JPS623190B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adhesive that forms an adhesive layer or a pressure-sensitive adhesive layer by applying ionizing radiation onto a substrate and polymerizing the adhesive.

Conventionally, solution-type or emulsion-type adhesive compositions have been widely used as adhesive compositions used to provide adhesive layers by coating onto base materials such as tapes and sheets. After applying these adhesive compositions onto a substrate, the solvent or water is evaporated to form an adhesive layer, and the composition is further covered with release paper to provide products such as adhesive tapes and sheets.

However, there are several problems with the use of these solution or emulsion type adhesives. For example, solution-based adhesives generally have a
% solids and requires large amounts of solvent. Therefore, there are problems such as flammability and toxicity at the coating site, and problems such as large energy loss and equipment costs associated with drying and recovering the solvent.
Furthermore, the use of emulsion type adhesives generally has problems such as a decrease in the water resistance of the adhesive and corrosion of metals. In addition, compared to solution-type products, there are fewer problems such as flammability and toxicity, but they have the disadvantage that a large amount of energy is required to dry water, and they cannot be used on substrates with poor heat resistance.

In order to solve these drawbacks of solution-type or emulsion-type adhesives, a solvent-free composition is applied onto a base material and irradiated with ionizing radiation such as ultraviolet rays or electron beams to form an adhesive layer. A method or a coating adhesive composition for the method has been proposed. For example, in Japanese Patent Publication No. 55-15217, acrylic acid alkyl ester alone or in combination with the side chain
A pressure-sensitive adhesive composition consisting of a mixture with a polymerizable monomer having a polar group such as COOH, CN, COOR, CONH ₂ , etc.; A composition in which an agent is dissolved in a monofunctional acrylate;
51-79131 discloses that a (meth)acrylic acid ester alone or a copolymer is a mixed monomer of a (meth)acrylic acid alkyl ester and a (meth)acrylic ester or acrylamide having a polar group such as a hydroxyl group. A diluted composition has been proposed.

However, the above-mentioned solvent-free pressure-sensitive adhesive compositions are not necessarily satisfactory in terms of cohesive strength and curing process of the resulting pressure-sensitive adhesive. In other words, in order to exhibit good properties as an adhesive, a combination of high adhesive strength and cohesive strength is required, and high adhesive strength can be achieved by using a polymer with a low Tg (glass transition point) or by using a tackifier. However, in order to provide a high cohesive force, it is necessary to increase the molecular weight of the binder resin and to have an appropriate crosslinked structure. When conventional monomer-only compositions are cured by radiation irradiation, a polymer with a low Tg is obtained and the adhesion is satisfactory, but it is difficult to increase the cohesive force by increasing the molecular weight, and Only slight improvements are obtained when irradiated at high doses. Also, the curing speed is slow. This situation is almost the same when the non-curable polymer and tackifier are diluted with a monofunctional monomer. Furthermore, these compositions are diluted with low molecular weight vinyl monomers to provide coating suitability and radiation curability; however, application of compositions containing these monomers degrades the working environment and also causes damage after curing. Problems such as bad odors caused by residual monomers in these products also remain.

The present invention provides an adhesive layer that can be applied substantially solvent-free and without containing low-molecular-weight monomers, and that has both high adhesive strength and cohesive strength by irradiating with ionizing radiation at a relatively low dose. The purpose is to provide an adhesive that can give

The adhesive of the present invention is aimed at achieving the above-mentioned object, and more specifically is made of an acrylic acid alkyl ester and a vinyl monomer having a polar group such as a carboxyl group, a hydroxyl group, an amino group, or an epoxy group. Per 1000 molecular weight of copolymer main chain,
It is characterized by being composed of an acrylic copolymer with a molecular weight of 1,000 to 50,000, which has been introduced with a side chain having 0.01 to 2 olefinic unsaturated bonds, and can be applied virtually without solvent and is free from ionizing radiation. It can be polymerized by

That is, the acrylic copolymer constituting the adhesive of the present invention has a copolymer main chain that exhibits a good adhesive property, and also has good polymerization curability due to the olefinic unsaturated bond in the side chain. and, through its polymerization, can provide an adhesive layer that exhibits a suitable crosslinking density and therefore good cohesion. Furthermore, since the molecular weight is kept low, it can be applied without a diluent.

The present invention will be explained in more detail below. In the following description, "%", "part" and component ratio are based on weight unless otherwise specified.

The hand chain of the acrylic copolymer of the present invention is a copolymer (hereinafter referred to as a ``main chain copolymer'') of an acrylic acid alkyl ester and a vinyl monomer having a polar group (hereinafter referred to as a ``polar vinyl monomer''). (referred to as "copolymer main chain").

As the acrylic acid alkyl ester which is a copolymerization component, those having an alkyl group having a carbon number of 2 to 12 are preferably used, and specifically, for example, ethyl acrylate, isoropyl acrylate,
Examples include butyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, lauryl acrylate, and the like.

The other copolymerization component, the polar vinyl monomer, has a polar group selected from a carboxyl group, a hydroxyl group, an amino group, and an epoxy group, and specifically includes, for example, acrylamide, hydroxyethyl acrylate, Acrylic acid, acrylonitrile, N-methylol, acrylamide, N-
T-butylacrylamide, itaconic acid, 2-hydroxy-3-phenoxypropyl acrylate, etc. are used. These polar vinyl monomers are used to improve adhesion and cohesive force with objects to be adhered, and their polar groups are used to introduce olefinic unsaturated bonds into side chains as described later. It will be done.

To obtain a copolymer main chain, 1 part of polar vinyl monomer is added to 100 parts of acrylic acid alkyl ester.
It can be obtained by mixing up to 100 parts, preferably 1 to 20 parts, and copolymerizing by a conventional method using, for example, a peroxide initiator. At this time, it is possible to suppress the molecular weight to a low molecular weight by using a relatively large amount of a chain transfer agent such as mercaptans, quinones, hydrocarbons, nitro compounds, and phenols. Specific examples of such chain transfer agents include n-butylmercaptan, n-dodecylmercaptan, thioglycolic acid ester, quinone, hydroquinone, chloranil, pyrogallol, 2,4-dinitrophenylhydrazine, 2,6-di-t -butyl-4-methylphenyl.

In addition, as another synthesis method, a copolymer can be obtained by dispersing an acrylic monomer in water, adding a suspending agent, and performing floatation polymerization.

In this case, the molecular weight can also be controlled by the acrylic monomer concentration and reaction time.

If the amount of polar vinyl monomer is less than 1 part per 100 parts of acrylic acid alkyl ester, the cohesive force of the adhesive layer obtained by curing the adhesive composition of the present invention will be insufficient, and the adhesiveness with the substrate will be poor. Also missing, 100
If the amount is exceeded, the adhesiveness will be insufficient.

The main chain copolymer obtained has polar groups resulting from the polar vinyl monomer. Utilizing this polar group, an olefinic unsaturated bond is introduced into the side chain. For its introduction, for example, the following method is used.

(a) A method in which a hydroxyl group or an epoxy group is applied to the carboxyl group of the main chain copolymer with an olefinic unsaturated monomer; (b) Contrary to (a), a hydroxyl group or an epoxy group of the main chain copolymer (c) A method of causing an olefinic unsaturated monomer having an isocyanate group to act on a hydroxyl group, a carboxyl group, or an amino group of the main chain copolymer. .

Monomers having an olefinic unsaturated bond used for this purpose include, for example, acrylic acid, cinnamic acid, 2-hydroxyethyl acrylate, glycidyl methacrylate, glycidyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxy- 3-phenoxypropyl acrylate, N-methylol acrylamide, etc.;
Or as having an isocyanate group,
Examples include 1:1 addition reaction products of tolylene diisocyanate, hexamethylene diisocyanate, xylene diisocyanate and an acrylic monomer having a hydroxyl group or a carboxyl group.

The olefinic unsaturated bond is introduced at an average rate of 0.01 to 2, preferably 0.1 to 1, per 1000 molecular weight of the main chain of the copolymer. If the number of unsaturated bonds is less than 0.01, the introduction effect will be poor and the curability will be insufficient, and if more than 2 are included, the adhesive layer will lack tackiness.

In this way, a copolymer (oligomer) having an olefinic unsaturated bond and having a molecular weight of 1,000 to 50,000 is obtained. Within the above-mentioned range, by mixing copolymers with different molecular weights and types as necessary, a viscosity suitable for coating, for example, 10~10 can be obtained.
A pressure-sensitive adhesive of the present invention having a strength of 1000 poise is obtained.

In addition, it goes without saying that the adhesive of the present invention may contain various fillers, tackifiers, plasticizers, etc. contained in ordinary adhesive compositions, if necessary, in the amounts normally used. It is.

The pressure-sensitive adhesive of the present invention thus obtained is generally coated on a base material such as paper, plastic film, metal box, or a laminate film thereof by a method such as roll coating, die coating, knife coating, or dip coating.
For example, it is applied at a rate of 10 to 30 g/ ^m2 ,
An adhesive layer is provided by curing by irradiating with ionizing radiation such as gamma rays or electron beams. Among them, 50~
Good results can be obtained by applying an electron beam with an energy of 1000 KeV, especially 100 to 300 KeV, at a dose of 1 to 20 Mrad. When irradiating with ionizing radiation,
It is advantageous to protect the coated surface with a paper or film that has release properties and to block oxygen before irradiation, since the generated radicals can be used effectively.

As described above, according to the present invention, an adhesive is provided which is mainly composed of a relatively low molecular weight copolymer containing an acrylic acid alkyl ester as a main component and having a polar group and an olefinic unsaturated bond. This composition is applied onto a substrate and irradiated with a relatively low dose of ionizing radiation to provide an adhesive layer with a good balance of adhesiveness and cohesive force. The resulting adhesive tapes, sheets, and other products are suitably used for adhering paper, various plastic films, and various metal plates, for example. In addition, this adhesive is solvent-free, so the flammability of the solvent
Problems such as toxicity, energy loss and equipment requirements associated with drying and solvent recovery are significantly improved, and since it does not substantially contain low molecular weight monomers, problems such as deterioration of the working environment and residual monomers are also avoided. There aren't many.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 100 parts of 2-ethylhexyl acrylate, 5 parts of acrylic acid, and 100 parts of toluene were placed in a 14-necked flask, and the flask was purged with nitrogen for about 2 hours while stirring with a stirrer. Furthermore, benzoyl peroxide (BPO) was added as a polymerization initiator. ) on a hot water bath.
After reacting at 60°C for 2 hours, 10 parts of n-dodecylmercaptan was added to prepare a viscous polymer.
Next, 1.5 parts of glycidyl acrylate was added dropwise.
The reaction was carried out by heating to 100°C and stirring for about 10 hours.

The solvent was removed from the solution of the acrylic copolymer (molecular weight approximately 5000) obtained in this manner, and the coating was applied to a 20μ thick polyester film in a solvent-free state to a coating thickness of 30μ. A polyethylene laminate paper with peelability is laminated on the object, and an electron beam of 5 Mrad is irradiated from the surface of the polyester film in a _N2 atmosphere using a low-energy electron accelerator (Electro Curtain CB20d 50/30, manufactured by Energy Science) to remove the adhesive. Polymerized and crosslinked.

After electron beam irradiation, the release paper was cut into 10 mm width pieces, the adhesive-coated polyester film was peeled off from the release paper to make an adhesive tape, and a stainless steel plate (SUS-
304), and the adhesive strength was measured by a 180° peel test specified in JIS-Z-0273. the result
Good results were shown at 350g/10mm.

In addition, for the 180° peel test specified in JIS-Z-0273, a stainless steel plate (SUS-304) is polished with sandpaper (#280) and then adhesive tape is attached.
After aging under certain conditions by rolling a 2 kg rubber roll back and forth once, the adhesive tape is folded 180 degrees against the stainless steel and peeled off at a speed of 300 mm/min, and the peeling force at this time is measured.

Example 2 In a reactor, 400 parts of water, 1 part of Triton 720 (alkyl allyl ether sulfonate), 1 to 2 parts of
Tergitol (2-methyl-7-ethylhendemyl-
4-Sodium sulfonate) and 0.01 part of ammonium persulfate. Stir the solution slowly.
Add 100 parts of methyl acrylate and 3 parts of acrylamide and heat the reactor. After heating and stirring at 70° C. for 1 hour, excess monomer is removed from the polymer suspension by steam distillation for 15 to 30 minutes. Next, add this 2
The mixture was poured into twice the volume of 5% hot saline solution, and the polymer was precipitated and separated to obtain an acrylic copolymer.

Separately, 2-hydroxyethyl acrylate and toluene diisocyanate were added at room temperature and stirred at 60°C for 2 hours to obtain a 1:1 adduct.
This 1:1 adduct was reacted with 100 parts of the previously synthesized acrylic copolymer by stirring at 60° C. for 4 hours to obtain an acrylic copolymer having a molecular weight of 10,000 and a viscosity of 40 poise.

This acrylic copolymer was coated on a polyester film in the same manner as in Example 1, cured to produce an adhesive tape, and evaluated by a 180° peel test, yielding a result of 450 g/10 mm.

Claims (1)

[Claims] 1 an acrylic acid alkyl ester and a polar compound selected from acrylamide, hydroxyethyl acrylate, acrylic acid, acrylonitrile, N-methylolacrylamide, N-t-butylacrylamide, itaconic acid, and 2-hydroxy-3-phenoxypropyl acrylate Molecular weight of copolymer main chain consisting of vinyl monomer having groups
Molecular weight 1000~ by introducing side chains having 0.01~2 olefinic unsaturated bonds per 1000
50,000 acrylic copolymer, which can be applied substantially without solvent and which can be polymerized by ionizing radiation.