JP6797499B2 - Polarizing plate with retardation layer and image display device using it - Google Patents

Description

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

In recent years, image display devices represented by liquid crystal display devices and electroluminescence (EL) display devices (for example, organic EL display devices and inorganic EL display devices) have rapidly become widespread. 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 recently, there is a strong demand for a thinner image display device. As a result, there is an increasing demand for thinner polarizing plates with retardation layers. Further, in recent years, there has been an increasing demand for a curved image display device and / or a bendable or bendable image display device, and further thinning and further flexibility of a polarizing plate and a polarizing plate with a retardation layer are required. ing. For the purpose of reducing the thickness of the polarizing plate with a retardation layer, the protective layer of the polarizing film and the retardation film, which greatly contribute to the thickness, are being thinned. However, when the protective layer and the retardation film are made thinner, the influence of shrinkage of the polarizing film becomes relatively large, which causes problems such as warpage 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 reduce the thickness of the polarizing film as well. However, if the thickness of the polarizing film is simply reduced, the optical characteristics are deteriorated. More specifically, one or both of the degree of polarization and the single transmittance, which are in a trade-off relationship, are reduced to a practically unacceptable degree. As a result, the optical characteristics of the polarizing plate with a retardation layer are also insufficient.

Japanese Patent No. 3325560

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

The polarizing plate with a retardation layer of the present invention has 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 made of a polyvinyl alcohol-based resin film containing a dichroic substance, has a thickness of 8 μm or less, and has a ratio of an orthogonal absorbance A550 at a wavelength of 550 nm to an orthogonal absorbance A210 at a wavelength of 210 nm (A ₅₅₀ / A _210). ) Is 1.4 to 3.5. The retardation layer is an orientation-solidified layer of a liquid crystal compound.
In one embodiment, the polarizing plate with a retardation layer has a unit weight of 6.5 mg / cm ² or less.
In one embodiment, the polarizing plate with a retardation layer has a total thickness of 60 μm or less.
In one embodiment, the retardation layer is a single layer of orientation-solidified layers of liquid crystal compounds, the Re (550) of the retardation layer is 100 nm to 190 nm, and the slow axis of the retardation layer and the above. The angle formed by the polarizing film with the absorption axis is 40 ° to 50 °.
In one embodiment, the retardation layer has a laminated structure of an oriented solidified layer of a first liquid crystal compound and an oriented solidified layer of a second liquid crystal compound; an oriented solidified layer of the first liquid crystal compound. The Re (550) of the second liquid crystal compound is 200 nm to 300 nm, and the angle formed by the slow axis thereof and the absorption axis of the polarizing film is 10 ° to 20 °; the Re (550) of the oriented solidification layer of the second liquid crystal compound. ) Is 100 nm to 190 nm, and the angle formed by the slow axis thereof 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 to 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 simple substance 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 outside the retardation layer, and the refractive index characteristic of the other retardation layer is nz> nx = ny. Show the relationship.
In one embodiment, the polarizing plate with a retardation layer further has a conductive layer or an isotropic base material with a conductive layer outside the retardation layer.
The present invention is also a polarizing plate with a retardation layer, comprising a polarizing film, a polarizing plate including a polarizing film on at least one side of the polarizing film, and a retardation layer, wherein the retardation layer is a liquid crystal. It is an orientation-solidified layer of a compound, and the polarizing film is composed of a polyvinyl alcohol-based resin film containing iodine and has a thickness of 8 μm or less. The polarizing film has an orthogonal absorbance A ₅₅₀ at a wavelength of ₅₅₀ nm and an orthogonal absorbance A at a wavelength of 210 nm. The ratio to ₂₁₀ (A ₅₅₀ / A ₂₁₀ ) is 1.4 to 3.5, and the ratio of the orthogonal absorbance A ₄₇₀ at a wavelength of ₄₇₀ nm to the orthogonal absorbance A ₆₀₀ at a wavelength of 600 nm (A ₄₇₀ / A _600). ) Is 0.7 to 2.00, and the orthogonal b value of the polarizing film is greater than −10 and less than +10, providing a polarizing plate with a retardation layer.
According to another aspect of the present invention, an image display device is provided. This image display device includes the above-mentioned polarizing plate with a retardation layer.
In one embodiment, the image display device is an organic electroluminescence display device or an inorganic electroluminescence display device.

According to the present invention, addition of a halide (typically potassium iodide) to a polyvinyl alcohol (PVA) -based resin, two-stage stretching including aerial auxiliary stretching and water stretching, and drying and shrinkage by a heating roll. By adopting these in combination, it is possible to obtain a polarizing film having extremely excellent optical characteristics while being thin. By using such a polarizing film, it is possible to realize a polarizing plate with a retardation layer which is thin, has excellent handleability, and has excellent optical characteristics.

It is schematic cross-sectional view of the polarizing plate with a retardation layer by one Embodiment of this invention. It is schematic cross-sectional view of the polarizing plate with a retardation layer according to another embodiment of this invention. It is schematic cross-sectional view of the polarizing plate with a retardation layer according to still another embodiment of this invention. It is the schematic which shows an example of the drying shrinkage treatment using a heating roll in the manufacturing method of the polarizing film used for the polarizing plate with a retardation layer of this 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 herein are as follows.
(1) Refractive index (nx, ny, nz)
“Nx” is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow-phase axis direction), and “ny” is the in-plane direction orthogonal to the slow-phase axis (that is, the phase-advance axis direction). Is the refractive index of, and "nz" is the refractive index in the thickness direction.
(2) In-plane phase difference (Re)
“Re (λ)” is an in-plane phase difference measured with light having a wavelength of λ nm at 23 ° C. For example, "Re (550)" is an in-plane phase difference measured with light having a wavelength of 550 nm at 23 ° C. Re (λ) is obtained by the formula: Re (λ) = (nx−ny) × d, where d (nm) is the thickness of the layer (film).
(3) Phase difference in the thickness direction (Rth)
“Rth (λ)” is a phase difference in the thickness direction measured with light having a wavelength of λ nm at 23 ° C. For example, "Rth (550)" is a phase difference in the thickness direction measured with light having a wavelength of 550 nm at 23 ° C. Rth (λ) is obtained by the formula: Rth (λ) = (nx−nz) × d, where d (nm) is the thickness of the layer (film).
(4) Nz coefficient The Nz coefficient is obtained by Nz = Rth / Re.
(5) Angle When referring to an angle herein, the angle includes both clockwise and counterclockwise with respect to the reference direction. Therefore, for example, "45 °" means ± 45 °.

A. Overall Configuration of Polarizing Plate with Difference Layer FIG. 1 is a schematic cross-sectional view of the polarizing plate with a retardation layer according to one embodiment of the present invention. The polarizing plate 100 with a retardation layer of the present embodiment has a polarizing plate 10 and a retardation layer 20. The polarizing plate 10 includes a polarizing film 11, a first protective layer 12 arranged on one side of the polarizing film 11, and a second protective layer 13 arranged on the other side of the polarizing film 11. .. Depending on the purpose, one of the first protective layer 12 and the second protective layer 13 may be omitted. For example, if the retardation layer 20 can also function as a protective layer for the polarizing film 11, the second protective layer 13 may be omitted. In the 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 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.

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 base material 60 with a conductive layer may be provided. Another retardation layer 50 and the conductive layer or the isotropic base material 60 with the conductive layer are typically provided on the outside of the retardation layer 20 (opposite to the polarizing plate 10). Another retardation layer typically exhibits a relationship in which the refractive index characteristic is nz> nz = ny. Another retardation layer 50 and the conductive layer or the isotropic base material 60 with the 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 the conductive layer are typically arbitrary layers provided as needed, and one or both of them may be omitted. For convenience, the retardation layer 20 may be referred to as a first retardation layer, and another retardation layer 50 may be referred to as a second retardation layer. When an isotropic base material with a conductive layer or a conductive layer is provided, the polarizing plate with a retardation layer is a so-called inner in which a touch sensor is incorporated between an image display cell (for example, an organic EL cell) and the polarizing plate. It can be applied to a touch panel type input display device.

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

The above embodiments may be combined as appropriate, and the components of the above embodiments may be modified in the art. For example, the polarizing plate 102 with a retardation layer in FIG. 3 may be provided with a second retardation layer 50 and / or an isotropic base material 60 with a conductive layer or a conductive layer. Further, for example, the configuration in which the isotropic base material 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). You may.

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

The polarizing plate with a retardation layer of the present invention may be single-wafered or elongated. As used herein, the term "long" means an elongated shape having a length sufficiently long with respect to the width, and for example, an elongated shape having a length of 10 times or more, preferably 20 times or more with respect to the width. Including. The elongated 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. Further, it is preferable that a release film is temporarily attached to the surface of the pressure-sensitive adhesive layer until a polarizing plate with a retardation layer is used. By temporarily attaching the release film, the pressure-sensitive adhesive layer can be protected and rolls can be formed.

The total thickness of the polarizing plate with a 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 can be, for example, 28 μm. According to the embodiment of the present invention, it is possible to realize such an extremely thin polarizing plate with a retardation layer. Such a polarizing plate with a retardation layer can have extremely excellent flexibility and bending durability. Such a polarizing plate with a retardation layer can be particularly preferably applied to a curved image display device and / or a bendable or bendable image display device. The total thickness of the polarizing plate with a retardation layer is the total thickness of all the layers constituting the polarizing plate with a retardation layer, except for the pressure-sensitive adhesive layer for bringing the polarizing plate into close contact with an external adherend such as a panel or glass. The total thickness (that is, the total thickness of the polarizing plate with a retardation layer is the peeling that can be temporarily attached to the pressure-sensitive adhesive layer for attaching the polarizing plate with a retardation layer to an adjacent member such as an image display cell and its surface. Does not include film thickness).

The unit weight of the polarizing plate with a retardation layer according to the embodiment of the present invention is, for example, 6.5 mg / cm ² or less, preferably 2.0 mg / cm ^{2 to} 6.0 mg / cm ² , and more preferably 3. ^{.0mg / cm 2 ~5.5mg / cm 2} , more preferably from ^{3.5mg / cm 2 ~5.0mg / cm 2} . When the display panel is thin, the weight of the polarizing plate with a retardation layer may cause the panel to be slightly deformed, resulting in display defects. Polarized light with a retardation layer having a unit weight of 6.5 mg / cm ² or less. According to the plate, such deformation of the panel can be prevented. Further, the polarizing plate with a retardation layer having the above-mentioned unit weight has good handleability even when it is thinned, 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. Polarizing plate 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 to the orthogonal absorbance A210 at a wavelength of 210 nm is 1.4 to 3.5. is there. The polarizing film used in the present invention has a very large ratio (A ₅₅₀ / A ₂₁₀ ) as compared with a normal 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 (having absorption in the ultraviolet region near 210 nm) that do not form a complex with PVA in the polarizing film is very small, and the content ratio of PVA-iodine complex (having absorption in the visible region). Means that is very large. More specifically, the polarizing film, _{PVA-I 5} having an absorption in the vicinity of 600 nm ^- content ratio of the complex is very large, and, _{PVA-I 3} has an absorption in the vicinity of 480 nm ^- content ratio of the complex is much It is maintained without diminishing. Here, since the thickness of the polarizing film means the length of the optical path length, if the thickness of the polarizing film is simply reduced, the optical path length is shortened and the polarization performance is also deteriorated. Since the amount of iodine that can be contained in the polarizing film is limited, it is essential to efficiently utilize the iodine contained in the polarizing film in order to achieve both high polarization performance and thinning of the polarizing film. In other words, by reducing iodine ions that have absorption in the ultraviolet and do not contribute to polarization performance, and by increasing the ratio of PVA-iodine complexes that have absorption in the visible region, both high polarization performance and thinning of the polarizing film can be achieved. Becomes possible. In other words, by increasing the ratio (A ₅₅₀ / A ₂₁₀ ), it is possible to achieve thinness and high optical characteristics. Furthermore, by maintaining the ratio (A ₄₇₀ / A ₆₀₀ ) above a predetermined value, good polarization performance can be realized over the entire visible light range. 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 ) by the conventional technique. The polarizing film used in the above can increase both of these. The ratio (A ₅₅₀ / A ₂₁₀ ) is preferably 1.8 or more, more preferably 2.0 or more, and even more preferably 2.2 or more. The upper limit of the ratio (A ₅₅₀ / A ₂₁₀ ) can 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. is there. The upper limit of the ratio (A ₄₇₀ / A ₆₀₀ ) is, for example, 2.00, preferably 1.33. The orthogonal absorbance is calculated by the following formula based on the orthogonal transmittance Tc measured when determining 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, further preferably 2 μm to 5 μm, particularly preferably 2 μm to 4 μm, and particularly preferably 2 μm to 3 μm.

The polarizing film preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The simple substance transmittance of the polarizing film is preferably 46.0% or less, and more preferably 45.0% or less. On the other hand, the simple substance transmittance is preferably 41.5% or more, more preferably 42.0% or more, and further 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 simple substance transmittance is typically a Y value measured with an ultraviolet-visible spectrophotometer and corrected for luminosity factor. The degree of polarization is typically obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc measured with an ultraviolet-visible spectrophotometer and corrected for luminosity factor.
Polarization degree (%) = {(Tp-Tc) / (Tp + Tc)} ^1/2 × 100

In one embodiment, the transmittance of a thin polarizing film of 8 μm or less is typically a lamination of a polarizing film (refractive index of the surface: 1.53) and a protective film (refractive index: 1.50). The body is measured using an ultraviolet-visible spectrophotometer. Depending on the refractive index of the surface of the polarizing film and / or the refractive index of the surface of the protective film in contact with the air interface, the reflectance at the interface of each layer may change, and as a result, the measured value of transmittance may change. .. Therefore, for example, when a protective film having a refractive index of not 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 transmittance correction value C is expressed by the following equation using the reflectance R ₁ (transmittance 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 of the transmission axis when a protective film having a refractive index of 1.50 is used, n ₁ is the refractive index of the protective film used, and T ₁ is the transmittance of the polarizing film. Is. For example, when a base material having a surface refractive index of 1.53 (cycloolefin film, film with hard coat layer, etc.) is used as the protective film, the correction amount C is about 0.2%. In this case, by adding 0.2% to the transmittance obtained by the measurement, the transmittance when a polarizing film having a surface refractive index of 1.53 is used and a protective film having a refractive index of 1.50 is used. It can be converted into a rate. 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 transmittance of the polarizing film is the correction value C. The effect on the value of is limited. Further, 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 more, and more preferably -5 or more. The orthogonal b value is preferably +10 or less, and more preferably +5 or less. The orthogonal b value indicates the hue when the polarizing film (finally, the polarizing plate with a retardation layer) is arranged in an orthogonal state, and the larger the absolute value of this numerical value, the more the orthogonal hue (black in the image display device). (Display) means that it looks tinted. For example, when the orthogonal b value is as low as −10 or less, the black display appears to be colored blue, 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 that can realize an excellent hue when displaying black. The orthogonal b value can be measured by a spectrophotometer represented by V-7100.

As the polarizing film, any suitable polarizing film can be adopted. The polarizing film can be typically made of a laminate of two or more layers.

Specific examples of the polarizing film obtained by using the laminated body include a polarizing film obtained by using a laminated body of a resin base material and a PVA-based resin layer coated and formed on the resin base material. The polarizing film obtained by using the laminate of the resin base material and the PVA-based resin layer coated and formed on the resin base material is, for example, a resin base material obtained by applying a PVA-based resin solution to the resin base material and drying it. It is produced by forming a PVA-based resin layer on the PVA-based resin layer to obtain a laminate of a resin base material and a PVA-based resin layer; stretching and dyeing the laminate to form a PVA-based resin layer as a polarizing film. obtain. In the present embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution for stretching. Further, stretching may further include, if necessary, stretching the laminate in the air at a high temperature (eg, 95 ° C. or higher) prior to stretching in boric acid aqueous solution. The obtained laminate of the resin base material / polarizing film may be used as it is (that is, the resin base material may be used as the protective layer of the polarizing film), or the resin base material is peeled off from the laminate of the resin base material / polarizing film. Then, an arbitrary appropriate protective layer according to the purpose may be laminated on the peeled surface. Details of the method for producing such a polarizing film are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. 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 base material to form a laminate. Then, the laminated body is subjected to an aerial auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment of shrinking by 2% or more in the width direction by heating while transporting in the longitudinal direction in this order. including. This can provide a polarizing film having excellent optical properties, having a thickness of 8 μm or less and a ratio (A ₅₅₀ / A ₂₁₀ ) of 1.4 to 3.5. That is, by introducing the auxiliary stretching, even when PVA is applied on the thermoplastic resin, the crystallinity of PVA can be enhanced, and high optical characteristics can be achieved. At the same time, by increasing the orientation of PVA in advance, it is possible to prevent problems such as deterioration of PVA orientation and dissolution when immersed in water in a subsequent dyeing step or stretching step, resulting in high optical characteristics. Will be possible to achieve. Further, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This makes it possible to improve the optical characteristics of the polarizing film obtained through a treatment step of immersing the laminate in a liquid, such as a dyeing treatment and a stretching treatment in water. Further, the optical characteristics can be improved by shrinking the laminated body in the width direction by the 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 for the polarizing film. Specific examples of the material that is 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 polysulfone-based. , Polystyrene-based, polycarbonate-based, polyolefin-based, (meth) acrylic-based, acetate-based transparent resins and the like. Further, thermosetting resins such as (meth) acrylic, urethane, (meth) acrylic urethane, epoxy, and silicone, or ultraviolet curable resins can also be mentioned. In addition to this, for example, glassy polymers such as siloxane-based polymers can also be mentioned. Further, the polymer film described in JP-A-2001-343529 (WO01 / 37007) can also be used. As the material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain. Can be used, and examples thereof include a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile / styrene copolymer. The polymer film can be, for example, an extruded product of the above resin composition.

As will be described later, the polarizing plate with a retardation layer of the present invention is typically arranged on the visible side of an image display device, and the first protective layer 12 is typically arranged on the visible side. Therefore, the first protective layer 12 may be subjected to surface treatment such as hard coat treatment, antireflection treatment, anti-sticking treatment, and anti-glare treatment, if necessary. Further / or, if necessary, the first protective layer 12 is provided with a process for improving visibility when visually recognizing through polarized sunglasses (typically, a (elliptical) circular polarization function is provided. (Giving an ultra-high phase difference) may be applied. By performing such processing, excellent visibility can be realized even when the display screen is visually recognized through a polarized lens such as polarized sunglasses. Therefore, the polarizing plate with a retardation layer can be suitably applied to an image display device that can be used outdoors.

The thickness of the first protective layer is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, and even more preferably 10 μm to 30 μm. When the surface treatment is applied, the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.

The second protective layer 13 is preferably optically isotropic in one embodiment. In the present specification, "optically isotropic" means that the in-plane retardation Re (550) is 0 nm to 10 nm and the thickness direction retardation Rth (550) is -10 nm to +10 nm. Say. The second protective layer 13 may, in one embodiment, 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, and even more preferably 10 μm to 30 μm. From the viewpoint of thinning and weight reduction, the second protective layer may be omitted preferably.

B-3. Method for manufacturing a polarizing film The polarizing film is, for example, a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin base material. To form a laminate, and to dry the laminate by aerial auxiliary stretching treatment, dyeing treatment, underwater stretching treatment, and heating while transporting in the longitudinal direction to shrink by 2% or more in the width direction. It can be produced by a method including shrinking treatment and applying in this order. The content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably carried out 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 laminate by the drying shrinkage treatment is preferably 2% or more. According to such a manufacturing method, the polarizing film described in the above item B-1 can be obtained. In particular, by preparing a laminate containing a PVA-based resin layer containing a halide, stretching the laminate to multi-step stretching including aerial auxiliary stretching and underwater stretching, and heating the stretched laminate with a heating roll. , A polarizing film having excellent optical properties (typically, simple substance transmittance and ratio (A ₅₅₀ / A ₂₁₀ )) can be obtained.

B-3-1. Preparation of Laminate As a method for preparing a laminate of a thermoplastic resin base material and a PVA-based resin layer, any appropriate method can be adopted. Preferably, a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin base material and dried to form a PVA-based resin layer on the thermoplastic resin base material. 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.

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

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

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

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

The thermoplastic resin base material preferably has a water absorption rate of 0.2% or more, more preferably 0.3% or more. The thermoplastic resin base material absorbs water, and the water can act as a plasticizer to plasticize. As a result, the stretching stress can be significantly reduced and the drawing can be performed at a high magnification. On the other hand, the water absorption rate of the thermoplastic resin base material is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin base material, it is possible to prevent problems such as deterioration of the appearance of the obtained polarizing film due to a significant decrease in dimensional stability of the thermoplastic resin base material during manufacturing. Further, it is possible to prevent the base material from breaking during stretching in water and the PVA-based resin layer from being peeled off from the thermoplastic resin base material. The water absorption rate of the thermoplastic resin base material can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption rate is a value obtained according to JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin base material is preferably 120 ° C. or lower. By using such a thermoplastic resin base material, it is possible to sufficiently secure the stretchability of the laminated body while suppressing the crystallization of the PVA-based resin layer. Further, in consideration of plasticizing the thermoplastic resin base material with water and satisfactorily stretching in water, the temperature is more preferably 100 ° C. or lower, more preferably 90 ° C. or lower. On the other hand, the glass transition temperature of the thermoplastic resin base material is preferably 60 ° C. or higher. By using such a thermoplastic resin base material, the thermoplastic resin base material is deformed (for example, unevenness, tarmi, wrinkles, etc. are generated) when the coating liquid containing the PVA-based resin is applied and dried. It is possible to satisfactorily produce a laminated body by preventing the above-mentioned problems. Further, the PVA-based resin layer can be well stretched at a suitable temperature (for example, about 60 ° C.). The glass transition temperature of the thermoplastic resin base material can be adjusted by, for example, heating with a crystallization material in which a modifying group is introduced into the constituent material. The glass transition temperature (Tg) is a value obtained according to JIS K 7121.

Any suitable thermoplastic resin can be adopted as the constituent material of the thermoplastic resin base material. Examples of the thermoplastic resin include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Can be mentioned. Among these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferable.

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

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

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

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

Any suitable method can be adopted as the method for stretching the thermoplastic resin base material. Specifically, it may be fixed-end stretching or free-end stretching. The stretching method may be a dry method or a wet method. The stretching of the thermoplastic resin base material may be carried out in one step or in multiple steps. When performed in multiple stages, the above-mentioned draw ratio is the product of the draw ratios 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 in which the halide and the PVA-based resin are dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Of these, water is preferred. The PVA-based resin concentration of the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film that adheres to the thermoplastic resin base material can be formed. The content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

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

As the PVA-based resin, any suitable resin can be adopted. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymers can be mentioned. Polyvinyl alcohol is obtained by saponification of polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying the 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. By using a PVA-based resin having such a degree of saponification, a polarizing film having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.

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

As the halide, any suitable halide can be adopted. For example, iodide and sodium chloride. Iodides include, for example, potassium iodide, sodium iodide, and lithium iodide. Of these, potassium iodide is preferred.

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

Generally, when the PVA-based resin layer is stretched, the orientation of the polyvinyl alcohol molecules in the PVA-based resin is increased. However, when the stretched PVA-based resin layer is immersed in a liquid containing water, the polyvinyl alcohol molecules become more oriented. The orientation may be disturbed and the orientation may decrease. In particular, when the laminate of the thermoplastic resin base material and the PVA-based resin layer is stretched in boric acid water, the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin base material. In the case of stretching, the tendency of the degree of orientation to decrease is remarkable. For example, while stretching a PVA film alone in boric acid water is generally performed at 60 ° C., stretching of a laminate of A-PET (thermoplastic resin base material) and a PVA-based resin layer is performed. It is carried out at a high temperature of about 70 ° C., and in this case, the orientation of PVA at the initial stage of stretching may decrease before it is increased by stretching in water. On the other hand, a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin base material is prepared, and the laminate is stretched at a high temperature (auxiliary stretching) in air before being stretched in boric acid water. , Crystallization of the PVA-based resin in the PVA-based resin layer of the laminated body after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This makes it possible to improve the optical characteristics of the polarizing film obtained through a treatment step of immersing the laminate in a liquid, such as a dyeing treatment and a stretching treatment in water.

B-3-2. Aerial Auxiliary Stretching Treatment In particular, in order to obtain high optical properties, a two-stage stretching method that combines dry stretching (auxiliary stretching) and boric acid water stretching is selected. By introducing the auxiliary stretching as in the two-stage stretching, the thermoplastic resin base material can be stretched while suppressing the crystallization of the thermoplastic resin base material, and the thermoplastic resin base material is excessively crystallized in the subsequent drawing in boric acid in water. This solves the problem that the stretchability is lowered, and the laminated body can be stretched at a higher magnification. Furthermore, when the PVA-based resin is applied on the thermoplastic resin base material, it is compared with the case where the PVA-based resin is applied on a normal metal drum in order to suppress the influence of the glass transition temperature of the thermoplastic resin base material. Therefore, it is necessary to lower the coating temperature, and as a result, the crystallization of the PVA-based resin becomes relatively low, which may cause a problem that sufficient optical characteristics cannot be obtained. On the other hand, by introducing the auxiliary stretching, even when the PVA-based resin is coated on the thermoplastic resin, the crystallinity of the PVA-based resin can be enhanced, and high optical characteristics can be achieved. Become. At the same time, by increasing the orientation of the PVA resin in advance, it is possible to prevent problems such as deterioration and dissolution of the orientation of the PVA resin when immersed in water in a subsequent dyeing step or stretching step. , It becomes possible to achieve high optical characteristics.

The stretching method of the aerial auxiliary stretching may be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). Good, but in order to obtain high optical properties, free end stretching can be positively adopted. In one embodiment, the aerial stretching treatment includes a heating roll stretching step of stretching the laminated body in the longitudinal direction due to a difference in peripheral speed between the heating rolls. The aerial stretching treatment typically includes a zone stretching step and a heating roll stretching step. The order of the zone stretching step and the heating roll stretching step is not limited, and the zone stretching step may be performed first, or the heating roll stretching step may be performed first. The zone stretching step may be omitted. In one embodiment, the zone stretching step and the heating roll stretching step are performed in this order. Further, in another embodiment, in the tenter stretching machine, the film is stretched by grasping the end portion of the film and widening the distance between the tenters in the flow direction (the widening of the distance between the tenters is the stretching ratio). At this time, the distance of the tenter in the width direction (perpendicular to the flow direction) is set to approach arbitrarily. Preferably, it can be set to be closer to the free end stretch with respect to the stretch ratio in the flow direction. In the case of free end stretching, the shrinkage rate in the width direction = (1 / stretching ratio) ^1/2 .

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

The draw ratio in the aerial auxiliary stretching is preferably 2.0 to 3.5 times. The maximum draw ratio when the aerial auxiliary stretching and the underwater stretching are combined is preferably 5.0 times or more, more preferably 5.5 times or more, still more preferably 6.0 times, the original length of the laminated body. That is all. In the present specification, the "maximum draw ratio" means the draw ratio immediately before the laminate breaks, and separately confirms the draw ratio at which the laminate breaks, and means a value 0.2 lower than that value.

The stretching temperature of the aerial auxiliary stretching can be set to an arbitrary appropriate value depending on the forming material of the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably the glass transition temperature (Tg) or more of the thermoplastic resin base material, more preferably the glass transition temperature (Tg) of the thermoplastic resin base material (Tg) + 10 ° C. or higher, and particularly preferably Tg + 15 ° C. or higher. On the other hand, the upper limit of the stretching temperature is preferably 170 ° C. By stretching at such a temperature, it is possible to suppress the rapid progress of crystallization of the PVA-based resin and suppress defects due to the crystallization (for example, hindering the orientation of the PVA-based resin layer due to stretching). it can. The crystallization index of the PVA-based resin after the aerial auxiliary stretching is preferably 1.3 to 1.8, and 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, the measurement is carried out using polarized light as the 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 spectra.
Crystallization index _{= (I} C _/ I R)
However,
I _C: intensity _{I R} of 1141cm ^-1 when measured by the incident measurement light: the intensity of 1440cm ^-1 when measured by the incident measurement light.

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

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

The staining solution is preferably an aqueous iodine solution. The blending amount of iodine is preferably 0.05 parts by weight to 0.5 parts by weight with respect to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add iodide to the aqueous iodine solution. Examples of 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. And so on. Of these, potassium iodide is preferred. The blending amount of iodide is preferably 0.1 parts by weight to 10 parts by weight, more preferably 0.3 parts by weight to 5 parts by weight, based on 100 parts by weight of water. The liquid temperature at the time of dyeing the dyeing liquid is preferably 20 ° C. to 50 ° C. in order to suppress the dissolution of the PVA-based resin. When the PVA-based resin layer is immersed in the dyeing solution, the immersion time is preferably 5 seconds to 5 minutes, more preferably 30 seconds to 90 seconds in order to secure the transmittance of the PVA-based resin layer.

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

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

B-3-5. Crosslinking treatment If necessary, a crosslinking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The cross-linking treatment is typically performed by immersing a PVA-based resin layer in an aqueous boric acid solution. By performing the cross-linking treatment, water resistance can be imparted to the PVA-based resin layer, and the orientation of PVA can be prevented from being lowered when immersed in high-temperature water by subsequent stretching in water. The concentration of the boric acid aqueous solution is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Further, when the cross-linking treatment is performed after the dyeing treatment, it is preferable to further add iodide. By blending iodide, elution of iodine adsorbed on 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 cross-linked 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, the thermoplastic resin base material or the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically about 80 ° C.), and the PVA-based resin layer is crystallized. Can be stretched at a high magnification while suppressing the above. As a result, a polarizing film having excellent optical characteristics can be produced.

Any suitable method can be adopted as the method for stretching the laminate. Specifically, it may be fixed-end stretching or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). Preferably, free end stretching is selected. The stretching of the laminate may be carried out in one step or in multiple steps. When performed in multiple stages, the draw ratio (maximum draw ratio) of the laminated body described later is the product of the draw ratios of each stage.

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

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

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

The stretching temperature (liquid temperature of the stretching bath) is preferably 40 ° C. to 85 ° C., more preferably 60 ° C. to 75 ° C. At such a temperature, the PVA-based resin layer can be stretched at a high magnification while suppressing dissolution. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin base material is preferably 60 ° C. or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40 ° C., it may not be stretched well even when the plasticization of the thermoplastic resin base material by water is taken into consideration. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and there is a possibility that excellent optical characteristics cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

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

B-3-7. Drying shrinkage treatment The drying shrinkage treatment may be carried out by heating the entire zone by zone heating, or by heating the transport roll (using a so-called heating roll) (heating roll drying method). Preferably, both are used. By drying with a heating roll, it is possible to efficiently suppress the heating curl of the laminate and produce a polarizing film having an excellent appearance. Specifically, by drying the laminate along the heating roll, the crystallization of the thermoplastic resin base material can be efficiently promoted and the crystallinity can be increased, which is relatively low. Even at the drying temperature, the crystallinity of the thermoplastic resin base material can be satisfactorily increased. As a result, the rigidity of the thermoplastic resin base material is increased so that it can withstand the shrinkage of the PVA-based resin layer due to drying, and curling is suppressed. Further, by using the heating roll, the laminated body can be dried while being maintained in a flat state, so that not only curling but also wrinkles can be suppressed. At this time, the laminated body can be improved in optical characteristics by shrinking in the width direction by a drying shrinkage treatment. This is because the orientation of PVA and the PVA / iodine complex can be effectively enhanced. The shrinkage ratio in the width direction of the laminate by the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roll, the laminated body can be continuously contracted in the width direction while being conveyed, and high productivity can be realized.

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

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

The heating roll may be provided in a heating furnace (for example, an oven) or in a normal production line (in a room temperature environment). Preferably, it is provided in a heating furnace provided with a blowing means. By using the drying with a heating roll and the hot air drying together, it is possible to suppress a steep temperature change between the heating rolls, and it is possible to easily control the shrinkage in the width direction. The temperature of hot air drying is preferably 30 ° C to 100 ° C. The hot air drying time is preferably 1 second to 300 seconds. The wind speed of hot air is preferably about 10 m / s to 30 m / s. The wind speed is the wind speed in the heating furnace and can be measured by a mini-vane type digital anemometer.

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

C. First Phase Difference Layer The first retardation layer 20 is an orientation-solidified layer of a liquid crystal compound as described above. By using the liquid crystal compound, the difference between nx and ny of the obtained retardation layer can be remarkably increased as compared with the non-liquid crystal material, so that the thickness of the retardation layer for obtaining a desired in-plane retardation can be obtained. Can be made much smaller. As a result, it is possible to further reduce the thickness and weight of the polarizing plate with a retardation layer. As used herein, the term "oriented solidified layer" refers to a layer in which a liquid crystal compound is oriented in a predetermined direction within the layer and the oriented state is fixed. The "oriented solidified layer" is a concept including an oriented cured layer obtained by curing a liquid crystal monomer as described later. In the present embodiment, the rod-shaped liquid crystal compounds are typically oriented in a state of being aligned in the slow-phase axial 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 liquid crystal expression mechanism 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 orientation state of the liquid crystal monomer can be fixed by polymerizing or cross-linking (that is, curing) the liquid crystal monomer. After the liquid crystal monomers are oriented, for example, if the liquid crystal monomers are polymerized or crosslinked with each other, the oriented state can be fixed. Here, the polymer is formed by polymerization, and the three-dimensional network structure is formed by cross-linking, but these are non-liquid crystal. Therefore, the formed first retardation layer does not undergo a transition to a liquid crystal phase, a glass phase, or a crystal phase due to a temperature change peculiar to a liquid crystal compound, for example. As a result, the first retardation layer becomes an extremely stable retardation layer that is not affected by temperature changes.

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

As the liquid crystal monomer, any suitable liquid crystal monomer can be adopted. For example, the polymerizable mesogen compounds described in Special Tables 2002-533742 (WO00 / 37585), EP358208 (US5211877), EP66137 (US4388453), WO93 / 22397, EP02671712, DE19504224, DE4408171, GB2280445 and the like can be used. Specific examples of such polymerizable mesogen compounds 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 treatment of the liquid crystal compound is applied to the surface of a predetermined base material, and a coating liquid containing the liquid crystal compound is applied to the surface to orient the liquid crystal compound in a direction corresponding to the orientation treatment. It can be formed by fixing the orientation state. In one embodiment, the substrate is any suitable resin film and the oriented solidified layer formed on the substrate can be transferred to the surface of the polarizing plate 10. In another embodiment, the substrate can be a second protective layer 13. In this case, the transfer step is omitted, and the stacking can be performed continuously by roll-to-roll from the formation of the oriented solidification layer (first retardation layer), so that the productivity is further improved.

As the orientation treatment, any appropriate orientation treatment can be adopted. Specific examples thereof include mechanical orientation treatment, physical orientation treatment, and chemical orientation treatment. Specific examples of the mechanical orientation treatment include a rubbing treatment and a stretching treatment. Specific examples of the physical orientation treatment include magnetic field orientation treatment and electric field orientation treatment. Specific examples of the chemical alignment treatment include an orthorhombic deposition method and a photoalignment treatment. As the treatment conditions for various orientation treatments, any appropriate conditions may be adopted depending on the purpose.

The orientation of the liquid crystal compound is performed by treating at a temperature indicating the liquid crystal phase according to the type of the liquid crystal compound. By performing such temperature treatment, the liquid crystal compound takes a liquid crystal state, and the liquid crystal compound is oriented according to the orientation treatment direction of the substrate surface.

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

Specific examples of the liquid crystal compound and details of the method for forming the oriented solidified layer are described in JP-A-2006-163343. The description of this publication is incorporated herein by reference.

Another example of the oriented solidified layer is a form in which the discotic liquid crystal compound is oriented in any of vertical orientation, hybrid orientation, and inclined orientation. In the discotic liquid crystal compound, typically, the disk surface of the discotic liquid crystal compound is oriented substantially perpendicular to the film surface of the first retardation layer. When the discotic liquid crystal compound is substantially vertical, the average value of the angles formed by the film surface and the disk surface of the discotic liquid crystal compound is preferably 70 ° to 90 °, more preferably 80 ° to 90 °. , More preferably it means 85 ° to 90 °. Discotic liquid crystal compounds generally have cyclic mother nuclei such as benzene, 1,3,5-triazine, and calix arene in the center of the molecule, and have linear alkyl groups, alkoxy groups, and substituted benzoyls. A liquid crystal compound having a disk-like molecular structure in which oxy groups and the like are radially substituted as its side chains. As a typical example of a discotic liquid crystal, C.I. Research report by Destrade et al., Mol. Crystal. Liq. Crystal. Benzene derivatives, triphenylene derivatives, tolucene derivatives, phthalocyanine derivatives, and B.I., described in Vol. 71, p. 111 (1981). Research report by Kohne et al., Angew. Chem. Cyclohexane derivatives described in Volume 96, p. 70 (1984), and J. Mol. M. Research report by Lehn et al., J. Mol. Chem. Soc. Chem. Commun. , 1794 (1985), J. Mol. Research report by Zhang et al., J. Mol. Am. Chem. Soc. Examples thereof include azacrown-based and phenylacetylene-based macrocycles described in Vol. 116, p. 2655 (1994). Further specific examples of the discotic liquid crystal compound include the compounds described in JP-A-2006-133652, JP-A-2007-108732, and JP-A-2010-2404038. The above documents and publications are incorporated herein by reference.

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

The first retardation layer typically shows a relationship in which the refractive index characteristic is nx> ny = nz. The first retardation layer is typically provided to impart antireflection characteristics to the polarizing plate, and functions as a λ / 4 plate when the first retardation layer is a single layer of an orientation solidification layer. Can be done. 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, and even more preferably 130 nm to 160 nm. Here, "ny = nz" includes not only the case where ny and nz are completely equal, but also the case where they are substantially equal. Therefore, ny> nz or ny <nz may occur 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, and more preferably 0.9 to 1.3. By satisfying such a relationship, a very excellent reflected hue can be achieved when the obtained polarizing plate with a retardation layer is used in an image display device.

The first retardation layer may exhibit a reverse dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light, and a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light. It may be shown, or may show a flat wavelength dispersion characteristic in which the phase difference value hardly changes with the wavelength of the measurement light. In one embodiment, the first retardation layer exhibits inverse dispersion wavelength characteristics. In this case, Re (450) / Re (550) of the retardation layer is preferably 0.8 or more and less than 1, and 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 formed by 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 even more preferably about. It is 45 °. If the angle θ is in such a range, by using the λ / 4 plate as the first retardation layer as described above, very excellent circular polarization characteristics (as a result, very excellent antireflection characteristics). A polarizing plate with a retardation layer having the above can be obtained.

In another embodiment, the first retardation layer 20 may have a laminated structure of a first orientation solidification layer 21 and a second orientation solidification layer 22 as shown in FIG. In this case, either one of the first oriented solidified layer 21 and the second oriented solidified layer 22 may function as a λ / 4 plate, and the other may function as a λ / 2 plate. Therefore, the thicknesses of the first oriented solidified layer 21 and the second oriented solidified layer 22 can be adjusted so as to obtain a desired in-plane phase difference between the λ / 4 plate or the λ / 2 plate. For example, when the first oriented solidified layer 21 functions as a λ / 2 plate and the second oriented solidified layer 22 functions as a λ / 4 plate, the thickness of the first oriented solidified layer 21 is, for example, 2.0 μm or more. It is 3.0 μm, and the thickness of the second oriented solidified layer 22 is, for example, 1.0 μm to 2.0 μm. In this case, the in-plane retardation Re (550) of the first oriented solidified layer is preferably 200 nm to 300 nm, more preferably 230 nm to 290 nm, and further preferably 250 nm to 280 nm. The in-plane retardation Re (550) of the second oriented solidified layer is as described above for the single oriented solidified layer. The angle formed by the slow axis of the first oriented solidification layer and the absorption axis of the polarizing film is preferably 10 ° to 20 °, more preferably 12 ° to 18 °, and even more preferably about 15 °. is there. The angle formed by the slow axis of the second oriented solidification layer and the absorption axis of the polarizing film is preferably 70 ° to 80 °, more preferably 72 ° to 78 °, and even more preferably about 75 °. is there. With such a configuration, it is possible to obtain characteristics close to the ideal reverse wavelength dispersion characteristic, and as a result, it is possible to realize extremely excellent antireflection characteristics. The liquid crystal compounds constituting the first oriented solidified layer and the second oriented solidified layer, the method for forming the first oriented solidified layer and the second oriented solidified layer, the optical properties, and the like are described above with respect to the single oriented solidified layer. As explained in.

D. Second Phase Difference Layer The second phase difference layer may be a so-called positive C plate in which the refractive index characteristic shows a relationship of nz> nz = ny as described above. By using the positive C plate as the second retardation layer, it is possible to satisfactorily prevent reflection in the oblique direction, and it is possible to widen the viewing angle of the antireflection function. In this case, the retardation Rth (550) in the thickness direction of the second retardation layer is preferably −50 nm to −300 nm, more preferably −70 nm to −250 nm, still more preferably −90 nm to −200 nm, and particularly preferably. It is -100 nm to -180 nm. Here, "nx = ny" includes not only the case where nx and ny are exactly equal, but also the case where nx and ny are substantially equal. That is, the in-plane retardation Re (550) of the second retardation layer can be less than 10 nm.

The second retardation layer with a refractive index characteristic of nz> nx = ny can be formed of any suitable material. The second retardation layer preferably consists of a film containing a liquid crystal material fixed in a homeotropic orientation. The liquid crystal material (liquid crystal compound) that can be homeotropically oriented 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 compounds described in [0020] to [0028] of JP-A-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, and even more preferably 0.5 μm to 5 μm.

E. Conductive layer or isotropic base material with conductive layer The conductive layer is made of any suitable base material by any suitable film forming method (for example, vacuum deposition method, sputtering method, CVD method, ion plating method, spray method, etc.). It can be formed by forming a metal oxide film on top of it. 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. Of these, indium-tin composite oxide (ITO) is preferable.

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.

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

As the optically isotropic base material (isotropic base material), any suitable isotropic base material can be adopted. Examples of the material constituting the isotropic base material include a material having a resin having no conjugate system such as a norbornene resin and an olefin resin as a main skeleton, and an acrylic resin having a cyclic structure such as a lactone ring and a glutarimide ring. Examples include the material contained in the main chain. When such a material is used, when an isotropic base material is formed, the expression of the phase difference due to the orientation of the molecular chains can be suppressed to be small. The thickness of the isotropic substrate is preferably 50 μm or less, more preferably 35 μm or less. The lower limit of the thickness of the isotropic substrate is, for example, 20 μm.

The conductive layer and / or the conductive layer of the isotropic base material with the conductive layer can be patterned, if necessary. By patterning, a conductive portion and an insulating portion can be formed. As a result, electrodes can be formed. The electrode can function as a touch sensor electrode that senses contact with the touch panel. As the patterning method, any suitable method can be adopted. 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 according to the above items A to E can be applied to an image display device. Therefore, the present invention includes an image display device using such a polarizing plate with a retardation layer. Typical examples of the image display device include a liquid crystal display device and an electroluminescence (EL) display device (for example, an organic EL display device and an inorganic EL display device). The image display device according to the embodiment of the present invention includes the polarizing plate with a retardation layer according to the above items A to E on the visible side thereof. The polarizing plate with a retardation layer is laminated so that the retardation layer is on the image display cell (for example, liquid crystal cell, organic EL cell, inorganic EL cell) side (so that the polarizing film is on the visual recognition side). In one embodiment, the image display device has a curved shape (substantially a curved display screen) and / or is bendable or bendable. In such an image display device, the effect of the polarizing plate with a retardation layer of the present invention becomes remarkable.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows. Unless otherwise specified, "parts" and "%" in Examples and Comparative Examples are based on weight.
(1) Thickness The thickness of 10 μm or less was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name “MCPD-3000”). The thickness exceeding 10 μm was measured using a digital micrometer (manufactured by Anritsu, product name “KC-351C”).
(2) Single-unit transmittance and orthogonal absorbance For the polarizing plates (protective film / polarizing film) of the examples and comparative examples, the single-unit transmittance Ts measured using an ultraviolet-visible spectrophotometer (V-7100 manufactured by JASCO Corporation), The parallel transmittance Tp and the orthogonal transmittance Tc were defined as Ts, Tp and Tc of the polarizing film, respectively. These Ts, Tp, and Tc are Y values measured by the JIS Z8701 two-degree visual field (C light source) and corrected for luminosity factor. 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.
Moreover, the orthogonal absorbance was determined by the following formula using the Tc measured at each wavelength.
Orthogonal absorbance = log10 (100 / Tc)
The orthogonal absorbance A ₂₁₀ was obtained from the orthogonal transmittance Tc ₂₁₀ having a measurement wavelength of 210 nm, and the orthogonal absorbance A ₅₅₀ was obtained from the orthogonal transmittance Tc ₅₅₀ having a measurement wavelength of 550 nm, respectively, using UV-3150 manufactured by Shimadzu Corporation. Further, the orthogonal absorbance A ₄₇₀ was obtained from the orthogonal transmittance Tc ₄₇₀ having a measurement wavelength of 470 nm, and the orthogonal absorbance A ₆₀₀ was obtained from the orthogonal transmittance Tc ₆₀₀ having a measurement wavelength of 600 nm, respectively, using V-7100 manufactured by Nippon Kogaku Co., Ltd.
For A ₄₇₀ and A ₆₀₀ , the same measurement can be performed with LPF-200 manufactured by Otsuka Electronics Co., Ltd.
(3) Orthogonal b value The polarizing plate used in the Examples and Comparative Examples was measured using an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product name "V7100"), and the hue in the cross-nicol state was determined. .. The lower the orthogonal b value (negative value and larger absolute value), the more the hue is blue rather than neutral.
(4) Warpage The polarizing plates with retardation layers obtained in Examples and Comparative Examples were cut out to a size of 110 mm × 60 mm. At this time, the polarizing film was cut out so that the absorption axis direction was the long side direction. The cut-out polarizing plate with a retardation layer was attached to a glass plate having a size of 120 mm × 70 mm and a thickness of 0.2 mm via an adhesive to prepare a test sample. The test sample was put into a heating oven maintained at 85 ° C. for 24 hours, and the amount of warpage after taking out was measured. When the test sample was allowed to stand on a flat surface with the glass plate facing down, the height of the highest portion from the flat surface was defined as the amount of warpage.
(5) Unit weight The polarizing plate with a retardation layer obtained in Examples and Comparative Examples is cut out to a predetermined size, and the weight (mg) is divided by the area (cm ² ) to obtain a polarizing plate with a retardation layer. The weight per unit area (unit weight) was calculated.
(6) Bending resistance The polarizing plates with retardation layers obtained in Examples and Comparative Examples were cut out to a size of 50 mm × 100 mm. At this time, the polarizing film was cut out so that the absorption axis direction was the short side direction. Using a folding resistance tester with a constant temperature and humidity chamber (CL09 type-D01 manufactured by YUASA), the cut polarizing plate with a retardation layer was subjected to a bending test under the condition of 20 ° C. and 50% RH. Specifically, the polarizing plate with a 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 cracks, peeling, film breakage, etc. that cause display defects occur. The number of bends until the occurrence was measured and evaluated according to the following criteria (folding diameter: 2 mmφ).
<Evaluation criteria>
Less than 10,000 times: Bad 10,000 times or more and less than 30,000 times: Good 30,000 times or more: Excellent

[Example 1]
1. 1. Preparation of Polarizing Film An amorphous isophthal copolymer polyethylene terephthalate film (thickness: 100 μm) having a long shape, a water absorption of 0.75%, and a Tg of about 75 ° C. was used as the thermoplastic resin base material. One side of the resin base material was corona-treated.
100 weight of PVA-based resin in which polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer Z410") are mixed at a ratio of 9: A PVA aqueous solution (coating solution) was prepared by dissolving 13 parts by weight of potassium iodide in water.
The PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60 ° C. to form a PVA-based resin layer having a thickness of 13 μm to prepare a laminate.
The obtained laminate was uniaxially stretched at the free end 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130 ° C. (aerial auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath at a liquid temperature of 40 ° C. (an aqueous boric acid solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).
Next, the finally obtained polarizing film is placed in a dyeing bath having a liquid temperature of 30 ° C. (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water). Immersion was carried out for 60 seconds while adjusting the concentration so that the simple substance transmittance (Ts) and the ratio (A ₅₅₀ / A ₂₁₀ ) became desired values (dyeing treatment).
Next, it was immersed in a cross-linked bath at a liquid temperature of 40 ° C. (an aqueous boric acid solution obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds. (Crossing treatment).
Then, while immersing the laminate in a boric acid aqueous solution (boric acid concentration 4.0% by weight) at a liquid temperature of 70 ° C., the total draw ratio is 5.5 in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds. Uniaxial stretching was performed so as to double (underwater stretching treatment).
Then, the laminate was immersed in a washing bath at a liquid temperature of 20 ° C. (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment).
Then, while drying in an oven kept at 90 ° C., it was brought into contact with a heating roll made of SUS whose surface temperature was kept at 75 ° C. for about 2 seconds (dry shrinkage treatment). The shrinkage rate in the width direction of the laminate 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 base material.

2. 2. Fabrication of Polarizing Plate Acrylic film (surface refractive index 1.50, 40 μm) is applied as a protective layer on the surface of the polarizing film obtained above (the surface opposite to the resin substrate), and an ultraviolet curable adhesive is applied. It was pasted together. Specifically, the curable adhesive was coated so as to have a total thickness of 1.0 μm, and bonded using a roll machine. Then, UV light was irradiated from the protective layer side to cure the adhesive. Next, after slitting both ends, the resin base material was peeled off to obtain a long polarizing plate (width: 1300 mm) having a protective layer / polarizing film structure. The simple substance transmittance of the polarizing plate (substantially the polarizing film) is 43.5%, A ₅₅₀ / A ₂₁₀ is 1.50, A ₄₇₀ / A ₆₀₀ is 0.87, and the orthogonal b value is Was -3.00.

3. 3. Preparation of First Oriented Solidified Layer and Second Oriented Solidified Layer Constituting the Phase Difference Layer With 10 g of polymerizable liquid crystal (manufactured by BASF: trade name "Pariocolor LC242", represented by the following formula) showing a nematic liquid crystal phase. , 3 g of a photopolymerization initiator (manufactured by BASF: trade name “Irgacure 907”) for the polymerizable liquid crystal compound 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 with a rubbing cloth and subjected to an orientation treatment. The direction of the alignment treatment was set to be 15 ° when viewed from the visual side with respect to the direction of the absorption axis of the polarizing film when the polarizing film was attached to the polarizing plate. The liquid crystal coating liquid was applied to the alignment-treated surface with a bar coater, and the liquid crystal compound was oriented by heating and drying at 90 ° C. for 2 minutes. The liquid crystal layer thus formed 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 oriented solidified layer A on the PET film. The thickness of the liquid crystal oriented solidified layer A was 2.5 μm, and the in-plane retardation Re (550) was 270 nm. Further, the liquid crystal oriented solidified layer A had a refractive index distribution of nx> ny = nz.
On the PET film in the same manner as above, except that the coating thickness was changed and the orientation treatment direction was set to be 75 ° when viewed from the visual side with respect to the direction of the absorption axis of the polarizing film. A liquid crystal oriented solidified layer B was formed. The thickness of the liquid crystal oriented solidified layer B was 1.5 μm, and the in-plane retardation Re (550) was 140 nm. Further, the liquid crystal oriented solidified layer B had a refractive index distribution of nx> ny = nz.

4. Fabrication of polarizing plate with retardation layer 2. On the surface of the polarizing film of the polarizing plate obtained in 3. above. The liquid crystal oriented solidified layer A and the liquid crystal oriented solidified layer B obtained in the above were transferred in this order. At this time, the angle between the absorption axis of the polarizing film and the slow axis of the alignment solidification layer A is 15 °, and the angle between the absorption axis of the polarizing film and the slow axis of the alignment solidification layer B is 75 °. Transferred (bonded). In addition, each transfer (bonding) is performed in the above 2. It was carried out through the ultraviolet curable adhesive (thickness 1.0 μm) used in. In this way, a polarizing plate with a retardation layer having a structure of a protective layer / adhesive layer / polarizing film / adhesive layer / retardation layer (first orientation solidification layer / adhesion layer / second orientation solidification layer) is obtained. It was. The total thickness of the obtained polarizing plate with a retardation layer was 52 μm. The obtained polarizing plate with a retardation layer was subjected to the evaluations (4) to (6) above. The amount of warpage was 1.8 mm.

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

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

[Comparative Example 1]
1. 1. Preparation of Polarizer A polyvinyl alcohol-based resin film having an average degree of polymerization of 2,400, a saponification degree of 99.9 mol%, and a thickness of 30 μm was prepared. The polyvinyl alcohol film was immersed in a swelling bath (water bath) at 20 ° C. for 30 seconds between rolls having different peripheral speed ratios and stretched 2.4 times in the transport direction while swelling (swelling step). Dyeing by immersing in a dyeing bath at 30 ° C. (an aqueous solution having an iodine concentration of 0.03% by weight and a potassium iodide concentration of 0.3% by weight) so that the single transmittance after final stretching becomes a desired value. At the same time, the original polyvinyl alcohol film (polyvinyl alcohol film not stretched at all in the transport direction) was stretched 3.7 times in the transport direction (dyeing step). The immersion time at this time was about 60 seconds. Next, the original polyvinyl alcohol film is immersed in a crosslinked bath at 40 ° C. (an aqueous solution having a boric acid concentration of 3.0% by weight and a potassium iodide concentration of 3.0% by weight). It was stretched up to 4.2 times in the transport direction as a reference (crosslinking step). Further, the obtained polyvinyl alcohol film is immersed in a stretching bath at 64 ° C. (an 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 to obtain the original polyvinyl alcohol film. After stretching up to 6.0 times in the transport direction with reference to the alcohol film (stretching step), it was immersed in a washing bath at 20 ° C. (an aqueous solution having a potassium iodide concentration of 3.0% by weight) for 5 seconds (washing). Process). The washed polyvinyl alcohol film was dried at 30 ° C. for 2 minutes to prepare a polarizer (thickness 12 μm).

2. 2. Preparation of polarizing plate As an adhesive, a polyvinyl alcohol resin containing an acetoacetyl group (average degree of polymerization of 1,200, saponification degree of 98.5 mol%, acetoacetylation degree of 5 mol%) and methylol melamine are used. An aqueous solution containing 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 was applied to one surface of the above-mentioned polarizer, and a TAC film having a thickness of 25 μm was applied to the other surface of the polarizer. After laminating with a roll laminating machine, it is heated and dried in an oven (temperature is 60 ° C., time is 5 minutes) to protect layer 1 (thickness 25 μm) / adhesive layer / polarizer / adhesive layer / protective layer 2 ( A polarizing plate having a structure having a thickness of 25 μm) was produced.

3. 3. Fabrication of polarizing plate with retardation layer 2. The liquid crystal oriented solidified layer A and the liquid crystal oriented solidified layer B are transferred in this order to the surface of the protective layer 2 of the polarizing plate obtained in the above manner in the same manner as in Example 1, and the protective layer 1 / adhesive layer / polarizer / adhesion A polarizing plate with a retardation layer having a structure of a layer / protective layer 2 / adhesive layer / retardation layer (first alignment solidification layer / adhesion layer / second orientation solidification 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]
Potassium iodide was not added to the PVA aqueous solution (coating liquid), the thickness of the polarizing film obtained by changing the PVA aqueous solution (coating liquid) was 3.3 μm, and no heating roll was used in the drying shrinkage treatment. The polarizing film and the polarizing plate are the same as in Example 1 except that the shrinkage rate in the width direction is 0.1% or less and the single transmittance of the polarizing film is adjusted by adjusting the concentration of the dyeing bath. Was produced. The simple substance transmittance of the polarizing plate (substantially, the polarizing film) was 43.4%, and that of 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. 1. Preparation of Polarizing Plate A long polarizing plate (width: 1300 mm) having a protective layer / polarizing film configuration was obtained in the same manner as in Example 1 except that a TAC film having a thickness of 25 μm was used as the protective layer.

2. 2. Preparation 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 a stirring blade and a reflux condenser controlled at 100 ° C. Bis [9- (2-phenoxycarbonylethyl) fluoren-9-yl] methane 29.60 parts by mass (0.046 mol), isosorbide (ISB) 29.21 parts by mass (0.200 mol), spiroglycol (SPG) 42 .28 parts by weight (0.139 mol), diphenyl carbonate (DPC) 63.77 parts by weight (0.298 mol) and calcium acetate monohydrate 1.19 × ^{10 -2} parts by weight as a catalyst (6.78 × 10 ^{- 5} mol) was charged. After substituting nitrogen under reduced pressure in the reactor, heating was performed with a heat medium, and stirring was started when the internal temperature reached 100 ° C. The internal temperature was brought to 220 ° C. 40 minutes after the start of the temperature rise, and the depressurization was started at the same time as controlling to maintain this temperature, and the temperature was 13.3 kPa 90 minutes after reaching 220 ° C. The phenol vapor produced as a by-product of the polymerization reaction was guided to a reflux condenser at 100 ° C., the monomer component contained in a small amount in the phenol vapor was returned to the reactor, and the uncondensed phenol vapor was guided to a condenser at 45 ° C. for recovery. Nitrogen was introduced into the first reactor and the pressure was once restored to atmospheric pressure, and then the oligomerized reaction solution in the first reactor was transferred to the second reactor. Then, the temperature rise and depressurization in the second reactor were started, and the internal temperature was 240 ° C. and the pressure was 0.2 kPa in 50 minutes. Then, the polymerization was allowed to proceed until the stirring power became a predetermined value. When the predetermined power was reached, nitrogen was introduced into the reactor to repressurize, the produced polyester carbonate-based resin was extruded into water, and the strands were cut to obtain pellets.

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

3. 3. Fabrication of polarizing plate with retardation layer 1. On the surface of the polarizing film of the polarizing plate obtained in 2. above. The retardation film obtained in (1) was bonded via an acrylic pressure-sensitive adhesive (thickness: 5 μm). At this time, the absorption axis of the polarizing film and the slow axis of the retardation film were bonded so as to form an angle of 45 °. In this way, a polarizing plate with a retardation layer having a structure of a protective layer / adhesive layer / polarizing film / adhesive layer / retardation layer was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 89 μm. The obtained polarizing plate with a retardation layer was subjected to the evaluations (5) and (6) above.

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

[Evaluation]
As is clear from Table 1 and the comparison between Example 1 and Comparative Example 2, the polarizing plate with a retardation layer of the embodiment of the present invention is thin, suppresses warpage after a heating test, and has optical characteristics. Excellent. Further, it can be seen that the bending resistance is improved when the weight per unit area of the polarizing plate with a retardation layer is not more than a predetermined value.

The polarizing plate with a retardation layer of the present invention is suitably used as a circular polarizing plate for a liquid crystal display device, an organic EL display device, and an inorganic EL display device.

10 Polarizing plate 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 (11)

It has 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 made of a polyvinyl alcohol-based resin film containing a dichroic substance, has a thickness of 8 μm or less, and has a ratio of orthogonal absorbance A ₅₅₀ at a wavelength of ₅₅₀ nm to 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 orientation-solidified layer of a liquid crystal compound.
The total thickness is 60 μm or less.
Polarizing plate with retardation layer. The retardation layer is a single layer of the orientation solidification layer of the liquid crystal compound.
The Re (550) of the retardation layer is 100 nm to 190 nm.
The angle formed by the slow axis of the retardation layer and the absorption axis of the polarizing film is 40 ° to 50 °.
The polarizing plate with a retardation layer according to claim 1 . The retardation layer has a laminated structure of an oriented solidified layer of a first liquid crystal compound and an oriented solidified layer of a second liquid crystal compound.
The Re (550) of the oriented solidified layer of the first liquid crystal compound is 200 nm to 300 nm, and the angle formed by the slow axis thereof and the absorption axis of the polarizing film is 10 ° to 20 °.
The Re (550) of the oriented solidified layer of the second liquid crystal compound is 100 nm to 190 nm, and the angle formed by the slow axis thereof and the absorption axis of the polarizing film is 70 ° to 80 °.
The polarizing plate with a retardation layer according to claim 1 . The method according to any one of claims 1 to 3 , wherein the ratio (A ₄₇₀ / A ₆₀₀ ) of the orthogonal absorbance A ₄₇₀ at a wavelength of ₄₇₀ nm to the orthogonal absorbance A ₆₀₀ at a wavelength of 600 nm of the polarizing film is 0.7 to 2.00. Polarizing plate with retardation layer. The polarizing plate with a retardation layer according to any one of claims 1 to 4 , wherein the orthogonal b value of the polarizing film is greater than -10 and less than +10. The polarizing plate with a retardation layer according to any one of claims 1 to 5 , wherein the polarizing film has a single transmittance of 42.5% or more. The position according to any one of claims 1 to 6 , further comprising another retardation layer outside the retardation layer, and the refractive index characteristics of the other retardation layer show a relationship of nz> nz = ny. Polarizing plate with phase difference layer. The polarizing plate with a retardation layer according to any one of claims 1 to 7 , further comprising a conductive layer or an isotropic substrate with a conductive layer on the outside of the retardation layer. A polarizing plate with a retardation layer, comprising 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 orientation-solidified layer of a liquid crystal compound.
The polarizing film is made of a polyvinyl alcohol-based resin film containing iodine, and has a thickness of 8 μm or less.
The ratio of the orthogonal absorbance A ₅₅₀ at a wavelength of ₅₅₀ nm to the orthogonal absorbance A ₂₁₀ at a wavelength of 210 nm (A ₅₅₀ / A ₂₁₀ ) 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.
The total thickness is 60 μm or less.
Polarizing plate with retardation layer. An image display device comprising the polarizing plate with a retardation layer according to any one of claims 1 to 9 . The image display device according to claim 10 , which is an organic electroluminescence display device or an inorganic electroluminescence display device.