Manufacturing method of optical laminates

Abstract

The present invention relates to a method for manufacturing an optical laminate capable of suppressing curling. The solution is that the method for manufacturing the optical laminate 100 of the present invention includes the following steps: a separator bonding step ST4, in which the separator 4 is bonded to a polarizing plate 10 through an adhesive layer 3 formed on the separator 4; and a separator peeling / bonding step ST5, in which, after the separator bonding step, the separator is peeled from the adhesive layer and then bonded to the polarizing plate through the adhesive layer. In the separator peeling / bonding step, at least the peeling of the separator is performed after humidification to an absolute humidity of 10 g / m³. Implemented in environments with a strength of 3 or higher.

Description

Technical Field

[0001] This invention relates to a method for manufacturing an optical laminate comprising at least a polarizing plate and a separating element. More particularly, this invention relates to a method for manufacturing an optical laminate capable of suppressing curling. Prior Technology

[0002] Traditionally, polarizing plates have been used as constituent materials for liquid crystal display devices or organic EL display devices. Polarizing plates include polarizing films, and, depending on the application, also include retardation films. The polarizing film is, for example, composed of a polarizing element dyed with a dichroic substance such as iodine and a protective film protecting the polarizing element. A strip-shaped polarizing film is manufactured by laminating a strip-shaped protective film onto at least one side of a strip-shaped polarizing element. A strip-shaped retardation film is then laminating onto one side of the manufactured strip-shaped polarizing film to produce a strip-shaped polarizing plate. A strip-shaped release film is then laminating onto one side of the manufactured strip-shaped polarizing plate, and a strip-shaped surface protective film is laminating onto the other side to produce a strip-shaped optical laminate. The lamination of these strip-shaped films is typically performed in a roll-to-roll or roll-to-sheet manner. The manufactured strip-shaped optical laminate system is cut into sizes or shapes suitable for its application in liquid crystal display devices, etc. Furthermore, when used in liquid crystal display devices, the separator is removed, and the remaining components of the optical laminate are attached to the liquid crystal display device, etc.

[0003] Figure 6 is a flowchart showing a general example of the steps in a conventional optical laminate manufacturing method. As shown in Figure 6, the conventional optical laminate manufacturing method includes a polarizing film manufacturing step ST1', a phase difference film bonding step ST2', a humidity adjustment step ST3', a separator bonding step ST4', an inspection step ST5', and a surface protective film bonding step ST6'. In the polarizing film manufacturing step ST1', a strip-shaped resin film is used as a preform film. While conveying the preform film along its long side, it is immersed in various processing baths to perform various treatments such as dyeing or stretching, thereby manufacturing a strip-shaped polarizing element. Then, a strip-shaped protective film is laminated onto at least one side of the strip-shaped polarizing element, thereby manufacturing a strip-shaped polarizing film. In the phase retardation film bonding step ST2', a long strip-shaped phase retardation film (1 / 2 wavelength plate or 1 / 4 wavelength plate, etc.) is bonded to one side of the long strip-shaped polarizing film to create a long strip-shaped polarizing plate.

[0004] In the humidity adjustment step ST3', humidification is performed while the long strip polarizing plate is conveyed along its long side, thereby adjusting the moisture content of the polarizing plate. In the separation component bonding step ST4', an adhesive is applied while the long strip-shaped separation component is conveyed along its long side. The applied adhesive is then heated and dried using an oven or similar appliance to harden it and form an adhesive layer. Next, the adhesive layer side of the long strip-shaped separation component (the separation component with the adhesive layer) is bonded to one side of a long strip-shaped polarizing plate, thereby creating a long strip-shaped intermediate body formed by laminating the polarizing plate, the adhesive layer, and the separation component. In inspection step ST5', with the adhesive layer between the separator and the polarizing plate remaining on the polarizing plate side, only the separator is peeled off to inspect the polarizing plate. Methods for inspecting the polarizing plate include transmission inspection, crossed polarization inspection, and reflection inspection. In inspection step ST5', after inspecting the polarizing plate, the peeled-off separator is reattached to the polarizing plate, thereby restoring the original state of the intermediate component. Furthermore, previous inspection steps ST5' were performed in a non-humidified environment, i.e., in a normal gas environment without humidification.

[0005] In the surface protective film bonding step ST6', a long strip of surface protective film is bonded to the side opposite to the side where the separator is bonded. By using the polarizing film manufacturing steps ST1' to surface protective film bonding step ST6' described above, a long strip-shaped optical laminate can be manufactured.

[0006] However, optical laminates manufactured in the above manner may experience curling (end warping) after being cut to the product size, which poses a problem for their use. For example, in Patent Document 1, a method for suppressing the curling of polarizing films is proposed, which involves specifying the material of the protective film protecting the polarizing element as a particular material. However, because the material of the protective film is limited, it is not universally applicable. A method is sought that can suppress curling without requiring significant changes to the constituent elements of conventionally used optical laminates. Previous technical documents Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2007-256568 Summary of the Invention

[0008] The problem the invention aims to solve The present invention was made to solve the problems of the prior art mentioned above, and its objective is to provide a method for manufacturing an optical laminate that can suppress curling.

[0009] The means to solve the problem To address the aforementioned issues, the inventors conducted extensive research and discovered that the reduction in moisture content of the polarizing plate in conventional optical laminate manufacturing methods may be one of the main causes of curling in the optical laminate. Specifically, we believe that, for example, in the polarizing film manufacturing step ST1', the moisture content of the polarizing plate (polarizing film) decreases because it is dried by heating in an oven or similar device after the protective film is bonded to the polarizing element. Furthermore, we believe that, for example, in the retardation film bonding step ST2', when the retardation film bonded to the polarizing film is a layer formed by polymerizing a polymeric liquid crystal, the curing heat generated during polymerization causes a reduction in the moisture content of the polarizing plate. Thus, we believe that because conventional optical laminate manufacturing methods include steps that cause a reduction in the moisture content of the polarizing plate, even if the moisture content of the polarizing plate is adjusted by the humidity adjustment step ST3', it is still impossible to maintain sufficient moisture content, resulting in curling of the optical laminate. The inventors actively investigated the main causes of the above-mentioned occurrence and found that if the polarizing plate is humidified at the time point when the separation piece formed by the material with low moisture permeability is generally peeled off, as in step ST5', the moisture content of the polarizing plate can be increased efficiently through the adhesive layer remaining on the polarizing plate, thereby suppressing the curling of the optical laminate. This invention is based on the knowledge and insights of the inventors described above.

[0010] In other words, to solve the aforementioned problems, the present invention provides a method for manufacturing an optical laminate, comprising the following steps: a separator bonding step, wherein the separator is bonded to a polarizing plate through an adhesive layer formed on the separator; and a separator peeling / bonding step, wherein after the separator bonding step, the separator is peeled from the adhesive layer and then bonded to the polarizing plate through the adhesive layer; and, in the separator peeling / bonding step, at least the peeling of the separator is performed in an environment humidified to an absolute humidity of 10 g / m³ or higher.

[0011] The separation component peeling / bonding step of this invention is not limited to the step of inspecting the polarizing plate, but also includes the step of bonding the separation component after peeling it off without inspecting the polarizing plate. Furthermore, in the separation component peeling / bonding step of this invention, the peeled separation component and the bonded separation component can be the same separation component or different new separation components. That is, the separation component peeling / bonding step of this invention includes cases where, after peeling the separation component from the adhesive layer (peeling the separation component while the adhesive layer remains on the polarizing plate), the same separation component is bonded back to the polarizing plate through the adhesive layer, and cases where a new separation component different from the peeled separation component is bonded (replaced) to the polarizing plate through the adhesive layer. According to the present invention, in the separation / bonding step, since the separation of at least the separation is carried out in an environment humidified to an absolute humidity of 10 g / m³ or higher, the moisture content of the polarizing plate can be increased efficiently, thereby suppressing the curling of the optical laminate.

[0012] Preferably, in the aforementioned separation / bonding step, at least the separation of the separation element is carried out inside the humidified frame. According to the preferred method described above, since only the inside of the frame of the separation element can be humidified (the outside of the frame may not need to be humidified), the moisture content of the polarizing plate can be increased more efficiently.

[0013] Preferably, the present invention includes a surface protective film bonding step of bonding the surface protective film to the aforementioned polarizing plate after the aforementioned separation member peeling / bonding step.

[0014] Preferably, the aforementioned separation / bonding step also serves as an inspection step for the aforementioned polarizing plate after the separation is removed. According to the preferred method described above, since the separation / bonding step also serves as the inspection step for the polarizing plate, it has the advantage of simplifying the manufacturing process compared to the case where the separation / bonding step and the inspection step are set separately.

[0015] Preferably, the aforementioned separation / bonding step is performed in an environment with a higher absolute humidity than the aforementioned separation / bonding step.

[0016] Invention Effects According to the present invention, curling can be effectively suppressed without changing the materials of the constituent elements of conventional optical laminates. Simple Explanation of the Diagram

[0017] Figure 1 is a schematic cross-sectional view showing the general structure of an optical laminate manufactured by a manufacturing method according to an embodiment of the present invention. Figure 2 is a flowchart showing the general steps of a method for manufacturing an optical laminate according to an embodiment of the present invention. Figure 3 is a schematic diagram showing an example of the general configuration of the apparatus for performing the separation / bonding step ST5 shown in Figure 2. Figure 4 is a schematic diagram showing another example of the general configuration of the apparatus for performing the separation / bonding step ST5 shown in Figure 2. Figure 5 is an explanatory diagram illustrating the evaluation method for curling. Figure 6 is a flowchart showing a general example of the steps in a conventional method for manufacturing optical laminates. Implementation

[0018] Hereinafter, with appropriate reference to the accompanying drawings, a method for manufacturing an optical laminate according to an embodiment of the present invention will be described. Furthermore, the figures are for illustrative purposes only, and it should be noted that the dimensions, scale, and shape of the constituent elements of the optical laminate or device shown in the figures may sometimes differ from the actual object.

[0019] <Composition of Optical Laminates> First, the structure of the optical laminate manufactured by the manufacturing method of this embodiment will be explained. Figure 1 is a schematic cross-sectional view showing the general structure of an optical laminate manufactured by the manufacturing method of this embodiment. As shown in Figure 1, the optical laminate 100 of this embodiment includes a polarizing film 1, a phase retardation film 2, an adhesive layer 3, a separator 4, and a surface protective film 5. The laminate of the polarizing film 1 and the phase retardation film 2 constitutes a polarizing plate 10. The laminate of the polarizing plate 10 and the adhesive layer 3 constitutes a first intermediate body M1. The laminate of the first intermediate body M1 and the separator 4 constitutes a second intermediate body M2. The constituent elements of the optical laminate 100 will be described below.

[0020] [Polarizing film 1] The polarizing film 1 is composed of a polarizing element 11 and protective films 12 and 13 protecting the polarizing element 11. In this embodiment, protective films 12 and 13 are attached to both sides of the polarizing element 11, but it is not limited to this. As long as a protective film is attached to at least one side of the polarizing element 11, it is sufficient.

[0021] (Polarizer 11) Polarizing element 11 is composed of a resin film containing a dichroic substance. The resin film can be any suitable resin film that can be used as a polarizing element. The resin film refers to a polyvinyl alcohol-based resin (hereinafter referred to as "PVA-based resin") film.

[0022] The PVA-based resin used to form the above-mentioned PVA-based resin film can be any suitable resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymers can be obtained by saponifying ethylene-vinyl acetate copolymers.

[0023] The average degree of polymerization of PVA-based resins can be appropriately selected according to the purpose. The average degree of polymerization is usually 1000~10000, preferably 1200~4500, and even more preferably 1500~4300. In addition, the average degree of polymerization can be obtained according to JIS K 6726-1994.

[0024] Examples of dichroic substances contained in resin films include iodine and organic dyes. These can be used alone or in combination of two or more. Iodine is preferred.

[0025] The resin film can be a single-layer resin film or a laminate of two or more layers.

[0026] A specific example of a polarizing element composed of a single-layer resin film can be a polarizing element for which a PVA-based resin film has undergone dyeing and stretching treatment using iodine (represented by uniaxial stretching treatment). The dyeing treatment using iodine is performed, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of uniaxial stretching is preferably 3 to 7 times. Stretching can be performed after dyeing, or it can be performed simultaneously with dyeing. Alternatively, dyeing can be performed after stretching. Depending on the requirements, the PVA-based resin film may undergo swelling treatment, crosslinking treatment, washing treatment, and drying treatment.

[0027] Specific examples of polarizing elements composed of laminates include those composed of a resin substrate and a laminate of a PVA-based resin layer (PVA-based resin film) deposited on the resin substrate, or those composed of a resin substrate and a laminate coated with a PVA-based resin layer formed on the resin substrate. A polarizing element composed of a resin substrate and a laminate coated with a PVA-based resin layer formed on the resin substrate can be manufactured, for example, by coating a PVA-based resin solution onto a resin substrate and allowing it to dry, forming a PVA-based resin layer on the resin substrate, and then, after obtaining the laminate of the resin substrate and the PVA-based resin layer, extending and dyeing the laminate to form a polarizing element from the PVA-based resin layer. In this embodiment, extending typically includes immersing the laminate in an aqueous boric acid solution and extending it. Alternatively, depending on the requirement, extending may also include air-stretching the laminate at a high temperature (e.g., above 95°C) before extending it in the aqueous boric acid solution. 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 any suitable protective layer of the desired purpose can be laminated on the peeled surface for use. Detailed description of the manufacturing method of the polarizing element is described, for example, in Japanese Patent Application Publication No. 2012-73580. This specification incorporates the entire description of that publication.

[0028] The thickness of the polarizing element 11 should preferably be less than 15μm, more preferably 1μm~12μm, even more preferably 3μm~10μm, and especially preferably 3μm~8μm.

[0029] The polarizer 11 preferably exhibits dichroism at any wavelength within the range of 380 nm to 780 nm. The transmittance of a single element of the polarizer 11 is preferably 40.0% to 45.0%, more preferably 41.5% to 43.5%. The polarization degree of the polarizer 11 is preferably 97.0% or higher, more preferably 99.0% or higher, and even more preferably 99.9% or higher.

[0030] (Protective film 12, 13) Protective films 12 and 13 are made of any suitable resin film. Examples of resin film forming materials include: (meth)acrylic resins, cellulose resins such as cellulose diacetate and cellulose triacetate, cyclic olefin resins such as norbornene resins, olefin resins such as polypropylene, ester resins such as polyethylene terephthalate resins, polyamide resins, polycarbonate resins, and copolymers thereof. Furthermore, "(meth)acrylic resins" refers to acrylic resins and / or methacrylic resins. The forming materials of protective films 12 and 13 may be the same or different. As described later, in order to increase the moisture content of the polarizing plate 10 by performing the separation / bonding step ST5 in a humidified environment, the forming material of either protective film 12 or 13 should preferably be a cellulose resin such as cellulose triacetate with high moisture permeability. The moisture permeability of the material forming either of the protective films 12 and 13 is preferably 25 g / (m 2·24 hours) to 100 g / (m 2·24 hours) when the film thickness is 1 μm, and more preferably 40 g / (m 2·24 hours) to 75 g / (m 2·24 hours) when the film thickness is 1 μm. On the other hand, the protective film 12 located on the side opposite to the adhesive layer 3 and the separator 4 of the polarizing element 11 is sometimes formed of a low moisture permeability forming material such as a cyclic olefin resin. The moisture permeability of the forming material with low moisture permeability is preferably 0.2 g / (m²·24h) to 3.4 g / (m²·24h) per μm, and preferably 0.3 g / (m²·24h) to 1.7 g / (m²·24h) per μm. Even in the case described above, in this embodiment, as described later, by peeling off the separator 4 in the separator peeling / bonding step ST5 performed in a humidified environment, the moisture content of the polarizing plate 10 can be increased through the adhesive layer 3.

[0031] The thickness of protective films 12 and 13 is typically 10μm to 100μm, preferably 10μm to 40μm, and more preferably 20μm to 40μm. The thicknesses of protective films 12 and 13 can be the same or different.

[0032] On the surfaces of the protective films 12 and 13 opposite to the polarizer 11, surface treatments such as hard coating, anti-reflective treatment, anti-sticking treatment, and anti-glare treatment may be applied as needed. Furthermore / or, on the surfaces of the protective films 12 and 13 opposite to the polarizer 11, treatments may be applied to improve visibility when viewed through polarized sunglasses (represented by treatments to impart (elliptical) polarization or to impart ultra-high phase difference). Moreover, when a surface treatment layer is formed, the thickness of the protective films 12 and 13 includes the thickness of the surface treatment layer.

[0033] Furthermore, protective films 12 and 13 are laminated onto the polarizer 11 by means of any suitable adhesive layer (not shown). Examples of adhesives constituting the adhesive layer include PVA-based adhesives or activated energy line curing adhesives.

[0034] [Phase difference film 2] The phase retardation film 2 can be, for example, a compensation plate that provides a wide viewing angle, or a phase retardation plate (circular polarizer) used together with a polarizing film to generate circularly polarized light, such as a 1 / 2 wavelength plate or a 1 / 4 wavelength plate. The thickness of the phase retardation film 2 is, for example, 1~200 μm.

[0035] Phase retardation thin film 2 is, for example, a layer formed by polymerizing a polymerizable liquid crystal or formed with resin. A polymerizable liquid crystal refers to a compound having a polymerizable group and liquid crystal properties. A polymerizable group means a group that participates in the polymerization reaction, and preferably a photopolymerizable group. Here, a photopolymerizable group refers to a group that can participate in the polymerization reaction through active free radicals or acids generated from a photopolymerization initiator. Examples of polymerizable groups include: vinyl, ethoxy, 1-chlorovinyl, isopropenyl, 4-vinylphenyl, acryloxy, methacryloxy, ethylene oxide, oxetane, etc. Among these, acryloxy, methacryloxy, ethoxy, ethylene oxide, and oxetane are preferred, with acryloxy being more suitable. The liquid crystal properties of a polymerizable liquid crystal can be thermotropic or lyotropic. If classified by degree of order, thermotropic liquid crystals can be nematic or lamellar liquid crystals. Furthermore, examples of resins forming the phase difference film 2 include: polyarylates, polyamides, polyimides, polyesters, polyaryl ether ketones, polyamide-imides, polyester-imides, polyvinyl alcohol, polyfuric acid esters, polyether tin, polytin, norbornene resins, polycarbonate resins, cellulose resins, and polyurethane. These resins can be used alone or in combination.

[0036] Furthermore, the phase retardation film 2 is laminated onto the polarizing film 1 (protective film 13) by means of any suitable adhesive layer or bonding agent layer (not shown). Examples of adhesives constituting the adhesive layer include PVA-based adhesives or activated energy line curing adhesives.

[0037] [Adhesive layer 3] The adhesive layer 3 is formed by applying adhesive to one side of the separating member 4 and drying the applied adhesive by heating it in an oven or similar means. The heating temperature of the adhesive should preferably be set in the range of 100℃ to 160℃, and more preferably in the range of 140℃ to 160℃. At this heating temperature, it is preferable to heat for 20 seconds to 3 minutes, and more preferably for 1 minute to 3 minutes.

[0038] Specific examples of adhesives forming adhesive layer 3 include: acrylic adhesives, rubber adhesives, polysiloxane adhesives, polyester adhesives, carbamate adhesives, epoxy adhesives, and polyether adhesives. By adjusting the type, quantity, combination, and blending ratio of monomers in the base resin forming the adhesive, as well as the amount of crosslinking agent, reaction temperature, and reaction time, an adhesive with desired properties can be formulated. The base resin of the adhesive can be used alone or in combination of two or more types. From the viewpoints of transparency, processability, and durability, acrylic adhesives are preferable. Detailed information about the adhesives constituting the adhesive layer is described in, for example, Japanese Patent Application Publication No. 2014-115468, which is referenced in this specification. The thickness of the adhesive layer can be set, for example, 10μm~100μm, preferably 10μm~40μm, and more preferably 10μm~30μm.

[0039] [Separable Part 4] The separator 4 can be any suitable separator. Specific examples include plastic films, non-woven fabrics, or paper coated with a release agent. Specific examples of release agents include polysiloxane-based release agents, fluorine-based release agents, and long-chain alkyl acrylate-based release agents. Specific examples of plastic films 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.

[0040] [Surface protective film 5] The surface protective film 5 represents a substrate and an adhesive layer. In this embodiment, the thickness of the surface protective film 5 is, for example, 30 μm or more. The upper limit of the thickness of the surface protective film 5 is, for example, 150 μm. Furthermore, in this specification, "the thickness of the surface protective film" refers to the combined thickness of the substrate and the adhesive layer.

[0041] The substrate can be any suitable resin film. Examples of resin film forming materials include: ester resins such as polyethylene terephthalate resins, cyclic olefin resins such as norbornene resins, olefin resins such as polypropylene resins, polyamide resins, polycarbonate resins, and copolymers thereof. Ester resins (especially polyethylene terephthalate resins) are preferred.

[0042] The adhesive used to form the adhesive layer can be any suitable adhesive. Examples of base resins for adhesives include: acrylic resins, styrene resins, polysiloxane resins, carbamate resins, and rubber resins.

[0043] <Manufacturing Method of This Embodiment> The manufacturing method of the optical laminate 100 of the present embodiment, which is used to manufacture the optical laminate 100 having the above-described structure, will be described below. Figure 2 is a flowchart showing the general steps of the manufacturing method of the optical laminate 100 of this embodiment. As shown in Figure 2, the manufacturing method of this embodiment includes a polarizing film manufacturing step ST1, a phase difference film bonding step ST2, a humidity adjustment step ST3, a separator bonding step ST4, a separator peeling / bonding step ST5, and a surface protective film bonding step ST6. Steps ST1 to ST6 will be described below.

[0044] [Polarization film manufacturing step ST1] In the polarizing film manufacturing step ST1, a strip-shaped resin film is used as a preform film. While conveying the preform film along its long side direction (MD direction), it is immersed in various processing baths to perform various treatments such as dyeing or stretching, thereby manufacturing a strip-shaped polarizing element 11. Then, strip-shaped protective films 12 and 13 are attached to the strip-shaped polarizing element 11, thereby manufacturing the strip-shaped polarizing film 1.

[0045] [Phase difference film bonding step ST2] In the phase retardation film bonding step ST2, a long strip phase retardation film 2 is bonded to one side (protective film 13) of the long strip polarizing film 1, thereby manufacturing a long strip polarizing plate 10. Furthermore, if the optical stack 100 does not have a phase difference film 2 (the polarizer 10 does not have a phase difference film 2), then the phase difference film bonding step ST2 is not required.

[0046] [Humidity Adjustment Step ST3] In humidity adjustment step ST3, humidification is performed while the long strip polarizing plate 10 is conveyed along its long side (MD direction), thereby adjusting the moisture content of the polarizing plate 10. The humidification of the polarizing plate 10 can be performed, for example, using a general-purpose electric heating humidifier. In humidity control step ST3, the temperature of the gas environment is, for example, 20~50℃, the relative humidity of the gas environment is, for example, 60~95%, and the humidification time is, for example, 1~60 minutes.

[0047] [Separated component bonding step ST4] In the separation element bonding step ST4, while conveying the elongated strip-shaped separation element 4 along its long side direction (MD direction), an adhesive is applied, and the applied adhesive is dried by heating in an oven or the like, thereby hardening it and performing an adhesive layer forming step to form the adhesive layer 3. Then, the separation element 4 is bonded to the elongated strip-shaped polarizing plate 10 through the adhesive layer 3 formed on the elongated strip-shaped separation element 4. Specifically, the adhesive layer 3 side of the elongated strip-shaped separation element 4 (the separation element 4 with the adhesive layer 3) is bonded to one side (phase difference film 2) of the elongated strip-shaped polarizing plate 10. In this way, a second intermediate body M2 is manufactured by laminating the polarizing plate 10, the adhesive layer 3, and the separation element 4.

[0048] [Separation / Lamination Step ST5] In the separation / bonding step ST5, the separation element 4 is peeled off from the adhesive layer 3 (while the adhesive layer 3 between the separation element 4 and the polarizing plate 10 remains on the polarizing plate 10 side, only the separation element 4 is peeled off), and then the separation element 4 is bonded to the polarizing plate 10 through the adhesive layer 3. In this separation / bonding step ST5, at least the peeling of the separation element 4 is carried out in an environment humidified to an absolute humidity of 10 g / m³ or higher. The humidified environment is preferably an absolute humidity of 11 g / m³ or higher, more preferably 12 g / m³ or higher, and even more preferably 13 g / m³ or higher. Specifically, at least the peeling of the separation element 4 is carried out inside the frame 20 humidified to an absolute humidity of 10 g / m³ or higher. In this embodiment, the separation / bonding step ST5 also serves as an inspection step for checking the polarizer 10 after the separation component 4 is removed. The peeling / bonding step ST5 of this embodiment will be explained in more detail below.

[0049] Figure 3 is a schematic diagram showing one example of the general configuration of the apparatus for performing the separation / bonding step ST5. Figure 3(a) is a side view (viewed from a horizontal direction orthogonal to the transport direction of each film), showing the interior of the frame 20. Figure 3(b) is a view of the frame 20 shown in Figure 3(a) in the direction of arrow X1 shown in Figure 3(a). Figure 3(c) is a view of the frame 20 shown in Figure 3(a) in the direction of arrow X2 shown in Figure 3(a). The remaining small arrows in Figure 3(a) indicate the transport direction of each film. In the separation / bonding step ST5, the second intermediate body M2, produced in the separation bonding step ST4 as described above, is wound around the release roller R1 shown in FIG3 and positioned at the upstream side of the device (the upstream side in the conveying direction of the second intermediate body M2). Then, the second intermediate body M2 delivered from the release roller R1 is conveyed toward the peeling roller R2. At the peeling roller R2, the separation part 4 is peeled off from the second intermediate body M2 (only the separation part 4 is peeled off while the adhesive layer 3 remains on the polarizing plate 10 side), and the peeled separation part 4 is conveyed toward the bonding roller R3.

[0050] On the other hand, the first intermediate M1, which is a laminate of polarizing plate 10 and adhesive layer 3 obtained by peeling off the separating member 4 from the second intermediate M2 by peeling off the peeling roller R2, is inspected by inspection device 40. The inspection device 40 shown in Figure 3 is a device for performing transmission inspection, which includes a light source 40a, a camera mechanism 40b, and a calculation mechanism (not shown). The camera mechanism 40b of the inspection device 40 receives light emitted from the light source 40a and transmitted through the first intermediate M1 to form an image, and outputs an electrical signal corresponding to the light intensity as an image signal to the calculation mechanism. The calculation mechanism generates a transmission image based on the input image signal. Then, the calculation mechanism applies well-known image processing techniques, such as binarization, to the generated transmission image to extract pixel regions whose brightness values ​​(pixel values) differ from other pixel regions, thereby detecting defects present in the first intermediate M1 (polarizing plate 10). Furthermore, the inspection performed using the separation / bonding step ST5 of this embodiment, which also serves as an inspection step, is not limited to the aforementioned transmission inspection. Orthogonal polarization inspection can also be used, which generates an orthogonal polarized image by using an inspection polarizing filter and transmitting light through the first intermediate body M1, and detects defects in the first intermediate body M1 (polarizing plate 10) based on this orthogonal polarized image. The aforementioned inspection polarizing filter is configured to be orthogonally polarized relative to the polarizing axis of the polarizing element 11 provided with the polarizing plate 10. Alternatively, reflection inspection can be used, which generates a reflected image by using light reflected from the first intermediate body M1, and detects defects in the first intermediate body M1 (polarizing plate 10) based on this reflected image. Furthermore, any combination of transmission inspection, orthogonal polarization inspection, and reflection inspection can be performed.

[0051] The first intermediate body M1, after being inspected by the inspection device 40, is conveyed to the bonding roller R3. Then, the separating element 4 is bonded back to the first intermediate body M1 by the bonding roller R3. That is, the separating element 4 is bonded to the polarizing plate 10 constituting the first intermediate body M1 through the adhesive layer 3 constituting the first intermediate body M1. In this way, the second intermediate body M2 can be manufactured and wound by the take-up roller R4. The separating element 4 of the second intermediate body M2 delivered from the release roller R1 and the separating element 4 of the second intermediate body M2 wound by the take-up roller R4 are the same separating element.

[0052] As mentioned above, in the separation / bonding step ST5 of this embodiment, at least the separation of the separation element 4 is performed inside the frame 20, which has been humidified to an absolute humidity of 10 g / m³ or higher. In the example shown in FIG3, the separation of the separation element 4 performed by the separation roller R2, the inspection performed by the inspection device 40, and the bonding of the separation element 4 performed by the bonding roller R3 are all performed inside the frame 20. Specifically, any one of the peeling roller R2, the inspection device 40, and the bonding roller R3 is disposed inside the frame 20. Then, as shown in FIG3(b), an opening 21 with a size larger than the cross-sectional size of the second intermediate body M2 is provided on the upstream side of the frame 20 (upstream side in the conveying direction of the second intermediate body M2), and the second intermediate body M2, delivered from the release roller R1 disposed outside the frame 20, is conveyed toward the peeling roller R2 through the opening 21. Also, as shown in FIG3(c), an opening 22 with a size larger than the cross-sectional size of the second intermediate body M2 is provided on the downstream side of the frame 20 (downstream side in the conveying direction of the second intermediate body M2), and the second intermediate body M2 produced by the bonding roller R3 is conveyed toward the take-up roller R4 disposed outside the frame 20 through the opening 22. If the openings 21 and 22 are too large, they may affect the humidification state inside the frame 20. Therefore, if the maximum cross-sectional size of the second intermediate body M2 or the changes in the conveying path of the second intermediate body M2 are taken into account, and the conveying of the second intermediate body M2 is not hindered, it is advisable to make them as small as possible. Then, a humidifier 30 is installed inside the frame 20, and the interior of the frame 20 is humidified to an absolute humidity of 10 g / m3 or higher by means of the humidifier 30. The humidifier 30 is not limited to this, and for example, a general commercial humidifier with electric heating can be used (such as the electric steam humidifier "UC-MG series" manufactured by UCAN Co., Ltd.).

[0053] As described above, in the separation / bonding step ST5, since the separation of the separation 4 is carried out inside the frame 20 which is humidified to an absolute humidity of 10 g / m3 or higher by the humidifier 30, the moisture content of the polarizing plate 10 can be effectively increased through the adhesive layer 3 remaining in the first intermediate body M1 after the separation of the separation 4 is removed.

[0054] In the example shown in Figure 3, the peeled-off separator 4 and the bonded separator 4 are the same separator, but the bonded separator 4 may also be a new separator that is different from the peeled-off separator 4. Hereinafter, the case where the peeled-off separator 4 and the bonded separator 4 are different in the separator peeling / bonding step ST5 will be explained. Furthermore, in the following explanation, the properly peeled-off separator 4 (the separator 4 bonded in the separator bonding step ST4) will be referred to as "separator 4a", and the new separator 4 bonded in the separator peeling / bonding step ST5 will be referred to as "separator 4b" to distinguish between the two.

[0055] Figure 4 is a schematic diagram showing another example of the general configuration of the apparatus for performing the separation / bonding step ST5. Figure 4(a) is a side view (viewed from a horizontal direction orthogonal to the transport direction of each film), showing the interior of the frame 20A. Figure 4(b) is a view of the frame 20A shown in Figure 4(a) in the direction of arrow X1 shown in Figure 4(a). Figure 4(c) is a view of the frame 20A shown in Figure 4(a) in the direction of arrow X2 shown in Figure 4(a). The remaining small arrows in Figure 4(a) indicate the transport direction of each film. In the separation peeling / bonding step ST5 using the apparatus shown in FIG4, the second intermediate body M2 produced in the separation bonding step ST4, as described above, is wound around the release roller R5 shown in FIG4 and positioned at the upstream side of the apparatus (the upstream side in the conveying direction of the second intermediate body M2). Then, the second intermediate body M2 delivered from the release roller R5 is conveyed toward the peeling roller R6. At the peeling roller R6, the separation part 4a is peeled off from the second intermediate body M2 (only the separation part 4a is peeled off while the adhesive layer 3 remains on the polarizing plate 10 side), and the peeled separation part 4a is wound up by the take-up roller R7.

[0056] On the other hand, the first intermediate body M1, which is a laminate of polarizing plate 10 and adhesive layer 3 obtained by peeling the separator 4a from the second intermediate body M2 using the peeling roller R6, is conveyed to the bonding roller R8 after being inspected using the same inspection device 40 as described above. A new separator (separator without adhesive layer 3) 4b, already wound on the release roller R9, is prepared and conveyed from the release roller R9 to the bonding roller R8. Then, the separator 4b is bonded to the first intermediate body M1 by the bonding roller R8. That is, the separator 4b is bonded to the polarizing plate 10 constituting the first intermediate body M1 through the adhesive layer 3 constituting the first intermediate body M1. In this way, the second intermediate body M2 can be manufactured and wound by the take-up roller R10. The separator 4 of the second intermediate body M2 fed out by the release roller R5 is separator 4a, but the separator 4 of the second intermediate body M2 wound by the take-up roller R10 is separator 4b.

[0057] In the separation / bonding step ST5 using the apparatus shown in Figure 4, at least the separation of separation element 4a is performed inside the frame 20A, which has been humidified to an absolute humidity of 10 g / m³ or higher. In the example shown in Figure 4, the separation of separation element 4a performed using the separation roller R6, the inspection performed using the inspection device 40, and the bonding of separation element 4b performed using the bonding roller R8 are all performed inside the frame 20A. Specifically, any one of the peeling roller R6, the inspection device 40, and the bonding roller R8 is disposed inside the frame 20A. Then, as shown in FIG4(b), an opening 21a with a size larger than the cross-sectional size of the second intermediate body M2 and an opening 21b with a size larger than the cross-sectional size of the separator 4a are provided on the upstream side of the frame 20A (upstream side of the conveying direction of the second intermediate body M2). The second intermediate body M2, delivered from the release roller R5 disposed outside the frame 20A, is conveyed to the peeling roller R6 through the opening 21a. The separator 4a, peeled off by the peeling roller R6, is conveyed to the take-up roller R7 disposed outside the frame 20A through the opening 21b. Furthermore, as shown in Figure 4(c), an opening 22a larger than the cross-sectional size of the second intermediate body M2 and an opening 22b larger than the cross-sectional size of the separator 4b are provided on the downstream side of the frame 20A (downstream of the conveying direction of the second intermediate body M2). The second intermediate body M2, produced by the bonding roller R8, is conveyed through the opening 22a toward the take-up roller R10 located outside the frame 20A. The separator 4b, delivered from the release roller R9 located outside the frame 20A, is conveyed through the opening 22b toward the bonding roller R8. If the openings 21a, 21b, 22a, and 22b are too large as required, it may affect the humidification state inside the frame 20A. Therefore, regarding openings 21a and 22a, considering the maximum cross-sectional size of the second intermediate body M2 or variations in its transport path, and without obstructing the transport of the second intermediate body M2, they should be made as small as possible. Similarly, regarding openings 21b and 22b, considering the maximum cross-sectional size of the separators 4a and 4b or variations in their transport paths, and without obstructing the transport of the separators 4a and 4b, they should be made as small as possible. Then, a humidifier 30, the same as that shown in Figure 3, is also installed inside the frame 20A. Through the humidifier 30, the interior of the frame 20A will be humidified to an absolute humidity of 10 g / m3 or higher.

[0058] In the separation / bonding step ST5 of the device shown in Figure 4, since the separation of the separation element 4a is carried out inside the frame 20A which is humidified to an absolute humidity of 10 g / m3 or higher by the humidifier 30, the moisture content of the polarizing plate 10 can be efficiently increased through the adhesive layer 3 remaining in the first intermediate body M1 after the separation of the separation element 4a is removed.

[0059] [Surface Protective Film Lamination Step ST6] In this embodiment, the surface protective film bonding step ST6 is performed after the separator peeling / bonding step ST5. In the surface protective film bonding step ST6, a strip-shaped surface protective film 5 is bonded to the strip-shaped second intermediate body M2. Specifically, the strip-shaped surface protective film 5 is bonded to the surface of the polarizing plate 10 constituting the second intermediate body M2, opposite to the side where the separator 4 is bonded. This allows the fabrication of a strip-shaped optical laminate 100.

[0060] According to the manufacturing method of this embodiment described above, in the separation / bonding step ST5, since the separation of at least the separation element 4 is carried out in an environment humidified to an absolute humidity of 10 g / m³ or higher, the moisture content of the polarizing plate 10 can be effectively increased. Therefore, without specially changing the materials of the constituent elements of the conventionally used optical laminate 100, curling can be effectively suppressed. Furthermore, in this embodiment, the separation member peeling / bonding step ST5 is described as also serving as an inspection step for the polarizing plate 10. However, the present invention is not limited to this, and the inspection step and the separation member peeling / bonding step ST5 may be performed separately. Alternatively, an embodiment in which no inspection is performed (i.e., the separation member peeling / bonding step ST5 is performed only for peeling and bonding the separation member 4) may be adopted.

[0061] Furthermore, in this embodiment, the description focuses on the implementation of each of the separation component bonding step ST4 to the surface protective film bonding step ST6 in the form of a long strip, but the present invention is not limited to this. For example, the following implementation may also be adopted: after the long strip polarizing plate 10 manufactured by the phase difference film bonding step ST2 is humidified by the humidity adjustment step ST3 and cut into the product size, the separation component bonding step ST4 to the surface protective film bonding step ST6 are performed.

[0062] Furthermore, in this embodiment, the description is based on the example of a polarizing plate 10 being a laminate of a polarizing film 1 and a phase difference film 2, but the present invention is not limited thereto. The polarizing plate 10 may also be in the following forms: a laminate of a polarizing film 1, a phase difference film 2, and other constituent elements; or a laminate of a polarizing film 1 and other constituent elements without a phase difference film 2; or a polarizing plate 10 containing only a polarizing film 1.

[0063] The following description will explain one example of the results of evaluating the curling of the optical laminate 100 and the moisture content of the second intermediate M2 produced by the manufacturing method (executive) of the present embodiment shown in FIG2, and another example of the results of evaluating the curling of the optical laminate and the moisture content of the second intermediate produced by the conventional manufacturing method (comparative example) shown in FIG6. The optical laminate 100 fabricated in the embodiment and the optical laminate fabricated in the comparative example both have a structure formed by laminating layers in the following order. (1) Surface protective film 5 (substrate: PET, thickness 38μm, adhesive layer: acrylic adhesive, thickness 10μm) (2) Cycloolefin protective film 12 with a hard coating (thickness 3μm) (total thickness 29μm) (1μm of cycloolefin protective film 12 has a moisture permeability of 0.9g / (m2·24h) (3) Adhesive (4) Polyvinyl alcohol polarizing element 11 (thickness 12μm) (5) Adhesive (6) Cellulose triacetate protective film 13 (thickness 20μm) (1μm of cellulose triacetate protective film 13 is converted to a moisture permeability of 60g / (m2·24h) (7) Adhesive (8) Polymerized liquid crystal system 1 / 2 wavelength plate 2 (thickness 2.5μm) (9) Polymerizable liquid crystal 1 / 4 wavelength plate 2 (thickness 1.5μm) (10) Acrylic adhesive layer 3 (thickness 28μm) (11) Separator 4 (PET, thickness 38μm) Furthermore, in the embodiment, the optical laminate 100 produced is formed by bonding a separator 4 identical to the peeled separator 4 to the inspected polarizing plate 10 (in the separation bonding step ST4, a new separator 4 is not replaced). The optical laminate produced in the comparative example is the same. The second intermediate M2 is the structure obtained by removing the surface protective film 5 from the optical laminate 100 of the embodiment described above. The second intermediate of the comparative example is also the same.

[0064] <Assessment of Moisture Content> In the embodiment, the moisture content of the second intermediate M2 was determined by humidifying the absolute humidity inside the frame 20 used in the separation peeling / bonding step ST5 to 13 g / m³ using a humidifier 30. Samples of predetermined sizes were cut from the strip of the second intermediate M2 before it entered the frame 20 and from the strip of the second intermediate M2 immediately after it exited the frame 20, and the absorbance of these samples was measured for evaluation. Specifically, the absorbance of each sample was measured using a Kurabo Industries Ltd. positive reflective infrared film thickness gauge "RX-200" at a temperature of 23°C ± 5°C and a relative humidity of 55% ± 10%. Furthermore, in the separation peeling / bonding step ST5, the absolute humidity outside the frame 20 was 9.5 g / m³. Also, the separation bonding step ST4, preceding the separation peeling / bonding step ST5, was performed in an environment with an absolute humidity of 9.5 g / m³. Regarding the comparative example, except that the humidifier 30 installed inside the frame 20 was stopped (creating a non-humidified environment) to set the absolute humidity inside the frame 20 to the same point as the outside of 9.5 g / m³, similarly to the embodiment, samples were cut from the second intermediate body before entering the frame 20 and the second intermediate body after exiting the frame 20, and the absorbance of these samples was measured.

[0065] Table 1 shows the absorbance measurement results of the examples and comparative examples. [Table 1] As shown in Table 1, in the comparative example, the absorbance of the second intermediate M2 did not change before entering the interior of the frame 20 and immediately after exiting it. In contrast, in the embodiment, the absorbance of the second intermediate M2 immediately after exiting the interior of the frame 20 was greater than that before entering it. Since absorbance is positively correlated with moisture content, it can be indirectly confirmed in the embodiment that the moisture content of the second intermediate M2 (polarizing plate 10) has increased.

[0066] <Evaluation of Curl> Figure 5 is an explanatory diagram illustrating the evaluation method for curling. As shown in Figure 5(a), in this embodiment, a plurality of rectangular optical laminates 100S with a product size (148 mm long × 70 mm wide) are cut along the TD direction of the long optical laminate 100. In Figure 5(a), three optical laminates 100S are shown for convenience, but in reality, ten optical laminates 100S are cut along the TD direction of one optical laminate 100. The aforementioned cutting is performed at the front and rear ends of the optical laminate 100, respectively, to obtain a total of 20 optical laminates 100S. Then, the curling of the 20 optical laminates 100S is evaluated. Furthermore, as shown in Figure 5(b), when cutting the optical laminates 100S, the cutting is performed at an angle of 45° relative to the long and short sides of the optical laminate 100S, with the MD direction of the optical laminate 100 (corresponding to the absorption axis of the polarizer 11) being perpendicular to the long and short sides of the optical laminate 100S.

[0067] As shown in Figure 5(c), during the evaluation of warping, the optical laminate 100S is placed on a flat stage 50 with the lower side of the optical laminate 100S convex (so that the warping of the four corners of the optical laminate 100S faces upward in the vertical direction). The vertical distance H from the upper surface of the stage 50 to the corner is measured for each of the four corners of the optical laminate 100S. The distance H is measured by visually reading the scale of a vertically extending scale erected near the corner of the optical laminate 100S. When the optical laminate 100S is placed on the stage 50 with its lower side convex, positive curl is considered when the side containing the separator 4 of the optical laminate 100S faces downward (and the side containing the surface protective film 5 faces upward), and the measured distance H is directly used as the curl value. On the other hand, when the optical laminate 100S is placed on the stage 50 with its lower side convex, negative curl is considered when the side containing the separator 4 of the optical laminate 100S faces upward (and the side containing the surface protective film 5 faces downward), and the value obtained by multiplying the measured distance H by -1 is directly used as the curl value.

[0068] Next, as shown in Figure 5(d), the separator 4 is peeled off from the optical laminate 100S. Then, for the laminate (the laminate of the first intermediate M1 and the surface protective film 5) after the separator 4 has been peeled off, the curl values ​​of the four corners are calculated using the same procedure as described above.

[0069] Then, the case where the curl values ​​of the four corners of the optical laminate 100S and the curl values ​​of the four corners of the laminate after peeling and separation 4 both meet the condition of -5mm ≤ curl value ≤ 5mm is considered qualified, and the case where the condition is not met is considered unqualified. For the comparative example, the curl value was calculated using the same procedure as in the embodiments described above, and it was determined to be either qualified or unqualified.

[0070] Table 2 shows the evaluation results of the curling of the embodiments and comparative examples. [Table 2] As shown in Table 2, 14 out of 20 optical laminates in the comparative example were qualified (70% pass rate), while in the embodiment, 19 out of 20 optical laminates 100S were qualified (95% pass rate), indicating that curling was suppressed.

[0071] 1:Polarizing film 2: Phase retardation thin film 3: Adhesive layer 4, 4a, 4b: Separators 5: Surface protective film 10:Polarizing plate 11:Polarizer 12, 13: Protective film 20,20A: Frame 21,21a,21b,22,22a,22b: Openings 30: Humidifier 40: Inspection device 40a: Light source 40b: Camera Structure 50: Platform 100, 100S: Optical laminates H: Distance M1: First intermediate M2: Second Intermediate TD, MD: Direction X1, X2: Arrows R1, R5, R9: Release rollers R2, R6: Stripping rollers R3, R8: Lamination rollers R4, R7, R10: Take-up rollers ST1: Polarizing Film Manufacturing Steps ST2: Phase Difference Film Lamination Steps ST3: Humidity Adjustment Steps ST4: Separator bonding steps ST5: Separator Peeling / Laying Steps ST6: Surface Protective Film Lamination Steps ST1': Polarizing film manufacturing steps ST2': Phase difference film bonding steps ST3': Humidity Adjustment Steps ST4': Separator bonding steps ST5': Inspection Steps ST6': Surface Protective Film Lamination Steps

Claims

1. A method for manufacturing an optical laminate, comprising the following steps: a separator bonding step, wherein the separator is bonded to a polarizing plate through an adhesive layer formed on the separator; and a separator peeling / bonding step, wherein after the separator bonding step, the separator is peeled from the adhesive layer and then bonded to the polarizing plate through the adhesive layer; and, in the separator peeling / bonding step, at least the peeling of the separator is performed in an environment humidified to an absolute humidity of 10 g / m³ or higher.

2. The method for manufacturing an optical laminate as claimed in claim 1, wherein in the aforementioned separation / bonding step, at least the separation of the separation is performed inside a humidified frame.

3. The method for manufacturing the optical laminate as claimed in claim 1 or 2, which includes, after the aforementioned separation / bonding step, a surface protective film bonding step of bonding the surface protective film to the aforementioned polarizing plate.

4. The method for manufacturing an optical laminate as claimed in claim 1 or 2, wherein the aforementioned separation / bonding step also serves as an inspection step for inspecting the aforementioned polarizing plate after the separation is removed.

5. The method for manufacturing an optical laminate as claimed in claim 1 or 2, wherein the aforementioned separation / bonding step is performed in an environment with a higher absolute humidity than the aforementioned separation / bonding step.

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