JPH05112618A - Method for producing solvent-based acrylic pressure-sensitive adhesive - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for obtaining a solvent-type acrylic pressure-sensitive adhesive having excellent curved surface adhesiveness and excellent balance between cohesive force at high temperature and low-speed peel strength. [Constitution] (Meth) acrylic acid alkyl ester 52-
97% by weight, polar monomers 3 to 15% by weight and --OH group-containing monomer 0.05 to 3% by weight, and 0 to 30% by weight of other monomers copolymerizable with the above monomers, In the method for producing an acrylic pressure-sensitive adhesive composition that is crosslinked with an isocyanate compound,
A method for producing a solvent-type acrylic pressure-sensitive adhesive, which comprises dividing or continuously adding a group-containing monomer to polymerize the monomer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a solvent-type acrylic pressure-sensitive adhesive that is crosslinked with a polyisocyanate compound, and particularly shows excellent curved surface adhesiveness and cohesive force and low-speed peel strength at high temperature. The invention relates to a method for producing a solvent-based acrylic pressure-sensitive adhesive having an excellent balance.

[0002]

2. Description of the Related Art Solvent-based acrylic pressure-sensitive adhesives, especially cross-linked acrylic pressure-sensitive adhesives, are excellent in adhesive properties such as adhesive force and cohesive force, as well as in weather resistance and oil resistance. Widely used. As a cross-linking agent used for the cross-linking acrylic pressure-sensitive adhesive, a polyisocyanate compound having excellent properties is widely used. When using a polyisocyanate compound as a cross-linking agent, in order to increase heat resistance, in the production of an acrylic pressure-sensitive adhesive, in addition to a carboxyl group-containing monomer such as acrylic acid or itaconic acid, hydroxyethyl methacrylate or hydroxyethyl acrylate is used. -OH like
Group-containing monomers are often copolymerized. In the production of this type of solvent-based acrylic pressure-sensitive adhesive, each of the above monomers is charged in a suitable solvent all at once, and heat-polymerized by using a polymerization initiator such as a peroxide or an azo compound.

By the way, --O for forming a cross-linking origin is used.
The polymerization reactivity of the H group-containing monomer with the main base monomer, ie, the (meth) acrylic acid alkyl ester or other polymerizable vinyl monomer, is significantly different. Therefore, when the solvent-type acrylic pressure-sensitive adhesive is prepared by using the above-mentioned polymerization method, it is difficult to uniformly distribute the —OH group-containing monomer in the produced polymer. In particular, when the -OH group-containing monomer is consumed at the initial stage of the polymerization reaction, the -OH group-containing monomer for forming the cross-linking starting point does not exist in the polymer produced in the latter stage of the reaction. As a result, it has been a cause of deterioration of curved surface adhesiveness and low-speed peel strength, particularly deterioration of low-speed peel strength at high temperatures.

[0004]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems of the conventional method for producing a solvent-based acrylic pressure-sensitive adhesive, and an object thereof is to have excellent curved surface adhesiveness and It is an object of the present invention to provide a method for producing a solvent-based acrylic pressure-sensitive adhesive having an excellent balance between cohesive force at high temperature and low-speed peel strength.

[0005]

The method for producing a solvent-type acrylic pressure-sensitive adhesive of the present invention comprises: (meth) acrylic acid alkyl ester 52 to 97% by weight; polar monomer 3 to 15% by weight; In a method for producing an acrylic pressure-sensitive adhesive, which is obtained by polymerizing 0.05 to 3% by weight of a monomer and 0 to 30% by weight of another monomer copolymerizable with these monomers, and which is crosslinked with a polyisocyanate compound, A method for producing a solvent-based acrylic pressure-sensitive adhesive, characterized by polymerizing by dividingly or continuously introducing a —OH group-containing monomer for constituting a cross-linking starting point.

That is, the present invention focuses on the difference in the polymerization reactivity of the -OH group-containing monomer with the main monomer,
When the group-containing monomer is polymerized in a divided or continuous manner to carry out the polymerization, -OH is added to the polymer produced.
The group-containing monomer is allowed to uniformly exist to achieve the above object. The (meth) acrylic acid alkyl ester has 1 to 14 carbon atoms, preferably 4 to 4 carbon atoms.
A (meth) acrylic acid alkyl ester having 12 alkyl groups is used. Preferred examples of such (meth) acrylic acid alkyl ester include n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate and the like.

As the polar monomer, ethyl (meth) acrylate, methyl (meth) acrylate,
(Meth) acrylonitrile, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, N-substituted acrylamide, N-vinylpyrrolidone, N-methylolacrylamide and the like are used. Examples of the —OH group-containing monomer for forming the cross-linking origin include 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, a caprolactone adduct, an ethylene oxide adduct, and the like.

As the other copolymerizable monomer in the present invention, an ethylenically unsaturated group-containing monomer can be copolymerized, whereby the cohesive force of the acrylic pressure-sensitive adhesive composition can be further enhanced. Examples of the ethylenically unsaturated group-containing monomer that can be used include vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile and styrene. However, if the copolymerization ratio of the ethylenically unsaturated group-containing monomer becomes high, the tackiness is impaired, so the copolymerization ratio of the ethylenically unsaturated group-containing monomer must be 30% by weight or less.

In the present invention, in the solvent-type acrylic pressure-sensitive adhesive, the above-mentioned (meth) acrylic acid alkyl ester, polar monomer and --OH group-containing monomer are used in the above-mentioned specific proportions. The mixing ratio of the ester, the polar monomer and the —OH group-containing monomer is the same as in the conventionally known method for producing a solvent-type acrylic pressure-sensitive adhesive. The feature of the present invention resides in that the above-OH group-containing monomer is dividedly or continuously added during the polymerization.

As a method of dividing or continuously charging the --OH group-containing monomer during the polymerization, --O is added after the initiation of the polymerization.
A method in which the H group-containing monomer is divided into a plurality of times and charged into the polymerization system, a part of the —OH group-containing monomer is added to the (meth) acrylic acid alkyl ester and the polar monomer to start the polymerization, and then the remaining -A method of adding the OH group-containing monomer to the polymerization system at once or in multiple steps,-
Polymerization system using a dropping funnel, etc., from before initiation of polymerization to before initiation of polymerization or before completion of polymerization using a dropping funnel or the like, or between after initiation of polymerization and before completion of polymerization. A method of continuously charging the same is used. In some cases, a main monomer, that is, a part of the (meth) acrylic acid alkyl ester and / or a polar monomer is mixed with the —OH group-containing monomer that is charged after the initiation of the polymerization, and a part of the main monomer is added. After the initiation of the polymerization, it may be added to the polymerization system together with the —OH group-containing monomer.

In short, in the present invention, the expression "divided charge" means that the --OH group-containing monomer is charged at least twice, while continuous charge means --OH.
It means a method of continuously introducing the group-containing monomer from a dropping funnel or the like. In addition, in the production of the solvent-type acrylic pressure-sensitive adhesive of the present invention, a predetermined amount of a polymerization initiator is used in addition to the (meth) acrylic acid alkyl ester, the polar monomer and the —OH group-containing monomer. As the polymerization initiator, a peroxide such as benzoyl peroxide and an azo compound such as azobisisobutyronitrile, which are conventionally used in the production of solvent-type acrylic pressure-sensitive adhesives, are appropriately used.

In the acrylic pressure-sensitive adhesive obtained by the present invention, the (meth) acrylic acid alkyl ester,
In addition to polar monomers and -OH group-containing monomers and polymerization initiators, tackifying resins such as petroleum resin, terpene resin, coumarone-indene resin or phenol resin, various colorants, antiaging agents, fillers, etc. Known additives may be added.

[0013]

In the method for producing a solvent-type acrylic pressure-sensitive adhesive of the present invention, when the (meth) acrylic acid alkyl ester, the polar monomer and the --OH group-containing monomer and, if necessary, the above-mentioned other monomer are polymerized, The contained monomer is divided or continuously charged as described above. Therefore,
Since the —OH group-containing monomer is not completely consumed immediately after the initiation of polymerization, it is considered that the —OH group-containing monomer component is uniformly dispersed in the produced polymer. Therefore, when an isocyanate compound as a cross-linking agent is added, the -OH group-containing monomer component constituting the cross-linking starting point is uniformly dispersed in the polymer, and therefore the solvent-type acrylic pressure-sensitive adhesive of the present invention has the same gel content. The value of the swelling ratio compared with the ratio is larger than that of the conventional solvent-based acrylic adhesive,
The low speed peel strength can be enhanced without lowering the cohesive strength of the pressure-sensitive adhesive, and the range of the mixing ratio of the crosslinking agent to the solvent-based acrylic pressure-sensitive adhesive can be made wide.

[0014]

The present invention will be clarified below by giving non-limiting examples and comparative examples of the present invention. Example 1 95 parts by weight of n-butyl acrylate, 5 parts by weight of acrylic acid, 0.1 part by weight of 2-hydroxyethyl methacrylate were placed in a flask equipped with a reflux condenser, a stirrer, a thermometer and a dropping funnel. 0.02 parts by weight of lauryl mercaptan as a chain transfer agent and ethyl acetate 80 as a solvent
Parts by weight were charged so that the total amount was 1 kg, and the components were dissolved by stirring. Then, the temperature of this solution is raised to 1
Refluxed for 0 minutes to remove dissolved oxygen in the solution. Next, a diluted solution of benzoyl peroxide in ethyl acetate (a mixture of 0.05 part by weight of benzoyl peroxide and 3.7 parts by weight of ethyl acetate) was added dropwise to the above solution, and the mixture was reacted under reflux for 5 hours. Further, a diluted solution of benzoyl peroxide in ethyl acetate (a mixture of 0.03 parts by weight of benzoyl peroxide and 3 parts by weight of ethyl acetate) was added dropwise and the mixture was aged for 2 hours.

In parallel with the above, after the first dilute solution of benzoyl peroxide-ethyl acetate was added dropwise, a dilute solution of 2-hydroxyethyl (meth) acrylate in ethyl acetate (2-hydroxyethyl methacrylate 0. A mixture of 4 parts by weight and 4 parts by weight of ethyl acetate) was continuously added dropwise at a constant rate over 5 hours. After the aging, 10 parts by weight of toluene was added to the reaction solution. The resin solution thus obtained had a solid content of 50% by weight and a viscosity of 20,000 cps (23
℃). To the resin solution obtained as described above, 1.0 part by weight of triisocyanate (manufactured by Nippon Polyurethane Company, trade name; Coronate L) was added as a cross-linking agent, and the mixture was stirred to prepare an acrylic pressure-sensitive adhesive composition. ..
This acrylic adhesive composition was subjected to corona discharge treatment 3
On a polyethylene terephthalate film with a thickness of 8 μm,
A pressure-sensitive adhesive sheet was prepared by applying an applicator so that the dried pressure-sensitive adhesive layer had a thickness of 25 μm, and drying in an oven for 5 minutes.

Example 2 Example 1 except that the compounding ratio of polyisocyanate (trade name; Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) as a crosslinking agent was changed from 1.0 part by weight to 1.5 parts by weight. 1
In exactly the same manner as above, to prepare an acrylic pressure-sensitive adhesive composition,
A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1.

Comparative Example 1 95 parts by weight of n-butyl acrylate, 5 parts by weight of acrylic acid, 0.5 parts by weight of 2-hydroxyethyl methacrylate, and lauryl mercaptan 0.02 as a chain transfer agent.
Parts by weight and 80 parts by weight of ethyl acetate as a solvent were charged so that the total amount was 1 kg, and the mixture was stirred and dissolved. Next, the temperature of this solution is raised and refluxed for 10 minutes to remove dissolved oxygen in the solution, and then a diluted solution of benzoyl peroxide in ethyl acetate (0.05 parts by weight of benzoyl peroxide and 3.7 parts by weight of ethyl acetate) is added. Part) was added dropwise, and the mixture was reacted under reflux for 5 hours. Then, a diluted solution of benzoyl peroxide in ethyl acetate (0.03 parts by weight of benzoyl peroxide and 3 parts by weight of ethyl acetate were mixed). ) Was added dropwise and aged for 2 hours to complete the reaction. After the reaction, 10 parts by weight of toluene was added to the reaction solution. The solid content of the obtained resin solution was 50% by weight, and the viscosity was 20,000 cps (23 ° C.). A polyisocyanate was added to the resin solution obtained as described above in the same manner as in Example 1 to prepare an acrylic pressure-sensitive adhesive composition, and a pressure-sensitive adhesive sheet was prepared in the same manner as in Example 1.

Comparative Example 2 Polyisocyanate (Nippon Polyurethane Company, trade name;
An acrylic pressure-sensitive adhesive composition was prepared in the same manner as in Comparative Example 1 except that the proportion of Coronate L) was changed from 1.0 parts by weight to 1.5 parts by weight. A pressure-sensitive adhesive sheet was produced in the same manner.

Evaluation Each of the acrylic pressure-sensitive adhesive compositions obtained in Examples 1 and 2 and Comparative Examples 1 and 2 was immersed in tetrahydrofuran, and the gel fraction and swelling ratio were measured. The results are shown in Table 1 below. Also,
Regarding the pressure-sensitive adhesive sheets obtained in Examples 1 and 2 and Comparative Examples 1 and 2, the 90 ° peel holding force (90 ° peel strength when a constant load is applied) and the shear holding force with respect to the stainless steel plate and the glass plate are as follows. It was measured at. The results are shown in Table 1. 90 ° peeling retention force: An adhesive sheet with a width of 20 mm is attached to a stainless steel plate or a glass plate, the adhesive sheet is kept horizontal with the lower side, and a suspension load of 100 g is applied to one end of the adhesive sheet, and the peeling distance per unit time Is measured
The 90 ° peel holding force was used as a measure of the low speed peel strength. Shear retention force: A pressure-sensitive adhesive sheet was attached to a stainless plate in an area of 20 mm × 20 mm, a load of 1 kg was applied, and the shift length of the pressure-sensitive adhesive sheet after 1 hour was measured.

[0020]

[Table 1]

As is clear from Table 1, in the acrylic adhesives of Example 1 and Comparative Example 1, the same gel fraction (70
The swelling ratio was 31 times in Comparative Example 1, while the swelling ratio was 37 times in Example 1. Similarly, when the acrylic pressure-sensitive adhesives of Example 2 and Comparative Example 2 were compared, the gel fraction was almost the same, while the swelling ratio was 10 times in Comparative Example 2, while the swelling ratio was 10 times. In Example 2, it was as high as 15 times.

Comparing the pressure-sensitive adhesive sheets prepared in Example 1 and Comparative Example 1, the pressure-sensitive adhesive sheets obtained in Example 1 were evaluated for both 90 ° peel holding force for a stainless plate and 90 ° peel holding force for a glass plate. As for the sheet, it can be seen that the peeling distance of the adhesive sheet is quite small. In addition, the pressure-sensitive adhesive sheet of Comparative Example 1 has 8
In contrast to the peeling distance of the pressure-sensitive adhesive sheet being considerably large at 0 ° C., the peeling distance of the pressure-sensitive adhesive sheet of Example 1 did not change at 40 ° C. even when the temperature was 80 ° C. .. Similarly, in the pressure-sensitive adhesive sheet of Example 2, as compared with the pressure-sensitive adhesive sheet of Comparative Example 2, when bonded to either a stainless plate or a glass plate,
It can be seen that the peeling distance is small. Moreover, the temperature is 80 ℃
Even in the case of, the peeling distance is much smaller than that of Comparative Example 2 in both cases where the stainless plate and the glass plate are bonded together.

[0023]

As described above, according to the present invention, the -OH group-containing monomer forming the cross-linking origin is dividedly or continuously added during the polymerization to produce the acrylic pressure-sensitive adhesive. However, it is possible to provide a solvent-type acrylic pressure-sensitive adhesive that exhibits a high swelling ratio and has an excellent balance between cohesive force at high temperature and low-speed peel strength.

Claims (1)

[Claims] 1. A (meth) acrylic acid alkyl ester 5
2 to 97% by weight, polar monomer 3 to 15% by weight,
Production of an acrylic pressure-sensitive adhesive obtained by polymerizing 0.05 to 3% by weight of an OH group-containing monomer and 0 to 30% by weight of another monomer copolymerizable with these monomers, and being crosslinked with a polyisocyanate compound. In the method, a method for producing a solvent-type acrylic pressure-sensitive adhesive, which comprises dividing or continuously introducing a —OH group-containing monomer that serves as a cross-linking starting point to polymerize the monomer.