JP6690228B2 - Golf ball - Google Patents

Description

  The present invention relates to golf balls. More specifically, the present invention relates to a golf ball having a core having a two-layer structure, an intermediate layer and a cover, and further having a plurality of dimples on the surface thereof.

  A golf player's primary concern with golf balls is flight distance. Players attach particular importance to flight distance on driver shots. The initial velocity, spin rate, and launch angle of a ball when hit with a golf club are referred to as the initial three factors. The flight distance of a golf ball is affected by the initial three factors. The higher the initial velocity of the ball, the greater the flight distance. A proper spin speed and a proper launch angle also contribute to the flight distance.

  Various proposals for improving flight performance have been made, focusing on the initial three factors. Japanese Unexamined Patent Publication No. 11-206920 discloses a golf ball having an inner core and an outer core. Golf balls having two core layers are disclosed in JP-A-2003-190331, JP-A-2006-289065, JP-A-2007-190382, JP-A-10-328326, JP-A-10-328328, and JP-A-2000. It is also disclosed in -60997 and Japanese Patent Application Laid-Open No. 2009-219871.

  A golf ball has a large number of dimples on its surface. The dimples disturb the flow of air around the golf ball during flight, causing turbulent flow separation. This phenomenon is called "turbulence". Due to the turbulent flow, the separation point of air from the golf ball shifts backward, and the drag force is reduced. The turbulent flow promotes the deviation between the upper separation point and the lower separation point of the golf ball due to backspin, and the lift force acting on the golf ball is enhanced. A good dimple will disturb the air flow better. A good dimple produces a great flight distance.

  Various proposals regarding dimples have been made. Japanese Patent Laid-Open No. 2009-172192 discloses a golf ball in which dimples are randomly arranged. The dimple pattern of this golf ball is called a random pattern. The random pattern can contribute to the flight performance of the golf ball. JP 2012-10822A also discloses a golf ball having a random pattern.

  Japanese Unexamined Patent Application Publication No. 2007-175267 discloses a dimple pattern in which the number of units in the high latitude region and the number of units in the low latitude region are different. Japanese Unexamined Patent Application Publication No. 2007-195591 discloses a dimple pattern in which the number of dimple types in the low latitude region is larger than the number of dimple types in the high latitude region. Japanese Unexamined Patent Application Publication No. 2013-153966 discloses a dimple pattern having a high dimple density and a small dimple size variation.

JP, 11-206920, A JP, 2003-190331, A JP, 2006-289065, A JP, 2007-190382, A JP, 10-328326, A JP, 10-328328, A Japanese Patent Laid-Open No. 2000-60997 JP 2009-219871 A JP, 2009-172192, A JP2012-10822A JP 2007-175267 A JP 2007-195591 A JP, 2013-153966, A

  Player demand for flight distance is escalating. An object of the present invention is to provide a golf ball having excellent flight performance when hit by a driver.

The golf ball according to the present invention includes an inner core, an outer core located outside the inner core, an intermediate layer located outside the outer core, and a cover located outside the intermediate layer.
Diameter D1 (mm), volume V1 (mm ³ ), center hardness H1o (Shore C), boundary hardness H1in (Shore C), and difference De1 between hardness H1in and hardness H1o in the inner core;
The volume V2 (mm ³ ) in the outer core, and the difference De2 between the surface hardness H2s (Shore C) and the outside boundary hardness H2out (Shore C);
Thickness Tm (mm) and hardness Hm (Shore D) in the intermediate layer;
And the thickness Tc (mm) and hardness Hc (Shore D) of the cover
Satisfies the following formulas (1)-(4).
1.0 <V2 / V1 <7.0 (1)
De2-De1 <0 (2)
600 <(H1o + H1in) * (D1 / 2) / 2 <1000 (3)
620 <Tc.Hc.Hm/Tm <900 (4)
This golf ball has a plurality of dimples on its surface. These dimples include a plurality of small dimples area is less than 8.0 mm ^2, and a plurality of large dimples is area of 8.0 mm ² or more. The ratio PS of the total area of the small dimples to the surface area of the phantom sphere of the golf ball is less than 2.0%. The ratio PL of the total area of the large dimples to the surface area of the phantom sphere is 79.0% or more. The unity G of the area (mm ² ) of the large dimples is 1.15 or less.

Preferably, the golf ball satisfies the following formula.
2.0 <V2 / V1 <6.0

Preferably, the golf ball satisfies the following formula.
700 <(H1o + H1in) * (D1 / 2) / 2 <900

Preferably, the golf ball satisfies the following formula.
640 <Tc.Hc.Hm/Tm <800

  Preferably, the ratio PS is 0.7% or more. Preferably, the number NS of small dimples is 6 or more and 20 or less. Preferably, the ratio (NS / N) of the number NS of small dimples to the total number N of dimples is 0.01 or more and 0.07 or less.

  Preferably, the depth of the deepest part of each dimple from the surface of the virtual sphere is 0.10 mm or more and 0.65 mm or less.

Preferably, the total volume of the dimples is 450 mm ³ or more and 750 mm ³ or less.

  Preferably, the ratio PL is 79.5% or more, and the uniformity G is 1.10 or less.

  Preferably, the ratio PL is 80.0% or more, and the uniformity G is 1.05 or less.

  When the golf ball according to the present invention is hit with a driver, the spin rate is low and the initial velocity of the ball is high. Further, in this golf ball, the dimples promote turbulence. With the proper initial three factors and proper aerodynamic characteristics, this golf ball provides a large flight distance on driver shots.

FIG. 1 is a sectional view showing a golf ball according to an embodiment of the present invention. FIG. 2 is an enlarged front view showing the golf ball of FIG. FIG. 3 is a rear view showing the golf ball of FIG. FIG. 4 is a plan view showing the golf ball of FIG. FIG. 5 is a bottom view showing the golf ball of FIG. FIG. 6 is a left side view showing the golf ball of FIG. FIG. 7 is a right side view showing the golf ball of FIG. FIG. 8 is an enlarged cross-sectional view showing a part of the golf ball of FIG. FIG. 9 is a front view showing the golf ball according to the first embodiment of the present invention. FIG. 10 is a plan view showing the golf ball of FIG.

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

  The golf ball 2 shown in FIG. 1 has a spherical inner core 4, an outer core 6 located outside the inner core 4, an intermediate layer 8 located outside the outer core 6, and an intermediate layer 8 And a cover 10 located outside the. This golf ball 2 has a plurality of dimples 12 on its surface. A portion of the surface of the golf ball 2 other than the dimple 12 is a land 14. The golf ball 2 includes a paint layer and a mark layer on the outside of the cover 10, but these layers are not shown. The golf ball 2 may include another layer between the outer core 6 and the mid layer 8. The golf ball 2 may include another layer between the mid layer 8 and the cover 10.

  The diameter of the golf ball 2 is preferably 40 mm or more and 45 mm or less. From the viewpoint that the standards of the US Golf Association (USGA) are satisfied, the diameter is particularly preferably 42.67 mm or more. From the viewpoint of suppressing air resistance, the diameter is more preferably 44 mm or less, and particularly preferably 42.80 mm or less. The weight of the golf ball 2 is preferably 40 g or more and 50 g or less. From the viewpoint that a large inertia can be obtained, the mass is more preferably 44 g or more, and 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.

  The inner core 4 is formed by crosslinking a rubber composition. Examples of preferable base rubber include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer and natural rubber. From the viewpoint of a large ball initial velocity, polybutadiene is preferable. When polybutadiene and other rubber are used in combination, it is preferable that polybutadiene is the main component. Specifically, the ratio of polybutadiene to the total base rubber is preferably 50% by mass or more, and particularly preferably 80% by mass or more. Polybutadiene having a cis-1,4 bond ratio of 80% or more is particularly preferable.

  The rubber composition of the inner core 4 preferably contains a co-crosslinking agent. A preferable co-crosslinking agent from the viewpoint of a large ball initial velocity is a monovalent or divalent metal salt of an α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms. Examples of preferable co-crosslinking agents include zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. From the viewpoint of resilience performance, zinc acrylate and zinc methacrylate are particularly preferable.

  The rubber composition may include an α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms and a metal oxide. Both react in the rubber composition to give a salt. This salt functions as a co-crosslinking agent. Preferred α, β-unsaturated carboxylic acids include acrylic acid and methacrylic acid. Preferred metal oxides include zinc oxide and magnesium oxide.

  From the viewpoint of a large initial velocity of the ball, the amount of the co-crosslinking agent is preferably 10 parts by mass or more, and particularly preferably 15 parts by mass or more, relative to 100 parts by mass of the base rubber. From the viewpoint of a low spin rate on driver shots, this amount is preferably 40 parts by mass or less, and particularly preferably 35 parts by mass or less. As will be described in detail later, a large spin distance on driver shots can be achieved with a low spin rate.

  Preferably, the rubber composition of the inner core 4 contains an organic peroxide. The organic peroxide functions as a crosslinking initiator. The organic peroxide contributes to the resilience performance of the golf ball 2. Suitable organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t-butyl). Examples are peroxy) hexane and di-t-butyl peroxide. A particularly versatile organic peroxide is dicumyl peroxide.

  From the viewpoint of a large initial velocity of the ball, the amount of the organic peroxide is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and 0.5 parts by mass or more with respect to 100 parts by mass of the base rubber. Particularly preferred. From the viewpoint of a small spin rate, this amount is preferably 3.0 parts by mass or less, more preferably 2.8 parts by mass or less, and particularly preferably 2.5 parts by mass or less.

  Preferably, the rubber composition of the inner core 4 contains an organic sulfur compound. The organic sulfur compounds include naphthalene thiol compounds, benzene thiol compounds and disulfide compounds.

  As a naphthalene thiol compound, 1-naphthalene thiol, 2-naphthalene thiol, 4-chloro-1-naphthalene thiol, 4-bromo-1-naphthalene thiol, 1-chloro-2-naphthalene thiol, 1-bromo-2-naphthalene Examples are thiol, 1-fluoro-2-naphthalenethiol, 1-cyano-2-naphthalenethiol and 1-acetyl-2-naphthalenethiol.

  As the benzenethiol compound, benzenethiol, 4-chlorobenzenethiol, 3-chlorobenzenethiol, 4-bromobenzenethiol, 3-bromobenzenethiol, 4-fluorobenzenethiol, 4-iodobenzenethiol, 2,5-dichlorobenzenethiol , 3,5-dichlorobenzenethiol, 2,6-dichlorobenzenethiol, 2,5-dibromobenzenethiol, 3,5-dibromobenzenethiol, 2-chloro-5-bromobenzenethiol, 2,4,6-tri Chlorobenzenethiol, 2,3,4,5,6-pentachlorobenzenethiol, 2,3,4,5,6-pentafluorobenzenethiol, 4-cyanobenzenethiol, 2-cyanobenzenethiol, 4-nitrobenzenethiol and 2 -Nito Benzenethiol are exemplified.

  Examples of disulfide compounds include diphenyl disulfide, bis (4-chlorophenyl) disulfide, bis (3-chlorophenyl) disulfide, bis (4-bromophenyl) disulfide, bis (3-bromophenyl) disulfide, bis (4-fluorophenyl) disulfide. , Bis (4-iodophenyl) disulfide, bis (4-cyanophenyl) disulfide, bis (2,5-dichlorophenyl) disulfide, bis (3,5-dichlorophenyl) disulfide, bis (2,6-dichlorophenyl) disulfide, bis (2,5-Dibromophenyl) disulfide, bis (3,5-dibromophenyl) disulfide, bis (2-chloro-5-bromophenyl) disulfide, bis (2-cyano-5-bromophenyl) disulfide Bis (2,4,6-trichlorophenyl) disulfide, bis (2-cyano-4-chloro-6-bromophenyl) disulfide, bis (2,3,5,6-tetrachlorophenyl) disulfide, bis (2,3 , 4,5,6-Pentachlorophenyl) disulfide and bis (2,3,4,5,6-pentabromophenyl) disulfide.

  From the viewpoint of a large initial velocity of the ball, the amount of the organic sulfur compound is preferably 0.1 part by mass or more, and particularly preferably 0.2 part by mass or more based on 100 parts by mass of the base rubber. From the viewpoint of a small spin rate, this amount is preferably 1.5 parts by mass or less, more preferably 1.0 part by mass or less, and particularly preferably 0.8 parts by mass or less. Two or more organic sulfur compounds may be used in combination.

  The rubber composition of the inner core 4 may include a filler for the purpose of adjusting specific gravity and the like. Examples of suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. The amount of the filler is appropriately determined so that the intended specific gravity of the inner core 4 is achieved. This rubber composition may contain various additives such as sulfur, carboxylic acid, carboxylic acid salt, antioxidant, colorant, plasticizer and dispersant in appropriate amounts. The rubber composition may include crosslinked rubber powder or synthetic resin powder.

  The diameter D1 of the inner core 4 is preferably 15.0 mm or more. In the golf ball 2 having the inner core 4 having the diameter D1 of 15.0 mm or more, spin on driver shots is suppressed. From this viewpoint, the diameter D1 is more preferably 18.0 mm or more, and particularly preferably 20.0 mm or more. From the viewpoint that the outer core 6 can have a sufficient thickness, the diameter D1 is preferably 32.0 mm or less, more preferably 29.0 mm or less, and particularly preferably 27.0 mm or less.

The volume V1 of the inner core 4 is preferably 1700 mm ³ or more. In the golf ball 2 having the inner core 4 having the volume V1 of 1700 mm ³ or more, spin on driver shots is suppressed. In this respect, the volume V1 is more preferably 3000 mm ³ or more, 4200 mm ³ or more is particularly preferable. From the standpoint of the outer core 6 may have a sufficient volume V2, the volume V1 is preferably 17000Mm ³ or less, more preferably 13000Mm ³ or less, 10300Mm ³ or less is particularly preferred.

  The mass of the inner core 4 is preferably 10 g or more and 30 g or less. The crosslinking temperature of the inner core 4 is 140 ° C. or higher and 180 ° C. or lower. The crosslinking time of the inner core 4 is 10 minutes or more and 60 minutes or less.

  In this golf ball 2, the difference De1 between the hardness H1o at the center of the inner core 4 and the in-boundary hardness H1in of the inner core 4 is large. The inner core 4 having a large difference De1 has a so-called outer-hard / inner-soft structure. The spin rate when the golf ball 2 having the inner core 4 is hit with a driver is small. When the golf ball 2 having the inner core 4 is hit with a driver, a large launch angle is obtained.

  The driver shot requires an appropriate trajectory height and an appropriate flight time. The golf ball 2 that achieves trajectory height and flight time at a high spin rate has a small run after falling. In the golf ball 2 that achieves the trajectory height and the flight time at a large launch angle, the run after dropping is large. From the viewpoint of flight distance, the golf ball 2 that achieves trajectory height and flight time at a large launch angle is preferable. The inner core 4 having the outer-hard / inner-soft structure can contribute to a large launch angle and a small spin rate, as described above. The golf ball 2 having the inner core 4 has excellent flight performance.

  From the viewpoint of flight performance, the difference De1 is preferably 5 or more, more preferably 8 or more, and particularly preferably 10 or more. From the viewpoint of easy production of the inner core 4, the difference (H1in-H1o) is preferably 40 or less, and particularly preferably 30 or less. Preferably, the hardness of the inner core 4 gradually increases from the center toward the surface.

  From the viewpoint of a large ball initial velocity, the central hardness H1o is preferably 40 or more, more preferably 45 or more, and particularly preferably 50 or more. From the viewpoint of a small spin rate, the hardness H1o is preferably 80 or less, more preferably 75 or less, and particularly preferably 70 or less.

  The hardness H1o is measured by a Shore C type hardness meter attached to an automatic hardness meter (trade name “Digitest II” manufactured by H. Barreith Co., Ltd.). This hardness meter is pressed against the center of the cross section of the hemisphere obtained by cutting the golf ball 2. The measurement is performed in an environment of 23 ° C.

  From the viewpoint of a small spin rate, the in-boundary hardness H1in is preferably 60 or more, more preferably 65 or more, and particularly preferably 70 or more. From the viewpoint of the durability of the golf ball 2, the hardness H1in is preferably 85 or less, more preferably 80 or less, and particularly preferably 78 or less.

  The hardness H1in is measured by a Shore C type hardness meter attached to an automatic hardness meter (trade name “Digitest II” manufactured by H. Barreith Co., Ltd.). This hardness meter is pressed against the cross section of the hemisphere obtained by cutting the golf ball 2. The hardness tester is pressed at a point moved 1 mm radially inward from the boundary between the inner core 4 and the outer core 6. The measurement is performed in an environment of 23 ° C.

In this inner core 4, the value Va calculated by the following mathematical formula is more than 600 and less than 1000.
Va = (H1o + H1in) * (D1 / 2) / 2
In other words, the inner core 4 satisfies the following formula (3).
600 <(H1o + H1in) * (D1 / 2) / 2 <1000 (3)
The value Va is approximate to the integral of the hardness distribution of the inner core 4. The golf ball 2 having the inner core 4 having a value Va of more than 600 has a low spin rate on driver shots. In the golf ball 2 having the inner core 4 having a value Va of less than 1000, the initial velocity of the ball on driver shots is high. A large flight distance is achieved by a small spin speed and a large initial velocity of the ball. From this viewpoint, it is more preferable that the golf ball 2 satisfies the following mathematical formula.
700 <(H1o + H1in) * (D1 / 2) / 2 <900
In other words, the value Va is preferably more than 700 and less than 900.

  The outer core 6 is formed by crosslinking a rubber composition. This composition may include the base rubber described above for the inner core 4.

  The rubber composition of the outer core 6 preferably contains a co-crosslinking agent. A preferable co-crosslinking agent from the viewpoint of a large ball initial velocity is a monovalent or divalent metal salt of an α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms. Examples of preferable co-crosslinking agents include zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. From the viewpoint of a large ball initial velocity, zinc acrylate and zinc methacrylate are particularly preferable.

  The rubber composition may include an α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms and a metal oxide. Both react in the rubber composition to give a salt. This salt functions as a co-crosslinking agent. Preferred α, β-unsaturated carboxylic acids include acrylic acid and methacrylic acid. Preferred metal oxides include zinc oxide and magnesium oxide.

  From the viewpoint of a large initial velocity of the ball, the amount of the co-crosslinking agent is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, and particularly preferably 35 parts by mass or more with respect to 100 parts by mass of the base rubber. From the viewpoint of feel at impact, this amount is preferably 55 parts by mass or less, more preferably 50 parts by mass or less, and particularly preferably 45 parts by mass or less.

  Preferably, the rubber composition of the outer core 6 contains an organic peroxide. The organic peroxide functions as a crosslinking initiator. The organic peroxide contributes to the resilience performance of the golf ball 2. The rubber composition of the outer core 6 may include the organic peroxide described above for the inner core 4.

  From the viewpoint of a large initial velocity of the ball, the amount of the organic peroxide is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and 0.5 parts by mass or more with respect to 100 parts by mass of the base rubber. Particularly preferred. From the viewpoint of shot feeling, this amount is preferably 3.0 parts by mass or less, more preferably 2.8 parts by mass or less, and particularly preferably 2.5 parts by mass or less.

  Preferably, the rubber composition of the outer core 6 contains an organic sulfur compound. The rubber composition may include the organic sulfur compound described above for the inner core 4.

  From the viewpoint of a large initial velocity of the ball, the amount of the organic sulfur compound is preferably 0.1 part by mass or more, and particularly preferably 0.2 part by mass or more based on 100 parts by mass of the base rubber. From the viewpoint of feel at impact, this amount is preferably 1.5 parts by mass or less, more preferably 1.0 part by mass or less, and particularly preferably 0.8 parts by mass or less.

  The rubber composition of the outer core 6 may include a filler for the purpose of adjusting specific gravity and the like. Examples of suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. The amount of the filler is appropriately determined so that the intended specific gravity of the outer core 6 is achieved. This rubber composition may contain various additives such as sulfur, carboxylic acid, carboxylic acid salt, antioxidant, colorant, plasticizer and dispersant in appropriate amounts. The rubber composition may include crosslinked rubber powder or synthetic resin powder.

  The diameter D2 of the outer core 6 is preferably 37.0 mm or more. The golf ball 2 having the outer core 6 having the diameter D2 of 37.0 mm or more has a high initial velocity on a driver shot. From this viewpoint, the diameter D2 is more preferably 37.5 mm or more, and particularly preferably 38.0 mm or more. From the viewpoint that the mid layer 8 and the cover 10 can have a sufficient thickness, the diameter D2 is preferably 40.5 mm or less, more preferably 40.0 mm or less, and particularly preferably 39.5 mm or less.

The volume V2 of the outer core 6 is preferably 18000 mm ³ or more. The golf ball 2 having the outer core 6 having a volume V2 of 18000 mm ³ or more has a high initial velocity on driver shots. In this respect, the volume V2 more preferably 19500Mm ³ or more, 21000Mm ³ or more are particularly preferred. In light of the intermediate layer 8 and the cover 10 may have a sufficient thickness, the volume V2 is preferably 29000Mm ³ or less, more preferably 27000Mm ³ or less, 26000Mm ³ or less is particularly preferred. In the present embodiment, the volume V2 is calculated by subtracting the volume of the inner core 4 from the volume of the sphere composed of the inner core 4 and the outer core 6.

  The mass of the outer core 6 is preferably 10 g or more and 30 g or less. The crosslinking temperature of the outer core 6 is 140 ° C. or higher and 180 ° C. or lower. The crosslinking time of the outer core 6 is 10 minutes or more and 60 minutes or less.

  In this golf ball 2, the difference De2 between the surface hardness H2s and the outer boundary hardness H2out of the outer core 6 is preferably −2 or more and 2 or less. The hardness distribution of this outer core 6 is close to flat. The outer core 6 has a small energy loss when hit by a driver. The golf ball 2 having the outer core 6 has a high initial velocity on a driver shot. The outer core 6 can contribute to the flight performance of the golf ball 2. From the viewpoint of flight performance, the difference De2 is preferably -1 or more and 1 or less. The difference De2 may be zero.

  From the boundary between the inner core 4 and the outer core 6 to the surface of the outer core 6, the difference between the Shore C hardness at the highest hardness point and the Shore C hardness at the lowest hardness point is preferably 5 or less, 4 or less is more preferable, and 3 or less is particularly preferable.

  From the viewpoint of a large initial velocity of the ball, the out-of-bounds hardness H2out is preferably 60 or more, more preferably 70 or more, and particularly preferably 75 or more. From the viewpoint of shot feeling, the hardness H2out is preferably 90 or less, more preferably 87 or less, and particularly preferably 85 or less.

  The hardness H2out is measured by a Shore C type hardness meter attached to an automatic hardness meter (trade name “Digitest II” manufactured by H. Barreith Co., Ltd.). This hardness meter is pressed against the cross section of the hemisphere obtained by cutting the golf ball 2. The hardness tester is pressed at a point moved 1 mm outward in the radial direction from the boundary between the inner core 4 and the outer core 6. The measurement is performed in an environment of 23 ° C.

  From the viewpoint of spin suppression on driver shots, the surface hardness H2s is preferably 70 or higher, more preferably 72 or higher, and particularly preferably 74 or higher. From the viewpoint of durability of the golf ball 2, the hardness H2s is preferably 90 or less, more preferably 88 or less, and particularly preferably 86 or less.

  The hardness H2s is measured by a Shore C type hardness meter attached to an automatic hardness meter (trade name “Digitest II” manufactured by H. Barreith Co., Ltd.). This hardness meter is pressed against the surface of the outer core 6. The measurement is performed in an environment of 23 ° C.

  A core having a small difference De2 can be obtained by a two-step crosslinking process. Specifically, in the first crosslinking step, the rubber composition is crosslinked at a predetermined temperature. This rubber composition is crosslinked in the second crosslinking step at a temperature higher than the temperature in the first crosslinking step.

The ratio (V2 / V1) of the volume V2 of the outer core 6 and the volume V1 of the inner core 4 satisfies the following mathematical formula (1).
1.0 <V2 / V1 <7.0 (1)
In other words, the ratio (V2 / V1) is more than 1.0 and less than 7.0. With the golf ball 2 having a ratio (V2 / V1) of more than 1.0, the initial velocity of the ball on driver shots is high. The golf ball 2 having a ratio (V2 / V1) of less than 7.0 has a low spin rate on driver shots. A large flight distance is achieved by a large initial velocity of the ball and a small spin speed. From this viewpoint, it is more preferable that the golf ball 2 satisfies the following mathematical formula.
2.0 <V2 / V1 <6.0
It is particularly preferable that the golf ball 2 satisfies the following formula.
2.5 <V2 / V1 <5.0

In this golf ball 2, the hardness difference De2 in the outer core 6 and the hardness difference De1 in the inner core 4 satisfy the following formula (2).
De2-De1 <0 (2)
In the golf ball 2 satisfying the above formula, a large initial velocity and a small spin velocity are compatible with each other on driver shots. From this viewpoint, it is more preferable that the golf ball 2 satisfies the following mathematical formula.
De2-De1 <-5
It is particularly preferable that the golf ball 2 satisfies the following formula.
De2-De1 <-10

  The mid layer 8 is located between the outer core 6 and the cover 10. The mid layer 8 is formed from a resin composition. Examples of the base polymer of this resin composition include ionomer resins, polyesters, polyamides, polyurethanes, polyolefins and polystyrenes. Particularly, an ionomer resin is preferable. The ionomer resin has high elasticity. The golf ball 2 having the mid layer 8 containing an ionomer resin has excellent flight performance on driver shots.

  The ionomer resin and another resin 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 85% or more.

  As a preferable ionomer resin, a binary copolymer of α-olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms can be mentioned. A preferable binary copolymer contains 80% by mass or more and 90% by mass or less of an α-olefin and 10% by mass or more and 20% by mass or less of an α, β-unsaturated carboxylic acid. This binary copolymer has excellent resilience performance. As another preferable ionomer resin, a ternary copolymer of an α-olefin, an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α, β-unsaturated carboxylic acid ester having 2 to 22 carbon atoms is used. Polymers may be mentioned. A preferable terpolymer is 70% by mass or more and 85% by mass or less of α-olefin, 5% by mass or more and 30% by mass or less of α, β-unsaturated carboxylic acid, and 1% by mass or more and 25% by mass or less. It includes an α, β-unsaturated carboxylic acid ester. This terpolymer has excellent resilience performance. In the binary copolymer and the terpolymer, preferred α-olefins are ethylene and propylene, and preferred α, β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. A particularly preferred ionomer resin is a copolymer of ethylene and acrylic acid. Another particularly preferred ionomer resin is a copolymer of ethylene and methacrylic acid.

  In the binary copolymer and the ternary copolymer, some of the carboxyl groups are neutralized with metal ions. Examples of the metal ion for neutralization include sodium ion, potassium ion, lithium ion, zinc ion, calcium ion, magnesium ion, aluminum ion and neodymium ion. Neutralization may be done with more than one metal ion. Particularly suitable metal ions from the viewpoint of resilience performance and durability of the golf ball 2 are sodium ion, zinc ion, lithium ion and magnesium ion.

  Specific examples of the ionomer resin include trade names “HIMIRAN 1555”, “HIMIRAN 1557”, “HIMIRAN 1605”, “HIMIRAN 1706”, “HIMIRAN 1707”, “HIMIRAN 1856”, and “HIMIRAN 1855” manufactured by Mitsui DuPont Polychemical Co., Ltd. "Himilan AM7311", "Himilan AM7315", "Himilan AM7317", "Himilan AM7329" and "Himilan AM7337"; DuPont trade names "Sarlin 6120", "Sarlin 6910", "Sarrin 7930", "Sarrin 7940", "Surin 8140", "Surin 8150", "Surin 8940", "Surin 8945", "Surin 9120", "Surin 9150", "Surin 9910", "Surin 9945", "Saari" AD8546 "," HPF1000 "and" HPF2000 "; and ExxonMobil Chemical Co. under the trade name of" IOTEK7010 "," IOTEK7030 "," IOTEK7510 "," IOTEK7520 "includes" IOTEK8000 "and" IOTEK8030 ". Two or more ionomer resins may be used in combination.

  The resin composition of the mid layer 8 may include a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer includes a polystyrene block as a hard segment and a soft segment. A typical soft segment is a diene block. Examples of compounds of the diene block include butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Butadiene and isoprene are preferred. Two or more compounds may be used in combination.

  The styrene block-containing thermoplastic elastomer includes styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-butadiene-styrene block copolymer (SIBS), The hydrogenated product of SBS, the hydrogenated product of SIS, and the hydrogenated product of SIBS are included. Examples of hydrogenated products of SBS include styrene-ethylene-butylene-styrene block copolymer (SEBS). Examples of hydrogenated products of SIS include styrene-ethylene-propylene-styrene block copolymer (SEPS). Examples of hydrogenated products of SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

  From the viewpoint of the resilience performance of the golf ball 2, the content of the styrene component in the styrene block-containing thermoplastic elastomer is preferably 10% by mass or more, more preferably 12% by mass or more, and particularly preferably 15% by mass or more. From the viewpoint of feel at impact, the content is preferably 50% by mass or less, more preferably 47% by mass or less, and particularly preferably 45% by mass or less.

  In the present invention, the styrene block-containing thermoplastic elastomer includes an alloy of one or more selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS and SEEPS, and an olefin. It is presumed that the olefin component in this alloy contributes to improving the compatibility with other base polymer. This alloy can contribute to the resilience performance of the golf ball 2. Olefins having 2 to 10 carbon atoms are preferable. Examples of suitable olefins include ethylene, propylene, butene and pentene. Ethylene and propylene are particularly preferred.

  Specific examples of the polymer alloy include Mitsubishi Chemical Co., Ltd. product names “Lavalon T3221C”, “Lavalon T3339C”, “Lavalon SJ4400N”, “Lavalon SJ5400N”, “Lavalon SJ6400N”, “Lavalon SJ7400N”, “Lavalon SJ8400N”, “Lavalon”. SJ9400N "and" Lavalon SR04 ". Other specific examples of the styrene block-containing thermoplastic elastomer include Daicel Chemical Industries' trade name "Epofriend A1010" and Kuraray's trade name "Septon HG-252".

  From the viewpoint of shot feeling, the ratio of the styrene block-containing thermoplastic elastomer to the total base polymer is preferably 1% by mass or more, and particularly preferably 2% by mass or more. From the viewpoint of suppressing spin on driver shots, this ratio is preferably 15% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less.

  The resin composition of the mid layer 8 may include polyamide. In the golf ball 2 in which the mid layer 8 contains polyamide, spin on driver shots is suppressed. Specific examples of the polyamide include polyamide 6, polyamide 11, polyamide 12, polyamide 66, and polyamide 610. Polyamide 6 is preferable from the viewpoint of versatility.

  From the viewpoint of spin suppression, the ratio of polyamide to the total base polymer is preferably 5% by mass or more, more preferably 10% by mass or more, and particularly preferably 15% by mass or more. From the viewpoint of feel at impact, this ratio is preferably 50% by mass or less, more preferably 45% by mass or less, and particularly preferably 40% by mass or less.

  The resin composition of the mid layer 8 may include a filler for the purpose of adjusting specific gravity and the like. Examples of suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. This resin composition may contain a powder made of a metal with a high specific gravity as a filler. Specific examples of high specific gravity metals include tungsten and molybdenum. The amount of the filler is appropriately determined so that the intended specific gravity of the mid layer 8 is achieved. The resin composition may contain a colorant, a crosslinked rubber powder or a synthetic resin powder. When the hue of golf ball 2 is white, a typical colorant is titanium dioxide.

  The hardness Hm of the mid layer 8 is preferably 55 or more. The golf ball 2 having the mid layer 8 having a hardness Hm of 55 or more has a low spin rate on driver shots. The mid layer 8 can contribute to the flight performance of the golf ball 2. From this viewpoint, the hardness Hm is more preferably 58 or higher, and particularly preferably 61 or higher. From the viewpoint of shot feeling, the hardness Hm is preferably 80 or less, more preferably 75 or less, and particularly preferably 72 or less.

  The hardness Hm of the mid layer 8 is measured in accordance with the regulations of "ASTM-D 2240-68". The hardness Hm is measured by a Shore D type hardness meter attached to an automatic hardness meter (trade name “Digitest II” manufactured by H. Barreith Co., Ltd.). For the measurement, a sheet formed by hot pressing and made of the same material as the material of the intermediate layer 8 and having a thickness of about 2 mm is used. Sheets are stored at a temperature of 23 ° C. for 2 weeks prior to measurement. At the time of measurement, three sheets are superposed.

  The thickness Tm of the mid layer 8 is preferably 0.3 mm or more and 2.5 mm or less. The golf ball 2 having the mid layer 8 having a thickness Tm of 0.3 mm or more has a low spin rate on driver shots. From this viewpoint, the thickness Tm is more preferably 0.5 mm or more, and particularly preferably 0.8 mm or more. The golf ball 2 having the mid layer 8 having a thickness Tm of 2.5 mm or less is excellent in shot feeling. From this viewpoint, the thickness Tm is more preferably 2.0 mm or less, and particularly preferably 1.8 mm or less. The thickness Tm is measured immediately below the land 14.

  The golf ball 2 may have two or more mid layers 8 located between the outer core 6 and the cover 10. In this case, the thickness of each intermediate layer 8 is preferably within the above range.

  The cover 10 is the outermost layer except the mark layer and the paint layer. The cover 10 is molded from a resin composition. Examples of the base polymer of this resin composition include polyurethane, ionomer resin, polyester, polyamide, polyolefin and polystyrene. From the viewpoint of controllability when hit with a short iron, the preferred base polymer is polyurethane. When polyurethane and another resin are used in combination for the cover 10, the ratio of polyurethane to the total base resin is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

  Polyurethane has a urethane bond in the molecule. This urethane bond can be formed by the reaction of a polyol and a polyisocyanate. In addition to the reaction for the urethane bond, a chain extension reaction may be performed. The chain extension reaction can be done with polyamines or low molecular weight polyols.

As polyurethane,
(A1) Polyurethane containing a polyisocyanate component and a high molecular weight polyol component,
(A2) Polyurethane containing a polyisocyanate component, a high molecular weight polyol component, and a low molecular weight polyol,
(A3) Polyurethane containing a polyisocyanate component, a high molecular weight polyol component, and a polyamine component,
Examples of the polyurethane include (A4) a polyisocyanate component, a high molecular weight polyol component, a low molecular weight polyol component, and a polyamine component.

  The polyol, which is a raw material for the urethane bond, has a plurality of hydroxyl groups. Low molecular weight polyols and high molecular weight polyols can be used.

  Low molecular weight polyols include diols, triols, tetraols and hexaols. Specific examples of the diol include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, dipropylene glycol, 1,2-butanediol. 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2,3-dimethyl-2,3-butanediol, neopentyl glycol, pentanediol, hexanediol, heptanediol, octanediol And 1,6-cyclohexanedimethylol are exemplified. Aniline diol or bisphenol A diol may be used. Specific examples of triols include glycerin, trimethylolpropane and hexanetriol. Specific examples of tetraol include pentaerythritol and sorbitol.

  As high molecular weight polyols, polyether polyols such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG) and polytetramethylene ether glycol (PTMG); polyethylene adipate (PEA), polybutylene adipate (PBA). ) And polyhexamethylene adipate (PHMA); condensation type polyester polyols; lactone type polyester polyols such as poly-ε-caprolactone (PCL); polycarbonate polyols such as polyhexamethylene carbonate; and acrylic polyols. Two or more polyols may be used in combination. From the viewpoint of feel at impact of the golf ball 2 on driver shots, the number average molecular weight of the high molecular weight polyol is preferably 400 or more, more preferably 1000 or more. The number average molecular weight is preferably 10,000 or less. A particularly preferred polyol is a diol.

  Polyisocyanate, which is a raw material for the urethane bond, has two or more isocyanate groups. Examples of polyisocyanates include aromatic polyisocyanates, alicyclic polyisocyanates, and aliphatic polyisocyanates. Two or more polyisocyanates may be used in combination.

  As the aromatic polyisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, a mixture of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3′-bitrylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethyl xylylene diisocyanate (TMXDI) and paraphenylene diisocyanate (PPDI) Is mentioned.

As the alicyclic polyisocyanate, 4,4′-dicyclohexylmethane diisocyanate (H ₁₂ MDI), 1,3-bis (isocyanatomethyl) cyclohexane (H ₆ XDI), isophorone diisocyanate (IPDI) and trans-1,4- An example is cyclohexane diisocyanate (CHDI).

  Hexamethylene diisocyanate (HDI) is illustrated as an aliphatic polyisocyanate.

From the viewpoint of scratch resistance, aromatic polyisocyanates are preferred. From the viewpoint of weather resistance, TMXDI, XDI, HDI, H ₆ XDI, IPDI, H ₁₂ MDI and NBD are preferable, and H ₁₂ MDI is particularly preferable. H ₁₂ MDI is excellent in both scratch resistance and weather resistance.

  Polyamines for chain extension reactions have more than one amino group. Polyamines include aliphatic polyamines such as ethylenediamine, propylenediamine, butylenediamine and hexamethylenediamine; cycloaliphatic polyamines such as isophoronediamine and piperazine; and aromatic polyamines.

  In aromatic polyamines, the amino group is attached to the aromatic ring. The amino group may be directly bonded to the aromatic ring. The amino group may be indirectly bonded to the aromatic ring via the lower alkylene group.

  Aromatic polyamines include monocyclic aromatic polyamines and polycyclic aromatic polyamines. In the monocyclic aromatic polyamine, two or more amino groups are bonded to one aromatic ring. The polycyclic aromatic polyamine has two or more aminophenyl groups. In this aminophenyl group, one or more amino groups are bonded to one aromatic ring.

  Examples of the monocyclic aromatic polyamine include a polyamine in which an amino group is directly bonded to an aromatic ring and a polyamine in which an amino group is bonded to an aromatic ring through a lower alkylene group. Specific examples of the monocyclic aromatic polyamine having an amino group directly bonded to the aromatic ring include phenylenediamine, toluenediamine, diethyltoluenediamine and dimethylthiotoluenediamine. A specific example of the monocyclic aromatic polyamine in which the amino group is bonded to the aromatic ring via the lower alkylene group is xylylenediamine.

  Examples of polycyclic aromatic polyamines include poly (aminobenzene) in which two or more aminophenyl groups are directly bonded and polyamine in which two or more aminophenyl groups are bonded via a lower alkylene group or alkylene oxide group. To be done. A diaminodiphenylalkane in which two aminophenyl groups are bonded via a lower alkylene group is preferable, and 4,4'-diaminodiphenylmethane and a derivative thereof are particularly preferable.

  The cover 10 may include a thermoplastic polyurethane or a thermosetting polyurethane. From the viewpoint of productivity, thermoplastic polyurethane is preferable. The thermoplastic polyurethane contains a polyurethane component as a hard segment and a polyester component or a polyether component as a soft segment. Thermoplastic polyurethane is soft. The cover 10 using this polyurethane has excellent scratch resistance.

  Specific examples of the thermoplastic polyurethane include BASF Japan's trade names “Elastollan NY80A”, “Elastollan NY82A”, “Elastollan NY84A”, “Elastollan NY85A”, “Elastollan NY86A”, “Elastollan NY88A”, "Elastollan NY90A", "Elastollan NY92A", "Elastollan NY95A", "Elastollan NY97A", "Elastollan NY585", "Elastollan KP016N" and "Elastollan 1190ATR"; and products of Dainichi Seika Kogyo Co., Ltd. The names "Resamine P4585LS" and "Resamine PS62490" are mentioned.

  The resin composition of the cover 10 may include an appropriate amount of a colorant, a filler, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, a fluorescent brightening agent and the like. When the hue of golf ball 2 is white, a typical colorant is titanium dioxide.

  From the viewpoint of the durability of the cover 10, the Shore D hardness Hc of the cover 10 is preferably 15 or more, more preferably 18 or more, and particularly preferably 20 or more. From the viewpoint of controllability of the golf ball 2, the hardness Hc is preferably 40 or less, more preferably 37 or less, and particularly preferably 34 or less.

  The hardness Hc of the cover 10 is measured according to the standard of "ASTM-D 2240-68". The hardness Hc is measured by a Shore D type hardness meter attached to an automatic hardness meter (trade name “Digitest II” manufactured by H. Barreith Co., Ltd.). For the measurement, a sheet made of the same material as the material of the cover 10 and having a thickness of about 2 mm, which is formed by hot pressing, is used. Sheets are stored at a temperature of 23 ° C. for 2 weeks prior to measurement. At the time of measurement, three sheets are superposed.

  From the viewpoint of control performance, the thickness Tc of the cover 10 is preferably 0.1 mm or more, more preferably 0.3 mm or more, and particularly preferably 0.4 mm or more. From the viewpoint of suppressing spin on driver shots, the thickness Tc is preferably 2.0 mm or less, more preferably 1.5 mm or less, and particularly preferably 1.0 mm or less. The thickness Tc is measured immediately below the land 14.

  A known method such as an injection molding method or a compression molding method can be used to form the cover 10. When the cover 10 is molded, the dimples 12 are formed by the pimples formed on the cavity surface of the mold.

  The golf ball 2 may include a reinforcing layer between the mid layer 8 and the cover 10. The reinforcing layer firmly adheres to the mid layer 8 and also firmly adheres to the cover 10. The reinforcing layer suppresses peeling of the cover 10 from the mid layer 8. The reinforcing layer is formed of a resin composition. As a preferable base polymer for the reinforcing layer, a two-component curing type epoxy resin and a two-component curing type urethane resin are exemplified.

  The amount of compressive deformation Sb of the golf ball 2 is preferably 2.0 mm or more and 3.5 mm or less. The golf ball 2 having a compression deformation amount Sb of 2.0 mm or more is excellent in shot feeling. From this viewpoint, the amount of compressive deformation Sb is preferably 2.2 mm or more, and particularly preferably 2.3 mm or more. In the golf ball 2 having the amount of compressive deformation Sb of 3.5 mm or less, the initial velocity on driver shot is high. From this viewpoint, the amount of compressive deformation Sb is more preferably 3.2 mm or less, and particularly preferably 3.0 mm or less.

  A YAMADA type compression tester is used to measure the amount of compressive deformation Sb. In this tester, the golf ball 2 is placed on a hard plate made of metal. A metal cylinder gradually descends toward the golf ball 2. The golf ball 2 sandwiched between the bottom surface of the cylinder and the rigid plate is deformed. The moving distance of the cylinder from the state where the initial load of 98 N is applied to the golf ball 2 to the state where the final load of 1274 N is applied is measured. The moving speed of the cylinder until the initial load is applied is 0.83 mm / s. The moving speed of the cylinder from the initial load to the final load is 1.67 mm / s.

In this golf ball 2, the value Vb calculated by the following mathematical formula exceeds 620 and is less than 900.
Vb = Tc.Hc.Hm / Tm
In other words, this golf ball 2 satisfies the following formula (4).
620 <Tc.Hc.Hm/Tm <900 (4)
According to the knowledge obtained by the present inventor, the golf ball 2 having the value Vb of more than 620 and less than 900 has both flight performance and control performance. From this viewpoint, it is more preferable that the golf ball 2 satisfies the following mathematical formula.
640 <Tc.Hc.Hm/Tm <800

  In the golf ball 2 having the cover 10 having a small hardness Hc and a small thickness Tc, the above mathematical expression (4) can be satisfied.

  As shown in FIGS. 2-7, the contour of the dimple 12 is a circle. This golf ball 2 has a dimple A having a diameter of 4.50 mm, a dimple B having a diameter of 4.40 mm, a dimple C having a diameter of 4.30 mm, and a dimple D having a diameter of 4.20 mm. And dimples E having a diameter of 3.00 mm. The number of types of dimples 12 is five. The golf ball 2 may have non-circular dimples instead of or together with the circular dimples 12.

  The number of dimples A is 80, the number of dimples B is 74, the number of dimples C is 62, the number of dimples D is 96, and the number of dimples E is 12. The total number of dimples 12 is 324. The dimples 12 and the lands 14 form a dimple pattern.

  FIG. 8 shows a cross section of the golf ball 2 along a plane passing through the center of the dimple 12 and the center of the golf ball 2. The vertical direction in FIG. 8 is the depth direction of the dimple 12. What is indicated by a chain double-dashed line 16 in FIG. 8 is a virtual sphere. The surface of the phantom sphere 16 is the surface of the golf ball 2 when it is assumed that the dimples 12 do not exist. The diameter of the phantom sphere 16 is the same as the diameter of the golf ball 2. The dimple 12 is recessed from the surface of the phantom sphere 16. The land 14 coincides with the surface of the virtual sphere 16. In the present embodiment, the cross-sectional shape of the dimple 12 is substantially an arc. The cross-sectional shape may be a curve whose curvature changes.

  What is indicated by an arrow Dm in FIG. 8 is the diameter of the dimple 12. The diameter Dm is the distance between the one contact Ed and the other contact Ed when the tangent line Tg common to both sides of the dimple 12 is drawn. The contact point Ed is also the edge of the dimple 12. The edge Ed defines the contour of the dimple 12. In FIG. 8, what is indicated by a double-headed arrow Dp1 is the first depth of the dimple 12. The first depth Dp1 is the distance between the deepest part of the dimple 12 and the surface of the virtual sphere 16. In FIG. 8, what is indicated by a double-headed arrow Dp2 is the second depth of the dimple 12. The second depth Dp2 is the distance between the deepest part of the dimple 12 and the tangent line Tg.

  The diameter Dm of each dimple 12 is preferably 2.0 mm or more and 6.0 mm or less. The dimple 12 having a diameter Dm of 2.0 mm or more contributes to turbulence. From this viewpoint, the diameter Dm is more preferably 2.5 mm or more, and particularly preferably 2.8 mm or more. The dimple 12 having a diameter Dm of 6.0 mm or less does not impair the essence of the golf ball 2 that is substantially a sphere. From this viewpoint, the diameter Dm is more preferably 5.5 mm or less, and particularly preferably 5.0 mm or less.

  From the viewpoint that the hop of the golf ball 2 is suppressed, the first depth Dp1 of the dimple 12 is preferably 0.10 mm or more, more preferably 0.13 mm or more, and particularly preferably 0.15 mm or more. From the viewpoint that the drop of the golf ball 2 is suppressed, the first depth Dp1 is preferably 0.65 mm or less, more preferably 0.60 mm or less, and particularly preferably 0.55 mm or less.

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

In the golf ball 2 shown in Figure 2-7, the area of the dimple A is 15.9 mm ^2, the area of the dimple B is 15.2 mm ^2, the area of the dimple C is 14.5 mm ^2, the dimple The area of D is 13.9 mm ² , and the area of the dimple E is 7.1 mm ² .

In the present invention, the ratio of the total area S of all the dimples 12 to the surface area of the phantom sphere 16 is called the occupancy rate. From the viewpoint of flight distance on driver shots, the occupancy rate is preferably 80% or more, more preferably 81% or more, and particularly preferably 82% or more. The occupation rate is preferably 95% or less. In the golf ball 2 shown in FIGS. 2-7, the total area of the dimples 12 is 4712.8 mm ² . Since the surface area of the virtual sphere 16 of this golf ball 2 is 5718.0 mm ² , the occupancy rate is 82.3%.

  From the viewpoint of achieving a sufficient occupation ratio, the total number N of the dimples 12 is preferably 250 or more, more preferably 280 or more, and particularly preferably 300 or more. From the viewpoint that each dimple 12 can contribute to turbulence, the total number N is preferably 450 or less, more preferably 400 or less, and particularly preferably 380 or less.

In the present invention, the “volume of dimples” means the volume of the portion surrounded by the surface of the phantom sphere 16 and the surface of the dimple 12. From the viewpoint of rising of the golf ball 2 is suppressed, the total volume of the dimples 12 is preferably 450 mm ³ or more, more preferably 480 mm ³ or more, 500 mm ³ or more is particularly preferable. In view of dropping of the golf ball 2 is suppressed, the total volume is preferably 750 mm ³ or less, more preferably 730 mm ³ or less, 710 mm ³ or less is particularly preferred.

In the present invention, the dimples 12 whose area is less than 8.0 mm ² are referred to as “small dimples 12S”. In the golf ball 2 shown in FIGS. 2-7, the dimple E is a small dimple 12S. In this golf ball 2, the number NS of the small dimples 12S is 12.

In the present invention, the dimples 12 having an area of 8.0 mm ² or more are referred to as “large dimples 12L”. In the golf ball 2 shown in FIGS. 2-7, the dimples AD are large dimples 12L. In this golf ball 2, the number NL of the large dimples 12L is 312. The sum of the number NS and the number NL is equal to the total number N.

  In the dimple pattern having only the large dimples 12L, the land 14 tends to be biased on the surface of the virtual sphere 16. This bias is referred to herein as distortion. In the golf ball 2 according to the present invention, the small dimple 12S suppresses distortion. In this golf ball 2, the small dimples 12S promote turbulence. With this golf ball 2, a great flight distance can be obtained on driver shots.

  In the pattern in which the small dimples 12S exist excessively, the size of the dimples 12 largely varies. Turbulence is insufficient for a pattern with a large variation. In the golf ball 2 having an appropriate number of small dimples 12S, sufficient turbulence can be obtained. With the golf ball 2 having an appropriate number of small dimples 12S, a large flight distance can be obtained on driver shots.

  From the viewpoint of flight distance on a driver shot, the ratio PS of the total area of the small dimples 12S to the surface area of the phantom sphere 16 is preferably 0.7% or more, more preferably 0.9% or more, and 1.0% or more. Is particularly preferable. From the viewpoint of flight distance on driver shots, this ratio PS is preferably less than 2.0%, more preferably 1.8% or less, and particularly preferably 1.7% or less. In the golf ball 2 shown in FIG. 2-7, this ratio PS is 1.5%.

  From the viewpoint of flight distance on driver shots, the number NS of the small dimples 12S is preferably 6 or more, more preferably 8 or more, and particularly preferably 10 or more. From the viewpoint of flight distance on driver shots, the number NS is preferably 20 or less, more preferably 18 or less, and particularly preferably 16 or less.

  From the viewpoint of flight distance on driver shots, the ratio (NS / N) of the number NS of the small dimples 12S to the total number N of the dimples 12 is preferably 0.01 or more, more preferably 0.02 or more, and 0.03. The above is particularly preferable. From the viewpoint of flight distance on driver shots, this ratio (NS / N) is preferably 0.07 or less, more preferably 0.06 or less, and particularly preferably 0.05 or less. In the golf ball 2 shown in FIG. 2-7, this ratio (NS / N) is 0.04.

  As described above, the presence of the small dimples 12S is essential from the viewpoint of suppressing distortion of the dimple pattern. On the other hand, the degree of contribution of the small dimples 12S to the turbulence is smaller than that of the large dimples 12L. A dimple pattern in which an appropriate number of small dimples 12S exists and a sufficient number of large dimples 12L exists has excellent flight performance.

  From the viewpoint of flight performance on driver shots, the ratio PL of the total area of the large dimples 12L to the surface area of the phantom sphere 16 is preferably 79.0% or more, more preferably 79.5% or more, and 80.0%. The above is particularly preferable. The ratio PL is preferably 90% or less. In the golf ball 2 shown in FIG. 2-7, the ratio PL is 80.8%.

  In a pattern in which the dimples 12 have large variations in size, turbulence is insufficient. From the viewpoint that sufficient turbulence can be obtained, the unity G of the area of the large dimple 12L is preferably 1.15 or less, more preferably 1.10 or less, and particularly preferably 1.05 or less. The uniformity G is preferably 0.50 or more.

The uniformity G is a standard deviation of the area (mm ² ) of the large dimple 12L. In the golf ball 2 shown in FIGS. 2-7, the average area of the large dimples 12L is 14.9 mm ² . The uniformity G of the golf ball 2 is calculated based on the following mathematical formula.
G = (((15.9-14.9) ² * 80 + (15.2-14.9) ² * 74 + (14.5-14.9) ² * 62
+ (13.9-14.9) ² * 96) / 312) ^1/2
The uniformity G of the golf ball 2 is 0.801.

  Hereinafter, the effects of the present invention will be clarified by examples, but the present invention should not be limitedly interpreted based on the description of the examples.

[Example 1]
100 parts by mass of high-cis polybutadiene (trade name "BR-730" of JSR Corporation), 26.0 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 0.7 parts by mass of dicumyl peroxide were kneaded to obtain a rubber composition (b). This rubber composition (b) was put into a mold having upper and lower molds each having a hemispherical cavity and heated at 170 ° C. for 15 minutes to obtain an inner core having a diameter D1 of 24 mm. The amount of barium sulphate was adjusted to obtain the desired ball mass.

  100 parts by mass of high cis polybutadiene (JSR's trade name "BR-730"), 41.5 parts by mass of zinc acrylate, 5 parts by mass of zinc oxide, an appropriate amount of barium sulfate, 0.1 parts by mass of antioxidant. The agent (H-BHT), 0.5 parts by mass of diphenyl disulfide and 0.7 parts by mass of dicumyl peroxide were kneaded to obtain a rubber composition (d). A half shell was molded with this rubber composition (d). The inner core was covered with two half shells. The inner core and the half shell are put into a mold including an upper mold and a lower mold each having a hemispherical cavity, and a core composed of an inner core and an outer core is molded in a first crosslinking step and a second crosslinking step. did. In the first crosslinking step, the crosslinking temperature was 140 ° C and the crosslinking time was 20 minutes. In the second crosslinking step, the crosslinking temperature was 160 ° C and the crosslinking time was 10 minutes. The core diameter was 38.5 mm.

  50 parts by weight of an ionomer resin (the above-mentioned "Surlyn 8150"), 50 parts by weight of another ionomer resin (the above-mentioned "Himilan AM7329") and 4 parts by weight of titanium dioxide were kneaded in a biaxial kneading extruder to obtain a resin composition. The thing (M2) was obtained. This resin composition (M2) was coated around the inner core by an injection molding method to form an intermediate layer. The thickness of this intermediate layer was 1.6 mm.

  A coating composition containing a two-component curing type epoxy resin as a base polymer (trade name "Porin 750LE", manufactured by Shinto Paint Co., Ltd.) was prepared. And 70 parts by mass of the solvent The curing agent liquid of this coating composition contains 40 parts by mass of the modified polyamidoamine, 55 parts by mass of the solvent, and 5 parts by mass of titanium dioxide. The mass ratio to the curing agent liquid is 1 / 1.This coating composition was applied to the surface of the intermediate layer with a spray gun and kept at 23 ° C. for 12 hours to obtain a reinforcing layer. The thickness of the reinforcing layer was 10 μm.

  100 parts by weight of a thermoplastic polyurethane elastomer (the aforementioned "Elastollan NY84A"), 0.2 parts by weight of a light stabilizer (trade name "Tinuvin 770"), 4 parts by weight of titanium dioxide and 0.04 parts by weight of Ultra. Marine blue was kneaded with a twin-screw kneading extruder to obtain a resin composition (C2). A half shell was obtained from this resin composition (C2) by a compression molding method. Two half shells covered a sphere consisting of an inner core, an outer core, an intermediate layer and a reinforcing layer. These half shells and spheres were placed in a final mold having an upper mold and a lower mold each having a hemispherical cavity and a large number of pimples on the cavity surface, and a cover was obtained by a compression molding method. The cover had a thickness of 0.5 mm. Dimples having an inverted shape of the pimples were formed on the cover.

  A clear paint having a two-component curing type polyurethane as a base material was applied around the cover to obtain a golf ball of Example 1 having a diameter of about 42.7 mm and a mass of about 45.6 g. Details of the dimple specifications D2 of this golf ball are shown in Tables 5 and 6 below. FIG. 9 is a front view of this golf ball, and FIG. 10 is a plan view of this golf ball.

[Example 2-8 and Comparative Example 1-7]
Golf of Examples 2-9 and Comparative Examples 1-7 in the same manner as in Example 1 except that the specifications of the inner core, the outer core, the mid layer, the cover and the dimples were as shown in Table 7-10 below. Got the ball Details of the specifications of the inner core and the outer core are shown in Tables 1 and 2 below. The details of the specifications of the intermediate layer are shown in Table 3 below. Details of the cover specifications are shown in Table 4 below. Details of the dimple specifications are shown in Tables 5 and 6 below. The dimple pattern of the golf ball according to Comparative Example 3 is the same as the dimple pattern of the golf ball according to Comparative Example 4 of JP 2006-20820A. The dimple pattern of the golf ball according to Comparative Example 4 is the same as the dimple pattern of the golf ball according to Example 2 of JP-A-2005-137692.

[Flight test]
A driver (Dunlop Sports Co., Ltd., product name “Z745”, shaft hardness: S, loft angle: 8.5 °) was attached to a swing machine manufactured by Golf Laboratories. The golf ball was hit under the condition that the head speed was 50 m / sec, and the initial speed, spin rate and flight distance of the golf ball were measured. The flight distance is the distance between the hitting point and the point where the ball is stationary. The average values of the data obtained from 12 measurements are shown in Table 7-10 below.

  As shown in Table 7-10, the golf balls of the respective examples are excellent in flight performance on driver shots. From this evaluation result, the superiority of the present invention is clear.

  The golf ball according to the present invention is suitable for play on a golf course, practice in a driving range, and the like.

2 ... Golf ball 4 ... Inner core 6 ... Outer core 8 ... Mid layer 10 ... Cover 12 ... Dimple 14 ... Land 16 ... Virtual sphere

Claims (11)

A golf ball comprising an inner core, an outer core located outside the inner core, an intermediate layer located outside the outer core, and a cover located outside the intermediate layer,
Diameter D1 (mm), volume V1 (mm ³ ), center hardness H1o (Shore C), in-boundary hardness H1in (Shore C), and difference De1 between the hardness H1in and the hardness H1o in the inner core;
Volume V2 (mm ³ ) in the outer core, and a difference De2 between the surface hardness H2s (Shore C) and the out-of-bounds hardness H2out (Shore C);
Thickness Tm (mm) and hardness Hm (Shore D) in the intermediate layer;
And the thickness Tc (mm) and hardness Hc (Shore D) of the cover
Satisfies the following formulas (1)- (4 ′) ,
1.0 <V2 / V1 <7.0 (1)
De2-De1 <0 (2)
600 <(H1o + H1in) * (D1 / 2) / 2 <1000 (3)
639 ≦ Tc · Hc · Hm / Tm ≦ 698 (4 ′)
It has multiple dimples on its surface,
The dimples, a plurality of small dimples area is less than 8.0 mm ^2, area includes a plurality of large dimples is 8.0 mm ² or more,
The ratio PS of the total area of the small dimples to the surface area of the phantom sphere of the golf ball is less than 2.0%,
The ratio PL of the total area of the large dimples to the surface area of the virtual sphere is 79.0% or more,
The unity G of the area (mm ² ) of the large dimple is 1.15 or less,
A golf ball having a total of 250 or more and 380 or less dimples. The golf ball according to claim 1, which satisfies the following formula.
2.0 <V2 / V1 <6.0 The golf ball according to claim 1, which satisfies the following formula.
700 <(H1o + H1in) * (D1 / 2) / 2 <900 The golf ball according to claim 1, which satisfies the following formula.
640 <Tc.Hc.Hm/Tm <800   The golf ball according to claim 1, wherein the ratio PS is 0.7% or more.   The golf ball according to claim 1, wherein the number NS of the small dimples is 6 or more and 20 or less.   7. The golf ball according to claim 1, wherein a ratio (NS / N) of the number NS of the small dimples to the total number N of the dimples is 0.01 or more and 0.07 or less.   The golf ball according to any one of claims 1 to 7, wherein a depth of the deepest part of each dimple from the surface of the virtual sphere is 0.10 mm or more and 0.65 mm or less. 9. The golf ball according to claim 1, wherein the total volume of the dimples is 450 mm ³ or more and 750 mm ³ or less.   The golf ball according to claim 1, wherein the ratio PL is 79.5% or more and the uniformity G is 1.10 or less. The golf ball according to claim 10, wherein the ratio PL is 80.0% or more and the uniformity G is 1.05 or less.

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