Window film

Abstract

[Problem] To provide a window film in which blocking during production is suppressed, and which has good visibility through the window film. [Solution] A window film comprising a base material, an adhesive layer that is disposed on one main surface of the base material, and a release sheet that is disposed on the adhesive layer, wherein a main surface of the adhesive layer and a release surface of the release sheet are in contact, and the release surface has an arithmetic average height Sa of not more than 20 nm and a peak density Spd of not less than 4000 / mm2.

Description

Window film

[0001] The present invention relates to a window film.

[0002] A window film is an adhesive film that is attached to windows of moving bodies such as automobiles and buildings, and is widely used.

[0003] A window film usually has a base material and an adhesive layer, and further, in order to protect the adhesive layer, a release sheet is disposed on the adhesive layer. The window film is fixed to a window as an adherend through the adhesive layer, but it is required that the visibility from the outside through the window film is good.

[0004] Patent Document 1 discloses an adhesive sheet with a release film used for optical applications. In this adhesive sheet, in order to suppress the reduction in visibility through the adhesive sheet caused by orange peel or streaks present on the adhesive surface, the maximum height Rz of the surface on the adhesive surface side of the release film is set to 400 nm or less to increase the smoothness of the adhesive surface.

[0005] Japanese Patent Application Laid-Open No. 2021-161192

[0006] A window film is usually manufactured by forming an adhesive layer on a release sheet or a base material and then laminating the adhesive layer and the base material or the release sheet. The release sheet is wound in a roll for storage and transportation, and during the manufacture of the window film, the release sheet is unwound from the roll and comes into contact with the adhesive layer.

[0007] As in Patent Document 1, when the smoothness of the contact surface with the adhesive layer in the release sheet is increased, in the roll of the release sheet, the contact area between the main surface (contact surface) on the side in contact with the adhesive layer and the main surface (non-contact surface) on the side not in contact with the adhesive layer becomes large, and the contact surface with the adhesive layer and the non-contact surface with the adhesive layer are likely to stick together. Such a phenomenon is called blocking. When blocking occurs, there is a problem that it becomes difficult to unwind the release sheet.

[0008] Furthermore, when winding the release sheet into a roll, the tension of winding generates stress inside the roll, compressing the radially laminated release sheets. This stress tends to be greater near the core of the roll. As a result, the contact between the contact surface with the adhesive layer and the non-contact surface with the adhesive layer becomes stronger near the core, making blocking more likely when unwinding the release sheet located near the core. Moreover, when blocking occurs, the surface texture of the contact surface with the adhesive layer becomes rough due to the pressure during contact (fine irregularities are formed). Consequently, during the manufacture of window film, in addition to a decrease in production efficiency due to blocking, the fine irregularities formed on the contact surface with the adhesive layer were transferred to the adhesive layer, sometimes resulting in an orange peel texture on the surface of the adhesive layer.

[0009] When window film is applied to a substrate (window) via an adhesive layer that has developed an orange peel texture, the light entering the window is dispersed in the adhesive layer, resulting in a problem where visibility to the outside through the window film is reduced.

[0010] This invention has been made in view of the above circumstances, and aims to provide a window film that suppresses blocking during manufacturing and provides good visibility through the window film.

[0011] The embodiments of the present invention are as follows: [1] A window film having a substrate, an adhesive layer disposed on one main surface of the substrate, and a release sheet disposed on the adhesive layer, wherein the main surface of the adhesive layer and the release surface of the release sheet are in contact, the arithmetic mean height Sa of the release surface is 25 nm or less, and the peak density Spd is 4000 pins / mm 2 That concludes our description of window film.

[0012] [2] The window film according to [1], having a functional layer disposed on the other main surface of the base material.

[0013] [3] The window film described in [2], wherein the functional layer is a hard coat layer.

[0014] According to the present invention, blocking during manufacturing is suppressed, and a window film with good visibility through the window film can be provided.

[0015] Figure 1A is a schematic cross-sectional view showing an example of the configuration of the window film according to this embodiment. Figure 1B is a schematic cross-sectional view showing another example of the configuration of the window film according to this embodiment.

[0016] The present invention will now be described in detail based on specific embodiments.

[0017] (1. Window Film) As shown in Figure 1A, the window film 1 according to this embodiment comprises a base material 10, an adhesive layer 20, and a release sheet 30 for protecting the adhesive layer 20 until it is attached to an object. In the release sheet 30, at least the main surface that contacts the main surface 20b of the adhesive layer 20 is a release surface 30a that has release properties. Furthermore, the window film may have other components as long as the effects of the present invention are obtained. That is, the window film may have layers other than the base material, adhesive layer, and release sheet.

[0018] When the window film 1 is used, the release sheet 30 is peeled off from the main surface 20b of the adhesive layer 20, and the main surface 20b is attached to the adherend (mainly the windows of automobiles and buildings), and performs the predetermined function.

[0019] As mentioned above, in window films, improving the smoothness of the adhesive layer surface reduces the occurrence of orange peel texture on the adhesive layer surface. To achieve this, it is necessary to improve the smoothness of the release sheet surface (release surface) that comes into contact with the adhesive layer surface.

[0020] However, simply improving the smoothness of the release surface of the release sheet led to a problem where the release sheets would easily stick together on the roll, causing blocking. Furthermore, the surface roughness of the release surface caused by the sticking of the release sheets was transferred to the surface of the adhesive layer, resulting in an orange peel texture.

[0021] Therefore, in this embodiment, by controlling the surface properties of the release sheet's contact surface with the adhesive layer (release surface) as follows, both blocking resistance and reduction of the orange peel texture of the adhesive layer are achieved. The configuration of the window film will be described in detail below.

[0022] (2. Release Sheet) The release sheet protects the adhesive until the window film is used and is peeled off from the adhesive layer when the window film is applied to the substrate. The thickness of the release sheet may be 10 to 250 μm, 15 to 200 μm, 20 to 150 μm, or 25 to 100 μm.

[0023] In this embodiment, the surface properties of the peeled surface are controlled as follows.

[0024] Specifically, if Sa is the arithmetic mean height of the release surface of the release sheet, then Sa is 20 nm or less. The arithmetic mean height of the surface is one of the height parameters classified as surface roughness parameters as defined in ISO 25178, and is the average value of the absolute values ​​of the peak height and valley depth on the measured surface. Sa represents the average surface roughness over the entire measured surface, with the influence of local irregularities suppressed.

[0025] Because Sa is within the above range, the surface roughness of the release surface of the release sheet is smooth overall. As a result, even if the surface properties of the release surface are transferred to the adhesive layer, the occurrence of orange peel texture on the surface of the adhesive layer is reduced.

[0026] Sa may be 25 nm or less, 23 nm or less, or 20 nm or less. On the other hand, from a manufacturing standpoint, the lower limit of Sa may be 8 nm.

[0027] Sa can be controlled by adjusting the smoothness of the surface on which the release agent layer composition is applied to the substrate of the release sheet described later, the method of applying the release agent layer composition, the composition of the coating liquid containing the release agent layer composition, and so on.

[0028] Furthermore, if we denote the density of peaks on the release surface of the release sheet as Spd, then Spd is 4000 peaks / mm². 2That concludes the explanation. Peak density is one of the morphological parameters classified as surface roughness parameters in ISO 25178, and is a value that represents the number of peaks per unit area on the measured surface. Spd indicates the proportion of protrusions on the measured surface. Protrusions that are 5% or more of the maximum height Sz of the measured surface are counted as peaks.

[0029] When Spd is within the above range, the area of ​​surface contact between the release surface and the other surface of the release sheet decreases, and the area of ​​minute point contact increases. As a result, compared to when Spd is smaller than the above range, the contact area between the release surface and the other surface of the release sheet decreases, and blocking can be suppressed.

[0030] Therefore, by having Sa and Spd within the above range, instead of relatively large bumps that would cause an orange peel texture, minute protrusions that are not recognizable as orange peel texture are formed on the release surface within a predetermined range, thereby achieving both high smoothness and reduced contact area on the release surface. As a result, blocking during the unwinding of the release sheet is suppressed, and furthermore, even if the surface properties of the release surface are transferred to the surface of the adhesive layer, the occurrence of orange peel texture is suppressed.

[0031] Spd can be controlled by adjusting the amount and size of particles added to the substrate for the release sheet. Silica particles and / or calcium carbonate can be used as particles.

[0032] The surface properties of the release surface of a release sheet can be measured as follows. When the release surface is represented as an XY plane using mutually orthogonal X and Y axes, the surface properties of the release surface can be represented as a displacement in the Z-axis direction perpendicular to the XY plane. In other words, the surface roughness of the release surface is represented as a three-dimensional (X, Y, Z) shape.

[0033] Therefore, the surface roughness parameters, arithmetic mean height Sa and Spd, are calculated from the measurement results of the displacement in the Z-axis direction within the measurement area. The size of the measurement area can be, for example, a rectangular area of ​​200-2000 μm × 200-2000 μm.

[0034] In this embodiment, it is preferable to use a non-contact white light interference microscope for measuring surface properties. In a white light interference microscope, the optical path of light emitted from a white light source is divided into two; one path is directed to a reference mirror, and the other to the sample surface, and the light reflected from both is imaged by a camera. In the obtained image, the three-dimensional shape of the sample surface is obtained by converting the information of interference fringes caused by the optical path difference due to the unevenness of the sample surface into height information. The magnification of the white light interference microscope can be appropriately set according to the values ​​of Sa and Spd.

[0035] The measurement results of the surface properties of a measurement surface, obtained as three-dimensional shape data, mainly include factors attributable to the shape of the measurement surface, factors attributable to the surface roughness of the measurement surface, and factors attributable to the waviness of the measurement surface. Therefore, the measurement results of the surface properties of a measurement surface are a contour curve obtained by combining these factors. These factors are distinguished by the length of their period (wavelength): factors attributable to surface roughness have short periods (short wavelengths), factors attributable to shape have long periods (long wavelengths), and factors attributable to waviness have periods intermediate between these two.

[0036] Based on the obtained surface roughness curve, Sa and Spd are calculated in accordance with the method specified in ISO 25178. That is, they can be measured using the same method as specified in ISO 25178, but they may also be measured under conditions different from those described in ISO 25178.

[0037] The surface roughness curve can be obtained from the measurement results by known filtering, planarization, etc. For example, analysis software included with a white light interference microscope or commercially available analysis software can be used.

[0038] (2.1. Composition of the release sheet) The composition of the release sheet can be any configuration as long as Sa and Spd on the release surface are controlled within the above range. For example, the release sheet may consist of one layer (single layer) or two or more layers of substrate, or the surface of the substrate may be treated to release from the viewpoint of controlling the release force, Sa and Spd. That is, the surface of the substrate may be modified, or a material not derived from the substrate (for example, a release agent layer) may be formed on the surface of the substrate.

[0039] In this embodiment, from the viewpoint of making it easier to keep Sa and Spd within the above range, the structure of the release sheet is preferably one that includes a base material, more preferably one in which the surface of the base material is peeled, and even more preferably one in which the base material and a release agent layer are present. That is, it is preferable that the peeling surface is the surface of the release agent layer. This makes it easier to control the surface properties of the peeling surface in the release sheet.

[0040] (2.2. Substrate) The substrate of the release sheet can be any material that can support the adhesive layer until it is attached to the substrate. It is usually composed of a film mainly made of resin-based material (hereinafter referred to as "resin film").

[0041] Specific examples of the resin film include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene vinyl acetate copolymer film, ionomer resin film, ethylene-(meth)acrylic acid copolymer film, ethylene-(meth)acrylate copolymer film, polystyrene film, polycarbonate film, polyimide film, fluororesin film, etc. Cross-linked films of these may also be used. Further, laminated films of these may also be used. From the perspective of SDGs, as the material constituting the resin film, a material with a high biomass content may be used, a material that can be recycled or reused may be used, or a recycled or reused material may be used.

[0042] The base material may contain various additives such as a colorant, a flame retardant, a plasticizer, an antistatic agent, a lubricant, a filler, etc. in the above resin film.

[0043] The thickness of the base material is not particularly limited within the range of the thickness of the above release sheet as long as it can support the adhesive layer. The thickness of the base material may be 10 to 250 μm, or 15 to 200 μm, or 20 to 150 μm, or 25 to 100 μm.

[0044] (2.3. Release agent layer) When the release sheet has a base material and a release agent layer, the release agent layer of the release sheet imparts releasability from the adhesive layer to the release sheet and constitutes the release surface. The release agent layer is preferably a layer obtained by curing a composition for the release agent layer described later.

[0045] The thickness of the release agent layer is not particularly limited as long as it can exhibit the desired releasability. From the perspective of adjusting the surface properties of the release sheet within the above range, it may be 30 to 250 nm, or 50 to 200 nm, or 70 to 150 nm.

[0046] The composition for the release agent layer can include, for example, an alkyd-based release agent, a silicone-based release agent, a fluorine-based release agent, an unsaturated polyester-based release agent, a polyolefin-based release agent, and a wax-based release agent. In this embodiment, the composition for the release agent layer preferably includes a silicone-based release agent.

[0047] (2.4. Silicone-based release agent) As the silicone-based release agent, it is preferable to use a silicone-based release agent containing a silicone having a dimethylpolysiloxane as a basic skeleton.

[0048] When the total weight of the composition for the release agent layer (excluding the catalyst described later) is 100 parts by mass, the content of the silicone composed of dimethylpolysiloxane may be less than 100 parts by mass, or less than 90 parts by mass, or less than 80 parts by mass, or less than 70 parts by mass. The lower limit value of the content is 0 parts by mass.

[0049] The silicone may be any of addition reaction type, condensation reaction type, and energy ray curing type such as ultraviolet curing type and electron beam curing type, but it is preferably an addition reaction type silicone. The addition reaction type silicone has high reactivity and excellent productivity, and has advantages such as easy stability of the release force after production and no curing shrinkage compared with the condensation reaction type.

[0050] Specific examples of the addition reaction type silicone include organopolysiloxanes having two or more alkenyl groups having 2 to 10 carbon atoms such as vinyl group, allyl group, propenyl group, and hexenyl group at the terminal and / or side chain of the molecule.

[0051] When using such an addition reaction type silicone, it is preferable to use a crosslinking agent and a catalyst in combination. [[ID= XVII]]

[0052] Examples of crosslinking agents include organopolysiloxanes having at least two hydrogen atoms bonded to silicon atoms in one molecule. Specifically, examples include dimethylhydrogensiloxy group-ended dimethylsiloxane-methylhydrogensiloxane copolymers, trimethylsiloxy group-ended dimethylsiloxane-methylhydrogensiloxane copolymers, trimethylsiloxy group-ended methylhydrogenpolysiloxanes, and poly(hydrogensilsesquioxanes).

[0053] Examples of catalysts include particulate platinum, particulate platinum adsorbed on a carbon powder support, chloroplatinic acid, alcohol-modified chloroplatinic acid, olefin complexes of chloroplatinic acid, palladium, and platinum group metal compounds such as rhodium.

[0054] By using such a catalyst, the curing reaction of the release agent layer composition can be made to proceed more efficiently.

[0055] The content of the silicone-based release agent when the total weight of the release agent layer composition (excluding the catalyst) is 100 parts by mass may be 30 to 100 parts by mass or 50 to 100 parts by mass, from the viewpoint of keeping the release force within the range described above.

[0056] (3. Substrate) The substrate according to this embodiment is a material that provides rigidity to the window film and has the function of supporting the adhesive layer. The material of the substrate is not particularly limited as long as it has the above function. In this embodiment, a resin material is preferably used as the substrate.

[0057] Examples of resin materials include polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polyolefin resins such as polyethylene, polypropylene, poly-methylpentene-1, and polybutene-1; polyurethane resins; polycarbonate resins; polyvinyl chloride resins; polyethersulfone resins; polyethylene sulfide resins; styrene resins; acrylic resins; polyamide resins; and cellulose resins such as cellulose acetate. These are used to create films or laminated films of these materials.

[0058] Among these, films made of polyolefin resins and polyester resins, or laminated films thereof, are preferred due to their excellent mechanical strength and cost-effectiveness. From the viewpoint of easily obtaining window films that satisfy the optical properties described later, films made of polyester resins or laminated films thereof are particularly preferred, and among these, polyethylene terephthalate films or laminated films containing polyethylene terephthalate are preferred.

[0059] The laminated film described above is preferably a film made by laminating one or more types of resin materials, and such laminated films include wavelength-selective laminated films that have a multilayer structure having at least two nanoscale layers. If a window film that satisfies the optical properties described later can be obtained, a laminated film without wavelength selectivity or a laminated film with wavelength selectivity can be appropriately selected and used. Wavelength selectivity here refers to the property of absorbing or reflecting in a specific wavelength range, and a wavelength-selective laminated film means a laminated film that can control the transmittance in a specific wavelength range.

[0060] To improve adhesion with the layer provided on the substrate, one or both sides of the substrate may be surface-treated by oxidation, embossing, or other methods, or another layer such as a primer layer may be formed. Examples of oxidation methods include corona discharge treatment, chromic acid treatment (wet), flame treatment, hot air treatment, and ozone / ultraviolet irradiation treatment. Examples of embossing methods include sandblasting and solvent treatment.

[0061] The thickness of the base material is not particularly limited as long as it exhibits a predetermined rigidity, and can be set appropriately according to the intended use. In this embodiment, from the viewpoint of ensuring mechanical strength suitable for workability during construction, the thickness of the base material may be 5 to 200 μm, 10 to 150 μm, or 15 to 100 μm.

[0062] The substrate may be transparent or colored. Furthermore, the substrate may have metals such as aluminum, gold, silver, copper, nickel, cobalt, chromium, tin, or indium deposited onto it.

[0063] (4. Adhesive Layer) The adhesive layer according to this embodiment fixes the window film to the surface of the window, allowing the window film to perform its predetermined functions. The window to which the adhesive layer according to this embodiment is attached may be made of glass material or of a glass substitute material such as plastic. The adhesive layer is formed by the adhesive described later being arranged in layers.

[0064] The adhesive layer may consist of one layer (single layer) or of two or more layers. If the adhesive layer has multiple layers, these layers may be identical or different from each other, and there are no particular restrictions on the combination of layers that make up these multiple layers.

[0065] The thickness of the adhesive layer may be 1 to 100 μm, 3 to 70 μm, 5 to 50 μm, or 7 to 35 μm. This allows for the development of desirable adhesive properties and optical properties.

[0066] (4.1. Composition of the adhesive) The composition of the adhesive according to this embodiment may be any of the following: acrylic adhesive, polyester adhesive, polyurethane adhesive, rubber adhesive, silicone adhesive, etc. Furthermore, the adhesive may be an emulsion type, a solvent type, or a solvent-free type. In addition, the adhesive may or may not have a crosslinked structure.

[0067] In this embodiment, from the viewpoint of ease of realizing the above-mentioned physical properties, and from the viewpoint of adhesive properties, optical properties, etc., an acrylic adhesive is preferred, and an acrylic adhesive having a crosslinked structure is more preferred.

[0068] Specifically, the adhesive is preferably an adhesive obtained from an adhesive composition containing a (meth)acrylic acid polymer (A) (hereinafter sometimes referred to as "adhesive composition P"), and more preferably an adhesive obtained by crosslinking an adhesive composition containing a (meth)acrylic acid polymer (A) and a crosslinking agent (B), that is, an adhesive containing a crosslinked product of a (meth)acrylic acid polymer (A) and a crosslinking agent (B). Such an adhesive is likely to satisfy the above-mentioned physical properties. In this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. Furthermore, the concept of "polymer" is also included in the concept of "polymer".

[0069] (4.1.1. (Meth)acrylic acid ester polymer (A)) The (meth)acrylic acid ester polymer (A) preferably contains units derived from monomers, including units derived from alkyl (meth)acrylic acid ester and units derived from monomers having reactive functional groups in the molecule (reactive functional group-containing monomers).

[0070] The (meth)acrylic acid ester copolymer (A) contains units derived from (meth)acrylic acid alkyl ester, thereby enabling the adhesive to exhibit desirable tackiness. As the (meth)acrylic acid alkyl ester, an alkyl ester having 1 to 20 carbon atoms in the alkyl group is preferred. The alkyl group may be linear, branched, or have a cyclic structure.

[0071] Examples of alkyl (meth)acrylate esters having 1 to 20 carbon atoms in the alkyl group 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.

[0072] Among these, alkyl (meth)acrylate esters having 1 to 8 carbon atoms in the alkyl group are preferred. Specifically, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred, and methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, and 2-ethylhexyl acrylate are particularly preferred. These may be used individually, but it is preferable to use them in combination.

[0073] The (meth)acrylic acid ester polymer preferably contains 50 to 99% by mass of units derived from alkyl (meth)acrylic acid esters having 1 to 20 carbon atoms in the alkyl group, as units derived from monomers that constitute the polymer. It may also contain 60 to 98% by mass or 70 to 97.5% by mass. This makes it easier for the resulting adhesive to exhibit suitable tackiness. In addition, other monomer components can be introduced into the (meth)acrylic acid ester polymer (A) in any desired amount.

[0074] The (meth)acrylic acid ester polymer (A) contains units derived from a monomer containing a reactive functional group. Through these reactive functional groups, the (meth)acrylic acid ester polymer reacts with the crosslinking agent (B), described later, forming a crosslinked structure (three-dimensional network structure) in the adhesive. As a result, an adhesive with the desired cohesive force is obtained. Note that the reactive functional group may be used solely to alter the properties of the adhesive, and it is not necessary for the reactive functional group to react with the crosslinking agent (B).

[0075] Preferred monomers containing reactive functional groups include monomers having a hydroxyl group in the molecule (hydroxyl group-containing monomers), monomers having a carboxyl group in the molecule (carboxyl group-containing monomers), and monomers having an amino group in the molecule (amino group-containing monomers). These reactive functional group-containing monomers may be used individually or in combination of two or more. Among these, hydroxyl group-containing monomers or carboxyl group-containing monomers are preferred. This facilitates the formation of a crosslinked structure via the crosslinking agent (B), and makes it easier to satisfy the above-mentioned physical properties related to adhesiveness.

[0076] Examples of hydroxyl group-containing monomers include hydroxyalkyl esters of (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. Among these, hydroxyalkyl esters of (meth)acrylates having a hydroxyalkyl group with 1 to 4 carbon atoms are preferred from the viewpoint of easily achieving the above-mentioned adhesive properties. Specifically, for example, 2-hydroxyethyl (meth)acrylate or 4-hydroxybutyl (meth)acrylate are preferred, and 2-hydroxyethyl (meth)acrylate is more preferred. These may be used alone or in combination of two or more.

[0077] 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 or methacrylic acid is preferred, and acrylic acid is particularly preferred, from the viewpoint of the reactivity of the carboxyl group in the resulting (meth)acrylic acid ester polymer (A) with the crosslinking agent and copolymerizability with other monomers. These may be used alone or in combination of two or more.

[0078] The (meth)acrylic acid ester polymer may contain, as units derived from monomers constituting the polymer, 1 to 30% by mass, 1.5 to 22% by mass, 2 to 16% by mass, or 2.5 to 12% by mass of units derived from monomers.

[0079] It is preferable that the (meth)acrylic acid ester polymer (A) does not contain carboxyl group-containing monomers as monomer units constituting the polymer. By not containing carboxyl group-containing monomers, the increase in adhesive strength to the adherend (e.g., glass) over time is suppressed, and the generation of adhesive residue when peeling is easily suppressed. Furthermore, since the carboxyl group is an acidic component, even if the object to be attached contains transparent conductive films such as tin-doped indium oxide (ITO), metal films, or metal meshes that are susceptible to problems caused by acid, it is possible to suppress problems caused by acid (corrosion, change in resistance, etc.).

[0080] Here, "not containing carboxyl group-containing monomers" means substantially not containing carboxyl group-containing monomers, and includes not only cases where no carboxyl group-containing monomers are present at all, but also cases where carboxyl group-containing monomers are present to an extent that does not cause corrosion of transparent conductive films or metal wiring due to carboxyl groups. Specifically, the (meth)acrylic acid ester polymer (A) may contain carboxyl group-containing monomers as monomer units in an amount of 0.1% by mass or less, preferably 0.01% by mass or less, and more preferably 0.001% by mass or less.

[0081] In this embodiment, it is preferable that the (meth)acrylic acid ester polymer (A) contains monomers that do not contain reactive functional groups as monomer units constituting the polymer. This is because it does not inhibit the effects of monomers containing reactive functional groups as described above. Examples of such monomers include unreactive nitrogen atom-containing monomers such as N-vinyl-2-pyrrolidone, alkoxyalkyl (meth)acrylate esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, vinyl acetate, and styrene. Among these, it is preferable to include vinyl acetate from the viewpoint that the resulting adhesive will easily exhibit the desired adhesive strength. These may be used individually or in combination of two or more.

[0082] The (meth)acrylic acid ester polymer (A) preferably contains 1 to 15% by mass of units derived from monomers that do not contain reactive functional groups, more preferably 2 to 10% by mass, and even more preferably 3 to 8% by mass, as monomer units constituting the polymer. This makes it easier to satisfy the above-mentioned physical properties related to adhesiveness.

[0083] The polymerization mode of the (meth)acrylic acid ester polymer (A) may be a random copolymer or a block copolymer.

[0084] The weight-average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 200,000 to 2,000,000, more preferably 300,000 to 1,400,000, even more preferably 400,000 to 1,100,000, particularly preferably 450,000 to 900,000, and most preferably 500,000 to 800,000. This makes it easier to satisfy the above-mentioned physical properties related to adhesiveness. The weight-average molecular weight in this specification is the value on a standard polystyrene basis measured by gel permeation chromatography (GPC).

[0085] In the adhesive composition P, the (meth)acrylic acid ester polymer (A) may be used alone or in combination of two or more types.

[0086] (4.1.2. Crosslinking agent (B)) The crosslinking agent (B) according to this embodiment crosslinks the (meth)acrylic acid ester polymer (A) when the adhesive composition P containing the crosslinking agent (B) is heated, etc., to form a crosslinked structure (three-dimensional network structure). As a result, the cohesive force of the resulting adhesive is improved, and the initial adhesive strength of the adhesive layer can be increased.

[0087] The crosslinking agent (B) can be any agent that reacts with the reactive groups of the (meth)acrylic acid ester polymer (A). Examples include isocyanate crosslinking agents, epoxy crosslinking agents, amine crosslinking agents, melamine crosslinking agents, aziridine crosslinking agents, hydrazine crosslinking agents, aldehyde crosslinking agents, oxazoline crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, and ammonium salt crosslinking agents. Among these, isocyanate crosslinking agents, metal chelate crosslinking agents, and epoxy crosslinking agents are preferred from the viewpoint of crosslinkability with the (meth)acrylic acid ester polymer (A). Note that the crosslinking agent (B) can be used alone or in combination of two or more types.

[0088] The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of polyisocyanate compounds include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate; aliphatic polyisocyanates such as hexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate; and their biuret and isocyanurate forms, as well as adducts which are reaction products with low molecular weight active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Among these, from the viewpoint of reactivity with hydroxyl groups, the biuret form of aliphatic polyisocyanate is more preferred, and the biuret form of hexamethylene diisocyanate is particularly preferred.

[0089] As metal chelating crosslinking agents, metal chelating compounds in which the metal atoms are aluminum, zirconium, titanium, zinc, iron, tin, etc., can be used. Among these, aluminum chelating compounds are preferred. Examples of aluminum chelating compounds include aluminum trisacetylacetonate, aluminum trisethylacetoacetate, and aluminum ethylacetoacetate diisopropylate.

[0090] Examples of epoxy crosslinking agents include 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidylaniline, and diglycidylamine. Among these, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane or N,N,N',N'-tetraglycidyl-m-xylylenediamine are preferred from the viewpoint of reactivity with carboxyl groups.

[0091] The content of the crosslinking agent (B) in the adhesive composition P is preferably 0.01 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, particularly preferably 0.15 to 1 part by mass, even more preferably 0.2 to 0.7 parts by mass, and most preferably 0.25 to 0.5 parts by mass, per 100 parts by mass of the (meth)acrylic acid ester polymer (A). This makes it easier to satisfy the above-mentioned physical properties related to adhesive strength.

[0092] (4.1.3. UV absorber (C)) The adhesive according to this embodiment preferably contains a UV absorber in order to impart a UV shielding function to the window film.

[0093] Examples of UV absorbers include compounds such as benzophenone-based, benzotriazole-based, benzoate-based, benzooxazinon-based, methine-based, triazine-based, phenyl salicylate-based, cyanoacrylate-based, and nickel complex salt-based compounds. One type may be used alone, or two or more types may be used in combination. Among the above UV absorbers (C), it is preferable to use benzophenone-based, benzotriazole-based, or triazine-based compounds, and it is more preferable to use benzophenone-based or triazine-based compounds.

[0094] Examples of benzophenone compounds include 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,4-dihydroxybenzophenone, and 2-hydroxy-4-octoxybenzophenone.

[0095] Examples of triazine compounds include 2,4-bis(2-hydroxy-4-butoxyphenyl)-6-(2,4-dibutoxyphenyl)-1,3,5-triazine, 2,4,6-tris(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine, 2,4,6-tris[2-hydroxy-4-(3-butoxy-2-hydroxypropyloxy)phenyl]-1,3,5-triazine, and 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine.

[0096] Examples of benzotriazole compounds include 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3'-tert-amyl-5'-isobutylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3'-isobutyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3'-isobutyl-5'-propylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, and 2-[2'-hydroxy-5'-(1,1,3,3-tetramethyl)phenyl]benzotriazole.

[0097] The content of the ultraviolet absorber (C) in the adhesive composition P is preferably 0.1 to 25 parts by mass, more preferably 0.5 to 18 parts by mass, even more preferably 1 to 12 parts by mass, and particularly preferably 4 to 10 parts by mass, per 100 parts by mass of the (meth)acrylic acid ester polymer (A). As a result, the resulting adhesive layer can exhibit excellent ultraviolet shielding properties.

[0098] (4.1.4. Other Additives) The adhesive composition P may contain additives commonly used in acrylic adhesives, as needed. Examples of such additives include tackifiers, coupling agents, fillers, softeners, antioxidants, light stabilizers, colorants, modifiers, rust inhibitors, flame retardants, hydrolysis inhibitors, surface lubricants, corrosion inhibitors, heat stabilizers, lubricants, antistatic agents, polymerization inhibitors, catalysts, leveling agents, thickeners, dispersants, defoamers, and surfactants. Polymerization solvents and diluent solvents described later are not included in the additives constituting the adhesive composition P.

[0099] (4.2. Physical properties of the adhesive) In this embodiment, the adhesive preferably has the following physical properties.

[0100] (4.2.1. Initial Adhesion of the Adhesive Layer) In this embodiment, it is preferable that the adhesive strength of the adhesive layer attached to the float glass is 1 N / 25 mm or more when peeled off the float glass after being left at 23°C and 50% relative humidity for 24 hours. This adhesive strength is assumed to be the initial adhesive strength when the window film is attached to the substrate. In this embodiment, this adhesive strength is defined as the initial adhesive strength.

[0101] By keeping the initial adhesive strength within the above range, strong adhesion to the substrate (such as the window surface) is achieved, allowing the window film to be stably fixed to the substrate. As a result, the window film can exhibit excellent shatterproof functionality.

[0102] The initial adhesive strength is preferably 1 to 100 N / 25 mm, more preferably 2 to 75 N / 25 mm, even more preferably 2.5 to 50 N / 25 mm, preferably 3 to 40 N / 25 mm, particularly preferably 4 to 30 N / 25 mm, and most preferably 6 to 25 N / 25 mm. The specific measurement conditions for the initial adhesive strength will be described later in the examples.

[0103] (4.2.2. Storage modulus of adhesive) In this embodiment, the storage modulus of the adhesive at 23°C is preferably 0.001 to 1 MPa, more preferably 0.01 to 0.8 MPa, even more preferably 0.03 to 0.6 MPa, preferably 0.05 to 0.5 MPa, particularly preferably 0.07 to 0.4 MPa, and most preferably 0.09 to 0.3 MPa.

[0104] The storage modulus at 80°C is preferably 0.001 to 1 MPa, more preferably 0.01 to 0.5 MPa, more preferably 0.02 to 0.4 MPa, and most preferably 0.025 to 0.3 MPa. When the storage modulus at 23°C and the storage modulus at 80°C are within the above ranges, the initial adhesion tends to be good.

[0105] The storage modulus can be adjusted, for example, by changing the composition of the adhesive, the crosslinking structure, the viscoelasticity, the weight-average molecular weight of the main polymer constituting the adhesive, and the glass transition temperature.

[0106] The storage modulus (G') can be measured by known methods. For example, the adhesive layer is prepared as a sample of a predetermined size, and the elastic modulus is measured by applying strain to the sample at a predetermined frequency within a predetermined temperature range using a dynamic viscoelasticity measuring device. From the measured elastic modulus, the storage modulus under the above conditions can be calculated. Specific measurement methods will be described in the examples below.

[0107] (4.2.3. Gel fraction of the adhesive) The gel fraction of the adhesive according to this embodiment is preferably 30 to 100%. This makes it easier to satisfy the adhesive strength and storage modulus described above.

[0108] The gel fraction of the adhesive according to this embodiment is more preferably 40 to 95%, even more preferably 45 to 90%, particularly preferably 50 to 87%, preferably 55 to 85%, and most preferably 60 to 80%. The gel fraction of the adhesive may be measured by the method shown in the test examples described later.

[0109] (5. Functional Layer) The window film according to this embodiment may have a functional layer in addition to the substrate, adhesive layer, and release sheet. This allows the window film to be given various functions. Examples of functions that the functional layer may have include hard coating properties, anti-glare properties, anti-reflection properties, ultraviolet absorption properties, infrared absorption properties, improved writing feel, Newton ring prevention properties, transparency, semi-permeability, antibacterial properties, antiviral properties, anti-fogging properties, water repellency, hydrophilicity, oil repellency, lipophilicity, sebum resistance (sebum wiping properties, sebum compatibility, sebum absorption, etc.), decorative properties, and stain resistance.

[0110] In this embodiment, as shown in Figure 1B, when the window film 1 according to this embodiment has a functional layer 40, it is preferable that the functional layer 40 is arranged on the main surface 10b of the substrate 10, opposite to the main surface 10a on which the adhesive layer 20 is arranged. Alternatively, the functional layer may be arranged between the substrate 10 and the adhesive layer 20.

[0111] The functional layer may consist of one layer having one or more of the above functions, or it may consist of multiple layers having one or more of the above functions. In this embodiment, the functional layer is preferably a hard coat layer having hard coat properties, and more preferably a hard coat layer having hard coat properties and at least one of the following functions: anti-glare, anti-reflection, ultraviolet absorption, infrared absorption, improved writing feel, Newton ring prevention, transparency, semi-permeability, antibacterial, antiviral, anti-fogging, water repellency, hydrophilicity, oil repellency, lipophilicity, sebum resistance (sebum wiping ability, sebum compatibility, sebum absorption, etc.), decorative properties, and stain resistance. The case where the functional layer is a hard coat layer will be described below.

[0112] The hard coat layer is made of a material that is superior to the base material in terms of hardness, scratch resistance, and weather resistance. In window films, the adhesive layer is attached to the substrate, so the hard coat layer is exposed to the outside. Therefore, even if some force is applied from the outside after installation, the external force is less likely to be transmitted directly to the adhesive layer and the substrate (windows of automobiles or buildings, etc.), thus exhibiting excellent impact resistance. Furthermore, even if the substrate breaks, the scattering of fragments is suppressed, thus exhibiting excellent shatterproof properties. Therefore, safety can be enhanced while maintaining the appearance of moving objects such as automobiles and buildings.

[0113] The thickness of the hard coat layer is preferably 0.5 to 20 μm, more preferably 1 to 15 μm, particularly preferably 1.5 to 10 μm, and most preferably 2 to 6 μm, from the viewpoint of surface hardness, scratch resistance, and weather resistance of the window film.

[0114] The constituent material of the hard coat layer is not particularly limited as long as it is a material that is superior to the substrate in terms of hardness, scratch resistance, weather resistance, etc. The hard coat layer according to this embodiment is preferably a cured product of a hard coat layer forming composition containing an energy ray curable resin.

[0115] (5.1. Composition for forming a hard coat layer) In this embodiment, the composition Q for forming a hard coat layer may be composed of a thermosetting material or an energy ray curable material. From the viewpoint of productivity and ease of obtaining the desired scratch resistance, the composition Q for forming a hard coat layer is preferably composed of an energy ray curable material, more preferably contains an energy ray curable resin (a), and even more preferably contains an energy ray curable resin (a) and a photopolymerization initiator (b).

[0116] (5.2. Energy-ray curable resin (a)) The energy-ray curable resin is not particularly limited and can be selected from those that are conventionally known. Examples include energy-ray curable monomers, oligomers, or compositions containing them.

[0117] Examples of energy-ray curable monomers include polyfunctional (meth)acrylates. Examples of energy-ray curable oligomers include urethane (meth)acrylates, polyester (meth)acrylates, polyether (meth)acrylates, and silicone (meth)acrylates.

[0118] Examples of polyfunctional (meth)acrylates include 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol polyfunctional (meth)acrylates such as pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, glycerol tri(meth)acrylate, triallyl(meth)acrylate, and the like.

[0119] Of these, pentaerythritol polyfunctional (meth)acrylate or dipentaerythritol polyfunctional (meth)acrylate is more preferable because it can impart appropriate hardness, scratch resistance, weather resistance, etc., to the hard coat layer.

[0120] (5.3. Photopolymerization initiator (b)) When ultraviolet light is used as the energy ray for curing the hard coat layer forming composition Q, it is preferable that the hard coat layer forming composition Q contains a photopolymerization initiator (b). By including a photopolymerization initiator, a hard coat layer can be efficiently formed when the hard coat layer forming composition Q is irradiated with ultraviolet light. Here, a photopolymerization initiator refers to a compound that generates radical species when irradiated with energy rays such as ultraviolet light.

[0121] As photopolymerization initiators, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, benzoin isobutyl ether, acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}-2-methylpropan-1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1-one, 4-( Examples include 2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone, benzophenone, p-phenylbenzophenone, 4,4-diethylaminobenzophenone, dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyldimethyl ketal, acetophenone dimethyl ketal, p-dimethylamine benzoate, oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propan-1-one], etc. One of these may be used alone, or two or more may be used in combination.

[0122] The content of the photopolymerization initiator (b) is preferably 1 to 30 parts by mass, more preferably 2 to 20 parts by mass, and even more preferably 3 to 10 parts by mass, per 100 parts by mass of the energy ray curable resin (a). This makes it easier for the resulting hard coat layer to exhibit the desired surface hardness and scratch resistance.

[0123] (5.4. Infrared absorbent (c)) The hard coat layer forming composition Q according to this embodiment may also preferably contain an infrared absorbent (c) in order to impart heat shielding performance to the window film. The infrared absorbent (c) is preferably an infrared absorbent that has excellent near-infrared absorption properties.

[0124] Examples of infrared absorbers (c) include organic infrared absorbers and inorganic infrared absorbers.

[0125] Examples of organic infrared absorbers include cyanine compounds, squalylium compounds, thiol nickel complex salt compounds, naphthalocyanine compounds, phthalocyanine compounds, triallylmethane compounds, naphthoquinone compounds, anthraquinone compounds, and amino compounds such as perchlorate of N,N,N',N'-tetrakis(p-di-n-butylaminophenyl)-p-phenylenediaminium, chlorate of phenylenediaminium, hexafluoroantimonate of phenylenediaminium, borate of phenylenediaminium, fluoride of phenylenediaminium, perchlorate of phenylenediaminium, compounds containing copper compounds and bisthiourea compounds, compounds containing phosphorus compounds and copper compounds, and copper phosphate compounds obtained by the reaction of phosphate ester compounds and copper compounds. These can be appropriately selected depending on the weather resistance and required optical properties.

[0126] Examples of inorganic infrared absorbers include titanium dioxide, zirconium oxide, tantalum oxide, niobium oxide, zinc oxide, indium oxide, tin-doped indium oxide (ITO), tin oxide, antimond-doped tin oxide (ATO), zinc antimonate, cesium oxide, zinc sulfide, hexaborides (LaB6, CeB6, PrB6, NdB6, GdB6, TbB6, DyB6, HoB6, YB6, SmB6, EuB6, ErB6, TmB6, YbB6, LuB6, SrB6, CaB6, etc.), and tungsten oxide compounds. Among these, tungsten oxide compounds, tin-doped indium oxide (ITO), and antimond-doped tin oxide (ATO) are preferred.

[0127] The amount of infrared absorbent (c) in the hard coat layer forming composition Q is preferably 10 to 300 parts by mass, and more preferably 20 to 200 parts by mass, per 100 parts by mass of energy ray curable resin (a). This makes it possible to obtain a window film that satisfies optical properties such as near-infrared transmittance, which will be described later.

[0128] In this embodiment, from the viewpoint of scratch resistance of the window film, it is also preferable that the hard coat layer does not contain an infrared absorber. By not including an infrared absorber, it becomes possible to increase the content ratio of energy ray curing resin in the hard coat layer or to separately incorporate materials that can enhance scratch resistance, making it easier to design for improved scratch resistance and surface hardness.

[0129] Here, "does not contain infrared absorbers" means substantially does not contain infrared absorbers, and includes not only cases where no infrared absorbers are contained at all, but also cases where infrared absorbers are contained to an extent that does not cause an increase in adhesive strength due to the infrared absorbers. Specifically, the hard coat layer forming composition Q may contain an infrared absorber in an amount of 0.1% by mass or less, preferably 0.01% by mass or less, and particularly preferably 0.001% by mass or less.

[0130] (5.5. Leveling Agent (d)) The hard coat layer forming composition Q according to this embodiment preferably contains a leveling agent (d) from the viewpoint of weather resistance, stain resistance, etc. of the window film. Examples of leveling agents include silicone-based leveling agents, fluorine-based leveling agents, acrylic-based leveling agents, vinyl-based leveling agents, etc. Among these, silicone-based leveling agents are preferred from the viewpoint of the above effects, and silicone-based leveling agents having a cyclic siloxane structure are more preferred. Note that one type of leveling agent may be used alone, or two or more types may be used in combination.

[0131] The content of the leveling agent (d) in the hard coat layer forming composition Q is preferably 0.001 to 1 part by mass, more preferably 0.01 to 0.5 parts by mass, even more preferably 0.02 to 0.1 parts by mass, and particularly preferably 0.04 to 0.08 parts by mass, per 100 parts by mass of the energy ray curable resin (a). This improves the weather resistance, stain resistance, etc., of the window film without interfering with the optical properties described later.

[0132] (5.6. Other Additives) The hard coat layer forming composition Q according to this embodiment may optionally contain other additives, as long as the effects of the present invention are not impaired. Examples of other additives include antioxidants, ultraviolet absorbers, antistatic agents, colorants, polymerization accelerators, polymerization inhibitors, plasticizers, antiviral agents, antibacterial agents, fillers, and diluent solvents.

[0133] (6. Physical properties of the window film) The window film according to this embodiment preferably has the following physical properties.

[0134] In this embodiment, the window film preferably has a light transmittance (ultraviolet transmittance) of 10% or less in the wavelength range of 300 to 380 nm. This allows the window film to exhibit good ultraviolet shielding function, suppressing the deterioration of materials inside buildings and automobiles, and preventing skin irritation and sunburn for people inside buildings and automobiles.

[0135] From the above perspective, the ultraviolet transmittance is preferably 5% or less, more preferably 1% or less, and most preferably 0%. The lower limit of the ultraviolet transmittance is usually 0% or more.

[0136] The window film according to this embodiment preferably has a light transmittance (visible light transmittance) of 98% or less in the wavelength range of 380 to 780 nm, and more preferably 95% or less. This allows the presence of the window to be visually recognized. For example, highly transparent window glass offers excellent visibility, but there is a risk of bumping into the window without noticing its presence and causing it to break. Therefore, from a safety standpoint, it is preferable to have high transparency while still allowing the presence of the window to be recognized. On the other hand, when visibility through a window is required, from the viewpoint of improving visibility, the visible light transmittance is preferably 10% or more, more preferably 30% or more, even more preferably 50% or more, particularly preferably 70% or more, and most preferably 80% or more, and most preferably 90% or more. This allows for a good view of the scenery through the window in a building, and a good view of the outside in a car window, thereby increasing safety while driving.

[0137] In this embodiment, the window film preferably has a light transmittance (near-infrared transmittance) of 90% or less in the wavelength range of 780 to 2500 nm. This allows the window film to exhibit good infrared heat shielding performance, suppressing the rise in surface temperature of components and people inside buildings and automobiles, as well as suppressing the rise in temperature of the interior space.

[0138] From the above viewpoint, the near-infrared transmittance is preferably 70% or less, more preferably 50% or less, more preferably 40% or less, and even more preferably 30% or less. The lower limit of the near-infrared transmittance is usually 0%, and from the viewpoint of compatibility with visible light transmittance, it is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more.

[0139] Furthermore, the ultraviolet transmittance, visible light transmittance, and near-infrared transmittance of the aforementioned window film can be measured by the method shown in the test examples described later.

[0140] In this embodiment, it is preferable that the haze value of the window film is 3% or less. This ensures good visibility of objects seen through the window film, even when the window film is applied to a window. In particular, even when viewing a light source through the window film, the light from the light source is less likely to diffuse, resulting in good visibility of the light source.

[0141] The above haze value is more preferably 2% or less, and even more preferably 1% 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. Detailed measurement methods will be described in the examples.

[0142] The total thickness of the window film according to this embodiment is preferably 5 to 200 μm, more preferably 10 to 160 μm, particularly preferably 20 to 140 μm, preferably 40 to 120 μm, even more preferably 50 to 100 μm, and most preferably 60 to 80 μm. This makes the window film easy to handle and readily exhibits the desired adhesive properties.

[0143] (7. Manufacture of the adhesive composition) The adhesive composition P can be manufactured, for example, by first manufacturing a (meth)acrylic acid ester polymer (A), and then mixing the obtained (meth)acrylic acid ester polymer (A) with a crosslinking agent (B). Additives may be added as needed.

[0144] (Meth)acrylic acid ester polymer (A) can be produced, for example, by polymerizing a mixture of monomers constituting the polymer using a conventional radical polymerization method. Polymerization of (meth)acrylic acid ester polymer (A) can be carried out by solution polymerization using a polymerization initiator as needed.

[0145] Examples of polymerization solvents used in solution polymerization include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, and methyl ethyl ketone. One type of polymerization solvent may be used, or two or more may be used in combination. Examples of polymerization initiators include azo compounds and organic peroxides, and two or more may be used in combination. Furthermore, the weight-average molecular weight of the resulting polymer can be adjusted by incorporating a chain transfer agent such as 2-mercaptoethanol during the polymerization process.

[0146] Next, a crosslinking agent (B) and, if necessary, an ultraviolet absorber (C), a diluent, etc., are added to the solution of the obtained (meth)acrylic acid polymer (A), and the mixture is thoroughly mixed to obtain a solvent-diluted adhesive composition P (coating solution). Additives may be added as needed.

[0147] If any of the above components is a solid component, or if it precipitates when mixed with other components in an undiluted state, that component may be dissolved or diluted in a diluting solvent beforehand before mixing it with the other components.

[0148] Examples of diluent 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 solvents such as ethyl cellosolve.

[0149] The concentration and viscosity of the prepared coating solution can be selected as appropriate depending on the situation, as long as they are within the range of coating. For example, the adhesive composition P is diluted to a concentration of 10 to 60% by mass. Note that the addition of a diluent is not a necessary condition when obtaining the coating solution; if the adhesive composition P has a viscosity suitable for coating, a diluent may not be added. In this case, the adhesive composition P becomes a coating solution in which the polymerization solvent of the (meth)acrylic acid ester polymer (A) is used directly as the diluent.

[0150] (7.1. Manufacturing of the adhesive) The adhesive constituting the adhesive layer is preferably obtained by crosslinking the adhesive composition P described above. Crosslinking of the adhesive composition P can usually be carried out by heat treatment. This heat treatment can also be combined with the drying treatment when volatilizing the diluent solvent etc. from the coating film of the adhesive composition P applied to the desired object.

[0151] The heating temperature for the heat treatment is preferably 50 to 150°C, and more preferably 70 to 120°C. The heating time is preferably 10 seconds to 10 minutes, and more preferably 50 seconds to 2 minutes.

[0152] After heat treatment, a curing period of 1 to 2 weeks at room temperature (e.g., 23°C, 50% relative humidity) may be provided as needed. If curing is necessary, an adhesive with a cross-linked structure will be obtained after the curing period. If curing is not necessary, an adhesive with a cross-linked structure will be obtained after the heat treatment is completed.

[0153] (8. Manufacturing of release sheets) Release sheets can be manufactured by known methods. For example, if the release sheet has a base material and a release agent layer, the base material and release agent layer composition described above are prepared. After applying a coating solution containing the release agent layer composition to one side of the prepared base material, the coating film is dried and cured to form the release agent layer. This gives rise to a release sheet. In this embodiment, the obtained release sheet is wound up by a winding machine to form a roll.

[0154] (9. Manufacturing of Window Film) The method for manufacturing the window film is not particularly limited and may be manufactured by known methods. For example, the coating solution of the above-mentioned adhesive composition P is applied to one main surface of the substrate, and a coating layer having a predetermined thickness is formed by crosslinking the adhesive composition P by heat treatment, and the release surface of the release sheet is placed on top of the coating layer. Alternatively, the coating solution of the above-mentioned adhesive composition P is applied to the release surface of the release sheet, and a coating layer having a predetermined thickness is formed by crosslinking the adhesive composition P by heat treatment, and one main surface of the substrate is placed on top of the coating layer.

[0155] If curing is required, the coating layer becomes an adhesive layer after a predetermined curing period. If curing is not required, the coating layer becomes the adhesive layer directly. This results in a window film.

[0156] When a window film has a hard coat layer, it is preferable to form the hard coat layer on the other main surface of the substrate before forming an adhesive layer on one main surface of the substrate. In this case, first, the coating solution of the hard coat layer forming composition Q is applied to the other main surface of the substrate and dried. After drying, the hard coat layer forming composition Q, from which the solvent has been evaporated, is cured by irradiating it with energy rays such as ultraviolet rays or electron beams, thereby forming a hard coat layer on the substrate.

[0157] When using ultraviolet light as the energy source, known devices such as high-pressure mercury lamps, xenon lamps, and metal halide lamps can be used as ultraviolet irradiation devices.

[0158] Examples of methods for applying the coating solution of the adhesive composition P and the hard coat layer forming composition Q include the bar coating method, knife coating method, roll coating method, blade coating method, die coating method, and gravure coating method.

[0159] In this specification, when "X to Y" (where X and Y are any numbers) is written, unless otherwise specified, it includes the meaning of "greater than or equal to X and less than or equal to Y," as well as "preferably greater than X" or "preferably less than Y." Similarly, when "greater than or equal to X" (where X is any number) is written, unless otherwise specified, it includes the meaning of "preferably greater than X," and when "less than or equal to Y" (where Y is any number) is written, unless otherwise specified, it also includes the meaning of "preferably less than Y."

[0160] Although embodiments of the present invention have been described above, the present invention is not limited in any way to the embodiments described above, and may be modified in various ways within the scope of the present invention.

[0161] The invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0162] (Example 1) 1. Preparation of (meth)acrylic acid ester polymer (A) 44 parts by mass of n-butyl acrylate, 44 parts by mass of isobutyl acrylate, 5 parts by mass of vinyl acetate, and 7 parts by mass of 2-hydroxyethyl methacrylate were copolymerized to prepare (meth)acrylic acid ester polymer (A). The molecular weight of the obtained (meth)acrylic acid ester polymer (A) was measured by the method shown below, and the weight-average molecular weight (Mw) was 700,000.

[0163] The weight-average molecular weight (Mw) is the weight-average molecular weight in polystyrene terms, measured using gel permeation chromatography (GPC) under the following conditions (GPC measurement). (Measurement conditions) ・GPC analyzer: HLC-8020, manufactured by Tosoh Corporation ・GPC column (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

[0164] 2. Preparation of the adhesive composition 100 parts by mass (solid content equivalent; the same applies hereinafter) of the (meth)acrylic acid ester polymer (A) obtained in 1 above, 0.35 parts by mass (B1) of an isocyanate-based crosslinking agent (manufactured by Mitsui Chemicals, product name "Takenate D-165N") as a crosslinking agent (B), and 5 parts by mass (C1) of a benzophenone-based ultraviolet absorber (manufactured by Solvay Japan, product name "Siasorb UV-24") as an ultraviolet absorber (C) were mixed and thoroughly stirred, and diluted with methyl ethyl ketone to obtain a coating solution of the adhesive composition with a solid content of 30% by mass.

[0165] 3. Preparation of the composition for forming a hard coat layer 50 parts by mass of dipentaerythritol pentaacrylate as an energy ray curable resin (a), 50 parts by mass of dipentaerythritol hexaacrylate as an energy ray curable resin, 5.0 parts by mass of 2,2-dimethoxy-2-phenylacetophenone as a photopolymerization initiator (b), and 0.05 parts by mass of octamethylcyclotetrasiloxane as a leveling agent (d) were mixed and thoroughly stirred, and diluted with propylene glycol monomethyl ether to obtain a coating solution of the composition for forming a hard coat layer with a solid content of 30% by mass.

[0166] 4. Preparation of the release sheet roll A polyethylene terephthalate (PET) film with a thickness of 25 μm and an arithmetic mean height (Sa) of 18.2 nm was prepared as the base material for the release sheet. A coating solution of a release agent layer composition containing a silicone-based release agent was applied to one main surface of the PET film so that the thickness after drying would be 100 nm, and a long release sheet A was obtained by drying.

[0167] Using a winding machine, the obtained long piece of release sheet was wound into a roll on a resin core to obtain a roll of release sheet A. The length of the wound release sheet was 8000 m.

[0168] 5. A polyethylene terephthalate (PET) film with a thickness of 50 μm was prepared as the manufacturing base material for the window film. The coating solution of the hard coat layer forming composition prepared in 3 above was applied to one main surface of the PET film using gravure coating so that the thickness after drying was 3 μm. The film was heated at 70°C for 1 minute to thoroughly remove the diluting solvent. Next, under a nitrogen atmosphere, the hard coat layer forming composition was cured by irradiating it with ultraviolet light using an ultraviolet irradiation device (manufactured by GS Yuasa Corporation, product name "Nitrogen Purge Small Conveyor Type UV Irradiation Device CSN2-40") under the following conditions to form a hard coat layer (thickness: 3 μm) and obtain a PET film with a hard coat layer. [Ultraviolet Irradiation Conditions] ・Light source: High-pressure mercury lamp ・Lamp power: 1.4 kW ・Conveyor speed: 1.2 m / min ・Illuminance: 120 mW / cm 2 ・Light amount: 240mJ / cm 2

[0169] Next, the release sheet A prepared in step 4 was unwound from the roll, and the adhesive composition coating solution prepared in step 2 was applied to its release surface using a die coat so that the thickness after drying was 25 μm. Then, it was heated at 90°C for 1 minute to thoroughly remove the dilution solvent and form an adhesive layer, obtaining a laminate of the release sheet and the adhesive layer. The adhesive layer of this laminate and the main surface of the PET film with a hard coat layer on the side where the hard coat layer is not formed were bonded together so that they were in contact with each other to obtain a window film.

[0170] (Examples 2 to 5, Comparative Examples 1 to 2) Window films were manufactured in the same manner as in Example 1, except that the composition of the (meth)acrylic acid ester polymer (A) constituting the adhesive layer, the type and amount of the crosslinking agent (B), the type and amount of the ultraviolet absorber (C), and the type and amount of the photopolymerization initiator and infrared absorber (c) added to the hard coat layer were changed as shown in Table 1, and the release sheets shown in Table 1 were used as the release sheets.

[0171] Release sheets B, C, and D were obtained using the same method as release sheet A, except that the Sa of the release sheet substrate was selected to match the values ​​in Table 1.

[0172]

[0173] Details of the abbreviations and other terms listed in Table 1 are as follows: [Hard coat layer] (Curable resin (a)) DPPA: Dipentaerythritol pentaacrylate DPHA: Dipentaerythritol hexaacrylate (Photopolymerization initiator (b)) b1: 2,2-dimethoxy-2-phenylacetophenone b2: 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one b3: 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}-2-methylpropan-1-one (Infrared absorber (c)) c1: Cesium-containing tungsten oxide (manufactured by Sumitomo Metal Mining Co., Ltd., product name "YMF-02AS") c2: Indium tin oxide (Leveling agent (d)) d1: Octamethylcyclotetrasiloxane [Adhesive layer] ((meth)acrylic acid ester polymer (A)) BA: n-butyl acrylate i-BA: isobutyl acrylate Vac: vinyl acetate HEMA: 2-hydroxyethyl methacrylate 2EHA: 2-ethylhexyl acrylate MA: methyl acrylate AA: acrylic acid EA: ethyl acrylate MMA: methyl methacrylate HEA: 2-hydroxyethyl acrylate (Crosslinking agent (B)) B1: Isocyanate crosslinking agent (manufactured by Mitsui Chemicals, product name "Takenate D-165N") B2: Metal chelate crosslinking agent (aluminum trisacetylacetonate) B3: Epoxy crosslinking agent (N,N,N,N'-tetraglycidyl-m-xylylenediamine) (UV absorber (C)) C1: Benzophenone UV absorber (manufactured by Solvay Japan, product name "Siasorb UV-24") C2: Triazine-based UV absorber (BASF product name "Chinubin 477")

[0174] The following evaluations were performed using the window films prepared in the examples and comparative examples.

[0175] (Surface properties of release sheets) Release sheets A to D, used in the preparation of window films according to the examples and comparative examples, were cut to a size of 50 mm x 50 mm. The surface roughness of the release surfaces of the cut release sheets A to D was measured using a scanning white light interference microscope (VS-1550, Hitachi High-Tech Corporation) with the light source facing it, under Wave measurement mode. The measurement was performed on a 2000 μm x 2000 μm area. From the measurement results, the arithmetic mean height (Sa) and peak density (Spd) were calculated in accordance with ISO 25178. The results are shown in Table 1.

[0176] (Optical Properties of Window Films) The visible light transmittance, ultraviolet light transmittance, and near-infrared light transmittance of the window films were measured as follows. The release sheets were peeled off from the window films prepared in the examples and comparative examples, and the exposed adhesive layer was attached to a 3 mm thick float glass plate. In accordance with JIS A 5759:2016, the light transmittance of the window films was measured by irradiating them with light in the wavelength range of 300 to 2500 nm using an ultraviolet-visible-near-infrared spectrophotometer (Shimadzu UV-3600). From the measurement results, the light transmittance (ultraviolet light transmittance) in the wavelength range of 300 to 380 nm, the light transmittance (near-infrared light transmittance) in the wavelength range of 780 to 2500 nm, and the light transmittance (visible light transmittance) in the wavelength range of 380 to 780 nm were calculated, respectively. The results are shown in Table 2.

[0177] Furthermore, for the samples whose light transmittance was measured, the haze value of the window film was measured using a spectroscopic haze meter (SH7000, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136:2000. The results are shown in Table 2.

[0178] (Initial Adhesion of the Adhesive Layer) The initial adhesion of the window films prepared in the examples and comparative examples was measured as follows. The obtained window films were cut to a width of 25 mm and a length of 100 mm. Under conditions of 23°C and 50% relative humidity, the release sheet was peeled off the window film and the exposed adhesive layer was attached to a float glass plate with a thickness of 3 mm. At this time, the window film was attached by applying pressure with a 2 kg roller for one back-and-forth motion, and this was used as the sample for measuring adhesion. The obtained sample was left for 24 hours under conditions of 23°C and 50% relative humidity. After standing, the adhesion (N / 25 mm) of the adhesive layer was measured using a tensile testing machine (Tensilon, manufactured by Orientec Co., Ltd.) under conditions of a peeling speed of 0.3 m / min and a peeling angle of 180°, and this was taken as the initial adhesion of the adhesive layer. Other conditions not described herein were measured in accordance with JIS Z0237:2009. The results are shown in Table 2.

[0179] (Evaluation of the gel fraction of the adhesive) The laminate of the release sheet and adhesive layer obtained when producing the window films according to the examples and comparative examples was cut to a size of 50 mm x 50 mm, and the adhesive layer was wrapped in a polyester mesh (product name: Tetron Mesh #200), and its mass was weighed using a precision balance. The mass of the adhesive alone was calculated by subtracting the mass of the mesh alone from the weighed value. This mass was designated as M1.

[0180] Next, the adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23°C) for 24 hours. The mesh was then removed and air-dried for 24 hours at 23°C and 50% relative humidity, followed by 12 hours of drying in an oven at 80°C. After drying, its mass was weighed using a precision balance. The mass of the adhesive alone was calculated by subtracting the mass of the mesh alone from the weighed value. This mass was designated as M2. Using the obtained M1 and M2, the gel fraction was calculated using the following formula. The results are shown in Table 2. Gel fraction (%) = (M2 / M1) × 100

[0181] (Storage modulus of adhesive G') Multiple adhesive layers of the laminates of release sheets and adhesive layers obtained when producing window films according to the examples and comparative examples were laminated to a thickness of 800 μm. From the obtained adhesive layer laminate, a cylindrical body with a diameter of 8 mm (height 800 μm) was punched out and used as a sample for measuring the storage modulus.

[0182] For the samples used for measurement, the storage modulus was measured using the torsional shear method with a viscoelasticity measuring device (Anton Paar MCR301) in accordance with JIS K7244-1, under the conditions of a measurement temperature range of -20 to 140°C, a measurement frequency of 1 Hz, and a heating rate of 4°C / min. From the measurement results, the storage modulus at 23°C and 80°C was calculated. The results are shown in Table 2.

[0183] (Image Quality Evaluation) In each example and comparative example, a window film was prepared by unwinding a release sheet located on the surface of the roll and bonding it to the surface of the adhesive layer, and a window film was prepared by unwinding a release sheet located near the core of the roll and bonding it to the surface of the adhesive layer.

[0184] The release sheet was peeled off the prepared window film, exposing the adhesive layer. The exposed adhesive layer was directed towards the light source of an image quality measuring device (Suga Test Instruments Co., Ltd., ICM-1T), and the image clarity was measured under the conditions of measurement mode: 45° transmission, comb width: 0.125 mm to evaluate the image quality. In addition, the exposed adhesive layer was visually inspected and evaluated according to the following criteria. The results for each are shown in Table 2. A: Almost no orange peel, good visibility F1: Orange peel present, some image distortion F2: Significant orange peel, poor visibility

[0185] (Blocking Resistance) Based on "4. Preparation of Rolls of Release Sheets," samples of the surface layer (at 100m of the unwound section) and core (at 7900m of the unwound section) of a long roll of release sheet were taken, and the surface condition of the release surface was visually inspected and evaluated according to the following criteria. The results are shown in Table 2. A: No change in appearance F: Change in appearance

[0186]

[0187] Table 2 shows that the window films of Examples 1 to 5 exhibited suppressed blocking during manufacturing and provided good visibility through the window film.

[0188] The window film of the present invention can be suitably used by being applied to windows of moving objects such as automobiles, or windows of buildings. Furthermore, the window film of the present invention can be applied to glass other than window glass, or to glass substitute materials (for example, plastics, etc.).

[0189] 1... Window film 10... Substrate 20... Adhesive layer 30... Release sheet 40... Hard coat layer

Claims

1. A window film comprising a substrate, an adhesive layer disposed on one main surface of the substrate, and a release sheet disposed on the adhesive layer, wherein the main surface of the adhesive layer and the release surface of the release sheet are in contact, the arithmetic mean height Sa of the release surface is 25 nm or less, and the peak density Spd is 4000 pins / mm 2 That's all for window film.

2. The window film according to claim 1, having a functional layer disposed on the other main surface of the substrate.

3. The window film according to claim 2, wherein the functional layer is a hard coat layer.

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