Adhesive Composition and Adhesive Film

Abstract

To provide an adhesive composition which can obtain an adhesive layer having a low water vapor transmission rate and excellent water vapor barrier properties, even though being an adhesive composition containing only acrylic monomers having a general structure and to provide an adhesive film using the same.SOLUTION: A water vapor transmission rate of an adhesive layer having a thickness of 25 μm obtained by cross-linking an adhesive composition, which comprises an acrylic polymer obtained by copolymerization of (A-1) an alkyl (meth) acrylate having 14 or more and 20 or less carbon atoms or (A-2) an alkyl (meth) acrylate having 14 or more and 20 or less carbon atoms, a (meth)acrylate containing an alkyl group having 1 or more and 13 or less carbon atoms, an alicyclic hydrocarbon group or an aromatic ring structure, (B) a (meth)acrylate containing a hydroxyl group without incorporating a vinyl monomer containing a carboxy group and a nitrogen-containing vinyl monomer and (C) a crosslinking agent, is 100 g / (m2 / day) or less under an atmosphere of 32°C×90% RH.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an adhesive composition capable of forming an adhesive layer having a low water vapor transmission rate and excellent water vapor barrier properties, and an adhesive film using the same.

Background Art

[0002] Conventionally, in specific pharmaceuticals, organic EL (organic electroluminescence) displays, electronic papers, etc., in order to avoid the adverse effects of moisture and oxygen in the atmosphere on the pharmaceuticals, light-emitting elements, etc. of the contents, the contents are sealed using a gas barrier film. In recent years, organic EL displays using self-luminous light-emitting elements have been gradually spreading as displays for televisions, smartphones, digital signage, etc. because the images are clearer than those of liquid crystal displays. In particular, since the light-emitting elements of organic EL displays are formed of organic substances with low moisture resistance, they are extremely vulnerable to moisture in the atmosphere. Therefore, conventionally, a thin glass substrate having gas barrier properties and heat resistance has been used as the base material and sealing member of the light-emitting element. However, in recent years, the flexibility of organic EL displays has been advanced, and a gas barrier film is used as a transparent base material to replace the thin glass substrate. In addition, an adhesive layer having gas barrier properties is used to bond the gas barrier films. For example, Patent Document 1 discloses a gas barrier film used for packaging applications of foods and pharmaceuticals that require high gas barrier properties, and for applications of electronic members such as solar cells, electronic papers, and organic EL displays.

[0003] In the conventional method of forming a gas barrier layer with a vapor deposition film mainly composed of silicon oxide by the plasma CVD method, the water vapor transmission rate required for organic EL display and electronic paper applications is 1×10 -3 g / (m 2· In order to obtain the following high gas barrier properties, it is necessary to thicken the vapor deposition film. However, since the formed gas barrier layer is a very dense and high-hardness layer, in the case of such a thick vapor deposition film, when the gas barrier film is bent, cracks occur in the vapor deposition film, resulting in a problem that the gas barrier property deteriorates.

[0004] Therefore, the gas barrier film of the invention according to Patent Document 1 is a gas barrier film having a gas barrier layer made of a vapor deposition film on at least one side of a polymer film substrate. The gas barrier layer includes, in order from the side of the polymer film substrate, a first layer mainly composed of a compound containing at least one element among the metal elements belonging to Groups 3 to 14 of the periodic table, and a second layer mainly composed of a silicon compound laminated in this order. Furthermore, by setting the thickness of each layer within a specific range, a gas barrier film having a high gas barrier property that is difficult to deteriorate even in a high-temperature environment or under bending can be obtained.

[0005] In addition, Patent Document 2 discloses a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet obtained from the composition, which are preferably used for sealing electronic devices such as display devices such as organic EL elements. According to the pressure-sensitive adhesive composition of the invention of Patent Document 2, by using a polyisobutylene-based resin and a polybutene resin having a specific molecular weight, the target pressure-sensitive adhesive properties can be exhibited, the water vapor transmission rate can be reduced, and the intrusion of moisture from the outside can be prevented.

[0006] In addition, Patent Document 3 discloses a pressure-sensitive adhesive composition that does not turn white even under humid heat conditions and has excellent transparency and gas barrier properties. According to the pressure-sensitive adhesive composition of the invention of Patent Document 3, by using a pressure-sensitive adhesive composition containing a tackifier resin, the gas barrier property is remarkably improved and the compatibility becomes good.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

[0008] However, the gas barrier film according to the invention described in Patent Document 1 exhibits gas barrier properties by forming a vapor deposition film of a metal thin film layer on one side of a base material using a sputtering / CVD apparatus. Therefore, for example, it is necessary to use a base material having a considerable rigidity, such as a polyester film with a thickness of 188 μm, and it could not be applied to a pressure-sensitive adhesive layer having appropriate flexibility by laminating a vapor deposition film thereon to provide gas barrier properties. In addition, since the pressure-sensitive adhesive composition according to the invention described in Patent Document 2 contains a polybutene resin which is an olefin-based resin, there is a problem that even if discoloration due to deterioration by ultraviolet rays is prevented by an antioxidant, it is inevitable that the composition will potentially discolor over time. For this reason, a pressure-sensitive adhesive composition that does not discolor due to ultraviolet rays has been demanded. In addition, in the pressure-sensitive adhesive sheet using the pressure-sensitive adhesive composition according to the invention described in Patent Document 3, in the pressure-sensitive adhesive sheets of Examples 1 to 6 in which a pressure-sensitive adhesive layer with a thickness of 100 μm was formed, the water vapor transmission rate was 70 to 110 g / (m 2 ·day). However, since the pressure-sensitive adhesive layer with a thickness of 100 μm is a thick film, it is restricted in its application range. For this reason, it has been demanded that even a thin pressure-sensitive adhesive layer has excellent water vapor barrier properties. Furthermore, in the optical pressure-sensitive adhesive film used for various displays, high transparency is required to improve visibility.

[0009] In view of the above problems, an object of the present invention is to provide an adhesive composition that can obtain an adhesive layer having a low water vapor transmission rate and excellent water vapor barrier properties, despite containing only acrylic monomers having a general structure, and an adhesive film using the same.

Means for Solving the Problems

[0010] Regarding an adhesive composition having a low moisture permeability, generally, in an adhesive layer with a thickness of 100 μm obtained from an acrylic polymer, when measuring the water vapor transmission rate, it shows a high value of 300 g / (m 2 ·day) or more. Further, since the water vapor barrier property deteriorates as the thickness of the adhesive layer becomes thinner, when the adhesive layer is made into a thin film, the value of the water vapor transmission rate will show an even higher value. The adhesive composition of the present invention that solves the above problems is characterized in that the water vapor transmission rate when the thickness of the adhesive layer is 25 μm is 100 g / (m 2 ·day) or less, and an adhesive layer having excellent water vapor barrier properties can be obtained.

[0011] The present invention uses, as an adhesive composition, at least (A-1) at least one or more alkyl (meth) acrylates having 14 to 20 carbon atoms in the alkyl group, and (B) at least one or more (meth) acrylates containing a hydroxyl group, copolymerized without containing a vinyl monomer containing a carboxyl group and a nitrogen-containing vinyl monomer such as an amino group, and (C) an adhesive composition containing a polyfunctional isocyanate compound having three or more functional groups as a crosslinking agent, and using an adhesive layer obtained by crosslinking the adhesive composition as the technical idea. As a result, it has been found that an adhesive layer having an unprecedentedly low moisture permeability can be obtained despite being an adhesive composition containing only acrylic monomers having a general structure, and the present invention has been completed.

[0012] To solve the above problems, the present invention provides an adhesive composition containing an acrylic polymer obtained by copolymerizing only (meth)acrylate as a monomer component and a (C) crosslinking agent, wherein when the thickness of the adhesive layer formed by crosslinking the adhesive composition is 25 μm, the water vapor transmission rate of the adhesive layer, measured using the infrared sensor method in accordance with JIS K7129, is 100 g / (m 2 ·day) or less in an atmosphere of 32°C × 90% RH.

[0013] The acrylic polymer contained in the adhesive composition is (A-1) at least one or more alkyl (meth)acrylates having 14 to 20 carbon atoms in the alkyl group, with a total of 100 parts by weight, or (A-2) at least one or more alkyl (meth)acrylates having 14 to 20 carbon atoms in the alkyl group, with a total of 85 to 100 parts by weight, and at least one or more selected from the group of compounds consisting of alkyl (meth)acrylates having 1 to 13 carbon atoms in the alkyl group, (meth)acrylates containing an alicyclic hydrocarbon group, and (meth)acrylates containing an aromatic ring structure, with a total of 15 to 0.0 parts by weight, and the total is 100 parts by weight, (B) at least one or more (meth)acrylates containing a hydroxyl group, with a total of 0.1 to 5.0 parts by weight, and is an acrylic polymer having a weight average molecular weight of 50,000 to 1,500,000 copolymerized without containing a vinyl monomer containing a carboxyl group and a nitrogen-containing vinyl monomer, Preferably, the adhesive composition contains a polyfunctional isocyanate compound having three or more functional groups as the (C) crosslinking agent in a proportion of 0.01 to 2.0 parts by weight with respect to 100 parts by weight of the acrylic polymer.

[0014] The SP value of the acrylic polymer is preferably 9.0 (cal / cm 3 ) 0.5 or less.

[0015] A pressure-sensitive adhesive film is formed by laminating a pressure-sensitive adhesive layer with a thickness of 25 μm, obtained by crosslinking the pressure-sensitive adhesive composition, on one side of a polyester film substrate with a thickness of 50 μm. When the adhesive strength of the pressure-sensitive adhesive layer is measured in accordance with JIS Z0237, the adhesive strength of the pressure-sensitive adhesive layer with respect to a high-density polyethylene resin is preferably 10 N / 25 mm or more.

[0016] It is preferable that the acrylic polymer contains, in a proportion of 80 parts by weight or more in total, at least one or more alkyl (meth) acrylates having 14 to 20 carbon atoms in the alkyl group, based on 100 parts by weight of the acrylic polymer.

[0017] It is preferable that the (meth) acrylate containing a hydroxyl group in (B) is at least one selected from the group of compounds consisting of 8-hydroxyoctyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 2-hydroxyethyl (meth) acrylate.

[0018] When the thickness of the pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition is 25 μm, the total light transmittance is preferably 90% or more and the haze value is preferably 1.0% or less.

[0019] The present invention also provides a pressure-sensitive adhesive film formed by forming a pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition on at least one side of a substrate.

Advantages of the Invention

[0020] Despite being a pressure-sensitive adhesive composition containing only acrylic monomers having a general structure, the pressure-sensitive adhesive composition of the present invention can provide a pressure-sensitive adhesive layer with a low water vapor transmission rate and excellent water vapor barrier properties.

Embodiments for Carrying Out the Invention

[0021] Hereinafter, the present invention will be described based on preferred embodiments.

[0022] The pressure-sensitive adhesive composition of this embodiment is a pressure-sensitive adhesive composition containing an acrylic polymer obtained by copolymerizing only (meth)acrylate as a monomer component and a (C) crosslinking agent. When the thickness of the pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition is 25 μm, the water vapor transmission rate of the pressure-sensitive adhesive layer, when measured using the infrared sensor method in accordance with JIS K7129, is 100 g / (m 2 ·day) or less under the atmosphere of 32 °C × 90% RH, which is characterized by this.

[0023] The acrylic polymer functions as the main component of the pressure-sensitive adhesive composition. As the monomer component constituting the acrylic polymer, (meth)acrylate is preferable. The (meth)acrylate may be one or more kinds of acrylate, one or more kinds of methacrylate, or a mixture of one or more kinds of acrylate and one or more kinds of methacrylate. Further, in order for the pressure-sensitive adhesive composition of the present invention to be a pressure-sensitive adhesive composition containing only acrylic monomers having a general structure, the acrylic polymer does not contain copolymerizable monomer components other than (meth)acrylate, such as amide monomers such as (meth)acrylamide, nitrile monomers such as (meth)acrylonitrile, olefin monomers such as styrene, vinyl esters such as vinyl acetate, etc., which is preferable. Furthermore, when the adherend of the pressure-sensitive adhesive layer is a metal surface such as indium tin oxide (ITO), the acrylic polymer preferably does not contain a (meth)acrylate ester monomer having a carboxy group and a compound that causes corrosion of the metal surface, such as (meth)acrylic acid and (meth)acrylate, although it will be described in detail later.

[0024] Examples of the (meth)acrylate that is the main component of the monomer component include at least one or more of (A-1) alkyl (meth)acrylates having 14 to 20 carbon atoms in the alkyl group, or (A-2) at least one or more of alkyl (meth)acrylates having 14 to 20 carbon atoms in the alkyl group and at least one or more selected from the group consisting of alkyl (meth)acrylates having 1 to 13 carbon atoms in the alkyl group, (meth)acrylates containing an alicyclic hydrocarbon group, and (meth)acrylates containing an aromatic ring structure.

[0025] Specific examples of the alkyl (meth)acrylate having 14 to 20 carbon atoms in the alkyl group, which is commonly used in (A-1) and (A-2), include alkyl (meth)acrylates having 14 carbon atoms in the alkyl group, such as tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, myristyl (meth)acrylate, and isomyristyl (meth)acrylate; alkyl (meth)acrylates having 15 carbon atoms in the alkyl group, such as pentadecyl (meth)acrylate and isopentadecyl (meth)acrylate; alkyl (meth)acrylates having 16 carbon atoms in the alkyl group, such as hexadecyl (meth)acrylate, isohexadecyl (meth)acrylate, cetyl (meth)acrylate, and isocetyl (meth)acrylate; alkyl (meth)acrylates having 17 carbon atoms in the alkyl group, such as heptadecyl (meth)acrylate and isooctadecyl (meth)acrylate; alkyl (meth)acrylates having 18 carbon atoms in the alkyl group, such as octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (meth)acrylate; alkyl (meth)acrylates having 19 carbon atoms in the alkyl group, such as nonadecyl (meth)acrylate and isononadecyl (meth)acrylate; and alkyl (meth)acrylates having 20 carbon atoms in the alkyl group, such as icosyl (meth)acrylate and isicosyl (meth)acrylate. At least one or more selected from the group consisting of them are included.

[0026] Among the above (A-2), examples of the alkyl (meth)acrylate in which the alkyl group has 1 to 13 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, isohexyl (meth)acrylate, heptyl (meth)acrylate, isoheptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, isoundecyl (meth)acrylate, dodecyl (meth)acrylate, isododecyl (meth)acrylate, tridecyl (meth)acrylate, isotridecyl (meth)acrylate, and the like.

[0027] Among the above (A-2), specific examples of the (meth)acrylate containing an alicyclic hydrocarbon group include at least one selected from the group consisting of (meth)acrylates containing a monocyclic alicyclic hydrocarbon group such as cyclopentyl (meth)acrylate and cyclohexyl (meth)acrylate; and (meth)acrylates containing a polycyclic alicyclic hydrocarbon group such as isobornyl (meth)acrylate, bicycloheptyl (meth)acrylate, bicyclooctyl (meth)acrylate, dimethylbicycloheptyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentenyl oxyethyl (meth)acrylate.

[0028] Among the above (A-2), examples of the (meth)acrylate containing an aromatic ring structure include at least one or more of benzyl (meth)acrylate, naphthyl (meth)acrylate, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxybutyl (meth)acrylate, phenoxyethoxyethyl (meth)acrylate, 2-(1-naphthyloxy)ethyl (meth)acrylate, 2-(2-naphthyloxy)ethyl (meth)acrylate, 6-(1-naphthyloxy)hexyl (meth)acrylate, 6-(2-naphthyloxy)hexyl (meth)acrylate, 8-(1-naphthyloxy)octyl (meth)acrylate, 8-(2-naphthyloxy)octyl (meth)acrylate, etc. The (meth)acrylate containing an aromatic ring structure is preferably a (meth)acrylate that does not contain a hydroxyl group, a carboxyl group, or a nitrogen atom. For example, (meth)acrylates containing an aromatic hydrocarbon group, alkyl (meth)acrylates containing an aromatic hydrocarbon group, alkyl (meth)acrylates containing an aromatic ether group, etc. can be mentioned.

[0029] The above (A-1) may be composed of a total of 100 parts by weight of two or more alkyl (meth)acrylates having 14 to 20 carbon atoms in the alkyl group. Also, among the total 100 parts by weight of the above (A-2), the total of at least one or more alkyl (meth)acrylates having 14 to 20 carbon atoms in the alkyl group is 85 to 100 parts by weight, and the total of at least one or more selected from the group of compounds consisting of alkyl (meth)acrylates having 1 to 13 carbon atoms in the alkyl group, (meth)acrylates containing an alicyclic hydrocarbon group, and (meth)acrylates containing an aromatic ring structure is 15 to 0.0 parts by weight. Further, among the total 100 parts by weight of the above (A-2), it is preferable in terms of reducing the water vapor transmission rate of the pressure-sensitive adhesive layer that the total of at least one or more alkyl (meth) acrylates having an alkyl group with 14 to 20 carbon atoms is 85 to 100 parts by weight, and at least one or more specific (meth) acrylates selected from the group of compounds consisting of alkyl (meth) acrylates having an alkyl group with 1 to 13 carbon atoms, (meth) acrylates containing an alicyclic hydrocarbon group, and (meth) acrylates containing an aromatic ring structure are contained in a specific ratio range.

[0030] For example, with respect to 100 parts by weight of the acrylic polymer, it is preferably contained in a ratio such that the total of one or more alkyl (meth) acrylates having an alkyl group with 14 to 20 carbon atoms is 80 parts by weight or more, more preferably 85 parts by weight or more, and particularly preferably 90 parts by weight or more. Also, with respect to 100 parts by weight of the acrylic polymer, it is preferably contained in a ratio such that the total of at least one or more selected from alkyl (meth) acrylates having an alkyl group with 1 to 13 carbon atoms, (meth) acrylates containing an alicyclic hydrocarbon group, or (meth) acrylates containing an aromatic ring structure is 20 parts by weight or less, more preferably 15 parts by weight or less, and particularly preferably 10 parts by weight or less. Further, in order to suppress the influence of ultraviolet rays and the like, as the (meth) acrylate containing an alicyclic hydrocarbon group and the (meth) acrylate containing an aromatic ring structure, it is preferable to select a compound having no olefinic double bond in the side chain portion of the acrylic polymer.

[0031] Incidentally, the reason why the pressure-sensitive adhesive layer obtained by using the pressure-sensitive adhesive composition according to the present invention has excellent gas barrier properties is not clear at present, but it is presumed as follows. That is, out of 100 parts by weight of the acrylic polymer, an alkyl (meth)acrylate having a long-chain alkyl group and having 14 or more and 20 or less carbon atoms in the alkyl group is contained in a proportion of 80 parts by weight or more. As a result, the hydrophilicity of the acrylic polymer is suppressed and the hydrophobicity becomes stronger, so that the moisture that has penetrated into the pressure-sensitive adhesive layer is difficult to be absorbed by the pressure-sensitive adhesive layer and is also difficult to permeate through the pressure-sensitive adhesive layer. It is presumed that the water vapor transmission rate of the pressure-sensitive adhesive layer is reduced. Therefore, further, if the number of carbon atoms in the long-chain alkyl group is increased to more than 20 to lengthen the molecular structure of the alkyl (meth)acrylate, it is considered that the hydrophobicity of the acrylic polymer becomes stronger. However, in this case, since the viscosity of the pressure-sensitive adhesive composition in which the acrylic polymer is dissolved increases, there is a problem that it becomes difficult to apply it to a substrate and laminate a pressure-sensitive adhesive layer. Therefore, in the pressure-sensitive adhesive composition according to the present embodiment, out of 100 parts by weight of the acrylic polymer, the total of at least one or more alkyl (meth)acrylates having 14 or more and 20 or less carbon atoms in the alkyl group is contained in a proportion of 80 to 100 parts by weight. This is preferable because a practical pressure-sensitive adhesive composition for solving the problems of the present invention can be obtained.

[0032] Specific examples of the (B) (meth)acrylate containing a hydroxyl group include at least one or more of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2,3-dihydroxypropyl (meth)acrylate, polyethylene glycol mono (meth)acrylate, polypropylene glycol mono (meth)acrylate, and other polyalkylene glycol mono (meth)acrylates.

[0033] The (meth)acrylate containing a hydroxyl group (B) is preferably contained in a proportion of 0.1 to 5.0 parts by weight, more preferably 0.6 to 5.0 parts by weight, and particularly preferably 1.2 to 5.0 parts by weight, based on 100 parts by weight in total of the above (A-1) or (A-2). Further, the (meth)acrylate containing a hydroxyl group (B) is preferably a hydroxyl group-substituted alkyl (meth)acrylate having 2 or more to 8 or less carbon atoms in the alkyl group. Among them, at least one selected from the group of compounds consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate is preferable. Furthermore, the (meth)acrylate containing a hydroxyl group (B) is more preferably a hydroxyl group-substituted alkyl (meth)acrylate having 4 or more to 8 or less carbon atoms in the alkyl group, and at least one selected from the group of compounds consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate is particularly preferable because it can increase the cohesive force of the pressure-sensitive adhesive layer and thus increase the adhesive force.

[0034] The acrylic polymer is preferably an acrylic polymer copolymerized without containing a vinyl monomer containing a carboxy group. Examples of the vinyl monomer containing a carboxy group include carboxy group-containing monomers having no ester group such as (meth)acrylic acid, itaconic acid, crotonic acid, maleic acid, and fumaric acid; (meth)acrylate monomers having a carboxy group such as carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl maleic acid, carboxypolycaprolactone mono(meth)acrylate, and 2-(meth)acryloyloxyethyl tetrahydrophthalic acid, but are not limited thereto.

[0035] The acrylic polymer is preferably an acrylic polymer copolymerized without containing a nitrogen-containing vinyl monomer. Examples of the nitrogen-containing vinyl monomer include cyclic (meth)acrylamides such as N-(meth)acryloylmorpholine, N-(meth)acryloylpyrrolidine, and N-(meth)acryloylpiperidine; N-vinyl group-containing cyclic monomers such as N-vinylpyrrolidone; acyclic (meth)acrylamides such as (meth)acrylamide, N-alkyl (meth)acrylamide, and N,N-dialkyl (meth)acrylamide; substituted amino group-containing (meth)acrylates such as N,N-dialkylaminoalkyl (meth)acrylate; substituted amino group-containing (meth)acrylamides such as N,N-dialkylaminoalkyl (meth)acrylamide; nitrile group-containing vinyl monomers such as (meth)acrylonitrile; isocyanate group-containing vinyl monomers; quaternary ammonium group-containing vinyl monomers such as (meth)acryloyloxyalkyltrimethylammonium salt, but are not limited thereto.

[0036] Note that the pressure-sensitive adhesive sheet according to the invention described in Patent Document 3 mentioned above requires copolymerizing an acrylate polymer with an amide group-containing monomer as an essential requirement. However, the pressure-sensitive adhesive composition of the present embodiment does not have an amide group-containing monomer as an essential component. Therefore, according to the present embodiment, even a pressure-sensitive adhesive composition containing an acrylic polymer obtained by copolymerizing only (meth)acrylate as a monomer component can have a low water vapor transmission rate and obtain a pressure-sensitive adhesive layer excellent in water vapor barrier properties.

[0037] The polymerization method of the copolymer used as the acrylic polymer is not particularly limited, and known polymerization methods such as solution polymerization method and emulsion polymerization method can be appropriately used. The acrylic polymer is preferably an acrylic polymer having a weight average molecular weight of 50,000 to 1,500,000, more preferably an acrylic polymer having a weight average molecular weight of 150,000 to 1,500,000, and particularly preferably an acrylic polymer having a weight average molecular weight of 300,000 to 1,500,000.

[0038] The acrylic polymer is preferably an acrylic polymer having an acid value of 0. The acrylic polymer is preferably a copolymerized acrylic polymer that does not contain acidic monomers such as vinyl monomers containing a sulfonic acid group and vinyl monomers containing a phosphonic acid group, in addition to vinyl monomers containing a carboxy group. Since acidic groups such as carboxy groups have high hydrophilicity, copolymerizing an acidic monomer with the acrylic polymer may increase the water vapor transmission rate and reduce the water vapor barrier properties. In addition, when the adherend is a metal surface such as indium tin oxide (ITO), a pressure-sensitive adhesive layer containing an acrylic polymer copolymerized with a vinyl monomer containing a carboxy group may corrode the metal surface and cause a change in the resistance value of the transparent conductive film. Therefore, the acrylic polymer is preferably a copolymerized acrylic polymer that does not contain a vinyl monomer containing a carboxy group, which is a compound that causes corrosion of the metal surface.

[0039] Examples of the crosslinking agent (C) include at least one or more polyisocyanate compounds such as diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate; biuret modified products thereof; isocyanurate modified products thereof; and adducts with polyhydric alcohols having a valency of 3 or more such as trimethylolpropane and glycerin. The polyisocyanate compound can crosslink the pressure-sensitive adhesive composition by reacting with the (meth)acrylate containing a hydroxyl group (B), even if it is an acrylic polymer copolymerized without containing a vinyl monomer containing a carboxy group. It is preferable that the pressure-sensitive adhesive composition contains an isocyanate compound having a functionality of 3 or more in a proportion of 0.01 to 2.0 parts by weight with respect to 100 parts by weight of the acrylic polymer as the crosslinking agent (C). When the polyisocyanate compound has a functionality of 3 or more, a higher density of crosslinking becomes possible compared to the case of a bifunctional compound. If the amount of the crosslinking agent (C) used is too large, gaps may occur between the polymer chains of the acrylic polymer, increasing the water vapor transmission rate and possibly reducing the water vapor barrier properties.

[0040] As optional components, the pressure-sensitive adhesive composition can be appropriately blended with known additives such as silane coupling agents, antioxidants, antistatic agents, surfactants, curing accelerators, plasticizers, fillers, crosslinking catalysts, crosslinking retardants, curing retardants, processing aids, and anti-aging agents. These can be used alone or in combination of two or more. Note that the pressure-sensitive adhesive sheet of Patent Document 3 has a tackifier resin such as terpene phenol resin as an essential component, but the pressure-sensitive adhesive composition of the present embodiment does not have a tackifier resin as an essential component. Therefore, according to the present embodiment, a pressure-sensitive adhesive composition having only the acrylic polymer as a resin component, and even a pressure-sensitive adhesive composition containing only acrylic monomers having a general structure, can obtain a pressure-sensitive adhesive layer with a low water vapor transmission rate and excellent water vapor barrier properties. Therefore, the pressure-sensitive adhesive composition of the present embodiment can produce a high-quality pressure-sensitive adhesive layer that can also be bonded to high-quality optical members.

[0041] The pressure-sensitive adhesive layer according to this embodiment can be obtained by applying the pressure-sensitive adhesive composition to a base material or a release film and then crosslinking the pressure-sensitive adhesive composition. The gel fraction of the pressure-sensitive adhesive layer after crosslinking is preferably, in some cases, 40 to 85%, 60 to 90%, or 95 to 100%. In order to advance the reaction of the crosslinking agent (C), it is preferable to store the pressure-sensitive adhesive layer under predetermined temperature conditions for aging. The thickness of the pressure-sensitive adhesive layer can be appropriately set depending on the application and the like. For example, the thickness can be 1 to 50 μm, and a thickness of 1 to 25 μm is preferable.

[0042] When the thickness of the pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition is 25 μm, the water vapor transmission rate of the pressure-sensitive adhesive layer, when measured using the infrared sensor method in accordance with JIS K7129, is 2 100 g / (m 2 ·day) or less, preferably 90 g / (m 2 ·day) or less, in an atmosphere of 32 °C × 90% RH. Details of the method for measuring the water vapor transmission rate are described in Method B of JIS K7129 "Plastics - Films and Sheets - Method for Determining Water Vapor Transmission Rate (Instrumental Measurement Method)" revised in 2008, or JIS K7129-2 "Plastics - Films and Sheets - Method for Determining Water Vapor Transmission Rate - Part 2: Infrared Sensor Method" established in 2019.

[0043] The SP value (solubility parameter) of the acrylic polymer is preferably 3 9.0 (cal / cm 3 ) 0.5 or less. Also, the SP value of the polymer used in the pressure-sensitive adhesive composition according to this embodiment is a value calculated using Fedors' equation, which is a measure for determining the compatibility when mixing polymers. According to Fedors' equation, the cohesive energy ΔE i (cal / mol) and molar volume ΔV i (cm 3 / mol) values are used to calculate the SP value by the following equation. Note that the 0.5 power (or 1 / 2 power) is synonymous with the square root. SP = (ΣΔE i / ΣΔV i ) 0.5

[0044] In the Fedors' equation, the subscript i represents the number assigned to each structural unit, and Σ represents the sum with respect to the subscript i. When there are multiple identical structural units in the molecule, if the number corresponding to the subscript i is n i then, instead of ΣΔE i we can use Σ(n i ×ΔE i ), and instead of ΣΔV i we can use Σ(n i ×ΔV i ). When it is difficult to represent the proportion of each structural unit as an integer ratio, non-integer ratios (such as mole fractions) can be used for n i .

[0045] The pressure-sensitive adhesive composition is a pressure-sensitive adhesive film obtained by laminating a pressure-sensitive adhesive layer with a thickness of 25 μm formed by crosslinking the pressure-sensitive adhesive composition on one side of a polyester film substrate with a thickness of 50 μm. When the adhesive strength of the pressure-sensitive adhesive layer is measured in accordance with JIS Z0237, it is preferable that the adhesive strength of the pressure-sensitive adhesive layer with respect to a high-density polyethylene resin is 10 N / 25 mm or more. Examples of the adherend used in the adhesive strength test include polyethylene resins such as high-density polyethylene. Since the SP value of polyethylene is about 7.7 to 8.4, if the SP value of the acrylic polymer is greater than 9.0, it will cause a decrease in the adhesive strength with respect to the polyethylene resin as the adherend.

[0046] When the pressure-sensitive adhesive layer is used for bonding optical members such as optical films and optical glasses, in order to reduce the reflection of light at the interface between the pressure-sensitive adhesive layer and the optical member, it is desirable that the difference in refractive index is as small as possible. For this reason, it is preferable that the refractive index of the pressure-sensitive adhesive layer is 1.47 to 1.50. The refractive index of the pressure-sensitive adhesive layer can be adjusted by the addition ratio of monomer components such as (meth)acrylates containing an aromatic ring structure. By containing 3 to 30 parts by weight of a (meth)acrylate monomer containing an aromatic ring structure out of a total of 100 parts by weight of the component (A-2), the refractive index of the pressure-sensitive adhesive layer can be set to a value of 1.47 to 1.50.

[0047] When the pressure-sensitive adhesive layer is used in a display device such as an organic EL display, a liquid crystal display, or an electronic paper, it is preferably a pressure-sensitive adhesive layer having excellent transparency. Specifically, for the pressure-sensitive adhesive composition, the total light transmittance of the pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition is preferably 90% or more, more preferably 92% or more, and particularly preferably 94% or more when the thickness is 25 μm. Also, for the pressure-sensitive adhesive composition, the haze value of the pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition is preferably 1.0% or less, more preferably 0.8% or less, and particularly preferably 0.6% or less when the thickness is 25 μm. According to the pressure-sensitive adhesive composition of the present embodiment, a pressure-sensitive adhesive layer having a low water vapor transmission rate and excellent water vapor barrier properties can be obtained without adding additives such as fillers. Therefore, light scattering by additives and the like is suppressed, and a pressure-sensitive adhesive layer having a high total light transmittance, a low haze value, and excellent transparency can be obtained.

[0048] The pressure-sensitive adhesive film of the present embodiment is formed by forming a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition on at least one side of a base material. As the base material film used for forming the pressure-sensitive adhesive layer and the release film (separator) for protecting the pressure-sensitive adhesive surface, a resin film such as a polyester film can be used. The base material film can be subjected to an antifouling treatment with a silicone-based, fluorine-based release agent or coating agent, silica fine particles, etc., and an antistatic treatment by coating or kneading an antistatic agent on the surface opposite to the side where the pressure-sensitive adhesive layer of the resin film is formed.

[0049] The release film is subjected to a release treatment on the surface that is mated with the adhesive surface of the adhesive layer, using a silicone-based or fluorine-based release agent or the like. By laminating the surfaces of the adhesive layer that have been subjected to the release treatment of the release film on both sides, a structure of "release film / adhesive layer / release film" can also be formed. In this case, the peeling force required to peel the release film from the adhesive layer may be the same on both sides of the adhesive layer, or may be different from each other.

[0050] By peeling at least one of the release films from the adhesive film to expose the adhesive surface of the adhesive layer, it becomes possible to laminate with an optical member such as an optical film. Examples of the optical film include a polarizing film, a retardation film, an antireflection film, an antiglare film, an ultraviolet absorption film, an infrared absorption film, an optical compensation film, a brightness enhancement film, and a substrate film for a light-emitting element in an organic EL display. The optical film may be various optical films for an organic EL display, various optical films for a liquid crystal display, various optical films for a touch panel, or various optical films for an electronic paper. Since the optical film laminated with the adhesive layer or the adhesive film of the present embodiment can be applied to, for example, an organic EL display, a liquid crystal display, a touch panel, an electronic paper, etc., the adhesive composition according to the present invention and the adhesive film using the same have great industrial utility value.

Example

[0051] Hereinafter, the present invention will be specifically described with reference to examples.

[0052] <Production of acrylic polymer and adhesive composition> [Example 1] A nitrogen gas was introduced into a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet tube to replace the air in the reaction apparatus with the nitrogen gas. Thereafter, tetradecyl methacrylate (95 parts by weight), benzyl acrylate (5 parts by weight), and 8-hydroxyoctyl acrylate (3.0 parts by weight) were added to the reaction apparatus together with a solvent (ethyl acetate) at the following ratios. Thereafter, azobisisobutyronitrile as a polymerization initiator was added dropwise over 2 hours, and then the polymerization reaction was continued to obtain a solution of the acrylic polymer of Example 1. To the solution of the acrylic polymer of Example 1, Coronate (registered trademark) L as a crosslinking agent was added at a ratio of 0.4 part by weight, and then stirred and mixed to obtain the adhesive composition of Example 1.

[0053] [Examples 2 to 6 and Comparative Examples 1 to 7] Solutions of acrylic polymers of Examples 2 to 6 and Comparative Examples 1 to 7 were obtained in the same manner as the solution of the acrylic polymer of Example 1 above, except that the monomer compositions were used as described in Groups (A) and (B) of Table 1, respectively. Also, adhesive compositions of Examples 2 to 6 and Comparative Examples 1 to 7 were obtained in the same manner as the adhesive composition of Example 1 above, except that the crosslinking agents were used as described in Group (C) of Table 1.

[0054] [Table 1]

[0055] In Examples 1, 3, 4, 6 and Comparative Examples 4 to 7 in Table 1, the monomers in group (A) contain at least one or more of (A-2) alkyl (meth) acrylates having 14 or more and 20 or less carbon atoms in the alkyl group, and alkyl (meth) acrylates having 1 or more and 13 or less carbon atoms in the alkyl group, (meth) acrylates containing an alicyclic hydrocarbon group, and at least one or more selected from the group of compounds consisting of (meth) acrylates containing an aromatic ring structure. In Examples 2 and 5, the monomers in group (A) are at least one or more of (A-1) alkyl (meth) acrylates having 14 or more and 20 or less carbon atoms in the alkyl group. In Examples 1 to 7 and Comparative Examples 4 to 7, with respect to 100 parts by weight of the acrylic polymer, the total of at least one or more of alkyl (meth) acrylates having 14 or more and 20 or less carbon atoms in the alkyl group contains 80 parts by weight or more. In Comparative Examples 1 to 3, with respect to 100 parts by weight of the acrylic polymer, the total of at least one or more of alkyl (meth) acrylates having 14 or more and 20 or less carbon atoms in the alkyl group is less than 80 parts by weight.

[0056] In Table 1, the value in parts by weight obtained by setting the total of the monomers in group (A) to 100 parts by weight is shown with an abbreviation corresponding to the compound name. Further, in groups (B) and (C), the numerical value in parts by weight obtained by setting the acrylic polymer to 100 parts by weight is shown in parentheses ( ). The abbreviations corresponding to the compound names used in Table 1 are as follows.

[0057] In Table 1, among group (A), for alkyl (meth) acrylates having 14 or more and 20 or less carbon atoms in the alkyl group, tetradecyl methacrylate is denoted as "TDMA", tetradecyl acrylate as "TDA", pentadecyl acrylate as "PDA", hexadecyl methacrylate as "HDMA", and isostearyl acrylate as "ISTA". Also, among the group (A), for the (meth)acrylate containing an alicyclic hydrocarbon group and the (meth)acrylate containing an aromatic ring structure, benzyl acrylate was denoted as "BZA" and isobornyl acrylate was denoted as "IBOA". Also, among the group (A), for the alkyl (meth)acrylate having 1 to 13 carbon atoms in the alkyl group and the nitrogen-containing vinyl monomer, 2-ethylhexyl acrylate was denoted as "2EHA", n-butyl acrylate was denoted as "BA", methyl acrylate was denoted as "MA", and N,N-dimethylacrylamide was denoted as "DMAA".

[0058] Also, in Table 1, for the group (B), 8-hydroxyoctyl acrylate was denoted as "8HOA", 6-hydroxyhexyl acrylate was denoted as "6HHA", 4-hydroxybutyl acrylate was denoted as "4HBA", 2-hydroxyethyl acrylate was denoted as "HEA", and acrylic acid was denoted as "AAc".

[0059] Also, in Table 1, for the group (C), Coronate (registered trademark) L (trade name of Tosoh Corporation: TMP adduct of TDI) was denoted as "L", Coronate (registered trademark) HX (trade name of Tosoh Corporation: isocyanurate of HDI) was denoted as "HX", Coronate (registered trademark) HL (trade name of Tosoh Corporation: HDI adduct) was denoted as "HL", and Takenate (registered trademark) D-110N (trade name of Mitsui Chemicals, Inc.: XDI adduct) was denoted as "D-110N". Here, "TDI" means tolylene diisocyanate, "TMP" means trimethylolpropane, "HDI" means hexamethylene diisocyanate, and "XDI" means xylylene diisocyanate, respectively.

[0060] <Manufacture of Adhesive Layer and Adhesive Film> The pressure-sensitive adhesive compositions of Examples 1 to 6 and Comparative Examples 1 to 7 were each applied to the surface of a release film (a polyethylene terephthalate (PET) film coated with a silicone resin). After removing the solvent by drying at 90°C after application, they were aged for 7 days in an atmosphere of 23°C and 50% RH. Thereby, pressure-sensitive adhesive films of Examples 1 to 6 and Comparative Examples 1 to 7 having a pressure-sensitive adhesive layer with a thickness of 25 μm formed by crosslinking the pressure-sensitive adhesive composition on one side of the release film were obtained.

[0061] <Test Methods and Evaluations> From the pressure-sensitive adhesive films of Examples 1 to 6 and Comparative Examples 1 to 7, the release film (PET film coated with a silicone resin) was peeled off to expose the pressure-sensitive adhesive layer.

[0062] <Method for Measuring Water Vapor Transmission Rate> The water vapor transmission rate [g / (m 2 ·day)] of the pressure-sensitive adhesive layer with a thickness of 25 μm was measured by the infrared sensor method in accordance with Method B of JIS K7129 using the MOCON (registered trademark) water vapor transmission rate measuring device PERMATRAN-W (registered trademark) 3 / 34G of Hitachi High-Tech Science Corporation. It was measured by converting from the amount of water vapor (g) that permeated in 24 h in an atmosphere of 32°C × 90% RH to per square meter of area. 2 When the measured value was 900 g / (m 2 ·day) or more, since the upper limit value of the measurement of the measuring device was reached, the measured value was not specified and was taken as "900 g / (m 2 ·day) or more".

[0063] <Method for Measuring Adhesive Strength> A pressure-sensitive adhesive layer with a thickness of 25 μm was transferred onto one side of a polyester film substrate with a thickness of 50 μm to obtain a pressure-sensitive adhesive film (an optical film with a pressure-sensitive adhesive layer) as a sample. The obtained pressure-sensitive adhesive film was bonded to the surface of a high-density polyethylene resin with a thickness of 2 mm using a pressure roller, and then autoclave-treated under the conditions of 50 °C and 0.5 MPa for 20 minutes. After that, it was returned to the atmosphere of 23 °C and 50% RH and left for 1 hour. As a method for measuring the adhesive force when peeling the pressure-sensitive adhesive film from the surface of the high-density polyethylene resin, the peel strength of the pressure-sensitive adhesive film was measured by a tensile tester in accordance with JIS Z0237 (Test Method for Pressure-Sensitive Tape and Pressure-Sensitive Sheet), and the peel strength when peeling at a speed of 300 mm / min in the 180° direction was taken as the adhesive force (N / 25 mm) of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive film.

[0064] <Method for Measuring Total Light Transmittance> Regarding the pressure-sensitive adhesive layer with a thickness of 25 μm, using a haze meter (product name: NDH4000) manufactured by Nippon Denshoku Industries Co., Ltd., in accordance with JIS K7361-1 (Plastics - Test Method for Total Light Transmittance of Transparent Materials - Part 1: Single Beam Method), the total light transmittance (%) of the pressure-sensitive adhesive layer was measured.

[0065] <Method for Measuring Haze Value> Regarding the pressure-sensitive adhesive layer with a thickness of 25 μm, using a haze meter (product name: NDH4000) manufactured by Nippon Denshoku Industries Co., Ltd., in accordance with JIS K7136 (Plastics - Method for Determining Haze of Transparent Materials), the haze value (%) of the pressure-sensitive adhesive layer was measured.

[0066] Table 2 shows the measurement results related to the evaluation of the pressure-sensitive adhesive layer. Further, in Table 2, the weight average molecular weight and SP value of the acrylic polymer are shown in the columns of "Polymer Molecular Weight" and "Polymer SP Value", respectively.

[0067]

Table 2

[0068] According to the test results in Table 2, for the pressure-sensitive adhesive films of Examples 1 to 6 of the present invention, when the water vapor transmission rate of the pressure-sensitive adhesive layer with a thickness of 25 μm was measured using the infrared sensor method in accordance with JIS K7129, it was 100 g / (m 2 ·day) or less under the atmosphere of 32 °C × 90% RH, and the water vapor barrier property of the pressure-sensitive adhesive layer was excellent. In addition, the pressure-sensitive adhesive films of Examples 1 to 6 of the present invention were pressure-sensitive adhesive films in which a pressure-sensitive adhesive layer with a thickness of 25 μm was laminated on one side of a polyester film substrate with a thickness of 50 μm. When the adhesive strength of the pressure-sensitive adhesive layer was measured in accordance with JIS Z0237, the adhesive strength of the pressure-sensitive adhesive layer with respect to the high-density polyethylene resin was 10 N / 25 mm or more, and the adhesive strength of the pressure-sensitive adhesive layer was excellent. In addition, for the pressure-sensitive adhesive films of Examples 1 to 6 of the present invention, the total light transmittance of the pressure-sensitive adhesive layer with a thickness of 25 μm was 90% or more, and the haze value was 1.0% or less, and the transparency of the pressure-sensitive adhesive layer was excellent. That is, according to the pressure-sensitive adhesive films of Examples 1 to 6 of the present invention, the problems of the present invention can be solved.

[0069] In addition, for the pressure-sensitive adhesive films of Comparative Examples 1 to 3 of the present invention, since the acrylic polymer is mainly composed of an alkyl (meth) acrylate having 8 or 4 carbon atoms in the alkyl group, the water vapor transmission rate is high and the water vapor barrier property is poor. In addition, the adhesive strength of the pressure-sensitive adhesive films of Comparative Examples 1 to 3 of the present invention with respect to the high-density polyethylene resin was low.

[0070] In addition, for the pressure-sensitive adhesive films of Comparative Examples 4 and 6 of the present invention, since the acrylic polymer does not contain a (meth) acrylate containing a hydroxyl group and contains a vinyl monomer containing a carboxyl group, the water vapor transmission rate is high and the water vapor barrier property is poor. In addition, the adhesive strength of the pressure-sensitive adhesive films of Comparative Examples 4 and 6 of the present invention with respect to the high-density polyethylene resin was low.

[0071] In addition, in the pressure-sensitive adhesive films of Comparative Examples 5 and 7 of the present invention, since there is an excessive amount of a crosslinking agent for crosslinking the acrylic polymer, the crosslinking points of the acrylic polymer are unevenly distributed, and it is considered that the reason is that there are many gaps in the network structure of the acrylic polymer. However, the water vapor transmission rate of the pressure-sensitive adhesive layer is high, and the water vapor barrier property is poor. In addition, the adhesive force to the high-density polyethylene resin is low. Further, in the pressure-sensitive adhesive films of Comparative Examples 5 and 7 of the present invention, it is considered that the reason is that the crosslinking points of the acrylic polymer are unevenly distributed, but the haze value of the pressure-sensitive adhesive layer is high and the total light transmittance is low. Incidentally, the pressure-sensitive adhesive film of Comparative Example 5 of the present invention is such that the acrylic polymer of Comparative Example 5 of the present invention is the same as the acrylic polymer of Example 1 of the present invention in terms of monomer composition, weight average molecular weight, and SP value, and both are crosslinked using an isocyanate compound having a functionality of 3 or more as a crosslinking agent. However, in the pressure-sensitive adhesive films of Example 1 and Comparative Example 5, significant differences were shown in the measurement results of both only due to the difference in the content of the crosslinking agent.

Claims

1. A pressure-sensitive adhesive composition comprising an acrylic polymer obtained by copolymerizing only (meth)acrylate as a monomer component, and (C) a crosslinking agent, The acrylic polymer contained in the pressure-sensitive adhesive composition is (A-1) 100 parts by weight of a total of at least two or more alkyl (meth)acrylates having an alkyl group with a carbon number of 14 to 20, or (A-2) 100 parts by weight of a total of at least one alkyl (meth)acrylate having an alkyl group carbon number of from C14 to C20, and more than 0.0 part by weight and 15 parts by weight or less of a total of at least one selected from the group consisting of alkyl (meth)acrylates having an alkyl group carbon number of from C1 to C13, (meth)acrylates containing an alicyclic hydrocarbon group, and (meth)acrylates containing an aromatic ring structure, (B) at least one (meth)acrylate containing a hydroxyl group; an acrylic polymer having a weight average molecular weight of 50,000 to 1,500,000, which is copolymerized with only acrylic acid and tertiary ester without containing a vinyl monomer containing a carboxyl group and a vinyl monomer containing a nitrogen group; the acrylic polymer contains at least one alkyl (meth)acrylate having an alkyl group carbon number of 14 to 20 in a total amount of 80 parts by weight or more per 100 parts by weight of the acrylic polymer, the pressure-sensitive adhesive composition contains, relative to 100 parts by weight of the acrylic polymer, 0.01 to 2.0 parts by weight of the (C) crosslinking agent, a trifunctional or higher isocyanate compound; When the pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition has a thickness of 25 μm, the water vapor transmission rate of the pressure-sensitive adhesive layer is 100 g / (m) in an atmosphere of 32° C.×90% RH when measured using an infrared sensor method in accordance with JIS K7129. ２ .day) or less.

2. The SP value of the acrylic polymer is 9.0 (cal / cm ３ ) ０．５ The pressure-sensitive adhesive composition according to claim 1, characterized in that:

3. 3. The pressure-sensitive adhesive composition according to claim 1 or 2, characterized in that an adhesive layer having a thickness of 25 μm, which is formed by crosslinking the pressure-sensitive adhesive composition, is laminated on one side of a polyester film substrate having a thickness of 50 μm to form an adhesive film, and when the adhesive strength of the adhesive layer is measured in accordance with JIS Z0237, the adhesive strength of the adhesive layer to a high-density polyethylene resin is 10 N / 25 mm or more.

4. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, characterized in that the (B) hydroxyl group-containing (meth)acrylate is at least one member selected from the group consisting of 8-hydroxyoctyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate.

5. The pressure-sensitive adhesive composition according to any one of claims 1 to 4, characterized in that a pressure-sensitive adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition has a total light transmittance of 90% or more and a haze value of 1.0% or less when the thickness is 25 µm.

6. 6. A pressure-sensitive adhesive film comprising a substrate and a pressure-sensitive adhesive layer formed by crosslinking the pressure-sensitive adhesive composition according to claim 1 on at least one side of the substrate.

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