JP6448455B2 - Golf ball - Google Patents

Description

  The present invention relates to a golf ball.

  A golfer's greatest demand for a golf ball is flight performance. In order to achieve a large flight distance, an appropriate ballistic height is required. The ballistic height depends on the spin speed and launch angle. A golf ball that achieves a high trajectory with a high spin rate has insufficient flight distance. A golf ball that achieves a high trajectory with a large launch angle can provide a large flight distance. By adopting an outer-hard / inner-soft core, a small spin speed and a large launch angle are achieved.

  From the viewpoint of achieving these various performances, various combinations of hardness distributions of the multi-layer core have been studied. For example, in Patent Documents 1 to 4, a solid core is covered with one or more covers, and the solid core is a spherical first layer, a second layer covering the first layer, and the A third layer covering the second layer, wherein the first layer has a diameter of 3 to 24 mm, and the third layer is formed of a rubber composition mainly composed of polybutadiene rubber; The cross-sectional hardness of the core center when the solid core is cut in half, the first layer 1 mm inside from the boundary surface between the first layer and the second layer, the second layer 1 mm outside from the boundary surface, the second layer A multi-piece solid golf ball is described in which the relationship between the hardness of the second layer 1 mm inside the boundary surface between the layer and the third layer, the third layer 1 mm outside the boundary surface and the surface of the third layer is specified. (Patent Document 1 (paragraph 0007), Patent Document 2 (paragraph 007), Patent Document 3 (paragraph 0007) Patent Document 4 (paragraph 0007)).

JP 2012-223569 A JP 2012-223570 A JP 2012-223571 A JP2012-223572A

  The demand for golfers' flight performance has been escalating in recent years, and further improvement in flight distance is expected. In addition, golfers desire a great flight distance even in a shot with a middle iron, and a technique for improving that point is not sufficient. The present invention has been made in view of the above circumstances, and an object thereof is to provide a golf ball having a large flight distance on a middle iron shot.

The golf ball of the present invention that has solved the above problems has a spherical core, an intermediate layer disposed outside the spherical core, and a cover disposed outside the intermediate layer, and the spherical ball The core has an inner layer and an outer layer, the hardness (H _{x + 1} ) at a point 1 mm outside in the radial direction from the boundary between the inner layer and the outer layer of the spherical core, and the radial direction from the boundary between the inner layer and the outer layer of the spherical core The difference (H _{x + 1} -H _x-1 ) from the hardness (H _x-1 ) of the point 1 mm inside is 0 or more in Shore C hardness, and the surface hardness (H _{X + Y} ) of the spherical core is Shore C The hardness α is greater than 65, the angle α of the inner layer hardness gradient calculated by the equation (1) is 0 ° or more, the angle α and the angle β of the outer layer hardness gradient calculated by the equation (2), Difference (α−β) is 0 ° or more, and among the components of the golf ball, Wherein the bar is the most high hardness.
α = (180 / π) × atan [{H _x−1 −Ho} / (X−1)] (1)
β = (180 / π) × atan [{H _{X + Y} −H _{x + 1} } / (Y−1)] (2)
[Wherein, X is the radius of the inner layer (mm), Y is the thickness of the outer layer (mm), Ho is the central hardness of the spherical core (Shore C), H _x-1 is the radius from the boundary between the inner and outer layers of the spherical core The hardness at the point 1 mm inside in the direction (Shore C), H _{x + 1} is the hardness at the point 1 mm outside from the boundary between the inner and outer layers of the spherical core (Shore C), and H _{X + Y} is the surface hardness of the spherical core (Shore C) ). ]

  In the golf ball of the present invention, the relationship between the hardness gradient of the inner layer of the spherical core and the hardness gradient of the outer layer, the relationship between the inner layer hardness and the outer layer hardness in the vicinity of the boundary between the inner layer and the outer layer of the spherical core, and the hardness of the cover are appropriate. It has become. Therefore, the golf ball of the present invention has a high initial ball speed during a middle iron shot, and excessive spin is suppressed. Therefore, the golf ball of the present invention increases the flight distance on the middle iron shot.

The difference (Hm−H _{X + Y} ) between the hardness (Hm) of the intermediate layer and the surface hardness (H _{X + Y} ) of the spherical core is preferably more than 1 in Shore C hardness. If the hardness difference (Hm−H _{X + Y} ) is greater than 1, an excessive spin amount during middle iron shot is suppressed, and the initial ball speed is further improved.

  The total thickness of the intermediate layer (Tm) and the cover (Tc) is preferably 3 mm or less. When the total thickness (Tc + Tm) is 3 mm or less, the feel at impact of the golf ball is further improved.

  The golf ball of the present invention has a large middle iron shot flight distance.

It is a figure which shows an example of the hardness distribution of a spherical core. It is a figure which shows another example of the hardness distribution of a spherical core. It is a figure which shows another example of the hardness distribution of a spherical core. It is a figure which shows another example of the hardness distribution of a spherical core. It is a figure which shows another example of the hardness distribution of a spherical core. 1 is a partially cutaway sectional view showing a golf ball according to an embodiment of the present invention.

The golf ball of the present invention has a spherical core, an intermediate layer arranged outside the spherical core, and a cover arranged outside the intermediate layer, and the spherical core has an inner layer and an outer layer. The hardness (H _{x + 1} ) at a point 1 mm outside in the radial direction from the boundary between the inner layer and the outer layer of the spherical core, and the hardness (H at a point 1 mm inward in the radial direction from the boundary between the inner layer and the outer layer of the spherical core. _x-1 ) (H _{x + 1} -H _x-1 ) is 0 or more in Shore C hardness, the surface hardness (H _{X + Y} ) of the spherical core is more than 65 in Shore C hardness, and the formula ( The angle α of the hardness gradient of the inner layer calculated by 1) is 0 ° or more, and the difference (α−β) between the angle α and the angle β of the hardness gradient of the outer layer calculated by the equation (2) is 0. The cover must have the highest hardness among the components of the golf ball. And butterflies.
α = (180 / π) × atan [{H _x−1 −Ho} / (X−1)] (1)
β = (180 / π) × atan [{H _{X + Y} −H _{x + 1} } / (Y−1)] (2)
[Wherein, X is the radius of the inner layer (mm), Y is the thickness of the outer layer (mm), Ho is the central hardness of the spherical core (Shore C), H _x-1 is the radius from the boundary between the inner and outer layers of the spherical core The hardness at the point 1 mm inside in the direction (Shore C), H _{x + 1} is the hardness at the point 1 mm outside from the boundary between the inner and outer layers of the spherical core (Shore C), and H _{X + Y} is the surface hardness of the spherical core (Shore C) ). ]

  With the above configuration, it is possible to increase the initial ball speed while suppressing excessive spin during the middle iron shot.

[Construction]
[Spherical core]
The spherical core has a two-layer structure including an inner layer and an outer layer. The spherical core is preferably formed from a rubber composition.

(Hardness Ho)
The center hardness Ho is a hardness (Shore C) measured at the center of the cut surface by cutting the spherical core into a hemisphere. The hardness Ho is preferably 48 or more, more preferably 49 or more, still more preferably 50 or more, and is preferably less than 65, more preferably 64 or less, and still more preferably 63 or less. When the hardness Ho is 48 or more, the resilience performance is further improved, and when the hardness Ho is less than 65, an excessive spin amount is suppressed at the middle iron shot.

(Hardness H _X-1 )
The hardness H _X-1 is a hardness (Shore C) measured at a point 1 mm inside in the radial direction from the boundary between the inner layer and the outer layer by cutting the spherical core into a hemispherical shape. That is, H _X-1 is the hardness measured at a point where the distance from the center is X-1 (mm). The hardness H _X-1 is preferably 63 or more, more preferably 65 or more, still more preferably 67 or more, and is preferably 82 or less, more preferably 80 or less, and still more preferably 78 or less. When the hardness H _X-1 is 63 or more, the resilience performance is improved, and when the hardness H _X-1 is 82 or less, an excessive spin amount is suppressed during the middle iron shot.

(Hardness H _{X + 1} )
The hardness H _{X + 1} is a hardness (Shore C) measured at a point 1 mm outside in the radial direction from the boundary between the inner layer and the outer layer by cutting the spherical core into a hemispherical shape. That is, the H _{X + 1} is a hardness measured at a point where the distance from the center is X + 1 (mm). The hardness H _{X + 1} is preferably 70 or more, more preferably 73 or more, further preferably 75 or more, preferably 90 or less, more preferably 88 or less, and still more preferably 86 or less. If the hardness H _{X + 1} is 70 or more, the resilience performance is improved, and if it is 90 or less, the feeling is good.

(Hardness H _{X + Y} )
The hardness H _{X + Y} is a hardness (Shore C) measured at the surface portion of the spherical core (outer layer core). The hardness H _{X + Y} is preferably 70 or more, more preferably 73 or more, still more preferably 75 or more, preferably 90 or less, more preferably 88 or less, and still more preferably 86 or less. If the hardness H _{X + Y} is 70 or more, the resilience performance is improved, and if it is 90 or less, the feeling is good.

(Hardness difference (H _X-1 -Ho))
The hardness difference between the central hardness Ho and the hardness H _X-1 (H _X-1 -Ho), that is, the hardness difference between the central hardness of the inner layer and the hardness near the boundary surface is preferably 4 or more, more preferably 5 or more. More preferably, it is 6 or more, preferably 27 or less, more preferably 26 or less, still more preferably 25 or less. If the hardness difference (H _X-1 -Ho) is 4 or more, an excessive spin amount is suppressed at the middle iron shot, and if it is 27 or less, the resilience performance is improved.

(Hardness difference (H _{X + 1} -H _X-1 ))
The hardness difference between the hardness H _X-1 and the hardness H _{X + 1} (H _{X + 1} -H _X-1 ), that is, the hardness difference between the inner layer hardness and the outer layer hardness in the vicinity of the boundary surface between the inner layer and the outer layer is preferably 0 or more. More preferably, it is 5 or more, More preferably, it is 7 or more, Most preferably, it is 8 or more, 20 or less is preferable, More preferably, it is 18 or less, More preferably, it is 16 or less. If the hardness difference (H _{X + 1} -H _X-1 ) is 0 or more, an excessive spin amount is suppressed at the middle iron shot, and if it is 20 or less, durability is improved.

(Hardness difference (H _{X + Y} −H _{X + 1} ))
The hardness difference between the surface hardness H _{X + 1} and the hardness H _{X + Y} (H _{X + Y} −H _{X + 1} ), that is, the hardness difference between the hardness near the boundary surface of the outer layer and the surface hardness is preferably −7 or more, more preferably −6 or more. More preferably, it is −5 or more, preferably 10 or less, more preferably 7 or less, still more preferably 5 or less. If the hardness difference (H _{X + Y} −H _{X + 1} ) is −7 or more, an excessive spin amount is suppressed at the middle iron shot, and if it is 10 or less, the resilience performance is improved.

(Hardness difference (H _{X + Y} -Ho))
The hardness difference between the central hardness Ho and the surface hardness H _{X + Y} (H _{X + Y} −Ho), that is, the hardness difference between the central hardness and the surface hardness of the spherical core is preferably 14 or more, more preferably 16 or more, and still more preferably. 18 or more, preferably 35 or less, more preferably 33 or less, and still more preferably 30 or less. If the hardness difference (H _{X + Y} −Ho) is 14 or more, the excessive spin amount during middle iron shot is suppressed, and if it is 35 or less, the durability is improved.

(Angle α)
The angle α is calculated by the equation (1). The angle α (°) represents the hardness gradient of the inner layer. The angle α is preferably 0 or more, more preferably 15 or more, still more preferably 20 or more, and is preferably 75 or less, more preferably 73 or less, and even more preferably 70 or less. If the angle α is equal to or greater than 0, an excessive spin amount is suppressed at the middle iron shot, and if it is equal to or smaller than 75, the resilience performance is improved.

(Angle β)
The angle β is calculated by equation (2). The angle β (°) represents the hardness gradient of the outer layer. The angle β is preferably −20 or more, more preferably −19 or more, further preferably −18 or more, preferably +20 or less, more preferably +19 or less, and still more preferably +18 or less. If the angle β is −20 or more, the excessive spin amount is suppressed during the middle iron shot, and if it is +20 or less, the resilience performance is improved.

(Angle difference (α-β))
The difference (α−β) between the angle α and the angle β is 0 or more. An example of an aspect in which the difference (α−β) is 0 or more is shown in FIGS. 1-5 is a figure which shows an example of the hardness distribution of a spherical core. As an aspect in which the difference (α−β) is 0 or more, the angle α and the angle β are positive, and the angle β is not more than the angle α (FIG. 1); the angle α is positive, and Embodiment in which angle β is 0 (FIG. 2); Embodiment in which angle α is positive and angle β is negative (FIG. 3); Embodiment in which both angle α and angle β are 0 (FIG. 4); An embodiment in which the angle α is 0 and the angle β is negative (FIG. 5) can be mentioned. With this configuration, it is possible to increase the initial ball speed while suppressing excessive spin during the middle iron shot.

  The difference (α−β) is preferably 5 or more, more preferably 10 or more, preferably 85 or less, more preferably 80 or less, and still more preferably 75 or less. If the difference (α−β) is 85 or less, the resilience performance is improved.

(Inner layer radius X)
The radius X is the radius (mm) of the inner layer of the core. The radius X is preferably 7 mm or more, more preferably 9 mm or more, further preferably 10 mm or more, preferably 16 mm or less, more preferably 15 mm or less, and further preferably 14 mm or less. If the radius X is 7 mm or more, excessive spin at the middle iron shot is suppressed, and if it is 16 mm or less, the resilience performance is improved.

(Outer layer thickness Y)
The thickness Y is the thickness (mm) of the outer layer of the core. The thickness Y is preferably 3 mm or more, more preferably 4 mm or more, further preferably 5 mm or more, preferably 12 mm or less, more preferably 11 mm or less, and further preferably 10 mm or less. When the thickness Y is 3 mm or more, the resilience performance is improved, and when the thickness Y is 12 mm or less, an excessive amount of spin is suppressed during the middle iron shot.

(Ratio (Y / X))
The ratio (Y / X) of the radius X to the thickness Y is preferably 0.2 or more, more preferably 0.3 or more, still more preferably 0.4 or more, and preferably 2.0 or less, more Preferably it is 1.7 or less, More preferably, it is 1.5 or less. When the ratio (Y / X) is 0.2 or more, the resilience performance is improved. When the ratio (Y / X) is 2.0 or less, the excessive spin amount is suppressed during the middle iron shot.

  The diameter of the spherical core is preferably 36.5 mm or more, more preferably 37.0 mm or more, further preferably 37.5 mm or more, preferably 42.0 mm or less, more preferably 41.0 mm or less, still more preferably. 40.2 mm or less. If the diameter of the spherical core is 36.5 mm or more, the spherical core is large and the resilience performance of the golf ball is further improved.

  When the spherical core has a diameter of 36.5 mm to 42.0 mm, the amount of compressive deformation (the amount by which the center contracts in the compression direction) from when the initial load 98 N is applied to when the final load 1275 N is applied is 2.0 mm. The above is preferable, More preferably, it is 2.5 mm or more, 4.8 mm or less is preferable, More preferably, it is 4.5 mm or less. If the amount of compressive deformation is 2.0 mm or more, the feel at impact is better, and if it is 4.8 mm or less, the resilience is better.

[Middle layer]
The golf ball has an intermediate layer disposed outside the spherical core. The intermediate layer may be a single layer or two or more layers. The intermediate layer is preferably formed from a resin composition.

  The intermediate layer has a hardness Hm (Shore C) of preferably 75 or more, more preferably 77 or more, still more preferably 79 or more, preferably 98 or less, more preferably 96 or less, and still more preferably 90 or less. If the hardness of the intermediate layer is 75 or more, the initial ball speed at the middle iron shot is improved, and the spin rate is reduced. If the hardness is 98 or less, the feel at impact is improved. The hardness of the intermediate layer is the slab hardness of the material forming the intermediate layer.

The hardness difference (Hm−H _{X + Y} ) between the hardness Hm of the intermediate layer and the surface hardness H _{X + Y} of the spherical core is preferably more than 1, more preferably 5 or more, preferably 35 or less, more preferably 30 or less. More preferably, it is 25 or less. If the hardness difference (Hm−H _{X + Y} ) is more than 1, an excessive spin amount during middle iron shot is suppressed, and the initial ball speed is improved. If the hardness difference (Hm−H _{X + Y} ) is 35 or less, the difference between the surface hardness of the spherical core and the intermediate layer hardness will not be too large, and the shot feeling will be good. When the intermediate layer is a multilayer, the hardness difference (Hm−H _{X + Y} ) refers to the difference in hardness between the hardness of the intermediate layer disposed on the innermost side and the surface hardness of the spherical core.

  The thickness Tm of the intermediate layer is preferably 0.5 mm or more, more preferably 0.6 mm or more, further preferably 0.7 mm or more, preferably 2.0 mm or less, more preferably 1.9 mm or less, Preferably it is 1.8 mm or less. If the thickness of the intermediate layer is 0.5 mm or more, the durability is good, and if it is 2.0 mm or less, the resilience performance is improved. In addition, what is necessary is just to adjust total thickness, when an intermediate | middle layer is a multilayer.

〔cover〕
The golf ball has a cover disposed outside the intermediate layer. The cover constitutes the outermost layer of the golf ball main body and is formed from a resin composition.

The cover of the golf ball has the highest hardness among the constituent members. That is, the central hardness Ho of the spherical core, the hardness H _{x + 1} at a point 1 mm outside in the radial direction from the boundary between the inner layer and the outer layer of the spherical core, and the hardness at a point 1 mm inside in the radial direction from the boundary between the inner layer and the outer layer of the spherical core The cover hardness Hc is the highest among the H _x-1 , the spherical core surface hardness H _{X + Y} , the intermediate layer hardness Hm, and the cover hardness Hc. By setting the cover hardness Hc to the highest hardness, excessive spin can be suppressed in the middle iron shot, and the flight distance is further improved.

  The cover has a hardness Hc (Shore C) of preferably 75 or more, more preferably 77 or more, still more preferably 79 or more, preferably 98 or less, and more preferably 96 or less. If the cover has a hardness of 75 or more, the ball initial speed at the middle iron shot is improved and the spin rate is reduced. If the cover has a hardness of 98 or less, the feel at impact is improved. The hardness of the cover is the slab hardness of the material forming the cover.

  The hardness difference (Hc−Hm) between the hardness Hc of the cover and the hardness Hm of the intermediate layer is preferably 4 or more, more preferably 5 or more, still more preferably 6 or more, and preferably 10 or less, more preferably 9 Hereinafter, it is more preferably 8 or less. If the hardness difference (Hc−Hm) is 4 or more, the spin rate during the middle iron shot is further reduced. Moreover, if the hardness difference (Hc−Hm) is 10 or less, the shot feeling becomes better. When the intermediate layer is a multilayer, the hardness difference (Hc−Hm) refers to the difference in hardness between the hardness of the innermost layer arranged on the inner side and the hardness of the cover.

The hardness difference (Hc−H _{X + Y} ) between the hardness Hc of the cover and the surface hardness H _{X + Y} of the spherical core is preferably 10 or more, more preferably 11 or more, still more preferably 12 or more, and preferably 16 or less. More preferably, it is 15 or less, More preferably, it is 14 or less. If the hardness difference (Hc−H _{X + Y} ) is 10 or more, the spin amount at the middle iron shot is further reduced. Moreover, if the hardness difference (Hc−H _{X + Y} ) is 16 or less, the shot feeling becomes better.

  The thickness Tc of the cover is preferably 0.5 mm or more, more preferably 0.6 mm or more, further preferably 0.7 mm or more, preferably 2.5 mm or less, more preferably 2.4 mm or less, and further preferably. Is 2.3 mm or less. If the cover thickness is 0.5 mm or more, the cover can be easily molded, and the cracking durability of the cover is improved. If the cover thickness is 2.5 mm or less, the feel at impact is improved.

  The total thickness (Tc + Tm) of the cover thickness Tc and the intermediate layer thickness Tm is preferably 3 mm or less, more preferably 2.9 mm or less, and even more preferably 2.8 mm or less. When the total thickness (Tc + Tm) is 3 mm or less, the feel at impact of the golf ball is further improved.

  The ratio (Tc / Tm) of the cover thickness Tc to the intermediate layer thickness Tm is preferably 1.00 or more, more preferably 1.05 or more, and even more preferably 1.10 or more. 00 or less is preferable, more preferably 4.90 or less, and still more preferably 4.80 or less. If the ratio (Tc / Tm) is 1.00 or more, the ball initial speed at the middle iron shot is improved and the spin amount is reduced. If the ratio (Tc / Tm) is 5.0 or less, the feel at impact is improved.

(Reinforcement layer)
The golf ball may have a reinforcing layer between the intermediate layer and the cover. By having the reinforcing layer, the adhesion between the intermediate layer and the cover is improved, and the durability of the golf ball is improved. The thickness of the reinforcing layer is preferably 3 μm or more, more preferably 5 μm or more, 100 μm or less, preferably 50 μm or less, and more preferably 20 μm or less.

  The golf ball preferably has a diameter of 40 mm to 45 mm. The diameter is particularly preferably equal to or greater than 42.67 mm from the viewpoint that US Golf Association (USGA) standards are satisfied. In light of suppression of air resistance, the diameter is more preferably equal to or less than 44 mm, and particularly preferably equal to or less than 42.80 mm. The mass of the golf ball is preferably 40 g or more and 50 g or less. In light of attainment of great inertia, the mass is more preferably equal to or greater than 44 g, and particularly preferably equal to or greater than 45.00 g. In light of satisfying the USGA standard, the mass is particularly preferably equal to or less than 45.93 g.

  When the golf ball has a diameter of 40 mm to 45 mm, the amount of compressive deformation (the amount by which the golf ball shrinks in the compression direction) when a final load of 1275 N is applied from a state in which an initial load of 98 N is applied is 1.5 mm or more. More preferably, it is 1.6 mm or more, More preferably, it is 1.7 mm or more, Most preferably, it is 1.8 mm or more, It is preferable that it is 3.0 mm or less, More preferably, it is 2.9 mm or less It is. A golf ball having a compression deformation amount of 1.5 mm or more does not become too hard and has a good shot feeling. On the other hand, when the amount of compressive deformation is 3.0 mm or less, the resilience is increased.

  The golf ball of the present invention includes, for example, a two-layer spherical core, a single-layer intermediate layer disposed so as to cover the spherical core, and a cover disposed so as to cover the intermediate layer. A four-piece golf ball having a two-layer spherical core, a two-layer intermediate layer arranged to cover the spherical core, and a cover arranged to cover the intermediate layer Golf ball; 6-piece or more golf having a spherical core having a two-layer structure, three or more intermediate layers arranged to cover the spherical core, and a cover arranged to cover the intermediate layer Ball; and the like. The present invention can be suitably used for golf balls having any of the above structures.

  FIG. 6 is a partially cutaway cross-sectional view showing a golf ball 1 according to an embodiment of the present invention. The golf ball 1 has a spherical core 2, an intermediate layer 3 located outside the spherical core 2, and a cover 4 located outside the intermediate layer 3. The spherical core 2 has an inner layer 21 and an outer layer 22 located outside the inner layer 21. A large number of dimples 41 are formed on the surface of the cover 4. Of the surface of the cover 4, a portion other than the dimples 41 is a land 42.

[material]
Conventionally known materials can be used for the core, intermediate layer, and cover of the golf ball.

  A known rubber composition (hereinafter sometimes simply referred to as “core rubber composition”) may be used for the core. For example, a rubber composition containing a base rubber, a co-crosslinking agent, and a crosslinking initiator. Can be formed by hot pressing.

  As the base rubber, it is particularly preferable to use a high-cis polybutadiene having a cis bond advantageous for rebound of 40% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more. The co-crosslinking agent is preferably an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metal salt thereof, more preferably a metal salt of acrylic acid or a metal salt of methacrylic acid. As the metal of the metal salt, zinc, magnesium, calcium, aluminum, and sodium are preferable, and zinc is more preferable. The amount of the co-crosslinking agent used is preferably 20 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the base rubber. When an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms is used as the co-crosslinking agent, it is preferable to add a metal compound (for example, magnesium oxide). As the crosslinking initiator, an organic peroxide is preferably used. Specifically, dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t-butylperoxy) Organic peroxides such as hexane and di-t-butyl peroxide can be mentioned, and among them, dicumyl peroxide is preferably used. The amount of the crosslinking initiator is preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, and preferably 3 parts by mass or less, more preferably 100 parts by mass of the base rubber. 2 parts by mass or less.

  The rubber composition for a core may further contain an organic sulfur compound. As the organic sulfur compound, diphenyl disulfides (for example, diphenyl disulfide, bis (pentabromophenyl) persulfide), thiophenols, and thionaphthols (for example, 2-thionaphthol) can be preferably used. The compounding amount of the organic sulfur compound is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and preferably 5.0 parts by mass or less with respect to 100 parts by mass of the base rubber. Preferably it is 3.0 mass parts or less. The core rubber composition may further contain a carboxylic acid and / or a salt thereof. The carboxylic acid and / or salt thereof is preferably a carboxylic acid having 1 to 30 carbon atoms and / or a salt thereof. As said carboxylic acid, both aliphatic carboxylic acid and aromatic carboxylic acid (benzoic acid etc.) can be used. The compounding quantity of carboxylic acid and / or its salt is 1 to 40 mass parts with respect to 100 mass parts of base rubber.

  The intermediate layer and the cover are molded from a resin composition. The resin composition contains a thermoplastic resin as a resin component. Examples of the thermoplastic resin include ionomer resins, thermoplastic olefin copolymers, thermoplastic polyamides, thermoplastic polyurethanes, thermoplastic styrene resins, thermoplastic polyesters, thermoplastic acrylic resins, thermoplastic polyolefins, thermoplastic polydienes, A thermoplastic resin such as a thermoplastic polyether may be mentioned. Among the thermoplastic resins, a thermoplastic elastomer having rubber elasticity is preferable. Examples of the thermoplastic elastomer include thermoplastic polyurethane elastomers, thermoplastic polyamide elastomers, thermoplastic styrenic elastomers, thermoplastic polyester elastomers, and thermoplastic acrylic elastomers.

(Ionomer resin)
As the ionomer resin, an ionomer resin (hereinafter referred to as “binary ionomer resin”) comprising a neutralized product of a binary copolymer of an olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms. ); A metal ion neutralized product of a terpolymer of an olefin, an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α, β-unsaturated carboxylic acid ester ( Hereinafter, an ionomer resin composed of a “ternary ionomer resin” may be used; or a mixture thereof.

  As said olefin, a C2-C8 olefin is preferable, For example, ethylene, propylene, butene, pentene, hexene, heptene, octene etc. are mentioned, Ethylene is preferable. Examples of the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid, and acrylic acid or methacrylic acid is preferable.

  The α, β-unsaturated carboxylic acid ester is preferably an alkyl ester of 3 to 8 carbon atoms, α, β-unsaturated carboxylic acid, more preferably an alkyl ester of acrylic acid, methacrylic acid, fumaric acid or maleic acid. In particular, acrylic acid alkyl esters or methacrylic acid alkyl esters are preferred. Examples of the alkyl group constituting the ester include methyl, ethyl, propyl, n-butyl, and isobutyl ester.

  The binary ionomer resin is preferably a metal ion neutralized product of an ethylene- (meth) acrylic acid binary copolymer. The ternary ionomer resin is preferably a metal ion neutralized product of a ternary copolymer of ethylene, (meth) acrylic acid, and (meth) acrylic acid ester. Here, (meth) acrylic acid means acrylic acid and / or methacrylic acid.

Examples of metal ions that neutralize at least part of the carboxyl groups of the binary ionomer resin and / or ternary ionomer resin include monovalent metal ions such as sodium, potassium, and lithium; magnesium, calcium, and zinc , Divalent metal ions such as barium and cadmium; trivalent metal ions such as aluminum; and other ions such as tin and zirconium. The binary ionomer resin and the ternary ionomer resin are neutralized with at least one metal ion selected from the group consisting of Na ⁺ , Mg ²⁺ , Ca ²⁺ , and Zn ^2+. preferable.

  Examples of the binary ionomer resin include Himiran (registered trademark) 1555 (Na), 1557 (Zn), 1605 (Na), 1706 (Zn), 1707 (Na), AM7311 (Mg), AM7329 (Zn), and AM7337. (Mitsui DuPont Polychemical Co., Ltd.); Surlyn (registered trademark) 8945 (Na), 9945 (Zn), 8140 (Na), 8150 (Na), 9120 (Zn), 9150 (Zn), 6910 (Mg) 6120 (Mg), 7930 (Li), 7940 (Li), AD8546 (Li) (manufactured by DuPont); Iotech (registered trademark) 8000 (Na), 8030 (Na), 7010 (Zn), 7030 (Zn) (ExxonMobil Chemical Co., Ltd.).

  Examples of the ternary ionomer resins include Himiran AM7327 (Zn), 1855 (Zn), 1856 (Na), AM7331 (Na) (manufactured by Mitsui DuPont Polychemical Co., Ltd.); Surlyn 6320 (Mg), 8120 (Na) 8320 (Na), 9320 (Zn), 9320W (Zn), HPF1000 (Mg), HPF2000 (Mg) (manufactured by DuPont); Iotech 7510 (Zn), 7520 (Zn) (manufactured by ExxonMobil Chemical) Can be mentioned.

(Thermoplastic olefin copolymer)
Examples of the thermoplastic olefin copolymer include a binary copolymer of an olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms (hereinafter referred to as “binary copolymer”). A terpolymer of an olefin, an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α, β-unsaturated carboxylic acid ester (hereinafter referred to as “terpolymer”). Or a mixture thereof. The thermoplastic olefin copolymer is a nonionic one whose carboxyl group is not neutralized.

  As said olefin, the same thing as the olefin which comprises the said ionomer resin can be mentioned, Especially it is preferable that it is ethylene. Examples of the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and esters thereof are the same as the α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and esters thereof constituting the ionomer resin. Can be mentioned.

  The binary copolymer is preferably a binary copolymer of ethylene and (meth) acrylic acid. As the ternary copolymer, a ternary copolymer of ethylene, (meth) acrylic acid and (meth) acrylic acid ester is preferable.

  Examples of the binary copolymer include Nukurel (registered trademark) N1050H, N2050H, N1110H, N0200H (manufactured by Mitsui DuPont Polychemical Co., Ltd.); Primacor (registered trademark) 5980I (manufactured by Dow Chemical Co., Ltd.), and the like. . Examples of the ternary copolymer include Nucrel AN4318, AN4319 (Mitsui / DuPont Polychemical), Primacol AT310, AT320 (Dow Chemical). Na, Zn, Li, Mg, etc. described in parentheses after the trade name indicate the metal species of these neutralized metal ions.

(Thermoplastic styrene elastomer)
As the thermoplastic styrenic elastomer, a thermoplastic elastomer containing a styrene block can be suitably used. 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 component 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 components 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), SBS hydrogenated, SIS hydrogenated and SIBS hydrogenated are included. Examples of the hydrogenated product of SBS include styrene-ethylene-butylene-styrene block copolymer (SEBS). As a hydrogenated product of SIS, styrene-ethylene-propylene-styrene block copolymer (SEPS) can be mentioned. Examples of the hydrogenated product of SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

  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. In light of the feel at impact of the obtained golf ball, the content is preferably equal to or less than 50% by weight, more preferably equal to or less than 47% by weight, and particularly preferably equal to or less than 45% by weight.

  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 hydrogenated products thereof, and polyolefin. It is. The olefin component in the alloy is presumed to contribute to the improvement of compatibility with the ionomer resin. By using this alloy, the resilience performance of the golf ball is improved. Preferably, an olefin having 2 to 10 carbon atoms is used. Suitable olefins include ethylene, propylene, butene and pentene. Ethylene and propylene are particularly preferred.

  Specific examples of the polymer alloy include Lavalon (registered trademark) T3221C, T3339C, SJ4400N, SJ5400N, SJ6400N, SJ7400N, SJ8400N, SJ9400N, SR04 (manufactured by Mitsubishi Chemical Corporation). Examples of the styrene block-containing thermoplastic elastomer include Epofriend A1010 (manufactured by Daicel Chemical Industries) and Septon HG-252 (manufactured by Kuraray).

(Thermoplastic polyurethane and thermoplastic polyurethane elastomer)
Examples of the thermoplastic polyurethane and the thermoplastic polyurethane elastomer include thermoplastic resins and thermoplastic elastomers having a plurality of urethane bonds in the main chain of the molecule. The polyurethane is preferably obtained by reacting a polyisocyanate component and a polyol component. Examples of the thermoplastic polyurethane elastomer include Elastollan (registered trademark) NY84A10, XNY85A, XNY90A, XNY97A, ET885, ET890 (manufactured by BASF Japan).

  The resin composition further includes a pigment component such as a white pigment (for example, titanium oxide), a blue pigment, a weight adjusting agent, a dispersant, an anti-aging agent, an ultraviolet absorber, a light stabilizer, a fluorescent material, or a fluorescent whitening agent. Such additives can be contained. Examples of the weight adjuster include inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder.

  The content of the white pigment (for example, titanium oxide) is preferably 0.05 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, relative to 100 parts by mass of the thermoplastic resin. Part or less is more preferable. By setting the content of the white pigment to 0.05 parts by mass or more, concealment can be imparted to the obtained golf ball constituent member. Further, when the content of the white pigment exceeds 10 parts by mass, the durability of the obtained golf ball constituent member may be lowered.

  The resin composition can be obtained, for example, by dry blending a thermoplastic resin, an additive, or the like. Further, the dry blended mixture may be extruded to be pelletized. For dry blending, for example, it is preferable to use a mixer capable of blending pellet-shaped raw materials, and more preferably a tumbler type mixer. For the extrusion, a known extruder such as a single screw extruder, a twin screw extruder, or a twin screw single screw extruder can be used.

  The resin composition used for the intermediate layer preferably contains an ionomer resin as a resin component, and particularly preferably contains a binary ionomer resin. If the intermediate layer material contains an ionomer resin, the resilience of the intermediate layer is further improved, and the flight distance of the middle iron shot is further improved. In the resin composition used for the intermediate layer, the content of the ionomer resin in the resin component is preferably 50% by mass or more, more preferably 65% by mass or more, and further preferably 70% by mass or more.

  Moreover, it is also preferable that the resin composition used for the said intermediate | middle layer contains an ionomer resin and a styrene block containing thermoplastic elastomer as a resin component. In this case, the ratio of the styrene block-containing thermoplastic elastomer to the ionomer resin in the resin component (ionomer resin / styrene block-containing thermoplastic elastomer) is preferably 1.3 or more, and more preferably 1.5 or more.

  The resin composition used for the cover preferably contains an ionomer resin as a resin component, and particularly preferably contains a binary ionomer resin. If the cover material contains an ionomer resin, the resilience of the cover is further improved, and the flight distance of the middle iron shot is further improved. In the resin composition used for the cover, the content of the ionomer resin in the resin component is preferably 50% by mass or more, more preferably 65% by mass or more, and further preferably 70% by mass or more.

  The reinforcing layer is formed from a reinforcing layer composition containing a resin component. As the resin component, a two-component curable thermosetting resin is preferably used. Specific examples of the two-component curable thermosetting resin include an epoxy resin, a urethane resin, an acrylic resin, a polyester resin, and a cellulose resin. From the viewpoint of the strength and durability of the reinforcing layer, a two-component curable epoxy resin and a two-component curable urethane resin are preferable.

  The composition for a reinforcing layer may contain additives such as a coloring material (for example, titanium dioxide), a phosphoric acid stabilizer, an antioxidant, a light stabilizer, a fluorescent brightener, an ultraviolet absorber, and an antiblocking agent. . The additive may be added to the main component of the two-component curable thermosetting resin, or may be added to the curing agent.

[Production method]
The hot-press molding conditions for the core rubber composition may be appropriately set depending on the rubber composition, but are usually heated at 130 ° C. to 200 ° C. for 10 minutes to 60 minutes or at 130 ° C. to 150 ° C. for 20 After heating for 40 minutes for 40 minutes, it is preferable to heat at 160 ° C. to 180 ° C. for 5 minutes to 15 minutes.

  The method for forming the intermediate layer is not particularly limited. For example, a resin composition is molded into a half-shell half shell in advance, and the core is wrapped with two sheets of the half-shell, or a resin is molded. Examples thereof include a method in which the composition is directly injection molded on the core and the core is wrapped.

  When the intermediate layer is formed by injection molding the resin composition on the core, it is preferable to use a mold having a hemispherical cavity as the upper and lower molds for molding. The intermediate layer can be formed by injection molding by projecting a hold pin, inserting a coated sphere and holding it, and then injecting a heat-melted resin composition and cooling.

  When the intermediate layer is formed by the compression molding method, the half shell can be molded by either the compression molding method or the injection molding method, but the compression molding method is preferred. The conditions for compression molding the resin composition into a half shell include, for example, a molding temperature of −20 ° C. or more and + 70 ° C. or less with respect to the flow start temperature of the resin composition at a pressure of 1 MPa or more and 20 MPa or less. Can be mentioned. By setting the molding conditions, a half shell having a uniform thickness can be molded. As a method for forming the intermediate layer using a half shell, for example, a method in which a sphere is covered with two half shells and compression-molded can be mentioned. As conditions for compression-molding the half shell into the intermediate layer, for example, at a molding pressure of 0.5 MPa or more and 25 MPa or less, the flow start temperature of the resin composition is −20 ° C. or more and + 70 ° C. or less. A molding temperature can be mentioned. By setting the molding conditions, an intermediate layer having a uniform thickness can be molded.

  The mode of molding the cover using the resin composition is not particularly limited, but the mode in which the resin composition is directly injection-molded on the intermediate layer, or the hollow shell-shaped shell is molded from the resin composition, and the intermediate layer is formed. An embodiment (preferably a method in which a hollow shell-shaped half shell is formed from a resin composition, and an intermediate layer is covered with two half shells and compression-molded) is covered with a plurality of shells and compression-molded. it can. The golf ball body in which the cover is molded is preferably taken out from the mold and subjected to surface treatment such as deburring, washing, and sandblasting as necessary. Moreover, a mark can be formed if desired.

  The total number of dimples formed on the cover is preferably 200 or more and 500 or less. If the total number of dimples is less than 200, the dimple effect is difficult to obtain. Further, when the total number of dimples exceeds 500, the size of each dimple becomes small and it is difficult to obtain the dimple effect. The shape (plan view shape) of the dimple formed is not particularly limited, and a circular shape; a polygon such as a substantially triangular shape, a substantially square shape, a substantially pentagonal shape, or a substantially hexagonal shape; Alternatively, two or more kinds may be used in combination.

  The film thickness of the coating film is not particularly limited, but is preferably 5 μm or more, more preferably 7 μm or more, preferably 50 μm or less, more preferably 40 μm or less, and further preferably 30 μm or less. When the film thickness is less than 5 μm, the coating tends to wear away due to continuous use, and when the film thickness exceeds 50 μm, the dimple effect decreases and the flight performance of the golf ball decreases.

  Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited to the following examples, and all modifications and embodiments without departing from the gist of the present invention are not limited thereto. Included in range.

[Evaluation method]
(1) Core hardness distribution (Shore C hardness)
Using an automatic rubber hardness meter P1 type manufactured by Kobunshi Keiki Co., Ltd. equipped with a spring type hardness meter Shore C type, the Shore C hardness measured at the surface of the spherical core (outer layer core) was defined as the surface hardness of the outer layer core. Further, the core was cut into a hemisphere, and the hardness was measured at the center of the cut surface and at a predetermined distance from the center. The hardness was calculated by measuring the hardness at four points at a predetermined distance from the center and averaging these.

(2) Slab hardness (Shore C hardness)
Using the resin composition, a sheet having a thickness of about 2 mm was produced by injection molding and stored at 23 ° C. for 2 weeks. This sheet was measured using an automatic rubber hardness meter P1 type manufactured by Kobunshi Keiki Co., Ltd. equipped with a spring type hardness meter Shore C type in a state where three or more sheets were stacked so as not to affect the measurement substrate.

(3) Compression deformation (mm)
The amount of deformation in the compression direction (the amount by which the golf ball or spherical core shrinks in the compression direction) from when the initial load of 98 N was applied to the golf ball or spherical core to when the final load of 1275 N was applied was measured.

(4) Spin speed of middle iron shot, initial ball speed, carry No. 5 iron (Dunlop Sports, trade name “Srixon Z725”, shaft hardness: S, loft angle: 25.0 ° ). The golf ball was hit under the condition that the head speed was 38.5 m / sec. The initial ball velocity (m / s), spin rate (rpm), and carry (distance from the firing point to the falling point (yd)) of the golf ball immediately after hitting were measured. The measurement was performed 10 times for each golf ball, and the average value was taken as the measured value of the golf ball. In addition, the spin speed of the golf ball immediately after hitting was measured by taking continuous photographs of the hit golf ball.

(5) Feeling of hitting A golf ball was hit by 10 golfers with a 5 iron, and the feeling of hitting was evaluated. Based on the number of golfers who replied that “the feel at impact is soft,” the following ratings were assigned.
◎: 9 or more ○: 6 or more and 8 or less △: 3 or more and 5 or less ×: 2 or less

[Production of golf balls]
(1) Production of spherical core 1-22, 24-27
Each raw material was kneaded with a kneading roll so as to have the composition shown in Table 1 to obtain a rubber composition. The rubber compositions shown in Tables 3 to 5 were heated and pressed at 170 ° C. for 25 minutes in upper and lower molds having hemispherical cavities to obtain inner layer cores. Next, half shells were molded using the rubber compositions shown in Tables 3 to 5. The inner core was covered with these two half shells. The inner core and the half shell were both hot-pressed at 140 to 170 ° C. for 25 minutes in an upper and lower mold having a hemispherical cavity to obtain a spherical core. In Table 1, the compounding amount of barium sulfate was adjusted so that the specific gravity of the inner layer and the specific gravity of the outer layer were the same value.

Golf ball no. 23
Each raw material was kneaded with a kneading roll so as to have the composition shown in Table 1 to obtain a rubber composition. The rubber composition shown in Table 5 was heated and pressed at 150 to 170 ° C. for 25 minutes in an upper and lower mold having hemispherical cavities to obtain a single layer core. In Table 1, the blending amount of barium sulfate was adjusted so that the ball weight was in the range of 45.00 g to 45.92 g.

ポリブタジエンゴム：ＪＳＲ社製、「ＢＲ７３０（シス結合含有率：９６質量％）」
酸化マグネシウム：共和化学工業社製、「マグサラット（登録商標）１５０ＳＴ」
メタクリル酸：三菱レイヨン社製
アクリル酸亜鉛：三新化学工業社製、「サンセラー（登録商標）ＳＲ」
酸化亜鉛：東邦亜鉛社製、「銀嶺（登録商標）Ｒ」
硫酸バリウム：堺化学社製、「硫酸バリウムＢＤ」
ジクミルパーオキサイド：日油社製、「パークミル（登録商標）Ｄ」
ＰＢＤＳ：川口化学工業社製、ビス（ペンタブロモフェニル）ペルスルフィド
ＤＰＤＳ：住友精化社製、ジフェニルジスルフィド
２−チオナフトール：Zhejiang shou & Fu Chemical社製
安息香酸：Emerald Kalama Chemical 社製
老化防止剤：本州化学工業社製、「Ｈ−ＢＨＴ」（ジブチルヒドロキシトルエン）

Polybutadiene rubber: “BR730 (cis bond content: 96 mass%)” manufactured by JSR Corporation
Magnesium oxide: “Magsarat (registered trademark) 150ST” manufactured by Kyowa Chemical Industry Co., Ltd.
Methacrylic acid: Mitsubishi Rayon Co., Ltd. Zinc acrylate: Sanshin Chemical Industry Co., Ltd., "Sunseller (registered trademark) SR"
Zinc oxide: Toho Zinc Co., Ltd., “Ginseng (registered trademark) R”
Barium sulfate: Sakai Chemical Co., Ltd. “Barium sulfate BD”
Dicumyl peroxide: NOF Corporation, “Park Mill (registered trademark) D”
PBDS: manufactured by Kawaguchi Chemical Industry Co., Ltd., bis (pentabromophenyl) persulfide DPDS: manufactured by Sumitomo Seika Co., Ltd., diphenyl disulfide 2-thionaphthol: manufactured by Zhejiang shou & Fu Chemical, benzoic acid: manufactured by Emerald Kalama Chemical Co., Ltd. “H-BHT” (dibutylhydroxytoluene), manufactured by Honshu Chemical Industry Co., Ltd.

(2) Preparation of Resin Composition Materials having the composition shown in Table 2 were mixed with a twin-screw kneading type extruder to prepare a pellet-shaped resin composition. The extrusion conditions were a screw diameter of 45 mm, a screw rotation speed of 200 rpm, and a screw L / D = 35, and the blend was heated to 160-230 ° C. at the die position of the extruder.

The raw materials used in Table 2 are as follows.
High Milan (registered trademark) 1605: Mitsui DuPont Polychemical Co., Ltd., sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin Himiran AM 7329: Mitsui DuPont Polychemical Co., Ltd., zinc ion neutralized ethylene-methacrylic acid co Polymer ionomer resin HiMilan AM7337: manufactured by Mitsui DuPont Polychemical Co., Ltd., sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin Himiran 1555: manufactured by Mitsui DuPont Polychemical Co., Ltd., sodium ion neutralized ethylene-methacrylic acid co Polymer ionomer resin Lavalon (registered trademark) T3221C: manufactured by Mitsubishi Chemical Corporation, thermoplastic styrene elastomer Nucrel (registered trademark) N1050H: manufactured by Mitsui DuPont Polychemical Co., Ltd., ethylene-methacrylic acid copolymer Body barium sulfate: manufactured by Sakai Chemical Industry Co., Ltd., "barium sulfate BD"
JF-90: manufactured by Johoku Chemical Industry Co., Ltd., light stabilizer

(3) Production of Intermediate Layer Golf Ball No. 2-27
The resin compositions shown in Tables 3 to 5 were injection-molded on the core obtained as described above to form an intermediate layer. In Table 2, the compounding amount of barium sulfate was adjusted so that the slab hardness would be a desired value.

(4) Production of cover Golf ball no. 1-27
The resin compositions shown in Tables 3 to 5 were injection-molded on the spherical core or intermediate layer-coated sphere obtained as described above to form a cover layer. In Table 2, the compounding amount of barium sulfate was adjusted so that the slab hardness would be a desired value. A large number of dimples were formed on the cover.

  The surface of the obtained golf ball main body was sandblasted and marked, and then a clear paint was applied and the paint was dried in an oven to obtain a golf ball. Tables 3 to 5 show the evaluation results of the obtained golf balls.

Golf ball No. 1 having the same composition and thickness of the intermediate layer and the cover Compare 4, 5, 13, 16-25. Golf ball no. 19 is the case where the difference (α−β) between the angle α of the hardness gradient of the inner layer and the angle β of the hardness gradient of the outer layer is less than 0 °. Golf ball no. 20 is the case where the angle α of the hardness gradient of the inner layer is less than 0 °. Golf ball no. 21 is the case where the surface hardness (H _{X + Y} ) is 65 or less in Shore C hardness. Golf ball no. 22 is a case where the difference (H _{x + 1} −H _x−1 ) is less than 0 in Shore C hardness. Golf ball no. Reference numeral 23 denotes a case where the spherical core is a single layer. These golf balls No. 19-23 have a small carry in the middle iron shot.

Golf balls having the same spherical core No. Compare 6-15. Golf ball no. 6 to 12 are cases where the difference (Hm−H _{X + Y} ) is 1 or less. Golf ball no. 13 to 15 are cases where the difference (Hm−H _{X + Y} ) is greater than 1. When these are compared, a golf ball No. having a difference (Hm−H _{X + Y} ) of more than 1 is shown. 13-15 have improved carry.

1: golf ball, 2: spherical core, 21: inner layer, 22: outer layer, 3: intermediate layer, 4: cover, 41: dimple, 42: land

Claims (9)

A spherical core, an intermediate layer disposed outside the spherical core, and a cover disposed outside the intermediate layer;
The spherical core has an inner layer and an outer layer;
The hardness (H _{X + 1} ) at a point 1 mm outside in the radial direction from the boundary between the inner layer and the outer layer of the spherical core, and the hardness (H at a point 1 mm in the radial direction from the boundary between the inner layer and the outer layer of the spherical core _X-1 ) is a Shore C hardness of 0 or more and 16 or less (H _{X + 1} -H _X-1 ),
The spherical core has a surface hardness (H _{X + Y} ) of more than 65 in Shore C hardness,
The hardness difference (H _{X + Y} −Ho) between the central hardness (Ho) and the surface hardness (H _{X + Y} ) of the spherical core is 18 to 35 in Shore C hardness,
The angle α of the hardness gradient of the inner layer calculated by the formula (1) is 0 ° or more,
The angle β of the hardness gradient of the outer layer calculated by the equation (2) is −20 ° or more and + 20 ° or less,
It said angle alpha and the difference between the angle β (α-β) is not less 0 ° or more,
A golf ball characterized in that the cover has the highest hardness among the components of the golf ball.
α = (180 / π) × atan [{H _X−1 −Ho} / (X−1)] (1)
β = (180 / π) × atan [{H _{X + Y} −H _{X + 1} } / (Y−1)] (2)
[Where X is the radius of the inner layer (mm), Y is the thickness of the outer layer (mm), Ho is the central hardness of the spherical core (Shore C), and H _X-1 is the radius from the boundary between the inner and outer layers of the spherical core. The hardness at the point 1 mm inside in the direction (Shore C), H _{X + 1} is the hardness at the point 1 mm outside in the radial direction from the boundary between the inner and outer layers of the spherical core (Shore C), and H _{X + Y} is the surface of the spherical core Represents hardness (Shore C). ] 2. The golf ball according to claim 1, wherein a difference (Hm−H _{X + Y} ) between a hardness (Hm) of the intermediate layer and a surface hardness (H _{X + Y} ) of the spherical core is greater than 1 in Shore C hardness. .   The golf ball according to claim 1 or 2, wherein a total thickness of the intermediate layer (Tm) and the cover (Tc) is 3 mm or less.   4. The golf ball according to claim 1, wherein the spherical core has a center hardness (Ho) of Shore C hardness of less than 65. 5. The hardness (H _X-1 ) is Shore C hardness of 63 to 82,
The hardness difference (H _X-1 -Ho) between the center hardness (Ho) and the hardness (H _X-1 ) is 4 to 27 in Shore C hardness. 5. Golf ball. The cover hardness (Hc) is in Shore C hardness state, and are more than 75,
The hardness difference (Hc−H _{X + Y} ) between the hardness (Hc) of the cover and the surface hardness (H _{X + Y} ) of the spherical core is 10 to 16 in Shore C hardness . The golf ball according to any one of the above. The hardness of the intermediate layer (Hm) is in Shore C hardness state, and are more than 75,
The golf according to claim 1 , wherein a hardness difference (Hc−Hm) between the hardness (Hc) of the cover and the hardness (Hm) of the intermediate layer is 4 to 10 in Shore C hardness. ball. The hardness (H _{X + 1} ) Is Shore C hardness of 70-90,
Surface hardness (H _{X + 1} ) And hardness (H _{X + Y} ) And hardness difference (H _{X + Y} -H _{X + 1} ) Is a shore C hardness of -7 to 10, and the golf ball according to any one of claims 1 to 7. The golf ball according to claim 1, wherein the spherical core is formed from a rubber composition containing a base rubber, a co-crosslinking agent, and a crosslinking initiator.

Images