JP5057048B2 - Golf ball - Google Patents

Description

  The present invention relates to a golf ball having excellent resilience.

  Conventionally, in order to impart excellent resilience to golf balls, the focus has been on one or more of the Mooney value, polymerization catalyst, solution viscosity, molecular weight distribution, and other indicators of polybutadiene used as a base rubber. (For example, Patent Document 1: Japanese Patent Laid-Open No. 2004-292667, Patent Document 2: US Pat. No. 6,818,705, Patent Document 3: Japanese Patent Laid-Open No. 2002-355336, Patent Document 4: JP 2002-355337 A, Patent Document 5: JP 2002-355338 A, Patent Document 6: JP 2002-355339 A, Patent Document 7: JP 2002-355340 A, Patent Document 8 : JP 2002-356581 A).

  For example, in Patent Document 1: Japanese Patent Application Laid-Open No. 2004-292667, polybutadiene having a Mooney viscosity of 30 to 42 and a molecular weight distribution (Mw / Mn) of 2.5 to 3.8 is disclosed. No. 6,818,705 describes polybutadiene having a molecular weight of 200,000 or more and a resilience index of 40 or more as a base rubber for golf balls.

  However, there are many users who demand a golf ball with a longer flight distance, and there has been a demand for the development of a golf ball with excellent resilience.

JP 2004-292667 A US Pat. No. 6,818,705 JP 2002-355336 A JP 2002-355337 A JP 2002-355338 A JP 2002-355339 A JP 2002-355340 A Japanese Patent Laid-Open No. 2002-356581

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a golf ball having excellent resilience.

As a result of intensive studies to achieve the above object, the present inventor has determined that the core has a specific T ₈₀ value in a multi-piece solid golf ball comprising a core, an inner layer cover, and an outer layer cover. The inner layer cover has a Shore D hardness of 10 to 10 and is formed from a heat-molded rubber composition containing a base rubber compounded with polybutadiene, an unsaturated carboxylic acid and / or a metal salt thereof, and an organic peroxide. 60, It was found that the shore D hardness of the outer layer cover is in the range of 50 to 80, and the outer layer cover is formed to be harder than the inner layer cover, so that the ball resilience is maintained well. Furthermore, the golf ball of the present invention has a multi-function that can achieve a soft and good hitting feeling and an increased flight distance by optimizing the material of the core and optimizing the hardness between the inner layer cover and the outer layer cover. The present inventors have found that it is a piece solid golf ball and have come to make the present invention.

That is, the present invention provides the following golf balls.
[1] In a multi-piece solid golf ball comprising a core, an inner layer cover, and an outer layer cover, the core has (a) a stress relaxation time (T ₈₀ ) defined as follows: 1.5 Heat molding of a rubber composition containing a base rubber containing solid polybutadiene of 2.5 or less , (b) an unsaturated carboxylic acid and / or metal salt thereof, and (c) an organic peroxide. A golf club characterized in that the inner layer cover has a Shore D hardness of 10 to 60, the outer layer cover has a Shore D hardness of 50 to 80, and has a Shore D hardness higher than that of the inner layer cover. ball.
[Stress relaxation time ( _T80 )]
ML _{1 + 4} (100 ° C.) value (measured according to ASTM D-1646-96, Mooney viscosity measured at 100 ° C.) Immediately after the rotor rotation was stopped, the ML _{1 + 4} value was 80%. This is the time (seconds) required to decrease.
[2] The golf ball of [1], wherein the rubber composition contains (d) an organic sulfur compound.
[3] The golf ball of [1] or [2], wherein the proportion of the polybutadiene having a stress relaxation time (T ₈₀ ) of 1.5 or more and 2.5 or less in the base rubber is 40% by mass or more.
[4] The polybutadiene having a stress relaxation time (T ₈₀ ) of 1.5 or more and 2.5 or less is a polybutadiene formed using a rare earth element catalyst, [1] to [3] Golf ball.
[5] The polybutadiene having a stress relaxation time (T ₈₀ ) of 1.5 or more and 2.5 or less is a polybutadiene formed by terminal modification after polymerization using a rare earth element-based catalyst [1] to [4] The golf ball according to any one of the above.

According to the golf ball of the present invention, a heat-molded product of a rubber composition having very excellent resilience is used for the core, and therefore, the resilience of the entire ball is very excellent.
In addition, the golf ball of the present invention is soft and has a good hit feeling and can increase the flight distance.

Hereinafter, the present invention will be described in more detail.
The golf ball of the present invention is formed by a core of a rubber composition using polybutadiene as a base rubber. Specifically, the core comprises the following components (a) to (c):
(A) a base rubber containing polybutadiene (hereinafter sometimes abbreviated as “BR1”) having a stress relaxation time (T ₈₀ ) defined as follows of 1.5 or more and 2.5 or less ;
(B) an unsaturated carboxylic acid and / or a metal salt thereof,
(C) an organic peroxide,
It is formed by a heat-molded product of a rubber composition containing

[Stress relaxation time ( _T80 )]
ML _{1 + 4} (100 ° C.) value (measured according to ASTM D-1646-96, Mooney viscosity measured at 100 ° C.) Immediately after the rotor rotation was stopped, the ML _{1 + 4} value was 80%. The time (seconds) it takes to drop.

The Mooney viscosity referred to in the present invention is an industrial viscosity index measured with a Mooney viscometer which is a kind of rotational plasticity meter, and ML _{1 + 4} (100 ° C.) is used as a unit symbol. M represents Mooney viscosity, L represents a large rotor (L type), 1 + 4 represents a preheating time of 1 minute, and a rotor rotation time of 4 minutes, which means a value measured at 100 ° C.

In the present invention, wherein the polybutadiene contained in the component (a), a stress relaxation time (T ₈₀₎ is Ru contains 1.5 to 2.5 in the polybutadiene (BR1). When the T ₈₀ value exceeds 2.5 , the object of the present invention is not achieved. On the other hand, if the T ₈₀ value is too small, there may be a problem in workability.

The Mooney viscosity (ML _{1 + 4} (100 ° C.)) of BR1 is preferably 20 or more and 80 or less, but is not particularly limited.

  The BR1 has a cis 1,4 bond content of 60% or more, preferably 80% or more, more preferably 90% or more, most preferably 95% or more, and a 1,2 vinyl bond content of 2 % Or less, preferably 1.7% or less, more preferably 1.5% or less, and most preferably 1.3% or less. If the cis 1,4 bond content or the 1,2 vinyl bond content is out of the above range, the resilience may be lowered.

  The BR1 in the present invention is preferably a polybutadiene formed using a rare earth element-based catalyst from the viewpoint of resilience.

  Here, a known catalyst can be used as the rare earth element-based catalyst. For example, a catalyst comprising a combination of a lanthanum series rare earth element compound, an organoaluminum compound, an alumoxane, a halogen-containing compound, and a Lewis base as necessary. Can be used.

  Examples of the lanthanum series rare earth element compounds include metal halides having an atomic number of 57 to 71, carboxylates, alcoholates, thioalcolates, amides, and the like.

Examples of the organoaluminum compound include AlR ¹ R ² R ³ (wherein R ¹ , R ² and R ³ may be the same or different, and each represents hydrogen or a hydrocarbon residue having 1 to 8 carbon atoms. Can be used.

  As said alumoxane, the compound which has a structure shown by following formula (I) or following formula (II) can be mentioned suitably. In this case, Fine Chemicals, 23, (9), 5 (1994), J. Am. Am. Chem. Soc. 115, 4971 (1993); Am. Chem. Soc. 117, 6465 (1995) may be used.

（式中、Ｒ⁴は、炭素数１〜２０の炭素原子を含む炭化水素基、ｎは２以上の整数である。）

(In the formula, R ⁴ is a hydrocarbon group containing a carbon atom having 1 to 20 carbon atoms, and n is an integer of 2 or more.)

Examples of the halogen-containing compound include AlX _n R _3-n (where X represents a halogen, R is a hydrocarbon residue having 1 to 20 carbon atoms, such as an alkyl group, an aryl group, an aralkyl group, N represents 1, 1.5, 2 or 3), strontium halides such as Me ₃ SrCl, Me ₂ SrCl ₂ , MeSrHCl ₂ and MeSrCl ₃ , and others, silicon tetrachloride, four Metal halides such as tin chloride and titanium tetrachloride are used.

  The Lewis base can be used to complex a lanthanum series rare earth element compound, and examples thereof include acetylacetone and ketone alcohol.

  In the present invention, the use of a lanthanum series rare earth element compound, particularly the use of a neodymium catalyst using a neodymium compound, is a polybutadiene rubber having a high content of 1,4-cis bonds and a low content of 1,2-vinyl bonds. Are preferable from the viewpoint of obtaining excellent polymerization activity, and specific examples of these rare earth element-based catalysts include those described in JP-A No. 11-35633.

  Here, when butadiene is polymerized in the presence of a rare earth element-based catalyst, a solvent may be used, or bulk polymerization or gas phase polymerization may be performed without using a solvent. The polymerization temperature is preferably −30 ° C. to 150 ° C., more preferably 10 to 100 ° C.

  In addition, the BR1 in the present invention can be obtained as a terminal-modified polybutadiene by reacting a terminal modifier on the active terminal of the polymer subsequent to the polymerization with the rare earth element-based catalyst. This is preferable from the viewpoint of manufacturing a golf ball.

  As the terminal modifier, known compounds can be used, and for example, compounds described in the following (1) to (6) can be used.

^{_{(1) R 5 n M'X 4}} -n, M'X 4, M'X 3, R 5 n M '(- R 6 -COOR 7) 4-n or _{^{R 5 n M' (- R}} 6 - COR ⁷ ) _4-n (wherein R ⁵ and R ⁶ may be the same or different and each represents a hydrocarbon group containing 1 to 20 carbon atoms, R ⁷ is a carbon atom having 1 to 20 carbon atoms) Which may contain a carbonyl group or an ester group in the side chain, M ′ is a tin atom, silicon atom, germanium atom or phosphorus atom, X is a halogen atom, and n is an integer of 0 to 3 A halogenated organometallic compound, a halogenated metal compound or an organometallic compound)

  (2) heterocumulene containing Y = C = Z bond in the molecule (wherein Y represents a carbon atom, oxygen atom, nitrogen atom or sulfur atom, and Z represents an oxygen atom, nitrogen atom or sulfur atom) Compound

  (3) Hetero 3-membered ring compound containing the following bond in the molecule

（式中、Ｙは、酸素原子、チッ素原子又はイオウ原子を示す）

(In the formula, Y represents an oxygen atom, a nitrogen atom or a sulfur atom)

  (4) Halogenated isocyano compound

^{(5) R 8 - (COOH} ) m, R 9 (COX) m, R 10 - (COO-R 11), R 12 -OCOO-R 13, R 14 - (COOCO-R 15) m, or the following formula Carboxylic acid, acid halide, ester compound, carbonate compound or acid anhydride represented by

（式中、Ｒ⁸〜Ｒ¹⁶は、同一でも異なっていてもよく、炭素数１〜５０の炭素原子を含む炭化水素基、Ｘはハロゲン原子、ｍは１〜５の整数を示す）

(In formula, R < ⁸ > -R < ¹⁶ > may be same or different, The hydrocarbon group containing a C1-C50 carbon atom, X is a halogen atom, m shows the integer of 1-5.)

_{^{(6) R 17 l M "}} (OCOR 18) 4-l, R 19 l M" (OCOR 20 -COOR 21) 4-l, or a metal salt of a carboxylic acid represented by the following formula

（式中、Ｒ¹⁷〜Ｒ²³は、同一でも異なっていてもよく、炭素数１〜２０の炭素原子を含む炭化水素基、Ｍ”はスズ原子、ケイ素原子又はゲルマニウム原子、ｌは０〜３の整数を示す。）

(In formula, R < ¹⁷ > -R < ²³ > may be same or different, A hydrocarbon group containing a C1-C20 carbon atom, M "is a tin atom, a silicon atom, or a germanium atom, l is 0-3. Indicates an integer.)

  Specific examples of the terminal modifiers shown in the above (1) to (6) and the reaction method thereof include those described in, for example, JP-A Nos. 11-35633 and 7-268132, and the like. Can be mentioned.

  In the present invention, the BR1 is contained in the base rubber, and the proportion of the BR1 in the base rubber is preferably 40% by mass or more, more preferably 50% by mass or more, and further Preferably it is 60 mass% or more, and may be 100 mass%. If the ratio is too small, the resilience may decrease.

In addition to the BR1, the rubber compound that may be blended in the base rubber is not particularly limited. For example, a polybutadiene rubber having a stress relaxation time T ₈₀ exceeding 3.5 may be blended. Alternatively, styrene butadiene rubber (SBR), natural rubber, polyisoprene rubber, ethylene propylene diene rubber (EPDM) or the like may be blended. These may be used alone or in combination of two or more.

  Here, the Mooney viscosity of such a compounding rubber is preferably 80 or less and 20 or more, but is not particularly limited.

  As such a compounding rubber, a rubber synthesized with a Group VIII catalyst can be used. Specific examples of the Group VIII catalyst include the following nickel-based catalysts and cobalt-based catalysts.

  That is, as the nickel-based catalyst, for example, a one-component system such as nickel diatomaceous earth, a two-component system such as Raney nickel / titanium tetrachloride, and a three-component system such as nickel compound / organometallic / boron trifluoride etherate. The thing etc. can be mentioned. As the nickel compound, reduced nickel with support, Raney nickel, nickel oxide, nickel carboxylate, organic nickel complex salt, or the like is used. Examples of the organic metal include trialkylaluminum such as triethylaluminum, tri-n-propylaluminum, triisobutylaluminum, and tri-n-hexylaluminum, n-butyllithium, sec-butyllithium, tert-butyllithium, 1, Examples include alkyl lithium such as 4-dilithium butane, and dialkyl zinc such as diethyl zinc and dibutyl zinc.

  In addition, as cobalt-based catalysts, cobalt and its compounds include Raney cobalt, cobalt chloride, cobalt bromide, cobalt iodide, cobalt oxide, cobalt sulfate, cobalt carbonate, cobalt phosphate, cobalt phthalate, cobalt carbonyl, cobalt acetyl. Examples thereof include acetonate, cobalt diethyldithiocarbamate, cobalt anilinium nitrite, cobalt dinitrosilkyl chloride and the like. Particularly, these compounds and dialkylaluminum monochloride such as diethylaluminum monochloride and diisobutylaluminum monochloride, triethylaluminum, -Trialkylaluminum such as n-propylaluminum, triisobutylaluminum, tri-n-hexylaluminum, ethylaluminum sesquik Aluminum alkyl sesquichloride of chloride etc., can be preferably exemplified a combination of aluminum chloride and the like.

  When the polymerization is performed using the Group VIII-based catalyst, particularly a nickel-based catalyst or a cobalt-based catalyst, usually, the reactor is continuously charged together with a solvent and a butadiene monomer, for example, the reaction temperature is 5 to 60 ° C, An example is a method in which the reaction pressure is appropriately selected in the range of atmospheric pressure to 70 several atmospheres, and the operation is performed so as to obtain the Mooney viscosity.

  Examples of the unsaturated carboxylic acid as the component (b) include acrylic acid, methacrylic acid, maleic acid, and fumaric acid. Acrylic acid and methacrylic acid can be particularly preferably used. Moreover, as a metal salt of unsaturated carboxylic acid, zinc salt of unsaturated fatty acids, such as zinc methacrylate and zinc acrylate, a magnesium salt, etc. can be mentioned, Especially zinc acrylate can be used conveniently.

  The amount of the component (b) is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and the upper limit is preferably 60 parts by mass or less, more preferably 100 parts by mass of the base rubber. It is recommended that the amount be 50 parts by mass or less, more preferably 45 parts by mass or less, and most preferably 40 parts by mass or less. When the blending amount of the component (b) is too large, the heat-molded product of the rubber composition may become hard and unbearable feel may occur, and when it is too small, the resilience may decrease.

  As said (c) component, a commercial item can be used, for example, park mill D (made by Nippon Oil & Fats Co., Ltd.), perhexa C (made by Nippon Oils & Fats Co., Ltd.), Luperco 231XL (made by Atochem Co., Ltd.), etc. can be used. If necessary, two or more different organic peroxides may be mixed and used.

  As a compounding quantity of the said (c) component, Preferably it is 0.1 mass part or more with respect to 100 mass parts of said base rubber, More preferably, it is 0.3 mass part or more, Preferably it is 5 mass parts or less as an upper limit. It is recommended that the amount be 4 parts by mass or less, more preferably 3 parts by mass or less, and most preferably 2 parts by mass or less. If the blending amount is too large or too small, a suitable hardness distribution, that is, hit feeling, durability and resilience may be inferior.

From the viewpoint of further improving the resilience, the rubber composition in the present invention includes the following component (d):
(D) It is suitable to mix an organic sulfur compound.

  Examples of such organic sulfur compounds include thiophenols, thionaphthols, halogenated thiophenols, or metal salts thereof, and more specifically, pentachlorothiophenol, pentafluorothio. Examples thereof include zinc salts such as phenol, pentabromothiophenol, and parachlorothiophenol, diphenyl polysulfide having 2 to 4 sulfur atoms, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, and dithiobenzoyl polysulfide. These may be used alone or in combination of two or more. Among these, a zinc salt of pentachlorothiophenol and / or diphenyl disulfide can be preferably used.

  The amount of the component (d) is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, still more preferably 0.5 parts by mass or more with respect to 100 parts by mass of the base rubber. The upper limit is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and still more preferably 3 parts by mass or less. If the amount is too large, the hardness of the heat-molded product of the rubber composition may become too soft. On the other hand, if the amount is too small, improvement in resilience may not be expected.

  The rubber composition in the present invention may further contain additives such as inorganic fillers and anti-aging agents. Examples of the inorganic filler include zinc oxide, barium sulfate, calcium carbonate and the like, and the blending amount thereof is preferably 5 parts by mass or more, more preferably 7 parts by mass with respect to 100 parts by mass of the base rubber. Or more, more preferably 10 parts by mass or more, most preferably 13 parts by mass or more, and the upper limit is preferably 80 parts by mass or less, more preferably 50 parts by mass or less, still more preferably 45 parts by mass or less, and most preferably 40 parts by mass. It is recommended that: If the amount is too large or too small, it may not be possible to obtain an appropriate mass and suitable resilience.

  From the standpoint of increasing the resilience, the inorganic filler preferably contains 50% by mass or more of zinc oxide, more preferably 75% by mass or more, particularly 100% by mass (inorganic filler) And zinc oxide is preferably 100%).

  The average particle diameter of zinc oxide (by the air permeation method) is preferably 0.01 μm or more, more preferably 0.05 μm or more, particularly 0.1 μm or more, and the upper limit is preferably 2 μm or less, more preferably 1 μm or less. It is done.

  Moreover, as an anti-aging agent, 2,2'-methylenebis (4-methyl-6-t-butylphenol) (Noklak NS-6, manufactured by Ouchi Shinsei Chemical Co., Ltd.), 2,2'-methylenebis (4 -Ethyl-6-t-butylphenol) (NOCRAK NS-5, manufactured by Ouchi Shinsei Chemical Co., Ltd.) and the like. The blending amount is preferably 0 parts by mass or more, more preferably 0.05 parts by mass or more, still more preferably 0.1 parts by mass or more, and most preferably 0.2 parts by mass with respect to 100 parts by mass of the base rubber. As described above, the upper limit is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, still more preferably 1 part by mass or less, and most preferably 0.5 parts by mass or less. Recommended from the point of view.

  The core in the present invention can be obtained by vulcanizing and curing the above-described rubber composition in the same manner as a known golf ball rubber composition. Examples of the vulcanization conditions include conditions carried out at a vulcanization temperature of 100 to 200 ° C. and a vulcanization time of 10 to 40 minutes.

  Regarding the core (vulcanized molded product) in the present invention, the hardness difference obtained by subtracting the JIS-C hardness at the center of the thermoformed product from the JIS-C hardness of the surface of the thermoformed product is preferably 15 or more, more preferably 16 More preferably, it is 17 or more, most preferably 18 or more, and the upper limit is preferably 50 or less, more preferably 40 or less. Adjusting the hardness in this way is preferable from the viewpoint of realizing a golf ball having both a soft feel and good resilience and durability.

  Further, the core (heat-molded product) in the present invention preferably has a deflection amount of 2.0 mm or more, more preferably 2 when a final load of 1275 N (130 kgf) is applied from a state in which an initial load of 98 N (10 kgf) is applied. 0.5 mm or more, more preferably 2.8 mm or more, and the upper limit is preferably 6.0 mm or less, more preferably 5.5 mm or less, still more preferably 5.0 mm or less, and most preferably 4.5 mm or less. Recommended. If the amount of deformation is too small, the feeling of hitting will worsen, and in particular, long shots that cause large deformation of the ball, such as a driver, may cause excessive spin and will not fly, while if too soft, the feeling of hitting will be dull and rebounded. May not be sufficient and will not fly, and crack durability due to repeated impacts may deteriorate.

  The core diameter is preferably 30.0 mm or more, more preferably 32.0 mm or more, still more preferably 35.0 mm or more, most preferably 37.0 mm or more, and the upper limit is preferably 41.0 mm or less, more preferably It is recommended that the thickness be 40.5 mm or less, more preferably 40.0 mm or less, and most preferably 39.5 mm or less.

  Further, the diameter of the solid core of the three-piece solid golf ball is preferably 30.0 mm or more, more preferably 32.0 mm or more, still more preferably 34.0 mm or more, most preferably 35.0 mm or more. It is recommended that the thickness be 40.0 mm or less, more preferably 39.5 mm or less, and still more preferably 39.0 mm or less.

  The specific gravity of the core is preferably 0.9 or more, more preferably 1.0 or more, still more preferably 1.1 or more, and the upper limit is preferably 1.4 or less, more preferably 1.3 or less, still more preferably Is recommended to be 1.2 or less.

  The golf ball of the present invention is a multi-piece solid golf ball having a cover of two or more layers comprising an inner layer cover and an outer layer cover, and these covers can be manufactured using a known cover material. In any case, as a main material, specifically, thermoplastic or thermosetting polyurethane elastomer, polyester elastomer, ionomer resin, ionomer resin having a relatively high degree of neutralization, polyolefin An elastomer or a mixture thereof can be exemplified. These can be used alone or in admixture of two or more. Particularly preferred are thermoplastic polyurethane elastomers, ionomer resins, ionomer resins having a relatively high degree of neutralization, and polyester elastomers. be able to.

  Commercially available products can be used as the thermoplastic polyurethane elastomer, for example, diisocyanates such as Pandex T7298, T7295, T7890, TR3080, T8290, T8295, T8295, and T1188 (manufactured by DIC Bayer Polymer). In which is aliphatic or aromatic. Commercially available ionomer resins include Surlyn 6320, 8945, 9945, 8120 (manufactured by DuPont, USA), High Milan 1706, 1605, 1855, 1557, 1601, and AM7316 (Mitsui / Dupont Poly). Chemical) and the like. Moreover, as a commercial item of a polyester-type elastomer, Hytrel 4047, the same 3078 (made by Toray DuPont) etc. are mentioned.

  Furthermore, a polymer such as a thermoplastic elastomer other than the above can be blended as an optional component in the main material of the cover. Specifically, as an optional polymer, a polyamide-based elastomer, a styrene-based block elastomer, a hydrogenated polybutadiene, an ethylene-vinyl acetate (EVA) copolymer, or the like can be blended.

  The golf ball of the present invention can be manufactured by a known method and is not particularly limited. However, the solid core is disposed in a predetermined molding die, and the intermediate layer material and the cover material are provided. A method of injecting according to a predetermined method in this order, or making a pair of half cups with these cover materials, enclosing the solid core, and compressing and compressing, etc. can be suitably employed.

  In the golf ball of the present invention, the hardness of the outer layer cover is required to be higher than the Shore D hardness of the inner layer cover.

  Here, the Shore D hardness of the inner layer cover is 10 or more, preferably 20 or more, more preferably 25 or more, most preferably 30 or more, and the upper limit is 60 or less, preferably 55 or less, more preferably 50 or less, most preferably. It is recommended to be 45 or less.

  Further, the Shore D hardness of the outer layer cover is 50 or more, preferably 53 or more, more preferably 56 or more, most preferably 59 or more, and the upper limit is 80 or less, preferably 75 or less, more preferably 70 or less, most preferably 65. It is recommended that:

  In the present invention, the Shore D hardness of the outer layer cover and the inner layer cover needs to be higher than the Shore D hardness of the inner layer cover, and the Shore D hardness difference between the hardness of the outer layer cover and the inner layer cover is preferably Is preferably 2 or more, more preferably 5 or more, still more preferably 7 or more, particularly preferably 9 or more, and the upper limit is preferably 30 or less, more preferably 25 or less, and even more preferably 20 or less.

  The thicknesses of the inner layer cover and the outer layer cover of the present invention are preferably 0.7 mm or more, more preferably 1.0 mm or more, and the upper limit is preferably 3.0 mm or less, more preferably 2.5 mm or less. It is recommended that it is preferably 2.2 mm or less, and most preferably 2.0 mm or less.

  The golf ball of the present invention can be used in competition and comply with the golf rules, and can be formed with a diameter of 42.67 mm or more and a weight 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 weight is preferably 44.5 g or more, particularly preferably 45.0 g or more, more preferably 45. It is recommended that it be at least 1 g, most preferably at least 45.2 g.

  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 and 2 and Comparative Examples 1 to 4]
Each raw material was kneaded with a kneader in the composition shown in Table 1 below to prepare a rubber composition, and vulcanized at 160 ° C. for 20 minutes in a spherical mold to obtain a diameter of 35.3 mm and a weight of 26. A 9 g core (spherical molded product) was prepared.

The details of the above blending are as follows.
・ Polybutadiene rubber: Trade name “EC140” (manufactured by Firestone Polymer)
Polymerization with Nd-based catalyst / Mooney viscosity “43” / T ₈₀ value: 2.3
・ Polybutadiene rubber: Trade name “BR51” (manufactured by JSR)
Polymerized with Nd-based catalyst / Mooney viscosity “39” / T ₈₀ value: 5.0
・ Polybutadiene rubber: Trade name “BR60” (manufactured by POLIMER Srl)
Polymerized with Nd-based catalyst / Mooney viscosity “57” / T ₈₀ value: 4.6
・ Polybutadiene rubber: Trade name “BR11” (manufactured by JSR)
Polymerized with Ni catalyst / Mooney viscosity “44” / T ₈₀ value: 4.9
・ Organic peroxide: Dicumyl peroxide Trade name “Park Mill D” (manufactured by NOF Corporation)
・ Zinc oxide: manufactured by Sakai Chemical Co., Ltd., trade name "Three kinds of zinc oxide", average particle size 0.6μm
-Anti-aging agent: Trade name "NOCRACK NS-30" (manufactured by Ouchi Shinsei Chemical Co., Ltd.)
・ Zinc acrylate: Trade name “ZN-DA85S” (manufactured by Nippon Shokubai Co., Ltd.)

  The obtained core was examined for deflection when a final load of 1275 N (130 kgf) was applied from a state in which an initial load of 98 N (10 kgf) was applied. The results are shown in Table 3.

  Next, the obtained core was placed in a predetermined mold, the resin shown in Table 2 was injection-molded to produce an inner layer coated core having a diameter of about 38.7 mm, and then transferred to a predetermined mold. A three-piece solid golf ball having a diameter of about 42.7 mm and a weight of about 45.3 g was manufactured. The main product names are as follows.

High Milan: Made by Mitsui DuPont, Ionomer Resin Surlyn: Made by DuPont, Ionomer Resin Hytrel: Made by Toray DuPont, Thermoplastic Polyester Elastomer Pandex: Made by DIC Bayer Polymer, Thermoplastic Polyurethane Elastomer

The performance of the obtained golf ball was examined as follows. The results are shown in Table 3.
The Shore D hardness of the material physical property inner layer and the outer layer cover indicates the material surface hardness measured by the ASTM D2240 test method.
A golf ball physical property hitting machine was used to measure the carry and total when hitting with a driver (W # 1) at a head speed of 40 m / s.
Based on the actual hitting test with the first wood (driver) and putter by 5 feeling golfers and 5 top golfers, each ball is evaluated with the highest rating, “too hard / good / too soft”. It was evaluated.

  As shown in Table 3, it can be seen that the golf balls of Comparative Examples 1 to 4 are significantly inferior in flight distance compared to the Examples, and Comparative Example 1 has a poor feel.

Claims (5)

In a multi-piece solid golf ball comprising a core, an inner layer cover, and an outer layer cover, the core has (a) a stress relaxation time (T ₈₀ ) defined as follows: 1.5 to 2. In a heat-molded product of a rubber composition comprising a base rubber containing 5 or less solid polybutadiene, (b) an unsaturated carboxylic acid and / or metal salt thereof, and (c) an organic peroxide. A golf ball characterized in that the inner layer cover has a Shore D hardness of 10 to 60, the outer layer cover has a Shore D hardness of 50 to 80, and has a higher Shore D hardness than the inner layer cover.
[Stress relaxation time ( _T80 )]
ML _{1 + 4} (100 ° C.) value (measured according to ASTM D-1646-96, Mooney viscosity measured at 100 ° C.) Immediately after the rotor rotation was stopped, the ML _{1 + 4} value was 80%. This is the time (seconds) required to decrease.   The golf ball according to claim 1, wherein the rubber composition contains (d) an organic sulfur compound. 3. The golf ball according to claim 1, wherein a proportion of the polybutadiene having a stress relaxation time (T ₈₀ ) of 1.5 or more and 2.5 or less in the base rubber is 40% by mass or more. The golf ball according to claim 1, wherein the polybutadiene having a stress relaxation time (T ₈₀ ) of 1.5 or more and 2.5 or less is a polybutadiene formed using a rare earth element-based catalyst. 5. The polybutadiene having a stress relaxation time (T ₈₀ ) of 1.5 or more and 2.5 or less is a polybutadiene formed by terminal modification after polymerization using a rare earth element-based catalyst. The golf ball described.