KR20210130707A - Polarizing film, polarizing plate, and manufacturing method of the polarizing film - Google Patents

Abstract

A polarizing film in which bending in the absorption axis direction is suppressed and having excellent bendability is provided. The polarizing film of the present invention is composed of a polyvinyl alcohol-based resin film containing iodine, and after standing at 85° C. for 120 hours, the shrinkage rate in the absorption axis direction (S _MD ) and the shrinkage rate in the direction orthogonal to the absorption axis direction (S _TD ) The ratio S _MD /S _TD of the family is 0.5 to 1.5. In one embodiment, the polarizing film has a thickness of 8 μm or less. The polarizing plate of the present invention includes the polarizing film and a protective layer disposed on at least one side of the polarizing film.

Description

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

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

In a liquid crystal display device, which is a typical image display device, polarizing films are disposed on both sides of a liquid crystal cell due to its image forming method. As a method for manufacturing a polarizing film, for example, a method of obtaining a polarizing film on a resin substrate by stretching a laminate including a resin substrate and a polyvinyl alcohol (PVA)-based resin layer, followed by dyeing treatment has been proposed (eg, Patent Document 1). According to such a method, since a thin polarizing film is obtained, it attracts attention because it can contribute to thickness reduction of the image display apparatus in recent years. However, the thin polarizing film as described above has a problem in that it tends to bend in the absorption axis direction. Such a problem is remarkable when a thin polarizing film is applied to an organic electroluminescent (EL) display apparatus. Specifically, since the organic EL display device itself is thin and a polarizing film (in fact, a polarizing plate) is disposed only on one side of the device, the device may have significant warpage.

Japanese Laid-Open Patent Publication No. 2001-343521

The present invention has been made in order to solve the above conventional problems, and its main object is to provide a polarizing film in which warpage in the absorption axis direction is suppressed and has excellent bendability.

The polarizing film of the present invention is composed of a polyvinyl alcohol-based resin film containing a dichroic material, and the shrinkage rate in the absorption axis direction (S _MD ) and the shrinkage rate in the direction orthogonal to the absorption axis direction after standing at 85 ° C. for 120 hours (S) _TD ) and the ratio S _MD /S _TD is 0.5 to 1.5.

In one embodiment, the thickness of the said polarizing film is 8 micrometers or less.

In one embodiment, the polarizing film has a single transmittance of 40.0% or more and a polarization degree of 99.0% or more.

In one embodiment, the shrinkage ratio (S _MD ) in the absorption axis direction and the shrinkage ratio (S _TD ) in the direction orthogonal to the absorption axis direction are 0.4% or less, respectively.

In one embodiment, the polarizing film has an orientation function of 0.30 or less.

According to another aspect of the present invention, a polarizing plate is provided. The polarizing plate includes the polarizing film and a protective layer disposed on at least one side of the polarizing film.

According to another aspect of the present invention, a method for manufacturing the polarizing film is provided. This manufacturing method comprises forming a polyvinyl alcohol-type resin layer containing iodide or sodium chloride and a polyvinyl alcohol-type resin on one side of a long thermoplastic resin base material, and setting it as a laminated body; and performing, in this order, an aerial auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment for shrinking the laminate by 2% or more in the width direction by heating while conveying in the longitudinal direction; do. The total magnification of the stretching of the aerial auxiliary stretching treatment and the underwater stretching treatment is 3.0 to 4.0 times the original length of the laminate; The draw ratio of the said aerial auxiliary drawing process is larger than the draw ratio of the said underwater drawing process.

According to the present invention, by optimizing the ratio of the shrinkage in the absorption axis direction to the shrinkage in the direction orthogonal to the absorption axis direction, a polarizing film with curvature in the absorption axis direction suppressed can be obtained. Optimization of the shrinkage ratio in the above two directions can be realized in a polarizing film obtained by a manufacturing method that typically combines air-assisted stretching and underwater stretching, adjusting these draw ratios, and reducing the total draw ratio. . Moreover, in one embodiment, the polarizing film which has the outstanding bendability can be obtained by making the thickness of a polarizing film into predetermined value (for example, 8 micrometers) or less.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing of the polarizing plate which concerns on one Embodiment of this invention.
2 is a schematic diagram showing an example of a drying shrinkage treatment using a heating roll.

EMBODIMENT OF THE INVENTION Hereinafter, although embodiment of this invention is described, this invention is not limited to these embodiment.

A. Polarizing film

The polarizing film according to an embodiment of the present invention is composed of a polyvinyl alcohol (PVA)-based resin film containing a dichroic substance (typically iodine, dichroic dye), and the absorption axis direction after standing at 85° C. for 120 hours of the shrinkage (S _MD) and the absorption axis direction (hereinafter referred to as the transmission axis direction is in the case referred to) is 0.5 to 1.5 ratio S _MD / S _TD of the shrinkage (S _TD) of orthogonal to the direction. That is, the polarizing film according to the embodiment of the present invention has remarkably small anisotropy of heat shrinkage. Hereinafter, in the present specification, such a characteristic related to heat shrinkage is sometimes referred to as 'isotropic shrinkage'. If it is such a structure, the curvature of the absorption axis direction of a polarizing film can be suppressed remarkably. Such a polarizing film (and consequently, a polarizing plate) can be suitably applied to an organic EL display device. Since the organic EL display device is thin and a polarizing film (substantially, a polarizing plate) is disposed only on one side, the warpage of the device becomes large. Ratio S _MD /S _TD becomes like this. Preferably it is 0.7-1.3, More preferably, it is 0.8-1.2, More preferably, it is 0.9-1.1, Especially preferably, it is 0.94-1.16.

The shrinkage ratio (S _MD ) in the absorption axis direction is preferably 0.4% or less, more preferably 0.3% or less, and still more preferably 0.2% or less. The shrinkage ratio (S _TD ) in the transmission axis direction is, for example, 0.42% or less, preferably 0.4% or less, more preferably 0.3% or less, and still more preferably 0.2% or less. The _{smaller both of S MD} and S _TD are, the more preferable, and ideally it is zero. The polarizing film according to the embodiment of the present invention not only has isotropic shrinkage, but also has small shrinkage rates in the absorption axis direction and in the transmission axis direction itself. As a result, curvature can be further suppressed. In addition, the polarizing film is typically provided as a component of a polarizing plate or a polarizing plate with a pressure-sensitive adhesive layer, and S _MD and ST _TD may vary depending on the type and/or characteristics of the protective layer and/or pressure-sensitive adhesive layer of the polarizing plate, respectively. On the other hand, the ratio S _MD /S _TD may be maintained in a substantially constant range regardless of the type and/or characteristics of the protective layer and/or the pressure-sensitive adhesive layer.

The thickness of the polarizing film is preferably 8 µm or less, more preferably 7 µm or less, still more preferably 5 µm or less, particularly preferably 3 µm or less, and very particularly preferably 2 µm or less. The lower limit of the thickness of the polarizing film may be, for example, 1 μm. The thickness of the polarizing film is 2 µm to 6 µm in one embodiment, 2 µm to 4 µm in another embodiment, 2 µm to 3 µm in still another embodiment, 5 µm to 7.5 µm in still another embodiment, and another In embodiment, 5.5 micrometers - 7 micrometers may be sufficient. By making the thickness of the polarizing film very thin in this way, the shrinkage rate in the absorption axis direction and the shrinkage rate in the transmission axis direction can be made very small. Moreover, by making the thickness of a polarizing film very thin in this way, the polarizing film which has the outstanding bendability can be obtained. As a result, preferably a polarizing film applicable to a curved image display device, more preferably a bendable image display device, and still more preferably a foldable image display device can be obtained.

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 40.0% or more, and more preferably 41.0% or more. The upper limit of the single transmittance may be, for example, 49.0%. The single transmittance of the polarizing film is 40.0% to 45.0% in one embodiment. The polarization degree of the polarizing film is preferably 99.0% or more, and more preferably 99.4% or more. The upper limit of the degree of polarization may be, for example, 99.999%. The degree of polarization of the polarizing film is 99.0% to 99.99% in one embodiment. According to the present invention, although the total draw ratio in the production of a polarizing film as described later is very small, such a practically acceptable single transmittance and polarization degree can be realized. This is presumed to originate in the manufacturing method mentioned later. In addition, the single transmittance|permeability is the Y value which measured using the ultraviolet/visible spectrophotometer typically, and performed visibility correction|amendment. In addition, the single transmittance is a value when the refractive index of one surface of a polarizing plate is converted into 1.50, and the refractive index of the other surface of a polarizing plate is converted into 1.53. Polarization degree can be calculated|required by the following formula based on the parallel transmittance|permeability (Tp) and orthogonal transmittance|permeability (Tc) typically measured using an ultraviolet/visible light spectrophotometer and corrected for visibility.

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

The polarizing film has an orientation function of, for example, 0.30 or less, and, for example, 0.25 or less, preferably 0.22 or less, more preferably 0.20 or less, still more preferably 0.18 or less, particularly preferably 0.15 or less. If the orientation function is within such a range, desired isotropic shrinkage can be realized. The lower limit of the orientation function may be, for example, 0.05. The smaller the orientation function, the less acceptable single transmittance and/or polarization degree may be obtained.

The orientation function f can be calculated|required by ATR:attenuated total reflection (ATR) measurement using, for example, a Fourier transform infrared spectrophotometer (FT-IR), using polarized light as a measurement light. Specifically, the measurement is performed in a state in which the stretching direction of the polarizing film is parallel to and perpendicular to the polarization direction of the measurement light, and the obtained absorbance spectrum is ^{calculated using the intensity of 2941 cm -1} , according to the following formula. Here, the intensity (I) is to 3330cm ^-1 for the reference peak, and the value of 2941cm ^-1 / 3330cm ^-1. Also, when f=1, it is fully oriented, and when f=0, it becomes random. In addition, ^{the peak at 2941 cm -1} is considered to be absorption resulting from the vibration of _{the main chain (-CH 2} -) of PVA in the polarizing film.

f=(3<cos ² θ>-1)/2

=(1-D)/[c(2D+1)]

=-2×(1-D)/(2D+1)

step,

c = (3cos ² β-1)/2, but in the case of a vibration of ^{2941 cm -1, β = 90°.}

θ: the angle of the molecular chain with respect to the stretching direction

β: angle of transition dipole moment with respect to the molecular chain axis

D=(I _⊥ )/(I _// ) (in this case, the more the PVA molecules are oriented, the larger D)

I _⊥ : Absorption intensity when the polarization direction of the measurement light and the stretching direction of the polarizing film are perpendicular to each other

I _// : Absorption intensity when the polarization direction of the measurement light and the stretching direction of the polarizing film are parallel

As described above, the polarizing film is composed of a PVA-based resin film containing iodine. Preferably, the PVA-based resin constituting the PVA-based resin film (substantially, the polarizing film) contains an acetoacetyl-modified PVA-based resin. With such a configuration, a polarizing film having a desired puncture strength can be obtained. The blending amount of the acetoacetyl-modified PVA-based resin is preferably 5 to 20% by weight, more preferably 8 to 12% by weight, when the total PVA-based resin is 100% by weight. The puncture strength can be made into a more suitable range as a compounding quantity is such a range.

The polarizing film may be typically manufactured 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 to the said resin base material is mentioned. A polarizing film obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate is applied, for example, by applying a PVA-based resin solution to the resin substrate, drying it, and forming a PVA-based resin layer on the resin substrate to form a resin obtaining a laminate of a base material and a PVA-based resin layer; stretching and dyeing the laminate to use the PVA-based resin layer as a polarizing film; In this embodiment, Preferably, the polyvinyl alcohol-type resin layer containing a halide and polyvinyl alcohol-type resin is provided on one side of a resin base material. Stretching typically includes stretching by immersing the laminate in an aqueous boric acid solution. In addition, the stretching preferably further includes aerial stretching of the laminate at a high temperature (eg, 95°C or higher) before stretching in an aqueous boric acid solution. In embodiment of this invention, the total magnification of extending|stretching is 3.0 times - 4.5 times, for example, and it is remarkably small compared with usual. Even at such a total magnification of stretching, a polarizing film having acceptable optical properties can be obtained by adding a halide and combining the drying shrinkage treatment. Moreover, in embodiment of this invention, the draw ratio of aerial auxiliary drawing is larger than the draw ratio of boric-acid underwater drawing. By setting it as such a structure, even if the total magnification of extending|stretching is small, the polarizing film which has an acceptable optical characteristic can be obtained. Further, the laminate is preferably subjected to a drying shrinkage treatment in which it is shrunk by 2% or more in the width direction by heating while being conveyed in the longitudinal direction. In one embodiment, the manufacturing method of a polarizing film includes giving an aerial auxiliary extending|stretching process, a dyeing|staining process, an underwater extending|stretching process, and a drying shrinkage process to a laminated body in this order. By introducing auxiliary stretching, even when PVA is applied on a thermoplastic resin, it becomes possible to increase the crystallinity of PVA, and it becomes possible to achieve high optical properties. In addition, by simultaneously raising the orientation of PVA in advance, it is possible to prevent problems such as a decrease in orientation and dissolution of PVA when immersed in water in a subsequent dyeing process or stretching process, so that it is possible to achieve high optical properties do. In addition, in the case where the PVA-based resin layer is immersed in a liquid, as compared to the case in which the PVA-based resin layer does not contain a halide, disorder in the orientation of polyvinyl alcohol molecules and a decrease in orientation can be suppressed. Thereby, the optical characteristic of the polarizing film obtained through the processing process performed by immersing a laminated body in a liquid, such as a dyeing process and an underwater extending|stretching process, can be improved. Moreover, an optical characteristic can be improved by shrinking|contracting a laminated body in the width direction by dry shrinkage process. The obtained laminate of the resin substrate / polarizing film may be used as it is (that is, the resin substrate may be used as a protective layer of the polarizing film), or the resin substrate is peeled from the laminate of the resin substrate / polarizing film, Any suitable protective layer may be laminated and used. The detail of the manufacturing method of a polarizing film is mentioned later in Section C.

B. Polarizer

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing of the polarizing plate which concerns on one Embodiment of this invention. The polarizing plate 100 includes a polarizing film 10 , a first protective layer 20 disposed on one side of the polarizing film 10 , and a second protective layer disposed on the other side of the polarizing film 10 ( 30). The polarizing film 10 is the polarizing film of the present invention described in section A above. One of the first protective layer 20 and the second protective layer 30 may be omitted. Moreover, as mentioned above, the resin base material used for manufacture of said polarizing film may be sufficient as one of a 1st protective layer and a 2nd protective layer.

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 used as the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyester, polyvinyl alcohol, polycarbonate, polyamide, polyimide, polyethersulfone, and transparent resins such as polysulfone-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based and acetate-based resins. Moreover, thermosetting resins, such as (meth)acrylic type, a urethane type, a (meth)acrylic urethane type, an epoxy type, a silicone type, or ultraviolet curable resin, etc. are mentioned. In addition, for example, glassy polymers, such as a siloxane type polymer, are mentioned. Moreover, the polymer film described in Unexamined-Japanese-Patent No. 2001-343529 (WO01/37007) 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 the side chain can be used, for example, isobutene and N- and a resin composition comprising an alternating copolymer composed of methylmaleimide and an acrylonitrile/styrene copolymer. The polymer film may be, for example, an extrusion molding of the resin composition.

When the polarizing plate 100 is applied to an image display device, the thickness of the protective layer (outer protective layer) disposed on the opposite side to the display panel is typically 300 μm or less, preferably 100 μm or less, more preferably It is 5 micrometers - 80 micrometers, More preferably, it is 10 micrometers - 60 micrometers. In addition, when surface treatment is performed, the thickness of an outer side protective layer is the thickness including the thickness of a 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, still more preferably is 10 μm to 60 μm. 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 can be 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), 'ny' is the refractive index in the direction orthogonal to the slow axis in the plane (ie, the fast axis direction), and ' nz' is the refractive index in the thickness direction, and 'd' is the thickness (nm) of the layer (film).

C. Manufacturing method of polarizing film

In the method for manufacturing a polarizing film according to an embodiment of the present invention, a polyvinyl alcohol-based resin layer (PVA-based resin layer) comprising a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin substrate ) to form a laminate, and to the laminate, an aerial auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment for shrinking the laminate by 2% or more in the width direction by heating while conveying in the longitudinal direction, This includes performing sequentially. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. 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 ratio 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 item A above can be obtained. In particular, by producing a laminate including a PVA-based resin layer containing a halide, stretching the laminate in multi-step stretching including air-assisted stretching and underwater stretching, and heating the laminate after stretching with a heating roll, excellent A polarizing film having optical properties (typically, single transmittance and unit absorbance) can be obtained.

C-1. Fabrication of laminates

Any suitable method can be employed as a method for producing a laminate of the thermoplastic resin substrate and the PVA-based resin layer. Preferably, a coating liquid 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 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

Any suitable method can be employ|adopted as a coating method of a coating liquid. For example, the roll coat method, the spin coat method, the wire bar coat method, the dip coat method, the die coat method, the curtain coat method, the spray coat method, the knife coat method (comma coat method, etc.) etc. are mentioned. The coating/drying temperature of the coating liquid is preferably 50°C or higher.

The thickness of the PVA-based resin layer is preferably 2 µm to 30 µm, more preferably 2 µm to 20 µm. By making the thickness of the PVA-based resin layer before stretching very thin in this way and reducing the total draw ratio as described later, a polarizing film having both isotropic shrinkage and acceptable single transmittance and polarization degree can be obtained.

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

C-1-1. Thermoplastic base material

As the thermoplastic resin substrate, any suitable thermoplastic resin film may be employed. About the detail of a thermoplastic resin base material, it describes in Unexamined-Japanese-Patent No. 2012-73580, for example. This publication is incorporated herein by reference in its entirety.

C-1-2. coating liquid

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-based 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. have. These can be used individually or in combination of 2 or more types. Among these, water is preferable. The concentration of the PVA-based resin in the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. If it is such a resin density|concentration, the uniform coating film closely_contact|adhered to a thermoplastic resin base material can be formed. 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.

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 suitable resin may be employed as the PVA-based resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying the ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. Saponification degree can be calculated|required according to JISK6726-1994. By using the PVA-based resin having such a degree of saponification, a polarizing film having excellent durability can be obtained. When the degree of saponification is too high, there is a possibility of gelation. As described above, the PVA-based resin preferably includes an acetoacetyl-modified PVA-based resin.

The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually from 1000 to 10000, preferably from 1200 to 4500, more preferably from 1500 to 4300. In addition, an average degree of polymerization can be calculated|required according to JISK6726-1994.

Any suitable halide may be employed as the halide. Examples include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide and lithium iodide. Among these, potassium iodide is preferable.

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 with respect to 100 parts by weight of the PVA-based resin exceeds 20 parts by weight, the halide may bleed out and the finally obtained polarizing film may become cloudy.

In general, when the PVA-based resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA-based resin is increased, but when the stretched PVA-based resin layer is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules is disturbed, Orientation may fall. In particular, in the case of stretching a laminate of a thermoplastic resin and a PVA-based resin layer in boric acid water, when stretching the laminate in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin, the orientation degree tends to decrease. remarkable For example, in general, stretching of a PVA film alone in boric acid water is performed at 60°C, whereas stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a high temperature of around 70°C. In this case, the orientation of the PVA at the initial stage of stretching may be lowered at a stage before rising by underwater stretching. On the other hand, by producing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate, and stretching the laminate at a high temperature in air (auxiliary stretching) before stretching the laminate in boric acid water, PVA of the laminate after auxiliary stretching Crystallization of the PVA-based resin in the resin-based layer can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, as compared to the case where the PVA-based resin layer does not contain a halide, disorder in the orientation of polyvinyl alcohol molecules and a decrease in orientation can be suppressed. Thereby, the optical characteristic of the polarizing film obtained through the processing process performed by immersing a laminated body in a liquid, such as a dyeing process and an underwater extending|stretching process, can be improved.

C-2. Aerial Auxiliary Stretch Treatment

In particular, in order to obtain high optical properties, a method of two-stage stretching in which dry stretching (auxiliary stretching) and stretching in boric acid water are combined is selected. Like two-stage stretching, by introducing auxiliary stretching, stretching can be performed while suppressing crystallization of the thermoplastic resin substrate. Furthermore, when applying the PVA-based resin on the thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, it is necessary to lower the application temperature compared to the case of applying the PVA-based resin on a conventional metal drum. As a result, crystallization of the PVA-based resin becomes relatively low, and there may be a problem that sufficient optical properties cannot be obtained. On the other hand, by introducing auxiliary stretching, even when the PVA-based resin is applied on the thermoplastic resin, it becomes possible to increase the crystallinity of the PVA-based resin, and it becomes possible to achieve high optical properties. At the same time, by increasing the orientation of the PVA-based resin in advance, problems such as a decrease in the orientation and dissolution of the PVA-based resin when immersed in water in a subsequent dyeing process or stretching process can be prevented, and high optical properties are achieved it becomes possible to do

The stretching method of the aerial assisted stretching may be fixed-end stretching (eg, stretching using a tenter stretching machine) or free-end stretching (eg, uniaxial stretching by passing a laminate between rolls having different circumferential speeds) However, free-end stretching can be actively employed in order to obtain high optical properties. In one embodiment, the aerial stretching treatment includes a heating roll stretching step of stretching the laminate by a difference in circumferential speed between heating rolls while conveying the laminate in its longitudinal direction. The aerial stretching process typically includes a zone stretching process and a hot roll stretching process. In addition, the order of a zone extending|stretching process and a heated roll extending process is not limited, A zone extending|stretching process may be performed first, and a hot roll extending|stretching process may be performed first. The zone stretching step may be omitted. In one embodiment, the zone stretching process and the heated roll stretching process are performed in this order. Moreover, in another embodiment, in a tenter stretching machine, it is extended|stretched by holding|gripping a film edge part and expanding the distance between tenters in a flow direction (extension of the distance between tenters becomes a draw ratio). At this time, the distance of the tenter in the width direction (direction perpendicular to the flow direction) is set so as to approach arbitrarily. Preferably, with respect to the draw ratio in the flow direction, it may be set to be close to the free end elongation. In the case of free-end stretching, it is calculated as the shrinkage ratio in the width direction = (1/stretch ratio) ^1/2.

Aerial assisted stretching may be performed in one step, and may be performed in multiple steps. When carrying out in multiple steps, the draw ratio is the product of the draw ratios of each step. The stretching direction in the aerial assisted stretching is preferably substantially the same as the stretching direction in the underwater stretching.

The draw ratio in aerial auxiliary stretching is preferably 1.0 to 4.0, more preferably 1.5 to 3.5, and still more preferably 2.0 to 3.0. If the draw ratio of the aerial assisted stretching is within such a range, the total magnification of the stretching can be set in a desired range when combined with the underwater stretching, and a desired isotropic shrinkage can be realized. As a result, a polarizing film with curvature in the absorption axis direction suppressed can be obtained. Moreover, as mentioned above, the draw ratio of aerial auxiliary drawing is larger than the draw ratio of boric-acid underwater drawing. By setting it as such a structure, even if the total magnification of extending|stretching is small, the polarizing film which has an acceptable optical characteristic can be obtained.

The stretching temperature of the aerial auxiliary stretching can be set to any appropriate value depending on the forming material of the thermoplastic resin substrate, the stretching method, and the like. The stretching temperature is preferably at least the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably at least the glass transition temperature (Tg) of the thermoplastic resin substrate +10°C, particularly preferably at least Tg+15°C. On the other hand, the upper limit of extending|stretching temperature becomes like this. Preferably it is 170 degreeC. By stretching at such a temperature, it is possible to suppress the rapid progress of crystallization of the PVA-based resin, thereby suppressing problems due to the crystallization (eg, hindering the orientation of the PVA-based resin layer by stretching).

C-3. Insolubilization treatment, dyeing treatment and crosslinking treatment

If necessary, insolubilization treatment is performed after the aerial auxiliary stretching treatment and before the underwater stretching treatment or dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). If necessary, a crosslinking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. Details of the insolubilization treatment, the dyeing treatment and the crosslinking treatment are described in, for example, Japanese Unexamined Patent Publication No. 2012-73580 (above).

C-4. Underwater stretching treatment

The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, stretching can be performed at a temperature lower than the glass transition temperature (typically about 80° C.) of the thermoplastic resin substrate or the PVA-based resin layer, and the PVA-based resin layer can be stretched while suppressing its crystallization. . As a result, a polarizing film having excellent optical properties can be manufactured.

Any suitable method can be employ|adopted for the extending|stretching method of a laminated body. Specifically, fixed-end stretching may be used, or free-end stretching (for example, a method of uniaxial stretching by passing a laminated body between rolls having different circumferential speeds) may be used. Preferably free-end stretching is selected. Extending|stretching of a laminated body may be performed in one step, and may be performed in multiple steps. When carrying out in multiple stages, the total magnification of stretching is the product of the stretching magnifications of each stage.

Stretching in water is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water). By using the boric acid aqueous solution as a stretching bath, rigidity to withstand the tension applied at the time of stretching to the PVA-based resin layer, and water resistance that does not dissolve in water can be imparted. Specifically, boric acid can be crosslinked by hydrogen bonding with the PVA-based resin by generating a tetrahydroxyboric acid anion in an aqueous solution. As a result, rigidity and water resistance are provided to the PVA-based resin layer, so that it can be stretched favorably, and a polarizing film having excellent optical properties can be manufactured.

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

Preferably, an iodide is blended in the stretching bath (aqueous boric acid solution). By mix|blending an iodide, the elution of the iodine made to adsorb|suck to the PVA-type resin layer can be suppressed. Specific examples of the iodide are as described above. The concentration of iodide is preferably 0.05 parts by weight to 15 parts by weight, more preferably 0.5 parts by weight to 8 parts by weight based on 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 a temperature, it can extend|stretch at a 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 higher in relation to the formation of the PVA-based resin layer. In this case, when extending|stretching temperature is less than 40 degreeC, even if it considers plasticization of the thermoplastic resin base material by water, there exists a possibility that it may not be able to extend|stretch favorably. On the other hand, as the temperature of the stretching bath increases, the solubility of the PVA-based resin layer increases, and there is a fear that excellent optical properties may not be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The draw ratio by extending|stretching in water becomes like this. Preferably they are 1.0 times - 3.0 times, More preferably, they are 1.0 times - 2.0 times, More preferably, they are 1.0 times - 1.5 times. If the draw ratio in the underwater stretching is within such a range, the total stretching ratio can be set in a desired range, and desired isotropic shrinkage can be realized. As a result, a polarizing film with curvature in the absorption axis direction suppressed can be obtained. The total magnification of stretching (the sum of the magnifications in the case of combining air-assisted stretching and underwater stretching) is, for example, 3.0 to 4.5 times, preferably 3.0 to 4.0 times, with respect to the original length of the laminate as described above, more Preferably it is 3.0 times - 3.5 times. By appropriately combining the addition of the halide to the coating solution, the adjustment of the draw ratios of the aerial assisted stretching and the underwater stretching, and the drying shrinkage treatment, a polarizing film having acceptable optical properties even at such a total stretching ratio can be obtained.

C-5. dry shrinkage treatment

The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or may be performed by heating a conveyance roll (using a so-called heating roll) (heating 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 an external appearance can be manufactured. Specifically, by drying in a state in which the laminate is poured on a heating roll, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the crystallinity, and even at a relatively low drying temperature, the crystallinity of the thermoplastic resin substrate can be favorably increased. can As a result, the rigidity of the thermoplastic resin substrate increases, and it becomes a state capable of withstanding the shrinkage of the PVA-based resin layer due to drying, and curling (warpage) is suppressed. Moreover, by using a heating roll, since a laminated body can be dried, maintaining a flat state, generation|occurrence|production of not only curls but wrinkles can also be suppressed. At this time, the optical properties can be improved by shrinking the laminate in the width direction by drying shrinkage treatment. It is because the orientation of PVA and a PVA/iodine complex can be improved effectively. 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%.

2 is a schematic diagram showing an example of a drying shrinkage treatment. In the drying shrinkage treatment, the laminate 200 is dried while being conveyed by the conveying rolls R1 to R6 and the guide rolls G1 to G4 heated to a predetermined temperature. In the illustrated example, the conveying 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 substrate. For example, only one surface of the laminate 200 (eg, the surface of the thermoplastic resin substrate) You may arrange|position conveyance rolls R1-R6 so that it may heat continuously.

Drying conditions are controllable by adjusting the heating temperature (temperature of a heating roll) of a conveyance roll, the number of heating rolls, contact time with a heating roll, etc. The temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. While the crystallinity degree of a thermoplastic resin can be increased favorably and curl can be suppressed favorably, the optical laminated body extremely excellent in durability can be manufactured. In addition, the temperature of a heating roll can be measured with a contact thermometer. Although six conveyance rolls are provided in the example of illustration, if there are several conveyance rolls, there will be no restriction|limiting in particular. The number of conveyance rolls is 2-40 normally, Preferably 4-30 pieces are provided. The contact time (total contact time) between the laminate and the heating roll is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and still more preferably 1 to 10 seconds.

A heating roll may be provided in a heating furnace (for example, oven), and may be provided in a normal production line (under a room temperature environment). Preferably, it is provided in the heating furnace provided with the blowing means. By using together drying by a heating roll and hot air drying, the rapid temperature change between heating rolls can be suppressed, and the contraction|shrinkage of the width direction can be controlled easily. The temperature of hot air drying becomes like this. Preferably it is 30 degreeC - 100 degreeC. Further, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the 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.

C-6. other processing

Preferably, a washing process is performed after an underwater extending|stretching process and before a dry shrinkage process. The washing treatment is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

[Example]

Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these Examples. The measuring method of each characteristic is as follows. In addition, unless otherwise specified, 'part' and '%' in Examples and Comparative Examples are based on weight.

(1) thickness

It was measured using the interference film thickness measuring meter (made by Otsuka Electronics, product name "MCPD-3000").

(2) Shrinkage S _MD and S _TD

The polarizing films obtained in Examples and Comparative Examples were cut out in a square of 10 cm in the absorption axis direction x 10 cm in the transmission axis direction to prepare a test sample. Precise dimensions in the absorption axis direction and transmission axis direction of the test sample were measured with a 'CNC image measuring machine' manufactured by Mitutoyo, and the respective dimensions were designated as S _MD0 and S _TD0 . After dimension measurement, the test sample was heated at 85 degreeC for 120 hours, and the dimension after heating was carried out similarly, and it measured. The dimensions after heating were designated as S _MD1 and S _TD1 , respectively. The shrinkage rate (S _MD ) in the absorption axis direction was calculated as (S _MD0 -S _MD1 )/S _MD0 × 100. The shrinkage rate (S _TD ) in the transmission axis direction was calculated as (S _TD0 -S _TD1 )/S _TD0 ×100. _{S MD} /S _TD was calculated from the obtained S _MD and S _TD.

(3) Single transmittance and polarization degree

For the laminate (polarizing plate) of the polarizing film/protective layer obtained in Examples and Comparative Examples, the single transmittance (Ts) measured using an ultraviolet/visible light spectrophotometer ('V-7100' manufactured by Nippon Bunko Co., Ltd.), parallel The transmittance (Tp) and the orthogonal transmittance (Tc) were defined as Ts, Tp, and Tc of the polarizing film, respectively. These Ts, Tp, and Tc are Y values which measured with the 2 degree field of view (C light source) of JIS Z8701, and performed visibility correction|amendment. In addition, the refractive index of the protective layer was 1.50 or 1.53, and the refractive index of the surface of the polarizing film opposite to the protective layer was 1.53.

Polarization degree (P) was calculated|required by the following formula from the obtained Tp and Tc.

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

In addition, it is confirmed that the spectrophotometer can perform equivalent measurement with "LPF-200" manufactured by Otsuka Denshi Co., Ltd., etc., and equivalent measurement results can be obtained even when any spectrophotometer is used.

(4) Warpage of the panel

The laminated body (polarizing plate) of the polarizing film/protective layer obtained by the Example and the comparative example was pasted together to the thin glass plate (0.1mm in thickness), and it was set as the image display panel correspondence sample. This image display panel corresponding sample was subjected to a heating test at 80°C for 24 hours, and the warpage after the test was measured. The average of the curvature amounts of the four corners of the image display panel correspondence sample was made into the curvature amount of a panel, and the following reference|standard evaluated.

○: Deflection amount less than 4 mm

×: Deflection amount is 4 mm or more

(5) bending test

The polarizing film/protective layer laminate (polarizing plate) obtained in Examples and Comparative Examples was cut to a size of 120 mm (absorption axis direction of the polarizing film) × 30 mm (direction orthogonal to the absorption axis direction of the polarizing film), and was used as a measurement sample. A continuous bending test was performed on this measurement sample using a continuous bending test apparatus (manufactured by Yuasa Systems Instruments Co., Ltd., product name 'DLDMLH-FS') in the no-load U-shaped expansion and contraction mode. The bending speed was 60 rpm, the bending amplitude was 20 mm, the bending radius of the bending was 1.0 mm, and the number of bending was 100000 times. Evaluation was made on the basis of the following criteria.

○: No fold marks were found.

x: A fold trace was confirmed

[Example 1]

As the thermoplastic resin substrate, an amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 µm) having a long, water absorption rate of 0.75% and a Tg of about 75°C was used. Corona treatment (treatment conditions: 55 W·min/m ² ) was performed on one side of the resin substrate.

Potassium iodide 13 in 100 parts by weight of a 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 'Goseimer Z410') were mixed in 9:1 A PVA aqueous solution (coating solution) was prepared by adding parts by weight.

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

The obtained laminate was uniaxially stretched at the free end by 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different circumferential speeds in an oven at 130°C (air-assisted stretching treatment).

Next, the laminate was immersed in an insolubilization bath (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubilization treatment).

Next, in a dyeing bath at a liquid temperature of 30°C (an aqueous solution of iodine obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with respect to 100 parts by weight of water) so that the single transmittance (Ts) of the finally obtained polarizing film is 41.0% It was immersed for 60 seconds while adjusting the density|concentration (dyeing process).

Then, it was immersed in a crosslinking bath (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide with respect to 100 parts by weight of water and 5 parts by weight of boric acid) with a liquid temperature of 40°C for 30 seconds (crosslinking treatment).

Thereafter, while immersing the laminate in an aqueous boric acid solution (boric acid concentration of 4.0% by weight, potassium iodide 5.0% by weight) at a liquid temperature of 62°C, the total draw ratio is 3.0 times in the longitudinal direction (longitudinal direction) between rolls having different circumferential speeds. Uniaxial stretching was performed as much as possible (underwater stretching treatment: the draw ratio in the underwater stretching treatment was 1.25 times).

Thereafter, the laminate was immersed in a washing bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) having a liquid temperature of 20°C (washing treatment).

Thereafter, while drying in an oven maintained at 90°C, it was brought into contact with a heating roll made of SUS whose surface temperature was maintained at 75°C for about 2 seconds (dry shrinkage treatment). The shrinkage ratio in the width direction of the laminate by the drying shrinkage treatment was 2%.

In this way, a polarizing film having a thickness of 6.8 µm was formed on the resin substrate.

On the surface (surface opposite to the resin substrate) of the polarizing film obtained above, as a protective film, an unstretched cycloolefin-based film (“Zeonoa Film: ZF14” manufactured by Nippon Zeon, surface refractive index 1.53, thickness 25 μm) was applied with ultraviolet rays. It was bonded together through a curable adhesive. Specifically, it coated so that the total thickness of a curable adhesive might be set to 1.0 micrometer, and it bonded together using the roll machine. Thereafter, UV rays were irradiated from the protective film side to cure the adhesive. Next, the resin base material was peeled, and the polarizing plate which has the structure of a protective film/polarizing film was obtained. A polarizing plate with an adhesive layer (protective film / polarizing film / adhesive) by bonding the adhesive from which the creep amount becomes 70 micrometers/h when the load of 500 g is applied to the polarizing plate obtained above for 1 hour to the surface which peeled the resin base material of a polarizing film, layer) was obtained.

About the obtained polarizing film or polarizing plate, S _MD , S _TD and S _MD /S _TD , single transmittance|permeability, polarization degree, and also the result of the bending and bending test are shown in Table 1.

[Example 2]

A polarizing plate and a polarizing plate with an adhesive layer were prepared in the same manner as in Example 1 except that a diagonally stretched cycloolefin film ('Zeonoa film: ZD12' manufactured by Nippon Zeon, 1.53 surface refractive index, 25 µm in thickness) was used as a protective film. . The obtained polarizing film or polarizing plate was used for evaluation similar to Example 1. A result is shown in Table 1.

[Example 3]

Except having used the 20-micrometer-thick acrylic film as a protective film, it carried out similarly to Example 1, and produced the polarizing plate and the polarizing plate with an adhesive layer. The obtained polarizing film or polarizing plate was used for evaluation similar to Example 1. A result is shown in Table 1.

[Example 4]

A polarizing film having a thickness of 6.4 µm was produced in the same manner as in Example 1 except that the draw ratio of the underwater stretching treatment was set to 1.45 times and the total draw ratio was made 3.5 times. Except having used this polarizing film, it carried out similarly to Example 3, and produced the polarizing plate and the polarizing plate with an adhesive layer. The obtained polarizing film or polarizing plate was used for evaluation similar to Example 1. A result is shown in Table 1.

[Example 5]

A polarizing film having a thickness of 5.9 µm was produced in the same manner as in Example 1 except that the draw ratio of the underwater stretching treatment was 1.67 times and the total draw ratio was 4.0 times. Except having used this polarizing film, it carried out similarly to Example 3, and produced the polarizing plate and the polarizing plate with an adhesive layer. The obtained polarizing film or polarizing plate was used for evaluation similar to Example 1. A result is shown in Table 1.

[Comparative Example 1]

A polarizing film having a thickness of 5.0 µm was produced in the same manner as in Example 1, except that the draw ratio of the underwater stretching treatment was 2.4 times, the total draw ratio was 5.5 times, and the liquid temperature of the stretching bath was 70°C. Except having used this polarizing film, it carried out similarly to Example 1, and produced the polarizing plate and the polarizing plate with an adhesive layer. The obtained polarizing film or polarizing plate was used for evaluation similar to Example 1. A result is shown in Table 1.

[Comparative Example 2]

A polarizing plate and a polarizing plate with an adhesive layer were produced in the same manner as in Comparative Example 1 except that the diagonally stretched cycloolefin-based film was used as the protective film. The obtained polarizing film or polarizing plate was used for evaluation similar to Example 1. A result is shown in Table 1.

[Comparative Example 3]

Except having used the acrylic resin film as a protective film, it carried out similarly to the comparative example 1, and produced the polarizing plate and the polarizing plate with an adhesive layer. The obtained polarizing film or polarizing plate was used for evaluation similar to Example 1. A result is shown in Table 1.

[Comparative Example 4]

A long roll of 30 μm thick PVA-based resin film (manufactured by Kuraray, product name 'PE3000') is uniaxially stretched in the long direction with a total draw ratio of 6.0 by a roll stretching machine, while simultaneously swelling, dyeing, crosslinking and washing. The 12-micrometer-thick polarizer was produced by giving a process and drying process finally. A polarizing plate was produced by bonding the diagonally stretched cycloolefin-based film to one side of this polarizer. Moreover, except having used this polarizing plate, it carried out similarly to Example 1, and produced the polarizing plate with an adhesive layer. The obtained polarizer or polarizing plate was used for evaluation similar to Example 1. A result is shown in Table 1.

[Comparative Example 5]

A polarizer having a thickness of 17 µm was produced in the same manner as in Comparative Example 4 except that the total draw ratio was set to 3.0 times. Except having used this polarizer, it carried out similarly to Example 1, and produced the polarizing plate and the polarizing plate with an adhesive layer. The obtained polarizer or polarizing plate was used for evaluation similar to Example 1. A result is shown in Table 1.

[Table 1]

As is clear from Table 1, the polarizing film of Examples of the present invention suppresses warpage and has excellent bendability.

Industrial Applicability

The polarizing film and polarizing plate of this invention are used suitably for a liquid crystal display device.

10: polarizing film
20: first protective layer
30: second protective layer
100: polarizer

Claims (7)

_{The ratio of the shrinkage ratio in the absorption axis direction (S MD} ) to the shrinkage ratio in the direction orthogonal to the absorption axis direction (S _TD ) after it is composed of a polyvinyl alcohol-based resin film containing a dichroic material and left at 85° C. for 120 hours S _MD /S _TD of 0.5 to 1.5, the polarizing film. According to claim 1,
A polarizing film having a thickness of 8 μm or less. 3. The method of claim 1 or 2,
A polarizing film having a single transmittance of 40.0% or more and a polarization degree of 99.0% or more. 4. The method according to any one of claims 1 to 3,
The polarizing film, wherein the shrinkage ratio (S _MD ) in the absorption axis direction and the shrinkage ratio (S _TD ) in the direction orthogonal to the absorption axis direction are 0.4% or less, respectively. 5. The method according to any one of claims 1 to 4,
A polarizing film having an orientation function of 0.30 or less. A polarizing plate comprising the polarizing film according to any one of claims 1 to 5, and a protective layer disposed on at least one side of the polarizing film. As the manufacturing method of the polarizing film in any one of Claims 1-5,
forming a polyvinyl alcohol-based resin layer containing iodide or sodium chloride and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate to obtain a laminate; and
The laminate is subjected to an aerial auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment for shrinking the laminate by 2% or more in the width direction by heating while conveying in the longitudinal direction, in this order,
A total magnification of the stretching of the aerial auxiliary stretching treatment and the underwater stretching treatment is 3.0 to 4.0 times the original length of the laminate,
The draw ratio of the aerial auxiliary drawing process is larger than the draw ratio of the said underwater drawing process,
manufacturing method.

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