With very special thanks to Mr. L. Paul Brossette for his contribution!
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3,241,834HIGHLY RESILIENT POLYBUTADIENE BALL Norman H. Stingley, Garden Grove, Calif., assignor to Wham-O Manufacturing Company, San Gabriel, Calif., a corporation of CaliforniaFiled Aug. 25, 1965, Ser. No. 482,5843 Claims. (Cl. 273—58) This is a continuation-in-part of application
Serial No. 462,081 filed June 7, 1965, and now abandoned. This invention relates to a toy and more
particularly to a ball or sphere having extremely high resilience and a high
coefficient of friction. The resilience of rubber balls is one of their
most important characteristics. This
is because the resilience of the ball material determines the “liveliness”
and “bounce” of the ball and hence its utility in
various sporting games and attractiveness as a toy for children. The resilient material normally used for
making rubber balls is a polymer such as natural rubber or some synthetic
analog of natural rubber such as polyisoprene. The present invention is concerned with a
material other than rubber and polyisoprene as the
base polymer in rubber toys and sporting articles. It has been found that this new material
imparts some highly unusual qualities to articles fabricated with it. Such articles have been found to have a
substantially greater resiliency than those manufactured from more conventional
materials. The greater resiliency is
thought to be due to the nature of the base polymer used in the mixture and
the unique quality of the mixture which comprises the article of being able
to conserve the energy which is imparted to it rather than dissipating a
substantial portion of it in the form of heat. The higher resilience means that balls made
from the material of this invention have a resilience factor in excess of
90%. This resilience factor is the
resilience of the material as measured by the Yerzley
method, ASTM D945-59. Another unusual quality of balls and toys of
this invention is their coefficient of friction. In this instance the coefficient friction
is substantially higher than in other similar items. This quality combined with the
significantly higher resilience causes a ball to react in an extraordinary
and unpredictable manner when bounced or struck. This higher coefficient of friction also
provides a means whereby the spin or “English” on a thrown, struck or dropped
ball can be accentuated resulting in unusual reactions by the ball whenever
rebounds from a hard surface. This
novel combination of qualities means that one natural application for balls
manufactured with the base polymer with which this invention is concerned is in
trick ball uses. In addition, as a
sports implement a ball of this invention presents a greater challenge to the
user. As an article of play, the
eccentricity of reaction makes the ball a highly entertaining and amusing
toy. The invention in the present case
contemplates a molded, vulcanized, highly resilient ball comprising a mixture
of Polybutadiene, a sulfurous vulcanizing agent and
a Polybutadiene reinforcing agent. In addition to the inherent resilience of
the base polymer, the degree of cross linkage between polymer chains is
important in optimizing the bounce or liveliness of balls fabricated with
it. The degree of cross linkage is
primarily determined by the amount of vulcanizing agent used. By limiting the amount of vulcanizing agent
introduced into the mixture to the quantities specified below, a ball having a Yerzley resilience in excess
of 90% is obtained. Such a resilience
factor is substantially higher that that found in balls manufactured from
natural rubber or polyisoprene. In addition to resilience and cross linkage,
the ability |
5 10 15 20 25 30 35 40 45 50 55 60 65 70 |
of the material to conserve energy is of
importance. It has been found that balls
manufactured according to the present invention dissipate very little energy
imparted to it in the form of heat.
The present invention embodies these and other properties as will be
observed from the following detailed description. The accompanying diagrammatic drawing with
legends illustrates the ball. Products according to this invention are
manufactured from a formulation consisting of the following:
In
the formulation above Polybutadiene is the base
polymer of the mixture. To produce
cross linkage between polybutadiene chains, that
is, to vulcanize or cure the polymer, sulfur is added to the mixture. A greater amount of vulcanizing agent is
used in the mixture than in such products as tires thereby producing a
greater degree of vulcanization. Put
another way, the degree of cross linkage relative to saturation (hard rubber)
is increased over tires and the like.
The more complete vulcanization is believed to result in the improved
resilience of the finished product.
The addition of sulfur in the range indicated will result in balls
having a Yerzley Resilience in excess of 90%. Oil extended polybutadiene
having as much as 50 parts by weight of oil per hundred parts by weight of polybutadiene can also be used as the base polymer. Because the natural curing rate of a mixture
of polybutadiene and sulfur is quite slow, certain
other additives are combined with this basic mixture to initiate the curing
cycle and accelerate the rate of vulcanization. The zinc oxide and stearic
acid are added to the basic mixture to provide this activation function. Acceleration accomplishes two purposes,
one, it shortens the length of the molding cycle, and two, it equalizes heat
throughout the mixture during the curing cycle. In the preceding formulation, the
accelerators are N-oxydiethylene benzothiazole 2 sulfenamide, di-orthotolylguanidine and bismuth dimethyldithiocarbonate. For ease of reference, the trade names
AMAX, DOTG and Bismate respectively will be used to
designate the accelerators. This activation of these accelerators occurs
as the mixture reaches a specific temperature. For Bismate and
DOTG the activation temperature is approximately 230° F, while that of AMAX is
approximately 260° F. By insuring that the heat
of reaction is equalized throughout the mixture a more uniform rate of
vulcanization and improved consistency in the end product is obtained. Hydrated silica is added to the mixture as a filler. As
specific hydrated silica suitable for use in this mixture is marked under the
trademark Hi-Sil 233. This material and certain other materials
perform the function of providing tear and abrasion resistance. The basic criteria for
selection of the filler material is its ability to improve the
durability of polybutadiene with unduly increasing
the specific gravity. Carbon black and
lithium oxide have also been found to fill these requirements and are
satisfactory substitutes for hydrated silica. |
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3,241,834 |
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In addition to the ingredients just
previously discussed, 4 methyl-6 tertiary-butyl phenol
is also added to the mixture. This
substance has been given the trade name of Antioxidant 2246 and prevents
discoloration and staining and inhibits aging of the finished product. Examples of substitutes for Antioxidant
2246 are phenyl B naphthylamine, alkyl
diphenylamine, and hindered alkyl phenols.
Pigmenting agents for obtaining the desired color of the end product
are optional additives. The
mixture and molding of the constituents of this formulation proceeds
according to the following steps. The
various elements of the formulation are brought together in a mixing machine
and agitated thoroughly to insure uniform mixing and distribution of the
elements throughout the mixture. The
result is a plastic mass ready for insertion in a mold. To complete the process, the mixture is
placed in a mold and subjected to a pressure of between 500 and 3,000 p.s.i. for a period of approximately 10-30 minutes. Simultaneously, the temperature of the
mixture is raised to approximately 285-340° F.
To a certain extent the length of the molding operation, the pressure,
and the temperature to which the formulation is subjected are co-variant and
one may be adjusted to compensate for a variation of the other. Preferably the time and temperature for the
molding operation is 15-20 minutes at approximately 320° F. and 1,000
p.s.i. An alternate formulation to the one outlined
above is as follows:
The above formulation is mixed in the same
manner as the preceding formulation.
To insure a good dispersion of all ingredients in the mixture, the
batch is normally given a two-pass mix.
In the above formulation, the zinc oxide and the stearic
acid perform the same functions, viz., activation of
polymer curing, as they did in the first formulation. Akron 544 Red and Akron 626 Blue are trade
designations for organic coloring agents manufactured by Akron Chemical
Co. Titanium dioxide is also a
coloring agent. These three
constituents in combination are the pigmenting agent for the mixture. Zeolex is a
proprietary brand name for a series of precipitated, highly hydrated sodium silico-aluminates and sodium calcium silico-aluminates. Its function is to strengthen the finished
product and to act as a filler in the same manner as
the Hi-Sil 233 does in the preceding formulation. Sulfur is the vulcanizing agent. Vandex is a
proprietary name for finely ground selenium.
Its function is to supplement sulfur as a vulcanizing agent. As in the first formulation, several
constituents of the mixture (AMAX and M. Tuads) are
added to serve as accelerators for the polymerization. |
5 10 15 20 25 30 35 40 45 50 55 60 65 |
As is normal in molding techniques, the curing
temperature must be carefully selected in order to prevent imperfections in
the finished product. Too high a
molding temperature will contribute to a condition designated
”backrind.”
This condition is characterized by an indented fracture around the
body of the molded product defining the point where the two halves of the
mold are brought together and is due to thermal expansion in this area during
and after the molding cycle. Subject to the proper choice of injection
pressure, injection time, and the combination of mixture constituents,
preheat, and mold temperature, this mixture can also
be molded by means of a conventional injection-molding technique. Combinations of ingredients of which the two
formulations listed above are representative have been found to result in a
product with a specific gravity of approximately 1.0 to 1.3. For greatest resilience, it has been found
that a sufficient amount of filler should be added to produce a product
having a specific gravity of 1.02. What is claimed is: 1. A highly resilient solid ball in the form
of a sphere, the ball material having a specific gravity of from about 1 to
about 1.3, and comprising in combination a vulcanized polymer characterized
by the use of 100 parts by weight of polybutadiene
and 0.5 to 15 parts by weight of a sulfur vulcanizing agent, and further
comprising, in addition to any activators and accelerators used for
vulcanization, 5 to 15 parts by weight of an inorganic reinforcement
material. 2. A ball is in accordance with claim 1
in which the reinforcing material is selected from the class consisting of
hydrated silica, carbon black and lithium oxide. 3. A ball in accordance with claim 2 in which the sulfur vulcanizing agent is approximately 5.25 parts by weight and the reinforcing material is approximately 7.5 parts by weight. References
Cited by the Examiner UNITED STATES PATENTS
FOREIGN PATENTS
OTHER REFERENCES “Rubber and Plastics Age,” vol. 38, No. 10,
October 1957, pages 880-883, 885, 887, 889, 891 and 892. “Rubber Chemistry and Technology,” vol.
XXXII, No. 2, April-June 1959, pages 614-627. “Rubber and Plastics Age,” March 1961, pages
276-282. DELBERT
B. LOWE, Primary Examiner. G.J.
MARLO, Assistant Examiner. |
March 22, 1966 |
N.
H. STINGLEY
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3,241,834 |
HIGHLY RESILIENT POLYBUTADIENE BALL
Filed Aug. 25, 1965
BALL
MATERIAL:
SPECIFIC GRAVITY - 1-1.3
POLYBUTADIENE - ABOUT 100 PARTS
SULFUR VULCAN. AGENT - 0.5 to 15 PARTS
HYDRATED SILICA or
}
CARBON BLACK or
} - 5 to 15 PARTS
LITHIUM OXIDE }
INVENTOR
BY Christie, Packer & Hale
ATTORNEYS