JP7370177B2 - Polarizing plate with retardation layer and image display device using the same - Google Patents

Description

The present invention relates to a polarizing plate with a retardation layer and an image display device using the same.

In recent years, image display devices typified by liquid crystal display devices and electroluminescent (EL) display devices (eg, organic EL display devices and inorganic EL display devices) have rapidly become popular. Polarizing plates and retardation plates are typically used in image display devices. In practice, a polarizing plate with a retardation layer that integrates a polarizing plate and a retardation plate is widely used (for example, Patent Document 1), but recently there has been a strong demand for thinner image display devices. With this trend, there is an increasing demand for thinner polarizing plates with retardation layers. In addition, in recent years, there has been an increasing demand for curved image display devices and/or bendable or foldable image display devices, and polarizing plates and polarizing plates with retardation layers are also required to be thinner and more flexible. ing. In order to make polarizing plates with retardation layers thinner, protective layers and retardation films of polarizing films, which contribute significantly to the thickness, are becoming thinner. However, when the protective layer and the retardation film are made thinner, the effect of shrinkage of the polarizing film becomes relatively large, causing problems such as warping of the image display device and deterioration of the operability of the polarizing plate with the retardation layer.

In order to solve the above problems, it is necessary to reduce the thickness of the polarizing film as well. However, simply reducing the thickness of the polarizing film deteriorates the optical properties. More specifically, one or both of the degree of polarization and the single transmittance, which are in a trade-off relationship, decrease to a practically unacceptable degree. As a result, the optical properties of the polarizing plate with a retardation layer also become insufficient.

Patent No. 3325560

The present invention has been made to solve the above-mentioned conventional problems, and its main purpose is to provide a polarizing plate with a retardation layer that is thin, easy to handle, and has excellent optical properties. .

The polarizing plate with a retardation layer of the present invention includes a polarizing plate including a polarizing film and a protective layer on at least one side of the polarizing film, and a retardation layer. The polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic substance, has a thickness of 8 μm or less, a single transmittance of 48% or more, and a polarization degree of 85% or more. The retardation layer is an alignment solidified layer of a liquid crystal compound.
In one embodiment, the polarizing plate with a retardation layer has a unit weight of 6.5 mg/cm ² or less.
In one embodiment, the polarizing plate with a retardation layer has a total thickness of 60 μm or less.
In one embodiment, the retardation layer is a single layer of an alignment solidified layer of a liquid crystal compound, the Re(550) of the retardation layer is 100 nm to 190 nm, and the slow axis of the retardation layer and the above The angle between the polarizing film and the absorption axis is 40° to 50°.
In one embodiment, the retardation layer has a laminated structure of a first fixed alignment layer of a liquid crystal compound and a second fixed alignment layer of a liquid crystal compound; The Re(550) of the alignment solidified layer of the second liquid crystal compound is 200 nm to 300 nm, and the angle between the slow axis and the absorption axis of the polarizing film is 10° to 20°; ) is 100 nm to 190 nm, and the angle between its slow axis and the absorption axis of the polarizing film is 70° to 80°.
In one embodiment, the difference between the maximum value and the minimum value of the single transmittance within a 50 cm ² area of the polarizing film is 0.5% or less.
In one embodiment, the polarizing plate with a retardation layer has a width of 1000 mm or more, and the difference between the maximum value and the minimum value of the single transmittance at a position along the width direction of the polarizing film is 1% or less. be.
In one embodiment, the polarizing film has a single transmittance of 50% or less and a polarization degree of 92% or less.
In one embodiment, the polarizing plate with a retardation layer further includes another retardation layer outside the retardation layer, and the retardation index characteristic of the another retardation layer satisfies nz>nx=ny. Show relationships.
In one embodiment, the polarizing plate with a retardation layer further includes a conductive layer or an isotropic substrate with a conductive layer on the outside of the retardation layer.
According to another aspect of the present invention, an image display device is provided. This image display device includes the above polarizing plate with a retardation layer.
In one embodiment, the image display device is an organic electroluminescent display device or an inorganic electroluminescent display device.

According to the present invention, addition of a halide (typically potassium iodide) to polyvinyl alcohol (PVA)-based resin, two-stage stretching including aerial assisted stretching and underwater stretching, and drying and shrinkage using heated rolls. By employing these in combination, it is possible to obtain a polarizing film that is thin and yet has extremely excellent optical properties. By using such a polarizing film, it is possible to realize a polarizing plate with a retardation layer that is thin, easy to handle, and has excellent optical properties.

1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to another embodiment of the present invention. FIG. 7 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to yet another embodiment of the present invention. FIG. 2 is a schematic diagram showing an example of a dry shrinkage treatment using a heating roll in a method for manufacturing a polarizing film used in a polarizing plate with a retardation layer of the present invention.

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

(Definition of terms and symbols)
Definitions of terms and symbols used herein are as follows.
(1) Refractive index (nx, ny, nz)
"nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., slow axis direction), and "ny" is the direction perpendicular to the slow axis in the plane (i.e., fast axis direction) "nz" is the refractive index in the thickness direction.
(2) In-plane phase difference (Re)
"Re(λ)" is an in-plane retardation measured with light having a wavelength of λnm at 23°C. For example, "Re(550)" is an in-plane retardation measured with light having a wavelength of 550 nm at 23°C. Re(λ) is determined by the formula: Re(λ)=(nx−ny)×d, where d (nm) is the thickness of the layer (film).
(3) Phase difference in thickness direction (Rth)
"Rth (λ)" is a retardation in the thickness direction measured with light having a wavelength of λ nm at 23°C. For example, "Rth (550)" is the retardation in the thickness direction measured with light having a wavelength of 550 nm at 23°C. Rth(λ) is determined by the formula: Rth(λ)=(nx−nz)×d, where d (nm) is the thickness of the layer (film).
(4) Nz coefficient The Nz coefficient is determined by Nz=Rth/Re.
(5) Angle When an angle is referred to in this specification, the angle includes both clockwise and counterclockwise directions with respect to the reference direction. Therefore, for example, "45°" means ±45°.

A. Overall Configuration of Polarizing Plate with Retardation Layer FIG. 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention. A polarizing plate with a retardation layer 100 of this embodiment includes a polarizing plate 10 and a retardation layer 20. The polarizing plate 10 includes a polarizing film 11, a first protective layer 12 disposed on one side of the polarizing film 11, and a second protective layer 13 disposed on the other side of the polarizing film 11. . Depending on the purpose, one of the first protective layer 12 and the second protective layer 13 may be omitted. For example, if the retardation layer 20 can also function as a protective layer for the polarizing film 11, the second protective layer 13 may be omitted. In an embodiment of the present invention, the polarizing film is composed of a polyvinyl alcohol resin film containing a dichroic substance. The thickness of the polarizing film is 8 μm or less, the single transmittance is 48% or more, and the polarization degree is 85% or more.

As shown in FIG. 2, in a polarizing plate 101 with a retardation layer according to another embodiment, another retardation layer 50 and/or a conductive layer or an isotropic base material 60 with a conductive layer may be provided. Another retardation layer 50 and a conductive layer or an isotropic substrate with a conductive layer 60 are typically provided outside the retardation layer 20 (on the opposite side to the polarizing plate 10). Another retardation layer typically exhibits a refractive index characteristic of nz>nx=ny. Another retardation layer 50 and a conductive layer or an isotropic substrate with a conductive layer 60 are typically provided in this order from the retardation layer 20 side. Another retardation layer 50 and a conductive layer or an isotropic substrate with a conductive layer 60 are typically arbitrary layers provided as needed, and either or both may be omitted. Note that, for convenience, the retardation layer 20 may be referred to as a first retardation layer, and the other retardation layer 50 may be referred to as a second retardation layer. Note that when a conductive layer or an isotropic substrate with a conductive layer is provided, the polarizing plate with a retardation layer is a so-called inner polarizing plate in which a touch sensor is incorporated between an image display cell (for example, an organic EL cell) and a polarizing plate. It can be applied to a touch panel type input display device.

In an embodiment of the present invention, the first retardation layer 20 is an alignment solidified layer of a liquid crystal compound. The first retardation layer 20 may be a single layer of an alignment fixed layer as shown in FIGS. 1 and 2, or a first alignment fixed layer 21 and a second alignment fixed layer 22 as shown in FIG. It may have a laminated structure with.

The above embodiments may be combined as appropriate, and the components in the above embodiments may be modified in a manner obvious to those skilled in the art. For example, the second retardation layer 50 and/or a conductive layer or an isotropic substrate 60 with a conductive layer may be provided on the polarizing plate 102 with a retardation layer shown in FIG. For example, the configuration in which the isotropic base material 60 with a conductive layer is provided outside the second retardation layer 50 is replaced with an optically equivalent configuration (for example, a laminate of a second retardation layer and a conductive layer). It's okay.

The polarizing plate with a retardation layer according to the embodiment of the present invention may further include another retardation layer. Other optical properties (for example, refractive index properties, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, arrangement position, etc. of the retardation layer can be appropriately set depending on the purpose.

The polarizing plate with a retardation layer of the present invention may have a single leaf shape or may have an elongated shape. In this specification, "elongated shape" means an elongated shape whose length is sufficiently longer than its width; for example, an elongated shape whose length is at least 10 times, preferably at least 20 times its width. include. The elongated polarizing plate with a retardation layer can be wound into a roll.

Practically, an adhesive layer (not shown) is provided on the opposite side of the retardation layer to the polarizing plate, and the polarizing plate with the retardation layer can be attached to the image display cell. Furthermore, it is preferable that a release film is temporarily attached to the surface of the adhesive layer until the polarizing plate with a retardation layer is used. Temporarily attaching a release film protects the adhesive layer and enables roll formation.

The total thickness of the polarizing plate with a retardation layer is preferably 60 μm or less, more preferably 55 μm or less, even more preferably 50 μm or less, particularly preferably 40 μm or less. The lower limit of the total thickness may be, for example, 28 μm. According to the embodiments of the present invention, it is possible to realize such an extremely thin polarizing plate with a retardation layer. Such a polarizing plate with a retardation layer can have extremely excellent flexibility and bending durability. Such a polarizing plate with a retardation layer can be particularly suitably applied to a curved image display device and/or a bendable or bendable image display device. The total thickness of a polarizing plate with a retardation layer refers to the total thickness of all the layers that make up the polarizing plate with a retardation layer, excluding the adhesive layer for adhering the polarizing plate to an external adherend such as a panel or glass. The total thickness of the polarizing plate with a retardation layer is the adhesive layer for attaching the polarizing plate with a retardation layer to an adjacent member such as an image display cell, and the peeling layer that can be temporarily attached to the surface of the adhesive layer. (not including film thickness).

The unit weight of the polarizing plate with a retardation layer according to the embodiment of the present invention is, for example, 6.5 mg/cm ² or less, preferably 2.0 mg/cm ² to 6.0 mg/cm ² , more preferably 3 .0mg/cm ² to 5.5mg/cm ² , more preferably 3.5mg/cm ² to 5.0mg/cm ² . If the display panel is thin, the weight of the polarizing plate with a retardation layer may cause the panel to be ^slightly deformed and display defects may occur. According to the plate, such deformation of the panel can be prevented. Moreover, the polarizing plate with a retardation layer having the above unit weight has good handling properties even when made thin, and can exhibit extremely excellent flexibility and bending durability.

Hereinafter, the constituent elements of the polarizing plate with a retardation layer will be explained in more detail.

B. Polarizing plate B-1. Polarizing Film As described above, the polarizing film 11 has a thickness of 8 μm or less, a single transmittance of 48% or more, and a polarization degree of 85% or more. Generally, the single transmittance and the degree of polarization are in a trade-off relationship with each other; increasing the single transmittance may decrease the degree of polarization, and increasing the degree of polarization may decrease the single transmittance. For this reason, it has conventionally been difficult to put into practical use a thin polarizing film that satisfies the optical characteristics of a single transmittance of 48% or more and a polarization degree of 85% or more. A feature of the present invention is to use a thin polarizing film that has excellent optical properties such as a single transmittance of 48% or more and a polarization degree of 85% or more, and suppresses variations in optical properties. There is one.

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

The polarizing film preferably exhibits absorption dichroism at a wavelength of 380 nm to 780 nm. The single transmittance of the polarizing film is preferably 50% or less. The degree of polarization of the polarizing film is preferably 86% or more, more preferably 87% or more, and still more preferably 88% or more. On the other hand, the degree of polarization is preferably 92% or less. The above-mentioned single transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction. The degree of polarization is typically determined by the following formula based on parallel transmittance Tp and cross transmittance Tc measured using an ultraviolet-visible spectrophotometer and corrected for visibility.
Degree of polarization (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

In one embodiment, the transmittance of a thin polarizing film 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 using 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 of the protective film in contact with the air interface, the reflectance at the interface of each layer may change, and as a result, the measured value of transmittance may change. . Therefore, for example, when using a protective film with a refractive index other than 1.50, the measured value of transmittance may be corrected according to the refractive index of the surface of the protective film that is in contact with the air interface. Specifically, the transmittance correction value C is expressed by the following formula 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 using a protective film with a refractive index of 1.50, 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 base material (cycloolefin film, film with a hard coat layer, etc.) having a surface refractive index of 1.53 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 measurement, it is possible to convert it to the transmittance when using a protective film with a surface refractive index of 1.50. According to the calculation based on the above formula, when the transmittance _T1 of the polarizing film is changed by 2%, the amount of change in the correction value C is 0.03% or less, and the transmittance of the polarizing film is less than the correction value C. The effect on the value of is limited. Furthermore, when the protective film has absorption other than surface reflection, appropriate correction can be made depending on the amount of absorption.

In one embodiment, the polarizing plate with a retardation layer has a width of 1000 mm or more, and therefore the width of the polarizing film also has a width of 1000 mm or more. In this case, the difference (D1) between the maximum value and the minimum value of the single transmittance at a position along the width direction of the polarizing film is preferably 1% or less, more preferably 0.8% or less, and Preferably it is 0.6% or less. The smaller D1 is, the more preferable it is, and the lower limit of D1 may be, for example, 0.01%. If D1 is within the above range, a polarizing plate with a retardation layer having excellent optical properties can be industrially produced. In another embodiment, the polarizing film has a difference (D2) between the maximum value and the minimum value of the single transmittance within a 50 cm ² area, preferably 0.5% or less, more preferably 0.25%. It is not more than 0.15%, more preferably not more than 0.15%. The smaller D2 is, the more preferable it is, and the lower limit of D2 may be, for example, 0.01%. If D2 is within the above range, variations in brightness on a display screen can be suppressed when the polarizing plate with a retardation layer is used in an image display device.

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

A specific example of a polarizing film obtained using a laminate includes a polarizing film obtained using a laminate of a resin base material and a PVA-based resin layer coated on the resin base material. A polarizing film obtained using a laminate of a resin base material and a PVA resin layer coated on the resin base material can be obtained by, for example, applying a PVA resin solution to the resin base material and drying it. Forming a PVA-based resin layer thereon to obtain a laminate of a resin base material and a PVA-based resin layer; stretching and dyeing the laminate to make the PVA-based resin layer a polarizing film; obtain. In this embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution and stretching. Furthermore, the stretching may further include stretching the laminate in air at a high temperature (for example, 95° C. or higher) before stretching in the boric acid aqueous solution, if necessary. The obtained resin base material/polarizing film laminate may be used as is (that is, the resin base material may be used as a protective layer for the polarizing film), or the resin base material may be peeled from the resin base material/polarizing film laminate. However, any appropriate protective layer may be laminated on the peeled surface depending on the purpose. Details of the method for manufacturing such a polarizing film are described in, for example, Japanese Patent Application Publication No. 2012-73580. The entire description of this publication is incorporated herein by reference.

A method for producing a polarizing film typically involves forming a polyvinyl alcohol resin layer containing a halide and a polyvinyl alcohol resin on one side of a long thermoplastic resin base material to form a laminate; and subjecting the laminate to, in this order, an auxiliary stretching process in the air, a dyeing process, a stretching process in water, and a drying shrinkage process in which the laminate is shrunk by 2% or more in the width direction by heating while conveying in the longitudinal direction. including. Thereby, it is possible to provide a polarizing film having a thickness of 8 μm or less, a single transmittance of 48% or more, and a polarization degree of 85% or more, which has excellent optical properties and suppresses variations in optical properties. . That is, by introducing auxiliary stretching, even when PVA is applied onto a thermoplastic resin, it becomes possible to improve the crystallinity of PVA, and it becomes possible to achieve high optical properties. At the same time, by increasing the orientation of PVA in advance, it is possible to prevent problems such as deterioration of orientation and dissolution of PVA when it is immersed in water during the subsequent dyeing and stretching processes, resulting in high optical properties. becomes possible to achieve. Furthermore, when the PVA-based resin layer is immersed in a liquid, disturbance in the orientation of polyvinyl alcohol molecules and deterioration of orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of a polarizing film obtained through a treatment process performed by immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment. Furthermore, optical properties can be improved by shrinking the laminate in the width direction by drying shrinkage treatment.

B-2. Protective Layer The first protective layer 12 and the second protective layer 13 are each formed of any suitable film that can be used as a protective layer of a polarizing film. Specific examples of materials that are the main components of the film include cellulose resins such as triacetylcellulose (TAC), polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, and polysulfones. Examples include transparent resins such as polystyrene, polynorbornene, polyolefin, (meth)acrylic, and acetate. Further, thermosetting resins or ultraviolet curable resins such as (meth)acrylic, urethane, (meth)acrylic urethane, epoxy, and silicone resins may also be mentioned. Other examples include glassy polymers such as siloxane polymers. Furthermore, the polymer film described in JP-A-2001-343529 (WO01/37007) can also be used. Materials for this film include, for example, 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 nitrile group in its side chain. For example, a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile/styrene copolymer can be used. The polymer film may be, for example, an extrusion molded product of the resin composition.

The polarizing plate with a retardation layer of the present invention is typically placed on the viewing side of an image display device, as will be described later, and the first protective layer 12 is typically placed on the viewing side. Therefore, the first protective layer 12 may be subjected to surface treatments such as hard coat treatment, antireflection treatment, antisticking treatment, and antiglare treatment, as necessary. Furthermore/or, the first protective layer 12 may be treated, if necessary, to improve visibility when viewed through polarized sunglasses (typically, an (elliptical) circularly polarizing function is applied); (imparting an ultra-high phase difference) may also be applied. By performing such processing, excellent visibility can be achieved even when the display screen is viewed through polarized lenses such as polarized sunglasses. Therefore, the polarizing plate with a retardation layer can be suitably applied to an image display device that can be used outdoors.

The thickness of the first protective layer is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, even more preferably 10 μm to 30 μm. In addition, when surface treatment is performed, the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.

In one embodiment, the second protective layer 13 is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane retardation Re (550) is 0 nm to 10 nm and the thickness direction retardation Rth (550) is -10 nm to +10 nm. say. The second protective layer 13 may be a retardation layer having any suitable retardation value in one embodiment. In this case, the in-plane retardation Re (550) of the retardation layer is, for example, 110 nm to 150 nm. The thickness of the second protective layer is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, even more preferably 10 μm to 30 μm. From the viewpoint of reducing the thickness and weight, the second protective layer can preferably be omitted.

B-3. Method for manufacturing a polarizing film A polarizing film is produced by, for example, forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin base material. The laminate is subjected to an auxiliary stretching process in the air, a dyeing process, a stretching process in water, and a drying process in which the laminate is contracted by 2% or more in the width direction by heating while conveying in the longitudinal direction. and shrinkage treatment in this order. The content of the halide in the PVA resin layer is preferably 5 parts by weight to 20 parts by weight based on 100 parts by weight of the PVA resin. The drying shrinkage treatment is preferably carried out using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is preferably 2% or more. According to such a manufacturing method, the polarizing film described in the above section B-1 can be obtained. In particular, by producing a laminate including a PVA resin layer containing a halide, stretching the laminate in multiple stages including auxiliary stretching in the air and stretching in water, and heating the laminate after stretching with a heating roll. , it is possible to obtain a polarizing film that has excellent optical properties (typically, single transmittance and degree of polarization) and suppresses variations in optical properties. Specifically, by using a heating roll in the drying shrinkage process, the entire laminate can be uniformly shrunk while being transported. This not only makes it possible to improve the optical properties of the resulting polarizing film, but also allows stable production of polarizing films with excellent optical properties, and suppresses variations in the optical properties (especially single transmittance) of the polarizing film. can do.

B-3-1. Preparation of Laminate Any suitable method may be adopted as a method for producing a laminate of a thermoplastic resin base material and a PVA-based resin layer. Preferably, a coating liquid containing a halide and a PVA resin is applied to the surface of the thermoplastic resin base material and dried to form a PVA resin layer on the thermoplastic resin base material. As mentioned above, the content of the halide in the PVA resin layer is preferably 5 parts by weight to 20 parts by weight based on 100 parts by weight of the PVA resin.

Any suitable method can be adopted as a method for applying the coating liquid. Examples include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, knife coating (comma coating, etc.). The coating and drying temperature of the coating liquid 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 base material may be subjected to surface treatment (for example, corona treatment, etc.), or an easily adhesive layer may be formed on the thermoplastic resin base material. By performing such a treatment, the adhesion between the thermoplastic resin base material and the PVA resin layer can be improved.

B-3-1-1. Thermoplastic resin base material The thickness of the thermoplastic resin base material 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, it may take a long time for the thermoplastic resin base material to absorb water in the underwater stretching treatment described below, and an excessive load may be required for stretching.

The thermoplastic resin base material 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 can be plasticized by the water acting as a plasticizer. As a result, stretching stress can be significantly reduced and stretching can be performed at a high magnification. On the other hand, the water absorption rate of the thermoplastic resin base material is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin base material, it is possible to prevent problems such as a significant decrease in the dimensional stability of the thermoplastic resin base material during production, resulting in deterioration of the appearance of the resulting polarizing film. Furthermore, it is possible to prevent the base material from breaking during underwater stretching or from peeling off the PVA resin layer from the thermoplastic resin base material. Note that the water absorption rate of the thermoplastic resin base material can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption rate is a value determined according to JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin base material is preferably 120°C or lower. By using such a thermoplastic resin base material, it is possible to sufficiently ensure the stretchability of the laminate while suppressing crystallization of the PVA-based resin layer. Furthermore, in consideration of plasticizing the thermoplastic resin base material with water and performing underwater stretching satisfactorily, 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 base material is preferably 60°C or higher. By using such a thermoplastic resin base material, the thermoplastic resin base material may be deformed (e.g., unevenness, sagging, wrinkles, etc.) when applying and drying a coating solution containing the above-mentioned PVA-based resin. It is possible to prevent this problem and produce a good laminate. Further, the PVA resin layer can be stretched well at a suitable temperature (for example, about 60° C.). Note that the glass transition temperature of the thermoplastic resin base material can be adjusted by, for example, heating using a crystallizing material that introduces a modifying group into the constituent material. The glass transition temperature (Tg) is a value determined according to JIS K 7121.

Any suitable thermoplastic resin may be employed as the constituent material of the thermoplastic resin base material. Examples of thermoplastic resins 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. can be mentioned. Among these, norbornene resins and amorphous polyethylene terephthalate resins are preferred.

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 copolymers further containing isophthalic acid and/or cyclohexane dicarboxylic acid as a dicarboxylic acid, and copolymers further containing cyclohexanedimethanol or diethylene glycol as a glycol.

In a preferred embodiment, the thermoplastic resin base material is comprised of a polyethylene terephthalate-based resin having isophthalic acid units. This is because such a thermoplastic resin base material has extremely excellent stretchability and can suppress crystallization during stretching. This is thought to be due to the fact that the introduction of the isophthalic acid unit imparts a large bend to the main chain. Polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content 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 base material with extremely excellent stretchability can be obtained. On the other hand, the content 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 the content to such a content ratio, the degree of crystallinity can be favorably increased in the drying shrinkage treatment described below.

The thermoplastic resin base material may be stretched in advance (before forming the PVA-based resin layer). In one embodiment, the elongated thermoplastic resin base material is stretched in the lateral direction. The lateral direction is preferably a direction perpendicular to the stretching direction of the laminate described below. In addition, in this specification, "orthogonal" also includes a case where they are substantially orthogonal. Here, "substantially orthogonal" includes a case where the angle is 90°±5.0°, preferably 90°±3.0°, and more preferably 90°±1.0°.

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

Any suitable method may be employed as a method for stretching the thermoplastic resin base material. Specifically, fixed end stretching or free end stretching may be used. The stretching method may be a dry method or a wet method. The thermoplastic resin base material may be stretched in one step or in multiple steps. In the case of multi-stage stretching, the above-mentioned stretching ratio is the product of the stretching ratios of each stage.

B-3-1-2. Coating Liquid The coating liquid contains a halide and a PVA resin as described above. The coating liquid is typically a solution in which the halide and the PVA resin are dissolved in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Among these, water is preferred. The concentration of the PVA resin in the solution is preferably 3 to 20 parts by weight based on 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film that adheres to the thermoplastic resin base material can be formed. The content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight based on 100 parts by weight of the PVA resin.

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

Any suitable resin may be employed as the PVA resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer can be obtained by saponifying 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 degree of saponification can be determined according to JIS K 6726-1994. By using a PVA resin having such a degree of saponification, a polarizing film with 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 depending on the purpose. The average degree of polymerization is usually 1,000 to 10,000, preferably 1,200 to 4,500, and more preferably 1,500 to 4,300. Note that the average degree of polymerization can be determined according to JIS K 6726-1994.

Any suitable halide may be employed as the halide. Examples include iodide and sodium chloride. Iodides include, for example, potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.

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

Generally, by stretching the PVA resin layer, the orientation of the polyvinyl alcohol molecules in the PVA resin increases. However, when the stretched PVA resin layer is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules increases. The orientation may be disturbed and the orientation may be deteriorated. In particular, when stretching a laminate of a thermoplastic resin base material and a PVA resin layer in boric acid water, the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin base material. When stretching, the above-mentioned tendency for the degree of orientation to decrease is remarkable. For example, while it is common for a PVA film alone to be stretched in boric acid water at 60°C, a laminate of A-PET (thermoplastic resin base material) and a PVA resin layer is stretched. It is carried out at a high temperature of around 70°C, and in this case, the orientation of PVA at the initial stage of stretching may decrease before it increases due to underwater stretching. In contrast, by producing a laminate of a PVA resin layer containing a halide and a thermoplastic resin base material, and stretching the laminate at high temperature in air (auxiliary stretching) before stretching it in boric acid water. , crystallization of the PVA resin in the PVA resin layer of the laminate after auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, disturbance in the orientation of polyvinyl alcohol molecules and deterioration of orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of a polarizing film obtained through a treatment process performed by immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment.

B-3-2. Auxiliary Stretching Treatment in Air In particular, in order to obtain high optical properties, a two-stage stretching method is selected that combines dry stretching (auxiliary stretching) and stretching in boric acid water. By introducing auxiliary stretching as in two-stage stretching, it is possible to stretch while suppressing crystallization of the thermoplastic resin base material, and prevent excessive crystallization of the thermoplastic resin base material during subsequent stretching in boric acid water. This solves the problem that the stretchability is lowered due to this, and the laminate can be stretched to a higher magnification. Furthermore, in order to suppress the influence of the glass transition temperature of the thermoplastic resin base material, when applying PVA resin on a thermoplastic resin base material, compared to the case where PVA resin is applied on a normal metal drum, As a result, the crystallization of the PVA-based resin becomes relatively low, which may cause a problem that sufficient optical properties cannot be obtained. On the other hand, by introducing auxiliary stretching, it is possible to increase the crystallinity of PVA-based resin even when applying PVA-based resin onto thermoplastic resin, making it possible to achieve high optical properties. 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 orientation and dissolution of the PVA resin when it is immersed in water during the subsequent dyeing and stretching processes. , it becomes possible to achieve high optical properties.

The stretching method for aerial auxiliary stretching may be fixed end stretching (for example, stretching using a tenter stretching machine) or free end stretching (for example, uniaxial stretching by passing the laminate between rolls with different circumferential speeds). However, in order to obtain high optical properties, free end stretching may be actively employed. In one embodiment, the aerial stretching process includes a heating roll stretching step of stretching the laminate using a difference in peripheral speed between heating rolls while conveying the laminate in its longitudinal direction. The aerial stretching process typically includes a zone stretching process and a heated roll stretching process. Note that 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. In another embodiment, the film is stretched in a tenter stretching machine by gripping the end portion of the film and widening the distance between the tenters in the machine direction (the widening of the distance between the tenters becomes 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, the stretching ratio in the machine direction can be set closer to free end stretching. In the case of free end stretching, the shrinkage rate in the width direction is calculated as (1/stretching ratio) ^1/2 .

Aerial assisted stretching may be performed in one step or in multiple steps. In the case of multi-stage stretching, the stretching ratio is the product of the stretching ratios of each stage. The stretching direction in the aerial auxiliary stretching is preferably substantially the same as the stretching direction in the underwater stretching.

The stretching ratio in the aerial auxiliary stretching is preferably 2.0 times to 3.5 times. The maximum stretching ratio when the aerial auxiliary stretching and underwater stretching are combined 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 all. In this specification, the "maximum stretching ratio" refers to the stretching ratio immediately before the laminate breaks, and the stretching ratio at which the laminate breaks is separately confirmed, and it refers to 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 base material, the stretching method, etc. The stretching temperature is preferably at least the glass transition temperature (Tg) of the thermoplastic resin base material, more preferably at least the glass transition temperature (Tg) of the thermoplastic resin base material +10°C, particularly preferably at least Tg +15°C. 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 the rapid progress of crystallization of the PVA-based resin and to suppress defects caused by the crystallization (for example, preventing the orientation of the PVA-based resin layer due to stretching). can. The crystallization index of the PVA-based resin after in-air assisted stretching is preferably 1.3 to 1.8, more preferably 1.4 to 1.7. The crystallization index of the PVA-based resin can be measured by the ATR method using a Fourier transform infrared spectrophotometer. Specifically, measurements are performed using polarized light as measurement light, and the crystallization index is calculated according to the following formula using the intensities at 1141 cm ^-1 and 1440 cm ^-1 of the obtained spectrum.
Crystallization index = (I _C /I _R )
however,
I _C : Intensity of 1141 cm ⁻¹ when measured with measurement light incident. I _R : Intensity of 1440 cm ⁻¹ when measured with measurement light incident.

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

B-3-4. Dyeing Process The above dyeing process is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). Specifically, this is carried out by adsorbing iodine to the PVA resin layer. The adsorption method includes, for example, immersing the PVA resin layer (laminate) in a dye containing iodine, applying the dye to the PVA resin layer, and applying the dye to the PVA resin layer. Examples include a method of spraying. Preferably, the method involves immersing the laminate in a dyeing solution (dyeing bath). This is because iodine can be adsorbed well.

The staining solution is preferably an aqueous iodine solution. The amount of iodine blended is preferably 0.05 part by weight to 0.5 part by weight per 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add iodide to the iodine aqueous solution. Examples of iodides 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 preferred. The amount of iodide to be blended is preferably 0.1 parts by weight to 10 parts by weight, more preferably 0.3 parts by weight to 5 parts by weight, based on 100 parts by weight of water. The temperature of the dyeing solution during dyeing 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 dyeing liquid, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds, in order to ensure the transmittance of the PVA resin layer.

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

When dyeing is performed continuously after immersing the laminate in a treatment bath containing boric acid (typically, insolubilization treatment), the boric acid contained in the treatment bath may mix into the dyeing bath. The boric acid concentration in the dye bath may change over time, resulting in unstable dyeing properties. In order to suppress the destabilization of dyeability as described above, the upper limit of the concentration of boric acid in the dyeing bath is preferably 4 parts by weight, more preferably 2 parts by weight, based on 100 parts by weight of water. be 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, and still more preferably 0.5 part by weight, based on 100 parts by weight of water. It is. In one embodiment, the dyeing process is carried out using a dye bath pre-blended with boric acid. This can reduce the rate of change in boric acid concentration when boric acid in the treatment bath is mixed into the dyeing bath. The amount of boric acid added to the dyeing bath in advance (that is, the content of boric acid not derived from the treatment bath) is preferably 0.1 parts by weight to 2 parts by weight based on 100 parts by weight of water. , more preferably 0.5 parts by weight to 1.5 parts by weight.

B-3-5. Crosslinking treatment If necessary, crosslinking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The above crosslinking treatment is typically performed by immersing the PVA resin layer in a boric acid aqueous solution. By performing the crosslinking treatment, water resistance is imparted to the PVA-based resin layer, and in the subsequent underwater stretching, it is possible to prevent a decrease in the orientation of PVA when immersed in high-temperature water. The concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight per 100 parts by weight of water. Moreover, when crosslinking treatment is performed after the above-mentioned dyeing treatment, it is preferable to further include an iodide. By blending iodide, it is possible to suppress elution of iodine adsorbed to the PVA-based resin layer. The amount of iodide to be blended is preferably 1 to 5 parts by weight per 100 parts by weight of water. Specific examples of iodides are as described above. The temperature of the crosslinking bath (boric acid aqueous solution) is preferably 20°C to 50°C.

B-3-6. 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 base material or the PVA resin layer, and the PVA resin layer can be It is possible to stretch to a high magnification while suppressing the As a result, a polarizing film having excellent optical properties can be manufactured.

Any suitable method can be used to stretch the laminate. Specifically, fixed-end stretching or free-end stretching (for example, a method in which the laminate is passed between rolls having different circumferential speeds and uniaxially stretched) may be used. Preferably, free end stretching is chosen. The laminate may be stretched in one step or in multiple steps. When performing multi-stage stretching, the stretching ratio (maximum stretching ratio) of the laminate described below is the product of the stretching ratios of each stage.

Stretching in water is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water). By using a boric acid aqueous solution as a stretching bath, it is possible to impart rigidity to the PVA-based resin layer to withstand 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 and crosslink with the PVA-based resin through hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer, which can be stretched well, and a polarizing film having excellent optical properties can be manufactured.

The aqueous boric acid solution is preferably obtained by dissolving boric acid and/or a borate salt in water, which is a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 2.5 to 6 parts by weight, particularly preferably 3 to 5 parts by weight, based on 100 parts by weight of water. It is. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film with higher characteristics can be manufactured. In addition to boric acid or a borate salt, 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 stretching bath (boric acid aqueous solution). By blending iodide, it is possible to suppress elution of iodine adsorbed to the PVA-based resin layer. Specific examples of iodides are as described above. The concentration of iodide is preferably 0.05 parts by weight to 15 parts by weight, more preferably 0.5 parts by weight to 8 parts by weight, based on 100 parts by weight of water.

The stretching temperature (the liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such a temperature, it is possible to stretch to a high magnification while suppressing dissolution of the PVA-based resin layer. 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., there is a possibility that the stretching cannot be performed satisfactorily even if the plasticization of the thermoplastic resin base material by water is taken into account. On the other hand, as the temperature of the stretching bath increases, the solubility of the PVA-based resin layer increases, and there is a possibility that excellent optical properties may not be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio by underwater stretching is preferably 1.5 times or more, more preferably 3.0 times or more. The total stretching ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, relative to the original length of the laminate. By achieving such a high stretching ratio, a polarizing film with extremely excellent optical properties can be manufactured. Such a high stretching ratio can be achieved by employing an underwater stretching method (boric acid underwater stretching).

B-3-7. Drying Shrinkage Treatment The drying shrinkage treatment described above may be performed by zone heating performed by heating the entire zone, or may be performed by heating a conveyance roll (using a so-called heating roll) (heated roll drying method). Preferably, both are used. By drying using a heating roll, heating curl of the laminate can be efficiently suppressed, and a polarizing film with excellent appearance can be manufactured. Specifically, by drying the laminate along a heating roll, it is possible to efficiently promote crystallization of the thermoplastic resin base material and increase the degree of crystallinity, which is relatively low. Even at drying temperatures, the degree of crystallinity of the thermoplastic resin base material can be increased favorably. As a result, the thermoplastic resin base material has increased rigidity and is in a state where it can withstand shrinkage of the PVA resin layer due to drying, thereby suppressing curling. Furthermore, by using a heating roll, the laminate can be dried while maintaining it in a flat state, so that not only curling but also wrinkles can be suppressed. At this time, the optical properties of the laminate can be improved by shrinking the laminate in the width direction by drying shrinkage treatment. This is because the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, 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 achieved.

FIG. 4 is a schematic diagram showing an example of drying shrinkage treatment. In the drying shrinkage process, the laminate 200 is dried while being transported by transport rolls R1 to R6 heated to a predetermined temperature and guide rolls G1 to G4. In the illustrated example, 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 base material. The transport rolls R1 to R6 may be arranged so as to continuously heat only the resin base material surface).

The drying conditions can be controlled by adjusting the heating temperature of the conveying roll (temperature of the heating roll), the number of heating rolls, the contact time with the heating roll, etc. The temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, particularly preferably 70°C to 80°C. It is possible to satisfactorily increase the degree of crystallinity of the thermoplastic resin, to satisfactorily suppress curling, and to produce an optical laminate having extremely excellent durability. Note that the temperature of the heating roll can be measured with a contact thermometer. In the illustrated example, six conveyance rolls are provided, but there is no particular restriction on the number of conveyance rolls as long as there is a plurality of conveyance rolls. Usually 2 to 40 conveyance rolls, preferably 4 to 30 conveyance 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 even more preferably 1 to 10 seconds.

The heating roll may be provided within a heating furnace (for example, an oven) or may be provided on a normal production line (at room temperature). Preferably, it is provided in a heating furnace equipped with air blowing means. By using both heating roll drying and hot air drying, a sharp 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. Further, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10 m/s to 30 m/s. Note that the wind speed is the wind speed within the heating furnace, and can be measured with a mini-vane digital anemometer.

B-3-8. Other Treatments Preferably, a washing treatment is performed after the underwater stretching treatment and before the drying shrinkage treatment. The above cleaning treatment is typically performed by immersing the PVA resin layer in an aqueous potassium iodide solution.

C. First Retardation Layer The first retardation layer 20 is, as described above, an alignment solidified layer of a liquid crystal compound. By using a liquid crystal compound, the difference between nx and ny of the obtained retardation layer can be made much larger than that of non-liquid crystal materials, so the thickness of the retardation layer can be adjusted to obtain the desired in-plane retardation. can be made significantly smaller. As a result, it is possible to further reduce the thickness and weight of the polarizing plate with a retardation layer. As used herein, the term "orientation-fixed layer" refers to a layer in which a liquid crystal compound is oriented in a predetermined direction and the orientation state is fixed. In addition, the "alignment hardened layer" is a concept that includes an orientation hardened layer obtained by curing a liquid crystal monomer as described below. In this embodiment, the rod-shaped liquid crystal compounds are typically aligned in the slow axis direction of the first retardation layer (homogeneous alignment).

Examples of the liquid crystal compound include a liquid crystal compound whose liquid crystal phase is a nematic phase (nematic liquid crystal). As such a liquid crystal compound, for example, a liquid crystal polymer or a liquid crystal monomer can be used. The mechanism for developing liquid crystallinity of a liquid crystal compound may be either lyotropic or thermotropic. The liquid crystal polymer and the liquid crystal monomer may be used alone or in combination.

When the liquid crystal compound is a liquid crystal monomer, the liquid crystal monomer is preferably a polymerizable monomer and a crosslinkable monomer. This is because the alignment state of the liquid crystal monomer can be fixed by polymerizing or crosslinking (that is, curing) the liquid crystal monomer. After aligning the liquid crystal monomers, for example, by polymerizing or crosslinking the liquid crystal monomers, the alignment state can be fixed. Here, a polymer is formed by polymerization, and a three-dimensional network structure is formed by crosslinking, but these are non-liquid crystalline. Therefore, the formed first retardation layer does not undergo a transition to a liquid crystal phase, a glass phase, or a crystal phase due to a temperature change, which is characteristic of liquid crystal compounds, for example. As a result, the first retardation layer becomes an extremely stable retardation layer that is not affected by temperature changes.

The temperature range in which a liquid crystal monomer exhibits liquid crystallinity differs depending on its type. Specifically, the temperature range is preferably 40°C to 120°C, more preferably 50°C to 100°C, and most preferably 60°C to 90°C.

Any suitable liquid crystal monomer may be employed as the liquid crystal monomer. For example, described in Special Table 2002-533742 (WO00/37585), EP358208 (US5211877), EP66137 (US4388453), WO93/22397, EP0261712, DE19504224, DE4408171, and GB2280445, etc. Polymerizable mesogenic compounds and the like can be used. Specific examples of such polymerizable mesogenic compounds include, for example, BASF's product name LC242, Merck's product name E7, and Wacker-Chem's product name LC-Sillicon-CC3767. As the liquid crystal monomer, for example, a nematic liquid crystal monomer is preferable.

The alignment solidified layer of a liquid crystal compound is obtained by subjecting the surface of a predetermined base material to an alignment treatment, applying a coating liquid containing a liquid crystal compound to the surface to align the liquid crystal compound in a direction corresponding to the alignment treatment, It can be formed by fixing the orientation state. In one embodiment, the base material is any suitable resin film, and the alignment solidified layer formed on the base material can be transferred to the surface of the polarizing plate 10. In another embodiment, the substrate may be the second protective layer 13. In this case, the transfer step is omitted and lamination can be performed continuously from the formation of the orientation-fixed layer (first retardation layer) by roll-to-roll, thereby further improving productivity.

Any suitable orientation treatment may be employed as the orientation treatment. Specifically, mechanical alignment treatment, physical alignment treatment, and chemical alignment treatment can be mentioned. Specific examples of mechanical alignment treatment include rubbing treatment and stretching treatment. Specific examples of physical alignment treatment include magnetic field alignment treatment and electric field alignment treatment. Specific examples of chemical alignment treatment include oblique vapor deposition and photo alignment treatment. As the treatment conditions for various orientation treatments, any appropriate conditions may be adopted depending on the purpose.

The alignment of the liquid crystal compound is carried out by treatment at a temperature at which it exhibits a liquid crystal phase depending on the type of liquid crystal compound. By performing such temperature treatment, the liquid crystal compound assumes a liquid crystal state, and the liquid crystal compound is oriented in accordance with the orientation treatment direction of the substrate surface.

In one embodiment, the alignment state is fixed by cooling the liquid crystal compound oriented as described above. When the liquid crystal compound is a polymerizable monomer or a crosslinkable monomer, the alignment state is fixed by subjecting the liquid crystal compound oriented as described above to a polymerization treatment or a crosslinking treatment.

Specific examples of the liquid crystal compound and details of the method for forming the alignment solidified layer are described in JP-A No. 2006-163343. The description of the publication is incorporated herein by reference.

Another example of the alignment solidified layer includes a form in which the discotic liquid crystal compound is aligned in any one of vertical alignment, hybrid alignment, and oblique alignment. In the discotic liquid crystal compound, typically, the disc plane of the discotic liquid crystal compound is oriented substantially perpendicularly to the film plane of the first retardation layer. The fact that the discotic liquid crystal compound is substantially perpendicular means that the average value of the angle between the film surface and the disk surface of the discotic liquid crystal compound is preferably 70° to 90°, more preferably 80° to 90°. , more preferably 85° to 90°. Discotic liquid crystal compounds generally have a cyclic core such as benzene, 1,3,5-triazine, calixarene, etc. at the center of the molecule, and have linear alkyl groups, alkoxy groups, substituted benzoyl groups, etc. A liquid crystal compound having a disc-shaped molecular structure in which oxy groups and the like are substituted radially as side chains. A typical example of discotic liquid crystal is C. Research report by Detrade et al., Mol. Cryst. Liq. Cryst. 71, p. 111 (1981), benzene derivatives, triphenylene derivatives, truxene derivatives, phthalocyanine derivatives, and B. Research report by Kohne et al., Angew. Chem. 96, p. 70 (1984), and the cyclohexane derivatives described in J. M. Research report of Lehn et al., J. Chem. Soc. Chem. Commun. , p. 1794 (1985), J. Research report of Zhang et al., J. Am. Chem. Soc. Examples include azacrown-based and phenylacetylene-based macrocycles described in Vol. 116, p. 2655 (1994). Further specific examples of discotic liquid crystal compounds include compounds described in JP-A No. 2006-133652, JP-A No. 2007-108732, and JP-A No. 2010-244038. The descriptions of the above-mentioned documents and publications are incorporated herein by reference.

In one embodiment, the first retardation layer 20 is a single layer of an alignment solidified layer of a liquid crystal compound as shown in FIGS. 1 and 2. When the first retardation layer 20 is composed of a single layer of an alignment solidified layer of a liquid crystal compound, its thickness is preferably 0.5 μm to 7 μm, more preferably 1 μm to 5 μm. By using a liquid crystal compound, it is possible to achieve an in-plane retardation equivalent to that of a resin film with a thickness much thinner than that of a resin film.

The first retardation layer typically exhibits a refractive index characteristic of nx>ny=nz. The first retardation layer is typically provided to impart antireflection properties to the polarizing plate, and functions as a λ/4 plate when the first retardation layer is a single layer of an alignment solidified layer. It is possible. In this case, the in-plane retardation Re (550) of the first retardation layer is preferably 100 nm to 190 nm, more preferably 110 nm to 170 nm, even more preferably 130 nm to 160 nm. Note that "ny=nz" here includes not only the case where ny and nz are completely equal, but also the case where they are substantially equal. Therefore, there may be cases where ny>nz or ny<nz as long as the effects of the present invention are not impaired.

The Nz coefficient of the first retardation layer is preferably 0.9 to 1.5, more preferably 0.9 to 1.3. By satisfying such a relationship, when the obtained polarizing plate with a retardation layer is used in an image display device, an extremely excellent reflected hue can be achieved.

The first retardation layer may exhibit inverse dispersion wavelength characteristics in which the retardation value increases according to the wavelength of the measurement light, and positive wavelength dispersion characteristics in which the retardation value decreases in accordance with the wavelength of the measurement light. Alternatively, the phase difference value may exhibit flat wavelength dispersion characteristics that hardly change depending on the wavelength of the measurement light. In one embodiment, the first retardation layer exhibits inverse dispersion wavelength characteristics. In this case, Re(450)/Re(550) of the retardation layer is preferably 0.8 or more and less than 1, more preferably 0.8 or more and 0.95 or less. With such a configuration, extremely excellent antireflection properties can be achieved.

The angle θ between the slow axis of the first retardation layer 20 and the absorption axis of the polarizing film 11 is preferably 40° to 50°, more preferably 42° to 48°, and still more preferably about It is 45°. If the angle θ is in this range, by using the λ/4 plate as the first retardation layer as described above, very good circular polarization properties (as a result, very good antireflection properties) can be obtained. A polarizing plate with a retardation layer can be obtained.

In another embodiment, the first retardation layer 20 may have a laminated structure of a first alignment fixed layer 21 and a second alignment fixed layer 22, as shown in FIG. In this case, either the first orientation fixed layer 21 or the second orientation fixed layer 22 may function as a λ/4 plate, and the other may function as a λ/2 plate. Therefore, the thicknesses of the first alignment fixed layer 21 and the second alignment fixed layer 22 can be adjusted so as to obtain a desired in-plane retardation of the λ/4 plate or the λ/2 plate. For example, when the first oriented solidified layer 21 functions as a λ/2 plate and the second oriented solidified layer 22 functions as a λ/4 plate, the thickness of the first oriented solidified layer 21 is, for example, 2.0 μm or more. The thickness of the second alignment fixed layer 22 is, for example, 1.0 μm to 2.0 μm. In this case, the in-plane retardation Re (550) of the first alignment fixed layer is preferably 200 nm to 300 nm, more preferably 230 nm to 290 nm, and still more preferably 250 nm to 280 nm. The in-plane retardation Re (550) of the second alignment fixed layer is as explained above for the single layer alignment fixed layer. The angle between the slow axis of the first alignment fixed layer and the absorption axis of the polarizing film is preferably 10° to 20°, more preferably 12° to 18°, and even more preferably about 15°. be. The angle between the slow axis of the second alignment fixed layer and the absorption axis of the polarizing film is preferably 70° to 80°, more preferably 72° to 78°, and even more preferably about 75°. be. With such a configuration, it is possible to obtain characteristics close to ideal reverse wavelength dispersion characteristics, and as a result, extremely excellent antireflection characteristics can be realized. Regarding the liquid crystal compounds constituting the first alignment fixed layer and the second alignment fixed layer, the formation method of the first alignment fixed layer and the second alignment fixed layer, optical properties, etc., please refer to the above for the single layer alignment fixed layer. As explained in .

D. Second Retardation Layer As described above, the second retardation layer may be a so-called positive C plate whose refractive index characteristics exhibit the relationship nz>nx=ny. By using a positive C plate as the second retardation layer, reflection in an oblique direction can be effectively prevented, and the antireflection function can provide a wide viewing angle. In this case, the retardation Rth (550) in the thickness direction of the second retardation layer is preferably -50 nm to -300 nm, more preferably -70 nm to -250 nm, still more preferably -90 nm to -200 nm, particularly preferably -100 nm to -180 nm. Here, "nx=ny" includes not only the case where nx and ny are strictly equal, but also the case where nx and ny are substantially equal. That is, the in-plane retardation Re (550) of the second retardation layer may be less than 10 nm.

The second retardation layer having a refractive index characteristic of nz>nx=ny may be formed of any suitable material. The second retardation layer preferably consists of a film containing liquid crystal material fixed in homeotropic alignment. The liquid crystal material (liquid crystal compound) that can be homeotropically aligned may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method for forming the retardation layer include the liquid crystal compound and the method for forming the retardation layer described in [0020] to [0028] of JP-A No. 2002-333642. In this case, the thickness of the second retardation layer is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, and even more preferably 0.5 μm to 5 μm.

E. Conductive layer or isotropic base material with conductive layer The conductive layer can be formed on any suitable base material by any suitable film forming method (e.g., vacuum evaporation method, sputtering method, CVD method, ion plating method, spray method, etc.). It can be formed by depositing a metal oxide film thereon. Examples of metal oxides include indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimony composite oxide, zinc-aluminum composite oxide, and indium-zinc composite oxide. Among them, indium-tin composite oxide (ITO) is preferred.

When the conductive layer contains a metal oxide, the thickness of the conductive layer is preferably 50 nm or less, more preferably 35 nm or less. The lower limit of the thickness of the conductive layer is preferably 10 nm.

The conductive layer may be transferred from the base material to the first retardation layer (or the second retardation layer if present) and the conductive layer alone may be used as a constituent layer of a polarizing plate with a retardation layer. Often, it may be laminated on the first retardation layer (or the second retardation layer if present) as a laminate with a base material (base material with conductive layer). Preferably, the base material is optically isotropic, and therefore, the conductive layer can be used as an isotropic base material with a conductive layer in a polarizing plate with a retardation layer.

Any suitable isotropic base material can be employed as the optically isotropic base material (isotropic base material). Materials constituting the isotropic base material include, for example, materials whose main skeleton is a resin without a conjugated system such as norbornene resins and olefin resins, and materials with cyclic structures such as lactone rings and glutarimide rings such as acrylic resins. Examples include materials contained in the main chain. When such a material is used, when an isotropic base material is formed, the development of retardation due to the orientation of molecular chains can be suppressed to a small level. The thickness of the isotropic base material is preferably 50 μm or less, more preferably 35 μm or less. The lower limit of the thickness of the isotropic base material is, for example, 20 μm.

The conductive layer and/or the conductive layer of the isotropic base material with a conductive layer may be patterned as necessary. A conductive part and an insulating part can be formed by patterning. As a result, an electrode can be formed. The electrode can function as a touch sensor electrode that senses contact with the touch panel. Any suitable method can be adopted as the patterning method. Specific examples of patterning methods include wet etching and screen printing.

F. Image display device The polarizing plate with a retardation layer described in the above items A to E can be applied to an image display device. Therefore, the present invention includes an image display device using such a polarizing plate with a retardation layer. Typical examples of image display devices include liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices). The image display device according to the embodiment of the present invention includes the polarizing plate with a retardation layer described in the above sections A to E on the viewing side. The polarizing plate with a retardation layer is laminated so that the retardation layer is on the image display cell (eg, liquid crystal cell, organic EL cell, inorganic EL cell) side (with the polarizing film on the viewing side). In one embodiment, the image display device has a curved shape (substantially a curved display screen) and/or is bendable or foldable. In such an image display device, the effect of the polarizing plate with a retardation layer of the present invention becomes remarkable.

なお、例えば、アンチグレア（ＡＧ）の表面処理や拡散性能を有する粘着剤を備える偏光板を測定対象とする場合、分光光度計に依存して異なる測定結果が得られ得るが、この場合、同一の偏光板をそれぞれの分光光度計で測定したときの測定値に基づいて数値換算を行うことにより、分光光度計に依存する測定値の差を補償することが可能である。
（３）長尺状の偏光膜の光学特性のバラつき
実施例および比較例に用いた偏光板から、幅方向に沿って等間隔に５か所の各位置で測定サンプルを切り出し、５つの各測定サンプルの中央部分の単体透過率を上記（２）と同様にして測定した。次いで、各測定位置において測定された単体透過率のうちの最大値と最小値との差を算出し、この値を長尺状の偏光膜の光学特性のバラつきとした。
（４）枚葉状の偏光膜の光学特性のバラつき
実施例および比較例に用いた偏光板から、１００ｍｍ×１００ｍｍの測定サンプルを切り出し、枚葉状の偏光板（５０ｃｍ^２）の光学特性のバラつきを求めた。具体的には、測定サンプルの４辺の各辺の中点から内側に約１．５ｃｍ～２．０ｃｍ付近の位置および中央部分の計５か所の単体透過率を上記（２）と同様にして測定した。次いで、各測定位置において測定された単体透過率のうちの最大値と最小値との差を算出し、この値を枚葉状の偏光膜の光学特性のバラつきとした。
（５）反り
実施例および比較例で得られた位相差層付偏光板を１１０ｍｍ×６０ｍｍサイズに切り出した。このとき、偏光膜の吸収軸方向が長辺方向となるように切り出した。切り出した位相差層付偏光板を、１２０ｍｍ×７０ｍｍサイズ、厚み０．２ｍｍのガラス板に粘着剤を介して貼り合わせ、試験サンプルとした。試験サンプルを、８５℃に保持された加熱オーブンに２４時間投入し、取り出した後の反り量を測定した。ガラス板を下にして試験サンプルを平面上に静置した時に、当該平面から最も高い部分の高さを反り量とした。
（６）単位重量
実施例および比較例で得られた位相差層付偏光板を所定のサイズに切り出し、重量（ｍｇ）を面積（ｃｍ^２）で除することにより、位相差層付偏光板の単位面積当たりの重量（単位重量）を算出した。
（７）耐折り曲げ性
実施例および比較例で得られた位相差層付偏光板を５０ｍｍ×１００ｍｍサイズに切り出した。このとき、偏光膜の吸収軸方向が短辺方向となるように切り出した。恒温恒湿チャンバー付耐折試験機（ＹＵＡＳＡ社製、ＣＬ０９ ｔｙｐｅ－Ｄ０１）を用いて、２０℃５０％ＲＨの条件下で、切り出した位相差層付偏光板を折り曲げ試験に供した。具体的には、位相差層付偏光板を、位相差層側が外側となるように、吸収軸方向に平行な方向に繰り返し折り曲げて、表示不良となるようなクラック、剥がれやフィルムの破断などが発生するまでの折り曲げ回数を測定し、以下の基準で評価した（折り曲げ径：２ｍｍφ）。
＜評価基準＞
１万回未満：不良
１万回以上３万回未満：良
３万回以上：優 EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples. The method for measuring each characteristic is as follows. Note that unless otherwise specified, "parts" and "%" in Examples and Comparative Examples are based on weight.
(1) Thickness The thickness of 10 μm or less was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name “MCPD-3000”). Thickness exceeding 10 μm was measured using a digital micrometer (manufactured by Anritsu Corporation, product name “KC-351C”).
(2) Single transmittance and polarization degree The polarizing film/protective layer laminate (polarizing plate) used in Examples and Comparative Examples was measured using an ultraviolet-visible spectrophotometer (V-7100 manufactured by JASCO Corporation). Single transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc were defined as Ts, Tp, and Tc of the polarizing film, respectively. These Ts, Tp, and Tc are Y values measured using a 2-degree visual field (C light source) according to JIS Z8701 and subjected to visibility correction. The refractive index of the protective layer was 1.50, and the refractive index of the surface of the polarizing film opposite to the protective layer was 1.53.
The degree of polarization P was determined from the obtained Tp and Tc using the following formula.
Polarization degree P (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 ×100
Note that a spectrophotometer such as LPF-200 manufactured by Otsuka Electronics Co., Ltd. can also perform equivalent measurements. As an example, Table 1 shows the measured values of the single transmittance Ts and polarization degree P obtained by measurements using V-7100 and LPF-200 for polarizing plates Samples 1 to 3 having the same configuration as in the example below. 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 less than 0.1%, and both spectrophotometers were used. It can be seen that equivalent measurement results can be obtained even if the

For example, when measuring a polarizing plate equipped with an anti-glare (AG) surface treatment or an adhesive with diffusion performance, different measurement results may be obtained depending on the spectrophotometer. By performing numerical conversion based on the measured values when the polarizing plate is measured with each spectrophotometer, it is possible to compensate for differences in the measured values depending on the spectrophotometer.
(3) Variation in optical properties of long polarizing film Measurement samples were cut out from the polarizing plates used in the Examples and Comparative Examples at five positions equally spaced along the width direction, and five measurements were taken. The single transmittance of the central portion of the 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 transmittance measured at each measurement position was calculated, and this value was taken as the variation in the optical properties of the long polarizing film.
(4) Variation in the optical properties of the sheet-shaped polarizing film A 100 mm x 100 mm measurement sample was cut out from the polarizing plate used in the Examples and Comparative Examples, and the variation in the optical properties of the sheet-shaped polarizing plate (50 cm ² ) was determined. Ta. Specifically, the single transmittance was determined in the same way as in (2) above at a total of five locations, including positions approximately 1.5 cm to 2.0 cm inward from the midpoint of each of the four sides of the measurement sample, and the central portion. It was measured using Next, the difference between the maximum value and the minimum value of the single transmittance measured at each measurement position was calculated, and this value was taken as the variation in the optical properties of the sheet-shaped polarizing film.
(5) Warpage The polarizing plates with retardation layers obtained in Examples and Comparative Examples were cut into a size of 110 mm x 60 mm. At this time, the polarizing film was cut out so that the absorption axis direction was in the long side direction. The cut out polarizing plate with a retardation layer was bonded to a glass plate with a size of 120 mm x 70 mm and a thickness of 0.2 mm via an adhesive to prepare a test sample. The test sample was placed in a heating oven maintained at 85° C. for 24 hours, and the amount of warpage after taking it out was measured. When the test sample was placed on a flat surface with the glass plate facing down, the height of the highest part from the flat surface was defined as the amount of warpage.
(6) Unit weight The polarizing plates with retardation layers obtained in Examples and Comparative Examples are cut out to a predetermined size, and the weight (mg) is divided by the area (cm ² ). The weight per unit area (unit weight) was calculated.
(7) Bending resistance The polarizing plates with retardation layers obtained in Examples and Comparative Examples were cut into a size of 50 mm x 100 mm. At this time, the polarizing film was cut out so that the absorption axis direction was in the short side direction. Using a folding tester with a constant temperature and humidity chamber (manufactured by YUASA, CL09 type-D01), the cut out polarizing plate with a retardation layer was subjected to a bending test under conditions of 20° C. and 50% RH. Specifically, a polarizing plate with a retardation layer is repeatedly bent in a direction parallel to the absorption axis direction with the retardation layer side facing outward to prevent cracks, peeling, or film breakage that would result in poor display. The number of times the bending occurred was measured and evaluated based on the following criteria (bending diameter: 2 mmφ).
<Evaluation criteria>
Less than 10,000 times: Poor 10,000 times or more and less than 30,000 times: Good 30,000 times or more: Excellent

[Example 1]
1. Preparation of Polarizing Film As a thermoplastic resin base material, a long, amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a water absorption rate of 0.75% and a Tg of about 75° C. was used. One side of the resin base material was subjected to corona treatment.
100 weight PVA resin prepared by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., trade name "Gosefaimer Z410") at a ratio of 9:1. 13 parts by weight of potassium iodide was added to 13 parts by weight of potassium iodide and dissolved in water to prepare a PVA aqueous solution (coating liquid).
The PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60° C. to form a PVA-based resin layer with a thickness of 13 μm, thereby producing a laminate.
The obtained laminate was uniaxially stretched free end to 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different circumferential speeds in an oven at 130° C. (in-air auxiliary stretching treatment).
Next, the laminate was immersed for 30 seconds in an insolubilization bath (boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. (insolubilization treatment).
Next, the final polarizing film was added to a dyeing bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 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 48% or more (staining treatment).
Next, it was immersed for 30 seconds in a crosslinking bath (an aqueous boric acid 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) at a liquid temperature of 40°C. (Crosslinking treatment).
Thereafter, while immersing the laminate in a boric acid aqueous solution (boric acid concentration 4.0% by weight) at a liquid temperature of 70°C, the total stretching ratio was 5.5 in the longitudinal direction between rolls having different circumferential speeds. Uniaxial stretching was performed to double the size (underwater stretching treatment).
Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (cleaning treatment).
Thereafter, while drying in an oven maintained at 90°C, it was brought into contact with a SUS heating roll whose surface temperature was maintained at 75°C for about 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment was 5.2%.
In this way, a polarizing film with a thickness of 5 μm was formed on the resin base material.

2. Preparation of polarizing plate An acrylic film (surface refractive index 1.50, 40 μm) as a protective layer and an ultraviolet curable adhesive were applied to the surface of the polarizing film obtained above (the surface opposite to the resin base material). Attached through. Specifically, the curable adhesive was applied to have a total thickness of 1.0 μm, and then bonded together using a roll machine. Thereafter, the adhesive was cured by irradiating UV light from the protective layer side. Next, after slitting both ends, the resin base material was peeled off to obtain a long polarizing plate (width: 1300 mm) having a protective layer/polarizing film configuration. The single transmittance of the polarizing plate (substantially, a polarizing film) was 48.48%, and the degree of polarization was 87.036%. Further, the variation in the optical properties of the long polarizing film was 0.58%, and the variation in the optical properties of the sheet polarizing film was 0.14%.

ポリエチレンテレフタレート（ＰＥＴ）フィルム（厚み３８μｍ）表面を、ラビング布を用いてラビングし、配向処理を施した。配向処理の方向は、偏光板に貼り合わせる際に偏光膜の吸収軸の方向に対して視認側から見て１５°方向となるようにした。この配向処理表面に、上記液晶塗工液をバーコーターにより塗工し、９０℃で２分間加熱乾燥することによって液晶化合物を配向させた。このようにして形成された液晶層に、メタルハライドランプを用いて１ｍＪ/ｃｍ^２の光を照射し、当該液晶層を硬化させることによって、ＰＥＴフィルム上に液晶配向固化層Ａを形成した。液晶配向固化層Ａの厚みは２．５μｍ、面内位相差Ｒｅ（５５０）は２７０ｎｍであった。さらに、液晶配向固化層Ａは、ｎｘ＞ｎｙ＝ｎｚの屈折率分布を有していた。
塗工厚みを変更したこと、および、配向処理方向を偏光膜の吸収軸の方向に対して視認側から見て７５°方向となるようにしたこと以外は上記と同様にして、ＰＥＴフィルム上に液晶配向固化層Ｂを形成した。液晶配向固化層Ｂの厚みは１．５μｍ、面内位相差Ｒｅ（５５０）は１４０ｎｍであった。さらに、液晶配向固化層Ｂは、ｎｘ＞ｎｙ＝ｎｚの屈折率分布を有していた。 3. Preparation of the first alignment fixed layer and the second alignment fixed layer constituting the retardation layer 10 g of polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF, trade name "Paliocolor LC242", represented by the following formula) A liquid crystal composition (coating liquid) was prepared by dissolving 3 g of a photopolymerization initiator for the polymerizable liquid crystal compound (manufactured by BASF, trade name "Irgacure 907") in 40 g of toluene.

The surface of a polyethylene terephthalate (PET) film (thickness: 38 μm) was rubbed using a rubbing cloth to perform orientation treatment. The direction of the alignment treatment was set to be 15° when viewed from the viewing side with respect to the direction of the absorption axis of the polarizing film when bonding to the polarizing plate. The above-mentioned liquid crystal coating solution was applied to this alignment-treated surface using a bar coater, and the liquid crystal compound was aligned by heating and drying at 90° C. for 2 minutes. The thus formed liquid crystal layer was irradiated with light of 1 mJ/cm ² using a metal halide lamp to cure the liquid crystal layer, thereby forming a liquid crystal alignment solidified layer A on the PET film. The thickness of the liquid crystal alignment solidified layer A was 2.5 μm, and the in-plane retardation Re (550) was 270 nm. Furthermore, the liquid crystal alignment solidified layer A had a refractive index distribution of nx>ny=nz.
The coating was applied on the PET film in the same manner as above, except that the coating thickness was changed and the orientation treatment direction was set at 75° when viewed from the viewing side with respect to the direction of the absorption axis of the polarizing film. A liquid crystal alignment solidified layer B was formed. The thickness of the liquid crystal alignment solidified layer B was 1.5 μm, and the in-plane retardation Re (550) was 140 nm. Furthermore, the liquid crystal alignment solidified layer B had a refractive index distribution of nx>ny=nz.

4. Preparation of polarizing plate with retardation layer 2 above. The above 3. is applied to the surface of the polarizing film of the polarizing plate obtained in step 3. The liquid crystal alignment solidified layer A and the liquid crystal alignment solidified layer B obtained in the above were transferred in this order. At this time, the angle between the absorption axis of the polarizing film and the slow axis of alignment fixed layer A is 15°, and the angle between the absorption axis of the polarizing film and the slow axis of alignment fixed layer B is 75°. Transfer (pasting) was performed using In addition, each transfer (pasting) is performed as described in 2. above. This was done using the same ultraviolet curable adhesive (thickness: 1.0 μm). In this way, a polarizing plate with a retardation layer having the structure of protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer (first alignment fixed layer/adhesive layer/second alignment fixed layer) was obtained. Ta. The total thickness of the obtained polarizing plate with a retardation layer was 52 μm. The obtained polarizing plate with a retardation layer was subjected to the evaluations (5) to (7) above. The amount of warpage was 1.8 mm.

[Example 2]
A polarizing plate with a retardation layer was produced in the same manner as in Example 1 except that an acrylic film with a thickness of 20 μm was used as the protective layer. The total thickness of the obtained polarizing plate with a retardation layer was 32 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The amount of warpage was 1.5 mm.

[Example 3]
A polarizing plate with a retardation layer was produced in the same manner as in Example 1 except that a 25 μm thick triacetyl cellulose (TAC) film was used as the protective layer. The total thickness of the obtained polarizing plate with a retardation layer was 37 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The amount of warpage was 1.3 mm.

[Comparative example 1]
1. Preparation of Polarizer A polyvinyl alcohol resin film having an average degree of polymerization of 2,400, a degree of saponification of 99.9 mol %, and a thickness of 30 μm was prepared. The polyvinyl alcohol film was immersed in a 20°C swelling bath (water bath) for 30 seconds between rolls with different circumferential speed ratios and stretched 2.4 times in the transport direction while swelling (swelling step). Dye by immersing in a dyeing bath at 30°C (an aqueous solution with an iodine concentration of 0.03% by weight and a potassium iodide concentration of 0.3% by weight) so that the single transmittance after final stretching becomes the desired value. Meanwhile, the original polyvinyl alcohol film (polyvinyl alcohol film not stretched at all in the transport direction) was stretched 3.7 times in the transport direction (dying step). The immersion time at this time was about 60 seconds. Next, the dyed polyvinyl alcohol film was immersed in a 40°C crosslinking bath (an aqueous solution with a boric acid concentration of 3.0% by weight and a potassium iodide concentration of 3.0% by weight) while the original polyvinyl alcohol film was immersed. The film was stretched to 4.2 times in the transport direction (crosslinking step). Furthermore, the obtained polyvinyl alcohol film was immersed for 50 seconds in a 64°C stretching bath (an aqueous solution with a boric acid concentration of 4.0% by weight and a potassium iodide concentration of 5.0% by weight) to restore the original polyvinyl alcohol film. After stretching the alcohol film up to 6.0 times in the transport direction (stretching step), the film was immersed in a 20°C cleaning bath (an aqueous solution with a potassium iodide concentration of 3.0% by weight) for 5 seconds (cleaning). process). The washed polyvinyl alcohol film was dried at 30° C. for 2 minutes to produce a polarizer (thickness: 12 μm).

2. Preparation of polarizing plate As an adhesive, polyvinyl alcohol resin containing an acetoacetyl group (average degree of polymerization 1,200, degree of saponification 98.5 mol%, degree of acetoacetylation 5 mol%) and methylolmelamine were used. An aqueous solution containing them at a weight ratio of 3:1 was used. Using this adhesive, attach a 25 μm thick triacetyl cellulose (TAC) film with a hard coat layer to one side of the polarizer obtained above, and attach a 25 μm thick TAC film to the other side of the polarizer. After laminating with a roll laminating machine, it was heated and dried in an oven (temperature: 60°C, time: 5 minutes) to form protective layer 1 (thickness 25 μm)/adhesive layer/polarizer/adhesive layer/protective layer 2 ( A polarizing plate having a thickness of 25 μm was produced.

3. Preparation of polarizing plate with retardation layer 2 above. Liquid crystal alignment solidified layer A and liquid crystal alignment solidified layer B were transferred in this order onto the surface of protective layer 2 of the polarizing plate obtained in Example 1 to form protective layer 1/adhesive layer/polarizer/adhesive. A polarizing plate with a retardation layer having a configuration of layer/protective layer 2/adhesive layer/retardation layer (first alignment fixed layer/adhesive layer/second alignment fixed layer) was produced. The total thickness of the obtained polarizing plate with a retardation layer was 68 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The amount of warpage was 4.2 mm.

[Comparative example 2]
Example except that potassium iodide was not added to the PVA aqueous solution (coating solution), the stretching ratio in the aerial auxiliary stretching treatment was 1.8 times, and no heating roll was used in the drying shrinkage treatment. An attempt was made to produce a polarizing film in the same manner as in Example 1, but the PVA-based resin layer was dissolved during the dyeing process and the underwater stretching process, making it impossible to produce a polarizing film. Therefore, a polarizing plate with a retardation layer could not be produced.

[Comparative example 3]
1. Preparation of Polarizing Plate A long polarizing plate (width: 1300 mm) having a protective layer/polarizing film configuration was obtained in the same manner as in Example 1 except that a 25 μm thick TAC film was used as the protective layer.

2. Preparation of retardation film constituting retardation layer 2-1. Polymerization of polyester carbonate resin Polymerization was carried out using a batch polymerization apparatus consisting of two vertical reactors equipped with a stirring blade and a reflux condenser controlled at 100°C. Bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane 29.60 parts by mass (0.046 mol), isosorbide (ISB) 29.21 parts by mass (0.200 mol), spiroglycol (SPG) 42 .28 parts by mass (0.139 mol), 63.77 parts by mass (0.298 mol) of diphenyl carbonate (DPC), and 1.19×10 ⁻² parts by mass (6.78×10 −2 of calcium acetate monohydrate as a catalyst ^{). 5} mol) was prepared. After the inside of the reactor was replaced with nitrogen under reduced pressure, it was heated with a heating medium, and when the internal temperature reached 100°C, stirring was started. 40 minutes after the start of temperature rise, the internal temperature was controlled to reach 220°C, and at the same time, pressure reduction was started to maintain this temperature, and the pressure was reduced to 13.3 kPa in 90 minutes after reaching 220°C. Phenol vapor produced as a by-product during the polymerization reaction was led to a reflux condenser at 100°C, a small amount of monomer component contained in the phenol vapor was returned to the reactor, and uncondensed phenol vapor was led to a condenser at 45°C for recovery. After nitrogen was introduced into the first reactor and the pressure was once restored to atmospheric pressure, the oligomerized reaction liquid in the first reactor was transferred to the second reactor. Next, temperature increase and pressure reduction in the second reactor were started, and the internal temperature was 240° C. and the pressure was 0.2 kPa in 50 minutes. Thereafter, polymerization was allowed to proceed until a predetermined stirring power was reached. When a predetermined power was reached, nitrogen was introduced into the reactor to restore the pressure, the produced polyester carbonate resin was extruded into water, and the strands were cut to obtain pellets.

2-2. Preparation of retardation film After drying the obtained polyester carbonate resin (pellets) in vacuum at 80°C for 5 hours, a single-screw extruder (manufactured by Toshiba Machine Co., Ltd., cylinder temperature setting: 250°C) and a T-die (width 200mm) were used. A long resin film with a thickness of 135 μm was produced using a film forming apparatus equipped with a chill roll (set temperature: 250° C.), a chill roll (set temperature: 120 to 130° C.), and a winder. The obtained elongated resin film was stretched in the width direction at a stretching temperature of 133° C. and a stretching ratio of 2.8 times to obtain a retardation film with a thickness of 53 μm. The obtained retardation film had Re(550) of 141 nm, Re(450)/Re(550) of 0.82, and Nz coefficient of 1.12.

3. Preparation of polarizing plate with retardation layer 1. The above 2. is applied to the surface of the polarizing film of the polarizing plate obtained in 2. The retardation films obtained in the above were bonded together via an acrylic adhesive (thickness: 5 μm). At this time, they were bonded together so that the absorption axis of the polarizing film and the slow axis of the retardation film formed an angle of 45°. In this way, a polarizing plate with a retardation layer having the structure of protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 89 μm. The obtained polarizing plate with a retardation layer was subjected to the evaluations in (6) and (7) above.

Table 2 shows the configurations and evaluation results of the polarizing plates with retardation layers obtained in Examples 1 to 3 and Comparative Examples 1 and 3.

[evaluation]
As is clear from Table 2 and the comparison between Example 1 and Comparative Example 2, the polarizing plate with a retardation layer of the Example of the present invention is thin, has suppressed warping after the heating test, and has excellent optical properties. Excellent. Furthermore, it can be seen that when the weight per unit area of the polarizing plate with a retardation layer is equal to or less than a predetermined value, the bending resistance is improved.

The polarizing plate with a retardation layer 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 plate 11 Polarizing film 12 First protective layer 13 Second protective layer 20 Retardation layer 100 Polarizing plate with retardation layer 101 Polarizing plate with retardation layer 102 Polarizing plate with retardation layer

Claims (10)

A polarizing film that is composed of a polyvinyl alcohol resin film containing a dichroic substance, has a thickness of 8 μm or less, has a single transmittance of 48% or more, and has a polarization degree of 85% or more, and at least one of the polarizing films. A method for producing a polarizing plate with a retardation layer, comprising a polarizing plate including a protective layer on the side thereof, and a retardation layer which is an alignment solidified layer of a liquid crystal compound,
A polyvinyl alcohol resin layer containing iodide or sodium chloride and a polyvinyl alcohol resin is formed on one side of a long thermoplastic resin base material to form a laminate, and the laminate is provided with an aerial support. Stretching treatment, dyeing treatment, underwater stretching treatment, and heating in a heating furnace using heating rolls while conveying in the longitudinal direction so that the total contact time with the heating rolls is 20 seconds or less. Producing the polarizing film by a production method including performing in this order a drying shrinkage treatment to shrink the polarizing film by 2% to 10% ;
obtaining the polarizing plate by disposing the protective layer on at least one side of the polarizing film; disposing the alignment solidified layer of the liquid crystal compound on one side of the polarizing plate;
including;
The liquid crystal compound orientation solidified layer is a layer in which the liquid crystal compound is oriented in a predetermined direction within the layer, and the orientation state is fixed.
A method for manufacturing a polarizing plate with a retardation layer. By performing an alignment treatment on the surface of the base material, applying a coating liquid containing the liquid crystal compound to the surface to align the liquid crystal compound in a direction corresponding to the alignment treatment, and fixing the alignment state, The method for manufacturing a polarizing plate with a retardation layer according to claim 1, further comprising obtaining an alignment solidified layer of the liquid crystal compound. A method of manufacturing a polarizing plate with a retardation layer having a total thickness of 60 μm or less, the method of manufacturing a polarizing plate with a retardation layer according to claim 1 or 2. The retardation layer is a single layer of an alignment solidified layer of a liquid crystal compound,
Re(550) of the retardation layer is 100 nm to 190 nm,
The angle between the slow axis of the retardation layer and the absorption axis of the polarizing film is 40° to 50°.
A method for manufacturing a polarizing plate with a retardation layer according to any one of claims 1 to 3. The retardation layer has a laminated structure of a first alignment solidified layer of a liquid crystal compound and a second alignment solidified layer of a liquid crystal compound,
Re(550) of the alignment solidified layer of the first liquid crystal compound is 200 nm to 300 nm, and the angle between the slow axis and the absorption axis of the polarizing film is 10° to 20°,
Re(550) of the alignment solidified layer of the second liquid crystal compound is 100 nm to 190 nm, and the angle between the slow axis and the absorption axis of the polarizing film is 70° to 80°;
A method for manufacturing a polarizing plate with a retardation layer according to any one of claims 1 to 3. Manufacturing the polarizing plate with a retardation layer according to any one of claims 1 to 5, wherein the difference between the maximum value and the minimum value of the single transmittance within a 50 cm ² area of the polarizing film is 0.5% or less. Method. The phase difference according to any one of claims 1 to 5, wherein the polarizing film has a width of 1000 mm or more, and a difference between a maximum value and a minimum value of single transmittance at a position along the width direction is 1% or less. A method for manufacturing a layered polarizing plate. 8. The method for manufacturing a polarizing plate with a retardation layer according to claim 1, wherein the polarizing film has a single transmittance of 50% or less and a polarization degree of 92% or less. The polarizing plate with a retardation layer further has another retardation layer outside the retardation layer,
Providing the other retardation layer outside the retardation layer,
9. The method for manufacturing a polarizing plate with a retardation layer according to claim 1, wherein the refractive index characteristics of the other retardation layer exhibit a relationship of nz>nx=ny. The polarizing plate with a retardation layer further has a conductive layer or an isotropic base material with a conductive layer on the outside of the retardation layer,
The method for producing a polarizing plate with a retardation layer according to any one of claims 1 to 9, comprising providing the conductive layer or the isotropic base material with the conductive layer on the outside of the retardation layer.

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