Window film and method for manufacturing front window equipped with window film

Abstract

Provided is a window film having a high heat-insulating performance that is capable of suppressing the occurrence of wrinkles in a resin film when forming a hard coat layer and of following the shape of an adherend at the time of sticking. A window film (1) has a resin film (10) and a hard coat layer (11) disposed on one main surface of the resin film (10). Assuming that the shrinkage rate in an MD direction of the resin film (10) when the resin film (10) is held at 180°C for 5 minutes is A% and that the shrinkage rate in a CD direction is B%, A-B is 0.4% or more. The hard coat layer (11) contains tin-doped indium oxide.

Description

Window film and method for manufacturing front window with window film

[0001] The present invention relates to a window film and a method for manufacturing a front window with a window film.

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

[0003] Window films typically have a resin film as a substrate, which generally tends to have low hardness and, as a result, tends to be poor in scratch resistance, weather resistance, and the like.

[0004] For this reason, window films often have, in addition to a resin film, a hard coat layer that is superior to the resin film in hardness, scratch resistance, weather resistance, etc. The hard coat layer is mainly obtained by applying a composition for forming the hard coat layer onto a resin film and curing the composition.

[0005] Furthermore, window films are sometimes applied to curved windows, such as automobile windows. When a flat window film is applied to a curved surface, excess film tends to be produced in the window film, which can easily cause the window film to sag, and this is one of the causes of wrinkles in the window film after application.

[0006] Patent Document 1 describes a window film that can suitably prevent scratches and wrinkles from occurring when the film is attached to an adherend by controlling the heat shrinkage rates of the substrate and hard coat layer to be within a predetermined range.

[0007] JP 2019-171781 A

[0008] Patent Document 1 describes that it is preferable to set the heat shrinkage rates of a substrate in two mutually perpendicular directions within a predetermined range, that is, to set the heat shrinkage rates in the two mutually perpendicular directions to approximately the same. However, as a result of intensive research, the present inventors have found that when the heat shrinkage rates of a substrate in two mutually perpendicular directions are set to approximately the same, particularly when a window film is attached to an adherend having a large area and a curved surface, the window film cannot sufficiently conform to the shape of the adherend, and wrinkles are likely to occur.

[0009] Furthermore, the present inventors have found that when an infrared absorbing agent is contained in a hard coat layer-forming composition to impart heat-shielding properties to a window film, heat is generated during the formation of the hard coat layer. When such heat is generated, a resin film located near the hard coat layer-forming composition undergoes thermal shrinkage, resulting in the problem of wrinkles occurring in the resin film after the hard coat layer is formed. That is, there is a problem that wrinkles occur in the resin film due to the formation of the hard coat layer, resulting in poor appearance of the manufactured window film.

[0010] The present invention has been made in consideration of the above-described circumstances, and aims to provide a window film with high heat insulation properties, which can suppress the occurrence of wrinkles in the resin film when a hard coat layer is formed, can conform to the shape of the substrate when applied, and has a method for manufacturing a front window with a window film.

[0011] The aspects of the present invention are as follows.

[0012] [1] A window film having a resin film and a hard coat layer disposed on one main surface of the resin film, wherein, after heating the resin film and holding it at 180°C for 5 minutes, the shrinkage percentage in the MD direction before and after heating is A%, and the shrinkage percentage in the CD direction before and after heating is B%, where A - B is 0.4% or more, and the hard coat layer contains tin-doped indium oxide.

[0013] [2] The window film according to [1], wherein the shrinkage rate in the MD direction is 0.75% or more.

[0014] [3] The window film according to [1] or [2], wherein the window film has a visible light transmittance of 80% or more.

[0015] [4] The window film according to any one of [1] to [3], wherein the near-infrared transmittance of the window film is 20% or less.

[0016] [5] The window film according to any one of [1] to [4], wherein the window film is for a front window of a vehicle.

[0017] [6] A method for manufacturing a front window with a window film, comprising a step of aligning the MD direction of the resin film with the long side direction of the front window and attaching the window film described in [5] to the front window.

[0018] According to the present invention, it is possible to provide a window film that suppresses the occurrence of wrinkles in the resin film when a hard coat layer is formed, that can follow the shape of the adherend when applied, and that has high heat insulation properties, and a method for manufacturing a front window with a window film.

[0019] Fig. 1A is a cross-sectional view showing an example of a window film according to the present embodiment, and Fig. 1B is a cross-sectional view showing another example of a window film according to the present embodiment.

[0020] The present invention will be described in detail below based on specific embodiments.

[0021] (1. Window Film) A window film has, for example, a substrate made of a resin film and a hard coat layer that is harder than the substrate.

[0022] In order to impart heat-shielding properties to window films, an infrared absorbing agent is typically incorporated into the hard coat layer. During the manufacture of window films, the hard coat layer is typically obtained by applying a composition for forming the hard coat layer onto a resin film and curing the composition by, for example, ultraviolet irradiation. The light source used for irradiation emits not only light with wavelengths belonging to the ultraviolet ray range but also light with wavelengths belonging to the visible ray range. Therefore, if the hard coat layer contains an infrared absorbing agent with a predetermined absorptivity in the wavelength range of visible light, the infrared absorbing agent will absorb visible light and generate heat. When this heat is generated in the hard coat layer, the heat propagates to the resin film, causing the resin film to shrink. Shrinkage of the resin film causes wrinkles, resulting in poor appearance of the window film.

[0023] However, because window films are flat, when a window film is applied to a curved substrate, excess portions are left unattached, leading to slack in the window film. Such slack prevents the window film from conforming adequately to the substrate, resulting in poor appearance. Therefore, it is preferable to utilize the thermal shrinkage of a resin film to improve the window film's ability to conform to the substrate by heating the window film to shrink it in a specific direction when applying the window film to a curved substrate.

[0024] However, when an attempt is made to improve conformability by using a resin film with large thermal shrinkage, the shrinkage of the resin film caused by the heat generated by the infrared absorber described above also increases. Therefore, when an attempt is made to improve conformability to an adherend by utilizing the shrinkage of the resin film, there is a problem that wrinkles of the resin film that occur during the formation of the hard coat layer increase. In other words, it has been difficult to achieve both conformability to an adherend by utilizing the shrinkage of the resin film and reduction of wrinkles of the resin film during the production of a window film.

[0025] In this embodiment, as described below, by incorporating a specific infrared absorbing agent and controlling the physical properties of the resin film, it is possible to achieve both conformability to an adherend by utilizing the shrinkage of the resin film and reduction in wrinkles in the resin film during production of the window film. The components of the window film will be described in detail below.

[0026] As shown in FIG. 1A , the window film 1 according to this embodiment includes a resin film 10 as a substrate and a hard coat layer 11 .

[0027] Furthermore, as long as the effects of the present invention are achieved, the window film may include other components. That is, the window film may include layers other than the substrate and the hard coat layer. For example, in order to securely fix the window film to the adherend (window), as shown in FIG. 1B , a pressure-sensitive adhesive layer 12 may be disposed on the main surface 10b of the resin film 10 opposite the main surface 10a on which the hard coat layer 11 is formed. When the pressure-sensitive adhesive layer 12 is disposed, a release sheet (not shown) may be disposed on the main surface 12a of the pressure-sensitive adhesive layer 12 to protect the pressure-sensitive adhesive layer 12 until it is attached to the adherend.

[0028] (1.1. Resin Film) The resin film according to this embodiment is a material that provides the rigidity of the window film, and functions as a substrate that supports the hard coat layer.

[0029] Resin films are generally formed by stretching molten resin into a sheet. The direction in which the molten resin flows is referred to as the MD (machine direction), and the direction perpendicular to the MD is referred to as the CD (cross direction). The orientation of the molecular chains constituting the resin tends to differ between the MD and CD directions. As a result, the physical properties of the resin film may differ between the MD and CD directions. In other words, anisotropy may occur in the physical properties of the resin film between the MD and CD directions.

[0030] The resin film according to this embodiment shrinks differently in the MD and CD directions before and after heating. First, when a predetermined length of the resin film before heating is taken as 100%, if the length of the resin film after holding at 180°C for 5 minutes is X%, the percentage of shrinkage due to heating ((100-X)%) is defined as the shrinkage rate in the MD direction (A%). For example, if the length of the resin film after holding at 180°C for 5 minutes is 95%, the shrinkage rate in the MD direction is 5%. Similarly, when a predetermined length of the resin film before heating is taken as 100%, if the length of the resin film after holding at 180°C for 5 minutes is Y%, the percentage of shrinkage due to heating ((100-Y)%) is defined as the shrinkage rate in the CD direction (B%).

[0031] In this embodiment, the difference (A - B) obtained by subtracting the shrinkage percentage in the CD direction of the resin film from the shrinkage percentage in the MD direction of the resin film is 0.4% or more. That is, in the resin film according to this embodiment, the shrinkage percentage in the MD direction is greater than the shrinkage percentage in the CD direction.

[0032] The resin film's shrinkage rate exhibits anisotropy in the machine direction and the cross direction, allowing the resin film to shrink significantly in a specific direction when heated during application of the window film. This allows the window film to more easily conform to the shape of the adherend, improving application of the window film.

[0033] The difference (A-B) between the shrinkage percentage in the MD direction and the shrinkage percentage in the CD direction is preferably 0.6% or more, more preferably 0.8% or more. The upper limit of the difference (A-B) between the shrinkage percentage in the MD direction and the shrinkage percentage in the CD direction is preferably 10%, more preferably 3%, from the viewpoint of the production conditions of the resin film and from the viewpoint of further suppressing wrinkling of the resin film during formation of the hard coat layer.

[0034] In addition, the shrinkage rate (A%) in the MD direction is preferably 0.75% or more, more preferably 1.5% or more, as long as the above shrinkage rate difference is satisfied. This makes it easier for the window film to follow the shape of the adherend, further improving the application properties of the window film. The upper limit of the shrinkage rate in the MD direction is preferably 10%, more preferably 4%, from the viewpoint of the manufacturing conditions of the resin film and the viewpoint of further suppressing wrinkles in the resin film when forming the hard coat layer.

[0035] Any resin film can be selected as the resin film as long as the shrinkage percentages in the MD and CD directions are within the above ranges. Specific examples of such resin films include films made of polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polyolefin resins such as polyethylene, polypropylene, poly4-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 laminated films thereof.

[0036] Among these, films made of polyolefin-based resins and polyester-based resins, which have excellent mechanical strength and economy, or laminate films thereof are preferred, and from the viewpoint of easily obtaining the above-mentioned physical properties, films made of polyester-based resins or laminate films thereof are particularly preferred, and polyethylene terephthalate films or laminate films containing polyethylene terephthalate are particularly preferred.

[0037] A metal layer may be formed on the resin film as long as the resin film satisfies the above physical properties. By providing a metal layer on the resin film, the optical properties of the window film can be easily adjusted. The metal layer may be a layer containing metal, or a layer consisting of metal alone. Examples of metals contained in the metal layer include aluminum, gold, silver, copper, nickel, cobalt, chromium, tin, indium, and the like, alloys thereof, and oxides thereof. Methods for forming the metal layer include vacuum deposition and sputtering. While a metal layer easily reflects infrared rays, it tends to reduce the light transmittance of the window film. Therefore, in applications requiring high visibility to the outside of the window, such as when the window film is used as a front window for a vehicle, it is preferable that a metal layer not be formed on the resin film. The window film according to this embodiment has excellent heat-shielding properties even without a metal layer formed on the resin film because the hard coat layer contains an infrared absorber.

[0038] For the purpose of improving adhesion to a layer provided on the resin film, one or both sides of the substrate 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 the resin film can exhibit a predetermined rigidity, and may be appropriately set depending on the intended use. In this embodiment, from the viewpoint of further improving workability and further suppressing the occurrence of wrinkles in the resin film during production, the thickness of the resin film is preferably 10 to 200 μm, more preferably 15 to 150 μm, and even more preferably 20 to 80 μm.

[0040] The window film according to this embodiment may have multiple layers of substrate made of resin film, but from the viewpoint of easily controlling the shrinkage characteristics of the window film, it is preferable that it has only one layer of substrate made of resin film.

[0041] (1.2. Hard Coat Layer) The hard coat layer according to this embodiment is superior to resin films in hardness, scratch resistance, weather resistance, and other hard coat properties. The window film is attached to the adherend so that the hard coat layer is exposed to the outside. Therefore, even if some external force is applied after application, the resin film is less likely to be scratched. In addition, since it is difficult for external force to be directly transmitted to the adherend (such as the window of an automobile or building), it is possible to exhibit excellent impact resistance. Furthermore, even if the adherend is broken, it is possible to prevent fragments from scattering, thereby exhibiting excellent shatterproof properties. Therefore, it is possible to improve safety while maintaining the appearance of moving bodies such as automobiles and buildings.

[0042] The hard coat layer may have a function other than hard coat properties. In this embodiment, the hard coat layer has heat shielding properties (infrared absorbing properties) in order to impart heat shielding properties to the window film.

[0043] The thickness of the hard coat layer is preferably 1 to 20 μm, more preferably 3 to 15 μm, from the viewpoint of improving the surface hardness, scratch resistance, weather resistance, and heat insulation properties of the window film.

[0044] The weight of the hard coat layer per area is 1 to 20 g / m from the viewpoint of improving the surface hardness, scratch resistance, weather resistance, and heat insulation properties of the window film. 2 It is preferable that the density is 3 to 15 g / m 2 More preferably, it is 3 to 10 g / m 2 It is more preferable that:

[0045] The hard coat layer is preferably composed of a material that can impart the above-described hardness, scratch resistance, weather resistance, and heat shielding property. The hard coat layer according to this embodiment is preferably a cured product formed by curing a composition for forming a hard coat layer.

[0046] (1.2.1. Composition for Forming Hard Coat Layer) In this embodiment, the composition Q for forming a hard coat layer is preferably active energy ray-curable, and particularly preferably ultraviolet ray-curable, from the viewpoint of productivity and ease of obtaining desired scratch resistance.

[0047] Specifically, the hard coat layer-forming composition Q preferably contains an active energy ray-curable resin (a) and an infrared absorber (c), and more preferably contains an active energy ray-curable resin (a), a photopolymerization initiator (b), and an infrared absorber (c).

[0048] (1.2.2. Active energy ray-curable resin (a)) The active energy ray-curable resin is not particularly limited and can be selected from conventionally known resins. Examples thereof include active energy ray-curable monomers, oligomers, and compositions containing them.

[0049] Examples of the active energy ray-curable monomer include polyfunctional (meth)acrylates. Examples of the active energy ray-curable oligomer include urethane (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, and silicone (meth)acrylate.

[0050] 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 polyfunctional (meth)acrylates such as pentaerythritol tri(meth)acrylate and pentaerythritol tetra(meth)acrylate, dipentaerythritol polyfunctional (meth)acrylates such as dipentaerythritol penta(meth)acrylate and dipentaerythritol hexa(meth)acrylate, glycerol tri(meth)acrylate, triallyl (meth)acrylate, and the like.

[0051] Among these, pentaerythritol polyfunctional (meth)acrylate or dipentaerythritol polyfunctional (meth)acrylate is more preferred because it can impart appropriate rigidity, scratch resistance, weather resistance, and the like to the hard coat layer.

[0052] (1.2.3. Infrared absorbent (c)) The infrared absorbent (c) is preferably an infrared absorbent having excellent near-infrared absorbing properties.

[0053] In this embodiment, the infrared absorber (c) is tin-doped indium oxide (ITO). ITO has a lower absorptivity in the visible light wavelength range than other infrared absorbers. Therefore, even when the hard coat layer forming composition Q containing ITO is cured by irradiating it with ultraviolet light, the ITO generates less heat due to the absorption of visible light. As a result, less heat is transmitted to the resin film, which suppresses shrinkage of the resin film and the associated occurrence of wrinkles. Furthermore, because the visible light absorption is low, the window film can maintain high transparency while exhibiting high heat-shielding properties.

[0054] The content of ITO in the hard coat layer-forming composition Q is preferably 10 to 300 parts by mass, more preferably 20 to 250 parts by mass, and even more preferably 40 to 200 parts by mass, relative to 100 parts by mass of the active energy ray-curable resin (a). This allows the resulting window film to exhibit high heat-shielding properties while further suppressing shrinkage of the resin film during hard coat layer formation.

[0055] (1.2.4. Photopolymerization initiator (b)) When ultraviolet rays are used as the active energy rays for curing the hard coat layer-forming composition Q, the hard coat layer-forming composition Q preferably contains a photopolymerization initiator (b). By containing a photopolymerization initiator, a hard coat layer can be efficiently formed when the hard coat layer-forming composition Q is irradiated with ultraviolet rays. Here, the photopolymerization initiator refers to a compound that generates radical species when irradiated with active energy rays such as ultraviolet rays.

[0056] Examples of the photopolymerization initiator include 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-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-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, benzyl dimethyl ketal, acetophenone dimethyl ketal, p-dimethylamine benzoate, and oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propan-1-one]. These may be used alone or in combination of two or more.

[0057] 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, relative to 100 parts by mass of the active energy ray-curable resin (a). This makes it easier for the resulting hard coat layer to exhibit the desired surface hardness and scratch resistance.

[0058] (1.2.5. Other Additives) Furthermore, within the scope of not impairing the effects of the present invention, the hard coat layer-forming composition Q may contain other additives as appropriate. Examples of other additives include antioxidants, ultraviolet absorbers, antistatic agents, colorants, polymerization accelerators, polymerization inhibitors, leveling agents, plasticizers, antiviral agents, antibacterial agents, fillers, and dilution solvents.

[0059] (1.3. Pressure-sensitive adhesive layer) In this embodiment, the window film preferably has a pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer can be attached to the surface of an adherend to favorably fix the window film to the adherend. The pressure-sensitive adhesive layer is a layer of a pressure-sensitive adhesive, which will be described later.

[0060] The pressure-sensitive adhesive layer may be composed of one layer (single layer) or two or more layers. When the pressure-sensitive adhesive layer has multiple layers, these multiple layers may be the same or different from each other, and the combination of layers constituting these multiple layers is not particularly limited.

[0061] The thickness of the 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.

[0062] The composition of the adhesive constituting the adhesive layer is not particularly limited. For example, it may be any of an acrylic adhesive, a polyester adhesive, a polyurethane adhesive, a rubber adhesive, a silicone adhesive, etc. The adhesive may be an emulsion type, a solvent type, or a solventless type. Furthermore, the adhesive may or may not have a crosslinked structure.

[0063] When the adhesive composition is an acrylic adhesive having a crosslinked structure, the adhesive is exemplified by an adhesive having a crosslinked structure obtained by crosslinking an adhesive composition containing a (meth)acrylic acid ester polymer and a crosslinking agent. In this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. In addition, the term "polymer" also includes the concept of "copolymer."

[0064] Examples of the (meth)acrylic acid ester polymer include a polymer containing, as monomer units, a unit derived from a (meth)acrylic acid alkyl ester and a unit derived from a monomer having a reactive functional group in the molecule (a reactive functional group-containing monomer).

[0065] Examples of the (meth)acrylic acid alkyl ester include (meth)acrylic acid alkyl esters in which the alkyl group has a carbon number of 1 to 20. 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 carboxy group in the molecule (carboxy group-containing monomer), and the like.

[0066] The crosslinking agent is preferably one that reacts with the reactive functional group of the (meth)acrylic acid ester polymer, and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-based crosslinking agents.

[0067] The pressure-sensitive adhesive may contain additives commonly used in pressure-sensitive adhesives, as needed. Examples of such additives include ultraviolet absorbers, infrared absorbers, tackifiers, 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, antifoaming agents, surfactants, etc.

[0068] (1.4. Physical Properties of Window Film) The window film according to this embodiment preferably has the following physical properties.

[0069] The window film according to this embodiment preferably has a light transmittance (visible light transmittance) of 80% or more in the wavelength range of 380 to 780 nm. This ensures sufficient transparency of the window film. As a result, visibility through the window to which the window film is attached can be improved. For example, when the window film is attached to the window of an automobile or the like, the view outside the vehicle can be clearly seen through the window film, thereby increasing safety while driving.

[0070] The visible light transmittance is preferably 82% or more, and more preferably 84% or more. The upper limit of the visible light transmittance may be 100%.

[0071] The window film according to this embodiment preferably has a light transmittance (near-infrared transmittance) of 20% or less in the wavelength range of 780 to 2500 nm. This allows the window film to exhibit good heat-shielding properties, suppressing increases in the surface temperature of components and people inside buildings and automobiles, as well as suppressing temperature increases in the interior space. Such low near-infrared transmittance is achieved by the inclusion of an infrared absorber in the hard coat layer; however, the lower the near-infrared transmittance, the greater the heat generated during the formation of the hard coat layer. Therefore, in window films that require such low near-infrared transmittance, it is even more important to use ITO as an infrared absorber to suppress heat generation.

[0072] The near-infrared transmittance is preferably 18% or less, more preferably 16% or less. The lower limit of the near-infrared transmittance may be 0%. The following can be said as a guideline for controlling the near-infrared transmittance: The near-infrared transmittance tends to decrease as the amount of infrared absorber contained in the hard coat layer increases. Furthermore, the near-infrared transmittance tends to decrease as the formation weight per area of ​​the hard coat layer increases. Furthermore, the near-infrared transmittance tends to decrease as the particle size of the infrared absorber decreases and it is more uniformly dispersed in the hard coat layer.

[0073] The visible light transmittance and near-infrared transmittance of the window film can be measured in accordance with JIS S 3107. Specific measurement methods will be described in the examples below.

[0074] (1.5. Production of Window Film) The method for producing the window film is not particularly limited, and it may be produced by a known method. For example, a hard coat layer may be formed on one main surface of a resin film. Specifically, a coating liquid of the above-mentioned hard coat layer-forming composition Q is applied to one main surface of the resin film and dried. The coating liquid of the hard coat layer-forming composition Q can be prepared by mixing the components constituting the hard coat layer-forming composition Q and, if necessary, using a known dilution solvent. Examples of methods for applying the coating liquid include bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating. The dried hard coat layer-forming composition Q is irradiated with active energy rays such as ultraviolet rays to cure it, thereby forming a hard coat layer on the resin film.

[0075] When ultraviolet rays are used as the active energy rays, known ultraviolet ray irradiators such as high-pressure mercury lamps, xenon lamps, and metal halide lamps can be used.

[0076] When ultraviolet rays are used as active energy rays, the illuminance is 50 to 1000 mW / cm 2 It is preferable that the intensity is about 100 to 500 mW / cm 2 It is more preferable that the light amount is 25 to 2000 mJ / cm. 2 is preferred, and 50 to 1000 mJ / cm 2 More preferably, 70 to 500 mJ / cm 2 is more preferable.

[0077] When the window film has a pressure-sensitive adhesive layer, a coating liquid of a composition for forming the pressure-sensitive adhesive layer (pressure-sensitive adhesive composition) can be applied to the other main surface of the resin film on which the hard coat layer is not formed, and the coating liquid is then dried to obtain the pressure-sensitive adhesive layer. When the pressure-sensitive adhesive composition contains a crosslinking agent, the pressure-sensitive adhesive layer containing a crosslinked structure may be obtained, as necessary, by heating, curing, or the like of the pressure-sensitive adhesive composition.

[0078] (2. Use of Window Film) The window film according to this embodiment is used by being attached to an adherend. The adherend is a window, and examples thereof include windows of mobile bodies such as automobiles, and windows of buildings, etc. In this embodiment, the adherend is preferably a window having a curved surface, and more preferably a window having a curved surface with a large curvature, or a window with a large change in curvature. An example of such a window is an automobile window. The automobile window may be a front window, a rear window, a side window, or a door window, but the adherend is preferably a front window having a large area and a curved surface with a large curvature.

[0079] The window film according to the present embodiment is preferably processed into a predetermined shape that matches the shape of the adherend before being attached to the adherend. The method for processing into the predetermined shape may be any known method. For example, the window film may be temporarily attached to the adherend, and then the window film may be deformed into the shape of the adherend and cut out in advance.

[0080] When the window film according to this embodiment is applied to the front window of an automobile, it is preferable to align the MD direction of the resin film with the long side (vehicle width) direction of the front window. Typically, the curvature of the edge of a front window in the long side direction is greater than that of the center, and the curvature changes significantly, but the curvature does not change much in the short side (vehicle height) direction. Therefore, when a window film is applied to a front window, it is likely that portions (slack) will occur where the window film cannot follow the front window, particularly at the edges in the long side direction. If the window film is applied to a front window in a slack state, the window film is likely to wrinkle after application, resulting in an appearance problem.

[0081] As described above, the window film according to this embodiment suppresses wrinkles in the resin film before application, and the difference between the shrinkage rate in the MD direction and the shrinkage rate in the CD direction is controlled within a predetermined range. Therefore, even if the resin film has few wrinkles before application and the window film becomes loose during application, the loosened portion can be heated to cause the window film to shrink significantly in the MD direction, allowing it to conform to the windshield. As a result, the occurrence of wrinkles after application can be suppressed while providing the windshield with a predetermined heat-shielding property.

[0082] In this way, a front window with a window film can be obtained using the window film according to this embodiment.

[0083] 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 means "preferably greater than X" or "preferably smaller than Y". Furthermore, when it is stated that "X or more" (X is any number), it means "preferably greater than X" unless otherwise specified, and when it is stated that "Y or less" (Y is any number), it also means "preferably smaller than Y" unless otherwise specified.

[0084] 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.

[0085] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0086] The measurement and evaluation methods in the present examples are as follows.

[0087] (Shrinkage of Resin Film) A resin film was cut into a 12 cm x 12 cm sample. A benchmark was drawn in the MD and CD directions 1 cm inside the outer periphery of the sample, and the distance between the benchmarks was measured with a vernier caliper. The sample was then heat-treated at 180°C for 5 minutes. The benchmark distances in the MD and CD directions of the heat-treated sample were again measured with a vernier caliper. The difference between the initial benchmark distance and the benchmark distance after heat treatment in each of the MD and CD directions was divided by the initial benchmark distance to obtain the shrinkage percentage. The shrinkage difference (A-B)% was calculated from the obtained shrinkage percentage in the MD direction (A%) and the shrinkage percentage in the CD direction (B%).

[0088] (Evaluation of application properties of window films) The release sheets of the window films produced in the examples and comparative examples were attached and temporarily applied to the front window of a general passenger vehicle that had been sprayed with an application liquid (a 0.1% aqueous solution of neutral detergent). At this time, the MD direction of the resin film was aligned with the vehicle width direction of the front window. Next, a heat gun was used to shrink the window film so that it conformed to the curved front window, and the window film was applied to the front window. The workability when adapting the window film was evaluated according to the following criteria: A: It can be adapted very easily B: It can be adapted easily C: It is possible to adapt, although it takes time F: It is not possible to adapt

[0089] (Transparency Evaluation of Window Film) The release sheet was peeled from the window films produced in the Examples and Comparative Examples, and the exposed pressure-sensitive adhesive layer was attached to a 3 mm thick float glass plate. In accordance with JIS S3107, the window film was irradiated with light in the wavelength range of 300 to 2500 nm using an ultraviolet-visible-near-infrared spectrophotometer (Shimadzu Corporation, UV-3600) to measure the light transmittance of the window film. From the measurement results, the light transmittance in the wavelength range of 380 to 780 nm (visible light transmittance) was calculated. From the calculated visible light transmittance, transparency was evaluated according to the following criteria: A: Visible light transmittance is 80% or more F: Visible light transmittance is less than 80%

[0090] (Evaluation of Heat Shielding Property of Window Film) In the measurement of light transmittance performed in the transparency evaluation described above, the light transmittance in the wavelength range of 780 to 2500 nm was taken at 5 nm intervals, and the average of the taken values ​​was taken as the near-infrared transmittance. From the calculated near-infrared transmittance, the heat shielding property was evaluated according to the following criteria: A: Near-infrared transmittance is 20% or less F: Near-infrared transmittance is more than 20%

[0091] (Evaluation of shrinkage wrinkles during window film production) When the composition for hard coat layer applied to the resin film is cured by ultraviolet irradiation, the strength of wavy wrinkles that occur in the CD direction of the resin film was visually evaluated according to the following criteria: A: No wrinkles at all, good appearance B: Almost no wrinkles, good appearance C: Weak wrinkles occur during curing, but the wrinkles become invisible after the window film is applied to the front window in the above-mentioned workability evaluation F: Strong wrinkles occur during curing, and the wrinkles are visible even after the window film is applied to the front window in the above-mentioned workability evaluation

[0092] (Example 1) 1. Hard Coat Layer Forming Composition A hard coat layer forming composition (manufactured by Mitsubishi Materials Corporation) containing an acrylate compound and a photopolymerization initiator, tin-doped indium oxide particles (c1) as an infrared absorber (c), and a urethane acrylate resin as an active energy ray-curable oligomer was prepared as a coating liquid. The infrared absorber was contained in an amount of 60 mass% relative to 100 mass% of the hard coat layer forming composition.

[0093] 2. Production of Window Film A 25 μm thick biaxially oriented polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Corporation) was prepared as a resin film. The prepared coating solution of the hard coat layer-forming composition was gravure coated onto one main surface of the PET film, and heated at 70°C for 1 minute to thoroughly remove the dilution solvent. Next, in a nitrogen atmosphere, the hard coat layer-forming composition was cured by irradiating it with ultraviolet light under the following conditions using an ultraviolet irradiation device (manufactured by GS Yuasa Corporation, product name "Nitrogen-purged small conveyor-type UV irradiation device CSN2-40"), forming a hard coat layer (formation weight per area: 5 g / m2 ) was formed to obtain a PET film with a hard coat layer. [UV irradiation conditions] Light source: high-pressure mercury lamp Lamp power: 1.4 kW Conveyor speed: 10 m / min Illuminance: 250 mW / cm 2 ・Light amount: 100mJ / cm 2

[0094] Next, a coating solution of the acrylic pressure-sensitive adhesive composition was applied by die coating to the release-treated surface of a release sheet (manufactured by Lintec Corporation, product name "SP-PET381031"), one side of which had been release-treated with a silicone-based release agent. After application, the coating was heated at 90°C for 1 minute to thoroughly remove the dilution solvent, and a pressure-sensitive adhesive layer (formation weight per area: 10 g / m) was formed. 2 The adhesive layer of the laminate and the main surface of the hard coat layer-attached PET film on the side where the hard coat layer was not formed were attached to each other so that they were in contact with each other, thereby obtaining a window film.

[0095] (Example 2) A window film was obtained in the same manner as in Example 1, except that the resin film in Example 1 was changed to a 25 μm thick biaxially stretched polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Corporation) whose stretching conditions during production were different from those in Example 1.

[0096] (Example 3) A window film was obtained in the same manner as in Example 1, except that the resin film in Example 1 was changed to a biaxially stretched polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Corporation) having a thickness of 25 μm, which was stretched under different conditions during production than in Example 1.

[0097] Example 4 A window film was obtained in the same manner as in Example 1, except that the resin film in Example 1 was changed to a biaxially oriented polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Corporation) having a thickness of 100 μm.

[0098] Comparative Example 1 A window film was obtained in the same manner as in Example 1, except that the resin film in Example 1 was changed to a biaxially stretched polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Corporation) having a thickness of 25 μm, which was produced under different stretching conditions from those in Example 1.

[0099] Comparative Example 2 A window film was obtained in the same manner as in Example 1, except that the resin film in Example 1 was changed to a biaxially stretched polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Corporation) having a thickness of 25 μm, which was produced under different stretching conditions from those in Example 1, and the hard coat layer-forming composition in Example 1 was changed to a hard coat layer-forming composition containing 40 mass % of cesium-doped tungsten oxide particles (manufactured by Sumitomo Metal Mining Co., Ltd., product name "YMF-02AS") (c2) as the infrared absorber (c).

[0100] Comparative Example 3 A window film was obtained in the same manner as in Example 1, except that the resin film in Example 1 was changed to a biaxially stretched polyethylene terephthalate (PET) film (manufactured by Mitsubishi Chemical Corporation) having a thickness of 25 μm, which was produced under different stretching conditions from those in Example 1, and the hard coat layer-forming composition in Example 1 was changed to a hard coat layer-forming composition containing 40 mass % of antimony-doped tin oxide particles (manufactured by Sumitomo Metal Mining Co., Ltd.) (c3) as the infrared absorber (c).

[0101] The window films produced in the examples and comparative examples (Examples 1 to 4 and Comparative Examples 1 to 3) were subjected to the above measurements and evaluations. The results are shown in Table 1.

[0102]

[0103] From Table 1, it was confirmed that the window films of the examples had excellent application properties, could suppress the occurrence of shrinkage wrinkles during production, and had excellent heat insulation properties.

[0104] The window film of the present invention can be suitably used by being attached to, for example, windows of mobile bodies such as automobiles, windows of buildings, etc. It is particularly suitable for use as a front window of an automobile, which has a large area and a large curvature.

[0105] REFERENCE SIGNS LIST 1... window film 10... resin film 11... hard coat layer 12... adhesive layer

Claims

1. A window film having a resin film and a hard coat layer disposed on one main surface of the resin film, wherein the resin film is heated and held at 180°C for 5 minutes, and then, when the shrinkage rate in the MD direction before and after heating is A% and the shrinkage rate in the CD direction before and after heating is B%, A-B is 0.4% or more, and the hard coat layer contains tin-doped indium oxide.

2. The window film according to claim 1, wherein the shrinkage rate in the machine direction is 0.75% or more.

3. The window film according to claim 1 or 2, wherein the window film has a visible light transmittance of 80% or more.

4. The window film according to claim 1 or 2, wherein the near-infrared transmittance of the window film is 20% or less.

5. The window film according to claim 1 or 2, which is for use on the front window of a vehicle.

6. A method for manufacturing a front window with a window film, comprising a step of aligning the MD direction of the resin film with the long side direction of the front window and attaching the window film according to claim 5 to the front window.

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