JP4369196B2 - Golf ball - Google Patents

Description

  The present invention relates to a golf ball. More specifically, the present invention relates to a golf ball that includes a core and a cover, and dimples are formed on the cover.

  A general golf ball on the market has a core and a cover. A golfer's greatest demand for a golf ball is flight distance. Golfers place particular importance on the flight distance on driver shots. The flight distance of the driver shot correlates with the resilience performance of the golf ball. Golf balls that use a hard cover and have improved resilience performance are commercially available. This golf ball is excellent in a flight distance on a driver shot.

  Since the golf club head has a loft angle, a golf ball hit with this golf club is launched obliquely upward. The angle of the traveling direction of the golf ball immediately after hitting with respect to the horizontal is called the launch angle. An appropriate launch angle contributes to the flight distance.

  A large number of dimples are formed on the surface of the cover. The role of the dimples is to cause turbulent separation by disturbing the air flow around the golf ball during flight. Due to the turbulent separation, the separation point of the air from the golf ball shifts backward, and the drag coefficient (Cd) decreases. Turbulent separation promotes the difference in separation point between the upper side and the lower side of the golf ball due to backspin, and increases the lift acting on the golf ball.

  The dimple cross-sectional shape affects flight performance. Various proposals have been made for improving the cross-sectional shape of dimples intended to improve flight performance. For example, single radius dimples, double radius dimples, dimples with a recessed center, and dimples with a protruding center are proposed.

Various proposals regarding dimple density have been made. Japanese Patent Publication No. 58-50744 discloses a golf ball having a pitch between dimples of 1.62 mm or less. Japanese Patent Laid-Open No. 62-192181 discloses a golf ball in which dimples are densely arranged so that a new dimple having an area larger than the average area cannot be formed. Japanese Patent Application Laid-Open No. 4-347177 discloses a golf ball in which dimples are arranged extremely densely and the number of lands on which a rectangle having a predetermined dimension can be drawn is 40 or less. All of the golf balls disclosed in these known documents have densely arranged dimples, in other words, dimple occupancy is increased. The importance of densely arranged dimples is recognized by those skilled in the art.
Japanese Patent Publication No. 58-50744 JP-A-62-192181 JP-A-4-347177

  When a golf ball using a hard cover is hit with an iron, the launch angle tends to be excessive. An excessive launch angle results in an excessive ballistic height, which reduces the flight distance.

  When hit with a golf club, the surface of the golf ball may be damaged and fluffy. In particular, the damage is significant when hit with a short iron. Scratching reduces the appearance of the golf ball. Scratch resistance is important for golf balls.

  An object of the present invention is to provide a golf ball excellent in resilience performance, flight performance on an iron shot, and scratch resistance.

  The golf ball according to the present invention includes a core, a cover, and a large number of dimples formed on the surface of the cover. The Shore D hardness of this cover is 58 or more and 70 or less. The ratio P of the number of dimples in which the curvature radius of the curved surface from the position where the depth is 10% lower than the dimple edge to the position where the depth is 50% lower than the dimple edge is 0.5 mm or more and 3.0 mm or less in the total number of dimples is , 50% or more. The occupation ratio of the total area of the dimples with respect to the surface area of the phantom sphere is 73% or less.

  Preferably, the average value of the contour length of the dimples is not less than 10.8 mm and not more than 14.2 mm.

  Since the golf ball cover is hard, the golf ball has excellent resilience performance. The cross-sectional shape of the dimple of this golf ball contributes to a reduction in drag. Since this golf ball has a small occupancy rate, it has excellent scratch resistance despite the fact that the dimple having the aforementioned cross-sectional shape is formed. Small occupancy also contributes to ballistic optimization on iron shots.

  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. The core 4 is a layer inside the cover 6 and in contact with the cover 6. A large number of dimples 8 are formed on the surface of 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 outside the cover 6, but these layers are not shown.

  In the present invention, the cover 6 means the outermost layer excluding the paint layer and the mark layer. There is also a golf ball whose cover is referred to as having a two-layer structure. In this case, the outer layer corresponds to the cover 6 in the present invention.

  The golf ball 2 has a diameter of 40 mm to 45 mm, and further 42 mm to 44 mm. From the viewpoint of reducing air resistance within a range that satisfies the standards of the US Golf Association (USGA), the diameter is particularly preferably 42.67 mm or greater and 42.80 mm or less. The golf ball 2 has a mass of 40 g or more and 50 g or less, and further 44 g or more and 47 g or less. From the viewpoint of increasing the inertia within a range where the USGA standard is satisfied, the mass is particularly preferably 45.00 g or more and 45.93 g or less.

  The cover 6 is hard. Specifically, the hardness Ho of the cover 6 is 58 or more. The hard cover 6 contributes to the resilience performance of the golf ball 2. In light of resilience performance, the hardness Ho is more preferably equal to or greater than 60, and particularly preferably equal to or greater than 62. If the hardness Ho is too large, the spin rate will be insufficient and the control performance will be insufficient. From the viewpoint of control performance, the hardness Ho is preferably 70 or less, more preferably 67 or less, and particularly preferably 65 or less. The hardness Ho is measured by a Shore D spring type hardness tester in accordance with the standard of “ASTM-D 2240-68”. For the measurement, three sheets of 2 mm thick made of the same material as the cover 6 are used in a stacked manner.

  A suitable polymer for the cover 6 is an ionomer resin. In particular, it is preferable that a carboxylic acid in a copolymer of an α-olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms is neutralized with a metal ion. Preferred α-olefins are ethylene and propylene. Preferred α, β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. 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. Neutralization may be performed with two or more metal ions. Particularly suitable metal ions from the viewpoint of the resilience performance and durability of the golf ball are sodium ions, zinc ions, lithium ions and magnesium ions.

  As specific examples of the ionomer resin, trade names “HIMILAN 1555”, “HIMILAN 1557”, “HIMILAN 1605”, “HIMILAN 1706”, “HIMILAN 1707”, “HIMILAN AM7311”, “HIMILAN AM7315” of Mitsui Dupont Polychemical Co., Ltd. "High Milan AM 7317", "Hi Milan AM 7318" and "High Milan MK 7320"; DuPont's trade names "Surlin 7930", "Surlin 7940", "Surlin 8140", "Surlin 8940", "Surlin 8945", "Surlin 9120" , "Surlin 9910" and "Surlin 9945"; and Exxon's trade names "IOTEK 7010", "IOTEK 7030", "IOTEK 8000" and "IOTEK 8030".

  Other polymers may be used in place of or in conjunction with the ionomer resin. Examples of other polymers include thermoplastic styrene elastomers, thermoplastic polyurethane elastomers, thermoplastic polyamide elastomers, thermoplastic polyester elastomers, and thermoplastic polyolefin elastomers.

  A preferred polymer used in combination with the ionomer resin is a thermoplastic resin styrene elastomer. The thermoplastic styrene elastomer contains a styrene block as a hard segment in its molecule. Thermoplastic styrene elastomers include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-butadiene-styrene block copolymer (SIBS), and SBS. Includes hydrogenated products, SIS hydrogenated products and SIBS hydrogenated products. Examples of the hydrogenated product of SBS include styrene-ethylene-butylene-styrene block copolymer (SEBS). As a hydrogenated product of SIS, styrene-ethylene-propylene-styrene block copolymer (SEPS) can be mentioned. Examples of the hydrogenated product of SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

  In the present invention, a polymer alloy of a thermoplastic elastomer containing a styrene block and an olefin is also referred to as a “thermoplastic styrene elastomer”. The olefin component in the polymer alloy is presumed to contribute to the improvement of compatibility with the ionomer resin. By using this polymer alloy, the resilience performance of the golf ball 2 is improved. An olefin having 2 to 10 carbon atoms is used for the polymer alloy. Suitable olefins include ethylene, propylene, butene and tempen. Ethylene and propylene are particularly preferred. Specific examples of the polymer alloy include Mitsubishi Chemical's trade names “Lavalon SJ4400N”, “Lavalon SJ5400N”, “Lavalon SJ6400N”, “Lavalon SJ7400N”, “Lavalon SJ8400N”, “Lavalon SJ9400N” and “Lavalon SR04”. It is done.

  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 0.5 mm to 2.5 mm, particularly 0.8 mm to 2.2 mm. The specific gravity of the cover 6 is 0.90 or more and 1.10 or less, particularly 0.95 or more and 1.05 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 usually 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.

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

  The diameter of the core 4 is 30.0 mm or more and 42.0 mm or less, and further 38.0 mm or more and 41.5 mm or less. The core 4 may be composed of two or more layers. The hardness Hi of the surface of the core 4 is preferably 40 or greater and 70 or less. When the hardness Hi is less than the above range, the resilience performance of the golf ball 2 may be insufficient. In this respect, the hardness Hi is more preferably equal to or greater than 45, and particularly preferably equal to or greater than 50. If the hardness Hi exceeds the above range, the shot feeling and scratch resistance of the golf ball 2 may be insufficient. In this respect, the hardness Hi is more preferably equal to or less than 65, and particularly preferably equal to or less than 60. The hardness Hi is measured by pressing a Shore D-type spring hardness meter against the surface of the core 4.

  The difference (Ho−Hi) between the hardness Ho of the cover 6 and the hardness Hi of the surface of the core 4 is preferably 5 or more and 50 or less. If the difference (Ho−Hi) is less than the above range, the shot feeling and scratch resistance of the golf ball 2 may be insufficient. In this respect, the difference (Ho−Hi) is more preferably equal to or greater than 10, and particularly preferably equal to or greater than 14. When the difference (Ho−Hi) exceeds the above range, the resilience performance of the golf ball 2 may be insufficient. In this respect, the difference (Ho−Hi) is more preferably equal to or less than 35, and particularly preferably equal to or less than 22.

  FIG. 2 is an enlarged plan view showing the golf ball 2 of FIG. As is apparent from FIG. 2, the planar shape of all the dimples 8 is circular. In FIG. 2, the types of the dimples 8 are indicated by reference signs A to D in one unit when the surface of the golf ball 2 is partitioned into 20 equivalent units. The golf ball 2 includes a dimple A having a diameter of 4.15 mm, a dimple B having a diameter of 3.50 mm, a dimple C having a diameter of 3.30 mm, and a dimple D having a diameter of 3.05 mm. I have. The number of dimples A is 50, the number of dimples B is 210, the number of dimples C is 110, and the number of dimples D is 40. The total number of dimples 8 of this golf ball 2 is 410.

  FIG. 3 is an enlarged cross-sectional view showing a part of the golf ball 2 of FIG. In this figure, a surface passing through the deepest point P1 of the dimple 8 and the center of the golf ball 2 is shown. The vertical direction in FIG. 3 is the depth direction of the dimple 8. The depth direction is a direction from the center of gravity of the dimple 8 toward the center of the golf ball 2. In FIG. 3, the phantom sphere 12 is indicated by a two-dot chain line. The surface of the phantom sphere 12 is the surface of the golf ball 2 when it is assumed that the dimple 8 does not exist. The dimple 8 is recessed from the phantom sphere 12. The land 10 coincides with the phantom sphere 12.

  In FIG. 3, what is indicated by a double-headed arrow Di is the diameter of the dimple 8. The diameter Di is a distance between one contact E and the other contact E when a common tangent line T is drawn on both sides of the dimple 8. The contact E is also an edge of the dimple 8. The edge E defines the planar shape of the dimple 8. The distance between the tangent line T and the deepest point P1 is the depth Dp of the dimple 8.

  In FIG. 3, a point indicated by a reference symbol P <b> 2 is a point below the edge E by a distance of (Dp · 0.8). What is indicated by the reference symbol P3 is a point below the edge E by a distance of (Dp · 0.5). What is indicated by a reference symbol P4 is a point below the edge E by a distance of (Dp · 0.3). What is indicated by reference numeral P5 is a point below the edge E by a distance of (Dp · 0.1).

  What is indicated by an arrow R in FIG. 3 is the radius of curvature of the bottom surface. The radius of curvature R is the radius of this arc when a circular arc passing through the point P2, the other point P2 opposite the point P2 across the deepest part P1, and the deepest point P1 is assumed. is there. The bottom surface is convex inward of the golf ball 2.

  In FIG. 3, what is indicated by an arrow r is the radius of curvature of the side wall 14 from the point P3 to the point P5. The radius of curvature r is the radius of this arc when an arc passing through the points P3, P4 and P5 is assumed. The side wall 14 is convex inward of the golf ball 2. The curvature radius r is 0.5 mm or more and 3.0 mm or less. The curvature radius r is smaller than the curvature radius of the side wall of a general golf ball. It is presumed that the dimple 8 having a small curvature radius r contributes to the drag reduction of the golf ball 2 in flight. This golf ball 2 is excellent in a flight distance on a driver shot due to a synergistic effect of the resilience performance caused by the hard cover 6 and the dimple 8 having a small radius of curvature r.

  In light of drag reduction, the radius of curvature r is more preferably equal to or less than 2.0 mm, and particularly preferably equal to or less than 1.5 mm. When the curvature radius r is less than the above range, it is difficult to mold the golf ball 2. In this respect, the curvature radius r is more preferably equal to or greater than 0.6 mm, and particularly preferably equal to or greater than 0.7 mm.

  From the viewpoint of drag reduction, it is preferable that the radius of curvature r is in the above range in all the dimples 8. When the radius of curvature r is in the above range in some of the dimples 8 and the radius of curvature r is out of the above range in the remaining dimples 8, the number of dimples 8 having the radius of curvature r within the above range is the total number N of the dimples 8. The ratio P occupied in is set to 50% or more. The ratio P is more preferably 75% or more, and particularly preferably 85% or more.

The area of the dimple 8 is an area of an area surrounded by the edge line (that is, an area of a planar shape) when the center of the golf ball 2 is viewed from infinity. In the case of the dimple 8 having a circular planar shape, the area s is calculated by the following mathematical formula.
s = (Di / 2) ² · π
In the golf ball 2 shown in FIG. 2, the area of the dimple A is 13.53 mm ² , the area of the dimple B is 9.62 mm ² , the area of the dimple C is 8.55 mm ² , and The area is 7.31 mm ² . The total area of these dimples 8 is 3929.6 mm ² . The total area is divided by the surface area of the phantom sphere 12 to calculate the occupation ratio Y. In this golf ball 2, the occupation ratio Y is 68.6%. This occupation ratio Y is smaller than the occupation ratio Y of a general golf ball on the market.

  The golf ball 2 provided with the hard cover 6 and the dimple 8 having a small curvature radius r may have a too high trajectory in an iron shot. In the golf ball 2 according to the present invention, since the occupation ratio Y is small, lift is suppressed. In the golf ball 2, the trajectory in the iron shot can be optimized. This golf ball 2 is excellent in flight performance on an iron shot.

  The dimple 8 having a small radius of curvature r is likely to be damaged and fluffed when hit with an iron. In the golf ball 2 according to the present invention, since the occupation ratio Y is small, damage is suppressed. The reason that the damage is suppressed is presumed to be because the pressure applied to the land 10 at the time of hitting is small.

  Occupancy rate Y is preferably 73% or less, more preferably 71% or less, and particularly preferably 69% or less from the viewpoints of ballistic optimization and scratch resistance performance in iron shots. If the occupancy Y is too small, the golf ball 2 drops on a driver shot, so the occupancy Y is preferably 60% or more, and particularly preferably 63% or more.

In the present invention, the term “contour length” means a distance actually measured along the contour line of the dimple 8. For example, in the case of the dimple 8 whose planar shape is a triangle, the sum of the lengths of the three sides is the contour length. Since this side exists on a spherical surface, strictly speaking, it is not a straight line but an arc shape. The length of this arc is the side length. In the case of the circular dimple 8, the contour length x is calculated by the following mathematical formula.
x = Di · π

  In the golf ball 2 shown in FIG. 2, the contour length x of the dimple A is 13.04 mm, the contour length x of the dimple B is 11.000 mm, and the contour length x of the dimple C is 10.4 mm. The contour length x of the dimple D is 9.58 mm. In the golf ball 2, the total contour length is 4485.9 mm. Since this golf ball 2 includes 410 dimples 8, the average value of the contour length is 10.94 mm.

  In order to reduce the occupation ratio Y, it is necessary to reduce the individual dimples 8 or the total number N of the dimples 8. By reducing the total number N and maintaining the size of the individual dimples 8, the drag reduction effect by the dimples 8 is maintained while the small occupation ratio Y is achieved. In this respect, the average value of the contour length is preferably 10.8 mm or more, more preferably 11.5 mm or more, and particularly preferably 12.0 mm or more. If the average value of the contour length is too large, the iron shot is easily damaged. From this viewpoint, the average value of the contour length is preferably 14.2 mm or less, and particularly preferably 13.5 mm or less. The contour length of each dimple 8 is preferably 6.3 mm or more and 19.0 mm or less.

  A double arrow F in FIG. 3 indicates the distance between the phantom sphere 12 and the deepest portion P1. The distance F is preferably 0.05 mm or greater and 0.60 mm or less. If the distance F is less than the above range, a hopping trajectory may occur. In this respect, the distance F is more preferably 0.10 mm or more, and particularly preferably 0.15 mm or more. If the distance F exceeds the above range, the trajectory may drop. In this respect, the distance F is more preferably equal to or less than 0.55 mm, and particularly preferably equal to or less than 0.50 mm.

In FIG. 3, the volume of the portion surrounded by the phantom sphere 12 and the dimple 8 is the volume of the dimple 8. The total volume of the dimples 8 is preferably 300 mm ³ or more and 750 mm ³ or less. If the total volume is less than the above range, a hopping trajectory may occur. In this respect, the total volume is more preferably 400 mm ³ or more, and particularly preferably 450 mm ³ or more. If the total volume exceeds the above range, the trajectory may drop. In this respect, the total volume is more preferably 700 mm ³ or less, 650 mm ³ or less is particularly preferred.

  The total number N of the dimples 8 is preferably 200 or more and 500 or less. If the total number N is less than the above range, the dimple effect is difficult to obtain. In this respect, the total number N is more preferably 240 or more, and particularly preferably 260 or more. If the total number N exceeds the above range, the dimple effect is difficult to obtain due to the small size of the individual dimples 8. In this respect, the total number N is more preferably 480 or less, and particularly preferably 460 or less.

  FIG. 4 is a schematic cross-sectional view showing a golf ball 16 according to another embodiment of the present invention. The golf ball 16 includes a spherical core 18, an intermediate layer 20, and a cover 22. The intermediate layer 20 is a layer inside the cover 22 and in contact with the cover 22. A large number of dimples 24 are formed on the surface of the cover 22. A portion of the surface of the golf ball 16 other than the dimples 24 is a land 26. The golf ball 16 includes a paint layer and a mark layer on the outside of the cover 22, but these layers are not shown. The hardness Ho of the cover 22 is 58 or more. The hardness Ho is more preferably 60 or more, and particularly preferably 62 or more. The hardness Ho is preferably 70 or less, more preferably 67 or less, and particularly preferably 65 or less.

  The mid layer 20 is made of a synthetic resin composition. Examples of suitable synthetic resins include ionomer resins, thermoplastic styrene elastomers, thermoplastic polyurethane elastomers, thermoplastic polyamide elastomers, thermoplastic polyester elastomers, and thermoplastic polyolefin elastomers. In particular, an ionomer resin and a thermoplastic styrene elastomer are preferable. The intermediate layer 20 has a thickness of 0.5 mm to 2.5 mm, particularly 0.8 mm to 2.2 mm. The specific gravity of the intermediate layer 20 is 0.90 or more and 1.10 or less, particularly 0.95 or more and 1.05 or less.

  The hardness Hi of the surface of the intermediate layer 20 is preferably 40 or greater and 70 or less. When the hardness Hi is less than the above range, the resilience performance of the golf ball 16 may be insufficient. In this respect, the hardness Hi is more preferably equal to or greater than 45, and particularly preferably equal to or greater than 50. When the hardness Hi exceeds the above range, the feel at impact may be insufficient. In this respect, the hardness Hi is more preferably equal to or less than 65, and particularly preferably equal to or less than 60. The hardness Hi is measured by pressing a Shore D-type spring hardness meter against the surface of a sphere composed of the core 18 and the intermediate layer 20.

  The difference (Ho−Hi) between the hardness Ho of the cover 22 and the hardness Hi of the surface of the intermediate layer 20 is preferably 5 or more and 50 or less. When the difference (Ho-Hi) is less than the above range, the golf ball 16 may have an insufficient shot feeling and scratch resistance. In this respect, the difference (Ho−Hi) is more preferably equal to or greater than 10, and particularly preferably equal to or greater than 14. When the difference (Ho−Hi) exceeds the above range, the resilience performance of the golf ball 16 may be insufficient. In this respect, the difference (Ho−Hi) is more preferably equal to or less than 35, and particularly preferably equal to or less than 22.

  FIG. 5 is an enlarged plan view showing the golf ball 16 of FIG. As is clear from FIG. 5, the planar shape of all the dimples 24 is circular. In FIG. 5, the type of the dimple 24 is indicated by a symbol A or B in one unit when the surface of the golf ball 16 is partitioned into 16 equivalent units. The golf ball 16 includes dimples A having a diameter of 4.35 mm and dimples B having a diameter of 3.30 mm. The number of dimples A is 168, and the number of dimples B is 168. The total number of dimples 24 of this golf ball 16 is 336.

  Also in this golf ball 16, the ratio P of the number of dimples 24 having a radius of curvature r of 0.5 mm to 3.0 mm to the total number N of dimples 24 is preferably 50% or more, more preferably 75% or more, and 85%. The above is particularly preferable. The ratio P is ideally 100%. Also in this golf ball 16, the occupation ratio Y is 60% or more and 73% or less, and the average value of the contour length of the dimple 24 is 10.8mm or more and 14.2mm 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 mass of polybutadiene (trade name “BR-11” of JSR Corporation), 24.5 parts by mass of zinc acrylate, 10 parts by mass of zinc oxide, an appropriate amount of barium sulfate and 0.8 parts by mass of dicumyl peroxide were kneaded. A rubber composition was obtained. 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 39.9 mm. The amount of compressive deformation of this core was 3.8 mm, and the surface hardness (Shore D) was 48. On the other hand, 50 parts by mass of ionomer resin (trade name “HIMILAN 1605” from Mitsui DuPont Polychemical Co.), 45 parts by mass of other ionomer resins (trade name “HIMILAN 1706” from Mitsui DuPont Polychemical Co., Ltd.), thermoplastic styrene elastomer (Mitsubishi Chemical Co., Ltd. trade name “Lavalon SR04”) 5 parts by mass and titanium dioxide 3 parts by mass were kneaded to obtain a resin composition. The core was put into a mold having a large number of protrusions on the inner peripheral surface, and the resin composition was injected around the core to form a cover having a thickness of 1.4 mm. A large number of dimples having a shape in which the shape of the protrusion was inverted were formed on the cover. The cover was painted to obtain a golf ball of Example 1 having a diameter of 42.7 mm. The dimple specification of this golf ball is type II shown in Table 2 below.

[ Examples 2 and 4 to 5 and Comparative Examples 1 to 2 ]
Golf balls of Examples 2 and 4 to 5 and Comparative Examples 1 to 2 were obtained in the same manner as Example 1 except that the mold was deformed and the dimple specifications were as shown in Table 1 below. Details of the dimple specifications are shown in Table 2 below.

[Examples 6 and 7]
Golf balls of Examples 6 and 7 were obtained in the same manner as in Example 1 except that the resin composition of the cover was as shown in Table 1 below. Details of the cover specifications are shown in Table 3 below.

[Example 8]
100 parts by mass of polybutadiene (the above-mentioned “BR-11”), 22 parts by mass of zinc acrylate, 10 parts by mass of zinc oxide, an appropriate amount of barium sulfate and 0.8 parts by mass of dicumyl peroxide were kneaded to obtain a rubber composition. . The 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 36.7 mm. The amount of compressive deformation of this core was 3.2 mm, and the Shore D hardness of the surface was 44. On the other hand, 40 parts by mass of ionomer resin (previously referred to as “HIMILAN 1605”), 30 parts by mass of other ionomer resin (previously referred to as “HIMILAN 1706”), 30 parts by weight of thermoplastic styrene elastomer (previously referred to as “Lavalon SR04”), and titanium dioxide. A resin composition composed of 3 parts by mass was coated around the core to form an intermediate layer having a thickness of 1.6 mm. A cover similar to that of Example 1 was formed around the intermediate layer, whereby a golf ball of Example 8 was obtained.

[Comparative Example 3]
A golf ball of Comparative Example 3 was obtained in the same manner as in Example 8 except that the dimple specifications and the resin composition of the cover were as shown in Table 1 below.

[Measurement of compression deformation]
First, the golf ball was placed on a metal rigid plate. Next, the metal cylinder was gradually lowered toward the golf ball, and the golf ball sandwiched between the bottom surface of the cylinder and the rigid plate was deformed. And the movement distance of the cylinder from the state where the initial load of 98N was applied to the golf ball to the state where the final load of 1274N was applied was measured. The results are shown in Table 1 below.

[Measurement of coefficient of restitution]
An aluminum hollow cylinder having a mass of 200 g was caused to collide with the golf ball at a speed of 45 m / s. Then, the velocity of the hollow cylinder before and after the collision and the velocity of the golf ball after the collision were measured, and the restitution coefficient of the golf ball was obtained. The average value of the data obtained by measuring 12 times is shown in Table 1 below as an index when the coefficient of restitution of the golf ball of Comparative Example 1 is 1.00.

[Flight distance test]
A No. 5 iron (trade name “XXIO” of Sumitomo Rubber Industries, Ltd., shaft hardness: S) was mounted on a swing machine manufactured by Tsurutemper. The machine conditions were set so that the head speed was 38 m / sec, the golf ball was hit, and the distance from the launch point to the rest point was measured. The average value of 12 measurements is shown in Table 1 below.

[Abrasion resistance]
A pitching wedge was attached to a golf laboratory swing machine. The machine conditions were set so that the head speed was 36 m / sec, and a golf ball was hit. The degree of scratches on the golf ball after hitting was visually observed. Those having an excellent appearance were rated A, and those having a poor appearance were rated B. The rank of concentrated evaluation is shown in Table 1 below.

  In Table 1, the golf balls of the examples are excellent in all of resilience performance, flight performance on iron shots, and scratch resistance. From this evaluation result, the superiority of the present invention is clear.

  The golf ball according to the present invention gives a refreshing feeling to the golfer who hits it, and contributes to the improvement of the score.

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 an enlarged cross-sectional view showing a part of the golf ball of FIG. FIG. 4 is a schematic cross-sectional view showing a golf ball according to another embodiment of the present invention. FIG. 5 is an enlarged plan view showing the golf ball of FIG. 6 is a plan view showing a golf ball according to Comparative Example 2. FIG.

Explanation of symbols

2, 16 ... Golf ball 4, 18 ... Core 6, 22 ... Cover 8, 24 ... Dimple 10, 26 ... Land 12 ... Virtual sphere 14 ... Side wall 20 ...・ Intermediate layer A ... Dimple A
B ... Dimple B
C ... Dimple C
D ... Dimple D
E ... Edge

Claims (2)

A core, a cover, and a large number of dimples formed on the surface of the cover;
The Shore D hardness of this cover is 58 or more and 70 or less,
The ratio P of the number of dimples with the curvature radius of the curved surface from the position where the depth is 10% lower than the dimple edge to the position where the depth is 50% lower than the dimple edge is 1.0 mm or more and 2.0 mm or less in the total number of dimples is 50% or more,
The occupation ratio of the total area of the dimples relative to the surface area of the phantom sphere is 73% or less,
A golf ball in which a difference (Ho-Hi) between the Shore D hardness (Ho) of the cover and the Shore D hardness (Hi) of the surface of the layer inside the cover and in contact with the cover is 14 or more and 22 or less.   The golf ball according to claim 1, wherein an average value of contour lengths of the dimples is 10.8 mm or more and 14.2 mm or less.

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