Games using tangible projectile – Golf – Ball
Reexamination Certificate
2000-08-31
2003-06-10
Sewell, Paul T. (Department: 3711)
Games using tangible projectile
Golf
Ball
C473S365000, C473S351000
Reexamination Certificate
active
06575850
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a golf ball which produces high spin and thus stops easily like a balata covered ball even when shot from a rough or in the rain, in other words, a golf ball which is superior in so-called controllability.
2. Description of the Background Art
Balata covered golf balls have widely been used generally by skilled and professional golfers because of excellent shot feeling and controllability. However, such balata covered golf balls are produced through complicated manufacturing steps and exhibit poor resistance to cutting. Then, various flexible covers are proposed these days as a substitute for the balata cover.
For example, U.S. Pat. No. 4,884,814 discloses a technique of using flexible ionomer resin as a base resin material for a cover.
Japanese Patent Laying-Open No. 10-179802 proposes a golf ball having a base resin material for a cover structured to have as a main component a heated mixture of two components, that is, ionomer resin and a styrene-butadiene-styrene block copolymer having a polybutadiene block containing epoxy group or a styrene-isoprene-styrene block copolymer having a polyisoprene block containing epoxy group. A cover composition constituting the cover has a flexural modulus of 50 to 300 MPa and a shore D hardness of 40 to 60.
Further, Japanese Patent Laying-Open No. 10-179801 proposes a golf ball having a base resin material for a cover that has as a main component a heated mixture of three components, that is, ionomer resin, acid-modified thermoplastic elastomer or thermoplastic elastomer having an OH group at the end of the polymer chain, and a styrene-butadiene-styrene block copolymer having a polybutadiene block containing epoxy group or a styrene-isoprene-styrene block copolymer having a polyisoprene block containing epoxy group. A cover composition constituting the cover has a flexural modulus of 50 to 300 MPa and a shore D hardness of 40 to 60.
These techniques achieve improvement in shot feeling, controllability and resistance to cutting, however, they are unsatisfactory in spin retention which is represented by a ratio of spin rate under a wet condition to spin rate under a dry condition.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a golfball exhibiting a high ratio of spin rate under a wet condition to spin rate under a dry condition, that is, a high spin retention.
A golf ball according to the present invention is formed of a core and a cover. The cover has a loss tangent (tan &dgr;) of 0.15 to 0.70 at −10° C. in a temperature distribution curve for dynamic viscoelasticity measured in a tensile mode under conditions that temperature increasing rate is 4° C./min, frequency is 10 Hz and initial strain is 1.0 mm.
Preferably, a base resin material of the cover is ionomer resin only, or structured by mixing ionomer resin and one or at least two of elastomer materials containing a rubber element, and mixing therewith 5 to 50 parts by weight of tackifier such as terpene resin and rosin ester resin.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Inventors of the present invention have found that the spin retention is enhanced in proportion to increase of a value of loss tangent (tan &dgr;) of a cover material measured at −10° C. The loss tangent generally refers to a characteristic concerning energy loss of a material. The smaller a value of the loss tangent, the smaller the energy loss and the higher the impact resilience. The loss tangent value is made small according to conventional techniques for the purpose of increasing the impact resilience. On the contrary, according to the present invention, the loss tangent value is set to fall in a range of relatively great values, that is, from at least 0.15 to less than 0.7, preferably from at least 0.25 to less than 0.5. Although the impact resilience slightly deteriorates due to the loss tangent set at 0.15 or more, the impact resilience of an entire golf ball is not significantly influenced by its cover. Therefore, according to the present invention, the influence of a core to the impact resilience is enhanced and accordingly degradation of the impact resilience of the entire golf ball is avoided.
If the loss tangent value is less than 0.15, the spin retention is insufficient. On the other hand, if the loss tangent value exceeds 0.7, the impact resilience and shot feeling are impaired.
Elastic modulus (E*) of the cover of the present invention can be set at a value preferably ranging from 300 to 5000 kg/cm
2
, more preferably 500 to 3000 kg/cm
2
, and most preferably 500 to 1500 kg/cm
2
in order to keep excellent controllability and shot feeling. For example, an elastic modulus exceeding 5000 kg/cm
2
, for example, produces hard shot feeling and controllability deteriorates (spin is not easily produced). If the elastic modulus is less than 300 kg/cm
2
, spin is readily produced and controllability is excellent while shot feeling is soft, a flight carry decreases, and the surface is prone to marring and durability deteriorates.
According to the present invention, the ionomer resin used as a base resin material for the cover is a binary copolymer, for example, of &agr;-olefin and &agr;,&bgr;-unsaturated carboxylic acid with 3 to 8 carbons, and at least a part of a carboxyl group thereof is neutralized by metallic ion. Another example of the ionomer resin as a base resin material for the cover is a ternary copolymer of &agr;-olefin, &agr;,&bgr;-unsaturated carboxylic acid with 3 to 8 carbons, and &agr;,&bgr;-unsaturated carboxylic acid ester with 2 to 22 carbons, and at least a part of a carboxyl group thereof is neutralized by metallic ion. If the base polymer of the ionomer resin is the binary copolymer of &agr;-olefin and &agr;,&bgr;-unsaturated carboxylic acid with 3 to 8 carbons, preferably &agr;-olefin is 80 to 90% by weight and &agr;,&bgr;-unsaturated carboxylic acid is 10 to 20% by weight. If the base polymer is the ternary copolymer of &agr;-olefin, &agr;,&bgr;-unsaturated carboxylic acid with 3 to 8 carbons, and &agr;,&bgr;-unsaturated carboxylic acid ester with 2 to 22 carbons, preferably &agr;-olefin is 70 to 85% by weight, &agr;,&bgr;-unsaturated carboxylic acid is 5 to 20% by weight, and &agr;,&bgr;-unsaturated carboxylic acid ester is 10 to 25% by weight. Preferably, melt index (MI) of these ionomer resin materials is 0.1 to 20 and more preferably 0.5 to 15.
As the &agr;-olefin mentioned above, ethylene, propylene, 1-butene, 1-pentene and the like, for example, are used, and particularly ethylene is preferred. As the &agr;,&bgr;-unsaturated carboxylic acid with 3 to 8 carbons, acrylic acid, methacrylic acid, fumaric acid, maleic acid, crotonic acid and the like, for example, are used and particularly acrylic acid and methacrylic acid are preferred. As the unsaturated carboxylic acid ester, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate and the like of fumaric acid, maleic acid, for example, are used, and particularly acrylic acid ester and methacrylic acid ester are preferred. As the metallic ion for neutralizing at least a part of the carboxyl group of the copolymer of &agr;-olefin and &agr;,&bgr;-unsaturated carboxylic acid, or the ternary copolymer of &agr;-olefin, &agr;,&bgr;-unsaturated carboxylic acid and &agr;,&bgr;-unsaturated carboxylic acid ester, for example, sodium ion, lithium ion, zinc ion, magnesium ion, potassium ion and the like are used. If the ionomer resin is a copolymer of ethylene and acrylic acid or methacrylic acid with a carboxyl group at least partially neutralized by metallic ion, preferably the ionomer resin has a melt index of 3 to 7 and a flexural modulus of 200 to 400 MPa and accordingly the ionomer resin is of highly rigid and high-flow type.
Specifically, the ionomer resin as described above
Hiraoka Hidenori
Iwami Satoshi
Kato Akira
Yokota Masatoshi
Birch & Stewart Kolasch & Birch, LLP
Hunter, Jr. Alvin A.
Sewell Paul T.
Sumitomo Rubber Industries Ltd.
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