US 3241834 A
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March 22, 1966 N. H. STINGLEY 3,241,834
HIGHLY RESILIENT POLYBUTADIENE BALL Filed Aug. 25. 1965 BALL MATERIAL:
SPECIFIC GRAVITY l-I.3
POLYBUTADIENE -ABOUT I00 PARTS SULFUR VULCAN. AGENT 05 I0 I5 PARTS HYDRATED SILICA 0r CARBON BLACK or A 5 I0 I5 PARTS LITHIUM OXIDE INVENTOR NORMAN H. STINGLEY BYM ATTORNEYS United States Patent 3,241,834 HIGHLY RESILIENT PGLYBUTADIENE BALL Norman H. Stingley, Garden Grove, (Zalifi, assignor to Wham-0 Manufacturing Company, San Gabriel, Calif, a corporation of California Filed Aug. 25, 1965, Ser. No. 432,584 3 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 coeflicient of friction.
The resiliency of rubber balls is one of their most important characteristics. This is because the resiliency 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. This 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 coefiicient 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 coeflicient 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 it 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 than that found in balls manufactured from natural rubber or polyisoprene.
In addition to resilience and cross linkage, the ability Preferred, Range, parts Constituent parts by wgt. by wgt.
Polybutadiene 100. 00 3-5 Zine oxide 4. 00 Stearic acid W, 2.00 0. 5-3 N-oxydrethylene benzothiazole 2 sulfenamide (AMAX) 1. 0. 5-2. 5 Di-ortho-tolylguanidine (DOTG) 1.00 0.5-2.5 Bismuttl; dimethyldithio-carbonate (Bis- 0.35 0. 25-0. 75
ma 6 4 methyl-6 tertiary-butyl phenol 1. 00 0. 5'2 Hydrated silica 7. 5 5-15 Sulfur 5. 25 0. 5-15 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 this 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 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.
The 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 ob-- tained.
Hydrated silica is added to the mixture as a filler. A specific hydrated silica suitable for use in this mixture is marketed under the trademark I-Ii-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 without unduly increasing the specific gravity. Carbon black and lithium oxide have also been found to fill these requirements and are satisfactory substitutes for the hydrated silica.
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 nold and subjected to a pressure of between 500 and 3,000 p.s.i. for a period of approximately 10 to 30 minutes. Simultaneously, the temperature of the mixture is raised to approximately 285340 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 in the other. Preferably the time and temperature for the molding operation is to 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.
As is normal in molding tehniques, 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:
l. 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 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 reinforcing material.
2. A ball 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 OTHER REFERENCES Rubber and Plastics Age, vol. 38, No. 10, October 1957, pages 880883, 885, 887, 889, 891 and 892.
Rubber Chemistry and Technology, vol. XXXII, No. 2, April-June 1959, pages 614-627.
Rubber Chemistry and Technology, vol. XXXIV, No. 1, January-March 1961, pages 176190.
Rubber and Plastics Age, March 1961, pages 276- 282.
DELBERT B. LOWE, Primary Examiner.
G. J. MARLO, Assistant Examiner.
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