JP2024063934A - Adhesive Film - Google Patents

Abstract

[Problem] To provide an adhesive film that can adhere to various three-dimensional surfaces such as rough surfaces, curved surfaces, and corners, and can provide an excellent metallic appearance. [Solution] An adhesive film in one embodiment includes a clear film layer and an acrylic pressure-sensitive adhesive layer, and exhibits a metallic appearance. The acrylic pressure-sensitive adhesive layer includes an acrylic adhesive polymer and a resin-coated metal pigment, the glass transition temperature of the acrylic adhesive polymer is -25°C or lower, and the acrylic pressure-sensitive adhesive layer includes 5 to 100 parts by mass of the resin-coated metal pigment based on 100 parts by mass of the acrylic adhesive polymer. [Selected Figure] Figure 1

Description

This disclosure relates to adhesive films.

Adhesive films with a metallic appearance are widely used in markings for vehicles, ships, aircraft, etc., interior and exterior decoration of buildings, illuminated signs, etc. Such adhesive films are generally laminates containing a film layer and a pressure-sensitive adhesive layer, and the film layer, the pressure-sensitive adhesive layer, or any other intermediate layer contains a metallic pigment, or a metal layer such as a metal plating, a metal vapor deposition film, or a metal foil is disposed on the surface of the film layer or between the layers that make up the adhesive film.

Patent document 1 (JP 2006-88593 A) describes a decorative metallic adhesive sheet that is "characterized in that it is made up of an acrylic resin layer (A) that contains an ultraviolet absorber and has a total light transmittance of 85% or more for visible light, a metallic adhesive layer (B) in which an acrylic adhesive contains aluminum metal powder and a pearl pigment, a colored soft vinyl chloride resin layer (C), and an acrylic adhesive layer (D) that are laminated in this order."

JP 2006-88593 A

The surfaces to which the adhesive film is applied, such as the interior or exterior walls of a building, are often rough. The adhesive film may be applied not only to flat surfaces, but also to curved surfaces or corners.

The present disclosure provides an adhesive film that can adhere to a variety of three-dimensional surfaces, including rough surfaces, curved surfaces, and corners, and can provide an excellent metallic appearance.

Generally, metal pigments used to impart a metallic appearance, such as aluminum pigments, have low compatibility with pressure-sensitive adhesives. The inventors have discovered that metal pigments with a resin coating have excellent compatibility with pressure-sensitive adhesives, and can impart a metallic appearance to the pressure-sensitive adhesive layer while maintaining adhesion and extensibility.

According to one embodiment, an adhesive film with a metallic appearance is provided, which includes a clear film layer and an acrylic pressure-sensitive adhesive layer, the acrylic pressure-sensitive adhesive layer includes an acrylic adhesive polymer and a resin-coated metal pigment, the glass transition temperature of the acrylic adhesive polymer is -25°C or lower, and the acrylic pressure-sensitive adhesive layer includes 5 to 100 parts by mass of the resin-coated metal pigment based on 100 parts by mass of the acrylic adhesive polymer.

The present disclosure provides an adhesive film that can adhere to a variety of three-dimensional surfaces, including rough surfaces, curved surfaces, and corners, and can provide an excellent metallic appearance.

The above description should not be construed as disclosing all embodiments of the present invention and all advantages associated with the present invention.

FIG. 1 is a schematic cross-sectional view of an adhesive film according to one embodiment.

The present invention will be described in more detail below with reference to the drawings to illustrate representative embodiments of the present invention, but the present invention is not limited to these embodiments.

In this disclosure, "(meth)acrylic" means acrylic or methacrylic, and "(meth)acrylate" means acrylate or methacrylate.

In this disclosure, "film" also includes articles called "sheets."

In this disclosure, "pressure-sensitive adhesion" refers to the property of a material or composition that adheres to a variety of surfaces with only slight pressure applied for a short period of time within the operating temperature range, e.g., from 0°C to 50°C, and does not exhibit a phase change (liquid to solid). In this disclosure, "adhesive" is used interchangeably with "pressure-sensitive adhesion."

The adhesive film of one embodiment includes a clear film layer and an acrylic pressure-sensitive adhesive layer, and exhibits a metallic appearance. The acrylic pressure-sensitive adhesive layer includes an acrylic adhesive polymer and a resin-coated metal pigment. The resin-coated metal pigment imparts a metallic appearance to the acrylic pressure-sensitive adhesive layer that can be seen through the clear film layer of the adhesive film.

The clear film layer and the acrylic pressure-sensitive adhesive layer may be in direct contact with each other, or other layers, such as a colored layer, a printed layer, a bulk layer, etc., may be interposed between these layers. Other layers, such as a colored layer, a printed layer, a bulk layer, a surface protection layer, etc., may be laminated on the clear film layer. The adhesive film may further have other functional layers, such as a primer layer that enhances the adhesion between the clear film layer and the acrylic pressure-sensitive adhesive layer. The surface of the clear film layer that comes into contact with the acrylic pressure-sensitive adhesive layer may be subjected to a surface treatment, such as a corona treatment or a plasma treatment.

The adhesive film may have a liner on the surface of the acrylic pressure-sensitive adhesive layer opposite the clear film layer. Liners, which are optional components, include, for example, plastic materials such as polyethylene, polypropylene, polyester, and cellulose acetate, paper, and laminated paper containing the plastic materials. These liners may have a surface that has been treated for release with silicone or the like. The thickness of the liner can usually be about 10 μm or more, or about 25 μm or more, and about 500 μm or less, or about 200 μm or less.

Figure 1 shows a schematic cross-sectional view of an adhesive film of one embodiment. The adhesive film 10 has a clear film layer 12, an acrylic pressure-sensitive adhesive layer 14, and optionally a liner 16. The acrylic pressure-sensitive adhesive layer 14 includes an acrylic adhesive polymer 142 and a resin-coated metal pigment 144 dispersed in the acrylic adhesive polymer 142.

As the clear film layer, for example, a plastic film such as a polyethylene film, a polypropylene film, a polyester film, an acrylic resin film, a polycarbonate film, a polyvinyl chloride film, a polyvinylidene chloride film, a polyurethane film, a polystyrene film, or a polyamide film can be used.

The thickness of the clear film layer may vary, for example, from about 5 μm or more, about 10 μm or more, or about 20 μm or more, to about 500 μm or less, about 300 μm or less, or about 200 μm or less.

In one embodiment, the visible light transmittance of the clear film layer is about 70% or more, about 80% or more, or about 90% or more. In this disclosure, "visible light transmittance" means the average visible light transmittance at wavelengths of 380 nm to 780 nm measured in accordance with JIS A 5759:2008.

The acrylic pressure-sensitive adhesive layer contains an acrylic adhesive polymer and a resin-coated metal pigment.

The acrylic adhesive polymer can be obtained by polymerizing or copolymerizing a polymerizable composition containing a (meth)acrylic monomer and, if necessary, other monomers having a monoethylenically unsaturated group. In this disclosure, the (meth)acrylic monomer and the other monomers having a monoethylenically unsaturated group are collectively referred to as the polymerizable component. The (meth)acrylic monomer and the other monomers having a monoethylenically unsaturated group may each be used alone, or two or more of them may be used in combination.

The (meth)acrylic monomer generally comprises an alkyl (meth)acrylate. The alkyl group of the alkyl (meth)acrylate may have 1 to 12 carbon atoms. Examples of the alkyl (meth)acrylate include linear or branched alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-methylbutyl (meth)acrylate, isoamyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, and n-dodecyl (meth)acrylate; and alicyclic (meth)acrylates such as cyclohexyl (meth)acrylate, 4-t-butylcyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. The alkyl (meth)acrylate preferably includes methyl acrylate, n-butyl acrylate, 2-methylbutyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, or a combination thereof.

The alkyl (meth)acrylate constitutes the main component of the acrylic adhesive polymer. In one embodiment, the acrylic adhesive polymer is obtained by copolymerizing a polymerizable composition containing alkyl (meth)acrylate in an amount of about 50% by mass or more, about 70% by mass or more, or about 80% by mass or more, about 99.5% by mass or less, about 99% by mass or less, or about 98% by mass or less, based on the mass of the polymerizable component, and contains structural units derived from alkyl (meth)acrylate in the above mass ratio.

The (meth)acrylic monomer may include aromatic (meth)acrylates such as phenyl (meth)acrylate and p-tolyl (meth)acrylate; phenoxyalkyl (meth)acrylates such as phenoxyethyl (meth)acrylate; alkoxyalkyl (meth)acrylates such as methoxypropyl (meth)acrylate and 2-methoxybutyl (meth)acrylate; or cyclic ether-containing (meth)acrylates such as glycidyl (meth)acrylate and tetrahydrofurfuryl (meth)acrylate.

The (meth)acrylic monomer or other monomer having a monoethylenically unsaturated group may include a polar monomer copolymerizable with the alkyl (meth)acrylate. Examples of polar monomers include carboxyl group-containing monomers such as (meth)acrylic acid, monohydroxyethyl phthalate (meth)acrylate, β-carboxyethyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, crotonic acid, itaconic acid, fumaric acid, citraconic acid, and maleic acid; aminoalkyl (meth)acrylates such as aminoethyl (meth)acrylate; monoalkylaminoalkyl (meth)acrylates such as butylaminoethyl (meth)acrylate; dialkylaminoalkyl (meth)acrylates such as N,N-dimethylaminoethyl acrylate (DMAEA) and N,N-dimethylaminoethyl methacrylate (DMAEMA); Examples of such monomers include amino group-containing monomers such as acrylate, dialkylaminoalkyl (meth)acrylamides such as N,N-dimethylaminopropyl acrylamide (DMAPAA) and N,N-dimethylaminopropyl methacrylamide, dialkylaminoalkyl vinyl ethers such as N,N-dimethylaminoethyl vinyl ether and N,N-diethylaminoethyl vinyl ether; amide group-containing monomers such as (meth)acrylamide, N-vinylpyrrolidone, and N-vinylcaprolactam; hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and unsaturated nitriles such as (meth)acrylonitrile. These polar monomers can increase the cohesive strength of the pressure-sensitive adhesive layer and improve the adhesive strength.

Other monomers having monoethylenically unsaturated groups include, for example, aromatic vinyl monomers such as styrene, α-methylstyrene, and vinyl toluene; and vinyl esters such as vinyl acetate.

The acrylic adhesive polymer is preferably a carboxy group-containing (meth)acrylic polymer. The carboxy group-containing (meth)acrylic polymer can be obtained by copolymerizing a polymerizable composition containing a carboxy group-containing monomer as a polymerizable component. The carboxy group-containing (meth)acrylic polymer can increase the cohesive strength and improve the adhesive strength due to the presence of the carboxy group. The carboxy group-containing (meth)acrylic polymer can also increase the adhesion between the clear film layer and the acrylic pressure-sensitive adhesive layer. The carboxy group-containing monomer is preferably (meth)acrylic acid.

In one embodiment, the carboxy group-containing (meth)acrylic polymer is obtained by copolymerizing a polymerizable composition containing a carboxy group-containing monomer in an amount of about 0.5% by mass or more, about 1% by mass or more, or about 2% by mass or more, about 15% by mass or less, about 10% by mass or less, or about 8% by mass or less, based on the mass of the polymerizable component, and contains constitutional units derived from the carboxy group-containing monomer in the above mass ratio.

The polymerization or copolymerization of the acrylic adhesive polymer can be carried out by radical polymerization. As radical polymerization, known polymerization methods such as solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization can be used. It is advantageous to use solution polymerization, which can easily synthesize high molecular weight polymers. As a polymerization initiator, for example, organic peroxides such as benzoyl peroxide, lauroyl peroxide, and bis(4-tert-butylcyclohexyl)peroxydicarbonate; or azo polymerization initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), dimethyl-2,2-azobis(2-methylpropionate), 4,4'-azobis(4-cyanovaleric acid), dimethyl 2,2'-azobis(2-methylpropionate), and azobis(2,4-dimethylvaleronitrile) (AVN) can be used. The amount of the polymerization initiator used is generally about 0.01 parts by mass or more, or about 0.05 parts by mass or more, and about 5 parts by mass or less, or about 3 parts by mass or less, per 100 parts by mass of the polymerizable component.

The glass transition temperature (Tg) of the acrylic adhesive polymer is about -25°C or less. By making the glass transition temperature of the acrylic adhesive polymer about -25°C or less, the acrylic pressure-sensitive adhesive layer can be imparted with pressure-sensitive adhesive properties at the use temperature (e.g., 5°C to 35°C) even when combined with a resin-coated metal pigment in an amount sufficient to give a metallic appearance. In one embodiment, the glass transition temperature of the acrylic adhesive polymer is about -30°C or less, or about -35°C or less. In one embodiment, the glass transition temperature of the acrylic adhesive polymer is about -70°C or more, about -65°C or more, or about -60°C or more. By making the glass transition temperature of the acrylic adhesive polymer about -70°C or more, the pressure-sensitive adhesive layer can be imparted with adhesive strength and holding strength.

を用いて計算ガラス転移温度として求めることができる。式中、Ｔｇ_ｉは成分ｉのホモポリマーのガラス転移温度（℃）、Ｘ_ｉは重合の際に添加した成分ｉのモノマーの質量分率をそれぞれ示し、ｉは１～ｎの自然数であり、

である。 The glass transition temperature (Tg) of acrylic adhesive polymers is calculated by the following FOX formula (Fox, TG, Bull. Am. Phys. Soc., 1 (1956), p. 123), assuming that each polymer is copolymerized with n kinds of monomers.

In the formula, Tg _i is the glass transition temperature (° C.) of a homopolymer of component i, X _i is the mass fraction of the monomer of component i added during polymerization, and i is a natural number from 1 to n.

It is.

In one embodiment, the weight average molecular weight (Mw) of the acrylic adhesive polymer is about 150,000 or more, about 200,000 or more, or about 250,000 or more, and about 2,000,000 or less, about 1,500,000 or less, or about 1,000,000 or less. In this disclosure, "weight average molecular weight" means the molecular weight calculated using standard polystyrene by gel permeation chromatography (GPC).

Resin-coated metal pigments are pigments in which at least a portion of the surface of the metal pigment is coated with resin, and have excellent miscibility with acrylic adhesive polymers. By using resin-coated metal pigments, it is possible to impart a metallic appearance to the acrylic pressure-sensitive adhesive layer while maintaining adhesion and extensibility. Resin-coated metal pigments may be used alone or in combination of two or more types.

The metal contained in the resin-coated metal pigment is not particularly limited, and examples include aluminum, zinc, iron, magnesium, copper, nickel, and alloys thereof. It is preferable that the resin-coated metal pigment contains aluminum, since it can effectively provide metallic luster with a smaller amount used and is inexpensive.

The material constituting the resin coating of the resin-coated metal pigment is not particularly limited, and examples include acrylic resins, polyolefins, polybutadiene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, fluororesins, polyvinyl ethers, polystyrene, and copolymers and blends thereof. It is preferable that the resin-coated metal pigment has an acrylic resin coating because of its excellent miscibility with acrylic adhesive polymers.

The shape of the resin-coated metal pigment is not particularly limited, and examples include flake, sphere, needle, and lump shapes. It is preferable that the resin-coated metal pigment is flake-shaped, since it can effectively provide metallic luster with a smaller amount used.

In one embodiment, the average particle size of the resin-coated metal pigment is about 5 μm or more, about 7 μm or more, or about 10 μm or more, and about 70 μm or less, about 50 μm or less, or about 40 μm or less. By setting the average particle size of the resin-coated metal pigment to the above range, the resin-coated metal pigment can be more uniformly dispersed in the acrylic pressure-sensitive adhesive layer. The average particle size of the resin-coated metal pigment is the volume cumulative particle size _D50 , which can be determined using laser diffraction/scattering particle size distribution measurement.

The acrylic pressure-sensitive adhesive layer contains about 5 parts by mass or more and about 100 parts by mass or less of the resin-coated metal pigment based on 100 parts by mass of the acrylic adhesive polymer. By making the content of the resin-coated metal pigment about 5 parts by mass or more, it is possible to impart a metallic appearance to the entire acrylic pressure-sensitive adhesive layer. By making the content of the resin-coated metal pigment about 100 parts by mass or less, it is possible to maintain the adhesiveness and extensibility of the acrylic pressure-sensitive adhesive layer. In one embodiment, the acrylic pressure-sensitive adhesive layer contains about 6 parts by mass or more, or about 8 parts by mass or more, and about 50 parts by mass or less, or about 30 parts by mass or less of the resin-coated metal pigment based on 100 parts by mass of the acrylic adhesive polymer.

In one embodiment, the content of the pigment other than the resin-coated metal pigment in the acrylic pressure-sensitive adhesive layer is less than about 5 parts by weight, less than about 3 parts by weight, or less than about 1 part by weight based on 100 parts by weight of the acrylic adhesive polymer. By making the content of the pigment other than the resin-coated metal pigment in the acrylic pressure-sensitive adhesive layer less than about 5 parts by weight, the quality of the metallic appearance of the acrylic pressure-sensitive adhesive layer can be improved.

The acrylic pressure-sensitive adhesive layer may further contain a dispersant that enhances the dispersibility of the resin-coated metal pigment in the acrylic adhesive polymer. Examples of dispersants include low-molecular dispersants including anionic compounds, cationic compounds, and nonionic compounds, and polymer dispersants having anionic, cationic, or nonionic polar groups. The dispersants may be used alone or in combination of two or more.

The dispersant preferably has a basic group. A dispersant having a basic group can more effectively disperse the resin-coated metal pigment in the acrylic adhesive polymer. In an embodiment in which the acrylic adhesive polymer includes a carboxyl group-containing (meth)acrylic polymer, the dispersant having a basic group can also interact with the carboxyl group-containing (meth)acrylic polymer to increase the cohesive strength of the acrylic pressure-sensitive adhesive layer, thereby increasing the adhesive strength and holding strength of the acrylic pressure-sensitive adhesive layer.

In one embodiment, the low molecular weight dispersant includes at least one selected from the group consisting of piperidyl compounds and benzotriazole compounds. The piperidyl compounds and benzotriazole compounds can further improve the dispersibility of the resin-coated metal pigment. In an embodiment in which the acrylic adhesive polymer includes a carboxyl group-containing (meth)acrylic polymer, the triazole ring or piperidine ring of the piperidyl compound and benzotriazole compound interacts with the carbonyl group of the carboxyl group-containing (meth)acrylic polymer to increase the cohesive strength of the acrylic pressure-sensitive adhesive layer, thereby increasing the adhesive strength and holding strength of the acrylic pressure-sensitive adhesive layer.

It is preferable that the piperidyl compound has at least two piperidyl groups, and these piperidyl groups are bonded via a divalent linking group having 4 or more, 6 or more, or 8 or more carbon atoms. A piperidyl compound in which piperidyl groups are bonded via a divalent linking group having 4 or more, 6 or more, or 8 or more carbon atoms has excellent compatibility with acrylic adhesive polymers.

The piperidyl compound may be one that can be used as a hindered amine light stabilizer (HALS). By using a hindered amine light stabilizer as the piperidyl compound, it is possible to impart ultraviolet resistance to the acrylic pressure-sensitive adhesive layer.

Examples of piperidyl compounds include bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)-[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl [1,2,2,6,6-pentamethyl-4-piperidyl)butane-1,2,3,4-tetracarboxylate, and tetrakis(2,2,6,6-tetramethyl-4-piperidyl)butane-1,2,3,4-tetracarboxylate.

The benzotriazole compound is preferably a 2H-benzotriazole compound, more preferably one having a substituted or unsubstituted hydroxyphenyl group at the 2-position. 2H-benzotriazole compounds, particularly 2H-benzotriazole compounds having a substituted or unsubstituted hydroxyphenyl group at the 2-position, have excellent compatibility with acrylic adhesive polymers.

The benzotriazole compound may be one that can be used as an ultraviolet absorber (UVA). By using a benzotriazole compound that has ultraviolet absorbing properties, it is possible to impart ultraviolet resistance to the acrylic pressure-sensitive adhesive layer.

Examples of benzotriazole compounds include 2-(2H-benzotriazole-2-yl)-p-cresol, 2-(2H-benzotriazole-2-yl)-4-methylphenol, 2-(2H-benzotriazole-2-yl)-4-methyl-6-(linear or branched)dodecylphenol, 2-(2H-benzotriazole-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol, 2-(5-chloro-2H-benzotriazole-2-yl)-6-(1,1 -dimethylethyl)-4-methylphenol, 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol, 2,2'-methylene-bis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol], and C7-9 branched and linear alkyl esters of 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoic acid.

In one embodiment, the polymer dispersant includes an amino group-containing (meth)acrylic polymer. The amino group-containing (meth)acrylic polymer not only enhances the dispersibility of the resin-coated metal pigment, but also has excellent compatibility with (meth)acrylic polymers having acidic groups such as carboxy groups. The amino group-containing (meth)acrylic polymer can be obtained by copolymerizing a polymerizable composition containing an amino group-containing monomer as a polymerizable component, among the polymerizable compositions described in relation to the acrylic adhesive polymer. As the amino group-containing monomer, a dialkylaminoalkyl (meth)acrylate such as N,N-dimethylaminoethyl acrylate (DMAEA) or N,N-dimethylaminoethyl methacrylate (DMAEMA) is preferred.

In one embodiment, the amino group-containing (meth)acrylic polymer is obtained by copolymerizing a polymerizable composition containing an amino group-containing monomer in an amount of about 0.5% by mass or more, about 1% by mass or more, or about 3% by mass or more, about 20% by mass or less, about 15% by mass or less, or about 10% by mass or less, based on the mass of the polymerizable component, and contains constitutional units derived from the amino group-containing monomer in the above mass ratio.

In one embodiment, the glass transition temperature (Tg) of the amino group-containing (meth)acrylic polymer is about 0° C. or more, about 20° C. or more, or about 40° C. or more, and about 150° C. or less, about 135° C. or less, or about 120° C. or less. The glass transition temperature of the amino group-containing (meth)acrylic polymer can be determined using the FOX formula in the same manner as the acrylic adhesive polymer.

The weight average molecular weight of the amino group-containing (meth)acrylic polymer is not particularly limited, and can be, for example, about 1,000 or more, about 5,000 or more, about 10,000 or more, about 200,000 or less, about 100,000 or less, or about 80,000 or less.

The content of the dispersant in the acrylic pressure-sensitive adhesive layer can be about 10 parts by weight or more, about 20 parts by weight or more, or about 40 parts by weight or more, about 500 parts by weight or less, about 300 parts by weight or less, or about 250 parts by weight or less, per 100 parts by weight of the resin-coated metal pigment.

The acrylic pressure-sensitive adhesive layer can be formed on the clear film layer, on other layers constituting the laminate including the clear film layer, or on the liner using a pressure-sensitive adhesive composition containing an acrylic adhesive polymer and a resin-coated metal pigment, and optionally a dispersant, a crosslinker, a solvent, and/or other additives.

The crosslinking agent is not particularly limited as long as it can form a crosslink between the polymer chains of the acrylic adhesive polymer. By using a crosslinking agent, the cohesive strength of the acrylic pressure-sensitive adhesive layer can be increased, and thus the adhesive strength and holding strength of the acrylic pressure-sensitive adhesive layer can be increased. For example, when the acrylic adhesive polymer is a carboxy group-containing (meth)acrylic polymer, the crosslinking agent can be an epoxy crosslinking agent, a bisamide crosslinking agent, an aziridine crosslinking agent, a carbodiimide crosslinking agent, an isocyanate crosslinking agent, or the like. The crosslinking agents may be used alone or in combination of two or more.

Epoxy crosslinking agents include, for example, N,N,N',N'-tetraglycidyl-1,3-benzenedi(methaneamine) (trade names include TETRAD-X (Mitsubishi Gas Chemical Company, Inc., Chiyoda-ku, Tokyo, Japan), E-AX and E-5XM (all from Soken Chemical & Engineering Co., Ltd., Toshima-ku, Tokyo, Japan)), and N,N'-(cyclohexane-1,3-diylbismethylene)bis(diglycidylamine) (trade names include TETRAD-C (Mitsubishi Gas Chemical Company, Inc., Chiyoda-ku, Tokyo, Japan), and E-5C (Soken Chemical & Engineering Co., Ltd., Toshima-ku, Tokyo, Japan)).

Examples of bisamide crosslinking agents include 1,1'-(1,3-phenylenedicarbonyl)bis(2-methylaziridine), 1,4-bis(ethyleneiminocarbonylamino)benzene, 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane, and 1,8-bis(ethyleneiminocarbonylamino)octane.

Examples of aziridine-based crosslinking agents include 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate (trade names: Chemitite (registered trademark) PZ-33 (Nippon Shokubai Co., Ltd., Osaka City, Osaka, Japan) and Crosslinker CX-100 (DSM Coating Resins B.V., Zwolle, Kingdom of the Netherlands).

Examples of carbodiimide crosslinking agents include Carbodilite V-03, V-05, and V-07 (all from Nisshinbo Chemical Inc., Chuo-ku, Tokyo, Japan).

Examples of isocyanate-based crosslinking agents include Coronate L and Coronate HK (both manufactured by Tosoh Corporation, Minato-ku, Tokyo, Japan).

The crosslinking agent can be used in an amount of about 0.01 parts by weight or more, about 0.02 parts by weight or more, or about 0.05 parts by weight or more, about 0.5 parts by weight or less, about 0.4 parts by weight or less, or about 0.3 parts by weight or less, based on 100 parts by weight of the acrylic adhesive polymer.

Examples of solvents include methanol, ethanol, hexane, heptane, toluene, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, etc., or mixtures of these solvents.

Other additives include, for example, ultraviolet absorbers, antioxidants, heat stabilizers, fillers, and tackifiers.

The thickness of the acrylic pressure-sensitive adhesive layer is not particularly limited, and can be, for example, about 5 μm or more, about 10 μm or more, or about 20 μm or more, and about 200 μm or less, about 100 μm or less, or about 80 μm or less.

The adhesive film can be produced by a known method. For example, the pressure-sensitive adhesive composition is applied to a liner by knife coating, bar coating, or the like, and dried to form an acrylic pressure-sensitive adhesive layer. In order to react with the optional crosslinking agent, the acrylic pressure-sensitive adhesive layer may be heated using hot air, an oven, or the like during drying. A clear film layer or a laminate including a clear film layer can be laminated on the obtained acrylic pressure-sensitive adhesive layer by a method such as dry lamination to produce an adhesive film. The pressure-sensitive adhesive composition can also be applied directly onto the clear film layer or onto another layer constituting the laminate including the clear film layer, and then dried to produce an adhesive film.

The acrylic pressure-sensitive adhesive layer may be solid, porous, or foamed. The adhesive surface of the acrylic pressure-sensitive adhesive layer may be flat or may have irregularities. The irregular adhesive surface includes an adhesive surface in which convex portions containing solids or reactants of the pressure-sensitive adhesive composition and concave portions surrounding the convex portions are formed on the adhesive surface of the acrylic pressure-sensitive adhesive layer, and in a state where the adhesive surface is adhered to an adherend, a communication path defined by the concave portions and communicating with the outside is formed between the adherend surface and the adhesive surface. An example of a method for forming an irregular adhesive surface is described below.

A liner is prepared with a release surface having a predetermined uneven structure. A pressure-sensitive adhesive composition is applied to the release surface of the liner and heated as necessary to form an acrylic pressure-sensitive adhesive layer. This transfers the uneven structure (negative structure) of the liner to the surface of the acrylic pressure-sensitive adhesive layer that comes into contact with the liner (this becomes the adhesive surface of the adhesive film), forming an uneven adhesive surface with a predetermined structure (positive structure) on the adhesive surface. As described above, the unevenness of the adhesive surface is designed in advance to include grooves that can form communication paths when the convex portions are adhered to the adherend.

As long as air bubbles can be prevented from remaining when the adhesive film is applied, the grooves of the acrylic pressure-sensitive adhesive layer may be arranged on the adhesive surface along a regular pattern to form a regular pattern of grooves, or may be arranged in an irregular pattern to form grooves of an indefinite shape. When multiple grooves are arranged approximately parallel to each other, the arrangement interval of the grooves is preferably about 10 μm or more and about 2000 μm or less. The depth of the groove (the distance from the adhesive surface to the bottom of the groove measured in the direction of the base layer) is usually about 10 μm or more and about 100 μm or less. The shape of the groove is not particularly limited as long as it does not impair the effects of the present invention. For example, the shape of the groove can be approximately rectangular (including trapezoidal), approximately semicircular, or approximately semielliptical in the cross section of the groove perpendicular to the adhesive surface.

The adhesive strength of the adhesive film in one embodiment is about 2.5 N/25 mm or more, about 3 N/25 mm or more, or about 4 N/25 mm or more when measured in accordance with JIS Z 0237:2009 using a SUS304 plate as an adherend. The adhesive strength of the adhesive film is generally about 50 N/25 mm or less, about 45 N/25 mm or less, or about 40 N/25 mm or less. In this disclosure, the measurement procedure and conditions for the adhesive strength of the adhesive film refer to "2-3. Adhesive Strength C" described in the Examples.

The adhesive film of the present disclosure can be used for markings on vehicles, ships, aircraft, etc., the interior and exterior of buildings, illuminated signs, etc., and is particularly suitable for use in applications that impart a metallic appearance to three-dimensional surfaces such as rough surfaces, curved surfaces, and corners.

The following examples illustrate specific embodiments of the present disclosure, but the invention is not limited thereto. All parts and percentages are by weight unless otherwise specified.

The materials used to prepare the adhesive film are shown in Table 1.

Example 1
A pressure-sensitive adhesive composition was prepared containing adhesive polymer 1 (ADH1), dispersant 1 (DPT1), aluminum paste 1 (AP1) and crosslinker 1 (CL1). The mass ratio of ADH1:DPT1:AP1:CL1 was 100:10:5:0.10 based on the non-volatile content. The pressure-sensitive adhesive composition was applied onto release liner 1 (L1) with a knife coater. The applied layer was dried at 95°C for 5 minutes. After drying, an acrylic pressure-sensitive adhesive layer having a thickness of 30 μm was obtained. The acrylic pressure-sensitive adhesive layer was transferred to film 1 (FL1) by laminating the acrylic pressure-sensitive adhesive layer and film 1 (FL1) to obtain the adhesive film of Example 1.

Examples 2 to 27
Adhesive films of Examples 2 to 27 were obtained in the same manner as in Example 1, except that the composition of the pressure-sensitive adhesive composition, the thickness of the acrylic pressure-sensitive adhesive layer, and the film were changed as shown in Table 2.

Comparative Example 1 and Comparative Example 2
Acrylic pressure-sensitive adhesive layers of Comparative Example 1 and Comparative Example 2 were formed in the same manner as in Example 1, except that the composition of the pressure-sensitive adhesive composition was changed as shown in Table 2. For Comparative Example 1 and Comparative Example 2, the appearance of the acrylic pressure-sensitive adhesive layer was unacceptable as described below, so no adhesive film was produced.

Comparative Example 3 and Comparative Example 4
Adhesive films of Comparative Example 3 and Comparative Example 4 were obtained in the same manner as in Example 1, except that the composition of the pressure-sensitive adhesive composition and the thickness of the acrylic pressure-sensitive adhesive layer were changed as shown in Table 2. The acrylic pressure-sensitive adhesive layer of the adhesive film of Comparative Example 4 did not contain aluminum paste.

The adhesive film was evaluated for the following items:

1. Appearance of the acrylic pressure-sensitive adhesive layer The appearance of the acrylic pressure-sensitive adhesive layer was visually observed. An acrylic pressure-sensitive adhesive layer in which the aluminum pigment was well dispersed and the surface was smooth was rated as A. An acrylic pressure-sensitive adhesive layer in which the aluminum pigment was aggregated and the surface was rough was rated as B. An acrylic pressure-sensitive adhesive layer in which the aluminum pigment was not dispersed and the color density was low was rated as C. A rating of A was deemed to be acceptable.

2-1. Adhesive strength A
The adhesive film was cut into a rectangle of 150 mm in length and 25 mm in width to prepare a test piece. The test piece was attached to a melamine-coated plate (Partec Co., Ltd., Hiratsuka City, Kanagawa Prefecture, Japan) at 20°C. The bonding method was in accordance with JIS Z 0237:2009. The test pieces were left at 20°C for 48 hours. A tensile tester (Tensilon (registered trademark) universal testing machine, model number: RTC-1210A, A&D Co., Ltd.) was used. The adhesive strength (N/25 mm) was measured when 180° peeling was performed at a temperature of 20° C. and a peeling speed of 300 mm/min using a tape (Toshima-ku, Tokyo, Japan).

2-2. Adhesive strength B
The adhesive film was cut into a rectangle of 150 mm in length and 25 mm in width to prepare a test piece. The test piece was attached to a melamine-coated plate (Partec Co., Ltd., Hiratsuka City, Kanagawa Prefecture, Japan) at 20°C. The method of application was in accordance with JIS Z 0237:2009. The test pieces were subjected to a thermal cycle of 80°C to -30°C seven times. The tensile tester (Tensilon (registered trademark) universal testing machine, model number: RTC-1210A The adhesive strength (N/25 mm) was measured at 180° peeling at a temperature of 20° C. and a peeling speed of 300 mm/min using a tape-adhesive tester (manufactured by A&D Co., Ltd., Toshima-ku, Tokyo, Japan).

2-3. Adhesive strength C
The adhesive film was cut into a rectangle of 150 mm in length and 25 mm in width to prepare a test specimen. The test specimen was attached to a SUS304BA panel (Partec Co., Ltd., Hiratsuka City, Kanagawa Prefecture, Japan) at 20°C. The method was in accordance with JIS Z 0237:2009. The test piece was left at 20°C for 1 minute. A tensile tester (Tensilon (registered trademark) universal testing machine, model number: RTC-1210A, A&D Co., Ltd., Japan) was used. The adhesive strength (N/25 mm) was measured when 180° peeling was performed at a temperature of 20° C. and a peeling speed of 300 mm/min using a tapered tape (Toshima-ku, Tokyo, Japan).

3. Heat shrinkage The adhesive film was cut into a rectangle of 100 mm in length and 50 mm in width to prepare a test specimen. The test specimen was attached to an aluminum panel with a roller in an environment of 23°C and left in an environment of 23°C for 24 hours. A cross cut was made in the test specimen with a cutter. The test specimen was then heated at 65°C for 48 hours. After heat aging, the shrinkage (mm) of the film was measured under a microscope and the maximum value was recorded.

4. Appearance during stretching The adhesive film was cut into a square of 50 mm to prepare a test specimen. The test specimen was attached to a stucco-painted board (Test Materials Co., Ltd., Chiyoda-ku, Tokyo, Japan) in an environment of 23°C. The maximum surface roughness (height from top to bottom) of the stucco-painted board was about 1.5 mm. The test specimen was pressed without heating using a PFA-1 rivet brush (3M Japan Co., Ltd., Shinagawa-ku, Tokyo, Japan). This caused the test specimen to stretch partially. The appearance of the adhesive film was then visually observed. Test specimens that did not change in appearance were rated A. Test specimens that changed in appearance were rated B. Evaluation A was considered to be pass.

5. Surface Gloss The adhesive film was cut into a 50 mm square to prepare a test specimen. The test specimen was attached to an aluminum panel in an environment of 23°C. The 60 degree gloss of the test specimen surface was measured using a portable gloss meter GMX-202 (Murakami Color Research Institute Co., Ltd., Chuo-ku, Tokyo, Japan).

6. Weather resistance The adhesive film was cut into a rectangle of 50 mm in length and 30 mm in width to prepare a test specimen. The test specimen was attached to an aluminum panel of 1 mm in thickness at room temperature using a squeegee. The test specimen was exposed to xenon light using a xenon weather resistance tester Ci5000 Weather-Ometer (Toyo Seiki Seisakusho Co., Ltd., Kita-ku, Tokyo, Japan). The test conditions were in accordance with JIS K 5600-7-7:2008. Test specimens that did not change in appearance were rated A. Test specimens that yellowed were rated B. Test specimens that peeled off from the aluminum panel were rated C. Evaluation A was considered to be pass.

7. Removability The adhesive film was cut into a rectangle of 150 mm in length and 25 mm in width to prepare a test specimen. The test specimen was attached to an aluminum panel at 20°C. The test specimen was subjected to a thermal cycle condition of 80°C to -30°C seven times. A tensile tester (Tensilon (registered trademark) universal testing machine, model number: RTC-1210A, A&D Co., Ltd., Toshima-ku, Tokyo, Japan) was used to perform 180° peeling at a temperature of 20°C and a peeling speed of 300 mm/min. The specimens in which no residue of the acrylic pressure-sensitive adhesive layer was observed on the aluminum panel were evaluated as A. The specimens in which separation was observed between the acrylic pressure-sensitive adhesive layer and the film were evaluated as B. The specimens in which residue of the acrylic pressure-sensitive adhesive layer was observed on the aluminum panel were evaluated as C.

8. Corrosion resistance The adhesive film was cut into a rectangle of 50 mm in length and 30 mm in width to prepare a test specimen. The test specimen was attached to an aluminum panel of 1 mm in thickness at room temperature using a squeegee. The test specimen was exposed to xenon light using a xenon weathering tester Ci5000 Weather-Ometer (Toyo Seiki Seisakusho Co., Ltd., Kita-ku, Tokyo, Japan). The test conditions were in accordance with JIS K 5600-7-7:2008. The adhesive film surface was exposed to xenon light for 500 hours. Test specimens that did not show corrosion were rated A. Test specimens that showed corrosion were rated B. Evaluation A was considered to be pass.

The evaluation results of the adhesive films of Examples 1 to 27 and Comparative Examples 1 to 4 are shown in Table 3.

It will be apparent to those skilled in the art that the above-described embodiments and examples can be modified in various ways without departing from the basic principles of the present invention. It will also be apparent to those skilled in the art that various improvements and modifications of the present invention can be implemented without departing from the spirit and scope of the present invention.

REFERENCE SIGNS LIST 10 adhesive film 12 clear film layer 14 acrylic pressure-sensitive adhesive layer 142 acrylic adhesive polymer 144 resin-coated metal pigment 16 liner

Claims (7)

An adhesive film having a metallic appearance, comprising a clear film layer and an acrylic pressure-sensitive adhesive layer,
The acrylic pressure-sensitive adhesive layer includes an acrylic adhesive polymer and a resin-coated metal pigment,
The glass transition temperature of the acrylic adhesive polymer is −25° C. or lower;
The acrylic pressure-sensitive adhesive layer comprises 5 parts by mass to 100 parts by mass of the resin-coated metal pigment based on 100 parts by mass of the acrylic adhesive polymer. The adhesive film according to claim 1, wherein the resin-coated metal pigment has an acrylic resin coating. The adhesive film according to claim 1 or 2, wherein the resin-coated metal pigment contains aluminum. The adhesive film according to any one of claims 1 to 3, wherein the resin-coated metal pigment is scaly. The adhesive film according to any one of claims 1 to 4, wherein the visible light transmittance of the clear film layer is 70% or more. The adhesive film according to any one of claims 1 to 5, wherein the adhesive film has an adhesive strength of 2.5 N/25 mm or more when measured using a SUS304 plate as an adherend in accordance with JIS Z 0237:2009. The adhesive film according to any one of claims 1 to 6, wherein the content of the pigment other than the resin-coated metal pigment in the acrylic pressure-sensitive adhesive layer is less than 5 parts by mass based on 100 parts by mass of the acrylic adhesive polymer.

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