Adhesive layer for overlaminate film, overlaminate film, and license plate

Abstract

To provide an adhesive layer for overlaminate films that exhibits strong adhesion to adherends and is less prone to cause visual defects during three-dimensional molding, as well as to provide an overlaminate film and a license plate.SOLUTION: The present invention provides an adhesive layer for overlaminate films and its applications, wherein the adhesive layer is formed from an adhesive composition comprising a (meth)acrylic polymer having reactive functional groups and a glass transition temperature of -45°C to -5°C, and an isocyanate-based crosslinking agent, wherein the gel fraction after heat treatment at 120°C for 1 hour is 60 mass% or more, and the gel fraction before heat treatment at 120°C for 1 hour is 30 mass% or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a pressure-sensitive adhesive layer for an overlaminate film, an overlaminate film, and a license plate. [Background technology]

[0002] Conventionally, inkjet-printed films have been used to decorate outdoor signs, vehicles (e.g., two-wheeled and four-wheeled vehicles), etc. Such films have a configuration including at least a printing film for printing and an overlaminate film for protecting the printing film, and in recent years have also been used for number plates (also called "license plates") (see, for example, Patent Documents 1 to 4). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-215672 A [Patent Document 2] JP 2017-177481 A [Patent Document 3] JP 2019-81330 A [Patent Document 4] JP 2019-206145 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, although commonly used overlaminate films have excellent adhesion to the adherend, during three-dimensional molding, cohesive failure and / or peeling of the pressure-sensitive adhesive layer may occur around the convex parts of the adherend, which may cause a loss of appearance.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances. The problem to be solved by one embodiment of the present disclosure is to provide a pressure-sensitive adhesive layer for an overlaminate film that has high adhesive strength to an adherend and is unlikely to cause poor appearance during three-dimensional molding. Another problem to be solved by another embodiment of the present disclosure is to provide an overlaminate film and a license plate comprising the above-mentioned pressure-sensitive adhesive layer for the overlaminate film. [Means for solving the problem]

[0006] Specific means for solving the problems include the following aspects. <1> It is formed from a pressure-sensitive adhesive composition containing a (meth)acrylic polymer having a reactive functional group and a glass transition temperature of −45° C. to −5° C., and an isocyanate-based crosslinking agent; An adhesive layer for an overlaminate film, having a gel fraction of 60% by mass or more after heat treatment at 120°C for 1 hour and a gel fraction of 30% by mass or less before heat treatment at 120°C for 1 hour. <2> The change in gel fraction before and after heat treatment at 120°C for 1 hour is 50% by mass or more. <1> 2. The pressure-sensitive adhesive layer for an overlaminate film according to claim 1 . <3> The gel fraction after heat treatment at 120°C for 1 hour is 60% by mass or more, and the gel fraction before heat treatment at 120°C for 1 hour is 10% by mass or less. <1> 2. The pressure-sensitive adhesive layer for an overlaminate film according to claim 1 . <4> The isocyanate crosslinking agent is a blocked isocyanate compound. <1> ~ <3> 10. The pressure-sensitive adhesive layer for an overlaminate film according to any one of the above items. <5> A surface protection film; Provided on one side of the surface protection film <1> ~ <4> The pressure-sensitive adhesive layer for an overlaminate film according to any one of the above items, An overlaminate film comprising: <6> A plate substrate; Provided on one side of the plate substrate <5> An overlaminate film according to claim 1, A license plate comprising: Effect of the Invention

[0007] According to one embodiment of the present disclosure, there is provided a pressure-sensitive adhesive layer for an overlaminate film that has high adhesive strength to an adherend and is less likely to cause poor appearance during three-dimensional molding. According to another embodiment of the present disclosure, there is provided an overlaminate film and a license plate comprising the above-mentioned pressure-sensitive adhesive layer for an overlaminate film. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a configuration of an overlaminate film of the present disclosure. [Diagram 2] FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a license plate of the present disclosure. [Diagram 3] FIG. 11 is a schematic cross-sectional view showing an example of another configuration of the license plate of the present disclosure. [Figure 4A] 1 is a photograph showing an example of the evaluation result "A" of cohesive failure in an example. [Figure 4B] 1 is a photograph showing an example of the evaluation result "B" of cohesive failure in an example. [Figure 4C] 1 is a photograph showing an example of the evaluation result "C" of cohesive failure in an example. [Diagram 5] 1 is a photograph showing an example of embossed letters in a peeling evaluation test in the Examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The adhesive layer for the overlaminate film, the overlaminate film, and the license plate of the present disclosure will be described in detail below. The following description of the requirements may be based on a representative embodiment of the present disclosure, but the present disclosure is not limited to such an embodiment, and can be modified as appropriate within the scope of the purpose of the present disclosure.

[0010] In the present disclosure, when an embodiment is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. In addition, the size of the members in each drawing is conceptual, and the relative relationship of the size between the members is not limited thereto. In addition, in each drawing, the same reference numerals are given to members having substantially the same functions, and duplicated descriptions may be omitted.

[0011] 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 limit and upper limit, respectively. 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 the upper or lower limit value of another numerical range described in the present disclosure. In addition, 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.

[0012] In the present disclosure, combinations of two or more preferred embodiments are more preferred embodiments.

[0013] In the present disclosure, when the adhesive composition contains multiple substances corresponding to each component, the amount of each component in the adhesive composition means the total amount of the multiple substances present in the adhesive composition, unless otherwise specified.

[0014] In the present disclosure, unless otherwise specified, "solid content" means components other than the solvent contained in the composition. In this disclosure, "solvent" means water and / or an organic solvent.

[0015] In the present disclosure, "(meth)acrylic monomer" means a monomer having a (meth)acryloyl group. In the present disclosure, "(meth)acrylic polymer" means a polymer that contains structural units derived from (meth)acrylic monomers and in which the proportion of structural units derived from (meth)acrylic monomers is 50 mass% or more.

[0016] In this 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".

[0017] In this disclosure, "n-" means normal, "i-" means iso, "s-" means secondary, and "t-" means tertiary.

[0018] In the present disclosure, "mass %" and "weight %" are synonymous, and "parts by mass" and "parts by weight" are synonymous.

[0019] In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0020] In the present disclosure, the term "layer" includes cases where the layer is formed over the entire area when the area is observed, as well as cases where the layer is formed over only a part of the area. The same applies to the term "film." In this disclosure, the term "lamination" refers to stacking layers, and a "lamination" may be two or more layers bonded together, or two or more layers may be detachable.

[0021] In the present disclosure, "poor appearance" refers to poor appearance caused by cohesive failure and / or peeling of the pressure-sensitive adhesive layer, and "peeling" also includes a state in which part of the pressure-sensitive adhesive layer is lifted from the adherend.

[0022] In the present disclosure, "a pressure-sensitive adhesive composition containing a (meth)acrylic polymer having a reactive functional group and a glass transition temperature of -45°C to -5°C, and an isocyanate-based crosslinking agent" is also referred to as "specific pressure-sensitive adhesive composition". In the present disclosure, "a (meth)acrylic polymer having a reactive functional group and a glass transition temperature of -45°C to -5°C" is also referred to as "a specific (meth)acrylic polymer".

[0023] [Adhesive layer for overlaminate film] The pressure-sensitive adhesive layer for an overlaminate film of the present disclosure (hereinafter also simply referred to as the "pressure-sensitive adhesive layer") is formed from a pressure-sensitive adhesive composition (i.e., a specific pressure-sensitive adhesive composition) containing a (meth)acrylic polymer (i.e., a specific (meth)acrylic polymer) having a reactive functional group and a glass transition temperature of -45°C to -5°C, and an isocyanate-based crosslinking agent, and has a gel fraction of 60 mass% or more after heat treatment at 120°C for 1 hour, and a gel fraction of 30 mass% or less before heat treatment at 120°C for 1 hour.

[0024] The pressure-sensitive adhesive layer of the present disclosure is used as a pressure-sensitive adhesive layer provided in an overlaminate film. Although the pressure-sensitive adhesive layer for a conventional general overlaminate film has excellent adhesion to an adherend, when the film is attached to the adherend and then three-dimensionally molded, cohesive failure and / or peeling may be observed around the protruding parts of the adherend after the three-dimensional molding. In contrast, the pressure-sensitive adhesive layer of the present disclosure is formed from a pressure-sensitive adhesive composition having the above-described configuration and has the above-described physical properties, and therefore has high adhesive strength to an adherend and is less likely to cause poor appearance during three-dimensional molding. The reason why the pressure-sensitive adhesive layer of the present disclosure can exhibit such an effect is unclear, but the present inventors speculate as follows, however, the following speculation is not intended to limit the pressure-sensitive adhesive layer of the present disclosure, but is merely an example.

[0025] The pressure-sensitive adhesive layer of the present disclosure is formed from a pressure-sensitive adhesive composition containing a (meth)acrylic polymer having a relatively low glass transition temperature, and therefore has excellent wettability to an adherend, and is considered to adhere closely to the adherend when attached to the adherend. Therefore, the pressure-sensitive adhesive layer of the present disclosure can function suitably as a pressure-sensitive adhesive layer provided in an overlaminate film. The adhesive composition of the present disclosure includes a (meth)acrylic polymer and an isocyanate-based crosslinking agent, and the (meth)acrylic polymer has a functional group capable of reacting with an isocyanate group of the isocyanate-based crosslinking agent to form a crosslinked structure, i.e., a reactive functional group. The adhesive layer of the present disclosure formed by the adhesive composition has a low gel fraction before heat treatment at 120°C for 1 hour, and a high gel fraction after heat treatment at 120°C for 1 hour, and the degree of crosslinking can be controlled by heating. For example, the adhesive layer before heat treatment has excellent wettability to the adherend due to the presence of a (meth)acrylic polymer with a relatively low glass transition temperature, and is soft due to the low gel fraction before heat treatment, so it is considered that the adhesive layer adheres closely to the adherend when it is attached to the adherend. The adhesive layer of the present disclosure can be heat-treated while in close contact with the adherend to increase its cohesive strength without decreasing its adhesive strength to the adherend, and it is therefore presumed that this adhesive layer has high adhesive strength to the adherend and can suppress the occurrence of cohesive failure and peeling around the convex parts of the adherend due to three-dimensional molding.

[0026] [Specific adhesive composition] The pressure-sensitive adhesive composition (i.e., specific pressure-sensitive adhesive composition) according to the present disclosure contains a (meth)acrylic polymer (i.e., specific (meth)acrylic polymer) having a reactive functional group and having a glass transition temperature of −45° C. to −5° C., and an isocyanate-based crosslinking agent. The pressure-sensitive adhesive layer of the present disclosure contains a cured product of a specific pressure-sensitive adhesive composition, and the cured product includes, for example, a crosslinked product of a specific (meth)acrylic polymer obtained by crosslinking and curing with an isocyanate-based crosslinking agent.

[0027] <Specific (meth)acrylic polymer> The specific pressure-sensitive adhesive composition contains a (meth)acrylic polymer having a reactive functional group and a glass transition temperature of -45°C to -5°C (that is, a specific (meth)acrylic polymer). The specific pressure-sensitive adhesive composition may contain only one type of specific (meth)acrylic polymer, or may contain two or more types.

[0028] In the present disclosure, a "reactive functional group" refers to a functional group that can react with an isocyanate group to form a crosslinked structure. Specific examples of the reactive functional group include a carboxy group, a hydroxyl group, an amino group, and a glycidyl group. In the present disclosure, an "amino group" includes a primary amino group, a secondary amino group, and a tertiary amino group. The reactive functional group preferably contains a carboxy group, and is more preferably a carboxy group, from the viewpoint of reactivity with an isocyanate group, for example.

[0029] The specific (meth)acrylic polymer may be a homopolymer or a copolymer. The specific (meth)acrylic polymer may be, for example, a homopolymer or copolymer of a (meth)acrylic monomer having no reactive functional group, into which a reactive functional group is introduced by substitution, or a copolymer of a (meth)acrylic monomer having no reactive functional group and a monomer having no reactive functional group and a monomer other than the (meth)acrylic monomer, into which a reactive functional group is introduced by substitution. The specific (meth)acrylic polymer may be, for example, a copolymer of a (meth)acrylic monomer having a reactive functional group and a (meth)acrylic monomer having no reactive functional group, a copolymer of a (meth)acrylic monomer having a reactive functional group and a monomer having no reactive functional group and a monomer other than the (meth)acrylic monomer, or a copolymer of a (meth)acrylic monomer having no reactive functional group and a monomer having a reactive functional group and a monomer other than the (meth)acrylic monomer.

[0030] A preferred embodiment of the specific (meth)acrylic polymer is an embodiment in which the specific (meth)acrylic polymer has a reactive functional group by including a constituent unit derived from a monomer having a reactive functional group described below.

[0031] <<Structural units derived from monomers having reactive functional groups>> The specific (meth)acrylic polymer preferably contains a structural unit derived from a monomer having a reactive functional group. In the present disclosure, a "structural unit derived from a monomer having a reactive functional group" refers to a structural unit formed by addition polymerization of a monomer having a reactive functional group.

[0032] An example of a monomer having a reactive functional group is a monomer having at least one reactive functional group and an ethylenically unsaturated group in one molecule. Specific examples of the reactive functional group are as described above. The ethylenically unsaturated group is not particularly limited, and examples thereof 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.

[0033] Examples of the monomer having a reactive functional group include a monomer having a carboxy group, a monomer having a hydroxyl group, a monomer having an amino group, and a monomer having a glycidyl group. As the monomer having a reactive functional group, a monomer having a carboxy group is preferable.

[0034] Specific examples of monomers having a carboxy group include (meth)acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, glutaconic acid, citraconic acid, ω-carboxy-polycaprolactone mono(meth)acrylate [e.g., ω-carboxy-polycaprolactone (n≒2) monoacrylate], and succinic acid derivatives (e.g., 2-acryloyloxyethyl-succinic acid). The monomer having a carboxy group is preferably a (meth)acrylic monomer having a carboxy group, more preferably (meth)acrylic acid, and even more preferably acrylic acid.

[0035] 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, a (meth)acrylic monomer having a hydroxyl group is preferable, a hydroxyalkyl (meth)acrylate is more preferable, a hydroxyalkyl (meth)acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms is further preferable, and 2-hydroxyethyl acrylate is particularly preferable.

[0036] Specific examples of the monomer having an amino group include 2-dimethylaminoethyl (meth)acrylate, 2-diethylaminoethyl (meth)acrylate, 2-diisopropylaminoethyl (meth)acrylate, and dimethylaminopropyl (meth)acrylamide.

[0037] Specific examples of monomers having a glycidyl group include glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, glycidyl vinyl ether, 3,4-epoxycyclohexyl vinyl ether, glycidyl (meth)allyl ether, 3,4-epoxycyclohexyl (meth)allyl ether, and 4-hydroxybutyl (meth)acrylate glycidyl ether.

[0038] The specific (meth)acrylic polymer may contain only one type of structural unit derived from a monomer having a reactive functional group, or may contain two or more types.

[0039] The content of the structural units derived from the monomer having a reactive functional group in the specific (meth)acrylic polymer is not particularly limited, but for example, it is preferably 1 mass% to 15 mass%, more preferably 2 mass% to 10 mass%, even more preferably 3 mass% to 8 mass%, and particularly preferably 4 mass% to 6 mass%, relative to all structural units of the specific (meth)acrylic polymer. When the content of the structural unit derived from the monomer having a reactive functional group in the specific (meth)acrylic polymer is 1% by mass or more based on the total structural units of the specific (meth)acrylic polymer, the cohesive strength of the pressure-sensitive adhesive layer is sufficiently increased, and the pressure-sensitive adhesive layer tends to be less susceptible to cohesive failure around the convex parts of the adherend during three-dimensional molding. In addition, the pressure-sensitive adhesive layer after heat treatment exhibits high cohesive strength, and the pressure-sensitive adhesive layer tends to be less susceptible to peeling around the convex parts of the adherend during three-dimensional molding. When the content of structural units derived from monomers having reactive functional groups in the specific (meth)acrylic polymer is 15 mass% or less relative to all structural units of the specific (meth)acrylic polymer, the cohesive strength of the pressure-sensitive adhesive layer does not become excessively high, and there is a tendency that a decrease in the adhesive strength of the pressure-sensitive adhesive layer to an adherend is better suppressed.

[0040] <<Structural units derived from (meth)acrylic acid alkyl ester monomers>> The specific (meth)acrylic polymer preferably contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer. 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. In addition, the "(meth)acrylic acid alkyl ester monomer" in the specific (meth)acrylic polymer refers to a (meth)acrylic acid alkyl ester monomer that does not have a carboxy group. In other words, in the specific (meth)acrylic polymer, the "(meth)acrylic acid alkyl ester monomer having a carboxy group" is classified as a monomer having a carboxy group.

[0041] The type of the (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. From the viewpoint of facilitating the production of a specific (meth)acrylic polymer having a glass transition temperature of −45° C. to −5° C., for example, an acrylic acid alkyl ester monomer is preferred. The alkyl group in the (meth)acrylic acid alkyl ester monomer may be unsubstituted or may have a substituent, but is preferably unsubstituted. The alkyl group contained in the (meth)acrylic acid alkyl ester monomer may be linear, branched, or cyclic. The alkyl group of the (meth)acrylic acid alkyl ester monomer preferably has 1 to 18 carbon atoms, more preferably 1 to 12 carbon atoms, further preferably 1 to 8 carbon atoms, and particularly preferably 1 to 4 carbon atoms.

[0042] 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 preferably contains at least one of methyl acrylate and n-butyl acrylate, and more preferably contains both methyl acrylate and n-butyl acrylate.

[0043] When the specific (meth)acrylic polymer contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer, the specific (meth)acrylic polymer may contain only one type of structural unit derived from the (meth)acrylic acid alkyl ester monomer, or may contain two or more types of structural units derived from the (meth)acrylic acid alkyl ester monomer.

[0044] When the specific (meth)acrylic polymer contains a structural unit derived from a (meth)acrylic acid alkyl ester monomer, the content of the structural unit derived from the (meth)acrylic acid alkyl ester monomer is not particularly limited, but for example, it is preferably 50 mass% or more, more preferably 50 mass% to 99 mass%, even more preferably 60 mass% to 97 mass%, and particularly preferably 70 mass% to 96 mass%, relative to all structural units of the specific (meth)acrylic polymer. Here, the content of the structural units derived from the (meth)acrylic acid alkyl ester monomer in the specific (meth)acrylic polymer being 50 mass% or more relative to the total structural units of the specific (meth)acrylic polymer means that the structural units derived from the (meth)acrylic acid alkyl ester monomer are contained as the main component of the structural units of the specific (meth)acrylic polymer.

[0045] <<Constituent units derived from other monomers>> The specific (meth)acrylic polymer may contain a structural unit derived from a monomer (so-called other monomer) that does not fall into either the monomer having a reactive functional group or the (meth)acrylic acid alkyl ester monomer. In the present disclosure, the term "structural units derived from other monomers" refers to structural units formed by addition polymerization of other monomers.

[0046] Examples of structural units derived from other monomers include structural units derived from (meth)acrylates having an aromatic ring, such as benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; structural units derived from alkoxyalkyl (meth)acrylates, such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; structural units derived from aromatic monovinyls, such as styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and vinyltoluene; structural units derived from vinyl cyanides, such as acrylonitrile and methacrylonitrile; and structural units derived from vinyl esters, such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate.

[0047] When the specific (meth)acrylic polymer contains a structural unit derived from another monomer, it may contain only one type of structural unit derived from the other monomer, or may contain two or more types of structural units derived from the other monomer.

[0048] When the specific (meth)acrylic polymer contains a structural unit derived from another monomer, the content of the structural unit derived from the other monomer can be appropriately set within a range that does not impair the effect of the pressure-sensitive adhesive layer of the present disclosure to be formed.

[0049] -Glass transition temperature of specific (meth)acrylic polymer- The glass transition temperature (also referred to as "Tg") of the specific (meth)acrylic polymer is -45°C to -5°C. When the glass transition temperature of the specific (meth)acrylic polymer is -45°C or higher, the cohesive strength of the pressure-sensitive adhesive layer is increased, and therefore the pressure-sensitive adhesive layer is less likely to undergo cohesive failure around the convex parts of the adherend during three-dimensional molding. From this viewpoint, the glass transition temperature of the specific (meth)acrylic polymer is preferably -40°C or higher, more preferably -35°C or higher, and even more preferably -30°C or higher. When the glass transition temperature of the specific (meth)acrylic polymer is -5°C or lower, the pressure-sensitive adhesive layer exhibits sufficient wettability to the adherend, and the adhesive strength of the pressure-sensitive adhesive layer to the adherend is increased, so that the adhesive strength of the pressure-sensitive adhesive layer to the adherend tends to be sufficiently increased. In addition, the pressure-sensitive adhesive layer after heat treatment exhibits high cohesive strength, and peeling of the pressure-sensitive adhesive layer around the convex parts of the adherend during three-dimensional molding tends to be unlikely to occur. From this viewpoint, the glass transition temperature of the specific (meth)acrylic polymer is preferably -10°C or lower, more preferably -15°C or lower. In one embodiment, the glass transition temperature of the specific (meth)acrylic polymer may be -40°C to -5°C, -40°C to -10°C, -40°C to -15°C, or -35°C to -15°C.

[0050] The glass transition temperature of the specific (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)

[0051] In formula 1, Tg1, Tg2, . . . , Tg(k-1), and Tgk respectively represent the glass transition temperatures expressed as absolute temperatures when each monomer constituting the specific (meth)acrylic polymer is made into a homopolymer. m1, m2, . . . , m(k-1), and mk respectively represent the molar fractions of each monomer constituting the specific (meth)acrylic polymer, and m1 + m2 + . . . + m(k-1) + mk = 1. Note that absolute temperatures can be converted to Celsius temperatures by subtracting 273 from the absolute temperature, and Celsius temperatures can be converted to absolute temperatures by adding 273 to the Celsius temperature.

[0052] In the present disclosure, the "glass transition temperature when made into a homopolymer" refers to a value described in a publicly known document or a value measured using a differential scanning calorimeter (DSC). The specific values ​​to be used are as follows:

[0053] For the "glass transition temperature when made into a homopolymer" of the monomers shown below, the respective values ​​shown are adopted. 2-Ethylhexyl acrylate: -70°C, 2-Ethylhexyl methacrylate: -10°C, n-butyl acrylate: -54°C, n-butyl methacrylate: 20°C, t-butyl acrylate: 43°C, t-butyl methacrylate: 118°C, i-butyl methacrylate: 53°C, methyl acrylate: 10°C, methyl methacrylate: 105°C, ethyl acrylate: -22°C, ethyl methacrylate: 65°C, methacrylic acid: 228°C, 4-hydroxybutyl acrylate: -80°C, 2-hydroxyethyl acrylate: -15°C, 2-hydroxyethyl methacrylate: acrylate: 85°C, acrylic acid: 106°C, n-octyl acrylate: -65°C, stearyl acrylate: 30°C, stearyl methacrylate: 38°C, lauryl acrylate: -3°C, lauryl methacrylate: -65°C, ω-carboxy-polycaprolactone (n≒2) monoacrylate: -30°C, phenoxyethyl acrylate: -22°C, methoxyethyl acrylate: -50°C, methoxypolyethylene glycol methacrylate: -60°C, 2-dimethylaminoethyl methacrylate: 18°C, 2-diethylaminoethyl methacrylate: 20°C.

[0054] Regarding the "glass transition temperature when made into a homopolymer" of a monomer other than the above-mentioned monomers, the value described in Polymer Handbook (4th edition, Wiley-Interscience; the same applies hereinafter) is adopted. When there is no description in the Polymer Handbook, the glass transition temperature of the homopolymer obtained by the following measurement method is adopted.

[0055] (Measurement of glass transition temperature of homopolymer) Using a differential scanning calorimeter (DSC), measurements are performed under conditions of a nitrogen gas flow, 10 mg of a measurement sample (i.e., homopolymer) and a heating rate of 10°C / min, and the inflection point of the obtained DSC curve is regarded as the glass transition temperature of the homopolymer. As the differential scanning calorimeter, for example, a differential scanning calorimeter (product name: Discovery DSC 2500) manufactured by TA Instruments Japan Co., Ltd. can be suitably used. However, the differential scanning calorimeter is not limited to this.

[0056] The glass transition temperature of the specific (meth)acrylic polymer can be appropriately adjusted, for example, by using two or more kinds of monomers having different glass transition temperatures when formed into homopolymers.

[0057] -Weight average molecular weight of specific (meth)acrylic polymer- The weight average molecular weight (also referred to as "Mw") of the specific (meth)acrylic polymer is not particularly limited, but is, for example, preferably 400,000 to 2.5 million, more preferably 500,000 to 2.5 million, and even more preferably 600,000 to 2.5 million. When the weight average molecular weight of the specific (meth)acrylic polymer is 400,000 or more, the pressure-sensitive adhesive layer tends to be less susceptible to thermal shrinkage caused by a decrease in cohesive strength. The specific (meth)acrylic polymer tends to be easier to produce when the weight average molecular weight is 2.5 million or less.

[0058] The weight average molecular weight of the specific (meth)acrylic polymer is a value measured by the following method, specifically, according to the following (1) to (3). (1) A solution of the specific (meth)acrylic polymer is applied to a release paper and dried at 100° C. for 1 minute to obtain a film of the specific (meth)acrylic polymer. (2) Using the film-like specific (meth)acrylic polymer obtained in (1) above and tetrahydrofuran, a sample solution having a solid content concentration of 0.2% by mass is obtained. Note that the "solid content concentration" here means the mass ratio of the specific (meth)acrylic polymer to the sample solution. (3) The weight average molecular weight of the specific (meth)acrylic polymer is determined, in terms of standard polystyrene, by gel permeation chromatography (GPC) under the following conditions.

[0059] ~Conditions~ Measurement equipment: High-speed GPC [Model: HLC-8420 GPC, manufactured by Tosoh Corporation] Detector: Differential refractometer (RI) [installed in HLC-8420, manufactured by Tosoh Corporation] Column: TSKgel GMH XL Two Tosoh products are used. Column temperature: 40℃ Eluent: Tetrahydrofuran Sample solution injection volume: 100μL Flow rate: 0.8mL / min

[0060] The weight average molecular weight of the specific (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.

[0061] -Content of specific (meth)acrylic polymer- The content of the specific (meth)acrylic polymer in the specific pressure-sensitive adhesive composition is not particularly limited, but for example, it is preferably 70% by mass to 99% by mass, more preferably 75% by mass to 99% by mass, and even more preferably 80% by mass to 99% by mass, relative to the total solid content in the specific pressure-sensitive adhesive composition.

[0062] 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.

[0063] -Method of manufacturing specific (meth)acrylic polymer- The method for producing the specific (meth)acrylic polymer is not particularly limited. The specific (meth)acrylic polymer can be produced by polymerizing the above-mentioned monomers by a known polymerization method typified by, for example, 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 specific pressure-sensitive adhesive composition after production are relatively simple and can be carried out in a short time.

[0064] In the solution polymerization method, a predetermined organic solvent, a monomer, a polymerization initiator, and a chain transfer agent used as required are generally charged into a polymerization tank, and the mixture is heated and reacted for several hours with stirring at the reflux temperature of the organic solvent. In this case, at least a part of the organic solvent, the monomer, the polymerization initiator, and the chain transfer agent used as required may be added successively. The reaction may also be carried out in a nitrogen gas flow.

[0065] 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 the organic solvent 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 oil; ester compounds such as methyl acetate, ethyl acetate, n-butyl acetate, n-amyl acetate, 2-hydroxyethyl acetate, 2-butoxyethyl acetate, 3-methoxybutyl acetate, and methyl benzoate; acetone, methyl Examples of the alcohol compounds include ketone compounds represented by ethyl ketone, methyl-i-butyl ketone, isophorone, cyclohexanone, and methylcyclohexanone, glycol ether compounds represented by 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 represented by methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, s-butyl alcohol, and t-butyl alcohol.

[0066] In producing the specific (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 methyl acetate and / or ethyl acetate from the viewpoints of the solubility of the specific (meth)acrylic polymer, ease of polymerization reaction, and the like.

[0067] During the polymerization reaction, only one type of organic solvent may be used, or two or more types may be used.

[0068] 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 peroxy-2-ethylhexanoate, 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-butyl peroxycyclopentasiloxane), peroxycyclohexyl)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.

[0069] In the polymerization reaction, only one type of polymerization initiator may be used, or two or more types may be used.

[0070] 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 target specific (meth)acrylic polymer.

[0071] In producing the specific (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, α-methylstyrene, aromatic compounds such as anthracene, phenanthrene, fluorene, and 9-phenylfluorene, p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, aromatic nitro compounds such as p-nitrophenol and p-nitrotoluene, benzoquinone and benzoquinone derivatives such as 2,3,5,6-tetramethyl-p-benzoquinone, borane derivatives such as tributylborane, carbon tetrabromide, ... Examples of the halogenated hydrocarbon compounds include 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.

[0072] When a chain transfer agent is used in producing the specific (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 specific (meth)acrylic polymer.

[0073] The polymerization temperature is not particularly limited and can be appropriately set depending on, for example, the molecular weight of the target specific (meth)acrylic polymer.

[0074] <Isocyanate compounds> The specific pressure-sensitive adhesive composition contains an isocyanate-based crosslinking agent. In the present disclosure, the "isocyanate-based crosslinking agent" includes a compound having two or more isocyanate groups in one molecule (also referred to as a "polyisocyanate-based compound") and a compound having two or more blocked isocyanate groups in one molecule (also referred to as a "blocked isocyanate-based compound"). In the present disclosure, the "polyisocyanate-based compound" is also referred to as an "unblocked isocyanate-based compound". The isocyanate crosslinking agent is preferably a blocked isocyanate compound, since the gel fraction can be easily controlled by heat treatment.

[0075] In the present disclosure, the term "blocked isocyanate group" refers to a group that is usually protected (so-called masked) with a blocking agent to suppress the reactivity of the isocyanate group, but which can be deprotected when heated to generate an active isocyanate group. That is, the term "blocked isocyanate compound" in the present disclosure is a compound in which two or more isocyanate groups of a polyisocyanate compound are protected with a blocking agent. In addition, in the present disclosure, the term "isocyanate group" simply refers to an isocyanate group that is not protected with a blocking agent.

[0076] The blocked isocyanate group has a partial structure represented by the following formula.

[0077] [ka]

[0078] In the above formula, X represents a structure obtained by removing a hydrogen atom from a blocking agent. The blocking agent is not particularly limited, and examples thereof include ketoxime compounds, amide compounds, nitrogen-containing heterocyclic compounds, and active methylene compounds.

[0079] Examples of the polyisocyanate compound before the isocyanate group is protected with a blocking agent include an aliphatic polyisocyanate compound, an alicyclic polyisocyanate compound, and an aromatic polyisocyanate compound.

[0080] The "aliphatic polyisocyanate compound" includes, for example, an aliphatic polyisocyanate compound, a polymer of an aliphatic polyisocyanate compound, an adduct of an aliphatic polyisocyanate compound and a polyol compound (e.g., trimethylolpropane (TMP); the same applies below), and a biuret of an aliphatic polyisocyanate compound. Specific examples of the aliphatic polyisocyanate compound include hexamethylene diisocyanate (HMDI), pentamethylene diisocyanate (PDI), tetramethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0081] The "alicyclic polyisocyanate compound" includes, for example, an alicyclic polyisocyanate compound, a polymer of an alicyclic polyisocyanate compound, an adduct of an alicyclic polyisocyanate compound and a polyol compound, and a biuret of an alicyclic polyisocyanate compound. Specific examples of the alicyclic polyisocyanate compound include isophorone diisocyanate (IPDI), hydrogenated tolylene diisocyanate, hydrogenated xylylene diisocyanate (H6XDI), hydrogenated 4,4'-diphenylmethane diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0082] The "aromatic polyisocyanate compound" includes, for example, an aromatic polyisocyanate compound, a polymer of an aromatic polyisocyanate compound, an adduct of an aromatic polyisocyanate compound and a polyol compound, and a biuret of an aromatic polyisocyanate compound. Specific examples of aromatic polyisocyanate compounds include tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), and 4,4'-diphenylmethane diisocyanate.

[0083] The polyisocyanate compound is preferably at least one selected from the group consisting of aliphatic polyisocyanate compounds and alicyclic polyisocyanate compounds, and more preferably at least one selected from the group consisting of isophorone diisocyanate, hexamethylene diisocyanate compounds, and hydrogenated xylylene diisocyanate compounds. The "isophorone diisocyanate-based compound" includes, for example, IPDI, IPDI polymers, adducts of IPDI and polyols, and biuret compounds of IPDI. As the isophorone diisocyanate compound, an adduct of IPDI and a polyol compound is preferred. The "hexamethylene diisocyanate-based compounds" include, for example, HMDI, HMDI polymers, adducts of HMDI and polyol-based compounds, and biuret forms of HMDI. As the hexamethylene diisocyanate compound, a polymer of HMDI or a biuret of HMDI is preferred. The "hydrogenated xylylene diisocyanate-based compound" includes, for example, H6XDI, an adduct of H6XDI and a polyol-based compound, and a biuret of H6XDI.

[0084] The dissociation temperature of the blocked isocyanate compound is not particularly limited, but is preferably 80° C. or higher from the viewpoint of commercial availability, for example. Also, the dissociation temperature of the blocked isocyanate compound is preferably 180° C. or lower from the viewpoint of suppressing deformation due to heating of a surface protection film provided in an overlaminate film attached to an adherend. The dissociation temperature of the blocked isocyanate compound is preferably 80°C to 180°C, more preferably 90°C to 180°C, and further preferably 100°C to 180°C.

[0085] Representative blocked isocyanate compounds and their dissociation temperatures are shown below. Dimethylpyrazole blocked isocyanate compounds (dissociation temperature: 100℃~120℃), active methylene blocked isocyanate compounds (dissociation temperature: 100℃~120℃), ketoxime blocked isocyanate compounds (dissociation temperature: 130℃~150℃), ε-caprolactam blocked isocyanate compounds (dissociation temperature: 160℃~180℃).

[0086] In the present disclosure, the "dissociation temperature of a blocked isocyanate compound" means the temperature at which the blocking agent dissociates. The dissociation temperature of a blocked isocyanate compound in the present disclosure refers to "the temperature of the endothermic peak accompanying the deprotection reaction of the blocked isocyanate when measured by DSC (Differential Scanning Calorimetry) analysis using a differential scanning calorimeter."

[0087] As the blocked isocyanate compound, commercially available products can be used. Examples of commercially available blocked isocyanate compounds include "Takenate (registered trademark) B-820NP" manufactured by Mitsui Chemicals, Inc., and "Duranate (registered trademark) 17B-60P," "Duranate (registered trademark) SBB-70P," "Duranate (registered trademark) TPA-B80E," and "Duranate (registered trademark) SBN-70D" manufactured by Asahi Kasei Corporation.

[0088] The specific pressure-sensitive adhesive composition may contain only one type of isocyanate-based crosslinking agent, or may contain two or more types.

[0089] The content of the isocyanate-based crosslinking agent in the specific pressure-sensitive adhesive composition is not particularly limited, but, for example, it is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, relative to 100 parts by mass of the specific (meth)acrylic polymer. When the content of the isocyanate-based crosslinking agent in the specific pressure-sensitive adhesive composition is 0.5 parts by mass or more relative to 100 parts by mass of the specific (meth)acrylic polymer, the cohesive strength of the pressure-sensitive adhesive layer is sufficiently increased, and the pressure-sensitive adhesive layer tends to be less susceptible to cohesive failure around the convex parts of the adherend during three-dimensional molding. In addition, the pressure-sensitive adhesive layer after heat treatment exhibits high cohesive strength, and the pressure-sensitive adhesive layer tends to be less susceptible to peeling around the convex parts of the adherend during three-dimensional molding. The upper limit of the content of the isocyanate-based crosslinking agent in the specific pressure-sensitive adhesive composition is, for example, preferably 44 parts by mass or less, more preferably 22 parts by mass or less, and even more preferably 18 parts by mass or less, relative to 100 parts by mass of the specific (meth)acrylic polymer. When the content of the isocyanate-based crosslinking agent in the specific pressure-sensitive adhesive composition is 44 parts by mass or less per 100 parts by mass of the specific (meth)acrylic polymer, the amount of the isocyanate-based crosslinking agent is not excessively large, and the transparency of the pressure-sensitive adhesive layer tends not to be impaired.

[0090] <<Ratio of the number of moles of isocyanate groups in an isocyanate-based crosslinking agent to the number of moles of reactive functional groups in a specific (meth)acrylic polymer>> In the specific pressure-sensitive adhesive composition, the ratio of the number of moles of isocyanate groups in the isocyanate-based crosslinking agent to the number of moles of reactive functional groups in the specific (meth)acrylic polymer is not particularly limited, but is preferably, for example, 0.025 or more, more preferably 0.05 or more, and even more preferably 0.1 or more. When the ratio of the number of moles of isocyanate groups in the isocyanate-based crosslinking agent to the number of moles of reactive functional groups in the specific (meth)acrylic polymer in the specific pressure-sensitive adhesive composition is 0.025 or more, the cohesive strength of the pressure-sensitive adhesive layer is sufficiently increased, and cohesive failure of the pressure-sensitive adhesive layer around convex parts of the adherend during three-dimensional molding tends to be less likely to occur. In the specific pressure-sensitive adhesive composition, the upper limit of the ratio of the number of moles of isocyanate groups in the isocyanate-based crosslinking agent to the number of moles of reactive functional groups in the specific (meth)acrylic polymer is, for example, preferably 1.0 or less, and more preferably 0.5 or less, from the viewpoint of the transparency of the pressure-sensitive adhesive layer.

[0091] The ratio of the number of moles of isocyanate groups in the isocyanate crosslinking agent to the number of moles of reactive functional groups in the specific (meth)acrylic polymer is calculated by the following formulas (1) to (3). When the isocyanate crosslinking agent is a blocked isocyanate compound, the "isocyanate group" in formula (1) refers to the isocyanate group in the blocked isocyanate group after the blocking agent is deprotected, that is, the isocyanate group in a state not protected by the blocking agent. When there are multiple types of monomers having reactive functional groups that form the specific (meth)acrylic polymer, calculations are performed for each monomer, and the obtained values ​​are then summed up.

[0092] Number of moles of isocyanate groups in the isocyanate crosslinking agent (unit: mmol) = [Isocyanate group content in isocyanate crosslinking agent (unit: mass%) / Solid content concentration of isocyanate crosslinking agent (unit: mass%) × Amount of isocyanate crosslinking agent [amount as solid content] (unit: g)] / Molecular weight of isocyanate group (unit: g / mol) × 1000 (1)

[0093] Number of moles of reactive functional groups in a specific (meth)acrylic polymer [unit: mmol] = [Content of the structural unit derived from the monomer having a reactive functional group in the specific (meth)acrylic polymer (unit: mass%) / 100 × blend amount of the specific (meth)acrylic polymer (unit: g) / molecular weight of the structural unit derived from the monomer having a reactive functional group (unit: g / mol) × number of reactive functional groups (valence) in the structural unit derived from the monomer having a reactive functional group × 1000] (2)

[0094] The ratio of the number of moles of isocyanate groups in an isocyanate-based crosslinking agent to the number of moles of reactive functional groups in a specific (meth)acrylic polymer = Value obtained by formula (1) / Value obtained by formula (2) (3)

[0095] <Organic solvent> The specific pressure-sensitive adhesive composition may contain an organic solvent. When the specific PSA composition contains an organic solvent, the application property and pot life can be improved. As the organic solvent, for example, the same organic solvents as those used in the polymerization reaction of the above-mentioned specific (meth)acrylic polymer can be mentioned.

[0096] When the specific pressure-sensitive adhesive composition contains an organic solvent, it may contain only one type of organic solvent, or may contain two or more types of organic solvent.

[0097] When the specific pressure-sensitive adhesive composition contains an organic solvent, the content of the organic solvent is not particularly limited and can be appropriately set depending on the purpose.

[0098] <Other ingredients> The specific pressure-sensitive adhesive composition may contain components other than the components already described (so-called other components) as necessary, within the scope that does not impair the effects of the pressure-sensitive adhesive layer of the present disclosure to be formed. Examples of other components include various additives such as polymers other than the specific (meth)acrylic polymer, crosslinking agents other than isocyanate-based crosslinking agents (e.g., epoxy-based crosslinking agents), crosslinking catalysts, antioxidants, light stabilizers (e.g., ultraviolet absorbers), and antistatic agents.

[0099] When the specific pressure-sensitive adhesive composition contains other components, the content of the other components can be appropriately set within a range that does not impair the effects of the pressure-sensitive adhesive layer of the present disclosure to be formed.

[0100] -Gel fraction of adhesive layer- The pressure-sensitive adhesive layer of the present disclosure has a gel fraction of 60 mass % or more after heat treatment at 120° C. for 1 hour, and a gel fraction of 30 mass % or less before heat treatment at 120° C. for 1 hour. The pressure-sensitive adhesive layer of the present disclosure has a gel fraction of 30% by mass or less before heat treatment at 120° C. for 1 hour, so that the pressure-sensitive adhesive layer before heat treatment is soft and tends to exhibit good adhesion to the adherend. In addition, the pressure-sensitive adhesive layer of the present disclosure has a gel fraction of 60% by mass or more after heat treatment at 120° C. for 1 hour, so that the pressure-sensitive adhesive layer after heat treatment has high cohesive strength, and when heat treatment is performed in a state where it is attached to the adherend, cohesive failure and peeling around the protrusions of the adherend due to three-dimensional molding tend to be suppressed without decreasing the adhesive strength to the adherend. From the above viewpoints, it is preferable that the pressure-sensitive adhesive layer of the present disclosure has a gel fraction of 60 mass% or more after heat treatment at 120°C for 1 hour and a gel fraction of 10 mass% or less before heat treatment at 120°C for 1 hour. The upper limit of the gel fraction of the pressure-sensitive adhesive layer after heat treatment at 120° C. for 1 hour is not particularly limited, and examples include 100% by mass or less, 95% by mass or less, 90% by mass or less, and 85% by mass or less. The lower limit of the gel fraction of the pressure-sensitive adhesive layer before heat treatment at 120° C. for 1 hour is not particularly limited, and examples include more than 0 mass %, 1 mass % or more, 2 mass % or more, and 3 mass % or more.

[0101] In the present disclosure, "the gel fraction of the adhesive layer before being heat-treated at 120°C for 1 hour" refers to the gel fraction of the adhesive layer formed by drying a coating film of a specific adhesive composition, before being heat-treated at 120°C for 1 hour. In the present disclosure, "the gel fraction of the adhesive layer after heat treatment at 120°C for 1 hour" refers to the gel fraction of the adhesive layer after the adhesive layer formed by drying a coating film of the specific adhesive composition is heat treated at 120°C for 1 hour.

[0102] The pressure-sensitive adhesive layer of the present disclosure preferably exhibits a change in gel fraction before and after heat treatment at 120° C. for 1 hour of 50% by mass or more, and more preferably 55% by mass or more. When the change in gel fraction of the pressure-sensitive adhesive layer before and after heat treatment at 120°C for 1 hour is 50% by mass or more, there is a tendency to be able to achieve a better balance between improved adhesion of the pressure-sensitive adhesive layer to the adherend and suppression of appearance defects in the pressure-sensitive adhesive layer during three-dimensional molding.

[0103] The gel fraction of the pressure-sensitive adhesive layer of the present disclosure is measured according to the following (1) to (4). (1) About 0.15 g of the adhesive layer is attached to a 250 mesh wire net (100 mm x 100 mm) whose mass has been accurately measured using a precision balance, and the wire net is folded five times with the attached adhesive layer on the inside to prevent the gel from leaking out, to prepare a sample. After that, the mass is accurately measured using a precision balance. (2) The obtained sample is immersed in 80 mL of ethyl acetate for 3 days. (3) Take out the sample, wash it with a small amount of ethyl acetate, and dry it at 120°C for 24 hours. Then, measure the mass accurately using a precision balance. (4) Calculate the gel fraction using the following formula. Gel fraction (unit: mass%) = (ZX) / (YX) x 100 where X is the mass of the wire mesh (unit: g), Y is the mass of the wire mesh with the adhesive layer attached before immersion (unit: g), and Z is the mass of the wire mesh with the adhesive layer attached after immersion and drying (unit: g).

[0104] In the present disclosure, the gel fraction of the pressure-sensitive adhesive layer before heat treatment at 120°C for 1 hour can be controlled by, for example, the blending of a polymer other than the specific (meth)acrylic polymer in the specific pressure-sensitive adhesive composition, the amount of the isocyanate-based crosslinking agent contained in the specific pressure-sensitive adhesive composition, and the drying temperature and drying time when drying the coating film of the specific pressure-sensitive adhesive composition. For example, the gel fraction of the pressure-sensitive adhesive layer before heat treatment at 120°C for 1 hour can be reduced by lowering the drying temperature, shortening the drying time, or reducing the amount of isocyanate-based crosslinking agent contained in the specific pressure-sensitive adhesive composition. In the present disclosure, the gel fraction of the pressure-sensitive adhesive layer after heat treatment at 120°C for 1 hour can be controlled by, for example, the weight-average molecular weight of the specific (meth)acrylic polymer, the amount of reactive functional groups possessed by the specific (meth)acrylic polymer, the amount of the isocyanate-based crosslinking agent contained in the specific pressure-sensitive adhesive composition, and the incorporation of a crosslinking catalyst in the specific pressure-sensitive adhesive composition. For example, the gel fraction after heat treatment at 120°C for 1 hour can be increased by increasing the amount of reactive functional groups in the specific (meth)acrylic polymer, by increasing the amount of isocyanate-based crosslinking agent contained in the specific pressure-sensitive adhesive composition, or by blending a crosslinking catalyst in the specific pressure-sensitive adhesive composition.

[0105] -Adhesive layer thickness- The thickness of the pressure-sensitive adhesive layer of the present disclosure is not particularly limited, but is, for example, preferably 3 μm to 40 μm, more preferably 5 μm to 35 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. When the thickness of the pressure-sensitive adhesive layer of the present disclosure is 3 μm or more, the adhesive strength of the pressure-sensitive adhesive layer to an adherend tends to be more sufficiently increased. When the thickness of the pressure-sensitive adhesive layer of the present disclosure is 40 μm or less, cohesive failure of the pressure-sensitive adhesive layer tends to be less likely to occur around convex parts of the adherend during three-dimensional molding.

[0106] In the present disclosure, the "thickness of the pressure-sensitive adhesive layer" means the average thickness of the pressure-sensitive adhesive layer. The average thickness of the pressure-sensitive adhesive layer is a value determined by the following method. The thickness of the adhesive layer is measured at 5 randomly selected locations in the thickness direction using a constant pressure thickness gauge (measuring probe diameter: 5 mm). The arithmetic mean of the measured values ​​is calculated and the obtained value is regarded as the average thickness of the adhesive layer.

[0107] [Overlamination film] The overlaminate film of the present disclosure comprises a surface protective film and a pressure-sensitive adhesive layer of the present disclosure provided on one side of the surface protective film. The overlaminate film of the present disclosure has a pressure-sensitive adhesive layer of the present disclosure, and therefore has high adhesive strength to an adherend and is less likely to cause poor appearance during three-dimensional molding.

[0108] The material of the adherend of the overlaminate film of the present disclosure is not particularly limited, and examples thereof include resins (such as polyurethane-based resins) and metals (such as aluminum plates).

[0109] The adhesive layer of the present disclosure has a low gel fraction before heat treatment at 120°C for 1 hour, and a high gel fraction after heat treatment at 120°C for 1 hour. The adhesive layer of the present disclosure is soft and has excellent adhesion to the adherend because of a low degree of crosslinking before heat treatment at 120°C for 1 hour. In addition, the adhesive layer of the present disclosure exhibits high cohesive strength due to the progress of the crosslinking reaction after heat treatment at 120°C for 1 hour. Therefore, the adhesive layer of the present disclosure has high adhesion to the adherend and is unlikely to cause poor appearance during three-dimensional molding. Therefore, the method of using the overlaminate film of the present disclosure is preferably, for example, a method of heating after bonding to the adherend, before three-dimensional molding, or during three-dimensional molding.

[0110] The material of the surface protection film is not particularly limited. Examples of the surface protection film 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), polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyurethane resins, (meth)acrylic resins, vinyl chloride resins, ABS (Acrylonitrile Butadiene Styrene) resins, and fluorine-based resins. The surface protection film is preferably a film containing a polyurethane resin, from the viewpoint of suppressing distortion of the molded portion that may occur during three-dimensional molding, for example.

[0111] The surface protective film may be colorless or colored, but is preferably colorless from the viewpoint of not interfering with the design of the decoration applied to the adherend. The surface protective film may be transparent or translucent, but is preferably transparent so as not to impair the visibility of the decoration applied to the adherend. In the present disclosure, "transparent" means that the average transmittance of visible light with a wavelength of 400 nm to 700 nm is 80% or more, and preferably 90% or more. In this disclosure, "transmittance" is a value measured using a spectrophotometer.

[0112] The surface of the surface protection film 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 surface protection film and the adhesive layer.

[0113] The surface protective film may contain various additives such as a crosslinking agent, a crosslinking catalyst, a plasticizer, a heat stabilizer, an ultraviolet absorber, a light stabilizer, an antistatic agent, a flame retardant, an antioxidant, a filler, an antifoaming agent, and a surfactant.

[0114] The thickness of the surface protection film is not particularly limited, but is, for example, preferably from 20 μm to 100 μm, more preferably from 25 μm to 90 μm, and further preferably from 30 μm to 80 μm.

[0115] In the present disclosure, the "thickness of the surface protection film" means the average thickness of the surface protection film. The average thickness of the surface protective film is a value determined by the following method. The thickness of the surface protection film is measured at five randomly selected locations in the thickness direction using a constant pressure thickness gauge (measuring probe diameter: 5 mm). The arithmetic mean of the measured values ​​is calculated, and the obtained value is regarded as the average thickness of the surface protection film.

[0116] The surface protective film may be a single layer film or may be formed of multiple layers. When the surface protection film is formed of a plurality of layers, the thickness of the surface protection film mentioned above refers to the total thickness of the plurality of layers forming the surface protection film.

[0117] The pressure-sensitive adhesive layer provided in the overlaminate film of the present disclosure is the same as the pressure-sensitive adhesive layer of the present disclosure described above, and preferred embodiments are also the same, so description thereof will be omitted here.

[0118] In the overlaminate film of the present disclosure, the exposed surface of the pressure-sensitive adhesive layer may be protected by a release sheet. In general, the release sheet protects the surface of the pressure-sensitive adhesive layer until the overlaminate film is put to practical use, and is peeled off when the film is used.

[0119] 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, one or both sides of which have been surface-treated with a release agent (so-called easy-release treatment), and composite sheets obtained by laminating two or more of these. 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 treating agent (so-called easy-release treatment) is also referred to as a "release film". Examples of the release agent include silicone-based release agents (eg, silicone), wax-based release agents (eg, paraffin wax), and fluorine-based release agents (eg, fluorine-based resins). An example of the resin film is a polyester film, typically a polyethylene terephthalate (PET) film. Examples of the 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.

[0120] FIG. 1 is a schematic cross-sectional view showing an example of the configuration of the overlaminate film of the present disclosure. The overlaminate film 10 shown in Fig. 1 includes a surface protective film 20 and a pressure-sensitive adhesive layer 30 provided on one side of the surface protective film 20. Details of the surface protective film 20 and the pressure-sensitive adhesive layer 30 are as described above.

[0121] The overlaminate film of the present disclosure may include layers (also referred to as "other layers") other than the surface protective film and the pressure-sensitive adhesive layer, as necessary. Examples of other layers include a decorative layer provided on the surface protective film and / or between the surface protective film and the adhesive layer. In this case, the decorative layer is a layer provided to impart design to the overlaminate film, and is a layer that expresses patterns, characters, pictures, etc. The decorative layer can be formed by known printing methods such as inkjet printing, screen printing, gravure printing, hot stamp printing, and baking printing. When the overlaminate film of the present disclosure is used for a license plate described later, a layer on which characters (numbers, kanji, hiragana, alphabet, etc.) are formed is provided as a decorative layer on the surface protective film. The characters can be formed, for example, by baking printing.

[0122] The overlaminate film of the present disclosure comprises the pressure-sensitive adhesive layer of the present disclosure, i.e., a pressure-sensitive adhesive layer that has high adhesive strength to an adherend and is unlikely to cause poor appearance during three-dimensional molding, and therefore can be suitably used not only for flat-shaped articles but also for three-dimensionally shaped articles. The overlaminate film of the present disclosure can be used, for example, as a constituent member of the license plate of the present disclosure described below. The overlaminate film of the present disclosure can also be used for applications such as the interior or exterior of a vehicle such as an automobile, and the interior of a building such as a wall, floor, or ceiling.

[0123] [How to make overlaminate film] The method for producing the overlaminate film of the present disclosure is not particularly limited. The overlaminate film of the present disclosure can be produced by a known method using the specific pressure-sensitive adhesive composition. Examples of the method for producing the overlaminate film of the present disclosure include the following methods.

[0124] The specific adhesive composition is applied to the easy-adhesion treated surface of the substrate film to be the surface protection film, to form a coating film on the substrate film.Then, the formed coating film is dried to form an adhesive film on the substrate film.Then, the exposed surface of the formed adhesive film is laminated on the easy-release treated surface of the release sheet, to produce the overlaminate film of the present disclosure having a laminated structure of substrate film (so-called surface protection film) / adhesive layer / release sheet.

[0125] Another method includes, for example, the following method. A specific adhesive composition is applied to the easy-release treated surface of a release sheet to form a coating film on the release sheet. Then, the formed coating film is dried to form an adhesive film on the release sheet. Then, the exposed surface of the formed adhesive film is laminated and stuck onto the easy-adhesion treated surface of a substrate film to be a surface protective film, thereby producing an overlaminate film of the present disclosure having a laminated structure of substrate film (so-called surface protective film) / adhesive layer / release sheet.

[0126] The method for applying the specific pressure-sensitive adhesive composition is not particularly limited. Examples of methods for applying the specific 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, and the like. The amount of the specific 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.

[0127] 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 appropriately set depending on the thickness of the coating film, the amount of the organic solvent in the coating film, and the like. The drying temperature for the coating film is preferably 100°C to 120°C, for example. Examples of drying conditions for the coated film include a drying temperature of 100°C and a drying time of 1 minute, a drying temperature of 100°C and a drying time of 5 minutes, a drying temperature of 110°C and a drying time of 1 minute, a drying temperature of 110°C and a drying time of 5 minutes, and a drying temperature of 120°C and a drying time of 1 minute.

[0128] [License plate] The license plate of the present disclosure comprises a plate substrate and an overlaminate film of the present disclosure provided on one side of the plate substrate. Since the license plate of the present disclosure is equipped with the overlaminate film of the present disclosure, appearance defects due to the use of the overlaminate film are less likely to occur. Hereinafter, in the license plate of the present disclosure, the "adhesive layer for the overlaminate film of the present disclosure" provided in the overlaminate film of the present disclosure will also be referred to as the "first adhesive layer."

[0129] The embodiment of the license plate of the present disclosure is not particularly limited as long as it comprises a plate substrate and an overlaminate film of the present disclosure provided on one side of the plate substrate. For example, it is preferable that the license plate has a surface protection film provided on the overlaminate film of the present disclosure as the outermost layer of the license plate. The license plate of the present disclosure may be, for example, an embodiment in which the first adhesive layer side of the overlaminate film of the present disclosure is attached to one side of the plate substrate, or an embodiment in which an image receiving layer capable of forming a decorative layer on the surface is provided between the plate substrate and the overlaminate film of the present disclosure. The image receiving layer may constitute an image receiving film together with a second adhesive layer that allows the image receiving layer to adhere to the plate substrate. In this case, the image receiving layer preferably contains a polyurethane resin and a (meth)acrylic resin, for example, from the viewpoint of imparting low-temperature impact resistance and printability. The image receiving layer preferably further contains a white pigment, for example, from the viewpoint of further improving whiteness. The second adhesive layer preferably contains a (meth)acrylic resin, for example, from the viewpoint of improving weather resistance, durability, and adhesion to the plate substrate. The second adhesive layer preferably further contains a pigment, for example, from the viewpoint of improving the appearance of the license plate. When the license plate of the present disclosure has an image receiving layer, a decorative layer may be provided on the image receiving layer as appropriate. In this case, the decorative layer is a layer provided to impart design to the license plate, and is a layer that expresses a pattern, a design, etc. As a method for forming a decorative layer on the image receiving layer, known printing methods such as inkjet printing, screen printing, and gravure printing can be applied. For example, a layer on which a design is formed by inkjet printing is provided as a decorative layer on the image receiving layer.

[0130] FIG. 2 is a schematic cross-sectional view showing an example of the configuration of the license plate of the present disclosure. The license plate 40 shown in Fig. 2 comprises a plate substrate 50 and an overlaminate film 10 of the present disclosure provided on one side of the plate substrate 50. The overlaminate film 10 comprises a surface protective film 20 and a first adhesive layer 30 provided on one side of the surface protective film 20. In the license plate 40, the surface of the overlaminate film 10 on the side of the first adhesive layer 30 is in contact with one side of the plate substrate 50. The license plate 40 also comprises a decorative layer 60 on the surface protective film 20 constituting the overlaminate film 10.

[0131] FIG. 3 is a schematic cross-sectional view showing an example of another configuration of the license plate of the present disclosure. The license plate 70 shown in FIG. 3 includes a plate substrate 50, an image receiving film 100 having an image receiving layer 80 and a second adhesive layer 90, and an overlaminate film 10 of the present disclosure. The overlaminate film 10 includes a surface protective film 20 and a first adhesive layer 30 provided on one side of the surface protective film 20. In the license plate 70, the surface of the image receiving film 100 on the second adhesive layer 90 side is in contact with one side of the plate substrate 50. In the license plate 70, the surface of the overlaminate film 10 on the first adhesive layer 30 side is in contact with the surface of the image receiving film 100 on the image receiving layer 80 side. The license plate 70 includes a decorative layer 60 on the surface protection film 20 that constitutes the overlaminate film 10. The license plate 70 also includes a decorative layer 60 on the image receiving layer 80 that constitutes the image receiving film 100. The details of the plate substrate 50 will be described later. The details of the overlaminate film 10, the decorative layer 60 and the image receiving film 100 are as described above.

[0132] The plate substrate may be a metal plate or a resin plate. Examples of the metal plate include an aluminum plate, a stainless steel plate, and an iron plate. Examples of resin plates include polycarbonate plates, polyester plates, polyvinyl chloride plates, acrylic plates, ABS plates, and PP plates. The plate substrate may be one obtained by forming the above-mentioned metal plate or resin plate into the shape of a frame or the like.

[0133] The method of manufacturing the license plate of the present disclosure is not particularly limited. The license plate of the present disclosure can be manufactured, for example, by the following method. First, the overlaminate film of the present disclosure is attached to a plate substrate before embossing the characters, etc. Next, the plate substrate to which the overlaminate film of the present disclosure is attached is heated, and then the plate substrate is embossed, or the plate substrate to which the overlaminate film of the present disclosure is attached is embossed while being heated. In this manner, the license plate of the present disclosure can be manufactured. EXAMPLES

[0134] The pressure-sensitive adhesive layer 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.

[0135] [Production of (meth)acrylic polymer (A)] [Manufacturing example A-1] A reactor equipped with a stirrer, a reflux condenser, a successive dropping device, and a thermometer was charged with 25 mass% of a monomer mixture consisting of 53.0 parts by mass of n-butyl acrylate (n-BA), 43.0 parts by mass of methyl acrylate (MA), and 4.0 parts by mass of acrylic acid (AA), 45.0 parts by mass of ethyl acetate (organic solvent), and 0.015 parts by mass of 2,2'-azobisisobutyronitrile (AIBN; polymerization initiator), and the mixture was heated to carry out polymerization at the reflux temperature for 20 minutes. Next, the remaining 75% by mass of the monomer mixture and a polymerization initiator solution consisting of 30.0 parts by mass of ethyl acetate and 0.15 parts by mass of 2,2'-azobisisobutyronitrile were successively dropped into the polymerization reaction product in the reactor maintained at reflux temperature over 1.5 hours, and the polymerization reaction was continued for 1 hour, and then a polymerization initiator solution consisting of 25.0 parts by mass of ethyl acetate and 0.30 parts by mass of 2,2'-azobisisobutyronitrile was successively dropped into the polymerization reaction product in one hour, and the polymerization reaction was continued for another 2 hours to obtain a polymerization reaction product. The obtained polymerization reaction product was diluted to a solid concentration of 35% by mass using methyl ethyl ketone (MEK), and then cooled to obtain a solution of (meth)acrylic polymer A-1.

[0136] The term "solid content concentration" used herein means the mass ratio of the (meth)acrylic polymer A-1 in the solution of the (meth)acrylic polymer A-1. The same applies to each of the solutions of the (meth)acrylic polymers A-2 to A-5 produced below.

[0137] [Manufacturing examples A-2 to A-5] In Production Examples A-2 to A-5, the same operation as in Production Example A-1 was carried out except that the monomer composition of the (meth)acrylic polymer was changed to the monomer composition shown in Table 1, and solutions of (meth)acrylic polymers A-2 to A-5 each having a solid content concentration of 35 mass% were obtained.

[0138] The monomer compositions (unit: mass%) and glass transition temperatures (represented as "Tg") (unit: °C) of the (meth)acrylic polymers A-1 to A-5 are shown in Table 1. The weight average molecular weight of each of the (meth)acrylic polymers A-1 to A-5 was 600,000.

[0139] The glass transition temperatures of the (meth)acrylic polymers A-1 to A-5 were determined by the same method as that for determining the glass transition temperature of the specific (meth)acrylic polymer described above. The weight average molecular weights of the (meth)acrylic polymers A-1 to A-5 were measured by the same method as the above-mentioned method for measuring the weight average molecular weight of the specific (meth)acrylic polymer.

[0140] Among the (meth)acrylic polymers A-1 to A-5, the (meth)acrylic polymers A-1 to A-3 correspond to the specific (meth)acrylic polymer in the present disclosure.

[0141] [Table 1]

[0142] Details of each monomer listed in Table 1 are as follows. <(Meth)acrylic acid alkyl ester monomer> "n-BA": n-butyl acrylate "MA": Methyl acrylate "2EHA": 2-Ethylhexyl acrylate <Monomers having reactive functional groups> "AA": acrylic acid (type of reactive functional group: carboxy group)

[0143] In Table 1, "-" in the monomer composition column means that the monomer in that column was not used.

[0144] [Production of (meth)acrylic polymer (B)] [Manufacturing example B-1] A reactor equipped with a stirrer, a reflux condenser, a successive dropping device, and a thermometer was charged with 20 mass% of a monomer mixture consisting of 80.0 parts by mass of methyl methacrylate (MMA), 14.0 parts by mass of ethyl acrylate (EA), and 6.0 parts by mass of 2-dimethylaminoethyl methacrylate (DM), 45.0 parts by mass of ethyl acetate (organic solvent), and 0.15 parts by mass of 2,2'-azobisisobutyronitrile (AIBN; polymerization initiator), and the mixture was heated to carry out polymerization at the reflux temperature for 20 minutes. The polymerization reaction product in the reactor, which was kept at reflux temperature, was successively dropped over 1.5 hours with the remaining 80% by mass of the monomer mixture, 30.0 parts by mass of ethyl acetate, and 0.15 parts by mass of 2,2'-azobisisobutyronitrile, followed by polymerization reaction for 1 hour. The polymerization reaction product was then successively dropped over 1 hour with the polymerization reaction product consisting of 25.0 parts by mass of ethyl acetate and 0.30 parts by mass of 2,2'-azobisisobutyronitrile, followed by polymerization reaction for another 2 hours to obtain a polymerization reaction product. The obtained polymerization reaction product was diluted to a solid concentration of 36% by mass with methyl ethyl ketone (MEK), and then cooled to obtain a solution of (meth)acrylic polymer B-1. The term "solids concentration" used herein means the mass proportion of the (meth)acrylic polymer B-1 in the solution of the (meth)acrylic polymer B-1.

[0145] The (meth)acrylic polymer B-1 had a glass transition temperature of 75.7° C. and a weight average molecular weight of 100,000.

[0146] The glass transition temperature of the (meth)acrylic polymer B-1 was determined by the same method as that for determining the glass transition temperature of the specific (meth)acrylic polymer described above. The weight average molecular weight of the (meth)acrylic polymer B-1 was measured by the same method as the above-mentioned method for measuring the weight average molecular weight of the specific (meth)acrylic polymer.

[0147] [Preparation of Adhesive Composition] [Manufacturing example X-1] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-1, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 4.4 parts by mass (solid content equivalent) of an isocyanate-based crosslinking agent (product name: Takenate B-820NP, blocked isocyanate-based compound, manufactured by Mitsui Chemicals, Inc.) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-1.

[0148] [Manufacturing example X-2] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-2, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 4.4 parts by mass (solid content equivalent) of an isocyanate-based crosslinking agent (product name: Takenate B-820NP, blocked isocyanate-based compound, manufactured by Mitsui Chemicals, Inc.) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-2.

[0149] [Manufacturing example X-3] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-3, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 4.4 parts by mass (solid content equivalent) of an isocyanate-based crosslinking agent (product name: Takenate B-820NP, blocked isocyanate-based compound, manufactured by Mitsui Chemicals, Inc.) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-3.

[0150] [Manufacturing example X-4] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-1, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 2.7 parts by mass (solid content equivalent) of an isocyanate-based crosslinking agent (product name: Duranate 17B-60P, blocked isocyanate-based compound, manufactured by Asahi Kasei Corporation) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-4.

[0151] [Manufacturing example X-5] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-1, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 3.2 parts by mass (solid content equivalent) of an isocyanate-based crosslinking agent (product name: Duranate SBB-70P, blocked isocyanate-based compound, manufactured by Asahi Kasei Corporation) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-5.

[0152] [Manufacturing example X-6] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-1, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 3.0 parts by mass (solid content equivalent) of an isocyanate-based crosslinking agent (product name: Duranate TPA-B80E, blocked isocyanate-based compound, manufactured by Asahi Kasei Corporation) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-6.

[0153] [Manufacturing example X-7] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-1, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 3.2 parts by mass (solid content equivalent) of an isocyanate-based crosslinking agent (product name: Duranate SBN-70D, blocked isocyanate-based compound, manufactured by Asahi Kasei Corporation) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-7.

[0154] [Manufacturing example X-8] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-1, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 2.2 parts by mass (solid content equivalent) of an isocyanate-based crosslinking agent (product name: Takenate B-820NP, blocked isocyanate-based compound, manufactured by Mitsui Chemicals, Inc.) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-8.

[0155] [Manufacturing example X-9] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-1 and 15.0 parts by mass (solid content equivalent) of an isocyanate-based crosslinking agent (product name: Takenate B-820NP, blocked isocyanate-based compound, manufactured by Mitsui Chemicals, Inc.) were mixed and stirred to obtain a pressure-sensitive adhesive composition X-9.

[0156] [Manufacturing example X-10] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-1, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 0.6 parts by mass (solid content equivalent) of an isocyanate-based crosslinking agent (product name: Takenate D-140N, unblocked isocyanate-based compound, manufactured by Mitsui Chemicals, Inc.) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-10.

[0157] [Manufacturing example X-11] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-4, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 4.4 parts by mass (solid content equivalent) of an isocyanate crosslinking agent (product name: Takenate B-820NP, blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-11.

[0158] [Manufacturing example X-12] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-5, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 4.4 parts by mass (solid content equivalent) of an isocyanate crosslinking agent (product name: Takenate B-820NP, blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-12.

[0159] [Manufacturing example X-13] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-1, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 0.3 parts by mass (solid content equivalent) of an isocyanate-based crosslinking agent (product name: Takenate D-140N, unblocked isocyanate-based compound, manufactured by Mitsui Chemicals, Inc.) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-13.

[0160] [Manufacturing example X-14] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-1, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 0.1 parts by mass (solid content equivalent) of an epoxy crosslinking agent (product name: TETRAD-C, manufactured by Mitsubishi Gas Chemical Company, Inc.) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-14.

[0161] [Manufacturing example X-15] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-1, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, 2.9 parts by mass (solid content equivalent) of an isocyanate crosslinking agent [product name: Takenate B-820NP, blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.], and 0.03 parts by mass (solid content equivalent) of an epoxy crosslinking agent [product name: TETRAD-C, manufactured by Mitsubishi Gas Chemical Company, Inc.] were mixed with stirring to obtain a pressure-sensitive adhesive composition X-15.

[0162] [Manufacturing example X-16] 100 parts by mass (solid content equivalent) of (meth)acrylic polymer A-1, 15 parts by mass (solid content equivalent) of (meth)acrylic polymer B-1, and 0.4 parts by mass (solid content equivalent) of an isocyanate crosslinking agent (product name: Takenate B-820NP, blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.) were mixed with stirring to obtain a pressure-sensitive adhesive composition X-16.

[0163] Among the pressure-sensitive adhesive compositions X-1 to X-16, the pressure-sensitive adhesive compositions X-1 to X-10 correspond to the specific pressure-sensitive adhesive composition of the present disclosure.

[0164] Table 2 shows the compositions of pressure-sensitive adhesive compositions X-1 to X-16.

[0165] [Table 2]

[0166] Details of the components listed in Table 2 are as follows: <Crosslinking agent> (Isocyanate-based crosslinking agent) "Takenate B-820NP" [Product name, blocked isocyanate compound, hydrogenated xylylene diisocyanate (H6XDI), solid content: 60% by mass, isocyanate group content (catalog value): 6.4% by mass, dissociation temperature: 100°C to 120°C, manufactured by Mitsui Chemicals, Inc.] "Duranate 17B-60P" [Product name, blocked isocyanate compound, biuret of hexamethylene diisocyanate (HMDI), solid content: 60% by mass, isocyanate group content (catalog value): 9.4% by mass, dissociation temperature: 130°C, manufactured by Asahi Kasei Corporation] "Duranate SBB-70P" [Product name, blocked isocyanate compound, biuret of hexamethylene diisocyanate (HMDI), solid content: 70% by mass, isocyanate group content (catalog value): 10.2% by mass, dissociation temperature: 110°C, manufactured by Asahi Kasei Corporation] "Duranate TPA-B80E" [Product name, blocked isocyanate compound, hexamethylene diisocyanate (HMDI) nurate (trimer), solids concentration: 80% by mass, isocyanate group content (catalog value): 12.4% by mass, dissociation temperature: 130°C, manufactured by Asahi Kasei Corporation] "Duranate SBN-70D" [Product name, blocked isocyanate compound, hexamethylene diisocyanate (HMDI) nurate (trimer), solids concentration: 70% by mass, isocyanate group content (catalog value): 10.2% by mass, dissociation temperature: 110°C, manufactured by Asahi Kasei Corporation] "Takenate D-140N" [product name, non-blocked isocyanate compound, adduct of isophorone diisocyanate (IPDI) and trimethylolpropane (TMP), solid content: 75% by mass, isocyanate group content (catalog value): 10.5% by mass, manufactured by Mitsui Chemicals, Inc.] The above "Takenate" and "Duranate" are both registered trademarks.

[0167] (Crosslinking agents other than isocyanate-based crosslinking agents) "TETRAD-C" [product name, epoxy crosslinking agent, solid content: 100% by mass, manufactured by Mitsubishi Gas Chemical Co., Ltd.] The above "TETRAD" is a registered trademark.

[0168] [Preparation of base film] In a reactor equipped with a stirrer, 90 parts by mass of polyurethane resin 1 [product name: Resamine NE-8836, one-component curing polycarbonate-based urethane resin, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.], 10 parts by mass of polyurethane resin 2 [product name: Resamine NE-8811, one-component curing polycarbonate-based urethane resin, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.], 20 parts by mass of crosslinking agent [product name: Resamine X-100, isocyanate-based crosslinking agent, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.], 0.1 parts by mass of crosslinking catalyst [product name: UA-38, tin 2-ethylhexyl acid, manufactured by TOKUSHIKI CORPORATION], and dilution solvent [N,N-dimethylformamide] were mixed and stirred for 10 minutes using a disper under an ambient temperature of 23° C. to obtain a composition for forming a base film. Next, the composition for forming a base film was applied to the easily peelable surface of a release film (trade name: P756050, polyethylene terephthalate (PET), thickness: 75 μm, manufactured by Lintec Corporation) that had been surface-treated (so-called easy peeling treatment) with a silicone-based release treatment agent, so that the thickness after drying would be 35 μm, forming a coating film. Next, the formed coating film was heated at 100° C. for 3 minutes using a hot air circulation dryer, and then further heated and dried at 160° C. for 3 minutes to produce a base film. In addition, the above-mentioned "Rezamin" is a registered trademark.

[0169] Example 1 (1) Preparation of adhesive film for gel fraction measurement An adhesive film for measuring the gel fraction was prepared using the adhesive composition X-1. The adhesive composition X-1 was applied to the easy-release treated surface of a release film X [trade name: PET75GS, material: polyethylene terephthalate (PET), thickness: 75 μm, manufactured by Lintec Corporation] that had been surface-treated (so-called easy-release treatment) with a silicone-based release treatment agent, so that the thickness after drying (i.e., the thickness of the adhesive layer) was 12 μm, to form a coating film. The formed coating film was then dried using a hot air circulation dryer under conditions of a drying temperature of 100° C. and a drying time of 1 minute, to form an adhesive film on the release film. Next, the exposed surface of the adhesive film was laminated on the easy-release treated surface of a release film Y [trade name: PET25LT, thickness: 25 μm, manufactured by Lintec Corporation] that had been surface-treated (so-called easy-release treatment) with a separately prepared silicone-based release treatment agent, to obtain an adhesive film for measuring the gel fraction of the adhesive layer before heat treatment (also referred to as "adhesive film for measuring gel fraction before heat treatment"). The pressure-sensitive adhesive film for gel fraction measurement before heat treatment was heat-treated at 120°C for 1 hour using a hot air circulation dryer to obtain a pressure-sensitive adhesive film for measuring the gel fraction of the pressure-sensitive adhesive layer after heat treatment (also referred to as "pressure-sensitive adhesive film for gel fraction measurement after heat treatment"). Both the "pressure-sensitive adhesive film for gel fraction measurement before heat treatment" and the "pressure-sensitive adhesive film for gel fraction measurement after heat treatment" have a configuration of release film X / pressure-sensitive adhesive layer / release film Y.

[0170] (2) Preparation of adhesive film for evaluation An adhesive film for evaluation was produced using the adhesive composition X-1. The adhesive composition X-1 was applied to the easy-release treated surface of a release film X (trade name: PET75GS, material: polyethylene terephthalate (PET), thickness: 75 μm, manufactured by Lintec Corporation) that had been surface-treated (so-called easy-release treatment) with a silicone-based release agent, so that the thickness after drying (i.e., the thickness of the adhesive layer) was 12 μm, forming a coating film. Next, the formed coating film was dried using a hot air circulation dryer under conditions of a drying temperature of 100° C. and a drying time of 1 minute, forming an adhesive film on the release film. Next, the exposed surface of the adhesive film was laminated on the substrate film prepared above to obtain an adhesive film for evaluation. The adhesive film for evaluation has a configuration of substrate film (so-called surface protection film) / adhesive layer / release film.

[0171] [Examples 2 to 10] In Examples 2 to 10, except that the composition of the adhesive composition was changed to the composition shown in Table 3, the same operation as in Example 1 was carried out to obtain adhesive films for gel fraction measurement (i.e., adhesive films for gel fraction measurement before heat treatment and adhesive films for gel fraction measurement after heat treatment) and adhesive films for evaluation.

[0172] [Examples 11 to 14] In Examples 11 to 14, the same operations as in Example 1 were performed except that the drying conditions for the formed coating film (i.e., drying temperature and drying time) were changed to the drying conditions in Table 3, to obtain adhesive films for gel fraction measurement (i.e., adhesive films for gel fraction measurement before heat treatment and adhesive films for gel fraction measurement after heat treatment) and adhesive films for evaluation.

[0173] [Comparative Examples 1, 2 and 6] In Comparative Examples 1, 2, and 6, the same operations as in Example 1 were carried out except that the composition of the adhesive composition was changed to the composition shown in Table 4, and adhesive films for gel fraction measurement (i.e., adhesive films for gel fraction measurement before heat treatment and adhesive films for gel fraction measurement after heat treatment) and adhesive films for evaluation were obtained.

[0174] [Comparative Examples 3 to 5] In Comparative Examples 3 to 5, the composition of the adhesive composition was changed to the composition shown in Table 4, and curing was performed under the conditions shown in Table 4 after the drying process. Except for this, the same operations as in Example 1 were performed to obtain adhesive films for gel fraction measurement and adhesive films for gel fraction measurement after heat treatment), and adhesive films for evaluation.

[0175] [Comparative Examples 7 and 8] In Comparative Examples 7 and 8, the same operations as in Example 1 were carried out except that the drying conditions for the formed coating film (i.e., the drying temperature and drying time) were changed to the drying conditions in Table 4, and adhesive films for gel fraction measurement (i.e., adhesive films for gel fraction measurement before heat treatment and adhesive films for gel fraction measurement after heat treatment) and adhesive films for evaluation were obtained.

[0176] [Measurement of gel fraction] The gel fractions before and after heat treatment were measured using the adhesive layers peeled off from the "adhesive film for measuring gel fraction before heat treatment" and "adhesive film for measuring gel fraction after heat treatment" prepared above, and the change in gel fraction before and after heat treatment was calculated according to the following (1) to (4). The results are shown in Tables 3 and 4. (1) Approximately 0.15 g of the adhesive layer was attached to a 250 mesh wire net (100 mm x 100 mm) whose mass was accurately measured using a precision balance, and the wire net was folded five times with the attached adhesive layer facing inward to prevent leakage of the gel, to prepare a sample. The mass was then accurately measured using a precision balance. (2) The obtained sample was immersed in 80 mL of ethyl acetate for 3 days. (3) The sample was taken out, washed with a small amount of ethyl acetate, and dried at 120° C. for 24 hours. Then, the mass was accurately measured using a precision balance. (4) The gel fraction was calculated using the following formula. Gel fraction (unit: mass%) = (ZX) / (YX) x 100 where X is the mass of the wire mesh (unit: g), Y is the mass of the wire mesh with the adhesive layer attached before immersion (unit: g), and Z is the mass of the wire mesh with the adhesive layer attached after immersion and drying (unit: g).

[0177] [Preparation of the substrate] A printing plate was prepared as an adherend to be used in the evaluation test, specifically, according to the following procedures (1) to (3).

[0178] (1) Formation of image-receiving layer In a reactor equipped with a stirrer, 100 parts by mass of a polyurethane resin (product name: REZAMIN NE-8811, one-component curing polycarbonate-based urethane resin, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), 15 parts by mass of a (meth)acrylic resin (product name: DIANAL MB-2593, methacrylic resin, manufactured by Mitsubishi Chemical Corporation), 42 parts by mass of a pigment (product name: NX-501, titanium oxide, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), and a dilution solvent (a mixed solvent of isopropyl alcohol and toluene (volume ratio 1:1)) were stirred and mixed for 10 minutes using a disper in an environment with an ambient temperature of 23° C. to obtain a composition for forming an image-receiving layer. Next, the composition for forming an image receiving layer was applied to the easily peelable surface of a release film (trade name: P756050, polyethylene terephthalate (PET), thickness: 75 μm, manufactured by Lintec Corporation) that had been surface-treated (so-called easily peelable) with a silicone-based release treatment agent, so that the thickness after drying would be 55 μm, forming a coating film. Next, the formed coating film was heated at 100° C. for 3 minutes using a hot air circulation dryer, and then further heated and dried at 160° C. for 3 minutes, thereby forming an image receiving layer on the release film. In addition, both "Rezamin" and "Dianal" are registered trademarks.

[0179] (2) Formation of the second adhesive layer 100 parts by mass of an acrylic copolymer obtained by polymerizing 90 parts by mass of n-butyl acrylate and 10.0 parts by mass of acrylic acid, 8.34 parts by mass of a white pigment [trade name: DAD-100, component: titanium dioxide, manufactured by DIC Corporation], 5.0 parts by mass of an isocyanate-based crosslinking agent [trade name: Coronate L-45E, manufactured by Mitsubishi Gas Chemical Co., Ltd.], and a dilution solvent [ethyl acetate] were mixed by stirring to obtain a composition for forming a second adhesive layer. Next, the composition for forming a second adhesive layer was applied to the easy-release treated surface of a release film [trade name: PET75GS, material: polyethylene terephthalate (PET), thickness: 75 μm, manufactured by Lintec Corporation] that had been surface-treated (so-called easy-release treatment) with a silicone-based release treatment agent, so that the thickness after drying was 40 μm, to form a coating film. The formed coating film was then dried by heating at 100° C. for 1 minute using a hot air circulation dryer, thereby forming a second pressure-sensitive adhesive layer on the release film. In addition, the above-mentioned "Coronate" is a registered trademark.

[0180] (3) Preparation of printing plates The exposed surface of the image receiving layer formed above was laminated to the exposed surface of the second adhesive layer to prepare an image receiving film. Next, in an environment of an atmospheric temperature of 23°C and 50% RH, the release film on the second adhesive layer side of the image receiving film was peeled off, and the exposed surface of the second adhesive layer was laminated to an aluminum plate. Next, the release film on the image receiving layer side of the image receiving film was peeled off, and solid printing of cyan and yellow was performed on the exposed surface of the image receiving layer using an inkjet printer [model number: JV-300, manufactured by Mimaki Engineering Co., Ltd.] to form a decorative layer. In this manner, a printing plate having a configuration of decorative layer / image receiving layer / second adhesive layer / aluminum plate was prepared.

[0181] [evaluation] 1. Adhesive strength The adhesive film for evaluation prepared above was cut to a size of 25 mm x 150 mm (long side), and the release film was peeled off. Next, the surface of the adhesive layer exposed by peeling was placed on the exposed surface of the decorative layer of the printing plate prepared above, and then the two were laminated by rolling a 2 kg roller back and forth twice. The laminate obtained by this lamination was subjected to a heat treatment at 120°C for 1 hour using a hot air circulation dryer, and used as a sample for adhesive strength evaluation test. For this adhesive strength evaluation test sample, the adhesive film for evaluation (structure: base film / adhesive layer) was peeled off from the printing plate at 180° in the long side (150 mm) direction, and the adhesive strength (unit: N / 25 mm) was measured by a method conforming to JIS Z 0237:2000. Specifically, a single column type material testing machine [model: RTG-1310] manufactured by A&D Co., Ltd. was used as the measuring device, and the measurement was performed under conditions of an atmospheric temperature of 23°C, 50% RH, and a peeling speed of 300 mm / min. Then, the adhesive strength to the adherend was evaluated according to the following evaluation criteria. The results are shown in Tables 3 and 4. In the following evaluation criteria, "A" and "B" are practically acceptable levels, with "A" being the most preferable.

[0182] -Evaluation criteria- A: The adhesive strength is 15N / 25mm or more. B: The adhesive strength is 5N / 25mm or more and less than 15N / 25mm. C: The adhesive strength is less than 5N / 25mm.

[0183] 2.Appearance during 3D molding 2-1. Cohesive failure The adhesive film for evaluation prepared above was cut to a size of 50 mm x 50 mm, and the release film was peeled off. Next, the surface of the adhesive layer exposed by peeling was placed on the exposed surface of the decorative layer of the printing plate prepared above, and then the two were laminated by rolling a 2 kg roller back and forth twice. The laminate obtained by this lamination was subjected to a heat treatment at 120°C for 1 hour using a hot air circulation dryer, and used as a sample for cohesive failure evaluation test. The cohesive failure evaluation test sample was subjected to a DuPont impact test from the aluminum plate side under the following conditions.

[0184] <DuPont impact test conditions> Falling weight: 1kg Drop height: 50cm Receiving jig: 1 / 4 inch recessed R shape Strike core: Flat tip, 1 / 2 inch diameter, 3 / 8 inch tip diameter

[0185] After the test, the evaluation adhesive film (structure: base film / adhesive layer) was stretched and deformed, and the deformed portion was observed under an optical microscope. The presence or absence and degree of air bubbles in the adhesive layer were confirmed, and the state of cohesive failure was evaluated according to the following evaluation criteria. The results are shown in Tables 3 and 4. The occurrence of air bubbles in the pressure-sensitive adhesive layer means that cohesive failure has occurred in the pressure-sensitive adhesive layer. In the following evaluation criteria, "A" and "B" are practically acceptable levels, with "A" being the most preferable.

[0186] -Evaluation criteria- A: No air bubbles were found in the adhesive layer (see FIG. 4A). B: A small amount of air bubbles were observed in the adhesive layer (see FIG. 4B). C: Air bubbles are noticeably generated in the adhesive layer (see FIG. 4C).

[0187] 2-2. Peeling The adhesive film for evaluation prepared above was cut to a size of 50 mm x 35 mm, and the release film was peeled off. Next, the surface of the adhesive layer exposed by peeling was placed on the exposed surface of the decorative layer of the printing plate prepared above, and then the two were laminated using a laminator. The laminate obtained by this lamination was subjected to a heat treatment at 120°C for 1 hour using a hot air circulation dryer, and used as a peel evaluation test sample. This peeling evaluation test sample was embossed with letters using a press machine and a die measuring 50 mm x 35 mm at a pressure of 1.3 t. An example of embossed letters is shown in Figure 5. Next, the peeling evaluation test sample 24 hours after embossing was subjected to a heat treatment at 120°C for 10 minutes using a hot air circulation dryer. After the heat treatment, the edges of the embossed letters were visually observed to confirm the presence or absence and the degree of lifting of the adhesive film (composition: base film / adhesive layer). The state of peeling was then evaluated according to the following evaluation criteria. The results are shown in Tables 3 and 4. In the following evaluation criteria, "A" and "B" are practically acceptable levels, with "A" being the most preferable.

[0188] -Evaluation criteria- A: No lifting was observed at all on the edges of the embossed letters. B: Slight lifting is observed at the edges of the embossed letters. C: The occurrence of lifting is clearly observed at the edges of the embossed letters.

[0189] [Table 3]

[0190] [Table 4]

[0191] As shown in Table 3, it was confirmed that the pressure-sensitive adhesive layers of Examples 1 to 14 had high adhesive strength to the adherend. It was also confirmed that the pressure-sensitive adhesive layers of Examples 1 to 14 were less susceptible to cohesive failure and peeling around the protrusions of the adherend during three-dimensional molding, and were less likely to cause poor appearance. On the other hand, as shown in Table 4, the adhesive layers of Comparative Examples 1 to 8 were confirmed to be inferior to the adhesive layers of Examples 1 to 14 in at least one of the evaluation results of adhesive strength to the adherend, and cohesive failure and peeling around the convex parts of the adherend during three-dimensional molding. [Explanation of symbols]

[0192] 10: Overlamination film 20: Surface protection film 30: Adhesive layer (first adhesive layer) 40, 70: License plate 50: Plate substrate 60:Decorative layer 80: Image receiving layer 90:Second adhesive layer 100: Image receiving film

Claims

1. The adhesive composition is formed from a pressure-sensitive adhesive composition including a (meth)acrylic polymer having a reactive functional group and a glass transition temperature of −45° C. to −5° C., and an isocyanate-based crosslinking agent; A pressure-sensitive adhesive layer for an overlaminate film, having a gel fraction of 60 mass% or more after heat treatment at 120°C for 1 hour and a gel fraction of 30 mass% or less before heat treatment at 120°C for 1 hour.

2. The pressure-sensitive adhesive layer for an overlaminate film according to claim 1 , wherein the change in gel fraction before and after heat treatment at 120° C. for 1 hour is 50% by mass or more.

3. The pressure-sensitive adhesive layer for an overlaminate film according to claim 1, wherein the gel fraction after heat treatment at 120°C for 1 hour is 60 mass% or more, and the gel fraction before heat treatment at 120°C for 1 hour is 10 mass% or less.

4. 2. The pressure-sensitive adhesive layer for an overlaminate film according to claim 1, wherein the isocyanate-based crosslinking agent is a blocked isocyanate-based compound.

5. A surface protection film; The pressure-sensitive adhesive layer for an overlaminate film according to any one of claims 1 to 4, which is provided on one side of a surface protective film; An overlaminate film comprising:

6. A plate substrate; The overlaminate film according to claim 5 provided on one surface side of a plate substrate; A license plate comprising:

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