Polarizing plate and image display device using the same

Abstract

To provide a polarizing plate that can achieve excellent photographing functions and face authentication functions without providing through holes or transparent portions when applied to an image display device having a camera unit. The polarizing plate according to an embodiment of the present invention has a polarizing element and a protective layer provided on at least one side of the polarizing element. The polarizing element is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and the reflection image contrast index of the polarizing plate is 15 or less.

Description

Technical Field

[0001] The present invention relates to a polarizing plate and an image display device using the same. Background Art

[0002] In an image display device (e.g., a liquid crystal display device, an organic EL display device, a quantum dot display device), due to its image formation method, a polarizing plate is disposed on at least one side of a display unit in most cases. In recent years, an image display device having a camera unit has been rapidly popularized, and the camera unit functions not only as a photographing device but also as a main component of a face authentication system. In order to fully exhibit such photographing function and face authentication function, a through hole or a transparent portion (non-polarizing portion) is provided in the polarizing plate at a position corresponding to the camera unit in most cases. However, since the through hole or the transparent portion mostly impairs the design, a polarizing plate capable of fully exhibiting the photographing function and the face authentication function without providing the through hole or the transparent portion is desired.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-081482 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] The present invention has been made to solve the above-described conventional problems, and a main object thereof is to provide a polarizing plate that can achieve excellent photographing function and face authentication function without providing a through hole or a transparent portion when applied to an image display device having a camera unit.

[0008] Means for Solving the Problems

[0009] The polarizing plate according to an embodiment of the present invention includes a polarizing member and a protective layer provided on at least one side of the polarizing member. The polarizing member is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and a reflection image contrast index of the polarizing plate is 15 or less.

[0010] In one embodiment, a thickness of the polarizing member is 12 μm or less.

[0011] In one embodiment, the reflection image contrast index is 13 or less.

[0012] In one embodiment, the polarizing plate has a protective layer only on one side of the polarizing member.

[0013] According to another aspect of the present invention, there is provided an image display device. The image display device includes: a display unit, and the above-described polarizing plate disposed on at least one side of the display unit.

[0014] Effect of the Invention

[0015] According to an embodiment of the present invention, by controlling the reflection image contrast index to 15 or less, a polarizing plate can be provided that can achieve excellent photographing function and face authentication function without providing a through hole or a transparent portion when applied to an image display device having a camera unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 FIG. is a cross-sectional schematic view of a polarizing plate according to an embodiment of the present invention.

[0017] Figure 2 FIG. is a schematic view showing an example of a drying shrinkage treatment using a heating roll in a method for manufacturing a polarizing element used in the polarizing plate according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0019] A. Overall Configuration of the Polarizing Plate

[0020] Figure 1 FIG. is a cross-sectional schematic view of a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 has: a polarizing element 10, a first protective layer (outer protective layer) 20 disposed on one side of the polarizing element 10 (for example, the side opposite to the display unit when the polarizing plate is applied to an image display device), and a second protective layer (inner protective layer) 30 disposed on the other side of the polarizing element 10 (for example, the display unit side when the polarizing plate is applied to an image display device). Depending on the purpose, etc., either the first protective layer 20 or the second protective layer 30 can be omitted. The polarizing element 10 is composed of a polyvinyl alcohol (PVA)-based resin film containing a dichroic substance (typically iodine, dichroic dye).

[0021] In an embodiment of the present invention, the reflection image contrast index is 15 or less, preferably 14.5 or less, more preferably 13 or less, and further preferably 12 or less. The smaller the reflection image contrast index, the more preferable it is, and its lower limit can be, for example, 5. When the reflection image contrast index is in such a range, it is possible to reduce the transmitted wavefront aberration (optical distortion of light passing through the polarizing plate, details of which will be described later). As a result, when applied to an image display device having a camera unit, it is possible to achieve excellent shooting and face authentication functions without providing through holes or transparent portions. Hereinafter, the technical meaning of defining the reflection image contrast index will be described. As one of the reasons for the increase in the transmitted wavefront aberration, it is presumed to be related to the surface roughness (e.g., arithmetic mean roughness Ra) of the polarizing member. The inventors of the present invention have conducted in-depth research on the relationship between the transmitted wavefront aberration and the surface roughness of the polarizing member, and as a result, it has been found that even if the surface roughness of the polarizing member is controlled, the transmitted wavefront aberration cannot be appropriately controlled. Based on such new insights, experiments were repeatedly conducted, and as a result, it was found that by controlling the reflection image contrast index, which is a characteristic of the entire polarizing plate, the transmitted wavefront aberration can be appropriately controlled, and thus the present invention was completed. The reason why the transmitted wavefront aberration can be appropriately controlled by controlling the reflection image contrast index instead of the surface roughness of the polarizing member is not yet clear theoretically, and it is presumed to be the result of the optimization of the individual and / or mutual optical elements of the components of the polarizing plate as a whole.

[0022] As described above, the reflection image contrast index reflects the individual and / or mutual optical elements (e.g., stripes of the polarizing member, refraction and / or scattering at the interface between the polarizing member and the protective layer, unevenness of the protective layer) of the components of the polarizing plate. The reflection image contrast index can be measured as follows. In a dark room environment, light from a special inspection lighting device (manufactured by Nippon Technology Center Co., Ltd., "S-Light") is irradiated onto the polarizing plate at an angle of 45°; the image of the reflection image is read in the form of digital data; image processing is performed on a 100 mm × 100 mm area to obtain the brightness unevenness as the standard deviation, which is used as the reflection image contrast index. More specifically, the brightness of the pixels of the image is numerically valued on a scale of 0 to 255, and the standard deviation is obtained and used as the reflection image contrast index.

[0023] The polarizing plate preferably has a small transmitted wavefront aberration as described above. Thus, when applied to an image display device having a camera unit, an excellent photographing function and a face authentication function can be achieved without providing a through hole or a transparent portion. The transmitted wavefront aberration is an index representing the optical distortion of the light transmitted through the polarizing plate, and refers to the deviation of the light transmitted through the polarizing plate from the ideal wavefront (spherical surface). Therefore, if the transmitted wavefront aberration is too large, the deviation of the light transmitted through the polarizing plate from the ideal wavefront becomes large, and the light beam emitted from one point of the object does not converge into one point, so there are cases where the image is blurred and distorted. Such an imaging defect particularly hinders correct authentication in a face authentication system. The transmitted wavefront aberration is preferably 100 nm or less, more preferably 50 nm or less, further preferably 30 nm or less, and particularly preferably 25 nm or less. The smaller the transmitted wavefront aberration, the more preferable, and the lower limit thereof can be, for example, 3 nm. Such a transmitted wavefront aberration can be achieved by controlling the reflection image contrast index to a value equal to or less than a specified value as described above. The transmitted wavefront aberration is typically represented by Pv·λ. Here, Pv represents the difference between the maximum value and the minimum value of the transmitted wavefront aberration in the measurement range (Peak-Valley), and represents the ratio of the distance to the wavelength of the incident light. For example, when the transmitted wavefront aberration is a distance of 1 / 10 of the wavelength of the incident light, Pv = 0.1. λ is the wavelength (nm) of the incident light. In one embodiment, the transmitted wavefront aberration can be measured using a HeNe laser with a wavelength of 632.8 nm.

[0024] A-1. Polarizing member

[0025] As described above, the polarizing member is composed of a PVA-based resin film containing a dichroic substance (typically, iodine, dichroic dye). The dichroic substance is preferably iodine. The polarizing member can be formed of a single-layer resin film or a laminate of two or more layers.

[0026] As a specific example of a polarizing element formed of a single-layer resin film, examples include those obtained by subjecting a hydrophilic polymer film such as a polyvinyl alcohol (PVA) - based film, a partially formalized PVA - based film, an ethylene - vinyl acetate copolymer - based partially saponified film, etc. to a dyeing treatment and a stretching treatment using a dichroic substance such as iodine or a dichroic dye, a dehydrated product of PVA, a dehydrochlorinated product of polyvinyl chloride, and other polyene - based oriented films. From the aspect of excellent optical properties, a polarizing element obtained by dyeing a PVA - based film with iodine and performing unidirectional stretching is preferably used. The iodine - based dyeing described above is performed, for example, by immersing the PVA - based film in an iodine aqueous solution. The stretching ratio of the above unidirectional stretching is preferably 3 to 7 times. The stretching can be performed after the dyeing treatment, or can be performed while dyeing. Alternatively, dyeing can be performed after stretching. As needed, a swelling treatment, a cross - linking treatment, a cleaning treatment, a drying treatment, etc. are performed on the PVA - based film. For example, by immersing the PVA - based film in water before dyeing for water washing, not only can the stains and anti - sticking agents on the surface of the PVA - based film be cleaned, but also the PVA - based film can be swollen to prevent uneven dyeing, etc.

[0027] As a specific example of a polarizing element obtained using a laminate, examples include a polarizing element obtained using a laminate of a resin substrate and a PVA - based resin layer (PVA - based resin film) laminated on the resin substrate, or a laminate of a resin substrate and a PVA - based resin layer formed by coating on the resin substrate. A polarizing element obtained using a laminate of a resin substrate and a PVA - based resin layer formed by coating on the resin substrate is manufactured, for example, as follows: A PVA - based resin solution is coated on a resin substrate and dried to form a PVA - based resin layer on the resin substrate, obtaining a laminate of the resin substrate and the PVA - based resin layer; the laminate is stretched and dyed to form a polarizing element from the PVA - based resin layer. In the present embodiment, stretching typically includes immersing the laminate in a boric acid aqueous solution and stretching. Further, stretching may optionally include air - stretching the laminate at a high temperature (for example, 95°C or higher) before stretching in the boric acid aqueous solution. The obtained laminate of the resin substrate / polarizing element can be used directly (that is, the resin substrate can be used as a protective film of the polarizing element), or the resin substrate can be peeled off from the laminate of the resin substrate / polarizing element, and any appropriate protective film suitable for the purpose can be laminated on the peeled surface for use. Details of such a manufacturing method of a polarizing element are described, for example, in Japanese Patent Application Laid - Open No. 2012 - 73580 and Japanese Patent No. 6470455. The entire disclosures of these publications are incorporated herein by reference.

[0028] As the PVA-based resin for forming the above-mentioned PVA-based resin film, any suitable resin can be used. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer can be cited. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer is obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.9 mol%, and more preferably 99.0 mol% to 99.5 mol%. The saponification degree can be determined according to JIS K 6726-1994. By using the PVA-based resin with such a saponification degree, a polarizing element with excellent durability can be obtained. When the saponification degree is too high, there is a concern about gelation.

[0029] The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 5000, and more preferably 1500 to 4500. It should be noted that the average degree of polymerization can be determined according to JIS K 6726-1994.

[0030] The iodine concentration in the PVA-based resin film (polarizing element) is, for example, 5.0 wt% to 12.0 wt%. In addition, the boric acid concentration in the PVA-based resin film is, for example, 12 wt% to 25 wt%.

[0031] The thickness of the polarizing element is, for example, 12 μm or less, preferably 8 μm or less, more preferably 7 μm or less, and further preferably 6 μm or less. On the other hand, the thickness of the polarizing element is preferably 1 μm or more, and more preferably 2 μm or more. The thicker the polarizing element, the easier it is to obtain the desired reflection image contrast index. However, according to the embodiments of the present invention, even such a thin polarizing element can achieve the desired reflection image contrast index.

[0032] The polarizing element preferably exhibits absorption dichroism at any wavelength in the wavelength range of 380 nm to 780 nm. The monomer transmittance of the polarizing element is preferably 40.0% to 46.0%, more preferably 40.5% to 43.0%. The degree of polarization of the polarizing element is preferably 99.9% or more, more preferably 99.95% or more, and further preferably 99.98% or more.

[0033] A-2. Protective layer

[0034] The first and second protective layers are formed of any suitable thin film that can be used as a protective layer for a polarizing member. Specific examples of the material that is the main component of the thin film include cellulose-based resins such as cellulose triacetate (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, polysulfone-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, acetate-based, and other transparent resins. In addition, thermosetting resins or ultraviolet curable resins such as (meth)acrylic-based, urethane-based, (meth)acrylic urethane-based, epoxy-based, and silicone-based resins can also be cited. Furthermore, for example, vitreous polymers such as siloxane-based polymers can also be cited. In addition, a polymer thin film described in Japanese Patent Application Laid-Open No. 2001-343529 (WO01 / 37007) can also be used. As the material of the thin film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used. For example, a resin composition having an alternating copolymer formed of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be cited. The polymer thin film can be, for example, an extrusion molded product of the above resin composition.

[0035] When the polarizing plate 100 is applied to an image display device, the thickness of the first protective layer (outer protective layer) 20 disposed on the side opposite to the display unit is typically 300 μm or less, preferably 100 μm or less, more preferably 5 μm to 80 μm, and further preferably 10 μm to 60 μm. It should be noted that in the case of performing surface treatment, the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.

[0036] When the polarizing plate 100 is applied to an image display device, the thickness of the second protective layer (inner protective layer) 30 disposed on the display unit side is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and still more preferably 10 μm to 60 μm. In one embodiment, the inner protective layer is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane retardation Re(550) is 0 nm to 10 nm and the thickness-direction retardation Rth(550) is -10 nm to +10 nm. In another embodiment, the inner protective layer is a retardation layer having any appropriate retardation value. In this case, the in-plane retardation Re(550) of the retardation layer is, for example, 110 nm to 150 nm, and the angle formed by the slow axis thereof and the absorption axis of the polarizing member is, for example, 40° to 50°. "Re(550)" is the in-plane retardation measured at 23 °C with light having a wavelength of 550 nm and is obtained by the formula: Re = (nx - ny) × d. "Rth(550)" is the thickness-direction retardation measured at 23 °C with light having a wavelength of 550 nm and is obtained by the formula: Re = (nx - nz) × d. Here, "nx" is the refractive index in the direction in which the in-plane refractive index is the largest (i.e., the slow-axis direction), "ny" is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast-axis direction), "nz" is the refractive index in the thickness direction, and "d" is the thickness (nm) of the layer (film). It should be noted that, as described above, it is preferable to omit the second protective layer (inner protective layer) 30.

[0037] B. Method for manufacturing a polarizing member

[0038] A polarizing member can be produced, for example, by a method including the following steps: forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a strip-shaped thermoplastic resin substrate to form a laminate; and sequentially performing an air-assisted stretching treatment, a dyeing treatment, a water stretching treatment, and a drying shrinkage treatment on the laminate. In the drying shrinkage treatment, the laminate is conveyed in the longitudinal direction while being heated to cause a shrinkage of 2% or more in the width direction. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roller, and the temperature of the heating roller is preferably 60°C to 120°C. The shrinkage rate in the width direction of the laminate due to the drying shrinkage treatment is preferably 2% or more. According to such a manufacturing method, the polarizing member described in Item B above can be obtained. In particular, by producing a laminate having a PVA-based resin layer containing a halide, subjecting the above laminate to multi-stage stretching including air-assisted stretching and water stretching, and heating the stretched laminate with a heating roller, a polarizing member having excellent optical properties (typically, monomer transmittance and degree of polarization) and in which deviations in optical properties are suppressed can be obtained. Specifically, by using a heating roller in the drying shrinkage treatment step, the laminate can be uniformly shrunk as a whole while being conveyed. Thereby, not only can the optical properties of the obtained polarizing member be improved, but also a polarizing member having excellent optical properties can be stably produced, and unevenness in the optical properties (especially monomer transmittance) of the polarizing member can be suppressed.

[0039] B-1. Production of laminate

[0040] As a method for producing a laminate of a thermoplastic resin substrate and a PVA-based resin layer, any suitable method can be adopted. It is preferable to coat a coating liquid containing a halide and a PVA-based resin on the surface of the thermoplastic resin substrate and dry it, thereby forming a PVA-based resin layer on the thermoplastic resin substrate. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

[0041] As a method for coating the coating liquid, any suitable method can be adopted. For example, roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, knife coating (comma coating, etc.) can be mentioned. The coating and drying temperature of the above coating liquid is preferably 50°C or higher.

[0042] The thickness of the PVA-based resin layer is preferably 3 μm to 40 μm, more preferably 3 μm to 20 μm.

[0043] Before forming the PVA-based resin layer, the thermoplastic resin substrate may be subjected to surface treatment (such as corona treatment, etc.), or an adhesion-promoting layer may be formed on the thermoplastic resin substrate. By performing such treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved.

[0044] B-1-1. Thermoplastic resin substrate

[0045] As the thermoplastic resin substrate, any suitable thermoplastic resin film can be used. Details of the thermoplastic resin substrate are described, for example, in Japanese Patent Laid-Open No. 2012-73580. The entire disclosure of this publication is incorporated herein by reference.

[0046] B-1-2. Coating solution

[0047] The coating solution contains a halide and a PVA-based resin as described above. The above coating solution is typically a solution in which the above halide and the above PVA-based resin are dissolved in a solvent. As the solvent, for example, water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, amines such as ethylenediamine and diethylenetriamine can be cited. These can be used alone or in combination of two or more. Among these, water is preferred. The PVA-based resin concentration in the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. At such a resin concentration, a uniform coating film that adheres to the thermoplastic resin substrate can be formed. The content of the halide in the coating solution is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

[0048] Additives can be blended in the coating solution. As additives, for example, plasticizers, surfactants, etc. can be cited. As plasticizers, for example, polyhydric alcohols such as ethylene glycol and glycerin can be cited. As surfactants, for example, nonionic surfactants can be cited. They can be used for the purpose of further improving the uniformity, dyeability, and stretchability of the obtained PVA-based resin layer.

[0049] As the above-mentioned PVA-based resin, any suitable resin can be used. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer can be mentioned. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer is obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The saponification degree can be determined according to JIS K 6726-1994. By using the PVA-based resin with such a saponification degree, a polarizing member with excellent durability can be obtained. If the saponification degree is too high, there is a concern about gelation. As described above, the PVA-based resin preferably contains a PVA-based resin modified with an acetoacetyl group.

[0050] The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1000 to 10,000, preferably 1200 to 4500, and more preferably 1500 to 4300. It should be noted that the average degree of polymerization can be determined according to JIS K 6726-1994.

[0051] As the above-mentioned halide, any suitable halide can be used. For example, iodide and sodium chloride can be mentioned. As the iodide, for example, potassium iodide, sodium iodide, and lithium iodide can be mentioned. Among these, potassium iodide is preferred.

[0052] The amount of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, and more preferably 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the PVA-based resin. If the amount of the halide exceeds 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, the halide may exude and the finally obtained polarizing member may become cloudy.

[0053] Generally, by stretching the PVA-based resin layer, the orientation of polyvinyl alcohol molecules in the PVA-based resin becomes higher. However, if the stretched PVA-based resin layer is immersed in a liquid containing water, the orientation of polyvinyl alcohol molecules sometimes becomes disordered and the orientation decreases. In particular, in the case of stretching a laminate of a thermoplastic resin and a PVA-based resin layer in boric acid water, when stretching the laminate in boric acid water at a relatively high temperature to stabilize the stretching of the thermoplastic resin, the tendency of the above-mentioned degree of orientation to decrease is significant. For example, the stretching of a PVA film itself in boric acid water is usually carried out at 60 °C, while the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is carried out at a relatively high temperature of about 70 °C. In this case, the orientation of PVA at the initial stage of stretching decreases before rising through stretching in water. In contrast, by producing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate and performing high-temperature stretching (auxiliary stretching) in air before stretching the laminate in boric acid water, the crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, compared with the case where the PVA-based resin layer does not contain a halide, the disorder of the orientation of polyvinyl alcohol molecules and the decrease in the orientation can be suppressed. Thereby, the optical properties of a polarizing element obtained through treatment steps such as dyeing treatment and stretching treatment in water, in which the laminate is immersed in a liquid, can be improved.

[0054] B-2. Air-assisted stretching treatment

[0055] In particular, in order to obtain high optical properties, a two-stage stretching method combining dry stretching (auxiliary stretching) and stretching in boric acid water is preferably used. By introducing auxiliary stretching as in two-stage stretching, stretching can be carried out while suppressing the crystallization of the thermoplastic resin substrate, the problem that the stretchability decreases due to excessive crystallization of the thermoplastic resin substrate during subsequent stretching in boric acid water can be solved, and the laminate can be stretched at a higher magnification. Furthermore, when a PVA-based resin is coated on a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, the coating temperature needs to be lowered compared with the case of usually coating a PVA-based resin on a metal roller. As a result, there is a problem that the crystallization of the PVA-based resin becomes relatively low and sufficient optical properties cannot be obtained. In contrast, by introducing auxiliary stretching, even when a PVA-based resin is coated on a thermoplastic resin, the crystallinity of the PVA-based resin can be improved and high optical properties can be achieved. In addition, by simultaneously increasing the orientation of the PVA-based resin in advance, problems such as a decrease in the orientation and dissolution of the PVA-based resin when immersed in water during subsequent dyeing and stretching processes can be prevented, and high optical properties can be achieved.

[0056] The stretching method of air-assisted stretching can be fixed-end stretching (for example, the method of stretching using a stentering machine), or free-end stretching (for example, the method of unidirectionally stretching a laminate by passing it between rollers with different circumferential speeds). In one embodiment, the stretching method of air-assisted stretching can be, for example, biaxial stretching using a stentering machine. By appropriately setting the stretching conditions of biaxial stretching, a predetermined biaxiality can be imparted to the obtained polarizing element. As a result, a polarizing element having a desired puncture strength can be achieved.

[0057] The stretching ratio in the length direction of air-assisted stretching is preferably 2.3 times or more, more preferably 2.4 to 3.5 times. In the embodiment of the present invention, the width residual rate (the width after shrinkage relative to the original width: %) is controlled by adopting biaxial stretching as described above. Specifically, the difference between the width residual rate of air-assisted stretching (that is, after air-assisted stretching) and the free shrinkage width residual rate is preferably 2% or more, more preferably 3% or more, and further preferably 5% or more. The maximum value of this difference can be, for example, 15%. Here, the free shrinkage width residual rate is the width residual rate when free-end stretching is performed in the length direction at the same stretching ratio. Specifically, the free shrinkage width residual rate when the stretching ratio is set to x times can be calculated by (1 / x 1 / 2 ) × 100. For example, when stretched to 2.4 times, the free shrinkage width residual rate is (1 / (2.4) 1 / 2 ) × 100 = 64.5%. It is considered that this is because when stretching in the length direction during free shrinkage, the width direction and the thickness direction shrink at the same ratio. It should be noted that when combining air-assisted stretching and water stretching, the maximum stretching ratio (in the length direction) relative to the original length of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, and further preferably 6.0 times or more. In this specification, the "maximum stretching ratio" refers to the stretching ratio just before the laminate breaks, and refers to the stretching ratio at which the breakage of the laminate is additionally confirmed and a value 0.2 lower than that value.

[0058] The stretching temperature for air-assisted stretching can be set to any appropriate value according to the forming material of the thermoplastic resin substrate, the stretching method, etc. The stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C, and particularly preferably equal to or higher than Tg + 15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, the crystallization of the PVA-based resin can be inhibited from proceeding rapidly, thereby suppressing the adverse conditions caused by this crystallization (for example, hindering the orientation of the PVA-based resin layer caused by stretching). The crystallization index of the PVA-based resin after air-assisted stretching is preferably 1.3 to 1.8, more preferably 1.4 to 1.7. The crystallization index of the PVA-based resin can be measured by the ATR method using a Fourier transform infrared spectrometer. Specifically, the measurement is carried out with polarized light as the measurement light, and the crystallization index is calculated according to the following formula using the intensities of 1141 cm -1 and 1440 cm -1 of the obtained spectrum.

[0059] Crystallization index = (I C / I R )

[0060] where,

[0061] I C : is the intensity of 1141 cm -1 when the measurement light is incident and the measurement is carried out

[0062] I R : is the intensity of 1440 cm -1 when the measurement light is incident and the measurement is carried out.

[0063] B-3. Insolubilization treatment, dyeing treatment and crosslinking treatment

[0064] If necessary, an insolubilization treatment is carried out after the air-assisted stretching treatment and before the water stretching treatment and the dyeing treatment. The above insolubilization treatment is typically carried out by immersing the PVA-based resin layer in a boric acid aqueous solution. The above dyeing treatment is typically carried out by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). If necessary, a crosslinking treatment is carried out after the dyeing treatment and before the water stretching treatment. The above crosslinking treatment is typically carried out by immersing the PVA-based resin layer in a boric acid aqueous solution. Details of the insolubilization treatment, dyeing treatment and crosslinking treatment are described, for example, in Japanese Patent Laid-Open No. 2012-73580 (above).

[0065] B-4. Water stretching treatment

[0066] The stretching treatment in water is carried out by immersing the laminate in a stretching bath. Through the stretching treatment in water, stretching can be carried out at a temperature lower than the glass transition temperature of the above-mentioned thermoplastic resin substrate and the PVA-based resin layer (typically around 80 °C), and it is possible to stretch the PVA-based resin layer at a high magnification while suppressing its crystallization. As a result, a polarizing element with excellent optical properties can be manufactured.

[0067] Any appropriate method can be adopted for the stretching method of the laminate. Specifically, it can be fixed-end stretching or free-end stretching (for example, a method of unidirectionally stretching the laminate by passing it between rollers with different circumferential speeds). Free-end stretching is preferably selected. The stretching of the laminate can be carried out in one stage or in multiple stages. In the case of multiple stages, the stretching ratio (maximum stretching ratio) of the laminate described later is the product of the stretching ratios of each stage.

[0068] The stretching in water is preferably carried out by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water). By using an aqueous boric acid solution as the stretching bath, it is possible to impart to the PVA-based resin layer the rigidity to withstand the tension applied during stretching and the water resistance of being insoluble in water. Specifically, boric acid generates tetra-hydroxyborate anions in an aqueous solution and crosslinks with the PVA-based resin through hydrogen bonds. As a result, it is possible to impart rigidity and water resistance to the PVA-based resin layer and thus stretch it well, and a polarizing element with excellent optical properties can be manufactured.

[0069] The above-mentioned aqueous boric acid solution is preferably obtained by dissolving boric acid and / or borate in water as a solvent. The boric acid concentration is preferably 1 part by weight to 10 parts by weight, more preferably 2.5 parts by weight to 6 parts by weight, and particularly preferably 3 parts by weight to 5 parts by weight relative to 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, it is possible to effectively suppress the dissolution of the PVA-based resin layer and obtain a polarizing element with higher properties. It should be noted that an aqueous solution obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, etc. in a solvent other than boric acid or borate can also be used.

[0070] It is preferable to mix an iodide in the above-mentioned stretching bath (aqueous boric acid solution). By mixing an iodide, it is possible to suppress the elution of iodine adsorbed on the PVA-based resin layer. Specific examples of the iodide are as described above. The concentration of the iodide is preferably 0.05 part by weight to 15 parts by weight, more preferably 0.5 part by weight to 8 parts by weight relative to 100 parts by weight of water.

[0071] The stretching temperature (the liquid temperature of the stretching bath) and the immersion time of the laminate in the stretching bath can be appropriately set according to the composition of the protective layer (representatively, the material, and whether it is disposed on one side or both sides of the polarizer). The stretching temperature can be, for example, 70°C or lower, and can be, for example, 67°C or lower, and can be, for example, 66°C or lower, and can be, for example, 65°C or lower. The lower limit of the stretching temperature can be, for example, 50°C, and can be, for example, 55°C. The immersion time of the laminate in the stretching bath can be, for example, 50 seconds or longer, and can be, for example, 55 seconds or longer, and can be, for example, 60 seconds or longer. The upper limit of the immersion time can be, for example, 100 seconds. The combination of the stretching temperature and the immersion time can be, for example, 55°C to 66°C / 55 seconds or longer, and can be, for example, 60°C to 66°C / 60 seconds to 80 seconds. Stretching in boric acid water is usually carried out at around 70°C for about 50 seconds, but the inventors have found that by lowering the stretching temperature by several degrees Celsius and extending the immersion time, the reflection image contrast index can be significantly reduced without degrading the optical properties of the polarizer. This is an unexpectedly excellent effect. Furthermore, it has also been found that the same effect can be obtained by only lowering the stretching temperature or only extending the immersion time using the composition of the protective layer.

[0072] The stretching ratio brought about by stretching in water is preferably 1.5 times or more, more preferably 3.0 times or more. The total stretching ratio of the laminate with respect to the original length of the laminate is preferably 5.0 times or more, and further preferably 5.5 times or more. By achieving such a high stretching ratio, a polarizer with extremely excellent optical properties can be manufactured. Such a high stretching ratio can be achieved by adopting a stretching method in water (stretching in boric acid water).

[0073] B-5. Drying shrinkage treatment

[0074] The above-mentioned dry shrinkage treatment can be carried out by area heating in which the entire area is heated, or by heating the conveying rollers (using so-called heating rollers) (heating roller drying method). It is preferred to use both. By drying using heating rollers, the heating curl of the laminate can be effectively suppressed, thereby manufacturing a polarizing element with excellent appearance. Specifically, by drying the laminate in a state along the heating roller, the crystallization of the above-mentioned thermoplastic resin substrate can be effectively promoted, thereby increasing the crystallinity. Even at a relatively low drying temperature, the crystallinity of the thermoplastic resin substrate can be increased well. As a result, the rigidity of the thermoplastic resin substrate increases, and thus it becomes a state capable of withstanding the shrinkage of the PVA-based resin layer caused by drying, and curling can be suppressed. In addition, by using heating rollers, the laminate can be dried while maintaining a flat state. Therefore, not only curling can be suppressed, but also the generation of wrinkles can be suppressed. At this time, by the dry shrinkage treatment, the laminate shrinks in the width direction, thereby improving the optical properties. This is because the orientation of PVA and the PVA / iodine complex can be effectively improved. The shrinkage rate of the laminate in the width direction caused by the dry shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using heating rollers, the laminate can be continuously shrunk in the width direction while being conveyed, and high productivity can be achieved.

[0075] Figure 2 It is a schematic diagram showing an example of the dry shrinkage treatment. In the dry shrinkage treatment, the laminate 200 is dried while being conveyed by the conveying rollers R1 to R6 and the guide rollers G1 to G4 heated to a specified temperature. In the illustrated example, the conveying rollers R1 to R6 are arranged in such a way that the surfaces of the PVA resin layer and the thermoplastic resin substrate are alternately and continuously heated. However, for example, the conveying rollers R1 to R6 may be arranged in such a way that only one surface of the laminate 200 (for example, the thermoplastic resin substrate surface) is continuously heated.

[0076] The drying conditions can be controlled by adjusting the heating temperature of the conveying rollers (the temperature of the heating rollers), the number of heating rollers, and the contact time with the heating rollers. The temperature of the heating rollers is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. An optical laminate can be manufactured that can well increase the crystallinity of the thermoplastic resin, thereby well suppressing curling and having very excellent durability. It should be noted that the temperature of the heating rollers can be measured by a contact thermometer. In the illustrated example, 6 conveying rollers are provided, but there is no particular limitation as long as there are a plurality of conveying rollers. The conveying rollers are usually provided in 2 to 40, preferably 4 to 30. The contact time (total contact time) of the laminate with the heating rollers is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and further preferably 1 to 10 seconds.

[0077] The heating roller can be arranged inside a heating furnace (such as an oven), or can be arranged in a normal production line (at room temperature environment). It is preferably arranged inside a heating furnace equipped with air supply means. By combining drying based on the heating roller and hot air drying, the sharp temperature change between the heating rollers can be suppressed, and the shrinkage in the width direction can be easily controlled. The temperature of the hot air drying is preferably 30°C to 100°C. In addition, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10 m / s to 30 m / s. It should be noted that this wind speed is the wind speed inside the heating furnace and can be measured by a mini vane type digital anemometer.

[0078] B-6. Other Treatments

[0079] The cleaning treatment is preferably carried out after the stretching treatment in water and before the drying shrinkage treatment. The above-mentioned cleaning treatment is typically carried out by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

[0080] C. Image Display Device

[0081] The polarizing plates described in the above Item A and Item B can be applied to an image display device. Therefore, such an image display device is also included in the embodiments of the present invention. The image display device includes: a display unit, and the polarizing plates described in the above Item A and Item B arranged on at least one side of the display unit. As the image display device, for example, a liquid crystal display device and an organic electro-luminescence (EL) display device can be cited. The configuration of the image display device is well-known in the industry, so its detailed description is omitted.

[0082] Examples

[0083] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by these examples. The evaluation items in the examples are as follows.

[0084] (1) Reflection Image Contrast Index

[0085] Place the polarizing plates obtained in the examples and comparative examples on the horizontal plane in a small dark room. Using a special inspection lighting device (manufactured by Nippon Technical Center Co., Ltd., "S-Light") as the light source, irradiate the polarizing plate with light from this light source at an angle of 45°. At this time, set the polarizing plate so that the absorption axis direction of the polarizing plate is perpendicular to the irradiation direction of the light source. The polarizing plate is adhered to a light-shielding black acrylic plate with an acrylic-based adhesive (thickness 20 μm). For a polarizing plate with a protective layer on one side, bring the polarizing element surface into contact with the adhesive, and for a polarizing plate with protective layers on both sides, bring the inner protective layer surface into contact with the adhesive. It should be noted that compared with the polarizing plate, the reflection image contrast index of the black acrylic plate is small enough not to affect the measurement results. Take a photograph of the reflection image projected onto the screen on the wall surface set in the dark room with a camera, and read the image of the reflection image in digital data form. Perform image processing on a 100 mm × 100 mm area of the read image, calculate the brightness unevenness as the standard deviation, and use it as the reflection image contrast index. More specifically, numerically represent the brightness of the pixels of the image on a scale of 0 to 255, calculate its standard deviation, and use it as the reflection image contrast index.

[0086] (2) Transmission wavefront aberration

[0087] Place the polarizing plates obtained in the examples and comparative examples in a measuring device (manufactured by ZYGO Corporation, Verifire interferometer system) for measurement. Use a HeNe laser with a wavelength of 632.8 nm as the light source, and set the spot diameter of the incident light to 1 mm. Use an application program for measuring the spherical transmission wavefront to obtain the transmission wavefront aberration calculated from the interference light.

[0088] [Example 1]

[0089] 1. Production of polarizing element

[0090] As the thermoplastic resin substrate, use a long strip-shaped amorphous isophthalic acid copolyethylene terephthalate film (thickness: 100 μm) with a Tg of about 75 °C, and perform corona treatment on one side of the resin substrate.

[0091] In 100 parts by weight of a PVA-based resin obtained by mixing polyvinyl alcohol (degree of polymerization 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER") in a ratio of 9:1, add 13 parts by weight of potassium iodide, dissolve the resulting substance in water, and prepare a PVA aqueous solution (coating solution).

[0092] Coat the above PVA aqueous solution on the corona-treated surface of the resin substrate and dry it at 60 °C to form a PVA-based resin layer with a thickness of 13 μm, and produce a laminate.

[0093] The obtained laminate is unidirectionally stretched longitudinally (in the length direction) to 2.4 times (air-assisted stretching treatment) in an oven at 130 °C.

[0094] Next, the laminate is immersed in an insolubilization bath at a liquid temperature of 40 °C (an aqueous boric acid solution obtained by compounding 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).

[0095] Next, in a dyeing bath at a liquid temperature of 30 °C (an aqueous iodine solution obtained by compounding iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water), the concentration is adjusted so that the monomer transmittance (Ts) of the finally obtained polarizing element becomes a desired value and it is immersed for 60 seconds (dyeing treatment).

[0096] Next, it is immersed in a crosslinking bath at a liquid temperature of 40 °C (an aqueous boric acid solution obtained by compounding 3 parts by weight of potassium iodide and compounding 5 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (crosslinking treatment).

[0097] Thereafter, the laminate is immersed in an aqueous boric acid solution at a liquid temperature of 64 °C (boric acid concentration 4 wt%, potassium iodide concentration 5 wt%) and unidirectionally stretched longitudinally (in the length direction) between rollers with different circumferential speeds so that the total stretching ratio becomes 5.5 times (stretching treatment in water). It should be noted that the immersion time of the laminate in the aqueous boric acid solution during the stretching treatment in water is 75 seconds.

[0098] Thereafter, the laminate is immersed in a cleaning bath at a liquid temperature of 20 °C (an aqueous solution obtained by compounding 4 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment).

[0099] Thereafter, while drying in an oven maintained at about 90 °C, it is brought into contact with a SUS heating roller having a surface temperature maintained at about 75 °C (dry shrinkage treatment).

[0100] By operating in this way, a polarizing element with a thickness of about 5 μm is formed on the resin substrate.

[0101] 2. Fabrication of polarizing plate

[0102] Using an ultraviolet curable adhesive, a polycarbonate resin film (40 μm) is laminated on the surface of the above-obtained polarizing element (the surface on the side opposite to the resin substrate) as a protective layer. Specifically, it is coated so that the total thickness of the curable adhesive becomes about 1.0 μm and laminated using a roll press. Thereafter, UV light is irradiated from the norbornene-based film side to cure the adhesive. Next, the resin substrate is peeled off to obtain a polarizing plate having a structure of polycarbonate resin film (protective layer) / polarizing element. The obtained polarizing plate is subjected to the evaluations in the above (1) and (2). The results are shown in Table 1.

[0103] It should be noted that the polycarbonate resin film is produced as follows. 47.19 parts by mass of tricyclodecane dimethanol (hereinafter sometimes abbreviated as "TCDDM"), 175.1 parts by mass of diphenyl carbonate (hereinafter sometimes abbreviated as "DPC"), and 0.979 parts by mass of a 0.2 mass% aqueous solution of cesium carbonate as a catalyst are put into a reaction vessel with respect to 81.98 parts by mass of isosorbide (hereinafter sometimes abbreviated as "ISB"). In a nitrogen atmosphere, as the first-stage process of the reaction, the temperature of the heating bath is heated to 150°C, and the raw materials are dissolved with stirring as needed (about 15 minutes). Then, the pressure is set from normal pressure to 13.3 kPa, and while raising the temperature of the heating bath to 190°C in 1 hour, the generated phenol is discharged out of the reaction vessel. After keeping the whole reaction vessel at 190°C for 15 minutes, as the second-stage process, the pressure inside the reaction vessel is set to 6.67 kPa, and the temperature of the heating bath is raised to 230°C in 15 minutes, and the generated phenol is discharged out of the reaction vessel. Since the stirring torque of the stirrer gradually increases, in order to raise the temperature to 250°C in 8 minutes and further remove the generated phenol, the pressure inside the reaction vessel is brought to 0.200 kPa or less. After reaching the specified stirring torque, the reaction is terminated, and the generated reaction product is extruded into water to obtain pellets of the polycarbonate copolymer. After vacuum-drying the obtained pellets at 80°C for 5 hours, a resin film is produced using a film-forming apparatus equipped with a single-screw extruder (manufactured by Toshiba Machine Co., Ltd., barrel set temperature: 250°C), a T-die (width 200 mm, set temperature: 250°C), a cooling roll (set temperature: 120 - 130°C), and a winder. The obtained strip-shaped resin film is stretched obliquely at a temperature of 135°C and a draw ratio of 2.2 times to obtain a polycarbonate resin film with a thickness of 40 μm.

[0104] [Example 2]

[0105] The temperature of the boric acid aqueous solution in the in-water stretching treatment was set to 66°C, the immersion time in the boric acid aqueous solution was set to 60 seconds, and a cycloolefin-based film (manufactured by Zeon Corporation, Japan, 17 μm) was used as the protective layer. Otherwise, the operation was the same as in Example 1 to produce a polarizing plate. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0106] [Example 3]

[0107] The temperature of the boric acid aqueous solution in the stretching treatment in water was set to 64 °C, the immersion time in the boric acid aqueous solution was set to 50 seconds, and an acrylic resin film (thickness: 40 μm) was used as the protective layer. Otherwise, the operation was the same as in Example 1 to produce a polarizing plate. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. Note that the acrylic resin film was produced as follows. An MS resin (copolymer of methyl methacrylate / styrene (molar ratio) = 80 / 20) was imidized with monomethylamine (imidization rate: 5%). The obtained imidized MS resin had a glutarimide unit, a (meth)acrylate unit, and a styrene unit, and an acid value of 0.5 mmol / g. The obtained imidized MS resin was formed into a film by melt extrusion molding. At this time, 0.66 parts by weight of an ultraviolet absorber was supplied with respect to 100 parts by weight of the resin.

[0108] [Example 4]

[0109] The same operation as in Example 2 was performed to form a polarizing element with a thickness of about 5 μm on the resin substrate. A cycloolefin-based film (manufactured by Zeon Corporation, Japan, 17 μm) was bonded as a protective layer to the surface of the obtained polarizing element (the surface on the side opposite to the resin substrate) by means of an ultraviolet curable adhesive. Specifically, the curable adhesive was applied so that the total thickness became about 1.0 μm, and bonding was performed using a roll press. Thereafter, UV light was irradiated from the cycloolefin-based film side to cure the adhesive. Then, the same operation as above was performed on the surface of the polarizing element exposed by peeling off the resin substrate to bond a polycarbonate-based resin film similar to that in Example 1. By such an operation, a polarizing plate having a structure of cycloolefin-based film (inner protective layer) / polarizing element / polycarbonate-based resin film (outer protective layer) was obtained. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. Note that the cycloolefin-based film was produced as follows. Pellets of a cycloolefin polymer (hydride of a ring-opening polymer of a norbornene-based monomer, trade name "ZEONOR1420R", manufactured by Zeon Corporation, Japan, glass transition temperature: 136 °C) were dried at 100.5 kPa and 100 °C for 12 hours. 1.5 parts by weight of a pigment compound represented by the following formula was added to the resin weight (100 parts by weight), and a cycloolefin-based film was formed using a T-mode film melt extrusion molding machine at a die temperature of 260 °C using a single-screw extruder.

[0110]

[0111] [Example 5]

[0112] The same acrylic resin film as in Example 3 was used as the inner protective layer, and the same cycloolefin-based film as in Example 4 was used as the outer protective layer. Otherwise, the operation was the same as in Example 4, and a polarizing plate having a structure of acrylic resin film (inner protective layer) / polarizer / cycloolefin-based film (outer protective layer) was obtained. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0113] [Example 6]

[0114] The temperature of the boric acid aqueous solution in the in-water stretching treatment was set to 70°C, and the immersion time in the boric acid aqueous solution was set to 60 seconds. Otherwise, the operation was the same as in Example 5, and a polarizing plate was produced. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0115] [Comparative Example 1]

[0116] The temperature of the boric acid aqueous solution in the in-water stretching treatment was set to 70°C, and the immersion time was set to 50 seconds. Otherwise, the operation was the same as in Example 2, and a polarizing plate was produced. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0117] [Comparative Example 2]

[0118] The temperature of the boric acid aqueous solution in the in-water stretching treatment was set to 70°C, and the immersion time was set to 50 seconds. Otherwise, the operation was the same as in Example 1, and a polarizer with a thickness of about 5 μm was formed on the resin substrate. A cycloolefin-based film (manufactured by Zeon Corporation, Japan, 17 μm) was adhered as a protective layer to the surface of the obtained polarizer (the side opposite to the resin substrate side) by means of an ultraviolet curable adhesive. Specifically, the coating was performed so that the total thickness of the curable adhesive became about 1.0 μm, and the adhesion was carried out using a roll press. Thereafter, UV light was irradiated from the cycloolefin-based film side to cure the adhesive. Then, an acrylic film (manufactured by Toyo Kohan Co., Ltd., 40 μm) was adhered in the same manner as above to the surface of the polarizer exposed by peeling off the resin substrate. By such an operation, a polarizing plate having a structure of acrylic film (inner protective layer) / polarizer / cycloolefin-based film (outer protective layer) was obtained. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0119] [Table 1]

[0120]

[0121] As is clear from Table 1, the reflection image contrast index of the polarizing plate according to the embodiment of the present invention is small, and as a result, the transmitted wavefront aberration is small. Therefore, it can be understood that when the polarizing plate according to the embodiment of the present invention is applied to an image display device having a camera unit, excellent photographing function and face authentication function can be achieved without providing a through hole or a transparent portion. Such a polarizing plate can be realized by lowering the temperature of the boric acid aqueous solution and extending the immersion time in the water stretching treatment in the manufacture of the polarizing member.

[0122] Industrial applicability

[0123] The polarizing plate according to the embodiment of the present invention is suitable for use in an image display device (for example, a liquid crystal display device, an organic EL display device, a quantum dot display device).

[0124] Explanation of reference numerals

[0125] 10 Polarizing member

[0126] 20 First protective layer

[0127] 30 Second protective layer

[0128] 100 Polarizing plate

Claims

1. A polarizing plate having a polarizer and a protective layer disposed on one side of the polarizer, the polarizer being composed of a polyvinyl alcohol-based resin film containing a dichroic substance, the protective layer being composed of a polycarbonate-based resin film containing isosorbide, tricyclodecane dimethanol, and diphenyl carbonate as structural units, or an acrylic-based resin film having a glutarimide unit, a (meth)acrylate unit, and a styrene unit, the reflection image contrast index of the polarizing plate being 13 or less, and the reflection image contrast index being measured as follows: In a darkroom environment, light from a light source is irradiated onto the polarizing plate at an angle of 45°. At this time, the polarizing plate is set so that the absorption axis direction of the polarizing plate is perpendicular to the irradiation direction of the light source. The reflection image projected onto a screen provided on the wall surface in the darkroom is photographed with a camera, and the image of the reflection image is read in digital data form. Image processing is performed on a 100 mm × 100 mm area of the read image, and the brightness unevenness is obtained as the standard deviation, which is used as the reflection image contrast index.

2. The polarizing plate according to claim 1, wherein, The thickness of the polarizer is 12 μm or less.

3. An image display device comprising: a display unit, and the polarizing plate according to claim 1 or 2 disposed on at least one side of the display unit.

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