JP7242884B2 - Polarizing plate with retardation layer and image display device using the same - Google Patents

Description

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

2. Description of the Related Art In recent years, image display devices typified by liquid crystal display devices and electroluminescence (EL) display devices (eg, organic EL display devices and inorganic EL display devices) have rapidly spread. Polarizing plates and retardation plates are typically used in image display devices. Practically, a polarizing plate with a retardation layer, in which a polarizing plate and a retardation plate are integrated, is widely used (for example, Patent Document 1). Recently, as the demand for thinner image display devices has increased, the demand for thinner polarizing plates with retardation layers has also increased. Also, in recent years, there has been an increasing demand for curved image display devices and/or bendable or bendable image display devices. Therefore, the polarizing plate and the polarizing plate with a retardation layer are also required to be made thinner and more flexible.

As a method for thinning the polarizing plate, it has been proposed to reduce the thickness of the protective layer and to laminate the protective layer only on one side of the polarizer. However, these methods cannot sufficiently protect the polarizer, and there is room for improvement in durability. Furthermore, there is a problem that cracks are likely to occur due to heat treatment.

JP-A-2001-343521

The present invention has been made to solve the above-described conventional problems, and a main object thereof is to provide a retardation layer-attached polarizing plate in which the occurrence of cracks during heating is suppressed.

A polarizing plate with a retardation layer according to an embodiment of the present invention has a polarizing plate including a polarizer and a protective layer disposed on one side of the polarizer, and a retardation layer. This polarizer is composed of a polyvinyl alcohol-based resin film, and the polyvinyl alcohol has an orientation function of 0.30 or less. It is below.
A polarizing plate with a retardation layer according to another embodiment of the present invention has a polarizing plate including a polarizer and a protective layer disposed on one side of the polarizer, and a retardation layer. This polarizer has a puncture strength of 30 gf/μm or more, this retardation layer is an alignment solidified layer of a liquid crystal compound, and the thickness of this protective layer is 10 μm or less.
In one embodiment, the total thickness of the retardation layer-attached polarizing plate is 30 μm or less.
In one embodiment, the polarizer has a thickness of 10 μm or less.
In one embodiment, the polarizer has a single transmittance of 40.0% or more and a degree of polarization of 99.0% or more.
In one embodiment, the protective layer is selected from the group consisting of a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin, a photo-cationically cured epoxy resin, and a solidified coating film of an organic solvent solution of an epoxy resin. It is composed of at least one selected.
In one embodiment, the thermoplastic acrylic resin has at least one repeating unit selected from the group consisting of lactone ring units, glutaric anhydride units, glutarimide units, maleic anhydride units and maleimide units.
In one embodiment, the protective layer is a photo-cationically cured epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton.
An image display device is provided in another aspect of the present invention. This image display device includes the retardation layer-attached polarizing plate.

According to an embodiment of the present invention, a polarizer having an orientation function of polyvinyl alcohol (PVA) of 0.30 or less, a protective layer having a thickness of 10 μm or less, and a retardation layer that is an alignment fixed layer of a liquid crystal alignment compound. A polarizing plate with a retardation layer is provided. Further, according to another embodiment of the present invention, a retardation having a polarizer having a puncture strength of 30 gf/μm or more, a protective layer having a thickness of 10 μm or less, and a retardation layer of an alignment solidification layer of a liquid crystal alignment compound. A layered polarizer is provided. By using such a retardation layer-attached polarizing plate, the retardation layer-attached polarizing plate can be made thinner, and the occurrence of cracks during heating can be suppressed. Furthermore, crack generation during bending can also be suppressed.

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

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

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

A. Overall Configuration of Retardation Layer-Equipped Polarizing Plate FIG. 1 is a schematic cross-sectional view of a retardation layer-attached polarizing plate according to one embodiment of the present invention. A polarizing plate 100 with a retardation layer of this embodiment has a polarizing plate 10 and a retardation layer 20 . The polarizing plate 10 includes a polarizer 11, a first protective layer 12 arranged on one side of the polarizer 11, and a second protective layer 13 arranged on the other side of the polarizer 11. . Depending on the purpose, one of the first protective layer 12 and the second protective layer 13 may be omitted. For example, if the retardation layer 20 can also function as a protective layer for the polarizer 11, the second protective layer 13 may be omitted. Retardation layer 20 is laminated to polarizer 11 or second protective layer 13 via any suitable adhesive layer or adhesive layer (not shown). In the embodiment of the present invention, the polarizer 11 is composed of a polyvinyl alcohol resin film, and the orientation function of polyvinyl alcohol is 0.30 or less. In another embodiment of the invention, the polarizer 11 has a puncture strength of 30 gf/μm or more. Moreover, the thickness of the protective layer is 10 μm or less. When the polarizing plate 100 includes the first protective layer 12 and the second protective layer 13, at least one of the protective layers may have a thickness of 10 μm or less, preferably the first protective layer 12 and the second protective layer. 13 have a thickness of 10 μm or less. In one embodiment, the polarizing plate 100 may have a hard-coded layer formed on the side of the viewer-side protective layer (eg, the first protective layer 12 ) that is not in contact with the polarizer 11 . In this embodiment, the sum of the thickness of the protective layer and the thickness of the hard coat layer is preferably 10 μm or less.

FIG. 2 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to another embodiment of the invention. As shown in FIG. 2, in a retardation layer-attached polarizing plate 101 according to another embodiment, another retardation layer 50 and/or a conductive layer or an isotropic substrate 60 with a conductive layer may be provided. Another retardation layer 50 and a conductive layer or an isotropic substrate with a conductive layer 60 are typically provided outside the retardation layer 20 (on the side opposite to the polarizing plate 10). Another retardation layer typically exhibits a refractive index characteristic of nz>nx=ny. Another retardation layer 50 and a conductive layer or an isotropic substrate 60 with a conductive layer are typically provided in this order from the retardation layer 20 side. The separate retardation layer 50 and the conductive layer or the isotropic substrate with a conductive layer 60 are typically optional layers provided as needed, and either or both of them may be omitted. For the sake of convenience, the retardation layer 20 may be referred to as a first retardation layer, and the other retardation layer 50 may be referred to as a second retardation layer. In addition, when a conductive layer or an isotropic substrate with a conductive layer is provided, the polarizing plate with a retardation layer is a so-called inner It can be applied to a touch panel type input display device.

FIG. 3 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to still another embodiment of the invention. In the embodiment of the present invention, the first retardation layer 20 is an alignment fixed layer of a liquid crystal compound. The first retardation layer 20 may be a single layer of orientation fixed layers as shown in FIGS. and may have a laminated structure.

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

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

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

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

The total thickness of the retardation layer-attached polarizing plate is preferably 30 μm or less, more preferably 25 μm or less, and still more preferably 20 μm or less. The total thickness can be, for example, 10 μm or more. According to the embodiment of the present invention, a polarizing plate with such an extremely thin retardation layer can be realized. Furthermore, the occurrence of cracks during heating can also be suppressed. Such a retardation layer-attached polarizing plate can have extremely excellent flexibility and bending durability. Such a retardation layer-attached polarizing plate can be particularly suitably applied to a curved image display device and/or a bendable or foldable image display device. The total thickness of the retardation layer-equipped polarizing plate refers to the total thickness of all layers composing the retardation layer-equipped polarizing plate, excluding the adhesive layer for adhering the polarizing plate to an external adherend such as a panel or glass. Refers to the total thickness (that is, the total thickness of the retardation layer-attached polarizing plate is the pressure-sensitive adhesive layer for attaching the retardation layer-attached polarizing plate to an adjacent member such as an image display cell, and the peeling that can be temporarily attached to the surface (not including film thickness).

The unit weight of the retardation layer-attached polarizing plate according to the embodiment of the present invention is, for example, 6.5 mg/cm ² or less, preferably 2.0 mg/cm ² to 6.0 mg/cm ² , more preferably 3 0 mg/cm ² to 5.5 mg/cm ² , more preferably 3.5 mg/cm ² to 5.0 mg/cm ² . If the display panel is thin, the weight of the retardation layer-attached polarizing plate may cause slight deformation of the panel, resulting in poor display. A polarizing plate with a retardation layer having a unit weight of 6.5 mg/cm ² or less can prevent such deformation of the panel. Further, the polarizing plate with a retardation layer having the above unit weight is easy to handle even when it is made thin, and can exhibit extremely excellent flexibility and bending durability.

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

B. Polarizing plate B-1. Polarizer A polarizer according to an embodiment of the present invention is composed of a polyvinyl alcohol (PVA) resin film and has an orientation function of 0.30 or less. With such a configuration, it is possible to suppress the occurrence of cracks during heating, particularly the occurrence of cracks along the absorption axis direction of the polarizer. In addition, it is possible to remarkably suppress the polarizer from tearing (breaking) along the absorption axis direction even when not heated. As a result, a polarizer (and, as a result, a polarizing plate) can be obtained that is extremely flexible. Such a polarizer (and consequently a polarizing plate) can preferably be applied to curved image display devices, more preferably foldable image display devices, even more preferably foldable image display devices. The orientation function is preferably 0.28 or less, more preferably 0.26 or less, and even more preferably 0.25 or less. The orientation function can be, for example, 0.05 or greater. An orientation function that is too small may not provide acceptable unitary transmission and/or degree of polarization.

The orientation function (f) is determined by attenuated total reflection (ATR) measurement using a Fourier transform infrared spectrophotometer (FT-IR) and polarized light as measurement light. Specifically, the measurement is performed with the stretching direction of the polarizer parallel and perpendicular to the polarization direction of the measurement light, and the intensity at 2941 cm ^-1 of the obtained absorbance spectrum is used to calculate according to the following formula. be done. Here, the intensity I is a value of 2941 cm ^-1 /3330 cm ^-1 with 3330 cm ^-1 as a reference peak. When f=1, the orientation is perfect, and when f=0, the orientation is random. Also, the peak at 2941 cm ⁻¹ is believed to be absorption due to vibration of the PVA main chain (—CH ₂ —) in the polarizer.
f=(3<cos ² θ>−1)/2
=(1−D)/[c(2D+1)]
=-2 x (1-D)/(2D+1)
however,
For c=(3cos ² β−1)/2 and a vibration of 2941 cm ⁻¹ β=90°.
θ: the angle of the molecular chain with respect to the stretching direction β: the angle of the transition dipole moment with respect to the molecular chain axis D=(I _⊥ )/(I _// ) (in this case, D increases as the PVA molecules are oriented)
I _⊥ : Absorption intensity when the polarization direction of the measurement light and the stretching direction of the polarizer are perpendicular I _// : Absorption intensity when the polarization direction of the measurement light and the stretching direction of the polarizer are parallel

The thickness of the polarizer is preferably 10 μm or less, more preferably 8 μm or less, still more preferably 7 μm or less. The thickness of the polarizer can be, for example, 1 μm or more. The thickness of the polarizer is 2 μm to 6 μm in one embodiment, 2 μm to 4 μm in another embodiment, 2 μm to 3 μm in still another embodiment, and 5.5 μm to 7.0 μm in still another embodiment. It may be 5 μm, and in yet another embodiment between 6 μm and 7.2 μm. This very small polarizer thickness allows for very small thermal shrinkage. It is speculated that such a configuration can also contribute to suppression of breakage in the direction of the absorption axis.

The polarizer preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm. The single transmittance of the polarizer is preferably 40.0% or more, more preferably 41.0% or more. Single transmittance can be, for example, 49.0% or less. The single transmittance of the polarizer is 40.0% to 45.0% in one embodiment. The polarization degree of the polarizer is preferably 99.0% or more, more preferably 99.4% or more. The degree of polarization can be, for example, 99.999% or less. The degree of polarization of the polarizer is between 99.0% and 99.99% in one embodiment. According to the present invention, although the orientation function is very small as described above, such practically acceptable single transmittance and degree of polarization can be realized. This is presumed to be due to the manufacturing method described later. The single transmittance is typically a Y value measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction. The degree of polarization is typically determined by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc, which are measured using an ultraviolet-visible spectrophotometer and subjected to visibility correction.
Degree of polarization (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100

In an embodiment of the present invention, the polarizer has a puncture strength of 30 gf/μm or more, preferably 35 gf/μm or more, more preferably 40 gf/μm or more, still more preferably 45 gf/μm or more, Particularly preferably, it is 50 gf/μm or more. The puncture strength can be, for example, 80 gf/μm or less. By setting the puncture strength of the polarizer within such a range, it is possible to significantly suppress the polarizer from tearing along the absorption axis direction. As a result, a polarizer (and, as a result, a polarizing plate) can be obtained that is extremely flexible. The puncture strength indicates the resistance to cracking of the polarizer when the polarizer is pierced with a predetermined strength. The piercing strength can be expressed, for example, as the strength (breaking strength) at which the polarizer is broken when a predetermined needle is attached to a compression tester and the needle is pierced into the polarizer at a predetermined speed. As is clear from the unit, the puncture strength means the puncture strength per unit thickness (1 μm) of the polarizer.

The polarizer is composed of a PVA-based resin film as described above. Preferably, the PVA-based resin constituting the PVA-based resin film (substantially, the polarizer) contains acetoacetyl-modified PVA-based resin. With such a configuration, a polarizer having a desired puncture strength can be obtained. The amount of the acetoacetyl-modified PVA-based resin is preferably 5-20% by weight, more preferably 8-12% by weight, when the total PVA-based resin is 100% by weight. . If the blending amount is in such a range, the puncture strength can be made in a more suitable range.

A polarizer can typically be made using a laminate of two or more layers. A specific example of a polarizer obtained using a laminate is a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate. A polarizer obtained by using a laminate of a resin base material and a PVA-based resin layer formed by coating on the resin base material is obtained, for example, by applying a PVA-based resin solution to the resin base material and drying the resin base material. forming a PVA-based resin layer thereon to obtain a laminate of a resin substrate and a PVA-based resin layer; stretching and dyeing the laminate to use the PVA-based resin layer as a polarizer; obtain. In this embodiment, preferably, a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin is formed on one side of the resin substrate. Stretching typically includes immersing the laminate in an aqueous boric acid solution for stretching. Furthermore, the stretching preferably further includes in-air stretching of the laminate at a high temperature (eg, 95° C. or higher) before stretching in an aqueous boric acid solution. In an embodiment of the present invention, the total draw ratio is, for example, 3.0 times to 4.5 times, which is significantly smaller than usual. Even with such a total draw ratio, a polarizer having acceptable optical properties can be obtained by a combination of halide addition and drying shrinkage treatment. Furthermore, in the embodiment of the present invention, it is preferable that the draw ratio of the in-air auxiliary drawing is higher than the draw ratio of the boric acid aqueous drawing. With such a configuration, it is possible to obtain a polarizer having acceptable optical properties even if the total draw ratio is small. In addition, the laminate is preferably subjected to a drying shrinkage treatment to shrink it in the width direction by 1% to 10% by heating it while transporting it in the longitudinal direction. In one embodiment, a method for manufacturing a polarizer includes subjecting a laminate to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order. By introducing auxiliary stretching, it is possible to improve the crystallinity of PVA and achieve high optical properties even when PVA is coated on a thermoplastic resin. At the same time, by increasing the orientation of PVA in advance, it is possible to prevent problems such as deterioration of orientation and dissolution of PVA when immersed in water in the subsequent dyeing process or stretching process, resulting in high optical properties. can be achieved. Furthermore, when the PVA-based resin layer is immersed in a liquid, disturbance of the orientation of the polyvinyl alcohol molecules and deterioration of the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This can improve the optical properties of the polarizer obtained through treatment steps such as dyeing treatment and underwater stretching treatment in which the laminate is immersed in a liquid. Furthermore, the optical properties can be improved by shrinking the laminate in the width direction by drying shrinkage treatment. The obtained resin substrate/polarizer laminate may be used as it is (that is, the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled off from the resin substrate/polarizer laminate. Then, any appropriate protective layer may be laminated on the release surface according to the purpose. Details of the method for manufacturing the polarizer will be described later in section B-2.

B-2. Method for producing a polarizer A method for producing a polarizer according to one embodiment of the present invention comprises polyvinyl alcohol containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin substrate. By forming a system resin layer (PVA system resin layer) to form a laminate, and by subjecting the laminate to an auxiliary stretching process in the air, a dyeing process, an underwater stretching process, and heating while conveying in the longitudinal direction. and drying shrinkage treatment for shrinking by 1% to 10% in the width direction. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin. The drying shrinkage treatment is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. The shrinkage ratio in the width direction of the laminate due to drying shrinkage treatment is preferably 1% to 10%. According to such a manufacturing method, the polarizer described in the above section B-1 can be obtained. In particular, a laminate containing a PVA-based resin layer containing a halide is produced, the laminate is stretched in multiple stages including auxiliary stretching in the air and stretching in water, and the laminate after stretching is heated with a heating roll. , a polarizer with excellent optical properties (typically unit transmittance and unit absorbance) can be obtained.

B-2-1. Production of Laminate Any appropriate method can be adopted as a method for producing a laminate of a thermoplastic resin substrate and a PVA-based resin layer. Preferably, a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin substrate and dried to form a PVA-based resin layer on the thermoplastic resin substrate. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.

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

The thickness of the PVA-based resin layer is preferably 2 μm to 30 μm, more preferably 2 μm to 20 μm. By making the thickness of the PVA-based resin layer before stretching very thin as described above and by reducing the total stretching ratio as described later, an allowable single transmittance and A polarizer with a degree of polarization can be obtained.

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

B-2-1-1. Thermoplastic Resin Substrate Any appropriate thermoplastic resin film can be employed as the thermoplastic resin substrate. Details of the thermoplastic resin base material are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580 and Japanese Patent No. 6470455. The publication is incorporated herein by reference in its entirety.

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

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

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

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

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

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

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

B-2-2. Aerial Auxiliary Stretching In order to obtain particularly high optical properties, a two-stage stretching method combining dry stretching (auxiliary stretching) and stretching in boric acid solution is selected. By introducing auxiliary stretching, such as two-stage stretching, it is possible to stretch while suppressing crystallization of the thermoplastic resin base material. Furthermore, when applying the PVA-based resin on the thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, compared to the case of applying the PVA-based resin on a normal metal drum As a result, the crystallization of the PVA-based resin becomes relatively low, which may cause a problem that sufficient optical properties cannot be obtained. On the other hand, by introducing auxiliary stretching, it is possible to increase the crystallinity of the PVA-based resin even when the PVA-based resin is applied on the thermoplastic resin, and it is possible to achieve high optical properties. Become. At the same time, by increasing the orientation of the PVA-based resin in advance, it is possible to prevent problems such as deterioration of the orientation and dissolution of the PVA-based resin when it is immersed in water in the subsequent dyeing process or stretching process. , making it possible to achieve high optical properties.

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

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

The draw ratio in the in-air auxiliary drawing is preferably 1.0 to 4.0 times, more preferably 1.5 to 3.5 times, still more preferably 2.0 to 3.0 times. be. If the stretch ratio of the in-air auxiliary stretching is within such a range, the total stretching ratio can be set within a desired range when combined with the underwater stretching, and a desired orientation function can be achieved. As a result, it is possible to obtain a polarizer in which breakage along the absorption axis direction is suppressed. Furthermore, as described above, the draw ratio of the in-air auxiliary drawing is preferably higher than the draw ratio of the boric acid aqueous drawing. With such a configuration, it is possible to obtain a polarizer having acceptable optical properties even if the total draw ratio is small.

The stretching temperature for the in-air auxiliary stretching can be set to any appropriate value depending on the material for forming the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably the glass transition temperature (Tg) of the thermoplastic resin substrate or higher, more preferably the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C or higher, and particularly preferably Tg + 15°C or higher. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, it is possible to suppress rapid crystallization of the PVA-based resin and suppress problems caused by the crystallization (for example, hindrance of orientation of the PVA-based resin layer due to stretching). can.

B-2-3. Insolubilization Treatment, Dyeing Treatment, and Crosslinking Treatment If necessary, an insolubilization treatment is performed after the auxiliary stretching treatment in the air and before the stretching treatment in water or the dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine). If necessary, a cross-linking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The cross-linking treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of boric acid. Details of the insolubilization treatment, dyeing treatment and cross-linking treatment are described, for example, in JP-A-2012-73580 (above).

B-2-4. Underwater Stretching Treatment Underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the thermoplastic resin substrate and the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80° C.), and the PVA-based resin layer undergoes its crystallization. can be stretched while suppressing As a result, a polarizer having excellent optical properties can be produced.

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

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

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

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

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

The draw ratio by underwater drawing is preferably 1.0 to 3.0 times, more preferably 1.0 to 2.0 times, still more preferably 1.0 to 1.5 times. . If the draw ratio in the underwater drawing is within such a range, the total draw ratio can be set within a desired range, and a desired orientation function can be achieved. As a result, it is possible to obtain a polarizer in which breakage along the absorption axis direction is suppressed. The total draw ratio (sum of draw ratios in the case of combining auxiliary in-air drawing and underwater drawing) is, as described above, for example 3.0 to 4.5 times the original length of the laminate. It is preferably 3.0 to 4.0 times, more preferably 3.0 to 3.5 times. By appropriately combining the addition of a halide to the coating liquid, the adjustment of the stretch ratios of the auxiliary stretching in air and the stretching in water, and the drying shrinkage treatment, it is possible to obtain acceptable optical properties even at such a total stretching ratio. A polarizer can be obtained.

B-2-5. Drying Shrinkage Treatment The drying shrinkage treatment may be performed by zone heating performed by heating the entire zone, or by heating the transport roll (using a so-called heating roll) (heated roll drying method). Preferably both are used. By drying using a heating roll, heat curling of the laminate can be efficiently suppressed, and a polarizer having an excellent appearance can be produced. Specifically, by drying the laminated body along the heating roll, the crystallization of the thermoplastic resin substrate can be efficiently promoted to increase the degree of crystallinity, which is relatively low. Even at the drying temperature, the degree of crystallinity of the thermoplastic resin substrate can be favorably increased. As a result, the thermoplastic resin base material has increased rigidity and is in a state capable of withstanding shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. Moreover, by using a heating roll, the layered product can be dried while being maintained in a flat state, so that not only curling but also wrinkling can be suppressed. At this time, the laminate can be shrunk in the width direction by drying shrinkage treatment, thereby improving the optical properties. This is because the orientation of PVA and PVA/iodine complex can be effectively enhanced. The shrinkage ratio of the laminate in the width direction due to drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%.

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

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

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

B-2-6. Other Treatments Preferably, a washing treatment is performed after the underwater stretching treatment and before the drying shrinkage treatment. The cleaning treatment is typically performed by immersing the PVA-based resin layer in an aqueous solution of potassium iodide.

B-3. Protective Layer In an embodiment of the present invention, the thickness of the protective layer is 10 μm or less. When the thickness of the protective layer is 10 μm or less, it can contribute to thinning of the polarizing plate. Even if the thickness of the protective layer of the retardation layer-attached polarizing plate is 10 μm or less, the occurrence of cracks during heating can be prevented. The thickness of the protective layer is preferably 7 μm or less, more preferably 5 μm or less, still more preferably 3 μm or less. The thickness of the protective layer is, for example, 1 μm or more.

The protective layer can be made of any suitable material. Cellulose resin such as triacetyl cellulose (TAC), polyester, polyvinyl alcohol, polycarbonate, polyamide, polyimide, polyethersulfone, polysulfone, polystyrene, polynorbornene, polyolefin, (meth) acrylic transparent resins such as acrylic, urethane, (meth)acrylic urethane, epoxy, silicone, and other thermosetting resins or ultraviolet curing resins; glassy resins such as siloxane polymers polymers.

The protective layer may be a film, a solidified product of a coating film, or a cured product (for example, a photo-cationically cured product). In one embodiment, the protective layer is composed of a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin (hereinafter simply referred to as an acrylic resin), a photo-cationically cured epoxy resin, and an organic solvent solution of an epoxy resin. is composed of at least one selected from the group consisting of the solidified product of the coating film. A specific description will be given below.

B-3-1. Solidified Coating Film of Organic Solvent Solution of Thermoplastic Acrylic Resin In one embodiment, the protective layer is composed of a solidified coating film of an organic solvent solution of thermoplastic acrylic resin.

B-3-1-1. Acrylic resin Acrylic resin preferably has a glass transition temperature (Tg) of 100°C or higher. As a result, Tg of the protective layer becomes 100° C. or higher. If the Tg of the acrylic resin is 100° C. or higher, the polarizing plate including the protective layer obtained from such a resin can be excellent in durability. Tg of the acrylic resin is preferably 110° C. or higher, more preferably 115° C. or higher, still more preferably 120° C. or higher, and particularly preferably 125° C. or higher. On the other hand, the Tg of the acrylic resin is preferably 300° C. or lower, more preferably 250° C. or lower, still more preferably 200° C. or lower, and particularly preferably 160° C. or lower. If the Tg of the acrylic resin is in such a range, the moldability can be excellent.

Any appropriate acrylic resin may be employed as the acrylic resin as long as it has the above Tg. An acrylic resin typically contains an alkyl (meth)acrylate as a main component as a monomer unit (repeating unit). As used herein, "(meth)acryl" means acryl and/or methacryl. Examples of the alkyl (meth)acrylate constituting the main skeleton of the acrylic resin include linear or branched alkyl groups having 1 to 18 carbon atoms. These can be used alone or in combination. Furthermore, any appropriate copolymerization monomer may be introduced into the acrylic resin by copolymerization. A repeating unit derived from an alkyl (meth)acrylate is typically represented by the following general formula (1):

In general formula (1), R ⁴ represents a hydrogen atom or a methyl group, and R ⁵ represents a hydrogen atom or an optionally substituted aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms. show. Examples of substituents include halogens and hydroxyl groups. Specific examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, t-(meth)acrylate, Butyl, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, (meth)acrylic dicyclopentanyl acid, chloromethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, (meth)acrylic acid 2, 3,4,5,6-pentahydroxyhexyl, 2,3,4,5-tetrahydroxypentyl (meth)acrylate, methyl 2-(hydroxymethyl)acrylate, ethyl 2-(hydroxymethyl)acrylate, 2 -(hydroxyethyl) methyl acrylate. In general formula (1), ^R5 is preferably a hydrogen atom or a methyl group. A particularly preferred alkyl (meth)acrylate is therefore methyl acrylate or methyl methacrylate.

The acrylic resin may contain only a single alkyl (meth)acrylate unit, or may contain a plurality of alkyl (meth)acrylate units in which R ⁴ and R ⁵ in the general formula (1) are different. good.

The content of alkyl (meth)acrylate units in the acrylic resin is preferably 50 mol% to 98 mol%, more preferably 55 mol% to 98 mol%, still more preferably 60 mol% to 98 mol%, particularly preferably 65 mol % to 98 mol %, most preferably 70 mol % to 97 mol %. If the content is less than 50 mol %, the effects derived from the alkyl (meth)acrylate units (eg, high heat resistance and high transparency) may not be exhibited sufficiently. If the content is more than 98 mol %, the resin becomes brittle and easily cracked, and high mechanical strength cannot be sufficiently exhibited, which may lead to poor productivity.

The acrylic resin preferably has a repeating unit containing a ring structure. Repeating units containing ring structures include lactone ring units, glutaric anhydride units, glutarimide units, maleic anhydride units, and maleimide (N-substituted maleimide) units. As for the repeating unit containing a ring structure, only one type may be included in the repeating unit of the acrylic resin, or two or more types may be included.

The lactone ring unit is preferably represented by general formula (2) below:

一般式（２）において、Ｒ^１、Ｒ^２およびＲ^３は、それぞれ独立して、水素原子または炭素数１～２０の有機残基を表す。なお、有機残基は酸素原子を含んでいてもよい。アクリル系樹脂には、単一のラクトン環単位のみが含まれていてもよく、上記一般式（２）におけるＲ^１、Ｒ^２およびＲ^３が異なる複数のラクトン環単位が含まれていてもよい。ラクトン環単位を有するアクリル系樹脂は、例えば特開２００８－１８１０７８号公報に記載されており、当該公報の記載は本明細書に参考として援用される。

In general formula (2), R ¹ , R ² and R ³ each independently represent a hydrogen atom or an organic residue having 1 to 20 carbon atoms. In addition, the organic residue may contain an oxygen atom. The acrylic resin may contain only a single lactone ring unit, or may contain a plurality of lactone ring units in which R ¹ , R ² and R ³ in the general formula (2) are different. . An acrylic resin having a lactone ring unit is described, for example, in JP-A-2008-181078, and the description of the publication is incorporated herein by reference.

The glutarimide unit is preferably represented by general formula (3) below:

In general formula (3), R ¹¹ and R ¹² each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms; R ¹³ is an alkyl group having 1 to 18 carbon atoms; or an aryl group having 6 to 10 carbon atoms. In general formula (3), preferably R ¹¹ and R ¹² are each independently hydrogen or methyl, and R ¹³ is hydrogen, methyl, butyl or cyclohexyl. More preferably, R ¹¹ is a methyl group, R ¹² is hydrogen and R ¹³ is a methyl group. The acrylic resin may contain only a single glutarimide unit, or may contain a plurality of glutarimide units in which R ¹¹ , R ¹² and R ¹³ in the general formula (3) are different. . Acrylic resins having a glutarimide unit, for example, JP-A-2006-309033, JP-A-2006-317560, JP-A-2006-328334, JP-A-2006-337491, JP-A-2006-337492 JP-A-2006-337493 and JP-A-2006-337569, and the descriptions in these publications are incorporated herein by reference. As for the glutaric anhydride unit, the above explanation regarding the glutarimide unit applies, except that the nitrogen atom substituted by R ¹³ in the general formula (3) becomes an oxygen atom.

As for the maleic anhydride unit and the maleimide (N-substituted maleimide) unit, their structures are specified by their names, so detailed descriptions thereof are omitted.

The content of repeating units containing a ring structure in the acrylic resin is preferably 1 mol % to 50 mol %, more preferably 10 mol % to 40 mol %, still more preferably 20 mol % to 30 mol %. If the content is too low, the Tg may be less than 100° C., and the resulting protective layer may have insufficient heat resistance, solvent resistance and surface hardness. If the content is too high, moldability and transparency may be insufficient.

The acrylic resin may contain repeating units other than repeating units containing alkyl (meth)acrylate units and ring structures. Examples of such repeating units include repeating units (other vinyl monomer units) derived from vinyl monomers copolymerizable with the monomers constituting the above units. Other vinyl monomers include, for example, acrylic acid, methacrylic acid, crotonic acid, 2-(hydroxymethyl)acrylic acid, 2-(hydroxyethyl)acrylic acid, acrylonitrile, methacrylonitrile, ethacrylonitrile, allyl glycidyl ether, maleic anhydride, itaconic anhydride, N-methylmaleimide, N-ethylmaleimide, N-cyclohexylmaleimide, aminoethyl acrylate, propylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethylaminopropyl methacrylate, methacryl cyclohexylaminoethyl acid, N-vinyldiethylamine, N-acetylvinylamine, allylamine, methallylamine, N-methylallylamine, 2-isopropenyl-oxazoline, 2-vinyl-oxazoline, 2-acryloyl-oxazoline, N-phenylmaleimide, phenylaminoethyl methacrylate, styrene, α-methylstyrene, p-glycidylstyrene, p-aminostyrene, 2-styryl-oxazoline and the like. These may be used alone or in combination. The kind, number, combination, content ratio, etc. of the other vinyl-based monomer units can be appropriately set according to the purpose.

The acrylic resin preferably has a weight average molecular weight of 1,000 to 2,000,000, more preferably 5,000 to 1,000,000, still more preferably 10,000 to 500,000, particularly preferably 50,000 to 500,000, and most preferably 60,000 to 150,000. The weight-average molecular weight can be determined, for example, by polystyrene conversion using a gel permeation chromatograph (GPC system, manufactured by Tosoh). Tetrahydrofuran can be used as the solvent.

The acrylic resin can be polymerized by any appropriate polymerization method using a suitable combination of the above monomer units.

In the embodiment of the present invention, acrylic resin and other resin may be used together. That is, a monomer component that constitutes an acrylic resin and a monomer component that constitutes another resin may be copolymerized, and the copolymer may be used to form a protective layer to be described later; may be subjected to forming the protective layer. Examples of other resins include thermoplastic resins such as styrenic resins, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyetheretherketone, polyester, polysulfone, polyphenylene oxide, polyacetal, polyimide, and polyetherimide. The type and blending amount of the resin to be used in combination can be appropriately set according to the purpose and desired properties of the resulting film. For example, a styrene resin (preferably an acrylonitrile-styrene copolymer) can be used together as a retardation control agent.

When an acrylic resin and another resin are used in combination, the content of the acrylic resin in the blend of the acrylic resin and the other resin is preferably 50% to 100% by weight, more preferably 60% to 100% by weight. % by weight, more preferably 70% to 100% by weight, particularly preferably 80% to 100% by weight. If the content is less than 50% by weight, the high heat resistance and high transparency inherent in the acrylic resin may not be fully reflected.

B-3-2. Photocationically Cured Epoxy Resin In one embodiment, the protective layer is composed of a photocationically cured epoxy resin. By using such a protective layer, it is possible to provide a polarizing plate and a polarizing plate with a retardation layer that achieve both excellent durability and excellent flexibility. As described above, since the protective layer is a photocationically cured product, the protective layer-forming composition contains a photocationic polymerization initiator. A photocationic polymerization initiator is a photosensitive agent having a function of a photoacid generator, and typically includes an ionic onium salt composed of a cation portion and an anion portion. In this onium salt, the cation portion absorbs light and the anion portion serves as an acid generation source. Ring-opening polymerization of the epoxy group proceeds by the acid generated from the photocationic polymerization initiator. The resulting protective layer, which is a photo-cationically cured product, has a high glass transition temperature and can reduce the iodine adsorption amount. Therefore, it is possible to provide a polarizing plate that achieves both excellent durability and excellent flexibility.

B-3-2-1. Epoxy Resin Any appropriate epoxy resin can be used as the epoxy resin. In embodiments of the present invention, epoxy resins preferably having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons can be used. Examples of aromatic skeletons include benzene ring, naphthalene ring, and fluorene ring. Epoxy resins may be used alone or in combination of two or more. An epoxy resin having a biphenyl skeleton as an aromatic skeleton is preferably used. By using an epoxy resin having a biphenyl skeleton, it is possible to provide a polarizing plate that achieves both superior durability and superior flexibility. As a representative example, an epoxy resin having a biphenyl skeleton will be described in detail below.

（式中、Ｒ^１４～Ｒ^２１は、それぞれ独立して、水素原子、炭素数１～１２の直鎖状もしくは分岐状の置換または非置換の炭化水素基、または、ハロゲン元素を表す）。In one embodiment, the epoxy resin having a biphenyl backbone is an epoxy resin containing the structure: Epoxy resins having a biphenyl skeleton may be used alone or in combination of two or more.

(In the formula, R ¹⁴ to R ²¹ each independently represent a hydrogen atom, a linear or branched substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms, or a halogen element).

R ¹⁴ to R ²¹ each independently represent a hydrogen atom, a linear or branched substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms, or a halogen element. Linear or branched substituted or unsubstituted hydrocarbon groups having 1 to 12 carbon atoms include, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, tert-pentyl group, cyclopentyl group, n-hexyl group, isohexyl group, cyclohexyl group, n-heptyl group, cycloheptyl group, methylcyclohexyl group, n- octyl group, cyclooctyl group, n-nonyl group, 3,3,5-trimethylcyclohexyl group, n-decyl group, cyclodecyl group, n-undecyl group, n-dodecyl group, cyclododecyl group, phenyl group, benzyl group, Methylbenzyl group, dimethylbenzyl group, trimethylbenzyl group, naphthylmethyl group, phenethyl group, 2-phenylisopropyl group and the like. The linear or branched substituted or unsubstituted hydrocarbon group having 1 to 12 carbon atoms preferably has 1 to 1 carbon atoms such as methyl group, ethyl group, n-propyl group, isopropyl group and n-butyl group. 4 alkyl groups. Halogen elements preferably include fluorine and bromine.

（式中、Ｒ^１４～Ｒ^２１は上記の通りであり、ｎは０～６の整数を表す）。In one embodiment, the epoxy resin having a biphenyl skeleton is an epoxy resin represented by the following formula.

(Wherein, R ¹⁴ to R ²¹ are as described above, and n represents an integer of 0 to 6).

In one embodiment, the epoxy resin having a biphenyl skeleton is an epoxy resin having only a biphenyl skeleton. By using an epoxy resin having only a biphenyl skeleton, the durability of the resulting protective layer can be further improved.

In one embodiment, the epoxy resin having a biphenyl skeleton may contain chemical structures other than the biphenyl skeleton. Chemical structures other than the biphenyl skeleton include, for example, a bisphenol skeleton, an alicyclic structure, an aromatic ring structure, and the like. In this embodiment, the proportion (molar ratio) of chemical structures other than the biphenyl skeleton is preferably less than that of the biphenyl skeleton.

A commercial product may be used as the epoxy resin having a biphenyl skeleton. Commercially available products include, for example, products manufactured by Mitsubishi Chemical Corporation under the trade names of jER YX4000, jER YX4000H, jER YL6121, jER YL664, jER YL6677, jER YL6810, and jER YL7399.

The epoxy resin having a biphenyl skeleton preferably has a glass transition temperature (Tg) of 90°C or higher. As a result, Tg of the protective layer becomes 90° C. or higher. If the Tg of the epoxy resin having a biphenyl skeleton is 90° C. or higher, the obtained polarizing plate including the protective layer tends to have excellent durability. The Tg of the epoxy resin having a biphenyl skeleton is preferably 100°C or higher, more preferably 110°C or higher, still more preferably 120°C or higher, and particularly preferably 125°C or higher. On the other hand, the Tg of the epoxy resin having a biphenyl skeleton is preferably 300° C. or lower, more preferably 250° C. or lower, still more preferably 200° C. or lower, and particularly preferably 160° C. or lower. If the Tg of the epoxy resin having a biphenyl skeleton is in such a range, moldability can be excellent.

The epoxy equivalent weight of the epoxy resin having a biphenyl skeleton is preferably 100 g/equivalent or more, more preferably 150 g/equivalent or more, still more preferably 200 g/equivalent or more. The epoxy equivalent weight of the epoxy resin having a biphenyl skeleton is preferably 3000 g/equivalent or less, more preferably 2500 g/equivalent or less, still more preferably 2000 g/equivalent or less. When the epoxy equivalent of the epoxy resin having a biphenyl skeleton is within the above range, a more stable protective layer (a sufficiently cured protective layer with less residual monomer) can be obtained. As used herein, the term "epoxy equivalent" refers to "the mass of an epoxy resin containing one equivalent of an epoxy group" and can be measured according to JIS K7236.

In an embodiment of the present invention, an epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton may be used in combination with another resin. That is, a blend of an epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton and another resin may be used to form the protective layer. Other resins include, for example, styrene resins, thermoplastic resins such as polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyetheretherketone, polyester, polysulfone, polyphenylene oxide, polyacetal, polyimide, and polyetherimide, acrylic resins and Oxetane-based resins and the like can be mentioned. Acrylic resins and oxetane resins are preferably used. The type and blending amount of the resin to be used in combination can be appropriately set according to the purpose and desired properties of the resulting film. For example, a styrenic resin can be used together as a retardation control agent.

Any appropriate acrylic resin can be used as the acrylic resin. For example, the (meth)acrylic compound includes, for example, a (meth)acrylic compound having one (meth)acryloyl group in the molecule (hereinafter also referred to as "monofunctional (meth)acrylic compound"), intramolecular includes (meth)acrylic compounds having two or more (meth)acryloyl groups (hereinafter also referred to as "polyfunctional (meth)acrylic compounds"). These (meth)acrylic compounds may be used alone or in combination of two or more. These acrylic resins are described, for example, in JP-A-2019-168500. The publication is incorporated herein by reference in its entirety.

Any appropriate compound having one or more oxetanyl groups in the molecule is used as the oxetane resin. For example, 3-ethyl-3-hydroxymethyloxetane, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, 3-ethyl-3-(phenoxymethyl)oxetane, 3-ethyl-3-(cyclohexyloxymethyl) Oxetane compounds having one oxetanyl group in the molecule such as oxetane, 3-ethyl-3-(oxiranylmethoxy)oxetane, (3-ethyloxetane-3-yl)methyl (meth)acrylate; 3-ethyl- 3 {[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, 1,4-bis[(3-ethyl-3-oxetanyl)methoxymethyl]benzene, 4,4'-bis[(3-ethyl oxetane compounds having two or more oxetanyl groups in the molecule such as 3-oxetanyl)methoxymethyl]biphenyl; These oxetane resins may be used alone or in combination of two or more.

As the oxetane resin, preferably 3-ethyl-3-hydroxymethyloxetane, 1,4-bis[(3-ethyl-3-oxetanyl)methoxymethyl]benzene, 3-ethyl-3-(2-ethylhexyloxymethyl) Oxetane, 3-ethyl-3-(oxiranylmethoxy)oxetane, (3-ethyloxetan-3-yl)methyl (meth)acrylate, 3-ethyl-3 {[(3-ethyloxetan-3-yl) Methoxy]methyl}oxetane and the like are used. These oxetane resins are readily available and can be excellent in dilutability (low viscosity) and compatibility.

In one embodiment, an oxetane resin that is liquid at room temperature (25° C.) and preferably has a molecular weight of 500 or less is used from the viewpoint of compatibility and adhesiveness. In one embodiment, preferably an oxetane compound containing two or more oxetanyl groups in the molecule, one oxetanyl group and one (meth)acryloyl group or one epoxy group in the molecule Oxetane compounds are used, more preferably 3-ethyl-3{[(3-ethyloxetan-3-yl)methoxy]methyl}oxetane, 3-ethyl-3-(oxiranylmethoxy)oxetane, (meth)acrylic (3-ethyloxetan-3-yl)methyl acid is used. By using these oxetane resins, the curability and durability of the protective layer can be improved.

A commercially available product may be used as the oxetane resin. Specifically, Aron oxetane OXT-101, Aron oxetane OXT-121, Aron oxetane OXT-212, and Aron oxetane OXT-221 (all manufactured by Toagosei Co., Ltd.) can be used. Aron oxetane OXT-101 and Aron oxetane OXT-221 can be preferably used.

When an epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton is used in combination with another resin, the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton The content of the epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton in a blend of an epoxy resin having at least one selected and other resins is preferably 50 wt % to 100 wt %, more preferably 60 wt % to 100 wt %, still more preferably 70 wt % to 100 wt %, particularly preferably 80 wt % to 100 wt %. If the content is less than 50% by weight, the protective layer may not have sufficient heat resistance and sufficient adhesion to the polarizer.

When an epoxy resin having a biphenyl skeleton and an oxetane resin are used in combination, the content of the oxetane resin is preferably 1 part by weight to 50 parts by weight with respect to 100 parts by weight of the total amount of the epoxy resin having a biphenyl skeleton and the oxetane resin. , more preferably 5 to 45 parts by weight, still more preferably 10 to 40 parts by weight. By setting the amount within the above range, the curability can be improved, and the adhesion between the protective layer and the polarizer can also be improved.

B-3-2-2. Photocationic Polymerization Initiator The photocationic polymerization initiator is a photosensitive agent having the function of a photoacid generator, and typically includes an ionic onium salt composed of a cation portion and an anion portion. In this onium salt, the cation portion absorbs light and the anion portion serves as an acid generation source. Ring-opening polymerization of the epoxy group proceeds by the acid generated from the photocationic polymerization initiator. As the photocationic polymerization initiator, any appropriate compound capable of curing an epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton upon irradiation with light such as ultraviolet rays. can be used. Only one type of photocationic polymerization initiator may be used, or two or more types may be used in combination.

Examples of photocationic polymerization initiators include triphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluorophosphate, p-(phenylthio)phenyldiphenylsulfonium hexafluoroantimonate, p-(phenylthio)phenyldiphenylsulfonium hexafluorophosphate, 4-chlorophenyldiphenylsulfonium hexafluorophosphate, 4-chlorophenyldiphenylsulfonium hexafluoroantimonate, bis[4-(diphenylsulfonio)phenyl]sulfide bishexafluorophosphate, bis[4-(diphenylsulfonio)phenyl ] sulfide bishexafluoroantimonate, (2,4-cyclopentadien-1-yl)[(1-methylethyl)benzene]-Fe-hexafluorophosphate, diphenyliodonium hexafluoroantimonate and the like. Preferably, a triphenylsulfonium salt-based hexafluoroantimonate-type photocationic polymerization initiator and a diphenyliodonium salt-based hexafluoroantimonate-type photocationic polymerization initiator are used.

You may use a commercial item as a photocationic polymerization initiator. Commercially available products include triphenylsulfonium salt-based hexafluoroantimonate type SP-170 (manufactured by ADEKA), CPI-101A (manufactured by San-Apro), WPAG-1056 (manufactured by Wako Pure Chemical Industries, Ltd.), diphenyliodonium salt-based Hexafluoroantimonate type WPI-116 (manufactured by Wako Pure Chemical Industries, Ltd.) and the like can be mentioned.

The content of the photocationic polymerization initiator is preferably from 0.1 parts by weight to 100 parts by weight of the epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton. 3 parts by weight, more preferably 0.25 to 2 parts by weight. If the content of the photocationic polymerization initiator is less than 0.1 parts by weight, it may not be sufficiently cured even when irradiated with light (ultraviolet rays).

B-3-3. Solidified Coating Film of Organic Solvent Solution of Epoxy Resin In one embodiment, the protective layer is composed of a solidified coating film of an organic solvent solution of epoxy resin.

B-3-3-1. Epoxy Resin In this embodiment, the epoxy resin preferably has a glass transition temperature (Tg) of 90° C. or higher. As a result, Tg of the protective layer becomes 90° C. or higher. If the Tg of the epoxy resin is 90° C. or higher, the polarizing plate including the protective layer obtained from such a resin tends to have excellent durability. The Tg of the epoxy resin is preferably 100° C. or higher, more preferably 110° C. or higher, still more preferably 120° C. or higher, and particularly preferably 125° C. or higher. On the other hand, the Tg of the epoxy resin is preferably 300° C. or lower, more preferably 250° C. or lower, still more preferably 200° C. or lower, and particularly preferably 160° C. or lower. If the Tg of the epoxy resin is in such a range, the moldability can be excellent.

Any appropriate epoxy resin can be employed as the epoxy resin as long as it has the above Tg. Epoxy resin typically refers to a resin having an epoxy group in its molecular structure. As the epoxy resin, an epoxy resin having an aromatic ring in its molecular structure is preferably used. By using an epoxy resin with an aromatic ring, an epoxy resin with a higher Tg can be obtained. Examples of the aromatic ring in the epoxy resin having an aromatic ring in its molecular structure include benzene ring, naphthalene ring, and fluorene ring. Epoxy resins may be used alone or in combination of two or more. When two or more epoxy resins are used, an epoxy resin containing an aromatic ring and an epoxy resin not containing an aromatic ring may be used in combination.

Specific examples of epoxy resins having an aromatic ring in the molecular structure include bisphenol A diglycidyl ether type epoxy resin, bisphenol F diglycidyl ether type epoxy resin, bisphenol S diglycidyl ether type epoxy resin, and resorcin diglycidyl ether. type epoxy resin, hydroquinone diglycidyl ether type epoxy resin, terephthalic acid diglycidyl ester type epoxy resin, bisphenoxyethanol fluorenediglycidyl ether type epoxy resin, bisphenol fluorenediglycidyl ether type epoxy resin, biscresol fluorenediglycidyl ether type epoxy resin, etc. epoxy resins having two epoxy groups; novolac type epoxy resins, N,N,O-triglycidyl-P- or -m-aminophenol type epoxy resins, N,N,O-triglycidyl-4-amino-m - or -Epoxy resins having three epoxy groups such as 5-amino-o-cresol type epoxy resins, 1,1,1-(triglycidyloxyphenyl)methane type epoxy resins; glycidylamine type epoxy resins (e.g., diamino Epoxy resins having four epoxy groups, such as diphenylmethane type, diaminodiphenylsulfone type, and metaxylenediamine type). In addition, glycidyl ester type epoxy resins such as hexahydrophthalic anhydride type epoxy resin, tetrahydrophthalic anhydride type epoxy resin, dimer acid type epoxy resin, and p-oxybenzoic acid type epoxy resin may be used.

The weight average molecular weight of the epoxy resin is preferably 1,000 to 2,000,000, more preferably 5,000 to 1,000,000, still more preferably 10,000 to 500,000, particularly preferably 50,000 to 500,000, and most preferably 60,000 to 150,000. The weight-average molecular weight can be determined, for example, by polystyrene conversion using a gel permeation chromatograph (GPC system, manufactured by Tosoh). Tetrahydrofuran can be used as the solvent.

The epoxy equivalent of the epoxy resin is preferably 1000 g/equivalent or more, more preferably 3000 g/equivalent or more, still more preferably 5000 g/equivalent or more. The epoxy equivalent of the epoxy resin is preferably 30000 g/equivalent or less, more preferably 25000 g/equivalent or less, still more preferably 20000 g/equivalent or less. When the epoxy equivalent is within the above range, a more stable protective layer can be obtained. As used herein, the term "epoxy equivalent" refers to "the mass of an epoxy resin containing one equivalent of an epoxy group" and can be measured according to JIS K7236.

In the embodiment of the present invention, epoxy resin and other resin may be used together. That is, a blend of epoxy resin and other resins may be used for forming the protective layer. Examples of other resins include thermoplastic resins such as styrenic resins, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyetheretherketone, polyester, polysulfone, polyphenylene oxide, polyacetal, polyimide, and polyetherimide. The type and blending amount of the resin to be used in combination can be appropriately set according to the purpose and desired properties of the resulting film. For example, a styrenic resin can be used together as a retardation control agent.

When an epoxy resin is used in combination with another resin, the content of the epoxy resin in the blend of the epoxy resin and the other resin is preferably 50% to 100% by weight, more preferably 60% to 100% by weight, More preferably 70% to 100% by weight, particularly preferably 80% to 100% by weight. If the content is less than 50% by weight, the protective layer may not have sufficient heat resistance and sufficient adhesion to the polarizer.

B-3-4. Structure and Properties of Protective Layer In one embodiment, as described above, the protective layer is composed of a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin, a photocationically cured epoxy resin, and an organic solvent solution of an epoxy resin. is composed of at least one selected from the group consisting of the solidified product of the coating film. With such a protective layer, the thickness can be made much thinner than that of an extruded film. The thickness of the protective layer is 10 μm or less as described above. In addition, although not theoretically clear, such a protective layer shrinks during film molding compared to cured products of other thermosetting resins or active energy ray-curable resins (e.g., UV-curable resins). It has the advantages of being able to suppress the deterioration of the film itself and suppressing the adverse effect on the polarizing plate (polarizer) caused by the residual monomer and the like because the residual monomer and the like are not contained. Furthermore, it has the advantage of being excellent in humidification durability because it has lower moisture absorption and moisture permeability than solidified aqueous coating films such as aqueous solutions or aqueous dispersions. As a result, it is possible to realize a highly durable polarizing plate that can maintain its optical properties even in a heated and humidified environment.

The Tg of the protective layer is as described for the acrylic resin and the epoxy resin.

The protective layer is preferably substantially optically isotropic. As used herein, the term “substantially optically isotropic” means that the in-plane retardation Re (550) is 0 nm to 10 nm, and the thickness direction retardation Rth (550) is −20 nm to +10 nm. Say something. The in-plane retardation Re(550) is more preferably 0 nm to 5 nm, still more preferably 0 nm to 3 nm, and particularly preferably 0 nm to 2 nm. The thickness direction retardation Rth(550) is more preferably −5 nm to +5 nm, still more preferably −3 nm to +3 nm, and particularly preferably −2 nm to +2 nm. If the Re(550) and Rth(550) of the protective layer are within such ranges, adverse effects on display characteristics can be prevented when a polarizing plate including the protective layer is applied to an image display device. Note that Re(550) is the in-plane retardation of the film measured at 23° C. with light having a wavelength of 550 nm. Re(550) is obtained by the formula: Re(550)=(nx−ny)×d. Rth(550) is the thickness direction retardation of the film measured at 23° C. with light having a wavelength of 550 nm. Rth(550) is obtained by the formula: Rth(550)=(nx−nz)×d. Here, nx is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow axis direction), and ny is the in-plane refractive index in the direction perpendicular to the slow axis (that is, the fast axis direction). is the refractive index, nz is the refractive index in the thickness direction, and d is the film thickness (nm).

The higher the light transmittance at 380 nm when the thickness of the protective layer is 3 μm, the better. Specifically, the light transmittance is preferably 85% or higher, more preferably 88% or higher, and even more preferably 90% or higher. If the light transmittance is in such a range, desired transparency can be ensured. Light transmittance can be measured, for example, by a method according to ASTM-D-1003.

The haze of the protective layer is preferably as low as possible. Specifically, the haze is preferably 5% or less, more preferably 3% or less, even more preferably 1.5% or less, and particularly preferably 1% or less. When the haze is 5% or less, the film can have a good clear feeling. Furthermore, even when it is used as a polarizing plate on the viewing side of an image display device, display contents can be visually recognized well.

YI at a protective layer thickness of 3 μm is preferably 1.27 or less, more preferably 1.25 or less, still more preferably 1.23 or less, and particularly preferably 1.20 or less. If the YI exceeds 1.3, the optical transparency may become insufficient. YI is obtained from the tristimulus values (X, Y, Z) of the color obtained by measurement using, for example, a high-speed integrating sphere type spectral transmittance meter (trade name DOT-3C: manufactured by Murakami Color Research Laboratory). , can be obtained by the following equation.
YI=[(1.28X−1.06Z)/Y]×100

The b value (scale of hue according to Hunter's color system) at a thickness of 3 μm of the protective layer is preferably less than 1.5, more preferably 1.0 or less. When the b value is 1.5 or more, an undesired tint may appear. For the b value, for example, a sample of the film constituting the protective layer is cut into 3 cm squares, and the hue is measured using a high-speed integrating sphere type spectral transmittance meter (trade name DOT-3C: manufactured by Murakami Color Research Laboratory). can be obtained by measuring and evaluating the hue according to Hunter's color system.

The protective layer (for example, a solidified product of a coating film or a photocationically cured product) may contain any suitable additive depending on the purpose. Specific examples of additives include ultraviolet absorbers; leveling agents; antioxidants such as hindered phenol, phosphorus, and sulfur; stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; Reinforcing materials such as carbon fiber; near-infrared absorbers; flame retardants such as tris(dibromopropyl) phosphate, triallyl phosphate, and antimony oxide; antistatic agents such as anionic, cationic, and nonionic surfactants; inorganic pigments , organic pigments, colorants such as dyes; organic fillers or inorganic fillers; resin modifiers; organic fillers or inorganic fillers; plasticizers; The additive may be added during polymerization of the acrylic resin, or added to the solution during film formation. The type, number, combination, addition amount, etc. of additives can be appropriately set according to the purpose.

An easy adhesion layer may be formed on the polarizer side of the protective layer. The easy-adhesion layer contains, for example, water-based polyurethane and an oxazoline-based cross-linking agent. By forming such an easy-adhesion layer, the adhesion between the protective layer and the polarizer can be enhanced. A hard coat layer may be formed on the protective layer. When the hard coat layer is formed, the hard coat layer may be formed so that the total thickness of the protective layer (for example, solidified coating film) and the hard coat layer is 10 μm or less. The hard coat layer can be formed when the protective layer is used as the protective layer on the viewer side of the viewer-side polarizing plate. When both the easy-adhesion layer and the hard coat layer are formed, typically they can be formed on different sides of the protective layer.

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

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

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

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

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

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

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

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

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

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

Another example of the alignment fixed layer includes a form in which a discotic liquid crystal compound is aligned in any one of vertical alignment, hybrid alignment and tilt alignment. In the discotic liquid crystal compound, typically, the discotic plane of the discotic liquid crystal compound is oriented substantially perpendicular to the film plane of the first retardation layer. When the discotic liquid crystal compound is substantially perpendicular, the average angle between the film surface and the disk surface of the discotic liquid crystal compound is preferably 70° to 90°, more preferably 80° to 90°. , more preferably 85° to 90°. Discotic liquid crystal compounds generally have a cyclic mother nucleus such as benzene, 1,3,5-triazine, or calixarene at the center of the molecule, and a linear alkyl group, alkoxy group, or substituted benzoyl A liquid crystal compound having a discotic molecular structure in which oxy groups and the like are radially substituted as side chains. Representative examples of discotic liquid crystals include C.I. Destrade et al., Mol. Cryst. Liq. Cryst. 71, 111 (1981), benzene derivatives, triphenylene derivatives, truxene derivatives and phthalocyanine derivatives; Kohne et al., Angew. Chem. 96, 70 (1984) and cyclohexane derivatives described in J. Am. M. In the report of Lehn et al., J. Am. Chem. Soc. Chem. Commun. , 1794 (1985); In the report of Zhang et al., J. Am. Am. Chem. Soc. 116, 2655 (1994), azacrown-based and phenylacetylene-based macrocycles. Further specific examples of discotic liquid crystal compounds include compounds described in JP-A-2006-133652, JP-A-2007-108732, and JP-A-2010-244038. The descriptions of the above documents and publications are incorporated herein by reference.

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

The first retardation layer typically exhibits a refractive index characteristic of nx>ny=nz. The first retardation layer is typically provided to impart antireflection properties to the polarizing plate, and when the first retardation layer is a single layer of the alignment fixed layer, it functions as a λ / 4 plate. can. In this case, the in-plane retardation Re(550) of the first retardation layer is preferably 100 nm to 190 nm, more preferably 110 nm to 170 nm, still more preferably 130 nm to 160 nm. Here, "ny=nz" includes not only the case where ny and nz are completely equal but also the case where they are substantially equal. Therefore, ny>nz or ny<nz may be satisfied within a range that does not impair the effects of the present invention.

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

The first retardation layer may exhibit a reverse wavelength dispersion characteristic in which the retardation value increases according to the wavelength of the measurement light, or has a positive wavelength dispersion characteristic in which the retardation value decreases according to the wavelength of the measurement light. It may also show a flat wavelength dispersion characteristic in which the phase difference value hardly changes even with the wavelength of the measurement light. In one embodiment, the first retardation layer exhibits reverse dispersion wavelength characteristics. In this case, Re(450)/Re(550) of the retardation layer is preferably 0.8 or more and less than 1, more preferably 0.8 or more and 0.95 or less. With such a configuration, very excellent antireflection properties can be achieved.

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

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

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

The second retardation layer having refractive index characteristics of nz>nx=ny can be made of any suitable material. The second retardation layer preferably consists of a film containing a liquid crystal material fixed in homeotropic alignment. A liquid crystal material (liquid crystal compound) that can be homeotropically aligned may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method for forming the retardation layer include the liquid crystal compound and the method for forming the retardation layer described in [0020] to [0028] of JP-A-2002-333642. In this case, the thickness of the second retardation layer is preferably 0.5 μm to 10 μm, more preferably 0.5 μm to 8 μm, still more preferably 0.5 μm to 5 μm.

E. Conductive layer or isotropic substrate with conductive layer It may be formed by depositing a metal oxide film thereon. Examples of metal oxides include indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimony composite oxide, zinc-aluminum composite oxide, and indium-zinc composite oxide. Among them, indium-tin composite oxide (ITO) is preferred.

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

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

Any appropriate isotropic substrate can be employed as the optically isotropic substrate (isotropic substrate). Materials constituting the isotropic base material include, for example, norbornene-based resins, olefin-based resins, and other resins that do not have a conjugated system as the main skeleton, and acrylic resins that have cyclic structures such as lactone rings and glutarimide rings. Examples include materials that are present in the main chain. By using such a material, it is possible to suppress the development of retardation due to the orientation of molecular chains when forming an isotropic base material. The thickness of the isotropic substrate is preferably 50 μm or less, more preferably 35 μm or less. The thickness of the isotropic base material is, for example, 20 μm or more.

The conductive layer and/or the conductive layer of the isotropic substrate with a conductive layer may be patterned as required. The patterning may form conductive portions and insulating portions. As a result, electrodes can be formed. The electrodes may function as touch sensor electrodes that sense contact with the touch panel. Any appropriate method can be adopted as a patterning method. Specific examples of the patterning method include wet etching and screen printing.

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

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows. "Parts" and "%" in Examples and Comparative Examples are by weight unless otherwise specified.

[Example 1]
1. Production of Polarizer As a thermoplastic resin substrate, a long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a water absorption of 0.75% and a Tg of about 75° C. was used. Corona treatment (treatment condition: 55 W·min/m ² ) was applied to one side of the resin substrate.
Polyvinyl alcohol (degree of polymerization: 4,200, degree of saponification: 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOSEFIMER Z410") mixed at 9:1: 100 weight of PVA-based resin 13 parts by weight of potassium iodide was added to 10 parts by weight to prepare a PVA aqueous solution (coating liquid).
The above PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60° C. to form a PVA-based resin layer having a thickness of 12 μm, thereby producing a laminate.
The obtained laminate was uniaxially stretched 2.4 times at the free end in the machine direction (longitudinal direction) between rolls with different peripheral speeds in an oven at 130° C. (in-air auxiliary stretching treatment).
Next, the laminate was immersed in an insolubilizing bath (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment).
Then, the finally obtained polarizer is added to a dyeing bath (iodine aqueous solution obtained by blending iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ° C. It was immersed for 60 seconds while adjusting the concentration so that the single transmittance (Ts) was 41.8% (dyeing treatment).
Next, it was immersed for 30 seconds in a cross-linking bath at a liquid temperature of 40°C (an aqueous solution of boric acid obtained by blending 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water). (crosslinking treatment).
After that, the laminate is immersed in an aqueous solution of boric acid (boric acid concentration: 4.0% by weight, potassium iodide: 5.0% by weight) at a liquid temperature of 62° C., and is moved between rolls having different peripheral speeds in the longitudinal direction (longitudinal direction). ) was uniaxially stretched so that the total stretch ratio was 3.0 times (underwater stretching treatment: the stretching ratio in the underwater stretching treatment was 1.25 times).
After that, the laminate was immersed in a washing bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (washing treatment).
After that, while drying in an oven kept at 90° C., it was brought into contact with a heating roll made of SUS whose surface temperature was kept at 75° C. for about 2 seconds (drying shrinkage treatment). The shrinkage rate in the width direction of the laminate due to the drying shrinkage treatment was 2%.
Thus, a polarizer having a thickness of 6.9 μm was formed on the resin substrate.

2. Preparation of polarizing plate Water-based polyurethane resin (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: Superflex 210-R) is dissolved in a mixed solvent of pure water and isopropyl alcohol, and the resulting solution is mixed with the resin obtained above. It was applied to the surface of the polarizer formed on the substrate. Then, the solvent was removed by drying at 60° C. to form an easy adhesion layer with a thickness of 0.15 μm. 20 parts of an acrylic resin having a methyl methacrylate unit (manufactured by Kusumoto Kasei Co., Ltd., trade name: B728) was dissolved in 80 parts of methyl ethyl ketone to obtain an acrylic resin solution (20%). This acrylic resin solution was applied to the easy-adhesion layer using a wire bar, and the coating film was dried at 60° C. for 5 minutes to form an acrylic resin layer configured as a solidified product of the coating film. The acrylic resin layer had a thickness of 2 µm and a Tg of 111°C. Then, dimethylol-tricyclodecane diacrylate (manufactured by Kyoeisha Chemical, trade name: Light Acrylate DCP-A) 70 parts by weight, isobornyl acrylate (manufactured by Kyoeisha Chemical, trade name: Light Acrylate IB-XA) 20 parts by weight, 1 , 9-nonanediol diacrylate (manufactured by Kyoeisha Chemical, trade name: Light Acrylate 1.9NA-A) 10 parts by weight, and a photopolymerization initiator (manufactured by BASF, trade name: Irgacure 907) 3 parts by weight, a solvent to obtain a coating liquid. The obtained coating liquid was applied onto the protective layer so that the coating liquid had a thickness of 3 μm after curing. Next, the solvent was dried, and ultraviolet rays were irradiated in a nitrogen atmosphere using a high-pressure mercury lamp so that the integrated light amount was 300 mJ/cm ² to form a hard coat layer. The thickness of the hard coat layer was 3 μm. Next, in order to stably perform the lamination operation with the retardation layer later, the pressure-sensitive adhesive layer of the pressure-sensitive adhesive layer-attached polyethylene terephthalate (PET) film was adhered to the protective layer for reinforcement. After that, the resin substrate is peeled off, and a polarizing plate having a configuration of a PET film with an adhesive layer/protective layer (hard coat layer/acrylic resin layer (solidified coating film))/adhesive layer/polarizer is obtained. Obtained.

ＰＥＴフィルム（厚み３８μｍ）表面を、ラビング布を用いてラビングし、配向処理を施した。配向処理の方向は、偏光板に貼り合わせる際に偏光子の吸収軸の方向に対して視認側から見て１５°方向となるようにした。この配向処理表面に、上記液晶塗工液をバーコーターにより塗工し、９０℃で２分間加熱乾燥することによって液晶化合物を配向させた。このようにして形成された液晶層に、メタルハライドランプを用いて１００ｍＪ/ｃｍ^２の光を照射し、当該液晶層を硬化させることによって、ＰＥＴフィルム上に液晶配向固化層Ａを形成した。液晶配向固化層Ａの厚みは２．５μｍ、面内位相差Ｒｅ（５５０）は２７０ｎｍであった。さらに、液晶配向固化層Ａは、ｎｘ＞ｎｙ＝ｎｚの屈折率分布を有していた。
塗工厚みを変更したこと、および、配向処理方向を偏光子の吸収軸の方向に対して視認側から見て７５°方向となるようにしたこと以外は上記と同様にして、ＰＥＴフィルム上に液晶配向固化層Ｂを形成した。液晶配向固化層Ｂの厚みは１．３μｍ、面内位相差Ｒｅ（５５０）は１４０ｎｍであった。さらに、液晶配向固化層Ｂは、ｎｘ＞ｎｙ＝ｎｚの屈折率分布を有していた。3. Production of the first alignment fixed layer and the second alignment fixed layer constituting the retardation layer Polymerizable liquid crystal exhibiting a nematic liquid crystal phase (manufactured by BASF: trade name “Paliocolor LC242”, represented by the following formula) 10 g , and 3 g of a photopolymerization initiator for the polymerizable liquid crystal compound (manufactured by BASF, trade name “Irgacure 907”) were dissolved in 40 g of toluene to prepare a liquid crystal composition (coating liquid).

The surface of a PET film (thickness: 38 μm) was rubbed with a rubbing cloth to give an orientation treatment. The direction of the orientation treatment was set to be 15° from the direction of the absorption axis of the polarizer when viewed from the viewing side when attached to the polarizing plate. The above liquid crystal coating solution was applied to the alignment-treated surface using a bar coater, and dried by heating at 90° C. for 2 minutes to align the liquid crystal compound. The liquid crystal layer thus formed was irradiated with light of 100 mJ/cm ² using a metal halide lamp to cure the liquid crystal layer, thereby forming a liquid crystal alignment solid layer A on the PET film. The liquid crystal alignment fixed layer A had a thickness of 2.5 μm and an in-plane retardation Re (550) of 270 nm. Furthermore, the liquid crystal alignment fixed layer A had a refractive index distribution of nx>ny=nz.
In the same manner as above, except that the coating thickness was changed and that the alignment treatment direction was set to be 75° to the direction of the absorption axis of the polarizer when viewed from the viewing side, A liquid crystal alignment fixed layer B was formed. The liquid crystal alignment fixed layer B had a thickness of 1.3 μm and an in-plane retardation Re (550) of 140 nm. Furthermore, the liquid crystal alignment fixed layer B had a refractive index distribution of nx>ny=nz.

4. Production of polarizing plate with retardation layer 2. The polarizer surface of the polarizing plate obtained in 3. above. The liquid crystal alignment fixed layer A and the liquid crystal alignment fixed layer B obtained in 1. were transferred in this order. At this time, the angle between the absorption axis of the polarizer and the slow axis of the oriented fixed layer A is 15°, and the angle between the absorption axis of the polarizer and the slow axis of the oriented fixed layer B is 75°. Then, transfer (bonding) was performed. It should be noted that each transfer (bonding) is the same as in 2. above. It was performed through the ultraviolet curable adhesive (thickness 1.0 μm) used in . Then, the pressure-sensitive adhesive layer-attached PET film was peeled off. In this way, a protective layer (hard coat layer/acrylic resin layer (solidified product of coating film))/easy adhesion layer/polarizer/adhesive layer/retardation layer (first orientation solidified layer/adhesive layer/second 2) was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 18 μm.

[Example 2]
A polarizer having a thickness of 6.4 μm was obtained in the same manner as in Example 1 except that the stretch ratio in the underwater stretching treatment was 1.46 times and the total stretch ratio was 3.5 times. A polarizing plate 2 with a retardation layer was obtained in the same manner as in Example 1 except that the obtained polarizer was used. The total thickness of the obtained polarizing plate with a retardation layer was 17 μm.

[Example 3]
A polarizer having a thickness of 6.0 μm was obtained in the same manner as in Example 1 except that the draw ratio in the underwater drawing treatment was 1.67 times and the total draw ratio was 4.0 times. A polarizing plate 3 with a retardation layer was obtained in the same manner as in Example 1 except that the obtained polarizer was used. The total thickness of the obtained polarizing plate with a retardation layer was 17 μm.

[Example 4]
A polarizer having a thickness of 5.6 μm was obtained in the same manner as in Example 1 except that the draw ratio in the underwater drawing treatment was 1.88 and the total draw ratio was 4.5. A polarizing plate 4 with a retardation layer was obtained in the same manner as in Example 1 except that the obtained polarizer was used. The total thickness of the obtained polarizing plate with a retardation layer was 16 μm.

[Example 5]
Except for using an acrylic resin that is polymethyl methacrylate having a lactone ring unit (30 mol% of the lactone ring unit) instead of the acrylic resin having a methyl methacrylate unit (manufactured by Kusumoto Kasei Co., Ltd., trade name: B728). A polarizing plate 5 with a retardation layer was obtained in the same manner as in Example 2. The total thickness of the obtained polarizing plate with a retardation layer was 17 μm.

[Example 6]
Acrylic resin (4 mol% of glutarimide ring units), which is polymethyl methacrylate having glutarimide ring units, was used instead of acrylic resin having methyl methacrylate units (manufactured by Kusumoto Kasei Co., Ltd., trade name: B728). A polarizing plate 6 with a retardation layer was obtained in the same manner as in Example 5 except for the above. The total thickness of the obtained polarizing plate with a retardation layer was 17 μm.

[Example 7]
Instead of the acrylic resin solution, an epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) YX6954BH30, weight average molecular weight: 36000, epoxy equivalent: 13000) 20 parts dissolved in 80 parts of methyl ethyl ketone, epoxy resin Except for forming a protective layer composed of a solidified coating film using a solution (20%), not forming a hard coat layer, and not forming an easy-adhesion layer on the polarizer. prepared a polarizing plate with a retardation layer in the same manner as in Example 5. Specifically, this epoxy resin solution was applied directly to the polarizer using a wire bar, and the applied film was dried at 60° C. for 3 minutes to form a protective layer. The protective layer had a thickness of 3 µm and a Tg of 130°C. Thus, a polarizing plate 7 with a retardation layer was obtained in the same manner as in Example 5 except that the protective layer was formed. The total thickness of the obtained polarizing plate with a retardation layer was 15 μm.

[Example 8]
Polarized light with a retardation layer in the same manner as in Example 2 except that a protective layer was formed as follows, an easy-adhesion layer was not formed on the polarizer, and a hard coat layer was not formed. Plate 8 was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 15 μm.
15 parts of an epoxy resin having a biphenyl skeleton (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) YX4000) was dissolved in 83.8 parts of methyl ethyl ketone to obtain an epoxy resin solution. To the resulting epoxy resin solution, 1.2 parts of a cationic photopolymerization initiator (manufactured by San-Apro, trade name: CPI (registered trademark)-100P) was added to obtain a composition for forming a protective layer. The obtained composition for forming a protective layer was applied directly to a polarizer using a wire bar, and the applied film was dried at 60° C. for 3 minutes. Next, ultraviolet rays were irradiated using a high-pressure mercury lamp so that the integrated light amount was 600 mJ/cm ² to form a protective layer. The thickness of the protective layer was 3 μm.

[Example 9]
A polarizing plate with a retardation layer was prepared in the same manner as in Example 8 except that a bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) 828) was used instead of the epoxy resin having a biphenyl skeleton. got 9. The total thickness of the obtained polarizing plate with a retardation layer was 15 μm.

[Example 10]
Polarized light with a retardation layer in the same manner as in Example 8 except that a hydrogenated bisphenol epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) YX8000) was used instead of the epoxy resin having a biphenyl skeleton. A plate 10 was obtained. The total thickness of the obtained polarizing plate with a retardation layer was 15 μm.

[Example 11]
Hydrogenated bisphenol type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) YX8000) 15 parts and oxetane resin (manufactured by Toagosei Co., Ltd., trade name: Aron Oxetane (registered trademark) OXT-221) 10 parts by weight was dissolved in 73 parts of methyl ethyl ketone to obtain an epoxy resin solution. To the resulting epoxy resin solution, 2 parts of a cationic photopolymerization initiator (manufactured by San-Apro Co., Ltd., trade name: CPI (registered trademark)-100P) was added to obtain a composition for forming a protective layer. A polarizing plate 11 with a retardation layer was obtained in the same manner as in Example 8 except that the obtained composition for forming a protective layer was used. The total thickness of the obtained polarizing plate with a retardation layer was 15 μm.

[Example 12]
A polarizing plate 12 with a retardation layer was obtained in the same manner as in Example 11, except that the thickness of the protective layer was changed to 8 μm.

[Example 13]
A polarizing plate 13 with a retardation layer was obtained in the same manner as in Example 11, except that the thickness of the protective layer was changed to 10 μm.

[Example 14]
A protective layer (cured product) was formed in the same manner as in Example 8, except that an ultraviolet curable epoxy resin (manufactured by Daicel, product name "Celoxide 2021P") was used. Specifically, a composition containing 95% by weight of the epoxy resin and 5% by weight of a photopolymerization initiator (CPI-100P, manufactured by San-Apro Co., Ltd.) is applied to the easy-adhesion layer and placed under an air atmosphere with a high-pressure mercury lamp. to form ^a cured layer (protective layer). A polarizing plate with a retardation layer was produced in the same manner as in Example 2 except that this protective layer was used. The thickness of the polarizing plate was 15 μm.

(Comparative example 1)
In the production of the polarizer, the same as in Example 1 except that the draw ratio in the underwater drawing treatment was 2.3 times and the total draw ratio was 5.5 times, and the liquid temperature of the drawing bath was 70°C. Then, a polarizer having a thickness of 5.1 μm was obtained. A polarizing plate C1 with a retardation layer was obtained in the same manner as in Example 1, except that an acrylic resin film having a thickness of 40 μm was laminated on the surface of the obtained polarizer via an ultraviolet curable adhesive to form a protective layer. rice field. The total thickness of the obtained polarizing plate with a retardation layer was 52 μm.

(Comparative example 2)
A polarizing plate C2 with a retardation layer was obtained in the same manner as in Comparative 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.

(Comparative Example 3)
A polarizing plate C3 with a retardation layer was obtained in the same manner as in Example 1 except that the polarizer obtained in Comparative Example 1 was used. The total thickness of the obtained polarizing plate with a retardation layer was 16 μm.

(Comparative Example 4)
A polarizer having a thickness of 5.1 μm was obtained in the same manner as in Comparative Example 1 except that the liquid temperature of the stretching bath in the underwater stretching treatment was 64° C. in the production of the polarizer. A polarizing plate C4 with a retardation layer was obtained in the same manner as in Comparative Example 3 except that the obtained polarizer was used. The total thickness of the obtained polarizing plate with a retardation layer was 16 μm.

(Comparative Example 5)
A polarizing plate C5 with a retardation layer was obtained in the same manner as in Comparative Example 3 except that a protective layer was formed in the same manner as in Example 7. The total thickness of the obtained polarizing plate with a retardation layer was 14 μm.

(Comparative Example 6)
A polarizing plate C6 with a retardation layer was obtained in the same manner as in Comparative Example 3 except that a protective layer was formed in the same manner as in Example 8. The total thickness of the obtained polarizing plate with a retardation layer was 14 μm.

[evaluation]
The following evaluations were performed using the polarizing plates with retardation layers obtained in Examples and Comparative Examples. Table 1 shows the results.
(1) Thickness The thickness of the polarizer was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name “MCPD-3000”). The calculation wavelength range used for thickness calculation was 400 nm to 500 nm, and the refractive index was 1.53. The thickness of the protective layer was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name: "MCPD-3000"), with the calculated wavelength range and refractive index selected as appropriate. The thickness of the easy-adhesion layer was obtained from scanning electron microscope (SEM) observation. A thickness exceeding 10 μm was measured using a digital micrometer (manufactured by Anritsu Co., Ltd., product name “KC-351C”).
(2) Orientation function For the polarizers used in Examples and Comparative Examples, a Fourier transform infrared spectrophotometer (FT-IR) (manufactured by Perkin Elmer, trade name: "Frontier") was used to measure polarized infrared light. Attenuated total reflection (ATR) of the surface of the polarizer was measured using light as measurement light. Germanium was used for the crystallite that adheres the polarizer, and the incident angle of the measurement light was set at 45°. The orientation function was calculated according to the following procedure. The incident polarized infrared light (measurement light) is polarized light (s-polarized light) that oscillates parallel to the surface where the germanium crystal sample is adhered, and the stretching direction of the polarizer is set perpendicular to the polarization direction of the measurement light ( ⊥) and parallel (//), and each absorbance spectrum was measured. From the obtained absorbance spectrum, (2941 cm ^-1 intensity) I was calculated with reference to (3330 cm ^-1 intensity). I _⊥ is (2941 cm ⁻¹ intensity)/(3330 cm ⁻¹ intensity) obtained from the absorbance spectrum obtained when the stretching direction of the polarizer is arranged perpendicular (⊥) to the polarization direction of the measurement light. In addition, I _// is obtained from the absorbance spectrum obtained when the stretching direction of the polarizer is arranged parallel (//) to the polarization direction of the measurement light (2941 cm ⁻¹ intensity) / (3330 cm ⁻¹ intensity) is. Here, (2941 cm ⁻¹ intensity) is the absorbance at 2941 cm ⁻¹ when 2770 cm ⁻¹ and 2990 cm ⁻¹ are the bottoms of the absorbance spectrum, and (3330 cm ⁻¹ intensity) is 2990 cm ⁻ Absorbance at 3330 cm ⁻¹ with ¹ and 3650 cm ⁻¹ as baseline. Using the obtained _I⊥ and I _// , the orientation function f was calculated according to Equation 1. When f=1, the orientation is perfect, and when f=0, the orientation is random. The peak at 2941 cm ⁻¹ is said to be absorption due to vibration of the PVA main chain (—CH ₂ —) in the polarizer. The peak at 3330 cm ⁻¹ is said to be absorption due to vibration of hydroxyl groups of PVA.
(Formula 1) f=(3<cos ² θ>−1)/2
=(1−D)/[c(2D+1)]
However, c=(3cos ² β−1)/2
β=90°⇒f=−2×(1−D)/(2D+1) when 2941 cm ⁻¹ is used as described above.
θ: Angle of molecular chain with respect to stretching direction β: Angle of transition dipole moment with respect to molecular chain axis D=( _I⊥ )/(I _// )
I _⊥ : Absorption intensity when the polarization direction of the measurement light and the stretching direction of the polarizer are perpendicular I _// : Absorption intensity when the polarization direction of the measurement light and the stretching direction of the polarizer are parallel (3) Crack occurrence rate Implementation The retardation layer-attached polarizing plates obtained in Examples and Comparative Examples were cut into 10 mm×10 mm sizes. The cut polarizing plate with a retardation layer was attached to a glass plate (thickness: 1.1 mm) via an acrylic pressure-sensitive adhesive layer having a thickness of 20 μm. After the sample attached to the glass plate was placed in an oven at 100° C. for 120 hours, the occurrence of cracks in the absorption axis direction (MD direction) of the polarizer was visually confirmed. This evaluation was performed using three polarizing plates with retardation layers, and the number of polarizing plates with retardation layers in which cracks were generated was evaluated.
(4) Bending Resistance Each polarizing plate with a retardation layer obtained in Examples and Comparative Examples was cut into a size of 50 mm×100 mm. At this time, the polarizer was cut so that the absorption axis direction of the polarizer was the long side direction. Using a bending tester (manufactured by Yuasa Systems Co., Ltd., product name: DLDM111LH), the cut polarizing plate with a retardation layer was subjected to a bending test at room temperature. Specifically, the polarizing plate with a retardation layer is rotated in the direction of the absorption axis at a rotation speed of 60 rpm so that the retardation layer side is inside and the protective layer or the hard coat layer formed on the protective layer is outside. The bending diameter was set to 1 mmφ (R is 0.5 mm), and the polarizing plate with the retardation layer was bent 50,000 times. Next, the presence or absence of cracks in the retardation layer-attached polarizing plate after the test was visually confirmed, and those in which cracks could not be confirmed were rated good, and those in which cracks were confirmed were rated unsatisfactory. The bending direction is the transmission axis direction of the polarizer.
(5) Single transmittance and degree of polarization For the polarizer (single polarizer) obtained by peeling and removing the resin substrate from the polarizer/thermoplastic resin substrate laminate used in the examples and comparative examples, the ultraviolet-visible spectrophotometer was used. (manufactured by JASCO Corporation, product name "V-7100"), the single transmittance Ts, the parallel transmittance Tp, and the orthogonal transmittance Tc were taken as Ts, Tp, and Tc of the polarizer, respectively. These Ts, Tp and Tc are Y values measured with a 2-degree field of view (C light source) according to JIS Z8701 and subjected to visibility correction.
From the obtained Tp and Tc, the degree of polarization P was determined by the following formula.
Degree of polarization P (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100
(6) Puncture strength The polarizer was peeled off from the polarizer/thermoplastic resin substrate laminate used in the examples and comparative examples, and a compression tester equipped with a needle (manufactured by Kato Tech Co., Ltd., product name "NDG5" needle Penetration force measurement specification), pierced at a piercing speed of 0.33 cm/sec in a room temperature (23°C ± 3°C) environment, and the strength when the polarizer was broken was taken as the breaking strength (piercing strength). As the evaluation value, the breaking strength of 10 test pieces was measured and the average value was used. The needle used had a tip diameter of 1 mmφ and 0.5R. For the polarizer to be measured, a jig having a circular opening with a diameter of about 11 mm was fixed on both sides of the polarizer, and the test was performed by piercing the center of the opening with a needle.

As is clear from Table 1, the polarizing plates with retardation layers of Examples 1 to 14 were inhibited from cracking even when subjected to heat treatment. Moreover, the durability at the time of bending was also excellent.

The retardation layer-attached polarizing plate of the present invention is suitably used for an image display device.

REFERENCE SIGNS LIST 10 polarizing plate 11 polarizer 12 first protective layer 13 second protective layer 20 retardation layer 100 polarizing plate with retardation layer 101 polarizing plate with retardation layer 102 polarizing plate with retardation layer

Claims (9)

a polarizing plate including a polarizer and a protective layer disposed on one side of the polarizer; and a retardation layer;
the polarizer is composed of a polyvinyl alcohol-based resin film, and the polyvinyl alcohol has an orientation function of 0.30 or less,
The retardation layer is an alignment fixed layer of a liquid crystal compound,
A polarizing plate with a retardation layer, wherein the protective layer has a thickness of 10 µm or less. a polarizing plate including a polarizer and a protective layer disposed on one side of the polarizer; and a retardation layer;
The polarizer has a puncture strength of 30 gf/μm or more,
The retardation layer is an alignment fixed layer of a liquid crystal compound,
A polarizing plate with a retardation layer, wherein the protective layer has a thickness of 10 µm or less. 3. The retardation layer-attached polarizing plate according to claim 1, wherein the total thickness is 30 [mu]m or less. 4. The polarizing plate with a retardation layer according to claim 1, wherein the polarizer has a thickness of 10 [mu]m or less. 5. The polarizing plate with a retardation layer according to claim 1, wherein the polarizer has a single transmittance of 40.0% or more and a degree of polarization of 99.0% or more. The protective layer is at least one selected from the group consisting of a solidified coating film of an organic solvent solution of a thermoplastic acrylic resin, a photo-cationically cured epoxy resin, and a solidified coating film of an organic solvent solution of an epoxy resin. The polarizing plate with a retardation layer according to any one of claims 1 to 5, comprising: 7. The position according to claim 6, wherein the thermoplastic acrylic resin has at least one repeating unit selected from the group consisting of lactone ring units, glutaric anhydride units, glutarimide units, maleic anhydride units and maleimide units. A polarizing plate with a retardation layer. 7. The retardation layer-attached polarizing plate according to claim 6, wherein the protective layer is a photo-cationically cured epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton. An image display device comprising the retardation layer-attached polarizing plate according to any one of claims 1 to 8.

Images