Golf ball and method of making same

A golf ball with a low spin rate is made by covering the center with a layer of uncured rubber, curing the rubber layer to make a rubber shell about the core, and then winding elastic threads about the cured rubber shell to form a golf ball core. A golf ball cover is then applied to the core to form a golf ball. The center is either a solid rubber sphere or a liquid-filled hollow envelope. The thickness of the rubber shell is between 0.16 cm and 0.64 cm.

This invention relates to golf balls and, more particularly, to wound golf 
balls with liquid centers. 
On the market today there are three main types of golf balls: one-piece, 
two-piece and wound. The one-piece ball is made of a homogeneous mass of 
thermoset or thermoplastic material, while the two-piece ball is made from 
a solid, homogeneous core around which a cover is molded. The wound, or 
three-piece, golf ball comprises a cover molded about a core that has been 
built up from a center around which elastic thread has been wound. The 
center of a wound ball is either a thin-walled, hollow sphere, commonly 
called an envelope, which is filled with a liquid or it is a solid 
homogeneous mass of a very resilient material such as polybutadiene or 
natural rubber. The liquid used to fill a liquid center is generally 
selected according to its specific gravity so that the overall weight of 
the ball is within the limit prescribed by the United States Golf 
Association, i.e. no greater than 1.62 ounces (45.93 gm). A typical liquid 
used is corn syrup, adjusted for specific gravity by the addition of an 
inert filler. The size of the center in wound balls typically varies from 
1 inch (2.54 cm) to 11/8 inch (2.86 cm), with a typical dimension being 1 
1/16 inch (2.7 cm). 
Balata covered three-piece golf balls have a higher spin rate than either 
Surlyn.RTM. covered three-piece balls or Surlyn.RTM. covered two-piece 
balls. Conventionally made two-piece golf balls having a Surlyn.RTM. cover 
typically have a spin rate of about 2200 rpm, while Surlyn.RTM. covered 
wound golf balls having a solid center typically have a spin rate of about 
3000 rpm. Balata covered wound golf balls having a liquid center typically 
have a spin rate of about 3700 rpm. 
It is known that lower spin rates result in a lower trajectory and a longer 
distance of travel for a given golf ball; however, many golfers prefer a 
balata cover over a Surlyn.RTM. cover because of the "click" and "feel" of 
the balata cover. "Click" is the sound made by the ball when it is hit by 
the club head, while "feel" is the overall sensation experienced by the 
golfer when the club head hits the ball. There is a need to reduce the 
rate of spin on a balata covered wound golf ball having a liquid center to 
make it comparable to the spin rate of the Surlyn.RTM. covered wound and 
two-piece golf balls. 
The applicants have discovered a new wound liquid-center golf ball which 
has lower spin than that of the conventional wound liquid-center golf 
ball. 
Broadly, the applicants have found that by surrounding a liquid-filled 
envelope with a hard cover prior to winding thread thereon, the wound golf 
ball so produced has a lower spin rate. More specifically, applicants have 
discovered a four-piece golf ball comprising a liquid-filled center; a 
hard, solid cover formed around said center; elastic thread wound around 
said hard cover; and an exterior dimpled cover formed over said elastic 
thread. 
This invention also relates to an improved liquid-filled center for a 
three-piece golf ball, said improved center comprising a liquid-filled 
envelope around which a hard cover has been formed. 
It has been found that forming a hard spherical cover around the 
liquid-filled center enables a larger liquid-filled center to be employed 
and requires the use of less thread while still having the same 
compression as compared to a conventional wound core having a liquid 
center. 
Envelopes are made in a conventional manner by using two sheets of a rubber 
material and two mold plates. Each mold plate has a plurality of half 
molds therein and a vacuum tube connected to the apex of each half mold. 
Under heat the vacuum causes the rubber sheet to take on the half mold 
shape. Water is sprayed across the bottom mold and the two mold plates are 
joined. The respective half molds also join to form a complete rubber 
envelope. This rubber envelope is subsequently subjected to additional 
heat to expand the envelope to a fully inflated hollow sphere. The 
envelope is then filled with a liquid in a conventional manner, usually by 
a hypodermic needle, and, finally, the hole left by the hypodermic needle 
is sealed. 
In accordance with the present invention, a heavy-walled sphere is formed 
around the liquid-filled envelope. Suitable means for forming the 
heavy-walled sphere around the liquid-filled envelope include wrapping 
pieces of uncured rubber around the envelope and then curing those pieces 
of uncured rubber around the envelope to form a heavy-walled sphere around 
the envelope. The pieces can be two half-shells which are preformed and 
subsequently joined around the liquid-filled half-shell. Good results have 
been obtained by merely cutting flat, rectangular pieces from a sheet of 
uncured rubber, wrapping the rectangular pieces of uncured rubber around 
the envelope, placing the wrapped center into a mold and subjecting the 
wrapped center to a temperature and pressure such that the rubber cures 
and forms a homogeneous, solid walled sphere around the liquid-filled 
envelope. Preferably, these strips measure about 1/16 inch (0.16 cm) 
thick, about 1/2 inch (1.3 cm) wide and about 1 feet (0.3 m) long. These 
strips are manually wrapped around a center to a uniform thickness. The 
mold used to cure the rubber is of sufficient size to hold the fully 
wrapped center. 
Because the wrapped envelope is subjected to heat and pressure to cure the 
rubber, it has been found that the liquid used to fill the center must 
have a sufficiently high boiling point to withstand boiling during the 
curing process of the wrap. Preferably, the liquid should have a boiling 
point of about 20.degree.-30.degree. C. above the cure temperature of the 
material used to wrap the center. When using 1'.times.1/2".times.1/16" 
(0.3 m.times.1.3 cm.times.0.16 cm) strips of uncured hard rubber compound, 
to wrap the center to a thickness of about 3/32 inch (0.24 cm), glycerine, 
1,2,3-propanetriol, which has a boiling point of about 290.degree. C. has 
been found to yield good results. 
Suitable materials for making the heavy-walled sphere are thermoset hard 
rubber compounds, thermoplastic plastic materials and castable urethane 
thermoset materials. Most preferred are thermoset hard rubber compounds 
such as natural rubber, polybutadiene or a mixture thereof. 
The solid walled sphere has a thickness of about 1/16 inch (0.16 cm) to 
about 1/4 inch (0.64 cm). Good results have been obtained with a wall 
thickness of about 3/32 inch (0.24 cm). 
The heavy-walled, solid sphere is hard. Preferably, it has a hardness in 
the range of about 80 to about 95, and most preferably about 90 to about 
95. Good results have been found with a hardness of about 90 when measured 
with a type-C Durometer hardness tester per ASTM No. D2240-75. 
The core having a hard wall surrounding the liquid-filled envelope has a 
diameter measuring between about 1 inch (2.54 cm) to about 11/2 inch (3.81 
cm). Preferably, the hard-walled core measures about 1.0 inch (2.54 cm) to 
about 13/8 inch (3.5 cm) in diameter. Good results have been obtained with 
a hard-walled core measuring 11/4 inch (3.175 cm). 
On top of this heavy walled, solid sphere, elastic thread is wound in a 
conventional manner. 
These and other aspects of the present invention may be more fully 
understood with reference to the accompanying drawings wherein: 
FIG. 1 illustrates a flow diagram for the method of the present invention; 
and 
FIG. 2 illustrates a golf ball made in accordance with the present 
invention.

Referring to FIG. 2, there is shown golf ball 10 having liquid center 11. 
The liquid center comprises rubber envelope 12 with liquid 14 therein. 
Golf ball cover 16 is about the exterior of the ball. The cover 16 is of 
conventional construction such as balata, gutta percha, Surlyn.RTM., 
polyurethane or a combination of the foregoing. Liquid-filled center 11 is 
surrounded by a hard cover 18. Between golf ball cover 16 and hard center 
cover 18 is elastic thread 20. The interface between envelope 12 and hard 
center cover 18 is shown by reference numeral 22. There is no space 
between hard center cover 18 and envelope 12. 
These and other aspects of the present invention may be more fully 
understood with reference to the following examples. 
EXAMPLE 1 
This example illustrates making a wound core of the present invention. As 
shown in FIG. 1, glycerine was injected into the envelope and the envelope 
was patched with an adhesive material. Next, strips measuring 
1'.times.1/2".times.1/16"(0.3 m.times.1.3 cm.times.0.16 cm) were cut from 
a sheet of uncured hard rubber compound. The sheet was formed in a 
conventional mixing of the components and then sheeted off and hand cut. 
The strips were manually wrapped around the liquid-filled center and then 
the wrapped center was placed into a smooth-walled ball mold which was 
subsequently closed and subjected to heat and pressure, about 320.degree. 
F. for about 4 minutes, in order to cure the hard rubber compound. The 
hard covered center was then demolded. 
EXAMPLE 2 
This example illustrates the reduced spin obtained with a golf ball having 
a liquid-filled, hard cover center of the present invention as compared to 
a hard center wound golf ball and a two-piece golf ball. Table I below 
illustrates the results: 
TABLE I 
______________________________________ 
DT Pinnacle Present 
Property Control Control Invention 
______________________________________ 
Ball diameter, 
1.68 (4.3) 1.68 (4.3) 
1.68 (4.3) 
inches (cm) 
PGA compression 
66 66 66 
Spin rate (rpm) 
3094 2309 2274 
______________________________________ 
The golf ball of the present invention had a glycerine-filled envelope 
measuring 1 1/16 inch (2.7 cm) and a cover of hard rubber compound around 
the envelope having a thickness of 3/16 inch (0.5 cm). 
The DT is a commercial three-piece ball having a solid rubber center sold 
by Acushnet Company and the Pinnacle is a commercial two-piece ball sold 
by Acushnet Company. All three balls had covers made of Surlyn.RTM.. 
Spin rate was determined by photographing the ball in flight at two points. 
For purposes of this example, each ball was hit using a dual pendulum 
machine having a 15.degree. face. The face was traveling at 454 RPM (138 
m/min.). The angle was measured from a vertical axis. Strobe lights and a 
single camera were used to get a double exposure of the ball on a single 
frame of film at two different points in the ball's line of travel. A 
yardstick was positioned just below tee ball's flight path such that the 
yardstick appeared in the double-exposed photograph. 
PGA compression was determined using a commercial PGA compression tester. 
The measurements were performed in a conventional manner well-known to 
those of skill in the art of golf ball manufacturing. 
It will be understood that each and every numerical value which appears in 
the claims herein is modified by the term "about" if the modifying term 
"about" does not appear in front of such numerical value. 
It will be understood that the claims are intended to cover all changes and 
modifications of the preferred embodiments of the invention herein chosen 
for the purpose of illustration which do not constitute a departure from 
the spirit and scope of the invention.