JPH0253471B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pressure-sensitive adhesive using a reaction product containing an acrylic acid alkyl ester as a main component, which can be applied in a hot molten state. Currently, pressure-sensitive adhesives are used as melt type, aqueous emulsion type, or hot melt type. In recent years, heat-melting types have attracted attention due to fire prevention, environmental pollution, energy conservation, resource conservation, productivity, etc., and their use has been growing rapidly. However, heat-melting type pressure-sensitive adhesives have a significant lack of heat resistance, and no one has been found that is of sufficient quality. Many studies have been carried out to improve these qualities, such as crosslinking, but nothing satisfactory has yet been obtained. Polystyrene-polybutadiene-polystyrene (SBS), polystyrene-
Block copolymers such as polyisoprene-polystyrene (SIS), ethylene-vinyl acetate copolymers (EVA), and polyacrylic acid alkyl esters are considered, and block copolymers and EVA have been commercialized and commercially available. However, it still has the drawbacks mentioned above. In order to improve these drawbacks, in the case of block copolymers, a method of crosslinking SBS with electron beams (Japanese Patent Laid-Open No.
55-71774 Furukawa Electric), there is a method in which SIS is blended with a transferable monomer and cross-linked with electron beams or ultraviolet light (Adhesives Age, March 1980, etc., p. 30). Although heat-melt pressure-sensitive adhesives can obtain fairly good cohesive strength and have improved heat resistance through crosslinking, they often have problems with heat stability and weather resistance, and they also do not contain polyfunctional monomers. Coating at high temperatures is not very desirable in terms of odor and toxicity. On the other hand, in the case of polyacrylic acid alkyl ester, there is a method in which an acrylic acid alkyl ester monomer is cross-linked with an electron beam (Ger. 2134468 Nitto Denko), and a method in which an acrylic acid alkyl ester monomer is mixed with a polymer and cross-linked with an electron beam (USP 3661618 Fire stone), and a method in which acrylic acid alkyl ester oligomer is applied in a hot melt state and cross-linked with an electron beam (USP3725115P.P.
G.) However, when using an acrylic acid alkyl ester monomer, it is unfavorable in terms of toxicity, odor, fire, etc., and the remaining unreacted monomer causes a significant decrease in adhesive performance. When using acrylic acid alkyl ester oligomer,
Although these points have been improved, in order to obtain the necessary heat resistance and cohesive strength, crosslinking must be carried out under considerably strong conditions, and the pressure-sensitive adhesives obtained in this way have a marked decrease in tack, and their adhesive strength and It is not possible to maintain a balance between the three properties of cohesion and adhesiveness. In addition, there are products in which photocrosslinkable monomers are copolymerized to facilitate crosslinking, but these also raise the Tg (glass transition point) of the system and reduce adhesiveness. In order to improve the shortcomings of these hot-melt pressure sensitive adhesives mainly made of block copolymers such as SIS and SBS and polyacrylic acid alkyl esters, the inventors of the present invention have conducted intensive research and developed a method using diene polymers. By using a product obtained by radical polymerization of a polymerizable monomer containing an acrylic acid alkyl ester as a main component in the presence of It was discovered that an adhesive that can be crosslinked by radiation was obtained, and that the crosslinked adhesive had excellent adhesive properties and heat resistance. Although it is possible to mix polyacrylic acid alkyl ester with the diene polymer, the compatibility is low and the mixture does not mix uniformly, resulting in separation.
A composition with good performance cannot be obtained. Furthermore, in the case of a hot-melt type pressure-sensitive adhesive in which a diene polymer is mixed with an acrylic acid alkyl ester monomer, problems associated with the monomer occur as described above. On the other hand, in the present invention, graft polymerization occurs, and a composition with good performance can be obtained without separation. The hot-melt pressure-sensitive adhesive of the present invention uses a reaction product of the following (1) and (2). (1) Diene polymer (2) Polymerizable monomer containing an acrylic acid alkyl ester as a main component (1) and (2) are explained below. (1) Diene polymers are usually commercially available natural rubber, styrene/butadiene rubber, SIS, and SBS.
Copolymers with diene bonds, such as block copolymers such as polybutadiene and polyisoprene. If these diene copolymers are not present, radiation crosslinking cannot be produced. Polymerizable monomer (2)
It is preferable that the diene polymer (1) is present in an amount of 0.3 to 10 parts by weight, particularly 0.3 to 5 parts by weight, per 100 parts by weight. If it is less than 0.3 parts by weight, the crosslinking property will be poor, and
If it exceeds 10 parts by weight, heat resistance, adhesiveness, hot melt coating properties, and solvent resistance will decrease. (2) Polymerizable monomers based on acrylic acid alkyl esters generally provide polymers useful as pressure-sensitive adhesives. For example, the polymerizable monomer has the following structure. (A) Acrylic acid alkyl ester (alkyl group has 1 to 10 carbon atoms) (B) Methacrylic acid alkyl ester (alkyl group has 1 to 12 carbon atoms), vinyl ester monomer, styrene, acrylonitrile, etc. 0 to 45 Weight% (C) Unsaturated carboxylic acid 0 to 30% by weight (A) such as methyl acrylate, ethyl acrylate, butyl acrylate, propyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, etc. One or more of these are used. For (B), methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, octyl methacrylate, lauryl methacrylate, pinyl acetate, vinyl propionate, styrene, acrylonitrile, 2-hydroxyethyl acrylate , acrylamide, etc., or two or more thereof may be used. As for (C), one or more of acrylic acid, methacrylic acid, maleic anhydride, itaconic acid, etc. can be used. These polymerizable monomers are mainly composed of (A) and can contain (B) and (C) as necessary, and the Tg (℃) of these polymers or copolymers is -10℃ to -50℃. It is preferable to set it as a range. The reaction product according to the present invention is obtained by adding a polymerizable monomer at 50 to 150°C in the presence of the diene polymer.
It is obtained by radical polymerization for 10 hours, but it is generally preferable to use a polymerization regulator. When polymerization is carried out in the absence of a polymerization modifier, the polymer may be gelled during the polymerization, or even without gelation, the degree of polymerization is high and heat meltability is lacking. In addition, if a large amount is used, a large amount of low-molecular-weight polymers containing acrylic acid alkyl ester as the main component will be produced, and even if crosslinked, the cohesive force will be low and the quality will be impaired. From this, it is preferable that the polymerization modifier be used in an amount of 0.05 to 2.0 parts by weight per 100 parts by weight of the polymerizable monomer containing an acrylic acid alkyl ester as a main component. This polymerization regulator is commonly used dodenlumercaptan,
2-ethylhexylthioglycol and the like. Solvents include benzene, toluene, xylene,
Methyl ethyl ketone, ethyl acetate, etc. can be used. Although the main components of the hot-melt pressure-sensitive adhesive of the present invention are as described above, in some cases, the above-mentioned products may include rosin-derived resins, polyterpenes, Resins used as tackifiers such as terpene phenol resins, petroleum hydrocarbon resins, and xylene resins may be blended. Furthermore, fillers commonly used in hot-melt pressure-sensitive adhesives may also be used. Since the present invention can be applied to various base materials during hot melting,
At 180℃, preferably less than 100000cps
Preferably, it has a viscosity of 30,000 cps or less. The composition of the present invention is then characterized by being capable of radiation crosslinking in the presence or absence of a sensitizer. Radiation includes ultraviolet rays, electron beams, gamma rays, and
rays, beta rays, etc., but when crosslinking with ultraviolet rays, it is desirable to use a sensitizer together.
Crosslinking with electron beams can be performed without a sensitizer. Of course, a sensitizer may also be used. Sensitizers used for this purpose include benzoyl, benzoin methyl ether, benzoin ethyl ether, 2-methylanthraquinone, diphenyl monosafite, diphenyl disulfite, acetophenone, benzophenone, P-toluenesulfonyl chloride, etc. Can be done. Examples of the present invention are described below. Example 1 Add 130g of ethyl acetate to a 500ml four-necked flask.
1 g of Kraton 1102 (manufactured by Ciel, SBS block copolymer) was charged, and the temperature was raised to 70°C while stirring to completely dissolve Kraton 1102. Next, the system was replaced with nitrogen gas, and 82 g of butyl acrylate, 18 g of vinyl acetate, and 0.2 g of dodecyl mercaptan were uniformly dissolved, and 0.3 g of radical initiator benzoyl peroxide was dissolved in 10 g of ethyl acetate. Drip. At first, it will generate heat, so cool it down as needed to keep it at 77-80℃. After 2 hours, 0.3 g of initiator was added to complete the reaction. The reaction rate was determined by solid content measurement during the course of the reaction, and the reaction was terminated 20 minutes after the reaction rate exceeded 90%. Next, the solvent is removed by increasing heating while blowing nitrogen gas under normal pressure. Further under reduced pressure (20mmHg,
Unreacted monomers are distilled off at ~100°C). Furthermore, in order to eliminate odor during melting, trace amounts of residual monomer are removed by steam distillation. then the product
Add 0.5g of benzophenone as a sensitizer to 100g and melt it on a piece of paper (approx. 190°C).
Apply 25μ coating. This was cross-linked with ultraviolet light under the following conditions,
The images were transferred to high-quality paper and polyester film (25μ), and an adhesion test was conducted based on JISZ1538 (adhesive paper for printing). The viscosity of the above adhesive was 11,250 cps at 190°C, and no increase in viscosity was observed even after 24 hours at 190°C. The conditions for ultraviolet crosslinking are as follows. Mercury lamp intensity: 80W (two lamps) Lamp height: 8cm Conveyor speed: 30m/min The above adhesion test results are shown in Table 1.

【table】

[Table] Reference example 1 In Example 1, an adhesive was made without using Kraton 1102 and cross-linked with UV rays, but the holding power was 120.
It was found that the adhesive was significantly impregnated into the high-quality paper within seconds, indicating that crosslinking had hardly progressed. Example 2 The adhesive prepared in Example 1 without adding any sensitizer was applied to high-quality paper in a heat-molten state (approximately 190° C.) to a thickness of approximately 25 μm. This was subjected to electron beam crosslinking under the following conditions, and an adhesion test was conducted based on JIS E1538 (adhesive paper for printing). The conditions for electron beam crosslinking are as follows. Accelerating voltage: 16 KV Irradiation dose: 5 to 20 Mrad Oxygen concentration: 500 ppm or less The results of the above adhesion test are shown in Table 2.

【table】

[Table] Example 3 In Example 1, the polymerizable monomer mainly consisting of alkyl acrylate was changed from butyl acrylate/vinyl acetate to 2-ethylhexyl acrylate/methyl methacrylate/vinyl acetate and butyl acrylate/methyl methacrylate. In addition, the diene copolymer Kraton 1102 (SBS block copolymer) is substituted with natural rubber, Kraton 1107 (SIS block copolymer manufactured by Ciel), SBR 1502 (styrene-butadiene random copolymer) and poly 1,2- Butadiene (polybutadiene manufactured by Nippon Soda B-1000) was substituted, and the amount of mercaptan was increased or decreased to obtain the adhesive of the present invention as shown in Table 3. The adhesion test was conducted in the same manner as in Example 2. However, the compositions shown in Table 3 are expressed by weight.

【table】

Claims (1)

[Scope of Claims] 1. A radiation-crosslinkable heat-melting pressure-sensitive adhesive using a product obtained by polymerizing a polymerizable monomer containing an acrylic ester as a main component in the presence of a diene polymer. . 2 In the presence of 0.3 to 10 parts by weight of a diene polymer,
The radiation-crosslinkable heat-melting pressure-sensitive adhesive according to claim 1, which is obtained by polymerizing 100 parts by weight of a polymerizable monomer.