JPH0368710B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field and Objectives] The present invention relates to the improvement of a non-pressure tennis ball, and an object of the present invention is to provide a non-pressure tennis ball that has excellent materials and shot feel comparable to pressurized tennis balls. [Background technology] A tennis ball for hard tennis is made of a hollow core ball made of rubber or a rubber-like elastic material, the inside of which is pressurized to about 0.6 to 0.9 kg/cm ² above atmospheric pressure with air or gas, and a hollow core ball made of woven or felt material. There are pressurized tennis balls covered with covers and non-pressure tennis balls, which are hollow core balls filled with air at atmospheric pressure and covered with textile or felt covers. By the way, in a pressurized tennis ball, air or gas at a pressure higher than atmospheric pressure sealed inside the core ball leaks out through the core ball wall due to the pressure difference with the outside, and loses pressure over a few months. I end up. As a result, the ball's repulsion, that is, its flight, decreases as the pressure decreases, making it impossible to use the ball satisfactorily as a tennis ball. Therefore, such pressurized tennis balls must be used within a certain period of time after manufacture or stored in a pressurized container before use to eliminate or reduce the drop in internal pressure. . However, they are expensive and inconvenient. In order to overcome this drawback, many attempts have been made to provide pressureless tennis balls. For example, U.S. Patent No. 2,896,949 proposes a pressureless tennis ball containing 10 to 45 parts by weight of high styrene resin in the core composition, and JP-A-55-96171 proposes a non-pressure tennis ball containing 10 to 45 parts by weight of high styrene resin in the core composition; EPM (ethylene-propylene copolymer) or EPDM (terpolymer of ethylene, propylene and non-conjugated diene monomer)
A pressureless tennis ball containing 60% by weight or less has been proposed. Furthermore, in JP-A No. 54-34934, the polymer composition of the core is ionomer resin 10 to 10.
30% by weight, natural rubber 30-70% by weight and cis-
A pressureless tennis ball containing 50 to 80% by weight of 1,4-polybutadiene has been proposed, and in Japanese Patent Publication No. 1989-25289, wood flour is added to the core composition at a ratio of 20 to 50% by weight of rubber.
A pressureless tennis ball containing % by weight has been proposed. However, none of the currently available unpressurized tennis balls have been accepted for advanced tennis championships. Either these non-pressure tennis balls are hard and give an unsatisfactory "feel" when hit with a racket, or the soft ones have poor flight and don't have the same feel at impact as a pressurized tennis ball, and also cause problems with the progress of the game and play. This is because there is a drawback that the deformation resistance decreases significantly due to repeated medium to strong blows. [Structure of the Invention] The present invention has been made in view of such circumstances, and the core ball is syndiotactic-1 and 2.
- Contains 5 to 30% by weight of polybutadiene and 40% or more of cis-1,4-polybutadiene (hereinafter referred to as VCR), which contains 5 to 60% by weight of the total rubber, and contains 3 to 10 carbon atoms. α,β-monoethylenically unsaturated carboxylic acid having atoms,
from a rubber composition comprising a metal ion having a valence of 1 to 4 and a peroxide in an amount sufficient to neutralize at least 10% of the carboxylic acid groups of the α,β-monoethylenically unsaturated carboxylic acid. By manufacturing this, it is possible to provide a non-pressure tennis ball that has physical properties and feel at impact comparable to those of a pressurized tennis ball. That is, in the present invention, the rubber component contains
VCR is contained in a specific proportion, and the rubber component is α,
By co-crosslinking with a metal salt of β-monoethylenically unsaturated carboxylic acid, impact resilience is improved,
In addition to increasing the bounce and setting the amount of deformation to an appropriate value, the ball has the feel of a pressurized ball and reduces the loss of shot feel caused by repeated hits, achieving physical properties and feel comparable to a pressurized tennis ball. This made it possible to obtain a pressureless tennis ball that has the following characteristics. Of course, since the tennis ball of the present invention is a non-pressure ball, the performance of the ball does not deteriorate due to a decrease in internal pressure, unlike in pressurized tennis balls. In the present invention, the rubber component of the composition for producing the core ball is natural rubber, cis-1,4-
Polybutadiene, styrene-butadiene rubber, etc.
VCR is blended and contains 5 to 60% by weight of VCR in the rubber. This is because VCR accounts for 60% by weight of all rubber.
If the VCR exceeds 5% by weight, the impact resilience decreases, and conversely, if the VCR is less than 5% by weight, it will become soft. This is because the amount must be increased, and as a result, it becomes impossible to obtain a tennis ball that gives a satisfying hard feel when hit. Similarly, Syndiotactic-1, 2 in VCR
- The amount of polybutadiene is between 5 and 30% by weight; if the syndiotactic -1,2-polybutadiene is less than this, it becomes soft and requires a similar operation as above to compensate for the hardness, resulting in ,
It became impossible to obtain a pressure-free tennis ball that gave a satisfying hard feel when hit, and Syndiotactic
This is because if the amount of 1,2-polybutadiene exceeds the above range, the rebound resilience will decrease and a satisfactory pressureless tennis ball will not be obtained. Further, the amount of cis-1,4-polybutadiene in the VCR must be 40% by weight or more, and if the amount is less than this, the impact resilience will decrease. Such a VCR can be obtained, for example, by carrying out conventional cis polymerization of polybutadiene and then continuing 1,2 syndiotactic polymerization in the same system. As a specific example of such a VCR, for example, UBEPOL- manufactured by Ube Industries, Ltd.
VCR309 (9% by weight of syndiotactic-1,2-polybutadiene, 89% by weight of cis-1,4-polybutadiene, 2% by weight of trans-1,4-polybutadiene), UBEPOL-VCR412 (syndiotactic-1,2-polybutadiene) 12% by weight of polybutadiene, 86% by weight of cis-1,4-polybutadiene, trans-
1,4-polybutadiene (2% by weight) and the like are commercially available and are preferably used in the present invention. Examples of the α,β-monoethylenically unsaturated carboxylic acid having 3 to 10 carbon atoms include methacrylic acid, acrylic acid, itaconic acid, and crotonic acid, with methacrylic acid and acrylic acid being particularly preferred. The amount of α,β-monoethylenically unsaturated carboxylic acid used is 100 parts of rubber (parts by weight,
(same below) is preferably in the range of 7 to 30 parts.
If the amount of α,β-monoethylenically unsaturated carboxylic acid used is less than 7 parts, it will become soft, if high styrene resin is added to give it hardness, it will give a hard feel, and if the amount of peroxide is increased, it will become soft. The vulcanized rubber becomes brittle, resulting in decreased durability and deformation resistance due to repeated hits, making it impossible to obtain a satisfactory tennis ball.On the other hand, if the amount exceeds 30 parts, it becomes too hard and the amount of deformation deviates from the standard value. It is. Examples of mono- to tetravalent metal ions that neutralize the α,β-monoethylenically unsaturated carboxylic acid include zinc ions, sodium ions, calcium ions, magnesium ions, zirconium ions, and especially zinc ions. is preferred. Normally, these metal ions are mixed in
For example, zinc ions are blended in the form of metal oxides such as zinc oxide. Neutralizing α,β-monoethylenically unsaturated carboxylic acid with metal ions is a method of co-crosslinking rubber with a metal salt of unsaturated carboxylic acid to improve rebound, increase bounce, and reduce deformation. This is to improve ball performance by adjusting the value to an appropriate value. If the amount of neutralization is less than 10%, the above-mentioned performance improvement effect cannot be sufficiently exhibited. α, β− due to metal ions
The higher the degree of neutralization of the monoethylenically unsaturated carboxylic acid is, the more preferable it is.
% is particularly preferable. In addition, when blending the α,β-monoethylenically unsaturated carboxylic acid and the metal ion, the α,β-monoethylenically unsaturated carboxylic acid and the metal ion may be mixed in the form of a neutralized salt. Examples of peroxides include dicumyl peroxide, beyzoyl peroxide, tert-butyl perbenzoate, 2,2'-di(tert-butylperoxy)butane, and 2,2'-azobisisobutyronitrile. Among these, dicumyl peroxide is particularly preferred. The amount of these peroxides used is preferably in the range of 0.5 to 5 parts per 100 parts of rubber. Core balls are made from a rubber composition containing the above-mentioned components as essential components and, if necessary, fillers such as zinc oxide, clay, silica, and calcium carbonate. A pressureless tennis ball is obtained by covering it with a textile or felt cover. To prepare the composition, components other than peroxide are uniformly kneaded using an appropriate kneading means such as a Banbury mixer or a kneader, and then peroxide is added to the above-mentioned kneaded material on a roll and kneaded uniformly using a roll. It is carried out by. The production of a core ball from the above composition, the production of a pressureless tennis ball using the obtained core ball, etc. can be carried out by means conventionally employed in the production of pressureless tennis balls. can. For example, to produce a core ball, the composition is first compression-molded in a half-shell (hemispherical shell) mold to produce a half-shell, and the resulting half-shell is divided into two to form a hollow sphere. This is done by stacking them in a core ball mold and compression molding them. At this time, only air at atmospheric pressure is sealed inside the core ball, and no foaming agent or the like used in the manufacture of pressurized tennis balls is sealed. In addition, high pressure air is applied to the obtained core ball.
Do not inject gas etc. Therefore, the internal pressure of the core ball obtained is substantially equal to atmospheric pressure. A pressureless tennis ball is manufactured by covering the core ball as described above with a cover made of woven fabric such as Melton or felt, and compression molding the ball with a mold. [Example] Next, the present invention will be explained in more detail with reference to Examples. Examples 1 to 7 and Comparative Examples 1 to 2 The compositions shown in Table 1 were prepared, a hollow core ball was made from the composition, and the obtained core ball was covered with a melton cover to form a non-pressure tennis ball. was manufactured. Note that the blended parts in Table 1 are based on parts by weight. For kneading to prepare the composition, compounding ingredients other than dicumyl peroxide, sulfur, and accelerator are kneaded with rubber using a Banbury mixer, and dicumyl peroxide, sulfur, and accelerator are added to the above-mentioned kneaded material on a roll. This was done by kneading with rolls. The composition prepared as above was formed into a sheet, extruded into a rod shape using an extruder, cut to fit a half-shell mold, placed in a half-shell mold, and heated at 160°C. A half shell was produced by compression molding for 5 minutes, two half shells were stacked to form a hollow sphere, placed in a core ball mold, and compression molded at 150°C for 15 minutes. This core ball was covered with a melton cover and heated to 150°C in a mold.
A pressureless tennis ball was manufactured by compression molding for 20 minutes. Table 2 shows the results of measuring the physical properties of the resulting pressureless tennis ball and the feel at impact.

【table】

〔Effect of the invention〕

As explained above, the non-pressure tennis ball of the present invention has excellent physical properties and shot feel comparable to those of pressurized tennis balls.

Claims (1)

[Scope of Claims] 1 Syndiotactic - Contains 5 to 30% by weight of 1,2-polybutadiene and 5 to 60% by weight of polybutadiene containing 40% or more of cis-1,4-polybutadiene based on the total rubber. , an α,β-monoethylenically unsaturated carboxylic acid having from 3 to 10 carbon atoms, sufficient to neutralize at least 10% of the carboxylic acid groups of the α,β-monoethylenically unsaturated carboxylic acid. A pressureless ball consisting of a core ball whose internal pressure is substantially equal to atmospheric pressure and which is made from a rubber composition containing a metal ion having a valence of 1 to 4 and a peroxide, and a cover that covers the core ball. tennis ball. 2 α,β-monoethylenically unsaturated carboxylic acid having 3 to 10 carbon atoms is 7 to 30 parts by weight per 100 parts by weight of rubber, and peroxide is 0.5 to 5 parts by weight per 100 parts by weight of rubber. The non-pressure tennis ball according to claim 1, which is parts by weight.