Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-05-23
2003-11-25
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S074000, C525S090000, C525S091000, C525S09200D, C473S373000, C473S374000
Reexamination Certificate
active
06653402
ABSTRACT:
This invention relates to a golf ball manufactured using a resin composition which has flexibility, resilience, toughness, flexural fatigue resistance and tear strength, exhibits a sufficiently smooth flow in the melt to injection mold, and produces a delamination resistant molded part, the golf ball featuring increased distance, pleasant feel upon impact and improved durability.
BACKGROUND OF THE INVENTION
Polyester block copolymers comprising hard segments composed of crystalline aromatic polyester units such as polybutylene terephthalate units and soft segments composed of aliphatic polyether units such as poly(alkylene oxide) glycol and/or aliphatic polyester units such as polylactone have satisfactory mechanical properties including strength, impact resistance, elastic recovery and flexibility, as well as low- and high-temperature properties, and are thermoplastic and easy to mold. These copolymers are of great interest in the golf art as the ball-forming resin composition as disclosed in JP-A 7-24084.
Despite such satisfactory physical properties, polyester block copolymers tend to lower mechanical properties such as modulus of resilience, strength and impact resistance and low-temperature properties as their hardness increases. Further improvements in physical properties are desired in order to increase the distance of golf balls manufactured using these copolymers.
On the other hand, ionomer resins in the form of copolymers of &agr;-olefin with &agr;,&bgr;-unsaturated carboxylic acids, neutralized with mono- to trivalent metal ions, are thermoplastic and easy to mold. The ionomer resins are very tough and fully resistant to rupture even when undergoing substantial deformation at a high speed. This feature is very advantageous in improving the scuff resistance and durability against repetitive hits of golf balls. Because of this feature, ionomer resins have long been used as the cover stock for golf balls.
However, ionomer resins are short of flexibility, giving a hard feel upon impact. It was then proposed to use in the golf ball-forming resin composition, softened ionomer resins in the form of copolymers of &agr;-olefin, &agr;,&bgr;-unsaturated carboxylic acids, and &agr;,&bgr;-unsaturated carboxylic esters, neutralized with mono- to trivalent metal ions. The softened ionomer resins, however, are inferior in resilience and low-temperature properties. Improvements in these properties are thus desired.
A further attempt was made to prepare golf balls from resin compositions in which polyester block copolymers are mixed with ionomer resins to compensate for the drawbacks of the respective components. For example, JP-A 56-83367 and JP-A 62-275480 disclose golf balls using resin compositions comprising polyester block copolymers in admixture with ionomer resins. Since polyester block copolymers having flexibility and resilience are mixed with ionomer resins having toughness and modulus of resilience though lacking flexibility, the resulting mixtures make use of the advantages of the respective components and are effective for improving rebound performance.
However, since polyester block copolymers and ionomer resins are not so compatible when mixed together, the golf ball-forming resin compositions proposed in the above patent references have uneven morphology. They suffer from the problem that since the respective resins are readily oriented during injection molding, the molded parts are likely to delaminate and less durable against repetitive hits.
Attempts have been made to further ameliorate these resin compositions. For example, WO 92/12206 discloses that a resin composition comprising a polyester block copolymer, an ionomer resin and an epoxy-containing compound is useful to form the golf ball core. JP-A 9-176429 discloses a golf ball using a resin composition comprising a polyester block copolymer, an ionomer resin and an epoxidized diene block copolymer. Since the resin compositions in these two patent references are formulated so as to improve the compatibility between the polyester block copolymer and the ionomer resin, they are golf ball-forming resin compositions having improved delamination resistance, flexibility and modulus of resilience. The inclusion of such epoxy-containing copolymers, however, increases the melt viscosity of the resin compositions. A high viscosity is advantageous for extrusion molding and blow molding, but inadequate for injection molding. The resin compositions are thus rather disadvantageous in molding golf balls.
Moreover, JP-A 10-147690 discloses that a thermoplastic polymer composition comprising a polyester resin, an addition polymerization type block copolymer, a polyester block copolymer and an ionomer resin is useful to form the golf ball cover. This thermoplastic polymer composition is a hard material having a high tensile strength and flexural strength and a very high flexural rigidity, but not a material having flexibility and a high modulus of resilience like rubber. The durability against hits of the composition is insufficient as the golf ball cover. Therefore, the composition is far apart from the desired golf ball material.
As discussed above, a golf ball-forming resin composition has not been available thus far which has flexibility, resilience, toughness, flexural fatigue resistance and tear strength, exhibits a sufficiently smooth flow in the melt to injection mold, and produces a delamination resistant molded part.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a golf ball which is manufactured using a resin composition which has flexibility, high resilience, toughness, flexural fatigue resistance and tear strength, exhibits a sufficiently smooth flow in the melt to injection mold, and produces a delamination resistant molded part, so that the golf ball may offer increased distance, pleasant feel upon impact and improved durability.
It has been found that a resin composition capable of meeting the above requirements is obtained by blending specific amounts of (A) a polyester block copolymer, (B) an ionomer resin, (C) a copolymer and (D) an epoxy-modified graft polymer as essential components. Since the polyester block copolymer (A) and the ionomer resin (B) can be mixed in a well compatible manner, the composition exhibits a smooth flow when melted and is thus suited for injection molding. Both the advantages of the polyester block copolymer (A) including good mechanical properties such as strength, impact resistance, elastic recovery and flexibility and good low- and high-temperature properties, thermoplasticity and ease of molding, and the advantages of the ionomer resin (B) including thermoplasticity, ease of molding, toughness, and rupture resistance (even when undergoing a substantial deformation at a high speed) are combined in a good balance so that the composition is endowed with not only improved durability-related properties such as rupture strength and impact strength, but also rubbery properties such as adequate flexibility and high resilience. Molded parts of the composition are markedly improved in durability (e.g., flexural fatigue resistance) and tear strength, and unsusceptible to cleavage or delamination.
It has also been found that a golf ball comprising a hot molded part of the above resin composition as its constituent component is improved in distance, feel and durability. A multi-piece solid golf ball comprising an intermediate layer formed of the above resin composition is endowed with excellent properties of both components (A) and (B) so that the ball is improved in distance and feel and remains highly durable.
According to the invention, there is provided a golf ball comprising as a constituent component a hot molded part of a resin composition comprising
(A) 5 to 95% by weight of a polyester block copolymer comprising as main constituents (a1) high melting, crystalline polymer segments composed of crystalline aromatic polyester units and (a2) low melting polymer segments composed of aliphatic polyether units and/or aliphatic polyester units,
(B) 95 to 5% by wei
Furuta Yoko
Ichikawa Yasushi
Bridgestone Sports Co. Ltd.
Buttner David J.
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