GB2351674A

GB2351674A - Four piece solid golf ball

Info

Publication number: GB2351674A
Application number: GB0025024A
Authority: GB
Inventors: Keiji Moriyama; Yoshinori Sano
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 1996-12-20
Filing date: 1997-12-19
Publication date: 2001-01-10
Anticipated expiration: 2017-12-19
Also published as: GB2351674B; GB0025024D0; GB0025025D0; GB2351675B; GB2351675A

Abstract

A four piece solid golf ball comprises:<BR> ```a centre (1),<BR> ```an intermediate layer (5) having two layers consisting of an inner layer (2) and an outer layer (3) formed on the centre (1), and<BR> ```a cover (4) covering the intermediate layer (5). The inner layer (2) and cover (4) are harder than the centre (1) and the outer layer (3) respectively, so that the hardness distribution of the portions (1) to (4) is arranged soft-hard-soft-hard from the centre (1) to the cover (4), and the centre (1) has a JIS-C hardness of from 50 to 80 and a diameter of from 30 to 35 mm, the inner layer (2) has a JIS-C hardness of from 70 to 100 and a thickness of from 0.5 to 2.5 mm, the outer layer (3) has a JIS-C hardness of from 40 to 80 and a thickness of from 0.5 to 2.5 mm and the cover (4) has a Shore D hardness of from 62 to 72 and a thickness of from 1.0 to 3.0 mm.

Description

2351674 FOUR PIECE SOLID GOLF BALL The present invention relates to a four

piece solid golf ball having a good flight performance and a good shot feel at the time of hitting. More particular, it relates to a four piece solid golf ball that exhibits a high launch angle when it is hit.

Golf balls are generally classified into two categories: thread wound golf balls and solid golf balls. A representative example of the-solid golf ball is a two piece solid golf ball which is composed of a solid centre formed from a vulcanised rubber and a cover formed on the centre and made from a thermoplastic resin.

is Although the two piece solid golf ball has a simple structure it has a very good flight performance and possesses excellent durability and therefore has proved popular with amateur golfers. However, the two piece solid golf ball has a high hardness and thus exhibits a poor shot feel at the time of hitting and poor controllability at an approach shot.

For improving the defects of the two piece solid golf ball, much effort has been made and it has hitherto been proposed that the core is made of two layers or, alternatively, that the cover is made of two layers. These structures improve the shot feel to some degree, but do not improve the other defects, and it is also desired to improve the shot feel further.

The present invention aims to provide a solid golf ball which addresses the above mentioned problems and which exhibits a good shot feel at the time of hitting and a long flight distance.

This object as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings.

Figure 1 is a drawing, by way of example, which shows a schematic cross section of an embodiment of the golf ball of the present invention.

The present inventors have intensely studied for achieving the above object and have found that the solid golf ball is made four piece and composed of a centre, an intermediate layer having two layers and a cover covering the intermediate layer and that their hardness is controlled as soft-hard-soft-hard in the order of centre-inner intermediate layer-outer intermediate layer-cover, which enlarges a launch angle of the golf ball when hitting and enhances flight performance, while keeping soft shot feel. The four piece solid golf ball of the present invention comprises:

a centre (1) an intermediate layer (5) having two layers consisting of an inner layer (2) inner layer (2) and an outer layer (3), formed on the center (1), and a cover (4) covering the intermediate layer (5), wherein the inner layer (2) and cover (4) are harder than the center (1) and the outer layer (3), so that the hardness distribution of the portions (1) to (4) is arranged soft - hard - soft - hard from the center (1) to the cover (4).

The present invention is explained with reference to Fig. 1 which shows a cross sectional view of one embodiment of the four piece solid golf ball of the present Invention. The four piece solid golf ball is composed of a center (1), an intermediate layer (5) formed on the center (1) and a cover (4) formed on the intermediate layer (5). The intermediate layer is composed of an inner layer (2) and an outer layer (3). In the present invention, the inner layer (2) and the cover (4) are harder than the center (1) and the outer layer (3), so that the hardness distribution of the portions (1) to (4) is arranged soft - hard - soft - hard from the center (1) to the cover (4). As long as the hardness distribution is controlled as above, the materials for producing each part of the four portions can be any one which has been used for golf balls, for example vulcanized rubber, thermoplastic resin (especially ionomer resin), thermoplastic elastomer and a mixture thereof. In order to realize the hardness distribution, the following three combinations are proposed for selecting the producing materials:

(A) Center = vulcanized rubber 3 Inner intermediate layer thermoplastic resin (e.g. ionomer resin) Outer intermediate layer vulcanized rubber Cover = thermoplastic resin (e.g. ionomer resin) (B) Center = vulcanized rubber Inner intermediate layer = vulcanized rubber Outer intermediate layer = thermoplastic elastomer or a mixture of thermoplastic elastomer and thermoplastic resin (e.g. ionomer resin) Cover = thermoplastic resin (e.g. ionomer resin) (C) Center = vulcanized rubber Inner intermediate layer = thermoplastic resin, thermoplastic elastomer or a mixture of thermoplastic elastomer and thermoplastic resin (e.g. ionomer resin) Outer intermediate layer = thermoplastic elastomer or a mixture of thermoplastic elastomer and thermoplastic resin (e.g. ionomer resin) Cover = thermoplastic resin (e.g. ionomer resin) As is apparent from the above combinations, the center is preferably formed from vulcanized rubber for imparting superior flight performance to the golf ball and the cover is preferably formed from thermoplastic resin, especially ionomer resin for providing the golf ball with strong durability. For intermediate layer, there are many combinations as 4 suggested above. The producing materials are firstly explained.

(Vulcanized rubber) The vulcanized rubber may be formed by vulcanizing a rubber composition. The hardness of the vulcanized rubber can be easily controlled by selecting ingredient, changing the formulating amount of the ingredient and changing condition for vulcanization. The rubber composition can be one which has been known to the art, but generally comprises a base rubber, a crosslinking agent, a metal salt of unsaturated carboxylic acid, filler and optional ly antioxidant. The base rubber employed can be one which has been used for solid golf ball, but includes natural rubber andlor synthetic rubber. Examples of the synthetic rubbers are butadiene rubber, polyisoprene rubber, styrene-butadiene rubber, ethylene-propylene-diene rubber and the like. Preferred is butadiene rubber having cls-1,4 bond of at least 40 %, preferably at least 80 % The crosslinking agent can be one which has been employed for the rubber composition of the golf ball, but includes an organic peroxide, such as dicurnyl peroxide and t-butyl peroxide. Preferred is dicurnyl peroxide. The crosslinking agent may be contained in the rubber composition in an amount of 1.0 to 2.0 parts by weight based on 100 parts by weight of the base rubber. Amounts of less than 1.0 parts by weight soften the rubber too much and reduce rebound characteristics, to result in poor flight distance. Those of more than 2.0 parts by weight harden the rubber too much and reduce shot feel.

The metal salt of unsaturated carboxylic acid is functioned as co-crosslinking agent. The (x,p-unsaturated carboxylic acid may have 3 to 8 carbon atoms and examples thereof can be acrylic acid and methacrylic acid. The metal for forming a metal salt of unsaturated carboxylic acid can be monovalent metal or divalent metal, such as sodium, potassium, lithium, magnesium, zinc and the like. The metal salt of (x,p-unsaturated carboxylic acid may be formed in the rubber composition in which cc, P-un saturated carboxylic acid is formulated with metal oxide to react. An amount of the metal salt of oc,p-unsatu rated carboxylic acid may be 15 to 30 parts by weight, based on 100 parts by weight of the base rubber. Amounts of more than 30 parts by weight harden the rubber too much and deteriorate shot feel and those of less than 15 parts by weight reduce rebound characteristics and reduce flight distance.

The filler can be one which has been used for the rubber composition of the core of the solid golf ball and includes inorganic salt, such as zinc oxide, barium sulfate, calcium carbonate etc.; metal powder having high specific gravity, such as tungsten powder, molybdenum powder etc.; and a mixture thereof. The rubber composition may further contain antioxidant or peptizer if necessary.

The rubber composition is prepared by mixing the above components by a conventional mixer, such as mixing roller, banbary mixer and the like. The resulting rubber composition is generally vulcanized in a mold at a temperature of 120 to 170 OC.

(Thermoplastic resin) The thermoplastic resin can generally be ionomer resin in the field of golf balls, but the other thermoplastic resins, such as polyester, polyurethane, polyamide, polyimide, polyolefin and the like, can also be 6 used. Especially, the cover of the four piece solid golf ball of the present invention is mainly formed from the ionomer resin. The ionomer resin can be one which has been used for the cover material of solid golf balls. The ionomer resin can be an ethyl ene-(meth)acrylic acid copolymer of which a portion of carboxylic acid groups is neutralized with metal ion. Examples of the metal ions are alkali metal ion, such as Na ion, K ion, Li ion etc.; divalent metal ion, such as Zn ion, Ca ion, Mg ion etc.; trivalent metal ion, such as A[ ion, Nd ion etc.; and a mixture thereof. Preferred are Na ion, Zn ion and Li ion, in view of rebound characteristics and durability. The ionomer resin is generally commercially available and includes Hi-milan 1557, 1605, 1652, 1705, 1706, 1707, 1855 and 1856 available from Mitsui Du Pont Polychemical Co., Ltd. and IOTEC 7010 and 800 available from Exxon Co.

In case of using the ionomer resin as cover material, the cover material may contains a filler, a colorant or an additive. Examples of the fillers are barium sulfate and the like. Examples of the colorants are titanium dioxide and the like. Examples of the additives are UV absorber, light stabilizer, fluorescent material or fluorescent whitener. The other material can be contained in the cover resin composition in such an amount that the characteristics of the cover is not damaged. The colorant may be present in an amount of 0.1 to 0.5 parts by weight based on 100 parts by weight of ionomer resin.

The cover may be formed by a method known to the art, for example injection molding or press molding. When forming a cover layer, many recesses, generally referred as "dimples", are formed thereon. The 7 golf ball is generally coated with a paint and marked with brand name or other informations to impart good appearance and to enhance product quality.

(Thermoplastic elastomer) The thermoplastic elastomer is a material which shows the characteristics of vulcanized rubber at room temperature but shows thermoplastic characteristics at an elevated temperature. The thermoplastic elastomer has soft segment showing rubber characteristics and hard segment preventing from plastic deformation in one molecule.

The thermoplastic elastomer generally includes polystyrene type, polyamide type, polyolefin type, polyester type, polyurethane type, 1,2 polybutadiene type, polyvinyl chloride type and the like. Preferred are polyurethane type thermoplastic elastomer and styrene-butadiene-styrene block copolymer having polybutadiene block with epoxy groups.

When the thermoplastic elastomer is used, it has thermoplastic properties at an elevated temperature and can be easily molded by conventional molding method, such as injection-molding or press molding.

(Mixture of thermoplastic resin and thermoplastic elastomer) The mixture can be any mixing ratio depending on which performance is made main. For example, if the performance of the thermoplastic elastomer is mainly used, the thermoplastic elastomer is mainly contained and the thermoplastic resin may be contained in an amount of less than 50 parts by weight based on 100 parts by weight of the thermoplastic elastomer. if the performance of the thermoplastic resin is 8 mainly used, the thermoplastic elastomer may be contained in an amount of less than 50 parts by weight of 100 parts by weight of the thermoplastic resin. In case of using ionomer resin as the thermoplastic resin to be mixed with the thermoplastic elastomer, the ionomer resin may preferably be one having relatively high melt index, such as Surlyn AD 8511 and 8512 available from Du Pont Co.

(Golf ball) The four piece solid golf ball of the present invention shows excellent flight performance and soft shot feel at the time of hitting, so long as the hardness distribution is controlled as soft - hard - soft hard from the center (1) to the cover (4), but there is the following three concrete embodiments in view of practical object. The present invention will be explained in more details using the I concrete embodiments.

The first one is a four piece solid golf ball in which the center (1) has a JIS-C hardness of 60 to 80 and a diameter of 15 to 30 mm, the inner layer (2) has a JIS-C hardness of 90 to 100 and a thickness of 1 to 3 mm, the outer layer (3) has a JIS-C hardness of 60 to 80 and a thickness of 2 to 12 mm and the cover (4) has a Shore D hardness of 62 to 72 and a thickness of 1 to 3 mm, wherein the inner layer (2) is harder than the center by 15 to 35 in JIS-C hardness and the outer layer (3) is softer than the inner layer (2) by 10 to 35 in J I S-C hardness.

The second one is a four piece solid golf ball in which the center (1) has a JIS-C hardness of 65 to 80 and a diameter of 15 to 25 mm, the inner layer (2) has a JIS-C hardness of 70 to 85 and a thickness of 2 to 13 mm, the outer layer (3) has a JIS-C hardness of 40 to 80 and a 9 thickness of 1.3 to 2.5 mm and the cover (4) has a Shore D hardness of 62 to 72 and a thickness of 1.7 to 2.9 mm, wherein the inner layer (2) is harder than the center (1) by 5 to 20 in JIS-C hardness and the outer layer (3) is softer than the inner layer (2) by 10 to 35 in JI S-C hardness.

The third one is a four piece solid golf ball in which the center (1) has a XS-C hardness of 50 to 80 and a diameter of 30 to 35 mm, the -inner layer (2) has a J IS-C hardness of 70 to 100 and a thickness of 0. 5 to 2.5 mm, the outer layer (3) has a JIS-C hardness of 40 to 80 and a thickness of 0.5 to 2.5 mm and the cover (4) has a Shore D hardness of 62 to 72 and a thickness of 1.0 to 3.0 mm, wherein the inner layer (2) is harder than the center (1) by 15 to 35 in JIS-C hardness and the outer layer (3) is softer than the inner layer (2) by 10 to 50 in JIS-C hardness.

(The First Embodiment) In this embodiment, the center has a JIS-C hardness of 60 to 80 and a diameter of 15 to 30 mm. If the JIS-C hardness is less than 60, the center is too soft and the golf ball has poor rebound performance and if it is more than 80, the center is too hard and the golf ball shows poor shot feel. If the diameter is less than 15 mm, it is difficult to feel soft shot event if the center is made soft. If it is more than 30 mm, the rebound performance of the golf ball significantly reduces and flight distance reduces.

The center is covered with the inner layer (2) of the intermediate layer (5) and the hardness difference therebetween is controlled within the range of 15 to 35 in JIS-C hardness. The inner layer (2) in the first embodiment may preferably be formed from thermoplastic resin, especially ionomer resin. The inner layer (2) may be formed by the same method for forming a cover, such as injection-molding or press molding.

The inner layer (2) has a thickness of 1 to 3 mm and a JIS-C hardness of 90 to 100, which enlarges the launch angle of a golf ball. If the thickness is less than 1.0 mm, rebound performance reduces and if it is more than 3.0 mm, shot feel is hard.

On the inner layer (2), an outer layer (3) is formed, which has a thickness of 2 to 12 mm and a JIS-C hardness of 60 to 80. The inner layer (2) and the outer layer (3) constitutes the intermediate layer (5). The outer layer can be obtained by any material as long as it has the JIS-C hardness range, but is generally formed by vulcanizing a rubber composition which is the same one as that used for the center (1) and thus contains a base rubber, a crosslinking agent, a metal salt of a,p unsaturated carboxylic acid, filler and optionally antioxidant. If the outer layer has a thickness of less than 2 mm, shot feel is hard and if it is more than 12 mm, rebound performance reduces. The outer layer (3) may be formed by art-knowp methods, for example a method comprising preparing two half shells from the rubber composition and putting the inner layer covered center into the shells, followed by vulcanizing. The outer layer (3) may be formed by injection-molding the rubber composition and then vulcanizing.

In the first embodiment, the outer layer (3) is softer than the inner layer (2) by 10 to 35, preferably 15 to 30 in JIS-C hardness. If the difference is less than 10, the resulting golf ball is poor in shot feel. If it is more than 35, the resulting golf ball is poor in flight distance.

11 The intermediate layer-covered center is then covered with a cover (4) which has a thickness of 1 to 3 mm and a Shore D hardness of 62 to 72. If the thickness is less than 1 mm, rebound performance reduces and flight distance also reduces. If it is more than 3 mm, shot feel is hard. If the Shore D hardness is less than 62, the resulting golf ball is poor in flight distance. If it is more than 72, the resulting golf ball is poor in shot feel.

(The Second Embodiment) In the second embodiment, a four piece solid golf ball comprises a center (1), an intermediate layer (5)having two layers consisting of an inner layer (2) and an outer layer (3), formed on the center (1), and a cover (4) covering the intermediate layer (5), wherein the center (1) has a JIS-C hardness of 65 to 80 and a diameter of 15 to 25 mm, the inner layer (2) has a JIS-C hardness of 70 to 85 and a thickness of 2 to 13 mm, the outer layer (3) has a JIS-C hardness of 40 to 80 and a thickness of 1.3 to 2.5 mm and the cover (4) has a Shore D hardness of 62 to 72 and a thickness of 1.7 to 2.9 mm, wherein the inner layer (2) is harder than the center (1) by 5 to 20 in JIS-C hardness and the outer layer (3) is softer than the inner layer (2) by 10 to 35 in JIS-C hardness.

In the second embodiment, the center (1) has a JIS-C hardness of 65 to 80 and a diameter of 15 to 25 mm. If the JIS-C hardness is less than 65, the center is too soft and the golf ball has poor rebound performance and if it is more than 80, the center is too hard and the golf ball shows poor shot feel. If the diameter is less than 15 mm, it is difficult to feel soft shot event if the center is made soft. If it is more than 25 mm, the rebound performance of the golf ball significantly reduces and flight 12 distance reduces.

The inner layer (2) has a thickness of 2 to 13 mm and a JIS-C hardness of 70 to 85, which enlarges the launch angle of a golf ball. If the thickness is less than 2.0 mm, rebound performance reduces and if it is more than 3.0 mm, shot feel is hard. The producing material of the inner layer (2) in the second embodiment is not limited so long as the hardness is controlled as above, but preferably is formed from vulcanized rubber.

The vulcanized rubber is explained above in detail, In the second embodiment, the hardness difference between the center (1) and the inner layer (2) is controlled within the range of 5 to 20, preferably 5 to 15 in JIS-C hardness. If the difference is less than 5, the resulting golf ball is poor in flight distance. If it is more than 20, the resulting golf ball is poor in flight distance.

The outer layer (3) has a thickness of 1.3 to 2.5 mm and a JIS C hardness of 40 to 80. If the outer layer has a thickness of less than 1. 3 mm, shot feel is hard and if it is more than 2.5 mm, rebound performance reduces. The outer layer can be formed from any material so long as the hardness is controlled as above, but is preferably formed from thermoplastic elastomer or a combination of thermoplastic resin and thermoplastic elastomer.

In the second embodiment, the outer layer (3) is softer than the inner layer (2) by 10 to 35, preferably 10 to 30 in JIS-C hardness. If the difference is less than 10, the resulting golf ball is poor in shot feel. If it is more than 35, the resulting golf ball is poor in flight distance.

The cover has a thickness of 1.7 to 2.9 mm and a Shore D 13 hardness of 62 to 72. If the thickness is less than 1.7 mm, rebound performance reduces and flight distance also reduces. If it is more than 2.9 mm, shot feel is hard. If the Shore D hardness is less than 62, the resulting golf ball is poor in flight distance. If it is more than 72, the resulting golf ball is poor in shot feel.

(The Third Embodiment) In the third embodiment, a four piece solid golf ball comprises a center (1), an intermediate layer (5)having two layers consisting of an inner layer (2) and an outer layer (3), formed on the center (1), and a cover (4) covering the intermediate layer (5), wherein the center (1) has a JIS- C hardness of 50 to 80 and a diameter of 30 to 35 mm, the inner layer (2) has a JIS-C hardness of 70 to 100 and a thickness of 0.5 to 2.5 mm, the outer layer (3) has a JIS-C hardness of 40 to 80 and a thickness of 0.5 to 2.5 mm and the cover (4) has a Shore D hardness of 62 to 72 and a thickness of 1.0 to 3.0 mm, wherein the inner layer (2) is harder than the center (1) by to 30 in JIS-C hardness and the outer layer (3) is softer than the inner layer (2) by 10 to 50 in J I S-C hardness.

In the third embodiment, the center (1) has a JIS-C hardness of 50 to 80 and a diameter of 30 to 35 mm. If the JIS-C hardness is less than 50, the center is too soft and the golf ball has poor rebound performance and if it is more than 80, the center is too hard and the golf ball shows poor shot feel. If the diameter is less than 30 mm, it is difficult to feel soft shot event if the center is made soft. If it is more than 35 mm, the rebound performance of the golf ball significantly reduces and flight distance reduces.

14 The inner layer (2) has a thickness of 0.5 to 2.5 mm and a JIS C hardness of 70 to 100, which enlarges the launch angle of a golf ball. If the thickness is less than 0.5 mm, rebound performance reduces and if it is more than 2.5 mm, shot feel is hard.

In the third embodiment, the hardness difference between the inner layer (2) and the center (1) is controlled within the range of 15 to 35, preferably 20 to 35 in JIS-C hardness. If the difference is less than 5, the resulting golf ball is poor in flight distance. If it is more than 20, the resulting golf ball is poor in flight distance.

The outer layer (3) has a thickness of 0.5 to 2.5 mm and a JIS C hardness of 40 to 80. If the outer layer has a thickness of less than 0. 5 mm, shot feel is hard and if it is more than 2.5 mm, rebound performance reduces.

In the third embodiment, the outer layer (3) is softer than the inner layer (2) by 10 to 50, preferably 20 to 40 in JIS-C hardness. If the difference is less than 10, the resulting golf ball is poor in shot feel. If it is more than 50, the resulting golf ball is poor in flight distance.

In the third embodiment, the inner layer and the outer layer can be formed from any material so long as the hardness is controlled as above, but is preferably formed from thermoplastic resin, thermoplastic elastomer or a combination of thermoplastic resin and thermoplastic elastomer.

The center has a thickness of 1.0 to 3.0 mm and a Shore D hardness of 62 to 72. If the thickness is less than 1.0 mm, rebound performance reduces and flight distance also reduces. If it is more than 3.0 mm, shot feel is hard. If the Shore D hardness is less than 62, the resulting golf ball is poor in flight distance. If it is more than 72, the resulting golf ball is poor in shot feel.

EXAMPLES

The following Examples and Comparative Examples further illustrate the present invention in detail but are not to be construed to limit the scope of the present invention to their details.

Examples 1 to 6 Preparation of a center A composition for center was prepared by mixing the ingredients shown in Table 1 and then press-molded at 140 IC for 25 minutes, followed by press-molding at 165 OC for 20 minutes to form a center. The diameter and JIS-C hardness are shown in Table 2.

Formation of gn inner layer of an intermediate laye The center obtained above was covered by injection molding with the resin composition for inner layer, of which ingredients were shown in Table 1. The thickness and JIS-C hardness of the inner layer are shown in Table 2.

Formation of an outer layer of an intermediate laye On the inner layer-covered center, a rubber composition for outer layer was covered and then press-molded at 155 OC for 20 minutes.

The ingredients of the rubber composition are shown in Table 1. The thickness and JIS-C hardness of the outer layer are shown in Table 2.

Formation Qf a cover 16 On the outer layer-covered center, a resin composition for cover was covered by injection molding and then painted thereon to obtain a four piece solid golf ball. The ingredients of the resin composition are shown in Table 1. The shore D hardness of the cover is shown in Table 2.

The resulting golf ball was subjected to evaluations in flight performance (i.e. launch angle, spin amount and flight distance) and shot feel and the results are shown in Table 2.

The evaluation methods are explained hereinafter.

(1) Flight distance A driver (No. 1 wood club) was equipped with a swing robot available from True Temper Co. and a golf ball was hit at a head speed of m/sec to determine a flight distance of carry. The term "carry" means a distance travelled by the golf ball before bouncing first time on the ground.

(2) Launch angle and spin amount As explained in flight distance, a driver was equipped with a swing robot and a golf ball was hit at a head speed of 40 m/sec.

Photographs of the impact point between the ball and the club were taken in a short period of time by two cameras. The launch angle and spin amount were determined from the photographs.

(3) Shot feel A professional golfer evaluated the golf ball by actually hitting with a driver (No. 1 wood club). The criteria of shot feel are as follow.

Good: Soft and good Poor: Hard and bad 17 Table 1

Examples

2 3 4 5 6 Center BR-1 1 1 100 100 100 100 100 100 Zinc acrylate 23 18 23 23 27 23 Zinc oxide 27.8 32.4 30.8 30.8 29.5 33.0 Antioxidant 2 0.5 0.5 0.5 0.5 0.5 0.5 Dicurnyl peroxide 2.0 2.0 2.0 2.0 2.0 2.0 Diphenylclisulfide 0.5 0.5 0.5 0.5 0.5 0.5.

Innerlayer Hi-milan 1605 3 50 50 50 50 50 50 Hi-milan 1706 4 50 so 50 50 50 50 Outer layer BR-1 1 100 100 100 100 100 100 Zinc acrylate 23 27 18 23 27 27 Zinc oxide 27.9 29.6 32.5 30.9 29.6 31.8 Antioxidant 0.5 0.5 0,5 0.5 0.5 0.5 Dicumyl peroxide 2.0 2.0 2.0 2.0 2.0 2.0 Diphenyidisuifide 0.5 0.5 0.5 0.5 0.5 0.5 Cover Hi-milan 1605 50 50 50 50 50 50 Hi-milan 1706 50 50 50 50 50 50 1 BR-1 1: High cis-polybutacliene rubber available from JSR Co., Ltd. (1.4-cis-butadiene content = 96 %) 2 Yoshinox 425 available from Yoshitomi Pharmaceutical Co., Ltd.

3 Hi-milan 1605: lonomer resin of ethylene-methacrylic acid neutralized with sodium ion (Melt index = 2.8, Flexural modulus = about 18 300 MPa), available from Mitsui Du Pont Polychemical co., Ltd.

4 Hi-milan 1706: lonorner resin of ethyl ene-methacrylic acid neutralized with zinc ion (Melt index = 0.8, Flexural modulus = about 260 MPa), available from Mitsui Du Pont Polychemical co., Ltd.

Table 2

Examples

2 3 4 5 6 Center Diameter (mm) 15.3 24.6 24.6 24.6 24.6 29.2 JIS-C hardness 75 65 75 75 78 75 Innerlayer Thickness (mm) 1.8 1.8 1.8 1.8 1.8 1.8 JIS-C hardness 95 95 95 95 95 95 Outer layer Thickness (mm) 9.6 4.95 4.95 4.95 4.95 2.65 JIS-C hardness -75 78 65 75 78 78 Cover Thickness (mm) 2.3 2.3 2.3 2.3 2.3 2.3 Shore D hardness 71 71 71 71 71 71 Ball evaluation Launch angle (0) 12.25 12.55 12.30 12.40 12.25 12.45 Spin amount (rpm) 2650 2550 2630 2605 2650 2560 Carry (yards) 201.0 203.8 201.3 201.9 202.7 201.5 Shot feel Good Good Good Good Good Good Examples 7 to 12 Preparation of a cente A composition for center was prepared by mixing the ingredients shown in Table 3 using a mixing roller and then press-molded 19 at 140 'C for 25 minutes, followed by press-molding at 165 OC for 8 minutes to form a center. The diameter and JIS-C hardness are shown in Table 4.

Formation of an inner layer of an intermediate laye On the center, arubber composition for inner layer was covered and then press-molded at 155 OC for 20 minutes. The ingredients of the rubber composition are shown in Table 3. The thickness and JIS-C hardness of the inner layer are shown in Table 4.

Formation of an outer layer of an intermediate laye The inner layer-covered center obtained above was covered by injection molding with the resin composition for outer layer, of which ingredients were shown in Table 3. The thickness and JIS-C hardness of the inner layer are shown in Table 4.

Formation of a cover On the outer layer-covered center, a resin composition for cover was covered by injection molding and then painted thereon to obtain a four piece solid golf ball. The ingredients of the resin composition are shown in Table 3. The shore D hardness of the cover is shown in Table 4.

The resulting golf ball was subjected to evaluations in flight performance (i.e. launch angle, spin amount and flight distance) and shot feel and the results are shown in Table 4.

The evaluation methods are the same as conducted in Examples 1-6.

Table 3

Examples

7 8 9 10 11 12 Center BR-1 1 1 100 100 100 100 100 100 Zinc acrylate 23 23 20 23 23 23 Zinc oxide 23.4 34.5 35.5 34.5 23.4 20.0 Antioxidant 2 0.5 0.5 0.5 0.5 0,5 0.5 Dicumy] peroxide 2.0 2.0 2.0 2.0 2.0 2.0 Diphenyidisuifide 0.5 0.5 0.5 0.5 0.5 0.5 Innerlayer BR-1 1 100 100 100 100 100 100 Zinc acrylate 28 28 31 31 28 31 Zinc oxide 21.7 33.1 32.1 32.1 21.7 17.1 Antioxidant 0.5 0.5 0.5 0.5 0.5 0.5 Dicumyl peroxide 2.5 2.5 2.5 2.5 2.5 2.5 Diphenyidisulficle 0.5 0.5 0.5 0.5 0.5 0.5 Outer layer Pandex T-7890N 6 - 100 100 Elastran ET 890 7 100 - AT 015 8 - 20 15 17.5 - - HG 252 9 60 45 52.5 - - Surlyn AD 8511 10 - 10 20 15 - - Surlyn AD 8512 11 - 10 20 15 - - Tungsten powder - - - - - 11.9 Cover Hi-milan 1605 50 50 50 50 50 50 Hi-milan 1706 50 50 50 50 50 50 6 Polyurethane thermoplastic elastomer available from Dai Nippon Ink & Chemicals Co., Ltd.

7 Polyurethane thermoplastic elastomer available from 21 Takeda Verdish Urethane Co., Ltd.

8 Styrene-butacliene-styrene block copolymer having polybutacliene block with epoxy groups, having JIS-A hardness of 67, styrene/butadiene weight ratio of 40/60 and epoxy content of about 1.5 to 1.7 % by weight, available from Daicel Chemical Industries Ltd.

9 Hydrogenated styrene-isoprene-styrene block copolymer having a terminal OH, having JIS-A hardness of 80 and styrene content of about 40 % by weight, available from Kuraray Co., Ltd.

lonomer resin of ethylene-methacrylic acid neutralized with zinc ion, having a melt index of 3.4 and a flexural modulus of about 220 MPa, available from Du Pont Co.

11 lonomer resin of ethylene-methacrylic acid neutralized with sodium ion, having a melt index of 4.4 and a flexural modulus of about 280 MPa, available from Du Pont Co.

'W 22 Table 4

Examples

7 8 9 10 11 12 Center Diameter (mm) 15.3 20.8 20.8 24.6 20.8 20.8 JIS-C hardness 75 75 67 75 75 75 Innerlayer Thickness (mm) 9.7 7.0 7.0 5.0 7.25 7.0 JIS-C hardness 80 80 83 83 80 83 Outer layer Thickness (mm) 1.8 1.8 1.8 1.8 1.85 1.8 JIS-C hardness 62 62 71 66 64 65 Cover Thickness (mm) 2.2 2.15 2.15 2.25 1.85 2.15 Shore D hardness 71 71 71 71 71 71 Ball evaluation Launch angle (0) 12.2 12.3 12.6 12.25 12.3 12.55 Spin amount (rpm) 2670 2490 2520 2635 2605 2550 Carry (yards) 201.5 202.8 203.2 201.9 202.7 203.8 Shot feel Good Good Good Good Good Good Examples 13 to 17 Preparation-of a center A composition for center was prepared by mixing the ingredients shown in Table 5 and then press-molded at 140 OC for 25 minutes, followed by press-molding at 165 IC for 8 minutes to form a center. The diameter and JIS-C hardness are shown in Table 6.

Formation of an inner layer of an intermediate layer The center obtained above was covered by injection molding 23 with the resin composition for inner layer, of which ingredients were shown in Table 5. The thickness and JIS-C hardness of the inner layer are shown in Table 6.

Formation-of an guter layer of an intermediate layer The inner layer-covered center obtained above was covered by injection molding with the resin composition for outer layer, of which ingredients were shown in Table 5. The thickness and JIS-C hardness of the inner layer are shown in Table 6.

Formation of a cover On the outer layer-covered center, a resin composition for cover was covered by injection molding and then painted thereon to obtain a four piece solid golf ball. The ingredients of the resin composition are shown in Table 5. The shore D hardness of the cover is shown in Table 6.

Comparative Example 1 A golf ball was prepared as generally described in Examples 1 to 6, with the exception that the intermeidate layer was not formed and the ingredients for the center, intermediate layer and cover were shown in Table 5

The resulting golf ball was subjected to evaluations in flight performance (i.e. launch angle, spin amount and flight distance) and shot feel and the results are shown in Table 6.

The evaluation methods are conducted as explained in Examples 1 to 6.

24 Table 5

12 Polyurethane thermoplastic elastomer, available from Takeda Virdish Co., Ltd.

13 Polyurethane thermoplastic elastomer, available from Japan Miractran Co., Ltd.

14 lonomer resin of ethyl ene-acrylic acid neutralized with zinc ion, having a melt index of 0.8, a flexural modulus of about 160 MPa Examples 1 Comp. Ex 13 14 15 16 1 17 1 Center BR-1 1 100 100 100 100 100 100 Zinc acrylate 18 21 24 21 21 24 Zinc oxide 5 5 5 5 5 24.5 Tungsten powder 31.9 31.1 28.8 28.8 28.8 - Antioxidant 0.5 0.5 0.5 0.5 0.5 0.5 Dicumyl peroxide 2.0 2.0 2.0 2.0 2.0 2.0 Diphenylclisulfide 0.5 0.5 0.5 0.5 0.5 0.5 Innerlayer Hi-milan 1606 50 50 50 50 50 Hi-milan 1706 50 50 50 50 50 Pandex T-7890N 6 100 Outer layer Extran ET 880 12 100 - - 100 100 Mixtran E 375 13 - 100 100 - - Cover Hi-milan 1605 50 50 50 50 Hi-milan 1706 50 - 50 50 50 IOTEC 7010 14 - 50 50 - IOTEC 8000 15 50 50 and a Shore D hardness of 57, available from Exxon Co.

lonomer resin of ethyl ene-acrylic acid neutralized with sodium ion, having a melt index of 0.8, a flexural modulus of about 370 MPa and a Shore D hardness of 57, available from Exxon Co.

Table 6

Examples Comp.

Ex.

13 14 15 16 17 1 Center Diameter (mm) 31.5 31.5 31.5 33.3 34.5 '35.3 JIS-C hardness 62 67 75 66 65 75 Innerlayer Thickness (mm) 1.8 1.8 1.8 1.0 1.0 1.85 JIS-C hardness 95 95 95 95 95 64 Outer layer Thickness (mm) 1.6 1.6 1.6 1.0 1.0 - JIS-C hardness 57 54 54 57 57 - Cover Thickness (mm) 2.2 2.2 2.2 1.7 2.0 2.3 Shore D hardness 71 72 72 71 71 71 Ball evaluation Launch angle 12.8 12.6 12.5 12.7 12.8 12.1 Spin amount (rpm) 2615 2645 2660 2605 2560 2730 Carry (yards) 204.2 203.5 202.8 203.8 202.5 200.3 Shot feel Good Good Good Good Good Good As is apparent from the above Examples, the four piece solid golf balls of the present invention exhibit long flight distance and excellent shot feel.

26

Claims

CLAIMS:

1. A four piece solid golf ball comprising:

a centre (1), an intermediate layer (5) having two layers consisting of an inner layer (2) and an outer layer (3) formed on the centre (1), and a cover (4) covering the intermediate layer (5), wherein the inner layer (2) and cover (4) are harder than the centre (1) and the outer layer (3) respectively, so that'the hardness distribution of the portions (1) to (4) is arranged soft-hard-soft-hard from the centre (1) to the cover (4), and wherein the centre (1) has a JIS-C hardness of from 50 to 80 and a diameter of from 30 to 35 mm, the inner layer (2) has a JIS-C hardness of from 70 to 100 and a thickness of from 0.5 to 2.5 mm, the outer layer (3) has a JIS-C hardness of from 40 to 80 and a thickness of from 0.5 to 2.5 mm and the cover (4) has a Shore D hardness of from 62 to 72 and a thickness of from 1.0 to 3.0 mm.

2. A four piece solid golf ball according to claim 1, wherein the centre (1) is formed from vulcanized rubber, the inner intermediate layer (2) is formed from thermoplastic resin, thermoplastic elastomer or a mixture of thermoplastic elastomer and thermoplastic resin, the outer intermediate layer (3) is formed from thermoplastic elastomer or a mixture of thermoplastic elastomer and thermoplastic resin, and the cover (4) is formed from thermoplastic resin.

3. A four piece solid golf ball according to claim 1 or claim 2, wherein the inner layer (2) has a thickness of from 1.0 to 1.8 mm.

4. A four piece solid golf ball according to any one of the preceding claims, wherein the outer layer (3) has a Shore D hardness of from 54 to 57.

5. A four piece solid golf ball according to any one of the preceding claims, wherein the inner layer (2) is harder than the centre (1) by from 15 to 35 in JIS-C hardness.

6. A four piece solid golf ball according to claim 5, wherein the outer layer (3) is softer than the inner layer (2) by from 10 to 50 in JIS-C hardness.

7. A method of making a four piece solid golf ball as defined in any one of claims 1 to 6, the method comprising the steps of:

(i) providing a centre (1); (ii) forming an intermediate layer (5) on the centre (1), wherein the intermediate layer (5) has an inner layer (2) and an outer layer (3); and (iii) covering the intermediate layer (5) covered centre (1) from step (ii) with a cover (4), wherein the inner layer (2) and cover (4) are harder than the centre (1) and the outer layer (3) respectively, so that the hardness distribution of the portions (1) to (4) is arranged soft-hard-soft-hard from the centre (1) to the cover (4), and wherein the centre (1) has a JIS-C hardness of from 50 to 80 and a diameter of from 30 to 35 mm, the inner layer (2) has a JIS-C hardness of from 70 to 100 and a thickness of from 0.5 to 2.5 mm, the outer layer (3) has a JIS-C hardness of from 40 to 80 and a thickness of from 0.5 to 2.5 mm and the cover (4) has a Shore D hardness of from 62 to 72 and a thickness of from 1.0 to 3.0 mm.

8. A four piece solid golf ball substantially as hereinbefore described with reference to any one of Examples 1 to 17.

9. A four piece solid golf ball substantially as hereinbefore described with reference to or as illustrated in Figure 1.