Manufacturing method of optical laminate

Abstract

To provide a manufacturing method of an optical laminate including a liquid crystal alignment solidification layer and capable of inhibiting a specific display unevenness when applied to an image display unit.SOLUTION: A manufacturing method of an optical laminate includes: a first lamination step of laminating a first laminate having a polarizer 11 and a first surface protective film 10, with a second laminate having a first liquid crystal alignment solidification layer 21 and a second surface protective film, interposing a first adhesion layer 12 so that the polarizer 11 and the first liquid crystal alignment solidification layer 21 face with each other, to produce a first intermediate laminate; a step of separating the second surface protective film from the first intermediate laminate to form a second intermediate laminate; and a second lamination step of laminating the second intermediate laminate with a third laminate having a second liquid crystal alignment solidification layer 31 and a third surface protective film 30, interposing a second adhesion layer 22 so that the first liquid crystal alignment solidification layer 21 and the second liquid crystal alignment solidification layer 31 face each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing an optical laminate. [Background technology]

[0002] In recent years, image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices and inorganic EL display devices), have rapidly become popular. Image display devices often use optical laminates containing retardation films (e.g., antireflection films integrating polarizing plates and retardation films). In recent years, as demand for thinner image display devices has increased, so has the demand for thinner optical laminates. To achieve thinner optical laminates, progress has been made in thinning the retardation layer (retardation film), which contributes significantly to the thickness of the optical laminate. A typical example of a thin retardation film is a film (hereinafter referred to as a liquid crystal film) in which a liquid crystal compound is oriented and the orientation state is fixed. Because liquid crystal compounds have a significantly higher birefringence (Δn) than resins, the thickness of a liquid crystal film required to achieve a desired in-plane retardation can be significantly smaller than that of a stretched resin film. However, image display devices using optical laminates containing liquid crystal films may exhibit display unevenness (specifically, a phenomenon in which a thin line with a particularly noticeable pink color is visible in the absorption axis direction of the polarizer) depending on the viewing environment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-222282 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made to solve the above-mentioned conventional problems, and its main object is to provide a method for manufacturing an optical laminate that includes a liquid crystal alignment solidified layer and that can suppress specific display unevenness when applied to an image display device. [Means for solving the problem]

[0005] [1] A method for manufacturing an optical laminate according to an embodiment of the present invention is a method for manufacturing an optical laminate having a polarizing plate and a retardation layer including a first liquid crystal alignment solidified layer and a second liquid crystal alignment solidified layer, and includes the following steps: a first lamination step of laminating a first laminate having the polarizing plate and a first surface protective film with a second laminate having the first liquid crystal alignment solidified layer and a second surface protective film through a first adhesive layer so that the polarizing plate and the first liquid crystal alignment solidified layer face each other to produce a first intermediate laminate; a step of peeling the second surface protective film from the first intermediate laminate to produce a second intermediate laminate; and a second lamination step of laminating the second intermediate laminate with a third laminate having the second liquid crystal alignment solidified layer and a third surface protective film through a second adhesive layer so that the first liquid crystal alignment solidified layer faces the second liquid crystal alignment solidified layer. At least one of the first surface protective film, the second surface protective film, and the third surface protective film comprises a substrate film and a pressure-sensitive adhesive layer. [2] The method of [1] above further includes peeling off the first surface protective film and the third surface protective film after the second laminating step. [3] In the above [1] or [2], the first adhesive layer and the second adhesive layer are made of an active energy ray-curable adhesive. [4] In any one of the above [1] to [3], at least one of the first surface protection film, the second surface protection film, and the third surface protection film contains a polyethylene terephthalate resin. [5] In any one of the above [1] to [4], at least one of the first surface protective film, the second surface protective film, and the third surface protective film has a thickness of 40 μm or more. [6] In any one of the above [1] to [5], the 90° peel strength of at least one of the first surface protection film, the second surface protection film, and the third surface protection film is 0.010 N / 15 mm or more. [7] In any one of the above [1] to [6], the bending angle of at least one of the first surface protective film, the second surface protective film, and the third surface protective film is less than 45°. [8] In any one of the above [1] to [7], the tensile load of at least one of the first surface protective film, the second surface protective film, and the third surface protective film is 20N or more and 50N or less. [Effects of the Invention]

[0006] According to an embodiment of the present invention, it is possible to realize an optical laminate that includes a liquid crystal alignment solidified layer and that can suppress specific display unevenness when applied to an image display device. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. [Figure 2A] 1 is a schematic cross-sectional view showing an example of a first laminate in one step of a method for producing an optical laminate according to one embodiment of the present invention. [Figure 2B] 2 is a schematic cross-sectional view showing an example of a second laminate in one step of a method for producing an optical laminate according to one embodiment of the present invention. FIG. [Figure 2C] 1 is a schematic cross-sectional view showing an example of a first intermediate laminate in one step of a method for producing an optical laminate according to one embodiment of the present invention. [Figure 2D] 3 is a schematic cross-sectional view showing an example of a second intermediate laminate in one step of a method for producing an optical laminate according to one embodiment of the present invention. FIG. [Figure 2E] FIG. 2 is a schematic cross-sectional view showing an example of a third laminate in one step of a method for producing an optical laminate according to one embodiment of the present invention. [Figure 2F]1 is a schematic cross-sectional view showing an example of an optical laminate produced by a method for producing an optical laminate according to one embodiment of the present invention. [Figure 2G] FIG. 2C is a schematic cross-sectional view showing an example of an optical laminate in which a surface protective film has been peeled off from the optical laminate shown in FIG. 2F. DETAILED DESCRIPTION OF THE INVENTION

[0008] Representative embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. Furthermore, in order to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part more schematically than in the embodiments, but these are merely examples and are not intended to limit the interpretation of the present invention. In this specification, "A and / or B" means either "A," "B," or "A and B."

[0009] (Definition of terms and symbols) The definitions of terms and symbols used in this specification are as follows. (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction in which the in-plane refractive index is greatest (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the plane (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. (2) In-plane phase difference (Re) "Re(λ)" is the in-plane retardation of a film measured with light of wavelength λ nm at 23°C. For example, "Re(550)" is the in-plane retardation of a film measured with light of wavelength 550 nm at 23°C. Re(λ) is calculated by the formula: Re=(nx-ny)×d, where d(nm) is the thickness of the film. (3) Retardation in the thickness direction (Rth) "Rth(λ)" is the retardation in the thickness direction of a film measured with light of wavelength λ nm at 23°C. For example, "Rth(550)" is the retardation in the thickness direction of a film measured with light of wavelength 550 nm at 23°C. Rth(λ) is calculated by the formula: Rth=(nx-nz)×d, where d (nm) is the thickness of the film. (4) Nz coefficient The Nz coefficient is calculated by Nz=Rth / Re. (5)Angle When angles are referred to herein, unless otherwise specified, the angles include angles in both clockwise and counterclockwise directions, so for example, "45°" includes ±45°.

[0010] A. Overview of the method for producing an optical laminate and the optical laminate In the manufacturing method according to the embodiment of the present invention, an optical laminate having a polarizing plate and a retardation layer including a first liquid crystal alignment solidified layer and a second liquid crystal alignment solidified layer can be manufactured. FIG. 1 is a schematic cross-sectional view of an optical laminate that can be produced by a method for producing an optical laminate according to one embodiment of the present invention. The illustrated optical laminate 5 includes a polarizing plate 11 and a retardation layer 40. The polarizing plate 11 and the retardation layer 40 are laminated via any suitable first adhesive layer 12 (e.g., an adhesive layer, a pressure-sensitive adhesive layer). The polarizing plate 11 typically includes a polarizer 111 and protective layers (a first protective layer 112 and a second protective layer 113) disposed on the main surface of the polarizer 111 (on both sides of the main surface in the illustrated example). Depending on the purpose, the first protective layer 112 and / or the second protective layer 113 may be omitted. Therefore, the polarizing plate may be a so-called double-protected polarizing plate, a so-called single-protected polarizing plate, or may be composed of a polarizer alone. In the illustrated optical laminate 5, surface protective films (a first surface protective film 10 and a third surface protective film 30) are disposed on both outermost layers, but the surface protective films may be peeled off in the optical laminate.

[0011] The retardation layer 40 includes, in order from the polarizing plate 11 side, a first liquid crystal alignment solidified layer 21 and a second liquid crystal alignment solidified layer 31 laminated on the first liquid crystal alignment solidified layer 21 via a second adhesive layer 22. By using a liquid crystal alignment solidified layer as a retardation layer, a desired in-plane retardation can be achieved with a thickness significantly thinner than that of a stretched resin film. As a result, the optical laminate can be significantly thinner. In one embodiment, the retardation layer 40 as a whole (specifically, as a laminate having the first liquid crystal alignment solidified layer 21 and the second liquid crystal alignment solidified layer 31) has a circular polarization function or an elliptically polarization function. In this specification, when the retardation layer is described simply as a "retardation layer," it refers to the retardation layer as a whole. In this specification, the "liquid crystal alignment solidified layer" refers to a layer in which liquid crystal compounds are aligned in a predetermined direction within the layer and the alignment state is fixed. The "liquid crystal alignment solidified layer" is a concept that encompasses an alignment-hardened layer obtained by hardening a liquid crystal monomer.

[0012] A method for manufacturing an optical laminate according to an embodiment of the present invention is a method for manufacturing an optical laminate having a polarizing plate and a retardation layer including a first liquid crystal alignment solidified layer and a second liquid crystal alignment solidified layer. The method includes a first lamination step of laminating a first laminate having a polarizing plate and a first surface protective film with a second laminate having a first liquid crystal alignment solidified layer and a second surface protective film via a first adhesive layer so that the polarizing plate faces the first liquid crystal alignment solidified layer to produce a first intermediate laminate; a step of peeling the second surface protective film from the first intermediate laminate to produce a second intermediate laminate; and a second lamination step of laminating the second intermediate laminate with a third laminate having the second liquid crystal alignment solidified layer and a third surface protective film via a second adhesive layer so that the first liquid crystal alignment solidified layer faces the second liquid crystal alignment solidified layer. At least one of the first surface protective film, the second surface protective film, and the third surface protective film comprises a substrate film and a pressure-sensitive adhesive layer.

[0013] In studying further thinning of an optical laminate including a liquid crystal alignment solidified layer as a retardation layer, the present inventors discovered a new problem: an image display device using an optical laminate including a liquid crystal alignment solidified layer as a retardation layer may exhibit specific display unevenness depending on the viewing environment. Specifically, the present inventors discovered that, in reflection under a three-wavelength light source, a phenomenon (sometimes referred to as linear unevenness) may occur in which a thin line with a particularly noticeable pink color in the absorption axis direction of the polarizer is visible throughout the display. As a result of extensive research into suppressing such linear unevenness, the present inventors discovered that linear unevenness can be suppressed by suppressing light interference in the optical laminate. In addition, the inventors investigated the cause of light interference in the optical laminate and found that unevenness in the thickness of the retardation layer including the adhesive layer can occur during the manufacturing process. Furthermore, they found that suppressing this unevenness in thickness can significantly suppress the above-mentioned linear unevenness, leading to the completion of the present invention. That is, such an effect of the embodiment of the present invention solves a newly discovered problem when considering further thinning of an optical laminate including a liquid crystal alignment solidified layer as a retardation layer, and is an unexpected and excellent effect. It goes without saying that the embodiment of the present invention can suppress the display unevenness that has been recognized in the past.

[0014] The reason why the optical laminate obtained by the manufacturing method according to the embodiment of the present invention exhibits the above-mentioned remarkable effects is not necessarily clear, but the following mechanism can be inferred. However, this mechanism is merely inferred and does not limit the present invention, nor does it restrict the present invention by this mechanism.

[0015] In the method for producing an optical laminate according to an embodiment of the present invention, the first laminate and the second laminate laminated in the first lamination step each have a surface protective film (a first surface protective film and a second surface protective film). Furthermore, the second intermediate laminate and the third laminate laminated in the second lamination step each have a surface protective film (a first surface protective film and a third surface protective film). That is, the first intermediate laminate produced in the first lamination step has a surface protective film lined on both sides of its outermost layer, and the laminate produced in the second lamination step has a surface protective film lined on both sides of its outermost layer. Furthermore, the lined surface protective film (i.e., at least one of the first surface protective film, the second surface protective film, and the third surface protective film) includes a base film and a pressure-sensitive adhesive layer. Because the laminates (the first laminate and the second laminate, and the second intermediate laminate and the third laminate) are each lined with a surface protective film before lamination, it is believed that the surface protective film reduces the effect of curing shrinkage of the adhesive layer, even if the adhesive layer is cured after lamination. In other words, by backing each laminate used for lamination with a surface protective film, even if the first adhesive layer used to prepare the first intermediate laminate undergoes cure shrinkage upon curing, shrinkage accompanying the cure of the first adhesive layer of the polarizing plate (particularly the polarizer). Furthermore, even if the second adhesive layer used to laminate the second intermediate laminate and the third laminate undergoes cure shrinkage, shrinkage accompanying the cure of the second adhesive layer of the polarizing plate (particularly the polarizer) and the retardation layer (the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer) is thought to be suppressed. As a result, when the adhesive layer cures, cure shrinkage of the entire optical stack (particularly the entire structure including the polarizing plate and the retardation layer) is suppressed, and thickness unevenness is thought to be suppressed. Therefore, in the method for producing an optical stack according to an embodiment of the present invention, thickness unevenness between the retardation layers of the optical stack is suppressed, and as a result, display unevenness (linear unevenness) due to light interference is thought to be suppressed even when the optical stack is applied to an image display device.

[0016] B. Details of the manufacturing method of the optical laminate Hereinafter, the method for producing an optical laminate according to an embodiment of the present invention will be described in more detail. 2A to 2G are schematic cross-sectional views for explaining the process steps of a method for producing an optical laminate according to one embodiment of the present invention. Each step of the method for producing an optical laminate will be described in detail below with reference to FIGS. 2A to 2G. Note that FIG. 2F is the same as FIG. 1.

[0017] B-1. First lamination process The first lamination step is a step of laminating a first laminate 1 (see FIG. 2A) and a second laminate 2 (see FIG. 2B). Specifically, in the first lamination step, a first laminate 1 having a polarizing plate 11 and a first surface protective film 10 is laminated with a second laminate 2 having a first liquid crystal alignment solidified layer 21 and a second surface protective film 20 via a first adhesive layer 22, with the polarizing plate 11 and the first liquid crystal alignment solidified layer 21 facing each other. This results in a first intermediate laminate 100 (see FIG. 2C). In the example shown in FIG. 2B, the second laminate 2 includes a first substrate 221 for forming the first liquid crystal alignment solidified layer 21. The first substrate 221 can typically be peeled off and removed in the end. Specifically, the first substrate 221 can be peeled off simultaneously with or after peeling off the second surface protective film during the production of a second intermediate laminate, which will be described later.

[0018] The first lamination step preferably includes conveying a long first laminate and a long second laminate using rolls. More preferably, it includes laminating the first laminate and the second laminate using lamination rolls. In this manner, a long first intermediate laminate can be produced. The long first intermediate laminate can be wound into a roll. In this specification, "long" means an elongated shape in which the length is sufficiently longer than the width, and includes, for example, an elongated shape in which the length is 10 times or more, preferably 20 times or more, the width.

[0019] B-1-1. Preparation of the first laminate As shown in Fig. 2A, a first laminate 1 having a polarizing plate 11 and a first surface protective film 10 is prepared. The first laminate 1 can be produced, for example, by preparing a polarizing plate 11 and arranging a surface protective film (first surface protective film 10) on the polarizing plate 11. Any appropriate method can be used to arrange the first surface protective film on the polarizing plate.

[0020] B-1-1-1. Polarizing plate B-1-1-1-1.Polarizer The polarizer 111 is typically made of a polyvinyl alcohol (PVA) resin film containing a dichroic material (e.g., iodine). Examples of PVA resins include polyvinyl alcohol, partially formalized polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and partially saponified ethylene-vinyl acetate copolymer.

[0021] The PVA resin preferably contains an acetoacetyl-modified PVA resin. With this configuration, a polarizer having desired mechanical strength can be obtained. The amount of the acetoacetyl-modified PVA resin is preferably 5% by weight to 20% by weight, and more preferably 8% by weight to 12% by weight, based on 100% by weight of the entire PVA resin. If the amount is within this range, a polarizer having better mechanical strength can be obtained.

[0022] The polarizer preferably contains iodide or sodium chloride (sometimes collectively referred to as a halide). Examples of iodides include potassium iodide, sodium iodide, and lithium iodide. The content of the halide in the polarizer is preferably 5 to 20 parts by weight, more preferably 10 to 15 parts by weight, relative to 100 parts by weight of the PVA-based resin. In the manufacturing method described below, the halide is blended into a coating liquid that forms a PVA-based resin layer, which is a precursor of the polarizer, and can be finally introduced into the polarizer. Introducing a halide into the polarizer can improve the orientation of PVA molecules in the polarizer, thereby achieving a polarizer with excellent optical properties (typically, both a high degree of polarization and a high single-unit transmittance).

[0023] The polarizer preferably exhibits absorptive dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is preferably 41.0% to 46.0%, more preferably 42.0% to 45.0%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more. According to an embodiment of the present invention, even if the single transmittance is within the above range, the degree of polarization can be maintained within this range.

[0024] The thickness of the polarizer is, for example, 12 μm or less, preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 7 μm or less. Meanwhile, the thickness of the polarizer is, for example, 1 μm or more, preferably 3 μm or more. By combining such a thin polarizer with a liquid crystal alignment solidified layer, the optical laminate can be significantly thinner. Furthermore, if the thickness of the polarizer is within the above range, curling during heating can be effectively suppressed.

[0025] The polarizer can be produced by any appropriate method. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

[0026] Specific examples of polarizers made of a single-layer resin film include hydrophilic polymer films such as PVA films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films that have been dyed with iodine or a dichroic substance such as a dichroic dye and stretched, and polyene-based oriented films such as dehydrated PVA films and dehydrochlorinated polyvinyl chloride films. A polarizer obtained by dyeing a PVA film with iodine and uniaxially stretching it is preferred because of its excellent optical properties.

[0027] The dyeing with iodine is carried out, for example, by immersing the PVA film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be carried out after the dyeing treatment or while dyeing. Alternatively, the PVA film may be stretched and then dyed. If necessary, the PVA film may be subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, or the like. For example, by immersing the PVA film in water and washing it before dyeing, it is possible to wash away dirt and antiblocking agents on the surface of the PVA film, and also to swell the PVA film, thereby preventing uneven dyeing.

[0028] Specific examples of polarizers obtained using 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 obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and drying the resin substrate to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer; and then stretching and dyeing the laminate to convert the PVA-based resin layer into a polarizer. In this embodiment, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is preferably formed on one side of the resin substrate. Stretching typically involves immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, stretching may optionally further include in-air stretching of the laminate at an elevated temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. Additionally, in this embodiment, the laminate is preferably subjected to a drying shrinkage treatment by heating while being transported in the longitudinal direction, thereby shrinking the laminate by 2% or more in the width direction. Typically, the manufacturing method of this embodiment includes subjecting the laminate to an auxiliary in-air stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment, in this order. By introducing auxiliary stretching, it is possible to increase the crystallinity of PVA, even when PVA is coated on a thermoplastic resin, thereby achieving high optical properties. Furthermore, by simultaneously increasing the orientation of PVA in advance, problems such as a decrease in orientation or dissolution of PVA when immersed in water in the subsequent dyeing or stretching steps can be prevented, thereby achieving high optical properties. Furthermore, when the PVA-based resin layer is immersed in a liquid, the disordering of the orientation of polyvinyl alcohol molecules and the decrease in orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of a polarizer obtained through treatment steps in which the laminate is immersed in a liquid, such as a dyeing treatment and an underwater stretching treatment. Furthermore, the optical properties can be improved by shrinking the laminate in the width direction through the drying shrinkage treatment.

[0029] B-1-1-1-2.Protective layer When the polarizing plate includes a protective layer, the protective layer may include a first protective layer and / or a second protective layer. The first protective layer and the second protective layer may have the same structure or different structures. The protective layer is composed of any appropriate resin film. Typical materials for the resin film include cellulose-based resins such as triacetyl cellulose (TAC), cycloolefin-based resins such as polynorbornene, (meth)acrylic resins, polyester-based resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefin-based resins such as polyethylene, and polycarbonate-based resins. Typical examples of (meth)acrylic resins include (meth)acrylic resins having a lactone ring structure. Examples of (meth)acrylic resins having a lactone ring structure are described in, for example, JP 2000-230016 A, JP 2001-151814 A, JP 2002-120326 A, JP 2002-254544 A, and JP 2005-146084 A. These publications are incorporated herein by reference. The material for the resin film is preferably a cellulose-based resin, more preferably TAC. From the viewpoint of obtaining a polarizing plate having low moisture permeability and excellent durability, cycloolefin resins and (meth)acrylic resins are preferred.

[0030] The optical laminate is typically disposed on the viewing side of an image display device, and the first protective layer 112 is typically disposed on the viewing side. Therefore, the first protective layer 112 may be subjected to a surface treatment as needed. Examples of surface treatments include hard coating, anti-reflection, anti-sticking, and anti-glare treatments. Additionally / alternatively, the first protective layer 112 may be subjected to a treatment to improve visibility when viewed through polarized sunglasses (typically, by providing an (elliptical) polarization function or an ultra-high phase difference). By performing such a treatment, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses. Therefore, the optical laminate may be suitably applied to image display devices that can be used outdoors.

[0031] The thickness of the protective layer is preferably 10 μm to 80 μm, more preferably 12 μm to 40 μm, and even more preferably 15 μm to 35 μm. If first protective layer 112 has been subjected to a surface treatment, the thickness of first protective layer 112 includes the thickness of the surface treatment layer.

[0032] B-1-1-1-3. Preparation of polarizing plates The polarizing plate can be produced, for example, as follows. In the case of a polarizer obtained using a single-layer resin film, a polarizing plate can be produced, for example, by bonding a protective layer to the polarizer via any appropriate adhesive layer (adhesive layer, pressure-sensitive adhesive layer). A polarizer obtained using a resin substrate / polarizer laminate can be produced, for example, by bonding a protective layer to the polarizer side of the resin substrate / polarizer of the laminate via any appropriate adhesive layer (adhesive layer, pressure-sensitive adhesive layer). If necessary, the resin substrate may be peeled from the laminate, and if necessary, another protective layer may be bonded to the surface from which the resin substrate has been peeled. Alternatively, the laminate may be produced as a polarizing plate by using the resin substrate as a protective layer. Details of the methods for producing such polarizers and polarizing plates are described, for example, in JP 2012-73580 A and Japanese Patent No. 6470455 A. The entire disclosures of these publications are incorporated herein by reference.

[0033] B-1-1-2. First surface protection film Next, the first surface protective film 10 is placed on the polarizing plate 11. The first surface protective film 10 is, for example, temporarily attached to the polarizing plate 11 in a releasable manner. Specifically, the first surface protective film 10 includes a base film and a pressure-sensitive adhesive layer (not shown), and the first surface protective film 10 and the polarizing plate 11 are bonded together via the pressure-sensitive adhesive layer. This allows a first laminate to be obtained (see FIG. 2A).

[0034] In the method for producing an optical laminate according to an embodiment of the present invention, the first surface protective film and the second and third surface protective films described below may be the same. Therefore, when describing the surface protective film in this specification, simply referring to the "surface protective film" means that the first surface protective film, the second surface protective film, and the third surface protective film are collectively described.

[0035] As the surface protection film, any appropriate surface protection film used for the purpose of protecting the surface of an optical film such as a polarizing plate or a retardation layer (film) can be used. Specifically, in the method for producing an optical laminate of this embodiment, the surface protection film can include a substrate film and a pressure-sensitive adhesive layer provided on the substrate film. As a result, in the method for producing an optical laminate of this embodiment, the surface protection film can have suitable mechanical properties. As a result, this can contribute to achieving the remarkable effects of the embodiment of the present invention.

[0036] The substrate film may be made of any suitable resin film. Examples of materials for forming the resin film include olefin resins such as polyethylene resins, ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. The surface protection film preferably contains a polyethylene terephthalate resin as the substrate film. In this case, when the first laminate and the second laminate are laminated via the first adhesive layer in the first lamination step, the cure shrinkage of the adhesive layer (first adhesive layer) can be particularly effectively suppressed. For example, the substrate film preferably has substantially no self-adhesiveness.

[0037] The thickness of the substrate film is preferably 10 μm to 100 μm, and more preferably 20 μm to 50 μm.

[0038] The tensile modulus of the base film is preferably 1.0×10 8 Pa ~ 5.0 × 10 9 Pa, more preferably 2.0×108 Pa ~ 3.0 × 10 9 The tensile modulus is Pa. The tensile modulus of the base film can be measured in accordance with JIS K 7161. The measurement conditions can be, for example, room temperature (about 23°C ± 5°C) and humidity of 50% ± 10%. In this specification, the tensile modulus of the surface protection film refers to the tensile modulus of the base film.

[0039] Any appropriate adhesive may be used as the adhesive forming the adhesive layer. Examples of base resins for adhesives include (meth)acrylic resins, styrene resins, and silicone resins. Examples of crosslinking agents that may be contained in the adhesive include isocyanate compounds, epoxy compounds, and aziridine compounds. The adhesive may also contain, for example, a silane coupling agent. The formulation of the adhesive may be appropriately set depending on the purpose.

[0040] The thickness of the pressure-sensitive adhesive layer may be, for example, 1 μm to 60 μm, and preferably 3 μm to 30 μm.

[0041] The thickness of the surface protection film is preferably 35 μm or more, more preferably 40 μm or more, and even more preferably 42 μm or more. The upper limit of the thickness of the surface protection film may be, for example, 100 μm. The thickness of the surface protection film refers to the total thickness of the base film and the pressure-sensitive adhesive layer. When the thickness is within this range, the overall cure shrinkage during production of the optical laminate can be particularly reduced.

[0042] The 90° peel strength of the surface protection film is preferably 0.010 N / 15 mm or more, more preferably 0.050 N / 15 mm or more, and even more preferably 0.10 N / 15 mm or more. Within this range, the overall cure shrinkage during production of the optical laminate can be particularly reduced. The upper limit of the 90° peel strength of the surface protection film is not particularly limited and can be, for example, 0.5 N / 15 mm. The 90° peel strength of the surface protection film can be measured by the method described in "(2-3) Peel Strength (90° Peel Force)" in the Examples below.

[0043] The bending angle of the surface protection film is preferably less than 45°. Within this range, the overall cure shrinkage during production of the optical laminate can be particularly reduced. The bending angle of the surface protection film can be measured as follows: A sample of the surface protection film having dimensions of 100 mm in length, 50 mm in width, and 30 μm to 50 μm in thickness is prepared. The sample is placed on a flat surface such as a desk so that 50% (or 50 mm) of its length protrudes into the air. The angle at which the protruding portion bends relative to the vertical direction is measured, and this angle is defined as the "bending angle of the surface protection film."

[0044] The tensile load of the surface protective film is preferably 20 N or more, more preferably 25 N or more, and even more preferably 30 N or more. On the other hand, the tensile load of the surface protective film is preferably 50 N or less, more preferably 45 N or less. Within this range, the overall cure shrinkage during the production of the optical laminate can be particularly reduced. The tensile load of the surface protective film refers to the minimum load required when a surface protective film having dimensions of 100 mm in length and 50 mm in width is stretched by +50% in the length direction while applying a certain tensile stress. Specifically, the tensile load of the surface protective film can be confirmed by measuring the tensile stress by stretching a surface protective film having dimensions of 100 mm in length and 50 mm in width by +50% in the length direction while applying a predetermined load using an autograph (precision universal testing machine). Details of the measurement method are as described in the examples below.

[0045] As long as the effects of the present invention are not impaired, the first surface protective film, the second surface protective film, and the third surface protective film may all be the same type of surface protective film, or may be different types of surface protective films, or two may be the same type of surface protective film and one may be a different type of surface protective film. Preferably, the first surface protective film, the second surface protective film, and the third surface protective film are all the same type of surface protective film.

[0046] B-1-2. Preparation of the second laminate 2B, the second laminate 2 can be produced by bonding a second surface protective film 20 to the first substrate 221 side of the first liquid crystal alignment solidified layer 21. As shown in FIG. 2C, the second laminate 2 is used to produce a first intermediate laminate 100.

[0047] B-1-2-1. Formation of the first liquid crystal alignment solidified layer In the method for manufacturing an optical laminate according to an embodiment of the present invention, the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer described later may be the same. Therefore, when the liquid crystal alignment solidified layer is described in this specification, simply referring to it as the "liquid crystal alignment solidified layer" means that the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer are described collectively.

[0048] The liquid crystal alignment solidified layer may be formed on, for example, any appropriate substrate. As shown in FIG. 2B, the first liquid crystal alignment solidified layer 21 may be formed on a first substrate 221. Specifically, the first liquid crystal alignment solidified layer 21 may be formed by performing an alignment treatment on the surface of the first substrate 221, applying a coating liquid containing a liquid crystal compound to the surface, aligning the liquid crystal compound in a direction corresponding to the alignment treatment, and fixing the alignment state. In one embodiment, the substrate is any appropriate resin film. Preferably, a triacetyl cellulose (TAC) film is used.

[0049] By using a liquid crystal compound, the difference between nx and ny of the resulting liquid crystal alignment solidified layer can be made significantly larger than that of a non-liquid crystal material, and the thickness of the liquid crystal alignment solidified layer required to obtain the desired in-plane retardation can be made significantly smaller. As a result, the optical laminate can be made thinner and lighter. In this embodiment, typically, rod-shaped liquid crystal compounds are aligned in the slow axis direction of the liquid crystal alignment solidified layer (homogeneous alignment).

[0050] Any appropriate alignment treatment can be adopted as the alignment treatment. Specific examples include mechanical alignment treatment, physical alignment treatment, and chemical alignment treatment. Specific examples of mechanical alignment treatment include rubbing treatment and stretching treatment. Specific examples of physical alignment treatment include magnetic field alignment treatment and electric field alignment treatment. Specific examples of chemical alignment treatment include oblique deposition and photoalignment treatment. Any appropriate treatment conditions can be adopted for the various alignment treatments depending on the purpose.

[0051] The alignment of the liquid crystal compound is achieved by treating the liquid crystal compound at a temperature at which the liquid crystal compound exhibits liquid crystallinity depending on the type of liquid crystal compound. By performing such temperature treatment, the liquid crystal compound assumes a liquid crystal state and is aligned in accordance with the alignment treatment direction of the substrate surface.

[0052] In one embodiment, the alignment state is fixed by cooling the liquid crystal compound aligned as described above. When the liquid crystal compound is a polymerizable monomer or a crosslinkable monomer, the alignment state is fixed by subjecting the liquid crystal compound aligned as described above to a polymerization treatment or a crosslinking treatment.

[0053] Specific examples of liquid crystal compounds and details of the method for forming the alignment solidified layer are described in JP-A-2006-163343, the disclosure of which is incorporated herein by reference.

[0054] When the liquid crystal compound is a liquid crystal monomer, the liquid crystal monomer is preferably a polymerizable monomer and a crosslinkable monomer. This is because the orientation state of the liquid crystal monomer can be fixed by polymerizing or crosslinking (i.e., curing) the liquid crystal monomer. After the liquid crystal monomer is aligned, for example, the alignment state can be fixed by polymerizing or crosslinking the liquid crystal monomers with each other. Here, a polymer is formed by polymerization, and a three-dimensional network structure is formed by crosslinking, but these are non-liquid crystals. Therefore, the formed liquid crystal alignment solidified layer does not undergo, for example, a transition to a liquid crystal phase, a glass phase, or a crystalline phase due to temperature changes, which is specific to liquid crystal compounds. As a result, the liquid crystal alignment solidified layer is not affected by temperature changes and has excellent stability.

[0055] Examples of liquid crystal compounds used in the liquid crystal alignment solidified layer include liquid crystal polymers and liquid crystal monomers. The liquid crystal compound is preferably polymerizable (i.e., a liquid crystal monomer). If the liquid crystal compound is polymerizable, the alignment state of the liquid crystal compound can be fixed by aligning the liquid crystal compound and then polymerizing it. Here, the polymer formed by polymerization is non-liquid crystal. Therefore, the formed liquid crystal alignment solidified layer does not undergo, for example, a transition to a liquid crystal phase, glass phase, or crystalline phase due to temperature changes, which is unique to liquid crystal compounds. As a result, the liquid crystal alignment solidified layer becomes a retardation layer that is not affected by temperature changes and has extremely excellent stability.

[0056] In one embodiment, the liquid crystal alignment solidified layer can be formed using a composition containing a polymerizable liquid crystal compound (polymerizable liquid crystal compound, i.e., liquid crystal monomer). In this specification, the polymerizable liquid crystal compound contained in the composition refers to a compound having a polymerizable group and liquid crystallinity. The polymerizable group refers to a group that participates in a polymerization reaction, preferably a photopolymerizable group. Here, the photopolymerizable group refers to a group that can participate in a polymerization reaction by an active radical or acid generated from a photopolymerization initiator. Examples of liquid crystal monomers that can be used include polymerizable mesogen compounds described in JP-A-2002-533742 (WO 00 / 37585), EP 358208 (US Pat. No. 5,211,877), EP 66137 (US Pat. No. 4,388,453), WO 93 / 22397, EP 0261712, DE 19504224, DE 4408171, and GB 2280445. Specific examples of such polymerizable mesogenic compounds include LC242 (trade name) from BASF, E7 (trade name) from Merck, and LC-Sillicon-CC3767 (trade name) from Wacker-Chem.

[0057] The mechanism by which the liquid crystal compound exhibits liquid crystallinity may be thermotropic or lyotropic. The liquid crystal phase may be nematic or smectic. From the viewpoint of ease of production, the liquid crystallinity is preferably thermotropic nematic liquid crystal.

[0058] The temperature range in which the liquid crystal monomer exhibits liquid crystallinity varies depending on the type of the liquid crystal monomer, and specifically, the temperature range is preferably 40°C to 120°C, more preferably 50°C to 100°C, and most preferably 60°C to 90°C.

[0059] The birefringence Δn of the liquid crystal alignment solidified layer is preferably 0.06 or more, more preferably 0.08 or more, even more preferably 0.09 or more, and particularly preferably 0.10 or more. The upper limit of Δn may be, for example, 0.13, or may be, for example, 0.12. If Δn is within this range, the desired in-plane retardation can be achieved with a very thin thickness. As a result, the liquid crystal alignment solidified layer and the optical laminate can be made even thinner, which can ultimately contribute to significantly thinner image display devices.

[0060] The liquid crystal alignment solidified layer may exhibit a reverse wavelength dispersion characteristic in which the retardation value increases with the wavelength of the measurement light, a positive wavelength dispersion characteristic in which the retardation value decreases with the wavelength of the measurement light, or a flat wavelength dispersion characteristic in which the retardation value hardly changes with the wavelength of the measurement light. In one embodiment, the liquid crystal alignment solidified layer exhibits a positive wavelength dispersion characteristic. In such cases, the effects of the present invention are remarkable.

[0061] In one embodiment, the Re(550) of the first liquid crystal alignment solidified layer is preferably 150 nm to 300 nm, more preferably 200 nm to 270 nm, and even more preferably 220 nm to 260 nm. In this case, the Re(550) of the second liquid crystal alignment solidified layer (described later) is preferably 100 nm to 200 nm, more preferably 110 nm to 160 nm, and even more preferably 110 nm to 130 nm. In this case, both the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer have in-plane retardation and therefore exhibit a refractive index characteristic of nx>ny. The first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer typically exhibit a refractive index characteristic of nx>ny=nz (positive A plate). Here, "ny=nz" encompasses not only the case where ny and nz are strictly equal, but also the case where ny and nz are substantially equal. That is, the Nz coefficients of the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer may each be 0.9 to 1.1.

[0062] The thickness of the first liquid crystal alignment solidified layer can be adjusted to obtain the desired in-plane retardation. In one embodiment, the thickness of the first liquid crystal alignment solidified layer can be, for example, 1.5 μm to 2.5 μm. As described above, according to an embodiment of the present invention, the thickness of the first liquid crystal alignment solidified layer can be made thinner than conventional layers, while further suppressing linear unevenness. The thickness of the second liquid crystal alignment solidified layer can also be adjusted to obtain the desired in-plane retardation. Specifically, the thickness can be, for example, 0.8 μm to 1.5 μm.

[0063] The angle between the slow axis of the first liquid crystal alignment solidified layer and the transmission axis of the polarizer is preferably 10° to 20°, more preferably 12° to 18°, and even more preferably 14° to 16°. In this case, the angle between the slow axis of the second liquid crystal alignment solidified layer and the transmission axis of the polarizer is preferably 70° to 80°, more preferably 72° to 78°, and even more preferably 74° to 76°. The direction of the slow axis of the first liquid crystal alignment solidified layer can be controlled by the above-mentioned alignment treatment. The angle between the slow axis of the first liquid crystal alignment solidified layer and the transmission axis of the polarizer and the angle between the slow axis of the second liquid crystal alignment solidified layer and the transmission axis of the polarizer may be reversed.

[0064] B-1-2-2. Second surface protection film The second surface protective film 20 can be disposed on the first liquid crystal alignment solidified layer 21 in the same manner as the first surface protective film 10 is disposed on the polarizing plate 11 in the above-described first laminate 1. Specifically, the second surface protective film 20 is temporarily and releasably attached to the side of the first liquid crystal alignment solidified layer 21 opposite to the side facing the polarizing plate 11 of the first laminate 1 (the side of the first substrate 221 in the illustrated example). In this way, the second laminate 2 can be obtained (see FIG. 2B). The second surface protection film 20 includes a base film and a pressure-sensitive adhesive layer (not shown), and any appropriate surface protection film can be used. As described above, the explanation for the first surface protection film in Section B-1-1-2 above can be applied to the second surface protection film.

[0065] B-1-3. Formation of the first adhesive layer Next, as shown in Fig. 2C, the first laminate 1 and the second laminate 2 are laminated together via a first adhesive layer 12. This produces a first intermediate laminate 100. The first adhesive layer can be formed by disposing or applying any appropriate pressure-sensitive adhesive or adhesive. Any appropriate configuration may be adopted for the first adhesive layer 12. As described above, the adhesive layer may be made of a pressure-sensitive adhesive or an adhesive.

[0066] The first adhesive layer is preferably made of an adhesive, more preferably an active energy ray curable adhesive, and in this case, the thickness of the adhesive layer is preferably 0.4 μm to 2.0 μm, more preferably 0.6 μm to 1.5 μm.

[0067] When laminating the first laminate and the second laminate using lamination rolls, it is preferable to supply an active energy ray-curable adhesive to at least one of the side of the first laminate opposite the first surface protective film (e.g., the polarizing plate side) and the side of the second laminate opposite the second surface protective film (e.g., the first liquid crystal alignment solidified layer side) while transporting the first laminate and the second laminate with the rolls, and then laminate them with the lamination rolls. In other words, in forming the first adhesive layer, it is preferable to supply an active energy ray-curable adhesive to the side of the first laminate that faces the polarizing plate and the first liquid crystal alignment solidified layer of the second laminate while transporting the first laminate and the second laminate with the rolls. The active energy ray-curable adhesive can be supplied by any appropriate method. For example, while transporting the first laminate and the second laminate, the active energy ray-curable adhesive is applied to the side of the polarizing plate opposite the first surface protective film and / or the side of the first liquid crystal alignment solidified layer opposite the second surface protective film. In this manner, a second laminate intermediate may be produced.

[0068] B-1-4. Hardening of the first adhesive layer When the first adhesive layer is composed of an active energy ray-curable adhesive, the first lamination step may preferably be followed by a curing step (hereinafter, sometimes referred to as a "first adhesive layer curing step") of curing the first adhesive layer. Specifically, in the first adhesive layer curing step, the first laminate and the second laminate are bonded together with the first adhesive layer interposed therebetween, and then the first adhesive layer is cured. More preferably, the first adhesive layer is cured before the second surface protective film is peeled off. In this case, by lining both surfaces of the outermost layer of the first intermediate laminate with surface protective films (first surface protective film 10 and second surface protective film 20 in the first intermediate laminate 100 shown in FIG. 2C), even if the first adhesive layer used to prepare the first intermediate laminate shrinks upon curing, shrinkage of the polarizing plate (particularly the polarizer) accompanying the curing of the first adhesive layer can be suppressed. Therefore, cure shrinkage of the entire first intermediate laminate can be suppressed. As a result, when a first intermediate laminate having a backed surface protective film is used to produce an optical laminate, it can contribute to further suppressing the curing shrinkage of the optical laminate as a whole, and when the optical laminate is applied to an image display device, it can significantly suppress display unevenness (linear unevenness) due to light interference.

[0069] The first adhesive layer can be cured by any appropriate method depending on the type and composition of the adhesive constituting the first adhesive layer. When the first adhesive layer is composed of an active energy ray-curable adhesive, the first adhesive layer can be cured preferably by irradiating it with active energy rays. The first adhesive layer curing step does not necessarily have to be performed after the first lamination step, and may be cured together with the second adhesive layer, for example, after the second lamination step described below. Furthermore, the first adhesive layer may be cured, for example, in the first lamination step.

[0070] In curing the first adhesive layer, preferably, a long first laminate and a long second laminate are roll-transported while being bonded together with the first adhesive layer interposed therebetween, and then the bonded first intermediate laminate is roll-transported while being cured by irradiating the first adhesive layer with active energy rays.

[0071] B-2. Preparation of second intermediate laminate Next, as shown in FIG. 2D , the second surface protective film 20 is peeled off from the first intermediate laminate 100. This allows the second intermediate laminate 200 to be produced. In this case, if the first substrate 221 is present, it is preferable to also peel off the first substrate 221. By peeling the second surface protective film 20 off from the first intermediate laminate 100, the second intermediate laminate 200 can be obtained in which the surface of the first liquid crystal alignment solidified layer 21 opposite to the first adhesive layer 12 is exposed. The second intermediate laminate 200 can be subjected to lamination with the third laminate 3.

[0072] B-3.Second lamination process The second lamination step is a step of laminating the second intermediate laminate 200 (see FIG. 2D) and the third laminate 3 (see FIG. 2E). Specifically, in the second lamination step, the second intermediate laminate 200 and the third laminate 3 are bonded together via the second adhesive layer 22 so that the first liquid crystal alignment solidified layer 21 and the second liquid crystal alignment solidified layer 31 face each other. This results in a laminate in which the second intermediate laminate and the third laminate are laminated (see FIG. 2F). In the example shown in FIG. 2E, the third laminate 3 includes a second substrate 331 for forming the second liquid crystal alignment solidified layer 31. The second substrate 331 can typically be peeled off and removed in the end. Specifically, it can be peeled off, for example, during the production of an image display device, which will be described later.

[0073] The second lamination step preferably includes conveying the long second intermediate laminate and the long second liquid crystal alignment solidified layer with rolls, and more preferably includes laminating the second intermediate laminate and the second liquid crystal alignment solidified layer with lamination rolls.

[0074] B-3-1. Preparation of the third laminate The third laminate can be produced, for example, by bonding a third surface protective film 30 to the second substrate 331 side of the second liquid crystal alignment solidified layer 31, as shown in Fig. 2E. The third laminate can be produced in the same manner as the second laminate. Therefore, the description of the second laminate in Section B-1-2 can be used to produce the third laminate.

[0075] B-3-1-1. Second liquid crystal alignment solidification layer Regarding the second liquid crystal alignment solidified layer, if the second liquid crystal alignment solidified layer has the same structure as the first liquid crystal alignment solidified layer (positive A plate), the explanation in the above section B-1-2-1 can be applied. Below, an example will be described in which the second liquid crystal alignment solidified layer is a positive C plate.

[0076] The refractive index characteristics of a positive C plate exhibit the relationship nz>nx=ny, for example. The thickness direction retardation Rth(550) of the positive C plate is preferably -20 nm to -300 nm, more preferably -30 nm to -250 nm, even more preferably -40 nm to -200 nm, and particularly preferably -50 nm to -150 nm. Here, "nx=ny" encompasses not only the case where nx and ny are strictly equal, but also the case where nx and ny are substantially equal. In other words, the in-plane retardation Re(550) of the positive C plate can be less than 10 nm.

[0077] The positive C plate can be formed, for example, using a composition containing a side-chain thermotropic liquid crystal polymer. As the side-chain thermotropic liquid crystal polymer, a copolymer having a liquid crystalline monomer unit represented by general formula (I) and a non-liquid crystalline monomer unit represented by general formula (II) is preferably used. [ka] [ka]

[0078] In formula (I), R 1 is a hydrogen atom or a methyl group, and R 2 is a cyano group, a fluoro group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms, and X 1 is —CO 2 — or —OCO—. a is an integer of 1 to 6, and b and c are each independently 1 or 2.

[0079] In formula (II), R 3is a hydrogen atom or a methyl group, and R 4 is an alkyl group having 7 to 22 carbon atoms, a fluoroalkyl group having 1 to 22 carbon atoms, or a group represented by the following general formula (III). [ka]

[0080] In formula (III), R 5 is an alkyl group having 1 to 5 carbon atoms, and d is an integer of 1 to 6.

[0081] The positive C plate can be produced, for example, by preparing a coating solution containing the side-chain thermotropic liquid crystal polymer, applying the coating solution to a substrate (e.g., a PET substrate) that has been subjected to a vertical alignment treatment by any appropriate method, and then heating and drying the coating solution under any appropriate heating conditions to align the liquid crystals to form a liquid crystal layer. The liquid crystal layer can be cured by irradiating it with ultraviolet light, thereby producing a laminate having a substrate / second liquid crystal alignment solidified layer (positive C plate) configuration.

[0082] Specific examples of methods for forming a positive C plate include the methods described in paragraphs

[0020] to

[0028] of Japanese Patent Application Laid-Open No. 2002-333642. In this case, the thickness of the positive C plate is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, and even more preferably 0.5 μm to 5 μm.

[0083] B-3-1-2. Third surface protection film The third surface protective film 30 can be disposed on the second liquid crystal alignment solidified layer 31 in the same manner as the first surface protective film 10 is disposed on the polarizing plate 11 in the first laminate 1. Specifically, the third surface protective film 30 is temporarily and releasably attached to the side of the second liquid crystal alignment solidified layer 31 opposite to the side facing the first liquid crystal alignment solidified layer 21 of the second intermediate laminate 200 (the side facing the second substrate 331 in the illustrated example). This allows the third laminate 3 to be obtained (see FIG. 2E). The third surface protection film 30 includes a base film and a pressure-sensitive adhesive layer (not shown), and any appropriate surface protection film can be used. As described above, the explanation for the first surface protection film in Section B-1-1-2 above can be applied to the third surface protection film.

[0084] B-3-2.Second adhesive layer 2F, the second intermediate laminate 200 and the third laminate 3 are laminated together via the second adhesive layer 22. The second adhesive layer 22 can be formed by disposing or applying any appropriate pressure-sensitive adhesive or adhesive. Any appropriate configuration may be adopted for the second adhesive layer 22. As described above, the adhesive layer may be made of a pressure-sensitive adhesive or an adhesive.

[0085] The second adhesive layer is preferably made of an active energy ray-curable adhesive. When the second adhesive layer is made of an active energy ray-curable adhesive, the effects of the present invention become more pronounced. The description of the first adhesive layer in Section B-1-3 can be used to explain the configuration of the second adhesive layer and the method for forming the second adhesive layer.

[0086] As in the first lamination step, it is also preferable to supply an active energy ray-curable adhesive to at least one of the side of the second intermediate laminate opposite to the first surface protective film (e.g., the side of the first liquid crystal alignment solidified layer) and the side of the third laminate opposite to the third surface protective film (e.g., the side of the second liquid crystal alignment solidified layer) while transporting the second intermediate laminate and the third laminate with rolls, and then laminate them using lamination rolls. In other words, in forming the second adhesive layer, it is preferable to supply an active energy ray-curable adhesive to the side where the first liquid crystal alignment solidified layer of the second intermediate laminate and the second liquid crystal alignment solidified layer of the third laminate face each other while transporting the second intermediate laminate and the third laminate with rolls.

[0087] B-4. Hardening of the second adhesive layer When the second adhesive layer is formed of an active energy ray-curable adhesive, the method preferably includes a curing step of curing the second adhesive layer (hereinafter also referred to as a second adhesive layer curing step). Specifically, in the second adhesive layer curing step, the second intermediate laminate 200 and the third laminate 3 are bonded together with the second adhesive layer 22 interposed therebetween, and then the second adhesive layer is cured. In this case, by lining both surfaces of the outermost layer of the laminate of the second intermediate laminate and the third laminate with surface protective films (first surface protective film 10 and third surface protective film 30 in FIG. 2F), even if the second adhesive layer used to prepare the laminate of the second intermediate laminate and the third laminate shrinks upon curing, shrinkage of the polarizing plate (particularly the polarizer) and the retardation layer (first liquid crystal alignment solidified layer and second liquid crystal alignment solidified layer) accompanying the curing of the second adhesive layer can be suppressed. As a result, when a laminate having a backed surface protective film is used to produce an optical laminate, it can contribute to further suppressing the curing shrinkage of the optical laminate as a whole, and even when the optical laminate is applied to an image display device, display unevenness (linear unevenness) due to light interference can be significantly suppressed.

[0088] In curing the second adhesive layer, preferably, the long second intermediate laminate and the long third laminate are roll-transported while being bonded together with the second adhesive layer interposed therebetween, and then the bonded laminate is roll-transported while being irradiated with active energy rays to cure the second adhesive layer.

[0089] In this way, the optical laminate according to the embodiment of the present invention can be manufactured. Even when the optical laminate manufactured in this way is applied to an image display device, since the laminate (including the intermediate laminate) used in the manufacturing process of the optical laminate has a surface protective film backed, the curing shrinkage of the first adhesive layer and the second adhesive layer, as well as the curing shrinkage of the entire optical laminate, can be suppressed, and display unevenness (linear unevenness) due to light interference in the optical laminate can be suppressed.

[0090] B-5. Surface protection film peeling process As shown in Figure 2G, the manufacturing method of one embodiment of the present invention may further include peeling off the first surface protective film and the third surface protective film after the second lamination step (also referred to as a surface protective film peeling step). After the surface protective film peeling step, an optical laminate 50 may be obtained. When an active energy ray-curable adhesive is used for the second adhesive layer, the manufacturing method may further include peeling off the first surface protective film and the third surface protective film after the second curing step.

[0091] The optical laminate obtained may be in a long shape or in a sheet-like shape. A long optical laminate can be wound into a roll. A long optical laminate can be produced, for example, by the so-called roll-to-roll process as described above. A sheet-like optical laminate may be produced by cutting a long optical laminate into a predetermined size (typically, a size corresponding to an image display device), or by cutting each of the long laminates (first laminate, second laminate, third laminate, first intermediate laminate, and second intermediate laminate) described above into a predetermined size and then bonding them together using the procedure described above.

[0092] The obtained optical laminate can be placed on an image display panel or the like, with, for example, an adhesive layer interposed between the optical laminate and the viewing side (specifically, the side from which the third surface protective film has been peeled off), to produce an image display device. [Example]

[0093] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Measurement and evaluation methods in the examples are as follows. Unless otherwise specified, "parts" and "%" in the examples are by weight.

[0094] (1) Thickness The thickness was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., "MCPD9800"). (2) Physical properties of surface protection film (2-1) Thickness As in (1) above, the thickness was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., "MCPD9800"). (2-2) Tensile modulus The tensile modulus of the surface protection film was measured by preparing a sample of the surface protection film having dimensions of 100 mm in length and 10 mm in width (the thickness is the thickness measured in (2-1) above; the same applies to (2-3) to (2-5) below). The sample was measured in accordance with JIS K 7161 using a tensile testing device (a precision universal testing machine autograph manufactured by Shimadzu Corporation) under conditions of a temperature of 23°C and a humidity of 50%. (2-3) Peel strength (90° peel force) First, a surface protection film sample measuring 100 mm in length and 15 mm in width was prepared. The sample was attached to a SUS plate (120 mm in length, 50 mm in width, 2.0 mm in thickness) using adhesive tape (double-sided tape). The sample was attached using a hand roller. Next, the sample was peeled using a variable angle peel tester at a peel angle of 90°, a peel rate of 1000 mm / min, and a measurement distance of 80 mm. The measured value obtained was taken as the peel strength (90° peel force). (2-4) Bending angle A sample of surface protection film measuring 100 mm in length and 50 mm in width was prepared and placed on a flat surface of a desk so that 50% (or 50 mm) of the sample's length protruded into the air. The angle at which the protruding portion bent relative to the vertical direction was measured. The angle obtained by the measurement was defined as the "bending angle of the surface protection film." (2-5) Tensile load The tensile load of the surface protection film was measured by preparing a sample of the surface protection film having dimensions of 100 mm in length and 10 mm in width, and using an autograph (precision universal testing machine) to measure the load when the sample reached a length of 150 mm in the longitudinal direction (the length obtained by stretching the original length of 100 mm in the longitudinal direction by 50%), and the lowest load among these was recorded as the tensile load. (3) Linear unevenness The image display devices obtained in the examples and comparative examples were visually observed under a three-band fluorescent lamp in a non-illuminated state, and evaluated according to the following criteria. 1 (Excellent): No linear irregularities were observed even when observing with a polarizing plate attached to a three-wavelength fluorescent lamp 2 (Good): No linear irregularities were observed under normal observation using a three-wavelength fluorescent lamp 3 (Acceptable): Slight linear irregularities were observed under normal observation with a three-wavelength fluorescent lamp. 4 (Unacceptable): Linear unevenness that is practically unacceptable was observed during normal observation using a three-wavelength fluorescent lamp. 5 (poor): Linear irregularities were evident during normal observation under a three-wavelength fluorescent lamp.

[0095] [Production Example 1: Preparation of Adhesive A1 Constituting the First Adhesive Layer and the Second Adhesive Layer] Hydroxyethyl acrylamide (trade name "HEAA", manufactured by KJ Chemicals Co., Ltd.) 10 parts, 2-acetoacetoxyethyl methacrylate (trade name "AAEM", manufactured by Mitsubishi Chemicals Corporation) 4 parts, acryloylmorpholine (trade name "ACMO", manufactured by KJ Chemicals Co., Ltd.) 60 parts, tripropylene glycol diacrylate (trade name "Aronix M-220", manufactured by Toagosei Co., Ltd.) 11 parts, 4-vinylphenylboronic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) 1 part, acrylic oligomer (trade name "ARUFON UP-1190", manufactured by Toagosei Co., Ltd.) 10 parts, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (trade name "Omnirad 819", manufactured by IGM Resins BV) 1 part, 1-hydroxycyclohexyl phenyl ketone (trade name "Omnirad 184", manufactured by IGM Resins BV) Two parts of ethylene glycol distearate (manufactured by BV Co., Ltd.) and one part of diethylthioxanthone (trade name "KAYACURE DETX-S", manufactured by Nippon Kayaku Co., Ltd.) were stirred at 50°C for one hour to prepare adhesive A1.

[0096] [Example 1] 1. Preparation of optical laminate 1-1. Preparation of the first laminate 1-1-1. Preparation of polarizer A long, amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a Tg of about 75° C. was used as the thermoplastic resin substrate, and one side of the resin substrate was subjected to a corona treatment. A PVA aqueous solution (coating solution) was prepared by dissolving 100 parts by weight of a PVA-based resin made by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFFIMER") in a 9:1 ratio, to which 13 parts by weight of potassium iodide was added, in water. The above PVA aqueous solution was applied to the corona treated surface of the resin substrate and dried at 60° C. to form a PVA resin layer with a thickness of 13 μm, thereby producing a laminate. The resulting laminate was uniaxially stretched 2.4 times in the machine direction (longitudinal direction) in an oven at 130°C (auxiliary in-air stretching treatment). Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubilizing treatment). Next, the film was immersed in a dye bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) at a liquid temperature of 30°C for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer would be a desired value (dyeing treatment). Next, the sample was immersed in a crosslinking bath (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (crosslinking treatment). The laminate was then immersed in a boric acid aqueous solution (boric acid concentration 4 wt %, potassium iodide concentration 5 wt %) at a liquid temperature of 70°C and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to a total stretch ratio of 5.5 times (underwater stretching treatment). Thereafter, the laminate was immersed in a cleaning bath (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (cleaning treatment). Thereafter, the film was dried in an oven maintained at about 90°C, and brought into contact with a heated roll made of SUS whose surface temperature was maintained at about 75°C (drying shrinkage treatment). In this way, a polarizer with a thickness of approximately 5 μm was formed on the resin substrate, and a long polarizing plate having a resin substrate / polarizer configuration was obtained. The polarizer had a single transmittance Ts of 43.3%. The polarizer had an absorption axis in the longitudinal direction. Hereinafter, the absorption axis direction (longitudinal direction) will be referred to as the "0° direction," and the transmission axis direction (width direction) will be referred to as the "90° direction."

[0097] 1-1-2. Preparation of polarizing plate (PL1) An HC-COP film was attached to the surface of the obtained polarizer (the surface opposite to the resin substrate) via a UV-curable adhesive. The HC-COP film was a cycloolefin resin (COP) film (thickness: 25 μm) with an HC layer (thickness: 4 μm) formed on it, and the COP film was attached so that it faced the polarizer. The COP film had an Re(550) of 100 nm. The HC-COP film was attached so that the angle between the slow axis of the COP film and the absorption axis of the polarizer was 45°. Next, the resin substrate was peeled off, and a triacetyl cellulose (TAC) film (thickness: 20 μm) was attached to the peeled surface via a UV-curable adhesive, thus obtaining a long polarizing plate PL1 having a structure of HC layer / COP film (first protective layer) / polarizer / TAC film (second protective layer).

[0098] 1-1-3. Lamination of the first surface protection film A surface protective film 1 (E-MASK RP109F, manufactured by Nitto Denko Corporation) was peelably laminated on the side of the polarizing plate opposite the second protective layer as a first surface protective film. The first surface protective film was laminated on the polarizing plate by a roll-to-roll process. This resulted in a long first laminate. The properties of Surface Protection Film 1 are shown in Table 1. In this way, a first laminate having a structure of first surface protective film / polarizing plate PL1 was obtained.

[0099] 1-2. Preparation of the second laminate 1-2-1. Preparation of the first liquid crystal alignment layer (LC1) A photopolymerizable liquid crystal compound exhibiting a nematic liquid crystal phase (BASF "Paliocolor LC242"; chemical formula shown below) was dissolved in cyclopentanone to prepare a solution with a solids concentration of 30% by weight. A surfactant (BYK-Chemie "BYK-360") and a photopolymerization initiator (IGM Resins "Omnirad907") were added to the solution to prepare a liquid crystal composition solution. The surfactant and polymerization initiator were added in amounts of 0.01 and 3 parts by weight, respectively, per 100 parts by weight of the photopolymerizable liquid crystal compound. A commercially available triacetyl cellulose (TAC) film (Fujifilm, thickness: 80 μm) was prepared as a substrate. The liquid crystal composition was applied to the substrate using a bar coater to achieve an Re(550) of 120 nm and heated at 100°C for 3 minutes to align the liquid crystal. After cooling to room temperature, the film was exposed to an integrated light dose of 400 mJ / cm under a nitrogen atmosphere. 2 The resulting laminate was then exposed to ultraviolet light for photo-curing, yielding a long laminate having a substrate / first liquid crystal alignment solidified layer LC1. The first liquid crystal alignment solidified layer was homogeneously aligned and had a thickness of 1.5 μm. [ka]

[0100] 1-2-2. Temporarily attaching the second surface protection film A surface protection film 1 (E-MASK RP109F, manufactured by Nitto Denko Corporation) was peelably laminated as a second surface protection film on the side opposite to the first liquid crystal solidified layer LC1 of the long laminate having a substrate / first liquid crystal alignment solidified layer LC1 structure. The second surface protection film was laminated using a roll-to-roll process. This resulted in a long second laminate having a structure of first liquid crystal alignment solidified layer LC1 / substrate (TAC film) / second surface protection film.

[0101] 1-3. Preparation of the third laminate 1-3-1. Preparation of the second liquid crystal alignment layer (LC2) A long laminate having a substrate / second liquid crystal alignment solidified layer LC2 structure was obtained in the same manner as the first liquid crystal alignment solidified layer, except that the coating thickness was changed so that Re(550) was 240 nm. The thickness of the second liquid crystal alignment solidified layer was 2.0 μm.

[0102] 1-3-2. Temporarily attaching the third surface protection film A surface protection film 1 (E-MASK RP109F, manufactured by Nitto Denko Corporation) was peelably laminated as a third surface protection film on the side opposite to the second liquid crystal alignment solidified layer LC2 of the long laminate having the second liquid crystal alignment solidified layer LC2. The third surface protection film was laminated by a roll-to-roll process. This resulted in a long third laminate.

[0103] 1-4.First lamination process While the long-shaped first laminate and long-shaped second laminate prepared above were each transported with a roll, adhesive A1 of Production Example 1 was applied to the second protective layer (TAC film) of the first laminate and the first liquid crystal alignment solidified layer of the second laminate, respectively, so that the thickness of the first adhesive layer after curing would be 1.0 μm. Then, using a lamination roll, the polarizing plate (specifically, the second protective layer on the opposite side of the first surface protective film) and the first liquid crystal alignment solidified layer were laminated via the first adhesive layer so that they faced each other. This produced a first intermediate laminate comprising the first surface protective film / polarizing plate (first protective layer / polarizer / second protective layer) / first adhesive layer / first liquid crystal alignment solidified layer / substrate / second surface protective film.

[0104] Next, while conveying the first intermediate laminate, ultraviolet light (integrated light amount 600 mJ / cm 2 ) to cure the first adhesive layer.

[0105] 1-5. Second intermediate laminate Next, the second surface protective film was peeled off from the first intermediate laminate with the first adhesive layer cured, to produce a long second intermediate laminate having a structure of first surface protective film / polarizer (first protective layer / polarizer / second protective layer) / first adhesive layer / first liquid crystal alignment solidified layer / substrate. The lamination and peeling were performed using a roll-to-roll process.

[0106] 1-6.Second lamination process First, the substrate (TAC film) of the first liquid crystal alignment solidified layer in the second intermediate laminate was peeled off. Next, while the second intermediate laminate from which the substrate had been peeled off and the long third laminate were transported using rolls, adhesive A1 from Production Example 1 was applied to the first liquid crystal alignment solidified layer of the second intermediate laminate and the second liquid crystal alignment solidified layer of the third laminate, respectively, so that the thickness of the second adhesive layer after curing would be 1.0 μm. Using a lamination roll, the first liquid crystal alignment solidified layer and the second liquid crystal alignment solidified layer were laminated via the second adhesive layer so that they faced each other. This produced a laminate comprising: first surface protective film / polarizer (first protective layer / polarizer / second protective layer) / first adhesive layer / first liquid crystal alignment solidified layer / second adhesive layer / second liquid crystal alignment solidified layer / substrate / third surface protective film.

[0107] 1-7. Formation and curing of the second adhesive layer Next, while conveying the laminate, ultraviolet light (integrated light amount 600 mJ / cm 2 ) to photocure the second adhesive layer. This resulted in an optical laminate with a surface protective film. In the optical laminate with the surface protective film, the first liquid crystal alignment solidified layer was homogeneously aligned and had a thickness of 1.5 μm. The slow axis direction of the first liquid crystal alignment solidified layer was in the 15° direction. The thickness of the second liquid crystal alignment solidified layer was 2.0 μm. The slow axis direction of the second liquid crystal alignment solidified layer was in the 75° direction.

[0108] 2. Fabrication of Image Display Device The first surface protective film and the third surface protective film were peeled off from the optical laminate with the surface protective films obtained above. Next, the cover glass and the optical film on the viewing side of a commercially available liquid crystal display device (manufactured by Apple Inc., product name "iPad (registered trademark)", IPS mode) were removed, and the removed surface was cleaned.The second liquid crystal alignment solidified layer side of the optical laminate obtained above was then bonded to the cleaned surface via an acrylic adhesive (thickness 10 μm), thereby obtaining an image display device.The obtained image display device was subjected to the evaluation of the above-mentioned (3) "linear unevenness".The results are shown in Table 1.

[0109] [Example 2, Comparative Examples 1 and 2] An optical laminate and an image display device were produced in the same manner as in Example 1, except that the first surface protective film, the second surface protective film, and the third surface protective film were changed to those shown in Table 1. The obtained image display device was subjected to the same evaluations as in Example 1. The results are shown in Table 1. The materials shown in the "Surface protection film" column in Table 1 are as follows.

[0110] (Surface protection film) Surface protection film 1: Product name "RP109F" manufactured by Nitto Denko Corporation (Film composition resin: polyethylene terephthalate resin. Adhesive layer composition: acrylic resin.) Surface protection film 2: Nitto Denko product name "HP300" (film composition resin: polyethylene terephthalate resin. Adhesive layer composition: acrylic resin.) Surface protection film 3: Toray Industries, Inc. product name "7832C" (film composition resin: polyethylene resin. Self-adhesive). Surface protection film 4: Toray Industries, product name "A521" (film composition resin: polyethylene resin. Self-adhesive).

[0111] [Table 1] [Industrial Applicability]

[0112] The optical laminate according to the embodiment of the present invention can be suitably used in image display devices (typically, liquid crystal display devices and organic EL display devices). [Explanation of symbols]

[0113] 1 First laminate 10 First surface protection film 11 Polarizing plate 111 Polarizer 112 Protective layer (1st protective layer) 113 Protective layer (second protective layer) 12 First adhesive layer 2 Second laminate 20 Second surface protection film 21 First liquid crystal alignment solidification layer 221 Base material (1st base material) 100 First intermediate laminate 200 Second intermediate laminate 22 Second adhesive layer 3 Third laminate 30 Third surface protection film 31 Second liquid crystal alignment solidification layer 331 Base material (second base material) 40 Retardation layer 5 Optical laminate 50 Optical laminate

Claims

1. A method for producing an optical laminate having a polarizing plate and a retardation layer including a first liquid crystal alignment solidified layer and a second liquid crystal alignment solidified layer, a first lamination step of laminating a first laminate having a polarizing plate and a first surface protective film and a second laminate having a first liquid crystal alignment solidified layer and a second surface protective film via a first adhesive layer so that the polarizing plate and the first liquid crystal alignment solidified layer face each other, thereby producing a first intermediate laminate; peeling the second surface protective film from the first intermediate laminate to obtain a second intermediate laminate; a second lamination step of laminating the second intermediate laminate and a third laminate having a second liquid crystal alignment solidified layer and a third surface protective film via a second adhesive layer so that the first liquid crystal alignment solidified layer faces the second liquid crystal alignment solidified layer; Including, At least one of the first surface protective film, the second surface protective film, and the third surface protective film includes a base film and a pressure-sensitive adhesive layer. A method for producing an optical laminate.

2. The method for producing an optical laminate according to claim 1 , further comprising peeling off the first surface protective film and the third surface protective film after the second lamination step.

3. The method for producing an optical laminate according to claim 1 , wherein the first adhesive layer and the second adhesive layer are made of an active energy ray-curable adhesive.

4. The method for producing an optical laminate according to claim 1 or 2, wherein at least one of the first surface protective film, the second surface protective film, and the third surface protective film contains a polyethylene terephthalate resin.

5. 3. The optical laminate according to claim 1, wherein at least one of the first surface protective film, the second surface protective film, and the third surface protective film has a thickness of 40 μm or more.

6. The method for producing an optical laminate according to claim 1 or 2, wherein the 90° peel strength of at least one of the first surface protective film, the second surface protective film, and the third surface protective film is 0.010 N / 15 mm or more.

7. The method for producing an optical laminate according to claim 1 or 2, wherein the bending angle of at least one of the first surface protective film, the second surface protective film, and the third surface protective film is less than 45°.

8. The method for producing an optical laminate according to claim 1 or 2, wherein a tensile load of at least one of the first surface protective film, the second surface protective film, and the third surface protective film is 20 N or more and 50 N or less.

Images