Game ball

A game ball is made by rotationally molding a hollow spherical shell from a blend of foamed ionomer resins (Surlyn 9450 and Surlyn 8528) and low density polyethylene resin. The center of the hollow spherical core may be filled with foamed polyurethane, and the spherical core may be covered by a leather cover. If desired, hollow ceramic microspheres or beads can be added to the resins before molding.

BACKGROUND 
This invention relates to game balls, and, more particularly, to a game 
ball with a spherical core formed from a blend of a foamed mixture of 
ionomer resins and low density polyethylene. 
This invention is an improvement over the game balls described in my prior 
U.S. Pat. No. 4,861,028. As described in my prior patent, soft balls have 
historically been made by forming a spherical core of cork, kapok, or 
similar material which is bound together. A layer of windings of string or 
yarn is wrapped over the core and a leather cover is placed over the 
windings and stitched together. 
In recent years, game balls, particularly softballs, have been made from 
molded plastic cores. For example, U.S. Pat. No. 4,149,720 describes a 
ball which includes a foamed polyurethane core and a leather cover. U.S. 
Pat. No. 4,364,565 describes a ball which includes a spherical core made 
from foamed ethylene vinyl acetate copolymer and Surlyn, an ionic 
copolymer which is available from E. I. DuPont de Nemours and Co. (DuPont) 
U.S. Pat. No. 4,610,071 describes a ball which includes a core which is 
molded from Nucrel (ethylene acid copolymer) and filled with polyurethane. 
A cover is sewn over the core. U.S. Pat. No. 3,069,170 describes a ball 
which includes a core of foamed polyethylene and a cover. U.S. Pat. No. 
4,463,951 describes a ball which is made by rotationally molding an outer 
layer of foamed polyvinyl chloride and injecting polyurethane foam into 
the cavity. 
The following U. S. Pat. Nos. describe balls which are formed from Surlyn: 
4,572,507, 4,529,200, 4,568,083,and 4,653,752. 
Specifications for softballs have been issued by two governing 
organizations, the United States Slow-pitch Softball Association (USSSA) 
and the Amateur Softball Association (ASA). The specifications of the 
USSSA in effect before 1989 permitted 11 and 12 inch softballs to have a 
coefficient of restitution (COR) ranging from 0.44 or under to 0.52, 
depending upon the category or class in which the ball was used. Different 
categories would be indicated for example, by the color of the stitching 
on the cover. Beginning in 1989 the COR of USSSA licensed balls could not 
exceed 0.50. 
Coefficient of restitution (COR) is one measure of the liveliness of the 
ball. COR is measured by propelling a ball against a hard surface at 60 
mph (88 fps) and measuring the rebound speed of the ball. COR is expressed 
in terms of the ratio of the rebound speed to 60 mph (88 fps). 
Other qualities of softballs are important which are not included in the 
foregoing "official" specifications. These qualities include the sound of 
the ball when batted, texture of the ball, the "feel off the bat" or, the 
feel which the batter experiences at the moment of impact, flight distance 
and consistency, and durability. 
My prior U.S. Pat. No. 4,861,028 describes a softball which includes a 
hollow core which is formed by rotationally molding low density 
polyethylene or a mixture of low density polyethylene and an ethylene acid 
copolymer. The specific ethylene acid copolymer described is available 
from DuPont under the name Nucrel. The low density polyethylene used is 
sold by the USI Division of Quantum Chemical Corporation under the 
designation Microthene MN718 and has a density of 0.915 grams/cc and a 
flexural modulus of 20.6 kpsi (1000 pounds per square inch). The softballs 
formed in accordance with my prior patent have not been well received. 
Those softballs did not carry as well as solid core balls, and the hollow 
balls had a tendency to fracture when played in temperatures below 
40.degree. F. 
SUMMARY OF THE INVENTION 
I have found that rotationally molding a blend of two different Surlyns 
(ionomer resins available from DuPont) substantially improves the 
performance of the core. The core can be further improved by adding a 
minor amount of low density polyethylene (LDPE), e.g., from 15 to 30% by 
weight, and a chemical blowing agent (CBA). The LDPE preferably has a 
density within the range of about 0.910 to 0.940 gm/cc. The LDPE serves as 
a compounding grinding agent and reduces the cost of an all-Surlyn core. 
The blowing agent forms a foamed core, and the thickness of the core wall 
is substantially greater than the thickness of the unfoamed core, thereby 
decreasing the size of the hollow interior. The foamed core also has 
greater resistance to deformation and plays and feels more like a solid 
core. The amounts of the Surlyn, the low density polyethylene, and the 
blowing agent can be varied as desired to vary the COR and the compression 
resistance (feel). The COR can be lowered and compression resistance can 
be improved by adding hollow ceramic microspheres. The hollow core can be 
filled with foamed polyurethane if desired.

DESCRIPTION OF SPECIFIC EMBODIMENTS 
The invention will be explained in conjunction with a softball 15. The 
particular softball illustrated in the drawings is a 12 inch circumference 
softball, but it will be understood that the invention can be used with 
other sizes of balls, for example, 9 and 11 inch circumference balls, and 
with other game balls with and without covers. 
The softball 15 includes a hollow spherical core or shell 16 and a cover 17 
which surrounds the core or shell. The cover is formed from two 
dumbbell-shaped pieces 18 and 19 which are stitched or sewn together along 
seams 20. The cover can be formed from leather, vinyl, or similar material 
which can be used to simulate the look and feel of leather covers. For a 
12 inch softball the outside diameter of the core or shell is within the 
range of 3.66 to 3.70inches, and the cover thickness is about 0.05 to 0.06 
inch. The wall thickness of the core or shell can be within the range of 
about 0.36to 0.56 inch. 
The core or shell 16 is formed from a blend of foamed resins, namely two 
different Surlyns (ionomer resins available from DuPont) and low density 
polyethylene resin. The preferred procedure for forming the core is 
rotational molding. Rotational molding is a well known art, and a detailed 
description of the procedure is unnecessary. The plastic resins are 
introduced into a mold, and the mold is rotated biaxially in a heated 
chamber. The mold is rotatably mounted on a spindle, and the mold is 
rotated by the spindle while the spindle is rotated about an axis which is 
perpendicular to the axis of the spindle. 
In rotational molding, there are essentially four basic steps: loading, 
molding or curing, cooling and unloading. In the loading step, either 
liquid or powdered polymer material is charged into a hollow mold. The 
mold halves are then closed and moved into an oven where the loaded mold 
spins biaxially. Rotation speeds should be variable at the heating 
station. 
In the oven, the heat penetrates the mold, causing the polymer material, if 
it is in powder form, to melt and conform to the mold surface, or if it is 
in liquid form, to start to gel. The heating is usually accomplished by 
air or by a liquid of a high specific heat, such as molten salt or where 
jacketed molds are used, by a liquid medium such as oil. 
As the molds are heated in the oven, they continue to rotate so that the 
polymer material will gradually become distributed evenly on the molded 
cavity through centrifugal force. As the heating continues, the polymer 
material melts completely forming a homogeneous layer of molten plastic. 
When the parts have been formed, the molds are transferred to a cooling 
chamber where cooling is accomplished by any means, preferably cold water 
spray or forced cold air. During cooling, the mold continues to rotate so 
that there are no distortions formed in the surface of the molded product. 
Lastly, the molds are opened and the parts removed either by manual or 
mechanical means. 
In forming game balls in accordance with the preferred embodiment of the 
invention, the mold is loaded with a blend of Surlyns, low density 
polyethylene (LDPE) resin, and a blowing agent. It is believed that Surlyn 
has not heretofore been rotomolded because Surlyn resin is not readily 
available in powder form and cannot be air ground. The LDPE serves as a 
compounding/grinding aid and also reduces the cost of an all-Surlyn ball. 
The LDPE is extrusion blended with the Surlyns, and the blend is ground 
into a powder. 
The preferred ball used 17% by weight Surlyn 8528 from DuPont, 68% by 
weight Surlyn 9450 from DuPont, and 15% NA 117LDPE in pellet form from the 
USI Division of Quantum Chemical Corporation. The comparable powder form 
of LDPE is MN-718. The chemical blowing agent (CBA) is a modified 
azodicarbonamide available from Uniroyal Chemical Company under the 
designation Celogen AZ 2990. The amount of the blowing agent is preferably 
in the range of 0.35 to 0.50 parts per hundred of the total of Surlyn and 
LDPE resins. The blowing agent expands the wall thickness of the core and 
makes the ball play and feel more like a solid ball. 
As will be explained hereinafter, the COR and compression resistance of the 
core can be varied by changing the ratio of Surlyn 8528 to Surlyn 9450. 
The core can be further improved by adding beads or microspheres to the 
resins in an amount of up to 10% of the total weight of the core. The 
preferred microspheres are available from Zeelan Industries of St. Paul, 
Minn. under the designation Z-Light W-1000. The microspheres are hollow 
silica-alumina ceramic alloy spheres having a diameter of 10 to 150 
microns, a specific gravity of 0.7 to 0.9 g/cc, a hardness of Mohs Scale 
5, and a compressive strength of 5000 psi. The microspheres increase the 
wall thickness of the core, lower the COR and I.V. (initial velocity), 
increase hardness slightly, and reduce the deformation (compression 
resistance) under a 400 pound load, especially at 100 degrees. 
FIG. 3 illustrates another 12 inch circumference softball 22 which includes 
a spherical core 24 formed in the same way as the core 16 and a cover 25. 
The center of the molded core is filled with low density polyurethane foam 
26. The PU foam makes a three-piece ball --the core, the cover, and the PU 
center -- and makes the ball play and feel more like a solid ball. The PU 
foam also prevents rattles if small pieces of the core break off during 
repeated impacts. The particular PU used is SWD-760-2, a two-part liquid 
polyurethane sold by SWD Urethane Co. of Mesa, Ariz. The molded core is 
provided with a suitable opening for introducing the mixed polyurethane 
components, which foam in place inside the core. 
Surlyn resins are ionic copolymers which are the sodium or zinc salts of 
the reaction product of an olefin having from 2to 8 carbon atoms and an 
unsaturated monocarboxylic acid having from 3 to 8 carbon atoms. The 
carboxylic acid groups of the copolymer may be totally or partially 
neutralized. Surlyn resins and the method of producing Surlyn resins are 
explained in detail in Rees U.S. Pat. No. 3,264,272. 
Surlyn 8528 is a sodium Surlyn and has the physical properties set forth in 
Table I. Surlyn 9450 is a zinc Surlyn and has the physical properties set 
forth in Table II. 
TABLE I 
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Density - g/cc: .94 ASTM D 792 
Melt Index - dg/min: 
1.3 ASTM D 1238 
Tensile - KPSI: 1.8 ASTM D 638 
Elongation - %: 450 ASTM D 638 
Flex Modulus - KPSI: 
32 ASTM D 790 
Hardness - Shore D: 
60 ASTM D 2240 
Vicat Softening - Deg. C: 
73 ASTM D 1525 
______________________________________ 
All of the above values are nominal: Measured values should be within 10% 
of the nominal values. Note: Melt index is highly influenced by moisture 
content and should be run on a sample from an unopened bag. 
TABLE II 
______________________________________ 
Density - g/cc: .94 ASTM D 792 
Melt Index - dg/min: 
5.5 ASTM D 1238 
Tensile - KPSI: 1.2 ASTM D 638 
Elongation - %: 500 ASTM D 638 
Flex Modulus - KPSI: 
19 ASTM D 790 
Hardness - Shore D: 
54 ASTM D 2240 
Vicat Softening - Deg. C: 
79 ASTM D 1525 
______________________________________ 
All of the above values are nominal: Measured values should be within 10% 
of the nominal values. Note: Melt index is highly influenced by moisture 
content and should be run on a sample from an unopened bag. 
Low density polyethylene sold under the designation NA 117 has the physical 
properties set forth in Table III. 
TABLE III 
______________________________________ 
Density - g/cc: .915 ASTM D 792 
Melt Index - dg/min: 
8 ASTM D 1238 
Tensile - KPSI: 1.7 ASTM D 638 
Elongation - %: 525 ASTM D 638 
Flex Modulus - KPSI 
20.6 ASTM D 790 
Hardness Shore D: 
48 ASTM D 2240 
Vicat Softening - Deg. C: 
88 ASTM D 1525 
______________________________________ 
All the above values are nominal: Measured values should be within 10% of 
the nominal values. 
One blend of resins used to make softballs in accordance with the invention 
used 17% by weight of Surlyn 8528, 68% by weight of Surlyn 9450, and 15% 
by weight of LDPE. This blend is called Blend X. Twelve inch softballs 
made from foamed Blend X cores were compared with commercial softballs 
sold under the names Red Dot and Thunder. The results are set forth in 
Table IV. 
TABLE IV 
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Deformation Carry 
@ 400 lbs. I.V. Distance 
Weight Size COR (inches) (feet/sec.) 
(feet) 
Ball (grams) 
(inches) 
at 80.degree. F. 
at 80.degree. F. 
at 100.degree. F. 
at 80.degree. F. 
at 80.degree. F. 
at 100.degree. F. 
__________________________________________________________________________ 
Blend X 
197.9 
12.01 
0.517 
0.286 0.472 
137.4 353 361 
Red Dot 
179.6 
11.87 
0.482 
0.241 0.278 
136.1 338 340 
Thunder 
180.3 
11.91 
0.501 
0.29 0.408 
137.7 347 358 
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FIG. 4 shows the effect of varying the percentages of Surlyn 8528 and 
Surlyn 9450 on the COR of the core. All cores had a total Surlyn content 
of 85% by weight of the total resin weight and 15% by weight LDPE. The 
data indicated by a square is for cores which also included 0.5 pph 
blowing agent. The data indicated by an + is for cores which included 0.4 
pph resin blowing agent and 10% by weight of the core of Z-Light ceramic 
beads or micropheres. 
FIG. 5 shows the effect of varying the amounts of Surlyn 8528 and Surlyn 
9450 on the compression resistance of the core. All cores had a total 
Surlyn content of 85% by weight of the total resin weight and 15% by 
weight LDPE. The cores were made with and without ceramic beads as 
indicated. The amount of beads is indicated as percent by weight of the 
total weight of the core, including the beads. 
FIG. 6 shows the effect of the amount of ceramic beads on the COR of the 
core. The cores were made from Blend X with 0.5 ppH blowing agent. 
FIGS. 7 through 11 show the effect of the amount of blowing agent on 
various properties of the core with 0, 5, and 10% by weight of ceramic 
beads. 
Table V is a matrix which shows the effect of varying amounts of blowing 
agent and Z Light ceramic beads on the physical properties of cores made 
from Blend X. 
TABLE V 
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Light Blowing Agent 
Level Level PPH 0 0.2 0.4 0.6 
______________________________________ 
0% Weight - gms. 152.3 150.6 151 149.4 
Size - in. circ. 
11.51 11.51 11.5 11.49 
Wall thickness - inch 
0.259 0.327 0.395 0.36 
Deform. @ 400 lb. 
@ 80 deg - inch 
0.389 0.355 0.343 0.311 
@ 100 deg - inch 
0.619 0.561 0.551 0.469 
Shore D Hardness 
50 38 30 26 
C.O.R. @ 88 FPS 
0.559 0.546 0.539 0.539 
I.V. @ 2.4 turns - FPS 
148.9 148.1 147.8 148.7 
5% Weight - gms. 152.9 152.1 150.9 150.3 
Size - in. circ. 
11.5 11.51 11.5 11.49 
Wall thickness - inch 
0.293 0.344 0.395 0.382 
Deform. @ 400 lb. 
@ 80 deg - inch 
0.312 0.295 0.262 0.268 
@ 100 deg - inch 
.532 .496 .451 .421 
Shore D Hardness 
52 38.5 31.5 27.5 
C.O.R. @ 88 FPS 
0.533 0.539 0.537 0.535 
I.V. @ 2.4 turns - FPS 
-- -- 145.7 148.4 
10% Weight - gms. 152.4 150.5 149.3 147.4 
Size - in. circ. 
11.51 11.51 11.49 11.51 
Wall thickness - inch 
0.269 0.358 0.477 0.432 
Deform. @ 400 lb. 
@ 80 deg - inch 
0.275 0.262 0.249 0.251 
@ 100 deg - inch 
0.473 0.434 0.429 0.393 
Shore D Hardness 
52 40 31 29 
C.O.R. @ 88 FPS 
0.543 0.525 0.52 0.511 
I.V. @ 2.4 turns - FPS 
147.3 145.8 146.1 145.0 
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Physical properties of softballs made from cores of two additional blends 
are set forth in Table VI. Blend X 0.4/10 was Blend X with 0.4 pph blowing 
agent and 10% Z Light beads. Blend 10.10 was 10% Surlyn 8528, 75% Surlyn 
9450, 15% LDPE, 0.4 pph blowing agent, and 10% Z-Light beads. 
TABLE VI 
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Deformation Carry 
@ 400 lbs. I.V. Distance 
Weight 
Size COR (inches) (feet/sec.) 
(feet) 
Ball (grams) 
(inches) 
@ 80.degree. F. 
@ 80.degree. F. 
100.degree. F. 
@ 80.degree. F. 
@ 80.degree. F. 
__________________________________________________________________________ 
.4/10 
186.7 
11.9 0.507 
0.269 0.411 137.6 358 
10.10 
189.7 
11.91 
0.492 
0.318 0.472 136.2 340 
__________________________________________________________________________ 
Table VII compares commercial Thunder and Red Dot softballs with softballs 
formed in accordance with the invention using 15, 20, 23, and 25% LDPE and 
varying amounts of Surlyn. The Thunder, Red Dot, and Blend X balls in 
Table VII are not the same balls which were tested in Table IV. The balls 
in Table VII were not tested for carry distance. 
TABLE VII 
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Deformation 
@ 400 lbs. I.V. 
Weight Size (inches) COR (feet/sec.) 
Ball (grams) 
(inches) 
at 80.degree. F. 
at 100.degree. F. 
at 80.degree. F. 
at 80.degree. F. 
__________________________________________________________________________ 
Thunder 
170.2 
11.89 
0.310 
0.480 
0.494 139.1 
Red Dot 
180.9 
11.81 
0.241 
0.301 
0.471 135.8 
Blend X 
187.8 
12.01 
0.294 
0.460 
0.525 139.3 
200 187.2 
11.87 
0.297 
0.469 
0.468 134.0 
212 190.9 
11.91 
0.260 
0.411 
0.493 135.6 
215 187.8 
11.88 
0.255 
0.412 
0.497 136.0 
__________________________________________________________________________ 
Blend 200 
Blend 212 
Blend 215 
__________________________________________________________________________ 
Surlyn 0% 12% 15% 
8528 
9450 80 65 60 
LDPE 20 23 25 
CBA 0.4 PPH 0.4 PPH 
0.4 PPH 
Z Spheres 9 9 9 
__________________________________________________________________________ 
Although I have found that a blend of Surlyn 8528 and Surlyn 9450 produces 
superior results, it is possible that other Surlyns could provide 
comparable results. Using two different Surlyns allows for varying certain 
physical properties of the ball as desired by varying the ratio of the 
Surlyns. 
The ceramic beads reduce the compression resistance under a 400 pound load, 
especially at 100.degree. F. It is believed that compression resistance is 
related to what players describe as "feel". A more compressible ball feels 
heavy and is not perceived as lively. A less compressible ball feels light 
and "jumps" off the bat. 
While in the foregoing specification detailed descriptions of specific 
embodiments of the invention were set forth for the purpose of 
illustration, it will be understand that many of the details herein given 
may be varied considerably by those skilled in the art without departing 
from the spirit and scope of the invention.