Tennis ball adhesive

Abstract

To provide an adhesive which is reduced in workload and can produce a tennis ball excellent in durability.SOLUTION: There is provided an adhesive for a tennis ball comprising a base material rubber. The main component of the base material rubber is a liquid rubber having a number average molecular weight of 10000 or more. The adhesive has a shear viscosity of 2000 Pa s or less. The tennis ball has a hollow core composed of a rubber material. The core is formed of two hemispherical half cores. The two half cores are bonded together using the adhesive for a tennis ball.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to adhesives, particularly to adhesives used in the manufacture of tennis balls. [Background technology]

[0002] A tennis ball has a core made of a rubber material. This core is a hollow sphere. The core is formed by bonding two hemispherical half cores together. An adhesive is used to bond the two half cores together. The outer surface of this core is covered with two dumbbell-shaped pieces of felt (also called Melton). An adhesive is also used to bond the Melton to the outer surface of the core. A seam is formed in the gap between the two pieces of Melton. A seam glue made of a rubber composition is used to form the seam.

[0003] Conventionally, solvent-based adhesives have been used in which rubber components, vulcanizing agents, vulcanization accelerators, etc. are dissolved in an organic solvent such as naphtha from the viewpoint of affinity with cores made of rubber material and adhesive strength. For example, Japanese Patent Laid-Open Publication No. 2004-148022 (Patent Document 1) discloses a solvent-based seam glue in which a rubber composition containing a base rubber such as natural rubber, titanium oxide, sulfur, etc. is dissolved in an organic solvent such as naphtha.

[0004] Solvent-based rubber adhesives are typically prepared by kneading solid rubber, such as natural rubber, with fillers, vulcanization accelerators, etc. in a mixer to reduce the molecular weight of the solid rubber, and then dissolving the resulting mixture in an organic solvent to liquefy it. Large amounts of organic solvent are required to dissolve this mixture. Because organic solvents are highly volatile, the viscosity of the adhesive gradually increases during storage and even during operation, making stable use difficult. Another problem is that workers are exposed to volatilized solvents in the work environment. Furthermore, growing concern about environmental issues in recent years has led to demands for the reduction of volatile organic compounds (VOCs).

[0005] For example, Japanese Patent Laid-Open Publication No. 57-179265 (Patent Document 2) discloses a melted seam adhesive based on depolymerized natural or synthetic rubber latex. Japanese Patent Laid-Open Publication No. 58-98372 (Patent Document 3) proposes a melted dumbbell adhesive that blends rubber latex with a high-temperature decomposition vulcanizing agent. Japanese Patent Laid-Open Publication No. 2020-059838 (Patent Document 4) proposes an aqueous adhesive containing rubber latex and a sulfenamide vulcanization accelerator. This aqueous adhesive is used to bond half cores together and vulcanize them. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-148022 [Patent Document 2] Japanese Patent Application Publication No. 57-179265 [Patent Document 3] Japanese Patent Application Publication No. 58-98372 [Patent Document 4] Japanese Patent Application Publication No. 2020-059838 Summary of the Invention [Problem to be solved by the invention]

[0007] When playing tennis, the ball is repeatedly hit. Cores made with adhesives that have weak adhesive strength may be damaged by repeated hits. Thus, to manufacture cores that require durability, an adhesive with excellent adhesive strength is necessary.

[0008] As proposed in Patent Documents 2 to 4, adhesives that use rubber latex as a primary component reduce the amount of organic solvent used, easing the burden on the environment and workers. However, because rubber latex contains a large amount of water with low volatility, the water remaining in the cured adhesive after vulcanization adhesion can affect the adhesive strength and reduce the durability of the tennis ball.

[0009] An object of the present invention is to provide an adhesive that is easy to work with and that can be used to produce tennis balls that are excellent in durability. [Means for solving the problem]

[0010] As a result of extensive research, the present inventors have noticed that the problem of residual moisture in the adhesive layer after vulcanization bonding can be avoided by using a liquid rubber that has fluidity in itself instead of rubber latex that contains a lot of moisture, and have completed the present invention.

[0011] That is, the tennis ball adhesive according to the present invention includes a base rubber, the main component of which is a liquid rubber with a number-average molecular weight of 10,000 or more, and the shear viscosity of the adhesive is 2,000 Pa s or less.

[0012] Preferably, the liquid rubber is an isoprene rubber or a butadiene rubber.

[0013] Preferably, the adhesive further includes a vulcanization accelerator. The amount of the vulcanization accelerator is preferably 1.5 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the base rubber.

[0014] From another perspective, the tennis ball according to the present invention includes a hollow core made of a rubber material. The core is formed from two hemispherical half cores. The two half cores are bonded together using any of the tennis ball adhesives described above. [Effects of the Invention]

[0015] The tennis ball adhesive of the present invention has a shear viscosity at working temperatures suitable for application to bonding surfaces. Furthermore, because the adhesive is substantially free of highly volatile organic solvents, it reduces the burden on the working environment and maintains a shear viscosity suitable for application during storage and operation. Furthermore, the adhesive provides high adhesive strength. Tennis balls obtained using this adhesive to bond cores exhibit excellent durability. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a partially cutaway cross-sectional view of a tennis ball obtained using an adhesive according to one embodiment of the present invention. [Figure 2] 2(a) and 2(b) are cross-sectional views showing the process of forming the core of the tennis ball of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below based on preferred embodiments, with reference to the accompanying drawings. In this specification, the range "X to Y" means "X or more and Y or less." Unless otherwise noted, all test temperatures are room temperature (20°C ± 5°C).

[0018] A tennis ball adhesive according to one embodiment of the present invention includes a base rubber. The base rubber mainly comprises a liquid rubber having a number-average molecular weight of 10,000 or more. In this specification, liquid rubber refers to a rubber that is fluid at room temperature and atmospheric pressure. By ensuring that the liquid rubber, which is the main component of the base rubber, has a number-average molecular weight of 10,000 or more, excellent adhesive strength suitable for laminating the core 4 can be obtained.

[0019] The shear viscosity of this tennis ball adhesive is 2,000 Pa·s or less. Adhesives with a shear viscosity of 2,000 Pa·s or less have good applicability. Workers can apply this adhesive evenly in the correct amount. Uniform application further improves the resulting adhesive strength. Furthermore, this adhesive achieves a shear viscosity suitable for application without using highly volatile organic solvents. In other words, this adhesive is substantially free of organic solvents. This adhesive reduces the burden on the environment and on workers who use it, and can maintain a shear viscosity suitable for application during storage or operation.

[0020] From the viewpoint of improving workability, the ratio of liquid rubber in the base rubber is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and particularly preferably 99% by mass or more. The entire amount of the base rubber may be liquid rubber. Furthermore, the base rubber may contain solid rubber as long as the effects of the present invention are not impaired. In this specification, solid rubber means rubber that does not flow at room temperature and atmospheric pressure.

[0021] From the viewpoint of improving adhesive strength, the number average molecular weight of the liquid rubber is preferably 15,000 or more, more preferably 20,000 or more, and even more preferably 26,000 or more. From the viewpoint of coatability, the number average molecular weight of the liquid rubber is preferably 60,000 or less, more preferably 40,000 or less. The number average molecular weight of the liquid rubber is measured by gel permeation chromatography and calculated as a value converted into standard polystyrene.

[0022] From the viewpoint of obtaining good application properties, the shear viscosity of the adhesive is preferably 1,800 Pa·s or less, and more preferably 1,500 Pa·s or less. From the viewpoint of ensuring an appropriate amount of adhesion to the application surface, the shear viscosity of the adhesive is preferably 80 Pa·s or more, more preferably 200 Pa·s or more, and particularly preferably 500 Pa·s or more. The shear viscosity of the adhesive is measured using a known rheometer at a temperature of 23°C and a shear rate of 10 (1 / s).

[0023] The type of liquid rubber is not particularly limited as long as the effects of the present invention can be obtained. Examples of liquid rubber include isoprene rubber, butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, chloroprene rubber, butyl rubber, ethylene-propylene rubber, and modified versions thereof. Examples of modified versions include rubbers modified with functional groups such as carboxyl groups, amine groups, and hydroxyl groups. Isoprene rubber or butadiene rubber is preferred.

[0024] Preferably, this tennis ball adhesive contains a vulcanization accelerator along with the base rubber. The type of vulcanization accelerator is not particularly limited as long as the effects of the present invention are not impaired. An appropriate vulcanization accelerator may be selected and used from aldehyde-ammonia-based vulcanization accelerators, aldehyde-amine-based vulcanization accelerators, thiazole-based vulcanization accelerators, sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, guanidine-based vulcanization accelerators, thiourea-based vulcanization accelerators, xanthogenate-based vulcanization accelerators, and the like. One or more vulcanization accelerators may be used in combination. A vulcanization accelerator selected from sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators is preferred.

[0025] From the viewpoint of obtaining an appropriate curing rate and high adhesive strength, the amount of vulcanization accelerator contained in the adhesive is preferably 1.5 parts by mass or more, and more preferably 2.5 parts by mass or more, per 100 parts by mass of base rubber. From the viewpoint of fluidity during vulcanization, the amount of vulcanization accelerator contained in the adhesive is preferably 5.0 parts by mass or less, and more preferably 4.0 parts by mass or less.

[0026] The adhesive may contain a vulcanizing agent, if necessary. Suitable vulcanizing agents include, for example, sulfur such as powdered sulfur, insoluble sulfur, precipitated sulfur, and colloidal sulfur; and sulfur compounds such as morpholine disulfide and alkylphenol disulfide.

[0027] The tennis ball adhesive may additionally contain a filler. One or more fillers selected from the group consisting of carbon black, silica, calcium carbonate, calcium hydroxide, magnesium hydroxide, talc, mica, diatomaceous earth, titanium oxide, zinc oxide, bismuth oxide, barium sulfate, magnesium carbonate, and alumina are preferred. From the standpoint of adhesive strength, the amount of filler in the adhesive is preferably 1 part by weight or more, more preferably 5 parts by weight or more, and particularly preferably 10 parts by weight or more, per 100 parts by weight of the base rubber. From the standpoint of flowability, the preferred amount of filler is 40 parts by weight or less.

[0028] The adhesive may further contain various additives such as a vulcanization accelerator, a thickener, a tackifier, an antioxidant, an antioxidant, a light stabilizer, a softener, a processing aid, and a colorant, as long as the effects of the present invention are not impaired.

[0029] The method for producing this tennis ball adhesive is not particularly limited, but for example, the adhesive can be produced by sequentially adding additives such as a vulcanization accelerator to a liquid rubber having a number-average molecular weight of 10,000 or more as a base rubber and mixing them. A known kneading machine such as a roll mill can be used for mixing.

[0030] This tennis ball adhesive can be suitably used, for example, in the production of hard tennis balls. FIG. 1 shows a tennis ball 2 obtained using an adhesive according to one embodiment of the present invention. This tennis ball 2 has a hollow core 4 made of a rubber material, two felt sections 6 covering this core 4, and a seam section 8 located in the gap between the two felt sections 6. The thickness of the core 4 is typically about 3 mm to 4 mm. The interior of the core 4 is filled with compressed gas. The two felt sections 6 are attached to the surface of the core 4 with an adhesive.

[0031] FIG. 2 is a cross-sectional view illustrating the process of forming the core 4 of the tennis ball 2 of FIG. 1. As shown in FIG. 2(a), in the process of forming this core 4, first, two half cores 20 are prepared. Each half core 20 is hemispherical and has an annular edge portion 21. Next, the rubber adhesive according to the present invention is applied to the edge portion 21 of each half core 20, and sodium chloride and sodium nitrite tablets and water are poured into one half core 20. Thereafter, as shown in FIG. 2(b), the two half cores 20 are bonded together at their edge portions 21. The sphere formed by the two half cores 20 is placed in a predetermined mold and heated and pressurized to form the hollow core 4.

[0032] The core 4 made of a rubber material is formed by crosslinking a rubber composition containing a base rubber, a vulcanizing agent, a vulcanization accelerator, a filler, etc. Suitable base rubbers include natural rubber, polybutadiene, polyisoprene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, polychloroprene, ethylene-propylene copolymer, ethylene-propylene-diene copolymer, isobutylene-isoprene copolymer, and acrylic rubber. Two or more of these may be used in combination. Natural rubber is more preferred. The rubber composition of the core 4 may further contain additives such as a vulcanization aid, an antioxidant, an antioxidant, a light stabilizer, a softener, a processing aid, and a colorant.

[0033] The method for producing the core rubber composition is not particularly limited as long as the object of the present invention is achieved. For example, the rubber composition may be produced by adding the base rubber and appropriately selected additives to a known mixer such as a Banbury mixer, kneader, or roll mixer, kneading the resulting mixture, and then heating and pressurizing the mixture. The kneading and vulcanization conditions are selected depending on the formulation of the rubber composition. The preferred kneading temperature is 50°C or higher and 180°C or lower. The preferred vulcanization temperature is 140°C or higher and 180°C or lower. The preferred vulcanization time is 2 minutes or higher and 60 minutes or lower.

[0034] The method for producing a tennis ball 2 having a core 4 obtained using this core rubber composition is not particularly limited. For example, a felt portion 6 that has been cut into a dumbbell shape in advance, has an adhesive applied to its back surface, and has seam glue applied to its cross section, is then bonded to the surface of the core 4 to obtain a tennis ball 2. An adhesive may be applied to the surface of the core 4 before the felt portion 6 is bonded. Any known adhesive may be appropriately selected and used for bonding the felt portion 6 and for the seam glue.

[0035] This tennis ball adhesive has high adhesive strength. Furthermore, because this adhesive has good workability, it can be applied evenly in the right amount to the edge portion 21 of the half core 20. This even application further improves the adhesive strength of the core 4. Tennis balls 2 equipped with this core 4 have high durability. [Example]

[0036] The effects of the present invention will be clarified below by examples, but the present invention should not be construed as being limited based on the descriptions of these examples.

[0037] [Example 1] The resulting mixture consisted of 100 parts by mass of liquid rubber (Kuraray's trade name "LIR30", number average molecular weight 28,000), 20 parts by mass of carbon black (Tokai Carbon's ISAF, trade name "Seat 6"), 5 parts by mass of zinc oxide (Toho Zinc's trade name "Ginrei R"), 1 part by mass of stearic acid (NOF Corporation's trade name "Beads Stearic Acid Tsubaki"), 5.26 parts by mass of sulfur (5% oil-containing sulfur, trade name "5% oil-containing fine powder sulfur"), and 10 parts by mass of sulfur dioxide (Tsurumi Chemical Industry Co., Ltd.'s trade name "Seast 6"). (200 mesh)"), 1.50 parts by mass of a vulcanization accelerator CBS (N-cyclohexyl-2-benzothiazole sulfenamide, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Noccela CZ-G"), and 1.74 parts by mass of a vulcanization accelerator DPG (1,3-diphenylguanidine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Noccela D") were charged into a three-roll mill and kneaded at 35-40°C for 0.5 hours to obtain the adhesive of Example 1.

[0038] [Examples 2-5 and Comparative Examples 1-2] Adhesives of Examples 2-5 and Comparative Examples 1-2 were obtained in the same manner as in Example 1, except that the base rubber and the formulation of each additive were changed as shown in Table 1-2 below.

[0039] [Shear viscosity measurement] Using a rheometer (manufactured by Anton Paar), the shear viscosity of the adhesives of Examples 1-5 and Comparative Examples 1-2 was measured at a temperature of 23°C and a shear rate of 10 (1 / s). The results obtained are shown in Table 1-2 below.

[0040] [Durability evaluation] 100 parts by weight of natural rubber (Astlett Rubber's product name "SMR CV60"), 15 parts by weight of carbon black (Cabot Japan's product name "N330"), 4 parts by weight of silica (Tosoh Silica's product name "Nipsil VN3"), 30 parts by weight of kaolin clay (Imerys' product name "ECKALITE 120"), 17 parts by weight of magnesium carbonate (Konoshima Chemical's product name "Kinsei"), and 5 parts by weight of zinc oxide (Seido Chemical's product name "Zinc Oxide Type 2") were added to a kneader and kneaded at 90°C for 5 minutes. 0.5 parts by weight of salicylic acid (Tokyo Chemical Industry Co., Ltd.), 2.3 parts by weight of 1,3-diphenylguanidine (Sansera D product name, Sanshin Chemical Industry Co., Ltd.), and 3.5 parts by weight of sulfur (Sunfel EX) were added to the resulting kneaded mixture and kneaded at 50°C for 3 minutes using an open roll mill to obtain a rubber composition.

[0041] The resulting rubber composition was poured into a mold and heated and pressurized at 150°C for 4 minutes to form two half cores (3.2 mm±0.4 mm thick). The edges of each half core were treated with sandpaper (#100), and then the adhesive from Example 1 was applied to the edges and dried at room temperature for at least 2 hours. Ammonium chloride, sodium nitrite, and water were then poured into one half core, which was then bonded to the other half core. The test cores were then prepared in the same manner, except that the adhesive from Example 1 was replaced with the adhesives from Examples 2-5 and Comparative Examples 1-2.

[0042] The obtained test core was repeatedly crashed into a steel wall 1m away at a speed of 50m / s, and the number of collisions until the core was destroyed was measured. Ten measurements were taken for each test core, and the average values ​​were calculated, and the results are shown in Table 1-2 below.

[0043] [Workability evaluation] When preparing the test cores described above, 10 workers were asked to subjectively evaluate the workability (ease of application and odor) when applying the adhesives of Examples 1-5 and Comparative Examples 1-2 to the edge portions using a three-point scale of A, B, and C. The best workability was given an "A," and the worst workability was given a "C." The results were averaged, with A = 5 points, B = 3 points, and C = 1 point, and are shown in Table 1-2 below.

[0044] [Table 1]

[0045] [Table 2]

[0046] Details of the compounds shown in Tables 1-2 are as follows: LIR30: Kuraray liquid polyisoprene rubber (number average molecular weight 28,000) LIR50: Kuraray liquid polyisoprene rubber (number average molecular weight 54,000) LBR305: Kuraray's liquid polybutadiene rubber (number average molecular weight 26,000) LBR352: Kuraray's liquid polybutadiene rubber (number average molecular weight 9,000) ISAF: Carbon black manufactured by Tokai Carbon Co., Ltd., product name "Seast 6" ZnO: Zinc oxide manufactured by Toho Zinc Co., Ltd., trade name "Ginrei R" Stearic acid: NOF Corporation's product name "Beads Stearic Acid Tsubaki" Sulfur: 5% oil-containing sulfur manufactured by Tsurumi Chemical Industry Co., Ltd., product name "5% oil-containing finely divided sulfur (200 mesh)" CBS: N-cyclohexyl-2-benzothiazole sulfenamide, product name "Noccela CZ-G" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. DPG: 1,3-diphenylguanidine, product name "Noccela D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0047] As shown in Table 1-2, the adhesives of the examples were rated higher than the adhesives of the comparative examples. These evaluation results clearly demonstrate the superiority of the present invention.

[0048] The tennis ball adhesive described above can be applied to the manufacture of various rubber products. [Explanation of symbols]

[0049] 2. Tennis balls 4 cores 6 Felt part 8. Seam part 20... Half Core 21 Edge

Claims

1. a base rubber, the main component of which is a liquid rubber having a number average molecular weight of 10,000 or more; The shear viscosity measured using a rheometer at a temperature of 23°C and a shear rate of 10 (1 / s) is 2,000 Pa s or less, A tennis ball adhesive that is substantially free of organic solvents.

2. 2. The adhesive of claim 1, wherein the liquid rubber is an isoprene rubber or a butadiene rubber.

3. 3. The adhesive according to claim 1, further comprising a vulcanization accelerator, the amount of the vulcanization accelerator being 1.5 parts by weight or more and 5.0 parts by weight or less per 100 parts by weight of the base rubber.

4. It has a hollow core made of rubber material, The core is formed from two hemispherical half cores, A tennis ball in which the two half cores are bonded together using the adhesive according to any one of claims 1 to 3.

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