CN112005144A

CN112005144A - Polarizing plate, polarizing plate roll, and method for producing polarizing film

Info

Publication number: CN112005144A
Application number: CN201980027817.9A
Authority: CN
Inventors: 后藤周作
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2018-04-25
Filing date: 2019-04-08
Publication date: 2020-11-27
Also published as: TW201945202A; KR20210005013A; TWI789514B; JP2019194657A; JP7219017B2

Abstract

The invention provides a toolA polarizing plate having excellent optical characteristics and suppressed variation in optical characteristics. The polarizing plate of the present invention comprises a polarizing film having a thickness of 8 μm or less, a monomer transmittance of 48% or more, and a polarization degree of 85% or more, and a protective layer disposed on at least one side of the polarizing film, and is 50cm in thickness²The difference between the maximum value and the minimum value of the single transmittance in the region (1) is 0.5% or less. Another polarizing plate of the present invention comprises a polarizing film having a thickness of 8 μm or less, a cell transmittance of 48% or more, and a degree of polarization of 85% or more, and a protective layer disposed on at least one side of the polarizing film, wherein the polarizing film has a width of 1000mm or more, and a difference between a maximum value and a minimum value of the cell transmittance at a position in a width direction of the polarizing film is 1% or less.

Description

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

Technical Field

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

Background

Along with the spread of thin displays, displays (OLEDs) having organic EL panels and displays (QLEDs) using display panels using inorganic light emitting materials such as quantum dots have been proposed. These panels have a metal layer with high reflectivity, and therefore, problems such as reflection of external light and reflection of a background tend to occur. It is known that these problems can be prevented 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, a method has been proposed in which a laminate having a resin substrate and a polyvinyl alcohol (PVA) -based resin layer is stretched and then subjected to a dyeing treatment to obtain a polarizing film on the resin substrate (for example, patent document 1). Since a polarizing film having a small thickness can be obtained by this method, it contributes to the thinning of image display devices in recent years and is attracting attention. Further, if the reflectance of the panel is suppressed to a low level as the performance of the display panel is improved, the required characteristics of the degree of polarization are reduced, and a polarizing plate having a higher transmittance is required. However, when it is desired to improve the transmittance of a conventional thin polarizing film, a problem of dissolution of a PVA type resin occurs, and thus a film that can withstand optical use has not been produced.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2001-343521

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above conventional problems, and a main object thereof is to provide a polarizing plate having excellent optical characteristics and suppressed variation in optical characteristics, a polarizing sheet roll, and a method for producing the polarizing film.

Means for solving the problems

The polarizing plate of the present invention comprises a polarizing film having a thickness of 8 μm or less, a monomer transmittance of 48% or more, and a polarization degree of 85% or more, and a protective layer disposed on at least one side of the polarizing film, and is 50cm in thickness²The difference between the maximum value and the minimum value of the single transmittance in the region (1) is 0.5% or less.

Another polarizing plate of the present invention comprises a polarizing film having a thickness of 8 μm or less, a cell transmittance of 48% or more, and a degree of polarization of 85% or more, and a protective layer disposed on at least one side of the polarizing film, wherein the polarizing film has a width of 1000mm or more, and a difference between a maximum value and a minimum value of the cell transmittance at a position in a width direction of the polarizing film is 1% or less.

In one embodiment, the polarizing film has a cell transmittance of 50% or less and a polarization degree of 92% or less.

According to another aspect of the present invention, a roll of polarizer is provided. The polarizer roll is formed by winding the polarizer in a roll shape.

According to another aspect of the present invention, there is provided a method of manufacturing a polarizing film. The polarizing film has a thickness of 8 μm or less, a monomer transmittance of 48% or more, and a degree of polarization of 85% or more, and the method comprises: forming a polyvinyl alcohol resin layer containing a halide and a polyvinyl alcohol resin on one side of a long thermoplastic resin base material to prepare a laminate; and subjecting the laminate to an auxiliary stretching treatment in a gas atmosphere having a stretching ratio of 2.0 times or more, a dyeing treatment, a stretching treatment in an aqueous solution, and a drying shrinkage treatment in this order, wherein in the drying shrinkage treatment, the laminate is shrunk by 2% or more in the width direction by heating while being conveyed in the longitudinal direction.

In one embodiment, the content of the halide in the polyvinyl alcohol resin layer is 5 to 20 parts by weight based on 100 parts by weight of the polyvinyl alcohol resin.

In one embodiment, the drying and shrinking treatment step is a step of heating the film using a heating roller.

In one embodiment, the temperature of the heating roll is 60 to 120 ℃, and the shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is 2% or more.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a polarizing plate having a polarizing film having a thickness of 8 μm or less, a monomer transmittance of 48% or more, and a degree of polarization of 85% or more, which has excellent optical characteristics and in which variations in optical characteristics are suppressed, can be provided.

Drawings

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

Fig. 2 is a schematic diagram showing an example of the drying shrinkage process using a heating roller.

Fig. 3 is a graph showing the optical characteristics of the polarizing plates obtained in examples and comparative examples.

Description of the symbols

10 polarizing film

20 st protective layer

30 nd 2 protective layer

100 polarizing plate

Detailed Description

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

A. Polarizing plate

Fig. 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. The polarizing plate 100 has: the polarizing film includes a polarizing film 10, a 1 st protective layer 20 disposed on one side of the polarizing film 10, and a 2 nd protective layer 30 disposed on the other side of the polarizing film 10. The polarizing film has a thickness of 8 [ mu ] m or less, a monomer transmittance of 48% or more, and a degree of polarization of 85% or more. One of the 1 st protective layer 20 and the 2 nd protective layer 30 may be omitted. One of the 1 st protective layer and the 2 nd protective layer may be a resin base material (described later) for producing a polarizing film.

The polarizing plate may be a long strip or a single sheet. When the polarizing plate is in a long form, it is preferably wound in a roll form to form a polarizing plate roll. The polarizing plate has excellent optical characteristics and also has small variations in optical characteristics. In one embodiment, the width of the polarizing plate is 1000mm or more, and the difference (D1) between the maximum value and the minimum value of the single transmittance at the position along the width direction is 1% or less. The upper limit of D1 is preferably 0.8%, more preferably 0.6%. The smaller the D1, the better, but the lower limit thereof is, for example, 0.01%. As long as D1 is within the above range, a polarizing plate having excellent optical characteristics can be industrially produced. In another embodiment, the polarizer is at 50cm²The difference (D2) between the maximum value and the minimum value of the single transmittance in the region is 0.5% or less. The upper limit of D2 is preferably 0.25%, more preferably 0.15%. The smaller the D2, the better, but the lower limit thereof is, for example, 0.01%. As long as D2 is within the above range, it is possible to suppress the luminance deviation of the display screen when the polarizing plate is used in an image display device.

A-1 polarizing film

The polarizing film has a thickness of 8 μm or less, a monomer transmittance of 48% or more, and a degree of polarization of 85% or more, as described above. In general, the monomer transmittance has a trade-off relationship with the degree of polarization, and if the monomer transmittance is increased, the degree of polarization is decreased, and if the degree of polarization is increased, the monomer transmittance is decreased. Therefore, it has been difficult to practically use a thin polarizing film satisfying optical characteristics of a single transmittance of 48% or more and a polarization degree of 85% or more. One of the results of the present invention is to realize a thin polarizing film (polarizing plate) having excellent optical characteristics such as a single transmittance of 48% or more and a degree of polarization of 85% or more, and in which variation in optical characteristics is suppressed. Such a polarizing film (polarizing plate) can be used for an image display device, and is particularly suitably used for 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 380nm to 780 nm. The monomer transmittance of the polarizing film is preferably 50% or less. The polarization degree of the polarizing film is preferably 86% or more, more preferably 87% or more, and further preferably 88% or more. On the other hand, the upper limit of the degree of polarization is preferably 92%. The monomer transmittance is typically a Y value measured by an ultraviolet-visible spectrophotometer and corrected for visibility. The degree of polarization is typically determined by the following equation based on the parallel transmittance Tp and the orthogonal transmittance Tc measured by an ultraviolet-visible spectrophotometer and corrected for visibility.

Degree of polarization (%) { (Tp-Tc)/(Tp + Tc) }^1/2×100

In one embodiment, the transmittance of a thin polarizing film having a thickness of 8 μm or less is typically measured using an ultraviolet-visible spectrophotometer with a laminate of a polarizing film (surface refractive index: 1.53) and a protective film (refractive index: 1.50) as a measurement target. The reflectance of the interface of each layer changes 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, and as a result, the measured value of the transmittance may change. Therefore, for example, when a protective film having a refractive index of not 1.50 is used, the measured value of the transmittance may be corrected based on the refractive index of the surface of the protective film in contact with the air interface. Specifically, the correction value C of the transmittance utilizes the reflectance R of polarized light parallel to the transmission axis of the interface between the protective film and the air layer₁(transmission axis reflectance) and is expressed by the following numerical expression.

C＝R₁－R₀

R₀＝((1.50－1)²/(1.50+1)²)×(T₁/100)

R₁＝((n₁－1)²/(n₁+1)²)×(T₁/100)

Herein, R is₀The transmission axis reflectance when a protective film having a refractive index of 1.50 was used, n₁Refractive index of protective film used, T₁Is the transmittance of the polarizing film. For example, in using surface refractionWhen the base material (cycloolefin film, film with hard coat layer, etc.) having a ratio of 1.53 was used as the protective film, the correction amount C was about 0.2%. In this case, the transmittance obtained by the measurement plus 0.2% can be converted into the transmittance when a protective film having a surface refractive index of 1.50 is used. In addition, if the calculation is performed based on the above formula, the transmittance T of the polarizing film is adjusted₁The amount of change in the correction value C when the change is 2% is 0.03% or less, and the influence of the transmittance of the polarizing film on the value of the correction value C is limited. In the case where the protective film has absorption other than surface reflection, appropriate correction can be made in accordance with the absorption amount.

Any suitable polarizing film may be used for the polarizing film. The polarizing film can be typically produced using a laminate of two or more layers.

Specific examples of the polarizing film obtained using the laminate include a polarizing film obtained using a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate by coating. A polarizing film obtained using a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate by coating can be produced, for example, as follows: coating the PVA resin solution on a resin base material, drying the resin base material, and forming a PVA resin layer on the resin base material to obtain a laminated body of the resin base material and the PVA resin layer; the laminate was stretched and dyed to obtain a polarizing film from the PVA type resin layer. In the present embodiment, the stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching. If necessary, the stretching may further include stretching the laminate at a high temperature (for example, 95 ℃ or higher) in a gas atmosphere before the stretching in the aqueous boric acid solution. The obtained laminate of the resin substrate and the polarizing film may be used as it is (that is, the resin substrate may be used as a protective layer for the polarizing film), or the resin substrate may be peeled off from the laminate of the resin substrate and the polarizing film, and an arbitrary appropriate protective layer may be laminated on the peeled surface according to the purpose. Details of such a method for producing a polarizing film are disclosed in, for example, japanese patent laid-open No. 2012 and 73580. The entire contents of this publication are incorporated herein by reference.

The method for manufacturing a polarizing film of the present invention comprises: forming a polyvinyl alcohol resin layer containing a halide and a polyvinyl alcohol resin on one side of a long thermoplastic resin base material to prepare a laminate; and subjecting the laminate to an auxiliary stretching treatment in a gas atmosphere having a stretching ratio of 2.0 times or more, a dyeing treatment, a stretching treatment in an aqueous solution, and a drying shrinkage treatment in this order, wherein the laminate is shrunk by 2% or more in the width direction by heating while being conveyed in the longitudinal direction. Thus, a polarizing film having excellent optical characteristics and suppressed variation in optical characteristics, which has a thickness of 8 μm or less, a monomer transmittance of 48% or more, and a degree of polarization of 85% or more, can be provided. That is, by introducing the auxiliary stretching, even when the PVA is coated on the thermoplastic resin, the crystallinity of the PVA can be improved, and high optical characteristics can be realized. Further, by simultaneously improving the orientation of the PVA in advance, it is possible to prevent problems such as degradation of the orientation and dissolution of the PVA when the PVA is immersed in water in the subsequent dyeing step and stretching step, and to realize high optical characteristics. In addition, when the PVA-based resin layer is immersed in a liquid, the alignment disorder and the decrease in alignment of the polyvinyl alcohol molecules can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. Thus, the optical properties of the polarizing film obtained through a treatment step of immersing the laminate in a liquid, such as dyeing treatment or stretching treatment in an aqueous solution, can be improved. Further, by shrinking the laminate in the width direction by the drying and shrinking treatment, the optical characteristics can be improved.

A-2 protective layer

The 1 st and 2 nd protective layers are formed of any suitable film that can be used as a protective layer for a polarizing film. Specific examples of the material to be the main component of the film include cellulose resins such as Triacetylcellulose (TAC), polyester resins, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth) acrylic acids, and transparent resins such as acetates. Further, thermosetting resins such as (meth) acrylic resins, urethane resins, (meth) acrylic urethane resins, epoxy resins, silicone resins, and the like, ultraviolet-curable resins, and the like can be mentioned. In addition to these, for example, a glassy polymer such as a siloxane-based polymer can be cited. Further, the polymer film described in Japanese patent application laid-open No. 2001-343529 (WO01/37007) can also be used. As a material of the film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in a side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in a side chain can be used, and examples thereof include a resin composition having an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film may be, for example, an extrusion molded product of the above resin composition.

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

When the polarizing plate 100 is applied to an image display device, the thickness of the protective layer (inner protective layer) disposed on the display panel side is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and still more preferably 10 μm to 60 μm. In one embodiment, the inner protective layer is a phase difference layer having any suitable phase difference value. In this case, the in-plane retardation Re (550) of the retardation layer is, for example, 110nm to 150 nm. "Re (550)" is an in-plane retardation measured at 23 ℃ with light having a wavelength of 550nm, and can be represented by the formula: re ═ x-ny) × d. Here, "nx" is a refractive index in a direction in which an in-plane refractive index becomes maximum (i.e., the slow axis direction), "ny" is a refractive index in a direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), "nz" is a refractive index in the thickness direction, and "d" is a thickness (nm) of the layer (film).

B. Method for producing polarizing film

The method for manufacturing a polarizing film according to one embodiment of the present invention includes: forming a polyvinyl alcohol resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol resin (PVA-based resin) on one side of a long thermoplastic resin base material to prepare a laminate; and subjecting the laminate to an auxiliary stretching treatment in a gas atmosphere having a stretching ratio of 2.0 times or more, a dyeing treatment, a stretching treatment in an aqueous solution, and a drying shrinkage treatment in this order, wherein the laminate is shrunk by 2% or more in the width direction by heating while being conveyed in the longitudinal direction. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably carried out using a heated roller, and the temperature of the heated roller is preferably 60 to 120 ℃. The shrinkage of the laminate in the width direction due to the drying shrinkage treatment is preferably 2% or more. According to such a production method, the polarizing film described in the above item a can be obtained. In particular, a polarizing film having excellent optical properties (typically, monomer transmittance and polarization degree) and suppressed variations in optical properties can be obtained by producing a laminate including a halide-containing PVA-based resin layer, subjecting the laminate to stretching in multiple stages including auxiliary stretching in a gas atmosphere and stretching in an aqueous solution, and heating the stretched laminate with a heating roller. Specifically, by using a heating roller in the drying and shrinking treatment step, the entire laminate can be uniformly shrunk while being conveyed. Thus, not only the optical characteristics of the obtained polarizing film can be improved, but also a polarizing film excellent in optical characteristics can be stably produced, and variations in optical characteristics (particularly, monomer transmittance) of the polarizing film can be suppressed.

B-1 preparation of laminate

Any appropriate method can be used for producing the laminate of the thermoplastic resin substrate and the PVA-based resin layer. Preferably, the PVA-based resin layer is formed on the thermoplastic resin substrate by applying a coating solution containing a halide and a PVA-based resin to the surface of the thermoplastic resin laminate and drying the coating solution. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin.

Any suitable method can be used for applying the coating liquid. Examples thereof include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and blade coating (e.g., doctor blade coating). The coating/drying temperature of the coating liquid is preferably 50 ℃ or higher.

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

Before the PVA-based resin layer is formed, the thermoplastic resin substrate may be subjected to a surface treatment (for example, corona treatment), or an easy-adhesion layer may be formed on the thermoplastic resin substrate. 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 base Material

The thickness of the thermoplastic resin substrate is preferably 20 to 300. mu.m, more preferably 50 to 200. mu.m. If the thickness is less than 20 μm, the PVA based resin layer may be difficult to form. If it exceeds 300. mu.m, for example, in the stretching treatment in an aqueous solution described later, it takes a long time for the thermoplastic resin substrate to absorb water, and an excessive load may be required for stretching.

The water absorption of the thermoplastic resin substrate is preferably 0.2% or more, and more preferably 0.3% or more. The thermoplastic resin substrate absorbs water, and the water acts as a plasticizer to plasticize the thermoplastic resin substrate. As a result, the tensile stress can be greatly reduced, and the stretching can be performed at a high magnification. On the other hand, the water absorption of the thermoplastic resin substrate is preferably 3.0% or less, and more preferably 1.0% or less. By using such a thermoplastic resin substrate, it is possible to prevent a problem that the dimensional stability of the thermoplastic resin substrate is significantly lowered at the time of production, and the appearance of the obtained polarizing film is deteriorated. Further, the substrate can be prevented from being broken and the PVA based resin layer can be prevented from being peeled off from the thermoplastic resin substrate when stretched in an aqueous solution. The water absorption of the thermoplastic resin base material can be adjusted by introducing a modifying group into the constituent material, for example. The water absorption is a value determined in accordance with JIS K7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120 ℃ or lower. By using such a thermoplastic resin substrate, the crystallization of the PVA type resin layer can be suppressed, and the stretchability of the laminate can be sufficiently ensured. In consideration of plasticization of the thermoplastic resin substrate with water and smooth stretching in an aqueous solution, the temperature is preferably 100 ℃ or lower, and more preferably 90 ℃ or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60 ℃ or higher. By using such a thermoplastic resin substrate, when the coating liquid containing the PVA-based resin is applied and dried, troubles such as deformation (for example, generation of unevenness, looseness, wrinkles, and the like) of the thermoplastic resin substrate can be prevented, and a laminate can be produced satisfactorily. Further, the PVA-based resin layer can be favorably stretched at an appropriate temperature (for example, about 60 ℃). The glass transition temperature of the thermoplastic resin substrate can be adjusted by, for example, using a crystallized material in which a modifying group is introduced into a constituent material and heating the crystallized material. The glass transition temperature (Tg) is a value determined in accordance with JIS K7121.

As the constituent material of the thermoplastic resin substrate, any suitable thermoplastic resin can be used. Examples of the thermoplastic resin include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. Of these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferable.

In one embodiment, an amorphous (noncrystalline) polyethylene terephthalate-based resin is preferably used. Among them, amorphous (less likely to crystallize) polyethylene terephthalate resins are particularly preferably used. Specific examples of the amorphous polyethylene terephthalate resin include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers further containing cyclohexanedimethanol and diethylene glycol as diols.

In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate resin having an isophthalic acid unit. This is because such a thermoplastic resin substrate is very excellent in stretchability and can be inhibited from crystallizing during stretching. This is considered to be because the introduction of the isophthalic acid unit imparts a large curve to the main chain. The polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content ratio of the isophthalic acid unit is preferably 0.1 mol% or more, and more preferably 1.0 mol% or more, based on the total of all the repeating units. This is because a thermoplastic resin substrate having very excellent stretchability can be obtained. On the other hand, the content ratio of the isophthalic acid unit is preferably 20 mol% or less, more preferably 10 mol% or less, relative to the total of all the repeating units. By setting such a content ratio, the crystallinity can be favorably improved in the drying shrinkage treatment described later.

The thermoplastic resin substrate may be stretched in advance (before the PVA-based resin layer is formed). In one embodiment, the elongated thermoplastic resin base material may be stretched in the transverse direction. The transverse direction is preferably a direction perpendicular to the stretching direction of the laminate described later. In the present specification, "orthogonal" means that the two are substantially orthogonal to each other. Here, "substantially orthogonal" includes 90 ° ± 5.0 °, preferably 90 ° ± 3.0 °, and more preferably 90 ° ± 1.0 °.

The stretching temperature of the thermoplastic resin substrate is preferably from Tg-10 ℃ to Tg +50 ℃ relative to the glass transition temperature (Tg). The stretch ratio of the thermoplastic resin base material is preferably 1.5 to 3.0 times.

Any suitable stretching method can be used for stretching the thermoplastic resin substrate. Specifically, the fixed end stretching may be performed, or the free end stretching may be performed. The stretching method may be dry or wet. The stretching of the thermoplastic resin substrate may be performed in one stage or in multiple stages. When the stretching is performed in multiple stages, the stretching ratio is the product of the stretching ratios in the respective stages.

B-1-2 coating liquid

The coating liquid contains the halide and the PVA-based resin as described above. The coating liquid may be typically a solution obtained by dissolving the halide and the PVA-based resin in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These may be used alone or in combination of two or more. Of these, water is preferred. The concentration of the PVA based resin in the solution is preferably 3 to 20 parts by weight based on 100 parts by weight of the solvent. When the resin concentration is such as this, a uniform coating film can be formed which adheres closely to the thermoplastic resin substrate. The content of the halide in the coating liquid is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin.

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

As the PVA-based resin, any suitable resin can be used. Examples thereof include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of 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 in accordance with JIS K6726-. By using the PVA-based resin having such a saponification degree, a polarizing film having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.

The average polymerization degree of the PVA-based resin may 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 polymerization degree can be determined in accordance with JIS K6726-.

As the halide, any suitable halide can be used. For example, iodide and sodium chloride may be mentioned. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Of these, potassium iodide is preferred.

The amount of the halide in the coating liquid is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin, and more preferably 10 to 15 parts by weight based on 100 parts by weight of the PVA-based resin. When the amount of the halide exceeds 20 parts by weight based on 100 parts by weight of the PVA-based resin, the halide may bleed out, and the polarizing film finally obtained may be clouded.

Generally, the orientation of polyvinyl alcohol molecules in a PVA type resin is improved by stretching the PVA type resin layer, but if the stretched PVA type resin layer is immersed in a liquid containing water, the orientation of polyvinyl alcohol molecules may be disturbed, and the orientation may be degraded. In particular, when a laminate of a thermoplastic resin and a PVA-based resin layer is stretched in an aqueous boric acid solution, the orientation degree tends to be significantly reduced when the laminate is stretched in an aqueous boric acid solution at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin. For example, while stretching of a PVA film monomer in an aqueous boric acid solution is generally performed at 60 ℃, stretching of a laminate of a-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a high temperature such as a temperature of about 70 ℃, and in this case, the orientation of PVA at the initial stage of stretching is reduced in a stage before it is raised by stretching in an aqueous solution. On the other hand, by preparing a laminate of a halide-containing PVA type resin layer and a thermoplastic resin substrate and stretching the laminate at a high temperature in air (auxiliary stretching) before stretching the laminate in an aqueous boric acid solution, crystallization of the PVA type resin in the PVA type resin layer of the laminate after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, disturbance of the orientation of the polyvinyl alcohol molecules and reduction 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 a treatment step of immersing the laminate in a liquid, such as a dyeing treatment or a stretching treatment in an aqueous solution.

B-2. auxiliary stretching treatment in gas atmosphere

In particular, in order to obtain high optical characteristics, a 2-stage stretching method combining dry stretching (auxiliary stretching) and stretching in an aqueous boric acid solution is selected. By introducing the auxiliary stretching as in the 2-stage stretching, the thermoplastic resin substrate can be stretched while suppressing crystallization, the problem of the reduction in stretchability due to excessive crystallization of the thermoplastic resin substrate at the time of subsequent stretching in an aqueous boric acid solution can be solved, and the laminate can be stretched at a higher magnification. Further, when the PVA type resin is coated on the thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, the coating temperature needs to be lowered as compared with the case where the PVA type resin is coated on a general metal drum, and as a result, there is a problem that crystallization of the PVA type resin is relatively lowered and sufficient optical characteristics cannot be obtained. On the other hand, by introducing the auxiliary stretching, even when the PVA type resin is coated on the thermoplastic resin, the crystallinity of the PVA type resin can be improved, and high optical characteristics can be realized. Further, by simultaneously improving the orientation of the PVA-based resin in advance, when the PVA-based resin is immersed in water in the subsequent dyeing step or stretching step, problems such as a decrease in the orientation and dissolution of the PVA-based resin can be prevented, and high optical characteristics can be realized.

The stretching method for assisting stretching in a gas atmosphere may be fixed-end stretching (for example, a method of stretching using a tenter) or free-end stretching (for example, a method of uniaxially stretching a laminate by passing the laminate between rolls having different peripheral speeds), and the free-end stretching is actively employed for obtaining high optical characteristics. In one embodiment, the stretching treatment in a gas atmosphere includes a heated roller stretching step of stretching the laminate by a difference in peripheral speed between heated rollers while conveying the laminate in the longitudinal direction thereof. The stretching treatment in a gas atmosphere typically includes a zone stretching step and a heated roller stretching step. The order of the area stretching step and the heating roller stretching step is not limited, and the area stretching step may be performed first or the heating roller stretching step may be performed first. The zone stretching process may also be omitted. In one embodiment, the zone stretching step and the heated roller stretching step are performed in this order. In addition, in another embodiment,in the tenter stretching machine, the film end is gripped, and the distance between the tenters is stretched by expanding in the transport direction (expansion of the distance between the tenters becomes the stretching magnification). At this time, the distance of the tenter in the width direction (the direction perpendicular to the conveying direction) is arbitrarily set close. Preferably, the stretching ratio in the transport direction may be set so as to stretch closer to the free end. In the case of free-end stretching, the degree of shrinkage in the width direction (1/stretch ratio) is determined by^1/2To calculate.

The auxiliary stretching in a gas atmosphere may be performed in one stage or in multiple stages. In the case of performing in multiple stages, the stretching magnification is the product of the stretching magnifications in each stage. The stretching direction in the auxiliary stretching in the gas atmosphere is preferably substantially the same as the stretching direction in the aqueous solution.

The stretching ratio in the auxiliary stretching in a gas atmosphere is preferably 2.0 to 3.5 times. The maximum stretching ratio in the case of auxiliary stretching in a combined gas atmosphere and stretching in an aqueous solution is preferably 5.0 times or more, more preferably 5.5 times or more, and even more preferably 6.0 times or more, with respect to the original length of the laminate. In the present specification, "maximum stretching ratio" means a stretching ratio immediately before the laminate is broken, and further, a stretching ratio at which the laminate is confirmed to be broken, and "maximum stretching ratio" means a value smaller than this value by 0.2.

The stretching temperature for assisting stretching in a gas atmosphere may be set to any appropriate value depending on the material for forming the thermoplastic resin substrate, 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 not less than the glass transition temperature (Tg) +10 ℃ of the thermoplastic resin substrate, and particularly preferably not less than Tg +15 ℃. On the other hand, the upper limit of the stretching temperature is preferably 170 ℃. By stretching at such a temperature, rapid progress of crystallization of the PVA type resin can be suppressed, and defects caused by the crystallization (for example, inhibition of orientation of the PVA type resin layer by stretching) can be suppressed. The crystallinity index of the PVA resin after auxiliary stretching in a gas atmosphere is preferably 1.3 to 1.8, and more preferably 1.4 to 1.7. The crystallinity index of the PVA based resin can be usedThe fourier transform infrared spectrophotometer was measured by the ATR method. Specifically, the measurement was carried out using polarized light as the measurement light, and the spectrum obtained was used at 1141cm^-1And 1440cm^-1The crystal index of (2) was calculated by the following formula.

Crystallization index ═ I (I)_C/I_R)

Wherein the content of the first and second substances,

I_C: 1141cm when measured by incidence of measuring light^-1Strength of

I_R: 1440cm in the measurement by incidence of measurement light^-1The strength of (2).

B-3. insolubilization treatment

If necessary, after the stretching treatment is assisted in a gas atmosphere, an insolubilization treatment is performed before the stretching treatment in an aqueous solution and the dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing insolubilization treatment, water resistance can be imparted to the PVA-based resin layer, and the PVA can be prevented from being degraded in orientation when immersed in water. The concentration of the aqueous boric acid solution is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilization bath (aqueous boric acid solution) is preferably 20 to 50 ℃.

B-4. dyeing treatment

The dyeing treatment is typically performed by dyeing the PVA-based resin layer with iodine. Specifically, iodine is adsorbed to the PVA-based resin layer. Examples of the adsorption method include: a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine; a method of applying the dyeing liquid to a PVA-based resin layer; a method of spraying the dyeing solution on the PVA-based resin layer, and the like. A method of immersing the laminate in a dyeing solution (dyeing bath) is preferable. This is because iodine can be adsorbed well.

The staining solution is preferably an aqueous iodine solution. The amount of iodine blended is preferably 0.05 to 0.5 parts by weight based on 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add iodide to the 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, titanium iodide, and the like. Of these, potassium iodide is preferred. The amount of the iodide is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, based on 100 parts by weight of water. In order to suppress the dissolution of the PVA based resin, the liquid temperature at the time of dyeing with the dyeing liquid is preferably 20 ℃ to 50 ℃. When the PVA-based resin layer is immersed in the dyeing liquid, the immersion time is preferably 5 seconds to 5 minutes, and more preferably 30 seconds to 90 seconds, in order to ensure the transmittance of the PVA-based resin layer.

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

When the dyeing treatment is continuously performed after the treatment (typically, insolubilization treatment) of immersing the laminate in a treatment bath containing boric acid, the boric acid contained in the treatment bath is mixed into the dyeing bath, whereby the boric acid concentration in the dyeing bath changes with time, and as a result, the dyeing property may become unstable. In order to suppress the instability of dyeing properties as described above, the upper limit of the boric acid concentration in the dyeing bath is adjusted so that it is preferably 4 parts by weight, more preferably 2 parts by weight, per 100 parts by weight of water. On the other hand, the lower limit of the boric acid concentration of the dyeing bath is preferably 0.1 part by weight, more preferably 0.2 part by weight, and further preferably 0.5 part by weight with respect to 100 parts by weight of water. In one embodiment, the dyeing treatment is performed using a dyeing bath previously compounded with boric acid. This can reduce the rate of change in the boric acid concentration when boric acid in the treatment bath is mixed into the dyeing bath. The amount of boric acid to be blended in the dyeing bath in advance (i.e., the content of boric acid not derived from the treatment bath) is preferably 0.1 to 2 parts by weight, more preferably 0.5 to 1.5 parts by weight, based on 100 parts by weight of water.

B-5. Cross-linking treatment

If necessary, the crosslinking treatment is performed after the dyeing treatment and before the stretching treatment in an aqueous solution. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing the crosslinking treatment, water resistance can be imparted to the PVA-based resin layer, and the orientation of the PVA can be prevented from being lowered when the PVA is immersed in high-temperature water during subsequent stretching in an aqueous solution. The concentration of the aqueous boric acid solution is preferably 1 to 5 parts by weight with respect to 100 parts by weight of water. In addition, when the crosslinking treatment is performed after the dyeing treatment, it is preferable to further incorporate an iodide. The iodine compound can suppress elution of iodine adsorbed on the PVA-based resin layer. The amount of the iodide is preferably 1 to 5 parts by weight based on 100 parts by weight of water. Specific examples of the iodide are as described above. The liquid temperature of the crosslinking bath (aqueous boric acid solution) is preferably 20 ℃ to 50 ℃.

B-6 stretching treatment in aqueous solution

The stretching treatment in an aqueous solution is performed by immersing the laminate in a stretching bath. The stretching treatment in an aqueous solution allows stretching at a temperature lower than the glass transition temperature (typically, about 80 ℃) of the thermoplastic resin substrate or the PVA type resin layer, and allows stretching at a high magnification while suppressing crystallization of the PVA type resin layer. As a result, a polarizing film having excellent optical characteristics can be produced.

Any suitable method can be used for stretching the laminate. Specifically, the stretching may be fixed-end stretching or free-end stretching (for example, a method of passing the laminate between rolls having different peripheral speeds to perform uniaxial stretching), and the free-end stretching is preferably selected. The stretching of the laminate may be performed in one stage or in multiple stages. In the case of performing in multiple stages, the stretching ratio (maximum stretching ratio) of the laminate described later is the product of the stretching ratios in the respective stages.

The stretching in an aqueous solution is preferably performed by immersing the laminate in an aqueous solution of boric acid (stretching in an aqueous solution of boric acid). By using an aqueous boric acid solution as a stretching bath, the PVA-based resin layer can be provided with rigidity capable of withstanding the tension applied during stretching and water resistance insoluble in water. Specifically, boric acid can generate tetrahydroxyborate anions in an aqueous solution and can be crosslinked with the PVA-based resin by hydrogen bonds. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, and the PVA-based resin layer can be stretched well, whereby 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 as 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, based on 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film having higher characteristics can be produced. An aqueous solution obtained by dissolving a boron compound such as borax other than boric acid or a borate, glyoxal, glutaraldehyde, or the like in a solvent may also be used.

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

The drawing temperature (liquid temperature of the drawing bath) is preferably 40 to 85 ℃ and more preferably 60 to 75 ℃. At such a temperature, the PVA-based resin layer can be stretched at a high magnification while dissolution thereof is suppressed. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60 ℃ or higher in view of the relationship with the formation of the PVA-based resin layer. In this case, when the stretching temperature is lower than 40 ℃, there is a possibility that the thermoplastic resin substrate cannot be stretched well even when plasticization of the thermoplastic resin substrate by water is considered. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and the less excellent optical characteristics may 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 an aqueous solution is preferably 1.5 times or more, and more preferably 3.0 times or more. The total stretch ratio of the laminate is preferably 5.0 times or more, and more preferably 5.5 times or more, the original length of the laminate. By realizing such a high stretch ratio, a polarizing film having very excellent optical characteristics can be produced. Such a high draw ratio can be achieved by employing a drawing method in an aqueous solution (drawing in an aqueous boric acid solution).

B-7. drying shrinkage treatment

The drying shrinkage treatment may be performed by heating the entire area to perform area heating, or may be performed by heating a transport roller (using a so-called hot roller) (hot roller drying method), and both of them are preferably used. By drying using a heating roller, the heating curl of the laminate can be efficiently suppressed, and a polarizing film having excellent appearance can be produced. Specifically, by drying the laminate in a state of being along the heating roller, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the crystallinity, and the crystallinity of the thermoplastic resin substrate can be favorably increased even at a relatively low drying temperature. As a result, the thermoplastic resin substrate has increased rigidity and is able to withstand shrinkage of the PVA type resin layer due to drying, and curling can be suppressed. Further, since the laminate can be dried while being kept flat by using the heating roller, not only curling but also wrinkles can be suppressed. At this time, the laminate is shrunk in the width direction by the drying shrinkage treatment, whereby the optical characteristics can be improved. This is because the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage rate of the laminate subjected to the drying shrinkage treatment in the width direction is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roller, the laminate can be continuously shrunk in the width direction while being conveyed, and high productivity can be achieved.

Fig. 2 is a schematic diagram showing an example of the drying shrinkage process. In the drying shrinkage process, the laminate 200 is dried while being conveyed by the conveying rollers R1 to R6 and the guide rollers G1 to G4 which are heated to a predetermined temperature. In the illustrated example, the conveying rollers 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 substrate, but the conveying rollers R1 to R6 may be disposed so as to continuously heat only one surface (for example, the surface of the thermoplastic resin substrate) of the laminate 200.

The drying conditions can be controlled by adjusting the heating temperature of the transport roller (temperature of the heating roller), the number of heating rollers, the contact time with the heating roller, and the like. The temperature of the heating roller is preferably 60 to 120 ℃, more preferably 65 to 100 ℃, and particularly preferably 70 to 80 ℃. The crystallinity of the thermoplastic resin can be favorably increased, the curling can be favorably suppressed, and an optical laminate having extremely excellent durability can be produced. The temperature of the heating roller may be measured by a contact thermometer. In the illustrated example, 6 transport rollers are provided, but there is no particular limitation as long as there are a plurality of transport rollers. The number of the transport rollers is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roller is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, and still more preferably 1 to 10 seconds.

The heating roller may be installed in a heating furnace (for example, an oven), or may be installed in a general manufacturing line (room temperature environment), and is preferably installed in a heating furnace provided with an air blowing mechanism. By using drying with a heating roller and hot air drying in combination, a rapid temperature change between the heating rollers can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of the hot air drying is preferably 30 to 100 ℃. The hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot wind is preferably about 10m/s to 30 m/s. The wind speed is the wind speed in the heating furnace and can be measured by a digital wind speed meter of a miniature blade type.

B-8 other treatment

It is preferable to perform the washing treatment after the stretching treatment in the aqueous solution and before the drying shrinkage treatment. The cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

Examples

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement method of each property is as follows. Unless otherwise specified, "parts" and "%" in examples and comparative examples are based on weight.

(1) Thickness of

The measurement was carried out by using an interferometric film thickness meter (product name "MCPD-3000" available from Otsuka Denshi Co., Ltd.).

(2) Transmittance and degree of polarization of monomer

For the polarizing plates (protective films/polarizing films) of examples and comparative examples, the single transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer (V-7100, manufactured by japan spectrographs) were used as Ts, Tp, and Tc of the polarizing films, respectively. These Ts, Tp and Tc are Y values obtained by measuring and correcting visibility with a 2-degree field of view (C light source) according to JIS Z8701. 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 is determined from Tp and Tc by the following equation.

Polarization degree P (%) { (Tp-Tc)/(Tp + Tc) }^1/2×100

The spectrophotometer may be the same as that of the measurement with an Otsuka electronic official LPF-200 or the like. For example, the measurement values of the transmittance Ts and the degree of polarization P of the obtained monomers are shown in table 1, in which samples 1 to 3 having polarizing plates having the same configurations as those of the following examples were measured using V-7100 and LPF-200. As shown in Table 1, the difference between the measured value of the monomer transmittance of V-7100 and the measured value of the monomer transmittance of LPF-200 was 0.1% or less, and it was found that the same measurement results were obtained by using any of the spectrophotometers.

[ Table 1]

For example, when a polarizing plate having an anti-glare (AG) surface treatment and a pressure-sensitive adhesive having a diffusing property is used as a measurement target, measurement results that differ depending on the spectrophotometer are obtained, and in this case, the difference between the measurement values depending on the spectrophotometer can be compensated by performing numerical conversion based on the measurement values obtained when the same polarizing plate is measured by each spectrophotometer.

(3) Variation in optical characteristics of long-strip polarizing plate

Measurement samples were cut out from the long polarizing plates of examples and reference examples at positions 5 at equal intervals in the width direction, and the cell transmittance at the central portion of each of the 5 measurement samples was measured in the same manner as in the above (2). Next, the difference between the maximum value and the minimum value of the individual transmittance measured at each measurement position is calculated, and this value is used as the deviation of the optical characteristics of the long polarizing plate (the difference between the maximum value and the minimum value of the individual transmittance at the position of the long polarizing plate in the width direction).

(4) Variation in optical characteristics of monolithic polarizing plate

A100 mm × 100mm measurement sample was cut from the long polarizing plates of examples and reference examples to obtain a single polarizing plate (50 cm)²) The deviation of the optical characteristics of (1). Specifically, the monomer transmittance was measured at 5 positions in total at positions and central portions of the sample in the vicinity of about 1.5cm to 2.0cm inward from the midpoint of each of the 4 sides in the same manner as in the above (2). Then, the difference between the maximum value and the minimum value of the single transmittance measured at each measurement position was calculated, and the calculated value was used as the deviation of the optical characteristics of the monolithic polarizing plate (at 50 cm)²The difference between the maximum and minimum of the monomer transmission within a region).

(5) Crystallization index of PVA resin layer after auxiliary stretching in gas atmosphere

The surface of the PVA-based resin layer was evaluated by ATR measurement using a fourier transform infrared spectrophotometer (product name "FT-IRFrontier" manufactured by PerkinElmer) as a measurement light for the laminate after stretching in a gas atmosphere. Specifically, measurement was carried out using 1141cm of the obtained spectrum^-1And 1440cm^-1The crystal index was calculated according to the following equation.

Crystallization index ═ I (I)_C/I_R)

Wherein the content of the first and second substances,

I_C: the incident measurement light was measured at 1141cm^-1Strength of

I_R: the incident measurement light was measured at 1440cm^-1Strength of

[ example 1]

1. Production of polarizing film

As the thermoplastic resin substrate, a long-sized amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100 μm) having a water absorption of 0.75% and a Tg of about 75 ℃ was used. One side of the resin substrate was subjected to corona treatment.

To 100 parts by weight of a PVA resin obtained by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (trade name "GOHSEFIMER Z410" available from Nippon synthetic chemical Co., Ltd.) at a ratio of 9:1, 13 parts by weight of potassium iodide was added to prepare an aqueous PVA solution (coating solution).

The aqueous PVA solution was applied to the corona-treated surface of the resin substrate, and dried at 60 ℃ to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.

The free end of the obtained laminate was stretched in one direction in the longitudinal direction (longitudinal direction) by a factor of 2.4 in an oven at 130 ℃ between rolls having different peripheral speeds (auxiliary stretching treatment in a gas atmosphere).

Next, the laminate was immersed in an insolubilization bath (an aqueous boric acid solution prepared by adding 4 parts by weight of boric acid to 100 parts by weight of water) at a liquid temperature of 40 ℃ for 30 seconds (insolubilization treatment).

Next, the polarizing film was immersed in a dyeing bath (aqueous iodine solution prepared by mixing iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ℃ for 60 seconds while adjusting the concentration so that the monomer transmittance (Ts) of the finally obtained polarizing film becomes 48% or more (dyeing treatment).

Subsequently, the substrate was immersed in a crosslinking bath (an aqueous boric acid solution containing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid per 100 parts by weight of water) at a liquid temperature of 40 ℃ for 30 seconds (crosslinking treatment).

Then, while immersing the laminate in an aqueous boric acid solution (boric acid concentration 5.0 wt%) having a liquid temperature of 70 ℃, uniaxial stretching (stretching treatment in an aqueous solution) was performed between rolls having different peripheral speeds so that the total stretching ratio in the longitudinal direction (longitudinal direction) was 5.5 times.

Then, the laminate was immersed in a cleaning bath (aqueous solution containing 4 parts by weight of potassium iodide per 100 parts by weight of water) at a liquid temperature of 20 ℃.

Then, while drying in an oven maintained at 90 ℃, the sheet was contacted with a SUS heating roll maintained at a surface temperature of 75 ℃ for about 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction by the drying shrinkage treatment was 5.2%.

Thus, a polarizing film having a thickness of 5 μm was formed on the resin substrate. Then, the same operation was repeated to produce 10 polarizing films in total.

2. Preparation of polarizing plate

An acrylic film (surface refractive index 1.50, 40 μm) as a protective film was bonded to the surface (the surface opposite to the resin substrate) of each of the polarizing films obtained above with an ultraviolet-curable adhesive. Specifically, the curable adhesive was applied so that the total thickness thereof became 1.0 μm, and was bonded using a roll machine. Then, UV light is irradiated from the protective film side to cure the adhesive. Then, both ends were slit, and the resin base material was peeled off, thereby obtaining 10 long polarizing plates (width: 1300mm) each having a protective film/polarizing film.

[ reference example 1]

12 polarizing films and polarizing plates were produced in the same manner as in example 1, except that dyeing treatment was performed so that the monomer transmittance (Ts) of the finally obtained polarizing film was 43% or more and less than 48%.

Comparative example 1

An attempt was made to produce a polarizing film in the same manner as in example 1, except that potassium iodide was not added to the PVA aqueous solution (coating solution), the stretching ratio of the auxiliary stretching treatment in a gas atmosphere was 1.8 times, and a heating roll was not used for the drying shrinkage treatment, but the PVA-based resin layer was dissolved in the dyeing treatment and the stretching treatment in an aqueous solution, and a polarizing film having a monomer transmittance of 48% or more could not be produced.

Comparative example 2

An attempt was made to produce 17 polarizing films and polarizing plates in the same manner as in example 1, except that the stretching ratio of the auxiliary stretching treatment in the gas atmosphere was 1.8 times and a heating roll was not used for the drying and shrinking treatment, but a polarizing film having a monomer transmittance of 48% or more could not be produced in the same manner as in comparative example 1.

[ reference example 2]

The polarizing film obtained in the same manner as in comparative example 2 was held in a constant temperature and humidity region set at a temperature of 60 ℃ and a humidity of 90% RH for 30 minutes. Then, a polarizing plate was produced in the same manner as in example 1.

The single transmittance and the degree of polarization of each polarizing plate of examples and comparative examples were measured. The results are shown in table 2 and fig. 3. Fig. 3 shows an approximate curve of the curve of example 1 and the curve of reference example 1, and an approximate curve of the curve of comparative example 2. Further, the approximation curve of comparative example 2 is an approximation curve based on 3 rd order polynomial approximation, and an extrapolated part of the approximation curve is represented by a broken line.

[ Table 2]

The polarizing film obtained by the manufacturing method of the comparative example does not satisfy both the monomer transmittance of 48% or more and the polarization degree of 85% or more. As shown by the approximate curve of the curve of comparative example 2, it is predicted that the degree of polarization is less than 85% when the monomer transmittance is 48% or more by the dyeing treatment in the production method of comparative example 2. In contrast, the polarizing film obtained by the production method of the example had excellent optical characteristics such as a single transmittance of 48% or more and a degree of polarization of 85% or more.

For each of the polarizing plates of example 1 and reference example 2, variations in optical characteristics of the long and monolithic polarizing plates were measured. The results are shown in Table 3.

[ Table 3]

	Deviation of transmission of monomer (strip shape)	Deviation of transmission of monomer (monomer)
			Example 1	0.58％	0.14％
Reference example 2	1.54％	0.68％

The variation in the individual transmittance of the long polarizing plate obtained by the manufacturing method of example was 1% or less, and the variation in the individual transmittance of the single polarizing plate obtained by the manufacturing method of example was 0.5% or less, and the variation in the optical characteristics was suppressed to such an extent that there was no problem. On the other hand, the polarizing plate of the reference example obtained through the step of humidifying the polarizing film had large variations in optical characteristics regardless of whether it was a long or single sheet.

In the polarizing films of examples and comparative examples, the crystallinity index of the PVA-based resin in the laminate after the auxiliary stretching in a gas atmosphere was measured based on the above (5). Further, it was confirmed whether or not the PVA based resin was dissolved in the dyeing treatment or the stretching treatment in an aqueous solution. The results are shown in Table 4.

[ Table 4]

Industrial applicability

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

Claims

1. A polarizing plate comprising a polarizing film and a protective layer disposed on at least one side of the polarizing film, wherein the polarizing film has a thickness of 8 μm or less, a monomer transmittance of 48% or more, and a degree of polarization of 85% or more,

the polarizer is 50cm²The difference between the maximum value and the minimum value of the single transmittance in the region (1) is 0.5% or less.

2. A polarizing plate comprising a polarizing film and a protective layer disposed on at least one side of the polarizing film, wherein the polarizing film has a thickness of 8 μm or less, a monomer transmittance of 48% or more, and a degree of polarization of 85% or more,

the width of the polarizing plate is 1000mm or more,

the difference between the maximum value and the minimum value of the single transmittance of the polarizing plate at the position along the width direction is 1% or less.

3. The polarizing plate according to claim 1 or 2,

the polarizing film has a monomer transmittance of 50% or less and a degree of polarization of 92% or less.

4. A polarizer roll obtained by winding the polarizer according to any one of claims 1 to 3 in a roll form.

5. A method for producing a polarizing film having a thickness of 8 μm or less, a monomer transmittance of 48% or more, and a degree of polarization of 85% or more, comprising:

forming a polyvinyl alcohol resin layer containing an iodide or sodium chloride and a polyvinyl alcohol resin on one side of a long thermoplastic resin base material to prepare a laminate; and

the laminate is subjected to an auxiliary stretching treatment in a gas atmosphere, a dyeing treatment, a stretching treatment in an aqueous solution, and a drying shrinkage treatment in this order, and in the drying shrinkage treatment, the laminate is heated while being conveyed in the longitudinal direction, thereby being shrunk by 2% or more in the width direction.

6. The method for producing a polarizing film according to claim 5, which is a method for producing a polarizing film having a monomer transmittance of 50% or less and a degree of polarization of 92% or less.

7. The manufacturing method according to claim 5 or 6,

in the polyvinyl alcohol resin layer, the content of the iodide or sodium chloride is 5 to 20 parts by weight based on 100 parts by weight of the polyvinyl alcohol resin.

8. The manufacturing method according to any one of claims 5 to 7,

the stretching ratio of the auxiliary stretching treatment in the gas atmosphere is more than 2.0 times.

9. The manufacturing method according to any one of claims 5 to 8,

the drying shrinkage treatment step is a step of heating using a heating roller.

10. The manufacturing method according to claim 9,

the temperature of the heating roller is 60 to 120 ℃, and the shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is 2% or more.