JP2009073920A - Removable adhesive sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a removable adhesive sheet excellent in stability when exfoliated. <P>SOLUTION: The removable adhesive sheet is obtained by forming an adhesive layer on a base material. The adhesive layer is formed from a water-dispersible adhesive composition including as essential components: an emulsion [A] of an (meth)acrylate copolymer, which contains an alkyl(meth)acrylate unit having a 4-12C alkyl group as a principal component and 0.1-2.0 mass% carboxyl group-containing unsaturated monomer unit; another emulsion [B] of an alkali-soluble or alkali-swellable (meth)acrylic acid copolymer containing the carboxyl group-containing unsaturated monomer unit; and a cross-linking agent [C]. A ratio of the adhesive layer to be gelated in tetrahydrofuran is 65-95 mass% when tetrahydrofuran is used as a solvent. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a releasable pressure-sensitive adhesive sheet excellent in adhesiveness to various adherends (metal plate, plastic plate, etc.) and excellent in peeling stability that can be easily peeled off after being stuck and left for a long period of time. Is.

Conventionally, an adhesive label, a masking tape or sheet, a surface protective film, and the like are often peeled off from an adherend after a certain period of time has elapsed after being attached to the adherend. At this time, part of the pressure-sensitive adhesive often remains on the adherend. Further, when the adherend is paper, the adherend or a substrate such as an adhesive label is often torn. In particular, when the adherend is a coated paper such as art paper or cast coated paper, the surface of the coated paper is smooth, so that the adhesive adheres to the coated paper surface and destroys the surface layer of the coated paper. There are many. Many re-peelable pressure-sensitive adhesives have been proposed in which a cohesive force is increased to reduce cohesive strength by adding a cross-linking agent so that it can be easily peeled off from the adherend without such a situation.
In particular, the re-peelable pressure-sensitive adhesive composition has been strongly studied from the viewpoint of environmental hygiene in recent years and has been strongly studied for a water-dispersed pressure-sensitive adhesive that does not use a solvent.
For example, Patent Literature 1 discloses an aqueous pressure-sensitive adhesive characterized by blending a polyglycidyl compound with an aqueous copolymer emulsion having a specific monomer composition, molecular weight, glass transition temperature, and particle size.
Patent Document 2 discloses an acrylic emulsion-type pressure-sensitive adhesive in which one or more kinds of crosslinking agents selected from a polyfunctional aziridine compound and a polyfunctional carbodiimide compound are added to a specific acrylic emulsion-type pressure-sensitive adhesive.
Patent Document 3 discloses a water-soluble crosslinking agent containing an oxazoline group in a specific acrylic emulsion-type pressure-sensitive adhesive, and 0.1 to 5 oxazoline groups per equivalent of carboxyl groups contained in the acrylic emulsion-type pressure-sensitive adhesive. Re-peelable pressure-sensitive adhesive which is blended so as to be equivalent, has a solvent-soluble content of 40% by mass or less, an elastic modulus of ² to 50 kg / cm ² and a re-peeling force of 500 g / 20 mm (width) or less. Agents have been proposed.
In Patent Document 4, a specific acrylic emulsion-type pressure-sensitive adhesive has a carbodiimide group-containing crosslinking agent, and the ratio of the carbodiimide group to the carboxyl group contained in the acrylic emulsion-type pressure-sensitive adhesive (carbodiimide group / carboxyl group). A water-dispersible pressure-sensitive adhesive for re-peeling having a re-peelability of 500 g / 20 mm (width) or less has been proposed.
Furthermore, Patent Document 5 discloses a water-dispersible cross-linking agent and an oil-soluble cross-linking agent for a water-dispersed pressure-sensitive adhesive composition containing (meth) acrylic acid alkyl ester as a main component and acrylic acid and methacrylic acid as functional monomers. An adhesive using an agent is disclosed.
However, all of the releasable adhesives have high cohesive strength and moderate adhesive strength, but are not yet satisfied with the required performance in recent years, and are excellent in more severe atmospheres and over long periods of time. Re-peelability (peeling stability) is required. Further, these technologies are still insufficient in terms of stain resistance, and further improvements are required.
By the way, alkali-soluble or alkali-swellable (meth) acrylic acid copolymer emulsions are known as one of acrylic emulsions, and are mainly used as additives such as viscosity improvers (for example, patent documents). 6-8 etc.).
However, a re-peelable pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer using an alkali-soluble or alkali-swellable (meth) acrylic acid copolymer as one of the cross-linked components in the pressure-sensitive adhesive has not been known.

Japanese Patent Publication No.5-075034 JP 7-278233 A Japanese Patent Laid-Open No. 10-114887 (Patent No. 3810490) JP 2001-131512 A JP 2001-152118 A JP 2002-332303 (Patent No. 3898773) JP 2004-18699 A JP 2005-515278 A

  Under such a background, the present invention has little increase in adhesive strength after a long period of time, and there is little contamination such as adhesive residue and imprints on the adherend during re-peeling, that is, it is resistant to contamination. An object of the present invention is to provide a releasable pressure-sensitive adhesive sheet having an excellent releasable water-dispersed pressure-sensitive adhesive composition as a pressure-sensitive adhesive layer.

As a result of intensive studies, the present inventors have found that a water-dispersed acrylic ester copolymer containing 0.1 to 2.0% by mass of a carboxyl group-containing unsaturated monomer unit, a carboxyl group-containing unsaturated monomer unit. Removability using a water-dispersible acrylic pressure-sensitive adhesive composition that contains an alkali-soluble or alkali-swellable (meth) acrylic acid copolymer containing as a cross-linked component and a cross-linking agent as an essential component The present inventors have found that the above problems can be solved by the pressure-sensitive adhesive sheet, and have completed the present invention.
The re-peelable pressure-sensitive adhesive sheet of the present invention has excellent substrate adhesion despite the slight adhesion.

That is, the present invention provides the following (1) to (6)
(1) In the releasable pressure-sensitive adhesive sheet formed by forming a pressure-sensitive adhesive layer on the surface substrate, the pressure-sensitive adhesive layer contains a C 4-12 (meth) acrylic acid alkyl ester unit as a main component of an alkyl group. Emulsion [A] of (meth) acrylic acid ester copolymer containing 0.1 to 2.0% by mass of carboxyl group-containing unsaturated monomer unit, alkali-soluble or alkali containing carboxyl group-containing unsaturated monomer unit When formed from a water-dispersed pressure-sensitive adhesive composition containing a swellable (meth) acrylic acid copolymer emulsion [B] and a crosslinking agent [C] as essential components, and using tetrahydrofuran in the pressure-sensitive adhesive layer as a solvent A re-peelable pressure-sensitive adhesive sheet, characterized in that the gel fraction is 65 to 95% by mass,
(2) The releasable pressure-sensitive adhesive sheet according to (1), wherein the alkyl group (meth) acrylic acid alkyl ester unit having 4 to 12 carbon atoms of the alkyl group is a 2-ethylhexyl acrylate unit,
(3) The alkali-soluble or alkali-swellable (meth) acrylic acid copolymer containing a (meth) acrylic acid alkyl ester unit having 3 or less carbon atoms in the alkyl group, as described in (1) or (2) above Peelable adhesive sheet,
(4) The releasable pressure-sensitive adhesive sheet according to any one of (1) to (3), wherein the alkali-soluble or alkali-swellable (meth) acrylic acid copolymer contains an internal crosslinking agent unit,
(5) In GPC measurement of the tetrahydrofuran-soluble component of the pressure-sensitive adhesive layer, the weight average molecular weight (Mw) is 20,000 to 200,000, and the molecular weight distribution (Mw / Mn, where Mn is the number average molecular weight) is The re-peelable pressure-sensitive adhesive sheet according to any one of (1) to (4) above and 2.0 to 5.0 and (6) the crosslinking agent [C] have two or more glycidyl groups in the molecule. The above (1) to (5), which is one or more selected from a polyglycidyl compound, an oxazoline compound having two or more oxazoline groups in the molecule, and a carbodiimide compound having two or more carbodiimide groups in the molecule. A re-peelable pressure-sensitive adhesive sheet according to any one of the above is provided.

  According to the present invention, there is provided a releasable pressure-sensitive adhesive sheet that is excellent in adhesiveness and can be easily peeled off from the surface of the adherend even after being left at a high temperature for a long time after being attached to the adherend. It is useful as a releasable pressure-sensitive adhesive sheet used for labels, sheets and the like.

Hereinafter, the releasable pressure-sensitive adhesive sheet of the present invention will be described in detail.
The (meth) acrylic acid ester copolymer emulsion which is the [A] component in the water-dispersed pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer in the releasable pressure-sensitive adhesive sheet of the present invention has a carbon number of an alkyl group. 4 to 12 (meth) acrylic acid alkyl ester (a1) as a main component, carboxyl group-containing unsaturated monomer (a2) is 0.1 to 2% by mass, and other impurities used as necessary. A monomer mixture containing a saturated monomer (a3) and a polyfunctional monomer (a4) is dispersed in water and subjected to emulsion polymerization. The method of emulsion polymerization is not particularly limited, and conventionally known methods can be employed.

a1 has an alkyl group having 4 to 12 carbon atoms such as an n-butyl group, isobutyl group, isoamyl group, hexyl group, heptyl group, 2-ethylhexyl group, isooctyl group, isononyl group, and isodecyl group. It is an alkyl ester of acrylic acid or methacrylic acid, and one or more alkyl esters selected from these groups can be used. The unit derived from a1 is preferably in a proportion of 50 to 99.9% by mass in the total monomer units constituting the copolymer in the component [A]. When the amount is less than 50% by mass, the initial adhesive strength of the pressure-sensitive adhesive layer may be reduced.
As a1, 2-ethylhexyl acrylate (2-EHA) is preferably used from the viewpoint of pressure-sensitive adhesive properties required for the pressure-sensitive adhesive layer formed on the re-peelable pressure-sensitive adhesive sheet, particularly re-peelability.

The carboxyl group-containing unsaturated monomer (a2) used in the present invention is used as an essential component in order to improve the cohesive force due to the crosslinking reaction.
Specific examples of a2 include monomers having a carboxyl group and a carbon-carbon unsaturated bond in one molecule, such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, crotonic acid, and the like. One or more selected from the above can be used. The content of the unit derived from a2 is 0.1 to 2.0% by mass, preferably 0.5 to 1.2% by mass in the unit derived from all monomers. When the content is less than 0.1% by mass, the cross-linking bond with the cross-linking agent [C] described later is small, so the cohesive force is not improved and the peeling stability such as adhesive residue is reduced. . Moreover, when there is more content of the unit derived from a2 than 2.0 mass%, the pot life after adding a crosslinking agent becomes short, and a problem arises in coating workability | operativity.

  Moreover, unsaturated monomers (a3) other than those copolymerizable with a1 and a2 can also be used. For example, the alkyl group such as methyl methacrylate, ethyl acrylate, isopropyl acrylate and the like having 1 to 3 carbon atoms in the alkyl group such as (meth) acrylic acid alkyl ester, tridecyl methacrylate, stearyl acrylate and the like has 13 to 13 carbon atoms. 18 (meth) acrylic acid alkyl ester, hydroxyl-containing monomer such as hydroxyalkyl (meth) acrylate such as hydroxyethyl (meth) acrylate, vinyl acetate, styrene, (meth) acrylonitrile, N-vinylpyrrolidone, (Meth) acryloylmorpholine, cyclohexylmaleimide, isopropylmaleimide, (meth) acrylamide, N, N-dimethyl (meth) acrylamide, glycidyl (meth) acrylate, dimethyl maleate, di-n-butyl maleate, di-maleate 2-Eth Maleic acid or fumaric acid ester such as hexyl, di-n-octyl maleate, dimethyl fumarate, di-n-butyl fumarate, di-2-ethylhexyl fumarate, di-n-octyl fumarate, etc. One or more selected from these groups can be used. The content of the unit derived from a3 is preferably 0 to 49.9% by mass in the unit derived from all monomers. When exceeding 49.9 mass%, the adhesiveness with the surface base material of the adhesive layer formed in a releasable adhesive sheet will become scarce.

  Furthermore, in addition to the above-mentioned monomers a1 to a3, (poly) ethylene glycol di (meth) acrylate, methylenebisacrylamide, 1,6-hexanedio- Examples thereof include polyfunctional monomers (a4) such as rudi (meth) acrylate, trimethylolpropane tri (meth) acrylate, and divinylbenzene, and one or more selected from these groups may be used. The content of the unit derived from a4 is preferably 0 to 2% by mass in all monomers. When the amount used exceeds 2% by mass, the adhesion to the surface substrate and the removability are reduced.

When the [A] component is prepared by an emulsion polymerization method using the monomers a1 to a2 and, if necessary, a3 and / or a4, a polymerization initiator is used. As polymerization initiators, azo compounds such as 2,2′-azobis (2-methylpropionamidine) dihydrochloride, 2,2′-azobis (2-amidinopropane) dihydrochloride, potassium persulfate, ammonium persulfate and the like Peroxides such as sulfate, benzoyl peroxide, t-butyl hydroperoxide, and hydrogen peroxide can be used. A redox initiator comprising a combination of persulfate and sodium bisulfite, a combination of peroxide and sodium ascorbate, or the like can also be used. These polymerization initiators may usually be added in a predetermined amount at each stage of emulsion polymerization to cause a polymerization reaction.
When the component [A] is prepared by an emulsion polymerization method, an appropriate amount of an anionic or nonionic emulsifier is used in order to ensure polymerization stability. Specific examples of anionic emulsifiers include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzene sulfonate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl sodium sulfate, and the like. Examples of nonionic emulsifiers include polyoxyethylene alkyl ether and polyoxyethylene alkyl phenyl ether. A radical polymerizable reactive emulsifier into which a propenyl group, an acryloyl group or the like is introduced can also be used. These emulsifiers can be used alone or in combination.
The conditions for emulsion polymerization are not particularly limited, and the conditions applied in normal emulsion polymerization can be applied as they are. In general, after the inside of the reactor is replaced with an inert gas, the temperature is increased while stirring under reflux, and the polymerization is carried out in a temperature range of about 40 to 100 ° C. for about 1 to 8 hours after the temperature is increased.

Next, the alkali-soluble or alkali-swellable (meth) acrylic acid copolymer as the component [B] in the water-dispersed pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer on the re-peelable pressure-sensitive adhesive sheet of the present invention. The emulsion will be described.
Component [B] is an emulsion containing a polymer having many hydrophilic groups such as carboxyl groups, and the polymer particles dispersed in water are dissolved or swelled by the addition of an alkali such as aqueous ammonia, resulting in a marked increase in viscosity. Therefore, it is used as a viscosity improver, a gelling agent, a thixotropic additive and the like in applications such as water-based paints, paper coating liquids, and water-based inks.
In the present invention, this is not used as a mere additive such as a conventional viscosity improver, but is used together with the above-mentioned [A] component as a crosslinkable component by a crosslinking agent which is the [C] component described later. .
The emulsion of the alkali-soluble or alkali-swellable (meth) acrylic acid copolymer as the component [B] is generally composed mainly of a (meth) acrylic acid alkyl ester having 3 or less carbon atoms such as ethyl (meth) acrylate. And a monomer having a hydrophilic group such as (meth) acrylic acid is usually added in an amount of 10% by mass or more, preferably 20% by mass or more, and moreover, such as the polyfunctional monomer (a4) A small amount of monomer (for example, about 0.01 to about 10% by mass) can be added to produce the polymer by emulsion polymerization.
In some cases, an associative monomer such as alkoxy polyethylene glycol (meth) acrylate is emulsion-copolymerized. The main component is a monomer having a hydrophilic group such as (meth) acrylic acid and a (meth) acrylic acid alkyl ester such as ethyl (meth) acrylate. In the emulsion polymerization process, about 20 to 40% by mass of an active ingredient is produced and sold by the dropping method of polymerizable monomer or the pre-emulsion dropping method. . Moreover, the usage-amount of the monomer which has hydrophilic groups like (meth) acrylic acid is 10-90 mass%, Preferably it is 20-80 mass%, More preferably, it is 20-60 mass%. When the content is less than 10% by mass, the polymerization stability is improved, but the resulting polymer having a large number of hydrophilic groups such as carboxyl groups may be reduced in alkali solubility. If it exceeds 90% by mass, the polymerization stability is remarkably lowered, and the solubility of the polymer in water becomes 10% by mass or more, and there is a possibility that it cannot be present in a stable state as an emulsion.
The emulsion of this alkali-soluble or alkali-swellable (meth) acrylic acid copolymer can be adjusted in crosslinkability depending on the amount and type of polyfunctional monomer, the molecular weight of the resulting polymer, and the type of associative monomer. And thereby the desired release stability can be prepared.
The conditions for emulsion polymerization for producing the component [B] are not particularly limited, and are the same as those for the component [A].
[B] The emulsion of the alkali-soluble or alkali-swellable (meth) acrylic acid copolymer as the component is commercially available, for example, “Aron B-300K” and “Aron A-7075” manufactured by Toa Gosei Co., Ltd. And “Primal TT-615” manufactured by Rohm and Haas Co., Ltd.

Next, the crosslinking agent which is the [C] component in the water-dispersed pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer on the releasable pressure-sensitive adhesive sheet of the present invention will be described.
[C] component which is a cross-linking agent used in the present invention cross-links carboxyl groups of the water-dispersed acrylic acid ester copolymer [A] and the alkali-swelling acrylic emulsion [B]. Epoxy-based, oxazoline-based, and carbodiimide-based compounds are superior in terms of adhesiveness of the adhesive layer and little increase in adhesive strength with time after being applied to the adherend, that is, excellent removability from the adherend and stain resistance. Mainly used.
In addition, these crosslinking agents may be used alone or in combination of two or more, and if necessary, an aziridine compound, polyisocyanate compound, melamine compound, metal complex compound, amine compound, adipic acid dihydrazide, sebacic acid Other crosslinking agents such as hydrazine derivatives such as dihydrazide may be used in combination.
The epoxy compound may be any compound having two or more epoxy groups or glycidyl groups in the molecule. For example, bisphenol A / epichlorohydrin type epoxy resin, sorbitol polyglycidyl ether (for example, manufactured by Nagase ChemteX Corporation) “Denacol EX-611”, “Denacol EX-612”, “Denacol EX-614”, “Denacol EX-614B”, “Denacol EX-622”, etc.), polyglycerol polyglycidyl ether (for example, manufactured by Nagase ChemteX Corporation) "Denacol EX-512", "Denacol EX-521", etc.), pentaerythritol polyglycidyl ether (eg, "Denacol EX-411" manufactured by Nagase ChemteX Corporation), diglycerol polyglycidyl ether (eg, Nagaseke). "Denacol EX-421" manufactured by Tex Corporation), glycerol polyglycidyl ether (for example, "Denacol EX-313", "Denacol EX-314" manufactured by Nagase ChemteX Corporation), etc.), trimethylolpropane polyglycidyl ether (for example, , "Denacol EX-321" manufactured by Nagase ChemteX Corporation), neopentyl glycol diglycidyl ether (for example, "Denacol EX-211" manufactured by Nagase ChemteX Corporation), 1,6-hexanediol diglycidyl ether ( For example, “Denacol EX-212” manufactured by Nagase ChemteX, Inc.), ethylene glycol diglycidyl ether (eg, “Denacol EX-810”, “Denacol EX-811” manufactured by Nagase ChemteX, Inc.), diethylene glycol diglycidyl, etc. Ether (for example, “Denacol EX-850”, “Denacol EX-851”, etc., manufactured by Nagase ChemteX Corporation), polyethylene glycol diglycidyl ether (for example, “Denacol EX-821”, “Denacol EX, manufactured by Nagase ChemteX Corporation) -830 "," Denacol EX-832 "," Denacol EX-841 "," Denacol EX-861 ", etc.), propylene glycol diglycidyl ether (for example," Denacol EX-911 "manufactured by Nagase ChemteX Corporation), Polypropylene glycol diglycidyl ether (for example, “Denacol EX-941”, “Denacol EX-920”, “Denacol EX-931”, etc., manufactured by Nagase ChemteX Corporation), diglycidylaniline, N, N, N ′, N ′ -Tetraglycidyl-m-xylene Examples thereof include diamine and 1,3-bis (N, N′-diglycidylaminomethyl) cyclohexane. Among these, an aqueous type cross-linking agent is preferable.
Examples of the oxazoline compound include addition-polymerizable 2-oxazoline (for example, 2-isopropenyl-2-oxazoline) having a substituent having an unsaturated carbon-carbon bond at the 2-position carbon position, and other unsaturated monomers. Examples of commercially available products include “Epocross WS-500”, “Epocross WS-700”, “Epocross K-2010E”, “Epocross K-2020E”, and “Epocross K-” manufactured by Nippon Shokubai Co., Ltd. 2030E "and the like.
As the carbodiimide-based compound, any compound having at least two carbodiimide groups may be used. For example, “Carbodilite V-02”, “Carbodilite V-02-L2”, “Carbodilite V-04” manufactured by Nisshinbo Co., Ltd., “ Carbodilite V-06 "," Carbodilite E-01 "," Carbodilite E-02 "," Carbodilite E-04 "and the like.

In order to obtain the releasable pressure-sensitive adhesive sheet of the present invention, it is necessary to apply a water-dispersed pressure-sensitive adhesive composition to a surface substrate as described later. It is necessary to adjust the viscosity and active ingredients of the water-dispersed pressure-sensitive adhesive composition depending on the coating method and coating conditions. For example, when adjusting the viscosity of the water-dispersed pressure-sensitive adhesive composition at 25 ° C. to be in the range of 50 to 30000 mPas, when the active ingredient of the component [A] is 50% by mass, the following blending ratio It becomes.
[A] component: 96.0-99.6 mass%
[B] component: 0.1-1.0 mass%
[C] component: 0.3-3.0 mass%
[The total amount of the three components is 100% by mass]
In the present invention, an emulsion of an alkali-soluble or alkali-swellable (meth) acrylic acid copolymer that is the component [B] is used, but the amount added is an appropriate amount to adjust the viscosity setting according to the coating method and coating conditions, And what is necessary is just to adjust so that the adhesive layer formed in a releasable adhesive sheet may enter into the range whose gel fraction is 65-95 mass%.
The pressure-sensitive adhesive layer formed on the releasable pressure-sensitive adhesive sheet of the present invention has an alkali-soluble or alkali-swellable (meth) acrylic component [B] to be used if the gel fraction is in the range of 65 to 95% by mass. The emulsion of the acid copolymer and the crosslinking agent as the [C] component may be in any combination.
By setting the gel fraction to 65% by mass or more, due to insufficient cohesive force of the pressure-sensitive adhesive layer, adhesive residue is contaminated on the adherend during re-peeling, or adhesive labels are cut off due to the pressure-sensitive adhesive layer protruding. Or it prevents that secondary workability, such as punching, falls. On the other hand, by setting the gel content to 95% by mass or less, for example, in the case of an adhesive label, the adhesiveness to the adherend becomes poor when it adheres to the rough surface of the adherend such as corrugated cardboard with light pressure. Prevent problems such as falling off naturally.
A gel fraction can be made into the range of 65-95 mass% by mix | blending the said [A] component, a [B] component, and a [C] component by the above ratios.

Further, in the GPC measurement of the tetrahydrofuran-soluble component of the pressure-sensitive adhesive layer, specifically, the weight average molecular weight (Mw) of the polymer component dissolved in tetrahydrofuran in the pressure-sensitive adhesive layer obtained at the time of measuring the gel fraction is 20,000 to 200,000 is preferred. Adhesiveness is ensured by setting it to 20,000 or more, and it prevents that it becomes easy to deform | transform excessively by external pressure by setting it to 200,000 or less. Moreover, it is preferable that Mw / Mn (number average molecular weight) is 2.0-5.0. By setting it as 2.0 or more, it prevents that the adhesive force with respect to various to-be-adhered bodies falls, and prevents it from becoming easy to produce adhesive residue at the time of peeling by being 5.0 or less.
By blending the [A] component, the [B] component, and the [C] component in the above ratio, the weight average molecular weight (Mw) can be set to 20,000 to 200,000, and Mw / Mn can be set to 2.0 to 5.0.
In the releasable pressure-sensitive adhesive sheet of the present invention, various additives such as a tackifier resin, other cross-linking agents, and the like within the water-dispersed pressure-sensitive adhesive composition as long as they do not affect the effects of the present invention as necessary. Plasticizers, softeners, fillers, pigments, dyes, anti-aging agents, thickeners, antifoaming agents, preservatives, and the like can be blended.

In the water-dispersed pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer on the releasable pressure-sensitive adhesive sheet of the present invention, the active ingredient concentration is usually 30 to 65% by mass, preferably 40 to 55% by mass. .
The viscosity is 50 to 12,000 mPa · s, preferably 100 to 10,000 mPa · s (BM type viscometer, 60 rotations, 25 ° C.). Furthermore, the pH is in the range of 7-9.
The active ingredient concentration, viscosity and pH in the pressure-sensitive adhesive composition are preferably within the above ranges from the viewpoints of drying property, coating property, and handling property.

Next, the surface substrate will be described in detail.
As a surface substrate, a sheet made of resin such as polyethylene terephthalate, polyethylene naphthalate, polyimide, polyetherimide, polyaramid, polyetherketone, polyetheretherketone, polyphenylene sulfide, poly (4-methylpentene-1), etc. And paper base materials such as film, fine paper, coated paper, glassine paper, and laminated paper are used.
The thickness of the surface base material is slightly different depending on the material used, but is usually about 5 to 300 μm, and preferably about 10 to 100 μm.

  In order to apply the water-dispersed pressure-sensitive adhesive composition to a surface substrate or a release sheet described later, a solution of the composition is prepared and applied to a conventional gravure coating method, bar coating method, spray coating. It can be performed using a method, spin coating method, roll coating method, die coating method, knife coating method, air knife coating method, hot melt coating method, curtain coating method and the like.

  The thickness of the pressure-sensitive adhesive layer formed on the surface base material after drying and curing is usually about 3 to 50 μm, preferably about 5 to 40 μm. By setting the thickness of the pressure-sensitive adhesive layer to 3 μm or more, it is possible to secure the adhesive force and cohesive force (holding force) necessary for the re-peelable pressure-sensitive adhesive sheet of the present invention. And prevents the pressure-sensitive adhesive layer from protruding from the end.

Next, the release sheet will be described in detail.
As a release sheet for protecting the pressure-sensitive adhesive layer formed on the surface substrate, a resin such as polyethylene terephthalate, polyethylene, or polypropylene coated with a release agent such as fluororesin, silicone resin, or long-chain alkyl group-containing carbamate A release sheet obtained by coating the release agent on a paper substrate such as a film, fine paper, glassine paper, or laminate paper can be used. The thickness of the release sheet varies somewhat depending on the material used, but is usually 10 to 250 μm, preferably 20 to 200 μm. The thickness of the release agent layer is usually about 0.1 to 5 μm, preferably about 0.5 to 2 μm.

  The re-peelable pressure-sensitive adhesive sheet of the present invention is obtained by directly applying a water-dispersed pressure-sensitive adhesive composition on the surface substrate and drying it according to a conventional method for producing pressure-sensitive adhesive sheets, or After coating on the release agent layer of the release sheet and drying, a pressure-sensitive adhesive layer is formed by transferring onto the surface substrate, and a sheet or tape-like roll or laminate Alternatively, it may be a releasable pressure-sensitive adhesive sheet that is a single leaf and affixed to a release sheet.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited only to a following example. In the following, “part” or “%” means “part by mass” or “mass%”.

<Example 1>
In a reactor equipped with a thermometer, a stirrer, a dropping device, a reflux condenser and a nitrogen inlet tube, weigh 28 parts of ion-exchanged water, enclose nitrogen and raise the internal temperature to 80 ° C., and maintain that temperature. However, immediately after adding 2 parts of 10% aqueous ammonium persulfate solution, 99 parts of 2-ethylhexyl acrylate and 1 part of acrylic acid prepared separately were added to a polyoxyethylene alkyl ether sulfate sodium salt (Kao Corporation). (Manufactured, trade name: Latemul E-118B) A monomer emulsion obtained by mixing and emulsifying 4 parts and 56 parts of ion-exchanged water was dropped dropwise continuously for 4 hours for emulsion polymerization. In parallel, 4 parts of an aqueous 5% ammonium persulfate solution was added dropwise. After completion of dropping, the mixture was aged at 80 ° C. for 4 hours and then cooled to room temperature. The mixture was neutralized with aqueous ammonia, and water was added to obtain an acrylate copolymer emulsion ([A] component) having an active ingredient of 50%, a viscosity of 50 mPa · s, and a pH of 8.0. To 200 parts of the emulsion, 1.0 part of an alkali-swelling acrylic acid copolymer emulsion (manufactured by Toagosei Co., Ltd., trade name: Aron B-300K) as a component [B] is added, and the viscosity is 10,000 mPa · s (BM Type pressure viscometer) to obtain an adhesive composition. Furthermore, to 100 parts of the above-mentioned pressure-sensitive adhesive composition, 0.5 part of a cross-linking agent “Denacol EX-313” manufactured by Nagase ChemteX Corporation is added as [C] component, mixed well, and water-dispersed. A pressure-sensitive adhesive composition was prepared. The obtained pressure-sensitive adhesive composition was dried using a roll knife coater on the release-treated surface of a release sheet (made by Lintec, glassine paper release-treated with a silicone resin, trade name: SP-8K Ao). The layer was coated to a thickness of 20 μm and dried at 90 ° C. for 2 minutes to form an adhesive layer. Subsequently, it was bonded to high-quality paper (64 g / m ² ) (manufactured by Nippon Paper Industries Co., Ltd., trade name: New NPi fine quality) and allowed to stand in an atmosphere of 23 ° C. and 50% relative humidity for 7 days to prepare a releasable pressure-sensitive adhesive sheet.
The re-peelable pressure-sensitive adhesive sheet was attached to a SUS plate, a polystyrene plate, and K liner paper, respectively, and the initial pressure-sensitive adhesive force, the time-dependent pressure-sensitive adhesive force, and the re-peelable property were measured.
Separately, the gel fraction and molecular weight (tetrahydrofuran soluble component) of the pressure-sensitive adhesive layer were measured. Table 1 shows each component ratio and measurement results.

<Examples 2 and 3>
As shown in Table 1, a water-dispersible pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the type and amount of the crosslinking agent [C] were changed to obtain a releasable pressure-sensitive adhesive sheet. In the same manner as in Example 1, the initial adhesive strength and the like were measured. The results are shown in Table 1.

<Examples 4 and 5>
As shown in Table 1, a water-dispersed pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the type and amount of the alkali-soluble or alkali-swelling acrylic emulsion as the component [B] were changed. A peelable pressure-sensitive adhesive sheet was obtained, and the initial adhesive force and the like were measured in the same manner as in Example 1. The results are shown in Table 1.

<Example 6>
[A] A water-dispersed pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the content of the carboxyl group-containing unsaturated monomer unit in the component was changed as shown in Table 1, and re-peeled. An adhesive sheet was obtained, and the initial adhesive strength and the like were measured in exactly the same manner as in Example 1. The results are shown in Table 1.

<Example 7>
[A] A water-dispersed pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the content of the (meth) acrylic acid alkyl ester unit as the main component in the component was changed as shown in Table 1. A re-peelable pressure-sensitive adhesive sheet was obtained, and the initial adhesive strength and the like were measured in exactly the same manner as in Example 1. The results are shown in Table 1.

<Comparative Examples 1-3>
A water-dispersible pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the amount of each of the alkali-swelling acrylic emulsions in Examples 1 to 3 was reduced. In the same manner, the initial adhesive strength and the like were measured. The results are shown in Table 1.

<Comparative example 4>
[A] A water-dispersed pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the content of the carboxyl group-containing unsaturated monomer unit in the component was changed as shown in Table 1, and re-peeled. An adhesive sheet was obtained, and the initial adhesive strength and the like were measured in exactly the same manner as in Example 1. The results are shown in Table 1.

<Measurement of physical properties of water-dispersed pressure-sensitive adhesive composition>
(1) Viscosity: Measured at 12 rotations / minute (unit: mPa · s) using a BM type viscometer (manufactured by Tokyo Keiki Co., Ltd.) under a 25 ° C. environment in accordance with JIS K-6833.
(2) Gel fraction: about 500 mg of the pressure-sensitive adhesive layer is wrapped in # 300 SUS mesh, immersed in tetrahydrofuran for 72 hours, taken out together with SUS mesh, dried at 120 ° C. for 3 hours, and calculated from the mass ratio before immersion. (Unit:%).
Weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn): Tetrahydrofuran soluble component at the time of gel fraction measurement was measured by GPC (manufactured by Tosoh: CCP8000, solvent: tetrahydrofuran, liquid feed rate: 1.0 ml / min). (Standard sample: polystyrene).

<Physical property test of releasable adhesive sheet>
(1) Initial adhesive strength and temporal adhesive strength Measured according to JIS Z-0237 180 ° peel adhesive strength measurement method. Cut the re-peelable adhesive sheet to a width of 25 mm, affix it to a SUS plate, polystyrene plate, K liner paper, and press and reciprocate once with a 2 kg mass roller. The time-dependent adhesive force measured after standing for 24 hours at 50% relative humidity was measured at a peeling speed of 300 mm / min. The unit of the measured value is N / 25 mm (width).
(2) Removability The releasable adhesive sheet is cut to a width of 25 mm and affixed to a SUS plate, polystyrene plate or K liner paper, left in a 40 ° C atmosphere for 7 days, and then oriented at 120 ° at a speed of 10 m / min. The film was peeled by hand and the peeled state was visually observed and evaluated according to the following criteria.
(Double-circle): It can peel neatly without adhesive residue and paper tearing.
○: There is a slight paper break at the edge, but there is no practical problem.
Δ: Residue remaining or paper tears partially.
X: There are adhesive residue and paper tears on the entire surface.

The numerical values for the [A], [B] and [C] components in Table 1 indicate the amounts of the active ingredients of [B] and [C] with respect to 100 parts by mass of the total monomer components of [A].
The abbreviations in the used [A] component are as follows.
2EHA: 2-ethylhexyl acrylate BA: n-butyl acrylate AA: acrylic acid MMA: methacrylic acid

The alkali-soluble or alkali-swelling acrylic emulsion used as the [B] component is as follows.
B-300K: “Aron B-300K” manufactured by Toagosei, 45% active ingredient
A-7075: “Aron A-7075” manufactured by Toagosei Co., Ltd., 20% active ingredient
TT-615: Rohm and Haas “Primal TT-61
5 ", 30% active ingredient

The crosslinking agent which is the [C] component used is as follows.
EX-313: manufactured by Nagase ChemteX Corporation, “Denacol EX-313 (glycerol polyglycidyl ether)”, active ingredient 100%
WS-700: Nippon Shokubai Co., Ltd., “Epocross WS-700”, 25% active ingredient
V-04: “Carbodilite V-04” manufactured by Nisshinbo Co., Ltd., active ingredient content 40%

Claims (6)

  In a releasable pressure-sensitive adhesive sheet formed by forming a pressure-sensitive adhesive layer on a surface base material, the pressure-sensitive adhesive layer contains a (meth) acrylic acid alkyl ester unit having 4 to 12 carbon atoms as the main component and also contains a carboxyl group Emulsion [A] of (meth) acrylic acid ester copolymer containing 0.1 to 2.0% by mass of unsaturated monomer unit, alkali-soluble or alkali swellable containing carboxyl group-containing unsaturated monomer unit ( Gel content when formed from a water-dispersed pressure-sensitive adhesive composition containing a meth) acrylic acid copolymer emulsion [B] and a cross-linking agent [C] as essential components, and using tetrahydrofuran in the pressure-sensitive adhesive layer as a solvent. A releasable pressure-sensitive adhesive sheet having a rate of 65 to 95% by mass.   The releasable pressure-sensitive adhesive sheet according to claim 1, wherein the alkyl group having 4 to 12 carbon atoms of the alkyl group is a 2-ethylhexyl acrylate unit.   The releasable pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the alkali-soluble or alkali-swellable (meth) acrylic acid copolymer contains a (meth) acrylic acid alkyl ester unit having 3 or less carbon atoms in an alkyl group.   The releasable pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the alkali-soluble or alkali-swellable (meth) acrylic acid copolymer contains an internal crosslinking agent unit.   In GPC measurement of the tetrahydrofuran-soluble component of the pressure-sensitive adhesive layer, the weight average molecular weight (Mw) is 20,000 to 200,000, and the molecular weight distribution (Mw / Mn, where Mn is the number average molecular weight) is 2.0. It is -5.0. The removable adhesive sheet in any one of Claims 1-4.   The crosslinking agent [C] is a polyglycidyl compound having two or more glycidyl groups in the molecule, an oxazoline compound having two or more oxazoline groups in the molecule, and a carbodiimide type having two or more carbodiimide groups in the molecule. It is 1 or more types chosen from a compound, The releasable adhesive sheet in any one of Claims 1-5.