JP2019194662A - Polarizing film, polarizing plate, polarizing plate roll, and method of manufacturing polarizing film - Google Patents

Abstract

To provide a polarizing film with superior optical characteristics.SOLUTION: A polarizing film of the present invention has a thickness of 8 μm or less, single transmittance of 45% or greater, and polarization degree of 97% or greater.SELECTED DRAWING: Figure 1

Description

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

  With the spread of thin displays, displays (OLEDs) equipped with 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 highly reflective metal layer and are liable to cause problems such as external light reflection and background reflection. Therefore, it is known to prevent these problems by providing a circularly polarizing plate having a polarizing film and a λ / 4 plate on the viewing side. As a method for producing the polarizing film, for example, there is a method in which a laminate having a resin base material and a polyvinyl alcohol (PVA) resin layer is stretched and then subjected to a dyeing treatment to obtain a polarizing film on the resin base material. It has been proposed (for example, Patent Document 1). According to such a method, a polarizing film having a small thickness can be obtained, and thus has been attracting attention as being able to contribute to the recent thinning of image display devices. However, the conventional thin polarizing film as described above has insufficient optical characteristics, and further improvement of the optical characteristics of the thin polarizing film is required.

JP 2001-343521 A

  The present invention has been made to solve the above-described conventional problems, and its main purpose is to provide a polarizing film, a polarizing plate, a polarizing plate roll, and a method for producing such a polarizing film having excellent optical properties. There is to do.

The polarizing film of the present invention has a thickness of 8 μm or less, a single transmittance of 45% or more, and a polarization degree of 97% or more.
In one embodiment, the single transmittance is 46% or less and the degree of polarization is 99% or less.
According to another aspect of the present invention, a polarizing plate is provided. This polarizing plate has a polarizing film and a protective layer disposed on at least one side of the polarizing film.
In one embodiment, the polarizing plate has a width of 1000 mm or more, and a difference between the maximum value and the minimum value of the single transmittance at a position along the width direction is 0.5% or less.
In one embodiment, the difference between the maximum value and the minimum value of the single transmittance in the region of 50 cm ² is 0.2% or less.
According to another aspect of the present invention, a polarizing plate roll is provided. The polarizing plate roll is formed by winding the polarizing plate into a roll.
According to another situation of this invention, the manufacturing method of a polarizing film is provided. This manufacturing method is a manufacturing method of the polarizing film, wherein a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of a long thermoplastic resin base material, And an air-assisted auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment that shrinks by 2% or more in the width direction by heating while transporting in the longitudinal direction. Including applying in order.
In one embodiment, content of the said halide in the said polyvinyl alcohol-type resin layer is 5 weight part-20 weight part with respect to 100 weight part of the said polyvinyl alcohol-type resin.
In one embodiment, the draw ratio in the said air auxiliary | assistant extending | stretching process is 2.0 times or more.
In one embodiment, the drying shrinkage treatment step is a step of heating using a heating roll.
In one embodiment, the temperature of the said heating roll is 60 to 120 degreeC, and the shrinkage | contraction rate of the width direction of the said laminated body by the said drying shrinkage process is 2% or more.

  According to the present invention, it is possible to provide a polarizing film having excellent optical properties having a thickness of 8 μm or less, a single transmittance of 45% or more, and a polarization degree of 97% or more.

It is a schematic sectional drawing of the polarizing plate by one Embodiment of this invention. It is the schematic which shows an example of the drying shrinkage process using a heating roll. It is a graph which shows the optical characteristic of the polarizing plate obtained by the Example and the comparative example.

  Hereinafter, although embodiment of this invention is described, this invention is not limited to these embodiment.

A. Polarizing Film The polarizing film according to one embodiment of the present invention has a thickness of 8 μm or less, a single transmittance of 45% or more, and a polarization degree of 97% or more. In general, the single transmittance and the degree of polarization are in a trade-off relationship with each other. Increasing the single transmittance can decrease the degree of polarization, and increasing the degree of polarization can decrease the single transmittance. For this reason, conventionally, it has been difficult to put into practical use a thin polarizing film that satisfies the optical characteristics of a single transmittance of 45% or more and a degree of polarization of 97% or more. As described above, the polarizing film according to one embodiment of the present invention has excellent optical characteristics such that the single transmittance is 45% or more and the degree of polarization is 97% or more. Furthermore, by using the polarizing film of this embodiment, it is possible to realize a polarizing plate in which variations in optical characteristics are suppressed. Realizing such a thin polarizing film (polarizing plate) is one of the achievements of the present invention. Such a polarizing film (polarizing plate) can be used for an image display device, and is particularly preferably used for a circular 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 further preferably 2 μm to 5 μm.

The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance of the polarizing film is preferably 46% or less. The polarization degree of the polarizing film is preferably 97.5% or more, more preferably 98% or more. On the other hand, the upper limit of the degree of polarization is preferably 99%. The single transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and corrected for visibility. The degree of polarization is typically obtained by the following equation based on the parallel transmittance Tp and orthogonal transmittance Tc measured by using an ultraviolet-visible spectrophotometer and corrected for visibility.
Polarization degree (%) = {(Tp−Tc) / (Tp + Tc)} ^1/2 × 100

In one embodiment, the transmittance of a thin polarizing film of 8 μm or less is typically a laminate of a polarizing film (surface refractive index: 1.53) and a protective film (refractive index: 1.50). It is measured using an ultraviolet-visible spectrophotometer with the body as the measurement object. Depending on the refractive index of the surface of the polarizing film and / or the refractive index of the surface in contact with the air interface of the protective film, the reflectance at the interface of each layer may change, and as a result, the measured value of transmittance may change. . Therefore, for example, when using a protective film whose refractive index is not 1.50, the measured value of the transmittance may be corrected according to the refractive index of the surface of the protective film in contact with the air interface. Specifically, the transmittance correction value C is expressed by the following equation using the reflectance R ₁ (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective film and the air layer.
C = R ₁ −R _{0
^{R 0 = ((1.50-1) 2}} /(1.50+1) 2) × (T 1/100)
^{_{R 1 = ((n 1 -1}} ) 2 / (n 1 +1) 2) × (T 1/100)
Here, R ₀ is the transmission axis reflectance when a protective film having a refractive index of 1.50 is used, n ₁ is the refractive index of the protective film used, and T ₁ is the transmittance of the polarizing film. It is. For example, when a substrate having a surface refractive index of 1.53 (such as a cycloolefin film or a film with a hard coat layer) is used as a protective film, the correction amount C is about 0.2%. In this case, by adding 0.2% to the transmittance obtained by the measurement, it is possible to convert to the transmittance when a protective film having a surface refractive index of 1.50 is used. According to the calculation based on the above formula, the change amount of the correction value C when the transmittance T _{1 of the} polarizing film is changed by 2% is 0.03% or less, and the transmittance of the polarizing film is the correction value C. The effect on the value of is limited. Moreover, when a protective film has absorption other than surface reflection, appropriate correction | amendment can be performed according to absorption amount.

  Any appropriate polarizing film can be adopted as 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 resin layer formed by coating on the resin substrate. For example, a polarizing film obtained by using a laminate of a resin base material and a PVA resin layer applied and formed on the resin base material may be obtained by applying a PVA resin solution to a resin base material and drying it. A PVA-based resin layer is formed thereon to obtain a laminate of a resin base material and a PVA-based resin layer; the laminate is stretched and dyed to form a PVA-based resin layer as a polarizing film; obtain. In the present embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching. Further, the stretching may further include, if necessary, stretching the laminate in the air at a high temperature (for example, 95 ° C. or higher) before stretching in the boric acid aqueous solution. The obtained resin substrate / polarizing film laminate may be used as it is (that is, the resin substrate may be used as a protective layer of the polarizing film), and the resin substrate is peeled from the resin substrate / polarizing film laminate. Any appropriate protective layer according to the purpose may be laminated on the release surface. Details of the method of manufacturing such a polarizing film are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. This publication is incorporated herein by reference in its entirety.

  The method for producing a polarizing film of the present invention includes forming a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin base material to form a laminate, and Including subjecting the laminate to an air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in which the shrinkage is contracted by 2% or more in the width direction by heating in the longitudinal direction in this order. . As a result, a polarizing film having excellent optical characteristics and a suppressed variation in optical characteristics, with a thickness of 8 μm or less, a single transmittance of 45% or more, and a degree of polarization of 97% or more can be provided. . That is, by introducing auxiliary stretching, even when PVA is applied onto a thermoplastic resin, the crystallinity of PVA can be increased and high optical properties can be achieved. At the same time, by increasing the orientation of the PVA in advance, it is possible to prevent problems such as a decrease in the orientation of the PVA and dissolution when immersed in water in the subsequent dyeing process or stretching process, and high optical properties. Can be achieved. Furthermore, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. Thereby, the optical characteristic of the polarizing film obtained through the process process performed by immersing a laminated body in a liquid, such as a dyeing | staining process and an underwater extending | stretching process, can be improved. Furthermore, optical properties can be improved by shrinking the laminate in the width direction by a drying shrinkage treatment.

B. Polarizing Plate FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present 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 30 disposed on the other side of the polarizing film 10. The polarizing film 10 is the polarizing film of the present invention described in the above section A. One of the first protective layer 20 and the second protective layer 30 may be omitted. As described above, one of the first protective layer and the second protective layer may be a resin base material used for manufacturing the polarizing film.

The polarizing plate may be long or single-wafer. When a polarizing plate is elongate, it is preferable that it is wound by roll shape and it is set as a polarizing plate roll. The polarizing plate has excellent optical properties and small variations in optical properties. In one embodiment, the polarizing plate has a width of 1000 mm or more, and a difference (D1) between the maximum value and the minimum value of the single transmittance at a position along the width direction is 0.5% or less. The upper limit of D1 is preferably 0.4%, more preferably 0.3%. D1 is preferably as small as possible, but the lower limit is, for example, 0.01%. If D1 is in the above range, a polarizing plate having excellent optical properties can be produced industrially. In another embodiment, the polarizing plate has a difference (D2) between the maximum value and the minimum value of the single transmittance within a region of 50 cm ² of 0.2% or less. The upper limit of D2 is preferably 0.15%, more preferably 0.1%. D2 is preferably as small as possible, but the lower limit is, for example, 0.01%. When D2 is within the above range, luminance variations on the display screen can be suppressed when the polarizing plate is used in an image display device.

  The first and second protective layers are formed of any appropriate film that can be used as a protective layer for the polarizing film. Specific examples of the material that is the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based materials. And transparent resins such as polystyrene, polynorbornene, polyolefin, (meth) acryl, and acetate. Further, thermosetting resins such as (meth) acrylic, urethane-based, (meth) acrylurethane-based, epoxy-based, and silicone-based or ultraviolet curable resins are also included. In addition to this, for example, a glassy polymer such as a siloxane polymer is also included. Moreover, the polymer film as described in Unexamined-Japanese-Patent No. 2001-343529 (WO01 / 37007) can also be used. Examples of the material of the film include a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain, and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain. For example, a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer can be mentioned. The polymer film can be, for example, an extruded product 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 side opposite to the display panel is typically 300 μm or less, preferably 100 μm or less, more preferably It is 5 μm to 80 μm, more preferably 10 μm to 60 μm. In addition, when the surface treatment is performed, 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 even more preferably 10 μm to 60 μm. is there. In one embodiment, the inner protective layer is a retardation layer having any suitable retardation value. In this case, the in-plane retardation Re (550) of the retardation layer is, for example, 110 nm to 150 nm. “Re (550)” is an in-plane retardation measured with light having a wavelength of 550 nm at 23 ° C., and is obtained by the formula: Re = (nx−ny) × d. Here, “nx” is the refractive index in the direction in which the in-plane refractive index is maximum (that is, the slow axis direction), and “ny” is the direction orthogonal to the slow axis in the plane (that is, fast phase). The refractive index in the axial direction), “nz” is the refractive index in the thickness direction, and “d” is the thickness (nm) of the layer (film).

C. Method for Producing Polarizing Film A method for producing a polarizing film according to one embodiment of the present invention comprises a polyvinyl alcohol containing a halide and a polyvinyl alcohol resin (PVA resin) on one side of a long thermoplastic resin substrate. By forming a laminated resin layer (PVA-based resin layer) to form a laminate, and heating the laminate while transporting it in the longitudinal direction, in-air auxiliary stretching treatment, dyeing treatment, underwater stretching treatment And a drying shrinkage treatment for shrinking 2% or more in the width direction in this order. 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 the above section A can be obtained. In particular, by producing a laminate including a PVA-based resin layer containing a halide, stretching the laminate to multistage stretching including air-assisted stretching and underwater stretching, and heating the stretched laminate with a heating roll Thus, it is possible to obtain a polarizing film having excellent optical characteristics (typically, single transmittance and degree of polarization) and suppressed variation in optical characteristics. Specifically, by using a heating roll in the drying shrinkage treatment step, the laminate can be uniformly shrunk over the entire laminate while being conveyed. As a result, not only can the optical characteristics of the obtained polarizing film be improved, but also a polarizing film with excellent optical characteristics can be stably produced, and variations in the optical characteristics (particularly the single transmittance) of the polarizing film are suppressed. can do.

C-1. Production of Laminate Any appropriate method can be adopted as a method of producing a laminate of a thermoplastic resin substrate and a PVA resin layer. Preferably, a PVA resin layer is formed on the thermoplastic resin substrate by applying a coating solution containing a halide and a PVA resin on the surface of the thermoplastic resin substrate 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 with respect to 100 parts by weight of the PVA-based resin.

  Any appropriate method can be adopted as a coating method of the coating solution. Examples thereof include a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (comma coating method and the like). The coating / drying temperature of the coating solution is preferably 50 ° C. or higher.

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

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

C-1-1. Thermoplastic resin substrate The thickness of the thermoplastic resin substrate is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If it is less than 20 μm, it may be difficult to form a PVA-based resin layer. If it exceeds 300 μm, for example, in the below-described underwater stretching treatment, it may take a long time for the thermoplastic resin substrate to absorb water, and an excessive load may be required for stretching.

  The thermoplastic resin substrate preferably has a water absorption rate of 0.2% or more, more preferably 0.3% or more. The thermoplastic resin substrate can absorb water and plasticize by acting as a plasticizer. As a result, the stretching stress can be greatly reduced, and the film can be stretched at a high magnification. On the other hand, the water absorption rate 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 problems such as the dimensional stability of the thermoplastic resin substrate being significantly reduced during production and the appearance of the resulting polarizing film being deteriorated. Moreover, it can prevent that a base material fractures | ruptures at the time of extending | stretching in water, or a PVA-type resin layer peels from a thermoplastic resin base material. In addition, the water absorption rate of a thermoplastic resin base material can be adjusted by introduce | transducing a modification group into a constituent material, for example. The water absorption is a value determined according to JIS K 7209.

  The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120 ° C. or lower. By using such a thermoplastic resin base material, the stretchability of the laminate can be sufficiently ensured while suppressing the crystallization of the PVA-based resin layer. Furthermore, in view of plasticizing the thermoplastic resin substrate with water and performing good stretching in water, it is more preferably 100 ° C. or lower, more preferably 90 ° C. or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60 ° C. or higher. By using such a thermoplastic resin base material, the thermoplastic resin base material is deformed (for example, generation of irregularities, talmi, wrinkles, etc.) when the coating solution containing the PVA resin is applied and dried. Thus, a laminate can be produced satisfactorily. In addition, the PVA-based resin layer can be satisfactorily stretched at a suitable temperature (for example, about 60 ° C.). In addition, the glass transition temperature of a thermoplastic resin base material can be adjusted by heating using the crystallizing material which introduce | transduces a modification group into a constituent material, for example. The glass transition temperature (Tg) is a value obtained according to JIS K7121.

  Any appropriate thermoplastic resin can be adopted as a constituent material of the thermoplastic resin substrate. Examples of the thermoplastic resin include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Is mentioned. Among these, preferred are norbornene resins and amorphous polyethylene terephthalate resins.

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

  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 extremely excellent in stretchability, and crystallization during stretching can be suppressed. This is thought to be due to the introduction of an isophthalic acid unit to give a large bend 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, more preferably 1.0 mol% or more, based on the total of all repeating units. This is because a thermoplastic resin substrate having extremely 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, based on the total of all repeating units. By setting to such a content rate, the crystallinity can be favorably increased in the drying shrinkage treatment described later.

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

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

  Any appropriate method can be adopted as a method for stretching the thermoplastic resin substrate. Specifically, it may be fixed end stretching or free end stretching. The stretching method may be dry or wet. The stretching of the thermoplastic resin substrate may be performed in one step or in multiple steps. When performing in multiple stages, the above-mentioned draw ratio is the product of the draw ratios of the respective stages.

C-1-2. Coating liquid The coating liquid contains a halide and a PVA resin as described above. The coating solution is typically a solution in which the halide and the PVA resin are dissolved in a solvent. Examples of the solvent include water, 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. Among these, water is preferable. The concentration of the PVA resin in the solution is preferably 3 to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film in close contact with the thermoplastic resin substrate can be formed. The content of the halide in the coating solution is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA resin.

  You may mix | blend an additive with a 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. Examples of the surfactant include nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability and stretchability of the resulting PVA-based resin layer.

  Any appropriate resin can be adopted as the PVA-based resin. Examples thereof include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA 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%. . The saponification degree can be determined according to JIS K 6726-1994. By using a 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, there is a risk of gelation.

  The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, more preferably 1500 to 4300. The average degree of polymerization can be determined according to JIS K 6726-1994.

  Any appropriate halide can be adopted as the halide. Examples include iodide and sodium chloride. Examples of iodide include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferable.

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

  In general, the orientation of the polyvinyl alcohol molecules in the PVA-based resin is increased by stretching the PVA-based resin layer. However, when the stretched PVA-based resin layer is immersed in a liquid containing water, The orientation may be disturbed and the orientation may be lowered. In particular, when the laminate of the thermoplastic resin and the PVA-based resin layer is stretched in boric acid water, when the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin, The tendency of the degree of orientation reduction is remarkable. For example, while stretching of a PVA film alone in boric acid water is generally performed at 60 ° C., stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA resin layer is performed. In this case, the orientation of the PVA at the initial stage of stretching can be lowered at a stage before it is increased by stretching in water. 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 high temperature (auxiliary stretching) in the air before stretching in boric acid water. The crystallization of the PVA resin in the PVA 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, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. Thereby, the optical characteristic of the polarizing film obtained through the process process performed by immersing a laminated body in a liquid, such as a dyeing | staining process and an underwater extending | stretching process, can be improved.

C-2. In-air auxiliary stretching treatment In particular, in order to obtain high optical properties, a two-stage stretching method combining dry stretching (auxiliary stretching) and boric acid water stretching is selected. By introducing auxiliary stretching, such as two-stage stretching, it is possible to stretch while suppressing crystallization of the thermoplastic resin substrate, and excessive crystallization of the thermoplastic resin substrate in subsequent boric acid water stretching Thus, the problem that the stretchability is lowered can be solved, and the laminate can be stretched at a higher magnification. Furthermore, in the case of applying a PVA resin on a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, compared to the case of applying a PVA resin on a normal metal drum. Therefore, it is necessary to lower the coating temperature. As a result, the crystallization of the PVA resin becomes relatively low, and a problem that sufficient optical characteristics cannot be obtained may occur. On the other hand, by introducing auxiliary stretching, it is possible to increase the crystallinity of the PVA resin even when applying the PVA resin on the thermoplastic resin, and to achieve high optical characteristics. Become. At the same time, by increasing the orientation of the PVA resin in advance, it is possible to prevent problems such as a decrease in the orientation and dissolution of the PVA resin when immersed in water in the subsequent dyeing process or stretching process. It becomes possible to achieve high optical properties.

The stretching method for air-assisted stretching may be fixed-end stretching (for example, stretching using a tenter stretching machine) or free-end stretching (for example, uniaxial stretching through a laminate between rolls having different peripheral speeds). Although good, free end stretching can be actively employed to obtain high optical properties. In one embodiment, the air stretching process includes a heating roll stretching process in which the laminate is stretched by a peripheral speed difference between heating rolls while being conveyed in the longitudinal direction. The aerial stretching process typically includes a zone stretching process and a heated roll stretching process. In addition, the order of a zone extending | stretching process and a heating roll extending process is not limited, A zone extending process may be performed previously and a heated roll extending process may be performed previously. The zone stretching step may be omitted. In one embodiment, a zone extending process and a heating roll extending process are performed in this order. In another embodiment, in a tenter stretching machine, the film is stretched by gripping the film end and expanding the distance between the tenters in the flow direction (the spread of the distance between the tenters becomes the stretching ratio). At this time, the distance of the tenter in the width direction (perpendicular to the flow direction) is set to be arbitrarily close. Preferably, it can be set to be closer to the free end stretching with respect to the stretching ratio in the flow direction. In the case of free end stretching, the shrinkage ratio in the width direction = (1 / stretch ratio) is calculated by ^1/2 .

  The air auxiliary stretching may be performed in one stage or in multiple stages. When performing in multiple stages, the draw ratio is the product of the draw ratios at each stage. The stretching direction in the air-assisted stretching is preferably substantially the same as the stretching direction in the underwater stretching.

  The stretching ratio in the air auxiliary stretching is preferably 2.0 times to 3.5 times. The maximum draw ratio when combining air-assisted stretching and underwater stretching is preferably 5.0 times or more, more preferably 5.5 times or more, and even more preferably 6.0 times the original length of the laminate. That's it. In this specification, the “maximum stretch ratio” refers to a stretch ratio immediately before the laminate is ruptured. Separately, a stretch ratio at which the laminate is ruptured is confirmed, and is a value 0.2 lower than the value.

  The stretching temperature for the air-assisted stretching can 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 10 ° C., particularly preferably not less than Tg + 15 ° C., more preferably glass transition temperature (Tg) of the thermoplastic resin substrate. On the other hand, the upper limit of the stretching temperature is preferably 170 ° C. By stretching at such a temperature, it is possible to suppress rapid progress of crystallization of the PVA-based resin, and to suppress problems due to the crystallization (for example, preventing the orientation of the PVA-based resin layer due to stretching). it can.

C-3. Insolubilization treatment If necessary, an insolubilization treatment is performed after the air auxiliary stretching treatment and before the underwater stretching treatment and dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA resin layer in an aqueous boric acid solution. By performing the insolubilization treatment, it is possible to impart water resistance to the PVA-based resin layer, and to prevent a decrease in the orientation of PVA when immersed in water. The concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilizing bath (boric acid aqueous solution) is preferably 20 ° C to 50 ° C.

C-4. Dyeing Process The dyeing process is typically performed by dyeing a PVA resin layer with iodine. Specifically, it is performed by adsorbing iodine to the PVA resin layer. As the adsorption method, for example, a method of immersing a PVA resin layer (laminate) in a staining solution containing iodine, a method of applying the staining solution to the PVA resin layer, and applying the staining solution to the PVA resin layer The method of spraying etc. are mentioned. Preferably, the laminate is immersed in a dyeing solution (dyeing bath). This is because iodine can be adsorbed well.

  The staining solution is preferably an iodine aqueous solution. The compounding amount of iodine is preferably 0.05 parts by weight to 0.5 parts by weight with respect to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add an 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, and titanium iodide. Etc. Among these, potassium iodide is preferable. The blending amount of iodide is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight with respect to 100 parts by weight of water. The liquid temperature during dyeing of the dyeing liquid is preferably 20 ° C. to 50 ° C. in order to suppress dissolution of the PVA resin. When the PVA resin layer is immersed in the staining solution, 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 resin layer.

  The staining conditions (concentration, liquid temperature, immersion time) can be set so that the single transmittance of the finally obtained polarizing film is 45% or more and the degree of polarization is 97% or more. As such staining conditions, preferably, an aqueous iodine solution is used as the staining solution, and the ratio of iodine and potassium iodide content in the aqueous iodine solution is 1: 5 to 1:20. The ratio of the content of iodine and potassium iodide in the aqueous iodine solution is preferably 1: 5 to 1:10. Thereby, the polarizing film which has the above optical characteristics can be obtained.

  When the dyeing treatment is performed continuously after the treatment (typically insolubilization treatment) in which the laminate is immersed in a treatment bath containing boric acid, boric acid contained in the treatment bath is mixed into the dyeing bath. The boric acid concentration of the dyeing bath changes with time, and as a result, the dyeability may become unstable. In order to suppress destabilization of the dyeability as described above, the upper limit of the boric acid concentration in the dyeing bath is preferably 4 parts by weight, more preferably 2 parts by weight with respect to 100 parts by weight of water. Adjusted. On the other hand, the lower limit of the boric acid concentration in the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and even more preferably 0.5 parts by weight with respect to 100 parts by weight of water. It is. In one embodiment, the dyeing process is performed using a dyeing bath in which boric acid is previously blended. Thereby, the rate of change of boric acid concentration when boric acid in the treatment bath is mixed in the dyeing bath can be reduced. The amount of boric acid blended in advance in the dyeing bath (that is, the content of boric acid not derived from the treatment bath) is preferably 0.1 to 2 parts by weight with respect to 100 parts by weight of water. More preferably, it is 0.5 to 1.5 parts by weight.

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

C-6. Underwater stretching treatment The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the thermoplastic resin substrate or the PVA resin layer can be stretched at a temperature lower than the glass transition temperature (typically about 80 ° C.), and the PVA resin layer is crystallized. It is possible to stretch at a high magnification while suppressing. As a result, a polarizing film having excellent optical characteristics can be manufactured.

  Arbitrary appropriate methods can be employ | adopted for the extending | stretching method of a laminated body. Specifically, it may be fixed end stretching or free end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). Preferably, free end stretching is selected. The stretching of the laminate may be performed in one stage or in multiple stages. When performed in multiple stages, the draw ratio (maximum draw ratio) of the laminate described later is the product of the draw ratios of the respective stages.

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

  The boric acid aqueous solution is preferably obtained by dissolving boric acid and / or borate in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 3 to 6.5 parts by weight, and particularly preferably 3.5 to 5 parts by weight with respect to 100 parts by weight of water. .5 parts by weight. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA resin layer can be effectively suppressed, and a polarizing film having higher characteristics can be produced. In addition to boric acid or borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like in a solvent can also be used.

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

  The stretching temperature (liquid temperature of the stretching bath) is preferably 40 ° C to 85 ° C, more preferably 60 ° C to 75 ° C. If it is such temperature, it can extend | stretch at 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 resin layer. In this case, when the stretching temperature is lower than 40 ° C., there is a possibility that stretching cannot be performed satisfactorily even in consideration of plasticization of the thermoplastic resin substrate with water. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and there is a possibility that excellent optical properties cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

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

C-7. Drying Shrinkage Treatment The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or by heating the transport roll (using a so-called heating roll) (heating roll drying method). Preferably both are used. By drying using a heating roll, it is possible to efficiently suppress the heating curl of the laminate and produce a polarizing film having an excellent appearance. Specifically, by drying the laminated body along the heating roll, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the crystallinity, which is relatively low. Even at the drying temperature, the crystallinity of the thermoplastic resin substrate can be increased satisfactorily. As a result, the thermoplastic resin base material increases in rigidity and can withstand the shrinkage of the PVA resin layer due to drying, and curling is suppressed. In addition, by using a heating roll, the laminate can be dried while maintaining a flat state, so that not only curling but also generation of wrinkles can be suppressed. At this time, the laminate can be improved in optical characteristics by being contracted in the width direction by a drying contraction process. This is because the orientation of PVA and PVA / iodine complex can be effectively increased. The shrinkage ratio in the width direction of the laminate by the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using a heating roll, the laminate can be continuously contracted in the width direction while being conveyed, and high productivity can be realized.

  FIG. 2 is a schematic diagram illustrating an example of the drying shrinkage process. In the drying shrinkage treatment, the laminate 200 is dried while being transported by the transport rolls R1 to R6 heated to a predetermined temperature and the guide rolls G1 to G4. In the example of illustration, although the conveyance rolls R1-R6 are arrange | positioned so that the surface of a PVA resin layer and the surface of a thermoplastic resin base material may be continuously heated alternately, for example, one surface (for example, thermoplasticity) of the laminated body 200 is arrange | positioned. You may arrange | position the conveyance rolls R1-R6 so that only the resin base-material surface) may be heated continuously.

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

  The heating roll may be provided in a heating furnace (for example, an oven) or may be provided in a normal production line (in a room temperature environment). Preferably, it is provided in a heating furnace provided with a ventilation means. By using drying with a heating roll and hot air drying in combination, a rapid temperature change between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of hot air drying is preferably 30 ° C to 100 ° C. The hot air drying time is preferably 1 second to 300 seconds. The wind speed of 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 minivan type digital anemometer.

C-8. Other treatments Preferably, a washing treatment is performed after the underwater stretching treatment and before the drying shrinkage treatment. The cleaning treatment is typically performed by immersing the PVA resin layer in an aqueous potassium iodide solution.

EXAMPLES 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. Unless otherwise specified, “parts” and “%” in Examples and Comparative Examples are based on weight.
(1) Thickness It measured using the interference film thickness meter (The product name "MCPD-3000" by Otsuka Electronics Co., Ltd.).
(2) Single transmittance and degree of polarization About the polarizing plate (protective film / polarizing film) of Examples and Comparative Examples, single transmittance Ts measured using an ultraviolet-visible spectrophotometer (V-7100 manufactured by JASCO Corporation), The parallel transmittance Tp and the orthogonal transmittance Tc were set to Ts, Tp and Tc of the polarizing film, respectively. These Ts, Tp, and Tc are Y values measured by a 2 degree visual field (C light source) of JIS Z8701 and corrected for visibility. In addition, the refractive index of the protective film was 1.50, and the refractive index of the surface on the opposite side to the protective film of a polarizing film was 1.53.
From the obtained Tp and Tc, the degree of polarization P was determined by the following formula.
Polarization degree P (%) = {(Tp−Tc) / (Tp + Tc)} ^1/2 × 100
The spectrophotometer can perform the same measurement with LPF-200 manufactured by Otsuka Electronics Co., Ltd. As an example, Table 1 shows measured values of single transmittance Ts and polarization degree P obtained by measurement using V-7100 and LPF-200 for Samples 1 to 3 of polarizing plates having the same configuration as the following examples. Show. As shown in Table 1, the difference between the measured value of the single transmittance of V-7100 and the measured value of the single transmittance of LPF-200 is 0.1% or less, and any spectrophotometer was used. Even in this case, it can be seen that an equivalent measurement result can be obtained.
Note that, for example, when a polarizing plate provided with an anti-glare (AG) surface treatment or a pressure-sensitive adhesive having diffusion performance is used as a measurement target, different measurement results can be obtained depending on the spectrophotometer. It is possible to compensate for the difference in the measured value depending on the spectrophotometer by performing numerical conversion based on the measured value when the polarizing plate is measured with each spectrophotometer.
(3) Variation in optical characteristics of long polarizing plate From the long polarizing plates of the examples and reference examples, measurement samples were cut out at five positions at equal intervals along the width direction. The single transmittance of the central portion of each measurement sample was measured in the same manner as in (2) above. Next, the difference between the maximum value and the minimum value of the single transmittances measured at each measurement position is calculated, and this value is used to vary the optical characteristics of the long polarizing plate (in the width direction of the long polarizing plate). The difference between the maximum value and the minimum value of the single transmittance at the position along the line.
(4) Variation in optical properties of single-wafer polarizing plate A measurement sample of 100 mm × 100 mm was cut out from the long polarizing plates of the examples and reference examples, and the optical properties of the single-wafer polarizing plate (50 cm ² ) were varied. Asked. Specifically, the single unit transmittance in a total of five locations in the vicinity of about 1.5 cm to 2.0 cm and the central portion from the midpoint of each of the four sides of the measurement sample to the inside is the same as in (2) above. Measured. Next, the difference between the maximum value and the minimum value of the single transmittance measured at each measurement position is calculated, and this value is used as the variation in the optical characteristics of the sheet-like polarizing plate (single transmittance in a 50 cm ² region). Difference between the maximum value and the minimum value).

[Example 1]
1. Production of Polarizing Film An amorphous isophthalic copolymer polyethylene terephthalate film (thickness: 100 μm) having a long shape, a water absorption of 0.75%, and a Tg of about 75 ° C. was used as the thermoplastic resin substrate. One side of the resin substrate was subjected to corona treatment.
100 weight of PVA 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 “Gosefimer Z410”) is mixed at 9: 1 13 parts by weight of potassium iodide was added to the part to prepare an aqueous PVA solution (coating solution).
The PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60 ° C., thereby forming a PVA resin layer having a thickness of 13 μm, thereby producing a laminate.
The obtained laminate was stretched uniaxially by 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130 ° C. (air-assisted stretching process).
Next, the laminate was immersed for 30 seconds in an insolubilizing bath having a liquid temperature of 40 ° C. (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with respect to 100 parts by weight of water) (insolubilization treatment).
Next, the polarizing film finally obtained in a dyeing bath (iodine aqueous solution obtained by blending iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ° C. It was immersed for 60 seconds while adjusting the concentration so that the single transmittance (Ts) was 45% or more (dyeing treatment).
Subsequently, it was immersed in a crosslinking bath having a liquid temperature of 40 ° C. (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds. (Crosslinking treatment).
Then, the total draw ratio is 5.5 in the machine direction (longitudinal direction) between rolls having different peripheral speeds while the laminate is immersed in a boric acid aqueous solution (boric acid concentration 4.5 wt%) at a liquid temperature of 70 ° C. Uniaxial stretching was performed so as to be doubled (underwater stretching treatment).
After that, the laminate was immersed in a cleaning bath having a liquid temperature of 20 ° C. (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) (cleaning treatment).
Then, while drying in an oven kept at 90 ° C., it was brought into contact with a SUS heating roll whose surface temperature was kept 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 5.2%.
In this way, a polarizing film having a thickness of 5 μm was formed on the resin substrate. Further, the same procedure was repeated to produce a total of five polarizing films.
2. Production of Polarizing Plate An acrylic film (surface refractive index: 1.50, 40 μm) as a protective film is attached to the surface of each polarizing film obtained above (the surface opposite to the resin base material) by ultraviolet curable bonding. It bonded together through the agent. Specifically, coating was performed so that the total thickness of the curable adhesive was 1.0 μm, and bonding was performed using a roll machine. Thereafter, UV light was irradiated from the protective film side to cure the adhesive. Next, after slitting both ends, the resin substrate was peeled off to obtain five long polarizing plates (width: 1300 mm) having a protective film / polarizing film configuration.

[Reference Example 1]
Six polarizing films and polarizing plates are produced in the same manner as in Example 1 except that the final polarizing film has a single transmittance (Ts) of 43% or more and less than 45%. did.

[Example 2]
Four polarizing films and polarizing plates were produced in the same manner as in Example 1 except that the oven temperature was 70 ° C. and the heating roll temperature was 70 ° C. in the drying shrinkage treatment. The shrinkage ratio in the width direction of the laminate by the drying shrinkage treatment was 2.5%.

[Reference Example 2]
Six polarizing films and polarizing plates were produced in the same manner as in Example 2, except that the final transmittance of the polarizing film obtained was dyed so that the single transmittance (Ts) was 43% or more and less than 45%. did.

[Comparative Example 1]
Example 1 except that potassium iodide was not added to the PVA aqueous solution (coating solution), the stretch ratio in the air auxiliary stretching process was 1.8 times, and the heating roll was not used in the drying shrinkage process. In the same manner as described above, an attempt was made to produce a polarizing film. However, the PVA resin layer was dissolved in the dyeing process and the underwater stretching process, and the polarizing film could not be produced.

[Comparative Example 2]
Nine polarizing films and polarizing plates were produced in the same manner as in Example 1 except that the draw ratio in the air auxiliary stretching process was 1.8 times and that no heating roll was used in the drying shrinkage process. However, a polarizing film having a single transmittance of 45% or more could not be produced.

[Reference Example 3]
The polarizing film obtained in the same manner as in Comparative Example 2 was held in a constant temperature and constant humidity zone set at a temperature of 60 ° C. and a humidity of 90% RH for 30 minutes. Thereafter, a polarizing plate was produced in the same manner as in Example 1.

  About each polarizing plate of the Example and the comparative example, the single-piece | unit transmittance | permeability and the polarization degree were measured. The results are shown in Table 2 and FIG. FIG. 3 illustrates an approximate curve of the plot of Example 1 and the plot of Reference Example 1, an approximate curve of the plot of Example 2 and the plot of Reference Example 2, and an approximate curve of the plot of Comparative Example 2.

  The polarizing film obtained by the production method of the comparative example did not satisfy the single transmittance of 45% or more and the polarization degree of 97% or more at the same time. As shown by the approximate curve of the plot of Comparative Example 2, in the manufacturing method of Comparative Example 2, the degree of polarization is less than 97% when the dyeing treatment is performed so that the single transmittance is 45% or more. Is predicted. On the other hand, the polarizing film obtained by the manufacturing method of the example had excellent optical characteristics with a single transmittance of 45% or more and a polarization degree of 97% or more.

  For each of the polarizing plates of Example 1 and Reference Example 3, variations in the optical properties of the long and single-wafer polarizing plates were measured. The results are shown in Table 3.

  The long polarizing plate obtained by the manufacturing method of the example has a single transmittance variation of 0.5% or less, and the single-wafer polarizing plate obtained by the manufacturing method of the example has a single transmittance. The variation in the optical properties is 0.2% or less, and the variation in the optical characteristics is suppressed to the extent that there is no problem. On the other hand, the polarizing plate of the reference example obtained through the process of humidifying the polarizing film had a large variation in optical characteristics in both the long shape and the single wafer shape.

  The polarizing plate having the polarizing film of the present invention is suitably used for a circular polarizing plate for organic EL display devices and inorganic EL display devices.

DESCRIPTION OF SYMBOLS 10 Polarizing film 20 1st protective layer 30 2nd protective layer 100 Polarizing plate

Claims (11)

  A polarizing film having a thickness of 8 μm or less, a single transmittance of 45% or more, and a degree of polarization of 97% or more.   The polarizing film according to claim 1, wherein the single transmittance is 46% or less and the degree of polarization is 99% or less.   A polarizing plate comprising the polarizing film according to claim 1 and a protective layer disposed on at least one side of the polarizing film. The width is 1000 mm or more,
The polarizing plate according to claim 3, wherein a difference between the maximum value and the minimum value of the single transmittance at a position along the width direction is 0.5% or less. The polarizing plate according to claim 3, wherein a difference between the maximum value and the minimum value of the single transmittance in a region of 50 cm ² is 0.2% or less.   A polarizing plate roll, wherein the polarizing plate of claim 4 or 5 is wound into a roll. It is a manufacturing method of the polarizing film according to claim 1 or 2,
Forming a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin base material to form a laminate, and, in the laminate, in-air auxiliary stretching treatment, A manufacturing method comprising: performing in this order a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment that shrinks 2% or more in the width direction by heating while being conveyed in the longitudinal direction.   The production method according to claim 7, wherein the content of the halide in the polyvinyl alcohol-based resin layer is 5 to 20 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin.   The production method according to claim 7 or 8, wherein a draw ratio in the air auxiliary drawing treatment is 2.0 times or more.   The manufacturing method according to claim 7, wherein the drying shrinkage treatment step is a step of heating using a heating roll. The manufacturing method of Claim 7 whose temperature of the said heating roll is 60 to 120 degreeC, and the shrinkage | contraction rate of the width direction of the said laminated body by the said drying shrinkage process is 2% or more.