US3428314A - Game ball - Google Patents

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US3428314A
US3428314A US467687A US3428314DA US3428314A US 3428314 A US3428314 A US 3428314A US 467687 A US467687 A US 467687A US 3428314D A US3428314D A US 3428314DA US 3428314 A US3428314 A US 3428314A
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Prior art keywords
playball
composition
shell
rubber
playballs
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US467687A
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Robert C Haines
Royce Pridgeon
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Dunlop Co Ltd
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Dunlop Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
    • B29D22/00—Producing hollow articles
    • B29D22/04—Spherical articles, e.g. balls
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2007/00—Use of natural rubber as moulding material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2009/00—Use of rubber derived from conjugated dienes, as moulding material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2055/00—Use of specific polymers obtained by polymerisation reactions only involving carbon-to-carbon unsaturated bonds, not provided for in a single one of main groups B29K2023/00 - B29K2049/00, e.g. having a vinyl group, as moulding material
    • B29K2055/02—ABS polymers, i.e. acrylonitrile-butadiene-styrene polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2061/00—Use of condensation polymers of aldehydes or ketones or derivatives thereof, as moulding material
    • B29K2061/04—Phenoplasts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2423/00—Use of polyalkenes or derivatives thereof as filler
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2711/00—Use of natural products or their composites, not provided for in groups B29K2601/00 - B29K2709/00, for preformed parts, e.g. for inserts
    • B29K2711/14—Wood, e.g. woodboard or fibreboard
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S524/00—Synthetic resins or natural rubbers -- part of the class 520 series
    • Y10S524/925—Natural rubber compositions having nonreactive materials, i.e. NRM, other than: carbon, silicon dioxide, glass titanium dioxide, water, hydrocarbon or halohydrocarbon

Definitions

  • a pressureless ball e.g. a tennis ball comprising a hollow sphere of a vulcanized elastomeric composition containing dispersed discrete particles of wood flour 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.
  • 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 -l2 lbs. per square inch above atmospheric pressure immediately after manufacture.
  • the presence of the gas at this super-atmospheric pressure modifies the properties of the playball so that desirable playing properties are obtained.
  • the presence of the gas imparts a higher resilience to the playball (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.
  • a tennis ball which may be regarded as a particular type of a 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.
  • playballs could be manufactured without the difficulties associated with the conventional pressurised 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 more nearly equal the values of pressure on either side of the wall of the shell the slower is the 'ice rate of diffusion of gas from inside the shell and if the pressures are equal, no diffusion will take place.
  • 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.
  • an internal pressure of up to about 6 lbs. per square inch above atmospheric pressure is regarded as substantially reduced compared to the conventional pressure of 1012 lbs. per square inch.
  • a playball is made with reduced or zero superatmospheric internal pressure
  • the wall of the hell must contribute significantly to or impart unaided the necessary properties of resilience and resistance to deforma tion.
  • 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.
  • a playball-shell comprises a self-supporting hollow sphere 1 of a rubber or rub ber-like composition, preferably a vulcanized elastomeric composition in which is dispersed a low-density reinforcing filler 2 comprising a finely divided cellulosic material.
  • 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.
  • the reinforcing filler 2 has a density of about 1 gram/cc, i.e. in the range 0.801.25 grams/co, the density being determined by measuring the variation in density of a rubber or rubber-like composition to which the reinforcing filler is added.
  • a textile covering 3 encloses the hollow sphere 1.
  • the cellulosic material may be in natural, chemicallytreated or regenerated form, the preferred forms being the natural and chemically-treated forms of commin-uted wood such as wood flour and chemically-treated wood flour (eg as sold under the name Solka Floc by Johnsen, Jorgensen & Wettre Ltd.)
  • the weight of the low density reinforcing filler may be up to 50 percent of the weight of the rubbery polymer, the preferred range being 20 to 40 percent.
  • wood flour is used as the filler, it should have a particle size not greater than 50 mesh.
  • particle size is below mesh, of the order of mesh.
  • 180 mesh indicates that the particle size is such that substantially all of the particles will pass through a mesh screen having 180 divisions to the inch.
  • the rubber or rubber-like composition may be any composition suitable to produce the properties required of a playballshell. It is preferred to use a vulcanized composition based on natural rubber 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.
  • a composition resilience as measured on the Dunlop Tripsometer, British Standard 903 Part A8
  • a composition hardness as measured in accordance with British Standard 903 Part A7 of above 65 degrees, particularly 75-80 degrees.
  • 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.
  • 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.
  • the wood flour used was made from Baltic spruce and had a density of 0.83 grams/cc.
  • the final composition had a density of 1.06 grams/ cc.
  • Half-shells were made from the composition given above and spherical playball-shells were formed by moulding the shells at a temperature of 160 C. for a period of seven minutes which vulcanized the composition. They were then made into tennis balls by applying conventional tennis ball melton 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 inches when dropped from a height of 100 inches (International Lawn Tennis Federation Specifications: 53-58 inches).
  • the composition characteristics when measured in a manner specified by 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.
  • Playballs having a substantially reduced super-atmos- I pheric internal pressure may be manufactured from the compositions given above, but as compared to Example I, the manufacturing details differ in the following re.- spects:
  • Tennis balls were made from these playball-shells by applying tennis ball melton as before and moulding for a further 10 minutes at C.
  • compositions described in any of the three applications may be blended together and satisfactory playballs and tennis balls with substantially reduced or zero superatmospheric internal pressure produced, given due attention to compounding and moulding conditions.
  • a satisfactory tennis ball has been produced from a composition including both wood fiour and Cellobond H. 831 which is a modified phenolic resin described in our application No. 467,755.
  • a pressureless playball-shell comprising a self-supporting hollow sphere of a vulcanized elastomeric composition and as a reinforcing filler about 20-40% by weight based on the weight of the elastomer in said composition of particles of a wood flour having a density in the range 08-125 grams/cc., a particle size not more than 50 mesh, and being evenly distributed throughout said composition.
  • a pressureless lawn tennis ball comprising a shell according to claim 1, and a textile medium covering said shell.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Compositions Of Macromolecular Compounds (AREA)
  • Dental Preparations (AREA)

Description

Feb. 18, 1969 R. 0. HAINES L 3,428,314
GAME BALL Filed June 28, 1965 VULCANIZED ELASTOMERIC COMPOSITION TEXTILE COVERING PARTICLES OF WOOD FLOUR HAVING A SIZE NOT MORE THAN 50 MESH AND A DENSITY OF 08 I-ZSq/cc.
United States Patent 28,326/ 64 U.S. Cl. 273-61 Int. Cl. A63b 39/00 4 Claims ABSTRACT OF THE DISCLOSURE A pressureless ball e.g. a tennis ball comprising a hollow sphere of a vulcanized elastomeric composition containing dispersed discrete particles of wood flour 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 -l2 lbs. per square inch above atmospheric pressure immediately after manufacture. The presence of the gas at this super-atmospheric 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 playball (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 a 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 pressurised 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 difficulties associated with the conventional pressurised 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 more nearly equal the values of pressure on either side of the wall of the shell the slower is the 'ice 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 substantially 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 of up to about 6 lbs. per square inch above atmospheric pressure is regarded as substantially reduced compared to the conventional pressure of 1012 lbs. per square inch.
If a playball is made with reduced or zero superatmospheric internal pressure, the wall of the hell must contribute significantly to or impart unaided the necessary properties of resilience and resistance to deforma tion. 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 certain reinforcing fillers having densities within the range 0.80-1.25 grams/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 rubber or rub ber-like composition, preferably a vulcanized elastomeric composition in which is dispersed a low-density reinforcing filler 2 comprising a finely divided cellulosic material. 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. Normally the reinforcing filler 2 has a density of about 1 gram/cc, i.e. in the range 0.801.25 grams/co, the density being determined by measuring the variation in density of a rubber or rubber-like composition to which the reinforcing filler is added. A textile covering 3 encloses the hollow sphere 1.
The cellulosic material may be in natural, chemicallytreated or regenerated form, the preferred forms being the natural and chemically-treated forms of commin-uted wood such as wood flour and chemically-treated wood flour (eg as sold under the name Solka Floc by Johnsen, Jorgensen & Wettre Ltd.)
Other examples of natural cellulosic materials which can be considered are finely-divided cork and wheat flour. An example of a regenerated cellulosic material is finely divided short fibres of rayon. The weight of the low density reinforcing filler may be up to 50 percent of the weight of the rubbery polymer, the preferred range being 20 to 40 percent.
If wood flour is used as the filler, it should have a particle size not greater than 50 mesh. Preferably the particle size is below mesh, of the order of mesh. The term 180 mesh indicates that the particle size is such that substantially all of the particles will pass through a mesh screen having 180 divisions to the inch.
The rubber or rubber-like composition may be any composition suitable to produce the properties required of a playballshell. It is preferred to use a vulcanized composition based on natural rubber 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 100.0 Wood flour (180 mesh) 26.0 Zinc oxide 3.0 Stearic acid 1.0 Sulphur 5.0 High abrasion furnace black 10.0 Diphenyl guanidine 2.0 Dibenzthiazyl disulphide 1.0 Benzoic acid 0.7 Antioxidant (Nonox WSL) 1.0
The wood flour used was made from Baltic spruce and had a density of 0.83 grams/cc. The final composition had a density of 1.06 grams/ cc.
Half-shells were made from the composition given above and spherical playball-shells were formed by moulding the shells at a temperature of 160 C. for a period of seven minutes which vulcanized the composition. They were then made into tennis balls by applying conventional tennis ball melton 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 inches when dropped from a height of 100 inches (International Lawn Tennis Federation Specifications: 53-58 inches). The composition characteristics when measured in a manner specified by 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 100.00
Solka Floc 30.00 Zinc oxide 3.00 Stearic acid 1.00
Sulphur 2.75 High abrasion furnace black 10.00 Diphenyl guanidine 1.40 Dibenzthiazyl disulphide 0.70 Benzoic acid 0.70 Antioxidant (Nonox WSL) 1.00
EXAMPLE III Playballs having a substantially reduced super-atmos- I pheric internal pressure may be manufactured from the compositions given above, but as compared to Example I, the manufacturing details differ in the following re.- spects:
(1) 0.09 gm. sodium nitrite and 0.08 gm. ammonium chloride crystals are introduced to the playball-shell prior to moulding. Nitrogen gas is evolved during the moulding operation which produces a super-atmospheric pressure of 5 lbs/square inch inside the playball-shell.
(2) The playball shell moulding operation is performed at 150 C. and 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 applications No. 467,704, filed June 28, 1965, entitled Improvements Relating to Playballs and No. 467,755, filed June 28, 1965, entitled Improvements in and Relating to Playballs and No. 28327/64 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 and satisfactory playballs and tennis balls with substantially reduced or zero superatmospheric internal pressure produced, given due attention to compounding and moulding conditions. For example a satisfactory tennis ball has been produced from a composition including both wood fiour and Cellobond H. 831 which is a modified phenolic resin described in our application No. 467,755.
Having now described our invention, what we claim is:
1. A pressureless playball-shell comprising a self-supporting hollow sphere of a vulcanized elastomeric composition and as a reinforcing filler about 20-40% by weight based on the weight of the elastomer in said composition of particles of a wood flour having a density in the range 08-125 grams/cc., a particle size not more than 50 mesh, and being evenly distributed throughout said composition.
2. A playball-shell according to claim 1, wherein the elastomeric composition comprises polybutadiene.
3. A playball-shell according to claim 1, wherein the elastomeric composition comprises natural rubber.
4. A pressureless lawn tennis ball comprising a shell according to claim 1, and a textile medium covering said shell.
References Cited UNITED STATES PATENTS 7/1959 Dunker 273-61 3/ 1966 Crompton 273218 GEORGE I. MARLO, Primary Examiner.
US467687A 1964-07-09 1965-06-28 Game ball Expired - Lifetime US3428314A (en)

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GB28326/64A GB1108556A (en) 1964-07-09 1964-07-09 Improvements in or relating to playballs

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US3428314A true US3428314A (en) 1969-02-18

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US (1) US3428314A (en)
DE (1) DE1478022B2 (en)
GB (1) GB1108556A (en)
MY (1) MY7000040A (en)
SE (1) SE326552B (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4065126A (en) * 1975-06-30 1977-12-27 David Mantz Practice tennis ball and apparatus
US4765853A (en) * 1987-10-07 1988-08-23 Hoffman Allan C Method of making a pressurized ball
US4853056A (en) * 1988-01-20 1989-08-01 Hoffman Allan C Method of making tennis ball with a single core and cover bonding cure
US5558325A (en) * 1993-08-05 1996-09-24 Gencorp Inc. Play balls or pressureless tennis balls
GB2390816B (en) * 2002-07-02 2006-07-19 Derek Price Lightweight 75mm ball

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT511909B1 (en) * 2011-08-16 2013-06-15 Chemiefaser Lenzing Ag USE OF CELLULOSE FIBERS WITH IMPROVED DOSAGE CAPACITY FOR REINFORCING COMPOSITE MATERIALS AND MOLDED BODIES MADE THEREFROM

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2896949A (en) * 1950-08-22 1959-07-28 Dunker Henry Christian Louis Tennis balls
US3239228A (en) * 1962-06-21 1966-03-08 Lord Corp Golf ball

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2896949A (en) * 1950-08-22 1959-07-28 Dunker Henry Christian Louis Tennis balls
US3239228A (en) * 1962-06-21 1966-03-08 Lord Corp Golf ball

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4065126A (en) * 1975-06-30 1977-12-27 David Mantz Practice tennis ball and apparatus
US4765853A (en) * 1987-10-07 1988-08-23 Hoffman Allan C Method of making a pressurized ball
US4853056A (en) * 1988-01-20 1989-08-01 Hoffman Allan C Method of making tennis ball with a single core and cover bonding cure
US5558325A (en) * 1993-08-05 1996-09-24 Gencorp Inc. Play balls or pressureless tennis balls
AU674417B2 (en) * 1993-08-05 1996-12-19 Penn Racquet Sports, Inc. Play balls or pressureless tennis balls
GB2390816B (en) * 2002-07-02 2006-07-19 Derek Price Lightweight 75mm ball

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MY7000040A (en) 1970-12-31
SE326552B (en) 1970-07-27
DE1478022B2 (en) 1976-02-12
GB1108556A (en) 1968-04-03
DE1478022A1 (en) 1970-07-23

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