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Golf ball material and golf ball

Golf ball material and golf ball description/claims

The present invention relates to golf ball materials which have good thermal stability, flow characteristics and moldability, and which are capable of providing high-performance golf balls endowed with outstanding rebound energy. The invention relates also to golf balls made with such golf ball materials.

Over the past few years, wide use has been made of ionomer resins in golf ball cover materials, also referred to hereinafter as “cover stock”. Ionomer resins are ionic copolymers composed of an olefin such as ethylene in combination with an unsaturated carboxylic acid such as acrylic acid, methacrylic acid or maleic acid, wherein the acidic groups are partially neutralized with metal ions such as sodium, lithium, zinc or magnesium ions. They have excellent characteristics such as durability, resilience and scuff resistance.

Ionomer resins account for most of the cover stock resin in current use. A variety of improvements have been made thereon because golfers are always on the lookout for golf balls having a high rebound and excellent flight characteristics.

Related improvements taught by the prior art (see U.S. Pat. No. 5,312,857, U.S. Pat. No. 5,306,760, and International Application WO 98/46671) include cover stock in which a large amount of metallic soap is added to the ionomer resin to improve the cost and rebound characteristics of the ionomer cover stock.

These cover stocks, however, fall far short of practical levels. During injection molding, the metallic soap in the cover stock decomposes and vaporizes to generate a large amount of fatty acid gas, often causing molding defects. In addition, gas constituents settle on the surface of the molded part to considerably lower the paintability thereof. Moreover, although such cover stock in which a large amount of metallic soap has been added to the ionomer resin does exhibit a rebound which is about the same as or better than that of metallic soap-free ionomer cover stock having the same degree of hardness, the improvement in rebound is not all that large. Indeed, depending on the type of metallic soap used, the moldability and rebound of cover stock may in fact be severely compromised.

Therefore, one object of the invention is to provide golf ball materials which have good thermal stability, flow and moldability, and which are capable of producing golf balls with outstanding rebound. Another object of the invention is to provide golf balls made using such golf ball materials.

Quite unexpectedly, it has been found that a mixture having good thermal stability, flow and moldability is obtained when 100 parts by weight of a base resin having (a) an olefin-unsaturated carboxylic acid binary random copolymer and/or a metal ion-neutralized olefin-unsaturated carboxylic acid binary random copolymer blended with (b) an olefin-unsaturated carboxylic acid-unsaturated carboxylate ternary random copolymer and/or a metal ion-neutralized olefin-unsaturated carboxylic acid-unsaturated carboxylate ternary random copolymer in a weight ratio of 0:100 to 30:70 is blended with (c) 5 to 80 parts by weight of a fatty acid and/or fatty acid derivative having a molecular weight of 280 to 1,500 and (d) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acidic groups left unneutralized in the base resin and component (c). The mixture is suitable for molding and a molded part thereof exhibits improved rebound characteristics.

The molded part of the above-described golf ball material can form any desired constituent component of a golf ball (which is selected from among a one-piece golf ball, solid core, solid center, cover and other components).

The golf ball thus constructed has very good rebound and improved initial velocity performance. The invention is predicated on these findings.

According to the invention, there is provided a golf ball material comprising a mixture which is composed of essential components:

100 parts by weight of a base resin having (a) an olef-in-unsaturated carboxylic acid binary random copolymer and/or a metal ion-neutralized olefin-unsaturated carboxylic acid binary random copolymer, blended with (b) an olefin-unsaturated carboxylic acid-unsaturated carboxylate ternary random copolymer and/or a metal ion-neutralized olefin-unsaturated carboxylic acid-unsaturated carboxylate ternary random copolymer in a weight ratio of 0:100 to 30:70,

(c) 5 to 80 parts by weight of a fatty acid and/or fatty acid derivative having a molecular weight of 280 to 1,500; and

(d) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing acidic groups left unneutralized in the base resin and component (c).

In a preferred embodiment, the mixture when molded has a Shore D hardness of 30 to 60; the mixture has a melt index of 0.5 to 20 dg/min.; the metal ion-neutralized random copolymer in the base resin includes a zinc ion-neutralized ionomer resin. The total content of random copolymers and the total content of metal ion-neutralized random copolymers in the base resin are preferably in a weight ratio of 0:100 to 60:40. Component (c) is typically selected from among stearic acid, behenic acid, arachidic acid, lignoceric acid and derivatives thereof. Typically, component (d) is calcium hydroxide.

In another aspect, the invention provides a golf ball comprising a molded part of the golf ball material set forth above as a constituent component.

The golf ball material of the invention contains as an essential component a base resin having (a) an olefin-unsaturated carboxylic acid binary random copolymer and/or a metal ion-neutralized olefin-unsaturated carboxylic acid binary random copolymer blended with (b) an olefin-unsaturated carboxylic acid-unsaturated carboxylate ternary random copolymer and/or a metal ion-neutralized olefin-unsaturated carboxylic acid-unsaturated carboxylate ternary random copolymer in a specific weight ratio.

In the base resin, the olefin, whether it belongs to component (a) or (b), generally has at least 2 carbon atoms, but not more than 8 carbon atoms, and preferably not more than 6 carbon atoms. Illustrative examples include ethylene, propylene, butene, pentene, hexene, heptene and octene. Ethylene is especially preferred.

Suitable examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid and fumaric acid. Of these, acrylic acid and methacrylic acid are especially preferred.

• Provisional Patent
• Utility Patent

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