Manufacturing method of image display panel, surface protective film and polarizing plate with surface protective film

Abstract

This invention provides a method for manufacturing an image display panel that suppresses the reduction in manufacturing efficiency, and a surface protective film that helps suppress the reduction in manufacturing efficiency of the image display panel. The method for manufacturing an image display panel according to an embodiment of this invention uses a surface protective film comprising a substrate having opposing first and second main surfaces, an adhesive layer disposed on the second main surface of the substrate, and is adhered to the viewing side of a polarizing plate disposed on the viewing side of the image display panel. The surface resistivity of the first main surface of the surface protective film is 1.0 × 10⁸ Ω / □ or higher, and the peel force of the surface protective film to the polarizing plate is 0.03 N / 25 mm or higher.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing an image display panel, a surface protective film, and a polarizing plate with the surface protective film attached. [Previous Technology]

[0002] Image display panels, represented by liquid crystal display devices and electroluminescent (EL) display panels (e.g., organic EL display devices, inorganic EL display devices), are rapidly gaining popularity. In image display panels, a polarizing plate is typically positioned on the viewing side. Here, during the manufacturing (including inspection) of the image display panel, a surface protective film is usually applied to the polarizing plate side of the image display panel to prevent damage to, for example, the surface of the image display panel (e.g., the surface of the polarizing plate). However, during the manufacturing (including inspection) of the image display panel, there is a problem of reduced manufacturing efficiency due to the quality of the surface protective film. Previous Art Documents Patent Documents

[0003] Patent Document 1: Japanese Patent Application Publication No. 2017-149923 [Summary of the Invention]

[0004] [The problem the invention aims to solve]

[0005] This invention was made to solve the aforementioned problems, and its main objective is to provide a method for manufacturing an image display panel that suppresses the reduction in manufacturing efficiency, and to provide a surface protective film that helps suppress the reduction in manufacturing efficiency of the image display panel. [Technical Means for Solving the Problem]

[0006] In an embodiment of the present invention, the method for manufacturing an image display panel uses a surface protective film. This surface protective film comprises a substrate having opposing first and second main surfaces, and an adhesive layer disposed on the second main surface side of the substrate. It is adhered to the viewing side of a polarizing plate disposed on the viewing side of the image display panel body. The surface resistivity of the surface protective film on the first main surface side is 1.0 × 10⁸ Ω / □ or higher, and the peel force of the surface protective film to the polarizing plate is 0.03 N / 25 mm or higher. In one embodiment, the manufacturing method includes preparing a polarizing plate having the polarizing plate and the surface protective film adhered to one side of the polarizing plate. In one embodiment, the reflectivity of the viewing side of the polarizing plate is 2.5% to 3.0%. In one embodiment, the water contact angle of the viewing side of the polarizing plate is 95° or higher. In one embodiment, the image display panel body includes a touch panel.

[0007] According to another aspect of the present invention, a surface protective film is provided. In this embodiment, the surface protective film comprises a substrate and an adhesive layer, wherein the substrate has opposing first and second main surfaces, and the adhesive layer is disposed on the second main surface side of the substrate. The surface resistivity of the surface protective film on the first main surface side is 1.0 × 10⁸ Ω / □ or higher. The adhesive layer contains an acrylic adhesive, which comprises a (meth)acrylic polymer having polar functional groups. The content of the monomer component having polar functional groups is 1.0 to 10.0 parts by weight relative to 100 parts by weight of the monomer forming the (meth)acrylic polymer. In one embodiment, the surface protective film further comprises a treatment layer, and the treatment layer is formed on the first main surface side of the substrate. In one embodiment, the treatment layer comprises a polymer containing quaternary ammonium cations. According to yet another aspect of the present invention, a polarizing plate with a surface protective film is provided. The polarizing plate with a protective film includes: the aforementioned polarizing plate, and the aforementioned protective film on the viewing side of the polarizing plate. [Effects of the Invention]

[0008] According to an embodiment of the present invention, in a method for manufacturing an image display panel, a surface protective film is used. The surface protective film includes a substrate having opposing first main surfaces and second main surfaces, and an adhesive layer disposed on the second main surface side of the substrate. It is adhered to the viewing side of a polarizing plate disposed on the viewing side of the image display panel body. The surface resistivity of the first main surface side of the surface protective film is 1.0 × 10⁸ Ω / □ or higher, and the peel force of the surface protective film to the polarizing plate is 0.03 N / 25 mm or higher. This suppresses the reduction in manufacturing efficiency of the image display panel.

[0009] According to another aspect of the present invention, the surface protective film comprises a substrate and an adhesive layer, wherein the substrate has a first main surface and a second main surface facing each other, and the adhesive layer is disposed on the second main surface side of the substrate, the surface resistivity of the first main surface side of the surface protective film is 1.0 × 10⁸ Ω / □ or more, the adhesive layer comprises an acrylic adhesive, the acrylic adhesive comprises a (meth)acrylic polymer having polar functional groups, and the content of the monomer component having polar functional groups is 1.0 part by weight to 10.0 parts by weight relative to 100 parts by weight of the monomer forming the (meth)acrylic polymer, thereby helping to suppress the reduction of manufacturing efficiency of the image display panel.

Implementation Method

[0011] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0012] (Definitions of Terms and Symbols) The terms and symbols used in this specification are defined as follows. (1) Refractive Index (nx, ny, nz) "nx" refers to the refractive index in the direction where the in-plane refractive index reaches its maximum (i.e., the direction of the late phase axis), "ny" refers to the refractive index in the direction orthogonal to the late phase axis (i.e., the direction of the advanced phase axis), and "nz" refers to the refractive index in the thickness direction. (2) In-plane Phase Difference (Re) "Re(λ)" refers to the in-plane phase difference measured at 23°C with light of wavelength λ nm. For example, "Re(550)" refers to the in-plane phase difference measured at 23°C with light of wavelength 550 nm. Re(λ) is calculated by the formula: Re(λ)=(nx-ny)×d when the thickness of the layer (film) is set to d (nm). (3) Phase difference in the thickness direction (Rth) "Rth(λ)" is the phase difference in the thickness direction measured at 23°C with light of wavelength λ nm. For example, "Rth(550)" is the phase difference in the thickness direction measured at 23°C with light of wavelength 550 nm. Rth(λ) is calculated by the formula: Rth(λ)=(nx-nz)×d when the thickness of the layer (film) is set to d (nm). (4) Nz coefficient The Nz coefficient is calculated by Nz=Rth / Re. (5) Angle When an angle is mentioned in this specification, the angle includes both clockwise and counterclockwise directions relative to the reference direction. Therefore, for example, "45°" means ±45°.

[0013] A. Method for Manufacturing an Image Display Panel The method for manufacturing an image display panel according to an embodiment of the present invention uses a surface protective film adhered to the viewing side of a polarizing plate disposed on the viewing side of the image display panel body. FIG1 is a schematic cross-sectional view showing an example of the schematic configuration of an image display panel obtained by the method for manufacturing an image display panel according to an embodiment of the present invention. Furthermore, in FIG1, an organic EL panel is used as an example of an image display panel for explanation.

[0014] The image display panel (organic EL panel) 100 includes an image display panel (organic EL panel) body 50 and a polarizing plate 200 with a surface protective film. The polarizing plate 200 with the surface protective film includes a polarizing plate 20 and a surface protective film 10 adhered to one side of the polarizing plate 20. In the example shown, the polarizing plate 200 with the surface protective film includes a phase retardation layer 30 and an adhesive layer 40 disposed on the other side of the polarizing plate 20. The surface protective film 10 can be peeled off during the manufacturing process of the final product (e.g., an image display device) or can be directly mounted on the final product.

[0015] A preferred method for manufacturing an image display panel according to an embodiment of the present invention includes preparing a polarizing plate with a surface protective film attached, the polarizing plate having a polarizing plate and a surface protective film adhered to one side of the polarizing plate. Specifically, an organic EL panel 100 is obtained by attaching a polarizing plate 200 with a surface protective film attached to an organic EL panel body 50. In the example shown in FIG1, the polarizing plate 200 with a surface protective film has a phase retardation layer 30 and an adhesive layer 40, but may include other components. For practicality, a release film (not shown) is temporarily adhered peelably to the adhesive layer 40 side of the polarizing plate 200 with a surface protective film. By temporarily adhering the release film, the adhesive layer is protected until the polarizing plate with a surface protective film is put into use, and the polarizing plate with a surface protective film can be roll-formed. Furthermore, any suitable adhesive layer (not shown) can be used in the lamination of the layers constituting the image display panel of the present invention.

[0016] Hereinafter, the constituent elements of the image display panel according to an embodiment of the present invention will be described in more detail.

[0017] B. Image Display Panel Body The image display panel (organic EL panel) body 50 typically includes a substrate and an upper structural layer, which includes a circuit layer containing thin-film transistors (TFTs), an organic light-emitting diode (OLED), and a sealing film for sealing the OLED (all not shown). The image display panel body 50 may further include a touch panel (not shown). The touch panel typically includes a conductive layer.

[0018] The conductive layer can be formed on any suitable substrate by forming a metal oxide film using any suitable film-forming method (e.g., vacuum evaporation, sputtering, CVD (Chemical Vapor Deposition), ion plating, spraying, etc.). Examples of metal oxides include indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimony composite oxide, zinc-aluminum composite oxide, and indium-zinc composite oxide. Indium-tin composite oxide (ITO) is preferred.

[0019] When the conductive layer contains a metal oxide, the thickness of the conductive layer is preferably 50 nm or less, more preferably 35 nm or less. The lower limit of the thickness of the conductive layer is preferably 10 nm.

[0020] The aforementioned conductive layer can be patterned as needed. Patterning can form conductive and insulating portions, resulting in electrodes. These electrodes can function as touch sensor electrodes that sense contact with the touch panel. Any suitable patterning method can be used. Specific examples of patterning methods include wet etching and screen printing.

[0021] C. Polarizing plate with surface protective film As shown in FIG1, the polarizing plate 200 with surface protective film includes a polarizing plate 20 and a surface protective film 10 attached to one side of the polarizing plate 20. As described above, the polarizing plate 200 with surface protective film may further include a phase retardation layer 30 and an adhesive layer 40. Hereinafter, the constituent elements of the polarizing plate with surface protective film will be described in more detail.

[0022] C-1. Polarizing Plate FIG2 is a schematic cross-sectional view showing an example of a polarizing plate constituting the image display panel shown in FIG1. ​​FIG3 is a schematic cross-sectional view showing an example of a functional layer constituting the polarizing plate shown in FIG2. As shown in FIG2, the polarizing plate 20 includes a polarizing element 21 and a protective layer 22. If necessary, a protective layer (not shown) may also be provided on the image panel body side of the polarizing element 21. Furthermore, in one embodiment of the present invention, the polarizing plate 20 has a functional layer 23 on the viewing side of the protective layer 22. Hereinafter, the constituent elements of the polarizing plate will be described in detail.

[0023] C-1-1. The polarizing element can be any suitable polarizing element. For example, the resin film forming the polarizing element can be a single-layer resin film. Alternatively, the polarizing element can be formed using two or more layers of laminate.

[0024] Specific examples of polarizing elements comprising a single-layer resin film include: hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films that have undergone dyeing and stretching treatments using iodine or dichroic dyes; and polyene alignment films such as PVA dehydration treatment products or polyvinyl chloride dehydrochlorination treatment products. In terms of superior optical properties, it is preferable to use a polarizing element obtained by dyeing a PVA film with iodine and performing uniaxial stretching.

[0025] The above-mentioned dyeing using iodine is performed, for example, by immersing the PVA membrane in an aqueous iodine solution. The uniaxial stretching ratio is preferably 3 to 7 times. Stretching can be performed after dyeing, or simultaneously with dyeing. Alternatively, dyeing can be performed after stretching. Swelling treatment, crosslinking treatment, washing treatment, drying treatment, etc., can be applied to the PVA membrane as needed. For example, by immersing the PVA membrane in water for washing before dyeing, not only can stains or anti-blocking agents on the surface of the PVA membrane be removed, but the PVA membrane can also swell to prevent uneven dyeing.

[0026] As a specific example of a polarizing element obtained using a laminate, examples include a laminate consisting of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate consisting of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizing element obtained using a laminate consisting of a resin substrate and a PVA-based resin layer coated on the resin substrate can be manufactured, for example, by the following steps: coating a PVA-based resin solution onto a resin substrate, drying it to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer; stretching and dyeing the laminate to form a polarizing element from the PVA-based resin layer. In this embodiment, it is preferable to form a polyvinyl alcohol-based resin layer comprising a halide and a polyvinyl alcohol-based resin on one side of the resin substrate. Regarding stretching, a representative method includes immersing the laminate in an aqueous boric acid solution for stretching. Furthermore, the stretching process may further include, as needed, air-stretching the laminate at a high temperature (e.g., above 95°C) before stretching in the boric acid aqueous solution. In this embodiment, it is preferable to heat the laminate while conveying it along its length, thereby subjecting it to a drying shrinkage treatment that results in a shrinkage of 2% or more in its width direction. A representative manufacturing method of this embodiment includes sequentially performing air-assisted stretching, dyeing, underwater stretching, and drying shrinkage on the laminate. By introducing assisted stretching, even when PVA is coated onto a thermoplastic resin, the crystallinity of PVA can be improved, thereby achieving higher optical properties. Furthermore, by simultaneously improving the orientation of PVA beforehand, problems such as reduced orientation or dissolution of PVA during immersion in water in subsequent dyeing or stretching steps can be prevented, achieving higher optical properties. Moreover, when the PVA-based resin layer is immersed in a liquid, compared to the case where the PVA-based resin layer does not contain halides, the disordered orientation and reduced orientation of polyvinyl alcohol molecules can be suppressed. This improves the optical properties of the polarizing element obtained by immersing the laminate in a liquid through dyeing and water stretching processes. Furthermore, by shrinking the laminate in the width direction through a drying shrinkage process, optical properties are further improved. The resulting resin substrate / polarizing element laminate can be used directly (i.e., the resin substrate can also be used as a protective layer for the polarizing element), or the resin substrate can be peeled off from the resin substrate / polarizing element laminate, and an appropriate protective layer can be applied to the peeled surface according to the desired laminate. Details of this method for manufacturing a polarizing element are described, for example, in Japanese Patent Application Publication No. 2012-73580 (Japanese Patent No. 5414738) and Japanese Patent No. 6470455. The entire description of these publications is incorporated herein by reference.

[0027] The thickness of the polarizing element is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 6 μm or less. The lower limit of the thickness of the polarizing element may be, for example, 1 μm.

[0028] The polarizing element preferably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The transmittance of the polarizing element is, for example, 41.5% to 46.0%, preferably 43.0% to 46.0%, and more preferably 44.5% to 46.0%. The polarization degree of the polarizing element is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0029] C-1-2. Protective Layer The aforementioned protective layer is formed from any suitable film. Specific examples of materials that are the main components of the film include: cellulose resins such as triacetyl cellulose (TAC), polyester resins, polyvinyl alcohol resins, polycarbonate resins, polyamide resins, polyimide resins, polyether resins, polyurethane resins, polystyrene resins, polyolefin resins, (meth)acrylic acid resins, acetate resins, and other transparent resins. Also, examples include: thermosetting resins or UV-curing resins such as (meth)acrylic acid resins, urethane resins, (meth)acrylate urethane resins, epoxy resins, silicone resins, etc. In addition, glassy polymers such as silicate polymers can also be used. Furthermore, polymer films described in Japanese Patent Application Publication No. 2001-343529 (WO01 / 37007) can also be used. As a material for the membrane, a resin composition may be used, for example, comprising: a thermoplastic resin having substituted or unsubstituted imine groups on its side chains, and a thermoplastic resin having substituted or unsubstituted phenyl and nitrile groups on its side chains. Examples include resin compositions comprising alternating copolymers of isobutylene and N-methylcis-butene diimide, and acrylonitrile-styrene copolymers. The polymer membrane may be, for example, an extruded product of the above resin composition.

[0030] The thickness of the above-mentioned protective layer is preferably 45 μm or less, more preferably 40 μm or less, and even more preferably 35 μm or less. The lower limit of the thickness of the protective layer is, for example, 10 μm.

[0031] For the protective layer disposed on the viewing side of the polarizing plate, surface treatments such as hard coating, anti-reflection treatment (low-reflection treatment), anti-adhesion treatment, and anti-glare treatment are performed as needed to form a functional layer. Furthermore, when a functional layer is formed, the thickness of the aforementioned protective layer includes the thickness of the functional layer.

[0032] A typical embodiment of the polarizing plate of the present invention is disposed on the viewing side of the image display panel body. Furthermore, as described above, a protective layer is disposed on the viewing side of the polarizing plate. Here, for example, when an organic EL panel (OLED) is used in a mobile device, there are cases where a glass plate is not disposed on the viewing side for purposes such as weight reduction. In this case, a surface treatment can be performed on the viewing side of the image display panel (i.e., the viewing side of the polarizing plate).

[0033] The reflectance of the viewing side of the above-mentioned polarizing plate is preferably 2.5% to 3.0%, and more preferably 2.6% to 2.9%. By keeping the reflectance of the viewing side of the polarizing plate within this range, the visibility of the user is improved.

[0034] The water contact angle on the viewing side of the aforementioned polarizing plate is preferably 95° or higher, more preferably 96° or higher, and even more preferably 97° or higher. By keeping the water contact angle on the viewing side of the polarizing plate within this range, the anti-fouling function of the viewing side of the polarizing plate is improved.

[0035] As shown in FIG2, the polarizing plate of the embodiment of the present invention has a functional layer 23 formed by the above-described surface treatment on its viewing side. The functional layer 23 is, for example, a layer formed by performing a hard coating treatment and an anti-reflection treatment on the protective layer 22. The functional layer 23 reduces reflectivity, for example, by utilizing light interference.

[0036] As shown in FIG. 3, in one embodiment of the present invention, the functional layer 23 includes a resin layer 23a and an anti-reflection layer 23b. The resin layer 23a is formed, for example, by coating a coating liquid containing resin, filler and solvent onto a polarizing plate to form a coating film, and then removing the solvent from the coating film. Examples of the resin include thermosetting resins and ionizing radiation-cured resins that are cured by ultraviolet light or light. Commercially available thermosetting resins or ultraviolet-cured resins can also be used as the resins.

[0037] As the aforementioned thermosetting or UV-curing resin, a curing compound having at least one acrylate or methacrylate group that is cured by heat, light (ultraviolet light, etc.), or an electron beam can be used. Examples include oligomers or prepolymers of acrylates or methacrylates of polyfunctional compounds such as silicone resin, polyester resin, polyether resin, epoxy resin, urethane resin, alkyd resin, spiroacetal resin, polybutadiene resin, polythiol polyene resin, and polyols. One of these can be used alone, or two or more can be used in combination. Silicone resin is preferred because by using silicone resin, the water contact angle on the viewing side of the polarizing plate can be kept within the aforementioned range, thereby ensuring antifouling function.

[0038] The antireflective layer 23b can be obtained by applying an antireflective layer forming coating liquid. The antireflective layer forming coating liquid may, for example, contain resin, additives containing fluorine, hollow particles, solid particles, and diluent solvent, and may be mixed to manufacture the antireflective layer. The hollow particles and solid particles may, for example, be silicon oxide particles.

[0039] By equipping the functional layer 23 with the configuration described above, the image display panel can be made lighter, and the user's visibility can be improved, thereby enhancing the anti-fouling function of the viewing side of the polarizing plate. Furthermore, the functional layer is described in Japanese Patent Application Publication No. 2020-030363. This publication is incorporated herein by reference.

[0040] C-1-3. Phase difference layer The phase difference layer 30 can be a single layer or have a stacked structure (essentially a two-layer structure).

[0041] When the retardation layer 30 is a single layer, it typically functions as a λ / 4 plate. The retardation layer is typically provided to impart anti-reflective properties to the image display panel. The refractive index characteristics of the retardation layer typically show a relationship of nx > ny = nz. The in-plane phase difference Re(550) of the retardation layer is preferably 100 nm to 190 nm, more preferably 110 nm to 170 nm, and even more preferably 120 nm to 160 nm. Furthermore, "ny = nz" here includes not only the case where ny and nz are exactly equal, but also the case where they are substantially equal. Therefore, within the scope of not impairing the effects of the present invention, there may be cases where ny > nz or ny < nz.

[0042] The Nz coefficient of the phase décor layer is preferably 0.9 to 1.5, and more preferably 0.9 to 1.3. By satisfying this relationship, an image display panel with excellent reflective hue can be obtained.

[0043] When the retardation layer is a single layer, it is preferable that the retardation layer exhibits anti-wavelength dispersion characteristics, where the phase difference value increases according to the wavelength of the measured light. In this case, the Re(450) / Re(550) of the retardation layer is preferably 0.8 or higher and less than 1, more preferably 0.8 or higher and less than 0.95. With this configuration, very excellent anti-reflection characteristics can be achieved.

[0044] The angle between the late phase axis of the retardation layer and the absorption axis of the polarizing element is preferably 40° to 50°, more preferably 42° to 48°, and even more preferably about 45°. If the angle is within this range, an image display panel with excellent anti-reflection properties can be obtained by fabricating the retardation layer into a λ / 4 plate as described above.

[0045] The retardation layer may contain any suitable material, as long as it can satisfy the characteristics described above. Specifically, the retardation layer may be an extension film of a resin film or an alignment and curing layer of a liquid crystal compound (hereinafter, liquid crystal alignment and curing layer).

[0046] When the phase difference layer is an extension of the resin film, representative examples of the resin constituting the resin film include: polycarbonate resin or polyester carbonate resin (hereinafter, sometimes simply referred to as polycarbonate resin). As a polycarbonate resin, any suitable polycarbonate resin can be used as long as the required moisture permeability can be obtained. For example, the polycarbonate resin contains: structural units derived from benzoyl dihydroxy compounds, structural units derived from isosorbide dihydroxy compounds, and structural units derived from at least one dihydroxy compound selected from the group consisting of alicyclic diols, alicyclic diethanols, di / triethylene glycols, and alkyl diols or spirodiols. Preferably, the polycarbonate resin contains structural units derived from genus dihydroxy compounds, structural units derived from isosorbide dihydroxy compounds, structural units derived from alicyclic diethanol, and / or structural units derived from di / tri or polyethylene glycol; more preferably, it contains structural units derived from genus dihydroxy compounds, structural units derived from isosorbide dihydroxy compounds, and structural units derived from di / tri or polyethylene glycol. The polycarbonate resin may also contain structural units derived from other dihydroxy compounds as needed. The retardation layer can be formed by stretching a film containing the polycarbonate resin described above under any suitable stretching conditions. Furthermore, details of the method for forming the polycarbonate resin and the phase retardation layer are described, for example, in Japanese Patent Application Publication No. 2014-10291, Japanese Patent Application Publication No. 2014-26266 (Japanese Patent No. 5528606), Japanese Patent Application Publication No. 2015-212816 (Japanese Patent No. 6189355), Japanese Patent Application Publication No. 2015-212817 (Japanese Patent No. 6823899), Japanese Patent Application Publication No. 2015-212818, Japanese Patent Application Publication No. 2017-54093 (Japanese Patent No. 6360821), and Japanese Patent Application Publication No. 2018-60014 (Japanese Patent No. 6321107). The descriptions in these publications are incorporated herein by reference.

[0047] When the retardation layer is a liquid crystal alignment and curing layer, by using a liquid crystal compound, the difference between nx and ny of the obtained retardation layer can be significantly increased compared to non-liquid crystal materials, thus significantly reducing the thickness of the retardation layer used to obtain the desired in-plane retardation. As a result, the polarizing plate with a surface protective film (and consequently, the image display panel) can be made thinner. In this specification, "alignment and curing layer" refers to a layer in which the liquid crystal compound is aligned in a specified direction within the layer, and its alignment state is fixed. Furthermore, "alignment and curing layer" includes the concept of an alignment and curing layer obtained by curing liquid crystal monomers. In this embodiment, a representative example is that the rod-shaped liquid crystal compound is aligned in a state of being aligned in the direction of the late phase axis of the retardation layer (horizontal alignment). Specific examples of liquid crystal compounds and details of the method for forming the liquid crystal alignment and curing layer are described, for example, in Japanese Patent Application Publication Nos. 2006-163343 and 2006-178389. The information contained in these gazettes is used in this specification for reference only.

[0048] The thickness of the retardation layer is typically set to a thickness that allows it to function appropriately as a λ / 4 plate. When the retardation layer is an extension film of a resin film, the thickness of the retardation layer is, for example, 10 μm to 60 μm. When the retardation layer is a liquid crystal alignment and curing layer, the thickness of the retardation layer is, for example, 1 μm to 5 μm.

[0049] When the retardation layer 30 has a multilayer structure, the retardation layer is typically a two-layer structure having a first liquid crystal alignment and curing layer and a second liquid crystal alignment and curing layer. In this case, either the first liquid crystal alignment and curing layer or the second liquid crystal alignment and curing layer can function as a λ / 2 plate, and the other can function as a λ / 4 plate. Here, the case where the first liquid crystal alignment and curing layer functions as a λ / 2 plate and the second liquid crystal alignment and curing layer functions as a λ / 4 plate will be described, but the reverse is also possible. The thickness of the first liquid crystal alignment and curing layer can be adjusted to obtain the in-plane retardation required for the λ / 2 plate, for example, it can be 2.0 μm to 4.0 μm. The thickness of the second liquid crystal alignment and curing layer can be adjusted to obtain the in-plane retardation required for the λ / 4 plate, for example, it can be 1.0 μm to 2.5 μm. The in-plane phase difference Re(550) of the first liquid crystal alignment and curing layer is preferably 200 nm to 300 nm, more preferably 230 nm to 290 nm, and even more preferably 250 nm to 280 nm. The in-plane phase difference Re(550) of the second liquid crystal alignment and curing layer, as described above, is preferably 100 nm to 190 nm, more preferably 110 nm to 170 nm, and even more preferably 120 nm to 160 nm. The angle between the late phase axis of the first liquid crystal alignment and curing layer and the absorption axis of the polarizing element is preferably 10° to 20°, more preferably 12° to 18°, and even more preferably about 15°. The angle between the late phase axis of the second liquid crystal alignment and curing layer and the absorption axis of the polarizing element is preferably 70° to 80°, more preferably 72° to 78°, and even more preferably about 75°. With this configuration, characteristics similar to ideal anti-wavelength dispersion can be obtained, resulting in excellent anti-reflection properties.

[0050] C-2. Surface Protective Film Figure 4 is a schematic cross-sectional view showing an example of a surface protective film constituting the image display panel shown in Figure 1. As shown in Figure 4, in one embodiment of the present invention, the surface protective film 10 includes a substrate 11 and an adhesive layer 12 of the surface protective film. The substrate 11 has opposing first main surfaces 11a and second main surfaces 11b, and the adhesive layer 12 of the surface protective film is disposed on the second main surface 11b of the substrate 11. Preferably, the surface protective film 10 further includes a processing layer 13, and the processing layer 13 is formed on the first main surface 11a of the substrate 11.

[0051] In one embodiment of the present invention, the surface resistivity of the first main surface side of the surface protective film is 1.0 × 10⁸ Ω / □ or higher, preferably 1.0 × 10⁹ Ω / □ or higher. By using such a surface protective film, the generation of touch panel sensor errors can be suppressed, thereby improving the manufacturing efficiency of the image display panel. Specifically, when the image display panel is used as a mobile machine, suppressing touch panel sensor errors becomes important. Touch panel sensor errors refer to the phenomenon that, during the manufacturing of the image display panel (image display device), especially during the inspection process, when confirming the operability of the touch panel, there is no response or the screen is difficult to respond when touched with a finger. When the above-mentioned surface protective film is applied to the image display panel and the viewing side of the surface protective film is touched with a finger, if the surface resistivity is 1.0 × 10⁸ Ω / □ or higher, the change in charge of the touched portion can be detected. That is, during the manufacturing of mobile machines, especially in the inspection process, the aforementioned touch panel sensor errors are suppressed, thereby reducing the manufacturing efficiency of the image display panel. The surface resistivity value is, for example, 1.0 × 10¹³ Ω / □ or less, preferably 1.0 × 10¹² Ω / □ or less, and more preferably 1.0 × 10¹¹ Ω / □ or less. If the surface resistivity value is above a fixed value, abnormalities such as adhesion to other films may occur. Here, for films with surface resistivity values ​​above a fixed value, surface treatment is required to reduce the surface resistivity value to below the fixed value. On the other hand, if the surface resistivity value of the film is below a fixed value, the aforementioned touch panel sensor errors may occur. Therefore, in this invention, by forming a treatment layer containing a specific antistatic agent in the surface protective film, it is superior in solving the above two problems.

[0052] In one embodiment of the present invention, the peel force of the surface protective film to the polarizing plate is 0.03 N / 25 mm or more, preferably 0.04 N / 25 mm or more, more preferably 0.05 N / 25 mm or more, and even more preferably 0.06 N / 25 mm or more. By using such a surface protective film, the surface protective film can be prevented from peeling off from the polarizing plate during the manufacturing of the image display panel, thereby improving the manufacturing efficiency of the image display panel. In one embodiment of the present invention, as described above, a functional layer is formed on the viewing side of the polarizing plate. The functional layer is typically composed of silicone resin to ensure anti-fouling function. In the functional layer containing silicone resin, the surface free energy of the functional layer becomes lower, and the adhesion to the adhesive becomes lower. If the adhesion between the polarizing plate and the surface protective film is low, the peeling of the surface protective film during the manufacturing process tends to occur more easily. Furthermore, for practical purposes, a release film is temporarily adhered to the adhesive layer side of the surface protective film in a peelable manner. In the step of peeling the release liner from the polarizing plate with the protective film, in order to fix the protective film side using a vacuum plate or the like, the peeling force of the protective film needs to be greater than that of the release liner. By ensuring that the peeling force of the protective film on the polarizing plate is 0.03 N / 25 mm or more, the protective film is prevented from peeling off from the polarizing plate, thereby suppressing the reduction in manufacturing efficiency of the image display panel. The upper limit of the peeling force is, for example, 0.50 N / 25 mm.

[0053] The thickness of the surface protective film is preferably 15 μm to 200 μm, more preferably 20 μm to 150 μm, even more preferably 30 μm to 100 μm, and particularly preferably 40 μm to 60 μm.

[0054] The constituent elements of the surface protective film will be described in more detail below.

[0055] C-2-1. The substrate material, as the forming material of the substrate, may include, for example, ester resins such as polyethylene terephthalate resins, cyclic olefin resins such as norethene resins, olefin resins such as polypropylene resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. Ester resins (especially polyethylene terephthalate resins) are preferred.

[0056] The thickness of the above-mentioned substrate is preferably 10 μm to 150 μm, more preferably 20 μm to 100 μm, and even more preferably 30 μm to 50 μm.

[0057] C-2-2. Adhesive Layer of Surface Protective Film The adhesive layer of the surface protective film contains an acrylic adhesive. A representative acrylic adhesive is a (meth)acrylic polymer containing a polar functional group. A representative (meth)acrylic polymer containing a polar functional group is a polymer containing an alkyl (meth)acrylate and a monomer with a polar functional group. Furthermore, (meth)acrylate refers to acrylates and / or methacrylates.

[0058] The content of the monomer component with polar functional groups is preferably 1.0 to 10.0 parts by weight, and more preferably 2.0 to 8.0 parts by weight, relative to 100 parts by weight of the monomer forming the above-mentioned (meth)acrylic polymer. If the content of the monomer component with polar functional groups is within the above range, the polar functional groups can form hydrogen bonds, for example, with the functional layer formed on the viewing side of the polarizing plate, thereby improving the adhesion.

[0059] Examples of alkyl (meth)acrylates include linear or branched alkyl groups with 1 to 18 carbon atoms. Examples of alkyl groups include: methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, hexyl, cyclohexyl, heptyl, 2-ethylhexyl, isooctyl, nonyl, decyl, isodecyl, dodecyl, isomycinyl, lauryl, tridecyl, pentadecyl, hexadecyl, heptadecanyl, octadecyl, etc. Alkyl (meth)acrylates can be used alone or in combination. The average number of carbon atoms in the alkyl group is preferably 3 to 10. Among the alkyl groups, 2-ethylhexyl is preferably an example.

[0060] The content of alkyl methacrylate relative to 100 parts by weight of the monomer forming the (meth)acrylate polymer is, for example, 20.0 parts by weight to 80.0 parts by weight, more preferably 30.0 parts by weight to 70.0 parts by weight.

[0061] Examples of monomers having polar functional groups include monomers containing carboxyl groups and monomers containing hydroxyl groups, with monomers containing carboxyl groups being a preferred example. Monomers having polar functional groups can be used alone or in combination.

[0062] A monomer containing a carboxyl group is a compound whose structure contains a carboxyl group and polymerizable unsaturated double bonds such as (meth)acrylic acid, vinyl, etc. Examples of monomers containing a carboxyl group include: (meth)acrylic acid, (meth)acrylic acid carboxyethyl ester, (meth)acrylic acid carboxypentyl ester, itconic acid, maleic acid, fumaric acid, butenoic acid, etc. Among these, acrylic acid is preferred. Acrylic polymers are preferably polymers containing (meth)acrylic acid alkyl esters and carboxyl-containing monomers, and more preferably polymers containing (meth)acrylic acid alkyl esters and acrylic acid.

[0063] In one embodiment, the acrylic polymer contains structural units derived from other comonomers. Examples of other comonomers include vinyl acetate, vinyl propionate, and other vinyl esters, with vinyl acetate being a preferred example. Other comonomers may be used alone or in combination.

[0064] The content of other comonomers is, for example, 1.0 to 20.0 parts by weight, more preferably 3.0 to 15.0 parts by weight, relative to 100 parts by weight of the monomers forming the (meth)acrylic polymer.

[0065] The weight average molecular weight (Mw) of the (meth)acrylic acid polymer is, for example, 300,000 to 600,000, preferably 400,000 to 500,000.

[0066] The crosslinking agent can react with a portion of the polar functional groups of the (meth)acrylic polymer. Organic crosslinking agents, multifunctional metal chelates, etc., can be used as crosslinking agents. Examples of organic crosslinking agents include isocyanate-based crosslinking agents, peroxide-based crosslinking agents, epoxy-based crosslinking agents, and imine-based crosslinking agents. Multifunctional metal chelates are those in which a multivalent metal is covalently or coordinately bonded to an organic compound. When the adhesive composition is of the radiation-curing type, a multifunctional monomer can be used as the crosslinking agent. The crosslinking agent can be used alone or in combination.

[0067] The amount of crosslinking agent is relative to 100 parts by weight of the (meth)acrylic polymer (base polymer), for example, 1.0 to 20.0 parts by weight, preferably 3.0 to 15.0 parts by weight.

[0068] The adhesive described above may contain any suitable additives as needed. Examples of such additives include: initiators, adhesive imparting agents, plasticizers, pigments, dyes, fillers, anti-aging agents, conductive materials, antistatic agents, ultraviolet absorbers, light stabilizers, peel modifiers, softeners, surfactants, flame retardants, antioxidants, etc.

[0069] The thickness of the adhesive layer of the surface protective film is preferably 3 μm to 100 μm, more preferably 4 μm to 60 μm, even more preferably 5 μm to 40 μm, and particularly preferably 10 μm to 25 μm.

[0070] C-2-3. As shown in FIG. 4, the surface protective film 10 may also have a treatment layer 13 on the first main surface 11a of the substrate 11. The treatment layer is formed by diluting an antistatic agent or the like with an organic solvent or water, coating the coating liquid onto the substrate layer, and drying it. Examples of the antistatic agent include polymers containing quaternary ammonium cations and polyaniline sulfonic acid-based antistatic agents, with polymers containing quaternary ammonium cations being preferred.

[0071] Examples of quaternary ammonium cations contained in the aforementioned polymers containing quaternary ammonium cations include: trimethylammonium cation, triethylammonium cation, tripropylammonium cation, methyldiethylammonium cation, ethyldimethylammonium cation, methyldipropylammonium cation, dimethylbenzylammonium cation, diethylbenzylammonium cation, methyldibenzylammonium cation, and ethyldibenzylammonium cation. Trimethylammonium cation is particularly suitable. Polymers containing these quaternary ammonium cations have both hydrophilic and lipophilic groups within their molecules. The hydrophilic groups absorb moisture from the air, thereby achieving excellent antistatic effects. [Example]

[0072] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. The methods for measuring each characteristic are as follows. Furthermore, unless otherwise specified, "parts" and "%" in the examples and comparative examples are based on weight.

[0073] (1) Thicknesses of 10 μm or less were measured using an interferometric film thickness gauge (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"). Thicknesses exceeding 10 μm were measured using a digital micrometer (manufactured by Anritsu Co., Ltd., product name "KC-351C"). (2) Peeling force: The second main surface side of the surface protective film obtained in the examples and comparative examples was bonded to the functional layer side of the polarizing plate MCIG1465CUZZ10 (manufactured by Nitto Denko Co., Ltd.) to create a short strip edge of 25 mm × 100 mm. The surface protective film of the obtained short strip edge was peeled off at a speed of 180° peel and 300 mm / min. Good: Peel strength is 0.03 N / 25 mm or higher. Poor: Peel strength is less than 0.03 N / 25 mm. (3) Surface resistivity: The surface protective film obtained in the examples and comparative examples was used, and the surface resistivity was measured by eddy current method using a non-contact surface resistivity meter manufactured by Napson Corporation, under the trade name "EC-80". The measurement temperature was set to 23°C. Good: Surface resistivity is 1.0 × 10⁸ Ω / □ or higher. Poor: Surface resistivity is less than 1.0 × 10⁸ Ω / □.

[0074] [Manufacturing Example 1] Adhesive composition A was prepared by polymerizing a monomer composition comprising 100 parts by weight of 2-ethylhexyl acrylate, 80 parts by weight of vinyl acetate and 5 parts by weight of acrylic acid to obtain an acrylic polymer. Adhesive composition A was prepared by mixing 100 parts by weight of the obtained acrylic polymer and 10.0 parts by weight of 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical, product name "TETRAD-C") as a crosslinking agent.

[0075] [Manufacturing Example 2] Adhesive Composition B was prepared by polymerizing a monomer composition comprising 100 parts by weight of 2-ethylhexyl acrylate and 4 parts by weight of 2-hydroxyethyl acrylate to obtain an acrylic polymer. Adhesive Composition B was prepared by mixing 100 parts by weight of the obtained acrylic polymer, 5 parts by weight of aliphatic polyisocyanate (Tosoh Corporation, product name "Coronate HX") as a crosslinking agent, 0.03 parts by weight of dioctyltin dilaurate (Tokyo Fine Chemicals Corporation, product name "Enbilizer OL-1") as a crosslinking aid, and 0.3 parts by weight of polyoxyethylene alkylpropylene phenyl ether ammonium sulfate (Daiichi Kogyo Pharmaceutical Co., Ltd., product name "AQUALON HS-10") as a release agent.

[0076] [Manufacturing Example 3] The adhesive composition C was prepared in the same manner as in Manufacturing Example 2, except that the release agent was not mixed in.

[0077] [Manufacturing Example 4] The adhesive composition D was prepared in the same manner as in Manufacturing Example 2, except that 3 parts by weight of aromatic polyisocyanate (manufactured by Tosoh, product name "Coronate L") as a crosslinking agent, 0.02 parts by weight of dioctyltin dilaurate (manufactured by Tokyo Fine Chemicals, product name "Enbilizer OL-1") as a crosslinking aid, and 0.5 parts by weight of polyoxypropylene glycol (manufactured by Sanyo Chemicals, product name "SANNIX PP-3000") as a release agent were mixed.

[0078] [Manufacturing Example 5] Treatment layer A is formed on the antistatic treated surface of a polyethylene terephthalate film "DIAFOIL T100N38" (manufactured by Mitsubishi Chemical) with an antistatic treatment layer. A coating solution is prepared by mixing 17% alkyl acetalized polyvinyl alcohol (manufactured by Sekisui Chemicals, product name "S-LEC KKW-10") and 83% octadecyl isocyanate (manufactured by Ohara Paragium Chemicals, product name "R-NCO") and diluting the substrate to 0.3% using a solvent such as xylene. The coating solution is heated at 130°C for 1 minute to dry it, forming a layer with a thickness of 40 to 60 nm, thereby forming treatment layer A.

[0079] [Manufacturing Example 6] Formation of Treatment Layer B: A coating solution is prepared by coating a polyethylene terephthalate film "DIAFOIL T100C38" (manufactured by Mitsubishi Chemical) with 74% of PEDOT-based conductive coating agent (manufactured by Chukyo Yushi, product name "T-670"), 8% of PEDOT-based conductive coating agent hardener (manufactured by Chukyo Yushi, "P-795"), 9% of polyaniline sulfonic acid-based antistatic agent (manufactured by Mitsubishi Rayon, product name "aquaPASS-F15P"), and 9% of antistatic agent additive (manufactured by Mitsubishi Rayon, product name "aquaPASS-A01") and diluting it to 0.35% with a solvent such as methanol. The solution is then heated at 130°C for 1 minute to dry it, forming a layer with a thickness of 40-60 nm, thereby forming Treatment Layer B.

[0080] [Example 1] Adhesive composition A prepared in Manufacturing Example 1 for side coating of a polyethylene terephthalate film (manufactured by Mitsubishi Chemical, product name "DIAFOIL T100F38") with an antistatic treatment layer was heated at 130°C for 1 minute. Then, treatment layer A was formed on the opposite side of the PET (polyethylene terephthalate) film according to Manufacturing Example 5, thereby obtaining a surface protective film. The obtained surface protective film was evaluated in (2) and (3) above. Furthermore, the above-mentioned antistatic treatment layer contains a polymer containing quaternary ammonium cations. The results are shown in Table 1.

[0081] [Example 2] An adhesive layer was formed on one side of a polyethylene terephthalate film (manufactured by Mitsubishi Chemical, product name "DIAFOIL T100C38") in the same manner as in Example 1 to obtain a surface protective film. The obtained surface protective film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0082] [Comparative Example 1] Except for using a polyethylene terephthalate film with an antistatic treatment layer formed according to Manufacturing Example 5, a surface protective film was obtained in the same manner as in Example 1. The obtained surface protective film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0083] [Comparative Example 2] A surface protective film was obtained in the same manner as in Example 1, except that the adhesive composition B prepared according to Manufacturing Example 2 was used. The obtained surface protective film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0084] [Comparative Example 3] Except that the adhesive composition C prepared according to Manufacturing Example 3 was used, and the polyethylene terephthalate film with the treatment layer B formed according to Manufacturing Example 6 was used, a surface protective film was obtained in the same manner as in Example 1. The obtained surface protective film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0085] [Comparative Example 4] A surface protective film was obtained in the same manner as in Example 2, except that the adhesive composition D prepared according to Manufacturing Example 4 was used. The obtained surface protective film was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0086] [Table 1] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Peel force (N / 25 mm) 0.065 0.065 0.065 0.015 0.010 0.024 Surface resistivity (Ω / □) 2.0×10 9 2.0×l0 1 5 2.0×l0 7 2.0×10 9 3.0×10 8 2.0×10 15

[0087] [Evaluation] As shown in Table 1, when using the surface protective film in the examples, both the peel strength and surface resistivity are good. Therefore, when this surface protective film is applied to an image display panel, the reduction in manufacturing efficiency of the image display panel can be suppressed. [Industrial Applicability]

[0088] The surface protective film of the present invention is suitable for use in image display panels. [Simplified Explanation of the Diagram]

[0010] FIG1 is a schematic cross-sectional view showing a schematic configuration of an example of the image display panel of the present invention. FIG2 is a schematic cross-sectional view showing a schematic configuration of an example of the polarizing plate constituting the image display panel of the present invention. FIG3 is a schematic cross-sectional view showing an example of the functional layer constituting the polarizing plate of the present invention. FIG4 is a schematic cross-sectional view showing an example of the surface protective film constituting the image display panel of the present invention.

Claims

1. A method for manufacturing an image display panel, which uses a surface protective film, the surface protective film comprising a substrate having opposing first and second main surfaces and a first adhesive layer disposed on the second main surface side of the substrate, and bonded to the viewing side of a polarizing plate disposed on the viewing side of an image display panel body, and comprising preparing a polarizing plate having the polarizing plate and the surface protective film bonded to one side of the polarizing plate, the polarizing plate having a functional layer comprising a resin layer and an anti-reflective layer on its viewing side, the resin layer comprising silicone resin, the polarizing plate with the surface protective film further comprising: a second adhesive layer located on the side of the polarizing plate opposite to the surface protective film, and a release film temporarily bonded to the second adhesive layer peelably, the surface resistivity of the first main surface side of the surface protective film being 1.0 × 10⁸ Ω / □ or higher. The peel force of the aforementioned surface protective film on the aforementioned functional layer is greater than the peel force of the release film on the aforementioned second adhesive layer, and is 0.03 N / 25 mm or more.

2. The manufacturing method of claim 1, wherein the reflectivity of the viewing side of the polarizing plate is 2.5% to 3.0%.

3. The manufacturing method of claim 1 or 2, wherein the water contact angle on the viewing side of the polarizing plate is 95° or more.

4. The manufacturing method of claim 1 or 2, wherein the image display panel body further comprises a touch panel.

5. A polarizing plate with a surface protective film, comprising a polarizing plate, a surface protective film located on the viewing side of the polarizing plate, a second adhesive layer located on the polarizing plate opposite to the surface protective film, and a release film temporarily adhered to the second adhesive layer, wherein the surface protective film comprises a substrate and a first adhesive layer, and the substrate has opposing first main surfaces and second main surfaces, and the first adhesive layer is disposed on the second main surface side of the substrate, the surface resistivity of the first main surface side of the surface protective film is 1.0 × 10⁸ Ω / □ or higher, the first adhesive layer comprises an acrylic adhesive, the acrylic adhesive comprises a (meth)acrylic polymer having polar functional groups, and the content of the monomer component having polar functional groups is 1.0 parts by weight to 10.0 parts by weight relative to 100 parts by weight of the monomer forming the (meth)acrylic polymer. The aforementioned polarizing plate has a functional layer comprising a resin layer and an anti-reflective layer on its viewing side. The resin layer comprises silicone resin. The peel force of the aforementioned surface protective film on the aforementioned functional layer is greater than the peel force of the release film on the aforementioned second adhesive layer, and is 0.03 N / 25 mm or more.

6. The polarizing plate with a surface protective film as claimed in claim 5, further comprising a processing layer, wherein the processing layer is formed on the first main surface side of the substrate.

7. The polarizing plate with a protective film as claimed in claim 6, wherein the treatment layer comprises a polymer containing a quaternary ammonium cation.

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