JP2001145709A - Solid golf ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid golf ball having favorable ball driving feel and controllability while keeping an excellent carry and durability. SOLUTION: In this solid golf ball comprising a core and a cover, a center hardness of the core as measured by a JIS-C hardness meter is within a range of 55-75, a surface hardness of the core is larger than the center hardness by 10 or more, and a hardness of the cover satisfies following inequalities (1), (2). Hardness of the cover - hardness of the core center <=17...(1) Hardness of the cover - hardness of the core surface <=5...(2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid golf ball having a core and a cover, and more particularly to a solid golf ball having a long flight distance, and excellent controllability and shot feeling.

[0002]

2. Description of the Related Art There are roughly two types of golf balls used so far. One is a thread wound golf ball. This thread-wound golf ball has a thread or rubber wound around a liquid or solid center and covered with a cover mainly composed of balata (trans polyisoprene) or an ionomer resin. The other is a solid golf ball such as a two-piece ball or a three-piece ball. This solid golf ball has a core made of a rubber member covered with a thermoplastic resin cover containing an ionomer resin and the like. Excellent flight distance. On the other hand, solid golf balls are generally hard, so there is a problem that the impact at the time of shot is large, spin is difficult to apply, and the controllability at approach shots etc. is insufficient,
He was often shunned by professional golfers and advanced amateur golfers who value the shot feeling and controllability.

[0003] In order to solve the above problems, various efforts have been made to improve the shot feeling and controllability by optimizing the hardness of the cover, the hardness of the core, the hardness distribution, and the like. For example, Japanese Patent Application Laid-Open No. 9-239067 discloses that the core has a surface hardness, a center hardness, and 5 m from the core surface.
There has been proposed a two-piece solid golf ball in which the hardness of each cover is specified within m, and the hardness and thickness of the cover and the number of dimples are specified.

[0004]

However, it has not been possible to sufficiently satisfy a good shot feeling and controllability while maintaining a long flight distance and excellent durability, and further improvement is desired. It is rare.

The present invention has been made in view of the above-mentioned requirements, and has as its object to provide a solid golf ball having a good shot feeling and controllability while maintaining excellent flight distance and durability. .

[0006]

According to the present invention, there is provided a solid golf ball having a core and a cover.
The center hardness of the core measured by a C-type hardness meter is 55 to 75;
Degree, and the surface hardness of the core is 1% less than the center hardness.
A solid golf ball is provided, wherein the solid golf ball is larger than 0 degree and the hardness of the cover satisfies the following inequalities (1) and (2).

(Cover hardness) − (Central hardness of core) ≦ 17 (1) (Cover hardness) − (Surface hardness of core) ≦ 5 (2) The thickness of the cover is desirably in the range of 1.0 to 1.8 mm.

[0008] The base resin of the cover includes the following (A)
(C) three components, (A) a thermoplastic polyamide-based elastomer, (B) an ethylene-unsaturated carboxylic acid binary copolymer ionomer and / or an ethylene-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary The copolymerization ionomer, the epoxidized diene block copolymer (C), and the mixing ratio of the above (A) to (C) are (A) :( B) = 1: 99 to 70:30 by mass ratio. Yes, it is preferable that the component (C) is blended in an amount of 1 to 40 parts by mass based on 100 parts by mass in total of the components (A) and (B).

The JIS-C hardness tester according to the present invention is
A spring-type hardness tester C type defined in JIS K 6301 (Vulcanized rubber physical test method).

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have developed a solid golf ball while maintaining excellent flight performance and durability.
As a result of various investigations as to whether or not a hitting feeling and controllability equivalent to or higher than that of a thread wound golf ball can be imparted, the core hardness of the core is set to a specific range, and the surface hardness of the core is made larger than the central hardness by a specific value or more, and the cover hardness and The present inventors have found that a golf ball having the above performance can be obtained by setting the core hardness and the surface hardness so as to satisfy a certain relationship, and have accomplished the present invention.

First, the first characteristic of the golf ball of the present invention is that the core has a center hardness of 5 as measured by a JIS-C hardness tester.
This is in the range of 5 to 75 degrees. That is, when the amount of deformation at impact is large, such as when shot with a driver, the deformation of the ball extends to the center of the core. For this reason, if the hardness of the central portion of the core is too large, the impact felt by the golfer at the time of shot increases, and the shot feeling decreases. In addition, the resilience of the core central portion affects the flight distance as well as the cover hardness and the core surface hardness. Therefore, when the center hardness is less than 55 degrees, the deformation at the center of the core is large, so that the repulsive force is reduced, and as a result, the flight distance is reduced. In addition, although the impact at the time of the shot is small, the shot feeling is reduced in the sense that the ball feels less rebound when hit and the ball feels difficult to fly. On the other hand, when the center hardness exceeds 75 degrees, the flight distance increases with the improvement in resilience, but the impact at the time of shot increases and the shot feeling decreases. A preferable lower limit of the center hardness is 65 degrees or more, more preferably 68 degrees or more.
The preferred upper limit of the center hardness is 72 degrees or less.

The second feature of the golf ball of the present invention is that
The point is that the surface hardness of the core is set to be at least 10 degrees higher than the center hardness. By increasing the surface hardness of the core by 10 degrees or more than the center hardness of the core, the entire core can be deformed by an optimum amount at the time of hitting the ball, and the flight angle can be maintained in a favorable range and the flight distance can be increased. Also, a good shot feeling is obtained. If the surface hardness of the core is not greater than the center hardness by 10 degrees or more, in other words, if the hardness distribution in the core is flat, only the core surface is greatly deformed at the time of hitting, the launch angle is reduced, and the flight distance is reduced. And the impact is increased to reduce the shot feeling. It is more preferable that the core surface hardness is at least 11 degrees greater than the center hardness.
A preferable upper limit of the difference between the surface hardness and the center hardness of the core is 30 degrees. A more preferred upper limit is 20 degrees, and a still more preferred upper limit is 15 degrees. If the difference between the surface hardness and the center hardness of the core is larger than 30 degrees, the deformation at the time of shot can be easily transmitted to the center of the core from the difference in hardness,
It feels like hitting a golf ball without a core and the shot feeling is not good. If the hardness difference between the surface and the center of the core is too large, the core is likely to be deformed, so that the energy received at the time of the shot cannot be stored, so that the energy loss eventually increases and the repulsive force decreases. The core surface hardness can take various hardnesses that satisfy the above requirements with respect to the hardness at the center of the core.
It is preferably at least 75 degrees, more preferably at least 80 degrees, most preferably at least 83 degrees. The upper limit of the surface hardness of the core is preferably 90 degrees or less, more preferably 87 degrees or less.
Degrees or less. If the surface hardness of the core is less than 75 degrees, the resilience is sharply reduced, and the flight distance is reduced. If the surface hardness is more than 90 degrees, the resilience is good, but the impact at the time of shot is large and the shot feeling is not good. It is.

The core of the golf ball of the present invention has a center hardness of the core that satisfies the above two characteristics, and can have various surface hardnesses having a hardness difference that satisfies the above requirements with respect to the core center hardness. Preferred combination of center hardness,
That is, a preferred embodiment of the core has a center hardness of 65 to 75.
A core having a surface hardness of 80 to 90 degrees, most preferably a core having a central hardness of 68 to 72 degrees and a surface hardness of 83 to 87 degrees.

The above-mentioned core is formed from a core composition containing a base rubber, a co-crosslinking agent, and a crosslinking initiator.
A core having a center hardness and a surface hardness in the above ranges can be obtained by appropriately selecting the type and amount of the co-crosslinking agent and the crosslinking initiator and vulcanization conditions such as the vulcanization temperature and time.

[0015] As the base rubber that can be used for the core, conventionally used natural rubber and synthetic rubber can be used. Among them, cis-1,4-polybutadiene rubber can be preferably used.
More than 80% is desirable. Polyisoprene rubber, styrene-butadiene rubber, EPDM, and the like may be appropriately added as long as the effects of the present invention are not impaired.

The co-crosslinking agent is not particularly limited, and examples thereof include a metal salt of an unsaturated carboxylic acid. Among these, monovalent or divalent metal salts having 3 to 8 carbon atoms, such as zinc acrylate and zinc methacrylate, are desirable. Of these, zinc acrylate is preferably used because of its excellent resilience. The compounding amount of the co-crosslinking agent is in the range of 20 to 35 parts by mass, preferably 25 to 32 parts by mass based on 100 parts by mass of the base rubber. If the compounding amount is less than 20 parts by mass, the hardness is insufficient due to insufficient crosslinking, the resilience upon shot is insufficient, causing a reduction in shot feeling, and the durability may be deteriorated. On the other hand, if the blending amount is more than 35 parts by mass, the crosslinking becomes excessive and the hardness is liable to be increased, and the impact at the time of shot is increased, and the shot feeling is reduced.

Examples of the crosslinking initiator include dicumyl peroxide and di-t-butyl peroxide. Among them, dicumyl peroxide can be preferably used. The amount of the crosslinking agent is not particularly limited, but is preferably 0.5 to 5 parts by mass, more preferably 1 to 3 parts by mass, per 100 parts by mass of the base rubber. If the amount is less than 0.5 part by mass, the crosslinking is insufficient, the hardness is insufficient, and the shot feeling is lowered, and the durability may be deteriorated. On the other hand, if the compounding amount is more than 5 parts by mass, the crosslinking becomes excessive and the hardness tends to increase, and the impact at the time of shot increases, resulting in a reduced shot feeling.

The rubber composition for the core may contain a filler such as zinc oxide, barium sulfate, silica, calcium carbonate, zinc carbonate, etc., in addition to the base rubber, the crosslinking initiator and the co-crosslinking agent. One or more of these fillers may be contained, and the total amount of the filler is 3 parts per 100 parts by mass of the base rubber.
The range is preferably from 40 to 40 parts by mass, more preferably from 5 to 30 parts by mass. If necessary, a thiol-based or sulfide-based sulfur additive, an antioxidant such as phenol, and a high specific gravity metal powder such as tungsten or molybdenum may be appropriately blended.

The rubber composition for the core is kneaded using a Banbury mixer or a roll kneader, and vulcanized in a mold to form a core. Vulcanization conditions may be appropriately determined from the type of the core composition and the desired hardness distribution, for example, as a vulcanization temperature in the range of 140 to 180 ° C,
The vulcanization time is preferably in the range of 10 to 60 minutes.

In the golf ball of the present invention, the hardness of the cover further satisfies the following formulas (1) and (2).

(Cover hardness) − (Central hardness of core) ≦ 17 (1) (Cover hardness) − (Surface hardness of core) ≦ 5 (2) ( Equation (1) indicates that the hardness of the cover is (the center hardness of the core + 17).
Degree) below. If the cover hardness exceeds 17 degrees higher than the core center hardness, the cover becomes too hard, so that the shot feeling is reduced or the spin is reduced, resulting in reduced controllability. That is, if the cover hardness is too high compared to the core center hardness until the difference between them exceeds 17 degrees, good shot feeling and resilience are maintained for various golf clubs (from wood type golf clubs to iron clubs). become unable. For example, if a good hitting feeling can be obtained with a wood type golf club, a heavy hitting feeling without a resilience can be obtained with an iron club, or the resilience decreases. On the other hand, if the difference between the core center hardness and the core hardness is not more than 17 degrees without increasing the cover hardness too much, the first characteristic described above for the core (the core center hardness is in the range of 55 to 75 degrees). Is difficult to satisfy, resulting in a decrease in resilience.

For the reasons described above, the difference between the hardness of the cover and the center hardness of the core is 17 degrees or less, preferably 16 degrees.
Degrees or less, more preferably 15 degrees or less. Also,
The lower limit of the difference between the two hardnesses represented by ((hardness of cover)-(center hardness of core)) is preferably 0 degree or more. When the center of the core is harder than the cover, the deformation at the time of hitting is concentrated on the outer portion of the ball, even though the hardness of the core is within the range of the present invention, so that the deformation of the core central portion is small. This gives the ball a hard shot feeling, and may reduce the launch angle, resulting in poor flight performance. In addition, it is preferable that there is a difference in hardness between the cover and the center of the core, because good flight performance and shot feeling can be achieved by deforming the entire golf ball by an optimum amount at the time of hitting. Therefore, the lower limit of the hardness difference is more preferably 10 or more, and further preferably 11 or more.

Equation (2) shows that the cover hardness is not more than [(core surface hardness) +5 degrees]. That is,
If the surface hardness of the core is set within the range of the present invention (10 degrees or more larger than the center hardness of the core) and the cover hardness is set to be larger than [(core surface hardness) +5 degrees], the cover hardness becomes large. It becomes too hard to spin and the controllability decreases. Therefore, the preferable upper limit of the difference between the two hardnesses represented by [(cover hardness)-(core surface hardness)] is 4 degrees or less, more preferably 3 degrees or less.
Degrees or less. On the other hand, the lower limit of the hardness difference between the two is preferably -10 degrees or more, more preferably -5 degrees or more, more preferably -3 degrees or more, and most preferably 0 degree or more. If the surface hardness of the core is excessively higher than the hardness of the cover, the resilience of the cover becomes too low and the resilience is lowered, or the surface hardness of the core becomes too high and the shot feeling is reduced. It's easy to do. If the cover hardness is excessively larger than the surface hardness of the core, the deformation amount of the entire golf ball at the time of hitting the ball cannot be maintained in the optimum range, and satisfactory hitting feeling, controllability and resilience are all satisfied. It becomes difficult.

Therefore, the specific JIS-C hardness of the cover is preferably 75 to 92 degrees. If the angle is less than 75 degrees, the resilience performance is sharply reduced, the flight distance is reduced, and the resilience at the time of a shot is too small, so that the shot feeling is not good. On the other hand, if it exceeds 92 degrees, the resilience performance is good, but it is hard and hard to spin, so that the controllability is reduced and the shot feeling is also hard.

The golf balls of the present invention include golf balls obtained by various combinations of hardness satisfying the requirements for the core and the requirements for the cover of the present invention. The golf ball of the present invention that satisfies the above-mentioned requirements is capable of deforming the ball at the time of driver shot by reducing the hardness so that the cover does not become too hard and having a certain difference from the cover to the center of the core. The amount is moderate to reduce energy loss. As a result, the resilience can be increased to increase the flight distance, and the shot impact can be reduced to improve the shot feeling. In addition, spin during an iron shot can be easily applied, and controllability can be secured.

Among the golf balls of the present invention satisfying the above requirements, a particularly preferred embodiment is that the core has a core hardness of 65 to 65.
75 degrees, surface hardness of 80-90 degrees, cover hardness of 8
0 to 90 degrees. In a most preferred embodiment, the core has a center hardness of 68 to 72 degrees, a surface hardness of 83 to 87 degrees, and a cover hardness of 83 to 88 degrees.

The cover is made of a resin composition containing a thermoplastic resin as a main component, and optionally adding pigments, dispersants, antioxidants, ultraviolet absorbers, light stabilizers, and the like as needed.

Examples of the thermoplastic resin used in the cover resin composition include an ionomer resin; a thermoplastic elastomer such as polyurethane, polyamide, or polyester; an epoxidized diene block copolymer; and a thermoplastic resin having a hydroxyl group at a terminal. Elastomers and the like can be mentioned, and these can be used alone or in combination of two or more. Preferably, a thermoplastic polyamide-based elastomer (hereinafter sometimes referred to as component (A)), an ethylene-unsaturated carboxylic acid binary copolymer ionomer and / or an ethylene-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary Copolymer ionomer (hereinafter, referred to as
Component (B), epoxidized diene-based block copolymer (hereinafter sometimes referred to as component (C))
Is a resin composition containing the following mass ratio.

Component (A): Component (B) = 1: 99-70: 30 A total of 100 parts by weight of the components (A) and (B) is mixed with 1 to 40 parts by weight of the component (C). I have.

The thermoplastic polyamide-based elastomer, which is the component (A), is a thermoplastic elastomer having a portion called a hard segment and a portion called a soft segment in a molecule and having polyamide as a hard segment. This thermoplastic polyamide-based elastomer has a relatively low hardness and a high flexural modulus. Therefore, by blending the thermoplastic polyamide-based elastomer with the cover material, the cover can be softened without lowering the rebound resilience of the cover. That is, a soft cover can be produced by using only the ionomer by increasing the blending ratio of the ethylene-unsaturated carboxylic acid-unsaturated carboxylic acid ester terpolymer ionomer, and the like. The decline is significant. On the other hand, by blending a polyamide-based thermoplastic elastomer that has a high flexural modulus even with low hardness, the flexural modulus is kept higher than that of an ionomer cover that has been softened to the same extent (lower hardness). Can be. Therefore, by using a cover that satisfies low hardness and retention of rebound resilience, it is possible to maintain control of the flight distance, which is a characteristic of a solid golf ball, and to easily control the spin when shot with an iron, thereby ensuring control. A golf ball that can be provided can be provided.

Specific examples of the thermoplastic polyamide elastomer (A) include those commercially available from Toray Industries, Inc. under the trade name "Pebax". The thermoplastic polyamide-based elastomer has a Shore D hardness in the range of 20 to 50 degrees, preferably 25 to 45 degrees.
Degree is desirable, and the flexural modulus is 10 to 10.
Those having a range of 150 MPa, preferably 20 to 130 MPa are preferably used. When the Shore D hardness of the thermoplastic polyamide-based elastomer is lower than 20 degrees, the cover to be produced becomes too soft, and the above-mentioned preferable cover hardness cannot be achieved. If the Shore D hardness is higher than 50 degrees, the produced cover is too hard, and the above-mentioned preferable cover hardness cannot be achieved. If the flexural modulus of the thermoplastic polyamide-based elastomer is lower than 10 MPa, the effect of containing the component (A) cannot be expected to prevent the decrease in flexural modulus, and the rebound resilience decreases. In the case of the component (A) having a flexural modulus higher than 150 MPa, the effect of softening the cover (the effect of reducing the cover hardness) is not so large, and ultimately, the shot feeling may not be improved.

The ethylene-unsaturated carboxylic acid binary copolymer ionomer, which is a copolymer-based ionomer as the component (B), has at least a carboxyl group in the ethylene-unsaturated carboxylic acid binary copolymer copolymer. An ionomer obtained by partially neutralizing with a metal ion, an ethylene-unsaturated carboxylic acid-unsaturated carboxylic acid ester terpolymer copolymer ionomer is an ethylene-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary copolymer. An ionomer obtained by neutralizing at least a part of the carboxyl groups in the polymer with a metal ion. Since these copolymer ionomers have a high flexural modulus, they have the effect of contributing to the improvement of the rebound resilience of the cover. In order to sufficiently obtain such an effect, it is preferable to use one having a flexural modulus of 200 MPa or more.

Examples of the α, β-unsaturated carboxylic acid of the copolymer type ionomer include acrylic acid, methacrylic acid, fumaric acid, maleic acid and crotonic acid, and acrylic acid and methacrylic acid are particularly preferred. Examples of the α, β-unsaturated carboxylic acid ester include, for example, methyl, ethyl, propyl, n-butyl, isobutyl esters such as acrylic acid, methacrylic acid, fumaric acid, and maleic acid, and in particular, acrylic acid esters And methacrylic acid esters are preferred. At least one of the carboxyl groups in the above-mentioned copolymer of ethylene and α, β-unsaturated carboxylic acid or terpolymer of ethylene, α, β-unsaturated carboxylic acid and α, β-unsaturated carboxylic acid ester Examples of metal ions that partially neutralize include sodium ions, lithium ions, zinc ions, magnesium ions, and potassium ions.

Specific examples of the binary copolymer ionomer of the above component (B) include Himilan 155 as an ionomer commercially available from Mitsui Dubon Polychemicals.
5 (Na), Himilan 1557 (Zn), Himilan 1601 (Na), Himilan 1605 (Na), Himilan 1706 (Zn), Himilan 1707 (N
a), Himilan AM7315 (Zn), Himilan A
M7317 (Zn), Himilan AM7311 (M
g), Himilan AK7320 (K) and the like,
Examples of ionomers commercially available from Dubon Corporation of the United States include Surlyn AD8511 (Zn) and Surlyn 8945.
(Na), Surlyn 8920 (Na), Surlyn 894
0 (Na), Surlyn 9910 (Zn), Surlyn AD
7930 (Li), Surlyn AD7940 (Li), Surlyn 9945 (Zn) and the like.

Specific examples of the terpolymer ionomer of the component (B) include Himilan 1856 as an ionomer commercially available from Mitsui Dubon Polychemicals Co., Ltd.
(Na), Himilan 1855 (Zn), Himilan A
M7316 (Zn) and the like.
8265 (Na), Surlyn AD8269 (Na), Surlyn AD8542 (Mg) and the like. In addition,
N described in the fox after the ionomer product name
a, Zn, K, Li, Mg, etc. indicate the metal species of the neutralizing metal ion.

The epoxidized diene-based block copolymer as the component (C) is obtained by epoxidizing a double bond derived from a conjugated diene compound of a block copolymer or a partially hydrogenated block copolymer. The block copolymer serving as the substrate is a block copolymer composed of a polymer block mainly composed of at least one vinyl aromatic compound and a polymer block mainly composed of at least one conjugated diene compound. . In addition, the partially hydrogenated block copolymer is obtained by hydrogenating the above block copolymer.

Examples of the vinyl aromatic compound constituting the block copolymer include styrene, α-methylstyrene, vinyltoluene, pt-butylstyrene,
One or two of 1,1-diphenylethylene and the like
More than one species can be used, but styrene is preferably used. As the conjugated diene compound, for example, one or more of butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene and the like can be used. And combinations thereof.

A preferred component (C) is a block copolymer in which the vinyl aromatic compound is styrene and the conjugated diene compound is butadiene. Particularly, a polystyrene block (S) having an epoxy group and a polybutadiene block (B) are preferred. However, in the block copolymer which couple | bonded by SBS type | mold is preferable. As a specific example of such a block copolymer, “Epo Friend” from Daicel Chemical Industries, Ltd.
And those marketed under the trade name.

The mixing ratio of the above three components in the cover composition is preferably (A) :( B) = 1: 99-70: 30, more preferably (A) :( B) = 5: 95-3.
5:65. Component (C) is added in an amount of 1 to 40 based on 100 parts by mass of the total of components (A) and (B).
Parts by mass, preferably 1 to 20 parts by mass.
When the mixing ratio of the component (A) is less than the above range, the softening effect is not sufficient. When the blending ratio of the component (B) is less than the above range, the flexural modulus becomes too low and the rebound resilience decreases. When the blending ratio is more than the above range, it becomes too hard and lacks flexibility. When the compounding ratio of the component (C) is less than the above range, the compatibility between the component (A) and the component (B) is deteriorated, so that the moldability of the cover is reduced and the appearance is likely to be poor. If it is too large, it will be too soft, and sufficient rebound resilience will not be obtained.

As the base resin contained in the resin composition for the cover, a resin other than the above-mentioned components (A), (B) and (C) may be contained. It is preferable that the content be 10% by weight or less based on the whole resin component.
Further, it is preferable to select a compounding composition so that the flexural modulus of the cover material is in the following range. That is, the lower limit of the flexural modulus is preferably 70 MPa or more, more preferably 100 MPa or more, and the upper limit is preferably 220 MPa or less, more preferably 210 MPa or less. If the flexural modulus of the cover is less than 70 MPa, the ball may lack rebound resilience even if the requirements of the present invention relating to hardness are satisfied. This is because the feeling is reduced.

The resin composition for the cover is prepared by mixing a base resin and, if necessary, additives such as a pigment, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer and the like, using a twin-screw kneading extruder or a bumper. It is prepared by heating and mixing at 150 to 250 ° C. for 0.5 to 15 minutes using an internal mixer such as a remixer or a kneader.

The golf ball of the present invention is preferably a two-piece golf ball in which the core is directly covered with the cover, but an intermediate layer may be interposed between the cover and the core. The method for covering the core with the cover is not particularly limited, and may be a conventionally known method. For example, a method in which the cover composition is preliminarily formed into a hemispherical shell-like half-shell shape, and the two are formed into a set and the core is wrapped therein to form a sphere, which is then heat-formed at 130 to 170 ° C. for 1 to 15 minutes, Alternatively, a method of forming a cover on the core by injection molding the cover composition on the core, or the like is employed.

The thickness of the cover is 1.0 to 1.8 mm
Is preferable, and the range of 1.3 to 1.6 mm is more preferable. When the thickness of the cover is less than 1.0 mm, the deformation of the cover at the time of hitting the ball becomes small, and the contact area with the club becomes too small. This reduces the spin rate when hit with a short iron, leading to a decrease in controllability. In addition, a cover that is too thin is difficult to mold and causes not only a decrease in productivity, but also a decrease in strength of the cover. On the other hand, when the thickness of the cover is more than 1.8 mm, particularly when the cover hardness is small, the resilience is reduced and the flight distance is reduced.

In forming the cover, dimples are formed on the ball surface as necessary. The number of dimples is 360-
A range of 450, preferably a range of 370 to 420 is desirable. In addition, paint finishing, stamping, etc. are performed as necessary.

[0045]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited thereto. Unless otherwise specified, "parts" described in Examples and Comparative Examples indicate parts by mass. [Measurement Evaluation Method] Hardness The JIS-C hardness referred to in the present invention is JIS K6.
301 (measured by a physical test method for vulcanized rubber) means a hardness measured by a spring type hardness tester C type.

The surface hardness of the core was measured by applying a pressing needle of a hardness meter to the surface of the manufactured core.

The core hardness of the core was measured by cutting the prepared core along the center line and applying a pressing needle of a hardness meter to the center of the cut surface.

The hardness of the cover was measured with the core covered with the cover and a pressing needle of a hardness meter applied to the surface of the cover. Flying performance A driver was attached to a swing robot manufactured by True Temper, and the golf ball was hit at a head speed of 49 m / sec. The launch angle (ballistic height) was measured by a sensor installed in a predetermined position in advance, and was continuously measured. The amount of spin of the ball was measured by photographing. In addition, the flight distance to the ball drop point (carry) was measured.

Next, the club was replaced with a sand wedge, hit at a head speed of 20 m / sec, and the spin rate was measured in the same manner as described above. Hitting feeling A driver's actual hitting test was performed by 10 professional golfers, and the following evaluation was made based on the number of persons who answered that the shot feeling was good. Here, the shot feeling is a feeling obtained by integrating the magnitude of impact received at the time of a shot and the resilience.

○: 8 to 10 Δ: 4 to 7 ×: 0 to 3 [Preparation of core] cis-1,4-polybutadiene (“BR
-18 "(manufactured by Nippon Synthetic Rubber Co.) 100 parts, 34 parts of zinc acrylate, 5.8 parts of zinc oxide, 0.5 parts of antioxidant (" Yoshinox 425 "manufactured by Yoshitomi Pharmaceutical Co., Ltd.), dicumyl A core composition containing 1.5 parts of peroxide, 0.3 parts of diphenyl disulfide, and 9.3 parts of tungsten was added at 155 ° C. for 15 minutes, and then 165 parts.
The core was vulcanized under pressure at 8 ° C. for 8 minutes to obtain a core having an average particle size of 39.6 mm. The core hardness of the obtained core was 72 and the surface hardness was 87. This core was designated as core A.

The core composition shown in Table 1 and the core A under the vulcanization conditions were used.
The cores B to E were produced in the same manner as described above.

[0052]

[Table 1]

[Production of Golf Balls] Cover compositions a, b, c, and d were produced with the compositions and amounts shown in Table 2, respectively.

Each of the prepared cover compositions was directly injection molded around the core A to prepare a golf ball, and the surface hardness was measured by a JIS-C hardness tester.

[0055]

[Table 2]

Ionomer 1: "Surlyn 9945", a zinc ion neutralized ethylene / methacrylic acid copolymer ionomer resin manufactured by Dupont. Ionomer 2: "Surlyn 8945," a sodium ion neutralized ethylene / methacrylic acid copolymer manufactured by Dupont. System ionomer resin Ionomer 3: "Surlyn AD8542" Magnesium ion-neutralized ethylene / methacrylic acid / isobutyl acrylate terpolymer copolymer manufactured by DuPont Ionomer 4: "Himilan 1555" in sodium ion manufactured by Mitsui Dupont Polychemicals Japanese ethylene /
Methacrylic acid copolymer ionomer resin Ionomer 5: "Himilan 1557" zinc ion neutralized ethylene / methacrylic acid copolymer ionomer resin from DuPont Mitsui Polychemicals Ionomer 6: "Himilan 1706" zinc from DuPont Mitsui Polychemicals Ion-neutralized ethylene / methacrylic acid copolymer ionomer resin Ionomer 7: "Himilan 1707" sodium ion-neutralized ethylene manufactured by DuPont Mitsui Polychemicals /
Methacrylic acid copolymer ionomer resin Ionomer 8: "Himilan 1855" Mitsui DuPont Polychemical Co., Ltd. zinc ion neutralized ethylene / methacrylic acid / isobutyl acrylate terpolymer copolymer ionomer resin Ionomer 9: "Himilan 1605" Mitsui Dupont Sodium ion neutralized ethylene made by Polychemicals /
Methacrylic acid copolymer-based ionomer resin Elastomer resin: Pebax 2533, a thermoplastic polyamide-based elastomer resin manufactured by Toray Epoxidized diene block copolymer: Epofriend A
1010 "Block copolymer having an SBS structure containing an epoxidized polybutadiene block manufactured by Daicel Chemical Industries, Ltd.Example 1 Cover composition b was directly injection-molded on the prepared core A to cover core A, A paint is applied to the obtained golf ball, the outer diameter is 42.7 mm, and the weight is 45.4 g.
Was manufactured. The following evaluation was performed about the obtained solid golf ball. Table 3 summarizes the results. Examples 2 to 5, Comparative Examples 1 to 3 Solid golf balls were prepared and evaluated in the same manner as in Example 1 using the core and cover compositions shown in Table 3.
Table 3 summarizes the results.

[0057]

[Table 3]

In the golf ball of Comparative Example 1 in which the difference between the center hardness and the surface hardness of the core is zero, the spin amount when hit with a driver is larger than that of the example, and the flight distance is 224.8 m. It was shorter than the example. Also,
The surface hardness of the core was determined by the cores A, B, and C used in Examples 1 to 5.
Despite being lower, the shot feeling was poor. The golf ball of Comparative Example 2 in which the difference between the center hardness and the surface hardness of the core is 5 degrees is not as large as Comparative Example 1, but has a larger spin rate when hit with a driver than the example, and The distance was short and the shot feeling was bad.

The golf ball of Comparative Example 3, which used the same core as in the example but did not satisfy the requirements of the present invention in terms of hardness with the cover, had too high a cover hardness and had a spin amount when hit with a sand wedge. The ball was small and the shot feeling when hit with a driver was poor.

On the other hand, the golf balls of Examples 1 to 5 satisfying the requirements of the present invention with respect to the center hardness and the surface hardness of the core, and the relationship between these hardnesses and the cover hardness, have a flight distance with a driver and a sand wedge. Excellent results were obtained with respect to both the spin rate and shot feeling. However, in Example 5 using the cover d made only of the blend of the ionomer resin, the flight distance was inferior to that of the other examples, and the spin amount when hit with a sand wedge was inferior (decrease in controllability), The shot feeling was also inferior to the other examples.

[0061]

According to the present invention, the distance and durability inherent to a solid golf ball can be improved by setting the center hardness of the core to a specific range and optimizing the hardness distribution from the cover surface to the center of the core. It is possible to improve the shot feeling and controllability while maintaining.

Claims (3)

[Claims] In a solid golf ball having a core and a cover, the center hardness of the core measured by a JIS-C hardness meter is in the range of 55 to 75 degrees, and the surface hardness of the core is 10% less than the center hardness. A solid golf ball characterized in that the cover has a hardness not less than a degree and the cover satisfies the following formulas (1) and (2). (Cover hardness) − (Central hardness of core) ≦ 17 (1) (Cover hardness) − (Core surface hardness) ≦ 5 (2) 2. The solid golf ball according to claim 1, wherein said cover has a thickness in a range of 1.0 to 1.8 mm. 3. The cover according to claim 1, wherein the base resin comprises:
(A) a thermoplastic polyamide-based elastomer, (B) an ethylene-unsaturated carboxylic acid binary copolymer ionomer and / or an ethylene-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary copolymer. Polymeric ionomer (C) Epoxidized diene-based block copolymer The compounding ratio of the above (A) to (C) is (A) by mass ratio:
(B) = 1: 99 to 70:30, and the component (C) is 1 to 4 based on 100 parts by mass in total of the above (A) and (B).
3. The solid golf ball according to claim 1, wherein 0 part by mass is blended.