KR20130132304A - Golf ball - Google Patents

Abstract

The present invention relates to a golf ball (2) including a core (4), an inner cover (8), a middle cover (10), and an outer cover (12). Nine points are obtained by dividing a section to the surface of the core (4) from the central point of the core (4) into 12.5% of the radius of the core (4). When the distance (%) from the central point among the nine points and hardness are plotted in a graph, the R2 Of the linear approximation curve obtained by the least square method is 0.95 or greater. The hardness Hi of the inner cover (8) is greater than the gradient Hs of the core (4). The hardness Ho of the outer cover (12) is greater than the Hi. The difference (Hi-Hs) is 1 or greater. The difference (Ho-Hi) is 5 or more to 30 or less.

Description

Golf ball {GOLF BALL}

The present application is related to Japanese Patent Application No. 2012-119167 filed on May 25, 2012, Japanese Patent Application No. 2012-119217 filed May 25, 2012, Japanese Patent Application No. 29 Japanese Patent Application No. 2012-121743 filed on May 29, 2012 is claimed as priority claim. The entire disclosure of these Japanese patent applications is incorporated herein by reference.

The present invention relates to a golf ball. Specifically, the present invention relates to a golf ball comprising a solid core and a cover having a plurality of layers.

The golfer's maximum demand for golf balls is flight performance. In particular, golfers value flying performance in shots using drivers and long irons. The flight performance correlates with the ball rebound performance. When hitting a golf ball with a good rebound performance, the golf ball is flying at high speed to achieve a long distance. A golf ball including a core having excellent repulsion performance is disclosed in JP 61-37178, JP2008-212681 (US2008 / 0214324), JP2008-523952 (US2006 / 0135287 and US2007 / 0173607), JP2009-119256 0124757).

The core disclosed in JP 61-37178 is obtained from a rubber composition comprising a co-crosslinking agent and a crosslinking aid. In this publication, palmitic acid, stearic acid and myristic acid are disclosed as crosslinking aids.

The core disclosed in JP2008-212681 is obtained from a rubber composition comprising an organic peroxide, a metal salt of an alpha, beta -unsaturated carboxylic acid and a copper salt of a fatty acid.

The core disclosed in JP2008-523952 is obtained from a rubber composition comprising a metal salt of an unsaturated monocarboxylic acid, a free radical initiator and a nonconjugated diene monomer.

The core disclosed in JP2009-119256 is obtained from a rubber composition comprising a polybutadiene having a vinyl content of 2% or less, a cis 1,4-bond content of 80% or more, and an active terminal thereof modified with an alkoxysilane compound.

Proper ballistic height is required to achieve long distance. The trajectory height depends on the spin speed and the launch angle. A golf ball achieving a high trajectory due to a large spin rate is insufficient in distance. The golf ball achieving high trajectory by large shot angle gets long distance. The use of an osseous / oil resistant structure in a golf ball can achieve a low spin rate and a large launch angle. Changes in the hardness distribution of the core are described in JP6-154357 (USP5,403,010), JP2008-194471 (USP7,344,455, US2008 / 0194358, US2008 / 0194359 and US2008 / 0214325), and JP2008-194473 US2008 / 0194357 and US2008 / 0312008).

In the core disclosed in JP6-154357, the JIS-C hardness H1 at the central point of the core is 58 to 73, and the JIS-C hardness H2 at the region where the distance from the center point is within the range of 5 mm to 10 mm is not less than 65 JIS-C hardness H3 at a point at a distance of 15 mm from the center point is 74 or more and 82 or less, and JIS-C hardness H4 at the surface of the core is 76 or more and 84 or less. The hardness H2 is larger than the hardness H1, the hardness H3 is larger than the hardness H2, and the hardness H4 is the hardness H3 or more.

In the core disclosed in JP2008-194471, the Shore D hardness at the center of the core is 30 or more and 48 or less, the Shore D hardness at the point at 4 mm from the center point is 34 or more and 52 or less, and the distance from the center point is 8 Mm, the Shore D hardness at the point located at a distance of 12 mm from the center point is not less than 43 and not more than 61, and the distance from the surface of the core is not less than 2 mm The Shore D hardness in the range of 3 mm or less is 36 or more and 54 or less, and the Shore D hardness at the surface is 41 or more and 59 or less.

In the core disclosed in JP2008-194473, the Shore D hardness at the center of the core is 25 or more and 45 or less, the Shore D hardness at the region where the distance from the center point is 5 mm or more to less than 10 mm is 39 or more and 58 or less, The Shore D hardness at the point located at a distance of 15 mm from the center of the core is not less than 36 and not more than 55 and the Shore D hardness at the surface of the core is not less than 55 and not more than 75. [

JP2010-253268 (US2010 / 0273575) discloses a golf ball including a core, a surrounding layer, an intermediate layer and a cover. In the core, the hardness gradually increases from the center of the core to the surface of the core. The difference between the JIS-C hardness at the surface and the JIS-C hardness at the center point is 15 or more. The hardness of the cover is larger than the hardness of the intermediate layer, and the hardness of the intermediate layer is larger than the hardness of the surrounding layer.

In the case of a tee shot in a par-three hole and a second shot in a par-for-hoe, a middle iron is often used. The golfer also hopes for a long distance on shorts using the middle irons. The object of the present invention is to provide a golf ball excellent in flight performance in a shot using a middle iron. It is another object of the present invention to provide a golf ball excellent in flight performance and excellent in hit feeling in a shot using a middle iron.

The golf ball according to the present invention includes a core, an inner cover positioned on the outer side of the core, a mid cover positioned on the outer side of the inner cover, and an outer cover positioned on the outer side of the mid cover. When plotting the distance (%) and the JIS-C hardness from the center point of the core of nine points obtained by dividing the area from the center of the core to the surface of the core by 12.5% of the radius of the core, The R ² of the linear approximation curve obtained by the square method is 0.95 or more. The JIS-C hardness Hi of the inner cover is larger than the JIS-C hardness Hs on the surface of the core. The JIS-C hardness Ho of the outer cover is larger than the hardness Hi. In the golf ball according to the present invention, the hardness distribution of the core and the inner cover is appropriate. In a golf ball, the energy loss is low when hitting a golf ball with a middle iron. When you hit a golf ball with a middle iron, the spin rate is low. A low spin rate achieves a long distance.

According to another aspect of the present invention, a golf ball according to the present invention includes a core, a first cover positioned on the outer side of the core, a second cover positioned on the outer side of the first cover, a third cover positioned on the outer side of the second cover, And a fourth cover located outside the cover. When plotting the distance (%) and the JIS-C hardness from the center point of the core of nine points obtained by dividing the area from the center of the core to the surface of the core by 12.5% of the radius of the core, The R ² of the linear approximation curve obtained by the square method is 0.95 or more. The JIS-C hardness H1 of the first cover is larger than the JIS-C hardness Hs on the surface of the core. The JIS-C hardness H4 of the fourth cover is larger than the JIS-C hardness H1 of the first cover. In the golf ball according to the present invention, the hardness distribution of the core and the first cover is appropriate. In a golf ball, the energy loss is low when hitting a golf ball with a middle iron. When you hit a golf ball with a middle iron, the spin rate is low. A low spin rate achieves a long distance.

According to still another aspect, a golf ball according to the present invention includes a core, an inner cover positioned on the outer side of the core, a mid cover positioned on the outer side of the inner cover, and an outer cover positioned on the outer side of the mid cover. When plotting the distance (%) and the JIS-C hardness from the center point of the core of nine points obtained by dividing the area from the center of the core to the surface of the core by 12.5% of the radius of the core, The R ² of the linear approximation curve obtained by the square method is 0.95 or more. The JIS-C hardness Hs at the surface of the core is larger than the JIS-C hardness Hi of the inner cover. The JIS-C hardness Ho of the outer cover is larger than the JIS-C hardness Hi of the inner cover. In the golf ball according to the present invention, the hardness distribution of the core, the inner cover and the outer cover is appropriate. In a golf ball, the energy loss is low when hitting a golf ball with a middle iron. When you hit a golf ball with a middle iron, the spin rate is low. A low spin rate achieves a long distance. In addition, the golf ball has excellent shot feel.

According to still another aspect, a golf ball according to the present invention includes a core, an inner cover positioned on the outer side of the core, a first mid cover positioned on the outer side of the inner cover, a second mid cover positioned on the outer side of the first mid cover, And an outer cover located outside the second mid cover. When plotting the distance (%) and the JIS-C hardness from the center point of the core of nine points obtained by dividing the area from the center of the core to the surface of the core by 12.5% of the radius of the core, The R ² of the linear approximation curve obtained by the square method is 0.95 or more. The JIS-C hardness Hs at the surface of the core is larger than the JIS-C hardness Hi of the inner cover. The JIS-C hardness Ho of the outer cover is larger than the JIS-C hardness Hi of the inner cover. In the golf ball according to the present invention, the hardness distribution of the core, the inner cover, the first mid cover, the second mid cover and the outer cover is appropriate. In a golf ball, the energy loss is low when hitting a golf ball with a middle iron. When you hit a golf ball with a middle iron, the spin rate is low. A low spin rate achieves a long distance. In addition, the golf ball has excellent shot feel.

1 is a partially cut-away sectional view of a golf ball according to a first embodiment of the present invention.
Fig. 2 is a line graph showing the hardness distribution of the core of the golf ball in Fig. 1. Fig.
3 is a partial cross-sectional view of a golf ball according to a second embodiment of the present invention.
Fig. 4 is a line graph showing the hardness distribution of the core of the golf ball in Fig. 3; Fig.
5 is a partially cut-away sectional view of a golf ball according to a third embodiment of the present invention.
Fig. 6 is a line graph showing the hardness distribution of the core of the golf ball in Fig. 5; Fig.
7 is a partially cut-away sectional view of a golf ball according to a fourth embodiment of the present invention.
8 is a line graph showing the hardness distribution of the core of the golf ball in Fig.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail based on preferred embodiments with reference to the accompanying drawings.

In the first embodiment

The golf ball 2 shown in Fig. 1 includes a spherical core 4 and a cover 6 covering the core 4. The cover 6 includes an inner cover 8, a mid cover 10 located outside the inner cover 8, and an outer cover 12 located outside the mid cover 10. On the surface of the outer cover 12, a plurality of dimples 14 are formed. Among the surfaces of the golf ball 2, the portion excluding the dimple 14 is the land 16. The golf ball 2 includes a paint layer and a mark layer outside the outer cover 12, and these layers are not shown in the drawings.

The golf ball 2 has a diameter of 40 mm or more and 45 mm or less. In terms of compliance with the rules set by the American Golf Association (USGA), the diameter is preferably greater than 42.67 mm. From the viewpoint of suppressing the air resistance, the diameter is preferably 44 mm or less, more preferably 42.80 mm or less. The golf ball 2 has a weight of 40 g or more and 50 g or less. With respect to obtaining a large inertia, the weight is preferably at least 44 g, more preferably at least 45.00 g. In terms of compliance with the rules set by the USGA, the weight is preferably 45.93 g or less.

2 is a line graph showing the hardness distribution of the core 4 of the golf ball 2 in Fig. The abscissa of the graph represents the ratio (%) of the distance from the center point of the core 4 to the radius of the core 4. The vertical axis of the graph represents JIS-C hardness. Nine measurement points obtained by dividing the region from the center point of the core 4 to the surface of the core 4 by 12.5% of the radius of the core 4 are plotted on the graph. The ratio of the distance from the center point of the core 4 to each of these measurement points with respect to the radius of the core 4 is as follows:

First point: 0.0% (center point)

2nd point: 12.5%

3rd point: 25.0%

4 points: 37.5%

5th point: 50.0%

6th point: 62.5%

7th: 75.0%

8th: 87.5%

9th: 100.0% (surface)

The JIS-C type hardness meter is pressed against the cut surfaces of the hemispheres obtained by cutting the core 4 to measure the hardness at points 1 to 8. The hardness Hs at the ninth point is measured by pressing a JIS-C type hardness meter on the surface of the spherical core 4. For the measurement, an automatic rubber hardness meter (trade name: "P1" manufactured by Kobunshi Keiki Co., Ltd.) equipped with the above hardness meter is used. In the present invention, JIS-C hardness at a measurement point where the distance from the center point of the core 4 is x (%) is represented by H (x). The hardness at the center of the core 4 is represented by H (0).

Fig. 2 also shows a linear approximation curve obtained by the least squares method based on the distance and hardness of nine measurement points. As is apparent from Fig. 2, the dashed line does not deviate greatly from the linear approximation curve. In other words, the broken line has a shape close to a linear approximation curve. In core 4, the hardness from its center point to its surface increases linearly. When the core (4) is hit with a middle iron, the energy loss is low. The core (4) has excellent rebound performance. When you hit the golf ball (2) with a middle iron, the distance is long.

In the core (4), R ² of the linear approximation curve obtained by the least squares method is 0.95 or more. R ² is an index indicating the linearity of the broken line. In the case of the core 4 having R ² of 0.95 or more, the shape of the broken line of the hardness distribution is close to a straight line. The core 4 having R ² of 0.95 or more is excellent in rebound performance. R ² is more preferably at least 0.96, particularly preferably at least 0.97. R ² is calculated by squaring the correlation coefficient R. The correlation coefficient R is calculated by dividing the covariance of the distance (%) from the center point and the hardness (JIS-C) by the standard deviation of the distance from the center point (%) and the standard deviation of hardness (JIS-C).

The core 4 is obtained by crosslinking the rubber composition. The rubber composition comprises

(a) base rubber;

(b) co-crosslinks;

(c) crosslinking initiators; And

(d) an acid and / or a salt.

During heating and molding of the core 4, the base rubber (a) is crosslinked by the co-crosslinking agent (b). The heat of the crosslinking reaction remains near the center point of the core 4. Therefore, at the time of heating and molding the core 4, the temperature at the center portion is high. The temperature is gradually reduced from the center point to the surface. In the rubber composition, it is presumed that the acid reacts with the metal salt of the co-crosslinking agent (b) and binds to the cation. In the rubber composition, it is presumed that the salt reacts with the metal salt of the co-crosslinking agent (b) to exchange cations. By bonding and exchange, the metal bridges are cut off. Such cutting is likely to occur at the center of the core 4 having a high temperature and will not occur near the surface of the core 4. As a result, the cross-link density of the core 4 increases from its center point toward its surface. In the core 4, an outer / inner oil structure can be achieved. When the golf ball 2 including the core 4 is hit with a middle iron, the spin rate is slow. The golf ball (2) achieves excellent flight performance in a shot using a middle iron.

Examples of the base rubber (a) of the core (4) include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer and natural rubber. From the viewpoint of rebound performance, polybutadiene is preferred. When polybutadiene and another rubber are used in combination, it is preferable that polybutadiene is contained as a main component. Specifically, the ratio of polybutadiene to the whole base rubber is preferably 50% by weight or more, and more preferably 80% by weight or more. The proportion of cis-1,4 bonds in the polybutadiene is preferably at least 40% by weight, more preferably at least 80% by weight.

Preference is given to polybutadienes having a proportion of 1,2-vinyl bonds of up to 2.0% by weight. Polybutadiene may contribute to the rebound performance of the core 4. From this viewpoint, the proportion of 1,2-vinyl bonds is preferably 1.7% by weight or less, particularly preferably 1.5% by weight or less.

From the viewpoint of obtaining a polybutadiene having a low 1,2-vinyl bond ratio and excellent polymerization activity, it is preferable that the rare earth element-containing catalyst is used for the synthesis of polybutadiene. Particularly, polybutadiene synthesized using a catalyst containing neodymium, which is a lanthanide rare earth element compound, is preferred.

The Mooney viscosity (ML _{1 + 4} (100 ° C)) of the polybutadiene is preferably 30 or more, more preferably 32 or more, particularly preferably 35 or more. The Mooney viscosity (ML _{1 + 4} (100 ° C)) is preferably 140 or less, more preferably 120 or less, still more preferably 100 or less, particularly preferably 80 or less. The Mooney viscosity (ML _{1 + 4} (100 ° C)) is measured according to the provisions of "JIS K6300". The measurement conditions are as follows:

Rotor: L Rotor

Warm-up time: 1 minute

Rotation time of rotor: 4 minutes

Temperature: 100 ℃

From the viewpoint of workability, the molecular weight distribution (Mw / Mn) of polybutadiene is preferably 2.0 or more, more preferably 2.2 or more, still more preferably 2.4 or more, particularly preferably 2.6 or more. From the viewpoint of rebound performance, the molecular weight distribution (Mw / Mn) is preferably 6.0 or less, more preferably 5.0 or less, still more preferably 4.0 or less, and particularly preferably 3.4 or less. 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:

Detector: differential refractometer

Column: GMHHXL (manufactured by TOSO CORPORATION)

Column temperature: 40 ° C

Mobile phase: tetrahydrofuran

The molecular weight distribution is calculated as the value obtained by conversion using a polystyrene standard material.

The preferred co-crosslinking agent (b)

(b1) an, -unsaturated carboxylic acid having 3 to 8 carbon atoms; And

(b2) a metal salt of an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms.

The rubber composition may comprise an alpha, beta -unsaturated carboxylic acid (b1) alone or a metal salt (b2) of an alpha, beta -unsaturated carboxylic acid as the co-crosslinking agent (b). The rubber composition may include both of 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 is graft-polymerized with the molecular chain of the base rubber to crosslink the rubber molecule. When the rubber composition contains an alpha, beta -unsaturated carboxylic acid (b1), it is preferable that the rubber composition further comprises a metal compound (f). The metal compound (f) reacts with the α, β-unsaturated carboxylic acid (b1) in the rubber composition. The salt obtained by this reaction is graft-polymerized together 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. Preference is given to compounds comprising divalent metals. Compounds containing divalent metals react with the co-crosslinking agent (b) to form metal crosslinks. The metal compound (f) is particularly preferably a zinc compound. 2 or more types of metal compounds can be used together.

Examples of?,? - 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, And zirconium ions. The metal salt (b2) of the alpha, beta -unsaturated carboxylic acid may include two or more types of ions. Divalent metal ions such as magnesium ion, calcium ion, zinc ion, barium ion and cadmium ion are preferred in that metal crosslinking is apt to occur between rubber molecules. The metal salt (b2) of the?,? - unsaturated carboxylic acid is particularly preferably zinc acrylate.

In view of the rebound performance of the golf ball 2, the amount of the crosslinking agent (b) is preferably 15 parts by weight or more, particularly preferably 20 parts by weight or more per 100 parts by weight of the base rubber. The amount thereof is preferably 50 parts by weight or less, more preferably 45 parts by weight or less, particularly preferably 40 parts by weight or less, per 100 parts by weight of the base rubber.

The crosslinking initiator (c) is preferably an organic peroxide. The organic peroxide contributes to the rebound performance of the golf ball 2. Examples of preferred organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl- Oxy) hexane and di-t-butyl peroxide. From the viewpoint of versatility, dicumyl peroxide is preferable.

In view of the rebound performance of the golf ball 2, the amount of the crosslinking initiator (c) is preferably 0.2 parts by weight or more, particularly preferably 0.5 parts by weight or more per 100 parts by weight of the base rubber. From the viewpoints of impact feel and durability of the golf ball 2, the amount thereof is preferably 5.0 parts by weight or less, particularly preferably 2.5 parts by weight or less, per 100 parts by weight of the base rubber.

The co-crosslinking agent (b) is not included in the concept of an acid and / or a salt (d). It is presumed that the acid and / or the salt (d) cut the metal bridges by the co-crosslinking agent (b) at the center of the core (4) during heating and molding of the core (4). Examples of the acid and / or salt (d) include oxo acids such as carboxylic acid, sulfonic acid and phosphoric acid and its salts; And hydrohalic acids such as hydrochloric acid and hydrofluoric acid and salts thereof. Oxoic acid and salts thereof are preferable. More preferred are carboxylic acids and / or salts thereof (d1). Carboxylate is particularly preferred.

The carbon number of the carboxylic acid component of the carboxylic acid and / or its salt (d1) is preferably 1 or more and 30 or less, more preferably 3 or more and 30 or less, still more preferably 5 or more and 28 or less. Examples of the carboxylic acid include an aliphatic carboxylic acid (fatty acid) and an aromatic carboxylic acid. Fatty acids and salts thereof are preferred.

The rubber composition may comprise saturated fatty acids or salts thereof or may comprise unsaturated fatty acids or salts thereof. Saturated fatty acids and salts thereof are preferred.

Examples of fatty acids include butyric acid (C4), valeric acid (C5), caproic acid (C6), ethanedic acid (C7), caprylic acid (C8), pelargonic acid (C9), capric acid (C12), myristic acid (C14), myristoleic acid (C14), pentadecylic acid (C15), palmitic acid (C16), palmitoleic acid (C16) (C18), aridic acid (C18), arachidic acid (C20), carrageenan (C18), oleic acid (C18), linoleic acid (C18), linolenic acid Erucic acid (C22), lignoceric acid (C24), nerubic acid (C24), heptanoic acid (C26), erucic acid (C22) , Montanic acid (C28) and melissic acid (C30). Two or more kinds of fatty acid salts can be used in combination. Caprylic acid (octanoic acid), lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid and behenic acid are preferable.

The aromatic carboxylic acid has an aromatic ring and a carboxyl group. Examples of the aromatic carboxylic acid 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), melotropic acid (benzene-1,2,3,4-tetracarboxylic acid), frenitic acid Tetracarboxylic acid), pyromellitic acid (benzene-1,2,4,5-tetracarboxylic acid), melitic acid (benzene hexacarboxylic acid), diphenic acid (biphenyl- (2, 3, 5-trimethylbenzoic acid), dicarboxylic acid (2, 3, 4-trimethylbenzoic acid), dicarboxylic acid (dicarboxylic acid), toluic acid (methylbenzoic acid), xylic acid, Trimethylbenzoic acid),? -Isoduric acid (2,4,6-trimethylbenzoic acid),? -Isodururic acid (3,4,5-trimethylbenzoic acid), citric acid (4-isopropylbenzoic acid) (5-methylisophthalic acid),? -Toluic acid (phenylacetic acid), hydratropic acid (2-phenylpropanoic acid), and hydrocinnamic acid (3-phenylpropano ) It can be given.

The rubber composition may include an aromatic carboxylic acid or a salt thereof substituted with a hydroxyl group, an alkoxy group or an oxo group. Examples of such carboxylic acids include salicylic acid (2-hydroxybenzoic acid), anisic acid (methoxybenzoic acid), cresotinic acid (hydroxy (methyl) benzoic acid), o-homosalicylic acid (2-hydroxy- ), m-homosalicylic acid (2-hydroxy-4-methylbenzoic acid), p-homosalicylic acid (2-hydroxy-5-methylbenzoic acid), o- (2,4-dihydroxybenzoic acid),? -resoric acid (2,6-dihydroxybenzoic acid), protocatechuic acid (3,4-dihydroxybenzoic acid),? (3,5-dihydroxybenzoic acid), vanillic acid (4-hydroxy-3-methoxybenzoic acid), isobanilic acid (3-hydroxy-4-methoxybenzoic acid), veratric acid (2,4-dihydroxy-6-methylbenzoic acid), m-hemipinic acid (4,5-dimethoxybenzoic acid) (4-hydroxy-3,5-dimethoxybenzoic acid), aspartic acid (2,4,5-tri (4-methoxyphenyl) acetic acid), mandelic acid (hydroxy (phenyl) acetic acid), vanillylmandelic acid (hydroxy , Homocysteic acid ((2,5-dihydroxyphenyl) acetic acid), homoprotocatechuic acid ((3,4-dihydroxyphenyl) acetic acid), homovanilic acid ((4-hydroxy- (3-hydroxy-4-methoxyphenyl) acetic acid), homobaric acid ((3,4-dimethoxyphenyl) acetic acid), o-homobaric acid (Carboxymethyl) benzoic acid), homoterephthalic acid (3- (carboxymethyl) benzoic acid), homoterephthalic acid (4- (Carboxybenzoic acid), benzylic acid (hydroxydiphenylacetic acid), terephthalic acid (4- (carboxycarbonyl) benzoic acid), isophthalic acid Lactic acid (2-hydroxy (3- (4-hydroxyphenyl) propanoic acid), terephthalic acid (3-hydroxy-2-phenylpropanoic acid), melilotic acid (3- (3,4-dihydroxyphenyl) propanoic acid), hydroperic acid (3- (4-hydroxy-3-methoxyphenyl) propanoic acid (3-hydroxyphenyl) propanoic acid), p-cumaric acid (3- (4-hydroxyphenyl) acrylic acid), umberic acid (3- (2,4-dihydroxyphenyl) acrylic acid), caffeic acid (3- (3,4-dihydroxyphenyl) acrylic acid), ferric acid (3- (3- (3-hydroxy-4-methoxyphenyl) acrylic acid) and isophthalic acid (3- (4-hydroxy-3,5-dimethoxyphenyl) acrylic acid).

The cationic component of the carboxylate is a metal ion or an organic cation. Examples of metal ions include sodium ions, potassium ions, lithium ions, silver ions, magnesium ions, calcium ions, zinc ions, barium ions, cadmium ions, copper ions, cobalt ions, nickel ions, Tin ions, zirconium ions, and titanium ions. Two or more kinds of ions can be used in combination.

Organic cations have carbon chains. Examples of organic cations 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 ions; And quaternary ammonium ions such as dioctyldimethylammonium ion and distearyldimethylammonium ion. Two or more types of organic cations can be used in combination.

Examples of preferred carboxylates include potassium salts, magnesium salts, aluminum salts, zinc salts, iron salts, copper salts, nickel salts of octanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid or behenic acid Or cobalt salts. Zinc salts of carboxylic acids are particularly preferred. Specific examples of preferred carboxylates include zinc octanoate, zinc laurate, zinc myristate and zinc stearate.

From the viewpoint of the linearity of the hardness distribution of the core 4, the amount of the acid and / or the salt (d) is preferably at least 0.5 part by weight, more preferably at least 1.0 part by weight, particularly preferably at least 2.0 Parts by weight or more. From the viewpoint of the rebound performance, the amount thereof is preferably 40 parts by weight or less, more preferably 30 parts by weight or less, particularly preferably 20 parts by weight or less, 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 3/7 to 9/1, and particularly preferably 4/6 to 8/2. From the rubber composition having such a weight ratio falling within the above range, it is possible to obtain the core 4 in which the hardness increases linearly from the center of the core toward the surface thereof.

As the co-crosslinking agent (b), it is preferable to use zinc acrylate. For the purpose of improving the dispersibility of the rubber, there is zinc acrylate whose surface is coated with stearic acid or zinc stearate. In the present invention, when the rubber composition contains such zinc acrylate, such a coating material is not included in the concept of an acid and / or a salt (d).

The rubber composition preferably further comprises an organic sulfur compound (e). The organo sulfur compound (e) has a linearity of the hardness distribution of the core (4); And can contribute to the control of the degree of the outer / inner oil structure. An example of the organic sulfur compound (e) is an organic compound having a thiol group or polysulfide bond having 2 to 4 sulfur atoms. The metal salt of such an organic compound is also included in the organic sulfur compound (e). Examples of the organic sulfur compounds (e) 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. Specific examples of the organic sulfur compound (e) include thiophenol, thionaphthol, polysulfide, thiocarboxylic acid, dithiocarboxylic acid, sulfenamide, thiuram, dithiocarbamate and thiazole. Preferred organic sulfur compounds (e) are thiophenol, diphenyl disulfide, thionaphthol, thiuram disulfide and metal salts thereof.

Specific examples of the organic sulfur compound (e) are represented by the following general formulas (1) to (4)

≪ Formula 1 >

In the general formula (1), R 1 to R 5 each represent H or a substituent.

(2)

In Formula 2, R 1 to R 10 each represent H or a substituent.

<Formula 3>

In Formula 3, R 1 to R 5 each represent H or a substituent, and M 1 represents a monovalent metal atom.

&Lt; Formula 4 >

In Formula 4, R 1 to R 10 each represent H or a substituent, and M 2 represents a divalent metal atom.

In the general formulas (1) to (4), each substituent is selected from the group consisting of a halogen group (F, Cl, Br, I), an alkyl group, a carboxyl group (-COOH), an ester of a carboxyl group (-COOR) ), An acyl group (-COR), a halogenated carbonyl group (-COX), a sulfo group (-SO ₃ H), an ester of sulfo group (-SO ₃ R), a halogenated sulfonyl group (-SO ₂ X) (-SO ₂ H), an alkylsulfinyl group (-SOR), a carbamoyl group (-CONH ₂ ), a halogenated alkyl group, a cyano group (-CN) and an alkoxy group (-OR) One or more selected groups.

Examples of the organosulfur compound represented by the formula (1) include thiophenol; Thiophenols substituted with a halogen group 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, 2,4,5-trichlorothiophenol, 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-triiodothiophenol, 2,4,5,6- Tetraiodothiophenol and pentaiodothiophenol; Thiophenols substituted with an alkyl group such as 4-methylthiophenol, 2,4,5-trimethylthiophenol, pentamethylthiophenol, 4-t-butylthiophenol, 2,4,5-tri- And penta-t-butyl thiophenol; Thiophenols substituted with carboxyl groups such as 4-carboxythiophenol, 2,4,6-tricarboxythiophenol and pentalcarboxythiophenol; Thiophenols substituted with alkoxycarbonyl groups such as 4-methoxycarbonylthiophenol, 2,4,6-trimethoxycarbonylthiophenol and penta-methoxycarbonylthiophenol; Thiophenols substituted with formyl groups such as 4-formylthiophenol, 2,4,6-trioformylthiophenol and pentafomylthiophenol; Thiophenols substituted with acyl groups such as 4-acetylthiophenol, 2,4,6-triacetylthiophenol and pentaacetylthiophenol; Thiophenols substituted with halogenated carbonyl groups such as 4-chlorocarbonylthiophenol, 2,4,6-tri (chlorocarbonyl) thiophenol and penta (chlorocarbonyl) thiophenol; Thiophenols substituted with sulfo groups such as 4-sulfothio phenol, 2,4,6-trisulfotio phenol and pentasulfothio phenol; Thiophenols substituted with an alkoxysulfonyl group such as 4-methoxysulfonylthiophenol, 2,4,6-trimethoxysulfonylthiophenol and pentamethoxysulfonylthiophenol; Thiophenols substituted with halogenated sulfonyl groups such as 4-chlorosulfonylthiophenol, 2,4,6-tri (chlorosulfonyl) thiophenol and penta (chlorosulfonyl) thiophenol; Thiophenols substituted with sulfino groups such as 4-sulfinothiophenol, 2,4,6-trisulfinothiophenol and pentasulfinothiophenol; Thiophenols substituted with an alkylsulfinyl group such as 4-methylsulfinylthiophenol, 2,4,6-tri (methylsulfinyl) thiophenol and penta (methylsulfinyl) thiophenol; Thiophenols substituted with carbamoyl groups such as 4-carbamoylthiophenol, 2,4,6-tricarbamoylthiophenol and pentacarbamoylthiophenol; Thiophenols substituted with halogenated alkyl groups such as 4-trichloromethylthiophenol, 2,4,6-tri (trichloromethyl) thiophenol and penta (trichloromethyl) thiophenol; Thiophenols substituted with cyano groups such as 4-cyanothiophenol, 2,4,6-tricyanothiophenol and pentacyanothiophenol; And thiophenols substituted with an alkoxy group such as 4-methoxythiophenol, 2,4,6-trimethoxythiophenol and pentamethoxythiophenol. Each of these thiophenols is substituted with one kind of substituent.

Another example of an organosulfur compound represented by formula (1) is a compound substituted with one or more of the above substituents and another substituent. Examples of other substituents include a nitro group (-NO ₂ ), an amino group (-NH ₂ ), a hydroxyl group (-OH) and a phenylthio group (-SPh). Specific examples of the compound include 4-chloro-2-nitrothiophenol, 4-chloro-2-aminothiophenol, 4-chloro-2-hydroxythiophenol, 4- Methyl-2-nitrothiophenol, 4-methyl-2-aminothiophenol, 4-methyl-2-hydroxytiophenol, 4-carboxy-2-aminothiophenol, 4-carboxy-2-hydroxythiophenol, 4-carboxy- 2-aminothiophenol, 4-methoxycarbonyl-2-hydroxythiophenol, 4-methoxycarbonyl-2-phenylthiothiophenol, 2-aminothiophenol, 4-formyl-2-hydroxythiophenol, 4-formyl-2-phenylthiothiophenol, Phenol, 4-acetyl-2-hydroxytiophenol, 4-acetyl-2-phenylthiothiophenol, 4-chlorocarbonyl-2-nitrothiophenol, 4-chlorocarbonyl-2-nitrothiophenol, 4-chlorocarbonyl- Sulfo-2-nitrothiophenol, 4-sulfo-2-aminothiophenol, 4-sulfo-2-hydroxythiophenol, 2-aminothiophenol, 4-methoxysulfonyl-2-hydroxytiophenol, 4-methoxysulfonyl-2-phenylthiothiophenol, 4- chlorosulfonyl- 2-nitrothiophenol, 4-chlorosulfonyl-2-aminothiophenol, 4-chlorosulfonyl-2-hydroxothiophenol, 4- 2-aminothiophenol, 4-sulfino-2-hydroxytiophenol, 4-sulfino-2-phenylthiothiophenol, 4-methylsulfinyl- 4-methylsulfinyl-2-aminothiophenol, 4-methylsulfinyl-2- 2-nitrothiophenol, 4-carbamoyl-2-aminothiophenol, 4-carbamoyl-2-hydroxy 4-trichloromethyl-2-nitrothiophenol, 4-trichloromethyl-2-aminothiophenol, 4-trichloromethyl-2-hydroxy 2-nitrothiophenol, 4-trichloromethyl-2-phenylthiothiophenol, 4-cyano-2-nitrothiophenol, 4-cyano- 4-methoxy-2-nitrothiophenol, 4-methoxy-2-nitrothiophenol, 4-methoxy-2- -2-phenylthiothiophenol.

Still another example of the organosulfur compound represented by formula (1) is a compound substituted with two or more substituents. Specific examples of the compound include 4-acetyl-2-chlorothiophenol, 4-acetyl-2-methylthiophenol, 4-acetyl-2-carboxythiophenol, Acetyl-2-formylthiophenol, 4-acetyl-2-chlorocarbonylthiophenol, 4-acetyl- Acetyl-2-methylsulfinylthiophenol, 4-acetyl-2-carbamoylthiophenol, 4-acetyl-2-trichloro Methylthiophenol, 4-acetyl-2-cyanothiophenol and 4-acetyl-2-methoxythiophenol.

Examples of the organosulfur compound represented by the formula (2) include diphenyl disulfide; A diphenyl disulfide substituted with a halogen group such as bis (4-fluorophenyl) disulfide, bis (2,5-difluorophenyl) disulfide, bis (2,4,5-trifluorophenyl) , Bis (2,4,5,6-tetrafluorophenyl) disulfide, bis (pentafluorophenyl) disulfide, bis (4-chlorophenyl) Bis (2,4,5-trichlorophenyl) disulfide, bis (2,4,5,6-tetrachlorophenyl) disulfide, bis (pentachlorophenyl) disulfide, bis Disulfide, bis (2,5-dibromophenyl) disulfide, bis (2,4,5-tribromophenyl) disulfide, bis (2,4,5,6-tetrabromophenyl) , Bis (pentabromophenyl) disulfide, bis (4-iodophenyl) disulfide, bis (2,5-diiodophenyl) Feed, bis (2,4,5,6-tetraiodophenyl) disulfide and bis (pentaiodophenyl) disulfide; Diphenyl disulfide substituted with an alkyl group such as bis (4-methylphenyl) disulfide, bis (2,4,5-trimethylphenyl) disulfide, bis (pentamethylphenyl) disulfide, bis Disulfide, bis (2,4,5-tri-t-butylphenyl) disulfide and bis (penta-t-butylphenyl) disulfide; Diphenyl disulfide substituted with a carboxyl group such as bis (4-carboxyphenyl) disulfide, bis (2,4,6-tricarboxyphenyl) disulfide and bis (pentacarboxyphenyl) disulfide; Diphenyl disulfide substituted with an alkoxycarbonyl group such as bis (4-methoxycarbonylphenyl) disulfide, bis (2,4,6-trimethoxycarbonylphenyl) disulfide and bis (pentamethoxycarbonyl Phenyl) disulfide; Diphenyl disulfides substituted with formyl groups such as bis (4-formylphenyl) disulfide, bis (2,4,6-triphorylphenyl) disulfide and bis (pentaformylphenyl) disulfide; Diphenyl disulfides substituted with an acyl group such as bis (4-acetylphenyl) disulfide, bis (2,4,6-triacetylphenyl) disulfide and bis (pentaacetylphenyl) disulfide; (4-chlorocarbonyl) phenyl disulfide and bis (penta (chlorocarbonyl) phenyl) disulfide group substituted with a halogenated carbonyl group such as bis (4-chlorocarbonylphenyl) disulfide, bis Phenyl) phenyl) disulfide; Diphenyl disulfides substituted with sulfo groups such as bis (4-sulfophenyl) disulfide, bis (2,4,6-trisulfophenyl) disulfide and bis (pentasulfophenyl) disulfide; Diphenyl disulfide substituted with alkoxysulfonyl group such as bis (4-methoxysulfonylphenyl) disulfide, bis (2,4,6-trimethoxysulfonylphenyl) disulfide and bis (pentamethysulfonylphenyl) Feed; Diphenyl disulfides substituted with halogenated sulfonyl groups such as bis (4-chlorosulfonylphenyl) disulfide, bis (2,4,6-tri (chlorosulfonyl) phenyl) disulfide and bis (penta ) Phenyl) disulfide; Diphenyl disulfide substituted with a sulfino group such as bis (4-sulfinophenyl) disulfide, bis (2,4,6-trisulfinophenyl) disulfide and bis (pentasulfinophenyl) disulfide; Diphenyl disulfides substituted with an alkylsulfinyl group such as bis (4-methylsulfinylphenyl) disulfide, bis (2,4,6-tri (methylsulfinyl) phenyl) disulfide and bis ) Phenyl) disulfide; Diphenyl disulfide substituted with a carbamoyl group such as bis (4-carbamoylphenyl) disulfide, bis (2,4,6-tricarbamoylphenyl) disulfide and bis (pentacarbamoylphenyl) Feed; Diphenyl disulfide substituted with a halogenated alkyl group such as bis (4-trichloromethylphenyl) disulfide, bis (2,4,6-tri (trichloromethyl) phenyl) disulfide and bis (penta (trichloromethyl) phenyl ) Disulfide; A diphenyl disulfide substituted with a cyano group such as bis (4-cyanophenyl) disulfide, bis (2,4,6-tricyanophenyl) disulfide and bis (pentacyanophenyl) disulfide; And diphenyl disulfides substituted with an alkoxy group such as bis (4-methoxyphenyl) disulfide, bis (2,4,6-trimethoxyphenyl) disulfide and bis (pentamethoxyphenyl) have. Each of these diphenyl disulfides is substituted with one substituent.

Another example of the organic sulfur compound represented by the formula (2) is a compound substituted with at least one of the above substituents and another substituent. Examples of other substituents include a nitro group (-NO ₂ ), an amino group (-NH ₂ ), a hydroxyl group (-OH) and a phenylthio group (-SPh). Specific examples of the compound include bis (4-chloro-2-nitrophenyl) disulfide, bis (4-chloro-2-aminophenyl) disulfide, bis Bis (4-methyl-2-nitrophenyl) disulfide, bis (4-methyl- Bis (4-carboxy-2-aminophenyl) disulfide, bis (4-carboxy-2-aminophenyl) disulfide, bis Bis (4-carboxy-2-hydroxyphenyl) disulfide, bis (4-carboxy-2-hydroxyphenyl) disulfide, bis 2-aminophenyl) disulfide, bis (4-methoxycarbonyl-2-hydroxyphenyl) disulfide, bis (4-methoxycarbonyl- Bis (4-formyl-2-nitrophenyl) disulfide, bis (4-formyl- Bis (4-acetyl-2-nitrophenyl) disulfide, bis (4-acetyl-2-nitrophenyl) disulfide, bis Bis (4-acetyl-2-hydroxyphenyl) disulfide, bis (4-acetyl-2-hydroxyphenyl) disulfide, bis Bis (4-chlorocarbonyl-2-hydroxyphenyl) disulfide, bis (4-chlorocarbonyl- Bis (4-sulfo-2-aminophenyl) disulfide, bis (4-sulfo-2-hydroxyphenyl) disulfide, bis ) Disulfide, bis (4-sulfo-2-phenylthiophenyl) disulfide, bis (4-methoxysulfonyl-2-nitrophenyl) , Bis (4-methoxysulfonyl-2-hydroxyphenyl) disulfide, bis (4-methoxysulfo Bis (4-chlorosulfonyl-2-aminophenyl) disulfide, bis (4-chlorosulfonyl-2-nitrophenyl) disulfide, bis Bis (4-sulfo-2-nitrophenyl) disulfide, bis (4-sulfosuccinyl-2-phenylthiophenyl) disulfide, bis Bis (4-sulfophenoxy) disulfide, bis (4-sulfino-2-hydroxyphenyl) disulfide, bis Bis (4-methylsulfinyl-2-aminophenyl) disulfide, bis (4-methylsulfinyl-2-hydroxyphenyl) disulfide, bis Bis (4-carbamoyl-2-nitrophenyl) disulfide, bis (4-carbamoyl-2-aminophenyl) disulfide, bis ) Disulfide, bis (4-carbamoyl-2-phenylthiophenyl) disulfide, bis (4-trichloromethyl- Bis (4-trichloromethyl-2-aminophenyl) disulfide, bis (4-trichloromethyl-2-hydroxyphenyl) disulfide, bis Bis (4-cyano-2-hydroxyphenyl) disulfide, bis (4-cyano-2-hydroxyphenyl) disulfide, bis (4-methoxy-2-nitrophenyl) disulfide, bis (4-methoxy-2-aminophenyl) disulfide, bis 4-methoxy-2-hydroxyphenyl) disulfide and bis (4-methoxy-2-phenylthiophenyl) disulfide.

Still another example of the organosulfur compound represented by formula (2) is a compound substituted with two or more substituents. Specific examples of the compound include bis (4-acetyl-2-chlorophenyl) disulfide, bis (4-acetyl-2-methylphenyl) disulfide, bis Acetyl-2-methoxycarbonylphenyl) disulfide, bis (4-acetyl-2-formylphenyl) disulfide, bis (4-acetyl-2-chlorosulfonylphenyl) disulfide, bis (4-acetyl-2-methoxysulfonylphenyl) disulfide, bis Bis (4-acetyl-2-trichloromethylphenyl) disulfide, bis (4-acetyl-2-methylsulfinylphenyl) disulfide, bis Disulfide, bis (4-acetyl-2-cyanophenyl) disulfide and bis (4-acetyl-2-methoxyphenyl) disulfide.

Examples of the organic sulfur compounds represented by the formula (3) include thiophenol sodium salt; Thiophenol sodium salt substituted with a halogen group 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-tris Sodium laurylthiophenol sodium salt, 2,4,5,6-tetrabromothiophenol sodium salt, pentabromothiophenol sodium salt, 4-iodothiophenol sodium salt, 2,5-diiodothiophenol sodium salt Sodium 2,4,5-triiodothiophenol sodium salt, 2,4,5,6-tetraiodothiophenol sodium salt and penta-iodothiophenol sodium salt; Thiophenol sodium salt substituted with an alkyl group such as 4-methylthiophenol sodium salt, 2,4,5-trimethylthiophenol sodium salt, pentamethylthiophenol sodium salt, 4-t-butylthiophenol sodium salt, 2,4 , 5-tri-t-butyl thiophenol sodium salt and penta (t-butyl) thiophenol sodium salt; Thiophenol sodium salts substituted with carboxyl groups such as 4-carboxythiophenol sodium salt, 2,4,6-tricarboxythiophenol sodium salt and pentacarboxythiophenol sodium salt; Thiophenol sodium salts substituted with an alkoxycarbonyl group such as 4-methoxycarbonylthiophenol sodium salt, 2,4,6-trimethoxycarbonylthiophenol sodium salt and pentamethoxycarbonylthiophenol sodium salt; Thiophenol sodium salts substituted with formyl groups such as 4-formylthiophenol sodium salt, 2,4,6-triformylthiophenol sodium salt and pentafomylthiophenol sodium salt; Thiophenol sodium salts substituted with acyl groups such as 4-acetylthiophenol sodium salt, 2,4,6-triacetylthiophenol sodium salt and pentaacetylthiophenol sodium salt; Thiophenol sodium salts substituted with a halogenated carbonyl group such as 4-chlorocarbonylthiophenol sodium salt, 2,4,6-tri (chlorocarbonyl) thiophenol sodium salt and penta (chlorocarbonyl) thiophenol sodium salt; Thiophenol sodium salts substituted with sulfo groups such as sodium 4-sulfothio phenol sodium salt, 2,4,6-trisulfotio phenol sodium salt and pentasulfotio phenol sodium salt; Thiophenol sodium salts substituted with an alkoxysulfonyl group such as 4-methoxy sulfonyl thiophenol sodium salt, 2,4,6-trimethoxy sulfonyl thiophenol sodium salt and pentamethoxy sulfonyl thiophenol sodium salt; Thiophenol sodium salts substituted with halogenated sulfonyl groups such as 4-chlorosulfonylthiophenol sodium salt, 2,4,6-tri (chlorosulfonyl) thiophenol sodium salt and penta (chlorosulfonyl) thiophenol sodium salt; Thiophenol sodium salts substituted with sulfino groups such as 4-sulfinothiophenol sodium salt, 2,4,6-trisulfinothiophenol sodium salt and pentasulfinothiophenol sodium salt; Thiophenol sodium salts substituted with an alkylsulfinyl group such as 4-methylsulfinylthiophenol sodium salt, 2,4,6-tri (methylsulfinyl) thiophenol sodium salt and penta (methylsulfinyl) thiophenol sodium salt; Thiophenol sodium salts substituted with carbamoyl groups such as 4-carbamoylthiophenol sodium salt, 2,4,6-tricarbamoylthiophenol sodium salt and pentacarbamoylthiophenol sodium salt; Thiophenol sodium salts substituted with halogenated alkyl groups such as 4-trichloromethylthiophenol sodium salt, 2,4,6-tri (trichloromethyl) thiophenol sodium salt and penta (trichloromethyl) thiophenol sodium salt; Thiophenol sodium salts substituted with cyano groups such as 4-cyanothiophenol sodium salt, 2,4,6-tricyanothiophenol sodium salt and pentacyanothiophenol sodium salt; And thiophenol sodium salts substituted with an alkoxy group such as 4-methoxythiophenol sodium salt, 2,4,6-trimethoxythiophenol sodium salt and pentamethoxythiophenol sodium salt. Each of these thiophenol sodium salts is substituted with one substituent.

Another example of the organosulfur compound represented by the formula (3) is a compound substituted with at least one of the above substituents and another substituent. Examples of other substituents include a nitro group (-NO ₂ ), an amino group (-NH ₂ ), a hydroxyl group (-OH) and a phenylthio group (-SPh). Specific examples of the compound include 4-chloro-2-nitrothiophenol sodium salt, 4-chloro-2-aminothiophenol sodium salt, 4-chloro-2-hydroxothiophenol sodium salt, Thiophenol sodium salt, 4-methyl-2-nitrothiophenol sodium salt, 4-methyl-2-aminothiophenol sodium salt, 4-methyl- Sodium thiophenol sodium salt, 4-carboxy-2-nitrothiophenol sodium salt, 4-carboxy-2-aminothiophenol sodium salt, 4-carboxy- Thiothiophenol sodium salt, 4-methoxycarbonyl-2-nitrothiophenol sodium salt, 4-methoxycarbonyl-2-aminothiophenol sodium salt, 4-methoxycarbonyl-2-hydroxothiophenol sodium Sodium 4-methoxycarbonyl-2-phenylthiothiophenol sodium salt, 4-formyl-2-nitrothiophenol sodium salt, 4-formyl- Sodium salt of 4-formyl-2-hydroxythiophenol, sodium salt of 4-acetyl-2-nitrothiophenol, sodium salt of 4-acetyl- Acetyl-2-hydroxytiophenol sodium salt, 4-acetyl-2-phenylthiothiophenol sodium salt, 4-chlorocarbonyl-2-nitrothiophenol sodium salt, 4- Sodium 4-chlorocarbonyl-2-hydroxytiophenol sodium salt, 4-chlorocarbonyl-2-phenylthiothiophenol sodium salt, 4-sulfo-2-nitrothiophenol sodium salt Sulfonium salt, 4-sulfo-2-aminothiophenol sodium salt, 4-sulfo-2-hydroxytiophenol sodium salt, 4-sulfo-2-phenylthiothiophenol sodium salt, 4-methoxysulfonyl- Phenol sodium salt, 4-methoxysulfonyl-2-aminothiophenol sodium salt, 4-methoxysulfonyl-2-hydroxothiophenol sodium salt, 4-methoxysulfonyl- Sodium thiothiophenol sodium salt, 4-chlorosulfonyl-2-nitrothiophenol sodium salt, 4-chlorosulfonyl-2-aminothiophenol sodium salt, 4-chlorosulfonyl-2-hydroxothiophenol sodium salt, 2-nitrothiophenol sodium salt, 4-sulfoso-2-aminothiophenol sodium salt, 4-sulfino-2-hydroxy Thiophenol sodium salt, 4-sulfino-2-phenylthiothiophenol sodium salt, 4-methylsulfinyl-2-nitrothiophenol sodium salt, 4-methylsulfinyl-2-aminothiophenol sodium salt, 2-hydroxy thiophenol sodium salt, 4-methylsulfinyl-2-phenylthiothiophenol sodium salt, 4-carbamoyl-2-nitrothiophenol sodium salt, 4-carbamoyl- Thiophenol sodium salt, 4-carbamoyl-2-hydroxothiophenol sodium salt, 4-carbamoyl-2-phenylthiothiophenol sodium salt, 4-trichloromethyl- 4-trichloromethyl-2-aminothiophenol sodium salt, 4-trichloromethyl-2-hydroxothiophenol sodium salt, 4-trichloromethyl-2-phenylthiothiophenol sodium salt, 4 -Cyano-2-nitrothiophenol sodium salt, 4-cyano-2-aminothiophenol sodium salt, 4-cyano-2-hydroxothiophenol sodium salt, 4-cyano- Methoxy-2-nitrothiophenol sodium salt, 4-methoxy-2-aminothiophenol sodium salt, 4-methoxy-2-hydroxytiophenol sodium salt and 4-methoxy-2- And sodium phenylthiothiophenol sodium salt.

Still another example of an organosulfur compound represented by formula (3) is a compound substituted with two or more substituents. Specific examples of the compound include 4-acetyl-2-chlorothiophenol sodium salt, 4-acetyl-2-methylthiophenol sodium salt, 4-acetyl-2-carboxythiophenol sodium salt, Acetyl-2-formylthiophenol sodium salt, 4-acetyl-2-chlorocarbonylthiophenol sodium salt, 4-acetyl-2-sulfothiophenol sodium salt, 4-acetyl 2-methylsulfonylthiophenol sodium salt, 4-acetyl-2-sulfinothiophenol sodium salt, 4-acetyl-2-methylsulfinylthiophenol sodium salt, Sodium 4-acetyl-2-carbamoylthiophenol sodium salt, 4-acetyl-2-trichloromethylthiophenol sodium salt, 4-acetyl-2-cyanothiophenol sodium salt, Sodium thiophenol sodium salt. Examples of the monovalent metal represented by M1 in the general formula (3) include sodium, lithium, potassium, copper (I) and silver (I).

Examples of the organic sulfur compounds represented by the formula (4) include thiophenol zinc salts; Thiophenol zinc salts substituted with a halogen group 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-tris Zinc bromide, zinc bromide, zinc bromide, zinc bromide, zinc bromide, zinc bromide, zinc bromide, zinc bromide, zinc bromide, zinc bromide, zinc bromide, zinc bromide, Salts, 2,4,5-triiodothiophenol zinc salts, 2,4,5,6-tetraiodothiophenol zinc salts, and penta-iodothiophenol zinc salts; Thiophenol zinc salts substituted with an alkyl group such as 4-methylthiophenol zinc salt, 2,4,5-trimethylthiophenol zinc salt, pentamethylthiophenol zinc salt, 4-t-butyl thiophenol zinc salt, 2,4 , 5-tri-t-butyl thiophenol zinc salt and penta-t-butyl thiophenol zinc salt; Thiophenol zinc salts substituted with carboxyl groups such as 4-carboxythiophenol zinc salt, 2,4,6-tricarboxythiophenol zinc salt and pentacarboxythiophenol zinc salt; Thiophenol zinc salts substituted with alkoxycarbonyl groups such as 4-methoxycarbonylthiophenol zinc salt, 2,4,6-trimethoxycarbonylthiophenol zinc salt and pentamethoxycarbonylthiophenol zinc salt; Thiophenol zinc salts substituted with formyl groups, such as 4-formylthiophenol zinc salts, 2,4,6-triformylthiophenol zinc salts and pentafomylthiophenol zinc salts; Thiophenol zinc salts substituted with acyl groups such as 4-acetylthiophenol zinc salt, 2,4,6-triacetylthiophenol zinc salt and pentaacetylthiophenol zinc salt; Thiophenol zinc salts substituted with halogenated carbonyl groups such as 4-chlorocarbonylthiophenol zinc salt, 2,4,6-tri (chlorocarbonyl) thiophenol zinc salt and penta (chlorocarbonyl) thiophenol zinc salt; Thiophenol zinc salts substituted with sulfo groups such as 4-sulfothiofenol zinc salt, 2,4,6-trisulfotio phenol zinc salt and pentasulfothiofenol zinc salt; Thiophenol zinc salts substituted with an alkoxysulfonyl group such as 4-methoxysulfonylthiophenol zinc salt, 2,4,6-trimethoxy sulfonylthiophenol zinc salt and pentamethoxysulfonylthiophenol zinc salt; Thiophenol zinc salts substituted with halogenated sulfonyl groups such as 4-chlorosulfonylthiophenol zinc salt, 2,4,6-tri (chlorosulfonyl) thiophenol zinc salt and penta (chlorosulfonyl) thiophenol zinc salt; Thiophenol zinc salts substituted with sulfino groups such as 4-sulfinothiophenol zinc salts, 2,4,6-trisulfinothiophenol zinc salts and pentasulfinothiophenol zinc salts; Thiophenol zinc salts substituted with an alkylsulfinyl group such as 4-methylsulfinylthiophenol zinc salt, 2,4,6-tri (methylsulfinyl) thiophenol zinc salt and penta (methylsulfinyl) thiophenol zinc salt; Thiophenol zinc salts substituted with carbamoyl groups such as 4-carbamoylthiophenol zinc salts, 2,4,6-tricarbamoylthiophenol zinc salts and pentacarbamoylthiophenol zinc salts; Thiophenol zinc salts substituted with halogenated alkyl groups such as 4-trichloromethylthiophenol zinc salt, 2,4,6-tri (trichloromethyl) thiophenol zinc salt and penta (trichloromethyl) thiophenol zinc salt; Thiophenol zinc salts substituted with cyano groups such as 4-cyanothiophenol zinc salt, 2,4,6-tricyanothiophenol zinc salt and pentacyanothiophenol zinc salt; And thiophenol zinc salts substituted with an alkoxy group such as 4-methoxythiophenol zinc salt, 2,4,6-trimethoxythiophenol zinc salt and pentamethoxythiophenol zinc salt. Each of these thiophenol zinc salts is substituted with one substituent.

Another example of the organic sulfur compound represented by the formula (4) is a compound substituted with at least one of the above substituents and another substituent. Examples of other substituents include a nitro group (-NO ₂ ), an amino group (-NH ₂ ), a hydroxyl group (-OH) and a phenylthio group (-SPh). Specific examples of the compound include 4-chloro-2-nitrothiophenol zinc salt, 4-chloro-2-aminothiophenol zinc salt, 4-chloro-2-hydroxytiophenol zinc salt, Thiophenol zinc salt, 4-methyl-2-nitrothiophenol zinc salt, 4-methyl-2-aminothiophenol zinc salt, 4-methyl- 2-nitrothiophenol zinc salt, 4-carboxy-2-aminothiophenol zinc salt, 4-carboxy-2-hydroxytiophenol zinc salt, 4-carboxy-2-phenyl Thiophenol zinc salt, 4-methoxycarbonyl-2-nitrothiophenol zinc salt, 4-methoxycarbonyl-2-aminothiophenol zinc salt, 4-methoxycarbonyl- 4-formyl-2-nitrothiophenol zinc salt, 4-formyl-2-aminothiophenol zinc salt, 4-formyl-2 - hydrocortisone 4-acetyl-2-nitrothiophenol zinc salt, 4-acetyl-2-aminothiophenol zinc salt, 4-acetyl-2-hydroxy Thiophenol zinc salts, 4-acetyl-2-phenylthiothiophenol zinc salts, 4-chlorocarbonyl-2-nitrothiophenol zinc salts, 4-chlorocarbonyl- Sulfonyl-2-nitrothiophenol zinc salt, 4-sulfo-2-aminothiophenol zinc salt, 4-chloro- Sulfo-2-hydroxythiophenol zinc salt, 4-sulfo-2-phenylthiothiophenol zinc salt, 4-methoxysulfonyl-2-nitrothiophenol zinc salt, 4-methoxysulfonyl- Phenothiophenol zinc salt, 4-chlorosulfonyl-2-nitrothiophenol zinc salt, 4-methoxysulfonyl-2-hydroxytiophenol zinc salt, 4- Chloro 2-aminothiophenol zinc salt, 4-chlorosulfonyl-2-hydroxytiophenol zinc salt, 4-chlorosulfonyl-2-phenylthiothiophenol zinc salt, 4-sulfino- Zinc salt, 4-sulfino-2-aminothiophenol zinc salt, 4-sulfino-2-hydroxytiophenol zinc salt, 4-sulfino- 2-nitrothiophenol zinc salt, 4-methylsulfinyl-2-aminothiophenol zinc salt, 4-methylsulfinyl-2-hydroxytiophenol zinc salt, 4-methylsulfinyl- 4-carbamoyl-2-nitrothiophenol zinc salt, 4-carbamoyl-2-aminothiophenol zinc salt, 4-carbamoyl- 2-nitrothiophenol zinc salt, 4-trichloromethyl-2-aminothiophenol zinc salt, 4-trichloromethyl-2-hydroxytiophenol zinc salt, Zinc salts, 4-tri 2-nitrothiophenol zinc salt, 4-cyano-2-aminothiophenol zinc salt, 4-cyano-2-hydroxytiophenol zinc salt 4-methoxy-2-nitrothiophenol zinc salt, 4-methoxy-2-aminothiophenol zinc salt, 4-methoxy-2- And zinc salt of 4-methoxy-2-phenylthiothiophenol.

Still another example of the organic sulfur compound represented by the formula (4) is a compound substituted with two or more substituents. Specific examples of the compound include 4-acetyl-2-chlorothiophenol zinc salt, 4-acetyl-2-methylthiophenol zinc salt, 4-acetyl-2-carboxythiophenol zinc salt, Acetyl-2-formylthiophenol zinc salt, 4-acetyl-2-chlorocarbonylthiophenol zinc salt, 4-acetyl-2- Acetyl-2-chlorosulfonylthiophenol zinc salt, 4-acetyl-2-sulfinothiophenol zinc salt, 4-acetyl-2-methylsulfinylthiophenol zinc salt, Acetyl-2-trichloromethylthiophenol zinc salt, 4-acetyl-2-cyanothiophenol zinc salt and 4-acetyl-2- Gt; thiophenol zinc salt. &Lt; / RTI &gt; (II), iron (II), cobalt (II), nickel (II), zirconium (II), zinc (II) And tin (II).

Examples of the naphthalene thiol include 2-naphthalene thiol, 1-naphthalene thiol, 2-chloro-1-naphthalene thiol, 2-bromo-1-naphthalene thiol, Naphthalene thiol, 1-fluoro-2-naphthalene thiol, 1-cyano-2-naphthalene thiol, Thiol, 1-acetyl-2-naphthalenethiol and metal salts thereof. 1-naphthalenethiol, 2-naphthalenethiol and zinc salts thereof are preferable.

Examples of organic sulfur compounds of the sulfenamide type include N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide and Nt-butyl- . Examples of the organosulfur compound of the thiuram type include tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethyl thiuram disulfide, tetrabutyl thiuram disulfide and dipentamethyl thiuram tetrasulfide. have. Examples of dithiocarbamates include, but are not limited to, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc ethylphenyldithiocarbamate, sodium dimethyldithiocarbamate, sodium diethyldithio (II) dimethyldithiocarbamate, iron (III) dimethyldithiocarbamate, selenium diethyldithiocarbamate, and tellurium diethyldithiocarbamate. Examples of thiazole-type organic sulfur compounds 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.

In view of rebound performance, the amount of the organic sulfur compound (e) is preferably 0.05 part by weight or more, particularly preferably 0.1 part by weight or more per 100 parts by weight of the base rubber. From the viewpoint of the rebound performance, the amount thereof is preferably 5.0 parts by weight or less, particularly preferably 2.0 parts by weight or less, per 100 parts by weight of the base rubber.

A filler may be included in the core 4 for the purpose of controlling specific gravity and the like. Examples of suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. The amount of filler is suitably determined so that the intended specific gravity of the core 4 is achieved. Particularly preferred fillers are zinc oxide. Zinc oxide functions not only as a specific gravity adjuster but also as a crosslinking aid.

An antioxidant, a colorant, a plasticizer, a dispersant, sulfur, a vulcanization accelerator and the like are added to the rubber composition of the core 4 as required. The crosslinked rubber powder or the synthetic resin powder may also be dispersed in the rubber composition.

In the core 4, the difference (Hs-H (0)) between the surface hardness Hs and the center hardness H (0) is preferably 15 or more. The difference is large. In other words, the core 4 has an outer / inner oil structure. When the core (4) is struck with a middle iron, recoil (twist return) is large and spin is suppressed. The core (4) contributes to the flight performance of the golf ball (2). In terms of flight performance, the difference (Hs-H (0)) is more preferably 20 or more, particularly preferably 25 or more. In view of the fact that the core 4 can be easily formed, the difference (Hs-H (0)) is preferably 50 or less.

The hardness H (0) at the center of the core 4 is preferably not less than 40.0 and not more than 70.0. The golf ball 2 whose hardness H (0) is 40.0 or more is excellent in repulsion performance. From this viewpoint, the hardness H (0) is more preferably 45.0 or more, particularly preferably 50.0 or more. The core (4) having a hardness H (0) of 70.0 or less can attain an outer / inner oil structure. In the golf ball 2 including the core 4, spin can be suppressed. From this viewpoint, the hardness H (0) is more preferably 68.0 or less, particularly preferably 66.0 or less.

The hardness Hs at the surface of the core 4 is preferably 76.0 or more and 95.0 or less. In the core (4) having a hardness Hs of 76.0 or more, an outer / inner oil structure can be achieved. In the golf ball 2 including the core 4, spin can be suppressed. From this viewpoint, the hardness Hs is more preferably not less than 78.0, particularly preferably not less than 80.0. The golf ball 2 whose hardness Hs is 95.0 or less is excellent in durability. From such a viewpoint, the hardness Hs is more preferably 93.0 or less, particularly preferably 90.0 or less.

The core 4 preferably has a diameter of 36.0 mm or more and 41.0 mm or less. The core (4) having a diameter of 36.0 mm or more can achieve excellent rebound performance of the golf ball (2). From this viewpoint, the diameter is more preferably at least 36.5 mm, and particularly preferably at least 37.0 mm. In the golf ball 2 including the core 4 having a diameter of 41.0 mm or less, the thickness of the inner cover 8, the mid cover 10 and the outer cover 12 may be sufficient. The golf ball 2 including the inner cover 8 having a large thickness, the mid cover 10 and the outer cover 12 has excellent durability. From such a viewpoint, the diameter is more preferably 40.0 mm or less, particularly preferably 39.0 mm or less. The core 4 may have a rib at its surface.

The core 4 preferably has a compressive deformation amount comp'n of 3.0 mm or more, particularly preferably 3.3 mm or more, from the viewpoint of shot feeling. From the viewpoint of the rebound performance, the amount of compressive deformation is preferably 4.6 mm or less, particularly preferably 4.3 mm or less.

In the case of the inner cover 8, a resin composition is suitably used. Examples of the base polymer of the resin composition include an ionomer resin, a styrene block-containing thermoplastic elastomer, a thermoplastic polyester elastomer, a thermoplastic polyamide elastomer and a thermoplastic polyolefin elastomer.

A particularly preferred base polymer is an ionomer resin. The golf ball 2 including the inner cover 8 including the ionomer resin is excellent in repulsion performance. The ionomer resin and another resin can be used in combination with the inner cover 8. In this case, the main component of the base polymer is preferably an ionomer resin. Specifically, the ratio of the ionomer resin to the total amount of the base polymer is preferably 50% by weight or more, more preferably 60% by weight or more, particularly preferably 70% by weight or more.

Examples of preferred ionomer resins include alpha-olefins and bidentate copolymers formed with alpha, beta -unsaturated carboxylic acids having 3 to 8 carbon atoms. Preferred binary copolymers comprise at least 80% and at most 90% by weight of an α-olefin and at least 10% and at most 20% by weight of an α, β-unsaturated carboxylic acid. Binary copolymers are excellent in rebound performance. Examples of other preferred ionomer resins include? -Olefins; Alpha, beta -unsaturated carboxylic acids having from 3 to 8 carbon atoms; And an alpha, beta -unsaturated carboxylate ester having 2 to 22 carbon atoms. Preferred ternary copolymers contain not less than 70% by weight and not more than 85% by weight of? -Olefins, not less than 5% by weight and not more than 30% by weight of?,? - unsaturated carboxylic acids and not less than 1% by weight and not more than 25% Unsaturated carboxylate esters. The ternary copolymer has excellent rebound performance. In the case of binary copolymers and ternary copolymers, preferred? -Olefins are ethylene and propylene, and preferred?,? - unsaturated carboxylic acids are acrylic acid and methacrylic acid. Particularly preferred ionomer resins are copolymers formed of ethylene and acrylic acid or methacrylic acid.

In binary copolymers and ternary copolymers, some of the carboxyl groups are neutralized with metal ions. Examples of 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 can be carried out using two or more metal ions. Particularly suitable metal ions from the viewpoint of the rebound performance and durability of the golf ball 2 are sodium ion, zinc ion, lithium ion and magnesium ion.

Specific examples of the ionomer resin include trade name "Himilan 1555", "HYMILAN 1557" and "HYMILAN 1557" manufactured by DuPont-MITSUI POLYCHEMICALS Co., &Quot; High Milan AM7311 ", "High Milan AM7317 "," High Milan AM7318 ", " "," High Milan AM7329 "," High Milan AM7337 "," High Milan MK7320 "and" High Milan MK7329 "; this child. Quot; Surlyn 6120 ", "Surlyn 6910 "," Surlyn 7930 ", "Surlyn 7940 "," Surlyn 8140 ", "Surlyn 6120 ", and " Surlyn 6140 ", manufactured by EI du Pont de Nemours and Company, 8150 "," Sullin 8940 "," Sullin 8945 "," Sullin 9120 "," Sullin 9150 "," Sullin 9910 "," Sullin 9945 "," Sullin AD8546 "," HPF 1000 "and" HPF 2000 "; IOTEK 7010 ", "IOTEC 7030 "," IOTEC 7510 ", "IOTEC 7520 "," IOTEC 8000 ", and "IOTEK ", manufactured by ExxonMobil Chemical Company. Otec 8030 ".

Two or more kinds of ionomer resins can be used in combination with the inner cover 8. An ionomer resin neutralized with a monovalent metal ion and an ionomer resin neutralized with a divalent metal ion can be used in combination.

A preferred resin that can be used in combination with the ionomer resin is a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer is excellent in compatibility with the ionomer resin. The resin composition comprising the styrene block-containing thermoplastic elastomer is excellent in 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 dienblock. Examples of the diene block compound include butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Butadiene and isoprene are preferred. Two or more compounds may be used in combination.

Examples of the styrene block-containing thermoplastic elastomer include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-butadiene-styrene block copolymer (SIBS) Hydrogenated SIS and hydrogenated SIBS. An example of hydrogenated SBS is styrene-ethylene-butylene-styrene block copolymer (SEBS). An example of a hydrogenated SIS is a styrene-ethylene-propylene-styrene block copolymer (SEPS). An example of hydrogenated SIBS is styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

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

In the present invention, the styrene block-containing thermoplastic elastomer includes at least one selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS and SEEPS and an alloy of olefins. It is presumed that the olefin component in the alloy contributes to improvement of compatibility with the ionomer resin. The use of such an alloy improves the rebound performance of the golf ball 2. It is preferred to use olefins having 2 to 10 carbon atoms. Examples of suitable olefins include ethylene, propylene, butene and pentene. Ethylene and propylene are particularly preferred.

Specific examples of the polymer alloy include trade names "Rabalon T3221C", "Lavalon T3339C", "Lavalon SJ4400N", "Lavalon SJ5400N", and "Lavalon SJ6400N" manufactured by Mitsubishi Chemical Corporation "," Lavalon SJ7400N "," Lavalon SJ8400N "," Lavalon SJ9400N "and" Lavalon SR04 ". Specific examples of the other styrene block-containing thermoplastic elastomer include trade name "Epofriend A1010" manufactured by Daicel Chemical Industries, Ltd. and trade name "Kuraray Co., Ltd." manufactured by Daicel Chemical Industries, Ltd. &Quot; Septon HG-252 "

The resin composition of the inner cover 8 contains an appropriate amount of a coloring agent such as titanium dioxide and a fluorescent pigment and a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, . The inner cover 8 may include a powder of a metal having a high specific gravity.

According to the discovery of the inventor of the present invention, the inner cover 8 greatly influences the deformation behavior of the golf ball 2 when striking the golf ball 2 with the middle irons. The golf ball 2 including the inner cover 8 having a high hardness Hi when hit with a middle iron has excellent flying performance. The inner cover 8 having an excessively large hardness Hi can contribute to a feeling of hit of the golf ball 2.

From the viewpoint of flight performance, the hardness Hi of the inner cover 8 is preferably 75 or more, more preferably 80 or more, particularly preferably 83 or more. From the viewpoint of feel of the golf ball 2, the hardness Hi is preferably 95 or less, particularly preferably 90 or less. The hardness Hi is measured using a JIS-C type hardness meter mounted on an automatic rubber hardness tester (trade name: "P1 ", manufactured by Kojundo Keiki Co., Ltd.). For the measurement, a slab with a thickness of about 2 mm is used, which is formed by a hot press. The slabs stored at 23 ° C for 2 weeks are used for the measurement. In the measurement, three slabs are stacked. A slab formed from the same resin composition as the resin composition of the inner cover 8 is used.

The hardness Hi of the inner cover 8 is set to be equal to the hardness Hi of the inner surface of the core 4 and the inner surface of the core 4 from the viewpoint that the outer / Is preferably larger than the hardness Hs. From the viewpoint of spin suppression, the difference (Hi-Hs) between the hardness Hi and the hardness Hs is preferably 1 or more, and particularly preferably 2 or more. The difference (Hi-Hs) is preferably 10 or less. In spheres with a difference (Hi-Hs) of 10 or less, the hardness increases linearly from its center point toward its surface. In the spheres whose hardness is increased linearly, the energy loss is low when the golf ball 2 is hit with a middle iron.

The inner cover 8 preferably has a thickness of 0.2 mm or more and 1.2 mm or less. The inner cover 8 having a thickness of 0.2 mm or more can be easily formed. From this viewpoint, the thickness is more preferably 0.4 mm or more, and particularly preferably 0.6 mm or more. The golf ball 2 including the inner cover 8 having a thickness of 1.2 mm or less has excellent rebound performance. From this viewpoint, the thickness is more preferably 1.0 mm or less, particularly preferably 0.9 mm or less.

In the case of forming the inner cover 8, a known method such as injection molding, compression molding and the like can be used.

In the case of the mid cover 10, a resin composition is suitably used. A preferred base polymer of the resin composition is an ionomer resin. The golf ball 2 including the mid cover 10 including the ionomer resin is excellent in repulsion performance. The ionomer resin described above for the inner cover 8 can be used for the mid cover 10.

An ionomer resin and another resin may be used in combination. In this case, from the viewpoint of the rebound performance, the ionomer resin is included as a main component of the base polymer. The ratio of the ionomer resin to the total amount of the base polymer is preferably not less than 50% by weight, more preferably not less than 60% by weight, particularly preferably not less than 70% by weight.

Other preferred resins that may be used in combination with the ionomer resin include styrene block-containing thermoplastic elastomers. The styrene block-containing thermoplastic elastomer described above with respect to the inner cover 8 can be used for the mid cover 10.

The mid cover 10 may contain an appropriate amount of a coloring agent such as titanium dioxide and a fluorescent pigment, a filler such as barium sulfate, a dispersing agent, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent and a fluorescent whitening agent.

The mid cover 10 preferably has a JIS-C hardness Hm of 75 or more and 96 or less. The golf ball 2 including the mid cover 10 having a hardness Hm of 75 or more is excellent in flight performance in a shot using a middle iron. From this viewpoint, the hardness Hm is more preferably 80 or more, particularly preferably 85 or more. The golf ball 2 including the mid cover 10 having a hardness Hm of 96 or less is excellent in shot feeling. From this viewpoint, the hardness Hm is more preferably 90 or less, particularly preferably 88 or less. The hardness Hm is measured in the same manner as the hardness Hi measurement method.

The hardness Hm of the mid cover 10 may be greater than the hardness Hi of the inner cover 8 or may be less than the hardness Hi of the inner cover 8. [

It is possible to achieve the outer / inner oil structure of the sphere consisting of the core 4, the inner cover 8 and the mid cover 10 in the golf ball 2 whose hardness Hm is larger than the hardness Hi. When the golf ball 2 is hit with a middle iron, the spin rate is low. The golf ball (2) has excellent flight performance in a shot using a middle iron. From the viewpoint of flight performance, the difference (Hm-Hi) between the hardness Hm and the hardness Hi is preferably 2 or more. The difference (Hm-Hi) is preferably 20 or less.

In the golf ball 2 in which the hardness Hm is smaller than the hardness Hi, the mid cover 10 absorbs the impact when striking the golf ball 2. The golf ball 2 is excellent in hit feeling. From the viewpoint of shot feeling, the difference (Hi-Hm) between the hardness Hi and the hardness Hm is preferably 2 or more. The difference (Hi-Hm) is preferably 20 or less.

The mid cover 10 preferably has a thickness of 0.2 mm or more and 1.2 mm or less. The mid cover 10 having a thickness of 0.2 mm or more can be easily formed. From this viewpoint, the thickness is more preferably 0.4 mm or more, and particularly preferably 0.6 mm or more. The golf ball 2 including the mid cover 10 having a thickness of 1.2 mm or less is excellent in repulsion performance. From this viewpoint, the thickness is more preferably 1.0 mm or less, particularly preferably 0.9 mm or less.

In the case of forming the mid cover 10, a known method such as injection molding, compression molding and the like can be used.

In the case of the outer cover 12, a resin composition is suitably used. A preferred base polymer of the resin composition is an ionomer resin. The golf ball 2 including the outer cover 12 including the ionomer resin is excellent in repulsion performance. The ionomer resin described above with respect to the inner cover 8 can be used for the outer cover 12.

An ionomer resin and another resin may be used in combination. In this case, from the viewpoint of the rebound performance, the ionomer resin is included as a main component of the base polymer. The ratio of the ionomer resin to the total amount of the base polymer is preferably not less than 50% by weight, more preferably not less than 60% by weight, particularly preferably not less than 70% by weight.

A preferred resin that can be used in combination with the ionomer resin is an ethylene- (meth) acrylic acid copolymer. The copolymer is obtained by a copolymerization reaction of a monomer composition containing ethylene and (meth) acrylic acid. In the copolymer, some of the carboxyl groups are neutralized with metal ions. The copolymer contains not less than 3 wt% and not more than 25 wt% (meth) acrylic acid component. Particular preference is given to ethylene- (meth) acrylic acid copolymers having polar functional groups. A specific example of the ethylene- (meth) acrylic acid copolymer is the trade name "NUCREL " produced by DuPont-Mitsui Polychemicals Company, Limited.

Another preferred resin that can be used in combination with the ionomer resin is a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer described above with respect to the inner cover 8 can be used for the outer cover 12.

The outer cover 12 contains an appropriate amount of a coloring agent such as titanium dioxide and a fluorescent pigment, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent and a fluorescent whitening agent.

The outer cover 12 preferably has a JIS-C hardness Ho of 83 or more and 98 or less. The golf ball 2 including the outer cover 12 having the hardness Ho of 83 or more is excellent in the rebound performance. The golf ball (2) is excellent in flight performance. From this viewpoint, the hardness Ho is more preferably 86 or more, particularly preferably 89 or more. The golf ball 2 including the outer cover 12 having a hardness Ho of 98 or less is excellent in hit feeling. From this viewpoint, the hardness Ho is more preferably 96 or less, particularly preferably 94 or less. The hardness Ho is measured in the same manner as the hardness Hi measurement method.

It is preferable that the hardness Ho of the outer cover 12 is larger than the hardness Hi of the inner cover 8. [ In the golf ball 2 in which the hardness Ho is greater than the hardness Hi, the spin can be suppressed. The golf ball (2) has excellent flight performance in a shot using a middle iron

From the viewpoint of flight performance, the difference between the hardness Ho and the hardness Hi (Ho-Hi) is preferably 5 or more, more preferably 6 or more, particularly preferably 7 or more. The difference (Ho-Hi) is preferably 30 or less.

It is preferable that the hardness Ho of the outer cover 12 is larger than the hardness Hm of the mid cover 10. [ In the golf ball 2 in which the hardness Ho is greater than the hardness Hm, an outer / inner oil structure can be achieved. When the golf ball 2 is hit with a middle iron, the spin rate is low. The golf ball (2) has excellent flight performance in a shot using a middle iron. From the viewpoint of flight performance, the difference (Ho-Hm) between the hardness Ho and the hardness Hm is preferably 2 or more. The difference (Ho-Hm) is preferably 20 or less.

The outer cover 12 preferably has a thickness of 0.2 mm or more and 1.2 mm or less. The outer cover 12 having a thickness of 0.2 mm or more can be easily formed. From this viewpoint, the thickness is more preferably 0.4 mm or more, and particularly preferably 0.6 mm or more. The golf ball 2 including the outer cover 12 having a thickness of 1.2 mm or less is excellent in repulsion performance. From this viewpoint, the thickness is more preferably 1.0 mm or less, particularly preferably 0.9 mm or less.

In the case of forming the outer cover 12, known methods such as injection molding, compression molding and the like can be used. In forming the outer cover 12, the dimples 14 are formed by a pimple formed on the cavity face of the mold.

The cover 6 preferably has a total thickness of 2.5 mm or less. The golf ball 2 including the cover 6 having a total thickness of 2.5 mm or less is excellent in shot feeling. From this viewpoint, it is particularly preferable that the total thickness is 2.4 mm or less. From the viewpoint of the durability of the golf ball 2, the total thickness is preferably 0.3 mm or more, more preferably 0.5 mm or more, particularly preferably 0.8 mm or more.

From the viewpoint of shot feel, the golf ball 2 has a compressive deformation amount comp'n of preferably 2.8 mm or more, more preferably 2.9 mm or more, particularly preferably 3.0 mm or more. From the viewpoint of the rebound performance, the amount of compressive deformation is preferably 3.6 mm or less, more preferably 3.5 mm or less, particularly preferably 3.4 mm or less.

For the measurement of compressive deformation (comp'n), a YAMADA type compression tester is used. In the tester, the sphere, for example, the core 4, the golf ball 2, and the like are placed on a metal-produced steel plate. Then, the metal-produced cylinder is gradually lowered toward the sphere. The spheres pushed between the bottom surface of the cylinder and the steel sheet are deformed. The moving distance of the cylinder is measured from a state where an initial load of 98 N is applied to the sphere to a state where a final load of 1,274 N is applied.

In the second embodiment

Figure 3 shows a golf ball 102 according to a second embodiment of the present invention. The golf ball 102 includes a spherical core 104 and a cover 106 covering the core 104. The cover 106 includes a first cover 108, a second cover 110 located outside the first cover 108, a third cover 112 located outside the second cover 110, And a fourth cover 114 located outside the cover 112. On the surface of the fourth cover 114, a plurality of dimples 116 are formed. Among the surfaces of the golf ball 102, the portion excluding the dimple 116 is the land 118. [ The golf ball 102 includes a paint layer and a mark layer outside the fourth cover 114, but these layers are not shown in the drawings.

The golf ball 102 has a diameter of 40 mm or more and 45 mm or less. In terms of compliance with the rules set by the USGA, the diameter is preferably greater than or equal to 42.67 mm. From the viewpoint of restraining air resistance, the diameter is preferably 44 mm or less, more preferably 42.80 mm or less. The golf ball 102 has a weight of 40 g or more and 50 g or less. With respect to obtaining a large inertia, the weight is preferably at least 44 g, more preferably at least 45.00 g. In terms of compliance with the rules set by the USGA, the weight is preferably 45.93 g or less.

Fig. 4 shows a line graph showing the hardness distribution of the core 104 of the golf ball 102 in Fig. The horizontal axis of the graph represents the ratio (%) of the distance from the center point of the core 104 to the radius of the core 104. The vertical axis of the graph represents JIS-C hardness. Nine measurement points obtained by dividing the region from the center point of the core 104 to the surface of the core 104 by 12.5% of the radius of the core 104 are plotted on the graph. The ratio of the distance of each of these measurement points from the center point of the core 104 to the radius of the core 104 is as follows:

First point: 0.0% (center point)

2nd point: 12.5%

3rd point: 25.0%

4 points: 37.5%

5th point: 50.0%

6th point: 62.5%

7th: 75.0%

8th: 87.5%

9th: 100.0% (surface)

The JIS-C type hardness meter is pressed against the cut surfaces of the hemispheres obtained by cutting the core 104 to measure the hardness at points 1 to 8. The hardness Hs at the ninth point is measured by pressing a JIS-C type hardness meter on the surface of the spherical core 104. For the measurement, an automatic rubber hardness tester (trade name: "P1", manufactured by Kobunshi Keiki Co., Ltd.) equipped with the above hardness meter is used. In the present invention, JIS-C hardness at a measurement point where the distance from the center point of the core 104 is x (%) is represented by H (x). The hardness at the center of the core 104 is represented by H (0).

The straight line indicated by the dotted line in FIG. 4 shows a linear approximation curve obtained by the least squares method based on the distance and hardness of nine measurement points. As is apparent from Fig. 4, the dashed line does not deviate greatly from the linear approximation curve. In other words, the broken line has a shape close to a linear approximation curve. In core 104, the hardness from its center point to its surface increases linearly. When the core 104 is hit with a middle iron, energy loss is low. The core 104 has excellent rebound performance. When the golf ball 102 is hit with a middle iron, the distance is long.

In the core 104, the R ² of the linear approximation curve obtained by the least squares method is 0.95 or more. R ² is an index indicating the linearity of the broken line. In the case of the core 104 having R ² of 0.95 or more, the shape of the broken line of the hardness distribution is close to a straight line. The core 104 having R ² of 0.95 or more has excellent rebound performance. R ² is more preferably at least 0.96, particularly preferably at least 0.97. R ² is calculated by squaring the correlation coefficient R. The correlation coefficient R is calculated by dividing the covariance of the distance (mm) from the center point and the hardness (JIS-C) by the standard deviation of the distance (mm) from the center point and the standard deviation of hardness (JIS-C).

The core 104 is obtained by crosslinking the rubber composition. The rubber composition comprises

(a) base rubber;

(b) co-crosslinks;

(c) crosslinking initiators; And

(d) an acid and / or a salt.

During heating and molding of the core 104, the base rubber (a) is crosslinked by the co-crosslinking agent (b). The heat of the crosslinking reaction remains near the center point of the core 104. Thus, at the time of heating and molding the core 104, the temperature at the center portion is high. The temperature is gradually reduced from the center point to the surface. In the rubber composition, it is presumed that the acid reacts with the metal salt of the co-crosslinking agent (b) and binds to the cation. In the rubber composition, it is presumed that the salt reacts with the metal salt of the co-crosslinking agent (b) to exchange cations. By bonding and exchange, the metal bridges are cut off. Such cutting is likely to occur at the center of the high temperature core 104 and not near the surface of the core 104. As a result, the cross-link density of the core 104 increases from its center point toward its surface. At the core 104, an outer / inner oil structure can be achieved. When the golf ball 102 including the core 104 is struck with a middle iron, the spin speed is slow. The golf ball (2) achieves excellent flight performance in a shot using a middle iron.

The rubber composition of the core 104 may comprise the base rubber (a) described above for the core 4 of the first embodiment.

The rubber composition of the core 104 may comprise the co-crosslinking agent (b) described above for the core 4 of the first embodiment. The preferred co-crosslinking agent (b)

(b1) an, -unsaturated carboxylic acid having 3 to 8 carbon atoms; And

(b2) a metal salt of an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms.

When the rubber composition contains an alpha, beta -unsaturated carboxylic acid (b1), it is preferable that the rubber composition further comprises a metal compound (f). The metal compound (f) reacts with the?,? - unsaturated carboxylic acid (b1) in the rubber composition. The salt obtained by this reaction is graft-polymerized with the molecular chain of the base rubber. The rubber composition of the core 104 may comprise the metal compound (f) described above for the core 4 of the first embodiment.

In view of the rebound performance of the golf ball 102, the amount of the crosslinking agent (b) is preferably 15 parts by weight or more, particularly preferably 20 parts by weight or more per 100 parts by weight of the base rubber. The amount thereof is preferably 50 parts by weight or less, more preferably 45 parts by weight or less, particularly preferably 40 parts by weight or less, per 100 parts by weight of the base rubber.

The rubber composition of core 104 may comprise the crosslinking initiator (c) described above for core 4 of the first embodiment. From the viewpoint of the rebound performance of the golf ball 102, the amount of the crosslinking initiator (c) is preferably at least 0.2 part by weight, particularly preferably at least 0.5 part by weight per 100 parts by weight of the base rubber. From the viewpoints of feeling of impact and durability of the golf ball 102, the amount thereof is preferably 5.0 parts by weight or less, particularly preferably 2.5 parts by weight or less, per 100 parts by weight of the base rubber.

The rubber composition of core 104 may comprise the acid and / or salt (d) described above for core 4 of the first embodiment. The co-crosslinking agent (b) is not included in the concept of an acid and / or a salt (d). It is believed that the acid and / or salt (d) cuts the metal bridges by the co-crosslinking agent (b) at the core of the core (104) during heating and molding of the core (104).

From the viewpoint of the linearity of the hardness distribution of the core 104, the amount of the acid and / or salt (d) is preferably 1.0 parts by weight or more, more preferably 2.0 parts by weight or more, particularly preferably 3.0 parts by weight or more, Parts by weight or more. From the viewpoint of the repulsion performance, the amount thereof is preferably 40 parts by weight or less, more preferably 35 parts by weight or less, particularly preferably 25 parts by weight or less, 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 3/7 to 9/1, and particularly preferably 4/6 to 8/2. It is possible to obtain the core 104 in which the hardness is linearly increased from the center of gravity of the rubber composition containing such a weight ratio within the above range toward the surface thereof.

As the co-crosslinking agent (b), it is preferable to use zinc acrylate. For the purpose of improving the dispersibility of the rubber, there is zinc acrylate whose surface is coated with stearic acid or zinc stearate. In the present invention, when the rubber composition contains such zinc acrylate, such a coating material is not included in the concept of an acid and / or a salt (d).

The rubber composition of core 104 may comprise the organosulfur compound (e) described above for core 4 of the first embodiment. The organosulfur compound (e) has a linearity of the hardness distribution of the core 104; And can contribute to the control of the degree of the outer / inner oil structure. In view of rebound performance, the amount of the organic sulfur compound (e) is preferably 0.05 part by weight or more, particularly preferably 0.1 part by weight or more per 100 parts by weight of the base rubber. From the viewpoint of the rebound performance, the amount thereof is preferably 5.0 parts by weight or less, particularly preferably 2.0 parts by weight or less, per 100 parts by weight of the base rubber.

A filler may be included in the core 104 for purposes such as controlling specific gravity. Examples of suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. The amount of filler is suitably determined so that the desired specific gravity of the core 104 is achieved. Particularly preferred fillers are zinc oxide. Zinc oxide functions not only as a specific gravity adjuster but also as a crosslinking aid.

An antioxidant, a colorant, a plasticizer, a dispersant, a sulfur, a vulcanization accelerator and the like are added to the rubber composition of the core 104 as required. The crosslinked rubber powder or the synthetic resin powder may also be dispersed in the rubber composition.

In the core 104, the difference (Hs-H (0)) between the surface hardness Hs and the center hardness H (0) is preferably at least 15. Such a difference is large. In other words, the core 104 has an outer / inner oil structure. When the core 104 is hit with a middle iron, recoil (twist return) is large and spin is suppressed. The core 104 contributes to the flight performance of the golf ball 102. In terms of flight performance, the difference (Hs-H (0)) is more preferably 20 or more, particularly preferably 25 or more. In view of the fact that the core 104 can be easily formed, the difference (Hs-H (0)) is preferably 50 or less.

The hardness H (0) at the center of the core 104 is preferably not less than 40.0 and not more than 70.0. The golf ball 102 having hardness H (0) of 40.0 or more is excellent in rebound performance. From this viewpoint, the hardness H (0) is more preferably 45.0 or more, particularly preferably 50.0 or more. In the core 104 having a hardness H (0) of 70.0 or less, an outer / inner oil structure can be achieved. In the golf ball 102 including the core 104, spin can be suppressed. From this viewpoint, the hardness H (0) is more preferably 68.0 or less, particularly preferably 66.0 or less.

The hardness Hs at the surface of the core 104 is preferably 76.0 or more and 95.0 or less. In the core 104 having a hardness Hs of 76.0 or more, an outer / inner oil structure can be achieved. In the golf ball 102 including the core 104, spin can be suppressed. From this viewpoint, the hardness Hs is more preferably not less than 78.0, particularly preferably not less than 80.0. The golf ball 102 having a hardness Hs of 95.0 or less is excellent in durability. From such a viewpoint, the hardness Hs is more preferably 93.0 or less, particularly preferably 90.0 or less.

The core 104 preferably has a diameter of 35.0 mm or more and 40.0 mm or less. The core 104 having a diameter of 35.0 mm or more can achieve excellent rebound performance of the golf ball 102. From such a viewpoint, the diameter is more preferably 35.5 mm or more, particularly preferably 36.0 mm or more. The first cover 108, the second cover 110, the third cover 112 and the fourth cover 114 are formed to have a thickness of not more than 40.0 mm in the golf ball 102 including the core 104 having a diameter of 40.0 mm or less . The golf ball 102 including the thick covers 108, 110, 112, and 114 has excellent durability. From such a viewpoint, the diameter is more preferably 39.0 mm or less, particularly preferably 38.0 mm or less. The core 104 may have a rib at its surface.

From the viewpoint of shot feel, the core 104 preferably has a compressive deformation amount comp'n of 3.0 mm or more, particularly preferably 3.3 mm or more. From the viewpoint of the rebound performance, the amount of compressive deformation is preferably 4.6 mm or less, particularly preferably 4.3 mm or less.

In the case of the first cover 108, the resin composition is suitably used. Examples of the base polymer of the resin composition include an ionomer resin, a styrene block-containing thermoplastic elastomer, a thermoplastic polyester elastomer, a thermoplastic polyamide elastomer and a thermoplastic polyolefin elastomer.

A particularly preferred base polymer is an ionomer resin. The golf ball 102 including the first cover 108 including the ionomer resin is excellent in repelling performance. The ionomer resin and another resin may be used in combination with the first cover 108. In this case, the main component of the base polymer is preferably an ionomer resin. Specifically, the ratio of the ionomer resin to the total amount of the base polymer is preferably 50% by weight or more, more preferably 60% by weight or more, particularly preferably 70% by weight or more.

The first cover 108 may comprise the ionomer resin described above for the golf ball 2 of the first embodiment. The first cover 108 may comprise the styrene block-containing thermoplastic elastomer described above for the golf ball 2 of the first embodiment.

The resin composition of the first cover 108 contains a coloring agent such as titanium dioxide and a fluorescent pigment, fillers such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, do. The first cover 108 may include a powder of a metal having a high specific gravity.

According to the discovery of the inventor of the present invention, the first cover 108 significantly affects the deformation behavior of the golf ball 102 when striking the golf ball 102 with a middle iron. The golf ball 102 including the first cover 108 having a large hardness H1 is excellent in flight performance when hitting with a middle iron. The first cover 108, whose hardness H1 is not excessively large, can contribute to the feeling of hit of the golf ball 102.

From the viewpoint of flight performance, the hardness H1 of the first cover 108 is preferably 75 or more, more preferably 80 or more, particularly preferably 83 or more. From the viewpoint of feel of the golf ball 102, the hardness H1 is preferably 95 or less, particularly preferably 90 or less. The hardness H1 is measured by a JIS-C type hardness meter mounted on an automatic rubber hardness tester (trade name: "P1", manufactured by Kojundo Keiki Co., Ltd.). For the measurement, a slab with a thickness of about 2 mm is used, which is formed by a hot press. The slabs stored at 23 ° C for 2 weeks are used for the measurement. In the measurement, three slabs are stacked. A slab formed from the same resin composition as the resin composition of the first cover 108 is used.

The hardness H1 of the first cover 108 is greater than the hardness H1 of the core 104 in view of achieving an extensible / oil resistant structure in the globe consisting of the core 104 and the first cover 108 and inhibiting the spin of the golf ball 102. [ Is preferably larger than the surface hardness Hs. From the viewpoint of spin suppression, the difference (H1-Hs) between the hardness H1 and the hardness Hs is preferably 1 or more, particularly preferably 2 or more. The difference (H1-Hs) is preferably 10 or less. In the sphere where the difference (H1-Hs) is 10 or less, the hardness increases linearly from its center point toward its surface. In a sphere whose hardness is increased linearly, energy loss is low when the golf ball 102 is hit with a middle iron.

The thickness T1 of the first cover 108 is 0.2 mm or more and 1.8 mm or less. The first cover 108 having a thickness T1 of 0.2 mm or more can be easily formed. From this viewpoint, the thickness T1 is more preferably 0.4 mm or more, and particularly preferably 0.6 mm or more. The golf ball 102 including the first cover 108 having a thickness T1 of 1.8 mm or less is excellent in repelling performance. From such a viewpoint, the thickness T1 is more preferably 1.4 mm or less, and particularly preferably 1.2 mm or less.

In the case of forming the first cover 108, known methods such as injection molding, compression molding and the like can be used.

In the case of the second cover 110, the resin composition is suitably used. A preferred base polymer of the resin composition is an ionomer resin. The golf ball 102 including the second cover 110 including the ionomer resin is excellent in repelling performance. The ionomer resin described above with respect to the first cover 108 may be used for the second cover 110.

An ionomer resin and another resin may be used in combination. In this case, from the viewpoint of the rebound performance, the ionomer resin is included as a main component of the base polymer. The ratio of the ionomer resin to the total amount of the base polymer is preferably not less than 50% by weight, more preferably not less than 60% by weight, particularly preferably not less than 70% by weight.

Other preferred resins that may be used in combination with the ionomer resin include styrene block-containing thermoplastic elastomers. The styrene block-containing thermoplastic elastomer described above for the first cover 108 can be used in the second cover 110.

The second cover 110 may contain an appropriate amount of a coloring agent such as titanium dioxide and a fluorescent pigment, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent and a fluorescent whitening agent.

The second cover 110 preferably has a JIS-C hardness H2 of 75 or more and 96 or less. The golf ball 102 including the second cover 110 having hardness H2 of 75 or more is excellent in flight performance in a shot using a middle iron. From this viewpoint, the hardness H2 is more preferably 80 or more, particularly preferably 85 or more. The golf ball 102 including the second cover 110 having hardness H2 of 96 or less is excellent in shot feeling. From this viewpoint, the hardness H2 is more preferably 94 or less, particularly preferably 92 or less. The hardness H2 is measured in the same manner as the hardness H1.

The hardness H2 of the second cover 110 is preferably larger than the hardness H1 of the first cover 108. [ In the golf ball 102 in which the hardness H2 is greater than the hardness H1, the steel / oil resistant structure of the sphere consisting of the core 104, the first cover 108 and the second cover 110 can be achieved. When the golf ball 102 is hit with a middle iron, the spin rate is low. The golf ball 102 has excellent flight performance in a shot using a middle iron. From the viewpoint of flight performance, the difference (H2-H1) between the hardness H2 and the hardness H1 is preferably 2 or more. The difference (H2-H1) is preferably 20 or less.

The hardness H2 of the second cover 110 may be smaller than the hardness H1 of the first cover 108. [ The second cover 110 absorbs shocks when hitting the golf ball 102. The golf ball 102 is excellent in hit feeling. From the viewpoint of shot feel, the difference (H1-H2) between the hardness H1 and the hardness H2 is preferably 2 or more. The difference (H1-H2) is preferably 20 or less.

The second cover 110 preferably has a thickness T2 of 0.2 mm or more and 1.8 mm or less. The second cover 110 having a thickness T2 of 0.2 mm or more can be easily formed. From such a viewpoint, the thickness T2 is more preferably 0.4 mm or more, particularly preferably 0.6 mm or more. The golf ball 102 including the second cover 110 having a thickness T2 of 1.8 mm or less is excellent in repelling performance. From such a viewpoint, the thickness T2 is more preferably 1.4 mm or less, and particularly preferably 1.2 mm or less.

In the case of forming the second cover 110, known methods such as injection molding, compression molding and the like can be used.

In the case of the third cover 112, a resin composition is suitably used. A preferred base polymer of the resin composition is an ionomer resin. The golf ball 102 including the third cover 112 including the ionomer resin is excellent in rebound performance. The ionomer resin described above with respect to the first cover 108 may be used in the third cover 112.

An ionomer resin and another resin may be used in combination. In this case, from the viewpoint of the rebound performance, the ionomer resin is included as a main component of the base polymer. The ratio of the ionomer resin to the total amount of the base polymer is preferably not less than 50% by weight, more preferably not less than 60% by weight, particularly preferably not less than 70% by weight.

Other preferred resins that may be used in combination with the ionomer resin include styrene block-containing thermoplastic elastomers. The styrene block-containing thermoplastic elastomer described above with respect to the first cover 108 may be used in the third cover 112.

The third cover 112 contains an appropriate amount of a coloring agent such as titanium dioxide and a fluorescent pigment, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent and a fluorescent whitening agent.

The third cover 112 preferably has a JIS-C hardness H3 of 75 or more and 96 or less. The golf ball 102 including the third cover 112 having the hardness H3 of 75 or more is excellent in flight performance in the shot using the middle irons. From such a viewpoint, the hardness H3 is more preferably 80 or more, particularly preferably 85 or more. The golf ball 102 including the third cover 112 whose hardness H3 is 96 or less is excellent in shot feeling. From such a viewpoint, the hardness H3 is more preferably 94 or less, particularly preferably 92 or less. The hardness H3 is measured in the same manner as the hardness H1.

The hardness H3 of the third cover 112 is preferably larger than the hardness H2 of the second cover 110. [ In the golf ball 102 in which the hardness H3 is greater than the hardness H2, the outer / inner oil structure of the sphere consisting of the core 104, the first cover 108, the second cover 110 and the third cover 112 is achieved . When the golf ball 102 is hit with a middle iron, the spin rate is low. The golf ball 102 has excellent flight performance in a shot using a middle iron. From the viewpoint of flight performance, the difference (H3-H2) between the hardness H3 and the hardness H2 is preferably 2 or more. The difference (H3-H2) is preferably 20 or less.

The hardness H3 of the third cover 112 may be smaller than the hardness H2 of the first cover 108. [ The third cover 112 absorbs impact when hit by the golf ball 102. The golf ball 102 is excellent in hit feeling. From the viewpoint of shot feeling, the difference (H2-H3) between the hardness H2 and the hardness H3 is preferably 2 or more. The difference (H2-H3) is preferably 20 or less.

The third cover 112 preferably has a thickness T3 of 0.2 mm or more and 1.8 mm or less. The third cover 112 having a thickness T3 of 0.2 mm or more can be easily formed. From this viewpoint, the thickness T3 is more preferably at least 0.4 mm, and particularly preferably at least 0.6 mm. The golf ball 102 including the third cover 112 having a thickness T3 of 1.8 mm or less is excellent in repelling performance. From such a viewpoint, the thickness T3 is more preferably 1.4 mm or less, and particularly preferably 1.2 mm or less.

In the case of forming the third cover 112, a known method such as injection molding, compression molding and the like can be used.

In the case of the fourth cover 114, a resin composition is suitably used. A preferred base polymer of the resin composition is an ionomer resin. The golf ball 102 including the fourth cover 114 including the ionomer resin is excellent in repelling performance. The ionomer resin described above with respect to the first cover 108 may be used in the fourth cover 114.

An ionomer resin and another resin may be used in combination. In this case, from the viewpoint of the rebound performance, the ionomer resin is included as a main component of the base polymer. The ratio of the ionomer resin to the total amount of the base polymer is preferably not less than 50% by weight, more preferably not less than 60% by weight, particularly preferably not less than 70% by weight.

Preferred resins that can be used in combination with ionomer resins are ethylene- (meth) acrylic acid copolymers. The copolymer is obtained by a copolymerization reaction of a monomer composition comprising ethylene and (meth) acrylic acid. In the copolymer, some of the carboxyl groups are neutralized with metal ions. The copolymer contains not less than 3 wt% and not more than 25 wt% (meth) acrylic acid component. Particular preference is given to ethylene- (meth) acrylic acid copolymers having polar functional groups. A specific example of the ethylene- (meth) acrylic acid copolymer includes the trade name "Nucrell " manufactured by DuPont-Mitsui Polychemicals Company, Limited.

Another preferred resin that can be used in combination with the ionomer resin is a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer described above with respect to the first cover 108 may be used in the fourth cover 114.

The fourth cover 114 may contain an appropriate amount of a coloring agent such as titanium dioxide and a fluorescent pigment, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent and a fluorescent whitening agent.

The fourth cover 114 preferably has a JIS-C hardness H4 of 83 or more and 98 or less. The golf ball 102 including the fourth cover 114 having a hardness H4 of 83 or more is excellent in rebound performance. The golf ball 102 is excellent in flight performance. From this viewpoint, the hardness H4 is more preferably 86 or more, particularly preferably 89 or more. The golf ball 102 including the fourth cover 114 having a hardness H4 of 98 or less is excellent in shot feeling. From such a viewpoint, the hardness H4 is more preferably 96 or less, particularly preferably 94 or less. The hardness H4 is measured in the same manner as the hardness H1 measurement method.

The hardness H4 of the fourth cover 114 is preferably larger than the hardness H1 of the first cover 108. [ In the golf ball 102 in which the hardness H4 is greater than the hardness H1, spin can be suppressed. The golf ball 102 has excellent flight performance in a shot using a middle iron.

From the viewpoint of flight performance, the difference (H4-H1) between the hardness H4 and the hardness H1 is preferably 3 or more, more preferably 5 or more, particularly preferably 6 or more. The difference (H4-H1) is preferably 30 or less.

The hardness H4 of the fourth cover 114 is preferably larger than the hardness H3 of the third cover 112. [ In the golf ball 102 in which the hardness H4 is greater than the hardness H3, an outer / inner oil structure can be achieved. When the golf ball 102 is hit with a middle iron, the spin rate is low. The golf ball 102 has excellent flight performance in a shot using a middle iron. From the viewpoint of flight performance, the difference (H4-H3) between the hardness H4 and the hardness H3 is preferably 2 or more. The difference (H4-H3) is preferably 20 or less.

The thickness T4 of the fourth cover 114 is preferably 0.2 mm or more and 1.8 mm or less. The fourth cover 114 having a thickness T4 of 0.2 mm or more can be easily formed. From this viewpoint, the thickness T4 is more preferably at least 0.4 mm, and particularly preferably at least 0.6 mm. The golf ball 102 including the fourth cover 114 having a thickness T4 of 1.8 mm or less is excellent in repelling performance. From this viewpoint, the thickness T4 is more preferably 1.4 mm or less, and particularly preferably 1.2 mm or less.

In the case of forming the fourth cover 114, a known method such as injection molding, compression molding and the like can be used. At the time of forming the fourth cover 114, the dimples 116 are formed by the pimples formed on the cavity surface of the mold.

The cover 106 preferably has a total thickness of 6.0 mm or less. The golf ball 102 including the cover 106 having a total thickness of 6.0 mm or less is excellent in hit feeling. In this respect, the total thickness is particularly preferably not more than 4.0 mm. In view of the durability of the golf ball 102, the total thickness is 0.4 mm or more, more preferably 0.8 mm or more, particularly preferably 1.2 mm or more.

From the viewpoint of the shot feel, the golf ball 102 is preferably at least 2.8 mm, more preferably at least 2.9 mm, and particularly preferably at least 3.0 mm in the compression deformation amount comp'n. From the viewpoint of the rebound performance, the amount of compressive deformation is preferably 3.6 mm or less, more preferably 3.5 mm or less, particularly preferably 3.4 mm or less.

The third embodiment

Figure 5 shows a golf ball 202 according to a third embodiment of the present invention. The golf ball 202 includes a spherical core 204 and a cover 206 covering the core 204. The cover 206 includes an inner cover 208, a mid cover 210 located outside the inner cover 208, and an outer cover 212 located outside the mid cover 210. At the surface of the outer cover 212, a plurality of dimples 214 are formed. Of the surfaces of the golf ball 202, the portion excluding the dimple 214 is the land 216. [ The golf ball 202 includes a paint layer and a mark layer outside the outer cover 212, and these layers are not shown in the drawings.

The golf ball 202 has a diameter of 40 mm or more and 45 mm or less. In terms of compliance with the rules set by the American Golf Association (USGA), the diameter is preferably greater than 42.67 mm. From the viewpoint of suppressing the air resistance, the diameter is preferably 44 mm or less, more preferably 42.80 mm or less. The golf ball 202 has a weight of 40 g or more and 50 g or less. With respect to obtaining a large inertia, the weight is preferably at least 44 g, more preferably at least 45.00 g. In terms of compliance with the rules set by the USGA, the weight is preferably 45.93 g or less.

6 is a line graph showing the hardness distribution of the core 204 of the golf ball 202 in Fig. The abscissa of the graph represents the ratio (%) of the distance from the center point of the core 204 to the radius of the core 204. The vertical axis of the graph represents JIS-C hardness. Nine measurement points obtained by dividing the region from the center point of the core 204 to the surface of the core 204 by 12.5% of the radius of the core 4 are plotted on the graph. The ratio of the distance of each of these measurement points from the center point of the core 204 to the radius of the core 204 is as follows:

First point: 0.0% (center point)

2nd point: 12.5%

3rd point: 25.0%

4 points: 37.5%

5th point: 50.0%

6th point: 62.5%

7th: 75.0%

8th: 87.5%

9th: 100.0% (surface)

The JIS-C type hardness meter is pressed against the cut surfaces of the hemispheres obtained by cutting the core 204 to measure the hardness at points 1 to 8. The hardness at the ninth point is measured by pressing a JIS-C type hardness meter on the surface of the spherical core 204. For the measurement, an automatic rubber hardness tester (trade name: "P1", manufactured by Kobunshi Keiki Co., Ltd.) equipped with the above hardness meter is used. In the present invention, JIS-C hardness at a measurement point where the distance from the center point of the core 204 is x (%) is represented by H (x). The hardness at the center of the core 204 is represented by H (0). Note that the hardness at the surface of the core 204 is represented by Hs.

Fig. 6 also shows a linear approximation curve obtained by the least squares method based on the distance and hardness of nine measurement points. As is apparent from Fig. 6, the dashed line does not deviate greatly from the linear approximation curve. In other words, the broken line has a shape close to a linear approximation curve. In core 204, the hardness from its center point to its surface increases linearly. When the core 204 is hit with a middle iron, the energy loss is low. The core 204 has excellent rebound performance. When the golf ball 202 is hit with a middle iron, the distance is long.

In the core 204, the R ² of the linear approximation curve obtained by the least squares method is 0.95 or more. R ² is an index indicating the linearity of the broken line. In the case of the core 204 having R ² of 0.95 or more, the shape of the broken line of the hardness distribution is close to a straight line. The core 204 having an R ² of 0.95 or more has excellent rebound performance. R ² is more preferably at least 0.96, particularly preferably at least 0.97. R ² is calculated by squaring the correlation coefficient R. The correlation coefficient R is calculated by dividing the covariance of the distance (%) from the center point and the hardness (JIS-C) by the standard deviation of the distance from the center point (%) and the standard deviation of hardness (JIS-C).

The core 204 is obtained by crosslinking the rubber composition. The rubber composition comprises

(a) base rubber;

(b) co-crosslinks;

(c) crosslinking initiators; And

(d) an acid and / or a salt.

During heating and molding of the core 204, the base rubber (a) is crosslinked by the co-crosslinking agent (b). The heat of the crosslinking reaction remains near the center point of the core 204. Thus, at the time of heating and molding the core 204, the temperature at the center portion is high. The temperature is gradually reduced from the center point to the surface. In the rubber composition, it is presumed that the acid reacts with the metal salt of the co-crosslinking agent (b) and binds to the cation. In the rubber composition, it is presumed that the salt reacts with the metal salt of the co-crosslinking agent (b) to exchange cations. By bonding and exchange, the metal bridges are cut off. Such cutting is likely to occur at the center of the high temperature core 204 and not near the surface of the core 204. As a result, the cross-link density of the core 204 increases from its center point toward its surface. At the core 204, an outer / inner oil structure can be achieved. When the golf ball 202 including the core 204 is struck with a middle iron, the spin rate is slow. The golf ball 202 achieves excellent flight performance in a shot using a middle iron.

The rubber composition of the core 204 may comprise the base rubber (a) described above for the core 4 of the first embodiment.

The rubber composition of core 204 may comprise the co-crosslinking agent (b) described above for core 4 of the first embodiment. The preferred co-crosslinking agent (b)

(b1) an, -unsaturated carboxylic acid having 3 to 8 carbon atoms; And

(b2) a metal salt of an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms.

When the rubber composition contains an alpha, beta -unsaturated carboxylic acid (b1), it is preferable that the rubber composition further comprises a metal compound (f). The metal compound (f) reacts with the α, β-unsaturated carboxylic acid (b1) in the rubber composition. The salt obtained by this reaction is graft-polymerized together with the molecular chain of the base rubber. The rubber composition of the core 204 may comprise the metal compound (f) described above for the core 4 of the first embodiment.

From the viewpoint of the rebound performance of the golf ball 202, the amount of the co-crosslinking agent (b) is preferably at least 15 parts by weight, particularly preferably at least 20 parts by weight, per 100 parts by weight of the base rubber. The amount thereof is preferably 50 parts by weight or less, more preferably 45 parts by weight or less, particularly preferably 40 parts by weight or less, per 100 parts by weight of the base rubber.

The rubber composition of core 204 may comprise the crosslinking initiator (c) described above for core 4 of the first embodiment. In view of the repulsive performance of the golf ball 202, the amount of the crosslinking initiator (c) is preferably at least 0.2 part by weight, particularly preferably at least 0.5 part by weight, per 100 parts by weight of the base rubber. From the viewpoints of impact feel and durability of the golf ball 202, the amount thereof is preferably 5.0 parts by weight or less, particularly preferably 2.5 parts by weight or less, per 100 parts by weight of the base rubber.

The rubber composition of core 204 may comprise the acid and / or salt (d) described above for core 4 of the first embodiment. The co-crosslinking agent (b) is not included in the concept of an acid and / or a salt (d). It is presumed that the acid and / or salt (d) cut the metal bridges by the co-crosslinking agent (b) at the center of the core (204) upon heating and molding of the core (204).

In view of the linearity of the hardness distribution of the core 204, the amount of the acid and / or salt (d) is preferably at least 0.5 part by weight, more preferably at least 1.0 part by weight, more preferably at least 0.5 part by weight, 2.0 parts by weight or more. From the viewpoint of rebound performance, the amount thereof is preferably 40 parts by weight or less, more preferably 30 parts by weight or less, 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 3/7 to 9/1, and particularly preferably 4/6 to 8/2. It is possible to obtain the core 204 in which the hardness is linearly increased from the center of gravity of the rubber composition containing such a weight ratio within the above range toward the surface thereof.

As the co-crosslinking agent (b), it is preferable to use zinc acrylate. For the purpose of improving the dispersibility of the rubber, there is zinc acrylate whose surface is coated with stearic acid or zinc stearate. In the present invention, when the rubber composition contains such zinc acrylate, such a coating material is not included in the concept of an acid and / or a salt (d).

The rubber composition of core 204 may comprise the organo sulfur compound (e) described above for core 4 of the first embodiment. The organosulfur compound (e) has a linearity of the hardness distribution of the core 204; And can contribute to the control of the degree of the outer / inner oil structure. In view of rebound performance, the amount of the organic sulfur compound (e) is preferably 0.05 part by weight or more, particularly preferably 0.1 part by weight or more per 100 parts by weight of the base rubber. From the viewpoint of the rebound performance, the amount thereof is preferably 5.0 parts by weight or less, particularly preferably 2.0 parts by weight or less, per 100 parts by weight of the base rubber.

A filler may be included in the core 204 for the purpose of controlling specific gravity and the like. Examples of suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. The amount of filler is suitably determined so that the desired specific gravity of the core 204 is achieved. Particularly preferred fillers are zinc oxide. Zinc oxide functions not only as a specific gravity adjuster but also as a crosslinking aid.

An antioxidant, a colorant, a plasticizer, a dispersant, a sulfur, a vulcanization accelerator, and the like are added to the rubber composition of the core 204 as needed. The crosslinked rubber powder or the synthetic resin powder may also be dispersed in the rubber composition.

In the core 204, the difference (Hs-H (0)) between the surface hardness Hs and the center hardness H (0) is preferably at least 15. Such a difference is large. In other words, the core 204 has an outer / inner oil structure. When the core 204 is struck with a middle iron, recoil (twist return) is large and spin is suppressed. The core 204 contributes to the flight performance of the golf ball 202. In terms of flight performance, the difference (Hs-H (0)) is more preferably 20 or more, particularly preferably 25 or more. In view of the fact that the core 204 can be easily formed, the difference (Hs-H (0)) is preferably 50 or less.

The hardness H (0) at the central point of the core 204 is preferably not less than 40.0 and not more than 70.0. The golf ball 202 having a hardness H (0) of 40.0 or more has excellent rebound performance. From this viewpoint, the hardness H (0) is more preferably 45.0 or more, particularly preferably 50.0 or more. The core 204 having a hardness H (0) of 70.0 or less can attain an outer / inner oil structure. In the golf ball 202 including the core 204, spin can be suppressed. From this viewpoint, the hardness H (0) is more preferably 68.0 or less, particularly preferably 66.0 or less.

The hardness Hs at the surface of the core 204 is preferably 76.0 or more and 95.0 or less. In the core 204 having a hardness Hs of 76.0 or higher, an outer / inner oil structure can be achieved. In the golf ball 202 including the core 204, spin can be suppressed. From this viewpoint, the hardness Hs is more preferably not less than 78.0, particularly preferably not less than 80.0. The golf ball 202 having a hardness Hs of 95.0 or less is excellent in durability. From such a viewpoint, the hardness Hs is more preferably 93.0 or less, particularly preferably 90.0 or less.

The core 204 preferably has a diameter of 36.0 mm or more and 41.0 mm or less. The core 204 having a diameter of 36.0 mm or more can achieve excellent rebound performance of the golf ball 202. From this viewpoint, the diameter is more preferably at least 36.5 mm, and particularly preferably at least 37.0 mm. In the golf ball 202 including the core 204 having a diameter of 41.0 mm or less, the thickness of the inner cover 208, the mid cover 210 and the outer cover 212 may be sufficient. The golf ball 202 including the inner cover 208 having a large thickness, the mid cover 210 and the outer cover 212 is excellent in durability. From such a viewpoint, the diameter is more preferably 40.0 mm or less, particularly preferably 39.0 mm or less. The core 204 may have a rib at its surface.

From the viewpoint of shot feel, the core 204 preferably has a compression deformation amount comp'n of 3.0 mm or more, particularly preferably 3.3 mm or more. From the viewpoint of the rebound performance, the amount of compressive deformation is preferably 4.6 mm or less, particularly preferably 4.3 mm or less.

In the case of the inner cover 208, a resin composition is suitably used. Examples of the base polymer of the resin composition include an ionomer resin, a styrene block-containing thermoplastic elastomer, a thermoplastic polyester elastomer, a thermoplastic polyamide elastomer and a thermoplastic polyolefin elastomer.

A particularly preferred base polymer is an ionomer resin. The golf ball 202 including the inner cover 208 including the ionomer resin is excellent in repulsion performance. The ionomer resin and another resin can be used in combination with the inner cover 208. In this case, the main component of the base polymer is preferably an ionomer resin. Specifically, the ratio of the ionomer resin to the total amount of the base polymer is preferably 50% by weight or more, more preferably 60% by weight or more, particularly preferably 70% by weight or more.

The inner cover 208 may comprise the ionomer resin described above for the golf ball 2 of the first embodiment. The inner cover 208 may comprise the styrene block-containing thermoplastic elastomer described above for the golf ball 2 of the first embodiment.

The resin composition of the inner cover 208 contains an appropriate amount of a coloring agent such as titanium dioxide and a fluorescent pigment and a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, . The inner cover 208 may include a metal powder having a high specific gravity.

According to the discovery of the inventor of the present invention, the inner cover 208 significantly affects the deformation behavior of the golf ball 202 when striking the golf ball 202 with the middle irons. The golf ball 202 including the inner cover 208 having a large hardness Hi is a middle iron, which is excellent in flight performance when hit. The inner cover 208 having an excessively large hardness Hi can contribute to a feeling of hit of the golf ball 202.

From the viewpoint of flight performance, the hardness Hi of the inner cover 208 is 68 or more, and more preferably 71 or more. From the viewpoint of feel of the golf ball 202, the hardness Hi is preferably 82 or less, and more preferably 79 or less. The hardness Hi is measured with a JIS-C type hardness meter mounted on an automatic rubber hardness tester (trade name: "P1", manufactured by Kojundo Keiki Co., Ltd.). For measurements, a slab with a thickness of about 2 mm is used, which is formed by a hot press. The slabs stored at 23 ° C for 2 weeks are used for the measurement. In the measurement, three slabs are stacked. A slab formed from the same resin composition as the resin composition of the inner cover 208 is used.

The inner cover 208 preferably has a thickness of 0.2 mm or more and 1.2 mm or less. The inner cover 208 having a thickness of 0.2 mm or more can be easily formed. From this viewpoint, the thickness is more preferably 0.4 mm or more, and particularly preferably 0.6 mm or more. The golf ball 202 including the inner cover 208 having a thickness of 1.2 mm or less has excellent repulsion performance. From this viewpoint, the thickness is more preferably 1.0 mm or less, particularly preferably 0.9 mm or less.

In the case of forming the inner cover 208, known methods such as injection molding, compression molding and the like can be used.

In the case of the mid cover 210, a resin composition is suitably used. A preferred base polymer of the resin composition is an ionomer resin. The golf ball 202 including the mid cover 210 including the ionomer resin is excellent in repelling performance. The ionomer resin described above with respect to the inner cover 208 may be used for the mid cover 210.

An ionomer resin and another resin may be used in combination. In this case, from the viewpoint of the rebound performance, the ionomer resin is included as a main component of the base polymer. The ratio of the ionomer resin to the total amount of the base polymer is preferably not less than 50% by weight, more preferably not less than 60% by weight, particularly preferably not less than 70% by weight.

Another preferred resin that may be used in combination with the ionomer resin is a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer described above with respect to the inner cover 208 may be used for the mid cover 210.

The intermediate cover 210 may contain an appropriate amount of a coloring agent such as titanium dioxide and a fluorescent pigment, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent and a fluorescent whitening agent.

The mid cover 210 preferably has a JIS-C hardness Hm of 68 or more and 89 or less. The golf ball 202 including the mid cover 210 having the hardness Hm of 68 or more has excellent flying performance in a shot using a middle iron. From such a viewpoint, the hardness Hm is more preferably 71 or more. The golf ball 202 including the mid cover 210 having a hardness Hm of 89 or less is excellent in shot feeling. From this viewpoint, the hardness Hm is more preferably 87 or less. The hardness Hm is measured in the same manner as the hardness Hi measurement method.

The mid cover 210 preferably has a thickness of 0.2 mm or more and 1.2 mm or less. The mid cover 210 having a thickness of 0.2 mm or more can be easily formed. From this viewpoint, the thickness is more preferably 0.4 mm or more, and particularly preferably 0.6 mm or more. The golf ball 202 including the mid cover 210 having a thickness of 1.2 mm or less is excellent in repulsion performance. From this viewpoint, the thickness is more preferably 1.0 mm or less, particularly preferably 0.9 mm or less.

In the case of forming the mid cover 210, known methods such as injection molding, compression molding and the like can be used.

In the case of the outer cover 212, a resin composition is suitably used. A preferred base polymer of the resin composition is an ionomer resin. The golf ball 202 including the outer cover 212 including the ionomer resin is excellent in repulsion performance. The ionomer resin described above with respect to the inner cover 208 can be used for the outer cover 212.

An ionomer resin and another resin may be used in combination. In this case, from the viewpoint of the rebound performance, the ionomer resin is included as a main component of the base polymer. The ratio of the ionomer resin to the total amount of the base polymer is preferably not less than 50% by weight, more preferably not less than 60% by weight, particularly preferably not less than 70% by weight.

Preferred resins that can be used in combination with ionomer resins are ethylene- (meth) acrylic acid copolymers. The copolymer is obtained by a copolymerization reaction of a monomer composition comprising ethylene and (meth) acrylic acid. In the copolymer, some of the carboxyl groups are neutralized with metal ions. The copolymer contains not less than 3 wt% and not more than 25 wt% (meth) acrylic acid component. Particular preference is given to ethylene- (meth) acrylic acid copolymers having polar functional groups. As a specific example of the ethylene- (meth) acrylic acid copolymer, there is a trade name "NUCLEAR" manufactured by DuPont-Mitsui Polychemicals Company, Limited.

Another preferred resin that can be used in combination with the ionomer resin is a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer described above with respect to the inner cover 208 may be used for the outer cover 212.

The outer cover 212 contains an appropriate amount of a coloring agent such as titanium dioxide and a fluorescent pigment, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent and a fluorescent whitening agent.

The outer cover 212 preferably has a JIS-C hardness Ho of 83 or more and 98 or less. The golf ball 202 including the outer cover 212 having a hardness Ho of 83 or more is excellent in repulsion performance. The golf ball 202 is excellent in flight performance. From this viewpoint, the hardness Ho is more preferably 86 or more, particularly preferably 89 or more. The golf ball 202 including the outer cover 212 having the hardness Ho of 98 or less is excellent in hit feeling. From this viewpoint, the hardness Ho is more preferably 96 or less, particularly preferably 94 or less. The hardness Ho is measured in the same manner as the hardness Hi measurement method.

The outer cover 212 preferably has a thickness of 0.2 mm or more and 1.2 mm or less. The outer cover 212 having a thickness of 0.2 mm or more can be easily formed. From this viewpoint, the thickness is more preferably 0.4 mm or more, and particularly preferably 0.6 mm or more. The golf ball 202 including the outer cover 212 having a thickness of 1.2 mm or less has excellent repulsion performance. From this viewpoint, the thickness is more preferably 1.0 mm or less, particularly preferably 0.9 mm or less.

In the case of forming the outer cover 212, known methods such as injection molding, compression molding and the like can be used. At the time of forming the outer cover 212, the dimples 214 are formed by the pimples formed on the cavity surface of the mold.

In the golf ball 202, the hardness Ho of the outer cover 212 is greater than the hardness Hi of the inner cover 208. In the golf ball 202 whose hardness Ho is greater than hardness Hi, spin can be suppressed. The golf ball 202 has excellent flying performance in a shot using a middle iron.

From the viewpoint of flight performance, the difference between the hardness Ho and the hardness Hi (Ho-Hi) is preferably 5 or more, more preferably 6 or more, particularly preferably 7 or more. The difference (Ho-H1) is preferably 30 or less.

The hardness Ho of the outer cover 212 is preferably larger than the hardness Hm of the mid cover 210. [ In the golf ball 202 in which the hardness Ho is greater than the hardness Hm, an outer / inner oil structure can be achieved in the cover 206. [ When the golf ball 202 is hit with a middle iron, the spin rate is low. The golf ball 202 has excellent flying performance in a shot using a middle iron. From the viewpoint of flight performance, the difference (Ho-Hm) between the hardness Ho and the hardness Hm is preferably 2 or more. The difference (Ho-Hm) is preferably 25 or less.

In the golf ball 202, the hardness Hi of the inner cover 208 is smaller than the surface hardness Hs of the core 204. [ In other words, the surface hardness Hs of the core 204 is larger than the hardness Hi of the inner cover 208. When the golf ball 202 is hit by a middle iron, the inner cover 208 absorbs the impact of the golf ball 202. The golf ball 202 is excellent in hit feeling. From the viewpoint of shot feel, the difference (Hs-Hi) between the hardness Hs and the hardness Hi is preferably 1 or more, particularly preferably 2 or more. The difference (Hs-Hi) is preferably 15 or less. In the sphere having the difference (Hs-Hi) of 15 or less, the impact of the inner cover 208 against the deformation behavior of the golf ball 202 when hitting the golf ball 202 with the middle iron is appropriately suppressed. In the sphere, energy loss is low when striking the golf ball 202 with a middle iron. In addition, in the golf ball 202, the flying distance and the spin speed are changed little when striking the golf ball 202 with the middle irons.

The hardness Hm of the mid cover 210 may be greater than the hardness Hi of the inner cover 208. [ In such a case, an outer / inner oil structure may be achieved in the cover 206. When the golf ball 202 is hit with a middle iron, the spin rate is low. The golf ball 202 is excellent in flight performance in a shot using a middle iron

The hardness Hm of the mid cover 210 may be smaller than the hardness Hi of the inner cover 208. [ The mid cover 210 absorbs the impact when hitting the golf ball 202. The golf ball 202 is excellent in hit feeling.

The difference (Hm-Hi) between the hardness Hm and the hardness Hi is preferably -5 or more, from the viewpoints of achieving both the predetermined flight performance and the predetermined hit feeling. The difference (Hm-Hi) is preferably 20 or less.

The cover 206 preferably has a total thickness of 2.5 mm or less. The golf ball 202 including the cover 206 having a total thickness of 2.5 mm or less is excellent in hit feeling. In this respect, the total thickness is particularly preferably not more than 2.4 mm. In view of the durability of the golf ball 202, the total thickness is preferably not less than 0.3 mm, more preferably not less than 0.5 mm, particularly preferably not less than 0.8 mm.

From the viewpoint of shot feel, the golf ball 202 is preferably a compressive deformation amount comp'n of 2.8 mm or more, more preferably 2.9 mm or more, particularly preferably 3.0 mm or more. From the viewpoint of the rebound performance, the amount of compressive deformation is preferably 3.6 mm or less, more preferably 3.5 mm or less, particularly preferably 3.4 mm or less.

Fourth embodiment

Fig. 7 shows a golf ball 302 according to a fourth embodiment of the present invention. The golf ball 302 includes a spherical core 304 and a cover 306 covering the core 304. The cover 306 includes an inner cover 308, a first mid cover 310 located outside the inner cover 308, a second mid cover 312 located outside the first mid cover 310, And an outer cover 314 located on the outer side of the second mid cover 312. At the surface of the outer cover 314, a plurality of dimples 316 are formed. Among the surfaces of the golf ball 302, a portion excluding the dimple 316 is a land 318. [ The golf ball 302 includes a paint layer and a mark layer outside the outer cover 314, and these layers are not shown in the drawings.

The golf ball 302 has a diameter of 40 mm or more and 45 mm or less. In terms of compliance with the rules set by the American Golf Association (USGA), the diameter is preferably greater than 42.67 mm. From the viewpoint of suppressing the air resistance, the diameter is preferably 44 mm or less, more preferably 42.80 mm or less. The golf ball 302 has a weight of 40 g or more and 50 g or less. With respect to obtaining a large inertia, the weight is preferably at least 44 g, more preferably at least 45.00 g. In terms of compliance with the rules set by the USGA, the weight is preferably 45.93 g or less.

8 is a line graph showing the hardness distribution of the core 304 of the golf ball 302 in Fig. The horizontal axis of the graph represents the ratio (%) of the distance from the center point of the core 304 to the radius of the core 304. The vertical axis of the graph represents JIS-C hardness. The nine measurement points obtained by dividing the region from the center point of the core 304 to the surface of the core 304 by 12.5% of the radius of the core 304 are plotted on the graph. The ratio of the distance of each of these measurement points from the center point of the core 304 to the radius of the core 304 is as follows:

First point: 0.0% (center point)

2nd point: 12.5%

3rd point: 25.0%

4 points: 37.5%

5th point: 50.0%

6th point: 62.5%

7th: 75.0%

8th: 87.5%

9th: 100.0% (surface)

The JIS-C type hardness meter is pressed against the cut surfaces of the hemispheres obtained by cutting the core 304 to measure the hardness at points 1 to 8. The hardness Hs at the ninth point is measured by pressing a JIS-C type hardness meter on the surface of the spherical core 304. For the measurement, an automatic rubber hardness tester (trade name: "P1", manufactured by Kobunshi Keiki Co., Ltd.) equipped with the above hardness meter is used. In the present invention, JIS-C hardness at a measurement point where the distance from the center point of the core 304 is x (%) is represented by H (x). The hardness at the center of the core 304 is represented by H (0).

Fig. 8 also shows a linear approximation curve obtained by the least squares method based on the distance and hardness of nine measurement points. As is apparent from Fig. 8, the dashed line does not deviate greatly from the linear approximation curve. In other words, the broken line has a shape close to a linear approximation curve. In core 304, the hardness from its center point to its surface increases linearly. When the core 304 is hit with a middle iron, energy loss is low. The core 304 has excellent rebound performance. When the golf ball 302 is hit with a middle iron, the distance is long.

In the core 304, the R ² of the linear approximation curve obtained by the least square method is 0.95 or more. R ² is an index indicating the linearity of the broken line. In the case of the core 304 having R ² of 0.95 or more, the shape of the broken line of the hardness distribution is close to a straight line. The core 304 having R ² of 0.95 or more has excellent rebound performance. R ² is more preferably at least 0.96, particularly preferably at least 0.97. R ² is calculated by squaring the correlation coefficient R. The correlation coefficient R is calculated by dividing the covariance of the distance (%) from the center point and the hardness (JIS-C) by the standard deviation of the distance from the center point (%) and the standard deviation of hardness (JIS-C).

The core 304 is obtained by crosslinking the rubber composition. The rubber composition comprises

(a) base rubber;

(b) co-crosslinks;

(c) crosslinking initiators; And

(d) an acid and / or a salt.

During heating and molding of the core 304, the base rubber (a) is crosslinked by the co-crosslinking agent (b). The heat of the crosslinking reaction remains near the center point of the core 304. Thus, at the time of heating and molding the core 304, the temperature at the center portion is high. The temperature is gradually reduced from the center point to the surface. In the rubber composition, it is presumed that the acid reacts with the metal salt of the co-crosslinking agent (b) and binds to the cation. In the rubber composition, it is presumed that the salt reacts with the metal salt of the co-crosslinking agent (b) to exchange cations. By bonding and exchange, the metal bridges are cut off. Such cutting will easily occur at the center of the high temperature core 304 and will not occur near the surface of the core 304. [ As a result, the cross-link density of the core 304 increases from its center point toward its surface. At core 304, an extensible / oil resistant structure can be achieved. When the golf ball 302 including the core 304 is hit with a middle iron, the spin speed is slow. The golf ball 302 achieves excellent flight performance in a shot using a middle iron.

The rubber composition of the core 304 may comprise the base rubber (a) described above for the core 4 of the first embodiment.

The rubber composition of the core 304 may comprise the co-crosslinking agent (b) described above for the core 4 of the first embodiment. The preferred co-crosslinking agent (b)

(b1) an, -unsaturated carboxylic acid having 3 to 8 carbon atoms; And

(b2) a metal salt of an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms.

When the rubber composition contains an alpha, beta -unsaturated carboxylic acid (b1), it is preferable that the rubber composition further comprises a metal compound (f). The metal compound (f) reacts with the α, β-unsaturated carboxylic acid (b1) in the rubber composition. The salt obtained by this reaction is graft-polymerized together with the molecular chain of the base rubber. The rubber composition of the core 304 may comprise the metal compound (f) described above for the core 4 of the first embodiment.

From the viewpoint of the rebound performance of the golf ball 302, the amount of the co-crosslinking agent (b) is preferably at least 15 parts by weight, particularly preferably at least 20 parts by weight, per 100 parts by weight of the base rubber. The amount thereof is preferably 50 parts by weight or less, more preferably 45 parts by weight or less, particularly preferably 40 parts by weight or less, per 100 parts by weight of the base rubber.

The rubber composition of the core 304 may comprise the crosslinking initiator (c) described above for the core 4 of the first embodiment. From the viewpoint of the rebound performance of the golf ball 302, the amount of the crosslinking initiator (c) is preferably at least 0.2 part by weight, particularly preferably at least 0.5 part by weight per 100 parts by weight of the base rubber. From the viewpoints of feeling of impact and durability of the golf ball 302, the amount thereof is preferably 5.0 parts by weight or less, particularly preferably 2.5 parts by weight or less, per 100 parts by weight of the base rubber.

The rubber composition of core 304 may comprise the acid and / or salt (d) described above for core 4 of the first embodiment. In the present invention, the co-crosslinking agent (b) is not included in the concept of acid and / or salt (d). As noted above, it is believed that the acid and / or salt (d) breaks the metal bridges at the center of core 304 during heating and shaping of core 304 by co-crosslinking agent (b).

In view of the linearity of the hardness distribution of the core 304, the amount of the acid and / or salt (d) is preferably at least 1 part by weight, more preferably at least 2 parts by weight, 3 parts by weight or more, particularly preferably 4 parts by weight or more. From the viewpoint of the rebound performance, the amount thereof is preferably 40 parts by weight or less, more preferably 30 parts by weight or less, particularly preferably 20 parts by weight or less, 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 3/7 to 9/1, and particularly preferably 4/6 to 8/2. It is possible to obtain the core 304 in which the hardness is linearly increased from the center of gravity of the rubber composition containing such a weight ratio within the above range toward its surface.

As the co-crosslinking agent (b), it is preferable to use zinc acrylate. For the purpose of improving the dispersibility of the rubber, there is zinc acrylate whose surface is coated with stearic acid or zinc stearate. In the present invention, when the rubber composition contains such zinc acrylate, such a coating material is not included in the concept of an acid and / or a salt (d).

The rubber composition of core 304 may comprise the organo sulfur compound (e) described above for core 4 of the first embodiment. The organosulfur compound (e) has a linearity of the hardness distribution of the core 304; And can contribute to the control of the degree of the outer / inner oil structure. In view of rebound performance, the amount of the organic sulfur compound (e) is preferably 0.05 part by weight or more, particularly preferably 0.1 part by weight or more per 100 parts by weight of the base rubber. From the viewpoint of the rebound performance, the amount thereof is preferably 5.0 parts by weight or less, particularly preferably 2.0 parts by weight or less, per 100 parts by weight of the base rubber.

A filler may be included in the core 304 for the purpose of adjusting specific gravity and the like. Examples of suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. The amount of filler is suitably determined so that the desired specific gravity of the core 304 is achieved. Particularly preferred fillers are zinc oxide. Zinc oxide functions not only as a specific gravity adjuster but also as a crosslinking aid.

An antioxidant, a colorant, a plasticizer, a dispersant, sulfur, a vulcanization accelerator, and the like are added to the rubber composition of the core 304 as needed. The crosslinked rubber powder or the synthetic resin powder may also be dispersed in the rubber composition.

In the core 304, the difference (Hs-H (0)) between the surface hardness Hs and the center hardness H (0) is preferably at least 15. Such a difference is large. In other words, the core 304 has an outer / inner oil structure. When the core 304 is hit with a middle iron, recoil (twist return) is large and spin is suppressed. The core 304 contributes to the flight performance of the golf ball 302. In terms of flight performance, the difference (Hs-H (0)) is more preferably 20 or more, particularly preferably 25 or more. In view of the fact that the core 304 can be easily formed, the difference (Hs-H (0)) is preferably 50 or less.

The hardness H (0) at the center of the core 304 is preferably not less than 40.0 and not more than 70.0. The golf ball 302 having a hardness H (0) of 40.0 or more is excellent in repulsion performance. From this viewpoint, the hardness H (0) is more preferably 45.0 or more, particularly preferably 50.0 or more. The core 304 having a hardness H (0) of 70.0 or less can achieve an outer / inner oil structure. In the golf ball 302 including the core 304, spin can be suppressed. From this viewpoint, the hardness H (0) is more preferably 68.0 or less, particularly preferably 66.0 or less.

The hardness Hs at the surface of the core 304 is preferably 76.0 or more and 95.0 or less. In the core 304 having a hardness Hs of 76.0 or more, an outer / inner oil structure can be achieved. In the golf ball 302 including the core 304, spin can be suppressed. From this viewpoint, the hardness Hs is more preferably not less than 78.0, particularly preferably not less than 80.0. The golf ball 302 having a hardness Hs of 95.0 or less is excellent in durability. From such a viewpoint, the hardness Hs is more preferably 93.0 or less, particularly preferably 90.0 or less.

The core 304 preferably has a diameter of 35.0 mm or more and 41.0 mm or less. The core 304 having a diameter of 35.0 mm or more can achieve excellent rebound performance of the golf ball 302. From such a viewpoint, the diameter is more preferably 35.5 mm or more, particularly preferably 36.0 mm or more. The inner cover 308, the first mid cover 310, the second mid cover 312, and the outer cover 314 have a thickness (thickness) of 41.0 mm or less in the golf ball 302 including the core 304, May be sufficient. The golf ball 302 having a large thickness of the inner cover 308, the first mid cover 310, the second mid cover 312 and the outer cover 314 is excellent in durability. From such a viewpoint, the diameter is more preferably 40.0 mm or less, particularly preferably 39.0 mm or less. Core 304 may have a rib at its surface.

From the viewpoint of feeling of impact, the core 304 preferably has a compressive strain (comp'n) of 3.0 mm or more, particularly preferably 3.3 mm or more. From the viewpoint of the rebound performance, the amount of compressive deformation is preferably 4.6 mm or less, particularly preferably 4.3 mm or less.

In the case of the inner cover 308, a resin composition is suitably used. Examples of the base polymer of the resin composition include an ionomer resin, a styrene block-containing thermoplastic elastomer, a thermoplastic polyester elastomer, a thermoplastic polyamide elastomer and a thermoplastic polyolefin elastomer.

A particularly preferred base polymer is an ionomer resin. The golf ball 302 including the inner cover 308 including the ionomer resin is excellent in repelling performance. The ionomer resin and another resin can be used in combination with the inner cover 308. In this case, the main component of the base polymer is preferably an ionomer resin. Specifically, the ratio of the ionomer resin to the total amount of the base polymer is preferably 50% by weight or more, more preferably 60% by weight or more, particularly preferably 70% by weight or more.

The inner cover 308 may comprise the ionomer resin described above for the golf ball 2 of the first embodiment. The inner cover 308 may comprise the styrene block-containing thermoplastic elastomer described above for the golf ball 2 of the first embodiment.

The resin composition of the inner cover 308 contains an appropriate amount of a coloring agent such as titanium dioxide and a fluorescent pigment, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, . The inner cover 308 may include a powder of a metal having a high specific gravity.

According to the discovery of the inventor of the present invention, the inner cover 308 significantly affects the deformation behavior of the golf ball 302 when striking the golf ball 302 with the middle irons. The golf ball 302 including the inner cover 308 having a large hardness Hi is excellent in flight performance when hitting with a middle iron. The inner cover 308 whose hardness H1 is not excessively large can contribute to the feeling of hit of the golf ball 302.

From the viewpoint of flight performance, the hardness Hi of the inner cover 308 is 68 or more, and more preferably 71 or more. From the viewpoint of feel of the golf ball 302, the hardness Hi is preferably 82 or less, and more preferably 79 or less. The hardness Hi is measured with a JIS-C type hardness meter mounted on an automatic rubber hardness tester (trade name: "P1", manufactured by Kojundo Keiki Co., Ltd.). For measurements, a slab with a thickness of about 2 mm is used, which is formed by a hot press. The slabs stored at 23 ° C for 2 weeks are used for the measurement. In the measurement, three slabs are stacked. A slab formed from the same resin composition as the resin composition of the inner cover 308 is used.

The inner cover 308 preferably has a thickness Ti of 0.2 mm or more and 1.8 mm or less. The inner cover 308 having a thickness Ti of 0.2 mm or more can be easily formed. From such a viewpoint, the thickness Ti is more preferably 0.4 mm or more, and particularly preferably 0.6 mm or more. The golf ball 302 including the inner cover 308 having a thickness of 1.8 mm or less has excellent repulsion performance. From such a viewpoint, the thickness Ti is more preferably not more than 1.6 mm, particularly preferably not more than 1.4 mm.

In the case of forming the inner cover 308, a known method such as injection molding, compression molding and the like can be used.

In the case of the first mid cover 310, a resin composition is suitably used. A preferred base polymer of the resin composition is an ionomer resin. The golf ball 302 including the first mid cover 310 including the ionomer resin is excellent in repulsion performance. The ionomer resin described above with respect to the inner cover 308 may be used for the first mid cover 310.

An ionomer resin and another resin may be used in combination. In this case, from the viewpoint of the rebound performance, the ionomer resin is included as a main component of the base polymer. The ratio of the ionomer resin to the total amount of the base polymer is preferably not less than 50% by weight, more preferably not less than 60% by weight, particularly preferably not less than 70% by weight.

Another preferred resin that may be used in combination with the ionomer resin is a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer described above with respect to the inner cover 308 can be used in the first mid cover 310.

The first mid cover 310 contains an appropriate amount of a coloring agent such as titanium dioxide and a fluorescent pigment, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, .

The first mid cover 310 preferably has a JIS-C hardness Hm1 of 68 or more and 89 or less. The golf ball 302 including the first mid cover 310 having a hardness Hm1 of 68 or more is excellent in flight performance in a shot using a middle iron. From this viewpoint, the hardness Hm1 is more preferably 71 or more. The golf ball 302 including the first mid cover 310 having a hardness Hm1 of 89 or less is excellent in shot feeling. From this viewpoint, the hardness Hm1 is more preferably 87 or less. The hardness Hm1 is measured in the same manner as the hardness Hi measurement method.

The first mid cover 310 preferably has a thickness Tm1 of 0.2 mm or more and 1.8 mm or less. The first mid cover 310 having a thickness Tm1 of 0.2 mm or more can be easily formed. From this viewpoint, the thickness Tm1 is more preferably at least 0.4 mm, and particularly preferably at least 0.6 mm. The golf ball 302 including the first mid cover 310 having a thickness Tm1 of 1.8 mm or less is excellent in repulsion performance. From this viewpoint, the thickness Tm1 is more preferably 1.6 mm or less, particularly preferably 1.4 mm or less.

In the case of forming the first mid cover 310, known methods such as injection molding, compression molding and the like can be used.

In the case of the second mid cover 312, a resin composition is suitably used. A preferred base polymer of the resin composition is an ionomer resin. The golf ball 302 including the second mid cover 312 including the ionomer resin is excellent in repulsion performance. The ionomer resin described above with respect to the inner cover 308 may be used in the second mid cover 312.

An ionomer resin and another resin may be used in combination. In this case, from the viewpoint of the rebound performance, the ionomer resin is included as a main component of the base polymer. The ratio of the ionomer resin to the total amount of the base polymer is preferably not less than 50% by weight, more preferably not less than 60% by weight, particularly preferably not less than 70% by weight.

A preferred resin that can be used in combination with the ionomer resin is a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer described above with respect to the inner cover 308 can be used for the second mid cover 312.

The second mid cover 312 contains an appropriate amount of a coloring agent such as titanium dioxide and a fluorescent pigment, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, .

The second mid cover 312 preferably has a JIS-C hardness Hm2 of 68 or more and 89 or less. The golf ball 302 including the second mid cover 312 having a hardness Hm2 of 68 or more is excellent in flight performance in a shot using a middle iron. From this viewpoint, the hardness Hm2 is more preferably 71 or more. The golf ball 302 including the second mid cover 312 having a hardness Hm2 of 89 or less is excellent in shot feeling. From this viewpoint, the hardness Hm2 is more preferably 87 or less. The hardness Hm2 is measured in the same manner as the hardness Hi measurement method.

The thickness Tm2 of the second mid cover 312 is preferably 0.2 mm or more and 1.8 mm or less. The second mid cover 312 having a thickness Tm2 of 0.2 mm or more can be easily formed. From this viewpoint, the thickness Tm2 is more preferably at least 0.4 mm, and particularly preferably at least 0.6 mm. The golf ball 302 including the second mid cover 312 having a thickness Tm2 of 1.8 mm or less is excellent in repelling performance. From this viewpoint, the thickness Tm2 is more preferably 1.6 mm or less, particularly preferably 1.4 mm or less.

In the case of forming the second mid cover 312, known methods such as injection molding, compression molding and the like can be used.

In the case of the outer cover 314, a resin composition is suitably used. A preferred base polymer of the resin composition is an ionomer resin. The golf ball 302 including the outer cover 314 including the ionomer resin is excellent in repelling performance. The ionomer resin described above with respect to the inner cover 308 can be used for the outer cover 314.

An ionomer resin and another resin may be used in combination. In this case, from the viewpoint of the rebound performance, the ionomer resin is included as a main component of the base polymer. The ratio of the ionomer resin to the total amount of the base polymer is preferably not less than 50% by weight, more preferably not less than 60% by weight, particularly preferably not less than 70% by weight.

Preferred resins that can be used in combination with ionomer resins are ethylene- (meth) acrylic acid copolymers. The copolymer is obtained by a copolymerization reaction of a monomer composition comprising ethylene and (meth) acrylic acid. In the copolymer, some of the carboxyl groups are neutralized with metal ions. The copolymer contains not less than 3 wt% and not more than 25 wt% (meth) acrylic acid component. Particular preference is given to ethylene- (meth) acrylic acid copolymers having polar functional groups. As a specific example of the ethylene- (meth) acrylic acid copolymer, there is a trade name "NUCLEAR" manufactured by DuPont-Mitsui Polychemicals Company, Limited.

Another preferred resin that can be used in combination with the ionomer resin is a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer described above with respect to the inner cover 308 can be used for the outer cover 314.

The outer cover 314 contains an appropriate amount of a coloring agent such as titanium dioxide and a fluorescent pigment, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent and a fluorescent whitening agent.

The outer cover 314 preferably has a JIS-C hardness Ho of 83 or more and 98 or less. The golf ball 302 including the outer cover 314 having the hardness Ho of 83 or more has excellent rebound performance. The golf ball 302 is excellent in flight performance. From this viewpoint, the hardness Ho is more preferably 86 or more, particularly preferably 89 or more. The golf ball 302 including the outer cover 314 having a hardness Ho of 98 or less is excellent in shot feeling. From this viewpoint, the hardness Ho is more preferably 96 or less, particularly preferably 94 or less. The hardness Ho is measured in the same manner as the hardness Hi measurement method.

The outer cover 314 preferably has a thickness To of 0.2 mm or more and 1.8 mm or less. The outer cover 314 having a thickness To of 0.2 mm or more can be easily formed. From such a viewpoint, the thickness To is more preferably 0.4 mm or more, particularly preferably 0.6 mm or more. The golf ball 302 including the outer cover 314 having a thickness To of 1.8 mm or less is excellent in repulsion performance. From this point of view, the thickness To is more preferably 1.6 mm or less, and particularly preferably 1.4 mm or less.

In the case of forming the outer cover 314, a known method such as injection molding, compression molding and the like can be used. At the time of forming the outer cover 314, the dimples 316 are formed by the pimples formed on the cavity surface of the mold.

In the golf ball 302, the hardness Ho of the outer cover 314 is greater than the hardness Hi of the inner cover 308. [ In the golf ball 302 whose hardness Ho is greater than hardness Hi, spin can be suppressed. The golf ball 302 is excellent in flight performance in a shot using a middle iron

From the viewpoint of flight performance, the difference between the hardness Ho and the hardness Hi (Ho-Hi) is preferably 5 or more, more preferably 6 or more, particularly preferably 7 or more. The difference (Ho-Hi) is preferably 30 or less.

The hardness Ho of the outer cover 314 is preferably larger than the hardness Hm1 of the first mid cover 310. [ In the golf ball 302 in which the hardness Ho is greater than the hardness Hm1, an outer / inner oil structure can be achieved in the cover 306. [ When the golf ball 302 is hit with a middle iron, the spin rate is low. The golf ball 302 is excellent in flight performance in a shot using a middle iron. From the viewpoint of flight performance, the difference (Ho-Hm1) between the hardness Ho and the hardness Hm1 is preferably 2 or more. The difference (Ho-Hm1) is preferably 25 or less.

The hardness Ho of the outer cover 314 is preferably larger than the hardness Hm2 of the second mid cover 312. [ In the golf ball 302 in which the hardness Ho is greater than the hardness Hm2, an outer / inner oil structure can be achieved in the cover 306. [ When the golf ball 302 is hit with a middle iron, the spin rate is low. The golf ball 302 is excellent in flight performance in a shot using a middle iron. From the viewpoint of flight performance, the difference (Ho-Hm2) between the hardness Ho and the hardness Hm2 is preferably 2 or more. The difference (Ho-Hm2) is preferably 25 or less.

In the golf ball 302, the hardness Hi of the inner cover 308 is smaller than the surface hardness Hs of the core 304. [ In other words, the surface hardness Hs of the core 304 is larger than the hardness Hi of the inner cover 308. [ When the golf ball 302 is struck by the middle irons, the inner cover 308 absorbs the impact of the golf ball 302. The golf ball 302 is excellent in hit feeling. From the viewpoint of shot feel, the difference (Hs-Hi) between the hardness Hs and the hardness Hi is preferably 1 or more, particularly preferably 2 or more. The difference (Hs-Hi) is preferably 15 or less. In the sphere having the difference (Hs-Hi) of 15 or less, the influence of the inner cover 308 on the deformation behavior of the golf ball 302 when striking the golf ball 302 with the middle iron is appropriately suppressed. In the sphere, energy loss is low when the golf ball 302 is hit with a middle iron. In addition, in the golf ball 302, the flying distance and the spin speed are less varied when striking the golf ball 302 with the middle irons.

The hardness Hm1 of the first mid cover 310 may be greater than the hardness Hi of the inner cover 308. [ In such a case, the outer cavity / oil resistant structure can be achieved in the cover 306. When the golf ball 302 is hit with a middle iron, the spin rate is low. The golf ball 302 is excellent in flight performance in a shot using a middle iron

The hardness Hm1 of the first mid cover 310 is lower than the hardness Hi of the inner cover 308. [ The first mid cover 310 absorbs the impact when hitting the golf ball 302. The golf ball 302 is excellent in hit feeling.

The difference (Hm1-Hi) between the hardness Hm1 and the hardness Hi is preferably -8 or more, from the viewpoint of attaining both the predetermined flying performance and the predetermined hit feeling. The difference (Hm1-Hi) is preferably 10 or less.

In the golf ball 302, the hardness Hm2 of the second mid cover 312 may be greater than the hardness Hm1 of the first mid cover 310. [ In such a case, the outer cavity / oil resistant structure can be achieved in the cover 306. When the golf ball 302 is hit with a middle iron, the spin rate is low. The golf ball 302 is excellent in flight performance in a shot using a middle iron

The hardness Hm2 of the second mid cover 312 may be smaller than the hardness Hm1 of the first mid cover 310. [ In this case, the second mid cover 312 absorbs the impact when striking the golf ball 302. The golf ball 302 is excellent in hit feeling.

The difference (Hm2-Hm1) between the hardness Hm2 and the hardness Hm1 is preferably -15 or more, from the viewpoint of achieving both of the predetermined flying performance and the predetermined hit feeling. The difference (Hm2-Hm1) is preferably 15 or less.

The cover 306 preferably has a total thickness of 6.0 mm or less. The golf ball 302 including the cover 306 having a total thickness of 6.0 mm or less is excellent in hit feeling. In this respect, the total thickness is particularly preferably 5.6 mm or less. From the viewpoint of the durability of the golf ball 302, the total thickness is preferably 0.6 mm or more, more preferably 0.8 mm or more, particularly preferably 1.0 mm or more.

From the viewpoint of shot feel, the golf ball 302 has a compressive deformation amount comp'n preferably equal to or greater than 2.8 mm, more preferably equal to or greater than 2.9 mm, and particularly preferably equal to or greater than 3.0 mm. From the viewpoint of the rebound performance, the amount of compressive deformation is preferably 3.6 mm or less, more preferably 3.5 mm or less, particularly preferably 3.4 mm or less.

Preferred embodiments of the present invention are specified in the following paragraphs.

1. An air conditioner comprising: a core; an inner cover located on the outer side of the core; a mid cover located on the outer side of the inner cover; and an outer cover located on the outer side of the mid cover,

When plotting the distance (%) and the JIS-C hardness from the center point of the core to the graph of nine points obtained by dividing the region from the center of the core to the surface of the core by 12.5% of the radius of the core, R ² of the linear approximation curve obtained by the least square method is 0.95 or more,

The JIS-C hardness Hi of the inner cover is larger than the JIS-C hardness Hs on the surface of the core,

Wherein a JIS-C hardness Ho of the outer cover is greater than a hardness Hi.

2. In paragraph 1, the difference between the hardness Hi and the hardness Hs (Hi-Hs) is 1 or more.

3. In paragraph 1, the golf ball having a difference between the hardness Ho and the hardness Hi (Ho-Hi) of 5 or more and 30 or less.

4. In paragraph 1, the difference between the hardness Hs and the JIS-C hardness H (0) at the center point of the core (Hs-H (0)) is 15 or more.

5. In paragraph 1, the thickness Ti of the inner cover is 1.2 mm or less,

The thickness Tm of the mid cover is 1.2 mm or less,

A golf ball having an outer cover thickness To of 1.2 mm or less.

6. In Paragraph 1, the sum (Ti + Tm + To) of the thickness Ti of the inner cover, the thickness Tm of the mid cover, and the thickness Tm of the outer cover is 2.5 mm or less.

7. In paragraph 1, the hardness Ho is greater than the JIS-C hardness Hm of the midcover,

The difference between the hardness Ho and the hardness Hm (Ho-Hm) is 2 or more.

8. In paragraph 1, the core is formed by crosslinking the rubber composition,

The rubber composition

(a) base rubber;

(b) co-crosslinks;

(c) crosslinking initiators; And

(d) an acid and / or a salt,

The co-crosslinking agent (b)

(b1) an, -unsaturated carboxylic acid having 3 to 8 carbon atoms; And / or

(b2) a metal salt of an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms.

9. The golf ball of Paragraph 8, wherein the amount of the acid and / or salt (d) is not less than 0.5 parts by weight and not more than 40 parts by weight per 100 parts by weight of the base rubber (a).

10. The golf ball of Paragraph 8, wherein the acid and / or salt (d) is a carboxylic acid and / or a salt thereof (d1).

11. In paragraph 10, the golf ball in which the carboxylic acid and / or its salt (d1) is a fatty acid and / or its salt.

12. The golf ball in paragraph 10, wherein the carboxylic acid component of the carboxylic acid and / or its salt (d1) has 1 to 30 carbon atoms.

13. In paragraph 10, the golf ball wherein the carboxylic acid and / or its salt (d1) is a zinc salt of a carboxylic acid.

14. In paragraph 13, the zinc salt of the carboxylic acid is at least one selected from the group consisting of zinc octanoate, zinc laurate, zinc myristate and zinc stearate.

15. The golf ball of Paragraph 8, wherein the rubber composition comprises from 15 to 50 parts by weight of a co-crosslinking agent (b) per 100 parts by weight of the base rubber (a).

16. The golf ball of Paragraph 8, wherein the rubber composition comprises not less than 0.2 parts by weight and not more than 5.0 parts by weight of the crosslinking initiator (c) per 100 parts by weight of the base rubber (a).

17. The golf ball of Paragraph 8, wherein the rubber composition further comprises an organosulfur compound (e).

18. The golf ball according to paragraph 17, wherein the organic sulfur compound (e) is at least one selected from the group consisting of thiophenol, diphenyl disulfide, thionaphthol, thiuram disulfide and metal salts thereof.

19. The golf ball of Paragraph 17, wherein the rubber composition comprises from 0.05 to 5 parts by weight of the organosulfur compound (e) per 100 parts by weight of the base rubber (a).

20. In paragraph 8, the rubber composition comprises an alpha, beta -unsaturated carboxylic acid (b1)

Wherein the rubber composition further comprises a metal compound (f).

21. A core, a first cover located on the outside of the core, a second cover located on the outside of the first cover, a third cover located on the outside of the second cover, and a fourth cover located on the outside of the third cover &Lt; / RTI &

When plotting the distance (%) and the JIS-C hardness from the center point of the core of nine points obtained by dividing the area from the center of the core to the surface of the core by 12.5% of the radius of the core, The R ² of the linear approximation curve obtained by the square method is 0.95 or more,

The JIS-C hardness H1 of the first cover is larger than the JIS-C hardness Hs on the surface of the core,

And the JIS-C hardness H4 of the fourth cover is larger than the JIS-C hardness H1 of the first cover.

22. In paragraph 21, the difference between the longitude H1 and the longitude Hs (H1-Hs) is 1.0 or greater.

23. In paragraph 21, the difference between the hardness H4 and the hardness H1 (H4-H1) is between 3 and 30.

24. In paragraph 21, the difference (Hs-H (0)) between the hardness Hs and the JIS-C hardness H (0) at the center of the core is 15 or more.

25. In paragraph 21,

The thickness T1 of the first cover is 1.8 mm or less,

The thickness T2 of the second cover is 1.8 mm or less,

The thickness T3 of the third cover is 1.8 mm or less,

And the thickness T4 of the fourth cover is 1.8 mm or less.

26. In paragraph 21, a golf ball having a total thickness (T1 + T2 + T3 + T4) of a thickness T1 of the first cover, a thickness T2 of the second cover, a thickness T3 of the third cover, .

27. In paragraph 21, the core is formed by crosslinking the rubber composition,

The rubber composition

(a) base rubber;

(b) co-crosslinks;

(c) crosslinking initiators; And

(d) an acid and / or a salt,

The co-crosslinking agent (b)

(b1) an, -unsaturated carboxylic acid having 3 to 8 carbon atoms; And / or

(b2) a metal salt of an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms.

28. The golf ball of Paragraph 27, wherein the amount of the acid and / or salt (d) is not less than 0.5 parts by weight and not more than 40 parts by weight per 100 parts by weight of the base rubber (a).

29. The golf ball of Paragraph 27, wherein the acid and / or salt (d) is a carboxylic acid and / or a salt thereof (d1).

30. In paragraph 29, the golf ball in which the carboxylic acid and / or its salt (d1) is a fatty acid and / or its salt.

31. The golf ball of paragraph 29 wherein the carboxylic acid component of the carboxylic acid and / or its salt (d1) has 1 to 30 carbon atoms.

32. In paragraph 29, the golf ball wherein the carboxylic acid and / or its salt (d1) is a zinc salt of a carboxylic acid.

33. In paragraph 32, the golf ball has a zinc salt of a carboxylic acid selected from the group consisting of zinc octanoate, zinc laurate, zinc myristate and zinc stearate.

34. The golf ball of Paragraph 27, wherein the rubber composition comprises from 15 to 50 parts by weight of a co-crosslinking agent (b) per 100 parts by weight of the base rubber (a).

35. The golf ball of Paragraph 27, wherein the rubber composition comprises not less than 0.2 parts by weight and not more than 5.0 parts by weight of the crosslinking initiator (c) per 100 parts by weight of the base rubber (a).

36. The golf ball of Paragraph 27, wherein the rubber composition further comprises an organosulfur compound (e).

37. The golf ball according to paragraph 36, wherein the organosulfur compound (e) is at least one selected from the group consisting of thiophenol, diphenyl disulfide, thionaphthol, thiuram disulfide and metal salts thereof.

38. The golf ball of Paragraph 36, wherein the rubber composition comprises from 0.05 to 5 parts by weight of the organosulfur compound (e) per 100 parts by weight of the base rubber (a).

39. In paragraph 27, the rubber composition comprises an alpha, beta -unsaturated carboxylic acid (b1)

Wherein the rubber composition further comprises a metal compound (f).

40. In paragraph 21,

The hardness H2 of the second cover is larger than the hardness H1,

The hardness H3 of the third cover is larger than the hardness H2,

A golf ball having a hardness H4 greater than a hardness H3.

41. In paragraph 40, the difference between the hardness H2 and the hardness H1 (H2-H1) is 2 or more.

42. In paragraph 40, the difference between the hardness H3 and the hardness H2 (H3-H2) is 2 or more.

43. In paragraph 40, the difference between the hardness H4 and the hardness H3 (H4-H3) is 2 or more.

44. An electronic device comprising: a core; an inner cover positioned on the outer side of the core; a mid cover positioned on the outer side of the inner cover; and an outer cover positioned on the outer side of the mid cover,

When plotting the distance (%) and the JIS-C hardness from the center point of the core of nine points obtained by dividing the area from the center of the core to the surface of the core by 12.5% of the radius of the core, The R ² of the linear approximation curve obtained by the square method is 0.95 or more,

The JIS-C hardness Hs at the surface of the core is larger than the JIS-C hardness Hi of the inner cover,

JIS-C hardness of outer cover Ho is larger than JIS-C Hardness Hi of inner cover.

45. In paragraph 44, the difference between the longitude Hs and the longitude Hi (Hs-Hi) is 1 or more.

46. In paragraph 44, a golf ball having a difference between a longitude Ho and a longitude Hi (Ho-Hi) of 5 or more and 30 or less.

47. In paragraph 44, the difference (Hs-H (0)) between the hardness Hs and the JIS-C hardness H (0) at the center point of the core is 15 or more.

48. In paragraph 44,

The thickness Ti of the inner cover is 1.2 mm or less,

The thickness Tm of the mid cover is 1.2 mm or less,

A golf ball having an outer cover thickness To of 1.2 mm or less.

49. In paragraph 44, the golf ball has a total thickness (Ti + Tm + To) of the inner cover thickness Ti, the mid cover thickness Tm and the outer cover thickness To equal to or less than 2.5 mm.

50. In Paragraph 44, a golf ball having JIS-C hardness Ho of the outer cover greater than JIS-C hardness Hm of the mid cover.

51. In paragraph 50, the difference between the longitude Ho and the longitude Hm (Ho-Hm) is 2 or more.

52. In paragraph 44, the core is formed by crosslinking the rubber composition,

The rubber composition

(a) base rubber;

(b) co-crosslinks;

(c) crosslinking initiators; And

(d) an acid and / or a salt,

The co-crosslinking agent (b)

(b1) an, -unsaturated carboxylic acid having 3 to 8 carbon atoms; And / or

(b2) a metal salt of an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms.

53. The golf ball of Paragraph 52, wherein the amount of the acid and / or salt (d) is not less than 0.5 parts by weight and not more than 40 parts by weight per 100 parts by weight of the base rubber (a).

54. The golf ball of Paragraph 52, wherein the acid and / or salt (d) is a carboxylic acid and / or a salt thereof (d1).

55. The golf ball of Paragraph 54, wherein the carboxylic acid component of the carboxylic acid and / or its salt (d1) has 1 to 30 carbon atoms.

56. In paragraph 54, the golf ball in which the carboxylic acid and / or its salt (d1) is a fatty acid and / or its salt.

57. The golf ball of Paragraph 52, wherein the rubber composition comprises from 15 to 50 parts by weight of a co-crosslinking agent (b) per 100 parts by weight of the base rubber (a).

58. The golf ball of Paragraph 52, wherein the rubber composition comprises not less than 0.2 parts by weight and not more than 5.0 parts by weight of the crosslinking initiator (c) per 100 parts by weight of the base rubber (a).

59. The golf ball of Paragraph 52, wherein the rubber composition further comprises an organosulfur compound (e).

60. The golf ball of Paragraph 59, wherein the organosulfur compound (e) is at least one selected from the group consisting of thiophenol, diphenyl disulfide, thionaphthol, thiuram disulfide and metal salts thereof.

61. The golf ball of Paragraph 59, wherein the rubber composition comprises from 0.05 to 5 parts by weight of the organosulfur compound (e) per 100 parts by weight of the base rubber (a).

62. In paragraph 52,

Wherein the rubber composition comprises an alpha, beta -unsaturated carboxylic acid (b1)

Wherein the rubber composition further comprises a metal compound (f).

63. In paragraph 52, the golf ball wherein the acid and / or salt (d) is a zinc salt of a carboxylic acid.

64. The golf ball of paragraph 63, wherein the zinc salt of the carboxylic acid is at least one selected from the group consisting of zinc octanoate, zinc laurate, zinc myristate and zinc stearate.

65. A method for manufacturing a core, comprising the steps of: providing a core, an inner cover located on the outer side of the core, a first mid cover located outside the inner cover, a second mid cover located outside the first mid cover, And an outer cover,

When plotting the distance (%) and the JIS-C hardness from the center point of the core of nine points obtained by dividing the area from the center of the core to the surface of the core by 12.5% of the radius of the core, The R ² of the linear approximation curve obtained by the square method is 0.95 or more,

The JIS-C hardness Hs at the surface of the core is greater than the JIS-C hardness Hi of the inner cover,

JIS-C hardness Ho of the outer cover is larger than JIS-C hardness Hi of the inner cover.

66. In paragraph 65, the difference between the longitude Hs and the longitude Hi (Hs-Hi) is 1 or more.

67. In paragraph 65, a golf ball having a difference between the longitude Ho and the longitude Hi (Ho-Hi) of 5 or more and 30 or less.

68. In paragraph 65, golf balls having a hardness Hs greater than the JIS-C hardness H (0) at the center of the core.

69. In paragraph 68, the difference between the longitude Hs and the longitude H (0) (Hs-H (0)) is 15 or more.

70. In paragraph 65,

The thickness Ti of the inner cover is 1.8 mm or less,

The thickness Tm1 of the first mid cover is 1.8 mm or less,

The thickness Tm2 of the second mid cover is 1.8 mm or less,

A golf ball having an outer cover thickness To of 1.8 mm or less.

71. In paragraph 70, the sum (Ti + Tm1 + Tm2 + To) of the thickness Ti of the inner cover, the thickness Tm1 of the first mid cover, the thickness Tm2 of the second mid cover and the thickness Tm of the outer cover is 6.0 mm or less Golf ball.

72. In paragraph 65, the core is formed by crosslinking the rubber composition,

The rubber composition

(a) base rubber;

(b) co-crosslinks;

(c) crosslinking initiators; And

(d) an acid and / or a salt,

The co-crosslinking agent (b)

(b1) an, -unsaturated carboxylic acid having 3 to 8 carbon atoms; And / or

(b2) a metal salt of an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms.

73. In paragraph 72, the golf ball has an amount of acid and / or salt (d) of at least 1 part by weight and less than 40 parts by weight per 100 parts by weight of the base rubber (a).

74. The golf ball of Paragraph 72, wherein the acid and / or salt (d) is a carboxylic acid and / or a salt thereof (d1).

75. The golf ball of Paragraph 74, wherein the carboxylic acid component of the carboxylic acid and / or its salt (d1) has 1 to 30 carbon atoms.

76. In paragraph 74, the golf ball in which the carboxylic acid and / or its salt (d1) is a fatty acid and / or its salt.

77. The golf ball of Paragraph 72, wherein the rubber composition comprises from 15 to 50 parts by weight of a co-crosslinking agent (b) per 100 parts by weight of the base rubber (a).

78. The golf ball according to paragraph 72, wherein the rubber composition comprises not less than 0.2 parts by weight and not more than 5.0 parts by weight of the crosslinking initiator (c) per 100 parts by weight of the base rubber (a).

79. The golf ball in paragraph 72, wherein the rubber composition further comprises an organosulfur compound (e).

80. The golf ball according to paragraph 79, wherein the organosulfur compound (e) is at least one selected from the group consisting of thiophenol, diphenyl disulfide, thionaphthol, thiuram disulfide and metal salts thereof.

81. The golf ball of paragraph 79, wherein the rubber composition comprises from 0.05 to 5 parts by weight of the organosulfur compound (e) per 100 parts by weight of the base rubber (a).

82. In paragraph 72, the rubber composition comprises an alpha, beta -unsaturated carboxylic acid (b1)

Wherein the rubber composition further comprises a metal compound (f).

83. In paragraph 72, the golf ball wherein the acid and / or salt (d) is a zinc salt of a carboxylic acid.

84. The golf ball of paragraph 83, wherein the zinc salt of the carboxylic acid is at least one selected from the group consisting of zinc octanoate, zinc laurate, zinc myristate and zinc stearate.

Example

Experiment 1

Example I-1

(Trade name "BR-730 ", manufactured by JSR Corporation), 27 parts by weight of zinc diacrylate (trade name" Sanceler SR ", Sanxin Chemical Industries Co., 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-naphthalenethiol, 10 parts by weight of zinc stearate and 0.75 parts by weight of dicumyl peroxide were kneaded A rubber composition was obtained. The rubber composition was placed in a mold including an upper mold and a lower mold each having a hemispherical cavity and heated at 170 DEG C for 25 minutes to obtain a core having a diameter of 37.9 mm. The amount of barium sulphate was adjusted so that the weight of the golf ball was 45.4 g.

24 parts by weight of an ionomer resin ("HYMILAN AM7337" described above), 50 parts by weight of another ionomer resin ("HYMILAN AM7329"), 26 parts by weight of a styrene block-containing thermoplastic elastomer And 6 parts by weight of titanium dioxide were kneaded by a twin screw extruder to obtain a resin composition. The core was placed in a mold. The resin composition was injected around the core by injection molding to form an inner cover having a thickness of 0.8 mm.

40 parts by weight of an ionomer resin ("HYMILAN AM7337" described above), 40 parts by weight of another ionomer resin ("HYMILAN AM7329"), 20 parts by weight of a styrene block-containing thermoplastic elastomer And 6 parts by weight of titanium dioxide were kneaded by a twin screw extruder to obtain a resin composition. The spheres consisting of the core and inner cover were placed in a mold. The resin composition was injection-molded around the sphere by injection molding to form a mid cover having a thickness of 0.8 mm.

5 parts by weight of an ionomer resin ("HYMILAN AM7337" described above), 10 parts by weight of another ionomer resin ("HYMILAN 1555"), 55 parts by weight still another ionomer resin ("HYMILAN AM7329" 30 parts by weight of an ethylene- (meth) acrylic acid copolymer (trade name "NUCLEAR N1050H ", DuPont-Mitsui Polychemicals Company, Limited), 3 parts by weight of titanium dioxide and 0.2 parts by weight of ultraviolet absorber (trade name" TINUVIN ) 770, manufactured by Ciba Japan KK) was kneaded with a twin-screw kneading extruder to obtain a resin composition. A sphere consisting of a core, an inner cover and a mid cover was placed in a final mold having a plurality of pimples on the cavity surface. The resin composition was injected around the sphere by injection molding to form an outer cover having a thickness of 0.8 mm. A dimple having a shape in which the shape of the pimple is reversed is formed on the outer cover. A clear paint containing a two-liquid curing polyurethane as a base material was applied to the outer cover to obtain a golf ball of Example I-1 having a diameter of 42.7 mm.

Examples I-2 to I-14 and Comparative Examples I-1 to I-9

Examples I-2 to I-14 and comparative examples were prepared in the same manner as in Example I-1, except that the specifications of the core, inner cover, mid cover and outer cover were as shown in Tables I-10 to I- Golf balls of Examples I-1 to I-9 were obtained. The composition of the cores is specifically shown in the following Tables I-1 and I-2. The composition of the inner cover, the mid cover and the outer cover is specifically shown in the following Tables I-3 and I-4. The hardness distributions of the cores are given in Tables I-5 to I-9 below. The golf ball according to Comparative Example I-7 has no mid cover.

Hitting by Middle Irons (I # 5)

A 5 iron (trade name "XXIO ", manufactured by DUNLOP SPORTS CO. LTD.) Was attached to a swing machine manufactured by Golf Laboratories, Inc., Shaft hardness: R, loft angle: 24 DEG). The golf ball was hit at a head speed of 34 m / sec. The spin speed immediately after the hit was measured. In addition, the distance from the point of ejection to the stop point was measured. The average values of the data obtained by 12 measurements are shown in Tables I-10 to I-14 below.

<Table I-1>

<Table I-2>

Details of the compounds shown in Tables I-1 and I-2 above are as follows:

BR-730: High-cis polybutadiene (cis-1,4-bond content: 96% by weight, 1,2-vinyl bond content: 1.3% by weight, Mooney viscosity (ML _{1 + 4} ° C)): 55, molecular weight distribution (Mw / Mn): 3)

San Siller SR: Zinc diacrylate (10 wt% stearic acid coated product) manufactured by Sanxin Chemical Industry Co., Ltd.,

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-naphthalene thiol: a product of Tokyo Chemical Industry Co., Ltd. (product of Tokyo Chemical Industry Co., Ltd.)

Zinc octanoate: a product of Mitsuwa Chemicals Co., Ltd.

Zinc laurate: Products of Mitsuwa Chemical Company, Limited

Zinc Myristate: Products of NOF Corporation

Zinc stearate: a product of Wako Pure Chemical Industries, Ltd.

Dicumyl Peroxide: The trade name "Percumyl D ", manufactured by ENOF Corp.,

<Table I-3>

<Table I-4>

<Table I-5>

<Table I-6>

<Table I-7>

<Table I-8>

<Table I-9>

<Table I-10>

<Table I-11>

<Table I-12>

<Table I-13>

<Table I-14>

As shown in Table I-10 to Table I-14, the golf ball according to the embodiment has excellent flying performance in a shot using the middle irons. From the evaluation results, the advantages of the present invention are obvious.

Experiment 2

Example II-1

27.0 parts by weight of zinc diacrylate (trade name "SANSELLER SR ", manufactured by SANSHIN CHEMICAL INDUSTRIAL COMPANY LIMITED), 5.0 parts by weight of high-cis-polybutadiene (trade name" BR- 730 ", manufactured by JSR Corporation) Zinc oxide, an appropriate amount of barium sulfate, 0.2 parts by weight of 2-naphthalene thiol, 10.0 parts by weight of zinc stearate and 0.75 part by weight of dicumyl peroxide were kneaded to obtain a rubber composition. The rubber composition was placed in a mold including an upper mold and a lower mold each having hemispherical cavities and heated at 170 DEG C for 25 minutes to obtain a core having a diameter of 36.3 mm. The amount of barium sulphate was adjusted so that the weight of the golf ball was 45.4 g.

40 parts by weight of an ionomer resin ("HYMILAN AM7337" described above), 40 parts by weight of another ionomer resin ("HYMILAN AM7329"), 20 parts by weight of a styrene block-containing thermoplastic elastomer And 6 parts by weight of titanium dioxide were kneaded by a twin screw extruder to obtain a resin composition. The core was placed in a mold. The resin composition was injected around the core by injection molding to form a first cover having a thickness of 0.8 mm.

45 parts by weight of ionomer resin ("HYMILAN AM7337"), 40 parts by weight of another ionomer resin ("HYMILAN AM7329"), 15 parts by weight of styrene block-containing thermoplastic elastomer (" And 6 parts by weight of titanium dioxide were kneaded by a twin screw extruder to obtain a resin composition. The sphere consisting of the core and the first cover was placed in the mold. The resin composition was injected around the sphere by injection molding to form a second cover having a thickness of 0.8 mm.

(The above-mentioned "Habilan AM7337"), 40 parts by weight of another ionomer resin (the aforementioned "HIMILAN AM7329"), 9 parts by weight of a styrene block-containing thermoplastic elastomer And 6 parts by weight of titanium dioxide were kneaded by a twin screw extruder to obtain a resin composition. The sphere consisting of the core, the first cover and the second cover was put into the mold. The resin composition was injection-molded around the sphere by injection molding to form a third cover having a thickness of 0.8 mm.

5 parts by weight of an ionomer resin ("HYMILAN AM7337" described above), 10 parts by weight of another ionomer resin ("HYMILAN 1555"), 55 parts by weight still another ionomer resin ("HYMILAN AM7329" 3 parts by weight of titanium dioxide and 0.2 parts by weight of an ultraviolet absorber (trade name "Tinuvin 770") were added to 30 parts by weight of an ethylene- (meth) acrylic acid copolymer (trade name "NUCLEAR N1050H ", DuPont- Mitsui Polychemicals Co., Manufactured by Shiba Japan K.K.) were kneaded by a twin-screw kneading extruder to obtain a resin composition. The sphere consisting of the core, the first cover, the second cover and the third cover was placed in a final mold having a plurality of pimples on the cavity surface. The resin composition was injected around the sphere by injection molding to form a fourth cover having a thickness of 0.8 mm. A dimple having a shape in which the shape of the pimple is reversed is formed on the fourth cover. The fourth cover was coated with a clear paint containing a two-liquid curing polyurethane as a base material to obtain a golf ball of Example II-1 having a diameter of 42.7 mm.

Examples II-2 to II-14 and Comparative Examples II-1 to II-10

In the same manner as in Example II-1 except that the specifications of the core, the first cover, the second cover, the third cover and the fourth cover were as shown in the following Tables II-9 to II-13, To II-14 and Comparative Examples II-1 to II-10. The composition of the core is specifically shown in the following Tables II-1 and II-2. The composition of the cover is specifically shown in Table II-3 below. The hardness distributions of the cores are given in Tables II-4 to II-8 below. The golf ball according to Comparative Example II-5 does not have the second cover and the third cover. The golf ball according to Comparative Example II-6 has no third cover. The golf ball according to Comparative Example II-7 has no third cover.

Hitting by Middle Irons (I # 5)

5 iron (trade name "JSCCIO" manufactured by Dunlop Sport Company, Limited, shaft hardness: R, loft angle: 24 °) was attached to a swing machine manufactured by Golf Laboratories, Respectively. The golf ball was hit at a head speed of 34 m / sec. The spin speed immediately after the hit was measured. In addition, the distance from the point of ejection to the stop point was measured. The average values of the data obtained by 12 measurements are shown in Tables II-9 to II-13.

<Table II-1>

<Table II-2>

Details of the compounds shown in Tables II-1 and II-2 above are as follows:

BR-730: High-cis polybutadiene (cis-1,4-bond content: 96% by weight, 1,2-vinyl bond content: 1.3% by weight, Mooney viscosity (ML _{1 + 4} ° C)): 55, molecular weight distribution (Mw / Mn): 3)

San Siller SR: Zinc diacrylate (10 wt% stearic acid coated product) manufactured by Sanxin Chemical Industry Co., Ltd.,

Zinc oxide: trade name "Ginrei R" manufactured by Toho Zinc Company, Limited,

Barium sulfate: trade name "barium sulfate BD" manufactured by Sakai Chemical Industry Co., Ltd.,

2-naphthalene thiol: product of Tokyo Chemical Industry Co., Ltd.

Zinc octanoate: product of Mitsuwa Chemical Co., Ltd.

Zinc laurate: Products of Mitsuwa Chemical Company, Limited

Myristic acid zinc: Products of ENOF Corporation

Zinc stearate: a product of Wako Pure Chemical Industries, Limited

Dicumyl peroxide: trade name "PERCUMIL D" manufactured by ENOF CORPORATION,

<Table II-3>

<Table II-4>

<Table II-5>

<Table II-6>

<Table II-7>

<Table II-8>

<Table II-9>

<Table II-10>

<Table II-11>

<Table II-12>

<Table II-13>

As shown in Tables II-9 to II-13, the golf ball according to the embodiment has excellent flight performance in the shot using the middle irons. From the evaluation results, the advantages of the present invention are obvious.

Experiment 3

Example III-1

(Trade name "SANSELLER SR ", manufactured by SANSHIN CHEMICAL INDUSTRIES COMPANY LIMITED), 27 parts by weight of a high-cis-polybutadiene (trade name" BR-730 ", manufactured by JSR Corporation) Zinc oxide, an appropriate amount of barium sulfate, 0.2 parts by weight of 2-thiophthol, 10 parts by weight of zinc stearate and 0.75 parts by weight of dicumyl peroxide were kneaded to obtain a rubber composition. The rubber composition was placed in a mold including an upper mold and a lower mold each having a hemispherical cavity and heated at 170 DEG C for 25 minutes to obtain a core having a diameter of 37.9 mm. The amount of barium sulphate was adjusted so that the weight of the golf ball was 45.4 g.

26 parts by weight of an ionomer resin ("HYMILAN AM7337" described above), 40 parts by weight of another ionomer resin ("HYMILAN AM7329"), 34 parts by weight of a styrene block-containing thermoplastic elastomer And 6 parts by weight of titanium dioxide were kneaded by a twin screw extruder to obtain a resin composition. The core was placed in a mold. The resin composition was injected around the core by injection molding to form an inner cover having a thickness of 0.8 mm.

45 parts by weight of ionomer resin ("HYMILAN AM7337"), 40 parts by weight of another ionomer resin ("HYMILAN AM7329"), 15 parts by weight of styrene block-containing thermoplastic elastomer (" And 6 parts by weight of titanium dioxide were kneaded by a twin screw extruder to obtain a resin composition. The spheres consisting of the core and inner cover were placed in a mold. The resin composition was injection-molded around the sphere by injection molding to form a mid cover having a thickness of 0.8 mm.

5 parts by weight of an ionomer resin ("HYMILAN AM7337" described above), 10 parts by weight of another ionomer resin ("HYMILAN 1555"), 55 parts by weight still another ionomer resin ("HYMILAN AM7329" 3 parts by weight of titanium dioxide and 0.2 parts by weight of an ultraviolet absorber (trade name "Tinuvin 770") were added to 30 parts by weight of an ethylene- (meth) acrylic acid copolymer (trade name "NUCLEAR N1050H ", DuPont- Mitsui Polychemicals Co., Manufactured by Shiba Japan K.K.) were kneaded with a twin-screw kneading extruder to obtain a resin composition. A sphere consisting of a core, an inner cover and a mid cover was placed in a final mold having a plurality of pimples on the cavity surface. The resin composition was injected around the sphere by injection molding to form an outer cover having a thickness of 0.8 mm. A dimple having a shape in which the shape of the pimple is reversed is formed on the outer cover. A clear paint containing a two-liquid curing polyurethane as a base material was applied to the outer cover to obtain a golf ball of Example III-1 having a diameter of 42.7 mm.

Examples III-2 to III-15 and Comparative Examples III-1 to III-9

In the same manner as in Example III-1, except that the specifications of the core, the inner cover, the mid cover and the outer cover were as shown in Tables III-8 to III-12 below, Golf balls III-1 to III-9 were obtained. The composition of the cores is specifically shown in the following Tables III-1 to III-3. The hardness distributions of the cores are given in Tables III-4 and III-5 below. The composition of the inner cover, the mid cover and the outer cover is specifically shown in Tables III-6 and III-7 below. The golf ball according to Comparative Example III-7 has no mid cover.

Hitting by Middle Irons (I # 5)

The golf club was equipped with a 5 iron (trade name "JCSIO ", manufactured by Dunlop Sport Company, Limited, shaft hardness: R) on a swing machine manufactured by Golf Laboratories, The golf ball was hit in the following condition 1, and the spin speed and the distance from the striking point to the stopping point were measured immediately after the striking. The average value S1 of the spin speed and the average value D1 of the distance obtained by ten measurements were calculated. In addition, the golf ball was struck under the following condition 2, and the spin rate and the distance from the striking point to the stopping point were measured immediately after striking. The average value S2 of the spin speed and the average value D2 of the flying distance obtained by ten measurements were calculated.

Condition 1

Head speed: 34 m / sec

Effective loft angle: 23.5 °

RB: Point 5 mm lower than the center of the face

Condition 2

Head speed: 34 m / sec

Effective loft angle: 20.5 °

RB: point 5 mm higher than the center of the face

The spin rate in condition 1 is greater than the spin rate in condition 2. The distance in Condition 1 is smaller than the distance in Condition 2. The average value S1 of the spin speed, the average value D1 of the distance, the average value S2 of the spin speed, the average value D2 of the distance, the difference (S1-S2) and the difference (D2-D1) are shown in Tables III-8 to III-12.

Feel

Ten golfers hit the golf ball with a middle iron (I # 5), and a score of 5.0 points is used to represent the feel of the golf ball. The average values of the indexes as the evaluation results are shown in Tables III-8 to III-12 below. The higher the number, the better the results.

<Table III-1>

<Table III-2>

<Table III-3>

Details of the compounds shown in Tables III-1 to III-3 above are as follows:

BR-730: High-cis polybutadiene (cis-1,4-bond content: 96% by weight, 1,2-vinyl bond content: 1.3% by weight, Mooney viscosity (ML _{1 + 4} ° C)): 55, molecular weight distribution (Mw / Mn): 3)

San Siller SR: Zinc diacrylate (10 wt% stearic acid coated product) manufactured by Sanxin Chemical Industry Co., Ltd.,

Zinc oxide: trade name "Ginrei R" manufactured by Toho Zinc Company, Limited,

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 octanoate: product of Mitsuwa Chemical Co., Ltd.

Zinc laurate: Products of Mitsuwa Chemical Company, Limited

Myristic acid zinc: Products of ENOF Corporation

Zinc stearate: a product of Wako Pure Chemical Industries, Limited

Dicumyl peroxide: trade name "PERCUMIL D" manufactured by ENOF CORPORATION,

<Table III-4>

<Table III-5>

<Table III-6>

<Table III-7>

<Table III-8>

<Table III-9>

<Table III-10>

<Table III-11>

<Table III-12>

As shown in Tables III-8 to III-12, the golf ball according to the embodiment is excellent in shot performance and excellent in flight performance in a shot using a middle iron. From the evaluation results, the advantages of the present invention are obvious.

Experiment 4

Example IV-1

(Trade name "SANSELLER SR ", manufactured by SANSHIN CHEMICAL INDUSTRIES COMPANY LIMITED), 27 parts by weight of a high-cis-polybutadiene (trade name" BR-730 ", manufactured by JSR Corporation) Zinc oxide, an appropriate amount of barium sulfate, 0.2 parts by weight of 2-thiophthol, 10 parts by weight of zinc stearate and 0.75 parts by weight of dicumyl peroxide were kneaded to obtain a rubber composition. The rubber composition was placed in a mold including an upper mold and a lower mold each having hemispherical cavities and heated at 170 DEG C for 25 minutes to obtain a core having a diameter of 36.3 mm. The amount of barium sulphate was adjusted so that the weight of the golf ball was 45.4 g.

26 parts by weight of an ionomer resin ("HYMILAN AM7337" described above), 40 parts by weight of another ionomer resin ("HYMILAN AM7329"), 34 parts by weight of a styrene block-containing thermoplastic elastomer And 6 parts by weight of titanium dioxide were kneaded by a twin screw extruder to obtain a resin composition. The core was placed in a mold. The resin composition was injected around the core by injection molding to form an inner cover having a thickness of 0.8 mm.

24 parts by weight of an ionomer resin ("HYMILAN AM7337" described above), 50 parts by weight of another ionomer resin ("HYMILAN AM7329"), 26 parts by weight of a styrene block-containing thermoplastic elastomer And 6 parts by weight of titanium dioxide were kneaded by a twin screw extruder to obtain a resin composition. The spheres consisting of the core and inner cover were placed in a mold. The resin composition was injected into the periphery of the sphere by injection molding to form a first mid cover having a thickness of 0.8 mm.

45 parts by weight of ionomer resin ("HYMILAN AM7337"), 40 parts by weight of another ionomer resin ("HYMILAN AM7329"), 15 parts by weight of styrene block-containing thermoplastic elastomer (" And 6 parts by weight of titanium dioxide were kneaded by a twin screw extruder to obtain a resin composition. A sphere consisting of a core, an inner cover and a first mid cover was placed in a mold. The resin composition was injected around the sphere by injection molding to form a second mid cover with a thickness of 0.8 mm.

5 parts by weight of an ionomer resin ("HYMILAN AM7337" described above), 10 parts by weight of another ionomer resin ("HYMILAN 1555"), 55 parts by weight still another ionomer resin ("HYMILAN AM7329" 3 parts by weight of titanium dioxide and 0.2 parts by weight of an ultraviolet absorber (trade name "Tinuvin 770") were added to 30 parts by weight of an ethylene- (meth) acrylic acid copolymer (trade name "NUCLEAR N1050H ", DuPont- Mitsui Polychemicals Co., Manufactured by Shiba Japan K.K.) were kneaded with a twin-screw kneading extruder to obtain a resin composition. The sphere consisting of the core, the inner cover, the first mid cover and the second mid cover was placed in a final mold having a plurality of pimples on the cavity surface. The resin composition was injected around the sphere by injection molding to form an outer cover having a thickness of 0.8 mm. A dimple having a shape in which the shape of the pimple is reversed is formed on the outer cover. A clear paint containing a two-liquid curing polyurethane as a substrate was applied to the outer cover to obtain a golf ball of Example IV-1 having a diameter of 42.7 mm.

Examples IV-2 to IV-14 and Comparative Examples IV-1 to IV-11

Except that the specifications of the core, the inner cover, the first mid cover, the second mid cover, and the outer cover were as shown in the following Tables IV-11 to IV-15. -2 to IV-14 and Comparative Examples IV-1 to IV-11 were obtained. The composition of the cores is specifically shown in the following Tables IV-1 to IV-3. The compositions of the inner cover, the first mid cover, the second mid cover and the outer cover are specifically shown in the following Tables IV-4 and IV-5. The hardness distributions of the cores are given in Tables IV-6 to IV-10 below. The golf ball according to Comparative Example IV-5 does not have the first mid cover and the second mid cover. Each golf ball according to Comparative Examples IV-6 and IV-7 has no second mid cover.

Hitting by Middle Irons (I # 5)

The golf club was equipped with a 5 iron (trade name "JCSIO ", manufactured by Dunlop Sport Company, Limited, shaft hardness: R) on a swing machine manufactured by Golf Laboratories, The golf ball was hit in the following condition 1, and the spin speed and the distance from the striking point to the stopping point were measured immediately after the striking. The average value S1 of the spin speed and the average value D1 of the distance obtained by ten measurements were calculated. In addition, the golf ball was struck under the following condition 2, and the spin rate and the distance from the striking point to the stopping point were measured immediately after striking. The average value S2 of the spin speed and the average value D2 of the flying distance obtained by ten measurements were calculated. In addition, the golf ball was hit in Condition 3, and the spin rate and the distance from the point of ejection to the stop point were measured immediately after the batting. The average value S3 of the spin speed and the average value D3 of the flying distance obtained by ten measurements were calculated. Conditions 1 and 2 are conditions for confirming the variation of the spin speed and the flying distance. Condition 3 is a normal condition for confirming the spin speed and distance.

Condition 1

Head speed: 34 m / sec

Effective loft angle: 23.5 °

RB: Point 5 mm lower than the center of the face

Condition 2

Head speed: 34 m / sec

Effective loft angle: 20.5 °

RB: Point 5 mm higher than the center of the face

Condition 3

Head speed: 34 m / sec

Effective loft angle: 23.0 °

RBI: Face center

The spin speed in condition 1 is higher than the spin speed in condition 2. The distance in Condition 1 is smaller than the distance in Condition 2. The average value S1 of spin speed, the average value D1 of distance, the average value S2 of spin speed, the average value D2 of distance, the difference S1-S2, the difference D2-D1, the average value S3 of spin speed and the average value D3 of distance, -11 to IV-15.

Feel

Ten golfers hit the golf ball with a middle iron (I # 5), and a score of 5.0 points is used to represent the feel of the golf ball. The average value of the index as the evaluation result is shown in Tables IV-11 to IV-15 below. The higher the number, the better the results.

<Table IV-1>

<Table IV-2>

<Table IV-3>

Details of the compounds shown in Tables IV-1 to IV-3 above are as follows:

BR-730: High-cis polybutadiene (cis-1,4-bond content: 96% by weight, 1,2-vinyl bond content: 1.3% by weight, Mooney viscosity (ML _{1 + 4} ° C)): 55, molecular weight distribution (Mw / Mn): 3)

San Siller SR: Zinc diacrylate (10 wt% stearic acid coated product) manufactured by Sanxin Chemical Industry Co., Ltd.,

Zinc oxide: trade name "Ginrei R" manufactured by Toho Zinc Company, Limited,

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 octanoate: product of Mitsuwa Chemical Co., Ltd.

Zinc laurate: Products of Mitsuwa Chemical Company, Limited

Myristic acid zinc: Products of ENOF Corporation

Zinc stearate: a product of Wako Pure Chemical Industries, Limited

Dicumyl peroxide: trade name "PERCUMIL D" manufactured by ENOF CORPORATION,

<Table IV-4>

<Table IV-5>

<Table IV-6>

<Table IV-7>

<Table IV-8>

<Table IV-9>

<Table IV-10>

<Table IV-11>

<Table IV-12>

<Table IV-13>

<Table IV-14>

<Table IV-15>

As shown in Tables IV-11 to IV-15, the golf ball according to the embodiment has excellent flight performance in the shot using the middle irons. From the evaluation results, the advantages of the present invention are obvious.

The golf ball according to the present invention can be used for playing in a golf course and for practice in a driving range. The foregoing description is presented by way of example only, and many modifications may be made without departing from the principles of the invention.

Claims (16)

A core, an inner cover positioned on the outer side of the core, a mid cover positioned on the outer side of the inner cover, and an outer cover positioned on the outer side of the mid cover,
When plotting the distance (%) and the JIS-C hardness from the center point of the core to the graph of nine points obtained by dividing the region from the center of the core to the surface of the core by 12.5% of the radius of the core, R ² of the linear approximation curve obtained by the least square method is 0.95 or more,
The JIS-C hardness Hi of the inner cover is larger than the JIS-C hardness Hs on the surface of the core,
Wherein a JIS-C hardness Ho of the outer cover is greater than a hardness Hi. The golf ball according to claim 1, wherein the difference (Hi-Hs) between the hardness Hi and the hardness Hs is 1 or more. The golf ball according to claim 1, wherein the difference (Ho-Hi) between the hardness Ho and the hardness Hi is 5 or more and 30 or less. The method of claim 1,
Wherein the core is formed by crosslinking the rubber composition,
The rubber composition
(a) base rubber;
(b) co-crosslinks;
(c) crosslinking initiators; And
(d) an acid or a salt or both,
The co-crosslinking agent (b)
(b1) an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms, or
(b2) a metal salt of an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms, or both. A core, a first cover located outside the core, a second cover located outside the first cover, a third cover located outside the second cover, and a fourth cover located outside the third cover, ,
When plotting the distance (%) and the JIS-C hardness from the center point of the core to the graph of nine points obtained by dividing the region from the center of the core to the surface of the core by 12.5% of the radius of the core, R ² of the linear approximation curve obtained by the least square method is 0.95 or more,
The JIS-C hardness H1 of the first cover is larger than the JIS-C hardness Hs on the surface of the core,
And the JIS-C hardness H4 of the fourth cover is larger than the JIS-C hardness H1 of the first cover. The golf ball according to claim 5, wherein the difference (H1-Hs) between the hardness H1 and the hardness Hs is 1.0 or more. The golf ball according to claim 5, wherein the difference (H4-H1) between the hardness H4 and the hardness H1 is 3 or more and 30 or less. 6. The method of claim 5, wherein the core is formed by crosslinking the rubber composition,
The rubber composition
(a) base rubber;
(b) co-crosslinks;
(c) crosslinking initiators; And
(d) an acid or a salt or both,
The co-crosslinking agent (b)
(b1) an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms, or
(b2) a metal salt of an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms, or both. A core, an inner cover positioned on the outer side of the core, a mid cover positioned on the outer side of the inner cover, and an outer cover positioned on the outer side of the mid cover,
When plotting the distance (%) and the JIS-C hardness from the center point of the core of nine points obtained by dividing the area from the center of the core to the surface of the core by 12.5% of the radius of the core, R ² of the linear approximation curve obtained by the square method is 0.95 or more,
The JIS-C hardness Hs at the surface of the core is larger than the JIS-C hardness Hi of the inner cover,
Wherein the JIS-C hardness Ho of the outer cover is greater than the JIS-C hardness Hi of the inner cover. The golf ball according to claim 9, wherein the difference (Hs-Hi) between the hardness Hs and the hardness Hi is 1 or more. The golf ball according to claim 9, wherein the difference (Ho-Hi) between the hardness Ho and the hardness Hi is 5 or more and 30 or less. The method according to claim 9, wherein the core is formed by crosslinking the rubber composition,
The rubber composition
(a) base rubber;
(b) co-crosslinks;
(c) crosslinking initiators; And
(d) an acid or a salt or both,
The co-crosslinking agent (b)
(b1) an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms, or
(b2) a metal salt of an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms, or both. The core, the inner cover positioned on the outer side of the core, the first mid cover positioned on the outer side of the inner cover, the second mid cover positioned on the outer side of the first mid cover, And an outer cover,
When plotting the distance (%) and the JIS-C hardness from the center point of the core to the graph of nine points obtained by dividing the region from the center of the core to the surface of the core by 12.5% of the radius of the core, R ² of the linear approximation curve obtained by the least square method is 0.95 or more,
The JIS-C hardness Hs at the surface of the core is larger than the JIS-C hardness Hi of the inner cover,
JIS-C hardness of outer cover Ho is larger than JIS-C Hardness Hi of inner cover. 14. The golf ball according to claim 13, wherein the difference (Hs-Hi) between the hardness Hs and the hardness Hi is 1 or more. 14. The golf ball according to claim 13, wherein the difference (Ho-Hi) between the hardness Ho and the hardness Hi is 5 or more and 30 or less. 14. The method of claim 13, wherein the core is formed by crosslinking the rubber composition,
The rubber composition
(a) base rubber;
(b) co-crosslinks;
(c) crosslinking initiators; And
(d) an acid or a salt or both,
The co-crosslinking agent (b)
(b1) an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms, or
(b2) a metal salt of an alpha, beta -unsaturated carboxylic acid having 3 to 8 carbon atoms, or both.

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