TWI762667B - Polarizing film, polarizing plate, polarizing plate roll, and manufacturing method of polarizing film - Google Patents

Abstract

The subject of the present invention is to provide a polarizing film having excellent optical properties. The solution is as follows: the thickness of the polarizing film of the present invention is 8 μm or less, the single transmittance is 44.5% or more, and the polarization degree is 99.90% or more.

Description

Polarizing film, polarizing plate, polarizing plate roll, and manufacturing method of polarizing film

The present invention relates to a polarizing film, a polarizing plate, a polarizing plate roll material and a manufacturing method of the polarizing film.

BACKGROUND OF THE INVENTION With the spread of thin-type 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 metal layers with high reflectivity, so problems such as external light reflection or background reflection are likely to occur. It is known that the circular polarizing plate with the polarizing film and the λ/4 plate is arranged on the viewing side at this time, which can prevent such problems. A method for producing a polarizing film, for example, a method of extending a laminate having a resin substrate and a polyvinyl alcohol (PVA)-based resin layer, and then applying a dyeing treatment to obtain a polarizing film on the resin substrate (eg. Patent Document 1). By this method, a polarizing film having a relatively thin thickness can be obtained, and it is therefore attracting attention for its contribution to the reduction in thickness of image display devices in recent years. However, since the optical properties of the conventional thin polarizing films as described above are insufficient, further improvement of the optical properties of the thin polarizing films is required.

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

SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION The present invention is made in order to solve the above-mentioned conventional problems, and its main object is to provide a polarizing film, a polarizing plate, a polarizing plate roll and a method for producing the polarizing film having excellent optical properties.

MEANS TO SOLVE THE PROBLEM The thickness of the polarizing film of this invention is 8 micrometers or less, the single transmittance is 44.5% or more, and the polarization degree is 99.0% or more. In one embodiment, the single transmittance is 45.0% or less, and the polarization degree is 99.9% or less. According to another aspect of the present invention, a polarizing plate is provided. The polarizing plate has: a polarizing film; and a protective layer, which is disposed on at least one side of the polarizing film. In one embodiment, 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 at the position along the width direction is 0.3% or less. In one embodiment, the difference between the maximum value and the minimum value of the single transmittance of the polarizing plate in an area of 50 cm ² is 0.2% or less. According to another aspect of the present invention, a polarizing plate coil is provided. The polarizing plate coil is formed by winding the polarizing plate in a roll shape. According to another aspect of the present invention, a method for manufacturing a polarizing film is provided. The manufacturing method is the manufacturing method of the above-mentioned polarizing film, and 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-shaped thermoplastic resin substrate, and producing a and a layered body is subjected to in-air auxiliary stretching treatment, dyeing treatment, underwater stretching treatment and drying shrinking treatment in this order, and the drying shrinkage treatment is carried out while conveying the above-mentioned layered body in the longitudinal direction while heating, thereby making It shrinks by more than 2% in the width direction. In one embodiment, the content of the halide in the polyvinyl alcohol-based resin layer is 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin. In one embodiment, the stretching magnification in the above-mentioned aerial auxiliary stretching process is 2.0 times or more. In one embodiment, the drying shrinkage treatment step is a step of heating using a heating roller. In one Embodiment, the temperature of the said heating roll is 60 degreeC - 120 degreeC, and the shrinkage rate of the width direction of the said laminated body obtained by performing the said drying shrinkage process is 2% or more.

Effects of the Invention According to the present invention, it is possible to provide a polarizing film having excellent optical properties, 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.

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

A. Polarizing film The polarizing film of one embodiment of the present invention has a thickness of 8 µm or less, a single transmittance of 44.5% or more, and a polarization degree of 99.0% or more. Generally speaking, the single transmittance and the degree of polarization have a trade-off relationship, so if the transmittance of the single unit is increased, the degree of polarization will decrease, and if the degree of polarization is increased, the transmittance of the single unit will decrease. Therefore, it has been difficult to apply a thin polarizing film that satisfies the optical properties of a single transmittance of 44.5% or more and a polarization degree of 99.0% or more. As described above, the polarizing film system according to one embodiment of the present invention has excellent optical properties such that the single transmittance is 44.5% or more and the polarization degree is 99.0% or more. Furthermore, by using the polarizing film of the present embodiment, a polarizing plate in which variation in optical properties is suppressed can be realized. One of the achievements of the present invention is to realize the thin polarizing film (polarizing plate). The polarizing film (polarizing plate) can be used in an image display device, and is especially 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 from 380nm to 780nm. The single transmittance of the polarizing film is preferably 45.0% or less. The degree of polarization of the polarizing film is preferably 99.2% or more, preferably 99.4% or more. On the other hand, the upper limit of the degree of polarization is preferably 99.9%. The above-mentioned monomer transmittance is representatively the Y value obtained by using an ultraviolet-visible light spectrophotometer to measure and correct the optical efficacy. The above-mentioned degree of polarization is representatively determined by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc obtained by measuring using an ultraviolet-visible light spectrophotometer and correcting the luminous efficacy. 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 layered product of a polarizing film (surface refractive index: 1.53) and a protective film (refractive index: 1.50) as the measurement object, using ultraviolet visible light spectroscopy. Photometer to measure. Depending on the refractive index of the surface of the polarizing film and/or the surface of the protective film in contact with the air interface, the reflectance of each layer at the interface will change, and as a result, the measured value of transmittance may change. Therefore, for example, when a protective film with a refractive index other than 1.50 is used, the measured value of transmittance can also be corrected according to the refractive index of the surface of the protective film in contact with the air interface. Specifically, the correction value C of the transmittance is represented by the following formula using 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. 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 reflectance of the transmission axis when a protective film with a refractive index of 1.50 is used, n ₁ is the refractive index of the protective film used, and T ₁ is the transmission of the polarizing film Rate. For example, when a substrate with a surface refractive index of 1.53 (cycloolefin-based film, film with a hard coat layer, etc.) is used as the protective film, the correction amount C is about 0.2%. In this case, the transmittance obtained by adding 0.2% can be converted into the transmittance when a protective film having a surface refractive index of 1.50 is used. In addition, after calculation according to the above formula, when the transmittance T1 _of the polarizing film is changed by 2%, the variation of the correction value C is 0.03% or less, so 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 performed according to the amount of absorption.

As the polarizing film, any appropriate polarizing film can be used. The polarizing film can be typically produced using a laminate of two or more layers.

As a specific example of the polarizing film obtained using a laminated body, the polarizing film obtained using the laminated body of the resin base material and the PVA-type resin layer formed in the resin base material by apply|coating is mentioned. A polarizing film obtained by using a laminate of a resin substrate and 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 It is dried to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; and the laminate is extended and dyed to make the PVA-based resin layer a polarizing film. In the present embodiment, the stretching represents that the layered body is immersed in a boric acid aqueous solution and stretched. Further, if necessary, the stretching may further include in-air stretching of the layered body at a high temperature (eg, 95° C. or higher) before stretching in a boric acid aqueous solution. The obtained laminate of resin substrate/polarizing film can be used directly (that is, the resin substrate can be used as a protective layer of the polarizing film), or the resin substrate can be peeled off from the laminate of resin substrate/polarizing film and the peeled surface Depending on the purpose, an arbitrary and appropriate protective layer is laminated and used later. The details of the manufacturing method of the polarizing film are described in, for example, Japanese Patent Laid-Open No. 2012-73580. In this specification, the entire description of this gazette is incorporated by reference.

The manufacturing method of the polarizing film of the present invention comprises 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 laminate; and, The above-mentioned laminated body is subjected to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order. 2% or more. Thereby, a polarizing film having excellent optical properties and suppressed variation in optical properties can be provided, the polarizing film has a thickness of 8 μm or less, a single transmittance of 44.5% or more, and a polarization degree of 99.0% or more. That is, by introducing the auxiliary extension, the crystallinity of the PVA can be improved even when the PVA is coated on the thermoplastic resin, and high optical properties can be achieved. In addition, by improving the orientation of PVA in advance, problems such as lowering of orientation and dissolution of PVA can be prevented when immersed in water in the subsequent dyeing step and stretching step, and high optical properties can be achieved. In addition, when the PVA-based resin layer is immersed in a liquid, the disorder of orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed more than when the PVA-based resin layer does not contain a halide. Therefore, the optical properties of the polarizing film obtained by the processing steps of immersing the laminated body in a liquid, such as dyeing treatment and underwater stretching treatment, can be improved. In addition, the transmission drying shrinkage treatment shrinks the laminate in the width direction, thereby improving optical properties.

B. 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 polarizing film 10 is the polarizing film of the present invention described in item A above. One of the first protective layer 20 and the second protective layer 30 may also be omitted. In addition, as mentioned above, one of the 1st protective layer and the 2nd protective layer may be a resin base material used for manufacture of the said polarizing film.

The polarizing plate can be elongated or thin. When the polarizer is in the shape of a long strip, it should be wound into a roll to make a polarizer coil. Then the polarizing plate has excellent optical properties and the variation of optical properties 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 at the position along the width direction is 0.3% or less. The upper limit of D1 is preferably 0.25%, and more preferably 0.2%. The smaller D1 is, the better, but its lower limit is, for example, 0.01%. As long as D1 is within the above range, a polarizing plate having excellent optical properties can be industrially produced. In another embodiment, the difference (D2) between the maximum value and the minimum value of the single transmittance of the polarizing plate in an area of 50 cm ² is 0.2% or less. The upper limit of D2 is preferably 0.1%, and more preferably 0.05%. The smaller D2 is, the better, but its lower limit is, for example, 0.01%. As long as D2 is within the above-mentioned range, when the polarizing plate is used in an image display device, the brightness variation of the display screen can be suppressed.

The first and second protective films 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 triacetyl cellulose (TAC), polyester-based, polyvinyl-alcohol-based, polycarbonate-based, polyamide-based, polyamide-based Imine-based, polyether-based, poly-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based and acetate-based transparent resins, etc. Moreover, (meth)acrylic type, urethane type, (meth)acrylate urethane type, epoxy type, polysiloxane type|system|group thermosetting resin, ultraviolet-curable resin, etc. are also mentioned. Other examples include glass-based polymers such as siloxane-based polymers. Moreover, the polymer film described in Unexamined-Japanese-Patent No. 2001-343529 (WO01/37007) can also be used. As the material of 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 the side chain can be used. , and, for example, a resin composition having an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer is mentioned. The polymer film may be, for example, an extruded product of the above-mentioned resin composition.

When the polarizing plate 100 is applied to an image display device, the thickness of the protective layer (outer protective layer) disposed on the opposite side of 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 the surface treatment is performed, the thickness of the outer protective layer includes 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 any suitable 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 the in-plane retardation measured at 23° C. with light having a wavelength of 550 nm, and is obtained by the transmission formula: Re=(nx−ny)×d. Here, "nx" is the refractive index in the direction in which the in-plane refractive index becomes the largest (that is, the slow axis direction), and "ny" is the refractive index in the in-plane direction 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).

C. Manufacturing method of polarizing film The manufacturing method of polarizing film according to one embodiment of the present invention includes the following steps: forming a halide-containing and polyvinyl alcohol-based resin (PVA-based resin) on one side of an elongated thermoplastic resin substrate The polyvinyl alcohol-based resin layer (PVA-based resin layer) is formed to form a laminated body; and, the laminated body is subjected to air-assisted stretching treatment, dyeing treatment, underwater stretching treatment and drying shrinkage treatment in sequence, and the drying shrinkage treatment is The layered body is heated while being conveyed in the longitudinal direction to shrink by 2% or more in the width direction. The halide content in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment should be carried out with a heating roller, and the temperature of the heating roller should be 60℃~120℃. The shrinkage rate in the width direction of the laminate obtained by the drying shrinkage treatment is preferably 2% or more. According to the above-mentioned production method, the polarizing film described in the above-mentioned item A can be produced. In particular, a polarizing film having excellent optical properties (representatively monomer transmittance and degree of polarization) and having suppressed variations in optical properties can be produced by producing a laminate comprising a PVA-based resin layer containing a halide After that, the stretching of the above-mentioned layered body was made into a multi-stage stretching including air-assisted stretching and underwater stretching, and the layered body after the stretching was heated with a heating roller. Specifically, by using a heating roller in the drying shrinkage treatment step, the entire layered body can be uniformly shrunk while conveying the layered body. By doing so, not only the optical properties of the prepared polarizing film can be improved, but also the polarizing film with excellent optical properties can be stably produced, and the variation in the optical properties (especially the transmittance of monomers) of the polarizing film can be suppressed.

C-1. Production of Laminated Product Any appropriate method can be adopted as a method of producing a laminate of a thermoplastic resin base material and a PVA-based resin layer. Preferably, a coating liquid containing a halide and a PVA-based resin is coated on the surface of the thermoplastic resin substrate and dried, thereby forming a PVA-based resin layer on the thermoplastic resin substrate. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

As the coating method of the coating liquid, an arbitrary and appropriate method can be adopted. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a blade coating method (comma coating method, etc.) etc. are mentioned. The coating and drying temperature of the above-mentioned coating liquid is preferably 50°C or higher.

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

Before forming the PVA-based resin layer, a surface treatment (eg, corona treatment, etc.) may be performed on the thermoplastic resin substrate, and an easily bonding layer may be formed on the thermoplastic resin substrate. The adhesiveness between the thermoplastic resin base material and the PVA-based resin layer can be improved by performing the above-mentioned treatment.

C-1-1. Thermoplastic resin substrate The thickness of the thermoplastic resin substrate is preferably 20 μm to 300 μm, 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 micrometers, it may take a long time for the thermoplastic resin base material to absorb water, for example, during the underwater stretching treatment described later, and there may be a possibility that an excessive load is also applied to the stretching.

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 water acts as a plasticizer for plasticization. As a result, elongation stress can be greatly reduced, and elongation at a high rate can be achieved. 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 base material, the dimensional stability of the thermoplastic resin base material at the time of production can be prevented from being remarkably lowered, and the appearance of the polarizing film produced can be prevented from deteriorating. It is possible to prevent the substrate from breaking or peeling off the PVA-based resin layer from the thermoplastic resin substrate when the substrate is extended in water. In addition, the water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a modified group into the constituent material. The water absorption rate is a value obtained by JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or lower. By using such a thermoplastic resin base material, the crystallization of the PVA-based resin layer can be suppressed, and the extensibility of the laminate can be sufficiently ensured. In addition, considering that the thermoplastic resin substrate can be plasticized by water and can be well stretched 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 such a thermoplastic resin substrate, it is possible to prevent defects such as deformation of the thermoplastic resin substrate (e.g., unevenness, slump, wrinkling, etc.) from occurring during application and drying of the coating liquid containing the PVA-based resin. In this case, a laminated body was produced favorably. In addition, the PVA-based resin layer can be well stretched at an appropriate temperature (for example, about 60° C.). In addition, the glass transition temperature of the thermoplastic resin substrate can be adjusted, for example, by heating using a crystallization material capable of introducing a modified group into the constituent material. The glass transition temperature (Tg) is a value determined in accordance with JIS K 7121.

Arbitrary and appropriate thermoplastic resins can be used as the constituent material of the thermoplastic resin base material. Examples of thermoplastic resins include ester-based resins such as polyethylene terephthalate-based resins, cycloolefin-based resins such as norbornene-based resins, olefin-based resins such as polypropylene, polyamide-based resins, and polycarbonate-based resins. , its copolymer resin, etc. Of these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferred.

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

In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate-based resin having an isophthalic acid unit. This is because the thermoplastic resin base material has extremely excellent extensibility and can suppress crystallization during extension. We speculate that it is due to the introduction of isophthalic acid units through transmission which imparts huge buckling to the main chain. The polyethylene terephthalate-based 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, more preferably 1.0 mol % or more, based on the total of all repeating units. This is because a thermoplastic resin substrate having extremely excellent extensibility can be obtained. On the other hand, the content ratio of the isophthalic acid unit is preferably 20 mol % or less, more preferably 10 mol % or less, based on the total of all repeating units. By setting it to the said content ratio, the crystallinity degree can be favorably increased in the drying shrinkage process mentioned later.

The thermoplastic resin base material may be stretched in advance (before the PVA-based resin layer is formed). In one embodiment, it extends along the width direction of the elongated thermoplastic resin substrate. The width direction is preferably a direction orthogonal to the extending direction of the laminate described later. In addition, the term "orthogonal" in this specification also includes the case where it is substantially orthogonal. In addition, "substantially orthogonal" includes the case of 90°±5.0°, preferably 90°±3.0°, more preferably 90°±1.0°.

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

An arbitrary and appropriate method can be adopted as the method for extending the thermoplastic resin substrate. Specifically, it can 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 it is carried out in multiple stages, the above stretching ratio is the product of the stretching ratio of each stage.

C-1-2. Coating liquid The coating liquid is as described above, and contains a halide and a PVA-based resin. The above-mentioned coating liquid represents a solution obtained by dissolving the above-mentioned halide and the above-mentioned PVA-based resin in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trimethylolpropane, ethylene glycol Amines such as diamine and ethylene triamine. These may be used alone or in combination of two or more. Among these, water is preferred. The concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. As long as it is the said resin density|concentration, a uniform coating film which adheres to a thermoplastic resin base material 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 resin.

Additives can also be mixed in the coating liquid. Examples of additives include plasticizers, surfactants, and the like. As a plasticizer, polyhydric alcohols, such as ethylene glycol and glycerol, are mentioned, for example. As a surfactant, a nonionic surfactant is mentioned, for example. These can be used in order to further improve the uniformity, dyeability, and extensibility of the obtained PVA-based resin layer.

Arbitrary and appropriate resin can be employ|adopted for the said PVA-type resin. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer are mentioned. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymers can be obtained by saponifying ethylene-vinyl acetate copolymers. The degree of saponification of the PVA resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. The degree of saponification is obtained according to JIS K 6726-1994. By using the PVA-based resin having the above degree of saponification, a polarizing film excellent in durability can be obtained. When the degree of saponification 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 1000~10000, preferably 1200~4500, more preferably 1500~4300. In addition, the average degree of polymerization can be calculated|required based on JISK6726-1994.

Any appropriate halide can be used as the above-mentioned halide. For example, iodide and sodium chloride are mentioned. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Among them, potassium iodide is preferred.

The amount of halide in the coating solution is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin, more preferably 10 to 15 parts by weight relative to 100 parts by weight of the PVA resin. If the amount of the halide is more than 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, the halide may overflow and the polarizing film finally obtained may become cloudy.

Generally speaking, when the PVA-based resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA-based resin layer will become higher, but if the stretched PVA-based resin layer is immersed in a water-containing liquid, there will be polyethylene The situation in which the orientation of alcohol molecules is disordered and the orientation is reduced. In particular, when a 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 above-mentioned degree of orientation is lowered when the laminate is stretched in boric acid water at a relatively high temperature. The tendency is obvious. For example, the extension of the PVA film monomer in boric acid water is generally carried out at 60° C. On the contrary, the extension of the laminate of A-PET (thermoplastic resin substrate) and the PVA resin layer is performed at 70° C. If the temperature before and after ℃ is carried out at a higher temperature, at this time, the orientation of the PVA at the beginning of the stretching will decrease at the stage before it rises due to the stretching in water. In this regard, after producing a laminate of a halide-containing PVA-based resin layer and a thermoplastic resin substrate, the laminate is stretched at high temperature (assisted stretching) in air before stretching in boric acid water, thereby promoting assisted stretching. Then, the crystallization of the PVA-based resin in the PVA-based resin layer of the laminate. As a result, when the PVA-based resin layer is immersed in a liquid, the disorder of orientation of the polyvinyl alcohol molecules and the decrease in orientation can be suppressed more than when the PVA-based resin layer does not contain a halide. Therefore, the optical properties of the polarizing film obtained by the processing steps of immersing the laminated body in a liquid, such as dyeing treatment and underwater stretching treatment, can be improved.

C-2. Aerial-assisted stretching treatment In particular, in order to obtain high optical properties, a two-stage stretching method combining dry stretching (assisted stretching) and boric acid water stretching is selected. As in the two-stage stretching method, by introducing auxiliary stretching, the crystallization of the thermoplastic resin substrate can be suppressed and the stretching can be performed, and the stretching caused by the excessive crystallization of the thermoplastic resin substrate during the subsequent stretching in boric acid water can be solved. The problem of lowering of the properties is eliminated, so that the laminate can be stretched at a higher magnification. In addition, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate when applying the PVA-based resin to the thermoplastic resin substrate, the application temperature must be higher than that of applying the PVA-based resin to a general metal drum In a lower case, as a result, the crystallization of the PVA-based resin becomes relatively low and sufficient optical properties cannot be obtained. In this regard, by introducing auxiliary stretching, the crystallinity of the PVA-based resin can be improved even when the PVA-based resin is coated on the thermoplastic resin, and high optical properties can be achieved. In addition, by improving the orientation of the PVA-based resin in advance, problems such as lowering of the orientation and dissolution of the PVA-based resin when immersed in water in the subsequent dyeing step and stretching step can be prevented, and high optical properties can be achieved.

The stretching method of aerial auxiliary stretching can be either fixed-end stretching (such as a method of stretching using a tenter stretching machine) or free-end stretching (such as a method of uniaxial stretching of the laminated body through rolls with different peripheral speeds) , but in order to obtain high optical properties, the free end extension can be actively used. In one embodiment, the in-air stretching treatment includes a heating roll stretching step in which the above-mentioned layered body is conveyed in the longitudinal direction thereof while being stretched using the difference in peripheral speed between the heating rolls. The in-air stretching process typically includes a zone stretching step and a heating roll stretching step. In addition, the sequence of the zone stretching step and the heating roller stretching step is not limited, and the zone stretching step may be performed first, or the heating roller stretching step may be performed first. The region extension step can also be omitted. In one embodiment, the zone stretching step and the heating roll stretching step are performed in sequence. Moreover, in another embodiment, the film end is held in a tenter stretching machine, and the distance between the tenters is expanded in the flow direction to stretch (the increase in the distance between the tenters is a stretching 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 close. Preferably, the extension ratio relative to the flow direction can be set to use the extension of the free end for approaching. When it is extended at the free end, it is calculated by the shrinkage rate in the width direction = (1/extension ratio) ^1/2 .

Aerial assist extension can be performed in one stage or in multiple stages. When it is carried out in multiple stages, the stretching ratio is the product of the stretching ratios of each stage. The extension direction of the aerial auxiliary extension should be slightly the same as the extension direction of the underwater extension.

The extension magnification of the aerial auxiliary extension should be 2.0 times to 3.5 times. The maximum stretching magnification when combining aerial auxiliary stretching and underwater stretching is preferably 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. In this specification, the "maximum stretching ratio" means the stretching ratio before the layered body breaks, and is a value lower than the value by 0.2 after confirming the stretching ratio at which the layered body breaks.

The stretching temperature of the air-assisted stretching can be set to an arbitrary and appropriate value according to the forming material of the thermoplastic resin base material, the stretching method, and the like. The elongation temperature is preferably higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably the glass transition temperature (Tg)+10°C or higher of the thermoplastic resin substrate, and particularly preferably Tg+15°C or higher. On the other hand, the upper limit of the stretching temperature is preferably 170°C. Stretching at such a temperature can suppress rapid progress of crystallization of the PVA-based resin, thereby suppressing inconveniences caused by the crystallization (eg, hindering the orientation of the PVA-based resin layer due to elongation).

C-3. Insolubilization Treatment If necessary, insolubilization treatment may be performed after the air-assisted extension treatment and before the water extension treatment or dyeing treatment. The above-mentioned insolubilization treatment is performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. By performing the insolubilization treatment, water resistance can be imparted to the PVA-based resin layer, and the orientation of the PVA 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 temperature of the insoluble bath (boric acid aqueous solution) is preferably 20°C to 50°C.

C-4. Dyeing treatment The above-mentioned dyeing treatment is performed by dyeing the PVA-based resin layer with iodine. Specifically, it is performed by adsorbing iodine to the PVA-based resin layer. The adsorption method includes, for example, a method of immersing a PVA-based resin layer (layered body) in an iodine-containing dyeing solution, a method of applying the dyeing solution to the PVA-based resin layer, and spraying the dyeing solution to PVA method on the resin layer, etc. A method of immersing the layered product in a dyeing liquid (dyeing bath) is preferably employed. This is because it can adsorb iodine well.

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

The dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the single transmittance of the polarizing film finally obtained is 44.5% or more and the polarization degree is 99.0% or more. The dyeing conditions are preferably to use an aqueous iodine solution as the dyeing solution, and the content ratio of iodine to potassium iodide in the aqueous iodine solution is set to 1:5 to 1:20. The content ratio of iodine and potassium iodide in the iodine aqueous solution is preferably 1:5~1:10. A polarizing film having the above-mentioned optical properties can be produced through the above procedure.

When the layered body is immersed in a treatment bath containing boric acid (representatively, an insolubility treatment) followed by a dyeing treatment, the boric acid contained in the treatment bath is mixed into the dyeing bath, and the concentration of boric acid in the dyeing bath varies with the As time changes, the dyeability may become unstable as a result. In order to suppress the instability of dyeability as described above, the upper limit of the boric acid concentration in the dyeing bath is preferably adjusted to 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 in the dyeing bath is preferably 0.1 part by weight, more preferably 0.2 part by weight, and still more preferably 0.5 part 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. Thereby, the ratio of the concentration change of boric acid when the boric acid of the above-mentioned treatment bath is mixed into the dyeing bath can be reduced. The blending amount of boric acid pre-blended into the dyeing bath (that is, the content of boric acid not derived from the above-mentioned treatment bath) is preferably 0.1 to 2 parts by weight relative to 100 parts by weight of water, more preferably 0.5 parts by weight ~1.5 parts by weight.

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

C-6. Underwater stretching treatment The underwater stretching treatment can be performed by immersing the layered body in a stretching bath. By the underwater stretching treatment, it can be stretched at a lower temperature than the glass transition temperature of the thermoplastic resin substrate or the PVA-based resin layer (representatively about 80°C), and the crystallization of the PVA-based resin layer can be suppressed. Simultaneous high-magnification extension. As a result, a polarizing film with excellent optical properties can be produced.

An arbitrary and appropriate method can be adopted as a method of extending the layered body. Specifically, it may be either fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching the layered body through rolls having different peripheral speeds). Preferably, the free end extension is selected. The extension of the laminate may be performed in one stage or in multiple stages. When it is carried out in multiple stages, the stretching ratio (maximum stretching ratio) of the layered body described later is the product of the stretching ratios of the respective stages.

The stretching in water is preferably performed by immersing the layered body in an aqueous solution of boric acid (stretching in water with boric acid). By using the boric acid aqueous solution as the stretching bath, the PVA-based resin layer can be provided with rigidity and water-insoluble water resistance capable of withstanding the tension applied during stretching. Specifically, boric acid generates tetrahydroxyboronic acid anion in an aqueous solution and can be cross-linked with PVA-based resin by hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, and good extension can be performed, thereby producing a polarizing film with excellent optical properties.

The above boric acid aqueous solution is preferably obtained by dissolving boric acid and/or borate in a solvent, ie, water. 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 2.5 to 6 parts by weight, particularly preferably 3 to 5 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 produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving boron compounds such as borax, glyoxal, and glutaraldehyde in a solvent can also be used.

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

The extension temperature (the liquid temperature of the extension bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. As long as it is within the above-mentioned temperature, the PVA-based resin layer can be suppressed from being dissolved, and at the same time, it can be stretched at a high magnification. Specifically, as described above, in consideration of the relationship with the formation of the PVA-based resin layer, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60° C. or higher. At this time, if the stretching temperature is lower than 40° C., even if it is considered that the thermoplastic resin base material can be plasticized with water, it may not be able to be properly stretched. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and there is a fear that excellent optical properties cannot be obtained. The immersion time for the layered body to be immersed in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio in the underwater stretching treatment is preferably 1.5 times or more, preferably 3.0 times or more. The total stretching ratio of the layered body is preferably 5.0 times or more, more preferably 5.5 times or more, relative to the original length of the layered body. By achieving the high draw ratio, a polarizing film having extremely excellent optical properties can be produced. The high elongation ratio can be achieved by using an underwater extension method (boric acid water extension).

C-7. Drying shrinkage treatment The above-mentioned drying shrinkage treatment may be performed through area heating by heating the entire area, or may be performed through heating a conveying roller (so-called heating roller) (heating roller drying method). It is preferable to use both. By drying it using a heating roll, the heating curl of a laminated body can be suppressed efficiently, and the polarizing film excellent in appearance can be manufactured. Specifically, by drying the layered body in a state where the layered body runs along the heating roller, the crystallization of the thermoplastic resin base material described above can be efficiently promoted to increase the degree of crystallinity even at a relatively low drying temperature , can still improve the crystallinity of thermoplastic resin substrates. As a result, the rigidity of the thermoplastic resin base material increases, and the shrinkage of the PVA-based resin layer due to drying is brought into a state, whereby curling is suppressed. Moreover, since the laminated body can be dried while maintaining a smooth state by using a heating roll, not only the generation of curls but also the generation of wrinkles can be suppressed. At this time, the layered body can be shrunk in the width direction by drying shrinkage treatment, and the optical properties can be improved. It is because it can effectively improve the orientation of PVA and PVA/iodine complexes. The shrinkage rate in the width direction of the laminate obtained by the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using a heating roller, the laminated body can be continuously shrunk in the width direction while being conveyed, and high productivity can be realized.

FIG. 2 is a schematic diagram showing an example of drying shrinkage treatment. In the drying shrinkage treatment, the layered body 200 is dried while being conveyed by the conveyance rollers R1 to R6 and the guide rollers G1 to G4 heated to a predetermined temperature. In the illustrated example, the conveying rollers R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but for example, the conveying rollers R1 to R6 may be arranged so as to continuously heat only the laminated body 200 on one side (eg, thermoplastic resin substrate side).

Drying conditions can be controlled by adjusting the heating temperature of the conveying roller (the 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 degree of crystallinity of the thermoplastic resin can be favorably increased, and curling can be favorably suppressed, and an optical laminate having extremely excellent durability can be produced. In addition, the temperature of the heating roller can be measured with a contact thermometer. In the illustrated example, six conveying rollers are provided, but there is no particular limitation 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) between the laminated body and the heating roller is preferably 1 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 (eg, an oven), or can be installed in a general manufacturing line (at room temperature). It should be installed in a heating furnace with an air supply mechanism. The rapid temperature change between the heating rollers can be suppressed by combining the drying with the heating roller and the hot air drying, and the shrinkage in the width direction can be easily controlled. The temperature of hot air drying should be 30℃~100℃. In addition, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air should be about 10m/s~30m/s. In addition, the wind speed is the wind speed in the heating furnace, which can be measured by a miniature fan-blade digital anemometer.

C-8. Other treatments Washing treatment should be performed after the water-stretching treatment and before the drying shrinkage treatment. The above-mentioned cleaning treatment can be typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution. Example

另，舉例而言，在以具備防眩(AG)之表面處理或具有擴散性能之黏著劑的偏光板為測定對象時，會依分光光度計而獲得不同的測定結果，此時，藉由將以各個分光光度計測定同一偏光板時所得之測定值作為基準進行數值換算，可補償依分光光度計所得測定值之差。 (3)長條狀偏光板的光學特性之參差 從實施例及參考例之長條狀偏光板沿寬度方向以等間隔在5處各位置裁切出測定試樣，再以與上述(2)相同方式測定出5個各測定試樣之中央部分的單體透射率。接著，算出在各測定位置測出之單體透射率之中最大值與最小值之差，並將該值作為長條狀偏光板的光學特性之參差(長條狀偏光板沿寬度方向之位置的單體透射率之最大值與最小值之差)。 (4)薄片狀偏光板的光學特性之參差 從實施例及參考例之長條狀偏光板裁切出100mm×100mm之測定試樣，並求得薄片狀偏光板(50cm² )的光學特性之參差。具體而言，係以與上述(2)相同方式測定出測定試樣之4邊各邊的中點起算往內側約1.5cm~2.0cm左右之位置及中央部分共計5處之單體透射率。接著，算出在各測定位置測出之單體透射率之中最大值與最小值之差，並將該值作為薄片狀偏光板的光學特性之參差(在50cm² 之區域內的單體透射率之最大值與最小值之差)。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. In addition, unless otherwise noted, "parts" and "%" in Examples and Comparative Examples are based on weight. (1) Thickness was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"). (2) Monomer transmittance and degree of polarization The polarizing plates (protective films/polarizing films) of the examples and comparative examples were measured using an ultraviolet-visible light spectrophotometer (V-7100 manufactured by JASCO Corporation), and the measured The single transmittance Ts, the parallel transmittance Tp, and the orthogonal transmittance Tc are used as Ts, Tp and Tc of the polarizing film, respectively. These Ts, Tp and Tc are the Y values obtained by measuring with the 2-degree field of view (C light source) of JIS Z8701 and correcting the luminous efficacy. In addition, the refractive index of the protective film was 1.50, and the refractive index of the surface of the polarizing film on the opposite side to the protective film was 1.53. The degree of polarization P was obtained from the obtained Tp and Tc by the following formula. Polarization degree P(%)={(Tp-Tc)/(Tp+Tc)} ^1/2 × 100 In addition, the spectrophotometer can also use LPF-200 made by Otsuka Electronics Co., Ltd. to perform the equivalent measurement. As an example, with respect to Samples 1 to 3 having polarizing plates having the same configuration as those in the following examples, the measurement was performed using V-7100 and LPF-200, and the measured values of the transmittance Ts and the degree of polarization P of the monomer were measured. The measured values are listed in Table 1. As shown in Table 1, the difference between the measured value of the single transmittance of V-7100 and the measured value of the single transmittance of LPF-200 is 0.1% or less, and it can be seen that the same measurement can be obtained regardless of whether any spectrophotometer is used. result. [Table 1]

In addition, for example, when a polarizing plate with anti-glare (AG) surface treatment or an adhesive with diffusive properties is used as the measurement object, different measurement results will be obtained depending on the spectrophotometer. Using the measured values obtained by each spectrophotometer to measure the same polarizing plate as a reference, the numerical conversion can be performed to compensate for the difference in the measured values obtained by the spectrophotometer. (3) Variation in optical properties of elongated polarizing plates The measurement samples were cut out from the elongated polarizing plates of Examples and Reference Examples at 5 positions at equal intervals in the width direction, and the same as the above (2) In the same manner, the single transmittance of the central portion of each of the five measurement samples was measured. Next, the difference between the maximum value and the minimum value of the single transmittance measured at each measurement position was calculated, and this value was used as the variation of the optical properties of the long polarizing plate (the position of the long polarizing plate in the width direction). The difference between the maximum value and the minimum value of the monomer transmittance). (4) Variation in optical properties of sheet polarizing plates A measurement sample of 100 mm×100 mm was cut out from the long polarizing plates of Examples and Reference Examples, and the optical properties of sheet polarizing plates (50 cm ² ) were obtained. uneven. Specifically, in the same manner as in (2) above, the single-body transmittance was measured at a total of 5 positions in the center of the measurement sample about 1.5 cm to 2.0 cm inward from the midpoint of each of the four sides of the measurement sample. Next, the difference between the maximum value and the minimum value of the single transmittance measured at each measurement position was calculated, and this value was used as the variation in the optical properties of the sheet-like polarizing plate (the single transmittance in the area of 50 cm ² ). difference between the maximum and minimum values).

[Example 1] 1. Production of polarizing film The thermoplastic resin substrate is a long strip of amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100 μm). Corona treatment is performed on one side of the resin substrate. The PVA system is a 9:1 mixture of polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetylacetate modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410") To 100 parts by weight of resin, 13 parts by weight of potassium iodide was added to prepare an aqueous PVA solution (coating liquid). The above-mentioned PVA aqueous solution was apply|coated to the corona-treated surface of a resin base material, and it dried at 60 degreeC, and the PVA-type resin layer of thickness 13 micrometers was formed by this, and the laminated body was produced. The obtained layered body was uniaxially stretched 2.4 times at the free end along the longitudinal direction (longitudinal direction) between rollers with different peripheral speeds in an oven at 130° C. (assisted stretching in the air). Next, the layered body was immersed in an insolubilization bath (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubility treatment). Next, adjust the concentration of a dyeing bath with a liquid temperature of 30° C. (an aqueous solution of iodine obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with respect to 100 parts by weight of water), so that the final polarizing film can be obtained in a single The volume transmittance (Ts) became 44.5% or more while being immersed therein for 60 seconds (dyeing treatment). Next, it was immersed in a crosslinking bath (a boric acid aqueous 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) for 30 seconds (crosslinking treatment) at a liquid temperature of 40°C. ). Then, while immersing the layered body in a boric acid aqueous solution (boric acid concentration: 4.0% by weight) at a liquid temperature of 70°C, uniaxial stretching was performed in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds so that the total stretching ratio was adjusted. Up to 5.5 times (extension treatment in water). Then, the layered body was immersed in a cleaning bath (aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 20°C (cleaning treatment). After that, while drying it in an oven kept at 90°C, the contact surface temperature was kept at 75°C with a heating roll made of SUS for about 2 seconds (drying shrinkage treatment). The shrinkage rate in the width direction of the laminate obtained by the drying shrinkage treatment was 5.2%. Through the above procedure, a polarizing film with a thickness of 5 μm was formed on the resin substrate. Then, the same steps were repeated to produce a total of seven polarizing films. 2. Preparation of polarizing plate An acrylic film (surface refractive index 1.50, 40 μm) was attached to the surface of each polarizing film prepared above (the surface opposite to the resin substrate) as a protective film through an ultraviolet curable adhesive. Specifically, it was applied so that the total thickness of the hardening adhesive was 1.0 μm, and was bonded using a rolling mill. Then, the adhesive was cured by irradiating UV light from the protective film side. Next, after cutting both ends, the resin base material was peeled off to obtain seven long polarizing plates (width: 1300 mm) having a protective film/polarizing film configuration.

[Reference Example 1] Five polarized lights were produced in the same manner as in Example 1, except that the dyeing treatment was performed so that the single transmittance (Ts) of the polarizing film finally produced was 43.0% or more and less than 44.5%. Films and polarizers.

[Example 2] Four polarizing films and polarizing plates were produced in the same manner as in Example 1, except that the oven temperature was set to 70°C and the heating roll temperature was set to 70°C in the drying shrinkage treatment. The shrinkage rate in the width direction of the laminate obtained by the drying shrinkage treatment was 2.5%.

[Reference Example 2] Five polarized lights were produced in the same manner as in Example 2, except that the dyeing treatment was performed so that the single transmittance (Ts) of the polarizing film finally produced was 43.0% or more and less than 44.5%. Films and polarizers.

[Comparative Example 1] Except that potassium iodide was not added to the PVA aqueous solution (coating solution), the stretching ratio in the air-assisted stretching treatment was set to 1.8 times, and the heating roller was not used in the drying shrinkage treatment, except that In Example 1, an attempt was made to produce a polarizing film in the same manner, but the PVA-based resin layer was dissolved during the dyeing treatment and the water stretching treatment, and a polarizing film could not be produced.

[Comparative Example 2] Nine polarizing films and polarizing films were produced in the same manner as in Example 1, except that the stretching ratio in the air-assisted stretching treatment was 1.8 times, and the heating roller was not used in the drying shrinkage treatment. plate. However, it is impossible to make a polarizing film with a single transmittance of more than 44.5%.

[Reference Example 3] The polarizing film produced in the same manner as in Comparative Example 2 was held in a constant temperature and humidity region set to a temperature of 60° C. and a humidity of 90% RH for 30 minutes. After that, a polarizing plate was produced in the same manner as in Example 1.

The individual transmittance and polarization degree were measured about each polarizing plate of the Example and the comparative example. The results are shown in Table 2 and FIG. 3 . FIG. 3 shows the approximate curve of the punctuation of Example 1 and the punctuation of Reference Example 1, the approximate curve of the punctuation of Example 2 and the punctuation of Reference Example 2, and the approximate curve of the punctuation of Comparative Example 2.

[Table 2]

The polarizing film produced by the manufacturing method of the comparative example did not satisfy the monomer transmittance of 44.5% or more and the monomer transmittance of 99.0% or more at the same time. In addition, as shown by the approximation curve of the punctuation point of Comparative Example 2, in the production method of Comparative Example 2, when dyeing was performed to make the transmittance of the monomers 44.5% or more, the degree of polarization was predicted to be less than 99.0%. On the other hand, the polarizing film obtained by the manufacturing method of the Example has the excellent optical characteristics that the single transmittance is 44.5% or more and the polarization degree is 99.0% or more.

For each of the polarizing plates of Example 1 and Reference Example 3, the variation in optical properties of the elongated and sheet-shaped polarizing plates was measured. The results are shown in Table 3.

[table 3]

The variation of the single transmittance of the elongated polarizing plate obtained by the manufacturing method of the embodiment is less than 0.3%, and the variation of the single transmittance of the thin polarizing plate obtained by the manufacturing method of the embodiment is At 0.2% or less, the variation in optical properties is suppressed to a level that does not cause problems. On the other hand, the polarizing plate of the reference example obtained through the step of humidifying the polarizing film has a large variation in optical properties regardless of the elongated shape and the thin sheet shape.

INDUSTRIAL APPLICABILITY The polarizing plate having the polarizing film of the present invention can be suitably used for circular polarizing plates for organic EL display devices and inorganic EL display devices.

10‧‧‧Polarizing film 20‧‧‧First protective layer 30‧‧‧Second protective layer 100‧‧‧Polarizing plate 200‧‧‧Laminated body R1~R6‧‧‧Conveying roller G1~G4‧‧‧Guide 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 diagram showing an example of a drying shrinkage treatment using a heated roll. FIG. 3 is a graph showing the optical properties of polarizing plates prepared in Examples and Comparative Examples.

10‧‧‧Polarizing film

20‧‧‧First protective layer

30‧‧‧Second protective layer

100‧‧‧Polarizer

Claims (5)

A manufacturing method of a polarizing film, which is a method for manufacturing a polarizing film, the thickness of the polarizing film is less than 8 μm, the transmittance of the monomer is more than 44.5% and the degree of polarization is more than 99.0%; the method comprises the following steps: heating a strip of A layered product is formed by forming a polyvinyl alcohol-based resin layer on one side of the plastic resin substrate, and the polyvinyl alcohol-based resin layer contains iodide or sodium chloride and contains a polyvinyl alcohol-based resin; and the layered product is sequentially In-air auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment are performed. The drying shrinkage treatment is performed by heating the above-mentioned laminate in the longitudinal direction, thereby shrinking it by 2% or more in the width direction. The method for producing a polarizing film according to claim 1, 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 of a polarizing film according to claim 1 or 2, wherein the stretching ratio in the above-mentioned air-assisted stretching treatment is 2.0 times or more. The manufacturing method of the polarizing film according to claim 1 or 2, wherein the drying shrinkage treatment step is a step of heating with a heating roller. The method for producing a polarizing film according to claim 4, wherein the temperature of the heating roll is 60°C to 120°C, and the shrinkage in the width direction of the laminate obtained by the drying shrinkage treatment is 2% or more.

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