IE57172B1 - Golf ball having improved playability properties - Google Patents

Abstract

A composition suitable for molding a cover for a golf ball, said cover having a Shore C hardness less than substantially 85 (but optionally in the range 70 to 85) comprises: (1) a thermoplastic urethane having a Shore A hardness less than substantially 95; and (2) an ionomer comprising olefinic groups having 2 to 4 carbon atoms copolymerized with a monocarboxylic acid having 3 or 4 carbon atoms, said acid groups being at least partly neutralized with metal ion(s), said ionomer having a Shore D hardness at least substantially 55. The cover improves characteristics of a golf ball, especially of golf balls having molded spherical cores, e.g. spin rate, short iron and wood playability, puttability, and durability.

Description

This invention related to a golf ball as hereinafter defined. The golf ball has superior short iron and other playability characteristics.

Balata and blends of balata with elastomeric or plastics materials were for 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 golf 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 shore iron play and can.be exploited only by relatively skilled players.

Balata and its synthetic substitutes, trans polybutadiene and trans polyisoprene, have today essentially been replaced by new materials. With the exception of a few lines of golf balls distributed through pro shops to professional golfers and those who would emulate them, newer synthetic polymers are the cover materials of choice. Of the new synthetics, by far the most commonly used are a line of ionomers sold by E.I. Dupont de Nemours & Company under the trademark SURLYN. These materials comprise copolymers of olefins, typically ethylene, with an alpha, beta ethylenically unsaturated carboxylic acid such as methacrylic acid. Metal ions such as sodium or zinc ions are used to neutralize some portion of the acidic groups in the copolumer, resulting in a thermoplastic elastomer which has several advantages including a cost advantage over balata. The ionomers may be manufactured with a wide variety of properties by altering the identity of the comonomers, the fraction of the polymer comprising the carboxylic acid, 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 results in ionomer resins of different melt index, hardness, resilience and other mechanical -2properties which, in a golf ball cover, affect cut resistance, shear resistance, general durability, and resilience.

U.S. Patent Specification No. 3,819,768 issued to R.P. Molitor 5 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 y production of an unexpectedly high coefficient of restitution of golf balls having the blended ionomer cover. 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 in the production of two-piece balls having covers which for all practical purposes cannot be cut in play, and which travel further when hit than any other USGA regulation ball as measured by controlled tests when hit by golfers or testing machines.

While the balata-covered, thread-wound balls are easily cut and vary expensive, they nevertheless have excellent short iron playability. It is much more difficult to impact spin to an ionomer covered two-piece ball. Frequently, experienced players note that the ionomer covered two-piece balls have an unsatisfactory feel.

The patent literature is replete with proposed cover formulations 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 of patent specifications are; U.S. 3,359,231; U.S. 4,398,000; U.S. 4,234,184; U.S. 4,295,652; U.S. 4,248,432; U.S. 3,989,568; U.S. 3,310,102; U.S. 4,337,947; U.S. 4,123,061; and U.S. 3,490,146.

The manufacture of two-piece balls (i.e. balls comprising a solid, molded, resilient, molded core and a cover) has many significant advantages over the more expensive wound balls. There is accordingly a ί 35 need for two-piece balls having shore iron playability characteristics comparable to wound, balata-covered golf balls.

The present invention provides a golf ball, comprising a cover having a -3Shore C hardness less than substantially 85, said cover comprising; a thermoplastic urethane having a Shore A hardness less than substantially 95; and an ionomer comprising olefinic groups having 2 to 4 carbon atoms copolymerized with a monocarboxylie acid having 3 or 4 carbon atoms, said acid group being at least partly neutralized with metal ions($), said ionomer having a Shore D hardness at least substantially 55.

Said golf ball of the present invention.may be embodied in any suitable 9 manner. Said Shore C hardness may be in the range 70 to 85, e.g. 75 to or substantially 78. Said Shore D hardness may be greater than 1 substantially 55. There may be substantially 8 parts by weight of said urethane to 1 to 4 parts by weight of said ionomer; there may be substantially 2 parts by weight of said ionomer. Said urethane may have a tensile strength of at least substantially 2500 lb/in2 (446.45 Kg/cm2), and at break an elongation greater than substantially 250 per cent. Said monocarboxylic acid may be acrylic acid or methacrylic acid. Said metal ion may be a sodium or zinc ion. Said composition may comprise titanium dioxide. Said cover may have a thickness no greater than substantially 0.06 inc (0.15 cm). Thinner covers appear to maximize the short iron playability characteristics of said golf ball. Said golf ball may comprise a thread wound core or a molded core. A molded spherical core may comprise a wound core. Said golf ball may comprise a coat of polyurethane paint. Said golf ball may be adapted to have a spin rate greater than substantially 9000 rpm, when hit with a nine iron.

Said golf ball of the present invention has short iron playability properties as good or better than balata-covered wound balls, but is significantly more durable. Said golf ball has better wood playability properties than conventional two-piece balls, and permits experienced golfers to apply spin so as to fade or draw a shot. Puttability is also improved. Said golf ball's cover composition can be injection molded or compression molded about a solid molded core to produce a golf ball cover that is more durable and cut resistant than balata rubber-covered balls. Said composition can enable the provision of a two-piece ball having shore iron and other playability characteristics * equal to or exceeding thread wound balata-covered balls. Said I -4composition can be compatible with urethane-based paints that resist chipping and peeling.

Tests have shown that the spin rate off a nine iron of a said golf ball 5 of the present invention may be about 9550 rpm vs. 5400 rpm for the state of the art, two-piece balls having ionomer covers. This compares favourably to balata-covered wound balls which under the same hitting conditions have a spin rate of about 9700 rpm. The phrase two-piece ball as used herein refers primarily to balls consisting of a molded core and a cover, but also includes e.g. balls having a separate solid layer beneath the cover as disclosed e.g. in U.S. Patent Specification No. 4,431,193 issued to Nesbitt, and other balls having non-wound cores.

The increased spin that can be applied during a proper hit to balls having a cover of the present 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 covers, and tests have shown that there is a greater area of contact between the ball and the club face. This permits the better player to impart fade, draw, or backspin to the ball as the situation dictates, and permits the player to execute better ships and other shots to the green. On shots of short range (e.g. less than 50 yards (45.7 metres)), the two-piece balls of the present invention often outperform balata-covered wound balls. Regarding puttability, two-piece balls including a cover of the present invention have a lower drop rebound relative to conventional two-piece balls, and have increased contact time on a putter face.

These characteristics combine to enable the player better to control the putting line and distance.

As some examples of use of cover compositions of the present invention, the cover compositions may be us?d to formulate golf ball covers by injection or compression molding about wound cores, solid molded cores of known composition, or high coefficient molded cores such as those disclosed in our U.K. Patent Specification No. 2,168,069 A. Various combinations of the solid core technologies may also be used.

The thermoplastic urethanes preferably comprise (e.g. consist essentially of) linear primary polymer chains having a preponderance -5of relatively long, flexible chain segments joined end to end by rigid chain segments through covalant chemical bonds. The flexible segments may be di isocyanate coupled, low melting polyester or polyether chains. The rigid segments may comprise single diurethane bridges resulting when a diisocyanate couples to polyester or polyether molecules. The rigid segments may comprise longer highmelting urethane chain segments formed by the reaction of a di isocyanate with a low molecular weight glycol chain extender component. The polar-nature of recurring rigid, urethane chain segments results in their strong '< mutual attraction, aggregation, and ordering into crystalline and polycrystalline domains in a mobile polymer matrix. Urethane hydrogen atoms and carbonyl and ether oxygen partners are believed to permit extensive hydrogen bonding among the polymer chains. This apparently restricts the mobility of the urethane chain segments in the domains.

These attractions and chain entaglements produce thermo-labile pseudo cross-links, and produce resins which can display the superficial properties of strong rubbery vulcanizates. Preferred thermoplastic urethanes have a tensile strength of at least 2500 lb/in (446.45 Kg/cm) and at break an elongation at least substantially 250 per cent. Most preferably, tensile strength and elongation at break are 4000 lb/in2 (0.71 Kg/cm2) and 400 per cent, respectively. Such materials are available commercially from Mobay Chemical Company under the trademark TEXIN, from B.F. Goodrich under the trademark ESTANE, from Upjohn Company under the trademark PELLETHANES, or from K.J. Quinn Company under the trademark Q THANES. Mobay chemical Company's TEXIN 480AR is an especially preferred thermoplastic urethane. TEXIN 591A may also be used.

The preferred thermoplastic polyurethane consists essentially of linear primary polymer chains. The structure of such chains preferably comprise long, flexible chain segments joined end to end by rigid chain segments through covalent chemical bonds. The flexible segments typically are diisocyanate-coupled, low melting polyester or polyether chains. The rigid segments include single diurethane bridges and high melting urethane chain segments formed by the reaction of di isocyanate , with small glycols. Hydrogen bonding and other attractive forces among the rigid chain segments are believed to produce domains which are 4 -6mutually attractive, behave somewhat like cross-links, and are reversible with heat and with solvation.

Monocarboxylic acid in the ionomers is preferably acrylic or methacrylic acid, at least partially neutralized (or cross-linked) with metal ion(s). The metal ions are preferably sodium and/or zinc ions. Examples of the ionomers are those sold under the trademark SURLYN by E.I. Dupont de Nemours Co. They come in a wide variety of grades which differ in average molecular weight, percent carboxylic acid monomer, ID degrees of neutralization, identity of neutralizing ion, and other factors. Any of the SURLYN ionomers or other ionomers of the type described having a shore D hardness of at least 55 may be used. An especially preferred material is SURLYN 1702. SURLYN 1702 is a copolymer of ethylene and methacrylic acid, and is believed to comprise about 96.5% by weight free acid and 1.2% by weight zinc. The copolymer's average melt index is about 14.

The preferred ionomer comprises olefinic groups having two or four carbon atoms copolymerized with acrylic or methacrylic acid groups, which are at least partially neutralized with a sodium or zinc ion, e.g. a SURLYN ionomer. Inclusion of the ionomer imparts to the cover a degree of cut resistance far in excess of balata, and helps to control the melt index of the blend in facilitate molding. Thus, the presence of the ionomer in the blend can serve to set the melt flow index to optimal levels for injection or compression molding, and imparts cut resistance and general durability to covers made with the blend.

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 if 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. -7The nature of the molded cores which may be used with the cover form no part of this invention, although molded cores are preferred compound with wound cores because of lower cost and superior performance. Thus the covers of the invention may be used with cores of the types described in U. S. Patent Specification Nos. 4,264,075; 4,169,599; or 4,141,559.

Conventional solid cores are typically compression molded from a slug of uncured or lightly cured elastomer composition comprising a high cis content polybutadiene and a metal salt of an alpha, beta, ethylenically unsaturated carboxylic acid such as zinc mono or di acrylate or methacrylate. To achieve high coefficient of restitution in the core, manufactures include a small amount of a metal oxide such as zinc oxide. Larger amounts of metal oxide than are needed for that coefficient may be included to increase core weight so that the finished ball more closely approaches the USGFA upper weight limit of 1.62 ounce (49.93 gram). Other materials may be used in the core composition, e.g. 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.

Our U.K. Patent Specification No. 2,168,069 A (the disclosure of which is incorporated herein by reference) discloses a golf ball core that is cured with a peroxide, and comprising a polyfunctional isocyanate having 3 to 30 carbon atoms. Balls having cores made using a small amount of such as an isocyanate (preferably a diisocyanate, e.g., 1.0% by weight of 4,41 diphenyl methane diisocyanate) have an improved, higher coefficient of restitution. 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 ft./sec. (38.1 metres/sec). The composition may otherwise be identical to prior art polybutadiene-metal acrylate core compositions.

These cores may be used with the cover composition of the invention to produce a ball of high coefficient and high initial velocity, closely approaching the USGA limit, and which has excellent short iron ρ1ayab i1i ty propert ies. j’ A U.S. Patent Application of ours (Attorney Docket No. SPH-007) filed on the same day as the U.S. application corresponding to the present application) 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 material 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 centre. An outer layer of the core (at least about 0.2 in (0.51 cm) thick) is cured differently because of the presence of e.g. sulfur or sulfur bearing material to produce a soft outer region, e.g. having a Shore A hardness of about 35. That type of core may also be used with the cover of this invention to produce balls of excellent short iron playability characteristics.

The invention will be further illustrated from the following non-limiting Examples.

Examples A cover composition according to the present invention was made by blending 80 parts by weight TEXIN 480AR thermoplastic urethane (Mobay); 20 parts by weight SURLYN 1702 (Dupont); and 0.4 parts by weight TiO?* After thorough blending, the composition had a melt flow index of 0.89. The composition was injection molded about conventional cores of the type described above at approximately 450°F (232.2°C) to produce covers 0.06 in (0.15 cm) thick. The balls were painted and their properties were tested versus a golf ball of similar construction, except that the cover material was a blend of a sodium ionomer with a zinc ionomer, and versus a wound ball having a balata cover.

Off a nine iron, balls having the above cover of the present invention had a spin rate of 9550 rpm, whereas ionomer covered balls had a spin rate of 5400 rpm, and balata covered balls a spin rate of 9700 rpm.

When bladed with a three iron, the balls of the present invention are very slightly bruised, the ionomer covered balls are unmarked, and the -9balata 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 for short iron playability.

The present invention includes equivalents and modifications within the scope of the above disclosures and/or of the appended claims. A preferred core is a molded, resilient, solid sphere.

Claims (15)

1. A golf ball, comprising a cover having a Shore C hardness less than substantially 85, said cover comprising: a thermoplastic urethane having a Shore A hardness less than substantially 95; and an ionomer comprising olefinic groups having 2 to 4 carbon atoms copolymerized with a monocarboxylic acid having 3 or 4 carbon atoms, said acid group being at least partly neutralized with metal ion(s), said ionomer having a Shore 0 hardness at least substantially 55.

2. A golf ball as claimed in claim 1, wherein said shore C hardness is in the range 70 to 85.

3. A golf ball as claimed in claim 1 or 2, wherein there are substantially 8 parts by weight of said urethane to 1 to 4 parts by weight of said ionomer.

4. A golf ball as claimed in claim 3, wherein there are substantially 2 parts by weight of said ionomer.

5. A golf ball as claimed in any one of claims 1 to 4, wherein said 2 urethane has a tensile strength of at least substantially 2500 lb/in 2 (446.45 Kg/cm ), and at break an elongation greater than substantially 250 per cent.

6. A golf ball as claimed in any one of claims 1 to 5, monocarboxylic acid is acrylic acid or methacrylic acid. wherein said

7. . metal A golf ball as claimed ion is a sodium or zinc in any one of claims 1 to 6, ion. wherein said

8. A golf ball as claimed in any one of claims 1 to 7, composition comprises titanium dioxide. wherein said

9. A golf ball as claimed in claim 1, wherein said composition is substantially as described in the Examples.

10.-1110. A golf ball as claimed in any one of claims 1 to 9, wherein said cover has a thickness no greater than substantially 0.06 in (0.15 cm).

11. A golf ball as claimed in any one of claims 1 to 10, wherein 5 said golf ball comprises a molded spherical core.

12. A golf ball as claimed in claim 11, wherein said molded spherical core comprises a wound core. 10.

13. A golf ball as claimed in any one of claims 1 to 12, comprising a coat of polyurethane paint. ι». 11.

14. A golf ball as claimed in any one of claims 1 to 13, when adapted to have a spin rate greater than substantially 9000 rpm, when 12 15. hit with a nine iron.

15. A golf ball as claimed in claim 1, substantially as hereinbefore described with reference to the Examples.