JPH02110183A - Acrylic pressure-sensitive adhesive - Google Patents

Abstract

PURPOSE:To obtain a pressure-sensitive adhesive excellent in resistance to polar solvents by copolymerizing two kinds of alkyl (meth)acrylates different in the number of carbon atoms with an ethylenically unsaturated monomer having polar groups. CONSTITUTION:The title adhesive is obtained by copolymerizing 20-80wt.% 16-24C alkyl (meth)acrylate (A), 20-80wt.% 2-12C alkyl (meth)acrylate (B), and 1-20wt.% ethylenically unsaturated monomer (C) having polar groups copolymerizable with components A and B [e.g., (meth)acrylic acid]. This type of adhesive conventionally used comprises a copolymer of the component B with a small amount of the component C and has a problem of a poor resistance to polar solvents. The use of the component A having 16-24C long-chain alkyl groups, as one of the monomers for synthesis of an acrylic polymer, can reduce the polarity of the polymer to thereby give an adhesive excellent in resistance to polar solvents and free from tape peeling, etc., in polar solvents.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an acrylic pressure-sensitive adhesive having excellent solvent resistance, particularly resistance to polar solvents.

[Conventional technology]

Conventionally, rubber-based adhesives and acrylic-based adhesives are known as pressure-sensitive adhesives. Among these, the former rubber type has advantages such as less selectivity of adherends and high tack, but has disadvantages such as inferior heat resistance and aging resistance compared to the latter acrylic type. be. For this reason, acrylic pressure-sensitive adhesives have recently been more widely used in various fields of application.

This acrylic pressure-sensitive adhesive is generally made of an acrylic acid alkyl ester and/or a methacrylic acid alkyl ester having an alkyl group having 2 to 12 carbon atoms, particularly 2 to 9 carbon atoms, as a raw monomer, and a small amount of acrylic acid or methacrylic acid. , is based on an acrylic polymer obtained by copolymerizing ethylenically unsaturated monomers containing polar groups in the molecule, such as acrylonitrile, and is made by blending various additives such as tackifiers and crosslinking agents as appropriate. When used, this adhesive is applied to one or both sides of a thin material such as plastic or paper as a pressure-sensitive adhesive tape for adhering and fixing various adherends.

[Problem to be solved by the invention]

However, the above-mentioned known acrylic pressure-sensitive adhesives
The polarity of the base acrylic polymer is much higher than that of rubber-based polymers, so it has excellent solvent resistance as an adhesive.
In particular, it has a drawback of being extremely poor in resistance to alcohols such as methanol and ethanol, and polar solvents such as dimethylformamide and γ-butyrolactone.

Therefore, after adhesively fixing various types of adherends with pressure-sensitive adhesive tape using this type of adhesive, if left in contact with polar solvents as described above, There is a problem in that the tape peels off over time, that is, the adhesive layer swells with the polar solvent and a part of it is eluted, causing the tape peeling.

For example, in electrolytic capacitors, acrylic pressure-sensitive adhesive tape is used to secure electrolytic paper, but in recent years, from the perspective of improving the characteristics of capacitors, dimethylformamide and γ- With the advent of polar solvents such as butyrolactone, when electrolytic paper is secured with the above adhesive tape, the tape peels off within a relatively short period of time after being impregnated with electrolyte. Problems are occurring frequently.

Therefore, in view of the above-mentioned conventional circumstances, the present invention has been developed to provide an acrylic material with excellent solvent resistance that can fully demonstrate its original adhesive and fixing function and that does not cause problems such as tape peeling over time even in polar solvents. The purpose is to provide pressure-sensitive adhesives.

[Means to solve the problem]

As a result of intensive studies to achieve the above object, the inventors found that acrylic acid or methacrylic acid containing a long chain alkyl group with 6 to 24 carbon atoms was used as one of the monomer components when synthesizing an acrylic polymer. When an acid alkyl ester is used, an acrylic polymer is obtained in which the polarity of the entire polymer is reduced by introducing the long-chain alkyl group into the side chain of the molecule, and pressure-sensitive adhesives based on this polymer are obtained. The adhesive has excellent resistance to polar solvents and does not cause problems such as swelling even if left in this solvent for a long period of time.This successfully solves the conventional problems such as tape peeling in polar solvents. I realized that this invention could be achieved and completed this invention.

That is, this invention comprises: a) 20 to 8% by weight of an acrylic acid alkyl ester and/or a methacrylic acid alkyl ester in which the alkyl group has 16 to 24 carbon atoms; and b) the alkyl group has 2 to 24 carbon atoms. 20 to 80% by weight of an acrylic acid alkyl ester and/or a methacrylic acid alkyl ester in the range of 12, and C) an ethylenically unsaturated heptamer containing a polar group in the molecule that can be copolymerized with the above components a and b. The present invention relates to an acrylic pressure-sensitive adhesive having excellent solvent resistance and containing as a main component an acrylic polymer consisting of a copolymer with 1 to 20% by weight.

[Structure and operation of the invention]

The acrylic acid alkyl ester and/or methacrylic acid alkyl ester (hereinafter both esters are collectively referred to as (meth)acrylic acid alkyl ester) used in this invention as component a has a carbon number in the range of 16 to 24. It is a monomer having a chain alkyl group, and as mentioned above, it is intended to contribute to improving the solvent resistance of acrylic polymers.

Specific examples of the monomer of component C include cetyl acrylate or cetyl methacrylate whose alkyl group has 16 carbon atoms, stearyl acrylate, stearyl methacrylate, eicosyl acrylate or eicosyl methacrylate whose alkyl group has 18 carbon atoms, and cetyl methacrylate whose alkyl group has 16 carbon atoms; Examples include tetraeicosyl acrylate and tetraeicosyl methacrylate.

The (meth)acrylic acid alkyl ester as component b used in this invention has an alkyl group having 2 to 2 carbon atoms, which has been used as the main monomer of conventional acrylic polymers.
12, particularly preferably in the range of 6 to 9, and this monomer is an essential component for obtaining an acrylic polymer with pressure-sensitive adhesive properties.

Specific examples of the monomer of component b include ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate,
2-ethylhexyl methacrylate, octyl acrylate, octyl methacrylate, nonyl acrylate,
Examples include nonyl methacrylate, isononyl acrylate, and isononyl methacrylate.

The ethylenically unsaturated monomer of component C used in this invention is a monomer that is copolymerizable with the monomers of components a and b above, and has a polar group such as a carboxyl group, nitrile group, hydroxyl group, or epoxy group in the molecule. It has a group and contributes to improving the adhesive force, adhesive force, and cohesive force of the pressure-sensitive adhesive.

Specific examples of monomers for component C include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid,
Acrylonitrile, methacrylate trile, hydroxyethyl acrylate, hydroxyethyl methacrylate,
Examples include glycidyl acrylate and glycidyl methacrylate.

The above a, b, C used in this invention
The proportions of the components to be used are 20 to 80% by weight of (meth)acrylic acid alkyl ester as component A, 20 to 80% by weight of (meth)acrylic acid alkyl ester as component B, and 20 to 80% by weight of (meth)acrylic acid alkyl ester as component C. The content of the ethylenically unsaturated monomer is 1 to 20% by weight, and if it is outside this range, either the adhesive properties or the solvent resistance will be impaired.

The above-mentioned usage ratio is particularly suitable for the C component being 30 to 80%.
% by weight, component B is 20-70% by weight, component C is 2-10%
Weight%.

In addition, as ethylenically unsaturated monomers other than the above-mentioned a, b, and C components, styrene and its derivatives, 69 vinyl, vinyl propionate, methyl acrylate, methyl methacrylate, and other conventionally known acrylic polymers are commonly used. Various modifying monomers may be used as necessary. The amount used is preferably 10% by weight or less based on the total monomers.

In this invention, the copolymerization of ethylenically unsaturated monomers that essentially contain components a, b, and C can be carried out by a conventional method using an appropriate polymerization initiator such as abbisisobutyronitrile or benzoyl peroxide. As for the polymerization method, any of various known methods such as solution polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization can be employed.

The acrylic polymer obtained by this copolymerization preferably has a weight average molecular weight in the range of 300,000 to 1,500,000; if this molecular weight is too low, it may be difficult to obtain good results in adhesive properties and solvent resistance. On the other hand, if it becomes too high, it will be disadvantageous in terms of handling such as coating workability, which is not preferable.

In this invention, even if the above acrylic polymer is used alone as an adhesive, desirable results in adhesive properties and solvent resistance can be obtained.

However, in order to better improve these properties, it is preferable to further crosslink the above polymer by appropriate means. This crosslinking may be performed after or before application to a thin sheet material or an adherend when forming a pressure-sensitive adhesive tape.

The crosslinking means may be electron beam irradiation, light irradiation, etc., but it is more convenient to include in advance a polyfunctional compound that reacts with the polar group of the acrylic polymer in the adhesive. Examples of such polyfunctional compounds include polyfunctional melamine compounds, polyfunctional epoxy compounds, and polyfunctional isocyanate compounds. The amount of these compounds used is 100% of the acrylic polymer.
It is usually 3 parts by weight or less.

In addition to the above-mentioned components, the acrylic pressure-sensitive adhesive of the present invention may contain various conventionally known additives such as tackifiers, softeners, antioxidants, antistatic agents, pigments, colorants, and fillers, as needed. It is optionally possible to include agents.

When using the acrylic pressure-sensitive adhesive of the present invention, it can be applied to one or both sides of a thin material such as a plastic sheet or paper and dried to form an adhesive layer with a thickness of usually 5 to 50 μm. It can be made into an adhesive tape or sheet, and as mentioned above, this adhesive product has excellent solvent resistance, so it is used as a tape for wrapping electrolytic capacitors, and for sanitary products such as alcohol-containing paper towels. Very useful as sealing labels, adhesive tapes, etc.

〔Effect of the invention〕

As described above, in this invention, the monomer component for obtaining the acrylic polymer has 16 to 24 carbon atoms.
By using an acrylic acid alkyl ester and/or a methacrylic acid alkyl ester having a long-chain alkyl group, it has excellent solvent resistance without causing any problems such as tape peeling in polar solvents as described above. An excellent acrylic pressure-sensitive adhesive can be provided.

[Examples] Below, examples of the present invention will be described in more detail. In addition, in the following, part 1% means 1% by weight, respectively. Moreover, the term "average molecular weight" means a weight average molecular weight measured by gel permeation chromatography in terms of standard polystyrene.

Example 1 30 parts of stearyl acrylate, 67 parts of 2-ethylhexyl acrylate, 3 parts of acrylic acid, 0.1 part of azobisisobutyronitrile as a polymerization initiation catalyst, and 200 parts of toluene as a polymerization solvent were placed in a three-neck flask. After the oxygen in the polymerization system was removed by stirring for 2 hours while introducing nitrogen gas, the temperature was raised to 60°C and the polymerization reaction was carried out for 8 hours. A polymer solution with a polymer concentration of 33% was obtained.

A polyfunctional isocyanate compound (B
Polymer 10
1 part to 0 part was added and thoroughly stirred to obtain an acrylic pressure-sensitive adhesive of the present invention.

Next, this adhesive was applied onto a polyethylene terephthalate film having a thickness of 25 μm so that the thickness after drying would be 20 μm, and the adhesive was dried by heating at 100° C. for 10 minutes to produce a pressure-sensitive adhesive tape.

Example 2 50 parts of cetyl acrylate, 45 parts of 2-ethylhexyl acrylate, 5 parts of acrylic acid, 0.1 part of abbisisobutyronitrile and 200 parts of toluene were charged into a three-hole flask, and the same procedure as in Example 1 was carried out. A polymer solution containing an acrylic polymer with an average molecular weight of 450,000 and a polymer concentration of 33% was obtained.

Next, an acrylic pressure-sensitive adhesive was prepared by adding and mixing the same amount of the same polyfunctional isocyanate compound as in Example 1 to this polymer solution, and using this adhesive, the same amount as in Example 1 was prepared. A pressure-sensitive adhesive tape was produced using the method described above.

Example 3 50 parts of stearyl methacrylate, 43 parts of isononyl acrylate, 7 parts of acrylic acid, 0.1 part of azobisisobutyronitrile and 200 parts of toluene were charged into a three-hole flask, and polymerization was carried out in the same manner as in Example 1. Therefore, the polymer concentration including an acrylic polymer with an average molecular weight of 580,000 is 3.
A 3% polymer solution was obtained.

Next, an acrylic pressure-sensitive adhesive was prepared by adding and mixing the same amount of the same polyfunctional isocyanate compound as in Example 1 to this polymer solution, and using this adhesive, the same amount as in Example 1 was prepared. A pressure-sensitive adhesive tape was produced using the method described above.

Example 4 65 parts of cetyl acrylate, 30 parts of 2-ethylhexyl methacrylate, 5 parts of hydroxyethyl acrylate,
0.1 part of azobisisobutyronitrile and 2 parts of toluene
00 parts were put into a three-hole flask and polymerized in the same manner as in Example 1 to obtain a polymer solution containing an acrylic polymer with an average molecular weight of 620,000 and a polymer concentration of 33%.

Next, an acrylic pressure-sensitive adhesive was prepared by adding and mixing the same amount of the same polyfunctional isocyanate compound as in Example 1 to this polymer solution, and using this adhesive, the same amount as in Example 1 was prepared. A pressure-sensitive adhesive tape was produced using the method described above.

Comparative Example 1 97 parts of 2-ethylhexyl acrylate, 3 parts of acrylic acid
1 part, 0.1 part of azobisisobutyronitrile, and 200 parts of toluene were placed in a three-necked flask, and the polymerization was carried out in the same manner as in Example 1 to obtain a polymer concentration of 3.3 parts, including an acrylic polymer with an average molecular weight of 470,000. % polymer solution was obtained.

Next, an acrylic pressure-sensitive adhesive was prepared by adding and mixing the same amount of the same polyfunctional isocyanate compound as in Example 1 to this polymer solution, and using this adhesive, the same amount as in Example 1 was prepared. A pressure-sensitive adhesive tape was produced using the method described above.

Comparative Example 2 93 parts of isononyl acrylate, 7 parts of acrylic acid, 0.1 part of azobisisobutyronitrile, and 200 parts of toluene
A portion of the solution was placed in a three-neck flask, and polymerization was carried out in the same manner as in Example 1 to obtain a polymer solution containing an acrylic polymer with an average molecular weight of 550,000 and a polymer concentration of 33%.

Next, an acrylic pressure-sensitive adhesive was prepared by adding and mixing the same amount of the same polyfunctional isocyanate compound as in Example 1 to this polymer solution, and using this adhesive, the same amount as in Example 1 was prepared. A pressure-sensitive adhesive tape was produced using the method described above.

For each of the pressure-sensitive adhesive tapes produced in Examples 1 to 4 and Comparative Example 1.2 above, a tape peeling test was conducted in the following manner as a solvent resistance test. The results were as shown in the table below.

<Tape peeling test> Each pressure-sensitive adhesive tape cut to a width of 10 mm was wrapped twice around a steel strip with a diameter of 5 mm, and then wrapped with dimethylformamide,
The tape was immersed in each polar solvent consisting of γ-butyrolactone or ethanol at 20° C. for 24 hours, and the state of peeling of the tape was observed and evaluated as follows.

◎...No peeling ○...Foil 1 peeling within 111 △...Peeling within 31■ of In or above ×...31
As is clear from the results in the table above, the use of an acrylic polymer containing an acrylic acid alkyl ester or a methacrylic acid alkyl ester with an alkyl group of 16 to 24 carbon atoms as a copolymerization component makes it possible to remove polar solvents. It can be seen that an acrylic pressure-sensitive adhesive tape with a reduced degree of swelling in the adhesive tape and less likely to peel off can be obtained.

Claims (3)

[Claims] (1) a) 20 to 80% by weight of an acrylic acid alkyl ester and/or a methacrylic acid alkyl ester in which the alkyl group has a carbon number in the range of 16 to 24, and b) an alkyl group in which the carbon number is in the range from 2 to 12. 20 to 80% by weight of a certain acrylic acid alkyl ester and/or methacrylic acid alkyl ester, and c) 1 to 20% by weight of an ethylenically unsaturated monomer containing a polar group in the molecule that can be copolymerized with the above components a and b. An acrylic pressure-sensitive adhesive with excellent solvent resistance that contains as a main component an acrylic polymer consisting of a copolymer with (2) Claim (1) wherein the acrylic polymer is crosslinked.
) Acrylic pressure-sensitive adhesive described in . (3) The method according to claim (1), which contains a polyfunctional compound consisting of a polyfunctional melamine compound, a polyfunctional epoxy compound, or a polyfunctional isocyanate compound for crosslinking this polymer together with the acrylic polymer. Acrylic pressure sensitive adhesive.