Method for producing optical laminate

Abstract

To provide a method for manufacturing an optical laminate capable of suppressing curl.SOLUTION: A method for manufacturing an optical laminate 100 includes: a separator sticking step ST3 of sticking a separator 4 to a polarizing plate 10 via an adhesive layer 3 formed in the separator; and a plurality of separator peeling and sticking steps ST4 of sticking the separator to the polarizing plate via the adhesive layer after peeling the separator from the adhesive layer. Of the plurality of separator peeling and sticking steps, at least one separator peeling and sticking step is a separator replacing step ST41 of sticking a new separator different from the peeled separator to the polarizing plate via the adhesive layer.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for producing an optical laminate including at least a polarizing plate and a separator, and in particular to a method for producing an optical laminate capable of suppressing curling. [Background technology]

[0002] Conventionally, polarizing plates are used as a constituent material of liquid crystal display devices, organic EL display devices, and the like. The polarizing plate includes a polarizing film and a retardation film or the like depending on the application. The polarizing film is composed of, for example, a polarizer dyed with a dichroic material such as iodine and a protective film that protects the polarizer. A long strip-shaped polarizing film is manufactured by laminating a long strip-shaped protective film to at least one side of a long strip-shaped polarizer. A long strip-shaped retardation film or the like is laminated to one side of the manufactured long strip-shaped polarizing film to manufacture a long strip-shaped polarizing plate. A long strip-shaped separator (release film) is laminated to one side of the manufactured long strip-shaped polarizing plate, and a long strip-shaped surface protective film is laminated to the other side to manufacture a long strip-shaped optical laminate. The lamination of these long strip-shaped films is usually performed by a roll-to-roll method or a roll-to-sheet method. The manufactured long strip-shaped optical laminate is cut into a size and shape depending on the application and used for a liquid crystal display device or the like. When the optical laminate is used in a liquid crystal display device or the like, the separator is peeled off and the remaining components of the optical laminate are attached to the liquid crystal display device or the like.

[0003] Fig. 7 is a flow diagram showing an outline of an example of a method for producing a conventional optical laminate. As shown in Fig. 7, the conventional method for producing an optical laminate includes a polarizing film production step ST1', a retardation film attachment step ST2', a separator attachment step ST3', an inspection step ST4', and a surface protection film attachment step ST5'. In the polarizing film manufacturing process ST1', a long strip-shaped resin film is used as a raw film, and the raw film is immersed in various treatment baths while being transported in the longitudinal direction, and various treatments such as dyeing and stretching are performed to manufacture a long strip-shaped polarizer. A long strip-shaped protective film is then attached to at least one surface of the long strip-shaped polarizer to manufacture a long strip-shaped polarizing film. In the retardation film laminating step ST2', a long strip-shaped retardation film (such as a half wavelength plate or a quarter wavelength plate) is laminated to one side of a long strip-shaped polarizing film to produce a long strip-shaped polarizing plate.

[0004] In the separator lamination process ST3', a long strip-shaped separator is coated with an adhesive while being transported in the longitudinal direction, and the coated adhesive is heated in an oven or the like to dry and harden to form an adhesive layer. Then, the adhesive layer side of this long strip-shaped separator (separator with adhesive layer) is laminated to one side of a long strip-shaped polarizing plate to produce a long strip-shaped intermediate in which the polarizing plate, the adhesive layer, and the separator are laminated. In the inspection process ST4', the separator is peeled off while leaving the adhesive layer between the separator and the polarizing plate on the polarizing plate side, and the polarizing plate is inspected. Inspection methods for polarizing plates include transmission inspection, crossed Nicol inspection, and reflection inspection. In the inspection process ST4', after inspecting the polarizing plate, the peeled separator is attached again to the polarizing plate to return it to its original intermediate state.

[0005] In the surface protective film laminating step ST5', a long strip-shaped surface protective film is laminated to the surface of the long strip-shaped polarizing plate opposite to the surface to which the separator is laminated. By the above-described polarizing film manufacturing step ST1' to surface protective film bonding step ST5', a long belt-like optical laminate is manufactured.

[0006] However, the optical laminate produced as described above may suffer from curling (warping of the edges) that is problematic in use after being cut into a product size. For example, Patent Document 1 proposes using a specific material for the protective film that protects the polarizer as a method for suppressing curling of the polarizing film, but since the material of the protective film is limited, it is not versatile. A method capable of suppressing curling without particularly changing the materials of the components of the conventionally used optical laminate is desired. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2007-256568 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made to solve the above-mentioned problems of the conventional technology, and an object of the present invention is to provide a method for producing an optical laminate capable of suppressing curling. [Means for solving the problem]

[0009] In order to solve the above problems, the present inventors have conducted extensive research and found that the formation of an adhesive layer on the separator in the separator lamination step (ST3' in FIG. 7) in the conventional method for producing an optical laminate may be one of the causes of curling of the optical laminate. Specifically, it is believed that when the adhesive applied to the separator is heated and dried, the separator shrinks and unevenness occurs in the thickness direction. When the separator is laminated to the polarizing plate in the separator lamination step, or when the separator is laminated to the polarizing plate again in the inspection step (ST4' in FIG. 7), the separator is laminated in a state in which the unevenness generated in the separator by heating is stretched out. However, after the passage of time from lamination, a force acts on the separator to return to the contracted state, which is believed to cause curling in the optical laminate. As a result of further intensive research focusing on the above-mentioned causes of curling, the inventors have found that performing the process of peeling off a separator and then laminating a separator multiple times, as in the conventional inspection process, and laminating (replacing) a new separator different from the peeled separator (a separator that has not been heated to form an adhesive layer) in at least one of these multiple processes is effective in suppressing curling. The present invention has been completed based on the above findings of the present inventors.

[0010] That is, in order to solve the above-mentioned problems, the present invention provides a method for producing a polarizing plate having a separator, the method comprising: a separator laminating step of laminating a separator to a polarizing plate via an adhesive layer formed on the separator; and a separator peeling / laminating step of peeling the separator from the adhesive layer and then laminating the separator to the polarizing plate via the adhesive layer multiple times, But before a separator replacement step of attaching a new separator different from the peeled separator to the polarizing plate via the pressure-sensitive adhesive layer. and attaching a separator identical to the peeled separator to the polarizing plate via the pressure-sensitive adhesive layer. The present invention provides a method for producing an optical laminate.

[0011] In the separator peeling / laminating step of the present invention, the peeled separator and the separator to be laminated are not limited to different separators, and may be the same separator. That is, the separator peeling / laminating step of the present invention is performed in the case where the separator is peeled from the adhesive layer (only the separator is peeled while the adhesive layer remains on the polarizing plate) and then the same separator is laminated again to the polarizing plate via the adhesive layer. And peel A process to attach a new separator, different from the one that was removed, to the polarizing plate via an adhesive layer. and, According to the present invention, by including a separator peeling / laminating step multiple times, the peeling and lamination of the separator are repeated. In other words, even if the separator to be laminated is the same as the separator to be peeled, curling can be suppressed by repeatedly laminating the separator to the polarizing plate in a state in which the irregularities of the separator are smoothed out multiple times. Furthermore, at least one separator peeling / laminating step is a separator replacement step in which a new separator different from the peeled separator (i.e., a separator that is not heated to form a pressure-sensitive adhesive layer and therefore is less likely to develop irregularities) is laminated, so curling can be further suppressed.

[0012] In the present invention, After the separator replacement step is performed, a step of attaching a separator identical to the peeled separator to the polarizing plate via the pressure-sensitive adhesive layer is performed. .

[0013] In the present invention, at least one of the separator peeling / laminating steps among the multiple separator peeling / laminating steps preferably also serves as an inspection step of inspecting the polarizing plate after the separator is peeled off. According to the above-mentioned preferred method, at least one separator peeling / laminating step also serves as a polarizing plate inspection step, which has the advantage of simplifying the manufacturing process compared to a case in which the separator peeling / laminating step and the inspection step are provided separately.

[0014] Preferably, the present invention further comprises a surface protective film laminating step of laminating a surface protective film to the polarizing plate after the separator replacement step.

[0015] The separator laminating step includes, for example, an adhesive layer forming step of applying an adhesive to the separator and heating and curing the applied adhesive to form the adhesive layer. In the separator replacement step, it is preferable that the elastic modulus of a new separator to be attached to the polarizing plate is higher than the elastic modulus of the separator after the pressure-sensitive adhesive layer formation step. As in the preferred method described above, if the elastic modulus of the new separator to be attached to the polarizing plate is higher than the elastic modulus of the separator after the adhesive layer formation process (i.e., after heating) included in the separator attachment process, the new separator to be attached (replaced) in the separator replacement process is less likely to deform, making it possible to further suppress curling.

[0016] Preferably, in the separator peeling / laminating step, the time from peeling the separator to laminating the separator is within one minute. According to the above-mentioned preferred method, the time from peeling off the separator to laminating the separator, in other words, the time for the adhesive layer to be exposed, is short, so that even if the humidity in the separator peeling / laminating process changes due to, for example, seasonal influences or daytime or nighttime influences, it is possible to suppress variations in curling caused by the polarizing plate absorbing moisture in the atmosphere from the adhesive layer side and swelling.

[0017] Preferably, in the separator peeling / laminating step, the separator and the polarizing plate are laminated together by a laminating roller, the separator enters the laminating roller at an angle of less than 90°, and the polarizing plate enters the laminating roller at an angle of less than 90°.

[0018] In the above-mentioned preferred method, the "approach angle of the separator to the lamination roller" means the angle between a vector perpendicular to a line passing through the rotation center of a pair of opposing rollers constituting the lamination roller, pointing to the exit side of the lamination roller, and a vector indicating the proceeding direction of the separator until it comes into contact with the lamination roller. Similarly, the "approach angle of the polarizing plate to the lamination roller" means the angle between a vector perpendicular to a line passing through the rotation center of a pair of rollers constituting the lamination roller, pointing to the exit side of the lamination roller, and a vector indicating the proceeding direction of the polarizing plate until it comes into contact with the lamination roller. According to the findings of the inventors, when the approach angle of the separator to the lamination roller is large (90° or more), the curl in the TD direction (direction perpendicular to the transport direction (MD direction) of the long, strip-shaped optical laminate) and negative curl (curl in which the side where the separator is located is concave) becomes large, and when the approach angle of the polarizing plate to the lamination roller is large (90° or more), the curl in the TD direction and positive curl (curl in which the side where the separator is located is convex) becomes large. According to the above-mentioned preferable method, curling can be further suppressed by making both the approach angles of the separator and the polarizing plate to the lamination roller less than 90°.

[0019] Preferably, the lamination roller is composed of a first roller that contacts the separator and a second roller that contacts the polarizing plate, and one surface of the first roller and the second roller is formed from resin and the other surface is formed from metal. If both the surface of the first roller and the surface of the second roller are made of metal, there is a risk of air bubbles being generated at the interface between the separator and the polarizing plate (the interface between the separator and the adhesive layer) when the separator and the polarizing plate are bonded together. If both the surface of the first roller and the surface of the second roller are made of resin, there is a risk of wrinkles being generated in the separator. According to the above-mentioned preferable method, the surface of one of the first roller and the second roller is made of resin and the surface of the other is made of metal, thereby making it possible to suppress the risk of air bubbles and wrinkles being generated.

[0020] Preferably, the surface of the first roller is made of metal, and the surface of the second roller is made of resin. The above preferred method not only reduces the risk of air bubbles and wrinkles, but also reduces the occurrence of appearance defects on the polarizing plate, such as scratches and dents, because the surface of the second roller that comes into contact with the polarizing plate is made of resin (and not metal). Effect of the Invention

[0021] According to the present invention, curling can be effectively suppressed without particularly changing the materials of the components of conventionally used optical laminates. [Brief description of the drawings]

[0022] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an optical laminate produced by a production method according to one embodiment of the present invention. [Diagram 2] FIG. 1 is a flow diagram showing schematic steps of a method for producing an optical laminate according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a side view (as viewed from a horizontal direction perpendicular to the conveyance direction of each film) that typically illustrates an example of a schematic configuration of an apparatus that performs the separator replacement step ST41 shown in FIG. 2. [Figure 4] 4 is an explanatory diagram for explaining lamination of the first intermediate M1 and the separator 4b by the laminating roller R4 shown in FIG. 3. FIG. [Diagram 5] FIG. 3 is a side view (as viewed from a horizontal direction perpendicular to the transport direction of each film) that typically illustrates an example of the schematic configuration of an apparatus that performs the inspection process ST42 shown in FIG. 2. [Figure 6] FIG. 2 is an explanatory diagram for explaining a method for evaluating curl. [Figure 7] FIG. 1 is a flow chart showing an example of schematic steps of a conventional method for producing an optical laminate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, a method for producing an optical laminate according to one embodiment of the present invention will be described with reference to the accompanying drawings. Note that each drawing is for reference only, and the dimensions, scale, and shapes of the optical laminate and the components of the device shown in each drawing may differ from the actual ones.

[0024] <Configuration of optical laminate> First, the configuration of the optical laminate produced by the production method according to this embodiment will be described. FIG. 1 is a cross-sectional view that illustrates a schematic configuration of an optical laminate produced by a production method according to this embodiment. As shown in Fig. 1, the optical laminate 100 of this embodiment includes a polarizing film 1, a retardation film 2, a pressure-sensitive adhesive layer 3, a separator 4, and a surface protective film 5. A laminate of the polarizing film 1 and the retardation film 2 constitutes a polarizing plate 10. A laminate of the polarizing plate 10 and the pressure-sensitive adhesive layer 3 constitutes a first intermediate M1. A laminate of the first intermediate M1 and the separator 4 constitutes a second intermediate M2. Each component of the optical laminate 100 will be described below.

[0025] [Polarizing film 1] The polarizing film 1 is composed of a polarizer 11 and protective films 12 and 13 that protect the polarizer 11. In this embodiment, the protective films 12 and 13 are attached to both sides of the polarizer 11, but the present invention is not limited thereto, and it is sufficient that a protective film is attached to at least one side of the polarizer 11.

[0026] (Polarizer 11) The polarizer 11 is typically made of a resin film containing a dichroic material. As the resin film, any appropriate resin film that can be used as a polarizer can be adopted. The resin film is typically a polyvinyl alcohol-based resin (hereinafter, referred to as "PVA-based resin") film.

[0027] Any appropriate resin can be used as the PVA resin forming the PVA resin film. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer can be mentioned. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer can be obtained by saponifying ethylene-vinyl acetate copolymer.

[0028] The average degree of polymerization of the PVA resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be determined in accordance with JIS K 6726-1994.

[0029] Examples of the dichroic material contained in the resin film include iodine, organic dyes, etc. These may be used alone or in combination of two or more. Iodine is preferably used.

[0030] The resin film may be a single-layer resin film or a laminate of two or more layers.

[0031] A specific example of a polarizer composed of a single-layer resin film is a PVA-based resin film that has been subjected to a dyeing treatment with iodine and a stretching treatment (typically, a uniaxial stretching treatment). The dyeing treatment with iodine is performed, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be performed after dyeing or while dyeing. Alternatively, the dyeing may be performed after stretching. If necessary, the PVA-based resin film is subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, or the like.

[0032] Specific examples of polarizers made of laminates include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a polarizer made of a laminate of a resin substrate and a PVA-based resin layer applied to the resin substrate. A polarizer made of a laminate of a resin substrate and a PVA-based resin layer applied to the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate, drying the resin substrate to form a PVA-based resin layer on the resin substrate, obtaining a laminate of the resin substrate and the PVA-based resin layer, and then stretching and dyeing the laminate to make the PVA-based resin layer a polarizer. In this embodiment, the stretching typically includes immersing the laminate in an aqueous solution of boric acid and stretching it. Furthermore, the stretching may include, as necessary, stretching the laminate in air at a high temperature (for example, 95° C. or higher) before stretching in the aqueous solution of boric acid. The obtained laminate of resin substrate / polarizer may be used as it is (i.e., the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled off from the laminate of resin substrate / polarizer, and any suitable protective layer may be laminated on the peeled surface depending on the purpose. Details of the method for producing such a polarizer are described in, for example, JP2012-73580A. The entire disclosure of this publication is incorporated herein by reference.

[0033] The thickness of the polarizer 11 is preferably 15 μm or less, more preferably 1 μm to 12 μm, further preferably 3 μm to 10 μm, and particularly preferably 3 μm to 8 μm.

[0034] The polarizer 11 preferably exhibits absorption dichroism at any wavelength within a wavelength range of 380 nm to 780 nm. The single transmittance of the polarizer 11 is preferably 40.0% to 45.0%, and more preferably 41.5% to 43.5%. The degree of polarization of the polarizer 11 is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0035] (Protective films 12 and 13) Any suitable resin film is used as the protective films 12 and 13. Examples of materials for forming the resin film include (meth)acrylic resins, cellulose resins such as diacetyl cellulose and triacetyl cellulose, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, ester resins such as polyethylene terephthalate resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. Note that "(meth)acrylic resin" means acrylic resin and / or methacrylic resin. The materials for forming the protective films 12 and 13 may be the same or different from each other.

[0036] The thickness of the protective films 12 and 13 is typically 10 μm to 100 μm, and preferably 20 μm to 40 μm. The thicknesses of the protective films 12 and 13 may be the same as or different from each other.

[0037] The surfaces of the protective films 12 and 13 opposite the polarizer 11 may be subjected to a surface treatment such as a hard coat treatment, an anti-reflection treatment, an anti-sticking treatment, an anti-glare treatment, etc., if necessary. Furthermore, the surfaces of the protective films 12 and 13 opposite the polarizer 11 may be subjected to a treatment for improving visibility when viewed through polarized sunglasses (typically, a treatment for imparting an (elliptical) polarizing function, a treatment for imparting an ultra-high phase difference) if necessary. When a surface treatment layer is formed by performing a surface treatment, the thickness of the protective films 12 and 13 includes the thickness of the surface treatment layer.

[0038] The protective films 12 and 13 are laminated by being attached to the polarizer 11 via any suitable adhesive layer (not shown). Representative examples of the adhesive constituting the adhesive layer include a PVA-based adhesive and an activation energy ray-curable adhesive.

[0039] [Retardation film 2] The retardation film 2 may be, for example, a compensation plate that provides a wide viewing angle, or a retardation plate (circular polarizing plate) such as a half-wave plate or a quarter-wave plate that is used together with a polarizing film to generate circularly polarized light. The thickness of the retardation film 2 is, for example, 1 to 200 μm.

[0040] The retardation film 2 is formed of, for example, a layer or resin formed by polymerizing a polymerizable liquid crystal. The polymerizable liquid crystal is a compound having a polymerizable group and liquid crystallinity. The polymerizable group means a group involved in a polymerization reaction, and is preferably a photopolymerizable group. Here, the photopolymerizable group means a group that can be involved in a polymerization reaction by an active radical or an acid generated from a photopolymerization initiator. Examples of the polymerizable group include a vinyl group, a vinyloxy group, a 1-chlorovinyl group, an isopropenyl group, a 4-vinylphenyl group, an acryloyloxy group, a methacryloyloxy group, an oxiranyl group, and an oxetanyl group. Among them, an acryloyloxy group, a methacryloyloxy group, a vinyloxy group, an oxiranyl group, and an oxetanyl group are preferred, and an acryloyloxy group is more preferred. The liquid crystallinity of the polymerizable liquid crystal may be a thermotropic liquid crystal or a lyotropic liquid crystal, and when the thermotropic liquid crystal is classified according to the degree of order, it may be a nematic liquid crystal or a smectic liquid crystal. Examples of the resin forming the retardation film 2 include polyarylate, polyamide, polyimide, polyester, polyaryletherketone, polyamideimide, polyesterimide, polyvinyl alcohol, polyfumaric acid ester, polyethersulfone, polysulfone, norbornene resin, polycarbonate resin, cellulose resin, and polyurethane. These resins may be used alone or in combination.

[0041] The retardation film 2 is laminated on the polarizing film 1 (protective film 13) via any suitable adhesive layer or pressure-sensitive adhesive layer (not shown). Representative examples of the adhesive constituting the adhesive layer include a PVA-based adhesive and an activation energy ray-curable adhesive.

[0042] [Adhesive layer 3] The adhesive layer 3 is formed by applying an adhesive to one surface of the separator 4 and then heating and drying the applied adhesive in an oven or the like to harden it. The heating temperature of the adhesive is preferably set in the range of 100° C. to 160° C., and more preferably in the range of 140° C. to 160° C. Heating at this heating temperature is preferably carried out for 20 seconds to 3 minutes, and more preferably for 1 minute to 3 minutes.

[0043] Specific examples of the adhesive forming the adhesive layer 3 include acrylic adhesives, rubber adhesives, silicone adhesives, polyester adhesives, urethane adhesives, epoxy adhesives, and polyether adhesives. By adjusting the type, number, combination, and compounding ratio of monomers forming the base resin of the adhesive, as well as the compounding amount of the crosslinking agent, reaction temperature, reaction time, and the like, an adhesive having desired properties according to the purpose can be prepared. The base resin of the adhesive may be used alone or in combination of two or more kinds. From the viewpoints of transparency, processability, durability, and the like, an acrylic adhesive is preferred. Details of the adhesive constituting the adhesive layer are described in, for example, JP 2014-115468 A, and the description of the publication is incorporated herein by reference. The thickness of the adhesive layer can be, for example, 10 μm to 100 μm.

[0044] [Separator 4] Any appropriate separator can be used as the separator 4. Specific examples include plastic films, nonwoven fabrics, and paper whose surfaces are coated with a release agent. Specific examples of the release agent include silicone-based release agents, fluorine-based release agents, and long-chain alkyl acrylate-based release agents. Specific examples of the plastic film include polyethylene terephthalate (PET) films, polyethylene films, and polypropylene films. The thickness of the separator 4 can be, for example, 10 μm to 100 μm.

[0045] [Surface protection film 5] The surface protection film 5 typically includes a substrate and a pressure-sensitive adhesive layer. In this embodiment, the thickness of the surface protection film 5 is, for example, 30 μm or more. The upper limit of the thickness of the surface protection film 5 is, for example, 150 μm. In this specification, the "thickness of the surface protection film" refers to the total thickness of the substrate and the pressure-sensitive adhesive layer.

[0046] The substrate can be made of any suitable resin film. Examples of materials for forming the resin film include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Ester resins (particularly polyethylene terephthalate resins) are preferred.

[0047] Any appropriate adhesive can be used as the adhesive for forming the adhesive layer. Examples of the base resin of the adhesive include acrylic resins, styrene resins, silicone resins, urethane resins, and rubber resins.

[0048] <Production method according to this embodiment> A method for producing the optical laminate 100 according to this embodiment for producing the optical laminate 100 having the configuration described above will be described below. FIG. 2 is a flow diagram showing an outline of steps in a method for producing the optical laminate 100 according to this embodiment. 2, the manufacturing method according to this embodiment includes a polarizing film manufacturing step ST1, a retardation film bonding step ST2, a separator bonding step ST3, a separator peeling / bonding step ST4 performed multiple times (twice in this embodiment), and a surface protection film bonding step ST5. Each of the steps ST1 to ST5 will be described below.

[0049] [Polarizing film manufacturing process ST1] In the polarizing film manufacturing process ST1, a long strip-shaped resin film is used as a raw film, and this raw film is immersed in various treatment baths while being transported in the longitudinal direction (MD direction) and subjected to various treatments such as dyeing and stretching to manufacture a long strip-shaped polarizer 11. Then, long strip-shaped protective films 12 and 13 are bonded to the long strip-shaped polarizer 11 to manufacture a long strip-shaped polarizing film 1.

[0050] [Retardation film lamination process ST2] In the retardation film laminating step ST2, a long strip-shaped retardation film 2 is laminated to one surface (protective film 13) of a long strip-shaped polarizing film 1 to produce a long strip-shaped polarizing plate 10. In addition, when the optical laminate 100 does not include the retardation film 2 (when the polarizing plate 10 does not include the retardation film 2), the retardation film bonding step ST2 is not necessary.

[0051] [Separator lamination process ST3] In the separator laminating step ST3, an adhesive is applied to the long strip separator 4 while it is being transported in the longitudinal direction (MD direction), and the applied adhesive is heated in an oven or the like to dry and harden, thereby forming an adhesive layer 3. Then, the separator 4 is laminated to the long strip polarizing plate 10 via the adhesive layer 3 formed on the long strip separator 4. Specifically, the adhesive layer 3 side of the long strip separator 4 (separator 4 with adhesive layer 3) is laminated to one side (retardation film 2) of the long strip polarizing plate 10. In this way, a second intermediate M2 in which the polarizing plate 10, the adhesive layer 3, and the separator 4 are laminated is manufactured.

[0052] [Separator peeling and lamination process ST4] In the separator peeling / laminating process ST4, the separator 4 is peeled off from the adhesive layer 3 (only the separator 4 is peeled off, leaving the adhesive layer 3 interposed between the separator 4 and the polarizing plate 10 on the polarizing plate 10 side), and then the separator 4 is laminated to the polarizing plate 10 via the adhesive layer 3. In this embodiment, the separator peeling / laminating step ST4 is performed twice, one of which is the separator replacement step ST41, and the other is the inspection step ST42. However, the present invention is not limited to this, and it is sufficient that at least one of the separator peeling / laminating steps ST4 performed multiple times is the separator replacement step ST41. The manufacturing method according to the present embodiment includes a separator peeling / laminating step ST4 multiple times, whereby the peeling and laminating of the separator 4 are repeated. In other words, even if the separator 4 to be laminated is the same as the separator 4 to be peeled, curling can be suppressed by repeatedly laminating the separator 4 to the polarizing plate 10 in a state in which the irregularities of the separator 4 are smoothed out multiple times. Furthermore, since the method includes a separator replacement step ST41 at least once where a new separator 4 different from the peeled separator 4 is laminated, curling can be further suppressed. The separator replacement step ST41 and the inspection step ST42 will be described in detail below.

[0053] (Separator replacement process ST41) In the separator replacement step ST41, a new separator 4 different from the peeled separator 4 is attached to the polarizing plate 10 via the pressure-sensitive adhesive layer 3. Hereinafter, the separator 4 to be peeled (the separator 4 attached in the separator attachment step ST3) will be referred to as "separator 4a" and the new separator 4 attached in the separator replacement step ST41 will be referred to as "separator 4b" to distinguish between the two.

[0054] 3 is a side view (as viewed from a horizontal direction perpendicular to the conveying direction of each film) showing a schematic configuration example of an apparatus for performing the separator replacement step ST41. The arrows shown in FIG. 3 indicate the conveying direction of each film. In the separator replacement step ST41, the second intermediate M2 manufactured in the separator laminating step ST3 as described above is wound around the pay-out roller R1 shown in Fig. 3 and disposed on the most upstream side of the apparatus (the most upstream side in the conveying direction of the second intermediate M2). Then, the second intermediate M2 paid out from the pay-out roller R1 is conveyed toward the peeling roller R2. At the peeling roller R2, the separator 4a is peeled off from the second intermediate M2, and the peeled separator 4a is taken up by the take-up roller R3.

[0055] Meanwhile, the first intermediate M1, which is a laminate of the polarizing plate 10 and the adhesive layer 3 obtained by peeling the separator 4a from the second intermediate M2 by the peeling roller R2, is conveyed toward the laminating roller R4. Also, a new separator 4b (i.e., a separator that is not heated to form the adhesive layer 3 and is therefore unlikely to develop unevenness) wound around the unwinding roller R5 is prepared, and this separator 4b is unwound from the unwinding roller R5 and conveyed toward the laminating roller R4. Then, the separator 4b is laminated to the first intermediate M1 by the laminating roller R4. That is, the separator 4b is laminated to the polarizing plate 10 constituting the first intermediate M1 via the adhesive layer 3 constituting the first intermediate M1. In this way, the second intermediate M2 is manufactured and taken up by the winding roller R6. The separator 4 of the second intermediate body M2 fed from the feed roller R1 is the separator 4a, while the separator 4 of the second intermediate body M2 taken up by the take-up roller R6 is the separator 4b. In this embodiment, the elastic modulus (elastic modulus in the TD direction) of the new separator 4b to be attached to the polarizing plate 10 in the separator replacement step ST41 is, for example, 6000 [N / mm 2 On the other hand, the elastic modulus (elastic modulus in the TD direction) of the separator 4a after the pressure-sensitive adhesive layer forming step (i.e., after heating) in the separator laminating step ST3 is, for example, 6000 [N / mm 2], and the elastic modulus of separator 4b is higher than that of separator 4a. If the elastic modulus of separator 4b is higher than that of separator 4a, the new separator 4b attached (replaced) in separator replacement step ST41 is less likely to shrink, and curling can be further suppressed. The upper limit of the elastic modulus of separator 4b (elastic modulus in the TD direction) is not particularly limited, but may be, for example, 7000 [N / mm 2 ] or less, and 6500 [N / mm 2 The lower limit of the elastic modulus (elastic modulus in the TD direction) of the separator 4a is not particularly limited, but is, for example, 5000 [N / mm 2 ] or more, and 5500 [N / mm 2 ] or more. The elastic modulus can be measured, for example, by using a tensile tester "Autograph" manufactured by Shimadzu Corporation. Specifically, a sample having a width (dimension in MD) of 10 mm and a length (dimension in TD) of 100 mm is cut out from each of the separators 4a and 4b alone, and the sample is set in the autograph and pulled in the TD direction at a speed of 50 mm / min. The elastic modulus can be calculated based on the force [N] applied to stretch the sample by a predetermined amount.

[0056] In this embodiment, in the separator replacement step ST41, the time from peeling the separator 4a to laminating the separator 4b is within 1 minute, preferably within 45 seconds, and more preferably within 30 seconds. Specifically, as shown in Fig. 3, when the length of the transport path of the first intermediate M1 from the peeling roller R2 to the laminating roller R4 is L and the transport speed is V, the length L of the transport path and the transport speed V are set so that L / V≦1 minute (preferably 45 seconds, and more preferably 30 seconds). As described above, in this embodiment, the time from peeling off separator 4a to bonding separator 4b, in other words, the time during which the adhesive layer 3 is exposed, is short, so that even if the humidity in the separator replacement process ST41 changes due to, for example, seasonal influences or daytime or nighttime influences, it is possible to suppress variations in curling that occurs when the polarizing plate 10 absorbs moisture in the atmosphere from the adhesive layer 3 side and swells.

[0057] Hereinafter, the lamination of the first intermediate M1 and the separator 4b by the laminating roller R4 will be described in more detail. 4 is an explanatory diagram for explaining lamination of the first intermediate M1 and the separator 4b by the laminating roller R4. As shown in FIG. 4, the laminating roller R4 is composed of a pair of opposing rollers, a first roller R41 and a second roller R42. The first roller R41 is a roller that contacts the separator 4b and transports the separator 4b between the first roller R41 and the second roller R42. The surface of the first roller R41 is made of metal (e.g., iron). The second roller R42 is a roller that contacts the first intermediate M1 and transports the first intermediate M1 between the first roller R41 and the second roller R42. The surface of the second roller R42 is made of resin (e.g., rubber).

[0058] As shown in FIG. 4, a straight line (virtual line) passing through the rotation center C1 of the first roller R41 and the rotation center C2 of the second roller R42 is defined as a straight line CL. A vector (virtual vector) perpendicular to the straight line CL and directed toward the exit side of the lamination roller R4 (the right side in FIG. 4) is defined as a vector VC. In this case, the approach angle α of the separator 4b to the lamination roller R4 means the angle between the vector VC and a vector indicating the moving direction of the separator 4b until it comes into contact with the lamination roller R4. In addition, the approach angle β of the first intermediate M1 to the lamination roller R4 (corresponding to the approach angle of the polarizing plate 10 to the lamination roller R4) means the angle between the vector VC and a vector indicating the moving direction of the first intermediate M1 until it comes into contact with the lamination roller R4 (corresponding to the moving direction of the polarizing plate 10). In this embodiment, both the approach angle α and the approach angle β are set to less than 90°. In FIG. 3, for convenience, α=90° and β=0° are illustrated, but in reality, α<90° and β<90°, preferably 10°<α<80°, and more preferably 20°<α<50°. Also, preferably 0°<β<80°, and more preferably 0°<β<75°. By increasing the approach angle α, the transportability of the first intermediate M1 (polarizing plate 10) is improved.

[0059] According to the findings of the inventors, when the approach angle α of the separator 4b to the laminating roller R4 is large (90° or more), the curl in the TD direction and the negative curl (the curl in which the side where the separator 4b is located is concave) becomes large, and when the approach angle β of the first intermediate M1 (polarizing plate 10) to the laminating roller R4 is large (90° or more), the curl in the TD direction and the positive curl (the curl in which the side where the separator 4b is located is convex) becomes large. Therefore, by making α<90° and β<90° as described above, curling can be further suppressed.

[0060] (Inspection process ST42) The inspection process ST42 of this embodiment is performed after the separator replacement process ST41. In the inspection process ST42, the separator 4b is peeled off from the adhesive layer 3 (only the separator 4b is peeled off while the adhesive layer 3 interposed between the separator 4b and the polarizing plate 10 is left on the polarizing plate 10 side), and then the polarizing plate 10 is inspected. Then, after inspecting the polarizing plate 10, the peeled separator 4b is attached again to the polarizing plate 10, thereby returning the polarizing plate 10 to its original state of the second intermediate M2.

[0061] 5 is a side view (as viewed from a horizontal direction perpendicular to the transport direction of each film) showing a schematic configuration example of an apparatus that performs the inspection process ST42. The arrows shown in FIG. 5 indicate the transport direction of each film. In the inspection process ST42, the second intermediate M2 manufactured in the separator replacement process ST41 as described above is wound around a feed roller R7 shown in FIG. 5 and disposed on the most upstream side of the apparatus (the most upstream side in the conveying direction of the second intermediate M2). Then, the second intermediate M2 fed from the feed roller R7 is conveyed toward a peeling roller R8. At the peeling roller R8, the separator 4b is peeled off from the second intermediate M2, and the peeled separator 4b is conveyed toward a laminating roller R9.

[0062] On the other hand, the first intermediate M1, which is a laminate of the polarizing plate 10 and the adhesive layer 3 obtained by peeling the separator 4b from the second intermediate M2 by the peeling roller R8, is inspected by the inspection device 20. The inspection device 20 shown in Fig. 5 is a device that performs a transmission inspection, and includes a light source 20a, an imaging means 20b, and a calculation means (not shown). The imaging means 20b of the inspection device 20 receives light emitted from the light source 20a and transmitted through the first intermediate M1, forms an image, and outputs an electrical signal according to the amount of light as an imaging signal to the calculation means. The calculation means generates a transmission image based on this input imaging signal. Then, the calculation means applies known image processing, such as binarization, to the generated transmission image to extract pixel regions that have a different luminance value (pixel value) from other pixel regions, thereby detecting defects present in the first intermediate M1 (polarizing plate 10). The inspection performed in the inspection step ST42 is not limited to the above-mentioned transmission inspection. It is also possible to adopt a crossed Nicol inspection in which a crossed Nicol image is generated by light transmitted through an inspection polarizing filter arranged to be in a crossed Nicol state with respect to the polarization axis of the polarizer 11 included in the polarizing plate 10 and the first intermediate M1, and defects present in the first intermediate M1 (polarizing plate 10) are detected based on this crossed Nicol image. It is also possible to adopt a reflection inspection in which a reflected image is generated by light reflected by the first intermediate M1, and defects present in the first intermediate M1 (polarizing plate 10) are detected based on this reflected image. Furthermore, it is also possible to perform any combination of the transmission inspection, the crossed Nicol inspection, and the reflection inspection.

[0063] After being inspected by the inspection device 20, the first intermediate M1 is conveyed toward the laminating roller R9. Then, the laminating roller R9 laminates the separator 4b to the first intermediate M1 again. That is, the separator 4b is laminated to the polarizing plate 10 constituting the first intermediate M1 via the adhesive layer 3 constituting the first intermediate M1. In this way, the second intermediate M2 is manufactured and taken up by the winding roller R10. The separator 4 of the second intermediate M2 unwound from the unwound roller R7 and the separator 4 of the second intermediate M2 taken up by the winding roller R10 are both the same separator 4b. In addition, in the inspection process ST42 as well as in the separator replacement process ST41, the time from peeling the separator 4b with the peeling roller R8 to laminating the separator 4b with the laminating roller R9 is within 1 minute, preferably within 45 seconds, more preferably within 30 seconds. In addition, in the inspection process ST42 as well as in the separator replacement process ST41, the surface of the roller that contacts the separator 4b and conveys the separator 4b between the pair of rollers, among the pair of opposing rollers that constitute the laminating roller R9, is made of metal (for example, iron). The surface of the roller that contacts the first intermediate M1 and conveys the first intermediate M1 between the pair of rollers is made of resin (for example, rubber). In addition, in the inspection process ST42 as well as in the separator replacement process ST41, both the approach angle α of the separator 4b to the laminating roller R9 and the approach angle β of the first intermediate M1 (polarizing plate 10) to the laminating roller R9 are set to less than 90°. As a result, curling can be further suppressed in the inspection process ST42. The approach angle α of the separator 4b to the lamination roller R9 and the approach angle β of the first intermediate M1 (polarizing plate 10) to the lamination roller R9 are preferably 10°<α<80°, and more preferably 20°<α<50°. Also, preferably 0°<β<80°, and more preferably 0°<β<75°. Increasing the approach angle α improves the transportability of the first intermediate M1 (polarizing plate 10).

[0064] [Surface protection film lamination process ST5] The surface protection film bonding step ST5 of this embodiment is performed after the separator replacement step ST41 (and further after the inspection step ST42). In the surface protection film bonding step ST5, a long strip-shaped surface protection film 5 is bonded to the long strip-shaped second intermediate M2. Specifically, the long strip-shaped surface protection film 5 is bonded to the surface of the polarizing plate 10 constituting the second intermediate M2 opposite to the side to which the separator 4b is bonded. In this way, a long strip-shaped optical laminate 100 is manufactured.

[0065] According to the manufacturing method according to the present embodiment described above, curling can be effectively suppressed without particularly changing the materials of the components of the optical laminate 100 that have been conventionally used. In this embodiment, an embodiment in which the separator peeling / laminating step ST4 is performed twice has been described; however, the present invention is not limited to this, and it is also possible to perform the separator peeling / laminating step ST4 three or more times.

[0066] In addition, in this embodiment, an aspect in which the separator replacement process ST41 is performed before the inspection process ST42 has been described, but the present invention is not limited to this, and it is also possible to perform the separator replacement process ST41 after the inspection process ST42.

[0067] In the present embodiment, the inspection process ST42 is described as a process in which the peeled separator 4b is bonded again to the polarizing plate 10 after inspecting the polarizing plate 10, but the present invention is not limited to this. In the inspection process ST42, as in the separator replacement process ST41, it is also possible to adopt a process in which a new separator different from the peeled separator 4b is bonded to the inspected polarizing plate 10.

[0068] In addition, in the present embodiment, the embodiment has been described in which the inspection step ST42 also serves as the separator peeling / bonding step ST4, but the present invention is not limited to this, and it is also possible to execute the separator peeling / bonding step ST4 separately from the inspection step ST42 and the separator replacement step ST41. Alternatively, it is also possible to adopt an embodiment in which no inspection is performed in the inspection step ST42 (i.e., the separator peeling / bonding step ST4 is simply performed by peeling and bonding the separator 4).

[0069] In the present embodiment, the separator laminating step ST3 to the surface protective film laminating step ST5 are performed in a state where each film is in a long strip shape, but the present invention is not limited to this. For example, it is also possible to adopt a mode in which the separator laminating step ST3 to the surface protective film laminating step ST5 are performed after the long strip shape polarizing plate 10 produced in the retardation film laminating step ST2 is cut to a product size.

[0070] Furthermore, in the present embodiment, the polarizing plate 10 is a laminate of the polarizing film 1 and the retardation film 2, but the present invention is not limited to this. It is also possible to adopt an embodiment in which the polarizing plate 10 is a laminate of the polarizing film 1, the retardation film 2, and other components, an embodiment in which the retardation film 2 is not present and the polarizing plate 10 is a laminate of the polarizing film 1 and other components, or an embodiment in which only the polarizing film 1 is present in the polarizing plate 10.

[0071] Below, we will explain an example of the results of evaluating the curl of the optical laminate 100 manufactured by the manufacturing method (example) of this embodiment shown in Figure 2, and an example of the results of evaluating the curl of the optical laminate manufactured by a conventional manufacturing method (comparison example) shown in Figure 7. The optical laminates 100 produced in the examples and comparative examples all had a configuration in which layers were laminated in the following order. (1) Surface protection film 5 (Base material: PET, thickness 38 μm, Adhesive layer: Acrylic adhesive, thickness 10 μm) (2) Cycloolefin-based protective film 12 (total thickness 32 μm) with a hard coat layer (thickness 7 μm) (3) Adhesive (4) Polyvinyl alcohol polarizer 11 (thickness 12 μm) (5) Adhesive (6) Triacetyl cellulose protective film 13 (thickness 25 μm) (7) Adhesive (8) Polymerizable liquid crystal half-wave plate 2 (thickness 2.5 μm) (9) Acrylic adhesive layer 3 (thickness 20 μm) (10) Separator 4 (PET, thickness 38 μm) In the optical laminate 100 produced in the example, a separator 4 identical to the peeled separator 4 was attached to the inspected polarizing plate 10 in the inspection step ST42 (the separator 4 was not replaced in the inspection step ST42).

[0072] FIG. 6 is an explanatory diagram for explaining a method for evaluating curl. As shown in FIG. 6(a), in the embodiment, a rectangular optical laminate 100S having a product size (148 mm long x 70 mm wide) was cut out along the TD direction of a long optical laminate 100. In FIG. 6(a), for convenience, three optical laminates 100S are shown, but in reality, 10 optical laminates 100S were cut out along the TD direction of one optical laminate 100. This was performed for a plurality of optical laminates 100 to obtain a total of 500 optical laminates 100S. Then, curl was evaluated for 100 randomly selected from the 500 optical laminates 100S. Note that, as shown in FIG. 6(b), when cutting out the optical laminate 100S, it was cut out obliquely so that the MD direction of the optical laminate 100 (corresponding to the direction of the absorption axis of the polarizer 11) was at an angle of 45° to the long side and short side of the optical laminate 100S.

[0073] 6(c), when evaluating curl, the optical laminate 100S was placed on a flat mounting table 30 so that the underside of the optical laminate 100S was convex (so that the warping of the four corners of the optical laminate 100S was directed vertically upward), and the vertical distance H from the upper surface of the mounting table 30 to each of the four corners of the optical laminate 100S was measured. The distance H was measured by setting up a scale extending vertically near the corners of the optical laminate 100S and visually reading the graduations of this scale. When the optical laminate 100S was placed on the mounting table 30 so that the bottom side thereof was convex, a positive curl was observed when the side of the optical laminate 100S where the separator 4 was located was facing down (the side where the surface protective film 5 was facing up), and the measured distance H was calculated as the curl value as it was. On the other hand, when the optical laminate 100S was placed on the mounting table 30 so that the bottom side thereof was convex, a negative curl was observed when the side of the optical laminate 100S where the separator 4 was located was facing up (the side where the surface protective film 5 was facing down), and the measured distance H was multiplied by -1 to calculate the curl value.

[0074] Next, as shown in Fig. 6(d), the separator 4 was peeled off from the optical laminate 100S. Then, for the laminate from which the separator 4 had been peeled off (the laminate of the first intermediate body M1 and the surface protective film 5), the curl values ​​of the four corners were calculated using the same procedure as above.

[0075] If the curl values ​​of the four corners of the optical laminate 100S and the curl values ​​of the four corners of the laminate from which the separator 4 has been peeled off all satisfied the condition -5 mm≦curl value≦5 mm, the product was deemed to have passed, and if they did not, the product was deemed to have failed. For the comparative examples, the curl value was calculated in the same manner as in the examples described above, and a pass or fail judgment was made.

[0076] Table 1 shows the evaluation results of curl for the examples and comparative examples. [Table 1] As shown in Table 1, in the comparative example, 44 out of 100 optical laminates passed (pass rate 44%), whereas in the example, 64 out of 100 optical laminates passed (pass rate 44%), demonstrating that curling was suppressed. [Explanation of symbols]

[0077] 1. Polarizing film 10...Polarizing plate 11... Polarizer 12, 13: Protective film 2. Retardation film 3. Adhesive layer 4. Separator 5. Surface protection film 100, 100S... Optical laminate ST1: Polarizing film manufacturing process ST2: Phase difference film lamination process ST3: Separator lamination process ST4: Separator peeling and lamination process ST41: Separator replacement process ST42: Inspection process ST5: Surface protection film lamination process

Claims

1. a separator lamination step of laminating the separator to a polarizing plate via a pressure-sensitive adhesive layer formed on the separator; and a separator peeling / sticking step of peeling the separator from the pressure-sensitive adhesive layer and then sticking the separator to the polarizing plate via the pressure-sensitive adhesive layer multiple times, the separator peeling / bonding step being repeated a plurality of times includes a separator replacement step of bonding a new separator different from the peeled separator to the polarizing plate via the pressure-sensitive adhesive layer, and a step of bonding the same separator as the peeled separator to the polarizing plate via the pressure-sensitive adhesive layer. A method for producing an optical laminate.

2. After the separator replacement step, a step of bonding a separator identical to the peeled separator to the polarizing plate via the adhesive layer is performed. A method for producing the optical laminate according to claim 1 .

3. At least one of the separator peeling / bonding steps among the multiple separator peeling / bonding steps also serves as an inspection step of inspecting the polarizing plate after peeling off the separator. A method for producing the optical laminate according to claim 1 or 2.

4. A surface protective film laminating step of laminating a surface protective film to the polarizing plate after the separator replacement step, A method for producing the optical laminate according to claim 1 .

5. The separator laminating step includes a pressure-sensitive adhesive layer forming step of applying a pressure-sensitive adhesive to the separator and heating and curing the applied pressure-sensitive adhesive to form the pressure-sensitive adhesive layer. A method for producing the optical laminate according to claim 1 .

6. In the separator replacement step, the elastic modulus of a new separator to be attached to the polarizing plate is higher than the elastic modulus of the separator after the pressure-sensitive adhesive layer formation step. A method for producing the optical laminate according to claim 5 .

7. In the separator peeling / laminating step, the time from peeling the separator to laminating the separator is within 1 minute. A method for producing the optical laminate according to claim 1 .

8. In the separator peeling / laminating step, the separator and the polarizing plate are laminated together by a laminating roller; an approach angle of the separator to the lamination roller being less than 90°, and an approach angle of the polarizing plate to the lamination roller being less than 90°; A method for producing the optical laminate according to claim 1 .

9. the lamination roller includes a first roller that contacts the separator and a second roller that contacts the polarizing plate, one of the first roller and the second roller has a surface made of resin and the other has a surface made of metal; The method for producing the optical laminate according to claim 8 .

10. the first roller has a surface made of metal; The second roller has a surface made of resin. The method for producing the optical laminate according to claim 9 .

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