JP7532310B2 - Polarizing plate, its manufacturing method, and image display device using said polarizing plate - Google Patents

Description

The present invention relates to a polarizing plate, a method for producing the same, and an image display device using the polarizing plate.

Some image display devices, such as mobile phones and notebook personal computers (PCs), are equipped with internal electronic components, such as cameras. In recent years, with the rapid spread of smartphones and touch panel type information processing devices, there is a demand for further improvements in camera performance, etc. Also, in order to accommodate the diversification of shapes and high functionality of image display devices, there is a demand for polarizing plates that have partial polarization performance. In order to meet these demands, polarizers have been proposed in which non-polarizing parts formed by chemical processing are formed in predetermined areas (for example, Patent Documents 1 and 2).

Korean Patent Publication No. 10-2015-0086159 JP 2015-215609 A

However, such polarizers have depressions in the chemically treated areas (i.e., the non-polarizing areas), and when such polarizers are used to construct a polarizing plate, air bubbles may be present in the depressions.

The present invention has been made to solve the above-mentioned newly recognized problems, and its main objective is to provide a polarizing plate that includes a polarizer having a thin portion as a non-polarizing portion at a specified portion, and that does not contain air bubbles in the thin portion.

The polarizing plate of the present invention comprises a polarizer having a thin portion on one side; and a protective layer attached to the thin portion side of the polarizer via an adhesive layer, and the thickness of the adhesive layer in the portion other than the thin portion is 23 μm or more.
According to another aspect of the present invention, there is provided a method for producing the above polarizing plate, which includes: treating a predetermined position on one surface of a polarizer with a treatment liquid to form a thin portion at the predetermined position; disposing a pressure-sensitive adhesive layer between the surface of the polarizer on which the thin portion is formed and a protective layer, the pressure-sensitive adhesive layer having a thickness of 23 μm or more at a portion other than the thin portion; and laminating the polarizer and the protective layer via the pressure-sensitive adhesive layer.
According to yet another aspect of the present invention, there is provided an image display device comprising the above-described polarizing plate, the thin portion of the polarizing plate being disposed at a position corresponding to a camera unit.

According to the present invention, in a polarizing plate including a polarizer having a thin portion as a non-polarizing portion, by optimizing the thickness of the adhesive layer that bonds the polarizer and the protective layer, a polarizing plate that does not contain air bubbles in the thin portion can be realized. Since air bubbles are easily noticeable to users in the camera portion of an image display device, the presence of air bubbles poses a problem of significantly reducing the commercial value of the image display device rather than affecting its actual performance. Therefore, by preventing the generation of air bubbles according to the present invention, the commercial value of the polarizing plate (and, as a result, the image display device) can be significantly increased.

1 is a schematic plan view of a polarizing plate according to one embodiment of the present invention. 2 is a schematic cross-sectional view of a main part of the polarizing plate of FIG. 1. FIG. 2 is a schematic perspective view of a polarizer in a polarizing plate according to another embodiment of the present invention. FIG. 2 is a schematic perspective view illustrating bonding of a polarizer and a first surface protective film in a method for producing a polarizing plate according to an embodiment of the present invention. 5A to 5C are schematic diagrams illustrating the formation of a non-polarizing portion in a method for producing a polarizing plate according to an embodiment of the present invention. 1 is a graph showing the relationship between the thickness of the pressure-sensitive adhesive layer and the number of bubbles generated in Examples and Comparative Examples.

Below, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. Note that, for ease of viewing, the scale and ratio of each figure may not correspond. Also, the thickness ratio of each layer in each figure may differ from the actual one.

A. Overall Configuration of Polarizing Plate FIG. 1 is a schematic plan view of a polarizing plate according to one embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view of a main part of the polarizing plate of FIG. 1. The polarizing plate 100 has a polarizer 10 having a thin portion 12 at a predetermined position, and a protective layer 30 attached to one side of the polarizer 10 via an adhesive layer 20. As shown in the illustrated example, the thin portion 12 typically has a recess 14 in which the surface on one side of the polarizer is recessed. As shown in the illustrated example, the protective layer 30 is typically attached to at least the recess 14 side of the polarizer 10. If necessary, another protective layer (not shown) may be attached to the other side of the polarizer via any appropriate adhesive layer (adhesive layer or adhesive layer). In an embodiment of the present invention, the thin portion 12 (recess 14) is substantially free of air bubbles. In this specification, "substantially free of air bubbles" means that no air bubbles are recognized when the thin portion of the polarizing plate is visually observed against a black background. The state where no bubbles are visually recognized may preferably be a state where no bubbles having a diameter of 30 μm or more, more preferably a state where no bubbles having a diameter of 20 μm or more are present. In an embodiment of the present invention, the polarizing plate 100 is bonded to the protective layer 30 and the polarizer 10 via the adhesive layer 20 so that substantially no bubbles are present between the protective layer 30 and the thin portion 12. Furthermore, in an embodiment of the present invention, the thickness of the adhesive layer 20 is 23 μm or more. By having the thickness of the adhesive layer be 23 μm or more, a state where substantially no bubbles are present in the thin portion can be realized. In addition, by using the adhesive layer, it is possible to significantly suppress streaks after a high-temperature and high-humidity durability test compared to the case where an adhesive layer is used.

B. Polarizer B-1. Overall structure of polarizer The polarizer 10 is typically made of a resin film containing a dichroic material. As described above, the polarizer 10 has a thin portion 12 at a predetermined position. As described above, the thin portion 12 typically has a recess 14 in which the surface on one side of the polarizer is recessed. The thin portion 12 may typically be a non-polarizing portion, and in one embodiment, may be a low-density portion having a lower content of the dichroic material than other portions of the polarizer. Therefore, in this specification, the thin portion may be referred to as a low-density portion or a non-polarizing portion depending on the matters to be described.

The thickness of the polarizer (thickness of the portion other than the thin portion) is typically 8 μm or less, preferably 6 μm or less, more preferably 5 μm or less, and even more preferably 4 μm or less. On the other hand, the thickness of the polarizer is preferably 0.5 μm or more, more preferably 1 μm or more. If the thickness of the polarizer is in such a range, the generation of bubbles in the thin portion (recess) can be substantially prevented by adopting an adhesive layer of a predetermined thickness. Furthermore, with such a thickness, a polarizer having excellent durability and optical properties can be obtained. Furthermore, the smaller the thickness, the better the non-polarized portion can be formed. For example, when the non-polarized portion is formed by decolorization through chemical treatment, the contact time between the treatment liquid (typically, a decolorizing liquid such as a basic solution: described later) and the polarizer can be shortened. Specifically, the non-polarized portion can be formed in a shorter time. Furthermore, by reducing the thickness of the resin film, the depth of the recess can be reduced, and as a result, the defect of the recess being visible can be suppressed.

The depth of the recess 14 is preferably 0.50 μm or less, more preferably 0.45 μm or less, and even more preferably 0.40 μm or less. On the other hand, the depth of the recess 14 is preferably 0.30 μm or more, and more preferably 0.35 μm or more. In this specification, the "depth of the recess" refers to the depth of the deepest part of the recess.

The polarizer (excluding the non-polarized portion) preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single transmittance (Ts) of the polarizer (excluding the non-polarized portion) is preferably 39% or more, more preferably 39.5% or more, even more preferably 40% or more, and particularly preferably 40.5% or more. The theoretical upper limit of the single transmittance is 50%, and the practical upper limit is 46%. The single transmittance (Ts) is the Y value measured using a 2-degree visual field (C light source) according to JIS Z8701 and corrected for visibility, and can be measured using, for example, a microspectroscopic system (LVmicro, manufactured by Lambda Vision). The degree of polarization of the polarizer (excluding the non-polarized portion) is preferably 99.9% or more, more preferably 99.93% or more, and even more preferably 99.95% or more.

B-2. Resin Film As the resin film, any appropriate resin film that can be used as a polarizer can be adopted. The resin film is typically a polyvinyl alcohol-based resin (hereinafter referred to as "PVA-based resin") film.

Any suitable resin can be used as the PVA-based resin forming the PVA-based resin film. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. 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 in accordance with JIS K 6726-1994. By using a PVA-based resin with such a saponification degree, a polarizer with excellent durability can be obtained. If the saponification degree is too high, there is a risk of gelation.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1,000 to 10,000, preferably 1,200 to 4,500, and more preferably 1,500 to 4,300. The average degree of polymerization can be determined in accordance with JIS K 6726-1994.

Examples of dichroic substances contained in the resin film include iodine and organic dyes. These can be used alone or in combination of two or more. Iodine is preferably used. For example, when forming a non-polarizing section by decolorization through chemical treatment, the iodine complex contained in the resin film (polarizer) is appropriately reduced, so that a non-polarizing section having suitable properties can be formed when used in, for example, a camera section.

B-3. Thin section (or low density section or non-polarized section)
As described above, the thin portion 12 typically has a recess 14 in which the surface on one side of the polarizer is recessed. The recess 14 can be formed, for example, by applying a bleaching liquid from only one side of the polarizer (polarizer intermediate). By forming a recess only on one side, the effect on the appearance can be further suppressed. In an embodiment of the present invention, the recess 14 is substantially free of air bubbles.

In one embodiment, the thin portion (non-polarizing portion) 12 is a low-density portion that contains a lower amount of dichroic material than other portions of the polarizer. This configuration avoids quality problems such as cracks, delamination, and glue overflow, compared to when the non-polarizing portion is formed mechanically (for example, by mechanically punching using an engraving blade, a plotter, a water jet, etc.). In addition, since the low-density portion contains a low amount of dichroic material itself, the transparency of the non-polarizing portion is maintained well, compared to when the non-polarizing portion is formed by decomposing the dichroic material using laser light or the like. Such a low-density portion can be typically formed by decolorization through chemical treatment (for example, decolorization through contact with a basic solution: described below).

The content of the dichroic substance in the low-density portion is preferably 1.0% by weight or less, more preferably 0.5% by weight or less, and even more preferably 0.2% by weight or less. If the content of the dichroic substance in the low-density portion is within this range, the desired transparency can be sufficiently imparted to the low-density portion. For example, when the low-density portion corresponds to the camera portion of an image display device, very excellent photographing performance can be realized in terms of both brightness and color. On the other hand, the lower limit of the content of the dichroic substance in the low-density portion is usually below the detection limit. When iodine is used as the dichroic substance, the iodine content can be determined, for example, from the X-ray intensity measured by fluorescent X-ray analysis, using a calibration curve prepared in advance using a standard sample.

The difference between the content of the dichroic material in the other portions and the content of the dichroic material in the low-density portion is preferably 0.5% by weight or more, and more preferably 1% by weight or more. If the difference in content is within this range, a low-density portion having the desired transparency can be formed.

The low-concentration portion has an alkali metal and/or alkaline earth metal content of 3.6% by weight or less, preferably 2.5% by weight or less, more preferably 1.0% by weight or less, and even more preferably 0.5% by weight or less. If the alkali metal and/or alkaline earth metal content in the low-concentration portion is within this range, the shape of the low-concentration portion formed by contact with a basic solution (decolorizing solution) described later can be well maintained (i.e., a low-concentration portion with excellent dimensional stability can be realized). The content can be determined, for example, from a calibration curve created in advance using a standard sample from the X-ray intensity measured by fluorescent X-ray analysis. Such a content can be achieved by reducing the alkali metal and/or alkaline earth metal in the contact portion in contact with the basic solution described later.

The transmittance of the non-polarized portion (for example, the transmittance measured with light of a wavelength of 550 nm at 23°C) is preferably 50% or more, more preferably 60% or more, even more preferably 75% or more, and particularly preferably 90% or more. With such a transmittance, the low-density portion has the desired transparency. As a result, when the polarizing plate is arranged so that the non-polarized portion corresponds to the camera portion of the image display device, adverse effects on the camera's shooting performance can be prevented. Furthermore, the higher the transmittance, the more pronounced the effect of the bubble suppression according to the present invention can be in a polarizer with a small thickness. This is because, even in a polarizer with a small thickness, the higher the transmittance, the deeper the recesses become, making it easier for bubbles to occur.

In the illustrated example, a small circular non-polarizing portion 12 is formed in the center of the upper end of the polarizer 10, but the arrangement, shape, size, etc. of the non-polarizing portion can be designed as appropriate. For example, it is designed according to the position, shape, size, etc. of the camera portion of the image display device to be mounted. Specifically, it is designed so that the non-polarizing portion does not correspond to the display screen of the image display device to be mounted.

The planar shape of the non-polarizing section 12 may be any suitable shape as long as it does not adversely affect the camera performance of the image display device in which the polarizer is used. Specific examples include a circle, an ellipse, a square, a rectangle, and a diamond. By appropriately setting the shape of the through holes in the surface protection film described in section F-2 below, a non-polarizing section having the desired planar shape can be formed.

C. Adhesive Layer Any suitable adhesive may be used as the adhesive constituting the adhesive layer 20. Examples of the adhesive include rubber-based adhesives, acrylic-based adhesives, silicone-based adhesives, urethane-based adhesives, vinyl alkyl ether-based adhesives, polyvinyl alcohol-based adhesives, polyvinyl pyrrolidone-based adhesives, polyacrylamide-based adhesives, cellulose-based adhesives, acrylic urethane-based adhesives, and organic-inorganic hybrid adhesives. Acrylic-based adhesives are preferred. This is because they have excellent optical transparency, exhibit appropriate adhesive properties (adhesion, cohesion, and adhesion), and are excellent in durability (weather resistance and heat resistance).

Acrylic adhesives typically contain an acrylic polymer with a main skeleton of a structural unit derived from an alkyl (meth)acrylate ester as the base polymer. The alkyl (meth)acrylate ester refers to an alkyl acrylate ester and/or an alkyl methacrylate ester. For example, C1 to C20 alkyl esters of (meth)acrylic acid are included. Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, isomyristyl (meth)acrylate, and lauryl (meth)acrylate. Preferably, the average number of carbon atoms in the alkyl group is 3 to 9. The alkyl (meth)acrylate esters may be used alone or in combination. The content of the structural units derived from (meth)acrylic acid alkyl ester is preferably 60 parts by weight or more, more preferably 80 parts by weight or more, and even more preferably 90 to 99.9 parts by weight, relative to 100 parts by weight of the base polymer.

The base polymer may contain, as necessary, a structural unit derived from another monomer component that is copolymerizable with the above-mentioned (meth)acrylic acid alkyl ester. Examples of such monomer components (copolymerization components) include hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)-methyl acrylate; (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, and the like. Examples of the monomers include carboxyl group-containing monomers such as acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid; acid anhydride group-containing monomers such as maleic anhydride and itaconic anhydride; caprolactone adducts of acrylic acid; sulfonic acid group-containing monomers such as styrene sulfonic acid, allyl sulfonic acid, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamide propanesulfonic acid, sulfopropyl (meth)acrylate, and (meth)acryloyloxynaphthalenesulfonic acid; and phosphoric acid group-containing monomers such as 2-hydroxyethyl acryloyl phosphate. Further, (N-substituted) amide monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-butyl(meth)acrylamide, N-methylol(meth)acrylamide, and N-methylolpropane(meth)acrylamide; alkylaminoalkyl(meth)acrylate monomers such as aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, and t-butylaminoethyl(meth)acrylate; alkoxyalkyl(meth)acrylate monomers such as methoxyethyl(meth)acrylate and ethoxyethyl(meth)acrylate; N-(meth)acryloyloxymethylene succinimide and N-(meth)acryloyloxymethylene succinimide; Succinimide monomers such as acryloyl-6-oxyhexamethylene succinimide, N-(meth)acryloyl-8-oxyoctamethylene succinimide, and N-acryloylmorpholine; maleimide monomers such as N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, and N-phenylmaleimide; and itaconimide monomers such as N-methylitaconimide, N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide, N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, and N-laurylitaconimide can also be used as copolymerization components for the purpose of modification. Furthermore, vinyl acetate, vinyl propionate, N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N-vinyl carboxylic acid amides, styrene, α-methylstyrene, vinyl monomers such as N-vinylcaprolactam; cyanoacrylate monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing acrylic monomers such as glycidyl (meth)acrylate; glycol-based acrylic ester monomers such as polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate; tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, silicone (meth)acrylate, and acrylic ester monomers such as 2-methoxyethyl acrylate can also be used as copolymerization components for the purpose of modification. By adjusting the type, combination, and blending ratio of the copolymerization components (and thus the content ratio of the structural units), it is possible to obtain an adhesive with the desired properties. Preferred copolymerization components include hydroxyl group-containing monomers and carboxyl group-containing monomers. These can act as reaction sites with the crosslinking agent, so an adhesive layer with excellent cohesiveness, heat resistance, etc. can be formed.

The weight average molecular weight of the base polymer is preferably 300,000 to 2.5 million, more preferably 1 million to 2.5 million, and even more preferably 1.4 million to 2 million. Within this range, a pressure-sensitive adhesive layer exhibiting an appropriate amount of creep can be formed. The weight average molecular weight is measured by GPC (gel permeation chromatography; solvent: THF) and calculated in terms of polystyrene.

The adhesive may further contain any suitable crosslinking agent. Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, peroxide-based crosslinking agents, melamine-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and amine-based crosslinking agents. Isocyanate-based crosslinking agents, epoxy-based crosslinking agents, and peroxide-based crosslinking agents are preferred. The crosslinking agents may be used alone or in combination of two or more.

The adhesive may further contain any suitable additive. Specific examples of additives include tackifiers, plasticizers, pigments, dyes, fillers, antioxidants, anti-aging agents, conductive materials, UV absorbers, light stabilizers, release regulators, softeners, surfactants, and flame retardants. The types, combinations, and amounts of additives may be appropriately set according to the purpose.

Details of the adhesive are described, for example, in JP 2013-254157 A. The disclosure of this publication is incorporated herein by reference.

The storage modulus at 25°C of the adhesive constituting the adhesive layer is preferably as low as possible, as long as the shape of the adhesive is maintained and the function of the adhesive can be expressed. The storage modulus is preferably 10 x ¹⁰⁵ Pa or less, more preferably 8 x ¹⁰⁵ Pa or less. The lower limit of the storage modulus is, for example, 1 x ¹⁰³ Pa. If the storage modulus of the adhesive is in such a range, the adhesive will well enter the recesses when laminating the polarizer and the protective layer. As a result, the generation of bubbles in the recesses can be well suppressed. The storage modulus can be determined by dynamic viscoelasticity measurement. The dynamic viscoelasticity measurement can be performed, for example, on a pressure-sensitive adhesive sample having a thickness of 2 mm and a diameter of 8 mm using an "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific, with a deformation mode of torsion, a measurement frequency of 1 Hz, a heating rate of 5°C/min, and a measurement temperature of -50°C to 150°C.

The thickness of the adhesive layer is 23 μm or more as described above. Although it is not theoretically clear, at a thickness having practically acceptable adhesive strength, the thicker the adhesive layer, the more the generation of bubbles in the recesses is suppressed, and by making the thickness 23 μm or more, the recesses can be made substantially free of bubbles. Such a critical effect was only discovered through trial and error to remove bubbles in the thin polarizer part of a polarizing plate using a polarizer having a thin part (non-polarizing part), and is an unexpectedly excellent effect. Note that as long as the thickness is 23 μm or more, the bubble prevention effect does not change even if the thickness is increased. The upper limit of the thickness of the adhesive layer is, for example, 50 μm from the viewpoints of cost, handling during production, optical properties, etc.

D. Protective Layer The protective layer 30 is formed of any suitable film that can be used as a protective layer for a polarizer. Specific examples of materials that are the main components of the film include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as polyester, polyvinyl alcohol, polycarbonate, polyamide, polyimide, polyethersulfone, polysulfone, polystyrene, polynorbornene, polyolefin, (meth)acrylic, and acetate. In addition, thermosetting resins or ultraviolet-curing resins such as (meth)acrylic, urethane, (meth)acrylic urethane, epoxy, and silicone are also included. In addition, glassy polymers such as siloxane polymers are also included. In addition, the polymer films described in JP-A-2001-343529 (WO01/37007) can also be used. As the material for this 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 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 protective layer 30 may be subjected to surface treatment such as hard coat treatment, anti-reflection treatment, and anti-glare treatment as necessary. In other words, a surface treatment layer such as a hard coat layer, an anti-reflection layer, and an anti-glare layer may be formed on the surface of the protective layer 30. The surface treatment layer is preferably a layer with low moisture permeability for the purpose of improving the moisture durability of the polarizing plate. The hard coat layer is provided for the purpose of preventing scratches on the polarizing plate surface. The hard coat layer can be formed by a method of adding a cured film having excellent hardness and slip properties to the surface using an appropriate ultraviolet curing resin such as an acrylic or silicone resin. The hard coat layer preferably has a pencil hardness of 2H or more. The anti-reflection layer is a low-reflection layer provided for the purpose of preventing reflection of external light on the polarizing plate surface. Examples of the anti-reflection layer include a thin layer type that prevents reflection by utilizing the cancellation effect of reflected light due to the interference of light as disclosed in JP-A-2005-248173, and a surface structure type that exhibits low reflectance by imparting a fine structure to the surface as disclosed in JP-A-2011-2759. The anti-glare layer is provided for the purpose of preventing external light from being reflected on the polarizing plate surface and impairing the visibility of light transmitted through the polarizing plate. The anti-glare layer is formed by imparting a fine uneven structure to the surface by an appropriate method such as a roughening method using a sandblasting method or an embossing method, or a method of blending transparent fine particles. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle expansion function) for diffusing light transmitted through the polarizing plate to expand the viewing angle.

The thickness of the protective layer 30 is typically 5 mm or less, preferably 1 mm or less, more preferably 1 μm to 500 μm, and even more preferably 5 μm to 150 μm. Note that if a surface treatment has been applied, the thickness of the protective layer includes the thickness of the surface treatment layer.

E. Other configurations of the polarizing plate The polarizing plate 100 may further have any suitable optical functional layer depending on the purpose. A typical example of the optical functional layer is a retardation film (optical compensation film). For example, a retardation film may be arranged on the opposite side of the polarizer 10 to the protective layer 30 (not shown). The optical characteristics of the retardation film (for example, index ellipsoid, in-plane retardation, thickness direction retardation) may be appropriately set depending on the purpose, characteristics of the image display device, etc. For example, when the image display device is an IPS mode liquid crystal display device, a retardation film having an index ellipsoid of nx>ny>nz and a retardation film having an index ellipsoid of nz>nx>ny may be arranged. The retardation film may also serve as the other protective layer. Note that "nx" is the refractive index in the direction in which the refractive index in the film plane is maximum (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the film plane, and "nz" is the refractive index in the thickness direction.

Up to this point, we have described an embodiment in which the polarizing plate is in the form of a sheet, but in another embodiment, the polarizing plate of the present invention may be in the form of a long sheet. The above-mentioned sheet-shaped polarizing plate can be obtained by cutting a long-shaped polarizing plate to a predetermined size or shape, or by cutting it out from a long-shaped polarizing plate. Below, we will briefly explain the polarizer in a long-shaped polarizing plate.

Figure 3 is a schematic perspective view of a long polarizer. The long polarizer 16 can be typically wound into a roll as shown in Figure 3. The polarizer 16 has non-polarizing sections (thin sections) 12 arranged at a predetermined interval (i.e., in a predetermined pattern) in the long direction and/or width direction. The arrangement pattern of the non-polarizing sections 12 can be appropriately set according to the purpose. Typically, the non-polarizing sections 12 are arranged at a position corresponding to the camera section of the image display device when the polarizer 16 (effectively a polarizing plate) is cut to a predetermined size (e.g., cut or punched in the long direction and/or width direction) to be attached to an image display device of a predetermined size. Therefore, when only one size of polarizer is cut from one long polarizer 16, the non-polarizing sections 12 can typically be arranged at substantially equal intervals in both the long direction and the width direction. With such a configuration, it is easy to control the cutting of the polarizer to a predetermined size according to the size of the image display device, and the yield can be improved. Furthermore, the variation in the position of the non-polarizing portion in the cut sheet-like polarizer can be suppressed. Note that "substantially equal intervals in both the longitudinal direction and the width direction" means that the intervals in the longitudinal direction are equal and the intervals in the width direction are equal, and the intervals in the longitudinal direction and the width direction do not need to be equal. For example, when the interval in the longitudinal direction is L1 and the interval in the width direction is L2, L1 may be equal to L2, or L1 may be ≠ L2. When polarizers of multiple sizes are cut from one long polarizer 16, the intervals of the non-polarizing portions 12 in the longitudinal direction and/or the width direction can be changed according to the size of the polarizer to be cut. For example, the non-polarizing portions 12 may be arranged at substantially equal intervals in the longitudinal direction and at different intervals in the width direction; or may be arranged at different intervals in the longitudinal direction and at substantially equal intervals in the width direction. When the non-polarized portions are arranged at different intervals in the longitudinal or width direction, the intervals between adjacent non-polarized portions may all be different, or only some (the intervals between specific adjacent non-polarized portions) may be different. Alternatively, a plurality of regions may be defined in the longitudinal direction of the polarizer 16, and the intervals between the non-polarized portions 12 in the longitudinal direction and/or width direction may be set for each region. In this way, non-polarized portions can be formed in any suitable arrangement pattern in a long polarizer according to the purpose. Details of the arrangement pattern of the non-polarized portions in the polarizer are described in, for example, JP 2016-27392 A, and the description of this publication is incorporated herein by reference.

For practical purposes, the polarizing plate 100 has a separate adhesive layer as the outermost layer (not shown). The separate adhesive layer is typically the outermost layer on the image display device side. A separator is temporarily and removably attached to the separate adhesive layer, protecting the separate adhesive layer until actual use and enabling roll formation.

F. Manufacturing Method of Polarizing Plate Hereinafter, a manufacturing method of the polarizing plate of the present invention will be described. For convenience, a manufacturing method of a long polarizing plate will be described. A sheet-shaped polarizing plate can be obtained by cutting the obtained long polarizing plate into a predetermined size or shape.

F-1. Preparation of Polarizer The resin film (typically, a PVA-based resin film) constituting the polarizer may be a single film, or may be a resin layer (typically, a PVA-based resin layer) formed on a resin substrate. The PVA-based resin layer may be formed by applying a coating liquid containing a PVA-based resin onto a resin substrate, or may be formed by laminating a PVA-based resin film onto a resin substrate. Hereinafter, the case where a PVA-based resin layer is formed by coating will be briefly described, but the same applies to the case where a PVA-based resin film is laminated. A polarizer obtained by using a laminate of a resin substrate and a PVA-based resin layer formed by coating 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 to obtain a laminate of the resin substrate and the PVA-based resin layer; and stretching and dyeing the laminate to make the PVA-based resin layer into a polarizer. In this embodiment, the stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching it. Furthermore, the stretching may further include air-stretching the laminate at a high temperature (e.g., 95°C or higher) before stretching in the boric acid aqueous solution, as necessary. The obtained resin substrate/polarizer laminate may be used as it is (i.e., the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled off from the resin substrate/polarizer laminate, and any suitable protective layer according to the purpose may be laminated on the peeled surface. Details of such a method for producing a polarizer are described in, for example, JP2012-73580A. The entire disclosure of this publication is incorporated herein by reference. Note that when the polarizer is a single PVA-based resin film, the polarizer may be produced by a method well known and commonly used in the art, and therefore a detailed description thereof will be omitted.

As described above, a polarizer (polarizer intermediate) is formed on the resin substrate. If necessary, a resin film constituting a protective layer (typically corresponding to another protective layer not shown in the above section A) is attached and/or the resin substrate is peeled off. For example, a resin film is attached to the polarizer surface of the resin substrate/polarizer laminate by roll-to-roll, and then the resin substrate is peeled off. In this way, a polarizer/protective layer laminate is obtained. Here, the polarizer intermediate means a polarizer before the non-polarizing portion is formed, and is intended to be distinguished from a polarizer having a non-polarizing portion. Therefore, in this specification, the polarizer intermediate may be simply referred to as a polarizer for the sake of context. A person skilled in the art can easily understand whether "polarizer" means a polarizer intermediate or a polarizer having a non-polarizing portion by looking at the description in this specification.

F-2. Formation of non-polarized portion Next, a non-polarized portion is formed at a predetermined position of the polarizer intermediate obtained in the above F-1. When the polarizer (polarizer intermediate) is formed from a PVA-based resin layer applied onto a resin substrate, typically, a laminate of resin substrate/polarizer or a laminate of protective layer/polarizer is used to form the non-polarized portion. When the polarizer (polarizer intermediate) is a single resin film, typically, a polarizer alone or a laminate of protective layer/polarizer is used to form the non-polarized portion. Hereinafter, the formation of the non-polarized portion will be specifically described. As a representative example, a case where a non-polarized portion is formed in a polarizer (polarizer intermediate) in a laminate of protective layer/polarizer (hereinafter, simply referred to as polarizing plate intermediate in this section) will be described. It is clear to a person skilled in the art that the same procedure can be applied to polarizer intermediates of other configurations (for example, a laminate of resin substrate/polarizer intermediate, a polarizer intermediate that is a single resin film).

The non-polarized portion can be typically formed by decolorization through a chemical treatment (hereinafter also referred to as chemical decolorization treatment). Chemical decolorization treatment can typically be performed by selectively treating a predetermined position of the polarizer (polarizer intermediate) with a treatment liquid (typically a decolorization liquid such as a basic solution: described below). Methods for selectively treating a predetermined portion include, for example, a method using a surface protection film (a so-called mask) with through holes arranged in a predetermined pattern, a method printing a decolorization liquid at a predetermined position, and a method spraying a decolorization liquid at a predetermined position. Below, a method using a surface protection film with through holes arranged in a predetermined pattern will be described as a representative example.

As shown in FIG. 4, a surface protection film having through holes arranged in a predetermined pattern is laminated by roll-to-roll to the polarizer side surface of the polarizing plate intermediate. In this specification, "roll-to-roll" refers to laminating rolled films while transporting them with their longitudinal directions aligned. The surface protection film having through holes is peelably laminated to the polarizer via any suitable adhesive. By using a surface protection film having through holes, decolorization treatment by immersion in a decolorizing solution is possible, so that the polarizing plate of the present invention can be obtained with very high manufacturing efficiency. For convenience, the surface protection film having through holes may be referred to as the first surface protection film.

The surface protection film has through holes arranged in a predetermined pattern. The positions at which the through holes are provided correspond to the positions at which the non-polarizing portions of the polarizer (polarizer intermediate) are formed. The arrangement pattern of the through holes shown in FIG. 4 corresponds to the arrangement pattern of the non-polarizing portions shown in FIG. 3. The through holes can be formed, for example, by mechanical punching (e.g., punching, engraving blade punching, plotter, water jet) or by removing predetermined portions of the film (e.g., laser ablation or chemical dissolution).

The surface protection film is preferably a film having a high hardness (e.g., elastic modulus). This is because deformation of the through hole during transportation and/or lamination can be prevented. Examples of materials for forming the surface protection film include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. The thickness of the surface protection film is typically 20 μm to 250 μm, and preferably 30 μm to 150 μm. Such a thickness has the advantage that deformation of the through hole is unlikely to occur even if tension is applied during transportation and/or lamination. The elastic modulus of the surface protection film is preferably 2.2 kN/mm ² to 4.8 kN/mm ^2. If the elastic modulus of the surface protection film is within such a range, it has the advantage that deformation of the through hole is unlikely to occur even if tension is applied during transportation and/or lamination. The elastic modulus is measured in accordance with JIS K 6781. The tensile elongation of the surface protection film is preferably 90% to 170%. If the tensile elongation of the first surface protection film is in this range, there is an advantage that it is difficult to break during transportation. The tensile elongation is measured in accordance with JIS K 6781.

On the other hand, another surface protective film (also referred to as a second surface protective film) is laminated to the protective layer side of the polarizing plate by roll-to-roll. The second surface protective film is peelably laminated to the protective layer via any suitable adhesive. By using the second surface protective film, the polarizing plate intermediate (polarizer intermediate/protective layer) can be appropriately protected in the decolorization treatment by immersion. The second surface protective film may be a film similar to the first surface protective film except that no through holes are provided. Furthermore, a soft (e.g., low elasticity) film such as a polyolefin (e.g., polyethylene) film can also be used as the second surface protective film. The second surface protective film may be laminated simultaneously with the first surface protective film, may be laminated before the first surface protective film is laminated, or may be laminated after the first surface protective film is laminated. Preferably, the second surface protective film is laminated before the first surface protective film is laminated. This procedure has the advantage that the protective layer is prevented from being scratched, and that the through holes formed in the first surface protective film are prevented from being transferred as marks to the protective layer during winding. When the second surface protective film is laminated before the first surface protective film is laminated, for example, a laminate of the protective layer and the second surface protective film can be produced, and the laminate can be laminated to a resin substrate/polarizer laminate, after which the resin substrate can be peeled off, and the first surface protective film can be laminated to the peeled surface.

Next, as shown in FIG. 5, the laminate of the first surface protective film/polarizer (polarizer intermediate)/protective layer/second surface protective film is subjected to a chemical bleaching treatment. The chemical bleaching treatment involves contacting the laminate with a treatment liquid (typically, a basic solution). When iodine is used as the dichroic material, the iodine content at the contact area can be easily reduced by contacting the desired area of the resin film with a basic solution.

The laminate may be brought into contact with the basic solution by any suitable means. Representative examples include immersion of the laminate in the basic solution, or application or spraying of the basic solution to the laminate. Immersion is preferred. This is because the decolorization process can be performed while transporting the laminate as shown in FIG. 5, which results in significantly high manufacturing efficiency. As described above, immersion is possible by using the first surface protective film (and, if necessary, the second surface protective film). Specifically, by immersing in the basic solution, only the portion of the polarizer (polarizer intermediate) corresponding to the through-hole of the first surface protective film comes into contact with the basic solution. For example, when the polarizer (polarizer intermediate) contains iodine as a dichroic material, the iodine concentration of the contact portion of the polarizer (polarizer intermediate) with the basic solution is reduced by contacting the polarizer (polarizer intermediate) with the basic solution, and as a result, a non-polarizing portion can be selectively formed only in the contact portion (which may be set by the through-hole of the first surface protective film). Thus, according to this embodiment, a non-polarized portion can be selectively formed in a predetermined portion of a polarizer (polarizer intermediate) with very high manufacturing efficiency without complicated operations. If iodine remains in the obtained polarizer, even if the iodine complex is destroyed to form a non-polarized portion, the iodine complex may be formed again with use of the polarizer, and the non-polarized portion may no longer have the desired characteristics. In this embodiment, the iodine itself is removed from the polarizer (substantially the non-polarized portion) by removing the basic solution described below. As a result, it is possible to prevent the characteristics of the non-polarized portion from changing with use of the polarizer. In addition, according to the contact method as described above, a recess can be formed only on one side of the resin film. In this case, it is significantly easier to control the depth of the recess than when recesses are formed on both sides of the resin film. As a result, it is easier to suppress the effect on the appearance.

The formation of a non-polarized portion by a basic solution will be described in more detail. After contacting a specific portion of the polarizer (polarizer intermediate), the basic solution penetrates into the specific portion. The iodine complex contained in the specific portion is reduced by the base contained in the basic solution to become iodine ions. By reducing the iodine complex to iodine ions, the polarization performance of the specific portion is substantially lost, and a non-polarized portion is formed in the specific portion. In addition, the reduction of the iodine complex improves the transmittance of the specific portion. The iodine that has become iodine ions moves from the specific portion into the solvent of the basic solution. As a result, by removing the basic solution described below, the iodine ions are also removed from the specific portion together with the basic solution. In this way, a non-polarized portion (low concentration portion) is selectively formed in a specific portion of the polarizer (polarizer intermediate), and the non-polarized portion becomes stable without any change over time. In addition, by adjusting the material, thickness, and mechanical properties of the first surface protection film, the concentration of the basic solution, and the time for which the laminate is immersed in the basic solution, it is possible to prevent the basic solution from penetrating into undesired areas (resulting in the formation of non-polarized areas in undesired areas).

As the basic compound contained in the basic solution, any appropriate basic compound can be used. Examples of basic compounds include hydroxides of alkali metals such as sodium hydroxide, potassium hydroxide, and lithium hydroxide, hydroxides of alkaline earth metals such as calcium hydroxide, inorganic alkali metal salts such as sodium carbonate, organic alkali metal salts such as sodium acetate, and aqueous ammonia. Among these, hydroxides of alkali metals and/or alkaline earth metals are preferably used, and sodium hydroxide, potassium hydroxide, and lithium hydroxide are more preferably used. The iodine complex can be efficiently ionized, and the non-polarized portion can be formed more easily. These basic compounds may be used alone or in combination of two or more.

Any suitable solvent can be used as the solvent for the basic solution. Specific examples include water, alcohols such as ethanol and methanol, ether, benzene, chloroform, and mixed solvents of these. Water and alcohol are preferred as the solvent because iodine ions migrate well into the solvent and can be easily removed later when removing the basic solution.

The concentration of the basic solution is, for example, 0.01N to 5N, preferably 0.05N to 3N, and more preferably 0.1N to 2.5N. If the concentration of the basic solution is in this range, the iodine concentration inside the polarizer (polarizer intermediate) can be efficiently reduced, and ionization of the iodine complex in parts other than the specified parts can be prevented. Furthermore, if the concentration is in this range, it becomes easy to control the depth of the recess that can be formed.

The temperature of the basic solution is, for example, 20°C to 50°C. The contact time between the laminate (essentially a specific portion of the polarizer intermediate) and the basic solution can be set according to the thickness of the polarizer intermediate, the type of basic compound contained in the basic solution used, and the concentration of the basic compound, and is, for example, 5 seconds to 30 minutes. If the contact time is within this range, a recess having an appropriate depth can be formed.

The polarizer may contain boric acid. For example, boric acid may be included by contacting the polarizer with a boric acid solution (e.g., an aqueous boric acid solution) during stretching or crosslinking to impart polarizing functionality. The boric acid content of the polarizer is, for example, 10% to 30% by weight. The boric acid content in the area in contact with the basic solution is, for example, 5% to 12% by weight.

After contact with the basic solution, the alkali metals and/or alkaline earth metals contained in the resin film are reduced in the contact area with the basic solution. By reducing the alkali metals and/or alkaline earth metals, a low-concentration area with excellent dimensional stability can be obtained. Specifically, the shape of the low-concentration area formed by contact with the basic solution can be maintained even in a humid environment.

By contacting the resin film with a basic solution, hydroxides of alkali metals and/or alkaline earth metals may remain at the contact area. In addition, by contacting the resin film with a basic solution, metal salts of alkali metals and/or alkaline earth metals may be generated at the contact area. These may generate hydroxide ions, and the generated hydroxide ions may act (decompose/reduce) on dichroic substances (e.g., iodine complexes) present around the contact area, expanding the non-polarized area (low concentration area). Therefore, it is believed that by reducing the alkali metal and/or alkaline earth metal salts, the expansion of the non-polarized area over time can be suppressed, and the desired shape of the non-polarized area can be maintained.

（式中、Ｘはアルカリ金属またはアルカリ土類金属を表す） Examples of metal salts capable of generating hydroxide ions include borates. Borates can be generated by neutralizing boric acid contained in a resin film with a basic solution (a solution of an alkali metal hydroxide and/or an alkaline earth metal hydroxide). Note that borates (metaborates) can be hydrolyzed to generate hydroxide ions as shown in the following formula, for example, when a polarizer is placed in a humid environment.

(wherein X represents an alkali metal or an alkaline earth metal)

Preferably, the content of alkali metals and/or alkaline earth metals in the contact area is reduced to 3.6% by weight or less, preferably 2.5% by weight or less, more preferably 1.0% by weight or less, and even more preferably 0.5% by weight or less.

The resin film may contain alkali metals and/or alkaline earth metals in advance by undergoing various treatments to make it into a polarizer. For example, potassium may be contained in the resin film by contacting it with a solution of an iodide such as potassium iodide. In this way, it is generally believed that the alkali metals and/or alkaline earth metals contained in the polarizer do not adversely affect the dimensional stability of the low concentration portion.

As the reduction method, a method of contacting the part in contact with the basic solution with a post-treatment liquid is preferably used. By using such a method, the alkali metal and/or alkaline earth metal can be transferred from the resin film to the post-treatment liquid, thereby reducing the content thereof.

Any appropriate method may be used for contacting the post-treatment liquid. For example, the post-treatment liquid may be dripped, applied, or sprayed onto the area in contact with the basic solution, or the area in contact with the basic solution may be immersed in the post-treatment liquid.

When the resin film is protected with any suitable protective material when it comes into contact with the basic solution, it is preferable to bring the post-treatment liquid into contact in that state (particularly when the temperature of the post-treatment liquid is 50°C or higher). In this manner, it is possible to prevent the polarization characteristics from being deteriorated by the post-treatment liquid in areas other than the area in contact with the basic solution.

The post-treatment liquid may contain any suitable solvent. Examples of the solvent include water, alcohols such as ethanol and methanol, ether, benzene, chloroform, and mixtures of these. Among these, water and alcohol are preferably used from the viewpoint of efficiently transferring the alkali metal and/or alkaline earth metal. Any suitable water may be used as the water. Examples include tap water, pure water, and deionized water.

The temperature of the post-treatment liquid at the time of contact is, for example, 20°C or higher, preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher. At such a temperature, the alkali metal and/or alkaline earth metal can be efficiently transferred to the post-treatment liquid. Specifically, the swelling ratio of the resin film can be significantly improved, and the alkali metal and/or alkaline earth metal in the resin film can be physically removed. Meanwhile, the temperature of the water is substantially 95°C or lower.

The contact time can be adjusted as appropriate depending on the contact method, the temperature of the post-treatment liquid, the thickness of the resin film, etc. For example, when immersed in warm water, the contact time is preferably 10 seconds to 30 minutes, more preferably 30 seconds to 15 minutes, and even more preferably 60 seconds to 10 minutes.

In one embodiment, an acidic solution is used as the post-treatment liquid. By using an acidic solution, the hydroxides of alkali metals and/or alkaline earth metals remaining in the resin film can be neutralized, and the alkali metals and/or alkaline earth metals in the resin film can be chemically removed.

As the acidic compound contained in the acidic solution, any appropriate acidic compound can be used. Examples of the acidic compound include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, hydrogen fluoride, and boric acid, and organic acids such as formic acid, oxalic acid, citric acid, acetic acid, and benzoic acid. The acidic compound contained in the acidic solution is preferably an inorganic acid, and more preferably hydrochloric acid, sulfuric acid, or nitric acid. These acidic compounds may be used alone or in combination of two or more.

Preferably, the acidic compound used is an acidic compound that is more acidic than boric acid. This is because it can also act on the metal salts (borates) of the above-mentioned alkali metals and/or alkaline earth metals. Specifically, it is possible to chemically remove the alkali metals and/or alkaline earth metals in the resin film by liberating boric acid from the borates.

The indicator of the acidity is, for example, the acid dissociation constant (pKa), and an acidic compound having a pKa smaller than that of boric acid (9.2) is preferably used. Specifically, the pKa is preferably less than 9.2, and more preferably 5 or less. The pKa may be measured using any appropriate measuring device, or values described in literature such as the 5th Revised Edition of the Basic Chemistry Handbook (edited by the Chemical Society of Japan, Maruzen Publishing) may be referenced. In addition, in acidic compounds that dissociate in multiple stages, the pKa value may change at each stage. When using such an acidic compound, one in which any of the pKa values at each stage is within the above range is used. In this specification, pKa refers to the value in an aqueous solution at 25°C.

The difference between the pKa of the acidic compound and the pKa of boric acid is, for example, 2.0 or more, preferably 2.5 to 15, and more preferably 2.5 to 13. Within such a range, the alkali metal and/or alkaline earth metal can be efficiently transferred to the post-treatment liquid, and as a result, the desired alkali metal and/or alkaline earth metal content in the low concentration portion can be achieved.

Examples of acidic compounds that can satisfy the above pKa include inorganic acids such as hydrochloric acid (pKa: -3.7), sulfuric acid ( _pK2 : 1.96), nitric acid (pKa: -1.8), hydrogen fluoride (pKa: 3.17), and boric acid (pKa: 9.2), and organic acids such as formic acid (pKa: 3.54), oxalic acid ( _pK1 : 1.04, _pK2 : 3.82), citric acid ( _pK1 : 3.09, _pK2 : 4.75, _pK3 : 6.41), acetic acid (pKa: 4.8), and benzoic acid (pKa: 4.0).

The solvent for the acidic solution (post-treatment liquid) is as described above, and even in this embodiment in which an acidic solution is used as the post-treatment liquid, the alkali metal and/or alkaline earth metal in the resin film may be physically removed.

The concentration of the acidic solution is, for example, 0.01N to 5N, preferably 0.05N to 3N, and more preferably 0.1N to 2.5N.

The temperature of the acidic solution is, for example, 20°C to 50°C. The contact time with the acidic solution can be set according to the thickness of the resin film, the type of acidic compound, and the concentration of the acidic solution, and is, for example, 5 seconds to 30 minutes.

In addition to the above treatments, the resin film may be subjected to any other appropriate treatments. Examples of other treatments include removal of basic and/or acidic solutions, washing, etc.

Specific examples of methods for removing the basic solution and/or acidic solution include wiping with a rag or the like, suction removal, natural drying, heat drying, air drying, and reduced pressure drying. The drying temperature is, for example, 20°C to 100°C. The drying time is, for example, 5 seconds to 600 seconds.

The cleaning process is carried out by any suitable method. Examples of solutions used in the cleaning process include pure water, alcohols such as methanol and ethanol, acidic aqueous solutions, and mixed solvents of these. Cleaning is typically carried out while the laminate is being transported, as shown in FIG. 5. The cleaning process can be carried out at any suitable stage. The cleaning process may be carried out multiple times.

In this manner, non-polarizing sections are formed in a predetermined arrangement pattern at predetermined positions on the long polarizer (polarizer intermediate). As described above, the non-polarizing sections are thin sections. According to the manufacturing method described above, the thin sections have a recessed portion on one side of the polarizer (the side facing the first surface protection film).

F-3. Preparation of Polarizing Plate Next, the first surface protective film is removed (typically peeled off) from the laminate. Furthermore, a pressure-sensitive adhesive (pressure-sensitive adhesive layer) is disposed between the surface of the laminate from which the first surface protective film has been removed (the surface on which the concave portion of the polarizer is formed) and the resin film constituting the protective layer. Specifically, the pressure-sensitive adhesive layer may be formed on the surface on which the concave portion of the polarizer is formed, or may be formed on the resin film constituting the protective layer. The polarizer and the resin film constituting the protective layer are laminated via the pressure-sensitive adhesive layer.

In this manner, a long polarizing plate having a structure of protective layer/polarizer/another protective layer can be obtained. A sheet-shaped polarizing plate can be obtained by cutting a long polarizing plate into a predetermined size or shape, as described above. When producing a polarizing plate having a protective layer/polarizer structure, a non-polarizing portion is formed in the resin substrate/polarizer laminate in the same manner as described above, and then the resin substrate is removed, and a protective layer is laminated on the removed surface. The second surface protective film can be removed at any appropriate time. Specifically, the second surface protective film may be removed from the laminate at the same time as the first surface protective film, may be removed after the long polarizing plate is formed, or may be removed after the sheet-shaped polarizing plate is formed.

G. Image display device The image display device of the present invention comprises the polarizing plate. The polarizing plate is cut to fit the size of the image display device. Examples of image display devices include liquid crystal display devices and organic EL devices. Specifically, the liquid crystal display device comprises a liquid crystal panel including a liquid crystal cell and the polarizing plate arranged on one or both sides of the liquid crystal cell. The organic EL device comprises an organic EL panel in which the polarizing plate is arranged on the viewing side. The polarizing plate is arranged so that the non-polarizing portion corresponds to the camera portion of the image display device.

The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples. The methods for measuring each characteristic are as follows.

(1) Thickness: Measurement was performed using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C").
(2) Depth of Recesses: Measurement was performed using a scanning electron microscope (manufactured by ZYGO Corporation, product name "New View 7300").
(3) Presence or absence of air bubbles and the number of air bubbles The presence or absence of air bubbles in the non-polarizing portions (thin portions) formed in the polarizing plates obtained in the Examples, Comparative Examples, and Reference Examples was confirmed at 5x magnification using an FPD scanning microscope (manufactured by Olympus, product name "MX61") and counted, and evaluated according to the following criteria.
◯: No air bubbles were observed △: A few air bubbles were observed ×: A large number of air bubbles were observed (4) Streaks The polarizing plates obtained in Example 1 and Reference Example 1 were each subjected to a durability test at 65° C./90% RH for 500 hours, and then the surface condition was visually confirmed.

[Example 1]
As the resin substrate, a long amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) having a water absorption rate of 0.75% and a Tg of 75° C. was used. One side of the substrate was subjected to a corona treatment, and an aqueous solution containing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (polymerization degree 1200, acetoacetyl-modification degree 4.6%, saponification degree 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., product name "GOHSEFYMER Z200") in a ratio of 9:1 was applied to the corona-treated surface and dried at 25° C. to form a PVA-based resin layer having a thickness of 13 μm, and a laminate was produced.
The resulting laminate was uniaxially stretched at its free end 2.4 times in the machine direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 120° C. (auxiliary air stretching).
Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 30° C. for 30 seconds (insolubilizing treatment).
Next, the polarizing plate was immersed in a dye bath at a liquid temperature of 30° C. while adjusting the iodine concentration and immersion time so that the polarizing plate had a predetermined transmittance. In this example, the polarizing plate was immersed for 60 seconds in an iodine aqueous solution obtained by mixing 0.2 parts by weight of iodine and 1.5 parts by weight of potassium iodide with respect to 100 parts by weight of water (dyeing treatment).
Next, the plate was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 30° C. for 30 seconds (crosslinking treatment).
Thereafter, the laminate was immersed in an aqueous boric acid solution (an aqueous solution obtained by blending 3 parts by weight of boric acid and 5 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 70° C., and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds so that the total stretch ratio was 5.5 times (underwater stretching).
Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 30° C. (cleaning treatment).
Next, the adhesive shown below was applied to the surface of the PVA-based resin layer of the laminate so that the adhesive layer would have a thickness of 1.0 μm after curing, and a Zeonoa-based resin film (thickness 17 μm) manufactured by Zeon Corporation that constitutes a protective layer (corresponding to another protective layer) was attached, and the Zeonoa-based resin film side was heated to 50° C. using an IR heater, and the adhesive was cured by irradiating it with ultraviolet light as described below. Thereafter, the substrate was peeled off from the PVA-based resin layer to obtain a long polarizing plate (polarizer/another protective layer) with a width of about 1300 mm. The polarizer had a thickness of 5 μm and a single transmittance of 40.8%.
(Adhesive Composition)
40 parts by weight of N-hydroxyethylacrylamide (HEAA), 60 parts by weight of acryloylmorpholine (ACMO), and 3 parts by weight of a photoinitiator "IRGACURE 819" (manufactured by BASF) were mixed to prepare an adhesive having a viscosity of 40 mPa·S before curing.
(Ultraviolet rays)
As the active energy ray, ultraviolet rays (gallium-filled metal halide lamp, irradiation device: Light HAMMER10 manufactured by Fusion UV Systems, Inc., bulb: V bulb, peak irradiance: 1600 mW/cm ² , cumulative irradiation amount 1000/mJ/cm ² (wavelength 380 to 440 nm)) were used. The irradiance of ultraviolet rays was measured using a Sola-Check system manufactured by Solatell.

One side of an ester-based resin film (thickness 38 μm) with a width of approximately 1,300 mm was coated with an adhesive (acrylic adhesive) to a thickness of 5 μm. Through holes with a diameter of 2.8 mm were formed in this adhesive-coated ester-based resin film at 250 mm intervals in the longitudinal direction and 400 mm intervals in the width direction using a Pinnacle (registered trademark) blade.

The above-mentioned adhesive ester resin film was laminated to the polarizer side of the polarizing plate obtained above by roll-to-roll bonding, and this was immersed in a 1 mol/L (1N) aqueous sodium hydroxide solution for 30 seconds, and then immersed in 1 mol/L (1N) hydrochloric acid for 10 seconds. It was then dried at 60°C to form a non-polarizing portion in the polarizer. The non-polarizing portion was a thin portion with a 0.5 μm deep recess on the ester resin film side.

The ester resin film was peeled off from the laminate obtained above, and an acrylic resin film (thickness: 40 μm) constituting a protective layer was attached to the peeled surface via an adhesive (thickness: 23 μm) having a storage modulus of 1 × 10 ⁵ Pa.

In this manner, a polarizing plate having a configuration of protective layer/polarizer/another protective layer was produced. The state of air bubble generation in the non-polarizing portion of the obtained polarizing plate was evaluated according to the criteria in (3) above. The results are shown in Table 1. Furthermore, when the presence or absence of streaks was checked according to the procedure in (4) above, no streaks were generated and the plate maintained a good condition.

[Comparative Example 1]
A polarizing plate was produced in the same manner as in Example 1, except that the thickness of the pressure-sensitive adhesive layer was set to 20 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
A polarizing plate was produced in the same manner as in Example 1, except that the thickness of the pressure-sensitive adhesive layer was 12 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[Comparative Example 3]
A polarizing plate was produced in the same manner as in Example 1, except that the thickness of the pressure-sensitive adhesive layer was set to 5 μm. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

Furthermore, Figure 6 shows a graph showing the relationship between the thickness of the adhesive layer and the number of bubbles generated in Example 1 and Comparative Examples 1 to 3.

[Reference Example 1]
A polarizing plate was produced in the same manner as in Example 1, except that the polarizer and the protective layer were bonded together using, instead of the pressure-sensitive adhesive, the ultraviolet-curable adhesive (thickness after curing: 2.5 μm) used in Example 1 to bond the polarizer and the other protective layer. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. Furthermore, when the presence or absence of streaks was confirmed by the above procedure (4), the occurrence of streaks was significant.

[evaluation]
As is clear from Table 1 and Figure 6, it is found that in a polarizing plate including a polarizer having a thin portion, the generation of bubbles in the thin portion can be prevented by adjusting the thickness of the adhesive layer that bonds the polarizer and the protective layer. Furthermore, it is suggested that there is a threshold thickness at which the generation of bubbles can be significantly suppressed between 5 μm and 10 μm of the adhesive layer, and that there may be a critical point at which the generation of bubbles that can be recognized under specified conditions can be substantially completely prevented when the adhesive layer is about 23 μm thick. Furthermore, as is clear from a comparison between Example 1 and Reference Example 1, it is found that the use of an adhesive layer can significantly suppress streaks after a durability test compared to the use of an adhesive layer.

The polarizing plate of the present invention is suitable for use in camera-equipped image display devices (liquid crystal display devices, organic EL devices) such as mobile phones such as smartphones, notebook PCs, and tablet PCs.

REFERENCE SIGNS LIST 10 Polarizer 12 Thin portion 14 Recess 20 Adhesive layer 30 Protective layer 100 Polarizing plate

Claims (5)

A polarizer having a thin portion as a non-polarizing portion on one side;
a protective layer attached to the thin portion side of the polarizer via a pressure-sensitive adhesive layer,
a surface of the non-polarizing portion on the surface on the thin-walled portion side is recessed from a surface of the portion other than the non-polarizing portion, and a surface of the non-polarizing portion and a surface of the portion other than the non-polarizing portion are at the same height on a surface opposite to the thin-walled portion side ,
The depth of the recess in the thin-walled portion is 0.3 μm to 0.5 μm,
The thickness of the pressure-sensitive adhesive layer in the portion other than the thin portion is 23 μm or more and 50 μm or less.
Polarizing plate. 2. The polarizing plate according to claim 1, wherein the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer has a storage modulus at 25° C. of 10×10 ⁵ Pa or less. treating a predetermined position on one surface of the polarizer with a treatment liquid to form a thin portion as a non-polarizing portion at the predetermined position, the thin portion having a recess depth of 0.3 μm to 0.5 μm;
disposing a pressure-sensitive adhesive layer between a surface of the polarizer on which the thin portion is formed and a protective layer, the thickness of the pressure-sensitive adhesive layer being 23 μm or more and 50 μm or less in a portion other than the thin portion; and laminating the polarizer and the protective layer with the pressure-sensitive adhesive layer interposed therebetween. The method for producing a polarizing plate according to claim 3 , wherein the pressure-sensitive adhesive layer has a storage modulus at 25° C. of 10×10 ⁵ Pa or less. An image display device comprising the polarizing plate according to claim 1 or 2, the thin portion of the polarizing plate being disposed in a position corresponding to a camera unit.

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