KR102521527B1 - Polarizing plate with retardation layer and image display using the same - Google Patents

Abstract

A polarizing plate with a retardation layer having a thin shape, excellent handleability, and excellent optical properties is provided.
The polarizing plate with a retardation layer of the present invention has a polarizing film and a polarizing plate including 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-based resin film containing a dichroic material, and has a thickness of 8 μm or less, and the ratio of the orthogonal absorbance A550 at a wavelength of 550 nm to the orthogonal absorbance A210 at a wavelength of 210 nm (A ₅₅₀ /A ₂₁₀ ) is 1.4 to 3.5. The retardation layer is an alignment hardening layer of a liquid crystal compound.

Description

Polarizing plate with retardation layer and image display device using the same

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

BACKGROUND OF THE INVENTION 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) are rapidly spreading. A polarizing plate and a retardation plate are typically used in the image display device. 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), and as the demand for thinning of image display devices has increased recently, the polarizing plate with a retardation layer has also been reduced in thickness. demand is getting stronger. Further, in recent years, a demand for a curved image display device and/or a bendable or bendable image display device has been increasing, and further thinning and further flexibility are required for polarizing plates and polarizing plates with retardation layers. For the purpose of thinning the polarizing plate with the retardation layer, thinning of the protective layer and retardation film of the polarizing film having a large contribution to the thickness is progressing. However, if the protective layer and the retardation film are made thinner, the effect of shrinkage of the polarizing film becomes relatively large, causing problems such as warping of the image display device and deterioration of operability of the polarizing plate with the retardation layer.

In order to solve the above problems, it is necessary to thin the polarizing film together. However, if the thickness of the polarizing film is merely thinned, the optical properties will deteriorate. More specifically, one or both of the polarization degree and single transmittance, which are in a trade-off relationship, decrease to a practically unacceptable level. As a result, the optical properties of the polarizing plate with the retardation layer also become insufficient.

Japanese Patent Publication No. 3325560

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

A polarizing plate with a retardation layer of the present invention has a polarizing film and a polarizing plate including 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-based resin film containing a dichroic material, has a thickness of 8 μm or less, and has a ratio between the orthogonal absorbance A550 at a wavelength of 550 nm and the orthogonal absorbance A210 at a wavelength of 210 nm (A ₅₅₀ /A ₂₁₀ ) is 1.4 to 3.5. The retardation layer is an alignment hardening layer of a liquid crystal compound.

In one embodiment, the basis weight of the said polarizing plate with a retardation layer is 6.5 mg/cm<2> or less.

In one embodiment, the polarizing plate with a retardation layer has a total thickness of 60 μm or less.

In one embodiment, the retardation layer is a single layer of an orientation fixing 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 polarizing film The angle formed by the absorption axis is 40° to 50°.

In one embodiment, the retardation layer has a laminated structure of an alignment-fixed layer of a first liquid crystal compound and an alignment-fixed layer of a second liquid crystal compound; Re (550) of the alignment-fixed layer of the first liquid crystal compound is 200 nm to 300 nm, and the angle between its 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 between its slow axis and the absorption axis of the polarizing film is 70° to 80°.

In one embodiment, the ratio (A ₄₇₀ /A ₆₀₀ ) of the orthogonal absorbance A ₄₇₀ at a wavelength of 470 nm and the orthogonal absorbance A ₆₀₀ at a wavelength of 600 nm of the polarizing film is 0.7 to 2.00.

In one embodiment, the orthogonal b value of the polarizing film is greater than -10 and less than +10.

In one embodiment, the single transmittance of the polarizing film is 42.5% or more.

In one embodiment, the polarizing plate with a retardation layer further has another retardation layer on the outside of the retardation layer, and the refractive index characteristic of the other retardation layer shows a relationship of nz > nx = ny.

In one embodiment, the said polarizing plate with a retardation layer further has a conductive layer or an isotropic base material with a conductive layer on the outside of the said retardation layer.

The present invention also relates to a polarizing plate comprising a polarizing film and a protective layer on at least one side of the polarizing film, and a polarizing plate with a retardation layer having a retardation layer, wherein the retardation layer is an alignment solidified layer of a liquid crystal compound, and the polarizing film contains iodine. The ratio (A 550 /A ₂₁₀ ) of the orthogonal absorbance A ₅₅₀ at a wavelength of 550 nm and the orthogonal absorbance A ₂₁₀ at a wavelength of 210 _nm of the polarizing film is composed of a polyvinyl alcohol-based resin film containing 1.4 to 3.5, the ratio (A ₄₇₀ /A ₆₀₀ ) between the orthogonal absorbance A ₄₇₀ at a wavelength of 470 nm and the orthogonal absorbance A ₆₀₀ at a wavelength of 600 nm of the polarizing film is 0.7 to 2.00, and the orthogonal b value of the polarizing film is -10 A polarizing plate with a retardation layer larger than +10 or less is provided.

According to another aspect of the present invention, an image display device is provided. This image display device is equipped with the said polarizing plate with a retardation layer.

In one embodiment, the image display device is an organic electroluminescent display device or an inorganic electroluminescent display device.

According to the present invention, a combination of two-step stretching including addition of a halide (typically, potassium iodide), air-assisted stretching and underwater stretching to a polyvinyl alcohol (PVA)-based resin, and drying and shrinking by a heating roll, By employing it, 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 that is thin, has excellent handling properties, and has excellent optical characteristics.

1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention.
2 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to another embodiment of the present invention.
3 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to still another embodiment of the present invention.
Fig. 4 is a schematic view showing an example of drying shrinkage treatment using a heating roll in the method for producing a polarizing film used for a polarizing plate with a retardation layer of the present invention.

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

(Definition of Terms and Symbols)

Definitions of terms and symbols in this specification 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 maximized (ie, the slow axis direction), 'ny' is the refractive index in the direction orthogonal to the slow axis in the plane (ie, the fast axis direction), , 'nz' is the refractive index in the thickness direction.

(2) In-plane phase difference (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 an in-plane retardation measured at 23° C. with light having a wavelength of 550 nm. Re(λ) can be obtained by the formula: Re(λ)=(nx-ny)×d when the thickness of the layer (film) is d(nm).

(3) Phase difference in thickness direction (Rth)

'Rth(λ)' is the phase difference in the thickness direction measured at 23°C with light having a wavelength of λ nm. For example, 'Rth(550)' is a phase difference in the thickness direction measured at 23° C. with light having a wavelength of 550 nm. Rth(λ) can be obtained by the formula: Rth(λ)=(nx-nz)×d when the thickness of the layer (film) is d(nm).

(4) Nz factor

The Nz coefficient can be 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 the reference direction. Thus, for example, '45°' means ±45°.

A. Overall configuration of polarizing plate with retardation layer

1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention. The 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 disposed on one side of the polarizing film 11, and a second protective layer 13 disposed on the other side of the polarizing film 11. ). Depending on the purpose, one of the first protective layer 12 and the second protective layer 13 may be omitted. For example, when the retardation layer 20 can also function as a protective layer of 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 thickness of the polarizing film is 8 μm or less, and the ratio (A ₅₅₀ /A ₂₁₀ ) between the orthogonal absorbance A550 at a wavelength of 550 nm and the orthogonal absorbance A210 at a wavelength of 210 nm is 1.4 to 3.5.

As shown in FIG. 2 , in the polarizing plate 101 with a retardation layer 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. The other retardation layer 50 and the conductive layer or the isotropic substrate 60 with a conductive layer are typically provided on the outside of the retardation layer 20 (opposite to the polarizing plate 10). The other retardation layer typically exhibits a relationship of nz>nx=ny in refractive index characteristics. The other retardation layer 50 and the conductive layer or the isotropic base material 60 with a conductive layer are typically provided in this order from the retardation layer 20 side. The other retardation layer 50 and the conductive layer or the isotropic base material 60 with a conductive layer are typically arbitrary layers provided as needed, and any one or both of them may be omitted. For convenience, the phase difference layer 20 is sometimes referred to as a first phase difference layer and the other phase difference layer 50 is referred to as a second phase difference layer. In addition, when a conductive layer or an isotropic base material with a conductive layer is provided, the polarizing plate with a retardation layer is a so-called inner touch panel type input display device in which a touch sensor is built in between an image display cell (e.g., an organic EL cell) and a polarizing plate. can be applied to

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

The above embodiments may be appropriately combined, and modifications obvious in the art may be added to the constituent elements in the above embodiments. For example, the second retardation layer 50 and/or a conductive layer or an isotropic substrate 60 with a conductive layer may be provided on the polarizing plate 102 with a retardation layer in FIG. 3 . Further, for example, even if the configuration in which the isotropic substrate 60 with a conductive layer is provided on the outside of 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) do.

The polarizing plate with a retardation layer according to the embodiment of the present invention may further include other retardation layers. Other optical characteristics of the retardation layer (eg, refractive index characteristics, in-plane retardation, Nz coefficient, photoelastic coefficient), thickness, placement position, etc. may be appropriately set according to the purpose.

The polarizing plate with a retardation layer of the present invention may be in the form of a sheet or a long picture. In this specification, "elongate" means an elongate shape that is sufficiently long with respect to width, and includes, for example, an elongated shape that is 10 times or more in length with respect to width, preferably 20 times or more. A long polarizing plate with a retardation layer can be wound in a roll shape.

Practically, an adhesive layer (not shown) is provided on the side opposite to the polarizing plate of the retardation layer, and the polarizing plate with the retardation layer can be attached to the image display cell. Moreover, it is preferable that the release film is temporarily attached to the surface of the pressure-sensitive adhesive layer until the polarizing plate with the retardation layer is put into use. Roll formation becomes possible while protecting an adhesive layer by temporarily attaching a peeling film.

The total thickness of the polarizing plate with the retardation layer 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. The lower limit of the total thickness may be, for example, 28 μm. According to the embodiment of the present invention, such an extremely thin polarizing plate with a retardation layer can be realized. Such a polarizing plate with a retardation layer can have extremely excellent flexibility and bending durability. Such a polarizing plate with a retardation layer can be particularly preferably applied to a curved image display device and/or a curved or bendable image display device. In addition, the total thickness of a polarizing plate with a retardation layer refers to the sum of the thicknesses of all layers constituting the polarizing plate with a retardation layer, excluding the pressure-sensitive adhesive layer for adhering the polarizing plate to an external adherend such as a panel or glass (ie, retardation layer). The total thickness of the polarizing plate with a layer does not include the thickness of the adhesive layer for attaching the polarizing plate with a retardation layer to an adjacent member such as an image display cell and the peeling film that can be attached to the surface).

The basis weight of the polarizing plate with retardation layer according to the embodiment of the present invention is, for example, 6.5 mg/cm 2 or less, preferably 2.0 mg/cm 2 to 6.0 mg/cm 2 , more preferably 3.0 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 panel is slightly deformed by the weight of the polarizing plate with a retardation layer, and there is a possibility that display defects may occur. deformation can be prevented. In addition, the polarizing plate with a retardation layer having the above-mentioned basis weight has good handleability even when it is reduced in thickness, and can exhibit extremely excellent flexibility and bending durability.

Hereinafter, the components of the polarizing plate with a retardation layer will be described in more detail.

B. Polarizer

B-1. polarizing film

As described above, the polarizing film 11 has a thickness of 8 μm or less, and the ratio (A ₅₅₀ /A ₂₁₀ ) of the orthogonal absorbance A550 at a wavelength of 550 nm and the orthogonal absorbance A210 at a wavelength of 210 nm is 1.4 to 3.5. The polarizing film used in the present invention has a very large ratio (A ₅₅₀ /A ₂₁₀ ) compared to a typical thin polarizing film, and in one embodiment, the ratio (A ₄₇₀ /A ₆₀₀ ) is also very large. This is because the content ratio of iodine ions (which have absorption in the ultraviolet region around 210 nm) that do not form complexes with PVA in the polarizing film is very small, and the content ratio of PVA-iodine complex (which has absorption in the visible region) is very large. it means. More specifically, the polarizing film has a very high content ratio of PVA-I ₅ ^-complex having absorption around 600 nm, and the content ratio of PVA-I ₃ ^-complex having absorption around 480 nm is maintained without a significant decrease. there is. Here, since the thickness of the polarizing film means the length of the optical path length, when the thickness of the polarizing film is simply reduced, the optical path length is shortened and the polarization performance is also reduced. Since there is also a limit to the amount of iodine that can be contained in the polarizing film, it is essential to efficiently utilize iodine contained in the polarizing film in order to achieve both high polarization performance and thinning of the polarizing film. That is, it is possible to achieve both high polarization performance and thinning of the polarizing film by reducing iodine ions that absorb light in ultraviolet light, reduce iodine ions that do not contribute to polarization performance, and improve the ratio of PVA-iodine complexes that absorb light in the visible region. In other words, by increasing the ratio (A ₅₅₀ /A ₂₁₀ ), it becomes possible to achieve thinness and high optical performance. Further, by maintaining the ratio (A ₄₇₀ /A ₆₀₀ ) below a predetermined value, good polarization performance over the entire visible light range can be realized. While the amount of iodine in the thin polarizing film is limited, it has been difficult to increase both the ratio (A ₅₅₀ /A ₂₁₀ ) and the ratio (A ₄₇₀ /A ₆₀₀ ) in the prior art. Both sides of can be enlarged. The ratio (A ₅₅₀ /A ₂₁₀ ) is preferably 1.8 or higher, more preferably 2.0 or higher, still more preferably 2.2 or higher. The upper limit of the ratio (A ₅₅₀ /A ₂₁₀ ) may be, for example, 3.5. Further, the ratio (A ₄₇₀ /A ₆₀₀ ) is typically 0.7 or more, preferably 0.75 or more, more preferably 0.80 or more, still more preferably 0.85 or more. The upper limit of the ratio (A ₄₇₀ /A ₆₀₀ ) is, for example, 2.00, preferably 1.33. In addition, the orthogonal absorbance can be obtained by the following formula based on the orthogonal transmittance Tc measured when obtaining the degree of polarization described later.

Orthogonal absorbance=log10(100/Tc)

It is one of the features of the present invention to use a thin polarizing film having such characteristics.

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, particularly preferably 2 μm to 4 μm, particularly preferably is 2 μm to 3 μm.

The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance of the polarizing film is preferably 46.0% or less, more preferably 45.0% or less. On the other hand, the single transmittance is preferably 41.5% or more, more preferably 42.0% or more, still more preferably 42.5% or more. The degree of polarization of the polarizing film is preferably 99.990% or more, and preferably 99.998% or less. The single transmittance is typically a Y value measured using an ultraviolet/visible ray spectrophotometer and corrected for visibility. The degree of polarization can be obtained by the following formula, based on the parallel transmittance Tp and the orthogonal transmittance Tc, which are typically measured using an ultraviolet/visible spectrophotometer and corrected for visibility.

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

In one embodiment, the transmittance of a thin polarizing film of 8 μm or less is typically measured for a laminate of a polarizing film (surface refractive index: 1.53) and a protective film (refractive index: 1.50), ultraviolet / visible light It is measured using a spectrophotometer. The reflectance at the interface of each layer changes depending on the refractive index of the surface of the polarizing film and/or the refractive index of the surface of the protective film in contact with the air interface, and as a result, the measured transmittance value may change. Therefore, for example, when a protective film having a refractive index other than 1.50 is used, the measured value of the transmittance may be corrected according to the refractive index of the surface of the protective film in contact with the air interface. Specifically, the correction value C of the transmittance 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 transmittance 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. For example, when a base material having a surface refractive index of 1.53 (such as a cycloolefin-based film or a film with a hard coat layer) is used as a protective film, the correction amount C is about 0.2%. In this case, by adding 0.2% to the transmittance obtained by the measurement, it is possible to convert the polarizing film having a surface refractive index of 1.53 into the transmittance in the case of using a protective film having a refractive index of 1.50. In addition, according to the calculation based on the above formula, the amount of change in the correction value C when the transmittance T ₁ of the polarizing film is changed by 2% is 0.03% or less, and the effect of the transmittance of the polarizing film on the value of the correction value C is limited. In addition, when the protective film has absorption other than surface reflection, appropriate correction can be performed according to the amount of absorption.

Further, the orthogonal b-value of the polarizing film is, for example, greater than -10, preferably -7 or greater, and more preferably -5 or greater. The orthogonal b value is preferably +10 or less, more preferably +5 or less. The orthogonal b value represents the color when the polarizing film (finally, the polarizing plate with the retardation layer) is arranged in an orthogonal state, and the larger the absolute value of this value, the orthogonal color (black display in the image display device) becomes color [ It means to have a color taste. For example, when the orthogonal b value is as low as -10 or less, the black display looks bluish and the display performance deteriorates. That is, according to the embodiment of the present invention, it is possible to obtain a polarizing plate with a retardation layer capable of realizing excellent color in black display. Also, the orthogonal b value can be measured by a spectrophotometer represented by V-7100.

As the polarizing film, any suitable polarizing film can be employed. The polarizing film can be typically manufactured using a laminate of two or more layers.

As a specific example of a polarizing film obtained using a laminate, a polarizing film obtained using a laminate of a resin substrate and a PVA-based resin layer coated and formed on the resin substrate is exemplified. A polarizing film obtained by using a laminate of a resin substrate and a PVA-based resin layer coated and formed on the resin substrate, for example, by applying a PVA-based resin solution to the resin substrate and drying it to form a PVA-based resin layer on the resin substrate, Obtaining a laminated body of a resin substrate and a PVA-based resin layer; Stretching and dyeing the layered product to use the PVA-based resin layer as a polarizing film. In this embodiment, extending|stretching typically includes immersing a layered product in boric acid aqueous solution and extending|stretching. Further, the stretching may further include air-stretching the laminate at a high temperature (eg, 95° C. or higher) before stretching in a boric acid aqueous 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), and the resin substrate is peeled from the resin substrate/polarizing film laminate, and Any suitable protective layer according to the above may be laminated and used. The details of the manufacturing method of such a polarizing film are described in Unexamined-Japanese-Patent No. 2012-73580, for example. The entire description of the publication is incorporated herein by reference.

A typical method for producing a polarizing film is to form a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate to form a laminate, and to the laminate, air-assisted stretching treatment. and dyeing treatment, underwater stretching treatment, and drying shrinkage treatment for shrinking by 2% or more in the width direction by heating while conveying in the longitudinal direction, in this order. Accordingly, a polarizing film having a thickness of 8 μm or less and a ratio (A ₅₅₀ /A ₂₁₀ ) of 1.4 to 3.5 and excellent optical characteristics can be provided. That is, by introducing auxiliary stretching, even when applying PVA on a thermoplastic resin, it becomes possible to increase the crystallinity of PVA and achieve high optical properties. In addition, at the same time, by increasing the orientation of PVA in advance, it is possible to prevent problems such as deterioration in orientation or dissolution of PVA when immersed in water in a subsequent dyeing step or drawing step, and to achieve high optical properties. do. Further, in the case where the PVA-based resin layer is immersed in a liquid, the disorder of orientation of polyvinyl alcohol molecules and the decrease in orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. Accordingly, the optical properties of the polarizing film obtained through a treatment process performed by immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment, can be improved. In addition, optical properties can be improved by shrinking the laminate in the width direction by drying shrinkage treatment.

B-2. protective layer

The first protective layer 12 and the second protective layer 13 are each formed of any suitable film that can be used as a protective layer of a polarizing film. Specific examples of the material serving as the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and transparent resins such as polysulfone, polystyrene, polynorbornene, polyolefin, (meth)acrylic, and acetate resins. Further, thermosetting resins such as (meth)acrylic, urethane-based, (meth)acrylurethane-based, epoxy-based, and silicone-based resins or ultraviolet curable resins may be used. In addition to this, glassy type polymers, such as a siloxane type polymer, are also mentioned, for example. Moreover, the polymer film of Unexamined-Japanese-Patent No. 2001-343529 (WO01/37007) can also be used. As the material for this film, a resin composition containing, for example, a thermoplastic resin having a substituted or unsubstituted imide group on its side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group on its side chain can be used. For example, isobutene and N- and a resin composition comprising an alternating copolymer of methyl maleimide and an acrylonitrile/styrene copolymer. The polymer film may be, for example, an extrusion molding of the resin composition.

As will be described later, the polarizing plate with a retardation layer of the present invention is typically disposed on the visual side of an image display device, and the first protective layer 12 is typically disposed on the visible side. Therefore, surface treatment such as hard coat treatment, antireflection treatment, anti-sticking treatment, and anticlare treatment may be applied to the first protective layer 12 as necessary. Further/or, if necessary, the first protective layer 12 is treated to improve visibility when viewed through polarized sunglasses (typically, imparting a (other) circular polarization function, imparting an ultra-high phase difference) may be implemented. By performing such a process, excellent visibility can be realized even when the display screen is visually recognized through a polarizing lens such as polarized sunglasses. Therefore, the polarizing plate with the retardation layer can also be preferably 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 applied, the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.

In one embodiment, the second protective layer 13 is preferably optically isotropic. In this specification, 'optically isotropic' means that the in-plane retardation Re (550) is 0 nm to 10 nm and the thickness direction retardation Rth (550) is -10 nm to +10 nm. The second protective layer 13, in one embodiment, may 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 lightening, the second protective layer may be omitted.

B-3. Manufacturing method of polarizing film

The polarizing film is, for example, formed by 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 to form a laminate, and lamination. Manufactured by a method comprising subjecting a sieve to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment for shrinking by 2% or more in the width direction by heating while conveying in the longitudinal direction in this order. It can be. The content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. The shrinkage rate in the width direction of the layered product by the drying shrinkage treatment is preferably 2% or more. According to this manufacturing method, the polarizing film described in the above item B-1 can be obtained. In particular, by preparing a laminate comprising a PVA-based resin layer containing a halide, stretching the laminate by multi-step stretching including air-assisted stretching and underwater stretching, and heating the laminate after stretching with a heating roll to obtain excellent optical properties. A polarizing film having characteristics (typically, single transmittance and ratio (A ₅₅₀ /A ₂₁₀ )) can be obtained.

B-3-1. Fabrication of the laminate

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

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

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

Before forming the PVA-based resin layer, surface treatment (for example, corona treatment) may be performed on the thermoplastic resin substrate, or an easily bonding layer may be formed on the thermoplastic resin substrate. By performing such a 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 it is less than 20 μm, there is a possibility that formation of the PVA-based resin layer becomes difficult. When it exceeds 300 μm, for example, in the underwater stretching treatment described later, while requiring a long time for the thermoplastic resin substrate to absorb water, there is a risk that 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. The thermoplastic resin substrate absorbs water and can be plasticized by the water acting as a plasticizer. As a result, the drawing stress can be significantly reduced, and the drawing can be performed at a high magnification. On the other hand, the water absorption of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin substrate, it is possible to prevent problems such as a significant decrease in dimensional stability of the thermoplastic resin substrate during production and deterioration in the appearance of the obtained polarizing film. In addition, it is possible to prevent breakage of the base material during stretching in water or peeling of the PVA-based resin layer from the thermoplastic resin base material. In addition, the water absorption of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifier into the constituent material. Water absorption is a value determined according to JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or lower. By using such a thermoplastic resin substrate, the stretchability of the laminate can be sufficiently secured while suppressing crystallization of the PVA-based resin layer. Further, considering that plasticization of the thermoplastic resin substrate with water and stretching in water are satisfactorily performed, the temperature is more preferably 100°C or less, and more preferably 90°C or less. 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, problems such as deformation of the thermoplastic resin substrate (e.g., occurrence of irregularities, sagging, wrinkles, etc.) are prevented when the coating solution containing the PVA-based resin is applied and dried, resulting in good results. It is possible to fabricate a laminate. In addition, stretching of the PVA-based resin layer can be satisfactorily performed at a desired temperature (eg, about 60° C.). In addition, the glass transition temperature of the thermoplastic resin substrate can be adjusted by, for example, heating using a crystallization material that introduces a modifier into the constituent material. The glass transition temperature (Tg) is a value determined according to JIS K 7121.

As a constituent material of the thermoplastic resin substrate, any suitable thermoplastic resin can be employed. Examples of the thermoplastic resin include ester-based resins such as polyethylene terephthalate-based resins, cycloolefin-based resins such as norbornene-based resins, olefin-based resins such as polypropylene, polyamide-based resins, polycarbonate-based resins, and copolymer resins thereof. can be heard Among these, norbornene-type resin and amorphous polyethylene terephthalate-type resin are preferable.

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

In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate-based resin having an isophthalic acid unit. This is because such a thermoplastic resin substrate has extremely excellent stretchability and can suppress crystallization during stretching. This is considered to be due to imparting large waviness to the main chain by introducing an isophthalic acid unit. The polyethylene terephthalate-based resin has a terephthalic acid unit and an ethylene glycol unit. The content of the isophthalic acid unit is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, based on the total of all repeating units. This is because a thermoplastic resin substrate extremely excellent in stretchability can be obtained. On the other hand, the content of the isophthalic acid unit is preferably 20 mol% or less, more preferably 10 mol% or less with respect 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, it is stretched in the transverse direction of a long thermoplastic resin base material. The transverse direction is preferably a direction orthogonal to the stretching direction of the laminate described later. In addition, in this specification, 'orthogonal' also includes the case of being substantially orthogonal. Here, 'substantially orthogonal' includes the case of 90°±5.0°, preferably 90°±3.0°, 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 suitable method can be employed as a method for stretching the thermoplastic resin substrate. Specifically, fixed-end stretching or free-end stretching may be used. The stretching method may be dry or wet. Stretching of the thermoplastic resin substrate may be performed in one step or in multiple steps. In the case of performing in multiple stages, the above-mentioned stretching ratio is the product of the stretching ratio of each stage.

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 obtained by dissolving the halide and the PVA-based resin in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. can These can be used individually or in combination of 2 or more types. Among these, water is preferable. The concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight based on 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film in close contact with the thermoplastic resin substrate can be formed. The content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

You may mix|blend additives with a coating liquid. As an additive, a plasticizer, surfactant, etc. are mentioned, for example. Examples of the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin. As surfactant, a nonionic surfactant is mentioned, for example. These can be used for the purpose of further improving the uniformity, dyeability, and stretchability of the obtained PVA-based resin layer.

Any suitable resin can be employed 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 degree of saponification of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The degree of saponification can be determined according to JIS K 6726-1994. A polarizing film with excellent durability can be obtained by using a PVA-based resin having such a degree of saponification. When the degree of saponification is too high, there is a possibility of gelation.

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

As the halide, any suitable halide can be employed. Examples include iodide and sodium chloride. As iodide, potassium iodide, sodium iodide, and lithium iodide are mentioned, for example. Among these, potassium iodide is preferable.

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-based resin, and more preferably 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the PVA-based resin. When the amount of the halide with respect to 100 parts by weight of the PVA-based resin exceeds 20 parts by weight, the halide may bleed out and the finally obtained polarizing film may become cloudy.

In general, when the PVA-based resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA-based resin increases, but when the stretched PVA-based resin layer is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules is disturbed, Orientation may deteriorate. In particular, in the case of stretching the laminate of the thermoplastic resin substrate and the PVA-based resin layer in boric acid, the degree of orientation decreases when the laminate is stretched in boric acid at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin substrate. The trend is remarkable. For example, it is common that stretching of a PVA film alone in boric acid is performed at 60° C., whereas stretching of a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a temperature of around 70° C. In this case, the orientation of the PVA at the beginning of the stretching may be lowered in the step before rising by the underwater stretching. In contrast, by preparing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate, and stretching the laminate in air at high temperature (auxiliary stretching) before stretching the laminate in boric acid, the PVA of the laminate after auxiliary stretching Crystallization of the PVA-based resin in the resin-based layer can be promoted. As a result, in the case where the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. Accordingly, the optical properties of the polarizing film obtained through a treatment process performed by immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment, can be improved.

B-3-2. Air Assisted Stretching Treatment

In particular, in order to obtain high optical properties, a two-step stretching method combining dry stretching (auxiliary stretching) and stretching in boric acid is selected. Like two-step stretching, by introducing auxiliary stretching, the thermoplastic resin substrate can be stretched while suppressing crystallization, and in the subsequent stretching in boric acid, the thermoplastic resin substrate is excessively crystallized to solve the problem of deterioration in stretchability, The laminate can be stretched at a higher magnification. Furthermore, in the case of 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, the application temperature should be lowered 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, and a problem that sufficient optical properties cannot be obtained may occur. In contrast, by introducing auxiliary stretching, even when the PVA-based resin is applied onto the thermoplastic resin, it becomes possible to increase the crystallinity of the PVA-based resin and achieve high optical properties. In addition, by simultaneously increasing the orientation of the PVA-based resin in advance, it is possible to prevent problems such as deterioration in the orientation of the PVA-based resin or dissolution when immersed in water in a subsequent dyeing step or drawing step, thereby achieving high optical properties. it becomes possible to do

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

Air-assisted stretching may be performed in one step or in multiple steps. When performed in multiple steps, the draw ratio is the product of the draw ratios of each step. The stretching direction in air assisted stretching is preferably substantially the same as that in underwater stretching.

The draw ratio in air assisted stretching is preferably 2.0 to 3.5 times. The maximum stretching ratio when air assisted stretching and underwater stretching are combined is preferably 5.0 times or more, more preferably 5.5 times or more, still more preferably 6.0 times or more of the original length of the laminate. In the present specification, 'maximum stretch ratio' refers to a stretch ratio immediately before the laminate is broken, and a value 0.2 lower than the value obtained by checking the stretch ratio at which the laminate is broken separately.

The stretching temperature of the air-assisted stretching can be set to any suitable value depending on the forming material of the thermoplastic resin substrate, the stretching method, and the like. The stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate (Tg) + 10°C, particularly preferably equal to or higher than Tg + 15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, rapid crystallization of the PVA-based resin can be suppressed, and problems caused by the crystallization (for example, obstruction of orientation of the PVA-based resin layer by stretching) can be suppressed. The crystallization index of the PVA-based resin after air-assisted stretching is preferably 1.3 to 1.8, more preferably 1.4 to 1.7. The crystallization index of the PVA-based resin can be measured by the ATR method using a Fourier transform infrared spectrophotometer. Specifically, measurement is performed using polarized light as measurement light, and the crystallization index is calculated according to the following formula using the intensities of 1141 cm ^-1 and 1440 cm ^-1 of the obtained spectrum.

Crystallization Index=(I _C /I _R )

but,

I _C : Intensity of 1141 cm ^-1 when measured by incident light

_IR : Intensity of 1440 cm ^-1 when measured by incident light

am.

B-3-3. insolubilization treatment

If necessary, insolubilization treatment is performed after the air-assisted stretching treatment and before the underwater stretching treatment or the dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. By performing the insolubilization treatment, water resistance can be imparted to the PVA-based resin layer, and orientation degradation of PVA when immersed in water can be prevented. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 4 parts by weight based on 100 parts by weight of water. The liquid temperature of the insolubilization bath (boric acid aqueous solution) is preferably 20°C to 50°C.

B-3-4. dye treatment

The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). Specifically, it is performed by adsorbing iodine to the PVA-based resin layer. As the adsorption method, for example, a method of immersing the PVA-based resin layer (laminate) in a dye containing iodine, a method of coating the dye solution on the PVA-based resin layer, and spraying the dye solution on the PVA-based resin layer. methods and the like. Preferably, it is the method of immersing a layered product in a dyeing solution (dyeing bath). This is because iodine can adsorb satisfactorily.

The staining solution is preferably an iodine aqueous solution. The blending amount of iodine is preferably 0.05 to 0.5 parts by weight based on 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to blend iodide in an aqueous solution of iodine. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide is preferable. The blending amount of iodide is preferably 0.1 part by weight to 10 parts by weight, more preferably 0.3 part by weight to 5 parts by weight, based on 100 parts by weight of water. The liquid temperature of the dyeing solution at the time of dyeing is preferably 20°C to 50°C in order to suppress dissolution of the PVA-based resin. In the case of immersing the PVA-based resin layer in the dye 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.

Dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the single transmittance and ratio (A ₅₅₀ /A ₂₁₀ ) of the finally obtained polarizing film have desired values. As such dyeing conditions, preferably, an iodine aqueous solution is used as the dyeing solution, and the iodine aqueous solution and the iodine potassium iodide content ratio are set to 1:5 to 1:20. The ratio of the contents of iodine and potassium iodide in the iodine aqueous solution is preferably 1:5 to 1:10. Accordingly, a polarizing film having the above optical properties can be obtained.

When the dyeing treatment is continuously performed after the treatment of immersing the layered product in a treatment bath containing boric acid (typically, insolubilization treatment), boric acid contained in the treatment bath is mixed into the dye bath, thereby increasing the boric acid concentration of the dye bath. It changes with time, and as a result, dyeability may become unstable. In order to suppress the destabilization of dyeability as described above, the upper limit of the concentration of boric acid in the dyeing bath is preferably adjusted to 4 parts by weight, more preferably 2 parts by weight with respect to 100 parts by weight of water. On the other hand, the lower limit of the concentration of boric acid in the dyeing bath is preferably 0.1 part by weight, more preferably 0.2 part by weight, and still more preferably 0.5 part by weight with respect to 100 parts by weight of water. In one embodiment, the dyeing treatment is performed using a dyeing bath in which boric acid has been mixed in advance. Accordingly, the rate of change in boric acid concentration when boric acid in the treatment bath is mixed in the dyeing bath can be reduced. The amount of boric acid blended in advance in the dyeing bath (i.e., the content of boric acid not derived from the treatment bath) is preferably 0.1 part by weight to 2 parts by weight, more preferably 0.5 part by weight, based on 100 parts by weight of water. -1.5 parts by weight.

B-3-5. cross-linking treatment

If necessary, a crosslinking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. By performing the crosslinking treatment, water resistance can be imparted to the PVA-based resin layer, and a decrease in the orientation of the PVA when immersed in high-temperature water can be prevented in the subsequent underwater stretching. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 5 parts by weight based on 100 parts by weight of water. In addition, when crosslinking treatment is performed after the above dyeing treatment, it is preferable to further incorporate iodide. By blending iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. The blending amount of iodide is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Specific examples of iodide are as described above. The liquid temperature of the crosslinking bath (boric acid aqueous solution) is preferably 20°C to 50°C.

B-3-6. Underwater stretching treatment

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

Arbitrary suitable methods can be employed for the stretching method of 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 circumferential speeds) may be used. Preferably, free end stretching is selected. Stretching of the laminate may be performed in one step or in multiple steps. In the case of performing in multiple steps, the draw ratio (maximum draw ratio) of the laminate described later is the product of the draw ratios of each step.

Stretching in water is preferably carried out by immersing the laminate in an aqueous boric acid solution (stretching in boric acid water). By using a boric acid aqueous solution as the stretching bath, the PVA-based resin layer can be imparted with rigidity that can withstand the tension applied during stretching and water resistance that does not dissolve in water. Specifically, boric acid generates tetrahydroxyboric acid anions in an aqueous solution and can be crosslinked with PVA-based resins by hydrogen bonding. As a result, rigidity and water resistance can be imparted to the PVA-based resin layer so that it can be stretched satisfactorily, and a polarizing film having excellent optical properties can be manufactured.

The aqueous solution of boric acid 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, based on 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film with higher characteristics can be manufactured. In addition to boric acid or borate salts, an aqueous solution obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, and the like in a solvent can also be used.

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

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such a temperature, it can be extended 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 formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40°C, there is a risk that satisfactory stretching may not be possible even if plasticization of the thermoplastic resin substrate by water is taken into consideration. On the other hand, as the temperature of the stretching bath becomes higher, the solubility of the PVA-based resin layer increases, and there is a possibility that excellent optical properties cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

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

B-3-7. dry shrink treatment

The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or may be performed by heating the conveying roll (using a so-called heating roll) (heating roll drying method). Preferably, both of these are used. By drying using a heating roll, heating curling of the layered product can be efficiently suppressed, and a polarizing film having an excellent appearance can be manufactured. Specifically, by drying in a state where the laminate is attached to a heating roll, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the crystallinity, and even at a relatively low drying temperature, the crystallinity of the thermoplastic resin substrate can be increased satisfactorily. can As a result, the rigidity of the thermoplastic resin base material is increased, and it is in a state capable of withstanding shrinkage of the PVA-based resin layer due to drying, and curling is suppressed. In addition, since the laminate can be dried while maintaining a flat state by using a heating roll, not only curling but also occurrence of wrinkles can be suppressed. At this time, optical properties can be improved by shrinking the laminate in the width direction by drying shrinkage treatment. This is because the orientation properties of PVA and PVA/iodine complexes can be effectively increased. The shrinkage in the width direction of the laminate by the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using a heating roll, the laminate can be continuously contracted in the width direction while conveying, and high productivity can be realized.

4 is a schematic view showing an example of drying shrinkage treatment. In the drying shrinkage treatment, the laminate 200 is dried while being conveyed by conveyance rolls R1 to R6 and guide rolls G1 to G4 heated to a predetermined temperature. In the illustrated example, conveyance rolls R1 to R6 are arranged so that the surface of the PVA resin layer and the surface of the thermoplastic resin substrate are continuously heated alternately. ) may be disposed so as to continuously heat only the conveying rolls R1 to R6.

Drying conditions can be controlled by adjusting the heating temperature of the conveying rolls (temperature of the heating rolls), the number of heating rolls, and the contact time with the heating rolls. The temperature of the heating roll is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. While the crystallinity of the thermoplastic resin can be increased satisfactorily and curling can be satisfactorily suppressed, an optical laminate having extremely excellent durability can be manufactured. In addition, the temperature of a heating roll can be measured with a contact thermometer. Although six conveyance rolls are provided in the illustrated example, the number of conveyance rolls is not particularly limited as long as there are a plurality of conveyance rolls. The conveyance rolls are usually 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roll is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, still more preferably 1 to 10 seconds.

The heating roll may be installed in a heating furnace (for example, an oven) or may be installed in a normal production line (in a room temperature environment). Preferably, it is installed in a heating furnace equipped with a blowing means. By using both heating roll drying and hot air drying, rapid temperature change between the heating rolls can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of hot air drying is preferably 30°C to 100°C. In addition, the hot air drying time is preferably 1 second to 300 seconds. The wind speed of the hot air is preferably about 10 m/s to 30 m/s. In addition, the said wind speed is the wind speed in a heating furnace, and can be measured with a miniven type digital anemometer.

B-3-8. other processing

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

C. The first retardation layer

As described above, the first retardation layer 20 is an alignment hardening layer of a liquid crystal compound. Since the difference between nx and ny of the retardation layer obtained by using a liquid crystal compound can be significantly increased compared to non-liquid crystal materials, the thickness of the retardation layer for obtaining a desired in-plane retardation can be significantly reduced. As a result, further thinning and weight reduction of the polarizing plate with the retardation layer can be realized. In this specification, the 'alignment fixed layer' refers to a layer in which liquid crystal compounds are aligned in a predetermined direction within the layer and the alignment state is fixed. In addition, the 'alignment hardened layer' is a concept including an alignment hardened layer obtained by curing a liquid crystal monomer as will be described later. In this embodiment, the rod-shaped liquid crystal compounds are typically aligned in a state aligned in the slow axis direction of the first retardation layer (homogeneous orientation).

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

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

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

As the liquid crystal monomer, any suitable liquid crystal monomer may be employed. For example, polymerizable mesogenic compounds described in Japanese Patent Application Publication Nos. 2002-533742 (WO00/37585), EP358208 (US5211877), EP66137 (US4388453), WO93/22397, EP0261712, DE19504224, DE4408171 and GB2280445 can be used. Specific examples of such a polymerizable mesogenic compound include, for example, BASF's trade name LC242, Merck's trade name E7, and Wacker-Chem's trade name LC-Sillicon-CC3767. As the liquid crystal monomer, for example, a nematic liquid crystal monomer is preferable.

The alignment hardening layer of the liquid crystal compound is formed by subjecting the surface of a predetermined base material to alignment treatment, applying a coating solution containing the liquid crystal compound to the surface, and aligning the liquid crystal compound in a direction corresponding to the alignment treatment, thereby forming the aligned state. It can be formed by fixing. In one embodiment, the substrate is any suitable resin film, and the orientation hardening layer formed on the substrate can be transferred to the surface of the polarizing plate 10 . In other embodiments, the substrate may be the second protective layer 13 . In this case, since the transfer process is omitted and lamination can be performed by roll-to-roll successively from the formation of the alignment-fixed layer (first retardation layer), productivity is further improved.

As the orientation treatment, any appropriate orientation treatment may be employed. Specifically, a mechanical orientation treatment, a physical orientation treatment, and a chemical orientation treatment are mentioned. Specific examples of the mechanical orientation treatment include rubbing treatment and stretching treatment. Specific examples of the physical orientation treatment include magnetic field orientation treatment and electric field orientation treatment. Specific examples of the chemical orientation treatment include an oblique deposition method and an optical orientation treatment. Arbitrary appropriate conditions may be employed for the treatment conditions of various alignment treatments depending on the purpose.

Alignment of the liquid crystal compound is performed by treatment at a temperature exhibiting a liquid crystal phase depending on the type of the liquid crystal compound. By performing such a temperature treatment, the liquid crystal compound assumes a liquid crystal state and aligns the liquid crystal compound according to the orientation treatment direction of the surface of the substrate.

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

The specific example of a liquid crystal compound and the details of the formation method of an alignment hardening layer are described in Unexamined-Japanese-Patent No. 2006-163343. The description of the publication is incorporated herein by reference.

Another example of the alignment hardening layer is a form in which the discotic liquid crystal compound is aligned in any of vertical alignment, hybrid alignment, and oblique alignment. In the discotic liquid crystal compound, the disk surface of the discotic liquid crystal compound is typically aligned substantially perpendicular to the film surface of the first retardation layer. When the discotic liquid crystal compound is substantially perpendicular, the average value of the angle between the film plane and the disk plane of the discotic liquid crystal compound is preferably 70° to 90°, more preferably 80° to 90°, and still more preferably means that it is 85 ° to 90 °. A discotic liquid crystal compound generally has a cyclic parent nucleus such as benzene, 1,3,5-triazine, calixarene, etc. arranged at the center of the molecule, and a straight-chain alkyl group, alkoxy group, substituted benzoyloxy group or the like is attached to its side chain. It refers to a liquid crystal compound having a disk-shaped molecular structure substituted radially. Representative examples of discotic liquid crystals include a research report by C. Destrade, Mol. Cryst. Liq. Cryst. 71, page 111 (1981), benzene derivatives, triphenylene derivatives, thruxene derivatives, phthalocyanine derivatives, and B. Kohne's research report, Angew. Chem. Cyclohexane derivatives described in Vol. 96, page 70 (1984), and research reports by J. M. Lehn, J. Chem. Soc. Chem. Commun., p. 1794 (1985), J. Zhang et al., J. Am. Chem. Soc. Azacrown type and phenylacetylene type macrocycles described in Volume 116, page 2655 (1994) are exemplified. As another specific example of the discotic liquid crystal compound, compounds described in, for example, Japanese Unexamined Patent Publication Nos. 2006-133652, 2007-108732, and 2010-244038 are exemplified. Descriptions of the above documents and publications are incorporated herein by reference.

In one embodiment, the 1st retardation layer 20 is a single layer of the alignment hardening layer of a liquid crystal compound, as shown in FIG.1 and FIG.2. When the first retardation layer 20 is composed of a single layer of an orientation fixing 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, an in-plane retardation equivalent to that of a resin film can be achieved with a significantly thinner thickness than that of the resin film.

The first retardation layer typically has a refractive index characteristic of nx>ny=nz. The first retardation layer is typically provided to impart antireflection characteristics to the polarizing plate, and may function as a λ/4 plate when the first retardation layer is a single layer of an orientation hardening layer. 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. In addition, 'ny=nz' here includes not only the case where ny and nz are completely equal, but also the case where they are substantially equal. Therefore, there may be cases where ny>nz or ny<nz is 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. When a polarizing plate with a retardation layer obtained by satisfying such a relationship is used for an image display device, very excellent reflected color can be achieved.

The first retardation layer may exhibit reverse dispersion wavelength characteristics in which the retardation value increases with the wavelength of the measurement light, or may exhibit positive wavelength dispersion characteristics in which the retardation value decreases with the wavelength of the measurement light. It may exhibit flat wavelength dispersion characteristics that hardly change even with the wavelength of 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 characteristics can be realized.

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 is about 45°. If the angle θ is in this range, a polarizing plate with a retardation layer having very excellent circular polarization characteristics (as a result, very excellent antireflection characteristics) can be obtained by using the λ/4 plate as the first retardation layer as described above.

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. 3 . In this case, one of the first alignment-fixed layer 21 and the second alignment-fixed layer 22 can function as a λ/4 plate, and the other can function as a λ/2 plate. Accordingly, the thickness of the first alignment-fixed layer 21 and the second alignment-fixed layer 22 may be adjusted to obtain a desired in-plane retardation of the λ/4 plate or the λ/2 plate. For example, when the first alignment-fixed layer 21 functions as a λ/2 plate and the second alignment-fixed layer 22 functions as a λ/4 plate, the thickness of the first alignment-fixed layer 21 is, for example, 2.0 μm to 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 alignment-hardened layer is as described above with respect to the single-layer alignment-hardened 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°. The angle between the slow axis of the second alignment-fixed layer and the absorption axis of the polarizing film is preferably 70° to 80°, more preferably 72° to 78°, still more preferably about 75°. With such a configuration, it is possible to obtain characteristics close to ideal reverse wavelength dispersion characteristics, and as a result, extremely excellent antireflection characteristics can be realized. The liquid crystal compounds constituting the first alignment fixed layer and the second alignment fixed layer, the formation method of the first alignment fixed layer and the second alignment fixed layer, and optical properties are as described above with respect to the single-layer alignment fixed layer.

D. Second retardation layer

As described above, the second retardation layer may be a so-called positive C plate having a refractive index characteristic of nz>nx=ny. By using the positive C plate as the second retardation layer, it is possible to favorably prevent reflection in an oblique direction, and a wide viewing angle of the antireflection function becomes possible. In this case, the phase difference Rth (550) in the thickness direction of the second retardation layer is preferably -50 nm to -300 nm, more preferably -70 nm to -250 nm, still more preferably -90 nm to -200 nm, particularly preferably -100 nm to -180 nm. Here, 'nx=ny' includes not only a case where nx and ny are strictly equal, but also a case where nx and ny are substantially equal. That is, the in-plane retardation Re (550) of the second retardation layer may be less than 10 nm.

The second retardation layer having a refractive index characteristic of nz>nx=ny may be formed of any suitable material. The second retardation layer is preferably made of a film containing a liquid crystal material fixed in a homeotropic orientation. The liquid crystal material (liquid crystal compound) capable of homeotropic alignment 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 described in [0020] to [0028] of Japanese Unexamined Patent Publication No. 2002-333642 and the method for forming the retardation layer. 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

The conductive layer can be formed by forming a metal oxide film on any suitable substrate by any suitable film formation method (eg, vacuum deposition method, sputtering method, CVD method, ion plating method, spray method, etc.). Examples of the metal oxide 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 substrate to the first retardation layer (or, if present, the second retardation layer), and the conductive layer alone may become a component layer of the polarizing plate with a retardation layer, or a laminate with the substrate (with a conductive layer) substrate) may be laminated on the first retardation layer (or the second retardation layer if present). Preferably, the substrate is optically isotropic, and therefore the conductive layer can be used for a polarizing plate with a retardation layer as an isotropic substrate with a conductive layer.

As the optically isotropic substrate (isotropic substrate), any suitable isotropic substrate can be employed. As the material constituting the isotropic base material, for example, a material whose main skeleton is a resin without a conjugated system such as norbornene-based resin or olefin-based resin, and a cyclic structure such as a lactone ring or glutarimide ring in the main chain of an acrylic resin. Materials etc. are mentioned. When such a material is used, when an isotropic substrate is formed, the expression of phase difference accompanying orientation of molecular chains can be suppressed to a small level. The thickness of the isotropic substrate is preferably 50 μm or less, and more preferably 35 μm or less. The lower limit of the thickness of the isotropic substrate 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 needed. By patterning, a conductive portion and an insulating portion can be formed. As a result, electrodes can be formed. The electrodes may function as touch sensor electrodes that detect contact with the touch panel. As the patterning method, any suitable method can be employed. Specific examples of the patterning method include a wet etching method and a screen printing method.

F. Image display device

The polarizing plate with a retardation layer described in the above items A to E can be applied to an image display device. Therefore, the present invention includes an image display device using such a polarizing plate with a retardation layer. Representative examples of the image display device include a liquid crystal display device and an electroluminescence (EL) display device (eg, an organic EL display device and an inorganic EL display device). An image display device according to an embodiment of the present invention includes the polarizing plate with a retardation layer described in Items A to E above on its viewing side. Polarizing plates with a retardation layer are laminated so that the retardation layer is on the side of an image display cell (for example, a liquid crystal cell, an organic EL cell, or an inorganic EL cell) (a polarizing film is on the viewing side). In one embodiment, the image display device has a curved shape (actually, 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.

[Example]

Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited by these examples. The measurement method of each characteristic is as follows. In addition, unless otherwise specified, 'parts' and '%' in Examples and Comparative Examples are based on weight.

(1) Thickness

The thickness of 10 µm or less was measured using an interference film thickness meter (manufactured by Otsuka Electronics, product name 'MCPD-3000'). The thickness exceeding 10 μm was measured using a digital micrometer (manufactured by Anritz, product name 'KC-351C').

(2) single transmittance and orthogonal absorbance

For the polarizing plates (protective film/polarizing film) of Examples and Comparative Examples, single transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc measured using an ultraviolet / visible ray spectrophotometer (V-7100 manufactured by Nippon Bunko Co., Ltd.), respectively, Ts, Tp and Tc of the polarizing film were used. These Ts, Tp and Tc are Y values measured by a 2-degree field of view (C light source) of JIS Z8701 and corrected for visibility. In addition, the refractive index of the protective film was 1.50, and the refractive index of the surface of the polarizing film opposite to the protective film was 1.53.

In addition, using the Tc measured at each wavelength, the orthogonal absorbance was obtained by the following formula.

Orthogonal absorbance=log10(100/Tc)

The orthogonal absorbance A ₂₁₀ from the orthogonal transmittance Tc ₂₁₀ at a measurement wavelength of 210 nm and the orthogonal absorbance A ₅₅₀ from the orthogonal transmittance Tc ₅₅₀ at a measurement wavelength of 550 nm were obtained using UV-3150 manufactured by Shimadzu Corporation, respectively. Further, the orthogonal absorbance A ₄₇₀ from the orthogonal transmittance Tc ₄₇₀ at a measurement wavelength of 470 nm and the orthogonal absorbance A ₆₀₀ from the orthogonal transmittance Tc ₆₀₀ at a measurement wavelength of 600 nm were obtained using V-7100 manufactured by Nippon Bunko Co., Ltd., respectively. In addition, about _A470 and _A600 , it is possible to carry out the same measurement with Otsuka Electronics Co., Ltd. LPF-200 grade|etc.,.

(3) orthogonal b value

The polarizing plate used in Examples and Comparative Examples was measured using an ultraviolet/visible ray spectrophotometer (manufactured by Nippon Bunko, product name 'V7100'), and the color in a cross-Nicol state was obtained. A polarizing plate having a low orthogonal b value (a negative value and a large absolute value) indicates that the color is blue rather than neutral.

(4) bending

The polarizing plate with the retardation layer obtained in Examples and Comparative Examples was cut into a size of 110 mm × 60 mm. At this time, the polarizing film was cut so that the direction of the absorption axis was in the direction of the long side. The cut out polarizing plate with the retardation layer was bonded to a glass plate having a size of 120 mm x 70 mm and a thickness of 0.2 mm through an adhesive to obtain a test sample. The test sample was put into a heating oven maintained at 85°C for 24 hours, and the amount of warping after being taken out was measured. When the test sample was left still on a plane with the glass plate facing down, the height of the highest part from the plane concerned was taken as the amount of warpage.

(5) unit weight

The weight (unit weight) per unit area of the polarizing plate with a retardation layer was calculated by cutting the polarizing plate with a retardation layer obtained in Examples and Comparative Examples into a predetermined size and dividing the weight (mg) by the area (cm ² ).

(6) bending resistance

The polarizing plate with the retardation layer obtained in Examples and Comparative Examples was cut into a size of 50 mm × 100 mm. At this time, the polarizing film was cut so that the direction of the absorption axis was in the direction of the short side. A polarizing plate with a retardation layer cut under conditions of 20° C. and 50% RH was subjected to a bending test using a folding resistance tester with a constant temperature and humidity chamber (manufactured by YU ASA, CL09 type-D01). Specifically, the polarizing plate with the retardation layer is repeatedly bent in a direction parallel to the absorption axis direction so that the retardation layer side is on the outside, and the number of times of bending until display defects such as cracks, peeling, breakage of the film, etc. occurs is measured. and evaluated according to the following criteria (bending diameter: 2 mmφ).

<Evaluation Criteria>

Less than 10,000 times: bad

10,000 or more and less than 30,000: Good

Over 30,000 times: excellent

[Example 1]

1. Fabrication of polarizing film

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

Polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name 'Gosefimer Z410') were mixed in a ratio of 9:1 to 100 parts by weight of a PVA-based resin containing potassium iodide 13 What was added by weight was dissolved in water to prepare a PVA aqueous solution (coating liquid).

A PVA-based resin layer having a thickness of 13 μm was formed by applying the PVA aqueous solution to the corona-treated surface of the resin substrate and drying at 60° C. to prepare a laminate.

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

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

Subsequently, the single transmittance (Ts) and ratio (A ₅₅₀ / A ₂₁₀ ) was immersed for 60 seconds while adjusting the concentration to a desired value (dyeing treatment).

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

Thereafter, while the laminate was immersed in an aqueous solution of boric acid (boric acid concentration: 4.0% by weight) at a liquid temperature of 70 ° C., uniaxial stretching was performed so that the total stretching ratio in the machine direction (longitudinal direction) was 5.5 times between rolls having different circumferential speeds. (underwater stretching treatment).

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

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

In this way, a polarizing film having a thickness of 4.6 μm was formed on the resin substrate.

2. Fabrication of polarizer

An acrylic film (surface refractive index: 1.50, 40 µm) was bonded as a protective layer to the surface of the polarizing film obtained above (surface opposite to the resin substrate) via an ultraviolet curable adhesive. Specifically, the coating was applied so that the total thickness of the curable adhesive was 1.0 μm, and bonding was performed using a roll machine. Thereafter, UV rays were irradiated 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 configuration of a protective layer/polarizing film. The single transmittance of the polarizing plate (actually, the polarizing film) was 43.5%, A ₅₅₀ /A ₂₁₀ was 1.50, A ₄₇₀ /A ₆₀₀ was 0.87, and the orthogonal b value was -3.00.

3. Preparation of the first alignment-fixed layer and the second alignment-fixed layer constituting the retardation layer

10 g of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF: trade name 'Paliocolor LC242', represented by the following formula) and a photopolymerization initiator for the polymerizable liquid crystal compound (manufactured by BASF: trade name 'Irgacure 907') 3 g was 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 using a rubbing cloth, and alignment treatment was performed. The direction of the alignment treatment was set to be 15° when viewed from the viewing side with respect to the direction of the absorption axis of the polarizing film when bonding to the polarizing plate. The liquid crystal compound was aligned by coating the liquid crystal coating solution on the orientation treated surface with a bar coater and heating and drying at 90°C for 2 minutes. The liquid crystal layer formed in this way was irradiated with light of 1 mJ/cm ² using a metal halide lamp, and the liquid crystal layer was cured to form a liquid crystal alignment hardened layer A on the PET film. The thickness of the liquid crystal alignment hardened layer A was 2.5 µm, and the in-plane retardation Re (550) was 270 nm. Moreover, the liquid-crystal orientation hardening layer A had the refractive index distribution of nx>ny=nz.

A liquid crystal alignment fixed layer B was formed on the PET film in the same manner as above except that the coating thickness was changed and the direction of the orientation treatment was 75 ° direction when viewed from the viewing side with respect to the direction of the absorption axis of the polarizing film. The thickness of the liquid crystal alignment fixed layer B was 1.5 μm, and the in-plane retardation Re (550) was 140 nm. Moreover, the liquid-crystal orientation hardening layer B had the refractive index distribution of nx>ny=nz.

4. Production of Polarizing Plate with Retardation Layer

The liquid-crystal orientation fixed layer A and the liquid-crystal orientation fixed layer B obtained in said 3. were transcribe|transferred to the polarizing film surface of the polarizing plate obtained by said 2. in this order. At this time, the transfer (bonding) was performed such that the angle between the absorption axis of the polarizing film and the slow axis of the alignment hardening layer A was 15 ° and the angle between the absorption axis of the polarizing film and the slow axis of the orientation hardening layer B was 75 °. In addition, each transfer (bonding) was performed through the ultraviolet curable adhesive (thickness 1.0 μm) used in 2. above. In this way, a polarizing plate with a retardation layer having a configuration of protective layer/adhesive layer/polarizing film/adhesive layer/retardation layer (first alignment-fixed layer/adhesive layer/second alignment-fixed layer) was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 52 μm. The obtained polarizing plate with a retardation layer was used for evaluation of the above (4) to (6). The amount of warp was 1.8 mm.

[Example 2]

A polarizing plate with a retardation layer was produced in the same manner as in Example 1 except for using an acrylic film having a thickness of 20 µm as the protective layer. The total thickness of the obtained polarizing plate with a retardation layer was 32 micrometers. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The amount of warp was 1.5 mm.

[Example 3]

A polarizing plate with a retardation layer was produced in the same manner as in Example 1 except for using a 25 μm-thick triacetyl cellulose (TAC) film as a 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. Fabrication of polarizer

A polyvinyl alcohol-based resin film having an average degree of polymerization of 2,400, a degree of saponification of 99.9 mol%, and a thickness of 30 µm was prepared. The polyvinyl alcohol film is immersed for 30 seconds in a swelling bath (water bath) at 20°C between rolls with different circumferential speed ratios, and stretched 2.4 times in the conveying direction while swelling (swelling step), followed by a dyeing bath (with an iodine concentration) of 30°C. The original polyvinyl alcohol film (a polyvinyl alcohol film that is not completely stretched in the conveying direction) is immersed and dyed so that the single transmittance after final stretching is a desired value in an aqueous solution having a potassium iodide concentration of 0.03% by weight and 0.3% by weight). As a reference, it was stretched 3.7 times in the transport direction (dyeing step). The immersion time at this time was about 60 seconds. Next, while immersing the dyed polyvinyl alcohol film in a 40°C crosslinking bath (aqueous solution having a boric acid concentration of 3.0% by weight and a potassium iodide concentration of 3.0% by weight), the original polyvinyl alcohol film is 4.2 times in the conveying direction. It was stretched to (crosslinking process). Further, the obtained polyvinyl alcohol film was immersed in a 64°C stretching bath (aqueous solution having a boric acid concentration of 4.0% by weight and a potassium iodide concentration of 5.0% by weight) for 50 seconds, and the original polyvinyl alcohol film was 6.0% by weight in the conveying direction. After stretching to the stomach (stretching step), it was immersed for 5 seconds in a 20°C washing bath (aqueous solution having a potassium iodide concentration of 3.0% by weight) (washing step). The washed polyvinyl alcohol film was dried at 30°C for 2 minutes to produce a polarizer (thickness: 12 µm).

2. Fabrication of polarizer

As an adhesive, an aqueous solution containing a polyvinyl alcohol resin containing an acetoacetyl group (average degree of polymerization of 1,200, degree of saponification of 98.5% by mole, degree of acetoacetylation of 5% by mole) and methylolmelamine at a weight ratio of 3:1 was used. Using this adhesive, a triacetyl cellulose (TAC) film with a hard coat layer having a thickness of 25 μm is placed on one side of the polarizer obtained above, and a TAC film having a thickness of 25 μm is rolled on the other side of the polarizer. After bonding together with an air conditioner, heat drying in an oven (temperature: 60° C., time: 5 minutes), protective layer (1) (thickness: 25 μm) / adhesive layer / polarizer / adhesive layer / protective layer (2) (thickness: 25 μm) ) A polarizing plate having a configuration was produced.

3. Production of Polarizing Plate with Retardation Layer

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. above, and the protective layer 1 / adhesive layer / polarizer / A polarizing plate with a retardation layer having a configuration of adhesive layer/protective layer (2)/adhesive layer/retardation layer (first alignment-fixed layer/adhesive layer/second alignment-fixed layer) was produced. The total thickness of the obtained polarizing plate with a retardation layer was 68 μm. The obtained polarizing plate with a retardation layer was subjected to the same evaluation as in Example 1. The amount of warpage was 4.2 mm.

[Comparative Example 2]

The PVA aqueous solution (coating solution) without adding potassium iodide, the thickness of the polarizing film obtained by changing the PVA aqueous solution (coating solution) was 3.3 μm, and the shrinkage rate in the width direction was measured without using a heating roll in the drying shrinkage treatment. A polarizing film and a polarizing plate were produced in the same manner as in Example 1 except that the concentration was 0.1% or less and the single transmittance of the polarizing film was adjusted by adjusting the concentration of the dyeing bath. The single transmittance of the polarizing plate (actually, the polarizing film) was 43.4%, and A ₅₅₀ /A ₂₁₀ was 0.75. 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. Fabrication of polarizer

A long polarizing plate (width: 1300 mm) having a configuration of a 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. Production of retardation film constituting the retardation layer

2-1. Polymerization of polyester carbonate resin

Polymerization was carried out using a batch polymerization apparatus consisting of two vertical reactors equipped with stirring blades 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 mass part (0.139 mol), 63.77 parts by mass (0.298 mol) of diphenyl carbonate (DPC), and 1.19 × 10 ^-2 parts by mass (6.78 × 10 ^-5 mol) of calcium acetate monohydrate as a catalyst were added. After substituting the inside of the reactor with reduced pressure nitrogen, heating was performed with a heat medium, and stirring was started when the internal temperature reached 100°C. 40 minutes after the start of temperature increase, the internal temperature reached 220°C, and while controlling to maintain this temperature, pressure reduction was started, and after reaching 220°C, it was set to 13.3 kPa in 90 minutes. Phenol vapor produced as a by-product of the polymerization reaction was led to a reflux condenser at 100°C, monomer components contained in a small amount in the phenol vapor were returned to the reactor, and uncondensed phenol vapor was led to a condenser at 45°C for recovery. . After nitrogen was introduced into the first reactor to once restore the pressure to atmospheric pressure, the oligomerized reaction solution in the first reactor was transferred to the second reactor. Subsequently, the temperature increase and pressure reduction in the second reactor were started, and the internal temperature was 240°C and the pressure was 0.2 kPa in 50 minutes. Thereafter, polymerization was allowed to proceed until a predetermined agitation power was reached. When the predetermined power was reached, nitrogen was introduced into the reactor to restore pressure, the resulting polyester carbonate-based resin was extruded into water, and the strands were cut to obtain pellets.

2-2. Production of retardation film

After vacuum drying the obtained polyester carbonate-based resin (pellet) at 80 ° C. for 5 hours, a single screw extruder (manufactured by Toshiba Machinery Co., Ltd., cylinder set temperature: 250 ° C.), T die (width 200 mm, set temperature: 250 ° C.), A long resin film with a thickness of 135 μm was produced using a film forming apparatus equipped with a cooling roll (set temperature: 120 to 130° C.) and a winder. 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 having a thickness of 53 µm. Re(550) of the obtained retardation film was 141 nm, Re(450)/Re(550) was 0.82, and the Nz coefficient was 1.12.

3. Production of Polarizing Plate with Retardation Layer

The retardation film obtained in the above 2. was bonded to the surface of the polarizing film of the polarizing plate obtained in the above 1. through an acrylic pressure-sensitive adhesive (thickness: 5 µm). At this time, they were bonded together so that the absorption axis of the polarizing film and the slow axis of the retardation film formed an angle of 45°. In this way, a polarizing plate with a phase difference layer having a configuration of protective layer/adhesive layer/polarizing film/adhesive layer/phase difference 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 used for evaluation of the above (5) and (6).

Table 1 shows the structure and evaluation results of the polarizing plate with a retardation layer obtained in Examples 1 to 3 and Comparative Examples 1 and 3.

[Table 1]

[evaluation]

As is clear from Table 1 and comparison between Example 1 and Comparative Example 2, the polarizing plate with a retardation layer of Examples of the present invention is thin, suppresses warping after heating test, and has excellent optical properties. Moreover, it turns out that bending resistance improves when the weight per unit area of a polarizing plate with a retardation layer is below a predetermined value.

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

10: polarizer
11: polarizing film
12: first protective layer
13: second protective layer
20: phase difference layer
100: polarizing plate with retardation layer
101: polarizing plate with retardation layer
102: polarizing plate with retardation layer

Claims (13)

A polarizing film, a polarizing plate including 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-based resin film containing a dichroic material, the thickness of the polarizing film is 8 μm or less, and the ratio between the orthogonal absorbance A ₅₅₀ at a wavelength of 550 nm and the orthogonal absorbance A ₂₁₀ at a wavelength of 210 nm ( A ₅₅₀ /A ₂₁₀ ) is 1.4 to 3.5,
The retardation layer is an alignment hardening layer of a liquid crystal compound,
A polarizing plate with a retardation layer having a total thickness of 60 μm or less. According to claim 1,
The retardation layer is a single layer of an alignment hardening layer of a liquid crystal compound,
Re (550) of the retardation layer is 100 nm to 190 nm,
A polarizing plate with a retardation layer, wherein an angle between a slow axis of the retardation layer and an absorption axis of the polarizing film is 40° to 50°. According to claim 1,
The retardation layer has a laminated structure of an alignment-fixed layer of a first liquid crystal compound and an alignment-fixed layer of a second liquid crystal compound,
Re (550) of the alignment hardening layer of the first liquid crystal compound is 200 nm to 300 nm, and the angle between its 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 an angle formed between a slow axis thereof and an absorption axis of the polarizing film is 70° to 80°. According to claim 1,
A polarizing plate with a retardation layer, wherein the ratio (A ₄₇₀ /A ₆₀₀ ) of the orthogonal absorbance A ₄₇₀ at a wavelength of 470 nm and the orthogonal absorbance A ₆₀₀ at a wavelength of 600 nm of the polarizing film is 0.7 to 2.00. According to claim 1,
A polarizing plate with a retardation layer, wherein the orthogonal b-value of the polarizing film is more than -10 and is less than or equal to +10. According to claim 1,
A polarizing plate with a retardation layer, wherein the polarizing film has a single transmittance of 42.5% or more. According to claim 1,
The polarizing plate with a retardation layer further has another retardation layer outside the retardation layer, wherein the refractive index characteristic of the other retardation layer exhibits a relationship of nz > nx = ny. According to claim 1,
The polarizing plate with a retardation layer which further has a conductive layer or an isotropic base material with a conductive layer on the outside of the said retardation layer. A polarizing plate with a retardation layer having a polarizing film, a polarizing plate including a protective layer on at least one side of the polarizing film, and a retardation layer,
The retardation layer is an alignment hardening layer of a liquid crystal compound,
The polarizing film is composed of a polyvinyl alcohol-based resin film containing iodine and has a thickness of 8 μm or less,
The ratio (A 550 /A 210 ) of the orthogonal absorbance A ₅₅₀ at a wavelength _of 550 nm and the orthogonal absorbance A ₂₁₀ at a wavelength of 210 _nm of the polarizing film is 1.4 to 3.5,
The ratio (A 470 /A 600 ₎ of the orthogonal absorbance A ₄₇₀ at a wavelength of 470 nm and the orthogonal absorbance A ₆₀₀ at a wavelength of 600 _nm of the polarizing film is 0.7 to 2.00,
The orthogonal b value of the polarizing film is greater than -10 and less than +10,
A polarizing plate with a retardation layer having a total thickness of 60 μm or less. An image display device comprising the polarizing plate with a retardation layer according to any one of claims 1 to 9. According to claim 10,
An image display device that is an organic electroluminescent display device or an inorganic electroluminescent display device. delete delete

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