JPS61228040A - Rubber composition for sporting ball - Google Patents

Abstract

PURPOSE:A composition for providing a non-pressure ball having the same physical properties as those of an internal-pressure tennis ball, improved elasticity and resistance to deformation such as ball hardness, etc., obtained by blending rubber consisting essentially of a diene polymer with organic short fibers and a thermosetting resin. CONSTITUTION:Rubber consisting essentially of a diene polymer is blended with organic short fibers and a thermosetting resin.A phenolic resin is used as the thermosetting resin, and it may be blended in a state of raw material substances (a phenol and a substrate to make it into a three-dimensional polymer, preferably resorcin and hexamethylenetetramine). Polyester, wool, etc., are used as the organic short fibers and the short fibers having a ratio of length/diameter of 10-500, preferably 20-300 are blended.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rubber composition for a core ball of a game ball such as a tennis ball or a racquet ball.

Traditionally, the core ball of a game ball has been formed from rubber or a rubber-like material to provide suitable properties to the game ball. For example, in the case of tennis balls, the core ball usually contains gas with a pressure higher than atmospheric pressure, and this pressure is 0.7 to 0.85 kg lower than atmospheric pressure immediately after the ball is manufactured.
/-High degree. By maintaining a pressure higher than the atmospheric pressure applied to the core ball, it provides the ball with higher elasticity (resilience) and resistance to deformation when hit by a racket, etc., giving the ball favorable playability. give.

However, although this high pressure inside the core gives the ball good playability, it is difficult to maintain this high pressure inside the core as it is, and the pressure difference between the inside and outside of the core causes gas to gradually escape from inside the ball. As the core internal pressure fluctuates (decrease), the gaming characteristics deteriorate.

That is, since the game characteristics of the ball depend on the internal pressure of the core, which is higher than the atmosphere, if the internal pressure changes, the characteristics will change accordingly, making the game characteristics unsatisfactory. Therefore, in order to use the ball within a certain period of time after manufacture, or to reduce or eliminate the pressure difference between the inside and outside of the ball wall, devices to reduce the diffusion of gas in the core, such as before use, may be used. It is necessary to store game balls tightly in a pressurized tin can or other container so that they can be removed from the container when used.

However, these methods have problems in terms of cost and various inconveniences such as storage.Furthermore, the manufacturing method for applying appropriate internal pressure in the core is not easy, and equipment for this is required. In addition, there is a problem that the number of manufacturing steps increases.

In order to improve such problems, pressureless balls with a core internal pressure of atmospheric pressure (overpressure 0) have been proposed in recent years.For example,
No. 45-575, No. 45-3926, No. 25289-1989, No. 7049-1980, No. 34934-1983, No. 225079-1980, etc. disclose non-pressure balls. Disclosures have been made regarding a core rubber composition to provide properties equivalent to those of an internal pressure tennis ball. However, in the conventional proposals, it is not easy to make a non-pressure ball have the same physical properties as an internal pressure tennis ball due to the weight limit set by the certification body, and the feel at impact is worse than that of an internal pressure tennis ball. There are drawbacks. For example, in order to have properties equivalent to internal pressure balls, i.e. elasticity and resistance to deformation, within the weight limits established for non-pressure balls, conventional phenolic synthetic resins, polypropylene, acrylonitrile-butadiene, etc.
A composition in which a self-reinforcing thermoplastic resin such as a styrene copolymer, a finely divided fibrous material, a low-density reinforcing filler such as an ionomer is blended into a core rubber composition, or a metal salt of an unsaturated carboxylic acid. Compounds that are neutralized with rubber and co-crosslinked with rubber have been proposed.

However, among these, pressureless tennis balls that mainly use styrene-based resin as a reinforcing filler in the core rubber composition have been put into practical use, and some of them have reached a level that satisfies international standards for tennis balls. However, they generally have inferior physical properties such as elasticity and resistance to deformation compared to internal pressure tennis balls, and they also have inferior feel at impact.
It is rarely used as a competition ball in tournaments, etc.
It is mainly used as a practice ball.

lyB area! The present invention was made in view of the above circumstances, and it is possible to obtain a non-pressure tennis ball having excellent physical properties equivalent to that of an internal pressure tennis ball, and furthermore, a rubber composition that can be suitably used to obtain various other game balls. The purpose is to provide.

That is, as a result of extensive research in order to achieve the above object, the present inventors have found that thermosetting resins, such as phenols and their genols, which are raw materials thereof, are added to the core rubber composition together with organic short fibers in a three-dimensional manner. When compounded with a compound that polymerizes, a non-pressure tennis ball consisting of a core ball formed from this rubber composition has better elasticity (riband) and resistance to deformation such as ball hardness within the weight standard compared to conventional non-pressure tennis balls. It has excellent resistance and excellent feel at impact, has the same characteristics as an internal pressure tennis ball, and fully passes international standards, and is also suitable for manufacturing core balls such as racquet balls. It was discovered that this provides excellent gaming characteristics, and this led to the present invention.

The present invention will be explained in more detail below.

By felling 1 bed The rubber composition of the present invention manufactures core balls for various game balls such as tennis balls and racquet balls, which are made by blending organic short fibers and thermosetting resins in a rubber whose main component is a diene polymer. It is suitably used as a rubber composition for

In this case, the diene polymer is natural rubber, cis-
Rubbers such as 1,4-polybutadiene rubber, cis-1,4-polyisoprene rubber, and SBR can be mentioned, and one of these can be used alone or in a mixture of two or more, but Especially natural rubber and cis-1,4-
A mixture containing polybutadiene in a weight ratio of 100:3 to 4o is preferably used.

In addition, organic short fibers include polyester, nylon,
It is made by chopping synthetic fibers such as vinylon, natural fibers such as cotton, wool, and cellulose, and has a length N) and a diameter (
The ratio (l/d) to d) is preferably from 10 to 500, particularly preferably from 20 to 300. In this case, if the l/d is less than 10, the reinforcing effect of short fibers may not be sufficient, and if the l/d is more than 500, it is difficult to uniformly disperse the fibers in the composition, and processing thereof is also difficult. It may happen.

The blending amount of these organic short fibers is preferably 0.5 to 20 parts, particularly 2 to 15 parts, per 100 parts (by weight, same hereinafter) of rubber. When the amount is less than 0.5 parts, the hardness may not be sufficient, and when it is more than 20 parts, the elasticity may not be sufficiently exhibited.

Further, examples of the thermosetting resin used in the present invention include phenol resins, melamine resins, urea resins, etc., and among these, phenol resins are particularly preferred. In this case, these resins can be blended in advance into the rubber composition in the form of resin raw materials. As this raw material, phenols and compounds that convert them into three-dimensional polymers are preferably used. Here, the phenols include resorcinol, cresol, phenol, p-methylolphenol, O-methylolphenol, 2.4
-dimethylolphenol, 2,6-dimethylolphenol, catechol, hydroquinone, chloroglucine, pyrogallol, bisphenol A, chlorophenol, aminophenol, diphenolic pencunic acid, urushiol, cashew nut oil, quinones, phenylsulfonic acid, Examples include low molecular weight compounds such as triphenylborate, lignin, polyphenylene oxide, and polysulfone resin, and these may be used alone or in combination of two or more. Furthermore, among high molecular compounds such as resorcin-aldehyde resins and phenol-aldehyde resins, resol-type compounds with a molecular weight of up to 1000 and novolac-type compounds with a molecular weight of up to 2000 can also be suitably used. Can be used in combination. Among these, resorcinol is particularly preferably used.

In addition, raw materials for three-dimensional polymerization of the above phenols include hexamethylenetetramine, cyclic formal, polyaldehyde, polymethylolated TL (methylolphenol, methylolurea, methylolmelamine, trimethylolphosphine oxide, etc.), amine aldehyde. Examples include condensates (aniline resin, methylene diamine adducts, etc.), and these may be used alone or in combination of two or more. Among these, hexamethylenetetramine is most preferably used.

The blending amount of these thermosetting resins is preferably 0.5 to 25 parts per 100 parts of the total amount of rubber and thermoplastic resin. In particular, when using phenols and a compound that three-dimensionally polymerizes them, the amount of phenols is 0.2 to 15 parts, especially 2 parts.
The amount used is preferably 1 to 12 parts, and the amount of the compound that three-dimensionally polymerizes the phenol is preferably 0.1 to 10 parts, particularly 1 to 8 parts. Here, the ratio of phenols, which are the raw materials of the thermosetting resin, and the compound that turns the phenols into three-dimensional polymers is 1:0.1 to 1:1.5, particularly 1:0.1 to 1, as a weight ratio. :1.
It is preferable to set it to 0.

In addition to the above-mentioned components, the rubber composition of the present invention may contain crosslinking agents such as sulfur and peroxides, inorganic fillers, and other auxiliaries.

In this case, the crosslinking agent is the same as in the case of ordinary rubber compounding, and sulfur, sulfur derivatives, peroxides, etc. can be used, and any commonly used crosslinking agents can be used.

For example, examples of peroxides include dicumyl peroxide, benzoyl peroxide, tert-butyl perbenzoate, 2,2'-di(tert-butylperoxy)butane, and 2,2-azobisisobutyronitrile. Among these, dicumyl peroxide is preferably used. Note that the amount of sulfur blended is preferably 2 to 10 parts, and the amount of peroxide blended is preferably 0.5 to 3 parts. Further, examples of inorganic fillers to be blended in the rubber composition of the present invention include calcium carbonate, silicate compounds, etc., and these may be added in an amount of 0.5 to 15 parts per 100 parts of rubber, and if necessary, low-density fillers. As a reinforcing filler, a thermoplastic resin such as a self-reinforcing thermoplastic resin such as a styrene resin with a styrene content of 60 to 100% by weight, a polyester resin, a polyurethane resin, etc., is added in an amount of 5 to 40 parts per 100 parts of rubber.
It is also possible to mix it in parts.

In the present invention, the preparation of the rubber composition, the production of a core ball from the rubber composition, the production of a pressureless tennis ball using the formed core ball, etc. can be carried out by commonly employed methods.

For example, the rubber composition is prepared by uniformly kneading the constituent components using a kneading device such as a roll or a Banbury mixer. In addition, to create a core ball, first compression mold this rubber composition in a half shell mold to create a hemispherical shell, and then stack two of the resulting hemispherical shells to form a hollow sphere. This is done by placing the ball in a core ball mold and compression molding it. Furthermore, in the production of pressureless tennis balls, a method is employed in which the formed arbor is covered with a cover made of woven fabric or felt such as Melton, and then compression molded using a mold.

In addition, core balls for racquetballs are usually obtained by vulcanization molding a rubber composition into a solid spherical shape.
Racquet balls are formed by using the core ball as is or by covering the core ball with a suitable cover.

Here, as a preferable blending example for obtaining a racquet ball, in 100 parts of natural rubber and high styrene resin, 5 to 40 parts of high styrene resin and 5 to 30 parts of filler such as calcium carbonate, magnesium carbonate, silicate compound, etc. , sulfur 2
6 parts of accelerator, 1 to 5 parts of accelerator, and a thermosetting resin such as 0.2 to 20 parts of resorcin and 0.1 to 10 parts of hexamethylenetetramine. Although the core ball for racquetball differs from the core ball for tennis ball in specific gravity, weight, etc., other properties such as elasticity and hardness are almost the same.

The rubber composition according to the present invention contains short organic fibers and a thermosetting resin in the rubber, thereby producing a core ball of a non-pressure tennis ball that has excellent physical properties equivalent to those of an internal pressure tennis ball. The pressureless tennis ball obtained by using the rubber composition of the present invention has particularly excellent shot feel.

Furthermore, the rubber composition of the present invention can be suitably used not only for the production of non-pressure tennis balls, but also for the production of internal pressure tennis balls, softball baseball balls, center backs for thread-wound golf balls, and other game balls, particularly for the production of core balls. .

EXAMPLES Hereinafter, the present invention will be specifically explained by showing examples and comparative examples, but the present invention is not limited to the following examples.

[Examples 1 and 2] Rubber compositions shown in Table 1 were prepared, and core balls for tennis balls were made from the rubber compositions.

Furthermore, a pressureless tennis ball was manufactured using this core ball.

Stearic acid was kneaded in a Banbury mixer, hexamethylenetetramine, an accelerator, and sulfur were added to the kneaded product,
This was done by kneading with rolls.

Next, the rubber composition prepared as described above was formed into a sheet with a roll, three sheets were pasted together at an angle of 60 degrees, and the sheets were cut to fit a half shell mold. Thereafter, it was placed in a half shell mold and compression molded to create a hemispherical shell, and then two of the hemispherical shells were stacked and placed in a core ball mold to create a core ball. This core ball was covered with a melton cover and compression molded in a mold at 125° C. for 20 minutes to produce a pressureless tennis ball.

The vulcanization conditions for half shell molding, core ball molding, and pressureless tennis ball molding are such that the degree of vulcanization in all steps is 150.
1.5 of the time the rheometer torque reaches 90% at °C
The setting was made so that it would be equivalent to vulcanization taking twice as long.

Table 2 shows the physical properties of the obtained pressureless tennis ball.

[Comparative Example 1.2] A rubber composition shown in Table 1 was prepared, a core ball for a tennis ball was made from the rubber composition in the same manner as in the example, and this core ball was further used to perform a non-pressure test. Manufactured tennis balls.

Preparation of a rubber composition, production of a core ball, and production of a pressureless tennis ball were carried out in the same manner as in Examples. The physical properties of the pressureless ball are also listed in Table 2.

Table 1 $2 1.3 Diphenylguanidine*3 Dibenzothiazyl disulfide Table 2 From the results in Tables 1 and 2 of the International Tennis Federation, it is clear that the rubber composition of the present invention is suitable for use in hollow elastic compositions for ball games. It was found that it is suitable as That is, as shown in Table 2, the non-pressure tennis ball formed from the rubber composition of the present invention has better rebound and resistance to deformation (deformation) than the non-pressure tennis ball that passes international standards (Comparative Example 2). amount) are close to those of an internal pressure tennis ball.

Furthermore, all of the tennis balls according to the present invention had a good shot feel, and in particular, the ball of Example 1 had a shot feel that was almost the same as that of an internal pressure tennis ball.

Claims (1)

[Scope of Claims] 1. A rubber composition for game balls, characterized in that organic short fibers and a thermosetting resin are blended into a rubber containing a diene polymer as a main component. 2. The rubber composition according to claim 1, wherein the thermosetting resin is a phenolic resin.