US20080026873A1

US20080026873A1 - Golf ball

Info

Publication number: US20080026873A1
Application number: US11/493,541
Authority: US
Inventors: Toshihiko Manami; Eiji Takehana
Original assignee: Bridgestone Sports Co Ltd
Current assignee: Bridgestone Sports Co Ltd
Priority date: 2006-07-27
Filing date: 2006-07-27
Publication date: 2008-01-31
Also published as: JP2008029843A; JP5170374B2

Abstract

The invention provides a golf ball having a core and a cover of one or more layer, wherein at least one layer of the cover is made of a material obtained by molding a mixture of (a) a metal ion neutralization product of an olefin-unsaturated carboxylic acid random copolymer having a Shore D hardness of at least 60; (b) an unsaturated fatty acid; and (c) a basic inorganic metal compound capable of neutralizing acid groups in components (a) and (b). The golf ball has both a good feel on impact and excellent scuff resistance while retaining a good flight performance.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a golf ball having a core and cover of one or more layer. More specifically, the invention relates to a golf ball having both a good feel on impact and excellent scuff resistance while retaining a good flight performance.
In recent years, ionomer resins have been widely used in golf ball cover materials. Ionomer resins are ionic copolymers of an olefin such as ethylene with an unsaturated carboxylic acid such as acrylic acid, methacrylic acid or maleic acid, in which some of the acidic groups are neutralized with metal ions such as sodium, lithium, zinc or magnesium. In particular, ionomer resins have excellent characteristics such as durability and rebound resilience, and are thus well-suited for use as the base resin in a golf ball cover material.
Ionomer resins account for most of the cover material resin in use today, and enable the production of golf balls endowed with the above properties. Yet, golfers are always on the lookout for golf balls having a high rebound resilience and excellent flight characteristics. Examples of such improvements include the use of terpolymers obtained by copolymerizing a third component such as an alkyl acrylate with ethylene and an unsaturated carboxylic acid, as described in U.S. Pat. No. 6,653,382 and U.S. Pat. No. 6,815,480. However, the admixture of oleic acid with this terpolymer makes the resulting material too soft for use in golf balls, leading to such undesirable effects as a low ball initial velocity and a poor scuff resistance.
U.S. Pat. No. 6,762,246 teaches a material obtained by mixing a low-molecular-weight compound such as a wax with a ternary ionomer, but the overall performance of golf balls thereby obtained tends to decline.
Given the importance placed on the feel of the ball when played, the use of a low-hardness ionomer in the cover material has also been proposed. However, when a low-hardness ionomer is used, the initial velocity of the ball tends to decline and the scuff resistance tends to worsen.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a golf ball which, in addition to exhibiting an excellent flight performance, also has a more than satisfactory feel on impact and scuff resistance.
The inventors have conducted extensive investigations, as a result of which they have discovered that, in a golf ball having a core and a cover of one or more layer, when at least one layer of the cover is made of a material obtained by using (a) a metal ion neutralization product of an olefin-unsaturated carboxylic acid random copolymer having a Shore D hardness of at least 60, (b) an unsaturated fatty acid, and (c) a basic inorganic metal compound capable of neutralizing acid groups in foregoing components (a) and (b), and mixing and molding these components (a) to (c) in specific proportions, the ball can be imparted with both a good feel and an excellent scuff resistance while retaining a good rebound resilience.
Accordingly, the invention provides the following golf balls.

[1] A golf ball comprising a core and a cover of one or more layer, wherein at least one layer of the cover is made of a material obtained by molding a mixture comprising:

(a) 100 parts by weight of a metal ion neutralization product of an olefin-unsaturated carboxylic acid random copolymer having a Shore D hardness of at least 60;
(b) 5 to 60 parts by weight of an unsaturated fatty acid; and
(c) 1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (a) and (b).

[2] The golf ball of [1], wherein an outermost layer of the cover is made of the material obtained by molding the mixture comprising components (a) to (c).
[3] The golf ball of [1], wherein the mixture has a melt mass flow rate of at least 2.0 g/10 min.
[4] The golf ball of [1], wherein the unsaturated fatty acid (b) is at least one selected from the group consisting of oleic acid, elaidic acid, erucic acid, linoleic acid and linolenic acid.
[5] The golf ball of [1], wherein the basic inorganic metal compound (c) is calcium hydroxide.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described more fully below.
The golf ball of the invention has a core and a cover of one or more layer. The core is not limited to one layer, and may, if necessary, be composed of two or more layers.
A rubber composition obtained by a conventional method and controlled vulcanization conditions, ingredient proportions and the like may be used as the core material. The core formulation generally includes such ingredients as a base rubber, crosslinking agent, co-crosslinking agent and inert filler. Natural rubbers and/or synthetic rubbers hitherto used in solid golf balls may be employed as the base rubber. For example, 1,4-polybutadiene having a cis structure content of at least 40% may be used. If desired, other types of rubber, such as natural rubber, polyisoprene rubber or styrene-butadiene rubber may be suitably blended with the polybutadiene. The crosslinking agent is exemplified by organic peroxides such as dicumyl peroxide and di-t-butyl peroxide. The co-crosslinking agent is not subject to any particular limitation. Illustrative examples include the metal salts of unsaturated fatty acids, particularly the zinc salts and magnesium salts of unsaturated fatty acids having 3 to 8 carbon atoms (e.g., acrylic acid, methacrylic acid). Examples of inert fillers include zinc oxide, barium sulfate, silica, calcium carbonate and zinc carbonate. Aside from the foregoing rubber composition, use may be made of a thermoplastic resin or thermoplastic elastomer, such as an ionomer resin or a polyester elastomer, as the solid core material.
The solid core may be produced by using a known process to cure/vulcanize a rubber composition containing the various above ingredients. For example, core production may involve masticating the ingredients using a mixing apparatus such as a Banbury mixer or roll mill, compression molding or injection molding the masticated material in a core mold, then curing the molded body by suitably heating at a temperature sufficient for the peroxide and co-crosslinking agent to act. To illustrate, when dicumyl peroxide is used as the peroxide and zinc acrylate is used as the co-crosslinking agent, heating is typically carried out at from 130 to 170° C., and preferably 150 to 160° C., for a period of 10 to 40 minutes, and preferably 12 to 20 minutes.
The hardness of the solid core is not subject to any particular limitation and may be adjusted as appropriate. The core may have a hardness distribution such that the hardness is substantially the same from the center to the surface of the core, or the core may have a hardness difference between the center and surface thereof.
It is desirable for the solid core to have a diameter of at least 25 mm, and preferably at least 36 mm, but not more than 42 mm, and preferably not more than 24 mm. The core weight is preferably from 20 to 32 g, and more preferably from 27 to 30 g.
In the present invention, at least one layer of the cover of one or more layers is made of a material obtained by molding a mixture composed of the following essential ingredients:
(a) 100 parts by weight of a metal ion neutralization product of an olefin-unsaturated carboxylic acid random copolymer;
(b) 5 to 60 parts by weight of an unsaturated fatty acid; and
(c) 1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (a) and (b).
The olefin in component (a) is generally one having at least 2 carbons, but not more than 8 carbons, and preferably not more than 6 carbons. Illustrative examples include ethylene, propylene, butene, pentene, hexene, heptene and octene. Ethylene is especially preferred.
Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid and fumaric acid. Acrylic acid and methacrylic acid are preferred.
The random copolymer of the random copolymer metal salt used as component (a) may be obtained by random copolymerization of the above-mentioned ingredients according to a known method. It is recommended that the content of unsaturated carboxylic acid (acid content) included in the random copolymer be generally at least 2 wt % (here and below, “wt %” stands for percent by weight), preferably at least 6 wt %, and more preferably at least 8 wt %, but not more than 25 wt %, preferably not more than 20 wt %, and more preferably not more than 15 wt %. If the acid content is too low, the rebound resilience may decrease. On the other hand, if the acid content is too high, the processability may decrease.
The metal ion neutralization product of a random copolymer used as component (a) may be obtained by neutralizing some of the acid groups on the random copolymer with metal ions. Illustrative examples of metal ions for neutralizing the acid groups include Na⁺, K⁺, Li⁺, Zn⁺⁺, Cu⁺⁺, Mg⁺⁺, Ca⁺⁺, Co⁺⁺, Ni⁺⁺ and Pb⁺⁺. Of these, Na⁺, Li⁺, Zn⁺⁺ and Mg⁺⁺ are preferred, and Zn⁺⁺ is especially recommended. The degree to which the random copolymer is neutralized by these metal ions is not subject to any particular limitation. The neutralization product may be obtained by a known method, such as one that involves introducing to the random copolymer a suitable compound, examples of which include formates, acetates, nitrates, carbonates, bicarbonates, oxides, hydroxides and alkoxides of the above metal ions.
In the inventive golf ball, a binary polymer which is a metal ion neutralization product of an olefin-unsaturated carboxylic acid random copolymer is used in this way as component (a). The reason is that, while using the subsequently described unsaturated fatty acid with the above metal ion neutralization product of a binary copolymer serving as component (a) is essential for imparting the inventive ball with a soft feel and an excellent scuff resistance, a binary polymer better plasticizes the overall cover material than does a ternary polymer, enabling a good moldability to be maintained.
It is critical that the metal ion neutralization product of an olefin-unsaturated carboxylic acid random copolymer serving as component (a) have a Shore D hardness of at least 60, preferably at least 61, and more preferably at least 62. Given that component (a) serves as the base resin of the cover material, and that the material hardness of the base resin is largely responsible for the hardness, durability and scuff resistance of the ball, it is essential to set the Shore D hardness of component (a) within the foregoing range.
Illustrative examples of the metal salt of a random copolymer serving as component (a) include Himilan 1605, Himilan 1706, Himilan AM7317, Himilan AM7318 and Himilan AM7315 (all products of DuPont-Mitsui Polychemicals Co., Ltd.), and Surlyn 7930, Surlyn 8150, Surlyn 8220 and Surlyn 9150 (all products of E.I. DuPont de Nemours & Co.).
In the invention, the unsaturated fatty acid used as component (b) generally has one or more double bond on the molecule. Illustrative examples include those having one double bond, such as oleic acid (18 carbons), elaidic acid (the trans isomer of oleic acid) and erucic acid (22 carbons); those having two double bonds, such as linoleic acid (18 carbons); and those having three double bonds, such as linolenic acid. These may be used singly or as combinations of two or more. The use of oleic acid is especially preferred.
Above component (b) is included in an amount, per 100 parts by weight of component (a), of at least 5 parts by weight, preferably at least 8 parts by weight, and more preferably at least 10 parts by weight. Use in a smaller amount will prevent the hardness of the ionomer resin from being lowered to the desired level. The upper limit in the amount of component (b) is 60 parts by weight or less, preferably 50 parts by weight or less, and more preferably 40 parts by weight or less. At an amount greater than this upper limit, uptake by the resin becomes difficult and bleeding tends to arise.
The golf ball material of the invention includes as component (c) a basic inorganic metal compound capable of neutralizing acid groups on above components (a) and (b). It neutralizes un-neutralized carboxyl groups within the ionomer resin and carboxyl groups in component (b), thereby forming a metal salt. This results in strong crosslinkages, enhancing the scuff resistance.
In the golf ball of the invention, as noted above, an unsaturated fatty acid is included as component (b). The amount of component (b) is relatively small, which should help avoid problems such as molding defects.
The reason for using an unsaturated fatty acid having one or more double bond on the molecule is that the ionomer resin hardness-lowering effect is much larger than that of saturated fatty acids having no double bonds (e.g., stearic acid (18 carbons)).
Component (c) of the invention is a basic inorganic metal compound capable of neutralizing acid groups in above components (a) and (b), thus enabling the rebound resilience and processability to be freely controlled.
Illustrative examples of the metal ions used in the basic inorganic metal compound include Li⁺, Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺, Zn⁺⁺, Al⁺⁺⁺, Ni⁺, Fe⁺⁺, Fe⁺⁺⁺, Cu⁺⁺, Mn⁺⁺, Sn⁺⁺, Pb⁺⁺ and Co⁺⁺. Basic inorganic fillers containing these metal ions may be used as the inorganic metal compound. Specific examples include magnesium oxide, magnesium hydroxide, magnesium carbonate, zinc oxide, sodium hydroxide, sodium carbonate, calcium oxide, calcium hydroxide, lithium hydroxide and lithium carbonate. The use of calcium hydroxide, which has a high reactivity with the ionomer resin, is especially preferred.
Above component (c) is included in an amount, per 100 parts by weight of component (a), of at least 1 part by weight, preferably at least 1.2 parts by weight, and more preferably at least 1.5 parts by weight. Below this amount, the degree of neutralization falls shorts and a sufficient rebound resilience cannot be achieved. The upper limit in the amount of component (c) per 100 parts by weight of component (a) is not more than 10 parts by weight, preferably not more than 7 parts by weight, and more preferably not more than 6 parts by weight.
Other materials may be suitably included in the mixture of components (a) to (c), although it is recommended that the mixture have a melt mass flow rate (measured in accordance with JIS-K7210 at a test temperature of 190° C. and under a test load of 21 N (2.16 kgf)) of preferably at least 2.0 g/10 min, and more preferably at least 2.5 g/10 min, but preferably not more than 6 g/10 min, and more preferably not more than 5 g/10 min. If the melt mass flow rate of the hot mixture is too low, the processability will markedly decline.
Various additives may be optionally included in the mixture. For example, when the mixture is to be used as a cover material, additives such as pigments, dispersants, antioxidants, ultraviolet absorbers and light stabilizers may be included therein. Moreover, to improve the feel of the ball on impact, in addition to the above essential ingredients, various non-ionomeric thermoplastic elastomers may be included in the material of the invention. Examples of such non-ionomeric thermoplastic elastomers include olefin elastomers, styrene elastomers, ester elastomers, and urethane elastomers. The use of olefin elastomers and styrene elastomers is especially preferred.
The mixing method used to obtain the above mixture is not subject to any particular limitation. For example, mixture may be carried out at a heating temperature of from 150 to 250° C. using as the mixing apparatus an internal mixer such as a kneading-type twin-screw extruder, a Banbury mixer or a kneader. No limitation is place on the method of incorporating the various additives other than above essential ingredients (a) to (c). Examples include a method in which the additives are compounded with the above essential ingredients and simultaneously mixed under applied heat, and a method in which the essential ingredients are first mixed under heating, then the optional additives are added, following by additional mixing under applied heat. In particular, when a co-rotating twin-screw extruder is used, the unsaturated fatty acid may be injected from various vent ports on the twin-screw extruder using a plunger-type pump. The basic inorganic metal compound may be added from any desired point using a side feed.
To obtain the cover in the invention, use may be made of a method which involves placing within a mold a single-layer core or a multi-layer core of two or more layers that has been pre-fabricated according to the type of ball, mixing and melting the above mixture under applied heat, and injection-molding the molten mixture so as to encase the core within the desired cover. In this way, the cover-forming operation can be carried out in a state that ensures an outstanding heat stability, flow and moldability, enabling the golf ball ultimately obtained to have a high rebound resilience and also a good feel on impact and excellent scuff resistance. Alternatively, the method used to form the cover may be one in which first a pair of hemispherical half-cups is molded from the cover material of the invention, following which the half-cups are placed over a core and molded under pressure at 120 to 170° C. for 1 to 5 minutes.
In the practice of the invention, the cover is not limited to one layer only, and may instead be formed with a multilayer structure of two or more layers. If the cover has one layer, the thickness is preferably from 0.5 to 3 mm. If the cover has two layers, it is preferable for the outer cover layer to have a thickness in a range of 0.5 to 2.0 mm and for the inner cover layer to have a thickness in a range of 0.5 to 2.0 mm. When the cover has a multilayer structure, the cover material of the invention may be used either at the inner side of the multilayer structure or in the outermost layer cover. However, in the present invention, use as the outermost layer is preferred. That is, when the cover is formed of two or more layers, to obtain a good feel and to make the scuff resistance even better, it is advantageous for a molded material obtained from the mixture containing above components (a) to (c) to be used as the chief material of the outermost layer.
With regard to the cover hardness, it is desirable for the respective layers making up the cover (cover layers) to have a Shore D hardness of at least 40, and preferably at least 45, but not more than 60, and preferably not more than 58.
The surface of the outermost layer of the cover may have a plurality of dimples formed thereon, and the cover may be administered various treatment, such as surface preparation, stamping and painting. In particular, the ease of operation involved in administering such surface treatment to a golf ball cover made of the cover material of the invention can be improved on account of the good moldability of the cover surface.
The present invention provides a golf ball in which a material obtained by molding the above mixture is used in at least one cover layer. The type of golf ball is not subject to any particular limitation, provided the ball has a core and at least one cover layer. Exemplary golf balls include solid golf balls, such as two-piece golf balls having a solid core encased by a cover and multi-piece golf balls with three or more layers (e.g., three-piece solid golf balls); and thread-wound golf balls having a thread-wound core encased by a cover of one layer or having a multilayer structure of two or more layers.
The golf ball of the invention, which can be manufactured so as to conform with the Rules of Golf for competitive play, may be produced to a ball diameter of not less than 42.67 mm and a weight of not more than 45.93 g. The golf ball of the invention may be suitably used in all competitive play, whether by amateur golfers having a head speed of 30 to 40 m/s or by professional golfers having a head speed of 45 m/s.
As described above, the golf ball of the invention provides both a good feel on impact and an excellent scuff resistance while retaining a good flight performance.

EXAMPLES

Examples of the invention and Comparative Examples are given below by way of illustration, and not by way of limitation.

Examples 1 to 6, Comparative Examples 1 to 4

Using a core material composed primarily of the polybutadiene shown in Table 1 below, a solid core with a diameter of 35.3 mm, a weight of 27.1 g, and a deflection under 100 kg of loading of 4.0 mm was produced. The deflection was the measured amount of deformation by the core when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf).

	TABLE 1

	Amount (pbw)

Core	Polybutadiene (1)	50
formulation	Polybutadiene (2)	50
	Zinc acrylate	24.0
	Peroxide (1)	0.6
	Peroxide (2)	0.6
	Antioxidant	0.1
	Zinc salt of pentachlorothiophenol	0.1
	Zinc oxide	5
	Barium sulfate	20.8
Core	Diameter (mm)	35.3
properties	Weight (g)	27.1
	Deflection (mm)	4.0

Details of the above formulation are provided below.

Butadiene rubber (1): BR01 (trade name), available from JSR Corporation.
Butadiene rubber (2): BR51 (trade name), a grade of BR730 having improved extrudability available from JSR Corporation.
Peroxide (1): Dicumyl peroxide, available from NOF Corporation under the trade name Percumyl D.
Peroxide (2): 1,1-Bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, available from NOF Corporation under the trade name Perhexa 3M-40.
Antioxidant: Nocrac NS-6 (trade name), available from Ouchi Shinko Chemical Industry Co., Ltd.

Next, an intermediate layer material of the composition shown in Table 2 was injection-molded to a thickness of 1.65 mm in a mold within which the above solid core had been placed. The cover material was then mixed in a co-rotating twin-screw extruder (screw diameter, 32 mm; L/D=32; motor capacity, 7.5 kw; with vacuum vent) at 200° C. The resulting mixture was injected into a mold within which the intermediate layer material-covered core had been placed, and injection-molded to a cover thickness of 2.05 mm, thereby producing a three-piece solid golf ball having a diameter of 42.7 mm. The surface of the golf ball obtained in each example was coated with a non-yellowing urethane resin-based paint. The properties (initial velocity, feel on impact, scuff resistance, etc.) of the golf balls obtained in each example were evaluated as described below. The results are presented in Table 2.

	TABLE 2

	Example	Comparative Example

	1	2	3	4	5	6	1	2	3	4

Intermediate layer	Hytrel 4047	100	100	100	100	100	100	100	100	100	100
formulation (pbw)
Intermediate	Material hardness	40	40	40	40	40	40	40	40	40	40
layer	(Shore D)
properties	Specific gravity	1.12	1.12	1.12	1.12	1.12	1.12	1.12	1.12	1.12	1.12
Sphere composed of	Outside diameter	38.6	38.6	38.6	38.6	38.6	38.6	38.6	38.6	38.6	38.6
core covered by	(mm)
intermediate layer

Cover	Component	Himilan	100	100	100				100		50
formulation	(a)	1706
(pbw)		Himilan				100	100	100		100	50
		1605
		Himilan										50
		1601
		Himilan										50
		1557
	Component	Oleic	20	30	40	20	30	40
	(b)	acid
	Component	Calcium	1.83	3.41	5.2	3.03	4.92	5
	(c)	hydroxide

	Titanium	4	4	4	4	4	4	4	4	4	4
	dioxide
	Magnesium							2	2	2	2
	stearate
	Blue	0.05	0.05	0.05	0.05	0.05	0.05	0.05	0.05	0.05	0.05
	pigment
Cover	Melt mass flow	4.0	4.3	5.9	3.8	4.8	6.9	1.3	2.9	1.7	2.1
properties	rate (g/10 min)
	Cover hardness	50	50	46	58	56	54	62	63	63	60
	(Shore D)
	Specific gravity	1.00	1.00	0.99	0.98	0.97	0.99	0.99	0.97	0.98	0.97
Ball	Diameter (mm)	42.7	42.7	42.7	42.7	42.7	42.7	42.7	42.7	42.7	42.7
properties	Weight (g)	45.4	45.4	45.4	45.3	45.1	45.4	45.3	45.1	45.2	45.1
	Deflection (mm)	3.4	3.4	3.4	3.2	3.2	3.3	3.1	3.0	3.0	3.2
	Initial velocity	76.1	76.3	76.4	77.1	77.1	76.9	76.9	77.3	77.5	77.0
	(m/s)
	Scuff resistance	4.4	4.4	4.3	4.3	4.2	4.1	4.6	4.1	4.2	3.7
	(rating)
	Feel on impact	good	good	good	good	good	good	poor	poor	poor	poor

Details of the above formulation are provided below.

(I) Hytrel 4047 (trade name):
- Thermoplastic polyether ester elastomer available from DuPont-Toray Co., Ltd. (Shore D hardness, 40).
(II) Himilan 1706 (trade name):
- Ionomer resin of ethylene-methacrylic acid copolymer neutralized with zinc ions, available from DuPont-Mitsui Polychemicals Co., Ltd. (Shore D hardness, 64).
(III) Himilan 1605 (trade name):
- Ionomer resin of ethylene-methacrylic acid copolymer neutralized with sodium ions, available from DuPont-Mitsui Polychemicals Co., Ltd. (Shore D hardness, 65).
(IV) Himilan 1601 (trade name):
- Ionomer resin of ethylene-methacrylic acid copolymer neutralized with sodium ions, available from DuPont-Mitsui Polychemicals Co., Ltd. (Shore D hardness, 59).
(V) Himilan 1557 (trade name):
- Ionomer resin of ethylene-methacrylic acid copolymer neutralized with zinc ions, available from DuPont-Mitsui Polychemicals Co., Ltd. (Shore D hardness, 59).
(VI) Oleic acid:
- NAA-300 (trade name), available from NOF Corporation.
(VII) Magnesium stearate:
- Nissan Magnesium Stearate (trade name), available from NOF Corporation.
(VIII) Titanium oxide:
- Tipaque R550 (trade name), available from Ishihara Sangyo Kaisha, Ltd.
(IX) Blue pigment:
- Ultramarine Blue EP-62 (trade name), available from Holliday Pigments.
(X) Calcium hydroxide:
- CLS-B (trade name), available from Shiraishi Kogyo.

[Evaluation of Cover Material Properties]

Melt Mass Flow Rate

The melt mass flow rate (or melt index) of the material, as measured in accordance with JIS-K7210 (test temperature, 190° C.; test load, 21 N (2.16 kgf).

Material Hardnesses of Intermediate Layer and Cover Resin

The Shore D hardnesses measured according to ASTM D-2240 are shown.
[Evaluation of Ball Properties]

Ball Deflection (mm)

The amount of deformation (mm) by the golf ball when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) was determined.

Initial Velocity of Ball (m/s)

The initial velocity (m/s) was measured using an initial velocity measuring apparatus of the same type as that of the official golf ball regulating-body—R&A (USGA), and in accordance with R&A (USGA) rules.

Feel on Impact

Sensory evaluations were carried out with a panel of ten amateur golfers having head speeds of 35 to 40 m/s and using W#1 clubs. Ratings were based on the following criteria.

- Good: At least 7 of the 10 golfers thought the ball had a good feel.
- Fair: Five or six of the 10 golfers thought the ball had a good feel.
- Poor: Four or fewer of the 10 golfers thought the ball had a good feel.

Scuff Resistance

A non-plated X-WEDGE 03 (loft, 52°) manufactured by Bridgestone Sports Co., Ltd. was set in a swing robot, and the ball was hit at a head speed of 33 m/s with the club face open about 30° from square. The surface state of the ball was then visually examined by three golfers having handicaps of 10 or less, and rated according to the following criteria. The average of the ratings obtained for each example is shown in the table.

- 5: Surface of ball is either completely unchanged or bears a slight imprint from club face.
- 4: Surface of ball bears a clear imprint from club face, but is not frayed.
- 3: Surface is conspicuously frayed and scuffed.
- 2: Surface is frayed and cracked.
- 1: Some dimples have been obliterated.

It is apparent from the results in Table 1 that the golf balls obtained in the examples of the invention had excellent rebound resilience, scuff resistance and feel on impact. By contrast, the balls obtained in the comparative examples had a poor feel and showed no improvement in scuff resistance.

Claims

1. A golf ball comprising a core and a cover of one or more layer, wherein at least one layer of the cover is made of a material obtained by molding a mixture comprising:

(a) 100 parts by weight of a binary polymer which is a metal ion neutralization product of an olefin-unsaturated carboxylic acid random copolymer having a Shore D hardness of at least 60;

(b) 5 to 60 parts by weight of an unsaturated fatty acid;

(c) 1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acid groups in components (a) and (b); and

wherein said material does not comprise a ternary polymer.

2. The golf ball of claim 1, wherein an outermost layer of the cover is made of the material obtained by molding the mixture comprising components (a) to (c).

3. The golf ball of claim 1, wherein the mixture has a melt mass flow rate of at least 3.8 to 6.9 g/10 min.

4. The golf ball of claim 1, wherein the unsaturated fatty acid (b) is elaidic acid and/or erucic acid.

5. The golf ball of claim 1, wherein the basic inorganic metal compound (c) is calcium hydroxide.

6. The golf ball of claim 1, wherein the cover has a Shore D hardness of from 46 to 58.

7. The golf ball of claim 1, wherein the metal ion neutralization product of an olefin-unsaturated carboxylic acid randon copolymer serving as component (a) has a Shore D hardness of at least 62.