Window film

Abstract

[Problem] To provide a window film that is suitable for high-mix low-volume production and demonstrates concealing properties as well as visibility of external light sources. [Solution] This window film has a transparent first resin film, a transparent second resin film, and a colored intermediate layer. The intermediate layer is disposed between one main surface of the first resin film and one main surface of the second resin film. The window film has a total light transmittance of 60% or less and a haze value of 8% or less.

Description

window film

[0001] The present invention relates to window films.

[0002] BACKGROUND ART Window films are adhesive films that are attached to windows of vehicles such as automobiles, windows of buildings, etc. to impart predetermined functions to the windows, and are widely used.

[0003] One type of such window film is known, which is colored to prevent the interior from being seen from the perspective of privacy protection. Such a property of a window film may be hereinafter referred to as "visibility blocking property." Patent Document 1 discloses a colored laminate using a colored substrate made of a colored resin film.

[0004] Japanese Patent Application Laid-Open No. 2015-178082

[0005] However, resin films are usually produced in large quantities as wide, long sheets by stretching molten resin. Therefore, when coloring a resin film, it is produced using a molten resin containing a colorant, as described above. In other words, colored resin films are suitable for mass production of a small number of products.

[0006] On the other hand, window films are available in a wide variety of colors and with varying levels of light transmittance, so a large number of varieties are required.

[0007] Therefore, when a colored resin film is used for a window film, a resin film with a different color tone must be produced for each type of product, which poses a problem of reduced production efficiency.

[0008] Furthermore, when window films are tinted, the visibility of external light sources (such as lights from other cars, traffic lights, etc.) is reduced when viewed from inside, posing a safety risk.

[0009] The present invention has been made in view of the above circumstances, and has an object to provide a window film that is suitable for small-lot production of a wide variety of products, and that has a visibility blocking effect and allows visibility of an external light source.

[0010] The aspects of the present invention are as follows.

[0011] [1] A window film having a transparent first resin film, a transparent second resin film, and a colored intermediate layer, wherein the intermediate layer is disposed between one main surface of the first resin film and one main surface of the second resin film, and having a total light transmittance of 60% or less and a haze value of 8% or less.

[0012] [2] The window film according to [1], wherein the window film does not have a layer containing metal.

[0013] [3] The window film according to [1] or [2], wherein the intermediate layer is a pressure-sensitive adhesive layer made of an acrylic pressure-sensitive adhesive.

[0014] [4] The window film according to any one of [1] to [3], wherein the intermediate layer is formed from a pressure-sensitive adhesive composition containing a (meth)acrylic acid alkyl ester polymer, and the (meth)acrylic acid alkyl ester polymer contains a unit derived from a monomer having a carboxy group in the molecule.

[0015] According to the present invention, it is possible to provide a window film that is suitable for small-lot production of a wide variety of products and that has visibility blocking properties and allows visibility of external light sources.

[0016] Fig. 1 is a cross-sectional view showing an example of a window film according to the present embodiment. Fig. 2A is a cross-sectional view showing an example of another configuration of the window film according to the present embodiment. Fig. 2B is a cross-sectional view showing an example of another configuration of the window film according to the present embodiment.

[0017] The present invention will be described in detail below based on specific embodiments.

[0018] (1. Window Film) The window film of this embodiment includes a transparent resin film as a substrate. The intermediate layer, which is not in contact with the adherend and is disposed between the resin films, is colored in a predetermined color tone. This allows the total light transmittance to be controlled to a predetermined value or less, while controlling the haze value to a predetermined value or less, thereby preventing a decrease in light source visibility. Window films are required to be available in a wide variety of colors and light transmittances, depending on user preferences and local regulations. Therefore, if a resin film used as a substrate were to be colored to meet this requirement, it would be necessary to manufacture a wide variety of resin films with different color tones and light transmittances. However, as described above, resin films are suitable for mass production of a small number of products. In this embodiment, the colored intermediate layer allows the window film of this embodiment to satisfy the above-described optical properties while including a transparent resin film, i.e., without using a colored resin film. As a result, a wide variety of window films can be easily developed, while achieving both visibility and blocking properties.

[0019] Furthermore, after being applied to an adherend, a window film may be replaced with another window film due to deterioration over time. When a colored adhesive layer is used as the adhesive layer for fixing the window film to the adherend (window), a portion of the adhesive layer may remain on the surface of the adherend when the window film is peeled off from the adherend. It has been found that when the adhesive layer is colored, the remaining adhesive layer affects the appearance of the adherend and impairs the aesthetics of the adherend. In this embodiment, the intermediate layer does not come into contact with the adherend, and therefore has the advantage that the aesthetics of the adherend are not impaired even when the window film is peeled off.

[0020] As shown in Fig. 1 , the window film 1 according to this embodiment has a first resin film 11 and a second resin film 12 as base materials, and an intermediate layer 20. In this embodiment, the first resin film 11 and the second resin film 12 are transparent, and the intermediate layer 20 is colored. The intermediate layer 20 is disposed between the main surface 11a of the first resin film 11 and the main surface 12b of the second resin film 12. Therefore, the window film 1 according to this embodiment has a laminate in which the first resin film 11, the intermediate layer 20, and the second resin film 12 are laminated in this order.

[0021] As long as the effects of the present invention are obtained, the window film may have other components. For example, in order to easily fix the window film to an adherend, a pressure-sensitive adhesive layer (a second pressure-sensitive adhesive layer described below) may be formed on the main surface of the first resin film or the second resin film opposite the main surface on which the intermediate layer is formed. In this embodiment, the pressure-sensitive adhesive layer is preferably colorless and transparent.

[0022] Figure 2A shows a window film 1 having a configuration in which an adhesive layer 30 is formed on the main surface 12a of the second resin film 12 opposite the main surface 12b on which the intermediate layer 20 is formed.

[0023] Furthermore, in order to protect the pressure-sensitive adhesive layer 30 until it is attached to the adherend, a release sheet may be disposed on the main surface 22b of the pressure-sensitive adhesive layer 30. When using the window film 1, the release sheet is peeled off from the pressure-sensitive adhesive layer 30, and the main surface 22b of the pressure-sensitive adhesive layer 30 is attached to the adherend (window).

[0024] Furthermore, in order to impart weather resistance, scratch resistance, etc. to the window film, a hard coat layer may be formed on the main surface of the first resin film or the second resin film opposite the main surface on which the intermediate layer 20 is formed. Fig. 2B shows a window film 1 having a configuration in which a hard coat layer 40 is formed on the main surface 11b of the first resin film 11 opposite the main surface 11a on which the intermediate layer 20 is formed.

[0025] When a window film has a pressure-sensitive adhesive layer and a hard coat layer, if the pressure-sensitive adhesive layer is formed on the main surface of one resin film, the hard coat layer is usually formed on the main surface of the other resin film.

[0026] Note that window films may include a layer containing a metal to control light transmittance, increase visible light reflectance, and enhance visibility by reflecting external light. However, the window film according to the present embodiment mainly controls light transmittance and provides sufficient visibility by using a colored intermediate layer, so it is preferable that the window film does not include a layer containing a metal. A layer containing a metal may oxidize over time, causing a change in the color tone of the window film, but eliminating the metal-containing layer can prevent such a problem. The metal-containing layer may be a layer consisting solely of a metal. Examples of metals contained in the metal-containing layer include metals such as aluminum, gold, silver, copper, nickel, cobalt, chromium, tin, and indium, alloys of these, and oxides of these.

[0027] (1.1. Optical Properties of Window Film) The window film according to this embodiment has the following optical properties.

[0028] (1.1.1. Total Light Transmittance of Window Film) In this embodiment, the window film has a total light transmittance of 60% or less. This makes it difficult to see the inside of the window to which the window film is attached from the outside (high visibility), thereby providing excellent privacy protection.

[0029] The total light transmittance can be set depending on the degree of visibility, but is preferably 45% or less, more preferably 35% or less. In this embodiment, from the viewpoint of visibility, the lower limit of the total light transmittance is preferably 7%, more preferably 9%, and even more preferably 15%. The total light transmittance in this specification can be measured in accordance with JIS K7361-1:1997. A detailed measurement method will be described in the examples.

[0030] (1.1.2. Haze Value of Window Film) When a window film is colored to reduce light transmittance, the haze value tends to increase. As the haze value increases, light from the light source observed through the window film is more likely to diffuse, reducing the visibility of the light source. When window films are applied to windows of automobiles, etc., reduced visibility of the light source is undesirable because it reduces safety. In this embodiment, the haze value of the window film is 8% or less. This ensures good visibility of objects seen through the window film, even when the window film is attached to a window. In particular, the light from the light source is less likely to diffuse when viewed through the window film, resulting in good visibility of the light source.

[0031] The haze value is preferably 6% or less, more preferably 4.5% or less, and even more preferably 4% or less. The lower limit of the haze value is 0%. The haze value in this specification can be measured in accordance with JIS K7136:2000. The detailed measurement method will be described in the examples.

[0032] The components of the window film having the above optical properties will now be described in detail.

[0033] (1.2. Resin Film) The resin films (first resin film and second resin film) according to this embodiment are materials that provide the rigidity of the window film, and function as a substrate that supports the intermediate layer.

[0034] In this embodiment, the first resin film and the second resin film are transparent. In this specification, "transparent" means that the total light transmittance is 80% or more. The total light transmittance of the first resin film and the second resin film is preferably more than 80%, and more preferably 85% or more. Furthermore, the first resin film and the second resin film are preferably colorless. That is, the first resin film and the second resin film are preferably colorless and transparent. The first resin film and the second resin film preferably do not contain a colorant, and preferably have a lightness L* of 95 or more as defined by the CIE 1976 L*a*b* color system.

[0035] Examples of such resin films include films made of polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polyolefin resins such as polyethylene, polypropylene, poly-4-methylpentene-1 and polybutene-1; polyurethane resins; polycarbonate resins; polyvinyl chloride resins; polyethersulfone resins; polyethylene sulfide resins; styrene resins; acrylic resins; polyamide resins; cellulose resins such as cellulose acetate; and laminate films thereof.

[0036] Among these, films made of polyolefin resins and polyester resins, which are excellent in mechanical strength and economy, or laminate films thereof are preferred, and films made of polyester resins or laminate films thereof are particularly preferred, and polyethylene terephthalate films or laminate films including a layer made of polyethylene terephthalate are particularly preferred. The first resin film and the second resin film may have the same configuration or different configurations.

[0037] The transparent resin film described above can be mass-produced, for example, by biaxial stretching, etc. Therefore, even when producing a wide variety of window films having predetermined optical properties, it is not necessary to prepare resin films having different optical properties, and the transparent resin film can be used as a substrate as is.

[0038] In order to improve adhesion to a layer provided on the resin film, one or both sides of the resin film may be subjected to a surface treatment by an oxidation method, a roughening method, etc. Examples of the oxidation method include corona discharge treatment, chromic acid treatment (wet), flame treatment, hot air treatment, ozone / ultraviolet irradiation treatment, etc. Examples of the roughening method include sandblasting and solvent treatment.

[0039] The thickness of the resin film is not particularly limited as long as it exhibits a predetermined rigidity and may be set appropriately depending on the intended use. The thickness of the first resin film and the thickness of the second resin film may be the same or different. In this embodiment, from the viewpoint of ensuring mechanical strength suitable for workability during application, the thickness of the first resin film and the second resin film is preferably within the range of 5 to 200 μm, and more preferably within the range of 10 to 100 μm. Furthermore, from the viewpoint of adjusting optical properties mainly with layers other than the resin film and obtaining a thin window film, the thickness of the first resin film and the second resin film is more preferably within the range of 15 to 80 μm, and particularly preferably within the range of 20 to 60 μm.

[0040] (1.3. Intermediate Layer) The intermediate layer provided in the window film according to this embodiment is a colored intermediate layer. Furthermore, the intermediate layer is preferably a layer that fixes and integrates the first resin film and the second resin film. An example of such a layer is an adhesive layer. Therefore, the intermediate layer is preferably an adhesive layer.

[0041] The adhesive layer is formed by forming a layer of a predetermined adhesive. In this embodiment, the adhesive constituting the adhesive layer may be a thermosetting adhesive, a moisture-sensitive adhesive, a thermoplastic resin, or the like, but is preferably a pressure-sensitive adhesive. A pressure-sensitive adhesive is an adhesive that has a predetermined elasticity and generates tack on its surface, and is a substance that exhibits adhesion to an adherend (first resin film and second resin film) when pressed against the adherend. A pressure-sensitive adhesive is also called a pressure-sensitive adhesive. In other words, the adhesive layer may be a pressure-sensitive adhesive layer. Below, a case where the adhesive layer is a first pressure-sensitive adhesive layer will be described.

[0042] (1.3.1. First Pressure-Sensitive Adhesive Layer) The first pressure-sensitive adhesive layer may be composed of one layer (single layer), or may be composed of two or more layers. When the first pressure-sensitive adhesive layer has multiple layers, these multiple layers may be the same or different, and the combination of layers constituting these multiple layers is not particularly limited.

[0043] The thickness of the first pressure-sensitive adhesive layer may be 5 to 100 μm, preferably 7 to 70 μm, more preferably 10 to 50 μm, and even more preferably 10 to 40 μm, which makes it easier to exhibit suitable adhesiveness and optical properties.

[0044] (1.3.2. Composition of First Pressure-Sensitive Adhesive) The composition of the first pressure-sensitive adhesive constituting the first pressure-sensitive adhesive layer is not particularly limited. For example, it may be any of an acrylic pressure-sensitive adhesive, a polyester pressure-sensitive adhesive, a polyurethane pressure-sensitive adhesive, a rubber pressure-sensitive adhesive, a silicone pressure-sensitive adhesive, etc. Furthermore, the first pressure-sensitive adhesive may be any of an emulsion type, a solvent type, or a solventless type. Furthermore, the first pressure-sensitive adhesive may or may not have a cross-linked structure.

[0045] In this embodiment, from the viewpoint of adhesive properties and optical properties of the window film, the first adhesive is preferably an acrylic adhesive, and more preferably an acrylic adhesive having a crosslinked structure.

[0046] Specifically, the first pressure-sensitive adhesive is preferably a pressure-sensitive adhesive formed from a pressure-sensitive adhesive composition containing a (meth)acrylic acid ester polymer (A) (hereinafter sometimes referred to as "pressure-sensitive adhesive composition P"), and is preferably a pressure-sensitive adhesive obtained by crosslinking a pressure-sensitive adhesive composition containing a (meth)acrylic acid ester polymer (A) and a crosslinking agent (B), i.e., a pressure-sensitive adhesive having a crosslinked structure between the (meth)acrylic acid ester polymer (A) and the crosslinking agent (B). Such a pressure-sensitive adhesive is less likely to increase the haze value of the window film and has excellent adhesion to the resin film that is the adherend. In this specification, (meth)acrylic acid refers to both acrylic acid and methacrylic acid. The same applies to other similar terms. Furthermore, the term "polymer" also includes the concept of "copolymer."

[0047] (1.3.2.1. (Meth)acrylic acid ester polymer (A)) The (meth)acrylic acid ester polymer (A) preferably contains, as units derived from monomers constituting the polymer, units derived from a (meth)acrylic acid alkyl ester and units derived from a monomer having a reactive functional group in the molecule (reactive functional group-containing monomer).

[0048] The (meth)acrylic acid ester polymer (A) contains units derived from a (meth)acrylic acid alkyl ester, allowing the PSA to exhibit desirable adhesiveness. As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms is preferred. The alkyl group may be linear or branched, but for convenience, those having a cyclic structure are excluded in order to distinguish them from alicyclic structure-containing monomers described below.

[0049] Examples of (meth)acrylic acid alkyl esters having an alkyl group containing 1 to 20 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate.

[0050] Among these, preferred are (meth)acrylic acid alkyl esters in which the alkyl group has 1 to 8 carbon atoms. Specifically, preferred are methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, and particularly preferred are methyl acrylate, methyl methacrylate, n-butyl acrylate, and 2-ethylhexyl acrylate.

[0051] The (meth)acrylic acid ester polymer preferably contains 30 to 98.5 mass %, and more preferably 40 to 90 mass %, of units derived from a (meth)acrylic acid alkyl ester having an alkyl group containing 1 to 20 carbon atoms as units derived from the monomers constituting the polymer. By setting the content ratio of units derived from a (meth)acrylic acid alkyl ester within the above range, it is possible to impart suitable adhesiveness to the (meth)acrylic acid ester polymer. In addition, it is possible to introduce desired amounts of other monomer components into the (meth)acrylic acid ester polymer.

[0052] The (meth)acrylic acid ester polymer (A) contains units derived from a reactive functional group-containing monomer, and the (meth)acrylic acid ester polymer reacts with the crosslinking agent (B) described below via the reactive functional group derived from the reactive functional group-containing monomer, forming a crosslinked structure (three-dimensional network structure) in the pressure-sensitive adhesive. As a result, a pressure-sensitive adhesive having the desired cohesive strength is obtained. Note that the reactive functional group may be used only to change the properties of the pressure-sensitive adhesive, and the reactive functional group does not necessarily have to react with the crosslinking agent (B).

[0053] Preferred examples of the reactive functional group-containing monomer include a monomer having a hydroxyl group in the molecule (hydroxyl group-containing monomer), a monomer having a carboxyl group in the molecule (carboxyl group-containing monomer), a monomer having an amino group in the molecule (amino group-containing monomer), etc. These reactive functional group-containing monomers may be used alone or in combination of two or more.

[0054] The (meth)acrylic acid ester polymer preferably contains, as units derived from monomers constituting the polymer, units derived from a reactive functional group-containing monomer in an amount of 1.5 to 40 mass %, more preferably 5 to 35 mass %, and even more preferably 10 to 30 mass %.

[0055] In this embodiment, from the viewpoint of controlling the optical properties of the window film, the reactive functional group-containing monomer is preferably at least one selected from a hydroxyl group-containing monomer and a carboxyl group-containing monomer. When the (meth)acrylic acid ester polymer contains at least one selected from a unit derived from a hydroxyl group-containing monomer and a unit derived from a carboxyl group-containing monomer, an increase in the haze value of the resulting window film tends to be suppressed.

[0056] Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0057] Among these, (meth)acrylic acid hydroxyalkyl esters having a hydroxyalkyl group having 1 to 4 carbon atoms are preferred. Specifically, 2-hydroxyethyl (meth)acrylate is preferred. These may be used alone or in combination of two or more.

[0058] When the (meth)acrylic acid ester polymer contains units derived from hydroxyl group-containing monomers as units derived from monomers constituting the polymer, the content of the units derived from hydroxyl group-containing monomers is preferably 1% by mass or more relative to 100% by mass of the (meth)acrylic acid ester polymer, and the content of the units derived from hydroxyl group-containing monomers is more preferably 1% by mass or more and 35% by mass or less.

[0059] Examples of carboxyl group-containing monomers include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, acrylic acid is preferred because it is easily copolymerized with other monomers. These may be used alone or in combination of two or more.

[0060] When the (meth)acrylic acid ester polymer contains a unit derived from a carboxyl group-containing monomer as a unit derived from a monomer constituting the polymer, the (meth)acrylic acid ester polymer preferably contains 1.5 mass% or more of the unit derived from the carboxyl group-containing monomer relative to 100 mass% of the (meth)acrylic acid ester polymer. The content of the unit derived from the carboxyl group-containing monomer is more preferably 1.5 mass% or more and 25 mass% or less, even more preferably 5 mass% or more and 20 mass% or less, and particularly preferably 8 mass% or more and 15 mass% or less.

[0061] The (meth)acrylic acid ester polymer may contain both units derived from a hydroxyl group-containing monomer and units derived from a carboxyl group-containing monomer as units derived from the monomers constituting the polymer. In this case, it is sufficient that at least one of the content ratio of the units derived from the hydroxyl group-containing monomer and the content ratio of the units derived from the carboxyl group-containing monomer satisfies the above content ratio, and both content ratios may also satisfy the above content ratio.

[0062] The (meth)acrylic acid ester polymer contains units derived from a carboxyl group-containing monomer, which can improve the adhesiveness and cohesion of the first pressure-sensitive adhesive layer. This is also preferable from the viewpoint of improving the dispersibility of the colorant in the pressure-sensitive adhesive. In this case, if the window film has a metal-containing layer, the metal-containing layer is likely to be oxidized due to contact between the first pressure-sensitive adhesive layer and the metal-containing layer. However, if the window film does not have a metal-containing layer, this problem can be avoided.

[0063] The (meth)acrylic acid ester polymer may contain a unit derived from a monomer having an alicyclic structure in the molecule (alicyclic structure-containing monomer) as a unit derived from a monomer constituting the polymer. Since the alicyclic structure-containing monomer is bulky, it is presumed that the presence of a unit derived therefrom in the polymer increases the spacing between polymer molecules, and the resulting pressure-sensitive adhesive can have excellent flexibility.

[0064] Specific examples of the alicyclic structure-containing monomer include cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, adamantyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, etc. These may be used alone or in combination of two or more.

[0065] The (meth)acrylic acid ester polymer may contain a unit derived from a nitrogen atom-containing monomer as a unit derived from a monomer constituting the polymer. This imparts a predetermined polarity to the pressure-sensitive adhesive, and the pressure-sensitive adhesive layer has excellent affinity even for adherends having a certain degree of polarity. As the nitrogen atom-containing monomer, a monomer having a nitrogen-containing heterocycle is preferred from the viewpoint of imparting appropriate rigidity to the (meth)acrylic acid ester polymer (A).

[0066] Examples of monomers having a nitrogen-containing heterocycle include N-(meth)acryloylmorpholine, N-vinyl-2-pyrrolidone, N-(meth)acryloylpyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylaziridine, aziridinylethyl (meth)acrylate, 2-vinylpyridine, 4-vinylpyridine, 2-vinylpyrazine, 1-vinylimidazole, N-vinylcarbazole, and N-vinylphthalimide. These may be used alone or in combination of two or more.

[0067] In this embodiment, the (meth)acrylic acid ester polymer may contain other monomers as monomer units constituting the polymer, if desired. As the other monomers, monomers that do not contain reactive functional groups are preferred so as not to inhibit the above-described action of the reactive functional group-containing monomer. Examples of such monomers include (meth)acrylic acid alkoxyalkyl esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, vinyl acetate, and styrene. These may be used alone or in combination of two or more.

[0068] The polymerization mode of the (meth)acrylic acid ester polymer may be a random copolymer or a block copolymer.

[0069] The weight-average molecular weight (Mw) of the (meth)acrylic acid ester polymer is preferably 100,000 to 1,500,000, more preferably 200,000 to 1,200,000, and even more preferably 300,000 to 900,000. This makes it easier to obtain the desired adhesive strength. The weight-average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0070] In the pressure-sensitive adhesive composition P, the (meth)acrylic acid ester polymer may be used alone or in combination of two or more kinds.

[0071] (1.3.2.2. Crosslinking agent (B)) The pressure-sensitive adhesive composition P for forming the first pressure-sensitive adhesive preferably contains a crosslinking agent (B). The crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer and forms a crosslinked structure (three-dimensional network structure) upon heating or the like of the pressure-sensitive adhesive composition P containing the crosslinking agent. As a result, the cohesive strength of the resulting pressure-sensitive adhesive is improved.

[0072] The crosslinking agent (B) may be any agent that reacts with the reactive group of the (meth)acrylic acid ester polymer. Examples include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, amine-based crosslinking agents, melamine-based crosslinking agents, aziridine-based crosslinking agents, hydrazine-based crosslinking agents, aldehyde-based crosslinking agents, oxazoline-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, and ammonium salt-based crosslinking agents. Among these, metal chelate-based crosslinking agents and isocyanate-based crosslinking agents are preferred. The crosslinking agent (B) may be used alone or in combination of two or more.

[0073] As the metal chelate crosslinking agent, a metal chelate compound in which the metal atom is aluminum, zirconium, titanium, zinc, iron, tin, etc. Among these, aluminum chelate compounds are preferred.

[0074] Examples of aluminum chelate compounds include aluminum trisacetylacetonate, aluminum trisethylacetoacetate, and aluminum ethylacetoacetate diisopropylate.

[0075] The isocyanate-based crosslinking agent contains at least a polyisocyanate compound, such as aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, and alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate.

[0076] The content of the crosslinking agent (B) in the pressure-sensitive adhesive composition P is preferably 0.01 to 10 parts by mass, and more preferably 0.04 to 5 parts by mass, relative to 100 parts by mass of the (meth)acrylic acid ester polymer, which makes it easier to obtain the desired cohesive strength.

[0077] (1.3.2.3. Colorant (C)) The pressure-sensitive adhesive composition P for forming the first pressure-sensitive adhesive preferably contains a colorant (C). By containing a colorant, the resulting first pressure-sensitive adhesive layer (intermediate layer) is colored, and the optical properties such as the total light transmittance and haze value described above can be adjusted. Therefore, for example, by applying the window film to windows of automobiles or buildings, privacy protection (view blocking) can be improved.

[0078] The colorant (C) may be a pigment or a dye, but in this embodiment, a pigment is preferred. The pigment may be an organic pigment or an inorganic pigment. From the viewpoint of the durability of the colorant, an inorganic pigment is preferred. The color of the colorant can be appropriately selected depending on the user's preference, the color of surrounding components such as the window frame, etc., but from the viewpoint of improving visibility, a dark or deep color such as black, brown, navy blue, purple, or blue is generally preferred, and black is particularly preferred.

[0079] Examples of inorganic pigments include carbon black, cobalt-based pigments, iron-based pigments, chromium-based pigments, titanium-based pigments such as titanium dioxide and titanium nitride, vanadium-based pigments, zirconium-based pigments, molybdenum-based pigments, ruthenium-based pigments, platinum-based pigments, ITO (indium tin oxide)-based pigments, and ATO (antimony tin oxide)-based pigments.

[0080] Examples of organic pigments and organic dyes include aminium-based dyes, cyanine-based dyes, merocyanine-based dyes, croconium-based dyes, squarium-based dyes, azulenium-based dyes, polymethine-based dyes, naphthoquinone-based dyes, pyrylium-based dyes, phthalocyanine-based dyes, naphthalocyanine-based dyes, naphtholactam-based dyes, azo-based dyes, condensed azo-based dyes, indigo-based dyes, perinone-based dyes, perylene-based dyes, dioxazine-based dyes, quinacridone-based dyes, isoindolinone-based dyes, quinophthalone-based dyes, pyrrole-based dyes, thioindigo-based dyes, metal complex-based dyes (metal complex dyes), dithiol metal complex-based dyes, indolephenol-based dyes, triallylmethane-based dyes, anthraquinone-based dyes, naphthol-based dyes, azomethine-based dyes, benzimidazolone-based dyes, pyranthrone-based dyes, and threne-based dyes.

[0081] Examples of black pigments include carbon black, copper oxide, iron oxide, manganese dioxide, aniline black, activated carbon, etc. Examples of black dyes include high-concentration vegetable dyes and azo dyes.

[0082] The above pigments or dyes can be used in appropriate mixtures depending on the purpose.

[0083] Among the above colorants, inorganic pigments are preferred, and carbon black is preferred, from the viewpoint of easily satisfying the optical properties of the window film and easily exhibiting privacy protection. Note that the carbon black may or may not have been subjected to a predetermined surface treatment (for example, a solvent-philic treatment).

[0084] Furthermore, the colorant (C) has an average haze, which is the average of the haze at a wavelength of 780 nm and the haze at a wavelength of 380 nm, of a solution obtained by diluting the colorant 10,000 times with ethyl acetate. The lower limit of the average haze is preferably 0.1% or more, more preferably 0.3% or more, and even more preferably 0.5% or more. The upper limit of the average haze is particularly preferably 6% or less, and most preferably 5% or less. The use of such a colorant makes it possible to easily adjust the optical properties, such as the total light transmittance and haze value, of the window film according to this embodiment, and the window film according to this embodiment is likely to achieve both a low total light transmittance and a low haze value.

[0085] Furthermore, the colorant (C) is preferably such that the difference between the haze value at a wavelength of 780 nm and the haze value at a wavelength of 380 nm of a solution obtained by diluting the colorant 10,000 times with ethyl acetate is 8.3 points or less, and more preferably 8 points or less. By using such a colorant, the optical properties such as the total light transmittance and haze value of the window film according to this embodiment can be easily adjusted, and it is easy to achieve both a low total light transmittance and a low haze value.

[0086] The lower limit of the difference in haze value may be 0 points, but from the viewpoint of making it easier to adjust the optical properties of the window film to be suitable, it is preferably 0.1 points or more, more preferably 0.3 points or more, and even more preferably 0.5 points or more.

[0087] The haze value at a wavelength of 780 nm of a solution obtained by diluting colorant (C) 10,000 times with ethyl acetate is preferably 0.1 to 3%, and more preferably 0.3 to 2.8%. Furthermore, the haze value at a wavelength of 380 nm of a solution obtained by diluting colorant (C) 10,000 times with ethyl acetate is preferably 0.1 to 11.5%, more preferably 0.5 to 11%, and even more preferably 1 to 10.5%. This makes it easier to satisfy the above-mentioned difference in haze value.

[0088] Furthermore, the standard deviation of the haze value at each wavelength in 5 nm increments in the wavelength range of 380 nm to 780 nm (i.e., 380 nm, 385 nm, 390 nm, ..., 775 nm, 780 nm) of a solution obtained by diluting colorant (C) 10,000 times with ethyl acetate is preferably 2.2 or less, more preferably 2 or less, and even more preferably 1.8 or less. The lower limit of the standard deviation is most preferably 0, but may generally be 0.1 or more, or may be 0.15 or more. This makes it possible to easily adjust the optical properties, such as the total light transmittance and haze value, of the window film according to this embodiment.

[0089] The content of the colorant (C) in the pressure-sensitive adhesive composition P is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.7 parts by mass or more, relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A). Furthermore, the content is preferably 7 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 2.5 parts by mass or less. By ensuring that the content of the colorant (C) is within the above range, the optical properties of the window film according to this embodiment, such as the total light transmittance and haze value, can be easily adjusted.

[0090] (1.3.2.4. Ultraviolet absorber (D)) The pressure-sensitive adhesive composition P for forming the first pressure-sensitive adhesive preferably contains an ultraviolet absorber (D) in order to impart an ultraviolet shielding function to the window film.

[0091] Examples of ultraviolet absorbers include compounds such as benzophenones, benzotriazoles, benzoates, benzoxazinones, methines, triazines, phenyl salicylates, cyanoacrylates, and nickel complex salts. One ultraviolet absorber may be used alone, or two or more may be used in combination. Among the ultraviolet absorbers (D), it is preferable to use benzophenones, benzotriazoles, and triazines, and it is more preferable to use triazines.

[0092] (1.3.2.5. Other Additives) The adhesive composition P for forming the first adhesive may contain additives commonly used in adhesives, if necessary. Examples of such additives include tackifiers, silane coupling agents, fillers, infrared absorbers, softeners, antioxidants, light stabilizers, modifiers, rust inhibitors, flame retardants, hydrolysis inhibitors, surface lubricants, corrosion inhibitors, heat stabilizers, lubricants, antistatic agents, polymerization inhibitors, catalysts, leveling agents, thickeners, dispersants, antifoaming agents, surfactants, etc. It should be noted that the polymerization solvents and dilution solvents described below are not included in the additives constituting the adhesive composition P.

[0093] (1.4. Second Adhesive Layer) In this embodiment, as shown in FIG. 2A , the window film 1 preferably has an adhesive layer 30. When the intermediate layer 20 is the first adhesive layer, the adhesive layer 30 is the second adhesive layer. The second adhesive layer can be used to make it easier to fix and attach the window film to an adherend (window). The second adhesive layer is a layer of the second adhesive described below.

[0094] The second pressure-sensitive adhesive layer may be one layer (single layer) or two or more layers. When the second pressure-sensitive adhesive layer has multiple layers, the layers may have different compositions.

[0095] The thickness of the second pressure-sensitive adhesive layer may be 3 to 100 μm, 5 to 80 μm, or 10 to 50 μm, which makes it easy to attach and fix the window film to the adherend (window).

[0096] (1.4.1. Second Pressure-Sensitive Adhesive) The composition of the second pressure-sensitive adhesive constituting the second pressure-sensitive adhesive layer is not particularly limited. For example, it may be any of an acrylic pressure-sensitive adhesive, a polyester pressure-sensitive adhesive, a polyurethane pressure-sensitive adhesive, a rubber pressure-sensitive adhesive, a silicone pressure-sensitive adhesive, etc. Furthermore, the second pressure-sensitive adhesive may be any of an emulsion type, a solvent type, or a solventless type. Furthermore, the second pressure-sensitive adhesive may or may not have a cross-linked structure.

[0097] In this embodiment, from the viewpoint of the adhesive properties and optical properties of the window film, the adhesive is preferably an acrylic adhesive, and more preferably an acrylic adhesive having a crosslinked structure. As described above, the second adhesive layer is preferably colorless and transparent, and therefore the second adhesive layer preferably does not substantially contain a colorant.

[0098] Examples of acrylic pressure-sensitive adhesives having a crosslinked structure include those obtained by removing the colorant from the pressure-sensitive adhesive described above in (1.3.2. Composition of the First Pressure-Sensitive Adhesive). When the second pressure-sensitive adhesive is formed from a pressure-sensitive adhesive composition containing a (meth)acrylic acid ester polymer (A) (hereinafter sometimes referred to as "pressure-sensitive adhesive composition P'"), from the viewpoint of improving the adhesion of the second pressure-sensitive adhesive layer to glass, it is preferable that the (meth)acrylic acid ester polymer contains units derived from a carboxy group-containing monomer. This allows the adhesion of the second pressure-sensitive adhesive layer to glass to be easily improved even if the (meth)acrylic acid ester polymer (A) does not contain units derived from special monomers such as nitrogen atom-containing monomers. Furthermore, from the viewpoint of improving productivity, it is preferable that the (meth)acrylic acid ester polymer contained in pressure-sensitive adhesive composition P' is the same as the (meth)acrylic acid ester polymer contained in pressure-sensitive adhesive composition P.

[0099] When the window film according to the present embodiment has a second adhesive layer, its adhesive strength to glass is preferably 8 N / 25 mm or more, more preferably 13 N / 25 mm or more. The adhesive strength of the window film to glass is a characteristic value measured by the method described in the Examples below. The upper limit of the adhesive strength of the window film to glass is usually about 30 N / 25 mm, and may be about 27 N / 25 mm.

[0100] (1.5. Hard Coat Layer) The window film according to the present embodiment may have a hard coat layer in addition to the resin film, intermediate layer, and pressure-sensitive adhesive layer described above. In this case, as shown in Fig. 2B , in the window film 1 shown in Fig. 2A , the hard coat layer 40 may be disposed on the main surface 11b of the first resin film 11 opposite to the main surface 11a on which the intermediate layer (first pressure-sensitive adhesive layer) 20 is disposed.

[0101] The hard coat layer is made of a material that is superior in hardness, scratch resistance, weather resistance, etc. to resin films. When the window film 1 shown in FIG. 2B is attached to an adherend (a window) via the second pressure-sensitive adhesive layer 30, the hard coat layer 40 is exposed to the outside in the window film 1. Therefore, even if the surface of the window film is pressed with a tool such as a squeegee when attaching the window film to the window during installation, or even if some external force is applied after installation, the surface of the window film is unlikely to be scratched.

[0102] From the viewpoint of the surface hardness, scratch resistance and weather resistance of the window film, the thickness of the hard coat layer is preferably 0.3 to 20 μm, more preferably 0.5 to 15 μm, and even more preferably 0.8 to 6 μm.

[0103] The material for the hard coat layer is not particularly limited as long as it is a material that is superior to the resin film in hardness, scratch resistance, weather resistance, etc. For example, the hard coat layer may be a cured product of a composition containing an active energy ray-curable resin. An example of such a composition is a hard coat layer-forming composition containing an active energy ray-curable resin and a photopolymerization initiator. The hard coat layer-forming composition may also contain other additives such as an antioxidant, an infrared absorber, an ultraviolet absorber, an antistatic agent, a colorant, a polymerization accelerator, a polymerization inhibitor, a plasticizer, a leveling agent, an antiviral agent, an antibacterial agent, a filler, and a dilution solvent.

[0104] (2. Manufacturing of Window Film) The method for manufacturing the window film is not particularly limited, and it may be manufactured by a known method. For example, a coating liquid of a pressure-sensitive adhesive composition P for forming a first pressure-sensitive adhesive layer (intermediate layer) is applied to one main surface of a first resin film as a substrate, and a heat treatment is carried out to crosslink the pressure-sensitive adhesive composition P, thereby forming a first coating layer having a predetermined thickness. Subsequently, one main surface of a second resin film and the exposed surface of the first coating layer are superimposed to form a first laminate.

[0105] When the window film has a second pressure-sensitive adhesive layer, a coating solution of a pressure-sensitive adhesive composition P' for forming the second pressure-sensitive adhesive layer is applied to the release surface of the release sheet, and a heat treatment is carried out to crosslink the pressure-sensitive adhesive composition P', thereby forming a second coating layer having a predetermined thickness. The exposed surface of the second coating layer is superimposed on the main surface of the first laminate on which the intermediate layer of the second resin film is not formed, to form a second laminate.

[0106] (2.1. Production of Pressure-Sensitive Adhesive Compositions) Pressure-sensitive adhesive composition P and pressure-sensitive adhesive composition P' (hereinafter sometimes collectively referred to as "pressure-sensitive adhesive composition P+") can be produced, for example, by first producing a (meth)acrylic acid ester polymer (A) and then mixing the resulting (meth)acrylic acid ester polymer (A) with a crosslinking agent (B). When producing a pressure-sensitive adhesive composition for forming a first pressure-sensitive adhesive, a colorant (C) is further added. If desired, an additive such as an ultraviolet absorber (D) may be added at any stage.

[0107] The (meth)acrylic acid ester polymer can be produced, for example, by polymerizing a mixture of monomers constituting the polymer by a conventional radical polymerization method. The polymerization of the (meth)acrylic acid ester polymer can be carried out, for example, by a solution polymerization method using a polymerization initiator as necessary.

[0108] Next, a crosslinking agent (B) and, if necessary, an additive (such as a colorant (C)) are added to the obtained solution of the (meth)acrylic acid ester polymer (A) and mixed thoroughly to obtain a pressure-sensitive adhesive composition P+ (coating liquid) diluted with a solvent.

[0109] In addition, if any of the above components is a solid component, or a component that precipitates when mixed with other components in an undiluted state, or a liquid component that has high viscosity, the component may be dissolved or diluted in a dilution solvent before being mixed with the other components.

[0110] Examples of dilution solvents include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methylene chloride and ethylene chloride; alcohols such as methanol, ethanol, propanol, butanol, and 1-methoxy-2-propanol; ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; and cellosolve-based solvents such as ethyl cellosolve.

[0111] The concentration and viscosity of the prepared coating solution may be within a range that allows coating, and can be appropriately selected depending on the situation. For example, two or more components to be incorporated into the PSA composition P+ may be mixed and then diluted with the above-mentioned dilution solvent so that the concentration of the PSA composition P+ is 10 to 60% by mass. It should be noted that adding a dilution solvent or the like is not necessarily required to obtain the coating solution; as long as the PSA composition P+ has a viscosity that allows coating, adding a dilution solvent is not necessary. When the (meth)acrylic acid ester polymer is obtained by solution polymerization, the PSA composition P+ becomes a coating solution in which the polymerization solvent for the (meth)acrylic acid ester polymer itself serves as the dilution solvent.

[0112] (2.2. Production of Pressure-Sensitive Adhesive) The pressure-sensitive adhesive is preferably obtained by crosslinking the above-mentioned pressure-sensitive adhesive composition P+. Crosslinking of the pressure-sensitive adhesive composition P+ can usually be carried out by heat treatment. This heat treatment can also serve as a drying treatment for volatilizing diluent solvents and the like from a coating film of the pressure-sensitive adhesive composition P+ applied to a desired object.

[0113] The heating temperature for the heat treatment is preferably 50 to 150° C., more preferably 70 to 120° C. The heating time is preferably 10 seconds to 10 minutes, more preferably 50 seconds to 2 minutes.

[0114] After the heat treatment, the coating film is dried and the resulting coating layer may be cured for about 1 to 2 weeks at room temperature (e.g., 23°C, relative humidity 50%), if necessary. If curing is required, a pressure-sensitive adhesive having a crosslinked structure in the coating layer is obtained after the curing period has elapsed. If curing is not required, a pressure-sensitive adhesive having a crosslinked structure in the coating layer is obtained after the heat treatment is completed.

[0115] Examples of methods for applying the coating solution of the pressure-sensitive adhesive composition P+ include bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

[0116] If necessary, after a predetermined curing period, the pressure-sensitive adhesive layer is formed. A window film is obtained by forming a first laminate in which at least one main surface of the second resin film and the exposed surface of the first pressure-sensitive adhesive layer are superimposed.

[0117] When the window film has a hard coat layer, it is preferable to form the hard coat layer on the other main surface of the first resin film before forming the first pressure-sensitive adhesive layer on one main surface of the first resin film. For example, a coating liquid of a composition containing an active energy ray-curable resin is applied to the other main surface of the first resin film and dried to form a coating layer. The formed coating layer is cured by irradiating it with active energy rays such as ultraviolet rays or electron beams, thereby forming a hard coat layer on the resin film.

[0118] In this specification, when it is stated that "X to Y" (X and Y are any numbers), it means "X or more and Y or less" unless otherwise specified, and also includes the meaning of "preferably greater than X" or "preferably smaller than Y". Furthermore, when it is stated that "X or more" (X is any number), it also includes the meaning of "preferably greater than X" unless otherwise specified, and when it is stated that "Y or less" (Y is any number), it also includes the meaning of "preferably smaller than Y" unless otherwise specified. Furthermore, "solid content" means non-volatile components remaining in the composition after the solvent in the composition has been evaporated, and does not necessarily mean that the composition is solid.

[0119] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and may be modified in various ways within the scope of the present invention.

[0120] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0121] Example 1 1. Preparation of (meth)acrylic acid ester polymer (A) A (meth)acrylic acid ester polymer (A) was prepared by copolymerizing 55 parts by mass of 2-ethylhexyl acrylate, 32 parts by mass of methyl acrylate, 1 part by mass of methyl methacrylate, 10 parts by mass of acrylic acid, and 2 parts by mass of 2-hydroxyethyl methacrylate. The molecular weight of the resulting (meth)acrylic acid ester polymer (A) was measured by the method described below, and the weight average molecular weight (Mw) was found to be 650,000.

[0122] The weight average molecular weight (Mw) is a polystyrene-equivalent weight average molecular weight measured using gel permeation chromatography (GPC) under the following conditions (GPC measurement). (Measurement conditions) GPC measurement device: HLC-8020, manufactured by Tosoh Corporation GPC columns (passed in the following order): TSK guard column HXL-H, TSK gel GMHXL (x2), TSK gel G2000HXL, manufactured by Tosoh Corporation Measurement solvent: tetrahydrofuran Measurement temperature: 40°C

[0123] 2. Preparation of Pressure-Sensitive Adhesive Composition P1 100 parts by mass (solids content equivalent; the same applies hereinafter) of the (meth)acrylic acid ester polymer (A) obtained above, 0.5 parts by mass of a metal chelate crosslinking agent (manufactured by Toyochem Co., Ltd., product name "BXX4805") (B1) as the crosslinking agent (B), and 2.5 parts by mass of a triazine ultraviolet absorber (manufactured by BASF Corporation, product name "Tinuvin 477") (D1) as the ultraviolet absorber (D), were mixed, thoroughly stirred, and diluted with methyl ethyl ketone to obtain a coating liquid of Pressure-Sensitive Adhesive Composition P1 containing a polymerization solvent and a dilution solvent.

[0124] 3. Preparation of Pressure-Sensitive Adhesive Composition P2 100 parts by mass (solids content equivalent; the same applies hereinafter) of the (meth)acrylic acid ester polymer (A) obtained above, 0.5 parts by mass of a metal chelate crosslinking agent (manufactured by Toyochem Co., Ltd., product name "BXX4805") (B1) as the crosslinking agent (B), 2 parts by mass of a carbon black pigment (C1) having the properties shown in Table 2 as the colorant (C), and 2.5 parts by mass of a triazine ultraviolet absorber (manufactured by BASF Corporation, product name "Tinuvin 477") (D1) as the ultraviolet absorber (D) were mixed, thoroughly stirred, and diluted with methyl ethyl ketone to obtain a coating liquid of Pressure-Sensitive Adhesive Composition P2 containing a polymerization solvent and a dilution solvent.

[0125] 4. Manufacture of window film A 38 μm thick polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Corporation, product name "Diafoil T600E38") was prepared as a transparent first resin film. The prepared PSA composition P2 coating solution was applied to one main surface of the first resin film using a die coater. After coating, the film was heated at 90°C for 1 minute to thoroughly remove the dilution solvent, forming a 10 μm thick first PSA layer on the first resin film.

[0126] A 38 μm-thick polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Corporation, product name "Diafoil T600E38") was prepared as a transparent second resin film. The exposed main surface (the main surface not in contact with the first resin film) of the first pressure-sensitive adhesive layer formed on the first resin film was bonded to the main surface of the second resin film.

[0127] Next, the prepared PSA composition P1 coating solution was applied to the release-treated surface of a release sheet, one side of which had been release-treated with a silicone-based release agent, using a die coater. After coating, the sheet was heated at 90°C for 1 minute to thoroughly remove the dilution solvent, forming a second PSA layer 25 µm thick on the release sheet.

[0128] The main surface of the second resin film on which the first pressure-sensitive adhesive layer was not formed was laminated with the exposed main surface of the second pressure-sensitive adhesive layer formed on the release sheet (the main surface not in contact with the release sheet), and then cured for 7 days under conditions of 23°C and a relative humidity of 50%, to obtain a window film having a configuration of release sheet / second pressure-sensitive adhesive layer / second resin film / first pressure-sensitive adhesive layer / first resin film.

[0129] Examples 2 to 4, Comparative Examples 1 to 3 Window films were produced in the same manner as in Example 1, except that the first and second pressure-sensitive adhesive layers were formed using pressure-sensitive adhesive compositions P1 to P6 containing (meth)acrylic acid ester polymer (A) in which the mass ratios of monomers used for copolymerization and the weight-average molecular weights are as shown in Table 1, and other additives in the amounts shown in Table 1. The configurations of the produced window films are shown in Table 3.

[0130]

[0131] Details of the abbreviations and the like in Table 1 are as follows: ((Meth)acrylic acid ester polymer (A)) 2EHA: 2-ethylhexyl acrylate MA: methyl acrylate MMA: methyl methacrylate AA: acrylic acid HEMA: 2-hydroxyethyl methacrylate BA: n-butyl acrylate ACMO: N-acryloylmorpholine IBXA: isobornyl acrylate HEA: 2-hydroxyethyl acrylate (Crosslinking agent (B)) B1: metal chelate-based crosslinking agent (manufactured by Toyochem Co., Ltd., product name "BXX4805") B2: tolylene diisocyanate-based crosslinking agent (manufactured by Toyochem Co., Ltd., product name "BHS-8515") (Coloring agent (C)) C1: carbon black-based pigment (having the optical properties shown in Table 2) C2: carbon black-based pigment (having the optical properties shown in Table 2) (UV absorber (D)) D1: Triazine-based ultraviolet absorber (manufactured by BASF, product name "Tinuvin 477")

[0132] Regarding colorant (C), Table 2 shows the optical properties of solutions obtained by diluting colorants C1 and C2 listed in Table 1 by a factor of 10,000 with ethyl acetate. The optical properties shown in Table 2 were calculated from the haze values ​​(%) obtained for the diluted solutions using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "SH-7000") in accordance with JIS K7136:2000. The "haze value difference" is the difference between the haze value at a wavelength of 780 nm and the haze value at a wavelength of 380 nm, the "average haze" is the average value of the haze values ​​at a wavelength of 780 nm and the haze value at a wavelength of 380 nm, and the "standard deviation of the haze values" is the standard deviation of the haze values ​​at each wavelength in 5-nm increments in the wavelength range from 380 nm to 780 nm.

[0133]

[0134] The pressure-sensitive adhesive layers and window films prepared in the examples and comparative examples were evaluated as follows.

[0135] (Total Light Transmittance and Haze Value of Window Film) The release sheet was peeled from the window film obtained in the Examples and Comparative Examples, and the exposed pressure-sensitive adhesive layer was attached to a 3 mm thick float glass plate under an environment of 23 ° C and 50% relative humidity, and this was used as a measurement sample. After background measurement was performed using the float glass plate, the total light transmittance of the window film was measured for the measurement sample using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH-5000) in accordance with JIS K7361-1:1997. In addition, the haze value of the window film for the measurement sample was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH-5000) in accordance with JIS K7136:2000. The results are shown in Table 3.

[0136] (Adhesion Strength of Window Film When Second Pressure-Sensitive Adhesive Layer is Attached to Glass) The adhesion strength of the window films obtained in the Examples and Comparative Examples was measured as follows. The obtained window films were cut into a width of 25 mm and a length of 100 mm. Under an environment of 23°C and 50% relative humidity, the release sheet was peeled from the window film, and the exposed second pressure-sensitive adhesive layer was attached to a 3 mm-thick float glass plate. The window film was applied by pressing it back and forth once under the weight of a 2 kg roller, and this was used as a sample for measuring adhesion strength. The obtained measurement sample was left for 24 hours under conditions of 23°C and 50% relative humidity. After leaving the sample, the adhesion strength (N / 25 mm) of the second pressure-sensitive adhesive layer was measured using a tensile tester (Tensilon, manufactured by Orientec Co., Ltd.) at a peel speed of 0.3 m / min and a peel angle of 180°. Note that measurements were performed under conditions other than those described here in accordance with JIS Z0237:2009. The results are shown in Table 3.

[0137] (Evaluation of Visibility (Privacy Protection) of Window Film) Black acrylic plates were attached to each other to create a cubic container with one side open and 5 cm on each side. The container was placed with the open side facing up, and a piece of paper with alphanumeric characters written on it was placed on the bottom. Next, the open side was covered with a measurement sample (window film attached to a float glass plate) prepared for measuring the total light transmittance and haze value of the window film. Here, the side of the measurement sample with the window film attached faced the bottom of the container. The paper placed on the bottom of the container was observed from 30 cm above the measurement sample. The alphanumeric characters on the paper were created using word processing software (product name "Word" manufactured by Microsoft Corporation) and printed in either a 10-point font size or a 20-point font size, both of which were printed in black on white paper. The visibility was evaluated according to the following criteria. The results are shown in Table 3. A: 20-point characters are difficult to read. F: 10-point characters are easily readable.

[0138] (External Visibility Evaluation of Window Film) A measurement sample (window film attached to a float glass plate) prepared for measuring the total light transmittance and haze value of the window film was placed on the float glass plate side of the measurement sample. A flashlight from a smartphone (product name "iPhone (registered trademark) 14" manufactured by Apple Inc.) was turned on as a light source at the initial light intensity. The measurement sample was placed 2 cm away from the light source, and the presence or absence of a halo due to light diffusion was confirmed when the light source was viewed through the measurement sample. The visibility was evaluated according to the following criteria. The results are shown in Table 3. A: No halo with a diameter of 2 cm or more was observed. B: No clear halo with a diameter of 2 cm or more was observed, but a faint halo with a diameter of 2 cm or more was observed. F: A clear halo with a diameter of 2 cm or more was observed.

[0139]

[0140] From Table 3, it was confirmed that the window films of the examples had excellent visibility and blocking properties, since the total light transmittance and haze value satisfied the above-mentioned ranges.

[0141] The window film of the present invention can be suitably used, for example, as an adhesive film to be attached to an adherend where privacy protection and visibility are required.

[0142] REFERENCE SIGNS LIST 1... window film 11... first resin film 12... second resin film 20... intermediate layer (first adhesive layer) 30... adhesive layer (second adhesive layer)

Claims

1. A window film having a transparent first resin film, a transparent second resin film, and a colored intermediate layer, wherein the intermediate layer is disposed between one main surface of the first resin film and one main surface of the second resin film, and having a total light transmittance of 60% or less and a haze value of 8% or less.

2. The window film of claim 1, wherein the window film does not have a layer containing metal.

3. The window film according to claim 1 or 2, wherein the intermediate layer is an adhesive layer made of an acrylic adhesive.

4. A window film according to claim 1 or 2, wherein the intermediate layer is formed from an adhesive composition containing a (meth)acrylic acid alkyl ester polymer, and the (meth)acrylic acid alkyl ester polymer contains units derived from a monomer having a carboxy group in the molecule.

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