JPH06246018A - Tennis ball - Google Patents

Abstract

PURPOSE:To provide a tennis ball having satisfactory workability of rubber composition for unvulcanized core, proper precision and excellent repulsive property. CONSTITUTION:In a tennis ball consisting of a core and cover covering the core, the core is composed of vulcanized and molded rubber composition comprising 100 pts.wt. of natural rubber, 2-10 pts.wt. of liquefied polybutadiene rubber, 3-20 pts.wt. of zinc oxide, 20-60 pts.wt. of a filler, 2-5 pts.wt. of sulfur and 1-5 pts.wt. of an accelerator.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to tennis balls. More specifically, the present invention relates to a tennis ball which has an unvulcanized rubber composition for cores having good processability, proper compression, and excellent repulsion properties.

[0002]

2. Description of the Related Art Generally, a rubber composition is blended with a softening agent in order to improve the easiness of mixing and dispersibility of the compounding agent and to improve the rubber flow to facilitate molding operations such as extrusion and rolling. , Higher fatty acids such as stearic acid and palmitic acid, higher fatty acid esters such as cottonseed oil and castor oil, plant-based softeners such as pine tar and tall oil, and petroleum-based softeners such as spindle oil and process oil. It is compounded.

However, in the rubber composition for the core of the tennis ball, the above-mentioned softening agent has a drawback of increasing the compression which is important in the core characteristics (that is, softening the core).

Therefore, the amount of the vulcanizing agent is increased to increase the degree of vulcanization so as to obtain a proper compression. Will be lowered.

Therefore, in Japanese Examined Patent Publication No. 3-50779, 1 to 7 parts by weight of liquid polyisoprene rubber is blended in place of the conventional softening agent to improve the processability of the unvulcanized rubber composition. A rubber composition for a tennis ball core has been proposed.

However, the tennis ball using the above rubber composition for cores does not always have sufficient resilience, and users demand tennis balls having more excellent resilience.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the problems in the prior art as described above, has good workability of the rubber composition when not vulcanized, has proper compression, and has a repulsion property. It is intended to provide a tennis ball having excellent characteristics.

[0008]

According to the present invention, the core of a tennis ball is composed of 2 to 10 parts by weight of liquid polybutadiene rubber, 3 to 20 parts by weight of zinc oxide, and 20 to 60 parts by weight of a filler based on 100 parts by weight of natural rubber. The above object is achieved by comprising a vulcanized molded product of a rubber composition containing 1 part by weight, 2 to 5 parts by weight of sulfur and 1 to 5 parts by weight of an accelerator.

To explain the present invention in detail, in the present invention, the liquid polybutadiene is blended with the rubber composition for the core as described above.
It improves the processability of the rubber composition when unvulcanized, and unlike conventional softeners that do not participate in crosslinking at all, it is vulcanized by a vulcanizing agent, and after vulcanization itself also has rubber-like elasticity. As a result, unlike the conventional softeners, the rubber properties are not significantly deteriorated, the compression is made proper, and the repulsion properties are improved as compared with the liquid polyisoprene rubber. In addition, this liquid polybutadiene rubber has a good effect of improving the processability of the rubber composition when it is not vulcanized, and can be sufficiently used as a softening agent.

In the present invention, the liquid polybutadiene rubber having an average molecular weight of 20,000 to 60,000 is preferably used. This is because liquid polybutadiene rubber having an average molecular weight of less than 20,000 deteriorates the physical properties of the vulcanized rubber, and conversely, liquid crystalline polybutadiene rubber having an average molecular weight of more than 60,000 has processability such as easy mixing, dispersibility and extrusion. This is because there is little effect of improving the molding workability.

The blending amount of the liquid polybutadiene rubber with respect to the natural rubber is in the range of 2 to 10 parts by weight of the liquid polybutadiene rubber with respect to 100 parts by weight of the natural rubber as described above. This is because when the amount is less than the range, the effect of improving the mixing workability, dispersibility, and molding workability such as extrusion is small, and when the amount is more than the range, the physical properties of the vulcanized rubber are deteriorated.

In the present invention, the rubber composition for producing the core is prepared by mixing 2 to 10 parts by weight of liquid polybutadiene rubber with 100 parts by weight of natural rubber as described above,
Further, 3 to 20 parts by weight of zinc oxide, calcium carbonate, magnesium carbonate, a silicic acid compound, a filler such as clay 20
-60 parts by weight, 2 to 5 parts by weight of sulfur, and 1 to 5 parts by weight of an accelerator (vulcanization accelerator), and if necessary, other compounding agents for rubber are appropriately added.

In the above rubber composition for cores, natural rubber is used as the base rubber because natural rubber has excellent processability and vulcanization characteristics, and has good compatibility with liquid polybutadiene rubber. . Further, a part of the natural rubber may be replaced with solid polybutadiene rubber, ethylene propylene diene rubber, styrene butadiene rubber or the like within a range that does not impair the properties of the natural rubber.

Further, in the above rubber composition for core, zinc oxide, filler, sulfur, accelerator, etc. are blended in the above proportions. The blending proportions thereof are excellent in proper compression and excellent. This is because it is suitable for obtaining repulsive properties.

The core is usually obtained by molding the above rubber composition into a hemispherical shell shape, filling a hollow space with a gas generating agent, bonding two of them together, and vulcanizing them into a ball shape. The vulcanization is carried out by heating under pressure at 140 to 160 ° C. for 6 to 35 minutes, although the conditions are not particularly limited.

Then, a tennis ball is obtained by coating the obtained core with a woven fabric such as melton or a cover made of felt and compression-molding it in a ball mold.

[0017]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples. However, the present invention is not limited to only those examples.

Examples 1 and 2 and Comparative Examples 1 to 5 A rubber composition having the composition shown in Table 1 was prepared, and its Mooney viscosity and rubber physical properties after vulcanization were measured. The results are shown in Table 2.
Shown in.

The kneading in preparing the rubber composition was carried out by kneading sulfur and a compounding agent other than the accelerator with a rubber in a Banbury mixer, and adding the sulfur and the accelerator to the above kneaded material with a roll and kneading. Also, vulcanization was conducted at 141 ° C for 3
It is performed under pressure for 0 minutes, and the physical properties of vulcanized rubber are measured according to JIS K.
The test was performed according to the test method specified in 6301. In addition,
The blending amount of each component in Table 1 is based on parts by weight.

[0020]

[Table 1] Note * 1: 2-mercaptobenzothiazole * 2: Dibenzothiazyl disulfide

[0021]

[Table 2]

As shown in Table 2, the rubber compositions of Examples 1-2 have lower Mooney viscosities than the rubber compositions of Comparative Example 5 in which no softening agent was blended, whereby Examples 1-2 were used.
It has been clarified that the above rubber composition has good mixing property, dispersibility, and molding workability such as extrusion.

Further, the rubber compositions of Examples 1 and 2 have a higher modulus than those of the rubber compositions of Comparative Examples 3 and 4 in which a conventional softening agent (commercial softening agent of higher fatty acid type) is blended, and they are used for tennis balls. It is clear that it is suitable as the core rubber composition.

Next, except for the rubber composition of Comparative Example 5 having poor molding workability such as extrusion, Examples 1 and 2 and Comparative Example 1
A core for a tennis ball was produced using the rubber compositions of ~ 4 and its characteristics were measured. The results are shown in Table 3. The core was prepared by molding a rubber composition into a hemispherical shell shape, and filling two hollow particles with a gas generating agent consisting of a mixture of an ammonium salt and nitrous acid and bonding them into a spherical shape. It was carried out by vulcanizing under pressure at 10 ° C. for 10 minutes. The thickness of the core was set to 3.4 mm and the outer diameter of the core was set to 60.5 mm.

Among the characteristics shown in Table 3, the resilience height and compression are measured as follows.

Repulsion height: The core is naturally dropped from a position of 254 cm in height to a flat concrete surface having a thickness of 6 cm or more, and the bounce height of the core at that time (but below the core) is measured. This is repeated 3 times and the average value is calculated.

Compression: Initial load of 3.5 on the core
Variable (m) from when a load of 18 pounds (8.165 kg) is applied to when a load of 18 pounds (1.575 kg) is applied
m) is measured. The smaller the compression, the harder the core.

[0028]

[Table 3]

As shown in Table 3, the cores of Examples 1 and 2 were compared with the cores of Comparative Examples 1 and 2 containing liquid polyisoprene rubber and the cores of Comparative Examples 3 and 4 containing a commercially available softening agent. The repulsion height was high.

Further, the smaller the value of compression, the harder the core is, but it is considered that the range of 6.8 ± 0.2 mm is good for the core for a tennis ball.
The cores of Examples 1 and 2 all have a compression within the above range, and can be said to be preferable as a core for a tennis ball from the viewpoint of compression.

That is, the compression is 6.8 ±
A good shot feeling is obtained within the range of 0.2 mm, and when the compression is smaller than the above range, the shot feeling is hard and the impact is large, and when the compression is larger than the above range, the ball is too soft and the shot feeling is deteriorated. At the same time, the rebound characteristics are reduced and the rebound is reduced, but the core of Example 1 has a compression of 6.86 m.
m, the core of Example 2 has a compression of 6.95.
mm, both of which are within the range of 6.8 ± 0.2 mm, which can be said to be preferable as a core for a tennis ball.

Next, the above-mentioned Examples 1 and 2 and Comparative Example 1
A core of No. 4 to 4 was covered with a melton cover, and compression molded at 150 ° C. for 20 minutes in a ball mold to produce a tennis ball.

The results of measuring the physical properties of the obtained tennis ball are shown in Table 4. Table 4 shows the standard values of the International Tennis Federation. The various physical properties shown in Table 4 are measured as follows.

Forward Deformation Amount (mm) First, the ball is moved along the XYZ axes (3 at right angles to each other.
The compression of 2.54 cm each in one axial direction is repeated 3 times. Within 2 hours after this pre-compression, the deformation amount is measured by the following method using a Steven compression tester.

The ball has an initial load of 3.5 pounds (1.57
5 pounds) 18 pounds (8.165 kg)
The deformation amount (mm) of the ball up to the time when the load is applied is measured.

Return deformation amount (mm) After reading the forward deformation amount, the deformation amount is 2.5.
Load is further applied until it reaches 4 cm, and from that point 18
Restores deformation up to a load of 8 pounds (8.165 kg),
The amount of deformation (mm) at that time is measured.

Rebound (cm) The ball is naturally dropped from a height of 254 cm onto a flat concrete surface, and the jumped height of the ball (but below the ball) is measured. This is repeated 3 times and the average value is calculated.

[0038]

[Table 4]

As shown in Table 4, the tennis balls of Examples 1 and 2 all passed the International Tennis Federation standard, and the tennis balls of Comparative Examples 1 and 2 in which liquid polyisoprene rubber was blended were used. The rebound was higher than that of the tennis balls of Comparative Examples 3 to 4 containing a commercially available softener.

[0040]

As described above, in the present invention, by blending the liquid polybutadiene rubber into the rubber composition for the core of the tennis ball, the processability of the unvulcanized rubber composition is good and the rubber composition is suitable. It was possible to provide a tennis ball having compression and excellent repulsion characteristics.

Claims (1)

[Claims] 1. A tennis ball having a core and a cover covering the core, wherein the core is a natural rubber 1
A rubber composition in which 2 to 10 parts by weight of liquid polybutadiene rubber, 3 to 20 parts by weight of zinc oxide, 20 to 60 parts by weight of a filler, 2 to 5 parts by weight of sulfur and 1 to 5 parts by weight of an accelerator are compounded with respect to 00 parts by weight. A tennis ball comprising a vulcanized molded product.