatic vinyl compound that is randomly introduced into the intermediate blocks. In the present invention, to fully exhibit the working effects described above, it is particularly desirable to use the above polymer (elastomer) in a hydrogenated form.
Examples of the aromatic vinyl compound in the polymer include styrene, α-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylethylene, N,N-dimethyl-p-aminoethylstyrene and N,N-diethyl-p-aminoethylstyrene. These may be used singly or two or more may be used together. Of these aromatic vinyl compounds, styrene is preferred.
Examples of the conjugated diene compound in the polymer include butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene and 1,3-hexadiene. These may be used singly or two or more may be used together. Of these compounds, butadiene and isoprene are preferred. Butadiene is more preferred.
Units originating from the above conjugated diene compounds, such as units originating from butadiene, become ethylene units or butylene units when subjected to hydrogenation. For example, when a styrene-butadiene-styrene block copolymer (SBS) is hydrogenated, it becomes a styrene-ethylene/butylene-styrene block copolymer (SEBS).
As mentioned above, it is preferable for the aromatic vinyl elastomer used as component (II) to be one that has been hydrogenated; i.e., a hydrogenated aromatic vinyl elastomer. The hydrogenated aromatic vinyl elastomer is preferably an elastomer obtained by hydrogenating a polymer composed of polymer blocks made up primarily of an aromatic vinyl compound and random copolymer blocks made up of an aromatic vinyl compound and a conjugated diene compound; and more preferably an elastomer obtained by hydrogenating a polymer composed up of polymer blocks made up primarily of styrene and random copolymer blocks made up of styrene and butadiene. An elastomer obtained by hydrogenating a polymer composed of polymer blocks made up primarily of styrene and random copolymer blocks made up of styrene and butadiene, particularly a polymer having at both ends a polymer block made up primarily of styrene (especially one having at each of the two ends a polymer block consisting entirely of styrene) and having random copolymer blocks in between, is especially preferred. It is thought that a lower hardness and a lower resilience are both achieved by using a copolymer having this structure. In addition, the rate of solidification after molding is rapid and so the degree of tack is low. Also, the compatibility with (I) the polyurethane or polyurea serving as the base resin is excellent, enabling decreases in the physical properties owing to such blending to be held to a minimum.
Illustrative examples of the hydrogenated aromatic vinyl elastomer include styrene-ethylene/butylene-styrene block copolymers (SEBS), styrene-isobutylene-styrene block copolymers (SIBS), styrene-isoprene-styrene block copolymers (SIS), styrene-isobutylene block copolymers (SIB), styrene-ethylene/propylene-styrene block copolymers (SEPS), styrene-ethylene/ethylene/propylene-styrene block copolymers (SEEPS), styrene-butadiene/butylene-styrene block copolymers (SBBS) and styrene-ethylene-propylene block copolymers (SEP).
In the aromatic vinyl elastomer, the proportion of the copolymer accounted for by units originating from the aromatic vinyl compound (i.e., the aromatic vinyl compound content, preferably the styrene content) is preferably at least 30 wt %, more preferably at least 40 wt %, even more preferably at least 50 wt %, and most preferably at least 60 wt %. By thus setting the aromatic vinyl compound content, preferably the styrene content, to a high level, the compatibility with the polyurethane or polyurea serving as component (I) is good and, moreover, the desired hardness and moldability can be prevented from worsening. The content of units from the above aromatic vinyl compound (preferably the styrene content) can be determined by calculation from H′-NMR measurements.
In the aromatic vinyl elastomer, the glass transition temperature (Tg), as indicated by the tan 6 peak temperature obtained by dynamic viscoelasticity measurement with a dynamic mechanical analyzer (DMA), is preferably from −20 to 50° C., more preferably at least 0° C., and even more preferably at least 5° C. The thinking here is that, by having the tan 6 peak temperature be close to the temperature at which the golf ball is normally used, the rebound resilience of the overall resin composition is kept low in the temperature region at which the golf ball is normally used, enabling the desired effects of the invention to be increased.
A commercial product may be used as the aromatic vinyl elastomer serving as component (II). Examples of such commercial products include those available under the trade names S.O.E., Tuftec™ and Tufprene™ from Asahi Kasei Corporation, and those available under the trade name Dicstyrene from DIC Corporation.
Component (II) has a material hardness on the Shore D hardness scale which, to increase the spin rate on approach shots, is 30 or less, preferably 28 or less, and more preferably 26 or less. The lower limit is preferably at least 18, and more preferably at least 20.
Component (II) has a rebound resilience which, to maintain the spin rate of the ball on approach shots and keep the ball rebound on approach shots low so as achieve good controllability, is 30% or less, preferably 25% or less, and more preferably 22% or less. By thus keeping the rebound resilience very low, a small amount of addition will not have an adverse effect on the golf ball properties, enabling a decrease in the ball initial velocity on approach shots to be achieved. To minimize the decrease in rebound and the reduction in distance on shots with a driver, the lower limit of the rebound resilience is preferably at least 15%, and more preferably at least 20%. This rebound resilience is measured in accordance with JIS-K 6255: 2013.
The content of component (II) per 100 parts by weight of component (I) is preferably 30 parts by weight or less, more preferably 20 parts by weight or less, and even more preferably 15 parts by weight or less. The lower limit in this content is preferably at least 5 parts by weight, and more preferably at least 10 parts by weight. When the content of component (II) is too high, the scuff resistance and moldability may worsen. On the other hand, when the content of component (II) is too low, the low hardness and the desired rebound resilience as a cover resin material may not be obtained, and the ball initial velocity-lowering effect on approach shots may diminish.
A thermoplastic polyester elastomer (III) may be additionally included in the resin composition containing above components (I) and (II). Component (III) is described below.

(III) Thermoplastic Polyester Elastomer

The thermoplastic polyester elastomer (III) is a component which imparts at least a given level of resilience to the resin composition and, along with imparting such resilience, enables the ball to maintain a spin rate at or above a given level on approach shots. The thermoplastic polyester elastomer serving as component (III) has a good compatibility with above component (I) serving as the base resin, the compatibility being better than that of, in particular, hitherto used thermoplastic polyester elastomers, and so is able to impart the ball with a good scuff resistance. In addition, including the thermoplastic polyester elastomer as an essential ingredient in the resin composition provides at least a given level of melt viscosity, imparting the resin composition with hardenability 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 (I) 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 owing to an increased cooling time.
The thermoplastic polyester elastomer serving as component (III) is a resin composition made up of (III-a) a polyester block copolymer and (III-b) a rigid resin. Component (III-a) is made up of, in turn, (III-a1) a high-melting crystalline polymer segment and (III-a2) a low-melting polymer segment.
The high-melting crystalline polymer segment (III-a1) within the polyester block copolymer serving as component (III-a) is a polyester made of 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
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 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.
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.
These aromatic dicarboxylic acids, diols and derivatives thereof may be used singly or two or more may be used together.
In particular, the following may be suitably used as component (III-a1): 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.
The low-melting polymer segment serving as component (III-a2) is an aliphatic polyether and/or an aliphatic polyester.
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(E-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(E-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.
Component (III-a) 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.
The proportion of component (III-a) accounted for by component (III-a2) 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 (III-a2) 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 (III-a2) is too high, the rigidity of the resin composition (and the molded body) may be inadequate.
The rigid resin serving as component (III-b) 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 preferably used. More preferably, the use of polybutylene terephthalate and/or polybutylene naphthalate is recommended.
Component (III-a) and component (III-b) are blended in a ratio, expressed as (III-a): (III-b), 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 (III-a) is too low, the low-temperature impact resistance may be inadequate. On the other hand, when the proportion of (III-a) is too high, the rigidity of the composition (and the molded body), as well as the molding processability, may be inadequate.
A commercial product may be used as the thermoplastic polyester elastomer (III). Specific examples include those available as Hytrel® from DuPont-Toray Co. Ltd.
Component (III) 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 43 or less, and even more preferably 41 or less. The lower limit is a Shore D hardness of preferably at least 36, and more preferably at least 38.
Component (III) has a rebound resilience which, to lower the initial velocity on approach shots, is preferably 74% or less, more preferably 73% or less, and even more preferably 72% or less. The lower limit of this rebound resilience is preferably at least 50%, more preferably at least 52%, and even more preferably at least 60%. The rebound resilience is measured in accordance with JIS-K 6255: 2013.
The thermoplastic polyester elastomer serving as component (III) has a melt viscosity of 1.5×10⁴dPa·s or less, preferably 1.45×10⁴dPa·s or less, more preferably 1.0×10⁴dPa·s or less, and even more preferably 0.8×10⁴dPa·s or less. The lower limit is preferably at least 0.4×10⁴dPa·s, and more preferably at least 0.5×10⁴dPa·s. With this melt viscosity, hardenability after molding of the resin composition is imparted and a good moldability (productivity) can be maintained. This melt viscosity indicates the value measured with a Capilograph (a type of capillary rheometer) at a temperature of 200° C. and a shear rate of 243 sec⁻¹in accordance with ISO 11443: 1995.
The amount of component (III) included per 100 parts by weight of component (I) is 20 parts by weight or less, and preferably 15 parts by weight or less. At above this value, a decrease in the scuff resistance may occur. The lower limit in the amount of component (III) included per 100 parts by weight of component (I) is preferably at least 3 parts by weight, and more preferably at least 5 parts by weight.
In addition to the above resin components, other resin materials may be included in the resin composition containing components (I) to (III). The purposes for doing so are, for example, to further improve the flowability of the golf ball resin composition and to enhance such ball properties as the rebound and the durability to cracking.
Specific examples of other resin materials that may be used include 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.
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 enhanced. Moreover, the isocyanate has a plasticizing effect which increases the flowability of the resin composition, enabling the moldability to be improved.
Any isocyanate compound employed in ordinary 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.
The amount of the above isocyanate compounds included per 100 parts by weight of the polyurethane or polyurea serving as the base resin 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 improvement 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.
In addition, optional additives may be suitably included in the above resin composition according to the intended use thereof. Examples of optional additives include inorganic fillers, organic staple fibers, reinforcing agents, crosslinking agents, pigments, dispersants, antioxidants, ultraviolet absorbers and light stabilizers. 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.
The resin composition has a rebound resilience measured in accordance with JIS-K 6255: 2013 which, in order to increase the spin rate on approach shots, is preferably at least 50%, more preferably at least 52%, and even more preferably at least 54%. The upper limit is preferably 72% or less, more preferably 70% or less, and even more preferably 68% or less.
The resin composition has a material hardness on the Shore D hardness scale which, in order to increase the spin rate on approach shots, is preferably 49 or less, more preferably 48 or less, and even more preferably 47 or less. From the standpoint of moldability, the lower limit in the material hardness on the Shore D hardness scale is preferably at least 30, and more preferably at least 35.
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 at the time that the resin composition is to be injection-molded. In addition, when 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 at the time that the resin composition is to be injection-molded.
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 core. In this case, the molding temperature differs according to the type of polyurethane or polyurea (I) serving as the base resin, but is typically in the range of 150 to 270° C.
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.
In cases where an intermediate layer is interposed between the above core and the above cover, it is preferable to employ any of various types of thermoplastic resins used in golf ball cover materials, especially an ionomer resin, as the intermediate layer material. A commercial product may be used as the ionomer resin. In this case, the thickness of the intermediate layer may be set within a range similar to that for the thickness of the cover described above.
In the golf ball of the invention, for reasons having to do with the aerodynamic performance, numerous dimples are provided on the surface of the outermost layer. 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.
In the present invention, a coating layer is formed on the surface of the cover. This coating layer is formed of a urethane coating that includes an organic solvent having a boiling point of 80° C. or less and a silicone-based additive. It is preferable to use as the urethane coating a two-part curable urethane coating, specifically one that includes a base resin composed primarily of a polyol resin and a curing agent composed primarily of a polyisocyanate.
The polyol is not particularly limited, although one, two or more polyester polyols may be suitably used as the polyol. For example, two types of polyester polyol, designated here as Polyester Polyol A (or Component A) and Polyester Polyol B (or Component B), may be used as the base resin. These two types of polyester polyol have differing weight-average molecular weights (Mw), the weight-average molecular weight of
Component A being from 20,000 to 30,000, and the weight-average molecular weight of Component B being from 800 to 1,500. The weight-average molecular weight of Component A is more preferably from 22,000 to 29,000, and even more preferably from 23,000 to 28,000. The weight-average molecular weight of Component B is more preferably from 900 to 1,200, and even more preferably from 1,0000 to 1,100.
The two types of polyester polyol can each be obtained by the polycondensation of a polyol with a polybasic acid. Examples of the polyol include diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, hexylene glycol, dimethylolheptane, polyethylene glycol and polypropylene glycol; and triol, tetraol, and polyols having an alicyclic structure. Examples of the polybasic acid include aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, azelaic acid and dimer acid; aliphatic unsaturated dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid and citraconic acid; aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid and pyromellitic acid; dicarboxylic acids having an alicyclic structure, such as tetrahydrophthalic acid, hexahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and endomethylenetetrahydrophthalic acid; and tris-2-carboxyethylisocyanurate. In particular, a polyester polyol in which a cyclic structure has been introduced onto the resin skeleton may be used as the polyester polyol serving as Component A. Examples include polyester polyols obtained by the polycondensation of a polyol having an alicyclic structure, such as cyclohexane dimethanol, with a polybasic acid; and polyester polyols obtained by the polycondensation of a polyol having an alicyclic structure with a diol or triol and a polybasic acid. A polyester polyol having a hyperbranched structure may be used as the polyester polyol serving as Component B. Examples include polyester polyols having a branched structure, such as NIPPOLAN 800 from Tosoh Corporation.
The weight-average molecular weight (Mw) of the overall base resin composed of the above two types of polyester polyol is preferably from 13,000 to 23,000, and more preferably form 15,000 to 22,000. The number-average molecular weight (Mn) of the overall base resin composed of the above two types of polyester polyol is preferably from 1,100 to 2,000, and more preferably from 1,300 to 1,850. When these average molecular weights (Mw and Mn) fall outside of the above ranges, the wear resistance of the applied film (coat) may decrease. The weight-average molecular weight and the number-average molecular weight are measured values (polystyrene-equivalent values) obtained by gel permeation chromatography (GPC) measurement with differential refractometer detection. The contents of the above Polyester Polyols A and B are not particularly limited, although it is preferable for the Component A content to be from 20 to 30 wt % of the total amount of base resin and the Component B content to be from 2 to 18 wt % of the overall base resin.
In cases where only one type of polyester polyol is used as the polyol, the use of Polyester Polyol A is preferred.
The polyisocyanate includes two types of compound: an isocyanurate and an adduct of hexamethylene diisocyanate. Generally, isocyanate prepolymers are divided into three types of structures: adducts, biurets, and isocyanurates. As used herein, “adduct” refers to an addition product of a diisocyanate and trimethylolpropane, and “isocyanurate” refers to a diisocyanate trimer.
The above hexamethylene diisocyanate also includes modified forms thereof.
Examples of modified hexamethylene diisocyanates include polyester-modified hexamethylene diisocyanate and urethane-modified hexamethylene diisocyanate.
To increase the spin rate of the golf ball on approach shots, the mixing ratio by weight (A)/(B) between the hexamethylene diisocyanate isocyanurate (A) and the hexamethylene diisocyanate adduct (B) is preferably from 85/15 to 15/85, more preferably from 80/20 to 20/80, and even more preferably from 75/25 to 25/75.
Examples of hexamethylene diisocyanate (HMDI) isocyanurates include those available under the tradenames Coronate® 2357 (Tosoh Corporation), Sumidur N3300 (Sumika Covestro Urethane Co., Ltd.), Duranate™ TPA-100 (Asahi Kasei Corporation), Takenate™ D170N and Takenate™ D177N (both from Mitsui Chemicals, Inc.), and Burnock DN-980 (DIC Corporation). These may be used singly or two or more may be used in combination.
Examples of hexamethylene diisocyanate (HMDI) adducts include those available under the trade names Coronate® HL (Tosoh Corporation), Takenate™ D160N (Mitsui Chemicals, Inc.), Duranate™ E402-80B and Duranate™ E405-70B (both from Asahi Kasei Corporation), and Burnock DN-955 and Burnock DN-955S (both from DIC Corporation). These may be used singly or two or more may be used in combination.
The molar ratio between hydroxyl groups (OH groups) on the polyester polyol and isocyanate groups (NCO groups) on the polyisocyanate, expressed as NCO/OH, is preferably at least 0.6, and more preferably at least 0.65. The upper limit is preferably not more than 1.5, more preferably not more than 1.0, and even more preferably not more than 0.9. When this molar ratio is less than 0.6, unreacted hydroxyl groups remain and the performance and water resistance as a golf ball coat may worsen. On the other hand, at above 1.5, the large excess of isocyanate groups may react with moisture to form fragile urea bonds, as a result of which the performance as a golf ball coat may decline.
An amine catalyst or an organometallic catalyst may be used as the curing catalyst (organometallic compound). A metallic soap of aluminum, nickel, zinc, tin or the like that has hitherto been included as a curing agent for two-part curable urethane coatings may be suitably used as this organometallic compound.
In this invention, a silicone-based additive such as a silicone resin, silicone fluid or silicone rubber is included in the coating composition in order to lower the coefficient of friction at the golf ball surface and impart water repellency. A silicone-modified acrylate can be used as the silicone resin. As used herein, “silicone-modified acrylate” refers to a surface conditioner in which an acrylic structure and a silicone structure have been incorporated onto one molecule. Because a polysiloxane chain is attached to the acrylic skeleton, unlike ordinary polyrotaxane-type silicone resins, slip does not readily occur even when the amount of silicone-based additive included is increased, enabling the water-repellency to be enhanced. Examples of silicone-modified acrylates include those available under the trade names BYK-3550 and BYK-3700 (both from BYK-Chemie GmbH). Exemplary silicone fluids include methyl hydrogen silicone fluids and dimethyl silicone fluids.
To lower the coefficient of friction at the golf ball surface and impart sufficient water repellency, the silicone-based additive is included in a proportion relative to the overall coating composition that is preferably at least 0.01 wt %, more preferably at least 0.02 wt %, and even more preferably at least 0.03 wt %. The upper limit is preferably not more than 0.5 wt %. When this upper limit is exceeded, the desired controllability on approach shots may not be obtained.
Known compounding ingredients for coatings may be optionally included in the coating composition. For example, thickeners, ultraviolet absorbers, fluorescent brighteners, slip agents and pigments may be suitably included.
When the coating composition is used, a coating layer can be formed on the ball surface by first preparing the coating composition at the time of application, applying the composition onto the ball surface by an ordinary coating operation and then passing through a drying step. Although not particularly limited, preferred use can be made of spray painting, electrostatic painting or dipping as the method of application.
Various organic solvents may be mixed into the coating composition. Examples of such organic solvents include aromatic solvents such as toluene, xylene and ethylbenzene; ester solvents such as ethyl acetate, butyl acetate, propylene glycol methyl ether acetate and propylene glycol methyl ether propionate; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; ether solvents such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether and dipropylene glycol dimethyl ether; alicyclic hydrocarbon solvents such as cyclohexane, methyl cyclohexane and ethyl cyclohexane; and petroleum hydrocarbon-based solvents such as mineral spirits.
In this invention, an organic solvent having a boiling point of 80° C. or less is included in the coating composition. The purpose is to minimize the silicone component that rises to the surface during coating. Examples of suitable organic solvents having a boiling point of 80° C. or less include hydrocarbon solvents such as n-hexane (68° C.), cyclohexane (80° C.) and benzene (80° C.); ester solvents such as methyl acetate (57° C.) and ethyl acetate (77° C.); and ketone solvents such as acetone (56° C.) and methyl ethyl ketone (79° C.). The numbers within parentheses here indicate boiling points. Of these organic solvents having a boiling point of 80° C. or less, taking into consideration the effects of the solvent on the body and the environment, the use of ester solvents and ketone solvents is preferred.
The above organic solvent having a boiling point of 80° C. or less is included in a proportion, based on the overall amount of the coating composition, which, in order to fully ensure the effect of minimizing the silicone component that rises to the surface during coating, is preferably at least 20 wt %, more preferably at least 30 wt %, and even more preferably at least 40 wt %. The upper limit is preferably 80 wt % or less. Above this upper limit, good leveling of the coating layer surface may not occur and the gloss of the coated surface may decrease.
The drying step may be similar to that used for known two-part curable urethane coatings, with the drying temperature typically being set to at least about 40° C., especially between 40° C. and 60° C., and the drying time typically being set to from 20 to 90 minutes, especially from 40 to 50 minutes.
The thickness of the coating layer, although not particularly limited, is preferably from 3 to 50 μm, and more preferably from 5 to 20 μm.
In the golf ball of the invention having the above coating layer, the ball has a deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) of preferably at least 2.0 mm, more preferably at least 2.3 mm, and even more preferably at least 2.5 mm. The upper limit is preferably 3.3 mm or less, and more preferably 3.0 mm or less. When this value is too small, there is a possibility that the spin rate on shots with a driver will rise, resulting in a decreased distance. On the other hand, when this value is too large, the spin rate on approach shots may decrease, resulting in lower controllability.
Also, in the golf ball of the invention having the above coating layer, when the ball is allowed to fall freely onto an impact surface inclined 58° to the horizontal from a height position 3 m above the surface, the amount of sliding by the ball, designated as “Ds” and defined as the perpendicular displacement by the ball from where sliding of the ball on the impact surface begins to where sliding ends, is 2.0 mm or less, more preferably 1.5 mm or less, and even more preferably 1.2 mm or less. Within this range in values, the golfer has a sensation of the ball “clinging” to the clubface, giving the golf ball a good feel at impact. The sensation of the ball “clinging” to the clubface presumably refers to the phenomenon where, when the golfer hits a golf ball and the face of the golf club and the ball collide, the golf ball does not slide much along the surface of the clubface. The numerical value of the above-described sliding amount (Ds) is used as the metric for this sensory evaluation. For a more thorough explanation, reference can be made to paragraph [0043] and FIG. 3 of JP-A 2019-217078, a prior-art disclosure filed by the present applicant.
Moreover, in this golf ball, the contact time of the ball after sliding, designated as “Tc” and defined as the time from when sliding of the ball on the impact surface ends until the ball separates from the impact surface, is at least 400 μs, more preferably at least 500 μs, and even more preferably at least 540 μs. Within this range in values, the golfer has a sensation of the ball “riding” on the clubface, giving the golf ball a good feel at impact. The sensation of the ball “riding” on the clubface presumably refers to the phenomenon where, when the golfer hits a golf ball and the face of the golf club and the ball collide, the golf ball comes into prolonged contact with the clubface. The numerical value of the above-described sliding amount (Tc) is used as the metric for this sensory evaluation. For a more thorough explanation, reference can be made to paragraph [0048] and FIGS. 3 and 4 of JP-A 2019-217078, a prior-art disclosure filed by the present applicant. The above contact time after sliding (Tc) corresponds to the “second contact time” in JP-A 2019-217078.
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.

EXAMPLES

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

Examples 1 to 8, Comparative Examples 1 to 6

A 38.6 mm core is formed in each Example. The core formulation, which is common to all the Examples of the invention and the Comparative Examples, includes as the base rubber 20 parts by weight of Polybutadiene A (available under the trade name BR51 from JSR Corporation) and 80 parts by weight of Polybutadiene B (available under the trade name BR 730 from JSR Corporation), 29.5 parts by weight of zinc acrylate (Wako Pure Chemical Industries, Ltd.), 0.6 part by weight of dicumyl peroxide (available under the trade name Percumyl D from NOF Corporation) as an organic peroxide, 0.1 part by weight of 2,2-methylenebis(4-methyl-6-butylphenol) (available under the trade name Nocrac NS-6 from Ouchi Shinko Chemical Industry Co., Ltd.) as an antioxidant, 19.3 parts by weight of zinc oxide (available under the trade name Zinc Oxide Grade 3 from Sakai Chemical Co., Ltd.) and 0.3 part by weight of the zinc salt of pentachlorothiophenol (Wako Pure Chemical Industries, Ltd.) as an organosulfur compound. Vulcanization of the rubber composition is carried out at a temperature of 155° C. for a period of 15 minutes. The specific gravity of the composition is 1.138.

Formation of the Intermediate Layer

Next, an intermediate layer-forming resin material is injection-molded over the 38.6 mm diameter core, thereby producing an intermediate layer-encased sphere having a 1.25 mm thick intermediate layer. The resin material in the intermediate layer, which is common to all of the Examples and Comparative Examples, includes Himilan 1605, Himilan 1557 and Himilan 1706 (all trade names for ionomer resins available from Dow-Mitsui Polychemicals Co., Ltd.) in a weight ratio of 50:12:38. In addition, 1.1 parts by weight of trimethylolpropane (Tokyo Chemical Industry Co., Ltd.) is included per 100 parts by weight of the total amount of this ionomer resin.,

Formation of Cover (Outermost Layer)

Next, using a different injection mold, the cover (outermost layer)-forming resin material shown in Table 1 below is injection-molded over the above intermediate layer-encased sphere, thereby producing a 42.7 mm diameter three-piece golf ball having an outermost layer with a thickness of 0.8 mm
Details on the ingredients included in the cover materials in Table 1 are as follows.

- 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%)
- 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%)
- S.O.E. 51611: A hydrogenated aromatic vinyl-based elastomer available from Asahi Kasei Corporation (styrene content, 60 wt %; Shore D hardness, 23; rebound resilience, 20%)
- Hytrel 2401: A thermoplastic polyether ester elastomer available from DuPont-Toray Co., Ltd. (Shore D hardness, 40; rebound resilience, 67%; melt viscosity, 5,700 dPa·s)

Material Hardness of Cover

The resin material is molded into sheets having a thickness of 2 mm and left to stand for two weeks at a temperature of 23±2° C. At the time of measurement, three sheets are stacked together and the Shore D hardness is measured with a Shore D durometer in accordance with ASTM D2240. The P2 Automatic Rubber Hardness Tester from Kobunshi Keiki Co., Ltd. with a Shore D durometer mounted thereon is used for measuring the hardness. The maximum value is read off as the hardness value.

Formation of Coating Layer (Coat)

Next, in each Example, the coating composition made up of the base resins and curing agents in the coating formulation shown in Table 1 below is applied with an air spray gun onto the surface of the cover (outermost layer) having numerous dimples formed thereon, producing a golf ball with a 15 μm thick coating layer (coat) on top.

Base Resin

A polyester polyol synthesized by the following method is used as the polyol of the base resin.
A reactor equipped with a reflux condenser, a dropping funnel, a gas inlet and a thermometer is charged with 140 parts by weight of trimethylolpropane, 95 parts by weight of ethylene glycol, 157 parts by weight of adipic acid and 58 parts by weight of 1,4-cyclohexanedimethanol, following which the reaction is effected by raising the temperature to between 200 and 240° C. under stirring and heating for 5 hours. This yields a polyester polyol having an acid value of 4, a hydroxyl value of 170 and a weight-average molecular weight (Mw) of 28,000.
Aside from Comparative Examples 3, 5 and 6, ethyl acetate (boiling point, 77° C.) is used in the specific amount shown in Table 1 as the organic solvent included in the base resin. In Comparative Examples 3, 5 and 6, butyl acetate (boiling point, 126° C.) is used in the specific amount shown in Table 1. In Examples 1 to 8 and Comparative Examples 3, 5 and 6, a silicone-modified acrylate (available under the trade name BYK-3700 from BYK-Chemie GmbH) is included in the specific amount shown in Table 1 as the silicone-based additive in the base resin.

Curing Agent

An isocyanate of hexamethylene diisocyanate (HMDI) available under the product name Duranate™ TPA-100 from Asahi Kasei Corporation (NCO content, 23.1%; nonvolatiles, 100%) is used as the Curing Agent A isocyanate. An adduct of hexamethylene diisocyanate (HMDI) available under the product name Duranate™ E402-80B from Asahi Kasei Corporation (NCO content, 7.6%; nonvolatiles, 80%) is used as the Curing Agent B isocyanate.
In all of the Examples, butyl acetate (boiling point, 126° C.) is used in the specific amount shown in Table 1 as the organic solvent in the curing agent.
The ball deformation, static coefficient of friction, feel at impact and controllability on approach shots of the golf balls obtained in the respective Examples are evaluated. Those results are shown in Table 1.

Ball Deformation

The ball is placed on a hard plate and the amount of deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is measured. The deflection is a value measured after holding the ball isothermally at a temperature of 23.9° C.

Static Coefficient of Friction

The golf ball is mounted on a jig and the static coefficient of friction of the golf ball when pulled under the following conditions is measured.
Measurement Conditions

- Normal force: 3.5N
- Face plate: stainless steel
- Pull rate: 50 mm/min
- Temperature: 23° C.

Feel at Impact

A sand wedge (X-WEDGE H8101, from Bridgestone Sports Co., Ltd.; 58°) is mounted on a golf swing robot and the feel at impact of a golf ball hit at a head speed of 20 m/s is evaluated using the amount of sliding by the ball Ds (mm) when struck and the contact time after sliding Tc (μs) as the metrics.

Test Method

An evaluation system like that in FIG. 1 of JP-A 2019-217078 is furnished. That is, as shown in FIG. 1 of this published application, the evaluation system has a high-speed camera, an evaluation apparatus and a collision member.

- Step 1: The golf ball is allowed to fall freely from a height of 3 m.
- Step 2: The golf ball is made to strike an impact surface inclined 58° to the horizontal.
- Step 3: The state of the golf ball on the impact surface is observed with a high-speed camera, and the amount of sliding Ds (mm) by the golf ball and the contact time after sliding Tc (p,$) are analyzed and computed.

Evaluation of “Clinging” Sensation

- Excellent (Exc): Amount of sliding (Ds) is 1.30 mm or less
- Good: Amount of sliding (Ds) is in the range of 1.31 to 2.00 mm
- NG: Amount of sliding (Ds) is 2.01 mm or more

Evaluation of “Riding” Sensation

- Excellent (Exc): Amount of contact after sliding (Tc) is at least 540 μs
- Good: Amount of contact after sliding (Tc) is from 500 to 539 μs
- NG: Amount of contact after sliding (Tc) is 499 μs or less

Controllability on Approach Shots (under normal dry conditions)

A sand wedge (X-WEDGE H8101, from Bridgestone Sports Co., Ltd.; 58°) is mounted on a golf swing robot and the initial velocity (m/s) and backspin rate (rpm) of a golf ball hit at a head speed of 20 m/s are measured. Determinations of the controllability are carried out by sensory evaluations. The clubs used are the respective golfers' own sand wedges (SW). The golfers use the following criteria to evaluate the controllability on actual shots.

- Excellent (Exc): Controllability is excellent.
- Good: Controllability is good.
- NG: Controllability is poor.

A determination as to whether the controllability is good or not is based not only on the ball spin rate, but also on the length of the contact time between the ball and the clubface owing to the initial velocity of the ball.

Controllability on Approach Shots (under Wet Conditions)

In addition, to ascertain the water-repelling effects, the spin rate of the golf ball on approach shots when the ball is wet is evaluated under the following conditions.
The golf ball is immersed in a water-filled bucket, the backspin rate (rpm) of the ball when struck while drops of water still adhere to the ball is measured, and a determination is made based on the following criteria.

- Excellent (Exc): 5,750 rpm or more
- Good: from 5,000 to 5,749 rpm
- NG: 4,999 or less

	TABLE 1

	Example

	1	2	3	4	5	6	7	8

Core	common to all Examples
Intermediate layer	common to all Examples

Cover	Component	TPU 1	100	100	100	100	100	100	100
formulation	(I)	TPU 2								100
(pbw)	Component	S.O.E. S1611					5	10	15	5
	(II)
	Component	Hytrel 2401	14.5	14.5	14.5	14.5	14.5	14.5	14.5	14.5
	(III)

Material hardness of cover	43	43	43	43	43	43	43	47
(Shore D)

Coating	Base resin	Polyol	30	30	30	30	30	30	30	30
formulation		Butyl acetate
(pbw)		(solvent)
		Ethyl acetate	70	70	70	70	70	70	70	70
		(solvent)
		Silicone-based	0.05	0.05	0.05	0.05	0.05	0.05	0.05	0.05
		additive
	Curing agent	Curing Agent A	18	16	10	4	16	16	16	16
		(isocyanurate)
		Curing Agent B	2	4	10	16	4	4	4	4
		(adduct)
		Butyl acetate	30	30	30	30	30	30	30	30
		(solvent)

Ratio of solvent	47	47	47	47	47	47	47	47
that boils at 80° C. or less (%)

Ball	Deformation (mm)	2.64	2.64	2.64	2.64	2.64	2.64	2.64	2.56
	Static coefficient of friction	0.40	0.46	0.50	0.53	0.46	0.46	0.46	0.46

Evaluations	Feel at impact	Amount of	1.43	1.35	1.30	1.29	1.13	1.35	1.52	2.05
		sliding Ds (mm)
		“Clinging”	good	good	Exc	Exc	Exc	good	good	NG
		sensation
		Contact time Tc	507	533	543	548	562	548	530	406
		(μs)
		“Riding”	good	good	Exc	Exc	Exc	Exc	good	NG
		sensation
	Controllability	Initial velocity	16.11	16.12	16.12	16.14	16.07	16.06	16.05	15.99
	on approach	(m/s)
	shots	Spin rate (rpm)	6,803	6,835	6,843	6,893	6,860	6,842	6,852	6,775
		Rating	good	good	good	Exc	Exc	Exc	Exc	good
		Wet spin rate	5,580	6,024	5,863	6,320	5,790	5,830	5,840	6,030
		(rpm)
		Rating	good	Exc	Exc	Exc	Exc	Exc	Exc	Exc

Comparative Example

	1	2	3	4	5	6

	Core	common to all Examples
	Intermediate layer	common to all Examples

Cover	Component	TPU 1	100	100	100	100	100	100
formulation	(I)	TPU 2
(pbw)	Component	S.O.E. S1611				5	5	15
	(II)
	Component	Hytrel 2401	14.5	14.5	14.5	14.5	14.5	14.5
	(III)

	Material hardness of cover	43	43	43	43	43	43
	(Shore D)

Coating	Base resin	Polyol	30	30	30	30	30	30
formulation		Butyl acetate			70		70	70
(pbw)		(solvent)
		Ethyl acetate	70	70		70
		(solvent)
		Silicone-based			0.05		0.05	0.05
		additive
	Curing agent	Curing Agent A	20	16	16	16	16	16
		(isocyanurate)
		Curing Agent B		4	4	4	4	4
		(adduct)
		Butyl acetate	30	30	30	30	30	30
		(solvent)

	Ratio of solvent	47	47	0	47	0	0
	that boils at 80° C. or less (%)

	Ball	Deformation (mm)	2.64	2.64	2.64	2.64	2.64	2.64
		Static coefficient of friction	0.40	0.52	0.35	0.52	0.35	0.35

Evaluations	Feel at impact	Amount of	1.44	1.35	1.53	0.96	1.68	1.62
		sliding Ds (mm)
		“Clinging”	good	good	good	Exc	good	good
		sensation
		Contact time Tc	467	510	453	594	488	503
		(μs)
		“Riding”	NG	good	NG	Exc	NG	good
		sensation
	Controllability	Initial velocity	16.12	16.13	16.03	16.09	16.07	16.1
	on approach	(m/s)
	shots	Spin rate (rpm)	6,834	6,860	6,699	6,810	6,669	6,611
		Rating	good	Exc	NG	Exc	NG	NG
		Wet spin rate	2,950	3,154	5,730	3,047	6,240	6,020
		(rpm)
		Rating	NG	NG	good	NG	Exc	Exc

Referring to Table 1, in Examples 1 to 4, the coating includes a silicone-based additive, the curing agent includes an adduct of HMDI, and the results indicate a good controllability on approach shots (both under normal dry conditions and when wet). In Examples 5 to 7, the cover includes a urethane, a polyester and an aromatic vinyl elastomer, and the results indicate a good controllability compared with Example 2.
By contrast, in Comparative Example 1, because the coating does not include a silicone-based additive and the curing agent does not include an adduct of HMDI, the spin rate of the ball when wet is low.
In Comparative Example 2, because the coating does not include a silicone-based additive, the spin rate of the ball when wet is low.
In Comparative Example 3, because the coating does not include an organic solvent having a boiling point of 80° C. or less, the static coefficient of friction is small and the spin rate is low.
In Comparative Example 4, because the coating does not include a silicone-based additive, the spin rate of the ball when wet is low.
In Comparative Example 5, because the coating does not include an organic solvent having a boiling point of 80° C. or less, the static coefficient of friction is small and the spin rate is low.
In Comparative Example 6, because the coating does not include an organic solvent having a boiling point of 80° C. or less, the static coefficient of friction is small and the spin rate is low.

Japanese Patent Application No. 2021-102359 is incorporated herein by reference.

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 core, a cover and a coating layer, wherein the coating layer is formed of a urethane coating comprised of an organic solvent having a boiling point of 80° C. or less, a silicone-based additive and, as a curing agent, a polyisocyanate which includes an adduct and an isocyanurate of hexamethylene diisocyanate (HMDI).

2. The golf ball of claim 1, wherein the organic solvent having a boiling point of 80° C. or less is included in a proportion, based on the overall amount of the coating composition, of at least 20 wt %.

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

4. The golf ball of claim 1, wherein at least one layer of the cover is formed of a resin composition comprising:

(I) a polyurethane or a polyurea, and

(II) an aromatic vinyl elastomer, which aromatic vinyl elastomer has a Shore D hardness of 30 or less and a rebound resilience of 30% or less.

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

6. The golf ball of claim 4, wherein the resin composition further comprises (III) a thermoplastic polyester elastomer having a Shore D hardness of 45 or less, a rebound resilience of 74% or less, and a melt viscosity at 200° C. and a shear rate of 243 sec⁻¹of 1.5×10⁴dPa·s or less.

7. The golf ball of claim 1 wherein, when the ball is allowed to fall freely onto an impact surface inclined 58° to the horizontal from a height position 3 m above the surface, the amount of sliding by the ball, designated as “Ds” and defined as the perpendicular displacement by the ball from where sliding of the ball on the impact surface begins to where sliding ends, is 2.0 mm or less, and the contact time of the ball after sliding, designated as “Tc” and defined as the time from when sliding of the ball on the impact surface ends until the ball separates from the impact surface, is at least 400 μs.