Polarizing plate, polarizing plate roll, and method for producing polarizing film

Abstract

Provided is a polarizing plate which has excellent optical characteristics and in which variations in optical characteristics are suppressed. The polarizing plate according to the present invention has a polarizing film and a protective layer disposed on at least one side of the polarizing film, the thickness of the polarizing film being 8 [mu] m or less, the unit transmittance being 44.5% or more, the degree of polarization being 99.0% or more, and the difference between the maximum value and the minimum value of the unit transmittance of the polarizing plate in a 50 cm2 region being 0.2% or less. Another polarizing plate according to the present invention has a polarizing film and a protective layer disposed on at least one side of the polarizing film, and the polarizing film has a thickness of 8 [mu] m or less, a single transmittance of 44.5% or more, and a degree of polarization of 99.0% or more. The polarizer has a width of 1000 mm or more, and the difference between the maximum value and the minimum value of the single transmittance at a position along the width direction is 0.3% or less.

Description

[0001] This application is a divisional application of an application filed on September 6, 2018, with application number 201880059534.8 and invention name “Polarizer, Polarizer Roll, and Method for Manufacturing Polarizing Film”. Technical Field

[0002] The present invention relates to a method for manufacturing a polarizing plate, a polarizing plate roll, and a polarizing film. Background Art

[0003] With the popularity of thin displays, displays equipped with organic EL panels (OLED) and displays using display panels using inorganic light-emitting materials such as quantum dots (QLED) have been proposed. These panels have a highly reflective metal layer, which is prone to problems such as external light reflection and background reflection. Therefore, it is known to prevent these problems by providing a circular polarizer having a polarizing film and a λ / 4 wave plate on the visible side. As a method for manufacturing a polarizing film, the following method is proposed, for example: a laminate having a resin substrate and a polyvinyl alcohol (PVA) resin layer is stretched, and then dyed to obtain a polarizing film on the resin substrate (for example, Patent Document 1). According to such a method, a thin polarizing film is obtained, and therefore, it has attracted attention in recent years as a method that can contribute to the thinning of image display devices. However, the optical properties of the existing thin polarizing films as described above are not sufficient, and further improvement of the optical properties of the thin polarizing films is required.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-343521 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] The present invention has been made to solve the above-mentioned conventional problems, and a main object of the present invention is to provide a polarizing plate, a polarizing plate roll, and a method for producing a polarizing film, each having excellent optical properties and with suppressed variations in the optical properties.

[0009] Solutions to the problem

[0010] The polarizing plate of the present invention comprises a polarizing film and a protective layer disposed on at least one side of the polarizing film, wherein the thickness of the polarizing film is 8 μm or less, the single transmittance is 44.5% or more, and the polarization degree is 99.0% or more. 2 The difference between the maximum value and the minimum value of the single-element transmittance within the region is 0.2% or less.

[0011] The other polarizers of the present invention have a polarizing film and a protective layer arranged on at least one side of the polarizing film. The thickness of the polarizing film is less than 8 μm, the single transmittance is greater than 44.5%, and the polarization degree is greater than 99.0%. The width of the polarizer is greater than 1000 mm, and the difference between the maximum and minimum values ​​of the single transmittance at a position along the width direction is less than 0.3%.

[0012] In one embodiment, the polarizing film has a single body transmittance of 45.0% or less and a degree of polarization of 99.9% or less.

[0013] According to another aspect of the present invention, a polarizing plate roll is provided, wherein the polarizing plate roll is formed by winding the polarizing plate into a roll.

[0014] According to another aspect of the present invention, a method for manufacturing a polarizing film is provided, which is a method for manufacturing a polarizing film with a thickness of less than 8 μm, a monomer transmittance of more than 44.5%, and a polarization degree of more than 99.0%. The method comprises: forming a polyvinyl alcohol resin layer containing iodide or sodium chloride and a polyvinyl alcohol resin on one side of a long thermoplastic resin substrate to form a laminate; and sequentially performing an auxiliary stretching treatment in a gas atmosphere, a dyeing treatment, a stretching treatment in an aqueous solution, and a drying and shrinking treatment on the above-mentioned laminate, in which the laminate is heated while being transported along the length direction, so that it shrinks by more than 2% in the width direction.

[0015] In one embodiment, the polarizing film has a single body transmittance of 45.0% or less and a degree of polarization of 99.9% or less.

[0016] In one embodiment, in the polyvinyl alcohol-based resin layer, the content of the iodide or sodium chloride is 5 parts by weight to 20 parts by weight based on 100 parts by weight of the polyvinyl alcohol-based resin.

[0017] In one embodiment, the stretching ratio in the auxiliary stretching process in the atmosphere is 2.0 times or more.

[0018] In one embodiment, the drying and shrinking treatment step is a step of heating using a heating roller.

[0019] In one embodiment, the temperature of the heating roller is 60° C. to 120° C., and the shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is 2% or more.

[0020] Effects of the Invention

[0021] According to the present invention, a polarizing plate having excellent optical properties with suppressed variations in optical properties can be provided, including a polarizing film having a thickness of 8 μm or less, a single-piece transmittance of 44.5% or greater, and a polarization degree of 99.0% or greater. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram showing an example of a drying and shrinking process using a heating roller.

[0024] Figure 3 This is a graph showing the optical properties of polarizing plates obtained in Examples and Comparative Examples.

[0025] Explanation of symbols

[0026] 10 Polarizing film

[0027] 20 1st protective layer

[0028] 30 Second protective layer

[0029] 100 polarizers DETAILED DESCRIPTION

[0030] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0031] A. Polarizer

[0032] Figure 1 This is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 comprises a polarizing film 10, a first protective layer 20 disposed on one side of the polarizing film 10, and a second protective layer 30 disposed on the other side of the polarizing film 10. The thickness of the polarizing film is 8 μm or less, the single-body transmittance is 44.5% or more, and the polarization degree is 99.0% or more. One of the first protective layer 20 and the second protective layer 30 may be omitted. It should be noted that one of the first protective layer and the second protective layer may be a resin substrate (described later) used for the manufacture of the above-mentioned polarizing film.

[0033] The polarizer can be in the form of a long strip or a single sheet. In the case where the polarizer is in the form of a long strip, it is preferably wound into a roll to make a polarizer roll. The polarizer has excellent optical properties, and the deviation of the optical properties is small. In one embodiment, the width of the polarizer is greater than 1000 mm, and the difference (D1) between the maximum and minimum values ​​of the single transmittance in the position along the width direction is less than 0.3%. The upper limit of D1 is preferably 0.25%, more preferably 0.2%. The smaller D1 is, the more preferred, but the lower limit is, for example, 0.01%. When D1 is within the above range, polarizers with excellent optical properties can be produced industrially. In another embodiment, the polarizer is at 50 cm 2 The difference (D2) between the maximum and minimum values ​​of the single transmittance within the region is 0.2% or less. The upper limit of D2 is preferably 0.1%, and more preferably 0.05%. The smaller D2, the better, but the lower limit is, for example, 0.01%. When D2 is within the above range, it is possible to suppress brightness unevenness in the display screen when the polarizing plate is used in an image display device.

[0034] A-1. Polarizing film

[0035] As mentioned above, the thickness of the polarizing film is less than 8 μm, the single transmittance is greater than 44.5%, and the polarization degree is greater than 99.0%. Generally speaking, there is a trade-off relationship between single transmittance and absorbance. If the single transmittance is increased, the absorbance will decrease, and if the absorbance is increased, the single transmittance will decrease. Therefore, it has been difficult to put a thin polarizing film that meets the optical properties of a single transmittance of more than 44.5% and a polarization degree of more than 99.0% into practical use. As described above, the polarizing film of one embodiment of the present invention has excellent optical properties such as a single transmittance of more than 44.5% and a polarization degree of more than 99.0%. In addition, by using the polarizing film of this embodiment, a polarizer with suppressed deviation in optical properties can be realized. The realization of such a thin polarizing film (polarizer) is one of the achievements of the present invention. Such a polarizing film (polarizer) can be used in image display devices, and can be suitably used in circular polarizers for organic EL display devices, in particular.

[0036] The thickness of the polarizing film is preferably 1 μm to 8 μm, more preferably 1 μm to 7 μm, and even more preferably 2 μm to 5 μm.

[0037] The polarizing film preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single-unit transmittance of the polarizing film is preferably 45.0% or less. The polarization degree of the polarizing film is preferably 99.2% or more, more preferably 99.4% or more. On the other hand, the upper limit of the polarization degree is preferably 99.9%. The above-mentioned single-unit transmittance is typically a Y value obtained by measuring using an ultraviolet-visible spectrophotometer and correcting for visibility. The above-mentioned polarization degree is typically based on the parallel transmittance Tp and the orthogonal transmittance Tc obtained by measuring using an ultraviolet-visible spectrophotometer and correcting for visibility, and is calculated using the following formula.

[0038] Polarization degree (%) = {(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100

[0039] In one embodiment, the transmittance of a thin polarizing film of less than 8 μm is typically measured using a laminate of a polarizing film (refractive index of the surface: 1.53) and a protective film (refractive index: 1.50) as the measurement object, using an ultraviolet-visible spectrophotometer. The reflectivity at the interface of each layer changes depending on the refractive index of the polarizing film surface and / or the refractive index of the surface in contact with the air interface of the protective film, and as a result, the measured value of the transmittance sometimes changes. Therefore, for example, when a protective film with a refractive index other than 1.50 is used, the measured value of the transmittance can be corrected according to the refractive index of the surface in contact with the air interface of the protective film. Specifically, the correction value C of the transmittance uses the reflectivity R1 (transmission axis reflectivity) of polarized light parallel to the transmission axis in the interface between the protective film and the air layer, and is expressed by the following formula.

[0040] C=R1-R0

[0041] R0=((1.50-1) 2 / (1.50+1) 2 )×(T1 / 100)

[0042] R1=((n1-1) 2 / (n1+1) 2 )×(T1 / 100)

[0043] Among them, R0 is the transmission axis reflectivity when a protective film with a refractive index of 1.50 is used, n1 is the refractive index of the protective film used, and T1 is the transmittance of the polarizing film. For example, when a substrate with a surface refractive index of 1.53 (cycloolefin film, film with hard coating, etc.) is used as a protective film, the correction amount C is about 0.2%. In this case, 0.2% is added to the transmittance obtained by measurement, which can be converted into the transmittance when a protective film with a surface refractive index of 1.50 is used. It should be noted that according to the calculation based on the above formula, the change in the correction value C when the transmittance T1 of the polarizing film changes by 2% is less than 0.03%, and the influence of the transmittance of the polarizing film on the value of the correction value C is limited. In addition, when the protective film has absorption other than surface reflection, appropriate correction can be made according to the absorption amount.

[0044] Any appropriate polarizing film can be adopted as the polarizing film. The polarizing film can be typically produced using a laminate of two or more layers.

[0045] As a specific example of a polarizing film obtained using a laminate, a polarizing film obtained using a laminate of a resin substrate and a PVA-type resin layer formed on the resin substrate can be cited. The polarizing film obtained using a laminate of a resin substrate and a PVA-type resin layer formed on the resin substrate can be made by the following method: for example, a PVA-type resin solution is applied to a resin substrate, dried, and a PVA-type resin layer is formed on the resin substrate to obtain a laminate of the resin substrate and the PVA-type resin layer; the laminate is stretched and dyed to make the PVA-type resin layer into a polarizing film. In this embodiment, stretching typically includes immersing the laminate in a boric acid aqueous solution for stretching. In addition, stretching may further include stretching the laminate in a gas atmosphere at a high temperature (for example, above 95°C) before stretching in a boric acid aqueous solution as needed. The obtained resin substrate / polarizing film laminate can be used directly (that is, the resin substrate can be used as a protective layer for the polarizing film), and the resin substrate can be peeled off from the resin substrate / polarizing film laminate, and any appropriate protective layer according to the purpose can be laminated on the peeled surface for use. The details of the method for producing such a polarizing film are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580, the entire contents of which are incorporated herein by reference.

[0046] The method for manufacturing a polarizing film of the present invention comprises: forming a polyvinyl alcohol resin layer containing a halide and a polyvinyl alcohol resin on one side of a long thermoplastic resin substrate to form a laminate; and sequentially subjecting the laminate to an auxiliary stretching treatment in a gas atmosphere, a dyeing treatment, an aqueous solution stretching treatment, and a drying and shrinking treatment. In the drying and shrinking treatment, the laminate is heated while being transported in the longitudinal direction, thereby shrinking it by more than 2% in the width direction. This produces a polarizing film having a thickness of less than 8 μm, a single-body transmittance of more than 44.5%, and a polarization degree of more than 99.0%, with excellent optical properties and suppressed optical property deviations. Specifically, by introducing the auxiliary stretching process, the crystallinity of the PVA can be improved even when coating the thermoplastic resin with PVA, thereby achieving high optical properties. Furthermore, by simultaneously improving the orientation of the PVA in advance, problems such as a decrease in orientation and dissolution of the PVA during immersion in water during the subsequent dyeing and stretching processes can be prevented, thereby achieving high optical properties. Furthermore, when the PVA resin layer is immersed in a liquid, the orientation disorder of the polyvinyl alcohol molecules and the reduction in orientation can be suppressed compared to when the PVA resin layer does not contain a halide. This improves the optical properties of polarizing films obtained through treatments such as dyeing and stretching in an aqueous solution, where the laminate is immersed in a liquid. Furthermore, shrinking the laminate in the width direction through drying and shrinking can improve optical properties.

[0047] A-2. Protective layer

[0048] The first protective layer and the second protective layer can be formed by any appropriate film that can be used as a protective layer of a polarizing film. As a specific example of the material that becomes the main component of the film, cellulose resins such as triacetyl cellulose (TAC), polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth) acrylic acid, transparent resins such as acetates, etc. can be listed. In addition, thermosetting resins or ultraviolet curing resins such as (meth) acrylic acid, carbamates, (meth) acrylic acid carbamates, epoxies, silicones, etc. can also be listed. In addition, glassy polymers such as siloxane polymers can also be listed. In addition, the polymer film described in Japanese Patent Application Publication No. 2001-343529 (WO01 / 37007) can also be used. As a material for the film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in a side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in a side chain can be used. For example, a resin composition containing an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be used. The polymer film can be, for example, an extrusion molded product of the above resin composition.

[0049] When the polarizing plate 100 is used in an image display device, the thickness of the protective layer (outer protective layer) disposed on the side opposite to the display panel is typically 300 μm or less, preferably 100 μm or less, more preferably 5 μm to 80 μm, and even more preferably 10 μm to 60 μm. It should be noted that, when a surface treatment is applied, the thickness of the outer protective layer includes the thickness of the surface treatment layer.

[0050] When the polarizer 100 is applied to an image display device, the thickness of the protective layer (inner protective layer) arranged on the display panel side is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and further preferably 10 μm to 60 μm. In one embodiment, the inner protective layer is a phase difference layer having any appropriate phase difference value. In this case, the in-plane phase difference Re (550) of the phase difference layer is, for example, 110 nm to 150 nm. "Re (550)" is the in-plane phase difference measured at 23 ° C with light of a wavelength of 550 nm, which can be calculated by the formula: Re = (nx-ny) × d. Among them, "nx" is the refractive index in the direction where the in-plane refractive index reaches the maximum (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).

[0051] B. Method for manufacturing polarizing film

[0052] The manufacturing method of the polarizing film of one embodiment of the present invention includes: forming a polyvinyl alcohol resin layer (PVA resin layer) containing a halide and a polyvinyl alcohol resin (PVA resin) on one side of a long thermoplastic resin substrate to form a laminate; and sequentially subjecting the laminate to an auxiliary stretching treatment in a gas atmosphere, a dyeing treatment, a stretching treatment in an aqueous solution, and a drying and shrinking treatment, wherein the laminate is heated while being transported in the longitudinal direction, thereby shrinking by more than 2% in the width direction. The content of the halide in the PVA resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin. The drying and shrinking treatment is preferably carried out using a heating roller, and the temperature of the heating roller is preferably 60°C to 120°C. The shrinkage rate of the laminate in the width direction using the drying and shrinking treatment is preferably more than 2%. According to such a manufacturing method, the polarizing film described in the above-mentioned item A can be obtained. In particular, a laminate comprising a halide-containing PVA-type resin layer is prepared, and the laminate is stretched by multi-stage stretching including auxiliary stretching in a gas atmosphere and stretching in an aqueous solution, and the stretched laminate is heated with a heating roller, thereby obtaining a polarizing film having excellent optical properties (representatively, single-unit transmittance and polarization degree) and suppressed deviations in the optical properties. Specifically, a heating roller is used in the drying and shrinking treatment process, thereby allowing the laminate to be uniformly shrunk as a whole while being transported. In this way, not only can the optical properties of the obtained polarizing film be improved, but also polarizing films with excellent optical properties can be stably produced, and deviations in the optical properties (especially single-unit transmittance) of the polarizing film can be suppressed.

[0053] B-1. Preparation of laminate

[0054] Any appropriate method can be used to produce a laminate of a thermoplastic resin substrate and a PVA-based resin layer. Preferably, a coating solution containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin substrate and dried to form the PVA-based resin layer on the thermoplastic resin substrate. As described above, the halide content in the PVA-based resin layer is preferably 5 to 20 parts by weight per 100 parts by weight of the PVA-based resin.

[0055] Any appropriate method may be used to apply the coating liquid. Examples include roll coating, spin coating, wire rod coating, dip coating, die coating, flow coating, spray coating, and blade coating (such as a doctor blade). The coating / drying temperature of the coating liquid is preferably 50°C or higher.

[0056] The thickness of the PVA-based resin layer is preferably 3 μm to 40 μm, more preferably 3 μm to 20 μm.

[0057] Before forming the PVA type resin layer, the thermoplastic resin substrate can be subjected to surface treatment (e.g., corona treatment), or an easy-adhesion layer can be formed on the thermoplastic resin substrate. By carrying out such treatment, the adhesion between the thermoplastic resin substrate and the PVA type resin layer can be improved.

[0058] B-1-1. Thermoplastic resin substrate

[0059] The thickness of the thermoplastic resin substrate is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If the thickness is less than 20 μm, there is a concern that forming the PVA-based resin layer will be difficult. If the thickness exceeds 300 μm, for example, during the aqueous solution stretching treatment described later, the thermoplastic resin substrate may require a long time to absorb water, and there is a concern that excessive load may be required for stretching.

[0060] The water absorption rate of the thermoplastic resin substrate is preferably 0.2% or more, more preferably 0.3% or more. The thermoplastic resin substrate absorbs water, and the water acts like a plasticizer to plasticize. As a result, the tensile stress can be greatly reduced, and stretching at a high ratio can be performed. On the other hand, the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin substrate, it is possible to prevent undesirable situations such as a significant reduction in the dimensional stability of the thermoplastic resin substrate during manufacturing, which deteriorates the appearance of the resulting polarizing film. In addition, it is possible to prevent the substrate from breaking during stretching in an aqueous solution and the PVA-type resin layer from peeling off from the thermoplastic resin substrate. It should be noted that the water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption rate is a value calculated in accordance with JIS K7209.

[0061] The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or less. By using such a thermoplastic resin substrate, the crystallization of the PVA-based resin layer can be suppressed, and the stretchability of the laminate can be fully ensured. In addition, if the plasticization of the thermoplastic resin substrate by water and the good stretching in the aqueous solution are taken into consideration, it is more preferably 100°C or less, and further preferably 90°C or less. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60°C or more. By using such a thermoplastic resin substrate, it is possible to prevent the thermoplastic resin substrate from being deformed (for example, causing unevenness, relaxation, wrinkles, etc.) when the coating solution containing the PVA-based resin is applied / dried, and the laminate can be well produced. In addition, the PVA-based resin layer can be well stretched at a suitable temperature (for example, about 60°C). It should be noted that the glass transition temperature of the thermoplastic resin substrate can be adjusted by, for example, using a crystallizing material that introduces a modifying group into the constituent material and heating it. The glass transition temperature (Tg) is a value determined in accordance with JIS K 7121.

[0062] Any suitable thermoplastic resin can be used as the constituent material of the thermoplastic resin substrate. Examples of thermoplastic resins include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymers thereof. Of these, norbornene resins and amorphous polyethylene terephthalate resins are preferred.

[0063] In one embodiment, an amorphous (non-crystallized) polyethylene terephthalate resin is preferably used. Among them, an amorphous (hard to crystallize) polyethylene terephthalate resin is particularly preferred. Specific examples of amorphous polyethylene terephthalate resins include copolymers further containing isophthalic acid and / or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers further containing cyclohexanedimethanol and diethylene glycol as diols.

[0064] In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate resin having isophthalic acid units. This is because such a thermoplastic resin substrate has very excellent stretchability and can suppress crystallization during stretching. It is believed that this is because the introduction of isophthalic acid units can impart a large curvature to the main chain. Polyethylene terephthalate resins have terephthalic acid units and ethylene glycol units. The content of isophthalic acid units relative to the total of all repeating units is preferably 0.1 mol% or more, more preferably 1.0 mol% or more. This is because a thermoplastic resin substrate with very excellent stretchability can be obtained. On the other hand, the content of isophthalic acid units relative to the total of all repeating units is preferably 20 mol% or less, more preferably 10 mol% or less. By setting such a content ratio, the crystallinity can be well improved during the drying shrinkage treatment described later.

[0065] The thermoplastic resin substrate may be stretched in advance (before forming the PVA-type resin layer). In one embodiment, the long strip of thermoplastic resin substrate may be stretched in the transverse direction. The transverse direction is preferably a direction orthogonal to the stretching direction of the laminate described later. It should be noted that, in this specification, "orthogonal" refers to, and also includes, substantially orthogonal situations. Among them, "substantially orthogonal" refers to, including the situation of 90°±5.0°, preferably 90°±3.0°, and more preferably 90°±1.0°.

[0066] The stretching temperature of the thermoplastic resin substrate is preferably Tg-10° C. to Tg+50° C. relative to the glass transition temperature (Tg). The stretching ratio of the thermoplastic resin substrate is preferably 1.5 to 3.0 times.

[0067] Any appropriate method may be used to stretch the thermoplastic resin substrate. Specifically, it may be fixed-end stretching or free-end stretching. The stretching method may be dry or wet. The thermoplastic resin substrate may be stretched in a single stage or in multiple stages. When stretched in multiple stages, the stretch ratio is the product of the stretch ratios in each stage.

[0068] B-1-2. Coating liquid

[0069] As described above, the coating liquid contains a halide and a PVA-based resin. The coating liquid can typically be a solution obtained by dissolving the halide and the PVA-based resin in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Of these, water is preferred. The PVA-based resin concentration of the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film that adheres closely to the thermoplastic resin substrate can be formed. The halide content in the coating liquid is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

[0070] Additives may be added to the coating liquid. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyols such as ethylene glycol and glycerol. Examples of surfactants include nonionic surfactants. These additives are used to further improve the uniformity, dyeability, and stretchability of the resulting PVA-based resin layer.

[0071] As the above-mentioned PVA-based resin, any appropriate resin can be used. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer can be mentioned. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer is obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of PVA-based resin is generally 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 calculated according to JISK 6726-1994. By using a PVA-based resin with such a saponification degree, a polarizing film with excellent durability can be obtained. If the saponification degree is too high, there is a concern about gelation.

[0072] The average polymerization degree of the PVA-based resin can be appropriately selected depending on the intended purpose. The average polymerization degree is usually 1,000 to 10,000, preferably 1,200 to 4,500, and more preferably 1,500 to 4,300. The average polymerization degree can be determined in accordance with JIS K 6726-1994.

[0073] As the halide, any appropriate halide can be used. Examples include iodide and sodium chloride. Examples of iodide include potassium iodide, sodium iodide, and lithium iodide. Of these, potassium iodide is preferred.

[0074] The amount of the halide in the coating liquid is preferably 5 to 20 parts by weight, more preferably 10 to 15 parts by weight, relative to 100 parts by weight of the PVA resin. If the amount of the halide exceeds 20 parts by weight relative to 100 parts by weight of the PVA resin, the halide may bleed out, resulting in a cloudy polarizing film.

[0075] Generally speaking, by stretching a PVA resin layer, the orientation of the polyvinyl alcohol molecules in the PVA resin is improved. However, if the stretched PVA resin layer is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules may be disordered and the orientation may be reduced. In particular, when a laminate of a thermoplastic resin and a PVA resin layer is stretched in a boric acid aqueous solution, the orientation tends to decrease significantly when the laminate is stretched in a boric acid aqueous solution at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin. For example, the stretching of a PVA film monomer in a boric acid aqueous solution is usually carried out at 60°C. In contrast, the stretching of a laminate of an A-PET (thermoplastic resin substrate) and a PVA resin layer is carried out at a high temperature of about 70°C. In this case, the orientation of the PVA in the initial stretching stage will decrease before it is raised by stretching in an aqueous solution. In contrast, by preparing a laminate of a halide-containing PVA resin layer and a thermoplastic resin substrate and then subjecting the laminate to high-temperature stretching in air (secondary stretching) before stretching it in a boric acid aqueous solution, crystallization of the PVA resin in the PVA resin layer of the laminate after secondary stretching can be promoted. As a result, when the PVA resin layer is immersed in a liquid, the orientation disorder of the polyvinyl alcohol molecules and the reduction in orientation can be suppressed compared to a case where the PVA resin layer does not contain a halide. This improves the optical properties of polarizing films obtained through treatment steps such as dyeing and aqueous solution stretching, where the laminate is immersed in a liquid.

[0076] B-2. Assisted stretching in gas atmosphere

[0077] In particular, in order to obtain high optical properties, a two-stage stretching method combining dry stretching (auxiliary stretching) and stretching in a boric acid aqueous solution is selected. Like the two-stage stretching, an auxiliary stretching is introduced, whereby stretching can be performed while suppressing the crystallization of the thermoplastic resin substrate, which can solve the problem of reduced stretchability due to excessive crystallization of the thermoplastic resin substrate when stretched in a boric acid aqueous solution thereafter, and the laminate can be stretched at a higher ratio. In addition, when applying PVA-based resins on a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, it is necessary to lower the coating temperature compared to the usual case of applying PVA-based resins on a metal drum. As a result, the crystallization of the PVA-based resins is relatively reduced, and problems such as insufficient optical properties can be obtained. In contrast, by introducing an auxiliary stretching, even when applying PVA-based resins on a thermoplastic resin, the crystallinity of the PVA-based resins can be improved, and high optical properties can be achieved. Furthermore, by simultaneously improving the orientation of the PVA resin in advance, it is possible to prevent problems such as a decrease in orientation and dissolution of the PVA resin when immersed in water in the subsequent dyeing and stretching steps, thereby achieving high optical properties.

[0078] The stretching method for auxiliary stretching in a gas atmosphere can be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, a method of uniaxially stretching the laminate by passing it between rollers with different circumferential speeds). In order to obtain high optical properties, free-end stretching can be actively adopted. In one embodiment, the stretching treatment in a gas atmosphere includes a heating roller stretching process in which the above-mentioned laminate is transported along its length while being stretched by the difference in circumferential speed between the heating rollers. The stretching treatment in a gas atmosphere typically includes a regional stretching process and a heating roller stretching process. It should be noted that the order of the regional stretching process and the heating roller stretching process is not limited. The regional stretching process can be performed first, or the heating roller stretching process can be performed first. The regional stretching process can also be omitted. In one embodiment, the regional stretching process and the heating roller stretching process are performed sequentially. In addition, in another embodiment, in the tenter stretching machine, the end of the film is held and the distance between the tenters is expanded in the conveying direction for stretching (the expansion of the distance between the tenters becomes the stretching ratio). At this time, the distance between the tenters in the width direction (vertical to the conveying direction) is arbitrarily set close. Preferably, the stretching ratio in the transport direction can be set to be closer to the free end. In the case of free end stretching, the shrinkage ratio in the width direction = (1 / stretching ratio) 1 / 2 To calculate.

[0079] The auxiliary stretching in the gas atmosphere can be performed in one stage or in multiple stages. In the case of multiple stages, the stretching ratio is the product of the stretching ratios in each stage. The stretching direction in the auxiliary stretching in the gas atmosphere is preferably substantially the same as the stretching direction in the aqueous solution stretching.

[0080] The stretch ratio in the auxiliary stretching in the gas atmosphere is preferably 2.0 to 3.5 times. The maximum stretch ratio in the case of combining the auxiliary stretching in the gas atmosphere and the stretching in the aqueous solution is preferably 5.0 times or more, more preferably 5.5 times or more, and even more preferably 6.0 times or more relative to the original length of the laminate. In this specification, the "maximum stretch ratio" refers to the stretch ratio immediately before the laminate breaks. Alternatively, the stretch ratio at which the laminate breaks is confirmed, and the "maximum stretch ratio" refers to a value 0.2 less than this value.

[0081] The stretching temperature for auxiliary stretching in a gas atmosphere can be set to any appropriate value depending on the material forming the thermoplastic resin substrate, the stretching method, etc. The stretching temperature is preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C, and particularly preferably above 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 rapid crystallization of the PVA-based resin can be suppressed, and the disadvantages caused by this crystallization (for example, interference with the orientation of the PVA-based resin layer caused by stretching) can be suppressed.

[0082] B-3. ​​Insolubilization treatment

[0083] As needed, an insolubilization treatment is performed after the auxiliary stretching treatment in a gas atmosphere, the stretching treatment in an aqueous solution, and before the dyeing treatment. The above-mentioned insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing the insolubilization treatment, water resistance can be imparted to the PVA-based resin layer, thereby preventing the orientation of the PVA from being reduced when immersed in water. The concentration of the aqueous boric acid solution is preferably 1 to 4 parts by weight relative to 100 parts by weight of water. The liquid temperature of the insolubilization bath (aqueous boric acid solution) is preferably 20°C to 50°C.

[0084] B-4. Dyeing treatment

[0085] The dyeing treatment is typically performed by dyeing the PVA resin layer with iodine. Specifically, iodine is adsorbed onto the PVA resin layer. Examples of adsorption methods include immersing the PVA resin layer (laminated body) in a dyeing solution containing iodine; applying the dyeing solution to the PVA resin layer; and spraying the dyeing solution onto the PVA resin layer. Immersing the laminate in the dyeing solution (dye bath) is preferred because iodine is readily adsorbed.

[0086] The dyeing solution is preferably an aqueous iodine solution. The amount of iodine added is preferably 0.05 to 0.5 parts by weight per 100 parts by weight of water. To increase the solubility of iodine in water, an iodide is preferably added to the aqueous iodine solution. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Of these, potassium iodide is preferred. The amount of iodide added is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, per 100 parts by weight of water. To suppress dissolution of the PVA resin, the dyeing solution is preferably used at a temperature of 20°C to 50°C. When immersing the PVA resin layer in the dyeing solution, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds, to ensure the transmittance of the PVA resin layer.

[0087] The dyeing conditions (concentration, liquid temperature, and immersion time) can be set so that the resulting polarizing film has a single-piece transmittance of 44.5% or greater and a degree of polarization of 99.0% or greater. As such, it is preferred to use an iodine aqueous solution as the dyeing solution, with the ratio of iodine to potassium iodide in the iodine aqueous solution being between 1:5 and 1:20. The ratio of iodine to potassium iodide in the iodine aqueous solution is preferably between 1:5 and 1:10. This produces a polarizing film having the aforementioned optical properties.

[0088] When the laminate is immersed in a treatment bath containing boric acid (representatively an insolubilization treatment) and then subjected to a dyeing treatment continuously, the boric acid concentration of the dyeing bath changes over time by mixing the boric acid contained in the treatment bath into the dyeing bath. As a result, the dyeing property sometimes becomes unstable. In order to suppress the instability of the dyeing property as described above, the upper limit of the boric acid concentration of the dyeing bath is adjusted so that it is preferably 4 parts by weight, more preferably 2 parts by weight relative to 100 parts by weight of water. On the other hand, the lower limit of the boric acid concentration of the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and further preferably 0.5 parts by weight relative to 100 parts by weight of water. In one embodiment, the dyeing treatment is performed using a dyeing bath pre-mixed with boric acid. Thus, the ratio of change in the boric acid concentration when the boric acid of the above-mentioned treatment bath is mixed into the dyeing bath can be reduced. The amount of boric acid pre-mixed in the dyeing bath (i.e., the content of boric acid not coming from the above-mentioned treatment bath) is preferably 0.1 to 2 parts by weight, more preferably 0.5 to 1.5 parts by weight relative to 100 parts by weight of water.

[0089] B-5. Cross-linking treatment

[0090] If necessary, a cross-linking treatment is performed after the dyeing treatment and before the aqueous solution stretching treatment. The above-mentioned cross-linking treatment is typically performed by immersing the PVA-type resin layer in a boric acid aqueous solution. By performing the cross-linking treatment, water resistance can be imparted to the PVA-type resin layer, and during the subsequent aqueous solution stretching, the orientation of the PVA when immersed in high-temperature water can be prevented from decreasing. The concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. In addition, when the cross-linking treatment is performed after the above-mentioned dyeing treatment, it is preferably further combined with an iodide. By combining an iodide, the dissolution of iodine adsorbed on the PVA-type resin layer can be suppressed. The amount of iodide combined is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the cross-linking bath (boric acid aqueous solution) is preferably 20°C to 50°C.

[0091] B-6. Stretching in aqueous solution

[0092] The aqueous solution stretching treatment is performed by immersing the laminate in a stretching bath. This allows stretching at a temperature below the glass transition temperature (typically around 80°C) of the thermoplastic resin substrate and PVA resin layer, suppressing crystallization of the PVA resin layer. As a result, a polarizing film with excellent optical properties can be produced.

[0093] The stretching method of the laminate can adopt any appropriate method. Specifically, it can be fixed end stretching or free end stretching (for example, a method in which the laminate is stretched uniaxially by passing the laminate between rollers with different peripheral speeds), preferably free end stretching. The stretching of the laminate can be carried out in one stage or in multiple stages. When carried out in multiple stages, the stretching ratio (maximum stretching ratio) of the laminate described below is the product of the stretching ratios of each stage.

[0094] Stretching in aqueous solution is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in aqueous boric acid solution). By using an aqueous boric acid solution as a stretching bath, the PVA-based resin layer can be given rigidity that can withstand the tension applied during stretching, as well as water resistance that prevents it from dissolving in water. Specifically, boric acid can generate tetrahydroxyborate anions in aqueous solution and cross-link with the PVA-based resin through hydrogen bonds. As a result, the PVA-based resin layer can be given rigidity and water resistance, which can be well stretched, and a polarizing film with excellent optical properties can be produced.

[0095] The above-mentioned boric acid aqueous solution is preferably obtained by dissolving boric acid and / or borate in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, and particularly preferably 3 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, the dissolution of the PVA-type resin layer can be effectively suppressed, and a polarizing film with higher characteristics can be manufactured. It should be noted that an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, etc. other than boric acid or borate in a solvent can also be used.

[0096] It is preferred to add an iodide to the stretching bath (boric acid aqueous solution). Adding an iodide can suppress the dissolution of iodine adsorbed to the PVA-based resin layer. Specific examples of iodide are described above. The concentration of the iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, per 100 parts by weight of water.

[0097] The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. If it is such a temperature, the dissolution of the PVA-type resin layer can be suppressed, and stretching can be performed at a high ratio. Specifically, as mentioned above, due to the relationship with the formation of the PVA-type resin layer, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or above. In this case, when the stretching temperature is lower than 40°C, there is a concern that it cannot be stretched well even considering the plasticization of the thermoplastic resin substrate brought about by water. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-type resin layer, and there is a concern that excellent optical properties cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

[0098] The stretch ratio by aqueous solution stretching is preferably 1.5 times or more, more preferably 3.0 times or more. The total stretch ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, relative to the original length of the laminate. By achieving such a high stretch ratio, a polarizing film with very excellent optical properties can be produced. Such a high stretch ratio can be achieved by using an aqueous solution stretching method (stretching in a boric acid aqueous solution).

[0099] B-7. Drying shrinkage treatment

[0100] The above-mentioned drying shrinkage treatment can be carried out by regional heating by heating the entire area, or by heating the transport roller (using a so-called heating roller) (heating roller drying method). Preferably, both are used. By using a heating roller for drying, the heating curling of the laminate can be efficiently suppressed, thereby manufacturing a polarizing film with excellent appearance. Specifically, by drying the laminate along the heating roller, the crystallization of the above-mentioned thermoplastic resin substrate can be efficiently promoted, the crystallinity can be increased, and the crystallinity of the thermoplastic resin substrate can be well increased even at a relatively low drying temperature. As a result, the rigidity of the thermoplastic resin substrate is increased, and it becomes a state that can withstand the shrinkage of the PVA-based resin layer caused by drying, which can suppress curling. In addition, by using a heating roller, the laminate can be dried while being kept in a flat state, therefore, not only can curling be suppressed, but also the generation of wrinkles can be suppressed. At this time, the laminate is shrunk in the width direction by the drying shrinkage treatment, thereby improving the optical properties. This is because the orientation of PVA and PVA / iodine complex can be effectively improved. The shrinkage rate of the laminate in the width direction by the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using heated rollers, the laminate can be continuously shrunk in the width direction while being conveyed, achieving high productivity.

[0101] Figure 2 This is a schematic diagram illustrating an example of a drying and shrinking process. During the drying and shrinking process, the laminate 200 is dried while being transported by transport rollers R1 to R6 and guide rollers G1 to G4, both heated to a predetermined temperature. In the illustrated example, the transport rollers R1 to R6 are positioned to alternately and continuously heat the PVA resin layer surface and the thermoplastic resin substrate surface. However, the transport rollers R1 to R6 may alternatively be positioned to continuously heat only one side of the laminate 200 (e.g., the thermoplastic resin substrate surface).

[0102] The drying conditions can be controlled by adjusting the heating temperature of the conveying roller (temperature of the heating roller), the number of heating rollers, the contact time with the heating roller, etc. The temperature of the heating roller is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. The crystallinity of the thermoplastic resin can be well increased, curling can be well suppressed, and an optical laminate with excellent durability can be produced. It should be noted that the temperature of the heating roller 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 multiple conveying rollers. Conveying rollers are usually provided in 2 to 40 numbers, preferably 4 to 30 numbers. The contact time (total contact time) between the laminate and the heating roller is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and further preferably 1 to 10 seconds.

[0103] The heating roller can be set in a heating furnace (such as an oven) or in a conventional manufacturing line (under room temperature environment). It is preferably set in a heating furnace equipped with an air supply mechanism. By combining the drying using the heating roller and the hot air drying, the rapid 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 10m / s to 30m / s. It should be noted that the wind speed is the wind speed in the heating furnace and can be measured by a mini-vane digital anemometer.

[0104] B-8. Other treatments

[0105] It is preferable to perform a cleaning treatment after the stretching treatment in the aqueous solution and before the drying and shrinking treatment. The cleaning treatment is typically performed by immersing the PVA-based resin layer in a potassium iodide aqueous solution.

[0106] Example

[0107] The present invention will be described in detail below by way of examples, but the present invention is not limited to these examples. The measuring methods of various properties are as follows. It should be noted that, unless otherwise specified, the "parts" and "%" in the examples and comparative examples are by weight.

[0108] (1) Thickness

[0109] The thickness was measured using an interferometer film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name: "MCPD-3000").

[0110] (2) Single-unit transmittance and polarization degree

[0111] For the polarizers (protective films / polarizing films) of the Examples and Comparative Examples, the single transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc measured using a UV-visible spectrophotometer (V-7100 manufactured by JASCO Corporation) were used as the Ts, Tp, and Tc of the polarizing film. These Ts, Tp, and Tc are Y values ​​obtained by measuring the 2-degree field of view (light source C) of JIS Z8701 and correcting for visibility. It should be noted that the refractive index of the protective film is 1.50, and the refractive index of the surface of the polarizing film opposite to the protective film is 1.53.

[0112] The polarization degree P is calculated from the obtained Tp and Tc using the following formula.

[0113] Polarization degree P (%) = {(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100

[0114] It should be noted that equivalent measurements can be performed using a spectrophotometer such as the LPF-200 manufactured by Otsuka Electronics Co., Ltd. As an example, the single-element transmittance Ts and polarization degree P of polarizing plates Samples 1 to 3, having the same configuration as in the following examples, were measured using the V-7100 and LPF-200, and these measured values ​​are shown in Table 1. As shown in Table 1, the difference between the single-element transmittance measured using the V-7100 and the LPF-200 is less than 0.1%, indicating that equivalent measurement results were obtained using either spectrophotometer.

[0115] [Table 1]

[0116]

[0117] It should be noted that, for example, when a polarizing plate that has undergone an anti-glare (AG) surface treatment and has an adhesive with diffusion properties is used as the measurement object, different measurement results may be obtained depending on the spectrophotometer. In this case, numerical conversion is performed based on the measurement values ​​when the same polarizing plate is measured using different spectrophotometers, thereby compensating for the difference in measurement values ​​depending on the spectrophotometer.

[0118] (3) Deviation in the optical properties of long polarizers

[0119] From the long strip of polarizing plate used in the examples and reference examples, measurement samples were cut out at five locations at equal intervals along the width direction, and the single transmittance of the central portion of each of the five measurement samples was measured in the same manner as in (2) above. Next, the difference between the maximum and minimum values ​​of the single transmittance measured at each measurement position was calculated, and this value was defined as the deviation of the optical characteristics of the long strip of polarizing plate (the difference between the maximum and minimum values ​​of the single transmittance at each position along the width direction of the long strip of polarizing plate).

[0120] (4) Variation in the optical properties of a single polarizing plate

[0121] From the long strips of polarizing plates used in the examples and reference examples, a measurement sample of 100 mm × 100 mm was cut out, and the polarizing plate (50 cm) of the single sheet was obtained. 2 ) of the optical characteristics. Specifically, the single transmittance was measured at a total of five positions, including positions about 1.5 cm to 2.0 cm inward from the midpoint of each of the four sides of the measurement sample and the central part, in the same manner as in (2) above. Next, the difference between the maximum and minimum values ​​of the single transmittance measured at each measurement position was calculated, and this value was set as the deviation of the optical characteristics of the single-piece polarizer (50 cm 2 The difference between the maximum and minimum values ​​of the single transmittance in the region).

[0122] [Example 1]

[0123] 1. Production of polarizing film

[0124] As the thermoplastic resin substrate, a long amorphous polyethylene terephthalate copolymer film (thickness: 100 μm) having a water absorption of 0.75% and a Tg of approximately 75° C. was used. One surface of the resin substrate was corona treated.

[0125] To 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol %) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410") in a ratio of 9:1, 13 parts by weight of potassium iodide was added to prepare a PVA aqueous solution (coating solution).

[0126] The PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60° C. to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.

[0127] The obtained laminate was uniaxially stretched to 2.4 times in the longitudinal direction (longitudinal direction) at the free end between rolls of different peripheral speeds in an oven at 130° C. (auxiliary stretching treatment in an atmosphere).

[0128] Next, the laminate was immersed in an insolubilization bath (boric acid aqueous solution prepared by blending 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilization treatment).

[0129] Next, the film was immersed for 60 seconds (dyeing treatment) in a dyeing bath (an iodine aqueous solution obtained by combining iodine and potassium iodide in a weight ratio of 1:7 relative to 100 parts by weight of water) at a liquid temperature of 30°C while adjusting the concentration so that the monomer transmittance (Ts) of the polarizing film obtained finally becomes 44.5% or more.

[0130] Next, the film was immersed in a cross-linking bath (boric acid aqueous solution containing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid per 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (cross-linking treatment).

[0131] Then, while immersing the laminate in a boric acid aqueous solution (boric acid concentration 4.0 wt%) at a liquid temperature of 70°C, it was uniaxially stretched (stretching treatment in aqueous solution) between rollers with different peripheral speeds so that the total stretching ratio in the longitudinal direction (length direction) became 5.5 times.

[0132] Then, the laminate was immersed in a cleaning bath (an aqueous solution containing 4 parts by weight of potassium iodide per 100 parts by weight of water) at a liquid temperature of 20° C. (cleaning treatment).

[0133] Thereafter, the laminate was dried in an oven maintained at 90° C. and brought into contact with a SUS heating roll maintained at a surface temperature of 75° C. for about 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment was 5.2%.

[0134] In this manner, a polarizing film having a thickness of 5 μm was formed on the resin substrate. The same steps were repeated to produce a total of 7 polarizing films.

[0135] 2. Production of polarizer

[0136] An acrylic film (surface refractive index 1.50, 40 μm) was attached as a protective film to the surface (opposite to the resin substrate) of each polarizing film obtained above using a UV-curable adhesive. Specifically, the curable adhesive was applied to a total thickness of 1.0 μm and then attached using a roller. UV light was then irradiated from the protective film side to cure the adhesive. Next, the ends were notched and the resin substrate peeled off, resulting in seven long polarizing plates (width: 1300 mm) with a protective film / polarizing film structure.

[0137] [Reference Example 1]

[0138] Five polarizing films and five polarizing plates were produced in the same manner as in Example 1, except that the dyeing treatment was performed so that the single-piece transmittance (Ts) of the finally obtained polarizing film would be 43.0% or more and less than 44.5%.

[0139] [Example 2]

[0140] Four polarizing films and a polarizing plate were produced in the same manner as in Example 1, except that the oven temperature and the heating roller temperature during the drying and shrinking treatment were set at 70° C. The shrinkage rate of the laminate in the width direction due to the drying and shrinking treatment was 2.5%.

[0141] [Reference Example 2]

[0142] Five polarizing films and five polarizing plates were produced in the same manner as in Example 2, except that the dyeing treatment was performed so that the single-piece transmittance (Ts) of the finally obtained polarizing film would be 43.0% or more and less than 44.5%.

[0143] [Comparative Example 1]

[0144] No potassium iodide was added to the PVA aqueous solution (coating solution), the stretching ratio in the auxiliary stretching treatment in the gas atmosphere was set to 1.8 times, and no heating roller was used in the drying and shrinking treatment. Except for this, the production of the polarizing film was attempted in the same manner as in Example 1. However, the PVA resin layer dissolved during the dyeing treatment and the stretching treatment in the aqueous solution, and the polarizing film could not be produced.

[0145] [Comparative Example 2]

[0146] Nine polarizing films and polarizing plates were produced in the same manner as in Example 1, except that the stretching ratio in the in-air auxiliary stretching treatment was set to 1.8 times and no heating roller was used in the drying and shrinking treatment. However, no polarizing film having a single transmittance of 44.5% or more was produced.

[0147] [Reference Example 3]

[0148] The polarizing film obtained in the same manner as in Comparative Example 2 was kept in a constant temperature and humidity area set at a temperature of 60° C. and a humidity of 90% RH for 30 minutes.

[0149] The single transmittance and polarization degree of each polarizing plate of the embodiment and the comparative example were measured, and the results are shown in Table 2 and Table 3. Figure 3 .exist Figure 3 , approximate curves of the curves of Example 1 and Reference Example 1, approximate curves of the curves of Example 2 and Reference Example 2, and approximate curves of the curve of Comparative Example 2 are shown.

[0150] [Table 2]

[0151]

[0152] The polarizing film obtained by the manufacturing method of the comparative example cannot simultaneously achieve a single-element transmittance of 44.5% or higher and a single-element transmittance of 99.0% or higher. It should be noted that, as shown by the approximate curve of the curve of Comparative Example 2, when dyeing is performed to achieve a single-element transmittance of 44.5% or higher in the manufacturing method of Comparative Example 2, it is predicted that the polarization degree will be less than 99.0%. In contrast, the polarizing film obtained by the manufacturing method of the example has excellent optical properties, with a single-element transmittance of 44.5% or higher and a polarization degree of 99.0% or higher.

[0153] The variations in optical properties of the long strip and single-piece polarizing plates of each of Example 1 and Reference Example 3 were measured. The results are shown in Table 3.

[0154] [Table 3]

[0155] Single transmittance deviation (strip) Single piece transmittance deviation (single piece) Example 1 0.18％ 0.05％ Reference Example 3 0.55％ 0.45％

[0156] The transmittance variation of the elongated polarizer obtained by the manufacturing method of the example was less than 0.3%, and the transmittance variation of the single-piece polarizer obtained by the manufacturing method of the example was less than 0.2%, and the variation in optical properties was suppressed to a level that was not problematic. On the other hand, the polarizer of the reference example, which was obtained by humidifying the polarizing film, showed large variations in optical properties in both the elongated and single-piece polarizers.

[0157] Industrial Applicability

[0158] The polarizing plate having the polarizing film of the present invention can be suitably used as a circularly polarizing plate for an organic EL display device or an inorganic EL display device.

Claims

1. A method for manufacturing a polarizing film, wherein the polarizing film has a thickness of 8 μm or less, a single-body transmittance of 44.5% or more, and a degree of polarization of 99.0% or more, the method comprising: A polyvinyl alcohol-based resin layer containing iodide or sodium chloride and polyvinyl alcohol-based resin is formed on one side of a long thermoplastic resin substrate to prepare a laminate; as well as The laminate is sequentially subjected to auxiliary stretching treatment in a gas atmosphere, dyeing treatment, stretching treatment in an aqueous solution, and drying and shrinking treatment. In the drying and shrinking treatment, the laminate is heated while being transported in the longitudinal direction, thereby shrinking it in the width direction by more than 2%. 2 . The manufacturing method according to claim 1 , which is a method for manufacturing a polarizing film having a single-body transmittance of 45.0% or less and a polarization degree of 99.9% or less.

3. The manufacturing method according to claim 1 or 2, wherein: In the polyvinyl alcohol-based resin layer, the content of the iodide or sodium chloride is 5 parts by weight to 20 parts by weight based on 100 parts by weight of the polyvinyl alcohol-based resin.

4. The production method according to any one of claims 1 to 3, wherein The stretching ratio in the auxiliary stretching treatment in the gas atmosphere is 2.0 times or more.

5. The production method according to any one of claims 1 to 4, wherein The drying shrinkage treatment step is a step of applying heat using a heating roller.

6. The manufacturing method according to claim 5, wherein: The temperature of the heating roller is 60° C. to 120° C., and the shrinkage rate of the laminate in the width direction caused by the drying shrinkage treatment is 2% or more.

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