US 3428315 A
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Feb. 18, 1969 R. c. HAINES 3,
GAME BALL Filed June 28. 1965 VULCANIZED ELASTOMERIC COMPOSITION TEXTILE COVERING PARTICLES OF A THERMOSETTING PHENOLIC RESIN HAVING A SIZE OF NOT MORE THAN 50 MESH AND A DENSITY OF o.s-|-25 United States Patent 28,327 64 US. Cl. 273-61 9 Claims Int. Cl. A631) 39/00 ABSTRACT OF THE DISCLOSURE A pressureless ball e.g. a tennis ball comprising a ho]- low sphere of a vulcanized elastomeric composition containing dispersed discrete particles of a thermosetting phenolic resin as a reinforcing filler.
This invention relates to playballs, including in particular lawn tennis balls, which will be referred to hereafter as tennis balls.
A playball usually consists of a hollow sphere made of an elastic medium which is usually a composition of rubber or rubber-like material suitably formulated to give properties appropriate to the playball.
Usually the hollow sphere (hereinafter called the playball-shell) contains a gas at a pressure above that of the atmosphere, the excess pressure in the case of a conventional playball usually being of the order of 10-12 lbs. per square inch above atmospheric pressure immediately after manufacture. The presence of the gas at this superatmospheric pressure modifies the properties of the playball so that desirable playing properties are obtainedfln particular, the presence of the gas imparts a higher resilience to the playball (i.e. it bounces higher when dropped from a fixed height) and its also increases the resistance of the playball to deformation under a radially applied load, such as for instance, is applied by a racket when the ball is struck.
It will be appreciated that the above remarks apply equally to a tennis ball which may be regarded as a particular type of playball in which the surface is covered by a textile medium composed of natural and/or synthetic fibres in an arrangement whereby the particular desirable playing properties of a tennis ball are achieved.
Although the super-atmospheric pressure existing inside the playball-shell imparts desirable playing properties to the playball, corresponding undesirable characteristics are also attendant which are related to the slow diffusion of gas from the interior of the playball-shell due to the differential pressure existing on each side of the wall of the shell. Due to the effect of super-atmospheric internal pressure on the playing qualities of the ball, these qualities change accordingly and a stage is reached when the playing qualities are unsatisfactory. It is consequently necessary for playballs either to be used within a certain specified time after manufacture or for the balls to be enclosed in pressurized tins or other containers prior to use so that the pressure differential across the wall of the playball-shell is reduced or eliminated. Both procedures entail inconvenience and expense.
It will be appreciated that it would be an advantage if playballs could be manufactured without the difiiculties associated with the conventional pressurized playballshell. Such difficulties would be minimised or obviated if the excess pressure inside the playball-shell could be substantially reduced or made equal to zero. It will be appreciated that the near are the values of pressure on either side of the wall of the shell the slower is the rate of diffusion of gas from inside the shell and if the pressures are equal, no diffusion will take place.
The manufacture of playballs incorporating a substan stantially reduced or zero super-atmospheric internal pressure is accordingly an object of this invention.
By a substantially reduced super-atmospheric internal pressure there is meant a pressure which is substantially reduced as compared to the conventional internal pressure in playball-shells. In the case of a tennis ball, an internal pressure up to about 6 lbs. per square inch above atmospheric pressure is regarded as substantially reduced compared to the conventional pressure of 10-12 lbs. per square inch.
If a playball is made with a reduced or zero superatmospheric internal pressure, the wall of the shell must contribute significantly to or impart unaided the necessary properties of resilience and resistance r to deformation. Satisfactory playballs can be made with reduced or zero super-atmospheric pressure by using substantially conventional rubber or rubber-like compositions while increasing the wall thickness of the playball-shell by an appreciable amount. It is found, however, that by doing this the weight of the playball is substantially increased and in the case of a tennis ball, the resulting weight would be outside the limits set by the controlling authorities. Such a method is therefore not satisfactory.
It has been found that the desired properties of resilience, resistance to deformation and weight can be obtained by using special compositions of low density incorporating as reinforcing fillers certain synthetic resins having densities within the range 0.80-1.25 gms./cc.
Referring to the drawing, the sole figure is a cross sectional view of one embodiment of the invention.
According to the present invention, a playball-shell comprises a self-supporting hollow sphere 1 of a vulcanized elastomer composition, that is, a rubber or rubber-like composition in which is present a lo w-density reinforcing filler 2 constituted by a thermosetting synthetic resin of the phenolic type. By a self-supporting hollow sphere is meant a hollow sphere which returns after deformation to a substantially spherical shape without the support of an internal bladder or other internal reinforcement. Normally the reinforcing filler 2 has a density of about 1 gram/cc., i.e. in the range 0.08-1.25. A textile covering 3 encloses the hollow sphere 2.
If the composition is a rubber composition, the synthetic resin preferably hardens at about rubber vulcanising temperatures. The resin may be a modified phenolic resin incorporating an aldehyde donor.
The reinforcing filler normally has a particle size not greater than 50 mesh. Preferably the particle size is below mesh, e.g. of the order of mesh. The term 150 mesh indicates that the particle size is such that substantially all of the particles will pass through a mesh screen having 150 divisions to the inch.
The reinforcing filler may be incorporated in a composition of a natural and/or synthetic base polymer, at a loading of up to 50 percent by weight relative to the base polymer, the preferable range of loading being 20-45 percent. An example of a very suitable thermosetting synthetic resin of the phenolic type is the resin sold by British Resin Products Limited, Penarth, Glamorgan, under the name Cellobond H. 831. This is a modified phenolic resin having about 8 percent of an aldehyde donor (in this case hexamine) added during manufacture. The resin hardens at about rubber vulcanising temperatures.
The resin is a solid in powder form of particle size such that 99.85 percent passes through 60 mesh and 90 percent through 150 mesh. It has a softening point around 85 to 95 C., and a hardening time at 130 C. of 110 to 140 seconds. The density of the resin has been measured as 1.18 grams/cc.
The rubber or rubber-like composition may be any composition suitable to produce the properties required of a playball-shell. It is preferred to use a vulcanized composition based on natural rubber and/or a synthetic rubber similar in resilience properties to natural rubber, such as cis-polyisoprene or polybutadiene. Compounding ingredients such as vulcanization agents and accelerators and high density reinforcing fillers such as carbon black may be added as required. In general the requirements for a rubber composition to make a tennis ball shell are a composition resilience (as measured on the Dunlop Tripsometer, British Standard 903 Part A8) above 65 percent, particularly 75-80 percent, and a composition hardness (as measured in accordance with British Standard 903 Part A7) of above 65 degrees, particularly 75-80 degrees.
If desired a substantially reduced super-atmospheric internal pressure may be induced inside the playball-shell, for example by including a nitrogen-generating combination of ingredients in the composition so as to produce a playball-shell enclosing nitrogen at a super-atmospheric pressure of up to 6 lbs. per square inch.
The invention is illustrated in the following examples, in which all parts are parts by weight.
EXAMPLE I The formulation is given below of a composition from which satisfactory playballs having zero super-atmospheric internal pressure can be made in accordance with the present invention.
Natural rubber 25.0 Polybutadiene 75.0 Cellobond H. 831 30.0 Sulphur 3.0 Zinc oxide 5.0 Stearic acid 2.0 Oil (Dutrex R) 2.0 Dibenzthiazyl disulphide 1.0 Tetramethyl thiuram disulphide 0.4 General purpose furnace black 15.0
Half shells were made from the mixture given above and spherical playball-shells were formed by moulding the shells at a temperature of 150C. for 13 minutes which vulcanized the composition. They were then made into tennis balls by applying a conventional tennis ball melton covering and were further moulded for minutes at a temperature of 130 C. The resulting tennis balls were found to bounce to a height of 54 inches when dropped from a height of 100 inches (International Lawn Tennis Federation Specification: 53-58 inches); the compression characteristics when measured in the manner specified by the International Lawn Tennis Federation were also found to be satisfactory.
EXAMPLE II The formulation is given below of a further composition from which satisfactory playballs having zero superatmospheric internal pressure can be made in accordance with the present invention.
Natural rubber 50.00 Polybutadiene 50.00 Cellobond H. 831 40.00 Sulphur 3.50 Zinc oxide 3.00
Stearic acid 1.00 Oil (Dutrex R) 2.00 Diphenyl guanidine 1.40 Dibenzthiazyl disulphide 0.70 Benzoic acid 0.70 Antioxidant 1.00
Cellobond H. 831 is a modified phenolic resin having about 8 percent of added hexamine and is available from British Resin Products Limited.
Tennis balls were made using this composition in the manner described in Example I. These balls were found to bounce to a height of 54 inches when dropped from a height of inches, and the compression characteristics were satisfactory when measured in the manner specified by the International Lawn Tennis Federation.
EXAMPLE III Playballs having a substantially reduced internal pressure may be manufactured from the above compositions. As compared to Example I, the manufacturing details differ in the following respects.
(1) 0.09 gm. sodium nitrite and 0.08 gm. ammonium chloride crystals are introduced into the playball-shell prior to moulding. Nitrogen gas is evolved during the moulding operation which produces a super-atmospheric pressure of 5 lbs. per square inch inside the playball-shell.
(2) The playball-shell moulding operation is performed at a temperature 140 C. for 13 minutes.
Tennis balls were made from these playball-shells by applying tennis ball melton as before and moulding for a further 10 minutes at C.
The bounce and compression characteristics were found to be satisfactory as before.
Attention is drawn to our two copending patent applications No. 467,704, filed June 28, 1965, entitled, Improvements Relating to Playballs, and No. 467,687, filed June 28, 1965, entitled Improvements in or Relating to Playballs. In these applications alternative compositions are described which enable the present object to be achieved. It is to be understood that the compositions described in any of the three applications may be blended together in any proportion and satisfactory playballs or tennis balls with substantially reduced or zero super-atmospheric internal pressure produced, given due attention to compounding and moulding conditions.
For example a satisfactory tennis ball has been produced from a composition including Cellobond H. 831 and wood flour which is one of the cellulosic materials described as fillers in our application No. 467,687.
Having now described my invention, what is claimed is:
1. A pressureless playball-shell comprising a self supporting hollow sphere of a vulcanized elastomeric composition and as a reinforcing filler about 20-45% by Weight of the elastomer in said composition of particles of a thermosetting phenolic resin having a density in the range of 0.8-1.25 grams/cc, and said particles having a size of not more than 50 mesh, said filler being evenly distributed throughout said composition.
2. A playball-shell according to claim 1, wherein the resin is a phenolic resin incorporating a formaldehyde donor.
3. A playball-shell according to claim 1, wherein the particle size of the resin is below 100 mesh.
4. A playball-shell according to claim 1, wherein the phenolic resin reinforcing filler has a softening point in the range 85-95 C., a hardening time at 130 C. of 110- seconds, a density of about 1.18 grams/cc. and contains a minor amount of a formaldehyde donor.
5. A playball-shell according to claim 4, wherein the phenolic resin reinforcing filler has a particle size such that substantially all of it passes through a 60 mesh and at least 90 percent through a mesh.
6. A playball-shell according to claim 4, wherein the formaldehyde donor is hexamine which is present in an amount of about 8 percent of the weight of said filler.
5 6 7. A playball-shell according to claim 1, wherein the FOREIGN PATENTS elastomeric composition comprises natural rubber.
8. A playball-shell according to claim 1, wherein the 579,632 7/1959 Canada elastomeric composition comprises polybutadiene.
9. A pressureless lawn tennis ball comprising a shell GEORGE J, MARLO, P i Examiner.
according to claim 1 and a textile medium covering said 5 shell. US. Cl. X.R.
References Cited UNITED STATES PATENTS 260-2.5, 3, 845; 264-331; 273-65 3,206,201 9/1965 Hendricks 27363 10