Optical laminate and manufacturing method of optical laminate

Abstract

To provide an optical laminate capable of preventing a rupture and separating a second protective layer, and to provide a manufacturing method of the optical laminate.SOLUTION: An optical laminate includes: a polarizer; a first protective layer bonded to the polarizer interposing a first aqueous adhesive layer; and a second protective layer arranged on an opposite side to the first protective layer with regard to the polarizer, and bonded to the polarizer interposing a second aqueous adhesive layer. Thickness of each of the first aqueous adhesive layer and the second aqueous adhesive layer is 0.01 μm to 0.20 μm, inclusive. A peel force of the second protective layer to the second aqueous adhesive layer is 0.05 (N / 15 mm) to 1.0 (N / 15 mm), inclusive.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] It is known that polarizers are used in 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). Typically, a substrate (protective layer) for protecting the surface of the polarizer is attached to the polarizer via an adhesive layer. In recent years, the applications of image display devices have become more diverse, and there is a demand for thinner image display devices. In such cases, a laminate including a polarizer and a substrate is also required to be thinner, and a single-sided thin polarizing plate in which a substrate is attached to only one side of a polarizer may be adopted (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-124566 A Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for further thinning of laminates including such polarizers and substrates. Accordingly, studies have been conducted to reduce the thickness of the adhesive layer by using a water-based adhesive. However, when a substrate is attached to one side of a polarizer using a water-based adhesive to produce a laminate in which a substrate is provided on only one side, the edges of the single-sided thin polarizing plate may curl when the water-based adhesive is heated and dried (solidified and / or cured), which may result in breakage of the single-sided thin polarizing plate. The present invention has been made to solve the above-mentioned problems of the prior art, and a main object of the present invention is to provide an optical laminate that can suppress breakage and from which the second protective layer can be peeled off. [Means for solving the problem]

[0005] [1] An optical laminate according to an embodiment of the present invention includes a polarizer, a first protective layer, and a second protective layer. The first protective layer is bonded to the polarizer via a first aqueous adhesive layer. The second protective layer is disposed on the opposite side of the polarizer from the first protective layer. The second protective layer is bonded to the polarizer via a second aqueous adhesive layer. The thicknesses of the first aqueous adhesive layer and the second aqueous adhesive layer are each 0.01 μm or more and 0.20 μm or less. The peel strength of the second protective layer from the second aqueous adhesive layer is 0.05 (N / 15 mm) or more and 1.0 (N / 15 mm) or less. [2] In the optical laminate described in [1] above, the second protective layer may be a non-saponified triacetyl cellulose film. [3] A method for producing an optical laminate according to another aspect of the present invention includes the steps of attaching a first protective layer to one surface of a polarizer via a first aqueous adhesive layer, and attaching a second protective layer to the other surface of the polarizer via a second aqueous adhesive layer, wherein the thicknesses of the first aqueous adhesive layer and the second aqueous adhesive layer are each 0.01 μm or more and 0.20 μm or less, and the peel force of the second protective layer from the second aqueous adhesive layer is 0.05 (N / 15 mm) or more and 1.0 (N / 15 mm) or less. [4] The method for producing an optical laminate described in [3] above may further include the steps of: performing a saponification treatment on an alkyl ester group-containing film to prepare a first protective layer; and preparing the alkyl ester group-containing film as a second protective layer. [5] In the method for producing an optical laminate according to [4] above, in the step of preparing the second protective layer, the alkyl ester group-containing film may be washed with water and then heated and dried. [6] In the method for manufacturing an optical laminate described in any one of [3] to [5] above, the step of attaching a first protective layer to one surface of the polarizer and the step of attaching a second protective layer to the other surface of the polarizer may be carried out simultaneously. [Effects of the Invention]

[0006] According to the embodiments of the present invention, it is possible to realize an optical laminate that can suppress breakage and from which the second protective layer can be peeled. [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 2] FIG. 2 is a schematic cross-sectional view of an optical laminate according to another embodiment of the present invention. 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. In addition, in order to clarify the explanation, the width, thickness, shape, etc. of each part may be shown schematically in the drawings compared to the embodiments, but these are merely examples and do not limit the interpretation of the present invention.

[0009] A. Overall structure of the optical laminate FIG. 1 is a schematic cross-sectional view of an optical laminate according to one embodiment of the present invention. The illustrated optical laminate 1 includes a polarizer 2, a first protective layer 3, and a second protective layer 4. The first protective layer 3 is bonded to the polarizer 2 via a first aqueous adhesive layer 51. The second protective layer 4 is disposed on the opposite side of the polarizer 2 from the first protective layer 3. The second protective layer 4 is bonded to the polarizer 2 via a second aqueous adhesive layer 52. That is, the optical laminate 1 includes, in this order, the first protective layer 3, the first aqueous adhesive layer 51, the polarizer 2, the second aqueous adhesive layer 52, and the second protective layer 4. The thickness of each of the first aqueous adhesive layer 51 and the second aqueous adhesive layer 52 is 0.20 μm or less, preferably 0.15 μm or less, and more preferably 0.10 μm or less. The lower limit of the thickness of each of the first aqueous adhesive layer 51 and the second aqueous adhesive layer 52 is 0.01 μm. The peel strength of the second protective layer 4 from the second aqueous adhesive layer 52 is 1.0 (N / 15 mm) or less, preferably 0.8 (N / 15 mm) or less, and more preferably 0.5 (N / 15 mm) or less. The lower limit of the peel strength of the second protective layer 4 from the second aqueous adhesive layer 52 is 0.05 (N / 15 mm). The peel strength can be measured, for example, using a tensile tester in accordance with JIS K6854-1. According to this configuration, the first protective layer is attached to one surface of the polarizer via the first aqueous adhesive layer, and the second protective layer is attached to the other surface of the polarizer via the second aqueous adhesive layer, which can prevent the end of the optical laminate from curling, thereby preventing poor appearance of the optical laminate and preventing breakage of the optical laminate due to curling of the end of the optical laminate. Furthermore, since the thicknesses of the first aqueous adhesive layer and the second aqueous adhesive layer are each equal to or less than the upper limit, the optical laminate can be made thinner. Furthermore, since the peel strength of the second protective layer with respect to the second aqueous adhesive layer is equal to or less than the upper limit, when a thinner optical laminate is required depending on the application, the second protective layer can be smoothly peeled from the polarizer. After peeling the second protective layer, at least a portion of the second aqueous adhesive layer remains on the surface of the polarizer. Therefore, the remaining second aqueous adhesive layer can protect the surface of the polarizer.

[0010] In one embodiment, a first surface treatment layer 6 is provided on the surface of the first protective layer 3. The first surface treatment layer 6 is located on the opposite side of the first protective layer 3 from the polarizer 2. Any appropriate first surface treatment layer 6 is adopted depending on the application of the optical laminate 1. Examples of the first surface treatment layer 6 include a hard coat layer, an anti-reflection layer, an anti-sticking layer, a diffusion layer, and an anti-glare layer. In one embodiment, the first surface treatment layer 6 is a hard coat layer. The thickness of the first surface treatment layer 6 is, for example, 1 μm or more, preferably 3 μm or more, and for example, 20 μm or less, preferably 10 μm or less.

[0011] In one embodiment, a surface protective film 7 is attached to the surface of the second protective layer 4. The surface protective film 7 is located on the opposite side of the second protective layer 4 from the polarizer 2. When the optical laminate has a long shape, the optical laminate is typically stored rolled up on a shaft. In this case, if a surface protective film is attached to the second protective layer, blocking between the second protective layer and the first protective layer can be suppressed.

[0012] 2, a second surface treatment layer 8 is provided on the surface of the second protective layer 4. The second surface treatment layer 8 is located on the opposite side of the second protective layer 4 from the polarizer 2. When the second surface treatment layer is provided, blocking between the second protective layer and the first protective layer can be suppressed when the long optical laminate is wound. Any appropriate second surface treatment layer 8 is adopted depending on the application of the optical laminate 1. Examples of the second surface treatment layer 8 include an anti-glare layer and an anti-sticking layer. In one embodiment, the second surface treatment layer 8 is an anti-glare layer. The thickness of the second surface treatment layer 8 is, for example, 0.5 μm or more, preferably 1.0 μm or more, and for example, 20 μm or less, preferably 10 μm or less.

[0013] The thickness of the optical laminate 1 is typically 150 μm or less, preferably 120 μm or less, more preferably 100 μm or less, and typically 20 μm or more, preferably 30 μm or more.

[0014] The polarizer, the first protective layer, the second protective layer, and the water-based adhesive layer will be described in detail below.

[0015] B. Polarizer Any appropriate polarizer can be used as the polarizer 2. For example, the resin film forming the polarizer 2 may be a single-layer resin film or a laminate of two or more layers. The polarizer 2 contains a dichroic material. Examples of the dichroic material include iodine and organic dyes. The dichroic materials can be used alone or in combination. Of the dichroic materials, iodine is preferred.

[0016] Specific examples of polarizers made of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films that have been dyed with a dichroic substance and stretched, and polyene-based oriented films such as dehydrated PVA films and dehydrochlorinated polyvinyl chloride films. Polarizers obtained by dyeing PVA films with iodine and uniaxially stretching them are preferred because of their excellent optical properties.

[0017] 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.

[0018] 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 one embodiment, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of the resin substrate. Stretching typically involves immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, the stretching may optionally further include in-air stretching the laminate at an elevated temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. Additionally, in one embodiment, the laminate is subjected to a drying shrinkage treatment in which the laminate is heated 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 in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment, in this order. By introducing the auxiliary stretching, it is possible to increase the crystallinity of the PVA, even when the PVA is coated on a thermoplastic resin, thereby achieving high optical properties. Furthermore, by simultaneously increasing the orientation of the PVA in advance, problems such as a decrease in the orientation or dissolution of the 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 the polyvinyl alcohol molecules and the decrease in the 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 drying shrinkage treatment causes the laminate to shrink in the width direction, thereby improving the optical properties. The polarizer is obtained by peeling off the resin substrate from the resulting resin substrate / polarizer.Details of such a method for manufacturing a polarizer are described in, for example, JP 2012-73580 A and Japanese Patent No. 6470455. The entire disclosures of these publications are incorporated herein by reference.

[0019] The thickness of the polarizer 2 is preferably 15 μm or less, more preferably 12 μm or less, and typically 1 μm or more, preferably 3 μm or more. When the thickness of the polarizer is within this range, curling of the optical laminate can be more stably suppressed.

[0020] The polarizer 2 preferably exhibits absorptive dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer 2 is, for example, 41.5% to 46.0%, preferably 43.0% to 46.0%, and more preferably 44.5% to 46.0%. The degree of polarization of the polarizer 2 is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

[0021] Although not shown, the polarizer 2 may have a non-polarizing portion. The planar shape of the non-polarizing portion can be changed as appropriate depending on the application. The non-polarizing portion is typically a bleached portion bleached by any appropriate chemical treatment. The difference between the content of the dichroic material in the polarizer other than the non-polarizing portion and the content of the dichroic material in the non-polarizing portion is, for example, 0.5% by mass or more, preferably 1% by mass or more. If the difference in content is within this range, a non-polarizing portion with the desired transparency can be formed.

[0022] C. 1st protective layer The first protective layer 3 is provided on one surface of the polarizer 2. The first protective layer 3 is attached to the polarizer 2 with a first aqueous adhesive layer 51 interposed therebetween.

[0023] The first protective layer 3 is formed of any appropriate film that can be used as a protective layer for the polarizer 2. Specific examples of materials that can be used as the main component of the film include cycloolefin (COP) resins such as polynorbornene resins, polyester resins such as polyethylene terephthalate (PET) resins, cellulose resins such as triacetyl cellulose (TAC), and transparent resins such as polycarbonate (PC), (meth)acrylic resins, polyvinyl alcohol resins, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polyolefins, and acetate resins. Other examples include thermosetting or ultraviolet-curing resins such as (meth)acrylic resins, urethane resins, (meth)acrylic urethane resins, epoxy resins, and silicone resins. The term "(meth)acrylic resin" refers to an acrylic resin and / or a methacrylic resin. Other examples include glassy polymers such as siloxane polymers. The polymer films described in JP 2001-343529 A (WO 01 / 37007) can also be used. Examples of materials for this film include resin compositions containing a thermoplastic resin with substituted or unsubstituted imide groups in its side chains and a thermoplastic resin with substituted or unsubstituted phenyl and nitrile groups in its side chains. Examples include a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extrusion molded product of the above resin composition. The film materials can be used alone or in combination.

[0024] In one embodiment, the first protective layer 3 is a saponified film obtained by saponifying an alkyl ester group-containing film. Examples of materials for the alkyl ester group-containing film include triacetyl cellulose (TAC). The first protective layer 3 is preferably a saponified TAC film.

[0025] The arithmetic mean surface roughness Ra of the first protective layer 3 is, for example, 0.2 nm or more, preferably 0.5 nm or more, and for example, 5.0 nm or less, preferably 3.0 nm or less. The arithmetic mean surface roughness Ra can be measured, for example, by an atomic force microscope (AFM).

[0026] The water contact angle of the first protective layer 3 is, for example, 10° or more, preferably 15° or more, and for example, 40° or less, preferably 30° or less. The water contact angle can be measured, for example, in accordance with JIS R3257.

[0027] The thickness of the first protective layer 3 is typically 300 μm or less, preferably 100 μm or less, more preferably 5 μm to 80 μm, and even more preferably 10 μm to 60 μm.

[0028] D.Second protective layer The second protective layer 4 is provided on the other surface of the polarizer 2. The second protective layer 4 is attached to the polarizer 2 via a second aqueous adhesive layer 52.

[0029] The second protective layer 4 is formed of any appropriate film that can adjust the peel strength from the second aqueous adhesive layer 52 to the above upper limit or less.

[0030] In one embodiment, the second protective layer 4 is the alkyl ester group-containing film described above. In other words, the second protective layer 4 is a non-saponified film that has not been subjected to a saponification treatment. The second protective layer 4 is preferably a non-saponified TAC film.

[0031] The light transmittance of the second protective layer 4 for light with a wavelength of 550 nm is, for example, 90% or more, preferably 93% or more, and for example, 99.5% or less.

[0032] The arithmetic mean surface roughness Ra of the second protective layer 4 is, for example, 0.1 nm or more, preferably 0.2 nm or more, and for example, 5.0 nm or less, preferably 2.0 nm or less.

[0033] The water contact angle of the second protective layer 4 is, for example, 40° or more, preferably 50° or more, and for example, 70° or less, preferably 65° or less.

[0034] The thickness range of the second protective layer 4 is the same as the thickness range of the first protective layer 3 described above.

[0035] E. First Water-Based Adhesive Layer and Second Water-Based Adhesive Layer The first aqueous adhesive layer 51 is located between the polarizer 2 and the first protective layer 3 and is in direct contact with the polarizer 2 and the first protective layer 3. The second aqueous adhesive layer 52 is located between the polarizer 2 and the second protective layer 4 and is in direct contact with the polarizer 2 and the second protective layer 4. When the aqueous adhesive layer is in direct contact with the polarizer, the moisture contained in the aqueous adhesive may migrate to the polarizer (typically a PVA-based resin film). This reduces the stability of the iodine complex contained in the polarizer, making the iodine complex with low orientation particularly susceptible to decomposition. As a result, the decomposition of the iodine complex with low orientation can be selectively promoted.

[0036] Each of the first aqueous adhesive layer 51 and the second aqueous adhesive layer 52 is formed by solidifying and / or curing an aqueous adhesive. In other words, each of the first aqueous adhesive layer 51 and the second aqueous adhesive layer 52 contains a solidified and / or cured aqueous adhesive. The first aqueous adhesive layer 51 and the second aqueous adhesive layer 52 preferably contain a solidified and / or cured aqueous adhesive of the same aqueous adhesive, and more preferably contain a cured aqueous adhesive of the same aqueous adhesive.

[0037] Any suitable water-based adhesive may be used as the water-based adhesive. The water-based adhesive before solidification (curing) is typically liquid at room temperature (23°C). In one embodiment, the aqueous adhesive contains a polyvinyl alcohol (PVA) resin. The PVA resin preferably contains an acetoacetyl group. When the PVA resin of the aqueous adhesive contains an acetoacetyl group, the adhesion between the polarizer and the aqueous adhesive layer can be improved.

[0038] The average saponification degree of the acetoacetyl group-containing PVA resin is, for example, 85 mol% or more, preferably 90 mol% or more, and for example, 100 mol% or less. The average saponification degree can be measured, for example, by NMR or in accordance with JIS K6726.

[0039] The degree of acetoacetylation of the PVA resin containing acetoacetyl groups is, for example, 0.1 mol% or more, preferably 1 mol% or more, more preferably 2 mol% or more, and for example, 40 mol% or less, preferably 20 mol% or less, more preferably 7 mol% or less. The degree of acetoacetylation can be calculated, for example, from a spectrum measured by NMR.

[0040] The average degree of polymerization of the PVA resin in the aqueous adhesive is, for example, 100 or more, preferably 1000 or more, and for example, 5000 or less, preferably 4000 or less, more preferably 2000 or less.

[0041] The water-based adhesive may contain any suitable additive. Examples of the additive include a crosslinking agent, a refractive index adjuster, an ultraviolet absorber, an antioxidant, and a leveling agent. The additives may be used alone or in combination.

[0042] In one embodiment, the aqueous adhesive contains a crosslinking agent as an additive in addition to the PVA resin. The crosslinking agent crosslinks the PVA resin, thereby curing the aqueous adhesive. Examples of crosslinking agents include melamine resins such as methylolmelamine; alkylenediamines; isocyanates; epoxies; and aldehydes. The crosslinking agents can be used alone or in combination. The content of the crosslinking agent in the aqueous adhesive is, for example, 10 parts by mass or more, preferably 20 parts by mass or more, and for example, 50 parts by mass or less, preferably 40 parts by mass or less, per 100 parts by mass of the PVA resin.

[0043] F. Method for manufacturing optical laminate Next, a method for producing the optical laminate will be described. In one embodiment, the method for producing an optical laminate includes a step of attaching a first protective layer 3 to one surface of a polarizer 2 via a first aqueous adhesive layer 51 (first attaching step), and a step of attaching a second protective layer 4 to the other surface of the polarizer 2 via a second aqueous adhesive layer 52 (second attaching step). In these steps, the thicknesses of the first aqueous adhesive layer 51 and the second aqueous adhesive layer 52 are each set within the above-mentioned range, and the peel force of the second protective layer 4 from the second aqueous adhesive layer 52 is set within the above-mentioned range.

[0044] In the first attaching step, the above-mentioned first protective layer 3 is prepared. The first protective layer 3 is provided with a first surface treatment layer 6, if necessary.

[0045] When the first protective layer 3 is a saponified film, the above-mentioned alkyl ester group-containing film is subjected to a saponification treatment to prepare the first protective layer.

[0046] The saponification treatment may be carried out by any suitable method, typically by immersing the alkyl ester group-containing film in a saponification treatment solution.

[0047] The saponification treatment solution has basicity. The saponification treatment solution is prepared, for example, by dissolving an alkali metal hydroxide in water. Examples of the alkali metal hydroxide include sodium hydroxide and potassium hydroxide. The alkali metal hydroxides can be used alone or in combination. Of the alkali metal hydroxides, sodium hydroxide is preferred. The concentration of the alkali metal hydroxide in the saponification treatment liquid is, for example, 1% by mass or more, preferably 5% by mass or more, and for example, 30% by mass or less, preferably 15% by mass or less. The temperature of the saponification treatment liquid is, for example, 40°C or higher, preferably 50°C or higher, and, for example, 90°C or lower, preferably 80°C or lower. The immersion time is, for example, 1 second or more, preferably 10 seconds or more, and, for example, 3 minutes or less, preferably 1 minute or less.

[0048] If necessary, the saponified film is washed with water after the saponification treatment and then dried by heating.

[0049] The water washing treatment can be carried out by any suitable method, typically by immersing the saponified film in water. The temperature of the water is, for example, 10°C or higher, preferably 20°C or higher, and, for example, 50°C or lower, preferably 40°C or lower. The immersion time is, for example, 1 second or more, preferably 10 seconds or more, and, for example, 3 minutes or less, preferably 1 minute or less.

[0050] The heat drying after washing with water can be carried out by any suitable method, typically by heating the saponified film after washing in an oven. The heating temperature is, for example, 60°C or higher, preferably 70°C or higher, and, for example, 100°C or lower, preferably 95°C or lower. The heating time is, for example, 1 second or more, preferably 5 seconds or more, and, for example, 1 minute or less, preferably 20 seconds or less.

[0051] In this way, the first protective layer 3 is prepared.

[0052] Next, the polarizer 2 and the first protective layer 3 are bonded together using the aqueous adhesive. In one embodiment, the long polarizer 2 and the long first protective layer 3 are transported between a pair of nip rollers, and the aqueous adhesive is supplied between the polarizer 2 and the first protective layer 3. Thereafter, the aqueous adhesive is heated and dried to solidify and / or harden, thereby forming a first aqueous adhesive layer 51 that bonds the polarizer 2 and the first protective layer 3 together.

[0053] The heat drying treatment of the water-based adhesive may be carried out by any appropriate method. The heat drying treatment may be carried out in one step or in multiple steps.

[0054] The heating and drying temperature is, for example, 40°C or higher, preferably 50°C or higher, and, for example, 90°C or lower, preferably 70°C or lower. The heating and drying time (if multiple stages are used, the total time of the stages) is, for example, 1 minute or more, preferably 3 minutes or more, and for example, 20 minutes or less, preferably 10 minutes or less.

[0055] In the second attaching step, a second protective layer 4 is prepared. A second surface treatment layer 8 is provided on the second protective layer 4, if necessary.

[0056] When the second protective layer 4 is a non-saponified film, the above-mentioned alkyl ester group-containing film is prepared as the second protective layer.

[0057] The non-saponified film (alkyl ester group-containing film) is preferably washed with water and then heated and dried. When the non-saponified film is washed with water and then heated and dried, the appearance of the optical laminate can be improved.

[0058] The water washing treatment and heat drying are each carried out by any appropriate method. The water washing treatment and heat drying for the unsaponified film are typically explained in the same manner as the water washing treatment and heat drying for the saponified film described above. In this way, the second protective layer is prepared.

[0059] Next, the polarizer 2 and the second protective layer 4 are bonded together using the aqueous adhesive. In one embodiment, the long polarizer 2 and the long second protective layer 4 are transported between a pair of nip rollers, and the aqueous adhesive is supplied between the polarizer 2 and the second protective layer 4. Thereafter, the aqueous adhesive is heated and dried to solidify and / or harden, thereby forming a second aqueous adhesive layer 52 that bonds the polarizer 2 and the second protective layer 4 together.

[0060] The heat drying treatment of the water-based adhesive can be carried out by any appropriate method. The heat drying treatment in the second attachment step can be explained in the same manner as the heat drying treatment in the first attachment step.

[0061] The first and second attaching steps may be carried out simultaneously or sequentially, and in one embodiment, the first and second attaching steps are carried out simultaneously.

[0062] To simultaneously perform the first and second bonding steps, the long polarizer 2 is transported between a pair of nip rollers, and the long first protective layer 3 and second protective layer 4 are transported between the pair of nip rollers so that the first protective layer 3 is located on one side of the polarizer 2 and the second protective layer 4 is located on the other side of the polarizer 2. At this time, an aqueous adhesive is supplied between the polarizer 2 and the first protective layer 3, and an aqueous adhesive is supplied between the polarizer 2 and the second protective layer 4, on the upstream side of the pair of nip rollers in the transport direction. This allows the first and second bonding steps to be performed simultaneously, enabling efficient production of an optical laminate.

[0063] G. Image display device The optical laminates described in the above items A to F can be applied to image display devices. Typical examples of image display devices include liquid crystal display devices and organic EL display devices. The image display device typically includes an image display panel and the optical laminates described in the above items A to F. The image display panel includes an image display cell. Note that the image display device may be referred to as an optical display device, the image display panel may be referred to as an optical display panel, and the image display cell may be referred to as an optical display cell. The optical laminate may be applied to an image display device as it is, or may be applied to an image display device after the second protective layer is peeled off. [Example]

[0064] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each property are as follows.

[0065] (1) Thickness measurement of the water-based adhesive layer of the optical laminate The thicknesses of the aqueous adhesive layers (first aqueous adhesive layer and second aqueous adhesive layer) of the optical laminates obtained in the examples and comparative examples were measured using a transmission electron microscope (TEM). The results are shown in Table 1.

[0066] (2) Appearance evaluation of optical laminates The surface protective film was peeled off from the optical laminates obtained in the examples and comparative examples, and the appearance was visually observed and evaluated according to the following criteria. The results are shown in Table 1. ◯: No significant defects in appearance. △: There are defects in appearance such as foreign matter mixed in. ×: Significant appearance defects.

[0067] (3) Evaluation of conveyability (curl) of optical laminates In the preparation of the optical laminates described in the Examples and Comparative Examples, the transportability in a continuous oven was evaluated according to the following criteria. The results are shown in Table 1. It is believed that breakage occurs due to curling of the film in the continuous oven due to asymmetry. 〇: The film does not break when 100m is produced. ×: The film breaks when 100 m is produced.

[0068] (4) Measurement of peel strength of the second protective layer against the second water-based adhesive layer The optical laminates obtained in the examples and comparative examples were cut into rectangular samples with a length of 200 mm parallel to the stretching axis of the polarizer and a width of 15 mm perpendicular to the stretching axis. The samples were then attached to a glass plate so that the second protective layer faced the glass surface. An incision was then made with a utility knife between the polarizer and the second protective layer (more specifically, at the interface between the second aqueous adhesive layer and the second protective layer). The polarizer and the second protective layer were peeled in a 90° direction at a peel rate of 300 mm / min using a Tensilon universal testing machine RTC (manufactured by A&D Co., Ltd.), and the peel force (N / 15 mm) was measured. The results are shown in Table 1.

[0069] (5) Composition analysis of the peeled surface after peel force testing After the above-mentioned peel force test (measurement), the peeled surface of the second protective layer of the sample was examined using a scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX) and an infrared absorption spectrum using an attenuated total reflectance (ATR) method to determine whether or not there was a water-based adhesive layer on the polarizer surface.

[0070] Example 1 <<Making a polarizer>> A polyvinyl alcohol film with an average degree of polymerization of 2,400, a degree of saponification of 99.9 mol%, and a thickness of 30 μm was prepared. The polyvinyl alcohol film was immersed in a swelling bath (water bath) at 25°C for 30 seconds between rolls with different peripheral speed ratios, where it was stretched 2.2 times in the conveying direction while swelling (swelling step). Subsequently, the film was immersed in a dye bath at 30°C (iodine solution obtained by blending iodine and potassium iodide in a mass ratio of 1:7 with 100 parts by mass of water) while adjusting the iodine concentration so that the polarizer had the desired transmittance. The film was then dyed by immersion for 30 seconds while stretching 3.1 times in the conveying direction relative to the original polyvinyl alcohol film (polyvinyl alcohol film that was not stretched in the conveying direction at all) while being stretched (dyeing step). Next, the dyed polyvinyl alcohol film was immersed in a crosslinking bath (aqueous solution with a boric acid concentration of 5.0% by mass and a potassium iodide concentration of 3.0% by mass) at 40°C for 30 seconds and stretched to 3.7 times the original size in the conveying direction (crosslinking step). The resulting polyvinyl alcohol film was then immersed in a 66°C stretching bath (aqueous solution containing 4.3% by mass of boric acid and 5.0% by mass of potassium iodide) for 60 seconds to be stretched 6.0 times in the conveying direction relative to the original polyvinyl alcohol film (stretching step), followed by immersion in a 20°C washing bath (aqueous solution containing 3.6% by mass of potassium iodide) for 10 seconds (washing step). The washed polyvinyl alcohol film was dried at 30°C for 30 seconds to produce a polarizer. The polarizer had a thickness of 12 μm.

[0071] <<Preparation of water-based adhesive>> A water-based adhesive was prepared by dissolving and / or dispersing an acetoacetyl group-containing polyvinyl alcohol resin (average polymerization degree: 1,200, saponification degree: 98.5 mol%, acetoacetylation degree: 5 mol%) and methylol melamine in water at a mass ratio of 3:1.

[0072] <<Production of optical laminates>> A film (thickness: 32 μm) having a hard coat layer (first surface treatment layer, HC) formed on a triacetyl cellulose (TAC) film (an alkyl ester group-containing film, manufactured by Fujifilm Corporation, product name: TJ25UL, thickness: 25 μm) was immersed in a 64°C saponification treatment solution (aqueous solution with a sodium hydroxide concentration of 10.0% by mass) for 30 seconds for saponification treatment. The film was then immersed in a 30°C water washing bath for 30 seconds for water washing treatment, and then heated and dried in an oven (temperature: 85°C, treatment time: 10 seconds) to prepare a first protective layer. Next, a triacetyl cellulose film (TAC, manufactured by Fujifilm Corporation, product name: TJ25UL, thickness: 25 μm) was immersed in a water bath at 30°C for 30 seconds for a water washing treatment, and then heated and dried in an oven (temperature: 80°C, treatment time: 10 seconds) to prepare a second protective layer. The first protective layer prepared above was bonded to one surface of the polarizer obtained above, and the second protective layer prepared above was bonded to the other surface of the polarizer via the aqueous adhesive obtained above using a roll laminator.Then, the resulting laminate was successively heated and dried in multiple ovens (drying at a temperature of 60°C for a treatment time of 60 seconds, then at a temperature of 55°C for a treatment time of 120 seconds, then at a temperature of 60°C for a treatment time of 120 seconds, and finally at a temperature of 62°C for a treatment time of 30 seconds), and a surface protective film was bonded to the laminate using a roll laminator to produce an optical laminate.

[0073] <Example 2> An optical laminate was produced in the same manner as in Example 1, except that the triacetyl cellulose film was used as the second protective layer without being subjected to water washing treatment or heat drying.

[0074] <Comparative Example 1> An optical laminate was produced in the same manner as in Example 1, except that only the first protective layer was attached to the polarizer via a water-based adhesive, and the second protective layer was not attached to the polarizer.

[0075] <Comparative Example 2> An optical laminate was produced in the same manner as in Example 1, except that no aqueous adhesive was provided between the polarizer and the second protective layer.

[0076] <Comparative Example 3> An optical laminate was produced in the same manner as in Example 1, except that the triacetyl cellulose film was subjected to saponification treatment, water washing treatment and heat drying in the same manner as the first protective layer to produce a second protective layer.

[0077] [Table 1]

[0078] [evaluation] As is clear from Table 1, when a substrate is attached to only one surface of a polarizer using an aqueous adhesive, the edges of the optical laminate curl and the optical laminate breaks when the aqueous adhesive is heated and dried (Comparative Examples 1 and 2). In contrast, when substrates are attached to both surfaces of a polarizer using an aqueous adhesive and the peel force of the second protective layer relative to the aqueous adhesive layer is adjusted as described above, curling and / or breakage of the optical laminate can be suppressed, and the second protective layer of an optical laminate having an excellent appearance can be smoothly peeled from the polarizer. [Industrial Applicability]

[0079] The optical laminate 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]

[0080] 1 Optical laminate 2 Polarizers 3 1st protective layer 4 Second protective layer 51 1st water-based adhesive layer 52 Second water-based adhesive layer

Claims

1. A polarizer; a first protective layer bonded to the polarizer via a first aqueous adhesive layer; a second protective layer disposed on the opposite side of the polarizer from the first protective layer and bonded to the polarizer via a second aqueous adhesive layer, the thickness of each of the first aqueous adhesive layer and the second aqueous adhesive layer is 0.01 μm or more and 0.20 μm or less; An optical laminate, wherein the peel strength of the second protective layer from the second aqueous adhesive layer is 0.05 (N / 15 mm) or more and 1.0 (N / 15 mm) or less.

2. 2. The optical laminate according to claim 1, wherein the second protective layer is a non-saponified triacetyl cellulose film.

3. a step of attaching a first protective layer to one surface of the polarizer via a first aqueous adhesive layer; and attaching a second protective layer to the other surface of the polarizer via a second aqueous adhesive layer, a peeling force of the second protective layer from the second aqueous adhesive layer to a peel strength of the second protective layer from the first aqueous adhesive layer to a peel strength of the second aqueous adhesive layer from the second aqueous adhesive layer to a peel strength of the second protective layer from the second ...

4. a step of subjecting the alkyl ester group-containing film to a saponification treatment to prepare a first protective layer; The method for producing an optical laminate according to claim 3 , further comprising the step of: preparing an alkyl ester group-containing film as the second protective layer.

5. The method for producing an optical laminate according to claim 4 , wherein in the step of preparing the second protective layer, the alkyl ester group-containing film is washed with water and then dried by heating.

6. The method for producing an optical laminate according to claim 3 , wherein the step of attaching a first protective layer to one surface of the polarizer and the step of attaching a second protective layer to the other surface of the polarizer are carried out simultaneously.

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