JPH0237376B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an adhesive suitable for bonding a melton cloth and a core ball of a tennis ball. Tennis balls are manufactured by bonding together a spherical core ball and a flat melton cloth. Conventionally, to bond core balls and melton cloth, natural rubber or synthetic rubber, whose molecules have been excessively cut by repeated mastication using a kneading roll machine for a long period of time, is dissolved in a volatile organic solvent such as naphtha. A solvent paste is used in which a vulcanizing agent, a vulcanization accelerator, a vulcanization accelerator, a filler, etc. are dissolved or dispersed in this solution. However, such solvent glue exhibits Newtonian viscosity as its fluidity property [FIG. 1, 4], and has a small yield stress, so that the solvent glue applied to the surface of the core ball sags during drying. This makes it difficult to uniformly apply the solvent glue to the surface of the core ball, resulting in eccentricity and a decrease in sphericity of the ball, as well as swelling of the rubber wall of the core ball due to the solvent, resulting in a decrease in dimensional stability. There are drawbacks. The present invention was made to solve the above problems, and its gist is that the adhesive strength of the depolymerized adhesive is 20
The present invention relates to an adhesive for tennis balls whose base material is natural rubber latex and/or synthetic rubber latex having a weight of ~180 g/cm (at 25°C). The base component of the adhesive according to the invention is natural rubber and/or synthetic rubber, such as polyisoprene, polybutadiene, polychloroprene, nitrile rubber, styrene-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, or these. Depolymerization treatment of the mixture, such as heating in the coexistence of an organic peroxide or azo compound, radical reaction using a redox initiator containing persulfate as one component, or X-rays, α-rays, β-rays, γ-rays, etc. It can be obtained by subjecting it to radiation irradiation, etc. Particularly preferred rubbers are natural rubber and synthetic polyisoprene rubber latex. The degree of depolymerization of the above-mentioned rubber latex is not particularly limited, but usually, for example, when natural rubber latex has adhesive strength according to JIS-Z-1522 (cellophane adhesive tape test) and JIS-Z-1528 (double-sided adhesive tape test) 20-180g/cm when drying after water evaporation
Generally, if the adhesive force is less than 20 g/cm, the initial adhesive force required for the adhesive is too small and the internal cohesive force is too large, and if it is more than 180 g/cm, it is excessive. As a result of molecular cleavage, the surface adhesive force is too large, making it difficult to perform bonding operations. Various conventional additives are appropriately added to the rubber latex thus prepared. Such additives include tackifiers, e.g.
QE6503B (commercial product from Zeon Corporation), Claprene
LIR-700 (commercial product from Clarei Soprene Chemical Company),
Vulcanizing agents (sulfur), vulcanization accelerators such as 2-mercaptobenzothiazole zinc salt, zinc diethyldithiocarbamate, vulcanization accelerators such as zinc oxide, stearic acid, oleic acid, triethanolamine, fillers such as Calcium carbonate, kaolin, clay, barium sulfate, anti-aging agents such as 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-
ethyl-6-t-butylphenol), thickener,
For example, carboxymethyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose,
Examples include polyvinyl alcohol and polyethylene oxide. The total amount of these additives is the same as the rubber component.
It is usually 20 to 60 parts by dry weight per 100 parts by dry weight. The solid content of the adhesive prepared as described above is usually 35-70% by weight, and the viscosity is usually 3000-70% by weight.
It is preferable to adjust it to 70000cps (20℃). The adhesive according to the present invention exhibits thixotropy as its flow characteristics [Fig. 1 1 to 3], and when applied to the core ball, the apparent viscosity decreases in proportion to the rotation speed of the application device (for example, a rotating barrel). Efficiency is increased (see Figure 2), and because the yield stress (zero shear viscosity) is large, there is little downward sag even when the ball is left standing during drying, and eccentricity of the ball and decrease in sphericity are avoided, resulting in dimensional stability. Improves sex. Furthermore, since no organic solvent is used in the adhesive according to the present invention, problems such as swelling of the core ball rubber wall and generation of porosity during press vulcanization do not occur. The adhesive according to the present invention is particularly suitable for bonding the core ball of a tennis ball and the melton cloth, but the adhesive has a suitable balance between surface adhesion and internal cohesive force in an unvulcanized state, and a It can be used in a wide range of applications that require high adhesive strength. The present invention will be explained below with reference to Examples. Example 1 and Comparative Examples 1 to 3

【table】

[Table] Prepare an adhesive according to the formulation shown in Table 1, apply it to the surface of a tennis ball core ball (about 6 cm in diameter) using a conventional method, evaporate the water or solvent, and then laminate Melton cloth. Press vulcanization was performed at 120℃ for 15 minutes to create a tennis ball. (Amount of coating is about 1 g/piece after drying) In Table 1, Example 1 is an adhesive prepared from the depolymerized natural rubber latex of the present invention, Comparative Example 1
Comparative Example 2 is a natural rubber latex with a large amount of tackifier added to increase its adhesive strength, and Comparative Example 3 is a solvent-based adhesive in which natural rubber is dissolved in an organic solvent. Table 2 shows the adhesive strength of each adhesive after drying, the bonding properties of the melton cloth, and the physical properties of the tennis ball (core/melton cloth adhesive strength, outer diameter).

【table】

[Table] From Table 2, the adhesive of Example 1 had appropriate tackiness, could easily be bonded with melton cloth, and had high adhesive strength. On the other hand, in Comparative Example 2, in which normal natural rubber latex was used as a latex-based adhesive, the adhesive strength was poor, so it was not possible to bond the melton cloth, and even after press vulcanization, some parts of the melton cloth and adhesive layer There were parts of the ball that were not in close contact with each other, and I was unable to make a satisfactory tennis ball. In Comparative Example 3, in which a large amount of tackifier was blended to improve the tackiness of the natural rubber latex, the lamination properties of the melton cloth were improved, but the adhesive strength was significantly reduced and could not be put to practical use. Comparative Example 3 is a conventionally used solvent-based adhesive, but compared to Example 1, the thickness of the applied adhesive was uneven and the adhesive strength varied widely, and the core was damaged by the solvent. Since it swells, the outer diameter of the ball is also affected, resulting in poor dimensional stability. Examples 2 to 4 Adhesives were prepared according to the formulations shown in Table 3, and the relationship between shear stress and rotor rotation speed was measured using a B-type viscometer No. 4 rotor.
Measurements were made at 22.0°C and the results are shown in Figure 1. Furthermore, the relationship between rotor rotational speed and apparent viscosity for these adhesives was determined, and the results are shown in FIG.

【table】 [Brief explanation of drawings]

FIG. 1 shows the relationship between shear stress (horizontal axis: arbitrary units) and rotor rotational speed (vertical axis: rpm) for the adhesives according to the present invention and conventional solvent glues. Figure 2 shows the rotor rotational speed (horizontal axis: rp
m.) and apparent viscosity (vertical axis: cps). 1 to 3 indicate the adhesive according to the present invention, respectively, and 4 indicates a conventional solvent glue.

Claims (1)

[Claims] 1. Adhesive strength after depolymerization treatment: 20 to 180 g/cm (25°C)
An adhesive for tennis balls whose base component is natural rubber latex and/or synthetic rubber latex having the following properties. 2. The adhesive according to item 1, wherein the depolymerization treatment is performed by radical reaction or radiation irradiation. 3 Adhesive strength of rubber latex is 20 to 180 g/cm
(25°C).