JP2020012017A - Aqueous re-releasable adhesive and adhesive sheet - Google Patents

Abstract

To provide an aqueous adhesive and an adhesive sheet which have good storage stability of an adhesive after a curing agent has been mixed, suppress an increase in adhesive force over time after pasting, and can obtain good re-releasability.SOLUTION: An aqueous re-releasable adhesive contains acrylic polymer particles and a particle type curing agent, in which the acrylic polymer particles are an emulsion polymer of a monomer mixture and a tackier resin, and the monomer mixture contains alkyl (meth)acrylate and a carboxyl group-containing monomer and contains no polyfunctional monomer.SELECTED DRAWING: None

Description

  The present invention relates to an aqueous removable pressure-sensitive adhesive.

  BACKGROUND ART Adhesives are used in various applications such as masking tapes, double-sided tapes, surface protection films, and packaging tapes. A water-based pressure-sensitive adhesive that does not use an organic solvent is actively used from the viewpoint of environmental measures, resource saving, safety, and the like. As such an aqueous pressure-sensitive adhesive, an acrylic pressure-sensitive adhesive which is low in cost and easily satisfies various physical properties is mainly used for label applications.

  The problem of this label application is that the re-peelability decreases due to an increase in the adhesive force after the lamination, as compared to immediately after lamination to an adherend such as a metal plate or a plastic plate. Can be When the re-peelability is reduced, there is a problem that it is difficult to peel the material from the adherend.

  Thus, Patent Document 1 discloses an emulsion obtained by subjecting a monomer mixture containing an alkyl (meth) acrylate, a carboxyl group-containing monomer, and a polyfunctional monomer to emulsion polymerization in the presence of an anionic reactive emulsifier, and oxazoline. There is disclosed a removable aqueous pressure-sensitive adhesive containing a system crosslinking agent.

  Further, Patent Document 2 discloses an aqueous pressure-sensitive adhesive containing a polymer emulsion obtained by emulsion polymerization of a monomer mixture of an alkyl acrylate and a carboxyl group-containing monomer in the presence of a reactive emulsifier and a chain transfer agent. .

JP 2004-256789 A Japanese Patent No. 2006-045410

  However, the water-based pressure-sensitive adhesive disclosed in Patent Document 1 has a high cohesive force of the acrylic emulsion itself, and thus does not have sufficient adhesion to a substrate. In addition, the water-based pressure-sensitive adhesive disclosed in Patent Document 2 uses a chain transfer agent during emulsion polymerization. Therefore, there is a problem that the cohesive strength of the polymer emulsion itself is low, so that the adhesive strength after bonding to the adherend increases.

  Therefore, the present invention provides an aqueous re-peelable pressure-sensitive adhesive which has good storage stability of the pressure-sensitive adhesive after mixing of the curing agent, and suppresses an increase in the adhesive force after lamination with time, thereby obtaining a pressure-sensitive adhesive sheet having good re-peelability. The purpose is to provide.

  The aqueous removable pressure-sensitive adhesive of the present invention contains acrylic polymer particles and a particle-type curing agent, and the acrylic polymer particles are an emulsion polymer of a monomer mixture and a tackifier resin, and the monomer mixture is The present invention relates to an aqueous removable pressure-sensitive adhesive containing a (meth) acrylic acid alkyl ester and a carboxyl group-containing monomer and not containing a polyfunctional monomer.

The pressure-sensitive adhesive sheet using the acrylic polymer particles and the particle-type curing agent of the present invention has an extremely high cohesive force. Generally, the curing agent is composed of a hydrophobic raw material that is insoluble in water. However, in order to use the curing agent in an aqueous pressure-sensitive adhesive, it is necessary to add a hydrophilic raw material to the curing agent. Thereby, when the ratio of the hydrophilic raw material is high, it can be made water-soluble, so that the curing reaction with the adhesive proceeds uniformly, while the ratio of the hydrophilic raw material that does not contribute to the reaction with the adhesive increases. The adhesive strength after bonding to the adherend is likely to increase, and the removability will decrease, such as the occurrence of adhesive residue. On the other hand, when the ratio of the hydrophilic raw material is low, the curing agent becomes a particle-type curing agent, and the curing reaction with the pressure-sensitive adhesive hardly proceeds uniformly.
As described above, the removable pressure-sensitive adhesive of the present invention has a low content ratio of the particle-type curing agent that is a hydrophilic raw material that does not contribute to the reaction with the pressure-sensitive adhesive. High removability was obtained. Furthermore, the change in viscosity of the pressure-sensitive adhesive after mixing the curing agent could be suppressed, and a pressure-sensitive adhesive that could be used stably even with a one-pack type could be obtained.

  According to the present invention, while the storage stability of the pressure-sensitive adhesive after mixing the curing agent is good, an increase in the adhesive force after bonding to the adherend is suppressed, and the water-based re-peeling can obtain a pressure-sensitive adhesive sheet having good re-peelability. An adhesive can be provided.

  Before describing the present invention in detail, terms will be defined. The alkyl (meth) acrylate includes an alkyl acrylate and an alkyl methacrylate. The monomer is an ethylenically unsaturated double bond containing monomer. The adherend is a partner to which the adhesive sheet is to be attached. Adhesion refers to the adhesion of the pressure-sensitive adhesive layer to the substrate.

《Aqueous removable adhesive》
The aqueous removable pressure-sensitive adhesive of the present invention contains acrylic polymer particles and a particle-type curing agent, and the acrylic polymer particles are an emulsion polymer of a monomer mixture and a tackifier resin, and the monomer mixture is It contains an alkyl (meth) acrylate and a carboxyl group-containing monomer and does not contain a polyfunctional monomer.
Acrylic polymer particles that are an emulsion polymer of a mixture containing a monomer mixture and a tackifier resin, a particle-type curing agent and, if necessary, an amino group-containing compound, an antifoaming agent, a leveling agent, a preservative, and a thickening agent By adding other additives such as the above, an aqueous removable pressure-sensitive adhesive can be obtained.
By adding other additives such as an amino group-containing compound, an antifoaming agent, a leveling agent, a preservative, and a thickening agent to the emulsion polymer containing the acrylic polymer particles and the particle-type curing agent, if necessary, A release adhesive can be obtained.

Further, the aqueous removable pressure-sensitive adhesive of the present invention can be suitably used as a one-component aqueous removable pressure-sensitive adhesive because the storage stability of the pressure-sensitive adhesive after mixing the curing agent is good.
The viscosity change rate of the aqueous removable adhesive after 90 days at 40 ° C. is preferably 0% or more and less than 10%, more preferably 0% or more and less than 5%. When the rate of change in viscosity is 0% or more and less than 10%, the storage stability is improved, and the step of using up the pressure-sensitive adhesive after mixing the curing agent, such as a two-pack type pressure-sensitive adhesive, becomes unnecessary. Furthermore, the compounding step of mixing a curing agent before the application of the adhesive, which is usually performed with a two-part adhesive, becomes unnecessary, and the workability during application is improved.

Viscosity change rate (%) = [(viscosity after 90 days at 40 ° C.) / (Initial viscosity) −1] × 100 absolute value

<Acrylic polymer particles>
The acrylic polymer particles in the present invention are emulsion polymers obtained by emulsion polymerization of at least a mixture of acrylic monomers and a tackifier resin. As the acrylic monomer, a monomer mixture containing a (meth) acrylic acid alkyl ester and a carboxyl group-containing monomer and not containing a polyfunctional monomer is used.
The acrylic polymer particles of the present invention can be obtained by subjecting this monomer mixture to emulsion polymerization in the presence of a tackifier resin.
Further, it is preferable to add an amino group-containing compound to the acrylic polymer particles after the emulsion polymerization. By adding the amino group-containing compound, the storage stability of the pressure-sensitive adhesive after mixing the curing agent is more favorable, the suppression of the increase in the adhesive force after lamination and the removability are preferable because a pressure-sensitive adhesive sheet with better removability is obtained. .
At the time of emulsion polymerization, other resins such as an antifoaming agent, a leveling agent, a solvent, and a urethane resin or an epoxy resin may be used.

[Monomer mixture]
The monomer mixture of the present invention contains a (meth) acrylic acid alkyl ester and a carboxyl group-containing monomer and does not contain a polyfunctional monomer.
Since the polyfunctional monomer has two or more polymerizable double bonds, a crosslinking reaction occurs during polymerization. As a result, the degree of crosslinking of the obtained acrylic polymer particles is increased, and the increase in the adhesive force after bonding the obtained pressure-sensitive adhesive sheet to an adherend such as a metal plate can be suppressed, while the adhesion to the base material decreases. For this reason, after sticking the pressure-sensitive adhesive sheet to an adherend such as a metal plate, there is a problem that adhesive residue occurs when the adhesive sheet is peeled off from the adherend.

  Examples of the alkyl (meth) acrylate include ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and n-octyl ( (Meth) acrylate, iso-octyl (meth) acrylate, lauryl (meth) acrylate, iso-nonyl (meth) acrylate, cyclohexyl (meth) acrylate, and the like. Among these, n-butyl acrylate and 2-ethylhexyl acrylate are preferred. (Meth) acrylic acid alkyl esters can be used alone or in combination of two or more.

  The alkyl (meth) acrylate preferably contains 50 to 99.5% by weight, and more preferably 70 to 99% by weight, based on 100% by weight of the monomer mixture. When the content is 50 to 99.5% by weight, the adhesive strength, tack and removability at the time of forming the pressure-sensitive adhesive layer can be easily obtained.

  Examples of the carboxyl group-containing monomer include (meth) acrylic acid, β-carboxyethyl acrylate, itaconic acid, crotonic acid, fumaric acid, fumaric anhydride, maleic acid, maleic anhydride, and butyl maleate. The carboxyl group-containing monomers can be used alone or in combination of two or more. The carboxyl group-containing monomer includes an acid anhydride group-containing monomer.

  The carboxyl group-containing monomer is preferably contained in the monomer mixture in an amount of 0.5 to 5% by weight, more preferably 0.8 to 2% by weight. By containing 0.5 to 5% by weight, the adhesive strength and removability are further improved.

  As the monomer mixture, “other monomers” other than the alkyl (meth) acrylate and the carboxyl group-containing monomer can be used. For example, aminomethyl (meth) acrylate, dimethylaminomethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, (meth) acrylamide, acetoacetoxyethyl methacrylate, diacetone (meth) acrylamide, (Meth) acrylonitrile, N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide, N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N- 2-ethylhexylitaconimide, N-cyclohexylitaconimide, N-laurylitaconimide, N- (meth) acryloyloxymethylene succinimide, N- (meth ) Acryloyl-6-oxyhexamethylene succinimide, N- (meth) acryloyl-8-oxyoctamethylene succinimide, glycidyl (meth) acrylate, vinyl acetate, styrene, methylstyrene, vinyl toluene, 2-methoxyethyl (meth) acrylate, Examples include 2-ethoxyethyl (meth) acrylate, 2-phenoxyethyl (meth) acrylate, and methoxypolyethylene glycol (meth) acrylate. In addition, known polyfunctional (meth) acrylate compounds such as polyethylene glycol di (meth) acrylate and neopentyl glycol adipate di (meth) acrylate may be used. Other monomers can be used alone or in combination of two or more.

The average particle size of the acrylic polymer particles of the present invention is preferably from 100 to 500 nm, more preferably from 150 to 450 nm. By setting the average particle diameter to 100 to 500 nm, the stability of the acrylic polymer particles can be improved.
Here, the average particle diameter is a volume average diameter of a cumulative 50% particle diameter measured by a dynamic light scattering type apparatus “Nanotrack Wave” (manufactured by Microtrack Bell Co., Ltd.).

[Tackifying resin]
The tackifier resin is a resin that can exhibit tackiness or improve adhesive strength by being added to an acrylic resin. Further, when the emulsion polymerization is carried out by adding to a monomer mixture containing an alkyl (meth) acrylate and a carboxyl group-containing monomer, a chain transfer reaction can be caused.

  In the present invention, a tackifier resin is used at the time of emulsion polymerization in order to obtain a desired solvent-insoluble content and a weight average molecular weight. In general, acrylic polymer particles obtained by emulsion polymerization have a very large molecular weight and are hardly soluble even with a solvent having a dissolving power such as tetrahydrofuran, but are soluble in a solvent by using a tackifier resin. Ingredients can be increased.

As described above, the tackifier resin has a large chain transfer effect, not only facilitates the adjustment of the molecular weight of the acrylic polymer particles, but also improves the adhesion when the pressure-sensitive adhesive layer is formed.
In the case where a chain transfer agent such as a compound having a thiol group or a hydroxyl group is used to adjust the molecular weight, the cohesive force of the acrylic polymer particles decreases, and the adhesive force after bonding to the adherend increases. However, when a tackifier resin is used, the chain transfer effect proceeds gently, without reducing the cohesive force of the acrylic polymer particles, and the adhesive is excellent in removability. be able to.

As the tackifying resin, it is preferable to use one or more selected from the group consisting of, for example, a rosin resin, a terpene resin, an aromatic petroleum resin, and an aliphatic petroleum resin. Furthermore, the softening point of the tackifier resin is preferably 80 ° C. or less from the viewpoint of adhesion to the substrate. Examples of the rosin resin include natural rosin, rosin ester, hydrogenated rosin, hydrogenated rosin ester, polymerized rosin, polymerized rosin ester, disproportionated rosin, and disproportionated rosin ester. Examples of the terpene resin include an α-pinene resin, a β-pinene resin, a terpene phenol resin, and a hydrogenated terpene phenol resin. Examples of the aromatic petroleum resin include a styrene oligomer and an α-methylstyrene / styrene copolymer.
Tackifying resins can be used alone or in combination of two or more

  The tackifier resin is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 8 parts by weight, based on 100 parts by weight of the monomer mixture. By using 0.1 parts by weight or more, the adhesiveness when the pressure-sensitive adhesive layer is formed is improved. By using 10 parts by weight or less, the acrylic polymer particles can be designed to have a high molecular weight, and the cohesive force when the pressure-sensitive adhesive layer is formed is further increased.

  In the present invention, the acrylic polymer particles are obtained by emulsion polymerization of the above monomer mixture and a tackifier resin. The emulsifier used in the emulsion polymerization is appropriately selected from an anionic emulsifier and a nonionic emulsifier. The emulsifier may be a reactive emulsifier having a radically polymerizable functional group, a non-reactive emulsifier having no radically polymerizable functional group, or both may be used in combination. From the viewpoint of water whitening resistance, it is more preferable to use a reactive emulsifier.

  In the present invention, among the emulsifiers, the reactive emulsifier is an anionic emulsifier having one or more radically polymerizable unsaturated double bonds in the molecule. For example, a sulfosuccinate-based emulsifier, an alkylphenol ether-based emulsifier, and the like can be given.

  Non-reactive anionic emulsifiers include polyoxyethylene polycyclic phenyl ether sulfate, higher fatty acid salts such as sodium stearate, alkyl aryl sulfonates such as sodium dodecylbenzene sulfonate, alkyl sulfate salts such as sodium lauryl sulfate, And polyoxyethylene alkyl ether sulfates such as sodium polyoxyethylene lauryl ether sulfate, and polyoxyethylene alkyl aryl ether sulfates such as sodium polyoxyethylene nonylphenyl ether sulfate.

Non-reactive nonionic emulsifiers include polyoxyethylene alkyl phenyl ethers such as polyoxyethylene nonylphenyl ether and polyoxyethylene octyl phenyl ether; polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether such as polyoxyethylene oleyl ether. Oxyethylene alkyl ethers; polyoxy polycyclic phenyl ethers such as polyoxyethylene distyrenated phenyl ether; polyoxyethylene sorbitan fatty acid esters;
Emulsifiers can be used alone or in combination of two or more.

  Among the emulsifiers, it is preferable to use a reactive or non-reactive anionic emulsifier because good polymerization stability is obtained, and particularly preferable are reactive polyoxyethylene alkyl ether sulfate salts, Is more preferably an ammonium salt of a polyoxyethylene alkyl ether sulfate having an alkyl group of 9 to 14. The emulsifier is preferably used in an amount of 0.5 to 3 parts by weight based on 100 parts by weight of the monomer mixture.

As the polymerization initiator used for the emulsion polymerization, it is preferable to use a water-soluble polymerization initiator.
Examples of the water-soluble polymerization initiator include potassium persulfate, sodium persulfate, ammonium persulfate, ammonium (amine) salt of 4,4′-azobis-4-cyanovaleric acid, and 2,2′-azobis (2-methylamide Oxime) dihydrochloride, 2,2'-azobis (2-methylbutanamidooxime) dihydrochloride tetrahydrate, 2,2'-azobis @ 2-methyl-N- [1,1-bis (hydroxymethyl) -2 -Hydroxyethyl] -propionamide} and 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide]. Of these, potassium persulfate and sodium persulfate are preferred.

  Further, the polymerization initiator can be used as a redox-based polymerization initiator (using both an oxidizing agent and a reducing agent). Examples of the oxidizing agent include ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide, p-methane hydroperoxide and the like. Examples of the reducing agent include sodium sulfite, sodium acid sulfite, Rongalit, ascorbic acid, and the like. Among them, it is preferable to use a combination of an oxidizing agent: potassium persulfate or sodium persulfate and a reducing agent: sodium sulfite or sodium acid sulfite because of excellent polymerization reactivity.

  The polymerization initiator is preferably used in an amount of 0.01 to 0.5 part by weight, more preferably 0.02 to 0.3 part by weight, based on 100 parts by weight of the monomer mixture. When the amount is 0.01 to 0.5 part by weight, the polymerization reactivity and the mechanical stability of the aqueous removable pressure-sensitive adhesive can be further improved.

  In the present invention, the emulsion polymerization is preferably carried out, for example, after emulsifying a monomer to form an emulsion, followed by synthesis (pre-emulsification method). The method of emulsion polymerization is a method in which the whole amount of the emulsion is previously charged in a reaction vessel and then reacts, or a part of the emulsion is charged in a reaction vessel and the residue of the emulsion is divided into several times. A known method such as a method of adding or continuously dropping can be used.

  The acrylic polymer particles preferably have a gel fraction of 30 to 70%. By setting the gel fraction within the above range, it is possible to obtain a high level of adhesion, adhesive strength and removability.

The calculation of the gel fraction can be performed by the following method. The acrylic copolymer particles are applied on a polyethylene terephthalate film (hereinafter referred to as a PET film), and a dried film is formed so that the thickness after drying becomes about 20 g / m ² (referred to as a coated material). The obtained coated product is wrapped in a stainless steel mesh of 200 mesh, then put into ethyl acetate, immersed at 23 ° C. for 72 hours, and dried to remove ethyl acetate. The ratio of the weight of the dried film after immersion to the weight of the dried film before immersion (% by weight) is referred to as a gel fraction with respect to ethyl acetate. The gel fraction is determined according to the following equation.
Formula 1 Gel fraction (%) = (weight of dry film before immersion−weight of PET film) / (weight of dry film after immersion−weight of PET film) × 100

<Particle type curing agent>
The aqueous removable pressure-sensitive adhesive of the present invention contains a particle-type curing agent. The particle-type curing agent is a water-dispersed emulsion in which the appearance of the curing agent is opaque and the curing agent has an average particle diameter.
By using the particle type curing agent, the hydrophilic group part of the particle type curing agent protects the hydrophobic curing agent, thereby suppressing the reaction between the particle type curing agent and the carboxyl group of the acrylic polymer in the emulsion polymer. be able to. Therefore, by applying and drying the emulsion of the pressure-sensitive adhesive of the present invention, the particle structure of the particle-type curing agent collapses and the reaction proceeds promptly. Since the particle-type curing agent has a small amount of a hydrophilic component that does not participate in the crosslinking reaction, the crosslinking density is increased, and an excellent re-peelable pressure-sensitive adhesive is obtained in which the pressure-sensitive adhesive strength of the obtained pressure-sensitive adhesive sheet after aging is low.

  The average particle diameter of the particle-type curing agent is preferably from 1 to 100 nm, more preferably from 1 to 50 nm. By setting the average particle diameter of the particle-type curing agent to 100 nm or less, the curing reaction between the particle-type curing agent and the carboxyl group of the acrylic polymer more easily proceeds, and the removability is improved. The method for measuring the average particle diameter of the particle-type curing agent is the same as that for the acrylic polymer.

  Examples of the particle-type curing agent include an aziridine compound, a carbodiimide compound, and an oxazoline compound. Of these, carbodiimide compounds are preferred from the viewpoint of long pot life and improved adhesion to the substrate. The particle-type curing agents can be used alone or in combination of two or more.

  The curing agent is preferably used in an amount of 0.01 to 8 parts by weight, preferably 0.01 to 5 parts by weight, more preferably 0.03 to 2.5 parts by weight, based on 100 parts by weight of the acrylic polymer. By adding 0.01 to 5 parts by weight, the adhesion to the substrate and the cohesive force are further improved.

<Amino group-containing compound>
The aqueous removable pressure-sensitive adhesive of the present invention may further contain an amino group-containing compound. The use of the amino group-containing compound improves the smoothness of the obtained pressure-sensitive adhesive sheet, so that the pressure-sensitive adhesive force after the pasting can be suppressed, and the removability can be excellent. Furthermore, when compounding the aqueous removable adhesive, the curing reaction between the particle type curing agent and the carboxyl group of the acrylic polymer particles can be suppressed, the increase in the viscosity of the aqueous removable adhesive is suppressed, and the change in viscosity is suppressed. It is preferred because it can be.

Examples of the amino group-containing compound include primary amines such as monomethylamine, monoethylamine, monopropylamine, monobutylamine and monoethanolamine, and secondary amines such as dimethylamine, diethylamine, dibutylamine, diethanolamine and diisopropanolamine, and methylpropanolamine. Amines and tertiary amines such as trimethylamine, triethylamine, dimethylethylamine, dimethylmonoethanolamine and triethanolamine.
Among these, secondary amines and tertiary amines are preferred because they have a three-dimensionally umbrella structure and have a greater effect of suppressing the curing reaction with the carboxyl group of the acrylic polymer particles.

  The amount of the amino group-containing compound to be added is preferably such that the molar ratio of the amino group of the amino group-containing compound to the carboxyl group of the acrylic polymer particles is 0.1 / 1 to 5/1, and 0.25 / 1. ~ 2.5 / 1 is more preferred. The stability of the aqueous removable pressure-sensitive adhesive can be improved by adjusting the amount of the carboxyl group to the acrylic polymer particles in a molar ratio of 0.1 / 1 to 5/1.

  The aqueous removable pressure-sensitive adhesive of the present invention can contain a tackifier resin after emulsion polymerization. Adjustment of the adhesive force is facilitated by the addition of the tackifier resin.

<Production method of aqueous removable adhesive>
The acrylic polymer particles of the present invention are emulsion polymerized using an initiator in the presence of a monomer mixture containing an alkyl (meth) acrylate and a carboxyl group-containing monomer, a tackifier resin, water, and an emulsifier. And acrylic polymer particles. The emulsion here means a monomer mixture, a tackifier resin, water, and an emulsifier before emulsion polymerization, and an emulsion polymer is obtained by emulsion polymerization of the emulsion.
Since the tackifier resin is used by dissolving it in the monomer mixture, the particles of the tackifier resin and the acrylic polymer particles do not exist separately after the emulsion polymerization, and the tackifier resin is integrated into the acrylic polymer particles. Can be incorporated.
By adding other additives such as an amino group-containing compound, a particle-type curing agent, an antifoaming agent, a leveling agent, a preservative, and a thickener to the obtained acrylic polymer particles, an aqueous removable pressure-sensitive adhesive can be obtained. it can.
Since the removable adhesive of the present invention has good storage stability after mixing the curing agent, it can be suitably used as an aqueous removable adhesive used in a one-pack type.

《Adhesive sheet》
The pressure-sensitive adhesive sheet of the present invention includes a substrate and a pressure-sensitive adhesive layer that is a cured product of an aqueous removable pressure-sensitive adhesive.
Examples of the production method include (1) a method of applying an aqueous re-peelable pressure-sensitive adhesive to a release sheet, drying the pressure-sensitive adhesive layer, and then transferring the pressure-sensitive adhesive layer onto a substrate. And (2) a method in which an aqueous re-peelable pressure-sensitive adhesive is applied to a substrate, dried to form a pressure-sensitive adhesive layer, and then a release sheet is laminated. And the like.

  Examples of the coating method include known methods such as a Meyer bar, an applicator, a brush, a spray, a roller, a gravure coater, a die coater, a lip coater, a comma coater, a knife coater, a reverse coater, and a spin coater. Drying is usually performed during coating. Drying is not particularly limited, and a known method such as hot air drying, an infrared heater, and a reduced pressure method can be appropriately selected and used. The drying temperature is usually about 60 to 180 ° C.

  The thickness of the pressure-sensitive adhesive layer is generally about 5 to 100 μm, and more preferably 10 to 50 μm.

  Examples of the substrate include plate materials or sheets such as paper, cellophane, plastic sheet, rubber, foam, cloth, rubber cloth, resin impregnated cloth, glass plate, metal plate, wood, and optical film such as polarizing plate. The substrate may be a single or a plurality of laminates. Further, the base material may be subjected to a peeling treatment or an antistatic treatment on the back surface (the surface not in contact with the pressure-sensitive adhesive layer). In addition, the substrate can be improved in adhesion to the pressure-sensitive adhesive layer by performing a known easy adhesion treatment.

  The thickness of the substrate is generally about 10 to 100 μm, and more preferably 30 to 80 μm.

  The adherend of the pressure-sensitive adhesive sheet of the present invention can be used as a material for a wide range of materials such as metal, glass, plastic film, rubber, wood, cardboard, paper and paint-coated surfaces.

  The application of the pressure-sensitive adhesive sheet of the present invention is not particularly limited, but it can be suitably used for applications requiring re-peeling, such as various labels, masking tapes, and protective films.

  Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In the following description, “part” means “part by weight” and “%” means “% by weight”.

(Example 1)
98.5 parts of 2-ethylhexyl acrylate as an alkyl (meth) acrylate, 1.5 parts of acrylic acid as a carboxy group-containing monomer, and picolastic A-5 as a tackifying resin (styrene-based resin, manufactured by Eastman Chemical Company) 1.0 part was added and dissolved. Further, 1.0 part of "AQUALON KH-10" (polyoxyethylene-1- (allyloxymethyl) alkyl ether sulfate ammonium salt, Daiichi Kogyo Seiyaku Co., Ltd.) as an anionic reactive emulsifier, and 25.1 deionized water. The mixture was added and stirred to obtain an emulsion. The obtained emulsion was put into a dropping funnel.
Separately, 45.6 parts of deionized water and 1.0 part of the above emulsion were charged into a four-necked flask equipped with a stirrer, a condenser, a thermometer and the above-mentioned dropping funnel. And the internal temperature was heated to 70 ° C. while stirring. Thereafter, 10% ammonium persulfate was added to start the reaction. After the above emulsion was added dropwise over 180 minutes while maintaining the internal temperature at 70 ° C, the reaction was continued for 1 hour while maintaining the internal temperature at 70 ° C with further stirring. Thereafter, the internal temperature was cooled to 65 ° C., and 1.0 part of a 10% aqueous solution of oxidizing agent “Perbutyl H-69” (manufactured by NOF Corporation) and a reducing agent “Erbit N” (manufactured by Fuso Chemical Industry Co., Ltd.) were used. 1.0 part of a 10% strength aqueous solution was added three times every 10 minutes, and the reaction was further continued for 1 hour.
Thereafter, the mixture was cooled to obtain an emulsion polymer as acrylic polymer particles having a nonvolatile content of 50% and an average particle size of 300 nm. The gel fraction of the acrylic polymer particles was 40%.

Next, with respect to 100 parts of the emulsion polymer containing the acrylic polymer particles, 2 parts of triethylamine as a neutralizing agent, 0.3 parts of SN Deformer 364 (manufactured by San Nopco) as a defoaming agent, and Unichem as a preservative 0.05 parts of Flex BN-202 (manufactured by Union Chemical Co.), 0.2 parts of "Perex OT-P" (manufactured by Kao Corporation) as a leveling agent, and a carbodiimide-based particle-type curing agent, carbodilite E-, as a crosslinking agent Addition of 1.25 parts of Nitrogen 05 (particle size: 45 nm, non-volatile content: 40%, manufactured by Nisshinbo Chemical Co., Ltd.) and further thickening with an alkali thickener gave an aqueous removable adhesive.
The obtained aqueous re-peelable pressure-sensitive adhesive was applied on a release sheet using a comma coater so that the thickness after drying was 20 μm, dried in a drying oven at 100 ° C. for 75 seconds, and then commercially available PET The films were laminated to obtain an adhesive sheet.
The performance was evaluated by the test method described later, and the results are shown in Table 1.

(Examples 2 to 20, Comparative Examples 1 to 7)
An aqueous removable pressure-sensitive adhesive and pressure-sensitive adhesive sheet were obtained in the same manner as in Example 1, except that the composition of Example 1 was changed to the raw materials and the amounts (parts by weight) shown in Table 1.
In addition, by appropriately adjusting the internal temperature, the dropping rate, the reaction time, and the like during the emulsion polymerization, acrylic-based polymer particles having an average particle diameter shown in the table were obtained.

The abbreviations in Table 1 are as follows.
-EHA: 2-ethylhexyl acrylate-BA: butyl acrylate-MMA: methyl methacrylate-AA: acrylic acid-MAA: methacrylic acid-TPGDA: tripropylene glycol diacrylate-A-5: "picolastic A-5" ( Styrene resin, manufactured by Eastman Chemical Company)
・ KE364C: “KE364C” (rosin resin, Arakawa Chemical Co., Ltd.)
-OTG: octyl thioglycolate-KH-10: "AQUALON KH-10" (anionic reactive emulsifier, polyoxyethylene-1- (allyloxymethyl) alkyl ether sulfate ammonium salt, 100% non-volatile content, Daiichi Kogyo) Pharmaceutical company)
RA9612: "Newcol RA9612" (anionic non-reactive emulsifier, polyoxyethylene alkyl ether sulfate ammonium salt, nonvolatile content 25%, manufactured by Nippon Emulsifier Co.)
E-05: "Carbodilite E-05 (carbodiimide-based particle-type curing agent, particle diameter 45 nm, nonvolatile content 40%, manufactured by Nisshinbo Chemical Inc.)"
-K-2010E: "Epocross K-2010E" (oxazoline-based particle-type curing agent, particle diameter 208 nm, nonvolatile content 100%, manufactured by Nippon Shokubai Co., Ltd.)
DZ-22E: “Chemiteite DZ-22E” (aziridine-based particle-type curing agent, particle diameter 700 nm, volatile content 100%, manufactured by Nippon Shokubai Co., Ltd.)
SV-02: "Carbodilite SV-02 (carbodiimide-based solution-type curing agent, nonvolatile content 40%, manufactured by Nisshinbo Chemical Inc.)"
EX-313: "Denacol EX-313" (Epoxy-based solution-type curing agent, nonvolatile content 100%, manufactured by Nagase ChemteX Corporation)
-PZ-33: "Chemiteit PZ-33" (aziridine-based solution-type curing agent, volatile matter 100%, manufactured by Nippon Shokubai Co., Ltd.)
・ TEN: triethylamine ・ TEA: triethanolamine ・ DEA: diethylamine ・ PA: monopropylamine

[Test method]
(1) Room temperature adhesive strength
The obtained pressure-sensitive adhesive sheet was prepared as a sample in a size of 100 mm long × 25 mm wide under an environment of 23 ° C. and 50% RH. Next, in accordance with JIS Z 0237, the peelable sheet was peeled off from the sample, the exposed pressure-sensitive adhesive layer was stuck to a stainless steel plate (hereinafter referred to as SUS) whose surface was polished, and a 2 kg roll was reciprocated once, immediately after 24 hours. Was measured for adhesion. The adhesion was measured using a tensile tester at a peeling speed of 300 mm / min and a peeling angle of 180 °.

(2) High-Temperature Adhesive Force The obtained adhesive sheet was prepared as a sample in a size of 100 mm long × 25 mm wide under an environment of 23 ° C. and 50% RH. Next, the peelable sheet was peeled off from the sample, the exposed pressure-sensitive adhesive layer was pasted on a stainless steel plate (hereinafter referred to as SUS) whose surface was polished, and a 2 kg roll was reciprocated once. After standing for 7 days, 2 hours after removing from the oven, the adhesive strength was measured in an atmosphere of 23 ° C. and 50% RH. The adhesion was measured using a tensile tester at a peeling speed of 300 mm / min and a peeling angle of 180 °. The rate of increase in adhesive strength was calculated from the following equation.
Adhesive strength maintenance rate (%) = [(high temperature adhesive strength) / (normal temperature adhesive strength) −1] × 100
The determination of the adhesive strength maintenance rate was evaluated according to the following criteria.

：: Adhesive strength maintenance rate of 50% or less. Very good.
：: Adhesive strength maintenance rate of 50% or more and less than 100%. Good.
Δ: Adhesive strength maintenance rate of 100% or more and less than 200%. Practical.
×: Adhesion strength retention rate of 200 %% or more. Not practical.

(3) Removability The obtained pressure-sensitive adhesive sheet was prepared as a sample having a size of 100 mm long × 25 mm wide under an environment of 23 ° C. and 50% RH. Next, the peelable sheet of the sample was peeled off, the exposed pressure-sensitive adhesive layer was adhered to SUS, and pressure-bonded by reciprocating once with a 2 kg roll. The sample after crimping was allowed to stand in an oven at 40 ° C. for 7 days, taken out of the oven, two hours later, and then sampled at a speed of 300 mm / min from SUS using a tensile tester in an atmosphere of 23 ° C. and 50% RH. Then, the film was peeled in the 180 ° direction, and whether or not contamination derived from the pressure-sensitive adhesive layer adhered to the SUS surface was visually evaluated according to the following criteria.

A: The SUS surface was clean. Very good.
：: Stain was slightly adhered to the SUS surface, but good.
Δ: Slight contamination was observed on the SUS surface, but there was no practical problem.
X: Very large amount of contamination adhered to the SUS surface. Not practical.

(4) Water Whitening Resistance The peelable sheet was peeled off from the obtained pressure-sensitive adhesive sheet, a PET film was bonded, and the sheet was immersed in ion-exchanged water at 40 ° C. for 24 hours. The turbidity before and after the immersion was measured with a haze meter (NDH5000W, manufactured by Nippon Denshoku Industries Co., Ltd.).

A: Turbidity change before and after immersion is less than 0.5. Very good.
：: Change in turbidity before and after immersion is 0.5 or more and less than 1.0. Good.
Δ: Change in turbidity before and after immersion is 1.0 or more and less than 1.5. No problem in practical use.
X: The turbidity change before and after immersion is 1.5 or more. Not practical.

(5) Change in Viscosity The obtained aqueous removable pressure-sensitive adhesive was allowed to stand at 40 ° C. for 90 days, and the viscosity before and after the standing was measured with a B-type viscometer. The rate of change in viscosity was calculated from the following equation.
Viscosity change rate (%) = [(viscosity after 90 days at 40 ° C.) / (Initial viscosity) −1] × 100 The determination of the absolute value viscosity change rate was evaluated based on the following criteria.

A: Viscosity increase rate is 0% or more and less than 5%. Very good.
：: The rate of increase in viscosity is 5% or more and less than 10%. Good.
Δ: Viscosity increase rate of 10% or more and less than 20%. Practical.
X: Viscosity increase rate 20% or more. Not practical.

Claims (9)

Acrylic polymer particles, an aqueous removable adhesive containing a particle-type curing agent,
The acrylic polymer particles are an emulsion polymer of a monomer mixture and a tackifier resin,
An aqueous removable pressure-sensitive adhesive, wherein the monomer mixture contains a (meth) acrylic acid alkyl ester and a carboxyl group-containing monomer and does not contain a polyfunctional monomer.   The aqueous removable pressure-sensitive adhesive according to claim 1, wherein the acrylic polymer particles have an average particle size of 100 to 500 nm.   The aqueous removable pressure-sensitive adhesive according to claim 1, further comprising an amino group-containing compound.   The aqueous removable pressure-sensitive adhesive according to claim 3, wherein the amino group-containing compound is a secondary amine or a tertiary amine.   The aqueous removable pressure-sensitive adhesive according to claim 3, wherein the molar ratio of the amino group of the amino group-containing compound to the carboxyl group of the acrylic polymer particles is from 0.1 / 1 to 5/1.   The aqueous removable pressure-sensitive adhesive according to any one of claims 1 to 5, wherein the particle-type curing agent has an average particle size of 1 to 100 nm.   The aqueous removable pressure-sensitive adhesive according to any one of claims 1 to 6, which is used in a one-pack type.   The aqueous removable pressure-sensitive adhesive according to any one of claims 1 to 7, wherein a viscosity change rate after 90 days at 40 ° C is 0% or more and less than 10%.   An adhesive sheet comprising a substrate and an adhesive layer which is a cured product of the aqueous removable adhesive according to any one of claims 1 to 8.