Note: Descriptions are shown in the official language in which they were submitted.
~12~ 3
HIGH COEFFICIENT GOLF BALL CORE
Back~round
This invention relates to an improved ~olid core for a
golf ball, golf balls made with the new ~ores; and a
composition of matter ~uitable for moldin~ such cores~
Two-pie~e golf balls consisting of a molded resilient
~ore and a cover are now widely available. They consist of a
peroxide cross-linked, mixed pGlybutadiene-metal acrylate
molded core and a separately mol~ed ~over typically comprising
~n ionomer resin such as the type ~old by E. Io Dupont de
Nemours Company under the trademark SURLYN. The balls are
extremely popular because they can be manufactured to ~e
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
~distance~ is a function of many factor~ including ~ngle of
trajectory and clubhead speed. Amsng the factors of ~oncern to
manuacturers which affect distance are the coefficient of
restitution of the ball, and the ball's surface configuration,
i.e., dimple pattern. Coefficient of restitution is a
measurement amiliar to those skilled in the golf ball art.
One way ~co measure the coefficient is ~o propel a ball a~ a
given speed a~ainst a hard massive ~urface, and measure its
incoming and outgoing velocity electronically. The
coeffiecient of restitution is the ratio of the outgoing
~elocity tv incoming velocity~
The coefficient of restitution in solid core balls is
a function of the composition of the molded core and of the
cover. ~n so-called ~hree-piece balls comprising a li~uid or
~r~
'7~
solid center, elastic thread windinys9 and a ~ver, the
coefficient of the core is a funct ~n primarily of the
composition of the elastomeri~ thread windings and cen~er, and
the winding tension.
Those seeking to increase the coefficient of
restitution of golf balls ~re effectively restrained by the
United States Gslfers Association reg~lations which mandate
that a ~regulation" ball cannot have an initial velocity in
excess of 255 feet per second. All other things being equal,
as the coefficient of restitution of a ball is incr~ased, the
~all's initial velo~ity will also increase.
U ~ SD Patent No. 31819 f 768 to R. P. Molitor discloses
that the coefficient of restitution of golf balls having any
yiven core can be increased ~ignificantly by applying to the
core a cover ~aterial compri6ing a blend of a s~dium
neutralized ionomer resin with a zinc neutralized ionomer
resin~ Over the years~ di~tance in two-piece golf balls has
been steadily improved by virtue of the developmerlt of
embodiments of the Molitor invention which ~ive further
increases in coeff icient and the development of improved molded
cores .
Cores ~uitable or u e in manufacturing two-piece
ball~ are disclosed in UOSO 4,264"075, U.5. 4tl69~599i U.S.
4,165,877, and U.5. 4,141,559. Currently, it is believed that
the highest coeff icient molded cores comprise a high c:is
content pl~lybutadiene and a zinc ~alt of an alpha beta
ethylinic:ally unsaturated rnonocarboxylic acid, e.g~, t zinc di or
mono acrylate or methacrylate, cured wlth conventional free
radical ini~iator-type peroxide catalyst~D
~2~ 3
Summary of the Invention
It has now been discovered that the addition of small
amounts of polyfunctional isocyanates, preferably diisocyanates
having a 3 to 30 carbon atoms, to what otherwise may be a
conventional core composition of the type described above can
have the effect of significantly increasing the coefficient of
restitution of the resulting cores. Specifically, compositions
of the invention containing 0.01 to 10~ of a polyfunctional
isocyanate can be used ~Q make golf ball cores having an
increased coefficient of restitution relative to identical
coses made in the absence of the isocyanateO In ac~ordance
with the invention, ~ores having a coefficient in excess of
0.7B0 can be made. An average coeffi~ient for cores from
production lots of ~803 + ~005 measured with an incoming
veloci y of 125 ft.~ec., can be achieved. This permits the
golf ~all manufacturer to appro~ch more closely the USGA
initial velocity li~it even without the increase in the
coefficient that can be obtained using the cover composition
disclosed in the above~referenced Molitor patent.
The invention comprise~ a golf ball having a cover and
a core, and a composition for manufacturing the core. The
composition comprises an elastomer which can be cross-linked by
free radical initiator or other types of catalysts, preferably
a high sis corltent polybutadier~e elastomer, a metal salt or
ester of an alpha, beta, ethylinically unsaturated
monocarboxylic acid compoun~, a free radical initiator catalyst
for cross-linklng ~he elastomer and the monocarboxylic acid
compound, and a polyfunctional isocyanate having 3-30 carbon
atoms. The i~vention include~ cores comprising the product of
reaction of these componen~s having a coefficient of at least
-3-
.. . . . . .. . .. . _ . _ . _ . _, _ .. . . _ . . _ . _ _ . . .. . ... . ..... ..
.750. Preferably, the monocarboxylic acid compound is zincdiacrylate, zinc dimethacrylate, zinc monoacrylate, or zinc
monomethacrylate; the catalyst comprises a conventional ru~ber
curing peroxide compound, preferably n butyl 494' bis (butyl
peroxy valerate, dicumyl peroxide, l~l-bi~ gt-butyl peroxy)
3,3,5-trimethylcyclohexane, di-t-butyl peroxide~ or 2,5 di
(t-butyl peroxy)-2,5 dimethylhexane. The preferred
polyfunctional isocyanates are dii~ocyanatesc ~ost preferably
4,4' diphenylmethane diiso~yanateJ ~owever, other reactive,
relatively low mole~ular weight compounds having 2 or more
isocyanate groups may be used. In addition, the ~omposition
and golf ball core of the invention may comprise a low
molecular weight fatty acid such as stearic ~cid.
In general7 the golf ball core and the composition of
the invention ~an ~omprise 100 parts of polybutadiene~ 20-50
parts carboxylic acid ~altt 0-20 parts fatty acid, 1-10 parts
peroxide, and 0.01-10 parts isocyanate~ The core may ~1BO
include some inorganic filler such as zinc oxid* or barytes to
increase its specific gravity. At least a smal~ amount of zinc
oxide is preferably used as it seems to have the e~fect of
increasing coefficient. A preferred composition comprises 100
parts polybutadiene, 36 parts monocarboxylic acid zinc salt
~uch as zin~ diacrylate, 5 parts low molecular weight fatty
acid, 2 parts peroxide, e.g., dicumyl peroxide or n butyl 4,4'
bis (butyl peroxy) valerate, and at least 1 part of the
pref~rred d;isocyanatet 4,4' diphenylmethane diisocyanate.
Accordinglyy it is an object of the invention to
provide an elastomer composition useful in making core~ for
two-piece balls having 3 higher coefficient of restitutionO
Another object is to prov;de a golf ball having a cover and a
core which~ because of ~he composition v the core, has
-4--
.
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8~3
improved distance. Still another object is to provide a corefor a two piece golf ball, which core may be used toge~her with
relatively low resilience cover mater ials while still achieving
a ball ~oeff icient of restitution and associated initial
velocity closely approaching the USGA limit.
These and other objects and features of the invention
will be apparent from the following description and from the
claims.
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Description
~ x~ept for the addition of the polyfunctional
isocyanate, the core composition and spherical golf ball core
of the invention are manufactured using conventional
techniques. Thus, an elastomer, prefer~bly a polybu~adiene
elastomer comprising as much cis polybutadiene as possible~ is
~lended together with 1) an alpha, beta, ethylinically
unsaturated ester or metal salt such as zinc ~ono or di
acrylate or methacrylate, or various mixtures thereof~ 2)
optionally 8 relatively inert higher specific gravity filler
such as zinc oxide to increase the weight of the core, 3
optionally a low mol2cular wei~ht fatty acid having7 for
example, 10-40 carbon a oms, e.~., steari~ acidt 4~ a free
radical initiator catalyst suoh as a peroxide~ and 5) the
polyfunctional i~ocyanate.
Preferably, all ingredients except the peroxide and
the isocyanate are mixed and blended using conventional mixing
equipment and the peroxide and isocyanate are ad~ed while the
temperature of the mixture is ~n the order of 200F. ~he blend
is extruded to form slugs of a weight sli9htly greater than the
weight of the cores to be produced, and then the ~lugs are
compression molded to cure the composition.
The slugs are placed in the cavities of a two-part
mold, whi~h is closed ~o compress the elastomer composition,
and then heated~ for example, to over 295F. After curing the
cores for 1~ to 20 minutes, dependiny on the molding
temperature, the mold is opened and the flashing is removed. A
thin surface layer of the cores in ~hen ground off to produce a
core of the size required. The flash removed from the oenter
may be ground to a fine parti~le ~i~e and added to the core
formulation.
6-
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'73
l~hile the reaction which takes place is not well
understood, i~ is believed that a complex network of cross-
links between the unsaturated components of the blend are
formed. Also, a small amount of zinc oxide may react in
some way. Isocyanate groups, of course, react primarily
with amine or hydroxyl group. However, they are known to be
reactive with carboxylic acids with liberation oE 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 curlng process, and
no theoretical explanation for the beneficial efect~ 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 compositlons such as are disclosed in U.S. patent
No. 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 to further increase the coefficient of
restitution of the gol~ ball, a cover embodying the
invention disclosed in U.S. 3,819,768 may be usedO The
currently preferred cover for use on the golf ball imparts
~ - 7 -
mls/LCM
to the ball short iron and other playability character.istics
comparable to balata-covered wound balls. The cover ls
disclosed in detail in copending Canadian Application Serial
No. 495,471.
~ - 7a -
mls/LCM
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d~f#qYC~ Briefly~ this new cover comprises a blend of ~
thermoplastic urethane having a Shore A hardnes~ less ~han 95
and a ion~mer material ~uch as those disclosed in U.S. Pa~ent
No. 3,2S4,272 and sold by E.I. Dupont de Nemours Company under
the trademark SVRLYN having a Shore D hardness ~reater than 55
~t a weight ratio sufficient to produce a cover having a Shore
C hardness within the range of 70 to 85.
The currently preferred polyfunctional isocyanates for
use in the core composition and core o~ the invention are
diisocyanates, most preferably 4,4' diphenylmethane
diisocyanate. However, other reactive isocyanates having at
least two isocyanate groups may be used. Examples include
trimethylene diisocyanate, propylene-1,2 dii~ocyanate~
tetramethylene diisocyanate, butylene-1,3 dii~ocyanate,
decamethylene dii~ocyanate~ octad~camethylene diisocyanate, 1
propylene-1,2- diisocyanate, 3 butylene-1,2 diisocyanate,
l-butylene 1,3 diisocyanate t 1- butylene-2,3 diisocyanate~
ethylidene diisocyanate, propylidene~ diisocyanate,
propylidene 2~2-diisocyanate t CyC lopenty~ene-1,3 diisocyanate~
cyclohexylene 1,3 diisocyanate, cyclohexylene 1,2-diisocyanate,
~yclohexylene-1,4-diisocyanate~ cyclopentylidene diisocyanate,
cyclohexylidene dii ocyanate, m-phenylene d;isocyanate, o
phenylene diisocyanate, p-phenylene diisocyanate, 1 methyl -2,~
phenylene diisocyanate~ naphthalene-1,4- diisocyanate~
diphenylene-4,4' dii~ocyanate, 3,4 tolylene ~iisocyanate,
2,6-tolylene dii~ocyanate, 4,4' diphenylmethane diisocyanate~
1,5 naphthalene diisocyanate, 2,2- me~hylene-b;~
(4-phenylisocyan~te), propylene-bis-(4-phenylisocyanate)5
xylylene 1,4 diisocyanate, xylylene 4,6 diisocyanate, and 4~4
diphenylene methane dii~ocyanat*. ~he amount of a particular
diisocyanate which maximizes the coefficient of a particular
,,, , , , , , , , _, , _ , , . ,, _ ., , . _ _ . .. . . . . . .
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73
composition should be determined empirically. Generally, 0.1
to 10 parts per 100 p~rts polybutadiene or other elastomer may
be used.
The currently pre erred free radical initiator
catalyst is a per~xide, most prefer~bly n butyl 4~4' bis (butyl
peroxy) valerate. Other conventional ru~ber curing peroxides
may be u~ed. Not limiting examples include dic~myl peroxide,
l,l-bi~ (t-bu~yl pero~y)-3,3,5-trimethylcycl~hexane, di-t-butyl
peroxide, and 2,5 di (t-butylperoxy3-2,5-dimethyl hexane.
The cross-linkable elastomer, unsaturated carboxylic
acid metal ~al~ ree radical initiator c~talyst, and a
polyfunctional isucyanate are all necessary to achieve the
increased coefficient of cores of the invention. ~owever,
other materials may be included in the core. For example, low
molecular weight fatty acids such ~s stearic acid appear to
haYe beneficial effectsO High ~pecific gravity filler~ ~uch as
barium sulfate, lead oxide, or most preferably zinc oxide may
be added to the eore to increase the weight of the b~ll as
desirable or as necessary to have the ball reach or closely
approach the USGA weight limit of 1~620 ounce. In addition,
small amounts of ionomers of the type described previously,
natural or ~ynthetlc rubbers, and other compatible elastomers
may be used ~s diluents. It is alo possible to add other
Gross-linking aids such as low molecular weight liquid
polycarboxylic ac~d esters, e.~.~ trymethylolpropan~
trimethacryla~e, 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.
v_ _ , . ,,, , , , ,, _, , _ _ , ,,,, , , , _ ,,, , ~ ~, _ _, , ,, , _ _, _ _ _ _ __, ,_ , _, __, , _,, _, . . .
8~'73
Broadly, in preferred compositions, for each 100 parts
polybutadiene, ~he ~ore composition ~f the invention can
include 20-50 parts carbQxylic ~cid salt or ester~ 0-20 parts
low molecular weight fatty acid~ 1-10 parts peroxide, and
oOl~10 ~arts of the polyfunctional isocyanate. The ratios of
ingredients may vary and are best optimized empiri~ally. The
amount of 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 understood from the
following non-limiting examples:
Examples
Using the ingredients set forth below, golf ball cores
having a finish2d siæe of 1.545 inch were ~anufactured by
compression molding and then gxinding a ~urface layer off the
molded cores. Each core was formulated using 100 partS high
cis content polybutadiene, 5 parts zinc oxide~ ~nd 17~4 parts
ground flash. The am~unt6 o$ the remaining ingredients used in
the test cores ~in parts by weight) and the coeffi~ients of
restitution and Riehle compression of the cores are set forth
below~
73
T LE
Effe~t of Polyfunctional Is~cyanate
On Golf Ball Cores Coefficient
Ingredient 1 lA 2 2R 3 3A 4 4~
Stearic Acid 3.0 3~0 3.0 3.0 7.0 7 0 7 0 7 0
Zinc Diacrylate 3B 38 38 38 38 38 38 38
Dicumyl Peroxide 3.0 3.~ 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 ~ 1.0 0 1.0 0 1.0 0 1~0
Compression 61 56 58 57 55 51 S5 51
Coefficient .807 .811 ~809 .809 .8I2 .~1~ .806 o808
In~redient ~ 5A 6 6A 7 7A 8 8A
Stearic Acid 3O0 3O0 3.0 3.0 7.0 7.0 7.0 7 0
Zinc Diacrylate 43 43 43 43 43 43 43 43
~icumyl Peroxide 3O0 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
Dii~ocyanate O 1.0 0 1.0 0 1.0 0 l.û
Compression 53 49 52 48 50 46 47 47
Coefficient .808 .813 .805 .807 .811 .815 o808 ~811
As can be seen from the foregoing table, the inclusion
of 1 part tl~ based on weight of polybutadiene) polyfunctional
isocyanate (4,4' diphenyl methane diisocyanate) generally has
the effect of hardening the core tdecreases compression values3
and increasing coefficient.
The invention may be embodied in other specific forms
without departing from the ~pirit and scope thereof.
Accordingly, other emb~diments are within the following claims.
What is claimed ;s:
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