WO2020262067A1 - Polarizing plate and method for producing said polarizing plate - Google Patents

Abstract

The present invention provides a polarizing plate which has high single transmittance and has excellent durability in a high-temperature and high-humidity environment. A polarizing plate of the present invention includes: a polarizing film made of a polyvinyl alcohol-based resin film containing iodine; and an adjacent layer which is provided on at least one surface of the polarizing film and contains chlorine.

Description

Polarizing plate and method for manufacturing the polarizing plate

The present invention relates to a polarizing plate and a method for producing the polarizing plate.

A liquid crystal display device, which is a typical image display device, has polarizing films arranged on both sides of the liquid crystal cell due to the image forming method. As a method for producing a polarizing film, for example, a method has been proposed in which a laminate having a resin base material and a polyvinyl alcohol-based resin layer is stretched and then dyed to obtain a polarizing film on the resin base material. (For example, Patent Document 1). According to such a method, a thin polarizing film can be obtained, which is attracting attention as it can contribute to the thinning of image display devices in recent years. However, the thin polarizing film is required to have further improved durability in a high temperature and high humidity environment.

Japanese Unexamined Patent Publication No. 2001-343521

The present invention has been made to solve the above-mentioned conventional problems, and its main purpose is to provide a polarizing plate having a high single transmittance and excellent durability in a high temperature and high humidity environment, and such a polarizing plate. The present invention is to provide a method for manufacturing a polarizing plate.

According to one aspect of the present invention, a polarizing plate having a polarizing film made of a polyvinyl alcohol-based resin film containing iodine and an adjacent layer containing chlorine provided on at least one surface of the polarizing film. Is provided.
In one embodiment, the adjacent layer further comprises a polyvinyl alcohol-based resin.
In one embodiment, the concentration of chlorine in the adjacent layer is 0.3% by weight or more.
In one embodiment, the chlorine is derived from hydrogen chloride.
In one embodiment, the thickness of the polarizing film is 8 μm or less.
In one embodiment, the iodine concentration in the polarizing film is 3% by weight or more.
In one embodiment, the content of the alkali metal and the alkaline earth metal in the adjacent layer is 0.1% by weight or less.
According to another aspect of the present invention, the method for producing a polarizing plate includes applying a polyvinyl alcohol-based resin aqueous solution containing hydrogen chloride to at least one surface of a polarizing film to form an adjacent layer. A production method is provided in which the pH of the polyvinyl alcohol-based resin aqueous solution containing hydrogen chloride is 2.5 or less.

According to the present invention, it is possible to obtain a polarizing plate having a high single transmittance and excellent durability in a high temperature and high humidity environment. Such a polarizing plate can be obtained by providing a layer containing chlorine adjacent to the polarizing film.

It is the schematic sectional drawing of the polarizing plate by one Embodiment of this invention. It is the schematic sectional drawing of the polarizing plate by one Embodiment of this invention. It is the schematic which shows an example of the drying shrinkage treatment using a heating roll.

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

A. Polarizing Plate The polarizing plate according to the embodiment of the present invention has a polarizing film made of a polyvinyl alcohol-based resin film containing iodine, and an adjacent layer containing chlorine provided on at least one surface of the polarizing film. The polarizing plate may further have a protective layer, if necessary. In the embodiment of the present invention, the chlorine contained in the adjacent layer is preferably derived from hydrogen chloride, and the chlorine concentration in the adjacent layer is preferably 0.3% by weight or more. By providing such a layer adjacent to the polarizing film, the durability of the polarizing film in a high temperature and high humidity environment can be improved, and typically, ΔP, which will be described later, can be set within a predetermined range. it can. The effect of the adjacent layer can be remarkable in the thin polarizing film. The thin polarizing film has a higher iodine concentration than the thick polarizing film, the stability of iodine is insufficient, and the humidification durability tends to be insufficient. However, the humidification durability is remarkably improved by providing the adjacent layer. Can be improved.

FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 10a has a polarizing film 12 and an adjacent layer 14 provided adjacent to one surface of the polarizing film 12. Unlike the illustrated example, the adjacent layers may be provided on both sides of the polarizing film.

FIG. 2 is a schematic cross-sectional view of a polarizing plate according to another embodiment of the present invention. The polarizing plate 10b is a first arrangement of the polarizing film 12 and the adjacent layer 14 provided adjacent to one surface of the polarizing film 12 and the side opposite to the side provided with the adjacent layer 14 of the polarizing film 12. The protective layer 16 is provided with a second protective layer 18 arranged on the side opposite to the side on which the polarizing film 12 of the adjacent layer 14 is provided. One of the first protective layer 16 and the second protective layer 18 may be omitted. When the adjacent layer is provided only on one surface of the polarizing film, the protective layer on the adjacent layer side (second protective layer 18 in the illustrated example) can be typically omitted. One of the first protective layer and the second protective layer may be a resin base material used for producing the polarizing plate described in item B.

A-1. Polarizing film The polarizing film is composed of a polyvinyl alcohol (PVA) -based resin film containing iodine as described above. Preferably, the PVA-based resin constituting the PVA-based resin film (substantially, a polarizing film) contains an acetacetyl-modified PVA-based resin. With such a configuration, a polarizing film having a desired mechanical strength can be obtained. The blending amount of the acetoacetyl-modified PVA-based resin is preferably 5% by weight to 20% by weight, more preferably 8% by weight to 12% by weight, when the total PVA-based resin is 100% by weight. .. When the blending amount is in such a range, a polarizing film having more excellent mechanical strength can be obtained.

The thickness of the polarizing film is preferably 8 μm or less, more preferably 7 μm or less, further preferably 5 μm or less, and particularly preferably 3 μm or less. The lower limit of the thickness of the polarizing film can be 1 μm in one embodiment and 2 μm in another embodiment. Such a thickness is realized, for example, by producing a polarizing film using a laminate of a thermoplastic resin base material and a PVA-based resin layer coated and formed on the thermoplastic resin base material, as will be described later. obtain. When the polarizing film is made from a single PVA-based resin film, the thickness of the polarizing film can be, for example, 12 μm to 35 μm.

The iodine concentration in the polarizing film is preferably 3% by weight or more, more preferably 4% by weight to 10% by weight, and further preferably 4% by weight to 8% by weight. In addition, in this specification, "iodine concentration" means the amount of all iodine contained in a polarizing film. More specifically, the iodine in the polarizing film _{^{I -, I 2, I 3}} -, PVA / I 3 - complex, PVA / _{I 5} ^- where present in the form of such complexes, iodine concentrations herein , Means the concentration of iodine that includes all of these forms. The iodine concentration can be calculated from, for example, the fluorescence X-ray intensity by fluorescent X-ray analysis and the film (polarizing film) thickness.

The polarizing film has a simple substance transmittance of preferably 42.0% or more, more preferably 43.0% or more, and further preferably 44.0% or more. On the other hand, the simple substance transmittance is preferably 47.0% or less, more preferably 45.0% or less. A thin polarizing film having a high single transmittance may have reduced durability in a high temperature and high humidity environment. However, according to the embodiment of the present invention, when the thin polarizing film has such a high single transmittance. Even if it exists, excellent durability in a high temperature and high humidity environment can be realized. In addition, in this specification, the simple substance transmittance, the orthogonal transmittance and the degree of polarization mean the simple substance transmittance, the orthogonal transmittance and the degree of polarization before the durability test. The degree of polarization of the polarizing film is preferably 99.85% or more, more preferably 99.90% or more, and further preferably 99.95% or more. On the other hand, the degree of polarization is preferably 99.998% or less. According to the embodiment of the present invention, it is possible to achieve both a high single transmittance and a high degree of polarization as described above, and to realize excellent durability in a high temperature and high humidity environment as described later. it can. The simple substance transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and corrected for luminosity factor. The single transmittance is a value when the refractive index of one surface of the polarizing plate is converted to 1.50 and the refractive index of the other surface is converted to 1.53. The degree of polarization is typically obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured with an ultraviolet-visible spectrophotometer and corrected for luminosity factor.
Polarization degree (%) = {(Tp-Tc) / (Tp + Tc)} ^1/2 x 100

In one embodiment, the transmittance (single transmittance) of a thin polarizing film of 8 μm or less is typically a polarizing film (refractive index of the surface: 1.53) and a protective layer (protective film) (refraction). The laminate with the rate: 1.50) is measured using an ultraviolet-visible spectrophotometer. Depending on the refractive index of the surface of the polarizing film and / or the refractive index of the surface of the protective layer in contact with the air interface, the reflectance at the interface of each layer may change, and as a result, the measured value of transmittance may change. .. Therefore, for example, when a protective layer having a refractive index of not 1.50 is used, the measured value of the transmittance may be corrected according to the refractive index of the surface of the protective layer in contact with the air interface. Specifically, the correction value C of the transmittance with reflectance R _{1 (transmission} axis reflectance) of light polarized parallel to the transmission axis at the interface between the protective layer and the air layer is expressed by the following equation.
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 transmittance of the transmission axis when a protective layer having a refractive index of 1.50 is used, n ₁ is the refractive index of the protective layer to be used, and T ₁ is the transmittance of the polarizing film. Is. For example, when a base material having a surface refractive index of 1.53 (cycloolefin film, film with a hard coat layer, etc.) is used as the protective layer, the correction amount C is about 0.2%. In this case, by adding 0.2% to the transmittance obtained by the measurement, the transmittance when a polarizing film having a surface refractive index of 1.53 is used and a protective layer having a refractive index of 1.50 is used. It can be converted into a rate. According to the calculation based on the above formula, the amount of change in the correction value C when the transmittance T _{1 of the} polarizing film is changed by 2% is 0.03% or less, and the transmittance of the polarizing film is the correction value C. The effect on the value of is limited. Further, when the protective layer has absorption other than surface reflection, appropriate correction can be performed according to the amount of absorption.

In one embodiment, the amount of change ΔP in the degree of polarization of the polarizing film after a durability test at a temperature of 60 ° C. and a relative humidity of 95% for 240 hours is typically −0.05% or more, preferably − It can be 0.03% or more, more preferably −0.01% or more. The amount of change ΔP in the degree of polarization is expressed by the following equation.
ΔP = P ₂₄₀ −P ₀
(In the formula, P ₂₄₀ is the degree of polarization after the durability test, and P ₀ is the degree of polarization before the durability test (the degree of polarization described above)).

The polarizing film may be produced by using a single PVA-based resin film, or may be produced by using a laminate of two or more layers including a PVA-based resin layer. Specific examples of the polarizing film obtained by using the laminate include a polarizing film obtained by using a laminate of a thermoplastic resin base material and a PVA-based resin layer coated and formed on the thermoplastic resin base material. .. Details of the method for producing such a polarizing film will be described later in Section B.

A-2. Adjacent Layer Adjacent layers contain chlorine and typically further contain a base resin for forming the layer. In the adjacent layer, chlorine may be contained in the form of a chlorine-containing compound, may be contained in the form of chlorine ions derived from the chlorine-containing compound, or both.

The concentration of chlorine in the adjacent layer is preferably 0.3% by weight or more, more preferably 0.5% by weight to 10.0% by weight, and further preferably 1.0% by weight to 8.0% by weight. When the chlorine concentration is within the above range, a polarizing film having excellent durability in a high temperature and high humidity environment can be preferably obtained. The concentration of chlorine in the adjacent layer can be calculated from, for example, the fluorescence X-ray intensity by fluorescent X-ray analysis and the thickness of the adjacent layer.

The chlorine contained in the adjacent layer is preferably derived from a chlorine-containing compound other than the chloride of an alkali metal or an alkaline earth metal. Specifically, the content (total content) of the alkali metal and the alkaline earth metal in the adjacent layer is typically 0.1% by weight or less, preferably 0.05% by weight or less.

As the chlorine-containing compound from which chlorine contained in the adjacent layer is derived, an acid containing chlorine (preferably a strong acid with pKa <0) such as hydrogen chloride and oxo acid of chlorine (for example, chloric acid and perchloric acid) is preferable. It can be exemplified. Of these, hydrogen chloride can be preferably used. By providing such a layer containing an acid adjacent to the polarizing film, it is considered that the effect of the present invention is exhibited through the action of protons (H ⁺ ) derived from the acid. Therefore, the effect of the present invention can be preferably obtained by blending an acid containing chlorine so that the chlorine concentration in the adjacent layer is within the above-mentioned preferable range.

Examples of the base resin include water-soluble resins such as PVA-based resins and acrylic resins. Of these, PVA-based resins can be preferably used. The PVA-based resin has excellent adhesion to the polarizing film, can easily form an aqueous solution having excellent operability, and can impart appropriate mechanical strength to the obtained adjacent layer. As the PVA-based resin, any suitable PVA-based resin can be used. Examples of the PVA-based resin include those described later in Section B-1-1 regarding the method for producing a polarizing plate.

The thickness of the adjacent layer can be preferably 0.1 μm or more, more preferably 0.3 μm or more, and further preferably 0.5 μm or more. If the adjacent layer is too thin, the effect of improving durability in a high temperature and high humidity environment may be insufficient. On the other hand, the thickness of the adjacent layer can be 3 μm or less.

A-3. Protective Layer The first and second protective layers are formed of any suitable film that can be used as a protective layer for the polarizing film. Specific examples of the material that is the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based. , Polystyrene-based, polycarbonate-based, polyolefin-based, (meth) acrylic-based, acetate-based transparent resins and the like. Further, thermosetting resins such as (meth) acrylic, urethane, (meth) acrylic urethane, epoxy, and silicone, or ultraviolet curable resins can also be mentioned. In addition to this, for example, glassy polymers such as siloxane-based polymers can also be mentioned. Further, the polymer film described in JP-A-2001-343529 (WO01 / 37007) can also be used. As the material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain. Can be used, and examples thereof include a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer. The polymer film can be, for example, an extruded product of the above resin composition.

The thickness of the protective layer (outer protective layer) arranged on the opposite side of the display panel when the polarizing plate is applied to the image display device is typically 300 μm or less, preferably 100 μm or less, and more preferably 5 μm. It is ~ 80 μm, more preferably 10 μm to 60 μm. When the surface treatment is applied, the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.

The thickness of the protective layer (inner protective layer) arranged on the display panel side when the polarizing plate is applied to the image display device is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and further preferably 10 μm to 60 μm. .. In one embodiment, the inner protective layer is a retardation layer with any suitable retardation value. In this case, the in-plane retardation Re (550) of the retardation layer is, for example, 110 nm to 150 nm. “Re (550)” is an in-plane phase difference measured with light having a wavelength of 550 nm at 23 ° C., and is obtained by the formula: Re = (nx−ny) × d. Here, "nx" is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow-phase axis direction), and "ny" is the in-plane direction orthogonal to the slow-phase axis (that is, phase-advance). It is the refractive index in the axial direction), “nz” is the refractive index in the thickness direction, and “d” is the thickness (nm) of the layer (film).

B. Method for Producing Polarizing Plate The method for producing a polarizing plate according to the embodiment of the present invention includes applying an aqueous solution of a PVA-based resin containing hydrogen chloride to at least one surface of a polarizing film to form an adjacent layer. The pH of the aqueous resin solution is preferably 2.5 or less. According to the method for producing a polarizing plate of the present embodiment, the polarizing plate according to Item A can be preferably obtained.

B-1. Method for manufacturing a polarizing plate using a laminated body In the method for manufacturing a polarizing plate according to one embodiment of the present invention, a PVA-based resin layer is formed on one side of a long thermoplastic resin base material to form a laminated body. , The laminate is stretched and dyed to form the PVA-based resin layer as a polarizing film, and an aqueous PVA-based resin containing hydrogen chloride is applied to at least one surface of the polarizing film to form an adjacent layer. Including forming. By applying the above PVA-based resin aqueous solution to form an adjacent layer containing chlorine, a polarizing plate having excellent durability in a high-temperature and high-humidity environment can be realized. Preferably, the laminated body is subjected to an aerial auxiliary stretching treatment, a dyeing treatment, and an underwater stretching treatment in this order to form a PVA-based resin layer into a polarizing film. The manufacturing method can further include performing a drying shrinkage treatment of shrinking the laminate in the width direction by 2% or more by heating the laminated body after the stretching treatment in water while transporting it in the longitudinal direction. In this case, the application of the PVA-based resin aqueous solution containing hydrogen chloride may be performed after the underwater stretching treatment and before the drying shrinkage treatment, or after the drying shrinkage treatment.

B-1-1. Preparation of Laminate As a method for preparing a laminate of a thermoplastic resin base material and a PVA-based resin layer, any appropriate method can be adopted. Preferably, a coating liquid containing a PVA-based resin is applied to the surface of the thermoplastic resin base material and dried to form a PVA-based resin layer on the thermoplastic resin base material.

Any appropriate method can be adopted as the application method of the coating liquid. 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 knife coating method (comma coating method, etc.) and the like can be mentioned. The coating / drying temperature of the coating liquid is preferably 50 ° C. or higher.

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

Before forming the PVA-based resin layer, the thermoplastic resin base material may be surface-treated (for example, corona treatment or the like), or the easy-adhesion layer may be formed on the thermoplastic resin base material. By performing such a treatment, the adhesion between the thermoplastic resin base material and the PVA-based resin layer can be improved.

Any suitable thermoplastic resin film can be adopted as the thermoplastic resin base material. Details of the thermoplastic resin base material are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. The entire description of the publication is incorporated herein by reference. A polyester resin is preferably used, and a polyethylene terephthalate resin is more preferable.

The coating liquid contains PVA-based resin. Typically, the coating liquid is a solution in which a PVA-based resin is dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, the solvent is preferably water.

Any suitable resin can be used as the PVA-based resin. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymers can be mentioned. Polyvinyl alcohol is obtained by saponification of polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying the ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. .. The degree of saponification can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a degree of saponification, a polarizing film having excellent durability can be obtained. If 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 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average degree of polymerization can be determined according to JIS K 6726-1994.

The PVA-based resin preferably contains an acetoacetyl-modified PVA-based resin. With such a configuration, a polarizing film having a desired mechanical strength can be obtained. The blending amount of the acetoacetyl-modified PVA-based resin is preferably 5% by weight to 20% by weight, more preferably 8% by weight to 12% by weight, when the total PVA-based resin is 100% by weight. .. When the blending amount is in such a range, a polarizing film having more excellent mechanical strength can be obtained.

The PVA-based resin concentration in the coating liquid is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film that adheres to the thermoplastic resin base material can be formed.

The coating liquid preferably further contains a halide. As the halide, any suitable halide can be adopted. For example, iodide and sodium chloride. Iodides include, for example, potassium iodide, sodium iodide, and lithium iodide. Of these, potassium iodide is preferred.

The amount of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, and more preferably 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the PVA-based resin. It is a department. If the amount of the halide exceeds 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, the halide may bleed out and the finally obtained polarizing film may become cloudy.

Generally, when the PVA-based resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA-based resin is increased. However, when the stretched PVA-based resin layer is immersed in a liquid containing water, the polyvinyl alcohol molecules become more oriented. The orientation may be disturbed and the orientation may decrease. In particular, when the laminate of the thermoplastic resin base material and the PVA-based resin layer is stretched in boric acid water, the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin base material. In the case of stretching, the tendency of the degree of orientation to decrease is remarkable. For example, while stretching a PVA film alone in boric acid water is generally performed at 60 ° C., stretching of a laminate of A-PET (thermoplastic resin base material) and a PVA-based resin layer is performed. It is carried out at a high temperature of about 70 ° C., and in this case, the orientation of PVA at the initial stage of stretching may decrease before it is increased by stretching in water. On the other hand, a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin base material is prepared, and the laminate is stretched at a high temperature (auxiliary stretching) in air before being stretched in boric acid water. , Crystallization of the PVA-based resin in the PVA-based resin layer of the laminated body after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This makes it possible to improve the optical characteristics of the polarizing film obtained through a treatment step of immersing the laminate in a liquid, such as a dyeing treatment and a stretching treatment in water.

Additives may be further added to the coating liquid. Examples of the additive include a plasticizer, a surfactant and the like. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. Examples of the surfactant include nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability, and stretchability of the obtained PVA-based resin layer.

B-1-2. Aerial Auxiliary Stretching Treatment In particular, in order to obtain high optical properties, a two-stage stretching method that combines dry stretching (auxiliary stretching) and water stretching (preferably boric acid water stretching) is selected. By introducing auxiliary stretching as in the case of two-stage stretching, the thermoplastic resin base material can be stretched while suppressing crystallization, and the thermoplastic resin can be stretched in water (preferably boric acid in water). The problem that the stretchability is lowered due to excessive crystallization of the base material can be solved, and the laminate can be stretched at a higher magnification. Furthermore, when the PVA-based resin is applied on the thermoplastic resin base material, it is compared with the case where the PVA-based resin is applied on a normal metal drum in order to suppress the influence of the glass transition temperature of the thermoplastic resin base material. Therefore, it is necessary to lower the coating temperature, and as a result, the crystallization of the PVA-based resin becomes relatively low, which may cause a problem that sufficient optical characteristics cannot be obtained. On the other hand, by introducing the auxiliary stretching, even when the PVA-based resin is applied on the thermoplastic resin base material, the crystallinity of the PVA-based resin can be enhanced, and high optical characteristics can be achieved. It will be possible. At the same time, by increasing the orientation of the PVA resin in advance, it is possible to prevent problems such as deterioration and dissolution of the orientation of the PVA resin when immersed in water in a subsequent dyeing step or stretching step. , It becomes possible to achieve high optical characteristics.

The stretching method of the aerial auxiliary stretching may be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). Good, but in order to obtain high optical properties, free end stretching can be positively adopted. In one embodiment, the aerial stretching treatment includes a heating roll stretching step of stretching the laminated body in the longitudinal direction due to a difference in peripheral speed between the heating rolls. The aerial stretching treatment typically includes a zone stretching step and a heating roll stretching step. The order of the zone stretching step and the heating roll stretching step is not limited, and the zone stretching step may be performed first, or the heating roll stretching step may be performed first. The zone stretching step may be omitted. In one embodiment, the zone stretching step and the heating roll stretching step are performed in this order. Further, in another embodiment, in the tenter stretching machine, the film is stretched by grasping the end portion of the film and widening the distance between the tenters in the flow direction (the widening of the distance between the tenters is the stretching ratio). At this time, the distance of the tenter in the width direction (perpendicular to the flow direction) is set to approach arbitrarily. Preferably, it can be set to be closer to the free end stretch with respect to the stretch ratio in the flow direction. In the case of free end stretching, the shrinkage rate in the width direction = (1 / stretching ratio) ^1/2 .

The aerial auxiliary extension may be performed in one step or in multiple steps. When performed in multiple stages, the draw ratio is the product of the draw ratios of each stage. The stretching direction in the aerial auxiliary stretching is preferably substantially the same as the stretching direction in the underwater stretching.

The draw ratio in the aerial auxiliary stretching is preferably 2.0 to 3.5 times. The maximum draw ratio when the aerial auxiliary stretching and the underwater stretching are combined is preferably 5.0 times or more, more preferably 5.5 times or more, still more preferably 6.0 times, the original length of the laminated body. That is all. In the present specification, the "maximum draw ratio" means the draw ratio immediately before the laminate breaks, and separately confirms the draw ratio at which the laminate breaks, and means a value 0.2 lower than that value.

The stretching temperature of the aerial auxiliary stretching can be set to an arbitrary appropriate value depending on the forming material of the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably the glass transition temperature (Tg) or more of the thermoplastic resin base material, more preferably the glass transition temperature (Tg) of the thermoplastic resin base material (Tg) + 10 ° C. or higher, and particularly preferably Tg + 15 ° C. or higher. On the other hand, the upper limit of the stretching temperature is preferably 170 ° C. By stretching at such a temperature, it is possible to suppress the rapid progress of crystallization of the PVA-based resin and suppress defects due to the crystallization (for example, hindering the orientation of the PVA-based resin layer due to stretching). it can.

B-1-3. Insolubilization treatment, dyeing treatment and cross-linking treatment If necessary, an insolubilization treatment is performed after the aerial auxiliary stretching treatment and before the underwater stretching treatment or the dyeing treatment. The insolubilization treatment is typically performed by immersing a PVA-based resin layer in an aqueous boric acid solution. The dyeing treatment is typically performed by dyeing the PVA-based resin layer with iodine. If necessary, a cross-linking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The cross-linking treatment is typically performed by immersing a PVA-based resin layer in an aqueous boric acid solution. Details of the insolubilization treatment, the dyeing treatment and the crosslinking treatment are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580.

B-1-4. Underwater stretching treatment The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the thermoplastic resin base material or the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically about 80 ° C.), and the PVA-based resin layer is crystallized. Can be stretched at a high magnification while suppressing the above. As a result, a polarizing film having excellent optical characteristics can be produced.

Any appropriate method can be adopted as the stretching method of the laminated body. Specifically, it may be fixed-end stretching or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). Preferably, free end stretching is selected. The stretching of the laminate may be carried out in one step or in multiple steps. When performed in multiple stages, the draw ratio (maximum draw ratio) of the laminate described later is the product of the draw ratios of each stage.

The underwater stretching is preferably carried out by immersing the laminate in a boric acid aqueous solution (boric acid water stretching). By using an aqueous boric acid solution as the stretching bath, it is possible to impart rigidity to withstand the tension applied during stretching and water resistance that does not dissolve in water to the PVA-based resin layer. Specifically, boric acid can generate a tetrahydroxyboric acid anion in an aqueous solution and crosslink with a PVA-based resin by hydrogen bonding. As a result, the PVA-based resin layer can be imparted with rigidity and water resistance, can be stretched satisfactorily, and a polarizing film having excellent optical characteristics can be produced.

The boric acid aqueous solution is preferably obtained by dissolving boric acid and / or borate in water as a solvent. The boric acid concentration is preferably 1 part by weight to 10 parts by weight, more preferably 2.5 parts by weight to 6 parts by weight, and particularly preferably 3 parts by weight to 5 parts by weight with respect to 100 parts by weight of water. Is. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film having higher characteristics can be produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde or the like in a solvent can also be used.

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

The stretching temperature (liquid temperature of the stretching bath) is preferably 40 ° C. to 85 ° C., more preferably 60 ° C. to 75 ° C. At such a temperature, the PVA-based resin layer can be stretched at a high magnification while suppressing dissolution. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin base material is preferably 60 ° C. or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40 ° C., it may not be stretched well even when the plasticization of the thermoplastic resin base material by water is taken into consideration. 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 possibility that excellent optical characteristics cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio by stretching in water is preferably 1.5 times or more, more preferably 3.0 times or more. The total draw ratio of the laminated body is preferably 5.0 times or more, more preferably 5.5 times or more, with respect to the original length of the laminated body. By achieving such a high draw ratio, it is possible to manufacture a polarizing film having extremely excellent optical characteristics. Such a high draw ratio can be achieved by adopting an underwater stretching method (boric acid underwater stretching).

B-1-5. Other Treatments Preferably, a washing treatment is performed after the underwater stretching treatment and before the drying shrinkage treatment. The cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution containing an iodide such as potassium iodide. The iodide concentration in the cleaning liquid is preferably 0.5% by weight to 10% by weight, preferably 0.5% by weight to 5% by weight, and more preferably 1% by weight to 4% by weight. The temperature of the cleaning liquid is usually 10 ° C to 50 ° C, preferably 20 ° C to 35 ° C. The immersion time is usually 1 second to 1 minute, preferably 10 seconds to 1 minute.

B-1-6. Drying shrinkage treatment The drying shrinkage treatment may be carried out by heating the entire zone by zone heating, or by heating the transport roll (using a so-called heating roll) (heating roll drying method). Preferably, both are used. By drying with a heating roll, it is possible to efficiently suppress the heating curl of the laminate and produce a polarizing film having an excellent appearance. Specifically, by drying the laminate along the heating roll, the crystallization of the thermoplastic resin base material can be efficiently promoted and the crystallinity can be increased, which is relatively low. Even at the drying temperature, the crystallinity of the thermoplastic resin base material can be satisfactorily increased. As a result, the rigidity of the thermoplastic resin base material is increased, and the thermoplastic resin base material is in a state where it can withstand the shrinkage of the PVA-based resin layer (polarizing film) due to drying, and curling is suppressed. Further, by using the heating roll, the laminated body can be dried while being maintained in a flat state, so that not only curling but also wrinkles can be suppressed. At this time, the optical characteristics of the polarizing film can be improved by shrinking the laminated body in the width direction by the drying shrinkage treatment. This is because the orientation of PVA and the PVA / iodine complex can be effectively enhanced. The shrinkage ratio in the width direction of the laminate by the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%.

FIG. 3 is a schematic view showing an example of the drying shrinkage treatment. In the drying shrinkage treatment, the laminate 200 is dried while being transported by the transport rolls R1 to R6 heated to a predetermined temperature and the guide rolls G1 to G4. In the illustrated example, the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA-based resin layer (polarizing film) and the surface of the thermoplastic resin base material. For example, one of the laminate 200 is provided. The transport rolls R1 to R6 may be arranged so as to continuously heat only the surface (for example, the surface of the thermoplastic resin base material).

Drying conditions can be controlled by adjusting the heating temperature of the transport roll (temperature of the heating roll), the number of heating rolls, the contact time with the heating roll, and the like. The temperature of the heating roll is preferably 60 ° C. to 120 ° C., more preferably 65 ° C. to 100 ° C., and particularly preferably 70 ° C. to 80 ° C. The crystallinity of the thermoplastic resin can be satisfactorily increased, curling can be satisfactorily suppressed, and an optical laminate having extremely excellent durability can be produced. The temperature of the heating roll can be measured with a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular limitation as long as there are a plurality of transport rolls. The number of transport rolls is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roll is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and further preferably 1 to 10 seconds.

The heating roll may be provided in a heating furnace (for example, an oven) or in a normal production line (in a room temperature environment). Preferably, it is provided in a heating furnace provided with a blowing means. By using the drying with a heating roll and the hot air drying together, it is possible to suppress a steep temperature change between the heating rolls, and it is possible to easily control the shrinkage in the width direction. The temperature of hot air drying is preferably 30 ° C to 100 ° C. The hot air drying time is preferably 1 second to 300 seconds. The wind speed of hot air is preferably about 10 m / s to 30 m / s. The wind speed is the wind speed in the heating furnace and can be measured by a mini-vane type digital anemometer.

B-1-7. Formation of Adjacent Layer A PVA-based resin aqueous solution containing hydrogen chloride is applied to the surface of the polarizing film of the laminate (polarizing plate) of the thermoplastic resin base material and the polarizing film obtained as described above to form an adjacent layer. Form. As a result, a laminate (polarizing plate) of a thermoplastic resin base material / polarizing film / adjacent layer can be obtained. In this case, typically, the thermoplastic resin base material can be used as it is as the protective layer of the polarizing film. In another embodiment, a resin film (which serves as a protective layer) is bonded to the surface of the polarizing film of the laminate of the thermoplastic resin base material and the polarizing film to form a laminated body of the protective layer / polarizing film / thermoplastic resin base material. Is prepared, and the thermoplastic resin base material is peeled off from the laminated body to prepare a laminated body (polarizing plate) of a protective layer / polarizing film. A PVA-based resin aqueous solution containing hydrogen chloride is applied to the surface of the polarizing film of the obtained polarizing plate. As a result, a laminated body (polarizing plate) of the protective layer / polarizing film / adjacent layer can be obtained.

The PVA-based resin aqueous solution is typically an aqueous solution in which hydrogen chloride and PVA-based resin are dissolved in water. The PVA-based resin is as described in Section B-1-1.

The concentration of the PVA-based resin in the above-mentioned PVA-based resin aqueous solution can be set in consideration of operability (coatability). The concentration can be adjusted, for example, so that the viscosity of the PVA-based resin aqueous solution is 1 mPa · sec to 300 mPa · sec. The concentration of the PVA-based resin in the PVA-based resin aqueous solution can be, for example, 0.1% by weight to 15% by weight, more preferably 0.5% by weight to 10% by weight.

The concentration of hydrogen chloride in the PVA-based resin aqueous solution is appropriately set in consideration of the chlorine concentration desired for the adjacent layer (in other words, the proton (H ⁺ ) concentration desired for the adjacent layer). The pH of the PVA-based resin aqueous solution is preferably 2.5 or less, more preferably 2.0 or less, still more preferably 1.5 or less. The lower limit of the pH of the PVA-based resin aqueous solution is not particularly limited, but may be 0.5 or more in consideration of leaving stability.

The adjacent layer is formed by applying the above PVA-based resin aqueous solution to the surface of the polarizing film and drying it if necessary. As the coating method, any appropriate method can be adopted. As a specific example, the method described in Section B-1-1 can be mentioned as a method of applying a coating liquid for forming a PVA-based resin layer (polarizing film). The drying temperature is, for example, 40 ° C. to 100 ° C., and the drying time is, for example, 1 minute to 20 minutes.

B-2. Method for manufacturing a polarizing plate using a single PVA-based resin film In Section B-1, a polarizing plate using a laminate of a thermoplastic resin base material and a PVA-based resin layer coated and formed on the thermoplastic resin base material is manufactured. Although the method has been described, the present invention can also be applied to a method for producing a polarizing plate using a single PVA-based resin film. In such a production method, typically, a PVA-based resin film having self-supporting property is stretched and dyed to form the PVA-based resin film as a polarizing film, and a PVA-based resin aqueous solution containing hydrogen chloride is used. Is applied to at least one surface of the polarizing film to form an adjacent layer. More specifically, a long PVA-based resin film is uniaxially stretched in the long direction by a roll stretching machine and subjected to swelling, dyeing, cross-linking, and cleaning treatment to prepare a polarizing film, and after the cleaning treatment. A PVA-based resin aqueous solution containing hydrogen chloride is applied to the polarizing film. The application of the PVA-based resin aqueous solution containing hydrogen chloride can be carried out in the same manner as in Item B-1-7.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows. Unless otherwise specified, "parts" and "%" in Examples and Comparative Examples are based on weight.
(1) Thickness The polarizing plates of Examples and Comparative Examples were cut, the cross section of the polarizing plate was observed using a scanning electron microscope (“JSM7100F” manufactured by JEOL Ltd.), and the thickness of the adjacent layer was measured. The thickness of the polarizing film was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000").
(2) Single-unit transmittance, orthogonal transmittance and degree of polarization Regarding the polarizing plates of Examples and Comparative Examples (for single-unit transmittance, a laminate having a protective layer / polarizing film structure), an ultraviolet-visible spectrophotometer (Otsuka Denshi) The single transmittance Ts, the parallel transmittance Tp, and the orthogonal transmittance Tc measured using LPF200) manufactured by the same company were defined as Ts, Tp, and Tc of the polarizing film, respectively. These Ts, Tp, and Tc are Y values measured by the JIS Z8701 two-degree visual field (C light source) and corrected for luminosity factor. From the obtained Tp and Tc, the degree of polarization was determined using the following formula.
Polarization degree (%) = {(Tp-Tc) / (Tp + Tc)} ^1/2 x 100
Next, glass from which the alkaline component has been removed (non-alkali glass) is attached to the adjacent layer side of the polarizing plate via an adhesive, and the glass is placed in an oven set at a temperature of 60 ° C. and a relative humidity of 95% for 240 hours. A durability test was performed, and the degree of polarization P ₂₄₀ after the durability test was determined in the same manner as described above.
(3) Chlorine concentration (Cl concentration) in the adjacent layer
The chlorine concentration in the film (adjacent layer) is determined by the following procedure using a scanning fluorescent X-ray analyzer (ZSX PRIMUS IV manufactured by Rigaku): First, thickness (μm), chlorine concentration (% by weight). Measures the fluorescent X-ray intensity (kcps) of a known sample (for example, a PVA-based resin film to which a certain amount of NaCl is added) to prepare a calibration curve. The calibration curve of the chlorine concentration in the film is expressed by the following formula:
(Chlorine concentration) = A × (Fluorescent X-ray intensity) / (Film thickness) -B
Here, A and B are constants that differ depending on the measuring device. For example, when ZSX PRIMUS IV (measurement sample diameter: 30 mm) is used as the measuring device, A is "0.0024" and B is "0.0012".
(4) Sodium concentration (Na concentration) in the adjacent layer
The sodium concentration in the film (adjacent layer) is determined by the following procedure using a scanning fluorescent X-ray analyzer (ZSX PRIMUS IV manufactured by Rigaku): First, thickness (μm), sodium concentration (% by weight). Measures the fluorescent X-ray intensity (kcps) of a known sample (for example, a PVA-based resin film to which a certain amount of NaCl is added) to prepare a calibration curve. The calibration curve of the sodium concentration in the film is expressed by the following formula:
(Sodium concentration) = A × (Fluorescent X-ray intensity) / (Film thickness) -B
Here, A and B are constants that differ depending on the measuring device. For example, when ZSX PRIMUS IV (measurement sample diameter: 30 mm) is used as the measuring device, A is "0.0054" and B is "0.0027".

[Example 1-1]
As the thermoplastic resin base material, an amorphous isophthal copolymer polyethylene terephthalate film (thickness: 100 μm) having a long shape and a Tg of about 75 ° C. was used, and one side of the resin base material was subjected to corona treatment.
100 parts by weight of PVA-based resin in which polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimmer") are mixed at a ratio of 9: A PVA aqueous solution (coating solution) was prepared by dissolving 13 parts by weight of potassium iodide in water.
The PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60 ° C. to form a PVA-based resin layer having a thickness of 13 μm to prepare a laminate.
The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (longitudinal direction) in an oven at 130 ° C. (aerial auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath at a liquid temperature of 40 ° C. (an aqueous boric acid solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).
Next, the polarizing plate finally obtained is placed in a dyeing bath having a liquid temperature of 30 ° C. (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water). Immersion was carried out for 60 seconds while adjusting the concentration so that the simple substance transmittance (Ts) was 44.0% (dyeing treatment).
Next, it was immersed in a cross-linked bath at a liquid temperature of 40 ° C. (an aqueous boric acid solution obtained by blending 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. (Crossing treatment).
Then, while immersing the laminate in a boric acid aqueous solution (boric acid concentration 4% by weight, potassium iodide concentration 5% by weight) at a liquid temperature of 70 ° C., the total in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds. Uniaxial stretching was performed so that the stretching ratio was 5.5 times (underwater stretching treatment).
Then, the laminate was immersed in a washing bath at a liquid temperature of 20 ° C. (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment).
Then, while drying in an oven kept at about 90 ° C., it was brought into contact with a heating roll made of SUS whose surface temperature was kept at about 75 ° C. (dry shrinkage treatment). The shrinkage rate in the width direction of the laminate by the drying shrinkage treatment was 2%.
In this way, a polarizing film having a thickness of 5.0 μm is formed on the resin base material, and a cycloolefin-based film (manufactured by ZEON, product name “G-Film”) as a protective layer (protective film) is formed on the surface of the polarizing film. ) Was bonded with a UV curable adhesive (thickness 1.0 μm), and then the resin base material was peeled off to obtain a laminate having a protective layer / polarizing film structure. The simple substance transmittance (Ts) of the obtained laminated body is 44.0%, because the surface refractive index of the polarizing film / protective layer constituting the laminated body is 1.53 / 1.53. , The value is corrected by + 0.2% to the actual measured value and converted into the state of 1.53 / 1.50.
Next, a PVA-based resin aqueous solution containing hydrogen chloride (HCl-containing PVA aqueous solution) was applied to the surface of the polarizing film of the laminate. The HCl-containing PVA aqueous solution contained 0.7% by weight of hydrogen chloride and 3.5% by weight of polyvinyl alcohol (degree of polymerization 2600, degree of saponification 99.98 mol%), and had a pH of 0.9. The coating film of the HCl-containing PVA aqueous solution was dried at 60 ° C. for 5 minutes to form an adjacent layer having a thickness of 0.4 μm to obtain a polarizing plate having a protective layer / polarizing film / adjacent layer structure.

Table 1 shows the Cl concentration and Na concentration in the ΔP and the adjacent layer of the obtained polarizing plate (substantially, the polarizing film).

[Example 1-2]
A polarizing plate was prepared in the same manner as in Example 1-1 except that the HCl-containing PVA aqueous solution was applied so that the thickness of the adjacent layer was 1.2 μm. For the obtained polarizing plate (substantially, a polarizing film), the Cl concentration and Na concentration in ΔP and the adjacent layer are shown in Table 1.

[Example 2-1]
The HCl-containing PVA aqueous solution was applied so that the pH of the HCl-containing PVA aqueous solution was 1.2 (the hydrogen chloride concentration in the HCl-containing PVA aqueous solution was 0.35% by weight) and the thickness of the adjacent layer was 1.2 μm. A polarizing plate was prepared in the same manner as in Example 1-1 except for the above. For the obtained polarizing plate (substantially, a polarizing film), the Cl concentration and Na concentration in ΔP and the adjacent layer are shown in Table 1.

[Example 2-2]
The HCl-containing PVA aqueous solution was applied so that the pH of the HCl-containing PVA aqueous solution was 1.6 (the hydrogen chloride concentration in the HCl-containing PVA aqueous solution was 0.15% by weight) and the thickness of the adjacent layer was 1.1 μm. A polarizing plate was prepared in the same manner as in Example 1-1 except for the above. For the obtained polarizing plate (substantially, a polarizing film), the Cl concentration and Na concentration in ΔP and the adjacent layer are shown in Table 1.

[Example 2-3]
The HCl-containing PVA aqueous solution was applied so that the pH of the HCl-containing PVA aqueous solution was set to 1.8 (hydrogen chloride concentration in the HCl-containing PVA aqueous solution was 0.09% by weight) and the thickness of the adjacent layer was 1.5 μm. A polarizing plate was prepared in the same manner as in Example 1-1 except for the above. For the obtained polarizing plate (substantially, a polarizing film), the Cl concentration and Na concentration in ΔP and the adjacent layer are shown in Table 1.

[Example 2-4]
The HCl-containing PVA aqueous solution was applied so that the pH of the HCl-containing PVA aqueous solution was 2.0 (the hydrogen chloride concentration in the HCl-containing PVA aqueous solution was 0.06% by weight) and the thickness of the adjacent layer was 1.2 μm. A polarizing plate was prepared in the same manner as in Example 1-1 except for the above. For the obtained polarizing plate (substantially, a polarizing film), the Cl concentration and Na concentration in ΔP and the adjacent layer are shown in Table 1.

[Comparative Example 1]
The HCl-containing PVA aqueous solution was applied so that the pH of the HCl-containing PVA aqueous solution was 3.1 (the hydrogen chloride concentration in the HCl-containing PVA aqueous solution was 0.02% by weight) and the thickness of the adjacent layer was 1.2 μm. A polarizing plate was prepared in the same manner as in Example 1-1 except for the above. For the obtained polarizing plate (substantially, a polarizing film), the Cl concentration and Na concentration in ΔP and the adjacent layer are shown in Table 1.

[Comparative Example 2]
NaCl-containing PVA aqueous solution (pH = 6.3) containing 0.2% by weight of sodium chloride and 3.5% by weight of polyvinyl alcohol (polymerization degree 2600, saponification degree 99.98 mol%) instead of HCl-containing PVA aqueous solution. ) Was used, and a NaCl-containing PVA aqueous solution was applied so that the thickness of the adjacent layer was 1.2 μm. A polarizing plate was prepared in the same manner as in Example 1-1. For the obtained polarizing plate (substantially, a polarizing film), the Cl concentration and Na concentration in ΔP and the adjacent layer are shown in Table 1.

[Reference example]
A polarizing plate having a protective layer / polarizing film configuration (Ts: 44) in the same manner as in Example 1-1 except that the HCl-containing PVA aqueous solution was not applied (as a result, an adjacent layer was not formed). 0.0%) was obtained. Table 1 shows ΔP of the obtained polarizing plate (substantially, a polarizing film). The degree of polarization P ₀ of the obtained polarizing plate (substantially a polarizing film) before the durability test was 99.90%, which is the polarizing plate of Examples and Comparative Examples provided with the adjacent layer. It was almost the same value as P ₀ of.

As is clear from Table 1, the polarizing plate of the embodiment of the present invention has excellent durability in a high temperature and high humidity environment.

The polarizing plate of the present invention is suitably used for a liquid crystal display device.

10 Polarizing plate 12 Polarizing film 14 Adjacent layer 16 First protective layer 18 Second protective layer

Claims (8)

1. A polarizing plate having a polarizing film made of a polyvinyl alcohol-based resin film containing iodine and an adjacent layer containing chlorine provided on at least one surface of the polarizing film.
2. The polarizing plate according to claim 1, wherein the adjacent layer further contains a polyvinyl alcohol-based resin.
3. The polarizing plate according to claim 1 or 2, wherein the concentration of chlorine in the adjacent layer is 0.3% by weight or more.
4. The polarizing plate according to any one of claims 1 to 3, wherein the chlorine is derived from hydrogen chloride.
5. The polarizing plate according to any one of claims 1 to 4, wherein the thickness of the polarizing film is 8 μm or less.
6. The polarizing plate according to any one of claims 1 to 5, wherein the iodine concentration in the polarizing film is 3% by weight or more.
7. The polarizing plate according to any one of claims 1 to 6, wherein the content of the alkali metal and the alkaline earth metal in the adjacent layer is 0.1% by weight or less.
8. The method for manufacturing a polarizing plate according to any one of claims 1 to 7.
   Including applying a polyvinyl alcohol-based resin aqueous solution containing hydrogen chloride to at least one surface of a polarizing film to form an adjacent layer.
   A production method in which the pH of the polyvinyl alcohol-based resin aqueous solution containing hydrogen chloride is 2.5 or less.

Images