Golf ball Number:6,767,294 from the United States Patent and Trademark Office (PTO) owispatent The present invention is directed to a solid, non-wound, golf ball comprising two or more core components, and a cover component. The core components comprise i) a pressurized foamed inner, spherical center component comprising a first matrix material selected from the group consisting of thermoset material, a thermoplastic material, or combinations thereof, a blowing agent and a cross-linking agent and, ii) an outer core layer disposed about the spherical center component, formed from a second matrix material selected from the group consisting of a thermoset material, a thermoplastic material, or combinations thereof. The golf ball may further comprise an additional outer core layer(s) that surround the outer core layer. The cover may be single or multi-layered.<H ball, Golf, Golf, ball, 6767294.html, Patent, pto, 6767294

Title: Golf ball

Abstract: The present invention is directed to a solid, non-wound, golf ball comprising two or more core components, and a cover component. The core components comprise i) a pressurized foamed inner, spherical center component comprising a first matrix material selected from the group consisting of thermoset material, a thermoplastic material, or combinations thereof, a blowing agent and a cross-linking agent and, ii) an outer core layer disposed about the spherical center component, formed from a second matrix material selected from the group consisting of a thermoset material, a thermoplastic material, or combinations thereof. The golf ball may further comprise an additional outer core layer(s) that surround the outer core layer. The cover may be single or multi-layered.

Patent Number: 6,767,294 Issued on 07/27/2004 to Nesbitt

Inventors: Nesbitt; R. Dennis (Westfield, MA)
Assignee: Callaway Golf Company (Carlsbad, CA)

Appl. No.: 10/236,808

Filed: September 6, 2002

Current U.S. Class: 473/369 ; 473/351; 473/367

Current International Class: A63B 37/02 (20060101); A63B 37/00 (20060101)

Field of Search: 473/351-377

References Cited [Referenced By]

U.S. Patent Documents


4144223	March 1979	Kent
4714253	December 1987	Nakahara et al.
4836552	June 1989	Puckett et al.
5019319	May 1991	Nakamura et al.
5688192	November 1997	Aoyama
5725443	March 1998	Sugimoto et al.
5823889	October 1998	Aoyama
5873796	February 1999	Cavallaro et al.
5989136	November 1999	Renard et al.
6120390	September 2000	Dalton
6193618	February 2001	Sullivan et al.
6207784	March 2001	Rajagopalan
6217462	April 2001	Maruko et al.
6284840	September 2001	Rajagopalan et al.
6319152	November 2001	Takesue et al.
6386992	May 2002	Harris et al.

Primary Examiner: Graham; Mark S.
Assistant Examiner: Hunter, Jr.; Alvin A.

Claims

What is claimed is:

1. A golf ball comprising: a dual core assembly including a pressurized foamed center core and at least one core layer disposed about said center core, said center core comprising a pressurized gas wherein said gas contained in said center is at a pressure greater than atmospheric pressure, and said core layer comprising polybutadiene; and a cover layer assembly disposed about said dual core assembly.

2. The golf ball of claim 1, wherein said pressurized foamed center core exhibits a closed-cell structure.

3. The golf ball of claim 1, wherein said pressurized foamed center core exhibits an open-cell structure.

4. The golf ball of claim 1, wherein said center core further comprises a decomposed chemical blowing agent.

5. The golf ball of claim 4, wherein said decomposed chemical blowing agent is selected from the group consisting of p-toluene sulfonyl hydrazide, sodium bicarbonate, 2,2'-azobisisobutyronitrile, azodicarbonamide, 4,4'-oxy-bis(benzenesulfonyl hydrazide), dinitrosopentamethylene-tetramine, and combinations thereof.

6. The golf ball of claim 5, wherein said decomposed chemical blowing agent comprises p-toluene sulfonyl hydrazide.

7. The golf ball of claim 1, wherein said center core further comprises a cross-linking agent.

8. The golf ball of claim 1, wherein said gas contained in said center core includes nitrogen.

9. The golf ball of claim 1, wherein said center core has a center core outer region and said core layer has a core layer inner region immediately adjacent to said center core outer region, and said core layer inner region is bonded to said center core outer region.

10. The golf ball of claim 9, wherein said bonding between said core layer inner region and said center core outer region is achieved at least in part by chemical cross-linking.

11. The golf ball of claim 1, wherein said cover layer assembly includes at least one inner cover layer and an outer cover layer.

12. The golf ball of claim 1, wherein the specific gravity of said center core is less than about 1.1.

13. The golf ball of claim 1, wherein the pressurized foamed center has a diameter of about 0.15 inches to about 1.0 inches.

14. The golf ball of claim 1, wherein the core layer has a thickness of about 0.125 inches to about 0.725 inches.

15. The golf ball of claim 1, wherein said polymeric material comprises polyisoprene or a halobutyl rubber.

16. The golf ball of claim 1 further comprising at least one barrier layer, wherein said barrier layer is formed in between any one of the core and cover layers.

17. A golf ball comprising: a dual core assembly including a center core and at least one core layer disposed about said center core, said center core comprising cross-linked polymeric material and a plurality of interior cells containing a pressurized gas wherein said gas in said center core is at a pressure greater than atmospheric pressure; and a cover layer assembly disposed about said dual core assembly.

18. The golf ball of claim 17, wherein said center core is produced by foaming and exhibits a closed-cell structure.

19. The golf ball of claim 17, wherein said plurality of interior cells are produced by a chemical blowing agent and wherein the plurality of interior cells exhibit an open-cell structure.

20. The golf ball of claim 17, wherein said outer core layer comprises polybutadiene, a metal carboxylate cross-linking agent, a free radical initiator and a heavy weight filler having a specific gravity of 2.7 or more.

21. The golf ball of claim 17, wherein the plurality of interior cells are uniformly distributed throughout the center core.

Description

FIELD OF THE INVENTION

The present invention relates to golf balls and specifically to the construction of solid, non-wound, golf balls for regulation play. More particularly, the invention is directed to improved golf balls comprising multi-component core assemblies which have a pressurized foamed center component. The pressurized foam center is encapsulated by one or more core layers which are then surrounded by a cover. The golf balls of this invention are of the same size and weight as conventional balls and have comparable or better performance characteristics.

BACKGROUND OF THE INVENTION

Golf balls traditionally have been categorized into three different groups. These are one piece balls, multi-piece solid balls comprising two or more solid pieces and wound (three piece) balls.

The one piece ball typically is formed from a solid mass of moldable material which has been cured to develop the necessary degree of hardness. In many instances, the one piece solid ball does not possess any significant difference in composition between the interior and exterior of the ball. One piece balls are described, for example, in U.S. Pat. Nos. 3,313,545; 3,373,123; and, 3,384,612.

A wound ball is frequently referred to as a "three piece ball" since it is made with a vulcanized rubber thread wound under tension around a solid or semi-solid center to form a wound core and thereafter enclosed in a single or multi-layer covering of tough protective material. For many years the wound ball was desired by many skilled, low handicap golfers, due to reported enhanced playability characteristics.

More particularly, the three piece wound ball typically has a balata or balata like cover which is relatively soft and flexible. Upon impact, the balata cover compresses against the surface of the club producing high spin. Consequently, the soft and flexible balata covers, along with the wound cores, provide an experienced golfer with the ability to apply a spin to control the ball in flight. This allows a skilled golfer to produce a draw or a fade or a backspin which causes the ball to "bite" or stop abruptly on contact with the green. Moreover, the balata cover produces a soft "feel" to the low handicap player. Such playability properties of workability, feel, etc. are particularly important in short iron play with low swing speeds and are exploited significantly by highly skilled players.

However, a three piece wound ball also has several disadvantages. For example, a wound ball is relatively difficult to manufacture due to the number of production steps required and the careful control which must be exercised in each stage of manufacture to achieve suitable roundness, velocity, rebound, "click", "feel", and the like.

Moreover, wound balls can also be knocked "out of round". One or more severe hits can damage the windings and knock the center "off center". Such a ball is then unbalanced, making putting, etc. more difficult.

Additionally, a soft wound (three piece) ball is not well suited for use by the less skilled and/or high handicap golfer who cannot intentionally control the spin of the ball. For example, the unintentional application of side spin by a less skilled golfer produces hooking or slicing. The side spin reduces the golfer's control over the ball as well as reducing travel distance.

Similarly, despite all the benefits of balata, balata covered balls are easily cut and/or damaged if mishit. Consequently, golf balls produced with balata or balata containing cover compositions can exhibit relatively short life spans. As a result of this negative property, balata and its synthetic substitute, trans-polyisoprene, and resin blends, have been essentially replaced as the cover materials of choice by golf ball manufacturers by materials comprising ionomeric resins and other elastomers such as polyurethanes.

Conventional multi-piece solid golf balls, on the other hand, include a solid resilient core having single or multiple cover layers employing different types of material molded on the core. The one piece golf ball and the solid core for a multi-piece solid (nonwound) ball frequently are formed from a combination of materials such as polybutadiene and other rubbers cross linked with zinc diacrylate or zinc dimethacrylate, and containing fillers and curing agents which are molded under high pressure and temperature to provide a ball of suitable hardness and resilience. For multi-piece nonwound golf balls, the cover typically contains a substantial quantity of ionomeric resins that impart toughness and cut resistance to the covers.

Ionomeric resins are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of a 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, such as durability, for golf ball cover construction. However, some of the advantages gained in increased durability have been offset to some degree by decreases in playability. This is because, although the ionomeric resins are very durable, they also tend to be quite 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 most 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 "feel" 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 ions, 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 golf ball cover compositions exhibiting not only the improved impact resistance and carrying distance properties produced by the "hard" ionomeric resins, but also the playability (i.e. "spin", "feel", etc.) characteristics previously associated with the "soft" balata covers, properties which are still desired by the more skilled golfer.

Moreover, a number of multi-piece solid balls have also been produced to address the various needs of the golfing population. The different types of material used to formulate the core(s), cover(s), etc. of these balls dramatically alter the balls' overall characteristics.

In this regard, various structures have been suggested using multi-layer cores and single layer covers wherein the core layers have different physical characteristics. For example, U.S. Pat. Nos. 4,714,253; 4,863,167 and 5,184,828 relate to three piece solid golf balls having improved rebound characteristics in order to increase flight distance. The '253 patent is directed towards differences in the hardness of the layers. The '167 patent relates to a golf ball having a center portion and an outer layer having a high specific gravity. Preferably, the outer layer is harder than the center portion. The '828 patent suggests that the maximum hardness must be located at the interface between the core and the mantle, and the hardness must then decrease both inwardly and outwardly.

Similarly, a number of patents for multi-piece solid balls suggest improving the spin and feel by manipulating the core construction. For example, U.S. Pat. No. 4,625,964 relates to a solid golf ball having a core diameter not more than 32 mm, and an outer layer having a specific gravity lower than that of the core. In U.S. Pat. No. 4,650,193, it is suggested that a curable core elastomer be treated with a cure altering agent to soften an outer layer of the core. U.S. Pat. No. 5,002,281 is directed towards a three piece solid golf ball which has an inner core having a specific gravity greater than 1.0, but less than or equal to that of the outer shell which must be less than 1.3.

U.S. Pat. Nos. 4,848,707 and 5,072,944 disclose three-piece solid golf balls having center and outer layers of different hardness. Other examples of such dual layer cores can be found in, but are not limited to, the followings patents: U.S. Pat. Nos. 4,781,383; 4,858,924; 5,002,281; 5,048,838; 5,104,126; 5,273,286; 5,482,285 and 5,490,674. It is believed that all of these patents are directed to balls with single cover layers.

Multi-layer covers containing one or more ionomeric 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 in U.S. Pat. No. 4,431,193, where a multi-layered golf ball cover is described as having been produced by initially molding a first cover layer on a spherical core and then adding a second cover layer. The first or inner layer is comprised of a hard, high flexural modulus resinous material to provide a gain in coefficient of restitution while the outer layer is a comparatively soft, low flexural modulus resinous material to provide spin and control. 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 an advantageous "feel" and playing characteristics of a balata covered golf ball.

In various attempts to produce a durable, high spin ionomeric golf ball, the golfing industry has also blended the hard ionomer resins with a number of softer ionomer 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.

A dual core, dual cover ball is described in U.S. Pat. No. 4,919,434. However, the patent emphasizes the hardness characteristics of all layers, particularly the requirement for a soft inner cover layer and a hard outer cover layer. With respect to the core, it requires that the layers should not differ in hardness by more than 10 percent and should be elastomeric materials having a specific deformation range under a constant load.

U.S. Pat. No. 5,104,126 attempts to concentrate the weight of the golf ball in the center core region by utilizing a metal ball as the core component. However, that patent teaches the use of a solid metal ball as the core component which provides substantially different properties than a polymeric core.

Additionally, according to the U.S.G.A., the initial velocity of the ball must not exceed 250 ft/sec. with a 2% maximum tolerance (i.e., 255 ft/sec.) when struck at a set club head speed on a U.S.G.A. machine. Furthermore, the overall distance of the ball must not exceed 280 yards with a 6% tolerance (296.8 yards) when hit with a U.S.G.A. specified driver at 160 ft/sec. (clubhead speed) at a 10 degree launch angle as tested by the U.S.G.A. Lastly, the ball must pass the U.S.G.A. administered symmetry test, i.e., fly consistently (in distance, trajectory and time of flight) regardless of how the ball is placed on the tee.

While the U.S.G.A. regulates five (5) specifications for the purposes of maintaining golf ball consistency, alternative characteristics (i.e., spin, feel, durability, distance, sound, visibility, etc.) of the ball are constantly being improved upon by golf ball manufacturers. This is accomplished by altering the type of materials utilized and/or improving construction of the balls. For example, the proper choice of the materials for the cover(s) and core(s) are important in achieving certain distance, durability and playability properties. Other important factors controlling golf ball performance include, but are not limited to, cover thickness and hardness, core stiffness (typically measured as compression), ball size and surface configuration.

Accordingly, a wide variety of golf balls have been designed and are available to suit an individual player's game. In essence, different types of balls have been specifically designed or "tailor made" for high handicap versus low handicap golfers, men versus women, seniors versus juniors, etc. Moreover, improved golf balls are continually being produced by golf ball manufacturers with technological advancements in materials and manufacturing processes.

In view in part of the above information, a number of one-piece, two-piece (a solid resilient center or core with a molded cover), three-piece wound (a liquid or solid center, elastomeric winding about the center, and a molded cover), and multi-layer solid or wound golf balls have been produced to address the various needs of golfers exhibiting different skill levels. The different types of materials utilized to formulate the core(s), cover(s), etc. of these balls dramatically alter the balls' overall characteristics.

It would be useful to develop a golf ball exhibiting an increased resilience and feel without substantially affecting the ball's remaining characteristics. Additionally, it would also be useful to develop a golf ball with a light-weight center having the same overall weight and size as conventional golf balls.

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.

SUMMARY OF THE INVENTION

Accordingly, it is a feature of the present invention to provide a multi-piece, nonwound, solid golf ball. The core is of a multi-layer construction. It comprises a pressurized center or inner core layer which is encapsulated by an outer core layer of different material and construction. The characteristics of the core are such that the feel, compression and/or moment of inertia of the ball may be adjusted.

An additional feature of the invention is to provide a ball having a multi-layer polymeric core having a pressurized foamed center or nucleus enclosed by an outer core layer and a multi-layer cover. The ball has enhanced feel and compression properties.

Another feature of the present invention is the provision for a golf ball having a pressurized foamed inner core. The inner core component is constructed in such a manner as to incorporate many of the desirable features associated with various categories of balls traditionally employed.

A further feature of the present invention is the provision for a golf ball core structure with a foamed inner or center polymeric core and an outer polymeric core layer, with the inner core having a specific gravity that differs from that of the outer core layer.

Yet another feature is the provision for a multi-layer core having a pressurized center that is combined with a multi-layer cover wherein the outer cover layer has a lower hardness value than the inner cover layer.

A still further feature of the invention is the provision for a golf ball having a foamed center or nucleus, a high specific gravity core layer and a soft outer cover layer with good scuff resistance and cut resistance coupled with relatively high spin rates at low club head speeds.

The present invention provides in an additional aspect, a solid, nonwound golf ball. The ball comprises a pressurized, multi-core assembly that is concentrically positioned within the center of the golf ball, and a multi-layer cover assembly disposed about the multi-core assembly.

In yet another aspect, the present invention provides a golf ball comprising a pressurized foamed center core component which is concentrically disposed about a reference point located at the geometric center of the golf ball. The golf ball further comprises an outer core layer which generally surrounds and is disposed about the center core component. The golf ball further comprises a first inner cover layer disposed and positioned around the outer core layer, and a second outermost dimpled cover layer that is disposed about the first inner cover layer. Preferably, an ionomeric material is used in at least one of the cover layers.

In yet another aspect, the present invention provides a golf ball comprising a center core component that is pressurized. Preferably, the center core component is foamed and contains a plurality of interior voids or cells, which contain an effective amount of a gas such as nitrogen that is at an elevated pressure. In certain embodiments, the pressurized center core has relatively high or low densities.

In an additional aspect, the subject matter of the present invention provides a golf ball comprising a dual polymeric core and a cover. The dual core has an inner, low density, spherical center core and at least one outer core layer. A lower or higher density outer core layer is disposed about the low density spherical center or inner core layer. A cover is then molded about the dual core.

Moreover, one or more outer core layers can be disposed about the center, followed by one or more cover layers. The outer core and/or cover layers can be made lighter and/or heavier in order to produce an overall golf ball which conforms with the weight and size requirements of the U.S.G.A. This combination of weight and size displacement decreases or increases the moment of inertia and/or allows the radius of gyration of the ball to move closer to or further from the center.

The moment of inertia (i.e., "MOI") of a golf ball (also known as "rotational inertia") is the sum of the products formed by multiplying the mass (or sometimes the area) of each element of a figure by the square of its distance from a specified line such as the center of a golf ball. This property is directly related to the "radius of gyration" of a golf ball which is the square root of the ratio of the moment of inertia of a golf ball about a given axis to its mass. It has been found that the lower the moment of inertia (or the closer the radius of gyration is to the center of the ball) the higher the spin rate is of the ball with all other properties being held equal.

In all of the above aspects, the present invention is directed, in part, to providing a pressurized center core component. This increases the resilience and feel characteristics of the ball.

The present invention is also directed to decreasing or increasing the moment of inertia of a solid, non-wound, golf ball by varying the weight arrangement and composition of the pressurized core (preferably the inner spherical center). By varying the weight, size and density of the components of the golf ball, the moment of inertia of a golf ball can be decreased or increased. Additionally, different types of matrix materials and/or cross-linking agents, or lack thereof, can be utilized in the core construction in order to produce an overall solid, non-wound, golf ball exhibiting enhanced spin and feel while maintaining resiliency and durability.

In one other further aspect, the subject matter of the present invention provides a multi-layered covered golf ball comprising a dual core and a multi-layer cover. The dual core comprises a pressurized low or high density spherical center core layer and at least one outer core layer having a similar or different density. Preferably, the spherical center has a specific gravity of from about 0.02 to about 4.0, preferably about 0.10 to 2.0, and most preferably, about 0.30-1.0. The spherical center has a diameter from 0.15 inches to 1.0 inches, preferably about 0.25 inches to 0.75 inches and most preferably 0.0340 inches to 0.344 inches.

The golf balls of the present inventions having the foamed, pressurized nucleus are more durable and softer with an increased resilience than solid metal nucleus balls. The specific gravity of the center, or nucleus, is dependent upon the extent of foaming or cell size, the quantity and type of the material in nucleus, the amount and type of blowing agent, and the specific gravity of the chosen filler (if desired) so that the maximum U.S.G.A. golf ball weight is not exceeded.

These and other objects and features of the invention will be apparent from the following description and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings which are presented for the purposes of illustrating the invention and not for the purposes of limiting the same.

FIG. 1 is a cross-sectional view of a preferred embodiment golf ball in accordance with the present invention comprising a dual core component having a pressurized, spherical center comprising foamed cells dispersed in a first matrix material selected from thermosets, thermoplastics, or a combination thereof, an outer core layer comprising a second matrix material selected from thermosets, thermoplastics, or a combination thereof, and a single-layered cover; and

FIG. 2 is a cross-sectional view of yet another preferred embodiment golf ball in accordance with the present invention comprising a dual core component having a pressurized, spherical center comprising foamed cells dispersed in a first matrix material selected from thermosets, thermoplastics, or a combination thereof, an outer core layer comprising a second matrix material selected from thermosets, thermoplastics, or a combination thereof, an inner cover layer and an outer cover layer.

FIGS. 3 and 4 are the same as FIGS. 1 and 2 above, respectively, with an additional layer around the pressurized nucleus to reduce or eliminate pressure loss, over time, of the gas contained in the nucleus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to improved solid, non-wound, golf balls comprising a polymeric core component with a pressurized center, or nucleus, and one or more outer core layers and a polymeric cover component with either a single or multi-layer cover. Preferably, the pressurized center core component has a relatively low density. The golf balls of the present invention can be of standard or enlarged size.

In this regard, in the present invention, the nucleus is pressurized in-situ during the molding process of the surrounding core stock. Preferably, a small "plug" or "pill" of polymeric material containing a blowing agent is inserted into the middle of two uncured preformed hollow core halves. Both halves are cured together under heat and pressure to decompose the blowing agent and cure the rubber matrix and core stock. Alternately, the two hollow halves may be cured separately and joined together with rubber adhesive with the plug or pill of polymeric material containing the blowing agent inside. The assembly is reheated in a metal mold under pressure to decompose the blowing agent and release the gas pressure.

As explained herein, the resulting center core component is pressurized and exhibits a foam-like structure comprising a plurality of cells. These terms are defined as follows. The term "pressurized" as used herein refers to the center core component being at a relatively high pressure, and one that is greater than atmospheric pressure. As described herein, the preferred embodiment of the center core component is in the form of a matrix of cross-linked polymer. The center core component includes a plurality of relatively small voids or interior hollow spaces defined throughout the matrix. These voids or spaces are referred to herein as "cells" and are described in greater detail herein. The resulting structure of the described matrix is also generally referred to herein as "foamed" or obtained by subjecting the center core component to a foaming process. The interior voids or cells, as described in greater detail herein, contain one or more gases. And, the term "pressurized" refers to the pressure of that gas within the cells as being greater than atmospheric pressure.

The golf balls of the present invention utilize a unique dual or multi-component core configuration. Preferably, the core comprises (i) an interior spherical center component formed from a blend including a first matrix material such as a thermoset material, a thermoplastic material, or combinations thereof; a blowing agent and a cross-linking agent and (ii) a core layer disposed about the spherical center component, the core layer formed from a second matrix material such as a thermoset material, a thermoplastic material, or combinations thereof. The cores may further comprise (iii) an optional outer core layer(s) disposed about the core layer. The outer core layer may be formed from a third matrix material such as a thermoset material, a thermoplastic material, or combinations thereof. The first, second or third matrix materials can be of the same or different materials.

The center core component has a specific gravity of from about 0.02 to about 4.0, and preferably about 0.10 to 2.0, most preferably, from about 0.30 to about 1.0. The weight of the remaining components are adjusted so that the ball will not exceed the U.S.G.A. golf ball weight requirement.

In this regard, the present invention is directed to golf balls comprising a dual core component having a pressurized foamed spherical center having a diameter of from about 0.15 to 1.0 inches, preferably about 0.25 to 0.75 inches. Most preferably, the pressurized formed spherical center has a diameter of about 0.340 to 0.344 inches. The pressurized foamed center is formed from in a first matrix material selected from thermosets, thermoplastics, and combinations thereof, a blowing or gas releasing agent and a cross-linking agent. Preferably, the first matrix material is a polyisoprene.

An outer core layer is then disposed about the spherical center. The outer core layer comprises a second matrix material selected from thermosets, thermoplastics, and combinations thereof. Preferably, this second matrix material is a polybutadiene. The outer diameter of the core is from about 1.25" to 1.60", and most preferably, 1.47" to 1.56". A cover comprising one or more layers is subsequently molded about the dual core component to form a solid, non-wound golf ball.

In a particularly preferred form of the present invention, the golf ball comprises a dual core assembly that includes a pressurized and relatively small but light-weight spherical center component, a thick core layer disposed about the spherical center component, and a cover assembly disposed about the dual core assembly. The light-weight center of the core preferably comprises a foamed polyisoprene rubber having an effective amount of cells dispersed throughout the center core component to produce the compression and feel desired.

The cover assembly may include a single cover or a multi-layered cover configuration. Preferably, the multi-layer golf ball covers of the present invention include a first or inner layer or ply of a high acid (greater than 16 weight percent acid) ionomer blend or a low acid (16 weight percent acid or less) ionomer blend and second or outer layer or ply comprised of a comparatively softer, low modulus ionomer, ionomer blend or other non-ionomeric thermoplastic or thermosetting elastomer such as polyurethane or polyester elastomer. Most preferably, the inner layer or ply includes a blend of low and/or high acid ionomers and has a Shore D hardness of 58 or greater and the outer cover layer is comprised of ionomer or polyurethane and has a Shore D hardness of at least 1 point softer than the inner layer.

Although the present invention is primarily directed to solid, non-wound, golf balls comprising a dual core component and a multi-layer cover as described herein, the present invention also includes golf balls having a dual core component and conventional covers comprising ionomer, balata, various thermoplastic polyurethanes, cast polyurethanes, or any other cover materials capable of being cross-linked via radiation after cover molding.

Accordingly, the present invention is directed to golf balls having a dual-core configuration and a single or multi-layer cover which produces, upon molding each layer around a pressurized inner center, a golf ball exhibiting enhanced feel (i.e., compression) without adversely affecting the ball's resiliency (i.e., distance) and/or durability (i.e., cut resistance, scuff resistance, etc.) characteristics.

The term resilience is generally defined as the ability of a strained body, by virtue of high yield strength and low elastic modulus, to recover its size and form following deformation. Simply stated, resilience is a measure of the energy retained to the energy lost when the ball is impacted with the club.

In the field of golf ball production, resilience is determined by the coefficient of restitution (C.O.R.), the constant "e" which is the ratio of the relative velocity of an elastic sphere after direct impact to that before impact. As a result, the coefficient of restitution ("e") can vary from 0 to 1, with 1 being equivalent to a perfectly or completely elastic collision and 0 being equivalent to a perfectly or completely inelastic collision.

Resilience (C.O.R.), along with additional factors such as club head speed, club head mass, angle of trajectory, ball size, density, composition and surface configuration (i.e., dimple pattern and area of coverage) as well as environmental conditions (i.e., temperature, moisture, atmospheric pressure, wind, etc.) generally determine the distance a golf ball will travel when hit. Along this line, the distance a golf ball will travel under controlled environmental conditions is a function of the speed and mass of the club and the size, density, composition and resilience (C.O.R.) of the ball and other factors. The velocity of the club, the mass of the club and the angle of the ball's departure are essentially provided by the golfer upon striking. Since club head, club head mass, the angle of trajectory and environmental conditions are not determinants controllable by golf ball producers and the ball size and weight are set by the U.S.G.A., these are not factors of principal concern among golf ball manufacturers. The factors or determinants of interest with respect to improved distance are generally the coefficient of restitution (C.O.R.), spin and the surface configuration (dimple pattern, ratio of land area to dimple area, etc.) of the ball.

The coefficient of restitution (C.O.R.) in solid core balls (i.e., molded cores and covers) is a function of the composition of the molded core and of the cover. The molded core and/or cover may be comprised of one or more layers such as in multi-layered balls.

In balls containing a wound core (i.e., balls comprising a liquid or solid center, elastic windings, and a cover), the coefficient of restitution is a function of not only the composition of the center and cover, but also the composition and tension of the elastomeric windings. As in the solid core balls, center and cover of a wound core ball may also consist of one or more layers.

The resilience or coefficient of restitution of a golf ball can be analyzed by determining the ratio of the outgoing velocity to the incoming velocity. In the examples of this writing, the coefficient of restitution of a golf ball was measured by propelling a ball horizontally at a speed of 125+/-1 feet per second (fps) against a generally vertical, hard, flat steel plate and measuring the ball's incoming and outgoing velocities electronically. Speeds were measured with a pair of Oehler Mark 55 ballistic screens (available from Oehler Research Austin Tex.), which provide a timing pulse when an object passes through them. The screens are separated by 36" and are located 25.25" and 61.25" from the rebound wall. The ball speed was measured by timing the pulses from screen 1 to screen 2 on the way into the rebound wall (as the average speed of the ball over 36"), and then the exit speed was timed from screen 2 to screen 1 over the same distance. The rebound wall was tilted 2 degrees from a vertical plane to allow the ball to rebound slightly downward in order to miss the edge of the cannon that fired it.

As indicated above, the incoming speed should be 125+/-1 fps. Furthermore, the correlation between C.O.R. and forward or incoming speed has been studied and a correction has been made over the +/- fps range so that the C.O.R. is reported as if the ball had an incoming speed of exactly 125.0 fps.

The coefficient of restitution must be carefully controlled in all commercial golf balls if the ball is to be within the specifications regulated by the U.S.G.A. As discussed to some degree above, the U.S.G.A. standards indicate that a "regulation" ball cannot have an initial velocity exceeding 255 feet per second in an atmosphere of 75.degree. F. when tested on a U.S.G.A. machine. Since the coefficient of restitution of a ball is related to the ball's initial velocity, it is highly desirable to produce a ball having sufficiently high coefficient of restitution (C.O.R.) to closely approach the U.S.G.A. limit on initial velocity, while having an ample amount of softness (i.e., hardness) to produce the desired degree of playability (i.e., spin, etc.).

Furthermore, as mentioned above, the maximum distance a golf ball can travel (carry and roll) when tested on a U.S.G.A. driving machine set at a club head speed of 160 feet/second is 296.8 yards. While golf ball manufacturers design golf balls which closely approach this driver distance specification, there is no upper limit for how far an individual player can drive a ball. Thus, while golf ball manufacturers produce balls having certain resilience characteristics in order to approach the maximum distance parameter set by the U.S.G.A. under controlled conditions, the overall distance produced by a ball in actual play will vary depending on the specific abilities of the individual golfer.

The surface configuration of a ball is also an important variable in affecting a ball's travel distance. The size and shape of the ball's dimples, as well as the overall dimple pattern and ratio of land area to dimpled area are important with respect to the ball's overall carrying distance. In this regard, the dimples provide the lift and decrease the drag for sustaining the ball's initial velocity in flight as long as possible. This is done by displacing the air (i.e., displacing the air resistance produced by the ball from the front of the ball to the rear) in a uniform manner. Moreover, the shape, size, depth and pattern of the dimple affect the ability to sustain a ball's initial velocity.

Additionally, compression is another property involved in the overall performance of a golf ball. The compression of a ball will influence the sound or "click" produced when the ball is properly hit. Similarly, compression can effect the "feel" of the ball (i.e., hard or soft responsive feel), particularly in chipping and putting.

Moreover, while compression by itself has little bearing on the distance performance of a ball, compression can affect the playability of the ball on striking. The degree of compression of a ball against the club face and the softness of the cover strongly influence the resultant spin rate. Typically, a softer cover will produce a higher spin rate than a harder cover. Additionally, a harder core will produce a higher spin rate than a softer core. This is because at impact a hard core serves to compress the cover of the ball against the face of the club to a much greater degree than a soft core thereby resulting in more "grab" of the ball on the clubface and subsequent higher spin rates. In effect the cover is squeezed between the relatively incompressible core and clubhead. When a softer core is used, the cover is under much less compressive stress than when a harder core is used and therefore does not contact the clubface as intimately. This results in lower spin rates.

The term "compression" utilized in the golf ball trade generally defines the overall deflection that a golf ball undergoes when subjected to a compressive load. For example, PGA compression indicates the amount of change in golf ball's shape upon striking.

The development of solid core technology in two-piece balls has allowed for much more precise control of compression in comparison to thread wound three-piece balls. This is because in the manufacture of solid core balls, the amount of deflection or deformation is precisely controlled by the chemical formula used in making the cores. This differs from wound three-piece balls wherein compression is controlled in part by the winding process of the elastic thread. Thus, two-piece and multi-layer solid core balls exhibit much more consistent compression readings than balls having wound cores such as the thread wound three-piece balls.

Additionally, cover hardness and thickness are important in producing the distance, playability and durability properties of a golf ball. As mentioned above, cover hardness directly affects the resilience and thus distance characteristics of a ball. All things being equal, harder covers produce higher resilience. This is because soft materials detract from resilience by absorbing some of the impact energy as the material is compressed on striking.

However, soft covered balls are generally preferred by the more skilled golfer because he or she can impart high spin rates that give him or her better control or workability of the ball. Spin rate is an important golf ball characteristic for both the skilled and unskilled golfer. As mentioned, high spin rates allow for the more skilled golfer, such as PGA and LPGA professionals and low handicap players, to maximize control of the golf ball. This is particularly beneficial to the more skilled golfer when hitting an approach shot to a green. The ability to intentionally produce "back spin", thereby stopping the ball quickly on the green, and/or "side spin" to draw or fade the ball, substantially improves the golfer's control over the ball. Thus, the more skilled golfer generally prefers a golf ball exhibiting high spin rate properties.

The term or designation "2.times.2" or "2.times.2 construction" as used herein refers to a golf ball construction utilizing two central core components, e.g. a central core component and a core layer disposed about the core component, and two cover components, e.g. a first inner cover layer and a second outer cover layer. The present invention however is not limited to 2.times.2 configurations and includes 2.times.1 (two core components and a single cover component), 3.times.2 (three core components and two cover components), 2.times.3 configurations (two core components and three cover components), 3.times.3 configurations (three core components and three cover components), and additional configurations such as 4.times.2, 4.times.3, 4.times.4, 2.times.4, 3.times.4, . . . etc.

The term "moment of inertia," sometimes designated "MOI" herein, for the golf balls of the present invention is defined as the sum of the products formed by multiplying the mass of each element by the square of its distance from a specified line or point. This is also known as rotational inertia. Since the present invention golf balls comprise a number of components, the MOI of the resulting golf ball is equal to the sum of the moments of inertia of each of its various components, taken about the same axis or point. All of the moments of inertia of golf balls referred to herein are with respect to, or are taken with regard to, the geometric center of the golf ball.

FIGS. 1 and 2 illustrate preferred embodiments of the golf balls in accordance with the present invention. It will be understood that all of the figures referenced herein are schematic in nature and none of the referenced figures are to scale. And so, the thicknesses and proportions of the various layers and the diameter of the various core components are not necessarily as depicted.

The golf ball 8 comprises a single layer 11 (FIG. 1) or a multi-layered cover 12 (FIG. 2) disposed about a core 10. The core 10 of the golf ball is formed of a pressurized foamed spherical or center core layer center 20, preferably having a low density, and an outer core layer 22. The low density spherical center 20 is designed to produce a greater resilience and feel characteristics.

The multi-layered cover 12 (FIG. 2) comprises two layers: a first or inner layer or ply 14 and a second or outer layer or ply 16. The inner layer 14 can be ionomer, ionomer blends, non-ionomer, non-ionomer blends, or blends of ionomer and non-ionomer. The outer layer 16 is softer than the inner layer and can be ionomer, ionomer blends, non-ionomer, non-ionomer blends or blends of ionomer and non-ionomer.

In a first multi-layered cover embodiment, the inner layer 14 is comprised of a high acid (i.e. greater than 16 weight percent acid) ionomer resin or high acid ionomer blend. Preferably, the inner layer is comprised of a blend of two or more high acid (i.e., at least 16 weight percent acid) ionomer resins neutralized to various extents by different metal cations. The inner cover layer may or may not include a metal stearate (e.g., zinc stearate) or other metal fatty acid salt. The purpose of the metal stearate or other metal fatty acid salt is to lower the cost of production without affecting the overall performance of the finished golf ball.

In a second multi-layered cover embodiment, the inner layer 14 is comprised of a low acid (i.e., 16 weight percent acid or less) ionomer blend. Preferably, the inner layer is comprised of a blend of two or more low acid (i.e., 16 weight percent acid or less) ionomer resins neutralized to various extents by different metal cations. The inner cover layer may or may not include a metal stearate (i.e., zinc stearate) or other metal fatty acid salt.

It has been found that a hard inner layer in the multi-cover embodiment provides for a substantial increase in resilience (i.e., enhanced distance) over known multi-layer covered balls. The softer outer layer along with the particular multi-component core of the present invention provides the desirable "feel" and high spin rate characteristic while maintaining the golf ball's resiliency. The softer outer layer allows the cover to deform more during impact and increases the area of contact between the club face and the cover, thereby imparting more spin on the ball. As a result, the soft cover provides the ball with a balata-like feel and playability characteristics with improved distance and durability.

Consequently, the overall combination of the pressurized foamed inner center, one or more outer core layers and the inner and outer cover layers results in a golf ball having enhanced resilience (and improved soft feel due to the foamed rubber nucleus).

FIGS. 3 and 4 relate to further preferred embodiments of the present invention, where in a layer 23 is included around the pressurized nucleus 20 to reduce or eliminate pressure loss, over time, of the gas contained in the nucleus.

The specific components and characteristics of the solid, non-wound golf balls of the present invention are more particularly set forth below.

Core Assembly

As noted, the present invention golf balls utilize a unique dual core configuration. Preferably, the cores comprise (i) an inner, pressurized, spherical center or center core layer component formed from a first matrix material comprised of thermoset material, thermoplastic material, or combinations thereof, blowing agent(s) and a cross-linking agent(s), and (ii) an outer core layer disposed about the spherical center component, the core layer being formed from a second matrix material comprised of thermoset material, thermoplastic material, or combinations thereof.

More preferably, the pressurized core component of the present invention consists of a foamed, spherical center and comprises a mixed or blended matrix of polyisoprene, cross-linking agent(s) and blowing agent(s). As indicated below, other polymeric materials can also be utilized. The ingredients of the center core component are mixed together and formed into a spherical shape and then encapsulated within at least one outer core layer. The resulting assembly is then molded under heat and pressure. Heating causes cross-linking of the polyisoprene to occur and also results in activation of the blowing agent (i.e. conversion into a gaseous state). This process and the resulting foamed matrix are described in greater detail below.

The gas phase in the foamed core component is distributed in voids, pores, or pockets referred to herein as cells. If these cells are interconnected in such a manner that gas can pass from one to another, the material is termed open-celled. If the cells are discrete and the gas phase of each is independent of that of the other cells, the material is termed closed-celled.

For example, hydrazide blowing agents such as Celogen.RTM. TSH release nitrogen gas (N.sub.2) to produce closed cells. In turn, sodium bicarbonate and ammonium carbonate release CO.sub.2 gas to produce open cells. Nitrogen gas is preferred in the present invention as it has much lower permeability than carbon dioxide.

The nomenclature of cellular polymers is not standardized. Classifications have been made according to the properties of the base polymer, the methods of manufacture, the cellular structure, or some combination of these.

The foamed core component can be prepared by a variety of methods. The most preferred process comprises expanding a fluid polymer phase to a low density cellular state and then preserving this state. This is the foaming or expanding process.

The expansion process generally includes three steps: creating small discontinuities or cells in a fluid or plastic phase; causing these cells to grow to a desired volume; and stabilizing this cellular structure by physical or chemical means such as peroxides or cross-linking agents.

The initiation or nucleation of cells is the formation of cells of such size that they are capable of growth under the given conditions of foam expansion. Generally, the growth of a hole or cell in a fluid medium at equilibrium is controlled by the pressure difference between the inside and the outside of the cell, the surface tension of the fluid phase, and the radius of the cell. The pressure outside the cell is the pressure imposed on the fluid surface by its surroundings. The pressure inside the cell is the pressure generated by the blowing agent dispersed or dissolved in the polymer matrix. If blowing pressures are low, the radii of initiating cells must be large. The hole that acts as an initiating site can be filled with either a gas or a solid that breaks the fluid surface and thus enables blowing agent to surround it.

During the time of cell growth in a foam, a number of properties of the system change greatly. Cell growth can, therefore, be treated only qualitatively. The following considerations are of primary importance: (1) the fluid viscosity is changing considerably, influencing both the cell growth rate and the flow of polymer to intersections from cell walls leading to collapse; (2) the pressure of the blowing agent decreases, falling off less rapidly than an inverse volume relationship because new blowing agent diffuses into the cells as the pressure falls off; (3) the rate of growth of the cell depends on the viscoelastic nature of the polymer phase, the blowing agent pressure, the external pressure on the foam, and the permeation rate of blowing agent through the polymer phase; and (4) the pressure in a cell of small radius is greater than that in a cell of larger radius.

The increase in surface area corresponding to the formation of many cells in the plastic phase is accompanied by an increase in the free energy of the system; hence the foamed state is inherently unstable. Methods of stabilizing this foamed state can be classified as chemical, e.g. the polymerization of a fluid resin into a three-dimensional thermoset polymer, or physical, e.g. the cooling of an expanded thermoplastic polymer to a temperature below its melting point to prevent polymer flow.

Concerning chemical stabilization, the chemistry of the system determines both the rate at which the polymer phase is formed and the rate at which it changes from a viscous fluid to a dimensionally stable cross-linked polymer phase. It also governs the rate at which the blowing agent is activated, whether it is due to temperature rise or to insolubilization in the liquid phase.

The blowing agent should have a lower decomposition temperature than the decomposition temperature of the peroxide or cross-linking agent so that cells are formed first, then cross-linked to stabilize the structure.

The type and amount of blowing agent governs the amount of gas generated, the rate of generation, the pressure that can be developed to expand the polymer phase, and the amount of gas lost from the system relative to the amount retained in the cells.

Additives to the foaming system (cell growth-control agents) can greatly influence nucleation of foam cells, either through their effect on the surface tension of the system, or by acting as nucleating sites from which cells can grow. They can influence the mechanical stability of the final solid foam structure considerably by changing the physical properties of the plastic phase and by creating discontinuities in the plastic phase that allow blowing agent to diffuse from the cells to the surroundings. Environmental factors such as temperature and pressure also influence the behavior of thermoset foaming systems.

As to physical stabilization, the factors are essentially the same as for chemically stabilized systems but for somewhat different reasons. Chemical composition of the polymer phase determines the temperature at which foam must be produced, the type of blowing agent required, and the cooling rate of the foam necessary for dimensional stabilization. Blowing agent composition and concentration controls the rate at which gas is released, the amount of gas released, the pressure generated by the gas, escape or retention of gas from the foam cells for a given polymer, and heat absorption or release owing to blowing agent activation.

Additives have the same effect on thermoplastic foaming processes as on thermoset foaming processes. Environmental conditions are important in this case because of the necessity of removing heat from the foamed structure in order to stabilize it. The dimensions and size of the foamed structure are important for the same reason.

The following is an exemplary description for forming a preferred embodiment pressurized core component in accordance with the present invention. A decomposable blowing agent, along with vulcanizing systems and other additives, is compounded with the uncured elastomer at a temperature below the decomposition temperature of the blowing agent. When the uncured elastomer is heated in a forming mold, it undergoes a viscosity change. The blowing agent and vulcanizing systems are chosen to yield preferably closed-celled cellular rubber from the release of nitrogen gas from blowing agents such as 2,2'-azobisisobutyronitrile, azodicarbonamide, 4,4'-oxy-bis(benzenesulfonyl hydrazide), and dinitrosopentamethylenete-tramine. Sodium bicarbonate produces an open cell structure with CO.sub.2 gas.

A preferred blowing or foaming agent for use in forming the center cores described herein is Celogen.RTM. TSH. This is available from Crompton Uniroyal Chemical of Naugatuck Conn. Celogen.RTM. TSH is p-toluene sulfonyl hydrazide. Various data associated with this agent is set forth below:

Form: White powder. Specific Gravity: 1.48 at 25.degree. C. (77.degree. F.) Melting Point: 105-120.degree. C. (221-248.degree. F.) Decomposition Point: 140-150.degree. C. (284-302.degree. F.) Gas Yield: 115 cc/gram at 150.degree. C. (302.degree. F.) Decomposition Gases: N.sub.2 and H.sub.2 O Activated by: Weak activators including peroxides, treated urea (BIK .RTM. OT) and triethanolamine. Not readily activated by conventional activation systems for chemical f