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
2001-02-21
2002-05-07
Woodward, Ana (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S131000, C525S919000, C473S378000
Reexamination Certificate
active
06384135
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to cover stocks for golf balls having improved scuff resistance and golf balls having covers formed of the stocks.
2. Prior Art
In prior art golf balls, balata or trans-polyisoprene and ionomer resins are often used as the cover stock. Professional and skilled golfers prefer golf balls using balata as the cover stock, because the balata cover balls have good in feel upon full shots with a driver and the ease of control (or spin susceptibility) upon approach shots.
The balata cover balls, however, have the drawback that the ball surface is marred or fluffed as a consequence of iron shots because the cover surface can be scraped by grooves across the iron club face. In addition, balata cover stocks are expensive and low in productivity because of difficulty to mold and a need for vulcanization.
Efforts have been made to seek for cover stocks having good feel and controllability comparable to the balata while eliminating the drawbacks of the balata. For example, cover stocks using thermoplastic polyurethane elastomers as disclosed in U.S. Pat. Nos. 3,395,109, 4,248,432, and 4,442,282 are relatively inexpensive as compared with the balata and easy to mold. Golf balls using these cover stocks offer good feel and controllability comparable to the balata cover balls. However, covers of thermoplastic polyurethane elastomers are still unsatisfactory in scuff resistance upon iron shots. Particularly at low temperatures or in winter, there is a likelihood that the ball surface can be cracked and dimples be scraped off by the iron club face.
Additionally, in golf ball cover stocks, metals salts of fatty acids such as magnesium stearate are generally blended as a dispersant. In a conventional process involving injection molding a cover stock having a fatty acid metal salt blended therein around a core to form a cover and painting the surface of the cover, the left-over of the fatty acid metal salt on the cover surface can adversely affect the adhesion of a paint coating to the cover.
SUMMARY OF THE INVENTION
An object of the invention is to provide a novel and improved golf ball cover stock capable of producing a golf ball of improved performance that offers improved scuff resistance against iron shots, the ease of control upon approach shots, and a very soft feel without shocks upon driver shots. Another object of the invention is to provide a golf ball using the cover stock.
In search of a golf ball cover stock which can offer a pleasant feel and is improved in controllability and scuff resistance, the inventors found that a golf ball cover stock comprising as a main component a heated mixture of a thermoplastic polyurethane elastomer and a polyolefin oligomer or polyolefin which has been modified with functional groups is best suited for achieving the above and other objects.
More particularly, according to the invention, a heated mixture of (1) a thermoplastic polyurethane elastomer, especially a thermoplastic polyurethane elastomer having a Shore D hardness of 35 to 55 and comprising an aliphatic diisocyanate as the diisocyanate component and (2) a functional group-modified polyolefin oligomer or polyolefin which is expected to serve as a binder on account of the intermolecular interaction with polar groups (such as hydroxyl groups or urethane bonds) in the thermoplastic polyurethane elastomer, is used as the main component of the golf ball cover stock. Golf balls obtained by enclosing cores with this cover stock substantially solve the problem that as a consequence of iron shots, the cover surface can be scraped by grooves across the iron club face and the ball surface is marred or fluffed. Upon full shots with a driver, the balls offer a very soft feel without a shock and without a shortage of flight distance. Therefore, the cover stock of the above-described composition is significantly improved in function and effect over conventional cover stocks of thermoplastic polyurethane elastomers. Additionally, when a functional group-modified polyolefin oligomer with a relatively low molecular weight is used as component (2) of the heated mixture, the oligomer also serves as a dispersant for pigments and thus helps reduce the amount of a fatty acid metal salt (typically magnesium stearate) blended as the dispersant. The problem of poor adhesion of a paint coating caused by the presence of the fatty acid metal salt is thus substantially eliminated.
Accordingly, the present invention provides a golf ball cover stock comprising as a main component a heated mixture consisting essentially of a thermoplastic polyurethane elastomer and a polyolefin oligomer or polyolefin which has been modified with functional groups. Also contemplated herein is a golf ball comprising a core and a cover formed from the inventive cover stock.
DETAILED DESCRIPTION OF THE INVENTION
The cover stock for golf balls according to the invention uses as a main component a heated mixture of (1) a thermoplastic polyurethane elastomer and (2) a polyolefin oligomer or polyolefin which has been modified with functional groups.
The thermoplastic polyurethane elastomer (1) used herein has a molecular structure consisting of a polyol compound constituting a soft segment, a monomolecular chain extender constituting a hard segment, and a diisocyanate.
The polyol compound is not critical and may be any of polyester polyols, polyether polyols, copolyester polyols, and polycarbonate polyols. Exemplary polyester polyols include polycaprolactone glycol, poly(ethylene-1,4-adipate) glycol, and poly(butylene-1,4-adipate) glycol; an exemplary polyether polyol is polyoxytetramethylene glycol; an exemplary copolyester polyol is poly(diethylene glycol adipate) glycol; and an exemplary polycarbonate polyol is (hexanediol-1,6-carbonate) glycol. Their number average molecular weight is about 600 to 5,000, preferably about 1,000 to 3,000.
The diisocyanate may employ aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), tolidine diisocyanate (TODI), and naphthalene diisocyanate (NDI) are included although aliphatic diisocyanates are preferably used in consideration of the yellowing resistance of the cover. Examples of the aliphatic diisocyanate include hexamethylene diisocyanate (HDI), 2,2,4- or 2,4,4-trimethylhexamethylene diisocyanate (TMDI), and lysine diisocyanate (LDI). HDI is especially preferred for its compatibility with another resin upon blending.
The monomolecular chain extender is not critical and may be selected from conventional polyhydric alcohols and amines. Examples include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-propylene glycol, 1,6-hexylene glycol, 1,3-butylene glycol, dicyclohexylmethylmethanediamine (hydrogenated MDA), and isophoronediamine (IPDA).
For the thermoplastic polyurethane elastomers, those having a Shore D hardness of 35 to 55, especially 40 to 55 are preferred. With a Shore D hardness of less than 35, the ball would receive an increased spin rate and thus travel a short distance when hit with a driver. With a Shore D hardness of more than 55, the cover would be insufficiently soft and adversely affect the feel and control when hit. The specific gravity of the thermoplastic polyurethane elastomer is not critical and may be adjusted as appropriate insofar as the objects of the invention are achievable. Preferably the specific gravity is from 0.9 to 1.5, more preferably from 0.9 to 1.3, especially 1.0 to 1.2.
As the thermoplastic polyurethane elastomer, there may be used commercially available ones whose diisocyanate component is aliphatic, for example, Pandex T7298, EX7895, and T7890 (by Dai-Nippon Ink & Chemicals K.K.).
The second essential component of the cover stock according to the invention is (2-a) a polyolefin oligomer which has been modified with functional groups or (2-a) a polyolefin which has been modified with functional groups.
The modified polyolefin oligomers (2-a) usually have a number average molecular weight Mn of about 1,000 to 20,000, preferably about 1,500 to 17,000, more
Ichikawa Yasushi
Kashiwagi Shunichi
Takesue Rinya
Bridgestone Sports Co. Ltd.
Sughrue & Mion, PLLC
Woodward Ana
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