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 an adhesive layer for an overlaminate film, an overlaminate film, and a number plate.

Background Art

[0002] Conventionally, for decorations such as outdoor signs and vehicles (e.g., motorcycles and four-wheeled vehicles), films subjected to inkjet printing have been used. Such films have a configuration including at least a printing film for printing and an overlaminate film for protecting this printing film, and in recent years, they have also been used in number plates (also referred to as "license plates") (see, for example, Patent Documents 1 to 4).

Prior Art Documents

Patent Documents

[0006] The following are examples of specific means for solving the problem: <1> The adhesive 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 crosslinking agent. An adhesive layer for overlaminate film, wherein the gel fraction after heating at 120°C for 1 hour is 60% by mass or more, and the gel fraction before heating at 120°C for 1 hour is 30% by mass or less. <2> The change in gel fraction before and after heating at 120°C for 1 hour is 50% by mass or more. <1> The adhesive layer for overlaminate film described in [reference]. <3> The gel fraction after heating at 120°C for 1 hour is 60% by mass or more, and the gel fraction before heating at 120°C for 1 hour is 10% by mass or less. <1> The adhesive layer for overlaminate film described in [reference]. <4> Isocyanate crosslinking agents are blocked isocyanate compounds. <1> ~ <3> An adhesive layer for overlaminate film as described in any one of the following. <5> Surface protective film, Provided on one side of the surface protective film <1> ~ <4> An adhesive layer for overlaminate film as described in any one of the following, An overlaminate film equipped with [specific feature]. <6> Plate substrate and Provided on one side of the plate substrate <5> The overlaminate film described above, A license plate equipped with [a specific feature / feature]. [Effects of the Invention]

[0007] According to one embodiment of the present disclosure, an adhesive layer for an overlaminate film is provided that has high adhesive strength to the adherend and is less likely to cause appearance defects during three-dimensional molding. According to other embodiments of the present disclosure, an overlaminate film and a license plate are provided, each comprising the above-mentioned adhesive layer for the overlaminate film. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view showing an example of the configuration of the overlaminate film of this disclosure. [Figure 2] This is a schematic cross-sectional view showing an example of the configuration of a license plate in this disclosure. [Figure 3] This is a schematic cross-sectional view showing an example of another configuration of a license plate in this disclosure. [Figure 4A] This is a photograph showing an example of an evaluation result "A" for cohesive failure in the implemented example. [Figure 4B] This photograph shows an example of the evaluation result "B" for cohesive failure in the example. [Figure 4C] This is a photograph showing an example of the evaluation result "C" for cohesive failure in the embodiment. [Figure 5] This is a photograph showing an example of embossed lettering in a peeling evaluation test in the embodiment. [Modes for carrying out the invention]

[0009] The adhesive layer for overlaminate film, the overlaminate film, and the license plate of this disclosure will be described in detail below. The descriptions of the requirements below may be based on typical embodiments of this disclosure, but this disclosure is not limited to such embodiments and may be implemented with appropriate modifications within the scope of the purposes of this disclosure.

[0010] In the present disclosure, when describing embodiments with reference to the drawings, the configuration of the embodiments is not limited to the configuration shown in the drawings. Also, the sizes of the members in each figure are conceptual, and the relative size relationships between the members are not limited thereto. Further, in each drawing, members having substantially the same function may be given the same reference numerals throughout the drawings, and duplicate descriptions may be omitted.

[0011] In the present disclosure, the numerical range indicated using "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value, respectively. In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another numerically described stepwise range. Also, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.

[0012] In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

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

[0014] In the present disclosure, "solid content" means components other than the solvent contained in the composition, unless otherwise specified. In the present 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 containing structural units derived from (meth)acrylic monomers and having a proportion of structural units derived from (meth)acrylic monomers of 50% by 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 this disclosure, "mass%" and "weight%" are synonymous, and "parts by mass" and "parts by weight" are synonymous.

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

[0020] In this disclosure, the term "layer" includes cases where, when observing the region in which the layer exists, it is formed not only over the entire region but also over only a portion of that region. The same applies to the term "membrane." In this disclosure, the term "lamination" means stacking layers, and "lamination" may be two or more layers bonded together, or two or more layers may be detachable.

[0021] In this disclosure, “appearance defect” means an appearance defect caused by cohesive failure and / or peeling of the adhesive layer, and “peeling” includes a state in which a part of the adhesive layer is lifted away from the adherend.

[0022] In this disclosure, "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 crosslinking agent" is also referred to as "a specific adhesive composition." In this disclosure, a (meth)acrylic polymer having reactive functional groups 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 adhesive layer for overlaminate film of this disclosure (hereinafter also simply referred to as the "adhesive layer") is formed from an adhesive composition (i.e., a specific adhesive composition) comprising a (meth)acrylic polymer having reactive functional groups and a glass transition temperature of -45°C to -5°C [i.e., a specific (meth)acrylic polymer] and an isocyanate crosslinking agent, wherein 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 30% by mass or less.

[0024] The adhesive layer of this disclosure is used in the adhesive layer of an overlaminate film. Conventional adhesive layers for general overlaminate films have excellent adhesion to the substrate, but when three-dimensional molding is performed after bonding to the substrate, cohesive failure and / or peeling may be observed around the convex parts of the substrate after three-dimensional molding. In contrast, the adhesive layer of this disclosure is formed from an adhesive composition having the above-described structure and possesses the above-described physical properties, and therefore has high adhesive strength to the adherend and is less likely to cause appearance defects during three-dimensional molding. The reason why the adhesive layer of this disclosure may produce such effects is not clear, but the inventors speculate as follows. However, the following speculation is not intended to limit the interpretation of the adhesive layer of this disclosure, but is explained as an example.

[0025] Since the adhesive layer of this disclosure is formed from an adhesive composition containing a (meth)acrylic polymer with a relatively low glass transition temperature, it is expected to have excellent wettability to the adherend and adhere tightly to the adherend when bonded to it. For this reason, the adhesive layer of this disclosure can function suitably as an adhesive layer in an overlaminate film. The adhesive composition in this disclosure comprises a (meth)acrylic polymer and an isocyanate crosslinking agent, wherein the (meth)acrylic polymer has functional groups, i.e., reactive functional groups, that can react with the isocyanate groups of the isocyanate crosslinking agent to form a crosslinked structure. The adhesive layer formed by this adhesive composition has the property of having 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 is thought to have 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 its low gel fraction before heat treatment, so it is thought to adhere well to the adherend when bonded to it. The adhesive layer of this disclosure can be heat-treated while in close contact with the adherend to enhance its cohesive force without reducing its adhesive strength to the adherend. Therefore, it is presumed that it will have high adhesive strength to the adherend and 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 adhesive composition in this disclosure [i.e., the specific adhesive composition] comprises a (meth)acrylic polymer [i.e., a specific (meth)acrylic polymer] having reactive functional groups and a glass transition temperature of -45°C to -5°C, and an isocyanate crosslinking agent. The adhesive layer of this disclosure comprises a cured product of a specific adhesive composition, the cured product comprising, 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 polymers> The specific adhesive composition contains a (meth)acrylic polymer [i.e., a specific (meth)acrylic polymer] having reactive functional groups and a glass transition temperature of -45°C to -5°C. The specific adhesive composition may contain only one specific (meth)acrylic polymer, or it may contain two or more specific polymers.

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

[0029] The specified (meth)acrylic polymer may be a homopolymer or a copolymer. For example, the specified (meth)acrylic polymer may be a homopolymer or copolymer of (meth)acrylic monomers that do not have reactive functional groups, into which reactive functional groups have been introduced by substitution; or it may be a copolymer of a (meth)acrylic monomer that does not have reactive functional groups and a monomer that does not have reactive functional groups and is other than a (meth)acrylic monomer, into which reactive functional groups have been introduced by substitution. Furthermore, the specified (meth)acrylic polymer may be a copolymer of a (meth)acrylic monomer that has reactive functional groups and a (meth)acrylic monomer that does not have reactive functional groups; or it may be a copolymer of a (meth)acrylic monomer that has reactive functional groups and is other than a (meth)acrylic monomer; or it may be a copolymer of a (meth)acrylic monomer that does not have reactive functional groups and is a monomer that has reactive functional groups and is other than a (meth)acrylic monomer.

[0030] A preferred embodiment of the specific (meth)acrylic polymer is one in which the specific (meth)acrylic polymer contains constituent units derived from monomers having reactive functional groups, as described below, thereby having reactive functional groups.

[0031] <<Constituent units derived from monomers having reactive functional groups>> The specific (meth)acrylic polymer preferably contains constituent units derived from monomers having reactive functional groups. In this disclosure, "constituent unit derived from monomers having reactive functional groups" means a constituent unit formed by addition polymerization of monomers having reactive functional groups.

[0032] Examples of monomers having reactive functional groups include monomers having at least one reactive functional group and an ethylenically unsaturated group in one molecule. Specific examples of reactive functional groups are as previously described. The ethylenically unsaturated group is not particularly limited and includes, for example, a vinyl group, an allyl group, a vinylphenyl group, a (meth)acrylamide group, and a (meth)acryloyl group. A (meth)acryloyl group is preferred as the ethylenically unsaturated group.

[0033] Examples of monomers having reactive functional groups include monomers having a carboxyl group, monomers having a hydroxyl group, monomers having an amino group, and monomers having a glycidyl group. As monomers having reactive functional groups, monomers having carboxyl groups are preferred.

[0034] Specific examples of monomers having a carboxyl 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). As the monomer having a carboxyl group, a (meth)acrylic monomer having a carboxyl group is preferred, (meth)acrylic acid is more preferred, and acrylic acid is even more preferred.

[0035] Specific examples of monomers having hydroxyl groups 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 monomers having hydroxyl groups, (meth)acrylic monomers having hydroxyl groups are preferred, hydroxyalkyl (meth)acrylates are more preferred, hydroxyalkyl (meth)acrylates having a hydroxyalkyl group with 2 to 4 carbon atoms are even more preferred, and 2-hydroxyethyl acrylate is particularly preferred.

[0036] Specific examples of monomers 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] A specific (meth)acrylic polymer may contain only one or more constituent units derived from monomers having reactive functional groups.

[0039] The content of constituent units derived from monomers having reactive functional groups in a specific (meth)acrylic polymer is not particularly limited, but for example, it is preferably 1% to 15% by mass, more preferably 2% to 10% by mass, even more preferably 3% to 8% by mass, and particularly preferably 4% to 6% by mass, relative to the total constituent units of the specific (meth)acrylic polymer. When the content of constituent units derived from monomers having reactive functional groups in a specific (meth)acrylic polymer is 1% by mass or more relative to the total constituent units of the specific (meth)acrylic polymer, the cohesive force of the adhesive layer is sufficiently increased, and cohesive failure of the adhesive layer around the protrusions of the adherend tends to be less likely to occur during three-dimensional molding. Furthermore, high cohesive force is exhibited in the adhesive layer after heat treatment, and peeling of the adhesive layer around the protrusions of the adherend tends to be less likely to occur during three-dimensional molding. When the content of constituent units derived from monomers having reactive functional groups in a specific (meth)acrylic polymer is 15% by mass or less relative to the total constituent units of the specific (meth)acrylic polymer, the cohesive force of the adhesive layer does not become excessively high, and the decrease in the adhesive strength of the adhesive layer to the adherend tends to be suppressed more effectively.

[0040] <<Constituent units derived from alkyl methacrylate monomers>> The specific (meth)acrylic polymer preferably contains constituent units derived from alkyl (meth)acrylate monomers. In this disclosure, "constituent units derived from (meth)acrylate alkyl ester monomers" means constituent units formed by the addition polymerization of (meth)acrylate alkyl ester monomers. In the context of specific (meth)acrylic polymers, "(meth)acrylate alkyl ester monomer" refers to an (meth)acrylate alkyl ester monomer that does not have a carboxyl group. In other words, in the context of specific (meth)acrylic polymers, "(meth)acrylate alkyl ester monomer having a carboxyl group" is classified as a monomer having a carboxyl group.

[0041] The type of alkyl (meth)acrylate monomer is not particularly limited. The alkyl acrylate monomer may be an alkyl acrylate monomer or an alkyl methacrylate monomer, but from the viewpoint of easily obtaining a specific (meth)acrylic polymer with a glass transition temperature of -45°C to -5°C, for example, an alkyl acrylate monomer is preferred. The alkyl group in the alkyl (meth)acrylate monomer may be unsubstituted or substituted, but it is preferable that it be unsubstituted. The alkyl group of the alkyl (meth)acrylate monomer may be linear, branched, or cyclic. The number of carbon atoms in the alkyl group of the (meth)acrylate monomer is preferably 1 to 18, more preferably 1 to 12, even more preferably 1 to 8, and particularly preferably 1 to 4.

[0042] Specific examples of alkyl (meth)acrylate monomers 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 alkyl (meth)acrylate 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 a specific (meth)acrylic polymer contains constituent units derived from alkyl (meth)acrylate monomers, it may contain only one type of constituent unit derived from alkyl (meth)acrylate monomers, or it may contain two or more types.

[0044] When a specific (meth)acrylic polymer contains constituent units derived from alkyl (meth)acrylate monomers, the content of constituent units derived from alkyl (meth)acrylate monomers is not particularly limited, but is preferably 50% by mass or more, more preferably 50% to 99% by mass, even more preferably 60% to 97% by mass, and particularly preferably 70% to 96% by mass, relative to the total constituent units of the specific (meth)acrylic polymer. Here, the content of constituent units derived from alkyl (meth)acrylate monomers in a specific (meth)acrylic polymer being 50% by mass or more of the total constituent units of the specific (meth)acrylic polymer means that constituent units derived from alkyl (meth)acrylate monomers are included as the main component of the constituent units of the specific (meth)acrylic polymer.

[0045] <<Constituent units derived from other monomers>> The specific (meth)acrylic polymer may contain constituent units derived from monomers that do not fall under either monomers having reactive functional groups or alkyl (meth)acrylate monomers (so-called other monomers). In this disclosure, "constituent units derived from other monomers" means constituent units formed by the addition polymerization of other monomers.

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

[0047] If a specific (meth)acrylic polymer contains constituent units derived from other monomers, it may contain only one type of constituent unit derived from other monomers, or it may contain two or more types.

[0048] If the specific (meth)acrylic polymer contains constituent units derived from other monomers, the content of the constituent units derived from other monomers can be appropriately set within a range that does not impair the effect of the adhesive layer formed according to this disclosure.

[0049] -Glass transition temperature of specific (meth)acrylic polymers- The glass transition temperature (also called "Tg") of certain (meth)acrylic polymers is -45°C to -5°C. When the glass transition temperature of a specific (meth)acrylic polymer is -45°C or higher, the cohesive force of the adhesive layer increases, making it less likely for cohesive failure of the adhesive layer to occur around the protrusions 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 a specific (meth)acrylic polymer is -5°C or lower, the adhesive layer exhibits sufficient wettability to the adherend, increasing the adhesion of the adhesive layer to the adherend, and thus tending to have a sufficiently high adhesive strength. Furthermore, high cohesive force is developed in the adhesive layer after heat treatment, making it less likely for the adhesive layer to peel off around the protrusions of the adherend during three-dimensional molding. From this viewpoint, the glass transition temperature of the specific (meth)acrylic polymer is preferably -10°C or lower, and more preferably -15°C or lower. In some embodiments, the glass transition temperature of a particular (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 a specific (meth)acrylic polymer is the absolute temperature (unit: K) calculated from Equation 1 below and converted to Celsius temperature (unit: °C). 1 / Tg=m1 / Tg1+m2 / Tg2+ +m(k-1) / Tg(k-1)+mk / Tgk (Formula 1)

[0051] In Equation 1, Tg1, Tg2, ..., Tg(k-1), and Tgk represent the glass transition temperatures expressed in absolute temperature when each monomer constituting the specific (meth)acrylic polymer is a homopolymer. m1, m2, ..., m(k-1), and mk represent the mole fractions of each monomer constituting the specific (meth)acrylic polymer, and m1 + m2 + ... + m(k-1) + mk = 1. Furthermore, absolute temperature can be converted to Celsius temperature by subtracting 273 from it, and Celsius temperature can be converted back to absolute temperature by adding 273 to it.

[0052] In this disclosure, the "glass transition temperature when used as a homopolymer" shall be the value described in publicly available documents or the value measured using a differential scanning calorimetry (DSC). Specifically, the choice of which value to use is as follows:

[0053] For the "glass transition temperatures when the monomers listed below are homopolymers," the values ​​indicated for each monomer should be used. 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 Methacrylate: 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-Carboxypolycaprolactone (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] For monomers other than those mentioned above, the "glass transition temperature when used as a homopolymer" will be based on the values ​​listed in the Polymer Handbook (4th edition, Wiley-Interscience; hereafter the same). If the value is not listed in the Polymer Handbook, the glass transition temperature of the homopolymer obtained by the following measurement method will be used.

[0055] (Measurement of glass transition temperature of homopolymers) A differential scanning calorimetry (DSC) was used to measure the glass transition temperature of the homopolymer under conditions of a nitrogen atmosphere, with a sample of 10 mg and a heating rate of 10°C / min. The inflection point of the resulting DSC curve was defined as the glass transition temperature of the homopolymer. As a differential scanning calorimetry device, for example, a differential scanning calorimeter (product name: Discovery DSC 2500) manufactured by T.A. Instrument Japan Co., Ltd. can be suitably used. However, the differential scanning calorimetry device is not limited to this.

[0056] The glass transition temperature of a specific (meth)acrylic polymer can be appropriately adjusted, for example, by using two or more monomers that have different glass transition temperatures when used as a single polymer.

[0057] -Weight-average molecular weight of specific (meth)acrylic polymers- The weight-average molecular weight (also called "Mw") of the specific (meth)acrylic polymer is not particularly limited, but is preferably 400,000 to 2,500,000, more preferably 500,000 to 2,500,000, and even more preferably 600,000 to 2,500,000. When the weight-average molecular weight of a specific (meth)acrylic polymer is 400,000 or higher, thermal shrinkage of the adhesive layer due to a decrease in cohesive force tends to be less likely. Certain (meth)acrylic polymers tend to be easier to manufacture if their weight-average molecular weight is 2.5 million or less.

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

[0059] ~Conditions~ Measurement device: High-speed GPC [Model number: HLC-8420 GPC, manufactured by Tosoh Corporation] Detector: Differential Refractometer (RI) [Integrated into HLC-8420, manufactured by Tosoh Corporation] Column: TSKgel GMH XL Two units manufactured by Tosoh Corporation were used. Column temperature: 40℃ Eluent: Tetrahydrofuran Sample solution injection volume: 100 μL Flow rate: 0.8mL / min

[0060] The weight-average molecular weight of a specific (meth)acrylic polymer can be adjusted to a desired value by controlling the polymerization temperature, polymerization time, amount of organic solvent used, type of polymerization initiator, and amount of polymerization initiator used during the polymerization of the monomer.

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

[0062] In this disclosure, "total solid content in the adhesive composition" means the total mass of the adhesive composition if the adhesive composition does not contain a solvent, and the mass of the residue remaining after removing the solvent from the adhesive composition if the adhesive composition contains a solvent.

[0063] -Meth)acrylic polymer manufacturing method- The method for producing the specific (meth)acrylic polymer is not particularly limited. Specific (meth)acrylic polymers can be produced by polymerizing the monomers described above using known polymerization methods, such as solution polymerization, emulsion polymerization, suspension polymerization, and bulk polymerization. As for the polymerization method, solution polymerization is preferred because the processing steps for preparing the specific adhesive composition after manufacturing are relatively simple and can be carried out in a short time.

[0064] In solution polymerization, a predetermined organic solvent, monomer, polymerization initiator, and a chain transfer agent (if necessary) are generally placed in a polymerization tank, and the reaction is carried out by heating for several hours at, for example, the reflux temperature of the organic solvent while stirring. In this case, at least a portion of the organic solvent, monomer, polymerization initiator, and chain transfer agent (if necessary) may be added sequentially. Alternatively, the reaction may be carried out under a nitrogen atmosphere.

[0065] Examples of organic solvents used in polymerization reactions include aromatic hydrocarbon compounds, aliphatic hydrocarbon compounds, alicyclic hydrocarbon compounds, ester compounds, ketone compounds, glycol ether compounds, and alcohol compounds. More specifically, organic solvents used in polymerization reactions 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 spirits, 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; and methyl Examples 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 the production of specific (meth)acrylic polymers, it is preferable to use organic solvents that do not easily cause chain transfer during polymerization reactions, such as aromatic hydrocarbon compounds, ester compounds, and ketone compounds. In particular, from the viewpoint of solubility of the specific (meth)acrylic polymer and ease of polymerization reaction, the use of methyl acetate and / or ethyl acetate is preferred.

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

[0068] Examples of polymerization initiators include organic peroxides and azo compounds commonly used in conventional solution polymerization methods. Specific examples of organic peroxides include t-butylperoxy-2-ethylhexanoate, t-butylhydroperoxide, cumenehydroperoxide, dicumylperoxide, benzoylperoxide, lauroylperoxide, caproylperoxide, di-i-propylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate, t-butylperoxypivalate, and 2,2-bis(4,4-di-t-butylperoxycycline). Examples include 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-carbonitride), and 2,2'-azobis(isobutyric acid)dimethyl.

[0069] During the polymerization reaction, one polymerization initiator may be used, or two or more may be used.

[0070] The amount of polymerization initiator used is not particularly limited and can be appropriately set, for example, depending on the molecular weight of the target specific (meth)acrylic polymer.

[0071] In the production of specific (meth)acrylic polymers, chain transfer agents may be used as needed. Examples of chain transfer agents include cyanoacetic acid, alkyl ester compounds of cyanoacetic acid with 1 to 8 carbon atoms, bromoacetic acid, alkyl ester compounds of bromoacetic acid with 1 to 8 carbon atoms, aromatic compounds represented by α-methylstyrene, anthracene, phenanthrene, fluorene, and 9-phenylfluorene, aromatic nitro compounds represented by p-nitroaniline, nitrobenzene, dinitrobenzene, p-nitrobenzoic acid, p-nitrophenol, and p-nitrotoluene, benzoquinone derivatives represented by benzoquinone and 2,3,5,6-tetramethyl-p-benzoquinone, borane derivatives represented by tributylborane, carbon tetrabromide, and tetra- Examples include halogenated hydrocarbon compounds represented by carbon chloride, 1,1,2,2-tetrabromoethane, tribromoethylene, trichloroethylene, bromotrichloromethane, tribromomethane, and 3-chloro-1-propene; aldehyde compounds represented by chloral and furaldehyde; alkyl mercaptan compounds having 1 to 18 carbon atoms; aromatic mercaptan compounds represented by 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 represented by pinene and terpinolene.

[0072] When using a chain transfer agent in the production of a specific (meth)acrylic polymer, the amount of the chain transfer agent used is not particularly limited and can be appropriately set, for example, according to the molecular weight of the target specific (meth)acrylic polymer.

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

[0074] <Isocyanate compounds> The specific adhesive composition contains an isocyanate-based crosslinking agent. In this disclosure, "isocyanate-based crosslinking agents" include compounds having two or more isocyanate groups in one molecule (also referred to as "polyisocyanate compounds") and compounds having two or more blocked isocyanate groups in one molecule (also referred to as "blocked isocyanate compounds"). In this disclosure, "polyisocyanate compounds" are also referred to as "non-blocked isocyanate compounds." The isocyanate crosslinking agent is preferably a blocked isocyanate compound because it allows for easy control of the gel fraction through heat treatment.

[0075] In this disclosure, "blocked isocyanate group" refers to a group whose reactivity is normally suppressed by protecting it with a blocking agent (so-called masking), but which can be deprotected upon heating to generate an active isocyanate group. In other words, a "blocked isocyanate compound" in this disclosure is a compound in which two or more isocyanate groups of a polyisocyanate compound are protected with a blocking agent. In this disclosure, when simply referred to as "isocyanate group," it refers to an isocyanate group that is not protected with a blocking agent.

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

[0077] [ka]

[0078] In the above formula, X represents the structure obtained by removing hydrogen atoms from the blocking agent. The blocking agents are not particularly limited and include, for example, ketoxime compounds, amide compounds, nitrogen-containing heterocyclic compounds, and active methylene compounds.

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

[0080] "Aliphatic polyisocyanate compounds" include, for example, aliphatic polyisocyanate compounds, polymers of aliphatic polyisocyanate compounds, adduct compounds of aliphatic polyisocyanate compounds and polyol compounds [e.g., trimethylolpropane (TMP); the same applies hereinafter], and biuret compounds of aliphatic polyisocyanate compounds. Specific examples of aliphatic polyisocyanate compounds include hexamethylene diisocyanate (HMDI), pentamethylene diisocyanate (PDI), tetramethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0081] "Alicyclic polyisocyanate compounds" include, for example, alicyclic polyisocyanate compounds, polymers of alicyclic polyisocyanate compounds, adducts of alicyclic polyisocyanate compounds and polyol compounds, and biuret compounds of alicyclic polyisocyanate compounds. Specific examples of alicyclic polyisocyanate compounds include isophorone diisocyanate (IPDI), hydrogenated tolylene diisocyanate, hydrogenated xylylene diisocyanate (H6XDI), hydrogenated 4,4'-diphenylmethane diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0082] "Aromatic polyisocyanate compounds" include, for example, aromatic polyisocyanate compounds, polymers of aromatic polyisocyanate compounds, adduct compounds of aromatic polyisocyanate compounds and polyol compounds, and biuret compounds of aromatic polyisocyanate compounds. Specific examples of aromatic polyisocyanate compounds include tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), and 4,4'-diphenylmethane diisocyanate.

[0083] As the polyisocyanate compound, at least one selected from the group consisting of aliphatic polyisocyanate compounds and alicyclic polyisocyanate compounds is preferred, and at least one selected from the group consisting of isophorone diisocyanate, hexamethylene diisocyanate compounds and hydrogenated xylylene diisocyanate compounds is more preferred. "Isophorone diisocyanate compounds" include, for example, IPDI, IPDI polymers, IPDI adducts with polyols, and IPDI biuret compounds. As for isophorone diisocyanate compounds, adduct compounds of IPDI and polyol compounds are preferred. "Hexamethylene diisocyanate compounds" include, for example, HMDI, HMDI polymers, adduct compounds of HMDI and polyol compounds, and biuret compounds of HMDI. As the hexamethylene diisocyanate compound, a polymer of HMDI or a biuret of HMDI is preferred. "Hydrogenated xylylene diisocyanate compounds" include, for example, H6XDI, adduct compounds of H6XDI and polyol compounds, and biuret compounds of H6XDI.

[0084] The dissociation temperature of the blocked isocyanate compound is not particularly limited, but for example, from the viewpoint of readily available commercial products, it is preferably 80°C or higher. Furthermore, from the viewpoint of suppressing deformation of the surface protective film of the overlaminate film bonded to the adherend due to heating, the dissociation temperature of the blocked isocyanate compound is preferably 180°C or lower. The dissociation temperature of the blocked isocyanate compound is preferably 80°C to 180°C, more preferably 90°C to 180°C, and even more preferably 100°C to 180°C.

[0085] Representative block isocyanate compounds and their dissociation temperatures are shown below. Dimethylpyrazole block isocyanate compounds (dissociation temperature: 100°C to 120°C), activated methylene block isocyanate compounds (dissociation temperature: 100°C to 120°C), ketoxime block isocyanate compounds (dissociation temperature: 130°C to 150°C), ε-caprolactam block isocyanate compounds (dissociation temperature: 160°C to 180°C).

[0086] In this disclosure, "dissociation temperature of the blocked isocyanate compound" means the temperature at which the blocking agent dissociates. In this disclosure, the dissociation temperature of a blocked isocyanate compound refers to "the temperature of the endothermic peak associated with the deprotection reaction of the blocked isocyanate, as measured by differential scanning calorimetry (DSC) analysis using a differential scanning calorimeter."

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

[0088] The specific adhesive composition may contain only one isocyanate-based crosslinking agent, or it may contain two or more.

[0089] The content of isocyanate-based crosslinking agents in the specific 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, per 100 parts by mass of the specific (meth)acrylic polymer. When the content of isocyanate-based crosslinking agent in a specific adhesive composition is 0.5 parts by mass or more per 100 parts by mass of a specific (meth)acrylic polymer, the cohesive force of the adhesive layer is sufficiently increased, and cohesive failure of the adhesive layer around the protrusions of the adherend tends to be less likely to occur during three-dimensional molding. Furthermore, high cohesive force is exhibited in the adhesive layer after heat treatment, and peeling of the adhesive layer around the protrusions of the adherend tends to be less likely to occur during three-dimensional molding. The upper limit of the isocyanate-based crosslinking agent content in the specific adhesive composition is 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, per 100 parts by mass of the specific (meth)acrylic polymer. When the content of isocyanate-based crosslinking agents in a specific adhesive composition is 44 parts by mass or less per 100 parts by mass of a specific (meth)acrylic polymer, the transparency of the adhesive layer tends not to be impaired because the amount of isocyanate-based crosslinking agents is not excessively high.

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

[0091] The ratio of the number of moles of isocyanate groups in an isocyanate crosslinking agent to the number of moles of reactive functional groups in a specific (meth)acrylic polymer can be calculated using the following formulas (1) to (3). Note that if the isocyanate crosslinking agent is a blocked isocyanate compound, "isocyanate group" in formula (1) refers to the isocyanate group after the blocking agent has deprotected it, i.e., the isocyanate group that is not protected by the blocking agent. Furthermore, if there are multiple monomers having reactive functional groups that form the specific (meth)acrylic polymer, the calculation should be performed for each monomer and then the resulting values ​​should be summed.

[0092] Number of moles of isocyanate groups in isocyanate-based crosslinking agents [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] Mole count of reactive functional groups in specific (meth)acrylic polymers [unit: mmol] =[Content of constituent units derived from monomers having reactive functional groups in the specific (meth)acrylic polymer (unit: mass%) / 100 × Amount of specific (meth)acrylic polymer blended (unit: g) / Molecular weight of constituent units derived from monomers having reactive functional groups (unit: g / mol) × Number of reactive functional groups (valence) in the constituent units derived from monomers having reactive functional groups × 1000]...(2)

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

[0095] <Organic solvents> The specific adhesive composition may contain an organic solvent. The application properties and pot life of certain adhesive compositions may be improved when they contain organic solvents. Examples of organic solvents include those similar to those used in the polymerization reaction of the specific (meth)acrylic polymers described above.

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

[0097] When a specific adhesive composition contains an organic solvent, the content of the organic solvent is not particularly limited and can be set as appropriate depending on the purpose.

[0098] <Other ingredients> The specific adhesive composition may, if necessary, contain components other than those described above (so-called other components), as long as they do not impair the effect of the adhesive layer formed according to this disclosure. Other components include polymers other than specific (meth)acrylic polymers, crosslinking agents other than isocyanate-based crosslinking agents (e.g., epoxy-based crosslinking agents), crosslinking catalysts, antioxidants, light stabilizers (e.g., UV absorbers), antistatic agents, and various other additives.

[0099] If the specific adhesive composition contains other components, the content of these other components can be appropriately set within a range that does not impair the effect of the adhesive layer formed according to this disclosure.

[0100] -Gel fraction of the adhesive layer- The adhesive layer of this disclosure has 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. The adhesive layer of this disclosure has a gel fraction of 30% by mass or less before heat treatment at 120°C for 1 hour, so the adhesive layer before heat treatment is soft and tends to exhibit good adhesion to the adherend. Furthermore, the adhesive layer of this disclosure has a gel fraction of 60% by mass or more after heat treatment at 120°C for 1 hour, so the adhesive layer after heat treatment has high cohesive force, and when heat treatment is applied while bonded to an adherend, cohesive failure and peeling around the convex parts of the adherend caused by three-dimensional molding tend to be suppressed without reducing the adhesive force to the adherend. From the above viewpoint, it is preferable that the adhesive layer of this disclosure has a gel fraction of 60% by mass or more after heat treatment at 120°C for 1 hour, and a gel fraction of 10% by mass or less before heat treatment at 120°C for 1 hour. The upper limit of the gel fraction of the 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 adhesive layer before heat treatment at 120°C for 1 hour is not particularly limited, and examples include greater than 0% by mass, 1% or more by mass, 2% or more by mass, and 3% or more by mass.

[0101] In this disclosure, "gel fraction of the adhesive layer before heat treatment 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 heat treatment at 120°C for 1 hour. In this disclosure, "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 heat treatment at 120°C for 1 hour of the adhesive layer formed by drying a coating film of a specific adhesive composition.

[0102] The adhesive layer of this disclosure preferably has a change in gel fraction of 50% by mass or more, and more preferably 55% by mass or more, before and after heat treatment at 120°C for 1 hour. When the change in the gel fraction of the adhesive layer before and after heating at 120°C for 1 hour is 50% by mass or more, it tends to be possible to achieve a better balance between improving the adhesive strength of the adhesive layer to the adherend and suppressing the occurrence of appearance defects in the adhesive layer during three-dimensional molding.

[0103] The gel fraction of the adhesive layer of this disclosure is measured according to (1) to (4) below. (1) A 250-mesh wire mesh (100 mm x 100 mm) whose mass is accurately measured using a precision balance is covered with approximately 0.15 g of adhesive layer. The wire mesh is then folded five times with the adhesive layer facing inward to prevent leakage of the gel, and this is used as the sample. The mass is then accurately measured using a precision balance. (2) Immerse the obtained sample in 80 mL of ethyl acetate for 3 days. (3) Remove the sample, wash it with a small amount of ethyl acetate, and dry it at 120°C for 24 hours. Then, accurately measure the mass using a precision balance. (4) Calculate the gel fraction using the following formula. Gel fraction (unit: mass%) = (ZX) / (YX) × ​​100 However, X is the mass of the wire mesh (in grams), Y is the mass of the wire mesh with the adhesive layer attached before immersion (in grams), and Z is the mass of the wire mesh with the adhesive layer attached after immersion and drying (in grams).

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

[0105] -Thickness of the adhesive layer- The thickness of the adhesive layer of this disclosure is not particularly limited, but is 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 adhesive layer in this disclosure is 3 μm or more, the adhesive strength of the adhesive layer to the adherend tends to be more sufficiently high. When the thickness of the adhesive layer in this disclosure is 40 μm or less, cohesive failure of the adhesive layer tends to be less likely to occur around the protrusions of the adherend during three-dimensional molding.

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

[0107] [Overlaminate film] The overlaminate film of this disclosure comprises a surface protective film and an adhesive layer of this disclosure provided on one side of the surface protective film. The overlaminate film of this disclosure, having an adhesive layer of this disclosure, has high adhesive strength to the adherend and is less likely to cause appearance defects during three-dimensional molding.

[0108] The material of the substrate to which the overlaminate film of this disclosure is deposited is not particularly limited, and examples include resins (e.g., polyurethane resins) and metals (e.g., aluminum plates).

[0109] The adhesive layer of this disclosure has the physical properties of having 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. Before heat treatment at 120°C for 1 hour, the adhesive layer of this disclosure is soft due to its low degree of crosslinking and exhibits excellent adhesion to the adherend. Furthermore, after heat treatment at 120°C for 1 hour, the adhesive layer of this disclosure exhibits high cohesive force due to the progress of the crosslinking reaction. Therefore, the adhesive layer of this disclosure has high adhesive strength to the adherend and is less likely to cause appearance defects during three-dimensional molding. Accordingly, a preferred method of using the overlaminate film of this disclosure is, for example, to heat it after laminating it to the adherend, before three-dimensional molding, or during three-dimensional molding.

[0110] The material of the surface protective film is not particularly limited. Examples of surface protective films 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., triacetylcellulose), polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyurethane resins, (meth)acrylic resins, vinyl chloride resins, ABS (Acrylonitrile Butadiene Styrene) resins, and fluororesins. The surface protective film is preferably a film containing a polyurethane resin, for example, from the viewpoint of being able to suppress distortion of the molded part that may occur during three-dimensional molding.

[0111] The surface protective film may be colorless or colored, but it is preferable that it be colorless from the viewpoint of not interfering with the design of the decoration applied to the adherend. Furthermore, the surface protective film may be transparent or semi-transparent, but it is preferable that it be transparent so as not to obstruct the visibility of the decoration applied to the adherend. In this disclosure, "transparent" means that the average transmittance of visible light with wavelengths 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 side of the surface protective film on which the adhesive layer is provided may be subjected to surface treatments such as corona discharge treatment or plasma discharge treatment (so-called easy-adhesion treatments) from the viewpoint of improving the adhesion between the surface protective film and the adhesive layer.

[0113] The surface protective film may contain various additives such as crosslinking agents, crosslinking catalysts, plasticizers, heat stabilizers, UV absorbers, light stabilizers, antistatic agents, flame retardants, antioxidants, fillers, defoamers, and surfactants.

[0114] The thickness of the surface protective film is not particularly limited, but is preferably 20 μm to 100 μm, more preferably 25 μm to 90 μm, and even more preferably 30 μm to 80 μm.

[0115] In this disclosure, "thickness of the surface protective film" refers to the average thickness of the surface protective film. The average thickness of the surface protective film is determined by the following method. The thickness of the surface protective film is measured at five randomly selected points in the thickness direction using a constant-pressure thickness gauge (probe diameter: 5 mm). The arithmetic mean of the measured values ​​is calculated, and this value is taken as the average thickness of the surface protective film.

[0116] The surface protective film may be a single layer or may be formed from multiple layers. When a surface protective film is formed from multiple layers, the thickness of the surface protective film as described above refers to the total thickness of the multiple layers that make up the surface protective film.

[0117] The adhesive layer of the overlaminate film of this disclosure is the same as the adhesive layer of this disclosure described above, and the preferred embodiment is also the same; therefore, a description is omitted here.

[0118] In the overlaminate film of this disclosure, the exposed adhesive layer surface may be protected by a release sheet. Generally, the release sheet protects the surface of the adhesive layer until the overlaminate film is put into practical use and is peeled off at the time of use.

[0119] The release sheet is not particularly limited as long as it can be easily peeled off from the adhesive layer. Examples of release sheets include resin films, paper, synthetic paper, and composite sheets made by laminating two or more of these materials, all of which have been surface-treated with a release agent on one or both sides (so-called easy-peel treatment). In this disclosure, a release sheet in which one or both sides of a resin film are subjected to a surface treatment with a release agent (so-called easy-release treatment) is also referred to as a "release film." Examples of release agents include silicone-based release agents (e.g., silicone), wax-based release agents (e.g., paraffin wax), and fluorine-based release agents (e.g., fluorine-based resins). Examples of resin films include polyester films, such as polyethylene terephthalate (PET) film. Examples of paper include high-quality paper and coated paper. The film thickness of the release sheet is not particularly limited, but is generally between 20 μm and 180 μm.

[0120] Figure 1 is a schematic cross-sectional view showing an example of the configuration of the overlaminate film of this disclosure. The overlaminate film 10 shown in Figure 1 comprises a surface protection film 20 and an adhesive layer 30 provided on one side of the surface protection film 20. Details of the surface protection film 20 and the adhesive layer 30 are as previously described.

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

[0122] The overlaminate film of this disclosure is equipped with an adhesive layer, that is, an adhesive layer that has high adhesive strength to the adherend and is less likely to cause appearance defects during three-dimensional molding, and can therefore be suitably used not only for planar articles but also for three-dimensional articles. The overlaminate film of this disclosure can be used, for example, as a component of the license plate of this disclosure as described later. The overlaminate film of this disclosure can also be applied to the interior or exterior of vehicles such as automobiles, and to the interior of buildings such as walls, floors, and ceilings.

[0123] [How to make overlaminate film] The method for producing the overlaminate film described herein is not particularly limited. The overlaminate film of this disclosure can be prepared by known methods using a specific adhesive composition. Examples of methods for preparing the overlaminate film of this disclosure include the following:

[0124] A specific adhesive composition is applied to the easily adhesive treated surface of a base film that will serve as a surface protective film, thereby forming a coating film on the base film. Next, the formed coating film is dried to form an adhesive film on the base film. Then, the exposed surface of the formed adhesive film is laminated onto the easily peeled surface of a release sheet, thereby producing the overlaminate film of this disclosure having a laminated structure of base film (so-called surface protective film) / adhesive layer / release sheet.

[0125] Another method, for example, is as follows: A specific adhesive composition is applied to the easily removable 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. Next, the exposed surface of the formed adhesive film is laminated onto the easily removable surface of a base film that will serve as a surface protective film, thereby producing the overlaminate film of this disclosure having a laminated structure of base film (so-called surface protective film) / adhesive layer / release sheet.

[0126] The method of applying the specific adhesive composition is not particularly limited. Examples of known methods for applying specific adhesive compositions include gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, knife coaters, spray coaters, bar coaters, applicators, and the like. The amount of the specific adhesive composition applied is not particularly limited and can be appropriately set, for example, depending on the thickness of the adhesive layer to be formed.

[0127] The method for drying the coating film is not particularly limited. Methods for drying the coated film include, for example, natural drying, heat drying, hot air drying, and vacuum drying. The drying temperature and drying time of the coating film are not particularly limited and are set appropriately according to the thickness of the coating film, the amount of organic solvent in the coating film, etc. A preferred drying temperature for the coated film is, for example, 100°C to 120°C. 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 this disclosure comprises a plate base material and an overlaminate film of this disclosure provided on one side of the plate base material. The license plates described herein are equipped with the overlaminate film described herein, and therefore are less prone to appearance defects due to the use of the overlaminate film. Hereinafter, in the license plate of this disclosure, the "adhesive layer for the overlaminate film of this disclosure" provided in the overlaminate film of this disclosure will also be referred to as the "first adhesive layer."

[0129] The embodiments of the license plate of this disclosure are not particularly limited, as long as they comprise a plate base material and an overlaminate film of this disclosure provided on one side of the plate base material. However, for example, an embodiment is preferred in which the surface protective film provided on the overlaminate film of this disclosure is provided as the outermost layer of the license plate. Embodiments of the license plate of the present disclosure may, for example, be an embodiment in which the side of the first adhesive layer 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 its 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 enables adhesion of the image receiving layer 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 providing low-temperature impact resistance and printability. Furthermore, the image receiving layer preferably further contains a white pigment, 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. Furthermore, the second adhesive layer preferably further contains a pigment, from the viewpoint of improving the appearance of the license plate. If the license plate according to this 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 give the license plate an aesthetic appearance and is a layer that expresses patterns, designs, etc. As a method for forming the 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 has been formed by inkjet printing may be provided as a decorative layer on the image-receiving layer.

[0130] Figure 2 is a schematic cross-sectional view showing an example of the configuration of the license plate of this disclosure. The license plate 40 shown in Figure 2 comprises a plate base material 50 and an overlaminate film 10 provided on one side of the plate base material 50. The overlaminate film 10 comprises a surface protection film 20 and a first adhesive layer 30 provided on one side of the surface protection film 20. In the license plate 40, the side of the overlaminate film 10 facing the first adhesive layer 30 is in contact with one side of the plate base material 50. The license plate 40 also has a decorative layer 60 on the surface protection film 20 that constitutes the overlaminate film 10.

[0131] Figure 3 is a schematic cross-sectional view showing an example of another configuration of the license plate of this disclosure. The license plate 70 shown in Figure 3 comprises a plate base material 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 comprises a surface protection film 20 and a first adhesive layer 30 provided on one side of the surface protection film 20. In the license plate 70, the side of the image receiving film 100 facing the second adhesive layer 90 is in contact with one side of the plate base material 50. Also, in the license plate 70, the side of the overlaminate film 10 facing the first adhesive layer 30 is in contact with the side of the image receiving film 100 facing the image receiving layer 80. The license plate 70 has a decorative layer 60 on the surface protective film 20 that constitutes the overlaminate film 10. Furthermore, the license plate 70 has a decorative layer 60 on the image receiving layer 80 that constitutes the image receiving film 100. Details of the plate substrate 50 will be described later. Details of the overlaminate film 10, decorative layer 60, and image receiving film 100 are as previously described.

[0132] A metal plate or a resin plate can be used as the plate base material. Examples of metal sheets include aluminum sheets, stainless steel sheets, and iron sheets. Examples of resin sheets include polycarbonate sheets, polyester sheets, polyvinyl chloride sheets, acrylic sheets, ABS sheets, and PP sheets. The plate base material may be a metal plate or resin plate molded into a frame or the like.

[0133] The method for manufacturing license plates described herein is not particularly limited. The license plates described herein can be manufactured, for example, by the following method: First, the overlaminate film of this disclosure is bonded to a plate substrate before embossing with letters or the like. Next, the plate substrate to which the overlaminate film of this disclosure has been bonded is heated, and then the plate substrate is embossed, or the plate substrate to which the overlaminate film of this disclosure has been bonded is embossed while being heated. By doing so, the license plate of this disclosure can be manufactured. [Examples]

[0134] The adhesive layer of this disclosure will be described in more detail below with reference to examples. This disclosure is not limited to the following examples unless it exceeds the spirit of the disclosure.

[0135] [Production of (meth)acrylic polymer (A)] [Manufacturing example A-1] In a reactor equipped with a stirrer, reflux condenser, sequential dropper, and thermometer, 25% by 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), along with 45.0 parts by mass of ethyl acetate [organic solvent] and 0.015 parts by mass of 2,2'-azobisisobutyronitrile [AIBN; polymerization initiator] were added and heated, and polymerization was carried out at reflux temperature for 20 minutes. Next, to the polymerization reaction product in a reactor maintained at reflux temperature, 75% by mass of the remaining 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 sequentially added dropwise over 1.5 hours. The reaction was held for 1 hour to allow the polymerization to proceed. 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 sequentially added dropwise over 1 hour, and the polymerization reaction was allowed to proceed for a further 2 hours to obtain the polymerization reaction product. The obtained polymerization reaction product was diluted to a solid content concentration of 35% by mass using methyl ethyl ketone (MEK), cooled, and a solution of (meth)acrylic polymer A-1 was obtained.

[0136] Here, "solid content concentration" refers to the mass ratio of (meth)acrylic polymer A-1 to the solution of (meth)acrylic polymer A-1. The same applies to the solutions of (meth)acrylic polymers A-2 to A-5 prepared below.

[0137] [Manufacturing examples A-2 to A-5] In production examples A-2 to A-5, the same procedure as in production example A-1 was followed, except that the monomer composition of the (meth)acrylic polymer was changed to the monomer composition shown in Table 1, to obtain solutions of (meth)acrylic polymers A-2 to A-5, each with a solid content concentration of 35% by mass.

[0138] Table 1 shows the monomer composition [unit: mass%] and glass transition temperature (denoted as "Tg") [unit: °C] of (meth)acrylic polymers A-1 to A-5. The weight-average molecular weight of all (meth)acrylic polymers A-1 to A-5 was 600,000.

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

[0140] Of the (meth)acrylic polymers A-1 to A-5, (meth)acrylic polymers A-1 to A-3 correspond to the specified (meth)acrylic polymers in this disclosure.

[0141] [Table 1]

[0142] Details of each monomer listed in Table 1 are as follows: <(meth)acrylate alkyl monomer> "n-BA": n-butyl acrylate "MA": Methyl acrylate "2EHA": 2-ethylhexyl acrylate <Monomers with reactive functional groups> "AA": Acrylic acid (Type of reactive functional group: Carboxylic group)

[0143] In Table 1, a "-" in the monomer composition column indicates that the monomer corresponding to that column was not used.

[0144] [(Meth)acrylic polymer (B) production] [Manufacturing example B-1] In a reactor equipped with a stirrer, reflux condenser, sequential dropper, and thermometer, 20% by 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), along with 45.0 parts by mass of ethyl acetate [organic solvent] and 0.15 parts by mass of 2,2'-azobisisobutyronitrile [AIBN; polymerization initiator] were added and heated, and polymerization was carried out at reflux temperature for 20 minutes. In a reactor maintained at reflux temperature, 80% by mass of the remaining monomer mixture, 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 sequentially added dropwise over 1.5 hours to the polymerization reaction product. After holding for 1 hour, 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 sequentially added dropwise over 1 hour, and the polymerization reaction was continued for a further 2 hours to obtain the polymerization reaction product. The obtained polymerization reaction product was diluted to a solid content concentration of 36% by mass using methyl ethyl ketone (MEK), cooled, and a solution of (meth)acrylic polymer B-1 was obtained. In this context, "solid content concentration" refers to the mass ratio of (meth)acrylic polymer B-1 to the solution of (meth)acrylic polymer B-1.

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

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

[0147] [Preparation of adhesive composition] [Manufacturing example X-1] Adhesive composition X-1 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-1, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 4.4 parts by mass (solid content) of an isocyanate crosslinking agent [product name: Takenate B-820NP, blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.].

[0148] [Manufacturing example X-2] Adhesive composition X-2 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-2, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 4.4 parts by mass (solid content) of an isocyanate crosslinking agent [product name: Takenate B-820NP, blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.].

[0149] [Manufacturing example X-3] Adhesive composition X-3 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-3, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 4.4 parts by mass (solid content) of an isocyanate crosslinking agent [product name: Takenate B-820NP, blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.].

[0150] [Manufacturing example X-4] Adhesive composition X-4 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-1, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 2.7 parts by mass (solid content) of isocyanate crosslinking agent [product name: Duranate 17B-60P, blocked isocyanate compound, manufactured by Asahi Kasei Corporation].

[0151] [Manufacturing example X-5] Adhesive composition X-5 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-1, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 3.2 parts by mass (solid content) of an isocyanate crosslinking agent [product name: Duranate SBB-70P, blocked isocyanate compound, manufactured by Asahi Kasei Corporation].

[0152] [Manufacturing example X-6] Adhesive composition X-6 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-1, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 3.0 parts by mass (solid content) of an isocyanate crosslinking agent [product name: Duranate TPA-B80E, blocked isocyanate compound, manufactured by Asahi Kasei Corporation].

[0153] [Manufacturing example X-7] Adhesive composition X-7 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-1, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 3.2 parts by mass (solid content) of an isocyanate crosslinking agent [product name: Duranate SBN-70D, blocked isocyanate compound, manufactured by Asahi Kasei Corporation].

[0154] [Manufacturing example X-8] Adhesive composition X-8 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-1, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 2.2 parts by mass (solid content) of an isocyanate crosslinking agent [product name: Takenate B-820NP, blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.].

[0155] [Manufacturing example X-9] Adhesive composition X-9 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-1 and 15.0 parts by mass (solid content) of isocyanate crosslinking agent [product name: Takenate B-820NP, blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.].

[0156] [Manufacturing example X-10] Adhesive composition X-10 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-1, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 0.6 parts by mass (solid content) of an isocyanate crosslinking agent [product name: Takenate D-140N, non-blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.].

[0157] [Manufacturing example X-11] Adhesive composition X-11 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-4, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 4.4 parts by mass (solid content) of an isocyanate crosslinking agent [product name: Takenate B-820NP, blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.].

[0158] [Manufacturing example X-12] Adhesive composition X-12 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-5, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 4.4 parts by mass (solid content) of an isocyanate crosslinking agent [product name: Takenate B-820NP, blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.].

[0159] [Manufacturing example X-13] Adhesive composition X-13 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-1, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 0.3 parts by mass (solid content) of an isocyanate crosslinking agent [product name: Takenate D-140N, non-blocking isocyanate compound, manufactured by Mitsui Chemicals, Inc.].

[0160] [Manufacturing example X-14] Adhesive composition X-14 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-1, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 0.1 parts by mass (solid content) of epoxy crosslinking agent [product name: TETRAD-C, manufactured by Mitsubishi Gas Chemical Co., Ltd.].

[0161] [Manufacturing example X-15] Adhesive composition X-15 was obtained by stirring and mixing 100 parts by mass (solids equivalent) of (meth)acrylic polymer A-1, 15 parts by mass (solids equivalent) of (meth)acrylic polymer B-1, 2.9 parts by mass (solids equivalent) of isocyanate crosslinking agent [product name: Takenate B-820NP, blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.], and 0.03 parts by mass (solids equivalent) of epoxy crosslinking agent [product name: TETRAD-C, manufactured by Mitsubishi Gas Chemical Company, Inc.].

[0162] [Manufacturing example X-16] Adhesive composition X-16 was obtained by stirring and mixing 100 parts by mass (solid content) of (meth)acrylic polymer A-1, 15 parts by mass (solid content) of (meth)acrylic polymer B-1, and 0.4 parts by mass (solid content) of an isocyanate crosslinking agent [product name: Takenate B-820NP, blocked isocyanate compound, manufactured by Mitsui Chemicals, Inc.].

[0163] Of the adhesive compositions X-1 to X-16, adhesive compositions X-1 to X-10 correspond to the specified adhesive compositions in this disclosure.

[0164] The compositions of adhesive compositions X-1 to X-16 are shown in Table 2.

[0165] [Table 2]

[0166] The 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℃~120℃, manufactured by Mitsui Chemicals, Inc.] "Duranate 17B-60P" [Product name, blocked isocyanate compound, biuret form 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 form 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, nurate (trimer) of hexamethylene diisocyanate (HMDI), solid content: 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, nurate (trimer) 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] "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 terms, "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 concentration: 100% by mass, manufactured by Mitsubishi Gas Chemical Company, Inc.] 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: Rezamin NE-8836, one-component curing polycarbonate-based urethane resin, manufactured by Dainichi Seika Kogyo Co., Ltd.], 10 parts by mass of polyurethane resin 2 [product name: Rezamin NE-8811, one-component curing polycarbonate-based urethane resin, manufactured by Dainichi Seika Kogyo Co., Ltd.], 20 parts by mass of crosslinking agent [product name: Rezamin X-100, isocyanate-based crosslinking agent, manufactured by Dainichi Seika Kogyo Co., Ltd.], 0.1 parts by mass of crosslinking catalyst [product name: UA-38, 2-ethylhexyl tin, manufactured by Tokushiki Co., Ltd.], and diluent solvent [N,N-dimethylformamide] were stirred and mixed for 10 minutes using a disperser at an ambient temperature of 23°C to obtain a base film forming composition. Next, a base film forming composition was applied to the easily peeled surface of a release film [product name: P756050, polyethylene terephthalate (PET), thickness: 75 μm, manufactured by Lintec Corporation] that had been surface-treated with a silicone-based release agent (so-called easy-peel treatment), so that the thickness after drying would be 35 μm, and a coating film was formed. Then, the formed coating film was heated in a hot air circulation dryer at 100°C for 3 minutes, and then further heated at 160°C for 3 minutes to dry it, thereby producing a base film. Please note that "Rezamin" is a registered trademark.

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

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

[0171] [Examples 2-10] In Examples 2 to 10, the same procedure as in Example 1 was followed, except that the composition of the adhesive composition was changed to the composition shown 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.

[0172] [Examples 11-14] In Examples 11 to 14, the same procedure as in Example 1 was followed, except that the drying conditions for the formed coating film (i.e., drying temperature and drying time) were changed to those shown in Table 3. This yielded 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 procedure as in Example 1 was followed, except that the composition of the adhesive composition was changed to the composition shown in Table 4, 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.

[0174] [Comparative Examples 3-5] In Comparative Examples 3 to 5, the same procedure as in Example 1 was followed, except that 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. This yielded adhesive films for gel fraction measurement, 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 procedure as in Example 1 was followed, except that the drying conditions for the formed coating film (i.e., drying temperature and drying time) were changed to those shown in Table 4, to obtain adhesive films for gel fraction measurement (i.e., adhesive film for gel fraction measurement before heat treatment and adhesive film for gel fraction measurement after heat treatment) and an evaluation adhesive film.

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

[0177] [Preparation of the substrate] A printed plate was prepared as the substrate to be used for evaluation testing. Specifically, it was prepared according to the following procedures (1) to (3).

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

[0179] (2) Formation of the second adhesive layer A composition for forming the second adhesive layer was obtained by stirring and mixing 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 [product name: DAD-100, component: titanium dioxide, manufactured by DIC Corporation], 5.0 parts by mass of an isocyanate crosslinking agent [product name: Coronate L-45E, manufactured by Mitsubishi Gas Chemical Company, Inc.], and a diluent [ethyl acetate]. Next, the composition for forming the second adhesive layer was applied to the easily peeled surface of a release film [product name: PET75GS, material: polyethylene terephthalate (PET), thickness: 75 μm, manufactured by Lintec Corporation] that had been surface-treated with a silicone-based release agent (so-called easy-peel treatment) to form a coated film with a dry thickness of 40 μm. Next, the formed coating film was dried by heating it at 100°C for 1 minute using a hot air circulation dryer, thereby forming a second adhesive layer on the release film. Please note that "Coronate" is a registered trademark.

[0180] (3) Preparation of printing plates An image-receiving film was fabricated by bonding the exposed surface of the image-receiving layer formed above to the exposed surface of the second adhesive layer. Next, under ambient 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 bonded to an aluminum plate. Then, the release film on the image-receiving layer side of the image-receiving film was peeled off, and a solid cyan and yellow print was applied to 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 way, a printed plate having the configuration of decorative layer / image-receiving layer / second adhesive layer / aluminum plate was fabricated.

[0181] [evaluation] 1. Adhesive strength The evaluation adhesive film prepared as described above was cut to a size of 25 mm x 150 mm (long side), and the release film was peeled off. Next, the side of the adhesive layer exposed by peeling was placed on the exposed side of the decorative layer on the printing plate prepared as described above, and then bonded by passing a 2 kg roller back and forth twice. The resulting laminate was then heat-treated at 120°C for 1 hour using a hot air circulation dryer to obtain a sample for adhesive strength evaluation testing. For this adhesion strength evaluation test sample, the adhesion strength (unit: N / 25mm) was measured when the evaluation adhesive film (composition: base film / adhesive layer) was peeled from the printing plate at a 180° angle along the long side (150mm) using a method compliant with JIS Z 0237:2000. Specifically, a single-column type material testing machine [model number: RTG-1310] manufactured by A&D Co., Ltd. was used as the measuring device, and measurements were taken under conditions of an ambient temperature of 23°C, 50% RH, and a peeling speed of 300 mm / min. The adhesion strength to the adherend was then evaluated according to the evaluation criteria below. The results are shown in Tables 3 and 4. In the evaluation criteria below, "A" and "B" represent a usable level, 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 three-dimensional molding 2-1. Cohesive failure The evaluation adhesive film prepared as described 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 on the printing plate prepared as described above, and then bonded by passing a 2 kg roller back and forth twice. The laminate obtained by this bonding was heat-treated at 120°C for 1 hour using a hot air circulation dryer to obtain a sample for cohesive failure evaluation test. A DuPont impact test was performed on this cohesive failure evaluation sample from the aluminum plate side under the following conditions.

[0184] <DuPont Impact Test Conditions> Falling weight: 1kg Drop height: 50cm Receiving jig: recessed R shape 1 / 4 inch Impact point: Flat tip shape, 1 / 2 inch diameter, 3 / 8 inch tip diameter

[0185] After the test, the stretched and deformed portions of the evaluation adhesive film (composition: base film / adhesive layer) were observed using an optical microscope. The presence and extent of air bubbles in the adhesive layer were then checked, and the state of cohesive failure was evaluated according to the evaluation criteria below. The results are shown in Tables 3 and 4. The formation of bubbles in the adhesive layer indicates that cohesive failure is occurring in the adhesive layer. In the evaluation criteria below, "A" and "B" represent a usable level, with "A" being the most preferable.

[0186] -Evaluation Criteria- A: No air bubbles were observed in the adhesive layer (see Figure 4A). B: A small amount of air bubbles were observed in the adhesive layer (see Figure 4B). C: Significant bubble formation is observed in the adhesive layer (see Figure 4C).

[0187] 2-2. Peeling The evaluation adhesive film prepared as described above was cut to a size of 50 mm x 35 mm, and the release film was peeled off. Next, the side of the adhesive layer exposed by peeling was placed on the exposed side of the decorative layer on the printing plate prepared as described above, and then laminated using a laminator. The resulting laminate was then heat-treated at 120°C for 1 hour using a hot air circulation dryer to obtain a sample for peel evaluation testing. For the sample for the peeling evaluation test, using a press machine, under the condition of a press pressure of 1.3 t, embossing of characters was performed using a mold with a size of 50 mm × 35 mm. An example of the embossing of characters is shown in Fig. 5. Next, for the sample for the peeling evaluation test 24 hours after the embossing, using a hot air circulation dryer, heat treatment was performed at 120 °C for 10 minutes. After the heat treatment, the edge of the embossed characters was visually observed, and the presence and degree of lifting of the adhesive film (composition: base film / adhesive layer) were confirmed. Then, according to the following evaluation criteria, the state of peeling was evaluated. The results are shown in Tables 3 and 4. In the following evaluation criteria, "A" and "B" are practical levels, and "A" is most preferable.

[0188] - Evaluation Criteria - A: No lifting is observed at the edge of the embossed characters. B: A slight lifting is observed at the edge of the embossed characters. C: A significant lifting is observed at the edge of the embossed characters.

[0189]

Table 3

[0190]

Table 4

[0191] As shown in Table 3, it was confirmed that the adhesive layers of Examples 1 to 14 had a high adhesive force to the adherend. Also, it was confirmed that the adhesive layers of Examples 1 to 14 were less likely to cause cohesive failure and peeling around the convex portions of the adherend during three-dimensional molding, and were less likely to cause appearance defects. On the other hand, as shown in Table 4, it was confirmed that the adhesive layers of Comparative Examples 1 to 8 were inferior to the adhesive layers of Examples 1 to 14 in at least one of the evaluation results of the adhesive force to the adherend and the cohesive failure and peeling around the convex portion of the adherend during three-dimensional molding.

Explanation of Signs

[0192] 10: Overlaminate film 20: Surface protection film 30: Adhesive layer (first adhesive layer) 40, 70: Number plate 50: Plate base material 6o: Decoration layer 80: Image receiving layer 90: Second adhesive layer 100: Image receiving film

Claims

1. The adhesive is formed from a (meth)acrylic polymer having reactive functional groups and a glass transition temperature of -45°C to -5°C, and an isocyanate crosslinking agent. An adhesive layer for overlaminate film, wherein the gel fraction after heating at 120°C for 1 hour is 60% by mass or more, and the gel fraction before heating at 120°C for 1 hour is 30% by mass or less.

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

3. The adhesive layer for overlaminate film according to claim 1, wherein 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.

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

5. Surface protective film, An adhesive layer for overlaminate film according to any one of claims 1 to 4 is provided on one side of the surface protective film, An overlaminate film equipped with [specific feature].

6. Plate substrate and An overlaminate film according to claim 5 provided on one side of the plate substrate, A license plate equipped with [a specific feature / feature].

Images