JP2020101805A - Polarizing plate and polarizing plate roll - Google Patents

Abstract

To provide a polarizing film with superior optical characteristics.SOLUTION: An elongated polarizing plate 100 of the present invention comprises a polarizing film 10 having a thickness of 8 μm or less, single transmittance of 43.5% or greater, and polarization degree of 99.940% or greater, and a protective layer 20, 30 disposed at least on one surface of the polarizing film. A difference between the maximum and minimum values of single transmittance within a 50 cm2 area is 0.15% or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a polarizing plate and a polarizing plate roll.

In a liquid crystal display device which is a typical image display device, polarizing films are arranged on both sides of a liquid crystal cell due to its image forming method. Further, with the spread of thin displays, a display (OLED) equipped with an organic EL panel and a display (QLED) using a display panel using an inorganic light emitting material such as quantum dots have been proposed. Since these panels have a highly reflective metal layer, problems such as external light reflection and background reflection are likely to occur. Therefore, it is known to prevent these problems by providing a circularly polarizing plate having a polarizing film and a λ/4 plate on the viewing side. As a method for producing a polarizing film, for example, a method in which a laminate having a resin substrate and a polyvinyl alcohol (PVA)-based resin layer is stretched and then subjected to dyeing treatment to obtain a polarizing film on the resin substrate 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 therefore, it has been noted that it can contribute to the thinning of the image display device in recent years. However, the conventional thin polarizing film as described above has insufficient optical characteristics, and further improvement of the optical characteristics of the thin polarizing film is required.

JP 2001-343521 A

The present invention has been made to solve the above-described conventional problems, and a main object thereof is to provide a polarizing plate having excellent optical characteristics and suppressing variations in the optical characteristics.

The polarizing plate of the present invention has a thickness of 8 μm or less, a single transmittance of 43.5% or more, and a polarization degree of 99.940% or more, and a polarizing film disposed on at least one side of the polarizing film. And the protective layer is formed, and the difference between the maximum value and the minimum value of the single-piece transmittance in the region of 50 cm ² is 0.15% or less.
The polarizing plate of the present invention has a thickness of 8 μm or less, a single transmittance of 43.5% or more, and a polarization degree of 99.940% or more, and a polarizing film disposed on at least one side of the polarizing film. And a width of 1000 mm or more, and the difference between the maximum value and the minimum value of the single transmittance at the position along the width direction is 0.3% or less.
In one embodiment, the single transmittance of the polarizing film is 44.0% or less, and the polarization degree of the polarizing film is 99.990% or less.
According to another aspect of the present invention, a polarizing plate roll is provided. This polarizing plate roll is formed by winding the above polarizing plate in a roll shape.

According to the present invention, a polarizing film having a thickness of 8 μm or less, a simple substance transmittance of 43.5% or more, and a polarization degree of 99.940% or more is provided, and it has excellent optical characteristics. A polarizing plate in which variations in optical characteristics are suppressed can be provided.

1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present 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 in the Example and the comparative example.

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

A. Polarizing Plate FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 includes a polarizing film 10, a first protective layer 20 arranged on one side of the polarizing film 10, and a second protective layer 30 arranged on the other side of the polarizing film 10. The polarizing film has a thickness of 8 μm or less, a single transmittance of 43.5% or more, and a polarization degree of 99.940% or more. One of the first protective layer 20 and the second protective layer 30 may be omitted. Note that one of the first protective layer and the second protective layer may be a resin base material (described later) used for manufacturing the polarizing film.

The polarizing plate may have a long shape or a sheet shape. When the polarizing plate has a long shape, it is preferably wound into a roll to form a polarizing plate roll. The polarizing plate has excellent optical characteristics and has little variation in optical characteristics. 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 0.3% or less. The upper limit of D1 is preferably 0.25%, more preferably 0.2%. The smaller D1 is, the more preferable, but the lower limit is, for example, 0.01%. When D1 is within the above range, a polarizing plate having excellent optical characteristics can be industrially produced. In another embodiment, in the polarizing plate, the difference (D2) between the maximum value and the minimum value of the single transmittance in the region of 50 cm ² is 0.15% or less. The upper limit of D2 is preferably 0.1%, more preferably 0.08%. The smaller D2 is, the more preferable, but the lower limit is, for example, 0.01%. When D2 is within the above range, it is possible to suppress variations in brightness on the display screen when the polarizing plate is used in an image display device.

B-1. Polarizing Film As described above, the polarizing film has a thickness of 8 μm or less, a single transmittance of 43.5% or more, and a polarization degree of 99.940% or more. In general, the single-body transmittance and the polarization degree are in a trade-off relationship with each other. When the single-body transmittance is increased, the polarization degree may be decreased, and when the polarization degree is increased, the single-body transmittance may be decreased. Therefore, conventionally, it has been difficult to practically use a thin polarizing film that satisfies the optical characteristics of a single transmittance of 43.5% or more and a polarization degree of 99.940% or more. Realization of a thin polarizing film (polarizing plate) with excellent optical characteristics such as a single transmittance of 43.5% or more and a polarization degree of 99.940% or more, and suppressing variations in optical characteristics. What has been done is one of the achievements of the present invention. A polarizing plate having such a polarizing film can be used for an image display device, and is particularly preferably used for a back side polarizing plate of a liquid crystal 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 44.0% or less. The polarization degree of the polarizing film is preferably 99.950% or more, more preferably 99.960% or more. On the other hand, the upper limit of the polarization degree is preferably 99.990%. The single-piece transmittance is typically a Y value measured with an ultraviolet-visible spectrophotometer and subjected to luminosity correction. The degree of polarization is typically obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured by using an ultraviolet-visible spectrophotometer and subjected to the visibility correction.
Polarization degree (%)={(Tp−Tc)/(Tp+Tc)} ^1/2 ×100

In one embodiment, the transmittance of a thin polarizing film having a thickness of 8 μm or less is typically obtained by laminating 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 target. The reflectance at the interface of each layer may change depending on the refractive index of the surface of the polarizing film and/or the refractive index of the surface of the protective film in contact with the air interface, and as a result, the measured value of the transmittance may change. .. Therefore, for example, when 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 of polarized light parallel to the transmission axis (transmission axis reflectance) 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. Is. For example, when a base material having a surface refractive index of 1.53 (such as a cycloolefin film and a film with a hard coat layer) is used as the 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 it 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. When the protective film has absorption other than surface reflection, appropriate correction can be performed according to the amount of absorption.

Any appropriate polarizing film can be adopted as the polarizing film. The polarizing film can be typically manufactured by using a laminate of two or more layers.

Specific examples of the polarizing film obtained by using the laminate include a polarizing film obtained by using a laminate of a resin base material and a PVA-based resin layer formed by coating on the resin base material. A polarizing film obtained by using a laminate of a resin base material and a PVA-based resin layer formed by coating on the resin base material is, for example, a resin base material obtained by applying a PVA-based resin solution to the resin base material and drying the solution. 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 the PVA-based resin layer as a polarizing film. obtain. In the present embodiment, the stretching typically includes dipping the laminate in a boric acid aqueous solution and stretching. Further, the stretching may further include, if necessary, stretching the laminate at high temperature (for example, 95° C. or higher) in air before stretching in the aqueous boric acid 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 for the polarizing film), or the resin substrate is peeled from the resin substrate/polarizing film laminate. However, any appropriate protective layer depending on the purpose may be laminated on the peeled surface and used. The details of the method for manufacturing such a polarizing film are described in, for example, JP 2012-73580 A. The entire disclosure of this publication is incorporated herein by reference.

The method for producing a polarizing film of the present invention comprises forming a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate to form a laminate, and The above-mentioned laminated body is subjected to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment of shrinking 2% or more in the width direction by heating while conveying in the longitudinal direction in this order. .. As a result, a polarizing film having a thickness of 8 μm or less, a single transmittance of 43.5% or more, and a polarization degree of 99.940% or more, which has excellent optical characteristics and which suppresses variations in optical characteristics. Can be provided. That is, by introducing the auxiliary stretching, the crystallinity of PVA can be increased and high optical characteristics can be achieved even when PVA is applied onto the thermoplastic resin. At the same time, by preliminarily enhancing the orientation of PVA, it is possible to prevent problems such as reduction in orientation and dissolution of PVA when immersed in water in a subsequent dyeing step or stretching step, and high optical characteristics. Can be achieved. Furthermore, when the PVA-based resin layer is dipped in a liquid, the alignment disorder of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This can improve the optical characteristics of the polarizing film obtained through a treatment process such as a dyeing treatment and an underwater stretching treatment performed by immersing the laminate in a liquid. Further, the optical characteristics can be improved by shrinking the laminate in the width direction by the dry shrinking treatment.

B-2. Protective Layer The first and second protective layers are formed of any suitable film that can be used as a protective layer of 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 resins, polyvinyl alcohol resins, polycarbonate resins, polyamide resins, polyimide resins, polyether sulfone resins, and polysulfone resins. , Polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, acetate-based transparent resins and the like. Further, a thermosetting resin such as a (meth)acrylic resin, a urethane resin, a (meth)acrylic urethane resin, an epoxy resin, a silicone resin, or an ultraviolet curable resin may be used. In addition to these, for example, a glassy polymer such as a siloxane polymer may be used. Further, the polymer film described in JP 2001-343529 A (WO 01/37007) can also be used. Examples of the material of this film include a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in its side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in its side chain. Can be used, and examples thereof include a resin composition having an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile/styrene copolymer. 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) arranged on the side opposite to the display panel is typically 300 μm or less, preferably 100 μm or less, and more preferably It is 5 μm to 80 μm, more preferably 10 μm to 60 μm. When the surface treatment is applied, the thickness of the outer protective layer is the thickness including the thickness of the surface treated layer.

The thickness of the protective layer (inner protective layer) arranged on the display panel side when the polarizing plate 100 is applied to an image display device is preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, and further 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 in the surface in the direction orthogonal to the slow axis (that is, the fast phase). Is the refractive index in the axial direction, “nz” is the refractive index in the thickness direction, and “d” is the thickness (nm) of the layer (film).

C. Method for Manufacturing Polarizing Film A method for manufacturing a polarizing film according to one embodiment of the present invention is 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 system resin layer (PVA system resin layer) into a laminate, and by subjecting the laminate to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and heating while conveying in the longitudinal direction. And a drying shrinkage treatment for shrinking in the width direction by 2% or more in this order. The content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. According to such a manufacturing method, the polarizing film can be obtained. In particular, by producing a laminate including a PVA-based resin layer containing a halide, stretching the laminate by multistage stretching including in-air auxiliary stretching and underwater stretching, and heating the laminated body after heating with a heating roll. It is possible to obtain a polarizing film having excellent optical characteristics (typically, single-element transmittance and degree of polarization) and suppressing variations in optical characteristics. Specifically, by using a heating roll in the drying shrinkage treatment step, it is possible to uniformly shrink the entire laminate while transporting the laminate. As a result, not only can the optical properties of the obtained polarizing film be enhanced, but also a polarizing film with excellent optical properties can be stably produced, and variations in optical properties of the polarizing film (particularly, single transmittance) can be suppressed. can do.

C-1. Production of Laminated Body Any appropriate method can be adopted as a method for producing a laminated body of a thermoplastic resin substrate and a PVA-based resin layer. Preferably, a PVA-based resin layer is formed on the thermoplastic resin substrate by applying a coating liquid containing a halide and a PVA-based resin on the surface of the thermoplastic resin substrate and drying the coating liquid. 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 method of applying the coating liquid. For example, a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (a comma coating method, etc.) and the like can be mentioned. The coating/drying temperature of the coating liquid is preferably 50° C. or higher.

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

Prior to forming the PVA-based resin layer, the thermoplastic resin substrate may be subjected to surface treatment (for example, corona treatment), or the easily adhesive layer may be formed on the thermoplastic resin substrate. By performing such a treatment, the adhesion between the thermoplastic resin base material and the PVA-based 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 the PVA-based resin layer. If it exceeds 300 μm, it may take a long time for the thermoplastic resin substrate to absorb water in an underwater stretching treatment described below, 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 base material absorbs water, and the water acts as a plasticizer and can be plasticized. As a result, the stretching stress can be significantly reduced, and stretching can be performed at a high ratio. On the other hand, the water absorption of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin base material, it is possible to prevent problems such as the dimensional stability of the thermoplastic resin base material being significantly reduced during production, and the resulting polarizing film being deteriorated in appearance. In addition, it is possible to prevent the base material from breaking during the underwater stretching and the PVA-based resin layer from peeling off from the thermoplastic resin base material. The water absorption of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption rate is a value determined according to JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120° C. or lower. By using such a thermoplastic resin substrate, it is possible to sufficiently secure the stretchability of the laminate while suppressing the crystallization of the PVA-based resin layer. Further, in consideration of good plasticization of the thermoplastic resin substrate with water and favorable underwater stretching, the temperature is preferably 100° C. or lower, and 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 may be deformed (for example, unevenness, wrinkles, wrinkles, etc.) when the coating liquid containing the PVA-based resin is applied and dried. It is possible to prevent the problems described above and to produce a good laminate. Moreover, the PVA-based resin layer can be stretched well at a suitable temperature (for example, about 60° C.). The glass transition temperature of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material and heating it with a crystallization material. The glass transition temperature (Tg) is a value determined according to JIS K 7121.

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 resin, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, copolymer resins thereof, and the like. Are listed. Among these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferable.

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

In a preferred embodiment, the thermoplastic resin base material 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 can suppress crystallization during stretching. It is considered that this is because the introduction of the isophthalic acid unit gives the main chain a large bend. 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 such a content ratio, the crystallinity can be favorably increased in the drying shrinkage treatment described below.

The thermoplastic resin substrate may be stretched in advance (before forming the PVA-based resin layer). In one embodiment, the elongated thermoplastic resin substrate is stretched in the lateral direction. The lateral direction is preferably a direction orthogonal to the stretching direction of the laminate described below. In addition, in this specification, "orthogonal" also includes the case of being substantially orthogonal. Here, “substantially orthogonal” includes the case of 90°±5.0°, preferably 90°±3.0°, and 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 stretch ratio of the thermoplastic resin substrate is preferably 1.5 times 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. Stretching of the thermoplastic resin substrate may be performed in one stage or in multiple stages. When performing in multiple stages, the above-mentioned draw ratio is a product of the draw ratio of each stage.

C-1-2. Coating liquid The coating liquid contains a halide and a PVA-based resin as described above. The coating liquid is typically a solution prepared by dissolving the halide and the PVA resin in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These may be used alone or in combination of two or more. Of these, water is preferable. The PVA-based resin concentration of the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, it is possible to form a uniform coating film in close contact with the thermoplastic resin substrate. The content of the halide in the coating liquid is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

You may mix 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 obtained 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. The ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, 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, gelation may occur.

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

Any appropriate halide can be adopted as the above-mentioned halide. Examples include iodide and sodium chloride. Examples of iodides 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 with respect to 100 parts by weight of the PVA-based resin, and more preferably 10 to 15 parts by weight with respect to 100 parts by weight of the PVA-based resin. It is a department. If the amount of the halide exceeds 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, the halide may bleed out, and the finally obtained polarizing film may become cloudy.

Generally, when the PVA-based resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA-based resin becomes high. However, when the stretched PVA-based resin layer is immersed in a liquid containing water, the polyvinyl alcohol molecules The orientation may be disturbed and the orientation may be deteriorated. 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 tendency of the reduction of the degree of orientation is remarkable. For example, while stretching of a PVA film alone in boric acid water is generally performed at 60° C., stretching of a laminate of A-PET (thermoplastic resin base material) and PVA-based resin layer is performed. It is carried out at a high temperature of around 70° C. In this case, the orientation of PVA in the initial stage of stretching may be lowered in the stage before being raised by the 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 high temperature in air (auxiliary stretching) before stretching in boric acid water. The crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the disorder of the alignment of the polyvinyl alcohol molecules and the deterioration of the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This can improve the optical characteristics of the polarizing film obtained through a treatment process such as a dyeing treatment and an underwater stretching treatment performed by immersing the laminate in a liquid.

C-2. In-air auxiliary stretching treatment In order to obtain particularly high optical properties, a two-stage stretching method is selected in which dry stretching (auxiliary stretching) and boric acid in-water stretching are combined. By introducing auxiliary stretching like two-stage stretching, it is possible to perform stretching while suppressing crystallization of the thermoplastic resin substrate, and excessive crystallization of the thermoplastic resin substrate in subsequent boric acid underwater stretching. Thereby, the problem that the stretchability is lowered can be solved, and the laminate can be stretched at a higher magnification. Conventionally, when a PVA-based resin is applied onto a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, the application temperature is higher than when the PVA-based resin is applied onto a metal drum. Therefore, there is a problem in that crystallization of the PVA-based resin is relatively low and sufficient optical characteristics cannot be obtained. On the other hand, by introducing the auxiliary stretching, the crystallinity of the PVA-based resin can be increased even when the PVA-based resin is applied onto the thermoplastic resin, and high optical characteristics can be achieved. Become. Furthermore, by preliminarily enhancing the orientation of the PVA-based resin, it is possible to prevent problems such as reduction in orientation and dissolution of the PVA-based resin when immersed in water in the subsequent dyeing step or stretching step, It becomes possible to achieve high optical properties.

The stretching method for the in-air auxiliary stretching may be fixed-end stretching (for example, a stretching method using a tenter stretching machine) or free-end stretching (for example, a uniaxial stretching method in which a laminate is passed between rolls having different peripheral speeds). Although good, free-end stretching can be positively adopted in order to obtain high optical characteristics. In one embodiment, the in-air stretching treatment includes a heating roll stretching step of stretching the laminate by the difference in peripheral speed between the heating rolls while conveying the laminate in the longitudinal direction. The in-air stretching treatment typically includes a zone stretching step and a heating roll stretching step. The order of the zone stretching step and the heating roll stretching step is not limited, and the zone stretching step may be performed first or the heating roll stretching step may be performed first. The zone stretching step may be omitted. In one embodiment, the zone stretching step and the heated roll stretching step are performed in this order. Further, in another embodiment, in the tenter stretching machine, the film is stretched by gripping the end portions of the film and widening the distance between the tenter in the flow direction (the spread of the distance between the tenter is the stretching ratio). At this time, the distance of the tenter in the width direction (direction perpendicular to the flow direction) is set to be arbitrarily close. Preferably, it can be set so as to be closer to the free end stretching with respect to the stretching ratio in the machine direction. In the case of free end stretching, the shrinkage ratio in the width direction=(1/stretching ratio) ^1/2 is calculated.

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

The draw ratio in the in-air auxiliary drawing is preferably 2.0 to 3.5 times. The maximum draw ratio in the case of combining the in-air auxiliary drawing and the underwater drawing is preferably 5.0 times or more, more preferably 5.5 times or more, and further preferably 6.0 times the original length of the laminate. That is all. In the present specification, the "maximum stretch ratio" refers to the stretch ratio immediately before the laminate is broken, and the stretch ratio at which the laminate is broken is confirmed separately, and is a value 0.2 lower than that value.

The stretching temperature of the in-air 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 the glass transition temperature (Tg) or higher of the thermoplastic resin substrate, more preferably the glass transition temperature (Tg)+10° C. or higher of the thermoplastic resin substrate, and particularly preferably Tg+15° C. or higher. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, it is possible to suppress rapid crystallization of the PVA-based resin and suppress defects due to the crystallization (for example, to prevent 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 in-air auxiliary stretching treatment and before the underwater stretching treatment or the dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based 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 prevent the PVA from being lowered in orientation when immersed in water. The concentration of the aqueous boric acid solution is preferably 1 part by weight to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilization bath (boric acid aqueous solution) is preferably 20°C to 50°C.

C-4. Dyeing Treatment The dyeing treatment is typically performed by dyeing the PVA-based resin layer with iodine. Specifically, it is performed by adsorbing iodine on the PVA resin layer. Examples of the adsorption method include a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of applying the dyeing solution to the PVA-based resin layer, and a method of applying the dyeing solution to the PVA-based resin layer. Examples include a method of spraying. A preferred method is to immerse the laminate in a dyeing solution (dyeing bath). This is because iodine can be favorably adsorbed.

The dyeing solution is preferably an aqueous iodine solution. The blending 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 iodide to the aqueous iodine solution. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide. Etc. Among these, potassium iodide is preferable. The iodide content is preferably 0.1 parts by weight to 10 parts by weight, and more preferably 0.3 parts by weight 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-based resin. When the PVA-based resin layer is immersed in the dyeing solution, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds in order to secure the transmittance of the PVA-based resin layer.

The dyeing conditions (concentration, liquid temperature, immersion time) should be set so that the final transmittance of the polarizing film obtained is 43.5% or more and the polarization degree is 99.940% or more. You can As such a dyeing condition, preferably, an iodine aqueous solution is used as the dyeing solution, and the ratio of the contents of iodine and potassium iodide in the iodine aqueous solution is 1:5 to 1:20. The ratio of the contents of iodine and potassium iodide in the aqueous iodine solution is preferably 1:5 to 1:10. As a result, a polarizing film having the above optical characteristics can be obtained.

When the dyeing treatment is continuously performed after the treatment of dipping the laminate in a treatment bath containing boric acid (typically, the insolubilization treatment), the boric acid contained in the treatment bath is mixed in the dyeing bath. The concentration of boric acid in the dyeing bath may change over time, resulting in unstable dyeability. In order to suppress the instability 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, relative to 100 parts by weight of water. Adjusted. On the other hand, the lower limit of the concentration of boric acid in the dyeing bath is preferably 0.1 part by weight, more preferably 0.2 part by weight, still more preferably 0.5 part by weight, relative to 100 parts by weight of water. Is. In one embodiment, the dyeing process is performed using a dyeing bath in which boric acid is preliminarily blended. This can reduce the rate of change in boric acid concentration when boric acid in the treatment bath is mixed in the dyeing bath. The amount of boric acid blended in the dyeing bath in advance (that is, the content of boric acid not derived from the treatment bath) is preferably 0.1 part by weight to 2 parts by weight with respect to 100 parts by weight of water. , And more preferably 0.5 to 1.5 parts by weight.

C-5. Crosslinking Treatment If necessary, a crosslinking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The cross-linking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing the crosslinking treatment, it is possible to impart water resistance to the PVA-based resin layer and prevent the orientation of PVA from being lowered when it is immersed in high-temperature water in the subsequent underwater stretching. The concentration of the aqueous boric acid solution is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Further, when the crosslinking treatment is performed after the dyeing treatment, it is preferable to further add iodide. By blending iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The iodide content is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably 20°C to 50°C.

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, 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 is crystallized. It is possible to stretch at a high magnification while suppressing the above. As a result, it is possible to manufacture a polarizing film having excellent optical characteristics.

Any appropriate method can be adopted as a method for stretching the laminate. Specifically, it may be fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching by passing a laminate between rolls having different peripheral speeds). Preferably, free end stretching is selected. Stretching of the laminate may be performed in one stage or in multiple stages. When carrying out in multiple stages, the stretching ratio (maximum stretching ratio) of the laminate described below is the product of the stretching ratios in each stage.

The underwater stretching is preferably performed by immersing the laminate in a boric acid aqueous solution (boric acid underwater stretching). By using an aqueous boric acid solution as the stretching bath, the PVA-based 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 generate a tetrahydroxyborate anion in an aqueous solution to crosslink with a PVA-based resin by hydrogen bond. As a result, the PVA-based resin layer can be imparted with rigidity and water resistance, can be favorably stretched, and a polarizing film having excellent optical characteristics can be manufactured.

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

Preferably, iodide is added to the above stretching bath (boric acid aqueous solution). By blending iodide, the elution of iodine adsorbed on the PVA-based resin layer can be suppressed. Specific examples of iodide are as described above. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 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. At such a temperature, the PVA-based resin layer can be stretched at a high ratio while suppressing the dissolution. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin base material is preferably 60° C. or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40° C., it may not be possible to stretch well even if the plasticization of the thermoplastic resin substrate by water is taken into consideration. On the other hand, the higher the temperature of the drawing bath, the higher the solubility of the PVA-based resin layer, and there is a possibility that excellent optical characteristics will not be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The draw ratio by underwater stretching 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, and more preferably 5.5 times or more, with respect to the original length of the laminate. By achieving such a high draw ratio, a polarizing film having extremely excellent optical characteristics can be manufactured. Such a high draw ratio can be achieved by employing an underwater drawing method (boric acid underwater drawing).

C-7. Drying Shrinkage Treatment The above drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or may be performed by heating the transport roll (using a so-called heating roll) (heating roll drying method). Both are preferably used. By drying using a heating roll, it is possible to efficiently suppress the curling of the laminate by heating and to manufacture a polarizing film having an excellent appearance. Specifically, by drying the laminate 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 satisfactorily increased. As a result, the rigidity of the thermoplastic resin base material increases, and the thermoplastic resin base material can withstand the shrinkage of the PVA-based resin layer due to drying, and curling is suppressed. Further, by using the heating roll, the laminate can be dried while being kept flat, so that not only curling but also generation of wrinkles can be suppressed. At this time, the laminated body can be improved in optical characteristics by shrinking in the width direction by a drying shrinkage treatment. This is because the orientation of PVA and the PVA/iodine complex can be effectively enhanced. The shrinkage rate in the width direction of the laminate by the dry shrinkage treatment is preferably 2% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the 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 showing an example of the drying shrinkage treatment. In the drying shrinkage treatment, the laminate 200 is dried while being transported by the transport rolls R1 to R6 heated to a predetermined temperature and the guide rolls G1 to G4. In the illustrated example, the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but for example, one surface of the laminate 200 (for example, thermoplastic The transport rolls R1 to R6 may be arranged so as to continuously heat only the resin substrate surface).

The 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. It is possible to satisfactorily increase the crystallinity of the thermoplastic resin, satisfactorily suppress curling, and manufacture an optical laminate having extremely excellent durability. The temperature of the heating roll can be measured with a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular limitation as long as there are multiple transport rolls. The number of transport rolls is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roll is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and further preferably 1 to 10 seconds.

The heating roll may be provided in a heating furnace (for example, an oven) or may be provided in a normal production line (under room temperature environment). Preferably, it is provided in a heating furnace provided with a blowing means. By using the drying with the heating roll and the hot air drying together, a sharp temperature change between the heating rolls can be suppressed, and the 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. The wind velocity is the wind velocity in the heating furnace, and can be measured by a mini vane 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 washing treatment is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

D. Summary The polarizing film of the present invention has a thickness of 8 μm or less, a single transmittance of 43.5% or more, and a polarization degree of 99.940% or more.
In one embodiment, the single transmittance is 44.0% or less and the polarization degree is 99.990% 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 arranged on at least one side of the polarizing film.
According to another aspect of the present invention, a method for manufacturing a polarizing film is provided. This manufacturing method is a method for manufacturing the above 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 substrate to form a laminate. In addition, the above-mentioned laminate is subjected to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment of shrinking 2% or more in the width direction by heating while conveying in the longitudinal direction. Including applying in order.
In one embodiment, the content of the halide in the polyvinyl alcohol resin layer is 5 to 20 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol resin.
In one embodiment, the draw ratio in the above-mentioned in-air auxiliary drawing treatment is 2.0 times or more.
In one embodiment, the drying shrinkage treatment step is a step of heating using a heating roll.
In one embodiment, the temperature of the heating roll is 60°C to 120°C, and the shrinkage rate in the width direction of the laminate due to the drying shrinkage treatment is 2% or more.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The measuring method of each characteristic is as follows. In the examples and comparative examples, "parts" and "%" are based on weight unless otherwise specified.
(1) Thickness It was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000").
(2) Single Transmittance and Polarization Degree The single transmittance Ts of the polarizing plates (protective film/polarizing film) of Examples and Comparative Examples measured using an ultraviolet-visible spectrophotometer (V-7100 manufactured by JASCO Corporation), The parallel transmittance Tp and the orthogonal transmittance Tc are set as Ts, Tp, and Tc of the polarizing film, respectively. These Ts, Tp, and Tc are Y values measured by the 2-degree visual field (C light source) of JIS Z8701 and subjected to luminosity correction. The refractive index of the protective film was 1.50, and the refractive index of the surface of the polarizing film on the side opposite to the protective film was 1.53.
The degree of polarization P was determined from the obtained Tp and Tc by the following formula.
Polarization degree P(%)={(Tp−Tc)/(Tp+Tc)} ^1/2 ×100
Note that the spectrophotometer can also perform the same measurement by using LPF-200 manufactured by Otsuka Electronics Co., Ltd. As an example, Table 1 shows the measured values of the single-piece transmittance Ts and the polarization degree P obtained by the measurement using V-7100 and LPF-200 for Samples 1 to 3 of the polarizing plates having the same configurations 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 was 0.1% or less, and any spectrophotometer was used. It is understood that the same measurement result can be obtained even in the case.
Note that, for example, when a polarizing plate provided with an adhesive having an anti-glare (AG) surface treatment or a diffusion property is used as the measurement target, different measurement results may be obtained depending on the spectrophotometer, but in this case, the same It is possible to compensate for the difference in the measured values depending on the spectrophotometer by performing the numerical conversion based on the measured values when the polarizing plate is measured by each spectrophotometer.
(3) Variation in Optical Properties of Long Polarizing Plates From the long polarizing plates of Examples and Reference Examples, measurement samples were cut out at five positions at equal intervals along the width direction to obtain five samples. The simple substance 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-piece transmittances measured at each measurement position is calculated, and this value is used to calculate the variation in the optical characteristics of the long polarizing plate (the width direction of the long polarizing plate. The difference between the maximum value and the minimum value of the single-body transmittance at the position along with.
(4) Variation in optical characteristics of sheet-shaped polarizing plate Measurement samples of 100 mm×100 mm were cut out from the long-sized polarizing plates of Examples and Reference Examples, and variation in optical characteristics of sheet-shaped polarizing plate (50 cm ² ). I asked. Specifically, the single-piece transmittances at a position of about 1.5 cm to 2.0 cm inward from the midpoint of each side of the four sides of the measurement sample and a total of 5 places in the central part are the same as in (2) above. Was measured. Next, the difference between the maximum value and the minimum value of the single-body transmittances measured at each measurement position is calculated, and this value is used to calculate the variation in the optical characteristics of the sheet-shaped polarizing plate (the single-body transmittance in the region of 50 cm ² ). Difference between the maximum value and the minimum value of).

[Example 1]
1. Production of Polarizing Film As the thermoplastic resin substrate, 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. Corona treatment was applied to one side of the resin substrate.
Polyvinyl alcohol (polymerization degree: 4200, saponification degree: 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosephimmer Z410") in a ratio of 9:1 100 weight of PVA-based resin To 13 parts by weight, 13 parts by weight of potassium iodide was added to prepare a PVA aqueous solution (coating solution).
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, and a laminate was prepared.
The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130° C. (in-air auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) having a liquid temperature of 40° C. for 30 seconds (insolubilization treatment).
Then, a dyeing bath having a liquid temperature of 30° C. (an iodine aqueous solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with respect to 100 parts by weight of water) was used to prepare the finally obtained polarizing film. Immersion was performed for 60 seconds while adjusting the concentration so that the simple substance transmittance (Ts) was 43.5% or more (dyeing treatment).
Then, it was immersed for 30 seconds in a crosslinking bath at a liquid temperature of 40° C. (an aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water). (Crosslinking treatment).
Then, while the laminated body was immersed in a boric acid aqueous solution (boric acid concentration 4.0% by weight) having a liquid temperature of 70° C., the total draw ratio was 5.5 in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds. Uniaxial stretching was performed so as to double the length (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 mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment).
Then, while being dried in an oven kept at 90° C., it was contacted with a heating roll made of SUS 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 due to the dry 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 14 polarizing films.
2. Preparation of Polarizing Plate An acrylic film (surface refractive index 1.50, 40 μm) as a protective film was attached to the surface of each polarizing film obtained above (the surface opposite to the resin substrate) by UV-curing adhesion. It pasted together via the agent. Specifically, the curable adhesive was applied so that the total thickness was 1.0 μm, and the curable adhesive was attached using a roll machine. Then, UV rays were irradiated from the protective film side to cure the adhesive. Next, after slitting both ends, the resin base material was peeled off to obtain 14 elongated polarizing plates (width: 1300 mm) having a structure of protective film/polarizing film.

[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 due to the dry shrinkage treatment was 2.5%.

[Comparative Example 1]
Example 1 except that potassium iodide was not added to the PVA aqueous solution (coating solution), the draw ratio in the in-air auxiliary drawing process was set to 1.8 times, and no heating roll was used in the dry shrinking process. Eight polarizing films and polarizing plates were prepared in the same manner as in.

[Comparative example 2]
Six polarizing films and polarizing plates were produced in the same manner as in Example 1 except that the draw ratio in the in-air auxiliary drawing process was set to 1.8 and that no heating roll was used in the dry shrinking process.

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

For each of the polarizing plates of Examples and Comparative Examples, the single transmittance and the degree of polarization were measured. The results are shown in Table 2 and FIG.

The polarizing film obtained by the manufacturing method of the comparative example did not satisfy the single transmittance of 43.5% or more and the polarization degree of 99.940% or more at the same time. On the other hand, the polarizing film obtained by the manufacturing method of the example had excellent optical characteristics such as a single transmittance of 43.5% or more and a polarization degree of 99.940% or more.

With respect to each of the polarizing plates of Examples and Reference Examples, the variation in the optical characteristics of the long and sheet-shaped polarizing plates was measured. The results are shown in Table 3.

The long-sized polarizing plate obtained by the manufacturing method of the example has a variation in the single transmittance of 0.3% or less, and the single-wafer polarizing plate obtained by the manufacturing method of the example has the single transmittance. Variation is 0.15% or less, and variation in optical characteristics is suppressed to such an extent that there is no problem. On the other hand, the polarizing plate of the reference example obtained through the step of humidifying the polarizing film had a large variation in the optical characteristics in both the long shape and the sheet shape.

The polarizing plate of the present invention is suitably used as a circularly polarizing plate for liquid crystal display devices, organic EL display devices, and inorganic EL display devices.

10 Polarizing Film 20 First Protective Layer 30 Second Protective Layer 100 Polarizing Plate

Claims (4)

A polarizing film having a thickness of 8 μm or less, a single transmittance of 43.5% or more, and a polarization degree of 99.940% or more, and a protective layer disposed on at least one side of the polarizing film. A polarizing plate having
A polarizing plate in which the difference between the maximum value and the minimum value of the single-element transmittance in a region of 50 cm ² is 0.15% or less. A polarizing film having a thickness of 8 μm or less, a single transmittance of 43.5% or more, and a polarization degree of 99.940% or more, and a protective layer disposed on at least one side of the polarizing film. A polarizing plate having
The width is 1000 mm or more,
A polarizing plate in which the difference between the maximum value and the minimum value of the single-body transmittance at a position along the width direction is 0.3% or less. The polarizing plate according to claim 1 or 2, wherein the single transmittance of the polarizing film is 44.0% or less, and the polarization degree of the polarizing film is 99.990% or less. A polarizing plate roll obtained by winding the polarizing plate according to claim 1 in a roll shape.