JP4112334B2 - Tennis ball - Google Patents

Description

【００４１】
表１に示されるように、実施例のテニスボールは、比較例１から３のテニスボールに比べて耐久性に優れている。しかも、実施例のテニスボールは、比較例２及び４のテニスボールに比べて耐汚染性に優れている。この評価結果より、本発明の優位性は明らかである。
【００４２】
【発明の効果】
以上の説明から明らかなように、本発明のテニスボールではシーム部が汚染されにくく、汚染が目立ちにくい。しかも、本発明のテニスボールは、耐久性に優れる。本発明のテニスボールは、性能上は未だ寿命をむかえていないにもかかわらず寿命をむかえたと誤解されたり、古いものであると誤解されることがない。本発明は、省資源にも寄与しうる。
【図面の簡単な説明】
【図１】図１は、本発明の一実施形態にかかるテニスボールが示された一部切り欠き正面図である。
【図２】図２は、図１のテニスボールの一部が示された拡大断面図である。
【図３】図３は、図１のテニスボールが地面でバウンドする瞬間の状態が示された正面図である。
【符号の説明】
１・・・テニスボール
２・・・コア
３・・・フェルト部
４・・・シーム部
Ｇ・・・地面[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a tennis ball used for hard tennis. More specifically, the present invention relates to a tennis ball having an improved seam portion that constitutes a part of the outer skin.
[0002]
[Prior art]
The tennis ball includes a core made of rubber and a hollow sphere, and two felt parts (also referred to as “Melton”) covering the surface of the core. The felt part has a dumbbell shape and is attached to the surface of the core with an adhesive (rubber paste). The gap between the felt parts is filled with seam glue. This seam glue is adhered to the felt before being attached to the core, for example, by the method disclosed in Japanese Patent Publication No. 63-21544. A seam portion is formed by crosslinking the seam glue. Since the surface of the felt part is fluffy, the outer surface of the seam part is closer to the center in the radial direction than the tennis ball virtual spherical surface (a spherical surface including the outer surface of the felt part and a spherical surface when it is assumed that there is no seam part). To position. That is, the outer surface of the seam portion is recessed from the outer surface of the felt portion.
[0003]
Usually seam glue consists of a rubber composition. In this rubber composition, a base rubber such as natural rubber or polyisoprene is blended with a colorant such as titanium oxide. The seam portion is almost white due to the blending of titanium oxide. On the other hand, the felt part is dyed chromatic (usually yellow).
[0004]
As described above, since the outer surface of the seam portion is depressed from the outer surface of the felt portion, when the tennis ball is placed on the ground, the seam portion does not contact the ground. However, when the tennis ball is used for playing tennis and bounces on the ground, the outer surface of the seam portion contacts the ground due to deformation of the felt portion and the core. This grounding contaminates the seam and darkens it. As described above, since the seam portion is white at the new stage, the contamination is conspicuous and the appearance of the tennis ball is significantly impaired.
[0005]
Tennis balls lose their air from the core after a long period of use, and the felt part wears out. A tennis ball that has reached the end of its life is discarded because it interferes with play. A tennis ball having a contaminated seam portion has a poor appearance, and even if it has not yet reached the end of its performance, it may be misunderstood as having reached the end of its life and discarded. Such unnecessary disposal is uneconomical and is not preferable from the viewpoint of resource saving. For example, in a facility that allows customers to use tennis balls, such as a tennis school, customers are misunderstood that they provide old tennis balls even though they provide tennis balls that are not problematic in terms of performance. There is also a business problem.
[0006]
Japanese Patent Application Laid-Open No. 6-178829 discloses a tennis ball having no seam portion. With this tennis ball, dirt on the seam is not a problem. This tennis ball has an excellent appearance over a long period of time.
[0007]
[Patent Document 1]
Japanese Patent Publication No. 63-21544 [Patent Document 2]
Japanese Patent Laid-Open No. 6-178829
[Problems to be solved by the invention]
The seam portion contributes to relaxation of stress at the time of hitting and bounce. In the above tennis ball having no seam portion, the felt portion may be peeled off by repeated hitting.
[0009]
The present invention has been made in view of such problems, and an object of the present invention is to provide a tennis ball that is not easily contaminated and that is not easily noticeable even when it is contaminated and that has excellent durability.
[0010]
[Means for Solving the Problems]
The tennis ball according to the present invention includes a hollow core made of an elastic material, two felt parts covering the core, and a seam part located in a gap between the felt parts. The width of the seam portion is 0.2 mm or greater and 3.0 mm or less. The tensile strength Tb of the seam material that is a constituent material of the seam portion is 14.7 MPa or more.
[0011]
In this tennis ball, since the width of the seam portion is smaller than that of the conventional tennis ball, it is difficult for the seam portion to contact the ground when the tennis ball bounces on the ground. This seam portion is not easily contaminated. Even when the seam portion is contaminated, the width is small, so that the dirt is hardly noticeable. Furthermore, since the seam portion is excellent in strength, it is difficult to scrape even after repeated use. Seams that are difficult to cut are less susceptible to contamination.
[0012]
Preferably, the elongation at break Eb of the seam material is 500% or more. In this tennis ball, the seam easily follows the deformation of the core. In this seam portion, cracks and peeling from the core are unlikely to occur.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.
[0014]
FIG. 1 is a partially cutaway front view showing a tennis ball 1 according to an embodiment of the present invention. The tennis ball 1 includes a core 2, two felt parts 3, and a seam part 4. The core 2 is a hollow sphere and is formed from a crosslinked rubber (that is, an elastic material). The thickness of the core 2 is usually about 3 mm to 4 mm. An internal pressure (with respect to atmospheric pressure) of about 80 KPa is applied to the core 2. Thereby, the resilience performance is imparted to the tennis ball 1. The felt part 3 covers the surface of the core 2. The felt part 3 is attached to the surface of the core 2 with an adhesive (rubber glue) or the like. The shape of each felt part 3 is a dumbbell shape.
[0015]
FIG. 2 is an enlarged cross-sectional view showing a part of the tennis ball 1 of FIG. As is apparent from this figure, the seam portion 4 is located in the gap between the felt portions 3. The outer surface (upper surface in FIG. 2) of the seam portion 4 is recessed from the outer surface (outer peripheral surface) of the felt portion 3. In this figure, the boundary between the seam part 4 and the felt part 3 is clearly depicted for convenience. However, in the actual tennis ball 1, since the seam glue impregnates the felt part 3, the boundary between the two becomes ambiguous. Yes.
[0016]
The width of the seam portion 4 (indicated by a double arrow W in FIG. 2) is 3.0 mm or less. This width W is smaller than the width (about 3.5 mm to 5.0 mm) of the seam portion of the conventional tennis ball. When the tennis ball 1 bounces to the ground G, as shown in FIG. 3, the felt portions 3 on both sides of the seam portion 4 serve as bridge girders, and the outer surface of the seam portion 4 is difficult to ground. The seam portion 4 is not easily contaminated. Even when the seam portion 4 is grounded and the seam portion 4 is contaminated by the deformation of the tennis ball 1, dirt is not noticeable because the area ratio of the seam portion 4 to the outer peripheral surface of the tennis ball 1 is small.
[0017]
From the viewpoint of preventing contamination, the width W of the seam portion 4 is more preferably 1.5 mm or less, and particularly preferably 1.0 mm or less. If the width W is too small, the stress at the time of impact is difficult to be relaxed, the felt part 3 may be peeled off from the core 2, and cracks may occur in the seam part 4. From the viewpoint of durability of the tennis ball 1, the width W of the seam portion 4 is preferably 0.2 mm or more, more preferably 0.4 mm or more, and particularly preferably 0.5 mm or more.
[0018]
In the measurement of the width W, the boundary between the seam portion 4 and the felt portion 3 is determined by visual observation. From the external observation of the tennis ball 1, the boundary between the seam portion 4 color (usually white) region and the felt portion 3 color (usually yellow) region is determined, and this boundary is the seam portion 4 and the felt portion 3. It is considered as a boundary. The interval between the left and right boundaries of the seam portion 4 is the width W.
[0019]
The tensile strength Tb of the seam material that is a constituent material of the seam portion 4 is 14.7 MPa or more. Even if the seam portion 4 made of the seam material repeatedly collides with the racket or the ground G, the surface thereof is difficult to be scraped. Although the seam portion whose surface has been scraped to increase the roughness is easily soiled, contamination of the seam portion 4 is suppressed by using a seam material having a large tensile strength Tb. From the viewpoint of contamination resistance, the tensile strength Tb of the seam material is more preferably 16.0 MPa or more, and particularly preferably 20.0 MPa or more. In a seam material whose base material is a normally obtained polymer, the tensile strength Tb is 35.0 MPa or less.
[0020]
A seam material having a large tensile strength Tb can be obtained, for example, by the following method.
(1) A base polymer having excellent strength is selected.
(2) A large amount of a crosslinking agent is blended.
(3) A large amount of vulcanization accelerator is blended.
(4) A large amount of filler is blended.
[0021]
The elongation Eb when cutting the seam material is preferably 500% or more. The seam portion 4 using this seam material is excellent in the followability of the core 2 when the tennis ball 1 is deformed. In the seam portion 4, cracking and peeling from the core 2 are unlikely to occur. This tennis ball 1 is excellent in durability. From the viewpoint of durability, the elongation at break Eb is more preferably 530% or more, and particularly preferably 600% or more. A seam material having an extremely large elongation Eb at the time of cutting may cause a decrease in contamination resistance. In this respect, the elongation at break Eb is preferably equal to or less than 900%.
[0022]
The tensile strength Tb and the elongation at break Eb are measured according to the provisions of “JIS K 6301”. For the measurement, a slab having the same composition as the seam portion 4 is used. The thickness of this slab is 2 mm. A rubber composition is put into a mold having a cavity having a height of 2 mm, and a slab is obtained by heating and crosslinking. The crosslinking temperature is 132 ° C. and the crosslinking time is 10 minutes.
[0023]
Although the base rubber of the seam portion 4 is not particularly limited, natural rubber is preferable because it has good followability to the compression deformation of the tennis ball 1 at the time of hitting, is obtained at a low cost, and contributes to the hit feeling of the tennis ball 1. Alternatively, polyisoprene is preferably used. Natural rubber or polyisoprene and other rubber may be used in combination, but even in this case, natural rubber and polyisoprene are the main component of the base rubber (50 mass% or more, particularly 75 mass% or more). Is preferred.
[0024]
The rubber composition of the seam part 4 is preferably blended with 10 to 40 parts by mass of titanium oxide with respect to 100 parts by mass of the base rubber. Since titanium oxide functions as a white pigment, the whiteness of the seam portion 4 is improved by blending it. The compounding of titanium oxide also contributes to improving the strength of the seam portion 4. In this respect, the amount of titanium oxide is more preferably equal to or greater than 12 parts by weight, and particularly preferably equal to or greater than 13 parts by weight. If the blending amount of titanium oxide is too large, the elongation Eb at the time of cutting of the seam part 4 may be lowered. Therefore, the blending amount is more preferably 35 parts by weight or less, and particularly preferably 30 parts by weight or less.
[0025]
Although there is no restriction | limiting in the crosslinked form of a rubber composition, Usually, sulfur bridge | crosslinking is employ | adopted. The blending amount of sulfur is preferably 2.5 parts by mass or more and 6.0 parts by mass or less with respect to 100 parts by mass of the base rubber. There exists a possibility that the intensity | strength of the seam part 4 may become inadequate that the compounding quantity of sulfur is less than the said range. In this respect, the amount of sulfur is more preferably equal to or greater than 3.0 parts by mass. If the blending amount exceeds the above range, the seam portion 4 is likely to be chipped. In this respect, the amount to be blended is more preferably equal to or less than 5.0 parts by weight.
[0026]
A vulcanization accelerator may be used in combination with sulfur. There are no restrictions on the type of vulcanization accelerator, and one of dithiocarbamate vulcanization accelerator, thiazole vulcanization accelerator, sulfenamide vulcanization accelerator, guanidine vulcanization accelerator, etc. Or 2 or more types are selected. A dithiocarbamate vulcanization accelerator and a thiazole vulcanization accelerator are preferred, and it is particularly preferred that these are used in combination. The total amount of the vulcanization accelerator is preferably 0.3 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the base rubber. There exists a possibility that the intensity | strength of the seam part 4 may become inadequate that a compounding quantity is less than the said range. If the blending amount exceeds the above range, the seam portion 4 is likely to be chipped.
[0027]
An appropriate amount of a filler (magnesium carbonate, calcium carbonate, etc.) other than titanium oxide is blended in the rubber composition as necessary. A crosslinking aid such as zinc oxide, an anti-aging agent, and other additives may be blended. From the viewpoint of improving the strength of the seam portion 4, about 0.1 to 5.0 parts by mass of a silane coupling agent may be added to the rubber composition.
[0028]
In the manufacture of the tennis ball 1, the woven felt is first cut into a dumbbell shape to form the felt portion 3. Next, a predetermined rubber composition is dissolved in an organic solvent such as naphtha to obtain a seam paste. The felt part 3 on which a large number of sheets are superimposed is immersed in the seam glue. The seam glue adheres to the cut surface (side surface) of the felt part 3 by dipping. This felt part 3 is affixed to the core 2 with an adhesive, and is pressurized and heated. Then, the base rubber of the seam glue causes a crosslinking reaction, the seam portion 4 is formed, and the tennis ball 1 is completed.
[0029]
After the felt part 3 on which the seam glue is not attached to the cut surface is attached to the core 2, the rubber composition is filled in the gap between the felt parts 3, and the rubber composition is cross-linked so that the seam part 4 is cross-linked. May be formed.
[0030]
【Example】
Hereinafter, the effects of the present invention will be clarified based on examples, but the present invention should not be construed in a limited manner based on the description of the examples.
[0031]
[Example 1]
A rubber composition containing natural rubber, sulfur, a vulcanization accelerator and an inorganic filler was crosslinked to form a hemispherical half shell. Two half shells were bonded together to obtain a hollow spherical core. On the other hand, weaving felt was used to obtain many dumbbell-shaped felt parts.
[0032]
100 parts by mass of natural rubber, 5 parts by mass of zinc oxide (trade name “Zinc Hua 1” from Mitsui Mining & Smelting Co., Ltd.), 6 parts by mass of magnesium carbonate (“2 star” by Fukushima Chemical Co., Ltd.), titanium oxide (Ishihara Sangyo) Company name "A100") 13 parts by weight, anti-aging agent (trade name "ANTAGE SP-P" by Kawaguchi Chemical Co., Ltd.) 0.9 parts by weight, zinc diethyldithiocarbamate (Ouchi Shinsei Chemical) as a vulcanization accelerator 0.4 parts by mass of the trade name “Noxeller EZ” by Kogyo Co., Ltd. 2.0 parts by mass of dibenzothiazyl disulfide (trade name “Noxeller DM” by Ouchi Shinsei Chemical Co., Ltd.) and sulfur as other vulcanization accelerators 3.4 parts by mass were kneaded with a roll to obtain a rubber composition. This rubber composition was dissolved in 60 parts by mass of naphtha to obtain a seam paste.
[0033]
Dozens of dumbbell-shaped felt portions described above were overlapped and sandwiched between two end plates and immersed in seam glue for 20 seconds. The seam glue adhered to the side surface of the felt part by immersion. After the seam paste is dried, two felt parts are attached to the core with an adhesive, and the cross-linking reaction is caused to occur in the seam paste and the adhesive by heating in the mold to obtain the tennis ball of Example 1. It was.
[0034]
[Examples 2 and 5 and Comparative Examples 1 and 4]
The tennis balls of Examples 2 and 5 and Comparative Examples 1 and 4 were the same as Example 1 except that the width W of the seam part was changed as shown in Table 1 below by changing the size of the felt part. Obtained.
[0035]
[Comparative Example 2]
The amount of vulcanization accelerator EZ is 0.2 parts by mass, vulcanization accelerator DM is not added, and other vulcanization accelerators are tetramethylthiuram monosulfide (trade name “Noxeller of Ouchi Shinsei Chemical Industry Co., Ltd.). TS ”) A tennis ball of Comparative Example 2 was obtained in the same manner as Example 1 except that 0.5 part by mass was blended.
[0036]
[Example 4]
Example 1 except that 1.0 part by mass of zinc dibenzyldithiocarbamate (trade name “Noxeller ZTC” from Ouchi Shinsei Kagaku Kogyo Co., Ltd.) was used as another vulcanization accelerator instead of the vulcanization accelerator EZ. Similarly, a tennis ball of Example 4 was obtained.
[0037]
[Example 3 and Comparative Example 3]
Tennis balls of Example 3 and Comparative Example 3 were obtained in the same manner as in Example 1 except that the blending amount of the vulcanization accelerator EZ was changed as shown in Table 1 below.
[0038]
[Evaluation of durability]
Tennis balls were used for two months at a tennis school with a hard court with an asphalt surface. The appearance of the tennis ball after use was visually observed, and the number of the 100 tennis balls in which the seam portion cracked or the felt portion peeled was counted. The case where no cracking or peeling occurs is “A”, the case where the number of cracking or peeling is 1 to 5 is “B”, and the number where cracking or peeling occurs is 6 to 10. The case was “C”, and the case where the number of cracks or peeling was 11 or more was “D”. The results are shown in Table 1 below.
[0039]
[Evaluation of contamination resistance]
Using the tennis ball subjected to the durability evaluation, the degree of contamination of the seam portion was evaluated in four stages from “A” to “D”. The case where the dirt was the least was designated as “A”, and the case where the dirt was the most severe was designated as “D”. The results are shown in Table 1 below.
[0040]
[Table 1]

[0041]
As shown in Table 1, the tennis balls of the examples are superior in durability to the tennis balls of Comparative Examples 1 to 3. Moreover, the tennis balls of the examples are superior in contamination resistance as compared with the tennis balls of Comparative Examples 2 and 4. From this evaluation result, the superiority of the present invention is clear.
[0042]
【The invention's effect】
As is clear from the above description, the seam portion is hardly contaminated and the contamination is not conspicuous in the tennis ball of the present invention. Moreover, the tennis ball of the present invention is excellent in durability. The tennis ball of the present invention is not misunderstood as having a long life even though it has not yet reached its life in terms of performance or being misunderstood as being old. The present invention can also contribute to resource saving.
[Brief description of the drawings]
FIG. 1 is a partially cutaway front view showing a tennis ball according to an embodiment of the present invention.
FIG. 2 is an enlarged cross-sectional view illustrating a part of the tennis ball of FIG. 1;
FIG. 3 is a front view showing a state at a moment when the tennis ball of FIG. 1 bounces on the ground.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Tennis ball 2 ... Core 3 ... Felt part 4 ... Seam part G ... Ground

Claims (2)

A hollow core made of an elastic material, two felt parts covering the core, and a seam part located in a gap between the felt parts,
The width of this seam part is 0.2 mm or more and 3.0 mm or less,
This seam part is formed by crosslinking the rubber composition,
This rubber composition contains 100 parts by mass of base rubber and 2.5 parts by mass or more and 6.0 parts by mass or less of sulfur,
A tennis ball having a seam material constituting the seam portion having a tensile strength Tb of 18.2 MPa to 35 MPa .   The tennis ball according to claim 1, wherein the seam material has an elongation Eb of 500% or more when cut.

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