JP2017110123A - Aqueous adhesive and adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous adhesive from which an adhesive sheet can be formed that has good adhesiveness to a paper base material and a film base material, shows good removability after a lapse of time under high-temperature and high-humidity conditions, and shows improved processability.SOLUTION: The aqueous adhesive comprises an emulsion of an acrylic polymer that is a copolymer of a monomer mixture including an alkyl (meth)acrylate ester, a carboxyl group-containing monomer and an alkoxysilyl group-containing monomer with an emulsion of an acrylic polymer as a copolymer with a chain transfer agent, and the aqueous adhesive contains, in 100 wt.% of the monomer mixture, 0.5-5 wt.% of the carboxyl group-containing monomer and 0.5-5 wt.% of the alkoxysilyl group-containing monomer.SELECTED DRAWING: None

Description

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

  Conventionally, a pressure-sensitive adhesive sheet using an aqueous pressure-sensitive adhesive has been used as an inexpensive paper label. On the other hand, solvent-type adhesives have been used for relatively expensive film labels. However, a highly versatile water-based pressure-sensitive adhesive that can be used for film labels and paper labels has been demanded from the demand for cost reduction from the market.

  Among the film labels, the re-peeling label is required to have reworkability and stain resistance that does not leave contamination after reworking.When an aqueous adhesive is used, the adhesiveness between the adhesive layer and the film substrate is low. There was a problem with low reworkability. In addition, the water-based adhesive contains a large amount of extra components other than the polymer, such as an emulsifier, compared to the solvent-type adhesive, so that when the labels are punched into various sizes from the adhesive sheet, the adhesive layer is applied to the cutter blade. There was a problem of blade stains to which the adhesive adhered, and a problem that the adhesive layer protruded from the edge of the label.

  Therefore, in Patent Document 1, a weight obtained by copolymerizing 0.005 to 0.5 parts by weight of a silane monomer with respect to 100 parts by weight of a monomer mixture containing (meth) acrylic acid alkyl ester as a main component. An aqueous pressure-sensitive adhesive containing a coalescence and a crosslinking agent and having a solvent insoluble content of 20 to 80% is disclosed.

  Moreover, in patent document 2, it obtains by copolymerizing the monomer mixture which mix | blended 0.005-1 weight part of silane monomers with respect to 100 weight part of monomer mixtures which have a (meth) acrylic-acid alkylester as a main component. An aqueous pressure-sensitive adhesive containing a polymer is disclosed.

JP 2002-146212 A JP 2007-146170 A

  However, when a film adhesive tape using a conventional aqueous adhesive is affixed to an adherend and left under high temperature and high humidity conditions, the adhesive layer absorbs moisture, and thus the adhesive tape cannot be easily peeled off. Moreover, even if it was able to peel, there existed the problem of the removability in which an adhesive layer remains on a to-be-adhered body. Further, since the pressure-sensitive adhesive layer has a low cohesive force in the conventional pressure-sensitive adhesive tape, there is a problem of workability that contaminates the punching blade when the pressure-sensitive adhesive layer protrudes from the side surface of the label after punching.

  The present invention provides an aqueous pressure-sensitive adhesive that can form a pressure-sensitive adhesive sheet having good adhesion to paper and film substrates, good removability after aging under high temperature and high humidity conditions, and improved workability. Objective.

The aqueous pressure-sensitive adhesive of the present invention comprises an emulsion of an acrylic polymer that is a copolymer of a (meth) acrylic acid alkyl ester, a carboxyl group-containing monomer, and an alkoxysilyl group-containing monomer, and a chain transfer agent. An aqueous pressure-sensitive adhesive comprising
In 100% by weight of the monomer mixture, 0.5 to 5% by weight of the carboxyl group-containing monomer and 0.5 to 5% by weight of the alkoxysilyl group-containing monomer are included.

  According to the present invention, an acrylic polymer synthesized using an appropriate amount of a carboxyl group-containing monomer and an appropriate amount of an alkoxysilyl group-containing monomer is bonded to silanol groups hydrolyzed by an alkoxysilyl group and is hydrophobic. The hydrophobicity is improved by forming a high silanol bond. Moreover, the cohesive force which tends to become excessive by the coupling | bonding of the said silanol groups can be adjusted to a moderate level with a chain transfer agent. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from an aqueous pressure-sensitive adhesive containing an acrylic polymer emulsion has a high hydrophobicity of the acrylic polymer and the pressure-sensitive adhesive layer is difficult to absorb moisture. Good re-peelability after being left in a high temperature and high humidity environment. In addition, since the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet has an appropriate cohesive force, workability was improved by suppressing contamination of the punching blade while exhibiting good adhesion to the paper substrate and the film substrate.

  INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an aqueous pressure-sensitive adhesive that can form a pressure-sensitive adhesive sheet having good adhesion to a paper substrate and a film substrate, good removability after aging under high temperature and high humidity conditions, and improved workability.

  Prior to describing the present invention in detail, terms will be defined. The (meth) acrylic acid alkyl ester includes an acrylic acid alkyl ester and a methacrylic acid alkyl ester. The monomer is an ethylenically unsaturated double bond-containing monomer. The adherend is the other party to which the adhesive tape is attached. The adhesion refers to the adhesion of the pressure-sensitive adhesive layer to the substrate. Sheet and tape are synonymous.

The aqueous pressure-sensitive adhesive of the present invention comprises an emulsion of an acrylic polymer that is a copolymer of a (meth) acrylic acid alkyl ester, a carboxyl group-containing monomer, and an alkoxysilyl group-containing monomer, and a chain transfer agent. An aqueous pressure-sensitive adhesive containing 0.5% to 5% by weight of the carboxyl group-containing monomer and 0.5% to 5% by weight of the alkoxysilyl group-containing monomer in 100% by weight of the monomer mixture.
This aqueous pressure-sensitive adhesive is preferably used after being coated and processed into a pressure-sensitive adhesive sheet. This pressure-sensitive adhesive sheet is preferably used for label applications such as a permanent pressure-sensitive adhesive label and a re-peeling label, and more preferably a re-peeling label.

In the present invention, an acrylic polymer emulsion is a copolymer prepared by emulsion polymerization of a monomer mixture containing a (meth) acrylic acid alkyl ester, a carboxyl group-containing monomer, and an alkoxysilyl group-containing monomer in the presence of a chain transfer agent. It is a polymer.
The alkoxysilyl group-containing monomer is incorporated into the polymer by emulsion polymerization, and the silanol groups generated from the alkoxysilyl group are formed by mutual silanol bonds to improve the hydrophobicity of the polymer itself. In addition, the formation of silanol bonds tends to make the cohesive force of the acrylic polymer excessive, but by using a chain transfer agent, the molecular weight can be suppressed, so that an appropriate cohesive force can be obtained.

  Examples of the alkoxysilyl group-containing monomer include 3-methacryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropyltriethoxysilane, 3-acryloyloxypropyltriethoxysilane, and 3-methacryloyloxy. Propylmethyldimethoxysilane, 3-acryloyloxypropylmethyldimethoxysilane, 3-methacryloyloxypropylmethyldiethoxysilane, 3-acryloyloxypropylmethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 4-vinylbutyltrimethoxy Silane, 4-vinylbutyltriethoxysilane, 8-vinyloctyltrimethoxysilane, 8-vinyloctyltriethoxysilane, 0 Methacryloyloxydecyl trimethoxysilane, 10-acryloyloxydecyl trimethoxysilane, 10-methacryloyloxydecyl triethoxysilane, 10-acryloyl monomers such as oxy decyl triethoxy silane. Among these, from the viewpoint of copolymerization with an alkyl (meth) acrylate, 3-methacryloyl-based and 3-acryloyl-based alkoxysilyl group-containing monomers are more preferable. The alkoxysilyl group-containing monomer can be used alone or in combination of two or more.

  The alkoxysilyl group-containing monomer is preferably contained in an amount of 0.5 to 5% by weight, more preferably 0.5 to 3% by weight, in 100% by weight of the monomer mixture. By including 0.5 to 5% by weight, re-peelability and adhesion after aging at high temperature and high humidity, and processability are improved.

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

  The (meth) acrylic acid alkyl ester is preferably contained in 90 to 99% by weight in 100% by weight of the monomer mixture. By including 90 to 99% by weight, the adhesive strength and tackiness are further improved.

  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 is preferably contained in an amount of 0.5 to 5% by weight, more preferably 0.8 to 2% by weight, in 100% by weight of the monomer mixture. By including 0.5 to 5% by weight, the adhesive strength and removability are further improved.

  When the acrylic polymer is synthesized, the emulsion polymerization is performed in the presence of a chain transfer agent. 0.01-10 weight part is preferable with respect to 100 weight part of monomer mixtures, and, as for the usage-amount of a chain transfer agent, 0.02-8 weight part is more preferable. When a chain transfer agent is used, it becomes easy to adjust the molecular weight of the acrylic polymer, and it becomes easy to achieve both re-peelability and adhesion after aging at high temperature and high humidity.

The chain transfer agent is preferably, for example, a thiol group-containing compound, an alcohol, and a tackifier resin.
Examples of thiol group-containing compounds include mercaptans such as lauryl mercaptan, 2-mercaptoethyl alcohol, dodecyl mercaptan, and mercaptosuccinic acid; n-butyl mercaptopropionate, and alkyl mercaptopropionates such as octyl mercaptopropionate; Examples include mercaptopropionic acid alkoxyalkyl such as methoxybutyl.
Examples of the alcohol include methyl alcohol, n-propyl alcohol, isopropyl alcohol (IPA), t-butyl alcohol, and benzyl alcohol.
The tackifier resin not only has a large chain transfer effect but can easily adjust the molecular weight of the acrylic polymer, and can also improve the adhesion when the pressure-sensitive adhesive layer is formed.

The tackifying resin is preferably a rosin resin, a terpene resin, an aromatic petroleum resin, an aliphatic petroleum resin, or the like.
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 α-pinene resin, β-pinene resin, terpene phenol resin, and hydrogenated terpene phenol resin.
Examples of aromatic petroleum resins include styrene oligomers and α-methylstyrene / styrene copolymers.
Examples of the aliphatic petroleum resin include Quinton A100, B170, M100, and R100 (manufactured by Nippon Zeon Co., Ltd.) as commercial products.
Chain transfer agents can be used alone or in combination of two or more.

The chain transfer agent is preferably blended in an amount of 0.01 to 10 parts by weight with respect to 100 parts by weight of the monomer mixture. By using 0.01 weight part or more, it becomes easy to adjust a gel fraction and adhesiveness improves more. Moreover, cohesion force improves more by using 10 weight part or less.
Moreover, when using a thiol group containing compound or alcohol as a chain transfer agent, 0.01-1 weight part is preferable with respect to 100 weight part of monomer mixtures, and 0.02-0.8 weight part is more preferable.
Moreover, when using tackifying resin as a serial transfer agent, 0.1-10 weight part is preferable with respect to 100 weight part of monomer mixtures, and 0.2-8 weight part is more preferable.

  The acrylic polymer is synthesized by emulsion polymerization of a monomer mixture in the presence of a chain transfer agent. In the emulsion polymerization, an emulsifier is usually used, and the emulsifier is preferably appropriately selected from an anionic emulsifier and a nonionic emulsifier. From another aspect, the emulsifier is appropriately selected from an emulsifier having an ethylenically unsaturated double bond (hereinafter referred to as a reactive emulsifier) and an emulsifier having no ethylenically unsaturated double bond (hereinafter referred to as a non-reactive emulsifier). It is preferable to select.

The emulsifier is preferably a reactive anionic emulsifier, a reactive nonionic emulsifier, a nonreactive anionic emulsifier, or a nonreactive nonionic emulsifier.
Examples of the reactive anionic emulsifier include sulfosuccinate ester emulsifiers, (meth) acrylate sulfate ester emulsifiers, phosphate ester emulsifiers, and allyl sulfonate emulsifiers.
Examples of the reactive nonionic emulsifier include alkyl ether emulsifiers, alkylphenyl ether emulsifiers, alkylphenyl ester emulsifiers, and the like.

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

  Non-reactive nonionic emulsifiers include, for example, polyoxyethylene alkylphenyl ethers such as polyoxyethylene nonylphenyl ether and polyoxyethylene octylphenyl ether; polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether and the like And polyoxyethylene alkyl ethers; polyoxypolycyclic phenyl ethers such as polyoxyethylene distyrenated phenyl ether; and polyoxyethylene sorbitan fatty acid esters.

Among the emulsifiers, use of a reactive anionic emulsifier or a non-reactive anionic emulsifier is preferable because good polymerization stability can be obtained, and in particular, a non-reactive polyoxyethylene alkyl ether sulfate salt is more preferable. A polyoxyethylene alkyl ether sulfate ammonium salt having an alkyl group of 9 to 14 is more preferred. The emulsifier can be used alone or in combination of two or more.
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.

The polymerization initiator used for emulsion polymerization is preferably 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}, 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide] and the like. Among these, potassium persulfate and sodium persulfate are preferable.

  As the polymerization initiator, a redox polymerization initiator (a combination of an oxidizing agent and a reducing agent) can also be used. Examples of the oxidizing agent include ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide, and p-methane hydroperoxide. Examples of the reducing agent include sodium sulfite, acidic sodium sulfite, Rongalite, ascorbic acid and the like. Among these, it is preferable to use an appropriate combination of an oxidizing agent: potassium persulfate or sodium persulfate and a reducing agent: sodium sulfite or acidic sodium sulfite because they are excellent in polymerization stability and heat-resistant colorability.

  The polymerization initiator is preferably used in an amount of 0.01 to 0.5 parts by weight, more preferably 0.02 to 0.3 parts by weight, based on 100 parts by weight of the monomer mixture. By being 0.01 weight part or more, superposition | polymerization stability and the mechanical stability of an adhesive can be improved more. It becomes easy to adjust a gel fraction to an appropriate range by becoming 0.5 weight part or less.

  In the emulsion polymerization method, for example, it is preferable to synthesize a monomer by emulsifying the monomer before synthesis to prepare an emulsion (referred to as a pre-emulsion) and then charging the pre-emulsion into a polymerization field (reaction vessel). The charging method is a method in which the entire amount of the pre-emulsion is charged in the reaction vessel in advance, or a part of the pre-emulsion is charged in the reaction vessel and the remainder of the pre-emulsion is added in several portions. There are methods such as continuous dripping, which can be appropriately selected according to the intended use and performance.

  The acrylic polymer used in the present invention is preferably adjusted to have a gel fraction of the dry film of 30 to 70%. When the acrylic polymer has the gel fraction, it becomes easy to achieve both re-peelability and adhesion after aging at high temperature and high humidity.

The gel fraction can be calculated by the following method. After neutralizing the acrylic polymer, adjusting the viscosity to about 100 to 1000 mPas with a thickener, adjusting the leveling property with a leveling agent, coating on a polyethylene terephthalate film (hereinafter referred to as PET film), and after drying A dry film is formed so as to have a thickness of about 20 g / m ² (referred to as a coated product). The obtained coated product is wrapped in a 200 mesh stainless steel mesh, and then it is put into ethyl acetate and immersed at 23 ° C. for 72 hours, and then dried to remove the solvent. And what calculated | required the ratio (weight%) of the weight of the dry film after immersion with respect to the weight of the dry film before immersion is called the gel fraction with respect to a solvent. The insoluble content is determined according to the following formula 1.
Formula 1 Gel fraction (%) = (Dry coating weight before immersion−PET film weight) / (Dry coating weight after immersion−PET film weight) × 100

  The aqueous pressure-sensitive adhesive of the present invention can further contain a crosslinking agent. Forming a cross-linked polymer network with the cross-linking agent further improves processability and facilitates adjustment of adhesive strength.

  Examples of the crosslinking agent include titanium chelate compounds, aluminum chelate compounds, zirconium chelate compounds, zinc oxide, aziridine compounds, epoxy compounds, isocyanate compounds, carbodiimide compounds, and hydrazide compounds. Among these, a carbodiimide compound, an aziridine compound, and an epoxy compound are preferable from the viewpoint of pot life and adhesion to a substrate. The crosslinking agents can be used alone or in combination of two or more.

  The crosslinking agent is preferably blended in an amount of 0.01 to 10 parts by weight, more preferably 0.03 to 8 parts by weight, based on 100 parts by weight of the acrylic polymer. By blending 0.01 to 10 parts by weight, the adhesiveness and cohesive force of the pressure-sensitive adhesive layer are further improved.

  The aqueous pressure-sensitive adhesive of the present invention can further contain a fatty acid ester plasticizer. Since the fatty acid ester plasticizer easily suppresses the increase in adhesive strength with time, the removability after the adhesive sheet is pasted on the adherend and left in a high temperature environment or a high temperature and high humidity environment is further improved.

  Examples of the fatty acid ester plasticizer include oleic acid ester, adipic acid ester, sebacic acid ester, azelaic acid ester, succinic acid ester, maleic acid ester, fumaric acid ester, and citric acid ester. Among these, a citrate ester capable of improving removability is preferable, trialkyl acetyl citrate is more preferable, and triethyl acetyl citrate is particularly preferable.

  The fatty acid ester plasticizer is preferably blended in an amount of 0.5 to 6 parts by weight based on 100 parts by weight of the acrylic polymer. By being within the above range, the removability is further improved.

  The aqueous pressure-sensitive adhesive of the present invention can contain a tackifying resin after the synthesis of the acrylic polymer. By including the tackifier resin, it is easy to adjust the adhesive force.

  The aqueous pressure-sensitive adhesive of the present invention can contain known additives such as neutralizing agents, leveling agents, preservatives, antifoaming agents, thickeners, pigment dispersions, and resin fine particles as optional components.

  The pressure-sensitive adhesive sheet of the present invention includes a base material and a pressure-sensitive adhesive layer formed from an aqueous pressure-sensitive adhesive. Examples of production methods include (1) A method of forming a pressure-sensitive adhesive layer by applying an aqueous pressure-sensitive adhesive to a peelable sheet and drying, and then transferring the pressure-sensitive adhesive layer onto a substrate. And (2) A method of forming a pressure-sensitive adhesive layer by applying an aqueous pressure-sensitive adhesive to a substrate and drying, and then bonding a peelable sheet. Or the double-sided adhesive tape which laminated | stacked the adhesive layer, the base material, and the adhesive layer one by one by the well-known method is also preferable.

  Examples of the coating method include known methods such as Mayer 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, It can use suitably selecting from well-known methods, such as a hot-air drying, an infrared heater, and a pressure reduction method. 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 about 10 to 50 μm.

Examples of the substrate include paper, cellophane, plastic sheet, rubber, foam, cloth, rubber cloth, resin-impregnated cloth, glass plate, metal plate, and wood, and optical film plate materials such as polarizing plates and sheets thereof. It is done. The base material may be a laminate composed of a single sheet or a plurality of sheets. Moreover, the base material can perform a peeling process or an antistatic process on the back surface (surface in which the adhesive layer is not formed). Moreover, a base material can improve adhesiveness with an adhesive layer by performing a well-known easy-adhesion process.
The thickness of the substrate is generally about 10 to 100 μm, and more preferably about 30 to 80 μm.

  The adherend of the pressure-sensitive adhesive sheet of the present invention can be used 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 preferably used for applications requiring reworkability such as various labels, masking tape applications, and protect film applications.

  EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the following description, “part” means “part by weight” and “%” means “% by weight”. All the formulations in the table are based on weight.

Example 1
97.5 parts of 2-ethylhexyl acrylate as (meth) acrylic acid alkyl ester, 1.5 parts of acrylic acid as carboxy-containing monomer, 3-methacryloxypropyltrimethoxysilane “KBM-503” (Shin-Etsu Chemical) as alkoxysilyl group-containing monomer 0.06 part of octyl thioglycolate as a chain transfer agent was added to 1.0 part of Kogyo Co., Ltd. and dissolved. Furthermore, 7.0 parts of “New Coal RA9612” (polyoxyethylene alkyl ether sulfate ammonium salt having a C 12-13 alkyl group, produced by Nippon Emulsifier Co., Ltd.) was added as a non-reactive anionic emulsifier. .1 part was added and stirred to prepare a pre-emulsion, which was placed in a dropping funnel.
Separately, 45.6 parts of deionized water was charged into a four-necked flask equipped with a stirrer, a condenser, a thermometer, and the above dropping funnel while the inside of the flask was replaced with nitrogen gas. Only 1.0 part of the pre-emulsion was added dropwise. Next, the internal temperature was heated to 70 ° C. Thereafter, 10% concentration of ammonium persulfate was added to start the emulsion polymerization. Next, the residue of the pre-emulsion was dropped over 180 minutes while maintaining the internal temperature at 70 ° C., and then 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., 1.0 part of 10% aqueous solution of “Perbutyl H-69” (manufactured by NOF Corporation), 10% aqueous solution of “Erbit N” (manufactured by Fuso Chemical Industries) 0 parts was added three times every 10 minutes, and the reaction was continued for another hour. 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 concentration of 50%. The acrylic polymer had a gel fraction of 45%.
Next, 1 part of 25% ammonia water as a neutralizing agent, 0.3 part of SN deformer 364 (manufactured by San Nopco) as a defoaming agent, and 1 part of a non-preservative as a preservative are 100 parts of the nonvolatile content of the acrylic polymer emulsion. 0.05 part of Chemflex BN-202 (manufactured by Union Chemical Co., Ltd.), 0.2 part of “Perex OT-P (nonvolatile content 70%)” (manufactured by Kao Corporation) as a leveling agent, triethyl acetylcitrate 1 as a plasticizer 0.5 part was added, and 1.0 part of carbodiimide-based crosslinking agent Carbodilite V-04 (non-volatile content: 40%) was added as a crosslinking agent, followed by thickening with an alkali thickener to obtain an aqueous pressure-sensitive adhesive.
The obtained water-based 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, A pressure-sensitive adhesive sheet was obtained by bonding. Moreover, the adhesive sheet which uses a commercially available polyethylene terephthalate (PET) film for the base material by the same method as the above was obtained.

(Examples 2 to 10, Comparative Examples 1 to 4)
An aqueous pressure-sensitive adhesive and a pressure-sensitive adhesive sheet were prepared in the same manner as in Example 1 except that the raw materials and blending amounts in Table 1 were changed.

Abbreviations in Table 1 are as follows.
<Monomer>
EHA: 2-ethylhexyl acrylate BA: butyl acrylate AA: acrylic acid MAA: methacrylic acid

<Alkoxysilyl group-containing monomer>
KBM-503: 3-methacryloxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.)
KBE-502: 3-methacryloxypropylmethyldiethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.)
KBE-1003: Vinyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.)

<Chain transfer agent>
OTG: Octyl thioglycolate A-5: “Picolastic A-5” (styrene oligomer, manufactured by Eastman Chemical Co.)

<Emulsifier>
RA9612: “New Coal RA9612” (non-reactive anionic emulsifier, ammonium polyoxyethylene alkyl ether sulfate, nonvolatile content 25%, manufactured by Nippon Emulsifier Co., Ltd.)
KH-10: “AQUALON KH-10” (reactive anionic emulsifier, polyoxyethylene-1- (allyloxymethyl) alkyl ether sulfate ammonium salt, non-volatile content 100%, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)
<Curing agent>
EX-313: “Denacol EX-313” (epoxy curing agent, non-volatile content 100%, manufactured by Nagase ChemteX Corporation)
PZ-33: “Chemite PZ-33” (aziridine-based curing agent, non-volatile content 100%, manufactured by Nippon Shokubai Co., Ltd.)

[Test method]
(1) Adhesive strength
The obtained pressure-sensitive adhesive sheet was prepared as a sample in a size of 100 mm length × 25 mm width in 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 adhesive layer was attached to a polished stainless steel plate (hereinafter referred to as SUS), the 2 kg roll was reciprocated once, and immediately after pressure bonding. The adhesive strength was measured. Separately, the sample pressed in the same manner as described above was allowed to stand for 10 days in an atmosphere of 60 ° C. and 90% RH, and then further left for 1 hour in an atmosphere of 23 ° C. and 50% RH. ) Was measured. The adhesive strength was measured using a tensile tester at a peeling rate of 300 mm / min and a peeling angle of 180 °. Moreover, the rate of increase in adhesive strength was calculated from the following formula.
Adhesive strength increase rate (%) = [(Adhesive strength after heat aging) / (Adhesive strength immediately after pressure bonding) -1] × 100
The rate of increase was evaluated according to the following criteria.
A: Increase rate of less than 10%, good B: Increase rate of 10% or more, less than 20%, no problem in practical use.
Δ: Increase rate 20% or more, less than 40%, impractical.
X: Increase rate of 40% or more, impractical.

(2) Removability The obtained pressure-sensitive adhesive sheet was prepared as a sample in a size of length 100 mm × width 25 mm in 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 attached to SUS, and pressure was applied by reciprocating once with a 2 kg roll. The sample after crimping is left in an atmosphere of 60 ° C. and 90% RH for 24 hours, and further left in an atmosphere of 23 ° C. and 50% RH for 1 hour, and then the sample is removed from the SUS at a speed of 300 mm / min using a tensile tester. It peeled in the direction of 180 degree | times and evaluated by the following reference | standard by visual observation whether the contamination originating in an adhesive layer had adhered to the SUS surface.
A: There is no contamination. Good ○: Slightly contaminated, but no problem in practical use.
Δ: Slightly contaminated, impractical.
X: There was much adhesion of contamination. Not practical.

(3) Workability The obtained pressure-sensitive adhesive sheet was repeatedly cut with a paper cutter in an environment of 40 ° C., and the presence or absence of the pressure-sensitive adhesive layer was visually observed on the blade of the paper cutter. evaluated.
A: There is no adhesion of the adhesive layer even after cutting 100 times. Good.
◯: Adhesion layer is observed after 50 to 99 times of cutting. There is no problem in practical use.
(Triangle | delta): Attachment of the adhesion layer is seen by 10 to 49 times of cutting. Not practical.
X: Adhesion layer is observed after cutting 9 times. Not practical.

(4) Gel fraction The obtained acrylic polymer was coated and dried on a PET film so that the thickness after drying was about 20 g / m ² , and was wrapped in a 200 mesh stainless steel mesh to obtain a sample. Next, the sample was put in ethyl acetate, immersed for 72 hours at 23 ° C., dried, and the ratio (% by weight) of the weight of the polymer layer after immersion to the weight of the polymer layer before immersion was determined.

From the results of Table 1, Examples 1 to 10 use appropriate amounts of alkoxysilyl group-containing (meth) acrylic monomer and carboxyl group-containing monomer, respectively, so that the pressure-sensitive adhesive sheet has good removability. At the same time, since the substrate adhesiveness of the pressure-sensitive adhesive layer is necessary for the removability, the pressure-sensitive adhesive sheet having a good removability also has a good substrate adhesiveness.

Claims (3)

An aqueous pressure-sensitive adhesive comprising an emulsion of an acrylic polymer that is a copolymer of a chain transfer agent, and a monomer mixture containing a (meth) acrylic acid alkyl ester, a carboxyl group-containing monomer, and an alkoxysilyl group-containing monomer,
An aqueous pressure-sensitive adhesive comprising 0.5 to 5% by weight of the carboxyl group-containing monomer and 0.5 to 5% by weight of the alkoxysilyl group-containing monomer in 100% by weight of the monomer mixture.   The aqueous pressure-sensitive adhesive according to claim 1, wherein the chain transfer agent is 0.01 to 10 parts by weight with respect to 100 parts by weight of the monomer mixture. The adhesive sheet provided with the base material and the adhesive layer formed from the water-based adhesive of Claim 1 or 2.