US20130316851A1 - Golf ball - Google Patents

Golf ball Download PDF

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Publication number
US20130316851A1
US20130316851A1 US13/871,096 US201313871096A US2013316851A1 US 20130316851 A1 US20130316851 A1 US 20130316851A1 US 201313871096 A US201313871096 A US 201313871096A US 2013316851 A1 US2013316851 A1 US 2013316851A1
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United States
Prior art keywords
hardness
golf ball
acid
preferably equal
salt
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
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US13/871,096
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English (en)
Inventor
Takahiro Sajima
Hidetaka INOUE
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sumitomo Rubber Industries Ltd
Original Assignee
Dunlop Sports Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from JP2012119603A external-priority patent/JP6068002B2/ja
Priority claimed from JP2012120502A external-priority patent/JP5499084B2/ja
Priority claimed from JP2012122840A external-priority patent/JP6068004B2/ja
Priority claimed from JP2012124079A external-priority patent/JP6068007B2/ja
Application filed by Dunlop Sports Co Ltd filed Critical Dunlop Sports Co Ltd
Assigned to DUNLOP SPORTS CO. LTD. reassignment DUNLOP SPORTS CO. LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: INOUE, HIDETAKA, SAJIMA, TAKAHIRO
Publication of US20130316851A1 publication Critical patent/US20130316851A1/en
Assigned to SUMITOMO RUBBER INDUSTRIES, LTD. reassignment SUMITOMO RUBBER INDUSTRIES, LTD. MERGER (SEE DOCUMENT FOR DETAILS). Assignors: DUNLOP SPORTS CO. LTD.
Abandoned legal-status Critical Current

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    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B37/00—Solid balls; Rigid hollow balls; Marbles
    • A63B37/0003—Golf balls
    • A63B37/005—Cores
    • A63B37/0051—Materials other than polybutadienes; Constructional details
    • A63B37/0054—Substantially rigid, e.g. metal
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B37/00—Solid balls; Rigid hollow balls; Marbles
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B37/00—Solid balls; Rigid hollow balls; Marbles
    • A63B37/0003—Golf balls
    • A63B37/0038—Intermediate layers, e.g. inner cover, outer core, mantle
    • A63B37/0039—Intermediate layers, e.g. inner cover, outer core, mantle characterised by the material
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B37/00—Solid balls; Rigid hollow balls; Marbles
    • A63B37/0003—Golf balls
    • A63B37/005—Cores
    • A63B37/0051—Materials other than polybutadienes; Constructional details
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B37/00—Solid balls; Rigid hollow balls; Marbles
    • A63B37/0003—Golf balls
    • A63B37/005—Cores
    • A63B37/006—Physical properties
    • A63B37/0062—Hardness
    • A63B37/00622—Surface hardness
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B37/00—Solid balls; Rigid hollow balls; Marbles
    • A63B37/0003—Golf balls
    • A63B37/007—Characteristics of the ball as a whole
    • A63B37/0077—Physical properties
    • A63B37/0092—Hardness distribution amongst different ball layers
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B37/00—Solid balls; Rigid hollow balls; Marbles
    • A63B37/0003—Golf balls
    • A63B37/007—Characteristics of the ball as a whole
    • A63B37/0077—Physical properties
    • A63B37/0092—Hardness distribution amongst different ball layers
    • A63B37/00922—Hardness distribution amongst different ball layers whereby hardness of the cover is lower than hardness of the intermediate layers
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B37/00—Solid balls; Rigid hollow balls; Marbles
    • A63B37/02—Special cores
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B37/00—Solid balls; Rigid hollow balls; Marbles
    • A63B37/02—Special cores
    • A63B37/06—Elastic cores
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/04—Oxygen-containing compounds
    • C08K5/09—Carboxylic acids; Metal salts thereof; Anhydrides thereof
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/04—Oxygen-containing compounds
    • C08K5/14—Peroxides
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B37/00—Solid balls; Rigid hollow balls; Marbles
    • A63B37/0003—Golf balls
    • A63B37/0023—Covers
    • A63B37/0029—Physical properties
    • A63B37/0031—Hardness
    • A63B37/0032—Hardness gradient
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B37/00—Solid balls; Rigid hollow balls; Marbles
    • A63B37/0003—Golf balls
    • A63B37/0038—Intermediate layers, e.g. inner cover, outer core, mantle
    • A63B37/004—Physical properties
    • A63B37/0043—Hardness
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B37/00—Solid balls; Rigid hollow balls; Marbles
    • A63B37/0003—Golf balls
    • A63B37/007—Characteristics of the ball as a whole
    • A63B37/0072—Characteristics of the ball as a whole with a specified number of layers
    • A63B37/0076—Multi-piece balls, i.e. having two or more intermediate layers

Definitions

  • the present invention relates to golf balls. Specifically, the present invention relates to golf balls that include a solid core and a cover.
  • Flight performance correlates with the resilience performance of a golf ball.
  • the golf ball flies at a high speed, thereby achieving a large flight distance.
  • golf players also place importance on spin performance of golf balls.
  • a backspin rate is high, the run is short. It is easy for golf players to cause a golf ball, to which backspin is easily provided, to stop at a target point.
  • a sidespin rate is high, the golf ball easily curves. It is easy for golf players to intentionally cause a golf ball, to which sidespin is easily provided, to curve.
  • a golf ball to which spin is easily provided has excellent controllability. In particular, advanced golf players place importance on controllability upon a shot with a short iron.
  • Golf balls that include a core having excellent resilience performance are disclosed in JP61-37178, JP2008-212681 (US2008/0214324), JP2008-523952 (US2006/0135287 and US2007/0173607), and JP2009-119256 (US2009/0124757).
  • JP61-37178 is obtained from a rubber composition that includes a co-crosslinking agent and a crosslinking activator.
  • This publication discloses palmitic acid, stearic acid, and myristic acid as the crosslinking activator.
  • the core disclosed in JP2008-212681 is obtained from a rubber composition that includes an organic peroxide, a metal salt of an ⁇ , ⁇ -unsaturated carboxylic acid, and a copper salt of a fatty acid.
  • the core disclosed in JP2008-523952 is obtained from a rubber composition that includes a metal salt of an unsaturated monocarboxylic acid, a free radical initiator, and a non-conjugated diene monomer.
  • the core disclosed in JP2009-119256 is obtained from a rubber composition that includes a polybutadiene whose vinyl content is equal to or less than 2%, whose cis 1,4-bond content is equal to or greater than 80%, and which has an active end modified with an alkoxysilane compound.
  • An appropriate trajectory height is required in order to achieve a large flight distance.
  • a trajectory height depends on a spin rate and a launch angle. In a golf ball that achieves a high trajectory by a high spin rate, a flight distance is insufficient. In a golf ball that achieves a high trajectory by a high launch angle, a large flight distance is obtained.
  • Use of an outer-hard/inner-soft structure in a golf ball can achieve a low spin rate and a high launch angle. Modifications regarding a hardness distribution of a core are disclosed in JP6-154357 (U.S. Pat. No. 5,403,010), JP2008-194471 (U.S. Pat. No.
  • a JIS-C hardness H1 at the central point of the core is 58 to 73
  • a JIS-C hardness H2 in a region that extends over a distance range from equal to or greater than 5 mm to equal to or less than 10 mm from the central point is equal to or greater than 65 but equal to or less than 75
  • a JIS-C hardness H3 at a point located at a distance of 15 mm from the central point is equal to or greater than 74 but equal to or less than 82
  • a JIS-C hardness H4 at the surface of the core is equal to or greater than 76 but equal to or less than 84.
  • the hardness H2 is greater than the hardness H1
  • the hardness H3 is greater than the hardness H2
  • the hardness H4 is equal to or greater than the hardness H3.
  • a Shore D hardness at the central point of the core is equal to or greater than 30 but equal to or less than 48, a Shore D hardness at a point located at a distance of 4 mm from the central point is equal to or greater than 34 but equal to or less than 52, a Shore D hardness at a point located at a distance of 8 mm from the central point is equal to or greater than 40 but equal to or less than 58, a Shore D hardness at a point located at a distance of 12 mm from the central point is equal to or greater than 43 but equal to or less than 61, a Shore D hardness in a region that extends over a distance range from equal to or greater than 2 mm to equal to or less than 3 mm from the surface of the core is equal to or greater than 36 but equal to or less than 54, and a Shore D hardness at the surface is equal to or greater than 41 but equal to or less than 59.
  • a Shore D hardness at the central point of the core is equal to or greater than 25 but equal to or less than 45
  • a Shore D hardness in a region that extends over a distance range from equal to or greater than 5 mm to equal to or less than 10 mm from the central point is equal to or greater than 39 but equal to or less than 58
  • a Shore D hardness at a point located at a distance of 15 mm from the central point is equal to or greater than 36 but equal to or less than 55
  • a Shore D hardness at the surface of the core is equal to or greater than 55 but equal to or less than 75.
  • JP2010-253268 discloses a golf ball that includes a core, an envelope layer, an inner cover, and an outer cover.
  • the hardness gradually increases from the central point of the core toward the surface of the core.
  • the difference between a JIS-C hardness at the surface and a JIS-C hardness at the central point is equal to or greater than 15.
  • the hardness of the outer cover is greater than the hardness of the inner cover, and the hardness of the inner cover is greater than the hardness of the envelope layer.
  • a first object of the present invention is to provide a golf ball having excellent flight performance and excellent controllability.
  • a second object of the present invention is to provide a golf ball that exerts excellent flight performance also upon a shot with a fairway wood.
  • a third object of the present invention is to provide a golf ball that exerts excellent flight performance also upon a shot with a middle iron.
  • a fourth object of the present invention is to provide a golf ball that has both excellent flight performance and favorable feel at impact upon a shot with a driver.
  • a golf ball according to the present invention includes a core, an inner cover positioned outside the core, and an outer cover positioned outside the inner cover.
  • the core includes a center and an envelope layer positioned outside the center.
  • the center is formed by a rubber composition being crosslinked.
  • the envelope layer is formed by a rubber composition being crosslinked. At least one of the rubber composition of the center and the rubber composition of the envelope layer includes:
  • the co-crosslinking agent (b) is:
  • (b2) a metal salt of an ⁇ , ⁇ -unsaturated carboxylic acid having 3 to 8 carbon atoms.
  • a JIS-C hardness Hi of the inner cover is greater than a JIS-C hardness Hs at a surface of the core.
  • a JIS-C hardness Ho of the outer cover is less than the hardness Hi.
  • a hardness distribution of the core is appropriate. When the golf ball is hit, the energy loss is low in the core. With the golf ball, a large flight distance is achieved. In the golf ball, the outer cover can contribute to controllability. The golf ball has both excellent flight performance and excellent controllability.
  • a golf ball according to the present invention includes a core, an inner cover positioned outside the core, and an outer cover positioned outside the inner cover.
  • the core includes a center and an envelope layer positioned outside the center.
  • the center is formed by a rubber composition being crosslinked.
  • the envelope layer is formed by a rubber composition being crosslinked. At least one of the rubber composition of the center and the rubber composition of the envelope layer includes:
  • the co-crosslinking agent (b) is:
  • (b2) a metal salt of an ⁇ , ⁇ 3 -unsaturated carboxylic acid having 3 to 8 carbon atoms.
  • a JIS-C hardness Ho of the outer cover is greater than a JIS-C hardness Hs at a surface of the core.
  • the hardness Ho is greater than a JIS-C hardness Hi of the inner cover.
  • a hardness distribution of the core is appropriate. When the golf ball is hit with a fairway wood, the energy loss is low in the core. In the golf ball, a hardness distribution of the entire ball is also appropriate. With the golf ball, a large flight distance is achieved.
  • a golf ball according to the present invention includes a core, an inner cover positioned outside the core, a mid cover positioned outside the inner cover, and an outer cover positioned outside the mid cover.
  • the core includes a center and an envelope layer positioned outside the center.
  • the center is formed by a rubber composition being crosslinked.
  • the envelope layer is formed by a rubber composition being crosslinked. At least one of the rubber composition of the center and the rubber composition of the envelope layer includes:
  • the co-crosslinking agent (b) is:
  • (b2) a metal salt of an ⁇ , ⁇ -unsaturated carboxylic acid having 3 to 8 carbon atoms.
  • a JIS-C hardness Hi of the inner cover is greater than a JIS-C hardness Hs at a surface of the core.
  • a difference (Hi ⁇ Hs) between the hardness Hi and the hardness Hs is equal to or greater than 1.
  • a JIS-C hardness Ho of the outer cover is greater than the hardness Hi.
  • a hardness distribution of the core is appropriate. When the golf ball is hit with a middle iron, the energy loss is low in the core. In the entirety of the golf ball, an outer-hard/inner-soft structure is achieved. When the golf ball is hit with a middle iron, the spin rate is low. Due to the low spin rate, a large flight distance is obtained.
  • a golf ball according to the present invention includes a core, an inner cover positioned outside the core, a mid cover positioned outside the inner cover, and an outer cover positioned outside the mid cover.
  • the core includes a center and an envelope layer positioned outside the center.
  • the center is formed by a rubber composition being crosslinked.
  • the envelope layer is formed by a rubber composition being crosslinked. At least one of the rubber composition of the center and the rubber composition of the envelope layer includes:
  • the co-crosslinking agent (b) is:
  • (b2) a metal salt of an ⁇ , ⁇ -unsaturated carboxylic acid having 3 to 8 carbon atoms.
  • a difference (Hi ⁇ Hs) between a JIS-C hardness Hi of the inner cover and a JIS-C hardness Hs at a surface of the core is less than 1.
  • a JIS-C hardness Ho of the outer cover is greater than the hardness Hi.
  • a hardness distribution of the core is appropriate. When the golf ball is hit with a driver, the energy loss is low in the core. In the golf ball, a hardness distribution of the entire ball is also appropriate. With the golf ball, a flight distance upon a shot with a driver is further increased without impairing the feel at impact.
  • FIG. 1 is a partially cutaway cross-sectional view of a golf ball according to a first embodiment of the present invention
  • FIG. 2 is a line graph showing a hardness distribution of an envelope layer of the golf ball in FIG. 1 ;
  • FIG. 3 is a partially cutaway cross-sectional view of a golf ball according to a second embodiment of the present invention.
  • FIG. 4 is a line graph showing a hardness distribution of an envelope layer of the golf ball in FIG. 3 ;
  • FIG. 5 is a partially cutaway cross-sectional view of a golf ball according to a third embodiment of the present invention.
  • FIG. 6 is a line graph showing a hardness distribution of an envelope layer of the golf ball in FIG. 5 ;
  • FIG. 7 is a partially cutaway cross-sectional view of a golf ball according to a fourth embodiment of the present invention.
  • FIG. 8 is a line graph showing a hardness distribution of an envelope layer of the golf ball in FIG. 7 .
  • a golf ball 2 shown in FIG. 1 includes a spherical core 4 , an inner cover 6 positioned outside the core 4 , and an outer cover 8 positioned outside the inner cover 6 .
  • the core 4 includes a spherical center 10 and an envelope layer 12 positioned outside the center 10 .
  • On the surface of the outer cover 8 a large number of dimples 14 are formed.
  • a part other than the dimples 14 is a land 16 .
  • the golf ball 2 includes a paint layer and a mark layer on the external side of the outer cover 8 , but these layers are not shown in the drawing.
  • the golf ball 2 preferably has a diameter of 40 mm or greater but 45 mm or less. From the standpoint of conformity to the rules established by the United States Golf Association (USGA), the diameter is particularly preferably equal to or greater than 42.67 mm. In light of suppression of air resistance, the diameter is more preferably equal to or less than 44 mm and particularly preferably equal to or less than 42.80 mm.
  • the golf ball 2 preferably has a weight of 40 g or greater but 50 g or less. In light of attainment of great inertia, the weight is more preferably equal to or greater than 44 g and particularly preferably equal to or greater than 45.00 g. From the standpoint of conformity to the rules established by the USGA, the weight is particularly preferably equal to or less than 45.93 g.
  • JIS-C hardnesses are measured at 13 measuring points from the central point of the core 4 to the surface of the core 4 .
  • the distances from the central point of the core 4 to these measuring points are as follows.
  • Hardnesses at the first to twelfth points are measured by pressing a JIS-C type hardness scale against a cut plane of the core 4 that has been cut into two halves.
  • a hardness at the thirteenth point is measured by pressing the JIS-C type hardness scale against the surface of the spherical core 4 .
  • an automated rubber hardness measurement machine (trade name “P1”, manufactured by Kobunshi Keiki Co., Ltd.), to which this hardness scale is mounted, is used.
  • FIG. 2 is a line graph showing a hardness distribution of the envelope layer 12 of the golf ball 2 in FIG. 1 .
  • the horizontal axis of the graph indicates a distance (mm) from the central point of the core 4 .
  • the vertical axis of the graph indicates a JIS-C hardness.
  • the sixth point, the eighth point, and the tenth to thirteenth points are plotted.
  • FIG. 2 also shows a linear approximation curve obtained by a least-square method on the basis of the distances and the hardnesses of the six measuring points.
  • the linear approximation curve is indicated by a dotted line.
  • the broken line does not greatly deviate from the linear approximation curve.
  • the broken line has a shape close to the linear approximation curve.
  • the hardness linearly increases from its inside toward its outside.
  • the energy loss is low in the envelope layer 12 .
  • the golf ball 2 has excellent resilience performance.
  • the flight distance is large.
  • R 2 of the linear approximation curve for the envelope layer 12 which is obtained by the least-square method is preferably equal to or greater than 0.95.
  • R 2 is an index indicating the linearity of the broken line.
  • the shape of the broken line of the hardness distribution is close to a straight line.
  • the golf ball 2 that includes the envelope layer 12 for which R 2 is equal to or greater than 0.95 has excellent resilience performance.
  • R 2 is more preferably equal to or greater than 0.96 and particularly preferably equal to or greater than 0.97.
  • R 2 is calculated by squaring a correlation coefficient R.
  • the correlation coefficient R is calculated by dividing the covariance of the distance (mm) from the central point and the hardness (JIS-C) by the standard deviation of the distance (mm) from the central point and the standard deviation of the hardness (JIS-C).
  • the gradient a of the linear approximation curve is preferably equal to or greater than 0.30, more preferably equal to or greater than 0.33, and particularly preferably equal to or greater than 0.35.
  • a JIS-C hardness at a measuring point whose distance from the central point of the core 4 is x (mm) is represented by H(x).
  • the hardness at the central point of the core 4 is represented by H(0.0).
  • the JIS-C hardness at the surface of the core 4 is represented by Hs.
  • the difference (Hs ⁇ H(0.0)) between the surface hardness Hs and the central hardness H(0.0) is preferably equal to or greater than 15.
  • the core 4 in which the difference (Hs ⁇ H(0.0)) is equal to or greater than 15 has an outer-hard/inner-soft structure.
  • the core 4 contributes to the flight performance of the golf ball 2 .
  • the difference (Hs ⁇ H(0.0)) is more preferably equal to or greater than 23 and particularly preferably equal to or greater than 24. From the standpoint that the core 4 can easily be formed, the difference (Hs ⁇ H(0.0)) is preferably equal to or less than 50.
  • the hardness gradually increases from its central point toward its surface.
  • the center 10 is formed by crosslinking a rubber composition.
  • base rubbers for use in the rubber composition include polybutadienes, polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-diene copolymers, and natural rubbers. Two or more rubbers may be used in combination. In light of resilience performance, polybutadienes are preferred, and high-cis polybutadienes are particularly preferred.
  • the rubber composition of the center 10 includes a co-crosslinking agent.
  • co-crosslinking agents in light of resilience performance include zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate.
  • the rubber composition includes an organic peroxide together with a co-crosslinking agent.
  • preferable organic peroxides include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide.
  • the rubber composition includes a sulfur compound.
  • various additives such as a filler, sulfur, a vulcanization accelerator, an anti-aging agent, a coloring agent, a plasticizer, a dispersant, and the like are included in the rubber composition of the center 10 in an adequate amount.
  • Synthetic resin powder or crosslinked rubber powder may also be included in the rubber composition.
  • the center 10 is more flexible than the envelope layer 12 .
  • the center 10 can suppress spin.
  • the center 10 preferably has a diameter of 10 mm or greater but 20 mm or less.
  • spin can be suppressed.
  • the diameter is more preferably equal to or greater than 12 mm and particularly preferably equal to or greater than 14 mm.
  • the golf ball 2 that includes the center 10 having a diameter of 20 mm or less has excellent resilience performance even though the center 10 is flexible.
  • the diameter is more preferably equal to or less than 18 mm and particularly preferably equal to or less than 16 mm.
  • the envelope layer 12 is formed by crosslinking a rubber composition.
  • the rubber composition includes:
  • the base rubber (a) examples include polybutadienes, polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-diene copolymers, and natural rubbers. In light of resilience performance, polybutadienes are preferred. When a polybutadiene and another rubber are used in combination, it is preferred that the polybutadiene is included as a principal component. Specifically, the proportion of the polybutadiene to the entire base rubber is preferably equal to or greater than 50% by weight and more preferably equal to or greater than 80% by weight. The proportion of cis-1,4 bonds in the polybutadiene is preferably equal to or greater than 40% by weight and more preferably equal to or greater than 80% by weight.
  • a polybutadiene in which the proportion of 1,2-vinyl bonds is equal to or less than 2.0% by weight is preferred.
  • the polybutadiene can contribute to the resilience performance of the golf ball 2 .
  • the proportion of 1,2-vinyl bonds is preferably equal to or less than 1.7% by weight and particularly preferably equal to or less than 1.5% by weight.
  • a polybutadiene synthesized with a rare-earth-element-containing catalyst is preferred.
  • a polybutadiene synthesized with a catalyst containing neodymium, which is a lanthanum-series rare earth element compound is preferred.
  • the polybutadiene has a Mooney viscosity (ML 1+4 (100° C.)) of preferably 30 or greater, more preferably 32 or greater, and particularly preferably 35 or greater.
  • the Mooney viscosity (ML 1+4 (100° C.)) is preferably equal to or less than 140, more preferably equal to or less than 120, even more preferably equal to or less than 100, and particularly preferably equal to or less than 80.
  • the Mooney viscosity (ML 1+4 (100° C.)) is measured according to the standards of “JIS K6300”. The measurement conditions are as follows.
  • the polybutadiene has a molecular weight distribution (Mw/Mn) of preferably 2.0 or greater, more preferably 2.2 or greater, even more preferably 2.4 or greater, and particularly preferably 2.6 or greater.
  • Mw/Mn molecular weight distribution
  • the molecular weight distribution (Mw/Mn) is preferably equal to or less than 6.0, more preferably equal to or less than 5.0, even more preferably equal to or less than 4.0, and particularly preferably equal to or less than 3.4.
  • the molecular weight distribution (Mw/Mn) is calculated by dividing the weight average molecular weight Mw by the number average molecular weight Mn.
  • the molecular weight distribution is measured by gel permeation chromatography (“HLC-8120GPC” manufactured by Tosoh Corporation).
  • the measurement conditions are as follows.
  • the molecular weight distribution is calculated as a value obtained by conversion using polystyrene standard.
  • Examples of preferable co-crosslinking agents (b) include:
  • (b2) a metal salt of an ⁇ , ⁇ -unsaturated carboxylic acid having 3 to 8 carbon atoms.
  • the rubber composition may include only the ⁇ , ⁇ -unsaturated carboxylic acid (b1) or only the metal salt (b2) of the ⁇ , ⁇ -unsaturated carboxylic acid as the co-crosslinking agent (b).
  • the rubber composition may include both the ⁇ , ⁇ -unsaturated carboxylic acid (b1) and the metal salt (b2) of the ⁇ , ⁇ -unsaturated carboxylic acid as the co-crosslinking agent (b).
  • the metal salt (b2) of the ⁇ , ⁇ -unsaturated carboxylic acid graft-polymerizes with the molecular chain of the base rubber, thereby crosslinking the rubber molecules.
  • the rubber composition preferably further includes a metal compound (f).
  • the metal compound (f) reacts with the ⁇ , ⁇ -unsaturated carboxylic acid (b1) in the rubber composition.
  • a salt obtained by this reaction graft-polymerizes with the molecular chain of the base rubber.
  • Examples of the metal compound (f) include metal hydroxides such as magnesium hydroxide, zinc hydroxide, calcium hydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide, and copper hydroxide; metal oxides such as magnesium oxide, calcium oxide, zinc oxide, and copper oxide; and metal carbonates such as magnesium carbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithium carbonate, and potassium carbonate.
  • metal hydroxides such as magnesium hydroxide, zinc hydroxide, calcium hydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide, and copper hydroxide
  • metal oxides such as magnesium oxide, calcium oxide, zinc oxide, and copper oxide
  • metal carbonates such as magnesium carbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithium carbonate, and potassium carbonate.
  • a compound that includes a bivalent metal is preferred.
  • the compound that includes the bivalent metal reacts with the co-crosslinking agent (b) to form metal crosslinks.
  • the metal compound (f) is particularly preferably a zinc compound
  • Examples of the ⁇ , ⁇ -unsaturated carboxylic acids include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid.
  • Examples of the metal component in the metal salt (b2) of the ⁇ , ⁇ -unsaturated carboxylic acid include sodium ion, potassium ion, lithium ion, magnesium ion, calcium ion, zinc ion, barium ion, cadmium ion, aluminum ion, tin ion, and zirconium ion.
  • the metal salt (b2) of the ⁇ , ⁇ -unsaturated carboxylic acid may include two or more types of ions.
  • bivalent metal ions such as magnesium ion, calcium ion, zinc ion, barium ion, and cadmium ion are preferred.
  • the metal salt (b2) of the ⁇ , ⁇ -unsaturated carboxylic acid is particularly preferably zinc acrylate.
  • the amount of the co-crosslinking agent (b) is preferably equal to or greater than 15 parts by weight and particularly preferably equal to or greater than 20 parts by weight, per 100 parts by weight of the base rubber. In light of feel at impact, the amount is preferably equal to or less than 50 parts by weight, more preferably equal to or less than 45 parts by weight, and particularly preferably equal to or less than 40 parts by weight, per 100 parts by weight of the base rubber.
  • the crosslinking initiator (c) is preferably an organic peroxide.
  • the organic peroxide contributes to the resilience performance of the golf ball 2 .
  • examples of preferable organic peroxides include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. In light of versatility, dicumyl peroxide is preferred.
  • the amount of the crosslinking initiator (c) is preferably equal to or greater than 0.2 parts by weight and particularly preferably equal to or greater than 0.5 parts by weight, per 100 parts by weight of the base rubber. In light of feel at impact and durability of the golf ball 2 , the amount is preferably equal to or less than 5.0 parts by weight and particularly preferably equal to or less than 2.5 parts by weight, per 100 parts by weight of the base rubber.
  • the co-crosslinking agent (b) is not included in the concept of the acid and/or the salt (d). It is inferred that during heating and forming of the core 4 , the acid and/or the salt (d) breaks the metal crosslinks by the co-crosslinking agent (b) near the inner surface of the envelope layer 12 .
  • the acid and/or the salt (d) include oxo acids, such as carboxylic acids, sulfonic acids, and phosphoric acid, and salts thereof; and hydroacids, such as hydrochloric acid and hydrofluoric acid, and salts thereof. Oxo acids and salts thereof are preferred.
  • a carboxylic acid and/or a salt thereof (d1) is more preferred. Carboxylates are particularly preferred.
  • the carbon number of the carboxylic acid component of the carboxylic acid and/or the salt thereof (d1) is preferably equal to or greater than 1 but equal to or less than 30, more preferably equal to or greater than 3 but equal to or less than 30, and even more preferably equal to or greater than 5 but equal to or less than 28.
  • the carboxylic acid include aliphatic carboxylic acids (fatty acids) and aromatic carboxylic acids. Fatty acids and salts thereof are preferred.
  • the rubber composition may include a saturated fatty acid and/or a salt thereof, or may include an unsaturated fatty acid and/or a salt thereof.
  • the saturated fatty acid and the salt thereof are preferred.
  • fatty acids examples include butyric acid (C4), valeric acid (C5), caproic acid (C6), enanthic acid (C7), caprylic acid (C8), pelargonic acid (C9), capric acid (decanoic acid) (C10), lauric acid (C12), myristic acid (C14), myristoleic acid (C14), pentadecylic acid (C15), palmitic acid (C16), palmitoleic acid (C16), margaric acid (C17), stearic acid (C18), elaidic acid (C18), vaccenic acid (C18), oleic acid (C18), linolic acid (C18), linolenic acid (C18), 12-hydroxystearic acid (C18), arachidic acid (C20), gadoleic acid (C20), arachidonic acid (C20), eicosenoic acid (C20), behenic acid (C22), erucic acid (
  • aromatic carboxylic acid has an aromatic ring and a carboxyl group.
  • aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, hemimellitic acid (benzene-1,2,3-tricarboxylic acid), trimellitic acid (benzene-1,2,4-tricarboxylic acid), trimesic acid (benzene-1,3,5-tricarboxylic acid), mellophanic acid (benzene-1,2,3,4-tetracarboxylic acid), prehnitic acid (benzene-1,2,3,5-tetracarboxylic acid), pyromellitic acid (benzene-1,2,4,5-tetracarboxylic acid), mellitic acid (benzene hexacarboxylic acid), diphenic acid (biphenyl-2,2′-dicarboxylic acid), toluic acid (methylbenzoic acid), xylic acid, prehnitylic acid (2,3,
  • the rubber composition may include an aromatic carboxylate substituted with a hydroxyl group, an alkoxy group, or an oxo group.
  • this carboxylic acid can include salicylic acid (2-hydroxybenzoic acid), anisic acid (methoxybenzoic acid), cresotinic acid (hydroxy(methyl)benzoic acid), o-homosalicylic acid (2-hydroxy-3-methylbenzoic acid), m-homosalicylic acid (2-hydroxy-4-methylbenzoic acid), p-homosalicylic acid (2-hydroxy-5-methylbenzoic acid), o-pyrocatechuic acid (2,3-dihydroxybenzoic acid), ⁇ -resorcylic acid (2,4-dihydroxybenzoic acid), ⁇ -resorcylic acid (2,6-dihydroxybenzoic acid), protocatechuic acid (3,4-dihydroxybenzoic acid), ⁇ -resorcylic acid (3,5-dihydroxybenzoic acid), vanil
  • the cationic component of the carboxylate is a metal ion or an organic cation.
  • the metal ion include sodium ion, potassium ion, lithium ion, silver ion, magnesium ion, calcium ion, zinc ion, barium ion, cadmium ion, copper ion, cobalt ion, nickel ion, manganese ion, aluminum ion, iron ion, tin ion, zirconium ion, and titanium ion. Two or more types of ions may be used in combination.
  • the organic cation has a carbon chain.
  • Examples of the organic cation include organic ammonium ions.
  • Examples of organic ammonium ions include primary ammonium ions such as stearylammonium ion, hexylammonium ion, octylammonium ion, and 2-ethylhexylammonium ion; secondary ammonium ions such as dodecyl(lauryl)ammonium ion, and octadecyl(stearyl)ammonium ion; tertiary ammonium ions such as trioctylammonium ion; and quaternary ammonium ions such as dioctyldimethylammonium ion, and distearyldimethylammonium ion. Two or more types of organic cations may be used in combination.
  • preferable carboxylates include a potassium salt, a magnesium salt, an aluminum salt, a zinc salt, an iron salt, a copper salt, a nickel salt, or a cobalt salt of caprylic acid (octanoic acid), lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, or behenic acid.
  • Zinc salts of carboxylic acids are particularly preferred.
  • Specific examples of preferable carboxylates include zinc octoate, zinc laurate, zinc myristate, and zinc stearate.
  • a particularly preferable carboxylate is zinc octoate.
  • the amount of the acid and/or the salt (d) is preferably equal to or greater than 0.5 parts by weight, more preferably equal to or greater than 1.0 parts by weight, and particularly preferably equal to or greater than 2.0 parts by weight, per 100 parts by weight of the base rubber.
  • the amount is preferably equal to or less than 40 parts by weight, more preferably equal to or less than 30 parts by weight, and particularly preferably equal to or less than 20 parts by weight, per 100 parts by weight of the base rubber.
  • the weight ratio of the co-crosslinking agent (b) and the acid and/or the salt (d) in the rubber composition is preferably equal to or greater than 3/7 but equal to or less than 9/1, and is particularly preferably equal to or greater than 4/6 but equal to or less than 8/2. From the rubber composition in which this weight ratio is within the above range, the core 4 whose hardness linearly increases from its central point toward its surface can be obtained.
  • zinc acrylate is preferably used as the co-crosslinking agent (b).
  • Zinc acrylate whose surface is coated with stearic acid or zinc stearate for the purpose of improving dispersibility to rubber is present.
  • this coating material is not included in the concept of the acid and/or the salt (d).
  • the rubber composition preferably further includes an organic sulfur compound (e).
  • the organic sulfur compound (e) can contribute to control of: the linearity of the hardness distribution of the envelope layer 12 ; and the degree of the outer-hard/inner-soft structure.
  • An example of the organic sulfur compound (e) is an organic compound having a thiol group or a polysulfide linkage having 2 to 4 sulfur atoms. A metal salt of this organic compound is also included in the organic sulfur compound (e).
  • organic sulfur compound (e) examples include aliphatic compounds such as aliphatic thiols, aliphatic thiocarboxylic acids, aliphatic dithiocarboxylic acids, and aliphatic polysulfides; heterocyclic compounds; alicyclic compounds such as alicyclic thiols, alicyclic thiocarboxylic acids, alicyclic dithiocarboxylic acids, and alicyclic polysulfides; and aromatic compounds.
  • aliphatic compounds such as aliphatic thiols, aliphatic thiocarboxylic acids, aliphatic dithiocarboxylic acids, and aliphatic polysulfides
  • heterocyclic compounds such as alicyclic thiols, alicyclic thiocarboxylic acids, alicyclic dithiocarboxylic acids, and alicyclic polysulfides
  • aromatic compounds such as aliphatic thiols, aliphatic
  • organic sulfur compound (e) examples include thiophenols, thionaphthols, polysulfides, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, thiurams, dithiocarbamates, and thiazoles.
  • Preferable organic sulfur compounds (e) is at least one member selected from the group consisting of thiophenols, diphenyl disulfides, thionaphthols, thiuram disulfides, and metal salts thereof.
  • organic sulfur compound (e) are represented by the following chemical formulas (1) to (4).
  • R1 to R5 each represent H or a substituent.
  • R1 to R10 each represent H or a substituent.
  • R1 to R5 each represent H or a substituent, and M1 represents a monovalent metal atom.
  • R1 to R10 each represent H or a substituent
  • M2 represents a bivalent metal atom.
  • each substituent is at least one group selected from the group consisting of a halogen group (F, Cl, Br, I), an alkyl group, a carboxyl group (—COOH), an ester (—COOR) of a carboxyl group, a formyl group (—CHO), an acyl group (—COR), a carbonyl halide group (—COX), a sulfo group (—SO 3 H), an ester (—SO 3 R) of a sulfo group, a sulfonyl halide group (—SO 2 X), a sulfino group (—SO 2 H), an alkylsulfinyl group (—SOR), a carbamoyl group (—CONH 2 ), an alkyl halide group, a cyano group (—CN), and an alkoxy group (—OR).
  • a halogen group F, Cl, Br, I
  • an alkyl group a carboxyl group (
  • Examples of the organic sulfur compound represented by the chemical formula (1) include thiophenol; thiophenols substituted with halogen groups, such as 4-fluorothiophenol, 2,5-difluorothiophenol, 2,4,5-trifluorothiophenol, 2,4,5,6-tetrafluorothiophenol, pentafluorothiophenol, 2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol, 2,6-dichlorothiophenol, 2,4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol, pentachlorothiophenol, 4-bromothiophenol, 2,5-dibromothiophenol, 2,4,5-tribromothiophenol, 2,4,5,6-tetrabromothiophenol, pentabromothiophenol, 4-iodothiophenol, 2,5-diiodothiophenol, 2,4,5-trii
  • organic sulfur compound represented by the chemical formula (1) is a compound substituted with at least one type of the above substituents and another substituent.
  • substituents include a nitro group (—NO 2 ), an amino group (—NH 2 ), a hydroxyl group (—OH), and a phenylthio group (—SPh).
  • the compound include 4-chloro-2-nitrothiophenol, 4-chloro-2-aminothiophenol, 4-chloro-2-hydroxythiophenol, 4-chloro-2-phenylthiothiophenol, 4-methyl-2-nitrothiophenol, 4-methyl-2-aminothiophenol, 4-methyl-2-hydroxythiophenol, 4-methyl-2-phenylthiothiophenol, 4-carboxy-2-nitrothiophenol, 4-carboxy-2-aminothiophenol, 4-carboxy-2-hydroxythiophenol, 4-carboxy-2-phenylthiothiophenol, 4-methoxycarbonyl-2-nitrothiophenol, 4-methoxycarbonyl-2-aminothiophenol, 4-methoxycarbonyl-2-hydroxythiophenol, 4-methoxycarbonyl-2-phenylthiothiophenol, 4-formyl-2-nitrothiophenol, 4-formyl-2-aminothiophenol, 4-formyl-2-hydroxythiophenol, 4-formyl-2-phenylthiophenol
  • Still another example of the organic sulfur compound represented by the chemical formula (1) is a compound substituted with two or more types of substituents.
  • the compound include 4-acetyl-2-chlorothiophenol, 4-acetyl-2-methylthiophenol, 4-acetyl-2-carboxythiophenol, 4-acetyl-2-methoxycarbonylthiophenol, 4-acetyl-2-formylthiophenol, 4-acetyl-2-chlorocarbonylthiophenol, 4-acetyl-2-sulfothiophenol, 4-acetyl-2-methoxysulfonylthiophenol, 4-acetyl-2-chlorosulfonylthiophenol, 4-acetyl-2-sulfinothiophenol, 4-acetyl-2-methylsulfinylthiophenol, 4-acetyl-2-carbamoylthiophenol, 4-acetyl-2-trichloromethylthiophenol, 4-acetyl-2-cyano
  • Examples of the organic sulfur compound represented by the chemical formula (2) include diphenyl disulfide; diphenyl disulfides substituted with halogen groups, such as bis(4-fluorophenyl)disulfide, bis(2,5-difluorophenyl)disulfide, bis(2,4,5-trifluorophenyl)disulfide, bis(2,4,5,6-tetrafluorophenyl)disulfide, bis(pentafluorophenyl)disulfide, bis(4-chlorophenyl)disulfide, bis(2,5-dichlorophenyl)disulfide, bis(2,4,5-trichlorophenyl)disulfide, bis(2,4,5,6-tetrachlorophenyl)disulfide, bis(pentachlorophenyl)disulfide, bis(4-bromophenyl)disulfide, bis(2,5-
  • organic sulfur compound represented by the chemical formula (2) is a compound substituted with at least one type of the above substituents and another substituent.
  • substituents include a nitro group (—NO 2 ), an amino group (—NH 2 ), a hydroxyl group (—OH), and a phenylthio group (—SPh).
  • the compound include bis(4-chloro-2-nitrophenyl)disulfide, bis(4-chloro-2-aminophenyl)disulfide, bis(4-chloro-2-hydroxyphenyl)disulfide, bis(4-chloro-2-phenylthiophenyl)disulfide, bis(4-methyl-2-nitrophenyl)disulfide, bis(4-methyl-2-aminophenyl)disulfide, bis(4-methyl-2-hydroxyphenyl)disulfide, bis(4-methyl-2-phenylthiophenyl)disulfide, bis(4-carboxy-2-nitrophenyl)disulfide, bis(4-carboxy-2-aminophenyl)disulfide, bis(4-carboxy-2-hydroxyphenyl)disulfide, bis(4-carboxy-2-phenylthiophenyl)disulfide, bis
  • Still another example of the organic sulfur compound represented by the chemical formula (2) is a compound substituted with two or more types of substituents.
  • the compound include bis(4-acetyl-2-chlorophenyl)disulfide, bis(4-acetyl-2-methylphenyl)disulfide, bis(4-acetyl-2-carboxyphenyl)disulfide, bis(4-acetyl-2-methoxycarbonylphenyl)disulfide, bis(4-acetyl-2-formylphenyl)disulfide, bis(4-acetyl-2-chlorocarbonylphenyl)disulfide, bis(4-acetyl-2-sulfophenyl)disulfide, bis(4-acetyl-2-methoxysulfonylphenyl)disulfide, bis(4-acetyl-2-chlorosulfonylphenyl)d
  • Examples of the organic sulfur compound represented by the chemical formula (3) include thiophenol sodium salt; thiophenol sodium salts substituted with halogen groups, such as 4-fluorothiophenol sodium salt, 2,5-difluorothiophenol sodium salt, 2,4,5-trifluorothiophenol sodium salt, 2,4,5,6-tetrafluorothiophenol sodium salt, pentafluorothiophenol sodium salt, 4-chlorothiophenol sodium salt, 2,5-dichlorothiophenol sodium salt, 2,4,5-trichlorothiophenol sodium salt, 2,4,5,6-tetrachlorothiophenol sodium salt, pentachlorothiophenol sodium salt, 4-bromothiophenol sodium salt, 2,5-dibromothiophenol sodium salt, 2,4,5-tribromothiophenol sodium salt, 2,4,5,6-tetrabromothiophenol sodium salt, pentabromothiophenol sodium salt, 4-iodothiophenol sodium salt, 2,5-diiodothiophenol
  • organic sulfur compound represented by the chemical formula (3) is a compound substituted with at least one type of the above substituents and another substituent.
  • substituents include a nitro group (—NO 2 ), an amino group (—NH 2 ), a hydroxyl group (—OH), and a phenylthio group (—SPh).
  • the compound include 4-chloro-2-nitrothiophenol sodium salt, 4-chloro-2-aminothiophenol sodium salt, 4-chloro-2-hydroxythiophenol sodium salt, 4-chloro-2-phenylthiothiophenol sodium salt, 4-methyl-2-nitrothiophenol sodium salt, 4-methyl-2-aminothiophenol sodium salt, 4-methyl-2-hydroxythiophenol sodium salt, 4-methyl-2-phenylthiothiophenol sodium salt, 4-carboxy-2-nitrothiophenol sodium salt, 4-carboxy-2-aminothiophenol sodium salt, 4-carboxy-2-hydroxythiophenol sodium salt, 4-carboxy-2-phenylthiothiophenol sodium salt, 4-methoxycarbonyl-2-nitrothiophenol sodium salt, 4-methoxycarbonyl-2-aminothiophenol sodium salt, 4-methoxycarbonyl-2-hydroxythiophenol sodium salt, 4-methoxycarbonyl-2-phenylthiothiophenol sodium salt, 4-formyl-2-nitrothiophenol sodium salt,
  • Still another example of the organic sulfur compound represented by the chemical formula (3) is a compound substituted with two or more types of substituents.
  • the compound include 4-acetyl-2-chlorothiophenol sodium salt, 4-acetyl-2-methylthiophenol sodium salt, 4-acetyl-2-carboxythiophenol sodium salt, 4-acetyl-2-methoxycarbonylthiophenol sodium salt, 4-acetyl-2-formylthiophenol sodium salt, 4-acetyl-2-chlorocarbonylthiophenol sodium salt, 4-acetyl-2-sulfothiophenol sodium salt, 4-acetyl-2-methoxysulfonylthiophenol sodium salt, 4-acetyl-2-chlorosulfonylthiophenol sodium salt, 4-acetyl-2-sulfinothiophenol sodium salt, 4-acetyl-2-methylsulfinylthiophenol sodium salt, 4-acetyl-2-carbamoylthiophenol sodium salt, 4-
  • Examples of the organic sulfur compound represented by the chemical formula (4) include thiophenol zinc salt; thiophenol zinc salts substituted with halogen groups, such as 4-fluorothiophenol zinc salt, 2,5-difluorothiophenol zinc salt, 2,4,5-trifluorothiophenol zinc salt, 2,4,5,6-tetrafluorothiophenol zinc salt, pentafluorothiophenol zinc salt, 4-chlorothiophenol zinc salt, 2,5-dichlorothiophenol zinc salt, 2,4,5-trichlorothiophenol zinc salt, 2,4,5,6-tetrachlorothiophenol zinc salt, pentachlorothiophenol zinc salt, 4-bromothiophenol zinc salt, 2,5-dibromothiophenol zinc salt, 2,4,5-tribromothiophenol zinc salt, 2,4,5,6-tetrabromothiophenol zinc salt, pentabromothiophenol zinc salt, 4-iodothiophenol zinc salt, 2,5-diiodothio
  • organic sulfur compound represented by the chemical formula (4) is a compound substituted with at least one type of the above substituents and another substituent.
  • substituents include a nitro group (—NO 2 ), an amino group (—NH 2 ), a hydroxyl group (—OH), and a phenylthio group (—SPh).
  • the compound include 4-chloro-2-nitrothiophenol zinc salt, 4-chloro-2-aminothiophenol zinc salt, 4-chloro-2-hydroxythiophenol zinc salt, 4-chloro-2-phenylthiothiophenol zinc salt, 4-methyl-2-nitrothiophenol zinc salt, 4-methyl-2-aminothiophenol zinc salt, 4-methyl-2-hydroxythiophenol zinc salt, 4-methyl-2-phenylthiothiophenol zinc salt, 4-carboxy-2-nitrothiophenol zinc salt, 4-carboxy-2-aminothiophenol zinc salt, 4-carboxy-2-hydroxythiophenol zinc salt, 4-carboxy-2-phenylthiothiophenol zinc salt, 4-methoxycarbonyl-2-nitrothiophenol zinc salt, 4-methoxycarbonyl-2-aminothiophenol zinc salt, 4-methoxycarbonyl-2-hydroxythiophenol zinc salt, 4-methoxycarbonyl-2-phenylthiothiophenol zinc salt, 4-formyl-2-nitrothiophenol zinc salt,
  • Still another example of the organic sulfur compound represented by the chemical formula (4) is a compound substituted with two or more types of substituents.
  • the compound include 4-acetyl-2-chlorothiophenol zinc salt, 4-acetyl-2-methylthiophenol zinc salt, 4-acetyl-2-carboxythiophenol zinc salt, 4-acetyl-2-methoxycarbonylthiophenol zinc salt, 4-acetyl-2-formylthiophenol zinc salt, 4-acetyl-2-chlorocarbonylthiophenol zinc salt, 4-acetyl-2-sulfothiophenol zinc salt, 4-acetyl-2-methoxysulfonylthiophenol zinc salt, 4-acetyl-2-chlorosulfonylthiophenol zinc salt, 4-acetyl-2-sulfinothiophenol zinc salt, 4-acetyl-2-methylsulfinylthiophenol zinc salt, 4-acetyl-2-carbamoylthiophenol zinc salt,
  • Examples of the bivalent metal represented by M2 in the chemical formula (4) include zinc, magnesium, calcium, strontium, barium, titanium (II), manganese (II), iron (II), cobalt (II), nickel (II), zirconium (II), and tin (II).
  • thionaphthols examples include 2-thionaphthol, 1-thionaphthol, 2-chloro-1-thionaphthol, 2-bromo-1-thionaphthol, 2-fluoro-1-thionaphthol, 2-cyano-1-thionaphthol, 2-acetyl-1-thionaphthol, 1-chloro-2-thionaphthol, 1-bromo-2-thionaphthol, 1-fluoro-2-thionaphthol, 1-cyano-2-thionaphthol, 1-acetyl-2-thionaphthol, and metal salts thereof.
  • 1-thionaphthol, 2-thionaphthol, and zinc salts thereof are preferred.
  • Examples of sulfenamide type organic sulfur compounds include N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, and N-t-butyl-2-benzothiazole sulfenamide.
  • Examples of thiuram type organic sulfur compounds include tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, and dipentamethylenethiuram tetrasulfide.
  • dithiocarbamates include zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc ethylphenyldithiocarbamate, sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, copper (II) dimethyldithiocarbamate, iron (III) dimethyldithiocarbamate, selenium diethyldithiocarbamate, and tellurium diethyldithiocarbamate.
  • thiazole type organic sulfur compounds examples include 2-mercaptobenzothiazole (MBT); dibenzothiazyl disulfide (MBTS); a sodium salt, a zinc salt, a copper salt, or a cyclohexylamine salt of 2-mercaptobenzothiazole; 2-(2,4-dinitrophenyl) mercaptobenzothiazole; and 2-(2,6-diethyl-4-morpholinothio)benzothiazole
  • organic sulfur compounds (e) are 2-thionaphthol, bis(pentabromophenyl)disulfide, and 2,6-dichlorothiophenol.
  • the amount of the organic sulfur compound (e) is preferably equal to or greater than 0.05 parts by weight, more preferably equal to or greater than 0.1 parts by weight, and particularly preferably equal to or greater than 0.2 parts by weight, per 100 parts by weight of the base rubber.
  • the amount is preferably equal to or less than 5.0 parts by weight, more preferably equal to or less than 3.0 parts by weight, and particularly preferably equal to or less than 1.0 parts by weight, per 100 parts by weight of the base rubber.
  • a filler may be included in the envelope layer 12 .
  • suitable fillers include zinc oxide, barium sulfate, calcium carbonate, and magnesium carbonate.
  • the amount of the filler is determined as appropriate so that the intended specific gravity of the core 4 is accomplished.
  • a particularly preferable filler is zinc oxide. Zinc oxide serves not only as a specific gravity adjuster but also as a crosslinking activator.
  • an anti-aging agent a coloring agent, a plasticizer, a dispersant, sulfur, a vulcanization accelerator, and the like are added to the rubber composition of the envelope layer 12 .
  • Crosslinked rubber powder or synthetic resin powder may also be dispersed in the rubber composition.
  • the base rubber (a) is crosslinked by the co-crosslinking agent (b).
  • the heat of the crosslinking reaction remains near the central point of the core 4 .
  • the temperature at the central portion is high.
  • the temperature gradually decreases from the central point toward the surface.
  • the acid reacts with the metal salt of the co-crosslinking agent (b) to bond to cation.
  • the salt reacts with the metal salt of the co-crosslinking agent (b) to exchange cation. By the bonding and the exchange, metal crosslinks are broken.
  • the bonding and the exchange are likely to occur near the innermost portion of the envelope layer 12 where the temperature is high, and are unlikely to occur near the surface of the envelope layer 12 .
  • breaking of metal crosslinks is likely to occur near the innermost portion of the envelope layer 12 and is unlikely to occur near the surface of the envelope layer 12 .
  • the crosslinking density of the envelope layer 12 increases from its inside toward its outside.
  • the hardness linearly increases from its inside toward its outside.
  • the rubber composition includes the organic sulfur compound (e) together with the acid and/or the salt (d), the gradient of the hardness distribution can be controlled, and the degree of the outer-hard/inner-soft structure of the core 4 can be increased.
  • the hardness H(0.0) at the central point of the core 4 is preferably equal to or greater than 40.0 but equal to or less than 70.0.
  • the golf ball 2 having a hardness H(0.0) of 40.0 or greater has excellent resilience performance.
  • the hardness H(0.0) is more preferably equal to or greater than 45.0 and particularly preferably equal to or greater than 47.0.
  • an outer-hard/inner-soft structure can be achieved.
  • spin can be suppressed.
  • the hardness H(0.0) is more preferably equal to or less than 68.0 and particularly preferably equal to or less than 65.0.
  • the hardness Hs at the surface of the core 4 is preferably equal to or greater than 75.0 but equal to or less than 95.0.
  • an outer-hard/inner-soft structure can be achieved.
  • spin can be suppressed.
  • the hardness Hs is more preferably equal to or greater than 80.0 and particularly preferably equal to or greater than 82.0.
  • the golf ball 2 having a hardness Hs of 95.0 or less has excellent durability.
  • the hardness Hs is more preferably equal to or less than 94.0 and particularly preferably equal to or less than 92.0.
  • the core 4 preferably has a diameter of 38.0 mm or greater but 41.5 mm or less.
  • the core 4 having a diameter of 38.0 mm or greater can achieve excellent resilience performance of the golf ball 2 .
  • the diameter is more preferably equal to or greater than 38.5 mm and particularly preferably equal to or greater than 39.0 mm.
  • the inner cover 6 and the outer cover 8 can have sufficient thicknesses.
  • the golf ball 2 that includes the inner cover 6 and the outer cover 8 which have large thicknesses has excellent durability.
  • the diameter is more preferably equal to or less than 41.0 mm and particularly preferably equal to or less than 40.5 mm.
  • the core 4 has an amount of compressive deformation Dc of preferably 3.5 mm or greater and particularly preferably 3.8 mm or greater.
  • the amount of compressive deformation Dc is preferably equal to or less than 4.5 mm and particularly preferably equal to or less than 4.0 mm.
  • a resin composition is suitably used.
  • the base polymer of the resin composition include ionomer resins, polystyrenes, polyesters, polyamides, and polyolefins.
  • Particularly preferable base polymers are ionomer resins.
  • the golf ball 2 that includes the inner cover 6 including an ionomer resin has excellent resilience performance.
  • An ionomer resin and another resin may be used in combination for the inner cover 6 .
  • the principal component of the base polymer is preferably the ionomer resin.
  • the proportion of the ionomer resin to the entire base polymer is preferably equal to or greater than 50% by weight, more preferably equal to or greater than 60% by weight, and particularly preferably equal to or greater than 70% by weight.
  • preferable ionomer resins include binary copolymers formed with an ⁇ -olefin and an ⁇ , ⁇ -unsaturated carboxylic acid having 3 to 8 carbon atoms.
  • a preferable binary copolymer includes 80% by weight or greater but 90% by weight or less of an ⁇ -olefin, and 10% by weight or greater but 20% by weight or less of an ⁇ , ⁇ -unsaturated carboxylic acid.
  • the binary copolymer has excellent resilience performance.
  • Examples of other preferable ionomer resins include ternary copolymers formed with: an ⁇ -olefin; an ⁇ , ⁇ -unsaturated carboxylic acid having 3 to 8 carbon atoms; and an ⁇ , ⁇ -unsaturated carboxylate ester having 2 to 22 carbon atoms.
  • a preferable ternary copolymer includes 70% by weight or greater but 85% by weight or less of an ⁇ -olefin, 5% by weight or greater but 30% by weight or less of an ⁇ , ⁇ -unsaturated carboxylic acid, and 1% by weight or greater but 25% by weight or less of an ⁇ , ⁇ -unsaturated carboxylate ester.
  • the ternary copolymer has excellent resilience performance.
  • preferable ⁇ -olefins are ethylene and propylene, while preferable ⁇ , ⁇ -unsaturated carboxylic acids are acrylic acid and methacrylic acid.
  • Particularly preferable ionomer resins are a copolymer formed with ethylene and acrylic acid and a copolymer formed with ethylene and methacrylic acid.
  • some of the carboxyl groups are neutralized with metal ions.
  • metal ions for use in neutralization include sodium ion, potassium ion, lithium ion, zinc ion, calcium ion, magnesium ion, aluminum ion, and neodymium ion.
  • the neutralization may be carried out with two or more types of metal ions.
  • Particularly suitable metal ions in light 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 trade names
  • IOTEK 7010 du Pont de Nemours and Company; and trade names “IOTEK 7010”, “IOTEK 7030”, “IOTEK 7510”, “IOTEK 7520”, “IOTEK 8000”, and “IOTEK 8030”, manufactured by ExxonMobil Chemical Company.
  • Two or more ionomer resins may be used in combination for the inner cover 6 .
  • An ionomer resin neutralized with a monovalent metal ion, and an ionomer resin neutralized with a bivalent metal ion may be used in combination.
  • a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like are included in the resin composition of the inner cover 6 in an adequate amount.
  • the inner cover 6 preferably has a hardness Hi greater than the surface hardness Hs of the core 4 .
  • the difference (Hi ⁇ Hs) between the hardness Hi and the hardness Hs is preferably equal to or greater than 2, more preferably equal to or greater than 4, and particularly preferably equal to or greater than 6.
  • the hardness Hi is measured with a JIS-C type hardness scale mounted to an automated rubber hardness measurement machine (trade name “P1”, manufactured by Kobunshi Keiki Co., Ltd.).
  • a slab that is formed by hot press and that has a thickness of about 2 mm is used.
  • a slab kept at 23° C. for two weeks is used for the measurement.
  • three slabs are stacked.
  • a slab formed from the same resin composition as the resin composition of the inner cover 6 is used for the measurement.
  • the JIS-C hardness Hi of the inner cover 6 is preferably equal to or greater than 80, more preferably equal to or greater than 85, and particularly preferably equal to or greater than 90.
  • the hardness Hi is preferably equal to or less than 98 and particularly preferably equal to or less than 97.
  • the inner cover 6 preferably has a thickness Ti of 0.5 mm or greater but 1.6 mm or less.
  • the thickness Ti is particularly preferably equal to or greater than 0.7 mm.
  • the golf ball 2 that includes the inner cover 6 having a thickness Ti of 1.6 mm or less can include a large core 4 .
  • the large core 4 can contribute to the resilience performance of the golf ball 2 .
  • the thickness Ti is particularly preferably equal to or less than 1.2 mm.
  • a resin composition is suitably used.
  • the base polymer of the resin composition include ionomer resins, polystyrenes, polyesters, polyamides, and polyolefins.
  • Particularly preferable base polymers are ionomer resins.
  • the golf ball 2 that includes the outer cover 8 including an ionomer resin has excellent resilience performance.
  • An ionomer resin and another resin may be used in combination for the outer cover 8 .
  • the principal component of the base polymer is preferably the ionomer resin.
  • the proportion of the ionomer resin to the entire base polymer is preferably equal to or greater than 50% by weight, more preferably equal to or greater than 60% by weight, and particularly preferably equal to or greater than 70% by weight.
  • the outer cover 8 can include the ionomer resin described above for the inner cover 6 .
  • a preferable resin that can be used in combination with an ionomer resin is a styrene block-containing thermoplastic elastomer.
  • the styrene block-containing thermoplastic elastomer has excellent compatibility with ionomer resins.
  • a resin composition including the styrene block-containing thermoplastic elastomer has excellent fluidity.
  • the styrene block-containing thermoplastic elastomer includes a polystyrene block as a hard segment, and a soft segment.
  • a typical soft segment is a diene block.
  • Examples of compounds for the diene block include butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Butadiene and isoprene are preferred. Two or more compounds may be used in combination.
  • styrene block-containing thermoplastic elastomers examples include styrene-butadiene-styrene block copolymers (SBS), styrene-isoprene-styrene block copolymers (SIS), styrene-isoprene-butadiene-styrene block copolymers (SIBS), hydrogenated SBS, hydrogenated SIS, and hydrogenated SIBS.
  • hydrogenated SBS include styrene-ethylene-butylene-styrene block copolymers (SEBS).
  • hydrogenated SIS examples include styrene-ethylene-propylene-styrene block copolymers (SEPS).
  • SIBS styrene-ethylene-ethylene-propylene-styrene block copolymers
  • the content of the styrene component in the styrene block-containing thermoplastic elastomer is preferably equal to or greater than 10% by weight, more preferably equal to or greater than 12% by weight, and particularly preferably equal to or greater than 15% by weight.
  • 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.
  • styrene block-containing thermoplastic elastomers include an alloy of an olefin and one or more members selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS, and SEEPS.
  • the olefin component in the alloy is presumed to contribute to improvement of compatibility with ionomer resins. Use of this alloy improves the resilience performance of the golf ball 2 .
  • An olefin having 2 to 10 carbon atoms is preferably used. Examples of suitable olefins include ethylene, propylene, butene, and pentene. Ethylene and propylene are particularly preferred.
  • polymer alloys include trade names “Rabalon T3221C”, “Rabalon T3339C”, “Rabalon SJ4400N”, “Rabalon SJ5400N”, “Rabalon SJ6400N”, “Rabalon SJ7400N”, “Rabalon SJ8400N”, “Rabalon SJ9400N”, and “Rabalon SR04”, manufactured by Mitsubishi Chemical Corporation.
  • Other specific examples of styrene block-containing thermoplastic elastomers include trade name “Epofriend A1010” manufactured by Daicel Chemical Industries, Ltd., and trade name “Septon HG-252” manufactured by Kuraray Co., Ltd.
  • Another resin that can be used in combination with an ionomer resin is an ethylene-(meth) acrylic acid copolymer.
  • the copolymer is obtained by a copolymerization reaction of a monomer composition that contains ethylene and (meth) acrylic acid. In the copolymer, some of the carboxyl groups are neutralized with metal ions.
  • the copolymer includes 3% by weight or greater but 25% by weight or less of a (meth)acrylic acid component.
  • An ethylene-(meth) acrylic acid copolymer having a polar functional group is particularly preferred.
  • a specific example of ethylene-(meth) acrylic acid copolymers is trade name “NUCREL” manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.
  • a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like are included in the resin composition of the outer cover 8 in an adequate amount.
  • the outer cover 8 preferably has a JIS-C hardness Ho of 96 or less.
  • the hardness Ho is more preferably equal to or less than 94 and particularly preferably equal to or less than 92.
  • the hardness Ho is preferably equal to or greater than 70 and particularly preferably equal to or greater than 80.
  • the hardness Ho is measured by the same measurement method as that for the hardness Hi.
  • the hardness Ho of the outer cover 8 is less than the hardness Hi of the inner cover 6 .
  • the sphere consisting of the core 4 and the inner cover 6 becomes significantly distorted since the head speed is high. Since this sphere has an outer-hard/inner-soft structure, the spin rate is suppressed.
  • the hardness of the envelope layer 12 linearly changes.
  • the golf ball 2 is launched at a high speed due to deformation and restoration of the envelope layer 12 .
  • the suppression of the spin rate and the high launch speed achieve a large flight distance.
  • this sphere becomes less distorted since the head speed is low.
  • the behavior of the golf ball 2 mainly depends on the outer cover 8 . Since the outer cover 8 is flexible, a slip between the golf ball 2 and a clubface is suppressed. Due to the suppression of the slip, a high spin rate is obtained. The high spin rate achieves excellent controllability. In the golf ball 2 , both desired flight performance upon a shot with a driver and desired controllability upon a shot with a short iron are achieved.
  • the difference (Hi ⁇ Ho) between the hardness Hi of the inner cover 6 and the hardness Ho of the outer cover 8 is preferably equal to or greater than 1, more preferably equal to or greater than 2, and particularly preferably equal to or greater than 4.
  • the difference (Hi ⁇ Ho) is preferably equal to or less than 20.
  • the hardness Ho of the outer cover 8 may be less than the surface hardness Hs of the core 4 or may be greater than the surface hardness Hs of the core 4 .
  • the golf ball 2 in which the hardness Ho is less than the hardness Hs has particularly excellent controllability.
  • the golf ball 2 in which the hardness Ho is greater than the hardness Hs has particularly excellent flight performance.
  • the outer cover 8 has a thickness To of preferably 0.1 mm or greater and particularly preferably 0.2 mm or greater. In light of flight performance upon a shot with a driver, the thickness To is preferably equal to or less than 1.2 mm and particularly preferably equal to or less than 1.0 mm.
  • the outer cover 8 For forming the outer cover 8 , known methods such as injection molding, compression molding, and the like can be used. When forming the outer cover 8 , the dimples 14 are formed by pimples formed on the cavity face of a mold.
  • the sum (Ti+To) of the thickness Ti of the inner cover 6 and the thickness To of the outer cover 8 is preferably equal to or less than 2.5 mm, more preferably equal to or less than 2.3 mm, and particularly preferably equal to or less than 2.1 mm.
  • the sum (Ti+To) is preferably equal to or greater than 0.3 mm, more preferably equal to or greater than 0.5 mm, and particularly preferably equal to or greater than 0.8 mm.
  • the golf ball 2 has an amount of compressive deformation Db of preferably 2.2 mm or greater, more preferably 2.5 mm or greater, and particularly preferably 2.8 mm or greater.
  • the amount of compressive deformation Db is preferably equal to or less than 4.0 mm, more preferably equal to or less than 3.7 mm, and particularly preferably equal to or less than 3.4 mm.
  • a YAMADA type compression tester For measurement of the amount of compressive deformation, a YAMADA type compression tester is used. In the tester, a sphere such as the core 4 , the golf ball 2 , or the like is placed on a hard plate made of metal. Next, a cylinder made of metal gradually descends toward the sphere. The sphere, squeezed between the bottom face of the cylinder and the hard plate, becomes deformed. A migration distance of the cylinder, starting from the state in which an initial load of 98 N is applied to the sphere up to the state in which a final load of 1274 N is applied thereto, is measured.
  • the golf ball may include a center formed from a rubber composition that includes the acid and/or the salt (d); and an envelope layer formed from a rubber composition that does not include the acid and/or the salt (d).
  • the rubber composition of the center is the same as the rubber composition of the envelope layer 12 shown in FIG. 1 .
  • a hardness distribution of the center is appropriate.
  • the golf ball may include a center formed from a rubber composition that includes the acid and/or the salt (d); and an envelope layer formed from a rubber composition that includes the acid and/or the salt (d).
  • the rubber composition of the center is the same as the rubber composition of the envelope layer 12 shown in FIG. 1 .
  • the rubber composition of the envelope layer is the same as the rubber composition of the envelope layer 12 shown in FIG. 1 .
  • a hardness distribution of the center is appropriate.
  • a hardness distribution of the envelope layer is appropriate.
  • a golf ball 102 shown in FIG. 3 includes a spherical core 104 , an inner cover 106 positioned outside the core 104 , and an outer cover 108 positioned outside the inner cover 106 .
  • the core 104 includes a spherical center 110 and an envelope layer 112 positioned outside the center 110 .
  • On the surface of the outer cover 108 a large number of dimples 114 are formed.
  • a part other than the dimples 114 is a land 116 .
  • the golf ball 102 includes a paint layer and a mark layer on the external side of the outer cover 108 , but these layers are not shown in the drawing.
  • the golf ball 102 preferably has a diameter of 40 mm or greater but 45 mm or less. From the standpoint of conformity to the rules established by the United States Golf Association (USGA), the diameter is particularly preferably equal to or greater than 42.67 mm. In light of suppression of air resistance, the diameter is more preferably equal to or less than 44 mm and particularly preferably equal to or less than 42.80 mm.
  • the golf ball 102 preferably has a weight of 40 g or greater but 50 g or less. In light of attainment of great inertia, the weight is more preferably equal to or greater than 44 g and particularly preferably equal to or greater than 45.00 g. From the standpoint of conformity to the rules established by the USGA, the weight is particularly preferably equal to or less than 45.93 g.
  • a JIS-C hardness is measured at each measuring point based on the distance from the central point of the core 104 to the surface of the core 104 .
  • the distances from the central point of the core 104 to these measuring points are as follows.
  • Hardnesses at the first to twelfth points are measured by pressing a JIS-C type hardness scale against a cut plane of the core 104 that has been cut into two halves.
  • a hardness at the thirteenth point is measured by pressing the JIS-C type hardness scale against the surface of the spherical core 104 .
  • an automated rubber hardness measurement machine (trade name “P1”, manufactured by Kobunshi Keiki Co., Ltd.), to which this hardness scale is mounted, is used.
  • FIG. 4 is a line graph showing a hardness distribution of the envelope layer 112 of the golf ball 102 in FIG. 3 .
  • the horizontal axis of the graph indicates a distance (mm) from the central point of the core 104 .
  • the vertical axis of the graph indicates a JIS-C hardness.
  • the sixth point, the eighth point, and the tenth to thirteenth points among the points included in the envelope layer 112 are plotted.
  • FIG. 4 also shows a linear approximation curve obtained by a least-square method on the basis of the distance and the hardness of each measuring point.
  • the linear approximation curve is indicated by a dotted line.
  • the broken line does not greatly deviate from the linear approximation curve.
  • the broken line has a shape close to the linear approximation curve.
  • the hardness linearly increases from its inside toward its outside.
  • R 2 of the linear approximation curve for the envelope layer 112 which is obtained by the least-square method is preferably equal to or greater than 0.90.
  • R 2 is an index indicating the linearity of the broken line.
  • the shape of the broken line of the hardness distribution is close to a straight line.
  • the golf ball 102 that includes the envelope layer 112 for which R 2 is equal to or greater than 0.90 has excellent resilience performance.
  • R 2 is more preferably equal to or greater than 0.95 and particularly preferably equal to or greater than 0.97.
  • R 2 is calculated by squaring a correlation coefficient R.
  • the correlation coefficient R is calculated by dividing the covariance of the distance (mm) from the central point and the hardness (JIS-C) by the standard deviation of the distance (mm) from the central point and the standard deviation of the hardness (JIS-C).
  • the gradient a of the linear approximation curve is preferably equal to or greater than 0.30, more preferably equal to or greater than 0.33, and particularly preferably equal to or greater than 0.35.
  • a JIS-C hardness at a measuring point whose distance from the central point of the core 104 is x (mm) is represented by H(x).
  • the hardness at the central point of the core 104 is represented by H (0.0).
  • the JIS-C hardness at the surface of the core 104 is represented by Hs.
  • the difference (Hs ⁇ H(0.0)) between the surface hardness Hs and the central hardness H(0.0) is preferably equal to or greater than 15.
  • the core 104 in which the difference (Hs ⁇ H(0.0)) is equal to or greater than 15 has an outer-hard/inner-soft structure.
  • the recoil (torsional return) in the core 104 is great, and thus spin is suppressed.
  • the core 104 contributes to the flight performance of the golf ball 102 .
  • the difference (Hs ⁇ H(0.0)) is more preferably equal to or greater than 23 and particularly preferably equal to or greater than 24. From the standpoint that the core 104 can easily be formed, the difference (Hs ⁇ H(0.0)) is preferably equal to or less than 50.
  • the hardness gradually increases from its central point toward its surface.
  • the center 110 is formed by crosslinking a rubber composition.
  • base rubbers for use in the rubber composition include polybutadienes, polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-diene copolymers, and natural rubbers. Two or more rubbers may be used in combination. In light of resilience performance, polybutadienes are preferred, and high-cis polybutadienes are particularly preferred.
  • the rubber composition of the center 110 includes a co-crosslinking agent.
  • co-crosslinking agents in light of resilience performance include acrylic acid, methacrylic acid, zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate.
  • the rubber composition further includes a metal compound. Examples of the metal compound include magnesium oxide and zinc oxide.
  • the rubber composition includes an organic peroxide together with a co-crosslinking agent.
  • the rubber composition includes a sulfur compound.
  • the rubber composition includes an acid and/or a salt.
  • preferable acids and/or salts include zinc octoate, zinc laurate, zinc myristate, and zinc stearate.
  • various additives such as a filler, sulfur, a vulcanization accelerator, an anti-aging agent, a coloring agent, a plasticizer, a dispersant, and the like are included in the rubber composition of the center 110 in an adequate amount.
  • Synthetic resin powder or crosslinked rubber powder may also be included in the rubber composition.
  • the center 110 is preferably more flexible than the envelope layer 112 .
  • the center 110 can suppress spin.
  • the center 110 preferably has a diameter of 8 mm or greater but 20 mm or less.
  • spin can be suppressed.
  • the diameter is more preferably equal to or greater than 12 mm and particularly preferably equal to or greater than 14 mm.
  • the golf ball 102 that includes the center 110 having a diameter of 20 mm or less has excellent resilience performance even though the center 110 is flexible.
  • the diameter is more preferably equal to or less than 18 mm and particularly preferably equal to or less than 16 mm.
  • the envelope layer 112 is formed by crosslinking a rubber composition.
  • the rubber composition includes:
  • the rubber composition of the envelope layer 112 can include the base rubber (a) described above for the envelope layer 12 of the first embodiment.
  • Examples of preferable co-crosslinking agents (b) include:
  • (b2) a metal salt of an ⁇ , ⁇ -unsaturated carboxylic acid having 3 to 8 carbon atoms.
  • the rubber composition of the envelope layer 112 can include the co-crosslinking agent (b) described above for the envelope layer 12 of the first embodiment.
  • the metal salt (b2) of the ⁇ , ⁇ -unsaturated carboxylic acid graft-polymerizes with the molecular chain of the base rubber, thereby crosslinking the rubber molecules.
  • the rubber composition includes the ⁇ , ⁇ -unsaturated carboxylic acid (b1)
  • the rubber composition preferably further includes a metal compound (f).
  • the metal compound (f) reacts with the ⁇ , ⁇ -unsaturated carboxylic acid (b1) in the rubber composition.
  • a salt obtained by this reaction graft-polymerizes with the molecular chain of the base rubber.
  • the rubber composition of the envelope layer 112 can include the metal compound (f) described above for the envelope layer 12 of the first embodiment.
  • the amount of the co-crosslinking agent (b) is preferably equal to or greater than 15 parts by weight and particularly preferably equal to or greater than 20 parts by weight, per 100 parts by weight of the base rubber. In light of feel at impact, the amount is preferably equal to or less than 50 parts by weight, more preferably equal to or less than 45 parts by weight, and particularly preferably equal to or less than 40 parts by weight, per 100 parts by weight of the base rubber.
  • the rubber composition of the envelope layer 112 can include the crosslinking initiator (c) described above for the envelope layer 12 of the first embodiment.
  • the amount of the crosslinking initiator (c) is preferably equal to or greater than 0.2 parts by weight and particularly preferably equal to or greater than 0.5 parts by weight, per 100 parts by weight of the base rubber.
  • the amount is preferably equal to or less than 5.0 parts by weight and particularly preferably equal to or less than 2.5 parts by weight, per 100 parts by weight of the base rubber.
  • the acid component included in the acid and/or the salt (d) has reactivity with a cationic component.
  • the acid dissociates and reacts with the cationic component of the co-crosslinking agent (b). It is thought that within the envelope layer 112 , the acid inhibits formation of the metal crosslinks by the co-crosslinking agent (b).
  • the acid component included in the salt exchanges the cationic component with the co-crosslinking agent (b). It is inferred that during heating and forming of the envelope layer 112 , the salt breaks the metal crosslinks by the co-crosslinking agent (b).
  • the rubber composition of the envelope layer 112 can include the acid and/or the salt (d) described above for the envelope layer 12 of the first embodiment.
  • the co-crosslinking agent (b) is not included in the concept of the acid and/or the salt (d).
  • the amount of the acid and/or the salt (d) is preferably equal to or greater than 0.3 parts by weight, more preferably equal to or greater than 1.0 parts by weight, and particularly preferably equal to or greater than 2.0 parts by weight, per 100 parts by weight of the base rubber.
  • the amount is preferably equal to or less than 40 parts by weight, more preferably equal to or less than 30 parts by weight, and particularly preferably equal to or less than 20 parts by weight, per 100 parts by weight of the base rubber.
  • the weight ratio of the co-crosslinking agent (b) and the acid and/or the salt (d) in the rubber composition is preferably equal to or greater than 3/7 but equal to or less than 9/1, and is particularly preferably equal to or greater than 4/6 but equal to or less than 8/2. From the rubber composition in which this weight ratio is within the above range, the envelope layer 112 having an appropriate hardness distribution can be obtained.
  • zinc acrylate is preferably used as the co-crosslinking agent (b).
  • Zinc acrylate whose surface is coated with stearic acid or zinc stearate for the purpose of improving dispersibility to rubber is present.
  • the rubber composition includes this zinc acrylate, the stearic acid or zinc stearate coating the zinc acrylate is not included in the concept of the acid and/or the salt (d).
  • the rubber composition of the envelope layer 112 further includes the organic sulfur compound (e) described above for the envelope layer 12 of the first embodiment.
  • the organic sulfur compound (e) can contribute to control of: the linearity of the hardness distribution of the envelope layer 112 ; and the degree of the outer-hard/inner-soft structure.
  • the amount of the organic sulfur compound (e) is preferably equal to or greater than 0.05 parts by weight, more preferably equal to or greater than 0.1 parts by weight, and particularly preferably equal to or greater than 0.2 parts by weight, per 100 parts by weight of the base rubber.
  • the amount is preferably equal to or less than 5.0 parts by weight, more preferably equal to or less than 3.0 parts by weight, and particularly preferably equal to or less than 1.0 parts by weight, per 100 parts by weight of the base rubber.
  • a filler may be included in the envelope layer 112 .
  • suitable fillers include zinc oxide, barium sulfate, calcium carbonate, and magnesium carbonate.
  • the amount of the filler is determined as appropriate so that the intended specific gravity of the core 104 is accomplished.
  • a particularly preferable filler is zinc oxide. Zinc oxide serves not only as a specific gravity adjuster but also as a crosslinking activator.
  • an anti-aging agent a coloring agent, a plasticizer, a dispersant, sulfur, a vulcanization accelerator, and the like are added to the rubber composition of the envelope layer 112 .
  • Crosslinked rubber powder or synthetic resin powder may also be dispersed in the rubber composition.
  • the heat of a crosslinking reaction of the base rubber remains near the central point of the core 104 .
  • the temperature at the central portion is high.
  • the temperature gradually decreases from the central point toward the surface.
  • the acid and/or the salt (d) reacts with a metal salt of the co-crosslinking agent (b) to inhibit formation of metal crosslinks or break metal crosslinks, respectively.
  • This reaction is accelerated in a region where the temperature is high. In other words, inhibition of formation of metal crosslinks and breaking of metal crosslinks are likely to occur near the innermost portion of the envelope layer 112 where the temperature is high, and are unlikely to occur near the surface of the envelope layer 112 .
  • the crosslinking density of the envelope layer 112 increases from its inside toward its outside.
  • the hardness linearly increases from its inside toward its outside.
  • the rubber composition includes the organic sulfur compound (e) together with the acid and/or the salt (d)
  • the gradient of the hardness distribution can be controlled, and the degree of the outer-hard/inner-soft structure of the core 104 can be increased.
  • the hardness H(0.0) at the central point of the core 104 is preferably equal to or greater than 40.0 but equal to or less than 68.0.
  • the golf ball 102 having a hardness H(0.0) of 40.0 or greater has excellent resilience performance.
  • the hardness H(0.0) is more preferably equal to or greater than 45.0 and particularly preferably equal to or greater than 47.0.
  • an outer-hard/inner-soft structure can be achieved.
  • spin can be suppressed.
  • the hardness H(0.0) is more preferably equal to or less than 65.0 and particularly preferably equal to or less than 63.0.
  • the hardness Hs at the surface of the core 104 is preferably equal to or greater than 70.0 but equal to or less than 95.0.
  • the core 104 having a hardness Hs of 70.0 or greater an outer-hard/inner-soft structure can be achieved.
  • the golf ball 102 that includes the core 104 spin can be suppressed.
  • the hardness Hs is more preferably equal to or greater than 80.0 and particularly preferably equal to or greater than 82.0.
  • the golf ball 102 having a hardness Hs of 95.0 or less has excellent durability.
  • the hardness Hs is more preferably equal to or less than 94.0 and particularly preferably equal to or less than 92.0.
  • the core 104 preferably has a diameter of 38.0 mm or greater but 41.5 mm or less.
  • the core 104 having a diameter of 38.0 mm or greater can achieve excellent resilience performance of the golf ball 102 .
  • the diameter is more preferably equal to or greater than 38.5 mm and particularly preferably equal to or greater than 39.0 mm.
  • the inner cover 106 and the outer cover 108 can have sufficient thicknesses.
  • the golf ball 102 that includes the inner cover 106 and the outer cover 108 which have large thicknesses has excellent durability.
  • the diameter is more preferably equal to or less than 41.0 mm and particularly preferably equal to or less than 40.5 mm.
  • the core 104 has an amount of compressive deformation Dc of preferably 3.5 mm or greater and particularly preferably 3.8 mm or greater.
  • the amount of compressive deformation DC is preferably equal to or less than 4.5 mm and particularly preferably equal to or less than 4.0 mm.
  • a resin composition is suitably used.
  • the base polymer of the resin composition include ionomer resins, polystyrenes, polyesters, polyamides, and polyolefins.
  • Particularly preferable base polymers are ionomer resins.
  • the golf ball 102 that includes the inner cover 106 including an ionomer resin has excellent resilience performance.
  • An ionomer resin and another resin may be used in combination for the inner cover 106 .
  • the principal component of the base polymer is preferably the ionomer resin.
  • the proportion of the ionomer resin to the entire base polymer is preferably equal to or greater than 50% by weight, more preferably equal to or greater than 60% by weight, and particularly preferably equal to or greater than 70% by weight.
  • the inner cover 106 can include the ionomer resin described above for the golf ball 2 of the first embodiment.
  • the inner cover 106 can include the styrene block-containing thermoplastic elastomer described above for the golf ball 2 of the first embodiment.
  • the content of the styrene component in the styrene block-containing thermoplastic elastomer is preferably equal to or greater than 10% by weight, more preferably equal to or greater than 12% by weight, and particularly preferably equal to or greater than 15% by weight.
  • 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.
  • a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like are included in the resin composition of the inner cover 106 in an adequate amount.
  • the inner cover 106 has a JIS-C hardness Hi of preferably 65 or greater, more preferably 75 or greater, and particularly preferably 80 or greater.
  • the hardness Hi is preferably equal to or less than 95 and particularly preferably equal to or less than 90. The hardness Hi is measured by the method described above for the golf ball 2 of the first embodiment.
  • the JIS-C hardness Hi of the inner cover 106 may be less than the surface hardness Hs of the core 104 or may be greater than the surface hardness Hs of the core 104 .
  • the hardness Hi is greater than the hardness Hs, an outer-hard/inner-soft structure is achieved in the sphere consisting of the core 104 and the inner cover 106 .
  • the spin rate is low.
  • the golf ball 102 is hit with a high-number wood club, particularly excellent flight performance is exerted.
  • the outer-hard/inner-soft structure of the core 104 achieves further excellent flight performance.
  • the shock provided when the golf ball 102 is hit with a high-number wood club is alleviated by the inner cover 106 .
  • the feel at impact of the golf ball 102 is favorable.
  • the inner cover 106 preferably has a thickness Ti of 0.5 mm or greater but 1.6 mm or less.
  • the thickness Ti is particularly preferably equal to or greater than 0.7 mm.
  • the golf ball 102 that includes the inner cover 106 having a thickness Ti of 1.6 mm or less can include a large core 104 .
  • the large core 104 can contribute to the resilience performance of the golf ball 102 .
  • the thickness Ti is particularly preferably equal to or less than 1.2 mm.
  • a resin composition is suitably used.
  • the base polymer of the resin composition include ionomer resins, polystyrenes, polyesters, polyamides, and polyolefins.
  • Particularly preferable base polymers are ionomer resins.
  • the ionomer resin described above for the inner cover 106 can be used.
  • the golf ball 102 that includes the outer cover 108 including an ionomer resin has excellent resilience performance.
  • An ionomer resin and another resin may be used in combination for the outer cover 108 .
  • the principal component of the base polymer is preferably the ionomer resin.
  • the proportion of the ionomer resin to the entire base polymer is preferably equal to or greater than 50% by weight, more preferably equal to or greater than 60% by weight, and particularly preferably equal to or greater than 70% by weight.
  • the outer cover 108 can include the other resin described above for the inner cover 106 .
  • the outer cover 108 has a JIS-C hardness Ho greater than the hardness Hi of the inner cover 106 .
  • a great hardness Ho can be achieved.
  • a highly elastic resin in the resin composition a great hardness Ho may be achieved.
  • Specific examples of the highly elastic resin include polyamides.
  • a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like are included in the resin composition of the outer cover 108 in an adequate amount.
  • the hardness Ho of the outer cover 108 is preferably equal to or greater than 83, more preferably equal to or greater than 84, and particularly preferably equal to or greater than 85.
  • the hardness Ho is preferably equal to or less than 96, more preferably equal to or less than 95, and particularly preferably equal to or less than 93.
  • the hardness Ho is measured by the same measurement method as that for the hardness Hi.
  • the hardness Ho of the outer cover 108 is greater than the hardness Hi of the inner cover 106 .
  • the sphere consisting of the core 104 and the inner cover 106 becomes significantly distorted since the head speed is high. Since this sphere has an outer-hard/inner-soft structure, the spin rate is suppressed.
  • the hardness of the envelope layer 112 linearly changes. Thus, the golf ball 102 is launched at a high speed due to deformation and restoration of the envelope layer 112 . The suppression of the spin rate and the high launch speed achieve a large flight distance.
  • the difference (Ho ⁇ Hi) between the hardness Ho of the outer cover 108 and the hardness Hi of the inner cover 106 is preferably equal to or greater than 2, more preferably equal to or greater than 4, and particularly preferably equal to or greater than 6.
  • the difference (Ho ⁇ Hi) is preferably equal to or less than 30.
  • the hardness Ho of the outer cover 108 is preferably greater than the surface hardness Hs of the core 104 .
  • the difference (Ho ⁇ Hs) between the hardness Ho and the hardness Hs is preferably equal to or greater than 2, more preferably equal to or greater than 6, and particularly preferably equal to or greater than 8.
  • the difference (Ho ⁇ Hs) is preferably equal to or less than 30.
  • the outer cover 108 has a thickness To of preferably 0.1 mm or greater and particularly preferably 0.2 mm or greater. In light of flight performance, the thickness To is preferably equal to or less than 1.4 mm and particularly preferably equal to or less than 1.2 mm.
  • the outer cover 108 For forming the outer cover 108 , known methods such as injection molding, compression molding, and the like can be used. When forming the outer cover 108 , the dimples 114 are formed by pimples formed on the cavity face of a mold.
  • the sum (Ti+To) of the thickness Ti of the inner cover 106 and the thickness To of the outer cover 108 is preferably equal to or less than 2.5 mm, more preferably equal to or less than 2.3 mm, and particularly preferably equal to or less than 2.1 mm.
  • the sum (Ti+To) is preferably equal to or greater than 0.3 mm, more preferably equal to or greater than 0.5 mm, and particularly preferably equal to or greater than 0.8 mm.
  • the golf ball 102 has an amount of compressive deformation Db of preferably 2.2 mm or greater, more preferably 2.5 mm or greater, and particularly preferably 2.8 mm or greater.
  • the amount of compressive deformation Db is preferably equal to or less than 4.0 mm, more preferably equal to or less than 3.7 mm, and particularly preferably equal to or less than 3.4 mm.
  • the amount of compressive deformation is measured by the method described above for the golf ball 2 of the first embodiment.
  • the golf ball may include a center formed from a rubber composition that includes the acid and/or the salt (d); and an envelope layer formed from a rubber composition that does not include the acid and/or the salt (d).
  • the rubber composition of the center is the same as the rubber composition of the envelope layer 112 shown in FIG. 3 . A hardness distribution of the center is appropriate.
  • the golf ball may include a center formed from a rubber composition that includes the acid and/or the salt (d); and an envelope layer formed from a rubber composition that includes the acid and/or the salt (d).
  • the rubber composition of the center is the same as the rubber composition of the envelope layer 112 shown in FIG. 3 .
  • the rubber composition of the envelope layer is the same as the rubber composition of the envelope layer 112 shown in FIG. 3 .
  • a hardness distribution of the center is appropriate.
  • a hardness distribution of the envelope layer is appropriate.
  • a golf ball 202 shown in FIG. 5 includes a spherical core 204 , an inner cover 206 positioned outside the core 204 , amid cover 208 positioned outside the inner cover 206 , and an outer cover 210 positioned outside the mid cover 208 .
  • the core 204 includes a spherical center 212 and an envelope layer 214 positioned outside the center 212 .
  • On the surface of the outer cover 210 a large number of dimples 216 are formed. Of the surface of the golf ball 202 , a part other than the dimples 216 is a land 218 .
  • the golf ball 202 includes a paint layer and a mark layer on the external side of the outer cover 210 , but these layers are not shown in the drawing.
  • the golf ball 202 preferably has a diameter of 40 mm or greater but 45 mm or less. From the standpoint of conformity to the rules established by the United States Golf Association (USGA), the diameter is particularly preferably equal to or greater than 42.67 mm. In light of suppression of air resistance, the diameter is more preferably equal to or less than 44 mm and particularly preferably equal to or less than 42.80 mm.
  • the golf ball 202 preferably has a weight of 40 g or greater but 50 g or less. In light of attainment of great inertia, the weight is more preferably equal to or greater than 44 g and particularly preferably equal to or greater than 45.00 g. From the standpoint of conformity to the rules established by the USGA, the weight is particularly preferably equal to or less than 45.93 g.
  • a JIS-C hardness is measured at each measuring point based on the distance from the central point of the core 204 to the surface of the core 204 .
  • the distances from the central point of the core 204 to these measuring points are as follows.
  • Hardnesses at the first to twelfth points are measured by pressing a JIS-C type hardness scale against a cut plane of the core 204 that has been cut into two halves.
  • a hardness at the thirteenth point is measured by pressing the JIS-C type hardness scale against the surface of the spherical core 204 .
  • an automated rubber hardness measurement machine (trade name “P1”, manufactured by Kobunshi Keiki Co., Ltd.), to which this hardness scale is mounted, is used.
  • FIG. 6 is a line graph showing a hardness distribution of the envelope layer 214 of the golf ball 202 in FIG. 5 .
  • the horizontal axis of the graph indicates a distance (mm) from the central point of the core 204 .
  • the vertical axis of the graph indicates a JIS-C hardness.
  • the sixth point, the eighth point, and the tenth to thirteenth points among the points included in the envelope layer 214 are plotted.
  • FIG. 6 also shows a linear approximation curve obtained by a least-square method on the basis of the distance and the hardness of each measuring point.
  • the linear approximation curve is indicated by a dotted line.
  • the broken line does not greatly deviate from the linear approximation curve.
  • the broken line has a shape close to the linear approximation curve.
  • the hardness linearly increases from its inside toward its outside.
  • R 2 of the linear approximation curve for the envelope layer 214 which is obtained by the least-square method is preferably equal to or greater than 0.95.
  • R 2 is an index indicating the linearity of the broken line.
  • the shape of the broken line of the hardness distribution is close to a straight line.
  • the golf ball 202 that includes the envelope layer 214 for which R 2 is equal to or greater than 0.95 has excellent resilience performance.
  • R 2 is more preferably equal to or greater than 0.97 and particularly preferably equal to or greater than 0.99.
  • R 2 is calculated by squaring a correlation coefficient R.
  • the correlation coefficient R is calculated by dividing the covariance of the distance (mm) from the central point and the hardness (JIS-C) by the standard deviation of the distance (mm) from the central point and the standard deviation of the hardness
  • the gradient a of the linear approximation curve is preferably equal to or greater than 1.10, more preferably equal to or greater than 1.50, and particularly preferably equal to or greater than 1.70.
  • a JIS-C hardness at a measuring point whose distance from the central point of the core 204 is x (mm) is represented by H(x).
  • the hardness at the central point of the core 204 is represented by H(0.0).
  • the JIS-C hardness at the surface of the core 204 is represented by Hs.
  • the difference (Hs ⁇ H(0.0)) between the surface hardness Hs and the central hardness H(0.0) is preferably equal to or greater than 15.
  • the core 204 in which the difference (Hs ⁇ H(0.0)) is equal to or greater than 15 has an outer-hard/inner-soft structure.
  • the recoil (torsional return) in the core 204 is great, and thus spin is suppressed.
  • the core 204 contributes to the flight performance of the golf ball 202 .
  • the difference (Hs ⁇ H(0.0)) is more preferably equal to or greater than 23 and particularly preferably equal to or greater than 24. From the standpoint that the core 204 can easily be formed, the difference (Hs ⁇ H(0.0)) is preferably equal to or less than 50.
  • the hardness gradually increases from its central point toward its surface.
  • the center 212 is formed by crosslinking a rubber composition.
  • base rubbers for use in the rubber composition include polybutadienes, polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-diene copolymers, and natural rubbers. Two or more rubbers may be used in combination. In light of resilience performance, polybutadienes are preferred, and high-cis polybutadienes are particularly preferred.
  • the rubber composition of the center 212 includes a co-crosslinking agent.
  • co-crosslinking agents in light of resilience performance include acrylic acid, methacrylic acid, zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate.
  • the rubber composition further includes a metal compound.
  • the metal compound include magnesium oxide and zinc oxide.
  • the rubber composition includes an organic peroxide together with a co-crosslinking agent.
  • the rubber composition includes a sulfur compound.
  • the rubber composition may include an acid and/or a salt.
  • various additives such as a filler, sulfur, a vulcanization accelerator, an anti-aging agent, a coloring agent, a plasticizer, a dispersant, and the like are included in the rubber composition of the center 212 in an adequate amount.
  • Synthetic resin powder or crosslinked rubber powder may also be included in the rubber composition.
  • the center 212 is preferably more flexible than the envelope layer 214 .
  • the center 212 can suppress spin.
  • the center 212 preferably has a diameter of 8 mm or greater but 24 mm or less.
  • spin can be suppressed.
  • the diameter is more preferably equal to or greater than 12 mm and particularly preferably equal to or greater than 14 mm.
  • the golf ball 202 that includes the center 212 having a diameter of 24 mm or less has excellent resilience performance even though the center 212 is flexible.
  • the diameter is more preferably equal to or less than 18 mm and particularly preferably equal to or less than 16 mm.
  • the envelope layer 214 is formed by crosslinking a rubber composition.
  • the rubber composition includes:
  • the rubber composition of the envelope layer 214 can include the base rubber (a) described above for the envelope layer 12 of the first embodiment.
  • Examples of preferable co-crosslinking agents (b) include:
  • (b2) a metal salt of an ⁇ , ⁇ -unsaturated carboxylic acid having 3 to 8 carbon atoms.
  • the rubber composition of the envelope layer 214 can include the co-crosslinking agent (b) described above for the envelope layer 12 of the first embodiment.
  • the metal salt (b2) of the ⁇ , ⁇ -unsaturated carboxylic acid graft-polymerizes with the molecular chain of the base rubber, thereby crosslinking the rubber molecules.
  • the rubber composition includes the ⁇ , ⁇ -unsaturated carboxylic acid (b1)
  • the rubber composition preferably further includes a metal compound (f).
  • the metal compound (f) reacts with the ⁇ , ⁇ -unsaturated carboxylic acid (b1) in the rubber composition.
  • a salt obtained by this reaction graft-polymerizes with the molecular chain of the base rubber.
  • the rubber composition of the envelope layer 214 can include the metal compound (f) described above for the envelope layer 12 of the first embodiment.
  • the amount of the co-crosslinking agent (b) is preferably equal to or greater than 15 parts by weight and particularly preferably equal to or greater than 20 parts by weight, per 100 parts by weight of the base rubber. In light of feel at impact, the amount is preferably equal to or less than 50 parts by weight, more preferably equal to or less than 45 parts by weight, and particularly preferably equal to or less than 40 parts by weight, per 100 parts by weight of the base rubber.
  • the crosslinking initiator (c) is preferably an organic peroxide.
  • the organic peroxide contributes to the resilience performance of the golf ball 202 .
  • the rubber composition of the envelope layer 214 can include the crosslinking initiator (c) described above for the envelope layer 12 of the first embodiment.
  • the amount of the crosslinking initiator (c) is preferably equal to or greater than 0.2 parts by weight and particularly preferably equal to or greater than 0.5 parts by weight, per 100 parts by weight of the base rubber. In light of feel at impact and durability of the golf ball 202 , the amount is preferably equal to or less than 5.0 parts by weight and particularly preferably equal to or less than 2.5 parts by weight, per 100 parts by weight of the base rubber.
  • the rubber composition of the envelope layer 214 can include the acid and/or the salt (d) described above for the envelope layer 12 of the first embodiment.
  • the acid component included in the acid and/or the salt (d) has reactivity with a cationic component.
  • the acid dissociates and reacts with the cationic component of the co-crosslinking agent (b). It is thought that within the envelope layer 214 , the acid inhibits formation of the metal crosslinks by the co-crosslinking agent (b).
  • the acid component included in the salt exchanges the cationic component with the co-crosslinking agent (b).
  • the salt breaks the metal crosslinks by the co-crosslinking agent (b).
  • the co-crosslinking agent (b) is not included in the concept of the acid and/or the salt (d).
  • the amount of the acid and/or the salt (d) is preferably equal to or greater than 0.5 parts by weight, more preferably equal to or greater than 1.0 parts by weight, and particularly preferably equal to or greater than 2.0 parts by weight, per 100 parts by weight of the base rubber.
  • the amount is preferably equal to or less than 40 parts by weight, more preferably equal to or less than 30 parts by weight, and particularly preferably equal to or less than 20 parts by weight, per 100 parts by weight of the base rubber.
  • the weight ratio of the co-crosslinking agent (b) and the acid and/or the salt (d) in the rubber composition is preferably equal to or greater than 3/7 but equal to or less than 9/1, and is particularly preferably equal to or greater than 4/6 but equal to or less than 8/2. From the rubber composition in which this weight ratio is within the above range, the core 204 having an appropriate hardness distribution can be obtained.
  • zinc acrylate is preferably used as the co-crosslinking agent (b).
  • Zinc acrylate whose surface is coated with stearic acid or zinc stearate for the purpose of improving dispersibility to rubber is present.
  • the rubber composition includes this zinc acrylate, the stearic acid or zinc stearate coating the zinc acrylate is not included in the concept of the acid and/or the salt (d).
  • the rubber composition of the envelope layer 214 further includes the organic sulfur compound (e) described above for the envelope layer 12 of the first embodiment.
  • the organic sulfur compound (e) can contribute to control of: the linearity of the hardness distribution of the envelope layer 214 ; and the degree of the outer-hard/inner-soft structure.
  • the amount of the organic sulfur compound (e) is preferably equal to or greater than 0.05 parts by weight, more preferably equal to or greater than 0.1 parts by weight, and particularly preferably equal to or greater than 0.2 parts by weight, per 100 parts by weight of the base rubber.
  • the amount is preferably equal to or less than 5.0 parts by weight, more preferably equal to or less than 3.0 parts by weight, and particularly preferably equal to or less than 1.0 parts by weight, per 100 parts by weight of the base rubber.
  • a filler may be included in the envelope layer 214 .
  • suitable fillers include zinc oxide, barium sulfate, calcium carbonate, and magnesium carbonate.
  • the amount of the filler is determined as appropriate so that the intended specific gravity of the core 204 is accomplished.
  • a particularly preferable filler is zinc oxide. Zinc oxide serves not only as a specific gravity adjuster but also as a crosslinking activator.
  • an anti-aging agent a coloring agent, a plasticizer, a dispersant, sulfur, a vulcanization accelerator, and the like are added to the rubber composition of the envelope layer 214 .
  • Crosslinked rubber powder or synthetic resin powder may also be dispersed in the rubber composition.
  • the heat of a crosslinking reaction remains near the central point of the core 204 .
  • the temperature at the central portion is high.
  • the temperature gradually decreases from the central point toward the surface.
  • the acid and/or the salt (d) reacts with a metal salt of the co-crosslinking agent (b) to inhibit formation of metal crosslinks or break metal crosslinks, respectively.
  • This reaction is accelerated in a region where the temperature is high. In other words, inhibition of formation of metal crosslinks and breaking of metal crosslinks are likely to occur near the innermost portion of the envelope layer 214 where the temperature is high, and are unlikely to occur near the surface of the envelope layer 214 .
  • the crosslinking density of the envelope layer 214 increases from its inside toward its outside.
  • the hardness linearly increases from its inside toward its outside.
  • the rubber composition includes the organic sulfur compound (e) together with the acid and/or the salt (d)
  • the gradient of the hardness distribution can be controlled, and the degree of the outer-hard/inner-soft structure of the core 204 can be increased.
  • the hardness H(0.0) at the central point of the core 204 is preferably equal to or greater than 40.0 but equal to or less than 68.0.
  • the golf ball 202 having a hardness H(0.0) of 40.0 or greater has excellent resilience performance.
  • the hardness H(0.0) is more preferably equal to or greater than 45.0 and particularly preferably equal to or greater than 47.0.
  • an outer-hard/inner-soft structure can be achieved.
  • the hardness H(0.0) is more preferably equal to or less than 65.0 and particularly preferably equal to or less than 63.0.
  • the hardness Hs at the surface of the core 204 is preferably equal to or greater than 70.0 but equal to or less than 95.0.
  • an outer-hard/inner-soft structure can be achieved.
  • spin can be suppressed.
  • the hardness Hs is more preferably equal to or greater than 80.0 and particularly preferably equal to or greater than 82.0.
  • the golf ball 202 having a hardness Hs of 95.0 or less has excellent durability.
  • the hardness Hs is more preferably equal to or less than 94.0 and particularly preferably equal to or less than 92.0.
  • the core 204 preferably has a diameter of 34.0 mm or greater but 39.0 mm or less.
  • the core 204 having a diameter of 34.0 mm or greater can achieve excellent resilience performance of the golf ball 202 .
  • the diameter is more preferably equal to or greater than 35.0 mm and particularly preferably equal to or greater than 35.5 mm.
  • the inner cover 206 and the outer cover 210 can have sufficient thicknesses.
  • the golf ball 202 that includes the inner cover 206 and the outer cover 210 which have large thicknesses has excellent durability.
  • the diameter is more preferably equal to or less than 38.0 mm and particularly preferably equal to or less than 37.5 mm.
  • the core 204 has an amount of compressive deformation Dc of preferably 3.5 mm or greater and particularly preferably 3.8 mm or greater.
  • the amount of compressive deformation DC is preferably equal to or less than 4.5 mm and particularly preferably equal to or less than 4.0 mm.
  • a resin composition is suitably used.
  • the base polymer of the resin composition include ionomer resins, polystyrenes, polyesters, polyamides, and polyolefins.
  • Particularly preferable base polymers are ionomer resins.
  • the golf ball 202 that includes the inner cover 206 including an ionomer resin has excellent resilience performance.
  • An ionomer resin and another resin may be used in combination for the inner cover 206 .
  • the principal component of the base polymer is preferably the ionomer resin.
  • the proportion of the ionomer resin to the entire base polymer is preferably equal to or greater than 50% by weight, more preferably equal to or greater than 60% by weight, and particularly preferably equal to or greater than 70% by weight.
  • the inner cover 206 can include the ionomer resin described above for the golf ball 2 of the first embodiment.
  • the inner cover 206 can include the styrene block-containing thermoplastic elastomer described above for the golf ball 2 of the first embodiment.
  • a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like are included in the resin composition of the inner cover 206 in an adequate amount.
  • the inner cover 206 has a JIS-C hardness Hi of preferably 70 or greater, more preferably 72 or greater, and particularly preferably 74 or greater.
  • the hardness Hi is preferably equal to or less than 94, more preferably equal to or less than 93, and particularly preferably equal to or less than 92.
  • the hardness Hi is measured by the method described above for the golf ball 2 of the first embodiment.
  • the JIS-C hardness Hi of the inner cover 206 is greater than the surface hardness Hs of the core 204 .
  • the difference (Hi ⁇ Hs) between the hardness Hi and the hardness Hs is equal to or greater than 1.
  • the difference (Hi ⁇ Hs) is equal to or greater than 1
  • an outer-hard/inner-soft structure is achieved in the sphere consisting of the core 204 and the inner cover 206 .
  • the difference (Hi ⁇ Hs) is more preferably equal to or greater than 3 and particularly preferably equal to or greater than 5.
  • the inner cover 206 preferably has a thickness Ti of 0.5 mm or greater but 1.6 mm or less.
  • the thickness Ti is particularly preferably equal to or greater than 0.7 mm.
  • the golf ball 202 that includes the inner cover 206 having a thickness Ti of 1.6 mm or less can include a large core 204 .
  • the large core 204 can contribute to the resilience performance of the golf ball 202 .
  • the thickness Ti is particularly preferably equal to or less than 1.2 mm.
  • a resin composition is suitably used.
  • the base polymer of the resin composition include ionomer resins, polystyrenes, polyesters, polyamides, and polyolefins.
  • Particularly preferable base polymers are ionomer resins.
  • the ionomer resin described above for the inner cover 206 can be used.
  • the golf ball 202 that includes the mid cover 208 including an ionomer resin has excellent resilience performance.
  • An ionomer resin and another resin may be used in combination for the mid cover 208 .
  • the principal component of the base polymer is preferably the ionomer resin.
  • the proportion of the ionomer resin to the entire base polymer is preferably equal to or greater than 60% by weight, more preferably equal to or greater than 70% by weight, and particularly preferably equal to or greater than 80% by weight.
  • the mid cover 208 can include the other resin described above for the inner cover 206 .
  • the mid cover 208 preferably has a JIS-C hardness Hm greater than the hardness Hi of the inner cover 206 .
  • Hm JIS-C hardness
  • the highly elastic resin include polyamides.
  • a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like are included in the resin composition of the mid cover 208 in an adequate amount.
  • the hardness Hm is preferably equal to or greater than 70, more preferably equal to or greater than 72, and particularly preferably equal to or greater than 74. In light of feel at impact, the hardness Hm is preferably equal to or less than 94, more preferably equal to or less than 93, and particularly preferably equal to or less than 92. The hardness Hm is measured by the same measurement method as that for the hardness Hi.
  • the JIS-C hardness Hm of the mid cover 208 is greater than the surface hardness Hs of the core 204 .
  • the golf ball 202 that includes the sphere exerts excellent flight performance.
  • the hardness Hm is greater than the hardness Hi of the inner cover 206 .
  • the hardness Hm is greater than the hardness Hi, an outer-hard/inner-soft structure is achieved in the sphere consisting of the core 204 , the inner cover 206 , and the mid cover 208 .
  • the difference (Hm ⁇ Hi) between the hardness Hm and the hardness Hi is preferably equal to or greater than 2 and more preferably equal to or greater than 4. In light of durability, the difference (Hm ⁇ Hi) is preferably equal to or less than 20.
  • the mid cover 208 preferably has a thickness Tm of 0.5 mm or greater but 1.6 mm or less.
  • the thickness Tm is particularly preferably equal to or greater than 0.7 mm.
  • the golf ball 202 that includes the mid cover 208 having a thickness Tm of 1.6 m or less can include a large core 204 .
  • the large core 204 can contribute to the resilience performance of the golf ball 202 .
  • the thickness Tm is particularly preferably equal to or less than 1.2 mm.
  • a resin composition is suitably used.
  • the base polymer of the resin composition include ionomer resins, polystyrenes, polyesters, polyamides, and polyolefins.
  • Particularly preferable base polymers are ionomer resins.
  • the ionomer resin described above for the inner cover 206 can be used.
  • the golf ball 202 that includes the outer cover 210 including an ionomer resin has excellent resilience performance.
  • An ionomer resin and another resin may be used in combination for the outer cover 210 .
  • the principal component of the base polymer is preferably the ionomer resin.
  • the proportion of the ionomer resin to the entire base polymer is preferably equal to or greater than 50% by weight, more preferably equal to or greater than 60% by weight, and particularly preferably equal to or greater than 70% by weight.
  • the outer cover 210 can include the other resin described above for the inner cover 206 .
  • Another resin that can be used in combination with an ionomer resin is an ethylene-(meth)acrylic acid copolymer.
  • the copolymer is obtained by a copolymerization reaction of a monomer composition that contains ethylene and (meth)acrylic acid. In the copolymer, some of the carboxyl groups are neutralized with metal ions.
  • the copolymer includes 3% by weight or greater but 25% by weight or less of a (meth)acrylic acid component.
  • An ethylene-(meth) acrylic acid copolymer having a polar functional group is particularly preferred.
  • a specific example of ethylene-(meth)acrylic acid copolymers is trade name “NUCREL” manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.
  • the outer cover 210 preferably has a JIS-C hardness Ho greater than the hardness Hm of the mid cover 208 .
  • the resin composition of the outer cover 210 may include a highly elastic resin.
  • Specific examples of the highly elastic resin include polyamides.
  • a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like are included in the resin composition of the outer cover 210 in an adequate amount.
  • the hardness Ho of the outer cover 210 is preferably equal to or greater than 80, more preferably equal to or greater than 82, and particularly preferably equal to or greater than 84.
  • the hardness Ho is preferably equal to or less than 96, more preferably equal to or less than 95, and particularly preferably equal to or less than 93.
  • the hardness Ho is measured by the same measurement method as that for the hardness Hi.
  • the hardness Ho of the outer cover 210 is greater than the hardness Hi of the inner cover 206 .
  • the spin rate is low.
  • the flight distance of the golf ball 202 is large.
  • the difference (Ho ⁇ Hi) between the hardness Ho of the outer cover 210 and the hardness Hi of the inner cover 206 is preferably equal to or greater than 2, more preferably equal to or greater than 4, and particularly preferably equal to or greater than 6. In light of durability, the difference (Ho ⁇ Hi) is preferably equal to or less than 20.
  • the hardness Ho of the outer cover 210 is preferably greater than the hardness Hm of the mid cover 208 .
  • Ho is greater than the hardness Hi, an outer-hard/inner-soft structure of the entire ball is achieved in the golf ball 202 consisting of the core 204 , the inner cover 206 , the mid cover 208 , and the outer cover 210 .
  • the golf ball 202 is hit with a middle iron, a large flight distance is achieved.
  • the difference (Ho ⁇ Hm) between the hardness Ho of the outer cover 210 and the hardness Hm of the mid cover 208 is preferably equal to or greater than 3 and particularly preferably equal to or greater than 6. In light of durability, the difference (Ho ⁇ Hm) is preferably equal to or less than 20.
  • the outer cover 210 has a thickness To of preferably 0.1 mm or greater and particularly preferably 0.2 mm or greater. In light of flight performance, the thickness To is preferably equal to or less than 1.4 mm and particularly preferably equal to or less than 1.2 mm.
  • the outer cover 210 For forming the outer cover 210 , known methods such as injection molding, compression molding, and the like can be used. When forming the outer cover 210 , the dimples 216 are formed by pimples formed on the cavity face of a mold.
  • the sum (Ti+Tm+To) of the thickness Ti, the thickness Tm, and the thickness To is preferably equal to or less than 4.0 mm, more preferably equal to or less than 3.9 mm, and particularly preferably equal to or less than 3.5 mm.
  • the sum (Ti+Tm+To) is preferably equal to or greater than 0.3 mm, more preferably equal to or greater than 0.5 mm, and particularly preferably equal to or greater than 0.8 mm.
  • the golf ball 202 has an amount of compressive deformation Db of preferably 2.2 mm or greater, more preferably 2.5 mm or greater, and particularly preferably 2.8 mm or greater.
  • the amount of compressive deformation Db is preferably equal to or less than 4.0 mm, more preferably equal to or less than 3.7 mm, and particularly preferably equal to or less than 3.4 mm.
  • the amount of compressive deformation is measured by the method described above for the golf ball 2 of the first embodiment.
  • the golf ball may include a center formed from a rubber composition that includes the acid and/or the salt (d); and an envelope layer formed from a rubber composition that does not include the acid and/or the salt (d).
  • the rubber composition of the center is the same as the rubber composition of the envelope layer 214 shown in FIG. 5 . A hardness distribution of the center is appropriate.
  • the golf ball may include a center formed from a rubber composition that includes the acid and/or the salt (d); and an envelope layer formed from a rubber composition that includes the acid and/or the salt (d).
  • the rubber composition of the center is the same as the rubber composition of the envelope layer 214 shown in FIG. 5 .
  • the rubber composition of the envelope layer is the same as the rubber composition of the envelope layer 214 shown in FIG. 5 .
  • a hardness distribution of the center is appropriate.
  • a hardness distribution of the envelope layer is appropriate.
  • a golf ball 302 shown in FIG. 7 includes a spherical core 304 , an inner cover 306 positioned outside the core 304 , a mid cover 308 positioned outside the inner cover 306 , and an outer cover 310 positioned outside the mid cover 308 .
  • the core 304 includes a spherical center 312 and an envelope layer 314 positioned outside the center 312 .
  • On the surface of the outer cover 310 a large number of dimples 316 are formed. Of the surface of the golf ball 302 , a part other than the dimples 316 is a land 318 .
  • the golf ball 302 includes a paint layer and a mark layer on the external side of the outer cover 310 , but these layers are not shown in the drawing.
  • the golf ball 302 preferably has a diameter of 40 mm or greater but 45 mm or less. From the standpoint of conformity to the rules established by the United States Golf Association (USGA), the diameter is particularly preferably equal to or greater than 42.67 mm. In light of suppression of air resistance, the diameter is more preferably equal to or less than 44 mm and particularly preferably equal to or less than 42.80 mm.
  • the golf ball 302 preferably has a weight of 40 g or greater but 50 g or less. In light of attainment of great inertia, the weight is more preferably equal to or greater than 44 g and particularly preferably equal to or greater than 45.00 g. From the standpoint of conformity to the rules established by the USGA, the weight is particularly preferably equal to or less than 45.93 g.
  • a JIS-C hardness is measured at each measuring point based on the distance from the central point of the core 304 to the surface of the core 304 .
  • the distances from the central point of the core 304 to these measuring points are as follows.
  • Hardnesses at the first to twelfth points are measured by pressing a JIS-C type hardness scale against a cut plane of the core 304 that has been cut into two halves.
  • a hardness at the thirteenth point is measured by pressing the JIS-C type hardness scale against the surface of the spherical core 304 .
  • an automated rubber hardness measurement machine (trade name “P1”, manufactured by Kobunshi Keiki Co., Ltd.), to which this hardness scale is mounted, is used.
  • FIG. 8 is a line graph showing a hardness distribution of the envelope layer 314 of the golf ball 302 in FIG. 7 .
  • the horizontal axis of the graph indicates a distance (mm) from the central point of the core 304 .
  • the vertical axis of the graph indicates a JIS-C hardness.
  • the sixth point, the eighth point, and the tenth to thirteenth points among the points included in the envelope layer 314 are plotted.
  • FIG. 8 also shows a linear approximation curve obtained by a least-square method on the basis of the distance and the hardness of each measuring point.
  • the linear approximation curve is indicated by a dotted line. In FIG. 8 , the broken line does not greatly deviate from the linear approximation curve.
  • the broken line has a shape close to the linear approximation curve.
  • the hardness linearly increases from its inside toward its outside.
  • the energy loss is low in the envelope layer 314 .
  • the flight distance is large.
  • R 2 of the linear approximation curve for the envelope layer 314 which is obtained by the least-square method is preferably equal to or greater than 0.94.
  • R 2 is an index indicating the linearity of the broken line.
  • the shape of the broken line of the hardness distribution is close to a straight line.
  • the golf ball 302 that includes the envelope layer 314 for which R 2 is equal to or greater than 0.94 has excellent resilience performance.
  • R 2 is more preferably equal to or greater than 0.97 and particularly preferably equal to or greater than 0.99.
  • R 2 is calculated by squaring a correlation coefficient R.
  • the correlation coefficient R is calculated by dividing the covariance of the distance (mm) from the central point and the hardness (JIS-C) by the standard deviation of the distance (mm) from the central point and the standard deviation of the hardness (JIS-C).
  • the gradient ⁇ of the linear approximation curve is preferably equal to or greater than 0.70, more preferably equal to or greater than 1.10, and particularly preferably equal to or greater than 1.40.
  • a JIS-C hardness at a measuring point whose distance from the central point of the core 204 is x (mm) is represented by H(x).
  • the hardness at the central point of the core 304 is represented by H(0.0).
  • the JIS-C hardness at the surface of the core 304 is represented by Hs.
  • the difference (Hs ⁇ H(0.0)) between the surface hardness Hs and the central hardness H(0.0) is preferably equal to or greater than 15.
  • the core 304 in which the difference (Hs ⁇ H(0.0)) is equal to or greater than 15 has an outer-hard/inner-soft structure.
  • the recoil (torsional return) in the core 304 is great, and thus spin is suppressed.
  • the core 304 contributes to the flight performance of the golf ball 302 .
  • the difference (Hs ⁇ H(0.0)) is more preferably equal to or greater than 23 and particularly preferably equal to or greater than 24. From the standpoint that the core 304 can easilybe formed, the difference (Hs ⁇ H(0.0)) is preferably equal to or less than 50.
  • the hardness gradually increases from its central point toward its surface.
  • the center 312 is formed by crosslinking a rubber composition.
  • base rubbers for use in the rubber composition include polybutadienes, polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-diene copolymers, and natural rubbers. Two or more rubbers may be used in combination. In light of resilience performance, polybutadienes are preferred, and high-cis polybutadienes are particularly preferred.
  • the rubber composition of the center 312 includes a co-crosslinking agent.
  • co-crosslinking agents in light of resilience performance include acrylic acid, methacrylic acid, zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate.
  • the rubber composition further includes a metal compound.
  • the metal compound include magnesium oxide and zinc oxide.
  • the rubber composition includes an organic peroxide together with a co-crosslinking agent.
  • the rubber composition includes a sulfur compound.
  • the rubber composition may include an acid and/or a salt.
  • various additives such as a filler, sulfur, a vulcanization accelerator, an anti-aging agent, a coloring agent, a plasticizer, a dispersant, and the like are included in the rubber composition of the center 312 in an adequate amount.
  • Synthetic resin powder or crosslinked rubber powder may also be included in the rubber composition.
  • the center 312 is preferably more flexible than the envelope layer 314 .
  • the center 312 can suppress spin.
  • the center 312 preferably has a diameter of 8 mm or greater but 24 mm or less.
  • spin can be suppressed.
  • the diameter is more preferably equal to or greater than 12 mm and particularly preferably equal to or greater than 14 mm.
  • the golf ball 302 that includes the center 312 having a diameter of 24 mm or less has excellent resilience performance even though the center 312 is flexible.
  • the diameter is more preferably equal to or less than 18 mm and particularly preferably equal to or less than 16 mm.
  • the envelope layer 314 is formed by crosslinking a rubber composition.
  • the rubber composition includes:
  • the rubber composition of the envelope layer 314 can include the base rubber (a) described above for the envelope layer 12 of the first embodiment.
  • Examples of preferable co-crosslinking agents (b) include
  • (b2) a metal salt of an ⁇ , ⁇ -unsaturated carboxylic acid having 3 to 8 carbon atoms.
  • the rubber composition of the envelope layer 314 can include the co-crosslinking agent (b) described above for the envelope layer 12 of the first embodiment.
  • the metal salt (b2) of the ⁇ , ⁇ -unsaturated carboxylic acid graft-polymerizes with the molecular chain of the base rubber, thereby crosslinking the rubber molecules.
  • the rubber composition includes the ⁇ , ⁇ -unsaturated carboxylic acid (b1)
  • the rubber composition preferably further includes a metal compound (f).
  • the metal compound (f) reacts with the ⁇ , ⁇ -unsaturated carboxylic acid (b1) in the rubber composition.
  • a salt obtained by this reaction graft-polymerizes with the molecular chain of the base rubber.
  • the rubber composition of the envelope layer 314 can include the metal compound (f) described above for the envelope layer 12 of the first embodiment.
  • the amount of the co-crosslinking agent (b) is preferably equal to or greater than 15 parts by weight and particularly preferably equal to or greater than 20 parts by weight, per 100 parts by weight of the base rubber. In light of feel at impact, the amount is preferably equal to or less than 50 parts by weight, more preferably equal to or less than 45 parts by weight, and particularly preferably equal to or less than 40 parts by weight, per 100 parts by weight of the base rubber.
  • the rubber composition of the envelope layer 314 can include the crosslinking initiator (c) described above for the envelope layer 12 of the first embodiment.
  • the amount of the crosslinking initiator (c) is preferably equal to or greater than 0.2 parts by weight and particularly preferably equal to or greater than 0.5 parts by weight, per 100 parts by weight of the base rubber.
  • the amount is preferably equal to or less than 5.0 parts by weight and particularly preferably equal to or less than 2.5 parts by weight, per 100 parts by weight of the base rubber.
  • the acid component included in the acid and/or the salt (d) has reactivity with a cationic component.
  • the acid dissociates and reacts with the cationic component of the co-crosslinking agent (b). It is thought that within the envelope layer 314 , the acid inhibits formation of the metal crosslinks by the co-crosslinking agent (b).
  • the acid component included in the salt exchanges the cationic component with the co-crosslinking agent (b). It is inferred that during heating and forming of the envelope layer 314 , the salt breaks the metal crosslinks by the co-crosslinking agent (b).
  • the rubber composition of the envelope layer 314 can include the acid and/or the salt (d) described above for the envelope layer 12 of the first embodiment.
  • the co-crosslinking agent (b) is not included in the concept of the acid and/or the salt (d).
  • the amount of the acid and/or the salt (d) is preferably equal to or greater than 1.0 parts by weight, more preferably equal to or greater than 2.0 parts by weight, and particularly preferably equal to or greater than 3.0 parts by weight, per 100 parts by weight of the base rubber.
  • the amount is preferably equal to or less than 40 parts by weight, more preferably equal to or less than 30 parts by weight, and particularly preferably equal to or less than 20 parts by weight, per 100 parts by weight of the base rubber.
  • the weight ratio of the co-crosslinking agent (b) and the acid and/or the salt (d) in the rubber composition is preferably equal to or greater than 3/7 but equal to or less than 9/1, and is particularly preferably equal to or greater than 4/6 but equal to or less than 8/2. From the rubber composition in which this weight ratio is within the above range, the core 304 having an appropriate hardness distribution can be obtained.
  • zinc acrylate is preferably used as the co-crosslinking agent (b).
  • Zinc acrylate whose surface is coated with stearic acid or zinc stearate for the purpose of improving dispersibility to rubber is present.
  • the rubber composition includes this zinc acrylate, the stearic acid or zinc stearate coating the zinc acrylate is not included in the concept of the acid and/or the salt (d).
  • the rubber composition of the envelope layer 314 further includes the organic sulfur compound (e) described above for the envelope layer 12 of the first embodiment.
  • the organic sulfur compound (e) can contribute to control of: the linearity of the hardness distribution of the envelope layer 314 ; and the degree of the outer-hard/inner-soft structure.
  • the amount of the organic sulfur compound (e) is preferably equal to or greater than 0.05 parts by weight, more preferably equal to or greater than 0.1 parts by weight, and particularly preferably equal to or greater than 0.2 parts by weight, per 100 parts by weight of the base rubber.
  • the amount is preferably equal to or less than 5.0 parts by weight, more preferably equal to or less than 3.0 parts by weight, and particularly preferably equal to or less than 1.0 parts by weight, per 100 parts by weight of the base rubber.
  • a filler may be included in the envelope layer 314 .
  • suitable fillers include zinc oxide, barium sulfate, calcium carbonate, and magnesium carbonate.
  • the amount of the filler is determined as appropriate so that the intended specific gravity of the core 304 is accomplished.
  • a particularly preferable filler is zinc oxide. Zinc oxide serves not only as a specific gravity adjuster but also as a crosslinking activator.
  • an anti-aging agent a coloring agent, a plasticizer, a dispersant, sulfur, a vulcanization accelerator, and the like are added to the rubber composition of the envelope layer 314 .
  • Crosslinked rubber powder or synthetic resin powder may also be dispersed in the rubber composition.
  • the heat of a crosslinking reaction remains near the central point of the core 304 .
  • the temperature at the central portion is high.
  • the temperature gradually decreases from the central point toward the surface.
  • the acid and/or the salt (d) reacts with a metal salt of the co-crosslinking agent (b) to inhibit formation of metal crosslinks or break metal crosslinks, respectively.
  • This reaction is accelerated in a region where the temperature is high. In other words, inhibition of formation of metal crosslinks and breaking of metal crosslinks are likely to occur near the innermost portion of the envelope layer 314 where the temperature is high, and are unlikely to occur near the surface of the envelope layer 314 .
  • the crosslinking density of the envelope layer 314 increases from its inside toward its outside.
  • the hardness linearly increases from its inside toward its outside.
  • the rubber composition includes the organic sulfur compound (e) together with the acid and/or the salt (d)
  • the gradient of the hardness distribution can be controlled, and the degree of the outer-hard/inner-soft structure of the core 304 can be increased.
  • the hardness H(0.0) at the central point of the core 304 is preferably equal to or greater than 40.0 but equal to or less than 68.0.
  • the golf ball 302 having a hardness H(0.0) of 40.0 or greater has excellent resilience performance.
  • the hardness H(0.0) is more preferably equal to or greater than 45.0 and particularly preferably equal to or greater than 47.0.
  • an outer-hard/inner-soft structure can be achieved.
  • spin can be suppressed.
  • the hardness H(0.0) is more preferably equal to or less than 65.0 and particularly preferably equal to or less than 63.0.
  • the hardness Hs at the surface of the core 304 is preferably equal to or greater than 70.0 but equal to or less than 95.0.
  • an outer-hard/inner-soft structure can be achieved.
  • spin can be suppressed.
  • the hardness Hs is more preferably equal to or greater than 80.0 and particularly preferably equal to or greater than 82.0.
  • the golf ball 302 having a hardness Hs of 95.0 or less has excellent durability.
  • the hardness Hs is more preferably equal to or less than 94.0 and particularly preferably equal to or less than 92.0.
  • the core 304 preferably has a diameter of 34.0 mm or greater but 39.0 mm or less.
  • the core 304 having a diameter of 34.0 mm or greater can achieve excellent resilience performance of the golf ball 302 .
  • the diameter is more preferably equal to or greater than 35.0 mm and particularly preferably equal to or greater than 35.5 mm.
  • the inner cover 306 and the outer cover 310 can have sufficient thicknesses.
  • the golf ball 302 that includes the inner cover 306 and the outer cover 310 which have large thicknesses has excellent durability.
  • the diameter is more preferably equal to or less than 38.0 mm and particularly preferably equal to or less than 37.5 mm.
  • the core 304 has an amount of compressive deformation Dc of preferably 3.5 mm or greater and particularly preferably 3.8 mm or greater.
  • the amount of compressive deformation DC is preferably equal to or less than 4.5 mm and particularly preferably equal to or less than 4.0 mm.
  • a resin composition is suitably used.
  • the base polymer of the resin composition include ionomer resins, polystyrenes, polyesters, polyamides, and polyolefins.
  • Particularly preferable base polymers are ionomer resins.
  • the golf ball 302 that includes the inner cover 306 including an ionomer resin has excellent resilience performance.
  • An ionomer resin and another resin may be used in combination for the inner cover 306 .
  • the principal component of the base polymer is preferably the ionomer resin.
  • the proportion of the ionomer resin to the entire base polymer is preferably equal to or greater than 50% by weight, more preferably equal to or greater than 52% by weight, and particularly preferably equal to or greater than 64% by weight.
  • the resin composition of the inner cover 306 can include the ionomer resin described above for the golf ball 2 of the first embodiment.
  • the resin composition of the inner cover 306 can include the styrene block-containing thermoplastic elastomer described above for the golf ball 2 of the first embodiment.
  • a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like are included in the resin composition of the inner cover 306 in an adequate amount.
  • the inner cover 306 has a JIS-C hardness Hi of preferably 60 or greater, more preferably 62 or greater, and particularly preferably 64 or greater.
  • the hardness Hi is preferably equal to or less than 90, more preferably equal to or less than 88, and particularly preferably equal to or less than 86.
  • the hardness Hi is measured by the method described above for the golf ball 2 of the first embodiment.
  • the difference (Hi ⁇ Hs) between the JIS-C hardness Hi of the inner cover 306 and the hardness Hs is less than 1. If the difference (Hi ⁇ Hs) is less than 1, the feel at impact is soft when the golf ball 302 is hit with a driver. In light of intensity of the feel at impact which a golf player obtains when hitting, the difference (Hi ⁇ Hs) is preferably equal to or greater than ⁇ 15 and further preferably equal to or greater than ⁇ 10.
  • the inner cover 306 preferably has a thickness Ti of 0.5 mm or greater but 1.6 mm or less.
  • the sphere that includes the inner cover 306 having a thickness Ti of 0.5 mm or greater has excellent feel at impact.
  • the thickness Ti is particularly preferably equal to or greater than 0.7 mm.
  • the golf ball 302 that includes the inner cover 306 having a thickness Ti of 1.6 mm or less can include a large core 304 .
  • the large core 304 can contribute to the resilience performance of the golf ball 302 .
  • the thickness Ti is particularly preferably equal to or less than 1.2 mm.
  • a resin composition is suitably used.
  • the base polymer of the resin composition include ionomer resins, polystyrenes, polyesters, polyamides, and polyolefins.
  • Particularly preferable base polymers are ionomer resins.
  • the ionomer resin described above for the inner cover 306 can be used.
  • the golf ball 302 that includes the mid cover 308 including an ionomer resin has excellent resilience performance.
  • An ionomer resin and another resin may be used in combination for the mid cover 308 .
  • the principal component of the base polymer is preferably the ionomer resin.
  • the proportion of the ionomer resin to the entire base polymer is preferably equal to or greater than 60% by weight, more preferably equal to or greater than 70% by weight, and particularly preferably equal to or greater than 80% by weight.
  • the mid cover 308 can include the other resin described above for the inner cover 306 .
  • the mid cover 308 preferably has a JIS-C hardness Hm greater than the hardness Hi of the inner cover 306 .
  • Hm JIS-C hardness
  • the highly elastic resin include polyamides.
  • a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like are included in the resin composition of the mid cover 308 in an adequate amount.
  • the hardness Hm is preferably equal to or greater than 50, more preferably equal to or greater than 60, and particularly preferably equal to or greater than 68. In light of feel at impact, the hardness Hm is preferably equal to or less than 95, more preferably equal to or less than 92, and particularly preferably equal to or less than 91. The hardness Hm is measured by the same measurement method as that for the hardness Hi.
  • the hardness Hm is preferably greater than the hardness Hi of the inner cover 306 .
  • the shock by a hit with a driver is alleviated.
  • the difference (Hm ⁇ Hi) between the hardness Hm and the hardness Hi is preferably equal to or greater than 6 and more preferably equal to or greater than 10. In light of durability, the difference (Hm ⁇ Hi) is preferably equal to or less than 20.
  • the mid cover 308 preferably has a thickness Tm of 0.5 mm or greater but 1.6 mm or less.
  • the sphere that includes the mid cover 308 having a thickness Tm of 0.5 mm or greater has excellent durability.
  • the thickness Tm is particularly preferably equal to or greater than 0.7 mm.
  • the golf ball 302 that includes the mid cover 308 having a thickness Tm of 1.6 m or less can include a large core 304 .
  • the large core 304 can contribute to the resilience performance of the golf ball 302 .
  • the thickness Tm is particularly preferably equal to or less than 1.2 mm.
  • a resin composition is suitably used.
  • the base polymer of the resin composition include ionomer resins, polystyrenes, polyesters, polyamides, and polyolefins.
  • Particularly preferable base polymers are ionomer resins.
  • the ionomer resin described above for the inner cover 306 can be used.
  • the golf ball 302 that includes the outer cover 310 including an ionomer resin has excellent resilience performance.
  • An ionomer resin and another resin may be used in combination for the outer cover 310 .
  • the principal component of the base polymer is preferably the ionomer resin.
  • the proportion of the ionomer resin to the entire base polymer is preferably equal to or greater than 50% by weight, more preferably equal to or greater than 60% by weight, and particularly preferably equal to or greater than 70% by weight.
  • the outer cover 310 can include the other resin described above for the inner cover 306 .
  • Another resin that can be used in combination with an ionomer resin is an ethylene-(meth) acrylic acid copolymer.
  • the copolymer is obtained by a copolymerization reaction of a monomer composition that contains ethylene and (meth) acrylic acid. In the copolymer, some of the carboxyl groups are neutralized with metal ions.
  • the copolymer includes 3% by weight or greater but 25% by weight or less of a (meth)acrylic acid component.
  • An ethylene-(meth) acrylic acid copolymer having a polar functional group is particularly preferred.
  • a specific example of ethylene-(meth) acrylic acid copolymers is trade name “NUCREL” manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.
  • the outer cover 310 preferably has a JIS-C hardness Ho greater than the hardness Hm of the mid cover 308 .
  • the resin composition of the outer cover 310 may include a highly elastic resin.
  • Specific examples of the highly elastic resin include polyamides.
  • a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like are included in the resin composition of the outer cover 310 in an adequate amount.
  • the hardness Ho of the outer cover 310 is preferably equal to or greater than 80, more preferably equal to or greater than 82, and particularly preferably equal to or greater than 84.
  • the hardness Ho is preferably equal to or less than 96, more preferably equal to or less than 95, and particularly preferably equal to or less than 93.
  • the hardness Ho is measured by the same measurement method as that for the hardness Hi.
  • the hardness Ho of the outer cover 310 is greater than the hardness Hi of the inner cover 306 .
  • the difference (Ho ⁇ Hi) between the hardness Ho of the outer cover 310 and the hardness Hi of the inner cover 306 is preferably equal to or greater than 5, more preferably equal to or greater than 9, and particularly preferably equal to or greater than 15. In light of durability, the difference (Ho ⁇ Hi) is preferably equal to or less than 30.
  • the hardness Ho of the outer cover 310 is preferably greater than the hardness Hm of the mid cover 308 .
  • the hardness increases from its central portion to its surface. In the entirety of the golf ball 302 , an outer-hard/inner-soft structure is achieved. When the golf ball 302 is hit, the flight distance is large.
  • the difference (Ho ⁇ Hm) between the hardness Ho of the outer cover 310 and the hardness Hm of the mid cover 308 is preferably equal to or greater than 3 and particularly preferably equal to or greater than 7. In light of durability, the difference (Ho ⁇ Hm) is preferably equal to or less than 25.
  • the outer cover 310 has a thickness To of preferably 0.1 mm or greater and particularly preferably 0.2 mm or greater. In light of flight performance, the thickness To is preferably equal to or less than 1.4 mm and particularly preferably equal to or less than 1.2 mm.
  • the outer cover 310 For forming the outer cover 310 , known methods such as injection molding, compression molding, and the like can be used. When forming the outer cover 310 , the dimples 316 are formed by pimples formed on the cavity face of a mold.
  • the sum (Ti+Tm+To) of the thickness Ti, the thickness Tm, and the thickness To is preferably equal to or less than 4.0 mm, more preferably equal to or less than 3.9 mm, and particularly preferably equal to or less than 3.5 mm.
  • the sum (Ti+Tm+To) is preferably equal to or greater than 0.3 mm, more preferably equal to or greater than 0.5 mm, and particularly preferably equal to or greater than 0.8 mm.
  • the golf ball 302 has an amount of compressive deformation Db of preferably 2.2 mm or greater, more preferably 2.5 mm or greater, and particularly preferably 2.8 mm or greater.
  • the amount of compressive deformation Db is preferably equal to or less than 4.0 mm, more preferably equal to or less than 3.7 mm, and particularly preferably equal to or less than 3.4 mm.
  • the amount of compressive deformation is measured by the method described above for the golf ball 2 of the first embodiment.
  • the golf ball may include a center formed from a rubber composition that includes the acid and/or the salt (d); and an envelope layer formed from a rubber composition that does not include the acid and/or the salt (d).
  • the rubber composition of the center is the same as the rubber composition of the envelope layer 314 shown in FIG. 7 . A hardness distribution of the center is appropriate.
  • the golf ball may include a center formed from a rubber composition that includes the acid and/or the salt (d); and an envelope layer formed from a rubber composition that includes the acid and/or the salt (d).
  • the rubber composition of the center is the same as the rubber composition of the envelope layer 314 shown in FIG. 7 .
  • the rubber composition of the envelope layer is the same as the rubber composition of the envelope layer 314 shown in FIG. 7 .
  • a hardness distribution of the center is appropriate.
  • a hardness distribution of the envelope layer is appropriate.
  • a golf ball comprising a core, an inner cover positioned outside the core, and an outer cover positioned outside the inner cover, wherein
  • the core comprises a center and an envelope layer positioned outside the center
  • the center is formed by a rubber composition being crosslinked
  • the envelope layer is formed by a rubber composition being crosslinked
  • At least one of the rubber composition of the center and the rubber composition of the envelope layer includes:
  • the co-crosslinking agent (b) is:
  • a JIS-C hardness Hi of the inner cover is greater than a JIS-C hardness Hs at a surface of the core
  • a JIS-C hardness Ho of the outer cover is less than the hardness Hi.
  • the zinc salt of the carboxylic acid is one or more members selected from the group consisting of zinc octoate, zinc laurate, zinc myristate, and zinc stearate.
  • the rubber composition includes 15 parts by weight or greater but 50 parts by weight or less of the co-crosslinking agent (b) per 100 parts by weight of the base rubber (a).
  • organic sulfur compound (e) is at least one member selected from the group consisting of thiophenols, diphenyl disulfides, thionaphthols, thiuram disulfides, and metal salts thereof.
  • the rubber composition includes 0.05 parts by weight or greater but 5 parts by weight or less of the organic sulfur compound (e) per 100 parts by weight of the base rubber (a).
  • the rubber composition includes the ⁇ , ⁇ -unsaturated carboxylic acid (b1), and
  • the rubber composition further includes a metal compound (f).
  • a golf ball comprising a core, an inner cover positioned outside the core, and an outer cover positioned outside the inner cover, wherein
  • the core comprises a center and an envelope layer positioned outside the center
  • the center is formed by a rubber composition being crosslinked
  • the envelope layer is formed by a rubber composition being crosslinked
  • At least one of the rubber composition of the center and the rubber composition of the envelope layer includes:
  • the co-crosslinking agent (b) is:
  • a JIS-C hardness Ho of the outer cover is greater than a JIS-C hardness Hs at a surface of the core
  • the hardness Ho is greater than a JIS-C hardness Hi of the inner cover.
  • carboxylic acid and/or the salt thereof (d1) is one or more members selected from the group consisting of zinc octoate, zinc laurate, zinc myristate, and zinc stearate.
  • organic sulfur compound (e) is at least one member selected from the group consisting of thiophenols, diphenyl disulfides, thionaphthols, thiuram disulfides, and metal salts thereof.
  • the rubber composition includes the ⁇ , ⁇ -unsaturated carboxylic acid (b1), and
  • the rubber composition further includes a metal compound (f).
  • a golf ball comprising a core, an inner cover positioned outside the core, a mid cover positioned outside the inner cover, and an outer cover positioned outside the mid cover, wherein
  • the core comprises a center and an envelope layer positioned outside the center
  • the center is formed by a rubber composition being crosslinked
  • the envelope layer is formed by a rubber composition being crosslinked
  • At least one of the rubber composition of the center and the rubber composition of the envelope layer includes:
  • the co-crosslinking agent (b) is:
  • a JIS-C hardness Hi of the inner cover is greater than a JIS-C hardness Hs at a surface of the core
  • a difference (Hi ⁇ Hs) between the hardness Hi and the hardness Hs is equal to or greater than 1, and
  • a JIS-C hardness Ho of the outer cover is greater than the hardness Hi.
  • carboxylic acid and/or the salt thereof (d1) is one or more members selected from the group consisting of zinc octoate, zinc laurate, zinc myristate, and zinc stearate.
  • the rubber composition includes the ⁇ , ⁇ -unsaturated carboxylic acid (b1), and
  • the rubber composition further includes a metal compound (f).
  • organic sulfur compound (e) is at least one member selected from the group consisting of thiophenols, diphenyl disulfides, thionaphthols, thiuram disulfides, and metal salts thereof.
  • a JIS-C hardness Hm of the mid cover is greater than the hardness Hi
  • the hardness Ho is greater than the hardness Hm.
  • a golf ball comprising a core, an inner cover positioned outside the core, a mid cover positioned outside the inner cover, and an outer cover positioned outside the mid cover, wherein
  • the core comprises a center and an envelope layer positioned outside the center
  • the center is formed by a rubber composition being crosslinked
  • the envelope layer is formed by a rubber composition being crosslinked
  • At least one of the rubber composition of the center and the rubber composition of the envelope layer includes:
  • the co-crosslinking agent (b) is:
  • a difference (Hi ⁇ Hs) between a JIS-C hardness Hi of the inner cover and a JIS-C hardness Hs at a surface of the core is less than 1, and
  • a JIS-C hardness Ho of the outer cover is greater than the hardness Hi.
  • carboxylic acid and/or the salt thereof (d1) is one or more members selected from the group consisting of zinc octoate, zinc laurate, zinc myristate, and zinc stearate.
  • the rubber composition includes 1.0 parts by weight or greater but less than 40 parts by weight of the acid and/or the salt (d) per 100 parts by weight of the base rubber (a).
  • the rubber composition includes the ⁇ , ⁇ -unsaturated carboxylic acid (b1), and
  • the rubber composition further includes a metal compound (f).
  • organic sulfur compound (e) is at least one member selected from the group consisting of thiophenols, diphenyl disulfides, thionaphthols, thiuram disulfides, and metal salts thereof.
  • a JIS-C hardness Hm of the mid cover is greater than the hardness Hi
  • the hardness Ho is greater than the hardness Hm.
  • a rubber composition was obtained by kneading 100 parts by weight of a high-cis polybutadiene (trade name “BR-730”, manufactured by JSR Corporation), 28 parts by weight of methacrylic acid, 34 parts by weight of magnesium oxide, and 0.75 parts by weight of dicumyl peroxide.
  • This rubber composition was placed into a mold including upper and lower mold halves each having a hemispherical cavity, and heated at 170° C. for 25 minutes to obtain a center with a diameter of 15 mm.
  • a rubber composition was obtained by kneading 100 parts by weight of a high-cis polybutadiene (the aforementioned “BR-730”), 26 parts by weight of zinc diacrylate (trade name “Sanceler SR”, manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.), 5.0 parts by weight of zinc oxide, an appropriate amount of barium sulfate, 0.20 parts by weight of 2-thionaphthol, 10.0 parts by weight of zinc stearate, and 0.75 parts by weight of dicumyl peroxide.
  • Half shells were formed from this rubber composition. The center was covered with two of these half shells.
  • the center and the half shells were placed into a mold including upper and lower mold halves each having a hemispherical cavity, and heated at 150° C. for 20 minutes to obtain a core with a diameter of 39.1 mm.
  • An envelope layer was formed from the rubber composition. The amount of barium sulfate was adjusted such that the specific gravity of the envelope layer coincides with the specific gravity of the center and the weight of a golf ball is 45.4 g.
  • a resin composition was obtained by kneading 50 parts by weight of an ionomer resin (the aforementioned “Himilan 1605”), 50 parts by weight of another ionomer resin (the aforementioned “Himilan AM7329”), and 4 parts by weight of titanium dioxide with a twin-screw kneading extruder.
  • the core was placed into a mold including upper and lower mold halves each having a hemispherical cavity.
  • the resin composition was injected around the core by injection molding to form an inner cover with a thickness of 1.0 mm.
  • a resin composition was obtained by kneading 46 parts by weight of an ionomer resin (the aforementioned “Himilan 1555”), 45 parts by weight of another ionomer resin (the aforementioned “Himilan AM7329”), 9 parts by weight of a styrene block-containing thermoplastic elastomer (the aforementioned “Rabalon T3221C”, 3 parts by weight of titanium dioxide, and 0.2 parts by weight of an ultraviolet absorber (trade name “TINJVIN 770”, manufactured by Ciba Japan K. K.) with a twin-screw kneading extruder.
  • an ionomer resin the aforementioned “Himilan 1555”
  • another ionomer resin the aforementioned “Himilan AM7329”
  • 9 parts by weight of a styrene block-containing thermoplastic elastomer the aforementioned “Rabalon T3221C”
  • titanium dioxide titanium dioxide
  • an ultraviolet absorber
  • the sphere consisting of the core and the inner cover was placed into a final mold having a large number of pimples on its cavity face.
  • the resin composition was injected around the sphere by injection molding to form an outer cover with a thickness of 0.8 mm. Dimples having a shape that is the inverted shape of the pimples were formed on the outer cover.
  • a clear paint including a two-component curing type polyurethane as a base material was applied to this outer cover to obtain a golf ball of Example I-1 with a diameter of 42.7 mm.
  • a driver with a titanium head (trade name “XXIO”, manufactured by DUNLOP SPORTS CO. LTD., shaft hardness: R, loft angle: 11.0°) was attached to a swing machine manufactured by True Temper Co.
  • a golf ball was hit under the condition of a head speed of 40 m/sec.
  • the spin rate was measured immediately after the hit. Furthermore, the distance from the launch point to the stop point was measured.
  • the average value of data obtained by 10 measurements is shown in Tables I-10 to I-13 below.
  • a sand wedge (SW) was attached to the above swing machine.
  • a golf ball was hit under the condition of a head speed of 21 m/sec.
  • the spin rate was measured immediately after the hit.
  • the average value of data obtained by 10 measurements is shown in Tables I-10 to I-13 below.
  • E1 E2 E3 E4 E5 E6 BR-730 100 100 100 100 100 100 100 100 Sanceler SR 26.0 27.5 29.5 31.5 27.0 26.5 Zinc oxide 5.0 5.0 5.0 5.0 5.0 Barium sulfate * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
  • BR-730 a high-cis polybutadiene manufactured by JSR Corporation (cis-1,4-bond content: 96% by weight, 1,2-vinyl bond content: 1.3% by weight, Mooney viscosity (ML 1+4 (100° C.)): 55, molecular weight distribution (Mw/Mn): 3)
  • Methacrylic acid a product of MITSUBISHI RAYON CO., LTD.
  • Sanceler SR zinc diacrylate manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD. (a product coated with 10% by weight of stearic acid)
  • Magnesium oxide trade name “MAGSARAT 150ST” manufactured by Kyowa Chemical Industry Co., Ltd.
  • 2-thionaphthol a product of Tokyo Chemical Industry Co., Ltd.
  • Zinc octoate a product of Mitsuwa Chemicals Co., Ltd.
  • Zinc laurate a product of Mitsuwa Chemicals Co., Ltd.
  • Zinc myristate a product of NOF Corporation
  • Zinc stearate a product of Wako Pure Chemical Industries, Ltd.
  • Dicumyl peroxide a product of NOF Corporation
  • a rubber composition was obtained by kneading 100 parts by weight of a high-cis polybutadiene (trade name “BR-730”, manufactured by JSR Corporation), 34 parts by weight of magnesium oxide (trade name “MAGSARAT 150ST”, manufactured by Kyowa
  • a rubber composition was obtained by kneading 100 parts by weight of a high-cis polybutadiene (the aforementioned “BR-730”), 26.0 parts by weight of zinc diacrylate (trade name “Sanceler SR”, manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.), 5 parts by weight of zinc oxide, an appropriate amount of barium sulfate, 0.2 parts by weight of 2-thionaphthol, 10 parts by weight of zinc stearate, and 0.75 parts by weight of dicumyl peroxide.
  • Half shells were formed from this rubber composition. The center was covered with two of these half shells.
  • the center and the half shells were placed into a mold including upper and lower mold halves each having a hemispherical cavity, and heated at 150° C. for 20 minutes to obtain a core with a diameter of 39.1 mm.
  • An envelope layer was formed from the rubber composition. The amount of barium sulfate was adjusted such that the specific gravity of the envelope layer coincides with the specific gravity of the center and the weight of a golf ball is 45.4 g.
  • a resin composition was obtained by kneading 26 parts by weight of an ionomer resin (the aforementioned “HimilanAM7337”), 40 parts by weight of another ionomer resin (the aforementioned “Himilan AM7329”), 34 parts by weight of a styrene block-containing thermoplastic elastomer (the aforementioned “Rabalon T3221C”), 6 parts by weight of titanium dioxide with a twin-screw kneading extruder.
  • the core was placed into a mold including upper and lower mold halves each having a hemispherical cavity.
  • the resin composition was injected around the core by injection molding to form an inner cover with a thickness of 1.0 mm.
  • a resin composition was obtained by kneading 5 parts by weight of an ionomer resin (the aforementioned “Himilan AM7337”), 10 parts by weight of another ionomer resin (the aforementioned “Himilan 1555”), 55 parts by weight of still another ionomer resin (the aforementioned “Himilan AM7329”), 30 parts by weight of an ethylene-methacrylic acid copolymer (the aforementioned “NUCREL N1050H”), 3 parts by weight of titanium dioxide, and 0.2 parts by weight of an ultraviolet absorber (trade name “TINUVIN 770”, manufactured by Ciba Japan K.K.) with a twin-screw kneading extruder.
  • an ionomer resin the aforementioned “Himilan AM7337
  • the aforementioned “Himilan 1555” the aforementioned “Himilan 1555”
  • still another ionomer resin the aforementioned “Himilan AM7329”
  • the sphere consisting of the core and the inner cover was placed into a final mold having a large number of pimples on its cavity face.
  • the resin composition was injected around the sphere by injection molding to form an outer cover with a thickness of 0.8 mm. Dimples having a shape that is the inverted shape of the pimples were formed on the outer cover.
  • a clear paint including a two-component curing type polyurethane as a base material was applied to this outer cover to obtain a golf ball of Example II-1 with a diameter of 42.7 mm.
  • Examples II-2 to II-16 and Comparative Examples II-1 to II-6 were obtained in the same manner as Example II-1, except the specifications of the center, the envelope layer, the inner cover, and the outer cover were as shown in Tables II-11 to II-15 below.
  • the composition of the center is shown in detail in Table II-1 below.
  • the composition of the envelope layer is shown in detail in Tables II-2 and II-3 below.
  • the compositions of the inner cover and the outer cover are shown in detail in Tables II-4 and II-5 below.
  • a hardness distribution of the core is shown in Tables II-6 to II-10 below.
  • a wood club (trade name “XXIO”, manufactured by DUNLOP SPORTS CO. LTD., shaft hardness: R, loft angle: 18.0°) was attached to a swing machine manufactured by True Temper Co. A golf ball was hit under the condition of a head speed of 37 m/sec. The spin rate was measured immediately after the hit.
  • Type A B C BR-730 100 100 100 MAGSARAT 150ST 34 — — Methacrylic acid 28 — — Sanceler SR — 20 26 Zinc oxide — 5 5 Barium sulfate — * * 2-thionaphthol — 0.2 0.2 Zinc octoate — 5 — Zinc stearate — — 10 Dicumyl peroxide 0.75 0.75 0.75 Amount of acid/salt 0 5 10 * Appropriate amount
  • BR-730 a high-cis polybutadiene manufactured by JSR Corporation (cis-1,4-bond content: 96% by weight, 1,2-vinyl bond content: 1.3% by weight, Mooney viscosity (ML 1+4 (100° C.)): 55, molecular weight distribution (Mw/Mn): 3)
  • MAGSARAT 150ST magnesium oxide manufactured by Kyowa Chemical Industry Co., Ltd.
  • Methacrylic acid a product of MITSUBISHI RAYON CO., LTD.
  • Sanceler SR zinc diacrylate manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD. (a product coated with 10% by weight of stearic acid)
  • Zinc oxide trade name “Ginrei R” manufactured by Toho Zinc Co., Ltd.
  • Barium sulfate tradename “Barium Sulfate BD” manufactured by Sakai Chemical Industry Co., Ltd.
  • 2-thionaphthol a product of Tokyo Chemical Industry Co., Ltd.
  • Zinc octoate a product of Mitsuwa Chemicals Co., Ltd. (purity: 99% or greater)
  • Zinc stearate a product of Wako Pure Chemical Industries, Ltd. (purity: 99% or greater)
  • Zinc laurate a product of Mitsuwa Chemicals Co., Ltd. (purity: 99% or greater)
  • Zinc myristate a product of NOF Corporation (purity: 90 or greater)
  • Dicumyl peroxide a product of NOF Corporation
  • the golf balls according to Examples are excellent in various performance characteristics. From the results of evaluation, advantages of the present invention are clear.
  • a rubber composition was obtained by kneading 100 parts by weight of a high-cis polybutadiene (trade name “BR-730”, manufactured by JSR Corporation), 34 parts by weight of magnesium oxide (trade name “MAGSARAT 150ST”, manufactured by Kyowa Chemical Industry Co., Ltd.), 28 parts by weight of methacrylic acid, and 0.75 parts by weight of dicumyl peroxide.
  • This rubber composition was placed into a mold including upper and lower mold halves each having a hemispherical cavity, and heated at 170° C. for 25 minutes to obtain a center with a diameter of 15 mm.
  • a rubber composition was obtained by kneading 100 parts by weight of a high-cis polybutadiene (the aforementioned “BR-730”), 26.0 parts by weight of zinc diacrylate (trade name “Sanceler SR”, manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.), 5 parts by weight of zinc oxide, an appropriate amount of barium sulfate, 0.2 parts by weight of 2-thionaphthol, 10 parts by weight of zinc stearate, and 0.75 parts by weight of dicumyl peroxide.
  • Half shells were formed from this rubber composition. The center was covered with two of these half shells.
  • the center and the half shells were placed into a mold including upper and lower mold halves each having a hemispherical cavity, and heated at 150° C. for 20 minutes to obtain a core with a diameter of 37.1 mm.
  • An envelope layer was formed from the rubber composition. The amount of barium sulfate was adjusted such that the specific gravity of the envelope layer coincides with the specific gravity of the center and the weight of a golf ball is 45.4 g.
  • a resin composition was obtained by kneading 40 parts by weight of an ionomer resin (the aforementioned “HimilanAM7337”), 40 parts by weight of another ionomer resin (the aforementioned “Himilan AM7329”), 20 parts by weight of a styrene block-containing thermoplastic elastomer (the aforementioned “Rabalon T3221C”), 6 parts by weight of titanium dioxide with a twin-screw kneading extruder.
  • the core was placed into a mold including upper and lower mold halves each having a hemispherical cavity.
  • the resin composition was injected around the core by injection molding to form an inner cover with a thickness of 1.0 mm.
  • a resin composition was obtained by kneading 51 parts by weight of an ionomer resin (the aforementioned “HimilanAM7337”), 40 parts by weight of another ionomer resin (the aforementioned “Himilan AM7329”), 9 parts by weight of a styrene block-containing thermoplastic elastomer (the aforementioned “Rabalon T3221C”, and 6 parts by weight of titanium dioxide with a twin-screw kneading extruder.
  • the sphere consisting of the core and the inner cover was placed into a mold including upper and lower mold halves each having a hemispherical cavity.
  • the resin composition was injected around the sphere by injection molding to form a mid cover with a thickness of 1.0 mm.
  • a resin composition was obtained by kneading 5 parts by weight of an ionomer resin (the aforementioned “Himilan AM7337”), 10 parts by weight of another ionomer resin (the aforementioned “Himilan 1555”), 55 parts by weight of still another ionomer resin (the aforementioned “Himilan AM7329”), 30 parts by weight of an ethylene-methacrylic acid copolymer (the aforementioned “NUCREL N1050H”), 3 parts by weight of titanium dioxide, and 0.2 parts by weight of an ultraviolet absorber (trade name “TINUVIN 770”, manufactured by Ciba Japan K.K.) with a twin-screw kneading extruder.
  • an ionomer resin the aforementioned “Himilan AM7337
  • the aforementioned “Himilan 1555” the aforementioned “Himilan 1555”
  • still another ionomer resin the aforementioned “Himilan AM7329”
  • the sphere consisting of the core, the inner cover, and the mid cover was placed into a final mold having a large number of pimples on its cavity face.
  • the resin composition was injected around the sphere by injection molding to form an outer cover with a thickness of 0.8 mm. Dimples having a shape that is the inverted shape of the pimples were formed on the outer cover.
  • a clear paint including a two-component curing type polyurethane as a base material was applied to this outer cover to obtain a golf ball of Example III-1 with a diameter of 42.7 mm.
  • Examples III-2 to III-15 and Comparative Examples III-1 to III-7 were obtained in the same manner as Example III-1, except the specifications of the center, the envelope layer, the inner cover, the mid cover, and the outer cover were as shown in Tables III-10 to III-14 below.
  • the composition of the center is shown in detail in Table III-1 below.
  • the composition of the envelope layer is shown in detail in Tables III-2 and III-3 below.
  • the compositions of the inner cover, the mid cover, and the outer cover are shown in detail in Tables III-4 and III-5 below.
  • a hardness distribution of the core is shown in Tables III-6 to III-9 below.
  • a middle iron (trade name “XXIO”, manufactured by DUNLOP SPORTS CO. LTD., shaft hardness: R, loft angle: 24.0°) was attached to a swing machine manufactured by True Temper Co.
  • a golf ball was hit under the condition of a head speed of 35 m/sec.
  • the spin rate was measured immediately after the hit.
  • the distance from the launch point to the stop point was measured.
  • the average value of data obtained by 10 measurements is shown in Tables III-10 to III-14 below.
  • Type A B C BR-730 100 100 100 MAGSARAT 150ST 34 — — Methacrylic acid 28 — — Sanceler SR — 20 26 Zinc oxide — 5 5 Barium sulfate — * * 2-thionaphthol — 0.2 0.2 Zinc octoate — 5 — Zinc stearate — — 10 Dicumyl peroxide 0.75 0.75 0.75 Amount of acid/salt 0 5 10 * Appropriate amount
  • Envelope Layer parts by weight
  • Type E7 E8 E9 E10 E11 BR-730 100 100 100 100 100 100 Sanceler SR 25.5 25.0 25.5 26.0 25.5 Zinc oxide 5 5 5 5 5 5 Barium sulfate * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
  • BR-730 a high-cis polybutadiene manufactured by JSR Corporation (cis-1,4-bond content: 96% by weight, 1,2-vinyl bond content: 1.3% by weight, Mooney viscosity (ML 1+4 (100° C.)): 55, molecular weight distribution (Mw/Mn): 3)
  • MAGSARAT 150ST magnesium oxide manufactured by Kyowa Chemical Industry Co., Ltd.
  • Methacrylic acid a product of MITSUBISHI RAYON CO., LTD.
  • Sanceler SR zinc diacrylate manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD. (a product coated with 10% by weight of stearic acid)
  • Zinc oxide trade name “Ginrei R” manufactured by Toho Zinc Co., Ltd.
  • Barium sulfate trade name “Barium Sulfate BD” manufactured by Sakai Chemical Industry Co., Ltd.
  • 2-thionaphthol a product of Tokyo Chemical Industry Co., Ltd.
  • Zinc octoate a product of Mitsuwa Chemicals Co., Ltd. (purity: 99% or greater)
  • Zinc stearate a product of Wako Pure Chemical Industries, Ltd. (purity: 99% or greater)
  • Zinc laurate a product of Mitsuwa Chemicals Co., Ltd. (purity: 99% or greater)
  • Zinc myristate a product of NOF Corporation (purity: 90 or greater)
  • Dicumyl peroxide a product of NOF Corporation
  • a rubber composition was obtained by kneading 100 parts by weight of a high-cis polybutadiene (trade name “BR-730”, manufactured by JSR Corporation), 34 parts by weight of magnesium oxide (trade name “MAGSARAT 150ST”, manufactured by Kyowa Chemical Industry Co., Ltd.), 28 parts by weight of methacrylic acid, and 0.75 parts by weight of dicumyl peroxide.
  • This rubber composition was placed into a mold including upper and lower mold halves each having a hemispherical cavity, and heated at 170° C. for 25 minutes to obtain a center with a diameter of 15 mm.
  • a rubber composition was obtained by kneading 100 parts by weight of a high-cis polybutadiene (the aforementioned “BR-730”), 26.0 parts by weight of zinc diacrylate (trade name “Sanceler SR”, manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.), 5 parts by weight of zinc oxide, an appropriate amount of barium sulfate, 0.2 parts by weight of 2-thionaphthol, 10 parts by weight of zinc stearate, and 0.75 parts by weight of dicumyl peroxide.
  • Half shells were formed from this rubber composition. The center was covered with two of these half shells.
  • the center and the half shells were placed into a mold including upper and lower mold halves each having a hemispherical cavity, and heated at 150° C. for 20 minutes to obtain a core with a diameter of 37.1 mm.
  • An envelope layer was formed from the rubber composition. The amount of barium sulfate was adjusted such that the specific gravity of the envelope layer coincides with the specific gravity of the center and the weight of a golf ball is 45.4 g.
  • a resin composition was obtained by kneading 24 parts by weight of an ionomer resin (the aforementioned“HimilanAM7337”), 50 parts by weight of another ionomer resin (the aforementioned “Himilan AM7329”), 26 parts by weight of a styrene block-containing thermoplastic elastomer (the aforementioned “Rabalon T3221C”), 6 parts by weight of titanium dioxide with a twin-screw kneading extruder.
  • the core was placed into a mold including upper and lower mold halves each having a hemispherical cavity.
  • the resin composition was injected around the core by injection molding to form an inner cover with a thickness of 1.0 mm.
  • a resin composition was obtained by kneading 51 parts by weight of an ionomer resin (the aforementioned“HimilanAM7337”), 40 parts by weight of another ionomer resin (the aforementioned “Himilan AM7329”), 9 parts by weight of a styrene block-containing thermoplastic elastomer (the aforementioned “Rabalon T3221C”, and 6 parts by weight of titanium dioxide with a twin-screw kneading extruder.
  • the sphere consisting of the core and the inner cover was placed into a mold including upper and lower mold halves each having a hemispherical cavity.
  • the resin composition was injected around the sphere by injection molding to form a mid cover with a thickness of 1.0 mm.
  • a resin composition was obtained by kneading 5 parts by weight of an ionomer resin (the aforementioned “Himilan AM7337”), 10 parts by weight of another ionomer resin (the aforementioned “Himilan 1555”), 55 parts by weight of still another ionomer resin (the aforementioned “Himilan AM7329”), 30 parts by weight of an ethylene-methacrylic acid copolymer (the aforementioned “NUCREL N1050H”), 3 parts by weight of titanium dioxide, and 0.2 parts by weight of an ultraviolet absorber (trade name “TINUVIN 770”, manufactured by Ciba Japan K.K.) with a twin-screw kneading extruder.
  • an ionomer resin the aforementioned “Himilan AM7337
  • the aforementioned “Himilan 1555” the aforementioned “Himilan 1555”
  • still another ionomer resin the aforementioned “Himilan AM7329”
  • the sphere consisting of the core, the inner cover, and the mid cover was placed into a final mold having a large number of pimples on its cavity face.
  • the resin composition was injected around the sphere by injection molding to form an outer cover with a thickness of 0.8 mm. Dimples having a shape that is the inverted shape of the pimples were formed on the outer cover.
  • a clear paint including a two-component curing type polyurethane as a base material was applied to this outer cover to obtain a golf ball of Example IV-1 with a diameter of 42.7 mm.
  • Examples IV-2 to IV-15 and Comparative Examples IV-1 to IV-7 were obtained in the same manner as Example IV-1, except the specifications of the core, the envelope layer, the inner cover, the mid cover, and the outer cover were as shown in Tables IV-11 to IV-15 below.
  • the composition of the center is shown in detail in Table IV-1 below.
  • the composition of the envelope layer is shown in detail in Tables IV-2 and IV-3 below.
  • the compositions of the inner cover, the mid cover, and the outer cover are shown in detail in Tables IV-4 and IV-5 below.
  • a hardness distribution of the core is shown in Tables IV-6 to IV-10 below.
  • a driver with a titanium head (trade name “XXIO”, manufactured by DUNLOP SPORTS CO. LTD., shaft hardness: R, loft angle: 11°) was attached to a swing machine manufactured by True Temper Co.
  • a golf ball was hit under the condition of a head speed of 40 m/sec.
  • the spin rate was measured immediately after the hit. Furthermore, the distance from the launch point to the stop point was measured.
  • the average value of data obtained by 10 measurements is shown in Tables IV-11 to IV-15 below.
  • Type A B C BR-730 100 100 100 MAGSARAT 150ST 34 — — Methacrylic acid 28 — — Sanceler SR — 20 26 Zinc oxide — 5 5 Barium sulfate — * * 2-thionaphthol — 0.2 0.2 Zinc octoate — 5 — Zinc stearate — — 10 Dicumyl peroxide 0.75 0.75 0.75 Amount of acid/salt 0 5 10 * Appropriate amount
  • Envelope Layer (parts by weight)
  • Type E7 E8 E9 E10 E11 BR-730 100 100 100 100 100 100 100 Sanceler SR 25.5 25.0 25.5 26.0 25.5 Zinc oxide 5 5 5 5 5 5 Barium sulfate * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
  • BR-730 a high-cis polybutadiene manufactured by JSR Corporation (cis-1,4-bond content: 96% by weight, 1,2-vinyl bond content: 1.3% by weight, Mooney viscosity (ML 1+4 (100° C.)): 55, molecular weight distribution (Mw/Mn): 3)
  • MAGSARAT 150ST magnesium oxide manufactured by Kyowa Chemical Industry Co., Ltd.
  • Methacrylic acid a product of MITSUBISHI RAYON CO., LTD.
  • Sanceler SR zinc diacrylate manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD. (a product coated with 10% by weight of stearic acid)
  • Zinc oxide trade name “Ginrei R” manufactured by Toho Zinc Co., Ltd.
  • Barium sulfate trade name “Barium Sulfate BD” manufactured by Sakai Chemical Industry Co., Ltd.
  • 2-thionaphthol a product of Tokyo Chemical Industry Co., Ltd.
  • Zinc octoate a product of Mitsuwa Chemicals Co., Ltd. (purity: 99% or greater)
  • Zinc stearate a product of Wako Pure Chemical Industries, Ltd. (purity: 99% or greater)
  • Zinc laurate a product of Mitsuwa Chemicals Co., Ltd. (purity: 99% or greater)
  • Zinc myristate a product of NOF Corporation (purity: 90 or greater)
  • Dicumyl peroxide a product of NOF Corporation
  • the golf balls according to Examples are excellent in flight performance and feel at impact particularly when being hit with a driver. From the results of evaluation, advantages of the present invention are clear.
  • the golf ball according to the present invention can be used for playing golf on golf courses and practicing at driving ranges.
  • the above descriptions are merely for illustrative examples, and various modifications can be made without departing from the principles of the present invention.

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  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Physical Education & Sports Medicine (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Compositions Of Macromolecular Compounds (AREA)
US13/871,096 2012-05-25 2013-04-26 Golf ball Abandoned US20130316851A1 (en)

Applications Claiming Priority (8)

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JP2012-119603 2012-05-25
JP2012119603A JP6068002B2 (ja) 2012-05-25 2012-05-25 ゴルフボール
JP2012120502A JP5499084B2 (ja) 2012-05-28 2012-05-28 ゴルフボール
JP2012-120502 2012-05-28
JP2012122840A JP6068004B2 (ja) 2012-05-30 2012-05-30 ゴルフボール
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USD764160S1 (en) * 2014-10-02 2016-08-23 Drive Medical Design & Manufacturing Soccer ball cane tip
US20160310799A1 (en) * 2015-04-27 2016-10-27 Dunlop Sports Co. Ltd. Golf ball
US10046207B2 (en) 2014-12-17 2018-08-14 Bridgestone Sports Co., Ltd. Multi-piece solid golf ball
US20190351292A1 (en) * 2018-05-16 2019-11-21 Bridgestone Sports Co., Ltd. Multi-piece solid golf ball
US10653922B2 (en) 2014-12-17 2020-05-19 Bridgestone Sports Co., Ltd. Multi-piece solid golf ball
US10773130B2 (en) 2014-12-17 2020-09-15 Bridgestone Sports Co., Ltd. Multi-piece solid golf ball
US10946251B2 (en) 2014-12-17 2021-03-16 Bridgestone Sports Co., Ltd. Multi-piece solid golf ball
US11202938B2 (en) 2014-12-17 2021-12-21 Bridgestone Sports Co., Ltd. Multi-piece solid golf ball
US20220409962A1 (en) * 2021-06-28 2022-12-29 Sumitomo Rubber Industries, Ltd. Golf ball
EP4282496A3 (en) * 2022-05-27 2023-12-20 Sumitomo Rubber Industries, Ltd. Golf ball

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USD764160S1 (en) * 2014-10-02 2016-08-23 Drive Medical Design & Manufacturing Soccer ball cane tip
US10046207B2 (en) 2014-12-17 2018-08-14 Bridgestone Sports Co., Ltd. Multi-piece solid golf ball
US10363461B2 (en) 2014-12-17 2019-07-30 Bridgestone Sports Co., Ltd. Multi-piece solid golf ball
US10653922B2 (en) 2014-12-17 2020-05-19 Bridgestone Sports Co., Ltd. Multi-piece solid golf ball
US10773130B2 (en) 2014-12-17 2020-09-15 Bridgestone Sports Co., Ltd. Multi-piece solid golf ball
US10946251B2 (en) 2014-12-17 2021-03-16 Bridgestone Sports Co., Ltd. Multi-piece solid golf ball
US11202938B2 (en) 2014-12-17 2021-12-21 Bridgestone Sports Co., Ltd. Multi-piece solid golf ball
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US20190351292A1 (en) * 2018-05-16 2019-11-21 Bridgestone Sports Co., Ltd. Multi-piece solid golf ball
US20220409962A1 (en) * 2021-06-28 2022-12-29 Sumitomo Rubber Industries, Ltd. Golf ball
EP4282496A3 (en) * 2022-05-27 2023-12-20 Sumitomo Rubber Industries, Ltd. Golf ball

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CN103418116A (zh) 2013-12-04
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KR20130132326A (ko) 2013-12-04
EP3181201A1 (en) 2017-06-21
EP3181201B1 (en) 2018-08-15
EP2666522A1 (en) 2013-11-27
KR101443527B1 (ko) 2014-09-22

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