JP7321004B2 - Polarizing plate with retardation layer and image display device using the same - Google Patents

Description

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

2. Description of the Related Art In recent years, image display devices typified by liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices) have rapidly spread. Polarizing plates and retardation plates are typically used in image display devices. Practically, a polarizing plate with a retardation layer in which a polarizing plate and a retardation plate are integrated is widely used (for example, Patent Document 1). Along with this trend, there is an increasing demand for thinner polarizing plates with retardation layers. In recent years, as the demand for curved image display devices and/or bendable or foldable image display devices has increased, further thinning and further flexibility are required for polarizing plates and polarizing plates with retardation layers. ing. For the purpose of thinning the retardation layer-attached polarizing plate, thinning of the protective layer of the polarizing film and the retardation film, which greatly contribute to the thickness, is progressing. However, when the thickness of the protective layer and the retardation film is reduced, the influence of the contraction 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-mentioned problems, it is necessary to reduce the thickness of the polarizing film as well. However, if the thickness of the polarizing film is simply reduced, the optical characteristics will deteriorate. More specifically, one or both of the degree of polarization and the single transmittance, which are in a trade-off relationship, are reduced to a practically unacceptable level. As a result, the optical properties of the retardation layer-attached polarizing plate also become insufficient.

Japanese Patent No. 3325560

The present invention has been made to solve the above conventional problems, and a main object thereof is to provide a polarizing plate with a retardation layer which is thin, excellent in handleability, and excellent in optical properties. .

The polarizing plate with a retardation layer of the present invention has 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 44.0% or more, and a polarization degree of 99.50% or more. . The retardation layer is an alignment fixed layer of a liquid crystal compound.
In one embodiment, the retardation layer-attached polarizing plate has a unit weight of 6.5 mg/cm ² or less.
In one embodiment, the retardation layer-attached polarizing plate has a total thickness of 60 μm or less.
In one embodiment, the retardation layer is a single layer of an alignment fixed layer of a liquid crystal compound, 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 formed with the absorption axis of the polarizing film 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 first fixed alignment layer of a liquid crystal compound. is 200 nm to 300 nm, and the angle formed by the slow axis thereof and the absorption axis of the polarizing film is 10° to 20°; ) 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°.
In one embodiment, the difference between the maximum value and the minimum value of single transmittance in a 50 cm ² area of the polarizing film is 0.2% or less.
In one embodiment, the retardation layer-attached polarizing plate has a width of 1000 mm or more, and the difference between the maximum and minimum single transmittance values at positions along the width direction of the polarizing film is 0.3%. It is below.
In one embodiment, the polarizing film has a single transmittance of 44.5% or less and a degree of polarization of 99.95% or less.
In one embodiment, the retardation layer-attached polarizing plate further has another retardation layer outside the retardation layer, and the refractive index characteristic of the another retardation layer is nz>nx=ny. Show relationship.
In one embodiment, the retardation layer-attached polarizing plate further has a conductive layer or a conductive layer-attached isotropic substrate outside the retardation layer.
According to another aspect of the present invention, an image display device is provided. This image display device includes the retardation layer-attached polarizing plate described above.
In one embodiment, the image display device is an organic electroluminescence display device or an inorganic electroluminescence display device.

According to the present invention, addition of a halide (typically potassium iodide) to a polyvinyl alcohol (PVA) resin, two-stage stretching including auxiliary stretching in air and stretching in water, and drying and shrinkage with heated rolls can be used in combination, it is possible to obtain a thin polarizing film having extremely excellent optical properties. By using such a polarizing film, it is possible to realize a polarizing plate with a retardation layer which is thin, excellent in handleability, and excellent in 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. FIG. 4 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to another embodiment of the invention; FIG. 4 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to still another embodiment of the present invention; FIG. 2 is a schematic diagram showing an example of drying shrinkage treatment using a heating roll in the method for producing the polarizing film used in the 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 in-plane direction orthogonal to the slow axis (i.e., fast axis direction) and "nz" is the refractive index in the thickness direction.
(2) In-plane retardation (Re)
“Re(λ)” is an in-plane retardation measured at 23° C. with light having a wavelength of λ nm. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23°C. Re(λ) is obtained by the formula: Re(λ)=(nx−ny)×d, where d (nm) is the thickness of the layer (film).
(3) Thickness direction retardation (Rth)
“Rth(λ)” is the retardation in the thickness direction measured at 23° C. with light having a wavelength of λ nm. For example, “Rth(550)” is the retardation in the thickness direction measured at 23° C. with light having a wavelength of 550 nm. 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 obtained by Nz=Rth/Re.
(5) Angle When referring to an angle in this specification, the angle includes both clockwise and counterclockwise directions with respect to a reference direction. Thus, for example, "45°" means ±45°.

A. Overall Configuration of Retardation Layer-Equipped Polarizing Plate FIG. 1 is a schematic cross-sectional view of a retardation layer-attached polarizing plate according to one embodiment of the present invention. A polarizing plate 100 with a retardation layer of this embodiment has a polarizing plate 10 and a retardation layer 20 . The polarizing plate 10 includes a polarizing film 11, a first protective layer 12 arranged on one side of the polarizing film 11, and a second protective layer 13 arranged 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-based resin film containing a dichroic substance. The polarizing film has a thickness of 8 μm or less, a single transmittance of 44.0% or more, and a polarization degree of 99.50% or more.

As shown in FIG. 2, in a retardation layer-attached polarizing plate 101 according to another embodiment, another retardation layer 50 and/or a conductive layer or an isotropic substrate 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 side opposite 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 60 with a conductive layer are typically provided in this order from the retardation layer 20 side. The separate retardation layer 50 and the conductive layer or the isotropic substrate with a conductive layer 60 are typically optional layers provided as needed, and either or both of them may be omitted. For the sake of 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. In addition, 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 It can be applied to a touch panel type input display device.

In the embodiment of the present invention, the first retardation layer 20 is an alignment fixed layer of a liquid crystal compound. The first retardation layer 20 may be a single layer of orientation fixed layers as shown in FIGS. and may have a laminated structure.

The above-described embodiments may be combined as appropriate, and the constituent elements in the above-described embodiments may be modified as is obvious in the art. For example, the second retardation layer 50 and/or the conductive layer or the isotropic substrate 60 with the conductive layer may be provided on the polarizing plate 102 with the retardation layer of FIG. Further, for example, the configuration in which the isotropic substrate 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 the second retardation layer and the conductive layer). may

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

The retardation layer-attached polarizing plate of the present invention may be sheet-shaped or long-shaped. As used herein, the term "long shape" means an elongated shape whose length is sufficiently long relative to its width, for example, an elongated shape whose length is 10 times or more, preferably 20 times or more, its width. include. The elongated retardation layer-attached polarizing plate can be wound into a roll.

Practically, an adhesive layer (not shown) is provided on the side of the retardation layer opposite to the polarizing plate, so that 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 pressure-sensitive adhesive layer until the polarizing plate with the retardation layer is used. Temporarily attaching the release film protects the pressure-sensitive adhesive layer and enables roll formation.

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

The unit weight of the retardation layer-attached polarizing plate 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 0 mg/cm ² to 5.5 mg/cm ² , more preferably 3.5 mg/cm ² to 5.0 mg/cm ² . When the display panel is thin, the weight of the retardation layer-attached polarizing plate may ^slightly deform the panel, resulting in display failure. The plate can prevent such deformation of the panel. Further, the polarizing plate with a retardation layer having the above unit weight is easy to handle even when it is made thin, and can exhibit extremely excellent flexibility and bending durability.

The constituent elements of the retardation layer-attached polarizing plate will be described in more detail below.

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 44.0% or more, and a degree of polarization of 99.50% or more. In general, there is a trade-off between the single transmittance and the degree of polarization. Increasing the single transmittance may decrease the degree of polarization, and increasing the degree of polarization may decrease the single transmittance. For this reason, conventionally, it has been difficult to practically provide a thin polarizing film that satisfies optical characteristics such as a single transmittance of 44.0% or more and a degree of polarization of 99.50% or more. The use of a thin polarizing film having excellent optical properties such as a single transmittance of 44.0% or more and a degree of polarization of 99.50% or more and suppressed variations in optical properties is the present invention. This is one of the features of the invention.

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

The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance of the polarizing film is preferably 44.5% or less. The polarization degree of the polarizing film is preferably 99.70% or more, more preferably 99.80% or more. On the other hand, the degree of polarization is preferably 99.95% or less. The single transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction. The degree of polarization is typically obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction.
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 with the body as the measurement target. 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 each layer interface may change, resulting in a change in the measured transmittance. . Thus, for example, if a protective film with a refractive index not equal to 1.50 is used, the transmittance measurements may be corrected according to the refractive index of the surface of the protective film in contact with the air interface. Specifically, the transmittance correction value C is expressed by the following 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 a protective film having a refractive index of 1.50 is used, n ₁ is the refractive index of the protective film used, and T ₁ is the transmittance of the polarizing film. is. For example, when a substrate having a surface refractive index of 1.53 (a cycloolefin film, a film with a hard coat layer, etc.) is used as the protective film, the correction amount C is about 0.2%. In this case, by adding 0.2% to the transmittance obtained by the measurement, it is possible to convert the transmittance into the transmittance when using a protective film having a surface refractive index of 1.50. According to the calculation based on the above formula, the amount of change in the correction value C when the transmittance _T1 of the polarizing film is changed by 2% is 0.03% or less, and the transmittance of the polarizing film is equal to the correction value C has a limited effect on the value of Moreover, when the protective film has absorption other than surface reflection, appropriate correction can be performed according to the amount of absorption.

In one embodiment, the retardation layer-attached polarizing plate has a width of 1000 mm or more, and therefore the width of the polarizing film is also 1000 mm or more. In this case, the difference (D1) between the maximum and minimum single transmittance values at positions along the width direction of the polarizing film is preferably 0.3% or less, more preferably 0.29% or less. , more preferably 0.28% or less, and particularly preferably 0.27% or less. D1 is preferably as small as possible, and the lower limit of D1 can be, for example, 0.01%. When 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 preferably has a difference (D2) between the maximum and minimum values of single transmittance in an area of 50 cm ² of 0.2% or less, more preferably 0.15%. or less, more preferably 0.1% or less. D2 is preferably as small as possible, and the lower limit of D2 can be, for example, 0.01%. If D2 is within the above range, it is possible to suppress variations in luminance on a display screen when the polarizing plate with a retardation layer is used in an image display device.

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

A representative method for producing a polarizing film is to form a laminate by forming a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate, Then, the laminate is subjected in this order to an in-air auxiliary stretching process, a dyeing process, an underwater stretching process, and a drying shrinkage process that shrinks the laminate by 2% or more in the width direction by heating while being transported in the longitudinal direction. including. As a result, the polarizing film has a thickness of 8 μm or less, a single transmittance of 44.0% or more, and a degree of polarization of 99.50% or more, and has excellent optical properties and suppressed variations in optical properties. can be provided. That is, by introducing auxiliary stretching, it becomes possible to improve the crystallinity of PVA even when PVA is coated on a thermoplastic resin, and 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 immersed in water in the subsequent dyeing process or stretching process, resulting in high optical properties. can be achieved. Furthermore, when the PVA-based resin layer is immersed in a liquid, disturbance of the orientation of the polyvinyl alcohol molecules and deterioration of the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This can improve the optical properties of the polarizing film obtained through treatment steps such as dyeing treatment and underwater stretching treatment in which the laminate is immersed in a liquid. Furthermore, the optical properties can be improved by shrinking the laminate in the width direction by drying shrinkage treatment.

B-2. Protective Layers First protective layer 12 and second protective layer 13 are each formed of any suitable film that can be used as a protective layer for a polarizing film. Specific examples of materials that are the main component of the film include cellulose resins such as triacetyl cellulose (TAC), polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyethersulfones, and polysulfones. , polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, and acetate-based transparent resins. Thermosetting resins such as (meth)acrylic, urethane, (meth)acrylic urethane, epoxy, and silicone, or ultraviolet curable resins may also be used. In addition, for example, a glassy polymer such as a siloxane-based polymer can also be used. Further, polymer films 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 a side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and nitrile group in a side chain. can be used, for example, a resin composition comprising an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile/styrene copolymer. The polymer film can be, for example, an extrudate of the resin composition.

The retardation layer-attached polarizing plate of the present invention is typically arranged on the viewing side of an image display device, and the first protective layer 12 is typically arranged on the viewing side, as will be described later. Therefore, the first protective layer 12 may be subjected to surface treatment such as hard coat treatment, anti-reflection treatment, anti-sticking treatment, and anti-glare treatment, if necessary. Further/or, the first protective layer 12 may optionally be treated to improve visibility when viewed through polarized sunglasses (typically, imparting (elliptical) polarizing function, imparting an ultra-high retardation) may 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 retardation layer-attached polarizing plate can also 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, still more preferably 10 μm to 30 μm. In addition, when the surface treatment is performed, the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.

Second protective layer 13 is preferably optically isotropic in one embodiment. As used herein, “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, in one embodiment, can be a retardation layer having any suitable retardation value. In this case, the in-plane retardation Re(550) of the retardation layer is, for example, 110 nm to 150 nm. The thickness of the second protective layer is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, still more preferably 10 μm to 30 μm. From the viewpoint of thinning and weight reduction, the second protective layer can be preferably omitted.

B-3. Method for manufacturing polarizing film The polarizing film is formed 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 substrate. is formed to form a laminate, and the laminate is subjected to aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and heating while conveying in the longitudinal direction to shrink by 2% or more in the width direction Drying and shrinkage treatment in this order. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. The shrinkage ratio in the width direction of the laminate due to 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, a laminate containing a PVA-based resin layer containing a halide is produced, the laminate is stretched in multiple stages including auxiliary stretching in the air and stretching in water, and the laminate after stretching is heated with a heating roll. It is possible to obtain a polarizing film having excellent optical properties (typically, single transmittance and degree of polarization) and suppressed variations in optical properties. Specifically, by using a heating roll in the drying shrinkage treatment step, the entire laminate can be uniformly shrunk while being conveyed. As a result, it is possible not only to improve the optical properties of the obtained polarizing film, but also to stably produce a polarizing film with excellent optical properties, and to suppress variations in the optical properties of the polarizing film (in particular, the transmittance of a single unit). can do.

B-3-1. Production of Laminate Any appropriate method can be adopted as a method for producing a laminate of a thermoplastic resin substrate and a PVA-based resin layer. Preferably, a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin substrate and dried to form a PVA-based resin layer on the thermoplastic resin substrate. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

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

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

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

B-3-1-1. Thermoplastic Resin Substrate The thickness of the thermoplastic resin substrate is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If the thickness is less than 20 μm, it may be difficult to form the PVA-based resin layer. If it exceeds 300 μm, for example, in the later-described underwater stretching treatment, it may take a long time for the thermoplastic resin substrate to absorb water, and an excessive load may be required for stretching.

The thermoplastic resin substrate preferably has a water absorption of 0.2% or more, more preferably 0.3% or more. Thermoplastic resin substrates can absorb water and be plasticized with water acting like a plasticizer. As a result, the stretching stress can be greatly reduced, and the film can be stretched at a high draw ratio. On the other hand, the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin substrate, it is possible to prevent problems such as deterioration in the appearance of the obtained polarizing film due to a marked decrease in the dimensional stability of the thermoplastic resin substrate during production. In addition, it is possible to prevent breakage of the base material and separation of the PVA-based resin layer from the thermoplastic resin base material during stretching in water. The water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption is a value determined according to JIS K7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or lower. By using such a thermoplastic resin substrate, it is possible to sufficiently secure the stretchability of the laminate while suppressing the crystallization of the PVA-based resin layer. Furthermore, considering the plasticization of the thermoplastic resin substrate with water and the satisfactory stretching in water, the temperature is preferably 100° C. or lower, more preferably 90° C. or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60°C or higher. By using such a thermoplastic resin substrate, deformation of the thermoplastic resin substrate (for example, generation of unevenness, sagging, wrinkles, etc.) occurs when the coating liquid containing the PVA-based resin is applied and dried. It is possible to prevent the problem of and produce a good laminate. Moreover, the PVA-based resin layer can be satisfactorily stretched at a suitable temperature (for example, about 60°C). The glass transition temperature of the thermoplastic resin substrate can be adjusted, for example, by heating using a crystallization material that introduces a modifying group into the constituent material. The glass transition temperature (Tg) is a value determined according to JIS K7121.

Any appropriate thermoplastic resin can be employed as a 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. is mentioned. Among these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferred.

In one embodiment, an amorphous (not crystallized) polyethylene terephthalate resin is preferably used. Among them, amorphous (difficult to crystallize) polyethylene terephthalate resin is particularly preferably used. Specific examples of amorphous polyethylene terephthalate resins include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers further containing cyclohexanedimethanol or diethylene glycol as glycols.

In a preferred embodiment, the thermoplastic resin base material is composed of a polyethylene terephthalate-based resin having an isophthalic acid unit. This is because such a thermoplastic resin substrate is extremely excellent in stretchability and can suppress crystallization during stretching. This is probably because the introduction of the isophthalic acid unit gives the main chain a large bend. A polyethylene terephthalate-based resin has a terephthalic acid unit and an ethylene glycol unit. The isophthalic acid unit content is preferably 0.1 mol % or more, more preferably 1.0 mol % or more, relative to the total of all repeating units. This is because a thermoplastic resin base material having extremely excellent stretchability can be obtained. On the other hand, the isophthalic acid unit content is preferably 20 mol % or less, more preferably 10 mol % or less, relative to the total of all repeating units. By setting such a content ratio, the degree of crystallinity can be favorably increased in the drying shrinkage treatment described later.

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

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

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

B-3-1-2. Coating Liquid The coating liquid contains a halide and a PVA-based resin as described above. The coating liquid is typically a solution in which the halide and the PVA-based resin are dissolved in a solvent. Examples of solvents 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-based resin in the solution is preferably 3 to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, it is possible to form a uniform coating film in close contact with the thermoplastic resin substrate. The content of the halide in the coating liquid is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

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

Any appropriate resin can be adopted as the PVA-based resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. An ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. . The degree of saponification can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a degree of saponification, a polarizing film with excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1,000 to 10,000, preferably 1,200 to 4,500, more preferably 1,500 to 4,300. The average degree of polymerization can be determined according to JIS K 6726-1994.

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

In general, when the PVA-based resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA-based resin increases. Orientation may be disturbed and the orientation may be lowered. In particular, when a laminate of a thermoplastic resin substrate and a PVA-based resin layer is stretched 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 substrate. When the film is stretched, the tendency of the degree of orientation to decrease is remarkable. For example, the stretching of a single PVA film in boric acid water is generally carried out at 60° C., whereas the stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is It is carried out at a high temperature of about 70° C., and in this case, the orientation of PVA at the initial stage of stretching may be lowered before it is increased by stretching in water. On the other hand, by preparing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate and stretching the laminate at a high temperature (auxiliary stretching) in air before stretching in boric acid water, , the crystallization of the PVA-based resin in the PVA-based 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, the disturbance of the orientation of the polyvinyl alcohol molecules and the deterioration of the orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. This can improve the optical properties of the polarizing film obtained through treatment steps such as dyeing treatment and underwater stretching treatment in which the laminate is immersed in a liquid.

B-3-2. Aerial Auxiliary Stretching In order to obtain particularly high optical properties, a two-stage stretching method combining dry stretching (auxiliary stretching) and stretching in boric acid solution is selected. By introducing auxiliary stretching, such as two-step stretching, it is possible to stretch while suppressing crystallization of the thermoplastic resin substrate, and excessive crystallization of the thermoplastic resin substrate in the subsequent stretching in boric acid water. It is possible to solve the problem that stretchability is reduced by stretching, and stretch the laminate at a higher magnification. Furthermore, when applying the PVA-based resin on the thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, compared to the case of applying the PVA-based resin 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 improve the crystallinity of the PVA-based resin even when the PVA-based resin is coated on the thermoplastic resin, and it is possible to achieve high optical properties. Become. At the same time, by increasing the orientation of the PVA-based resin in advance, it is possible to prevent problems such as deterioration of the orientation and dissolution of the PVA-based resin when it is immersed in water in the subsequent dyeing process or stretching process. , making it possible to achieve high optical properties.

The stretching method of the in-air auxiliary stretching may be fixed edge stretching (e.g., a method of stretching using a tenter stretching machine) or free edge stretching (e.g., a method of uniaxially stretching the laminate through rolls having different peripheral speeds). Although good, free-end stretching may be positively employed to obtain high optical properties. In one embodiment, the in-air stretching process includes a heating roll stretching step in which the laminate is stretched by a peripheral speed difference between heating rolls while being conveyed in the longitudinal direction. The air drawing process typically includes a zone drawing process and a hot roll drawing process. The order of the zone stretching process and the heating roll stretching process is not limited, and the zone stretching process may be carried out first, or the heating roll stretching process may be carried out first. The zone drawing step may be omitted. In one embodiment, the zone drawing step and the heated roll drawing step are performed in this order. In another embodiment, in a tenter stretching machine, the film is stretched by gripping the ends of the film and increasing the distance between the tenters in the machine direction (the extension of the distance between the tenters is the stretching ratio). At this time, the distance between the tenters in the width direction (perpendicular to the machine direction) is set to be arbitrarily close. Preferably, the draw ratio in the machine direction can be set to be closer to the free end draw. In the case of free end stretching, the shrinkage ratio in the width direction is calculated by (1/stretching ratio) ^1/2 .

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

The draw ratio in the in-air auxiliary drawing is preferably 2.0 to 3.5 times. The maximum draw ratio when the auxiliary drawing in the air and the drawing in water are combined is preferably 5.0 times or more, more preferably 5.5 times or more, and still more preferably 6.0 times the original length of the laminate. That's it. As used herein, the term "maximum draw ratio" refers to the draw ratio immediately before the laminate breaks, and is 0.2 lower than the draw ratio at which the laminate breaks.

The stretching temperature for the in-air auxiliary stretching can be set to any appropriate value depending on the material for forming the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably the glass transition temperature (Tg) of the thermoplastic resin substrate or higher, more preferably the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C or higher, and particularly preferably Tg + 15°C or higher. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, it is possible to suppress rapid crystallization of the PVA-based resin and suppress problems caused by the crystallization (for example, hindrance of orientation of the PVA-based resin layer due to stretching). can. The crystallization index of the PVA-based resin after auxiliary stretching in air 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, measurement is 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 = ( _IC / _IR )
however,
I _C : Intensity at 1141 cm ⁻¹ when measured with incident measurement light I _R : Intensity at 1440 cm ⁻¹ when measured with incident measurement light.

B-3-3. Insolubilization Treatment If necessary, an insolubilization treatment is performed after the auxiliary stretching treatment in the air and before the stretching treatment in water or the dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The insolubilization treatment imparts water resistance to the PVA-based resin layer, and prevents deterioration of the orientation of the PVA when immersed in water. The concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight with respect to 100 parts by weight of water. The liquid temperature of the insolubilizing bath (boric acid aqueous solution) is preferably 20°C to 50°C.

B-3-4. Dyeing Treatment The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). Specifically, it is carried out by allowing the PVA-based resin layer to adsorb iodine. Examples of the adsorption method include a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of coating the PVA-based resin layer with the dyeing solution, and a method of applying the dyeing solution to the PVA-based resin layer. A spraying method and the like can be mentioned. A preferred method is to immerse the laminate in a dyeing solution (dyeing bath). This is because iodine can be well adsorbed.

The staining solution is preferably an iodine aqueous solution. The amount of iodine compounded is preferably 0.05 to 0.5 parts by weight per 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add an iodide to the 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 compounded is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, per 100 parts by weight of water. The liquid temperature of the dyeing liquid during dyeing is preferably 20° C. to 50° C. in order to suppress the dissolution of the PVA-based resin. When the PVA-based resin layer is immersed in the staining solution, 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-based resin layer.

The dyeing conditions (concentration, liquid temperature, immersion time) should be set so that the finally obtained polarizing film has a single transmittance of 44.0% or more and a degree of polarization of 99.50% or more. can be done. As for such dyeing conditions, it is preferable to use an iodine aqueous solution as a dyeing solution and to set the content ratio of iodine and potassium iodide in the iodine aqueous solution to 1:5 to 1:20. The content ratio of iodine and potassium iodide in the aqueous iodine solution is preferably 1:5 to 1:10. Thereby, a polarizing film having the optical properties as described above can be obtained.

When dyeing treatment is performed continuously after the treatment of immersing the laminate in a treatment bath containing boric acid (typically, insolubilization treatment), the boric acid contained in the treatment bath is mixed into the dyeing bath. The boric acid concentration in the dyeing bath may change over time, resulting in unstable dyeability. In order to suppress the destabilization of dyeability as described above, the upper limit of the boric acid concentration in the dyeing bath is preferably 4 parts by weight, more preferably 2 parts by weight with respect to 100 parts by weight of water. adjusted. On the other hand, the lower limit of the boric acid concentration in the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and still more preferably 0.5 parts by weight with respect to 100 parts by weight of water. is. In one embodiment, the dyeing process is performed using a dyeing bath pre-blended with boric acid. This can reduce the rate of change in boric acid concentration when the boric acid in the treatment bath is mixed into the dyeing bath. The amount of boric acid blended in advance in the dyeing bath (that is, the content of boric acid not derived from the treatment bath) is preferably 0.1 to 2 parts by weight with respect to 100 parts by weight of water. , more preferably 0.5 to 1.5 parts by weight.

B-3-5. Crosslinking Treatment If necessary, a crosslinking treatment is applied after the dyeing treatment and before the underwater stretching treatment. The cross-linking treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. The cross-linking treatment imparts water resistance to the PVA-based resin layer, and prevents deterioration of the orientation of the PVA when immersed in high-temperature water in the subsequent underwater stretching. The concentration of the boric acid aqueous solution is preferably 1 to 5 parts by weight with respect to 100 parts by weight of water. Moreover, when cross-linking treatment is carried out after the dyeing treatment, it is preferable to further add an iodide. By blending iodide, elution of iodine adsorbed on the PVA-based resin layer can be suppressed. The amount of iodide compounded is preferably 1 to 5 parts by weight per 100 parts by weight of water. Specific examples of iodides are as described above. The liquid temperature of the cross-linking bath (boric acid aqueous solution) is preferably 20°C to 50°C.

B-3-6. Underwater Stretching Treatment Underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the thermoplastic resin substrate and the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80° C.), and the PVA-based resin layer undergoes its crystallization. can be stretched at a high magnification while suppressing the As a result, a polarizing film having excellent optical properties can be produced.

Any appropriate method can be adopted as a method for stretching the laminate. Specifically, fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching a laminate by passing it between rolls having different peripheral speeds) may be used. Free-end drawing is preferably chosen. The laminate may be stretched in one step or in multiple steps. When the stretching is performed in multiple stages, the draw ratio (maximum draw ratio) of the laminate described below is the product of the draw ratios in each step.

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

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

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

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such a temperature, the film can be stretched at 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 substrate is preferably 60° C. or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40° C., it may not be possible to stretch well even if the plasticization of the thermoplastic resin base material by water is considered. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, which may make it impossible to obtain excellent optical properties. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

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

B-3-7. Drying Shrinkage Treatment The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or by heating the transport roll (using a so-called heating roll) (heated roll drying method). Preferably both are used. By drying using a heating roll, it is possible to efficiently suppress heat curling of the laminate and produce a polarizing film having an excellent appearance. Specifically, the crystallization of the thermoplastic resin substrate can be efficiently promoted and the crystallinity can be increased by drying the laminate while it is placed along the heating roll. Even at the drying temperature, the degree of crystallinity of the thermoplastic resin substrate can be favorably increased. As a result, the thermoplastic resin base material has increased rigidity and is in a state capable of withstanding shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. Moreover, by using a heating roll, the layered product can be dried while being maintained in a flat state, so that not only curling but also wrinkling can be suppressed. At this time, the laminate can be shrunk in the width direction by drying shrinkage treatment, thereby improving the optical properties. This is because the orientation of PVA and PVA/iodine complex can be effectively enhanced. The shrinkage ratio of the laminate in the width direction due to drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roll, the laminate can be continuously shrunk in the width direction while being transported, 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, the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate. The transport rolls R1 to R6 may be arranged so as to continuously heat only the surface of the resin base material.

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

The heating roll may be provided in a heating furnace (for example, oven), or may be provided in a normal production line (under room temperature environment). Preferably, it is provided in a heating furnace equipped with air blowing means. By using both heating roll drying and hot air drying, abrupt temperature changes between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature for hot air drying is preferably 30°C to 100°C. Moreover, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10m/s to 30m/s. The wind speed is the wind speed in 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 cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide.

C. First Retardation Layer As described above, the first retardation layer 20 is an alignment and solidification layer of a liquid crystal compound. By using a liquid crystal compound, the difference between nx and ny in the resulting retardation layer can be significantly increased compared to a non-liquid crystal material. can be significantly reduced. As a result, it is possible to further reduce the thickness and weight of the retardation layer-attached polarizing plate. As used herein, the term "fixed alignment layer" refers to a layer in which a liquid crystal compound is aligned in a predetermined direction and the alignment state is fixed. In addition, the "alignment fixed layer" is a concept including an alignment cured layer obtained by curing a liquid crystal monomer as described later. In the present embodiment, typically, rod-shaped liquid crystal compounds are aligned in the slow axis direction of the first retardation layer (homogeneous alignment).

Examples of liquid crystal compounds include liquid crystal compounds 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. Either lyotropic or thermotropic mechanism may be used to develop the liquid crystallinity of the liquid crystal compound. The liquid crystal polymer and 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 cross-linking (that is, curing) the liquid crystal monomer. After aligning the liquid crystal monomers, for example, the alignment state can be fixed by polymerizing or cross-linking the liquid crystal monomers. Here, a polymer is formed by polymerization and a three-dimensional network structure is formed by cross-linking, 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 change in temperature, which is peculiar to liquid crystalline compounds. As a result, the first retardation layer becomes a highly stable retardation layer that is not affected by temperature changes.

The temperature range in which the liquid crystal monomer exhibits liquid crystallinity varies depending on the 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 appropriate liquid crystal monomer can be employed as the liquid crystal monomer. For example, polymerizable mesopolymers described in JP-T-2002-533742 (WO00/37585), EP358208 (US5211877), EP66137 (US4388453), WO93/22397, EP0261712, DE19504224, DE4408171, and GB2280445 Gen compounds and the like can be used. Specific examples of such polymerizable mesogenic compounds include LC242 (trade name) available from BASF, E7 (trade name) available from Merck, and LC-Sillicon-CC3767 (trade name) available from Wacker-Chem. As the liquid crystal monomer, for example, a nematic liquid crystal monomer is preferable.

The alignment fixed layer of the liquid crystal compound is obtained by subjecting the surface of a predetermined substrate to alignment treatment, coating the surface with a coating liquid containing a liquid crystal compound, and orienting the liquid crystal compound in the 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 fixed layer formed on the base material can be transferred to the surface of the polarizing plate 10 . In another embodiment, the substrate can be the second protective layer 13 . In this case, the transfer step is omitted, and lamination can be performed by roll-to-roll continuously from the formation of the alignment fixed layer (first retardation layer), thereby further improving productivity.

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

Alignment of the liquid crystal compound is performed by treatment at a temperature at which a liquid crystal phase is exhibited depending on the type of liquid crystal compound. By performing such a temperature treatment, the liquid crystal compound assumes a liquid crystal state, and the liquid crystal compound is aligned in accordance with the orientation treatment direction of the base material surface.

In one embodiment, the alignment state is fixed by cooling the liquid crystal compound aligned as described above. When the liquid crystal compound is a polymerizable monomer or a crosslinkable monomer, the orientation 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 fixed layer are described in JP-A-2006-163343. The description of the publication is incorporated herein by reference.

Another example of the alignment fixed layer includes a form in which a discotic liquid crystal compound is aligned in any one of vertical alignment, hybrid alignment and tilt alignment. In the discotic liquid crystal compound, typically, the discotic plane of the discotic liquid crystal compound is oriented substantially perpendicular to the film plane of the first retardation layer. When the discotic liquid crystal compound is substantially perpendicular, the average 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 mother nucleus such as benzene, 1,3,5-triazine, or calixarene at the center of the molecule, and a linear alkyl group, alkoxy group, or substituted benzoyl A liquid crystal compound having a discotic molecular structure in which oxy groups and the like are radially substituted as side chains. Representative examples of discotic liquid crystals include C.I. Destrade et al., Mol. Cryst. Liq. Cryst. 71, 111 (1981), benzene derivatives, triphenylene derivatives, truxene derivatives and phthalocyanine derivatives; Kohne et al., Angew. Chem. 96, 70 (1984) and cyclohexane derivatives described in J. Am. M. In the report of Lehn et al., J. Am. Chem. Soc. Chem. Commun. , 1794 (1985); In the report of Zhang et al., J. Am. Am. Chem. Soc. 116, 2655 (1994), azacrown-based and phenylacetylene-based macrocycles. Further specific examples of discotic liquid crystal compounds include compounds described in JP-A-2006-133652, JP-A-2007-108732, and JP-A-2010-244038. The descriptions in the above documents and publications are incorporated herein by reference.

In one embodiment, the first retardation layer 20 is a single layer of an alignment fixed layer of a liquid crystal compound as shown in FIGS. When the first retardation layer 20 is composed of a single layer of a fixed alignment 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 realize 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 when the first retardation layer is a single layer of the alignment fixed layer, it functions as a λ / 4 plate. can. 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, still more preferably 130 nm to 160 nm. Here, "ny=nz" includes not only the case where ny and nz are completely equal but also the case where they are substantially equal. Therefore, ny>nz or ny<nz may be satisfied within a range that does not impair the effects of the present invention.

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, a very excellent reflection hue can be achieved.

The first retardation layer may exhibit a reverse wavelength dispersion characteristic in which the retardation value increases according to the wavelength of the measurement light, or has a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light. It may also show a flat wavelength dispersion characteristic in which the phase difference value hardly changes even with the wavelength of the measurement light. In one embodiment, the first retardation layer exhibits reverse 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, very 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 45°. If the angle θ is in such a 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.

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, one of the first fixed orientation layer 21 and the second fixed orientation layer 22 can function as a λ/4 plate, and the other can 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 the desired in-plane retardation of the λ/4 plate or the λ/2 plate. For example, when the first fixed orientation layer 21 functions as a λ/2 plate and the second fixed orientation layer 22 functions as a λ/4 plate, the thickness of the first fixed orientation layer 21 is, for example, 2.0 μm to 2.0 μm. 3.0 μm, and 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, still more preferably 250 nm to 280 nm. The in-plane retardation Re(550) of the second textured fixed layer is as described above for the single-layer textured fixed layer. The angle formed by 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°, still more preferably about 15°. be. The angle formed by 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°, still 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, very excellent antireflection characteristics can be realized. The liquid crystal compounds constituting the first alignment fixed layer and the second alignment fixed layer, the method for forming the first alignment fixed layer and the second alignment fixed layer, the optical characteristics, etc. are described above for the single-layer alignment fixed layer. As explained in

D. Second Retardation Layer As described above, the second retardation layer can be a so-called positive C plate whose refractive index characteristics exhibit a relationship of nz>nx=ny. By using a positive C plate as the second retardation layer, it is possible to satisfactorily prevent reflection in oblique directions and widen the viewing angle of the antireflection function. In this case, the thickness direction retardation Rth (550) 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 can be less than 10 nm.

The second retardation layer having a refractive index characteristic of nz>nx=ny can be made of any suitable material. The second retardation layer preferably consists of a film containing a liquid crystal material fixed in homeotropic alignment. A 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-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, still more preferably 0.5 μm to 5 μm.

E. Conductive layer or isotropic substrate with conductive layer It may 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 the polarizing plate with the retardation layer. It may be laminated on the first retardation layer (or, if present, on the second retardation layer) as a laminate with a substrate (a substrate with a conductive layer). Preferably, the substrate is optically isotropic, and therefore the conductive layer can be used as an isotropic substrate with a conductive layer in a polarizing plate with a retardation layer.

Any suitable isotropic substrate can be employed as the optically isotropic substrate (isotropic substrate). Materials constituting the isotropic base material include, for example, norbornene-based resins, olefin-based resins, and other resins that do not have a conjugated system as the main skeleton, and acrylic resins that have cyclic structures such as lactone rings and glutarimide rings. Examples include materials that are present in the main chain. By using such a material, it is possible to suppress the development of retardation due to the orientation of molecular chains when forming an isotropic base material. The thickness of the isotropic substrate 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 substrate with a conductive layer may be patterned as required. The patterning may form conductive portions and insulating portions. As a result, electrodes can be formed. The electrodes may function as touch sensor electrodes that sense contact with the touch panel. Any appropriate method can be adopted as a patterning method. Specific examples of the patterning method include wet etching and screen printing.

F. Image Display Device The polarizing plate with a retardation layer according to 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 retardation layer-attached polarizing plate. 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). An image display device according to an embodiment of the present invention includes the retardation layer-attached polarizing plate according to the above items A to E on the viewing side thereof. The retardation layer-attached polarizing plate is laminated so that the retardation layer is on the image display cell (eg, liquid crystal cell, organic EL cell, inorganic EL cell) side (so that the polarizing film is 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 bendable. 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 The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows. "Parts" and "%" in Examples and Comparative Examples are by weight unless otherwise specified.
(1) Thickness The thickness of 10 μm or less was measured using an interferometric film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name “MCPD-3000”). A thickness exceeding 10 μm was measured using a digital micrometer (manufactured by Anritsu Co., Ltd., product name “KC-351C”).
(2) Individual Transmittance and Degree of Polarization The polarizing film/protective layer laminates (polarizing plates) used in Examples and Comparative Examples were 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 with a 2-degree field of view (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.
From the obtained Tp and Tc, the degree of polarization P was determined by the following formula.
Degree of polarization P (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100
As for the spectrophotometer, LPF-200 manufactured by Otsuka Electronics Co., Ltd. can be used for equivalent measurement. As an example, Table 1 shows the measured values of the single transmittance Ts and the degree of polarization P obtained by measurement using V-7100 and LPF-200 for Samples 1 to 3 of polarizing plates having the same configuration as in the following examples. show. As shown in Table 1, the difference between the measured value of the single transmittance of V-7100 and the measured value of the single transmittance of LPF-200 is 0.1% or less, and any spectrophotometer was used. It can be seen that equivalent measurement results can be obtained even in the case.

In addition, for example, when measuring a polarizing plate provided with an anti-glare (AG) surface treatment or an adhesive having diffusion performance, different measurement results may be obtained depending on the spectrophotometer, but in this case, the same By performing numerical conversion based on the measured values obtained when the polarizing plate is measured by each spectrophotometer, it is possible to compensate for the difference in the measured values depending on the spectrophotometer.
(3) Variation in optical properties of long polarizing film From the polarizing plates used in Examples and Comparative Examples, measurement samples were cut out at five positions at equal intervals along the width direction, and five measurements were performed. 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 and minimum single transmittance values measured at each measurement position was calculated, and this value was used as the variation in the optical properties of the elongated polarizing film.
(4) Variation in optical properties of sheet-shaped polarizing film A measurement sample of 100 mm × 100 mm was cut out from the polarizing plate used in Examples and Comparative Examples, and the variation in optical properties of the sheet-shaped polarizing plate (50 cm ² ) was obtained. rice field. Specifically, the single transmittance at a total of 5 points in the vicinity of about 1.5 cm to 2.0 cm inside from the midpoint of each of the four sides of the measurement sample and the central portion is set in the same manner as in (2) above. measured by 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 used as the variation in the optical properties of the sheet-like polarizing film.
(5) Warp The retardation layer-attached polarizing plates obtained in Examples and Comparative Examples were cut into 110 mm×60 mm sizes. At this time, the polarizing film was cut so that the absorption axis direction of the polarizing film was the long side direction. The cut polarizing plate with a retardation layer was attached to a glass plate having a size of 120 mm×70 mm and a thickness of 0.2 mm via an adhesive to obtain 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 portion from the flat surface was taken as the amount of warpage.
(6) Unit weight The retardation layer-attached polarizing plate obtained in Examples and Comparative Examples was cut into a predetermined size, and the weight (mg) was divided by the area (cm ² ) to obtain the retardation layer-attached polarizing plate. The weight per unit area (unit weight) was calculated.
(7) Bending Resistance Each polarizing plate with a retardation layer obtained in Examples and Comparative Examples was cut into a size of 50 mm×100 mm. At this time, the cut was made so that the absorption axis direction of the polarizing film was aligned with the short side direction. Using a folding endurance tester with a constant temperature and humidity chamber (manufactured by YUASA, CL09 type-D01), the cut polarizing plate with a retardation layer was subjected to a bending test under conditions of 20° C. and 50% RH. Specifically, the retardation layer-attached polarizing plate is repeatedly bent in a direction parallel to the absorption axis direction so that the retardation layer side faces outward, and cracks, peeling, and film breakage that cause poor display are observed. The number of times of bending until occurrence was measured and evaluated according to 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 substrate, a long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a water absorption of 0.75% and a Tg of about 75° C. was used. Corona treatment was applied to one side of the resin substrate.
Polyvinyl alcohol (degree of polymerization: 4,200, degree of saponification: 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOSEFIMER Z410") mixed at 9:1: 100 weight of PVA-based resin A PVA aqueous solution (coating solution) was prepared by adding 13 parts by weight of potassium iodide.
The above 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 having a thickness of 13 μm, thereby producing a laminate.
The obtained laminate was uniaxially stretched 2.4 times at the free end in the machine direction (longitudinal direction) between rolls with different peripheral speeds in an oven at 130° C. (in-air auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment).
Next, the finally obtained polarizing film is placed in a dyeing bath (iodine aqueous solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ° C. It was immersed for 60 seconds while adjusting the concentration so that the single transmittance (Ts) was 44.0% or more (dyeing treatment).
Next, it was immersed for 30 seconds in a cross-linking bath at a liquid temperature of 40°C (an aqueous solution of boric acid 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). (crosslinking treatment).
Thereafter, the laminate is immersed in an aqueous boric acid solution (boric acid concentration: 4.0% by weight) at a liquid temperature of 70° C., and stretched between rolls with different circumferential speeds in the longitudinal direction (longitudinal direction) at a total draw ratio of 5.5. It was uniaxially stretched so as to double (stretching in water).
After that, the laminate was immersed in a washing bath (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. (washing treatment).
After that, while drying in an oven kept at 90° C., it was brought into contact with a heating roll made of SUS whose surface temperature was kept at 75° C. for about 2 seconds (drying shrinkage treatment). The shrinkage ratio in the width direction of the laminate due to the drying shrinkage treatment was 5.2%.
Thus, a polarizing film having a thickness of 5 μm was formed on the resin substrate.

2. Preparation of polarizing plate On the surface of the polarizing film obtained above (the surface opposite to the resin base material), an acrylic film (surface refractive index: 1.50, 40 μm) as a protective layer, and an ultraviolet curable adhesive is applied. pasted together through Specifically, the curable adhesive was applied so as to have a total thickness of 1.0 μm, and was bonded using a roll machine. After that, UV rays were applied from the protective layer side to cure the adhesive. Next, after slitting both ends, the resin substrate was peeled off to obtain a long polarizing plate (width: 1300 mm) having a structure of protective layer/polarizing film. The single transmittance of the polarizing plate (substantially, the polarizing film) was 44.12%, and the degree of polarization was 99.929%. Furthermore, the variation in the optical properties of the elongated polarizing film was 0.27%, and the variation in the optical properties of the sheet-like polarizing film was 0.10%.

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. Production of the first alignment fixed layer and the second alignment fixed layer constituting the retardation layer Polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF: trade name “Paliocolor LC242”, represented by the following formula) 10 g , and 3 g of a photopolymerization initiator for the polymerizable liquid crystal compound (manufactured by BASF, trade name “Irgacure 907”) were dissolved in 40 g of toluene to prepare a liquid crystal composition (coating liquid).

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

4. Production of polarizing plate with retardation layer 2. On the polarizing film surface of the polarizing plate obtained in 3. above. The liquid crystal alignment fixed layer A and the liquid crystal alignment fixed layer B obtained in 1. were transferred in this order. At this time, the angle between the absorption axis of the polarizing film and the slow axis of the oriented fixed layer A was 15°, and the angle between the absorption axis of the polarizing film and the slow axis of the oriented fixed layer B was 75°. Then, transfer (bonding) was performed. It should be noted that each transfer (bonding) is the same as in 2. above. It was performed through the ultraviolet curable adhesive (thickness 1.0 μm) used in . Thus, a polarizing plate with a retardation layer having a structure of protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer (first fixed alignment layer/adhesive layer/second fixed alignment layer) is obtained. rice field. 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 above evaluations (5) to (7). 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 having 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. A polyvinyl alcohol film is immersed in a swelling bath (water bath) at 20° C. for 30 seconds between rolls having different peripheral speed ratios, and stretched by 2.4 times in the conveying direction while swelling (swelling step). Dyeing by immersion in a dyeing bath (an aqueous solution with an iodine concentration of 0.03% by weight and a potassium iodide concentration of 0.3% by weight) at 30° C. so that the single transmittance after the final drawing becomes a desired value While doing so, the film was stretched 3.7 times in the transport direction based on the original polyvinyl alcohol film (a polyvinyl alcohol film not stretched in the transport direction at all) (dyeing step). The immersion time at this time was about 60 seconds. Next, the dyed polyvinyl alcohol film is immersed in a 40° C. cross-linking 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 is removed. It was stretched up to 4.2 times in the transport direction on the basis of the standard (crosslinking step). Further, the obtained polyvinyl alcohol film was immersed 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) for 50 seconds to stretch the original polyvinyl alcohol film. After stretching up to 6.0 times in the transport direction (stretching step) based on the alcohol film, it was immersed for 5 seconds in a washing bath (aqueous solution having a potassium iodide concentration of 3.0% by weight) at 20 ° C. (washing process). The washed polyvinyl alcohol film was dried at 30° C. for 2 minutes to prepare a polarizer (thickness: 12 μm).

2. Preparation of polarizing plate As an adhesive, a polyvinyl alcohol resin containing an acetoacetyl group (average degree of polymerization: 1,200, saponification degree: 98.5 mol%, acetoacetylation degree: 5 mol%) and methylolmelamine were used. An aqueous solution containing 3:1 weight ratio was used. Using this adhesive, a triacetyl cellulose (TAC) film with a hard coat layer having a thickness of 25 μm was attached to one surface of the polarizer obtained above, and a TAC film having a thickness of 25 μm was attached to the other surface of the polarizer. After bonding with a roll bonding machine, heat drying is performed in an oven (temperature is 60 ° C., time is 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. Production of polarizing plate with retardation layer 2. In the same manner as in Example 1, the liquid crystal alignment fixed layer A and the liquid crystal alignment fixed layer B were transferred in this order to the surface of the protective layer 2 of the polarizing plate obtained in 2. Protective layer 1 / adhesive layer / polarizer / adhesive A polarizing plate with a retardation layer having a structure of layer/protective layer 2/adhesive layer/retardation layer (first fixed alignment layer/adhesive layer/second fixed alignment 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 air auxiliary stretching treatment was set to 1.8 times, and the heating roll was not used in the drying shrinkage treatment. A polarizing film and a polarizing plate were produced in the same manner as in 1. The single transmittance of the polarizing plate (substantially, the polarizing film) was 43.23%, and the degree of polarization was 99.886%. A polarizing plate with a retardation layer was produced in the same manner as in Example 1 except that this polarizing plate was used.

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

2. Preparation of Retardation Film Constituting Retardation Layer 2-1. Polymerization of polyester carbonate-based 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 weight of calcium acetate monohydrate as a catalyst (6.78 × 10 ^{- 5} mol) was charged. After the interior of the reactor was replaced with nitrogen under reduced pressure, heating was performed with a heating medium, and stirring was started when the internal temperature reached 100°C. After 40 minutes from the start of heating, the internal temperature was allowed to reach 220°C, and the pressure was reduced at the same time as controlling to maintain this temperature. Phenol vapor produced as a by-product of the polymerization reaction was led to a reflux condenser at 100°C, a small amount of monomer components contained in the phenol vapor was returned to the reactor, and uncondensed phenol vapor was led to a condenser at 45°C and recovered. 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, the temperature rise and pressure reduction in the second reactor were started, and the internal temperature was brought to 240° C. and the pressure to 0.2 kPa in 50 minutes. After that, polymerization was allowed to proceed until a predetermined stirring power was obtained. When a predetermined power was reached, nitrogen was introduced into the reactor to restore the pressure, the polyester carbonate-based resin produced was extruded into water, and strands were cut to obtain pellets.

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

3. Production of polarizing plate with retardation layer 1 above. 2. on the surface of the polarizing film of the polarizing plate obtained in 2. above. The retardation film obtained in 1. was pasted together via an acrylic pressure-sensitive adhesive (thickness: 5 μm). At this time, the absorption axis of the polarizing film and the slow axis of the retardation film were attached so as to form an angle of 45°. Thus, a polarizing plate with a retardation layer having a 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 above evaluations (6) and (7).

Table 2 shows the structures and evaluation results of the retardation layer-attached polarizing plates obtained in Examples 1 to 3 and Comparative Examples 1 and 3.

[evaluation]
As is clear from Table 2 and a comparison between Example 1 and Comparative Example 2, the polarizing plate with a retardation layer of the example of the present invention is thin, suppresses warping after the heating test, and has excellent optical properties. Excellent. In addition, it can be seen that when the weight per unit area of the retardation layer-attached polarizing plate 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.

REFERENCE SIGNS LIST 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 (9)

A polarizing film composed of a polyvinyl alcohol resin film containing a dichroic substance, having a thickness of 8 μm or less, a single transmittance of 44.0% or more, and a polarization degree of 99.50% or more, and the polarizing film A method for producing a polarizing plate with a retardation layer, which has a polarizing plate including a protective layer on at least one side of the film and a retardation layer that is an alignment fixed layer of a liquid crystal compound,
Forming a polyvinyl alcohol-based resin layer containing iodide or sodium chloride and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate to form a laminate, and A stretching treatment, a dyeing treatment, and an underwater stretching treatment are carried out in the width direction by heating using a heating roll in a heating furnace while conveying in the longitudinal direction so that the total contact time with the heating roll is 20 seconds or less. drying shrinkage treatment to shrink 2% to 10% to 2% to 10% ;
The stretching ratio in the air auxiliary stretching is 2.0 times to 3.5 times.
A method for producing a polarizing plate with a retardation layer. 2. A method for producing a retardation layer-attached polarizing plate according to claim 1, wherein the total thickness is 60 [mu]m or less. The retardation layer is a single layer of an alignment fixed layer of a liquid crystal compound,
Re (550) of the retardation layer is 100 nm to 190 nm,
The angle formed by the slow axis of the retardation layer and the absorption axis of the polarizing film is 40° to 50°.
3. The method for producing the retardation layer-attached polarizing plate according to claim 1 or 2. The retardation layer has a laminated structure of a first liquid crystal compound alignment fixed layer and a second liquid crystal compound alignment fixed layer,
Re (550) of the alignment fixed layer of the first liquid crystal compound is 200 nm to 300 nm, the angle formed by the slow axis and the absorption axis of the polarizing film is 10 ° to 20 °,
Re (550) of the alignment fixed layer of the second liquid crystal compound is 100 nm to 190 nm, and the angle formed by the slow axis and the absorption axis of the polarizing film is 70° to 80°.
3. The method for producing the retardation layer-attached polarizing plate according to claim 1 or 2. 5. The production of the retardation layer-attached polarizing plate according to claim 1, wherein the difference between the maximum value and the minimum value of single transmittance in a region of 50 cm ² of the polarizing film is 0.2% or less. Method. 5. The polarizing film according to any one of claims 1 to 4, 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 positions along the width direction is 0.3% or less. A method for producing a polarizing plate with a retardation layer. 7. The method for producing a polarizing plate with a retardation layer according to claim 1, wherein the polarizing film has a single transmittance of 44.5% or less and a degree of polarization of 99.95% or less. The retardation layer-attached polarizing plate is a retardation layer-attached polarizing plate further having another retardation layer outside the retardation layer,
Providing the separate retardation layer outside the retardation layer,
8. The method for producing a polarizing plate with a retardation layer according to claim 1, wherein the refractive index characteristic of said another retardation layer exhibits a relationship of nz>nx=ny. The retardation layer-attached polarizing plate further has a conductive layer or a conductive layer-attached isotropic substrate outside the retardation layer,
9. The method for producing a polarizing plate with a retardation layer according to claim 1, comprising providing the conductive layer or the isotropic substrate with the conductive layer outside the retardation layer.

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