Pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet

Abstract

To provide an adhesive composition capable of forming an adhesive layer which is hardly peeled off from a low polarity adherend, has excellent transparency and suppresses coloring and to provide an adhesive sheet provided with the adhesive layer.SOLUTION: There are provided: an adhesive composition which comprises a (meth)acrylic polymer, a chlorinated polyolefin and a crosslinking agent and comprises no tackifier or has a tackifier content in the range of more than 0 pt.mass and less than 2.0 pts.mass based on 100 pts.mass of the (meth)acrylic polymer, wherein the content of the chlorinated polyolefin is 0.05 pt.mass to 2.0 pts.mass based on 100 pts.mass of the (meth)acrylic polymer; and an adhesive sheet.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet. [Background technology]

[0002] Polyolefin resins are highly versatile materials that are widely used in vehicle (e.g., automobile) parts (e.g., exterior and interior parts), building materials, office automation (OA) equipment, etc. However, because polyolefin resins have low polarity and low surface energy, it is difficult to securely fix a pressure-sensitive adhesive sheet to an adherend containing a polyolefin resin. For these reasons, pressure-sensitive adhesive sheets have been proposed in recent years that include a pressure-sensitive adhesive layer that exhibits high adhesive strength to low-polarity adherends containing polyolefin resins.

[0003] For example, Patent Document 1 describes a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing an adhesive polymer and a chlorinated polyolefin having a heat of fusion of 0 J / g to 5 J / g and a chlorine content of 16% by mass to 25% by mass. Patent Document 2 discloses an acrylic adhesive sheet in which an adhesive layer consisting of a multilayer structure of two or more layers, with an acrylic copolymer as the main component, is formed on one side of a substrate, and the adhesive layer located on the surface side has a higher affinity for low-polarity adherends than the adhesive layer located inside it. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-151485 [Patent Document 2] Japanese Patent Application Publication No. 10-46115 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, with the diversification of consumer preferences, high design quality is being demanded for articles such as vehicle parts, building materials, office automation equipment, etc. The design quality of these articles is enhanced by color and pattern, and pressure-sensitive adhesive compositions used in these articles are required to be able to form a pressure-sensitive adhesive layer that exhibits high adhesive strength to an adherend, as well as to form a pressure-sensitive adhesive layer that does not impair the color and pattern applied to the article.

[0006] An object of one embodiment of the present disclosure is to provide a pressure-sensitive adhesive composition that can form a pressure-sensitive adhesive layer that is difficult to peel from a low-polarity adherend, has excellent transparency, and is suppressed from coloring. The problem to be solved by another embodiment of the present disclosure is to provide a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer that is difficult to peel off from a low-polarity substrate, has excellent transparency, and is suppressed from discoloring. [Means for solving the problem]

[0007] Specific means for solving the problems include the following aspects. [1] A (meth)acrylic polymer, a chlorinated polyolefin; a cross-linking agent; Including, the content of the chlorinated polyolefin is 0.05 parts by mass to 2.0 parts by mass relative to 100 parts by mass of the (meth)acrylic polymer, A pressure-sensitive adhesive composition which does not contain a tackifier, or which contains the tackifier in an amount of more than 0 parts by mass and less than 2.0 parts by mass per 100 parts by mass of the (meth)acrylic polymer. [2] The pressure-sensitive adhesive composition according to [1], wherein the (meth)acrylic polymer has at least one of a carboxy group and a hydroxyl group. [3] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to [1] or [2]. [Effects of the Invention]

[0008] According to one embodiment of the present disclosure, there is provided a pressure-sensitive adhesive composition that can form a pressure-sensitive adhesive layer that is difficult to peel from a low-polarity adherend, has excellent transparency, and is suppressed from being discolored. According to another embodiment of the present disclosure, there is provided a pressure-sensitive adhesive sheet that is difficult to peel off from an adherend with low polarity, has excellent transparency, and includes a pressure-sensitive adhesive layer that is suppressed from being discolored. DETAILED DESCRIPTION OF THE INVENTION

[0009] The pressure-sensitive adhesive composition and pressure-sensitive adhesive sheet of the present disclosure are described in detail below. The following description of the requirements may be based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments and can be implemented with appropriate modifications within the scope of the object of the present disclosure.

[0010] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

[0011] In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0012] In the present disclosure, when the PSA composition contains a plurality of substances corresponding to each component, the amount of each component in the PSA composition means the total amount of the plurality of substances present in the PSA composition, unless otherwise specified.

[0013] In the present disclosure, "(meth)acrylic polymer" means a polymer in which the content of structural units derived from monomers having a (meth)acryloyl group is 50 mass% or more relative to all structural units (i.e., all structural units of the polymer). In the present disclosure, the term "(meth)acrylic monomer" means a monomer having a (meth)acryloyl group.

[0014] In the present disclosure, "(meth)acrylic" is a term that encompasses both "acrylic" and "methacrylic," "(meth)acrylate" is a term that encompasses both "acrylate" and "methacrylate," and "(meth)acryloyl" is a term that encompasses both "acryloyl" and "methacryloyl."

[0015] In this disclosure, "n-" means normal, "i-" means iso, "s-" means secondary, and "t-" means tertiary.

[0016] [Adhesive composition] The pressure-sensitive adhesive composition of the present disclosure comprises a (meth)acrylic polymer, a chlorinated polyolefin, and a crosslinking agent, wherein the content of the chlorinated polyolefin is 0.05 to 2.0 parts by mass relative to 100 parts by mass of the (meth)acrylic polymer, and the pressure-sensitive adhesive composition does not contain a tackifier, or the content of the tackifier is in the range of more than 0 to less than 2.0 parts by mass relative to 100 parts by mass of the (meth)acrylic polymer. The pressure-sensitive adhesive composition of the present disclosure has the above-described configuration, and thus can form a pressure-sensitive adhesive layer that is difficult to peel from an adherend with low polarity, has excellent transparency, and is suppressed from being discolored.

[0017] [(Meth)acrylic polymer] The pressure-sensitive adhesive composition of the present disclosure contains a (meth)acrylic polymer. The pressure-sensitive adhesive composition of the present disclosure may contain only one type of (meth)acrylic polymer, or may contain two or more types.

[0018] The (meth)acrylic polymer may be a homopolymer of one type of (meth)acrylic monomer, a copolymer of two or more types of (meth)acrylic monomers, or a copolymer of a (meth)acrylic monomer and another monomer. A preferred embodiment of the (meth)acrylic polymer is a copolymer of two or more kinds of (meth)acrylic monomers.

[0019] The (meth)acrylic polymer preferably has at least one of a carboxy group and a hydroxyl group. When the (meth)acrylic polymer has at least one of a carboxy group and a hydroxyl group, the adhesive strength of the formed pressure-sensitive adhesive layer to a low-polarity adherend tends to be higher than when the (meth)acrylic polymer has neither a carboxy group nor a hydroxyl group. When the (meth)acrylic polymer has at least one of a carboxy group and a hydroxy group, it may have either a carboxy group or a hydroxy group, or it may have both a carboxy group and a hydroxy group.

[0020] Examples of the (meth)acrylic polymer having at least one of a carboxy group and a hydroxyl group include the following modes (1) and (2), with mode (1) being preferred. (1) An embodiment in which the (meth)acrylic polymer contains at least one of a structural unit derived from a monomer having a carboxy group and a structural unit derived from a monomer having a hydroxy group, as described below, and thereby has at least one of a hydroxyl group and a carboxyl group. (2) An embodiment in which at least one of a carboxyl group and a hydroxyl group is introduced by substitution into a homopolymer or copolymer of a (meth)acrylic monomer having neither a carboxyl group nor a hydroxyl group, so that the (meth)acrylic polymer has at least one of a hydroxyl group and a carboxyl group.

[0021] The structural units that the (meth)acrylic polymer may contain will be described in detail below.

[0022] <Structural Units Derived from (Meth)acrylic Acid Alkyl Ester Monomers> The (meth)acrylic polymer preferably contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer. The structural units derived from the (meth)acrylic acid alkyl ester monomer can contribute to adjusting the adhesive strength of the pressure-sensitive adhesive layer that is formed.

[0023] In the present disclosure, the term "structural unit derived from a (meth)acrylic acid alkyl ester monomer" refers to a structural unit formed by addition polymerization of a (meth)acrylic acid alkyl ester monomer. The "(meth)acrylic acid alkyl ester monomer" in the present disclosure does not include monomers that fall under the category of monomers having a carboxy group, which will be described later, and monomers that fall under the category of monomers having a hydroxyl group, which will be described later.

[0024] The type of (meth)acrylic acid alkyl ester monomer is not particularly limited. The (meth)acrylic acid alkyl ester monomer may be an acrylic acid alkyl ester monomer or a methacrylic acid alkyl ester monomer, but is preferably an acrylic acid alkyl ester monomer. The (meth)acrylic acid alkyl ester monomer is preferably an unsubstituted (meth)acrylic acid alkyl ester monomer. The alkyl group of the (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic. The alkyl group preferably has 1 to 18 carbon atoms, and more preferably has 1 to 12 carbon atoms, for example.

[0025] Specific examples of the (meth)acrylic acid alkyl ester monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. The (meth)acrylic acid alkyl ester monomer is preferably at least one selected from the group consisting of, for example, n-butyl acrylate (n-BA), 2-ethylhexyl acrylate (2EHA), and methyl methacrylate (MMA).

[0026] When the (meth)acrylic polymer contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer, the polymer may contain only one type of structural unit derived from a (meth)acrylic acid alkyl ester monomer, or may contain two or more types of structural units derived from a (meth)acrylic acid alkyl ester monomer.

[0027] When the (meth)acrylic polymer contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer, the content of the structural unit derived from a (meth)acrylic acid alkyl ester monomer in the (meth)acrylic polymer is not particularly limited. The content of structural units derived from (meth)acrylic acid alkyl ester monomers in the (meth)acrylic polymer is, for example, preferably 50% by mass to 99.5% by mass, more preferably 60% by mass to 99.5% by mass, even more preferably 70% by mass to 99.5% by mass, and particularly preferably 80% by mass to 99.5% by mass, relative to all structural units of the (meth)acrylic polymer. Here, the content of structural units derived from (meth)acrylic acid alkyl ester monomers in the (meth)acrylic polymer being 50 mass% or more relative to all structural units of the (meth)acrylic polymer means that structural units derived from (meth)acrylic acid alkyl ester monomers are contained as the main component of the structural units constituting the (meth)acrylic polymer.

[0028] <Structural Units Derived from Monomers Having a Carboxy Group> The (meth)acrylic polymer preferably contains a structural unit derived from a monomer having a carboxy group. When the (meth)acrylic polymer contains a structural unit derived from a monomer having a carboxy group, the adhesive strength of the formed pressure-sensitive adhesive layer to a low-polarity substrate tends to be higher than when the (meth)acrylic polymer does not have a carboxy group.

[0029] In the present disclosure, the term "structural unit derived from a monomer having a carboxy group" refers to a structural unit formed by addition polymerization of a monomer having a carboxy group.

[0030] The type of the monomer having a carboxy group is not particularly limited. Examples of the monomer having a carboxy group include a monomer having at least one carboxy group and an ethylenically unsaturated group in one molecule. The type of the ethylenically unsaturated group is not particularly limited. Specific examples of the ethylenically unsaturated group include a vinyl group, an allyl group, a vinylphenyl group, a (meth)acrylamide group, and a (meth)acryloyl group. The ethylenically unsaturated group is preferably a (meth)acryloyl group, more preferably an acryloyl group.

[0031] Specific examples of the monomer having a carboxy group include (meth)acrylic acid and crotonic acid. ,Ma Examples include leic acid, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, ω-carboxy-polycaprolactone mono(meth)acrylate (e.g., ω-carboxy-polycaprolactone (n≒2) monoacrylate), succinic acid esters (e.g., 2-acryloyloxyethyl-succinic acid), vinyl formate, vinyl acetate, vinyl propionate, and vinyl neodecanoate. The monomer having a carboxy group is preferably acrylic acid (AA).

[0032] When the (meth)acrylic polymer contains a structural unit derived from a monomer having a carboxy group, the polymer may contain only one type of structural unit derived from a monomer having a carboxy group, or may contain two or more types of structural units derived from a monomer having a carboxy group.

[0033] When the (meth)acrylic polymer contains a structural unit derived from a monomer having a carboxy group, the content of the structural unit derived from a monomer having a carboxy group in the (meth)acrylic polymer is not particularly limited. The content of structural units derived from monomers having a carboxy group in the (meth)acrylic polymer is, for example, preferably 1.0 mass % to 10.0 mass %, more preferably 2.0 mass % to 8.0 mass %, and even more preferably 3.0 mass % to 6.0 mass %, relative to all structural units of the (meth)acrylic polymer. When the content of the structural units derived from the monomer having a carboxy group in the (meth)acrylic polymer is within the above range relative to all structural units of the (meth)acrylic polymer, the adhesive strength of the formed pressure-sensitive adhesive layer to a low-polarity adherend tends to be higher.

[0034] <Structural Units Derived from Monomers Having a Hydroxyl Group> The (meth)acrylic polymer preferably contains a structural unit derived from a monomer having a hydroxyl group. When a (meth)acrylic polymer contains a structural unit derived from a monomer having a hydroxyl group, the adhesive strength of the formed pressure-sensitive adhesive layer to a low-polarity substrate tends to be higher than when the (meth)acrylic polymer does not have a hydroxyl group.

[0035] In the present disclosure, the term "structural unit derived from a monomer having a hydroxyl group" refers to a structural unit formed by addition polymerization of a monomer having a hydroxyl group.

[0036] The type of the hydroxyl group-containing monomer is not particularly limited. Examples of the monomer having a hydroxyl group include a monomer having at least one hydroxyl group and an ethylenically unsaturated group in one molecule. The type of the ethylenically unsaturated group is not particularly limited. Specific examples of the ethylenically unsaturated group include a vinyl group, an allyl group, a vinylphenyl group, a (meth)acrylamide group, and a (meth)acryloyl group. The ethylenically unsaturated group is preferably a (meth)acryloyl group, more preferably an acryloyl group.

[0037] Specific examples of monomers having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,1-dimethyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, N-hydroxyethyl (meth)acrylamide, glycerin mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, and poly(ethylene glycol-propylene glycol) mono(meth)acrylate. As the monomer having a hydroxyl group, for example, from the viewpoint of good copolymerizability with other monomers, hydroxyalkyl(meth)acrylates are preferred, and from the viewpoint of good compatibility with other monomers, hydroxyalkyl(meth)acrylates having a hydroxyalkyl group with 1 to 5 carbon atoms are more preferred, hydroxyalkyl(meth)acrylates having a hydroxyalkyl group with 2 to 4 carbon atoms are even more preferred, and 2-hydroxyethyl acrylate (2HEA) is particularly preferred.

[0038] When the (meth)acrylic polymer contains a structural unit derived from a monomer having a hydroxyl group, the polymer may contain only one type of structural unit derived from a monomer having a hydroxyl group, or may contain two or more types of structural units derived from a monomer having a hydroxyl group.

[0039] When the (meth)acrylic polymer contains a structural unit derived from a monomer having a hydroxyl group, the content of the structural unit derived from a monomer having a hydroxyl group in the (meth)acrylic polymer is not particularly limited. The content of structural units derived from monomers having a hydroxyl group in the (meth)acrylic polymer is, for example, preferably 0.1% by mass to 5.0% by mass, more preferably 0.2% by mass to 3.0% by mass, and even more preferably 0.3% by mass to 1.0% by mass, relative to all structural units of the (meth)acrylic polymer. When the content of structural units derived from monomers having a hydroxyl group in the (meth)acrylic polymer is within the above range relative to all structural units of the (meth)acrylic polymer, the adhesive strength of the formed pressure-sensitive adhesive layer to low-polarity adherends tends to be higher.

[0040] <Other structural units> The (meth)acrylic polymer may contain structural units other than the structural units described above (so-called other structural units) as needed, as long as the effects of the pressure-sensitive adhesive composition of the present disclosure are not impaired.

[0041] Examples of monomers that constitute other structural units include (meth)acrylates having an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; alkoxyalkyl (meth)acrylates, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; aromatic monovinyls, such as styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and vinyltoluene; vinyl cyanides, such as acrylonitrile and methacrylonitrile; vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate; and derivatives thereof.

[0042] When the (meth)acrylic polymer contains other structural units, it may contain only one type of other structural unit, or may contain two or more types of other structural units.

[0043] When the (meth)acrylic polymer contains other structural units, the content of the other structural units in the (meth)acrylic polymer is not particularly limited and can be set appropriately depending on the purpose as long as the effects of the pressure-sensitive adhesive composition of the present disclosure are not impaired.

[0044] -Glass transition temperature of (meth)acrylic polymers- The glass transition temperature (also referred to as "Tg") of the (meth)acrylic polymer is not particularly limited, but is preferably -10°C or lower, more preferably -20°C or lower, and even more preferably -30°C or lower. When the glass transition temperature of the (meth)acrylic polymer is −10° C. or lower, the pressure-sensitive adhesive layer formed tends to have higher adhesive strength to adherends with low polarity, presumably because the polarity of the pressure-sensitive adhesive layer becomes lower. The lower limit of the glass transition temperature of the (meth)acrylic polymer is preferably, for example, −75° C. or higher.

[0045] The glass transition temperature of the (meth)acrylic polymer is a value obtained by converting the absolute temperature (unit: K) calculated from the following formula 1 into Celsius temperature (unit: ° C.). 1 / Tg=m1 / Tg1+m2 / Tg2+ +m(k-1) / Tg(k-1)+mk / Tgk (Formula 1)

[0046] In formula 1, Tg1, Tg2, . . . , Tg(k-1), and Tgk represent the glass transition temperatures expressed as absolute temperatures when each monomer constituting the (meth)acrylic polymer is made into a homopolymer. m1, m2, . . . , m(k-1), and mk represent the mole fractions of each monomer constituting the (meth)acrylic polymer, respectively, and the equation is m1 + m2 + . . . + m(k-1) + mk = 1. Note that absolute temperatures can be converted to Celsius degrees by subtracting 273 from the absolute temperature, and Celsius degrees can be converted to absolute temperatures by adding 273 to the Celsius degrees.

[0047] In the present disclosure, the "glass transition temperature expressed in absolute temperature when made into a homopolymer" refers to the glass transition temperature expressed in absolute temperature of a homopolymer produced by polymerizing the monomer alone. The glass transition temperature of the homopolymer was measured using a differential scanning calorimeter (DSC) under conditions of a nitrogen gas flow, a 10 mg measurement sample, and a heating rate of 10°C / min, and the inflection point of the obtained DSC curve was taken as the glass transition temperature of the homopolymer. As a differential scanning calorimeter, for example, EXSTAR6000 (model number) manufactured by Seiko Instruments Inc. can be used. However, the differential scanning calorimeter is not limited to this.

[0048] The glass transition temperatures of representative monomers when made into homopolymers, expressed in Celsius degrees, are: 2-ethylhexyl acrylate -76°C, 2-ethylhexyl methacrylate -10°C, n-butyl acrylate -57°C, n-butyl methacrylate -21°C, t-butyl acrylate -41°C, t-butyl methacrylate -107°C, i-butyl methacrylate -48°C, methyl acrylate -5°C, methyl methacrylate -103°C, isobornyl methacrylate -155°C, isobornyl acrylate -106°C, ethyl acrylate -27°C, and methacrylic acid -18°C. 5°C, 4-hydroxybutyl acrylate -39°C, 2-hydroxyethyl acrylate -15°C, 2-hydroxyethyl methacrylate 55°C, 2-hydroxypropyl acrylate -7°C, acrylic acid 106°C, n-octyl acrylate -65°C, i-octyl acrylate -75°C, i-decyl acrylate -62°C, lauryl acrylate 15°C, dimethylaminoethyl methacrylate 18°C, ω-carboxy-polycaprolactone (n≈2) monoacrylate -30°C, and 2-acryloyloxyethyl-succinic acid -40°C.

[0049] The glass transition temperature of the (meth)acrylic polymer can be appropriately adjusted, for example, by using two or more kinds of monomers that have different glass transition temperatures when made into homopolymers.

[0050] -Weight average molecular weight of (meth)acrylic polymer- The weight average molecular weight (also referred to as "Mw") of the (meth)acrylic polymer is not particularly limited, but is preferably from 100,000 to 1,000,000, more preferably from 200,000 to 900,000, and even more preferably from 300,000 to 800,000. When the weight average molecular weight of the (meth)acrylic polymer is within the above range, the pressure-sensitive adhesive layer formed tends to have higher adhesive strength to adherends with low polarity. It is believed that when the weight average molecular weight of the (meth)acrylic polymer is 100,000 or more, the cohesive strength of the pressure-sensitive adhesive layer formed is more appropriately high, and when it is 1,000,000 or less, the pressure-sensitive adhesive layer formed does not become excessively hard, resulting in better wettability of the pressure-sensitive adhesive layer to the adherend.

[0051] The weight average molecular weight of the (meth)acrylic polymer is a value determined by the following method, specifically, according to the following (1) to (3). (1) A solution of a (meth)acrylic polymer is applied to a release paper and dried at 100° C. for 1 minute to obtain a film of the (meth)acrylic polymer. (2) Using the film-like (meth)acrylic polymer obtained in (1) above and tetrahydrofuran, a sample solution having a solids concentration of 0.2% by mass is obtained. Note that the "solids concentration" here refers to the mass proportion of the (meth)acrylic polymer in the sample solution. (3) The weight average molecular weight of the (meth)acrylic polymer is determined as a standard polystyrene equivalent value by gel permeation chromatography (GPC) under the following conditions.

[0052] ~Conditions~ Measurement equipment: High-speed GPC [Model: HLC-8220 GPC, manufactured by Tosoh Corporation] Detector: Differential refractometer (RI) [built into HLC-8220, manufactured by Tosoh Corporation] Column: TSKgel GMH XL Four Tosoh Corporation products are used. Column temperature: 40℃ Eluent: tetrahydrofuran Sample solution injection volume: 100 μL Flow rate: 0.8mL / min

[0053] The weight average molecular weight of the (meth)acrylic polymer can be adjusted to a desired value by adjusting the polymerization temperature, polymerization time, amount of organic solvent used, type of polymerization initiator, amount of polymerization initiator used, etc. when polymerizing the monomer.

[0054] -(Meth)acrylic polymer content- The content of the (meth)acrylic polymer in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited, but is, for example, preferably 75.0 mass % to 99.91 mass %, more preferably 80.0 mass % to 99.85 mass %, and even more preferably 85.0 mass % to 98.97 mass %, relative to the total solid content in the pressure-sensitive adhesive composition. In the present disclosure, the "total solid content in the PSA composition" means the total mass of the PSA composition when the PSA composition does not contain a solvent, and means the mass of the residue remaining after removing the solvent from the PSA composition when the PSA composition contains a solvent. In this disclosure, "solvent" means water and organic solvents.

[0055] -Method for producing (meth)acrylic polymer- The method for producing the (meth)acrylic polymer is not particularly limited. The (meth)acrylic polymer can be produced by polymerizing the above-mentioned monomers by a known polymerization method, typically a solution polymerization method, an emulsion polymerization method, a suspension polymerization method, or a bulk polymerization method. As the polymerization method, a solution polymerization method is preferred in that the processing steps for preparing the pressure-sensitive adhesive composition after production are relatively simple and can be carried out in a short time.

[0056] In the solution polymerization method, a predetermined organic solvent, monomers, a polymerization initiator, and an optional chain transfer agent are generally charged into a polymerization vessel and reacted by heating for several hours with stirring, for example, at the reflux temperature of the organic solvent. In this case, at least a portion of the organic solvent, monomers, polymerization initiator, and optional chain transfer agent may be added sequentially. Alternatively, the reaction may be carried out in a nitrogen gas stream.

[0057] Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbon compounds, aliphatic hydrocarbon compounds, alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, and alcohol compounds. More specifically, examples of organic solvents used in the polymerization reaction include aromatic hydrocarbon compounds such as benzene, toluene, ethylbenzene, n-propylbenzene, t-butylbenzene, o-xylene, m-xylene, p-xylene, tetralin, decalin, and aromatic naphtha; aliphatic or alicyclic hydrocarbon compounds such as n-hexane, n-heptane, n-octane, i-octane, n-decane, dipentene, petroleum spirit, petroleum naphtha, and turpentine; ester compounds such as ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate; acetone; Examples of the alcohol compounds include ketones, methyl-i-butyl ketone, isophorone, cyclohexanone, and methylcyclohexanone; glycol ether compounds, such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, and diethylene glycol monobutyl ether; and alcohol compounds, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t-butyl alcohol.

[0058] In producing a (meth)acrylic polymer, it is preferable to use an organic solvent that is unlikely to cause chain transfer during the polymerization reaction, such as an aromatic hydrocarbon compound, an ester compound, or a ketone compound. In particular, it is preferable to use ethyl acetate from the viewpoints of the solubility of the (meth)acrylic polymer, ease of the polymerization reaction, etc.

[0059] During the polymerization reaction, only one type of organic solvent may be used, or two or more types may be used.

[0060] Examples of the polymerization initiator include organic peroxides and azo compounds that are used in ordinary solution polymerization methods. Specific examples of organic peroxides include t-butyl hydroperoxide, cumene hydroperoxide, dicumyl peroxide, benzoyl peroxide, lauroyl peroxide, caproyl peroxide, di-i-propyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-amylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-octylperoxycyclohexyl)propane, 2,2-bis(4,4-di-α-cumylperoxycyclohexyl)propane, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)butane, and 2,2-bis(4,4-di-t-octylperoxycyclohexyl)butane. Specific examples of azo compounds include 2,2'-azobisisobutyronitrile [AIBN], 2,2'-azobis(2,4-dimethylvaleronitrile) [ABVN], 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), and 2,2'-azobis(isobutyrate) dimethyl. In producing a (meth)acrylic polymer, it is preferable to use a polymerization initiator that does not cause a graft reaction during the polymerization reaction, and it is particularly preferable to use an azo compound.

[0061] In the polymerization reaction, only one type of polymerization initiator may be used, or two or more types may be used.

[0062] The amount of the polymerization initiator used is not particularly limited, and can be appropriately set depending on, for example, the molecular weight of the desired (meth)acrylic polymer.

[0063] In producing the (meth)acrylic polymer, a chain transfer agent may be used, if necessary. Examples of the chain transfer agent include cyanoacetic acid, alkyl ester compounds of cyanoacetic acid having 1 to 8 carbon atoms, bromoacetic acid, alkyl ester compounds of bromoacetic acid having 1 to 8 carbon atoms, aromatic compounds such as α-methylstyrene, anthracene, phenanthrene, fluorene, and 9-phenylfluorene, aromatic nitro compounds such as p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, and p-nitrotoluene, benzoquinone derivatives such as benzoquinone and 2,3,5,6-tetramethyl-p-benzoquinone, borane derivatives such as tributylborane, carbon tetrabromide, tetrabromide, tetrachloromethane, benzoquinone derivatives such as benzoquinone ... Examples of such compounds include halogenated hydrocarbon compounds such as carbon chloride, 1,1,2,2-tetrabromoethane, tribromoethylene, trichloroethylene, bromotrichloromethane, tribromomethane, and 3-chloro-1-propene, aldehyde compounds such as chloral and furaldehyde, alkyl mercaptan compounds having 1 to 18 carbon atoms, aromatic mercaptan compounds such as thiophenol and toluene mercaptan, mercaptoacetic acid, alkyl ester compounds of mercaptoacetic acid having 1 to 10 carbon atoms, hydroxyalkyl mercaptan compounds having 1 to 12 carbon atoms, and terpene compounds such as pinene and terpinolene.

[0064] When a chain transfer agent is used in producing a (meth)acrylic polymer, the amount of the chain transfer agent used is not particularly limited and can be appropriately set depending on, for example, the molecular weight of the target (meth)acrylic polymer.

[0065] The polymerization temperature is not particularly limited and can be appropriately set depending on, for example, the molecular weight of the desired (meth)acrylic polymer.

[0066] [Chlorinated polyolefin] The pressure-sensitive adhesive composition of the present disclosure contains a chlorinated polyolefin. The content of the chlorinated polyolefin in the pressure-sensitive adhesive composition of the present disclosure is 0.05 to 2.0 parts by mass per 100 parts by mass of the (meth)acrylic polymer described above. Although chlorinated polyolefins can contribute to improving the adhesive strength of a pressure-sensitive adhesive layer to adherends with low polarity, they have poor compatibility with (meth)acrylic polymers and can therefore cause a loss of transparency of the pressure-sensitive adhesive layer. By adjusting the content of chlorinated polyolefin to 0.05 to 2.0 parts by mass per 100 parts by mass of the (meth)acrylic polymer, the pressure-sensitive adhesive composition of the present disclosure can form a pressure-sensitive adhesive layer that combines excellent transparency with high adhesive strength to adherends with low polarity.

[0067] Chlorinated polyolefins are chlorinated polyolefins. The polyolefin may be a homopolymer of an olefin, or a copolymer of an olefin and another monomer (for example, an ethylene-vinyl acetate copolymer (so-called EVA)). When the polyolefin is a copolymer of an olefin and another monomer, the content of structural units derived from the olefin in the copolymer is not particularly limited, but is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, of the total structural units of the copolymer. The olefin is not particularly limited, and examples thereof include ethylene, propylene, butene, and pentene.

[0068] There are no particular limitations on whether or not the chlorinated polyolefin is modified and the type of modification. The chlorinated polyolefin may be, for example, an unmodified chlorinated polyolefin, an acrylic-modified chlorinated polyolefin, or an acid-modified chlorinated polyolefin. Among these, the chlorinated polyolefin is preferably at least one of unmodified chlorinated polyolefin and acrylic-modified chlorinated polyolefin, and more preferably acrylic-modified chlorinated polyolefin. Unmodified chlorinated polyolefins and acrylic-modified chlorinated polyolefins tend to have better compatibility with (meth)acrylic polymers than, for example, acid-modified chlorinated polyolefins. Therefore, when the chlorinated polyolefin is at least one of unmodified chlorinated polyolefins and acrylic-modified chlorinated polyolefins, it tends to be easier to form a pressure-sensitive adhesive layer with better transparency.

[0069] The chlorine content of the chlorinated polyolefin is not particularly limited, but is preferably, for example, 10% by mass or more, and more preferably 12% by mass or more. When the chlorine content of the chlorinated polyolefin is 10% by mass or more, the pressure-sensitive adhesive layer formed tends to have higher adhesive strength to adherends with low polarity. The upper limit of the chlorine content of the chlorinated polyolefin is preferably 45% by mass or less, and more preferably 40% by mass or less, from the viewpoint of reducing the burden on the environment and solubility in organic solvents, for example. In the present disclosure, the chlorine content of a chlorinated polyolefin is a value determined by a method in accordance with JIS K 7229:1995.

[0070] The weight average molecular weight of the chlorinated polyolefin is not particularly limited, but is preferably from 2,000 to 200,000, and more preferably from 2,000 to 150,000, for example. In the present disclosure, the weight average molecular weight of the chlorinated polyolefin is a value determined as a standard polystyrene equivalent by gel permeation chromatography (GPC) under the following conditions.

[0071] ~Conditions~ Measurement equipment: High-speed GPC [Model: HLC-8220 GPC, manufactured by Tosoh Corporation] Detector: Differential refractometer (RI) [built into HLC-8220, manufactured by Tosoh Corporation] Column: TSKgel GMH XL Four Tosoh Corporation products are used. Column temperature: 40℃ Eluent: tetrahydrofuran Sample solution injection volume: 100 μL Flow rate: 0.8mL / min

[0072] As the chlorinated polyolefin, commercially available products can be used. Examples of commercially available chlorinated polyolefins include "Superclone (registered trademark) 224H," "Superclone (registered trademark) 223M," "Superclone (registered trademark) 240H," "Superclone (registered trademark) 260F," "Superclone (registered trademark) 822," "Superclone (registered trademark) 892L," "Superclone (registered trademark) 930," "Superclone (registered trademark) 842LM," "Superclone (registered trademark) 851L," "Superclone (registered trademark) 3228S," "Superclone (registered trademark) 3221S," "Superclone (registered trademark) 2319S," "Superclone (registered trademark) 814B," "Superclone (registered trademark) 360T," "Superclone (registered trademark) 370M," "Superclone (registered trademark) 2027MB," "Superclone (registered trademark) C," "Superclone (registered trademark) L-206," "Superclone (registered trademark) 813A," and "Superclone (registered trademark) Examples of such cellulose esters include "Superclone (registered trademark) 803M," "Superclone (registered trademark) 803MW," "Superclone (registered trademark) 1026," "Superclone (registered trademark) 803L," "Superclone (registered trademark) 814HS," "Superclone (registered trademark) 390S," "Superclone (registered trademark) B," and "Superclone (registered trademark) BX" (all manufactured by Nippon Paper Industries Co., Ltd.).

[0073] The pressure-sensitive adhesive composition of the present disclosure may contain only one type of chlorinated polyolefin, or may contain two or more types of chlorinated polyolefin.

[0074] The content of the chlorinated polyolefin in the pressure-sensitive adhesive composition of the present disclosure is 0.05 to 2.0 parts by mass relative to 100 parts by mass of the (meth)acrylic polymer. The content of chlorinated polyolefin in the pressure-sensitive adhesive composition of the present disclosure being 0.05 parts by mass or more relative to 100 parts by mass of the (meth)acrylic polymer means that the pressure-sensitive adhesive composition of the present disclosure actively contains chlorinated polyolefin. The content of chlorinated polyolefin in the pressure-sensitive adhesive composition of the present disclosure is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the (meth)acrylic polymer. When the content of the chlorinated polyolefin in the pressure-sensitive adhesive composition of the present disclosure is 2.0 parts by mass or less relative to 100 parts by mass of the (meth)acrylic polymer, a pressure-sensitive adhesive layer with excellent transparency can be formed. From this viewpoint, the content of the chlorinated polyolefin in the pressure-sensitive adhesive composition of the present disclosure is 2.0 parts by mass or less, and preferably 1.5 parts by mass or less, relative to 100 parts by mass of the (meth)acrylic polymer.

[0075] [Crosslinking agent] The pressure-sensitive adhesive composition of the present disclosure contains a crosslinking agent. The type of crosslinking agent is not particularly limited. Examples of the crosslinking agent include an epoxy-based crosslinking agent, an isocyanate-based crosslinking agent, a metal chelate-based crosslinking agent, and an aziridine-based crosslinking agent. The crosslinking agent is preferably at least one selected from the group consisting of epoxy-based crosslinking agents, isocyanate-based crosslinking agents, and metal chelate-based crosslinking agents.

[0076] In this disclosure, "isocyanate-based crosslinking agent" refers to a compound having two or more isocyanate groups in one molecule (so-called polyisocyanate compound). Also, "epoxy-based crosslinking agent" refers to a compound having two or more epoxy groups in one molecule (so-called bifunctional or higher functional epoxy compound). Also, "metal chelate-based crosslinking agent" refers to a metal chelate compound that functions as a crosslinking agent. Also, "aziridine-based crosslinking agent" refers to a compound having two or more aziridine groups in one molecule (so-called bifunctional or higher functional aziridine compound).

[0077] The type of epoxy-based crosslinking agent is not particularly limited. Specific examples of epoxy crosslinking agents include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, tripropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polytetramethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol diglycidyl ether, Examples include glycerol polyglycidyl ether, resorcinol diglycidyl ether, 2,2-dibromoneopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol polyglycidyl ether, sorbitol polyglycidyl ether, adipic acid diglycidyl ester, phthalic acid diglycidyl ester, tris(glycidyl)isocyanurate, tris(glycidoxyethyl)isocyanurate, 1,3-bis(N,N-glycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidyl-1,3-benzenedi(methanamine).

[0078] As the epoxy-based crosslinking agent, commercially available products can be used. Examples of commercially available epoxy crosslinking agents include "TETRAD (registered trademark)-X" and "TETRAD (registered trademark)-C" (both manufactured by Mitsubishi Gas Chemical Company, Inc.), and "Denacol (registered trademark) EX-201" and "Denacol (registered trademark) EX-931" (both manufactured by Nagase ChemteX Corporation).

[0079] The type of isocyanate-based crosslinking agent is not particularly limited. Examples of the isocyanate crosslinking agent include an aliphatic polyisocyanate compound, an alicyclic polyisocyanate compound, and an aromatic polyisocyanate compound. Specific examples of aliphatic polyisocyanate compounds include hexamethylene diisocyanate (HMDI), pentamethylene diisocyanate (PDI), tetramethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate. Specific examples of the alicyclic polyisocyanate compound include isophorone diisocyanate (IPDI), hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, hydrogenated 4,4'-diphenylmethane diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate. Specific examples of aromatic polyisocyanate compounds include tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), 4,4'-diphenylmethane diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate. Further, examples of the isocyanate-based crosslinking agent include dimers, trimers, and pentamers of the above polyisocyanate compounds, adducts of the above polyisocyanate compounds with polyol compounds (e.g., trimethylolpropane (TMP)), and biuret forms of the above polyisocyanate compounds.

[0080] As the isocyanate-based crosslinking agent, commercially available products can be used. Examples of commercially available isocyanate crosslinking agents include "Coronate (registered trademark) HX," "Coronate (registered trademark) HL-S," "Coronate (registered trademark) L," "Coronate (registered trademark) L-45E," "Coronate (registered trademark) 2031," "Coronate (registered trademark) 2037," "Coronate (registered trademark) 2234," "Coronate (registered trademark) 2785," "Aquanate (registered trademark) 200," and "Aquanate (registered trademark) 210" (all manufactured by Tosoh Corporation), "Sumidur (registered trademark) N3300," "Desmodur (registered trademark) N3400," and "Sumidur (registered trademark) N75" (all manufactured by Sumika Covestro Urethane Co., Ltd.), "Duranate (registered trademark) D201," "Duranate (registered trademark) E405-70B," "Duranate (registered trademark) E405-80T," and "Duranate (registered trademark) AE700-100," "Duranate (registered trademark) 24A-100," and "Duranate (registered trademark) TSE-100" (all manufactured by Asahi Kasei Corporation), as well as "Takenate (registered trademark) D-110N," "Takenate (registered trademark) D-120N," "Takenate (registered trademark) D-140N," "Takenate (registered trademark) M-631N," "MT-Olestar (registered trademark) NP1200," and "STABIO (registered trademark) XD-340N" (all manufactured by Mitsui Chemicals, Inc.).

[0081] The type of metal chelate crosslinking agent is not particularly limited. Examples of metal chelate crosslinking agents include aluminum chelate compounds, titanium chelate compounds, zirconium chelate compounds, and cobalt chelate compounds. As the metal chelate crosslinking agent, an aluminum chelate compound is preferred. Specific examples of aluminum chelate compounds include aluminum monoacetylacetonate bis(ethylacetoacetate), aluminum tris(ethylacetoacetate), and aluminum tris(acetylacetonate).

[0082] As the metal chelate crosslinking agent, commercially available products can be used. Examples of commercially available metal chelate crosslinking agents include Aluminum Chelate A (trade name: aluminum tris(acetylacetonate), manufactured by Kawaken Fine Chemicals Co., Ltd.), Aluminum Chelate D (trade name: aluminum monoacetylacetonate bis(ethylacetoacetate), manufactured by Kawaken Fine Chemicals Co., Ltd.), and ALCH-TR (trade name: aluminum tris(ethylacetoacetate), manufactured by Kawaken Fine Chemicals Co., Ltd.).

[0083] The type of aziridine crosslinking agent is not particularly limited. Examples of the aziridine crosslinking agent include trimethylolpropane-tri-β-aziridinylpropionate, tetramethylolmethane-tri-β-aziridinylpropionate, trimethylolpropane-tri-β-(2-methylaziridine)propionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide), and N,N'-toluene-2,4-bis(1-aziridinecarboxamide).

[0084] As the aziridine-based crosslinking agent, commercially available products can be used. An example of a commercially available aziridine crosslinking agent is "ChemiTite (registered trademark) PZ-33" (manufactured by Nippon Shokubai Co., Ltd.).

[0085] The pressure-sensitive adhesive composition of the present disclosure may contain only one type of crosslinking agent, or may contain two or more types.

[0086] The content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is not particularly limited, but is preferably, for example, 0.01 to 5 parts by mass relative to 100 parts by mass of the (meth)acrylic polymer. When the content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is within the above range relative to 100 parts by mass of the (meth)acrylic polymer, the pressure-sensitive adhesive layer formed tends to have higher adhesive strength to low-polarity adherends.

[0087] Furthermore, when the crosslinking agent is an epoxy-based crosslinking agent, the content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is, for example, more preferably 0.01 to 3 parts by mass, even more preferably 0.01 to 2 parts by mass, and particularly preferably 0.01 to 1 part by mass, relative to 100 parts by mass of the (meth)acrylic polymer. Furthermore, when the crosslinking agent is an isocyanate-based crosslinking agent, the content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is, for example, more preferably 0.05 parts by mass to 5 parts by mass, even more preferably 0.1 parts by mass to 5 parts by mass, and particularly preferably 0.1 parts by mass to 4 parts by mass, relative to 100 parts by mass of the (meth)acrylic polymer. Furthermore, when the crosslinking agent is a metal chelate crosslinking agent, the content of the crosslinking agent in the pressure-sensitive adhesive composition of the present disclosure is, for example, more preferably 0.01 to 3 parts by mass, even more preferably 0.05 to 2 parts by mass, and particularly preferably 0.1 to 1 part by mass, relative to 100 parts by mass of the (meth)acrylic polymer.

[0088] [Tackifier] The pressure-sensitive adhesive composition of the present disclosure does not contain a tackifier, or the content of the tackifier is in the range of more than 0 parts by mass and less than 2.0 parts by mass per 100 parts by mass of the (meth)acrylic polymer. Some tackifiers have poor compatibility with (meth)acrylic polymers, which can cause a decrease in the transparency of the pressure-sensitive adhesive layer that is formed. In addition, some tackifiers themselves have a color, which can cause the pressure-sensitive adhesive layer that is formed to be discolored. The pressure-sensitive adhesive composition of the present disclosure does not contain a tackifier or contains a tackifier in a range of more than 0 parts by mass and less than 2.0 parts by mass per 100 parts by mass of the (meth)acrylic polymer, and therefore can form a pressure-sensitive adhesive layer that is excellent in transparency and resistant to coloration. From this perspective, the pressure-sensitive adhesive composition of the present disclosure preferably does not contain a tackifier or contains a tackifier in a range of more than 0 parts by mass and not more than 1.5 parts by mass per 100 parts by mass of the (meth)acrylic polymer, more preferably does not contain a tackifier or contains a tackifier in a range of more than 0 parts by mass and not more than 1.0 parts by mass per 100 parts by mass of the (meth)acrylic polymer, even more preferably does not contain a tackifier or contains a tackifier in a range of more than 0 parts by mass and not more than 0.5 parts by mass per 100 parts by mass of the (meth)acrylic polymer, and particularly preferably does not contain a tackifier.

[0089] In the present disclosure, the term "tackifier" refers to a compound that has the property of being able to impart tackiness when blended and has a molecular weight of less than 10,000 (preferably in the range of 500 or more and less than 10,000). Tackifiers are also called tackifiers.

[0090] The type of tackifier is not particularly limited. Examples of the tackifier include compounds having a rosin skeleton (e.g., rosin resins), compounds having a terpene skeleton (e.g., terpene resins), and compounds having a styrene skeleton (e.g., styrene resins). Examples of the tackifier include alicyclic saturated hydrocarbon resins.

[0091] Specific examples of compounds having a rosin skeleton include rosin compounds represented by abietic acid, neoabietic acid, and palustric acid, diol compounds having a rosin skeleton obtained by reacting hydrogenated rosin with diglycidyl ether, and hydrogenated rosin diol compounds. Specific examples of compounds having a terpene skeleton include copolymers of monocyclic monoterpene compounds such as α-pinene, β-pinene, and dipentene (limonene) with phenolic compounds such as phenol, cresol, and bisphenol A. Specific examples of the compound having a styrene skeleton include polystyrene and a copolymer of styrene and α-methylstyrene.

[0092] The tackifier may be a commercially available product. Examples of commercially available tackifiers include "YS Polystar U115," "YS Polystar U130," "YS Polystar T80," "YS Polystar T100," "YS Polystar T115," "YS Polystar T130," "YS Polystar TH30," "YS Polystar TH130," "YS Polystar T145," "YS Polystar T160," "YS Polystar S145," "YS Polystar G125," "YS Polystar G150," "YS Polystar N125," "YS Polystar K125," "YS Polystar K140," and "YS Resin CP" manufactured by Yasuhara Chemical Co., Ltd.; "FTR (registered trademark) 6100" manufactured by Mitsui Chemicals, Inc.; and "Pine Crystal (registered trademark) KE-359," "Pine Crystal (registered trademark) D-6011," and "Pensel (registered trademark)" manufactured by Arakawa Chemical Industries, Ltd. Examples of such compounds include "Alcon (registered trademark) P-125," "Alcon (registered trademark) P-140," "Alcon (registered trademark) P-90," "Tamanol (registered trademark) 803L," and "Tamanol (registered trademark) 901" (all of which are trade names).

[0093] When the pressure-sensitive adhesive composition of the present disclosure contains a tackifier, it may contain only one type of tackifier, or may contain two or more types of tackifiers.

[0094] [Crosslinking catalyst] The pressure-sensitive adhesive composition of the present disclosure may contain a crosslinking catalyst. The type of crosslinking catalyst is not particularly limited. Examples of crosslinking catalysts include organometallic compounds such as dioctyltin dilaurate (DOTDL) and 1,3-diacetoxytetrabutylstannoxane, and tertiary amine compounds such as triethylenediamine and N-methylmorpholine.

[0095] As the crosslinking catalyst, commercially available products can be used. An example of a commercially available crosslinking catalyst is Adeka STAB (registered trademark) OT-1 manufactured by ADEKA CORPORATION.

[0096] When the pressure-sensitive adhesive composition of the present disclosure contains a crosslinking catalyst, it may contain only one type of crosslinking catalyst, or may contain two or more types of crosslinking catalyst.

[0097] When the pressure-sensitive adhesive composition of the present disclosure contains a crosslinking catalyst, the content of the crosslinking catalyst is not particularly limited and can be set appropriately depending on the purpose.

[0098] [Organic solvent] The pressure-sensitive adhesive composition of the present disclosure may contain an organic solvent. When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, the coatability can be further improved. Examples of the organic solvent include the same organic solvents as those used in the polymerization reaction of the (meth)acrylic polymer described above.

[0099] When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, it may contain only one type of organic solvent, or may contain two or more types of organic solvents.

[0100] When the pressure-sensitive adhesive composition of the present disclosure contains an organic solvent, the content of the organic solvent is not particularly limited and can be set appropriately within a range that does not impair the effects of the pressure-sensitive adhesive composition of the present disclosure.

[0101] [Other ingredients] The pressure-sensitive adhesive composition of the present disclosure may contain components other than the components described above (so-called other components) as needed, as long as the effects of the pressure-sensitive adhesive composition of the present disclosure are not impaired. Examples of other components include polymers other than (meth)acrylic polymers, antioxidants, light stabilizers (for example, ultraviolet absorbers), antistatic agents, and other various additives.

[0102] When the pressure-sensitive adhesive composition of the present disclosure contains other components, the contents of the other components are not particularly limited and can be set appropriately within a range that does not impair the effects of the pressure-sensitive adhesive composition of the present disclosure.

[0103] <<Applications>> The pressure-sensitive adhesive composition of the present disclosure is capable of forming a pressure-sensitive adhesive layer that is difficult to peel off from a low-polarity substrate, has excellent transparency, and is suppressed from coloring. Therefore, the pressure-sensitive adhesive composition is suitable as a pressure-sensitive adhesive composition to be used on a low-polarity substrate that is provided with design features such as color, pattern, gloss, etc. Examples of low polarity adherends include adherends containing polyolefin resins (eg, polypropylene (PP), polyethylene (PE)). Specifically, examples of low-polarity adherends include vehicle (for example, automobile) parts (for example, exterior and interior parts) containing polyolefin resins as materials, building materials, and OA (office automation) equipment.

[0104] [Adhesive sheet] The pressure-sensitive adhesive sheet of the present disclosure includes a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of the present disclosure. The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of the present disclosure is resistant to peeling from a low-polarity adherend, has excellent transparency, and is inhibited from coloring. Therefore, the pressure-sensitive adhesive sheet of the present disclosure is suitable as a pressure-sensitive adhesive sheet that is provided with a design, for example, by color, pattern, gloss, etc., and is used on a low-polarity adherend.

[0105] The thickness of the pressure-sensitive adhesive layer provided in the pressure-sensitive adhesive sheet of the present disclosure is not particularly limited. The thickness of the pressure-sensitive adhesive layer is generally 1 μm to 300 μm, preferably 5 μm to 200 μm, and more preferably 10 μm to 100 μm.

[0106] In the present disclosure, the "thickness of the pressure-sensitive adhesive layer" refers to the average thickness of the pressure-sensitive adhesive layer. The average thickness of the pressure-sensitive adhesive layer is a value measured by the following method. The arithmetic mean value of the thicknesses of the adhesive layer measured at 10 randomly selected points in the thickness direction of the adhesive layer is calculated, and the obtained value is defined as the average thickness of the adhesive layer. The thickness of the adhesive layer is measured using a film thickness meter.

[0107] The pressure-sensitive adhesive sheet of the present disclosure may be a substrate-free pressure-sensitive adhesive sheet that does not have a substrate, or may be a substrate-containing pressure-sensitive adhesive sheet that has a pressure-sensitive adhesive layer on one or both sides of a substrate. When the pressure-sensitive adhesive sheet of the present disclosure is a substrate-free pressure-sensitive adhesive sheet that does not have a substrate, or when it is a substrate-containing pressure-sensitive adhesive sheet that has a pressure-sensitive adhesive layer on one side of a substrate, the exposed surface of the pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet of the present disclosure may be protected by a release sheet. Generally, the release sheet protects the surface of the pressure-sensitive adhesive layer until the pressure-sensitive adhesive sheet is put to practical use, and is peeled off at the time of use.

[0108] The release sheet is not particularly limited as long as it can be easily peeled off from the pressure-sensitive adhesive layer. Examples of release sheets include resin films, paper, synthetic paper, and composite sheets made by laminating two or more of these, each of which has been surface-treated with a release agent on one or both sides (so-called easy-release treatment). In the present disclosure, a release sheet in an embodiment in which one or both sides of a resin film have been surface-treated with a release treatment agent (so-called easy-release treatment) is also referred to as a "release film." Examples of release agents include silicone-based release agents (e.g., silicone), wax-based release agents (e.g., paraffin wax), and fluorine-based release agents (e.g., fluorine-based resins). Examples of resin films include polyester films such as polyethylene terephthalate (PET) films. Examples of paper include fine paper and coated paper. The thickness of the release sheet is not particularly limited, and is generally 20 μm to 180 μm.

[0109] When the pressure-sensitive adhesive sheet of the present disclosure includes a substrate, the substrate is not particularly limited as long as a pressure-sensitive adhesive layer can be formed on the substrate. Examples of the substrate include films containing resins such as polyolefin resins (e.g., polyethylene (PE) and polypropylene (PP)), polyester resins (e.g., polyethylene terephthalate (PET)), acetate resins (e.g., triacetyl cellulose resin), polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, acrylic resins, vinyl chloride resins, ABS (Acrylonitrile Butadiene Styrene) resins, and fluorine-based resins.

[0110] The surface of the substrate on which the adhesive layer is provided may be subjected to a surface treatment such as corona discharge treatment or plasma discharge treatment (so-called easy-adhesion treatment) in order to improve the adhesion between the substrate and the adhesive layer.

[0111] The substrate may contain various additives such as a plasticizer, a heat stabilizer, a light stabilizer, an antistatic agent, a flame retardant, and an antioxidant. The substrate may be partially or entirely patterned.

[0112] The thickness of the substrate is not particularly limited, but is generally 5 μm to 500 μm, preferably 10 μm to 300 μm, more preferably 10 μm to 200 μm, and even more preferably 10 μm to 100 μm.

[0113] In this disclosure, "thickness of the substrate" means the average thickness of the substrate. The average thickness of the substrate is a value measured by a method conforming to the above-mentioned method for measuring the average thickness of the pressure-sensitive adhesive layer.

[0114] [How to make adhesive sheets] The method for producing the pressure-sensitive adhesive sheet of the present disclosure is not particularly limited. The pressure-sensitive adhesive sheet of the present disclosure can be produced by a known method. The pressure-sensitive adhesive sheet of the present disclosure can be produced, for example, by the following method.

[0115] When the pressure-sensitive adhesive sheet of the present disclosure is a substrate-free type pressure-sensitive adhesive sheet, first, the pressure-sensitive adhesive composition of the present disclosure is applied to the easy-release treated surface of a release sheet to form a coating film on the release sheet. The formed coating film is then dried to form an adhesive film on the release sheet. Next, the exposed surface of the formed adhesive film is laminated onto the easy-release treated surface of a separately prepared release sheet, and then cured as necessary, thereby producing a substrate-free type pressure-sensitive adhesive sheet having a laminated structure of release sheet / adhesive layer / release sheet.

[0116] When the pressure-sensitive adhesive sheet of the present disclosure is a substrate-type pressure-sensitive adhesive sheet, first, the pressure-sensitive adhesive composition of the present disclosure is applied to an easily adhesive treated surface of the substrate to form a coating film on the substrate. The formed coating film is then dried to form a pressure-sensitive adhesive film on the substrate. Next, the exposed surface of the formed pressure-sensitive adhesive film is laminated onto the easily release treated surface of a release sheet, and then cured as necessary, thereby producing a substrate-type pressure-sensitive adhesive sheet having a laminate structure of release sheet / pressure-sensitive adhesive layer / substrate.

[0117] When the pressure-sensitive adhesive sheet of the present disclosure is a substrate-containing pressure-sensitive adhesive sheet, another method may be, for example, the following method. The pressure-sensitive adhesive composition of the present disclosure is applied to the easy-release treated surface of a release sheet to form a coating film on the release sheet. The formed coating film is then dried to form a pressure-sensitive adhesive film on the release sheet. The exposed surface of the formed pressure-sensitive adhesive film is then laminated to the easy-adhesion treated surface of a substrate, and then cured as necessary, to produce a substrate-type pressure-sensitive adhesive sheet having a laminated structure of substrate / pressure-sensitive adhesive layer / release sheet.

[0118] The method for applying the pressure-sensitive adhesive composition is not particularly limited. Examples of methods for applying the pressure-sensitive adhesive composition include known methods using a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, knife coater, spray coater, bar coater, applicator, etc. The amount of the pressure-sensitive adhesive composition to be applied is not particularly limited, and is set appropriately depending on, for example, the thickness of the pressure-sensitive adhesive layer to be formed.

[0119] The method for drying the coating film is not particularly limited. Examples of methods for drying the coating film include natural drying, heat drying, hot air drying, and vacuum drying. The drying temperature and drying time of the coating film are not particularly limited, and are set appropriately depending on the thickness of the coating film, the amount of organic solvent in the coating film, and the like. An example of the drying conditions is drying using a hot air dryer at 70°C to 120°C for 30 to 180 seconds.

[0120] When curing is performed, the curing conditions include, for example, an ambient temperature of 20°C to 35°C and a relative humidity of 45% to 55% (ie, 45% RH to 55% RH) for 2 to 7 days. [Example]

[0121] The pressure-sensitive adhesive composition and the like of the present disclosure will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples as long as it does not deviate from the gist of the disclosure.

[0122] [Production of (meth)acrylic polymer] [Manufacturing example A-1] A reactor equipped with a stirrer, reflux condenser, sequential dropping device, and thermometer was charged with 103.7 parts by mass of ethyl acetate (organic solvent for polymerization) and 0.07 parts by mass of 2,2'-azobisisobutyronitrile (AIBN; polymerization initiator). Next, 558.3 ​​parts by mass of a monomer mixture consisting of 524.8 parts by mass of n-butyl acrylate (n-BA) and 33.5 parts by mass of acrylic acid (AA) was prepared in a separate vessel. First, 122.8 parts by mass of this prepared monomer mixture was charged into the reactor, and the mixture was heated and refluxed at reflux temperature for 10 minutes. Next, under reflux temperature conditions, the remaining 435.5 parts by mass of the monomer mixture and a mixed solution of 449.3 parts by mass of ethyl acetate (organic solvent for polymerization) and 0.46 parts by mass of AIBN (polymerization initiator) were added dropwise to the reactor over 120 minutes, and the mixture was allowed to react for 70 minutes after the dropwise addition was completed. Then, a mixed solution of 61.0 parts by mass of ethyl acetate (organic solvent for polymerization) and 1.40 parts by mass of AIBN (polymerization initiator) was added dropwise over 60 minutes, and after the completion of the addition, the mixture was allowed to react for 90 minutes. After the completion of the reaction, the solution was diluted with ethyl acetate to obtain a solution of (meth)acrylic polymer A-1 having a solid content of 34.0% by mass.

[0123] The "solid content concentration" here means the mass proportion of the (meth)acrylic polymer A-1 in the solution of the (meth)acrylic polymer A-1. The same applies to the solutions of the (meth)acrylic polymers A-2 to A-5 produced below.

[0124] [Manufacturing examples A-2 to A-5] Solutions of (meth)acrylic polymers A-2 to A-5 were obtained in the same manner as in Production Example A-1, except that the monomer composition of the (meth)acrylic polymer in Production Example A-1 was changed to the monomer composition shown in Table 1 and that the polymerization temperature, polymerization time, amount of organic solvent used, amount of polymerization initiator used, etc. were appropriately adjusted. The solids concentrations of the obtained solutions of (meth)acrylic polymers A-2 to A-5 are shown below.

[0125] -Solids concentration of each solution of (meth)acrylic polymers A-2 to A-5- A-2: 33.5% by mass, A-3: 40.0% by mass, A-4: 33.0% by mass, A-5: 35.0% by mass

[0126] Table 1 shows the monomer compositions, glass transition temperatures (Tg), and weight average molecular weights (Mw) of the (meth)acrylic polymers A-1 to A-5.

[0127] The glass transition temperatures of the (meth)acrylic polymers A-1 to A-5 were calculated by the same method as the above-mentioned method for calculating the glass transition temperature of a (meth)acrylic polymer. The weight average molecular weights of the (meth)acrylic polymers A-1 to A-5 were measured by the same method as the method for measuring the weight average molecular weight of the (meth)acrylic polymer described above.

[0128] [Table 1]

[0129] Details of each monomer listed in Table 1 are as follows: <(Meth)acrylic acid alkyl ester monomer> "n-BA": n-butyl acrylate "2EHA": 2-ethylhexyl acrylate "MMA": Methyl methacrylate <Monomers having a carboxy group> "AA": acrylic acid <Monomers having a hydroxyl group> "2HEA": 2-hydroxyethyl acrylate

[0130] In Table 1, "-" in the column of monomer composition means that the monomer in that column was not used.

[0131] [Preparation of Pressure-Sensitive Adhesive Composition] Example 1 100 parts by mass (solid content equivalent) of the solution of (meth)acrylic polymer A-1, 3.00 parts by mass (solid content equivalent) of an isocyanate-based crosslinking agent, Coronate (registered trademark) L-45E (trade name, manufactured by Tosoh Corporation), and 1.0 part by mass (solid content equivalent) of a chlorinated polyolefin, Superchlorine (registered trademark) 224H (trade name, manufactured by Nippon Paper Industries Co., Ltd.) were thoroughly mixed to obtain a pressure-sensitive adhesive composition of Example 1.

[0132] [Examples 2 to 15] The same procedure as in Example 1 was carried out except that the formulation of the adhesive composition in Example 1 was changed to the formulation shown in Table 2, to obtain adhesive compositions of Examples 2 to 15.

[0133] [Comparative Examples 1 to 7] The same procedure as in Example 1 was carried out except that the formulation of the adhesive composition in Example 1 was changed to the formulation shown in Table 3, and adhesive compositions of Comparative Examples 1 to 7 were obtained.

[0134] [Table 2]

[0135] [Table 3]

[0136] Details of each component listed in Table 2 and / or Table 3 are as follows: [Crosslinking agent] <Epoxy-based crosslinking agent> "TETRAD-X" (product name, manufactured by Mitsubishi Gas Chemical Company, Inc.) <Isocyanate-based crosslinking agent> "Coronate L-45E" (trade name, adduct of tolylene diisocyanate (TDI) and trimethylolpropane (TMP), manufactured by Tosoh Corporation) "Duranate AE700-100" [product name, hexamethylene diisocyanate (HMDI), manufactured by Asahi Kasei Corporation] "Takenate D-140N" (trade name, adduct of isophorone diisocyanate (IPDI) and trimethylolpropane (TMP), manufactured by Mitsui Chemicals, Inc.) <Metal chelate crosslinking agent> "Aluminum Chelate A" (trade name, chemical name: aluminum tris(acetylacetonate), manufactured by Kawaken Fine Chemicals Co., Ltd.) The above "TETRAD," "Coronate," "Duranate," and "Takenate" are all registered trademarks.

[0137] [Crosslinking catalyst] "ADEKA STAB OT-1" (product name, chemical name: dioctyl tin dilaurate (DOTDL), manufactured by ADEKA Corporation) The above "ADK STAB" is a registered trademark.

[0138] [Chlorinated polyolefin] "Superchlorine 224H" (product name, chlorine content: 12.5% ​​by mass, weight-average molecular weight: 62908, acrylic-modified chlorinated polyolefin, manufactured by Nippon Paper Industries Co., Ltd.) "Superchlorine 813A" (product name, chlorine content: 30.0% by mass, weight-average molecular weight: 8072, unmodified chlorinated polyolefin, manufactured by Nippon Paper Industries Co., Ltd.) "Superchron" is a registered trademark.

[0139] [Tackifier] "Pensel D-125" (product name, rosin resin, manufactured by Arakawa Chemical Industries, Ltd.) "Arcon P-90" (product name, alicyclic saturated hydrocarbon resin, manufactured by Arakawa Chemical Industries, Ltd.) "Pensel" and "Alcon" are registered trademarks.

[0140] In Tables 2 and 3, "-" means that there is no corresponding item in that column. In Tables 2 and 3, the values ​​shown in the "content" column are all solid content equivalents.

[0141] [Preparation of adhesive sheets for evaluation] 1. Evaluation adhesive sheet A The pressure-sensitive adhesive composition prepared above was applied to the easily peelable surface of a release film (trade name: PET75GS, thickness: 75 μm, manufactured by Lintec Corporation) that had been treated with a silicone-based release agent to facilitate peeling, to form a coating film. The amount of pressure-sensitive adhesive composition applied was such that the thickness of the final pressure-sensitive adhesive layer formed would be 50 μm. The formed coating film was then dried using a hot air circulation dryer at a drying temperature of 100°C and a drying time of 1 minute to form a pressure-sensitive adhesive film on the release film. The exposed surface of the pressure-sensitive adhesive film formed on the release film was then placed on one side of a substrate film (trade name: DIAFOIL (registered trademark) S100-75, thickness: 75 μm, manufactured by Mitsubishi Chemical Corporation), and then pressed using a rubber roller in an environment with an ambient temperature of 23°C and 50% RH to form a laminate. The prepared laminate was then left to stand for 7 days in an environment with an atmospheric temperature of 23°C and 50% RH to cure the adhesive film, thereby preparing an evaluation adhesive sheet A. The evaluation adhesive sheet A thus prepared had a laminate structure of release film (thickness: 75 μm) / adhesive layer (thickness: 50 μm) / substrate film (thickness: 75 μm).

[0142] 2. Evaluation adhesive sheet B The pressure-sensitive adhesive composition prepared above was applied to the easily peelable surface of a release film X1 (trade name: PET75GS, thickness: 75 μm, manufactured by Lintec Corporation) that had been treated with a silicone-based release agent to facilitate peeling, to form a coating film. The amount of pressure-sensitive adhesive composition applied was such that the thickness of the finally formed pressure-sensitive adhesive layer would be 45 μm. The formed coating film was then dried using a hot air circulation dryer under drying conditions of a drying temperature of 100°C and a drying time of 1 minute, to form a pressure-sensitive adhesive film on the release film X1. Next, the pressure-sensitive adhesive composition prepared above was applied to the easily peelable surface of a release film X2 (trade name: PET75GS, thickness: 75 μm, manufactured by Lintec Corporation) that had been treated with a separately prepared silicone-based release agent to easily peel, to form a coating film. The amount of pressure-sensitive adhesive composition applied was such that the thickness of the finally formed pressure-sensitive adhesive layer would be 45 μm. Next, the formed coating film was dried using a hot air circulation dryer under drying conditions of a drying temperature of 100°C and a drying time of 1 minute, to form a pressure-sensitive adhesive film on the release film X2. Next, the exposed surface of the adhesive film formed on the surface of release sheet X1 was overlapped with the exposed surface of the adhesive film formed on the surface of release sheet X2, and then pressed together using a rubber roller in an environment with an atmospheric temperature of 23°C and 50% RH to produce a laminate. The produced laminate was then left to stand in an environment with an atmospheric temperature of 23°C and 50% RH for 7 days to allow the adhesive film to age, thereby producing an evaluation adhesive sheet B. The produced evaluation adhesive sheet B had a laminate structure of release film X1 (thickness: 75 μm) / adhesive layer (thickness: 90 μm) / release film X2 (thickness: 75 μm).

[0143] [Measurement and Evaluation] 1.Transparency The pressure-sensitive adhesive sheet A for evaluation prepared as described above was cut into a size of 50 mm x 50 mm. The release film was then peeled off from the cut pressure-sensitive adhesive sheet A for evaluation to obtain a pressure-sensitive adhesive sheet piece for evaluation. The pressure-sensitive adhesive sheet piece for evaluation had a laminated structure of a pressure-sensitive adhesive layer / substrate film. Next, the haze value (unit: %) of the evaluation pressure-sensitive adhesive sheet piece was measured using a haze meter (model number: NDH 2000, manufactured by Nippon Denshoku Industries Co., Ltd.). Evaluation was then performed according to the following evaluation criteria. The results are shown in Table 4. In the following evaluation criteria, "A" and "B" are at levels that are not problematic in practical use, with "A" being more preferable.

[0144] -Evaluation criteria- A: The haze value is less than 0.50%. B: The haze value is 0.50% or more and less than 1.10%. C: The haze value is 1.10% or more.

[0145] 2. Presence or absence of coloring The evaluation pressure-sensitive adhesive sheet B prepared above was cut into a size of 50 mm × 50 mm. Next, release film X1 and release film X2 were peeled off from the cut evaluation pressure-sensitive adhesive sheet B. The pressure-sensitive adhesive layer obtained by this peeling was visually observed to confirm the presence or absence of coloration. The results are shown in Table 4. In Table 4, if coloration was confirmed, it was recorded as "Yes," and if coloration was not confirmed, it was recorded as "No."

[0146] 3. Adhesion to polypropylene (PP) The pressure-sensitive adhesive sheet A for evaluation prepared above was cut into a size of 25 mm x 150 mm (long sides) to prepare one piece of pressure-sensitive adhesive sheet for evaluation. The release film was peeled off from the prepared piece of adhesive sheet for evaluation, and the surface of the adhesive layer exposed by the peeling was placed on one side of a polypropylene (PP) plate [product name: K20123PP, product number: PP-N-BN, size: 100 mm × 150 mm, thickness: 2 mm, manufactured by Paltec Co., Ltd.] (hereinafter referred to as "PP plate" as appropriate), and then the two plates were pressed together by moving a 2 kg roller back and forth twice to produce a laminate. Next, the prepared laminate was left to stand for 24 hours in an environment of an atmospheric temperature of 23°C and 50% RH to prepare a sample for measuring adhesive strength. Next, the adhesive strength (unit: N / 25 mm) of the prepared adhesive strength measurement sample was measured by peeling the evaluation adhesive sheet piece (composition: adhesive layer / substrate film) from the PP plate at an angle of 180° in the long side (150 mm) direction, using a method in accordance with JIS Z 0237:2000. Specifically, a single-column material testing machine (model number: RTG-1310) manufactured by A&D Co., Ltd. was used as the measuring device, and measurements were made under conditions of an ambient temperature of 23°C, 50% RH, and a peel speed of 300 mm / min. Evaluation was then carried out according to the following evaluation criteria. The results are shown in Table 4. In Table 4, if zipping occurred when peeling the evaluation adhesive sheet piece (composition: adhesive layer / substrate film) from the PP plate, this was recorded as "zipping," along with the minimum adhesive strength measured during peeling. The zipping phenomenon here refers to a phenomenon in which, when peeling the evaluation adhesive sheet piece from the PP plate, the peeling does not occur smoothly but produces a crackling noise. The more zipping occurs and the lower the minimum adhesive strength, the easier it is for the adhesive layer to peel from the PP plate. In the following evaluation criteria, "A" and "B" are at levels that are not problematic in practical use, with "A" being more preferable.

[0147] -Evaluation criteria- A: The adhesive strength is 15.0N / 25mm or more. B: The adhesive strength is in the range of 5.0 N / 25 mm or more and less than 15.0 N / 25 mm. C: The adhesive strength is less than 5.0 N / 25 mm (however, if zipping occurs, the minimum adhesive strength is less than 5.0 N / 25 mm).

[0148] [Table 4]

[0149] As shown in Table 4, it was confirmed that each of the pressure-sensitive adhesive layers formed using the pressure-sensitive adhesive compositions of Examples 1 to 15 had excellent transparency. Furthermore, no coloring was confirmed in each of the pressure-sensitive adhesive layers formed using the pressure-sensitive adhesive compositions of Examples 1 to 15. It was also confirmed that each of the pressure-sensitive adhesive layers formed using the pressure-sensitive adhesive compositions of Examples 1 to 15 was difficult to peel from a PP plate, which is an adherend with low polarity.

[0150] On the other hand, it was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 1, which did not contain chlorinated polyolefin, was easily peeled off from the PP plate, which is an adherend with low polarity. It was confirmed that the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition of Comparative Example 2, in which the content of chlorinated polyolefin exceeded 2.0 parts by mass per 100 parts by mass of the (meth)acrylic polymer, was inferior in transparency to the pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive compositions of the Examples. Coloring was confirmed in the pressure-sensitive adhesive layers formed from the pressure-sensitive adhesive compositions of Comparative Examples 3 to 5 and 7, in which the tackifier content was 2.0 parts by mass or more per 100 parts by mass of the (meth)acrylic polymer. Furthermore, the results of Comparative Examples 3, 4, and 5 revealed that transparency was impaired as the tackifier content increased. The adhesive layer formed from the adhesive composition of Comparative Example 6, which contained a tackifier instead of chlorinated polyolefin, tended to be difficult to peel from the PP plate, which is a low-polarity adherend, but was found to be inferior in transparency to the adhesive layers formed from the adhesive compositions of Examples 1 and 2. Furthermore, coloration was observed in the adhesive layer formed from the adhesive composition of Comparative Example 6.

Claims

1. a (meth)acrylic polymer; a chlorinated polyolefin; a crosslinking agent (excluding metal chelate crosslinking agents); Including, the chlorinated polyolefin is an acrylic-modified chlorinated polyolefin, the content of the acrylic-modified chlorinated polyolefin is 0.05 parts by mass to 2.0 parts by mass relative to 100 parts by mass of the (meth)acrylic polymer, the (meth)acrylic polymer contains a structural unit derived from a monomer having a carboxy group, and the content of the structural unit derived from the monomer having a carboxy group in the (meth)acrylic polymer is 3.0% by mass to 6.0% by mass with respect to all structural units of the (meth)acrylic polymer; does not contain a tackifier, or the content of the tackifier is in the range of more than 0 parts by mass and less than 2.0 parts by mass per 100 parts by mass of the (meth)acrylic polymer, A pressure-sensitive adhesive composition having a haze value of less than 1.10% when a pressure-sensitive adhesive layer having a thickness of 50 μm is formed.

2. The adhesive composition described in claim 1, wherein the (meth)acrylic polymer contains a structural unit derived from a monomer having a hydroxyl group.

3. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to claim 1 or 2.

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