JP6028288B2 - Re-peelable water pressure sensitive adhesive - Google Patents

Description

    The present invention relates to a re-peelable water-based pressure-sensitive adhesive used for a pressure-sensitive adhesive sheet or the like.

  In recent years, various studies have been made on aqueous pressure-sensitive adhesives for the purpose of improving the removability of the pressure-sensitive adhesive sheet and improving the stain resistance at the time of re-peeling. For example, (A) the number of carbon atoms is 2 to 14 An aqueous emulsion obtained by emulsion polymerization of 80 to 95% by weight of an acrylic acid ester and / or methacrylic acid ester having an alkyl group of 1 to 5% by weight of an aliphatic α, β-unsaturated carboxylic acid is used as a non-volatile component. Parts by weight of (B) phosphoric acid and / or phosphate ester of 0.001 part by weight or more and less than 0.1 part by weight and (C) an epoxy compound having an average of 2 or more glycidyl groups in the molecule. Re-peelable water-based pressure-sensitive adhesive composition containing 0.1 to 2 glycidyl groups with respect to one carboxyl group of the aqueous resin emulsion (for example, see Patent Document 1). (A1) 50 to 99.89% by weight of (meth) acrylic acid alkyl ester containing an alkyl group having 4 to 12 carbon atoms, (a2) 0.1 to 10% by weight of a carboxyl group-containing unsaturated monomer, ( A monomer mixture containing 0.01 to 10% by weight of a3) carbonyl group-containing unsaturated monomer and (a4) 0 to 49.89% by weight of another unsaturated monomer is used as an anionic reactive emulsifier. An emulsion obtained by emulsion polymerization in the presence of an acrylic resin having a glass transition temperature of more than −50 ° C. and not more than −25 ° C. and having a gel fraction of less than 70% by weight, [B] a hydrazine compound, and [C A re-peelable water-based pressure-sensitive adhesive (for example, see Patent Document 2) characterized by containing a phosphate ester compound has been proposed.

Japanese Patent Application Laid-Open No. 07-157741 JP 2006-241419 A

  However, the conventional pressure-sensitive adhesive sheet had a certain degree of removability after aging in a high-temperature atmosphere, but the re-peelability in a high-temperature atmosphere and the durability that the pressure-sensitive adhesive sheet is difficult to peel off in a high-temperature atmosphere. There was a problem that was difficult to balance.

  The present invention has little change in adhesive force after being attached to an adherend for a long period of time, and has good re-peelability after being placed in a high-temperature atmosphere after being attached to an adherend, but does not float off. An object of the present invention is to provide a re-peelable water-based pressure-sensitive adhesive capable of producing a pressure-sensitive adhesive tape having durability that hardly occurs.

The present invention relates to an ethylenically unsaturated monomer comprising 50 to 99 % by weight of a (meth) acrylic acid alkyl ester containing an alkyl group having 2 to 12 carbon atoms and 0.5 to 3% by weight of a carboxyl group-containing unsaturated monomer. An acrylic polymer emulsion obtained by emulsion polymerization of a monomer, and a phosphate ester compound having an alkyl group having 8 to 14 carbon atoms, wherein the phosphate ester compound has an alkylene oxide structure. In addition, the releasable water pressure-sensitive type , wherein the alkyl group has a branched structure, and the phosphoric ester compound is 0.5 to 5 parts by weight with respect to 100 parts by weight of the acrylic polymer. It is an adhesive.

  According to the present invention, when the re-peelable water-based pressure sensitive adhesive is processed into a pressure sensitive adhesive sheet, the combination of monomers used for the synthesis of the acrylic polymer and the specific phosphate ester By including a specific amount of the compound, the phosphate ester compound having poor compatibility with the acrylic polymer is likely to move to the interface with the pressure-sensitive adhesive layer, so that the cohesive force of the pressure-sensitive adhesive layer is increased in a high-temperature atmosphere. Since the decrease can be suppressed, good adhesive force can be obtained. Further, the present inventors have found that the phosphoric acid ester compound is easy to be re-peeled even though the pressure-sensitive adhesive sheet hardly floats or peels off in a high-temperature atmosphere because it easily exists at the interface.

  According to the present invention, there is little change in adhesive force after being applied to an adherend for a long period of time, and the removability after being placed in a high-temperature atmosphere after being attached to an adherend is good, but it does not float off. It was possible to provide a re-peelable water-based pressure sensitive adhesive capable of producing a pressure sensitive adhesive tape having durability that hardly occurs.

FIG. 1 is a side view showing a durability test method.

The re-peelable water-based pressure-sensitive adhesive of the present invention has 50 to 99 % by weight of a (meth) acrylic acid alkyl ester containing an alkyl group having 2 to 12 carbon atoms and 0.5 to 3 carboxyl group-containing unsaturated monomer. emulsion of ethylenically unsaturated monomers emulsion polymerization obtained by acrylic polymer, and carbon atoms saw containing a phosphoric ester compound having 8 to 14 alkyl groups containing by weight%, the phosphoric acid ester The system compound does not have an alkylene oxide structure, and the alkyl group has a branched structure . Moreover, 0.5-5 weight part of phosphate ester compounds are contained with respect to 100 weight part of acrylic polymers. The re-peelable water-based pressure-sensitive adhesive is preferably used as a pressure-sensitive adhesive sheet having a formed pressure-sensitive adhesive layer and a substrate by coating and drying. The re-peelable water pressure-sensitive adhesive of the present invention is excellent in adhesive strength, heat resistance and re-peelability. In the present invention, “sheet”, “tape” and “label” are synonymous. Further, the heat resistance means a property that hardly causes floating in an 80 ° C. atmosphere .

  The acrylic polymer contains 50 to 99.9% by weight of a (meth) acrylic acid alkyl ester containing an alkyl group having 2 to 12 carbon atoms and 0.5 to 3% by weight of a carboxyl group-containing unsaturated monomer. Obtained by emulsion polymerization of an ethylenically unsaturated monomer. In addition, (meth) means containing two compounds like methyl acrylate and methyl methacrylate, for example.

  The (meth) acrylic acid alkyl ester is preferably contained in the total unsaturated monomer in an amount of 50 to 99.9% by weight, and more preferably 70 to 99% by weight. Inclusion of 50 to 99.9% by weight facilitates obtaining adhesive strength, heat resistance and removability.

  Specific examples of the (meth) acrylic acid alkyl ester include ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, and 2-ethylhexyl (meth). Examples include acrylate, n-octyl (meth) acrylate, iso-octyl (meth) acrylate, lauryl (meth) acrylate, iso-nonyl (meth) acrylate, cyclohexyl (meth) acrylate, and benzyl (meth) acrylate.

  In the (meth) acrylic acid alkyl ester, it is also preferable to substitute a part of the hydrogen atom of the alkyl group with an alkoxy group. Specific examples include 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 2-phenoxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, and the like.

  The carboxyl group-containing unsaturated monomer is preferably included in the total unsaturated monomers in an amount of 0.5 to 3% by weight, more preferably 1.0 to 2.5% by weight. Inclusion of 0.5 to 3% by weight makes it easy to obtain adhesive strength, heat resistance and removability.

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

  Specific examples of the carboxyl group-containing unsaturated monomer include (meth) acrylic acid, β-carboxyethyl acrylate, itaconic acid, crotonic acid, fumaric acid, fumaric anhydride, maleic acid, maleic anhydride, maleic acid. Examples thereof include butyl acid.

  Specific examples of other unsaturated monomers that can be used in the synthesis of the acrylic polymer in the present invention include aminomethyl (meth) acrylate, dimethylaminomethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, Dimethylaminopropyl (meth) acrylate, (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylonitrile, N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide, N-methylitaconimide N-ethyl itaconimide, N-butyl itaconimide, N-octyl itaconimide, N-2-ethylhexylitaconimide, N-cyclohexyl leuconconimide, N-lauryl itaconimide, N- (meth) acryloylimide Simethylenesuccinimide, N- (meth) acryloyl-6-oxyhexamethylenesuccinimide, N- (meth) acryloyl-8-oxyoctamethylenesuccinimide, glycidyl (meth) acrylate, vinyl acetate, styrene, methylstyrene, vinyltoluene, etc. Can be mentioned. In addition, known polyfunctional (meth) acrylate compounds such as polyethylene glycol di (meth) acrylate and neopentyl glycol adipate di (meth) acrylate are (meth) acrylic acid alkyl ester single amount) and carboxyl group-containing unsaturated single amount. Included in monomers other than the body.

  Among the other unsaturated monomers, acetoacetoxyethyl (meth) acrylate is preferable because it can further improve removability and heat resistance. The amount used is 0.01 part by weight or more and less than 1 part by weight of the unsaturated monomer constituting the acrylic polymer, and more preferably 0.05 part by weight or more and less than 0.5 part by weight.

  In the present invention, the acrylic polymer emulsion can be obtained by emulsion polymerization of the unsaturated monomer. As the emulsifier used in the emulsion polymerization, an anionic emulsifier and a nonionic emulsifier can be used alone or in combination of two or more.

  The anionic emulsifier is a long chain alkyl skeleton such as “Adekaria Soap SE-10N” manufactured by Asahi Denka Kogyo Co., Ltd., “Aqualon HS-10, HS-20” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. “AQUALON KH-05, KH-10” manufactured by Ichi Kogyo Seiyaku Co., Ltd., “Adekaria Soap SR-10N” manufactured by Asahi Denka Kogyo Co., Ltd., “KAYARAD” manufactured by Nippon Kayaku Co., Ltd. with a phosphate ester skeleton, sodium stearate Higher alkyl fatty acid salts such as sodium dodecylbenzene sulfonate, alkyl sulfate salts such as sodium lauryl sulfate, polyoxyethylene alkyl ether sulfate salts such as sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene Nonylphenyl ether sulfate Polyoxyethylene alkylaryl ether sulfuric acid ester salts such as potassium can be exemplified.

  The nonionic emulsifier has an unsaturated double bond at the molecular terminal or middle part of polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, sorbitan higher fatty acid esters, glycerin higher fatty acid esters, etc. Asahi Denka Kogyo Co., Ltd. “Adekaria Soap NE-10”, Daiichi Kogyo Seiyaku Co., Ltd. “Aqualon RN-10, RN-20, RN-50”, Japan Emulsifier Stock "Antox NA-16" manufactured by the company, polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene alkyl phenyl ethers such as polyoxyethylene nonylphenyl ether, and higher sorbitan fatty acid esters such as sorbitan monostearate Oleic acid monog Glycerine higher fatty acid esters such as celite and the like.

  Among the emulsifiers, it is preferable to use an anionic emulsifier because good polymerization stability can be obtained. Particularly, polyoxyethylene alkyl ether sulfate ester salts are more preferable, and polyoxyethylene distyryl ether sulfate ammonium salt is more preferable. . The amount of the emulsifier used is preferably 0.5 to 3 parts by weight with respect to 100 parts by weight of the total monomers used for the emulsion polymerization. By using in the said range, superposition | polymerization stability and removability can be improved more.

  The polymerization initiator used for emulsion polymerization is not particularly limited, and both a water-soluble polymerization initiator and an oil-soluble polymerization initiator can be used. Specifically, for example, alkyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, p-methane hydroperoxide, lauroyl peroxide, 3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, t-Butylcumyl peroxide, benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethyl Cyclohexane, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, di-isobutyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butylperoxyisocarbonate Organic peroxides such as citrate, 2,2′-azobisisobutyronitrile, dimethyl-2,2′-azobisisobutyrate, 2,2′-azobis (2,4-dimethylvaleronitrile), 2 , 2′-azobis (2-methylbutyronitrile), potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, ammonium (amine) salt of 4,4′-azobis-4-cyanovaleric acid, 2 , 2′-azobis (2-methylamidooxime) dihydrochloride, 2,2′-azobis (2-methylbutanamidoxime) dihydrochloride tetrahydrate, 2,2′-azobis {2-methyl-N- [1 , 1-bis (hydroxymethyl) -2-hydroxyethyl] -propionamide}, 2,2′-azobis [2-methyl-N- (2-H Roxyethyl) -propionamide], various redox catalysts (in this case, as an oxidizing agent, ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide, p-methane hydroperoxide and the like, and as a reducing agent, sodium sulfite, acidic sodium sulfite, Rongalite, ascorbic acid, etc. are used. Of these, potassium persulfate, sodium persulfate, redox catalyst (oxidizing agent: potassium persulfate, sodium persulfate, reducing agent: sodium sulfite, acidic sodium sulfite are excellent in polymerization stability and heat-resistant colorability. And the like are preferred.

  The amount of the polymerization initiator used is preferably 0.01 to 2 parts by weight, more preferably 0.03 to 1.0 part by weight, based on 100 parts by weight of all monomers used for emulsion polymerization. By using 0.01 to 2 parts by weight, copolymerizability and removability can be further improved.

  In the present invention, a buffer may 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. Specifically, sodium bicarbonate, potassium bicarbonate, monosodium phosphate, monopotassium phosphate, disodium phosphate, phosphorus Examples include trisodium acid, sodium acetate, ammonium acetate, sodium formate, ammonium formate, and trisodium citrate. The buffering agent is preferably used in an amount of less than 5 parts by weight, more preferably less than 3 parts by weight, based on 100 parts of all monomers used for emulsion polymerization.

  In the present invention, the emulsion polymerization is preferably synthesized after, for example, preparing a monomer into an emulsion. In the emulsion polymerization method, the whole amount of the monomer emulsion may be charged in the reaction vessel in advance, or a part thereof may be charged in the reaction vessel, and the remainder may be added in portions or added dropwise. Alternatively, the entire amount may be added in portions or added dropwise.

  In the present invention, the molecular weight of the acrylic polymer can be appropriately adjusted using a chain transfer agent during emulsion polymerization. Specifically, for example, thiol compounds such as mercaptan compounds, thioglycol compounds, and β-mercaptopropionic acid are preferable.

  The re-peelable water-based pressure-sensitive adhesive of the present invention includes a phosphate ester compound having an alkyl group having 8 to 14 carbon atoms. By including the phosphate compound, the cohesive force and removability are improved. The reason for this is that the phosphate ester compound has a tendency to easily move to the interface with the pressure-sensitive adhesive layer because of its poor compatibility with the acrylic polymer. In addition, since the pressure-sensitive adhesive layer and the adherend are not brought into close contact with each other, a good adhesive force can be obtained. Further, since the phosphoric acid ester compound is likely to be present at the interface, it is easy to re-peel despite the fact that the pressure-sensitive adhesive sheet is unlikely to float or peel off in a high temperature atmosphere.

  The phosphoric ester compound is preferably used in an amount of 0.5 to 5 parts by weight, more preferably 1 to 3.5 parts by weight, based on 100 parts by weight of the acrylic polymer. By using 0.5 to 5 parts by weight, it becomes easy to achieve both cohesion and removability.

  In the present invention, the phosphoric acid ester compound having an alkyl group having 8 to 14 carbon atoms specifically includes, for example, ethylhexyl diphenyl phosphate, ethylhexyl acid phosphate, bis (2-ethylhexyl) phosphate, and isodecyl acid. Examples include phosphate, tridecyl phosphite, triisodecyl acid phosphate, oleyl acid phosphate, and the like.

  Moreover, it is preferable that the said phosphate ester type compound is a compound which does not have an alkylene oxide structure and an alkyl group has a branched structure. Due to the branched structure, the phosphoric ester compound can further improve the removability. Specifically, such a compound is preferably, for example, isodecyl acid phosphate, isotridecyl acid phosphate, or the like. These compounds do not function as an emulsifier.

  Examples of the method for introducing the phosphate ester-based compound into the re-peelable water-based pressure-sensitive adhesive in the present invention include the following methods. (1) A method in which an emulsion containing an acrylic polymer is synthesized and then added. (2) A method of synthesizing an acrylic polymer in the presence of a phosphate ester compound. Among these methods, the method (2) is preferable because the removability can be further improved. Moreover, the specific method of (2) is preferably an emulsion polymerization after the emulsion of the monomer is produced after the phosphoric ester compound and all the monomers are blended.

  The re-peelable water-based pressure sensitive adhesive of the present invention preferably contains a metal crosslinking agent. The releasability is further improved by the metal crosslinking agent, and further, contamination due to the pressure-sensitive adhesive is less likely to occur on the adherend after aging in a high temperature atmosphere.

  Examples of the metal crosslinking agent include titanium chelate compounds, aluminum chelate compounds, zirconium chelate compounds, and zinc oxide.

  The metal crosslinking agent is preferably blended in an amount of less than 1 part by weight with respect to 100 parts by weight of the acrylic polymer. The re-peelability is further improved by the blending.

The re-peelable water-based pressure sensitive adhesive of the present invention can be used in combination with a crosslinking agent other than the metal crosslinking agent. Specific examples include an aziridine compound, an epoxy compound, an isocyanate compound, a carbodiimide compound, and a hydrazide compound.

  In addition to the above, the re-peelable water-based pressure sensitive adhesive of the present invention may contain additives such as leveling agents, preservatives, antifoaming agents, thickeners, and pigment dispersions as optional components.

  The pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer formed from a re-peelable aqueous pressure-sensitive adhesive. Specific examples of the production method are as follows: (1) A re-peelable water-type pressure-sensitive adhesive is applied to a peelable sheet and dried to form a pressure-sensitive adhesive layer, and a substrate is further attached. Further, (2) a pressure-sensitive adhesive layer is formed by applying a re-peelable water-based pressure-sensitive adhesive to the substrate and drying it, and further a peelable sheet is attached.

  Examples of the coating method 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. There is no restriction | limiting in particular in a drying method, Hot air drying, infrared rays, a pressure reduction method, etc. can be used. The drying temperature is usually preferably about 60 to 180 ° C.

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

  In the present invention, the base material is a plate material or sheet such as paper, cellophane, plastic sheet, rubber, foam, cloth, rubber cloth, resin-impregnated cloth, glass plate, metal plate, wood, polarizing plate, etc. It is done. The substrate may be a single body or a laminate. Moreover, the said base material can perform a peeling process or an antistatic process in the back surface (opposite surface which bonded the pressure-sensitive-type adhesive layer directly). The base material may be coated with a known anchor agent.

  Further, the adherend on which the “pressure-sensitive adhesive sheet” of the present invention is used is not particularly limited, and can be widely applied to metals, glass, plastics, rubber, wood, paint coating surfaces, and the like.

  The use of the pressure-sensitive adhesive sheet of the present invention is not particularly limited, but can be suitably used for various labels, masking tapes, protect films, and the like.

  Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. In the following description, parts and% mean parts by weight and% by weight, respectively.

(Synthesis Example 1)
“AP-10” manufactured by Daihachi Chemical Industry Co., Ltd. as 2-ethylhexyl acrylate 94.9 parts, methyl methacrylate 3.0 parts, acrylic acid 2.0 parts, acetoacetoxyethyl methacrylate 0.1 part, and phosphate ester compound 2.7 parts of (isodecyl acid phosphate) was added and dissolved. Further, 1.75 parts of “Haitenol NF-08” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. as an anionic emulsifier was added to 7.0 parts of deionized water, and 215 parts of deionized water was further added and stirred. An emulsion was obtained. This was placed in a dropping funnel.
A four-necked flask equipped with a stirrer, a condenser, a thermometer and the dropping funnel was charged with 425 parts of deionized water and 1.0 part of the emulsion, and the inside of the flask was replaced with nitrogen gas. The internal temperature was raised to 70 ° C. while stirring. 30 parts of 10% aqueous ammonium persulfate solution and 3 parts of 1% aqueous sodium metabisulfite solution were added. Ten minutes later, the dropping of the rest of the emulsion was started from the dropping funnel, and at the same time, 27 parts of a 1% sodium metabisulfite aqueous solution was started to drop. While maintaining the internal temperature at 70 ° C., the above emulsion and 1% aqueous sodium metabisulfite solution were added dropwise over 210 minutes. Furthermore, after continuing reaction at 70 degreeC for 1 hour, internal temperature was cooled to 65 degreeC, 0.1 part of 10% aqueous solution of "Perbutyl H-69" made by NOF Corporation, Fuso Chemical Industries Co., Ltd. " 0.1 part of a 10% aqueous solution of “Erbit N” was added three times every 10 minutes, and the reaction was continued for another 60 minutes. Thereafter, the mixture was cooled and neutralized by adding 25% aqueous ammonia at 30 ° C. to obtain an acrylic polymer emulsion having a nonvolatile content of 55% and a pH of 7.5.

  Table 1 shows the weight ratio of the unsaturated monomer used in the emulsion polymerization and the phosphate ester compound.

(Synthesis Examples 2-3, Comparative Synthesis Examples 1-6)
Polymerization was performed in the same manner as in Synthesis Example 1 except that the monomer, phosphate ester (B), and emulsifier were changed to the compositions shown in Table 1, to obtain an acrylic copolymer.

(Synthesis Example 4)
94.9 parts of 2-ethylhexyl acrylate, 3.0 parts of methyl methacrylate, 2.0 parts of acrylic acid, 0.1 part of acetoacetoxyethyl methacrylate, and “Hitenol NF-” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. as an anionic emulsifier 08 "1.75 parts dissolved in 7.0 parts of deionized water was added, and further 215 parts of deionized water was added and stirred to obtain an emulsion. This was placed in a dropping funnel.
A four-necked flask equipped with a stirrer, condenser, thermometer and dropping funnel was charged with 425 parts of deionized water and 1.0 part of the above emulsion, and the inside of the flask was replaced with nitrogen gas and stirred. The internal temperature was raised to 70 ° C. 30 parts of 10% aqueous ammonium persulfate solution and 3 parts of 1% aqueous sodium metabisulfite solution were added. Ten minutes later, dropping of the residue of the emulsion was started from the dropping funnel, and at the same time, 27 parts of 1% aqueous sodium metabisulfite solution was added dropwise. While maintaining the internal temperature at 70 ° C., the above emulsion and 1% aqueous sodium metabisulfite solution were added dropwise over 210 minutes. Furthermore, after continuing reaction at 70 degreeC for 1 hour, internal temperature was cooled to 65 degreeC, 0.1 part of 10% aqueous solution of "Perbutyl H-69" made by NOF Corporation, Fuso Chemical Industries Co., Ltd. " 0.1 part of a 10% aqueous solution of “Erbit N” was added three times every 10 minutes, and the reaction was continued for another 60 minutes. Further, 2.7 parts of “AP-10” (isodecyl acid phosphate) manufactured by Daihachi Chemical Industry Co., Ltd. was added as a phosphate ester compound. Thereafter, the mixture was cooled and neutralized by adding 25% aqueous ammonia at 30 ° C. to obtain an acrylic polymer emulsion having a nonvolatile content of 55% and a pH of 7.5.

(Synthesis Example 5)
Synthesis was performed in the same manner except that “AP-10” in Synthesis Example 1 was replaced with phosphanol “RS-710” manufactured by Toho Chemical Industry Co., Ltd. An acrylic polymer having a nonvolatile content of 55% and a pH of 7.5 An emulsion was obtained.

(Comparative Synthesis Example 7)
91.8 parts of 2-ethylhexyl acrylate, 2.3 parts of methyl methacrylate, 3.5 parts of acrylic acid, 2.4 parts of vinyl acetate, and 3.5 parts of “Emar 10” manufactured by Kao Corporation as an anionic emulsifier 0.3% aqueous solution of potassium persulfate 0.3 part, 0.02 part of sodium citrate and 28.2 parts of deionized water were added and stirred to obtain an emulsion, which was placed in a dropping funnel. In a four-necked flask equipped with a stirrer, a condenser, a thermometer and the dropping funnel, 40 parts of deionized water and the inside of the flask were replaced with nitrogen gas, and the internal temperature was raised to 70 ° C. while stirring. 0.3 parts of a 2.5% aqueous ammonium persulfate solution and 1.0 parts of a 2.5% aqueous sodium metabisulfite solution were added. After 10 minutes, the emulsion was dropped from the dropping funnel over 3 hours while maintaining the internal temperature at 70 ° C. During the dropwise addition of the emulsion, 0.2 part of a 2.5% aqueous sodium metabisulfite solution was added four times every 30 minutes. After completion of the dropwise addition, the reaction was further continued for 2 hours, and 0.04 part of orthophosphoric acid was added as a phosphate ester compound. Thereafter, the mixture was cooled and neutralized by adding 25% aqueous ammonia at 30 ° C. to obtain an acrylic polymer emulsion having a nonvolatile content of 55% and a pH of 7.5.

(Comparative Synthesis Example 8)
83.0 parts of n-butyl acrylate, 2.0 parts of acrylic acid, 0.5 part of diacetone acrylamide, 14.5 parts of methyl methacrylate, 0.05 part of 1-dodecanethiol as a chain transfer agent, and Sanyo as an anionic emulsifier 3.16 parts of “Eleminol JS-2” manufactured by Kasei Kogyo Co., Ltd. and 41.4 parts of water were mixed and stirred to obtain an emulsion, which was put into a dropping funnel.
In a four-necked flask equipped with a stirrer, a condenser, a thermometer, and the dropping funnel, 31.7 parts of deionized water, 0.26 parts of the above-mentioned “Eleminol JS-2”, sodium acetate trihydrate After 41 parts were charged and heated to 75 ° C. with stirring, 5% (7.23 parts) of the above emulsion was added. Further, after raising the temperature to 80 ° C., 0.8 part of 3% potassium persulfate aqueous solution was added, and then 15 minutes later, the remaining 95% (137.38 parts) of the above emulsion and 3% potassium persulfate aqueous solution 3 .2 parts of the mixed solution was added dropwise over 3.5 hours. After completion of the dropping, the reaction was continued for 2 hours while maintaining the temperature at 80 ° C., then the internal temperature was cooled to 65 ° C., and 2.4 parts of 10% aqueous ammonia solution was added for neutralization. Then, after cooling to 55 ° C., 0.5 parts of “Perbutyl H-69” manufactured by NOF Corporation and 0.5 parts of 10% L-ascorbic acid aqueous solution were added and reacted for 15 minutes. Again, 0.5 parts of 10% aqueous solution of “Perbutyl H-69” manufactured by NOF Corporation and 0.5 parts of 10% L-ascorbic acid aqueous solution were added and reacted for 15 minutes. Then, after cooling to 30 ° C., the pH was adjusted to 8.0 using a 10% aqueous ammonia solution, and butyl acid phosphate (“AP-4” manufactured by Daihachi Chemical Industry Co., Ltd.) was used as the phosphate ester compound. ]) 0.5 parts was added to obtain an emulsion. In addition, when the dry coating film of this emulsion was immersed in toluene at 20 ° C. for 24 hours and dried, the ratio of the remaining coating film weight after immersion to the coating film weight before immersion was 50%. In addition, the glass transition temperature of the copolymer calculated from the calculation method described in Patent Document 2 was −37.2 ° C.

Example 1
For 100 parts of the acrylic polymer emulsion obtained in Synthesis Example 1, 0.1 part of ADEKAATE B-940 manufactured by ADEKA Co., Ltd. is used as an antifoaming agent, and 0 part of Unichem Flex BN-202 manufactured by Union Chemical is used as an antiseptic. .05 parts, 0.1 part of Perex OT-P manufactured by Kao Corporation as a wetting agent, and Zinc Oxide Solution No. 0.5 part of 1 (aqueous solution of carbonic acid, ammonium, zinc salt 2: 2: 1) was added, and further thickened with an alkali thickener to obtain a re-peelable aqueous pressure-sensitive adhesive. This was coated on a peelable sheet with a comma coater so that the dry coating amount was 25 g / m ² , dried in a drying oven at 100 ° C. for 120 seconds, laminated with commercially available high-quality paper, and wound up. A pressure-type adhesive sheet was obtained, and its performance was evaluated by the test method described later. The results are shown in Table 2.

(Examples 2-6, Comparative Examples 1-8)
An aqueous pressure-sensitive adhesive was obtained in the same manner as in Example 1 except that the acrylic polymer emulsion and the crosslinking agent were changed as shown in Table 2, and a pressure-sensitive adhesive sheet was prepared.
However, Examples 4 and 6 are reference examples.

Abbreviations in Table 1 are as follows.
EHA: 2-ethylhexyl acrylate BA: butyl acrylate AA: acrylic acid MMA: methyl methacrylate AAEM: acetoacetoxyethyl methacrylate VAc: vinyl acetate DAAM: diacetone acrylamide AP-10: isodecyl acid phosphate JP-513: isotridecyl acid Phosphate JP-310: Tridecyl phosphite AP-4: Butyl acid phosphate RS-710: Polyoxyethylene alkyl (C12-15) ether phosphate (content 90%)

[Test method]
(1) Adhesive strength After preparing a sample of a pressure-sensitive adhesive sheet in a shape of 100 mm length x 25 mm width in an environment of 23 ° C. and 50% RH, the peelable sheet is peeled off, and the surface is affixed to a polished stainless steel plate, 2 kg One reciprocation with a roll was performed to measure the adhesive force immediately after the press bonding. In addition, after pressure bonding, the measurement sample was allowed to stand for 78 hours in a 60 ° C. atmosphere, and then further left for 1 hour in a 23 ° C. atmosphere to measure the adhesive strength after heat aging. The adhesive force was measured at a peeling speed of 300 mm / min and a peeling angle of 180 °. Also, the rate of increase in adhesive strength was calculated from the following formula.
Adhesive strength increase rate (%) = [(Adhesive strength after thermal aging) / (Adhesive strength immediately after pressing) -1] × 100

(2) Removability After preparing a sample of a pressure-sensitive adhesive sheet in a shape of length 100 mm × width 25 mm in a 23 ° C. and 50% RH environment, the peelable sheet is peeled off and attached to a stainless steel plate whose surface is polished, One reciprocation with a 2 kg roll was performed for pressure bonding. Furthermore, after being left for 24 hours in a 120 ° C atmosphere and further left for 1 hour in a 23 ° C atmosphere, it was peeled off in a 180 ° direction at a speed of 300 mm / min. did.
○: Almost no contamination was observed on the adherend.
Δ: Slight contamination is observed on the adherend, but there is no practical problem.
X: Contamination was recognized remarkably on the adherend, and there was a problem in practical use.

(3) Durability In a 23 ° C. 50% RH environment, a pressure-sensitive adhesive sheet was prepared in a shape of 100 mm long × 10 mm wide, and then the peelable sheet was peeled by 80 mm. The exposed 80 mm portion of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet 2 was attached to a stainless steel plate 1 whose surface was polished, and was subjected to one reciprocal pressure bonding with a 2 kg roll. After leaving in an 80 ° C. atmosphere for 30 minutes to completely peel off the peelable sheet, the 50 g weight 3 is lowered with a string as shown in FIG. 1 on the 20 mm portion where the pressure-sensitive adhesive layer is not in contact with the stainless steel plate. The durability in a high temperature atmosphere (80 ° C.) was evaluated by applying a load 4 in the 90 ° direction of the pressure-sensitive adhesive sheet. The evaluation was performed for 10 minutes, and when the pressure-sensitive adhesive sheet was peeled off and dropped, the dropping time was recorded. Moreover, when the pressure-sensitive adhesive sheet did not fall, the length of the pressure-sensitive adhesive sheet peeled off from the stainless steel plate was recorded for the 80 mm portion where the pressure-sensitive adhesive sheet was initially bonded to the stainless steel plate.

The symbols in Table 2 are as follows.
-Crosslinking agent A: BASF Japan (made) Zinc Oxide Solution No. 1
B: Denacol EX-313 (epoxy curing agent manufactured by Nagase Chemitex Corp.)
C: 5% aqueous solution of adipic acid dihydrazide

  From the results shown in Table 2, Examples 1 to 6, which are the re-peelable water-based pressure-sensitive adhesives of the present invention, had a small change in adhesive strength after the lapse of time and satisfied re-peelability and durability. On the other hand, the pressure-sensitive adhesives of Comparative Examples 1 to 8 were inferior in any of adhesive force change, removability and durability after pasting, and could not satisfy all the characteristics.

1: Stainless steel plate 2: Pressure sensitive adhesive sheet 3: Weight of 50 g 4: Direction of load

Claims (5)

Emulsified ethylenically unsaturated monomer containing 50 to 99 wt% of (meth) acrylic acid alkyl ester containing alkyl group having 2 to 12 carbon atoms and 0.5 to 3 wt% of carboxyl group-containing unsaturated monomer An acrylic polymer emulsion obtained by polymerization, and a phosphate ester compound having an alkyl group having 8 to 14 carbon atoms,
The phosphate ester compound does not have an alkylene oxide structure, and the alkyl group has a branched structure,
A re-peelable water-based pressure sensitive adhesive, wherein the phosphoric ester compound is 0.5 to 5 parts by weight with respect to 100 parts by weight of the acrylic polymer. Further comprising a metal crosslinking agent, releasable aqueous pressure sensitive adhesive of claim 1 Symbol placement. The re-peelable water-based pressure-sensitive adhesive according to claim 1 or 2 , wherein the ethylenically unsaturated monomer includes acetoacetoxyethyl (meth) acrylate. Pressure sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the claims 1-3 releasable aqueous pressure sensitive adhesive according to any. It possesses an alkyl group with a carbon number of 8-14, and a branched structure, in the presence of a phosphoric ester compound having no alkylene oxide structure, containing an alkyl group having 2 to 12 carbon atoms (meth) acrylate A process for producing an emulsion of an acrylic polymer by emulsion polymerization of an ethylenically unsaturated monomer containing 50 to 99% by weight of an acid alkyl ester and 0.5 to 3% by weight of a carboxyl group-containing unsaturated monomer. seen including,
A method for producing a releasable water-based pressure-sensitive adhesive, wherein the phosphoric ester compound is 0.5 to 5 parts by weight with respect to 100 parts by weight of an acrylic polymer .

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