JP2003019229A - Tennis ball - Google Patents

Abstract

(57) [Summary] [Problem] To provide a tennis ball 1 having a seam portion excellent in appearance and durability even after being used at a new stage. A tennis ball includes a core, two felt portions, and a seam portion. Seam part 4
Is formed by adhering a rubber paste containing a rubber composition to the felt portion 3 before being attached to the core 2 and vulcanizing the rubber composition. This rubber composition
100 parts of a base rubber, 1.0 to 3.0 parts of a thiazole-based vulcanization accelerator, and 0.1 to 1.5 parts of a dithiocarbamate-based vulcanization accelerator. I have. The viscosity of rubber paste is 140dPa.s or more and 200dPa.s
The following is preferred. The hardness of the seam portion 4 is preferably 40 or more and 60 or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tennis ball used for hard tennis, and more particularly to a tennis ball having an improved seam portion which constitutes a part of the outer skin.

[0002]

2. Description of the Related Art A tennis ball has a core made of rubber and a hollow sphere, and two felt portions (also called "meltons") covering the surface of the core. The felt portion has a dumbbell shape and is attached to the surface of the core with an adhesive. The gap between the felt parts is a seam part. The seam portion is formed by crosslinking the rubber composition. Usually, crosslinking with sulfur (that is, vulcanization) is adopted, and a vulcanization accelerator is used together. The rubber composition contains a colorant such as titanium oxide. The seam is almost white due to the addition of titanium oxide. On the other hand, the felt part is dyed in a chromatic color (usually yellow).

An example of a seam forming method is disclosed in Japanese Examined Patent Publication No. 63-
It is disclosed in Japanese Patent Publication No. 21544. In this method, the felt part before being attached to the core is immersed in rubber latex with the front and back surfaces masked,
Be lifted. By the immersion, rubber latex adheres to the side surface of the felt portion. This rubber latex is vulcanized after the felt portion is attached to the core.

Since rubber latex generally has a low viscosity,
The immersion greatly penetrates the inside of the felt part.
Therefore, the apparent width of the seam portion tends to be extremely thick, and the width tends to be uneven. A tennis ball provided with such a seam portion has an inferior appearance.

Rubber glue is often used instead of rubber latex. The rubber paste is a rubber composition dissolved in a solvent. Rubber glue is clearly distinguished from rubber latex in that it is not a dispersion. With rubber glue, the viscosity can be easily adjusted by adjusting the amount of solvent. Since the degree of penetration during immersion is controlled by this viscosity adjustment, the tennis ball using rubber paste has an excellent appearance.

[0006]

When a tennis ball is used for playing tennis and bounces on the ground, the outer surface of the seam portion comes into contact with the ground due to deformation of the felt portion and the core, and rubs against the ground. When the bouncing is repeated, the surface roughness of the seam portion gradually increases. For seams with high surface roughness,
Dirt components easily migrate from the ground. The migration contaminates the seam and darkens it. As described above, since the seam portion is white when it is new, contamination is conspicuous and the appearance of the tennis ball is significantly impaired.

[0007] A tennis ball loses air from the core after being used for a long period of time, and the felt portion is worn away, so that the life of the tennis ball will eventually expire. A tennis ball that has reached the end of its life interferes with play and is discarded.

Since the appearance of a tennis ball having a contaminated seam portion is poor, it may be misunderstood that it has reached the end of its life even if it has not reached its end of life, and it may be discarded. Such unnecessary disposal is uneconomical and is not preferable from the viewpoint of resource saving. In addition, at facilities that let customers use tennis balls (for example, tennis schools), it is misunderstood by customers that they are providing old tennis balls even though they are providing tennis balls that are not problematic in terms of performance. There is also a business problem that it will end up.

Means for increasing the hardness of the seam portion by increasing the amount of sulfur blended can be considered. Since the seam portion having high hardness is evenly worn, the surface roughness is unlikely to increase and contamination is suppressed. However, when a large amount of sulfur is blended, the seam portion may be embrittled, and the sulfur may bloom so that the appearance may be deteriorated. Means for increasing the hardness of the seam portion by increasing the blending amount of the vulcanization accelerator can be considered. However, simply increasing the blending amount of the vulcanization accelerator deteriorates the color of the seam portion, resulting in poor appearance.

The present invention has been made in view of the above problems, and an object thereof is to provide a tennis ball which is excellent in the appearance of the seam portion at a new stage, has a good appearance of the seam portion for a long time, and is excellent in durability. It is what

[0011]

The invention made to achieve the above object is to provide a hollow core made of an elastic material,
The rubber composition includes two felt portions covering the core and a seam portion positioned in a gap between the felt portions, and the seam portion is included in the rubber paste attached to the side surface of the felt portion. Is formed by vulcanization of 100 parts of the base rubber and 1.
0 parts or more and 3.0 parts or less of a thiazole vulcanization accelerator,
A tennis ball containing 0.1 part or more and 1.5 parts or less of a dithiocarbamate vulcanization accelerator.

In this tennis ball, since rubber glue is used, an appropriate and uniform seam width can be achieved. In this tennis ball, since the kind and amount of the vulcanization accelerator compounded in the seam portion are devised, the high hardness of the seam portion is achieved without causing yellowing or bloom. Since the seam portion is less likely to be contaminated, the good appearance of the seam portion is maintained for a long time.

Preferably, the viscosity of the rubber paste at 20 ° C. is 140 dPa · s or more and 200 dPa · s or less. This further improves the appearance of the seam portion at the new stage. The viscosity is measured with a Rion viscometer.

Preferably, the hardness of the seam portion measured by a type A durometer (hereinafter also referred to as "A hardness")
Is 40 or more and 60 or less. This seam is tough and is unlikely to be contaminated by repeated bouncing.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on preferred embodiments with reference to the drawings.

FIG. 1 is a partially cutaway sectional view of a tennis ball 1 according to an embodiment of the present invention. The tennis ball 1 includes a core 2, two felt portions 3 and a seam portion 4. The core 2 is a hollow sphere and is made of vulcanized rubber (that is, elastic material). The thickness of the core 2 is usually about 3 mm to 4 mm. In core 2,
An internal pressure (relative to atmospheric pressure) of about 80 KPa is applied.
Thereby, the resilience performance is imparted to the tennis ball 1.
The felt portion 3 covers the surface of the core 2. The felt portion 3 is attached to the surface of the core 2 with an adhesive. The shape of the felt portion 3 before being attached is a dumbbell shape.

FIG. 2 is an enlarged sectional view showing a part of the tennis ball 1 shown in FIG. As you can see from this figure,
The seam portion 4 is located in the gap between the felt portions 3 and 3. The outer surface (upper surface in FIG. 2) of the seam portion 4 is
It is depressed from the outer surface (outer peripheral surface) of the felt portion 3. In this figure, the boundary between the seam portion 4 and the felt portion 3 is clearly drawn for convenience, but in the actual tennis ball 1, the rubber glue penetrates into the felt portion 3, so the boundary between the two is ambiguous.

The seam portion 4 is formed by vulcanizing the rubber composition. The base rubber of the rubber composition is not particularly limited, but it is a natural rubber because it has good followability to the compressive deformation of the tennis ball 1 at the time of hitting, can be obtained at low cost, and improves the shot feeling of the tennis ball 1. Preferably, polyisoprene or polybutadiene is used. Natural rubber, polyisoprene or polybutadiene may be used in combination with other rubbers, but in this case also, natural rubber, polyisoprene and polybutadiene are the main components of the base rubber (50% by mass or more, particularly 75% by mass or more). ) Is preferred.

For the vulcanization of the rubber composition, a thiazole vulcanization accelerator and a dithiocarbamate vulcanization accelerator are used together with sulfur. Unlike other vulcanization accelerators (for example, sulfenamide-based vulcanization accelerators), the thiazole-based vulcanization accelerator has a large amount of the seam portion 4 even if its content is increased for the purpose of increasing the hardness of the seam portion 4. Never turn yellow. In other words, by optimizing the blending amount of the thiazole vulcanization accelerator, both contamination and yellowing are prevented. When the thiazole-based vulcanization accelerator is used alone, the vulcanization rate is slow and the productivity of the tennis ball 1 is reduced. By using the thiazole vulcanization accelerator and the dithiocarbamate vulcanization accelerator in combination, the appearance of the seam portion 4 and the productivity of the tennis ball 1 are compatible with each other.

Specific examples of the thiazole vulcanization accelerator include dibenzothiazyl disulfide (for example, trade name "NOXCELLER DM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) and 2-mercaptobenzothiazole (for example, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.). Trade name "NOXCELLER M"), 2-mercaptobenzothiazole zinc salt (for example, trade name "NOXCELLER MZ" of Ouchi Shinko Chemical Industry Co., Ltd.), 2-mercaptobenzothiazole cyclohexylamine salt (for example of Ouchi Shinko Chemical Industry Co., Ltd.) Trade name "NOXCELLER M-60-OT"), 2- (N, N-diethylthiocarbamoylthio) benzothiazole (for example, trade name "NOXCELLER 64" of Ouchi Shinko Chemical Industry Co., Ltd.) and 2-
Examples include (4′-morpholinodithio) benzothiazole (for example, trade name “NOXCELLER MDB” manufactured by Ouchi Shinko Chemical Industry Co., Ltd.). Of these, dibenzothiazyl disulfide is preferable.

Specific examples of the dithiocarbamate vulcanization accelerator include zinc diethyldithiocarbamate (for example, trade name "NOXCELLER EZ" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) and zinc dimethyldithiocarbamate (for example, Ouchi Shinko Chemical Co., Ltd.). Brand name "NOXCELLER PZ"), zinc dibutyldithiocarbamate (eg brand name "NOXCELLER BZ" from Ouchi Shinko Chemical Industry Co., Ltd.) and tellurium diethyldithiocarbamate (eg brand name "NOXCELLER TT" from Ouchi Shinko Chemical Industry Co., Ltd.
TE ”). Of these, zinc diethyldithiocarbamate is preferable.

The amount of the thiazole vulcanization accelerator compounded is 1.0 part or more and 3.0 parts or less with respect to 100 parts of the base rubber. If the blending amount is less than the above range, the seam portion 4 has a low hardness, and the surface roughness is likely to increase, and thus the contamination tends to occur. From this viewpoint, the content is more preferably 1.2 parts or more, and particularly preferably 1.6 or more. If the blending amount exceeds the above range, the hardness of the seam portion 4 becomes too high, and the seam portion 4
Tend to become brittle and chip during use. From this viewpoint, the blending amount is more preferably 2.8 parts or less, and particularly preferably 2.4 parts or less. As used herein, "part"
The term means mass ratio (parts by weight).

The compounding amount of the dithiocarbamate vulcanization accelerator is 0.1 part or more and 1.5 parts or less with respect to 100 parts of the base rubber. If the blending amount is less than the above range, it takes a long time for vulcanization, and the seam portion 4 has low hardness and is easily contaminated. From this point of view, the compounding amount is more preferably 0.4 part or more. If the blending amount exceeds the above range, the vulcanization reaction of the rubber composition may be rapid and it may be difficult to control the physical properties of the seam portion 4. From this viewpoint, the compounding amount is more preferably 1.4 parts or less, and particularly preferably 0.8 parts or less.

Other vulcanization accelerators may be used in combination with the thiazole vulcanization accelerator and dithiocarbamate vulcanization accelerator. However, since other vulcanization accelerators may lead to a decrease in whiteness of the seam portion 4, insufficient hardness, and a decrease in production efficiency, the content thereof should be as small as possible. In particular,
The ratio of the total amount of the thiazole vulcanization accelerator and the dithiocarbamate vulcanization accelerator to the total vulcanization accelerator is 70.
It is made to be not less than mass%, more preferably not less than 85 mass%, and especially not less than 100 mass%.

The content of sulfur is preferably 1.0 part or more and 4.0 parts or less with respect to 100 parts of the base rubber. If the blending amount is less than the above range, the seam portion 4 may have insufficient strength. From this viewpoint, the blending amount is more preferably 2.0 parts or more. If the content of sulfur exceeds the above range, defective appearance due to chipping of the seam portion 4 or blooming is likely to occur. From this point of view, the content is particularly preferably 3.5 parts or less.

The rubber composition preferably contains 5 parts by weight or more and 30 parts by weight or less of titanium oxide based on 100 parts of the base rubber. Since titanium oxide functions as a white pigment, the whiteness of the seam portion 4 is increased and the appearance is improved by blending titanium oxide. Moreover, the titanium oxide is mixed in the seam 4
Also contributes to higher hardness. From this viewpoint, the blending amount is more preferably 8 parts or more, particularly preferably 12 parts or more. If the blending amount is too large, the seam portion 4 becomes too hard, so
The compounding amount is more preferably 25 parts or less, particularly preferably 20 parts or less.

A filler other than titanium oxide (magnesium carbonate, calcium carbonate, clay, etc.) may be appropriately blended in the rubber composition. A cross-linking aid such as zinc oxide, an antioxidant and other additives may be added to the rubber composition in an appropriate amount, if necessary.

In the manufacture of this tennis ball 1, first, the woven felt is cut into a dumbbell shape to form the felt portion 3. Next, a rubber composition having a predetermined composition is dissolved in an organic solvent such as naphtha to obtain rubber paste. With this rubber glue,
The felt portion 3 in which a large number of sheets are stacked is immersed. By the immersion, the rubber paste adheres to the cut surface (side surface) of the felt portion 3. The felt portion 3 is attached to the core 2 with an adhesive and is pressed and heated. Then, the rubber in the rubber paste is vulcanized, the seam portion 4 is formed, and the tennis ball 1 is completed.

The viscosity of the rubber paste is adjusted by adjusting the amount of the organic solvent. The viscosity is preferably 140 dPa · s or more and 200 dPa · s or less. If the viscosity is less than the above range, the rubber paste may excessively penetrate into the felt portion 3 and the appearance of the seam portion 4 at the new stage may be deteriorated. From this viewpoint, the viscosity is particularly preferably 160 dPa · s or more. If the viscosity exceeds the above range, the amount of rubber glue attached to the felt portion 3 may increase and the width of the seam portion 4 may become thicker than an appropriate value. From this viewpoint, the viscosity is 180 dP
It is particularly preferably a · s or less. The viscosity is measured with a Rion viscometer. The measurement temperature is 20 ° C.

The width of the seam portion 4 (indicated by a double-headed arrow W in FIG. 2) is not limited, and is 1.0 mm to 5.0 mm.
It is appropriately set within the range. Width W is 1.0 mm or more and 3.0
If it is made smaller than 1.0 mm, particularly 1.0 mm or more and 2.7 mm or less, the felt portions 3 on both sides of the seam portion 4 play a role of a bridge girder even when the tennis ball 1 bounces on the ground.
The outer surface of the seam portion 4 is hard to be grounded. Therefore, the seam section 4
Pollution is suppressed. Even if the seam portion 4 is contaminated, if the width W is small, the area ratio of the seam portion 4 occupying the outer peripheral surface of the tennis ball 1 is small, so that the dirt is not noticeable.

In measuring the width W, the boundary between the seam portion 4 and the felt portion 3 is visually determined. From the external observation of the tennis ball 1, a boundary between the seam portion 4 (usually white) area and the felt portion 3 color (usually yellow) is determined, and this boundary is formed between the seam portion 4 and the felt portion 3. Is the boundary of. The interval between the left and right boundaries of the seam portion 4 is the width W.

The A hardness of the seam portion 4 is preferably 40 or more and 60 or less. If the A hardness is less than the above range, the surface roughness of the seam portion 4 tends to increase due to bouncing, and the tackiness of the seam portion 4 tends to increase. In the seam portion 4 having high surface roughness and high adhesiveness, dirt components are easily transferred from the ground. From this viewpoint, the A hardness is particularly preferably 45 or more. If the A hardness exceeds the above range, the seam portion 4
Becomes brittle and is likely to chip when hit or bound. From this viewpoint, the A hardness is preferably 57 or less. A hardness is
It is measured with a type A durometer according to "JIS K 6253". For the sake of convenience, a rubber sheet having a thickness of 2.0 mm, which is obtained by vulcanizing a rubber composition having the same composition as the seam portion 4 under the same conditions as the seam portion 4, is used as a measurement sample. Two sheets of this sheet are overlaid and the hardness is measured.

[0033]

EXAMPLES The effects of the present invention will be clarified below based on Examples, but the present invention should not be construed in a limited way based on the description of the Examples.

[Example 1] A rubber composition containing natural rubber, sulfur, a vulcanization accelerator, an inorganic filler and the like was vulcanized,
A hemispherical half shell was formed. This half shell 2
The pieces were attached to each other to obtain a hollow spherical core. Moreover, the woven felt was punched out to obtain many dumbbell-shaped felt parts.

On the other hand, 100 parts of natural rubber, 5.0 parts of zinc oxide (trade name "Zinc Hua No. 1" of Mitsui Mining & Smelting Co., Ltd.), 5.0 parts of magnesium carbonate ("2 star" of Fukushima Chemical Industry Co., Ltd.) ,
Titanium oxide (trade name "A100" of Ishihara Sangyo Co., Ltd.) 14.
0 part, anti-aging agent (Styrenated Phenol, Kawaguchi Chemical Co., Ltd. trade name “ANTAGE SP-P”) 0.8 part, dibenzothiazyl disulfide as a thiazole vulcanization accelerator (trade name of Ouchi Shinko Chemical Industry Co., Ltd. "Nox Cellar DM") 2.
0 parts, 0.4 parts of zinc diethyldithiocarbamate (trade name "NOXCELLER EZ" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) as a dithiocarbamate vulcanization accelerator and sulfur (trade name "fine sulfur 200 mesh manufactured by Tsurumi Chemical Co., Ltd." ]) 3.0 was kneaded with a roll to obtain a rubber composition. 60% of this rubber composition
A rubber paste having a viscosity of 170 dPa · s was obtained by dissolving in some naphtha.

Then, dozens of the above-mentioned dumbbell-shaped felt parts were overlapped, sandwiched between two end plates, immersed in rubber paste for 20 seconds and pulled up. The rubber paste adhered to the side surface of the felt portion due to the immersion. After the rubber paste was dried, two felt parts were attached to the core with an adhesive and put into a mold. Then, the mold was heated to 135 ° C. and held for 20 minutes to vulcanize the rubber paste and the adhesive to obtain the tennis ball of Example 1.

[Examples 2 to 9 and Comparative Examples 1 to 3] The compounding amounts of the thiazole vulcanization accelerator and the dithiocarbamate vulcanization accelerator in the rubber paste are as shown in Tables 1 and 2 below. In the same manner as in Example 1 except that the variables were changed,
Tennis balls of Examples 2 to 9 and Comparative Examples 1 to 3 were obtained.

[Comparative Example 4] Comparative Example 4 was carried out in the same manner as in Example 1 except that the thiazole vulcanization accelerator was not added and the amount of the dithiocarbamate vulcanization accelerator was 0.6 part. Got a tennis ball.

[Comparative Example 5] 0.5 part of tetramethylthiuram monosulfide (trade name "NOXCELLER TS" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) as a thiuram vulcanization accelerator was used in place of the thiazole vulcanization accelerator. Example 1 except that the content of the dithiocarbamate vulcanization accelerator was 0.3 part.
A tennis ball of Comparative Example 5 was obtained in the same manner as in.

Comparative Example 6 N-cyclohexyl-2-benzothiazolylsulfenamide (sold by Ouchi Shinko Chemical Industry Co., Ltd. as a sulfenamide vulcanization accelerator in place of the thiazole vulcanization accelerator Nox Cellar CZ ") 2.0 was added, but no dithiocarbamate vulcanization accelerator was added, and a tennis ball of Comparative Example 6 was obtained in the same manner as in Example 1.

[Measurement of Hardness] After drying the rubber paste to volatilize the solvent, the remaining rubber composition is put into a mold and put into a mold 135.
The sheet was heated and pressed at 20 ° C. for 20 minutes to obtain a sheet having a thickness of 2.0 mm. Two sheets of this sheet are piled up, and "JIS K
The hardness was measured with a type A durometer according to "6253". The measurement results are shown in Tables 1 and 2 below.

[Measurement of Color Difference] Using a color difference meter (trade name “CR-221” manufactured by Minolta Co., Ltd.), L, a and b of the seam portion of the tennis ball immediately after being manufactured (before use) were measured. Also, using this tennis ball, two senior players were allowed to carry out a rally for 5 minutes on an asphalt hard court, and after that (after use), L, a and b of the seam were measured by the same method. . Here, "L" is an index representing lightness, and "a" and "b" are indices representing hue and saturation. L, a and b are “JIS Z 870”.
1 ”or the tristimulus lines X, Y, and Z defined in“ JIS Z 8728 ”, and are calculated based on the following mathematical formulas. L = 116 × (Y / Yn) ^1/3 −16 a = 500 × ((X / Xn) ^1/3 − (Y / Yn)
^1/3 ) b = 200 × ((Y / Yn) ^1/3 − (Z / Zn)
^1/3 ) In these mathematical expressions, Xn, Yn, and Zn represent tristimulus values in the XYZ system of the perfect diffuse reflection surface. Also, X /
Xn, Y / Yn and Z / Zn are all 0.0088
Greater than 56.

A color difference (ΔE) was calculated from the difference (ΔL, Δa and Δb) between L, a and b before and after use thus calculated based on the following mathematical formula. ΔE = ((ΔL) ² + (Δa) ² + (Δb) ² ) ^1/2 The results are shown in Tables 1 and 2 below. The color difference (ΔE) was measured at three locations for each tennis ball. Shown in Tables 1 and 2 below are average values of three color differences (ΔE).

[Evaluation of Durability] Ten tennis balls of each Example and each Comparative Example were prepared. Then, these were struck on the plate 1000 times at a ball speed of 25 m / s, and the presence or absence of chipping at the seam was visually determined.
The number (ball number) of the ten tennis balls in which any chipping was observed is shown in Tables 1 and 2 below.

[0045]

[Table 1]

[0046]

[Table 2]

As shown in Table 2, Comparative Example 1 containing a small amount of a thiazole vulcanization accelerator, Comparative Examples 4 and 5 containing no thiazole vulcanization accelerator, and a dithiocarbamate vulcanization accelerator. In the tennis ball of Comparative Example 3 containing a small amount of the agent, the color difference (the degree of change in color due to use)
Is big. In the tennis ball of Comparative Example 2 in which the amount of the thiazole-based vulcanization accelerator is large, many chips are generated. The tennis ball of Comparative Example 6 in which the sulfenamide-based vulcanization accelerator was used had a slight hue from the stage before use and had low lightness. On the other hand, the tennis balls of the respective examples have good color before use, there is little color difference before and after the specification, and chipping is unlikely to occur. From this evaluation result, the superiority of the present invention is clear.

[0048]

As is apparent from the above description, the tennis ball of the present invention is misunderstood as having expired its life or misunderstood as being old even though it has not yet expired in terms of performance. There is no. This tennis ball is
Also excellent in durability. This tennis ball can contribute to resource saving.

[Brief description of drawings]

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

FIG. 2 is an enlarged cross-sectional view showing a part of the tennis ball shown in FIG.

[Explanation of symbols]

1 ... Tennis Ball 2 ... core 3 ... felt part 4 ... Seam part

Claims (3)

[Claims] 1. A hollow core made of an elastic material, two felt portions covering the core, and a seam portion located in a gap between the felt portions. The seam portion is a felt portion. Is formed by vulcanizing the rubber composition contained in the rubber paste attached to the side surface of the rubber composition. This rubber composition contains 100 parts of the base rubber and 1.0 part or more and 3.0 parts or less. A tennis ball containing the thiazole-based vulcanization accelerator of 0.1 to 1.5 parts by weight of a dithiocarbamate-based vulcanization accelerator. 2. The viscosity of the rubber paste at 20 ° C. measured by a Rion viscometer is 140 dPa · s or more and 200 d or more.
The tennis ball according to claim 1, which has a Pa · s or less. 3. The tennis ball according to claim 1, wherein a hardness of the seam portion measured by a type A durometer is 40 or more and 60 or less.