TWI801395B - Polarizing film, polarizing plate, polarizing plate roll, and method for manufacturing polarizing film - Google Patents

Abstract

The object of the present invention is to provide a polarizing film with excellent optical properties. The solution is: the thickness of the polarizing film of the present invention is 8 μm or less, the single transmittance is 44.0% or more, and the polarization degree is 99.50% or more.

Description

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

The invention relates to a polarizing film, a polarizing plate, a polarizing plate coil and a method for manufacturing the polarizing film.

Background of the Invention In a liquid crystal display device, which is a typical image display device, polarizing films are arranged on both sides of a liquid crystal cell depending on the image forming method. Furthermore, with the popularization of thin displays, displays equipped with organic EL panels (OLEDs) and displays using display panels using inorganic light-emitting materials such as quantum dots (QLEDs) have also been proposed. These panels have a highly reflective metal layer, so they are prone to problems such as reflection of external light or reflection of the background. However, it is known that setting the circular polarizing plate with the polarizing film and the λ/4 plate on the viewing side can prevent these problems. A method for producing a polarizing film, for example, has been proposed in which a laminate having a resin substrate and a polyvinyl alcohol (PVA) resin layer is extended, and then dyed to obtain a polarizing film on the resin substrate (for example, Patent Document 1). A thinner polarizing film can be obtained by this method, so it can contribute to the thinning of image display devices in recent years and has attracted attention. However, the optical characteristics of the conventional thin polarizing film are insufficient, and further improvement of the optical characteristic of the thin polarizing film is required.

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

Summary of the Invention Problems to be Solved by the Invention The present invention was made to solve the aforementioned conventional problems, and its main purpose is to provide a polarizing film, a polarizing plate, a polarizing plate roll, and a method for manufacturing the polarizing film having excellent optical properties.

Means for Solving the Problems The polarizing film of the present invention has a thickness of 8 μm or less, a single transmittance of 44.0% or more, and a degree of polarization of 99.50% or more. In one embodiment, the single transmittance is 44.5% or less, and the degree of polarization is 99.95% or less. According to another aspect of the present invention, a polarizer is provided. The polarizing plate has: a polarizing film; and a protective layer 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 in a region of 50 cm ² of the polarizing plate is 0.2% or less. Another aspect of the present invention is to provide a polarizer roll. This polarizing plate roll material is formed by winding the above-mentioned 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 the manufacturing method of the above-mentioned polarizing film, and it 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 strip-shaped thermoplastic resin substrate to form a laminated body; and, the above-mentioned laminated body is sequentially subjected to air-assisted stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment. It shrinks more than 2% along the width direction. In one embodiment, the halide content 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 ratio in the 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 roll. In one embodiment, the temperature of the heating roll is 60° C. to 120° C., and the shrinkage rate of the laminate obtained by performing the drying shrinkage treatment in the width direction 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, the thickness of the polarizing film is 8 μm or less, the single transmittance is 44.0% or more, and the degree of polarization is 99.50% or more.

Modes for Carrying Out the Invention The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

A. Polarizing film The polarizing film according to an embodiment of the present invention has a thickness of 8 μm or less, a single transmittance of 44.0% or more, and a degree of polarization of 99.50% or more. Generally speaking, there is a trade-off relationship between the single transmittance and the degree of polarization. Therefore, if the single transmittance is increased, the polarization degree will be reduced, and if the polarization degree is increased, the single transmittance will be reduced. Therefore, conventional thin polarizing films satisfying the optical characteristics of a single transmittance of 44.0% or more and a degree of polarization of 99.50% or more are difficult to apply. As described above, the polarizing film according to one embodiment of the present invention has excellent optical characteristics such that the single transmittance is 44.0% or more and the degree of polarization is 99.50% or more. Furthermore, using the polarizing film of this embodiment, it is possible to realize a polarizing plate in which variations in optical characteristics are suppressed. 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 image display devices, and is especially suitable for circular polarizing plates used in organic EL display devices.

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 between 380nm and 780nm. The monomer transmittance of the polarizing film is preferably 44.5% or less. The degree of polarization of the polarizing film should be above 99.70%, more preferably above 99.80%. On the other hand, the upper limit of the degree of polarization is preferably 99.95%. The above-mentioned single transmittance is representatively the Y value obtained by measuring with an ultraviolet-visible spectrophotometer and correcting for optical performance. The above-mentioned degree of polarization is representatively obtained by the following formula based on the parallel transmittance Tp and the cross transmittance Tc obtained by measuring with an ultraviolet-visible spectrophotometer and performing light performance correction. Degree of polarization (%)={(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

In one embodiment, the transmittance of a thin polarizing film of 8 μm or less is typically measured using a laminate of a polarizing film (refractive index of the surface: 1.53) and a protective film (refractive index: 1.50) using ultraviolet-visible light spectroscopy. photometer to measure. Due to the refractive index of the surface of the polarizing film and/or the refractive index of the surface of the protective film in contact with the air interface, the reflectance of each layer on the interface will change, resulting in a change in the measured value of the transmittance. Therefore, for example, when using a protective film with a refractive index other than 1.50, the measured value of the 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 corrected value C of transmittance is represented by the following formula using 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 on the transmission axis when using a protective film with a refractive index of 1.50, n ₁ is the refractive index of the protective film used, and T ₁ is the transmittance of the polarizing film Rate. For example, when using a substrate with a surface refractive index of 1.53 (cycloolefin film, hard-coated film, etc.) as a protective film, the correction amount C is about 0.2%. At this time, add 0.2% to the measured transmittance to convert it to the transmittance when using a protective film with a surface refractive index of 1.50. In addition, after calculation according to the above formula, when the transmittance _T1 of the polarizing film is changed by 2%, the change of the correction value C 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. Also, when the protective film has absorption other than surface reflection, appropriate correction can be made according to the amount of absorption.

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

Specific examples of the polarizing film obtained using a laminate include a polarizing film obtained using a laminate of a resin base material and a PVA-based resin layer formed by coating on the resin base material. A polarizing film obtained by using a laminate of a resin substrate and a PVA-based resin layer coated and formed on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate, and making it dry to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; and stretching and dyeing the laminate to make the PVA-based resin layer into a polarizing film. In this embodiment, stretching typically includes immersing the laminate in an aqueous solution of boric acid and stretching it. Furthermore, if necessary, the stretching may further include stretching the laminate in air at a high temperature (for example, 95° C. or higher) before stretching in a boric acid aqueous solution. The laminate of the obtained 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 the resin substrate/polarizing film and placed on the peeled surface Depending on the purpose, an arbitrary and appropriate protective layer is laminated for later use. The details of the manufacturing method of the said polarizing film are described in Unexamined-Japanese-Patent No. 2012-73580, for example. In this specification, the entire description of the publication 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 laminate 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 above-mentioned laminated body while transporting it in the long-side direction, thereby shrinking it in the width direction. More than 2%. Thereby, a polarizing film with excellent optical properties and suppressed variation in optical properties can be provided. The thickness of the polarizing film is 8 μm or less, the single transmittance is 44.0% or more, and the degree of polarization is 99.50% or more. That is, by introducing auxiliary stretching, even when PVA is coated on a thermoplastic resin, the crystallinity of PVA can be improved, and high optical characteristics can be achieved. Also, at the same time, improving the orientation of PVA in advance can prevent problems such as decrease in orientation and dissolution of PVA when immersed in water in the subsequent dyeing step and stretching step, and can achieve high optical characteristics. In addition, when the PVA-based resin layer is immersed in a liquid, the disorder of polyvinyl alcohol molecules and the decrease in alignment can be suppressed more than when the PVA-based resin layer does not contain a halide. Therefore, it is possible to improve the optical characteristics of the polarizing film produced through the processing steps of immersing the laminate in liquid, such as dyeing processing and underwater stretching processing. In addition, the optical properties can be improved by shrinking the laminate in the width direction through drying shrinkage treatment.

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 has: 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. Moreover, as mentioned above, one of the 1st protective layer and the 2nd protective layer may be the resin base material used for manufacture of the said polarizing film.

The polarizing plate can be strip-shaped or thin-sheet-shaped. When the polarizing plate is long, it is preferably wound into a roll to make a polarizing plate roll. 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 0.29%, and more preferably 0.28%. The smaller D1 is, the better, but its lower limit is, for example, 0.01%. As long as D1 is within the above range, polarizing plates with excellent optical properties can be industrially produced. In another embodiment, the difference (D2) between the maximum value and the minimum value (D2) of the single transmittance in a region of 50 cm ² of the polarizing plate is 0.2% or less. The upper limit of D2 is preferably 0.15%, more preferably 0.1%. 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, it is possible to suppress the brightness variation of the display screen when the polarizing plate is used in an image display device.

The first and second protective films are formed of any appropriate film 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 resins, etc. Imine-based, polyether-based, polystyrene-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based and acetate-based transparent resins, etc. Further, thermosetting resins such as (meth)acrylic, urethane, (meth)acrylate urethane, epoxy, and silicone, or ultraviolet curable resins are also mentioned. Other examples include glassy polymers such as siloxane polymers. Furthermore, a polymer film described in Japanese Patent Laid-Open 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 the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl and nitrile group in the side chain can be used. , and, for example, a resin composition having an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer is mentioned. The polymer film can 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) arranged on the side opposite to the display panel is typically not more than 300 μm, preferably not more than 100 μm, more preferably 5 μm to 80 μm, and more preferably It is preferably 10 μm to 60 μm. In addition, when surface treatment is applied, 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 more preferably 10 μm to 60 μm. In one embodiment, the inner protective layer is a retardation layer having any 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 the in-plane retardation measured with light with a wavelength of 550nm at 23°C, and can be obtained by the transmission formula: Re=(nx-ny)×d. Here, "nx" is the refractive index in the direction where the in-plane refractive index becomes the largest (that is, the direction of the slow axis), and "ny" is the refractive index in the direction that is perpendicular to the slow axis in the plane (that is, the direction of the fast axis) , "nz" is the refractive index in the thickness direction, and "d" is the thickness (nm) of the layer (film).

C. Manufacturing method of a polarizing film The manufacturing method of a polarizing film according to an embodiment of the present invention includes the following steps: forming a polarizing film containing halides and polyvinyl alcohol-based resin (PVA-based resin) on one side of a strip-shaped thermoplastic resin substrate. The polyvinyl alcohol-based resin layer (PVA-based resin layer) is formed to form a laminate; and, the laminate is sequentially subjected to air-assisted stretching treatment, dyeing treatment, underwater stretching treatment and drying shrinkage treatment. The drying shrinkage treatment is The laminate is heated while being conveyed in the longitudinal direction, thereby shrinking the laminate 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 done with heating rollers, and the temperature of the heating rollers should be 60°C~120°C. The shrinkage rate in the width direction of the laminate obtained by drying and shrinking is preferably 2% or more. The polarizing film described in the above-mentioned item A can be produced according to the above-mentioned manufacturing method. In particular, a polarizing film having excellent optical properties (typically, single transmittance and degree of polarization) and with suppressed variation in optical properties can be produced by producing a laminate including a PVA-based resin layer containing a halide Afterwards, the stretching of the above-mentioned laminate is multi-stage stretching including aerial auxiliary stretching and underwater stretching, and the stretched laminate is heated with a heating roller. Specifically, by using a heating roll in the drying shrinkage treatment step, the entire laminate can be uniformly shrunk while conveying the laminate. In this way, the optical properties of the prepared polarizing film can not only be improved, but also the polarizing film with excellent optical properties can be stably produced, and the variation of the optical properties (especially the single transmittance) of the polarizing film can be suppressed.

C-1. Fabrication of Laminated Body Any appropriate method may be used for fabricating the laminated body of the thermoplastic resin base material and the PVA-based resin layer. Preferably, a coating solution containing halides and 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 mentioned above, the halide content in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

Any appropriate method can be adopted for the coating method of the coating liquid. Examples include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, knife coating (comma coating, etc.) and the like. The coating and drying temperature of the above-mentioned coating solution 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, surface treatment (such as corona treatment, etc.) can be performed on the thermoplastic resin substrate, and an easy-adhesive layer can also be formed on the thermoplastic resin substrate. By performing the above treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved.

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 is larger than 300 μm, for example, it may take a long time for the thermoplastic resin base to absorb water in the underwater stretching treatment described later, and there is a possibility that excessive load will be applied to the stretching.

The water absorption rate of the thermoplastic resin substrate is preferably above 0.2%, more preferably above 0.3%. The thermoplastic resin substrate absorbs water, and the water acts as a plasticizer for plasticization. As a result, elongation stress can be greatly reduced and high-magnification elongation can be achieved. On the other hand, the water absorption 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, it is possible to prevent problems such as deterioration of the appearance of the obtained polarizing film caused by a marked decrease in the dimensional stability of the thermoplastic resin base material during production. It can also prevent the substrate from breaking when it is stretched in water, or the PVA-based resin layer from peeling off from the thermoplastic resin substrate. In addition, the water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption is a value obtained in accordance with JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably below 120°C. By using such a thermoplastic resin base material, crystallization of the PVA-based resin layer can be suppressed, and sufficient extensibility of the laminate can be ensured. In addition, considering that the thermoplastic resin substrate can be plasticized by water and can be stretched well in water, it is more preferably not higher than 100°C, more preferably not higher than 90°C. 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, defects such as deformation of the thermoplastic resin substrate (such as unevenness, sagging, or wrinkling) can be prevented when coating and drying the coating liquid containing the above-mentioned PVA-based resin. situation, the laminated body can be produced well. In addition, the stretching of the PVA-based resin layer can be favorably performed 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 a crystallized material capable of introducing a modifying group into the constituent material. The glass transition temperature (Tg) is a value calculated based on 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 resins such as polyethylene terephthalate resins, cycloolefin resins such as norcamphene resins, olefin resins such as polypropylene, polyamide resins, and polycarbonate resins. , and other copolymer resins. Among these, norcamphene-based resins and amorphous polyethylene terephthalate-based resins are preferable.

In one embodiment, an amorphous (uncrystallized) polyethylene terephthalate resin is preferably used. Among them, it is particularly preferable to use an amorphous (difficult to crystallize) polyethylene terephthalate resin. Specific examples of amorphous polyethylene terephthalate resins include copolymers that further contain isophthalic acid and/or cyclohexane dicarboxylic acid as dicarboxylic acids, or copolymers that further contain cyclohexane dicarboxylic acid. Copolymers of methanol or diethylene glycol as glycol.

In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate resin having an isophthalic acid unit. This is because the thermoplastic resin base material has extremely excellent extensibility and suppresses crystallization at the time of elongation. We speculate that this is due to the large buckling imparted to the main chain by the introduction of isophthalic acid units. 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, more preferably 1.0 mol% or more, based on the total of all repeating units. This is because a thermoplastic resin substrate with 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 the above-mentioned content ratio, the degree of crystallization can be favorably increased in the drying shrinkage treatment described later.

The thermoplastic resin substrate may also have been pre-stretched (before forming the PVA-based resin layer). In one embodiment, it is extended along the width direction of the elongated thermoplastic resin substrate. The width direction is preferably a direction perpendicular to the extending direction of the laminate described later. In addition, the term "orthogonal" in this specification also includes the case of being substantially orthogonal. Also, "substantially orthogonal" includes 90°±5.0°, preferably 90°±3.0°, more preferably 90°±1.0°.

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

An arbitrary and appropriate method can be adopted for the stretching method of the thermoplastic resin base material. Specifically, it can be extended from a fixed end, or can be extended from a free end. The extension method can be dry or wet. The stretching of the thermoplastic resin substrate can be carried out in one stage or in multiple stages. When it is carried out in multiple stages, the above-mentioned elongation ratio is the product of the elongation ratios of each stage.

C-1-2. Coating liquid The coating liquid system contains a halide and a PVA-based resin as described above. The above-mentioned coating liquid represents a solution obtained by dissolving the above-mentioned halide compound and the above-mentioned PVA-based resin in a solvent. Examples of the solvent include water, dimethylsulfide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, ethylene glycol, and the like. Amines such as diamine and diethylenetriamine. These may be used alone or in combination of two or more. Among them, water is the best. 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 above-mentioned resin concentration, a uniform coating film can be formed in close contact with the thermoplastic resin substrate. The halide content in the coating solution is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.

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

Arbitrary and appropriate resins can be used for the above-mentioned PVA-based resin. Examples thereof include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer can be obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol %-100 mol %, preferably 95.0 mol %-99.95 mol %, more preferably 99.0 mol %-99.93 mol %. The degree of saponification is obtained in accordance with JIS K 6726-1994. A polarizing film excellent in durability can be obtained by using a PVA-based resin having such a degree of saponification. When the degree of saponification is too high, gelation may occur.

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 obtained according to JIS K 6726-1994.

Any appropriate halide may be used as the above-mentioned halide. Examples thereof include iodide and sodium chloride. Examples of iodide include potassium iodide, sodium iodide and lithium iodide. Among these, potassium iodide is preferable.

The amount of halide in the coating liquid is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin, 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 is greater than 20 parts by weight relative to 100 parts by weight of the PVA-based resin, the halide may overflow and the final polarizing film may become cloudy.

Generally speaking, the stretching of the PVA-based resin layer will increase the orientation of the polyvinyl alcohol molecules in the PVA resin layer, but if the stretched PVA-based resin layer is immersed in a liquid containing water, there will be polyethylene The situation where the alignment of alcohol molecules is disordered and the alignment is reduced. In particular, when stretching a laminate of a thermoplastic resin and a PVA-based resin layer in boric acid water, the degree of orientation decreases when the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin. The tendency is obvious. For example, the stretching of PVA film monomer in boric acid water is generally carried out at 60°C. In contrast, the stretching of the laminate of A-PET (thermoplastic resin substrate) and PVA-based resin layer is at 70°C. If the temperature is around ℃, that is, at a higher temperature, at this time, the orientation of the PVA at the beginning of the stretching will be lowered at the stage before it is raised by the stretching in water. In this regard, after fabricating a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin base material, the laminate is stretched at high temperature in air (assisted stretching) before being stretched in boric acid water, thereby facilitating auxiliary stretching. Crystallization of the PVA-based resin in the PVA-based resin layer of the subsequent 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, it is possible to improve the optical characteristics of the polarizing film produced through the processing steps of immersing the laminate in liquid, such as dyeing processing and underwater stretching processing.

C-2. In-air 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 underwater stretching is selected. Like the two-stage stretching method, by introducing auxiliary stretching, stretching can be carried out while suppressing the crystallization of the thermoplastic resin substrate, so as to solve the problem of stretching caused by excessive crystallization of the thermoplastic resin substrate in the subsequent stretching in boric acid water The problem of lowering the property can be solved, so that the laminate can be stretched at a higher magnification. 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 temperature must be lower than that of the PVA-based resin coated on a general metal roller. In the case of even lower cases, as a result, the crystallization of the PVA-based resin becomes relatively low, and there arises a problem that sufficient optical properties cannot be obtained. In contrast, by introducing auxiliary stretching, the crystallinity of the PVA-based resin can be improved even when the PVA-based resin is coated on a thermoplastic resin, and high optical characteristics can be achieved. Also, at the same time, improving the orientation of the PVA-based resin in advance can prevent problems such as lowering of orientation and dissolution of the PVA-based resin when immersed in water in the subsequent dyeing step and stretching step, and can achieve high optical characteristics.

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

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

The extension magnification of the auxiliary extension in the air should be 2.0 times to 3.5 times. The maximum elongation magnification when combining aerial auxiliary elongation and underwater elongation is preferably 5.0 times or more, 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 elongation ratio" in this specification means the elongation ratio immediately before the laminate is broken, and is a value 0.2 lower than the value obtained by separately confirming the elongation ratio of the laminate fracture.

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 substrate, the stretching method, and the like. The stretching temperature is preferably above the glass transition temperature (Tg) of the thermoplastic resin base material, and the glass transition temperature (Tg) of the thermoplastic resin base material is preferably above +10°C, especially above Tg+15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. Stretching at such a temperature suppresses rapid progress of crystallization of the PVA-based resin, thereby suppressing disadvantages caused by the crystallization (for example, interruption of orientation of the PVA-based resin layer due to stretching).

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

C-4. Dyeing treatment The above-mentioned dyeing treatment is typically carried out by dyeing the PVA-based resin layer with iodine. Specifically, it is performed by adsorbing iodine on the PVA-based resin layer. Examples of the adsorption method include: a method of immersing the PVA resin layer (laminate) in a dyeing solution containing iodine, a method of applying the dyeing solution to the PVA resin layer, and spraying the dyeing solution onto the PVA. The method on the resin layer, etc. A method of immersing the laminate in a dyeing solution (dyeing bath) is preferably employed. This is because iodine can be well adsorbed.

The above-mentioned dyeing solution is preferably iodine aqueous solution. The blending amount of iodine is preferably 0.05 to 0.5 parts by weight relative to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is advisable 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, titanium iodide and the like. Among these, potassium iodide is preferable. The blending amount of iodide is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, relative to 100 parts by weight of water. In order to inhibit the dissolution of PVA-based resin, the liquid temperature of the dyeing solution during dyeing should be 20°C~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.

Dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the monomer transmittance of the finally obtained polarizing film becomes 44.0% or more and the degree of polarization becomes 99.50% or more. The dyeing condition is preferably to use an iodine aqueous solution as the dyeing solution, and set the content ratio of iodine and potassium iodide in the iodine aqueous solution to 1:5-1:20. The content ratio of iodine and potassium iodide in the iodine aqueous solution should be 1:5~1:10. A polarizing film having the above-mentioned optical properties can be prepared through the above procedure.

When the dyeing treatment is carried out after the treatment of immersing the laminate in a treatment bath containing boric acid (typically insolubilization treatment), the boric acid contained in the treatment bath will be mixed into the dyeing bath, and the concentration of boric acid in the dyeing bath will vary with each other. As time changes, the dyeing properties may become unstable as a result. In order to suppress destabilization of dyeability as described above, the upper limit of the concentration of boric acid in the dyeing bath is adjusted to preferably 4 parts by weight, more preferably 2 parts by weight, relative to 100 parts by weight of water. On the other hand, the lower limit of the concentration of boric acid in the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and still more preferably 0.5 parts by weight with respect to 100 parts by weight of water. In one embodiment, the dyeing treatment is performed using a dyeing bath premixed with boric acid. Thereby, the rate at which the boric acid concentration changes when the boric acid in the treatment bath mentioned above is mixed into the dyeing bath can be reduced. The amount of boric acid mixed in the dyeing bath in advance (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, cross-linking treatment may be performed after the dyeing treatment and before the stretching treatment in water. Typically, the above-mentioned crosslinking treatment can be performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By performing cross-linking treatment, water resistance can be imparted to the PVA-based resin layer, and the orientation of 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 carrying out the crosslinking treatment after the above-mentioned dyeing treatment, it is preferable to further blend iodide. By mixing iodide, the elution of iodine adsorbed to 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 iodide are as described above. The liquid temperature of the cross-linking bath (boric acid aqueous solution) should be 20°C~50°C.

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

An arbitrary and appropriate method can be used for the stretching method of the laminate. Specifically, it may be fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching a laminate through rolls having different circumferential speeds). Preferably a free end extension is selected. The extension of the laminate may be performed in one step or in multiple steps. When it is carried out in multiple stages, the elongation ratio (maximum elongation ratio) of the laminate described later is the product of the elongation ratios of each stage.

The underwater stretching is preferably carried out by immersing the laminate in an aqueous solution of boric acid (boric acid underwater stretching). By using an aqueous solution of boric acid as a stretching bath, the PVA-based resin layer can be given rigidity to withstand tension during stretching and water resistance that is insoluble in water. Specifically, boric acid generates tetrahydroxyboric acid anion in aqueous solution, which can cross-link with PVA-based resin through hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, and good stretching 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 water which is a solvent. On the other hand, the concentration of boric acid 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 concentration of boric acid 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. Moreover, the aqueous solution which melt|dissolved boron compound, such as borax, glyoxal, glutaraldehyde, etc. in a solvent other than boric acid or borate, can also be used.

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

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C~85°C, more preferably 60°C~75°C. As long as it is within the above-mentioned temperature, the dissolution of the PVA-based resin layer can be suppressed, and at the same time, high-magnification stretching can be achieved. Specifically, as mentioned above, considering 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., good stretching may not be possible even considering the plasticization of the thermoplastic resin base material with water. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and it may not be possible to obtain excellent optical properties. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The elongation ratio in the underwater elongation treatment is preferably 1.5 times or more, preferably 3.0 times or more. The total elongation ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, relative to the original length of the laminate. By achieving such a high elongation ratio, a polarizing film with extremely excellent optical characteristics can be produced. The high elongation ratio can be achieved by adopting an underwater elongation method (boric acid elongation).

C-7. Drying shrinkage treatment The above-mentioned drying shrinkage treatment can be carried out by heating the entire region by heating the region, or by heating the conveying roller (so-called heating roller) (heating roller drying method). It is preferable to use both. By drying with a heating roll, heating curl of the laminate can be effectively suppressed, and a polarizing film having an excellent appearance can be produced. Specifically, by drying the laminate in a state along the heating roll, the crystallization of the above-mentioned thermoplastic resin substrate can be effectively promoted to increase the degree of crystallization even at a relatively low drying temperature. , can still increase the crystallinity of the thermoplastic resin substrate well. As a result, the rigidity of the thermoplastic resin substrate is increased to be able to withstand the shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. In addition, by using the heating roller, the laminate can be dried while maintaining a smooth state, so that not only the occurrence of curls but also the occurrence of wrinkles can be suppressed. At this time, the laminated body can be shrunk in the width direction through drying shrinkage treatment to improve optical properties. 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 drying and shrinking is preferably 1% to 10%, more preferably 2% to 8%, and especially preferably 4% to 6%. By using the heating roller, the laminate can be continuously shrunk in the width direction while being conveyed, and high productivity can be achieved.

Fig. 2 is a schematic view showing an example of drying shrinkage treatment. In the drying shrinkage process, the laminated body 200 is dried while being conveyed by conveying rollers R1 to R6 and guide rollers G1 to G4 heated to a predetermined temperature. 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 substrate can be alternately and continuously heated, but for example, the conveying rollers R1 to R6 can be arranged so as to continuously heat only the laminate One side of 200 (for example, the thermoplastic resin substrate side).

The drying conditions can be controlled by adjusting the heating temperature of the conveying roller (temperature of the heating roller), the number of the heating roller, and the contact time with the heating roller, etc. The temperature of the heating roller is preferably 60°C~120°C, more preferably 65°C~100°C, especially 70°C~80°C. While the degree of crystallization of the thermoplastic resin can be increased well to suppress curling well, an optical laminate with 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 laminate and the heating roller is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, more preferably 1 to 10 seconds.

The heating roller can be installed in a heating furnace (such as an oven), or it can be installed in a general production line (at room temperature). It should be installed in a heating furnace with an air supply mechanism. By combining drying with heating rolls and hot air drying, rapid temperature changes between heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of hot air drying should be 30℃~100℃. Moreover, the hot air drying time should be 1 second to 300 seconds. The wind speed of hot air should be around 10m/s~30m/s. In addition, the wind speed refers to the wind speed in the heating furnace, which can be measured by a mini fan-type digital anemometer.

C-8. Other treatments Washing should be performed after stretching in water and before drying shrinkage. Typically, the cleaning treatment described above can be 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 measuring method of each characteristic is as follows. In addition, "parts" and "%" in Examples and Comparative Examples are based on weight unless otherwise noted. (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 For the polarizing plates (protective film/polarizing film) of Examples and Comparative Examples, use an ultraviolet-visible light spectrophotometer (V-7100 manufactured by JASCO Corporation) to measure, and measure the Single transmittance Ts, parallel transmittance Tp, and crossed 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 optical performance. In addition, the refractive index of the protective film was 1.50, and the refractive index of the surface of the polarizing film opposite 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 manufactured by Otsuka Electronics Co., Ltd. for equivalent measurement. As an example, V-7100 and LPF-200 were used to measure samples 1 to 3 having polarizing plates having the same configuration as the following examples, and the measured single transmittance Ts and polarization degree P The measured values are listed in Table 1. As shown in Table 1, the difference between the measured value of the single-body transmittance of V-7100 and the measured value of the single-body transmittance of LPF-200 is 0.1% or less. It can be seen that the same measurement can be obtained no matter which spectrophotometer is used result. [Table 1]

Also, for example, when measuring a polarizing plate with an anti-glare (AG) surface treatment or an adhesive with diffusing properties, different measurement results will be obtained depending on the spectrophotometer. The measured value obtained by each spectrophotometer when measuring the same polarizing plate is used as the benchmark for numerical conversion, which can compensate for the difference in the measured value obtained by the spectrophotometer. (3) Variation in the optical properties of the strip-shaped polarizing plate Cut out the measurement samples at 5 positions at equal intervals along the width direction of the strip-shaped polarizing plate of the embodiment and the reference example, and then compare with the above (2) The single-body transmittance of the central portion of each of five measurement samples was measured in the same manner. Next, calculate the difference between the maximum value and the minimum value of the single transmittance measured at each measurement position, and use this value as the variance of the optical characteristics of the strip-shaped polarizing plate (the position of the strip-shaped 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 thin-sheet polarizing plates Cut out 100mm×100mm measurement samples from the strip-shaped polarizing plates of Examples and Reference Examples, and obtain the optical properties of thin-sheet polarizing plates (50cm ² ) uneven. Specifically, in the same manner as in (2) above, the single transmittance was measured at a total of 5 positions about 1.5 cm to 2.0 cm inward from the midpoint of each of the four sides of the measurement sample and the central part. Next, calculate the difference between the maximum value and the minimum value among the individual transmittances measured at each measurement position, and use this value as the variation in the optical characteristics of the sheet-shaped polarizing plate (the individual transmittance in the area of 50 ^cm2 difference between the maximum and minimum values).

[Example 1] 1. Making a polarizing film The thermoplastic resin substrate is an amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100μm). And corona treatment is applied to one side of the resin substrate. A PVA system made by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mole%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410") at a ratio of 9:1. To 100 parts by weight of resin, 13 parts by weight of potassium iodide was added to prepare an aqueous PVA solution (coating solution). The above-mentioned PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60° C. to form a PVA-based resin layer with a thickness of 13 μm, thereby producing a laminate. The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (long side direction) between rollers with different peripheral speeds in an oven at 130° C. (assisted stretching in the air). Next, the laminated body was immersed in an insolubility bath (an aqueous solution of boric acid obtained by mixing 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 iodine aqueous solution 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 single color of the polarizing film finally obtained can be adjusted. The volume transmittance (Ts) becomes 44% or more while dipping in it 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) at a liquid temperature of 40°C for 30 seconds (crosslinking treatment). ). Then, while immersing the laminate in a boric acid aqueous solution (boric acid concentration: 4.0% by weight) at a liquid temperature of 70°C, uniaxial stretching was carried out in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds so that the total stretching ratio Up to 5.5 times (extended treatment in water). Thereafter, the laminate was immersed in a cleaning bath (an 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. (washing treatment). Thereafter, 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 (drying shrinkage treatment). The shrinkage rate in the width direction of the laminate obtained by performing the drying shrinkage treatment was 5.2%. Through the above procedures, a polarizing film with a thickness of 5 μm was formed on the resin substrate. And a total of 9 polarizing films were produced by repeating the same procedure. 2. Fabrication of polarizing plates On the surface of each polarizing film prepared above (the side opposite to the resin substrate), an acrylic film (surface refractive index 1.50, 40 μm) was pasted through a UV-curable adhesive as a protective film. Specifically, it was applied so that the total thickness of the hardening adhesive was 1.0 μm, and bonded using a rolling mill. Thereafter, UV rays are irradiated from the protective film side to cure the adhesive. Next, after both ends were cut, the resin substrate was peeled off to obtain nine elongated polarizing plates (width: 1300 mm) having a protective film/polarizing film configuration.

[Example 2] 18 polarizing films and polarizing plates were produced in the same manner as in Example 1 except that the temperature of the oven was set to 70° C. and the temperature of the heating roller was set to 70° C. during the drying shrinkage treatment. The shrinkage rate in the width direction of the laminate obtained by performing the drying shrinkage treatment was 2.5%.

[Comparative Example 1] Potassium iodide was not added to the PVA aqueous solution (coating solution), and the stretching ratio in the air-assisted stretching process was set to 1.8 times, and no heating roller was used in the drying shrinkage process. Five polarizing films and polarizing plates were produced in the same manner as in Example 1.

[Comparative Example 2] Six polarizing films and polarizing films were produced in the same manner as in Example 1 except that the stretching ratio in the aerial auxiliary stretching process was set to 1.8 times, and no heating roller was used in the drying shrinkage process. plate.

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

The single transmittance and polarization degree were measured about each polarizing plate of an Example and a comparative example. The results are shown in Table 2 and Figure 3.

[Table 2]

The polarizing film produced by the manufacturing method of the comparative example did not satisfy the single transmittance of 44.0% or more and the polarization degree of 99.50% or more at the same time. On the other hand, the polarizing film produced by the manufacturing method of the example has excellent optical characteristics such that the single transmittance is 44.0% or more and the degree of polarization is 99.50% or more.

Regarding the polarizing plates of Example 1 and Reference Example 1, the variation in optical characteristics of the strip-shaped and sheet-shaped polarizing plates was measured. The results are listed in Table 3.

[table 3]

The variance of the individual transmittance of the strip-shaped polarizing plate prepared by the manufacturing method of the example is less than 0.3%, and the variance of the individual transmittance of the sheet-shaped polarizing plate prepared by the manufacturing method of the example is If it is less than 0.2%, the fluctuation of optical characteristics can be 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 large variations in optical characteristics regardless of whether it is in the shape of a strip or a sheet.

Industrial Applicability The polarizing plate having the polarizing film of the present invention can be suitably used as a circular polarizing plate for liquid crystal display devices, organic EL display devices, and inorganic EL display devices.

10‧‧‧Polarizing film 20‧‧‧First protective layer 30‧‧‧Second protective layer 100‧‧‧Polarizing plate 200‧‧‧Laminate 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 drying shrinkage treatment using a heating roll. Fig. 3 is a graph showing optical properties of polarizing plates produced in Examples and Comparative Examples.

10‧‧‧Polarizing film

20‧‧‧1st protective layer

30‧‧‧Second protective layer

100‧‧‧polarizer

Claims (6)

A method for manufacturing a polarizing film, which is a method for manufacturing a polarizing film with a thickness of 8 μm or less, a single transmittance of 44.0% or more, and a degree of polarization of 99.50% or more, and the method includes the following steps: A polyvinyl alcohol-based resin layer containing iodide or sodium chloride and a polyvinyl alcohol-based resin is formed on one side of the substrate to form a laminate; and, the above-mentioned laminate is sequentially subjected to air-assisted stretching and dyeing. treatment, underwater stretching treatment, and drying shrinkage treatment. The drying shrinkage treatment involves heating the above-mentioned laminate while transporting it along the longitudinal direction, thereby shrinking it by more than 2% in the width direction. The method of manufacturing a polarizing film according to claim 1, which is a method of manufacturing a polarizing film with a single transmittance of 44.5% or less and a degree of polarization of 99.95% or less. The method for producing a polarizing film according to claim 1 or 2, wherein the content of the aforementioned iodide or sodium chloride in the aforementioned polyvinyl alcohol-based resin layer is 5 parts by weight to 20 parts by weight relative to 100 parts by weight of the aforementioned polyvinyl alcohol-based resin. parts by weight. The method of manufacturing a polarizing film according to claim 1 or 2, wherein the stretching ratio in the above-mentioned air-assisted stretching process is 2.0 times or more. The method of manufacturing a polarizing film according to claim 1 or 2, wherein the drying and shrinking treatment step is a heating step using a heating roller. The method of manufacturing a polarizing film according to claim 5, wherein the temperature of the heating roller is 60°C to 120°C.

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