Water-based adhesive for rubber

Abstract

To provide an aqueous adhesive for rubber which reduces environmental load and exhibits stable adhesive force.SOLUTION: There is provided an aqueous adhesive for rubber which is composed of a main agent mainly composed of a rubber latex and an organic solvent capable of swelling a rubber component in the rubber latex. The amount of the organic solvent 25 mass% or more and 60 mass% or less based on the total amount of the main agent and the organic solvent. The organic solvent preferably has a melting point of 140°C or less. The tennis ball has a hollow core composed of a rubber material. The hollow core is formed of two hemispherical half cores. The two half cores are bonded together using the aqueous adhesive for rubber.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an aqueous adhesive. Specifically, the present invention relates to an aqueous adhesive used for bonding rubber materials.

Background Art

[0002] In the production of rubber products, it may be necessary to bond a plurality of members made of rubber materials (hereinafter also referred to as rubber members), or to bond a rubber member to a member made of fiber, metal, etc. For example, a tennis ball can be cited as a rubber product obtained by bonding a plurality of rubber members together. A tennis ball has a hollow core. The outer peripheral surface of this core is covered with two dumbbell-shaped melton (felt). A seam portion is formed in the gap between the two melton.

[0003] Normally, the core is formed by bonding two hemispherical half-cores. An adhesive is used for bonding these two half-cores. Also, an adhesive is used for bonding the melton to the outer peripheral surface of the core. A seam paste made of a rubber composition is used for forming the seam portion.

[0004] Conventionally, from the viewpoints of affinity and adhesion strength with rubber materials, solvent-based adhesives in which rubber components, vulcanizing agents, vulcanization accelerators, etc. are dissolved in organic solvents such as naphtha have been used. For example, Japanese Patent Application Laid-Open No. 2004-148022 (Patent Document 1) discloses a solvent-based seam paste 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.

[0005] Solvent-based rubber adhesives are usually prepared by kneading solid rubbers such as natural rubber together with fillers, vulcanization accelerators, etc. in a mixer to reduce the molecular weight of the solid rubber, and then dissolving the resulting kneaded product in an organic solvent to make it liquid. To dissolve this kneaded product, a large amount of organic solvent was required. Since organic solvents are highly volatile, there was a problem that workers were exposed to the solvents in the working environment. In recent years, due to the increasing concern about environmental issues, the reduction of volatile organic compounds (VOCs) has been demanded.

[0006] In Japanese Patent Application Laid-Open No. 2020-059838 (Patent Document 2), an aqueous adhesive containing rubber latex and a sulfenamide-based vulcanization accelerator has been proposed as an adhesive for tennis balls to replace solvent-based adhesives. This aqueous adhesive is used for bonding and vulcanizing half cores together.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] As proposed in Patent Document 2, according to the aqueous adhesive that does not contain an organic solvent, sufficient adhesive strength may not be obtained during vulcanization bonding, and poor bonding between rubber members may occur, leaving problems in terms of stable production.

[0009] An object of the present invention is to provide an aqueous rubber adhesive that exhibits stable adhesive strength.

Means for Solving the Problems

[0010] As a result of intensive studies, the inventors have found that poor adhesion caused by an aqueous adhesive occurs due to the low affinity between the aqueous adhesive and the rubber member. Then, by using an organic solvent capable of swelling the rubber component in the aqueous adhesive, it has been found that the affinity with the rubber member is significantly improved, and the present invention has been completed.

[0011] That is, the aqueous adhesive for rubber according to the present invention is composed of a main agent containing rubber latex as a main component and an organic solvent capable of swelling the rubber component in the rubber latex. The amount of the organic solvent used is 25% by mass or more and 60% by mass or less of the total amount of the main agent and the organic solvent. Preferably, the solid content concentration of the main agent is 45% by mass or more and 65% by mass or less.

[0012] The boiling point of the preferred organic solvent is 140°C or lower.

[0013] The preferred rubber latex is solid rubber latex and / or liquid rubber latex. Preferably, the rubber component of the rubber latex is natural rubber and / or synthetic rubber.

[0014] Preferably, the main agent contains a vulcanization accelerator of 0.1% by mass or more and 3.9% by mass or less in terms of solid content. Preferably, the main agent contains an inorganic filler of 0.1% by mass or more and 40% by mass or less in terms of solid content.

[0015] From another aspect, the tennis ball according to the present invention includes a hollow core made of a rubber material. This hollow core is formed from two hemispherical half-cores. The two half-cores are bonded together using any of the above-described aqueous adhesives for rubber.

Advantages of the Invention

[0016] In the aqueous adhesive for rubber according to the present invention, the affinity for the adhesive surface of the rubber material is improved by the organic solvent capable of swelling the rubber component in the rubber latex. According to this aqueous adhesive, sufficient adhesive strength can be obtained in the vulcanization adhesion of the rubber material with a smaller amount of organic solvent used than in conventional products.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0018] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings. In the present specification, "X to Y" indicating a range means "X or more and Y or less". Also, unless otherwise noted, all test temperatures are room temperature (20°C ± 5°C).

[0019] The aqueous rubber adhesive according to an embodiment of the present invention is composed of a main agent containing rubber latex as a main component and an organic solvent capable of swelling the rubber component in this rubber latex. In this aqueous rubber adhesive, the amount of the organic solvent used is 25% by mass or more and 60% by mass or less of the total amount of the main agent and the organic solvent. In the present specification, the main component means a component usually contained in an amount of 50% by mass or more, preferably 60% by mass or more, more preferably 75% by mass or more.

[0020] In the bonding step of the rubber members, first, the organic solvent is applied to the bonding surface of the rubber member. Subsequently, after the main agent containing rubber latex as a main component is applied to the bonding surface to which the organic solvent has been applied, leaching (washing) is performed. Next, after the bonding surface of this rubber member and the bonding surface of another rubber member are bonded together, heating and pressurization are performed. By this heating and pressurization, the vulcanization reaction of the rubber component derived from the rubber latex proceeds. By this vulcanization reaction of the rubber component, the adhesive hardens and the rubber members are joined together.

[0021] The rubber molecules in the rubber latex swell by coming into contact with the organic solvent applied to the bonding surface. This organic solvent can also swell the rubber member to be bonded, similar to the rubber component in the rubber latex. On the bonding surface where the main agent is applied together with the organic solvent, it is considered that the swollen rubbers come into contact with each other and the entanglement of molecules occurs, thereby improving the affinity between the aqueous adhesive and the rubber member. And it is considered that a strong adhesive force can be obtained by proceeding with the vulcanization reaction in a state where the entanglement of rubber molecules occurs on this bonding surface.

[0022] In the aqueous adhesive for rubber according to the present invention, since the organic solvent is directly applied to the bonding surface of the rubber member, even in an extremely small amount, it can swell the rubber component forming the bonding surface. Thereby, it is considered that the adhesive strength of the rubber member can be remarkably improved with an amount of the organic solvent that does not cause an environmental load and a burden on the operator.

[0023] Also, rubber latex means an emulsion in which rubber components are dispersed in fine particle form in a dispersion medium such as water or an aqueous solution. The main agent whose main component is rubber latex contains water as a component other than the solid content. The aqueous adhesive for rubber according to the present invention, in which the usage amount of the organic solvent is 25% by mass or more and 60% by mass or less of the total amount of the main agent and the organic solvent, uses less organic solvent compared to conventional solvent-based adhesives. In conventional solvent-based adhesives, since an organic solvent is used as a dispersion medium or a solvent, there is a limit to reducing its usage amount. However, according to the present invention, since water is used as the dispersion medium, the usage amount of the organic solvent with respect to the whole adhesive can be reduced.

[0024] As long as the effects of the present invention can be obtained, the concentration of the total solid content contained in the main agent is not particularly limited. From the viewpoint of adhesive strength, the solid content concentration is preferably 40% by mass or more, more preferably 45% by mass or more, and further preferably 50% by mass or more. From the viewpoints of fluidity and reduction of the burden on the operator, the solid content concentration is preferably 65% by mass or less, more preferably 60% by mass or less, and particularly preferably 55% by mass or less.

[0025] From the perspective of improving strength, the amount of the organic solvent used is preferably 27% by mass or more, more preferably 30% by mass or more, based on the total amount of the main agent and the organic solvent. From the perspectives of reducing the burden on the environment and workers and improving workability, the amount of the organic solvent used is 60% by mass or less, preferably 55% by mass or less, and more preferably 53% by mass or less, based on the total amount of the main agent and the organic solvent.

[0026] As long as the rubber component in the rubber latex can be swollen, the type of the organic solvent is not particularly limited. For example, aliphatic hydrocarbons such as n-hexane, isohexane, and cyclohexane, aromatic hydrocarbons such as toluene and xylene, rubber volatile oil, naphtha, petroleum fractions having a boiling range of 80 to 160 ° C, etc. are exemplified. Two or more organic solvents may be used in combination. From the perspective of being less likely to remain after vulcanization adhesion, an organic solvent having a boiling point of 140 ° C or lower is preferred. As long as the effects of the present invention are not inhibited, the organic solvent may contain additives such as a surfactant and a thickener.

[0027] As long as the effects of the present invention can be obtained, the type of the rubber latex which is the main component of the main agent is not particularly limited. It may be a solid rubber latex or a liquid rubber latex. A solid rubber latex and a liquid rubber latex may be used in combination. From the perspective of obtaining a large adhesive strength, a solid rubber latex is preferred. Here, the liquid rubber is a rubber having fluidity at normal temperature and atmospheric pressure, and the liquid rubber latex means an emulsion in which the liquid rubber is dispersed in fine particles in a dispersion medium. The solid rubber is a rubber that does not flow at normal temperature and atmospheric pressure, and the solid rubber latex means an emulsion in which the solid rubber is dispersed in fine particles in a dispersion medium.

[0028] The type of the rubber component in the rubber latex is not particularly limited, but natural rubber and / or synthetic rubber can be preferably used. The natural rubber may be depolymerized natural rubber. Examples of the synthetic rubber include acrylonitrile-butadiene rubber, chloroprene rubber, butadiene rubber, isoprene rubber, butyl rubber, ethylene-propylene rubber, or modified products thereof. Examples of the modified products include functional group-modified rubbers having a functional group such as a carboxyl group, an amine group, or a hydroxyl group. Two or more rubber components may be used in combination. From the viewpoint of the adhesion strength, natural rubber and / or depolymerized natural rubber is preferable.

[0029] From the viewpoint of the miscibility with slurries of various additives described later, the solid content concentration of the rubber latex is preferably 65% by mass or less, more preferably 60% by mass or less. From the viewpoint of the adhesion strength, the solid content concentration of the rubber latex is preferably 45% by mass or more, more preferably 50% by mass or more. The solid content concentration of the rubber latex is determined in accordance with the method described in JIS K6387-2 "Rubber latex - Part 2: Method for determining total solids".

[0030] The main agent may contain a vulcanization accelerator as necessary. Examples of this vulcanization accelerator include sulfenamide-based vulcanization accelerators, guanidine-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiourea-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, morpholine-based vulcanization accelerators, aldehyde-amine-based vulcanization accelerators, aldehyde-ammonia-based vulcanization accelerators, imidazoline-based vulcanization accelerators, xanthate-based vulcanization accelerators, and the like. Two or more vulcanization accelerators may be used in combination. A preferable vulcanization accelerator is a sulfenamide-based vulcanization accelerator.

[0031] A preferred example of the sulfenamide-based vulcanization accelerator is a compound represented by the general formula R 9 -S-N(-R 10 )-R 11 In this general formula, R 9 , R 10 and R 11Each is independently a hydrogen atom or a linear, branched or cyclic alkyl group having 3 to 20 carbon atoms, an alkyl ether group, an alkylphenyl group, a nitrogen-containing heterocyclic group, a sulfur-containing heterocyclic group or a nitrogen- and sulfur-containing heterocyclic group.

[0032] Specific examples of such compounds include N-cyclohexyl-2-benzothiazolesulfenamide, N-tert-butyl-2-benzothiazolesulfenamide, N,N'-dicyclohexyl-2-benzothiazolylsulfenamide, N-oxydiethylene-2-benzothiazolesulfenamide, N,N-diisopropyl-2-benzothiazolesulfenamide, N-ethyl-2-benzothiazolesulfenamide and the like. One or more selected from the group consisting of N-cyclohexyl-2-benzothiazolesulfenamide, N-tert-butyl-2-benzothiazolesulfenamide and N-oxydiethylene-2-benzothiazolesulfenamide are more preferable.

[0033] From the viewpoint of adhesion strength, the amount of the vulcanization accelerator contained in the main agent is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and still more preferably 0.3% by mass or more in terms of solid content. From the viewpoint of adhesion, the amount of the vulcanization accelerator contained in the aqueous adhesive is preferably 3.9% by mass or less, more preferably 3.5% by mass or less, and still more preferably 3.0% by mass or less in terms of solid content.

[0034] When a sulfenamide-based vulcanization accelerator is used in combination with other vulcanization accelerators, the proportion of the sulfenamide-based vulcanization accelerator in all the vulcanization accelerators is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0035] The main agent may further contain a vulcanizing agent. Suitable vulcanizing agents include, for example, sulfur such as powdered sulfur, insoluble sulfur, precipitated sulfur, colloidal sulfur; sulfur compounds such as morpholine disulfide, alkylphenol disulfide, etc. The amount of the vulcanizing agent in the main agent is not particularly limited, but from the viewpoint of adhesion strength, it is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 2.8% by mass or more in terms of solid content. From the viewpoint of optimizing the curing rate, the amount of the vulcanizing agent in the main agent is preferably 5% by mass or less in terms of solid content.

[0036] As long as the effects of the present invention can be obtained, the main agent may contain an inorganic filler. One or more inorganic fillers selected from the group consisting of silica, carbon black, calcium carbonate, calcium hydroxide, magnesium hydroxide, talc, mica, diatomaceous earth, titanium oxide, zinc oxide, bismuth oxide, barium sulfate, magnesium carbonate, and alumina are preferred. The amount of the inorganic filler in the main agent is not particularly limited, but from the viewpoint of adhesion to the adhesion surface, it is preferably 0.1% by mass or more, more preferably 1.0% by mass or more, and particularly preferably 10% by mass or more in terms of solid content. From the viewpoint of fluidity, the amount of the inorganic filler is preferably 40% by mass or less, more preferably 25% by mass or less in terms of solid content.

[0037] As long as the effects of the present invention are not inhibited, the main agent may further contain various additives such as a vulcanization accelerator co-thickener, tackifier, anti-aging agent, antioxidant, light stabilizer, softener, processing aid, colorant, etc.

[0038] From the viewpoint of adhesion to the adhesion surface, the viscosity of the main agent is preferably 20 cps or more, more preferably 50 cps or more, and particularly preferably 200 cps or more. From the viewpoints of coatability and fluidity, the viscosity of the aqueous adhesive is preferably 20,000 cps or less, more preferably 10,000 cps or less, and particularly preferably 3,000 cps or less. The viscosity of the main agent is measured according to the description in JIS Z8803 "Method for Measuring Viscosity of Liquids". Specifically, it is measured at a temperature of 23 ± 1 °C using a Brookfield type rotational viscometer (TVC-10 type viscometer manufactured by Toki Sangyo Co., Ltd.).

[0039] From the perspective of the stability of the latex, the pH of the main agent is preferably adjusted to be 7.0 or more and 12.0 or less, more preferably 8.0 or more and 11.5 or less, and particularly preferably 9.5 or more and 10.5 or less. The pH of the main agent is measured at a temperature of 23°C ± 1°C using a pH meter (TPX-999 manufactured by Dongxing Chemical Research Institute).

[0040] The method for producing the aqueous adhesive according to the present invention is (1) A step of adding a dispersant to water to prepare a dispersion medium, (2) A step of obtaining a slurry of each additive by introducing and mixing a plurality of additives for compounding into the rubber latex into this dispersion medium and then adjusting the pH to 8.0 or more and 12.0 or less, (3) A step of obtaining a main agent by adding the obtained slurry of each additive to this rubber latex, and (4) A step of preparing an organic solvent capable of swelling the rubber component in the rubber latex is included. The amount of the organic solvent to be prepared is 25% by mass or more and 60% by mass or less of the total amount of the main agent and the organic solvent.

[0041] Examples of the additives for compounding into the rubber latex include vulcanizing agents, vulcanization accelerators, vulcanization accelerator aids, inorganic fillers, thickeners, anti-aging agents, antioxidants, light stabilizers, softeners, processing aids, colorants, and the like.

[0042] The dispersion medium is used for preparing a slurry that disperses each of a plurality of additives. The type of the dispersant is not particularly limited, and it is appropriately selected and used from anionic, nonionic, and cationic surfactants according to the type of the additive and the concentration of the slurry. Examples of the anionic surfactant include alkyl sulfonates having 8 to 20 carbon atoms, alkyl aryl sulfates, sodium naphthalene sulfonate-formaldehyde condensates, alkali metal salts of rosin acid, and the like. Examples of the nonionic surfactant include aromatic polyglycol ethers, polyvinyl alcohol, polyoxyethylene alkyl ethers, polyoxyethylene monostearates, and the like. Examples of the cationic surfactant include dilauryldimethylammonium chloride, hexadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, and the like. An anionic or nonionic surfactant is preferred. Two or more surfactants may be used in combination.

[0043] From the viewpoint of the stability of the slurry, the concentration of the dispersant in the dispersion medium is preferably 0.5% by mass or more, and more preferably 1.0% by mass or more. From the viewpoint of the adhesive strength of the obtained adhesive, the concentration of the dispersant in the dispersion medium is preferably 20% by mass or less, and more preferably 15% by mass or less.

[0044] From the viewpoint of the dispersion stability of the latex, preferably, this production method further includes a step of adjusting the pH of the dispersion medium to 8.0 or more and 12.0 or less. For example, after dissolving the dispersant in purified water, the dispersion medium may be prepared by adding aqueous ammonia or the like until a predetermined pH is obtained.

[0045] In this manufacturing method, a plurality of additives are each introduced into a dispersion medium so as to have a predetermined solid content concentration, and after adjusting the pH to 8.0 or more and 12.0 or less, they are uniformly mixed by a ball mill or the like, whereby slurries of the respective additives are obtained. Thereafter, the obtained slurries of the respective additives are added to a rubber latex and uniformly mixed, whereby a main agent of the aqueous adhesive for rubber according to the present invention is obtained. This manufacturing method may further include a step of adding a diluent such as water after blending the slurries of the respective additives with the rubber latex to adjust the solid content concentration thereof.

[0046] The aqueous adhesive for rubber according to the present invention can be suitably used, for example, in the manufacture of tennis balls. FIG. 1 shows a tennis ball 2 obtained using the aqueous adhesive according to an embodiment of the present invention. This tennis ball 2 has a hollow core 4, two felt parts 6 covering the core 4, and a seam part 8 located in the gap between the two felt parts 6. The thickness of the core 4 is usually about 3 mm to 4 mm. The inside of the core 4 is filled with compressed gas. On the surface of the core 4, two felt parts 6 are attached by an adhesive.

[0047] FIG. 2 is a cross-sectional view for explaining the forming process of the core 4 of the tennis ball 2 in FIG. 1. As shown in FIG. 2(a), in this forming process of the core 4, first, two half-cores 20 are prepared. Each half-core 20 has a hemispherical shell shape and an annular edge part 21. Next, an organic solvent capable of swelling the rubber component is applied to the edge part 21 of each half-core 20. Subsequently, the main agent is applied to the edge part 21 to which the organic solvent has been applied, and sodium chloride and sodium nitrite tablets and water are introduced into one half-core 20. Thereafter, as shown in FIG. 2(b), the two half-cores 20 are bonded together at their edge parts 21. The sphere composed of the two half-cores 20 is put into a predetermined mold and heated and pressurized, whereby the hollow core 4 is formed.

[0048] From another aspect, the method of using this aqueous adhesive for rubber is (1) a first step of applying an organic solvent capable of swelling a rubber component to a bonding surface of a rubber member; (2) The second step is to apply a base material whose main component is rubber latex to the adhesive surface that has been coated with the organic solvent. and (3) The third process involves heating and pressurizing the organic solvent and base material applied to the bonding surface to crosslink the rubber component in the base material. Includes.

[0049] The amount of organic solvent used in the first step is 0.025 ml / cm2 of the adhesive surface area. 2 More than 0.14mL / cm 2 The organic solvent is preferably used in an amount of 25% by mass or more and 60% by mass or less of the total amount of the base material and the organic solvent. According to a method in which the organic solvent is used in an amount within this range, the affinity between the rubber component in the base material and the bonding surface of the rubber member is significantly improved, and stable adhesive strength is exhibited. Furthermore, the volatilization concentration of the organic solvent in the third step is reduced, thereby reducing the burden on workers and the environment.

[0050] Preferred materials for the core 4 (half core 20) of the tennis ball 2 in this embodiment will be described below, but the material for the core 4 (half core 20) can be changed within the scope in which the object of the present invention is achieved.

[0051] The core 4 is formed by crosslinking a rubber composition. 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 types of base rubbers may be used in combination. A more preferred base rubber is natural rubber.

[0052] The rubber composition of Core 4 may contain a vulcanizing agent and a vulcanization accelerator. The vulcanizing agent and the vulcanization accelerator described above for the main component of the rubber aqueous adhesive can be appropriately selected and used. The amounts of the vulcanizing agent and the vulcanization accelerator in the rubber composition of Core 4 are adjusted according to their types. From the viewpoint of the rebound performance, 0.5 part by mass or more is preferable, and 1.0 part by mass or more is more preferable with respect to 100 parts by mass of the base rubber. The compounding amount of the vulcanizing agent is preferably 5.0 parts by mass or less. From the viewpoint of the rebound performance, the compounding amount of the vulcanization accelerator is preferably 1.0 part by mass or more, and 2.0 part by mass or more is more preferable with respect to 100 parts by mass of the base rubber. The compounding amount of the vulcanization accelerator is preferably 6.0 parts by mass or less.

[0053] The rubber composition of Core 4 may further contain a filler. Examples of suitable fillers include talc, kaolin clay, graphite, graphene, bentonite, halloysite, montmorillonite, mica, beidellite, saponite, hectorite, nontronite, vermiculite, illite, allophane, carbon fiber, carbon nanotube, carbon black, silica, calcium carbonate, magnesium carbonate, barium sulfate, etc. Talc, kaolin clay, graphite and graphene are preferable. Two or more kinds may be used in combination.

[0054] The amount of the filler in the rubber composition of Core 4 is appropriately adjusted according to its type. From the viewpoints of the rebound performance and durability, 5 parts by mass or more is preferable, 10 parts by mass or more is more preferable, and 15 parts by mass or more is particularly preferable with respect to 100 parts by mass of the base rubber. From the viewpoint of the hitting feeling, the amount is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, and particularly preferably 80 parts by mass or less.

[0055] Within a range that does not inhibit the effects of the present invention, the rubber composition of Core 4 may further contain additives such as a vulcanization aid, an anti-aging agent, an antioxidant, a light stabilizer, a softening agent, a processing aid, a colorant, etc.

[0056] As long as the object of the present invention is achieved, the method for manufacturing the rubber composition for the core is not particularly limited. For example, a kneaded product obtained by charging a base rubber and appropriately selected additives into a known kneader such as a Banbury mixer, a kneader, or a roll and kneading them is heated and pressurized to produce this rubber composition. The kneading conditions and vulcanization conditions are selected according to the formulation of the rubber composition for the core. 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 vulcanization time is preferably 2 minutes or longer and 60 minutes or shorter.

[0057] The method for manufacturing the tennis ball 2 provided with the core 4 obtained by using this rubber composition for the core is also not particularly limited. For example, the felt part 6 which is previously cut into a dumbbell shape, an adhesive is applied to the back surface thereof, and a seam glue is adhered to the cross section thereof is bonded to the surface of the core 4 to obtain the tennis ball 2. Before bonding the felt part 6, an adhesive may be applied to the surface of the core 4. For the bonding of the felt part 6 and the seam glue, a known adhesive can be appropriately selected and used.

Examples

[0058] Hereinafter, the effects of the present invention will be clarified by examples, but the present invention should not be construed in a limited manner based on the description of these examples.

[0059] [Example 1] (Manufacture of aqueous rubber adhesive) First, 1.6 parts by mass of sodium naphthalene sulfonate-formaldehyde condensate (trade name "Tamol NN9104" manufactured by BASF) and 0.6 parts by mass of aromatic polyglycol ether (trade name "Emalbin WA" manufactured by LANXESS) are dissolved in 100 parts by mass of purified water, and the dispersion medium is prepared by adjusting the pH to 8.0 or higher and 12.0 or lower with commercially available aqueous ammonia (28% by mass).

[0060] Next, the above-mentioned dispersion medium was added to N-cyclohexyl-2-benzothiazolesulfenamide (CBS, a vulcanization accelerator manufactured by Sanshin Chemical Co., Ltd., trade name "Sunceler CM"), and after stirring with a ball mill for 8 hours or more, the pH was adjusted to 8.0 or more and 12.0 or less using the above-mentioned aqueous ammonia to obtain a slurry of CBS (solid content concentration: 20% by mass).

[0061] Subsequently, 122.4 parts by mass of depolymerized latex (trade name "DPL-51" manufactured by Regitex, solid content concentration: 50% by mass), 10.2 parts by mass of zinc oxide slurry (solid content concentration: 60% by mass, trade name "Disperacc ZnO60" of Behn Meyer), 51.0 parts by mass of titanium oxide slurry (solid content concentration: 60% by mass, trade name "Dispertint TB60" of Behn Meyer), 8.4 parts by mass of sulfur slurry (solid content concentration: 60% by mass, trade name "Disperacc Sulphur 60" of Behn Meyer), and 5.9 parts by mass of the CBS slurry were added to 102 parts by mass of natural rubber latex (trade name "Low Ammonia Latex" of Nomura Trading Co., Ltd., solid content concentration: 60% by mass) and uniformly mixed. An appropriate amount of aqueous ammonia (manufactured by Yoneyama Pharmaceutical Co., Ltd.) and pure water were added to obtain a main agent a with a solid content concentration of 50.9% by mass. The viscosity of the main agent a measured by the method described above was 225 cps, and the pH was 10.6. Separately, as an organic solvent, rubber volatile oil (trade name "LA Rubber Volatile Oil (G)", naphtha, manufactured by JXTG Energy Co., Ltd.) was prepared.

[0062] (Preparation of Test Core) 100 parts by mass of natural rubber (trade name "SMR CV60" manufactured by Astlett Rubber), 15 parts by mass of carbon black (trade name "N330" manufactured by Cabot Japan), 4 parts by mass of silica (trade name "Nipsil VN3" manufactured by Tosoh Silica), 30 parts by mass of kaolin clay (trade name "ECKALITE 120" manufactured by Imerys), 17 parts by mass of magnesium carbonate (trade name "Venus" manufactured by Kojima Chemical Industry), and 5 parts by mass of zinc oxide (trade name "Zinc Oxide No. 2" manufactured by Shoindo Chemical) were charged into a Banbury mixer and kneaded at 90°C for 5 minutes. To the obtained kneaded product, 0.5 part by mass of salicylic acid (manufactured by Tokyo Chemical Industry), 2.3 parts by mass of 1,3-diphenylguanidine (trade name "Sunceler D" manufactured by Sanshin Chemical), and 3.5 parts by mass of sulfur (trade name "Sunfel EX") were added, and kneaded at 50°C for 3 minutes using an open roll to obtain a rubber composition.

[0063] The obtained rubber composition was put into a mold and pressed at 140°C for 4 minutes to form two half-cores. After treating the edge portions of each half-core with sandpaper (#100), the prepared organic solvent was applied to the edge portions. Subsequently, the main agent a was applied to the edge portions to which the organic solvent was applied. The amount of the organic solvent used was 52.1% by mass of the total amount of the main agent and the organic solvent (0.136 ml / cm 2 ) with respect to the area of the bonding surface. Thereafter, in order to wash away the surfactant in the slurry, each half-core was washed with water (leaching), and ammonium chloride, sodium nitrite, and water were added to one of the half-cores, and then heated at 150°C for 6 minutes to prepare a test core.

[0064] [Examples 2 and Comparative Examples 1-2] In Examples 2 and Comparative Examples 1-2, the amount of the organic solvent used was as shown in Table 1 below. Otherwise, a test core was prepared in the same manner as in Example 1. In Table 1, the ratio (wt.%) of the organic solvent to the total amount of the main agent and the organic solvent and the amount used (ml / cm 2 ) with respect to the area of the bonding surface are shown as the "amount of organic solvent used".

[0065] [Examples 3-4] In Example 3-4, the formulation of the rubber latex and each slurry was the same as that of the main agent a, except that it was composed of 152.8 parts by mass of depolymerized latex (the aforementioned product name "DPL-51"), 6.4 parts by mass of zinc oxide slurry (the aforementioned product name "Disperacc ZnO60"), 31.8 parts by mass of titanium oxide slurry (the aforementioned product name "Dispertint TB60"), 5.2 parts by mass of sulfur slurry (the aforementioned product name "Disperacc Sulphur 60") and 3.7 parts by mass of CBS slurry. Thus, the main agent b with a solid content concentration of 50.9% by mass was obtained. The viscosity of the main agent b measured by the method described above was 220 cps, and the pH was 10.6. Separately, as the organic solvent, rubber volatile oil (product name "LA rubber volatile oil (G)" manufactured by JXTG Energy Corporation, naphtha) was prepared.

[0066] Using the main agent b and setting the amount of the organic solvent used as shown in Table 1 below, test cores were prepared in the same manner as in Example 1.

[0067] [Adhesion evaluation] From the test cores prepared for Examples 1-4 and Comparative Examples 1-2, 12 JIS No. 3 dumbbell pieces (thickness 2 mm) were cut out as test pieces respectively. At this time, each test piece was cut out so that the adhesive surfaces of the two half-cores were located at the central part of the dumbbell piece.

[0068] Using a tensile testing machine (product name "Autograph AGS-X" manufactured by Shimadzu Corporation), a tensile test was performed on each test piece at a tensile speed of 500 mm / min, and the cross-section of the test piece after fracture was observed. For each 12 test pieces, those with substrate fracture (fracture outside the adhesive surface) were judged as "good", and those with interfacial fracture (fracture at any edge part) or cohesive fracture (fracture in the adhesive layer) were judged as "bad". The number (pieces) and ratio (%) of the test pieces judged to have good adhesion are shown in Table 1 below.

[0069]

Table 1

[0070] As shown in Table 1, according to the aqueous adhesive of the example, more than 60% of the test pieces were judged to have good adhesion. From this evaluation result, the superiority of the present invention is clear.

Industrial Applicability

[0071] The aqueous adhesive for rubber described above can be applied to the production of various rubber products.

Explanation of Signs

[0072] 2 ··· Tennis ball 4 ··· Core 6 ··· Felt part 8 ··· Seam part 20 ··· Half core 21 ··· Edge part

Claims

1. It is composed of a main agent with rubber latex as the main component and an organic solvent capable of swelling the rubber component in this rubber latex, wherein the solid content concentration of the main agent is 45% by mass or more and 65% by mass or less, and the amount of the organic solvent used is 25% by mass or more and 60% by mass or less of the total amount of the main agent and the organic solvent, an aqueous rubber adhesive.

2. The aqueous rubber adhesive according to Claim 1, wherein the boiling point of the organic solvent is 140°C or lower.

3. The aqueous rubber adhesive according to Claim 1 or 2, wherein the rubber latex is a solid rubber latex and / or a liquid rubber latex.

4. The aqueous rubber adhesive according to any one of Claims 1 to 3, wherein the rubber component of the rubber latex is natural rubber and / or synthetic rubber.

5. The aqueous rubber adhesive according to any one of Claims 1 to 4, wherein the main agent contains a vulcanization accelerator in an amount of 0.1% by mass or more and 3.9% by mass or less in terms of solid content.

6. The aqueous rubber adhesive according to any one of Claims 1 to 5, wherein the main agent contains an inorganic filler in an amount of 0.1% by mass or more and 40% by mass or less in terms of solid content.

7. It has a hollow core made of a rubber material, wherein the hollow core is formed from two hemispherical half-cores, and the two half-cores are bonded together using the aqueous rubber adhesive according to any one of Claims 1 to 6, a tennis ball.

Images