Window film manufacturing method

Abstract

To provide a production method for suitably producing a window film which prevents a hardening reaction of an adhesive composition due to ultraviolet irradiation from being inhibited by an ultraviolet absorber, and has a sufficient ultraviolet absorption function.SOLUTION: A production method of a window film in the present invention includes steps of: applying an adhesive composition containing an ultraviolet cure type hot-melt adhesive and an ultraviolet absorber to one face side of a base material; and irradiating the adhesive composition with ultraviolet rays so as to harden the adhesive composition to form an adhesive layer. The ultraviolet cure type hot-melt adhesive is an acrylic polymer having a functional group having a benzophenone structure. In the adhesive composition, a ratio of the ultraviolet absorber based on 100 pts.mass of the acrylic polymer is 0.5 pt.mass or more and 20.0 pts.mass or less, and the adhesive layer has a spectral transmittance of a wavelength of 260 nm of 50% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a window film. Manufacturing method Regarding. [Background technology]

[0002] Window films are adhesive films that are applied to the window glass of vehicles such as automobiles, ships, and trains, as well as buildings such as houses, apartment buildings, and office buildings. They are widely used for blocking ultraviolet and / or infrared rays in sunlight, protecting privacy, preventing crime, preventing glass from shattering, and for decoration.

[0003] In particular, while ultraviolet rays are known to be harmful to the human body, ordinary clear glass is unable to block ultraviolet rays with wavelengths of 300nm to 400nm, so there is a growing need for window films that are highly transparent, achromatic, and yet can efficiently block ultraviolet rays.

[0004] Such window films include those containing an ultraviolet absorber in the adhesive layer (see, for example, Patent Document 1).

[0005] The window film can be formed, for example, by a method including the steps of applying a pressure-sensitive adhesive composition containing an organic solvent and an ultraviolet absorber onto a substrate, removing the organic solvent, and forming a pressure-sensitive adhesive layer containing the ultraviolet absorber by a thermal curing reaction.

[0006] On the other hand, in recent years, there have been attempts to use 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.

[0007] However, when a window film containing an ultraviolet absorber is produced using an ultraviolet-curable hot-melt adhesive composition instead of a conventional solvent-based heat-curable adhesive composition, the following problems arise.

[0008] That is, the ultraviolet light irradiated to cause the curing reaction of the ultraviolet-curable hot-melt pressure-sensitive adhesive composition is absorbed by the ultraviolet absorber contained in the pressure-sensitive adhesive composition, thereby inhibiting the curing reaction.

[0009] On the other hand, if the content of the ultraviolet absorber in the pressure-sensitive adhesive composition is reduced, the final window film will not be able to be imparted with sufficient ultraviolet absorbing function. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2020-012082 Summary of the Invention [Problem to be solved by the invention]

[0011] The object of the present invention is to provide a method for producing a window film using an ultraviolet-curable hot-melt adhesive, which can suitably produce a window film having sufficient ultraviolet absorption function without the curing reaction of the adhesive composition due to ultraviolet irradiation being inhibited by the ultraviolet absorber contained in the adhesive composition, and to provide a window film having sufficient ultraviolet absorption function, which has an adhesive layer made of a material in which the curing reaction has progressed sufficiently. [Means for solving the problem]

[0012] Such an object can be achieved by the present invention described below. The method for producing a window film of the present invention is a method for producing a window film including a substrate and a pressure-sensitive adhesive layer provided on one surface of the substrate, applying a pressure-sensitive adhesive composition containing an ultraviolet-curable hot-melt pressure-sensitive adhesive and an ultraviolet absorber to one surface of the substrate; The pressure-sensitive adhesive composition Includes wavelength bands between 220nm and 280nm and curing the pressure-sensitive adhesive composition by irradiating it with ultraviolet light to form the pressure-sensitive adhesive layer. the ultraviolet-curable hot-melt pressure-sensitive adhesive is an acrylic polymer having a functional group with a benzophenone structure, In the pressure-sensitive adhesive composition, a ratio of the ultraviolet absorber to 100 parts by mass of the acrylic polymer is 0.5 parts by mass or more and 20.0 parts by mass or less; The pressure-sensitive adhesive layer has a spectral transmittance of 50% or more at a wavelength of 260 nm. the law of nature, The ultraviolet absorption wavelength band of the ultraviolet absorber in the pressure-sensitive adhesive layer is 300 nm or more and 380 nm or less. .

[0013] The method for producing a window film of the present invention is a method for producing a window film including a substrate and a pressure-sensitive adhesive layer provided on one surface of the substrate, applying a pressure-sensitive adhesive composition containing an ultraviolet-curable hot-melt pressure-sensitive adhesive and an ultraviolet absorber to one surface of the substrate using a hot-melt coater; and curing the pressure-sensitive adhesive composition by irradiating the pressure-sensitive adhesive composition with ultraviolet light to form the pressure-sensitive adhesive layer. the ultraviolet-curable hot-melt pressure-sensitive adhesive is an acrylic polymer having a functional group with a benzophenone structure, In the pressure-sensitive adhesive composition, a ratio of the ultraviolet absorber to 100 parts by mass of the acrylic polymer is 0.5 parts by mass or more and 20.0 parts by mass or less; The pressure-sensitive adhesive layer has a spectral transmittance of 50% or more at a wavelength of 260 nm. In the present invention, the melt viscosity of the pressure-sensitive adhesive composition at 160° C. is preferably 2000 mPa·s or more and 13000 mPa·s or less. In the present invention, the pressure-sensitive adhesive layer is preferably formed by a melt extrusion method. In the present invention, the temperature of the pressure-sensitive adhesive composition when it is applied to the substrate is preferably 120°C or higher and 210°C or lower. In the present invention, the ultraviolet absorber preferably has a benzotriazole structure, a benzophenone structure, or a hydroxyphenyltriazine structure.

[0014] In the present invention, the ultraviolet absorber is preferably at least one of compounds represented by the following formulas (1) to (12).

[0015] [ka]

[0016] [ka]

[0017] [ka]

[0018] [ka]

[0019] [ka]

[0020] [ka]

[0021] [ka]

[0022] [ka]

[0023] [ka]

[0024] [ka]

[0025] [ka] (In formula (11), R is an alkyl group having from 10 to 12 carbon atoms.)

[0026] [ka]

[0027] 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.

[0028] In the present invention, the substrate is preferably made of a material containing polyester.

[0029] The present invention preferably further comprises a step of laminating a release liner on the surface of the substrate opposite to the surface of the pressure-sensitive adhesive composition applied to one surface of the substrate. [Effects of the Invention]

[0032] According to the present invention, there is provided a method for producing a window film using an ultraviolet-curable hot-melt adhesive, which is capable of suitably producing a window film having sufficient ultraviolet absorbing function, without the curing reaction of the adhesive composition due to ultraviolet irradiation being inhibited by an ultraviolet absorber contained in the adhesive composition. can be done. [Brief explanation of the drawings]

[0033] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an example of a method for producing a window film of the present invention. [Figure 2] 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

[0034] Preferred embodiments of the present invention will be described in detail below. [1] Window film manufacturing method First, a method for manufacturing a window film will be described. FIG. 1 is a cross-sectional view schematically illustrating an example of a method for producing a window film of the present invention.

[0035] The method for producing a window film of the present invention is a method for producing a window film 1 including a substrate 2 and a pressure-sensitive adhesive layer 3 provided on one surface of the substrate 2, and includes an adhesive composition applying step of applying an adhesive composition 3' containing an ultraviolet-curable hot-melt adhesive and an ultraviolet absorber to one surface of the substrate 2, and a curing step of irradiating the adhesive composition 3' with ultraviolet light to cure the adhesive composition 3' to form a pressure-sensitive adhesive layer 3. The ultraviolet-curable hot-melt adhesive is an acrylic polymer having a functional group with a benzophenone structure, and the ratio of the ultraviolet absorber to 100 parts by mass of the acrylic polymer in the pressure-sensitive adhesive composition 3' is 0.5 parts by mass or more and 20.0 parts by mass or less, and the pressure-sensitive adhesive layer 3 has a spectral transmittance at a wavelength of 260 nm of 50% or more.

[0036] According to the present invention, in the method for manufacturing a window film using an ultraviolet-curable hot-melt adhesive, the ultraviolet-curable hot-melt adhesive in the adhesive composition 3' is an acrylic polymer having a functional group with a benzophenone structure, so that the wavelength band for the ultraviolet curing reaction of the adhesive composition 3', in other words, the crosslinking reaction between the acrylic polymers, can be suitably shifted from the ultraviolet absorption wavelength band for blocking ultraviolet rays in the adhesive layer 3 to be formed.

[0037] Specifically, for example, the wavelength band for UV curing of the pressure-sensitive adhesive composition 3' can be 220 nm to 280 nm, and the wavelength band of UV absorption by the UV absorber in the pressure-sensitive adhesive layer 3 to be formed can be 300 nm to 380 nm.

[0038] Furthermore, in the adhesive composition 3', by setting the ratio of the ultraviolet absorber to 100 parts by mass of the acrylic polymer to 0.5 parts by mass or more and 20.0 parts by mass or less, the ultraviolet curing reaction of the adhesive composition 3' proceeds smoothly without being inhibited by the ultraviolet absorber, and the adhesive layer 3 formed can fully absorb ultraviolet light.

[0039] Furthermore, since the pressure-sensitive adhesive layer 3 has a transmittance of 50% or more for ultraviolet light with a wavelength of 260 nm, when the ultraviolet-curable pressure-sensitive adhesive composition 3' is irradiated with ultraviolet light with a wavelength of 260 nm for the curing reaction, the absorption of ultraviolet light by the ultraviolet absorber contained in the pressure-sensitive adhesive composition 3' is kept low, allowing more ultraviolet light to be irradiated, and the curing reaction of the pressure-sensitive adhesive composition 3' due to ultraviolet light irradiation to proceed smoothly.

[0040] Thus, according to the present invention, a method for manufacturing a window film can be provided that can suitably produce a window film 1 having sufficient ultraviolet absorption function without the curing reaction of the adhesive composition 3' due to ultraviolet irradiation being inhibited by the ultraviolet absorber contained in the adhesive composition 3'.

[0041] The excellent effects of the present invention can be obtained by the method for producing a window film having the above-mentioned configuration, and cannot be obtained if the method does not have the above-mentioned configuration.

[0042] For example, if the acrylic polymer in the adhesive composition does not have a functional group having a benzophenone structure, the wavelength band for UV curing of the adhesive composition 3' and the absorption wavelength band for UV blocking cannot be suitably shifted, and the intended effect of the present invention cannot be obtained.

[0043] Furthermore, if the ratio of the ultraviolet absorber to 100 parts by mass of the acrylic polymer in the pressure-sensitive adhesive composition is less than the lower limit, the pressure-sensitive adhesive layer formed will not be able to sufficiently absorb ultraviolet rays.

[0044] Furthermore, if the ratio of the ultraviolet absorber to 100 parts by mass of the acrylic polymer in the pressure-sensitive adhesive composition exceeds the upper limit, the ultraviolet absorber inhibits the ultraviolet curing reaction of the pressure-sensitive adhesive composition.

[0045] Furthermore, if the spectral transmittance of the pressure-sensitive adhesive layer at a wavelength of 260 nm is too low, when the pressure-sensitive adhesive composition is irradiated with ultraviolet light at a wavelength of 260 nm for a curing reaction, the ultraviolet light will be absorbed by the ultraviolet absorber contained in the pressure-sensitive adhesive composition, and the curing reaction of the pressure-sensitive adhesive composition due to ultraviolet light irradiation will not proceed smoothly.

[0046] The 260 nm spectral transmittance of the pressure-sensitive adhesive layer 3 is measured using a measuring device conforming to 5.3.1 of JIS R3106 by a method conforming to 5.3.2 of JIS R3106.

[0047] The spectral transmittance is measured using a substrate made of a material containing polypropylene, which does not substantially absorb ultraviolet light, since a substrate made of a material containing polyethylene terephthalate absorbs part of the ultraviolet light.

[0048] In the adhesive composition 3', the ratio of the ultraviolet absorber to 100 parts by mass of the acrylic polymer may be 0.5 parts by mass or more and 20.0 parts by mass or less, preferably 2.0 parts by mass or more and 18.0 parts by mass or less, and more preferably 5.0 parts by mass or more and 10.0 parts by mass or less. This makes it possible to make the above-mentioned effects more pronounced.

[0049] The spectral transmittance of the pressure-sensitive adhesive layer 3 at a wavelength of 260 nm may be 50% or more, preferably 80% or more, and more preferably 90% or more. This makes it possible to make the above-mentioned effects more pronounced.

[0050] [1-1] Pressure-sensitive adhesive composition application step As shown in FIG. 1(a), in the adhesive composition application step, an adhesive composition 3' containing an ultraviolet-curable hot-melt adhesive and an ultraviolet absorber is applied to one surface of a substrate 2.

[0051] [1-1-1] Base material The substrate 2 has the function of supporting the pressure-sensitive adhesive layer 3 . 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.

[0052] This improves the handleability of the window film 1 and improves the workability of attaching the window film 1 to an adherend, etc. Furthermore, the durability of the window film 1 is improved.

[0053] In this specification, the term "mainly" refers to the part of interest that has the highest content.

[0054] 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.

[0055] Examples of polyesters that form the base material 2 include polyethylene terephthalate and polybutylene terephthalate, with polyethylene terephthalate being preferred.

[0056] 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 improved.

[0057] The substrate 2 may contain components other than those mentioned above. Examples of such components include colorants, antioxidants, ultraviolet absorbers, light stabilizers, softeners, fillers, heat stabilizers, lubricants, and antistatic agents.

[0058] 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.

[0059] 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 promoter.

[0060] 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.

[0061] The thickness of the substrate 2 is not particularly limited, but is preferably 10 μm to 300 μm, more preferably 15 μm to 200 μm, and even more preferably 20 μm to 100 μm.

[0062] This not only provides shatterproof properties to 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.

[0063] [1-1-2] Pressure-sensitive adhesive composition The pressure-sensitive adhesive composition 3 ′ is used to form the pressure-sensitive adhesive layer 3 . The pressure-sensitive adhesive layer 3 formed using the pressure-sensitive adhesive composition 3' has the function of coming into contact with and bonding to an adherend when the window film 1 is stuck to the adherend.

[0064] The adhesive composition 3' contains an ultraviolet-curable hot-melt adhesive that undergoes a curing reaction upon irradiation with ultraviolet light, and an ultraviolet absorber.

[0065] The ultraviolet-curable hot-melt adhesive is an acrylic polymer having a functional group with a benzophenone structure as an ultraviolet-reactive group that contributes to a crosslinking reaction upon irradiation with ultraviolet light. As a result, the pressure-sensitive adhesive layer 3 formed is crosslinked by ultraviolet irradiation, and the cohesive strength is improved.

[0066] 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 having an alkyl group with 1 to 8 carbon atoms. Among alkyl (meth)acrylates having an alkyl group with 1 to 8 carbon atoms, 2-ethylhexyl (meth)acrylate and butyl (meth)acrylate are particularly preferred.

[0067] 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.

[0068] By providing a functional group having a benzophenone structure as the UV-reactive group, it is possible to improve the reactivity to UV rays and also improve the stability to stimuli other than UV rays. In particular, it is possible to suitably shift the wavelength band for UV curing of the pressure-sensitive adhesive composition 3′, in other words, the crosslinking reaction between acrylic polymers, from the UV absorption wavelength band for UV blocking in the pressure-sensitive adhesive layer 3 to be formed.

[0069] 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.

[0070] This makes it possible to make the above-mentioned effects more pronounced. Furthermore, the pot life of the pressure-sensitive adhesive composition 3' can be extended, and the pressure-sensitive adhesive layer 3 can have excellent adhesiveness.

[0071] Examples of acrylic polymers having a functional group with a benzophenone structure as a UV-reactive group 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."

[0072] The content of the acrylic polymer in the adhesive composition 3' is preferably 50.0% by mass or more and 99.5% by mass or less, more preferably 70.0% by mass or more and 99.2% by mass or less, and even more preferably 85.0% by mass or more and 98.0% by mass or less.

[0073] An ultraviolet absorber has the function of absorbing ultraviolet rays and converting them into energy such as heat, thereby preventing the effects of ultraviolet rays on the human body and articles.

[0074] The ultraviolet absorber preferably has an absorption maximum wavelength of 400 nm or less, particularly preferably 390 nm or less, and even more preferably 380 nm or less, in a wavelength range of 200 nm or more and 500 nm or less in a 0.1% by mass acetonitrile solution.

[0075] In addition, when there are multiple absorption maximum wavelengths of absorbance within the wavelength range of 200 nm or more and 500 nm or less, it is sufficient that at least one of the absorption maximum wavelengths is within the above range.

[0076] This allows the acrylic polymer to be sufficiently cured when irradiated with ultraviolet light without being inhibited by the ultraviolet absorber.

[0077] On the other hand, the lower limit of the absorption maximum wavelength is preferably 200 nm or more, more preferably 250 nm or more, and even more preferably 280 nm or more, from the viewpoint of preventing the effects of ultraviolet rays on the human body and articles.

[0078] Examples of ultraviolet absorbers include benzophenone-based, benzotriazole-based, benzoate-based, benzoxazinone-based, triazine-based, phenyl salicylate-based, cyanoacrylate-based, and nickel complex salt-based compounds, and one type may be used alone or two or more types may be used in combination.

[0079] Among these, it is preferable to use a compound having a benzotriazole structure, a benzophenone structure, or a hydroxyphenyltriazine structure as the ultraviolet absorber. These compounds have excellent compatibility with the aforementioned acrylic polymers and the like, and have high ultraviolet absorption function in the wavelength range of 300 nm or more and 380 nm or less, making it easier for the pressure-sensitive adhesive layer 3 formed to satisfy the aforementioned optical properties.

[0080] In particular, the ultraviolet absorber is preferably at least one of the compounds represented by the following formulas (1) to (12). This makes it possible to make the above-mentioned effects even more pronounced.

[0081] [ka]

[0082] [ka]

[0083] [ka]

[0084] [ka]

[0085] [ka]

[0086] [ka]

[0087] [ka]

[0088] [ka]

[0089] [ka]

[0090] [ka]

[0091] [ka] (In formula (11), R is an alkyl group having from 10 to 12 carbon atoms.)

[0092] [ka]

[0093] Commercially available examples of such ultraviolet absorbers include those sold by BASF under the trade names "Tinuvin (registered trademark) PS," "Tinuvin (registered trademark) 460," "Tinuvin (registered trademark) 477," "Tinuvin (registered trademark) 400," and "Tinuvin (registered trademark) 384-2," and those sold by Shipro Chemical Co., Ltd. under the trade names "SEESORB SB701," "SEESORB SB704," "SEESORB SB706," "SEESORB SB707," "SEESORB SB709," "SEESORB SB107," and "SEESORB SB106."

[0094] The pressure-sensitive adhesive composition 3' may contain components other than those described above. Hereinafter, in this section, such components will also be referred to as "other components."

[0095] Examples of other components include dispersants, tackifiers, antioxidants, polymerization initiators, light stabilizers, heat stabilizers, softeners, silane coupling agents, fillers, colorants, and antistatic agents. These may be used alone or in combination of two or more.

[0096] However, the content of other components in the pressure-sensitive adhesive composition 3' is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0097] The softening point of the pressure-sensitive adhesive composition 3' is preferably 90°C or higher and 150°C or lower, and more preferably 100°C or higher and 150°C or lower.

[0098] The melt viscosity of the pressure-sensitive adhesive composition 3' 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.

[0099] The melt viscosity of the pressure-sensitive adhesive composition 3' is measured by a method in accordance with JIS K6862:1984.

[0100] Although there are no particular limitations on the method for forming the pressure-sensitive adhesive layer 3, a melt extrusion method can be suitably employed. More specifically, the pressure-sensitive adhesive layer 3 can be suitably formed by supplying a molten pressure-sensitive adhesive composition 3' onto the substrate 2 from a T-die or the like using an extruder.

[0101] When supplying the adhesive composition 3' onto the substrate 2, the adhesive composition 3' may be heated so as to melt, but the temperature (coating temperature) of the adhesive composition 3' is preferably 120°C or higher and 210°C or lower, and more preferably 130°C or higher and 190°C or lower.

[0102] [1-2] Release liner lamination process In this embodiment, as shown in FIG. 1(b), a release liner lamination step is further provided in which a release liner 4 is laminated on the surface opposite to the substrate 2 of the pressure-sensitive adhesive composition 3' applied to one surface of the substrate 2.

[0103] 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.

[0104] In particular, by having a release liner lamination step between the above-mentioned pressure-sensitive adhesive composition application step and the below-described curing step, the surface of the pressure-sensitive adhesive layer 3 can be suitably flattened.

[0105] 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.

[0106] [1-2-1] 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.

[0107] 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.

[0108] 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.

[0109] [1-3]Curing process As shown in FIGS. 1(c) and 1(d), in the curing step, the pressure-sensitive adhesive composition 3' is irradiated with ultraviolet light to cure the pressure-sensitive adhesive composition 3' into the pressure-sensitive adhesive layer 3.

[0110] The pressure-sensitive adhesive layer 3 thus formed has a spectral transmittance of 50% or more at a wavelength of 260 nm. As a result, when the adhesive composition 3' is irradiated with ultraviolet light having a wavelength of 260 nm for the curing reaction, the absorption of ultraviolet light by the ultraviolet absorber contained in the adhesive composition 3' is kept low, allowing more ultraviolet light to be irradiated, and the curing reaction of the adhesive composition 3' due to ultraviolet light irradiation proceeds smoothly.

[0111] There are no particular limitations on the ultraviolet light source, and for example, a high-pressure mercury lamp, a metal halide lamp, a UV-LED, etc. may be used.

[0112] The pressure-sensitive adhesive layer 3 thus formed is made of a material containing a polymer containing an acrylic structure and an ultraviolet absorber.

[0113] 1(c), the pressure-sensitive adhesive composition 3' is irradiated with ultraviolet light from the release liner 4 side, but this is not limiting, and for example, the pressure-sensitive adhesive composition 3' may be irradiated with ultraviolet light from the base material 2 side. More specifically, for example, when the release liner 4 is a polypropylene film that transmits ultraviolet light with a wavelength of 260 nm, the pressure-sensitive adhesive composition 3' may be irradiated with ultraviolet light from the release liner 4 side, and when the base material 2 is a polypropylene film that transmits ultraviolet light with a wavelength of 260 nm, the pressure-sensitive adhesive composition 3' may be irradiated with ultraviolet light from the base material 2 side. Alternatively, the pressure-sensitive adhesive composition 3' may be irradiated with ultraviolet light without the release liner 4.

[0114] [2] Window film Next, the window film of the present invention will be described. FIG. 2 is a cross-sectional view schematically showing one example of the configuration of the window film of the present invention. The window film 1 includes a substrate 2 and a pressure-sensitive adhesive layer 3 provided on one surface of the substrate 2.

[0115] In particular, in the window film 1, the adhesive layer 3 is a cured product of an adhesive composition 3' containing an ultraviolet-curable hot-melt adhesive and an ultraviolet absorber, the ultraviolet-curable hot-melt adhesive is an acrylic polymer having a functional group with a benzophenone structure, the proportion of the ultraviolet absorber in the adhesive composition 3' relative to 100 parts by mass of the acrylic polymer is 0.5 parts by mass or more and 20.0 parts by mass or less, and the spectral transmittance of the adhesive layer 3 at a wavelength of 260 nm is 50% or more.

[0116] Such a window film 1 can be suitably produced by the production method described above. Such a window film 1 has an adhesive layer 3 made of a material in which the curing reaction has progressed sufficiently, and also has a sufficient ultraviolet absorbing function.

[0117] The spectral transmittance of the pressure-sensitive adhesive layer 3 at a wavelength of 260 nm may be 50% or more, preferably 80% or more, and more preferably 90% or more. This makes it possible to make the above-mentioned effects more pronounced.

[0118] 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.

[0119] This not only improves the durability and UV absorption performance 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. Furthermore, the film is also able to conform to the shape of a curved adherend, effectively preventing wrinkles and the like.

[0120] Furthermore, the pressure-sensitive adhesive layer 3 preferably has an ultraviolet transmittance of less than 3%, more preferably less than 1%, as measured in accordance with JIS A5759:2016. The reason for this is that when the ultraviolet transmittance value is less than 3%, the window film 1 can more effectively block ultraviolet rays.

[0121] The lower limit of the ultraviolet transmittance measured in accordance with JIS A5759:2016 is not particularly limited, and may be, for example, 0% or more, 0.01% or more, particularly 0.1% or more, or even 0.50% or more.

[0122] The substrate 2 preferably satisfies the conditions described in [1-1-1] above. 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 .

[0123] 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.

[0124] This not only improves the durability and UV absorption function 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.

[0125] 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.

[0126] The window film 1 is preferably transparent so as not to impair the appearance of the adherend. 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).

[0127] The yellowness index (YI) of the window film 1 is preferably 4 or less, more preferably 1 or more and 3.5 or less, and even more preferably 1.5 or more and 2.5 or less.

[0128] 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.

[0129] The yellowness index (YI) of the window film 1 can be measured by a method in accordance with JIS K 7373.

[0130] [3] Adherent Next, an adherend to which the window film 1 is attached will be described. The window film 1 is suitably applied to window glass of buildings such as houses and buildings, and vehicles such as automobiles and trains, as well as mirrors, glass cases, and show windows.

[0131] This makes it possible to suitably block ultraviolet rays contained in sunlight and the like, and to adequately protect the human body from the effects of ultraviolet rays and from deterioration of articles caused by ultraviolet rays.

[0132] [4] How to apply window film Next, a method for attaching the window film will be described. When the window film 1 is applied to an adherend such as a window glass, if a release liner 4 is present, the application can be performed by first peeling off the release liner 4 to expose the pressure-sensitive adhesive layer 3, and then adhering the pressure-sensitive adhesive layer 3 to the adherend. Here, application can also be performed using a method known as water application, in which application is performed at the interface between the pressure-sensitive adhesive layer 3 and the adherend via an application liquid prepared by adding a surfactant to water, and then scraping out the application liquid using a tool known as a squeegee.

[0133] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these.

[0134] 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.

[0135] The method for producing a window film of the present invention only needs to include a pressure-sensitive adhesive composition application step and a curing step, and may further include other steps.

[0136] Furthermore, in the above-described embodiment, the case where a pressure-sensitive adhesive composition is applied to one side of a substrate to form a pressure-sensitive adhesive layer on the substrate has been mainly described, but the pressure-sensitive adhesive layer may also be formed by applying a transfer method in which the pressure-sensitive adhesive layer is formed on one side of a release liner and then the release liner on which the pressure-sensitive adhesive layer is provided is bonded to the substrate. Even in such a case, the same effects as those described above can be obtained. When the transfer method is applied, it is preferable to perform the curing step before contacting the pressure-sensitive adhesive layer provided on the release liner with the substrate (in other words, before the step of applying the pressure-sensitive adhesive composition containing the ultraviolet-curable hot-melt pressure-sensitive adhesive and the ultraviolet absorber to the substrate). [Example]

[0137] The present invention will be described in detail below based on specific examples, but the present invention is not limited thereto. In the following examples, treatments and measurements for which no temperature conditions are specified were carried out at 23°C.

[0138] [5] Window film manufacturing Example 1 First, a 50 μm thick film made of polyethylene terephthalate (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4160") was prepared as a substrate.

[0139] Next, an ultraviolet-curable hot-melt adhesive composition was prepared by mixing an ultraviolet-curable hot-melt adhesive and an ultraviolet absorber. The ultraviolet-curable hot-melt adhesive used was a benzophenone group-containing acrylic hot-melt adhesive manufactured by BASF under the trade name "acResin (registered trademark) A204UV." The ultraviolet absorber used was Tinuvin 460 (manufactured by BASF), an ultraviolet absorber having a hydroxyphenyltriazine structure. The amount of ultraviolet absorber added was 4.0 parts by mass per 100 parts by mass of the acrylic polymer.

[0140] The adhesive composition was applied to one surface of the substrate using a hot melt coater to a thickness of 25 μm, to obtain a substrate with the adhesive composition attached thereto.

[0141] Next, a release liner was attached to the adhesive layer of the substrate with the adhesive composition. The release liner was a 40 μm thick polypropylene film with a silicone coating on the surface that would come into contact with the adhesive layer.

[0142] Next, a high-pressure mercury lamp (I-Grantage ECS-4011GX, manufactured by I-Graphics Co., Ltd.) was used as an ultraviolet irradiation device, and the irradiation intensity was 48 mW / cm from the release liner side. 2 , cumulative light intensity 60mJ / cm 2 The pressure-sensitive adhesive composition was cured by irradiation with light containing ultraviolet rays under the conditions of (a) to (c), thereby forming a pressure-sensitive adhesive layer, and thus a window film was obtained.

[0143] Examples 2 to 19 A window film was produced in the same manner as in Example 1, except that the type and amount of the ultraviolet absorber were changed to those shown in Table 1.

[0144] (Comparative Examples 1 to 8) A window film was produced in the same manner as in Example 1, except that the type and amount of the ultraviolet absorber were changed to those shown in Table 1.

[0145] (Comparative Example 9) A window film was produced in the same manner as in Example 1, except that no ultraviolet absorber was used.

[0146] [6] Window film evaluation The obtained window films were evaluated as follows.

[0147] [6-1]260nm transmittance The spectral transmittance at 260 nm of the pressure-sensitive adhesive layer of the obtained window film was measured using a measuring device conforming to 5.3.1 of JIS R3106 and a method conforming to 5.3.2 of JIS R3106.

[0148] [6-2] Holding power test The obtained window film was cut into a sample of 25 mm x 50 mm. The sample was attached to a stainless steel plate as an adherend, with an adhesive area of ​​25mm x 25mm. The stainless steel plate and sample were held vertically, a 1kg weight was attached to the sample, and the sample was left to stand at 40°C for 70,000 seconds. After the test, the length of displacement from the adhesive point was measured, and the holding strength was evaluated according to the following criteria.

[0149] ◎: Misalignment amount is 0.0 mm (no misalignment) ○: Misalignment is 0.1 mm or more and less than 5.0 mm △: Misalignment is 5.0mm or more and less than 15.0mm ×: Misalignment is 15.0 mm or more

[0150] [6-3] Weather resistance test The resulting window film was attached to a 3mm float glass and subjected to continuous UV irradiation for 2000 hours from the glass surface using a Sunshine Carbon accelerated weathering tester (Sunshine Weather Meter S80, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS A5759:2016, under test conditions of a temperature of 63°C ± 3°C indicated by a black panel thermometer and a relative humidity of 50% ± 5%. During the weathering test, the window film was subjected to 18 minutes of water spraying during the 120 minutes of irradiation.

[0151] ΔYI was calculated from the YI values ​​before and after the weather resistance test (ΔYI = YI after weather resistance test - YI before weather resistance test), and the weather resistance was judged according to the following criteria.

[0152] ◎: ΔYI is 0.0 or more and 1.0 or less ○: ΔYI is 1.1 or more and 3.0 or less △: ΔYI is 3.1 or more and less than 5.0 ×: ΔYI is 5.0 or more

[0153] The yellowness index (YI) was measured using a spectrocolorimeter (Spectro Color Meter SQ2000, manufactured by Nippon Denshoku Industries Co., Ltd.) according to the method of JIS K 7373. YI is a value defined by the following formula.

[0154] YI=100(1.28X-1.067Z) / Y (X and Y are the tristimulus values ​​in the XYZ coordinate system of the window film measured with a color difference meter.)

[0155] Table 1 shows the main components of the window films for each of the examples and comparative examples, as well as the results of the above evaluations.

[0156] In Table 1, acResin A204UV (manufactured by BASF), a benzophenone group-containing acrylic hot melt adhesive, is referred to as "acResin", the ultraviolet absorber represented by the above formula (1) is referred to as "formula (1)", the ultraviolet absorber represented by the above formula (2) is referred to as "formula (2)", the ultraviolet absorber represented by the above formula (3) is referred to as "formula (3)", the ultraviolet absorber represented by the above formula (4) is referred to as "formula (4)", the ultraviolet absorber represented by the above formula (5) is referred to as "formula (5)", the ultraviolet absorber represented by the above formula (6) is referred to as "formula (6)", and the ultraviolet absorber represented by the above formula (7) is referred to as "formula (8)". The absorber is shown as "Formula (7)", the ultraviolet absorber represented by the above formula (8) is shown as "Formula (8)", the ultraviolet absorber represented by the above formula (9) is shown as "Formula (9)", the ultraviolet absorber represented by the above formula (10) is shown as "Formula (10)", the ultraviolet absorber represented by the above formula (11) is shown as "Formula (11)", the ultraviolet absorber represented by the above formula (12) is shown as "Formula (12)", Tinuvin 477 (manufactured by BASF), which is an ultraviolet absorber having a hydroxyphenyltriazine structure, is shown as "T477", and CYASORB UV-24 (manufactured by Solvay), which is 2,2'-dihydroxy-4-methoxy benzophenone as an ultraviolet absorber, is shown as "UV-24".

[0157] [Table 1]

[0158] As is clear from Table 1, in each of the Examples, the UV curing reaction of the pressure-sensitive adhesive composition proceeded smoothly, and good results were obtained in the holding power test with small deviations. Furthermore, the pressure-sensitive adhesive layer had sufficient UV absorption function, and good results were obtained in the weather resistance test. Furthermore, the spectral transmittance of the pressure-sensitive adhesive layer formed at a wavelength of 260 nm was 50% or more in all cases.

[0159] In contrast, in comparative examples in which the proportion of ultraviolet absorber per 100 parts by mass of acrylic polymer was less than 0.5 parts by mass, the weather resistance of the pressure-sensitive adhesive layer formed was insufficient. Furthermore, in comparative examples in which the proportion of ultraviolet absorber exceeded 20.0 parts by mass, the ultraviolet curing reaction of the pressure-sensitive adhesive composition was inhibited by the ultraviolet absorber, resulting in insufficient curing properties. Furthermore, in comparative examples in which the proportion of ultraviolet absorber was 0.5 parts by mass or more and 20.0 parts by mass or less, but the pressure-sensitive adhesive layer had a spectral transmittance of less than 50% at a wavelength of 260 nm, the ultraviolet curing reaction of the pressure-sensitive adhesive composition did not proceed sufficiently, resulting in insufficient weather resistance.

[0160] In addition, window films were produced in the same manner as in each of the above-mentioned Examples and Comparative Examples, except that the laminate was produced by coating one side of a release liner with an ultraviolet-curable hot-melt pressure-sensitive adhesive composition to form a pressure-sensitive adhesive layer, and then laminating a substrate onto the pressure-sensitive adhesive layer.These window films were evaluated in the same manner as above, and the same results as above were obtained.

[0161] In addition, window films were manufactured in the same manner as in each of the above examples and comparative examples, except that the thickness of the adhesive layer was changed in various ways within the range of 1 μm or more and 100 μm or less, and these were evaluated in the same manner as above, and the same results as above were obtained. [Explanation of symbols]

[0162] 1:Window film 2: Base material 3': adhesive composition 3: Adhesive layer 4: Release liner

Claims

1. A method for manufacturing a window film comprising a substrate and a pressure-sensitive adhesive layer provided on one surface of the substrate, applying a pressure-sensitive adhesive composition containing an ultraviolet-curable hot-melt pressure-sensitive adhesive and an ultraviolet absorber to one surface of the substrate; and curing the pressure-sensitive adhesive composition by irradiating the pressure-sensitive adhesive composition with ultraviolet light having a wavelength band of 220 nm or more and 280 nm or less to form the pressure-sensitive adhesive layer, the ultraviolet-curable hot-melt pressure-sensitive adhesive is an acrylic polymer having a functional group with a benzophenone structure, In the pressure-sensitive adhesive composition, a ratio of the ultraviolet absorber to 100 parts by mass of the acrylic polymer is 0.5 parts by mass or more and 20.0 parts by mass or less, The pressure-sensitive adhesive layer has a spectral transmittance of 50% or more at a wavelength of 260 nm, The method for manufacturing a window film, wherein the ultraviolet absorption wavelength band of the ultraviolet absorber in the pressure-sensitive adhesive layer is 300 nm or more and 380 nm or less.

2. A method for manufacturing a window film comprising a substrate and an adhesive layer provided on one side of the substrate, applying a pressure-sensitive adhesive composition containing an ultraviolet-curable hot-melt pressure-sensitive adhesive and an ultraviolet absorber to one surface of the substrate using a hot-melt coater; and curing the pressure-sensitive adhesive composition by irradiating the pressure-sensitive adhesive composition with ultraviolet light to form the pressure-sensitive adhesive layer. the ultraviolet-curable hot-melt pressure-sensitive adhesive is an acrylic polymer having a functional group with a benzophenone structure, In the pressure-sensitive adhesive composition, a ratio of the ultraviolet absorber to 100 parts by mass of the acrylic polymer is 0.5 parts by mass or more and 20.0 parts by mass or less, A method for producing a window film, wherein the pressure-sensitive adhesive layer has a spectral transmittance of 50% or more at a wavelength of 260 nm.

3. A method for manufacturing a window film as described in claim 1 or 2, wherein the melt viscosity of the adhesive composition at 160°C is 2000 mPa·s or more and 13000 mPa·s or less.

4. A method for manufacturing a window film described in any one of claims 1 to 3, wherein the adhesive layer is formed by a melt extrusion method.

5. A method for manufacturing a window film described in any one of claims 1 to 4, wherein the temperature of the adhesive composition when applied to the substrate is 120°C or higher and 210°C or lower.

6. The method for manufacturing a window film according to any one of claims 1 to 5, wherein the ultraviolet absorber has a benzotriazole structure, a benzophenone structure, or a hydroxyphenyltriazine structure.

7. The method for manufacturing a window film according to any one of claims 1 to 6, wherein the ultraviolet absorber is at least one compound represented by the following formulas (1) to (12): 【Chemistry 1】 【Chemistry 2】 【Transformation 3】 【Chemistry 4】 【Transformation 5】 【Transformation 6】 【Transformation 7】 【Transformation 8】 【Chemistry 9】 【Chemistry 10】 【Chemistry 11】 (In formula (11), R is an alkyl group having from 10 to 12 carbon atoms.) 【Chemistry 12】

8. The method for manufacturing a window film according to any one of claims 1 to 7, 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.

9. The method for manufacturing a window film according to any one of claims 1 to 8, wherein the substrate is made of a material containing polyester.

10. The method for manufacturing a window film according to any one of claims 1 to 9, further comprising a step of laminating a release liner on a surface opposite to the substrate from which the pressure-sensitive adhesive composition is applied.

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