JP7290189B2 - Golf ball - Google Patents

Description

The present invention relates to golf balls. More particularly, the present invention relates to golf balls having microprojections on their surface.

A golf ball hit by a golf club flies in the air. This golf ball falls and rolls on the ground. When falling and rolling, the golf ball contacts the ground. This contact can deposit mud on the surface of the golf ball and contaminate this surface. A player cannot touch a golf ball when it is in the fairway or rough. Players are therefore unable to remove dirt from golf balls. On the green, players can remove dirt from golf balls. However, this removal work is troublesome. In some cases, even the work cannot sufficiently remove the dirt. Even washing with water may not remove the dirt. Golf balls that remain soiled are replaced. The exchange imposes a financial burden on the player.

A golf ball has a large number of dimples on its surface. The dimples disrupt the flow of air around the golf ball during flight, causing turbulent separation. This phenomenon is called "turbulization". Turbulence shifts the point of air separation from the golf ball rearward, reducing drag. The turbulence promotes the deviation between the upper separation point and the lower separation point of the golf ball due to backspin, and increases the lift acting on the golf ball. The reduction in drag and increase in lift is referred to as the "dimple effect." Better dimples disrupt airflow better. Good dimples produce great distance.

Backspin velocity correlates with trajectory height. A golf ball with a high backspin speed provides a high trajectory. Long iron shots tend to have a low trajectory height. Golf players desire a golf ball with a high spin rate on long iron shots.

Japanese Patent Application Laid-Open No. 2015-142599 discloses a golf ball having a highly rough surface. This roughness can be formed by blasting or the like. This roughness enhances the aerodynamic properties of the golf ball through a synergistic effect with the dimples.

Japanese Patent Application Laid-Open No. 2011-72776 discloses a golf ball having a coating formed by a paint containing particles. The particles enhance the aerodynamic properties of the golf ball through a synergistic effect with the dimples.

Japanese Patent Application Laid-Open No. 2-68077 discloses a golf ball having a dimple having a single projection on its bottom. The dimples having the protrusions enhance the aerodynamic characteristics of the golf ball.

Japanese Patent Application Laid-Open No. 2015-142599 Japanese Patent Application Laid-Open No. 2011-72776 JP-A-2-68077

SUMMARY OF THE INVENTION It is an object of the present invention to provide a golf ball that has a sufficiently high spin rate on shots with a long iron and is excellent in stain resistance and washability.

A golf ball according to the present invention has a core and a cover positioned outside the core. This cover has a plurality of microprotrusions on its surface. Each microprojection has an exposed portion exposed to the surface of the golf ball. The arithmetic mean height Sa of the surface of the golf ball is 0.5 μm or more and 30 μm or less. The average value Hav of the height H of the exposed portion is 0.5 μm or more and 50 μm or less.

Preferably, the ratio Pp of the total area of all the exposed portions to the surface area of the phantom sphere of the golf ball is 7% or more.

Preferably, the average value Dav of the diameter D of the exposed portion is 5 μm or more and 50 μm or less.

Preferably, the average value Pav of the pitch P between one exposed portion and another adjacent exposed portion is 100 μm or less.

Preferably, the maximum height Sz of the surface of the golf ball is 5 μm or more and 200 μm or less.

The golf ball may further have a paint layer partially covering the cover. The exposed portion protrudes from this paint layer.

In the golf ball according to the present invention, the exposed portion reduces the lift of the golf ball during flight. The trajectory of this golf ball is not too high. Therefore, with this golf ball, a long flight distance can be obtained on shots with a long iron.

FIG. 1 is a cross-sectional view showing a golf ball according to one embodiment of the present invention. 2 is an enlarged cross-sectional view showing a portion of the golf ball of FIG. 1; FIG. 3 is an enlarged perspective view showing a portion of the surface of the golf ball of FIG. 1; FIG. 4 is an enlarged cross-sectional view showing a portion of the golf ball of FIG. 1; FIG. 5 is a cross-sectional view taken along line VV of FIG. 4. FIG. FIG. 6 is a cross-sectional view showing a portion of a golf ball according to another embodiment of the invention. FIG. 7 is a cross-sectional view showing a portion of a golf ball according to still another embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

A golf ball 2 shown in FIG. 1 has a spherical core 4 , an intermediate layer 6 located outside the core 4 , and a cover 8 located outside the intermediate layer 6 . Core 4 , intermediate layer 6 and cover 8 are included in body 10 of golf ball 2 . This golf ball 2 does not have a paint layer. This golf ball 2 has a large number of dimples 12 on its surface. The land 14 is the portion of the surface of the golf ball 2 other than the dimples 12 . Body 10 may have a one-piece construction, a two-piece construction, a four-piece construction, a five-piece construction, and the like.

The diameter of the golf ball 2 is preferably 40 mm or more and 45 mm or less. A diameter of 42.67 mm or more is particularly preferable from the viewpoint that the standards of the United States Golf Association (USGA) are satisfied. From the viewpoint of air resistance suppression, the diameter is more preferably 44 mm or less, and particularly preferably 42.80 mm or less. The golf ball 2 according to this embodiment has a diameter of 42.7 mm.

The weight of the golf ball 2 is preferably 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, particularly preferably 45.00 g or more. From the viewpoint that the USGA standard is satisfied, the mass is particularly preferably 45.93 g or less.

Preferably, core 4 is formed by cross-linking 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 rubbers may be used in combination. From the viewpoint of resilience performance, polybutadiene is preferred, and high-cis polybutadiene is particularly preferred.

Core 4 may be formed from a resin composition. Core 4 may be formed from a mixture of a rubber composition and a resin composition. The resin composition described below for the intermediate layer 6 or the cover 8 can be used for the core 4 .

The rubber composition of core 4 contains a co-crosslinking agent. Preferred co-crosslinking agents from the viewpoint of resilience performance are zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. It is preferred 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-butylperoxy). oxy)hexane and di-t-butyl peroxide.

The rubber composition of core 4 may contain additives such as fillers, sulfur, vulcanization accelerators, sulfur compounds, anti-aging agents, colorants, plasticizers and dispersants. The rubber composition may contain a carboxylic acid or carboxylate. The rubber composition may comprise synthetic resin powder or crosslinked rubber powder.

The diameter of the core 4 is preferably 30.0 mm or more, particularly preferably 38.0 mm or more. The diameter of the core 4 is preferably 42.0 mm or less, particularly preferably 41.5 mm or less. Core 4 may have more than one layer. The core 4 may have ribs on its surface. Core 4 may be hollow.

The intermediate layer 6 is made of a resin composition. A preferred base polymer for this resin composition is an ionomer resin. Preferred ionomer resins include binary copolymers of α-olefins and α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms. Another preferred ionomer resin is a ternary combination 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. polymers. In the bi- and terpolymers, preferred α-olefins are ethylene and propylene, and preferred α,β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. In the bi- and terpolymers, some of the carboxyl groups are neutralized with metal ions. Examples of 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, or in addition to the ionomer resin, the resin composition of the intermediate layer 6 may contain other polymers. Other polymers include polystyrene, polyamides, polyesters, polyolefins and polyurethanes. The resin composition may contain two or more polymers.

The resin composition of the intermediate layer 6 contains 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 brightener, and the like. It's okay. For the purpose of specific gravity adjustment, the resin composition may contain powder of high specific gravity metal such as tungsten and molybdenum.

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

The cover 8 is molded from a thermoplastic resin composition or a thermosetting resin composition or a mixture of both. Preferably, cover 8 is molded from a thermoplastic resin composition. Examples of base polymers for this resin composition include ionomer resins, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, thermoplastic polyurethane elastomers, thermoplastic polyolefin elastomers, and thermoplastic polystyrene elastomers. In particular, ionomer resins are preferred. Ionomer resins are highly elastic. The golf ball 2 having the cover 8 containing ionomer resin has excellent resilience performance. This golf ball 2 has excellent flight distance on driver shots. The ionomer resins described above for intermediate layer 6 can be used for cover 8 .

The ionomer resin and other resins may be used in combination. When used in combination, the ionomer resin is the main component of the base polymer from the viewpoint of resilience performance. The ratio of the ionomer resin to the total base polymer is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more.

The resin composition of the cover 8 may contain a pigment. The resin composition may contain inorganic pigments and organic pigments. Inorganic pigments include red pigments such as red iron oxide (Fe ₂ O ₃ ), red lead (Pb ₃ O ₄ ), molybdenum red and cadmium red; titanium yellow (TiO ₂ —NiO—Sb ₂ O ₃ ), litharge (PbO). , yellow lead ( _PbCrO4 ), _iron oxide yellow (FeO(OH)) and cadmium yellow; blue pigments such as cobalt blue ( _CoO.Al2O3 ), Prussian blue and ultramarine blue. . Examples of organic pigments include azo pigments, phthalocyanine pigments and perylene pigments. Azo pigments are preferred. Examples of azo pigments include Pigment Yellow-1, Pigment Yellow-12, Pigment Red 3, Pigment Red 57 and Pigment Orange 13.

The resin composition of the cover 8 may contain appropriate amounts of fillers, dispersants, antioxidants, ultraviolet absorbers, light stabilizers, fluorescent agents, fluorescent whitening agents, and the like.

The thickness of the cover 8 is preferably 0.2 mm or more, particularly preferably 0.3 mm or more. The thickness of the cover 8 is preferably 2.5 mm or less, 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, particularly preferably 1.05 or less. The cover 8 may have two or more layers.

FIG. 2 shows a cross section of golf ball 2 along a plane passing through the center of dimple 12 and the center of golf ball 2 . The vertical direction in FIG. 2 is the depth direction of the dimples 12 . A phantom sphere is indicated by a chain double-dashed line 16 in FIG. The surface of phantom sphere 16 is the surface of golf ball 2 when it is assumed that dimples 12 and exposed portions (described in detail later) do not exist. The phantom sphere 16 has the same diameter as the golf ball 2 . Dimple 12 is recessed from the surface of phantom sphere 16 . Land 14 coincides with the surface of phantom sphere 16 .

The diameter of the dimple 12 is indicated by an arrow Dm in FIG. This diameter Dm is the distance between one contact point Ed and the other contact point Ed when a tangent line Tg common to both sides of the dimple 12 is drawn. The contact Ed is also the edge of the dimple 12 . Edge Ed defines the contour of dimple 12 .

The diameter Dm of each dimple 12 is preferably 2.0 mm or more and 6.0 mm or less. The dimples 12 having a diameter Dm of 2.0 mm or more contribute to turbulence. From this point of view, the diameter Dm is more preferably 2.5 mm or more, and particularly preferably 2.8 mm or more. The dimples 12 having a diameter Dm of 6.0 mm or less do not impair the nature of the golf ball 2, which is substantially spherical. From this point of view, the diameter Dm is more preferably 5.5 mm or less, particularly preferably 5.0 mm or less.

For a non-circular dimple, a circular dimple 12 having the same area as the non-circular dimple is assumed. The diameter of this hypothetical dimple 12 is considered the diameter of the non-circular dimple.

A double arrow Dp in FIG. 2 indicates the depth of the dimple 12 . This depth Dp is the distance between the deepest part of the dimple 12 and the tangent line Tg. The average depth Dpav is calculated by summing the depths Dp of all dimples 12 and dividing this sum by the total number of dimples 12 . The average depth Dpav is preferably 80 μm or more and 200 μm or less. A large run can be achieved with the golf ball 2 having an average depth Dpav of 80 μm or more. From this point of view, the average depth Dpav is more preferably 100 μm or more, particularly preferably 110 μm or more. A large carry can be achieved with the golf ball 2 having an average depth Dpav of 200 μm or less. From this point of view, the average depth Dpav is more preferably 180 μm or less, particularly preferably 160 μm or less.

FIG. 3 is an enlarged perspective view showing a portion of the surface of golf ball 2 of FIG. As described above, this golf ball 2 does not have a paint layer. Accordingly, the surface of cover 8 is the surface of golf ball 2 shown in FIG. As shown in FIG. 3, this cover 8 has a large number of minute projections 18 on its surface. Each microprotrusion 18 has a generally cylindrical shape. As is clear from FIG. 2, the minute protrusions 18 are formed on the surface of the dimples 12 and also formed on the surfaces of the lands 14 . Each minute protrusion 18 stands radially outward of the golf ball 2 . Microprotrusions 18 may be formed only on the surface of dimple 12 . Microprotrusions 18 may be formed only on the surface of land 14 . Since there is no paint layer, each minute projection 18 is exposed on the surface of the golf ball 2 as a whole. In a golf ball 2 that does not have a paint layer, the microprojections 18 are also exposed portions 19 as a whole.

Mud may contact the surface of the golf ball 2 when the golf ball 2 hits the ground or rolls on the ground. Since the mud flows between the exposed portion 19 and the adjacent exposed portion 19 as a channel, the mud is less likely to adhere to the golf ball 2 . This golf ball 2 is hard to get dirty. This golf ball 2 is excellent in antifouling properties.

Water easily flows between the exposed portion 19 and the adjacent exposed portion 19 . Therefore, even if mud adheres to the surface of the golf ball 2, when the surface is washed with water, the water takes in the dirt and flows. Dirt on this golf ball 2 is easily removed. This golf ball 2 is excellent in washability. The exposed portion 19 can also contribute to protection of the mark layer.

As described above, this golf ball 2 does not have a paint layer. Therefore, improvement in spin speed due to the paint layer cannot be expected. However, since the coefficient of friction between the golf ball 2 having the exposed portion 19 and the club face is large, the spin rate does not drop significantly compared to conventional golf balls. This golf ball 2 has excellent flight performance on shots with a long iron.

FIG. 3 shows a plurality of exposed portions 19 belonging to the first row I and a plurality of exposed portions 19 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 exposed portions 19 are arranged at equal pitches. In other words, the exposed portions 19 are regularly arranged. The exposed portions 19 belonging to the first row I and the exposed portions 19 belonging to the second row II are arranged in a zigzag pattern. The exposed portions 19 may be arranged irregularly on a portion of the surface of the golf ball 2 .

FIG. 4 is an enlarged cross-sectional view showing a portion of the golf ball 2 of FIG. The cover 8 has minute projections 18 (that is, exposed portions 19). The exposed portion 19 stands radially outward of the golf ball 2 . Reference numeral 24 in FIG. 4 indicates the bottom surface of the exposed portion 19 .

5 is a cross-sectional view taken along line VV of FIG. 4. FIG. FIG. 5 shows the bottom surface 24 of the exposed portion 19 . As described above, the microprotrusions 18 have a cylindrical shape. Therefore, the shape of the bottom surface 24 of the exposed portion 19 is circular.

Arrow D in FIG. 4 indicates the diameter of the bottom surface 24 and the diameter of the exposed portion 19 . By summing up the diameters D of all the exposed portions 19 and dividing this total by the number of exposed portions 19, the average diameter Dav is calculated. The average diameter Dav is preferably 5 μm or more and 50 μm or less. A golf ball 2 having an average diameter Dav within the above range is excellent in antifouling properties and washability. A golf ball 2 having an average diameter Dav within the above range has excellent flight distance on long iron shots. From these points of view, the average diameter Dav is more preferably 15 μm or more, particularly preferably 20 μm or more. From the same point of view, the average diameter Dav is more preferably 40 μm or less, particularly preferably 35 μm or less.

The area of exposed portion 19 is defined as the area of bottom surface 24 . The area Sp of the exposed portion 19 shown in FIGS. 4 and 5 can be calculated by the following formula.
Sp = (D / 2) ² * pi

The ratio Pp of the total area Sp of all the exposed portions 19 to the surface area of the phantom sphere 16 of the golf ball 2 is preferably 7% or more. A golf ball 2 having a ratio Pp of 7% or more has excellent antifouling properties and washability. This golf ball 2 is also excellent in flight distance on shots with a long iron. From these points of view, the ratio Pp is preferably 15% or more, particularly preferably 20% or more. From the viewpoint of easiness in manufacturing the mold for the golf ball 2, the ratio Pp is preferably 50% or less, more preferably 40% or less, and particularly preferably 35% or less.

In FIG. 5, along with the bottom surface 24c of the first exposed portion 19c, the bottom surface 24d of the second exposed portion 19d is also shown by a two-dot chain line. The second exposed portion 19d is adjacent to the first exposed portion 19c. A two-dot chain line 26 in FIG. 5 is a straight line passing through the center of gravity Oc of the bottom surface 24c of the first exposed portion 19c and the center of gravity Od of the bottom surface 24d of the second exposed portion 19d.

The arrow P in FIG. 5 indicates the pitch. The pitch P is the distance between the first exposed portion 19c and the second exposed portion 19d adjacent to the first exposed portion 19c. The pitch P is the distance between the center of gravity Oc of the bottom surface 24c of the first exposed portion 19c and the center of gravity Od of the bottom surface 24d of the second exposed portion 19d. The “second exposed portion 19d adjacent to the first exposed portion 19c” means the distance L (described later in detail) from the first exposed portion 19c among the exposed portions 19 existing around the first exposed portion 19c. ) is the smallest exposed portion 19 .

One pitch P is determined for each exposed portion 19 . The average pitch Pav is calculated by summing the pitches P of all the exposed portions 19 and dividing the sum by the number of the exposed portions 19 . The average pitch Pav is preferably 100 μm or less. A golf ball 2 having an average pitch Pav of 100 μm or less is excellent in antifouling properties, washability, and flight performance on shots with a long iron. From these points of view, the average pitch Pav is more preferably 80 μm or less, particularly preferably 70 μm or less. From the same point of view, the average pitch Pav is preferably 10 μm or more, more preferably 20 μm or more, and particularly preferably 25 μm or more.

The arrow L in FIG. 5 indicates the distance between the first exposed portion 19c and the second exposed portion 19d adjacent to the first exposed portion 19c. The distance L is the pitch P minus the radius of the bottom surface 24c of the first exposed portion 19c and the radius of the bottom surface 24d of the second exposed portion 19d. One distance L is determined for each exposed portion 19 . The average distance Lav is calculated by summing the distances L of all the exposed portions 19 and dividing this sum by the number of exposed portions 19 . The average distance Lav is preferably 5 μm or more and 50 μm or less. A golf ball 2 having an average distance Lav within this range is excellent in antifouling properties, washability, and flight performance on shots with a long iron. From these points of view, the average distance Lav is particularly preferably 10 μm or more and 40 μm or less.

What is indicated by an arrow H in FIG. 4 is the height of the minute projections 18 and the height of the exposed portion 19 . Height H is measured along the radial direction of golf ball 2 . The average height Hav is calculated by summing the heights H of all the exposed portions 19 and dividing this total by the number of the exposed portions 19 . The average height Hav is preferably 0.5 μm or more and 50 μm or less. A golf ball 2 having an average height Hav within this range is excellent in antifouling properties, washability, and flight performance on shots with a long iron. From these points of view, the average height Hav is preferably 2 μm or more, particularly preferably 3 μm or more. From the same point of view, the average height Hav is more preferably 40 μm or less, particularly preferably 35 μm or less.

The total number of exposed portions 19 is preferably 10,000 or more and 10,000,000 or less. The golf ball 2 having a total number of 10,000 or more is excellent in antifouling properties, washability, and flight performance on shots with a long iron. From these viewpoints, the total number is more preferably 20,000 or more, and particularly preferably 50,000 or more. Molds for golf balls 2 with a total number of 10 million or less are easy to manufacture. From this point of view, the total number is more preferably 7 million or less, and particularly preferably 5 million or less.

The arithmetic mean height Sa of the surface of the golf ball 2 is preferably 0.5 μm or more and 30 μm or less. A golf ball 2 having an arithmetic mean height Sa within this range is excellent in antifouling properties, washability, and flight performance on long iron shots. From these points of view, the arithmetic mean height Sa is more preferably 1.5 μm or more, and particularly preferably 2.0 μm or more. From the same point of view, the arithmetic mean height Sa is more preferably 25 μm or less, particularly preferably 20 μm or less.

The maximum height Sz of the surface of the golf ball 2 is preferably 5 μm or more and 200 μm or less. A golf ball 2 having a maximum height Sz within this range is excellent in antifouling properties, washability, and flight performance on long iron shots. From these points of view, the maximum height Sz is more preferably 10 μm or more, and particularly preferably 15 μm or more. From the same point of view, the maximum height Sz is more preferably 180 μm or less, particularly preferably 160 μm or less.

The arithmetic mean height Sa and the maximum height Sz are measured by a laser microscope (for example, a non-contact surface roughness/profile measuring instrument manufactured by Keyence Corporation) in accordance with ISO-25178. In this microscope, the surface of the golf ball 2 is scanned with a laser in the X and Y directions. Through this scanning, unevenness data on the surface of the golf ball 2 is obtained. The arithmetic average height Sa and the maximum height Sz are calculated from the three-dimensional image thus obtained. The measurement conditions are as follows.
Magnification: 1000
Measurement range X: 250 μm
Measurement range Y: 250 μm
Cutoff value: λc = 0.25
Observation area: X=1024 pixels, Y=768 pixels Total number of pixels: 786432 pixels

The glossiness of the surface of the golf ball 2 is preferably 0.1 or more and 20 or less. A golf ball 2 having a gloss within this range has an excellent appearance. From this point of view, the glossiness is more preferably 0.3 or more and 17 or less, and particularly preferably 0.5 or more and 15 or less. Gloss is measured according to the specification of "ASTM D523-60°".

FIG. 6 is a cross-sectional view showing a portion of a golf ball according to another embodiment of the invention. FIG. 6 shows a cover 28 which is part of the body. The cover 28 has microprotrusions 32 . This golf ball does not have a paint layer. Accordingly, the microprotrusion 32 is the exposed portion 34 as a whole. Reference numeral 36 in FIG. 6 indicates the bottom surface of the exposed portion 34 .

The microprotrusions 32 have a truncated conical shape. Therefore, the exposed portion 34 also has a truncated cone shape. The specifications of this golf ball are the same as those of the golf ball 2 shown in FIGS.

In this golf ball, the exposed portion 34 also contributes to antifouling properties, washability, and flight performance on long iron shots.

FIG. 7 is a cross-sectional view showing a portion of a golf ball according to still another embodiment of the invention. This golf ball has a cover 38 and a paint layer 40 . The cover 38 has microprotrusions 42 . The paint layer 40 is thin. Therefore, a portion of the minute protrusions 42 are not covered with the paint layer 40 . In other words, part of the minute projections 42 are exposed on the surface of the golf ball. This portion is referred to as the exposed portion 44 . The exposed portion 44 protrudes from the paint layer 40 . Reference numeral 46 in FIG. 7 indicates the bottom surface of the exposed portion 44 .

Also in this golf ball, the exposed portion 44 is excellent in antifouling properties, washability, and flight performance on long iron shots.

A golf ball may have microprojections having shapes such as cones, prisms, truncated pyramids, pyramids, partial spheres, and the like.

The effects of the present invention will be clarified by examples below, but the present invention should not be construed in a limited manner based on the description of these examples.

[Example 1]
100 parts by mass of high-cis polybutadiene (JSR's trade name "BR-730"), 27.4 parts by mass of zinc acrylate, 5 parts by mass of zinc oxide, an appropriate amount of barium sulfate, 0.5 parts by mass of diphenyl disulfide and 0.9 parts by mass of dicumyl peroxide were kneaded to obtain a rubber composition. This rubber composition was put into a mold consisting of an upper mold and a lower mold having a hemispherical cavity and heated at 160° C. for 20 minutes to obtain a core with a diameter of 38.20 mm. The amount of barium sulfate was adjusted to obtain cores of given mass.

26 parts by mass of ionomer resin ("Himilan AM7337", trade name of Mitsui DuPont Polychemical Co., Ltd.), 26 parts by mass of other ionomer resin ("Himilan AM7329", trade name of DuPont Mitsui Polychemical Co., Ltd.), 48 parts by mass of styrene block Thermoplastic elastomer (trade name “Lavalon T3221C” manufactured by Mitsubishi Chemical Corporation), 4 parts by mass of titanium dioxide (A220) and 0.2 parts by mass of light stabilizer (trade name “JF-90” manufactured by Johoku Chemical Industry Co., Ltd.) were kneaded with a twin-screw kneading extruder to obtain a resin composition. 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 1.00 mm.

47 parts by mass of ionomer resin (Mitsui DuPont Polychemicals, trade name "Himilan 1555"), 46 parts by mass of other ionomer resin (Mitsui DuPont Polychemicals, trade name "Himilan 1557"), 7 parts by mass of styrene block The contained thermoplastic elastomer (the above-mentioned "Lavalon T3221C"), 4 parts by mass of titanium dioxide (A220) and 0.2 parts by mass of a light stabilizer (the above-mentioned "JF-90") are kneaded with a twin-screw kneading extruder. , to obtain a resin composition. A sphere consisting of a core and an intermediate layer was put into a final mold having many pimples and micro-dents on the cavity surface. The above resin composition was coated around the intermediate layer by injection molding to form a cover. The thickness of this cover was 1.25 mm. The cover was formed with dimples having a shape that was the inverse of the shape of the pimples. The cover was further formed with minute protrusions (exposed portions) having a shape that was the reverse of the shape of the minute recesses.

[Examples 2-8 and Comparative Examples 1 and 3]
Golf balls of Examples 2-8 and Comparative Examples 1 and 3 were obtained in the same manner as in Example 1, except that the final mold was changed to form the exposed portions with the specifications shown in Table 1-3 below. . The golf ball according to Comparative Example 3 does not have an exposed portion.

[Comparative Example 2]
A golf ball of Comparative Example 2 was obtained in the same manner as in Comparative Example 3, except that the entire cover was covered with a paint layer. The thickness of the paint layer was 10 μm.

[Spin speed]
An iron club #5 (trade name “SRIXON” manufactured by Sumitomo Rubber Industries, shaft hardness: S) was attached to a swing machine manufactured by Golf Laboratory. A golf ball was hit at a head speed of 41 m/sec to measure the spin rate. The average values of data obtained from 20 measurements are shown in Tables 1-3 below. The spin speed ratios when Comparative Example 2 is used as a reference are also shown in Tables 1-3 below.

[Stain resistance]
A golf ball according to each example and each comparative example was placed in a bucket together with soil, and the soil was stirred. The degree of soiling of the golf balls thereafter was rated according to the following criteria.
A: very little dirt B: little dirt C: much dirt D: very much dirt The results are shown in Tables 1-3 below.

[Washability]
The golf balls subjected to the antifouling evaluation were put into a bucket together with water, and the water was stirred. The degree of soiling of the golf balls thereafter was rated according to the following criteria.
A: very little dirt B: little dirt C: much dirt D: very much dirt The results are shown in Tables 1-3 below.

As shown in Tables 1-3, the golf balls of each example are excellent in flight performance on long iron shots. Furthermore, the golf balls of each example are excellent in antifouling properties and washability. From these evaluation results, the superiority of the present invention is clear.

The aforementioned minute projections are applicable 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

2 Golf ball 4 Core 6 Intermediate layer 8 Cover 10 Body 12 Dimple 14 Land 16 Virtual sphere 18, 32, 42・Minor protrusions 19, 34, 44... Exposed parts 24, 36, 46... Bottom surface 40... Paint layer

Claims (5)

A golf ball comprising a core and a cover positioned outside the core,
The cover has a plurality of microprojections on its surface,
each microprojection has an exposed portion exposed on the surface of the golf ball,
The surface of the golf ball has an arithmetic mean height Sa of 0.5 μm or more and 30 μm or less,
The average value Hav of the height H of the exposed portion is 0.5 μm or more and 50 μm or less,
The cover has a thickness of 0.2 mm or more and 2.5 mm or less,
A golf ball, the surface of which is the surface of the cover. 2. The golf ball according to claim 1, wherein the ratio Pp of the total area of all the exposed portions to the surface area of the phantom sphere of the golf ball is 7% or more. 3. The golf ball according to claim 1, wherein the average value Dav of the diameter D of the exposed portion is 5 [mu]m or more and 50 [mu]m or less. 4. The golf ball according to any one of claims 1 to 3, wherein an average value Pav of pitches P between one exposed portion and another adjacent exposed portion is 100 [mu]m or less. 5. The golf ball according to any one of claims 1 to 4, wherein the maximum surface height Sz is from 5 [mu]m to 200 [mu]m.

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