Adhesive composition, adhesive layer, and adhesive film

Abstract

To provide an adhesive and an adhesive tape which are little in the increase of an adhesive force even after having been left under high temperature condition, and are less in the contamination on the surface of an adherend after having been peeled from the adherend.SOLUTION: An adhesive composition contains an acrylic polymer (A) and a crosslinking agent (B). The acrylic polymer (A) includes a unit derived from (meth)acrylic acid alkyl ester (a1), a unit derived from a nitrogen-containing monomer (a2) and a unit derived from an oxyalkylene chain-containing monomer (a3), and a percentage content of the unit derived from the nitrogen-containing monomer (a2) is 2 mass% or more in the acrylic polymer (A).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive layer, and a pressure-sensitive adhesive film. [Background technology]

[0002] Adhesive sheets are used in a variety of fields, including automobiles, construction, and electronic devices. In particular, in recent years, they have been used in many situations, such as for protecting the surfaces of portable electronic devices such as tablets and smartphones, for fixing components, and for protecting components during processing.

[0003] Examples of such adhesive sheets that have been proposed include a transparent adhesive film using a polymer containing units derived from an alkyl(meth)acrylate and units derived from a monomer having a saturated cyclic group (Patent Document 1), and adhesives using acrylic polymers formed from alkyl(meth)acrylate monomers, (meth)acrylate monomers having an aromatic group, nitrogen-containing vinyl monomers without a hydroxyl group, vinyl monomers having a carboxyl group, etc. (Patent Documents 2 to 7). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-48328 A [Patent Document 2] JP 2019-70148 A [Patent Document 3] JP 2019-70149 A [Patent Document 4] JP 2019-70152 A [Patent Document 5] JP 2019-77881 A [Patent Document 6] JP 2019-77882 A [Patent Document 7] JP 2019-90040 A Summary of the Invention [Problem to be solved by the invention]

[0005] Components used in electronic devices require more advanced processing, and are therefore processed under harsher conditions than before. Therefore, the surface protection film used in the processing of these components must be able to be cleanly peeled off from the components after the processing process is completed, even after being exposed to harsh conditions such as high temperatures. For this reason, such protection films are required to have properties such as a small increase in adhesive strength after heat history and not contaminating the adherend with adhesive residue or the like when the adhesive sheet is peeled off from the adherend surface. However, with conventionally known adhesive sheets, it was sometimes difficult to achieve the above properties when placed under harsher processing conditions (high temperature, high humidity).

[0006] In addition, conventionally, protective films used in processing steps were replaced for each process and the used protective films were discarded. However, in recent years, in order to reduce the environmental impact and costs, there has been a demand for protective films to be used in multiple processes, and the above properties are required to be achieved even when repeatedly exposed to harsh processing conditions (high temperature, high humidity).

[0007] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a pressure-sensitive adhesive and a pressure-sensitive adhesive tape which show only a small increase in adhesive strength even after repeated exposure to high temperature and high humidity conditions, and which cause only a small contamination of the surface of an adherend after being peeled off from the adherend. [Means for solving the problem]

[0008] Through investigations, the inventors have found that by using an acrylic polymer of a specific composition, it is possible to provide a pressure-sensitive adhesive that exhibits only a small increase in adhesive strength even after being placed under high temperature and high humidity conditions, and that causes only a small amount of contamination of the surface of an adherend after being peeled off from the adherend.

[0009] That is, the pressure-sensitive adhesive composition of the present invention comprises an acrylic polymer (A), a crosslinking agent (B) and a plasticizer (C), the acrylic polymer (A) comprises a unit derived from an (meth)acrylic acid alkyl ester (a1), a unit derived from a nitrogen-containing monomer (a2) and a unit derived from an oxyalkylene chain-containing monomer (a3), the content of the unit derived from the nitrogen-containing monomer (a2) being 2 mass% or more in the acrylic polymer (A), the crosslinking agent (B) comprises a metal chelate crosslinking agent (b1), the plasticizer (C) comprises an esterification product of a compound (c1) having a hydroxyl group and a compound (c2) having an acid group, and the SP value (Small equation) of the plasticizer (C) is 10 (cal / cm 2 ) 1 / 2 and the number average molecular weight of the plasticizer (C) is 6,000 or less. Effect of the Invention

[0010] According to the present invention, it is possible to provide a pressure-sensitive adhesive and a pressure-sensitive adhesive tape which show only a small increase in adhesive strength even after repeated exposure to high temperature and high humidity conditions and cause only a small contamination of the adherend surface after being peeled off from the adherend. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The pressure-sensitive adhesive composition of the present invention contains an acrylic polymer (A), a crosslinking agent (B), and a plasticizer (C).

[0012] The acrylic polymer (A) contains units derived from an alkyl (meth)acrylate ester (a1), units derived from a nitrogen-containing monomer (a2), and units derived from an oxyalkylene chain-containing monomer (a3).

[0013] The (meth)acrylic acid alkyl ester (a1) may be a (meth)acrylic acid alkyl ester having an alkyl group bonded to an ester bond. The number of carbon atoms in the alkyl group is preferably 1 or more, more preferably 3 or more, and even more preferably 4 or more, and is preferably 20 or less, more preferably 15 or less, even more preferably 12 or less, still more preferably 10 or less, and particularly preferably 8 or less.

[0014] The (meth)acrylic acid alkyl ester (a1) preferably includes a (meth)acrylic acid alkyl ester (a1-1) in which an alkyl group having 3 or more carbon atoms (preferably 4 or more) is bonded to an ester bond. The content of the (meth)acrylic acid alkyl ester (a1-1) in the (meth)acrylic acid alkyl ester (a1) is preferably 50 mass% or more, more preferably 60 mass% or more, even more preferably 70 mass% or more, and is preferably 100 mass% or less.

[0015] The (meth)acrylic acid alkyl ester (a1) preferably further contains a (meth)acrylic acid alkyl ester (a1-2) in which an alkyl group having 2 or less carbon atoms is bonded to an ester bond. When the (meth)acrylic acid alkyl ester (a1-2) is contained, the content thereof is preferably 1 mass% or more, more preferably 2 mass% or more, and is preferably 50 mass% or less, more preferably 40 mass% or less, and further preferably 30 mass% or less.

[0016] Examples of the alkyl group include linear alkyl groups such as a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, a lauryl group, and a stearyl group; and branched alkyl groups such as an isopropyl group, an isobutyl group, a t-butyl group, an isopentyl group, a neopentyl group, an isohexyl group, an isoheptyl group, an isooctyl group, a 2-ethylhexyl group, an isononyl group, an isodecyl group, and an isostearyl group.

[0017] The (meth)acrylic acid alkyl ester (a1) is preferably an acrylic acid alkyl ester.

[0018] The (meth)acrylic acid alkyl ester (a1) may be used alone or in combination. Examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (meth)acrylate.

[0019] In the acrylic polymer (A), the content of units derived from the (meth)acrylic acid alkyl ester (a1) is preferably 50 mass% or more, more preferably 60 mass% or more, and preferably 98 mass% or less, more preferably 95 mass% or less.

[0020] The nitrogen-containing monomer (a2) is a monomer having a nitrogen atom and a polymerizable double bond in the molecule, and is preferably a monomer having an amide bond and a polymerizable double bond in the molecule. Examples of the nitrogen-containing monomer (a2) include lactam compounds having a vinyl group; (meth)acrylamide monomers; and (meth)acrylate compounds having a functional group containing a nitrogen atom (e.g., an amino group, a mono-substituted amino group, a di-substituted amino group, a nitrile group, etc.).

[0021] Examples of the lactam compound having a vinyl group include N-vinylpyrrolidone and N-vinylcaprolactam.

[0022] The (meth)acrylamide monomer may be a compound in which a hydrogen atom or a hydrocarbon group (preferably an aliphatic hydrocarbon group, provided that -CH2- contained in the hydrocarbon may be replaced by -CO-, and a hydrogen atom contained in the hydrocarbon group may be replaced by a hydroxyl group) is bonded to a nitrogen atom of (meth)acrylamide. When two or more groups (the aforementioned hydrocarbon groups) are substituted for the nitrogen atom of (meth)acrylamide, the groups may be bonded to each other to form a ring containing the nitrogen atom.

[0023] The hydrocarbon group (preferably an aliphatic hydrocarbon group) substituting the nitrogen atom contained in the amide bond preferably has 1 or more carbon atoms, preferably 10 or less, and more preferably 6 or less carbon atoms.

[0024] The (meth)acrylamide monomer may be one or more of them. The (meth)acrylamide monomer may be any of (meth)acrylamide, N-1 substituted (meth)acrylamide, and N,N-2 substituted (meth)acrylamide.

[0025] The (meth)acrylamide monomer may be used alone or in combination. Examples of the (meth)acrylamide monomer include (meth)acrylamide; N-isopropyl(meth)acrylamide, N-(1,1-dimethyl-3-oxobutyl)acrylamide, N-methylol(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N-(2-hydroxymethyl)acrylamide, and N-(2-hydroxyethyl)acrylamide; and other N-1-substituted (meth)acrylamide compounds such as N-(2-hydroxyethyl)acrylamide. Examples of N-2 substituted (meth)acrylamide compounds include (meth)acryloylmorpholine, N-(meth)acryloylpiperidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloyl-4-piperidone, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-methylenebis(meth)acrylamide, and N,N-dimethylaminopropyl(meth)acrylamide.

[0026] Among them, the (meth)acrylamide monomer preferably contains a monomer represented by formula (1).

[0027] [ka] [In formula (1), R 1 R represents a hydrogen atom or a methyl group. 2 and R 3 each independently represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, -CH- contained in the hydrocarbon group may be replaced by -CO- or -O-, and a hydrogen atom contained in the hydrocarbon group may be replaced by a hydroxyl group; R 2 and R 3 may be bonded to each other to form a ring containing a nitrogen atom.

[0028] R 2 and R 3The hydrocarbon group represented by the formula (I) may be one or more types, and examples thereof include linear or branched saturated aliphatic hydrocarbon groups; linear or branched unsaturated aliphatic hydrocarbon groups; and the like.

[0029] The (meth)acrylamide monomer is R 2 and R 3 It is also preferable that the (meth)acrylamide monomer contains a (meth)acrylamide monomer in which both of R 2 and R 3 In the case where the acrylic polymer (A) contains a (meth)acrylamide monomer in which both of the above are hydrocarbon groups, the content of units derived from the monomer in the acrylic polymer (A) is preferably 0.2 mass % or more, more preferably 0.5 mass % or more, and is preferably 20 mass % or less, more preferably 15 mass % or less.

[0030] In the nitrogen-containing monomer (a2), the content of units derived from the acrylamide monomer is preferably 30% by mass or more, more preferably 60% by mass or more, and even more preferably 75% by mass or more, with the upper limit being 100% by mass.

[0031] Examples of the (meth)acrylate compound having a functional group containing a nitrogen atom (for example, an amino group, a mono-substituted amino group, a di-substituted amino group, a nitrile group, etc.) include (meth)acrylonitrile, t-butylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, etc. Examples of the (meth)acrylate compound having a functional group containing a nitrogen atom include a compound in which the functional group containing a nitrogen atom and a (meth)acryloxy group are bonded via a single bond or a hydrocarbon group (preferably an alkyl group) having 1 to 10 carbon atoms (preferably 1 to 5 carbon atoms).

[0032] The nitrogen-containing monomer (a2) preferably contains a nitrogen-containing monomer having a hydroxyl group. The nitrogen-containing monomer having a hydroxyl group is preferably a (meth)acrylamide monomer having a hydroxyl group, and in formula (1), R 2 and R3 More preferred is a monomer in which at least one of the above is a hydrocarbon group, and a hydrogen atom contained in the hydrocarbon group is replaced with a hydroxyl group.

[0033] The content of the nitrogen-containing monomer having a hydroxyl group in the nitrogen-containing monomer (a2) is preferably 50 mass% or more, more preferably 60 mass% or more, even more preferably 65 mass% or more, and is preferably 100 mass% or less, more preferably 95 mass% or less, even more preferably 90 mass% or less.

[0034] In the acrylic polymer, the content of units derived from the nitrogen-containing monomer (a2) is preferably 2% by mass or more, more preferably 2.5% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less.

[0035] The oxyalkylene chain-containing monomer (a3) ​​is a monomer having an oxyalkylene unit and a polymerizable double bond in the molecule. The number of carbon atoms in the oxyalkylene unit is preferably 2 or more, and preferably 5 or less, more preferably 4 or less, further preferably 3 or less, and particularly preferably 2. The oxyalkylene chain-containing monomer is preferably an alkoxy polyalkylene glycol (meth)acrylate. Examples of the alkoxy group in the alkoxy polyalkylene glycol (meth)acrylate include alkoxy groups having 1 to 5 carbon atoms (preferably 1 to 3), such as a methoxy group, an ethoxy group, and a propoxy group.

[0036] The oxyalkylene chain-containing monomer (a3) ​​may be used alone or in combination of two or more kinds, and examples thereof include methoxyethylene glycol methacrylate and methoxyethylene glycol acrylate.

[0037] The content of the alkoxy polyalkylene glycol (meth)acrylate in the oxyalkylene chain-containing monomer (a3) ​​is 0 mass% or more, preferably 10 mass% or more, more preferably 30 mass% or more, and is 100 mass% or less, preferably 90 mass% or less, more preferably 80 mass% or less.

[0038] The number of repeating oxyalkylene units in the oxyalkylene chain-containing monomer (a3) ​​is preferably 2 or more, more preferably 4 or more, and even more preferably 5 or more, and is preferably 100 or less, more preferably 30 or less, and even more preferably 20 or less.

[0039] In the acrylic polymer (A), the content of units derived from the oxyalkylene chain-containing monomer (a3) ​​is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, even more preferably 1.5 mass% or more, and is preferably 30 mass% or less, more preferably 20 mass% or less, even more preferably 15 mass% or less.

[0040] The acrylic polymer (A) may have units derived from a monomer (a4) other than the (meth)acrylic acid alkyl ester (a1), the nitrogen-containing monomer (a2), and the oxyalkylene chain-containing monomer (a3).

[0041] The other monomer (a4) may be one or more, and examples thereof include unsaturated monocarboxylic acids such as (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, and β-carboxyethyl (meth)acrylate; (meth)acrylic monomers having a hydroxyl group; epoxy ring-containing (meth)acrylic monomers such as glycidyl (meth)acrylate; alicyclic ring-containing (meth)acrylic monomers such as cyclohexyl (meth)acrylate; aromatic vinyl monomers such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ethylvinylbenzene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and parahydroxystyrene; and monomers having two or more vinyl groups.

[0042] Examples of the (meth)acrylic monomer having a hydroxyl group include a compound in which a hydroxyl group is bonded to the alkyl group of a (meth)acrylic acid alkyl ester; a (meth)acrylic acid polyalkylene glycol ester, and the like. Of these, a compound in which a hydroxyl group is bonded to the alkyl group of a (meth)acrylic acid alkyl ester is preferred, and a compound in which a hydroxyl group is bonded to the terminal of the alkyl group of a (meth)alkyl acid alkyl ester is more preferred.

[0043] The number of hydroxyl groups contained in the (meth)acrylic monomer having a hydroxyl group is preferably one. The (meth)acrylic monomer having a hydroxyl group is preferably an acrylic monomer having a hydroxyl group.

[0044] Examples of the alkyl acrylate include the same compounds as those exemplified as the alkyl (meth)acrylate (a1).

[0045] The (meth)acrylic monomer having a hydroxyl group may be used alone or in combination with another. Examples of the (meth)acrylic monomer having a hydroxyl group include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; and polyethylene glycol (meth)acrylate.

[0046] In the acrylic polymer (A), the content of units derived from the (meth)acrylic monomer having a hydroxyl group is preferably 0.01 mass% or more, more preferably 0.02 mass% or more, even more preferably 0.03 mass% or more, and is preferably 15 mass% or less, more preferably 12 mass% or less, even more preferably 10 mass% or less.

[0047] In the acrylic polymer (A), the content of units derived from the other monomer (a4) is 0 mass% or more, more preferably more than 0 mass%, even more preferably 0.01 mass% or more, and is preferably 20 mass% or less, more preferably 10 mass% or less, even more preferably 5 mass% or less.

[0048] The weight average molecular weight of the acrylic polymer (A) is preferably 100,000 or more, more preferably 200,000 or more, and even more preferably 300,000 or more, and is preferably 2,000,000 or less, more preferably 1,800,000 or less, and even more preferably 1,500,000 or less.

[0049] In this specification, the number average molecular weight and weight average molecular weight of the acrylic polymer (A) are expressed as converted values ​​measured by gel permeation chromatography (GPC) using polystyrene as a standard sample.

[0050] In the pressure-sensitive adhesive composition of the present invention, the content of the acrylic polymer (A) in the nonvolatile matter is preferably 15 mass % or more, more preferably 20 mass % or more, even more preferably 25 mass % or more, and is preferably 100 mass % or less.

[0051] In this specification, the non-volatile content of the PSA composition refers to the portion excluding the solvent component that is optionally contained in the PSA composition.

[0052] The acrylic polymer (A) can be produced by copolymerizing the (meth)acrylic acid alkyl ester (a1), the (meth)acrylamide monomer (a2), the oxyalkylene chain-containing monomer (a3) ​​and, if necessary, other monomers (a4) in the presence of a polymerization initiator.

[0053] As the polymerization initiator, for example, one or more thermal polymerization initiators can be used, and examples thereof include peroxide initiators such as benzoyl peroxide and lauroyl peroxide, and azo initiators such as azobisisobutylnitrile.

[0054] The pressure-sensitive adhesive composition of the present invention contains a crosslinking agent (B), and the crosslinking agent (B) contains a metal chelate crosslinking agent (b1).

[0055] Examples of the metal chelate crosslinking agent (b1) include compounds in which acetylene and ethyl acetoacetate are coordinated to polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium.

[0056] The metal chelate crosslinking agent (b1) may be dissolved in an organic solvent in advance and used as a metal chelate crosslinking agent (b1) solution. Examples of the organic solvent include the same compounds as the solvent (D) described below. When the metal chelate crosslinking agent (b1) is dissolved in an organic solvent in advance, the concentration is preferably, for example, 1 to 10 mass%.

[0057] The content of the metal chelate crosslinking agent (b1) in the crosslinking agent (B) is preferably 0.5 mass% or more, more preferably 1 mass% or more, and even more preferably 2 mass% or more, and is preferably 70 mass% or less, more preferably 50 mass% or less, and even more preferably 40 mass% or less.

[0058] The crosslinking agent (B) may contain other crosslinking agents (b2) in addition to the metal chelate crosslinking agent (b1). As the other crosslinking agents (b2), one or more types may be used, and examples thereof include isocyanate crosslinking agents, epoxy crosslinking agents, melamine crosslinking agents, aziridine crosslinking agents, polyvalent metal salt crosslinking agents, ketohydrazide crosslinking agents, oxazoline crosslinking agents, carbodiimide crosslinking agents, silane crosslinking agents, and glycidyl (alkoxy) epoxy silane crosslinking agents.

[0059] As the other crosslinking agent (b2), an isocyanate crosslinking agent, an epoxy crosslinking agent, a melamine crosslinking agent, an oxazoline crosslinking agent, a carbodiimide crosslinking agent, or a glycidyl (alkoxy) epoxy silane crosslinking agent is preferable, an isocyanate crosslinking agent, an epoxy crosslinking agent, a melamine crosslinking agent, or a carbodiimide crosslinking agent is more preferable, and an isocyanate crosslinking agent is particularly preferable.

[0060] The content of the isocyanate crosslinking agent in the crosslinking agent (B) is preferably 30% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more, and is preferably 100% by mass or less, and more preferably 98% by mass or less.

[0061] The content of the crosslinking agent (B) is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 3 parts by mass or more, relative to 100 parts by mass of the acrylic polymer (A), and is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less.

[0062] The pressure-sensitive adhesive composition of the present invention contains a plasticizer (C). The plasticizer (C) contains an esterification product of a compound (c1) having a hydroxyl group and a compound (c2) having an acid group.

[0063] The compound (c1) having a hydroxyl group is a compound having one or more hydroxyl groups in one molecule, and the number of hydroxyl groups in the compound (c1) having a hydroxyl group is preferably one or more, and preferably six or less, more preferably four or less, and even more preferably two or less, in one molecule.

[0064] The compound (c1) having a hydroxyl group may be a chain compound such as a linear or branched chain, a cyclic compound such as an alicyclic or aromatic ring, or a compound combining a chain group and a cyclic group, and is preferably a chain compound.

[0065] The compound (c1) having a hydroxyl group preferably includes a compound represented by the following formula (2) or (3).

[0066] [ka]

[0067] [In formula (2), R 4 represents a monovalent chain hydrocarbon group having 2 to 18 carbon atoms or a monovalent hydrocarbon group having 5 to 50 carbon atoms in which one or more -CH2- groups are replaced with -O-. In formula (3), R 5 represents a divalent chain hydrocarbon group having 2 to 18 carbon atoms or a divalent hydrocarbon group having 5 to 65 carbon atoms in which one or more -CH2- groups are replaced with -O-.]

[0068] R 4Examples of the chain hydrocarbon group represented by the formula (I) include alkyl groups such as ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, isobutyl group, n-pentyl group, isopentyl group, sec-pentyl group, tert-pentyl group, n-hexyl group, n-heptyl group, 2-heptyl group, isoheptyl group, sec-heptyl group, tert-heptyl group, n-octyl group, isooctyl group, sec-octyl group, tert-octyl group, 2-ethylhexyl group, n-nonyl group, isononyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, and octadecyl group, and may be linear or branched. 4 The chain hydrocarbon group represented by the following formula (I) preferably has 4 to 16 carbon atoms, and more preferably 6 to 13 carbon atoms.

[0069] R 4 Among the groups represented by the formula (I), examples of the group in which one or more -CH2- contained in the monovalent chain hydrocarbon group are replaced with -O- include groups having one or more oxyalkylene units having 2 to 10 carbon atoms. The number of carbon atoms in the oxyalkylene unit is preferably 2 to 6, more preferably 2 to 4, and even more preferably 3 to 4. In the compound (c1) having a hydroxyl group, the oxyalkylene unit may be one type or two or more types, and may, for example, contain both an oxyalkylene unit having 2 carbon atoms and an oxyalkylene unit having 3 or more carbon atoms.

[0070] R 4 In the group represented by the formula (I) in which one or more -CH2- groups contained in a monovalent chain hydrocarbon group are replaced with -O-, the number of oxyalkylene units is preferably 1 or more, and is preferably 20 or less, more preferably 15 or less, in total.

[0071] R 5Examples of the divalent chain hydrocarbon group represented by the formula (I) include alkanediyl groups such as ethanediyl group, propanediyl group, butanediyl group, pentanediyl group, hexanediyl group, heptanediyl group, octanediyl group, nonanediyl group, and decanediyl group, and may be linear or branched. 5 The chain hydrocarbon group represented by the following formula (I) preferably has 2 to 10 carbon atoms, more preferably 2 to 6 carbon atoms, and further preferably 3 to 4 carbon atoms.

[0072] R 5 Among the groups represented by the formula (I), examples of the group in which one or more -CH2- contained in the divalent chain hydrocarbon group are replaced with -O- include groups having one or more oxyalkylene units having 2 to 10 carbon atoms. The number of carbon atoms in the oxyalkylene unit is preferably 2 to 6, more preferably 2 to 4, and even more preferably 3 to 4. In the compound (c1) having a hydroxyl group, the oxyalkylene unit may be one type or two or more types, and may contain, for example, both an oxyalkylene unit having 2 carbon atoms and an oxyalkylene unit having 3 or more carbon atoms.

[0073] R 5 In the group represented by the formula (I) in which one or more -CH2- groups contained in a divalent chain hydrocarbon group are replaced with -O-, the number of oxyalkylene units is preferably 2 or more and is preferably 20 or less, more preferably 15 or less, in total.

[0074] The content of the compound represented by formula (2) or (3) in the compound (c1) having a hydroxyl group is preferably 80 mass% or more, more preferably 90 mass% or more, and even more preferably 95 mass% or more, with the upper limit being 100 mass%.

[0075] Among the compounds (c1) having a hydroxyl group, examples of compounds having three or more hydroxyl groups in one molecule include glycerin, trimethylolpropane, pentaerythritol, and dipentaerythritol.

[0076] The compound (c2) having an acid group is a compound having one or more acid groups in one molecule, and the number of acid groups in the compound (c2) having an acid group is preferably one or more, and is preferably not more than 6, more preferably not more than 4, even more preferably not more than 3, and even more preferably not more than 2. Examples of the acid group include a carboxyl group, a phosphoric acid group, a sulfonic acid group, and the like, and the carboxyl group is preferred.

[0077] The compound (c2) having an acid group may be a chain compound such as a straight chain or a branched chain, or may be a compound containing a ring structure such as an alicyclic ring or an aromatic ring. The compound (c2) having an acid group may or may not have other functional groups such as a hydroxyl group, an epoxy group, or a (meth)acryloyl group in addition to the acid group.

[0078] The compound (c2) having an acid group preferably includes a compound represented by the following formula (4) or (5).

[0079] [ka]

[0080] [In formulas (4) and (5), R 6 represents a monovalent aliphatic hydrocarbon group having 4 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms, 6 The aliphatic hydrocarbon group represented by the following formula may have a hydroxyl group as a substituent. R 7 represents a divalent aliphatic hydrocarbon group having 4 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 20 carbon atoms. R a represents an acid group.

[0081] R 6 Examples of the aliphatic hydrocarbon group represented by the formula (R) include alkyl groups such as butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl. 6 The aliphatic hydrocarbon group represented by R may be linear or branched.6 The aliphatic hydrocarbon group represented by the following formula (1) preferably has 4 to 16 carbon atoms, and more preferably 4 to 10 carbon atoms.

[0082] R 6 Examples of the aromatic hydrocarbon group represented by the formula (R) include monocyclic or polycyclic aromatic hydrocarbon groups such as a phenyl group, a tolyl group, and a xylyl group. 6 The aromatic hydrocarbon group represented by the following formula (1) preferably has 6 to 15 carbon atoms, and more preferably 6 to 10 carbon atoms.

[0083] R 6 is preferably a monovalent aliphatic hydrocarbon group having 4 to 10 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 10 carbon atoms.

[0084] R 7 Examples of the divalent aliphatic hydrocarbon group represented by the formula (I) include alkanediyl groups such as butanediyl, pentanediyl, hexanediyl, heptanediyl, octanediyl, nonanediyl, and decanediyl. 7 The divalent aliphatic hydrocarbon group represented by the formula (I) may be linear or branched. 7 The divalent aliphatic hydrocarbon group represented by the following formula (I) preferably has 4 to 16 carbon atoms, and more preferably 4 to 10 carbon atoms.

[0085] R 7 Examples of the divalent aromatic hydrocarbon group represented by the formula (I) include monocyclic or polycyclic divalent aromatic hydrocarbon groups such as a phenylene group, a tolylene group, and a xylylene group. 7 The divalent aromatic hydrocarbon group represented by the following formula (I) preferably has 6 to 15 carbon atoms, and more preferably 6 to 10 carbon atoms.

[0086] R 7 is preferably an aliphatic hydrocarbon group, and more preferably an aliphatic hydrocarbon group having 4 to 10 carbon atoms.

[0087] R a Examples of the acid group represented by the formula (I) include a carboxyl group, a phosphoric acid group, and a sulfonic acid group, and the carboxyl group is preferred.

[0088] The content of the compound represented by formula (4) or (5) in the compound (c2) having an acid group is preferably 80 mass% or more, more preferably 90 mass% or more, and even more preferably 95 mass% or more, with the upper limit being 100 mass%.

[0089] Among the compounds (c2) having an acid group, examples of compounds having three or more acid groups in one molecule include tricarboxylic acids; hydroxytricarboxylic acids such as citric acid; and aromatic polycarboxylic acids such as trimellitic acid and pyromellitic acid.

[0090] In the plasticizer (C), the content of the ester of the compound (c1) having a hydroxyl group and the compound (c2) having an acid group is preferably 80 mass% or more, more preferably 90 mass% or more, and even more preferably 95 mass% or more, with the upper limit being 100 mass%.

[0091] The number average molecular weight of the plasticizer (C) is 6,000 or less, preferably 3,000 or less, and more preferably 2,000 or less, and the lower limit may be, for example, 100 or more, or 150 or more.

[0092] The solubility parameter of the plasticizer (C) is 10 (cal / cm 3 ) 1 / 2 It is preferably 9.5 (cal / cm 3 ) 1 / 2 More preferably, it is 9.0 (cal / cm 3 ) 1 / 2 ≦7.5(cal / cm 3 ) 1 / 2 More preferably, 8.0 (cal / cm 3 ) 1 / 2 The solubility parameter of the plasticizer (C) is a value calculated based on Small's equation.

[0093] The content of the plasticizer (C) is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and preferably 40 parts by mass or less, more preferably 30 parts by mass or less, based on 100 parts by mass of the acrylic polymer (A).

[0094] The pressure-sensitive adhesive composition of the present invention preferably contains a solvent (D). As the solvent (D), one or more solvents may be used, and examples thereof include aromatic hydrocarbon solvents such as toluene and xylene; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as acetone and methyl ethyl ketone; and aliphatic hydrocarbon solvents such as hexane. Among them, it is preferable to contain an ester solvent.

[0095] The content of the ester solvent in the solvent (D) is preferably 50% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and is preferably 100% by mass or less.

[0096] The content of the solvent (D) in the pressure-sensitive adhesive composition is preferably 10 mass % or more, more preferably 30 mass % or more, even more preferably 50 mass % or more, and is preferably 90 mass % or less, more preferably 70 mass % or less, even more preferably 65 mass % or less.

[0097] In the pressure-sensitive adhesive composition of the present invention, in order to maintain low yellowing, the content of the tackifier resin is preferably reduced, and is preferably less than 10 parts by mass, more preferably 8 parts by mass or less, even more preferably 3 parts by mass or less, and even more preferably 1 part by mass or less, and is preferably 0 parts by mass, relative to 100 parts by mass of the acrylic polymer. By using an acrylic polymer (A) having a specific composition and weight-average molecular weight and adopting a configuration that does not contain a tackifier resin, it is possible to maintain low yellowing of the adhesive layer, maintain low adhesive strength even under high temperature / high humidity conditions, and suppress contamination of the adherend surface after peeling from the adherend.

[0098] The pressure-sensitive adhesive composition of the present invention may contain, as additives, a base (such as aqueous ammonia) or an acid for adjusting the pH; a foaming agent; a softener; an antioxidant; fillers such as glass or plastic fibers, balloons, beads, metal powder, etc.; colorants such as pigments and dyes; a pH adjuster; a film-forming auxiliary; a leveling agent; a thickener; a water repellent; an antifoaming agent; an acid catalyst; an acid generator, etc.

[0099] The pressure-sensitive adhesive composition can be applied onto a support and dried to form a pressure-sensitive adhesive layer. The support may be any of a release sheet, a pressure-sensitive adhesive sheet, and the like.

[0100] The coating method may be performed using a knife coater, a reverse coater, a die coater, a lip die coater, a slot die coater, a gravure coater, a curtain coater, or the like.

[0101] The thickness of the adhesive layer is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more, and is preferably 100 μm or less, more preferably 70 μm or less, and even more preferably 50 μm or less.

[0102] The adhesive sheet or adhesive tape of the present invention has the adhesive layer and the substrate.The substrate may be any of a film, sheet, tape, plate, three-dimensional shape, etc., and the material of the substrate may be a plastic such as polyester resin, polypropylene resin, polyethylene resin, polyimide resin, vinyl chloride resin, urethane resin, etc.; rubber; nonwoven fabric; metal foil; paper, etc., and plastic is preferable, and vinyl chloride resin is more preferable.In addition, the substrate may have a smooth surface, or may have an uneven surface such as a fibrous substrate or a foam substrate.

[0103] The thickness of the substrate is preferably 0.1 μm or more and preferably 1,000 μm or less. EXAMPLES

[0104] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is possible to carry out the present invention by making appropriate modifications within the scope of the above and below-mentioned aims, and all of these modifications are included in the technical scope of the present invention.

[0105] [Synthesis Example 1] <Synthesis of acrylic copolymer (A1)> In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, and a thermometer, 830 parts by mass of n-butyl acrylate (hereinafter sometimes referred to as "BA"), 50 parts by mass of methyl acrylate (hereinafter sometimes referred to as "MA"), 50 parts by mass of hydroxyethyl acrylamide (hereinafter sometimes referred to as "HEAA"), 10 parts by mass of acrylamide (hereinafter sometimes referred to as "AM"), 10 parts by mass of NK Ester AM-90G (manufactured by Shin-Nakamura Chemical Co., Ltd.), 40 parts by mass of NK Ester M-90G (manufactured by Shin-Nakamura Chemical Co., Ltd.), 10 parts by mass of hydroxyethyl acrylate (hereinafter sometimes referred to as "HEA"), and 1000 parts by weight of ethyl acetate were charged, and the temperature was raised to 65°C while blowing in nitrogen under stirring. After 1 hour, 10 parts by mass of 2,2'-azobis(2-methylbutyronitrile) solution (solid content 5% by mass) previously dissolved in ethyl acetate was added. After that, the mixture was held at 65°C for 10 hours under stirring, and then the contents were cooled and filtered through a 200 mesh wire screen to obtain an acrylic copolymer (A1) with a non-volatile content of 50% by mass, a viscosity of 240,000 mPa·s, and a weight average molecular weight of 900,000.

[0106] [Synthesis Example 2] <Synthesis of acrylic copolymer (A2)> In a reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer, 400 parts by mass of n-butyl acrylate, 310 parts by mass of 2-ethylhexyl acrylate (hereinafter, sometimes referred to as "2EHA"), 100 parts by mass of methyl acrylate, 100 parts by mass of hydroxyethyl acrylamide, 20 parts by mass of dimethyl acrylamide (hereinafter, sometimes referred to as "DMAA"), 40 parts by mass of NK Ester AM-130G (manufactured by Shin-Nakamura Chemical Co., Ltd.), 30 parts by mass of 4-hydroxybutyl acrylate (hereinafter, sometimes referred to as "4HBA"), and 1000 parts by weight of ethyl acetate were charged, and the temperature was raised to 70°C while blowing in nitrogen under stirring. After 1 hour, 10 parts by mass of 2,2'-azobis(2-methylbutyronitrile) solution (solid content 5% by mass) previously dissolved in ethyl acetate was added. After that, the mixture was held at 70°C for 8 hours under stirring, and then the contents were cooled and filtered through a 200 mesh wire screen to obtain an acrylic copolymer (A2) with a non-volatile content of 50% by mass, a viscosity of 120,000 mPa·s, and a weight-average molecular weight of 440,000.

[0107] [Synthesis Example 3] <Synthesis of acrylic copolymer (A3)> In a reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer, 735 parts by mass of n-butyl acrylate, 100 parts by mass of 2-ethylhexyl acrylate, 50 parts by mass of methyl acrylate, 20 parts by mass of acryloyl morpholine (hereinafter, sometimes referred to as "ACMO"), 50 parts by mass of hydroxyethyl acrylamide, 20 parts by mass of NK Ester AM-90G, 20 parts by mass of NK Ester M-90G, 5 parts by mass of hydroxyethyl methacrylate (hereinafter, sometimes referred to as "HEMA"), and 1000 parts by weight of ethyl acetate were charged, and the temperature was raised to 65°C while blowing in nitrogen under stirring. After 1 hour, 10 parts by mass of 2,2'-azobis(2-methylbutyronitrile) solution (solid content 5% by mass) previously dissolved in ethyl acetate was added. After that, the mixture was held at 65°C for 10 hours under stirring, and then the contents were cooled and filtered through a 200 mesh wire screen to obtain an acrylic copolymer (A3) with a non-volatile content of 50% by mass, a viscosity of 160,000 mPa·s, and a weight-average molecular weight of 1,050,000.

[0108] [Synthesis Example 4] <Synthesis of acrylic copolymer (A4)> In a reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer, 825 parts by mass of n-butyl acrylate, 50 parts by mass of methyl acrylate, 20 parts by mass of acryloyl morpholine, 50 parts by mass of dimethylacrylamide, 50 parts by mass of NK Ester M-230G (manufactured by Shin-Nakamura Chemical Co., Ltd.), 5 parts by mass of 4-hydroxybutyl acrylate, and 1000 parts by mass of ethyl acetate were charged, and the mixture was heated to 70°C while stirring and blowing in nitrogen. After 1 hour, 10 parts by mass of 2,2'-azobis(2-methylbutyronitrile) solution (solid content 5% by mass) previously dissolved in ethyl acetate was added. After that, the mixture was held at 70°C for 8 hours while stirring, and then the contents were cooled and filtered through a 200 mesh wire net to obtain an acrylic copolymer (A4) with a non-volatile content of 50% by mass, a viscosity of 150,000 mPa·s, and a weight average molecular weight of 650,000.

[0109] [Synthesis Example 5] <Synthesis of acrylic copolymer (A5)> In a reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer, 710 parts by weight of 2-ethylhexyl acrylate, 150 parts by weight of methyl acrylate, 50 parts by weight of hydroxyethyl acrylamide, 20 parts by weight of NK Ester AM-130G, 20 parts by weight of NK Ester M-90G, 50 parts by weight of hydroxyethyl acrylate, and 1000 parts by weight of ethyl acetate were charged, and the temperature was raised to 65°C while stirring and blowing in nitrogen. After 1 hour, 10 parts by weight of 2,2'-azobis(2-methylbutyronitrile) solution (solid content 5% by weight) previously dissolved in ethyl acetate was added. After that, the mixture was held at 65°C for 10 hours while stirring, and then the contents were cooled and filtered through a 200 mesh wire net to obtain an acrylic copolymer (A5) with a non-volatile content of 50% by weight, a viscosity of 420,000 mPa·s, and a weight average molecular weight of 1.15 million.

[0110] [Synthesis Example 6] <Synthesis of acrylic copolymer (A6)> In a reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer, 850 parts by mass of 2-ethylhexyl acrylate, 20 parts by mass of acryloyl morpholine, 40 parts by mass of acrylamide, 50 parts by mass of NK Ester AM-90G, 10 parts by mass of hydroxyethyl methacrylate, 30 parts by mass of acrylic acid (hereinafter sometimes referred to as "AA"), and 1000 parts by weight of ethyl acetate were charged, and the temperature was raised to 70°C while stirring and blowing in nitrogen. After 1 hour, 10 parts by mass of 2,2'-azobis(2-methylbutyronitrile) solution (solid content 5% by mass) previously dissolved in ethyl acetate was added. After that, the mixture was held at 70°C for 8 hours while stirring, and then the contents were cooled and filtered through a 200 mesh wire net to obtain an acrylic copolymer (A6) with a non-volatile content of 50% by mass, a viscosity of 125,000 mPa·s, and a weight average molecular weight of 580,000.

[0111] [Synthesis Example 7] <Synthesis of acrylic copolymer (A7)> In a reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer, 270 parts by mass of n-butyl acrylate, 400 parts by mass of 2-ethylhexyl acrylate, 50 parts by mass of hydroxyethyl acrylamide, 20 parts by mass of dimethyl acrylamide, 120 parts by mass of NK Ester M-90G, 40 parts by mass of 4-hydroxybutyl acrylate, 100 parts by mass of cyclohexyl acrylate (hereinafter sometimes referred to as "CHMA"), and 1000 parts by weight of ethyl acetate were charged, and the mixture was heated to 70°C while stirring and blowing in nitrogen. After 1 hour, 10 parts by mass of 2,2'-azobis(2-methylbutyronitrile) solution (solid content 5% by mass) previously dissolved in ethyl acetate was added. After that, the mixture was held at 65°C for 10 hours under stirring, and then the contents were cooled and filtered through a 200 mesh wire screen to obtain an acrylic copolymer (A7) with a non-volatile content of 50% by mass, a viscosity of 210,000 mPa·s, and a weight-average molecular weight of 1.25 million.

[0112] [Synthesis Example 8] <Synthesis of Acrylic Copolymer (A1')> In a reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer, 300 parts by weight of n-butyl acrylate, 350 parts by weight of 2-ethylhexyl acrylate, 150 parts by weight of methyl acrylate, 100 parts by weight of dimethylacrylamide, 100 parts by weight of hydroxyethyl acrylate, and 1000 parts by weight of ethyl acetate were charged, and the mixture was heated to 70°C while stirring and blowing in nitrogen. After 1 hour, 10 parts by weight of 2,2'-azobis(2-methylbutyronitrile) solution (solid content 5% by weight) previously dissolved in ethyl acetate was added. After that, the mixture was held at 70°C for 8 hours while stirring, and then the contents were cooled and filtered through a 200 mesh wire net to obtain a comparative acrylic copolymer (A1') with a non-volatile content of 50% by weight, a viscosity of 110,000 mPa·s, and a weight average molecular weight of 550,000.

[0113] [Synthesis Example 9] <Synthesis of acrylic copolymer (A2')> In a reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet, and thermometer, 790 parts by weight of 2-ethylhexyl acrylate, 150 parts by weight of NK Ester AM-90G, 50 parts by weight of hydroxyethyl methacrylate, 10 parts by weight of acrylic acid, and 1000 parts by weight of ethyl acetate were charged, and the mixture was heated to 70°C while stirring and blowing in nitrogen. After 1 hour, 10 parts by weight of 2,2'-azobis(2-methylbutyronitrile) solution (solid content 5% by weight) previously dissolved in ethyl acetate was added. After that, the mixture was held at 70°C for 8 hours while stirring, and then the contents were cooled and filtered through a 200 mesh wire net to obtain a comparative acrylic copolymer (A2') with a non-volatile content of 50% by weight, a viscosity of 110,000 mPa·s, and a weight average molecular weight of 520,000.

[0114] [Example 1] An acrylic adhesive composition was obtained by mixing and stirring 100 parts by mass of the acrylic copolymer (A) obtained in Synthesis Example 1, 3.5 parts by mass of diisononyl adipate, 5.0 parts by mass of aluminum acetylacetone solution (solid content 5% by mass), 2.5 parts by mass of an isocyanate-based crosslinking agent (Finetack hardener DN; manufactured by DIC Corporation), 1 part by mass of a hindered phenol-based antioxidant (Irganox1010; manufactured by BASF Japan Ltd.), and 260 parts by mass of ethyl acetate until homogeneous.

[0115] [Examples 2 to 11, Comparative Examples 1 to 6] Except for changing the types and amounts of the acrylic resin (A), crosslinking agent (B) and plasticizer (C), acrylic pressure-sensitive adhesive compositions were obtained in the same manner as in Example 1. Each resin is shown in Table 1, each crosslinking agent is shown in Table 2, the composition of each plasticizer is shown in Table 1, and the types and amounts of the acrylic resin, plasticizer and crosslinking agent used in each acrylic pressure-sensitive adhesive composition are shown in Tables 4 to 5.

[0116] [How to process adhesive film] [How to process adhesive film] The acrylic adhesive compositions obtained in the Examples and Comparative Examples were applied to the surface of a 50 μm-thick polyethylene terephthalate film (release PET50) with a release-treated surface so that the film thickness after solvent drying would be 5 μm. The solvent was then evaporated in a dryer at 80° C. for 3 minutes, and a 10 μm PET film was then laminated thereto.

[0117] [Method of measuring adhesive strength] The adhesive film prepared by the above method was cut into a 25 mm width to be used as a test piece. The adherend was a glass plate, and the film was attached to the adherend with a 2 kg roll, one round trip. One hour after attachment, the 180 degree peel strength was measured at a peel speed of 300 mm / min in an atmosphere of 23°C and 50% RH, and this was taken as the adhesive strength.

[0118] [Method for measuring adhesive strength after heat resistance] As in the adhesive strength measurement method described above, the test piece was attached to the adherend and left to stand for 1 hour. It was then left to stand for 1 hour in a 150°C RH atmosphere, and immediately left to stand for 30 minutes in a 23°C, 50% RH atmosphere. This was repeated 5 times, and then left to stand for 30 minutes in a 23°C, 50% RH atmosphere, after which the 180° peel strength was measured at a peel speed of 300 mm / min, and this was taken as the adhesive strength after heat resistance.

[0119] [Method for evaluating the staining of substrates under moist and heat conditions] The test piece was attached to the adherend in the same manner as in the adhesive strength measurement method described above. It was then left in an atmosphere of 65°C and 90% RH for 3 days and then removed. After leaving it in an atmosphere of 23°C and 50% RH for 24 hours, the test piece was peeled off and the peeled surface of the adherend (the part where the test piece was attached) was irradiated with an LED light to check for the presence or absence of contamination on the adherend surface, and this was used to evaluate the contamination resistance. 〇: No contamination △: No adhesive remains on the surface of the adherend, but there are white marks ×: Adhesive remains on the surface of the adherend

[0120] [Method for evaluating substrate contamination under heat-resistant conditions] The test piece was attached to the adherend in the same manner as in the adhesive strength measurement method described above. It was then left to stand in an atmosphere of 150°C and RH for 1 hour, and immediately left to stand in an atmosphere of 23°C and 50% RH for 30 minutes. This was repeated five times, and then left to stand in an atmosphere of 23°C and 50% RH for 30 minutes, after which the test piece was peeled off, and the peeled surface of the adherend (the part where the test piece was attached) was irradiated with an LED light to check for the presence or absence of contamination on the adherend surface, which was used to evaluate the contamination resistance. 〇: No contamination △: No adhesive remains on the surface of the adherend, but there are white marks ×: Adhesive remains on the surface of the adherend

[0121] [Method for evaluating water contact angle] The water contact angle A of the adherend was measured without the test piece attached and without being subjected to temperature conditions. Next, the test piece was attached to the adherend in the same manner as in the above-mentioned method for measuring adhesive strength. After that, it was left to stand in an atmosphere of 150°C and RH for 1 hour, and immediately after that, it was left to stand in an atmosphere of 23°C and 50% RH for 30 minutes. After repeating this five times, it was left to stand in an atmosphere of 23°C and 50% RH for 30 minutes, after which the test piece was peeled off and the water contact angle B of the peeled adherend surface (the part where the test piece was attached) was measured. The change in water contact angle was calculated from the following (Equation 1). (Formula 1) Contact angle B - Contact angle A ◎: Change in water contact angle is less than 10° ○: Change in water contact angle is 10° or more and less than 20° △: Change in water contact angle is 20° or more and less than 30° ×: Change in water contact angle is 30° or more

[0122] [Table 1]

[0123] [Table 2]

[0124] [Table 3]

[0125] [Table 4]

[0126] [Table 5]

Claims

1. The composition comprises an acrylic polymer (A), a crosslinking agent (B) and a plasticizer (C), the acrylic polymer (A) contains a unit derived from an alkyl (meth)acrylate ester (a1), a unit derived from a nitrogen-containing monomer (a2), and a unit derived from an oxyalkylene chain-containing monomer (a3), the content of units derived from the nitrogen-containing monomer (a2) in the acrylic polymer (A) is 5 to 20 mass%; the content of units derived from the oxyalkylene chain-containing monomer (a3) ​​in the acrylic polymer (A) is 0.5 to 30 mass%; The crosslinking agent (B) contains a metal chelate crosslinking agent (b1), The plasticizer (C) contains an ester of a compound (c1) having a hydroxyl group and a compound (c2) having an acid group, and the SP value (Small formula) of the plasticizer (C) is 10 (cal / cm ２ ) １／２ and the number average molecular weight of the plasticizer (C) is 6,000 or less.

2. The pressure-sensitive adhesive composition according to claim 1, wherein the content of the plasticizer (C) is from 1 part by mass to 40 parts by mass based on 100 parts by mass of the acrylic polymer (A).

3. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the crosslinking agent (B) further comprises an isocyanate crosslinking agent (b2).

4. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the content of the metal chelate crosslinking agent (b1) is 0.1 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the acrylic copolymer (A).

5. The pressure-sensitive adhesive composition according to claim 3, wherein the content of the isocyanate crosslinking agent (b2) is from 1 part by mass to 15 parts by mass based on 100 parts by mass of the acrylic copolymer (A).

6. An adhesive layer formed from the adhesive composition according to any one of claims 1 to 5.

7. A protective film having the adhesive layer according to claim 6.

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