GB2168069A - Golf balls and cores - Google Patents

Abstract

A composition suitable for preparing a golf ball core, comprises: an elastomer cross-linkable by a free radical initiator catalyst or any other suitable catalyst; a metal salt or ester of an alpha, beta ethylenically unsaturated monocarboxylic acid compound, or any mixture thereof; a free radical initiator catalyst or any other suitable catalyst, for cross-linking said elastomer and said metal salt or ester compound, and a polyfunctional isocyanate optionally having 3 to 30 carbon atoms. he polyfunctional isocyanate enables an increase in coefficient of restitution of a golf ball comprising a core made from such composition to be obtained.

Description

SPECIFICATION Golf balls and cores This invention relates to a composition for preparing a golf ball core; a golf ball core corresponding to the ingredients of a said composition; and a golf ball comprising a said core and a cover.

Two-piece golf balls comprising a molded resilient core and a cover are now widely available. They have a peroxide cross-linked, mixed polybutadiene-metal acrylate molded core and a separately molded cover typically comprising an ionomer resin such as the type sold by E.I. Dupont de Nemours Company under the trademark SURLYN. The balls are extremely popular because they can be manufactured to be substantially cutproof, and to travel further when hit than any other type of commercially available USGA regulation golf ball. The distance a ball will travel when hit (hereinafter called "distance") is a function of many factors including angle of trajectory and clubhead speed. Among the factors of concern to manufacturers which affect distance are the coefficient of restitution of the ball, and the ball's surface configuration, e.g. dimple pattern.Coefficient of restitution is a measurement familiar to those skilled in the golf ball art. One way to measure the coefficient of restitution is to propel a ball at a given speed against a hard massive surface, and measure its incoming and outgoing velocity electronically. The coefficient of restitution is the ratio of the outgoing velocity to incoming velocity.

The coefficient of restitution in solid core balls is a function of the composition of the molded core and of the cover. In so-called three-piece balls comprising a liquid or solid core, elastic thread windings, and a cover, the coefficient of restitution of the core is a function primarily of the composition of the elastomeric thread windings and core, and the winding tension.

Those seeking to increase the coefficient of restitution of golf balls are effectively restrained by the United States Golfers Association regulations which mandate that a "regulation" ball cannot have an initial velocity in excess of 255 feet per second (77.72 metres per second). All other things being equal, as the coefficient of restitution of a ball is increased, the ball's initial velocity will also increase.

U.S. Patent No. 3,819,768 issued to R.P. Molitor discloses that the coefficient of restitution of golf balls having any given core can be increased significantly by applying to the core a cover material comprising a blend of a sodium neutralized ionomer resin with a zinc neutralized ionomer resin. Over the years, distance in two-piece golf balls has been steadily improved by virtue of the development of embodiments of the Molitor invention which give further increases in coefficient of restitution, and the development of improved molded cores.

Cores suitable for use in manufacturing two-piece balls are disclosed in U.S. Patent Nos. 4,264,075; 4,169,599; 4,165,877; and 4,141,559. Currently it is believed that the highest coefficient of restitution molded cores comprise a high cis content polybutadiene and a zinc salt of an alpha beta ethylenically unsaturated monocarboxylic acid (e.g., zinc di or mono acrylate or methacrylate) cured with conventional free radical initiator-type peroxide catalysts.

In accordance with the present invention, it has now been discovered that the addition of polyfunctional isocyanates (preferably diisocyanates having 3 to 30 carbon atoms) in e.g. a small amount to what otherwise may be a conventional core composition of the type described above can significantly increase the coefficient of restitution of the resulting core. Golf ball cores according to the present invention have an increased coefficient of restitution relative to identical cores made in the absence of the isocyanate. The golf ball cores can have a coefficient of restitution in excess of e.g. substantially 0.75, for instance in excess of 0.78. For cores from some production lots, one example of an average coefficient of restitution is 0.803 + 0.005 measured with an incoming velocity of 125 ft/sec (38.1 metres/sec).The present invention permits a golf ball manufacturer to approach more closely the USGA initial velocity limit, even without the increase in the coefficient of restitution that can be obtained using the cover composition disclosed in the above-referenced Molitor patent.

The core composition in the present invention enables the corresponding golf ball to have greater distance.

Furthermore, the present invention provides a core for a two piece golf ball, which core may be used together with relatively low resilience cover material while still achieving a golf ball coefficient of restitution and associated initial velocity closely approaching the USGA limit.

A first aspect of the present invention provides a composition suitable for preparing a golf ball core, said composition comprising: an elastomer cross-linkable by a free radical initiator catalyst or any other suitable catalyst; a metal salt ar ester of an alpha, beta ethylenically unsaturated monocarboxylic acid compound, or any mixture thereof; a free radical initiator catalyst or any other suitable catalyst, for cross-linking said elastomer and said metal salt or ester; and a polyfunctional isocyanate optionally having 3 to 30 carbon atoms.

A second aspect of the present invention provides a core for a golf ball, wherein said core comprises a core corresponding to the ingredients of a composition of the first aspect of the present invention.

A third aspect of the present invention provides a golf ball, comprising: a core of the second aspect of the present invention; and a cover for said core.

Preferably, a said composition of the first aspect of the present invention comprises per 100 parts by weight of said elastomer: 20 to 50 parts by weight of said salt or ester; 1 to 10 parts by weight of said catalyst; and 0.01 to 10.0 parts by weight of said isocynate.

Preferably, said elastomer in the present invention comprises a polybutadiene, preferably a polybutadiene elastomer comprising a high cis content of or as much cis polybutadiene as possible.

Preferably, said metal salt or ester comprises zinc monoacrylate, zinc diacrylate, zinc monomethacrylate, zinc dimethacrylate, or any mixture chosen therefrom.

Preferably, said free radical initiator catalyst comprises a rubber curing peroxide. Preferably said free radical initiator catalyst comprises n butyl 4,4' - bis (butylperoxy) valerate; dicumyl peroxide; 1,1 - bis (tbutylperoxy)-3,3,5 - trimethylcyclohexane; di-t-butyl peroxide; 2,5 - di (t-butylperoxy) - 2,5 - dimethyl hexane; or any mixture chosen therefrom. n-Butyl 4,4'-bis (butylperoxy) valerate is most preferred.

Preferably, said polyfunctional isocyanate comprises a diisocyanate. However, the isocyaflate may have more than 2 isocyanate groups. Preferably, said diisocyanate comprises trimethylene diisocyanate; propylene-1 ,2 diisocyanate; tetramethylene diisocyanate; butylene-1,3 diisocyanate; decamethylene diisocyanate; octadecamethylene diisocyanate; 1 propylene-1,2- diisocyanate; 3butylene-1,2 diisocyanate; 1-butylene-1,3 diisocyanate; 1-butylene-2,3 diisocyanate; ethylidene diisocyanate; propylidene-1 ,1 -diisocyanate; propylidene 2,2-diisocyanate; cyclopentylene-1,3 diisocyanate; cyclohexylene-1,2 dissocyanate; cyclohexylene 1,3-diisocyanate; cyclohexylene-1 ,4-diisocyanate; cyclopentylidene diisocyanate; cyclohexyfidene diisocyanate; m-phenylene diisocyanate; o-phenylene diisocyanate; p-phenylene diisocyanate; 1 methyl -2,4 phenylene diisocyanate; naphthalene-1 ,4-diisocyanate; diphenylene-4,4' diisocyanate; 3,4-tolylene diisocyanate; 2,6-tolylene diisocyanate; 4,4' diphenylmethane diisocyanate; 1,5 naphthalene diisocyanate; 2,2 propylene-bis- (4-phenylisocyanate); propylene-bis-(4-phenylisocyanate); xylylene 1,4 diisocyanate, xylylene 4,6 diisocyanate; 4-4'-di-phenylene methane diisocyanate; or any mixture chosen therefrom. 4,4'-Diphenylmethane diisocyanate is most preferred. The amount of a particular polyisocyanate which maximizes the coefficient of restitution of a particular composition should be determined empirically. Preferably, there are 0.1 to 10.0 parts by weight of polyisocyanate to 100 parts by weight of said elastomer.

A said composition of the first aspect of the present invention can comprise a low molecular weight fatty acid, e.g. comprising 10 to 40 carbon atoms, for instance stearic acid. Preferably, there is up to at most substantially 20 parts by weight of said fatty acid, when present.

A said composition of the first aspect of the present invention can comprise inorganic filler to increase the specific gravity of the core, e.g. inorganic filler comprising zinc oxide, barium sulphate, or any mixture chosen therefrom. At least a small amount of zinc oxide is preferred because it seems to have the effect of increasing the coefficient of restitution. Barytes is also convenient.

One convenient example of a said composition of the first aspect of the present invention comprises: substantially 100 parts by weight of said elastomer; substantially 36 parts by weight of said salt or ester; substantially 2 parts by weight of said peroxide catalyst; at least substantially 1 part by weight of said diisocyanate; and substantially 5 parts by weight of said fatty acid.

Those ingredients are preferably chosen from corresponding preferred ingredients mentioned herein.

Except for the addition of the polyfunctional isocyanate, the core composition and golf ball core of the present invention are manufactured using conventional techniques. Thus, the elastomer (preferably a polybutadiene elastomer comprising as much cis polybutadiene as possible) can be blended together with: (1) said salt or ester or any mixture thereof; (2) said catalyst; (3) said isocyanate; (4) said fatty acid; and (5) said inert filler- and see above options.

Preferably, all ingredients except the peroxide and the isocyanate are mixed and blended using conventional mixing equipment, and the peroxide and isocyanate are added while the temperature of the mixture is substantially 93.3"C (220"F). The blend is extruded to form slugs of a weight slightly greater than the weight of the cores to be produced, and then the slugs are compression molded to cure the composition.

The slugs are placed in the cavities of a two-part mold, which is closed to compress the elastomer composition, and then heated, for example, to over substantially 146.1"C (2950F). After curing the cores for 10 to 20 minutes, depending on the molding temperature, the mold is opened and the flashing is removed. A thin surface layer of the cores is then ground off to produce a core of the size required. The flash removed from the centre may be ground to a fine particle size and added to the core formulation.

Although the reaction which takes place is not well understood, it is believed that there is formed a complex network of cross-links between the unsaturated components of the blend formed. Also, a small amount of zinc oxide may react in some way. Isocyanate groups react primarily with amine or hydroxyl groups. However, isocyanates are known to be reactive with carboxylic acids, with liberation of carbon dioxide. While it may be that some trace of free carboxylic acid is present in the blend as an impurity in association with the metal carboxylic acid salt or ester, no gas liberation has been observed during the curing process, and no theoretical explanation for the beneficial effects of the isocyanate is available.

Optionally, the core may be dipped in a solution of an adhesive, e.g., an epoxy-based adhesive, prior to injection or compression molding a cover.

The covers molded about the cores can comprise balata or blends of balata with other elastomeric or thermoplastic materials, various ionomers of the type known to those skilled in the art or blends thereof, and various resilient compositions such as are disclosed in U.S. patent Nos. 3,359,231, 4,398,000, 4,234,184, 4,295,652, 4,248,432, 3,989,516, 3,310,102, 4,337,947, 4,123,061 and 3,490,146. If it is desired further to increase the coefficient of restitution of the golf ball, a cover embodying the invention disclosed in U.S.

3,819,768 may be used. The currently preferred cover for use on the golf ball imparts to the ball short iron and other playability characteristics comparable to balata-covered wound balls. That cover is disclosed in detail in copending U.K. patent application No. (P.2304), the disclosure of which is incorporated herein by reference. Briefly, that cover comprises a blend of a thermoplastic urethane having a Shore A hardness less than 95, and an ionomer material such as those disclosed in U.S. Patent No. 3,264,272 and sold by E.l.

Dupont de Nemours Company under the trademark SURLYN having a Shore D hardness greater than 55 at a weight ratio sufficient to produce a cover having a Shore C hardness within the range of 70 to 85.

The elastomer, said salt or ester, said catalyst, and said polyfunctional isocyanate are all necessary to achieve the increased coefficient of restitution of cores in the present invention. However, other materials may be included in the core. For example, low molecular weight fatty acids (e.g. 10 to 40 carbon atoms, for instance stearic acid) appear to have beneficial effects. High specific gravity fillers e.g. barium sulfate, lead oxide, or most preferably zinc oxide may be added to the core to increase the weight of the ball as desirable or as necessary to have the ball reach or closely approach the USGA weight limit of 1.620 ounce (45.93 gram). In addition, small amounts of ionomers of the type described previously, natural or synthetic rubbers, and other compatible elastomers may be used as diluents.It is also possible to add other crosslinking aids such as low molecular weight liquid polycarboxylic acid esters, e.g. trymethylolpropane trimethacrylate, ethylene glycol dimethacrylate, or 1,3 butylene glycol dimethacrylate. Also, coagents useful in peroxide curing may be used, e.g. N,N' m-phenylene dimaleimide.

Broadly, in preferred compositions, for each 100 parts by weight polybutadiene, the core composition of the invention can include 20 to 50 parts by weight of said salt or ester, 1 to 10 parts by weight of said peroxide, 0.01 to 10.0 parts by weight of said polyfunctional isocyanate, and 0 to 20 parts by weight of said fatty acid.

The ratios of ingredients may vary and are best optimized empirically. The amount of polyfunctional or polyvalent isocyanate used will vary depending on the particular monocarboxylic acid, peroxide, and elastomer employed, and the relative amounts used.

The invention will be further illustrated by the following non-limiting Examples: Examples Using the ingredients set forth below, golf ball cores having a finished size of 1.545 inch (3.93 cm) were manufactured by compression molding, and then grinding a surface layer off the molded cores. Each core was formulated using 100 parts by weight high cis content polybutadiene; 5 parts by weight zinc oxide, and 17.4 parts by weight ground flash. The amounts of the remaining ingredients used in the test cores (in parts by weight) and the coefficients of restitution and Riehle compression of the cores are set forth in the Table below.

TABLE 1 Effect of Polyfunctional Isocyanate On Golf Ball Cores Coefficient of Restitution Ingredient 1 1A 2 2A 3 3A 4 4A Stearic Acid 3.0 3.0 3.0 3.0 7.0 7.0 7.0 7.0 Zinc Diacrylate 38 38 38 38 38 38 38 38 Dicumyl Peroxide 3.0 3.0 4.0 4.0 3.0 3.0 4.0 4.0 Barium Sulfate 14.3 14.3 14.3 14.3 14.3 14.3 14.3 14.3 Diisocyanate 0 1.0 0 1.0 0 1.0 0 1.0 Compression 61 56 58 57 55 51 55 51 Coefficient 0.807 0.811 0.809 0.809 0.812 0.815 0.806 0.808 Ingredient 5 5A 6 6A 7 7A 8 8A Stearic Acid 3.0 3.0 3.0 3.0 7.0 7.0 7.0 7.0 Zinc Diacrylate 43 43 43 43 43 43 43 43 Dicumyl Peroxide 3.0 3.0 4.0 4.0 3.0 3.0 4.0 4.0 Barium Sulfate 11.3 11.3 11.3 11.3 11.3 11.3 11.3 11.3 Diisocyanate 0 1.0 0 1.0 0 1.0 0 1.0 Compression 53 49 52 48 50 46 47 47 Coefficient 0.808 0.813 0.805 0.807 0.811 0.815 0.808 0,811 As can be seen from the foregoing table, the inclusion of 1 part by weight (1% by weight based on weight of polybutadiene) polyfunctional isocyanate (4,4' diphenylmethane diisocyanate) generally has the effect of hardening the core (decreases compression values) and increasing coefficient of restitution.

The present invention includes equivalents and modifications within the scope of the above disclosures and/or of the appended claims. A molded spherical core is preferred.

Claims (24)

1. A composition suitable for preparing a golf ball core, said composition comprising: an elastomer cross-linkable by a free radical initiator catalyst or any other suitable catalyst: a metal salt or ester of an alpha, beta ethylenically unsaturated monocarboxylic acid compound, or any mixture thereof; a free radical initiator catalyst or any other suitable catalyst, for cross-linking said elastomer and said metal salt or ester compound; and a polyfunctional isocyanate optionally having 3 to 30 carbon atoms.

2. A composition as claimed in claim 1, wherein said composition comprises per 100 parts by weight of said elastomer: 20 to 50 parts by weight of said salt or ester; 1 to 10 parts by weight of said catalyst; and 0.01 to 10.0 parts by weight of said isocyanate.

3. A composition as claimed in claim 1 or 2, wherein said elastomer comprises a polybutadiene.

4. A composition as claimed in any one of claims 1 to 3, wherein said metal salt comprises zinc diacrylate.

5. A composition as claimed in any one of claim 1 to 3, wherein said metal salt or ester comprises: zinc monoacrylate, zinc diacrylate, zinc monomethacrylate, zinc dimethacrylate, or any mixture chosen therefrom.

6. A composition as claimed in any one of claims 1 to 5, wherein there is a said free radical initiator catalyst.

7. A composition as claimed in claim 6, wherein said free radical initiator catalyst comprises a rubber curing peroxide.

8. A composition as claimed in claim 6 or 7, wherein said free radical initiator catalyst comprises n butyl 4,4'-bis (butylperoxy) valerate.

9. A composition as claimed in claim 6 or 7, wherein said free radical initiator catalyst comprises n butyl 4,4'-bis (butylperoxy) valerate; dicumyl peroxide; 1,1 -bis (t-butylperoxy)-3,3,5-trimethylcyclohexa ne; di-tbutyl peroxide; 2,5-di(t-butylperoxy) -2,5-dimethyl hexane; or any mixture chosen therefrom.

10. A composition as claimed in any one of claims 1 to 9, wherein said isocyanate comprises a diisocyanate.

11. A composition as claimed in claim 10, wherein said isocyanate comprises 4,4' diphenylmethane diisocyanate.

12. A composition as claimed in claim 10, wherein said isocyanate comprises trimethylene diisocyanate; propylene-1,2 diisocyanate; tetramethylene diisocyanate; butylene-1,3 diisocyanate; decamethylene diisocyanate; octadecamethylene diisocyanate; 1 propylene-1 ,2-diisocyanate; 3-butylene-1,2 diisocyanate; 1butylene 1,3-diisocyanate; 1-butylene-2,3 diisocyanate; ethylidene diisocyanate; propylidene-1 ,1 -diisocyan- ate; propylidene 2,2-diisocyanate; cyclopentylene-1,3 diisocyanate; cyclohexylene-1,2 diisocyanate; cyclohexylene 1,3-diisocyanate; cyclohexylene-1 ,4-diisocyanate; cyclopentylidene diisocyanate; cyclohexylidene diisocyanate; m-phenylene diisocyanate; o-phenylene diisocyanate; p-phenylene diisocyanate; 1 methyl 2,4 phenylene diisocyanate; naphthalene-1,4-diisocyanate; diphenylene-4,4' diisocyanate; 3,4-tolylene diisocyanate; 2,6-tolylene diisocyanate; 4,4' diphenylmethane diisocyanate; 1,5 naphthalene diisocyanate; 2,2 propylene-bis (4-phenylisocyanate); propylene-bis-)4-phenylisocyanate); xylylene 1,4 diisocyanate; xylylene 4, 6 diisocyanate; 4,4'-diphenylene methane diisocyanate; or any mixture chosen therefrom.

13. A composition as claimed in any one of claims 1 to 12, comprising a low melocular weight fatty acid.

14. A composition as claimed in claim 13, wherein there is up to at most substantially 20 parts by weight of said fatty acid.

15. A composition as claimed in claim 13 or 14, wherein said fatty acid comprises stearic acid.

16. A composition as claimed in any one of claims 1 to 15, comprising inorganic filler.

17. A composition as claimed in claim 16, wherein said filler comprises zinc oxide, barium sulphate, lead oxide, or any mixture chosen therefrom.

18. A composition as claimed in claim 1, substantially as described in the Examples.

19. A core for a golf ball, wherein said core comprises a core corresponding to the ingredients of a composition as claimed in any one of claims 1 to 18.

20. A core as claimed in claim 1, which is a molded spherical core.

21. A core as claimed in claim 19 or 20, wherein said cre has a coefficient of restitution of at least substantially 0.75.

22. A core as claimed in claim 19, substantially as described in the Examples.

23. A golf ball comprising a core as claimed in any one of claims 19 to 22; and a cover for said core.

24. A golf ball as claimed in claim 23, wherein said cover comprises a blend of a thermoplastic urethane and an ionomer material.