Rubber composition for tennis ball
A rubber composition for a tennis ball includes a base rubber and a high-flatness filler. The high-flatness filler has an average particle diameter D 50 of not less than 1 μm and not greater than 50 μm. A degree of flatness DL is not less than 40 and not greater than 200. An amount of the high-flatness filler per 100 parts by weight of the base rubber is not less than 5 parts by weight and not greater than 100 parts by weight. A ratio (E2/E1) of a tensile elastic modulus E2 in a tensile strain range from 70% to 100% to a tensile elastic modulus E1 in a tensile strain range from 10% to 30%, of a vulcanized rubber obtained by vulcanizing the rubber composition, is not less than 0.60 and less than 1.00. The tennis ball includes a hollow core formed from the rubber composition.
1. A rubber composition for a tennis ball, the rubber composition including a base rubber and a high-flatness filler, wherein
the high-flatness filler has an average particle diameter D 50 of not less than 1 μm and not greater than 50 μm,
a degree of flatness DL obtained by dividing the average particle diameter D 50 by an average thickness T of the high-flatness filler is not less than 40 and not greater than 200,
an amount of the high-flatness filler per 100 parts by weight of the base rubber is not less than 5 parts by weight and not greater than 100 parts by weight, and
when a tensile elastic modulus, of a vulcanized rubber obtained by vulcanizing the rubber composition with sulfur, in a tensile strain range from 10% to 30% that is measured at a temperature of 23±1° C. according to JIS K6251, is denoted by E1, and a tensile elastic modulus of the vulcanized rubber in a tensile strain range from 70% to 100% that is measured at a temperature of 23±1° C. according to JIS K6251, is denoted by E2, a ratio (E2/E1) is not less than 0.60 and less than 1.00.
2. The rubber composition according to claim 1 , further including a filler that does not correspond to the high-flatness filler, wherein
a total amount of the high-flatness filler and the filler that does not correspond to the high-flatness filler, per 100 parts by weight of the base rubber, is not less than 20 parts by weight and not greater than 150 parts by weight.
3. The rubber composition according to claim 2 , wherein the filler that does not correspond to the high-flatness filler has an average particle diameter D 50 of not less than 0.01 μm and not greater than 50 μm.
4. The rubber composition according to claim 2 , wherein a proportion of the high- flatness filler to the total amount of the high-flatness filler and the filler that does not correspond to the high-flatness filler is not less than 30% by weight.
5. The rubber composition according to claim 2 , wherein the filler that does not correspond to the high-flatness filler is selected from the group consisting of silica, carbon black, calcium carbonate, clay, talc, magnesium carbonate, mica, magnesium hydroxide, diatomaceous earth, titanium oxide, zinc oxide, and bismuth oxide.
6. The rubber composition according to claim 1 , wherein the high-flatness filler is selected from the group consisting of talc, graphites, and graphenes.
7. The rubber composition according to claim 1 , wherein the base rubber includes a butadiene rubber and a natural rubber, and a weight ratio B/N of an amount B of the butadiene rubber to an amount N of the natural rubber in the base rubber is not greater than 1.4.
8. The rubber composition according to claim 1 , wherein the rubber composition has a nitrogen gas permeability coefficient G at 40° C. of not greater than 1.5×10 −9 (cm 3 ·cm/cm 2 /sec/cmHg).
9. The rubber composition according to claim 1 , wherein the rubber composition has a sulfur content of not less than 0.01% by weight and not greater than 10% by weight.
10. The rubber composition according to claim 1 , wherein the rubber composition has a Shore A hardness Ha of not less than 20 and not greater than 88.
11. The rubber composition according to claim 1 , wherein a product EB×Ha of the hardness Ha and elongation at break EB (%) of the rubber composition obtained according to JIS K6251 is not less than 1,000 and not greater than 100,000.
12. A tennis ball comprising a core formed from the rubber composition according to claim 1 .