JP6763137B2 - Golf ball - Google Patents

Description

The present invention relates to a golf ball. 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 greatest concern with a golf ball is distance. Players place particular importance on distance on driver shots. The initial velocity, spin velocity, and launch angle of the ball when hit by 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 greater the initial velocity of the ball, the greater the flight distance. The proper spin speed and the proper launch angle also contribute to the flight distance.

Various proposals have been made regarding the improvement of flight performance, focusing on the initial three elements. 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 described in JP-A-2003-190331, JP-A-2006-289065, JP-A-2007-190382, JP-A-10-328326, JP-A-10-328328, JP-A-2000. It is also disclosed in Japanese Patent Application Laid-Open No. -60997 and Japanese Patent Application Laid-Open No. 2009-21971.

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 separation. This phenomenon is called "turbulence". The turbulence shifts the point of separation of air from the golf ball backwards, reducing drag. Due to the turbulence, the deviation between the upper peeling point and the lower peeling point of the golf ball due to the backspin is promoted, and the lift acting on the golf ball is enhanced. Good dimples better disrupt the flow of air. Excellent dimples produce a large flight distance.

Various proposals have been made regarding dimples. Japanese Unexamined Patent Publication 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. Random patterns can contribute to the flight performance of a golf ball. Japanese Patent Application Laid-Open No. 2012-10822 also discloses a golf ball having a random pattern.

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

Japanese Unexamined Patent Publication No. 11-20920 Japanese Patent Application Laid-Open No. 2003-190331 JP-A-2006-289065 JP-A-2007-190382 Japanese Unexamined Patent Publication No. 10-328326 Japanese Unexamined Patent Publication No. 10-328328 JP-A-2000-60997 JP-A-2009-21971 JP-A-2009-172192 JP2012-10822A JP-A-2007-175267 JP-A-2007-195591 Japanese Unexamined Patent Publication No. 2013-153966

Players' demands for distance are 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), in-boundary hardness H1in (shore C), and difference between hardness H1in and hardness H1o in the inner core De1;
Volume V2 (mm ³ ) in the outer core, and the difference between the surface hardness H2s (shore C) and the extraboundary hardness H2out (shore C) De2;
Thickness Tm (mm) and hardness Hm (Shore D) in the mesosphere;
And the thickness Tc (mm) and hardness Hc (shore D) of the cover.
Satisfies the following mathematical formulas (1.1)-(1.4).
1.0 <V2 / V1 <7.0 (1.1)
De2-De1 <0 (1.2)
600 <(H1o + H1in) ・ (D1 / 2) / 2 <1000 (1.3)
620 <Tc ・ Hc ・ Hm / Tm <900 (1.4)
This golf ball has a plurality of dimples on its surface. The ratio So of the total area of the dimples to the surface area of the virtual ball of the golf ball is 81.0% or more. The ratio Rs of the number of dimples whose diameter is 9.60% or more and 10.37% or less of the diameter of the golf ball to the total number of dimples is 50% or more. The hemispherical dimple pattern of a golf ball consists of three units that are rotationally symmetric with each other. The dimple pattern of each unit consists of two small units that are mirror-symmetrical to each other. This golf ball satisfies the following mathematical formula (2.1).
Rs ≧ −2.5 ・ So + 273 (2.1)

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 golf ball satisfies the following mathematical formula (2.2).
Rs ≧ −2.5 ・ So + 278 (2.2)

Preferably, the golf ball satisfies the following mathematical formula (2.3).
Rs ≧ −2.5 ・ So + 283 (2.3)

Preferably, the ratio Rs'of the number of dimples whose diameter is 10.10% or more and 10.37% or less of the diameter of the golf ball to the total number of dimples is 50% or more. Preferably, the golf ball satisfies the following mathematical formula (2.4).
Rs'≧ -2.2 ・ So + 245 (2.4)

Preferably, the golf ball satisfies the following mathematical formula (2.5).
Rs'≧ -2.2 ・ So + 252 (2.5)

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.

When the golf ball according to the present invention is hit by a driver, the spin speed is low and the initial velocity of the ball is high. Furthermore, in this golf ball, turbulence is promoted by dimples. With the right initial three elements and the right aerodynamics, this golf ball provides a great distance on driver shots.

FIG. 1 is a cross-sectional view showing a golf ball according to an embodiment of the present invention. FIG. 2 is an enlarged plane showing the golf ball of FIG. FIG. 3 is a front view showing the golf ball of FIG. FIG. 4 is an enlarged cross-sectional view showing a part of the golf ball of FIG. FIG. 5 is a graph showing the relationship between the ratio So and the ratio Rs. FIG. 6 is a graph showing the relationship between the ratio So and the ratio Rs'. FIG. 7 is a plan view showing a golf ball according to a second embodiment of the present invention. FIG. 8 is a front view showing the golf ball of FIG. 7. FIG. 9 is a plan view showing the golf ball according to Comparative Example 4. FIG. 10 is a front view showing the golf ball of FIG.

Hereinafter, the present invention will be described in detail based on a preferred embodiment 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 the intermediate layer 8. It is provided with a cover 10 located on the outside of the. The golf ball 2 has a plurality of dimples 12 on its surface. The portion of the surface of the golf ball 2 other than the dimples 12 is the land 14. The golf ball 2 has a paint layer and a mark layer on the outside of the cover 10, but the illustration of these layers is omitted. The golf ball 2 may have another layer between the outer core 6 and the intermediate layer 8. The golf ball 2 may have another layer between the intermediate layer 8 and the cover 10.

The diameter of the golf ball 2 is preferably 40 mm or more and 45 mm or less. A diameter of 42.67 mm or more is particularly preferred from the perspective of meeting the standards of the United States Golf Association (USGA). 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 diameter of the golf ball 2 according to the present embodiment is 42.70 mm. The 30 points above Land 14 are randomly selected. The diameter with each point as one end is measured. The diameter of the golf ball 2 is calculated by averaging these diameters.

The mass 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 cross-linking the rubber composition. Preferred base rubbers include polybutadiene, polyisoprene, styrene-butadiene copolymers, ethylene-propylene-diene copolymers and natural rubbers. Polybutadiene is preferred from the standpoint of large ball initial velocity. When polybutadiene and other rubbers 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 preferred co-crosslinking agent from the viewpoint of large ball initial velocity is a monovalent or divalent metal salt of α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms. Preferred 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 contain 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 the large initial velocity of the balls, the amount of the co-crosslinking agent is preferably 10 parts by mass or more, particularly preferably 15 parts by mass or more with respect to 100 parts by mass of the base rubber. From the viewpoint of a small spin rate on a driver shot, this amount is preferably 40 parts by mass or less, and particularly preferably 35 parts by mass or less. As will be explained in detail later, a small spin speed can achieve a large flight distance on a driver shot.

Preferably, the rubber composition of the inner core 4 contains an organic peroxide. The organic peroxide functions as a cross-linking 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). Peroxy) Hexane and di-t-butyl peroxide are exemplified. A particularly versatile organic peroxide is dicumyl peroxide.

From the viewpoint of the initial velocity of a large ball, the amount of organic peroxide is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and 0.5 part by mass or more with respect to 100 parts by mass of the base rubber. Especially preferable. 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. Organic sulfur compounds include naphthalenethiol compounds, benzenethiol compounds and disulfide compounds.

As naphthalenethiol compounds, 1-naphthalenethiol, 2-naphthalenethiol, 4-chloro-1-naphthalenethiol, 4-bromo-1-naphthalenethiol, 1-chloro-2-naphthalenethiol, 1-bromo-2-naphthalene Examples thereof include thiol, 1-fluoro-2-naphthalenethiol, 1-cyano-2-naphthalenethiol and 1-acetyl-2-naphthalenethiol.

As benzenethiol compounds, 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 -Nitrobenzenethiol is exemplified.

As disulfide compounds, 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) Examples thereof include 5,6-pentachlorophenyl) disulfide and bis (2,3,4,5,6-pentabromophenyl) disulfide.

From the viewpoint of the 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 with respect to 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 contain a filler for the purpose of adjusting the specific gravity and the like. 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. The rubber composition may contain an appropriate amount of various additives such as sulfur, carboxylic acid, carboxylic acid salt, antiaging agent, colorant, plasticizer, and dispersant. 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 an inner core 4 having a diameter D1 of 15.0 mm or more, spin on a driver shot 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 an inner core 4 having a volume V1 of 1700 mm ³ or more, spin on a driver shot 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 cross-linking temperature of the inner core 4 is 140 ° C. or higher and 180 ° C. or lower. The cross-linking 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 hardness H1in within the boundary of the inner core 4 is large. The inner core 4 having a large difference De1 has a so-called outer rigid inner flexible structure. The spin speed when the golf ball 2 having the inner core 4 is hit by the driver is small. When the golf ball 2 having the inner core 4 is hit by a driver, a large launch angle can be obtained.

For driver shots, an appropriate trajectory height and an appropriate flight time are required. The golf ball 2, which achieves ballistic height and flight time at a large spin speed, has a small run after falling. A golf ball 2 that achieves ballistic height and flight time at a large launch angle has a large run after falling. From the viewpoint of flight distance, a golf ball 2 that achieves ballistic height and flight time at a large launch angle is preferable. As described above, the inner core 4 having the outer rigid inner flexible structure can contribute to a large launch angle and a small spin velocity. The golf ball 2 having the inner core 4 is excellent in 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 easiness of manufacturing the inner core 4, the difference (H1in-H1o) is preferably 40 or less, and particularly preferably 30 or less. Preferably, the inner core 4 gradually increases in hardness from the center toward the surface.

From the viewpoint of the large initial velocity of the ball, 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.

Hardness H1o is measured by a Shore C type hardness tester attached to an automatic hardness tester (trade name "Digitest II" manufactured by H. Burleys). This hardness tester is pressed against the center of the cross section of the hemisphere obtained by cutting the golf ball 2. The measurement is made 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.

Hardness H1in is measured by a Shore C type hardness tester attached to an automatic hardness tester (trade name "Digitest II" manufactured by H. Burleys). This hardness tester is pressed against the cross section of the hemisphere obtained by cutting the golf ball 2. The hardness tester is pressed against a point moved 1 mm inward in the radial direction from the boundary between the inner core 4 and the outer core 6. The measurement is made 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 mathematical formula (1.3).
600 <(H1o + H1in) ・ (D1 / 2) / 2 <1000 (1.3)
The value Va approximates 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 small spin speed on a driver shot. 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 the driver shot is large. A large flight distance is achieved by a small spin speed and a large initial velocity of the ball. From this point of view, it is more preferable that the golf ball 2 satisfies the following 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 cross-linking the rubber composition. This composition may include the base rubber described above with respect to the inner core 4.

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

The rubber composition may contain 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 the large initial velocity of the balls, 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 shot feeling, 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 cross-linking initiator. The organic peroxide contributes to the resilience performance of the golf ball 2. The rubber composition of the outer core 6 may contain the organic peroxides described above with respect to the inner core 4.

From the viewpoint of the initial velocity of a large ball, the amount of organic peroxide is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and 0.5 part by mass or more with respect to 100 parts by mass of the base rubber. Especially preferable. 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. This rubber composition may contain the organic sulfur compounds described above for the inner core 4.

From the viewpoint of the 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 with respect to 100 parts by mass of the base rubber. From the viewpoint of shot feeling, 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 contain a filler for the purpose of adjusting the specific gravity and the like. Suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. The amount of filler is appropriately determined so that the intended specific gravity of the outer core 6 is achieved. The rubber composition may contain an appropriate amount of various additives such as sulfur, carboxylic acid, carboxylic acid salt, antiaging agent, colorant, plasticizer, and dispersant. 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 a diameter D2 of 37.0 mm or more has a large 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 intermediate 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 large initial velocity on a driver shot. 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 cross-linking temperature of the outer core 6 is 140 ° C. or higher and 180 ° C. or lower. The cross-linking time of the outer core 6 is 10 minutes or more and 60 minutes or less.

In the golf ball 2, the difference De2 between the surface hardness H2s and the out-of-boundary hardness H2out of the outer core 6 is preferably -2 or more and 2 or less. The hardness distribution of the outer core 6 is close to flat. In this outer core 6, the energy loss when hit by a driver is small. The golf ball 2 having the outer core 6 has a large 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 the large initial velocity of the ball, the hardness H2out outside the boundary 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.

Hardness H2out is measured by a Shore C type hardness tester attached to an automatic hardness tester (trade name "Digitest II" manufactured by H. Burleys). This hardness tester is pressed against the cross section of the hemisphere obtained by cutting the golf ball 2. The hardness tester is pressed against 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 made in an environment of 23 ° C.

From the viewpoint of spin suppression in driver shots, the surface hardness H2s is preferably 70 or more, more preferably 72 or more, and particularly preferably 74 or more. From the viewpoint of the 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.

Hardness H2s is measured by a Shore C type hardness tester attached to an automatic hardness tester (trade name "Digitest II" manufactured by H. Burleys). This hardness tester is pressed against the surface of the outer core 6. The measurement is made in an environment of 23 ° C.

A core with a small difference De2 can be obtained by a two-step cross-linking step. Specifically, in the first cross-linking step, the rubber composition is cross-linked at a predetermined temperature. In the second cross-linking step, this rubber composition is cross-linked at a temperature higher than the temperature of the first cross-linking step.

The ratio (V2 / V1) of the volume V2 of the outer core 6 to the volume V1 of the inner core 4 satisfies the following mathematical formula (1.1).
1.0 <V2 / V1 <7.0 (1.1)
In other words, the ratio (V2 / V1) is greater than 1.0 and less than 7.0. In the golf ball 2 having a ratio (V2 / V1) exceeding 1.0, the initial velocity of the ball on a driver shot is large. In the golf ball 2 having a ratio (V2 / V1) of less than 7.0, the spin speed on a driver shot is small. A large flight distance is achieved by a large ball initial velocity and a small spin velocity. From this point of view, it is more preferable that the golf ball 2 satisfies the following 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 mathematical formula (1.2).
De2-De1 <0 (1.2)
In the golf ball 2 that satisfies the above formula, a large initial velocity and a small spin velocity are compatible with each other in the driver shot. From this point of view, it is more preferable that the golf ball 2 satisfies the following formula.
De2-De1 <-5
It is particularly preferable that the golf ball 2 satisfies the following formula.
De2-De1 <-10

The intermediate layer 8 is located between the outer core 6 and the cover 10. The intermediate layer 8 is molded from the resin composition. Examples of the base polymer of this resin composition include ionomer resin, polyester, polyamide, polyurethane, polyolefin and polystyrene. In particular, ionomer resin is preferable. Ionomer resin has high elasticity. The golf ball 2 having the intermediate layer 8 containing the ionomer resin is excellent in flight performance on driver shots.

Ionomer resin and other resins may be used in combination. When used in combination, the ionomer resin is the main component of the base polymer from the viewpoint of resilience performance. The ratio of the ionomer resin to the total base polymer is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 85% or more.

Preferred ionomer resins include binary copolymers of α-olefins and α, β-unsaturated carboxylic acids having 3 or more and 8 or less carbon atoms. Preferred binary copolymers include 80% by mass or more and 90% by mass or less of α-olefins and 10% by mass or more and 20% by mass or less of α, β-unsaturated carboxylic acids. This binary copolymer is excellent in resilience performance. As other preferable ionomer resins, a ternary copolymer of an α-olefin, an α, β-unsaturated carboxylic acid having 3 or more and 8 or less carbon atoms and an α, β-unsaturated carboxylic acid ester having 2 or more and 22 or less carbon atoms Examples include copolymers. Preferred ternary copolymers are 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. Includes α, β-unsaturated carboxylic acid esters. This ternary copolymer is excellent in resilience performance. In the binary copolymer and the ternary copolymer, the preferred α-olefins are ethylene and propylene, and the 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. A particularly preferred other ionomer resin is a copolymer of ethylene and methacrylic acid.

In the binary copolymer and the ternary copolymer, a part of the carboxyl group is neutralized with metal ions. Examples of metal ions 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 two or more metal ions. 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 ionomer resins include the trade names "Himilan 1555", "Himilan 1557", "Himiran 1605", "Himiran 1706", "Himiran 1707", "Himiran 1856", "Himiran 1855", etc. "High-Milan AM7311", "High-Milan AM7315", "High-Milan AM7317", "High-Milan AM7329" and "High-Milan AM7337"; "Sarin 8140", "Sarin 8150", "Sarin 8940", "Sarin 8945", "Sarin 9120", "Sarin 9150", "Sarin 9910", "Sarin 9945", "Sarin AD8546", "HPF1000" and " HPF2000 ”; and the trade names“ IOTEK7010 ”,“ IOTEK7030 ”,“ IOTEK7510 ”,“ IOTEK7520 ”,“ IOTEK8000 ”and“ IOTEK8030 ”of Exxon Mobile Chemical Company. Two or more types of ionomer resins may be used in combination.

The resin composition of the intermediate layer 8 may contain 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 the diene block compound 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.

Examples of the styrene block-containing thermoplastic elastomer include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-butadiene-styrene block copolymer (SIBS), and the like. Includes SBS hydrohydrates, SIS adjuncts and SIBS adjuncts. Examples of hydrogenated SBS include styrene-ethylene-butylene-styrene block copolymer (SEBS). Examples of SIS hydrogenated products include styrene-ethylene-propylene-styrene block copolymer (SEPS). Examples of the hydrogenated product 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 shot feeling, this 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 the improvement of compatibility with other base polymers. This alloy can contribute to the resilience performance of the golf ball 2. An olefin having 2 or more and 10 or less carbon atoms is preferable. Suitable olefins include ethylene, propylene, butene and pentene. Ethylene and propylene are particularly preferred.

As specific examples of the polymer alloy, the trade names of Mitsubishi Chemical Corporation "Lavaron T3221C", "Lavaron T3339C", "Lavaron SJ4400N", "Lavaron SJ5400N", "Lavaron SJ6400N", "Lavaron SJ7400N", "Lavaron SJ8400N", "Lavaron SJ8400N" "SJ9400N" and "Lavalon SR04" can be mentioned. Other specific examples of the styrene block-containing thermoplastic elastomer include the trade name "Epofriend A1010" of Daicel Chemical Industries, Ltd. and the trade name "Septon HG-252" of Kuraray.

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 spin suppression in 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 intermediate layer 8 may contain a polyamide. In the golf ball 2 in which the intermediate layer 8 contains a polyamide, spin on a driver shot 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 shot feeling, 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 intermediate layer 8 may contain a filler for the purpose of adjusting the specific gravity and the like. Suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. This resin composition may contain a powder made of a high specific gravity metal 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 intermediate layer 8 is achieved. The resin composition may include a colorant, crosslinked rubber powder or synthetic resin powder. When the hue of the golf ball 2 is white, the typical colorant is titanium dioxide.

The hardness Hm of the intermediate layer 8 is preferably 55 or more. The golf ball 2 having the intermediate layer 8 having a hardness Hm of 55 or more has a small spin speed on a driver shot. The intermediate layer 8 can contribute to the flight performance of the golf ball 2. From this viewpoint, the hardness Hm is more preferably 58 or more, and particularly preferably 61 or more. 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 intermediate layer 8 is measured in accordance with the provisions of "ASTM-D 2240-68". Hardness Hm is measured by a Shore D type hardness tester attached to an automatic hardness tester (trade name "Digitest II" manufactured by H. Burleys). For the measurement, a sheet having a thickness of about 2 mm, which is made of the same material as the material of the intermediate layer 8 and is formed by heat pressing, is used. Prior to measurement, the sheet is stored at a temperature of 23 ° C. for 2 weeks. At the time of measurement, three sheets are overlapped.

The thickness Tm of the intermediate layer 8 is preferably 0.3 mm or more and 2.5 mm or less. The golf ball 2 having the intermediate layer 8 having a thickness Tm of 0.3 mm or more has a small spin speed on a driver shot. 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 intermediate 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 directly below the land 14.

The golf ball 2 may have two or more intermediate 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 for 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 control performance when hit with a short iron, a preferred base polymer is polyurethane. When polyurethane and other resins are used in combination with 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 the polyol with the polyisocyanate. In addition to the reaction for urethane bonding, a chain length extension reaction may be carried out. The chain length extension reaction can be carried out 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,
(A4) Polyurethane containing a polyisocyanate component, a high molecular weight polyol component, a low molecular weight polyol component, and a polyamine component is exemplified.

The polyol, which is the raw material for urethane bonding, 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 diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, dipropylene glycol, and 1,2-butanediol. , 1,3-Butanediol, 1,4-Butanediol, 2,3-Butanediol, 2,3-dimethyl-2,3-Butanediol, Neopentyl glycol, Pentandiol, Hexadiol, Heptanediol, Octanediol And 1,6-cyclohexanedimethylol are exemplified. Aniline-based diols or bisphenol A-based diols may be used. Specific examples of triol include glycerin, trimethylolpropane and hexanetriol. Specific examples of tetraol include pentaerythritol and sorbitol.

Polyester polyols such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG) and polytetramethylene ether glycol (PTMG) as high molecular weight polyols; polyethylene adipate (PEA), polybutylene adipate (PBA) ) And condensate polyester polyols such as polyhexamethylene adipate (PHMA); lactone-based polyester polyols such as poly-ε-caprolactone (PCL); polycarbonate polyols such as polyhexamethylene carbonate; and acrylic polyols. Two or more kinds of polyols may be used together. From the viewpoint of the shot feeling of the golf ball 2 on a driver shot, 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 urethane bonding, has two or more isocyanate groups. Examples of the polyisocyanate include aromatic polyisocyanates, alicyclic polyisocyanates and aliphatic polyisocyanates. Two or more kinds of polyisocyanates may be used in combination.

As aromatic polyisocyanates, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 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), tetramethylxylylene diisocyanate (TMXDI) and paraphenylenedi isocyanate (PPDI) Can be mentioned.

As alicyclic polyisocyanates, 4,4'-dicyclohexylmethane diisocyanate (H ₁₂ MDI), 1,3-bis (isocyanatomethyl) cyclohexane (H ₆ XDI), isophorone diisocyanate (IPDI) and trans-1,4- Cyclohexane diisocyanate (CHDI) is exemplified.

Hexamethylene diisocyanate (HDI) is exemplified as the aliphatic polyisocyanate.

From the viewpoint of scratch resistance, aromatic polyisocyanate is preferable. 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 length extension reactions have two or more amino groups. Examples of polyamines include aliphatic polyamines such as ethylenediamine, propylenediamine, butylenediamine and hexamethylenediamine; alicyclic polyamines such as isophoronediamine and piperazine; and aromatic polyamines.

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

Aromatic polyamines include monocyclic aromatic polyamines and polycyclic aromatic polyamines. In monocyclic aromatic polyamines, two or more amino groups are bonded to one aromatic ring. Polycyclic aromatic polyamines have 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 polyamines in which an amino group is directly bonded to an aromatic ring and polyamines in which an amino group is bonded to an aromatic ring via a lower alkylene group. Specific examples of monocyclic aromatic polyamines in which an amino group is directly bonded to an aromatic ring include phenylenediamine, toluenediamine, diethyltoluenediamine and dimethylthiotoluenediamine. Xylylenediamine is exemplified as a specific example of a monocyclic aromatic polyamine in which an amino group is bonded to an aromatic ring via a lower alkylene group.

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 an alkylene oxide group. Will be done. Diaminodiphenylalkane in which two aminophenyl groups are bonded via a lower alkylene group is preferable, and 4,4'-diaminodiphenylmethane and its derivatives are particularly preferable.

The cover 10 may contain thermoplastic polyurethane or may contain 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 is excellent in scratch resistance.

As specific examples of thermoplastic polyurethane, BASF Japan's product names "Elastran NY80A", "Elastran NY82A", "Elastran NY84A", "Elastran NY85A", "Elastran NY86A", "Elastran NY88A", "Elastran NY90A", "Elastran NY92A", "Elastran NY95A", "Elastran NY97A", "Elastran NY585", "Elastran KP016N" and "Elastran 1190ATR"; and products of Dainichiseika Kogyo Co., Ltd. The names "Resamine P4585LS" and "Resamine PS62490" are mentioned.

The resin composition of the cover 10 may contain an appropriate amount of a colorant, a filler, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, a fluorescent whitening agent and the like. When the hue of the golf ball 2 is white, the 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 the control performance 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 in accordance with the provisions of "ASTM-D 2240-68". Hardness Hc is measured by a Shore D type hardness tester attached to an automatic hardness tester (trade name "Digitest II" manufactured by H. Burleys). For the measurement, a sheet formed by hot pressing and made of the same material as the material of the cover 10 and having a thickness of about 2 mm is used. Prior to measurement, the sheet is stored at a temperature of 23 ° C. for 2 weeks. At the time of measurement, three sheets are overlapped.

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 spin suppression in driver shots, this 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 directly below the land 14.

A known method such as an injection molding method or a compression molding method can be adopted for forming the cover 10. When the cover 10 is molded, the dimples 12 are formed by the pimples formed on the cavity surface of the molding die.

The golf ball 2 may be provided with a reinforcing layer between the intermediate layer 8 and the cover 10. The reinforcing layer firmly adheres to the intermediate layer 8 and also firmly adheres to the cover 10. The reinforcing layer suppresses peeling of the cover 10 from the intermediate layer 8. The reinforcing layer is formed from a resin composition. Examples of the preferred base material polymer for the reinforcing layer include a two-component curable epoxy resin and a two-component curable urethane resin.

The amount of compression 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 compression deformation Sb is preferably 2.2 mm or more, and particularly preferably 2.3 mm or more. The golf ball 2 having a compression deformation amount Sb of 3.5 mm or less has a large initial velocity on a driver shot. From this viewpoint, the amount of compression deformation Sb is more preferably 3.2 mm or less, and particularly preferably 3.0 mm or less.

A YAMADA type compression tester (SCH) is used to measure the amount of compression deformation Sb. In this tester, the golf ball 2 is placed on a metal rigid plate. 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 98N is applied to the golf ball 2 to the state where the final load of 1274N 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 is more than 620 and less than 900.
Vb = Tc ・ Hc ・ Hm / Tm
In other words, the golf ball 2 satisfies the following mathematical formula (1.4).
620 <Tc ・ Hc ・ Hm / Tm <900 (1.4)
According to the knowledge obtained by the present inventor, in the golf ball 2 having a value Vb of more than 620 and less than 900, both flight performance and control performance are compatible. From this point of view, it is more preferable that the golf ball 2 satisfies the following formula.
640 <Tc ・ Hc ・ Hm / Tm <800

The above mathematical formula (1.4) can be satisfied in the golf ball 2 having the cover 10 having a small hardness Hc and a small thickness Tc.

As shown in FIGS. 2 and 3, the outline of the dimple 12 is a circle. The golf ball 2 includes a dimple A having a diameter of 4.60 mm, a dimple B having a diameter of 4.50 mm, a dimple C having a diameter of 4.35 mm, and a dimple D having a diameter of 4.00 mm. It is equipped with dimples E having a diameter of 3.00 mm. The number of types of dimple 12 is 5. The golf ball 2 may have non-circular dimples in place of or with the circular dimples 12.

The number of dimples A is 24, the number of dimples B is 12, the number of dimples C is 252, the number of dimples D is 24, and the number of dimples E is 12. The total number of dimples 12 is 324. A dimple pattern is formed by these dimples 12 and lands 14.

FIG. 4 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. 4 is the depth direction of the dimple 12. What is shown by the alternate long and short dash line 16 in FIG. 4 is a virtual sphere. The surface of the virtual sphere 16 is the surface of the golf ball 2 when the dimples 12 are assumed to be absent. The diameter of the virtual ball 16 is the same as the diameter of the golf ball 2. The dimple 12 is recessed from the surface of the virtual 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.

In FIG. 4, the arrow Dm indicates the diameter of the dimple 12. This diameter Dm is the distance between one contact Ed and the other contact Ed when a common tangent Tg is drawn on both sides of the dimple 12. The contact Ed is also the edge of the dimple 12. The edge Ed defines the contour of the dimple 12. In FIG. 4, the double-headed arrow Dp1 indicates 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. 4, the double-headed arrow Dp2 indicates the second depth of the dimple 12. This second depth Dp2 is the distance between the deepest part of the dimple 12 and the tangent 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 flight performance on a driver shot. 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 it is substantially a ball. From this viewpoint, the diameter Dm is more preferably 5.5 mm or less, and particularly preferably 5.0 mm or less.

In the case of non-circular dimples, circular dimples having the same area as the area of this non-circular dimple are virtualized. The diameter of this virtual dimple is considered the diameter of the non-circular dimple.

The ratio Pd of the diameter Dm of the dimple 12 to the diameter of the golf ball 2 is preferably 9.60% or more and 10.37% or less. Dimple 12 having this ratio of 9.60% or more contributes to turbulence. A golf ball having these dimples is excellent in flight performance on a driver shot. From this viewpoint, the ratio Pd is more preferably 9.90% or more, and particularly preferably 10.10% or more. The dimple 12 having this ratio Pd of 10.37% or less does not impair the essence of the golf ball 2 that it is substantially a ball. From this viewpoint, the ratio Pd is more preferably 10.32% or less, and particularly preferably 10.27% or less. In the golf ball 2 shown in FIGS. 2 and 3, the dimple C corresponds to "a dimple having a ratio Pd of 9.60% or more and 10.37% or less".

The ratio Rs of the number of dimples 12 having a ratio Pd of 9.60% or more and 10.37% or less to the total number of dimples 12 is preferably 50% or more. A dimple pattern having a ratio Rs of 50% or more contributes to flight performance on a driver shot. From this viewpoint, the ratio Rs is more preferably 60% or more, and particularly preferably 70% or more. The ratio Rs may be 100%. In the golf ball 2 shown in FIGS. 2 and 3, the number of dimples C is 252, and the total number is 324. Therefore, the ratio Rs is 77.8%.

The ratio of the number of dimples 12 having a ratio Pd of less than 9.60 to the total number of dimples 12 is preferably less than 50%. Dimple patterns with this ratio less than 50% contribute to turbulence. From this point of view, this ratio is more preferably 30% or less, and particularly preferably 10% or less. This ratio may be zero.

The ratio of the number of dimples 12 having a ratio Pd of more than 10.37% to the total number of dimples 12 is preferably less than 50%. In the dimple pattern in which this ratio is less than 50%, the degree of freedom in designing the dimple pattern is high, and therefore the width of the land 14 is unlikely to be excessive. From this point of view, this ratio is more preferably 30% or less, and particularly preferably 10% or less. This ratio may be zero.

The ratio Rs'of the number of dimples 12 having a ratio Pd of 10.10% or more and 10.37% or less to the total number of dimples 12 is preferably 50% or more. A dimple pattern with a ratio Rs'of 50% or more contributes to flight performance on driver shots. From this viewpoint, the ratio Rs'is more preferably 60% or more, and particularly preferably 70% or more. The ratio Rs'may be 100%. In the golf ball 2 shown in FIGS. 2 and 3, the dimple C corresponds to "a dimple having a ratio Pd of 10.10% or more and 10.37% or less". In this golf ball 2, the number of dimples C is 252, and the total number is 324. Therefore, the ratio Rs'is 77.8%.

From the viewpoint of suppressing the hops of the golf ball 2, 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 of suppressing the drop of the golf ball 2, 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 area 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 formula.
S = (Dm / 2) ²・ π

In the golf ball 2 shown in FIGS. 2 and 3, the area of the dimple A is 16.62 mm ² , the area of the dimple B is 15.90 mm ² , the area of the dimple C is 14.86 mm ² , and the dimple. The area of D is 12.57 mm ² , and the area of dimple E is 7.07 mm ² .

In the present invention, the ratio of the total area S of all the dimples 12 to the surface area of the virtual sphere 16 is referred to as the occupancy rate So. From the viewpoint of flight performance on driver shots, the occupancy rate So is preferably 81.0% or more, more preferably 82.0% or more, and particularly preferably 83.0% or more. The occupancy rate is preferably 95% or less. In the golf ball 2 shown in FIGS. 2 and 3, the total area of the dimples 12 is 4721.1 mm ² . Since the surface area of the virtual ball 16 of the golf ball 2 is 5278.0 mm ² , the occupancy rate is 82.4%.

From the viewpoint that a sufficient occupancy rate is achieved, 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 the dimples" means the volume of the portion surrounded by the surface of the virtual sphere 16 and the surface of the dimples 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 graph shown in FIG. 5, the horizontal axis is the occupancy rate So of the dimple 12. In this graph, the vertical axis is the ratio Rs of the number of dimples 12 having a ratio Pd of 9.60% or more and 10.37% or less to the total number of dimples 12. The straight line represented by the symbol L1 in this graph is represented by the following mathematical formula.
Rs = -2.5 ・ So + 273
In this graph, the golf ball 2 belonging to the zone above the straight line L1 satisfies the following mathematical formula (2.1).
Rs ≧ −2.5 ・ So + 273 (2.1)
In the golf ball 2 satisfying the above mathematical formula (2.1), turbulence is promoted. This golf ball 2 is excellent in flight performance on driver shots.

The straight line represented by the reference numeral L2 in the graph of FIG. 5 is represented by the following mathematical formula.
Rs = -2.5 ・ So + 278
In this graph, the golf ball 2 belonging to the zone above the straight line L2 satisfies the following mathematical formula (2.2).
Rs ≧ −2.5 ・ So + 278 (2.2)
In the golf ball 2 satisfying the above mathematical formula (2.2), turbulence is promoted. This golf ball 2 is excellent in flight performance on driver shots.

The straight line represented by the reference numeral L3 in the graph of FIG. 5 is represented by the following mathematical formula.
Rs = -2.5 ・ So + 283
In this graph, the golf ball 2 belonging to the zone above the straight line L3 satisfies the following mathematical formula (2.3).
Rs ≧ −2.5 ・ So + 283 (2.3)
In the golf ball 2 satisfying the above mathematical formula (2.3), turbulence is promoted. This golf ball 2 is excellent in flight performance on driver shots.

In the graph shown in FIG. 6, the horizontal axis is the occupancy rate So of the dimple 12. In this graph, the vertical axis is the ratio Rs'of the number of dimples 12 having a ratio Pd of 10.10% or more and 10.37% or less to the total number of dimples 12. The straight line represented by the symbol L4 in this graph is represented by the following mathematical formula.
Rs'= -2.2 ・ So + 245
In this graph, the golf ball 2 belonging to the zone above the straight line L4 satisfies the following mathematical formula (2.4).
Rs'≧ -2.2 ・ So + 245 (2.4)
In the golf ball 2 satisfying the above mathematical formula (2.4), turbulence is promoted. This golf ball 2 is excellent in flight performance on driver shots.

The straight line represented by the reference numeral L5 in the graph of FIG. 6 is represented by the following mathematical formula.
Rs'= -2.2 ・ So + 252
In this graph, the golf ball 2 belonging to the zone above the straight line L5 satisfies the following mathematical formula (2.5).
Rs'≧ -2.2 ・ So + 252 (2.5)
In the golf ball 2 satisfying the above formula (2.5), turbulence is promoted. This golf ball 2 is excellent in flight performance on driver shots.

As shown in FIG. 3, the surface of the golf ball 2 (or virtual sphere 16) can be partitioned into two hemispherical HEs by the equator Eq. Specifically, the surface can be partitioned into the Northern Hemisphere NH and the Southern Hemisphere SH. Each hemispherical HE has a pole P. The pole P corresponds to the deepest point of the molding for the golf ball 2.

FIG. 2 shows the Northern Hemisphere. The Southern Hemisphere has a pattern in which the dimple pattern of FIG. 2 is rotated around a pole P. Each of the line segments S1, S2 and S3 shown in FIG. 2 extends from the pole P. The angle between the line segment S1 and the line segment S2 at the pole P is 120 °. The angle between the line segment S2 and the line segment S3 at the pole P is 120 °. The angle between the line segment S3 and the line segment S1 at the pole P is 120 °.

On the surface of the golf ball 2 (or the virtual sphere 16), the zone surrounded by the line segment S1, the line segment S2, and the equator Eq is the first spherical triangle T1. On the surface of the golf ball 2 (or the virtual sphere 16), the zone surrounded by the line segment S2, the line segment S3, and the equator Eq is the second spherical triangle T2. On the surface of the golf ball 2 (or the virtual sphere 16), the zone surrounded by the line segment S3, the line segment S1 and the equator Eq is the third spherical triangle T3. Each spherical triangle is a unit. This hemispherical HE can be divided into three units.

When the dimple pattern of the first spherical triangle T1 is rotated by 120 ° about the straight line connecting the two poles P, it substantially overlaps with the dimple pattern of the second spherical triangle T2. When the dimple pattern of the second spherical triangle T2 is rotated by 120 ° about the straight line connecting the two poles P, it substantially overlaps with the dimple pattern of the third spherical triangle T3. When the dimple pattern of the third spherical triangle T3 is rotated by 120 ° about the straight line connecting the two poles P, it substantially overlaps with the dimple pattern of the first spherical triangle T1. In other words, the hemispherical dimple pattern consists of three units that are rotationally symmetric with each other.

The pattern in which the dimple pattern of the hemispherical HE is rotated by 120 ° about the straight line connecting the two poles P substantially overlaps with the dimple pattern before the rotation. The dimple pattern of the hemispherical HE is 120 ° rotationally symmetric.

The line segment S4 shown in FIG. 2 extends from the pole P. The angle between the line segment S4 and the line segment S1 at the pole P is 60 °. The angle between the line segment S4 and the line segment S2 at the pole P is 60 °. By the line segment S4, the first spherical triangle T1 (unit) can be partitioned into a small spherical triangle T1a and a small spherical triangle T1b. The spherical triangle T1a and the spherical triangle T1b are small units.

The pattern in which the dimple pattern of the spherical triangle T1a is inverted with respect to the plane including the straight line connecting the two poles P and the line segment S4 substantially overlaps with the dimple pattern of the spherical triangle T1b. In other words, the dimple pattern of the spherical triangle T1a (unit) consists of two small units that are mirror-symmetrical to each other.

Similarly, the dimple pattern of the second spherical triangle T2 consists of two small units that are mirror-symmetrical to each other. The dimple pattern of the third spherical triangle T3 also consists of two small units that are mirror-symmetrical to each other. This hemispherical HE dimple pattern consists of 6 small units.

According to the findings obtained by the present inventor, the golf ball 2 consists of three units in which the dimple patterns of the hemisphere are rotationally symmetric with each other by 120 °, and the dimple patterns of each unit consist of two small units with mirror symmetry with each other. Then, turbulence is promoted. This golf ball 2 is excellent in flight performance on driver shots.

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

[Example 1]
100 parts by mass of high cis polybutadiene (trade name "BR-730" of JSR Corporation), 26.0 parts by mass of zinc acrylate, 5 parts by mass of zinc oxide, appropriate amount of barium sulfate, 0.5 parts by mass of diphenyl disulfide And 0.7 parts by mass of dicumyl peroxide was kneaded to obtain a rubber composition (b). The rubber composition (b) was put into a mold composed of an upper mold and a lower mold both 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 sulfate was adjusted so that a predetermined ball mass was obtained.

100 parts by mass of high-cis polybutadiene (trade name "BR-730" of JSR), 41.5 parts by mass of zinc acrylate, 5 parts by mass of zinc oxide, 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 from 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 consisting of an upper mold and a lower mold both having a hemispherical cavity, and a core composed of an inner core and an outer core is formed in the first cross-linking step and the second cross-linking step. did. In the first cross-linking step, the cross-linking temperature was 140 ° C. and the cross-linking time was 20 minutes. In the second cross-linking step, the cross-linking temperature was 160 ° C. and the cross-linking time was 10 minutes. The diameter of the core was 38.5 mm.

50 parts by mass of ionomer resin (the above-mentioned "Sarrin 8150"), 50 parts by mass of another ionomer resin (the above-mentioned "Himilan AM7329") and 4 parts by mass of titanium dioxide are kneaded with a twin-screw kneading extruder to form a resin composition. I got the thing (M2). 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 (trade name "Porin 750LE" of Shinto Paint Co., Ltd.) using a two-component curable epoxy resin as a base polymer was prepared. The main component solution of this coating composition is 30 parts by mass of bisphenol A type epoxy resin. And 70 parts by mass of the solvent. The curing agent solution of this coating composition contains 40 parts by mass of the modified polyamide amine, 55 parts by mass of the solvent, and 5 parts by mass of titanium dioxide. The mass ratio with the curing agent solution is 1/1. This coating composition was applied to the surface of the intermediate layer with a spray gun and held at 23 ° C. for 12 hours to obtain a reinforcing layer. The thickness of the reinforcing layer was 10 μm.

100 parts by mass of thermoplastic polyurethane elastomer (“Elastolan NY84A” mentioned above), 0.2 parts by mass of light stabilizer (trade name “Chinubin 770”), 4 parts by mass of titanium dioxide and 0.04 parts by mass of ultra Marine blue was kneaded with a twin-screw kneading extruder to obtain a resin composition (C2). From this resin composition (C2), a half shell was obtained 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 put into a final mold consisting of 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 thickness of the cover was 0.5 mm. Dimples having an inverted shape of the pimples were formed on the cover.

A clear paint based on a two-component curable polyurethane was applied around the cover to obtain a golf ball of Example 1 having a diameter of about 42.7 mm and a mass of about 45.6 g.

[Example 2-8 and Comparative Example 1-6]
Golf in Examples 2-8 and Comparative Examples 1-6 in the same manner as in Example 1 except that the specifications of the inner core, outer core, intermediate layer, cover and dimples are as shown in Table 7-9 below. I got the ball. Details of the specifications of the inner core and outer core are shown in Tables 1 and 2 below. Details of the specifications of the mesosphere 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.

[Flight test]
A driver (Dunlop Sports' product name "Z745", shaft hardness: S, loft angle: 8.5 °) was attached to the swing machine of Golf Laboratory. The golf ball was hit under the condition that the head speed was 50 m / sec, and the initial speed, spin speed, 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 value of the data obtained in the 12 measurements is shown in Table 7-9 below.

As shown in Table 7-9, the golf balls of each embodiment 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 playing on a golf course, practicing in a driving range, and the like.

2 ... Golf ball 4 ... Inner core 6 ... Outer core 8 ... Middle layer 10 ... Cover 12 ... Dimple 14 ... Land 16 ... Virtual ball Eq ... Equator NH ... Northern Hemisphere SH ... Southern Hemisphere P ... Paul

Claims (8)

A golf ball having 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 between the hardness H1in and the hardness H1o in the inner core De1;
The volume V2 (mm ³ ) in the outer core, and the difference between the surface hardness H2s (shore C) and the out-of-boundary hardness H2out (shore C) De2;
Thickness Tm (mm) and hardness Hm (Shore D) in the mesosphere;
And the thickness Tc (mm) and hardness Hc (shore D) of the cover.
However, the following mathematical formulas (1.1)-(1.4) are satisfied.
1.0 <V2 / V1 <7.0 (1.1)
De2-De1 <0 (1.2)
600 <(H1o + H1in) ・ (D1 / 2) / 2 <1000 (1.3)
620 <Tc ・ Hc ・ Hm / Tm <900 (1.4)
It has multiple dimples on its surface
The ratio So of the total area of the dimples to the surface area of the virtual ball of the golf ball is 81.0% or more.
The diameter of the dimple where the diameter of a circular dimple having the same area as that of the non-circular dimples case when a circular dimples are non-circular dimples have a diameter of this circle, the diameter of the golf ball 9 The ratio Rs of the number of dimples of .60% or more and 10.37% or less to the total number of dimples is 50% or more.
The ratio Rs'of the number of dimples having a dimple diameter of 10.10% or more and 10.37% or less of the diameter of the golf ball to the total number of dimples is 50% or more.
The hemispherical dimple pattern of the golf ball consists of three units that are rotationally symmetric with each other.
The dimple pattern of each unit consists of two small units that are mirror-symmetrical to each other.
A golf ball that satisfies the following formulas (2.1) and (2.5) .
Rs ≧ −2.5 ・ So + 273 (2.1)
Rs'≧ -2.2 ・ So + 252 (2.5) 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 or 2, which satisfies the following formula.
700 <(H1o + H1in) ・ (D1 / 2) / 2 <900 The golf ball according to any one of claims 1 to 3, which satisfies the following formula.
640 <Tc ・ Hc ・ Hm / Tm <800 The golf ball according to any one of claims 1 to 4, which satisfies the following mathematical formula (2.2).
Rs ≧ −2.5 ・ So + 278 (2.2) The golf ball according to claim 5, which satisfies the following mathematical formula (2.3).
Rs ≧ −2.5 ・ So + 283 (2.3) The golf ball according to any one of claims 1 to 6 , wherein the deepest part of each dimple has a depth of 0.10 mm or more and 0.65 mm or less from the surface of the virtual sphere. The golf ball according to any one of claims 1 to 7 , wherein the total volume of the dimples is 450 mm ³ or more and 750 mm ³ or less.

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