Golf ball

Abstract

To provide a golf ball that sufficiently satisfies various performances required for a practice golf ball such as scratch resistance, peel resistance, and crack durability.SOLUTION: There is provided a golf ball which comprises a core and a cover covering the core, and in which a large number of dimples are formed on the outer surface of the cover. The ball has predetermined cover material hardness and a specific compressive deformation amount under a predetermined load. The outer surface of the cover has paint layers on the inner layer and the outer layer. The inner paint layer is formed from a paint composition containing an acrylic resin and an urethane resin, and the outer paint layer is formed from a two-component curable urethane paint composition comprising a polyol component and a polyisocyanate component. By including less than 5 mass% of an inorganic or organic filler relative to the solid content of the base resin of the paint composition, the thickness (film thickness) ratio of the paint layers formed at the center (bottom) and the edge of the dimple is optimized.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a golf ball such as a practice golf ball that includes a core and a cover, and a large number of dimples and two paint layers are formed on the surface of the cover.

Background Art

[0002] Golf balls used in golf practice ranges are required to have different performances from those used in general golf courses due to their usage environment. Since an unspecified user hits the ball in a golf practice range and the ball is used repeatedly over a long period of time, appearance characteristics are also emphasized. Sometimes, if there are problems with the appearance characteristics rather than the performance of the ball, it may lead to claims from users of the golf practice range.

[0003] Elements required for the appearance of a practice golf ball include excellent scratch resistance, no mark peeling, difficulty in discoloration, and excellent surface glossiness. In terms of the performance of a practice golf ball, as described above, since the ball is used repeatedly over a long period of time in a harsh environment, repeated crack durability is mainly required.

[0004] Therefore, for practice golf balls, in order to meet the above requirements, it is desirable to improve the paint layer (coating film) applied to the cover surface. As a paint composition used for ordinary golf balls, a two-component curable polyurethane paint that is mixed immediately before use using a polyol and a polyisocyanate is mainly used because it can withstand large deformations, impacts, and friction. However, in the paint composition conventionally used for golf balls, when applying to a golf ball, the film thickness at the edge of the dimple usually becomes thin. For this reason, this thin film thickness part easily becomes a part with weak scratch resistance and peelability.

[0005] As technologies for improving the two-component curable polyurethane paint composition of a golf ball, the following Patent Documents 1 to 4 are exemplified.

[0006] Patent Document 1 proposes a golf ball containing silica particles with an average particle diameter of 200 nm or less in a paint, and Patent Document 2 proposes a paint in which polymer gel fine particles such as an acrylic-styrene copolymer resin are dispersed. However, regarding the golf balls described in these documents, it cannot be said that the scratch resistance and peeling resistance of the paint layer have been sufficiently improved.

[0007] Patent Document 3 proposes forming two paint layers on the cover surface and forming the paint layer uniformly by using a low-boiling solvent. Patent Document 4 describes a technique for improving mark durability by forming a two-layer paint layer in which different types of paint layers of an epoxy resin and a urethane resin are separately formed as main agents.

[0008] However, regarding the golf balls described in Patent Document 3 and Patent Document 4, in any case, in addition to the repeated impact durability required in a harsh environment such as that used in a golf driving range, it has been difficult to obtain characteristics that satisfy all of the scratch resistance, mark peeling durability, and surface glossiness in the ball appearance.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention has been made in view of the above circumstances, and even in a harsh environment such as that used in a golf driving range, it has good scratch resistance, mark peeling durability, and surface glossiness in the appearance of the ball, and excellent cracking durability during repeated hitting. The purpose is to provide a golf ball.

Means for Solving the Problems

[0011] As a result of intensive studies to achieve the above object, the inventors of the present invention found that in a golf ball comprising a core and a cover composed of at least one layer covering the core, the material hardness of the cover is less than 60 in Shore D hardness, and the compression deformation amount of the whole ball under a predetermined load is specified within the range of 2.7 to 3.3 mm. At the same time, two coating layers, an inner layer and an outer layer, are formed on the outer surface of the cover. The inner coating layer is formed of a coating composition containing an acrylic resin and a urethane resin as main components, and the outer coating layer is formed of a two-component curable urethane coating composition composed of a polyol component and a polyisocyanate component. When the golf ball was designed to contain an inorganic or organic filler of less than 5% by mass based on the solid content of the base resin of the coating composition, this golf ball sufficiently satisfies the cracking durability during repeated hitting required in a harsh environment such as that used in a golf driving range, and all the ball appearance characteristics (scratch resistance, mark peeling durability, surface glossiness) required by users as a practice golf ball are good. The present invention has been completed based on this finding.

[0012] Therefore, the present invention provides the following golf ball. 1. A golf ball comprising a core and a cover consisting of at least one layer covering the core, wherein a large number of dimples are formed on the outer surface of the cover, the material hardness of the cover is less than 60 in Shore D hardness, the outer surface of the cover has a paint layer consisting of at least two layers of an inner layer and an outer layer, the paint inner layer is formed of a paint composition containing an acrylic resin and a urethane resin as main components, the paint outer layer is formed of a two-component curable urethane paint composition consisting of a polyol component and a polyisocyanate component, and the paint composition contains an inorganic or organic filler of less than 5% by mass based on the solid content of the base resin of the paint composition. When the ratio of the thickness (film thickness) of the paint layer formed at the center (bottom) and the edge portion of the dimple in the cross section of the dimple is defined as the edge ratio represented by the following formula: (Film thickness at the edge of the dimple) / (Film thickness at the center of the dimple) × 100 (%) The relationships between the edge ratio E1 of the paint inner layer, the edge ratio E2 of the paint outer layer, and the edge ratio ET of the entire paint layer are represented by the following two formulas -10 ≦ E2 - E1 ≦ 10, and ET - E2 ≧ 0 are satisfied, and the compression deformation amount when the final load of 1275 N (130 kgf) is applied from the state where an initial load of 98 N (10 kgf) is applied to the golf ball is 2.7 to 3.3 mm. A golf ball characterized by this. 2. The golf ball according to the above 1, wherein in the paint composition of the paint inner layer, the content of the acrylic resin is 50% by mass or more of the total resin of the main component. 3. The golf ball according to the above 1 or 2, wherein in the paint composition of the paint outer layer, the average particle diameter of the inorganic or organic filler is 0.1 to 1.0 μm in the average particle diameter based on the BET method. 4. The golf ball according to the above 1 or 2, wherein in the paint composition of the paint outer layer, the two-component curable urethane paint composition consists of a polyol component mainly composed of a hydroxyl group-containing polyester polyol having an alicyclic structure in the molecule and a non-yellowing polyisocyanate. 5. In the coating composition of the outer coating layer, the two-component curable urethane coating composition of the golf ball according to the above 1 or 2 is composed of a polyol component mainly composed of acrylic polyol and an isocyanate component mainly composed of elastic deformation polyisocyanate. 6. In the two-component curable urethane coating composition, the viscosity after mixing the two components is 0.025 Pa·s or more according to the test method of JIS K5600-2-2 (1999). The golf ball according to the above 1 or 2. 7. The golf ball according to the above 1 or 2, wherein the thickness of the inner coating layer is 5 to 15 μm. 8. The golf ball according to the above 1 or 2, wherein the thickness of the outer coating layer is 17 to 23 μm. 9. The diameter of the core is 40 mm or less, and the compression deformation amount when the final load of 1275 N (130 kgf) is applied from the state where the initial load of 98 N (10 kgf) is applied to the core is 3.0 to 4.0 mm. The golf ball according to the above 1 or 2. 10. At least one layer of the cover is formed of a resin composition containing the following component (a) and / or component (b). The golf ball according to the above 1 or 2. (a) An ionic ethylene-methacrylic acid-unsaturated carboxylic acid copolymer having an unsaturated carboxylic acid content of 5% by mass or more (b) An ionic ethylene-methacrylic acid-unsaturated carboxylic acid ester copolymer having an unsaturated carboxylic acid content of 5% by mass or more

Advantages of the Invention

[0013] According to the golf ball of the present invention, it is a golf ball that sufficiently satisfies various performances required for a practice golf ball, such as scratch resistance, mark peeling durability, and crack durability during repeated hitting. Therefore, the golf ball of the present invention is particularly useful as a practice golf ball (range ball).

Brief Description of the Drawings

[0014]

Figure 1

Embodiments for Carrying Out the Invention

[0015] Hereinafter, the present invention will be described in more detail. The golf ball of the present invention includes a core and a cover composed of at least one layer covering the core, and a large number of dimples are formed on the outer surface of the cover.

[0016] The above core can be formed using a known rubber material as a base material. As the base rubber, known base rubbers of natural rubber or synthetic rubber can be used. More specifically, it is recommended to mainly use polybutadiene, particularly cis-1,4-polybutadiene having at least 40% or more of a cis structure. Further, in the base rubber, if desired, natural rubber, polyisoprene rubber, styrene-butadiene rubber, etc. can be used in combination with the above-mentioned polybutadiene. Also, polybutadiene can be synthesized by Ziegler catalysts such as titanium-based, cobalt-based, nickel-based, neodymium-based catalysts, and metal catalysts such as cobalt and nickel.

[0017] To the above base rubber, co-crosslinking agents such as unsaturated carboxylic acids and their metal salts, inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, and organic peroxides such as dicumyl peroxide and 1,1-bis(t-butylperoxy)cyclohexane can be blended. Further, if necessary, commercially available anti-aging agents and the like can be appropriately added.

[0018] The above core is a heat-molded product obtained by heat-curing the above rubber material. The above core may be single-layer or multi-layer, and the above heat-molded product can be used for all or part of the single-layer or multi-layer core. For example, kneading is performed using a kneader such as a Banbury mixer or a roll, compression molding or injection molding is performed using a core mold, and the molded product is appropriately heated under conditions of about 100 to 200 °C and 10 to 40 minutes as a temperature sufficient for the action of an organic peroxide or a co-crosslinking agent, whereby the molded product is cured to produce a core.

[0019] The diameter of the above core is not particularly limited, but it is preferably 40 mm or less. If the diameter of the core exceeds 40 mm, the crack durability deteriorates, and there is a risk that it will be difficult to withstand long-term use.

[0020] The compression hardness (deformation amount) when the final load of 1,275 N (130 kgf) is applied from the state where the initial load of 98 N (10 kgf) is applied to the above core is not particularly limited, but is preferably 3.0 mm or more, more preferably 3.2 mm or more, and the upper limit is preferably 4.0 mm or less, more preferably 3.8 mm or less. If this compression hardness deviates from the above range, the hitting feeling will be too soft or too hard, resulting in a hardness that is only preferred by specific users, and it is particularly unsuitable as a practice golf ball. Also, if the compression hardness is particularly too hard, it will lead to early cracking of the ball and the characteristics as a practice golf ball will be impaired.

[0021] Regarding the cover material, there is no particular limitation, but various resin materials used for golf balls can be used. In particular, in the golf ball of the present invention, it is preferable that the cover material is formed of a resin composition containing the following component (a) and / or component (b). (a) An ionic ethylene-methacrylic acid-unsaturated carboxylic acid copolymer having an unsaturated carboxylic acid content of 5% by mass or more (b) An ionic ethylene-methacrylic acid-unsaturated carboxylic acid ester copolymer having an unsaturated carboxylic acid content of 5% by mass or more

[0022] (a) As the unsaturated carboxylic acid component, it is preferable to adopt either acrylic acid or methacrylic acid. As the unsaturated carboxylic acid ester component of (b), a lower alkyl ester is preferable, and in particular, butyl acrylate (n-butyl acrylate, butyl acrylate) is preferable. The content (acid content) of the unsaturated carboxylic acid in the components (a) and (b) is preferably 25% by mass or less as the upper limit value.

[0023] Both components (a) and (b) are ionic resins. In these components, the type of metal salt that neutralizes the acid group may be an inorganic metal species with a valence of 1 to 3. Specifically, they are zinc, sodium, magnesium, potassium, and calcium. In particular, it is preferable to use zinc or sodium.

[0024] Specific examples of components (a) and (b) include the "IOTEK" series manufactured by ExxonMobil, the "Himilan" series manufactured by Mitsui Dow Chemical, the ionomer resin manufactured by THE DOW CHEMICAL COMPANY, and the "Surlyn" series.

[0025] In addition to the above resin materials, other thermoplastic elastomers, fatty acids or their derivatives, basic inorganic metal compounds, fillers, various additives, etc. can be added to the cover.

[0026] To obtain the above cover, for example, a single-layer or multi-layer core prepared in advance according to the type of the ball is arranged in a mold, the above mixture is heated, mixed, and melted, and injection molding is performed to coat the desired cover around the core. In addition to the above, for example, a pair of hemispherical half-cups can be molded in advance with the cover material of the present invention, and the core can be wrapped with these half-cups and pressure-molded at 120 to 170 °C for 1 to 5 minutes.

[0027] The thickness of the above cover can be 0.3 to 3.0 mm, preferably in the range of 0.5 to 2.0 mm. Also, the material hardness of the above cover is not particularly limited, but it is preferably 40 or more in Shore D hardness, more preferably 50 or more, and the upper limit is preferably 60 or less.

[0028] A number of dimples are formed on the surface of the outermost layer of the above cover. There are no particular restrictions on these dimples, but preferably there are 250 or more, preferably 300 or more, and the upper limit can preferably be 420 or less, more preferably 400 or less. Regarding the shape of the dimples, one or a combination of two or more such as circular, various polygons, dumbbell shape, and other ellipses can be appropriately used. For example, when using circular dimples, the diameter can be about 2.5 mm or more and 6.5 mm or less, and the depth can be 0.08 mm or more and 0.30 mm or less.

[0029] A paint layer composed of at least two layers, an inner layer and an outer layer, is formed on the outer surface of the above cover. The inner paint layer is formed by a paint composition containing an acrylic resin and a urethane resin as main components. Since an ionomer resin, a urethane resin, etc. are blended as main components in the cover of the golf ball, by using an acrylic resin and a urethane resin for the inner paint layer that contacts both the cover and the outer paint layer, the affinity with the cover and the adhesion with the outer paint layer can be improved.

[0030] The ratio of the acrylic resin to the urethane resin (acrylic resin: urethane resin) is preferably 30:70 to 80:20, more preferably 50:50 to 80:20, and even more preferably 60:40 to 70:30 by mass ratio. In particular, by increasing the ratio of the acrylic resin, the adhesion with the ionomer resin blended in the cover material can be increased, so the ratio of the acrylic resin is preferably 50% by mass or more. On the other hand, when the ratio of the urethane resin is increased, since the urethane resin has flexibility, the wear resistance of the entire paint layer can be increased.

[0031] As the acrylic resin, for example, a resin obtained by polymerizing one or more acrylic monomers selected from the group consisting of acrylic acid, methacrylic acid and their esters, or a resin obtained by copolymerizing one or more acrylic monomers and one or more monomers other than acrylic monomers can be used. Among the acrylic monomers, specific examples of acrylic acid esters and methacrylic acid esters include, for example, alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, benzyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, glycidyl (meth)acrylate, etc. Specific examples of monomers other than acrylic monomers include styrene, etc. Among these, as the acrylic resin, it is preferable to use an acrylic acid ester in order to improve adhesion.

[0032] On the other hand, as the urethane resin, for example, a resin having a urethane bond obtained by the reaction of a polyol component and a polyisocyanate component can be used. Examples of the polyol component include polyesters, polyethers, polycarbonates, etc. Examples of the polyisocyanate component include tolylene diisocyanate (TDI), diphenylmethane - diisocyanate (MDI), dicyclohexylmethane diisocyanate (hydrogenated MDI), naphthalene - 1,5 - diisocyanate (NDI), xylylene diisocyanate (XDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), etc. Among these, as the urethane resin, from the viewpoint of imparting flexibility, it is preferable to use a polyether type.

[0033] The paint composition of the inner paint layer is preferably an aqueous paint composition. An aqueous paint composition refers to one in which the resin as the main component is dissolved or dispersed in water. Aqueous paint compositions are classified into water-soluble paint compositions and water-dispersible paint compositions according to the stabilization state of the resin in water. As a preferred embodiment of the present invention, it is preferably in the form of a water-dispersible paint composition. Water-dispersible paint compositions are classified into colloidal dispersion type (particle size about 0.005 to 0.05 μm) and emulsion type (particle size about 0.05 to 0.5 μm) according to the particle size of the resin. In the embodiments of the present invention, either the colloidal dispersion type or the emulsion type may be used. For example, an acrylic resin may be used as an emulsion-type paint, and a urethane resin may be used as a colloidal dispersion-type paint, and these may be mixed to form a water-dispersible paint composition.

[0034] The paint composition of the inner paint layer may contain a crosslinking agent in addition to the above-mentioned main component. When the acrylic resin or urethane resin has a crosslinking reactive group, the crosslinking agent can be formulated according to the crosslinking reactive group. Examples of the crosslinking agent include, but are not limited to, methylol compounds, polyepoxy compounds, amino resins, polyaziridine compounds, polyoxazoline compounds, polyisocyanate compounds, sulfur-based compounds, hydrazine-based compounds, silane coupling agents, chelating agents, etc. The crosslinking agent is preferably soluble in the solvent of the aqueous paint composition. Water is mainly used as the solvent of the aqueous paint composition. The blending amount of the crosslinking agent is preferably, for example, 0.1 to 5 parts by mass with respect to 100 parts by mass of the main component.

[0035] The thickness (film thickness) of the inner paint layer is preferably 5 μm or more, more preferably 6 μm or more, and even more preferably 7 μm or more in order to improve the impact resistance. The upper limit of this thickness (film thickness) is preferably 15 μm or less, more preferably 13 μm or less, in order to maintain the jumping-up property.

[0036] The method for forming the paint inner layer on the surface of the cover is not particularly limited, and known methods for painting a golf ball paint on the cover surface can be used. For example, methods such as spray painting method and electrostatic painting method can be used.

[0037] The paint outer layer is formed on the outer surface of the above-mentioned paint inner layer. The material of this paint outer layer is a two-component curable urethane paint composition composed of a polyol component and a polyisocyanate component. Specifically, as this paint outer layer, a two-component curable urethane paint composition composed of a polyol component mainly containing a hydroxyl group-containing polyester polyol having an alicyclic structure in the molecule and a non-yellowing polyisocyanate, or a two-component curable urethane paint composition composed of a polyol component mainly containing an acrylic polyol and a two-component curable urethane paint composition mainly containing an elastic deformation polyisocyanate are preferably employed.

[0038] Two-component curable urethane paint composed of a polyol component mainly containing a hydroxyl group-containing polyester polyol having an alicyclic structure in the molecule and a non-yellowing polyisocyanate The hydroxyl group-containing polyester polyol having an alicyclic structure in the molecule is obtained by reacting a polyhydric alcohol component having an alicyclic structure in the molecule with a polybasic acid component.

[0039] As the polyhydric alcohol component having an alicyclic structure in the molecule, preferably, diols such as 1,3-cyclohexanedimethanol and 1,4-cyclohexanedimethanol, or a mixture thereof can be mentioned. Further, as the polybasic acid component having an alicyclic structure in the molecule, preferably, dicarboxylic acids such as tetrahydrophthalic acid, hexahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid, acid anhydrides thereof, acid halides thereof, or a mixture thereof can be mentioned.

[0040] The polyhydric alcohol component and polybasic acid component having an alicyclic structure in the above molecule may be part or all of the constituent components of the hydroxyl group-containing polyester. The polyhydric alcohol component having an alicyclic structure in the molecule is preferably contained in an amount of 3% by mass or more, more preferably 5 to 40% by mass, in the total polyhydric alcohol component. The polybasic acid component having an alicyclic structure in the molecule is preferably contained in an amount of 5% by mass or more, more preferably 10 to 55% by mass, in the total polybasic acid component. When the contents of the polyhydric alcohol component and polybasic acid component having an alicyclic structure are outside the above ranges, the durability of the coated golf ball against sand abrasion and grass juice contamination becomes insufficient.

[0041] Examples of the polyhydric alcohol component having no alicyclic structure in the molecule that can be used in combination with the above polyhydric alcohol component having an alicyclic structure in 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, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, or a mixture thereof.

[0042] Examples of the polybasic acid component having no alicyclic structure in the molecule that can be used in combination with the above polybasic acid component having an alicyclic structure in the molecule include dicarboxylic acids such as adipic acid, sebacic acid, dimer acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, itaconic acid, acid anhydrides thereof, acid halides thereof, or a mixture thereof.

[0043] As described above, the hydroxyl group-containing polyester is obtained by subjecting the above polyhydric alcohol component and polybasic acid component to an esterification reaction. The mass average molecular weight of the hydroxyl group-containing polyester thus obtained is preferably 3,000 to 35,000 as measured by GPC, and its hydroxyl value is preferably 50 to 300, particularly preferably 150 to 250. If the mass average molecular weight and hydroxyl value of the hydroxyl group-containing polyester are outside the above ranges, the durability of the coated golf ball against sand abrasion and grass juice contamination will be insufficient.

[0044] On the other hand, as the non-yellowing polyisocyanate, for example, adducts such as hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, burette bodies, isocyanurate bodies, or mixtures thereof are suitable.

[0045] The above hydroxyl group-containing polyester and non-yellowing polyisocyanate are preferably used in a range where the ratio (molar ratio) of the isocyanate group of the non-yellowing polyisocyanate to the hydroxyl group of the hydroxyl group-containing polyester is 0.8 to 1.3.

[0046] Two-component curable urethane paint composed of a polyol component mainly containing an acrylic polyol and a two-component curable urethane paint mainly containing an elastic deformation polyisocyanate The acrylic polyol is composed of a main chain made of an acrylic polymer and side chains made of polyester and / or polyether.

[0047] There are no particular restrictions on the structure of the above acrylic polymer, and any structure may be used as long as it has an acrylic repeating unit as the basic skeleton. Also, the acrylic monomer constituting the main chain may be only one kind or two or more kinds, or it may be a copolymerized product with other monomers copolymerizable with the acrylic monomer.

[0048] Specific structures of the acrylic polyol include, for example, (i) those obtained by adding components constituting side chains such as lactone or alkylene oxide to the main chain of an acrylic polymer, (ii) those obtained by adding a new monomer and an initiator in the presence of an acrylic polymer and grafting a side chain to the main chain of the acrylic polymer by polymerization of the monomer, (iii) those obtained by homopolymerizing an acrylic monomer to which a polyester (hereinafter abbreviated as "polyester-containing acrylic monomer") and / or an acrylic monomer to which a polyether (hereinafter abbreviated as "polyether-containing acrylic monomer") is added, (iv) those obtained by copolymerizing a polyester-containing acrylic monomer and / or a polyether-containing acrylic monomer with other acrylic monomers, and the like.

[0049] On the other hand, the elastomeric modified polyisocyanate is a prepolymer having an NCO terminal obtained by using the above-mentioned diisocyanates such as tolylene diisocyanate (TDI), xylene diisocyanate (XDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI) as monomers and subjecting them to a urethane reaction with an active hydrogen-containing compound having elasticity. Note that there are no particular restrictions on the conditions of the urethane reaction and the like, and conventional conditions may be followed.

[0050] Examples of the active hydrogen-containing compound having elasticity for elastomeric modification of the above polyisocyanate include polyester polyol, polycarbonate polyol, polyether polyol, polyolefin polyol, animal and plant-based polyol, or copolyols thereof. In particular, it preferably contains a modified polyisocyanate modified with at least one polyol selected from the group consisting of polyester polyol, polyether polyol, polycarbonate polyol, polyolefin polyol, animal and plant-based polyol, and copolyols thereof. Further, from the viewpoint of further elastifying the resulting coating film and further improving the impact resistance, it is preferable that these polyols have a Tg of 0°C or lower. Note that these polyols can be used alone or in combination of two or more.

[0051] The above coating composition contains an inorganic or organic filler. As this inorganic or organic filler, various inorganic substances or organic substances can be adopted from the viewpoints of maintaining the transparency of the coating layer and imparting a reinforcing effect and a sag prevention effect. Specifically, polyurethane particles, silicon dioxide (silica), carbon, titanium oxide, etc. are exemplified. Examples of the polyurethane particles include thermoplastic polyurethane particles and three-dimensional crosslinked polyurethane particles. For example, the polyurethane particles described in JP-A-2017-78149 are exemplified.

[0052] Regarding the particle size of the inorganic or organic filler, the average particle size based on the BET method is preferably 0.1 μm or more, more preferably 0.2 μm or more, and the upper limit is preferably 10 μm or less. By adding an inorganic or organic filler having an average particle size within a predetermined range to the above coating composition, the sag of the paint can be suppressed, the film thickness edge ratio between the central portion and the edge portion of the dimple can be improved, and the scratch resistance, peeling resistance, and mark protection effect of the coating layer can be improved.

[0053] Regarding the blending amount of the above filler, it is less than 5% by mass based on the solid content of the base resin of the coating composition, preferably less than 3% by mass, more preferably less than 2% by mass. If it exceeds the above upper limit value, it may adversely affect the transparency of the coating film. On the other hand, the lower limit value of this blending amount is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and still more preferably 0.5% by mass or more. If this value is too small, the effect of improving the uniformity of the film thickness of the coating layer, which is the desired effect of the present invention, will be reduced.

[0054] As described above, the above coating composition uses acrylic polyol or polyester polyol as the main agent and polyisocyanate as the curing agent, and various organic solvents can be mixed depending on the coating conditions. 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, methylcyclohexane, and ethylcyclohexane; and petroleum hydrocarbon solvents such as mineral spirit.

[0055] In addition, known coating formulation components may be added to the above coating composition as necessary. Specifically, appropriate amounts of a thickener, an ultraviolet absorber, a fluorescent brightener, a slipping agent, a pigment, etc. can be blended.

[0056] Regarding the above coating composition, it is preferable that the viscosity after mixing the two components of the polyol component and the isocyanate component is 0.025 Pa·s or more, more preferably 0.030 Pa·s or more, as measured by the test method of JIS K5600-2-2 (1999), because it can suppress the sagging of the paint and improve the film thickness edge ratio between the central part and the edge part of the dimple.

[0057] When using the above coating composition, the coating composition is adjusted during coating on a golf ball manufactured by a known method, and the surface is coated by adopting a normal coating process, and a coating film layer can be formed on the ball surface through a drying process. In this case, as the coating method, a spray coating method, an electrostatic coating method, a dipping method, etc. can be preferably adopted, and there is no particular limitation.

[0058] Regarding the above drying process, it is the same as that of known two-component curable urethane paints, and the drying temperature can be about 40°C or higher, particularly 40 - 60°C, and the drying time can be 20 - 90 minutes, particularly 40 - 50 minutes.

[0059] As the coating method of the above coating composition, a method commonly used for the surface coating of golf balls can be adopted. For example, methods such as brush coating, spray coating, and electrostatic coating can be mentioned. The thickness of the coating film is preferably 10 - 30 μm, more preferably 17 - 23 μm.

[0060] In the golf ball of the present invention, when the ratio of the thickness (film thickness) of the paint layers formed at the central part (bottom) and the edge part of the dimple in the cross-section of the dimple is the edge ratio represented by the following formula, (Film thickness at the edge of the dimple) / (Film thickness at the central part of the dimple)×100(%) The relationship between the edge ratio E1 of the inner paint layer, the edge ratio E2 of the outer paint layer, and the edge ratio ET of the entire paint layer is the following two formulas -10≦E2 - E1≦10, and ET - E2≧0 It is characterized by satisfying these conditions. E2 - E1 means that the edge ratios of both the inner and outer paint layers are high and the variation in the edge ratio is small. Also, ET - E2 is the value obtained by subtracting the edge of the outer paint layer from the edge ratio of the entire paint layer, which means that the edge ratio of the inner paint layer is a relatively high value. By satisfying these two formulas, the film thickness edge ratio between the central part and the edge part of the dimple can be improved, and the scratch resistance, peeling resistance, and mark protection effect of the paint layer can be improved.

[0061] The edge ratio, which is the ratio of the film thickness at the edge portion of the dimple to the film thickness at the central portion (bottom) of the dimple, indicates that the film thickness in the dimple is more uniform as it approaches 100%, and it serves as an index for evaluating the uniformity of the coating film. The edge ratios (E1, E2) of each paint layer are preferably 50% or more, more preferably 70% or more. Usually, when attempting to form a thick coating film on the concave surface of the dimple, the film thickness at the edge portion, which is the shallower part of the depression, becomes thinner, and the film thickness at the deeper central portion of the depression becomes thicker. When forming a coating film with a high elastic recovery rate, this tendency becomes more prominent, and it becomes difficult to form a film thickness of 10 μm or more at the edge portion of the dimple. In the embodiments of the present invention, by using a solvent with a boiling point of 80°C or lower, even when forming an outer coating film with an elastic recovery rate of 50% or more at the edge portion of the dimple with a film thickness of 10 μm or more, the edge ratio can be made 50% or more.

[0062] Regarding the compression hardness (deformation amount) when the final load of 1,275 N (130 kgf) is applied starting from the state where an initial load of 98 N (10 kgf) is applied to the above golf ball, there are no particular restrictions, but it is preferably 2.7 mm or more, more preferably 2.8 mm or more, still more preferably 3.0 mm or more. As the upper limit, it is preferably 3.6 mm or less, more preferably 3.5 mm or less, still more preferably 3.4 mm or less. If this compression hardness deviates from the above range, the hitting feeling will be either too soft or too hard, resulting in a hardness that is only preferred by specific users, and it is particularly unsuitable as a practice golf ball. Also, especially if the compression hardness is too hard, it will lead to early cracking of the ball, and the characteristics of the practice golf ball will be impaired.

Examples

[0063] Hereinafter, examples and comparative examples will be shown to specifically explain the present invention, but the present invention is not limited to the following examples.

[0064] 〔Examples 1 to 6, Comparative Examples 1 to 5〕 A golf ball with dimples was prepared by injection molding and coating a core with a diameter of 39.3 mm with an ionomer resin cover having a thickness of 1.7 mm shown in Table 1.

[0065]

Table 1

[0066] The above “S8940”, “S9910”, and “S9320” are all ionomer resins manufactured by THE DOW CHEMICAL COMPANY, with the trade name “Surlyn” series

[0067] For the above golf balls, two-layer coating was performed as follows

[0068] Formation of a two-layer coating In Examples 1 to 3 and Comparative Examples 1 to 3, primer treatment was performed using an aqueous primer composition composed of the main agents shown in Table 2 to form a paint inner layer. That is, this aqueous primer composition was applied with an automatic spray gun so that the thickness of the paint inner layer was 8 to 9 μm. The aqueous primer composition is a material obtained by mixing “Acrylic Primer” (main agent) manufactured by Kashu Co., Ltd., “Crosslinker CX-100” (hardener), and water in a mass ratio of 100:1.5:3. This was dried at 55°C for 30 minutes and subjected to testing Next, after marking a specific logo (marking part) on the above paint inner layer, a paint composition composed of the main agent and hardener shown in Table 2 was used, and this was applied with an automatic spray gun so that the thickness of the paint outer layer was 20 μm. This was dried at 55°C for 1 hour and subjected to testing

[0069] In Examples 4 to 6 and Comparative Examples 4 and 5, in the same manner as above, primer treatment was performed using an aqueous primer composition composed of the main agents shown in Table 2 to form a paint inner layer, marking of a specific logo (marking part) was performed, and then a paint outer layer was formed using a paint composition composed of the main agent and hardener shown in Table 2

[0070]

Table 2

[0071] Viscosity measurement of the paint composition Regarding the measurement of the viscosity of the above paint composition, the viscosity was measured immediately after mixing the two components of polyol and polyisocyanate. The measurement was carried out by the flow cup method, and the viscosity was specified in accordance with JIS K5600-2-2-1999. The measuring instrument used was the product named "NK-2" manufactured by Anest Iwata Corporation, and the measurement was carried out in a room at a temperature of 22.8°C.

[0072] For each of the obtained golf balls, the scratch resistance, mark peeling property, surface gloss were evaluated, and the crack durability was evaluated by the following test methods. The results are shown in Table 3.

[0073] Water abrasion resistance test Approximately 4 kg of sand and water with a size of around 5 mm were put into a pot mill with an outer diameter of 210 mm, and 15 balls were put into this pot mill. Then, it was stirred in the pot mill at a rotational speed of 50 - 60 rpm for 120 minutes. After that, the golf balls were taken out from the pot mill, and a UV light (IDHR-100S-UV-365 manufactured by Raimac Co., Ltd., the same hereinafter) was irradiated onto the golf balls to evaluate the three items of "scratch resistance", "mark peeling property" and "surface gloss" described below.

[0074] [Scratch resistance] For the scratch resistance, the surface of the golf ball was magnified with a magnifying glass to observe the degree of damage to the fine paint film. It was evaluated according to the following criteria, and the average value of the evaluation results of 5 golf balls was described in Table 3. 5 points: No damage 4 points: Slight scratches 3 points: Many scratches 2 points: Prickly scratches occurred 1 point: Gouged scratches occurred

[0075] [Mark peeling property] The mark peeling property is observed by irradiating a golf ball with UV light and observing the degree of peeling of the marks due to wear on the surface of each golf ball. It is scored according to the following criteria, and the average value of the evaluation results of 5 golf balls is described in Table 3. 7 points: No peeling 6 points: Slight peeling 5 points: Some peeling 4 points: Considerable peeling, but the marks can still be read 3 points: Considerable peeling, but the marks can still be read with some difficulty 2 points: Considerable peeling, and the marks cannot be read 1 point: All marks have peeled off

[0076] 〔Surface gloss〕 Regarding the surface gloss, the surface of the golf ball is magnified with a magnifying glass to observe the presence or absence of surface gloss on the dimples and the land portions. It is evaluated according to the following criteria, and the average value of the evaluation results of 5 golf balls is described in Table 3. 7 points: Glossy both on the land portions and inside the dimples 6 points: Slightly dull on the land portions, glossy inside the dimples 5 points: Considerably dull on the land portions, glossy inside the dimples 4 points: Almost no gloss on the land portions, slightly dull inside the dimples 3 points: No gloss on the land portions, considerably dull inside the dimples 2 points: No gloss on the land portions, very considerably dull inside the dimples 1 point: No gloss both on the land portions and inside the dimples

[0077] Edge ratio (%) In the cross-section of the dimple D shown in Fig. 1, the thickness (film thickness) t of the paint layer (each layer of the inner paint layer and the outer paint layer) P at the center M and the edge portions E, E of the dimple is determined. Note that for the edge portion of the dimple, first, at a location excluding the vicinity of the equator and the vicinity of the apex on the ball surface, a portion including the largest dimple is cut by about φ10 mm, and then further cut so that the cross-section of the largest dimple portion is exposed. Thereafter, the dimple cross-section is observed with a microscope, and the positions where the height on the surface is maximum as shown in Fig. 1 are defined as the edge portions E, E. Further, the position under the normal line extending from the half position of the length of the straight line connecting E, E is defined as the center portion M of the dimple. And the edge ratio is given by the following formula: (Average value of the film thickness of the edge portions E, E of the dimple) / (Film thickness of the center portion M of the dimple) × 100 (%) The edge ratio (%) is calculated thereby. The closer the edge ratio is to 100%, the more uniform the film thickness is. Represent the edge ratio E1 of the inner paint layer, the edge ratio E2 of the outer paint layer, and the edge ratio ET of the paint layer (overall), and the values of E2 - E1 and ET - E2 are shown in Table 3.

[0078] Crack durability The durability of the ball is evaluated using an ADC Ball COR Durability Tester manufactured by Automated Design Corporation, USA. This tester has a function of continuously colliding a golf ball against two metal plates installed in parallel after launching the golf ball by air pressure. The incident velocity on the metal plate is set to 43 m / s. The number of launches required until the golf ball cracks is measured, and the average value of the measured values of 10 golf balls is calculated.

[0079]

Table 3

[0080] As shown in Table 3, in Examples 1 to 6, the surface of the ball has good scratch resistance, almost no mark peeling, excellent glossiness, and excellent crack durability. In contrast, it can be seen from Table 3 that Comparative Examples 1 to 5 are inferior to each of the Examples in the following points. In Comparative Example 1, the outer paint layer does not contain an organic or inorganic filler, the edge ratio relationship is ET - E2 < 0, there is a lot of mark peeling, and the surface glossiness is poor. In Comparative Example 2, the material hardness of the cover becomes as high as 60 or more, the scratch resistance is poor, and there is a lot of mark peeling. In Comparative Example 3, the material hardness of the cover is as high as 60 or more, and the compression hardness of the ball product becomes less than 2.7 mm, and the scratch resistance and crack durability are poor. In Comparative Example 4, the compression hardness of the ball product is greater than 3.3 mm, becoming soft, and the scratch resistance is poor. In Comparative Example 5, the content of the organic or inorganic filler in the outer paint layer is high, the scratch resistance is poor, the surface glossiness is poor, and there is also a lot of mark peeling.

Claims

1. A golf ball comprising a core and a cover composed of at least one layer covering the core, wherein a large number of dimples are formed on the outer surface of the cover. In this golf ball, the material hardness of the cover is less than 60 in Shore D hardness, and the outer surface of the cover has a paint layer composed of at least two layers, an inner layer and an outer layer. The inner paint layer is formed of a paint composition containing an acrylic resin and a urethane resin as main components, and the outer paint layer is formed of a two-component curable urethane paint composition composed of a polyol component and a polyisocyanate component. The paint composition contains an inorganic or organic filler of less than 5% by mass based on the solid content of the base resin of the paint composition. When the ratio of the thickness (film thickness) of the paint layer formed at the center (bottom) and the edge of the dimple in the cross section of the dimple is defined as the edge ratio represented by the following formula: (Film thickness at the edge of the dimple) / (Film thickness at the center of the dimple) × 100 (%) The relationship between the edge ratio E1 of the inner paint layer, the edge ratio E2 of the outer paint layer, and the edge ratio ET of the entire paint layer satisfies the following two formulas -10 ≤ E2 - E1 ≤ 10, and ET - E2 ≥ 0 And the compression deformation amount when the final load of 1275 N (130 kgf) is applied from the state where an initial load of 98 N (10 kgf) is applied to the golf ball is 2.7 to 3.3 mm. A golf ball characterized by this.

2. The golf ball according to claim 1, wherein in the paint composition of the inner paint layer, the content of the acrylic resin is 50% by mass or more of the total resin of the main component.

3. The golf ball according to claim 1 or 2, wherein in the paint composition of the outer paint layer, the average particle size of the inorganic or organic filler is 0.1 to 1.0 μm in terms of the average particle size based on the BET method.

4. The golf ball according to claim 1 or 2, wherein in the paint composition of the outer paint layer, the two-component curable urethane paint composition is composed of a polyol component mainly composed of a hydroxyl group-containing polyester polyol having an alicyclic structure in the molecule and a non-yellowing polyisocyanate.

5. The golf ball according to claim 1 or 2, wherein in the paint composition of the outer paint layer, the two-component curable urethane paint composition is composed of a polyol component mainly composed of an acrylic polyol and an isocyanate component mainly composed of an elastic deformation polyisocyanate.

6. The golf ball according to claim 1 or 2, wherein in the two-component curable urethane coating composition, the viscosity after mixing the two components is 0.025 Pa·s or more as measured by the test method of JIS K5600-2-2 (1999).

7. The golf ball according to claim 1 or 2, wherein the thickness of the inner coating layer is 5 to 15 μm.

8. The golf ball according to claim 1 or 2, wherein the thickness of the outer coating layer is 17 to 23 μm.

9. The golf ball according to claim 1 or 2, wherein the diameter of the core is 40 mm or less, and the compression deformation amount when the final load of 1275 N (130 kgf) is applied starting from the state where an initial load of 98 N (10 kgf) is applied to the core is 3.0 to 4.0 mm.

10. The golf ball according to claim 1 or 2, wherein at least one layer of the cover is formed of a resin composition containing the following component (a) and / or component (b). (a) An ionic ethylene-methacrylic acid-unsaturated carboxylic acid copolymer having an unsaturated carboxylic acid content of 5% by mass or more (b) An ionic ethylene-methacrylic acid-unsaturated carboxylic acid ester copolymer having an unsaturated carboxylic acid content of 5% by mass or more

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