Golf Ball

This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2024-097477 filed in Japan on Jun. 17, 2024, the entire contents of which are hereby incorporated by reference.

The present invention relates to a golf ball whose surface is coated with a two-part curable urethane coating. More specifically, the invention relates to a golf ball which exhibits a gloss-free appearance and has an excellent spin performance on approach shots.

Golf balls are often coated on the surface with a coating composition so as to protect the ball surface and maintain a good aesthetic appearance. Two-part curable polyurethane coatings obtained by mixing together a polyol and a polyisocyanate just prior to use are generally employed as such golf ball coating compositions because of their ability to withstand large deformation, impact and friction.

In recent years, many matte golf balls, i.e., balls to which a matte coating has been applied, have appeared on the market on account of their high-end feel and visibility. A matte coating is a coating which, by formulating the coating composition with a delustering agent and conferring texture to the golf ball surface, imparts a matte appearance. For example, JP-A 2006-051357 describes a golf ball in which the coating composition contains silica particles having an average particle size of 200 nm or less. JP-A 2020-000624 describes a golf ball which has a delustering particle-containing coating layer on the surface, which coating layer has an average surface roughness Ra of from 0.5 to 1.0. JP-A 2023-001696 describes a golf ball on which a delusterant-containing coating layer is formed, the average surface roughness Ra of the coating layer is set to 0.35 or more, and the static coefficient of friction at the ball surface is set to 0.20 or more.

These prior-art golf balls, by having a coating layer which contains a delusterant such as silica, do exhibit a gloss-free appearance, but their spin rate on approach shots leaves something to be desired. That is, in general, a coating layer formed using a delusterant-containing coating composition, as compared with a coating layer formed with a coating composition that does not contain delusterant, increases the roughness of the golf ball surface, making the ball surface more slippery. As a result, the backspin rate of the ball on approach shots greatly decreases and a sufficient amount of spin cannot be obtained.

It is therefore an object of the present invention to provide a golf ball which exhibits a gloss-free appearance and also has an excellent spin performance on approach shots.

As a result of intensive investigations, we have discovered that, in a golf ball having a coating of one or more layer on a golf ball surface with numerous dimples thereon, by forming at least one coating layer of a two-part curable urethane coating composition which has a polyol component and a polyisocyanate component and contains silica and polyurethane as delusterants, and by adjusting the delusterant content within a range of 8 to 30 parts by weight per 100 parts by weight of coating solids, the golf ball exhibits a matte appearance that is free of gloss and the spin performance of the ball on approach shots can be improved.

Accordingly, the invention provides a golf ball having a coating of one or more layer on a golf ball surface with numerous dimples thereon, wherein at least one coating layer is formed of a two-part curable urethane coating composition which has a polyol component and a polyisocyanate component and contains silica and polyurethane as delusterants, the delusterant content being from 8 to 30 parts by weight per 100 parts by weight of coating solids.

In a preferred embodiment of the golf ball of the invention, the delusterant is a mixture of silica particles and polyurethane particles.

In another preferred embodiment of the inventive golf ball, the silica is included in an amount of from 0.6 to 15 parts by weight per 100 parts by weight of coating solids.

In yet another preferred embodiment, the polyurethane is included in an amount of from 1 to 25 parts by weight per 100 parts by weight of coating solids.

In still another preferred embodiment, the delusterant has an average particle size as determined by the BET method of from 0.1 to 20 μm.

In a further preferred embodiment, the polyol component is an acrylic polyol or a polyester polyol.

In a yet further preferred embodiment, the two-part curable urethane paint composition contains a polyol component made up primarily of a hydroxyl group-containing polyester polyol having an alicyclic structure on the molecule, and a non-yellowing polyisocyanate.

In a still further preferred embodiment, the two-part curable urethane paint composition contains a polyol component made up primarily of an acrylic polyol, and an isocyanate component made up primarily of an elastically modified polyisocyanate.

In another preferred embodiment, the golf ball has a surface energy of from 30 to 40 mN/m.

In still another preferred embodiment, the golf ball has a static coefficient of friction that is from 0.26 to 0.40.

The golf ball of the invention exhibits a matte appearance that is free of gloss and also has an improved spin performance on approach shots.

The objects, features and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the appended diagram.

The golf ball of the invention has a coating layer obtained by applying a coating composition to a ball surface having numerous dimples thereon. The role of this coating layer is to protect the overall ball and to impart the ball surface with glossiness and an aesthetic appearance. Specifically, a two-part curable urethane coating composition having a polyol component and a polyisocyanate component is used, with the use of a two-part curable urethane coating composition containing a polyol component made up primarily of a hydroxyl group-containing polyester polyol having an alicyclic structure on the molecule and a non-yellowing polyisocyanate or a two-part curable urethane coating composition containing a polyol component made up primarily of an acrylic polyol and an isocyanate component made up primarily of an elastically modified polyisocyanate being more preferred.

[Two-Part Curable Urethane Coating Having Polyol Component Made Up Primarily of Hydroxyl Group-Containing Polyester Polyol Having Alicyclic Structure on Molecule, and Non-Yellowing Polyisocyanate]

As used herein, “hydroxyl group-containing polyester polyol having an alicyclic structure on the molecule” refers to a polyester polyol obtained by reacting a polyhydric alcohol component having an alicyclic structure on the molecule with a polybasic acid component having an alicyclic structure on the molecule.

Preferred examples of the polyhydric alcohol component having an alicyclic structure on the molecule include diols such as 1,3-cyclohexanedimethanol and 1,4-cyclohexanedimethanol, and mixtures of these. Preferred examples of the polybasic acid component having an alicyclic structure on the molecule include dicarboxylic acids such as tetrahydrophthalic acid, hexahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid, acid anhydrides of these, acid halides of these, and mixtures thereof.

The foregoing polyhydric alcohol component and polybasic acid component having an alicyclic structure on the molecule may account for some or all of the ingredients making up the hydroxyl group-containing polyester. The polyhydric alcohol component having an alicyclic structure on the molecule accounts for preferably at least 3 wt %, and more preferably from 5 to 40 wt %, of the overall polyhydric alcohol component. The polybasic acid component having an alicyclic structure on the molecule accounts for preferably at least 5 wt %, and more preferably from 10 to 55 wt %, of the overall polybasic acid component. When the contents of the alicyclic structure-containing polyhydric alcohol component and the polybasic acid component fall outside of the above ranges, the durability of the coated golf ball to sand abrasion and grass stains is inadequate.

Examples of polyhydric alcohol components which do not have an alicyclic structure on the molecule that may be used together with the above polyhydric alcohol component having an alicyclic structure on the molecule include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, 1,6-hexanediol, neopentyl glycol, 3,3-dimethylolheptane, polyethylene glycol, polypropylene glycol, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, and mixtures thereof.

Examples of polybasic acid components which do not have an alicyclic structure on the molecule that may be used together with the above polybasic acid component having an alicyclic structure on the molecule include dicarboxylic acids such as adipic acid, sebacic acid, dimer acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid and itaconic acid, acid anhydrides of these, acid halides of these, and mixtures thereof.

As mentioned above, the hydroxyl group-containing polyester is a compound that can be obtained by subjecting the above polyhydric alcohol component and polybasic acid component to an esterification reaction. The hydroxyl group-containing polyester thus obtained is preferably one having a weight-average molecular weight as determined by gel permeation chromatography of from 3,000 to 35,000 and a hydroxyl value of from 50 to 300, especially from 150 to 250. When the weight-average molecular weight and hydroxyl value of the hydroxyl group-containing polyester fall outside of the above ranges, the durability of the coated golf ball to sand abrasion and grass stains is inadequate.

Preferred examples of the non-yellowing polyisocyanate include adducts, biurets and isocyanurates of, for example, hexamethylene diisocyanate, isophorone diisocyanate and hydrogenated xylylene diisocyanate, and mixtures of these.

The above hydroxyl group-containing polyester and non-yellowing polyisocyanate are preferably used in such manner that the molar ratio of isocyanate groups on the non-yellowing polyisocyanate to hydroxyl groups on the hydroxyl group-containing polyester falls within the range of 0.8 to 1.3.

As used herein, “acrylic polyol” refers to a compound having an acrylic polymer backbone and polyester and/or polyether side chains.

The acrylic polyol is not particularly limited as to the structure thereof and may have any structure so long as the basic skeleton includes acrylic recurring units. The acrylic monomer making up the backbone may be of one type only or may be of two or more types. Alternatively, the acrylic polymer may be one that has been copolymerized from an acrylic monomer and other monomers that are copolymerizable therewith.

The specific structure of the acrylic polyol is exemplified by (i) structures obtained by adding a lactone or alkylene oxide side chain-forming component to an acrylic polymer backbone; (ii) structures obtained by adding a novel monomer and an initiator in the presence of an acrylic polymer, and grafting side chains onto the acrylic polymer backbone by monomer polymerization; (iii) structures obtained by homopolymerizing an acrylic monomer to which a polyester has been added (abbreviated below as “polyester-containing acrylic monomer”) and/or an acrylic monomer to which a polyether has been added (abbreviated below as “polyether-containing acrylic monomer”); and (iv) structures obtained by copolymerizing a polyester-containing acrylic monomer and/or a polyether-containing acrylic monomer with another acrylic monomer.

The elasticity-modified polyisocyanate is obtained by using as the monomer a diisocyanate such as the above-mentioned tolylene diisocyanate (TDI), xylene diisocyanate (XDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI) and subjecting this to a urethane-forming reaction with an active hydrogen-containing compound having elasticity to give an NCO-terminated prepolymer. The conditions for the urethane-forming reaction are not particularly limited and may be in line with conventional conditions.

Examples of the active hydrogen-containing compound having elasticity that is used for modifying the elasticity of the above polyisocyanate include polyester polyols, polycarbonate polyols, polyether polyols, polyolefin polyols, animal and plant polyols, and copolyols of these. It is especially preferable to include a modified polyisocyanate that has been modified with at least one type of polyol selected from the group consisting of polyester polyols, polyether polyols, polycarbonate polyols, polyolefin polyols, animal and plant polyols and copolymers of these. To make the resulting coating layer more elastic and further improve the impact resistance, it is preferable for these polyols to have a glass transition temperature of 0° C. or less. These polyols may be used singly or two or more may be used in admixture.

In this invention, silica and polyurethane are included together as delusterants in the coating composition. Silica is known to be normally highly effective as a delusterant. However, because silica is very hard, there is a tendency for the static coefficient of friction at the golf ball surface to decrease, as a result of which the golf ball may have a lower spin rate on approach shots. By using urethane, which is relatively soft, in this invention as a delusterant together with silica, there is less of a decline in the static coefficient of friction at the golf ball surface and so the golf ball maintains a high spin rate on approach shots. Moreover, including urethane as a delusterant results in a good compatibility with the urethane coating. In addition, although the silica must be included in at least a given amount to obtain a delustering effect, by using urethane together as a delusterant in this invention, the silica content can be set to a relatively low level. Also, silica generally has a poor dispersibility in coating compositions and tends to form lumps, and so stirring must be carried out for a long time. However, in this invention, by including urethane, the silica content can be set to a relatively low level, which reduces the amount of stirring work required and improves the silica dispersibility.

Examples of silicas that may be used include, of the family of products available under the trade name Nipsil from Tosoh Corporation: SS-50B, SS-170X, SS-178B and SS-50A. This invention is not limited to the use of hydrophilic surface-treated silica as the delusterant; silica that has not been subjected to hydrophilic surface treatment may also be used. Examples of the latter type of silica include, of the family of products available under the trade name Nipsil from Tosoh Corporation: E-200A, E-220A, K-500, E-1009, E-1011, E-1030, E-150J, E-170, E-200 and E-220. When there is a need to use a highly dispersible delusterant, a silica that has not been subjected to hydrophilic surface treatment is preferred. A hydrophilic surface-treated silica and a silica that has not been subjected to hydrophilic surface treatment may be used together.

The silica content per 100 parts by weight of the coating composition solids (resin component) is preferably 0.6 part by weight or more, more preferably 1 part by weight or more, and even more preferably 3 parts by weight or more. The upper limit is preferably not more than 15 parts by weight, more preferably not more than 11 parts by weight, and even more preferably not more than 8 parts by weight. When the silica content is too high, the spin rate of the ball on approach shots may decrease. On the other hand, when the silica content is too low, a sufficient delustering effect cannot be obtained.

The coating composition in this invention includes polyurethane together with the silica. A polyurethane in the form of particles is preferably used as the polyurethane. The polyurethane particles are exemplified by thermoplastic polyurethane particles and three-dimensionally crosslinked polyurethane particles, such as the polyurethane particles described in JP-A 2017-78149. The polyurethane particles have an average particle size based on the BET method of preferably at least 0.1 μm, and more preferably at least 0.2 μm. The upper limit is preferably not more than 30 μm, and more preferably not more than 10 μm. By adding such polyurethane particles to the coating composition, sagging of the coating can be suppressed and the film thickness edge ratio between the film thicknesses at center and edge portions of the dimples can be improved.

The polyurethane particle content per 100 parts by weight of coating composition solids is preferably at least 1 part by weight, more preferably at least 2 parts by weight, and even more preferably at least 5 parts by weight. The upper limit is preferably not more than 25 parts by weight, more preferably not more than 20 parts by weight, and even more preferably not more than 15 parts by weight. At a low polyurethane particle content, a sufficient delustering effect is not obtained; at a high content, there is a tendency for the viscosity of the coating composition to rise and the coating workability to worsen, or for the surface of the coating film to become rough and the ball appearance to worsen.

In the practice of the invention, silica and polyurethane are included as the delusterant in the coating composition. Use can be made of a mixture of silica particles and polyurethane particles, or of a composite prepared by combining polyurethane and silica.

The delusterant has an average particle size based on the BET method of preferably at least 1 μm, and more preferably at least 2 μm. The upper limit is preferably not more than 20 μm, and more preferably not more than 10 μm. When this value is greater than 20 μm, the ball surface becomes coarse, which may adversely affect the spin performance by lowering the spin rate. On the other hand, when this value is smaller than 1 μm, the delustering effect may decrease.

The delusterant content is from 8 to 30 parts by weight per 100 parts by weight of the coating solids. When this content is too low, a sufficient delustering effect is not obtained; when the content is too high, the viscosity of the coating composition tends to rise and coating tends to be more difficult to carry out. The delusterant content is preferably 10 parts by weight or more, more preferably 12 parts by weight or more; the upper limit is preferably not more than 25 parts by weight, and more preferably not more than 22 parts by weight.

As noted above, the coating composition uses an acrylic polyol or a polyester polyol as the base resin and uses a polyisocyanate as the curing agent. Various organic solvents may be admixed depending on the coating conditions. Examples of organic solvents that may be used 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, methylcyclohexane and ethylcyclohexane; and petroleum hydrocarbon-based solvents such as mineral spirits.

Known compounding ingredients may be optionally added to the coating composition. Specifically, suitable amounts of, for example, thickeners, ultraviolet absorbers, fluorescent whiteners, slip agents and pigments may be added.

To suppress sagging of the coating and improve the film thickness edge ratio between the film thicknesses at the center and edge portions of the dimples, following mixture of the two parts—the polyol component and the isocyanate component, the coating composition preferably has a viscosity, as tested by the method of JIS K5600-2-2 (1999), of at least 0.025 Pa·s, and more preferably at least 0.030 Pa·s.

When the above coating composition is used, a coating layer can be formed on the surface of conventionally manufactured golf balls via the steps of preparing the coating composition at the time of application, applying the coating composition to the surface using a conventional coating operation, and drying. Preferred, non-limiting examples of the coating method used in this case include spray painting, electrostatic painting and dipping.

In the above drying step, which is similar to that used with known two-part curable urethane coatings, the drying temperature may be set to about 40° C. or more, especially between 40° C. and 60° C., and the drying time may be set to from 20 to 90 minutes, especially from 40 to 50 minutes.

When the above coating composition is applied onto a ball surface that has been subjected to dry surface treatment such as corona treatment, plasma treatment, ultraviolet irradiation treatment or electron beam irradiation treatment, the advantageous effects of such treatment become clearly apparent. In this case, it is especially preferable to apply plasma treatment.

Methods commonly used for surface coating golf balls may be used to apply the above coating composition. Examples of such methods include brush painting, spray painting and electrostatic painting. The thickness of the coating layer is preferably from 5 to 50 μm, and more preferably from 10 to 30 μm.

The coating layer edge ratio (%), which serves as an indicator of the uniformity of the coating layer, is preferably 50% or more, and more preferably 70% or more.