CELLULOID-FREE, SUBSTANTIALLY SPHERICAL HOLLOW BODY AND FABRICATION THEREOF

Abstract

A substantially spherical hollow body, having a diameter of from 37 mm to 45 mm, in particular a diameter of 39.7 mm to 40.75 mm, and a weight of from 2.5 g to 3.5 g, in particular a weight of 2.6 g to 2.85 g, comprising a shell and an inner hollow space, wherein the shell has a wall thickness of 0.2 mm to 1.3 mm, in particular 0.3 mm to 0.8 mm, characterized in that the shell is free of celluloid and comprises at least one styrene-containing copolymer.

Claims

1.-20. (canceled)

21. A substantially spherical hollow body with a diameter of from 37 mm to 45 mm, in particular with a diameter of from 39.7 mm to 40.75 mm, and a weight of from 2.5 g to 3.5 g, in particular a weight of from 2.6 g to 2.85 g, comprising a shell and an internal cavity, said shell having a wall thickness of from 0.2 mm to 1.3 mm, in particular of from 0.3 mm to 0.8 mm, wherein the shell is free of celluloid and comprises at least one styrene comprising copolymer selected from the group comprising acrylonitrile-butadiene-styrene copolymer (ABS), styrene-butadiene copolymer (SBC), methyl methacrylate-butadiene-styrene copolymer (MBS) and methyl methacrylate-acrylonitrile-butadiene styrene (MABS), and at least a second organic polymer, wherein the second organic polymer is a homopolymer selected from the group comprising polycarbonate and polystyrene, or a copolymer selected from the group comprising acrylonitrile-butadiene-styrene copolymer (ABS) and styrene-butadiene copolymer (SBC).

22. The substantially spherical hollow body of claim 21, wherein the styrene comprising copolymer has a Charpy notched impact strength according to ISO 179 of from 1 kJ/m.sup.2 to 50 kJ/m.sup.2, in particular of from 2 kJ/m.sup.2 to 20 kJ/m.sup.2 measured at 23 C.

23. The substantially spherical hollow body of claim 21, wherein the styrene comprising copolymer has an elasticity modulus according to ISO 527 of from 1200 MPa to 3000 MPa, in particular of from 1500 MPa to 2500 MPa.

24. The substantially spherical hollow body of claim 21, wherein the styrene comprising copolymer has a density according to ISO 1183 of from 0.8 g/cm.sup.3 to 1.2 g/cm.sup.3, in particular of from 1 g/cm.sup.3 to 1.1 g/cm.sup.3.

25. The substantially spherical hollow body of claim 21, wherein the second organic polymer has a Charpy notched impact strength according to ISO 179 of from 1 kJ/m.sup.2 to 10 kJ/m.sup.2 and a Shore D hardness according to ISO 868 of from 65 to 80.

26. The substantially spherical hollow body of claim 21, wherein the concentration ratio of the styrene comprising copolymer to the second organic polymer is from 1:0.05 to 1:1, in particular from 1:0.25 to 1:0.75.

27. The substantially spherical hollow body of claim 21, wherein the shell comprises at least one further additive selected from the group comprising fibres, platelets, spherical particles, inorganic substances and organic substances, in particular plasticizers and/or colour pigments.

28. A process for the manufacture of a substantially spherical hollow body according to claim 21, comprising the steps of: producing two substantially identical substantially hemispherical shells by injection molding; and joining of the two half-shells along their edges to form a hollow body.

29. The manufacturing process of claim 28, wherein the joining of the two half-shells occurs by welding, in particular by ultrasonic welding, vibration welding, hot plate welding, laser welding or rotation welding, or by gluing.

30. The manufacturing process of claim 28, wherein the expansion of a material thickening formed on the inside of the hollow body during joining of the two half-shells in either direction is at the most five times, preferably at the most two and a half times, more preferably at most one and a half times the average wall thickness of the hollow body.

31. The manufacturing process of claim 28, wherein the further step of post-processing of the hollow body, in particular by cutting, grinding, blasting, lapping, polishing, tumbling with inorganic, organic and/or polymeric substances, blasting with inorganic, organic and/or polymeric substances and/or coating with at least a soluble or insoluble substance.

32. The manufacturing process of claim 31, wherein in the post-processing of the hollow body, a material thickening formed on the outside of the hollow body during joining of the two half-shells is at least partially removed.

33. A substantially spherical hollow body produced by a manufacturing process of claim 28, wherein at least one of the following properties: roundness tolerance of at the most 0.20.06 mm, surface finish of the outer surface between Ra=1.0 and Ra=5.0, difference of the barycentre radii of gyration for the three axes x, y and z of at the most 0.25 mm, difference of the outer diameters in various spatial directions of at the most 0.3 mm.

34. A use of a styrene comprising copolymer selected from the group comprising acrylonitrile-butadiene-styrene copolymer (ABS), styrene-butadiene copolymer (SBC), methyl methacrylate-butadiene-styrene copolymer (MBS) and methyl methacrylate-acrylonitrile-butadiene styrene (MABS) for the manufacture of a celluloid-free substantially spherical hollow body having a diameter of from 37 mm to 45 mm and a weight of from 2.5 g to 3.5 g, wherein the styrene comprising copolymer is in the form of a polymer blend, which further comprises at least a second organic polymer, in particular wherein the second organic polymer is a homopolymer selected from the group comprising polycarbonate and polystyrene, or a copolymer selected from the group comprising acrylonitrile-butadiene-styrene copolymer (ABS) and styrene-butadiene copolymer (SBC).

Description

[0085] Further advantages, features and possible applications of the present invention will follow from the description below in conjunction with FIG. 1.

[0086] FIG. 1 shows how two experienced players assessed the feel of a table tennis ball made of 25-35% polycarbonate and 75-65% ABS during play compared to prior art celluloid balls and celluloid-free balls.

EXAMPLES

Example 1: Manufacture and Characterization of Celluloid-Free Table Tennis Balls

[0087] Table tennis balls having a diameter of approximately 40 mm were produced by injection molding two respective hemispherical half-shells and thereafter joining the two half-shells together by welding. Different styrene-containing copolymers and polymer blends of a styrene-containing copolymer and a second organic polymer were used as the material. The table tennis balls thereby manufactured were compared to prior art celluloid and celluloid-free table tennis balls with respect to different ITTF criteria such as weight, diameter, sphericity, deviation, veer from a centerline upon straight-line rolling on an even surface, bounce and hardness.

[0088] The materials used and their mechanical properties are listed in Table 1.

TABLE-US-00001 Charpy impact Ball Modulus of strength indentation Density elasticity ISO 179 hardness Table tennis Principal component ISO 1183 ISO 527 at 23 C. ISO 2039-1 ball Polymer [g/cm.sup.3] [MPa] [kJ/m.sup.2] [MPa] 1 styrene-butadiene 1.02 1800 2 copolymer 1 2 acrylonitrile-butadiene- 1.04 2300 19 99 styrene copolymer 3 methyl methacrylate- 1.08 2000 5 70 acrylonitrile-butadiene- styrene copolymer 4 methyl methacrylate- 1.05 2100 4 60 butadiene-styrene copolymer 5 styrene-butadiene 1.01 1500 4 copolymer 2 Polymer mixtures at specific mixing ratios: 6 acrylonitrile-butadiene- 1.07 2000 40 85 styrene copolymer + polycarbonate 7 styrene-butadiene copolymer 1 + 30% polystyrene 8 styrene-butadiene copolymer 1 + 50% polystyrene 9 styrene-butadiene copolymer 2 + 30% polystyrene 10 styrene-butadiene copolymer 2 + 50% polystyrene

[0089] Table 2 summarizes the properties profile of the resulting manufactured table tennis balls compared to prior art table tennis balls.

TABLE-US-00002 Bounce Hardness Table tennis Deviation [mm] [mm] ball Material (veer) [mm] min. max. Seam line 45 Pole Std. ITTF 175 240 260 0.72-0.83 0.68-0.81 0.08 specifications Prior art Manufacturer 1 celluloid 175 > veer > 225 250 60 Manufacturer 2 celluloid Fail 230 255 0.74 0.8 0.69 0.05 Manufacturer 3 celluloid 175 > veer > 230 250 60 Manufacturer 4 celluloid 175 < veer > 235 250 60 1 (see Table 1) SBC 1 175 > veer > 240 250 0.96 0.95 0.93 0.03 60 2 ABS 175 < veer > 265 265 0.7325 0.7 0.8 0.097 60 3 MABS 175 > veer > 240 245 0.5 0.52 0.56 60 4 MBS 175 > veer > 240 250 0.73 0.78 0.68 60 5 SBC 2 175 > veer > 230 240 1.01 1.35 1.25 60 6 ABS + Veer < 60 240 255 0.72 0.76 0.71 PC 7 SBC 1 + 175 > veer > 245 255 0.74 0.82 0.73 30% PS 60 8 SBC 1 + 175 > veer > 250 255 0.68 0.76 0.68 50% PS 60 9 SBC 2 + 175 > veer > 230 245 0.75 0.99 0.78 30% PS 60 10 SBC 2 + 175 > veer > 245 250 0.8 0.86 0.77 50% PS 60

[0090] Playing Feel

[0091] The playing feel of the table tennis ball from Example 1 (25-35% PC+75-65% ABS) was compared by two impartial experienced table tennis players to that of the Nittaku celluloid ball, one of the best celluloid balls currently on the market.

[0092] The results are shown in FIG. 1. The two squares/crosses/circles on each line represent the assessments of the two players.

[0093] The zero point of the scale indicates the celluloid ball test results in the different categories. The table tennis ball of 25-35% PC+75-65% ABS conveys a comparable feel during play to that of the celluloid ball. This particularly applies to the playing feel upon dynamic and slow strokes as well as the player's sensation of racket/ball transfer, reverse spin rotation transfer, subjective ball hardness and evenness of bounce. The spin of the celluloid-free ball was rated much worse than that of the celluloid ball. All in all, however, the players indicated that the table tennis ball of 25-35% PC+75-65% ABS can be played unproblematically and that it is substantially comparable to the ITTF-approved balls.