CA1266144A - Golf ball having improved playability properties - Google Patents

Abstract

Abstract of the Disclosure Disclosed is a golf ball having improved short iron and wood playability and improved puttability relative conventional, inonomer covered balls. The golf balls comprise a novel cover which is far more durable than balata-covered balls yet closely approach or exceed their playability characteristics. The cover comprises a blend of a thermoplastic urethane having a Shore A hardness less than 95 and an inonomer having a Shore D hardness greater than 55. The relative amounts of the urethane and ionomer are set so that the cover has a Shore C hardness within the range of 70 to 85.

Description

f ~ abili~

SPH-003 (P-2113) 8ack~round of the Inven~lon This invention relates to golf balls and more par~icularly to an improved golf ball c~ver use~ul in making balls, pargicularly two-piece balls, having ~uperior ghort iron and other playa~ility characteristics.

Balata ~nd blends of balata with elastomeric vr plastic materials were ~or many years the materials of choice in the manufacture of covers for top grade golf balls. These materials have good molding properties and accordingly could be readily compression molded about a spherical wound core to produce a high quality gol~ ball. An experienced player can apply spin to a balata covered wound ball such that it will fade or draw in flight or have the backspin necessary to stop abruptly on the green. These playability properties are most important in ~hort iron play and can be exploited ~ignificantly only by relatively ~killed players.

Balata and it~ synthetic substitutes, trans polybutadiene and trans polyisoprene, have today essentially been replaced by new material~. With the exception of a few lines of golf balls distri~uted through pro ~hops to professional ~olfers and those who-would emulate ~hem, newer synthetic polymer~ are the cover materials of choice.

Of the new synthetic~, by far the most commonly used are a line of ionomer~ ~old by E. I. Dupont de Nemour6 &
Company under the trademark SURLYN. These materials comprise copolymers of olefins, typically ethylenet with an alpha, beta, ethylinically uncaturated carboxylic acid such as methacrylic acid. Metal io~s ~uch a~ s~dium or zinc are used ~o neutralize ~ome p~rtion of the acidic groups in the copolymer resul~ing in a thexmoplastic elastomer which has ~everal advantages including a cost advantage over balata. The ionomerC- may be manufactured with a wide variety of proper~ie6 by al~ering the identity of the comonomers, the fraction of the polymer comprising the carboxylic ac~d, the molecular weight of the polymer, the degree of neutralization of the polymer~ and the identity of the metal ions used~ Control of these parameters resul~s in ionomer resins of different melt index, hardness, resiii nce and other mechanical properties which, in a gol ball cover, affect cut resistance, ~hear resistance, general durability, and resilience~

U.S. Patent 3,819,768 to R. P~ Molitor discloses that blends of sodium neutralized ionomer resins with zinc neutralized ionomer resins, as a class, have certain advantages which have not been achievable in any other way. Among these is the production of an unexpectedly high coefficient of restitution of golf balls having the blended ionomer ~over.
Such covers also resist cold cracking~ have excellent aging properties, and are unexpectedly durable. The development of the SURLYN blended cover has been a major factor ~n ~he production of two-piece balls having cover~ which for all practical purposes cannot be cut in play, ~nd which travel further when hit than any other VSGA regulation ball as measured by controlled te5t5 when hit by golfers or testing machines.

. .

While the balata-covered, thread-wound balls are easily cut and very expensive, they nevertheles~ have excellent short iron playability. It is much ~nore difficul~ to impart spin to an ionc~mer covered two-piece ball. ~requently, experienced players note that the ionomer covered two-piece balls have an unsatisfactory "feeln.

The patent literature is replete wi~ch propo5ed cover formulatiDns seeking to improve upon the balata and ionomer covers which have been commercially successful. Polyurethanes, thermoplastic rubbers, various block copolymers, polyesters, and polyamides, as well as various blends including such materials, have been proposed. Examples include: U.S.
3,359,231, ll.S. 4,398,000, U.S. 4,234,184, U.S. 4,295,652, IJ.S.
4,248,432, U.S. 3,989,568, U.~. 3,310,1~2, U.S. 4,337,947, U.S.
4,123,061, and U.S.. 3,490,146~

The manufacture of two-piece balls i4e., balls comprising a solid, molded, resilient core and a cover, has many significant advantages over 'che more expensive wound ball~. There is accordingly a need for two-piece balls having short iron playability characteristics comparable to wound, balata covered balls.

.. . . .. .. .. ..

Summary _f the_Inventlon It has now been discovered that a key to manufacturing a two-piece hall having playability properties similar ko wound, balata-covered balls is to provide about an inner resilient molded core a cover having a shore C hardness less than 85. The cover of khe novel golf ball of khe invenkion i5 made o~ a composition comprising a blend of 1) a thermoplastic urethane having a shore A hardness less than 95 and 2) an ionomer having a ~hore D hardness greater than 55. The ionomer comprises ole~inic groups having two to four carbon atoms copolymerized with acrylic or methacrylic acid groups and cross-linked wikh metal ions, preferably sodium or zinc ions. The primary componen~s of the blended cover are set at a weight ratio so as to result in a cover material after molding having a shore C
hardness within the rànge of 70 to 85. Preferably, the urethane component o~ the cover material has a tensile strength of at least 2500 psi and an elongation at break of at least 250~. A
preferred cover material comprises about 8 parts of the thermoplastic urethane and between 1 and 4 parts ionomer.
Preferably, the cover is no greater than 0~060 inch thick.
Thinner covers appear to maximize the short iron playability characteristics of the balls.
The cover composition of the invention may be used in connection with the manufacture of thread-wound balls, but is preferably used in the manufacture of balls having molded cores.
Two-piece balls made with the cover of the invention JJ ,ci.

have short ir~n playability pr~perties as g~od as or better than balata-covered wound balls but are ~ignificantly more durable. They also have better w~od playabili~y properties than conven~ional two-piece ball~, and permit experienced golfers ~o apply spin so as ~o fade or draw a shot~
Puttability is slso improved.

Tests have sho~n that ~he spin rate off a nine iron of tw~-piece balls c~mprising the cover material of the invention is about 9,550 rpm vs. about 5,400 rpm for state of the art, two-pie~e balls having ionvmer covers. This compares favorably to balata-covered wound balls which under the same hitting conditions have a spin rate of about 9,700 rpm. The phrase "two-piece ball" as used herein refers primarily to balls consisting of a molded core and a ~over, but also incl~des balls having a separate solid layer beneath the cover as disclosed, for example, in U.S. Patent No. 4~431,193 to Nesbitt, and other balls having nonwound cores.

The increased spin that can be applied during a proper hit to balls having the cover of the invention is believed to be due primarily to the softness of the blended cover material. On impact, the cover deforms significantly more than balls having ionomer cover~, and tests have ~hown that there is a greater area of contact between the ball and the club face.
This permits the better playér to impart ~ade, draw, or backspin to the ball as the ~ituation dictates, and permits the player to execute be~ter chips and other ~hot6 to ~he green.
On ~hot~ of ~hort range, e.g., less than 50 yard~, the two-piece ball~ of the invention often outperform .. .. . ....

~ $~
balata-covered wound balls. Regarding pu~tability~ two-p~ece balls including ~he cover of the inven~io~ have a lower drop rebound relative to c~nventional two-piece balls, and have increased contact time on th~ p~tter ~ace. These c~Jarac~eri~tics combine to enable the player better to control the putting line and distance.

Th~ preferred components o~ the cover ma~erial comprise a thermoplastic polyurethane consisting essentially of linear primary polymer chains. ~he stru~ture of such chains preferably comprises long, flexible chain segments joined end to end by rigid chain ~egments through covalent chemical bonds. The flexible ~egments typically are diisocyanate-coupled, low melting polyester or polyether ~hains. The rigid ~egment~ include ~ingle diurethane bridges and high melting urethane chain segments ~ormed by the reaction of diioscyanate with ~mall glycols. Hydrogen bonding and other ~tractive forces among the rigid chain segments are believed to produce domains which are mutually attractive, behave ~omewhat like cross-links, and are reversible with heat and with ~olvation.

The preferred second component of the cover composition is an ionomer comprising olefinic groups having two four carbon atoms copolymerized with acrylic or methacrylic acid groups which are ~t leagt partially neutralized with a ~odium or zinc ion, e.g., 8 SU~LYN ionomer. Inclusion of the ionomer imparts to the cover a degree of cut resistence far in excess of balata and helps to control the melt index of the blend to facilitate molding.

The cover composition oE the invention may be used to formulate golf ball covers by injection or compression moldiny about wound cores, solid molded cores of known composition, high coefficient molded cores such as those disclosed in U.S0 Patent No. 4,726,590, or cores of the type claimed in U.S. Patent No.
4,650,193 which has an inner, hard centxal portion and a soft outer layer. Various combinations of the solid core technologies may also be used.
Accordingly, it is an object of the invention to provide a cover composition which can be injection molded or compression molded about a solid molded core to produce golf ball covers which are more durable and cut resistent than balata rubber-covered balls. Another object is to provide a two-piece ball having short iron and other playability characteristics equal to or exceeding thread-wound balata-covered balls. Another object is to provide a cover composition compatible with urethan-based paints which resists chipping and peeling.
These and other objects and features of the invention will be apparent from the following description and from the claims.

JJ~ 7 i~

escri~on The cover compDsiti~n of the inventi~n in i~ ~roadest aspects c~mprise~ a blend of a thermoplas~ic urethane having a shore ~ hardness less than 95 t~gether with an ionomer resin having a shore D hardness greater than 55 ~t weight ratios ~ufficient to result in a golf ball cover having a shore C hardness wit~in the xange of 70 to 85, preferably within the ranqe of 75 to 80, and most preferably about 78.

The thermoplastic urethanes useful in the cover preferably consist essentially of linear primary polymer chains having a preponderence ~f relatively long, flexible chain segments joined end to end by rigid chain segments through covalent chemical bonds~ The flexible ~egment~ may be diisocyanate coupled, low melting polyester or polyether chains. The rigid segments include single diurethane bridges resulting when a diisocyanate couples to polyester or polyether molecules. The rigid segments may comprise longer high melting urethane chain segments formed by the reaction of diisocyanate with a low molecular weight glycol chain extende~ component.

The polar nature of the recurring rigid, urethane chain segments results in their strong mutual attraction, aggregation, and ordering into ~rystalline and polycrystalline domainc in the mobile polymer matrix. Urethane hydrogen atoms and carbonyl and ether oxygen partners are believed to permit extensive hydrogen bonding among ~he polymer chains. This apparantly restricts the m~bility of the urethane chain segments in the domains. These attractions and chain entanglements prod~ce ~herm~-la~ile pseudo cross-links and prod~ce resins ~hich can display the superficial proper~ieS of strong rubbery vulcani~tes. Preferred ~herm~plas~ic urethanes in the cover compositi~n of the inven~ion have a tensile strength of at least 2500 lb/in2 and an elongation at break of at least 250 percentO Most preferably, tensile s~rength and elongation at break are 40DOlb/in~ and 400 percent, respectively, Such materials are available commercially from Mobay Chemical Company under the trademark T~XIN, from B~Fo ~oodrich under the trademark ESTANE, fr~m Upjohn Company under ~he trademark PELLETHANES, or from X. J. Quinn Company under the trademark Q THANES. Mobay Chemical Company's TEXIN 480~R is the currently preferred thermoplastic urethane for use in the composition of the invention. TEXIN ~9lA may also be used.

The other major component of the cover composition is an ionomer resin comprising a copolymer of an olefin having ~u~e-to four carb~n atoms with a monocarboxylic, typically acrylic or methacrylic, acid, ~t least partially neutral~zed with a metal ion. These materials are ~old under the trademark SURLYN
by E. I. Dupont de Nemours Co. and, as noted previously, come in a wide variety of grades which differ in average molecular weight, percent carboxylic acid monomer, degree of neutralization, identity of neutralizing ion, and other factors. Any of the SURLYN ionomers or other ionomers of the type described having a ~hore D hardness of ~t lea~t 55 may ~e used. The currently preferred ~aterial i~ SURLYN 1702. SURLYN

1702 is a copolymer of ethylene and methacrylic acid which is _9_ believed to comprise about 96.5~ free ~ci~ and 1.2~ zinc. Its average melt index is about 14.
The presence of the ionomer in the blend serves to set the melt flow index to optimal levels for injection or compression molding and also imparts cut resistance and general durability to covers made with the blend.
In a preferred embodiment, the cover is comprised of 8 parts of the urethane and between 1 and 4 parts of the ionomer.
The urethane and ionomer resin components thus coact in use to provide a unique combination of durability, playability, and ease of manufacture. The nature of the cover material is such that better players can fade, draw, or apply backspin to the ball even though it is of two-piece construction, yet the cover is more cut resistant and has generally better durability than balata~covered wound balls.
It is believed that the primary reason why more spin can be given to the ball during a hit is that the cover material deforms more easily than do ionomer covers. Thus, irons, particularly short irons, tend to "bite" into the ball without permanently deforming it.
The nature of the molded cores which may be used with the cover form no part of this invention, although molded cores are preferred over wound cores because of their lower cost and superior performance. Thus the covers of the invention may be used with cores of the type described in U.S. patent nu~bers 4,264,075, 4,169,599, or 4,141,559.

JJ/sd ~ .

Conventional soli~ cores are typically compressio~
molded from a slug of uncured or lightly cured elastomer composition comprising a high ci~ content polybutadiene and a metal salt of an alpha, beta, ethylinically unsaturated carboxylic acid such as zinc mono or di acrylate or methacrylate.
To achieve high coefficient of restitution in the core, manufacturer include a small amount of a metal oxide such as zinc oxide. Larger amounts o~ metal oxide than are needed to achieve coe~ficient may be included to increase core weight so that the *inished ball more closely approaches the USGA upper weight limit of 1.620 ounce~ Other materials may be used in the core composition including compatible rubbers or ionomers, and low molecular weight fatty acids such as stearic acid. Free radical initiator catalysts such as peroxides are admixed with the core composition so that, on the application of heat and pressure, a complex curing or cross-linking reaction takes place.
U.S. Patent No. 4,726,590 discloses a golf ball aore that is cured with a peroxide and a poly~un~tional isocyanate having 3-30 carbon atoms~ Balls having cores made using a small amount of such as isocyanate, preferably a diisocyanate, e.g., 1.0%, 4,4' diphenyl methane diisocyanate, have an improved, higher coefficient of reskitution. Coefficient of restitution is defined as the ratio of outgoing to incoming velocity of the test core or ball projected against a hard plate at a selected initial velocity, e.g., 125 fk./sec. The composition may otherwise be identical to prior art polybutadiene-metal acrylate core compositions~

JJ ~c~S 11 These cores may be used with the cover composition of the invention to produce a ball of high coefficient and high initi~l velocity, closely approaching the USGA limit, which nevertheless has excellent short iron playability properties.
U.S. Patent No. 4,650,193 discloses a core consisting of a hard, inner central portion and a softer outer layer. The core may be manufactured by formulating a conventional core composition of the type described above, extruding slugs of the proper size, applying a ma~erial which alters cross-linking to surface layers of the slug, e.g., sulfur or sulfur bearing materials, and then compression molding. Inner portions of the core cure in the normal way to produce a hard, resilient center.
An outer layer of the core, at least about 0.20 inches thick, is cured differently because of the presence of the sulfur or sulfur bearing material to produce a soft outer region, e.g., having a Shore A hardness o~ about 35. This type of core may also be used with the cover of this invention to produce ball~ of excellent short iron playability characteristics.
The invention will be further understood from the following non-limiting example.
A cover composition according to the present invention was made by bl~nding 80 parts TEXIN 480AR thermoplastic urethane (Mobay), 20 parts SURLYN 1702 (Dupont) and 0.4 parts Tio2. After thorough blending, the cover stock had a melt flow index of 0.89.
It was injection molded about "' 12 -conventional cores of the type described above at approximately 450 degrees F to produce covers .060 in. ~hick. The balls were p~inted and their properties were ~ested ver~us a golf ball of ~imilar construc~ion, except that ~he cover material was a blend o~ a sodium ionomer with a zinc ionomer, and versus a wou~d ball having a balata cover.

Off a nine iron, balls having the cover of the invention had a spin rate of 9550 rpm, whereas ionomer covered balls had a spin rate of 5400 rpm and the balata covered balls a spin rate of 9700 rpm. When ~bladed~ with a three iron, the balls of the invention are very ~lightly bruised, the ionomer covered ball~ are unmarked, and the bala~a covered ball is cut through to the threads. When tested by professional golfers, the balls of the invention were perceived as being equal or superior to balata covered balls ~or ~hort iron playability.

The invention may be embodied an other specific forms without departing from the spirit and ~cope thereof.
Accordingly, other embodimentR are within the following claims.

Claims (18)

Claims

1. A composition of matter for molding a cover for a golf ball, said composition comprising a thermoplastic urethane polymer having a Shore A hardness less than 95 and an ionomer comprising olefinic groups having 2 to 4 carbon atoms copolymerized with a monocarboxylic acid having 3 to 4 carbon atoms, said acid groups being at least partially neutralized with a metal ion, said ionomer having a Shore D hardness greater than 55, the relative amounts of said urethane and said ionomer being sufficient to produce a cover having a Shore C
hardness with the range of 70 to 85.

2. The composition of claim 1 wherein said ionomer is neutralized with a metal selected from the group consisting of sodium and zinc.

3. The composition of claim 1 comprising 8 parts of said urethane and between 1 and 4 parts of said ionomer.

4. The composition of claim 1 further comprising titanium dioxide.

5. The composition of claim 1 wherein said urethane has a tensile strength of at least 2500 lb/in2 and an elongation at break of at least 250 percent.

6. In a golf ball having a core and a cover, the im-provement wherein the cover comprises a blend of a thermoplastic urethane polymer having a Shore A hardness less than 95 and an ionomer having a Shore D hardness greater than 55, said ionomer comprising olefinic groups having 2 to 4 carbon atoms copolymerized with acrylic or methacrylic acid groups, said acid groups being at least partly neutralized with a metal ion, the relative amounts of said urethane polymer and said ionomer being sufficient to produce a cover having a Shore C hardness within the range of 70 to 85.

7. The improvement of claim 6 wherein said core comprises a molded, resilient, solid sphere.

8. The improvement of claim 6 wherein said ionomer is neutralized with a metal selected from the group consisting of sodium and zinc.

9. The improvement of claim 6 comprising 8 parts of said urethane polymer and between 1 and 4 parts of said ionomer.

10. The improvement of claim 9 comprising about 2 parts of said ionomer.

11. The improvement of claim 6 wherein said cover has a thickness no greater than 0.60 inch.

12. The improvement of claim 6 further comprising a coat of polyurethane paint.

13. The improved golf ball of claim 6 characterized in that it has a spin rate when hit with a nine iron greater than 9,000 rpm.

14. A golf ball cover comprising a blend of a thermoplastic urethane having a Shore A hardness less than 95 and an ionomer comprising olefinic groups having 2 to 4 carbon atoms copolymerized with a monocarboxylic acid having 3 to 4 carbon atoms, said acid groups being at least partially neutralized with a metal ion, said ionomer having a Shore D
hardness greater than 55, the relative amounts of said urethane and said ionomer being sufficient to produce a cover having a Shore C hardness with the range of 70 to 85.

15. The cover of claim 14 wherein said ionomer is neutralized with a metal selected from the group consisting of sodium and zinc.

16. The cover of claim 14 comprising 8 parts of said urethane and between 1 and 4 parts of said ionomer.

17. The cover of claim 14 further comprising titanium dioxide.

18. The cover of claim 14 wherein said urethane has a tensile strength of at least 2500 lb/in2 and an elongation at break of at least 250 percent.