JP3498123B2 - Acrylic pressure-sensitive adhesive composition - Google Patents

Description

Description: TECHNICAL FIELD [0001] The present invention relates to a pressure-sensitive adhesive composition containing an acrylic polymer as a main adhesive component. More specifically, the present invention relates to a pressure-sensitive adhesive composition which has a high adhesive strength, is excellent in heat resistance, and hardly peels off when a constant load is continuously applied. [0002] In recent years, pressure-sensitive adhesives made of acrylic polymers have been used in various fields such as industrial adhesive tapes, adhesive sheets, labels, and liquid crystal display panels. These pressure-sensitive adhesives have high adhesive strength,
With diversification of uses, it is also necessary to have high heat resistance. Incidentally, among such pressure-sensitive adhesives, there are those which are used under conditions where a constant load is always applied, such as an adhesive for a wall-mounted hook. Adhesives used under these conditions essentially need to have a high initial adhesive strength, but a high initial adhesive strength alone does not necessarily mean constant load releasability (when a constant relatively light load is applied for a long period of time). And the holding power does not increase. In order to improve the constant load peelability and holding power, the stress (peeling force) applied to the adhesive is dispersed and absorbed in the adhesive before it directly acts on the interface between the adhesive and the adherend. There is a need to. Accordingly, the present inventor has conducted repeated studies to improve the constant load releasability and the holding power of the pressure-sensitive adhesive. As a result, the acrylic adhesive has a specific epoxy compound and the molecular weight of the acrylic adhesive is reduced. The inventors have found that the formation of a crosslinked structure at a relatively low density therebetween significantly improves the constant load releasability and the holding force of the adhesive, thereby completing the present invention. [0005] Japanese Patent Application Laid-Open No. 4-18478 discloses that a telechelic oligomer having a weight average molecular weight of 1,000 to 30,000 is blended into an acrylic adhesive. This telechelic oligomer is an oligomer having two or more functional groups at the molecular terminals. Examples of the functional groups include an isocyanate group, an epoxy group, an amino group, a carboxyl group, and a hydroxyl group. It is formed of ethylene chains, polyoxypropylene chains, and the like. In Example 3, n-butyl acrylate
Acrylic acid copolymer (monomer weight composition; 9: 1) 10
There is shown an example in which 0.5 parts by weight of a bifunctional epoxy-based telechelic oligomer having a weight average molecular weight of 2,000 is blended with 0 parts by weight. However, in such an adhesive, the stress applied to the adhesive is three-dimensionally dispersed and absorbed by a uniform crosslinked structure formed by the telechelic oligomer having an epoxy group. Even if such a telechelic oligomer having a large molecular weight is used, the compatibility with the acrylic polymer is poor and uniform crosslinking is not formed, so that the effect of stress dispersion at high temperatures is small. In other words, in order to disperse and absorb the stress applied to the adhesive, a low-density and uniform crosslinked structure is formed between the acrylic polymers, and the crosslinked structure thus formed does not impair the cohesive force of the adhesive. It needs to be formed. An object of the present invention is to provide an acrylic pressure-sensitive adhesive having particularly excellent constant load peel strength. Another object of the present invention is to provide an acrylic pressure-sensitive adhesive having high adhesive strength at high temperature and high peel strength under constant load. [0008] The acrylic pressure-sensitive adhesive composition of the present invention is an acrylic pressure-sensitive adhesive composition comprising an acrylic polymer and an epoxy compound. Acrylic acid, itaconic acid, crotonic acid,
Maleic acid monobutyl and β-carboxyethyl acrylate containing a repeating unit having a carboxyl group derived from at least one compound selected from the group consisting of 0.5 to 20 parts by weight, The compound is a linear glycidyl-based bifunctional epoxy compound having an epoxy equivalent of 250 to 400, and contains the epoxy compound in an amount of 0.02 to 2 parts by weight based on 100 parts by weight of the acrylic polymer. In addition, a repeating unit derived from a (meth) acrylic acid ester is copolymerized in the acrylic polymer in an amount within a range of 60 to 99.5 parts by weight. You
A repeating unit having a carboxyl group,
Residues other than repeating units derived from acrylates
The part is copolymerized with a monomer having another functional group,
The other functional group-containing monomer includes a hydroxyl group-containing monomer, an amide group-containing monomer, an amide group and a methylol group-containing monomer, an amino group-containing monomer, an α, β-unsaturated dibasic acid Diester , vinyl ester
Stele, vinyl ether, vinyl aromatic compound and
It is characterized in that it is at least one kind of monomer selected from the group consisting of (meth) acrylonitrile. It is already known to mix an epoxy compound with an acrylic pressure-sensitive adhesive as described above, and by containing an epoxy compound, the heat-resistant holding power of the acrylic pressure-sensitive adhesive is improved. However, with the epoxy compounds that have been used in the past, constant load releasability (there is difficulty in peeling when a constant relatively light load is applied for a long time)
Was a weak point. However, when a specific epoxy compound is blended in a specific amount to form a crosslinked structure, the constant load releasability which has conventionally been regarded as a weak point of the acrylic pressure-sensitive adhesive is remarkably improved. [0010] Further, by forming a crosslinked structure with such an epoxy compound, the adhesiveness under heat is also improved. Next, the acrylic pressure-sensitive adhesive composition of the present invention will be described in detail. The acrylic pressure-sensitive adhesive composition of the present invention contains an acrylic polymer and a specific epoxy compound. The acrylic polymer is a main component of the adhesion, and is usually composed of an alkyl (meth) acrylate monomer having an alkyl group having about 1 to 18 carbon atoms and a monomer having a carboxyl group. It is produced by copolymerizing Examples of the alkyl (meth) acrylate monomer used herein include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, and sec- (meth) acrylate. -Propyl,
N-butyl (meth) acrylate, sec- (meth) acrylate
Butyl, tert-butyl (meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate,
Examples include cyclohexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, undecyl (meth) acrylate, and lauryl (meth) acrylate. it can. The alkyl (meth) acrylate is usually copolymerized in an acrylic polymer in an amount of 60 to 99.5 parts by weight. Examples of the monomer having a carboxyl group that forms the acrylic polymer of the present invention include carboxyl groups such as (meth) acrylic acid, itaconic acid, crotonic acid, maleic acid, monobutyl maleate, and β-carboxyethyl acrylate. The contained monomer can be mentioned. In the acrylic polymer which is the main component of the adhesive of the present invention, the repeating unit having a carboxyl group is copolymerized in an amount of 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight. Have been. When the group having a carboxyl group is less than 0.5 parts by weight, the reactivity with the epoxy compound is reduced, and unreacted epoxy groups often remain in the adhesive. The acrylic polymer has a high glass transition temperature, and does not exhibit good adhesive performance at room temperature. The acrylic polymer used in the present invention may be copolymerized with a monomer having another functional group as long as the properties of the acrylic polymer are not impaired. Examples of the monomer having another functional group include monomers having a hydroxyl group such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate and allyl alcohol; Monomers containing an amide group such as acrylamide, N-methyl (meth) acrylamide and N-ethyl (meth) acrylamide; containing an amide group such as N-methylol (meth) acrylamide and dimethylol (meth) acrylamide and a methylol group Monomer, aminomethyl (meth)
Monomers having a functional group such as monomers having an amino group such as acrylate, dimethylaminoethyl (meth) acrylate and vinylpyridine can be exemplified. Further, in addition to the above-mentioned acrylic monomers, monomers having an ethylenic double bond can be used. Examples of the monomer having an ethylenic double bond include diesters of α, β-unsaturated dibasic acids such as dibutyl maleate, dioctyl maleate and dibutyl fumarate; vinyl esters such as vinyl acetate and vinyl propionate Vinyl ether; styrene, α
-Vinyl aromatic compounds such as methylstyrene and vinyltoluene; (meth) acrylonitrile; The above acrylic polymer is prepared by charging the above monomer into an organic solvent and reacting the mixture at a reaction temperature of 50 to 100 ° C. and a reaction time of 2 to 2 under an atmosphere of an inert gas such as nitrogen gas.
It can be produced by reacting for 0 hours. In this reaction, a reaction initiator such as azobisisobutyronitrile is used. The weight average molecular weight of the acrylic polymer thus obtained is usually 100,000 to 1
It is in the range of 500,000. By reacting in an organic solvent as described above, the acrylic polymer is obtained as an organic solvent solution. The organic solvent solution of the acrylic polymer thus obtained can be used as it is without separating the organic solvent. The acrylic pressure-sensitive adhesive of the present invention contains a specific epoxy compound. This epoxy compound has a linear structure and is a glycidyl-based bifunctional epoxy compound having epoxy groups at both ends of the molecule. Further, the epoxy equivalent of the epoxy compound must be in the range of 250 to 400.
This epoxy equivalent, though indirect, indicates the length of the crosslinked structure formed by the epoxy compound.
The epoxy compound bonds to a carboxyl group in the acrylic polymer to form a crosslinked structure. Then, when an epoxy compound having an epoxy equivalent of 250 to 400 is used,
A uniform crosslinked structure is formed with the acrylic polymer, and a loose constraint is formed between the adhesive molecules. It is considered that the stress applied to the adhesive layer is absorbed by the deformation of the uniform crosslinked structure between the adhesive molecules loosely constrained as described above. Therefore, when an epoxy compound having an epoxy equivalent of less than 250 is used, the cohesive force of the acrylic polymer is increased and the holding power is improved, but the deformability of the crosslinked structure is small, so that the constant load peeling property is deteriorated.
In addition, the epoxy compound having an epoxy equivalent of more than 400 has low compatibility with the acrylic polymer, has poor cross-linking structure, has poor deformability, and has low holding power and constant load peelability. Specific examples of epoxy compounds that can be used in the present invention are shown below. Embedded image Such an epoxy compound mainly binds to a carboxyl group in the acrylic polymer to form a uniform crosslinked structure between the acrylic polymer molecules. The crosslinked structure thus formed must be formed to such an extent that the acrylic polymer is gently restrained.
It is necessary to use in an amount of 0.02 to 2 parts by weight based on parts by weight to form a crosslinked structure. If the amount of the epoxy compound is less than 0.02 parts by weight, a crosslinked structure having a density effective for absorbing stress cannot be formed. On the other hand, if it exceeds 2 parts by weight, the crosslinking density becomes too high, and the constant-load releasability deteriorates. In order to quickly form such a crosslinked structure by the epoxy compound, it is preferable to use a reaction accelerator in the present invention. Examples of the reaction accelerator include amino compounds such as imidazole. When such a reaction accelerator is used, the reaction accelerator is used in an amount of usually 0.01 to 5 parts by weight, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the acrylic polymer. You. The acrylic pressure-sensitive adhesive composition of the present invention comprises:
Usually, it is used as a two-pack type pressure-sensitive adhesive composed of a main agent composed of an acrylic polymer and an epoxy-based crosslinking component. Furthermore, you may mix | blend other components with the pressure-sensitive adhesive composition of this invention. Other components that can be incorporated into the acrylic pressure-sensitive adhesive composition of the present invention include tackifiers, plasticizers and dyes. As the other components described above, known components can be used alone or in combination. The acrylic pressure-sensitive adhesive composition of the present invention comprises:
It can be used in the same manner as a normal two-part pressure-sensitive adhesive. For example, a predetermined amount of an epoxy compound is added to an acrylic polymer dissolved or dispersed in an organic solvent and mixed well. At this time, other components such as a tackifier are blended if necessary and mixed. Next, this mixture is applied on a release paper, and after removing the solvent, the mixture is transferred to a support and used as an adhesive. In particular, the acrylic pressure-sensitive adhesive composition of the present invention is transferred at 5 to 1
It is preferably used after aging for about 0 days. The acrylic pressure-sensitive adhesive composition of the present invention comprises:
Good adhesion to metals, glass, etc., high-durability industrial adhesive tapes, industrial adhesive sheets, label adhesives, liquid crystal display adhesives (especially a polarizing plate or a polarizing plate It is highly useful as an adhesive for bonding a laminate with a retardation plate. Since the acrylic pressure-sensitive adhesive composition of the present invention comprises an acrylic polymer and a specific epoxy compound, a uniform crosslinked structure is mainly formed between the acrylic polymers by the epoxy compound. The stress applied to the adhesive can be dispersed by the crosslinked structure.
Therefore, the acrylic pressure-sensitive adhesive composition of the present invention is particularly excellent in constant load peel strength. Furthermore, the acrylic pressure-sensitive adhesive composition of the present invention has a high adhesive strength to an adherend, and particularly has excellent adhesiveness and cohesiveness under high-temperature conditions. In addition, the pressure-sensitive adhesive composition of the present invention has a high temperature of, for example, 90 ° C.
Since ℃ adhesive strength in the vicinity of high, it is excellent in <br/> especially as heat-resistant adhesive. EXAMPLES The present invention will be described in more detail with reference to Production Examples and Examples, which should not be construed as limiting the present invention. In the examples and the like below, the expression “parts” means “parts by weight” unless otherwise specified. [Production Example 1] [Production of acrylic polymer] Ethyl acetate 80 was placed in a reactor equipped with a stirrer, a cooling pipe, a thermometer and a nitrogen introduction pipe.
Parts, 30 parts of toluene, 50 parts of butyl acrylate, 47 parts of 2-ethylhexyl acrylate, 2.5 parts of acrylic acid, and 0.5 part of 2-hydroxyethyl methacrylate. Was raised to about 75 ° C. The reaction was started by adding 0.2 parts of azobisisobutyronitrile to the reaction solution. After 2 hours, 0.3 parts of azobisisobutyronitrile was further added, and the reaction solution was added. The temperature was raised to 80 ° C., and stirring was continued at this temperature for 5 hours. 40 parts of cooled toluene was added to the reaction solution, and the solid content was 39.1% and the viscosity at 23 ° C was 4%.
A polymer solution with 800 cps and a weight average molecular weight (Mw) of 540,000 was obtained. Example 1 100 parts (solid content, the same applies hereinafter) of the polymer obtained in Production Example 1 were used as a crosslinking agent by the following formula (1)
0.4 parts of an epoxy compound having an epoxy equivalent of about 280 [Denacol EX-832; manufactured by Nagase Kasei Kogyo Co., Ltd.] and 0.4 parts of imidazole as a crosslinking accelerator.
5 parts were added, and the resultant was coated on a release paper so that the thickness after drying was 25 μm, and after drying, transferred to a polyester film. After removing the solvent with a dryer, the mixture was aged at 23 ° C. for 7 days to obtain an adhesive tape. Embedded image Example 2 An epoxy compound having a structure represented by the following formula (2) and having an epoxy equivalent of about 382 [Denacol E] was used as a crosslinking agent for 100 parts of the polymer obtained in Production Example 1 above.
X-841; manufactured by Nagase Kasei Kogyo Co., Ltd.], 0.4 parts of imidazole as a crosslinking accelerator and 0.5 parts of a dried paper having a thickness of 25 μm on a release paper. Transferred to film. After removing the solvent with a dryer, the mixture was aged at 23 ° C. for 7 days to obtain an adhesive tape. Embedded image Comparative Example 1 An epoxy compound having a structure of the following formula (3) and having an epoxy equivalent of about 135 [Denacol EX- was used as a crosslinking agent for 100 parts of the polymer obtained in Production Example 1.
810; manufactured by Nagase Kasei Kogyo Co., Ltd.] and 0.1 part of imidazole as a cross-linking accelerator are added, coated on a release paper so that the thickness after drying is 25 μm, and then dried to obtain a polyester. Transferred to film. After removing the solvent with a dryer, the mixture was aged at 23 ° C. for 7 days to obtain an adhesive tape. Embedded image Comparative Example 2 An epoxy compound having an epoxy equivalent of about 100 [Tetrad X; manufactured by Mitsubishi Gas Chemical Co., Ltd.] was used as a crosslinking agent for 100 parts of the polymer obtained in Production Example 1.
03 parts were added, and the resultant was coated on a release paper so that the thickness after drying was 25 μm, and after drying, transferred to a polyester film. After removing the solvent with a dryer, the mixture was aged at 23 ° C. for 7 days to obtain an adhesive tape. Comparative Example 3 To 100 parts of the polymer obtained in Production Example 1, 0.5 part of a polyisocyanate compound [Coronate L; manufactured by Nippon Polyurethane Co., Ltd.] was added as a cross-linking agent, and the mixture was placed on a release paper. Apply so that the thickness after drying is 25 μm,
After drying, it was transferred to a polyester film. After removing the solvent with a dryer, the mixture was aged at 23 ° C. for 7 days to obtain an adhesive tape. Test Examples The adhesive performance of the tapes of Examples 1 and 2 and Comparative Tapes of Comparative Examples 1 to 3 prepared as described above was examined by the following method. The results are shown in Table 1. (Test method) Adhesive performance SUS304 obtained by polishing an adhesive test tape with a No. 280 abrasive
The plate and the glass plate were pressed back and forth with a 2 kg hand roller once. After leaving for 1 hour, the strength of the test tape when peeled at a peel angle of 180 ° and a pulling speed of 300 mm / min was measured (peeling temperature 23 ° C. (normal temperature) and 9 ° C.).
0 ° C, g / 25 mm). Holding force The above SUS304 plate was used as an adherend, and a sticking area of 20 ×
A load of 1 kg was applied to a test tape of 20 mm ² , and the displacement after 60 minutes in an atmosphere of 80 ° C. was measured (mm). A constant load peeling test tape was stuck on SUS304 and a glass plate so that the area was 20 mm in width and 50 mm in length.
A load of 200 g was applied in the peeling direction of 90 °. The peeling distance or falling time of the test tape thus applied after 60 minutes was measured (mm or minute). Table 1 shows the results of tests conducted on the above-mentioned adhesive strength, constant weight peelability and holding power. [Table 1] From the results shown in Table 1, it is clear that only the acrylic pressure-sensitive adhesive composition of the present invention shows excellent adhesive performance.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-46982 (JP, A) JP-A-6- 1957 (JP, A) JP-A-7-173445 (JP, A) JP-A-7-173 178035 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C09J 163/00-163/10 C08G 59/40-59/66

Claims (1)

(57) [Claim 1] An acrylic pressure-sensitive adhesive composition comprising an acrylic polymer and an epoxy compound, wherein the acrylic polymer comprises (meth) acrylic acid, itaconic acid, A repeating unit having a carboxyl group derived from at least one compound selected from the group consisting of crotonic acid, monobutyl maleate and β-carboxyethyl acrylate in an amount of 0.5 to 20 parts by weight; The epoxy compound is a linear glycidyl-based bifunctional epoxy compound having an epoxy equivalent of 250 to 400, and contains the epoxy compound in an amount of 0.02 to 2 parts by weight based on 100 parts by weight of the acrylic polymer. And a repeating unit derived from a (meth) acrylate in the acrylic polymer is 60 to 99.5 parts by weight. In an amount within the range have been copolymerized, furthermore, acrylic poly
A repeating unit having a carboxyl group in the mer,
Repeating unit derived from (meth) acrylate
The remainder other than the position is copolymerized with monomers having other functional groups.
The other functional group-containing monomers include a hydroxyl group-containing monomer, an amide group-containing monomer, an amide group and a methylol group-containing monomer, an amino group-containing monomer, and an α, β- Diester of saturated dibasic acid , vinyl ester
Stele, vinyl ether, vinyl aromatic compound and
An acrylic pressure-sensitive adhesive composition comprising at least one monomer selected from the group consisting of (meth) acrylonitrile.