US3432165A - Game ball - Google Patents

Description

March 11, 1969 R- c. HAINES ETAL 3,432,165

GAME BALL Filed June 28, 1965 VULCANIZED ELASTOMERI'C Q N A w 5 m f. O WSL I m m 5 V O O ETE P N M M um O YND C ZPE TIH OmGS M N Y W L A G O H N P. A m aw W ORM M o snw EN 5 KLMMQ L T E n R TC X ACNI E PAlM T United States Patent 28,325/64 US. Cl. 273-61 Int. Cl. A63b 39/06 6 Claims ABSTRACT OF THE DISCLOSURE A prcssureless ball, e.g., a tennis ball comprising a hoilow sphere of a vulcanised elastomeric composition containing dispersed discrete particles of a reinforcing filler comprising acrylonitrile-butadienc-styrene copoiymers or polypropylene.

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 obtained. in particular, the presence of the gas imparts a higher resilience to the playbali (i.e., it bounces higher when dropped from a fixed height) and it 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 specitied time after manufacture or for the balls to be enclosed in pressurised tins or other containers prior to use so that the pressure dillerential across the wall of the playballshell 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 difiicultles associated with the conventional pressurised playball-shcil. Such diliicultles 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 appreciatcd that the nearer are the values of pressure on either side of the wall of the shell the slower is the rate of dif- 3,432,165 Patented Mar. 11, 1969 'ice fusion of gas from inside the shell and if the pressures are equal, no diffusion will take place.

' The manufacture of playballs incorporating a substantially reduced or zero superatmospheric 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 piayball-shells. in the ease of a tennis ball, an internal pressure up to about 6 lbs. per sq. inch above atmospheric pressure is regarded as "substantially reduced" compared to the conventional pressure of 10-12 lbs. per sq. inch.

If a playball is made with a reduced or zero superatmosphcric internal pressure, the wall of the shell must contribute significantly to or impart unaided the necessary properties of resilience and resistance 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 piayball-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 thermoplastic synthetic resins having densities. within the range 0.80- 1.25 gm./cc., in dispersed form.

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-sheli comprises a self-supporting hollow sphere 1 of a vulcanized elastomeric composition, that is, a vulcanized natural and/or synthetic rubber composition in which is present a low density reinforcing filler 2 constituted by a thermoplastic synthetic resin of the self-reinforcing type, particles of which are dispersed in a matrix of the vulcanized natural and/or synthetic rubber composition. A textile covering 3 encloses the hollow sphere 1.

By a self-supporting hollow sphere there is meant a sphere which returns after deformation to a substantially spherical shape without the support of an internal bladder or other internal reinforcement. By a synthetic resin of the self-reinforcing type there is meant a synthetic resin capable of forming articles of commerce in an uncompoundcd state. The present application does not include the use of resins of the conventional reinforcing type such as the resinous copolymers of butadiene and styrene which are normally used as compounding ingredients in the preparation of rubber compositions. Resins of the selfreiniorcing type are capable of being processed on conventional plastics equipment without the addition of other ingredients. Some examples of thermoplastic synthetic resins of the self-reinforcing type useful as the filler 2 are polypropylene, and acrylonitrile/butadienc/styrcnc inter polymers.

Normally the reinforcing filler has a density of about i gram/cc, l.e., in the range O.80-l.25 grams/cc. The densities of the resins referred to above are as follows:

Polypropylene 0.9 ABS. i.0l-l.06

These materials can be dispersed in natural and/or synthetic rubber compositions, c.g., in a proportion of up to 50% particulraly 20% to 40% by weight referred to the rubber content in the rubber composition, so that they are present in the form of small discrete particles. This csn be verified by observation of thin sections of the resulting composition under a high-powered microscope. It must be emphasised that the synthetic resins used here do not form homogeneous mixtures with the rubber composition matrix and do not take part in the vulcanization process (normally carried out with sulphur as vulcanising agent under the action of heat, assuming the composition is in fact a sulphur-vulcanisabie composition).

it has been found that due attention must be paid to the temperature at which the synthetic resin is mixed into the rubber composition, if fully satisfactory playbail properties are to be obtained. Thus if the synthetic resin used is polypropylene or an acryionitriie-butadienestyrene interpolymer for instance, mixing should be perforated so that the final temperature lies within the range l60-l90 C. The size of the discrete synthetic resin particles is found to be critically dependent on final mixing temperature, and their diameter size should preferably be within the range I to 5 microns. if larger particles are present, as occurs if the final mixing temperature is below 160 C. in the case of the particular synthetic resins just mentioned, the endurance of the playball-shell is appreciably reduced. if the final mixing temperatures higher than l90 C. are used, referring still to these particular synthetic resins, it is found that the resilience of the rubber composition matrix is markedly reduced owing to thermal degradation, and the bouncing properties of the resulting playball are adversely affected.

The rubber composition is preferably a composition of 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 re quircd. in general the requirements for a rubber composition to make a tennis ball shell are a composition resiliencc (as measured on the Dunlop Tripsomcter, British Standard 903 Part A 8) above 65% particularly 75-80%, and a composition hardness (as measured in accordance with British Standard 903 Part A 7) of above 65 degrees, particularly 75-80 degrees. When the filler is A.B.S. an amount of -40 weight percent may be used to advantage.

If desired a substantially reduced super-atmospheric internal pressure may be induced inside the playball-sheli. for example, by including a nitrogen-generating combination of ingredients in the composition so as to produce a playbail-shell enclosing nitrogen at a super-atmospheric pressure of up to 6 lbs. per sq. inch.

The invention is illustrated in the following examples. in which all parts are parts by weight.

EXAMPLE I Natural 100. A.B.8. 86.

Sulphur Di honyl uenldtne DI mth yldlsulphide I AJLB. is an serylonltrfle/butsdIsne/styrene tntorpoiymer.

Playball-shells made from the mixtures given above, which were mixed so that the final temperature was 165' C. were formed by moulding the shells at a temperature of U5 C. for a period of seven minutes. They were then made into tennis balls by applying a conventional tennis ball meiton covering and were further moulded for 10 minutes at a temperature of 130 C.

The resulting tennis balls were found to bounce to a height of 54" when dropped from a eight of (international Lawn Tennis Federation Specification: 53-58). The compression characteristics when measured in the. manner specified by the International Lawn Tennis Feel eration were also found to be satisfactory.

EXAMPLE Il ilayballs having a substantially reduced super-atmos pherie internal pressure may be manufactured from the Compositions given above but the manufacturing detail differ in the following respects:

(l) 0.09 gm. sodium nitrite and 0.08 gm. ammonium chloride crystals are introduced into the playball-sheli prior to moulding. Nitrogen gas is evolved during the moulding operation which produces a super-atmospheric pressure of 5 lbs/square inch inside the piayball-shell.

(2) The playbail-shell moulding operation is performed at a temperature of 145 C. for a period of seven 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 appiications No. 467,687, filed June 28, 1965, entitled "improvements in or Relating to Playballs" and No. 467,755, tiled June 28, 1965. entitled improvements in and 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.

We claim:

1. A pressureless playball-shcll comprising a self supporting hollow sphere of a vulcanised clastomeric composition and a reinforcing filler present in an amount of about 20-40% by weight of the elastnmer in said composition, said fiiler being selected from the group consisting of acrylonitrile-butadiene-styrene interpoiymers and polypropylene, said filler having a density in the range of 0.8-1.25 grams/co, and being evenly distributed throughout said composition in the form of particles having diameters in the range of 1-5 microns.

2. A playball-sheil according to claim I, wherein the eiastomerie composition comprises natural rubber.

3. A playball-sheli according to claim 2, wherein the reinforcing filler is an aerylonitriie-butadiene-styrene interpoiymcr which is present in an amount of 30-40 percent by weight of the rubber.

4. A playball-shell according to claim 2, wherein the reinforcing filler is polypropylene.

5. A playbail-shell according to claim 1, wherein theelastomeric composition comprises polybutndlene.

6. A pressureless lawn tennis ball comprising a shell as claimed in claim I, and a textile medium covering the shell.

References Cited FORElGN PATENTS 609,566 ll/l960 Canada. 636,395 2/1962 Canada.

GEORGE l. MARLO, Primary Examiner.

U.S. Cl. X.R. 260-4, 889, 893, 894; 273-65; 264-33l, 349

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