CA2147823A1 - Golf ball cover - Google Patents

Abstract

A cover material for a golf ball, produced by blending a sodium neutralized ionomer and a zinc neutralized ionomer, wherein each ionomer has 15.5 to 19.5% by weight carboxylic acid. Golf balls using this cover material exhibit superior coefficient of restitution and initial velocity properties as compared to individual non-blended ionomers and prior art blends.

Description

GOLF BALL COVER
BACKGROUND OF THE INVENTION
This lnvention relates in general to golf balls and, more partlcularly, to a golf ball havlng an improved cover material.
Golf balls having cover compositlons which comprise a copolymer of an olefin and at least one unsaturated monocarboxylic acid are known in the art. The cover material compositions are sold under the trademark "Surlyn" by the E.
I. du Pont de Nemours Company, Wilmington, Delaware and have been very successful. Their success lles in part to the fact that the resulting covers are extremely cut and abrasion resistant. Balls made from Surlyn polymers have achieved widespread consumer acceptance on a worldwide basis.
Moreover, the properties of a SURLYN cover material can be controlled and varied to produce golf balls having different playing characterlstlcs and propertles whlch may be controlled and varled in hardness, cut resistance, shear resistance and resillence. These propertles can be varled by selection of suitable ethylene-methacrylic acid ratios, degree of neutralization and the particular metal lon employed.
While being extremely advantageous from a cut resistance point of view, the prior art golf balls have short comings in that they do not have optimal coefficient of restitution (COR) properties or initial velocity properties.
It is noted that the coefficient of restitution can be directly related to the distance which a golf ball can be 21~7823 driven, and initial velocity properties relate to maximizing flight distance.
These polymers have been produced with various physical properties to overcome the negative factors once associated with them. One solution was the use of neutralization with ionomers in an attempt to produce optimal physical properties.
Typically, for golf ball covers, there are two kinds of ionomer resins that are used commercially. One is an ionomer resin in which carboxyl groups are neutralized with sodium (hereinafter sodium neutralized ionomer resin) and the other is an ionomer resin in which carboxyl groups are neutralized with zinc (hereinafter zinc neutralized ionomer resin). It has been found that the sodium neutralized ionomer resin is superior in impact resistance to the zinc neutralized one, but is inferior in low temperature durability.
U.S. Pat. No. 4,911,451 to Sullivan et al teaches the use of blends of an ethylene-acrylic acid copolymer neutralized with a sodium ion and of an ethylene-acrylic acid copolymer neutralized with a zinc ion to produce a golf ball cover.
U.S. Pat. No. 3,819,768 shows a golf ball cover of mixtures of ionic copolymers of olefins and unsaturated monocarboxylic acid salts, such as a mixture of sodium and zinc salts of the copolymers.
Mixtures of these two neutralized ionomer resins have not been found to overcome the problems in physical properties of the resulting covers made from either resin alone.
U.S. Pat. No. 4,984,804 describes a golf ball cover material prepared by mixing three ionomer resins in specific amount ratios. The three ionomer resins are a sodium neutralized ionomer resin, a zinc or magnesium neutralized ionomer resin and a sodium and zinc or magnesium neutrallzed ionomer resln. As descrlbed in that reference, the cover material blend wlll be a sodlum/sodlumfzinc blend of ionomer reslns or a sodlum/sodlum/magneslum blend. All physlcal properties of a cover produced from this blend are not optlmlzed.
Accordlngly, lt ls an object of the present lnventlon to provlde a golf ball havlng a synthetlc cover materlal.
Another ob~ect of the present lnventlon ls to provlde an lmproved synthetlc cover materlal for a golf ball.
It ls another ob~ect of the present lnventlon to provlde a golf ball havlng a synthetlc cover materlal that achleves the click, feel, playability and flight performance qualities of high performance golf balls.
A further object of the present invention is to provlde a golf ball havlng a cover materlal that has lmproved process manufacturlng as well as durabllity and resillence.
SUMMARY OF THE INVENTION
The present lnvention is a cover material for a hlgh performance golf ball. The cover materlal ls a speciflc blend of a sodlum neutrallzed lonomer and a zlnc neutralized 21~7823 ionomer, wherein each ionomer has 15.5 to 19.5% by weight carboxylic acid. Golf balls utilizing this cover material have been found to have superior coefficient of restitution and initial velocity properties as compared to individual non-blended ionomers and prior art blends.
These and other objects and features of the present invention will be apparent from a reading of the following detailed description of the invention, taken along with the figure.
BRIEF DESCRIPTION OF THE DRAWINGS
The figure illustrates the increased C.O.R./initial velocity and significant synergy over expected values for balls produced according to the concepts of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates generally to golf balls having an improved cover material. The improved cover material is produced by blending a zinc ionomer and a sodium ionomer, each ionomer containing 15.5 to 19.5~ carboxylic acid.
For the purposes of the present invention, the term "sodium ionomer" shall be defined as a copolymer having 80.5-84.5% of an olefin, and 15.5-19.5% by weight of an a, ~
ethylenically unsaturated carboxylic acid, with 10-90% of the carboxylic acid groups being neutralized with sodium metal ions. The sodium ionomer shall have a melt index of 0.5-5.0 g/10 min, Shore "D" hardness of 65 or greater, and a flexural modulus of 40,000-80,000 psi.

21~7~2~

In addition, the term "zinc ionomer" shall be defined as a copolymer having 80.5-84.5% of an olefin, and 15.5-19.5% by weight of an a, ~ ethylenically unsaturated carboxyllc acid, with 10-gO% of the carboxylic acid groups being neutralized with zinc metal ions. The zinc ionomer shall have a melt index of 0.5-5.0 g/10 min, Shore "D"
hardness of 60 or greater, and a flexural modulus of 30,000-60,000 psi.
In a preferred embodiment of the present invention, the olefin shall be ethylene and the carboxylic acid shall be acrylic acid, methacrylic acid and mixtures of acrylic and methacrylic acid.
A cover material for a golf ball, according to a preferred embodiment of the present invention, shall include:
a) 25-75% of a sodium ionomer, having 80.5-81.5% by weight of ethylene, and 18.5-19.5% by weight of a carboxylic acid, 10-90% of which is neutralized with sodium ions, the ionomer having a melt index of 0.5-5.0 gtlO min, Shore D harness of 65 or greater, and a flexural modulus of 40,000-80,000 psi.
b) 75-25% of a zinc ionomer, having 80.5-81.5% by weight of ethylene, and 18.5-19.5% by weight of a carboxylic acid, 10-90% of which is neutralized with zinc ions, the zinc ionomer having a melt index of 0.5-5.0 g/10 min, Shore D hardness of 60 or greater, and a flexural modulus of 30,000-60,000 psi.
Examples of ionomers useful in the present invention are listed below:

Ion % Flexural Shore Material TY~e Acid Modulus _ M.I
Surlyn AD 8444 Na 19 70,000 psi 70 2.4 g/10 min Surlyn AD 8195 Zn 19 40,000 pSi 66 1.0 g/10 min Surlyn 8940 Na 15 51,000 psi 65 2.8 g/10 min Surlyn 9910 Zn 15 48,000 psi ,~64 0.7 g/10 min -Flexural Modulus - using test methods according to ASTM D-790 -Shore D - using test methods according to ASTM D-2240 -Melt Index - using test methods according to D-1238 It may be desirable for the cover material of the present invention to include various additives, such as pigments, lubricants, a UV absorber, dyes, fillers, stabilizers and the like. Colorants are often used.
Typically, the colorant will consist of titanium dioxide, ultramarine blue, ultramarine violet and an ionomeric carrier.
A suitable colorant is available from AMERICHEM Inc. of Cuyahuga, Ohio. If used, the additives will generally be present in the composition in an amount up to 5 parts per hundred polymer (p.h.p.) of the composition.
The blends are made and produced into a golf ball cover by processes known in the art for producing golf ball covers, processes such as extrusion molding or injection molding. It is within the skill of those in the field to produce a material for a golf ball cover from the components of the present invention.
The present invention will be described by way of the following examples, which are provided for illustration, but are not to be considered as limiting.

Example ~

Haterial 1 2 3 4 5 6 7 8 Surlyn 25 33 50 67 75 100 Surlyn 75 67 50 33 25 100 Surlyn 50 Surlyn 50 Americhem 5 5 5 5 5 5 5 5 R1 cc Weight 45.57 45.43 45.45 45.35 45.3345.30 45.25 45.02 (a) PGA Com- 100 101 101 100 100 99 90 94 pression (b) Shore D 69 70 71 70 70 69 66 67 ( c ) Rebound 79.3 79.8 79.7 79.5 79.3 78.6 76.8 78.1 (d) C.O.R. 0.740 0.740 0.741 0.738 0.7380.734 0.715 0.727 (e) Initial 254.1 254.7 254.9 254.5 254.3253.9 251.5 253.2 Velocity (f) Cold 10+ 10+ 10+ 10+ 10+ 2 3 7 Pound (a) Weight = grams (b) PGA measures deformation under a fixed static load of 200 lbs.
(c) Shore D Hardness, ASTM 2240 (d) Rebound = inches from a 100-inch drop test (e) COR = coefficient of restitution = rebound velocity/
forward velocity (f) Initial Velocity = feet/second Examples 1-5 list blends which fall within the range of the principles of the present invention. It is evident 21~7823 that C.O.R. and initial velocity properties are greatly enhanced with the blends incorporatlng a zlnc lonomer and sodium ionomer each having 15.5 to 19.5% acid values.
For purposes of the present lnventlon, low temperature durabllity ls tested wlth an impact tester, as known ln the art. Low Temperature Durablllty ls determlned ln a cold pound test, ln whlch slx (6) balls are condltloned to -20F for 24 hours and placed at the lmpact tester to hlt once. If the ball does not spllt or crack, lt was returned to the freezer and hlt agaln after 24 hours. This cycle was repeated for up to 10 days or 10 hlts.
Golf balls are typically deslgned to yleld PGA
compresslon values of over 120 to attaln lnltlal veloclty that will approach 255 feet/sec., the maximum value allowed by the U.S.G.A.. The preferred range of PGA compresslon ls 90 to 110, so as to get the benefit of the sensation during club and ball impact by the player. The present invention offers the range of PGA compression that will provide a soft feel to the golfer, and still maximize the inltial velocity that ls very important in providlng the maximum flight distance performances of the golf ball.
Examples 6 and 7 are provided to compare the physical properties of cover materlal formulatlons uslng a slngle ionomer (example 6, zinc, and example 7, sodlum) havlng a 19%
acld level. Balls prepared wlth cover formulatlons as described in Examples 6 and 7 are known ln the art. Blends produced according to the present invention show lncreased COR
and initial veloclty values over the single ionomer 2I47~23 formulations. Those improved physical properties are evident from a review of the figure, wherein the expected linear prediction is surpassed with the actual blends as described in the present invention.
Example 8 is provided to compare the physical properties of a cover material formulation incorporating a sodium/zinc ionomer blend, having 15% acid known in the art, with the blends according to the present invention. Again, the blends according to the present invention show significant improvement in COR and initial velocity parameters.
The compositions of the present invention produce a cover for a golf ball that is cost effective to produce, and yet yields superior playability and flight performance qualities as compared to known formulations of golf balls having synthetic covers.
It will be appreciated that the instant specification and claims are set forth by way of illustration and not limitation and that various changes and modifications may be made without departing from the spirit and scope of the present invention.

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Claims (9)

1. A golf ball having a cover, wherein the cover comprises:
25-75% of a sodium ionomer, said sodium ionomer having 80.5 to 84.5% of an olefin and 15.5 to 19.5% by weight of an .alpha. .beta.
unsaturated carboxylic acid, with 10-90% of the carboxylic acid groups being neutralized with sodium metal ions; and 75-25% of a zinc ionomer, said zinc ionomer having 80.5 to 84.5% of an olefin and 15.5 to 19.5% by weight of an .alpha. .beta.
unsaturated carboxylic acid, with 10-90% of the carboxylic acid groups being neutralized with zinc metal ions.

2. The golf ball of claim 1 wherein in the sodium ionomer and zinc ionomer, the olefin comprises ethylene and the carboxylic acid is selected from the group consisting of acrylic acid, methacrylic acid and mixtures of acrylic and methacrylic acid.

3. The golf ball of claim 1 wherein in the cover, the sodium ionomer has a melt index of 0.5 to 5.0 g/10 min, Shore D hardness of 65 or greater and a flexural modulus of 40,000 to 80,000 psi.

4. The golf ball of claim 1 wherein in the cover, the zinc ionomer has a melt index of 0.5 to 5.0 g/10 min, Shore D hardness of 60 or greater and a flexural modulus of 30,000 to 60,000 psi.

5. The golf ball of claim 2, wherein the cover comprises 25 to 75% of a sodium ionomer, said sodium ionomer having 80.5 to 81.5% by weight ethylene and 18.5 to 19.5% by weight of a carboxylic acid, 10-90% of the carboxylic acid groups neutralized with sodium metal ions; and 75 to 25% of a zinc ionomer, said zinc ionomer having 80.5-81.5% by weight ethylene and 18.5 to 19.5% by weight of a carboxylic acid, 10-90% of the carboxylic acid groups neutralized with zinc metal ions.

6. The golf ball of claim 1 further comprising a colorant in amounts of up to 5 parts per hundred polymer.

7. The golf ball of claim 1, wherein the cover comprises:
33% of a sodium ionomer, said sodium ionomer having 80.5 to 84.5% of an olefin and 15.5 to 19.5% by weight of an .alpha. .beta.
unsaturated carboxylic acid, with 10-90% of the carboxylic acid groups being neutralized with sodium metal ions; and 67% of a zinc ionomer, said zinc ionomer having 80.5 to 84.5% of an olefin and 15.5 to 19.5% by weight of an .alpha. .beta.
unsaturated carboxylic acid, with 10-90% of the carboxylic acid groups being neutralized with zinc metal ions.

8. The golf ball of claim 1, wherein the cover comprises:
50% of a sodium ionomer, said sodium ionomer having 80.5 to 84.5% of an olefin and 15.5 to 19.5% by weight of an .alpha. .beta.
unsaturated carboxylic acid, with 10-90% of the carboxylic acid groups being neutralized with sodium metal ions; and 50% of a zinc ionomer, said zinc ionomer having 80.5 to 84.5% of an olefin and 15.5 to 19.5% by weight of an a ~
unsaturated carboxylic acid, with 10-90% of the carboxylic acid groups being neutralized with zinc metal ions.

9. The golf ball of claim 1, wherein the cover comprises:
67% of a sodium ionomer, said sodium ionomer having 80.5 to 84.5% of an olefin and 15.5 to 19.5% by weight of an .alpha. .beta.
unsaturated carboxylic acid, with 10-90% of the carboxylic acid groups being neutralized with sodium metal ions; and 33% of a zinc ionomer, said zinc ionomer having 80.5 to 84.5% of an olefin and 15.5 to 19.5% by weight of an .alpha. .beta.
unsaturated carboxylic acid, with 10-90% of the carboxylic acid groups being neutralized with zinc metal ions.