WO2019054273A1

WO2019054273A1 - Polarizing plate, polarizing plate roll, and method for producing polarizing film

Info

Publication number: WO2019054273A1
Application number: PCT/JP2018/033045
Authority: WO
Inventors: 後藤　周作; 幸佑 ▲高▼永; 亮嶋津
Original assignee: 日東電工株式会社
Priority date: 2017-09-13
Filing date: 2018-09-06
Publication date: 2019-03-21
Also published as: CN118311705A; TW201921053A; TWI775940B

Abstract

Provided is a polarizing plate that exhibits excellent optical properties and for which variability in the optical properties is suppressed. The polarizing plate according to the present invention is a polarizing plate that has a polarizing film having a thickness of not more than 8 μm, a single transmittance of at least 46%, and a degree of polarization of at least 92%, and that has a protective layer disposed on at least one side of the polarizing film, wherein the difference between the maximum value and the minimum value of the single transmittance in a 50 cm2 region is not more than 0.3%. Another polarizing plate according to the present invention is a polarizing plate that has a polarizing film having a thickness of not more than 8 μm, a single transmittance of at least 46%, and a degree of polarization of at least 92%, and that has a protective layer disposed on at least one side of the polarizing film, wherein the polarizing plate has a width of at least 1000 mm and the difference between the maximum value and the minimum value of the single transmittance at locations along the width direction is not more than 0.7%.

Description

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

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

With the spread of thin displays, displays (OLEDs) on which organic EL panels are mounted and displays (QLEDs) using display panels using inorganic light emitting materials such as quantum dots have been proposed. These panels have highly reflective metal layers and are prone to problems such as external light reflection and background reflection. Therefore, it is known to prevent these problems by providing a circularly polarizing plate having a polarizing film and a λ / 4 plate on the viewing side. As a method for producing a polarizing film, for example, there is a method of stretching a laminate having a resin base and a polyvinyl alcohol (PVA) based resin layer and then subjecting it to a dyeing treatment to obtain a polarizing film on the resin base It is proposed (for example, patent document 1). According to such a method, since a thin polarizing film can be obtained, it is noted that it can contribute to thinning of the image display apparatus in recent years. However, the conventional thin polarizing film as described above has insufficient optical characteristics, and further improvement of the optical characteristics of the thin polarizing film is required.

JP 2001-343521 A

The present invention has been made to solve the above-described conventional problems, and its main object is to provide a polarizing plate, a polarizing plate roll, and a polarizing plate having excellent optical properties and suppressing variation in optical properties. It is an object of the present invention to provide a method of producing a membrane.

The polarizing plate of the present invention has a thickness of 8 μm or less, a single transmittance of 46% or more, and a polarizing film having a polarization degree of 92% or more, and a protective layer disposed on at least one side of the polarizing film. The difference between the maximum value and the minimum value of the single transmittance in the region of 50 cm ² is 0.3% or less.
Another polarizing plate of the present invention is disposed on at least one side of a polarizing film having a thickness of 8 μm or less, a single transmittance of 46% or more, and a polarization degree of 92% or more. A width of at least 1000 mm, and a difference between a maximum value and a minimum value of single transmittance at a position along the width direction is 0.7% or less.
In one embodiment, the single transmittance of the polarizing film is 48% or less, and the polarization degree is 97% or less.
According to another aspect of the present invention, a polarizing plate roll is provided. The polarizing plate is formed by winding the polarizing plate in a roll shape.
According to still another aspect of the present invention, a method of producing a polarizing film is provided. This manufacturing method is a method for manufacturing a polarizing film having a thickness of 8 μm or less, a single transmittance of 46% or more, and a polarization degree of 92% or more, and one side of a long thermoplastic resin base material Forming a polyvinyl alcohol-based resin layer containing iodide or sodium chloride and a polyvinyl alcohol-based resin to form a laminate, and the above-mentioned laminate, air-assisted stretching treatment, dyeing treatment, and underwater stretching treatment And drying and shrinking treatment in which the film is shrunk by 2% or more in the width direction by heating while being conveyed in the longitudinal direction.
In one embodiment, the single transmittance of the polarizing film is 48% or less, and the polarization degree is 97% or less.
In one embodiment, the content of the iodide or sodium chloride 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 draw ratio in the above-described air-assisted 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 contraction rate in the width direction of the laminate due to the drying contraction treatment is 2% or more.

According to the present invention, it has a polarizing film having a thickness of 8 μm or less, a single transmittance of 46% or more, and a polarization degree of 92% or more, and has excellent optical characteristics and dispersion of optical characteristics. It is possible to provide a polarizing plate with suppressed.

It is a 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 process using a heating roll. It is a graph which shows the optical characteristic of the polarizing plate obtained by the Example and the comparative example.

Hereinafter, although the embodiment of the present invention is described, the present invention is not limited to these embodiments.

A. Polarizer FIG. 1 is a schematic cross-sectional view of a polarizer according to one 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 has a thickness of 8 μm or less, a single transmittance of 46% or more, and a polarization degree of 92% or more. One of the first protective layer 20 and the second protective layer 30 may be omitted. In addition, one of the first protective layer and the second protective layer may be a resin base material (described later) used for the production of the above-mentioned polarizing film.

The polarizing plate may be elongated or sheet-like. When the polarizing plate has a long shape, it is preferable that the polarizing plate be wound in a roll shape to be a polarizing plate roll. The polarizing plate has excellent optical properties and small variation in optical properties. In one embodiment, the polarizing plate has a width of 1000 mm or more, and the difference (D1) between the maximum value and the minimum value of the single transmittance at a position along the width direction is 0.7% or less. The upper limit of D1 is preferably 0.6%, more preferably 0.5%. It is preferable that D1 be as small as possible, but the lower limit is, for example, 0.01%. If D1 is within the above range, a polarizing plate having excellent optical properties can be industrially produced. In another embodiment, in the polarizing plate, the difference (D2) between the maximum value and the minimum value of the single transmittance in the region of 50 cm ² is 0.3% or less. The upper limit of D2 is preferably 0.2%, more preferably 0.15%. The smaller D2 is, the better, but the lower limit is, for example, 0.01%. If D2 is within the above range, it is possible to suppress variations in luminance on the display screen when the polarizing plate is used in the image display device.

A-1. Polarizing Film As described above, the polarizing film has a thickness of 8 μm or less, a single transmittance of 46% or more, and a polarization degree of 92% or more. In general, the single transmittance and the degree of polarization are in a trade-off relationship with each other. Increasing the single transmittance may decrease the degree of polarization, and increasing the degree of polarization may decrease the single transmittance. Therefore, conventionally, it has been difficult to put to practical use a thin polarizing film that satisfies the optical characteristics of single transmittance of 46% or more and polarization degree of 92% or more. As described above, the polarizing film according to one embodiment of the present invention has excellent optical characteristics that the single transmittance is 46% or more and the degree of polarization is 92% or more. Furthermore, by using the polarizing film of the present embodiment, it is possible to realize a polarizing plate in which variations in optical characteristics are suppressed. The realization of such a thin polarizing film (polarizing plate) is one of the results of the present invention. Such a polarizing film (polarizing plate) can be used in an image display device, and in particular, is suitably used in a circularly polarizing plate for an organic EL display device.

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

The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance of the polarizing film is preferably 48% or less. The polarization degree of the polarizing film is preferably 92.5% or more, more preferably 93% or more. On the other hand, the upper limit of the degree of polarization is preferably 97%. The single transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and subjected to visual sensitivity correction. The degree of polarization is typically determined by the following equation based on the parallel transmittance Tp and the orthogonal transmittance Tc which are measured using an ultraviolet-visible spectrophotometer and subjected to visual sensitivity 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 a laminate of a polarizing film (refractive index of the surface: 1.53) and a protective film (refractive index: 1.50). It is measured using a UV-visible spectrophotometer with the body as the measurement target. Depending on 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 at the interface of each layer may change, and as a result, the measured value of transmittance may change. . Therefore, for example, when using a protective film whose refractive index is not 1.50, the measured value of transmittance may be corrected according to the refractive index of the surface of the protective film in contact with the air interface. Specifically, the correction value C of the transmittance is expressed by the following equation using the reflectance R ₁ (transmission axis reflectance) of polarized light parallel to the transmission axis at 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 transmission axis reflectance when a protective film having a refractive index of 1.50 is used, n ₁ is the refractive index of the protective film used, and T ₁ is the transmittance of a polarizing film. It is. For example, when a substrate having a surface refractive index of 1.53 (a cycloolefin film, a film with a hard coat layer, etc.) is used as a protective film, the correction amount C is about 0.2%. In this case, by adding 0.2% to the transmittance obtained by the measurement, it is possible to convert to the transmittance when the protective film having a surface refractive index of 1.50 is used. According to the calculation based on the above equation, the change amount of the correction value C when changing the transmittance T _{1 of the} polarizing film by 2% is 0.03% or less, and the transmittance of the polarizing film is the correction value C The impact on the value of is limited. In addition, when the protective film has absorption other than surface reflection, appropriate correction can be performed according to the amount of absorption.

Any appropriate polarizing film may be employed as the polarizing film. The polarizing film can be typically produced using a laminate of two or more layers.

As a specific example of the polarizing film obtained using a laminated body, the polarizing film obtained using the laminated body of the resin base material and the PVA-type resin layer apply | coated and formed by the said resin base material is mentioned. The polarizing film obtained by using a laminate of a resin substrate and a PVA-based resin layer applied and formed on the resin substrate is, for example, applying a PVA-based resin solution to the resin substrate and drying it. Forming a PVA-based resin layer thereon to obtain a laminate of a resin substrate and a PVA-based resin layer; stretching and dyeing the laminate to make the PVA-based resin layer into a polarizing film; obtain. In the present embodiment, stretching typically includes dipping the laminate in a boric acid aqueous solution and stretching. Furthermore, stretching may optionally further comprise air-stretching the laminate at a high temperature (eg, 95 ° C. or higher) prior to stretching in an aqueous boric acid solution. The resulting laminate of resin substrate / polarizing film may be used as it is (that is, the resin substrate may be used as a protective layer of polarizing film), and the resin substrate is peeled off from the laminate of resin substrate / polarizing film Alternatively, any appropriate protective layer depending on the purpose may be laminated on the peeled surface. The details of the method for producing such a polarizing film are described, for example, in JP-A-2012-73580. The publication is incorporated herein by reference in its entirety.

In the method for producing a polarizing film of the present invention, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of a long thermoplastic resin substrate to form a laminate, The above-mentioned laminate includes, in this order, airborne auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment in which the film is shrunk by 2% or more in the width direction by heating while being conveyed in the longitudinal direction. . Thereby, it is possible to provide a polarizing film having excellent optical properties having a thickness of 8 μm or less, a single transmittance of 46% or more, and a polarization degree of 92% or more, and suppressing variation in optical properties. . That is, by introducing the auxiliary stretching, even in the case of coating PVA on a thermoplastic resin, it becomes possible to enhance the crystallinity of PVA, and it becomes possible to achieve high optical characteristics. At the same time, by raising the orientation of PVA in advance, it is possible to prevent problems such as the decrease in the orientation of PVA and the dissolution when it is immersed in water in the subsequent dyeing step or drawing step, and high optical characteristics It will be possible to achieve Furthermore, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of 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 can improve the optical properties of the polarizing film obtained through processing steps performed by immersing the laminate in a liquid, such as dyeing processing and underwater stretching processing. Furthermore, the optical characteristics can be improved by shrinking the laminate in the width direction by the drying shrinkage treatment.

A-2. Protective Layers The first and second protective layers are formed of any suitable film that can be used as a protective layer of a 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, polyether sulfone-based, and polysulfone-based Transparent resins such as polystyrenes, polynorbornenes, polyolefins, (meth) acrylics and acetates can be mentioned. In addition, thermosetting resins such as (meth) acrylic resins, urethane resins, (meth) acrylic urethane resins, epoxy resins, and silicone resins, ultraviolet curable resins, and the like can also be mentioned. Besides, for example, glassy polymers such as siloxane polymers can also be mentioned. Further, a polymer film described in JP-A-2001-343529 (WO 01/37007) can also be used. As a material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in a side chain, and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in a side chain For example, a resin composition having an alternating copolymer of isobutene and N-methyl maleimide and an acrylonitrile / styrene copolymer can be mentioned. The polymer film may be, for example, an extrusion of the resin composition.

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

The thickness of the protective layer (inner protective layer) disposed on the display panel side when the polarizing plate 100 is applied to an image display device is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and still more preferably 10 μm to 60 μm. is there. In one embodiment, the inner protective layer is a retardation layer having 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 retardation 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 (ie, the slow axis direction), and “ny” is the direction orthogonal to the in-plane slow axis (ie, the phase advance “N” 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 Film A method for producing a polarizing film according to one embodiment of the present invention is a polyvinyl alcohol comprising a halide and a polyvinyl alcohol resin (PVA resin) on one side of a long thermoplastic resin substrate By forming a base resin layer (PVA base resin layer) to form a laminate, and heating the laminate while conveying it in the air-assisted stretching treatment, dyeing treatment, underwater stretching treatment, and in the longitudinal direction And d) applying a drying shrinkage treatment to shrink in the width direction by 2% or more in this order. The content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60 ° C. to 120 ° C. The shrinkage rate in the width direction of the laminate by the drying shrinkage treatment is preferably 2% or more. According to such a manufacturing method, the polarizing film described in the above section A can be obtained. In particular, a laminate including a PVA-based resin layer containing a halide is prepared, stretching of the laminate is multistage stretching including air-assisted stretching and underwater stretching, and the laminate after stretching is heated by a heating roll. Thus, it is possible to obtain a polarizing film having excellent optical properties (typically, single transmittance and polarization degree) and suppressing variation in optical properties. Specifically, by using the heating roll in the drying and shrinking treatment step, the entire stack can be uniformly shrunk while being transported. As a result, it is possible not only to improve the optical properties of the obtained polarizing film, but also to stably produce a polarizing film having excellent optical properties, and to suppress variations in the optical properties of the polarizing film (in particular, single transmittance). can do.

B-1. Production of Laminate As a method of producing a laminate of a thermoplastic resin base material and a PVA-based resin layer, any appropriate method may be employed. Preferably, a coating solution containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin substrate and dried to form a PVA-based resin layer on the thermoplastic resin substrate. As described above, the content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

Any appropriate method can be adopted as a method of applying the coating solution. 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 (a comma coating method etc.) and the like can be mentioned. The coating / drying temperature of the coating solution is preferably 50 ° C. or more.

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

Before forming a PVA-type resin layer, you may surface-treat (for example, corona treatment etc.) to a thermoplastic resin base material, and may form an easily bonding layer on a thermoplastic resin base material. By performing such treatment, the adhesion between the thermoplastic resin substrate and the PVA-based resin layer can be improved.

B-1-1. Thermoplastic resin substrate The thickness of the thermoplastic resin substrate is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. There exists a possibility that formation of a PVA-type resin layer may become difficult as it is less than 20 micrometers. If it exceeds 300 μm, for example, in the in-water stretching process described later, the thermoplastic resin base material takes a long time to absorb water, and there is a possibility that the stretching may require an excessive load.

The thermoplastic resin substrate preferably has a water absorption of 0.2% or more, more preferably 0.3% or more. The thermoplastic resin substrate absorbs water and the water acts as a plasticizer and can be plasticized. As a result, the stretching stress can be significantly reduced and the film can be stretched at a high magnification. On the other hand, the water absorption rate of the thermoplastic resin base material is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin base material, the dimensional stability of the thermoplastic resin base material significantly decreases at the time of production, and defects such as deterioration of the appearance of the obtained polarizing film can be prevented. Moreover, it can prevent that a base material fractures at the time of extending | stretching in water, or peeling of a PVA-type resin layer from a thermoplastic resin base material. The water absorption rate of the thermoplastic resin base material can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption rate is a value determined according to JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120 ° C. or less. By using such a thermoplastic resin base material, the stretchability of a laminated body can fully be ensured, suppressing crystallization of a PVA-type resin layer. Furthermore, it is more preferable that the temperature is 100 ° C. or less, and more preferably 90 ° C. or less, in consideration of good plasticization of the thermoplastic resin base material by water and stretching in water. On the other hand, the glass transition temperature of the thermoplastic resin base material is preferably 60 ° C. or higher. By using such a thermoplastic resin base material, the thermoplastic resin base material is deformed (for example, generation of unevenness, sagging, wrinkles, etc.) when applying and drying a coating solution containing the PVA-based resin Can be prevented, and the laminate can be manufactured well. In addition, stretching of the PVA-based resin layer can be favorably performed at a suitable temperature (for example, about 60 ° C.). In addition, the glass transition temperature of a thermoplastic resin base material can be adjusted by heating using a crystallization material which introduce | transduces a modified group to a constituent material, for example. The glass transition temperature (Tg) is a value determined according to JIS K 7121.

Any appropriate thermoplastic resin may be employed as a constituent material of the thermoplastic resin base material. Examples of the thermoplastic resin include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, copolymer resins thereof, etc. Can be mentioned. Among these, norbornene resins and amorphous polyethylene terephthalate resins are preferable.

In one embodiment, amorphous (non-crystallized) polyethylene terephthalate resin is preferably used. Among them, amorphous (hard to crystallize) polyethylene terephthalate resins are particularly preferably used. Specific examples of the amorphous polyethylene terephthalate resin include a copolymer further containing isophthalic acid and / or cyclohexanedicarboxylic acid as a dicarboxylic acid, and a copolymer further containing cyclohexanedimethanol and diethylene glycol as a glycol.

In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate resin having an isophthalic acid unit. Such a thermoplastic resin base material is extremely excellent in stretchability, and crystallization at the time of stretching can be suppressed. This is considered to be due to the fact that the main chain is given a large bend by introducing an isophthalic acid unit. The polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content ratio of isophthalic acid units is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, based on the total of all the repeating units. This is because a thermoplastic resin substrate extremely excellent in stretchability can be obtained. On the other hand, the content ratio of isophthalic acid units is preferably 20 mol% or less, more preferably 10 mol% or less, based on the total of all the repeating units. By setting to such a content rate, crystallinity degree can be made to increase favorably in the below-mentioned drying shrinkage process.

The thermoplastic resin base material may be stretched in advance (before forming the PVA-based resin layer). In one embodiment, the elongated thermoplastic resin base material is stretched in the transverse direction. The lateral direction is preferably a direction orthogonal to the stretching direction of the laminate described later. In the present specification, “orthogonal” also includes the case of being substantially orthogonal. Here, “substantially orthogonal” includes the case of 90 ° ± 5.0 °, preferably 90 ° ± 3.0 °, more preferably 90 ° ± 1.0 °.

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

Any appropriate method may be employed as a method of stretching the thermoplastic resin substrate. Specifically, it may be fixed end stretching or free end stretching. The stretching method may be dry or wet. Stretching of the thermoplastic resin substrate may be performed in one step or in multiple steps. When carrying out in multiple steps, the above-mentioned draw ratio is the product of the draw ratio of each step.

B-1-2. Coating Solution The coating solution contains a halide and a PVA-based resin as described above. The coating solution is typically a solution in which the halide and the PVA resin are dissolved in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferred. The PVA-based resin concentration of the solution 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, it is possible to form a uniform coating film in close contact with the thermoplastic resin substrate. The content of the halide in the coating solution is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

You may mix | blend an additive with a coating liquid. As an additive, a plasticizer, surfactant, etc. are mentioned, for example. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. As surfactant, a nonionic surfactant is mentioned, for example. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the obtained PVA-based resin layer.

Any appropriate resin may be employed as the PVA-based resin. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer can be mentioned. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree 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 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 depending on 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.

Any appropriate halide can be adopted as the above-mentioned halide. For example, iodide and sodium chloride can be mentioned. The iodide includes, for example, potassium iodide, sodium iodide and lithium iodide. Among these, preferred is potassium iodide.

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

Generally, when the PVA-based resin layer is stretched, the orientation of polyvinyl alcohol molecules in the PVA-based resin becomes high, but when the stretched PVA-based resin layer is immersed in a liquid containing water, the polyvinyl alcohol molecule is The orientation may be disturbed and the orientation may be reduced. In particular, when a laminate of a thermoplastic resin and a PVA-based resin layer is stretched in boric acid in water, the above laminate is stretched in boric acid water at a relatively high temperature to stabilize the stretching of the thermoplastic resin, The tendency of the above-mentioned degree of orientation reduction is remarkable. For example, while stretching of 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 PVA-based resin layer is 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 drawing can be lowered before it is raised by drawing in water. On the other hand, a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate is prepared, and the laminate is subjected to high temperature stretching (auxiliary stretching) in air before stretching in boric acid water. The crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after the auxiliary stretching may be promoted. As a result, when the PVA-based resin layer is immersed in liquid, the disorder of the orientation of 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 can improve the optical properties of the polarizing film obtained through processing steps performed by immersing the laminate in a liquid, such as dyeing processing and underwater stretching processing.

B-2. Air-Assisted Stretching In particular, in order to obtain high optical properties, a two-stage stretching method is selected in which dry stretching (auxiliary stretching) and boric acid in-water stretching are combined. As in the two-stage drawing, by introducing the auxiliary drawing, the drawing can be performed while suppressing the crystallization of the thermoplastic resin base material, and the excessive crystallization of the thermoplastic resin base material in the subsequent boric acid aqueous drawing Solves the problem that the stretchability is lowered, and the laminate can be stretched at a higher magnification. Furthermore, when applying 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, compared to the case of applying a PVA-based resin on a normal metal drum 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 can not be obtained. On the other hand, by introducing the auxiliary stretching, the crystallinity of the PVA-based resin can be enhanced even when the PVA-based resin is applied on the thermoplastic resin, and high optical characteristics can be achieved. Become. At the same time, by raising the orientation of the PVA-based resin in advance, it is possible to prevent problems such as a decrease in the orientation of the PVA-based resin and dissolution when it is immersed in water in a later dyeing or drawing step. It is possible to achieve high optical properties.

The method of air-assisted 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 uniaxially stretching through a laminate between rolls having different peripheral speeds) Although good, in order to obtain high optical properties, free end stretching can be actively employed. In one embodiment, the in-air stretching process includes a heating roll stretching step of stretching by the circumferential speed difference between the heating rolls while conveying the laminate in the longitudinal direction. The air-drawing process typically includes a zone drawing process and a heating roll drawing process. The order of the zone drawing process and the heating roll drawing process is not limited, and the zone drawing process may be performed first, and the heating roll drawing process 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. In another embodiment, in the tenter stretching machine, the film end is gripped and stretched by extending the distance between the tenters in the flow direction (the spread of the distance between the tenters becomes the stretching ratio). At this time, the distance of the tenter in the width direction (perpendicular to the flow direction) is set to be arbitrarily close. Preferably, the draw ratio in the flow direction may be set closer to the free end draw. In the case of free end stretching, the shrinkage rate in the width direction = (1 / stretch ratio) ^1/2 is calculated.

The air-assisted extension may be performed in one step or in multiple steps. When performing in multiple steps, the draw ratio is the product of the draw ratio of each step. The stretching direction in the airborne auxiliary stretching is preferably substantially the same as the stretching direction of the underwater stretching.

The draw ratio in the air-assisted drawing is preferably 2.0 times to 3.5 times. The maximum draw ratio in the case of combining the air-assisted extension and the in-water stretching 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 laminate. It is above. In the present specification, the "maximum stretch ratio" refers to the stretch ratio immediately before the laminate breaks, separately confirms the stretch ratio at which the laminate breaks, and refers to a value 0.2 lower than that value.

The stretching temperature of the air-assisted stretching can be set to any appropriate value depending on the forming material of the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably not less than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably the glass transition temperature (Tg) of the thermoplastic resin substrate + 10 ° C. or more, and particularly preferably Tg + 15 ° C. or more. 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 rapid progress of crystallization of the PVA-based resin and to suppress a defect due to the crystallization (for example, to prevent the orientation of the PVA-based resin layer by stretching). it can.

B-3. Insolubilization treatment If necessary, after in-air auxiliary stretching treatment, insolubilization treatment is carried out before underwater stretching treatment or dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in a boric acid aqueous solution. Water resistance can be imparted to the PVA-based resin layer by performing the insolubilization treatment, and the decrease in alignment of PVA when immersed in water can be prevented. The concentration of the aqueous boric acid solution is preferably 1 part by weight to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilization bath (boric acid aqueous solution) is preferably 20 ° C to 50 ° C.

B-4. Dyeing Treatment The dyeing treatment is typically performed by dyeing the PVA-based resin layer with iodine. Specifically, this is performed by adsorbing iodine to the PVA-based resin layer. As the adsorption method, for example, a method of immersing a PVA-based resin layer (laminated body) in a staining solution containing iodine, a method of applying the staining solution to a PVA-based resin layer, the staining solution to a PVA-based resin layer The method of spraying etc. are mentioned. Preferably, the method is a method of immersing the laminate in a staining solution (staining bath). It is because iodine can be adsorbed well.

The staining solution is preferably an aqueous iodine solution. The compounding amount of iodine is preferably 0.05 parts by weight to 0.5 parts by weight with respect to 100 parts by weight of water. In order to enhance the solubility of iodine in water, it is preferable to add an iodide to an aqueous iodine solution. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide and titanium iodide. Etc. Among these, preferred is potassium iodide. The compounding amount of iodide is preferably 0.1 parts by weight to 10 parts by weight, more preferably 0.3 parts by weight to 5 parts by weight with respect to 100 parts by weight of water. The liquid temperature at the time of dyeing of the staining solution is preferably 20 ° C. to 50 ° C. in order to suppress the dissolution of the PVA-based resin. In the case of immersing the PVA-based resin layer in the staining solution, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds, in order to secure the transmittance of the PVA-based resin layer.

The dyeing conditions (concentration, liquid temperature, immersion time) can be set such that the single transmittance of the polarizing film finally obtained is 46% or more and the degree of polarization is 92% or more. As such staining conditions, preferably, an aqueous iodine solution is used as a staining solution, and the ratio of the contents of iodine and potassium iodide in the aqueous iodine solution is set to 1: 5 to 1:20. The ratio of the contents of iodine and potassium iodide in the aqueous iodine solution is set to 1: 5 to 1:20. The ratio of the content of iodine and potassium iodide in the aqueous iodine solution is preferably 1: 5 to 1:10. Thereby, the polarizing film which has the above optical characteristics may be obtained.

In the case where the dyeing process is continuously performed after the treatment (typically, the insolubilization treatment) of immersing the laminate in the treatment bath containing boric acid, the boric acid contained in the treatment bath is mixed into the dyeing bath. The boric acid concentration in the dyeing bath may change with time, resulting in instability of the dyeability. The upper limit of the boric acid concentration of the dyeing bath is preferably 4 parts by weight, more preferably 2 parts by weight with respect to 100 parts by weight of water, in order to suppress the destabilization of the dyeability as described above. Adjusted. On the other hand, the lower limit of the boric acid concentration 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. It is. In one embodiment, the dyeing process is carried out using a dyeing bath in which boric acid has been previously incorporated. This can reduce the rate of change in boric acid concentration when boric acid in the treatment bath is mixed in the dyeing bath. The compounding amount of boric acid (that is, the content of boric acid not derived from the above-mentioned treatment bath) previously blended in the dyeing bath is preferably 0.1 part by weight to 2 parts by weight with respect to 100 parts by weight of water. And more preferably 0.5 to 1.5 parts by weight.

B-5. Crosslinking treatment If necessary, after dyeing treatment, crosslinking treatment is carried out before in-water stretching treatment. The above crosslinking treatment is typically performed by immersing the PVA-based resin layer in a boric acid aqueous solution. By subjecting the PVA-based resin layer to water resistance by performing the crosslinking treatment, it is possible to prevent the decrease in alignment of the PVA when it is immersed in high-temperature water by stretching in water later. The concentration of the aqueous boric acid solution is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Moreover, when performing a crosslinking process after the said dyeing | staining process, it is preferable to mix | blend iodide further. By blending an iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. The compounding amount of iodide is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably 20 ° C to 50 ° C.

B-6. Underwater Stretching Process The underwater stretching process is performed by immersing the laminate in a stretching bath. According to the in-water stretching process, stretching can be performed at a temperature lower than the glass transition temperature (typically, about 80 ° C.) of the thermoplastic resin base material or the PVA-based resin layer, and the PVA-based resin layer is crystallized. Can be stretched at a high magnification while suppressing the As a result, it is possible to manufacture a polarizing film having excellent optical properties.

Any appropriate method can be adopted as a method of stretching the laminate. Specifically, it may be fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching through a laminate between rolls having different peripheral speeds). Preferably, free end stretch is selected. Stretching of the laminate may be performed in one step or in multiple steps. When it carries out in multiple steps, the draw ratio (maximum draw ratio) of the below-mentioned layered product is the product of the draw ratio of each step.

Stretching in water is preferably carried out by immersing the laminate in an aqueous solution of boric acid (stretching in boric acid). By using a boric acid aqueous solution as a stretching bath, the PVA resin layer can be provided with rigidity to withstand the tension applied during stretching and water resistance which is not dissolved in water. Specifically, boric acid can form a tetrahydroxyborate anion in an aqueous solution and crosslink it with a PVA resin by hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, the film can be stretched satisfactorily, and a polarizing film having excellent optical properties can be produced.

The aqueous boric acid solution is preferably obtained by dissolving boric acid and / or a borate in water which is a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 3.5 to 7 parts by weight, and particularly preferably 4 to 6 parts by weight with respect to 100 parts by weight of water. It 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 with higher characteristics can be manufactured. In addition to boric acid or a 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 blended in the above-mentioned stretching bath (boric acid aqueous solution). By blending an iodide, 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 parts by weight to 15 parts by weight, 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. If it is such temperature, it can extend | stretch to high magnification, suppressing melt | dissolution of a PVA-type resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60 ° C. or more in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is less than 40 ° C., there is a possibility that the film can not be stretched well even in consideration of the plasticization of the thermoplastic resin base material by water. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, which may make it impossible to obtain excellent optical properties. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

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

B-7. Drying Shrinkage Treatment The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or may be performed by heating the transport roll (using a so-called heating roll) (heated roll drying method). Preferably, both are used. By drying using a heating roll, the heating curl of a laminated body can be suppressed efficiently and the polarizing film excellent in the external appearance can be manufactured. Specifically, by drying the laminated body along the heating roll, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the degree of crystallization, which is relatively low. Even at the drying temperature, the crystallinity of the thermoplastic resin substrate can be favorably increased. As a result, the rigidity of the thermoplastic resin base material is increased to be able to withstand the shrinkage of the PVA-based resin layer due to drying, and the curling is suppressed. Moreover, since it can dry, maintaining a laminated body in a flat state by using a heating roll, generation | occurrence | production of not only curl but wrinkles can be suppressed. At this time, the optical property can be improved by shrinking the laminate in the width direction by drying shrinkage treatment. This is because the orientation of PVA and 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%. By using the heating roll, the laminate can be continuously shrunk in the width direction while being conveyed, and high productivity can be realized.

FIG. 2 is a schematic view showing an example of the drying shrinkage process. In the drying shrinkage process, the laminate 200 is dried while being conveyed by the conveyance 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 disposed so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin base material, for example, one surface of the laminate 200 (for example, thermoplasticity The transport rolls R1 to R6 may be arranged to continuously heat only the resin base material surface).

The drying conditions can be controlled by adjusting the heating temperature of the transport roll (the 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., particularly preferably 70 ° C. to 80 ° C. While being able to increase the crystallinity degree of a thermoplastic resin favorably, a curl can be suppressed favorably, and an optical layered product extremely excellent in durability can be manufactured. The temperature of the heating roll can be measured by a contact thermometer. Although six transport rolls are provided in the illustrated example, the number of transport rolls is not particularly limited as long as it is plural. The number of transport rolls is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) of the laminate with the heating roll is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and still more preferably 1 to 10 seconds.

The heating roll may be provided in a heating furnace (for example, an oven) or may be provided in a normal production line (under a room temperature environment). Preferably, it is provided in a heating furnace provided with blowing means. By combining the drying by the heating roll and the hot air drying, it is possible to suppress a sharp temperature change between the heating rolls, and to easily control the contraction 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. In addition, the said wind speed is a wind speed in a heating furnace, and can be measured with a mini-vane type digital anemometer.

B-8. Other Treatment Preferably, after the in-water stretching treatment, a washing treatment is performed before the drying shrinkage treatment. The washing treatment is typically performed by immersing the PVA-based resin layer in a potassium iodide aqueous solution.

EXAMPLES Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by these examples. The measuring method of each characteristic is as follows. In the examples and comparative examples, "parts" and "%" are by weight unless otherwise specified.
(1) Thickness The thickness was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name “MCPD-3000”).
(2) Single transmittance and polarization degree Single transmittance Ts measured using an ultraviolet-visible spectrophotometer (V-7100 manufactured by JASCO Corporation) for the polarizing plates (protective film / polarizing film) of Examples and Comparative Examples. The parallel transmittance Tp and the orthogonal transmittance Tc are respectively taken as Ts, Tp and Tc of the polarizing film. These Ts, Tp and Tc are Y values measured by the visual field (C light source) according to JIS Z 8701 and subjected to the visual sensitivity correction. 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 determined from the obtained Tp and Tc according to the following equation.
Degree of polarization P (%) = {(Tp-Tc) / (Tp + Tc)} ^1/2 × 100
In addition, it is possible to measure an equivalent spectrophotometer also with Otsuka Electronics LPF-200 etc. As an example, measurement values of single transmittance Ts and polarization degree P obtained by measurement using V-7100 and LPF-200 for the sample 1 to sample 3 of the polarizing plate having the same configuration as the following embodiment are shown in Table 1 Show. As shown in Table 1, the difference between the measured value of the single transmittance of V-7100 and the measured value of the single transmittance of LPF-200 was 0.1% or less, and any of the spectrophotometers was used. It is understood that even in the case, equivalent measurement results can be obtained.

For example, when a polarizing plate provided with an adhesive having antiglare (AG) surface treatment or diffusion performance is to be measured, different measurement results may be obtained depending on the spectrophotometer, but in this case, the same results may be obtained. By performing numerical conversion based on the measured values when the polarizing plates are measured by the respective spectrophotometers, it is possible to compensate for differences in measured values depending on the spectrophotometer.
(3) Variations in Optical Properties of Long Polarizing Plates From the long polarizing plates of Examples and Reference Examples, five measurement samples are cut out at five positions at equal intervals along the width direction. The single transmittance of the central part of each measurement sample was measured in the same manner as (2) above. Next, the difference between the maximum value and the minimum value of the single transmittances measured at each measurement position is calculated, and this value is used to vary the optical characteristics of the long polarizing plate (width direction of the long polarizing plate The difference between the maximum value and the minimum value of the single transmittance at the position along
(4) Dispersion of optical characteristics of sheet-like polarizing plate A measurement sample of 100 mm × 100 mm is cut out from the long polarizing plate of Example and Reference Example, and dispersion of optical characteristics of sheet-like polarizing plate (50 cm ² ) I asked for. Specifically, the unitary transmittances of a total of five locations in the vicinity of about 1.5 cm to 2.0 cm and the central part from the middle point of each side of the four sides of the measurement sample are the same as in (2) above. Measured. Next, the difference between the maximum value and the minimum value of the single transmittances measured at each measurement position is calculated, and this value is used as the variation in the optical characteristics of the sheet-like polarizing plate (single transmittance in the 50 cm ² area) Difference between the maximum value and the minimum value of

Example 1
1. Preparation of Polarizing Film As a thermoplastic resin substrate, an amorphous isophthalic copolymer polyethylene terephthalate film (thickness: 100 μm) having a long water absorption coefficient of 0.75% and a Tg of about 75 ° C. was used. Corona treatment was applied to one side of the resin substrate.
100 weight of PVA-based resin in which polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gaucefimer Z410") are mixed at 9: 1 To a part, 13 parts by weight of potassium iodide was added to prepare a PVA aqueous 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 13 μm-thick PVA-based resin layer, thereby producing a laminate.
The obtained laminate was subjected to free-end uniaxial stretching at 2.4 times in the longitudinal direction (longitudinal direction) between rolls with different circumferential speeds in an oven at 130 ° C. (air-assisted extension treatment).
Then, the laminate was immersed in an insolubilization bath (a solution of boric acid obtained by blending 4 parts by weight of boric acid with respect to 100 parts by weight of water) having a liquid temperature of 40 ° C. for 30 seconds (insolubilization treatment).
Next, a polarizing film finally obtained in a dyeing bath (a solution of iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water) obtained at a liquid temperature of 30 ° C. It was immersed for 60 seconds while adjusting the concentration so that the single-piece transmittance (Ts) was 46% or more (staining treatment).
Then, it was immersed in a crosslinking bath having a liquid temperature of 40 ° C. (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 100 parts by weight of water and 5 parts by weight of boric acid) for 30 seconds (Crosslinking treatment).
Thereafter, while immersing the laminate in a boric acid aqueous solution (boric acid concentration: 5.0% by weight) having a liquid temperature of 70 ° C., a total draw ratio is 5.5 in the longitudinal direction (longitudinal direction) between rolls different in peripheral speed. Uniaxial stretching was performed so as to be doubled (in-water stretching treatment).
Thereafter, the laminated body was immersed in a washing bath having a liquid temperature of 20 ° C. (an aqueous solution obtained by blending 4 parts by weight of potassium iodide to 100 parts by weight of water) (washing treatment).
Thereafter, while drying in an oven maintained at 90 ° C., it was brought into contact with a SUS heating roll whose surface temperature was maintained at 75 ° C. for about 2 seconds (drying shrinkage treatment). The shrinkage ratio in the width direction of the laminate due to the drying shrinkage treatment was 5.2%.
Thus, a 5 μm-thick polarizing film was formed on the resin substrate. Furthermore, the same procedure was repeated to make a total of five polarizing films.
2. Preparation of Polarizing Plate As a protective film, an acrylic film (surface refractive index: 1.50, 40 μm) was attached to the surface (surface on the opposite side to the resin base material) of each polarizing film obtained above by UV curing Pasted through the agent. Specifically, the curable adhesive was applied so as to have a total thickness of 1.0 μm, and was bonded using a roll machine. Thereafter, UV light was irradiated from the protective film side to cure the adhesive. Subsequently, after slitting both ends, the resin base material was exfoliated and five long polarizing plates (width: 1300 mm) which have the composition of a protective film / polarizing film were obtained.

[Reference Example 1]
Seven polarizing films and polarizing plates were prepared in the same manner as in Example 1 except that the dyeing process was performed so that the single transmittance (Ts) of the polarizing film finally obtained would be 43% or more and less than 46%. did.

Comparative Example 1
Example 1 except that potassium iodide was not added to the PVA aqueous solution (coating solution), the draw ratio in air-assisted drawing was 1.8 times, and no heating roll was used in the drying shrinkage treatment. The preparation of a polarizing film was tried in the same manner as in the above, but the PVA-based resin layer was dissolved in the dyeing treatment and the stretching treatment in water, so that the polarizing film could not be prepared.

Comparative Example 2
Seventeen polarizing films and polarizing plates were produced in the same manner as in Example 1 except that the draw ratio in the air-assisted extension treatment was 1.8 times and that the heating roll was not used in the drying shrinkage treatment. However, it was not possible to produce a polarizing film having a single transmittance of 46% or more.

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

The single transmittance and the degree of polarization of each of the polarizing plates of the example and the comparative example were measured. The results are shown in Table 2 and FIG. In FIG. 3, the approximate curves of the plot of Example 1 and the plot of Reference Example 1 and the approximate curves of the plot of Comparative Example 2 are illustrated. The approximate curve of Comparative Example 2 is an approximate curve based on third-order polynomial approximation, and the broken line indicates an extrapolated portion of the approximate curve.

The polarizing film obtained by the manufacturing method of the comparative example did not simultaneously satisfy the single transmittance of 46% or more and the polarization degree of 92% or more. As shown in the approximate curve of the plot of Comparative Example 2, in the production method of Comparative Example 2, the degree of polarization is less than 92% when the dyeing process is performed so that the single transmittance is 46% or more. Is predicted. On the other hand, the polarizing film obtained by the manufacturing method of the example had excellent optical characteristics having a single transmittance of 46% or more and a polarization degree of 92% or more.

About each polarizing plate of Example 1 and the reference example 2, the dispersion of the optical characteristic of a long sheet-like and sheet-like polarizing plate was measured. The results are shown in Table 3.

The sheet-like polarizing plate obtained by the manufacturing method of the example has a variation of the single transmittance of 0.7% or less, and the sheet-like polarizing plate obtained by the manufacturing method of the example has the single transmittance Of 0.3% or less, and the variation of the optical characteristics is 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 subjecting the polarizing film to a humidification treatment had large variations in optical characteristics in both long and sheet-like shapes.

The polarizing plate having the polarizing film of the present invention is suitably used as a circularly polarizing plate for an organic EL display device and an inorganic EL display device.

10 polarizing film 20 first protective layer 30 second protective layer 100 polarizing plate

Claims

A polarizing plate having a polarizing film having a thickness of 8 μm or less, a single transmittance of 46% or more, and a polarization degree of 92% or more, and a protective layer disposed on at least one side of the polarizing film. There,
A polarizing plate, wherein the difference between the maximum value and the minimum value of the single transmittance in the region of 50 cm 2 is 0.3% or less.
A polarizing plate having a polarizing film having a thickness of 8 μm or less, a single transmittance of 46% or more, and a polarization degree of 92% or more, and a protective layer disposed on at least one side of the polarizing film. There,
The width is 1000 mm or more,
A polarizing plate, wherein the difference between the maximum value and the minimum value of single transmittance at a position along the width direction is 0.7% or less.
The polarizing plate according to claim 1 or 2, wherein the single transmittance of the polarizing film is 48% or less and the polarization degree is 97% or less.
The polarizing plate roll in which the polarizing plate in any one of Claim 1 to 3 is wound by roll shape.
A method for producing a polarizing film, which has a thickness of 8 μm or less, a single transmittance of 46% or more, and a polarization degree of 92% or more.
A polyvinyl alcohol-based resin layer containing iodide or sodium chloride and a polyvinyl alcohol-based resin is formed on one side of the long thermoplastic resin base material to form a laminate, and the above-mentioned laminate is subjected to aerial assisted stretching. A manufacturing method comprising performing in this order a treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment which shrinks in the width direction by 2% or more by heating while conveying in the longitudinal direction.
It is a manufacturing method of the polarizing film which is 48% or less in single-piece | unit transmittance | permeability, and is 97% or less of polarization degree, Comprising: The manufacturing method of Claim 5.
7. The method according to claim 5, wherein the content of the iodide or sodium chloride 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.
The manufacturing method in any one of Claim 5 to 7 whose draw ratio in the said air-aided extending | stretching process is 2.0 times or more.
The manufacturing method according to any one of claims 5 to 8, wherein the drying and shrinking treatment step is a step of heating using a heating roll.
10. The method according to claim 9, wherein the temperature of the heating roll is 60 ° C. to 120 ° C., and the shrinkage ratio in the width direction of the laminate due to the drying shrinkage treatment is 2% or more.