GB2200849A

GB2200849A - Tennis balls

Info

Publication number: GB2200849A
Application number: GB08703264A
Authority: GB
Inventors: Robert Christopher Haines
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1987-02-12
Filing date: 1987-02-12
Publication date: 1988-08-17
Also published as: DE3804104A1; ZA88331B; FR2610833A1; GB8703264D0

Description

25200849 TENNIS BALLS W V This invention relates to tennis balls.

Conventional tennis balls consist of a hollow spherical core of a compounded thermosetting rubber covered by means of a melton cloth. In some tennis balls, the internal pressure of the hollow core is at atmospheric pressure and in others the core is inflated to about 0.84 Kg/CM2 above atmospheric pressure by means of an inert gas.

All tennis balls are required to conform to the following specification laid down by the International Tennis

Federation (I.T.F.):

Ball diameter 6.35 to 6.67 cm Weight 56.7 to 58. g Rebound to 147 cm (The, ball is dropped from a height of 254 cm on to a concrete base).

Forward compression 0.56 to 0.74 cm Return Compression 0.89 to 1.08 cm (Forward and Return Compression are measured using a load of 8.165 Kg).

Hereinafter, the terms "rebound", "forward compression" and "return compression" will be used to denote the equivalent terms of the International Tennis Federation's Specification referred to in the immediately-preceding paragraph.

We have now"found that a tennis ball which meets the I.T.F. specification can be made from a thermoplastics material so that the considerable technical and economic advantages of plastics moulding and fabrication can be employed. Such a ball has been found not to require a cover and in order tb achieve the customary aerodynamic properties of a tennis ball, the surface of the ball may be provided with symmetricallyplaced discontinuities as a part of the plastics moulding and/or fabrication process.

2.

Accordingly, the present invention provides a tennis ball consisting of a coverless hollow spherical member of a thermoplastics imaterial and having a rebound (as hereinbefore defined) in the range 135 to 147 cm, a forward compression (as hereinbefore defined) in the range 0.56 to 0.74 cm, a ret urn compression (as hereinbefore defined) in the range 0.89 to 1.08 cm, a weight in the range 56.7 to 58.5 g, and an outer diameter in the range 6.35 to 6.67 cm.

is The thermoplastics material can suitably be formed from a mixture comprising a polyether ester elastomer and a plasticiser preferably in the ratio 2: 1 to 5: 1 by weight. -The exact ratio used will depend upon the hardness of the particular elastomer chosen.

The polyether ester elastomer may be derived from a mixture 6om-prising a phthalate ester, a low-molecular-weight glycol and a poly (alkylene ether) glycol.

Suitable polyether ester elastomers include the fhermoplastics materials available from E.I. du Pont de Nemours & Company under the Registered Trade Mark HYTREL.

The plasticiser may be an alkyl substituted aryl phosphate, for example 2-ethylhexyl diphenyl phosphate, available from Monsanto Limited as SANTICISER 141. (SANTICISER is a Registered Trade Mark).

Alternatively, the plasticiser may be a glycol ester, for example dipropylene glycol dibenzoate, available from Versicol Corporation as BENZOFLEX 9-88. (BENZOFLEX is a Registered Trade Mark).

The outer surface of the spherical hollow member may be provided with discontinuities, for example a symmetrical pattern of holes or a symmetrical pattern of dimples. Alternatively, the discontinuities may comprise a textured pattern which can readily be produced during moulding of the spherical hollow member.

i 11 f 3.

If a symmetrical pattern of holes is to be provided on the surface of the ball, the.thickness of the spherical hollow member is increased in order that the finished ball will meet the I.T.F. specificationIn respect of weight, forward compression and return compression.

Tennis balls according to the present invention may most conveniently be made by welding (as opposed to adhering) -two "half-shells" together.Such welding would not-be possible in the case_of conventional tennis ball cores (which are made of a thermosetting material).

Finally, we have found that the tennis balls according to the pr6int invention meet the I.T.F. specification without the need to inflate the spherical hollow member to above atmospheric pressure.

Also, the use of thermoplastics materials facilitates the production of timis balls which can have excellent bright colours (Z.T.F. speci ies; white or yellow) whereas conventional tennis ball cores have hitherto always required a separate cover layer in the appropriate colour.

The present invention will be illustrated by way of the following example.:

A polyether ester elastomer (HYTREL 4056; 100 parts by weight) and a plasticiser (SANTICISER 141; 25 parts by weight) were mixed together in a high-speed vane mixer. The resulting compound was extruded through a strand-die and -passed through a cooling bath to a granulator to produce injection-moulding pellets.

Two half-shells Y&e separately mouldd by an injection- '-moulding process and subsequently joine( together by hot-plate moulding to produce a hollow ball.

4.

In this example, the external radius of the half-shell mould was 34.6 mm and the internal radius was 30.9 mm, to allow for shrinkage of the pla, tics material after moulding.

1,11 The ball was found,to have the properties shown in the TABLE below:TABLE

Property I.T.F. Example Weight 56.7 to 58.5 g 57.1 g Rebound 135 to 147 cm 142.2 cm Forward Compression 0.56 to 0.74 cm 0.660 cm Return Compression 0.89 to 1.08 cm 1.003 cm Outer Diameter 6.35 to 6.67 cm 6.60 cm An alternative tennis ball according to the foregoing example was provided with 60 holes, each hole having a diameter of 4 mm and the holes being distributed symmetrically over the spherica 1 surface of the ball. It was found that this ball would meet the I.T.F. requirements if the wall thickness were increased by 0.2 mm to -compensate for the loss in weight caused by removal of material to make the holes.

.1 -ISC RACK - 10442 =/CBF t; 1 hi 5..

Claims

CLAIMS:

1. A tennis ball consisting of a coverless hollow spherical member of a thermoplastics material and having a rebound (as hereinbefore defined) in the range 135 to 147 cm, a forward compression (as hereinbefore defined) in the range 0.56 to 0.74 cm, a return compression (as hereinbefore defined) in the range 0.89 to 1.08 cm, a weight in the range 56.7 to 58.5 g and an outer diameter in the range 6.35 to 6.67 cm.

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2. A tennis ball according to Claim 1. in which the thermoplastics material is formed from a mixture comprising a polyether ester elastomer and a plasticiser.

3. A tennis ball according to Claim 2, in which the ratio is of the polyether ester elastomer and the plasticiser in the mixture-is from 2: 1 to 5': 1 by weight.

4. A tennis ball according to Claim 2 or 3, in which the polyether ester elastomer is derived from a mixture comprising a phthalatd ester, a low-molecular-weight glycol and a poly (alkylene ether) glycol.

5. A tennis ball according to any one of Claims 2 to 4, in which the plasticiser consists essentially of an alkyl substituted aryl phosphate.

6. A tennis ball according to Claim 5, in which the plasticiser is 2ethyl hexyl diphenyl phosphate.

7. A tennis ball according to any one of Claims 2 to 4, in which the plasticiser consists essentially of a glycol ester.

8. A tennis ball according to Claim 7, in which the plasticiser is dipropylene glycol dibenzoate.

9. A tennis ball according to any one of the preceding claims, in which the outer surface of the spherical hollow member is discontinuous.

1 1 6.

10. A tennis ball according to Claim 9, in which the outer surface of the spherical hollow member is provided with a symmetrical pattern of dimples.

11. A tennis ball according to Claim 9, in which the outer surface of the spherical hollow member is provided with a symmetrical pattern of holes.

12. A tennis ball accordinq-to Claim 9, in which the outer surface of the spherical hollow member is provided with a symmetrical moulded pattern.

13. A tennis ball, substantially as hereinbefore described with reference to the Example.

WK/CW - ISC RACK 10442 Published 1988 at The ?Went 021ce. Staw House, 55 71 High Holbori, Lozdon WCIR 4TF. Further eopies may be obtamed from The Patent Mce. Sales Branch. St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multaplex techniques HAL St Mary Cray. Kent Con. 1/87.

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