Adhesives and adhesive sheets for polyvinyl chloride

Abstract

To provide an adhesive sheet which has solvent resistance to a low polar solvent, curved surface property, and water paste suitability, and is also excellent in reworkability, and an adhesive for polyvinyl chloride forming the adhesive sheet.SOLUTION: An adhesive for a polyvinyl chloride contains an acrylic resin (A) and a curing agent (B), in which the acrylic resin (A) is a copolymer of a monomer mixture containing 15-60 mass% of a monomer (a1) represented by general formula (1) and 0.5-7 mass% of a monomer (a2) having a carboxyl group, and the curing agent (B) is at least one selected from the group consisting of a chelate curing agent, an isocyanate curing agent and an epoxy curing agent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an adhesive and adhesive sheet for polyvinyl chloride that can be suitably used for laminating polyvinyl chloride. [Background technology]

[0002] Labels and stickers applied to motorcycles, automobiles, signs, electrical appliances, etc., commonly use resin sheets made of polyvinyl chloride (PVC) as the base material due to their flexibility and weather resistance. The back of these PVC sheets has a release liner attached via an adhesive, while the surface of the sheet is printed. Such adhesive sheets made of PVC are used outdoors, especially on motorcycles, and are prone to dirt and gasoline contamination. As a result, the PVC may swell, and the adhesive may not be able to withstand the resulting stress, leading to lifting or peeling.

[0003] Furthermore, the surfaces to which adhesive sheets are applied, such as motorcycles, automobiles, signs, and electrical appliances, are almost always curved. Adhesive sheets must not peel off over time even when applied to curved surfaces (curved surface suitability), and in addition, they must be suitable for wet application to the bodies of motorcycles, automobiles, etc. (wet application suitability).

[0004] Furthermore, in recent years, from the perspective of reducing vehicle weight for energy conservation, resin parts are increasingly being used in vehicles. Marking film, which is a decorative adhesive sheet with colors, letters, patterns, etc. printed on a film, is increasingly being used on these resin parts. Marking film is made by laminating an adhesive layer onto a base material such as polyvinyl chloride, and is used by attaching the adhesive layer side to the substrate. In emerging countries, the automotive society is still expanding explosively, and the opportunities for marking film to be applied to rubber products such as tires and plastic products for interiors at mass retailers are also increasing dramatically. The marking films used on these vehicles are frequently exposed to gasoline, so high gasoline resistance is required.

[0005] Patent Document 1 describes the use of an adhesive for marking films in which the ratio of the mol% of carboxyl group-containing monomer to the average number of carbon atoms of the alkyl group of the alkyl acrylate is 1.5 to 4.5, and the gel fraction after crosslinking is 40 to 90%. Furthermore, Patent Document 2 discloses that in acrylic copolymers used as adhesives, gasoline resistance is improved by using acrylic copolymers obtained using carboxyl group-containing monomers and hydroxyl group-containing monomers.

[0006] Furthermore, in recent years, from a "sustainability" perspective, there has been a growing effort to utilize plant-derived bioethanol as an alternative fuel to gasoline, and the use of ethanol-blended gasoline in gasoline engine vehicles has also begun. As a result, adhesive sheets are required to be resistant to both low-polarity gasoline and high-polarity ethanol. Therefore, the selection and design of materials for adhesive sheets, including the adhesive itself, have become more stringent.

[0007] In contrast, Patent Document 3 discloses that an adhesive layer formed from an adhesive composition containing an acrylic copolymer and a crosslinking agent, obtained by copolymerizing an acrylic copolymer and a monomer mixture containing alkyl (meth)acrylate and a high-concentration carboxyl group-containing unsaturated monomer applied to a vinyl chloride resin film, has a weight-average molecular weight of 250,000 or more when immersed for 20 minutes in a mixed solvent of gasoline and ethanol (gasoline:ethanol = 90:10, volume ratio), so-called E10 fuel, and exhibits excellent resistance to mixed gasoline. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 10-46127 [Patent Document 2] Japanese Patent Publication No. 2016-210863 [Patent Document 3] Japanese Patent Publication No. 2019-70078 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, adhesive layers formed from acrylic copolymers obtained by copolymerizing high concentrations of carboxyl group-containing unsaturated monomers have a problem in that they have high initial adhesive strength when bonded to an adherend, making them unsuitable for repositioning, i.e., they have poor reworkability.

[0010] In other words, the problem that the present invention aims to solve is to provide an adhesive sheet that has solvent resistance to low-polarity solvents, suitability for curved surfaces, suitability for water application, and also excellent reworkability, as well as an adhesive for polyvinyl chloride that forms the adhesive sheet. [Means for solving the problem]

[0011] The inventors of this invention have conducted extensive research to solve the above problems and have found that the above problems can be solved by the polyvinyl chloride adhesive described below, thereby completing the present invention.

[0012] That is, the first invention comprises an acrylic resin (A) and a curing agent (B), The present invention relates to an adhesive for polyvinyl chloride, wherein the acrylic resin (A) is a copolymer of a monomer mixture containing 15 to 60% by mass of monomer (a1) represented by the following general formula (1) and 0.5 to 7% by mass of monomer (a2) having a carboxyl group, and the curing agent (B) is at least one selected from the group consisting of chelating curing agents, isocyanate curing agents, and epoxy curing agents. [ka] (In general formula (1), R 1 is an alkyl group having 1 to 2 carbon atoms, or a phenyl group, R 2 R is an alkylene group having 2 to 4 carbon atoms. 3 (where n represents a hydrogen atom or methyl group, and n is an integer from 1 to 4 representing a repeating unit.)

[0013] Further, in the second invention, the monomer mixture contains an alkyl (meth)acrylate monomer (a3) having an alkyl group with 1 to 2 carbon atoms, and the content of the alkyl (meth)acrylate monomer (a3) is 35 to 79.5% by mass in 100% by mass of the monomer mixture, relating to the adhesive for polyvinyl chloride.

[0014] Further, in the third invention, the monomer mixture contains an alkyl (meth)acrylate monomer (a5) having an alkyl group with 4 to 13 carbon atoms, and the content of the alkyl (meth)acrylate monomer (a5) is 0.5 to 10% by mass in 100% by mass of the monomer mixture, relating to the adhesive for polyvinyl chloride.

[0015] Further, in the fourth invention, the monomer mixture contains a monomer (a4) having a hydroxyl group, and the content of the monomer (a4) having a hydroxyl group is 0.5 to 7% by mass in 100% by mass of the monomer mixture, relating to the adhesive for polyvinyl chloride.

[0016] Further, in the fifth invention, the acrylic resin (A) has a weight average molecular weight of 200,000 to 600,000, relating to the adhesive for polyvinyl chloride.

[0017] Further, in the sixth invention, the curing agent (B) includes a chelate curing agent or an epoxy curing agent, relating to the adhesive for polyvinyl chloride.

[0018] Further, in the seventh invention, the curing agent (B) includes a chelate curing agent or an epoxy curing agent and an isocyanate curing agent, relating to the adhesive for polyvinyl chloride.

[0019] Further, in the eighth invention, it relates to an adhesive sheet including a base material and an adhesive layer formed from the adhesive for polyvinyl chloride.

[0020] Furthermore, the ninth invention relates to the adhesive sheet, wherein the base material is polyvinyl chloride. [Effects of the Invention]

[0021] The present invention provides an adhesive sheet that possesses solvent resistance to low-polarity solvents, suitability for curved surfaces, suitability for water application, and excellent reworkability, as well as an adhesive for polyvinyl chloride used to form the adhesive sheet. [Modes for carrying out the invention]

[0022] The following terms are defined for the purposes of this invention. First, sheet, film, and tape are synonymous. (Meth)acrylic acid means acrylic acid and methacrylic acid. Monomer means an ethylenically unsaturated double bond-containing monomer. Adhesion refers to the surface to which the adhesive sheet is attached. In this specification, adhesives for polyvinyl chloride, monomer (a1) represented by general formula (1), monomer (a2) having a carboxyl group, alkyl (meth)acrylate monomer having an alkyl group with 1 to 2 carbon atoms (a3), monomer (a4) having a hydroxyl group, and alkyl (meth)acrylate monomer having an alkyl group with 4 to 13 carbon atoms (a5) may be abbreviated as adhesive, monomer (a1), monomer (a2), monomer (a3), monomer (a4), and monomer (a5), respectively. Unless otherwise noted, the various components mentioned herein may be used individually or in combination of two or more. Furthermore, unless otherwise specified, the "~" symbol indicating a numerical range includes both the lower and upper limits. The embodiments of the present invention will be described in detail below, but the following description is merely an example (representative example) of the embodiments of the present invention, and the present invention is not limited to these contents unless it exceeds the gist of the invention.

[0023] Adhesives for polyvinyl chloride The adhesive of the present invention comprises an acrylic resin (A) and a curing agent (B), wherein the acrylic resin (A) is a copolymer of a monomer mixture containing 15 to 60% by mass of monomer (a1) represented by general formula (1) and 0.5 to 7% by mass of monomer (a2) having a carboxyl group, and the curing agent (B) is at least one selected from the group consisting of chelating curing agents, isocyanate curing agents, and epoxy curing agents. Monomer (a1) has 1 to 4 alkylene oxide groups, which imparts hydrophilicity and excellent resistance to hydrocarbons in gasoline. Monomer (a2) has carboxyl groups, exhibiting high adhesion to the adherend and acting as a crosslinking point with the curing agent. This adhesive uses an acrylic resin (A) in which monomer (a1) and monomer (a2) are in the above-mentioned specific ratio, and further combines it with the above-mentioned specific curing agent (B). As a result, it exhibits excellent resistance to solvents such as ethanol-mixed gasoline, excellent suitability for curved surfaces and wet application, and also has excellent reworkability without excessively high adhesion. This adhesive contains at least an acrylic resin (A) and a curing agent (B), and may contain other components to the extent that it achieves the effects of the present invention.

[0024] <Acrylic resin (A)> Acrylic resin (A) is a copolymer of a mixture containing at least 15 to 60% by mass of monomer (a1) and 0.5 to 7% by mass of monomer (a2) having a carboxyl group, and may further contain other monomers. In other words, acrylic resin (A) is a copolymer having at least constituent units derived from monomer (a1) and constituent units derived from monomer (a2), and may further contain constituent units derived from other monomers.

[0025] Other monomers besides monomers (a1) and (a2) include alkyl (meth)acrylate monomers having an alkyl group with 1 to 2 carbon atoms (a3), monomers having a hydroxyl group (a4), alkyl (meth)acrylate monomers having an alkyl group with 4 to 13 carbon atoms (a5), monomers having an amide bond, monomers having an epoxy group, monomers having an amino group, styrenes, vinyl ethers, vinyl esters, and the like.

[0026] Due to its excellent solvent resistance, suitability for curved surfaces, suitability for water application, and reworkability, acrylic resin (A) is a copolymer of a monomer mixture containing 15-60% by mass of monomer (a1) represented by general formula (1) and 0.5-7% by mass of monomer (a2) having a carboxyl group. Preferably, the copolymer is a monomer mixture further containing an alkyl (meth)acrylate monomer (a3) ​​having an alkyl group having 1 to 2 carbon atoms. Preferably, it is a copolymer of a monomer mixture further containing a monomer (a4) having a hydroxyl group. Preferably, the copolymer is a monomer mixture further containing an alkyl (meth)acrylate monomer (a5) having an alkyl group having 4 to 13 carbon atoms.

[0027] In the present invention, the weight-average molecular weight (hereinafter also referred to as Mw) of the acrylic resin (A) may be 10,000 or more, but is preferably 150,000 to 700,000, more preferably 200,000 to 600,000, even more preferably 200,000 to 500,000, and particularly preferably 200,000 to 400,000, from the viewpoint of excellent solvent resistance, suitability for curved surfaces, suitability for water application, and reworkability. A weight-average molecular weight of 150,000 or more ensures a sufficient number of crosslinking points with the curing agent (B), resulting in an adhesive that is less soluble in low-polarity solvents. On the other hand, a weight-average molecular weight of 700,000 or less is sufficient, providing excellent solvent resistance, suitability for curved surfaces, suitability for water application, and reworkability. In this invention, the weight-average molecular weight is a polystyrene-based value measured by gel permeation chromatography (GPC), and specific details can be found in the examples described later.

[0028] [Monomer (a1)] Monomer (a1) is a monomer represented by the following general formula (1). By using such a monomer having an alkoxyalkylene oxide group, an alkoxypolyalkylene oxide group, a phenoxyalkylene oxide group, or a phenoxypolyalkylene oxide group, polarity can be imparted to form an adhesive layer that is difficult to dissolve in a low-polarity solvent (such as gasoline). Preferably, it is a (meth)acrylic acid alkyl ester monomer having an alkoxyalkylene oxide group.

[0029] [Chemical formula] (In general formula (1), R 1 is an alkyl group having 1 to 2 carbon atoms or a phenyl group, R 2 is an alkylene group having 2 to 4 carbon atoms, R 3 is a hydrogen atom or a methyl group, and n represents a repeating unit and is an integer of 1 to 4.)

[0030] R 1 is an alkyl group having 1 to 2 carbon atoms or a phenyl group, specifically, a methyl group, an ethyl group, or a phenyl group, and is preferably a methyl group or an ethyl group in terms of water resistance and resistance to low-polarity solvents. R 2 is an alkylene group having 2 to 4 carbon atoms, which may be linear or branched. Specifically, it is an ethylene group, a propylene group, or a butylene group, and is preferably an ethylene group in terms of water resistance and resistance to low-polarity solvents. R 3 is a hydrogen atom or a methyl group. n represents a repeating unit and is an integer of 1 to 4, and preferably the repeating unit n is 1 in terms of water resistance and resistance to low-polarity solvents.

[0031] The monomer (a1) content is 15 to 60% by mass, preferably 20 to 30% by mass. A higher monomer (a1) content results in better resistance to low-polarity solvents, so 15% by mass or more is preferred. On the other hand, by setting the monomer (a1) content to 60% by mass or less, an adhesive with excellent water resistance and suitability for wet application is obtained.

[0032] Examples of monomers (a1) include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, ethoxypolypropylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, and phenoxypolypropylene glycol (meth)acrylate. The repeating unit n of the polyalkylene glycol chain is an integer between 2 and 4. Among these, 2-methoxyethyl (meth)acrylate or 2-ethoxyethyl (meth)acrylate is preferred from the viewpoint of balancing water resistance and resistance to low-polarity solvents, and 2-methoxyethyl (meth)acrylate is more preferred.

[0033] [Monomer (a2)] Monomer (a2) is a monomer that has a carboxyl group. The monomer (a2) imparts tackiness to the acrylic resin (A), and maintains its tackiness and cohesive force even when swollen with a low-polarity solvent, thereby suppressing lifting and peeling from the adherend. The monomer (a2) content is 0.5 to 7% by mass of 100% by mass of the monomer mixture constituting the acrylic resin. From the viewpoint of achieving both adhesive strength and reworkability, as well as storage stability, 1.0 to 6% by mass is preferred, 2 to 5% by mass is more preferred, and 2 to 4% by mass is even more preferred. Within this range, it is possible to satisfy the desired adhesive properties while maintaining reworkability and storage stability.

[0034] Examples of monomers (a2) include (meth)acrylic acid, monohydroxyethyl acrylic phthalate, p-carboxybenzyl acrylic acid, ethylene oxide-modified acrylic phthalate (number of moles of ethylene oxide added: (2~18)), monohydroxyethyl acrylic succinate, β-carboxyethyl acrylate, and itaconic acid. Among these, (meth)acrylic acid is preferred from the viewpoint of imparting tackiness and cohesiveness when expanded by a low-polarity solvent.

[0035] [Monomer (a3)] Monomer (a3) ​​is an alkyl (meth)acrylate monomer having an alkyl group with 1 to 2 carbon atoms, excluding monomers (a1), (a2), and (a4). It is preferable that the acrylic resin (A) further contains monomer (a3) ​​as a monomer. By including monomer (a3), the cohesive force of the acrylic resin is improved, and while maintaining the basic adhesive properties, solvent resistance and reworkability provided by monomer (a1) and solvent resistance to adhesive properties provided by monomer (a3) ​​can be added.

[0036] When monomer (a3) ​​is used, the monomer (a3) ​​content is preferably 35 to 79.5% by mass, more preferably 45 to 75% by mass, and even more preferably 55 to 70% by mass, of 100% by mass of the monomer mixture. By using monomer (a3) ​​within this range, cohesive force is imparted to the acrylic resin (A), maintaining cohesive force even in adhesives swollen with low-polarity solvents, and suppressing lifting and peeling of the polyvinyl chloride film due to swelling.

[0037] Examples of monomers (a3) ​​include methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate. Among these, methyl acrylate and ethyl acrylate, which have fewer carbon atoms in their side chains, are preferred from the viewpoint of low polarity solvents.

[0038] [Monomer (a4)] Monomer (a4) is a monomer that has a hydroxyl group. It is preferable that the acrylic resin (A) further contains monomer (a4) as a monomer. By including monomer (a4), the cohesive force of the acrylic resin (A) is further enhanced, and the cohesive force of the adhesive layer swollen by the low-polarity solvent can be further maintained. In addition, the polarity of the adhesive can be made higher, which suppresses the dissolution of the adhesive in the low-polarity solvent and suppresses lifting and peeling of the polyvinyl chloride film due to swelling when immersed in the low-polarity solvent. On the other hand, when prioritizing the storage stability of adhesives for polyvinyl chloride, it is preferable that the acrylic resin (A) does not contain monomer (a4). Adhesives using acrylic resin (A) that do not contain monomer (a4) exhibit suppressed viscosity changes even during long-term storage.

[0039] When monomer (a4) is used, the content of monomer (a4) is preferably 0.5 to 7% by mass, more preferably 1 to 6% by mass, and even more preferably 2 to 5% by mass, based on 100% by mass of the monomer mixture. By using monomer (a4) within this range, it is possible to impart both cohesive force and polarity to the acrylic resin (A) while maintaining its basic adhesive properties and solvent resistance. This allows the cohesive force to be maintained even in an adhesive layer swollen with a low-polarity solvent, suppressing lifting and peeling due to swelling of the polyvinyl chloride film. Furthermore, it is preferable because it can also provide excellent suitability for water application and curved surfaces.

[0040] Examples of monomers (a4) include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and 8-hydroxyoctyl (meth)acrylate; glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, and 1,4-cyclohexanedimethanol mono(meth)acrylate; caprolactone-modified (meth)acrylate; and N-hydroxyalkyl (meth)acrylamides such as N-hydroxymethyl (meth)acrylamide and N-hydroxyethyl (meth)acrylamide. Among these, 2-hydroxyethyl (meth)acrylate is preferred.

[0041] [Monomer (a5)] Monomer (a5) is an alkyl (meth)acrylate monomer having an alkyl group with 4 to 13 carbon atoms, excluding monomers (a1), (a2), and (a4). By further using monomer (a5) as a monomer constituting the acrylic resin (A), longer side chains can be introduced compared to monomers (a1) and (a3), thus providing cohesive force through entanglement of side chains. This cohesive force is maintained even in the adhesive layer swollen with a low-polarity solvent, and lifting and peeling due to swelling of the polyvinyl chloride film is suppressed, making it preferable. More preferably, an alkyl (meth)acrylate monomer having an alkyl group with 4 to 8 carbon atoms is used. The alkyl group may be linear or branched.

[0042] When monomer (a5) is used, the monomer (a5) content is preferably 0.5 to 10% by mass, more preferably 1.5 to 8% by mass, and even more preferably 2.5 to 6% by mass, based on 100% by mass of the monomer mixture. Using monomer (a5) within this range is preferable because it allows for the imparting of cohesive force through the entanglement of side chains, which maintains cohesive force even in the adhesive layer swollen with a low-polarity solvent, thereby suppressing lifting and peeling of the polyvinyl chloride film due to swelling.

[0043] Examples of monomers (a5) include, but are not limited to, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, neopentyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-pentyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, and tridecyl (meth)acrylate.

[0044] The acrylic resin (A) is preferable to contain at least one of monomer (a3) ​​and monomer (a5) because it is superior in solvent resistance, flexibility, water-bonding suitability, and reworkability. By combining monomer (a1) with monomer (a3) ​​and / or monomer (a5), resistance to both hydrophilic and hydrophobic solvents is improved, and resistance to solvents such as ethanol-blended gasoline is also excellent.

[0045] [Other monomers] The monomers constituting the acrylic resin (A) of the present invention may include other monomers other than the above monomers (a1), (a2), (a3), (a4), and (a5). Other monomers include monomers having amide bonds, monomers having epoxy groups, monomers having amino groups, monomers having aromatic rings, styrenes, vinyl ethers, vinyl esters, and vinyl cyanides.

[0046] Examples of monomers containing an amide bond include (meth)acrylamide compounds such as (meth)acrylamide, N-methyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, diacetone(meth)acrylamide, and N-(butoxymethyl)acrylamide; Examples include heterocyclic compounds such as N-vinylpyrrolidone, N-vinylcaprolactam, and acryloylmorpholine.

[0047] Examples of monomers having an epoxy group include glycidyl (meth)acrylate, methylglycidyl (meth)acrylate, and 3,4-epoxycyclohexylmethyl (meth)acrylate.

[0048] Examples of monomers having an amino group include monomethylaminoethyl (meth)acrylate, monoethylaminoethyl (meth)acrylate, monomethylaminopropyl (meth)acrylate, and monoethylaminopropyl (meth)acrylate, as well as monoalkylamino esters of (meth)acrylate.

[0049] Examples of monomers having an aromatic ring include phenoxyethyl acrylate, benzyl acrylate, phenoxydiethylene glycol (meth)acrylate, and ethylene oxide-modified nonylphenol (meth)acrylate.

[0050] From the viewpoint of adhesion, film hardness, weather resistance, etc., the monomer having an aromatic ring is preferably present in an amount of 0 to 7% by mass of 100% by mass of the monomer mixture.

[0051] Other monomers include cyclohexyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate; styrenes such as styrene and α-methylstyrene; vinyl ethers such as ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, and isobutyl vinyl ether; vinyl esters such as vinyl acetate and vinyl propionate; and vinyl cyanides such as acrylonitrile.

[0052] From the viewpoint of adhesiveness, the content of other monomers is preferably 0 to 10% by mass of 100% by mass of the monomer mixture. If the other monomers are monomers having amide bonds, monomers having epoxy groups, monomers having amino groups, or monomers having aromatic rings, their content is preferably 0 to 7% by mass of each, from the viewpoint of polarity, crosslinkability, and reactivity.

[0053] [Method for manufacturing acrylic resin (A)] Acrylic resin (A) can be produced by adding a polymerization initiator to a monomer mixture and appropriately selecting known production methods such as solution polymerization, bulk polymerization, emulsion polymerization, and various radical polymerizations. Among these, solution polymerization is preferred because it allows for easy adjustment of the weight-average molecular weight of the acrylic resin.

[0054] The solvent used in the solution polymerization is preferably, for example, methyl acetate, ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, xylene, hexane, acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, n-propanol, and isopropanol, with methyl ethyl ketone being more preferred. The solvent can be used alone or in combination of two or more types.

[0055] In the aforementioned solution polymerization, it is preferable to add approximately 0.001 to 1 part by mass of polymerization initiator to 100 parts by mass of monomer mixture. Typically, polymerization can be carried out under a nitrogen atmosphere at a temperature of approximately 50°C to 90°C for 4 to 12 hours. Furthermore, during polymerization, a chain transfer agent can be used to appropriately adjust the weight-average molecular weight of the acrylic resin.

[0056] Azo compounds and organic peroxides can be used as polymerization initiators.

[0057] Examples of azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane1-carbonitride), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl2,2'-azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), and 2,2'-azobis(2-(2-imidazolin-2-yl)propane).

[0058] Examples of organic peroxides include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl) peroxydicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxybivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, and diacetyl peroxide. Polymerization initiators can be used alone or in combination of two or more types and / or in combination with the following chain transfer agents.

[0059] Examples of chain transfer agents include n-dodecyl mercaptan, mercaptoisobutyl alcohol, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, glycidyl mercaptan, α-methylstyrene dimer, carbon tetrachloride, chloroform, and hydroquinone. The chain transfer agent can be used in an amount of approximately 0.01 to 1 part by mass per 100 parts by mass of the monomer mixture.

[0060] <Hardening agent (B)> The curing agent (B) is at least one selected from the group consisting of chelating curing agents, isocyanate curing agents, and epoxy curing agents. By using the curing agent (B), the adhesive according to the present invention can be made to have excellent solvent resistance to low-polarity solvents, suitability for curved surfaces, suitability for water application, and reworkability, while also maintaining storage stability. Of the curing agents (B), chelate curing agents or epoxy curing agents are preferred due to their superior solvent resistance to low-polarity solvents, suitability for curved surfaces, suitability for water application, reworkability, and storage stability. Furthermore, to enhance the effect of the chelating curing agent or epoxy curing agent, it is preferable to use an isocyanate curing agent in combination with these curing agents. That is, it is preferable that curing agent (B) comprises a chelating curing agent and an isocyanate curing agent, or that curing agent (B) comprises an epoxy curing agent and an isocyanate curing agent. When using an isocyanate curing agent in combination, the amount of isocyanate curing agent is preferably 0.1 to 65 parts by mass, and more preferably 0.5 to 25 parts by mass, per 100 parts by mass of the chelating curing agent or epoxy curing agent.

[0061] [Chelating agent] Chelate curing agents include, for example, coordination compounds of polyvalent metals such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium with acetylacetone or ethyl acetoethyl acetate.

[0062] The chelating curing agent is preferably included in an amount of 0.1 to 5 parts by mass per 100 parts by mass of acrylic resin (A). Including 0.1 to 5 parts by mass makes it easier to balance the cohesive force and adhesive force of the adhesive layer.

[0063] [Isocyanate hardening agent] Isocyanate compounds include, for example, adducts of isocyanate monomers such as tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethyl xylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate, and polyol compounds such as trimethylolpropane; burettes of the isocyanate monomers; isocyanurates of the isocyanate monomers; and compounds having three or more isocyanate groups in the molecule, such as adducts of the isocyanate monomers and known polyether polyols or polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, etc. Examples include isocyanate monomers such as tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethyl xylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate; and compounds having two isocyanate groups in the molecule, such as the allophanate of hexamethylene diisocyanate (Coronate 2770: manufactured by Nippon Polyurethane Industry Co., Ltd.). Among these, the trimethylolpropane adduct of tolylene diisocyanate is preferred because it suppresses performance degradation due to plasticizer absorption. Note that the number of isocyanate groups is the average number.

[0064] The isocyanate curing agent is preferably present in an amount of 0.01 to 1 part by mass, more preferably 0.01 to 0.6 parts by mass, even more preferably 0.05 to 0.6 parts by mass, and particularly preferably 0.1 to 0.6 parts by mass, per 100 parts by mass of the acrylic resin (A). Including 0.01 to 1 part by mass can improve the deformation-following properties and processability of the PVC film. The isocyanate curing agent can be used in combination with an epoxy curing agent or a chelating curing agent. For example, the hydroxyl groups generated by the reaction of carboxyl groups with the epoxy curing agent can be further crosslinked with the isocyanate curing agent.

[0065] [Epoxy curing agent] Examples of epoxy curing agents include bisphenol A-epichlorohydrin type epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidylaminophenylmethane.

[0066] The epoxy curing agent is preferably present in an amount of 0.01 to 1 part by mass per 100 parts by mass of acrylic resin (A). Including 0.01 to 1 part by mass makes it easier to balance the cohesive force and adhesive force of the adhesive layer.

[0067] <Adhesive-granting resin> This adhesive may contain a tackifying resin to the extent that it can solve the problems of the present invention. Preferred tackifying resins include, for example, rosin resins, terpene resins, alicyclic hydrocarbon resins, aliphatic petroleum resins, aromatic petroleum resins, and alkylphenol formaldehyde resins (oil-based phenolic resins). The tackifying resin can be used alone or in combination of two or more. Including a tackifying resin in the adhesive makes it easier to improve the adhesive strength to polyvinyl chloride.

[0068] The tackifying resin is preferably present in an amount of 10 to 30 parts by mass per 100 parts by mass of acrylic resin (A).

[0069] The softening point of the tackifying resin is preferably 80 to 140°C. Setting the softening point to 80 to 140°C makes it easy to achieve both adhesive strength and cohesive strength.

[0070] <Other optional ingredients> The adhesive of the present invention may also contain, to the extent that it can solve the problems of the present invention, various other resins, curing catalysts, silane coupling agents, ultraviolet absorbers, light stabilizers, antioxidants, ultraviolet absorbers, anti-aging agents, weather-resistant stabilizers, antistatic agents, defoamers, leveling agents, release agents, oils, softeners, dyes, pigments, fillers, and the like as optional components.

[0071] Adhesive sheet The adhesive sheet of the present invention comprises an adhesive layer formed from the polyvinyl chloride adhesive of the present invention described above. The adhesive sheet of the present invention is used to bond polyvinyl chloride and an adhesive layer, but the base material of the adhesive sheet may be polyvinyl chloride, or the adherend may be polyvinyl chloride. In other words, the adhesive of the present invention is suitable as an adhesive for bonding polyvinyl chloride, and can be used in general labels and seals, adhesive optical films, elastic wall materials, waterproof coatings, flooring materials, sealants, molding materials, urethane foam (rigid, semi-rigid, flexible), sound-absorbing materials, vibration-damping materials, various molding materials, elastic fibers, artificial leather, synthetic leather, etc., but is not limited to these. In particular, due to its excellent solvent resistance to low-polarity solvents, suitability for curved surfaces, and suitability for water application, it can be suitably used as an adhesive sheet with a polyvinyl chloride base material and as a marking film for resin parts of vehicles, etc., as the adherend.

[0072] The adhesive sheet preferably comprises a base material and an adhesive layer formed from the adhesive of the present invention. In other embodiments, it may be a double-sided adhesive sheet having adhesive layers on both sides of a core material, or a cast adhesive sheet consisting only of an adhesive layer without a base material or core material. The adhesive layer can be formed by coating the adhesive onto a release sheet, drying it to form the adhesive layer, and then bonding the base material. Alternatively, it can be formed by coating the adhesive onto a base material and drying it.

[0073] <Polyvinyl chloride> Polyvinyl chloride (PVC), used as a base material or adherend, is a resin produced by polymerizing vinyl chloride monomer and then softening and stabilizing it with additives such as plasticizers, which is then molded into a film. By adjusting the polymerization conditions and additives, it exhibits excellent durability, weather resistance, chemical resistance, transparency, and processability. Because it can be manufactured at a very low cost, it is widely used not only in industrial materials, building materials, and automotive components, but also as general consumer goods. The thickness of the polyvinyl chloride film used as the base material can be appropriately selected depending on the application and is not particularly limited, but is preferably around 25 μm to 2000 mm. The shape of the polyvinyl chloride used as the adherend can be any shape according to the application of the polyvinyl chloride, and the adherend surface may be curved.

[0074] <Adhesive layer> The adhesive layer comprises an acrylic resin (A) and a curing agent (B), and can be formed using an acrylic adhesive containing the acrylic resin (A) and the curing agent (B). This type of adhesive layer provides good solvent resistance, suitability for curved surfaces, and suitability for wet application.

[0075] The viscosity of the adhesive may be adjusted by adding the solvent exemplified in solution polymerization during coating.

[0076] There are no particular restrictions on the method of applying the adhesive, and examples include Meyer bars, applicators, brushes, sprays, rollers, gravure coaters, die coaters, lip coaters, comma coaters, knife coaters, reverse coaters, and spin coaters. It is preferable to perform a drying process during coating. There are no particular restrictions on the drying apparatus, and examples include hot air dryers, infrared heaters, and vacuum methods. The drying temperature is usually around 60 to 140°C.

[0077] The thickness of the adhesive layer is preferably 1 to 300 μm, and more preferably 5 to 100 μm. Being within the range of 1 to 300 μm allows for appropriate adjustment of the adhesive properties.

[0078] <Base material> The adhesive sheet substrate can be made from materials other than polyvinyl chloride, such as cellophane, other plastics, rubber, foam, cloth, rubberized cloth, resin-impregnated cloth, glass, and wood. The substrate can be in the form of a sheet or a film, but a film is preferred because it is easier to handle. The substrate can be used alone or as a laminate of two or more materials.

[0079] Examples of the aforementioned other plastic substrates include polyolefins such as polyvinyl alcohol, triacetylcellulose, polypropylene, polyethylene, polycycloolefin, and ethylene-vinyl acetate copolymer; polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; and polyurethane, polycarbonate, polynorbornene, polyarylate, polyacrylic, polyphenylene sulfide, polystyrene, polyamide, and polyimide. [Examples]

[0080] The present invention will now be described in more detail with reference to examples, but the present invention is not limited thereto. In the examples, "parts" means "parts by mass" and "%" means "mass percent". The amounts in the table are in parts by mass, and all except the solvent are calculated on a non-volatile content basis. A blank space in the table indicates that the ingredient was not included.

[0081] The method for measuring the weight-average molecular weight (Mw) of acrylic resins is shown below.

[0082] [Measurement of weight-average molecular weight (Mw)] Weight-average molecular weight (Mw) was measured using GPC. GPC is a liquid chromatography method that separates and quantifies substances dissolved in a solvent (THF; tetrahydrofuran) based on differences in their molecular size, and the Mw was determined in terms of polystyrene equivalent. Device name: Manufactured by Shimadzu Corporation, LC-GPC system "Prominence" Columns: Four Tosoh GMHXL columns and one Tosoh HXL-H column connected in series. Mobile phase solvent: tetrahydrofuran Flow rate: 1.0ml / min Column temperature: 40℃

[0083] The abbreviations for the materials used in the examples and comparative examples are listed below. <Monomer (a1)> MEA: 2-methoxyethyl acrylate EEA: 2-ethoxyethyl acrylate <Monomer (a2)> AA: Acrylic acid MAA: Methacrylic acid <Monomer (a3)> MA: Methyl acrylate (number of carbon atoms in the alkyl group: 1) EA: Ethyl acrylate (number of carbon atoms in the alkyl group: 2) <Monomer (a4)> HEA: 2-hydroxyethyl acrylate HEMA: 2-hydroxyethyl methacrylate <Monomer (a5)> BA: Butyl acrylate (number of carbon atoms in the alkyl group: 4) HA: n-hexyl acrylate (number of carbon atoms in the alkyl group: 6) 2EHA: 2-ethylhexyl acrylate (number of carbon atoms in the alkyl group: 8) DA: n-dodecyl acrylate (number of carbon atoms in the alkyl group: 12) <Hardening agent (B)> Aluminum Chelate A: Aluminum Trisacetylacetonate (manufactured by Kawaken Fine Chemical Co., Ltd.) TDI / TMP: Trimethylolpropane duct body of tolylene diisocyanate TETRAD-X: N,N,N',N'-Tetraglycidyl-1,3-Benzenedi(methanamine) <Polymerization initiator> AIBN: 2,2'-Azobisisobutyronitrile <Chain movement agent> Chain transfer agent; 2-ethylhexyl thioglycolate

[0084] <Manufacturing of acrylic resins> (Acrylic resin (A-1)) In a reaction vessel under a nitrogen atmosphere, 63.0 parts methyl acrylate, 10.0 parts butyl acrylate, 25.0 parts 2-methoxyethyl acrylate, 2.0 parts acrylic acid, 49.0 parts methyl ethyl ketone, and 0.04 parts 2,2'-azobisisobutyronitrile (hereinafter, AIBN) were charged. The mixture was heated with stirring to confirm the start of the polymerization reaction, and the reaction was carried out at reflux temperature for 3 hours. Next, 0.03 parts AIBN was added to the reaction solution and the reaction was carried out for 1 hour, and then another 0.03 parts AIBN was added to the reaction solution and the reaction was continued for 3 hours. After that, the reaction vessel was cooled to obtain an acrylic resin (A-1) solution with a weight-average molecular weight of 320,000.

[0085] (Acrylic resins (A-2 to A-25), acrylic resins (AC-1 to AC-3)) Acrylic resins (A-2 to 25) and acrylic resins (AC-1) to acrylic resins (AC-1 to 3) were obtained in the same manner as acrylic resin (A-1), except that the monomer compositions and blending amounts (parts by mass) were as shown in Tables 1 to 4.

[0086] (Acrylic resin (A-26)) In a reaction vessel (hereinafter simply referred to as "reaction vessel") equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube, 42 parts methyl ethyl ketone, 10.0 parts butyl acrylate, 61.0 parts methyl acrylate, 25.0 parts 2-methoxyethyl acrylate, 2.0 parts acrylic acid, 2.0 parts 2-hydroxyethyl acrylate, 0.04 parts 2,2'-azobisisobutyronitrile (hereinafter referred to as AIBN), and 0.05 parts 2-ethylhexyl thioglycolate were charged under a nitrogen atmosphere. The mixture was heated while stirring to confirm the start of the polymerization reaction, and the reaction was carried out at reflux temperature for 3 hours. Next, 0.03 parts AIBN was added to the reaction solution and the reaction was carried out for 1 hour, and then another 0.03 parts AIBN was added to the reaction solution and the reaction was continued for 3 hours. After that, the reaction vessel was cooled to obtain an acrylic resin (A-26) solution with a weight-average molecular weight of 150,000.

[0087] (Acrylic resin (A-27)) In a reaction vessel (hereinafter simply referred to as "reaction vessel") equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube, 42 parts methyl ethyl ketone, 10.0 parts butyl acrylate, 61.0 parts methyl acrylate, 25.0 parts 2-methoxyethyl acrylate, 2.0 parts acrylic acid, 2.0 parts 2-hydroxyethyl acrylate, 0.04 parts 2,2'-azobisisobutyronitrile (hereinafter referred to as AIBN), and 0.03 parts 2-ethylhexyl thioglycolate were charged under a nitrogen atmosphere. The mixture was heated while stirring to confirm the start of the polymerization reaction, and the reaction was carried out at reflux temperature for 3 hours. Next, 0.03 parts AIBN was added to the reaction solution and the reaction was carried out for 1 hour, and then another 0.03 parts AIBN was added to the reaction solution and the reaction was continued for 3 hours. After that, the reaction vessel was cooled to obtain an acrylic resin (A-27) solution with a weight-average molecular weight of 200,000.

[0088] (Acrylic resin (A-28)) In a reaction vessel (hereinafter simply referred to as "reaction vessel") equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube, 30 parts methyl ethyl ketone, 12 parts ethyl acetate, 10.0 parts butyl acrylate, 61.0 parts methyl acrylate, 25.0 parts 2-methoxyethyl acrylate, 2.0 parts acrylic acid, 2.0 parts 2-hydroxyethyl acrylate, and 0.04 parts 2,2'-azobisisobutyronitrile (hereinafter referred to as AIBN) were charged under a nitrogen atmosphere. The mixture was heated while stirring to confirm the start of the polymerization reaction, and the reaction was carried out at reflux temperature for 3 hours. Next, 0.03 parts AIBN was added to the reaction solution and the reaction was carried out for 1 hour, and then another 0.03 parts AIBN was added to the reaction solution and the reaction was continued for 3 hours. After that, the reaction vessel was cooled to obtain an acrylic resin (A-28) solution with a weight-average molecular weight of 600,000.

[0089] (Acrylic resin (A-29)) In a reaction vessel (hereinafter simply referred to as "reaction vessel") equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube, 21 parts methyl ethyl ketone, 21 parts ethyl acetate, 10.0 parts butyl acrylate, 61.0 parts methyl acrylate, 25.0 parts 2-methoxyethyl acrylate, 2.0 parts acrylic acid, 2.0 parts 2-hydroxyethyl acrylate, and 0.04 parts 2,2'-azobisisobutyronitrile (hereinafter referred to as AIBN) were charged under a nitrogen atmosphere. The mixture was heated while stirring to confirm the start of the polymerization reaction, and the reaction was carried out at reflux temperature for 3 hours. Next, 0.03 parts AIBN was added to the reaction solution and the reaction was carried out for 1 hour, and then another 0.03 parts AIBN was added to the reaction solution and the reaction was continued for 3 hours. After that, the reaction vessel was cooled to obtain an acrylic resin (A-29) solution with a weight-average molecular weight of 700,000.

[0090] (Example 1) In the acrylic resin solution obtained in the above synthesis example, 1.0 part of aluminum chelate A as a metal chelating agent and 0.2 parts of TDI / TMP (trimethylolpropane adduct of tolylene diisocyanate) as an isocyanate curing agent were added to 100 parts (non-volatile content) of acrylic resin (A-1) and an acrylic adhesive was obtained by further adjusting the non-volatile content to 50% by adding ethyl acetate as a solvent. The aforementioned acrylic adhesive was applied to a commercially available release sheet with a thickness of 75 μm using a comma coater so that the thickness after drying was 25 μm, and an adhesive layer was formed by drying at 100°C for 2 minutes. Next, a 50 μm thick polyvinyl chloride film was laminated to this adhesive layer, and an adhesive sheet with the structure of "release sheet / adhesive layer / PVC sheet" was obtained by aging at a temperature of 25°C and 50% RH for one week.

[0091] (Examples 2-33, Comparative Examples 1-5) Except for changing the composition and proportions of the materials as shown in Tables 1 to 4, the same procedure as in Example 1 was followed to obtain the acrylic adhesives and adhesive sheets of Examples 2 to 33 and Comparative Examples 1 to 5, respectively.

[0092] <Evaluation of adhesive sheets> The solvent resistance, flexibility to curved surfaces, suitability for wet application, and reworkability of the adhesive sheets were evaluated using the following methods. The results are shown in Tables 1-4. The "melamine-coated board" used in the evaluation is a metal plate with a surface coating of black melamine, measuring 70 mm in width and 150 mm in length.

[0093] <Solvent resistance> The obtained adhesive sheet was cut to a size of 30 mm in width and 50 mm in length. Under conditions of 23°C and 50% relative humidity, the release sheet was peeled off the cut adhesive sheet, and the exposed adhesive layer was attached to a melamine-coated board. The board was pressed down once using a 2 kg roll and left for 24 hours to prepare a sample. The sample prepared under the above conditions was placed in a plastic container measuring 100 mm in width, 200 mm in length, and 50 mm in height. 100 g of E25 fuel (gasoline:ethanol = 75:25, volume ratio) adjusted to 23°C was then added to the plastic container and left to stand for 30 minutes under conditions of 23°C and 50% relative humidity. After that, the melamine-coated board to which the adhesive sheet was attached was removed, and the degree of lifting and peeling of the adhesive sheet from the melamine-coated board was visually evaluated. Furthermore, the same solvent resistance tests were conducted by changing the temperature of the E25 fuel and the ambient temperature of the plastic container to 5°C, 10°C, and 35°C. The evaluation criteria are as follows. [Evaluation Criteria] ○: No lifting or peeling of the adhesive sheet was observed. Good. △: The adhesive sheet did not peel off, and fewer than 5 lifts were observed, but they returned to their original state after 1 hour of removal. Usable. ×: The adhesive sheet did not peel off, but lifting was observed, and it did not return to its original position after 1 hour of removal. Unusable and impractical.

[0094] <Suitability for curved surfaces> The obtained adhesive sheet was prepared to a size of 25 mm in width and 100 mm in length. Next, under an atmosphere of 25°C and 50% relative humidity, the adhesive sheet was attached to a metal rod with a diameter of 60 mm along its circumference to prepare a sample. After the sample was left to stand for 7 days under an atmosphere of 25°C and 50% relative humidity, the degree of lifting and peeling of the edges of the adhesive sheet from the metal rod was visually evaluated. The evaluation criteria were as follows. [Evaluation Criteria] ◎: No lifting or peeling observed at the edges of the adhesive sheet. Excellent. ○: There was some lifting / peeling of the adhesive sheet edges, less than 0.2mm. This does not affect practical use and is in good condition. △: There was lifting or peeling at the edge of the adhesive sheet, between 0.2mm and 0.5mm. Still usable. ×: The adhesive sheet has lifting or peeling at the edges (0.5mm or more) and is unusable. Not practical for use.

[0095] <Suitable for water application> The obtained adhesive sheet was cut to a size of 25 mm in width and 100 mm in length. Under an atmosphere of 23°C and 50% relative humidity, the release sheet was peeled off the cut adhesive sheet, and the exposed adhesive layer was attached to a melamine-coated board whose entire surface had been sprayed with distilled water. A 2 kg roll was passed back and forth to allow water droplets to escape from the surface of the melamine-coated board, and after wiping off the excess water, the board was pressed and left for 24 hours to prepare a sample. A standard sample was prepared in the same manner except that distilled water was not sprayed. The water-bonded sample and the standard sample were subjected to a peel test using a tensile testing machine under conditions of a peel speed of 300 mm / min and a peel angle of 180 degrees, and the peel strength (N / 25 mm) was compared to determine the peel strength ratio compared to the standard (without water bonding). Peel strength percentage (%) = Peel strength of water-attached sample / Peel strength of standard sample × 100 [Evaluation Criteria] ◎: Peel strength is 90% or more compared to the standard. Excellent. ○: Peel strength is 70% to less than 90% of the standard. No practical problems, good. △: Peel strength is 50% to less than 70% of the standard. Usable. ×: Peel strength is less than 50% of the standard and unusable. Not practical.

[0096] <Removable (reworkable)> The obtained adhesive sheet was cut to a size of 25 mm in width and 100 mm in length. Under conditions of 23°C and 50% relative humidity, the release sheet was peeled off the cut adhesive sheet, and the exposed adhesive layer was attached to a melamine-coated board to prepare a sample. Next, a test was conducted in which the adhesive sheet was peeled off by hand in a 180-degree direction immediately after attachment, and the sample after the hand-peel test was reattached to the melamine-coated board. The peeling force during hand-peeling and the appearance of the adhesive sheet after reattachment were evaluated on a four-point scale. [Evaluation Criteria] ◎: It requires no force to peel it off the melamine-coated board, and no cosmetic defects are observed when it is reattached. Excellent. ○: It requires little force to peel off the melamine-coated board, and there are few cosmetic defects when reattached. Excellent. △: Requires force to peel off melamine-coated boards, resulting in minimal cosmetic defects when re-bonded. Usable. ×: It requires force to peel off the melamine-coated board, and a poor appearance is observed when it is reattached. Not practical for use.

[0097] [Table 1]

[0098] [Table 2]

[0099] [Table 3]

[0100] [Table 4]

[0101] [Summary of results] Examples 1-6 in Table 1 are examples of adhesives for polyvinyl chloride using an acrylic resin (A) that does not contain monomer (a4). All of the adhesives in Examples 1-6 were shown to have excellent water-applicability and re-peelability, as well as good flexibility for curved surfaces and solvent resistance. Furthermore, the adhesives in Examples 1-6 showed good storage stability, with no significant increase in viscosity even when used after long-term storage. Examples 7-33 in Tables 2-4 are examples of adhesives for polyvinyl chloride using an acrylic resin (A) containing monomer (a4). Adhesives using acrylic resin (A) containing monomer (a4) all exhibited excellent water-bonding suitability and re-peelability, as well as good flexibility on curved surfaces and solvent resistance, with a particular tendency to show excellent solvent resistance at 35°C. As described above, the adhesive for polyvinyl chloride of the present invention, which comprises an acrylic resin (A) and a curing agent (B), wherein the acrylic resin (A) is a copolymer of a monomer mixture containing 15 to 60% by mass of monomer (a1) represented by general formula (1) and 0.5 to 7% by mass of monomer (a2) having a carboxyl group, and the curing agent (B) is at least one selected from the group consisting of chelating curing agents, isocyanate curing agents, and epoxy curing agents, was confirmed to have better solvent resistance to low-polarity solvents (E25 fuel (gasoline:ethanol = 75:25, volume ratio), suitability for curved surfaces, suitability for wet application, and re-peelability compared to the adhesive of the comparative example, even when using a polyvinyl chloride film as the substrate.

Claims

1. The material comprises an acrylic resin (A) and a hardening agent (B). Acrylic resin (A) is a copolymer of monomer mixtures containing 15 to 60% by mass of monomer (a1) represented by the following general formula (1), 0.5 to 7% by mass of monomer (a2) having a carboxyl group, and 35 to 79.5% by mass of alkyl (meth)acrylate monomer (a3) ​​having an alkyl group having 1 to 2 carbon atoms. The curing agent (B) contains at least an isocyanate curing agent, and may also contain a chelating curing agent or an epoxy curing agent. The isocyanate curing agent is contained in an amount of 0.01 to 1 part by mass per 100 parts by mass of acrylic resin (A). When the chelating curing agent is included, the amount of the chelating curing agent is 0.1 to 5 parts by mass per 100 parts by mass of the acrylic resin (A). If the epoxy curing agent is included, the epoxy curing agent is present in an amount of 0.01 to 1 part by mass per 100 parts by mass of acrylic resin (A) as an adhesive for polyvinyl chloride. 【Chemistry 1】 (In general formula (1), R １ is an alkyl group having 1 to 2 carbon atoms, or a phenyl group, R ２ R is an alkylene group having 2 to 4 carbon atoms. ３ (where is a hydrogen atom or methyl group, and n represents a repeating unit, an integer from 1 to 4.)

2. The monomer mixture contains an alkyl (meth)acrylate monomer (a5) having an alkyl group having 4 to 13 carbon atoms. The polyvinyl chloride adhesive according to claim 1, wherein the content of (meth)acrylate alkyl ester monomer (a5) is 0.5 to 10% by mass in 100% by mass of the monomer mixture.

3. The monomer mixture contains a monomer (a4) having a hydroxyl group, The polyvinyl chloride adhesive according to claim 1 or 2, wherein the content of the monomer having a hydroxyl group (a4) is 0.5 to 7% by mass in 100% by mass of the monomer mixture.

4. The acrylic resin (A) has a weight-average molecular weight of 200,000 to 600,000, and is an adhesive for polyvinyl chloride according to any one of claims 1 to 3.

5. The polyvinyl chloride adhesive according to any one of claims 1 to 4, wherein the curing agent (B) comprises a chelating curing agent or an epoxy curing agent and an isocyanate curing agent.

6. An adhesive sheet comprising a base material and an adhesive layer formed from the polyvinyl chloride adhesive described in any one of claims 1 to 5.

7. The adhesive sheet according to claim 6, wherein the base material is polyvinyl chloride.

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