Golf ball core by addition of dispersing agents

Golf balls exhibiting superior durability and improved coefficient of restitution is provided by the inclusion of a dispersing agent in the core formulation.

This invention relates to golf balls. More particularly, this invention 
relates to multi-ply solid golf balls having a high impact resilience and 
an excellent durability. 
Wound golf balls which have been widely employed have been particularly 
desirable in possessing high impact resilience and high initial velocity 
on impact. However, the wound golf balls suffer a major flaw in lacking 
durability. 
In order to improve the durability, there have been developed two-piece 
solid golf balls consisting of a solid core having a good impact 
resilience and a cover, either unitary or multi-ply, having an excellent 
resistance to cutting. 
There are several advantages of homogenous, unitary construction for a golf 
ball, in contrast to the wound golf balls of the earlier art. Unitary golf 
balls can be produced with an essentially perfect center of gravity with 
attendant desirable properties of superior roll and trueness of flight. 
Such golf balls are highly resistant to cutting, often indestructible in 
normal play, and return to round even when severely distorted, maintaining 
their superior flight characteristics even after extended use. 
Additionally, and in contrast to the wound golf balls, unitary balls 
maintain the integrity of their playing characteristics throughout widely 
varying temperature ranges, will not water log and possess an excellent 
shelf life. 
While golf balls have found wide acceptance and constitute by far the bulk 
of sales, the advantages gained in the properties enumerated have been 
offset to a degree by decreased impact resilience. 
It is, therefore, an object of the present invention to provide unitary 
golf balls exhibiting superior durability, and an improved coefficient of 
restitution. 
In accordance with the present invention, there is provided a unitary golf 
ball comprising a solid core and a cover therefor, the solid core 
comprising an elastomer or admixture of elastomers, at least one metallic 
salt of an unsaturated carboxylic acid, free radical initiator and a 
dispersing agent. 
It has been found that the addition of the dispersing agent to the core 
composition and the presence thereof during the cure cycle results in an 
increase of the coefficient of restitution of from about 0.5 to about 2.0 
percent over that exhibited by a similar core prepared in the absence of a 
dispersing agent. 
The core compositions of the prevent invention may be based on 
polybutadiene, and mixtures of polybutadiene with other elastomers. It is 
preferred that the base elastomer have a relatively high molecular weight. 
The broad range for the molecular weight of suitable base elastomers is 
from about 50,000 to about 500,000. A more preferred range for the 
molecular weight of the base elastomer is from about 100,000 to about 
500,000. As a base elastomer for the core composition, cis-polybutadiene 
is preferable employed, or a blend of cis-polybutadiene with other 
elastomers may also be utilized. Most preferably, cis-polybutadiene having 
a weight-average molecular weight of from about 100,000 to about 500,000 
is employed. 
The unsaturated carboxylic acid component of the core composition is the 
reaction product of the selected carboxylic acid or acids and an oxide or 
carbonate of a metal such as zinc, magnesium, barium, calcium, lithium, 
sodium, potassium, cadmium, lead, tin and the like. Preferably, the oxides 
of polyvalent metals such as zinc, magnesium and cadmium are used, and 
most preferably the oxide is zinc oxide. 
Exemplary of the unsaturated carboxylic acids which find utility in the 
present core compositions are acrylic acid, methacrylic acid, itaconic 
acid, crotonic acid, sorbic acid and the like, and mixtures thereof. 
Preferably, the acid component is either acrylic or methacrylic acid. 
Usually, from about 20 to about 50, and preferaby from about 25 to about 
40 parts by weight of the carboxylic acid salt is included in the core 
composition. 
The free radical initiator included in the core composition is any known 
polymerization initiator which decomposes during the cure cycle. The 
amount of the selected initiator present is dictated only by the 
requirements of catalytic activity as a polymerization initiator. Suitable 
initiators include peroxides, persulfates, azo compounds and hydrazides. 
Peroxides which are readily commercially available are conveniently used 
in the present invention, generally in amounts of from about 0.1 to about 
10.0 parts by weight per each 100 parts of rubber. 
Exemplary of suitable peroxides for the purposes of the present invention 
are dicumyl peroxide, n-butyl 4,4'-bis (butylperoxy) valerate, 
1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane, di-t-butyl peroxide 
and 2,5-di-(t-butylperoxy)-2,5 dimethyl hexane and the like, as well as 
mixtures thereof. 
The dispersing agent of the present core composition may be anionic, 
cationic, noionic or amphoteric in properties as a surfactant. If desired, 
mixtures of selected dispersing agents may be used. Suitable dispersing 
agents include alkali metal salts of fatty acids having from about 12 to 
about 20 carbon atoms, such as caprylic, lauric and stearic acid and the 
like; sulfated fats such as sulfated oleic acid, sulfated castor oil, 
sulfated coconut oil and the like; sodium salts of alkylated aromatic 
sulfonic acids such as naphthalene sulfonic acid, substituted benzoid 
alkyl sulfonic acids and the like; monoaryl and monoalkyl ethers of 
dialkylene glycols such as monomethyl and monophenyl ether of diethylene 
glycol and polyethylene glycol. Additionally, such dispersing agents as 
ammonium salts of alkyl phosphates, sodium salts of carboxylated 
electrolytes, sodium alkyl sulfates, monosodium salt of sulfated methyl 
oleate and the like may be used. Preferably, the dispersing agent is a 
sodium salt of polymerized alkyl naphthalene sulfonic acid or sodium salt 
of polymerized substituted benzoid alkyl sulfonic acids such as DARVAN (R. 
T. Vanderbilt Co.). 
The dispersing agent is included in an amount of from about 0.1 to about 
5.0, preferably from about 0.2 to about 2.0 parts by weight per 100 parts 
of rubber. 
The core compositions of the present invention may additionally contain any 
other suitable and compatible modifying ingredients including, but not 
limited to, fillers, metal oxides, fatty acids, and diisocyanates. 
As fillers, any known and conventional filler material, or mixtures 
thereof, may be used. Such fillers as are incorporated into the core 
compositions should be in finely divided form, as for example, in a size 
generally less than about 20 mesh and preferably less than about 100 mesh 
U.S. standard size. Suitable fillers include silica, silicates, zinc 
oxide, carbon black, cork, titania, cotton flock, cellulose flock, leather 
fiber, plastic and/or leather flour, asbestos, glass fibers, metal 
carbonates and talc. Particularly useful is the oxide or carbonate of the 
cation used in forming the metal salt of the unsaturated carboxylic acid 
component. 
The amount of filler included in the core composition is primarily dictated 
by weight restrictions and preferably is included in amounts of from about 
10 to about 100 parts by weight per 100 parts rubber. 
Fatty acids may also be included in the compositions, functioning to 
improve moldability and processing. Generally, free fatty acids having 
from 10 to about 40 carbon atoms, and preferably having from about 15 to 
about 20 carbon atoms, are used. Exemplary of suitable fatty acids are 
stearic acid and linoleic acids, as well as mixtures thereof. When 
included in the core compositions, the fatty acid component is present in 
amounts of from about 1 to about 15, preferably in amounts of from about 2 
to about 5 parts by weight based on 100 parts rubber. 
It is preferred that the core compositions include stearic acid as the 
fatty acid adjunct in an amount of from about 2 to about 5 parts by weight 
per 100 parts of rubber. 
Diisocyanates may also be optionally included in the core compositions when 
utilized, the diisocyanates are included in amounts of from about 0.2 to 
about 5.0 parts by weight based on 100 parts rubber. Exemplary of suitable 
diisocyanates is 4,4'-diphenylmethane diisocyanate and other 
polyfunctional isocyanates known to the art. 
In producing golf ball cores utilizing the present compositions, the 
selected components are intimately mixed using, for example, two roll 
mills or a Banbury mixer until the mixture is uniform, usually over a 
period of from about 5 to about 20 minutes. The sequence of addition of 
components is not critical. 
A preferred blending sequence is one wherein rubber, zinc salt, metal 
oxide, filler, fatty acid and surfactant are blended for about 7 minutes 
in an internal mixer such as a Banbury mixer. As a result of shear during 
mixing the temperature rises to about 200.degree. F. The initiator is then 
added and the mixing continued until the temperature reaches about 
220.degree. F. whereupon the batch is discharged onto a two roll mill, 
mixed for about one minute and sheeted out. 
The sheet is then placed in a Barwell preformer and slugs are produced. The 
slugs are then subjected to compression molding at about 325.degree. F. 
for about 14 minutes. After molding and cooling, the cooling effected at 
room temperature for about 4 hours, the molded cores are subjected to a 
centerless grinding operation whereby a thin layer of the molded core is 
removed to produce a round core having a diameter of 1.545 inches. 
Usually the curable component of the composition will be cured by heating 
the composition at elevated temperatures on the order of from about 
275.degree. F. to about 350.degree. F., preferably from about 295.degree. 
F. to about 325.degree. F., with molding of the composition effected 
simultaneously with the curing thereof. The composition can be formed into 
the core structure by any one of a variety of molding techniques, e.g., 
injection, compression or transfer molding. When the composition is cured 
by heating, the time required for curing will normally be of short 
duration, generally from about 10 to about 20 minutes, depending upon the 
amounts and activity of the selected curing agent. Those of ordinary skill 
in the art of free radical curing agents for polymers are conversant with 
adjustments of cure times and temperatures required to effect optimum 
results from any specific free radical agent. 
The core is then converted into a golf ball by providing at least one layer 
of covering material, ranging in thickness from about 0.050 to about 0.250 
inch, preferably from about 0.060 to about 0.090 inch. 
The cover composition is preferably made from ethylene-acrylic acid or 
ethylene-methacrylic acid copolymers neutralized with mono- or divalent 
metals such as sodium, potassium, lithium, calcium, zinc or magnesium. 
While the cover composition may be any of a number of covering materials 
known in the art, such as balata, polyolefins and the like, it is 
preferred, for imparting durability to the ball, to employ ionomeric 
resins, such as those produced by neutralizing the copolymers described in 
U.S. Pat. No. 3,421,766 and British Pat. No. 963,380 using the procedures 
set out in Canadian Pat. Nos. 674,595 and 713,631. In accordance with the 
procedures set forth in the aforementioned patents, the ionomeric resin is 
produced by copolymerizing a selected olefin and unsaturated carboxylic 
acid to provide a copolymer having the acid units randomly distributed 
along the polymer chain, with the relative amounts of reactants adjusted 
to provide a copolymer containing from about 9 to about 15 mole percent of 
the carboxylic acid moiety, at least about 18 percent, preferably from 
about 18 to about 60 percent of the acid groups are then neutralized by 
metal ions having a valence of from 1 to 4, including sodium potassium, 
zinc, calcium, magnesium, and the like. 
Suitable olefins include ethylene, propylene, butene-1, hexene-1 and the 
like. Unsaturated carboxylic acids which may be copolymerized with the 
selected olefin include acrylic acid, methacrylic acid, ethacrylic acid, 
alpha-chloroacrylic acid, crotonic acid, maleic acid, fumaric acid, 
itaconic acid and the like. Preferably, the ionomeric resin is a copolymer 
of ethylene with either acrylic or methacrylic acid having from about 9 to 
about 15 mole percent acid moiety. 
The golf ball can be produced by covering the core using one of several 
available methods. For example, a core may be placed in the center of a 
golf ball mold and the cover composition injected into and retained in the 
surrounding space for a period of time at a mold temperature of from about 
40.degree. F. to about 120.degree. F. 
Alternatively, the cover composition may be injection molded at 
temperatures of from about 200.degree. F. to about 450.degree. F. into 
smooth-surfaced hemispherical shells, a core enveloped with two such 
shells placed in a dimpled golf ball mold at temperatures on the order of 
from about 100.degree. F. to about 200.degree. F. 
Coloration of the golf ball may be effected by including a selected 
coloring agent uniformly dispersed in the cover composition, or by 
applying one or more coatings of paint to the ball after molding. Indicia 
is applied to complete the product. 
The invention is further described in the following examples wherein the 
parts are by weight unless otherwise specified.

EXAMPLES 
Employing the ingredients tabled below, golf ball cores having a finished 
diameter of 1.545 inches were produced by compression molding and 
subsequent removal of a surface layer by grinding. Each core was 
formulated using 100 parts high cis content polybutadiene. In the 
examples, the amounts of the remaining ingredients are expressed in parts 
by weight, and the degrees of coefficient of restitution and compression 
achieved set forth. 
______________________________________ 
EXAMPLES 
Ingredients 1 2 3 4 5 
______________________________________ 
Zinc Diacrylate 
40 40 40 40 40 
Zinc Oxide 17 17 17 17 17 
Stearic Acid 5.0 5.0 5.0 5.0 5.0 
4,4'-diphenyl 
1.0 1.0 1.0 1.0 1.0 
methane diisocyanate 
peroxide 1.2 1.2 1.2 1.2 1.2 
Dodecanethiol 
1.0 1.0 1.0 1.0 1.0 
Dispersing Agent 1 
-- 1.0 5.0 -- -- 
Dispersing Agent 2 
-- -- -- 1.0 5.0 
Weight gms. 37.5 37.6 38.0 37.7 37.2 
Compression 55 50 48 47 50 
Coefficient of 
.805 .814 .803 .816 .797 
Restitution 
______________________________________ 
(Dispersing Agent l sodium salt of polymerized naphthalene sulfonic acid 
Dispersing Agent 2 sodium salt of polymerized substituted benzoid alkyl 
sulfonic acid.) 
______________________________________ 
EXAMPLES 
Ingredients 6 7 8 9 
______________________________________ 
Zinc Diacrylate 
31 3l 31 31 
Ground Flash 18 18 18 18 
Zinc Oxide 17 17 17 17 
Zinc Stearate 
20 20 20 20 
n-Butyl 4,4-Bis- 
0.75 0.75 0.75 0.75 
(Butylperoxide) 
Valerate 
Dispersing Agent 1 
-- 0.1 0.2 1.0 
Dispersing Agent 2 
-- -- -- -- 
Weight gms. 39.9 39.8 39.8 40.0 
Compression 62 63 60 63 
Coefficient of 
.805 .805 .808 .804 
Restitution 
Size 1.545 1.545 1.545 1.545 
______________________________________ 
______________________________________ 
EXAMPLES 
Ingredients 10 11 12 
______________________________________ 
Zinc Diacrylate 
31 31 31 
Ground Flash 18 18 18 
Zinc Oxide 17 17 17 
Zinc Stearate 20 20 20 
n-Butyl 4,4-Bis- 
0.75 0.75 0.75 
(Butylperoxide) 
Valerate 
Dispersing Agent 1 
-- -- -- 
Dispersing Agent 2 
0.1 0.2 1.0 
Weight gms. 40.0 39.9 39.9 
Compression 60 62 64 
Coefficient of 
.806 .808 .804 
Restitution 
Size 1.545 1.545 1.545 
______________________________________ 
DISCUSSION OF THE EXAMPLES 
The data for examples 1 and 6 represent controls in that the cores produced 
in these examples do not incorporate dispersing agents. The average 
coefficient of restitution for these control cores is 0.805 with an 
average compression of 58.5. This difference in compression is thought to 
be due to the fact that the formulation for example 1 is different than 
that of example 6. 
Example 7 uses a dispersing agent at 0.1 parts, it can be seen that at this 
low level the use of a dispersing agent in accordance with this invention 
is ineffective. 
Examples 3 and 5 use a dispersing agent at 5.0 parts, a relative high 
concentration which is ineffective, note the significant decrease in the 
respective coefficient of restitutions. 
Examples 2, 4, 7, 8, 10 and 11 are compositions which use dispersing agents 
in accordance with this invention. As we mentioned above, the average 
coefficient of restitution for the control data of examples 1 and 6 is 
.805. The average coefficient of restitution for the examples in 
accordance with this invention is 809.5 for an increase in the coefficient 
of restitution of 4.5 points. This increase of 4.5 points is significant 
in that it represents an increase of approximately 3 to 6 yards in the 
distance which a golf ball will travel when struck under controlled 
conditions. This beneficial increase in coefficient of restitution is 
achieved while maintaining a relatively constant compression. 
From the above data, it can be seen that the optimum effective level of 
dispersing agent used in accordance with this invention varies from 
formulation to formulation. One skilled in the art arrives at the optimum 
effective level of the dispersing agent for a given formulation by 
experimentation. In this regard, see the data for examples 9 and 12 
wherein it can be seen that the use of dispersing agent 2 in the given 
formulation peaks at 1.0 parts. 
It is to be appreciated that the specification and examples are set forth 
by way of illustration and not limitation, and that various modifications 
and changes may be made without departing from the spirit and scope of the 
present invention.