TW201945202A - Polarizer, polarizer roll, and method for manufacturing polarizing film - Google Patents

Abstract

The present invention provides a polarizer with an excellent optical characteristic and minimizes variation in the optical characteristics. The polarizer according to the present invention comprises a polarizing film having the thickness of 8 [mu]m or less, a unit transmittance of 48% or greater, and a degree of polarization of 85% or greater, and a protective layer arranged on at least one side of the polarizing film, said polarizer having the difference of 0.5% or less between the maximum and the minimum unit transmittance in a region of 50 cm2. Another polarizer according to the present invention comprises a polarizing film having the thickness of 8 [mu]m or less, a unit transmittance of 48% or greater, and a degree of polarization of 85% or greater, and a protective layer arranged on at least one side of the polarizing film, said polarizer having the width of 1000 mm or greater and having the difference of 1% or less between the maximum and the minimum unit transmittance at a position along the width direction.

Description

Manufacturing method of polarizing plate, polarizing plate roll, and polarizing film

The present invention relates to a method for manufacturing a polarizing plate, a polarizing plate roll, and a polarizing film.

BACKGROUND OF THE INVENTION With the popularity of thin displays, displays (OLEDs) equipped with organic EL panels and displays (QLEDs) using display panels using inorganic light-emitting materials such as quantum dots have also been proposed. These panels have a highly reflective metal layer, so they easily cause problems such as external light reflection or background reflection. It is known that a circularly polarizing plate having a polarizing film and a λ / 4 plate is arranged on the viewing side at this time to prevent such problems. As a method for producing a polarizing film, for example, a method has been proposed in which a laminated body having a resin substrate and a polyvinyl alcohol (PVA) resin layer is extended and then subjected to a dyeing treatment to obtain a polarizing film on the resin substrate ( For example, Patent Document 1). A thinner polarizing film can be obtained by this method, and it has attracted much attention because it can contribute to the reduction in thickness of image display devices in recent years. In addition, if the reflectivity of the panel is suppressed to decrease as the performance of the display panel is improved, the required characteristics of the polarization degree are reduced, and a polarizing plate with a higher transmittance is required. However, in the past, in order to improve the transmittance of the existing thin polarizing film, a thin film capable of withstanding optical applications could not be produced due to problems such as dissolution of the PVA-based resin.

Prior Art Literature Patent Literature Patent Literature 1: Japanese Patent Laid-Open No. 2001-343521

SUMMARY OF THE INVENTION Problems to be Solved by the Invention The present invention has been made in order to solve the above-mentioned conventional problems. The main object of the present invention is to provide a polarizing plate, a polarizing plate roll, and a polarizing film having excellent optical characteristics and suppressing variations in optical characteristics. Production method.

Means for solving the problem The polarizing plate of the present invention has a polarizing film and a protective layer disposed on at least one side of the polarizing film, and the thickness of the polarizing film is 8 μm or less, the unit transmittance is 48% or more, and the degree of polarization It is 85% or more; and the difference between the maximum value and the minimum value of the monomer transmittance in the area of 50 cm ² of the polarizing plate is 0.5% or less.
Another polarizing plate of 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 is 8 μm or less, the single transmittance is 48% or more, and the polarization degree is 85% or more. In addition, the width of the polarizing plate is 1000 mm or more, and the difference between the maximum value and the minimum value of the single transmittance of the position in the width direction is 1% or less.
In one embodiment, a single transmittance of the polarizing film is 50% or less, and a polarization degree is 92% or less.
According to another aspect of the present invention, a polarizing plate coil is provided. The polarizing plate roll is obtained by winding the polarizing plate into a roll shape.
According to another aspect of the present invention, a method for manufacturing a polarizing film is provided. The manufacturing method is a method for manufacturing a polarizing film having a thickness of 8 μm or less, a monomer transmittance of 48% or more, and a polarization degree of 85% or more. The manufacturing method includes the following steps: forming a single side of a long thermoplastic resin substrate A laminated body is made of a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin; and the above-mentioned laminated body is sequentially subjected to an air-assisted stretching treatment, a dyeing treatment, and an underwater stretching treatment at an extension ratio of 2.0 times or more. In combination with the drying shrinkage treatment, the drying shrinkage treatment is carried out while heating the laminated body while conveying it in the longitudinal direction, thereby shrinking it by 2% or more in the width direction.
In one embodiment, the content of the halide in the polyvinyl alcohol-based resin layer is 5 to 20 parts by weight based on 100 parts by weight of the polyvinyl alcohol-based resin.
In one embodiment, the drying shrinkage treatment step is a step of heating using a heating roller.
In one embodiment, the temperature of the heating roller is 60 ° C. to 120 ° C., and the shrinkage rate in the width direction of the laminated body obtained by performing the drying shrinkage treatment is 2% or more.

Advantageous Effects of Invention According to the present invention, it is possible to provide a polarizing plate having excellent optical characteristics and suppressed optical characteristics, and the polarizing plate has a polarized light having a thickness of 8 μm or less, a single transmittance of 48% or more, and a polarization degree of 85% or more membrane.

Embodiments for Implementing the Invention Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

A. Polarizing Plate FIG. 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 includes 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 monomer transmittance is 48% or more, and the polarization degree is 85% or more. One of the first protective layer 20 and the second protective layer 30 may be omitted. One of the first protective layer and the second protective layer may be a resin substrate (to be described later) for producing a polarizing film.

The polarizing plate may be long or thin. When the polarizing plate is long, it should be wound into a roll to make a polarizing plate roll. Then, the polarizing plate has excellent optical characteristics and the variation in optical characteristics is also small. In one embodiment, the width of the polarizing plate is 1000 mm or more, and the difference (D1) between the maximum value and the minimum value of the single transmittance of the position in the width direction is 1% or less. The upper limit of D1 should be 0.8%, and more preferably 0.6%. The smaller D1 is, the better, but the lower limit is, for example, 0.01%. As long as D1 is within the above range, a polarizing plate having excellent optical characteristics can be industrially produced. In another embodiment, the difference (D2) between the maximum value and the minimum value of the single transmittance in a 50 cm ² area of the polarizing plate is 0.5% or less. The upper limit of D2 should be 0.25%, and more preferably 0.15%. The smaller D2 is, the better, but the lower limit is, for example, 0.01%. As long as D2 is within the above range, the brightness variation of the display screen can be suppressed when a polarizing plate is used in an image display device.

A-1. Polarizing film As described above, the polarizing film has a thickness of 8 μm or less, a single transmittance of 48% or more, and a polarization degree of 85% or more. Generally speaking, there is a trade-off relationship between the transmittance of the monomer and the degree of polarization, so if the transmittance of the monomer is increased, the degree of polarization will decrease, and if the degree of polarization is increased, the transmittance of the monomer will decrease. Therefore, it has been difficult to provide a thin polarizing film that has conventionally satisfied optical characteristics of 48% or more and 85% or more polarized light. One of the achievements of the present invention is that a thin polarizing film (polarizing plate) can be realized, which has excellent optical characteristics of a single transmittance of 48% or more and a polarization degree of 85% or more, and the optical characteristics are suppressed. The polarizing film (polarizing plate) can be used in an image display device, and is particularly suitable for a circular polarizing plate for an organic EL display device.

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

The polarizing film should exhibit absorption dichroism at any wavelength of 380nm ~ 780nm. The single transmittance of the polarizing film is preferably 50% or less. The polarization degree of the polarizing film should be more than 86%, more preferably 87% or more, and more preferably 88% or more. On the other hand, the upper limit of the degree of polarization should be 92%. The above-mentioned monomer transmittance represents a Y value measured by an ultraviolet-visible spectrophotometer and compensated for visual sensitivity. The above-mentioned polarization degree is representatively based on the parallel transmittance Tp and the orthogonal transmittance Tc measured with an ultraviolet-visible spectrophotometer and compensated for visual sensitivity, and is obtained by the following formula.
Polarization (%) = ((Tp-Tc) / (Tp + Tc)) ^1/2 × 100

In one embodiment, the transmittance of a thin polarizing film with a thickness of 8 μm or less is represented by a multilayer body of a polarizing film (refractive index on the surface: 1.53) and a protective film (refractive index: 1.50) as the measurement object, and ultraviolet and visible light are used for the spectroscopic analysis. Photometer to determine. Depending on the refractive index of the surface of the polarizing film and / or the refractive index of the surface of the protective film that is in contact with the air interface, the reflectance of each layer at the interface will change, and as a result, the measured value of the transmittance may change. Therefore, for example, when a protective film having a refractive index other than 1.50 is used, the measured value of the transmittance can also be corrected according to the refractive index of the surface of the protective film that is in contact with the air interface. Specifically, the correction value C of the transmittance is the reflectance R ₁ (transmission axis reflectance) of polarized light parallel to the transmission axis of the interface between the protective film and the air layer, and is expressed by the following formula.
C = R ₁ -R _{0
^{R 0 = ((1.50-1) 2}} /(1.50+1) 2) × (T 1/100)
_{R 1 = ((n 1 -1} ) 2 / (n 1 +1) 2) × (T 1/100)
Here, R ₀ is the transmission axis reflectance when a protective film having a refractive index of 1.50 is used, n ₁ is the refractive index of the protective film used, and T ₁ is the transmittance of the polarizing film. For example, when a substrate (cycloolefin-based film, film with hard coat layer, etc.) having a surface refractive index of 1.53 is used as the protective film, the correction amount C is about 0.2%. At this time, 0.2% of the transmittance obtained by the measurement can be converted into the transmittance when a protective film having a surface refractive index of 1.50 is used. In addition, according to the above formula, the change in the correction value C when the transmittance T1 of the polarizing film is changed by 2% is less than 0.03%, so the influence of the transmittance of the polarizing film on the value of the correction value C is limited. of. When the protective film has absorption other than surface reflection, appropriate correction can be performed depending on the amount of absorption.

Any polarizing film can be used as the polarizing film. The polarizing film is typically made by using a multilayer body of two or more layers.

Specific examples of the polarizing film obtained by using the laminated body include a polarizing film obtained by using a resin substrate and a laminate of a PVA-based resin layer formed on the resin substrate. A polarizing film obtained by using a resin substrate and a laminate of a PVA-based resin layer formed on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate and Forming a PVA-based resin layer on the resin substrate by drying to obtain a laminate of the resin substrate and the PVA-based resin layer; and extending and dyeing the laminate to form a PVA-based resin layer as a polarizing film. In this embodiment, stretching means that the laminated body is immersed in an aqueous boric acid solution and stretched. Moreover, if necessary, the stretching may further include performing air stretching at a high temperature (for example, 95 ° C. or higher) on the laminate before performing the stretching in an aqueous boric acid solution. The obtained resin substrate / polarizing film laminate can be directly used (that is, the resin substrate can be used as a protective layer of the polarizing film), or the resin substrate can be peeled from the resin substrate / polarizing film laminate and applied to This peeling surface is laminated with an arbitrary and appropriate protective layer according to the purpose, and is used later. Details of the method for producing the polarizing film are described in, for example, Japanese Patent Laid-Open No. 2012-73580. The entire description of the publication is referred to in this specification as a reference.

The method for manufacturing a polarizing film of the present invention includes the following steps: forming a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate to form a laminated body; and, The laminated body is sequentially subjected to air-assisted stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment with an extension magnification of 2.0 times or more. The drying shrinkage treatment is carried out while heating the laminated body in the longitudinal direction, thereby Make it shrink more than 2% in the width direction. Thereby, a polarizing film having excellent optical characteristics and suppressed optical characteristics can be provided. The thickness of the polarizing film is 8 μm or less, the monomer transmittance is 48% or more, and the polarization degree is 85% or more. That is, by introducing auxiliary extension, even when PVA is coated on a thermoplastic resin, the crystallinity of PVA can be improved and high optical characteristics can be achieved. In addition, by improving the directivity of PVA at the same time in advance, when the subsequent dyeing step and the extension step are immersed in water, problems such as the reduction or dissolution of the directivity of PVA can be prevented, and high optical characteristics can be achieved. In addition, when the PVA-based resin layer is immersed in a liquid, compared with the case where the PVA-based resin layer does not contain a halide, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed. Thereby, it is possible to improve the optical characteristics of the polarizing film obtained by a treatment step in which the laminated body is immersed in a liquid, such as a dyeing treatment and an elongation treatment in water. In addition, by shrinking the laminated body in the width direction by a drying shrinkage treatment, optical characteristics can be improved.

A-2. Protective layer The first and second protective layers are formed of arbitrary and appropriate films that can be used as a protective layer of a polarizing film. Specific examples of the material of the main component of the film include cellulose resins such as triethylammonium cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, and polyfluorene. Transparent resins such as imine, polyether fluorene, polyfluorene, polystyrene, polynorbornene, polyolefin, (meth) acrylic and acetate. In addition, thermosetting resins such as (meth) acrylic, urethane, urethane, (meth) acrylic, epoxy, and polysiloxane, and ultraviolet curable resins can also be mentioned. Other examples include glassy polymers such as siloxane polymers. In addition, a polymer film described in Japanese Patent Laid-Open No. 2001-343529 (WO01 / 37007) may be used. As a material of the film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted fluorene imine group in a side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in a side chain, and For example, a resin composition having an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be cited. The polymer film may be, for example, an extruded shape of the resin composition.

When the polarizing plate 100 is applied to an image display device, the thickness of the protective layer (outside 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 more It should be 10μm ~ 60μm. In addition, when a surface treatment is performed, the thickness of the outer protective layer is a thickness including the thickness of the surface treatment layer.

When the polarizing plate 100 is applied to an image display device, the thickness of the protective layer (inner protective layer) disposed on the display panel side is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and still more preferably 10 μm to 60 μm. In one embodiment, the inner protective layer is a retardation layer having an arbitrary and appropriate retardation value. At this time, the in-plane retardation Re (550) of the retardation layer is, for example, 110 nm to 150 nm. "Re (550)" is an in-plane phase difference measured with light having a wavelength of 550 nm at 23 ° C, and can be obtained by the formula: Re = (nx-ny) × d. Here, "nx" is the refractive index in the plane whose refractive index is the largest direction (that is, the slow axis direction), and "ny" is the refractive index in the plane that is orthogonal to the slow axis (that is, the fast axis direction). "Nz" is the refractive index in the thickness direction, and "d" is the thickness (nm) of the layer (thin film).

B. Manufacturing method of polarizing film The manufacturing method of a polarizing film according to an embodiment of the present invention includes the following steps: forming a halogen-containing compound and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin substrate; A polyvinyl alcohol-based resin layer (PVA-based resin layer) is used to form a laminated body; and the laminated body is sequentially subjected to an air-assisted extension treatment, a dyeing treatment, an underwater extension treatment, and a dry shrinkage treatment with an extension ratio of 2.0 times or more, This drying shrinkage treatment is performed by heating the laminated body while conveying it in the longitudinal direction, thereby shrinking it by 2% or more in the width direction. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin. The drying and shrinking treatment should be performed by using a heating roller, and the temperature of the heating roller should be 60 ° C to 120 ° C. The shrinkage of the laminated body in the width direction due to the drying shrinkage treatment should be more than 2%. According to the above manufacturing method, the polarizing film described in the above item A can be obtained. In particular, a polarizing film having excellent optical characteristics (represented by individual transmittance and polarization) and suppressed optical characteristics can be produced by the following methods: Production of a laminate including a halide-containing PVA-based resin layer Then, the extension of the laminated body is set as a multi-stage extension including aerial auxiliary extension and underwater extension, and the extended laminated body is heated by a heating roller. Specifically, by using a heating roller in the drying shrinkage treatment step, the entire laminated body can be uniformly contracted while being conveyed. This can not only improve the optical characteristics of the polarizing film produced, but also stably produce a polarizing film with excellent optical characteristics, and can suppress variations in the optical characteristics (especially the single transmittance) of the polarizing film.

B-1. Production of Laminated Body A method for producing a laminated body of a thermoplastic resin substrate and a PVA-based resin layer may be any appropriate method. It is preferable to form a PVA-based resin layer on the surface of the thermoplastic resin laminate by applying a coating solution containing a halide and a PVA-based resin and drying the coating liquid. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

The coating liquid may be applied by any appropriate method. Examples include a roll coating method, a spin coating method, a bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a doctor blade coating method (comma coating method, etc.), and the like. The coating and drying temperature of the coating liquid is preferably 50 ° C or higher.

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

Prior to forming the PVA-based resin layer, a surface treatment (for example, corona treatment) may be applied to the thermoplastic resin substrate, or an easy-adhesion layer may be formed on the thermoplastic resin substrate. By performing the treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved.

B-1-1. Thermoplastic resin substrate The thickness of the thermoplastic resin substrate is preferably 20 μm to 300 μm, and more preferably 50 μm to 200 μm. If it is less than 20 μm, it may be difficult to form a PVA-based resin layer. If it exceeds 300 μm, for example, the thermoplastic resin base material may take a long time to absorb water during an extension treatment in water described later, which may cause an excessive load on the extension.

The water absorption of the thermoplastic resin substrate is preferably 0.2% or more, and more preferably 0.3% or more. The thermoplastic resin substrate absorbs water, and water acts as a plasticizer to plasticize. As a result, the stretching stress can be greatly reduced, and the stretching can be performed at a high magnification. On the other hand, the water absorption of the thermoplastic resin substrate is preferably 3.0% or less, and more preferably 1.0% or less. By using the thermoplastic resin base material, it is possible to prevent the dimensional stability of the thermoplastic resin base material from being significantly reduced at the time of production, which can cause problems such as deterioration in appearance of the obtained polarizing film. Further, it is possible to prevent the substrate from being broken or the PVA-based resin layer from being peeled from the thermoplastic resin substrate when it is stretched in water. The water absorption of the thermoplastic resin substrate can be adjusted, for example, by introducing a modified base into a constituent material. The water absorption is a value obtained in accordance with JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120 ° C or lower. By using the thermoplastic resin substrate, the crystallization of the PVA-based resin layer can be suppressed, and at the same time, the extensibility of the laminated body can be sufficiently ensured. In addition, considering the plasticization of thermoplastic resin substrates based on water and the smooth extension in water, the temperature is preferably 100 ° C or lower, and more preferably 90 ° C or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60 ° C or higher. By using the thermoplastic resin substrate, it is possible to prevent the thermoplastic resin substrate from being deformed (for example, unevenness, sagging, wrinkles, etc.) and the like during coating and drying of the coating solution containing the PVA-based resin can be prevented. Laminates are produced well. The PVA-based resin layer can be stretched well at an appropriate temperature (for example, about 60 ° C). The glass transition temperature of the thermoplastic resin substrate can be adjusted, for example, by heating a crystallized material that introduces a modified material into a constituent material. The glass transition temperature (Tg) is a value obtained in accordance with JIS K 7121.

As a constituent material of the thermoplastic resin substrate, any appropriate thermoplastic resin can be used. Examples of the thermoplastic resin include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, Copolymer resins and the like. Of these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferred.

In one embodiment, an amorphous (uncrystallized) polyethylene terephthalate resin is preferably used. Among these, an amorphous (hardly crystallizable) polyethylene terephthalate-based resin is particularly preferably used. Specific examples of the amorphous polyethylene terephthalate-based resin include copolymers containing isophthalic acid and / or cyclohexanedicarboxylic acid as dicarboxylic acids, and further containing cyclohexane. Dimethyl or diethylene glycol is a copolymer of glycol.

In a preferred embodiment, the thermoplastic resin substrate is made of a polyethylene terephthalate resin having an isophthalic acid unit. The reason is that the thermoplastic resin substrate is extremely excellent in elongation, and can suppress crystallization during elongation. We believe that this is due to the introduction of isophthalic acid units, which results in a large bend in the main chain. The polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content ratio of the isophthalic acid unit is preferably 0.1 mol% or more, and more preferably 1.0 mol% or more, relative to the total of all the repeating units. This is because a thermoplastic resin substrate having excellent elongation can be obtained. On the other hand, the content ratio of the isophthalic acid unit is preferably 20 mol% or less, and more preferably 10 mol% or less, relative to the total of all the repeating units. By setting the content ratio as described above, the degree of crystallization can be favorably increased in the dry shrinkage treatment described later.

The thermoplastic resin substrate may be stretched in advance (before forming the PVA-based resin layer). In one embodiment, it extends in the lateral direction of the long thermoplastic resin substrate. The horizontal direction is preferably a direction orthogonal to the extending direction of the laminated body described later. In addition, the term "orthogonal" in this specification includes a case where it is substantially orthogonal. Here, the term “substantially orthogonal” includes a case of 90 ° ± 5.0 °, and is preferably 90 ° ± 3.0 °, and more preferably 90 ° ± 1.0 °.

Relative to the glass transition temperature (Tg), the extension temperature of the thermoplastic resin substrate should preferably be Tg-10 ° C ~ Tg + 50 ° C. The stretching ratio of the thermoplastic resin substrate should preferably be 1.5 to 3.0 times.

The thermoplastic resin substrate may be stretched by any appropriate method. Specifically, it may be a fixed end extension or a free end extension. The extension method can be dry or wet. The stretching of the thermoplastic resin substrate can be performed in one stage or in multiple stages. When carried out in multiple stages, the above-mentioned stretch magnification is the product of the stretch magnifications of each stage.

B-1-2. Coating liquid The coating liquid contains a halide and a PVA-based resin as described above. The coating liquid represents a solution obtained by dissolving the halide and the PVA-based resin in a solvent. Examples of the solvent include water, dimethylmethylene, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, and polyhydric alcohols such as trimethylolpropane. Amines such as ethylenediamine and diethylene glycol. These may be used alone or in combination of two or more kinds. Among them, 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. As long as the resin concentration is the same, a uniform coating film adhered to the thermoplastic resin substrate can be formed. The content of the halide in the coating liquid is 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin.

Additives can also be blended in the coating solution. Examples of the additives include plasticizers and surfactants. Examples of the plasticizer include a polyhydric alcohol such as ethylene glycol or glycerin. The surfactant may be, for example, a nonionic surfactant. These can be used in order to further improve the uniformity, dyeability, and elongation of the obtained PVA-based resin layer.

The PVA-based resin may be any appropriate resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of PVA 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 degree of saponification is determined in accordance with JIS K 6726-1994. By using the PVA-based resin having the saponification degree, a polarizing film having excellent durability can be obtained. When 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 according to the purpose. The average degree of polymerization is usually 1000 to 10,000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be obtained in accordance with JIS K 6726-1994.

The halide may be any appropriate halide. Examples include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Of these, potassium iodide is preferred.

The amount of the halide in the coating liquid is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin, and more preferably 10 to 15 parts by weight relative to 100 parts by weight of the PVA-based resin. If the amount of the halide relative to 100 parts by weight of the PVA-based resin exceeds 20 parts by weight, the halide may bleedout, which may cause the resulting polarized film to become cloudy.

In general, by extending the PVA-based resin layer, the orientation of the polyvinyl alcohol molecules in the PVA-based resin becomes higher. However, if the stretched PVA-based resin layer is immersed in a water-containing liquid, the Orientation will be disordered, and the orientation may be reduced. In particular, when the laminate of a thermoplastic resin and a PVA-based resin layer is stretched in boric acid water, in order to stabilize the stretching of the thermoplastic resin, the laminate is stretched in boric acid water at a relatively high temperature, and the orientation will tend to decrease. Significant. For example, the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is generally higher at about 70 ° C than when stretching a PVA film monomer in boric acid water at 60 ° C. In this case, the orientation of the PVA in the initial stage of stretching may decrease in the stage before it rises by stretching in water. In contrast, a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate is produced, and the laminate is stretched at high temperature (assisted stretching) in the air before the laminate is stretched in boric acid water, thereby facilitating the lamination after the auxiliary stretching. Crystallization of the PVA-based resin in the bulk PVA-based resin layer. As a result, when the PVA-based resin layer is immersed in a liquid, as compared with the case where the PVA-based resin layer does not contain a halide, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed. Thereby, it is possible to improve the optical characteristics of the polarizing film obtained by a treatment step in which the laminated body is immersed in a liquid, such as a dyeing treatment and an elongation treatment in water.

B-2. Auxiliary extension processing in the air In particular, in order to obtain a high degree of optical characteristics, a two-stage extension method combining dry extension (auxiliary extension) and boric acid water extension will be selected. For two-stage extension, by introducing auxiliary extension, the crystallization of the thermoplastic resin substrate can be suppressed and extended at the same time, and the reduction in extensibility caused by the excessive crystallization of the thermoplastic resin substrate in the subsequent boric acid water extension can be solved. Problem, so the laminate can be extended at a higher rate. In addition, when coating a PVA-based resin on a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, the coating must be reduced compared to the case where a PVA-based resin is coated on a normal metal cylinder. As a result of the cloth temperature, the crystallization of the PVA-based resin may be relatively low, which may cause a problem that sufficient optical characteristics cannot be obtained. In contrast, by introducing auxiliary extension, when the PVA-based resin is coated on a thermoplastic resin, the crystallinity of the PVA-based resin can be improved, and high optical characteristics can be achieved. In addition, by improving the orientation of the PVA-based resin at the same time in advance, when the subsequent dyeing step and the extension step are immersed in water, problems such as a decrease in the orientation of the PVA-based resin and dissolution can be prevented, and high optical characteristics can be achieved.

The extension method of aerial auxiliary extension can be fixed-end extension (such as the method using a tenter extension machine) or free-end extension (such as a method of uniaxial extension of the laminated body through rollers with different peripheral speeds) However, in order to obtain high optical characteristics, free-end extension can be actively used. In one embodiment, the air-stretching process includes a heating roller stretching step. The step is to convey the layered body along its long side direction, and at the same time to stretch by the peripheral speed difference between the heating rollers. The aerial stretching process includes a zone stretching step and a heating roller stretching step. In addition, the order of the zone extension step and the heating roller extension step is not limited, and the zone extension step may be performed first, or the heat roller extension step may be performed first. The region extension step may also be omitted. In one embodiment, the area extending step and the heating roller extending step may be performed sequentially. In another embodiment, the tenter stretcher is configured to hold the film end portion and extend the distance between the tenter stretchers in the direction of flow (the expansion of the distance between the tenter stretchers is the stretch magnification). At this time, the distance of the tenter in the width direction (vertical direction with respect to the flow direction) is set to be arbitrarily accessible. Ideally, the extension ratio with respect to the flow direction can be set to use the free end extension to approach. In the case of free-end extension, the shrinkage ratio in the width direction = (1 / extension ratio) ^{1/2 is} calculated.

Aerial assisted extension can be performed in one stage or in multiple stages. When carried out in multiple stages, the stretch magnification is the product of the stretch magnifications at each stage. The extension direction in the aerial auxiliary extension is preferably slightly the same as the extension direction in the water.

The extension magnification in the air assisted extension should be 2.0 times to 3.5 times. The maximum extension ratio when combining aerial assisted extension and underwater extension should be 5.0 times or more, preferably 5.5 times or more, and more preferably 6.0 times or more relative to the original length of the laminate. The "maximum extension ratio" in this specification means the extension ratio before the multilayer body is fractured, and it is a value that is 0.2 lower than the value after confirming the extension ratio of the multilayer body after fracture.

The air-assisted elongation extension temperature can be set to an arbitrary and appropriate value in accordance with the forming material and extension method of the thermoplastic resin substrate. The elongation temperature is preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably the glass transition temperature (Tg) of the thermoplastic resin substrate + 10 ° C or more, and more preferably Tg + 15 ° C or more. On the other hand, the upper limit of the elongation temperature is preferably 170 ° C. Stretching at the temperature can suppress rapid progress of crystallization of the PVA-based resin, and can suppress adverse conditions caused by the crystallization (for example, obstructing the orientation of the PVA-based resin layer due to stretching). The crystallization index of the PVA-based resin after air-assisted extension should be 1.3 to 1.8, and more preferably 1.4 to 1.7. The crystallization index of the PVA resin can be measured by a Fourier transform infrared spectrophotometer using the ATR method. Specifically, the measurement was performed using polarized light as the measurement light, and the crystallization index was calculated by the following formula using the intensity of 1141 cm ^-1 and 1440 cm ^-1 of the obtained spectrum.
Crystallization Index = (I _C / I _R )
but,
I _C : intensity of 1141 cm ^-1 when measured by incident measuring light
I _R : Intensity of 1440 cm ^-1 when the measurement light is incident.

B-3. Insolubilization treatment If necessary, an insolubilization treatment is performed after the air-assisted extension treatment and before the water extension treatment or dyeing treatment. The said insolubilization process can be performed by immersing a PVA-type resin layer in a boric-acid aqueous solution. By applying the insolubilization treatment, water resistance can be imparted to the PVA-based resin layer, and the orientation of the PVA resin can be prevented from being lowered when immersed in water. The concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight relative to 100 parts by weight of water. The liquid temperature of the insoluble bath (aqueous boric acid solution) is preferably 20 ° C to 50 ° C.

B-4. Dyeing process The dyeing process mentioned above is performed by dyeing the PVA-based resin layer with iodine. Specifically, this is performed by adsorbing iodine on the PVA-based resin layer. Examples of the adsorption method include a method of immersing a PVA-based resin layer (layered body) in a dye solution containing iodine, a method of applying the dye solution to a PVA-based resin layer, and spraying the dye solution to PVA. Method on the resin layer. A method of immersing the laminated body in a dyeing solution (dyeing bath) is preferable. This is because iodine can be adsorbed well.

The above-mentioned dyeing solution is preferably an iodine aqueous solution. The blending amount of iodine with respect to 100 parts by weight of water is preferably 0.05 parts by weight to 0.5 parts by weight. In order to improve the solubility of iodine in water, it is suitable to mix iodide with iodine solution. Examples of the iodide 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. Relative to 100 parts by weight of water, the blending amount of iodide is preferably 0.1 to 10 parts by weight, and more preferably 0.3 to 5 parts by weight. In order to suppress the dissolution of the PVA-based resin, the temperature of the dyeing liquid during dyeing should be 20 ° C to 50 ° C. When the PVA-based resin layer is immersed in the dyeing liquid, in order to ensure the transmittance of the PVA-based resin layer, the immersion time is preferably 5 seconds to 5 minutes, and preferably 30 seconds to 90 seconds.

The dyeing conditions (concentration, liquid temperature, and immersion time) can be set such that the monomer transmittance of the finally obtained polarizing film is 48% or more and the polarization degree is 85% or more. The dyeing conditions are preferably using an iodine aqueous solution as the dyeing solution, and the ratio of the content of iodine and potassium iodide in the iodine aqueous solution is set to 1: 5 to 1:20. The ratio of the content of iodine and potassium iodide in the iodine aqueous solution is preferably 1: 5 to 1:10. Thereby, a polarizing film having the optical characteristics as described above can be obtained.

When the laminated body is immersed in a treatment bath containing boric acid (represented as insoluble treatment) and then subjected to a dyeing treatment, mixing the boric acid contained in the treatment bath into the dyeing bath will cause the boric acid concentration of the dyeing bath to develop over time. As a result, the dyeability may become unstable as a result. In order to suppress the instability of the dyeability as described above, the upper limit of the concentration of boric acid in the dyeing bath is preferably adjusted to 4 parts by weight, more preferably 2 parts by weight, with respect to 100 parts by weight of water. On the other hand, with respect to 100 parts by weight of water, the lower limit of the boric acid concentration in the dyeing bath is preferably 0.1 parts by weight, preferably 0.2 parts by weight, and more preferably 0.5 parts by weight. In one embodiment, the dyeing treatment is performed using a dyeing bath in which boric acid is mixed in advance. This makes it possible to reduce the rate of change in the concentration of boric acid when boric acid in the treatment bath is mixed in the dyeing bath. The blending amount of boric acid (that is, the content of boric acid that is not derived from the above-mentioned treatment bath) previously blended in the dyeing bath with respect to 100 parts by weight of water is preferably 0.1 to 2 parts by weight, and preferably 0.5 to 1.5 parts by weight Serving.

B-5. Cross-linking treatment If necessary, a cross-linking treatment is performed after the dyeing treatment and before the water extension treatment. The above-mentioned crosslinking treatment is typically performed by immersing a PVA-based resin layer in an aqueous boric acid solution. By performing a cross-linking treatment, water resistance can be imparted to the PVA-based resin layer, which prevents the orientation from lowering when the PVA is immersed in high-temperature water during subsequent water extension. The concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight relative to 100 parts by weight of water. When the crosslinking treatment is performed after the dyeing treatment, it is preferable to further mix iodide. By blending iodide, the elution of iodine which has been adsorbed on the PVA-based resin layer can be suppressed. The blending amount of the iodide with respect to 100 parts by weight of water is preferably 1 to 5 parts by weight. Specific examples of the iodide are as described above. The liquid temperature of the crosslinking bath (aqueous boric acid solution) should preferably be 20 ° C to 50 ° C.

B-6. Extension treatment in water The extension treatment in water is performed by immersing the laminate in an extension bath. It can be stretched at a temperature lower than the glass transition temperature of the above-mentioned thermoplastic resin substrate or PVA-based resin layer (typically about 80 ° C) by the elongation treatment in water, while suppressing crystallization of the PVA-based resin layer and It can be extended at a high magnification. As a result, a polarizing film having excellent optical characteristics can be manufactured.

The laminated body can be extended by any appropriate method. Specifically, the extension may be a fixed end extension or a free end extension (for example, a method in which the laminated body is extended uniaxially through rollers having different peripheral speeds). Ideally, the free end extension is chosen. The extension of the laminate can be performed in one stage or in multiple stages. When carried out in multiple stages, the stretching magnification (maximum stretching magnification) of the laminated body described later is the product of the stretching magnifications at each stage.

Extension in water is preferably performed by immersing the laminate in an aqueous solution of boric acid (extension in boric acid). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be provided with rigidity capable of withstanding the tension applied during stretching and water resistance insoluble in water. Specifically, boric acid generates a tetrahydroxyborate anion in an aqueous solution, and can be crosslinked with a PVA-based resin through hydrogen bonding. As a result, it is possible to impart rigidity and water resistance to the PVA-based resin layer, to extend well, and to produce a polarizing film having excellent optical characteristics.

The aqueous boric acid solution is preferably obtained by dissolving boric acid and / or a borate in water of a solvent. On the other hand, the boric acid concentration is preferably 1 to 10 parts by weight relative to 100 parts by weight of water, more preferably 3.5 to 7 parts by weight, and even more preferably 4 to 6 parts by weight. By setting the boric acid concentration to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film with higher characteristics can be manufactured. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, etc. in a solvent may be used.

Ideally, the above-mentioned extension bath (aqueous boric acid solution) is blended with iodide. By blending iodide, the elution of iodine which has been adsorbed on the PVA-based resin layer can be suppressed. Specific examples of the iodide are as described above. Relative to 100 parts by weight of water, the concentration of iodide is preferably 0.05 to 15 parts by weight, and more preferably 0.5 to 8 parts by weight.

The extension temperature (bath temperature of the extension bath) should preferably be 40 ° C to 85 ° C, and more preferably 60 ° C to 75 ° C. As long as the temperature is the same, the PVA-based resin layer can be suppressed from dissolving and can be stretched at a high rate. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60 ° C. or higher in relation to the formation of the PVA-based resin layer. At this time, if the stretching temperature is lower than 40 ° C, even if it is considered that the thermoplastic resin substrate can be plasticized with water, it may not be stretched well. On the other hand, the higher the temperature of the extension bath, the higher the solubility of the PVA-based resin layer, and it is feared that excellent optical characteristics cannot be obtained. The immersion time of the laminated body in the extension bath is preferably 15 seconds to 5 minutes.

The stretching magnification performed in the water stretching is preferably 1.5 times or more, and more preferably 3.0 times or more. Relative to the original length of the laminated body, the total extension ratio of the laminated body should be 5.0 times or more, more preferably 5.5 times or more. By achieving such a high stretch ratio, a polarizing film having extremely excellent optical characteristics can be manufactured. The high elongation ratio can be achieved by an elongation method in water (extension in boric acid).

B-7. Dry shrinkage treatment The above-mentioned dry shrinkage treatment can be performed by zone heating by heating the entire area, or by heating a conveying roller (using a so-called heating roller) (heating roller drying method). It is desirable to use both. By using a heating roller to dry it, it is possible to efficiently suppress the heat bending of the laminated body, and to produce a polarizing film with excellent appearance. Specifically, drying the laminated body along the heating roller can effectively promote the crystallization of the above thermoplastic resin substrate and increase the degree of crystallization. Even at a low drying temperature, it can still perform well. Increase the crystallinity of thermoplastic substrates. As a result, the rigidity of the thermoplastic resin substrate can be increased, the PVA-based resin layer can withstand the shrinkage due to drying, and curl can be suppressed. In addition, since the laminated body can be maintained in a flat state and dried by using a heating roller, the occurrence of wrinkles can be suppressed not only by bending. At this time, the laminated body is shrunk in the width direction by the drying shrinkage treatment, and the optical characteristics can be improved. This is because it can effectively improve the orientation of PVA and PVA / iodine complex. The shrinkage of the laminated body in the width direction due to the drying shrinkage treatment is preferably 1% to 10%, preferably 2% to 8%, and particularly preferably 4% to 6%. By using a heating roller, the laminated body can be continuously contracted in the width direction while being conveyed, and high productivity can be achieved.

FIG. 2 is a schematic diagram showing an example of a dry shrinkage treatment. In the drying shrinkage process, the laminated body 200 is conveyed by the conveying rollers R1 to R6 and the guide rollers G1 to G4 that have been heated to a predetermined temperature, and is simultaneously dried. In the example shown in the figure, the conveying rollers R1 to R6 are arranged so that the surface of the PVA resin layer and the surface of the thermoplastic resin laminate are alternately and continuously heated. Material surface), the conveying rollers R1 to R6 are arranged.

The drying conditions can be controlled by adjusting the heating temperature (temperature of the heating roller) of the conveying roller, the number of heating rollers, and the time of contacting the heating roller. 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. Increasing the degree of crystallization of the thermoplastic resin well can suppress the bending well, and can produce an optical laminate having excellent durability. The temperature of the heating roller can be measured with a contact thermometer. Although six conveying rollers are provided in the example in the figure, there are no particular restrictions as long as there are a plurality of conveying rollers. The number of conveying rollers is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) of the laminated body and the heating roller is preferably 1 second to 300 seconds, preferably 1 to 20 seconds, and more preferably 1 to 10 seconds.

The heating roller can be installed in a heating furnace (such as an oven), and can also be installed in a general manufacturing production line (under room temperature environment). It is preferable to install in a heating furnace provided with a ventilation mechanism. By using the heating roller and the hot-air drying together, it is possible to suppress rapid temperature changes between the heating rollers, and it is possible to easily suppress shrinkage in the width direction. The temperature of hot air drying should be 30 ℃ ~ 100 ℃. In addition, the hot air drying time should be 1 second to 300 seconds. The wind speed of hot wind should be about 10m / s ~ 30m / s. In addition, the wind speed is the wind speed in the heating furnace, and can be measured by a small impeller-type digital anemometer.

B-8. Other treatments are preferably performed after the water elongation treatment and before the drying shrinkage treatment. The said washing | cleaning process is representatively performed by immersing a PVA-type resin layer in the potassium iodide aqueous solution.
Examples

Hereinafter, the present invention will be specifically described with examples, but the present invention is not limited by these examples. The measurement method of each characteristic is as follows. Moreover, "part" and "%" in an Example and a comparative example are a weight basis, unless there is particular notice.
(1) The thickness was measured using an interference film thickness meter (manufactured by Otsuka Electronics Corporation, product name "MCPD-3000").
(2) Transmittance and polarization of the monomer The polarizing plates (protective film / polarizing film) of the examples and comparative examples were measured using a UV-visible spectrophotometer (V-7100, manufactured by JASCO Corporation), and measured. The single transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc are taken as Ts, Tp, and Tc of the polarizing film, respectively. These Ts, Tp, and Tc are Y values obtained by measuring and compensating visual sensitivity in accordance with JIS Z8701's 2-degree field of view (C light source). The refractive index of the protective film is 1.50, and the refractive index of the surface of the polarizing film on the side opposite to the protective film is 1.53.
From the obtained Tp and Tc, the degree of polarization P was obtained by the following formula.
Polarization P (%) = ((Tp-Tc) / (Tp + Tc)) ^1/2 × 100
In addition, the spectrophotometer can be equivalently measured by LPF-200 manufactured by Otsuka Electronics Corporation. As an example, V-7100 and LPF-200 are used to measure samples 1 to 3 having polarizing plates having the same structure as the following examples, and the measured values of the single transmittance Ts and the polarization degree P The measured values are shown in Table 1. As shown in Table 1, the difference between the measured value of the monomer transmittance of V-7100 and the measured value of the monomer transmittance of LPF-200 is less than 0.1%. It can be seen that the same measurement can be obtained regardless of the use of any spectrophotometer. result.
[Table 1]

In addition, for example, when a polarizing plate having an anti-glare (AG) surface treatment or an adhesive having a diffusion property is used as a measurement object, different measurement results are obtained according to a spectrophotometer. At this time, by Using the measured value obtained when each spectrophotometer measures the same polarizing plate as a reference for numerical conversion, the difference between the measured values obtained by the spectrophotometer can be compensated.
(3) Variations in the optical characteristics of the long polarizing plate From the long polarizing plate of the examples and reference examples, the measurement samples were cut out at five positions at equal intervals along the width direction, and then the same as (2) above. The monomer transmittance of the central portion of each of the five measurement samples was measured in the same manner. Next, the difference between the maximum value and the minimum value of the unit transmittance measured at each measurement position is calculated, and this value is used as the difference in the optical characteristics of the long polarizing plate (the position of the long polarizing plate in the width direction) (The difference between the maximum and minimum values of the monomer transmission).
(4) Variations in the optical characteristics of the sheet-shaped polarizing plate A 100 mm × 100 mm measurement sample was cut out from the strip-shaped polarizing plate of the examples and reference examples, and the optical characteristics of the sheet-shaped polarizing plate (50 cm ² ) were obtained. Staggered. Specifically, in the same manner as in the above (2), the unit transmittance of the measurement sample at a position of approximately 1.5 cm to 2.0 cm from the midpoint of each of the four sides of the measurement sample and at a total of five points in the center was measured. Next, calculate the difference between the maximum value and the minimum value of the monomer transmittance measured at each measurement position, and use this value as the difference in optical characteristics of the sheet-shaped polarizer (unit transmittance in a 50 cm ² area). Difference between the maximum and minimum values).
(5) Crystallization index of PVA-based resin layer after air-assisted extension. For the laminated body after air-assisted extension, a Fourier transform infrared spectrophotometer (manufactured by Perkin Elmer, product name "FT-IR Frontier") is used. Polarized light was used as the measurement light, and the surface of the PVA-based resin layer was evaluated by ATR measurement. Specifically, measurement is performed, and the crystallization index is calculated by the following formula using the intensities of 1141 cm ^-1 and 1440 cm ^-1 of the obtained spectrum.
Crystallization Index = (I _C / I _R )
but,
I _C : intensity of 1141 cm ^-1 when measured by incident measuring light
I _R : intensity of 1440 cm ^-1 when measured by incident measuring light

[Example 1]
1. The polarizing film thermoplastic resin substrate is made of an amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100 μm) having a long strip shape with a water absorption of 0.75% and a Tg of about 75 ° C. Corona treatment is performed on one side of the resin substrate.
PVA (Polymer alcohol (degree of polymerization: 4200, degree of saponification: 99.2 mole%)) and acetamidine modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gohsefimer Z410", 9: 1) To 100 parts by weight of the resin, 13 parts by weight of potassium iodide was added to prepare a PVA aqueous solution (coating solution).
A laminated body was produced by applying the above-mentioned PVA aqueous solution to the corona-treated surface of a resin substrate and drying it at 60 ° C. to form a PVA-based resin layer having a thickness of 13 μm.
The obtained laminated body was subjected to free-end uniaxial extension of 2.4 times in the longitudinal direction (long-side direction) between rolls having different peripheral speeds in an oven at 130 ° C. (air-assisted extension treatment).
Next, the layered product was immersed in an insoluble bath (aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40 ° C. (insolubilization treatment).
Next, the concentration of the dyeing bath (the aqueous iodine solution obtained by mixing iodine and potassium iodide at a weight ratio of 1: 7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ° C. is adjusted so that the single unit of the polarizing film finally obtained is The volume transmittance (Ts) became 48% or more and was simultaneously immersed therein for 60 seconds (dyeing treatment).
Next, it was immersed in a crosslinking bath (aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40 ° C (crosslinking treatment) ).
Then, while the laminate was immersed in a boric acid aqueous solution (boric acid concentration of 5.0% by weight) at a liquid temperature of 70 ° C, uniaxial stretching was performed in the longitudinal direction (long side direction) between rolls having different peripheral speeds so as to obtain a total stretching ratio. Up to 5.5 times (extension treatment in water).
Then, the laminated body was immersed in a washing bath (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20 ° C (washing treatment).
After that, while drying it in an oven kept at 90 ° C, it was brought into contact with a SUS heating roller whose surface temperature was kept at 75 ° C for about 2 seconds (dry shrinkage treatment). The shrinkage ratio in the width direction of the laminated body obtained by the drying shrinkage treatment was 5.2%.
Through the above procedure, a polarizing film having a thickness of 5 μm was formed on the resin substrate. Then, the same procedure was repeated to produce a total of 10 polarizing films.
2. Fabrication of a polarizing plate On the surface (the surface opposite to the resin substrate) of each of the polarizing films obtained above, an acrylic film (surface refractive index: 1.50, 40 μm) was bonded with a UV-curable adhesive as a protective film. Specifically, the total thickness of the hardening-type adhesive was 1.0 μm, and bonding was performed using a roll mill. Then, UV rays are irradiated from the protective film side to harden the adhesive. Next, after cutting both end portions, the resin substrate was peeled off to obtain 10 long polarizing plates (width: 1300 mm) having a structure of a protective film / polarizing film.

[Reference Example 1]
Dyeing treatment was performed so that the monomer transmittance (Ts) of the finally obtained polarizing film was 43% or more and less than 48%. Except for this, twelve polarizing films and polarizing plates were produced in the same manner as in Example 1.

[Comparative Example 1]
An attempt was made to produce polarized light in the same manner as in Example 1 except that potassium iodide was not added to the PVA aqueous solution (coating solution), the stretching ratio was 1.8 times in the air-assisted stretching treatment, and the heating roller was not used in the drying shrinkage treatment. Film, but the PVA-based resin layer was dissolved in the dyeing treatment and the water elongation treatment, and a polarizing film with a monomer transmittance of 48% or more was not successfully produced.

[Comparative Example 2]
An attempt was made to produce 17 polarizing films and polarizing plates in the same manner as in Example 1 except that the stretching ratio of the air-assisted stretching treatment was 1.8 times and that no heating roller was used in the drying shrinkage treatment. A polarizing film with a monomer transmittance of 48% or more was not successfully produced.

[Reference Example 2]
The polarizing film produced in the same manner as in Comparative Example 2 was held in a constant temperature and constant humidity region set to a temperature of 60 ° C. and a humidity of 90% RH for 30 minutes. Thereafter, a polarizing plate was produced in the same manner as in Example 1.

For each of the polarizing plates of Examples and Comparative Examples, the individual transmittance and polarization degree were measured. The results are shown in Table 2 and Fig. 3. In FIG. 3, the approximate curves of the punctuation points in Example 1 and Reference Example 1 and the approximate curves of the punctuation points in Comparative Example 2 are plotted and displayed. In addition, the approximate curve of Comparative Example 2 is an approximate curve of a cubic polynomial, and an extrapolated portion of the approximate curve is indicated by a dashed line.

[Table 2]

The polarizing film produced by the manufacturing method of the comparative example did not satisfy both a monomer transmittance of 48% or more and a polarization degree of 85% or more. In addition, as shown by the approximate curve of the punctuation point in Comparative Example 2, in the manufacturing method of Comparative Example 2, when the dyeing treatment is performed so that the transmittance of the monomer is 48% or more, the degree of polarization can be predicted to be less than 85%. In contrast, the polarizing film prepared by the manufacturing method of the example has excellent optical characteristics of a single transmittance of 48% or more and a polarization degree of 85% or more.

For each of the polarizing plates of Example 1 and Reference Example 2, the difference in optical characteristics between the long and thin polarizing plates was measured. The results are shown in Table 3.

[table 3]

The variation in the unit transmittance of the long polarizing plate produced by the manufacturing method of the example is 1% or less, and the variation in the unit transmittance of the thin plate polarizing plate produced by the manufacturing method of the embodiment is Below 0.5%, variations in optical characteristics are suppressed to the extent that there is no problem. On the other hand, the polarizing plate of the reference example obtained through the step of humidifying the polarizing film has a large difference in optical characteristics regardless of the long shape and the thin shape.

In addition, for the polarizing films of the examples and comparative examples, the crystallization index of the PVA-based resin in the laminate after the air-assisted stretching was measured according to the above (5). It was confirmed whether the PVA-based resin was dissolved in the dyeing treatment or the water-stretching treatment. The results are shown in Table 4.

[Table 4]

INDUSTRIAL APPLICABILITY A polarizing plate having the polarizing film of the present invention can be suitably used as a circular polarizing plate for an organic EL display device and an inorganic EL display device.

10‧‧‧ polarizing film

20‧‧‧The first protective layer

30‧‧‧ 2nd protective layer

100‧‧‧ polarizing plate

200‧‧‧Laminated body

G1 ~ G4‧‧‧Guide roller

R1 ~ R6‧‧‧ Conveying roller

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

FIG. 2 is a schematic view showing an example of a drying shrinkage treatment using a heating roller.

FIG. 3 is a graph showing optical characteristics of polarizing plates obtained in Examples and Comparative Examples.

Claims (10)

A polarizing plate having a polarizing film and a protective layer disposed on at least one side of the polarizing film, and the thickness of the polarizing film is 8 μm or less, the single transmittance is 48% or more, and the polarization degree is 85% or more; and The difference between the maximum value and the minimum value of the monomer transmittance in a region of 50 cm ² is 0.5% or less. A polarizing plate having a polarizing film and a protective layer disposed on at least one side of the polarizing film, and the thickness of the polarizing film is 8 μm or less, the single transmittance is 48% or more, and the polarization degree is 85% or more; and The width of the polarizer is more than 1000mm, and The difference between the maximum value and the minimum value of the unit transmittance at the position in the width direction is 1% or less. For example, the polarizing plate of claim 1 or 2, wherein a single transmittance of the aforementioned polarizing film is 50% or less, and a polarization degree is 92% or less. A polarizing plate roll is obtained by winding a polarizing plate according to any one of claims 1 to 3 into a roll shape. A method for manufacturing a polarizing film. The thickness of the polarizing film is 8 μm or less, the monomer transmittance is 48% or more, and the polarization degree is 85% or more. The manufacturing method includes the following steps: A laminated body is formed by forming a polyvinyl alcohol-based resin layer on one side of a long thermoplastic resin substrate, wherein the polyvinyl alcohol-based resin layer contains: iodide or sodium chloride, and a polyvinyl alcohol-based resin; and The aforementioned laminated body is sequentially subjected to air-assisted stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment. The drying shrinkage treatment is to heat the laminated body while conveying it in the longitudinal direction, thereby shrinking it in the width direction. 2% or more. For example, the method for manufacturing a polarizing film according to claim 5, wherein a single transmittance of the polarizing film is 50% or less, and a polarization degree is 92% or less. The method according to claim 5 or 6, wherein the content of the iodide or sodium chloride in the polyvinyl alcohol-based resin layer is 5 to 20 parts by weight relative to 100 parts by weight of the polyvinyl alcohol-based resin. The manufacturing method according to any one of claims 5 to 7, wherein the stretching ratio of the aforementioned aerial auxiliary stretching treatment is 2.0 times or more. The manufacturing method according to any one of claims 5 to 8, wherein the drying shrinkage treatment step is a step of heating using a heating roller. The manufacturing method according to claim 9, wherein the temperature of the heating roller is 60 ° C to 120 ° C, and the widthwise shrinkage of the laminated body obtained by performing the drying shrinkage treatment is 2% or more.