JP7375451B2 - adhesive composition - Google Patents

Description

The present invention relates to an adhesive composition.

Adhesive sheets are used in various fields such as automobiles, architecture, and electronic devices. Particularly in recent years, it has been used in many situations, such as protecting the surfaces of portable electronic devices such as tablets and smartphones, securing components, and protecting the components used during processing processes.

Examples of such adhesive sheets include transparent adhesive films using polymers containing units derived from alkyl (meth)acrylates and units derived from monomers having a saturated cyclic group (Patent Document 1), alkyl (meth)acrylate Adhesives using acrylic polymers formed from acrylate monomers, (meth)acrylate monomers having aromatic groups, nitrogen-containing vinyl monomers not having hydroxyl groups, vinyl monomers having carboxyl groups, etc. (Patent Documents 2 to 7), etc. is proposed.

JP2017-48328A JP 2019-70148 Publication JP 2019-70149 Publication JP 2019-70152 Publication JP2019-77881A JP2019-77882A Japanese Patent Application Publication No. 2019-90040

Components used in electronic devices require more advanced processing, so they are processed under harsher conditions than in the past. Therefore, the surface protection film used in the processing of these members needs to be able to be peeled cleanly from the member after the processing is completed, even after being exposed to harsh conditions such as high temperatures. Therefore, these protective films are required to have characteristics such as a small increase in adhesive strength after heat history, and the ability to not contaminate the adherend with adhesive residue when the adhesive sheet is peeled off from the surface of the adherend. There is. However, with conventionally known pressure-sensitive adhesive sheets, it is sometimes difficult to achieve the above characteristics when placed under harsher processing conditions (high temperature, high humidity).

The present invention has been made in view of the above-mentioned circumstances, and provides an adhesive and adhesive that exhibits less increase in adhesive strength even after being placed in high-temperature conditions and less contamination of the surface of the adherend after being peeled off from the adherend. Our goal is to provide adhesive tape.

The present inventors investigated and found that by using an acrylic polymer with a specific composition, there was little increase in adhesive strength even after being placed in high temperature and high humidity conditions, and the adhesive strength could be maintained even after being peeled off from the adherend. It has been found that it is possible to provide an adhesive with less surface contamination.

That is, the adhesive composition of the present invention contains an acrylic polymer (A) and a crosslinking agent (B), and the acrylic polymer (A) contains a unit derived from an alkyl (meth)acrylic acid ester (a1), The acrylic polymer (A) contains units derived from the nitrogen-containing monomer (a2) and units derived from the oxyalkylene chain-containing monomer (a3), and the content of the units derived from the nitrogen-containing monomer (a2) is Medium content is characterized by being 2% by mass or more.

According to the present invention, it is possible to provide an adhesive and an adhesive tape that exhibit little increase in adhesive strength even after being placed in high temperature and high humidity conditions, and that cause less contamination on the surface of an adherend after being peeled off from the adherend. I can do it.

The adhesive composition of the present invention contains an acrylic polymer (A) and a crosslinking agent (B).

The acrylic polymer (A) has a unit derived from a (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). include.

Examples of the (meth)acrylic acid alkyl ester (a1) include (meth)acrylic acid alkyl esters in which an alkyl group is bonded to an ester bond. The number of carbon atoms in the alkyl group is preferably 1 or more, more preferably 3 or more, even more preferably 4 or more, preferably 20 or less, more preferably 15 or less, still more preferably 12 or less, even more preferably 10 It is particularly preferably 8 or less.

The (meth)acrylic acid alkyl ester (a1) 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. It is preferable. The content of the (meth)acrylic acid alkyl ester (a1-1) is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass in the (meth)acrylic acid alkyl ester (a1). % or more, preferably 100% by mass or less.

The (meth)acrylic acid alkyl ester (a1) preferably further includes 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 included, its content is preferably 1% by mass or more, more preferably 2% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or more. It is not more than 30% by mass, more preferably not more than 30% by mass.

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

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

As the (meth)acrylic acid alkyl ester (a1), one type or two or more types can be used, for example, 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, isostearyl (meth)acrylate ) acrylate, etc.

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

The nitrogen-containing monomer (a2) is a monomer having a nitrogen atom and a polymerizable double bond in the molecule, and is a monomer having an amide bond and a polymerizable double bond in the molecule. For example, a lactam compound having a vinyl group; a (meth)acrylamide monomer; a functional group containing a nitrogen atom (for example, an amino group, a monosubstituted amino group, a disubstituted amino group, a nitrile group, etc.) ( Examples include meth)acrylate compounds.

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

The (meth)acrylamide monomer has a hydrogen atom or a hydrocarbon group (preferably an aliphatic hydrocarbon group) in the nitrogen atom of (meth)acrylamide. However, -CH ₂ - contained in the hydrocarbon is -CO - may be substituted with -, and the hydrogen atom contained in the hydrocarbon group may be substituted with a hydroxyl group). Furthermore, when the nitrogen atom of (meth)acrylamide is substituted with two or more groups (the hydrocarbon groups), these groups may be bonded to each other to form a ring containing a nitrogen atom.

The number of carbon atoms in the hydrocarbon group (preferably an aliphatic hydrocarbon group) substituting the nitrogen atom contained in the amide bond is preferably 1 or more, preferably 10 or less, and more preferably 6 or less.

As the (meth)acrylamide monomer, one type or two or more types can be used. The (meth)acrylamide monomer may be any of (meth)acrylamide, N-1 substituted (meth)acrylamide, and N,N-2 substituted (meth)acrylamide.

As the (meth)acrylamide monomer, one type or two or more types can be used, for example, (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, N-(2-hydroxyethyl)acrylamide, etc. N-1 substituted (meth)acrylamide compound; N-(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, N,N-dimethylamino Examples include N-2-substituted (meth)acrylamide compounds such as propyl (meth)acrylamide.

Among these, it is preferable that the (meth)acrylamide monomer includes a monomer represented by formula (1).

［式（１）中、Ｒ¹は、水素原子又はメチル基を表す。Ｒ²及びＲ³は、それぞれ独立に、水素原子又は炭素原子数１～２０の炭化水素基を表し、該炭化水素基に含まれる－ＣＨ₂－は、－ＣＯ－又は－Ｏ－に置き換わっていてもよく、該炭化水素基に含まれる水素原子は水酸基に置き換わっていてもよく、Ｒ²及びＲ³は、互いに結合して、窒素原子を含む環を形成していてもよい。］

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

The hydrocarbon groups represented by R ² and R ³ may be one or more types, such as linear or branched saturated aliphatic hydrocarbon groups; linear or branched aliphatic hydrocarbon groups; Examples include unsaturated aliphatic hydrocarbon groups such as

It is also preferable that the (meth)acrylamide monomer includes a (meth)acrylamide monomer in which both R ² and R ³ are the hydrocarbon groups. When both R ² and R ³ contain a (meth)acrylamide monomer in which the hydrocarbon group is the hydrocarbon group, the content of units derived from the monomer is preferably 0. The content is 2% by mass or more, more preferably 0.5% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less.

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, still more preferably 75% by mass or more, and the upper limit is It is 100% by mass.

As the (meth)acrylate compound having a functional group containing a nitrogen atom (for example, an amino group, a monosubstituted amino group, a disubstituted amino group, a nitrile group, etc.), (meth)acrylonitrile, t-butylaminoethyl (meth) Acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and the like. In the (meth)(meth)acrylate compound having a nitrogen atom-containing functional group, the nitrogen atom-containing functional group and the (meth)acryloxy group may be a single bond or have a carbon atom number of 1 to 10 (preferably Examples include compounds bonded via a hydrocarbon group (preferably an alkyl group) having 1 to 5 carbon atoms.

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), at least one of R ² and R ³ is a hydrocarbon group, and More preferable are monomers in which the hydrogen atoms in the monomer are replaced with hydroxyl groups.

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

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 is 15% by mass or less.

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, preferably 5 or less, more preferably 4 or less, still more preferably 3 or less, particularly preferably 2. The oxyalkylene chain-containing monomer is preferably alkoxypolyalkylene 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 methoxy, ethoxy, and propoxy groups.

As the oxyalkylene chain-containing monomer (a3), one type or two or more types can be used, and examples thereof include methoxyethylene glycol methacrylate and methoxyethylene glycol acrylate.

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

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

In the acrylic polymer (A), the content of units derived from the oxyalkylene chain-containing monomer (a3) is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1. The content is at least .5% by mass, preferably at most 30% by mass, more preferably at most 20% by mass, even more preferably at most 15% by mass.

The acrylic polymer (A) is 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). It may have a unit of

As the other monomer (a4), one type or two or more types can be used, for example, (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, β-carboxyethyl Unsaturated monocarboxylic acids such as (meth)acrylate; (meth)acrylic monomers having hydroxyl groups; epoxy ring-containing (meth)acrylic monomers such as glycidyl (meth)acrylate; cyclohexyl (meth)acrylate, etc. Alicycle-containing (meth)acrylic monomer; styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ethylvinylbenzene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p - Aromatic vinyl monomers such as phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, parahydroxystyrene; monomers having two or more vinyl groups, and the like.

Examples of the (meth)acrylic monomer having a hydroxyl group include a compound in which a hydroxyl group is bonded to an alkyl group of an alkyl (meth)acrylate; a polyalkylene glycol (meth)acrylate ester; preferably (meth)acrylic acid; It is a compound in which a hydroxyl group is bonded to the alkyl group of an acrylic acid alkyl ester, and more preferably a hydroxyl group is bonded to the terminal of the alkyl group in a (meth)alkylic acid alkyl ester.

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

Examples of the acrylic acid alkyl ester include the same compounds as those exemplified as the (meth)acrylic acid alkyl ester (a1).

As the (meth)acrylic monomer having a hydroxyl group, one type or two or more types can be used, for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl Hydroxyl alkyl (meth)acrylates such as (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; examples include polyethylene glycol (meth)acrylate, etc. .

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

In the acrylic polymer (A), the content of units derived from other monomers (a4) is 0% by mass or more, more preferably more than 0% by mass, even more preferably 0.01% by mass or more. The content is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less.

The weight average molecular weight of the acrylic polymer (A) is preferably 100,000 or more, more preferably 200,000 or more, even more preferably 300,000 or more, and preferably 2,000,000 or less, more preferably 1,800,000 or less, even more preferably is less than 1.5 million.

In this specification, the number average molecular weight and weight average molecular weight of the acrylic polymer (A) represent converted values measured using gel permeation chromatography (GPC) using polystyrene as a standard sample. .

In the adhesive composition of the present invention, the content of the acrylic polymer (A) is preferably 15% by mass or more, more preferably 20% by mass or more, and still more preferably 25% by mass or more in the nonvolatile matter, Preferably it is 100% by mass or less.

In this specification, the non-volatile content of the adhesive composition refers to the portion of the adhesive composition excluding a solvent component included as necessary.

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

As the polymerization initiator, for example, one or more types of thermal polymerization initiators can be used, including peroxide initiators such as benzoyl peroxide and lauroyl peroxide, and azo initiators such as azobisisobutylnitrile. Examples include.

The adhesive composition of the present invention contains a crosslinking agent (B). As the crosslinking agent, one type or two or more types can be used, for example, isocyanate crosslinking agent, epoxy crosslinking agent, aziridine crosslinking agent, polyvalent metal salt crosslinking agent, metal chelate crosslinking agent, keto hydrazide crosslinking agent, oxazoline. Examples include crosslinking agents, carbodiimide crosslinking agents, silane crosslinking agents, glycidyl(alkoxy)epoxysilane crosslinking agents, and the like.

Among these, isocyanate crosslinkers, epoxy crosslinkers, oxazoline crosslinkers, carbodiimide crosslinkers, and glycidyl (alkoxy)epoxysilane crosslinkers are preferred, isocyanate crosslinkers, epoxy crosslinkers, and carbodiimide crosslinkers are more preferred, and isocyanate crosslinkers are particularly preferred. .

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, still more preferably 80% by mass or more, even more preferably 90% by mass or more. , preferably 100% by mass or less.

The content of the crosslinking agent (B) is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass, based on 100 parts by mass of the acrylic polymer (A). The amount is at least 10 parts by mass, preferably at most 10 parts by mass, more preferably at most 7 parts by mass, even more preferably at most 5 parts by mass.

The pressure-sensitive adhesive composition of the present invention preferably contains a solvent (D). As the solvent (D), one type or two or more types can be used, for example, 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. ; Examples include aliphatic hydrocarbon solvents such as hexane. Among these, it is preferable to include an ester solvent.

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

The content of the solvent (D) in the adhesive composition is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, and preferably 90% by mass or less, more preferably Preferably it is 70% by mass or less, more preferably 65% by mass or less.

In the adhesive composition of the present invention, in order to maintain low yellowing, the content of the tackifying resin is preferably reduced, and is preferably less than 10 parts by mass based on 100 parts by mass of the acrylic polymer. , more preferably 8 parts by weight or less, still more preferably 3 parts by weight or less, even more preferably 1 part by weight or less, and preferably 0 parts by weight. By using an acrylic polymer (A) having a specific composition and weight average molecular weight and not containing a tackifying resin, the adhesive layer maintains low yellowing and can be used even under high temperature/high humidity conditions. , it is possible to maintain high adhesive strength and suppress migration of plasticizer.

The adhesive composition of the present invention contains, as additives, bases (such as aqueous ammonia) and acids for adjusting pH; blowing agents; softeners; antioxidants; fibers, balloons, beads, and metals made of glass or plastic. Even if it contains fillers such as powder; colorants such as pigments and dyes; pH adjusters; film-forming aids; leveling agents; thickeners; water repellents; antifoaming agents; acid catalysts; acid generators, etc. good.

An adhesive layer can be formed by applying the adhesive composition onto a support and drying it. The support may be any base material such as a release sheet or an adhesive sheet.

As the coating method, methods such as a knife coater, reverse coater, die coater, lip die coater, slot die coater, gravure coater, curtain coater, etc. can be used.

The thickness of the adhesive layer is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 15 μm or more, and preferably 100 μm or less, more preferably 70 μm or less, and still more preferably 50 μm or less.

The adhesive sheet or adhesive tape of the present invention includes the adhesive layer and the base material. The base material may be in the form of a film, sheet, tape, plate, three-dimensional shape, etc., and the material of the base material includes polyester resin, polypropylene resin, polyethylene resin, polyimide resin, vinyl chloride. Examples include plastics such as resins and urethane resins; rubber; nonwoven fabrics; metal foils; and paper; plastics are preferred, and vinyl chloride resins are more preferred. Further, the base material may have a smooth surface, or may have an uneven surface such as a fibrous base material or a foam base material.

The thickness of the base material is preferably 0.1 μm or more, and preferably 1,000 μm or less.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the Examples below, and modifications may be made as appropriate within the scope of the spirit of the preceding and following. Of course, other implementations are also possible, and all of them are included within the technical scope of the present invention.

[Synthesis example 1]
<Synthesis of acrylic resin (A1)>
830 parts by mass of n-butyl acrylate, 50 parts by mass of methyl acrylate, 50 parts by mass of hydroxyethyl acrylamide, 10 parts by mass of acrylamide, and NK ester AM-90G were placed in a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, and a thermometer. (manufactured by Shin Nakamura Chemical Industry Co., Ltd.), 40 parts by weight of NK Ester M-90G (manufactured by Shin Nakamura Chemical Industry Co., Ltd.), 10 parts by weight of hydroxyethyl acrylate, and 1000 parts by weight of ethyl acetate were charged, and under stirring. The temperature was raised to 70° C. while blowing nitrogen. After 1 hour, 10 parts by mass (solid content: 5%) of 2,2'-azobis(2-methylbutyronitrile) solution previously dissolved in ethyl acetate was added. Thereafter, after holding at 70°C for 8 hours while stirring, the contents were cooled and filtered through a 200-mesh wire gauze.Acrylic resin (A1 ) was obtained.

[Synthesis example 2]
<Synthesis of acrylic resin (A1)>
In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, and a 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 acryloylmorpholine, and hydroxyethyl. 50 parts by weight of acrylamide, 20 parts by weight of NK Ester AM-90G, 20 parts by weight of NK Ester M-90G, 5 parts by weight of hydroxyethyl methacrylate, and 1000 parts by weight of ethyl acetate were charged, and the temperature was raised to 70°C while stirring and blowing nitrogen. did. After 1 hour, 10 parts by mass (solid content: 5%) of 2,2'-azobis(2-methylbutyronitrile) solution previously dissolved in ethyl acetate was added. Thereafter, after holding at 70°C for 8 hours while stirring, the contents were cooled and filtered through a 200-mesh wire gauze.Acrylic resin (A2 ) was obtained.

[Synthesis example 3]
<Synthesis of acrylic resin (A3)>
In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, and a thermometer, 400 parts by mass of n-butyl acrylate, 310 parts by mass of 2-ethylhexyl acrylate, 100 parts by mass of methyl acrylate, 100 parts by mass of hydroxyethyl acrylamide, and dimethyl acrylamide. 20 parts by mass, 40 parts by mass of NK ester AM-130G (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.), 30 parts by mass of 4-hydroxybutyl acrylate, and 1000 parts by weight of ethyl acetate were heated to 70°C while stirring and blowing nitrogen. The temperature rose. After 1 hour, 10 parts by mass (solid content: 5%) of 2,2'-azobis(2-methylbutyronitrile) solution previously dissolved in ethyl acetate was added. Thereafter, after holding at 70°C for 8 hours while stirring, the contents were cooled and filtered through a 200-mesh wire gauze.Acrylic resin (A3 ) was obtained.

[Synthesis example 4]
<Synthesis of acrylic resin (A4)>
In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, and a thermometer, 825 parts by mass of n-butyl acrylate, 50 parts by mass of methyl acrylate, 20 parts by mass of acryloylmorpholine, 50 parts by mass of dimethylacrylamide, and NK ester M- 50 parts by weight of 230G (manufactured by Shin Nakamura Chemical Industry Co., Ltd.), 5 parts by weight of 4-hydroxybutyl acrylate, and 1000 parts by weight of ethyl acetate were charged, and the temperature was raised to 70° C. while stirring and blowing nitrogen. After 1 hour, 10 parts by mass (solid content: 5%) of 2,2'-azobis(2-methylbutyronitrile) solution previously dissolved in ethyl acetate was added. Thereafter, after holding at 70°C for 8 hours with stirring, the contents were cooled and filtered through a 200-mesh wire gauze.The contents were then cooled and filtered using an acrylic resin (A4 ) was obtained.

[Synthesis example 5]
<Synthesis of acrylic resin (A5)>
In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, and a thermometer, 710 parts by mass of 2-ethylhexyl acrylate, 150 parts by mass of methyl acrylate, 50 parts by mass of hydroxyethyl acrylamide, 20 parts by mass of NK ester AM-130G, and NK were added. 20 parts by weight of 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 70°C while stirring and blowing nitrogen. After 1 hour, 10 parts by mass (solid content: 5%) of 2,2'-azobis(2-methylbutyronitrile) solution previously dissolved in ethyl acetate was added. Thereafter, after holding at 70°C for 8 hours while stirring, the contents were cooled and filtered through a 200-mesh wire gauze.Acrylic resin (A5 ) was obtained.

[Synthesis example 6]
<Synthesis of acrylic resin (A6)>
In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, and a thermometer, 875 parts by mass of 2-ethylhexyl acrylate, 20 parts by mass of acryloylmorpholine, 40 parts by mass of acrylamide, 50 parts by mass of NK ester AM-90G, and hydroxyethyl. 10 parts by weight of methacrylate, 5 parts by weight of acrylic acid, and 1000 parts by weight of ethyl acetate were charged, and the temperature was raised to 70° C. while stirring and blowing nitrogen. After 1 hour, 10 parts by mass (solid content: 5%) of 2,2'-azobis(2-methylbutyronitrile) solution previously dissolved in ethyl acetate was added. Thereafter, after holding at 70°C for 8 hours while stirring, the contents were cooled and filtered through a 200-mesh wire gauze.Acrylic resin (A6 ) was obtained.

[Synthesis example 7]
<Synthesis of acrylic resin (A7)>
In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, and a 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 dimethylacrylamide, and NK ester. 120 parts by weight of M-90G, 40 parts by weight of 4-hydroxybutyl acrylate, 100 parts by weight of cyclohexyl acrylate, and 1000 parts by weight of ethyl acetate were charged, and the temperature was raised to 70°C while stirring and blowing nitrogen. After 1 hour, 10 parts by mass (solid content: 5%) of 2,2'-azobis(2-methylbutyronitrile) solution previously dissolved in ethyl acetate was added. Thereafter, after holding at 70°C for 8 hours while stirring, the contents were cooled and filtered through a 200-mesh wire gauze.Acrylic resin (A7 ) was obtained.

[Synthesis example 8]
<Synthesis of comparative acrylic resin (A1')>
In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, and a thermometer, 50 parts by mass of n-butyl acrylate, 670 parts by mass of 2-ethylhexyl acrylate, 210 parts by mass of methyl acrylate, 60 parts by mass of 4-hydroxybutyl acrylate, 10 parts by weight of acrylic acid and 1000 parts by weight of ethyl acetate were charged, and the temperature was raised to 70° C. while stirring and blowing nitrogen. After 1 hour, 10 parts by mass (solid content: 5%) of 2,2'-azobis(2-methylbutyronitrile) solution previously dissolved in ethyl acetate was added. Thereafter, after holding at 70°C for 8 hours while stirring, the contents were cooled and filtered through a 200-mesh wire gauze.A comparative acrylic resin (nonvolatile content: 50% by mass, viscosity: 130,000mPa・s, weight average molecular weight: 650,000) A1') was obtained.

[Synthesis example 9]
<Synthesis of comparative acrylic resin (A2')>
In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, and a thermometer, 300 parts by mass of n-butyl acrylate, 350 parts by mass of 2-ethylhexyl acrylate, 150 parts by mass of methyl acrylate, 100 parts by mass of dimethyl acrylamide, and hydroxyethyl acrylate. 100 parts by weight and 1000 parts by weight of ethyl acetate were charged, and the temperature was raised to 70°C while stirring and blowing nitrogen. After 1 hour, 10 parts by mass (solid content: 5%) of 2,2'-azobis(2-methylbutyronitrile) solution previously dissolved in ethyl acetate was added. Thereafter, after holding at 70°C for 8 hours while stirring, the contents were cooled and filtered through a 200-mesh wire gauze.A comparative acrylic resin (non-volatile content: 50% by mass, viscosity: 110,000 mPa・s, weight average molecular weight: 550,000) A2') was obtained.

[Synthesis example 10]
<Synthesis of comparative acrylic resin (A3')>
In a reaction vessel equipped with a stirrer, reflux condenser, nitrogen inlet tube, and thermometer, 790 parts by mass of 2-ethylhexyl acrylate, 150 parts by mass of NK Ester AM-90G, 50 parts by mass of hydroxyethyl methacrylate, 10 parts by mass of acrylic acid, and acetic acid. 1000 parts by weight of ethyl was charged, and the temperature was raised to 70°C while stirring and blowing nitrogen. After 1 hour, 10 parts by mass (solid content: 5%) of 2,2'-azobis(2-methylbutyronitrile) solution previously dissolved in ethyl acetate was added. Thereafter, after holding at 70°C for 8 hours while stirring, the contents were cooled and filtered through a 200-mesh wire gauze.A comparative acrylic resin (nonvolatile content: 50% by mass, viscosity: 110,000 mPa・s, weight average molecular weight: 520,000) A3') was obtained.

[Synthesis example 11]
<Synthesis of comparative acrylic resin (A4')>
In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen introduction tube, and a thermometer, 700 parts by mass of n-butyl acrylate, 100 parts by mass of 2-ethylhexyl acrylate, 15 parts by mass of acryloylmorpholine, and 50 parts by mass of NK ester AM-130G. , 50 parts by weight of NK Ester M-90G, 80 parts by weight of 4-hydroxybutyl acrylate, 5 parts by weight of acrylic acid, and 1000 parts by weight of ethyl acetate, and the mixture was heated to 70°C while stirring and blowing nitrogen. After 1 hour, 10 parts by mass (solid content: 5%) of 2,2'-azobis(2-methylbutyronitrile) solution previously dissolved in ethyl acetate was added. Thereafter, after holding at 70°C for 8 hours with stirring, the contents were cooled and filtered through a 200-mesh wire gauze.A comparative acrylic resin (non-volatile content: 50% by mass, viscosity: 100,000mPa・s, weight average molecular weight: 490,000) A4') was obtained.

[Example 1]
To 100 parts by mass of the acrylic resin (A1) obtained in Synthesis Example 1, 4 parts by mass of an isocyanate crosslinking agent (Fine Tac Curing Agent D-40; manufactured by DIC Corporation) was stirred and mixed uniformly. In this way, an acrylic adhesive composition (1) was obtained.

[Examples 2 to 7, Comparative Examples 1 to 4]
An acrylic adhesive was prepared in the same manner as in Example 1, except that acrylic resins (A2) to (A7) or comparative acrylic resins (A1') to (A4') were used instead of 100 parts by mass of acrylic resin (A1). Compositions (2) to (7) and comparative acrylic adhesive compositions (1') to (4') were obtained.

[Adhesive film processing method]
The film obtained in Examples 1 to 7 and Comparative Examples 1 to 4 was coated on the surface of a 50 μm thick polyethylene terephthalate film (release PET50) whose surface had been subjected to mold release treatment so that the film thickness after drying with the solvent was 12 μm. After applying the acrylic adhesive composition and the comparative acrylic adhesive composition and volatilizing the solvent in a dryer at 80° C. for 3 minutes, a PET 38 μm film was attached.

[Method of measuring adhesive strength]
A test piece was prepared by cutting the adhesive film prepared by the method described above into a 25 mm width piece. The adherend was a glass plate, and the adhesive was attached to the adherend using a 2 kg roll x 2 reciprocations. One hour after pasting, the 180 degree peel strength was measured at a peel rate of 300 mm/min in an atmosphere of 23° C. and 50% RH, and this was taken as the adhesive strength.

[Method of measuring adhesive strength after heat resistance]
A test piece was attached to the adherend in the same manner as in the method for measuring adhesive strength described above. Thereafter, it was left in an atmosphere of 140° C. for 1 hour and then taken out. After being left in an atmosphere of 23° C. and 50% RH for 30 minutes, the 180 degree peel strength was measured at a peel rate of 300 mm/min, and the adhesive strength after heat resistance was measured.

[Method for evaluating contamination of adherend]
A test piece was attached to the adherend in the same manner as in the method for measuring adhesive strength described above. Thereafter, it was left in an atmosphere of 60° C. and 90% RH for 3 days, and then taken out. After leaving it in an atmosphere of 23°C and 50% RH for 30 minutes, peel off the test piece and irradiate the peeled adherend surface (the part that was pasted) with an LED light to check whether there is any contamination on the adherend surface. This was confirmed and the stain resistance was evaluated.
〇: No contamination △: No adhesive remains on the surface of the adherend, but there are white marks ×: There is residual adhesive on the surface of the adherend

The results are shown in Tables 1 and 2.

Examples 1 to 7 are examples of the present invention, and even after being placed under high temperature conditions, there was little increase in adhesive strength, and there was little contamination on the surface of the adherend after it was peeled off from the adherend. Comparative Example 1 is an example that does not contain a nitrogen-containing monomer or an oxyalkylene chain-containing monomer, and the adhesive strength increases after being placed in high temperature conditions. Adhesive residue was confirmed on the body surface. Comparative Example 2 is an example that does not contain an oxyalkylene chain-containing monomer, and the adhesive strength increases after being placed in high temperature conditions. Remaining adhesive was confirmed. Comparative Example 3 is an example that does not contain a nitrogen-containing monomer, and the adhesive strength increases after being placed in high temperature conditions. was confirmed to remain. Comparative Example 4 is an example in which the content of units derived from the nitrogen-containing monomer (a2) is less than 2% by mass, and the adhesive strength increases after being placed in high temperature conditions. After the adhesive was placed on the surface of the adherend, it was confirmed that adhesive remained on the surface of the adherend.

Claims (4)

Contains an acrylic polymer (A) and a crosslinking agent (B),
The acrylic polymer (A) has a unit derived from a (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). including;
The (meth)acrylic acid alkyl ester (a1) contains a monomer whose homopolymer has a glass transition temperature of −15° C. or higher,
The nitrogen-containing monomer (a2) includes a nitrogen-containing monomer (a2-1) having a hydroxyl group and a nitrogen-containing monomer (a2-2) having no hydroxyl group,
An adhesive composition in which the content of units derived from the nitrogen-containing monomer (a2) is 2% by mass or more in the acrylic polymer (A). The adhesive composition according to claim 1 , wherein the nitrogen-containing monomer (a2) is a (meth)acrylamide monomer. An adhesive layer formed from the adhesive composition according to claim 1 or 2 . A protective film having the adhesive layer according to claim 3 .