JPH0512950B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a hard tennis ball suitable for practicing hitting speed balls. [Prior art] Tennis balls for hard courts include pressurized tennis balls (pressured tennis balls) that have a hollow core filled with air or other gas that exerts a pressure 0.6 to 1.0 kg/ ^cm2 higher than atmospheric pressure. There are two types of tennis balls: pressure tennis balls (pressure tennis balls) and pressureless tennis balls (pressureless tennis balls) in which the pressure inside the core is equal to atmospheric pressure. Among these, there are first-class balls that pass the International Tennis Federation standards, and low-priced practice balls whose shot feel and characteristics are slightly lower than those of the first-class balls. However, practice balls are only slightly inferior in shot feel and characteristics, and their characteristics are not significantly or essentially different from those of first-class balls. By the way, there are various ways to practice to improve your tennis skills, but in order to get used to the speedball in baseball, the pitcher throws the ball in front of the normal position, shortening the distance from the pitching position to the batter. be. This method of improving by practicing under conditions that are more severe than the actual situation can be applied to any sport. Tennis has also recently become faster around the world, and various training methods have been adopted as a countermeasure. The basic technique for ground strokes is to get to the ball hitting point quickly, pull the racket early, and hit the ball with a lowered back (bending the knees) in response to a sliding fast ball. The quickest way to master these basics is to practice under the harsher conditions mentioned above. Specifically, there are various methods, but as far as current balls are used, the most common method is to use the ball at a faster speed than at short distances. [Problem to be solved by the invention] In the above-mentioned case, the person throwing out the ball only throws out a large number of balls one after another, but never continues a normal rally. This is because, as mentioned above, practice balls are made with the goal of making them as close as possible to balls that pass the International Tennis Federation standards, so if you keep rallying, your opponent will not be able to hit the speed ball with ease and control. This is because it is not a practice for hitting speed balls. [Means for Solving the Problems] Therefore, in practicing ground strokes, the present inventor continued rallying each other, that is, practiced more realistically, while at the same time developing a ball with low bounce and As a result of various researches in order to create a tennis ball that can be used to practice hitting against a speed ball that has a high horizontal speed after bouncing, we found that 3 to 50% of epoxidized natural rubber with an epoxidation rate of 10 to 60 mol% was added to the total polymer. When making a core with a rubber composition containing % by weight, the diameter must be within the range that passes the International Tennis Federation standard and the weight must be 54.0%.
~58.0g, forward deformation of 5.90~7.50mm, return deformation of 8.5~10.0mm, which meet or are close to the standard values stipulated by the International Tennis Federation standards, while rebounding is ~70~.
At 130 cm, it is lower than the International Tennis Federation standard value, and the feel and flight of the ball are not much different from a first-class tennis ball that passes International Tennis Federation standards.The ball's reflection angle after bouncing is smaller than conventional balls, and after the bounce It was discovered that a tennis ball having a higher horizontal velocity than conventional balls could be obtained, and the present invention was completed. When a tennis ball having the above characteristics is actually hit, it exhibits ball behavior after bouncing that cannot be obtained with a conventional tennis ball, as described above. In other words, the speed after bouncing is high and the behavior is low and slips. the result,
By using the tennis ball of the present invention, it is possible to practice ground strokes under harsh conditions with a low bounce that cannot be obtained with conventional balls and a high horizontal speed after the bounce, which is the basic skill for improving speed balls. You will be able to more reliably master the ability to pull the racket quickly and lower your hips (bend your knees) to hit the ball. Therefore, if you can reliably return the tennis ball of the present invention as intended, you will be able to return the ball with ground strokes without difficulty even in a match with a player who is several steps faster than the opponent with whom you practice regularly. be able to. In other words, the tennis ball of the present invention can be said to be an optimal practice ball for improving ball returns against speed balls. In the present invention, the epoxidized natural rubber used to produce the core is a part of natural rubber that has been epoxidized, and this was developed by the Malaysian Rubber Research Institute. In the invention, epoxidized natural rubber with an epoxidation rate of 10 to 60 mol% is used. The amount of epoxidized natural rubber used is 3 to 50% by weight of the total polymer, but this is because if the amount of epoxidized natural rubber used is less than 3% by weight, the rebound will be too large and the rebound will be 70 to 130 cm.
This is because it is difficult to keep the angle within this range, and if the amount of epoxidized natural rubber used exceeds 50% by weight, the angle of reflection after bouncing becomes extremely small, making it difficult to practice. Within the above range, when the proportion of the total polymer used in the epoxidized natural rubber is A weight %, and the epoxidation rate of the epoxidized natural rubber is B mol %, A×
The most preferable results are obtained when B has the relationship shown below. 1.5≦A×B/100≦9 Polymers constituting the core other than the above epoxidized natural rubber include natural rubber, polybutadiene, styrene butadiene rubber (SBR), high styrene resin, ethylene propylene diene rubber ( (EPDM) etc., but natural rubber or high-cis polybutadiene is usually preferred. The core is made by adding fillers such as clay, magnesium carbonate, calcium carbonate, and silica fillers, vulcanization accelerators such as zinc oxide and stearic acid, vulcanizing agents, vulcanization accelerators, etc. to the above polymer. It can be obtained by vulcanizing a rubber composition prepared as follows. Specifically, the polymer, filler, and vulcanization accelerator are kneaded using a kneading machine such as a Banbury mixer or a roll, and then a vulcanizing agent and a vulcanization accelerator are mixed and kneaded. The obtained rubber composition is made into a sheet shape, which is formed into a rod shape using an extruder, and the obtained rod-shaped rubber composition is put into a half shell mold and compression molded to form a pair of hemispherical shells. A gas generating agent made of a mixture of ammonium salt and nitrite is filled in the recess of one of the obtained hemispherical shells, and the other hemispherical shell is filled with this so that the other hemispherical shell becomes spherical. A core is produced by overlapping and compression molding. Further, it may be used as a core for a pressureless tennis ball without adding a gas generating agent as described above. Compression molding to produce hemispherical shells is usually carried out at 140 to 160°C for 3 to 6 minutes, and the thickness of the hemispherical shells is usually
Made into 3.1-3.6mm. Compression molding for core production is usually carried out at 140-160°C for 15-25 minutes. A tennis ball is produced by covering the core obtained as described above with a felt cover such as a melton cover and compression molding it in a ball mold. Compression molding for making tennis balls is usually carried out at 130 to 150°C for 15 to 20 minutes, and the ball diameter is usually 64 to 66.5 mm. In the present invention, the weight of the tennis ball obtained is 54.0 to 58.0 g, and the amount of forward deformation is 5.90 to 7.50.
The reason why the return deformation amount is specified as 8.5 to 10.0 mm is that while these characteristics meet or are as close to the International Tennis Federation standard values as possible, since this is a practice ball, there may be slight deviations from the International Tennis Federation standard values. It is based on the idea that deviations can be used for practical reasons. The reason why the rebound is set at 70 to 130 cm is because if the rebound is less than 70 cm, the flight and feel of the ball will be too far from the ball that passes the International Tennis Federation standards, and if the rebound is less than 70 cm, the rebound is 130 cm.
The larger the value, the smaller the reflection angle after bouncing.
This is also because it becomes impossible to increase the horizontal speed after the bounce. [Example] Next, the present invention will be explained in more detail by giving examples. Examples 1 to 3 and Comparative Example 1 A core rubber composition having the formulation shown in Table 1 was formed into a sheet, formed into a rod shape using an extruder, placed in a half shell mold, and heated at 150°C for 5 minutes. A pair of hemispherical shells with a thickness of 3.3 mm were obtained by compression molding. The amounts of each component in Table 1 are based on parts by weight. Of the pair of hemispherical shells obtained as described above, a gas generating agent made of a mixture of ammonium salt and nitrite is filled into the recess of one of the hemispherical shells, and the other hemispherical shell is shaped into a spherical shape. They were stacked one on top of the other, placed in a core mold, and compression molded at 150°C for 20 minutes to obtain a tennis ball core. The above core was covered with a melton cover in a conventional manner, placed in a tennis ball mold, and compression molded at 140° C. for 18 minutes to obtain a pressurized tennis ball with a diameter of 65 mm. The weight, forward deformation, return deformation, and rebound of the tennis balls obtained were measured in accordance with International Tennis Federation standards, and the ball was actually hit to examine the feel and flight.
Shown in the table. In addition, the bounce characteristics of the tennis balls obtained during ground strokes when hit flat on a hard court were investigated, and the results are shown in Table 3.

【table】

【table】

〔Effect of the invention〕

As explained above, in the present invention, by using a specific proportion of epoxidized natural rubber in the polymer constituting the core, the rebound of the ball is lowered than the International Tennis Federation standard value, and the reflection after the bounce is lowered. The angle is smaller than that of conventional balls, and the horizontal speed after the ball bounces can be increased. Therefore, according to the tennis ball of the present invention, even when continuing a normal rally, it is possible to practice hitting against a speed ball that has a low bounce and a high horizontal speed after bouncing, which was impossible with conventional balls. Now I can do it. In addition, if the balls are released one after another at a high speed from short distances as in the past, the bounce will be low, which could not be achieved with conventional balls, and the conditions will be more severe for speed balls that have a high horizontal speed after bouncing. This allows you to practice more appropriately when returning a speed ball with a ground stroke.

Claims (1)

[Claims] 1 A core made of a rubber composition containing 3 to 50% by weight of epoxidized natural rubber with an epoxidation rate of 10 to 60 mol% in the total polymer, and a cover covering the core, weighing 54.0 to 58.0 g. , the amount of forward deformation is
5.90~7.50mm, return deformation amount is 8.5~10.0mm,
A tennis ball characterized by a rebound of 70 to 130 cm.