JP2985139B2 - Pressure-sensitive adhesive layer, method for producing the same, and adhesive sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acrylic pressure-sensitive adhesive layer excellent in adhesion or adhesion and repulsion resistance, a method for producing the same, and an adhesive sheet having such a pressure-sensitive adhesive layer.

[0002]

2. Description of the Related Art Conventionally, various acrylic pressure-sensitive adhesive layers mainly composed of an acrylic polymer containing an acrylic acid alkyl ester as a component have been proposed. And repulsion resistance.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to develop an acrylic pressure-sensitive adhesive layer having excellent adhesion or adhesion and excellent rebound resistance, and an adhesive sheet thereof.

[0004]

According to the present invention, there is provided an acrylic polymer comprising an acrylic acid alkyl ester having 4 to 18 carbon atoms in the alkyl group (provided that ethylene-
(T) Tertiary copolymer of butyl acrylate (meth) acrylate
Excludes coalescence. ) , Wherein the average concentration of carboxyl groups in at least one surface layer is higher than that in the inside, and oxidizing the surface layer of the pressure-sensitive adhesive layer; The method for producing a pressure-sensitive adhesive layer described above, wherein pressure-sensitive adhesive layers having different average content concentrations are laminated, and an adhesive sheet comprising such a pressure-sensitive adhesive layer on a supporting substrate. To provide.

[0005] Regarding the point that the average concentration of carboxyl groups in the surface layer of the pressure-sensitive adhesive layer is higher than that in the inside, the present invention includes the case where no carboxyl group is contained in the pressure-sensitive adhesive layer.

[0006]

The present inventors have intensively studied to achieve a balance between the adhesion or adhesive strength of the acrylic pressure-sensitive adhesive layer and the rebound resistance, and found that the average concentration of carboxyl groups in the pressure-sensitive adhesive layer is high. It is found that the adhesion or adhesion to the adherend is improved because of the involvement of hydrogen bonding, but the hardness is increased by increasing the glass transition point, the deformability is reduced, and the repulsion resistance is poor.

The present invention makes use of the above relationship to improve the adhesion or adhesion on a layer having a relatively low average concentration of carboxyl groups, which is advantageous for improving rebound resistance. By forming a composite layer structure in which a layer having a high average concentration of carboxyl groups is provided, compatibility between adhesion or adhesion and repulsion resistance is achieved.

[0008]

The pressure-sensitive adhesive layer of the present invention is an acrylic polymer containing one or more acrylic acid alkyl esters having 4 to 18 carbon atoms in the alkyl group.
(However, ethylene-butyl (meth) acrylate (meth
(T) Excluding acrylate terpolymers. ) . If the carbon number of the alkyl group is out of the above range, the pressure-sensitive adhesive property tends to be impaired. The polymerization may be performed by an appropriate polymerization method such as a radical polymerization method. The weight average molecular weight of the acrylic polymer is preferably 300,000 or more.

Examples of the above-mentioned acrylic acid alkyl esters include (n-, t-) butyl, amyl, 2-ethylhexyl, octyl, nonyl, decyl, dodecyl, lauryl and stearyl. Has 4 carbon atoms such as
And alkyl esters of acrylic acid or methacrylic acid having an alkyl group of from 18 to 18. Above all, acrylic acid alkyl esters having an alkyl group having 8 to 18 carbon atoms are preferable, and alkyl methacrylate is particularly preferable from the viewpoint of easy modification treatment such as surface oxidation.

In the present invention, the alkyl group has 4 to 18 carbon atoms for the purpose of modifying the acrylic polymer to be obtained.
A suitable unsaturated monomer other than the above-mentioned acrylic acid alkyl ester can be used in combination. Examples of such unsaturated monomers generally used include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, (anhydride) maleic acid, itaconic acid, fumaric acid, crotonic acid, methyl group, ethyl group and propyl group. Such as acrylic acid alkyl esters having an alkyl group having a carbon number outside the above range, acrylic acid esters having a functional organic group such as hydroxyethyl group, hydroxypropyl group and glycidyl group, vinyl acetate and vinyl propionate. Vinyl esters such as
Styrene derivatives such as styrene or α-methylstyrene, vinylpyrrolidone, acrylonitrile, methacrylonitrile, acrylamide, N-methylolacrylamide, methacrylamide and the like.

Incidentally, the copolymerization ratio of the unsaturated carboxylic acids is such that the number of carbon atoms of the alkyl group is 4 to 1 from the viewpoint of pressure-sensitive adhesive properties.
20 parts by weight or less per 100 parts by weight of the acrylic acid alkyl ester of No. 8 is suitable. In addition, the copolymerization ratio of the other unsaturated monomer is as follows: from the viewpoint of pressure-sensitive adhesive properties, the acrylic acid alkyl ester 1 to 4 having 18 to 18 carbon atoms in the alkyl group.
50 parts by weight or less per 100 parts by weight is appropriate.

In the pressure-sensitive adhesive layer of the present invention, the average content of carboxyl groups in at least one surface layer is higher than that in the inside. In the present invention, from the viewpoint of compatibility between adhesion or adhesion and repulsion resistance, based on the case where the average content concentration of carboxyl groups in only one surface layer is high, carboxyl groups in the surface layer having a thickness of 10% of all layers are high. Average content of groups 2
It is preferable that the number be twice or more. The thickness of the pressure-sensitive adhesive layer is appropriately determined according to the purpose of use.
μm.

The pressure-sensitive adhesive layer of the present invention is formed, for example, by a method of treating the surface layer of the pressure-sensitive adhesive layer by an appropriate oxidation treatment method such as a corona discharge treatment or a heat treatment, in which the copolymerization ratio of unsaturated carboxylic acids is different. It can be performed by a method of laminating a pressure-sensitive adhesive layer or the like. The pressure-sensitive adhesive layer itself may be formed according to a conventional method such as a method of applying and drying a pressure-sensitive adhesive.

The method of oxidizing the surface layer by heating is as follows.
It can be preferably applied to a pressure-sensitive adhesive layer using an acrylic polymer containing an alkyl methacrylate having 8 to 18 carbon atoms in the alkyl group as a component, and can usually achieve the object by heat treatment at 150 to 220 ° C. .

The pressure-sensitive adhesive layer of the present invention has a crosslinked structure as required. Cross-linking treatment, for example, ethylene glycol diacrylate, pentaerythritol diacrylate, trimethylol propane triacrylate, trimethylol propane trimethacrylate multifunctional monomers such as copolymerization in an acrylic polymer, a method of internal cross-linking, Isocyanate compounds, epoxy compounds,
A method may be used in which a crosslinking agent such as a peroxide-based compound is blended with a pressure-sensitive adhesive and external crosslinking is performed via the crosslinking agent, or a method of irradiating a radiation such as an electron beam or ultraviolet light to perform crosslinking, and the like. .

In the case of the internal crosslinking method by copolymerization of the above-mentioned polyfunctional monomers, the copolymerization ratio of the polyfunctional monomers is preferably 0.01 to 1% by weight. In the case of the external cross-linking method via a cross-linking agent, the compounding amount of the cross-linking agent is 20 parts by weight or less, preferably 0.01 to 100 parts by weight, per 100 parts by weight of the acrylic polymer.
10 parts by weight are preferred.

In the pressure-sensitive adhesive layer of the present invention, if necessary, a suitable compounding agent such as a tackifier, a plasticizer, a softener, a filler, a pigment, a dye, etc., which is usually used for a pressure-sensitive adhesive, is used. Can also be contained.

The adhesive sheet of the present invention is provided with a pressure-sensitive adhesive layer having a high average carboxyl group content in at least one surface layer on one or both sides of a supporting substrate. As the supporting base material, an appropriate thin body made of, for example, paper, laminated paper, cloth or nonwoven fabric, plastic film, metal foil, foam sheet, or the like may be used. A separator obtained by treating a thin leaf with a release agent may be used. When the surface layer having a high average concentration of carboxyl groups in the pressure-sensitive adhesive layer is only on one side, the surface layer may be on the supporting base material side or on the adherend to be bonded.

[0019]

According to the present invention, based on a layer structure having a surface layer having a high average concentration of carboxyl groups, an acrylic pressure-sensitive adhesive layer having excellent adhesion or adhesion to an adherend and excellent repulsion resistance. Can be obtained.

[0020]

【Example】

Example 1 190 parts (parts by weight, hereinafter the same) of octyl methacrylate and 10 parts of methacrylic acid were added to azobisisobutyronitrile 0.1 part by weight.
4 parts and 200 parts of ethyl acetate were polymerized at 60 ° C. for 10 hours.
Two parts of an epoxy crosslinking agent (N, N, N ', N'-tetraglycidyl-m-xylenediamine) are added, the pressure-sensitive adhesive solution A is applied on a separator, and the mixture is applied at 100 ° C. for 5 minutes. After drying, a pressure-sensitive adhesive layer having a thickness of 5 μm was formed.

Using 198 parts of octyl methacrylate and 2 parts of methacrylic acid, a pressure-sensitive adhesive solution B was obtained in the same manner as described above, coated on a 25 μm-thick polyester film, and dried at 100 ° C. for 5 minutes. A pressure-sensitive adhesive layer having a thickness of 45 μm was formed. Then, the above-mentioned pressure-sensitive adhesive layers were laminated to obtain an adhesive sheet of the present invention.

COMPARATIVE EXAMPLE 1 A pressure-sensitive adhesive solution A was used in a thickness of 25 μm according to Example 1.
An adhesive sheet was obtained by forming a pressure-sensitive adhesive layer having a thickness of 50 μm on a polyester film having a thickness of 50 μm.

Example 2 Using 198 parts of isodecyl methacrylate and 2 parts of acrylic acid, a pressure-sensitive adhesive solution C was obtained in the same manner as in Example 1 and applied to a 25 μm-thick polyester film at 100 ° C.
For 5 minutes to form a pressure-sensitive adhesive layer having a thickness of 50 μm, and then subjected to a heat treatment at 200 ° C. for 5 minutes to obtain an adhesive sheet of the present invention.

Comparative Example 2 To the pressure-sensitive adhesive solution C obtained in Example 2, 1 part of benzoyl peroxide was added per 100 parts of the polymer, and the mixture was coated on a 25 μm-thick polyester film to obtain 1 part.
After drying at 00 ° C. for 5 minutes, a pressure-sensitive adhesive layer having a thickness of 50 μm was formed to obtain an adhesive sheet.

Example 3 A solution obtained according to Example 1 using 187.8 parts of butyl acrylate, 12 parts of acrylic acid and 0.2 part of hydroxyethyl acrylate was added in an amount of 3 parts per 100 parts of the polymer. An isocyanate-based cross-linking agent (trimethylolpropane hexamethylene diisocyanate adduct) is added, and the pressure-sensitive adhesive solution D is applied on a separator and
After drying for 5 minutes, a pressure-sensitive adhesive layer having a thickness of 5 μm was formed.

Using 199.8 parts of butyl acrylate and 0.04 parts of hydroxyethyl acrylate, a pressure-sensitive adhesive solution E was obtained in the same manner as described above, and the solution was applied on a 25 μm-thick polyester film to give 100%. After drying at a temperature of 5 ° C. for 5 minutes, a pressure-sensitive adhesive layer having a thickness of 45 μm was formed. Then, the above-mentioned pressure-sensitive adhesive layers were laminated to obtain an adhesive sheet of the present invention.

Comparative Example 3 According to Example 3, a 25 μm-thick
An adhesive sheet was obtained by forming a pressure-sensitive adhesive layer having a thickness of 50 μm on a polyester film having a thickness of 50 μm.

Example 4 A solution obtained according to Example 1 using 100 parts of butyl acrylate, 96 parts of 2-ethylhexyl acrylate, and 4 parts of acrylic acid was mixed with 20 parts of wood rosin (adhesive) per 100 parts of the polymer. And 0.1 part of benzoyl peroxide, and the resulting pressure-sensitive adhesive solution F was coated on a separator and dried at 100 ° C. for 5 minutes to form a pressure-sensitive adhesive layer having a thickness of 5 μm. .

A pressure-sensitive adhesive solution G was obtained in the same manner as described above except that wood rosin was not blended, coated on a polyester film having a thickness of 25 μm and dried at 100 ° C. for 5 minutes to obtain a pressure-sensitive adhesive solution having a thickness of 45 μm. After forming the adhesive layer, the two pressure-sensitive adhesive layers were laminated to obtain the adhesive sheet of the present invention.

Comparative Example 4 According to Example 4, a 25 μm-thick
An adhesive sheet was obtained by forming a pressure-sensitive adhesive layer having a thickness of 50 μm on a polyester film having a thickness of 50 μm.

Evaluation Test Adhesive Strength Adhesive sheets (width 20 mm) obtained in Examples and Comparative Examples were adhered to a stainless steel plate in accordance with JIS Z 0237.
At 3 ° C., the force required for peeling (180 ° peel) was measured.

Rebound Resistance A 10 mm-wide tape made of the adhesive sheet obtained in each of Examples and Comparative Examples was wound around a stainless steel rod having a diameter of 2.0 mm three times.
After standing at 48 ° C for 48 hours, the tape edge floats (peels off)
The length was measured.

The results are shown in Table 1. The table also shows
Carboxyl group content in pressure-sensitive adhesive layer (average concentration)
showed that. In the table, "whole" indicates the average concentration of carboxyl groups in all layers of the pressure-sensitive adhesive layer, and "surface" indicates the average concentration of carboxyl groups in the surface layer having a thickness of 10% of the total thickness of the pressure-sensitive adhesive layer. Shows the average concentration.

The average concentration of carboxyl groups can be determined by a neutralization titration method or a microscopic FT-IR method. In the case of Example 2, the average concentration was determined by a neutralization titration method. That is, a sample is cut from the surface of the pressure-sensitive adhesive layer by a predetermined thickness, sampled, dissolved in tetrahydrofuran, 0.1N-NaOH aqueous solution is added to the solution to react with a carboxyl group, and then phenol is added. The amount of unreacted NaOH was determined by titration with 0.01N-HCl aqueous solution using red as an indicator.
The amount was calculated and the value was converted to the amount of carboxyl groups.

[Table 1]

Table 1 shows that the examples of the present invention have excellent adhesive strength and rebound resistance.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-226586 (JP, A) JP-A-3-121167 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C09J 7/00-7/04

Claims (4)

(57) [Claims] 1. An acrylic polymer comprising an acrylic acid alkyl ester having an alkyl group having 4 to 18 carbon atoms as a component.
(However, ethylene-butyl (meth) acrylate (meth
(T) Excluding acrylate terpolymers. ) , Wherein the average content of carboxyl groups in at least one surface layer is higher than that in the inside. 2. The method for producing a pressure-sensitive adhesive layer according to claim 1, wherein the surface layer of the pressure-sensitive adhesive layer is oxidized to increase the average content of carboxyl groups in the surface layer. 3. The method for producing a pressure-sensitive adhesive layer according to claim 1, wherein pressure-sensitive adhesive layers having different average carboxyl group concentrations are laminated. 4. An adhesive sheet comprising the pressure-sensitive adhesive layer according to claim 1 on a supporting substrate.