JP5279881B2 - Multi-piece solid golf ball - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a golf ball capable of exerting excellence in repulsion, feeling of hitting the ball and durability at the same time. <P>SOLUTION: The multi-piece solid golf ball includes: a core formed of base rubber as a main material; a middle layer for covering the core; and a cover for covering the middle layer and having a plurality of dimples on the outer surface, and appropriately has the followings: a Shore D-scale hardness difference between the cover and the middle layer; an initial-velocity difference between the core and the ball; (a deflection hardness of a ball body with the core covered with the middle layer)/(a deflection hardness of the core); a total thickness (mm) of the middle layer and the cover; (a deflection hardness of the golf ball)/(a deflection hardness of the ball body with the core covered with the middle layer); a specific gravity of the core and that of the middle layer; and a Shore D-scale hardness difference between the surface and center of the core. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a multi-piece solid golf ball having a core surrounded by a cover of two or more layers. More specifically, the present invention relates to a multi-piece solid golf ball having excellent feeling, resilience, flight distance, and controllability.

  In recent years, the demand for golf balls from players has been diversified and individualized due to an increase in the golf population, and various studies have been made on ball structures in order to meet such demands.

  For example, in Japanese Patent Laid-Open No. 9-313643, by optimizing the hardness distribution of the core, and also by optimizing the hardness distribution of the entire ball including the core, the intermediate layer, and the cover, good flying performance and A golf ball capable of simultaneously satisfying durability and good hit feeling and controllability has been proposed, and Japanese Patent Application Laid-Open No. 10-305114 includes a solid core, an intermediate layer, and a cover. In golf balls formed with a large number of dimples, the balance of hardness between the core, intermediate layer and cover is optimized, and by optimizing the dimple elements, the feel and flying performance can be achieved regardless of the head speed. Improved golf balls have been proposed. Other prior art documents include golf balls described in JP-A-2001-218873, JP-A-2001-218875, JP-A-2005-212656, and JP-A-2005-218858.

  However, these golf balls still have room for improvement from the viewpoint of resilience. In addition to an increase in flight distance, there has been a demand for a golf ball having an overall advantage that can provide excellent feeling and durability, as well as good controllability.

Japanese Patent Laid-Open No. 9-313643 JP 10-305114 A JP 2001-218873 A JP 2001-218875 A Japanese Patent Laid-Open No. 2005-21656 JP 2005-218858 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a golf ball that imparts excellent resilience and imparts excellent feel, durability, and controllability.

As a result of intensive studies to achieve the above object, the present inventors have determined that a core formed using a base rubber as a main material, an intermediate layer covering the core, and covering the intermediate layer, A golf ball having a cover having a large number of dimples formed thereon, a Shore D hardness balance between the intermediate layer and the cover, an initial speed balance between the core and the entire ball, and an intermediate layer coated on the core and the core Optimize the deflection hardness balance between the sphere and the total thickness of the intermediate layer and the cover, balance of the deflection hardness between the golf ball and the sphere coated with the intermediate layer on the core, the diameter of the core, the specific gravity of the core, And by knowing that the Shore D hardness difference between the core surface and the core center has been optimized, it is possible to realize a golf ball that can achieve both good resilience, feel, durability, and excellent controllability. , Leading to the completion of the invention.

That is, the present invention provides the following multi-piece solid golf ball.
Claim 1:
In a golf ball comprising a core formed of a base rubber as a main material, an intermediate layer covering the core, and a cover covering the intermediate layer and having a large number of dimples formed on the outer surface, (1) to (4), (11) and (12),
(1): (Shore D hardness of cover) − (Shore D hardness of intermediate layer)> 5,
(2 ′): (initial velocity of the core (m / s)) − (initial velocity of the ball (m / s)) ≧ 0.2 (Here, the initial velocity is a USGA drum rotation-type initial velocity meter. Means the initial speed measured using the same initial speed measuring instrument)
(3): 0.87 ≦ [(the deflection hardness of the sphere with the intermediate layer coated on the core) / (the deflection hardness of the core)] ≦ 0.93 (where the deflection hardness is the initial load on the spherical object) The amount of deformation (mm) from when 98 N (10 kgf) is loaded to when the final load of 1275 N (130 kgf) is loaded)
(4): The total thickness of the intermediate layer thickness (mm) and the cover thickness (mm) is 3.0 mm or less,
(11): (deflection hardness of golf ball / deflection hardness of sphere in which core is covered with intermediate layer) ≦ 0.98
(12): (Shore D hardness of core surface) − (Shore D hardness of core center) ≧ 15
The core diameter is 36.8 mm or more and 38.8 mm or less, the core specific gravity is 1.15 g / cm ³ or more and 1.35 g / cm ³ or less, and the intermediate layer is softer than the core surface. And the intermediate layer is
(A-1) Metal ion neutralized product of olefin-unsaturated carboxylic acid binary random copolymer and / or olefin-unsaturated carboxylic acid binary random copolymer and (a-2) olefin-unsaturated carboxylic acid -(A-1) / (a-) an unsaturated carboxylic acid ester ternary random copolymer and / or a metal ion neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer. 2) (A) an ionomer resin included at a ratio of 100/0 to 0/100 (mass ratio);
(B) an olefinic thermoplastic elastomer;
(A) / (B) = 85/15 to 60/40 (mass ratio)
(C) 5 to 80 parts by mass of an organic fatty acid having a molecular weight of 280 to 1500 and / or a derivative thereof;
(D) 0.1 to 10 parts by mass of a basic inorganic metal compound capable of neutralizing an unneutralized acid group in the resin component and the component (C);
A multi-piece solid golf ball, wherein the intermediate layer has a Shore D hardness of 40 or more and 60 or less, and the cover is formed of an ionomer resin as a main material .
Claim 2:
About 0.05 to 0.5 parts by mass of sulfur and 0.05 to 5 parts by mass of an organic sulfur compound with respect to 100 parts by mass of the base rubber of the core, and about 5 to 5 parts by mass of the sulfur and the organic sulfur compound. The multi-piece solid golf ball according to claim 1, wherein ≦ (the amount of organic sulfur compound / the amount of sulfur) ≦ 20.
Claim 3:
The number of dimples formed on the ball surface is 280 to 360, the lift coefficient CL of the ball when the ball is hit at a Reynolds number of 70,000 and a spin rate of 2000 rpm is 0.165 or more, and the Reynolds number is 180,000. The multi-piece solid golf ball according to claim 1 or 2, wherein a drag coefficient CD of the ball when the ball is hit at a spin rate of 2520 rpm is 0.230 or less.
Claim 4:
Further, the following conditions (5), (6), (7) and (9):
(5): The thickness (mm) of the cover is 0.5 mm or more and 2.0 mm or less,
(6): Shore D hardness of the cover is 52 or more and 62 or less,
(7): The thickness (mm) of the intermediate layer is 0.5 mm or more and 1.6 mm or less ,
(9): The initial velocity of the golf ball is 76.5 m / s or more,
The multi-piece solid golf ball according to claim 1, wherein:
Claim 5:
Furthermore, the following condition (10):
(10): The melt flow rate of the cover is 2 g / 10 min or more,
The multi-piece solid golf ball according to claim 1, wherein:
Claim 6:
6. The condition according to (11) above, wherein the deflection hardness of the golf ball / the deflection hardness of the sphere in which the core is coated with the intermediate layer is 0.85 or more and 0.95 or less. Peace solid golf ball.
Claim 7:
The multi-piece solid golf ball according to any one of claims 1 to 6, wherein a Shore D hardness of the core surface is in a range of 55.1 to 57.5.

  The multi-piece solid golf ball of the present invention is excellent in resilience, imparts excellent feel and durability, and also has good controllability.

It is explanatory drawing for demonstrating the relationship between the lift and drag of the golf ball in flight. It is a top view of the ball | bowl which showed the dimple used in the Example of this invention.

Hereinafter, the present invention will be described in more detail.
The present invention comprises a core formed using a base rubber as a main material, an intermediate layer covering the core, a cover with the intermediate layer, and a large number of dimples on the outer surface. The following conditions (1) to (4), (11) and (12),
(1): (Shore D hardness of cover) − (Shore D hardness of intermediate layer)> 5
(2 ′): (initial velocity of the core (m / s)) − (initial velocity of the ball (m / s)) ≧ 0.2 (Here, the initial velocity is a USGA drum rotation-type initial velocity meter. Means the initial speed measured using the same initial speed measuring instrument)
(3): 0.87 ≦ [(the deflection hardness of the sphere with the intermediate layer coated on the core) / (the deflection hardness of the core)] ≦ 0.93 (where the deflection hardness is the initial load on the spherical object) The amount of deformation (mm) from when 98 N (10 kgf) is loaded to when the final load of 1275 N (130 kgf) is loaded)
(4): The total thickness of the intermediate layer thickness (mm) and the cover thickness (mm) is 3.0 mm or less,
(11): (deflection hardness of golf ball / deflection hardness of sphere in which core is covered with intermediate layer) ≦ 0.98
(12): (Shore D hardness of core surface) − (Shore D hardness of core center) ≧ 15
The core diameter is 36.8 mm or more and 38.8 mm or less, the core specific gravity is 1.15 g / cm ³ or more and 1.35 g / cm ³ or less, and the intermediate layer is softer than the core surface. A multi-piece solid golf ball.
Here, in the present invention, the flexural hardness means that when a final load 1275 (130 kgf) is applied from a state in which an initial load 98 N (10 kgf) is applied to a spherical object such as a core, a sphere coated with an intermediate layer, and a golf ball. The amount of deformation (mm) up to.

As the material of the intermediate layer and / or cover in the present invention,
(A-1) a metal ion neutralized product of an olefin-unsaturated carboxylic acid binary random copolymer and / or an olefin-unsaturated carboxylic acid binary random copolymer;
(A-2) Metal ion neutralized product of olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ternary random copolymer and / or olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ternary random copolymer And
(A-1) / (a-2) = 100/0 to 0/100 (mass ratio) (A) ionomer resin included,
(B) an olefinic thermoplastic elastomer ,
It is preferable that (A) / (B) = 85/15 to 60/40 (mass ratio).
For 100 parts by mass of the resin component containing the (A) ionomer resin and the (B) olefin-based thermoplastic elastomer at a ratio of (A) / (B) = 85/15 to 60/40 (mass ratio),
(C) 5 to 80 parts by mass of an organic fatty acid having a molecular weight of 280 to 1500 and / or a derivative thereof;
(D) 0.1 to 10 parts by mass of a basic inorganic metal compound capable of neutralizing an unneutralized acid group in the resin component and the component (C);
It is more preferable that the mixture is formed by blending.

  As the olefin in the component (a-1) and the component (a-2), an olefin having 2 or more carbon atoms and having an upper limit of 8 or less, particularly 6 or less is preferably used. More specific examples of such olefins include ethylene, propylene, butene, pentene, hexene, heptene, octene and the like, and ethylene is particularly preferably used.

  Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid and the like, and acrylic acid and methacrylic acid are particularly preferably used.

  Examples of the unsaturated carboxylic acid ester in the component (a-2) include lower alkyl esters of the above-mentioned unsaturated carboxylic acid, and more specifically, methyl methacrylate, ethyl methacrylate, propyl methacrylate. Butyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate and the like, and butyl acrylate (n-butyl acrylate, i-butyl acrylate) is particularly preferably used.

  The olefin-unsaturated carboxylic acid binary random copolymer of component (a-1) and the olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer of component (a-2) (hereinafter referred to as these) Are generally abbreviated as “random copolymer”), and are obtained by random copolymerizing the above-mentioned olefin, unsaturated carboxylic acid, and if necessary, unsaturated carboxylic acid ester by a known method. be able to.

  The random copolymer is preferably one having an unsaturated carboxylic acid content (acid content) adjusted. In this case, the content of the unsaturated carboxylic acid contained in the component (a-1) is 4% by mass or more, preferably 6% by mass or more, more preferably 8% by mass or more, further preferably 10% by mass or more, and the upper limit. 30 mass% or less, Preferably it is 20 mass% or less, More preferably, it is 18 mass% or less, More preferably, it is 15 mass% or less. The content of the unsaturated carboxylic acid contained in the component (a-2) is 4% by mass or more, preferably 6% by mass or more, more preferably 8% by mass or more, and the upper limit is 15% by mass or less, preferably 12% by mass. % Or less, more preferably 10% by mass or less. If the content of the unsaturated carboxylic acid contained in the component (a-1) and / or the component (a-2) is too small, the resilience may be lowered, and if it is too much, the workability may be lowered.

  Metal ion neutralized product of olefin-unsaturated carboxylic acid binary random copolymer of component (a-1) and olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer of component (a-2) The polymer metal ion neutralized product (hereinafter sometimes collectively referred to as “random copolymer metal ion neutralized product”) is a part of the acid group in the random copolymer. Alternatively, it can be obtained by neutralizing the whole with metal ions.

Examples of metal ions that neutralize the acid groups in the random copolymer include Na ⁺ , K ⁺ , Li ⁺ , Zn ⁺⁺ , Cu ⁺⁺ , Mg ⁺⁺ , Ca ⁺⁺ , Co ⁺⁺ , and Ni. ⁺⁺ , Pb ^{++ and the} like can be mentioned. Among these, Na ⁺ , Li ⁺ , Zn ⁺⁺ and Mg ⁺⁺ are preferable, and Na ⁺ is particularly preferable from the viewpoint of improving resilience. is there.

  As a method of obtaining the metal ion neutralized product of the random copolymer using such metal ions, for example, the metal ion formate, acetate, nitrate of the random copolymer having an acid group. Carbonate, bicarbonate, oxide, hydroxide, alkoxide and the like may be added for neutralization. The degree of neutralization of the acid groups by these metal ions is not particularly limited in the present invention.

  A commercial item can be used as said (a-1) component and said (a-2) component, for example, as a random copolymer of said (a-1) component, for example, Nukurel 1560, 1214, 1035 (all manufactured by Mitsui & DuPont Polychemical Co., Ltd.), ESCOR 5200, 5100, and 5000 (all manufactured by EXXONMOBIL CHEMICAL), etc., as the metal ion neutralized product of the random copolymer of the above component (a-1) For example, High Milan 1554, 1557, 1601, 1601, 1605, 1706, AM7311 (all manufactured by Mitsui DuPont Polychemical), Surlyn 7930 (manufactured by DuPont, USA), Iotech 3110, 4200 (manufactured by EXXONMOBILCHEMICAL) Etc., the random co As a combination, for example, Nukurel AN4311, AN4318 (all manufactured by Mitsui & DuPont Polychemical Co., Ltd.), ESCOR ATX325, ATX320, ATX310 (all manufactured by EXXONMOBIL CHEMICAL), etc. As polymer metal ion neutralized products, for example, Himiran 1855, 1856, and AM7316 (all manufactured by Mitsui DuPont Polychemical Co., Ltd.), Surlyn 6320, 8320, 9320, and 8120 (all manufactured by DuPont, USA) , Iotech 7510, 7520 (both manufactured by EXXONMOBIL CHEMICAL) and the like. These may be used alone or in combination of two or more. Examples of the sodium neutralized ionomer resin suitable as the metal ion neutralized product of the random copolymer include Himiran 1605, 1601 and Surlyn 8120.

  The proportion of the component (a-2) in the total amount of the component (a-1) and the component (a-2) is 0% by mass or more, preferably 50% by mass or more, and the upper limit is 100% by mass. % Or less.

The (B) olefin-based thermoplastic elastomer is a component that is suitably blended from the viewpoint of further improving the feeling and resilience when hitting a golf ball. In the present invention, the above (A) ionomer resin and (B) olefin-based thermoplastic elastomer may be collectively referred to as “resin component”.

A commercial item may be used as such (B) component, and Dynalon (made by JSR ) etc. can be mentioned as an olefin type elastomer. These may be used alone or in combination of two or more.

The proportion of the component (B) in the resin component is 15% by mass or more, and the upper limit is 40% by mass or less. If the proportion of the component (B) in the resin component exceeds 40% by mass , the compatibility of the components may be reduced, and the durability of the golf ball may be significantly reduced.

  The component (C) in the present invention is an organic fatty acid having a molecular weight of 280 or more and 1500 or less and / or a derivative thereof. The molecular weight is extremely small as compared with the resin component, and the melt viscosity of the mixture is appropriately adjusted. Since it is a component which contributes to the improvement of property, it mix | blends suitably.

  The molecular weight of the organic fatty acid component (C) is 280 or more, preferably 300 or more, more preferably 330 or more, still more preferably 360 or more, and the upper limit is 1500 or less, preferably 1000 or less, more preferably 600 or less, and more Preferably it is 500 or less. If the molecular weight is too small, the heat resistance may be inferior, and if it is too large, the fluidity may not be improved.

  Examples of such organic fatty acids of component (C) include unsaturated organic fatty acids having a double bond or triple bond in the alkyl group, and saturated organic fatty acids in which the bond in the alkyl group is composed of only a single bond. It can be used suitably.

  The number of carbon atoms in one molecule of the organic fatty acid is 18 or more, preferably 20 or more, more preferably 22 or more, still more preferably 24 or more, and the upper limit is 80 or less, preferably 60 or less, more preferably 40 or less, still more preferably. Is 30 or less. If the number of carbon atoms is too small, not only may the result be inferior in heat resistance, but the content of acid groups will be too high, resulting in excessive interaction with acid groups contained in the resin component, and fluidity. The improvement effect may be reduced. On the other hand, when the number of carbon atoms is too large, the molecular weight increases, and thus the effect of fluidity modification may not be noticeable.

  More specifically, examples of the organic fatty acid of component (C) in the present invention include stearic acid, 12-hydroxystearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, arachidic acid, lignoceric acid, and the like. Of these, stearic acid, arachidic acid, behenic acid, lignoceric acid, particularly behenic acid are preferably used.

Examples of the organic fatty acid derivative of the component (C) include metal soaps in which protons contained in the acid groups of the organic fatty acids described above are substituted with metal ions. In this case, examples of the metal ions include Na ⁺ , Li ⁺ , Ca ⁺⁺ , Mg ⁺⁺ , Zn ⁺⁺ , Mn ⁺⁺ , Al ⁺⁺⁺ , Ni ⁺⁺ , Fe ⁺⁺ , Fe ⁺⁺⁺ , Cu ⁺⁺ , Sn ⁺⁺ , Pb ⁺⁺ , Co ^{++ and the} like can be used, and Ca ⁺⁺ , Mg ⁺⁺ , and Zn ⁺⁺ are particularly preferable.

  More specifically, as the organic fatty acid derivative of the component (C), for example, magnesium stearate, calcium stearate, zinc stearate, 12-hydroxy magnesium stearate, 12-hydroxy calcium stearate, 12-hydroxy zinc stearate, arachidic acid Examples include magnesium, calcium arachidate, zinc arachidate, magnesium behenate, calcium behenate, zinc behenate, magnesium lignocerate, calcium lignocerate, zinc lignocerate, among others, magnesium stearate, calcium stearate, stearic acid Zinc, magnesium arachidate, calcium arachidate, zinc arachidate, magnesium behenate, calcium behenate, behenic acid sub , Can be preferably used magnesium lignoceric acid, calcium lignoceric acid, lignoceric acid zinc. These may be used alone or in combination of two or more.

  Moreover, as such (C) component compounding quantity, it is 5 mass parts or more with respect to 100 mass parts of said resin components which consist of (A) and (B), Preferably it is 10 mass parts or more, More preferably, it is 15 The upper limit is 80 parts by weight or less, preferably 40 parts by weight or less, more preferably 25 parts by weight or less, still more preferably 22 parts by weight or less. If the blending amount of the component (C) is too small, the melt viscosity may be too low and the workability may be lowered, and if it is too much, the durability may be lowered.

  In the invention, a known metal soap-modified ionomer (USP5312857, USP5306760, WO98 / 46671, etc.) may be used as a mixture of the above (A) ionomer resin and the above (C) component.

  The component (D) in the present invention is a basic inorganic metal compound capable of neutralizing an unneutralized acid group in the resin component and the component (C). When the component (D) is not blended and, for example, a metal soap-modified ionomer resin is used alone, an exchange reaction between the metal soap and the unneutralized acid group contained in the ionomer resin occurs during heating and mixing. In some cases, defects such as poor molding, poor coating film adhesion, and low rebound of the resulting molded product may occur. In view of such points, the component (D) is suitably blended in the present invention.

  The component (D) preferably has high reactivity with the resin component and does not contain an organic acid in the reaction byproduct.

Examples of the metal ion in the component (D) include Li ⁺ , Na ⁺ , K ⁺ , Ca ⁺⁺ , Mg ⁺⁺ , Zn ⁺⁺ , Al ⁺⁺⁺ , Ni ⁺⁺ , Fe ⁺⁺ and Fe ^{+. ++} , Cu ⁺⁺ , Mn ⁺⁺ , Sn ⁺⁺ , Pb ⁺⁺ , Co ^++, etc. can be mentioned, and these may be used alone or in combination of two or more. As the component (D), known basic inorganic fillers containing these metal ions can be used. More specifically, for example, magnesium oxide, magnesium hydroxide, magnesium carbonate, zinc oxide, sodium hydroxide, Examples thereof include sodium carbonate, calcium oxide, calcium hydroxide, lithium hydroxide, and lithium carbonate. In particular, hydroxides or monoxides are recommended, and calcium hydroxide and magnesium oxide having high reactivity with the base resin are preferably used.

  As a compounding quantity with respect to 100 mass parts of said resin components of the said (D) component, 0.1 mass part or more, Preferably it is 0.5 mass part or more, More preferably, it is 1 mass part or more, More preferably, it is 2 mass parts or more, As an upper limit, it is 10 mass parts or less, Preferably it is 8 mass parts or less, More preferably, it is 6 mass parts or less, More preferably, it is 5 mass parts or less. When the blending amount of the component (D) is too small, the heat stability and the resilience may not be improved, and when it is too large, the heat resistance of the golf ball material is lowered due to the excessive basic inorganic metal compound. There is.

  The degree of neutralization of the mixture obtained by mixing the components (A) to (D) is 50 mol% or more, preferably 60 mol% or more, more preferably based on the total amount of acid groups in the mixture. It is 70 mol% or more, more preferably 80 mol% or more. By such high neutralization, for example, even when a metal soap-modified ionomer resin is used, an exchange reaction between the metal soap and unneutralized acid groups contained in the ionomer resin hardly occurs during heating and mixing, and thermal The possibility of impairing stability, moldability, and resilience is reduced.

  In the material of the intermediate layer and / or cover in the present invention, in addition to the components (A) to (D), a pigment, a dispersant, an anti-aging agent, an ultraviolet absorber, a light stabilizer, and the like. Additives can be blended. The blending amount is not particularly limited, but is 0.1 parts by mass or more, preferably 0.5 parts by mass with respect to 100 parts by mass of the resin component composed of the component (A) and the component (B). Part or more, more preferably 1 part by weight or more, and the upper limit is 10 parts by weight or less, preferably 6 parts by weight or less, more preferably 4 parts by weight or less.

  The intermediate layer and / or cover material in the present invention can be obtained by heating and mixing the above-described components. For example, under a heating temperature of 150 to 250 ° C., a kneading type twin screw extruder, Banbury, kneader, etc. It can obtain by kneading using an internal mixer.

  The core in the present invention is manufactured according to a conventional method using a base rubber as a main material. For example, with respect to 100 parts by mass of cis-1,4-polybutadiene, α, β-monoethylenically unsaturated carboxylic acid such as acrylic acid or methacrylic acid or neutralized product thereof, functional monomer such as trimethylolpropane methacrylate, etc. 10 parts by mass or more and 60 parts by mass or less of fillers such as zinc oxide and barium sulfate, one kind selected from these crosslinking agents alone or a mixture of two or more, and dicumyl After peroxide such as peroxide is blended in an amount of 0.5 parts by mass or more and 5 parts by mass or less, and an anti-aging agent is blended in an amount of 0 parts by mass or more and 1 part by mass or less as required. The solid core can be formed by a method of heating and compressing at 140 ° C. to 170 ° C. for 10 minutes to 40 minutes to form a spherical shape.

  It is preferable to contain sulfur in the base rubber which is the main material of the core. In this case, powder sulfur can be mentioned as sulfur, and specifically, trade name “Z sulfur” (manufactured by Tsurumi Chemical Co., Ltd.) is exemplified.

  The amount of sulfur is 0.05 parts by mass or more, preferably 0.07 parts by mass or more, more preferably 0.09 parts by mass or more, with respect to 100 parts by mass of the core base rubber. The value is 0.5 parts by mass or less, preferably 0.3 parts by mass or less, and more preferably 0.2 parts by mass or less. If the amount of sulfur is too small, the difference in hardness between the core surface and the center may not be increased beyond a certain level. Moreover, when there are too many compounding quantities of sulfur, there exists a possibility that impact resilience may become low and a flight distance may become small.

  Further, from the viewpoint of improving the resilience of the golf ball, it is preferable to contain an organic sulfur compound in the base rubber which is the main material of the core. The organic sulfur compound is not particularly limited as long as it can improve the resilience of the golf ball, and examples thereof include thiophenols, thionaphthol, halogenated thiophenols, and metal salts thereof. More specifically, pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, zinc salt of pentachlorothiophenol, zinc salt of pentafluorothiophenol, zinc salt of pentabromothiophenol, Examples include zinc salt of parachlorothiophenol, diphenyl polysulfide having 2 to 4 sulfur atoms, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, dithiobenzoyl polysulfide, etc., especially zinc salt of pentachlorothiophenol, diphenyl Disulfide is preferably used.

  The amount of the organic sulfur compound is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and most preferably 0.2 parts by mass or more with respect to 100 parts by mass of the base rubber. is there. If the blending amount is too small, the effect of improving the resilience cannot be expected. Moreover, as an upper limit, Preferably it is 5 mass parts or less, More preferably, it is 4 mass parts or less, Most preferably, it is 2 mass parts or less. If the amount is too large, the core becomes too soft, and the feel of hitting may worsen, or the durability to cracking when repeatedly hitting may deteriorate.

Here, about the compounding ratio of the sulfur and organic sulfur compound mentioned above, it is desirable to satisfy the following formula.
1 ≦ (the amount of organic sulfur compound / the amount of sulfur) ≦ 30

  The value of (the amount of organic sulfur compound / the amount of sulfur) is more preferably 3 or more, most preferably 5 or more, and the upper limit is more preferably 25 or less, most preferably 20 or less. be able to. If this value is too small, the resilience may be low and the flight distance may not be achieved. On the other hand, if this value is too large, the ball hardness may become too soft, or the difference in hardness between the core surface and the center may not be sufficient, resulting in an increase in spin and a loss of flight distance.

  The deflection hardness of such a core is 2.5 mm or more, preferably 3.0 mm or more, more preferably 3.3 mm or more, and the upper limit is 5.5 mm or less, preferably 4.5 mm or less, more preferably 4.0 mm or less. It is. If the deflection hardness is less than 2.5 mm, the spin of the golf ball may increase too much to fly or the feel of hitting may become hard. On the other hand, if it exceeds 5.5 mm, the resilience will be low and fly away. It may disappear, the feeling of hitting may become too soft, or the durability to cracking when hitting repeatedly may deteriorate.

The diameter of the core not less than 36.8 mm, preferably at least 37.2 mm, more preferably 37.6mm or more. The upper limit value of the diameter of the core, or less 38.8 mm.

The specific gravity of the core is 1.15 g / cm ³ or more, and the upper limit is 1.35 g / cm ³ or less, preferably 1.25 g / cm ³ or less.

  Further, the core surface hardness is 45 or more, preferably 50 or more, more preferably 53 or more, and the upper limit is 65 or less, preferably 62 or less, more preferably 60 or less as the Shore D hardness. If the Shore D hardness of the core surface exceeds 65, the spin of the golf ball may increase and may not fly or the feel of hitting may become hard. On the other hand, if the Shore D hardness of the core surface is less than 45, rebound In some cases, it becomes difficult to fly due to its low nature, the feeling of hitting becomes too soft, and the durability to cracking when repeatedly hitting may deteriorate.

  On the other hand, the core center hardness is 30 or more as Shore D hardness, preferably 33 or more, more preferably 35 or more, and the upper limit is 50 or less, preferably 45 or less, more preferably 40 or less. If the Shore D hardness exceeds 50, the spin of the golf ball may increase too much to fly or the feel of hitting may become hard. On the other hand, if the Shore D hardness is less than 30, the resilience will be low and fly away. It may disappear, the feeling of hitting may become too soft, or the durability to cracking when hitting repeatedly may deteriorate.

  The intermediate layer is formed softer than the core surface. If the intermediate layer is harder than the core surface, the feeling may deteriorate.

  In the present invention, a golf ball including a core, an intermediate layer covering the core, and a cover covering the intermediate layer is formed using each of the materials described above. Is the Shore D hardness balance between the intermediate layer and the cover (condition (1) above), the initial velocity balance between the core and the ball (condition (2 ') above), and the core and core cover the intermediate layer. Optimize the flexural hardness balance (the above condition (3)) with the formed sphere, and optimize the total thickness of the intermediate layer and the cover (the above condition (4)). Is a deflection hardness balance between the ball and a sphere whose core is covered with an intermediate layer (condition (11) above), and a Shore D hardness balance between the core surface and the core center (condition (12) above). ) To optimize the feel and durability , Resilience and flight distance, is intended to provide an excellent golf ball in control.

Further, from the viewpoint of providing a more excellent golf ball, the following conditions (5) to (11) can be preferably employed.
(5): The thickness (mm) of the cover is 0.5 mm or more and 2.0 mm or less,
(6): Shore D hardness of the cover is 52 or more and 62 or less,
(7): The thickness (mm) of the intermediate layer is 0.5 mm or more and 1.6 mm or less,
(8): Shore D hardness of the intermediate layer is 40 or more and 60 or less,
(9): The initial velocity of the golf ball is 76.5 m / s or more,
(10): MFR of the cover is 2 g / min or more,
(11): 0.85 ≦ (deflection hardness of golf ball / deflection hardness of sphere in which core is covered with intermediate layer) ≦ 0.95,

[Conditions for (1)]
In the golf ball of the present invention, the value of (Shore D hardness of the cover) − (Shore D hardness of the intermediate layer) is 5 or more , and the upper limit is 30 or less, preferably 20 or less, more preferably 15 or less. If the difference is 5 or less, too much spin is applied and the flight distance is reduced, and if the difference exceeds 30, the rebound is reduced and the flight distance is reduced.

[Regarding condition (2 ')]
In the golf ball of the present invention, the value of (core initial velocity (m / s)) − (ball initial velocity (m / s)) is 0.2 or more, preferably 0.4 or more. If the difference is less than 0.2, a ball having both good resilience, controllability and feeling may not be made. As a means satisfying the condition (2 ′), a high resilience material is required for the intermediate layer. If the intermediate layer is hardened and the core is made soft and has a low rebound, the condition (2 ′) is satisfied. However, if the other requirements of the claim are not satisfied at the same time, the effect of the present invention cannot be achieved.

  The “initial speed (m / s)” was measured using an initial speed measuring device of the same type as a USGA drum rotary initial speed meter approved by R & A. The ball was temperature-controlled at 23 ± 1 ° C. for 3 hours or more and then tested in a room at room temperature 23 ± 2 ° C. 5. Using a 250 pound (113.4 kg) head (striking mass), hit the ball at a hitting speed of 143.8 ft / s (43.83 m / s) and hit a dozen balls 4 times each. The initial speed (m / s) was calculated by measuring the time required to pass between 28 ft (1.91 m). This cycle was performed in about 15 minutes.

[Regarding condition (3)]
In the golf ball of the present invention, the value of (deflection hardness of the sphere with the core covered with the intermediate layer) / (deflection hardness of the core) is 0.87 or more, preferably 0.88 or more, more preferably 0.90 or more. The upper limit is 0.93 or less. When the ratio is less than 0.87, the feeling of hitting with the putter becomes hard, or the spin by the W # 1 hit increases and the flight distance does not come out. If the ratio exceeds 0.93 , the spin will increase when the W # 1 is hit and the flying distance will not be obtained, or the repeated hitting durability will deteriorate.

  As specific means for designing the golf ball so as to satisfy the condition (3), the shore D hardness of the intermediate layer is set in the range of about 40 to 60, and the intermediate layer thickness and core hardness are set to appropriate values. The method of setting to can be adopted.

[Regarding condition (4)]
In the golf ball of the present invention, the total thickness of the intermediate layer (mm) and the cover (mm) is 0.5 mm or more, preferably 1.0 mm or more, more preferably 2.0 mm or more, and the upper limit is 3 It is 0.0 mm or less, preferably 2.8 mm or less, more preferably 2.6 mm or less. If the total thickness is less than 0.5 mm, the crack durability during repeated hitting deteriorates, and if the total thickness exceeds 3.0 mm, the spin at the time of hitting W # 1 increases and the flight distance does not appear.

[Regarding condition (5)]
In the golf ball of the present invention, the cover thickness (mm) is 0.5 mm or more, preferably 0.9 mm or more, more preferably 1.1 mm or more, and the upper limit is 2.0 mm or less, preferably 1.6 mm or less. Preferably it is 1.3 mm or less. If the cover thickness is less than 0.5 mm, the durability to cracking during repeated impacts may deteriorate, while if it exceeds 2.0 mm, the feel during approach or putter impacts may deteriorate.

[Regarding condition (6)]
In the golf ball of the present invention, the cover has a Shore D hardness of 52 or more, preferably 55 or more, more preferably 57 or more, and an upper limit of 62 or less, preferably 61 or less, more preferably 60 or less. If the Shore D hardness is less than 52, the spin may be excessively applied, the repulsion may be insufficient, the flight distance may be decreased, and the scratch resistance may be deteriorated. On the other hand, if the Shore D hardness exceeds 62, the durability against cracking due to repeated hitting may deteriorate, the feeling of hitting a short game or putter may deteriorate, and the controllability in the approach may be insufficient.

[Regarding condition (7)]
In the golf ball of the present invention, the intermediate layer has a thickness (mm) of 0.5 mm or more, preferably 0.8 mm or more, more preferably 1.1 mm or more, and an upper limit of 1.6 mm or less, preferably 1.4 mm or less. More preferably, it is 1.3 mm or less. If the thickness of the intermediate layer is less than 0.5 mm, the durability against cracking due to repeated impacts may deteriorate, or the rebound may decrease and the flight distance may not be obtained. On the other hand, if it exceeds 1.6 mm, the spin at the time of hitting with the driver may increase so that the flight distance may not be obtained.

[Regarding condition (8)]
In the golf ball of the present invention, the Shore D hardness of the intermediate layer is 40 or more, preferably 45 or more, more preferably 48 or more, and the upper limit is 60 or less, preferably 55 or less, more preferably 52 or less. In addition, the shore D hardness of an intermediate | middle layer means the shore D hardness when the material which forms an intermediate | middle layer is made into a sheet form. If the Shore D hardness is less than 40, the spin distance may be excessively applied or the rebound may be insufficient, resulting in a decrease in flight distance. On the other hand, if the Shore D hardness exceeds 60, the durability against cracking due to repeated hitting may deteriorate, and the hit feeling of a short game or putter may deteriorate.

[Regarding condition (9)]
In the golf ball of the present invention, the initial velocity of the golf ball is 76.5 m / s or more, preferably 76.8 m / s or more, more preferably 77.1 m / s or more, and the upper limit is 77.724 m / s or less. . If it is too low, the flight distance will not come out. If it exceeds the upper limit of 77.724 m / s, it becomes out of the standard defined by R & A (USGA) and cannot be registered as a certified ball.

[Regarding condition (10)]
In the golf ball of the present invention, the MFR of the cover material is 2.0 g / 10 min or more, preferably 2.2 g / 10 min or more, more preferably 2.6 g / 10 min or more. If the MFR is less than 2.0 g / 10 min, molding may be difficult, or the sphericity of the ball obtained by molding may be reduced, resulting in increased variation in flying. Here, the melt flow rate (sometimes abbreviated as “MFR”) is a value (g / 10) measured at a test temperature of 190 ° C. and a test load of 21.18 N (2.16 kgf) in accordance with JIS-K6760. And the same applies in the present invention.

[Regarding condition (11)]
In the golf ball of the present invention, (the deflection hardness of the golf ball / the deflection hardness of the sphere whose core is covered with the intermediate layer) is 0.98 or less, preferably 0.85 or more, more preferably 0.88 or more. The upper limit is preferably 0.95 or less, more preferably 0.92 or less. If the value is too small or too large, the spin at W # 1 may increase too much and the flight distance may not be obtained.
As a specific means for designing the golf ball so as to satisfy the condition (11), a method of setting the cover hardness, the cover thickness, and the deflection hardness of the sphere covered with the intermediate layer to appropriate values can be adopted. .

[Regarding condition (12)]
In the golf ball of the present invention, (Shore D hardness of core surface) − (Shore D hardness of core center) is 15 or more, preferably 16 or more, more preferably 17 or more, and the upper limit is 30 or less, preferably 25. Below, more preferably 23 or less. If the hardness difference of the Shore D hardness is too small, the spin may be applied too much and the flight distance may not be obtained. On the other hand, if the hardness difference is too large, the durability to cracking when hitting repeatedly may deteriorate, or the initial speed when hitting with W # 1 may be lowered and the flight distance may not be obtained.

In the present invention, a large number of dimples are formed on the cover surface. The number of dimples arranged on the cover surface is 280 to 360, preferably 300 to 350, and more preferably 320 to 340. If the number of dimples exceeds the above range, the trajectory of the ball may be lowered and the flight distance may not be achieved. Further, if the number of dimples is too small, the trajectory becomes high and the flight distance may not be extended. The shape of the dimple can be appropriately used by combining one type or two or more types such as a circular shape, various polygonal shapes, a dew drop shape, and other elliptical shapes. For example, when circular dimples are used, the diameter can be set in the range of 2.5 mm to 6.5 mm and the depth can be set in the range of 0.08 to 0.30 mm. Further, the V ₀ value (value obtained by dividing the space volume of the dimple below the plane surrounded by the edge of the dimple by the cylindrical volume having the plane as the bottom surface and the maximum depth of the dimple from the bottom surface as the height). The SR value (the ratio of the total dimple area defined by the surface edge of the plane surrounded by the edges of the dimples to the area of the ball sphere assuming that no dimples are present) in the range of 0.35 to 0.80 60 to 90%, VR value (ratio of the total volume of dimples formed downward from the plane surrounded by the edges of the dimples to the ball ball volume assuming no dimples) is in the range of 0.6 to 1 The dimples can be selected as appropriate.

  In order to improve the flight distance, low CD under high speed conditions and high CL under low speed conditions are considered good. In the multi-piece solid golf ball of the present invention, when the ball is hit at a Reynolds number of 70,000 and a spin rate of 2000 rpm, the lift coefficient CL of the ball is 0.165 or more, and the Reynolds number is 180,000 and the spin rate is 2520 rpm. It is preferable that the ball has a drag coefficient CD of 0.230 or less. This point will be described below.

Balls hit by clubs such as Wood Club # 1 (driver) have a great flight distance, especially in the wind, and the balance of lift and drag is appropriate to obtain a ball that runs well. In addition to the structure and the materials used, it depends in particular on the type, total number, surface occupancy, total volume, etc. of the dimples used.
Further, as shown in FIG. 1, the golf ball G in flight hit by the club receives gravity 6, resistance (drag) 7 by air, and lift 8 due to the Magnus effect because the ball has spin. It has been known. In the figure, 9 indicates the flight direction, and the ball G rotates in 11 directions.

In this case, the force acting on the golf ball is represented by the following ballistic equation (1).
F = FL + FD + Mg (1)
F: force acting on the golf ball FL: lift FD: drag Mg: gravity

Further, the lift force F and the drag force FD of the ballistic equation (1) are respectively expressed by the following equations (2) and (3).
FL = 0.5 × CL × ρ × A × V ² (2)
FD = 0.5 × CD × ρ × A × V ² (3)
CL: Lift coefficient
CD: Drag coefficient
ρ: Air density
A: Golf ball maximum cross-sectional area
V: Golf ball vs. air velocity

  In order to improve the flight distance of the hit ball, it is not very effective to reduce only the drag or drag coefficient CD. When only the drag coefficient is reduced, the position of the highest point of the hit ball is extended, but the flying distance tends to be lost due to a drop due to insufficient lift in the low speed region after the highest point.

  Therefore, in the multi-piece solid golf ball of the present invention, the drag coefficient CD when the ball is hit at a Reynolds number of 180,000 and a spin rate of 2520 rpm is preferably 0.230 or less, more preferably 0.225 or less, and still more preferably. The lift coefficient CL of the ball when the ball is hit at a Reynolds number of 70000 and a spin rate of 2000 rpm is preferably 0.165 or more, more preferably 0.170 or more, and further preferably 0.180 or more. It is. Note that the Reynolds number of 180,000 immediately after the ball is hit is approximately 66 m / s at the ball speed, and in this case, the Reynolds number of 70,000 corresponds to a speed of 26 m / s.

  In addition, the golf ball of the present invention can conform to the golf rules for competition purposes, and can be formed with a diameter of 42.67 mm or more and a mass of 45.93 g or less. The upper limit of the diameter is preferably 44.0 mm or less, more preferably 43.5 mm or less, most preferably 43.0 mm or less, and the lower limit of the mass is preferably 44.5 g or more, more preferably 45.0 g or more, still more preferably. Is 45.1 g or more, particularly preferably 45.2 g or more.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

[Examples 1 to 3, Comparative Examples 1 to 5]
A rubber composition obtained by blending (parts by mass) shown in Table 1 was vulcanized at 157 ° C. for 15 minutes to prepare a three-piece golf ball core. The core was coated with an intermediate layer material and a cover material shown in Table 2 by injection molding to obtain a three-piece solid golf ball.
Table 3 shows the evaluation results of the obtained golf balls.

Polybutadiene (1)
Product name BR01 (manufactured by JSR)
Polybutadiene (2)
Product name BR730 (manufactured by JSR)
Polyisoprene product name IR2200 (JSR Co., Ltd.)
Peroxide (1)
Dicumyl peroxide, trade name Park Mill D (manufactured by NOF Corporation)
Peroxide (2)
A mixture of 1,1 di (t-butylperoxy) cyclohexane and silica, trade name Perhexa C-40 (manufactured by NOF Corporation)
Sulfur Z sulfur (mixture of 95% sulfur / 5% zinc oxide) manufactured by Tsurumi Chemical Co., Ltd.
Anti-aging agent NOCRACK NS-6 (Ouchi Shinsei Chemical Co., Ltd.)

Said MFR (g / 10min) is the melt flow rate of the material measured by the test temperature of 190 degreeC and the test load of 21.18N (2.16kgf) based on JIS-K6760. The details of the above materials are as follows.
Surlyn 8120
DuPont ionomer
AM7331
Ionomer made by Mitsui DuPont Polychemical Co., Ltd.
AM7311, 7317, 7318
An ionomer manufactured by Mitsui DuPont Polychemicals. 7311; Magnesium ionomer, 7317; Zinc ionomer with 18% acid content, 7318; Sodium ionomer with 18% acid content
High Milan 1557, 1605, 1855
Ionomer made by Mitsui DuPont Polychemical Co., Ltd.
AN4318
Nucler made by Mitsui DuPont Polychemical Co., Ltd.
Hytrel 3046
Polyester elastomer made by Toray DuPont
Dynalon E6100P
Hydrogenated polymer manufactured by JSR
Behenic acid manufactured by NOF Corporation NAA222-S (beads)
CLS-B made by calcium hydroxide Shiroishi Kogyo Co., Ltd.

Carry when struck at a head speed of 47m / s with a W # 1 club in the golf swing robot fly, total, the spin was measured. As the W # 1 club, TourStage X500 Loft 10 ° manufactured by Bridgestone Sports was used. The flight distance was evaluated according to the following criteria.
○: Total flight distance of 224.0 m or more ×: Total flight distance of less than 224.0 m

W # 1 feeling and putter feeling A sensory evaluation was performed by 10 amateur golfers with a head speed of 40 to 50 m / s. Evaluation was performed according to the following criteria.
○: 7 or more out of 10 felt good hit feeling ×: Less than 4 out of 10 people felt good hit feeling

Cracking when you repeatedly hit at a head speed of 45m / s with a W # 1 club in durability golf swing robot, it was evaluated by the number of times when the cracks began to enter the surface of the ball. The average value of each ball N = 3 was used as the evaluation target value. Each index when the number of cracks in Example 2 that started to be cracked was 100 was evaluated according to the following criteria.
○: Index 95 or higher ×: Index less than 95

A scratch-resistant non-plated pitching sand wedge was set on a hitting robot, hit once at a head speed of 40 m / s, visually observed on the ball surface, and evaluated according to the following criteria.
○: Can still be used ×: Cannot be used anymore

Dimple characteristics In this example, the following dimples were used.

Dimple definition
Diameter : Diameter of a plane surrounded by dimple edges
Depth : Maximum dimple depth from a plane surrounded by dimple edges
V ₀ : A value obtained by dividing the space volume of the dimple below the plane surrounded by the edge of the dimple by the cylindrical volume having the plane as the bottom surface and the maximum depth of the dimple from the bottom surface as the height.
SR : The ratio of the total dimple area defined by the surface edge of the plane surrounded by the edge of the dimple to the ball sphere area on the assumption that no dimple exists
VR : The ratio of the total dimple volume formed below the plane surrounded by the edge of the dimple to the volume of the ball sphere assumed that no dimple exists

Aerodynamic characteristics (low speed CL ratio and high speed CD value)
The low speed CL ratio was calculated by using UBL (Ultra Ball Launcher) to calculate the lift coefficient CL of the ball when the ball was launched at a Reynolds number of 70000 and a spin rate of 2000 rpm. Similarly, the high-speed CD value is a drag coefficient obtained when a ball is hit at a Reynolds number of 180,000 and a spin rate of 2520 rpm. These values are as follows:

  The UBL is a device that places two pairs of drums on the upper and lower sides, puts belts on the upper and lower drums, rotates them, and inserts the balls between them to hit the balls under desired conditions. UBL is made by Automated Design Corporation.

From the results in the above table, the golf balls of Examples 1 to 3 are all excellent in flying performance and excellent in feeling, cracking durability and scratch resistance. On the other hand, in Comparative Example 1, since the total thickness of the intermediate layer gauge and the cover gauge is too thick, the rebound of the ball is slightly lowered and the spin amount at the time of hitting W # 1 is increased, so that the flight distance is inferior. .
As for Comparative Example 2, (the deflection hardness of the sphere in which the core is coated with the intermediate layer) / (the core deflection hardness) is less than 0.87, and the intermediate layer is too hard than the cover, so that the putter feeling feels hard. In addition, it is inferior in cracking durability when repeatedly hit.
For Comparative Example 3, (the deflection hardness of the sphere in which the core is coated with the intermediate layer) / (the deflection hardness of the core) exceeds 0.97, so the spin amount at the time of hitting W # 1 is large and the flight distance is inferior. It is inferior in cracking durability when repeatedly hit.
In Comparative Example 4, since the value of (core surface shore D hardness−core center shore D hardness) is less than 15, the low spin effect is insufficient and the flight distance does not appear.
For Comparative Example 5, the cover is soft, the resilience is low, and the flight distance does not come out.

Claims (7)

In a golf ball comprising a core formed of a base rubber as a main material, an intermediate layer covering the core, and a cover covering the intermediate layer and having a large number of dimples formed on the outer surface, (1) to (4), (11) and (12),
(1): (Shore D hardness of cover) − (Shore D hardness of intermediate layer)> 5,
(2 ′): (initial velocity of the core (m / s)) − (initial velocity of the ball (m / s)) ≧ 0.2 (Here, the initial velocity is a USGA drum rotation-type initial velocity meter. Means the initial speed measured using the same initial speed measuring instrument)
(3): 0.87 ≦ [(the deflection hardness of the sphere with the intermediate layer coated on the core) / (the deflection hardness of the core)] ≦ 0.93 (where the deflection hardness is the initial load on the spherical object) The amount of deformation (mm) from when 98 N (10 kgf) is loaded to when the final load of 1275 N (130 kgf) is loaded)
(4): The total thickness of the intermediate layer thickness (mm) and the cover thickness (mm) is 3.0 mm or less,
(11): (deflection hardness of golf ball / deflection hardness of sphere in which core is covered with intermediate layer) ≦ 0.98
(12): (Shore D hardness of core surface) − (Shore D hardness of core center) ≧ 15
The core diameter is 36.8 mm or more and 38.8 mm or less, the core specific gravity is 1.15 g / cm ³ or more and 1.35 g / cm ³ or less, and the intermediate layer is softer than the core surface. And the intermediate layer is
(A-1) Metal ion neutralized product of olefin-unsaturated carboxylic acid binary random copolymer and / or olefin-unsaturated carboxylic acid binary random copolymer and (a-2) olefin-unsaturated carboxylic acid -(A-1) / (a-) an unsaturated carboxylic acid ester ternary random copolymer and / or a metal ion neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer. 2) (A) an ionomer resin included at a ratio of 100/0 to 0/100 (mass ratio);
(B) an olefinic thermoplastic elastomer;
(A) / (B) = 85/15 to 60/40 (mass ratio)
(C) 5 to 80 parts by mass of an organic fatty acid having a molecular weight of 280 to 1500 and / or a derivative thereof;
(D) 0.1 to 10 parts by mass of a basic inorganic metal compound capable of neutralizing an unneutralized acid group in the resin component and the component (C);
A multi-piece solid golf ball, wherein the intermediate layer has a Shore D hardness of 40 or more and 60 or less, and the cover is formed of an ionomer resin as a main material .   About 0.05 to 0.5 parts by mass of sulfur and 0.05 to 5 parts by mass of an organic sulfur compound with respect to 100 parts by mass of the base rubber of the core, and about 5% by mass of sulfur and the organic sulfur compound The multi-piece solid golf ball according to claim 1, wherein ≦ (the amount of organic sulfur compound / the amount of sulfur) ≦ 20.   The number of dimples formed on the ball surface is 280 to 360, the lift coefficient CL of the ball when the ball is hit at a Reynolds number of 70,000 and a spin rate of 2000 rpm is 0.165 or more, and the Reynolds number is 180,000. The multi-piece solid golf ball according to claim 1 or 2, wherein a drag coefficient CD of the ball when the ball is hit at a spin rate of 2520 rpm is 0.230 or less. Further, the following conditions (5), (6), (7) and (9):
(5): The thickness (mm) of the cover is 0.5 mm or more and 2.0 mm or less,
(6): Shore D hardness of the cover is 52 or more and 62 or less,
(7): The thickness (mm) of the intermediate layer is 0.5 mm or more and 1.6 mm or less,
(9): The initial velocity of the golf ball is 76.5 m / s or more,
The multi-piece solid golf ball according to claim 1, wherein: Furthermore, the following condition (10):
(10): The melt flow rate of the cover is 2 g / 10 min or more,
The multi-piece solid golf ball according to claim 1, wherein:   6. The condition according to (11) above, wherein the deflection hardness of the golf ball / the deflection hardness of the sphere in which the core is coated with the intermediate layer is 0.85 or more and 0.95 or less. Peace solid golf ball.   The multi-piece solid golf ball according to any one of claims 1 to 6, wherein a Shore D hardness of the core surface is in a range of 55.1 to 57.5.

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