JP2018033479A - Golf ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a golf ball having an excellent anti-soiling property and cleanability.SOLUTION: The golf ball has a plurality of dimples 12 and a land 14 on a surface thereof. The golf ball further has a large number of minute projections 18 formed on surfaces of the dimples 12 and the land 14. An average pitch Pav of these minute projections 18 is equal to or greater than 100 μm. An average height Hav of these minute projections 18 is not less than 0.5 μm and not greater than 50 μm. The golf ball satisfies the following mathematical formula. Lav>0.5 Tav In the mathematical formula, Lav represents an average value of distances L between the minute projections 18 and other minute projections 18 adjacent to the minute projections 18, and Tav represents an average value of widths T of these minute projections 18.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a golf ball. Specifically, the present invention relates to a golf ball having dimples on its surface.

  The golf ball has a large number of dimples on its surface. The dimples enhance the aerodynamic characteristics of the golf ball.

  A golf ball having a minute protrusion or a minute dent together with a dimple has been proposed. These protrusions and dents can contribute to aerodynamic characteristics, spin performance, appearance, manufacturability, and the like.

  Japanese Patent Application Laid-Open No. 2015-142599 discloses a golf ball having a paint layer with a large roughness. This roughness can be formed by blasting or the like. This paint layer enhances the aerodynamic characteristics of the golf ball.

JP-A-2015-142599

  A golf ball hit with a golf club flies in the air. The golf ball falls and rolls on the ground. When falling and rolling, the golf ball comes in contact with the ground. Due to this contact, mud adheres to the surface of the golf ball, and this surface may become dirty. When the golf ball is on the fairway or rough, the player cannot touch the golf ball. Therefore, the player cannot remove the dirt on the golf ball. On the green, the player can remove the dirt on the golf ball. However, this removal work is troublesome. Depending on the operation, the dirt may not be sufficiently removed. Even if washed with water, dirt may not be removed. The golf ball that remains dirty is replaced. The exchange imposes an economic burden on the player.

  The golf ball disclosed in Japanese Patent Application Laid-Open No. 2015-142599 is liable to adhere to mud because the paint layer has a large roughness. The antifouling property of this golf ball is not sufficient. Even if this golf ball is washed with water, mud is hardly removed. This golf ball is not sufficiently cleanable.

  An object of the present invention is to provide a golf ball having excellent antifouling properties and cleanability.

  The golf ball according to the present invention includes a plurality of dimples and a land. The golf ball further includes a large number of minute protrusions formed on the surface of the dimples and / or lands. The average pitch Pav of these microprotrusions is 100 μm or more.

  Preferably, the average height Hav of the microprojections is not less than 0.5 μm and not more than 50 μm.

Preferably, the golf ball satisfies the following mathematical formula.
Lav> 0.5 ・ Tav
In this equation, Lav represents the average value of the distance L between the microprotrusions and other microprotrusions adjacent to the microprotrusions, and Tav represents the average value of the widths T of the microprotrusions.

  A golf ball may have a plurality of rows. Preferably, a plurality of minute protrusions are arranged at an equal pitch in each row.

  The golf ball may have a main body and a paint layer located outside the main body. Preferably, the microprojection has a shape reflecting the surface shape of the main body.

  When the golf ball according to the present invention falls or rolls on the ground, mud may come into contact with the surface of the golf ball. Since mud flows between the microprotrusions and the microprotrusions adjacent thereto, the mud hardly adheres to the golf ball. This golf ball is hard to get dirty.

  Water easily flows between the microprotrusions and the microprotrusions adjacent thereto. Therefore, even if mud adheres to the surface, if the water is washed with water, the water will take in dirt and flow. In this golf ball, dirt is easily removed.

FIG. 1 is a partially cutaway sectional view showing a golf ball according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of the golf ball of FIG. FIG. 3 is an enlarged perspective view showing a part of the surface of the golf ball of FIG. FIG. 4 is an enlarged cross-sectional view showing a part of the golf ball of FIG. FIG. 5 is a cross-sectional view taken along line VV in FIG. 6 is an enlarged cross-sectional view showing a part of the golf ball in FIG.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  The golf ball 2 shown in FIG. 1 includes a spherical core 4, an intermediate layer 6 located outside the core 4, and a cover 8 located outside the intermediate layer 6. The core 4, the mid layer 6, and the cover 8 are included in the main body 10 of the golf ball 2. The golf ball 2 has a large number of dimples 12 on the surface thereof. A portion of the surface of the golf ball 2 other than the dimples 12 is a land 14. Although not shown in FIG. 1, the golf ball 2 further has a paint layer described later. The paint layer is located outside the main body 10. The main body 10 may have a one-piece structure. The main body 10 may have a two-piece structure, a four-piece structure, a five-piece structure, or the like.

  The golf ball 2 preferably has a diameter of 40 mm or greater and 45 mm or less. The diameter is particularly preferably equal to or greater than 42.67 mm from the viewpoint that US Golf Association (USGA) standards are satisfied. In light of suppression of air resistance, the diameter is more preferably equal to or less than 44 mm, and particularly preferably equal to or less than 42.80 mm. In the golf ball 2 according to this embodiment, the diameter is 42.7 mm.

  The golf ball 2 preferably has a mass of 40 g or more and 50 g or less. From the viewpoint of obtaining a large inertia, the mass is more preferably 44 g or more, and particularly preferably 45.00 g or more. In light of satisfying the USGA standard, the mass is particularly preferably equal to or less than 45.93 g.

  The core 4 is formed by crosslinking a rubber composition. Examples of the base rubber of the rubber composition include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, and natural rubber. Two or more kinds of rubbers may be used in combination. From the viewpoint of resilience performance, polybutadiene is preferred, and high cis polybutadiene is particularly preferred.

  The rubber composition of the core 4 contains a co-crosslinking agent. From the viewpoint of resilience performance, preferred co-crosslinking agents are zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. It is preferable that the rubber composition contains an organic peroxide together with a co-crosslinking agent. Preferred organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t-butylperoxide). Oxy) hexane and di-t-butyl peroxide.

  The rubber composition of the core 4 may contain additives such as a filler, sulfur, a vulcanization accelerator, a sulfur compound, an anti-aging agent, a colorant, a plasticizer, and a dispersant. The rubber composition may contain a carboxylic acid or a carboxylate. The rubber composition may include a synthetic resin powder or a crosslinked rubber powder.

  The diameter of the core 4 is preferably 30.0 mm or more, and particularly preferably 38.0 mm or more. The diameter of the core 4 is preferably 42.0 mm or less, and particularly preferably 41.5 mm or less. The core 4 may have two or more layers. The core 4 may have a rib on its surface. The core 4 may be hollow.

  The mid layer 6 is made of a resin composition. A preferred base polymer of this resin composition is an ionomer resin. A preferable ionomer resin includes a binary copolymer of an α-olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms. As another preferable ionomer resin, a ternary copolymer of an α-olefin, an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α, β-unsaturated carboxylic acid ester having 2 to 22 carbon atoms is used. A polymer is mentioned. In this binary copolymer and ternary copolymer, preferred α-olefins are ethylene and propylene, and preferred α, β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. In this binary copolymer and ternary copolymer, some of the carboxyl groups are neutralized with metal ions. Examples of the metal ions for neutralization include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions.

  Instead of the ionomer resin, the resin composition of the mid layer 6 may contain another polymer. Examples of other polymers include polystyrene, polyamide, polyester, polyolefin, and polyurethane. The resin composition may contain two or more kinds of polymers.

  The resin composition of the intermediate layer 6 includes a colorant such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, a fluorescent whitening agent, and the like. But you can. For the purpose of adjusting the specific gravity, the resin composition may contain a powder of a high specific gravity metal such as tungsten or molybdenum.

  The thickness of the mid layer 6 is preferably 0.2 mm or more, and particularly preferably 0.3 mm or more. The thickness of the mid layer 6 is preferably 2.5 mm or less, and particularly preferably 2.2 mm or less. The specific gravity of the mid layer 6 is preferably 0.90 or more, particularly preferably 0.95 or more. The specific gravity of the mid layer 6 is preferably 1.10 or less, particularly preferably 1.05 or less. The intermediate layer 6 may have two or more layers.

  The cover 8 is formed from a resin composition. A preferred base polymer of this resin composition is an ionomer resin. The golf ball 2 having the cover 8 containing an ionomer resin is excellent in resilience performance. The ionomer resin described above for the mid layer 6 can be used for the cover 8.

  Instead of the ionomer resin, the resin composition of the cover 8 may contain another polymer. Examples of other polymers include polystyrene, polyamide, polyester, polyolefin, and polyurethane. The resin composition may contain two or more kinds of polymers.

  The resin composition of the cover 8 may contain an appropriate amount of a colorant, a filler, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, a fluorescent whitening agent, and the like. When the color of the golf ball 2 is white, a typical colorant is titanium dioxide.

  The thickness of the cover 8 is preferably 0.2 mm or more, more preferably 0.4 mm or more, and particularly preferably 0.6 mm or more. The thickness of the cover 8 is preferably 2.5 mm or less, and particularly preferably 2.2 mm or less. The specific gravity of the cover 8 is preferably 0.90 or more, particularly preferably 0.95 or more. The specific gravity of the cover 8 is preferably 1.10 or less, and particularly preferably 1.05 or less.

  FIG. 2 shows a cross section of the golf ball 2 along a plane passing through the center of the dimple 12 and the center of the golf ball 2. The vertical direction in FIG. 2 is the depth direction of the dimple 12. What is indicated by a two-dot chain line 16 in FIG. 2 is a virtual sphere. The surface of the phantom sphere 16 is the surface of the golf ball 2 when it is assumed that there are no dimples 12 and minute protrusions (detailed later). The diameter of the phantom sphere 16 is the same as the diameter of the golf ball 2. The dimple 12 is recessed from the surface of the phantom sphere 16. The land 14 coincides with the surface of the phantom sphere 16.

  In FIG. 2, what is indicated by an arrow Dm is the diameter of the dimple 12. The diameter Dm of each dimple 12 is preferably 2.0 mm or greater and 6.0 mm or less. In FIG. 2, what is indicated by a double-headed arrow Dp is the depth of the dimple 12. This depth Dp is the distance between the deepest part of the dimple 12 and the surface of the phantom sphere 16. The depth Dp is preferably 0.10 mm or greater and 0.65 mm or less.

The area s of the dimple 12 is an area of a region surrounded by the outline of the dimple 12 when the center of the golf ball 2 is viewed from infinity. In the case of the circular dimple 12, the area S is calculated by the following mathematical formula.
S = (Dm / 2) ² * π

  In the present invention, the ratio of the total area S of all the dimples 12 to the surface area of the phantom sphere 16 is referred to as an occupation ratio. From the viewpoint that sufficient turbulence can be obtained, the occupation ratio So is preferably 75% or more. The occupation ratio is preferably 95% or less.

  From the viewpoint of achieving a sufficient occupation ratio, the total number N of the dimples 12 is preferably 250 or more. From the standpoint that each dimple 12 can contribute to turbulence, the total number N is preferably 450 or less.

In the present invention, the “dimple volume” means the volume of the portion surrounded by the surface of the phantom sphere 16 and the surface of the dimple 12. From the viewpoint of suppressing hops of the golf ball 2 during flight, the total volume of the dimples 12 is preferably 450 mm ³ or more. From the viewpoint of suppressing the drop of the golf ball 2 in flight, the total volume is preferably 750 mm ³ or less.

  FIG. 3 is an enlarged perspective view showing a part of the surface of the golf ball 2 of FIG. As is apparent from FIG. 3, the golf ball 2 has a large number of microprojections 18 on the surface thereof. As is clear from FIG. 2, the minute protrusions 18 are formed on the surface of the dimple 12 and also on the surface of the land 14. Each minute protrusion 18 stands up outward in the radial direction of the golf ball 2. The microprojections 18 may be formed only on the surface of the dimple 12. The microprojections 18 may be formed only on the surface of the land 14.

  FIG. 3 shows three minute protrusions 18a belonging to the first row I and three minute protrusions 18b belonging to the second row II. The direction indicated by arrow A in FIG. 3 is the extending direction of the columns. In each row, the minute protrusions 18 are arranged at an equal pitch. In other words, the microprojections 18 are regularly arranged. The minute protrusions 18 may be irregularly arranged on a part of the surface of the golf ball 2.

  The microprojections 18a belonging to the first row I and the microprojections 18b belonging to the second row II may be arranged in a zigzag manner. In other words, the position of the minute protrusion 18a belonging to the first row I may be shifted from the position of the minute protrusion 18b belonging to the second row II in the extending direction A.

  FIG. 4 is an enlarged cross-sectional view showing a part of the golf ball 2 of FIG. In FIG. 4, a cover 8 that is a part of the main body 10 and a paint layer 20 are shown. FIG. 4 shows the minute protrusion 18. The cover 8 has a convex portion 22. The microprojections 18 are formed by the convex portions 22 and the paint layer 20. Since the protrusions 22 are erected outward in the radial direction of the golf ball 2 (upward in FIG. 4), the minute protrusions 18 are also erected outward in the radial direction of the golf ball 2. In other words, the microprotrusions 18 have a shape reflecting the surface shape of the main body 10 (cover 8). In FIG. 4, what is indicated by reference numeral 24 is the bottom surface of the minute protrusion 18.

  FIG. 5 is a cross-sectional view taken along line VV in FIG. FIG. 5 shows the bottom surface 24 of the minute protrusion 18. The bottom surface 24 includes the cover 8 and the paint layer 20.

  What is indicated by an arrow P in FIG. 3 is a pitch. The pitch P is a distance between the first microprojection 18 and the second microprojection 18 adjacent to the first microprojection 18. The pitch P is the distance between the center of gravity of the bottom surface 24 of the first microprojection 18 and the center of gravity of the bottom surface 24 of the second microprojection 18. “The second microprotrusion adjacent to the first microprotrusion” is a microprotrusion 18 having the shortest distance from the first microprotrusion 18 among the microprotrusions 18 present around the first microprotrusion 18. It is. This “distance” is the distance between the centers of gravity of the bottom surface 24 of the microprojections 18.

  One pitch P is determined for each minute protrusion 18. The pitch P of all the microprotrusions 18 is summed, and this sum is divided by the number of microprotrusions 18, whereby the average pitch Pav is calculated. The average pitch Pav is preferably 100 μm or more. Even when mud comes into contact with the golf ball 2 having an average pitch Pav of 100 μm or more, the mud flows between the microprojections 18 and the microprojections 18 adjacent thereto. Mud hardly adheres to the golf ball 2. This golf ball 2 is excellent in antifouling property. In the golf ball 2 having an average pitch Pav of 100 μm or more, water also flows through the flow path between the minute protrusion 18 and the minute protrusion 18 adjacent thereto. Therefore, even when the surface of the golf ball 2 is dirty, when the water is washed with water, the water flows in with mud. This golf ball 2 is excellent in cleanability. From the viewpoint of antifouling properties and cleaning properties, the average pitch Pav is more preferably 110 μm or more, and particularly preferably 120 μm or more. The average pitch Pav is preferably 2 mm or less from the viewpoint that the flow path is easily formed.

  In FIG. 3, an arrow L indicates a distance between the first microprotrusion 18 and the second microprotrusion 18 adjacent to the first microprotrusion 18. The direction of the distance L is the same as the direction of the pitch P.

  One distance L is determined for each minute protrusion 18. The distance L of all the microprotrusions 18 is summed, and this sum is divided by the number of microprotrusions 18, whereby the average distance Lav is calculated. In light of easy formation of the flow path, the average distance Lav is preferably 40 μm or more, more preferably 60 μm or more, and particularly preferably 75 μm or more. The average distance Lav is preferably 400 μm or less.

  FIG. 5 also shows the bottom surface 24d of the second microprotrusion 18d along the two-dot chain line along with the bottom surface 24c of the first microprotrusion 18c. The second minute protrusion 18d is adjacent to the first minute protrusion 18c. In FIG. 5, what is indicated by a two-dot chain line 26 is a straight line passing through the center of gravity Oc of the bottom surface 24c of the first microprojection 18c and the center of gravity Od of the bottom surface 24d of the second microprojection 18d. What is indicated by an arrow T in FIG. 5 is the width of the first microprotrusion 18c. The width T is measured along the straight line 26. The width T is the distance of the portion of the straight line 26 included in the contour of the bottom surface 24c.

  In FIG. 6, the bottom surface 24 e of the second microprotrusion 18 e is also shown by a two-dot chain line along with the bottom surface 24 c of the first microprotrusion 18 c. The second minute protrusion 18e is adjacent to the first minute protrusion 18c. In FIG. 6, what is indicated by a two-dot chain line 28 is a straight line passing through the center of gravity Oc of the bottom surface 24c of the first microprojection 18c and the center of gravity Oe of the bottom surface 24e of the second microprojection 18e. In FIG. 6, what is indicated by an arrow T is the width of the first minute protrusion 18c. The width T is measured along the straight line 28. The width T is the distance of the portion included in the outline of the bottom surface 24 c of the straight line 28. The width T shown in FIG. 6 is larger than the width T shown in FIG.

  The distance between the first microprojection 18c and the second microprojection 18d shown in FIG. 5 is equal to the distance between the first microprojection 18c and the second microprojection 18e shown in FIG. The first minute protrusion 18c is adjacent to the two second minute protrusions 18d and 18e. Accordingly, the first microprotrusion 18 c can have a plurality of widths T. In this case, the largest width T is adopted as the width of the first minute protrusion 18c.

  One width T is determined for each minute protrusion 18. The average width Tav is calculated by summing the widths T of all the microprotrusions 18 and dividing the sum by the number of microprotrusions 18. From the viewpoint of antifouling properties, the average width Tav is preferably 40 μm or more, more preferably 50 μm or more, and particularly preferably 75 μm or more. The average width Tav is preferably 400 μm or less from the viewpoint that the flow path is easily formed.

This golf ball 2 satisfies the following mathematical formula.
Lav> 0.5 ・ Tav
In the golf ball 2, a flow path is easily formed between the minute protrusion 18 and the minute protrusion 18 adjacent thereto. When the golf ball 2 is washed with water, the water flows in with mud. Therefore, this golf ball 2 is excellent in antifouling properties and cleanability. From the viewpoint of antifouling properties and cleaning properties, it is preferable that the golf ball 2 satisfies the following mathematical formula.
Lav ≧ Tav
It is preferable that the golf ball 2 satisfies the following mathematical formula.
Lav <1.5 ・ Tav

  In FIG. 4, what is indicated by an arrow H is the height of the minute protrusion 18. The height H is measured along the radial direction of the golf ball 2. The heights H of all the microprotrusions 18 are summed, and this sum is divided by the number of microprotrusions 18, whereby the average height Hav is calculated. From the viewpoint that a flow path is easily formed between the minute protrusion 18 and the minute protrusion 18 adjacent thereto, the average height Hav is preferably 0.5 μm or more, more preferably 1.0 μm or more, and 2.0 μm or more. Is particularly preferred. In light of flight performance of the golf ball 2, the average height Hav is preferably equal to or less than 50 μm, more preferably equal to or less than 40 μm, and particularly preferably equal to or less than 30 μm.

From the viewpoint of antifouling property and detergency, the average area is preferably 100 [mu] m ² or more bottom 24, more preferably 225 .mu.m ² or more, 400 [mu] m ² or more is particularly preferable. From the viewpoint of antifouling property, the average area is preferably 3600Myuemu ² or less, more preferably 2500 [mu] m ² or less, 1600 .mu.m ² or less is particularly preferred.

  From the viewpoint of antifouling properties and cleaning properties, the ratio of the total area of the bottom surfaces 24 of all the microprojections 18 to the surface area of the phantom sphere 16 is preferably 5% or more, more preferably 15% or more, and particularly preferably 20% or more. preferable. From the viewpoint of antifouling properties, this ratio is preferably 80% or less, more preferably 60% or less, and particularly preferably 50% or less.

  From the standpoint of antifouling properties and cleaning properties, the total number of microprojections 18 is preferably 500 or more, more preferably 1000 or more, and particularly preferably 2000 or more. From the viewpoint of antifouling properties, the total number is preferably 500000 or less, more preferably 300000 or less, and particularly preferably 100000 or less.

  As described above, the minute protrusion 18 includes the convex portion 22 of the main body 10 and the paint layer 20 (see FIG. 4). Therefore, even if the paint layer 20 peels from the main body 10, the shape of the microprojections 18 is generally maintained and the flow path is maintained. No special paint is required to form the microprojections 18. This golf ball 2 can be easily manufactured.

  In the golf ball 2, contamination is prevented by the physical action of the minute protrusions 18. Therefore, it is not necessary to employ the cover 8 and the paint layer 20 having special chemical properties for the purpose of antifouling.

  The convex portion 22 of the main body 10 is formed at the same time as the main body 10 is formed. For this molding, a molding die is used. The cavity surface of this mold has a number of minute recesses. Each concave portion has a shape in which the shape of the convex portion 22 is substantially inverted. This mold can be obtained from a master mold. Etching is an example of the master mold manufacturing method. Many fine maskings are used during etching. By the masking, a convex portion is formed on the master mold. A concave portion is formed in the mold by the convex portion of the master mold. The masking position corresponds to the position of the convex portion of the master mold, corresponds to the position of the concave portion of the mold, and corresponds to the position of the minute protrusion 18 of the golf ball 2. The master mold can be manufactured by various methods other than etching. Laser irradiation processing is exemplified as a method other than etching.

  As described above, the fine protrusions 18 are formed on the surface of the dimple 12 and also on the surface of the land 14 (see FIG. 2). The minute protrusions 18 prevent the dimples 12 from being contaminated and also prevent the land 14 from being contaminated.

  The shape of the microprojections 18 shown in FIGS. 2-6 is generally a quadrangular prism. The golf ball 2 may have microprojections having other shapes. Examples of other shapes include a prism other than a quadrangular prism, a cylinder, a truncated pyramid, a truncated cone, a truncated pyramid, and a cone. The shape of the minute protrusion may be a part of a sphere. The microprotrusions may have a shape in which a plurality of solids are combined.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
100 parts by weight of high-cis polybutadiene (trade name “BR-730” from JSR), 25.5 parts by weight of zinc acrylate, 12 parts by weight of zinc oxide, appropriate amount of barium sulfate, 0.5 parts by weight of diphenyl disulfide 0.9 parts by mass of dicumyl peroxide, 0.1 parts by mass of 2-naphthalenethiol and 2 parts by mass of benzoic acid were kneaded to obtain a rubber composition. This rubber composition was put into a mold composed of an upper mold and a lower mold each having a hemispherical cavity and heated at 160 ° C. for 20 minutes to obtain a core having a diameter of 38.7 mm. The amount of barium sulfate was adjusted so that a core with a predetermined mass was obtained.

  26 parts by mass of ionomer resin (trade name “HIMILAN AM7337” from Mitsui DuPont Polychemical Co., Ltd.), 26 parts by mass of other ionomer resin (trade name “HIMILAN AM7329” from Mitsui DuPont Polychemical Co., Ltd.), 48 parts by mass of styrene block Biaxially contained thermoplastic elastomer (Mitsubishi Chemical's trade name "Lavalon T3221C"), 4 parts by weight of titanium dioxide and 0.2 parts by weight of light stabilizer (Johoku Chemical Industry's trade name "JF-90") The resin composition was obtained by kneading with a kneading extruder. This resin composition was coated around the core by an injection molding method to form an intermediate layer. The thickness of this intermediate layer was 1.0 mm.

  55 parts by mass of ionomer resin (trade name “HIMILAN AM7329” from Mitsui DuPont Polychemical Co., Ltd.), 45 parts by weight of other ionomer resins (trade name “HIMILAN 1555” from Mitsui DuPont Polychemical Co., Ltd.), 4 parts by mass of titanium dioxide And 0.2 parts by mass of a light stabilizer (trade name “JF-90” from Johoku Chemical Industry Co., Ltd.) were kneaded with a twin-screw kneading extruder to obtain a resin composition. A sphere composed of a core and an intermediate layer was put into a final mold composed of an upper mold and a lower mold each having a hemispherical cavity and having a large number of pimples and minute recesses on the cavity surface. The resin composition was coated around the intermediate layer by an injection molding method to form a cover. The thickness of this cover was 1.0 mm. A dimple having a shape obtained by inverting the shape of the pimple was formed on the cover. The cover was further formed with a minute convex portion having a shape obtained by inverting the shape of the minute concave portion.

  A clear paint based on a two-component curable polyurethane was applied around the cover to obtain a golf ball of Example 1 having a diameter of about 42.7 mm and a mass of about 45.6 g. This golf ball has a large number of minute protrusions on its surface. The specifications of these microprotrusions are shown in Table 1 below.

[Examples 2-4 and 8 and Comparative Example 1]
Example 2-4 and Example 2-4 were changed in the same manner as in Example 1 except that the final mold was changed and minute projections having an average pitch Pa, an average distance La, and an average width Ta shown in Table 1-2 below were formed. 8 and Comparative Example 1 golf balls were obtained.

[Example 5-7]
A golf ball of Example 5-7 was obtained in the same manner as in Example 1 except that the final mold was changed and minute protrusions having an average height Ha shown in Table 1-2 below were formed.

[Comparative Example 2]
A golf ball of Comparative Example 2 was obtained in the same manner as in Example 1 except that the final mold was changed and no fine protrusion was formed.

[Anti-fouling]
Dirt and water were mixed to obtain mud. Along with the mud, the golf balls according to the examples and the comparative examples were put into buckets, and the mud was stirred. The degree of dirt on the golf ball thereafter was rated according to the following criteria.
A: Very little dirt B: Little dirt C: Many dirt D: Very much dirt This result is shown in Tables 1 and 2 below.

[Cleanability]
The golf ball subjected to the antifouling property evaluation was put into a bucket together with water, and the water was stirred. The degree of dirt on the golf ball thereafter was rated according to the following criteria.
A: Very little dirt B: Little dirt C: Many dirt D: Very much dirt This result is shown in Tables 1 and 2 below.

  As shown in Tables 1 and 2, the golf balls of the examples are excellent in antifouling properties and cleanability. From this evaluation result, the superiority of the present invention is clear.

  The above-mentioned minute protrusions are applied not only to three-piece golf balls but also to golf balls having various structures such as one-piece golf balls, two-piece golf balls, four-piece golf balls, five-piece golf balls, six-piece golf balls, and wound golf balls. Can be done.

2 ... Golf ball 4 ... Core 6 ... Intermediate layer 8 ... Cover 10 ... Main body 12 ... Dimple 14 ... Land 16 ... Virtual sphere 18 ... Micro projection 20 ... Paint layer 22 ... Convex part 24 ... Bottom surface

Claims (5)

A golf ball having a plurality of dimples and a land,
A plurality of minute protrusions formed on the surface of the dimple and / or the land,
A golf ball having an average pitch Pav of the fine protrusions of 100 μm or more.   2. The golf ball according to claim 1, wherein an average height Hav of the minute protrusions is not less than 0.5 μm and not more than 50 μm. The golf ball according to claim 1 or 2 satisfying the following mathematical formula.
Lav> 0.5 ・ Tav
(In the above formula, Lav represents the average value of the distance L between the microprotrusions and other microprotrusions adjacent to the microprotrusions, and Tav represents the average value of the widths T of the microprotrusions.)   4. The golf ball according to claim 1, wherein the golf ball has a plurality of rows, and a plurality of minute protrusions are arranged at an equal pitch in each row. It has a main body and a paint layer located outside this main body,
The golf ball according to claim 1, wherein the minute protrusion has a shape reflecting a surface shape of the main body.

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