Solid construction golf ball incorporating compressible materials

The subject invention relates to a golf ball having the beneficial characteristics of both a wound and solid construction ball. The invention is directed to a non-wound golf ball incorporating a compressible material, such as a gas, as part of its core. The compressible material can be dispersed throughout the entire core or only in a part of the core. The compressible material or gas can be incorporated into the core by including or dispersing microspheres having a flexible shell containing the compressible material or gas. The golf balls of this invention combine the feel and playing characteristics of a wound construction ball with the shelf-life, manufacturing simplicity and durability of solid construction golf balls.

BACKGROUND OF THE INVENTION 
Present day golf balls can be classified under one of two categories: solid 
balls and wound balls. The first category of solid balls includes unitary 
or one-piece golf balls as well as multi-piece balls. One-piece golf 
balls, seldomly used as playing balls, are typically made from a solid 
piece of polybutadiene rubber, with dimples molded into its surface. 
Although inexpensive and durable, these unitary balls are generally 
limited to use as practice balls because they do not give the desired 
distance when hit. In contrast, multi-piece solid balls usually consist of 
a core of hard, polymeric materials enclosed in a distinct, cut-proof 
cover made of DuPont's SURLYN, an ionomer resin. Because of its durability 
and low spin, which produces greater distance and reduced hooking and 
slicing, this type of ball is the most popular among ordinary players. 
Wound golf balls are manufactured by wrapping elastic windings under high 
tension around a solid rubber or liquid filled center. A cover, usually 
SURLYN or balata is molded over the windings to form the ball. This 
winding process naturally incorporates a certain amount of trapped air 
within the layer of windings. The air trapped within a wound construction 
ball provides certain characteristics which are considered by many golfers 
to be desirable. It creates a soft feel at impact due to its compressible 
nature and high resiliency due to its high efficiency (low damping) as a 
spring. For skilled golfers, these wound balls typically provide a higher 
spin rate and offer more control over the ball's flight than solid balls. 
Unfortunately, the wound construction is also more difficult and expensive 
to manufacture than solid construction golf balls. Also, wound golf balls 
have comparatively shorter shelf life and lower resistance to certain 
types of damage than solid balls. 
Various attempts have been made to mimic these wound construction benefits 
using solid construction manufacturing techniques. However, these balls 
generally have used softer core materials, softer cover materials, layers 
of soft materials combined with conventional materials or combinations 
thereof. Examples of such balls include the Titleist HP2, Pinnacle 
Performance, Ultra Competition, Ultra Tour Balata, Maxfli HT Hi Spin, 
Precept EV Extra Spin, Altus Newing, Top-Flite Tour Z-Balata, Top-Flite 
Tour and Kasco's "Dual Core" balls. Likewise U.S. Pat. No. 4,650,193 to 
Molitor also discloses a golf ball made from relatively "soft" materials. 
While these solid constructions sometimes produce improved feel or playing 
characteristics which simulate those of wound balls, they fail to 
completely capture the same desired characteristics. In addition, the soft 
materials often produce compromised resilience or durability or both. 
This invention takes a different approach. Instead of using soft but 
incompressible materials, it employs compressible materials such as gases 
in the core of a solid construction golf ball. This approach provides a 
much better simulation of the effects of the trapped air in a wound 
construction golf ball while using a manufacturing process similar to that 
for solid golf balls. The result is a ball having the soft feel and high 
resilience of wound construction balls combined with the manufacturing 
simplicity, shelf life and durability of solid construction balls. 
Although prior art golf balls have employed such a gaseous component, these 
balls have been typically special purpose balls or balls where only the 
covers incorporate such a material as disclosed in U.S. Pat. Nos. 
5,150,906 and 4,274,637 to Molitor et al. and U.S. Pat. No. 4,431,193 to 
Nesbitt. Representative of special purpose balls are short-distance balls 
such as those disclosed in U.S. Pat. No. 4,836,552 to Puckett et al., 
floater balls such as those described in U.S. Pat. No. 4,085,937 to Schenk 
and "Nerf" type toy and practice balls. These balls incorporate gas in the 
ball materials for the purposes of reducing the ball's weight and/or its 
potential for causing damage to a struck object. They do not feel or 
perform in any way like a normal wound or solid construction golf ball. 
SUMMARY OF THE INVENTION 
This invention relates to multi-piece golf balls and their method of 
manufacture. In particular, this invention is directed towards golf balls 
comprising a core of a material incorporating a compressible gaseous 
material or cellular material, and a spherical cover or shell of polymeric 
material. 
In addition this invention provides a solid construction golf ball having 
the beneficial characteristics of both wound and solid construction type 
balls. The golf balls of this invention combine the feel and playing 
characteristics of a wound construction with the shelf life and durability 
of a solid construction golf ball. 
Furthermore, the golf balls of this invention will have advantages over 
both conventional solid as well as wound construction balls in cold 
weather. Under such conditions, solid construction balls develop a very 
hard feel due to the stiffening of the materials. They do, however, retain 
most of their resilience so they do not lose much distance. On the other 
hand, wound construction balls retain much of their soft feel (because the 
entrapped air does not stiffen significantly), but they lose distance due 
to a loss of resilience in the high tension windings. A ball made 
according to this invention will retain softness like a wound ball, and 
retain resilience like a solid construction ball. 
Another objective of this invention to provide a golf ball having the 
desired characteristics of a wound construction ball and the manufacturing 
simplicity and cost-savings of a solid construction ball. 
This invention is further directed towards the manufacture of a solid 
construction golf ball possessing the performance characteristics of a 
wound ball and benefits of solid construction balls.

A DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The key to this invention is that compressible materials are incorporated 
into the construction of the golf ball. "Compressible materials" are 
materials whose density is strongly affected by pressure or temperature. 
Gases would generally be considered to be compressible materials while 
liquids and solids would not be. 
As defined in this invention the word "core" refers to unitary cores as 
well as multi-layered cores. The compressible materials of this invention 
can be incorporated into the entire core or into at least one layer of the 
core. Preferably the compressible gaseous material is incorporated into 
the outer layer of a multi-layered core so that the golf ball behaves and 
plays more like a wound ball. The thickness of the layer containing the 
Compressible material preferably ranges from about 0.05 inches to 0.80 
inches, which is generally the diameter of the entire core. More 
preferably, the thickness of such layer ranges from about 0.10 to 0.25 
inches. 
The figures exemplify two embodiments of this invention. These figures are 
provided to further the understanding of this invention and are not to be 
construed as limiting the claims in any manner. FIG. 1 illustrates a golf 
ball 1 which includes the compressible material in the entire core 2. To 
complete the ball, a cover 3 is molded over the core 2. In FIG. 2, the 
ball 1 comprises a multiple layered core 2 comprising an inner core layer 
4 and an outer core layer 5. The compressible material is incorporated 
into the outer core layer 5. 
Suitable core materials into which the compressible gaseous material can be 
incorporated include solids and liquids. In general, the core material 
will essentially be incompressible. Among these materials is 
polybutadiene, a polymer which is presently used to make cores for nearly 
all commercial golf balls. Also, various thermoplastic materials such as 
DuPont's SURLYN, an ionomer resin, DuPont's Hytrel, or B.F. Goodrich's 
Estane, or blends thereof, could be used. Furthermore, materials which are 
not normally resilient enough for use in golf ball cores but may be 
satisfactory when the compressible gaseous material is incorporated into 
it may be used. One such example is polyurethane. 
The proportions of compressible gaseous material to core material that are 
suitable will depend upon the core materials used as well as the 
performance characteristic or effects that are desired of the golf ball. 
In general, a range of about 5% to 50% compressible material by volume of 
the core layer containing the compressible material is suitable. For outer 
core layers which have thicknesses equivalent to that of the winding layer 
in wound balls, 10-15% compressible material by volume of the outer core 
layer is preferred. However, for thinner layers or layers made of stiffer 
materials, a higher proportion of compressible material to core material 
is recommended. Preferably, the compressible material is distributed 
uniformly in the core layer or entire core. 
The gaseous materials can be incorporated into the core polymer in a number 
of ways. The core polymeric materials can be "foamed" by various 
techniques which include, but are not limited to the use of blowing 
agents, gas injection, mechanical aeration and two-component reactive 
systems. U.S. Pat. No. 4,274,637 to Molitor describes the use of blowing 
agents and gas injection to foam polymeric materials. Blowing agents foam 
the core polymeric materials by decomposing to form gases which are 
absorbed by the materials. The gas then expands to form the foamed core 
materials or cellular core material. Foaming by gas injection can be 
achieved by injecting a gas under pressure such as nitrogen, air, carbon 
dioxide, etc. into the material. When the gas expands, the material is 
foamed. 
In addition, the gas can be added to the core material by the inclusion of 
gases encapsulated in microspheres. This addition can be done by mixing 
gas-filled microspheres into the polymer composition. However, the 
encapsulating envelope of such gas must be of a material flexible enough 
to permit compression of the gas inside during impact. Such encapsulating 
materials include polymeric microspheres, such as acrylonitrile copolymer 
microspheres, as well as expandable microspheres. However, glass 
microspheres would not be appropriate for this invention because of their 
rigidity. 
Regardless of the materials from which they are made appropriate 
microspheres must be of a size such that they be small enough to act like 
a continuous medium when incorporated into the core material. Typically a 
microsphere diameter on the order of at most 10% of the thickness of the 
core layer incorporating the compressible material is suitable. 
Moreover, various crosslinkers and fillers can be added to the core 
materials along with the gaseous material. Suitable cross-linking agents 
include metallic salts of an unsaturated carboxylic acid. These salts are 
generally zinc diacrylate or zinc dimethacrylate. Of these two 
crosslinkers, zinc diacrylate has been found to produce golf balls with 
greater initial velocity than zinc dimethacrylate. 
Suitable fillers that can be used in this invention include free radical 
initiators used to promote crosslinking of the salt and the polybutadiene. 
The free radical initiator is suitably a peroxide compound such as dicumyl 
peroxide, 1,1-di (T-butylperoxy) 3,3,5-trimethyl cyclohexane, a--a bis 
(T-butylperoxy) diisopropylbenzene, 2,5-dimethyl-2,5 di (T-butylperoxy) 
hexane, or di-T-butyl peroxide, and mixtures thereof. Also other 
substantially inert fillers such as zinc oxide, barium sulfate and 
limestone as well as additives can be added to the mixture. The maximum 
amount of fillers utilized in a composition is governed by the specific 
gravity of the fillers as well as the maximum weight requirement 
established by the U.S.G.A. Appropriate fillers generally used range in 
specific gravity from 2.0-5.6. 
There are generally two basic techniques used in the manufacture of golf 
balls: Compression molding and injection molding. Both these techniques 
are well-known in the art. For an inventive ball having the compressible 
material dispersed throughout the core, the gas is incorporated by adding 
the microspheres or by some other foaming technique into polybutadiene or 
some other suitable core material. After the addition of the compressible 
materials, the core material composition is then extruded into preforms 
suitable for molding. The preforms are then compression molded into 
spherical cores. The cover, typically of a thermoplastic material, is then 
either injection molded directly around the core or compression molded 
using pre-formed hemispheres of cover material placed around the core. 
Such cover materials, such as SURLYN or balata rubber, are known in the 
art. 
For an inventive ball where the compressible material is incorporated into 
the outer layer of the core, the center of the core would be formed by 
compression molding a core material to form a sphere with a diameter less 
than that of the finished core. The outer layer of the core which 
incorporates the compressible material is then either injection molded or 
compression molded around the center of the core. Finally, the cover would 
be injection molded or compression molded around the core by conventional 
means. 
While it is apparent that the invention disclosed herein is well calculated 
to fulfill the objects stated above, it will be appreciated that numerous 
modifications and embodiments may be devised by those skilled in the art. 
Therefore, it is intended that the appended claims cover all such 
modifications and embodiments as falling within the true spirit and scope 
of the present invention.