Optical laminate

Abstract

To provide an optical laminate capable of simultaneously achieving heat resistance and moisture resistance in a good balance.SOLUTION: An optical laminate includes: a polarizer; a buffer layer disposed on a surface of the polarizer and including a polyvinyl alcohol resin; and a retardation layer located opposite to the polarizer with regard to the buffer layer, and adhered to the buffer layer interposing a joint layer. The retardation layer is an oriented and solidified layer of a liquid crystal compound. A ratio of thickness of the polarizer to thickness of the buffer layer is 70 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to 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 typically use optical laminates including a polarizing plate and a retardation layer. Furthermore, to reduce the thickness of the optical laminate, a layer of oriented and solidified liquid crystal compounds may be used as the retardation layer. As such an optical laminate, for example, a retardation layer-attached polarizing plate is known, in which a layer of oriented and solidified liquid crystal compounds is attached to a polarizing plate via a UV-curable adhesive (see, for example, Patent Document 1). However, such retardation layer-attached polarizing plates have insufficient heat resistance and moisture resistance. More specifically, the retardation layer-attached polarizing plate described in Patent Document 1 may deform in a high-temperature environment (e.g., 85°C or higher), causing cracks in the polarizer. Furthermore, the polarizer may be discolored and lose its color in a high-temperature and high-humidity environment (e.g., a temperature of 65°C and a humidity of 95% RH or higher). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-63975 Summary of the Invention [Problem to be solved by the invention]

[0004] 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 layered body that can achieve excellent heat resistance and moisture resistance in a well-balanced manner. [Means for solving the problem]

[0005] [1] An optical laminate according to an embodiment of the present invention includes a polarizer, a buffer layer, and a retardation layer. The buffer layer is provided on the surface of the polarizer. The buffer layer contains a polyvinyl alcohol-based resin. The retardation layer is located on the opposite side of the buffer layer from the polarizer. The retardation layer is attached to the buffer layer via an adhesive layer. The retardation layer is an alignment-solidified layer of a liquid crystal compound. The ratio of the thickness of the polarizer to the thickness of the buffer layer is 70 or more. [2] In the optical laminate according to the above [1], the ratio of the thickness of the polarizer to the thickness of the buffer layer may be 120 or more. [3] In the optical laminate according to the above [1] or [2], the polarizer may contain a polyvinyl alcohol-based resin. [4] In the optical laminate according to any one of [1] to [3] above, the ratio of the thickness of the bonding layer to the thickness of the buffer layer may be 7 or more. [5] In the optical laminate according to any one of [1] to [4] above, the buffer layer may have a thickness of 0.15 μm or less. [Effects of the Invention]

[0006] According to an embodiment of the present invention, an optical laminate that can achieve excellent heat resistance and moisture resistance in a well-balanced manner can be realized. [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] 2 is a schematic cross-sectional view of an intermediate laminate used in the production of the optical laminate of FIG. 1. FIG. 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] (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.

[0010] 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 optical laminate 1 in the illustrated example includes a polarizer 2, a buffer layer 52, and a retardation layer 8. The buffer layer 52 is provided on the surface of the polarizer 2. The buffer layer 52 contains a polyvinyl alcohol (PVA) resin. The retardation layer 8 is located on the opposite side of the buffer layer 52 from the polarizer 2. The retardation layer 8 is a layer in which a liquid crystal compound is aligned and fixed. In this specification, the term "alignment and fixed layer" refers to a layer in which a liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state is fixed. The term "alignment and fixed layer" is a concept that encompasses an alignment and fixed layer obtained by curing a polymerizable liquid crystal compound (typically a liquid crystal monomer). The retardation layer 8 is attached to the buffer layer 52 via the bonding layer 7. That is, the optical laminate 1 includes the polarizer 2, the buffer layer 52, the bonding layer 7, and the retardation layer 8 in this order. The ratio of the thickness of the polarizer 2 to the thickness of the buffer layer 52 (polarizer thickness / buffer layer thickness) is 70 or more, preferably 80 or more, more preferably 100 or more, even more preferably 120 or more, and particularly preferably 150 or more. The upper limit of the polarizer thickness / buffer layer thickness is typically 250, and preferably 200. According to this configuration, a buffer layer is provided between the polarizer and the bonding layer. Therefore, even if dimensional changes occur in the bonding layer due to heat in a high-temperature environment (e.g., 85°C or higher), the buffer layer can prevent the dimensional changes in the bonding layer from affecting the polarizer. Therefore, cracks can be prevented from occurring in the polarizer in a high-temperature environment, and the heat resistance of the optical laminate can be improved. Furthermore, because the polarizer thickness / buffer layer thickness is equal to or greater than the above-mentioned lower limit, the amount of moisture retained by the buffer layer can be reduced in a high-temperature, high-humidity environment (e.g., a temperature of 65°C and a humidity of 95% RH or higher). This prevents the polarizer from losing its color due to moisture, and improves the moisture resistance of the optical laminate. In other words, according to the above configuration, the optical laminate can achieve a good balance between excellent heat resistance and moisture resistance.

[0011] In one embodiment, the ratio of the thickness of the bonding layer 7 to the thickness of the buffer layer 52 (thickness of the bonding layer / thickness of the buffer layer) is, for example, more than 6, preferably 7 or more, more preferably 10 or more, and even more preferably 13 or more. When the thickness of the bonding layer / thickness of the buffer layer is equal to or greater than the above-mentioned lower limit, the moisture resistance of the optical laminate can be stably improved. The upper limit of the thickness of the buffer layer / thickness of the bonding layer is typically 100, preferably 50, and more preferably 20.

[0012] In one embodiment, the thickness of the buffer layer 52 is, for example, 0.17 μm or less, preferably 0.15 μm or less, more preferably 0.10 μm or less, and even more preferably 0.08 μm or less. If the thickness of the buffer layer is equal to or less than the above upper limit, the moisture resistance of the optical laminate can be improved more stably. The lower limit of the thickness of the buffer layer is typically 0.01 μm.

[0013] In one embodiment, the optical laminate 1 further includes a protective layer 3. The protective layer 3 is located on the opposite side of the polarizer 2 from the buffer layer 52. The protective layer 3 is typically attached to the polarizer 2 via a water-based adhesive layer 51. That is, the optical laminate 1 in the illustrated example includes the protective layer 3, the water-based adhesive layer 51, the polarizer 2, the buffer layer 52, the bonding layer 7, and the retardation layer 8, in this order.

[0014] The thickness of the optical laminate 1 is typically 170 μm or less, preferably 140 μm or less, more preferably 120 μm or less, and is typically 20 μm or more, preferably 30 μm or more.

[0015] The polarizer, protective layer, water-based adhesive layer, buffer layer, retardation layer, and bonding layer will be described in detail below.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] As described above, the polarizer 2 preferably contains a PVA-based resin. In this embodiment, both the polarizer and the buffer layer contain a PVA-based resin. This can improve the adhesion between the polarizer and the buffer layer.

[0021] 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 in a high-temperature environment can be suppressed, and the heat resistance of the optical laminate can be further improved.

[0022] 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.

[0023] 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.

[0024] C. Protective layer The protective layer 3 is provided on one surface of the polarizer 2. In the illustrated example, the protective layer 3 is attached to the polarizer 2 via a water-based adhesive layer 51.

[0025] The 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 resins or UV-curable resins such as (meth)acrylic resins, urethane resins, (meth)acrylic urethane resins, epoxy resins, and silicone resins. Note that "(meth)acrylic" refers to acrylic and / or methacrylic. Other examples include glassy polymers such as siloxane polymers. 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.

[0026] In one embodiment, the 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 protective layer 3 is preferably a saponified TAC film.

[0027] The arithmetic mean surface roughness Ra of the 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).

[0028] The water contact angle of the 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.

[0029] The thickness of the 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.

[0030] In one embodiment, a first surface treatment layer 6 is provided on the surface of the protective layer 3. The first surface treatment layer 6 is located on the opposite side of the 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 antireflection layer, an anti-sticking layer, a diffusion layer, and an anti-glare layer. The first surface treatment layer 6 is preferably 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.

[0031] D. Water-based adhesive layer The water-based adhesive layer 51 is located between the polarizer 2 and the protective layer 3 and is in direct contact with the polarizer 2 and the protective layer 3 . 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.

[0032] The water-based adhesive layer 51 is formed by solidifying and / or curing the water-based adhesive. In other words, the water-based adhesive layer 51 contains a solidified and / or cured product of the water-based adhesive.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] E. Buffer layer The buffer layer 52 is formed on the surface of the polarizer 2. The buffer layer 52 is located between the polarizer 2 and the bonding layer 7 and is in direct contact with the polarizer 2 and the bonding layer 7.

[0040] In one embodiment, the buffer layer 52 is formed by solidifying and / or curing a water-based adhesive containing a PVA-based resin. In other words, the buffer layer 52 includes a solidified and / or cured product of the water-based adhesive containing a PVA-based resin. The aqueous adhesive used in the buffer layer is similar to the aqueous adhesive used in the aqueous adhesive layer described above. The aqueous adhesive layer 51 and the buffer layer 52 preferably contain a solidified and / or cured product of the same aqueous adhesive, and more preferably contain a cured product of the same aqueous adhesive. This can prevent curling of the edges of the intermediate laminate (described later), and ultimately prevent poor appearance of the optical laminate. The buffer layer 52 is typically elastic.

[0041] F. Retardation layer The retardation layer 8 is located on the opposite side of the buffer layer 52 from the polarizer 2. The retardation layer 8 is attached to the buffer layer 52 via an adhesive layer 7. The retardation layer 8 has any appropriate in-plane retardation.

[0042] As described above, the retardation layer 8 is an oriented and solidified layer of a liquid crystal compound. In one embodiment of the present invention, the retardation layer 8 contains a rod-shaped liquid crystal compound. The rod-shaped liquid crystal compound is oriented in a state aligned in the slow axis direction of the retardation layer 8 (homogeneous orientation). Examples of the rod-shaped liquid crystal compound include a liquid crystal polymer and a liquid crystal monomer. The liquid crystal polymer and the liquid crystal monomer may be used alone or in combination. The liquid crystal compound is preferably polymerizable. If the liquid crystal compound is polymerizable, the orientation state of the liquid crystal compound can be fixed by aligning the liquid crystal compound and then polymerizing it.

[0043] The retardation layer 8, which is an alignment and solidification layer of a liquid crystal compound, can be formed using a composition containing a polymerizable liquid crystal compound (polymerizable liquid crystal compound). In this specification, the polymerizable liquid crystal compound contained in the composition refers to a compound that has a polymerizable group and has liquid crystal properties. The polymerizable group refers to a group that participates in a polymerization reaction, and is 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.

[0044] Examples of polymerizable liquid crystal compounds include polymerizable and / or crosslinkable liquid crystal monomers. The orientation state of the liquid crystal monomers can be fixed by polymerizing or crosslinking (i.e., curing) the liquid crystal monomers. After the liquid crystal monomers are aligned, the orientation state can be fixed by, for example, 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 retardation layer does not undergo, for example, a transition to a liquid crystal phase, glass phase, or crystalline phase due to temperature changes, which is specific to liquid crystal compounds. As a result, the retardation layer is an extremely stable retardation layer that is not affected by temperature changes.

[0045] The manifestation of liquid crystallinity may be thermotropic or lyotropic. Also, as the constitution of the liquid crystal phase, it may be a nematic liquid crystal or a smectic liquid crystal. From the viewpoint of ease of production, thermotropic nematic liquid crystals are preferred for liquid crystallinity. When the liquid crystal compound is thermotropic, the temperature range in which it exhibits liquid crystallinity varies depending on its type. This temperature range is, for example, 40°C to 120°C, preferably 50°C to 100°C, and more preferably 60°C to 90°C.

[0046] As the polymerizable liquid crystal compound, any suitable liquid crystal monomer can be adopted. For example, the polymerizable mesogenic compounds described in JP-T 2002-533742 (WO00 / 37585), EP358208 (US5211877), EP66137 (US4388453), WO93 / 22397, EP0261712, DE19504224, DE4408171, and GB2280445 can be used. Specific examples of such polymerizable mesogenic compounds include, for example, the product name LC242 from BASF, the product name E7 from Merck, and the product name LC-Sillicon-CC3767 from Wacker-Chem.

[0047] Such a retardation layer 8 may have a single-layer structure or a laminated structure in which two or more layers are laminated. In one embodiment, the retardation layer 8 has a laminated structure including a first retardation layer and a second retardation layer. Each of the first retardation layer and the second retardation layer is typically an alignment and solidification layer of the above-described liquid crystal compound.

[0048] The first retardation layer and the second retardation layer each typically exhibit a refractive index characteristic of nx > ny = nz. Note that "ny = nz" includes not only the case where ny and nz are exactly equal but also the case where they are substantially equal. Therefore, within a range that does not impair the effects of the present invention, ny > nz or ny < nz may occur.

[0049] Typically, either the first retardation layer or the second retardation layer can function as a λ / 2 plate, and the other can function as a λ / 4 plate. Here, a case where the first retardation layer can function as a λ / 2 plate and the second retardation layer can function as a λ / 4 plate will be described, but these may be reversed. When the first retardation layer can function as a λ / 2 plate and the second retardation layer can function as a λ / 4 plate, the in-plane retardation Re(550) of the first retardation layer is, for example, 200 nm to 300 nm, preferably 230 nm to 290 nm, and more preferably 250 nm to 280 nm. The angle between the slow axis of the first retardation layer and the absorption axis of the polarizer is, for example, 10° to 20°, preferably 12° to 18°, and more preferably about 15°. The in-plane retardation Re(550) of the second retardation layer is, for example, 100 nm to 190 nm, preferably 110 nm to 170 nm, and more preferably 130 nm to 160 nm. The angle between the slow axis of the second retardation layer and the absorption axis of the polarizer is, for example, 70° to 80°, preferably 72° to 78°, and more preferably about 75°. With this configuration, it is possible to obtain characteristics close to ideal reverse wavelength dispersion characteristics, and as a result, it is possible to realize very excellent antireflection characteristics.

[0050] The thickness of the first retardation layer can be adjusted to obtain a desired in-plane retardation of the λ / 2 plate, for example, 1.5 μm to 2.5 μm, and the thickness of the second retardation layer can be adjusted to obtain a desired in-plane retardation of the λ / 4 plate, for example, 0.5 μm to 1.5 μm. The Nz coefficient of each of the first retardation layer and the second retardation layer is, for example, 0.9 to 1.5, and preferably 0.9 to 1.3.

[0051] The first retardation layer and the second retardation layer may each exhibit an inverse dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light, a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light, or a flat wavelength dispersion characteristic in which the retardation value changes little depending on the wavelength of the measurement light.

[0052] The alignment and solidification layer of the liquid crystal compound can be formed, for example, by the following procedure. First, a coating solution for forming an alignment film is applied to an arbitrary suitable substrate and dried to form a coating film. The coating film is then subjected to an alignment treatment to form an alignment film on the substrate. Typical alignment treatments include rubbing and photoalignment. An alignment film generally contains a polymer material as its main component. Typical examples of polymer materials include polyvinyl alcohol, polyimide, and their derivatives. Next, a solution containing a polymerizable liquid crystal compound is applied to the alignment film and heated. The heating removes the solvent and promotes the alignment of the liquid crystal compound. This heating may be performed in a single step or in multiple steps at different temperatures. Next, the polymerizable liquid crystal compound is polymerized by ultraviolet irradiation to fix the alignment of the liquid crystal compound. In this way, a retardation layer consisting of an alignment and solidification layer of the liquid crystal compound is formed on the substrate (substantially on the alignment film). Note that methods for aligning rod-shaped liquid crystal compounds are described, for example, in JP-A 2006-163343 and JP-A 2006-178389. The disclosures of these publications are incorporated herein by reference. In one embodiment, the liquid crystal alignment solidified layer (first retardation layer) formed on the substrate can be transferred to the surface of the polarizer via a bonding layer. Similarly, the liquid crystal alignment solidified layer (second retardation layer) formed on the substrate can be transferred to the surface of the first retardation layer via an adhesive.

[0053] G. Bonding layer The bonding layer 7 is located between the buffer layer 52 and the retardation layer 8, and bonds the buffer layer 52 to the retardation layer 8. The bonding layer 7 is in direct contact with the buffer layer 52 and the retardation layer 8.

[0054] The bonding layer 7 may be a pressure-sensitive adhesive layer or an adhesive layer. When the bonding layer 7 is a pressure-sensitive adhesive layer, examples of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer include (meth)acrylic pressure-sensitive adhesives. The thickness of the pressure-sensitive adhesive layer is, for example, 3.5 μm or more and 35 μm or less. When the bonding layer 7 is an adhesive layer, examples of the adhesive constituting the adhesive layer include a thermosetting adhesive and an ultraviolet curing adhesive, and more preferably an ultraviolet curing adhesive. The thickness of the adhesive layer is, for example, 0.4 μm or more and 3.0 μm or less. The bonding layer 7 is preferably an adhesive layer, more preferably an ultraviolet curable adhesive layer.

[0055] H. Method for manufacturing optical laminate Next, a method for producing the optical laminate will be described. As shown in FIG. 2, in one embodiment, the method for manufacturing an optical laminate includes the steps of: preparing an intermediate laminate 10 including a polarizer 2, a buffer layer 52, and a release liner 4 (preparation step); peeling the release liner 4 from the buffer layer 52 (peeling step); and attaching a retardation layer 8 to the buffer layer 52 via an adhesive layer 7 (attachment step).

[0056] The intermediate laminate 10 prepared in the preparation step includes at least the above-described polarizer 2, the above-described buffer layer 52, and a release liner 4. The release liner 4 is attached to the buffer layer 52 in a releasable manner.

[0057] The peel strength of the release liner 4 from the buffer layer 52 is, for example, 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. If the peel strength of the release liner from the buffer layer is within the above range, the release liner can be smoothly peeled off from the buffer layer. The lower limit of the peel strength of the release liner 4 from the buffer 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.

[0058] The release liner 4 is formed of any appropriate film that can adjust the release force from the buffer layer 52 to the above upper limit or less.

[0059] In one embodiment, the release liner 4 is the alkyl ester group-containing film described above. In other words, the release liner 4 is a non-saponified film that has not been subjected to a saponification treatment. The release liner 4 is preferably a non-saponified TAC film.

[0060] The light transmittance of the release liner 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.

[0061] The arithmetic mean surface roughness Ra of the release liner 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.

[0062] The water contact angle of the release liner 4 is, for example, 40° or more, preferably 50° or more, and for example, 70° or less, preferably 65° or less.

[0063] The range of thickness of the release liner 4 is the same as the range of thickness of the protective layer 3 described above.

[0064] The illustrated intermediate laminate 10 includes the polarizer 2, the buffer layer 52, and the release liner 4, as well as the protective layer 3 and the aqueous adhesive layer 51. That is, the illustrated intermediate laminate 10 includes the protective layer 3, the aqueous adhesive layer 51, the polarizer 2, the buffer layer 52, and the release liner 4 in this order.

[0065] The preparation process of such an intermediate laminate 10 includes, for example, a step of attaching a protective layer 3 to one surface of the polarizer 2 via a water-based adhesive layer 51 (protective layer attachment step); and a step of attaching a release liner 4 to the other surface of the polarizer 2 via a buffer layer 52 (release liner attachment step).

[0066] In the protective layer attaching step, the above-mentioned protective layer 3 is prepared. The protective layer 3 is provided with a first surface treatment layer 6 as needed.

[0067] When the protective layer 3 is a saponified film, the above-mentioned alkyl ester group-containing film is subjected to a saponification treatment to prepare the protective layer.

[0068] 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.

[0069] 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.

[0070] If necessary, the saponified film is washed with water after the saponification treatment and then dried by heating.

[0071] 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.

[0072] 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. In this way, the protective layer 3 is prepared.

[0073] Next, the polarizer 2 and the protective layer 3 are bonded together using the aqueous adhesive. In one embodiment, the long polarizer 2 and the long protective layer 3 are transported between a pair of nip rollers, and the aqueous adhesive is supplied between the polarizer 2 and the protective layer 3. Thereafter, the aqueous adhesive is heated and dried to solidify and / or harden, thereby forming an aqueous adhesive layer 51 that bonds the polarizer 2 and the protective layer 3 together.

[0074] 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.

[0075] 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.

[0076] In the release liner attaching step, the above-mentioned release liner 4 is prepared. For example, the above-mentioned non-saponified film (a film containing alkyl ester groups) is used as the release liner.

[0077] 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.

[0078] 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 release liner 4 is prepared.

[0079] Next, the polarizer 2 and the release liner 4 are bonded together, typically using the water-based adhesive. In one embodiment, the long polarizer 2 and the long release liner 4 are transported between a pair of nip rollers, and the water-based adhesive is supplied between the polarizer 2 and the release liner 4. The water-based adhesive is then heated and dried to solidify and / or harden, thereby forming a buffer layer 52 that bonds the polarizer 2 and the release liner 4 together.

[0080] The heat drying treatment of the water-based adhesive can be carried out by any appropriate method. The heat drying treatment in the release liner attachment step can be explained in the same manner as the heat drying treatment in the protective layer attachment step.

[0081] The protective layer attaching step and the release liner attaching step may be carried out simultaneously or sequentially. In one embodiment, the protective layer attaching step and the release liner attaching step are carried out simultaneously.

[0082] To simultaneously perform the protective layer attaching step and the release liner attaching step, the long polarizer 2 is transported between a pair of nip rollers, and the long protective layer 3 and release liner 4 are transported between the pair of nip rollers so that the protective layer 3 is located on one side of the polarizer 2 and the release liner 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 protective layer 3 on the upstream side of the pair of nip rollers in the transport direction, and an aqueous adhesive is also supplied between the polarizer 2 and the release liner 4. This allows the above-mentioned protective layer attaching step and release liner attaching step to be performed simultaneously, enabling efficient production of an intermediate laminate.

[0083] Next, in the peeling step, the release liner 4 is peeled from the buffer layer 52. Because the peeling force of the release liner against the buffer layer is equal to or less than the upper limit, the release liner can be smoothly peeled from the polarizer. Note that, in the release liner peeling step, the buffer layer 52 does not substantially follow the release liner 4 and remains on the surface of the polarizer.

[0084] Next, in the bonding step, the retardation layer 8 is bonded to the buffer layer 52 via the bonding layer 7. The bonding layer 7 is formed by any appropriate method depending on the material that constitutes the bonding layer. In this manner, the optical laminate 1 shown in FIG. 1 is manufactured.

[0085] I. Image display device The optical laminates described in the above items A to H 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 H. 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. [Example]

[0086] 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.

[0087] (1) Thickness measurement of optical laminates The thicknesses of the polarizer, buffer layer, and bonding layer included in 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.

[0088] (2) Durability test under heated environment The optical laminates obtained in the Examples and Comparative Examples were cut into 150 x 50 mm pieces with the absorption axis of the polarizer aligned along the long side, and the optical laminates were attached to a glass plate via a 20 μm thick acrylic adhesive layer on the retardation side. They were then placed in a hot air oven at 85°C for 500 hours, and the appearance after heating was visually evaluated according to the following criteria. The results are shown in Table 1. ◯: No cracks of 100 μm or more occur at the edge of the optical laminate. ×: Cracks of 100 μm or more occur at the edge of the optical laminate.

[0089] (3) Durability test in a humid environment The optical laminates obtained in the examples and comparative examples were cut into 40 x 40 mm pieces so that the absorption axis of the polarizer was parallel to the sides, and the retardation surface of the optical laminate was attached to a glass plate via a 20 μm thick acrylic adhesive layer. The laminates were then left to stand in an oven at 65°C and 95% RH for 500 hours, and the degree of polarization (ΔP) was measured before and after humidification. The degree of polarization was determined by measuring the optical properties using a UV-visible spectrophotometer (Otsuka Electronics Co., Ltd., "LPF-200"). The measurement wavelength was 380 to 780 nm (5 nm intervals). ΔP(%)=P500-P0 Here, P0 is the initial degree of polarization (before humidification), and P500 is the degree of polarization after 500 hours of humidification. ΔP was evaluated according to the following criteria. The results are shown in Table 1. ○: ΔP ≦ 0.5. △:0.5<ΔP≦1 ×: 1<ΔP.

[0090] 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.

[0091] <<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.

[0092] <<Fabrication of retardation layer>> <Preparation of the first alignment layer and the second alignment layer constituting the retardation layer> A liquid crystal composition (coating liquid) was prepared by dissolving 10 g of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF: trade name "Paliocolor LC242", represented by the following formula) and 3 g of a photopolymerization initiator for the polymerizable liquid crystal compound (manufactured by BASF: trade name "Irgacure 907") in 40 g of toluene. [ka] The surface of a polyethylene terephthalate (PET) film (thickness: 38 μm) was rubbed with a rubbing cloth to perform an alignment treatment. The direction of the alignment treatment was set to be 15° from the viewing side with respect to the absorption axis direction of the polarizing film when it was attached to the polarizing film. The above liquid crystal coating solution was applied to this alignment-treated surface using a bar coater, and the liquid crystal compound was aligned by heating and drying at 90°C for 2 minutes. The liquid crystal layer thus formed was irradiated with 1 mJ / cm using a metal halide lamp. 2 The liquid crystal layer was cured by irradiating the liquid crystal layer with light of 1000 nm to form a liquid crystal alignment layer A on the PET film. The liquid crystal alignment layer A had a thickness of 2.5 μm and an in-plane retardation Re(550) of 270 nm. Furthermore, the liquid crystal alignment layer A had a refractive index distribution of nx>ny=nz. A liquid crystal alignment layer B was formed on the PET film in the same manner as above, except that the coating thickness was changed and the alignment treatment direction was set to a 75° angle with the absorption axis of the polarizing film when viewed from the viewing side. The liquid crystal alignment layer B had a thickness of 1.5 μm and an in-plane retardation Re(550) of 140 nm. Furthermore, the liquid crystal alignment layer B had a refractive index distribution of nx>ny=nz.

[0093] <<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 protective layer. Next, a triacetyl cellulose film (TAC, manufactured by Fujifilm Corporation, product name: TJ25UL, thickness: 25 μm) was immersed in a water washing 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 release liner. The protective layer prepared above was attached to one side of the polarizer obtained above, and the release liner prepared above was attached to the other side of the polarizer via the aqueous adhesive obtained above using a roll laminator, and then the resulting films were heated and dried continuously in multiple ovens (drying at 60°C for 60 seconds, followed by drying at 55°C for 120 seconds, then at 60°C for 120 seconds, and finally drying at 62°C for 30 seconds). This resulted in the protective layer being attached to the polarizer via the aqueous adhesive layer, and the release liner being attached to the polarizer via the buffer layer (aqueous adhesive layer), thereby obtaining an intermediate laminate. Next, the release liner was peeled off from the intermediate laminate. The liquid crystal alignment solidified layer A and liquid crystal alignment solidified layer B obtained above were then transferred, in this order, to the release surface of the buffer layer. The transfer (lamination) was performed so that the angle between the absorption axis of the polarizer and the slow axis of the alignment solidified layer A was 15°, and the angle between the absorption axis of the polarizer and the slow axis of the alignment solidified layer B was 75°. Each transfer (lamination) was performed via a UV-curable adhesive (thickness 1 μm), which was cured by UV irradiation. As a result, a bonding layer composed of the UV-curable adhesive bonded the buffer layer and the retardation layer. In this manner, an optical laminate having a structure of protective layer / water-based adhesive layer / polarizer / buffer layer / bonding layer / retardation layer was produced.

[0094] <Example 2> An optical laminate was produced in the same manner as in Example 1, except that the UV-curable adhesive was changed to an acrylic adhesive and the buffer layer and the retardation layer were bonded together by a bonding layer made of an acrylic adhesive.

[0095] Example 3 Except for changing the 12 μm thick polarizer to an 8 μm thick polarizer, an optical laminate was produced in the same manner as in Example 1. The 8 μm thick polarizer was produced using polyvinyl alcohol having a thickness of 20 μm.

[0096] Example 4 Comparative Example 2 An optical laminate was produced in the same manner as in Example 1, except that the thickness of the buffer layer was changed to the value shown in Table 1.

[0097] <Comparative Example 1> An optical laminate was produced in the same manner as in Example 1, except that the buffer layer was not formed and the retardation layer was directly attached to the polarizer with a UV-curable adhesive.

[0098] [Table 1]

[0099] [evaluation] As is clear from Table 1, when the polarizer and the retardation layer are bonded with a bonding layer made of an adhesive, the heat resistance and moisture resistance of the optical laminate are insufficient (Comparative Example 1).In addition, even when a buffer layer is provided between the polarizer and the bonding layer, if the ratio of the polarizer thickness to the buffer layer thickness exceeds the upper limit, the moisture resistance decreases (Comparative Example 2). In contrast, it is found that by providing a buffer layer between the polarizer and the bonding layer and adjusting the ratio of the thickness of the polarizer to the thickness of the buffer layer to the above upper limit or less, it is possible to achieve a good balance between heat resistance and moisture resistance. [Industrial Applicability]

[0100] 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]

[0101] 1 Optical laminate 2 polarizers 7 Bonding layer 8 Retardation layer 52 Buffer layer

Claims

1. A polarizer; a buffer layer provided on a surface of the polarizer and containing a polyvinyl alcohol-based resin; a retardation layer located on the opposite side of the buffer layer from the polarizer and attached to the buffer layer via a bonding layer, the retardation layer is a layer in which a liquid crystal compound is aligned and solidified, An optical laminate, wherein the ratio of the thickness of the polarizer to the thickness of the buffer layer is 70 or more.

2. The optical laminate according to claim 1 , wherein the ratio of the thickness of the polarizer to the thickness of the buffer layer is 120 or more.

3. The optical laminate according to claim 1 , wherein the polarizer contains a polyvinyl alcohol-based resin.

4. The optical laminate according to claim 1 , wherein a ratio of the thickness of the bonding layer to the thickness of the buffer layer is 7 or more.

5. The optical laminate according to claim 1 or 2, wherein the buffer layer has a thickness of 0.15 μm or less.

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