KR20200042411A - Polarizing plate with retardation layer and image display device using the same - Google Patents

Abstract

Provided is a polarizing plate with a retardation layer which is thin, has excellent handling properties, and has excellent optical characteristics. The polarizing plate with a retardation layer of the present invention has a polarizing plate including a polarizing film and a protective layer on at least one side of the polarizing film, and a retardation layer. The polarizing film is composed of a polyvinyl alcohol-based resin film containing a dichroic material, has the thickness of 8 μm or less, has the simple substance transmittance of 46% or more, and has the polarization degree of 92% or more. The retardation layer is an alignment-solidified layer of a liquid crystal compound.

Description

Polarizing plate with retardation layer and image display device using the same {POLARIZING PLATE WITH RETARDATION LAYER AND IMAGE DISPLAY DEVICE USING THE SAME}

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

In recent years, image display devices represented by liquid crystal display devices and electroluminescent (EL) display devices (for example, organic EL display devices and inorganic EL display devices) have been rapidly spread. Polarizing plates and retardation plates are typically used for image display devices. Practically, since 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), as the demand for thinning of an image display device has recently increased, the polarizing plate with a retardation layer is also thinned. Demands are getting stronger. In addition, as the demand for a curved image display device and / or a bendable or bendable image display device has increased recently, thinning of the thin layer and softening of the thin layer are also required for the polarizing plate and the polarizing plate with a retardation layer. For the purpose of reducing the thickness of the polarizing plate with a retardation layer, thinning of the protective layer and the retardation film of the polarizing film having a large contribution to thickness is in progress. However, when the protective layer and the retardation film are thinned, the effect of shrinking the polarizing film becomes relatively large, resulting in problems such as warp of the image display device and deterioration of operability of the polarizing plate with the retardation layer.

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

Japanese Patent Publication No. 3325560

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

The polarizing plate with a retardation layer of the present invention has a polarizing film, a polarizing plate comprising a protective layer on at least one side of the polarizing film, and a retardation layer. The polarizing film is composed of a polyvinyl alcohol-based resin film containing a dichroic material, the thickness of which is 8 µm or less, the simple substance transmittance is 46% or more, and the polarization degree is 92% or more. The retardation layer is an alignment-solidified layer of a liquid crystal compound.

In one embodiment, the polarizing plate with a retardation layer has a unit weight of 6.5 mg / cm 2 or less.

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

In one embodiment, the retardation layer is a single layer of the alignment-solidified layer of the liquid crystal compound, Re (550) of the retardation layer is 100 nm to 190 nm, the slow axis of the retardation layer and the polarizing film The angle formed by the absorption axis is 40 ° to 50 °.

In one embodiment, the retardation layer has a stacked structure of an alignment-solidified layer of the first liquid crystal compound and an alignment-solidified layer of the second liquid crystal compound; Re (550) of the alignment-solidified layer of the first liquid crystal compound is 200 nm to 300 nm, and an angle formed between the slow axis and the absorption axis of the polarizing film is 10 ° to 20 °; Re (550) of the alignment-solidified layer of the second liquid crystal compound is 100 nm to 190 nm, and an angle formed between the slow axis and the absorption axis of the polarizing film is 70 ° to 80 °.

In one embodiment, the difference between the maximum value and the minimum value of the simplex transmittance in the area of 50 cm 2 of the polarizing film is 0.3% or less.

In one embodiment, the polarizing plate with a retardation layer has a width of 1000 mm or more, and a difference between a maximum value and a minimum value of simplex transmittance at a position along the width direction of the polarizing film is 0.7% or less.

In one embodiment, the simplex transmittance of the polarizing film is 48% or less, and the polarization degree is 97% or less.

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

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

According to another aspect of the present invention, an image display device is provided. This image display device includes the polarizing plate with the retardation layer described above.

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

According to the present invention, a polyvinyl alcohol (PVA) -based resin is combined with the addition of halides (typically potassium iodide), two-stage stretching including air assisted stretching and underwater stretching, and drying and shrinking by a heating roll. By adopting, it is possible to obtain a polarizing film having a thin shape and extremely excellent optical properties. By using such a polarizing film, it is possible to realize a polarizing plate with a retardation layer that is thin, has excellent handling properties, and has excellent optical properties.

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

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

(Definition of terms and symbols)

Definitions of terms and symbols in the present specification are as follows.

(1) Refractive index (nx, ny, nz)

'nx' is the refractive index in the direction in which the in-plane refractive index becomes the maximum (ie, the slow axis direction), and 'ny' is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the direction of the true axis). , '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 λnm 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) can be obtained by the formula: Re (λ) = (nx-ny) × d when the thickness of the layer (film) is d (nm).

(3) Phase difference in thickness direction (Rth)

'Rth (λ)' is a phase difference in the thickness direction measured with light having a wavelength of λnm 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. When the thickness of the layer (film) is set to d (nm), Rth (λ) can be obtained by the formula: Rth (λ) = (nx-nz) × d.

(4) Nz coefficient

The Nz coefficient can be determined by Nz = Rth / Re.

(5) angle

When referring to an angle in the present specification, the angle includes both a clockwise direction and a counterclockwise direction with respect to the reference direction. Thus, for example, '45 ° 'means ± 45 °.

A. Overall configuration of polarizing plate with retardation layer

1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention. The polarizing plate 100 with a phase difference layer of this embodiment has a polarizing plate 10 and a phase difference layer 20. The polarizing plate 10 includes a polarizing film 11, a first protective layer 12 disposed on one side of the polarizing film 11, and a second protective layer 13 disposed on the other side of the polarizing film 11 ). Depending on the purpose, one of the first protective layer 12 and the second protective layer 13 may be omitted. For example, when the retardation layer 20 can also function as a protective layer of the polarizing film 11, the second protective layer 13 may be omitted. In the embodiment of the present invention, the polarizing film is composed of a polyvinyl alcohol-based resin film containing a dichroic material. The thickness of the polarizing film is 8 µm or less, the simple substance transmittance is 46% or more, and the polarization degree is 92% or more.

As shown in FIG. 2, in the polarizing plate 101 with a retardation layer according to another embodiment, another retardation layer 50 and / or a conductive layer or an isotropic substrate 60 with a conductive layer may be provided. The other retardation layer 50 and the conductive layer or the isotropic substrate 60 with a conductive layer are typically provided outside the retardation layer 20 (opposite the polarizing plate 10). Other retardation layers typically have a refractive index characteristic of nz> nx = ny. The other retardation layer 50 and the conductive layer or the isotropic substrate 60 with a conductive layer are typically provided in this order from the retardation layer 20 side. The other retardation layer 50 and the conductive layer or the isotropic substrate 60 with a conductive layer are typically arbitrary layers provided as necessary, and either or both of them may be omitted. In addition, for convenience, the retardation layer 20 may be referred to as a first retardation layer, and the other retardation layer 50 may be referred to as a second retardation layer. Further, when a conductive layer or an isotropic substrate with a conductive layer is provided, a polarizer with a retardation layer has a so-called inner touch panel type input display device in which a touch sensor is embedded between an image display cell (eg, an organic EL cell) and a polarizing plate. Can be applied to.

In the embodiment of the present invention, the first retardation layer 20 is an alignment-solidified layer of a liquid crystal compound. The first retardation layer 20 may be a single layer of the oriented solidification layer as shown in FIGS. 1 and 2, and the first oriented solidification layer 21 and the second oriented solidification layer 22 as shown in FIG. 3. It may have a laminated structure of.

The above-described embodiments may be combined as appropriate, or modifications apparent in the art may be added to the components in the above-described embodiments. For example, the second phase difference layer 50 and / or the conductive layer or the isotropic substrate 60 with a conductive layer may be provided on the polarizing plate 102 with a phase difference layer in FIG. 3. In addition, even if, for example, the configuration in which the isotropic substrate 60 with a conductive layer is provided outside the second retardation layer 50 is replaced with an optically equivalent configuration (for example, a laminate of the second retardation layer and the conductive layer). do.

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

The polarizing plate with a retardation layer of the present invention may be a single leaf shape or a long shape. In the present specification, the term "long-length shape" means a long length shape that is sufficiently long with respect to the width, and includes, for example, a long shape with a length of 10 times or more, preferably 20 times or more with respect to the width. The long-shaped polarizing plate with a retardation layer can be wound in a roll shape.

Practically, an adhesive layer (not shown) is provided on the opposite side to the polarizing plate of the retardation layer, and the polarizing plate with the retardation layer can be attached to the image display cell. Moreover, it is preferable that the release film is temporarily attached to the surface of the pressure-sensitive adhesive layer until a polarizing plate with a retardation layer is provided for use. By attaching the release film, it is possible to protect the pressure-sensitive adhesive layer and form a roll.

The total thickness of the polarizing plate with a retardation layer is preferably 60 μm or less, more preferably 55 μm or less, further preferably 50 μm or less, and particularly preferably 40 μm or less. The lower limit of the total thickness may be, for example, 28 μm. According to the embodiment of the present invention, such an extremely thin polarizing plate with a retardation layer can be realized. Such a polarizing plate with a retardation layer may have extremely excellent flexibility and bending durability. Such a polarizing plate with a retardation layer can be particularly preferably applied to a curved image display device and / or a curved or bendable image display device. In addition, the total thickness of the polarizing plate with a retardation layer means the sum of the thicknesses 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 (that is, retardation). The total thickness of the layered polarizing plate does not include the thickness of the adhesive layer for attaching the polarizing plate with the retardation layer to adjacent members such as an image display cell and the thickness of the release film that can be attached to the surface).

The unit weight of the polarizing plate with a retardation layer according to the embodiment of the present invention is, for example, 6.5 mg / cm 2 or less, preferably 2.0 mg / cm 2 to 6.0 mg / cm 2, more preferably 3.0 mg / cm 2 to 5.5 mg / Cm 2, more preferably 3.5 mg / cm 2 to 5.0 mg / cm 2. When the display panel is thin, the panel may be slightly deformed by the weight of the polarizing plate with a retardation layer, and display defects may occur. According to the polarizing plate with a retardation layer having a unit weight of 6.5 mg / cm 2 or less, such a panel Can prevent deformation. In addition, even when the polarizing plate with a retardation layer having the unit weight is thinned, it has good handleability and can exhibit extremely excellent flexibility and bending durability.

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

B. Polarizer

B-1. Polarizing film

As described above, the polarizing film 11 has a thickness of 8 µm or less, a simple substance transmittance of 46% or more, and a polarization degree of 92% or more. Generally, the simplex transmittance and the polarization degree are in a trade-off relationship with each other, and the higher the single transmittance may decrease the polarization degree, and the higher the polarization degree, the lower the simple transmittance. For this reason, it has been difficult to provide a thin polarizing film for practical use that satisfies the optical properties of a single element transmittance of 46% or more and a polarization degree of 92% or more. It is one of the features of the present invention to use a thin polarizing film having a simple optical transmittance of 46% or more and a polarization degree of 92% or more, and to suppress variation (non-uniformity) in optical properties.

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

The polarizing film preferably exhibits absorption dichroism at a wavelength of 380 nm to 780 nm. The simplex transmittance of the polarizing film is preferably 48% or less. The polarization degree of the polarizing film is preferably 92.5% or more, and more preferably 93% or more. On the other hand, the polarization degree is preferably 97% or less. The group transmittance is typically a Y value measured by using an ultraviolet / visible ray spectrophotometer and correcting visibility. The polarization degree can be obtained by the following equation, based on the parallel transmittance Tp and the orthogonal transmittance Tc, which are typically measured using an ultraviolet / visible ray spectrophotometer and corrected for visibility.

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

In one embodiment, the transmittance of a thin polarizing film of 8 µm or less is typically measured by using a laminate of a polarizing film (refractive index on the surface: 1.53) and a protective film (refractive index: 1.50) as the measurement object, ultraviolet / visible light It is measured using a spectrophotometer. Depending on the refractive index of the surface of the polarizing film and / or the refractive index of the surface contacting the air interface of the protective film, the reflectance at the interface of each layer changes, and as a result, the measured value of the transmittance may change. Therefore, for example, when a protective film having a refractive index other than 1.50 is used, the measured value of the transmittance may be corrected according to the refractive index of the surface contacting the air interface of the protective film. Specifically, the correction value C of the transmittance is expressed by the following equation using the reflectance R ₁ (transmission axis reflectance) of polarized light parallel to the transmission axis at the interface between the protective film and the air layer.

C = R ₁ -R ₀

^{_{R 0 = ((1.50-1) 2}} /(1.50+1) 2) × (T 1/100)

_{R 1 = ((n 1 -1} ) 2 / (n 1 +1) 2) × (T 1/100)

Here, R ₀ is a transmission axis reflectance when a protective film having a refractive index of 1.50 is used, n ₁ is a refractive index of the protective film used, and T ₁ is a transmittance of the polarizing film. For example, when a base material having a surface refractive index of 1.53 (cycloolefin-based film, film with a hard coat layer, etc.) is used as the protective film, the correction amount C is about 0.2%. In this case, by adding 0.2% to the transmittance obtained by the measurement, it is possible to convert the transmittance when a protective film having a surface refractive index of 1.50 is used. Further, 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 influence of the transmittance of the polarizing film on the value of the correction value C is limited. In addition, when the protective film has absorption other than surface reflection, appropriate correction can be performed depending on the amount of absorption.

In one embodiment, the polarizing plate with a retardation layer has a width of 1000 mm or more, and thus the width of the polarizing film is 1000 mm or more. In this case, the difference (D1) between the maximum value and the minimum value of the simplex transmittance at a position along the width direction of the polarizing film is preferably 0.7% or less, more preferably 0.6% or less, still more preferably 0.5% or less , Particularly preferably 0.44% or less. The smaller D1 is, the more preferable. The lower limit of D1 may be, for example, 0.01%. When D1 is in the above range, a polarizing plate with a retardation layer having excellent optical properties can be industrially produced. In another embodiment, the polarizing film has a difference (D2) between the maximum value and the minimum value of simplex transmittance in the region of 50 cm 2, preferably 0.3% or less, more preferably 0.2% or less, and even more preferably 0.15%. Is below. The smaller the D2, the better. The lower limit of D2 may be, for example, 0.01%. When D2 is within the above range, fluctuations in luminance on the display screen can be suppressed when a polarizing plate with a retardation layer is used in the image display device.

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

As a specific example of the polarizing film obtained using a laminated body, the polarizing film obtained using the laminated body of a resin base material and the PVA system resin layer formed and apply | coated to the said resin base material is mentioned. A polarizing film obtained by using a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate is applied, for example, by applying a PVA-based resin solution to the resin substrate and drying to form a PVA-based resin layer on the resin substrate, To obtain a laminate of a resin substrate and a PVA-based resin layer; And stretching and dyeing the laminate to make the PVA-based resin layer a polarizing film. In this embodiment, extending | stretching typically includes extending | stretching by immersing a laminated body in aqueous boric acid solution. In addition, the stretching may further include air stretching the laminate at a high temperature (eg, 95 ° C. or higher) before stretching in a boric acid aqueous solution, if necessary. The obtained laminate of the resin substrate / polarizing film may be used as it is (ie, the resin substrate may be used as a protective layer of the polarizing film), the resin substrate is peeled from the laminate of the resin substrate / polarizing film, and the release surface is used for the purpose. Any suitable protective layer according to the above may be stacked and used. Details of the manufacturing method of such a polarizing film are described, for example, in JP 2012-73580 A. This publication is incorporated by reference in its entirety.

The manufacturing method of the polarizing film is typically to form a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate to form a laminate, and to the laminate, air assisted stretching This includes performing treatment, dyeing treatment, underwater stretching treatment, and drying shrinkage treatment that shrinks by 2% or more in the width direction by heating while conveying in the longitudinal direction. Accordingly, a polarizing film having a thickness of 8 µm or less, a simple substance transmittance of 46% or more, and a polarization degree of 92% or more, having excellent optical properties, and suppressing fluctuations in optical properties can be provided. That is, by introducing the auxiliary stretching, even when PVA is applied on a thermoplastic resin, it is possible to increase the crystallinity of PVA, and it is possible to achieve high optical properties. In addition, by simultaneously increasing the orientation of the PVA, problems such as degradation or dissolution of the orientation of the PVA can be prevented when immersed in water in a subsequent dyeing step or stretching step, so that high optical properties can be achieved. do. In addition, in the case where the PVA-based resin layer is immersed in a liquid, the disorder of orientation of the polyvinyl alcohol molecule and the deterioration of the orientation can be suppressed compared to the case where the PVA-based resin layer does not contain a halide. Accordingly, the optical properties of the polarizing film obtained through a treatment process performed by immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment, can be improved. Further, the optical properties can be improved by shrinking the laminate in the width direction by a dry shrinkage treatment.

B-2. Protective layer

The first protective layer 12 and the second protective layer 13 are each formed of any suitable film that can be used as a protective layer of 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, and polyethersulfone-based resins, And transparent resins such as polysulfone, polystyrene, polynorbornene, polyolefin, (meth) acrylic, and acetate. In addition, thermosetting resins such as (meth) acrylic, urethane-based, (meth) acryl-urethane-based, epoxy-based, and silicone-based resins, or ultraviolet curable resins are also exemplified. In addition to this, for example, glassy polymers such as siloxane polymers can also be mentioned. Further, the polymer film described in JP 2001-343529 A (WO01 / 37007) can also be used. As the material of the 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 nitrile group in the side chain can be used, such as isobutene and N- And a resin composition having an alternating copolymer composed of methyl maleimide and an acrylonitrile-styrene copolymer. The polymer film may be, for example, an extruded product of the resin composition.

As described later, the polarizing plate with a retardation layer of the present invention is typically disposed on the viewer side of the image display device, and the first protective layer 12 is typically disposed on the viewer side. Therefore, the first protective layer 12 may be subjected to surface treatments such as hard coat treatment, anti-reflection treatment, anti-sticking treatment, and anti-clear treatment, if necessary. In addition, the first protective layer 12 is treated to improve the visibility when viewed through polarized sunglasses, if necessary (typically, (g) to provide a circular polarization function, to give an ultra-high phase difference) May be carried out. By performing such a process, it is possible to realize excellent visibility even when the display screen is viewed through a polarizing lens such as polarized sunglasses. Therefore, the polarizing plate with a retardation layer can be preferably applied to an image display device that can be used outdoors.

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

In one embodiment, the second protective layer 13 is preferably optically isotropic. In the present specification, 'optically isotropic' means that the in-plane retardation Re (550) is 0 nm to 10 nm, and the retardation Rth (550) in the thickness direction is -10 nm to +10 nm. The second protective layer 13 may be, in one embodiment, a retardation layer having any suitable retardation value. In this case, the in-plane retardation Re (550) of the retardation layer is 110 nm to 150 nm, for example. 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 lightening, preferably, the second protective layer can be omitted.

B-3. Manufacturing method of polarizing film

The polarizing film is formed into a laminate by forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin substrate, for example, and stacking It is produced by a method including performing an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a dry shrinkage treatment that shrinks by 2% or more in the width direction by heating while conveying in the longitudinal direction to the sieve in this order. Can be. The content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight based on 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably processed 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 dry shrinkage treatment is preferably 2% or more. According to such a manufacturing method, the polarizing film demonstrated in the said B-1 item can be obtained. In particular, a laminate comprising a PVA-based resin layer containing a halide is produced, and the stretching of the laminate is made into multi-stage stretching including air assisted stretching and underwater stretching, and the laminate after heating is heated with a heating roll. A polarizing film having optical characteristics (representatively, simple substance transmittance and polarization degree) and suppressing fluctuations in optical characteristics can be obtained. Specifically, by using a heating roll in the drying shrinkage treatment step, it is possible to uniformly shrink over the entire laminate while conveying the laminate. Thereby, not only the optical properties of the obtained polarizing film can be improved, but also a polarizing film excellent in optical properties can be stably produced, and variations in the optical properties (especially, simple substance transmittance) of the polarizing film can be suppressed.

B-3-1. Production of laminate

Any suitable method can be adopted as a method for producing a laminate of a thermoplastic resin substrate and a PVA-based resin layer. Preferably, a PVA-based resin layer is formed on the thermoplastic resin substrate by applying a coating liquid containing a halide and a PVA-based resin to the surface of the thermoplastic resin substrate and drying it. 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 a method for applying the coating liquid. For example, roll coat method, spin coat method, wire bar coat method, dip coat method, die coat method, curtain coat method, spray coat method, knife coat method (comma coat method, etc.) can be mentioned. The coating and 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, a surface treatment (for example, corona treatment) may be performed on the thermoplastic resin substrate, or an easily adhesive layer may be formed on the thermoplastic resin substrate. By performing such treatment, the adhesiveness between the thermoplastic resin substrate and the PVA-based resin layer can be improved.

B-3-1-1. Thermoplastic resin substrate

The thickness of the thermoplastic resin substrate is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If it is less than 20 µm, there is a fear that formation of the PVA-based resin layer becomes difficult. If it exceeds 300 µm, for example, in the underwater stretching treatment described later, the thermoplastic resin substrate needs a long time to absorb water, and there is a fear that excessive stretching is required.

The thermoplastic resin substrate preferably has an absorbency of 0.2% or more, and more preferably 0.3% or more. The thermoplastic resin substrate absorbs water and can plasticize by acting as a plasticizer. As a result, the stretching stress can be drastically reduced, and stretching can be performed at a high magnification. Meanwhile, the water absorption of the thermoplastic resin substrate is preferably 3.0% or less, and more preferably 1.0% or less. By using such a thermoplastic resin substrate, problems such as deterioration of the dimensional stability of the thermoplastic resin substrate at the time of manufacture and deterioration of the appearance of the resulting polarizing film can be prevented. In addition, it is possible to prevent the substrate from breaking during stretching in water or peeling of the PVA-based resin layer from the thermoplastic resin substrate. In addition, the absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a transformer into the constituent material. The water absorption rate is a value determined according to JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120 ° C. or less. By using such a thermoplastic resin substrate, it is possible to sufficiently secure stretchability of the laminate while suppressing crystallization of the PVA-based resin layer. In addition, considering that plasticization of the thermoplastic resin substrate with water and stretching under water are satisfactory, it is more preferably 100 ° C or lower, and further preferably 90 ° C or lower. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60 ° C or higher. By using such a thermoplastic resin substrate, it is preferable to prevent problems such as deformation of the thermoplastic resin substrate (for example, unevenness, sagging, wrinkles, etc.) when applying and drying the coating liquid containing the PVA-based resin. Laminate can be produced. In addition, the stretching of the PVA-based resin layer can be performed satisfactorily at a desirable temperature (for example, about 60 ° C). Moreover, the glass transition temperature of a thermoplastic resin base material can be adjusted, for example, by heating using a crystallization material which introduces a transformer into the constituent material. The glass transition temperature (Tg) is a value determined according to JIS K 7121.

Any suitable thermoplastic resin may be employed as the constituent material of the thermoplastic resin substrate. Examples of the thermoplastic resin include ester-based resins such as polyethylene terephthalate-based resins, cycloolefin-based resins such as norbornene-based resins, olefin-based resins such as polypropylene, polyamide-based resins, polycarbonate-based resins, and copolymer resins thereof. Can be mentioned. Among these, it is preferably a norbornene-based resin and an amorphous polyethylene terephthalate-based resin.

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

In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate-based resin having an isophthalic acid unit. This is because such a thermoplastic resin substrate is extremely excellent in stretchability and crystallization during stretching can be suppressed. This is thought to be due to the fact that the main chain is imparted with a large curvature by introducing an isophthalic acid unit. The polyethylene terephthalate-based resin has a terephthalic acid unit and an ethylene glycol unit. The content ratio of the isophthalic acid unit is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, based on the total of all repeating units. This is because a thermoplastic resin substrate having 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 to such a content ratio, the crystallinity can be favorably increased in the dry shrinkage treatment described later.

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

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

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

B-3-1-2. Coating liquid

The coating liquid contains a halide and a PVA-based resin as described above. The coating solution is typically a solution in which the halide and the PVA-based resin are dissolved in a solvent. Examples of the solvent include polyhydric alcohols such as water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. You can. These can be used alone or in combination of two or more. Among these, water is preferable. The PVA-based resin concentration of the solution is preferably 3 parts by weight to 20 parts by weight based on 100 parts by weight of the solvent. With such resin concentration, a uniform coating film in close contact with the thermoplastic resin substrate can be formed. The content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

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

Any suitable resin may be employed as the PVA-based resin. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymers are mentioned. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, more preferably 99.0 mol% to 99.93 mol%. Saponification degree can be obtained according to JIS K 6726-1994. A polarizing film having excellent durability can be obtained by using a PVA-based resin having such saponification degree. When the saponification degree is too high, there is a fear that it will gel.

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

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

The amount of halide in the coating solution is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, and more preferably 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the PVA-based resin. When the amount of the halide relative to 100 parts by weight of the PVA-based resin exceeds 20 parts by weight, the halide may bleed out and the polarizing film finally obtained may become cloudy.

In general, the orientation of the polyvinyl alcohol molecule in the PVA-based resin is increased by stretching the PVA-based resin layer, but if the PVA-based resin layer after stretching is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecule is disturbed. Orientation may fall. In particular, in the case of stretching the laminate of the thermoplastic resin substrate and the PVA-based resin layer in boric acid, when the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin substrate, the orientation is also lowered. The trend is remarkable. For example, the stretching of the PVA film alone in boric acid water is generally performed at 60 ° C, whereas the stretching of the laminate of the A-PET (thermoplastic resin substrate) and the PVA-based resin layer is about 70 ° C or higher. It is carried out at a temperature, in this case, the orientation of the PVA at the beginning of stretching may be lowered in the step before rising by underwater stretching. On the other hand, a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate is produced, and the laminate is subjected to high temperature stretching (auxiliary stretching) in air before stretching in boric acid water, so that the PVA of the laminate after auxiliary stretching Crystallization of the PVA-based resin in the system-based resin layer can be promoted. As a result, in the case where the PVA-based resin layer is immersed in a liquid, the disorder of orientation of the polyvinyl alcohol molecule and the deterioration of the orientation can be suppressed as compared to the case where the PVA-based resin layer does not contain a halide. Accordingly, the optical properties of the polarizing film obtained through a treatment process performed by immersing the laminate in a liquid, such as dyeing treatment and underwater stretching treatment, can be improved.

B-3-2. Aerial assisted stretching treatment

In particular, in order to obtain high optical properties, a two-stage stretching method in which dry stretching (auxiliary stretching) and boric acid underwater stretching are combined is selected. As in the case of two-stage stretching, by introducing auxiliary stretching, it is possible to stretch while suppressing crystallization of the thermoplastic resin substrate, and in the subsequent stretching in boric acid, the problem that stretchability is lowered due to excessive crystallization of the thermoplastic resin substrate is solved. The laminate can be stretched at a higher magnification. Furthermore, when applying a PVA-based resin on a thermoplastic resin substrate, in order to suppress the effect of the glass transition temperature of the thermoplastic resin substrate, compared with the case of applying a PVA-based resin on a conventional metal drum, the coating temperature may be lowered. There is a need, and as a result, the crystallization of the PVA-based resin becomes relatively low, which may cause a problem that sufficient optical properties cannot be obtained. On the other hand, by introducing the auxiliary stretching, even when a PVA-based resin is applied on a thermoplastic resin, it is possible to increase the crystallinity of the PVA-based resin, and it is possible to achieve high optical properties. In addition, by simultaneously increasing the orientation of the PVA-based resin, problems such as degradation or dissolution of the orientation of the PVA-based resin can be prevented when immersed in water in a subsequent dyeing step or stretching step, thereby achieving high optical properties. It becomes possible to do.

The method of stretching the aerial assisted stretching may be fixed-end stretching (for example, a method using a tenter stretching machine) or free-end stretching (for example, a uniaxial stretching by passing a laminate between rolls having different circumferential speeds). However, free end stretching can be actively employed to obtain high optical properties. In one embodiment, the aerial stretching treatment includes a heating roll stretching step of stretching the circumferential speed difference between the heating rolls while conveying the laminate in its longitudinal direction. The aerial stretching treatment typically includes a zone stretching step and a heating roll stretching step. Further, 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 process and the heating roll stretching process are performed in this order. Further, in another embodiment, in the tenter stretching machine, the film end is gripped and stretched by extending the distance between the tenters in the flow direction (expansion of the distance between the tenters becomes the stretching magnification). At this time, the distance of the tenter in the width direction (vertical to the flow direction) is set to be arbitrarily close. Preferably, with respect to the draw ratio in the flow direction, it can be set to be closer by free end stretching. In the case of free end stretching, the shrinkage ratio in the width direction = (1 / stretch magnification) is calculated as ^1/2 .

The aerial assisted stretching may be performed in one step or in multiple steps. When performing in multiple steps, the draw ratio is the product of the draw ratio of each step. The stretching direction in the aerial assisted stretching is preferably almost the same as the stretching direction of underwater stretching.

The draw ratio in the aerial assisted stretching is preferably 2.0 to 3.5 times. The maximum draw ratio in the case of combining air assisted stretching and underwater stretching is preferably 5.0 times or more, more preferably 5.5 times or more, and even more preferably 6.0 times or more with respect to the original length of the laminate. In the present specification, the term 'maximum stretching ratio' refers to a stretching ratio immediately before the laminate breaks, and separately refers to a value lower than 0.2 by checking the stretching ratio that the laminate breaks.

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

Crystallization Index = (I _C / I _R )

but,

I _C : 1141cm ^-1 intensity when measured by measuring light incident

I _R : 1440cm ^-1 intensity when measured by measuring light incident

to be.

B-3-3. Insolubilization treatment

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

B-3-4. Dyeing treatment

The dyeing treatment is typically performed by dyeing a PVA-based resin layer with a dichroic material (typically, iodine). Specifically, it is performed by adsorbing iodine to a PVA-based resin layer. Examples of the adsorption method include a method of immersing a PVA-based resin layer (laminate) in a dye solution containing iodine, a method of coating the dye solution on a PVA-based resin layer, and spraying the dye solution on the PVA-based resin layer. And methods. Preferably, it is a method of immersing a laminate in a dyeing solution (dyeing bath). This is because iodine can adsorb well.

The dye is preferably an aqueous solution of iodine. The blending amount of iodine is preferably 0.05 parts by weight to 0.5 parts by weight based on 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to blend iodide with an aqueous solution of iodine. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, and the like. Among these, potassium iodide is preferable. The blending amount of iodide is preferably 0.1 part by weight to 10 parts by weight, more preferably 0.3 part by weight to 5 parts by weight with respect to 100 parts by weight of water. The liquid temperature during dyeing of the dyeing solution 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 ensure the transmittance of the PVA-based resin layer.

The dyeing conditions (concentration, liquid temperature, immersion time) can be set such that the finally obtained polarizing film has a simple substance transmittance of 46% or more and a polarization degree of 92% or more. As such dyeing conditions, an aqueous solution of iodine is preferably used as the dyeing solution, and the ratio of the content of iodine and potassium iodide in the aqueous solution of iodine is 1: 5 to 1:20. The ratio of the content of iodine and potassium iodide in the aqueous solution of iodine is preferably 1: 5 to 1:10. Accordingly, a polarizing film having the above optical properties can be obtained.

When the dyeing treatment is continuously performed after the treatment of dipping the laminate in a treatment bath containing boric acid (typically, insolubilization treatment), the concentration of boric acid in the dyeing bath is caused by the incorporation of boric acid contained in the treatment bath into the dyeing bath Changes over time, and as a result, dyeability may become unstable. In order to suppress the destabilization of the dyeability as described above, the upper limit of the concentration of boric acid in the dyeing bath is adjusted to preferably 4 parts by weight, more preferably 2 parts by weight with respect to 100 parts by weight of water. On the other hand, the lower limit of the concentration of boric acid in the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and even more preferably 0.5 parts by weight with respect to 100 parts by weight of water. In one embodiment, a dyeing treatment is performed using a dyeing bath in which boric acid was previously blended. Thereby, the proportion of the change in the concentration of boric acid in the case where the boric acid in the treatment bath is incorporated in the dyeing bath can be reduced. The amount of boric acid to be blended in the dyeing bath in advance (that is, the content of boric acid not derived from the treatment bath) is preferably 0.1 parts by weight to 2 parts by weight, more preferably 0.5 parts by weight with respect to 100 parts by weight of water. -1.5 parts by weight.

B-3-5. Crosslinking treatment

If necessary, crosslinking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing the crosslinking treatment, water resistance is imparted to the PVA-based resin layer, and it is possible to prevent deterioration of the orientation of PVA when immersed in high-temperature water by subsequent underwater stretching. The concentration of the aqueous boric acid solution is preferably 1 part by weight to 5 parts by weight with respect to 100 parts by weight of water. Moreover, when performing a crosslinking process after the said dyeing process, it is preferable to mix | blend an 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 crosslinking bath (boric acid aqueous solution) is preferably 20 ° C to 50 ° C.

B-3-6. Underwater stretching treatment

The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the thermoplastic resin substrate 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 stretched at a high magnification while suppressing its crystallization. can do. As a result, a polarizing film having excellent optical properties can be produced.

Any appropriate method can be adopted as the stretching method of the laminate. Specifically, fixed-end stretching may be used, or free-end stretching may be used (for example, a method of uniaxially stretching a laminate between rolls having different circumferential speeds). Preferably, free end stretching is selected. Stretching of the laminate may be performed in one step or in multiple steps. When performing in multiple steps, the draw ratio (maximum draw ratio) of the laminate described later is a product of the draw ratio of each step.

Stretching in water is preferably performed by immersing the laminate in an aqueous solution of boric acid (boric acid stretching in water). By using a boric acid aqueous solution as the stretching bath, the PVA-based resin layer can be provided with rigidity withstanding the tension applied during stretching and water resistance that does not dissolve in water. Specifically, boric acid may be crosslinked by hydrogen bonding with a PVA-based resin by generating a tetrahydroxyboric acid anion in an aqueous solution. As a result, the PVA-based resin layer can be stretched satisfactorily by imparting rigidity and water resistance, and a polarizing film having excellent optical properties can be produced.

The aqueous boric acid solution is preferably obtained by dissolving boric acid and / or borate in water as a solvent. The concentration of boric acid 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. By setting the boric acid concentration to 1 part by weight or more, the dissolution of the PVA-based resin layer can be effectively suppressed, and a more highly polarizing film can be produced. Further, 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 (aqueous solution of boric acid). 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 with respect to 100 parts by weight of water.

The stretching temperature (liquid temperature of the stretching bath) is preferably 40 ° C to 85 ° C, more preferably 60 ° C to 75 ° C. At such a temperature, it is possible to stretch at a high magnification while suppressing dissolution of the PVA-based resin layer. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60 ° C. or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is less than 40 ° C, there is a fear that the stretching cannot be satisfactorily performed even if plasticization of the thermoplastic resin substrate with water is considered. On the other hand, the higher the temperature of the stretching bath becomes, the higher the solubility of the PVA-based resin layer becomes, and there is a fear that excellent optical properties cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

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

B-3-7. Dry shrink treatment

The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or may be performed by heating (using a so-called heating roll) (heat roll drying method). Preferably, both of them are used. By drying using a heating roll, it is possible to efficiently suppress the heating curl of the laminate and to produce a polarizing film excellent in appearance. Specifically, by drying in a state in which the laminate is poured on a heating roll, crystallinity of the thermoplastic resin substrate can be efficiently promoted to increase the crystallinity, and crystallinity of the thermoplastic resin substrate can be favorably increased even at a relatively low drying temperature. You can. As a result, the stiffness of the thermoplastic resin substrate increases, and thus the state of being able to withstand shrinkage of the PVA-based resin layer due to drying is suppressed. In addition, by using the heating roll, the laminate can be dried while being kept flat, so that not only curls but also wrinkles can be suppressed. At this time, the optical properties can be improved by shrinking the laminate in the width direction by a dry shrinkage treatment. This is because the orientation of the PVA and PVA / iodine complex can be effectively increased. The shrinkage in the width direction of the laminate by the dry shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roll, it is possible to continuously shrink in the width direction while conveying the laminate, and high productivity can be realized.

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

Drying conditions can be controlled by adjusting the heating temperature of the conveying roll (temperature of the heating roll), the number of heating rolls, and the contact time with the heating roll. 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. By increasing the crystallinity of the thermoplastic resin satisfactorily, the curl can be satisfactorily suppressed, and an optical laminate having extremely excellent durability can be produced. In addition, the temperature of a heating roll can be measured with a contact thermometer. In the illustrated example, six conveying rolls are provided, but the number of conveying rolls is not particularly limited. Two to 40 conveying rolls are usually provided, 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, further preferably 1 to 10 seconds.

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

B-3-8. Other processing

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

C. First retardation layer

The first retardation layer 20 is an alignment-solidified layer of a liquid crystal compound as described above. By using a liquid crystal compound, the difference between nx and ny of the resulting retardation layer can be significantly increased compared to a non-liquid crystal material, so that the thickness of the retardation layer for obtaining a desired in-plane retardation can be significantly reduced. As a result, thinning and weight reduction of the thin layer of the polarizing plate with a retardation layer can be realized. In the present specification, the term “orientation-solidifying layer” refers to a layer in which a liquid crystal compound is oriented in a predetermined direction within a layer, and the alignment state is fixed. In addition, the 'oriented solidification layer' is a concept including an alignment hardened layer obtained by curing a liquid crystal monomer as described later. In this embodiment, typically, the rod-like liquid crystal compound is oriented in a state arranged in the slow axis direction of the first retardation layer (homogeneous orientation).

As a liquid crystal compound, the liquid crystal compound (nematic liquid crystal) whose liquid crystal phase is a nematic phase is mentioned, for example. As such a liquid crystal compound, a liquid crystal polymer or a liquid crystal monomer can be used, for example. The liquid crystal compound may have a lyotropic or thermotropic expression mechanism. The liquid crystal polymer and the liquid crystal monomer may be used alone or in combination.

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

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

Any suitable liquid crystal monomer may be employed as the liquid crystal monomer. For example, polymerizable mesogen compounds described in Japanese Patent Application Publications 2002-533742 (WO00 / 37585), EP358208 (US5211877), EP66137 (US4388453), WO93 / 22397, EP0261712, DE19504224, DE4408171 and GB2280445, etc. can be used. As a specific example of such a polymerizable mesogen compound, BASF's brand name LC242, Merck's brand name E7, and Wacker-Chem's brand name LC-Sillicon-CC3767 are mentioned, for example. As the liquid crystal monomer, for example, a nematic liquid crystal monomer is preferable.

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

As the orientation treatment, any suitable orientation treatment may be employed. Specifically, mechanical orientation treatment, physical orientation treatment, and chemical orientation treatment are exemplified. As a specific example of a mechanical orientation treatment, rubbing treatment and extending | stretching treatment are mentioned. As a specific example of a physical orientation treatment, a magnetic field orientation treatment and an electric field orientation treatment are mentioned. Specific examples of the chemical alignment treatment include an oblique vapor deposition method and a photo-alignment treatment. Any suitable conditions may be adopted as the treatment conditions for the various alignment treatments depending on the purpose.

The alignment of the liquid crystal compound is performed by treating at a temperature representing the liquid crystal phase depending on the type of the liquid crystal compound. By performing such a temperature treatment, the liquid crystal compound takes a liquid crystal state, and the liquid crystal compound is aligned in accordance with the orientation treatment direction of the substrate surface.

The fixing of the alignment state is performed in one embodiment by cooling the oriented liquid crystal compound. When the liquid crystal compound is a polymerizable monomer or a crosslinkable monomer, fixation of the alignment state is performed by subjecting the liquid crystal compound oriented as described above to polymerization treatment or crosslinking treatment.

Details of the specific example of the liquid crystal compound and the method of forming the alignment-solidified layer are described in Japanese Patent Laid-Open No. 2006-163343. The description of this publication is incorporated herein by reference.

As another example of the alignment-solidified layer, a form in which the discotic liquid crystal compound is oriented in any of vertical alignment, hybrid alignment and oblique alignment is mentioned. As for the discotic liquid crystal compound, the disc face 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 perpendicular, the average value of the angle formed by the film surface and the disc surface of the discotic liquid crystal compound is preferably 70 ° to 90 °, more preferably 80 ° to 90 °, and more preferably Means 85 ° to 90 °. As a discotic liquid crystal compound, cyclic parent nuclei such as benzene, 1,3,5-triazine, and calix arene are generally arranged at the center of a molecule, and linear alkyl groups, alkoxy groups, and substituted benzoyloxy groups are side chains thereof. Refers to a liquid crystal compound having a radially substituted disk-like molecular structure. As a representative example of discotic liquid crystal, research reports of C. Destrade, Mol. Cryst. Liq. Cryst. A study report of benzene derivatives, triphenylene derivatives, truxene derivatives, phthalocyanine derivatives, or B. Kohne, described in Vol. 71, p. 111 (1981), Angew. Chem. The cyclohexane derivative described in Vol. 96, p. 70 (1984), and a study report by J. M. Lehn, J. Chem. Soc. Chem. Commun., 1794 (1985), J. Zhang's research report, J. Am. Chem. Soc. Azacrown or phenylacetylene-based macrocycles described in 116, page 2655 (1994). As another specific example of the discotic liquid crystal compound, for example, the compounds described in Japanese Unexamined Patent Publication No. 2006-133652, Japanese Unexamined Patent Publication No. 2007-108732, and Japanese Unexamined Patent Publication No. 2010-244038 are exemplified. The above documents and publications are incorporated herein by reference.

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

The first retardation layer typically has a refractive index characteristic of nx> ny = nz. The first retardation layer is typically provided to impart anti-reflection properties to the polarizing plate, and can function as a λ / 4 plate when the first retardation layer is a single layer of the oriented solidification layer. In this case, the in-plane retardation Re (550) of the first retardation layer is preferably 100 nm to 190 nm, more preferably 110 nm to 170 nm, still more preferably 130 nm to 160 nm. In addition, here, 'ny = nz' includes not only cases where ny and nz are exactly the same, but also cases where they are substantially the same. Therefore, there may be a case where ny> nz or ny <nz is 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. When the polarizing plate with a retardation layer obtained by satisfying such a relationship is used in an image display device, a very excellent reflection color can be achieved.

The first retardation layer may exhibit a reverse-dispersion wavelength characteristic in which the phase difference value increases according to the wavelength of the measurement light, or may exhibit a positive wavelength dispersion characteristic in which the phase difference value decreases according to the wavelength of the measurement light, and the phase difference value is measured A flat wavelength dispersion characteristic that hardly changes even with the wavelength of light may be exhibited. In one embodiment, the first retardation layer exhibits a reverse dispersion wavelength characteristic. In this case, Re (450) / Re (550) of the retardation layer is preferably 0.8 or more and less than 1, more preferably 0.8 or more and 0.95 or less. With such a structure, it is possible to realize very excellent antireflection characteristics.

The angle θ between the slow axis of the first retardation layer 20 and the absorption axis of the polarizing film 11 is preferably 40 ° to 50 °, more preferably 42 ° to 48 °, even more preferably Is about 45 °. When the angle θ is such a range, a polarizing plate with a retardation layer having very good circular polarization properties (resulting in very good anti-reflection properties) can be obtained by setting the first retardation layer to a λ / 4 plate as described above.

In another embodiment, the first retardation layer 20 may have a stacked structure of the first oriented solidified layer 21 and the second oriented solidified layer 22 as shown in FIG. 3. In this case, either of the first oriented solidified layer 21 and the second oriented solidified layer 22 can function as a λ / 4 plate, and the other can function as a λ / 2 plate. Accordingly, the thickness of the first oriented solidified layer 21 and the second oriented solidified layer 22 can be adjusted to obtain a desired in-plane retardation of the λ / 4 plate or the λ / 2 plate. For example, when the first oriented solidified layer 21 functions as a λ / 2 plate, and the second oriented solidified layer 22 functions as a λ / 4 plate, the thickness of the first oriented solidified layer 21 is, for example, 2.0 Μm to 3.0 µm, and the thickness of the second oriented solidification 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 solidification layer is preferably 200 nm to 300 nm, more preferably 230 nm to 290 nm, and even more preferably 250 nm to 280 nm. The in-plane retardation Re (550) of the second oriented solidified layer is as described above with respect to the oriented solidified layer of a single layer. The angle between 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 still more preferably about 15 °. The angle between 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 still more preferably about 75 °. With such a configuration, it is possible to obtain characteristics close to ideal reverse wavelength dispersion characteristics, and as a result, very excellent antireflection characteristics can be realized. The liquid crystal compound constituting the first alignment-solidified layer and the second alignment-solidified layer, the method for forming the first alignment-solidified layer and the second alignment-solidified layer, and optical properties are as described above with respect to the single-layered alignment-solidified layer.

D. Second phase difference layer

The second retardation layer may be a so-called positive C plate having a refractive index characteristic of nz> nx = ny as described above. By using a positive C plate as the second retardation layer, reflection in the oblique direction can be satisfactorily prevented, and wide viewing angle of the antireflection function is enabled. 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, further preferably -90 nm to -200 nm, particularly preferably -100nm to -180nm. Here, 'nx = ny' includes not only cases where nx and ny are strictly identical, but also cases where nx and ny are substantially identical. That is, the in-plane retardation Re (550) of the second retardation layer may be less than 10 nm.

The second retardation layer having a refractive index characteristic of nz> nx = ny can be formed of any suitable material. The second retardation layer preferably consists of a film comprising a liquid crystal material fixed in a homeotropic orientation. The liquid crystal material (liquid crystal compound) capable of homeotropic alignment may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the method for forming the liquid crystal compound and the retardation layer include a liquid crystal compound described in Japanese Patent Application Laid-Open No. 2002-333642 and a 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 substrate with conductive layer

The conductive layer can be formed by depositing a metal oxide film on any suitable substrate by any suitable deposition method (eg, vacuum deposition, sputtering, CVD, ion plating, spraying, etc.). Examples of the metal oxide include indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimony composite oxide, zinc-aluminum composite oxide, and indium-zinc composite oxide. Especially, it is indium-tin composite oxide (ITO).

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

The conductive layer may be transferred from the above substrate to the first retardation layer (or, if present, the second retardation layer), and the conductive layer alone may be a constituent layer of a polarizing plate with a retardation layer, or a laminate with a substrate (with a conductive layer) It may be laminated on the first retardation layer (or, if present, the second retardation layer). Preferably, the substrate is optically isotropic, and thus the conductive layer can be used for a polarizing plate with a retardation layer as an isotropic substrate with a conductive layer.

As the optically isotropic substrate (isotropic substrate), any suitable isotropic substrate can be employed. As a material constituting the isotropic substrate, for example, a material having a resin having no conjugate system such as norbornene-based resin or olefin-based resin as a main skeleton, and having a cyclic structure such as a lactone ring or a glutarimide ring in the main chain of an acrylic resin And materials. By using such a material, when an isotropic substrate is formed, the expression of the phase difference accompanying the orientation of the molecular chain can be suppressed to a small extent. The thickness of the isotropic substrate is preferably 50 μm or less, and more preferably 35 μm or less. The lower limit of the thickness of the isotropic substrate is, for example, 20 µm.

The conductive layer and / or the conductive layer of the isotropic substrate with the conductive layer may be patterned as necessary. By patterning, a conductive portion and an insulating portion can be formed. As a result, an electrode can be formed. The electrode can function as a touch sensor electrode that senses contact with the touch panel. Any appropriate method can be adopted as the patterning method. A wet etching method and a screen printing method are mentioned as a specific example of a patterning method.

F. Image display device

The polarizing plates with retardation layers described in items A to E can be applied to an image display device. Accordingly, the present invention includes an image display device using such a polarizing plate with a retardation layer. Representative examples of the image display device include a liquid crystal display device and an electroluminescence (EL) display device (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 plates with retardation layers described in items A to E on the viewer side. The polarizing plate with a retardation layer is laminated such that the retardation layer is on the image display cell (eg, liquid crystal cell, organic EL cell, inorganic EL cell) side (so that the polarizing film is on the viewing side). In one embodiment, the image display device has a curved shape (actually, a curved display screen) and / or can be bent or bent. In such an image display device, the effect of the polarizing plate with a retardation layer of the present invention becomes remarkable.

[Example]

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

(1) thickness

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

(2) Single group transmittance and polarization degree

For the laminate (polarizing plate) of the polarizing film / protective layer used in Examples and Comparative Examples, simplex transmittance Ts, parallel transmittance Tp, orthogonal measured using an ultraviolet / visible ray spectrophotometer (V-7100 manufactured by Nippon Bunko Co., Ltd.) Transmittance Tc was made into Ts, Tp, and Tc of a polarizing film, respectively. These Ts, Tp, and Tc are Y values measured by a two-degree field of view (C light source) of JIS Z8701 to perform visibility correction. Moreover, the refractive index of the protective layer was 1.50, and the refractive index of the surface on the opposite side to the protective layer of the polarizing film was 1.53.

From the obtained Tp and Tc, the polarization degree P was calculated by the following formula.

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

In addition, the spectrophotometer can perform the same measurement with Otsuka Denshi LPF-200 etc. As an example, Table 1 shows the measured values of the single transmittance Ts and the polarization degree P obtained by the measurement using V-7100 and LPF-200 for samples 1 to 3 of the polarizing plates having the same configuration as the following examples. As shown in Table 1, the difference between the measured value of simplex transmittance of V-7100 and the measured value of simplex transmittance of LPF-200 is 0.1% or less, and it can be seen that equivalent measurement results can be obtained even when using any spectrophotometer. .

[Table 1]

In addition, for example, when a polarizing plate having an adhesive having surface treatment or diffusion performance of anti-glare (AG) as a measurement object, different measurement results may be obtained depending on the spectrophotometer, but in this case, the same polarizing plate may be used for each spectroscopy. By performing numerical conversion based on the measured value when measured with a photometer, it is possible to compensate for the difference in measured values depending on the spectrophotometer.

(3) Variation of optical properties of the long polarized film

The measurement samples were cut out at five positions at equal intervals along the width direction from the polarizing plates used in Examples and Comparative Examples, and the group transmittance of the central portion of each of the five measurement samples was measured in the same manner as in (2) above. . Subsequently, the difference between the maximum value and the minimum value in the single transmittance measured at each measurement position was calculated, and this value was used as the variation in the optical properties of the long-length polarizing film.

(4) Variation of optical properties of sheet-fed polarizing film

Measurement samples of 100 mm × 100 mm were cut out from the polarizing plates used in Examples and Comparative Examples, and variations in optical properties of the single-leaf polarizing plates (50 cm 2) were determined. Specifically, the measurement was performed in the same manner as in (2) above, in which the total positions of five positions in the vicinity of the center and the center portion of each of the four sides of the measurement sample were approximately 1.5 cm to 2.0 cm from the midpoint of each side. Subsequently, the difference between the maximum value and the minimum value in the single transmittance measured at each measurement position was calculated, and this value was used as a variation in the optical properties of the single-leaf polarizing film.

(5) bending

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

(6) Unit weight

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

(7) bending resistance

The polarizing plate with a retardation layer obtained in Examples and Comparative Examples was cut into a size of 50 mm × 100 mm. At this time, it cut out so that the direction of the absorption axis of the polarizing film becomes the short side direction. A polarization plate with a retardation layer cut under the condition of 50% RH at 20 ° C was used for a bending test using a constant temperature and humidity chamber-attached tester (YU ASA, CL09 type-D01). 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 outward, and the number of bendings until cracks, peeling, film breakage, etc., which are poor display is generated. It measured and evaluated based on the following criteria (bending diameter: 2 mmφ).

<Evaluation criteria>

Less than 10,000 times: Bad

10,000 to 30,000: Good

30,000 or more: Excellent

[Example 1]

1. Preparation of polarizing film

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

Potassium iodide in 100 parts by weight of 100 parts by weight of PVA-based resin mixed with polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Co., Ltd., trade name `` Kose Finemer Z410 '') 9: 1 The PVA aqueous solution (coating solution) was prepared by dissolving what was added by weight in water.

The PVA aqueous solution was applied to a corona-treated surface of a resin substrate and dried at 60 ° C. to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.

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

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

Subsequently, the single transmittance (Ts) of the polarizing film finally obtained in a dyeing bath at a liquid temperature of 30 ° C (aqueous solution obtained by mixing iodine and potassium iodide in a weight ratio of 1: 7 with respect to 100 parts by weight of water) is 46% or more. It was immersed for 60 seconds while adjusting the concentration (staining treatment).

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

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

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

Thereafter, while drying in an oven maintained at 90 ° C., the SUS-made heating roll was kept at 75 ° C. for about 2 seconds (dry shrinkage treatment). The shrinkage rate in the width direction of the laminate by the dry shrinkage treatment was 5.2%.

Thus, a polarizing film having a thickness of 5 µm was formed on the resin substrate.

2. Preparation of polarizer

An acrylic film (surface refractive index of 1.50, 40 µm) was bonded as a protective layer to the surface of the polarizing film obtained above (the side opposite to the resin substrate) via an ultraviolet curing adhesive. Specifically, coating was performed so that the total thickness of the curable adhesive was 1.0 µm, and bonding was performed using a roll machine. Thereafter, the UV light was irradiated from the protective layer side to cure the adhesive. Subsequently, after slitting both ends, the resin substrate was peeled off to obtain a long polarizing plate (width: 1300 mm) having a configuration of a protective layer / polarizing film. The polarizing plate (substantially, the polarizing film) had a simple substance transmittance of 46.82% and a polarization degree of 93.238%. In addition, the fluctuation of the optical properties of the long polarizing film was 0.44%, and the fluctuation of the optical properties of the single-phase polarizing film was 0.14%.

3. Preparation of first oriented solidified layer and second oriented solidified layer constituting retardation layer

10 g of a polymerizable liquid crystal showing a nematic liquid crystal phase (manufactured by BASF: trade name 'Paliocolor LC242', represented by the following formula), and a photopolymerization initiator for the polymerizable liquid crystal compound (manufactured by BASF: trade name 'Irgacure 907') A liquid crystal composition (coating solution) was prepared by dissolving 3 g in 40 g of toluene.

The surface of a polyethylene terephthalate (PET) film (38 µm thick) was rubbed using a rubbing cloth to perform orientation treatment. The direction of the alignment treatment was set to be 15 ° when viewed from the viewing side with respect to the direction of the absorption axis of the polarizing film when affixed to the polarizing plate. The liquid crystal coating solution was coated on this alignment treatment surface with a bar coater, and the liquid crystal compound was aligned by heating and drying at 90 ° C for 2 minutes. The liquid crystal layer thus formed was irradiated with 1 mJ / cm 2 of light using a metal halide lamp, and the liquid crystal layer was cured to form a liquid crystal alignment solidified layer A on the PET film. The thickness of the liquid crystal aligning solidified layer A was 2.5 µm, and the in-plane retardation Re (550) was 270 nm. In addition, the liquid crystal aligning solidified layer A had a refractive index distribution of nx> ny = nz.

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

4. Preparation of polarizing plate with retardation layer

The liquid crystal aligning solidified layer A and liquid crystal aligning solidified layer B obtained in 3. were transferred to the surface of the polarizing film of the polarizing plate obtained in 2. At this time, the angle between the absorption axis of the polarizing film and the slow axis of the oriented solidification layer A was 15 °, and the angle between the absorption axis of the polarizing film and the slow axis of the oriented solidification layer B was 75 ° to perform transfer (bonding). . In addition, each transfer (bonding) was performed through the ultraviolet curing adhesive (thickness: 1.0 µm) used in 2. above. Thus, a polarizing plate with a retardation layer having a configuration of a protective layer / adhesive layer / polarizing film / adhesive layer / phase difference layer (first oriented solidification layer / adhesive layer / second oriented solidified layer) was obtained. The obtained polarizing plate with a retardation layer had a total thickness of 52 µm. The obtained polarizing plate with a retardation layer was provided for evaluation of said (5)-(7). The amount of warpage was 1.8 mm.

[Example 2]

A polarizing plate with a retardation layer was produced in the same manner as in Example 1 except that an acrylic film having a thickness of 20 μm was used as the protective layer. The total thickness of the obtained polarizing plate with a retardation layer was 32 µm. The obtained polarizing plate with a retardation layer was provided in the same evaluation as Example 1. The amount of warping 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 provided in the same evaluation as Example 1. The amount of warpage was 1.3 mm.

[Comparative Example 1]

1. Production of polarizer

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

2. Preparation of polarizer

As an adhesive, an aqueous solution containing a polyvinyl alcohol resin containing an acetoacetyl group (average polymerization degree of 1,200, saponification degree of 98.5 mol%, acetoacetylation degree of 5 mol%) and methylol melamine in a weight ratio of 3: 1 was used. Using this adhesive, a triacetylcellulose (TAC) film with a hard coat layer having a thickness of 25 µm was rolled onto one side of the polarizer obtained above, and a TAC film having a thickness of 25 µm was rolled onto the other side of the polarizer. After bonding with aikido, it is heated and dried in an oven (temperature is 60 ° C., time is 5 minutes), and the protective layer 1 (25 µm thick) / adhesive layer / polarizer / adhesive layer / protective layer 2 (25 µm thick) ) Was prepared.

3. Preparation of polarizing plate with retardation layer

The liquid crystal alignment-solidified layer A and the liquid crystal alignment-solidified layer B were transferred in this order to the surface of the protective layer 2 of the polarizing plate obtained in 2. above in the same manner as in Example 1, to thereby protect the protective layer 1 / adhesive layer / polarizer / A polarizing plate with a retardation layer having a configuration of an adhesive layer / protective layer (2) / adhesive layer / phase difference layer (first oriented solidification layer / adhesive layer / second oriented solidified 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 provided in the same evaluation as Example 1. The amount of warpage was 4.2 mm.

[Comparative Example 2]

In the same manner as in Example 1, except that potassium iodide was not added to the PVA aqueous solution (coating solution), the draw ratio in the air-assisted stretching treatment was increased to 1.8 times, and the heating roll was not used in the drying shrinkage treatment. By attempting to prepare a polarizing film, the PVA-based resin layer was dissolved in the dyeing treatment and the underwater stretching treatment, so that the polarizing film could not be produced. Therefore, a polarizing plate with a retardation layer could not be produced.

[Comparative Example 3]

1. Preparation of polarizer

A long polarizing plate (width: 1300 mm) having a configuration of a protective layer / polarizing film was obtained in the same manner as in Example 1 except that a TAC film having a thickness of 25 μm was used as the protective layer.

2. 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 wing and a reflux cooler controlled at 100 ° C. Bis [9- (2-phenoxycarbonylethyl) fluorene-9-yl] methane 29.60 parts by mass (0.046 mol), isosorbide (ISB) 29.21 parts by mass (0.200 mol), spiroglycol (SPG) 42.28 parts by mass Part (0.139 mol), diphenyl carbonate (DPC) 63.77 parts by mass (0.298 mol) and 1.19 x 10 ^-2 parts by mass of calcium acetate monohydrate (6.78 x 10 ^-5 mol) were added as a catalyst. After nitrogen substitution in the reactor under reduced pressure, heating was performed with heat, and stirring was started when the internal temperature reached 100 ° C. After 40 minutes from the start of the temperature rise, the internal temperature was reached to 220 ° C, control was carried out to maintain the temperature, and decompression was started, and after reaching 220 ° C, the temperature was 13.3 kPa at 90 minutes. The phenol vapor by-product along with the polymerization reaction was led to a reflux cooler at 100 ° C, the monomer component containing a small amount in the phenol vapor was returned to the reactor, and the phenol vapor that was not condensed was led to a condenser at 45 ° C for recovery. . Nitrogen was introduced into the first reactor, and once the pressure was restored to atmospheric pressure, the oligomerized reaction solution in the first reactor was transferred to the second reactor. Subsequently, the temperature rise and decompression in the second reactor were started, and the internal temperature was 240 ° C and the pressure was 0.2 kPa in 50 minutes. Subsequently, polymerization proceeded until it became a predetermined stirring power. When the desired power was reached, nitrogen was introduced into the reactor and pressurized, and the resulting polyester carbonate-based resin was extruded in water, and the strand was cut to obtain pellets.

2-2. Production of retardation film

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

3. Preparation of polarizing plate with retardation layer

The retardation film obtained in 2. above was pasted on the surface of the polarizing film of the polarizing plate obtained in 1. through an acrylic pressure-sensitive adhesive (5 µm thick). At this time, the absorption axis of the polarizing film and the slow axis of the retardation film were brought together to form an angle of 45 °. Thus, a polarizing plate with a retardation layer having a configuration of a protective layer / adhesive layer / polarizing film / adhesive layer / phase difference layer was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 89 µm. The obtained polarizing plate with a retardation layer was provided for evaluation of said (6) and (7).

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

[Table 2]

[evaluation]

As is apparent from the comparison between Table 2 and Example 1 and Comparative Example 2, the polarizing plate with a retardation layer of the example of the present invention is thin, curvature after heating test is suppressed, and optical properties are excellent. Moreover, it turns out that bending resistance improves because the weight per unit area of the polarizing plate with a retardation layer is below a predetermined value.

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

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

Claims (12)

A polarizing plate comprising a polarizing film and a protective layer on at least one side of the polarizing film, and a retardation layer,
The polarizing film is composed of a polyvinyl alcohol-based resin film containing a dichroic material, the thickness of which is 8 µm or less, the simple substance transmittance is 46% or more, and the polarization degree is 92% or more,
A polarizing plate with a phase difference layer, wherein the phase difference layer is an alignment-solidified layer of a liquid crystal compound. According to claim 1,
Unit weight is 6.5mg / ㎠ The following is a polarizing plate with a retardation layer. According to claim 1,
A polarizing plate with a retardation layer having a total thickness of 60 µm or less. According to claim 1,
The retardation layer is a single layer of the alignment solidification layer of the liquid crystal compound,
Re (550) of the retardation layer is 100nm ~ 190nm,
The angle between the slow axis of the retardation layer and the absorption axis of the polarizing film is 40 ° to 50 °, a polarizing plate with a retardation layer. According to claim 1,
The retardation layer has a layered structure between the alignment-solidified layer of the first liquid crystal compound and the alignment-solidified layer of the second liquid crystal compound,
Re (550) of the alignment-solidified layer of the first liquid crystal compound is 200 nm to 300 nm, and the angle formed by the slow axis and the absorption axis of the polarizing film is 10 ° to 20 °,
The Re (550) of the alignment solidification layer of the second liquid crystal compound is 100 nm to 190 nm, and the angle between the slow axis and the absorption axis of the polarizing film is 70 ° to 80 °, a polarizing plate with a retardation layer. According to claim 1,
The polarizing plate with a phase difference layer whose difference between the maximum value and the minimum value of simple substance transmittance in the area of 50 cm <2> of the polarizing film is 0.3% or less. According to claim 1,
A polarizing plate with a retardation layer having a width of 1000 mm or more and a difference between the maximum value and the minimum value of simple substance transmittance at a position along the width direction of the polarizing film is 0.7% or less. According to claim 1,
The polarizing plate with a retardation layer whose single-transmittance of the said polarizing film is 48% or less and polarization degree is 97% or less. According to claim 1,
A polarizing plate with a retardation layer further comprising another retardation layer outside the retardation layer, wherein the refractive index characteristics of the other retardation layer exhibit a relationship of nz> nx = ny. According to claim 1,
A polarizing plate with a retardation layer further comprising a conductive layer or an isotropic substrate with a conductive layer on the outside of the retardation layer. An image display device comprising the polarizing plate with a retardation layer according to any one of claims 1 to 10. The method of claim 11,
An image display device which is an organic electroluminescent display device or an inorganic electroluminescent display device.

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