JP2001218878A - Tennis ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tennis ball 1 providing the good feeling in ball speed and the superior ball hitting feeling. SOLUTION: This tennis ball 1 has a hollow core 2 and a melton layer 3 adhered to an outer surface of the core 2. A ratio (Vf/Vi) of a bounce velocity Vf to an entrance velocity Vi is 0.685 or more in colliding the tennis ball 2 with a tennis court under a conditions that an angle of entrance is 16 deg.C±2 deg.C and a velocity is 30m/s ±2 m/s. A relationship of (Vf/Vi) and FD (mm) as a value of the forward deformation measured in accordance with the standard of the international tennis federation satisfies a mathematical expression of (I); 0.116×FD<=(Vf/Vi)<=0.152×FD...(I).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a tennis ball used for hard tennis.

[0002]

2. Description of the Related Art A tennis ball for hard tennis includes a spherical core and a melton layer attached to an outer surface of the core. The core is usually made of rubber and hollow. Such a tennis ball is, for example,
No. 59333, JP-A-9-239069 and the like.

[0003] By the way, tennis is different from golf and the like.
There is no opportunity for the player to select the type of ball to be used in the competition. In a tennis competition, players who compete against each other hit the same ball back, so that there are few advantages and disadvantages depending on the type of ball as in golf.
For this reason, tennis players are relatively reckless about the performance of tennis balls. Also, in the development of tennis balls, there is a tendency that more emphasis is placed on homogenization of physical properties and reduction of manufacturing costs than introduction of new technology.

[0004] In the old days, natural turf courts and clay courts were the mainstream, but in recent years, various tennis courts such as antuka courts, hard courts, carpet courts, and artificial turf courts with sand have been developed. I have. The speed of the tennis ball decreases as it bounces on the tennis court, but the rate of this reduction differs depending on the type of tennis court. For example, clay coat, antu coat,
In artificial turf courts containing sand, the ball speed after bouncing tends to be lower.

[0005]

As described above, various tennis courts have been developed, and as players become accustomed to playing on these tennis courts, clay courts, antuca courts, artificial turf courts containing sand, etc., have been developed. You may feel unsatisfactory on a tennis court with a small ball speed after the bounce. There is also a problem that the timing at which the player swings the racket must be delayed on a tennis court having a low ball speed after bouncing, as compared to playing on a large tennis court.
These problems can be solved by using a tennis ball having a sense of speed. However, as described above, the technical development of the tennis ball has not progressed so much, and the player has not yet been satisfied with the sense of speed.

[0006] The incident velocity V when colliding with the tennis court
When the ratio (Vf / Vi) of the reflection speed Vf to i is increased, that is, the resilience performance of the tennis ball is enhanced, the ball speed after the bouncing is increased and the sense of speed is enhanced. However,
In a tennis ball having a large (Vf / Vi), the value of the forward deformation (FD) defined in the standards of the International Tennis Federation tends to be small. FD
If is small, the impact transmitted to the player when hitting the ball is large,
The player feels that the shot feeling is poor. Players want a tennis ball that has a sense of speed and a good shot feeling.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a tennis ball having a feeling of speed and a good shot feeling.

[0008]

Means for Solving the Problems The present inventor has proposed (Vf / V
Even if i) is a large tennis ball, FD and (Vf /
If the relationship with Vi) is within a predetermined range, the impact force felt by the player when hitting the ball is not necessarily large,
The inventor has invented a tennis ball that is excellent in both feeling of speed and shot feeling. In the tennis ball of the present invention, it is the ratio of the reflection velocity Vf to the incident velocity Vi when colliding with the tennis court under the conditions that the incident angle is 16 ° ± 2 ° and the velocity is 30 m / s ± 2 m / s (Vf / Vi). ) And FD (mm), which is the value of the forward deformation measured according to the International Tennis Federation (ITF) standard, satisfy the relationship shown in the following equation (I). In this tennis ball, the value of (Vf / Vi) is 0.685 or more. 0.116 × FD ≦ (Vf / Vi) ≦ 0.152 × FD (I)

In this tennis ball, since the value of (Vf / Vi) is 0.685 or more, a decrease in ball speed due to bouncing can be suppressed. Therefore, the player can obtain a sense of speed. In this tennis ball, F
Since D and (Vf / Vi) satisfy the relationship of the above formula (I), the FD is in an appropriate range in the relative relationship with (Vf / Vi), so that the shot feeling is good.

Preferably, FD (mm) and (Vf / V
i) satisfies the relationship shown in the following equation (II). As a result, a balance between a sense of speed and a sense of hitting is better achieved. 0.120 × FD ≦ (Vf / Vi) ≦ 0.144 × FD (II)

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
Embodiments of the present invention will be described in detail.

FIG. 1 is a partially cutaway sectional view showing a tennis ball 1 according to an embodiment of the present invention. This tennis ball 1 is for hard tennis and has a hollow core 2
And a melton layer 3 attached to the outer surface of the core 2. The outside diameter (diameter) of the tennis ball 1 is usually in the range of 64.4 mm to 67.3 mm, and the mass is in the range of 56.7 g to 58.5 g.

The value of (Vf / Vi) of the tennis ball 1 is 0.685 or more, particularly 0.687 or more. This suppresses a reduction in ball speed due to a collision with the tennis court. Therefore, the ball speed after the bouncing is higher than that of a normal tennis ball, and the player can feel a sense of speed.

The measurement of (Vf / Vi) is performed according to the rules of the international tennis standard (ITF CS 01/01). That is, the incident angle is 16 ° ± 2 ° and the incident speed is 3 °.
The tennis ball 1 is hit against a tennis court under the condition that the number of revolutions per second is 0 m / s ± 2 m / s or less than 3 times. Then, the ball speed Vi immediately before the collision and the ball speed V immediately after the collision
is measured, and (Vf / Vi) is calculated from this value. The measurement is performed on three balls per type, and each ball is measured three times. Then, an average value of the nine data is calculated. Prior to the measurement, each ball is hit against the tennis court three times under the same conditions as the measurement (preliminary collision). This preliminary collision removes permanent hardness from the tennis ball 1,
(Vf / Vi) is measured in a state close to practical use.

As described above, the incident angle has a tolerance of ± 2 ° similarly to the incident angle defined in the ITF standard.
Further, the incident speed has an allowable range of ± 2 m / s similarly to the incident speed defined in the ITF standard. Strictly speaking, when the measurement conditions fluctuate within this allowable range, (Vf / V
The measured value of i) may fluctuate. For example, the measured value may be slightly different between the case where the incident speed is 14 ° which is the lower limit and the case where the incident speed is 18 ° which is the upper limit. However, in an actual measurement, the measurement error caused by the above-mentioned allowable range is very narrow in relation to the effect of the present invention, and the measurement was performed under the conditions within this allowable range (Vf
It can be said that the value of / Vi) is considerably accurate.
Therefore, when verifying whether or not the tennis ball is within the scope of the present invention, it is sufficient to use (Vf / Vi) measured under any one of the conditions within the allowable range. And it was measured under any one condition (Vf / Vi)
Is equal to or greater than 0.685 and when (Vf / Vi) satisfies the above formula (I), the tennis ball is included in the scope of the present invention.

[0016] The measured value of (Vf / Vi) is affected by the type of tennis court. In the present invention, an artificial turf coat containing sand (trade name “Omnicoat LT2” of Sumitomo Rubber Industries, Ltd.)
0 ”) is measured (Vf / Vi). In this artificial turf coat with sand, the mass per 10,000 m is 80.
An artificial turf made of polypropylene having a length of about 19.0 mm and a weight of about 00 g is provided at a basis weight of 980 g per square meter. In this artificial turf coat containing sand, sand having an average particle diameter of about 0.5 mm is uniformly filled at a filling amount of 25 kg per square meter.

In this tennis ball 1, FD and (Vf /
Vi) satisfies the relationship of the above formula (I). That is,
(Vf / Vi) is equal to or less than the value of (0.152 × FD), and (Vf / Vi) is equal to or more than the value of (0.116 × FD). Thereby, as described above, (Vf / Vi)
Is set to 0.685 or more, so that the player can obtain a good shot feeling while improving the sense of speed.

When (Vf / Vi) is larger than (0.152 × FD), the FD becomes relatively small, the impact upon hitting the ball becomes large, and the shot feeling may be deteriorated. From this viewpoint, (Vf / Vi) is (0.144 × F
It is preferably not more than the value of D). Conversely, (Vf / V
If i) is smaller than (0.116 × FD), the FD becomes relatively large, and the player feels heavier on the tennis ball 1, which may also deteriorate the shot feeling.
From this viewpoint, (Vf / Vi) is (0.120 × FD)
Is preferably equal to or greater than

The FD is measured in accordance with "Ball Forward Deformation" which is a standard of the International Federation of Tennis. In this measurement method, the tennis ball 1 is first compressed by 2.54 cm in each of three orthogonal directions (X axis, Y axis and Z axis). Within two hours after the compression in three directions is repeated three times, the FD is measured by the steven compression tester. Specifically, the deformation amount (m) of the tennis ball 1 from the state in which the initial compression load of 15.435 N is applied to the state in which the final compression load of 80.017 N is applied to the tennis ball 1
m) is measured. The measurement is performed in three directions of the X-axis, the Y-axis, and the Z-axis, and the average value of the three measured values is defined as the FD. The measurement is performed in an atmosphere at a temperature of 20 ° C. and a relative humidity of 60%.

Generally, in the tennis ball 1, (Vf / Vi) tends to increase as the amount of fluff of the melton layer 3 decreases, and (Vf / Vi) tends to decrease as the amount of fluff increases. Further, as the thickness of the core 2 becomes larger (Vf / V
i) tends to increase and the FD tends to decrease, and conversely, as the thickness decreases, (Vf / Vi) decreases and the FD tends to increase. Further, the higher the crosslinking density of the core 2 (Vf
/ Vi) tends to increase and the FD tends to decrease. Conversely, the lower the ratio, the lower the (Vf / Vi) tends to increase the FD. Furthermore, the higher the internal pressure of the core 2 (Vf
/ Vi) tends to increase and the FD tends to decrease. Conversely, the lower the ratio, the lower the (Vf / Vi) tends to increase the FD. By adjusting the fuzz amount of the melton layer 3, the core thickness, the crosslinking density of the core 2, the internal pressure and the like to appropriate values, (Vf / Vi) becomes 0.685 or more, and F
D and (Vf / Vi) satisfy the relationship of the above formula (I).

Particularly, the relation between (Vf / Vi) of 0.685 or more and FD and (Vf / Vi) satisfying the above-mentioned formula (I) by the core composition which is relatively flexible but has low energy loss and high repulsion. Are more easily achieved. Examples of such a core compound include a rubber composition containing a small amount of a filler. In addition, by devising the type and amount of the crosslinking agent, crosslinking assistant, vulcanization accelerator, etc., the core 2 having the most efficient crosslinking density can be obtained in the compounding system. (Vf / Vi), and the relationship between FD and (Vf / Vi) satisfying the above formula (I) are more easily achieved.

The core 2 is usually a crosslinked rubber molding. As the base rubber used for the core 2, natural rubber (N
R), polybutadiene (BR), styrene-butadiene copolymer (SBR), polyisoprene (IR) and the like. Further, syndiotactic-1,2-polybutadiene (VCR), high styrene resin and the like are also suitably used as the base rubber. These base rubbers may be used alone or in combination of two or more.
Preferred examples of the combined use of the base rubber include, for example, natural rubber in which 80% by mass or less of syndiotactic-1,2-polybutadiene and 30% by mass or less of high styrene resin are blended.

The core 2 may contain an inorganic filler. Suitable inorganic fillers include, for example, magnesium carbonate, zinc white, clay, calcium carbonate, silica, talc and the like. These inorganic fillers may be used alone, or two or more kinds may be used in combination. The amount of the inorganic filler is not particularly limited, but is preferably 30 parts or more and 95 parts or less, particularly preferably 50 parts or more and 85 parts or less with respect to 100 parts of the base rubber. If the blending amount of the inorganic filler is optimized, the values of FD and (Vf / Vi) tend to be within desired ranges. In addition, in this specification, the numerical value shown by "part" means a ratio based on mass.

The form of crosslinking of the core 2 is not particularly limited, but sulfur crosslinking is usually employed. The blending amount of sulfur is preferably 2.0 parts or more and 10.0 parts or less with respect to 100 parts of the base rubber, and particularly preferably 3.0 parts or more and 6.5 parts or less. In the case of sulfur crosslinking, a thiazole-based vulcanization accelerator, a sulfenamide-based vulcanization accelerator, a guanidine-based vulcanization accelerator, or the like may be used as a crosslinking modifier. These vulcanization modifiers may be used alone or in combination of two or more. The compounding amount of the vulcanization modifier is usually 7.0 parts or less, particularly 0.5 part or more and 5.0 parts or less, and more preferably 2.0 parts or more and 5.0 parts or less based on 100 parts of the base rubber. You. The core 2 may be blended with an anti-scorch agent such as phthalic anhydride and salicylic acid, if necessary. If a preferable type of the vulcanization regulator and the scorch inhibitor is selected, and if the amounts of the sulfur, the vulcanization regulator and the scorch inhibitor are optimized, the values of FD and (Vf / Vi) are within the desired ranges. It is easy to be.

If the thickness of the core 2 is optimized, the values of FD and (Vf / Vi) tend to be within desired ranges. Specifically, the thickness of the core 2 is preferably from 3.0 mm to 4.8 mm, and particularly preferably from 3.2 mm to 4.5 mm. If the thickness is less than the above range, the resilience of the tennis ball 1 may be reduced and the sense of speed may be deteriorated. Conversely, if the thickness exceeds the above range, the impact force may increase and the shot feeling may decrease.

The inner and outer diameters of the core 2 are appropriately set so that the thickness is within the above range. The preferred inner diameter is 50.
3 mm or more and 55.3 mm or less, particularly 50.9 mm or more and 54.7 mm or less. The preferred outer diameter is 5
9.5 mm or more and 61.5 mm or less, particularly 59.8 mm
It is at least 61.3 mm. If the outer diameter is too small, the impact force at the time of hitting the ball may increase. Conversely, if the outer diameter is too large, the air resistance may increase and the sense of speed may decrease.

The melton layer 3 is made of a felt-shaped and gourd-shaped (dumbbell-shaped) meltton cloth that is attached to the core 2. If the thickness of the melton cloth is optimized, FD and (Vf / V
The value of i) tends to be within a desired range. Specifically, the thickness of the melton cloth is preferably 2.5 mm or more and 3.8 mm or less, and particularly preferably 2.7 mm or more and 3.7 mm or less. When the thickness is less than the above range, the ball speed becomes high and the vibration absorption is poor, so that the impact is easily transmitted to the player, and the shot feeling may be reduced.
Conversely, if the thickness exceeds the above range, the air resistance increases, the ball speed decreases, and the sense of speed may decrease.

Here, an example of a method for manufacturing the tennis ball 1 of the present invention will be described. First, a rubber composition is obtained by kneading a base rubber, a crosslinking agent, a filler, and the like with a kneader, a Banbury mixer, an open roll, or the like. Next, this rubber composition is extruded by a screw type extruder, a vacuum press type extruder, or the like, and is put into a mold having an outer mold having a hemispherical cavity and an inner mold having a hemispherical convex portion. Then, the crosslinking temperature is from 140 ° C. to 160 ° C., and the crosslinking time is from 0.5 minute to 10 minutes.
Heating and pressurizing under the condition of 1 minute to obtain a hemispherical half shell. An adhesive is applied to the edge of the half shell, and 2
The half shells are joined so that their edge portions come into contact with each other to obtain a spherical body. The spherical body is put into a mold, and heated and pressed under the conditions of a crosslinking temperature of 145 ° C. to 175 ° C. and a crosslinking time of 4 minutes to 12 minutes to obtain a core 2. When the internal pressure of the core 2 needs to be increased, for example, ammonium chloride and sodium nitrite are charged into the spherical body, and nitrogen gas may be generated by a thermal reaction at the time of crosslinking the spherical body. Also, when the spherical body is pressed, the internal pressure of the mold is set to 0.06.
The internal pressure of the core 2 may be increased by bonding the half shells at a pressure from about MPa to about 0.11 MPa.

On the other hand, two melton cloths punched in a gourd shape are prepared and attached to the surface of the core 2.
This is put into a mold and the crosslinking temperature is from 120 ° C. to 150 ° C.
The melt ball 3 is formed by heating and pressurizing at a temperature of 7 ° C. and a crosslinking time of 7 to 20 minutes to obtain the tennis ball 1. By applying an adhesive also to the edge of the melton cloth at the time of bonding the melton cloth, a seam in which the adhesive has solidified is formed between the two melton cloths. In addition, since the surface roughness of the core 2 is previously increased by sandblasting, sandpaper polishing, or the like, the adhesion between the core 2 and the melton layer 3 is improved.

[0030]

EXAMPLES Hereinafter, the effects of the present invention will be clarified based on examples, but it is needless to say that the present invention should not be construed as being limited based on the description of the examples.

Example 1 100 parts of natural rubber, clay 3
8 parts, magnesium carbonate 40 parts, silica 4 parts, salicylic acid 0.2 parts, stearic acid 1 part, zinc white 5 parts, N-cyclohexyl-2-benzothiazolylsulfenamide 2 parts as vulcanization modifier, etc. 1,3 as vulcanization modifiers
After 3 parts of diphenylguanidine and 6.5 parts of sulfur were charged into a kneader and kneaded, the mixture was extruded with an extruder to obtain a rubber composition. Next, this rubber composition is charged into a mold having an outer mold having a hemispherical cavity and an inner mold having a hemispherical convex portion, and heated and pressed at 160 ° C. for 3 minutes to crosslink the rubber composition. Thus, a hemispherical half shell was obtained. Next, the two half shells were joined with an adhesive to obtain a spherical body. This spherical body is put into a mold, heated and pressed at 165 ° C. for 5 minutes,
Got the core. In addition, it is 97 mass% beforehand in the spherical body.
215 mg of tablets containing ammonium chloride and 3% by mass of a binder and 280 mg of tablets containing 96% by mass of sodium nitrite and 4% by mass of a binder were charged, and nitrogen gas was generated during heating and pressurization. . The thickness of the core was 3.4 mm. The surface of the core was subjected to a sandblast treatment to increase the surface roughness. On the other hand, two melton cloths having a thickness of 2.8 mm punched out in a gourd mold were prepared, and these were adhered to the surface of the core with an adhesive to form a melton layer. This is put into a mold,
For 10 minutes to obtain a tennis ball of Example 1.

[Examples 2 to 9 and Comparative Examples 1 to 5] Except that the types and amounts of the components of the core, the thickness of the core and the thickness of the melton cloth were as shown in Tables 1 and 2, In the same manner as in Example 1, Examples 2 to 9 and Comparative Example 1
Got 5 tennis balls.

[0033]

[Table 1]

[0034]

[Table 2]

The details of the compounding agent and the melton cloth used in each of the examples and comparative examples are as follows. Natural rubber: ribbed smoked sheet (RSS) # 3 Syndiotactic-1,2-polybutadiene: trade name “VCR412” of Ube Industries, Ltd. high styrene resin: trade name “Nippol 2007J” of Zeon Corporation Polyethylene powder: Mitsui Chemicals Brand name “Miperone X17220” Vulcanization regulator N-cyclohexyl-2-benzothiazolylsulfenamide: Ouchi Shinko Chemical Co., Ltd. “Noxeller CZ” Vulcanization regulator 1,3 diphenylguanidine: Ouchi Noxeller D, a brand name of Shinko Chemical Co., Ltd. Vulcanization modifier dibenzothiazyl sulfide: Noxeller DM, a name of Ouchi Shinko Chemical Co., Ltd. Melton Cross: manufactured by Milliken

[Measurement of Diameter and Mass] The diameter and mass of each tennis ball were measured. These results are shown in Table 3 below.
And in Table 4.

[Measurement of FD] In accordance with the standard of the International Tennis Federation “Ball Forward Deformation”,
FD (mm) was measured. The results are shown in Tables 3 and 4 below.

[Measurement of (Vf / Vi)] The incident speed Vi (m / s), the incident angle (deg), and the reflection speed are measured by a high-speed video camera according to the rules of the international tennis standard (ITF CS 01/01). Vf (m / s) and reflection angle (d
eg) was measured. The measurement was performed under the conditions of a temperature of 19 ° C. and a relative humidity of 57%. As the tennis court, the above-mentioned artificial turf court containing sand (trade name “Omni Court LT20” of Sumitomo Rubber Industries, Ltd.) was used. Then, from the incident speed Vi and the reflection speed Vf, (Vf / V
The value of i) was calculated. The results are shown in Tables 3 and 4 below.

[Actual hit evaluation] 5 including 2 professional players
Zero senior players were given the same racket and made a rally using the tennis balls of each example and each comparative example. A sense of speed (the speed at which the tennis ball was hit at the moment the tennis ball hit the racket and The extent to which the tennis ball bounces on the tennis court.
Low impact (the degree of force transmitted to the hand or arm when the tennis ball hits the racket) and lightness (good or bad ball separation when the tennis ball hits the racket, feeling of impact sound, etc.) About the degree). And it evaluated by the following method. Sense of speed (the number of players who answered that there was a sense of speed) ◎: 45 or more ○: 35 or more and less than 45 □: 35 or more and less than 45 △: 25 or more and less than 35 ×: less than 15 Minimal impact (number of players who answered that the impact felt by the hand was small (small)) ◎: 45 or more ○: 35 or more and less than 45 □: 35 or more and less than 45 △: 25 or more and less than 35 ×: less than 15 ・ Lightness (number of players who answered light) ◎: 45 or more ○: 35 or more but less than 45 □: 35 or more and less than 45 △: 25 or more and less than 35 ×: 15 Less than These results are shown in Tables 3 and 4 below.

[0040]

[Table 3]

[0041]

[Table 4]

In Table 4, (Vf / Vi) is (0.1
The tennis balls of Comparative Example 1, Comparative Example 2, and Comparative Example 5 smaller than (16 × FD), (Vf / Vi) being (0.152 ×
Comparative Example 3 tennis ball larger than (FD) and (V)
In the tennis ball of Comparative Example 4 in which f / Vi) is smaller than 0.685, one of the evaluation items is “×”. On the other hand, as shown in Table 3, (Vf / V
i) is equal to or greater than the value of (0.116 × FD) and (0.
In the tennis ball of each embodiment that is equal to or less than (152 × FD) and equal to or more than 0.685, all the evaluation items are “項目” or more. In particular, Examples 2, 3, 4,
For the tennis balls 6, 7, and 8, all the evaluation items are “○” or more.

FIG. 2 shows FD and (Vf) in Tables 3 and 4.
/ Vi) is a graph with the horizontal axis and the vertical axis respectively. In this graph, all the examples show straight lines A, D
And E, and all comparative examples are outside this area. From this, (Vf / Vi) becomes
(0.116 × FD) or more, and (0.152 × FD)
It can be understood that the evaluation of the tennis ball is high when the value is equal to or less than the value of FD) and equal to or more than 0.685. Further, the embodiment in the region surrounded by the straight lines B, C and E is an embodiment with a particularly high evaluation. From this, (Vf / Vi) is equal to or more than the value of (0.120 × FD) and (0.144 × FD).
× FD) is preferred. From these evaluation results, the superiority of the present invention was confirmed.

[0044]

As described above, by using the tennis ball of the present invention, the player can obtain both a good feeling of speed and a good shot feeling.

[Brief description of the drawings]

FIG. 1 is a partially cutaway sectional view showing a tennis ball according to an embodiment of the present invention.

FIG. 2 is a graph showing evaluation results of tennis balls according to an example of the present invention and a comparative example.

[Explanation of symbols]

 1. Tennis ball 2. Core 3. Melton layer

Claims (2)

[Claims] 1. An incident angle of 16 ° ± 2 ° and a speed of 30 m /
It is the ratio of the reflection velocity Vf to the incident velocity Vi when colliding with the tennis court under the condition of s ± 2 m / s (Vf /
Vi) is equal to or greater than 0.685, and (Vf / V
A tennis ball in which i) and the FD (mm), which is the value of the fore deformation measured according to the International Tennis Federation's standards, satisfy the following formula (I). 0.116 × FD ≦ (Vf / Vi) ≦ 0.152 × FD (I) 2. The tennis ball according to claim 1, wherein (Vf / Vi) and FD (mm) satisfy a relationship represented by the following equation (II). 0.120 × FD ≦ (Vf / Vi) ≦ 0.144 × FD (II)