Golf ball cover of neutralized poly(ethylene-acrylic acid) copolymer

An improved golf ball comprising a core and a cover therefor, said cover comprises singularly or blends of a zinc neutralized ethylene-acrylic acid copolymer and a sodium neutralized ethylene-acrylic acid copolymer, or a blend of two or more zinc-neutralized ethylene-acrylic acid copolymers and a sodium-neutralized ethylene acrylic acid copolymer.

This invention relates to golf balls. More particularly, this invention 
relates to an improved golf ball cover useful in producing golf balls, 
particularly two-piece golf balls, exhibiting superior playability 
characteristics. 
BACKGROUND OF THE INVENTION For many years balata and blends of balata with 
various elastomeric or plastic materials were the principal materials 
utilized in the manufacture of top quality golf balls. Balata and 
balata-containing cover compositions possess the desirable property of 
being readily adaptable to molding and, accordingly, can be easily 
compression molded about a spherical core to produce a high quality golf 
balls. 
The relative softness of the balata cover is particularly advantageous in 
that a relatively experienced golfer can apply a spin to a balata-covered 
ball to control the ball in flight to produce a draw or a fade, or a 
backspin to cause the ball to "bite" or stop abruptly on contact with the 
green. Such playability is particularly important in short iron play where 
accuracy overrides distance considerations, and is exploited significantly 
by the more highly skilled players. 
However, golf balls utilizing balata-based compositions as the covering are 
also quite susceptible to being cut easily if mis-hit and therefore such 
golf balls have a relatively short life span. 
Due to this negative property, balata and it's synthetic substitutes, 
trans-polybutadiene and trans-polyisoprene, have today been essentially 
replaced by new cover materials, primarily by a copolymer of ethylene and 
methacrylic acid, sold by E. I. DuPont de Nemours and Company under the 
trademark SURLYN. Neutralization of a number of the acidic functional 
groups, generally on the order of from about 18 to about 73 percent, is 
effected with metal ions, such as zinc or sodium, producing a 
thermoplastic which has several advantages over balata when employed as 
the cover material for golf balls. 
In addition to cost-saving and ready availability vis-a-vis balata, the 
properties of SURLYN may be controlled and varied to produce golf balls 
having different playing characteristics and properties which may be 
controlled and varied in hardness, cut resistance, shear resistance, and 
resilience. These properties can be varied by selection of suitable 
ethylene-methacrylic acid ratios, degree of neutralization and the 
particular metal ion employed. 
While the use of SURLYN salts of poly(ethylene-methacrylic acid) copolymers 
as golf ball covers has been a major factor in the production of two-piece 
balls which for all practical purposes cannot be cut in play and which 
travel further when hit than any other USGA regulation ball as measured by 
controlled tests, the coefficient of restitution exhibited is an extremely 
important factor, with increased values resulting in increased distances 
which the ball will travel. 
The golfing industry has therefor attempted for a numbers of years to 
develop a cover composition which possesses both the durability of the 
SURLYN salts of poly(ethylene-methacrylic copolymer) and increased 
coefficients of restitution. 
It is therefore an object of the present invention to provide a golf ball 
which is resistant to cutting during play and which exhibits a markedly 
elevated coefficient of restitution. 
It is another object of the invention to provide a golf ball which is 
longer, i.e., which does not have a distance shortcoming when struck with 
a golf club. 
A further object of the present invention is to provide a golf ball which 
exhibits a bright white coloration and which does not yellow upon aging. 
Still another object is to provide a golf ball cover composition which can 
be easily processed. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided a golf ball 
comprising a core and a cover, said cover comprises a ionomer which has 
from about 10 to about 90 percent by weight of a poly ethylene-acrylic 
acid copolymer characterized by containing about 11 percent by weight 
acrylic acid with about 40 percent of the carboxylic acid groups 
neutralized by sodium ions, and ionomers which are from about 90 to about 
10 percent by weight of at least one poly ethylene-acrylic acid 
characterized by containing from about 11 to 16 percent acrylic acid with 
from about 10 to about 40 percent of the carboxylic acid groups 
neutralized by zinc ions. Ionomers which are neutralized with lithium 
magnesium or other metal ions are also within the scope of this invention. 
Blends of ionomers as described above may also be used. The cover 
composition may further contain about 2.4 percent by weight of known 
additives, such as pigments, brightening agents and the like. 
Examples of ethylene-acrylic acid copolymers found suitable for use in 
accordance with this invention either singularly or as blends are ionomers 
produced by Exxon Chemical Company and sold under the trademark ESCOR as 
ESCOR 562, 900, 906, 4000 and 4200. 
ESCOR 562 is a zinc-neutralized copolymer of ethylene and acrylic acid 
containing 16 percent by weight acrylic acid with 40 percent of the acid 
groups zinc-neutralized and characterized by a melt index of 1.5 and a 
Shore D Hardness of 55. 
ESCOR 900 is a sodium-neutralized copolymer of ethylene and acrylic acid 
containing 11 percent by weight acrylic acid with 40 percent of the acid 
groups sodium-neutralized and characterized by a melt index of 0.8 and a 
Shore D Hardness of 61. 
ESCOR 906 is a zinc-neutralized copolymer of ethylene and acrylic acid 
containing 16 percent by weight acrylic acid with 10 percent of the acid 
groups zinc-neutralized and characterized by a melt index of 16 and a 
Shore D Hardness of 52. 
ESCOR 4000 is a zinc-neutralized copolymer of ethylene and acrylic acid 
containing 16 percent by weight acrylic acid with 30 percent of the acid 
groups zinc-neutralized and characterized by a melt index of 2.5 and a 
Shore D Hardness of 55. 
ESCOR 4200 is a zinc-neutralized copolymer of ethylene and acrylic acid 
containing 11 percent by weight acrylic acid with 15 percent of the acid 
groups zinc-neutralized and characterized by a melt index of 3.3 and a 
Shore D Hardness of 50. 
As is discussed above in accordance with one embodiment of this invention, 
blends of sodium and zinc ionomers of poly ethylene-acrylic acid 
copolymers may be used as cover compositions. When blends of sodium and 
zinc ionomers are used the ratio of sodium ionomer to zinc ionomer can be 
from about 90% to about 10% and from about 10% to about 90%. A more 
preferred range is from about 75% to about 25% and from about 25% to about 
75%. The preferred composition for use in this invention is 50% sodium 
ionomer and 50% zinc ionomer. 
In formulating the novel blended cover compositions of the present 
invention, the sodium-neutralized copolymer, preferably ESCOR 900 may be 
blended with a single zinc-neutralized copolymer, preferably ESCOR 4000, 
or with blends of the zinc-neutralized copolymer within the blending 
parameters hereinbefore specified, as for example a blend of ESCOR 900 
with ESCOR 562 and ESCOR 4000. Preferably, the cover compositions comprise 
a blend of ESCOR 900 and ESCOR 4000 and most preferably a blend wherein 
the ESCOR 900 and ESCOR 4000 are present in about 50% to 50% weight ratio. 
It is within the purview of the present invention, as stated, to include in 
the cover compositions compatible materials which do not adversely affect 
the basic novel characteristics thereof including such art-recognized 
ingredients as pigments, stabilizers, optical brighteners, antioxidants 
and the like. Particularly, desirable ingredients are the pigments and 
optical brighteners disclosed in U.S. Pat. No. 4,679,795 to Melvin, et al, 
the disclosure of which is herein incorporated by reference thereto. 
The preferred white basic color of the golf balls is formulated by 
pigmentation of the selected cover formulation. Suitable white pigments 
for use in accordance with this invention include titanium dioxide, zinc 
oxide and zinc sulfide. Fluorescent and non-fluorescent colored pigments 
may also be used in this invention. It is to be understood by those 
skilled in the art that covers other than white can be produced by adding 
colored dyes or pigments to the basic polymeric blend. 
The amount of pigment used in conjunction with the polymeric cover 
composition naturally depends upon, inter alia, the particular pigment 
utilized, generally from about 1 to about 3 percent by weight based upon 
the weight of the ionomer. The most preferred pigment is titanium dioxide 
present in amounts of from about 0.5 to about 5 percent by weight based on 
the weight of ESCOR ionomers. A most preferred concentration for the 
titanium dioxide is about 2 percent based on the weight of the ionomers. 
One of skill in the art is aware of the fact that there are various hues of 
white, e.g. blue white, yellow whites and the like. Preferably, in the 
present cover compositions, trace amount of a blue pigment are added to 
impart a blue white appearance thereto. 
The subject invention is adapted to utilize a wide variety of optical 
brighteners. 
One skilled in the art must choose an optical brightener which is 
compatible with the polymer used as a base cover stock and with the 
pigment used therein. In that optical brighteners have been utilized for a 
width variety of purposes in many different environments for many years, 
non-functional optical brighteners exist. Optical brighteners have been 
commercially utilized for the brightening of textiles in order to impart a 
desirable blue-white appearance. The applicant does not understand fully 
the ramifications of why some optical brighteners are functional while 
other optical brighteners are not functional. It is within the purview of 
one skilled in the art to select a functional optical brightener for use 
in the cover compositions of the present invention. 
Examples of suitable optical brighteners which can be used in accordance 
with this invention are Uvitex OB as sold by the Ciba-Geigy Chemical 
Company, Ardsley, N.Y. Uvitex OB is thought to be 
2,5-Bis(5-tert-butyl-2-benzoxazoly)thiopene. Examples of other optical 
brighteners suitable for use in accordance with this invention are as 
follows: Leucopure EGM as sold by Sandoz, East Hanover, N.J. 07936. 
Leucopure EGM is thought to be 
7-(2h-naphthol(1,2-d)-triazol-2yl)-3phenyl-coumarin. Phorwhite K-2002 is 
sold by Mobay Chemical Corporation, P. O. Box 385, Union Metro Park, 
Union, N.J. 07083 is throught to be a pyrazoline derivative, Eastobrite 
OB-1 as sold by Eastman Chemical Products, Inc. Kingsport, Tenn. is 
thought to be 4,4-Bis(-benzoxazoly)stilbene. 
Many optical brighteners are colored. The percentage of optical brighteners 
utilized must not be excessive in order to prevent the optical brightener 
from functioning as a pigment or dye in its own right. 
The above-mentioned Uvitex and Eastobrite OB-1 are preferred optical 
brighteners for use in accordance with this invention. 
The percentage of optical brighteners which can be used in accordance with 
this invention is from about 0.01% to about 0.5% as based on the weight of 
the polymer used as a cover stock. A more preferred range is from about 
0.05% to about 0.25% with the most preferred range from about 0.5% to 
about depending on the optical properties of the particular optical 
brightner used and the polymeric environment in which it is a part. 
Usually, the additives are admixed with a copolymer to be used in the cover 
composition to provide a masterbatch of desired concentration and an 
amount of the masterbatch sufficient to provide the desired amounts of 
additive is then admixed with the copolymer blend. 
A most preferred cover composition for use in accordance with this 
invention consists of: 
ESCOR 4000: 52.40 pbw 
ESCOR 900: 45.2 
Titanium dioxide: 2.35 
Ultra-Blue: 0.024 
Uvitex OB: 0.102 
Golf balls utilizing the unique cover compositions of the present invention 
may be produced by the techniques currently employed in the art. For 
example, selected blends of ESCOR 4000 and ESCOR 900, admixed with the 
optional ingredients, can be injection molded on a prepositioned core in 
accordance with injection molding techniques commonly employed in the art. 
Likewise, covers can be produced by injection molding cover half shells, 
two of which can then be positioned around a golf ball core. The core and 
enveloping half shells are then placed in a compression mold, the shells 
fused together and dimples formed thereon in accordance with commonly 
accepted procedures. 
The cover compositions may be applied to both solid and would type cores as 
are currently used in the art. 
Experience has demonstrated that the average golfer prefers a glossy golf 
ball. In order to produce glossy golf balls, the balls of this invention 
may be coated with a clear epoxy-urethane or urethane-urethane system 
subsequent to molding. The system in question consists of a clear epoxy 
primer, followed by a clear urethane coat. Use of this clear coat system 
subsequent to the molding operation is not mandatory in order to achieve 
the desirable results of this invention; however, it is highly desirable. 
In the preferred embodiment, a water borne urethane primer is first 
applied followed by a clear solvent based urethane coating. In addition to 
high initial gloss, the above-mentioned system produces a golf ball which 
is durable and maintaining its gloss during play. It is understood by one 
skilled in the art that other clear coat systems can likewise be utilized. 
One qualification for the optical brightener which is used in accordance 
with this invention is that the optical brightener in question must be 
compatible with the polymer system utilized and it must be stable at 
temperatures necessary for the injection molding of the golf ball cover 
onto a prepositioned core. This qualification is necessary if the 
above-described injection molding technique is utilized. If the 
compression molding technique is used in the formation of the ball, the 
optical brightener used in accordance with this invention must be stable 
at the temperature necessary for the injection molding of the half shell 
and the compression molding of the half shells around a preformed core. 
The subject invention is useful in producing white golf balls wherein the 
whiteness of the ball is observed through a clear coat finish. It should 
be noted that this invention is likewise very useful in that it can 
provide a superior substrate if it is deemed to be desirable to paint the 
golf ball in a conventional manner with a white pigmented paint system. 
This procedure is advantageous in this instance in that a base of maximum 
whiteness is provided for the paint coating. Painting of a surface is 
desirable in situations where as a result of contamination by foreign 
matter the resulting finished golf ball must be painted. In the trade this 
is generally referred to as a dirty manufacturing process wherein 
impurities sometimes appear in the resulting finished product in such a 
manner that the overall appearance of the finished golf ball is 
cosmetically detrimentally affected. These slight cosmetic defects can be 
hidden by using a single coat of white paint over the optically brightened 
surface of this invention in place of the more standard two coats of white 
paint. In this manner the cosmetic defects are hidden and a truly superior 
product is produced. 
In the subject specification and claims, the term "core" is utilized to 
define the central part of the finished golf ball. As used in this 
specification and claims the term "core" refers to both solid centers as 
are used in two-piece golf balls, and to wound centers which are commonly 
used in balls which are referred to in the trade as three-piece golf balls 
.

The following examples serve to illustrate the present invention, such 
examples given for the purpose of illustration and not to be considered as 
limiting the invention. In the examples, all values are expressed as parts 
by weight unless otherwise indicated. 
EXAMPLES 
In the following examples, golf balls were produced using the cover 
compositions of the present invention, controls and comparative cover 
compositions by positioning a solid, preformed, cross-linked polybutadiene 
core in an infection molding cavity in such a manner as to permit the 
uniform injection of the selected cover composition around each core. All 
materials were molded under essentially identical settings. 
In conducting the comparative prior art testing, SURLYN 9910 and SURLYN 
8940 ionomers were utilized. Further, these surlyn ionomers were blended 
with various ESCOR copolymers to evaluate the properties of the cover 
composition of this invention. 
SURLYN 9910 is a zinc-neutralized copolymer of ethylene and methacrylic 
acid characterized by a melt index of 0.7 and a Shore D Hardness of 64. 
SURLYN 8940 is a sodium-neutralized copolymer of ethylene and methacrylic 
acid characterized by a melt index of 2.8 and a Shore D Hardness of 65. 
In the examples as set forth in Table I, SURLYN White MB refers to a 
masterbatch having the following composition. 
SURLYN 8528: 50 parts by weight (pbw) 
Titanium dioxide: 15.86 
Ultra-Blue: 0.16 
Uvitex OB: 0.70 
Santonex R: 0.025 
In the examples as set forth in Table I Escor masterbatch (escor White MB) 
has the following composition: 
ESCOR 4000: 50 parts by weight (pbw) 
Unitane 0-110: 15.86 
Ultra-Blue: 0.16 
Uvitex OB: 0.70 
Santonex R: 0.025 
Coefficient of restitution was measured by firing the resulting golf ball 
in an air cannon at a velocity of 125 feet per second against a steel 
plate which is positioned 12 feet from the nozzle of the cannon. The 
rebound velocity was then measured. The rebound velocity was divided by 
the forward velocity to give the coefficient of restitution. The superior 
coefficients of restitution of the cover compositions of the present 
invention, are detailed in Table I. 
3 TABLE I 
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 
27 ESCOR 4000 -- 90.4 45.2 -- -- -- -- -- -- -- -- -- 45.2 45.2 45.2 
22.6 21.9 -- 45.2 81.4 72.3 63.3 54.2 36.2 27.1 18.1 9.0 ESCOR 562 -- -- 
-- 90.4 -- -- 45.2 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
-- -- ESCOR 900 -- -- -- -- 90.4 -- -- 45.2 -- -- -- 45.2 -- 45.2 45.2 
22.6 68.5 -- 45.2 9.0 18.1 27.1 36.2 54.2 63.3 72.3 81.4 SURLYN 8940 
68.5 -- 33.9 -- -- 68.5 33.9 33.9 -- 90.4 68.5 33.9 33.9 -- -- 33.9 -- 
68.5 -- -- -- -- -- -- -- -- -- SURLYN 9910 21.9 -- 11.3 -- -- 21.9 11.3 
11.3 90.4 -- 21.9 11.3 11.3 -- -- 11.3 -- 21.9 -- -- -- -- -- -- -- -- 
-- SURLYN White MB 9.6 9.6 9.6 9.6 9.6 9.6 9.6 9.6 9.6 9.6 9.6 9.6 9.6 
9.6 -- 9.6 -- 9.6 -- -- -- -- -- -- -- -- -- ESCOR White MB -- -- -- -- 
-- -- -- -- -- -- -- -- -- -- 9.6 -- 9.6 -- 9.6 9.6 9.6 9.6 9.6 9.6 9.6 
9.6 9.6 Compression 62 60 54 55 56 54 55 53 57 55 48 48 50 47 48 47 49 
51 52 51 51 52 54 50 50 52 51 C.O.R. 799 787 800 796 794 796 797 797 797 
795 809 805 806 811 811 808 808 814 819 814 817 818 818 828 818 816 813 
Durability.sup.c NB 2B NB NB NB NB 1B 1B NB 4B NB NB NB NB NB NB NB NB 
NB NB NB NB NB NB NB 1B NB Cold Crack.sup.b NB 1B NB 11b NB NB 3B NB NB 
4B NB NB NB 3B NB NB NB NB NB NB NB NB NB NB NB NB NB Cut Resistance.sup. 
d 3-4 3 3-4 2-3 3-4 3-4 3-4 4 4 3-4 4-5 4-5 4-5 4-5 4-5 4-5 4-5 4-5 4-5 
4-5 4-5 4-5 4-5 4-5 4-5 4-5 4-5 
.sup.a Controls Examples 1-3, 4-10, 11-17 and 18-27 were run as separate 
sets 
.sup.b One dozen tested each Example, NB = none broke 
.sup.c 300 blows, 1 dozen tested each Example, NB = none broke 
.sup.d Graded 1 through 5 from 1 = clean cut to 5 = no mark 
Shore hardness was measured in accordance with ASTM Test D-2240. 
Cut resistance was measured in accordance with the following procedure. A 
golf ball is fired at 135 feet per second against the leading edge of a 
pitching wedge, wherein the leading edge radius is 1/32 inch, the loft 
angle is 51 degrees, the sole radius is 2.5 inches, and the bounce angle 
is 7 degrees. 
The cut resistance of the balls tested herein was evaluated on a scale of 
1-5. 1 represents a cut that extends completely through the cover to the 
core; a 2 represents a cut that does not extend completely through the 
cover but that does break the surface; a 3 does not break the surface of 
the cover but does leave a permanent dent; a 4 leaves only a slight crease 
which is permanent but not as severe as 3; and a 5 represents virtually no 
visible indentation or damage of any sort. 
DISCUSSION OF THE EXAMPLES 
The examples set forth in the foregoing table compares the properties of 
the golf balls of the present invention (Examples 14, 15, 17 and 19-27) 
with those of standard SURLYN cover balls of the prior art (Examples 1, 6, 
11 and 18), with those of golf balls utilizing single ESCOR polymer-based 
covers (Examples 2, 4, 5) with those incorporating various ESCOR-SURLYN 
blends (Examples 3, 7, 8, 12, 13, 16) and with those utilizing single 
SURLYN ionomers (Examples 9 and 10). 
As can be readily appreciated from review of the tabled results, the novel 
cover compositions of the present invention, while exhibiting the 
durability associated with golf balls having SURLYN neutralized 
poly(ethylene-methacrylic acid) copolymer-based cover compositions, 
clearly provides for a pronounced elevated coefficient of restitution. 
It should also be noted that, in addition to providing golf balls of 
superior play properties, the use of the ESCOR blends of the present 
invention results in substantial cost saving when compared to prior art 
golf balls. 
The invention has been described with reference to particular embodiments, 
but it is to be understood that variations and modifications can be 
effected without departing from the spirit and scope of the invention.