CA1147489A - Homogeneous molded golf ball - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
In a homogeneous molded golf ball comprising a filled elastomer highly cross-linked into a three dimensional network with long flexible cross-links formed of a polymerized cross-linking monomer, the improvement which comprises using as said cross-linking monomer a metal-containing cross-linkable monomer whereby said comonomer simultaneously functions as said fil-ler at least in part. The preferred elastomer is cis-polybutadiene. The metal-containing cross-linkable monomer can be formed in situ or added as such and preferably comprises a salt of at least one metal selected from the group consisting of zinc, magnesium and calcium, and at least one acid se-lected from the group consisting of methacrylic, acrylic, cinnamic, acotinic, crotonic, vinylacetic, itaconic, styrenesulfonic and benzoylacrylic acids.
Additional filler may be added to adjust the density to the desired value.
The composition is preferably preheated prior to molding and produces golf balls of superior properties with respect to durability, cannon life, sound and distance properties.

Description

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The present illvention relates to molding compositions containing cis-polybutadiene or other elastomers, and a monomer capable of cross-linking the elastomer into a three-dimensional net-~ork. More specifically, the cross-links which are capable of being produced by the monomer are relatively long an~ flexible.
Such molding compositions are eminently suitable for the production of molded golf balls, particularly unitary molded golf balls.
Molding compositions of this general class, and golf balls which can be reproduced from them, are described U.S. Patents 3,313,545, issued April 11, 1967, and 3,438,933, issued April 15, 1969~
There are se~eral advantages of homogeneous, unitary construction for a golf ball, in contrast to the wound balls of the earlier art. Unitary golf balls can be produced with a perfect center of gravity and thus have excellent aero-dynamic properties, superior roll, and trueness of flight. ~Such golf balls are highly-resistant to cutting and often indestructible in normal play. These balls will return to round even when severly distorted, and thus maintain their superior 1ight characteristics after extended use. ~-Homogeneous, uni-~ary golf balls may be manufactured with better quality control than conventional wound balls.
As contrasted to the conventionally covered wound balls, unitary balls maintain their playing characteristics better in hot and in cold weather, have an excellent shelf-life, and will not waterlog. If the paint on the ball becomes worn or damaged ! the balls may be very readily reclaimed by removing or stripping off ~he old paint and repainting the - same. By contrast, conventional covered wound balls seldom - . ~
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last long enough -to allow repain-ting.
Above-noted Pa-tents 3,313,545 and 3,43i3,933 disclose production oE
such homogeneous golf balls by molding a composition comprising an elastomer, a cross-linking monomer present to the exten-t of about 20 to 95% and about 20 to 90% of a filler, both based on the weight oE the elastomer, the monomer ending up in the molded structure as long flexible cross-links. The filler is distributed throughout the structure ancl serves a variety of func-tions, e.g. improving the tensile strength and compressive strength, as well as bringing the density to the accepted value for golf balls, imparting the proper play characteristics, click, and the like.
While such balls are quite satisfactory it is an object of the in-vention to improve the properites of such molded balls still further with respect to hardness, distance, durability, cut and chip resistance, flight characteristics, and the like.
These and other objects and advantages are realized in accordance with the present invention which represents a refinement in the production of superior homogeneous molded golf balls described in the above-identified patents. Specifically, the monomer used in cross-linking the elastomer is metal-containing so that it simultaneously functions at least in part as the filler. When cured under heat and pressure, preferably in the presence of a polymerization initiator, the novel compositions yield structures consisting of elastomer cross-linked into a three dimensional network containing a large proportion of relatively long flexible cross-links, the cross-links incorpor-ating metallic ions.
Thus, the invention provides a solid unitary golf ball prepared from a composition comprising a cross-linkable elastomer and as a cross-linking agent a metal salt of an organic acid, the me-tal being selected from the class consisting of monovalent, divalent, and trivalent metals, the organic acid being selected from the class consisting of ~,~-ethylenically unsaturated mono- and di-carboxylic acids containing from three to eight carbon atoms, the cross-linking agent being present in sufficient quantity to cross-link said elastomer and form said solid unitary golf ball, when said :

-composition is cured in a standard golf ball mold under standard unitary golf ball molding condi-tions.
In another aspect, the invention provides in a hornogeneous molded ball having the density and click and rebound required in a golf ball and comprising a filled elastomer highly cross-linked into a three dimensional network with long, flexible cross-links formed of a polymerized cross-linking monomer, the improvement wherein said cross-linking monomer comprises a me-tal-containing cross-linking monomer and is present in about 0.046 to 0.41 equivalents per mole of elastomer base whereby said monomer simultaneously functions as said filler at least in part, said ball in addition to said filler-functioning cross-linking monomer containing up to about 30 parts of a further filler per 100 parts by weight of said elastomer, the amount of said further filler being sufficient to impart to said golf ball a weight of about 1.500 to 1.620 ounces.
Golf balls produced according to the present invention have superi-or distance, improved durability, excellen-t click and feel, superior cut and chip resistance, and excellent flight characteristics, when compared to con-ventional wound golf balls and prior art unitary golf balls.
The elastomer preferred in the present invention is cis-polybuta-diene rubber containing at least 40% cis configuration.

- 3a -The monomer consists generally of a normally solid metal compound of a polymerizable organic moiety, and a preferred group of such monomers are the metal salts of unsaturated~ polymerizable organic acids. Preferably the monomer is soluble in the elastomer base; or readily dispersible in the elastomer under the usual conditions of rubber compounding; or else the mon-omer is capable of being formed in situ from at least one precursor which is readily soluble in the elastomer base.
An example of in situ formation is by predispersion of a suitable basic metal compound in the cis-polybutadiene rubber, such as zinc oxide or carbonate, followed by the addition of a suitable polymerizable acid, such as acrylic or methacrylic acid. The resulting monomer, zinc diacrylate or zinc dimethacrylate is thus formed during compounding, and is therefore pres-ent in a desirably high degree of dispersion or solution in the elastomer matrix.
Examples of suitable metals include but are not restricted to zinc, magnesium, calcium, lithium, sodium, potassium, cadmium, lead, barium, zir-conium, beryllium, copper, aluminum, tin, iron, antimony and bismuth. Poly-valent metals, i.e. those having a valence higher than 1, and especially the divalent metals zinc, magnesium, and calcium are a preferred sub-group.
Examples of metal salts of polymerizable organic acids include but are not restricted to salts of the following general formulas:
(a) carboxylates, sulfonates, and sulfinates of the formulas ~RC02)m M, R(S03)m.M, R~S02)m.M, ~RC02)p .M0, ~RS03)p .M0, R~S02)p .M0;
~b) phosphonates of the formulas ~R2P02)m.M, ~R~P02)p M0, ~RP03)q.M, ~RP03).M'0;
~c) imide salts of the formulas O

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(d) tin salts of the formula R" OCR
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whereln each R independently is a group having at least one polymerizable olefinic unsaturation, R' is a divalent group having a polymerizable olefinic unsatura-tion, each R" independently is an alkyl, aryl or alalkyl group, M is a metal ion having a valence, m, of from 1 to 5, M' is a metal ion having a valence of ~, M" is a metal ion having a valence of 1 or 2, p is m-2 when m is greater than 2, and q has the value m/2 when m is 2 or ~.
In ~a), ~b~, ~c), and ~d), the R's may be alkenyl, aralkenyl, alkenylaryl, h~terocyclic, or cycloalXenyl, and contain halogen, nitro, cyano, keto, ester~ ether and or amido substituents, provided that the metal containing cross-linking monomer contains at least one polymerizable olefinic unsaturation per molecule. The alkenyl radicals, when present, preferably are lower alkenyl and the aryl radicals, when present, are preferably phenyl, each of which may be substituted as indicated.
Mixtures ~f different metal-containing polymerizable monomers may also be used within tIle scope of the present invention, provided that at least one member of the mixture be homopolymerizable. Other members of the mixture may be copolymerizable or homopolymerizable, or else only copolymer-izable. An example of the second type of monomer is zinc dimaleate, which is copolymerizable with zinc dimethacrylate but not homopolymerizable.
Mixtures of different metal-containing monomers may be used to ad-vantag~ for the purpose of adjusting the polymerization rate or the final X `.

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density of the ball3 the density of the ball is desirably below about 1.13 and preferably between about 1.11 and 1.12, corresponding to a weight of about 1.5 to 1.62 ounces for a standard golf ball of about 1.6g to 1.685 inches in diameter. For example, zinc diacrylate when used as the sole metal-containing monomer polymerizes very rapidly during curing, making the curing operation excessively exothermic and difficult to control. Thus, it may be advantageous to use mixtures of zinc diacrylate and zinc dimethacryl-ate in order to achieve a better balance of ease of processing, and final characteristics of the ball.
F.xamples of polymerizable salt-forming acids which are useful in the present invention are acrylic, methacrylic, 2-acetaminoacrylic, ~,~-di-methacrylic, ethacrylic, ~-chloroacrylic, 2-ethyl-3-propylacrylic, acotinic, ~-benzoylacrylic, crotonic, aminocrotonic, allylacetic, 2-allyloxypropionic,

2-furfurylacrylic, vinylacetic, allyloxyacetic, 2-vinylpropionic, vinylhydro-gen phthalic, ~-acryloxypropionic, 2-butene-1,~-dicarboxylic, sorbic, acetyl-ene dicarboxylic, N-butylmaleamic, maleic, chloromaleic, di-n-butylmaleamic, N,N-dimethylmaleamic, N-ethylmaleamic, N-phenylmaleamic, dichloromaleic, di-hydroxymaleic, allylarsonic~ chlorandic, fumaric, itaconic, styrenesulfonic, divinylbenzenesulfonic, styrenephosphonic, and styrenesulfinic acids; male-imide, and methylmaleimide. Methacrylic, acrylic, cinnamic, acotinic, crot-onic, vinylacetic, itaconic, styrenesulfonic, and benzoylacrylic acids are a preferred sub-group.
The term "metal-containing polymerizable monomers" as employed herein includes such monomers which have been at least partially prepolymer-ized before compounding, or after compounding or processing, and before cur-ing. Also included are salts of carboxylic polymers such as butadiene-acrylonitrile-acrylic acid, acrylonitrile-butadiene-sorbic acid, styrene-butadiene-sorbic acid" butadiene-vinylacrylic acid, butadiene-sorbic acid, and the like, provided that these polymers contain residual polymerizable unsaturations. An advantage of using such prepolymerized cross-linking ~.~

salts is that the amount of heat generated when the ball is cured is minim-ized, in contrast to USillg unpolymerized monome~s. The reduced exotherm makes the molding operation more easily controlled.
The amount of the metal-containing cross-linking monomer should correspond to at least about 0.046 equi~alents of polymerizable unsaturation per mole of butadiene in the elastomer base, but may be as high as 0.41 equivalents per mole. A preferred level of cross-linking monomer is in the range 0.08 to 0.28 equivalents per mole, while a more preferable range is ~.10 to 0.23 equivalents per mole. Thus, if the cross-lin~ing monomer se-lected is zinc dimethacrylate, more preferable amounts are in the range ofabout 20 to 50 parts by weight of zinc dimethacrylate per hundred parts of cis-butadiene polymer.
Without departing from the scope of the present invention, mixtures of metal-containing and metal-free polymerizable monomers such as esters of unsaturated acids, may also be used. Examples of metal-free polymerizable monomers include but are not restricted to vinyl, allyl, methallyl, furfuryl, crotyl and cinnamyl esters of monobasic and polybasic acids such as acetic, propionic, butyric, benzoic, phenylacetic, chloroacetic, trichloroacetic, oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, maleic, itaconic, citraconic, mesaconic, fumaric, citric, acotinic, phthalic, isophthalic, terephthalic, naphthalenedicarboxylic, mellitic, pyro-mellitic, tumesic, acrylic, methacrylic, ethacrylic, cinnamic, crotonic, cy- ~ ~-anuric; polyolesters and anhydrides of acrylic, methacrylic, ethacrylic, crotonic, and cinnamic acids, the said polyols including ethylene glycol, di-, tri-, and tetraethylene glycol, glycerol, 1,3-butylene glycol, 1,~-butylene glycol, trimethylolpropane, pentaerythritol, propylene glycol, di-, tri-, and tetrapropylene glycols, polyethylene glycol, and polypropylene gly-col; vinyl and divinyl benzene; allyl and di-allyl benzene, mono-, di-~ and triallylmelamine; allyl and diallylamine; allyl ether, allyl glycolates;
mono-, di-, tri-, and tetraallyl and vinyl silanes; methyl, ethyl, propyl, .~.

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butyl, pentyl, hexyl, benzyl, phenyl, cyclohexyl, chloroethyl, ~-cyanoethyl, dimethylaminoethyl, glycidyl, lauryl, 2-methoxyethyl, tetrahydrofurfuryl, hydroxyethyl and hydroxypropyl esters of acrylic, methacrylic, ethacrylic) cinnamic, crotonic, cyanuric, fumaric, malcic, and methylmaleic acids, tri-allyl phosphate and phosphite. Further examples include low molecular weight reactive polymers such as polymers of butadiene, isoprene, chloroprene, and epoxidized derivatives of these materials.
A preferred group of metal-free polymerizable monomers are di-acrylates, dimethacrylates of ethylene glycol, propylene glycol, butylene glycol, di-, and triacrylates and methacrylates of trimethylolpropane, and di-, tri-, and tetraacrylates and methacrylates of pentaerythritol. In gen-eral, metal-free monomers containing more than one polymerizable unsatura-tion per molecule are preferred, but monoacrylates and monomethacrylates of polyols such as ethylene glycol are also highly suitable.
In order to vary the density so ~hat the finished ball will have the desired weight and will not exceed the maximum allowable weight, some filler may be required. However, because the metal-containing monomer will contribute a higher density to the stock than other types of monomers such as esters of unsaturated acids, when required, the amount of filler needed to adjust the density will usually and advantageously be relatively low.
If an inert filler is desired, any known or conventional filler may be used which should be in finely divided form as, for example, in a form less than about 20 mesh, and preferably less than about 60 mesh United States Standard screen size. Suitable fillers are silica and silicates, zinc oxide, carbon black, cork, titania, cotton flock, cellulose flock, leather fiber, plastic fiber, plastic flour, leather flour, fibrous fillers such as asbestos, glass and synthetic fibers, metal oxide and carbonates, and talc. Particularly useful is the oxide or carbonate of the same metal which is present in the metal-containing monomer. Impact modifiers such as ultra-high molecular weight polyethylene and acrylonitrile-butadiene-styrene ~7~

resin can also be used.
The amount of inert filler is dic~ated mainly by its type, and is preferably less than about 30 parts per hundred parts of elastomer base, and more preferably less than about 15 parts.
Advantageously, a polymerization initiator is used, which decom-poses to produce free radicals during the cure cycle. ~he polymerization initiator need only be present in the cataLytic amount required ~or this function and may be in general used in the amount that the particular agent is generally used as a polymerization catalyst. Suitable initiators include peroxides, persulfates, azo compounds, ~ydrazines, amine oxides, ionizing radiation, and the like. Peroxides such as dicumyl peroxide, l,l-di-t-butyl-peroxy-3,3,5-trimethylcyclohexane, di-t-butyl peroxide, and 2,5-bis~t-butyl-peroxy)-2,5-dimethylhexane are commercially available and conveniently usedJ
usually in amounts of about 0.2-10% by weight of the elastomer. -For the production of golf balls, the ingredients should initially be intimately mixed using, for example, rubber mixing rolls or a Banbury mixer, until the composition is uniform. In order to promote good disper-sion, the metal-containing monomer may advantageously be formed in situ, for example from the metal oxide and corresponding acid, as has been described above. Otherwise, the mixing is basically done in a manner which is common in the elastomer art.
The temperature of the mixing is not critical but should, of course, be below curing temperature, and the mixing is generally affected at room temperature, though through friction the ingredients may be warmed.
This again follows rubber milling practice and involves no new technique.
The molding is effected in mating, precision hemisphere molds or dies whose molding surface is covered with multiple regular projections to give the molded ball conventional dimpled or waffled surface appearance in order to improve its aero-dynamic characteristics. The molding is a simple?
straight-forward operation effected in the conventional manner used in pre-_ g _ cision molding. The material, after being thoroughly mixed may be formedinto slugs in the customary manner and the slugs, which may be cylindrical or any other desired shape which will facili-tate the insertion in the mold, should be proportioned so that the mold is fully filled.
In cross-linking there is about a 2.4% linear contraction but this is sometimes less than the expansion due to mold heating and the heat gener-ated by curing. Therefore, in accordance with a preferred aspect of the in-vention the slugs are preheated to about 100 C, as in an oven, preferably an RF oven, whereby they undergo some initial expansion which would otherwise occur within the heated mold. Thus there is less pressure built up within the closed mold which eliminates the tendency, otherwise sometimes exhibited, for the mold halves to separate slightly, change the internal dimensions and produce out-of-round balls. The mating halves of the mold are then closed on the preheated slug so that the mold cavity is entirely filled. The mold halves may be held together with pressures between about 100 and 15,000 psi, preferably about 5,000 to 10,000 psi.
Molding temperature may vary depending on the particular composi-tion used and may, for example, range between 130 and 200C. During times may range from 1 to 50 minutes, and preferably from 5 to 30 minutes.
It is preferred to optimize the curing ~ime and temperature in order to obtain the best properties of the golf ball. The best curing condi-tions are usually different for each different formulation selected. Because of the highly exother~ic nature of the curing process, the properties of the present golf balls are highly sensi~ive to curing conditions, in contrast to the prior art balls made using only metal-free monomers.
After molding, the balls are removed from the mold and any mold marks buffed off, and the ball is painted and marked, and is then ready for use. Painting may be effected in the conventional manner using the conven-tional paints used for golf balls, as for example, enamel, polyurethane, epoxy, acrylic, or vinyl paints.

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The invention will be further described in the ~ollowing illustra-tive examples wherein all parts are by weight unloss otherwise expressed.
In these examples, the properties of the golf balls are measured by a variety of tests.
The cannon life test is a measure of the durability of a golf ball under severe impact conditions. In this test J a box is constructed of 1/4-inch thick steel plate in the shape of a r,ectangular prism wi$h edges 2 ft.
by 2 ft. by 3 ft. One end of a steel tube 1.687 inches in internal diameter by 5 ft. long is sealed to one 2 ft. by 3 ft. face of the box at a point which is one foot from a 2 ft. edge and the same distance from a 3 ft. edge.
The axis of the tube is inclined 45 to a line parallel to the 2 ft. edge of said face, and 80 to a line parallel to the 3 ft. edge of the face. The other end of the tube is connected to a 20-gallon air tank via a fast-acting valve and contains a port for introducing a golf ball. The tube thus consti-tutes an air cannon.
In operation, the air tank is pressuri7ed to 40 pounds per square inch, and the ball is shot into the box by sudden release of the air pres-sure. The "cannon life" given in Table I is the average number of succes-sive shots which a golf ball will withstand before rupturing or otherwise becoming unplayable. Usually at least six or ten balls are tested for can-non life, and the results are averaged.
"Rebound" is the height to which a ball will bounce, expressed as a percentage of the height from which it is dropped onto a hard, flat, hori-zontal surface, such as a thick marble slab. A ball with higher rebound is "livelier" in play and is thus more acceptable to serious or professional golfers. For two golf balls equal in compression and hardness the ball with the higher rebound generally also has the more acceptable "click".
The distance of various kinds of golf balls are compared using a driving machine. The driving machine consists essentially of a golf club face attached to the periphery of a steel flywheel, 2~ inches in diameter, ~ .

and weighing 300 pounds. The golf club face is adjusted to strike the test golf balls while making an angle of L7 to the vertical. In operationl the flywheel is rotated at a speed of 1200 revolutions per minute~ corresponding to a club face velocity of 150 ft./sec., and a means is provided to hit the balls at the rate of 120 balls per minute. At this rate variations in wind or other weather factors do not affect the validity of a direct comparison among the distances of different balls thus struck within a very short period of time. To compare balls for distance, alternate sample balls of the different types are driven at the rate of about 120 balls per minute, caught in a sand trap, and their distances measured. Several balls of each type, usually 10, are tested and the results are averaged.
The term "Compression" in the golf ball industry relates to an arbitrary value expressed by a number which can range from 0 to over 100, and that defines the deflection that a golf ball undergoes when subjected to a compressive loading. The specific test is made in an apparatus fashioned in the form of a small press with an upper and a lower anvil. The upper an-vil is at rest against a 200-pound die spring, and the lower anvil is mov-able through .300 inches by means of a crank mechanism. In its open posi-tion the gap between the anvils is 1.780 inches allowing a clearance of .100 inches for insertion of the ball. As the lower anvil is raised by the crank, it compresses the ball against the upper anvil, such compression occurring during the last .200 inches of stroke of the lower anvil, the ball then lead-ing the upper anvil which in ~urn loads the spring. The equilibrium point of the upper anvil is measured by a dial micrometer if the anvil is deflect-ed by the ball more than .100 inches (less deflection is simply regarded as zero compression) and the reading on the micrometer dial is referred to as the compression of the ball. In practice, tournament quality balls have compression ratings a:round 90 or 100 which means that the upper anvil was deflected a total of .190 or .200 inches.

- 12 _ Example 1 One hundred parts of cis-polybutadiene were blended with 30 parts of glacial methacrylic acid and 15 parts of ~inc oxide in a Brabender Plasti-Corder mixing machine. The temperature of the stoc~ increased from an ini-tial 100C to about 150C over the mixing period of 10 minutes. The batch was removed, allowed to cool, then blended on a mill with 4 parts of Di-Cup ~ 40-C, which is a commercial polymerization initiator consisting of 40%
dicumyl peroxide supported on calcium carb~nate. The batch was formed into suitable slugs and molded into homogeneous, unitary golf balls in a commer-cial golf ball press for a total cure cycle of 15 minutes at 170 C.
Example 2Homogeneous unitary golf balls were made following the teaching of Bartsch United States Patents 3,313,545 and 3,438,933, using the following formulation:
Parts by Weight cis-Polybutadiene 100 Trimethylolpropane trimethacrylate 37 High density polyethylene - 14.3 Magnesium oxide 3.8 Titanium dioxide 2.8 Reinforcing silica 35 2,2'-Methylene bois ~4-methyl-6-tertiarybutylphenol) 40% dicumyl peroxide supported on calcium 3.8 carbonate.
The batch was cured 15 minutes at 170 C in a commercial press to yield homogeneous golf balls.
Table I

Top-Grade Commercial Example Number: 1 2 Wound Ball Rebound, percent 81 72 69 ~`

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Table I Cont'd Top-Grade Commercial Example Number: 1 _2~ Wound BA11 Click excellent good excellent Compression 85 81 90 Shore Hardness, C 79 ~2 75 Cannon Life, Shots (average) 10 4.1 o The characteristics of the balls of Examples 1 and 2 are compared with those of a commercial top-grade conventional wound ball in Table I.
The golf ball made according to the method of the present inven-tion, Example 1, is more durable than either the conventional wound ball, or the homogeneous ball of the previous art, as indicatad by the higher cannon life. The ball also has excellent click, equal to that of the top-grade wound ball, and better than that of the best previous homogeneous ball.
Example 3 Cis-polybutadiene ~100 parts) was blended on a two-roll rubber mill with 30.4 parts of zinc dimethacrylate and 6.3 parts of Di-Cup ~ 40-C, a commercial polymerization initiator containing 40% by weight of dicumyl per-oxide and 60% by weight of inert carrier. When thoroughly blended the stock was sheeted off the mill~ formed into suitable slugs, and molded into golf balls on a production press for 15 minutes at 180 C.
Example 4 One hundred parts of cis-polybutadiene were blended on a mill with 17 parts of zinc oxide. 22.2 parts of methacrylic acid was slowly added and blended until thoroughly dispersed. After a few minutes there was very little odor of methacrylic acid from the stock, indicating that the acid had thoroughly reacted with the zinc oxide to form zinc dimethacrylate. 6.3 parts of Di-Cup ~ 40-C was then blended into the rubber. Golf balls were molded as in Example 3.
The level of zinc oxide plus methacrylic acid in Example 4 is stoichiometrically equivalent to the level of zinc oxide plus zinc dimeth-'~

acrylate in Example 3, in each case constituting 30.4 parts of re~ctive fil-ler ~zinc dimethacrylate) and 6.3 parts of inert filler (zinc oxide).
Table II
Example Number: 3 4 Rebound, percent 82 80 Click good excellent Compression 32 88 Shore llardness, C 83 gO
The balls of Examples 3 and 4 had excellent playing characteristics, and were durable and cut-resistant. As shown in Table II, the ball made by reacting zinc oxide and methacrylic acid in situ (Example 4) had somewhàt better click and compression than the ball made using zinc dime~hacrylate.
Both balls were very lively in play, as evidenced by high rebound.
Examples 5 through 14 Batches were blended on a mill using the formulations given in Table III. In Examples 6 through 14, the appropriate metal carbonate or ox-ide other than zinc oxide was first blended with the cis-polybutadiene gum, and then, the methacrylic acid added. Blending was continued for several minutes until the methacrylic acid had substantially reacted, as evidenced by a relatively low odor of residual methacrylic acid. In Examples 6, 7, and 13, the zinc oxide was then blended into the batch. Finally Di-Cup ~ ~
40-C, a mixture of 40% dicumyl peroxide supported on calcium carbonate, was blended into the batch.
Each batch was sheeted off the mill, formed into suitable slugs, and molded into golf balls.

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Examples 6 through l~ can be molded into golf balls which exhibit excellent playing characteristics, high durability, and good distance. Ex-ample 5 is a control which contains no metal-containing polymerizable cross-linking monomer; balls molded from this stock exhibit no click and are very soft.
Examples 15 through 18 In Table IV, examples are given of other embodiments of the present invention which utilize various other metal-containing polymerizable cross-linking monomers, viz, zinc dicinnama*e, zinc dicrotonate, zinc diacrylate, and magnesium diacrylate. In these formulations each of the monomers has been introduced by reaction in situ, in order to favor a high degree of dis-persion within the polybutadiene base.
Each of the compositions of Table IV can be molded into golf balls with good playing characteristics, high durability, and acceptable click.

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L~ ¦ O --I b4 J~ r 1~ o .~ , Examples 19, 20, and 21 If desired, within tne scope of the present invention metal-contain-ing polymerizable monomers may be blended ~ith metal-free polymerizable mon-omers, for example, methacrylate esters such as trimethylolpropane trimeth-acrylate or hydroxyethyl methacrylate.
The formulations of Examples 19, ~0, and 21, Table V, were blended and molded into golf balls which exhibited high compression, good or excel-lent click, high durability, and excellent playing characteristics.

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Examples 22 ancl 23 The distances of balls made in accordance with the present inven-tion was compared with that of prior art homogeneous balls, and top-grade wound balls, using a driving machine.
Example 22 represents balls made according to the formulation de-scribed in Example 1, except that the batch was blended in a Banbury mixer.
Example 23 similarly represents balls made according to the formulation of Example 2, and mixed in a Banbury mixer. Each batch of ~xamples 22 and 23 were cured in production presses for 15 minutes total cure cycle at 180C.
Table VI
Example Number: 22 _ 23 Control Type of golf ball:present prior art top-grade invention homogeneous commercial ball wound ball Average distance, yards, lQ in driving machine: 234 217 225 Thus, it is seen from the results in Table VI that balls made ac-cording to the method of the present invention have greater distances than homogeneous unitary balls of the prior art, or than top-grade commercial wound balls.
Examples 24 to 30 The following batch was blended in a Banbury mixer for about 20 min-utes; the maximum temperature reached during mixing was about 220F.
cis-polybutadiene 80.7 lb.
zinc oxide 16.7 lb.
methacrylic acid 19 lb.
2,2'-methylene bis (4-methyl-6-tertiary butyl phenol) 0.20 lb.
40% dicumyl peroxide on calcium carbonate 5.25 lb.
The batch was then sheeted on a 2-roll mill, extruded and cut into cylindri-cal slugs, and then molded into golf balls at various cure times and temper-.

atures as indicated in Table VII. The compression, relative driving machine distance) average cannon life, and rebound shown in Table VII indicate the large effect of curing time and temperature on the properties of the ball.
It is thus a matter of ordinary skill to optimize the curing time and tem-perature for a given formulation.
TABLE VII
Example No.: 24 25 26 27 28 29 30 .
Cure Time, min. 30 30 30 20 20 15 10 Cure Temperature, C150 155 160 160 180 180180 Ball Characteristics .
Compression 0 95 100 35 85 88 85 Relative Distance, yds. 221 218 222 222225 226 225 Rebound, % 70 75 78 74 79 80 78 Cannon Life, Average4 >20 9 3 0 1 2 Example 31 Cis-polybutadiene (100 parts) was blended with 40 parts of dibutyl-tin diacrylate, 30 parts of reinforcing silica, and 2 parts of dicumyl per-oxide. The batch was molded 15 minutes at 170 C to yield a ball with excel-lent click, 79% rebound, a compression of 60, good durability and excellent playing characteristics.
Example 32 The process of Example 1 was repeated with the -following differ-ences: the weight of zinc oxide filler was increased to 18 parts and the methacrylic acid monomer decreased to 25 parts, the two interacting to form zinc dimethacrylate which func~ions both as filler and cross-linking mon-omer; there is an excess of unreacted zinc oxide which`also serves as filler to bring the density to the desired overall value. The slugs were preheated in an RF oven to raise their temperature throughuut to 100C prior to being placed in the mold. The balls were cured at 165C for 16 minutes, the exo-therm peak temperature rising to 225 C. The balls were characterized by less '~g . . ~ , . . .

9Lq~

than 5 points Shore C variation in hardness between the center and outside.
The balls are characterized by good si~e, cannon life, seam and distance properties and by most accurate flight characteristics.
It will be appreciated that the instant 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.

Claims (35)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a homogeneous molded ball having the density and click and rebound required in a golf ball and comprising a filled elastomer highly cross-linked into a three dimensional network with long, flexible cross-links formed of a polymerized cross-linking monomer, the improvement wherein said cross-linking monomer comprises a metal-containing cross-linking monomer and is present in about 0.046 to 0.41 equivalents per mole of elastomer base whereby said monomer simultaneously functions as said filler at least in part, said ball in addition to said filler-functioning cross-linking monomer containing up to about 30 parts of a further filler per 100 parts by weight of said elastomer, the amount of said further filler being sufficient to impart to said golf ball a weight of about 1.500 to 1.620 ounces.

2. A golf ball according to claim l wherein said filler is present in up to about 15 parts per 100 parts by weight of said elastomer.

3. A golf ball according to claim l wherein said metal-containing cross-linking monomer comprises a salt of at least one metal selected from the group consisting of zinc, magnesium and calcium, and at least one acid selected from the group consisting of methacrylic, acrylic, cinnamic, acotinic, crotonic, vinylacetic, itaconic and benzoylacrylic acids.

4. A golf ball according to claim l wherein said elastomer comprises polybutadiene and said metal-containing cross-linking monomer comprises zinc dimethacrylate present in about 20 to 50 parts per 100 parts by weight of the poly-butadiene.

5. A golf ball according to claim 4 wherein the composition additionally contains up to about 15 parts by weight of zinc oxide per 100 parts by weight of polybutadiene.

6. In the process for producing an homogeneous molded golf ball comprising a filled elastomer highly cross-linked into a three dimensional network with long flexible cross-links comprising molding an intimate mixture of an elastomer, a cross-linking monomer, a metal containing filler, and a free radical catalyst, the improvement which comprises using as said cross-linking monomer about 0.046 to 0.41 moles per mole of elastomer base of a metal-containing cross-linking monomer selected from the group consisting of (RCO2)m?M, R(SO3)m?M, R(SO2)m?M, (RCO2)p?MO, (RSO3)p?MO, R(SO2)p?MO, (R2PO2)m?M, (R2PO2)p?MO, (RPO3)q?M, (RPO3)?M'O, , , and wherein each R independently is a group having at least one polymerizable olefinic unsaturation, R' is a divalent group having a polymerizable olefinic unsaturation, each R" independently is an alkyl, aryl or aralkyl group, M is a metal ion having a valence, m, of from 1 to 5, M' is a metal ion having a valence of 4, M" is a metal ion having a valence of 1 or 2, p is m-2 when m is greater than 2, and q has the value m/2 when m is 2 or 4, whereby it simultaneously functions as said filler at least in part.

7. The process according to claim 6, wherein said intimate mixture is formed by mixing said elastomer with a cross-linking monomer and with at least the stoichiometric amount of a metal-containing compound reactive with said monomer under the conditions of mixing or molding whereby said metal-containing cross-linking monomer is formed in situ.

8, The process according to claim 6, wherein said metal-containing compound is used in an excess of the stoichiometric amount up to about 30 parts by weight per 100 parts of the elastomer.

9. The process according to claim 6, wherein said metal-containing compound is used in an excess of the stoichiometric amount up to about 15 parts by weight per 100 parts of the elastomer.

10. The process according to claim 6, wherein said metal-containing cross-linking monomer comprises a salt of at least one metal selected from the group consisting of zinc, magnesium and calcium, and at least one acid selected from the group consisting of methacrylic, acrylic, cinnamic, acotinic, crotonic, vinylacetic, itaconic and benzoylacrylic acids.

11. The process according to claim 8 wherein the elastomer comprises polybutadiene, the monomer comprises methacrylic acid anct said metal-containing compound is zinc oxide present in amount sufficient to form about 20 to 50 parts of zinc dimetacryl-ate based on 100 parts by weigh of polybutadiene and to leave up to about 15 parts of unreacted zinc oxide per 100 parts by weight of polybutadiene.

12. A solid unitary golf ball prepared from a composition comprising 100 parts of polybutadiene having a cis 1,4 poly-butadiene content of at least 40% and a divalent metal salt of a monoethylenically unsaturated carboxylic acid present in sufficient quantity to cross-link said polybutadiene and form said solid unitary golf ball when said composition is cured in a standard golf ball mold at a temperature between 266°F. and 392°F. for from 1 to 50 minutes.

13. A solid unitary golf ball prepared from a composition comprising a cross linkable elastomer and as a cross linking agent a metal salt of an organic acid, the metal being selected from the class consisting of monoval-ent, divalent, and trivalent metals, the organic acid being selected from the class consisting of .alpha.,.beta.-ethylenically unsaturated mono- and di-carbox-ylic acids containing from three to eight carbon atoms, the cross linking agent being present in sufficient quantity to cross link said elastomer and form said solid unitary golf ball, when said composition is cured in a stan-dard golf ball mold under standard unitary golf ball molding conditions.

14. A solid unitary golf ball prepared from a composition comprising a cross linkable elastomer and as a cross linking agent a metal salt of an organic acid, which is selected from the class consisting of neutral and basic zinc methacrylate, the cross linking agent being present in sufficient quantity to cross link said elastomer and form said solid unitary golf ball, when said composition is cured in a standard golf ball mold under standard unitary golf ball molding conditions.

15. A solid unitary golf ball prepared from a composition comprising a cross linkable polybutadiene and as a cross linking agent a metal salt of an organic acid, the metal being selected from the class consisting of mono-valent, divalent and trivalent metals, the organic acid being selected from the class consisting of .alpha.,.beta.-ethylenically unsaturated mono- and di-carboxylic acids containing from three to eight carbon atoms, the cross linking agent being present in sufficient quantity to cross link said polybutadiene and form said solid unitary golf ball, when said composition is cured in a stan-dard golf ball mold under standard unitary golf ball molding conditions.

16. A solid unitary golf ball prepared from a composition comprising a cross linkable polybutadiene and as a cross linking agent a metal salt of an organic acid which is selected from the class consisting of neutral and basic zinc methacrylate, the cross linking agent being present in sufficient quantity to cross link said polybutadiene and form said solid unitary golf ball, when said composition is cured in a standard golf ball mold under standard unitary golf ball molding conditions.

17. A solid unitary golf ball prepared from a composition comprising a cross linkable cis polybutadiene and as a cross linking agent a metal salt of an organic acid, which is selected from the class consisting of neutral and basic zinc methacrylate, the cross linking agent being present in suffi-cient quantity to cross link, said cispolybutadiene and form said solid uni-tary golf ball, when said composition is cured in a standard golf ball mold under standard unitary golf ball molding conditions.

18. A process of manufacture of a solid unitary golf ball from a com-position comprising a cross linkable elastomer and as a cross linking agent a metal salt of an organic acid, the metal being selected from the class con-sisting of monovalent, divalent, and trivalent metals, the organic acid being selected from the class consisting of .alpha.,.beta.-ethylenically unsaturated mono- and di-carboxylic acid containing from three to eight carbon atoms, the cross linking agent being present in sufficient quantity to cross link said elasto-mer, the process comprising forming said composition, molding said composi-tion and curing said molded composition.

19. A process of manufacture of a solid unitary golf ball from a com-position comprising a cross linkable elastomer and as a cross linking agent, a metal salt of an organic acid, the metal being selected from the class con-sisting of monovalent, divalent, and trivalent metals, the organic acid being selected from the class consisting of .alpha.,.beta.-ethylenically unsaturated mono- and di-carboxylic acid containing from three to eight carbon atoms, the cross linking agent being present in sufficient quantity to cross link said elasto-mer, the process comprising forming said composition, molding said composi-tion and curing said molded composition, where said cross linking agent is formed in situ.

20. A process of manufacture of a solid unitary golf ball from a com-position, comprising a cross linkable elastomer and as a cross linking agent a metal salt of an organic acid, which is selected from the class consisting of neutral and basic zinc methacrylate, the cross linking agent being pres-ent in sufficient quantity to cross link said elastomer, the process com-prising forming said composition, molding said composition and curing said molded composition.

21. A process of manufacture of a solid unitary golf ball from a com-position comprising a cross linkable elastomer and as a cross linking agent a metal salt of an organic acid, which is selected from the class consisting of neutral and basic zinc methacrylate, the cross linking agent being present in sufficient quantity to cross link said elastomer, the process comprising forming said composition, molding said composition and curing said molded composition, where said cross linking agent is formed in situ.

22. A process of manufacture of a solid unitary golf ball from a com-position comprising a cross linkable polybutadiene and as a cross linking agent, a metal salt of an organic acid, the metal being selected from the class consisting of monovalent, divalent, and trivalent metals, the organic acid being selected from the class consisting of .alpha.,.beta.-ethylenically unsatur-ated mono- and di-carboxylic acid containing from three to eight carbon atoms, the cross linking agent being present in sufficient quantity to cross link said polybutadiene, the process comprising forming said composition, molding said composition and curing said molded composition.

23. A process of manufacture of a solid unitary golf ball from a com-position comprising a cross linkable polybutadiene and as a cross linking agent a metal salt of an organic acid, the metal being selected from the class consisting of monovalent, divalent and trivalent metals, the organic acid being selected from the class consisting of .alpha.,.beta.-ethylenically unsaturat-ed mono- and di-carboxylic acids containing from three to eight carbon atoms, the cross linking agent being present in sufficient quantity to cross link said polybutadiene, the process comprising forming said composition, molding said composition and curing said molded composition, where said cross linking agent is formed in situ.

24. A process of manufacture of a solid unitary golf ball from a composition comprising a cross linkable polybutadiene and as a cross linking agent a metal salt of an organic acid, which is selected from the class con-sisting of neutral and basic zinc methacrylate, the cross linking agent being present in sufficient quantity to cross link said polybutadiene, the process comprising forming said composition, molding said composition and curing said molded composition.

25. A process of manufacture of a solid unitary golf ball from a composition comprising a cross linkable polybutadiene and as a cross linking agent a metal salt of an organic acid, which is selected from the class con-sisting of neutral and basic zinc methacrylate, the cross linking agent being present in sufficient quantity to cross link said polybutadiene, the process comprising forming said composition, molding said composition and curing said molded composition, where said cross linking agent is formed in situ.

26. A process of manufacture of a solid unitary golf ball from a com-position comprising a cross linkable cispolybutadiene and as a cross linking agent a metal salt of an organic acid, which is selected from the class con-sisting of neutral and basic zinc methacrylate, the cross linking agent being present in sufficient quantity to cross link said cispolybutadiene, the pro-cess comprising forming said composition, molding said composition and curing said molded composition.

27. A process of manufacture of a solid unitary golf ball from a composition comprising a cross linkable cispolybutadiene and as a cross link-ing agent a metal salt of an organic acid, which is selected from the class consisting of neutral and basic zinc methacrylate, the cross linking agent being present in sufficient quantity to cross link said cispolybutadiene, the process comprising forming said composition, molding said composition and curing said molded composition, where said cross linking agent is formed in situ.

28. A golf ball as in claim 14, wherein there is not more than 1.5 moles of zinc oxide per mole of methacrylic acid.

29. A golf ball as in claim 16, wherein there is not more than 1.5 moles of zinc oxide per mole of methacrylic acid.

30. A golf ball as in claim 17, wherein there is not more than 1.5 moles of zinc oxide per mole of methacrylic acid.

31. A process as in claim 25, wherein there is not more than 1.5 moles of zinc oxide per mole of methacrylic acid.

32. A process as in claim 26, wherein there is not more than 1.5 moles of zinc oxide per mole of methacrylic acid.

33. A process as in claim 27, wherein there is not more than 1.5 moles of zinc oxide per mole of methacrylic acid.

34. A solid unitary golf ball, cured under standard unitary golf ball molding conditions in a standard golf ball mold, comprising poly-butadiene having a high cis-1,4-polybutadiene content crosslinked by metal-carboxyl groups attached to the polybutadiene, wherein said metal is at least one of mono-, di-, and trivalent metals, and said carboxyl group is derived from an .alpha.,.beta.-ethylenically unsaturated mono- or di-carboxylic acid comprising from three to eight carbon atoms.

35. A process of manufacture of a solid unitary golf ball, under standard unitary golf ball molding conditions in a standard golf ball mold, by crosslinking polybutadiene having a high cis-1,4 polybutadiene content by means of metallic and carboxyl groups sufficient to crosslink said polybutadiene, the process comprising molding and curing a composition polybutadiene, metallic and carboxyl groups, wherein said metallic groups are at least one of mono-, di-, or trivalent metals, and said carboxyl groups are derived from an .alpha.,.beta.-ethylenically unsaturated mono- or di-carboxylic acid comprising from three to eight carbon atoms.