The present invention relates to golf balls and, more particularly, to improved golf balls comprising multi-layer covers which have a comparatively hard inner layer and a relatively soft outer layer, and a dual or triple core, a cellular or liquid core, or a wound core. The improved multi-layer golf balls provide enhanced distance and durability properties over single layer cover golf balls while at the same time offering enhanced xe2x80x9cfeelxe2x80x9d and spin characteristics generally associated with soft balata and balata-like covers of the prior art. The present invention further relates to golf balls and, more particularly, to golf balls comprising one or more optional mantle layers. The golf balls may contain a filled inner layer comprising at least 50 parts by weight of non-ionomeric polyolefin material. The golf balls may additionally comprise an optional polymeric outer cover and/or an inner polymeric hollow sphere substrate.
Traditional golf ball covers have been comprised of balata or blends of balata with elastomeric or plastic materials. The traditional balata covers are relatively soft and flexible. Upon impact, the soft balata covers compress against the surface of the club producing high spin. Consequently, the soft and flexible balata covers provide an experienced golfer with the ability to apply a spin to control the ball in flight in order to produce a draw or a fade, or a backspin which causes the ball to xe2x80x9cbitexe2x80x9d or stop abruptly on contact with the green. Moreover, the soft balata covers produce a soft xe2x80x9cfeelxe2x80x9d to the low handicap player. Such playability properties (workability, feel, etc.) are particularly important in short iron play with low swing speeds and are exploited significantly by relatively skilled players.
Despite all the benefits of balata, balata covered golf balls are easily cut and/or damaged if mis-hit. Golf balls produced with balata or balata-containing cover compositions therefore have a relatively short lifespan.
As a result of this negative property, balata and its synthetic substitutes, transpolybutadiene and transpolyisoprene, have been essentially replaced as the cover materials of choice by new cover materials comprising ionomeric resins.
Ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability and flight characteristics, various ionomeric resins sold by E. I. DuPont de Nemours and Company under the trademark xe2x80x9cSurlyn(copyright)xe2x80x9d and more recently, by the Exxon Corporation (see U.S. Pat. No. 4,911,451) under the trademarks xe2x80x9cESCOR(copyright)xe2x80x9d and the trade name xe2x80x9cotek,xe2x80x9d have become the materials of choice for the construction of golf ball covers over the traditional xe2x80x9cbalataxe2x80x9d (transpolyisoprene, natural or synthetic) rubbers. As stated, the softer balata covers, although exhibiting enhanced playability properties, lack the durability (cut and abrasion resistance, fatigue endurance, etc.) properties required for repetitive play.
Ionomeric resins are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacrylic acid, or maleic acid. Metal ions, such as sodium or zinc, are used to neutralize some portion of the acidic group in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e. durability, etc., for golf ball cover construction over balata. However, some of the advantages gained in increased durability have been offset to some degree by the decreases produced in playability. This is because although the ionomeric resins are very durable, they tend to be very hard when utilized for golf ball cover construction, and thus lack the degree of softness required to impart the spin necessary to control the ball in flight. Since the ionomeric resins are harder than balata, the ionomeric resin covers do not compress as much against the face of the club upon impact, thereby producing less spin. In addition, the harder and more durable ionomeric resins lack the xe2x80x9cfeelxe2x80x9d characteristic associated with the softer balata related covers.
As a result, while there are currently more than fifty (50) commercial grades of ionomers available both from DuPont and Exxon, with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (i.e., relative content of ethylene and methacrylic and/or acrylic acid groups) and additive ingredients such as reinforcement agents, etc., a great deal of research continues in order to develop a golf ball cover composition exhibiting not only the improved impact resistance and carrying distance properties produced by the xe2x80x9chardxe2x80x9d ionomeric resins, but also the playability (i.e., xe2x80x9cspin,xe2x80x9d xe2x80x9cfeel,xe2x80x9d etc.) characteristics previously associated with the xe2x80x9csoftxe2x80x9d balata covers, properties which are still desired by the more skilled golfer.
Consequently, a number of two-piece (a solid resilient center or core with a molded cover) and three-piece (a liquid or solid center, elastomeric winding about the center, and a molded cover) golf balls have been produced to address these needs. The different types of materials utilized to formulate the cores, coves, etc. of these balls dramatically alters the balls"" overall characteristics. In addition, multi-layered covers containing one or more ionomer resins have also been formulated in an attempt to produce a golf ball having the overall distance, playability and durability characteristics desired.
This was addressed by Spalding Sports Worldwide, Inc., the assignee of the present invention, in U.S. Pat. No. 4,431,193 where a multi-layered golf ball is produced by initially molding a first cover layer on a spherical core and then adding a second layer. The first layer is comprised of a hard, high flexural modulus resinous material such as type 1605 Surlyn(copyright) (now designated Surlyn(copyright) 8940). Type 1605 Surlyn (Surlyn(copyright) 8940) is a sodium ion based low acid (less than or equal to 15 weight percent methacrylic acid) ionomer resin having a flexural modulus of about 51,000 psi. An outer layer of a comparatively soft, low flexural modulus resinous material such as type 1855 Surlyn(copyright) (now designated Surlyn(copyright) 9020) is molded over the inner cover layer. Type 1855 Surlyn(copyright) (Surlyn(copyright) 9020) is a zinc ion based low acid (10 weight percent methacrylic acid) ionomer resin having a flexural modulus of about 14,000 psi.
The ""193 patent teaches that the hard, high flexural modulus resin which comprises the first layer provides for a gain in coefficient of restitution over the coefficient of restitution of the core. The increase in the coefficient of restitution provides a ball which serves to attain or approach the maximum initial velocity limit of 255 feet per second as provided by the United States Golf Association (U.S.G.A.) rules. The relatively soft, low flexural modulus outer layer provides for the advantageous xe2x80x9cfeelxe2x80x9d and playing characteristics of a balata covered golf ball.
In various attempts to produce a durable, high spin ionomer golf ball, the golfing industry has blended the hard ionomer resins with a number of softer ionomeric resins. U.S. Pat. Nos. 4,884,814 and 5,120,791 are directed to cover compositions containing blends of hard and soft ionomeric resins. The hard copolymers typically are made from an olefin and an unsaturated carboxylic acid. The soft copolymers are generally made from an olefin, an unsaturated carboxylic acid, and an acrylate ester. It has been found that golf ball covers formed from hard-soft ionomer blends tend to become scuffed more readily than covers made of hard ionomer alone. It would be useful to develop a golf ball having a combination of softness and durability which is better than the softness-durability combination of a golf ball cover made from a hard-soft ionomer blend.
Most professional golfers and good amateur golfers desire a golf ball that provides distance when hit off a driver, control and stopping ability on full iron shots, and high spin on short xe2x80x9ctouch and feelxe2x80x9d shots. Many conventional two-piece and thread wound performance golf balls have undesirable high spin rates on full shots. The excessive spin on full shots is a sacrifice made in order to achieve more spin which is desired on the shorter touch shots. It would be beneficial to provide a golf ball which has high spin for touch shots without generating excessive spin on full shots.
Prior artisans have attempted to incorporate metal layers or metal filler particles in golf balls to alter the physical characteristics and performance of the balls. For example, U.S. Pat. No. 3,031,194 to Strayer is directed to the use of a spherical inner metal layer that is bonded or otherwise adhered to a resilient inner constituent within the ball. The ball utilizes a liquid filled core. U.S. Pat. No. 4,863,167 to Matsuki, et al. describes golf balls containing a gravity filler which may be formed from one or more metals disposed within a solid rubber-based core. U.S. Pat. Nos. 4,886,275 and 4,995,613, both to Walker, disclose golf balls having a dense metal-containing core. U.S. Pat. No. 4,943,055 to Corley is directed to a weighted warmup ball having a metal center.
Prior artisans have also described golf balls having one or more interior layers formed from a metal, and which feature a hollow center. Davis disclosed a golf ball comprising a spherical steel shell having a hollow air-filled center in U.S. Pat. No. 697,816. Kempshall received numerous patents directed to golf balls having metal inner layers and hollow interiors, such as 704,748; 704,838; 713,772; and 739,753. In U.S. Pat. Nos. 1,182,604 and 1,182,605, Wadsworth described golf balls utilizing concentric spherical shells formed from tempered steel. U.S. Pat. No. 1,568,514 to Lewis describes several embodiments for a golf ball, one of which utilizes multiple steel shells disposed within the ball, and which provide a hollow center for the ball.
Prior artisans have attempted to provide golf balls having liquid filled centers. Toland described a golf ball having a liquid core in U.S. Pat. No. 4,805,914. Toland describes improved performance by removing dissolved gases present in the liquid to decrease the degree of compressibility of the liquid core. U.S. Pat. No. 5,037,104 to Watanabe, et al. and U.S. Pat. No. 5,194,191 to Nomura, et al. disclose thread wound golf balls having liquid cores. Similarly, U.S. Pat. No. 5,421,580 to Sugimoto, et al. and U.S. Pat. No. 5,511,791 to Ebisuno, et al. are both directed to thread wound golf balls having liquid cores limited to a particular range of viscosities or diameters. Moreover, Molitor, et al. described golf balls with liquid centers in U.S. Pat. No. 5,150,906 and 5,480,155.
The only known U.S. patents disclosing a golf ball having a metal mantle layer in combination with a liquid core are U.S. Pat. No. 3,031,194 to Strayer and the previously noted U.S. Pat. No. 1,568,514 to Lewis. Unfortunately, the ball constructions and design teachings disclosed in these patents involve a large number of layers of different materials, relatively complicated or intricate manufacturing requirements, and/or utilize materials that have long been considered unacceptable for the present golf ball market.
Concerning attempts to provide golf balls with cellular or foamed polymeric materials utilized as a core, few approaches have been proposed. U.S. Pat. No. 4,839,116 to Puckett, et al. discloses a short distance golf ball. It is believed that artisans considered the use of foam or a cellular material undesirable in a golf ball, perhaps from a believed loss or decrease in the coefficient of restitution of a ball utilizing a cellular core.
Although satisfactory in at least some respects, all of the foregoing ball constructions, particularly the few utilizing a metal shell and a liquid core, are deficient. This is most evident when considered in view of the stringent demands of the current golf industry. Moreover, the few disclosures of a golf ball comprising a cellular or foam material do not motivate one to employ a cellular material in a regulation golf ball. Specifically, there is a need for a golf ball that exhibits a high initial velocity or coefficient of restitution (C.O.R.), may be driven relatively long distances in regulation play, and which may be readily and inexpensively manufactured.
These and other objects and features of the invention will be apparent from the following summary and description of the invention, the drawings and from the claims.
In one aspect, the present invention provides a golf ball comprising a dual core comprising a core, an outermost cover layer disposed about the core, at least one inner layer disposed within the ball between the core and the outermost cover layer, and at least 50 parts by weight of non-ionomeric polyolefin material.
In yet another aspect, the present invention provides a multi-layer golf ball comprising a core, an outermost cover layer disposed about the core, at least one inner layer disposed within the ball between the core and the outermost cover layer, and at least 50 parts by weight of non-ionomeric polyolefin material disposed in the inner layer. The outermost cover layer exhibits a Shore D hardness less than 55. The inner layer exhibits a Shore D hardness of at least 60.
In yet another aspect, the present invention provides a golf ball comprising a core, an outer cover layer disposed about the core, an inner cover layer positioned between the core and the outer cover layer and at least 75 parts by weight of non-ionomeric polyolefin material. The outer cover layer exhibits a Shore D hardness less than 55. And, the inner cover layer exhibits a Shore D hardness of at least 60.
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