JP5604321B2 - Alkali-peelable pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet using the same - Google Patents

Description

  The present invention relates to an alkali-peelable pressure-sensitive adhesive composition, and more specifically, a pressure-sensitive adhesive composition that peels easily in an alkaline aqueous solution, has excellent unevenness followability, and is also excellent in water whitening resistance and water-resistant adhesion maintenance. And an adhesive sheet using the same.

  Recycling of glass and plastic is progressing in the trend of environmental protection and resource reuse. In order to reuse the glass or plastic with the adhesive sheet attached, it is necessary to remove the adhesive sheet. As a method for removing the pressure-sensitive adhesive sheet, there is a method of detaching the pressure-sensitive adhesive sheet by immersing in an alkaline aqueous solution.

  By making the pressure-sensitive adhesive water-soluble, the pressure-sensitive adhesive sheet can be easily peeled off in an alkaline aqueous solution. For example, if a starch-based or polyvinyl alcohol-based pressure-sensitive adhesive is used, it is easily peeled off in an alkaline aqueous solution. In addition, an acrylic pressure-sensitive adhesive is disclosed in which water-solubility is imparted by neutralizing a carboxyl group in a polymer with a neutralizing agent (Patent Document 1). However, such a water-soluble pressure-sensitive adhesive is liable to cause peeling or whitening due to moisture, so that the usage environment and application are limited. For example, it cannot be used in a product that gets wet or in a high humidity environment, and is not suitable for a transparent adhesive label from the viewpoint of design and optical properties.

  On the other hand, the present applicant dissolves in an alkaline aqueous solution by metal chelate crosslinking of an acrylic polymer copolymerized with a carboxyl group-containing monomer and a monomer having an ether bond, but in a neutral or acidic aqueous solution. The adhesive which does not melt | dissolve is proposed (patent document 2). This pressure-sensitive adhesive achieves both alkali solubility and water resistance. However, since the pressure-sensitive adhesive dissolves in the alkaline aqueous solution, there is a problem that the alkaline aqueous solution is contaminated.

  Furthermore, when the adherend is a glass container such as a beer bottle or a liquor bottle, an uneven structure is often present on the surface in terms of design and function. If there is not enough follow-up to such a concavo-convex structure, it is easy to entrain air bubbles when a label is attached, which causes subsequent peeling or poor appearance. For this reason, the pressure-sensitive adhesive for the label is also required to have high followability to the concavo-convex structure.

  Thus, various characteristics are required for the pressure-sensitive adhesive sheet for reuse treatment with an alkaline aqueous solution. However, there is basically a trade-off between the ease of peeling with an aqueous alkaline solution and the water resistance (water-resistant adhesion maintenance and water whitening resistance), and in order to prevent contamination of the alkaline aqueous solution, dissolution in an alkaline aqueous solution is required. Realizing this is very difficult because it requires an approach that is different from the conventional method to improve the performance.

  Patent Document 3 discloses that an adhesive polymer copolymerized with butyl acrylate, 2-ethylhexyl acrylate and acrylic acid, a non-adhesive polymer having a molecular weight of 70,000 copolymerized with N, N-dimethylaminoethyl methacrylate, and a crosslinking agent. A pressure-sensitive adhesive composition using the above is disclosed. However, this pressure-sensitive adhesive composition is not intended for reuse treatment in an alkaline aqueous solution, and because the non-adhesive polymer has a large molecular weight, it lacks alkali releasability and unevenness followability and is suitable for the application. Absent.

Japanese Patent Laid-Open No. 10-226776 JP-A-6-184508 Japanese Patent No. 2009-35602

  Accordingly, there is a strong demand for the development of a pressure-sensitive adhesive sheet that easily peels in an alkaline aqueous solution, has excellent adhesion resistance, water whitening resistance, and unevenness followability, and does not contaminate the alkaline aqueous solution. An object of the present invention is to provide such an adhesive sheet.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have a nitrogen-containing adhesive acrylic polymer having a carboxyl group in which alkyl acrylates having different glass transition temperatures are combined in a specific blending amount. By combining with a non-adhesive acrylic polymer, it is possible to obtain a pressure-sensitive adhesive that is excellent in unevenness followability, adhesion resistance maintenance, and water whitening resistance, and that promptly peels off in an alkaline aqueous solution without causing contamination of the alkaline aqueous solution. As a result, the present invention has been completed.

That is, the present invention provides the following components (A) to (C):
(A) At least the following components (a1) to (a3)
(A1) The glass transition temperature of the homopolymer is −80 ° C. or higher and lower than −60 ° C. (Meta)
Acrylic acid alkyl ester 10-50% by mass
(A2) Acrylic acid alkyl ester having a glass transition temperature of −60 ° C. or more and 10 ° C. or less of homopolymer 40 to 85% by mass
(A3) Carboxyl group-containing radical polymerizable monomer 5 to 20% by mass
100 parts by mass of an acrylic polymer obtained by copolymerizing (B) the following components (b1) and (b2)
(B1) Nitrogen-containing radical polymerizable monomer 1 to 10% by mass
(B2) (Meth) acrylic acid alkyl ester 90-99% by mass
The molecular weight is 1000-50,000 and the glass transition temperature is 0-15.
3 to 30 parts by mass of acrylic polymer at 0 ° C. (C) An alkali-peelable pressure-sensitive adhesive composition containing a polyfunctional crosslinking agent.

  Moreover, this invention is an adhesive sheet formed by providing the adhesive layer formed from the said adhesive composition on a base material.

  In the pressure-sensitive adhesive sheet of the present invention, the entire pressure-sensitive adhesive layer is not dissolved in an alkaline aqueous solution, but can be quickly peeled off by losing the bond with the interface. As a result, it is possible to prevent contamination of the alkaline aqueous solution and increase the efficiency of the regeneration work. Moreover, since it is excellent in water-resistant adhesion maintenance and water-whitening resistance, it does not easily peel off or whiten even when water adheres to it or is placed in a humid heat environment. Furthermore, since the unevenness followability is high, it can be flexibly applied even to an adherend having an uneven structure such as a glass bottle, and peeling and appearance defects do not occur.

  The acrylic polymer of component (A) used in the pressure-sensitive adhesive composition of the present invention (hereinafter sometimes referred to as “polymer (A)”) has a glass transition temperature of at least (a1) homopolymer of −80 ° C. or higher and −60 ° C. (Meth) acrylic acid alkyl ester having a temperature lower than ℃, (a2) homopolymer having a glass transition temperature of -60 ° C to 10 ° C, and (a3) a carboxyl group-containing radical polymerizable monomer. It is obtained by polymerization.

  (A1) The (meth) acrylic acid alkyl ester whose homopolymer has a glass transition temperature of −80 ° C. or higher and lower than −60 ° C. includes 2-ethylhexyl acrylate, octyl acrylate, lauryl methacrylate, tetradecyl methacrylate, and the like. 1 type (s) or 2 or more types can be used. Among them, those having a glass transition temperature of −80 to −65 ° C. are preferable in terms of improving the followability of the obtained pressure-sensitive adhesive to unevenness, and specific examples include 2-ethylhexyl acrylate and octyl acrylate.

  The content of (a1) with respect to the entire constituent monomer of the polymer (A) is 10 to 50% by mass (hereinafter referred to as “%”), preferably 12 to 30%. When it is less than 10%, sufficient unevenness followability cannot be obtained, and when it is more than 50%, the cutting property and punching property are poor, and the workability is very poor in applications such as labels.

  (A2) Examples of the acrylic acid alkyl ester whose homopolymer has a glass transition temperature of −60 ° C. or higher and 10 ° C. or lower include n-butyl acrylate, ethyl acrylate, methyl acrylate, octyl methacrylate, and the like. More than seeds can be used. Among them, a pressure-sensitive adhesive having a glass transition temperature of −55 to −20 ° C. is preferable in terms of imparting adhesiveness to a glass container and improving cutability and punching property, specifically, n-butyl. Examples include acrylate, ethyl acrylate, octyl methacrylate, and the like.

  Content of (a2) with respect to the whole constituent monomer of polymer (A) is 40 to 85%, preferably 60 to 80%. If it is less than 40%, sufficient adhesion cannot be obtained, and if it is more than 85%, followability to unevenness becomes insufficient, such being undesirable.

  The (a3) carboxyl group-containing radical polymerizable monomer is a monomer having a carboxyl group and radical polymerizability in the molecule, and specifically includes (meth) acrylic acid, 2-carboxyethyl (meth) acrylate, 3 -Carboxypropyl (meth) acrylate, 4-carboxybutyl (meth) acrylate, itaconic acid, crotonic acid, maleic acid, fumaric acid, etc. are mentioned, These 1 type (s) or 2 or more types can be used. Among these, acrylic acid and methacrylic acid are preferably used in terms of good copolymerizability with (a1) and (a2).

  The content of (a3) with respect to the entire constituent monomer of the polymer (A) is 5 to 30%, preferably 8 to 15%. If it is less than 5%, the formation of a crosslinked structure due to the reaction with a crosslinking agent described later becomes insufficient, or the formation of a pseudo-crosslinked structure due to electrostatic bonding with a nitrogen atom of the polymer (B) described later is insufficient. Therefore, it is not preferable because the adhesive strength becomes insufficient, or the cutting property and punching property are inferior, and when it exceeds 30%, the formation of the crosslinked structure becomes excessive and the followability to unevenness and curved surface pasting property are inferior. It is not preferable.

  The polymer (A) can be blended with other radical polymerizable monomers. Specifically, (meth) acrylic acid alkyl esters other than (a1) and (a2) such as i-octyl acrylate, t-butyl acrylate, n-butyl methacrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, etc. Having an alkylene oxide chain such as cyclo ring-containing (meth) acrylate such as aryl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, methoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate ) Acrylate, styrene, vinyl acetate and the like can be used. Content of the other radical polymerizable monomer with respect to the whole constituent monomer of the component (A) acrylic polymer is 0 to 20%, preferably 0 to 10%. If it is more than 20%, it is not preferable because there is a risk of impairing the follow-up to unevenness, adhesive force, and alkali peelability, which are the effects of the present invention.

  The polymer (A) can be produced by polymerizing the mixture of the monomer components by a conventionally known polymerization method such as a solution polymerization method, a bulk polymerization method, an emulsion polymerization method, a suspension polymerization method or the like. Among these, those produced by a solution polymerization method that can easily control the reaction and contain less impurities are preferable.

  The polymer (A) obtained as described above preferably has a weight average molecular weight (Mw) of 200 to 2,000,000, more preferably 400,000 to 1,000,000. This range is preferable because the coating property of the pressure-sensitive adhesive solution is good. In addition, in this specification, a weight average molecular weight means the value calculated | required by the measuring method described in the Example.

  The polymer (A) preferably has a glass transition temperature (Tg) of −65 to −30 ° C., more preferably −60 to −40 ° C. This range is preferable because the balance between the ability to follow unevenness and the adhesive force is good. In the present specification, the glass transition temperature of the copolymer is a value calculated by the following FOX equation. Table 1 below shows the glass transition temperatures of typical homopolymers of the respective monomers. For monomers not listed in Table 1, values described in the literature (Polymer Handbook 3rd edition: J. Brandrup, E. H. Immergut, Wiley-Interscience, 1989) can be used.

(Form of FOX)
1 / Tg = Wa / Tga + Wb / Tgb + ...
Tg: Glass transition temperature of copolymer Tga, Tgb,...: Glass transition temperature of homopolymer of monomer a, monomer b,.
Degree Wa, Wb, ...: Weight fraction of monomer a, monomer b, ...

  On the other hand, the acrylic polymer of component (B) used in the pressure-sensitive adhesive composition of the present invention (hereinafter sometimes referred to as “polymer (B)”) is (b1) a nitrogen-containing radical polymerizable monomer and (b2). Copolymerized with (meth) acrylic acid alkyl ester.

  (B1) Examples of the nitrogen-containing radical polymerizable monomer include dialkylaminoalkyl (meth) acrylates such as N, N-dimethylaminoethyl methacrylate (DMAEMA); (meth) acryloylmorpholine, dimethylacrylamide, and the like. These 1 type (s) or 2 or more types can be used. Among them, a monomer having a tertiary amino group is preferable, N, N-dimethylaminoethyl methacrylate (DMAEMA) has good copolymerizability with (b2), and good electrostatic bondability with the polymer (A). It is preferably used in that it is.

(B2) (Meth) acrylic acid alkyl ester includes methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, pentyl (Meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, lauryl (meth) acrylate, etc. 1 type or 2 types or more can be used. Among these, methyl acrylate and methyl methacrylate are preferably used in that the Tg of the polymer (B) is adjusted to a preferable range and the peelability when treated with an alkaline aqueous solution can be improved.
In the polymer (B), it is preferable not to use a monomer having a carboxyl group or a hydroxyl group, which is highly reactive with the crosslinking agent (C) described later. When these functional groups are present in the polymer (B), the polymer (B) forms a crosslinked structure by the crosslinking agent (C), and the fluidity of the polymer (B) is insufficient when immersed in an alkaline solution. Therefore, the peelability may be reduced.

  The polymer (B) has (b1) and (b2) as constituent monomers, the content of (b1) is 1 to 10%, the content of (b2) is 90 to 99%, preferably (b1) The content is 2 to 5%, and the content of (b2) is 98 to 95%. Within this range, the electrostatic bondability with the polymer (A) is good, and sufficient alkali peelability is obtained.

  The polymer (B) is produced by polymerizing a mixture of the above components (b1) and (b2) by a conventionally known polymerization method such as a solution polymerization method, a bulk polymerization method, an emulsion polymerization method or a suspension polymerization method. Can do. Among these, those produced by a solution polymerization method are preferable in that reaction control is easy and impurities are hardly mixed.

  The weight average molecular weight (Mw) of the polymer (B) thus obtained is 1000 to 50,000, preferably 5000 to 30,000. When the weight average molecular weight is less than 1000, the cut property and punching property are deteriorated, and when it is more than 50,000, the fluidity when immersed in an alkali solution is lowered and the peelability is deteriorated.

  In addition, the polymer (B) has a glass transition temperature (Tg) of 0 to 150 ° C, preferably 50 to 120 ° C. If it is lower than 0 ° C., the polymer (B) itself has adhesiveness even when the polymer (B) moves to the adhesive layer interface when immersed in an alkaline solution, so that the alkali peelability may be lowered. If the temperature is higher than 150 ° C., the compatibility with the polymer (A) decreases, and a pseudo-crosslinked structure due to electrostatic bonding between the polymer (A) and the polymer (B) cannot be formed uniformly. It is not preferable.

  The polyfunctional crosslinking agent of the component (C) used in the present invention is not particularly limited as long as it can bond carboxyl groups in the acrylic polymer of the component (A), and is an epoxy crosslinking agent or an isocyanate crosslinking agent. A metal chelate crosslinking agent or the like can be used, and two or more kinds can be used in combination. Of these, epoxy crosslinkers and metal chelate crosslinkers are preferred. Moreover, when it is desired to ensure adhesion with the substrate, it is effective to use an isocyanate crosslinking agent in combination with the epoxy crosslinking agent and / or the metal chelate crosslinking agent. For example, when an epoxy crosslinking agent and an isocyanate crosslinking agent are used in combination, they can be used in a mass ratio of 1: 0.1 to 1:10, preferably 1: 0.5 to 1: 5.

  Epoxy crosslinking agents include bisphenol A epichlorohydrin type epoxy resin, ethylene diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane tri Examples include glycidyl ether, diglycidyl aniline, diamine glycidyl amine, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine, 1,3-bis (N, N′-diamine glycidylaminomethyl) cyclohexane, and the like. It is done. Among these, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine is preferably used.

  Isocyanate crosslinking agents include tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), chlorophenylene diisocyanate, hexamethylene diisocyanate (HDI), tetramethylene diisocyanate, isophorone diisocyanate (IPDI), diphenylmethane diisocyanate ( MDI), diisocyanate compounds such as hydrogenated diphenylmethane diisocyanate, isocyanate compounds obtained by adding trimethylolpropane or the like to these diisocyanate compounds, isocyanurate modified products, burette modified products, and the like. Among these, adducts such as tolylene diisocyanate or trimethylolpropane are preferable because adhesion to a plastic film can be improved.

  Examples of the metal chelate crosslinking agent include compounds in which acetylacetone, ethyl acetoacetate and the like are coordinated to a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium and zirconium. It is done.

  The compounding quantity of the component (B) in the adhesive composition of this invention is 3-30 parts with respect to 100 mass parts (henceforth "part") of a component (A), Preferably it is 5-15 parts. It is. If less than 3 parts, sufficient alkali peelability cannot be obtained. If more than 30 parts, the Tg of the component (B) is high, and the pseudo-crosslinked structure with the component (A) becomes too dense. This is not preferable because the pressure-sensitive adhesive layer becomes hard and the followability to unevenness and adhesion are deteriorated.

  Moreover, the compounding quantity of a component (C) is 0.01-5 parts with respect to 100 parts of components (A), Preferably it is 0.05-3 parts. If the amount is less than 0.01 part, sufficient adhesive strength cannot be obtained, and processability is deteriorated. If the amount is more than 5 parts, the crosslinking density becomes too high, and the unevenness followability and adhesion are deteriorated. It is not preferable.

  The pressure-sensitive adhesive composition of the present invention is prepared by blending the above components (A) to (C) with other optional components as necessary and mixing them according to a conventional method. Examples of optional components that can be used include ultraviolet absorbers, antistatic agents, tackifiers, dyes, pigments, fillers, and antioxidants. These arbitrary components can be mix | blended in the range which does not impair the effect of this invention.

The pressure-sensitive adhesive sheet of the present invention is obtained by forming a pressure-sensitive adhesive layer on a substrate using the pressure-sensitive adhesive composition thus obtained. The pressure-sensitive adhesive layer is formed by applying a pressure-sensitive adhesive composition to the surface of a substrate according to a conventional method, drying and aging. Similarly, an adhesive layer may be formed on the separator and transferred to the substrate. Drying is usually 50 to 180 ° C., 1 to
It takes about 10 minutes. The aging is performed at 20 to 60 ° C. for about 1 to 14 days. The thickness of the pressure-sensitive adhesive layer is usually 5 to 100 μm, preferably about 10 to 60 μm.

  As the substrate, PET, a heat-shrinkable film (shrink film) or the like can be used. Among these, when a heat-shrinkable film is used, it is possible to further shorten the peeling time in an alkaline aqueous solution. This is because, when the temperature of the alkaline aqueous solution is set to a high temperature, the film shrinks, and the film easily peels off from the adherend due to the force. The heat shrinkable film is not particularly limited as long as it has heat shrinkability. A generally used polystyrene heat-shrinkable film, polyester heat-shrinkable film, or composite heat-shrinkable film can be suitably used.

  The pressure-sensitive adhesive sheet of the present invention is suitably used as a sheet or label that is affixed to various products or their packaging containers and displays information such as product names. And since it can peel easily in alkaline aqueous solution after use, it is suitable as a label for reusable containers such as glass containers and plastic containers such as beer bottles and liquor bottles. In particular, the pressure-sensitive adhesive sheet of the present invention has a curved surface and is suitable for beer bottles having a concavo-convex structure because it has excellent concavo-convex followability. Furthermore, such labels and the like often require transparency from the viewpoint of design and optical properties. However, this pressure-sensitive adhesive sheet is suitable because water adheres to it and is not easily whitened even in a humid heat environment.

The pressure-sensitive adhesive sheet of the present invention is excellent in releasability in an alkaline aqueous solution, but has a feature that there is little contamination of the alkaline aqueous solution, and further has excellent water resistance adhesion maintenance and water whitening resistance, and also has high unevenness followability. The reason is as follows.
That is, in the pressure-sensitive adhesive sheet of the present invention, the acrylic polymer of component (A) and the acrylic polymer of component (B) (hereinafter sometimes referred to as “(A) polymer” and “(B) polymer” respectively) A pseudo-crosslinking network is formed by electrostatic bonding between the carboxyl group and the nitrogen atom. When (A) the carboxyl group of the polymer is neutralized with an aqueous alkali solution, (B) the polymer does not participate in crosslinking at all. The polymer (B) which has lost the binding due to crosslinking has a low molecular weight and thus has high fluidity, and moves to the pressure-sensitive adhesive interface by nitrogen atoms having high water solubility. The polymer (B) having a high Tg and a low molecular weight is a non-adhesive component in itself, and the interfacial bonding force is greatly reduced by being unevenly distributed at the adherend-adhesive interface. Easy interface peeling. Thus, since the adhesive is not dissolved in the alkaline aqueous solution but peeled off by interfacial peeling, the alkaline aqueous solution is not contaminated.

  On the other hand, highly polar carboxyl groups and nitrogen atoms disperse water molecules that have infiltrated the interface between the adhesive and the adherend throughout the adhesive layer. It works to avoid the decline. The reason why the adhesive is whitened by moisture is that the moisture that has entered the vicinity of the interface or the adhesive layer becomes minute droplets and diffusely reflects light. Since highly polar carboxyl groups and nitrogen atoms disperse water molecules throughout the pressure-sensitive adhesive layer, it is possible to prevent water from forming droplets, and as a result, to suppress whitening of the pressure-sensitive adhesive. And (A) In a polymer, (meth) acrylic-acid alkylester whose glass transition temperature is less than -60 degreeC is added in a specific range, A softness | flexibility is born and uneven | corrugated followability is obtained. .

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not restrict | limited at all by these Examples.

Manufacturing example 1
Production of acrylic polymer ((A) polymer):
In a flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser, 15 parts by mass of 2-ethylhexyl acrylate (2-EHA), 75 parts by mass of n-butyl acrylate (BA), and acrylic acid (AA) 10 The contents of the flask were heated to 70 ° C. while charging 100 parts by mass of ethyl acetate and introducing nitrogen gas into the flask. Next, 0.1 part by mass of a polymerization initiator azobisisobutyronitrile (AIBN) sufficiently substituted with nitrogen gas was added to the flask under stirring. Heating and cooling were performed for 8 hours so that the temperature of the contents in the flask could be maintained at 70 ° C., and finally 30 parts of ethyl acetate was added to obtain an acrylic polymer A1 solution. Moreover, except having replaced with the monomer composition shown in Table 2, the acrylic polymer A2-A6 solution was obtained similarly.

Manufacturing example 2
Production of acrylic polymer ((B) polymer):
A flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser is charged with 2 parts by mass of dimethylaminoethyl methacrylate (DMAEMA), 98 parts by mass of methyl methacrylate (MMA), and 100 parts by mass of toluene. The contents of the flask were heated to 90 ° C. while introducing gas. Next, 0.1 part by mass of a polymerization initiator azobisisobutyronitrile (AIBN) sufficiently substituted with nitrogen gas was added to the flask under stirring. Heating and cooling were performed for 8 hours so that the temperature of the contents in the flask could be maintained at 90 ° C., and finally 30 parts of toluene was added to obtain an acrylic polymer B1 solution. Moreover, except having replaced with the monomer composition shown in Table 3, the acrylic polymer B2-3 and B6-B9 solution were obtained similarly. The acrylic polymer B4 has the same monomer composition as that of B1, but was made into a low molecular weight body by increasing the amount of toluene initially charged during the production conditions. On the other hand, B5 was also made into a high molecular weight product by reducing the amount of toluene added in the initial charge.

  About obtained acrylic polymer B1-B9, the weight average molecular weight (Mw) was measured according to the following GPC measurement conditions. The glass transition temperature (Tg) was determined from the FOX equation. The results are shown in Table 3 together with the monomer composition.

<GPC measurement conditions>
Measuring device: HLC-8120GPC (manufactured by Tosoh Corporation)
GPC column configuration: The following five columns (all manufactured by Tosoh Corporation)
(1) TSK-GEL HXL-H (guard column)
(2) TSK-GEL G7000HXL
(3) TSK-GEL GMHXL
(4) TSK-GEL GMHXL
(5) TSK-GEL G2500HXL
Diluted with tetrahydrofuran so that the sample concentration is 1.0 mg / cm ³ Mobile phase solvent: Tetrahydrofuran Flow rate: 1 ml / min
Column temperature: 40 ° C

Example 1
Production of adhesive sheet:
The solid content of acrylic polymer B1 is 10 parts by mass with respect to the solid content of 100 parts by mass of the obtained acrylic polymer A1, and the epoxy crosslinker tetrad X (N, N, N ′, N′-tetraglycidyl-m- Xylylenediamine (manufactured by Mitsubishi Gas Chemical Co., Inc.) (0.3 parts by mass) was added and mixed to prepare an adhesive composition. This was coated on a 38 μm PET film that had been subjected to a release treatment so that the thickness after drying was 50 μm, and dried at 80 ° C. for 2 minutes. After drying, a 38 μm PET film was bonded to the pressure-sensitive adhesive layer side and aged at 23 ° C. for 7 days to obtain a pressure-sensitive adhesive sheet.

Examples 2-8
A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the acrylic polymers (A) and (B) and the crosslinking agent were changed as shown in Table 4 below. Moreover, the adhesive sheet was produced like Example 1 using the obtained adhesive composition. However, in Example 6, a 20 μm styrene-based heat-shrinkable film was used as the base material.

Comparative Examples 1-12
A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the acrylic polymers (A) and (B) and the crosslinking agent were changed as shown in Table 5 below. Moreover, the adhesive sheet was produced like Example 1 using the obtained adhesive composition.

Test example 1
About the adhesive sheet obtained in Examples 1-8 and Comparative Examples 1-12, the water resistant adhesion maintenance property, wet heat whitening property, uneven | corrugated followable | trackability, and alkali peelability were evaluated with the following method. These results are summarized in Table 6.

(Water resistant adhesion maintenance)
After pasting the sample on the glass, it was immersed in room temperature water and taken out one day later, and the adhesive strength was measured immediately after that (adhesive strength after water resistance). Moreover, after sticking a sample on glass, the adhesive residual was calculated | required from the following formula by making what measured the adhesive force 20 minutes after that into initial stage adhesive force.
Adhesive remaining (%) = viscosity after water resistance ÷ initial adhesive strength × 100

(Wet heat whitening)
After pasting the sample on the glass, it was placed in 60 ° C.-95% RH for 24 hours, and then allowed to stand in a 23 ° C.-50% RH environment for 2 hours, and the haze was measured. When the haze value exceeds 1%, whitening starts to be recognized visually, so that the haze value does not exceed 1% after wet heat durability.

(Concavity and convexity followability: micro creep)
A sample is pasted on a glass plate so that the pasting area becomes 10 mm × 10 mm, a constant load of 800 g is given in the shearing direction under a 60 ° C.-dry environment for 1000 seconds, and the deviation width (μm) in the shearing direction at that time is given. It was measured. When the deviation width is 300 μm or less, it is too hard and the unevenness followability is insufficient, and when it is 550 μm or more, it is too soft and the workability is difficult.

(Alkali peelability)
A sample cut to 25 mm × 25 mm was made into a glass plate, stored at room temperature for 1 day, submerged in an aqueous NaOH solution (3 mass%) at 80 ° C., and the time (min) required for the film to peel naturally was measured. From the viewpoint of workability, it is desirable to peel within 10 minutes.

The pressure-sensitive adhesive sheet of the present invention can be promptly peeled off in an aqueous alkali solution. Moreover, since it is excellent in water-resistant adhesion maintenance property and water whitening resistance, even if water adheres, peeling and whitening hardly occur, and uneven follow-up property is high. Therefore, it is useful as a sheet or label attached to a reused container such as a beer bottle.
that's all

Claims (3)

Next component (A) thru | or (C)
(A) At least the following components (a1) to (a3)
(A1) The glass transition temperature of the homopolymer is −80 ° C. or higher and lower than −60 ° C. (Meta)
Acrylic acid alkyl ester 10-50% by mass
(A2) Acrylic acid alkyl ester having a glass transition temperature of −60 ° C. or more and 10 ° C. or less of homopolymer 40 to 85% by mass
(A3) Carboxyl group-containing radical polymerizable monomer 5 to 20% by mass
100 parts by mass of an acrylic polymer obtained by copolymerizing (B) the following components (b1) and (b2)
(B1) Nitrogen-containing radical polymerizable monomer 1 to 10% by mass
(B2) (Meth) acrylic acid alkyl ester 90-99% by mass
The molecular weight is 1000 to 50,000 and the glass transition temperature is 0 to 15
3 to 30 parts by mass of an acrylic polymer at 0 ° C. (C) A pressure-sensitive adhesive composition for labels, which contains a polyfunctional epoxy crosslinking agent.   The adhesive sheet which provides the adhesive layer formed from the adhesive composition of Claim 1 on a base material. The pressure-sensitive adhesive sheet according to claim 2, wherein the substrate is a heat-shrinkable film.