JP2007260317A - Golf ball - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a golf ball 2 having an extremely thin cover 6 and having superior carrying property. <P>SOLUTION: This golf ball 2 is provided with a core 4, a cover 6 and multiple dimples 8. The thickness of the cover 6 is 0.20 mm or less. The dimples 8 are piercedly provided in the cover 6. The dimple 8 has a side wall 14 and a bottom 16. the side wall 14 has a shape of the side face of a truncated cone. The bottom 16 is accorded with the surface of the core 4. The bottom 16 is outward projecting radially. This golf ball 2 is exposed with the surface of the core 4. The ratio (D2/D1) of the diameter D2 of the bottom 16 to the diameter D1 of the dimple 8 is not less than 0.50 and not more than 0.85. The total area of the dimples 8 is not less than 250 mm<SP>3</SP>and not more than 400 mm<SP>3</SP>. The bottom 16 is applied with surface roughening. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a golf ball. More specifically, the present invention relates to an improvement in golf ball dimples.

  A general golf ball includes a core and a cover. The golf ball further includes a large number of dimples. The dimple is formed on the surface of the cover. The dimples disturb the air flow around the golf ball during flight and cause turbulent separation. Turbulent separation shifts the separation point of air from the golf ball backwards, reducing drag. Turbulent separation 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 of drag and the improvement of lift are referred to as “dimple effect”. Excellent dimples better disturb the air flow. Excellent dimples produce a great flight distance.

For golf balls, control performance is important as well as flight distance. A golf ball having an extremely thin cover and having both flight distance and control performance has been proposed. For example, Japanese Patent Application Laid-Open No. 2006-34773 discloses a golf ball including a cover having a thickness of 0.1 mm to 0.6 mm.
JP 2006-34773 A

  From the viewpoint of the dimple effect, the dimple needs to have a sufficient volume. As described above, the dimple is formed on the cover. Dimples deeper than the cover thickness cannot be formed. In a golf ball having an extremely thin cover, the dimple volume is insufficient. With this golf ball, a sufficient dimple effect cannot be obtained. This golf ball is inferior in flight performance.

  An object of the present invention is to provide a golf ball having an extremely thin cover and excellent flight performance.

  The golf ball according to the present invention includes a core, a cover, and dimples. The cover is laminated on the core. The thickness of this cover is 0.20 mm or less. The dimple is drilled in the cover. The bottom surface of the dimple coincides with the surface of the core.

Preferably, the ratio (D2 / D1) of the bottom surface diameter D2 to the dimple diameter D1 is not less than 0.50 and not more than 0.85. Preferably, the side wall of the dimple has a shape of a side surface of the truncated cone. Preferably, the total volume of the dimples is 250 mm ³ or more and 400 mm ³ or less. Preferably, the bottom surface is roughened.

  In this golf ball, since the dimple penetrates the cover, a sufficient dimple volume is achieved even though the cover is extremely thin. This golf ball is excellent in flight performance. In this golf ball, an extremely thin cover can contribute to control performance, feel at impact, and the like.

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

  FIG. 1 is a schematic cross-sectional view showing a golf ball 2 according to an embodiment of the present invention. The golf ball 2 includes a spherical core 4 and a cover 6. A large number of dimples 8 are formed on the cover 6. A portion of the surface of the golf ball 2 other than the dimples 8 is a land 10. The golf ball 2 includes a paint layer and a mark layer, but these layers are not shown.

  The golf ball 2 has a diameter of 40 mm or greater and 45 mm or less. From the viewpoint of satisfying the standards of the US Golf Association (USGA), the diameter is more preferably 42.67 mm or more. 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. The golf ball 2 has a mass of 40 g or more and 50 g or less. In light of attainment of great inertia, the mass is more preferably equal to or greater than 44 g, and particularly preferably equal to or greater than 45.00 g. From the viewpoint that the USGA standard is satisfied, the mass is more preferably 45.93 g or less.

  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.

  For crosslinking of the core 4, a co-crosslinking agent is preferably used. From the viewpoint of resilience performance, preferred co-crosslinking agents are zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. It is preferable that an organic peroxide is blended with the co-crosslinking agent in the rubber composition. Suitable organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t- Butyl peroxy) hexane and di-t-butyl peroxide.

  In the rubber composition of the core 4, various additives such as a filler, a sulfur compound, an anti-aging agent, a colorant, a plasticizer, and a dispersant are blended in appropriate amounts as necessary. Crosslinked rubber powder or synthetic resin powder may be blended with the rubber composition.

  The core 4 may be composed of a spherical center and an intermediate layer covering the center. Typically, the center is made of rubber and the intermediate layer is made of rubber or thermoplastic resin. The core 4 may include three or more layers.

  A suitable polymer for the cover 6 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. Other preferable ionomer resins include ternary α-olefin, α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and α, β-unsaturated carboxylic acid ester having 2 to 22 carbon atoms. A copolymer is mentioned. In the 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 the 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.

  A thermoplastic polyurethane elastomer may be used for the cover 6. The thermoplastic polyurethane elastomer is soft. When the golf ball 2 having the cover 6 made of a thermoplastic polyurethane elastomer is hit with a short iron, the spin rate is high. The cover 6 made of a thermoplastic polyurethane elastomer contributes to control performance in a shot with a short iron. The thermoplastic polyurethane elastomer also contributes to the scratch resistance performance of the cover 6.

  The thermoplastic polyurethane elastomer includes a polyurethane component as a hard segment and a polyester component or a polyether component as a soft segment. Examples of the curing agent for the polyurethane component include alicyclic diisocyanate, aromatic diisocyanate and aliphatic diisocyanate. In particular, alicyclic diisocyanates are preferred. Since the alicyclic diisocyanate does not have a double bond in the main chain, yellowing of the cover 6 is suppressed. In addition, since the alicyclic diisocyanate is excellent in strength, damage to the cover 6 is suppressed. Two or more diisocyanates may be used in combination.

  Other polymers may be used for the cover 6. Examples of the other polymer include a thermoplastic styrene elastomer, a thermoplastic polyamide elastomer, a thermoplastic polyester elastomer, and a thermoplastic polyolefin elastomer.

  If necessary, the cover 6 may contain an appropriate amount of 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, and a fluorescent brightening agent. Blended. For the purpose of adjusting the specific gravity, the cover 6 may be mixed with powder of a high specific gravity metal such as tungsten or molybdenum.

  The cover 6 has a thickness of 0.20 mm or less. When the golf ball 2 is hit with a driver, the cover 4 is thin, and the core 4 is sufficiently deformed. In this golf ball 2, the core 4 sufficiently contributes to the resilience performance. Even when the control performance, feel at impact, scratch resistance and the like are emphasized and a polymer having inferior resilience performance is used for the cover 6, the cover 6 does not impair resilience performance. In this golf ball 2, both resilience performance and other performance are achieved. From this viewpoint, the thickness of the cover 6 is more preferably 0.18 mm or less, and particularly preferably 0.17 mm or less. From the viewpoint of easy molding, the thickness of the cover 6 is preferably 0.05 mm or more.

  FIG. 2 is an enlarged plan view showing the golf ball 2 of FIG. 1, and FIG. 3 is a front view thereof. The surface of the golf ball 2 can be partitioned into 10 units whose dimple patterns are equivalent to each other. In FIG. 2, the types of the dimples 8 are indicated by reference signs A to D for one unit. The planar shape of the dimple 8 is a circle. This golf ball 2 includes a dimple A having a diameter of 4.00 mm, a dimple B having a diameter of 3.45 mm, a dimple C having a diameter of 3.30 mm, and a dimple D having a diameter of 3.15 mm. I have. The number of dimples A is 132, the number of dimples B is 180, the number of dimples C is 60, and the number of dimples D is 60. The total number of dimples 8 is 432.

  FIG. 4 is an enlarged cross-sectional view showing a part of the golf ball 2 of FIG. FIG. 4 shows a cross section along a plane passing through the center of the dimple 8 and the center of the golf ball 2. The vertical direction in FIG. 4 is the depth direction of the dimple 8. In FIG. 4, what is indicated by a two-dot chain line 12 is a virtual sphere. The dimple 8 is recessed from the phantom sphere 12. The land 10 coincides with the phantom sphere 12.

  The dimple 8 is formed in the cover 6. The dimple 8 includes a side wall 14 and a bottom surface 16. The side wall 14 has the shape of the side surface of a truncated cone. The bottom surface 16 coincides with the surface of the core 4. In other words, the dimple 8 passes through the cover 6. The bottom surface 16 is convex outward in the radial direction. The planar shape of the bottom surface 16 is a circle. In this golf ball 2, the surface of the core 4 is exposed. Although not shown, the paint layer covers the land 10, the side wall 14, and the bottom surface 16.

  In FIG. 4, what is indicated by a double-headed arrow D <b> 1 is the diameter of the dimple 8. The diameter D1 is a distance between one contact point Ed and the other contact point Ed when a common tangent line 18 is drawn on both sides of the dimple 8. The contact point Ed is also an edge of the dimple 8. The edge Ed defines the contour of the dimple 8. In the case of a non-circular dimple, a circle having the same area as that of the contour shape is assumed, and the diameter of the circle is regarded as the diameter D1 of the non-circular dimple.

  In FIG. 4, what is indicated by a double arrow D2 is the diameter of the bottom surface 16, and what is indicated by a double arrow d1 is the minimum depth from the tangent line 18 to the bottom surface 16, and is indicated by a double arrow d2. It is the maximum depth from the tangent line 18 to the bottom surface 16. When the bottom surface 16 is non-circular, a circle having the same area as the contour shape of the bottom surface 16 is assumed, and the diameter of the circle is regarded as the diameter D2 of the bottom surface 16. The volume of the space surrounded by the plane including the outline of the dimple 8, the side wall 14, and the bottom surface 16 is the volume V of the dimple 8.

  As described above, the cover 6 is very thin. However, since the dimple 8 penetrates the cover 6, the volume V is sufficiently large. The golf ball 2 exhibits a large dimple effect. The direction of air from the land 10 toward the center of the dimple 8 varies greatly at the boundary 20 between the side wall 14 and the bottom surface 16. This change further enhances the dimple effect. This golf ball 2 is excellent in flight performance.

  The ratio of the diameter D2 to the diameter D1 (D2 / D1) is preferably 0.50 or more and 0.85 or less. In the dimple 8 having the ratio (D2 / D1) of 0.50 or more, the direction of air greatly changes at the boundary 20. Large changes contribute to the dimple effect. In this respect, the ratio (D2 / D1) is more preferably equal to or greater than 0.55, and particularly preferably equal to or greater than 0.59. In the dimple 8 having a ratio (D2 / D1) of 0.85 or less, the air flow does not separate at the boundary 20 and moves toward the center of the dimple 8. This air flow enhances the dimple effect. In this respect, the ratio (D2 / D1) is more preferably 0.75 or less and particularly preferably 0.71 or less.

  The bottom surface 16 is preferably roughened. The rough bottom surface 16 enhances the dimple effect. By the rough surface processing, a number of smiling holes are formed in the bottom surface 16. This hole increases the volume V. For the convenience of the manufacturing method, it is preferable that the rough surface processing is performed not only on the bottom surface 16 but also on the entire surface of the core 4. Specific examples of the rough surface processing include blasting, brushing, and barrel polishing.

  The 10-point average roughness of the bottom surface 16 is preferably 0.005 mm or more, more preferably 0.01 mm or more, and particularly preferably 0.05 mm or more. The 10-point average roughness is preferably 0.4 mm or less. The 10-point average roughness is measured by a surface roughness meter in accordance with “JIS B 0601”. The average diameter of the holes in the bottom surface 16 is preferably 0.002 mm or more and 0.3 mm or less. The average depth of the holes in the bottom surface 16 is preferably 0.002 mm or more and 0.2 mm or less.

  From the viewpoint of the dimple effect, the diameter D1 is preferably 2.0 mm or more, more preferably 2.2 mm or more, and particularly preferably 2.4 mm or more. In light of maintaining the original characteristics of the golf ball 2 being substantially a sphere, the diameter D1 is preferably 6.0 mm or less, more preferably 5.8 mm or less, and particularly preferably 5.6 mm or less.

The area s of the dimple 8 is an area of a region surrounded by a contour line when the center of the golf ball 2 is viewed from infinity. In the case of the circular dimple 8, the area s is calculated by the following mathematical formula.
s = (D1 / 2) ²・ π
In the golf ball 2 shown in FIGS. 1 to 4, the area of the dimple A is 12.57 mm ² , the area of the dimple B is 9.35 mm ² , and the area of the dimple C is 8.55 mm ² , The area of the dimple D is 7.79 mm ² .

In the present invention, the ratio of the total area s of all the dimples 8 to the surface area of the phantom sphere 12 is referred to as an occupation ratio. From the viewpoint of obtaining a sufficient dimple effect, the occupation ratio is preferably 70% or more, more preferably 72% or more, and particularly preferably 74% or more. The occupation ratio is preferably 90% or less, more preferably 88% or less, and particularly preferably 86% or less. In the golf ball 2 shown in FIGS. 1 to 4, the total area of the dimples 8 is 4322.6 mm ² . Since the surface area of the phantom sphere 12 of this golf ball 2 is 5728.0 mm ² , the occupation ratio is 75.5%.

From the viewpoint of rising of the golf ball 2 is suppressed, the total volume of the dimples 8 is preferably 250 mm ³ or more, more preferably 270 mm ³ or more, 280 mm ³ or more is particularly preferable. In view of dropping of the golf ball 2 is suppressed, the total volume is preferably 400 mm ³ or less, more preferably 380 mm ³ or less, 370 mm ³ or less is particularly preferred. In the golf ball 2, since the dimple 8 penetrates the cover 4, a sufficient total volume can be achieved even though the cover 4 is thin.

  From the viewpoint of the dimple effect, the number of the dimples 8 is preferably 200 or more, more preferably 220 or more, and particularly preferably 240 or more. From the viewpoint that each dimple 8 can contribute to the dimple effect, the number is preferably 500 or less, more preferably 480 or less, and particularly preferably 460 or less.

  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 polybutadiene (trade name “BR-730” from JSR), 30 parts by weight of zinc acrylate, 6 parts by weight of zinc oxide, 10 parts by weight of barium sulfate, 0.5 parts by weight of diphenyl disulfide and 0.5 parts by mass of dicumyl peroxide was 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 170 ° C. for 18 minutes to obtain a core having a diameter of 42.37 mm. On the other hand, 50 parts by mass of ionomer resin (trade name “HIMILAN 1605” from Mitsui DuPont Polychemical Co.), 50 parts by mass of other ionomer resins (trade name “HIMILAN 1706” from Mitsui DuPont Polychemical Co., Ltd.) and 3 parts by mass Part of titanium dioxide was kneaded to obtain a resin composition. The core was put into a final mold having a large number of pimples on the inner peripheral surface, and the resin composition was injected around the core by an injection molding method to form a cover having a thickness of 0.165 mm. A large number of dimples having a reversed pimple shape were formed on the cover. A clear paint based on a two-component curable polyurethane was applied to the cover to obtain a golf ball of an example having a diameter of 42.7 mm and a mass of about 45.4 g. The golf ball has a PGA compression of about 85. This golf ball has the dimple pattern shown in FIGS. Details of the dimple specifications are shown in Table 1 below.

[Examples 2 to 7]
Golf balls of Examples 2 to 7 were obtained in the same manner as in Example 1 except that the core diameter, cover thickness, and dimple specifications were as shown in Tables 1 and 2 below.

[Example 8]
A golf ball of Example 8 was obtained in the same manner as in Example 1 except that the cover was molded after the core was subjected to blasting. The 10-point average roughness of the surface of this core was 0.10 mm.

[Comparative example]
A golf ball of a comparative example was obtained in the same manner as in Example 1 except that the core diameter, cover thickness, and dimple specifications were as shown in Table 3 below. The cross-sectional shape of this golf ball is shown in FIG. The golf ball dimple does not penetrate the cover.

[Flight distance test]
A driver with a titanium head (trade name “XXIO”, Sumitomo Rubber Industries, Ltd., shaft hardness: X, loft angle: 9 °) equipped with a titanium head was attached to a swing machine manufactured by Tsurutemper. A golf ball was hit under the condition that the head speed was 49 m / sec, and the distance from the launch point to the rest point was measured. During the test, there was almost no wind. The average values of the 20 measurement results are shown in Tables 1 to 3 below.

  As shown in Tables 1 to 3, the flight distance of the golf ball of the example is large. From this evaluation result, the superiority of the present invention is clear.

  The dimple according to the present invention can be applied not only to a two-piece golf ball but also to a multi-piece golf ball and a thread wound golf ball.

FIG. 1 is a schematic cross-sectional view showing a golf ball according to an embodiment of the present invention. FIG. 2 is an enlarged plan view showing the golf ball of FIG. FIG. 3 is a front view showing 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 illustrating a part of the golf ball according to Comparative Example 1.

Explanation of symbols

2 ... Golf ball 4 ... Core 6 ... Cover 8 ... Dimple 10 ... Land 12 ... Virtual sphere 14 ... Side wall 16 ... Bottom 18 ... Tangent 20 ... ·boundary

Claims (5)

  A golf ball comprising a core, a cover laminated on the core and having a thickness of 0.20 mm or less, and dimples formed in the cover and having a bottom surface coinciding with the surface of the core.   2. The golf ball according to claim 1, wherein a ratio (D2 / D1) of a bottom surface diameter D2 to a diameter D1 of the dimple is 0.50 or more and 0.85 or less.   The golf ball according to claim 1, wherein a side wall of the dimple has a shape of a side surface of a truncated cone. 4. The golf ball according to claim 1, wherein a total volume of the dimples is 250 mm ³ or more and 400 mm ³ or less.   The golf ball according to claim 1, wherein the bottom surface is roughened.

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