JP5200452B2 - Water-based adhesive and method for producing the same - Google Patents

Description

  The present invention relates to an aqueous pressure-sensitive adhesive suitably used for forming a pressure-sensitive adhesive layer such as a pressure-sensitive adhesive label, tape, or sheet, and a method for producing the same.

  In recent years, plastic products have become widespread, but an adhesive is applied to one side of a substrate such as paper in order to display the trademark, price, etc. on the plastic product, or to package and bind the plastic product. Adhesive labels, tapes, sheets and the like (hereinafter simply referred to as “adhesive labels / tapes”) having an adhesive layer formed thereon are used. Further, in industrial fields such as automobiles, OA equipment, home appliances, and building materials, adhesive tapes are used for the purpose of bonding to various plastics, foam bodies, metal parts and members. In these industrial applications, solvent-based acrylic pressure-sensitive adhesives have been used in the past because of the need to achieve more stringent performance such as adhesion reliability under severe environmental conditions. Development of water-based adhesives is required from the viewpoint of pollution control.

  As an aqueous adhesive, for example, in Patent Document 1, a (meth) acrylic acid ester monomer and a vinyl monomer having an acidic group are emulsion-polymerized in an aqueous medium using a specific water-soluble azo initiator, and branched. Alternatively, it is disclosed to obtain a water-based pressure-sensitive adhesive that has a low cross-linking structure and therefore has a moderately reduced cohesive force and can exhibit a high initial adhesive force to an adherend having irregularities on the surface.

  However, adhesive labels and tapes using the above-mentioned adhesives have problems that sufficient adhesiveness may not be obtained due to insufficient cohesive force, and productivity during polymerization is inferior.

JP 2006-274143 A

The present invention has been made based on the circumstances as described above, and the object thereof is to obtain a sufficient cohesive force and to exhibit high adhesiveness, and to have high permeability to a substrate. It is to provide an aqueous adhesive.
Another object of the present invention is to provide a method for producing a water-based pressure-sensitive adhesive capable of producing the above water-based pressure-sensitive adhesive with high productivity.

The aqueous pressure-sensitive adhesive of the present invention contains polymer particles of an aqueous emulsion,
The polymer constituting the polymer particles of the aqueous emulsion is an acrylic polymer or a styrene-acrylic polymer,
The weight average molecular weight (Mw) is 600,000 to 10 million, the gel fraction is 30% or less ,
In addition, 0.7 to 5 parts by weight of at least one selected from a half-ester of a carboxyl group-containing monomer and methacrylic acid is obtained in 100 parts by weight of all the monomers for forming the polymer. The difference between the total acid titration value and the conductivity titration value (ΔAE) is 10 to 200 μeq / g.

  The aqueous pressure-sensitive adhesive of the present invention preferably further contains a crosslinking agent.

The method for producing an aqueous adhesive of the present invention is a method for producing the above aqueous adhesive,
Supplying a redox polymerization initiator and a polymerizable monomer in an aqueous medium, and polymerizing the polymerizable monomer in the aqueous medium to obtain polymer particles of the aqueous emulsion;
The redox polymerization initiator is continuously supplied even after the supply of the polymerizable monomer is completed to complete the polymerization reaction.

According to the water-based pressure-sensitive adhesive of the present invention, sufficient cohesive force can be obtained because it has a sufficiently high molecular weight, and since the polymer has a sufficiently large content of carboxyl groups defined by ΔAE, A high cohesive force is obtained by the interaction between them, and thus a high heat-resistant holding force is obtained, and furthermore, since a specific low gel fraction is obtained, a high penetrating power to the substrate is obtained when an adhesive layer is formed. In addition, double-sided tapes can also be formed as adhesive labels.
Moreover, according to the manufacturing method of the aqueous adhesive of this invention, said aqueous adhesive can be manufactured with high productivity.

  Hereinafter, embodiments of the present invention will be described in detail.

The water-based pressure-sensitive adhesive of the present invention can be applied to one or both sides of a substrate to form a pressure-sensitive adhesive layer, and can constitute a sticky label, tape, sheet, etc. Double-sided tapes and sheets can also be configured.
The aqueous adhesive of the present invention has (a) a weight average molecular weight (Mw) of 600,000 to 10,000,000, (b) a gel fraction of 30% or less, preferably 20% or less, and (c) total acid amount titration. And an aqueous emulsion of polymer particles made of a polymer having a difference ΔAE between 10 and 200 μeq / g (hereinafter referred to as “specific polymer”).

(A) Weight average molecular weight (Mw)
Specifically, the weight average molecular weight (Mw) of the specific polymer in the water-based pressure-sensitive adhesive is in terms of polystyrene measured using a gel permeation chromatography apparatus “HCL-8020” (manufactured by Tosoh Corporation).
When this weight average molecular weight (Mw) is in the above range, the water-based pressure-sensitive adhesive can exhibit a high cohesive force.

  Further, the value of the weight average molecular weight (Mw) / number average molecular weight (Mn) (hereinafter referred to as “molecular weight dispersion ratio”) of the specific polymer in the water-based pressure-sensitive adhesive is preferably 40 to 800, more preferably. It is 50-700, More preferably, it is 60-600.

(B) Gel fraction The gel fraction of the specific polymer in the water-based pressure-sensitive adhesive is indicated by the tetrahydrofuran-insoluble matter.
Specifically, after immersing a sample (weight W ₁ mg) in tetrahydrofuran at room temperature for 1 week, the insoluble matter was taken out, this insoluble matter was dried at 100 ° C. for 3 hours, and its weight (W ₂ mg) was measured. And can be calculated according to the following formula (1).
Formula (1): Gel fraction (%) = W ₂ / W ₁ × 100
When the gel fraction of this specific polymer is 30% or less, sufficient penetration of the water-based pressure-sensitive adhesive into the tape base material is obtained when an adhesive layer such as a tape is formed using the water-based pressure-sensitive adhesive. Can do.

(C) Difference ΔAE between total acid titration value and conductivity titration value
The difference between the total acid titration value (α) of the specific polymer in the water-based adhesive and the conductometric titration value (β), specifically, from the total acid titration value (α) to the conductometric titration value ( The value ΔAE obtained by subtracting β) indicates the degree of carboxyl group content in the polymer particles made of the specific polymer. Hereinafter, this value is referred to as “carboxyl group content in polymer particles”.
When the carboxyl group content ΔAE in the polymer particles is in the above range, the aqueous pressure-sensitive adhesive has a high cohesive force due to the interaction between the carboxyl groups, and thus can exhibit high adhesiveness.

In the carboxyl group content ΔAE in the polymer particles, the total acid titration value (α) is a value measured according to JIS K 2501, and specifically, a sample dried in a 250 mL Erlenmeyer flask (Specific polymer) To 100 g of toluene and 0.5 mL of p-naphtholbenzein solution were added to 0.2 g and dissolved over 1 day, and then 0.1 mol / L potassium hydroxide (KOH) in 2-propanol And the time when the color changed from yellow to green is the end point (V ₁ mL), and the blank titer is V ₀ mL, and is calculated by the following formula (2).
Formula (2): α [μeq / g] = KOH concentration [N] × (V ₁ −V ₀ ) [mL] × 1000 / weight of sample [g]

In addition, in the carboxyl group content ΔAE in the polymer particles, the conductivity titration value (β) is a value measured using “AT-410” manufactured by KYOTO ELECTRONICS, specifically, 300 mL. 0.87 g of a sample (a water-based emulsion of polymer particles of a specific polymer) was collected in a beaker of 1 and diluted to 200 mL with pure water, and a 1 mol / L sodium hydroxide aqueous solution was used with a dropper with stirring until it became 320 to 360 μS. The solution stirred for about 30 seconds was titrated with 0.01 N sulfuric acid, and the titration amount for the surface of the polymer particles and the aqueous phase by the specific polymer was obtained from the obtained conductivity titration curve. It is calculated according to the following formula (3) using titration.
Formula (3): β [μeq / g] = sulfuric acid concentration [mol / L] × titration amount [mL] × 1000 / weight of sample [g]

  The carboxyl group content ΔAE in the polymer particles of the specific polymer in the water-based pressure-sensitive adhesive is a relatively hydrophobic carboxyl such as a half-ester of a carboxyl group-containing monomer or a methacrylic acid among the polymerizable monomers described later. The amount of the group-containing monomer can be adjusted by controlling the amount used in all monomers. For example, by using 0.5 to 7 parts by weight in 100 parts by weight of all monomers, the carboxyl in the polymer particles The group content ΔAE can be adjusted to the above range.

Further, the glass transition temperature of the specific polymer constituting the water-based pressure-sensitive adhesive is −40 ° C. or lower, preferably −90 ° C. to −50 ° C. When the glass transition temperature of the specific polymer exceeds −40 ° C., the adhesive label / tape having an adhesive layer made of the aqueous adhesive has a low ball tack of the adhesive layer. The ball tack is one index representing the adhesive strength.
The glass transition temperature is a value measured using a differential scanning calorimeter “SSC-5000 type” (manufactured by Seiko Denshi Kogyo Co., Ltd.).

An aqueous emulsion of polymer particles composed of a specific polymer constituting the aqueous adhesive is obtained by emulsion polymerization of an appropriate polymerizable monomer or a mixture thereof using, for example, a redox polymerization initiator.
The polymerizable monomer or a mixture thereof is not particularly limited as long as a specific polymer can be obtained, but contains at least one selected from a half-ester of a carboxyl group-containing monomer and methacrylic acid. A monomer mixture is preferable, and examples of the carboxyl group-containing monomer half ester include monoalkyl maleate, monoalkyl itaconate, and mono [2- (meth) acryloyloxyethyl] phthalate. be able to.
Examples of the other polymerizable monomer constituting the monomer mixture include, for example, an alkyl alkyl ester having 4 to 12 carbon atoms in an alkyl group and / or an alkyl alkyl methacrylate having 4 to 12 carbon atoms in an alkyl group. Components (hereinafter referred to as “component A”), components composed of α, β-unsaturated carboxylic acid (hereinafter referred to as “component B”), and the like. Depending on the above, a component comprising a copolymerizable monomer copolymerizable therewith (hereinafter referred to as “C component”) can also be mentioned.
Hereinafter, a polymer obtained from such a monomer mixture is referred to as a “specific acrylic polymer”.

  Specific examples of the acrylic acid alkyl ester having 4 to 12 carbon atoms in the alkyl group constituting the component A for polymerizing a specific acrylic polymer include n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, Examples include 2-ethylhexyl acrylate, n-octyl acrylate, isononyl acrylate, and lauryl acrylate. Specific examples of the alkyl methacrylate having 4 to 12 carbon atoms in the alkyl group include n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, and isononyl methacrylate. And lauryl methacrylate. These acrylic acid alkyl esters and methacrylic acid alkyl esters can be used alone or in combination of two or more. Among these, 2-ethylhexyl acrylate, isononyl acrylate, or lauryl methacrylate is preferable.

  The proportion of component A used in the monomer mixture is preferably 80 to 99% by weight, more preferably 85 to 99% by weight, and still more preferably 90 to 98% by weight. When the proportion of component A used in the monomer mixture is outside the above range, the adhesive label / tape having an adhesive layer made of the water-based adhesive is capable of following the expansion and contraction of the adherend. It becomes a low thing, and it becomes easy to produce what is called a suki which peels an adhesive label and tapes partially from the surface of a to-be-adhered body.

  Specific examples of the α, β-unsaturated carboxylic acid, which is a B component for polymerizing a specific acrylic polymer, include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and half ester. Can do. These α, β-unsaturated carboxylic acids can be used alone or in combination of two or more. Of these, methacrylic acid or mono [2- (meth) acryloyloxyethyl] phthalate is preferable. The proportion of component B used in the monomer mixture is preferably 1.2 to 8% by weight, more preferably 1.2 to 7% by weight, and still more preferably 1.5 to 5% by weight. When the ratio of the component B in the monomer mixture is outside the above range, the pressure-sensitive adhesive labels / tapes having the pressure-sensitive adhesive layer made of the water-based pressure-sensitive adhesive are inferior in the pressure-sensitive adhesive force, heat resistance holding power, and storage stability. It will be a thing.

  Specific examples of the copolymerizable monomer that is a C component for polymerizing a specific acrylic polymer include carbon number of alkyl groups such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, isopropyl acrylate, and isopropyl methacrylate. Acrylic acid alkyl ester or methacrylic acid alkyl ester having 3 or less; (meth) acrylic acid cyclic alkyl ester such as cyclohexyl (meth) acrylate; aromatic (meth) acrylic such as phenoxymethyl (meth) acrylate and benzyl (meth) acrylate Acid ester; hydroxyalkyl acrylate, hydroxyalkyl methacrylate, polyoxyethylene (meth) acrylate, methoxyethyl acrylate, ethoxymethyl acrylate, glycy Aliphatic (meth) acrylic acid esters such as polyacrylate and glycidyl methacrylate; (meth) acrylic acid amides such as acrylamide, methacrylamide, N-methylolacrylamide, N-methoxymethylacrylamide, N-methoxybutylacrylamide; vinyl methyl ketone, Vinyl ethyl ketone, vinyl-n-propyl ketone, vinyl-i-propyl ketone, vinyl-n-butyl ketone, vinyl-i-butyl ketone, vinyl-t-butyl ketone, vinyl phenyl ketone, vinyl benzyl ketone, divinyl ketone, diacetone acrylamide Aldo group and / or keto group-containing radical polymerizable monomers such as: (meth) acrylonitrile, crotonnitrile, 2-cyanoethyl (meth) acrylate, 2-cyanopropyl ( Nitrile group-containing unsaturated compounds such as acrylate and 3-cyanopropyl (meth) acrylate; styrene, o-vinyltoluene, m-vinyltoluene, p-vinyltoluene, p-ethylvinylstyrene, α-methylstyrene, α -Monovinyl aromatic compounds such as fluorostyrene; vinyl halides such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl propionate. By appropriately selecting these copolymerizable monomers, an aqueous pressure-sensitive adhesive having characteristics corresponding to the monomers used can be obtained.

  The proportion of component C used in the monomer mixture is preferably 10% by weight or less. When this ratio exceeds 5% by weight, adhesive labels / tapes having an adhesive layer made of the water-based adhesive are liable to cause a crack or bleed phenomenon from the adherend.

  The monomer mixture is preferably subjected to a polymerization reaction treatment by an emulsion polymerization method. Specifically, the monomer mixture is emulsified with an emulsifier to form a pre-emulsion, which is a redox polymerization initiator. In addition, the polymerization reaction treatment is usually performed under an inert atmosphere by the molecular weight regulator, and thereby, an aqueous emulsion of polymer particles made of a specific polymer is obtained.

In the polymerization reaction treatment, the monomer mixture is polymerized while continuously supplying the pre-emulsion and the redox polymerization initiator to the reaction system, and the redox polymerization starts even after the supply of the pre-emulsion to the reaction system is completed. It is preferable to complete the polymerization reaction by continuously supplying the agent. Here, when the redox polymerization initiator is composed of, for example, a plurality of types of oxidizers and / or a plurality of types of reducing agents, the continuously supplied redox-based initiator is the oxidizer and the reducing agent. Any combination that includes at least one of them may be used.
By using a redox polymerization initiator and allowing the polymerization reaction to proceed in this way, the polymerization reaction can be efficiently performed, and the aqueous pressure-sensitive adhesive can be obtained with high productivity.

A redox polymerization initiator is a polymerization initiator in which an oxidizing agent and a reducing agent are combined.
Examples of the oxidizing agent include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; hydrogen peroxide, t-butyl hydroperoxide, t-butyl peroxymaleic acid, succinic peroxide, benzoyl peroxide, Cumene hydroperoxide, diisopropyl peroxydicarbonate, cumyl peroxyneodecanoate, cumyl peroxy octoate, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 2,2-bis (4,4-di- and peroxides such as t-butylperoxycyclohexyl) propane.
On the other hand, examples of the reducing agent include acidic sodium sulfite, sodium dithionite, sodium thiosulfate, Rongalite, ascorbic acid, fructose and other reducing saccharides, ferrous sulfate, ferric sulfate and other iron salts. Can do. Moreover, you may use together chelating agents, such as sodium ethylenediaminetetraacetate, as needed.
Preferable examples of these combinations include the following combinations (1) to (3).
(1) Persulfate, acidic sodium sulfite, ferrous sulfate (2) t-butyl hydroperoxide, acidic sodium sulfite, ferrous sulfate (3) p-menthane hydroperoxide, ferrous sulfate, ethylenediamine tetra The proportion of sodium acetate, sodium formaldehyde sulfoxylate redox polymerization initiator used is preferably 0.01 to 5% by weight of the monomer mixture, more preferably 0.05 to 3% by weight, still more preferably 0.1 to 1% by weight.

  As the emulsifier, surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl sulfate ester salt, sodium polyoxyethylene alkyl succinate, sodium lauryl sulfate, sodium dodecylbenzene sulfonate can be used. “Latemul S-180A” and “PD-104” manufactured by Kao Corporation; “Eleminol JS-2” manufactured by Sanyo Chemical Co., Ltd .; “Aqualon KH-10” manufactured by Daiichi Kogyo Seiyaku Co., Ltd .; “Adekaria Soap SE-10N”, “SR-10N” manufactured by Asahi Denka Kogyo Co., Ltd .; “AntoxMS-60” manufactured by Nippon Emulsifier Co., Ltd .; “Surfmer FP-120” manufactured by Toho Chemical Industry Co., Ltd. Any reactive emulsifier can be used. The use ratio of the emulsifier is preferably 0.2 to 7% by weight of the monomer mixture, more preferably 0.5 to 5% by weight, and still more preferably 0.7 to 5% by weight. By appropriately selecting the type and use ratio of this emulsifier, an aqueous emulsion of polymer particles having an average particle size of a target size can be obtained.

  As the molecular weight regulator, butyl mercaptan, dodecyl mercaptan, octyl thioglycolate, isopropyl alcohol, methanol, carbon tetrachloride and the like can be used. The use ratio of the molecular weight regulator is preferably 0.001 to 0.5% by weight of the monomer mixture, more preferably 0.003 to 0.3% by weight, and still more preferably 0.005 to 0.005%. 1% by weight. By appropriately selecting the type and use ratio of the molecular weight regulator, an aqueous emulsion of polymer particles made of a polymer having a weight average molecular weight (Mw) of a target size can be obtained.

The average particle size of the polymer particles of the aqueous emulsion in this aqueous adhesive is 100 to 500 nm, preferably 150 to 450 nm, and more preferably 180 to 400 nm. When the average particle diameter of the polymer particles is less than 100 nm, the pressure-sensitive adhesive label / tape having the pressure-sensitive adhesive layer made of the water-based pressure-sensitive adhesive has excessive pressure-sensitive adhesive force to the adherend. End up. On the other hand, when the average particle diameter of the polymer particles exceeds 500 nm, the adhesive label / tape having an adhesive layer made of the water-based adhesive has a low adhesive force of the adhesive layer.
The average particle diameter of the polymer particles is measured using a nanosizer (manufactured by Coulter).

  This water-based pressure-sensitive adhesive is preferably obtained by adding a crosslinking agent to a water-based emulsion of polymer particles made of a specific polymer.

  As the crosslinking agent constituting the water-based pressure-sensitive adhesive, commonly used crosslinking agents can be used. For example, polyfunctional isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, metal chelate-based ones Examples thereof include a crosslinking agent and dihydrazide compounds such as adipic acid dihydrazide. This cross-linking agent may be either oil-soluble or water-soluble. These crosslinking agents can be used alone or in combination of two or more.

  As the crosslinking agent, for example, when the polymer constituting the polymer particles of the water-based emulsion is the specific acrylic polymer as described above, among the epoxy-based crosslinking agents, particularly ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether. , Propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, dibromoneopentyl glycol diglycidyl ether, o-phthalic acid diglycidyl ester, glycerin polyglycidyl ether , Trimethylolpropane polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol poly Ricidyl ether, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine, N, N, N ′, N′-pentaglycidyldiethylenetriamine, N, N, N ′, N′-tetraglycidylethylenediamine It is preferable to use a polyglycidyl compound containing two or more epoxy groups.

When the polymer constituting the polymer particles of the aqueous emulsion is the specific acrylic polymer as described above, the addition ratio of the crosslinking agent is such that the epoxy group introduced by the crosslinking agent constitutes the polymer particles of the aqueous emulsion. The ratio is preferably 0.005 to 2 equivalents relative to 1 equivalent of carboxyl groups in the specific polymer. Further, when an aldo group and / or keto group-containing radical polymerizable monomer is used, the amount of the crosslinking agent having two or more hydrazide groups is 0.01 to 1 with respect to 1 equivalent of the aldo group and / or keto group. Equivalent range.
Examples of the crosslinking agent having two or more hydrazide groups include oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, sebacic acid dihydrazide, phthalic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, Dicarboxylic acid dihydrazides having a total carbon number of 2 to 10, preferably 4 to 6, such as maleic acid dihydrazide, fumaric acid dihydrazide, itaconic acid dihydrazide; citric acid trihydrazide, nitriloacetic acid trihydrazide, cyclohexanetricarboxylic acid trihydrazide, ethylenediamine Trifunctional or higher functional hydrazides such as tetraacetic acid tetrahydrazide; ethylene-1,2-dihydrazine, propylene-1,2-dihydrazine, propylene-1,3-hydride Jin, butylene-1,3-dihydrazine, butylene-1,4-dihydrazine, the total number of carbon atoms, such as butylene-2,3-hydrazine aliphatic dihydrazine is 2-4.
When the ratio of the cross-linking agent is within such a range, the pressure-sensitive adhesive labels / tapes having the pressure-sensitive adhesive layer made of the water-based pressure-sensitive adhesive have heat resistant holding power. When the ratio of the cross-linking agent is excessive, the adhesive label / tape having an adhesive layer made of the water-based adhesive is insufficiently adhered to the adherend because of the adhesive force of the adhesive layer to the adherend. It becomes easy to generate | occur | produce and the biting of the adhesive with respect to a base material will become inferior.

  In the water-based pressure-sensitive adhesive of the present invention, various additives used for general water-based pressure-sensitive adhesives, such as white pigments, thickeners, wetting agents, alkali agents, stabilizers and emulsifiers, preservatives, fungicides, and the like are added. be able to.

  In the case of forming an adhesive layer of adhesive labels / tapes using the aqueous adhesive of the present invention, the base material of the adhesive labels / tapes is paper, cloth, polyvinyl chloride, polypropylene, polyester, polyimide Although a foam, a metal foil, etc. can be used, since the said aqueous adhesive has a high cohesion force, it can also be comprised as a base material-less double-sided tape without using a base material. Examples of the adherend on which the adhesive label / tape is used include plastic, metal, paper, glass, silicone, ceramic, and skin.

According to the above water-based pressure-sensitive adhesive, since it has a sufficiently high molecular weight, sufficient cohesive force can be obtained, and the polymer particles made of the specific polymer have a sufficiently large content of carboxyl groups defined by ΔAE. High cohesive force is obtained by the interaction between the carboxyl groups, and thus high heat-resistant retention force is obtained. Furthermore, since it has a specific low gel fraction, it has a high penetrating power to the substrate when an adhesive layer is formed. Therefore, a double-sided tape can be formed as an adhesive label.
Moreover, according to the manufacturing method of the above aqueous adhesive, said aqueous adhesive can be manufactured with high productivity.

  Specific examples of the present invention will be described below, but the present invention is not limited to these examples.

In the following examples and comparative examples, the average particle size of the polymer particles was measured using a nanosizer (manufactured by Coulter).
Moreover, the weight average molecular weight of polystyrene conversion was measured using the gel permeation chromatography apparatus "HCL-8020" (made by Tosoh Corporation).
Further, the gel fraction and the carboxyl group content ΔAE in the polymer particles were measured by the same method as described above.
Furthermore, the glass transition temperature was measured using a differential scanning calorimeter “SSC-5000 type” (manufactured by Seiko Electronics Co., Ltd.).

<Example 1>
(Preparation of monomer mixture)
A simple substance comprising 81.4 parts by weight of 2-ethylhexyl acrylate, 10 parts by weight of methyl methacrylate, 5 parts by weight of 2-hydroxyethyl methacrylate, 3.3 parts by weight of methacrylic acid, and 0.3 parts by weight of 2-methacryloyloxyethyl succinic acid. A monomer mixture was prepared.

(Preparation of aqueous emulsion)
In an autoclave equipped with a stirrer, a temperature controller and a reflux condenser, 47 parts by weight of water, 0.02 part by weight of sodium dodecylbenzenesulfonate as an emulsifier, and 0.4 part by weight of potassium persulfate as a polymerization initiator were added. Charged and heated to 40 ° C. In this autoclave, the above monomer mixture (100 parts by weight), 0.05 part by weight of lauryl mercaptan as a molecular weight regulator, 1.0 part by weight of “KH1025” (Daiichi Kogyo Seiyaku Co., Ltd.) and 29 of water After adding parts by weight, a pre-emulsion was prepared by stirring and emulsifying. The total amount of this pre-emulsion was continuously fed into the autoclave over 4 hours, and started with 9.85 parts by weight of water, 0.1 parts by weight of sodium hydrogen sulfite, and 0.03 parts by weight of ferrous sulfate. While continuously supplying the agent solution over 5 hours, the first 4 hours are stirred at 40 ° C. to carry out the polymerization reaction of the monomer mixture, and then the temperature is raised to 50 ° C. and stirred for 3 hours. An aqueous emulsion composed of a copolymer of 2-ethylhexyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, methacrylic acid, and 2-methacryloyloxyethyl succinic acid is obtained by conducting a polymerization reaction for 7 hours to complete the reaction. It was.
The glass transition temperature of the polymer particles in this water-based emulsion is −51 ° C., the average particle diameter is 280 nm, and the weight average molecular weight (Mw) in terms of polystyrene of the copolymer constituting the polymer particles, the gel fraction, and Table 1 shows the carboxyl group content ΔAE in the polymer particles.

[Production of water-based adhesive]
The aqueous emulsion is adjusted to pH 8.5 with ammonia, a polycarboxylic acid thickener “ASE-60” (Rohm & Haas) is added, and the viscosity (Brookfield viscometer, No. 4 spindle) is added. , 6 r.p.m.) was adjusted to 2 × 10 ⁴ cp. Next, polyethylene glycol diglycidyl ether is added to this aqueous emulsion, and 0.1 equivalent of epoxy group in polyethylene glycol diglycidyl ether is equivalent to 1 equivalent of carboxyl group in the copolymer constituting the polymer particles of the aqueous emulsion. The water-based pressure-sensitive adhesive [1] was produced by adding at a ratio of:

<Example 2>
An aqueous emulsion was prepared in the same manner as in Example 1 except that the monomer mixture was prepared according to the formulation shown in Table 1 below.
The glass transition temperature of the polymer particles in this aqueous emulsion was −54 ° C., and the average particle size was 276 nm. Table 1 shows the polystyrene-reduced weight average molecular weight (Mw), gel fraction, and carboxyl group content ΔAE in the polymer particles constituting the polymer particles.
Using this aqueous emulsion, an aqueous adhesive [2] was produced in the same manner as in Example 1.

<Example 3>
An aqueous emulsion was prepared in the same manner as in Example 1 except that the monomer mixture was prepared according to the formulation shown in Table 1 below.
The glass transition temperature of the polymer particles in this aqueous emulsion was −52 ° C., and the average particle size was 277 nm. Table 1 shows the polystyrene-reduced weight average molecular weight (Mw), gel fraction, and carboxyl group content ΔAE in the polymer particles constituting the polymer particles.
Using this aqueous emulsion, an aqueous pressure-sensitive adhesive [3] was produced in the same manner as in Example 1.

<Example 4>
A monomer mixture was prepared according to the formulation shown in Table 1 below, and an aqueous emulsion was prepared in the same manner as in Example 1 except that the amount of lauryl mercaptan used was changed from 0.05 parts by weight to 0.02 parts by weight. did.
The glass transition temperature of the polymer particles in this aqueous emulsion was −51 ° C., and the average particle size was 280 nm. Table 1 shows the polystyrene-reduced weight average molecular weight (Mw), gel fraction, and carboxyl group content ΔAE in the polymer particles constituting the polymer particles.
Using this aqueous emulsion, an aqueous pressure-sensitive adhesive [4] was produced in the same manner as in Example 1.

<Comparative Example 1>
A monomer mixture was prepared according to the formulation shown in Table 2 below, and an aqueous emulsion was prepared in the same manner as in Example 1 except that the amount of lauryl mercaptan used was changed from 0.05 parts by weight to 0.1 parts by weight. did.
The glass transition temperature of the polymer particles in this aqueous emulsion was −52 ° C., and the average particle size was 280 nm. Table 2 shows the polystyrene-equivalent weight average molecular weight (Mw), gel fraction, and carboxyl group content ΔAE in the polymer particles constituting the polymer particles.
Using this aqueous emulsion, a comparative aqueous adhesive [5] was produced in the same manner as in Example 1.

<Comparative example 2>
A monomer mixture was prepared according to the formulation shown in Table 2 below, and an aqueous emulsion was prepared in the same manner as in Example 1 except that the monomer mixture was polymerized at 70 ° C.
The glass transition temperature of the polymer particles in this aqueous emulsion was −51 ° C., and the average particle size was 271 nm. Table 2 shows the polystyrene-equivalent weight average molecular weight (Mw), gel fraction, and carboxyl group content ΔAE in the polymer particles constituting the polymer particles.
Using this aqueous emulsion, a comparative aqueous adhesive [6] was produced in the same manner as in Example 1.

<Comparative Example 3>
A monomer mixture was prepared according to the formulation shown in Table 2 below, and the same procedure as in Example 1 was performed except that the monomer mixture was polymerized at 75 ° C. without using lauryl mercaptan (molecular weight regulator). An aqueous emulsion was prepared.
The glass transition temperature of the polymer particles in this aqueous emulsion was −50 ° C., and the average particle size was 268 nm. Table 2 shows the polystyrene-equivalent weight average molecular weight (Mw), gel fraction, and carboxyl group content ΔAE in the polymer particles constituting the polymer particles.
Using this aqueous emulsion, a comparative aqueous adhesive [7] was produced in the same manner as in Example 1.

<Comparative example 4>
An aqueous emulsion was prepared in the same manner as in Example 1 except that the monomer mixture was prepared according to the formulation shown in Table 2 below.
The glass transition temperature of the polymer particles in this aqueous emulsion was −54 ° C., and the average particle size was 273 nm. Table 2 shows the polystyrene-equivalent weight average molecular weight (Mw), gel fraction, and carboxyl group content ΔAE in the polymer particles constituting the polymer particles.
A comparative water-based adhesive [8] was produced in the same manner as Example 1 using each water-based emulsion.

<Comparative Example 5>
An aqueous emulsion was prepared in the same manner as in Example 1 except that the monomer mixture was prepared according to the formulation shown in Table 2 below.
The glass transition temperature of the polymer particles in this aqueous emulsion was −50 ° C., and the average particle size was 272 nm. Table 2 shows the polystyrene-equivalent weight average molecular weight (Mw), gel fraction, and carboxyl group content ΔAE in the polymer particles constituting the polymer particles.
A comparative aqueous adhesive [9] was produced using each aqueous emulsion in the same manner as in Example 1.

<Comparative Example 6>
(1) Preparation of emulsion:
In a container, 4 parts by weight of an anionic surfactant “Latemul E-118B” (manufactured by Kao Corporation) and 20 parts by weight of deionized water were uniformly dissolved. Thereto, 48.5 parts by weight of 2-ethylhexyl acrylate, 48.5 parts by weight of n-butyl acrylate, 3 parts by weight of acrylic acid and 0.1 part by weight of lauryl mercaptan were added and emulsified to obtain an emulsion [A] (124 0.1 parts by weight).
(2) Preparation of aqueous emulsion:
Put 0.02 parts by weight of “Latemul E-118B” and 70 parts by weight of deionized water in a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, a thermometer, and a dropping funnel. The temperature rose. Under stirring, 1 part by weight of an aqueous solution of an anionic water-soluble polymerization initiator “V-501” (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and then 1.23 parts by weight of the emulsion [A] was charged to 55 ° C. The polymerization reaction was carried out for 1 hour. Subsequently, the remaining emulsified liquid [A] (122.8 parts by weight) and 8 parts by weight of an aqueous solution of “V-501” were dropped over 8 hours while maintaining the reaction vessel at 55 ° C. using a separate dropping funnel. After completion of dropping, the mixture was stirred at the same temperature for 2 hours, and then the contents were cooled to prepare an aqueous emulsion.
The glass transition temperature of the polymer particles in this water-based emulsion is −57 ° C., the average particle diameter is 270 nm, and the weight average molecular weight (Mw), gel fraction, and the inside of the polymer particles constituting the polymer particles Table 2 shows the carboxyl group content ΔAE.
(3) Production of water-based adhesive:
The aqueous emulsion was adjusted to pH 7.5 with ammonia, filtered through a 200-mesh wire mesh, 0.24 parts by weight of “Surfinol 420” (manufactured by Air Products Japan) as a leveling agent, “Epocross WS-” After adding 0.2 part by weight of “500” (manufactured by Nippon Shokubai Co., Ltd.), the mixture is filtered through a 100-mesh wire mesh, and rosin-based resin “E-200” (manufactured by Arakawa Chemical Industries, Ltd.) is used as a tackifier resin in solid content. 4 parts by weight was added to obtain a comparative water-based adhesive [10].

[Evaluation of water-based adhesive]
Using the above water-based pressure-sensitive adhesive, the following (1) pressure-sensitive adhesive storage stability was evaluated. The results are shown in Tables 3 and 4.
Moreover, the double-sided adhesive tape by which the adhesion layer was laminated | stacked on both surfaces of the base material using the above aqueous adhesive was produced. That is, each of the aqueous adhesives [1] to [4] obtained in Examples 1 to 4 and Comparative Examples 1 to 6 and the comparative aqueous adhesives [5] to [10] were each used as a release paper. The adhesive layer having a thickness of 40 to 50 g / m ² was formed by coating and drying at a time, and then sandwiching the adhesive layer on both sides of the rayon nonwoven fabric (base material) and passing the roll once to transfer it to the rayon nonwoven fabric. After curing for 1 week, a test piece was prepared by cutting into a size of 25 × 25 mm. Using this test piece, the following (2) to (5) were evaluated. The results are shown in Tables 3 and 4.

(1) Adhesive storage stability The viscosity of the water-based adhesive was measured using a viscometer “B-type viscometer” (manufactured by Tokyo Keiki Co., Ltd.) under the conditions of initial viscosity and 50 ° C. under measurement conditions of 25 ° C. and 60 revolutions The viscosity after standing for 7 days was measured, and when the viscosity change rate was within ± 40%, it was evaluated as “good”, and when it was larger than that, it was evaluated as “thickening”.

(2) Substrate permeability The double-sided pressure-sensitive adhesive tape obtained on black paper was pasted, and the degree of permeability was visually observed. The degree of penetration is such that the more the water-based adhesive penetrates into the base material, the greater the transparency and the black of the black drawing paper can be seen through. Therefore, the whiteness of the base material (rayon nonwoven fabric) that does not have an adhesive layer made of water-based adhesive Can be judged.
In particular,
Evaluate the case where it is the same as rayon non-woven (white) as “bad”
Unlike the rayon nonwoven fabric (white), the case where it looks black was evaluated as “good”.

(3) Heat resistance retention A stainless steel plate (SUS304) was used as a measurement adherend, and the above test piece was affixed to this stainless steel plate (attachment area 25 × 25 mm) and pressure-bonded with a 1 kg weight for 1 minute, and further measured atmosphere After curing at 80 ° C. or 120 ° C. for 20 minutes, a load of 1 kg was applied in a measurement atmosphere, and the evaluation was made based on the deviation width (mm) after 1 hour or the presence or absence of a drop.

(4) Adhesive force A stainless steel plate (SUS304) was used as an adherend to be measured, and the above test piece was attached to this stainless steel plate, and left for 20 minutes in an atmosphere at a temperature of 23 ° C. and a humidity of 65 RH%. A peel test was performed by the method, and the adhesive strength was determined in units of N / 25 mm.

(5) Ball tack Measured by the method of JIS Z 0237. The ball tack is one index representing the adhesive strength.

  As is clear from Tables 3 and 4 above, the water-based pressure-sensitive adhesives according to Examples 1 to 4 have sufficient storage stability, base material permeability, heat resistance retention, and excellent adhesiveness. Met. On the other hand, the water-based adhesives according to Comparative Examples 1 to 6 were unsuitable as described below.

Comparative Example 1 is an example in which the resin has a weight average molecular weight (Mw) outside the range defined by the present invention, specifically, a resin having an excessively low weight average molecular weight (Mw). It was confirmed that lack of retainability.
Comparative Example 2 is an example in which a resin having a gel fraction before cross-linking of 43%, which is outside the range defined in the present invention, was confirmed to lack substrate permeability.
In Comparative Example 3, the weight average molecular weight (Mw) of the resin is outside the range defined in the present invention, specifically, the weight average molecular weight (Mw) is excessive, and the gel fraction before crosslinking is 71%. It is an example in the case of using a resin that is outside the range defined in the present invention, but it was confirmed that the base material lacks permeability.
Comparative Example 4 is an example in which a resin having a ΔAE outside the range defined by the present invention, specifically, an excessively low value, was confirmed to lack heat resistance at high temperatures.
Comparative Example 5 is an example in which ΔAE is outside the range defined by the present invention, specifically, when the resin is too small, but it was confirmed that the storage stability is low and the viscosity is increased. .
Comparative Example 6 is an example in the case of using a resin whose ΔAE is outside the range defined in the present invention, specifically, too low, but lacks heat resistance at high temperatures, and also has an adhesive strength shown in the ball tack. It was confirmed to be low. Moreover, productivity was low.

Claims (3)

Containing polymer particles of an aqueous emulsion,
The polymer constituting the polymer particles of the aqueous emulsion is an acrylic polymer or a styrene-acrylic polymer,
The weight average molecular weight (Mw) is 600,000 to 10 million, the gel fraction is 30% or less ,
In addition, 0.7 to 5 parts by weight of at least one selected from a half-ester of a carboxyl group-containing monomer and methacrylic acid is obtained in 100 parts by weight of all the monomers for forming the polymer. And a difference (ΔAE) between the total acid titration value and the conductivity titration value is 10 to 200 μeq / g.   The aqueous pressure-sensitive adhesive according to claim 1, further comprising a crosslinking agent. A method for producing the water-based pressure-sensitive adhesive according to claim 1,
Supplying a redox polymerization initiator and a polymerizable monomer in an aqueous medium, and polymerizing the polymerizable monomer in the aqueous medium to obtain polymer particles of the aqueous emulsion;
A method for producing a water-based pressure-sensitive adhesive, wherein the redox polymerization initiator is continuously supplied even after the supply of the polymerizable monomer is completed to complete the polymerization reaction.