JP6702115B2 - Water-based removable adhesive - Google Patents

Description

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

  A removable adhesive sheet using a paper base material generally uses an aqueous adhesive in many cases. Since it is important that the re-peelable pressure-sensitive adhesive sheet firmly adheres to the adherend while it is attached and that it can be easily peeled off after use, it has been a conventional improvement of the water-based pressure-sensitive adhesive for the purpose of improving re-peelability. Is being done.

  For example, Patent Document 1 discloses an aqueous removable pressure-sensitive adhesive containing an acrylic polymer, a phosphate ester-based surfactant, a rosin-based tackifying resin, and a polyisocyanate-based curing agent.

JP-A-2005-089490

  However, the conventional water-based removable pressure-sensitive adhesive has a problem that the removable property is difficult for various materials such as stainless steel, polyolefin, and polyvinyl chloride, although it has some removable property.

  An object of the present invention is to provide a water-based removable pressure-sensitive adhesive capable of producing a pressure-sensitive adhesive sheet having removability for various materials such as stainless steel, polyolefin, and polyvinyl chloride.

  The water-based removable pressure-sensitive adhesive of the present invention is an acrylic polymer which is an emulsion polymer of a monomer mixture containing 50 to 99.9% by weight of a (meth)acrylic acid alkyl ester and 0.1 to 8% by weight of a carboxyl group-containing monomer. It contains a system polymer (A), a surfactant having 18 mol or more of alkylene oxide units, and a first plasticizer (excluding the surfactant).

  According to the above-mentioned present invention, the water-based removable pressure-sensitive adhesive containing an acrylic polymer (A) copolymerized with a surfactant having 18 mol or more of alkylene oxide units and a plasticizer has an adhesive force to an adherend. Since it is possible to achieve both a high level of peelability and a high level of releasability, it is possible to obtain good releasability not only for olefins having low polarity but also for polyvinyl chloride having high polarity.

  INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an aqueous removable pressure-sensitive adhesive capable of producing a pressure-sensitive adhesive sheet having removability for various materials such as stainless steel, polyolefin, and polyvinyl chloride.

The water-based removable pressure-sensitive adhesive of the present invention is an acrylic polymer which is an emulsion polymer of a monomer mixture containing 50 to 99.9% by weight of a (meth)acrylic acid alkyl ester and 0.1 to 8% by weight of a carboxyl group-containing monomer. The polymer (A), a surfactant having 18 mol or more of alkylene oxide units, and a first plasticizer.
The water-based removable pressure-sensitive adhesive of the present invention is preferably used as a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed by coating and drying and a substrate.
The water-based removable pressure-sensitive adhesive of the present invention has little change in adhesive strength after being adhered to an adherend for a long time, has good removability, and is good for various adherends having different polarities. Has removability. In the present invention, "sheet", "tape" and "label" are synonyms. The monomer is an ethylenically unsaturated group-containing monomer. Further, the adherend refers to the other party to which the adhesive sheet is attached.

  The acrylic copolymer (A) used in the present invention is an emulsion polymer of a monomer mixture containing 50 to 99.9% by weight of (meth)acrylic acid alkyl ester and 0.1 to 8% by weight of a carboxyl group-containing monomer. Is. Note that (meth)acrylic is acrylic and methacrylic, and (meth)acrylate is acrylate and methacrylate.

  The (meth)acrylic acid alkyl ester is, for example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, 2-Ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, iso-octyl (meth)acrylate, lauryl (meth)acrylate, iso-nonyl (meth)acrylate, cyclohexyl (meth)acrylate, Benzyl (meth)acrylate and the like can be mentioned. Among these, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, and (meth)acrylic acid 2-methacrylate are available from the viewpoints of availability and emulsion stability of the monomer mixture. It is more preferred to use ethylhexyl.

The (meth)acrylic acid alkyl ester also includes a compound in which a part of hydrogen atoms of an alkyl group is substituted with an alkoxy group or the like. Examples of such compounds include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, and methoxypolyethylene glycol (meth)acrylate.
The (meth)acrylic acid alkyl ester can be used alone or in combination of two or more kinds.

  The (meth)acrylic acid alkyl ester is preferably contained in an amount of 50 to 99.9% by weight, more preferably 70 to 99% by weight, in 100% by weight of the monomer mixture. By containing 50 to 99.9% by weight, it is easy to achieve both adhesive strength and removability.

  The carboxyl group-containing monomer contains an acid anhydride group-containing compound in addition to the carboxyl group.

Examples of the carboxyl group-containing monomer include (meth)acrylic acid, β-carboxyethyl (meth)acrylate, itaconic acid, crotonic acid, fumaric acid, fumaric anhydride, maleic acid, maleic anhydride, and butyl maleate. Be done. Among these, acrylic acid and methacrylic acid are preferable, and the combined use of acrylic acid and methacrylic acid is more preferable. By the combined use, the polymerization stability during emulsion polymerization is further improved, and the adhesiveness with the paper substrate is further improved.
The (meth)acrylic acid alkyl ester can be used alone or in combination of two or more kinds.

  The carboxyl group-containing monomer is preferably contained in an amount of 0.1 to 8% by weight, more preferably 0.8 to 5.0% by weight, in 100% by weight of the monomer mixture. By containing 0.1 to 8% by weight, it is easy to achieve both adhesive strength and removability.

Examples of the monomer other than the (meth)acrylic acid alkyl ester and the carboxyl group-containing monomer that can be used in the synthesis of the acrylic polymer (A) include, for example, a hydroxyl group-containing monomer, a self-crosslinking monomer, an amino group-containing monomer, and an amide group-containing monomer. Monomers, imide group-containing monomers and other vinyl monomers are preferred.
Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate.
Examples of the self-crosslinking monomer include diallyl phthalate, acetoacetoxyethyl (meth)acrylate, and 3-(trimethoxysilyl)propyl (meth)acrylate.
Examples of the amino group-containing monomer include aminomethyl (meth)acrylate, dimethylaminomethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and dimethylaminopropyl (meth)acrylate.
Examples of the amide group-containing monomer include (meth)acrylamide and diacetone (meth)acrylamide.
Examples of the imide group-containing monomer include 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)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, N-(meth) Acryloyl-8-oxyoctamethylenesuccinimide may be mentioned.
Other vinyl monomers include, for example, vinyl acetate, styrene, methylstyrene, vinyltoluene, and acrylonitrile.
In addition, known polyfunctional (meth)acrylic acid compounds such as polyethylene glycol di(meth)acrylate and neopentyl glycol adipate di(meth)acrylate are included in other vinyl monomers.

  It is preferable that the monomer mixture contains a self-crosslinking monomer. The self-crosslinking monomer self-crosslinks with the acrylic copolymer (A). This improves the cohesive force of the water-based removable pressure-sensitive adhesive and further improves the removability.

  The self-crosslinking monomer is preferably 0.01 part by weight or more and less than 2% by weight, more preferably 0.1 part by weight or more and 1 part by weight or less, in 100% by weight of the monomer mixture.

  Since the acrylic polymer (A) is an emulsion polymer and has a very large molecular weight, the weight average molecular weight cannot be usually measured.

  The glass transition temperature of the acrylic polymer (A) is preferably −80 to 0° C., more preferably −70 to −20° C.

The acrylic polymer (A) can be synthesized by emulsion-polymerizing a monomer mixture. A surfactant is usually used for emulsion polymerization. As the surfactant used in the present invention, a surfactant having 18 mol or more of alkylene oxide units is used.
When a surfactant having an alkylene oxide unit of 18 moles or more is used, it is possible to suppress the increase in the adhesive strength with time after the adhesive sheet is attached to polyvinyl chloride having a high polarity and after a long period of time. Peelability is obtained.
The alkylene oxide unit of the surfactant having 18 mol or more of the alkylene oxide unit has no particular upper limit and is not particularly limited as long as it can be applied to emulsion polymerization. In this respect, the generally commercially available surfactant has an upper limit of about 100 mol. For this reason, the upper limit is 100 moles, if strongly stated. Therefore, the alkylene oxide unit of the surfactant is preferably 18 to 100 mol, more preferably 40 to 100 mol, and further preferably 50 to 70. The number of alkylene oxide units shown here is an average value. Examples of the alkylene oxide unit include ethylene oxide, propylene oxide, butylene oxide and the like. Among these, ethylene oxide is preferable in terms of polymerization stability and mechanical stability of the acrylic polymer (A).

  Examples of the surfactant having 18 mol or more of alkylene oxide unit include polyoxyalkylene alkyl ether sulfuric acid ester salts such as sodium polyoxyethylene lauryl ether sulfate (ethylene oxide unit is 18 mol or more), polyoxyethylene polycyclic phenyl ether sulfuric acid. Polyoxyethylene alkylaryl ether sulfuric acid ester salts such as salts (ethylene oxide units are 18 mol or more), sodium polyoxyethylene nonylphenyl ether sulfate (ethylene oxide units are 18 mol or more), polyoxyethylene alkyl ethers (ethylene oxide units are 18 mol or more), polyoxyethylene polyoxypropylene alkyl ether (the total of ethylene oxide units and propylene oxide units is 18 mol or more), polyoxyethylene alkylphenyl ether (the ethylene oxide unit is 18 mol or more), and the like.

  The surfactant having 18 mol or more of alkylene oxide units is preferably 0.5 to 5 parts by weight, and more preferably 0.8 to 2 parts by weight, based on 100 parts by weight of the monomer mixture.

  For the emulsion polymerization, a surfactant other than the surfactant having 18 mol or more of alkylene oxide units can be used. Other surfactants include anionic surfactants and nonionic surfactants. These surfactants may be reactive surfactants having an ethylenically unsaturated bond.

  Examples of the anionic surfactant include higher fatty acid salts such as sodium stearate, alkylaryl sulfonates such as sodium dodecylbenzenesulfonate, alkyl sulfate ester salts such as sodium lauryl sulfate, and polyoxyethylene lauryl ether sulfate such as sodium polyoxyethylene lauryl ether sulfate. Examples thereof include oxyalkylene alkyl ether sulfate ester salts, polyoxyethylene polycyclic phenyl ether sulfate salts, and polyoxyethylene alkylaryl ether sulfate ester salts such as sodium polyoxyethylene nonylphenyl ether sulfate.

  Nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene alkyl phenyl ethers such as polyoxyethylene nonyl phenyl ether, sorbitan higher fatty acid esters such as sorbitan monostearate, and oleic acid monoglyceride. Glycerin higher fatty acid ester and the like. Other surfactants can be used alone or in combination of two or more kinds.

  Among the other surfactants, anionic surfactants that can obtain good polymerization stability are preferred, and polyoxyalkylene alkyl ether sulfate ester salts are more preferred.

  The other surfactant is preferably used in an amount of 0.5 to 3 parts by weight based on 100 parts by weight of the monomer mixture. When used in the above range, the polymerization stability is further improved.

As the polymerization initiator used in emulsion polymerization, a water-soluble polymerization initiator can be appropriately selected and used.
The water-soluble initiator is preferably a peroxide or an azo compound.
Examples of the peroxide include alkyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, p-methane hydroperoxide, lauroyl peroxide, 3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, t-butyl cumyl peroxide, benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethyl Organic peroxides such as cyclohexane, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, di-isobutylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate and t-butylperoxyisobutyrate Inorganic peroxides such as potassium persulfate, sodium persulfate and ammonium persulfate.
Examples of the azo compound include 2,2′-azobisisobutyronitrile, dimethyl-2,2′-azobisisobutyrate, 2,2′-azobis(2,4-dimethylvaleronitrile), and 2,2′. -Azobis(2-methylbutyronitrile), ammonium (amine) salt of 4,4'-azobis-4-cyanovaleric acid, 2,2'-azobis(2-methylamidooxime) dihydrochloride, 2,2 '-Azobis(2-methylbutanamide oxime) dihydrochloride tetrahydrate, 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]-propionamide} , 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide] and the like.

Further, by using a reducing agent in combination with the water-soluble polymerization initiator, the polymerization rate can be increased or the polymerization can be carried out at a low reaction temperature.
Examples of the reducing agent include reducing compounds such as sodium ascorbate, sodium erythorbate, sodium tartrate, sodium citrate, glucose, sodium sulfite, sodium bisulfite, and sodium metabisulfite.
The reducing agent is preferably used in an amount of 0.01 to 2 parts by weight based on 100 parts by weight of the monomer mixture.

In the present invention, a buffer can be used to adjust the pH as necessary during emulsion polymerization.
The buffering agent is not particularly limited as long as it has a pH buffering action, and for example, sodium hydrogen carbonate, potassium hydrogen carbonate, monosodium phosphate, monopotassium phosphate, disodium phosphate, trisodium phosphate, acetic acid. Examples thereof include sodium, ammonium acetate, sodium formate, ammonium formate, trisodium citrate and the like.

  The buffer is preferably used in an amount of 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight, based on 100 parts by weight of the monomer mixture.

  For emulsion polymerization, a known method can be used, but in the present invention, a method of first emulsifying the monomer mixture in advance and polymerizing the emulsion (referred to as pre-emulsion method) is preferable. Next, the emulsion can be polymerized by charging the whole amount in a reaction vessel in advance. Alternatively, a part of the emulsion can be charged into a reaction vessel and the remaining amount can be dividedly added or polymerized while dropping. Alternatively, the whole amount of the emulsion can be added in portions or added dropwise to carry out the polymerization.

  During the emulsion polymerization, the molecular weight of the acrylic polymer (A) can be appropriately adjusted by using a chain transfer agent. Examples of the chain transfer agent include mercaptan compounds, thioglycol compounds, and thiol compounds such as β-mercaptopropionic acid.

  The chain transfer agent is preferably used in an amount of 0.01 to 0.15 part by weight, more preferably 0.3 to 0.1 part by weight, based on 100 parts by weight of the monomer mixture.

  The water-based removable adhesive of the present invention needs to contain the first plasticizer. Further, it is preferable to include a second plasticizer. When the water-based removable adhesive contains a plasticizer, the elasticity of the adhesive is reduced, and good removable properties can be obtained for plastics having different polarities such as polyolefin and vinyl chloride. In addition, when the water-based removable pressure-sensitive adhesive contains the first plasticizer and the second plasticizer, a new effect of good removability with respect to the cardboard can be obtained.

  The first plasticizer and the second plasticizer (hereinafter sometimes collectively referred to as plasticizer) can be appropriately selected from phosphoric acid ester, fatty acid ester, polyalkylene glycol and the like. The phosphoric acid ester is a compound other than a compound that can emulsify a monomer and can be used as a surfactant.

Examples of the phosphoric acid ester include ethylhexyl diphenyl phosphate, ethylhexyl acid phosphate, bis(2-ethylhexyl) phosphate, isodecyl acid phosphate, tridecyl phosphite, triisodecyl acid phosphate, and oleyl acid phosphate. Be done.
Examples of the fatty acid ester include tributyl acetate citrate, di2-ethylhexyl phthalate, trioctyl trimellitate, trioctyl adipate, ethyl laurate, isopropyl myristate and the like. Among these, tributyl citrate, trioctyl trimellitate, and trioctyl adipate are preferable.
Examples of the polyalkylene glycol include polyoxyethylene glycol, polyoxypropylene glycol, polyoxypropylene glyceryl ether, poly(oxyethyleneoxypropylene) glycol monoether, polyoxypropylene monobutyl ether, polyoxyethylene/polyoxypropylene block polymer, etc. Is mentioned. Among these, polyoxypropylene glycol and polyoxypropylene glyceryl ether are preferable.

  One of the first plasticizer and the second plasticizer used in the present invention is preferably a phosphate ester. The inclusion of the phosphate ester improves the cohesive strength and removability to a higher level. The reason is that the phosphoric acid ester tends not to be compatible with the acrylic polymer (A), so that it easily migrates to the surface of the pressure-sensitive adhesive layer. Since the migration is promoted in a high temperature atmosphere, after sticking the pressure-sensitive adhesive sheet to an adherend and aging in a high temperature atmosphere, the cohesive force of the pressure-sensitive adhesive layer is not reduced, and the pressure-sensitive adhesive layer and the adherend are further reduced. The adhesiveness and the removability can be compatible at a high level since they are not adhered excessively. The compatibility is particularly effective when applied to polyvinyl chloride.

  The phosphate ester preferably has an alkyl group having 8 to 14 carbon atoms. Further, since the phosphoric acid ester is not a surfactant as described above, it is more preferable that it is a compound having no alkylene oxide structure and having an alkyl group having a branched structure. The phosphate ester having the branched structure further improves removability. Such phosphoric acid esters are isodecyl acid phosphate and isotridecyl acid phosphate among the examples already mentioned.

  The first plasticizer is preferably added in an amount of 0.2 to 10 parts by weight, more preferably 0.2 to 6 parts by weight, and more preferably 0.5 to 100 parts by weight, based on 100 parts by weight of the acrylic polymer (A). ˜3.5 parts by weight is more preferred. By using 0.2 to 10 parts by weight, it becomes easy to achieve both a high level of cohesive force and removability.

  The second plasticizer is preferably added in an amount of 0.2 to 10 parts by weight, more preferably 1.0 to 6.0 parts by weight, based on 100 parts by weight of the acrylic polymer (A). By using 0.2 to 10 parts by weight, it becomes easy to obtain good removability even for an adherend that is easy to break like cardboard and hard to obtain removability.

  100-6000 are preferable and, as for the molecular weight of a plasticizer, 100-3000 are more preferable. When the molecular weight is 100 to 6000, the removability is further improved.

  The water-based removable pressure-sensitive adhesive of the present invention may contain a crosslinking agent as an optional component. The water-based removable pressure-sensitive adhesive of the present invention has a good removability without adding a crosslinking agent, but a crosslinking agent can be added in order to further improve the removability. The cross-linking agent is preferably a titanium chelate compound, an aluminum chelate compound, a zirconium chelate compound, a metal cross-linking agent such as zinc oxide, an aziridine compound, an epoxy compound, an isocyanate compound, a carbodiimide compound, or a hydrazide compound.

  The water-based removable adhesive of the present invention may further contain additives such as a leveling agent, an antiseptic, an antifoaming agent, a thickener, and a pigment dispersion as optional components.

  The method for producing the water-based removable adhesive is a (meth)acrylic acid alkyl ester in the presence of a surfactant having an alkylene oxide unit of 18 mol or more and a first plasticizer (excluding the surfactant). It is preferable to include a step of emulsion-polymerizing a monomer mixture containing 50 to 99.9% by weight of (a1) and 0.1 to 5% by weight of a carboxyl group-containing monomer (a2) to obtain an acrylic polymer (A). Next, it is preferable to further mix optional components. Above, the first manufacturing method.

Alternatively, a method of synthesizing the acrylic polymer (A), blending the first plasticizer, and then blending optional components. Above, the second manufacturing method.
Alternatively, a method of synthesizing the acrylic polymer (A) in the presence of the first plasticizer and the second plasticizer, and then blending optional components. Above, the third manufacturing method.

  Among these methods, the first manufacturing method and the third manufacturing method are preferable because the removability of the pressure-sensitive adhesive sheet can be further improved. Further, in the first and third production methods, it is preferable to mix a plasticizer and a monomer to prepare a pre-emulsion and then carry out emulsion polymerization.

  The pressure-sensitive adhesive sheet of the present invention includes a base material and a pressure-sensitive adhesive layer containing an aqueous re-peelable pressure-sensitive adhesive. The pressure-sensitive adhesive sheet manufacturing method is, for example, (1) a method in which a water-based removable pressure-sensitive adhesive is applied to a peelable sheet and dried to form a pressure-sensitive adhesive layer, and then a substrate is attached. Further, (2) a method in which an aqueous re-peelable pressure-sensitive adhesive is applied to a substrate and dried to form a pressure-sensitive adhesive layer, and a release sheet is attached to the pressure-sensitive adhesive layer is preferable.

  Examples of the coating include known methods such as Meyer bar, applicator, brush, spray, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater and spin coater. When coating, it is usually dried. The drying method is not particularly limited, and hot air drying, infrared rays, a pressure reducing method and the like can be used. Usually, the drying temperature is preferably about 60 to 180°C.

  The thickness of the adhesive layer is generally about 5 μm to 100 μm, preferably 10 μm to 50 μm.

Examples of the base material include paper, plastic, rubber, foam, fiber, non-woven fabric, glass, metal and wood. Among these, paper and plastic are preferable, and paper is more preferable.
The substrate may be a single material or a laminate.
In addition, the back surface (the surface opposite to the surface on which the pressure-sensitive adhesive layer is directly attached) of the base material can be subjected to a peeling treatment or an antistatic treatment. The base material may be coated with a known anchor agent.

  The thickness of the substrate is generally about 10 m to 200 μm, preferably 20 μm to 80 μm.

  The release sheet may be a known release paper or release film obtained by coating a release agent on paper such as woodfree paper or a plastic film, and the thickness of the release sheet is usually 10 μm to 200 μm.

  The adherend to which the pressure-sensitive adhesive sheet of the present invention can be applied is, for example, a wide range such as polyolefin (polyethylene, polypropylene, etc.), polyvinyl chloride, other plastics, metal (stainless steel, etc.), rubber, wood, cardboard, glass, paint coating surface, etc. Can be mentioned.

  Further, the adhesive sheet of the present invention is applied to various adherends such as logistics labels used for shipping products, labels having bar codes printed thereon, masking tapes, protect film applications, etc. In addition to the repeeling use where it is required to be peeled from the adherend after the predetermined purpose is fulfilled, it can be used for the permanent sticking use.

  Next, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In the following description, parts are parts by weight and% is% by weight.

(Example 1)
2-Ethylhexyl acrylate 95.9 parts as a (meth)acrylic acid alkyl ester, 1.0 part of acrylic acid and methacrylic acid as a carboxyl group-containing monomer, and acetoacetoxy methacrylamide 0 as other monomers. 1 part, 2.0 parts of isodecyl acid phosphate as the first plasticizer, and 0.06 part of octyl thioglycolate as the chain transfer agent were added and dissolved. Further, as a surfactant, 6.0 parts of a 25% aqueous solution of a polyoxyethylene lauryl ether sulfate ammonium salt in which the addition mole number of ethylene oxide is 18 is added, and further 28.8 parts of deionized water is added and stirred to emulsify. I got a thing. This was placed in a dropping funnel. Separately, 50.5 parts of deionized water and 1.0 part of the above emulsion were charged into a four-necked flask equipped with a stirrer, a cooling tube, a thermometer and the dropping funnel, and the inside of the flask was filled with nitrogen gas. The internal temperature was raised to 78° C. with stirring. Thereafter, 3.0 parts of a 10% ammonium persulfate aqueous solution was added. Ten minutes later, the dropping of the rest of the emulsion was started from the dropping funnel. The above emulsion was added dropwise over 180 minutes while maintaining the internal temperature at 78°C, and the reaction was continued for 1 hour while maintaining the internal temperature at 78°C while further stirring. Then, 1.0 part of a 10% aqueous solution of t-butyl hydroperoxide and 1.0 part of a 10% aqueous solution of sodium ascorbate were added, and the reaction was continued for another hour. Then, the mixture was cooled and neutralized by adding 25% ammonia water at 30° C. to obtain an emulsion having a nonvolatile content concentration of 55% and a pH of 7.5 containing an acrylic polymer. An appropriate amount of a defoaming agent, a preservative, a leveling agent, and a thickening agent were added to 100 parts of the acrylic polymer in the obtained emulsion to obtain an aqueous removable pressure-sensitive adhesive. The obtained water-based removable pressure-sensitive adhesive was coated on a peelable sheet using a comma coater so that the thickness after drying was 18 μm, dried in a drying oven at 100° C. for 75 seconds, and then commercialized. A high-quality paper was attached to obtain an adhesive sheet. The performance was evaluated by the test method described below, and the results are shown in Table 2.

(Example 2)
An aqueous re-peelable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner as in Example 1, except that the surfactant was changed to polyoxyethylene lauryl ether sulfate ammonium salt having an addition mole number of ethylene oxide of 40.

(Example 3)
An aqueous re-peelable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner as in Example 1, except that the surfactant was changed to polyoxyethylene lauryl ether sulfate ammonium salt having an ethylene oxide addition mole number of 60.

(Example 4)
An aqueous re-peelable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner except that the surfactant of Example 1 was changed to polyoxyethylene lauryl ether sulfate ammonium salt in which the number of moles of ethylene oxide added was 100.

(Example 5)
The same procedure was followed except that the monomers used in the synthesis of the acrylic copolymer of Example 3 were changed to 98.0 parts of 2-ethylhexyl acrylate, 1.0 part of acrylic acid and 3.0 parts of methacrylic acid, and the aqueous reconstitution was performed. A peelable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared.

(Example 6)
Monomers used in the synthesis of the acrylic copolymer of Example 3 were added to 94.7 parts of 2-ethylhexyl acrylate, 1.0 part of acrylic acid and 3.0 parts of methacrylic acid, and 1.3 parts of acetoacetoxyethyl methacrylate. The same procedure was performed except that the water-based removable pressure-sensitive adhesive and the pressure-sensitive adhesive sheet were changed.

(Example 7)
The monomers used for the synthesis of the acrylic copolymer of Example 3 were changed to 2-ethylhexyl acrylate 95.5 parts, acrylic acid 1.0 parts and methacrylic acid 3.0 parts, and diallyl phthalate 0.5 parts. Except for this, the same procedure was performed to prepare an aqueous re-peelable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet.

(Example 8)
Monomers used in the synthesis of the acrylic copolymer of Example 3 were added to 98.4 parts of 2-ethylhexyl acrylate, 0.4 parts of acrylic acid and 0.3 parts of methacrylic acid, and 0.1 parts of acetoacetoxyethyl methacrylate. The same procedure was performed except that the water-based removable adhesive and the pressure-sensitive adhesive sheet were changed.

(Example 9)
Monomers used in the synthesis of the acrylic copolymer of Example 3 were added to 97.4 parts of 2-ethylhexyl acrylate, 1.0 part of acrylic acid and 5.0 parts of methacrylic acid, and 0.1 part of acetoacetoxyethyl methacrylate. The same procedure was performed except that the water-based removable pressure-sensitive adhesive and the pressure-sensitive adhesive sheet were changed.

(Example 10)
An aqueous re-peelable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner as in Example 3, except that the amount of isotridecyl acid phosphate was changed to 0.2 part.

(Example 11)
An aqueous re-peelable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner as in Example 3, except that the amount of isotridecyl acid phosphate was changed to 6.0 parts.

(Example 12)
A water-based removable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner as in Example 3 except that 0.5 part of tributyl acetate citrate was added as a second plasticizer to the water-based removable pressure-sensitive adhesive.

(Example 13)
A water-based removable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner as in Example 3 except that 5 parts of tributyl acetate citrate was added as a second plasticizer to the water-based removable pressure-sensitive adhesive.

(Example 14)
A water-based removable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner except that 7 parts of tributyl acetate citrate was added as the second plasticizer to the water-based removable pressure-sensitive adhesive of Example 3.

(Example 15)
An aqueous re-peelable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner as in Example 3, except that the isotridecyl acid phosphate was changed to butyl acid phosphate.

(Example 16)
A water-based removable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner as in Example 3 except that 5.0 parts of polypropylene glycol (number average molecular weight 400) was added as the second plasticizer to the water-based removable pressure-sensitive adhesive. ..

(Example 17)
As the surfactant of Example 1, 2.0 parts of a 25% aqueous solution of a polyoxyethylene lauryl ether sulfate ammonium salt having an ethylene oxide addition mole number of 60 and polyoxyethylene lauryl having an ethylene oxide addition mole number of 8 were used. An aqueous re-peelable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner except that the amount was changed to 4.0 parts of a 25% aqueous solution of ammonium ether sulfate ester.

(Example 18)
The same procedure as in Example 1 was repeated except that the surfactant used in Example 1 was changed to 12.0 parts of a 25% aqueous solution of ammonium polyoxyethylene lauryl ether sulfate having an added mole number of ethylene oxide of 60. And the adhesive sheet was created.

(Comparative Example 1)
Monomers used in the synthesis of the acrylic copolymer of Example 3 were added to 90.9 parts of 2-ethylhexyl acrylate, 2.0 parts of acrylic acid and 7.0 parts of methacrylic acid, and 0.1 part of acetoacetoxyethyl methacrylate. A water-based removable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner except that 5.0 parts of tributyl acetate citrate was added as the second plasticizer.

(Comparative example 2)
The surfactant of Example 3 was changed to polyoxyethylene lauryl ether sulfate ammonium salt having an ethylene oxide addition mole number of 8, and 5.0 parts of tributyl citrate citrate was added as a second plasticizer. The same operation was performed to prepare an aqueous re-peelable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet.

(Comparative example 3)
2-Ethylhexyl acrylate 95.9 parts as a (meth)acrylic acid alkyl ester, acrylic acid 1.0 part and methacrylic acid 3.0 parts as a carboxyl group-containing monomer, and acetoacetoxy methacrylamide 0.1 as other monomers. Parts, 0.06 parts of octyl thioglycolate as a chain transfer agent was added and dissolved. Further, as a surfactant, 6.0 parts of a 25% aqueous solution of polyoxyethylene lauryl ether sulfate ammonium salt having an added mole number of ethylene oxide of 60 was added, and further 28.8 parts of deionized water was added and stirred to emulsify. A water-based removable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner except that the obtained product was obtained.

(Comparative example 4)
2-Ethylhexyl acrylate 89.9 parts as a (meth)acrylic acid alkyl ester, acrylic acid 2.0 parts and methacrylic acid 8.0 parts as a carboxyl group-containing monomer, and acetoacetoxy methacrylamide 0.1 as other monomers. Parts and 0.06 parts of octyl thioglycolate as a chain transfer agent were added and dissolved. Further, as a surfactant, 6.0 parts of a 25% aqueous solution of polyoxyethylene lauryl ether sulfate ammonium salt having an added mole number of ethylene oxide of 60 was added, and further 28.8 parts of deionized water was added and stirred to emulsify. A water-based removable pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner except that the obtained product was obtained.

In Table 1, the first surfactant described in the description of the above Examples and Comparative Examples is referred to as the first surfactant, and similarly, the second surfactant described in Table 1 is referred to as the second surfactant in Table 1. In addition, the blending amount in Table 1 describes the weight of the raw material in terms of nonvolatile content.
The symbols in Table 1 are as follows.
Monomer 2EHA: 2-ethylhexyl acrylate AA: acrylic acid MAA: methacrylic acid AAEM: acetoacetoxyethyl methacrylate DAP: diallyl phthalate

-Surfactant The AO addition mole number means the alkylene oxide addition mole number.
-Plasticizer BP: Butyl acid phosphate IDP: Isodecyl acid phosphate TMS: Tributyl acetate citrate (formula weight 402)
PPG400: Polypropylene glycol (number average molecular weight 400)

[Test method]
(1) Adhesive Strength The obtained adhesive sheet was prepared as a sample in a size of 100 mm in length×25 mm in width under an environment of 23° C. and 50% RH. Then, the peelable sheet of the sample was peeled off, the sample was attached to a stainless steel plate (hereinafter referred to as SUS) whose surface was polished, and a 2 kg roll was reciprocated once to measure the adhesive force immediately after pressure bonding. After pressure-bonding separately, the sample was left in an atmosphere of 40° C. for 7 days, and further left in an atmosphere of 23° C. and 50% RH for 1 hour, and then the adhesive strength was measured. The adhesive strength was measured at a peel rate of 300 mm/min and a peel angle of 180°.
Adhesion was measured in the same manner as above except that the stainless steel plate of the adherend was changed to a polypropylene plate (hereinafter referred to as PP), a polyvinyl chloride plate, and a cardboard.

(2) Adhesive force change rate The adhesive force change rate was calculated from the following formula (1): 100 to 110% was ⊚, 111 to 120% was ∘, 121 to 130% was Δ, and 131% or more was x. ..
(Adhesive force change rate%) =
[(Adhesive strength after 7 days of pasting)/(Adhesive strength immediately after pressure bonding)]×100... Formula (1)
⊚: Almost no increase in adhesive strength. Are better.
◯: A slight increase in adhesive strength is observed. Good.
Δ: A slight increase in adhesive strength is seen. No problem in practical use x: Practical use is impossible due to a large increase in adhesive strength.

(3) Removability (contamination of adherend)
It was confirmed whether or not the adherends (SUS, PP, polyvinyl chloride, cardboard) after the test of (1) had contamination derived from the pressure-sensitive adhesive layer. The results in Table 3 are shown by the following symbols.
⊚: No contamination is attached. Are better.
◯: Slight contamination was attached. Good.
Δ: A small amount of contamination was observed. No problem in practical use x: A lot of contamination is attached. Not practical.

(4) Removability (base material state)
The state of the base material during the test of (1) is shown. The results in Table 3 are shown by the following symbols.
◯: There was no abnormality on the base material, and it could be peeled off cleanly. There is no problem in practical use.
X: The adhesive strength was high, and paper or blurring occurred during peeling. Not practical.

  From the results of Table 2 and Table 3, Examples 1 to 18, which are the water-based removable pressure-sensitive adhesives of the present invention, show little change in the adhesive force after pasting, and similarly good removability is obtained for any adherend. It exhibited peelability. On the other hand, in Comparative Examples 1 to 3, all of the properties could not be satisfied because either the change in adhesive strength over time of each adherend or the removability was poor.

Claims (5)

Acrylic, which is an emulsion polymer of a monomer mixture containing 50 to 99 % by weight of (meth)acrylic acid alkyl ester, 0.1 to 8% by weight of a carboxyl group-containing monomer, and 0.01 to 2% by weight of a self-crosslinking monomer. system polymer (a), seen containing surfactants having 18 or more moles of alkylene oxide units, and a first plasticizer,
The water-based removable pressure-sensitive adhesive , wherein the first plasticizer is a phosphoric acid ester .   The water-based removable pressure-sensitive adhesive according to claim 1, further comprising a second plasticizer. The first of the acrylic polymer plasticizer (A) containing 0.2 to 10 parts by weight per 100 parts by weight, according to claim 1 or 2 Symbol mounting aqueous removable pressure-sensitive adhesive. A pressure-sensitive adhesive sheet comprising a base material and a pressure-sensitive adhesive layer containing the water-based removable pressure-sensitive adhesive according to claim 1. 50 to 99 % by weight of a (meth)acrylic acid alkyl ester (a1) and a carboxyl group-containing monomer (a2) 0.1 in the presence of a surfactant having 18 moles or more of alkylene oxide units and a first plasticizer. and 8% by weight, the monomer mixture by emulsion polymerization viewing including the step of obtaining the acrylic polymer (a) containing a 0.01 wt% self-crosslinking monomer,
The method for producing an aqueous removable pressure-sensitive adhesive , wherein the first plasticizer is a phosphoric acid ester .