JP2592876B2 - Pressure sensitive adhesive - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an acrylic pressure-sensitive adhesive, that is, a pressure-sensitive adhesive using an acrylic polymer as an adhesive main component.

[Conventional technology]

In recent years, pressure-sensitive adhesives have been used in many fields because of their good bonding workability. Among them, acrylic pressure-sensitive adhesives are required to have these properties because of their excellent weather resistance, heat resistance, and deterioration resistance. Has been especially awarded in certain fields.

By the way, such a pressure-sensitive adhesive exhibits excellent initial adhesive strength due to excellent wettability to adherends, particularly rough surface adherends, and resists stress remaining on adherends after bonding. It has excellent residual stress resistance that can substantially maintain the above initial adhesive strength with a large cohesive strength that can be achieved, and under severe conditions such as when left for a long time under high temperature and high humidity It is desired to have excellent durability that can sufficiently resist even a stress newly generated in the adherend when placed.

From this viewpoint, in acrylic pressure-sensitive adhesives,
Until today, devising the monomer composition of the acrylic polymer used as the main adhesive component, or blending this polymer with an appropriate tackifying resin, plasticizer, etc., and adding various crosslinking agents to crosslink the polymer Various attempts have been made to improve the adhesive properties such as the above.

[Problems to be solved by the invention]

However, despite the above-mentioned attempts, acrylic pressure-sensitive adhesives which are excellent in both the above-mentioned initial adhesive strength, particularly the rough surface adhesive strength and the residual stress resistance, and which are highly satisfactory in durability have been found. Absent. For this reason,
For example, when this kind of adhesive is applied to the adhesive part of the elastic rough surface such as foam, the adhesion failure of the overlapped part, or the elastic return of the metal plate when applied to the curved surface adhesive part between the metal plate and the molded product It is still an unsolved problem that adhesion failures due to the above-mentioned problems often occur under severe conditions, particularly when left under high temperature and high humidity for a long time.

Accordingly, the present invention provides an acrylic pressure-sensitive adhesive which is excellent in both initial adhesive strength, particularly rough surface adhesive strength and residual stress resistance, and has high durability, which can solve the above-mentioned problems. It is intended to be.

[Means for solving the problem]

The present inventors have conducted intensive studies to achieve the above object, and as a result, as an acrylic polymer used as an adhesive main component, a main monomer mainly composed of alkyl (meth) acrylate and a polyfunctional unsaturated monomer. When using an acrylic polymer having a specific molecular weight composed of a copolymer of the formula (1), a large cohesive force capable of withstanding the residual stress of the adherend after bonding is obtained in addition to having excellent rough surface adhesion, that is, the residual stress resistance The inventor has found that a pressure-sensitive adhesive having excellent durability and high durability capable of maintaining its adhesive strength even under severe conditions can be obtained, and the present invention has been completed.

That is, the present invention provides the following general formula: (Wherein, R ₁ is a hydrogen atom or a methyl group, and R ₂ is
To a main monomer mainly composed of a (meth) acrylic acid alkyl ester represented by the formula:
According to gel permeation chromatography comprising a copolymer of a polyfunctional unsaturated monomer having two or more polymerizable carbon-carbon double bonds in one molecule at a ratio of 0.001 to 5 parts by weight. The measured weight average molecular weight is
The present invention relates to a pressure-sensitive adhesive characterized by containing an acrylic polymer in a range of 500,000 to 1.5 million and a low molecular weight component having a molecular weight of 100,000 or less and 15% by weight or less.

As described above, in the present invention, the acrylic polymer serving as an adhesive main component is a copolymer of a main monomer mainly composed of an alkyl (meth) acrylate and a polyfunctional unsaturated monomer, and is a gel permeation. The weight average molecular weight measured by the chromatographic method was in the range of 500,000 to 1.5 million, and a low molecular weight component having a molecular weight of 100,000 or less and a low molecular weight component having a small amount of 15% by weight or less were used. As a result, both the rough surface adhesive strength and the residual stress resistance are excellent, and the durability is highly satisfied,
In addition, acrylic pressure-sensitive adhesives that exhibit these properties stably in a wide variety of additives, such as tackifier resins, plasticizers, and cross-linking agents, are commonly formulated for the purpose of adjusting the monomer composition and adhesive properties. According to this, an excellent effect that it is possible to avoid all the problems such as poor adhesion of the overlapped portion of the foam or the like under the severe conditions as described above and poor adhesion due to elastic return of the metal plate and the like. Was achieved.

The reason why such an effect can be obtained is not always clear at present. It is presumed that the use of a polyfunctional unsaturated monomer causes the acrylic polymer to have a moderately branched chain, thereby improving the flowability due to the branching effect, and increasing the cohesive force due to an increase in entanglement between the polymer chains. Because of the improvement, good results were obtained in all of the properties of rough surface adhesion, residual stress resistance and durability, and the low molecular weight component of the acrylic polymer reduced residual stress resistance. And even better results in improving durability, and these properties are stably obtained in the above-mentioned wide monomer composition and a wide blending composition, while the presence of the low-molecular weight component is important in maintaining rough surface adhesion. It is not a significant factor, and it is more preferable to reduce this component in terms of stabilizing the adhesive strength, particularly based on the use of the polyfunctional unsaturated monomer. Improvement of surface adhesive force is thought whether not to be well expressed than by connexion to reduce the low molecular weight component.

In this specification, the molecular weight of an uncrosslinked acrylic polymer measured by gel permeation chromatography (hereinafter referred to as GPC method) is 10%.
The weight percentage of low molecular weight components of 10,000 or less (hereinafter referred to as low molecular percentage A), and the molecular weight of the crosslinked acrylic polymer measured by the same method as described above.
The weight percentage of low molecular weight components of 100,000 or less (hereinafter referred to as low molecular weight B) is measured and calculated by the following method.

That is, the dried sample polymer is passed through an infinite number of pores (0.2
μm) and immersed in ethyl acetate at 20 ° C. for 240 hours, and the weight percentage of the soluble polymer eluted in ethyl acetate (hereinafter referred to as percentage X) is measured. Next, the weight percentage of the low molecular weight component having a molecular weight of 100,000 or less (hereinafter, referred to as percentage Y) is measured from the molecular weight distribution curve by the GPC method using the soluble polymer. From these percentages X and Y, the low molecular percentages A and B are calculated according to the following formula.

Most of the uncrosslinked acrylic polymer is a soluble polymer, that is, the percentage X = 100. Therefore, the low molecular percentage A substantially matches the percentage Y which is a measured value by the GPC method. On the other hand, the crosslinked acrylic polymer usually contains a crosslinked polymer and an uncrosslinked polymer, and the latter uncrosslinked polymer is mostly a soluble polymer, while the former crosslinked polymer has a higher degree of crosslinking and Depending on the molecular weight configuration before cross-linking, the polymer becomes a soluble polymer, a non-soluble polymer, or a mixed polymer thereof. That is, since the weight percentage X of the soluble polymer takes various values according to the above-mentioned embodiment, the low molecular percentage B does not always coincide with the percentage Y measured by the GPC method, and even if the insoluble polymer is slight, If it exists, it becomes smaller than the above percentage Y.

The measurement conditions of the molecular weight distribution curve by the GPC method are a sample concentration of 1 mg / ml, a sample introduction amount of 500 mg, a column temperature of 40 ° C., and a flow rate of 1.0 ml / min.

[Structure and operation of the invention]

As the alkyl (meth) acrylate represented by the above general formula used in the present invention,
Various alkyl acrylates or alkyl methacrylates in which R ₂ is an alkyl group having 1 to 18 carbon atoms can be used. Specifically, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, acrylic acid Examples thereof include 2-ethylhexyl, octyl acrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and octyl methacrylate.

Such a (meth) acrylic acid alkyl ester may be used alone as a main monomer, or may be used together with another monomer copolymerizable therewith. As other monomers, any of various monomers known as monomers for modifying acrylic pressure-sensitive adhesives such as vinyl acetate, styrene, acrylonitrile, acrylamide, acrylic acid, methacrylic acid, hydroxyethyl acrylate, glycidyl methacrylate, etc. Can be used. These other monomers are desirably 50% by weight or less based on the total amount of the (meth) acrylic acid alkyl ester in terms of adhesive properties.

Examples of the polyfunctional unsaturated monomer having two or more polymerizable carbon-carbon double bonds in one molecule used together with these main monomers include the following general formulas: (Wherein, R ₃ and R ₄ are hydrogen atoms or methyl groups, and n is 1 to 3
2, preferably an integer of 1 to 15) represented by ethylene glycol or polyethylene glycol diacrylate or dimethacrylate,
Examples include trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, and 1,4-butanediol diacrylate. Of course, other monomers can be widely used as long as they have two or three or more polymerizable carbon-carbon double bonds in one molecule.

The amount of this polyfunctional unsaturated monomer used depends on the main monomer
0.001 to 5 parts by weight, preferably 0.01 to 2 parts by weight per 100 parts by weight
It is the ratio to be parts by weight. If the amount is less than 0.001 part by weight or exceeds 5 parts by weight, any of the properties of the rough surface adhesion, the residual stress resistance and the durability is extremely lowered, which is not preferable. The optimum amount of the polyfunctional unsaturated monomer is also related to the molecular weight of the acrylic polymer. Generally, when a polymer having a low average molecular weight is used, a polymer having a high average molecular weight is used in an amount larger than the above range. It is preferable to use a small amount.

The acrylic polymer used as the main adhesive component in the present invention comprises a copolymer of a main monomer mainly composed of the alkyl (meth) acrylate and a polyfunctional unsaturated monomer as described above, and is measured by a GPC method. The weight average molecular weight is in the range of 500,000 to 1.5 million, and the low molecular weight component having a molecular weight of 100,000 or less is 15% by weight or less, that is, the low molecular percentage A is 15% or less, preferably 10% or less. It has a specific molecular weight configuration characterized by the following.

When the low molecular percentage A exceeds 15%, all of the initial adhesive strength, residual stress resistance and durability can be improved even if various additives for adjusting adhesive properties such as a tackifying resin and a crosslinking agent are added. Obtaining an acrylic pressure-sensitive adhesive having a highly improved adhesive property as the object of the present invention, which is difficult to be highly satisfied and hard to stably exhibit these properties in a wide range of monomer compositions and a wide range of compounding compositions. Becomes difficult.

In the present invention, the acrylic polymer having the molecular weight composition as described above is prepared by subjecting the monomer to a polymerization method such as a solution polymerization method, an emulsion polymerization method, or a bulk polymerization method using a polymerization catalyst such as an azo compound or a peroxide. After the polymerization in the polymerization solution, a method of separating and removing the above components by adding an organic solvent capable of dissolving only the low molecular weight components to the polymerization solution, or a tape obtained by adding the above polymerization solution or a mixture obtained by adding a necessary compounding agent thereto. It can be easily obtained by, for example, a method in which the low molecular weight component is eluted by treating with the same organic solvent as described above after forming into a form such as a shape.

Further, for example, in a solution polymerization method, a solvent having a small chain transfer coefficient such as benzene, methyl acetate, or tert-butyl alcohol is used as a polymerization solvent, and the polymerization is carried out at a temperature as low as possible by increasing the monomer concentration. That is, it is possible to obtain the acrylic polymer having the molecular weight composition of the present invention by selecting the operation conditions at the time of polymerization, and further to select such polymerization operation conditions and to reduce the polymerization after the polymerization. It is also an effective method to appropriately combine the operation of removing the molecular weight component with the operation of removing the molecular weight component.

In the pressure-sensitive adhesive of the present invention, in addition to using the above-mentioned acrylic polymer as an adhesive main component, a tackifier resin generally used for the purpose of adjusting the adhesive properties may be added thereto. In order to maintain heat resistance, it is preferable to use, for example, those having a softening point of 100 ° C. or higher from terpene phenol, xylene resin and the like. As additives other than the tackifying resin, various known additives such as plasticizers, fillers such as calcium carbonate and finely divided silica, coloring agents, and ultraviolet absorbers may be used. Any of these additives may be used in a usual amount applied to an acrylic pressure-sensitive adhesive.

The pressure-sensitive adhesive of the present invention can contain a crosslinking agent. If the acrylic polymer is crosslinked by the crosslinking agent, the cohesive force of the adhesive can be further increased. Instead of such a crosslinking agent, a photosensitizer such as benzophenone and a photocrosslinkable compound such as N.N-methylenebisacrylamide may be blended to cause photocrosslinking. In this case, the same effect as described above may be obtained. Can play.
The same effect as described above can also be obtained by employing other crosslinking means such as electron beam irradiation in addition to crosslinking by these crosslinking agents and photocrosslinking.

In the cross-linking with the above-mentioned cross-linking agent, conventionally known cross-linking agents are widely used. Among them, polyfunctional melamine compounds and / or polyfunctional epoxy compounds such as methylated trimethylol melamine, butyl Hexamethylol melamine, diglycidyl aniline, glycerin diglycidyl ether and the like are particularly preferable as the crosslinking agent of the present invention. The amount used is 0.0 to 100 parts by weight of the acrylic polymer.
The content is preferably in the range of 01 to 10 parts by weight, preferably 0.01 to 2 parts by weight.

It is also preferable to use a polyfunctional isocyanate compound. Examples of such a compound include tolylene diisocyanate, hexamethylene diisocyanate, polymethylene polyphenyl isocyanate, diphenylmethane diisocyanate, a dimer of diphenylmethane diisocyanate, and trimethylol. Reaction products of propane and tolylene diisocyanate, reaction products of trimethylolpropane and hexamethylene diisocyanate, polyether polyisocyanates, polyester polyisocyanates, and the like. Of these, the reaction product of 1 mol of trimethylolpropane and 3 mol of tolylene diisocyanate is most preferred. The amount of these compounds to be used is in the range of 0.01 to 20 parts by weight, preferably 0.05 to 15 parts by weight, based on 100 parts by weight of the acrylic polymer.

The pressure-sensitive adhesive of the present invention may be, for example, a solution-type adhesive applied directly to an adherend, or may be a solution-type adhesive such as paper, nonwoven fabric, plastic sheet, or foam sheet. Adhesive tape with a base material coated on one or both sides of the base material to form an adhesive layer with a predetermined thickness, or a baseless adhesive tape coated on a release material to form an adhesive layer with a predetermined thickness May be applied to the adherend.

At the time of these applications, the acrylic polymer constituting the adhesive layer is appropriately cross-linked by a drying step after applying to an adherend, a base material or a release material, or a light irradiation or electron beam irradiation step after this step. Is done. At that time, the low molecular weight component having a molecular weight of 100,000 or less as measured by the GPC method in the crosslinked acrylic polymer is adjusted to 10% by weight or less in the whole polymer, that is, the low molecular percentage B is 10% or less. In this case, more preferable results can be obtained in satisfying all of the initial adhesive strength, the residual stress resistance and the durability.

〔The invention's effect〕

As described above, in the present invention, the acrylic polymer serving as the main adhesive component is a copolymer of a main monomer mainly composed of alkyl (meth) acrylate and a polyfunctional unsaturated monomer, and By using a material with a specific molecular weight so that its low molecular weight component is a specific amount, it has excellent initial adhesion, especially rough surface adhesion and residual stress resistance, and highly satisfactory durability In addition, an acrylic pressure-sensitive adhesive capable of stably exhibiting these properties in a wide range of monomer compositions and a wide range of compounding compositions can be obtained.

Therefore, according to the pressure-sensitive adhesive according to the present invention,
Problems such as poor adhesion when applied to adherends having a rough surface such as foam, and poor adhesion due to elastic return of the metal plate when applied to a curved surface adhesive portion between a metal plate and a molded product,
An excellent effect can be obtained in that it hardly occurs even under severe conditions such as when left for a long time under high temperature and high humidity. For this reason, the pressure-sensitive adhesive according to the present invention can be advantageously used not only for ordinary adhesives but also for applications exposed to severe conditions as described above.

〔Example〕

Next, an embodiment of the present invention will be described in more detail. Hereinafter, "parts" means parts by weight, and the acrylic polymer solutions P-1 to P-9 used in the following Examples and Comparative Examples were prepared by the following method.

<Acrylic polymer solution P-1> n-butyl acrylate 87 parts, methyl acrylate 10 parts,
3 parts of acrylic acid, 0.15 part of triethylene glycol diacrylate and 300 parts of ethyl acetate as a polymerization solvent were charged into a three-necked flask, and stirred for 2 hours while introducing nitrogen gas. After removing the oxygen in the polymerization system in this manner, 0.08 parts of azobisisobutyronitrile was added, and 55 ° C.
The temperature rose. Six hours later, 0.04 part of azobisisobutyronitrile was further added, the temperature was raised to 65 ° C, and the polymerization reaction was continued for 6 hours to obtain an acrylic polymer solution P-1 having a polymer concentration of 25% by weight.

<Acrylic polymer solution P-2> To 100 parts of the above-mentioned acrylic polymer solution P-1 was dropped 500 parts of n-heptane over 6 hours while stirring, and the mixture was allowed to stand for 24 hours, after which the supernatant was separated. Thereafter, 200 parts of toluene was added to the polymer solution from which the supernatant was separated to dissolve the polymer, and then 250 parts of n-heptane was added in the same manner as described above, and the operation of separating the supernatant was repeated 5 times. After adding 100 parts of toluene to the final polymer solution thus obtained, the solution was concentrated to obtain an acrylic polymer solution P-2 having a polymer concentration of 15% by weight.

<Acrylic polymer solution P-3> All the supernatant liquids separated during the preparation of the above acrylic polymer solution P-2 were collected and concentrated to give an acrylic polymer solution P-3 having a polymer concentration of 35% by weight. I got

<Acrylic polymer solution P-4> The acrylic polymer solution P-1 and the acrylic polymer solution P-2 are mixed so that the weight ratio becomes 1: 1. A system polymer solution P-4 was obtained.

<Acrylic polymer solution P-5> An acrylic polymer solution having a polymer concentration of 25% by weight was prepared in the same manner as in the acrylic polymer solution P-1, except that 0.15 part of triethylene glycol diacrylate was not used. Got 5

<Acrylic polymer solution P-6> The same acrylic polymer solution P-5 was subjected to the same low molecular weight component removal operation as in the case of the acrylic polymer solution P-2, and the polymer concentration was reduced to 15% by weight. An acrylic polymer solution P-6 was obtained.

<Acrylic polymer solution P-7> All the supernatants separated in the preparation of the above acrylic polymer solution P-6 were collected, concentrated, and concentrated to obtain an acrylic polymer solution P-7 having a polymer concentration of 35% by weight. I got

<Acrylic polymer solution P-8> 90 parts of n-butyl acrylate, 5 parts of vinyl acetate, 5 parts of acrylic acid, 1 part of trimethylolpropane trimethacrylate, 0.5 part of lauryl mercaptan, and three parts of 150 parts of toluene as a polymerization solvent The resulting mixture was put into a neck flask, and an acrylic polymer solution was obtained in the same manner as in the case of the acrylic polymer solution P-1.

Next, 120 parts of n-heptane was added to 100 parts of the polymer solution.
The mixture was dropped over 6 hours while stirring, and allowed to stand for 24 hours, after which the supernatant was separated. Thereafter, 260 parts of toluene was added to and dissolved in the polymer solution from which the supernatant was separated, and then 330 parts of n-heptane was added in the same manner as described above, and the operation of separating the supernatant was repeated four more times. 150 parts of toluene was added to the final polymer solution thus obtained, followed by concentration to obtain an acrylic polymer solution P-8 having a polymer concentration of 10% by weight.

<Acrylic polymer solution P-9> 2-ethylhexyl acrylate 65 parts, acrylic acid n-
Butyl 30 parts, acrylic acid 5 parts, triethylene glycol diacrylate 0.05 part, ethyl acetate 23 as a polymerization solvent
Three parts were charged into a three-necked flask, and an acrylic polymer solution was obtained in the same manner as in the case of the acrylic polymer solution P-1.

Next, 120 parts of methanol was added dropwise to 100 parts of the polymer solution over a period of 6 hours with stirring. Thereafter, 360 parts of ethyl acetate was added to and dissolved in the polymer solution from which the supernatant was separated, and then 450 parts of methanol was added in the same manner as described above, and the operation of separating the supernatant was repeated four more times. After adding 45 parts of ethyl acetate to the final polymer solution thus obtained, the solution was concentrated to obtain an acrylic polymer solution P-9 having a polymer concentration of 15% by weight.

In addition, these acrylic polymer solutions P-1 to P-9 were each composed of a weight percentage of the soluble polymer constituting each polymer (the above percentage X), a weight average molecular weight of this soluble polymer by a GPC method, and a molecular weight of 100,000. The following weight percentages of the low molecular weight components (low molecular weight percentage A) had the molecular weight constitutions shown in Table 1 below.

Example 1 Acrylic polymer 1 was added to acrylic polymer solution P-2.
A polyfunctional isocyanate compound [Bayer Co., Ltd. trade name; reaction product of trimethylolpropane and tolylene diisocyanate] was added at a ratio of 1 part to 00 parts to obtain a pressure-sensitive adhesive solution. .

Example 2 A pressure-sensitive adhesive solution was prepared in the same manner as in Example 1, except that the acrylic polymer solution P-4 was used instead of the acrylic polymer solution P-2.

Comparative Example 1 A pressure-sensitive adhesive solution was prepared in the same manner as in Example 1, except that the acrylic polymer solution P-1 was used instead of the acrylic polymer solution P-2.

Comparative Example 2 In the same manner as in Example 1, except that the acrylic polymer solution P-3 was used instead of the acrylic polymer solution P-2, and the amount of the polyfunctional isocyanate compound was changed to 5 parts. A pressure-sensitive adhesive solution was prepared.

Comparative Example 3 A pressure-sensitive adhesive solution was prepared in the same manner as in Example 1, except that the acrylic polymer solution P-5 was used instead of the acrylic polymer solution P-2.

Comparative Example 4 A pressure-sensitive adhesive solution was prepared in the same manner as in Example 1, except that the acrylic polymer solution P-6 was used instead of the acrylic polymer solution P-2.

Comparative Example 5 In the same manner as in Example 1, except that the acrylic polymer solution P-7 was used instead of the acrylic polymer solution P-2, and the amount of the polyfunctional isocyanate compound used was changed to 5 parts. A pressure-sensitive adhesive solution was prepared.

Example 3 Acrylic polymer solution P-8 was used alone as a pressure-sensitive adhesive solution.

Example 4 Acrylic polymer solution 1 was added to acrylic polymer solution P-9.
A polyfunctional melamine compound (methylated trimethylol melamine) was added at a ratio of 0.3 part to 00 parts to obtain a pressure-sensitive adhesive solution.

For each of the pressure-sensitive adhesive solutions of the above Examples and Comparative Examples, the rough surface adhesion, the residual stress resistance and the durability were examined by the following methods.

<Rough Surface Adhesion> Each pressure-sensitive adhesive solution was cast and applied on a 38 μm-thick polyethylene terephthalate film so that the thickness after drying was about 50 μm, and Example 4 was at 140 ° C. for 10 minutes. 120
After heating and drying at 10 ℃ for 10 minutes, width 20mm, length 100m
A sample piece was prepared by cutting to a size of m. This sample piece was adhered to a cloth made of 85 pieces of sufomusulin by one reciprocation of a 2 kg roller at 20 ° C., and T-peeled at a peeling rate of 300 mm / min at the same temperature by a Schopper type peeling tester to measure the adhesive force.

<Residual stress resistance> Each of the pressure-sensitive adhesive solutions was cast and applied to an aluminum plate having a thickness of 0.4 mm so that the thickness after drying became about 50 μm. After heating and drying at 120 ° C. for 10 minutes, the sample was cut into a size of 10 mm in width and 80 mm in length to produce a sample piece. This sample piece was bent and attached to an aluminum cylinder having a diameter of 50 mm, and after storing at 40 ° C. for 24 hours, the distance that the sample piece floated up from the cylinder was measured.

<Durability> 10mm in width and 80mm in length as in the case of rough surface adhesion test
A sample piece was prepared and bonded to a stainless steel plate specified in ZIS Z-0237 at 20 ° C so that the adhesive area was 10 mm × 20 mm, and then a vertical load of 500 g was applied in an atmosphere at 80 ° C. And the time to fall was measured.

The results of these tests are as shown in Table 2 below. In the table, for reference, the weight percentage of the soluble polymer (percentage X) and the low molecular weight of 100,000 or less for the acrylic polymer constituting the adhesive layer of the sample piece prepared in each test are shown. The weight percentages of the components (the aforementioned low molecular weight percentages B) are also shown.

From the results in Table 2 above, it is clear that the pressure-sensitive adhesive according to the present invention satisfies all of the properties of rough surface adhesion, residual stress resistance and durability.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naomata Tanaka 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nichidenki Kogyo Co., Ltd. (72) Inventor Noboru Itano 1-1-1, Shimohozumi, Ibaraki-shi, Osaka No. 2 Nitto Denki Kogyo Co., Ltd. (56) References JP-A-56-155268 (JP, A) JP-A-61-47772 (JP, A) JP-A-58-40377 (JP, A) 58-87171 (JP, A)

Claims (3)

(57) [Claims] 1. The following general formula: (Wherein, R ₁ is a hydrogen atom or a methyl group, and R ₂ is
To a main monomer mainly composed of a (meth) acrylic acid alkyl ester represented by the formula:
According to gel permeation chromatography comprising a copolymer of a polyfunctional unsaturated monomer having two or more polymerizable carbon-carbon double bonds in one molecule at a ratio of 0.001 to 5 parts by weight. The measured weight average molecular weight is
A pressure-sensitive adhesive comprising an acrylic polymer having a molecular weight of 500,000 to 1.5 million and a low molecular weight component having a molecular weight of 100,000 or less and 15% by weight or less. 2. The pressure-sensitive adhesive according to claim 1, wherein the acrylic polymer is crosslinked. 3. A low molecular weight component having a molecular weight of 100,000 or less as measured by gel permeation chromatography in an acrylic polymer after crosslinking is 10% by weight or less in the whole polymer. The pressure-sensitive adhesive according to the item 2).