window film

Abstract

To provide a window film capable of suitably maintaining adhesive force to an adherend, even when placed under high-humidity environment in a state of being adhered to the adherend.SOLUTION: A window film of the present invention is a window film comprising a base material and an adhesive layer provided on one side of the base material. The adhesive layer is formed with a material containing a hot-melt adhesive containing an ultraviolet curable acrylic polymer and a material containing a silane coupling agent. The acrylic polymer preferably has a functional group having a benzophenone structure. It is preferable that a ratio of the functional group having the benzophenone structure to an entire acrylic polymer is 0.1 mass% or more and 5.0 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to window films. [Background technology]

[0002] Window films are adhesive films that are applied to the window glass of vehicles such as automobiles, ships, and trains, and buildings such as houses, condominiums, and office buildings, and are widely used for purposes such as blocking ultraviolet and / or infrared rays in sunlight, protecting privacy, preventing crime, preventing glass from shattering, preventing fogging, preventing dirt from adhering, and decoration (e.g., Patent Document 1).

[0003] Furthermore, films similar to those described above are used on mirrors in washrooms, bathrooms, etc., primarily for the purposes of preventing glass from shattering, preventing fogging, and preventing dirt from adhering (for example, Patent Document 2). Hereinafter, in this specification, the term "window film" will be explained as a concept that includes not only films that are attached to windows, but also films that are attached to mirrors.

[0004] On the other hand, in recent years, there have been attempts to use hot-melt pressure-sensitive adhesive compositions, particularly ultraviolet-curable hot-melt pressure-sensitive adhesive compositions, instead of conventional solvent-based heat-curable pressure-sensitive adhesive compositions, because they do not require a drying step to remove the organic solvent, do not require equipment for a drying step, contribute to energy conservation, and are advantageous from the perspective of reducing the generation of volatile organic compounds (VOCs) and reducing the environmental load.

[0005] However, window films produced using ultraviolet-curable hot-melt pressure-sensitive adhesive compositions instead of conventional solvent-based heat-curable pressure-sensitive adhesive compositions have had the problem that, when used in humid environments or environments where the window films are wet with water, the adhesive strength to adherends such as mirrors and window glass decreases significantly over time. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-012082 [Patent Document 2] Japanese Patent Application Publication No. 2019-038140 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a window film that can favorably maintain its adhesive strength to an adherend even when the film is placed in a humid environment while attached to the adherend. [Means for solving the problem]

[0008] Such an object can be achieved by the present invention described below. The window film of the present invention is a window film comprising a substrate and a pressure-sensitive adhesive layer provided on one surface side of the substrate, The adhesive layer is characterized by being formed using a material containing a hot-melt adhesive containing an ultraviolet-curable acrylic polymer and a silane coupling agent.

[0009] In the present invention, the content of the silane coupling agent in the material is preferably 0.005 parts by mass or more and 7.0 parts by mass or less relative to 100 parts by mass of the hot melt pressure-sensitive adhesive.

[0010] In the present invention, the acrylic polymer preferably has a functional group having a benzophenone structure.

[0011] In the present invention, the proportion of the functional group having a benzophenone structure relative to the entire acrylic polymer is preferably 0.1% by mass or more and 5.0% by mass or less.

[0012] In the present invention, the substrate is preferably made of a material containing polyester.

[0013] In the present invention, the thickness of the pressure-sensitive adhesive layer is preferably 1 μm or more and 100 μm or less.

[0014] In the present invention, it is preferable that a release liner be provided on the surface of the pressure-sensitive adhesive layer opposite to the substrate. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a window film that can favorably maintain its adhesive strength to an adherend even when the window film is placed in a humid environment while attached to the adherend. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view showing one example of the configuration of a window film of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Preferred embodiments of the present invention will be described in detail below. [1] Window film First, the window film of the present invention will be described. FIG. 1 is a cross-sectional view showing an example of the structure of the window film of the present invention.

[0018] The window film 1 includes a substrate 2 and an adhesive layer 3 provided on one surface of the substrate 2. The adhesive layer 3 is formed using a material containing a hot-melt adhesive containing an ultraviolet-curable acrylic polymer and a silane coupling agent.

[0019] This allows the window film 1 to maintain its adhesive strength to the adherend even when the window film 1 is placed in a humid environment while attached to the adherend.

[0020] In particular, when at least a portion of the surface of the adherend is made of glass, the adhesive layer 3 adheres to the glass surface through hydrogen bonding or forms a covalent bond of -O-Si-O- with the glass, thereby achieving excellent adhesion between the adhesive layer 3 and the glass.

[0021] [1-1] Base material The substrate 2 has the function of supporting the pressure-sensitive adhesive layer 3 .

[0022] The substrate 2 may be made of any material. For example, the constituent material of the substrate 2 may be various resin materials, but it is preferable that the substrate 2 be made of a material containing polyester, and it is more preferable that the substrate 2 be made mainly of polyester.

[0023] This improves the handleability of the window film 1 and the workability of attaching the window film 1 to an adherend, etc. Also, the durability of the window film 1 is improved. Furthermore, the adhesion between the substrate 2 and the pressure-sensitive adhesive layer 3 can be further improved.

[0024] In this specification, the term "mainly" refers to the part of interest that has the highest content.

[0025] In particular, the content of polyester in the base material 2 is preferably 90% by mass or more, and more preferably 95% by mass or more.

[0026] Examples of polyesters that can be used to form the substrate 2 include polyethylene terephthalate and polybutylene terephthalate, with polyethylene terephthalate being preferred.

[0027] This improves the handleability of the window film 1 and the workability of attaching the window film 1 to an adherend, etc. Also, the durability of the window film 1 is improved. Also, the adhesion to the pressure-sensitive adhesive layer 3 made of a material described below is further improved.

[0028] The substrate 2 may contain components other than those mentioned above. Examples of such components include colorants, antioxidants, ultraviolet absorbers, light stabilizers, softeners, modifiers, rust inhibitors, fillers, surface lubricants, corrosion inhibitors, heat stabilizers, lubricants, antistatic agents, polymerization inhibitors, crosslinking agents, catalysts, leveling agents, thickeners, and dispersants.

[0029] The substrate 2 may have a substantially uniform composition throughout, or may have regions with different compositions. For example, the substrate 2 may be a laminate including multiple layers with regions with different compositions (including, for example, resin materials with different molecular weights), or may be made of a gradient material whose composition changes gradually along the thickness direction.

[0030] The substrate 2 may be subjected to a surface treatment to enhance adhesion to the pressure-sensitive adhesive layer 3. Examples of such surface treatments include corona treatment and application of an adhesion improver such as a urethane-based, polyester-based, polyethylene-based, polyethyleneimine-based, or acrylic-based one.

[0031] These surface treatment methods are appropriately selected depending on the material constituting the substrate 2, but generally, application of an adhesion improver is preferred in terms of effectiveness and operability.

[0032] The thickness of the substrate 2 is not particularly limited, but is preferably 10 μm or more and 300 μm or less, more preferably 15 μm or more and 200 μm or less, and even more preferably 20 μm or more and 100 μm or less.

[0033] This not only improves the durability of the window film 1, but also improves the handleability of the window film 1, facilitating tasks such as application to an adherend. In addition, the ability to conform to the shape of a curved adherend is improved, effectively preventing wrinkles and the like.

[0034] [1-2] Adhesive layer The pressure-sensitive adhesive layer 3 has the function of coming into contact with and bonding to an adherend when the window film 1 is stuck to the adherend.

[0035] The adhesive layer 3 is formed using a material containing a hot-melt adhesive containing an ultraviolet-curable acrylic polymer and a silane coupling agent.

[0036] [1-2-1] Hot melt adhesive The hot melt adhesive contains an ultraviolet curable acrylic polymer.

[0037] By including an ultraviolet-curable acrylic polymer in the hot-melt pressure-sensitive adhesive, a crosslinking reaction can be promoted by irradiation with ultraviolet light, and as a result, the pressure-sensitive adhesive layer 3 formed has high cohesive strength.

[0038] The ultraviolet-curable acrylic polymer preferably has an ultraviolet C wave reactive group.

[0039] This allows the ultraviolet-C reactive group to function as an ultraviolet-reactive group that contributes to a crosslinking reaction due to irradiation with ultraviolet light, particularly ultraviolet-C radiation.

[0040] Examples of such ultraviolet C wave reactive groups include functional groups having a benzophenone structure, functional groups having a benzyl structure, functional groups having an o-benzoylbenzoic acid ester structure, functional groups having a thioxanthone structure, functional groups having a 3-ketocoumarin structure, functional groups having a 2-ethylanthraquinone structure, and functional groups having a camphorquinone structure, with functional groups having a benzophenone structure being preferred.

[0041] This allows the crosslinking reaction to proceed more favorably. The benzophenone structure described above is converted into a diphenylmethanol structure by the crosslinking reaction caused by irradiation with ultraviolet light.

[0042] The acrylic polymer is a polymer or copolymer of acrylic monomers. Examples of acrylic monomers include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, and lauryl (meth)acrylate. In particular, the acrylic polymer preferably contains, as the acrylic monomer, an alkyl (meth)acrylate whose alkyl group has 1 to 8 carbon atoms. Among alkyl (meth)acrylates whose alkyl group has 1 to 8 carbon atoms, 2-ethylhexyl (meth)acrylate and butyl (meth)acrylate are particularly preferred.

[0043] The UV-reactive group is excited by UV irradiation to generate radicals that trigger a curing reaction (crosslinking reaction). The UV-reactive group is introduced, for example, into the side chain of an acrylic polymer.

[0044] By providing a functional group having a benzophenone structure as the ultraviolet-reactive group, it is possible to improve the reactivity to ultraviolet light and also improve the stability to stimuli other than ultraviolet light.

[0045] The proportion of functional groups having a benzophenone structure in the entire acrylic polymer is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.2% by mass or more and 3.0% by mass or less.

[0046] This makes it possible to make the above-mentioned effects more pronounced. In addition, the pot life of the hot-melt adhesive used to form the adhesive layer 3 can be extended, and the adhesive layer 3 can have excellent adhesiveness.

[0047] Examples of acrylic polymers having a functional group with a benzophenone structure include "acResin (registered trademark)" manufactured by BASF. Examples of "acResin (registered trademark)" include "acResin (registered trademark) A250 UV," "acResin (registered trademark) A260 UV," "acResin (registered trademark) A204 UV," and "acResin (registered trademark) UV 3532."

[0048] [1-2-2] Silane coupling agents The adhesive layer 3 is formed using a material containing the above-mentioned hot melt adhesive and a silane coupling agent.

[0049] This allows the window film 1 to maintain its adhesive strength to the adherend even when placed in a humid environment while attached to the adherend.

[0050] The silane coupling agent may be any compound that contains a silicon atom and has two or more different reactive groups in the molecule, but it is preferable that the silane coupling agent satisfies the following conditions.

[0051] Examples of the silane coupling agent include polymerizable unsaturated group-containing silicon compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacryloxypropyltrimethoxysilane; silicon compounds having an epoxy structure such as 3-glycidoxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; mercapto group-containing silicon compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyldimethoxymethylsilane; 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane; and amino group-containing silicon compounds such as 3-chloropropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, 3-trimethoxysilylpropylsuccinic anhydride, 1,6-bis(trimethoxysilyl)hexane, and condensates of at least one of these with alkyl group-containing silicon compounds such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, and ethyltrimethoxysilane. One or a combination of two or more selected from these can be used.

[0052] The content of the silane coupling agent in the material, i.e., the material used to form the adhesive layer 3, is preferably 0.005 parts by mass or more and 7.0 parts by mass or less, more preferably 0.05 parts by mass or more and 5.0 parts by mass or less, and even more preferably 0.1 parts by mass or more and 3.0 parts by mass or less, per 100 parts by mass of the hot melt adhesive.

[0053] This makes it possible to more suitably maintain the adhesive strength of the window film 1 to the adherend, particularly when the window film 1 is placed in a humid environment while attached to the adherend. If the content of the silane coupling agent is too high, the cohesive strength of the adhesive will decrease, causing the adhesive to deform when attached, or making it more likely that adhesive residue will remain when the window film 1 is peeled off.

[0054] [1-2-3] Other ingredients The pressure-sensitive adhesive layer 3 may contain components other than those mentioned above. Hereinafter, in this section, such components will be referred to as "other components."

[0055] Examples of other components include ultraviolet absorbers, antioxidants, polymerization initiators, light stabilizers, heat stabilizers, softeners, fillers, colorants, and antistatic agents, and one or more selected from these may be used in combination.

[0056] However, the content of other components in the pressure-sensitive adhesive layer 3 is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0057] [1-2-4] Other conditions The thickness of the pressure-sensitive adhesive layer 3 is preferably 1 μm or more and 100 μm or less, more preferably 5 μm or more and 80 μm or less, and even more preferably 10 μm or more and 60 μm or less.

[0058] This not only improves the durability of the window film 1, but also improves the handleability of the window film 1, making it easier to perform tasks such as attaching the film to an adherend. In addition, the film is able to conform to the shape of a curved adherend, effectively preventing wrinkles and the like.

[0059] [1-3] Release liner In the window film 1 , a release liner 4 may be disposed on the surface of the pressure-sensitive adhesive layer 3 opposite to the substrate 2 .

[0060] This effectively prevents dust and the like from adhering to the adhesive layer 3 and the adhesive layer 3 from adhering to undesired areas during storage, transportation, etc. of the manufactured window film 1.

[0061] The release liner 4 is peeled off from the pressure-sensitive adhesive layer 3 when the window film 1 is to be stuck to an adherend.

[0062] The release liner 4 may be, for example, a sheet made of various resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene, polypropylene, polyarylate, etc., or a base material made of various paper materials such as polyethylene-laminated paper, polypropylene-laminated paper, clay-coated paper, resin-coated paper, glassine paper, or high-quality paper, with the surface of this base material in contact with the adhesive layer 3 being subjected to a release treatment as necessary.

[0063] Examples of the release treatment include forming a release agent layer made of a release agent such as a silicone resin, a long-chain alkyl resin, or a fluorine-based resin.

[0064] The thickness of the release liner 4 is not particularly limited, but is preferably, for example, 10 μm to 400 μm. Furthermore, when the release layer is provided, the thickness of the release layer is preferably, for example, 0.01 μm to 5 μm.

[0065] [1-4] Other conditions The thickness of the window film 1 is not particularly limited, but is preferably 11 μm to 400 μm, more preferably 18 μm to 230 μm, and even more preferably 20 μm to 100 μm.

[0066] This not only improves the durability of the window film 1, but also improves the handleability of the window film 1, making it easier to apply the film to an adherend. In addition, the film is more easily conformable to the shape of a curved adherend, more effectively preventing wrinkles and the like.

[0067] The thickness of the window film 1 does not include the thickness of the release liner 4. In other words, it is the thickness of only the portion that is attached to the adherend.

[0068] The window film 1 is preferably transparent so as not to impair the appearance of the adherend.

[0069] In this specification, "transparent" means that the transmittance in the visible light region is 60% or more (upper limit 100%), and preferably 80% or more (upper limit 100%). The transmittance of the window film 1 can be measured by a method in accordance with JIS A5759:2016 (Films for architectural glazing - Visible light transmittance test).

[0070] The window film 1 preferably has a yellowness index (YI) of 4 or less, more preferably 3.5 or less, and even more preferably 2.5 or less.

[0071] This makes it possible to obtain a window film 1 in which coloring is more suitably suppressed, and which has better transparency and colorlessness, making it more suitable as a window film 1.

[0072] The yellowness index (YI) of the window film 1 can be measured by a method in accordance with JIS K7373:2006.

[0073] In accordance with the adhesive strength measurement method of JIS A5759:2016, the window film 1 is cut to a width of 25 mm and pressed onto a float glass plate using a 2 kg roller with one back and forth motion.After leaving the film for 24 hours in an environment of 23°C and relative humidity of 50%, the adhesive strength measured at an angle of 180° and a peel rate of 300 mm / min is preferably 7.5 N / 25 mm or more, more preferably 8.5 N / 25 mm or more, and even more preferably 9.0 N / 25 mm or more.

[0074] This allows the window film 1 to have better adhesion to the adherend.

[0075] Furthermore, in accordance with the adhesive strength measurement method of JIS Z0237:2009, the window film 1 is cut to a width of 25 mm and pressed onto a float glass plate using a 2 kg roller with one back-and-forth motion. After leaving the film for 24 hours in an environment of 30°C and relative humidity of 80%, the adhesive strength measured at an angle of 180° and a peeling speed of 300 mm / min is preferably 5.0 N / 25 mm or more, more preferably 7.5 N / 25 mm or more, and even more preferably 8.0 N / 25 mm or more. This allows the effects of the present invention to be more pronounced.

[0076] [2] Window film manufacturing method Next, a method for manufacturing a window film will be described.

[0077] The window film 1 can be suitably produced, for example, by a method including a pressure-sensitive adhesive composition application step of applying a composition containing a hot-melt pressure-sensitive adhesive containing an ultraviolet-curable acrylic polymer and a silane coupling agent to one side of the substrate 2, and a curing step of irradiating the composition with ultraviolet light to cure the composition and form the pressure-sensitive adhesive layer 3.

[0078] [2-1] Pressure-sensitive adhesive composition application step When the composition is supplied onto the substrate 2, it is sufficient that the composition is heated so as to be melted, and the temperature of the composition (coating temperature) is preferably 120°C or higher and 210°C or lower, and more preferably 130°C or higher and 190°C or lower.

[0079] The softening point of the composition is preferably 90°C or higher and 150°C or lower, and more preferably 100°C or higher and 150°C or lower.

[0080] The melt viscosity of the composition at 160° C. is preferably 2000 mPa·s or more and 13000 mPa·s or less, and more preferably 4000 mPa·s or more and 12000 mPa·s or less.

[0081] The melt viscosity of the composition is measured by a method in accordance with JIS K6862:1984.

[0082] The method for applying the composition is not particularly limited, but a melt extrusion method can be preferably used. More specifically, a method in which the molten composition is supplied onto the substrate 2 from a T-die or the like using an extruder can be preferably used.

[0083] [2-2] Curing process In the curing step, the composition supplied onto the substrate 2 is irradiated with ultraviolet light to cure the composition and form the pressure-sensitive adhesive layer 3 .

[0084] There are no particular limitations on the ultraviolet light source, and examples thereof include high-pressure mercury lamps, metal halide lamps, UV-LEDs, and electrodeless lamp bulbs such as H bulbs. The ultraviolet light is preferably applied from the composition side.

[0085] [2-3] Release liner lamination process After the composition is supplied onto the substrate 2, a release liner 4 for protecting the pressure-sensitive adhesive layer 3 may be attached onto the composition (pressure-sensitive adhesive layer 3).

[0086] This effectively prevents dust and the like from adhering to the adhesive layer 3 and the adhesive layer 3 from adhering to undesired areas during storage, transportation, etc. of the window film 1.

[0087] The release liner 4 is peeled off from the pressure-sensitive adhesive layer 3 when the window film 1 is to be stuck to an adherend.

[0088] [2-3-1] Release liner The release liner 4 may be, for example, a sheet made of various resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene, polypropylene, polyarylate, etc., or a base material made of various paper materials such as polyethylene-laminated paper, polypropylene-laminated paper, clay-coated paper, resin-coated paper, glassine paper, or high-quality paper, with the surface of this base material in contact with the adhesive layer 3 being subjected to a release treatment as necessary.

[0089] Examples of the release treatment include forming a release agent layer made of a release agent such as a silicone resin, a long-chain alkyl resin, or a fluorine-based resin.

[0090] The thickness of the release liner 4 is not particularly limited, but is preferably, for example, 10 μm to 400 μm. Furthermore, when the release layer is provided, the thickness of the release layer is preferably, for example, 0.01 μm to 5 μm.

[0091] The method for producing the window film 1 is not limited to the above-described method, and the window film 1 may also be produced, for example, by applying a composition for forming the adhesive layer 3 to a release liner 4, and then contacting the composition applied to the release liner 4 with the substrate 2.

[0092] The pressure-sensitive adhesive layer 3 can be formed on the release liner 4 in the same manner as described above.

[0093] The order of the release liner laminating step and the curing step may be reversed. This allows the surface of the pressure-sensitive adhesive layer 3 to be suitably flattened.

[0094] The curing step is preferably carried out by irradiating the surface side of the pressure-sensitive adhesive with ultraviolet light before the release liner lamination step.

[0095] [3] Adherent Next, an adherend to which the window film 1 is attached will be described.

[0096] The window film 1 is suitably applied to mirrors in bathrooms and washrooms, windowpanes in buildings such as houses and offices, and vehicles such as automobiles and trains, mirrors, glass cases, and show windows.

[0097] In particular, the window film 1 is preferably used in a high temperature and high humidity environment, more specifically, in an environment where the temperature is 30° C. or higher and the relative humidity is 70% or higher (for example, in a bathroom). This allows the effects of the present invention to be more pronounced.

[0098] Furthermore, the adherend preferably has a chemical structure of —Si—OH on the surface to which the window film 1 is applied.

[0099] [4] How to apply window film Next, a method for applying the window film 1 will be described.

[0100] When attaching the window film 1 to an adherend, if a release liner 4 is present, the release liner 4 is first peeled off to expose the pressure-sensitive adhesive layer 3, and the pressure-sensitive adhesive layer 3 is then brought into contact with the adherend, thereby enabling attachment. Here, attachment may also be performed using a method known as wet attachment, in which attachment is performed at the interface between the pressure-sensitive adhesive layer 3 and the adherend via a working liquid prepared by adding a surfactant to water, and then the working liquid is scraped off using a tool known as a squeegee.

[0101] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these.

[0102] For example, the window film may have a configuration other than those described above. More specifically, for example, the window film may have at least one intermediate layer between the substrate and the pressure-sensitive adhesive layer, or may further have at least one coating layer (such as a hard coating layer) on the outer surface side of the substrate. [Example]

[0103] The present invention will be described in detail below based on specific examples, but the present invention is not limited thereto. Treatments and measurements in the following examples, for which no temperature conditions are specified, were carried out at room temperature (23°C).

[0104] [5] Window film manufacturing Example 1 First, a 50 μm thick film made of polyethylene terephthalate (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4360") was prepared as a substrate.

[0105] Next, an ultraviolet-curable hot-melt adhesive composition was prepared by mixing an ultraviolet-curable hot-melt adhesive and a silane coupling agent in a predetermined ratio. The ultraviolet-curable hot-melt adhesive used was a benzophenone group-containing acrylic hot-melt adhesive manufactured by BASF, trade name "acResin (registered trademark) A250 UV." The silane coupling agent used was 3-glycidoxypropyltrimethoxysilane. The amount of silane coupling agent added was 0.1 parts by mass per 100 parts by mass of the ultraviolet-curable hot-melt adhesive.

[0106] A pressure-sensitive adhesive composition was melted at 140° C. using a hot melt coater and applied to one surface of the substrate to a thickness of 25 μm, to obtain a substrate with the pressure-sensitive adhesive composition.

[0107] Next, a high-pressure mercury lamp (I-Grantage ECS-4011GX, manufactured by I-Graphics Co., Ltd.) was used as an ultraviolet irradiation device to irradiate the adhesive composition coated on the substrate from the surface side at an irradiation intensity of 48 mW / cm. 2 , cumulative light intensity 60mJ / cm 2 The pressure-sensitive adhesive composition was cured by irradiation with light including ultraviolet rays under the conditions of (a) to (c), thereby forming a pressure-sensitive adhesive layer.

[0108] Next, a release liner was attached to the surface of the adhesive layer to obtain a window film with a release liner. The release liner was a 38 μm thick polyethylene terephthalate film with a release treatment applied to the surface that would come into contact with the adhesive layer.

[0109] Examples 2 to 14 A window film was produced in the same manner as in Example 1, except that the type of silane coupling agent used in preparing the ultraviolet-curable hot-melt adhesive composition and the amount of silane coupling agent added to the ultraviolet-curable hot-melt adhesive were changed as shown in Table 1.

[0110] (Comparative Example 1) A window film was produced in the same manner as in Example 1, except that an ultraviolet-curable hot-melt adhesive containing no silane coupling agent was used as the ultraviolet-curable hot-melt adhesive composition.

[0111] [6] Evaluation of adhesive strength The obtained window films were evaluated as follows. First, a window film was cut into a sample 25 mm wide and 250 mm long in accordance with the adhesive strength measurement method of JIS A5759: 2016. Next, the release film was removed and the adhesive layer of the window film was pressed against a float glass plate using a 2 kg rubber roller, which was moved back and forth once in an environment of 23°C and 50% relative humidity.

[0112] After leaving the sample in an environment of 23°C and 50% relative humidity for 24 hours, the sample was peeled off at an angle of 180° and at a peeling speed of 300 mm / min using a tensile tester in accordance with the adhesive strength measurement method of JIS A5759:2016, and the adhesive strength at that time was measured.

[0113] In addition, the atmosphere during application of the window film and when the float glass was left to stand after application of the window film was changed to a temperature of 30°C and a relative humidity of 80%, and the adhesive strength of the sample window film when peeled off was measured in accordance with JIS Z0237:2009.

[0114] Adhesive strength of 7.5 N / 25 mm or more was rated as "○" (pass), adhesive strength of 5.0 N / 25 mm or more but less than 7.5 N / 25 mm was rated as "△" (pass), and adhesive strength of less than 5.0 N / 25 mm was rated as "×" (fail).

[0115] The results of the above evaluations, along with the structure of the pressure-sensitive adhesive layer, for each of the Examples and Comparative Examples are summarized in Table 1. In Table 1, the benzophenone group-containing acrylic hot-melt pressure-sensitive adhesive acResin UV (manufactured by BASF) is indicated as "acResin," 3-glycidoxypropyltrimethoxysilane as "C1," 3-glycidoxypropylmethyldiethoxysilane as "C2," 8-glycidoxyoctyltrimethoxysilane as "C3," 1,6-bis(trimethoxysilyl)hexane as "C4," mercapto group-containing oligomer KR-519 (manufactured by Shin-Etsu Chemical Co., Ltd.) as "C5," 3-aminopropyltrimethoxysilane as "C6," 3-trimethoxysilylpropylsuccinic anhydride as "C7," 3-isocyanatopropyltriethoxysilane as "C8," and 1,6-bis(trimethoxysilyl)hexane as "C9." In Table 1, the amount of silane coupling agent added is shown as a ratio to 100 parts by mass of hot melt pressure sensitive adhesive.

[0116] [Table 1]

[0117] As is clear from Table 1, in each of the above examples in which a silane coupling agent was used in combination with a hot melt adhesive containing a UV-curable acrylic polymer, high adhesive strength was maintained even after the adhesive was left in a humid environment while attached to the adherend, and good results were obtained. In contrast, the comparative examples did not produce satisfactory results. [Explanation of symbols]

[0118] 1:Window film 2: Base material 3: Adhesive layer 4: Release liner

Claims

1. A window film comprising a substrate and a pressure-sensitive adhesive layer provided on one surface of the substrate, The window film is characterized in that the adhesive layer is formed using a material containing a hot-melt adhesive containing an ultraviolet-curable acrylic polymer and a silane coupling agent.

2. The window film according to claim 1, wherein the content of the silane coupling agent in the material is 0.005 parts by mass or more and 7.0 parts by mass or less per 100 parts by mass of the hot melt adhesive.

3. 3. The window film according to claim 1, wherein the acrylic polymer has a functional group having a benzophenone structure.

4. The window film according to claim 3 , wherein the proportion of the functional group having a benzophenone structure relative to the entire acrylic polymer is 0.1% by mass or more and 5.0% by mass or less.

5. The window film according to any one of claims 1 to 4, wherein the substrate is made of a material containing polyester.

6. 6. The window film according to claim 1, wherein the thickness of the pressure-sensitive adhesive layer is 1 μm or more and 100 μm or less.

7. 7. The window film according to claim 1, wherein a release liner is provided on the surface of the pressure-sensitive adhesive layer opposite to the substrate.

Images