JPH0263020B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improvement of a pressureless tennis ball, and an object of the present invention is to provide a pressureless tennis ball that has excellent physical properties comparable to internal pressure tennis balls. Hardball tennis balls include internal pressure tennis balls, which are made of rubber or rubber-like elastic material and have an internal pressure of about twice the atmospheric pressure, and are covered with a cover made of fabric or felt, and tennis balls with no internal pressure.
There is a so-called pressureless tennis ball that has a pressureless core ball covered with a cover made of fabric or felt. By the way, methods for applying internal pressure to internal pressure tennis balls include filling the hollow core ball with gas at a pressure higher than atmospheric pressure, or using a foaming agent that decomposes by heat or chemical reaction to generate gas during molding of the core ball. There is a method of enclosing a foaming agent and applying internal pressure using the gas generated by causing a decomposition reaction in the enclosed foaming agent, but it is not easy to apply an appropriate internal pressure, and it is difficult to manufacture a core ball with the desired internal pressure. The problem is that it is difficult. On the other hand, pressureless tennis balls have no internal pressure, so
In order to have the same physical properties as an internal pressure tennis ball,
The wall pressure of the core ball must be increased, resulting in an increase in weight and exceeding the weight limit set by the certification body. It is difficult to obtain a compressed tennis ball. Another disadvantage is that the feel at impact is worse than that of an internal pressure tennis ball. In view of such circumstances, the present inventors have conducted various studies and found that α, having 3 to 8 carbon atoms,
At least 10% of the carboxylic acid groups of β-monoethylenically unsaturated carboxylic acid are neutralized with metal ions having a valence of 1 to 3, and natural rubber, cis-1,4-polybutadiene is treated with peroxide. It was discovered that when co-crosslinked with rubber such as, a pressureless tennis ball having excellent physical properties equivalent to that of an internal pressure tennis ball can be obtained without increasing the thickness of the core ball, which led to the completion of the present invention. . That is, by co-crosslinking the α,β-monoethylenically unsaturated carboxylic acid with a rubber such as natural rubber or cis-1,4-bolybutadiene,
The resultant ball has improved rebanding and deformation properties, resulting in an unpressurized tennis ball that meets international standards for rebanding and deformation within the weight limit set by international standards without increasing the thickness of the core ball. It became possible to obtain it. In the present invention, the composition for obtaining the core ball includes a rubber such as natural rubber, cis-1,4-polybutadiene, the above α,β-monoethylenically unsaturated carboxylic acid, and a carboxylic acid group of the unsaturated carboxylic acid. metal ions having a valence of 1 to 3, and a peroxide as a crosslinking agent, in an amount sufficient to neutralize at least 10% of the In the above composition, the composition ratio of each component is, for example, 10 parts of α,β-monoethylenically unsaturated carboxyl to 100 parts (by weight, the same applies hereinafter) of rubber.
~30 parts, peroxide 0.5 to 3 parts, and metal ions in an amount sufficient to neutralize at least 10% of the carboxylic acid groups of the α,β-monoethylenically unsaturated carboxylic acid. preferable. As the rubber, natural rubber and cis-1,4-polybutadiene can be used alone or in combination. When using both together, natural rubber 20 to 60
80 to 40 parts of cis-1,4-polybutadiene. Examples of the α,β-monoethylenically unsaturated carboxylic acid having 3 to 8 carbon atoms include methacrylic acid, acrylic acid, itaconic acid, crotonic acid, and sorbic acid, but methacrylic acid is particularly preferred. preferable. The amount of α,β-monoethylenically unsaturated carboxylic acid to be used is determined from the rubber
A range of 10 to 30 parts per 100 parts is preferred. This is because if the amount of α,β-monoethylenically unsaturated carboxylic acid used is less than the above range, the rebanding of the resulting core ball cannot be sufficiently increased, and the α,β-monoethylenically unsaturated carboxylic acid This is because if the amount of acid used exceeds the above range, the hardness of the resulting core ball will become too high, exceeding the specifications. Examples of metal ions having a valence of 1 to 3 used to neutralize the α,β-monoethylenically unsaturated carboxylic acid include zinc ions, sodium ions, calcium ions, magnesium ions, etc. Zinc ions are particularly preferred, and when actually blended, the zinc ions are blended in the form of zinc oxide. α、β
- Neutralizing a monoethylenically unsaturated carboxylic acid with a metal ion having a valence of 1 to 3 as described above is a method of co-crosslinking the unsaturated carboxylic acid with rubber as a metal salt and improving the performance of the ball. This is to improve the results. The amount of these metal ions used is sufficient to neutralize at least 10% of the α,β-monoethylenically unsaturated carboxylic acid. This is because if it is less than 10%, the aforementioned performance improvement effect cannot be fully exhibited. The degree of neutralization is preferably as high as 10% or more, particularly 100%. Note that the α,β-monoethylenically unsaturated carboxylic acid and the metal ion may be combined in the form of a neutralized salt. Examples of peroxides for co-crosslinking the α,β-monoethylenically unsaturated carboxylic acid with rubber include dicumyl peroxide, benzoyl peroxide, tert-butyl perbenzoate, 2,2-di(tert-butyl Examples include peroxy)butane, 2,2'-azobisisobutyronitrile, and dicumyl peroxide is particularly preferred. . As mentioned above, the amount of peroxide used is 100% of rubber.
The range of 0.5 to 3 parts per part is preferred. Preparation of the composition, production of a core ball from the composition, production of a pressureless tennis ball using the obtained core ball, etc. can be carried out by commonly employed means. For example, the composition is prepared by uniformly kneading the constituent components using an appropriate kneading means such as a roll or a Banbury mixer, and the core ball is produced by first compressing the composition in a half-shell mold. This is carried out by molding to produce a hemispherical shell, stacking two of the obtained hemispherical shells to form a hollow sphere, placing them in a core ball mold, and compression molding. A pressureless tennis ball is manufactured by covering the obtained core ball with a cover made of woven fabric or felt such as Melton, and pressing the ball with a mold. Note that as a method similar to the present invention, a method has been proposed in which a copolymer of ethylene and an unsaturated carboxylic acid having 3 to 8 carbon atoms is blended with natural rubber and cis-1,4-polybutadiene. In this case, the above-mentioned copolymer of ethylene and unsaturated carboxylic acid is simply mixed with rubber, and α,β-monoethylenically unsaturated carboxylic acid is not co-crosslinked with rubber as in the present invention. In this respect, the proposed method differs in configuration from the present invention, and also has different effects as will be described later. Next, the present invention will be explained with reference to Examples. Examples 1 to 3 The tissues shown in Table 1 were prepared, core balls were created from the compositions, and pressureless tennis balls were manufactured using the obtained core balls. The numbers in the table indicate the number of parts mixed.

[Table] The composition was prepared by kneading the components other than dicumyl peroxide using a Banbury mixer, and adding dicumyl peroxide to the above-mentioned kneaded product on a roll. The composition prepared as described above was formed into a sheet, extruded into a rod shape using an extruder, cut to fit a half-shell mold, and then placed in a half-shell mold and compression-molded. A hemispherical shell was produced, and two of the obtained hemispherical shells were stacked so as to form a hollow sphere, placed in a core ball mold, and compression molded to produce a core ball. The core ball was then covered with a melton cover and compression molded in a mold at 150° C. for 20 minutes to produce a pressureless tennis ball. Table 3 shows the results of measuring the physical properties of the obtained pressureless tennis ball. In addition, the wall thickness of the core ball in Examples 1 to 3 was 4.1.
It was warm in mm. Comparative Examples 1-2 Compositions shown in Table 2 were prepared, core balls were produced from the compositions, and pressureless tennis balls were produced using the obtained core balls.

[Table] The composition was prepared by kneading the other components except for sulfur using a Banbury mixer, and adding sulfur to the above-mentioned kneaded product on a roll. The production of the core ball and the production of the pressureless tennis ball were carried out in the same manner as in Example 1. Table 3 shows the results of measuring the physical properties of the obtained pressureless tennis ball. The wall thickness of the core balls in Comparative Examples 1 and 2 is the same as in Examples 1 and 3.
It was 4.1mm.

[Table] As shown in Table 3, the non-pressure tennis ball of the present invention has a larger reband than the ball of Comparative Example 1, which is a conventional non-pressure tennis ball, and the amount of deformation is almost the same as that of the internal pressure tennis ball. The amount of deformation was moderate. Furthermore, the tennis ball of the present invention contains ethylene and 3
Even compared to the ball of Comparative Example 2, which contained a copolymer with an unsaturated carboxylic acid having ~8 carbon atoms, the rebanding was higher and the amount of deformation was also moderate. The reason why the physical properties of the ball of Comparative Example 2 are worse than those of the present invention is considered to be that the physical properties are deteriorated because the copolymer is simply mixed and no co-crosslinking is performed. Furthermore, all of the tennis balls of the present invention have good shot feel, especially in Example 1.
The ball had an excellent shot feel, almost equivalent to that of an internal pressure tennis ball. The feel at impact of the balls of Examples 2 and 3 was also much better than that of conventional non-pressure tennis balls, and was close to that of internal pressure tennis balls.

Claims (1)

[Scope of Claims] 1 Rubber, α,β- having 3 to 8 carbon atoms
a monoethylenically unsaturated carboxylic acid, 1 in an amount sufficient to neutralize at least 10% of the unsaturated carboxylic acid;
A pressureless tennis ball comprising a core ball obtained from a composition comprising a metal ion having a valence of ~3 and a peroxide, and a cover covering the core ball. 2 α,β-monoethylenically unsaturated carboxylic acid having 3 to 8 carbon atoms in an amount of 10 to 30 parts by weight per 100 parts by weight of rubber, and peroxide in an amount of 0.5 to 3 parts by weight per 100 parts by weight of rubber. The pressureless tennis ball according to claim 1, which is a non-pressure tennis ball. 3. The pressureless tennis ball according to claim 1 or 2, wherein the rubber is at least one selected from the group consisting of natural rubber and cis-1,4-volibutadiene.