TWI891822B - Polarizing plate with phase difference layer and image display device using the same - Google Patents

Abstract

The present invention provides a polarizing plate with a phase difference layer that can suppress cracking when heated. The polarizing plate with a phase difference layer of the present invention comprises a polarizing plate and a phase difference layer. The polarizing plate includes a polarizer and a protective layer. The polarizer is composed of a polyvinyl alcohol-based resin film containing a dichroic substance. The protective layer is arranged on one side of the polarizer. The phase difference layer is an alignment cured layer of a liquid crystal compound. The thickness of the protective layer is less than 10 μm. In one embodiment, when the monomer transmittance of the polarizer is set to x% and the birefringence of the polyvinyl alcohol-based resin is set to y, the following formula (1) is satisfied. In one embodiment, when the monomer transmittance of the polarizer is set to x% and the in-plane phase difference of the polyvinyl alcohol resin film is set to znm, the following formula (2) is satisfied. In one embodiment, when the monomer transmittance of the polarizer is set to x% and the alignment function of the polyvinyl alcohol resin is set to f, the following formula (3) is satisfied. y＜-0.011x+0.525    (1) z＜-60x+2875          (2) f＜-0.018x+1.11        (3)

Description

Polarizing plate with phase difference layer and image display device using the same

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

Background Technology

In recent years, image display devices represented by liquid crystal display devices and electroluminescent (EL) display devices (such as organic EL display devices and inorganic EL display devices) have become rapidly popular. In image display devices, polarizing plates and phase difference plates are generally used. In practice, polarizing plates with phase difference layers, which are formed by integrating a polarizing plate and a phase difference plate, are widely used (for example, Patent Document 1). Recently, as the demand for thinner image display devices increases, the demand for thinner polarizing plates with phase difference layers is also increasing. In addition, in recent years, the demand for curved image display devices and/or bendable or foldable image display devices is increasing. Therefore, there is a demand for further thinning and further flexibility of polarizing plates and polarizing plates with phase difference layers.

Some methods for thinning polarizing plates include reducing the thickness of the protective layer and laminating the protective layer only on one side of the polarizer. However, these methods are insufficient for protecting the polarizer, and their durability needs improvement. Furthermore, there is the problem that heat treatment can easily crack not only the polarizer but also the polarizing plate. Prior Art Patent

Patent document 1: Japanese Patent Application Publication No. 2001-343521

Summary of the invention Problem to be solved by the invention

This invention was developed to address the aforementioned problems. Its primary purpose is to provide a polarizing plate with a phase difference layer that can suppress cracking during heating. Means for Solving the Problem

The polarizing plate with a phase difference layer according to an embodiment of the present invention comprises a polarizing plate and a phase difference layer. The polarizing plate includes a polarizer and a protective layer. The polarizer is composed of a polyvinyl alcohol resin film containing a dichroic substance. The protective layer is disposed on one side of the polarizer. The phase difference layer is an alignment cured layer of a liquid crystal compound. The thickness of the protective layer is less than 10 μm. When the monomer transmittance of the polarizer is set to x% and the birefringence of the polyvinyl alcohol resin is set to y, the following formula (1) is satisfied. y＜-0.011x+0.525       (1) Another embodiment of the present invention is a polarizing plate with a phase difference layer, comprising a polarizing plate and a phase difference layer, wherein the polarizing plate includes a polarizer and a protective layer, wherein the polarizer is composed of a polyvinyl alcohol resin film containing a dichroic substance, and the protective layer is disposed on one side of the polarizer. The phase difference layer is an alignment cured layer of a liquid crystal compound, and the thickness of the protective layer is less than 10 μm. When the monomer transmittance of the polarizer is set to x%, and the in-plane phase difference of the polyvinyl alcohol resin film is set to z nm, the following formula (2) is satisfied. z＜-60x+2875            (2) Another embodiment of the present invention is a polarizing plate with a phase difference layer, comprising a polarizing plate and a phase difference layer, wherein the polarizing plate comprises a polarizer and a protective layer, wherein the polarizer is composed of a polyvinyl alcohol resin film containing a dichroic substance, and the protective layer is disposed on one side of the polarizer. The phase difference layer is an alignment cured layer of a liquid crystal compound, and the thickness of the protective layer is 10 μm or less. When the monomer transmittance of the polarizer is set to x%, and the alignment function of the polyvinyl alcohol resin is set to f, the following formula (3) is satisfied. f＜-0.018x+1.11         (3) In one embodiment, the total thickness of the polarizing plate with a phase difference layer 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-element transmittance of 40.0% or greater and a degree of polarization of 99.0% or greater. In one embodiment, the protective layer is composed of at least one member selected from the group consisting of a cured product of a coating film of an organic solvent solution of a thermoplastic (meth)acrylic resin, a photo-cured product of an epoxy resin, and a cured product of a coating film of an organic solvent solution of an epoxy resin. In one embodiment, the thermoplastic (meth)acrylic resin comprises 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 another embodiment, the protective layer is a photo-cured epoxy resin comprising at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons. According to another aspect of the present invention, an image display device is provided. The image display device comprises the polarizing plate with a retardation layer. Effects of the Invention

The present invention provides a polarizing plate with a retardation layer. The polarizing plate comprises: a polarizer whose monomer transmittance satisfies a specific relationship with the birefringence of polyvinyl alcohol (PVA) or the in-plane retardation of a PVA-based resin film; a protective layer having a thickness of 10 μm or less; and a retardation layer comprising an alignment-cured layer of a liquid crystal alignment compound. This polarizing plate with a retardation layer can be thinned and cracking during heating can be suppressed. Furthermore, cracking during flexing can be suppressed.

The following describes the embodiments of the present invention, but the present invention is not limited to these embodiments.

(Definition of terms and symbols) The definitions of terms and symbols in this manual are as follows. (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction where the in-plane refractive index is the largest (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. (2) In-plane phase difference (Re) "Re(λ)" is the in-plane phase difference measured at 23°C using light of a wavelength of λnm. For example, "Re(550)" is the in-plane phase difference measured at 23°C using light of a wavelength of 550nm. Re(λ) is calculated using the formula: Re(λ) = (nx-ny) × d, assuming the thickness of the layer (thin film) is d (nm). (3) Retardation in the thickness direction (Rth) "Rth(λ)" is the retardation in the thickness direction measured at 23°C using light of wavelength λnm. For example, "Rth(550)" is the retardation in the thickness direction measured at 23°C using light of wavelength 550nm. Rth(λ) is calculated using the formula: Rth(λ) = (nx - nz) × d, when the thickness of the layer (film) is set to d (nm). (4) Nz coefficient The Nz coefficient is calculated by Nz = Rth/Re. (5) Angle When an angle is mentioned in this specification, the angle includes both clockwise and counterclockwise angles relative to the reference direction. Therefore, for example, "45°" means ±45°.

A. Overall Structure of a Polarizing Plate with a Retardation Layer Figure 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention. The polarizing plate with a retardation layer 100 of this embodiment comprises a polarizing plate 10 and a retardation layer 20. The polarizing plate 10 includes a polarizer 11, a first protective layer 12 disposed on one side of the polarizer 11, and a second protective layer 13 disposed on the other side of the polarizer 11. Depending on the intended purpose, either the first protective layer 12 or 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. The phase difference layer 20 is laminated on the polarizer 11 or the second protective layer 13 via any suitable adhesive layer or bonding agent layer (not shown). In an embodiment of the present invention, the polarizer 11 is composed of a polyvinyl alcohol resin film containing a dichroic substance, and when the monomer transmittance is set to x% and the birefringence of the polyvinyl alcohol resin is set to y, the following equation (1) is satisfied. In another embodiment of the present invention, the polarizer 11 is composed of a polyvinyl alcohol resin film containing a dichroic substance, and when the monomer transmittance is set to x% and the in-plane phase difference of the polyvinyl alcohol resin film is set to znm, the following equation (2) is satisfied. In one embodiment, when the monomer transmittance of the polarizer 10 is set to x% and the alignment function of the polyvinyl alcohol-based resin constituting the polarizer is set to f, the following equation (3) is satisfied. y＜-0.011x+0.525       (1) z＜-60x+2875            (2) f＜-0.018x+1.11        (3)

FIG2 is a schematic cross-sectional view of a polarizing plate with a phase difference layer according to another embodiment of the present invention. As shown in FIG2 , another phase difference layer 50 and/or a conductive layer or an isotropic substrate 60 with a conductive layer may also be provided in the polarizing plate with a phase difference layer according to another embodiment. The another phase difference layer 50 and the conductive layer or the isotropic substrate 60 with a conductive layer are typically provided on the outer side of the phase difference layer 20 (on the side opposite to the polarizing plate 10). The refractive index characteristics of the another phase difference layer typically exhibit the relationship nz>nx=ny. The another phase difference layer 50 and the conductive layer or the isotropic substrate 60 with a conductive layer are typically provided in sequence starting from the phase difference layer 20 side. The other phase difference layer 50 and the conductive layer or the isotropic substrate 60 with a conductive layer are generally optional layers provided as needed; either or both may be omitted. Furthermore, for convenience, the phase difference layer 20 is sometimes referred to as the first phase difference layer, and the other phase difference layer 50 is sometimes referred to as the second phase difference layer. Furthermore, when a conductive layer or an isotropic substrate with a conductive layer is provided, the polarizing plate with a phase difference layer can be used in a so-called internal touch panel input display device, in which a touch sensor is incorporated between an image display unit (e.g., an organic EL unit) and the polarizing plate.

Figure 3 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to another embodiment of the present invention. In this embodiment, the first retardation layer 20 is an alignment-cured layer of a liquid crystal compound. The first retardation layer 20 can be a single alignment-cured layer as shown in Figures 1 and 2 , or it can have a laminated structure comprising a first alignment-cured layer 21 and a second alignment-cured layer 22 as shown in Figure 3 .

The above embodiments may be combined as appropriate, and modifications that are self-explanatory in the industry may be made to the components of the above embodiments. For example, a second phase difference layer 50 and/or a conductive layer or an isotropic substrate 60 with a conductive layer may be further provided on the polarizing plate 102 with a phase difference layer in Figure 3 . Furthermore, for example, the configuration in which the isotropic substrate 60 with a conductive layer is provided outside the second phase difference layer 50 may be replaced with an optically equivalent configuration (e.g., a laminate of a second phase difference layer and a conductive layer).

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

The polarizing plate with a retardation layer of the present invention can be in the form of a single sheet or a long strip. As used herein, "long strip" refers to an elongated shape whose length is significantly longer than its width, including, for example, a length of at least 10 times, and preferably at least 20 times, its width. Long strips of polarizing plates with a retardation layer can be rolled into a cylindrical shape.

In practice, an adhesive layer (not shown) is placed on the side of the retardation layer opposite the polarizing plate, allowing the polarizing plate with retardation layer to be attached to the image display unit. Furthermore, a release film is preferably temporarily attached to the surface of the adhesive layer until the polarizing plate with retardation layer is ready for use. This temporary release film protects the adhesive layer and allows for the formation of a cylinder.

The total thickness of the polarizing plate with a phase difference layer is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less. For example, the total thickness can be 10 μm or greater. According to embodiments of the present invention, such an extremely thin polarizing plate with a phase difference layer can be achieved. Furthermore, cracking during heating can be suppressed. Such a polarizing plate with a phase difference layer can have excellent flexibility and flexing durability. Such a polarizing plate with a phase difference layer is particularly suitable for use in curved image display devices and/or bendable or foldable image display devices. Furthermore, the so-called total thickness of the polarizing plate with a phase difference layer refers to the total thickness of all layers constituting the polarizing plate with a phase difference layer, excluding the adhesive layer used to adhere the polarizing plate to an external adherend such as a panel or glass (that is, the total thickness of the polarizing plate with a phase difference layer does not include the thickness of the adhesive layer used to adhere the polarizing plate with a phase difference layer to an adjacent component such as an image display unit and the peeling film that can be temporarily adhered to its surface).

The unit weight of the polarizing plate with a phase difference layer in embodiments of the present invention is, for example, 6.5 mg/ ^cm² or less, preferably 2.0 mg/ ^cm² to 6.0 mg/ ^cm² , more preferably 3.0 mg/ ^cm² to 5.5 mg/ ^cm² , and even more preferably 3.5 mg/ ^cm² to 5.0 mg/ ^cm² . When display panels are thin, there is a risk that the panel may be slightly deformed by the weight of the polarizing plate with a phase difference layer, resulting in display defects. A polarizing plate with a phase difference layer having a unit weight of 6.5 mg/ ^cm² or less can prevent such panel deformation. Furthermore, a polarizing plate with a phase difference layer having such a unit weight maintains good handleability even after thinning and exhibits excellent flexibility and flexural durability.

The following describes in more detail the components of a polarizing plate with a phase difference layer.

B. Polarizing Plate B-1. Polarizer A polarizer in one embodiment of the present invention is composed of a PVA resin film containing a dichroic substance, and when the monomer transmittance is set to x% and the birefringence of the PVA resin is set to y, the following equation (1) is satisfied. Furthermore, a polarizer in another embodiment of the present invention is composed of a PVA resin film containing a dichroic substance, and when the monomer transmittance is set to x% and the in-plane phase difference of the PVA resin film is set to znm, the following equation (2) is satisfied. In one embodiment, when the monomer transmittance of the polarizer is set to x% and the alignment function of the polyvinyl alcohol resin constituting the polarizer is set to f, the following equation (3) is satisfied. y＜-0.011x+0.525 (1) z＜-60x+2875 (2) f＜-0.018x+1.11 (3)

The birefringence of the PVA resin in the polarizer (hereinafter referred to as PVA birefringence or PVA Δn) and the in-plane retardation of the PVA resin film (hereinafter referred to as "PVA in-plane retardation") are both values related to the alignment of the molecular chains of the PVA resin constituting the polarizer, and the values increase with increasing alignment. Because the molecular chains of the PVA resin in the polarizer are more loosely aligned toward the absorption axis than in previous polarizers, cracking along the absorption axis is suppressed. As a result, a polarizer (and ultimately a polarizing plate) with exceptionally excellent flexibility is achieved. Such a polarizer (resulting in a polarizing plate) is preferably used in a curved image display device, preferably a bendable image display device, and even more preferably a foldable image display device. Previously, it was difficult to obtain acceptable optical properties (typically, single-element transmittance and polarization degree) for polarizers with low orientation. However, a polarizer that satisfies the above formula (1) and/or formula (2) can achieve both a lower orientation of the PVA-based resin than previously possible and acceptable optical properties.

The polarizer of the embodiment of the present invention preferably satisfies the following formula (1a) and/or formula (2a), and preferably satisfies the following formula (1b) and/or formula (2b). The above-mentioned polarizer preferably satisfies the following formula (1a) and/or formula (2a), and preferably satisfies the following formula (1b) and/or formula (2b). -0.004x+0.18＜ y ＜ -0.011x+0.525   (1a) -0.003x+0.145＜ y ＜ -0.011x+0.520   (1b) -40x+1800＜ z ＜ -60x+2875               (2a) -30x+1450＜ z ＜ -60x+2850               (2b)

In this specification, the in-plane retardation of PVA is the in-plane retardation value of the PVA resin film at 23°C and a wavelength of 1000 nm. By setting the measurement wavelength in the near-infrared region, the influence of iodine absorption in the polarizer is eliminated, making it possible to measure the retardation. Furthermore, the birefringence (in-plane birefringence) of PVA is the value obtained by dividing the in-plane retardation of PVA by the thickness of the polarizer.

The in-plane retardation of PVA is evaluated as follows. First, the retardation values are measured at multiple wavelengths above 850nm. The measured retardation values, R(λ), are plotted against the wavelength, λ, and then fitted using the least squares method to the following unit Myers equation. A and B are fitting parameters, coefficients determined using the least squares method. R(λ) = A + B / (λ ² -600 ² ) At this point, the retardation value R(λ) can be separated into the in-plane retardation of PVA (Rpva), which has no wavelength dependence, and the in-plane retardation of iodine (Ri), which has a strong wavelength dependence, as follows. Rpva = A Ri = B / (λ ² -600 ² ) Based on this separation formula, the in-plane retardation of PVA at a wavelength of λ = 1000nm (i.e., Rpva) can be calculated. Furthermore, the evaluation method of the in-plane phase difference of PVA is also described in Patent No. 5932760, which can be referred to as needed. In addition, the birefringence (Δn) of PVA can be calculated by dividing the phase difference by the thickness.

Examples of commercially available devices for measuring the in-plane retardation of PVA at the aforementioned wavelength of 1000 nm include the KOBRA-WR/IR series and KOBRA-31X/IR series manufactured by Oji Scientific Instruments.

The alignment function (f) of the polyvinyl alcohol-based resin constituting the polarizer used in the present invention preferably satisfies the following formula (3a), and more preferably satisfies the following formula (3b). If the alignment function is too small, it may be impossible to obtain an acceptable monomer transmittance and/or polarization degree. -0.01x+0.50＜f＜-0.018x+1.11 (3a) -0.01x+0.57＜f＜-0.018x+1.1    (3b)

The alignment function (f) is determined, for example, by measuring attenuated total reflection (ATR) using Fourier transform infrared spectroscopy (FT-IR) with polarized light as the measurement light. Specifically, germanium is used as the microcrystal for bonding the polarizer, the measurement light is incident at a 45° angle, and the incident polarized infrared light (measurement light) is polarized (s-polarized) oscillating parallel to the plane of the sample to which the germanium crystal is bonded. Measurements are performed with the polarizer extending in a direction parallel or perpendicular to the polarization direction of the measurement light. The intensity at 2941 cm ^-1 in the obtained absorbance spectrum is used to calculate the alignment function according to the following formula. The intensity I is calculated using the reference peak at 3330 cm ^-1 as the value of 2941 cm ^-1 /3330 cm ^-1 . Note that f = 1 indicates perfect alignment, and f = 0 indicates random alignment. The peak at 2941 cm ^-1 is believed to be due to absorption caused by the vibration of the PVA main chain (-CH ₂ -) in the polarizer. f = (3 < cos ² θ > -1)/2 = (1-D)/[c(2D+1)] = -2×(1-D)/(2D+1) Where c = (3cos ² β-1)/2, and for the vibration at 2941 cm ^-1 , β = 90°. θ: Angle of the molecular chain relative to the extension direction β: Angle of the transition dipole moment relative to the molecular chain axis D = (I _⊥ ) / (I _// ) (At this time, the greater the orientation of the PVA molecules, the greater the D) I _⊥ : The absorption intensity when the polarization direction of the measured light is perpendicular to the extension direction of the polarizer I _// : The absorption intensity when the polarization direction of the measured light is parallel to the extension direction of the polarizer

The thickness of the polarizer is preferably 10 μm or less, more preferably 8 μm or less. The lower limit of the polarizer thickness can be, for example, 1 μm. In one embodiment, the thickness of the polarizer can be 2 μm to 10 μm, and in another embodiment, it can be 2 μm to 8 μm. Making the polarizer this thin significantly reduces thermal shrinkage. This structure is also believed to help suppress cracking along the absorption axis.

The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single transmittance of the polarizer is preferably 40.0% or higher, preferably 41.0% or higher. The upper limit of the single transmittance may be, for example, 49.0%. In one embodiment, the single transmittance of the polarizer is 40.0% to 45.0%. The polarization degree of the polarizer is preferably 99.0% or higher, preferably 99.4% or higher. The upper limit of the polarization degree may be, for example, 99.999%. In one embodiment, the polarization degree of the polarizer is 99.0% to 99.99%. One of the characteristics of the polarizer of the embodiment of the present invention is that the orientation degree of the PVA-based resin constituting the polarizer is lower than before, and despite having the above-mentioned in-plane phase difference, birefringence and/or orientation function, the above-mentioned practically acceptable monomer transmittance and polarization degree can be achieved. The reason is presumably due to the manufacturing method described later. Furthermore, the monomer transmittance is usually measured using an ultraviolet-visible spectrometer, and the Y value is corrected for the sensitivity. The polarization degree is usually calculated based on the parallel transmittance Tp and the perpendicular transmittance Tc measured using an ultraviolet-visible spectrometer and corrected for the sensitivity, using the following formula. Polarization degree (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100

The puncture strength of the polarizer is, for example, 30 gf/μm or more, preferably 35 gf/μm or more, more preferably 40 gf/μm or more, even more preferably 45 gf/μm or more, and particularly preferably 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 to such a range, the rupture of the polarizer along the absorption axis can be significantly suppressed. As a result, a polarizer (the result is a polarizing plate) with very excellent flexibility can be obtained. The puncture strength indicates the rupture resistance of the polarizer when the polarizer is punctured with a specific strength. The puncture strength can be expressed as, for example, the strength (fracture strength) of the polarizer rupture when a specific needle is installed in a compression tester and the needle pierces the polarizer at a specific speed. Furthermore, it can be understood from the unit that the puncture strength refers to the puncture strength per unit thickness (1 μm) of the polarizer.

As described above, the polarizer is composed of a PVA-based resin film containing a dichroic substance. Preferably, the PVA-based resin constituting the PVA-based resin film (essentially the polarizer) includes an acetyl-modified PVA-based resin. This configuration allows for a polarizer with the desired puncture strength. When the total PVA-based resin is assumed to be 100% by weight, the amount of the acetyl-modified PVA-based resin blended is preferably 5% to 20% by weight, preferably 8% to 12% by weight. A blending amount within this range achieves a more suitable puncture strength.

Polarizers are typically manufactured using a laminate of two or more layers. A specific example of a polarizer manufactured using a laminate includes a laminate comprising a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer obtained by laminating a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by applying a PVA-based resin solution to the resin substrate, drying it, and forming the PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; stretching and dyeing the laminate, and then using the PVA-based resin layer as a polarizer. In this embodiment, a polyvinyl alcohol-based resin layer comprising a halogenated compound and a polyvinyl alcohol-based resin is preferably formed on one side of the resin substrate. Stretching typically involves immersing the laminate in an aqueous boric acid solution and then stretching it. Furthermore, the stretching preferably further includes stretching the laminate in the air at a high temperature (for example, above 95°C) before stretching in the boric acid aqueous solution. In the embodiment of the present invention, the total stretching ratio is preferably 3.0 times to 4.5 times, which is significantly smaller than the general ratio. Even with such a total stretching ratio, a polarizer with acceptable optical properties can be obtained by combining the addition of halides and a drying and shrinking treatment. Furthermore, in the embodiment of the present invention, it is preferred that the stretching ratio of the air-assisted stretching is greater than the stretching ratio of the stretching in boric acid water. By forming such a structure, a polarizer with acceptable optical properties can be obtained even if the total stretching ratio is smaller. Furthermore, the laminate is preferably subjected to a drying and shrinking treatment, which involves heating the laminate while conveying it in its longitudinal direction, thereby shrinking it by at least 2% in its widthwise direction. In one embodiment, a method for manufacturing a polarizer includes sequentially subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying and shrinking treatment. By introducing the auxiliary stretching treatment, the crystallinity of the PVA resin can be enhanced, even when coating the PVA resin on a thermoplastic resin, achieving high optical properties. Furthermore, by simultaneously enhancing the orientation of the PVA resin beforehand, problems such as a decrease in orientation or dissolution of the PVA resin during immersion in water during subsequent dyeing or stretching steps can be prevented, thereby achieving high optical properties. Furthermore, when the PVA resin layer is immersed in a liquid, the orientational disturbance of the polyvinyl alcohol molecules and a decrease in orientation can be suppressed compared to a PVA resin layer without a halogenated compound. This improves the optical properties of polarizers obtained after treatment steps involving immersion of the laminate in a liquid, such as dyeing and underwater stretching. Furthermore, shrinking the laminate in the width direction during a drying and shrinking process can further enhance optical properties. The resulting resin substrate/polarizer laminate can be used directly (i.e., the resin substrate can be used as a protective layer for the polarizer). Alternatively, the resin substrate can be peeled off from the resin substrate/polarizer laminate and any suitable protective layer can be applied to the peeled surface. The detailed polarizer manufacturing method will be described later.

B-2. Polarizer Manufacturing Method A polarizer manufacturing method according to one embodiment of the present invention comprises the following steps: forming a polyvinyl alcohol resin layer (PVA resin layer) comprising a halogenated compound and a polyvinyl alcohol resin (PVA resin) on one side of a long thermoplastic resin substrate to form a laminate; and sequentially subjecting the laminate to an air-assisted stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying and shrinking treatment. The drying and shrinking treatment involves heating while conveying the laminate in the longitudinal direction to achieve a widthwise shrinkage of 1% to 10%. The halogenated compound content in the PVA resin layer is preferably 5 to 20 parts by weight per 100 parts by weight of the PVA resin. The drying and shrinking treatment is preferably performed using a heating roller, and the temperature of the heating roller is preferably 60°C to 120°C. The shrinkage rate of the laminate in the width direction caused by the drying and shrinking treatment is preferably 1% to 10%. According to such a manufacturing method, the polarizer described in the above-mentioned item B-1 can be obtained. In particular, by producing a laminate containing a PVA-based resin layer containing a halogenated compound, setting the extension of the laminate to a multi-stage extension including air-assisted extension and underwater extension, and then heating the laminate after heat extension with a heating roller, a polarizer with excellent optical properties (usually single-element transmittance and polarization degree) can be obtained.

B-2-1. Laminated Product Formation Any suitable method can be employed to form the laminate of the thermoplastic resin substrate and the PVA-based resin layer. Preferably, the PVA-based resin layer is formed on the thermoplastic resin substrate by applying a coating solution containing a halogenated compound and a PVA-based resin to the surface of the thermoplastic resin substrate and then drying the solution. As mentioned above, the halogenated compound content in the PVA-based resin layer is preferably 5 to 20 parts by weight per 100 parts by weight of the PVA-based resin.

The coating liquid can be applied using any suitable method. Examples include roll coating, spin coating, wire rod coating, dip coating, die coating, curtain coating, spray coating, knife coating (comma coating, etc.). The application and drying temperature of the coating liquid should preferably be above 50°C.

The thickness of the PVA resin layer is preferably 2μm to 30μm, more preferably 2μm to 20μm. By making the thickness of the PVA resin layer very thin before stretching and reducing the total stretching ratio as described below, a polarizer with acceptable monomer transmittance and polarization degree can be obtained despite a very small alignment function.

Before forming the PVA resin layer, the thermoplastic resin substrate can be subjected to a surface treatment (e.g., corona treatment) or a bonding layer can be formed on the thermoplastic resin substrate. Such treatment can improve the adhesion between the thermoplastic resin substrate and the PVA resin layer.

B-2-1-1. Thermoplastic Resin Substrate Any suitable thermoplastic resin film can be used as the thermoplastic resin substrate. Details regarding thermoplastic resin substrates are described, for example, in Japanese Patent Application Publication No. 2012-73580 and Japanese Patent No. 6470455. All of the contents of these publications are incorporated herein by reference.

B-2-1-2. Coating Liquid As described above, the coating liquid comprises a halogenated compound and a PVA-based resin. The coating liquid is typically a solution of the halogenated compound and the PVA-based resin dissolved in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trihydroxymethylpropane, and amines such as ethylenediamine and diethylenetriamine. These solvents can be used alone or in combination. Water is preferred. The PVA-based resin concentration in the solution is preferably 3 to 20 parts by weight per 100 parts by weight of the solvent. This resin concentration allows for the formation of a uniform coating film that adheres closely to the thermoplastic resin substrate. The content of the halogenated compound in the coating solution is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin.

Additives can also be added to the coating liquid. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyols such as ethylene glycol and glycerin. Examples of surfactants include non-ionic surfactants. These can be used to further improve the uniformity, dyeability, and extensibility of the resulting PVA resin layer.

Any suitable resin may be used as the PVA resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer is obtained by saponifying ethylene-vinyl alcohol copolymer. The saponification degree of PVA resin is generally 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The saponification degree can be determined in accordance with JIS K 6726-1994. By using a PVA resin with such a saponification degree, a polarizer with excellent durability can be obtained. If the saponification degree is too high, there is a risk of gelation. As described above, the PVA-based resin preferably includes an acetyl-modified PVA-based resin.

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

Any suitable halides may be used as the halides. Examples include iodides and sodium chloride. Examples of iodides include potassium iodide, sodium iodide, and lithium iodide. Among these, potassium iodide is preferred.

The amount of halogen in the coating solution should preferably be 5 to 20 parts by weight, more preferably 10 to 15 parts by weight, per 100 parts by weight of the PVA resin. If the amount of halogen exceeds 20 parts by weight per 100 parts by weight of the PVA resin, the halogen may bleed out, resulting in a cloudy polarizer.

Generally speaking, stretching a PVA resin layer increases the orientation of the polyvinyl alcohol molecules within the PVA resin. However, immersing the stretched PVA resin layer in a liquid containing water can disrupt the orientation of the polyvinyl alcohol molecules, reducing this orientation. This tendency to reduce orientation is particularly pronounced when stretching a laminate of a thermoplastic resin and a PVA resin layer in boric acid water at relatively high temperatures to stabilize the stretching of the thermoplastic resin. For example, while stretching of a PVA film monomer in boric acid water is typically performed at 60°C, stretching of a laminate of an A-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a higher temperature of around 70°C. At this time, the orientation of the PVA in the initial stretching phase decreases before it begins to rise due to stretching in water. In contrast, when preparing a laminate of a PVA-based resin layer containing a halogenated compound and a thermoplastic resin substrate, stretching the laminate in air at a high temperature (assisted stretching) before stretching the laminate in boric acid water promotes crystallization of the PVA resin in the PVA-based resin layer of the laminate after the assisted stretching. As a result, when the PVA resin layer is immersed in a liquid, the disordered alignment of the polyvinyl alcohol molecules and the reduction in orientation are suppressed compared to a case where the PVA resin layer does not contain a halogenated compound. This improves the optical properties of polarizers obtained by immersing the laminate in a liquid, such as through dyeing and underwater stretching.

B-2-2. In-Air Assisted Stretching To achieve particularly high optical properties, a two-stage stretching method combining dry stretching (assisted stretching) with stretching in boric acid water can be used. As with two-stage stretching, the introduction of an auxiliary stretching process allows stretching to be performed while suppressing crystallization of the thermoplastic resin substrate. Furthermore, when coating a PVA resin on a thermoplastic resin substrate, the coating temperature must be lower than when coating the PVA resin on a conventional metal drum to suppress the influence of the thermoplastic resin substrate's glass transition temperature. This results in a relatively slow crystallization of the PVA resin, preventing the achievement of sufficient optical properties. In contrast, by introducing assisted stretching, the crystallinity of the PVA resin can be enhanced even when coating it on a thermoplastic resin, achieving high optical properties. Furthermore, by simultaneously enhancing the orientation of the PVA resin beforehand, problems such as a decrease in orientation or dissolution of the PVA resin during subsequent dyeing or stretching steps can be prevented, ultimately achieving high optical properties.

The stretching method of aerial assisted stretching can be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, a method of passing the laminate through rollers with different circumferential speeds for uniaxial stretching). In order to obtain high optical properties, free-end stretching can be actively adopted. In one embodiment, the aerial stretching process includes a heating roller stretching step in which the laminate is transported in its longitudinal direction while being stretched using the circumferential speed difference between the heating rollers. The aerial stretching process usually includes a regional stretching step and a heating roller stretching step. Furthermore, the order of the regional stretching step and the heating roller stretching step is not limited, and the regional stretching step can be performed first, or the heating roller stretching step can be performed first. The regional stretching step can also be omitted. In one embodiment, the zone stretching step and the heated roller stretching step are performed sequentially. In another embodiment, the film ends are clamped in tenter stretching machines, and the distance between the tenters is increased in the flow direction to achieve stretching (the distance between the tenters is the stretch ratio). In this case, the distance between the tenters in the width direction (perpendicular to the flow direction) can be set to any desired distance. Preferably, the stretch ratio relative to the flow direction is set to achieve closeness by free-end stretching. When performing free-end stretching, the widthwise contraction ratio is calculated as (1/stretch ratio) ^½ .

Air-assisted stretching can be performed in a single stage or in multiple stages. When performed in multiple stages, the stretching ratio is the product of the stretching ratios of each stage. The stretching direction of air-assisted stretching should preferably be substantially the same as the stretching direction of underwater stretching.

The stretching ratio in the air-assisted stretching is preferably 1.0 times to 4.0 times, more preferably 1.5 times to 3.5 times, and even more preferably 2.0 times to 3.0 times. If the stretching ratio of the air-assisted stretching is in such a range, the total stretching ratio can be set to the desired range when combined with the underwater stretching, and the desired orientation function can be achieved. As a result, a polarizer in which the fracture along the absorption axis direction is suppressed can be obtained. Furthermore, as mentioned above, it is preferable that the stretching ratio of the air-assisted stretching is greater than the stretching ratio of the boric acid water stretching. By having such a structure, even if the total stretching ratio is small, a polarizer with acceptable optical properties can be obtained. More specifically, the ratio of the stretching ratio of the air-assisted stretching to the stretching ratio of the underwater stretching (underwater stretching/air-assisted stretching) is preferably 0.4-0.9, more preferably 0.5-0.8.

The stretching temperature for air-assisted stretching can be set to any appropriate value depending on the thermoplastic resin substrate material, stretching method, and other factors. The stretching temperature is preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably above the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C, and even more preferably above Tg + 15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. Stretching at this temperature can suppress the rapid crystallization of the PVA resin, thereby minimizing problems caused by this crystallization (for example, preventing the alignment of the PVA resin layer during stretching).

B-2-3. Insolubilization, Dyeing, and Crosslinking If necessary, an insolubilization treatment is performed after the air-assisted stretching treatment and before the underwater stretching treatment or dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA resin layer in an aqueous boric acid solution. The dyeing treatment is typically performed by dyeing the PVA resin layer with a dichroic substance (typically iodine). If necessary, a crosslinking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The crosslinking treatment is typically performed by immersing the PVA resin layer in an aqueous boric acid solution. Details regarding the insolubilization treatment, dyeing treatment, and crosslinking treatment are described, for example, in Japanese Patent Application Laid-Open No. 2012-73580 (cited above).

B-2-4. Underwater Stretching Underwater stretching is performed by immersing the laminate in a stretching bath. This allows stretching at temperatures lower than the glass transition temperature (typically around 80°C) of the thermoplastic resin substrate or PVA resin layer, suppressing crystallization of the PVA resin layer. As a result, polarizers with excellent optical properties can be produced.

Any suitable method may be used for stretching the laminate. Specifically, it may be fixed-end stretching or free-end stretching (for example, a method in which the laminate passes between rollers of varying circumferential speeds for uniaxial stretching). Free-end stretching is preferred. Stretching of the laminate may be performed in a single stage or in multiple stages. When a multi-stage stretching method is used, the total stretching ratio is the product of the stretching ratios of each stage.

Underwater stretching is preferably performed by immersing the laminate in an aqueous boric acid solution (boric acid underwater stretching). Using an aqueous boric acid solution as the stretching bath imparts the PVA resin layer with the rigidity necessary to withstand the tension applied during stretching, as well as water resistance, preventing it from dissolving in water. Specifically, boric acid forms tetrahydroxyboric acid anions in aqueous solution, which crosslink with the PVA resin via hydrogen bonds. This imparts rigidity and water resistance to the PVA resin layer, enabling excellent stretchability and producing polarizers with superior optical properties.

The boric acid aqueous solution can be preferably obtained by dissolving boric acid and/or a boric acid salt in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, preferably 2.5 to 6 parts by weight, and more preferably 3 to 5 parts by weight, per 100 parts by weight of water. Setting the boric acid concentration to 1 part by weight or higher effectively inhibits the dissolution of the PVA resin layer, enabling the production of polarizers with higher performance. Furthermore, in addition to boric acid or a boric acid salt, aqueous solutions obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, etc. in a solvent may also be used.

It is preferred to add an iodide to the stretching bath (boric acid aqueous solution). This addition can suppress the dissolution of iodine adsorbed by the PVA-based resin layer. Specific examples of iodide are described above. The concentration of iodide is preferably 0.05 to 15 parts by weight, 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 dissolution of the PVA resin layer can be suppressed while stretching at a high rate. Specifically, as mentioned above, due to the relationship with the formation of the PVA resin layer, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably above 60°C. At this time, if the stretching temperature is lower than 40°C, even considering the plasticization of the thermoplastic resin substrate by water, there is a risk that it will not be stretched well. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA resin layer, and there is a risk that excellent optical properties may not be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio of the underwater stretching is preferably 1.0 times to 3.0 times, more preferably 1.0 times to 2.0 times, and more preferably 1.0 times to 1.5 times. If the stretching ratio of the underwater stretching is in this range, the total stretching ratio can be set to the desired range, and the desired orientation function can be achieved. As a result, a polarizer in which cracks along the absorption axis are suppressed can be obtained. The total stretching ratio (the sum of the stretching ratios when combining the air-assisted stretching and the underwater stretching) is as described above, for example, 3.0 times to 4.5 times, preferably 3.0 times to 4.0 times, and more preferably 3.0 times to 3.5 times relative to the original length of the laminate. By appropriately combining the addition of halides to the coating solution, adjusting the stretching ratios of in-air assisted stretching and underwater stretching, and drying and shrinking treatment, a polarizer with acceptable optical properties can be obtained even at such a total stretching ratio.

B-2-5. Drying and Shrinking Treatment The drying and shrinking treatment can be performed using either localized heating (heating the entire area) or heated conveyor rollers (using so-called heating rollers) (heating roller drying). Using both methods is preferred. Using heating rollers for drying effectively suppresses heat warping of the laminate, resulting in the production of a polarizer with excellent appearance. Specifically, drying the laminate while it travels along the heating rollers effectively promotes crystallization of the thermoplastic resin substrate, increasing its degree of crystallization. This allows for a significant increase in the degree of crystallization of the thermoplastic resin substrate even at relatively low drying temperatures. As a result, the thermoplastic resin substrate's rigidity increases, making it resistant to shrinkage caused by drying of the PVA-based resin layer and thus preventing curling. Furthermore, because the use of heated rollers allows the laminate to be maintained flat while drying, not only curling but also wrinkling can be suppressed. The drying and shrinking treatment shrinks the laminate in the width direction, thereby improving its optical properties. This is because it effectively improves the orientation of the PVA and PVA/iodine complex. The shrinkage rate in the width direction of the laminate treated by the drying and shrinking treatment is preferably 1% to 10%, preferably 2% to 8%, and even more preferably 4% to 6%.

Figure 4 schematically illustrates an example of a drying and shrinking process. During the drying and shrinking process, transport rollers R1-R6 and guide rollers G1-G4, heated to specific temperatures, transport the laminate 200 while drying it. In the illustrated example, while transport rollers R1-R6 are positioned to alternately and continuously heat the PVA resin layer surface and the thermoplastic resin substrate surface, they could alternatively be positioned to continuously heat only one surface of the laminate 200 (e.g., the thermoplastic resin substrate surface).

The drying conditions can be controlled by adjusting the heating temperature of the conveyor rollers (heating roller temperature), the number of heating rollers, and the contact time with the heating rollers. The temperature of the heating rollers is preferably 60°C to 120°C, more preferably 65°C to 100°C, and even more preferably 70°C to 80°C. This can significantly increase the degree of crystallization of the thermoplastic resin, effectively suppress curling, and produce optical laminates with extremely excellent durability. Furthermore, the temperature of the heating rollers can be measured using a contact thermometer. In the example shown, six conveyor rollers are provided, but there is no particular limitation as long as there are multiple conveyor rollers. Typically, there are 2 to 40 conveyor rollers, preferably 4 to 30. The contact time (total contact time) between the laminate and the heated roller is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

The heating rollers can be placed inside a heating furnace (such as an oven) or on a general production line (at room temperature). They are preferably placed inside a heating furnace equipped with an air supply mechanism. By combining drying with the heating rollers and hot air drying, rapid temperature fluctuations between the heating rollers can be suppressed, making it easier to suppress shrinkage in the width direction. The hot air drying temperature is preferably 30°C to 100°C. Furthermore, the hot air drying time is preferably 1 second to 300 seconds. The hot air velocity is preferably approximately 10m/s to 30m/s. Furthermore, this velocity is the velocity inside the heating furnace and can be measured using a Minivan digital anemometer.

B-2-6. Other Treatments It is best to perform a cleaning treatment after the water stretching treatment and before the drying and shrinking treatment. This cleaning treatment is typically performed by immersing the PVA resin layer in an aqueous potassium iodide solution.

B-3. Protective Layer In embodiments of the present invention, the protective layer has a thickness of 10 μm or less. A protective layer thickness of 10 μm or less also contributes to a thinner polarizing plate. Even with a protective layer thickness of 10 μm or less, the polarizing plate with a retardation layer described above can prevent cracking during heating. The protective layer thickness is preferably 7 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. For example, the protective layer thickness is 1 μm or greater.

The protective layer can be formed from any suitable material. Examples include: cellulose-based resins such as triacetate (TAC); transparent resins such as polyesters, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyether sulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, (meth)acrylic acids, and acetates; thermosetting or UV-curing resins such as (meth)acrylic acids, urethanes, (meth)acrylic urethanes, epoxies, and silicones; and glassy polymers such as silicone polymers.

The protective layer can be a thin film, a cured product of a coating film, or a hardened product (e.g., a photopolymer cured product). In one embodiment, the protective layer is composed of at least one selected from the group consisting of a cured product of a coating film obtained from an organic solvent solution of a thermoplastic (meth)acrylic resin (hereinafter sometimes referred to as an acrylic resin), a photopolymer cured product of an epoxy resin, and a cured product of a coating film obtained from an organic solvent solution of an epoxy resin. This is described in detail below.

B-3-1. Cured Film of a Thermoplastic Acrylic Resin Organic Solvent Solution In one embodiment, the protective layer is formed from a cured film of a thermoplastic acrylic resin organic solvent solution.

B-3-1-1. Acrylic Resin The glass transition temperature (Tg) of acrylic resins is preferably 100°C or higher. Consequently, the Tg of the protective layer is 100°C or higher. When the Tg of an acrylic resin is 100°C or higher, a polarizing plate including a protective layer made from such a resin exhibits excellent durability. The Tg of an acrylic resin is preferably 110°C or higher, preferably 115°C or higher, more preferably 120°C or higher, and even more preferably 125°C or higher. On the other hand, the Tg of an acrylic resin is preferably 300°C or lower, preferably 250°C or lower, more preferably 200°C or lower, and even more preferably 160°C or lower. Acrylic resins with a Tg within this range exhibit excellent moldability.

As for acrylic resins, any suitable acrylic resin can be used as long as it has the above-mentioned Tg. Acrylic resins generally have monomer units (repeating units) containing (meth) alkyl acrylate as the main component. In this specification, "(meth) acrylic acid" refers to acrylic acid and/or methacrylic acid. As for the (meth) alkyl acrylate constituting the main skeleton of the acrylic resin, examples include linear or branched alkyl groups with 1 to 18 carbon atoms. These can be used alone or in combination. Furthermore, any suitable copolymer monomer can be introduced into the acrylic resin by copolymerization. The repeating units derived from the (meth) alkyl acrylate are generally represented by the following general formula (1):

[Chemical formula 1]

In general formula (1), ^R4 represents a hydrogen atom or a methyl group, and ^R5 represents a hydrogen atom or an optionally substituted aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms. Examples of the substituent include halogen and hydroxyl groups. Specific examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, benzyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, dicyclopentane (meth)acrylate, chloromethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate, 2,3,4,5-tetrahydroxypentyl (meth)acrylate, methyl 2-(hydroxymethyl)acrylate, ethyl 2-(hydroxymethyl)acrylate, and methyl 2-(hydroxyethyl)acrylate. In the general formula (1), ^R5 is preferably a hydrogen atom or a methyl group. Therefore, the preferred (meth)acrylate is 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.

The content of alkyl (meth)acrylate units in acrylic resins is preferably 50 mol% to 98 mol%, more preferably 55 mol% to 98 mol%, more preferably 60 mol% to 98 mol%, even more preferably 65 mol% to 98 mol%, and most preferably 70 mol% to 97 mol%. If the content is less than 50 mol%, the effects of the alkyl (meth)acrylate units (such as high heat resistance and high transparency) may not be fully realized. If the content exceeds 98 mol%, the resin may become brittle and easily cracked, failing to fully demonstrate its high mechanical strength, and may result in poor productivity.

The acrylic resin preferably has repeating units containing a ring structure. Examples of repeating units containing a ring structure include lactone ring units, glutaric anhydride units, glutarimide units, maleic anhydride units, and maleimide (N-substituted maleimide) units. The acrylic resin may contain only one repeating unit containing a ring structure, or two or more repeating units containing a ring structure.

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

[Chemical formula 2] 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. Furthermore, the organic residue may also 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. Acrylic resins containing lactone ring units are described, for example, in Japanese Patent Application Laid-Open No. 2008-181078, the contents of which are incorporated herein by reference.

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

[Chemical formula 3]

In general formula (3), R ¹¹ and R ¹² each independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ¹³ represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aryl group having 6 to 10 carbon atoms. In general formula (3), preferably, R ¹¹ and R ¹² each independently represent hydrogen or a methyl group, and R ¹³ represents hydrogen, a methyl group, a butyl group, or a cyclohexyl group. More preferably, R ¹¹ represents a methyl group, R ¹² represents hydrogen, and R ¹³ represents a methyl group. The acrylic resin may contain only a single pentylimide unit, or may contain a plurality of pentylimide units in which R ¹¹ , R ¹² , and R ¹³ in the general formula (3) are different. Acrylic resins having a glutarimide unit are described, for example, in Japanese Patent Application Laid-Open Nos. 2006-309033, 2006-317560, 2006-328334, 2006-337491, 2006-337492, 2006-337493, and 2006-337569, the contents of which are incorporated herein by reference. Regarding the glutaric anhydride unit, the above description regarding the glutarimide unit is applicable, except that the nitrogen atom substituted for R ¹³ in the general formula (3) is replaced by an oxygen atom.

Since the structures of the maleic anhydride unit and the maleimide (N-substituted maleimide) unit are clearly apparent from their names, a detailed description thereof will be omitted.

The content of repeating units containing a ring structure in acrylic resins is preferably 1 mol% to 50 mol%, more preferably 10 mol% to 40 mol%, and even 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, formability and transparency may be insufficient.

The acrylic resin may also contain repeating units other than the (meth)acrylate unit and the repeating unit containing a ring structure. Examples of such repeating units include repeating units derived from vinyl monomers copolymerizable with the monomers constituting the above-mentioned units (other vinyl monomer units). Examples of other vinyl monomers include 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, methyl Examples of the vinyl monomers include ethylaminopropyl acrylate, cyclohexylaminoethyl methacrylate, N-vinyldiethylamine, N-acetylvinylamine, allylamine, methallylamine, N-methylallylamine, 2-isopropenyl-oxazoline, 2-vinyl-oxazoline, 2-acryl-oxazoline, N-phenylmaleimide, phenylaminoethyl methacrylate, styrene, α-methylstyrene, p-epoxypropylstyrene, p-aminostyrene, and 2-phenylvinyl-oxazoline. These monomers may be used alone or in combination. The type, amount, combination, and content ratio of other vinyl monomer units may be appropriately determined depending on the intended purpose.

The weight average molecular weight of the acrylic resin is preferably 1,000 to 2,000,000, more preferably 5,000 to 1,000,000, more preferably 10,000 to 500,000, even more 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 gel permeation chromatography (GPC system, manufactured by Tosoh) in terms of polystyrene. Tetrahydrofuran can be used as the solvent.

Acrylic resins can be used by appropriately combining the above-mentioned monomer units and polymerizing them using any appropriate polymerization method.

In the embodiment of the present invention, acrylic resins and other resins may be used in combination. That is, the monomer components constituting the acrylic resin may be copolymerized with the monomer components constituting the other resins, and the copolymer may be provided for forming the protective layer described later; or a mixture of the acrylic resin and other resins may be provided for forming the protective layer. Examples of other resins include thermoplastic resins such as styrene resins, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyetheretherketone, polyester, polysulfone, polyphenylene ether, polyacetal, polyimide, and polyetherimide. The type and amount of the resins used in combination may be appropriately set according to the purpose and the desired properties of the obtained film. For example, a styrene resin (preferably an acrylonitrile-styrene copolymer) can be used as a phase difference control agent.

When using acrylic resins in combination with other resins, the acrylic resin content in the mixture is preferably 50% to 100% by weight, more preferably 60% to 100% by weight, more preferably 70% to 100% by weight, and even more preferably 80% to 100% by weight. If the content is less than 50% by weight, the inherent high heat resistance and high transparency of acrylic resins may not be fully exhibited.

B-3-2. Photocurable Epoxy Resin In one embodiment, the protective layer is formed from a photocurable epoxy resin. Using such a protective layer allows for the provision of polarizing plates and polarizing plates with retardation layers that exhibit both excellent durability and excellent flexibility. As described above, since the protective layer is a photocurable epoxy resin, the protective layer-forming composition includes a photocurable epoxy resin. A photocurable epoxy resin is a photosensitive agent that functions as a photoacid generator and is typically an ionic onium salt containing a cationic portion and an anionic portion. In this onium salt, the cationic portion absorbs light, while the anionic portion becomes an acid generator. The acid generated from this photocationic polymerization initiator causes ring-opening polymerization of the epoxy groups. The resulting protective layer of the photocationic cured product has a higher glass transition temperature and reduced iodine adsorption. This enables the provision of a polarizing plate that combines excellent durability with superior flexibility.

B-3-2-1. Epoxy Resin Any suitable epoxy resin can be used as the epoxy resin. In embodiments 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 is preferably used. Examples of aromatic skeletons include benzene rings, naphthalene rings, and fluorene rings. A single epoxy resin may be used, or a combination of two or more may be used. An epoxy resin having a biphenyl skeleton as the aromatic skeleton is preferably used. Using an epoxy resin having a biphenyl skeleton allows for the provision of a polarizing plate with both superior durability and superior flexibility. Hereinafter, an epoxy resin having a biphenyl skeleton will be described in detail as a representative example.

In one embodiment, the epoxy resin having a biphenyl skeleton is an epoxy resin having the following structure. One type of epoxy resin having a biphenyl skeleton may be used alone, or two or more types may be used in combination. [Chemical Formula 4] (wherein, R ¹⁴ to R ²¹ independently represent a hydrogen atom, a linear or branched substituted or unsubstituted alkyl 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 alkyl group having 1 to 12 carbon atoms, or a halogen element. Examples of the linear or branched substituted or unsubstituted alkyl group having 1 to 12 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, t-butyl, n-pentyl, isopentyl, neopentyl, t-pentyl, cyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, cycloheptyl, methylcyclohexyl, n-octyl, cyclooctyl, n-nonyl, 3,3,5-trimethylcyclohexyl, n-decyl, cyclodecyl, n-undecyl, n-dodecyl, cyclododecyl, phenyl, benzyl, methylbenzyl, dimethylbenzyl, trimethylbenzyl, naphthylmethyl, phenethyl, and 2-phenylisopropyl. Preferred examples of linear or branched substituted or unsubstituted alkyl groups having 1 to 12 carbon atoms include alkyl groups having 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, and n-butyl. Preferred examples of halogen elements include fluorine and bromine.

In one embodiment, the epoxy resin having a biphenyl skeleton is an epoxy resin represented by the following formula: [Chemical Formula 5] (wherein, R ¹⁴ to R ²¹ are as described above, and n represents an integer from 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 also contain chemical structures other than the biphenyl skeleton. Examples of chemical structures other than the biphenyl skeleton include a bisphenol skeleton, an alicyclic structure, and an aromatic ring structure. In this embodiment, the ratio (molar ratio) of chemical structures other than the biphenyl skeleton is preferably less than that of the biphenyl skeleton.

Commercially available epoxy resins having a biphenyl skeleton may also be used. Examples of commercially available epoxy resins include those manufactured by Mitsubishi Chemical Corporation, trade names: jER YX4000, jER YX4000H, jER YL6121, jER YL664, jER YL6677, jER YL6810, and jER YL7399.

The glass transition temperature (Tg) of the epoxy resin having a biphenyl skeleton is preferably 90°C or higher. As a result, the Tg of the protective layer is 90°C or higher. If the Tg of the epoxy resin having a biphenyl skeleton is 90°C or higher, the polarizing plate including the resulting protective layer tends to have excellent durability. The Tg of the epoxy resin having a biphenyl skeleton is preferably 100°C or higher, preferably 110°C or higher, more preferably 120°C or higher, and even more 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, preferably 250°C or lower, more preferably 200°C or lower, and even more preferably 160°C or lower. If the Tg of the epoxy resin with a biphenyl skeleton is within this range, excellent moldability can be achieved.

The epoxy equivalent weight of the epoxy resin having a biphenyl skeleton is preferably 100 g/equivalent or greater, more preferably 150 g/equivalent or greater, and more preferably 200 g/equivalent or greater. Furthermore, the epoxy equivalent weight of the epoxy resin having a biphenyl skeleton is preferably 3000 g/equivalent or less, preferably 2500 g/equivalent or less, and more preferably 2000 g/equivalent or less. By having the epoxy equivalent weight of the epoxy resin having a biphenyl skeleton within the above range, a more stable protective layer (a sufficiently cured protective layer with less residual monomers) can be obtained. In this specification, "epoxy equivalent" refers to the mass of an epoxy resin containing one equivalent of epoxy groups and can be measured according to JIS K7236.

In embodiments 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 other resins. Specifically, a mixture of an epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton and other resins may be used to form the protective layer. Examples of other resins include thermoplastic resins such as styrene-based resins, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyetheretherketone, polyester, polysulfone, polyphenylene oxide, polyacetal, polyimide, and polyetherimide, as well as curing resins such as acrylic resins and cyclohexane-based resins. Acrylic resins and cyclohexane resins are preferred. The type and amount of the resin used can be appropriately determined based on the intended purpose and the desired properties of the resulting film. For example, a styrene resin can be used as a phase difference control agent.

Any suitable acrylic resin can be used. For example, (meth)acrylic compounds include (meth)acrylic compounds having one (meth)acrylic group in the molecule (hereinafter also referred to as "monofunctional (meth)acrylic compounds") and (meth)acrylic compounds having two or more (meth)acrylic groups in the molecule (hereinafter also referred to as "polyfunctional (meth)acrylic compounds"). These (meth)acrylic compounds can be used alone or in combination of two or more. These acrylic resins are described, for example, in Japanese Patent Application Laid-Open No. 2019-168500. All the contents of this publication are incorporated herein by reference.

As for the oxetane resin, any suitable compound having one or more oxetane groups in the molecule can be used. Examples include 3-ethyl-3-hydroxymethyloxetane, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, 3-ethyl-3-(phenoxymethyl)oxetane, 3-ethyl-3-(cyclohexyloxymethyl)oxetane, 3-ethyl-3-(oxiranylmethoxy)oxetane, (meth)acrylate (3-ethyloxetane-3-yl)methyl, etc. Cyclooxetane compounds having one cyclooxetane group; cyclooxetane compounds having two or more cyclooxetane groups in the molecule, such as 3-ethyl-3{[(3-ethylcyclooxetane-3-yl)methoxy]methyl}cyclooxetane, 1,4-bis[(3-ethyl-3-cyclooxetane)methoxymethyl]benzene, and 4,4'-bis[(3-ethyl-3-cyclooxetane)methoxymethyl]biphenyl. These cyclooxetane resins may be used alone or in combination of two or more.

Preferred oxetane resins include 3-ethyl-3-hydroxymethyloxetane, 1,4-bis[(3-ethyl-3-oxetane-1-yl)methoxymethyl]benzene, 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane, 3-ethyl-3-(oxiranylmethoxy)oxetane, (3-ethyloxetane-3-yl)methyl (meth)acrylate, and 3-ethyl-3{[(3-ethyloxetane-3-yl)methoxy]methyl}oxetane. These oxetane resins are readily available and have excellent diluting properties (low viscosity) and compatibility.

In one embodiment, from the perspective of compatibility and adhesion, it is preferred to use an oxetane resin having a molecular weight of 500 or less and being liquid at room temperature (25°C). In one embodiment, it is preferred to use an oxetane compound containing two or more oxetane groups in the molecule, or an oxetane compound containing one oxetane group and one (meth)acryloyl group or one epoxy group in the molecule. More preferred are 3-ethyl-3{[(3-ethyloxetane-3-yl)methoxy]methyl}oxetane, 3-ethyl-3-(oxiranylmethoxy)oxetane, and (meth)acrylic acid (3-ethyloxetane-3-yl)methyl. Use of such oxetane resins can improve the curability and durability of the protective layer.

As the oxetane resin, commercially available products can be used. Specifically, ARONE OXETANE OXT-101, ARONE OXETANE OXT-121, ARONE OXETANE OXT-212, and ARONE OXETANE OXT-221 (all manufactured by Toagosei Co., Ltd.) can be used. ARONE OXETANE OXT-101 and ARONE OXETANE OXT-221 are 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 content of the epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton in the mixture of the epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton 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, and even more preferably 80% to 100% by weight. If the content is less than 50% by weight, the heat resistance of the protective layer and sufficient adhesion to the polarizer may not be achieved.

When using a biphenyl-based epoxy resin and a cyclopentane resin together, the cyclopentane resin content is preferably 1 to 50 parts by weight, more preferably 5 to 45 parts by weight, and even more preferably 10 to 40 parts by weight, per 100 parts by weight of the combined biphenyl-based epoxy resin and cyclopentane resin. This range improves curability and enhances adhesion between the protective layer and the polarizer.

B-3-2-2. Photocationic Polymerization Initiators Photocationic polymerization initiators are photosensitive agents that function as photoacid generators. Typical examples include ionic onium salts composed of a cationic portion and an anionic portion. In this onium salt, the cationic portion absorbs light, while the anionic portion becomes a source of acid. The acid generated by this photocationic polymerization initiator causes ring-opening polymerization of the epoxy group. Any suitable compound that can cure 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 light can be used as the photocationic polymerization initiator. The photocatalytic polymerization initiator may be used alone or in combination of two or more.

Examples of photocatalytic polymerization initiators include triphenylsulphide hexafluoroantimonylate, triphenylsulphide hexafluorophosphate, p-(phenylthio)phenyldiphenylsulphide hexafluoroantimonylate, p-(phenylthio)phenyldiphenylsulphide hexafluoroantimonylate, 4-chlorophenyldiphenylsulphide hexafluorophosphate, 4-chlorophenyldiphenylsulphide hexafluoroantimonylate, bis[4-(diphenyldihydrosulfanyl)phenyl]sulfide bis[hexafluorophosphate], bis[4-(diphenyldihydrosulfanyl)phenyl]sulfide bis[hexafluoroantimonylate], (2,4-cyclopentadien-1-yl)[(1-methylethyl)benzene]-Fe-hexafluorophosphate, and diphenyliodonium hexafluoroantimonylate. Preferred are triphenylsulphide hexafluoroantimony salt-based photocatalytic polymerization initiators and diphenyliodonium hexafluoroantimony salt-based photocatalytic polymerization initiators.

Commercially available photocatalytic polymerization initiators may also be used. Examples include triphenylsulfonium hexafluoroantimonate-based SP-170 (ADEKA), CPI-101A (SANAPRO), WPAG-1056 (Wako Junyaku Industries), and diphenylisocyanate hexafluoroantimonate-based WPI-116 (Wako Junyaku Industries).

The amount of the photocatalytic polymerization initiator is preferably 0.1 to 3 parts by weight, more preferably 0.25 to 2 parts by weight, per 100 parts by weight of the epoxy resin having at least one member selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton. If the amount of the photocatalytic polymerization initiator is less than 0.1 parts by weight, sufficient curing may not be achieved even with irradiation with light (UV light).

B-3-3. Cured Film of an Epoxy Resin Organic Solvent Solution In one embodiment, the protective layer is formed from a cured film of an epoxy resin organic solvent solution.

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

Regarding epoxy resins, any suitable epoxy resin can be used as long as it has the above-mentioned Tg. Epoxy resins generally refer to resins having an epoxy group in their molecular structure. Epoxy resins having an aromatic ring in their molecular structure are preferably used. By using epoxy resins having an aromatic ring, an epoxy resin having a higher Tg can be obtained. Examples of aromatic rings in epoxy resins having an aromatic ring in their molecular structure include benzene rings, naphthalene rings, and fluorene rings. Epoxy resins may be used alone or in combination of two or more. When using two or more epoxy resins, an epoxy resin containing an aromatic epoxy group and an epoxy resin not containing an aromatic epoxy group may be used in combination.

Epoxy resins with aromatic rings in their molecular structure include: bisphenol A diglycidyl ether epoxy resin, bisphenol F diglycidyl ether epoxy resin, bisphenol S diglycidyl ether epoxy resin, resorcinol diglycidyl ether epoxy resin, Hydroquinone diglycidyl ether type epoxy resin, terephthalate diglycidyl ester type epoxy resin, bisphenoxyethanol fluorene diglycidyl ether type epoxy resin, bisphenol fluorene diglycidyl ether type epoxy resin, biscresol fluorene diglycidyl ether type epoxy resin, etc. have two Epoxy resins containing epoxy groups; epoxy resins having three epoxy groups, such as phenolic epoxy resins, N,N,O-triglycyrrhizic-p- or m-aminophenol epoxy resins, N,N,O-triglycyrrhizic-4-amino-m- or -5-amino-o-cresol epoxy resins, and 1,1,1-(triglycyrrhizic-propyloxyphenyl)methane epoxy resins; epoxy resins having four epoxy groups, such as glycyrrhizic-amine epoxy resins (e.g., diaminodiphenylmethane type, diaminodiphenylsulfonium type, and m-xylenediamine type). Furthermore, hexahydrophthalic anhydride type epoxy resin, tetrahydrophthalic anhydride type epoxy resin, dimer acid type epoxy resin, p-oxybenzoic acid type epoxy resin, or other glycidyl ester type epoxy resin can also 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, more preferably 10,000 to 500,000, even more 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 gel permeation chromatography (GPC system, manufactured by Tosoh) in terms of polystyrene. Tetrahydrofuran can be used as the solvent.

The epoxy equivalent weight of the epoxy resin is preferably 1000 g/equivalent or greater, more preferably 3000 g/equivalent or greater, and more preferably 5000 g/equivalent or greater. Furthermore, the epoxy equivalent weight of the epoxy resin is preferably 30,000 g/equivalent or less, more preferably 25,000 g/equivalent or less, and more preferably 20,000 g/equivalent or less. An epoxy equivalent weight within this range provides a more stable protective layer. As used herein, "epoxy equivalent weight" refers to the mass of the epoxy resin containing one equivalent of epoxy groups and can be measured in accordance with JIS K7236.

In embodiments of the present invention, epoxy resins may be used in combination with other resins. Specifically, a mixture of epoxy resins and other resins may be used to form the protective layer. Examples of other resins include thermoplastic resins such as styrene-based resins, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyetheretherketone, polyester, polysulfone, polyphenylene ether, polyacetal, polyimide, and polyetherimide. The type and amount of the resin used in combination can be appropriately determined based on the intended purpose and the desired properties of the resulting film. For example, a styrene-based resin can be used in combination as a phase difference controller.

When using epoxy resin in combination with other resins, the epoxy resin content in the mixture is preferably 50% to 100% by weight, more preferably 60% to 100% by weight, more preferably 70% to 100% by weight, and even more preferably 80% to 100% by weight. If the content is less than 50% by weight, the heat resistance of the protective layer and sufficient adhesion to the polarizer may not be achieved.

B-3-4. Composition and Properties of the Protective Layer In one embodiment, as described above, the protective layer is composed of at least one selected from the group consisting of a cured product obtained from a coating film of a thermoplastic acrylic resin in an organic solvent solution, a photo-cured product of an epoxy resin, and a cured product obtained from a coating film of an organic solvent solution of an epoxy resin. Such a protective layer can achieve a significantly reduced thickness compared to extruded films. As described above, the protective layer thickness is 10 μm or less. Furthermore, while the theory remains unclear, this protective layer exhibits less shrinkage during film formation and contains no residual monomers compared to cured products made from other thermosetting resins or active energy ray-curing resins (e.g., UV-curing resins). This offers the following advantages: It suppresses degradation of the film itself and any adverse effects on the polarizing plate (polarizer) caused by residual monomers. Furthermore, compared to cured products made from aqueous coatings such as aqueous solutions or dispersions, it exhibits lower moisture absorption and permeability, resulting in superior durability under humidification. As a result, optical properties are maintained even in heated and humidified environments, enabling the realization of a highly durable polarizing plate.

The Tg of the protective layer is the same as that described for acrylic resin and epoxy resin, respectively.

The protective layer is preferably substantially optically isotropic. In this specification, "substantially optically isotropic" means that the in-plane phase difference Re(550) is 0nm~10nm and the phase difference Rth(550) in the thickness direction is -20nm~+10nm. The in-plane phase difference Re(550) is preferably 0nm~5nm, more preferably 0nm~3nm, and even more preferably 0nm~2nm. The phase difference Rth(550) in the thickness direction is preferably -5nm~+5nm, more preferably -3nm~+3nm, and even more preferably -2nm~+2nm. If the Re(550) and Rth(550) of the protective layer are within such a range, when the polarizing plate including the protective layer is applied to an image display device, adverse effects on the display characteristics can be prevented. Furthermore, Re(550) is the in-plane phase difference of the film measured at 23°C with light of a wavelength of 550 nm. Re(550) is calculated by the formula: Re(550) = (nx-ny) × d. Rth(550) is the phase difference in the thickness direction of the film measured at 23°C with light of a wavelength of 550 nm. Rth(550) is calculated by the formula: Rth(550) = (nx-nz) × d. Among them, nx is the refractive index in the direction where the in-plane refractive index is the largest (i.e., the slow axis direction), ny is the refractive index in the direction orthogonal to the slow axis (i.e., the fast axis direction), nz is the refractive index in the thickness direction, and d is the thickness of the film (nm).

The light transmittance of a 3 μm thick protective layer at 380 nm is preferably as high as possible. Specifically, the light transmittance is preferably 85% or higher, more preferably 88% or higher, and even more preferably 90% or higher. Light transmittance within this range ensures the desired transparency. Light transmittance can be measured, for example, according to ASTM D-1003.

The lower the haze of the protective layer, the better. Specifically, the haze is preferably 5% or less, more preferably 3% or less, even more preferably 1.5% or less, and even more preferably 1% or less. A haze of 5% or less imparts a clean feel to the film. Furthermore, even when used as a polarizing plate on the viewing side of an image display device, the displayed content remains clearly visible.

The YI of a 3μm thick protective layer is preferably 1.27 or less, more preferably 1.25 or less, more preferably 1.23 or less, and even more preferably 1.20 or less. If the YI exceeds 1.3, optical transparency may be insufficient. Furthermore, the YI can be calculated from the tristimulus values (X, Y, Z) of a color measured using a high-speed integrating sphere spectrophotometer (trade name DOT-3C: manufactured by Murakami Color Technology Laboratory) using the following formula: YI = [(1.28X - 1.06Z) / Y] × 100

The b-value (a measure of hue according to the Hunter color system) of a 3μm-thick protective layer should preferably be less than 1.5, more preferably 1.0 or less. A b-value of 1.5 or greater may result in undesirable color. The b-value can be obtained, for example, by cutting a sample of the film constituting the protective layer into 3cm squares, measuring the hue using a high-speed integrating sphere spectrophotometer (trade name DOT-3C, manufactured by Murakami Color Technology Laboratory), and evaluating the hue according to the Hunter color system.

The protective layer (e.g., cured product of the coating film or photo-cured product) may also contain any appropriate additives according to the purpose. Specific examples of additives include: UV absorbers; leveling agents; antioxidants such as hindered phenols, phosphorus, and sulfur; stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fiber and carbon fiber; near-infrared absorbers; tris(dibromopropyl)phosphate, triallylphosphine, and thiazolinone. Flame retardants such as acid salts and antimony oxide; antistatic agents such as anionic, cationic, and nonionic surfactants; colorants such as inorganic pigments, organic pigments, and dyes; organic and inorganic fillers; resin modifiers; organic and inorganic fillers; plasticizers; lubricants; antistatic agents; and flame retardants. Additives can be added during the polymerization of acrylic resins or to the solution during film formation. The type, amount, combination, and dosage of additives can be appropriately adjusted based on the intended use.

An easy-to-adhesive layer can also be formed on the polarizer side of the protective layer. The easy-to-adhesive layer contains, for example, a water-based polyurethane and an oxazoline-based crosslinking agent. By forming such an easy-to-adhesive layer, the adhesion between the protective layer and the polarizer can be improved. In addition, a hard coating layer can also be formed on the protective layer. In addition, when forming the hard coating layer, the hard coating layer can be formed in such a way that the total thickness of the protective layer (for example, a cured product of a coating film) and the thickness of the hard coating layer is less than 10 μm. The hard coating layer can be formed when the protective layer is used as a protective layer on the viewing side of a polarizing plate on the viewing side. When both the easy-to-adhesive layer and the hard coating layer are formed, they can usually be formed on different sides of the protective layer.

C. First Retardation Layer As described above, the first retardation layer 20 is an alignment-cured layer of liquid crystal compounds. By using liquid crystal compounds, the difference between nx and ny in the resulting retardation layer can be significantly larger than with non-liquid crystal materials. This allows for a significantly smaller thickness of the retardation layer required to achieve the desired in-plane retardation. Consequently, the polarizing plate with the retardation layer can be further reduced in thickness and weight. As used in this specification, the term "aligned-cured layer" refers to a layer in which the liquid crystal compounds are aligned in a specific direction within the layer, fixing this alignment. Furthermore, as described below, the term "aligned-cured layer" encompasses alignment-cured layers obtained by curing liquid crystal monomers. In this embodiment, the rod-shaped liquid crystal compounds are typically aligned in the slow-axis direction of the first retardation layer (parallel alignment).

Examples of liquid crystal compounds include those with a nematic phase (nematic liquid crystals). Liquid crystal compounds such as liquid crystal polymers or liquid crystal monomers can be used. Liquid crystal compounds can exhibit either lyotropic or thermotropic liquid crystal properties. Liquid crystal polymers and liquid crystal monomers can 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 cross-linking monomer. The reason is that by polymerizing or cross-linking (i.e., curing) the liquid crystal monomer, the alignment state of the liquid crystal monomer can be fixed. After the liquid crystal monomer is aligned, for example, if the liquid crystal monomers are polymerized or cross-linked with each other, the above-mentioned alignment state can be fixed. Here, a polymer is formed by polymerization, and a three-dimensional mesh structure is formed by cross-linking, but these are non-liquid crystal. Therefore, the first phase difference layer formed will not undergo a transition to a liquid crystal phase, a glass phase, or a crystalline phase due to temperature changes unique to liquid crystal compounds. As a result, the first phase difference layer becomes a phase difference layer with extremely excellent stability that is not affected by temperature changes.

The temperature range in which a liquid crystal monomer exhibits liquid crystallinity varies depending on its 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 suitable liquid crystal monomer can be used as the liquid crystal monomer. For example, polymerizable mesogen compounds described in Japanese Patent Application Publication No. 2002-533742 (WO00/37585), EP358208 (US5211877), EP66137 (US4388453), WO93/22397, EP0261712, DE19504224, DE4408171, and GB2280445 can be used. Specific examples of such polymerizable mesogen compounds include BASF's LC242, Merck's E7, and Wacker-Chem's LC-Sillicon-CC3767. The liquid crystal monomer is preferably a nematic liquid crystal monomer.

The aligned solidified layer of the liquid crystal compound can be formed by applying an alignment treatment to the surface of a specific substrate, applying a coating liquid containing the liquid crystal compound to the surface, aligning the liquid crystal compound in a direction corresponding to the alignment treatment, and fixing the alignment state. In one embodiment, the substrate is any suitable resin film, and the aligned solidified layer formed on the substrate 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 can be omitted, and the lamination can be carried out continuously using a roll-to-roll process starting with the formation of the aligned solidified layer (first phase difference layer), thereby further improving productivity.

Any suitable alignment treatment can be used for the alignment treatment described above. Specifically, mechanical alignment treatment, physical alignment treatment, and chemical alignment treatment can be used. Specific examples of mechanical alignment treatment include rubbing treatment and stretching treatment. Specific examples of physical alignment treatment include magnetic field alignment treatment and electric field alignment treatment. Specific examples of chemical alignment treatment include tilted evaporation and photo-alignment treatment. The treatment conditions for each alignment treatment can be any suitable conditions depending on the intended purpose.

The alignment of the liquid crystal compound is achieved by treating the liquid crystal compound at a temperature that exhibits a liquid crystal phase, depending on the type of liquid crystal compound. This temperature treatment causes the liquid crystal compound to enter a liquid crystal state, where it aligns in the direction of the alignment treatment on the substrate surface.

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

Specific examples of liquid crystal compounds and details of the method for forming the alignment cured layer are described in Japanese Patent Application Laid-Open No. 2006-163343, which is incorporated herein by reference.

Other examples of aligned cured layers include those in which the discotic liquid crystal compound is aligned in any of homeotropic, hybrid, and tilted alignments. The discotic liquid crystal compound is typically aligned such that the disc plane of the discotic liquid crystal compound is substantially perpendicular to the film plane of the first retardation layer. The term "substantially perpendicular" means that the average angle between the film plane and the disc plane of the discotic liquid crystal compound is preferably 70° to 90°, preferably 80° to 90°, and even more preferably 85° to 90°. Discotic liquid crystal compounds generally refer to compounds with a disc-like molecular structure, characterized by a cyclic core of benzene, 1,3,5-triazine, or calixarene at the center of the molecule, and radially substituted side chains of linear alkyl, alkoxy, or substituted benzyloxy groups. Representative examples of discotic liquid crystals include benzene derivatives, tris-benzene ring derivatives, indene acene derivatives, and phthalocyanine derivatives as reported in the research report of C. Destrade et al., Mol. Cryst. Liq. Cryst., Vol. 71, p. 111 (1981); cyclohexane derivatives as reported in the research report of B. Kohne et al., Angew. Chem., Vol. 96, p. 70 (1984); and nitrogen crown-based or phenylacetylene-based macrocycles as reported in the research report of J. M. Lehn et al., J. Chem. Soc. Chem. Commun., p. 1794 (1985); and in the research report of J. Zhang et al., J. Am. Chem. Soc., Vol. 116, p. 2655 (1994). Further specific examples of discotic liquid crystal compounds include those described in Japanese Patent Application Publication No. 2006-133652, Japanese Patent Application Publication No. 2007-108732, and Japanese Patent Application Publication No. 2010-244038. The contents of these documents and publications are incorporated herein by reference.

In one embodiment, the first retardation layer 20, as shown in Figures 1 and 2, is a single layer of an aligned and cured liquid crystal compound. When the first retardation layer 20 is composed of a single layer of an aligned and cured 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, a significantly thinner thickness than a resin film can be achieved, while achieving an in-plane retardation comparable to that of a resin film.

The refractive index characteristics of the first phase difference layer usually show the relationship of nx>ny=nz. The first phase difference layer is usually provided to impart anti-reflection properties to the polarizing plate. When the first phase difference layer is a single layer of the alignment cured layer, it can function as a λ/4 plate. At this time, the in-plane phase difference Re(550) of the first phase difference layer is preferably 100nm~190nm, preferably 110nm~170nm, and more preferably 130nm~160nm. Furthermore, here "ny=nz" not only includes the case where ny and nz are completely equal, but also includes the case where they are substantially equal. Therefore, within the scope that does not impair the effect of the present invention, there may be a case where ny>nz or ny<nz.

The Nz coefficient of the first phase difference layer is preferably 0.9-1.5, more preferably 0.9-1.3. By satisfying this relationship, the polarizing plate with phase difference layer can achieve excellent reflection color when used in image display devices.

The first retardation layer can exhibit an inverse dispersion wavelength characteristic, in which the retardation value increases with the wavelength of the measurement light, a positive dispersion wavelength characteristic, in which the retardation value decreases with the wavelength of the measurement light, or a flat wavelength dependence, in which the retardation value remains almost constant regardless of the wavelength of the measurement light. In one embodiment, the first retardation layer exhibits an inverse dispersion wavelength characteristic. In this case, the Re(450)/Re(550) ratio of the retardation layer is preferably 0.8 or greater and less than 1, more preferably 0.8 or greater and 0.95 or less. With such a configuration, very excellent anti-reflection properties can be achieved.

The angle θ formed 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 even more preferably approximately 45°. If the angle θ is within this range, by using the first retardation layer as a λ/4 plate as described above, a polarizing plate with a retardation layer having excellent circular polarization properties (and consequently, excellent anti-reflection properties) can be obtained.

In another embodiment, as shown in FIG3 , the first retardation layer 20 may have a laminated structure comprising a first aligned solidified layer 21 and a second aligned solidified layer 22. In this case, either the first aligned solidified layer 21 or the second aligned solidified layer 22 may function as a λ/4 plate, while the other may function as a λ/2 plate. Therefore, the thicknesses of the first aligned solidified layer 21 and the second aligned solidified layer 22 can be adjusted to achieve the desired in-plane retardation of either the λ/4 plate or the λ/2 plate. For example, when the first aligned solidified layer 21 functions as a λ/2 plate and the second aligned solidified layer 22 functions as a λ/4 plate, the thickness of the first aligned solidified layer 21 is, for example, 2.0 μm to 3.0 μm, and the thickness of the second aligned solidified layer 22 is, for example, 1.0 μm to 2.0 μm. In this case, the in-plane retardation Re(550) of the first aligned solidified layer is preferably 200 nm to 300 nm, more preferably 230 nm to 290 nm, and even more preferably 250 nm to 280 nm. The in-plane retardation Re(550) of the second aligned solidified layer is the same as described above for a single aligned solidified layer. The angle formed by the slow axis of the first alignment solidified layer and the absorption axis of the polarizer is preferably 10°~20°, preferably 12°~18°, and more preferably about 15°. The angle formed by the slow axis of the second alignment solidified layer and the absorption axis of the polarizer is preferably 70°~80°, preferably 72°~78°, and more preferably about 75°. If so configured, characteristics close to the ideal reverse wavelength dispersion characteristics can be obtained, and as a result, very excellent anti-reflection characteristics can be achieved. The liquid crystal compounds constituting the first alignment solidified layer and the second alignment solidified layer, the formation methods of the first alignment solidified layer and the second alignment solidified layer, the optical characteristics, etc. are the same as the above description related to the single-layer alignment solidified layer.

D. Second Phase Difference Layer As described above, the second phase difference layer can be a so-called positive C plate, whose refractive index characteristics exhibit the relationship nz>nx=ny. Using a positive C plate as the second phase difference layer effectively prevents reflection in the tilted direction, extending the anti-reflection function to a wider viewing angle. In this case, the thickness-direction phase difference Rth(550) of the second phase difference layer is preferably -50nm to -300nm, more preferably -70nm to -250nm, more preferably -90nm to -200nm, and even more preferably -100nm to -180nm. Here, "nx=ny" includes not only the case where nx and ny are completely equal, but also the case where nx and ny are substantially equal. That is, the in-plane phase difference Re(550) of the second phase difference layer can be less than 10nm.

The second phase difference layer having the refractive index characteristic of nz＞nx=ny can be formed of any suitable material. The second phase difference layer is preferably composed of a thin film containing a liquid crystal material fixed in a vertical alignment. The liquid crystal material (liquid crystal compound) that can be vertically aligned can be a liquid crystal monomer or a liquid crystal polymer. Specific examples of the liquid crystal compound and the method for forming the phase difference layer can be exemplified by the liquid crystal compound and the method for forming the phase difference layer described in [0020] to [0028] of Japanese Patent Publication No. 2002-333642. At this time, the thickness of the second phase difference layer is preferably 0.5μm~10μm, preferably 0.5μm~8μm, and more preferably 0.5μm~5μm.

E. Conductive Layer or Isotropic Substrate with Conductive Layer The conductive layer can be formed by depositing a metal oxide film on any suitable substrate using any suitable film-forming method (e.g., vacuum evaporation, sputtering, CVD, ion plating, spray coating, etc.). 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. Indium-tin composite oxide (ITO) is preferred.

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

The conductive layer can be transferred from the substrate to the first retardation layer (or the second retardation layer, if present) to form a single conductive layer as a constituent layer of the polarizing plate with retardation layer, or it can be laminated onto the first retardation layer (or the second retardation layer, if present) as a laminate with the substrate (the substrate with the conductive layer). Preferably, the substrate is optically isotropic, so the conductive layer can be used in the polarizing plate with retardation layer in the form of an isotropic substrate with a conductive layer.

Regarding the optically isotropic substrate (isotropic substrate), any suitable isotropic substrate can be used. Regarding the materials constituting the isotropic substrate, for example, there can be listed: materials with resins without a conjugated system such as norbornene resins or olefin resins as the main skeleton, materials with cyclic structures such as lactone rings or pentamido rings in the main chain of acrylic resins, etc. If such materials are used, the phase difference caused by the alignment of the molecular chain can be suppressed to a small extent when forming the isotropic substrate. The thickness of the isotropic substrate is preferably less than 50μm, and more preferably less than 35μm. The thickness of the isotropic substrate is, for example, more than 20μm.

The conductive layer and/or the conductive layer of the isotropic substrate with the conductive layer can be patterned as needed. Patterning can form conductive and insulating portions. This results in electrodes, which can function as touch sensor electrodes that detect contact with the touch panel. Any suitable patterning method can be employed. Specific examples include wet etching and screen printing.

F. Image Display Device The polarizing plates with phase difference layers described in Items A through E above can be used in image display devices. Therefore, the present invention includes image display devices using such polarizing plates with phase difference layers. Representative examples of image display devices include liquid crystal display devices and electroluminescent (EL) display devices (e.g., organic EL display devices, inorganic EL display devices). An embodiment of the image display device of the present invention includes the polarizing plates with phase difference layers described in Items A through E above on its viewing side. The polarizing plates with phase difference layers are laminated such that the phase difference layers are on the side of the image display unit (e.g., liquid crystal unit, organic EL unit, inorganic EL unit) (i.e., such that the polarizer is on the viewing side). In one embodiment, the image display device may have a curved shape (essentially a curved display screen) and/or be bendable or flexible. In such an image display device, the polarizing plate with a phase difference layer of the present invention is particularly effective. [Example]

The present invention is described in detail below using examples, but the present invention is not limited to these examples. The methods for measuring various properties are described below. Furthermore, unless otherwise specified, "parts" or "%" in the examples and comparative examples are by weight.

[Example 1] 1. Preparation of Polarizers: A long, amorphous, isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100 μm) with a water absorption of 0.75% and a Tg of approximately 75°C was used as a thermoplastic resin substrate. One side of the resin substrate was subjected to a corona treatment (treatment conditions: 55 W min/m ² ). A PVA aqueous solution (coating solution) was prepared by adding 13 parts by weight of potassium iodide to 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (DP4200, saponification degree 99.2 mol %) and acetyl-modified PVA (manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., trade name "Gosefaimer Z410") in a 9:1 ratio. The PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60°C to form a 13.5μm-thick PVA resin layer to produce a laminate. The laminate was then uniaxially stretched to 2.4 times its free end in the longitudinal direction (lengthwise) between rolls at different circumferential speeds in a 130°C oven (air-assisted stretching). The laminate was then immersed in an insolubilization bath (a boric acid aqueous solution containing 4 parts by weight of boric acid per 100 parts by weight of water) at 40°C for 30 seconds (insolubilization treatment). Next, the film was immersed in a dye bath (an iodine aqueous solution prepared by mixing iodine and potassium iodide at a weight ratio of 1:7 per 100 parts by weight of water) at a temperature of 30°C for 60 seconds, adjusting the concentration so that the resulting polarizer's monomer transmittance (Ts) reached 40.5%. This was followed by immersion in a crosslinking bath (an aqueous boric acid solution prepared by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid per 100 parts by weight of water) at a temperature of 40°C for 30 seconds (crosslinking). The laminate was then immersed in a boric acid aqueous solution (boric acid concentration 4.0 wt%, potassium iodide 5.0 wt%) at a temperature of 62°C and uniaxially stretched in the longitudinal direction (lengthwise) between rollers of varying circumferential speeds at a total stretch ratio of 3.0 (in-water stretching treatment: the stretch ratio in the in-water stretching treatment was 1.25). The laminate was then immersed in a cleaning bath (an aqueous solution of 4 parts potassium iodide per 100 parts water) at a temperature of 20°C (cleaning treatment). The laminate was then dried in an oven maintained at 90°C while contacting a SUS heated roller maintained at a surface temperature of 75°C for approximately 2 seconds (drying and shrinking treatment). The shrinkage rate of the laminate in the width direction due to the drying and shrinking treatment was 2%. In this way, a polarizer with a thickness of 7.4μm was formed on the resin substrate.

2. Polarizing Plate Preparation: A water-based polyurethane resin (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: SUPER FLEX 210-R) was dissolved in a mixed solvent of pure water and isopropyl alcohol. The resulting solution was applied to the surface of the polarizer formed on the resin substrate. The solution was then dried at 60°C to remove the solvent, forming a 0.15μm thick adhesive layer. An acrylic resin containing methyl methacrylate units (manufactured by Kusumoto Chemicals Co., Ltd., trade name: B728) was dissolved in 80 parts of methyl ethyl ketone to obtain a 20% acrylic resin solution. The acrylic resin solution was applied to the adhesive layer using a wire bar. The coated film was dried at 60°C for 5 minutes to form an acrylic resin layer, which served as a cured product of the coated film. The acrylic resin layer had a thickness of 2 μm and a Tg of 116°C. Next, 70 parts by weight of dihydroxymethyl-tricyclodecane diacrylate (Kyoei Chemicals, trade name: LIGHTACRYLATE DCP-A), 20 parts by weight of isobornyl acrylate (Kyoei Chemicals, trade name: LIGHTACRYLATE IB-XA), 10 parts by weight of 1,9-nonanediol diacrylate (Kyoei Chemicals, trade name: LIGHTACRYLATE 1.9NA-A), and 3 parts by weight of a photopolymerization initiator (BASF, trade name: IRGACURE 907) were mixed in a solvent to prepare a coating solution. This coating solution was applied to the protective layer to a cured thickness of 3 μm. Next, the solvent is dried and irradiated with UV light using a high-pressure mercury lamp at a cumulative light intensity of 300 mJ/ ^cm² in a nitrogen atmosphere to form a hard coat layer. The hard coat layer has a thickness of 3 μm. To ensure stable lamination with the subsequent phase difference layer, an adhesive layer of polyethylene terephthalate (PET) film with an adhesive layer is bonded to the protective layer for reinforcement. The resin substrate is then peeled off, resulting in a polarizing plate having a structure of PET film with an adhesive layer/protective layer (hard coat layer/acrylic resin layer (cured coating film))/easy-adhesion layer/polarizer.

3. Preparation of the First and Second Alignment Cured Layers Constituting the Phase Difference Layer: 10 g of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (BASF product: "Paliocolor LC242," represented by the following formula) and 3 g of a photopolymerization initiator for the polymerizable liquid crystal compound (BASF product: "IRGACURE 907") were dissolved in 40 g of toluene to prepare a liquid crystal composition (coating solution). [Chemical Formula 6] The surface of the polyethylene terephthalate (PET) film (thickness 38 μm) was rubbed with a rubbing cloth to perform an alignment treatment. The direction of the alignment treatment is 15° relative to the absorption axis of the polarizer when attached to the polarizing plate, as viewed from the viewing side. The above-mentioned liquid crystal coating liquid was applied to the alignment-treated surface using a rod coater, and heated and dried at 90°C for 2 minutes to align the liquid crystal compound. The liquid crystal layer thus formed was irradiated with 100 mJ/ ^cm2 of light using a metal halogen lamp to harden the liquid crystal layer, thereby forming a liquid crystal alignment cured layer A on the PET film. The thickness of the liquid crystal alignment cured layer A is 2.5 μm, and the in-plane phase difference Re(550) is 270 nm. Furthermore, the liquid crystal alignment cured layer A has a refractive index distribution of nx＞ny=nz. A liquid crystal alignment cured layer B was formed on the PET film in the same manner as above, except that the coating thickness was changed and the alignment treatment direction was oriented at 75° relative to the polarizer's absorption axis when viewed from the viewing side. The liquid crystal alignment cured layer B had a thickness of 1.5 μm and an in-plane retardation Re(550) of 140 nm. Furthermore, the liquid crystal alignment cured layer B had a refractive index distribution of nx>ny=nz.

4. Preparation of a Polarizing Plate with a Retardation Layer The liquid crystal alignment cured layer A and liquid crystal alignment cured layer B obtained in step 3 were sequentially transferred onto the polarizer surface of the polarizing plate obtained in step 2. The transfer (lamination) was performed so that the angle between the absorption axis of the polarizer and the slow axis of alignment cured layer A was 15°, and the angle between the absorption axis of the polarizer and the slow axis of alignment cured layer B was 75°. Each transfer (lamination) was performed using the UV-curable adhesive (1.0 μm thick) used in step 2. Next, the PET film with the adhesive layer was peeled off. This resulted in a polarizing plate with a retardation layer structure consisting of a protective layer (hard coat layer/acrylic resin layer (cured coating film))/adhesive layer/polarizer/adhesive layer/retardation layer (first alignment cured layer/adhesive layer/second alignment cured layer). The total thickness of the resulting polarizing plate with a retardation layer was 19 μm.

[Examples 2-4] A polarizer with a thickness of 7.4 μm was formed on a resin substrate using the same method as in Example 1, except that dye baths with different iodine concentrations (weight ratio of iodine to potassium iodide = 1:7) were used. A polarizing plate with a retardation layer was obtained using the same method as in Example 1, except that the obtained laminate with a polarizer/resin substrate structure was used. The structure consisted of a protective layer (hard coat layer/acrylic resin layer (cured coating film))/easy adhesive layer/polarizer/adhesive layer/retardation layer (first alignment cured layer/adhesive layer/second alignment cured layer). The total thickness of the resulting polarizing plate with a retardation layer was 19 μm.

[Examples 5-8] A 6.7μm-thick polarizer was formed on a resin substrate using the same method as in Example 1, except that the underwater stretching treatment was set to a stretching ratio of 1.46x, the total stretching ratio was set to 3.5x, and dye baths with varying iodine concentrations (the weight ratio of iodine to potassium iodide = 1:7) were used. A polarizing plate with a retardation layer having a structure of protective layer (hard coat layer/acrylic resin layer (cured coating film))/easy adhesive layer/polarizer/adhesive layer/retardation layer (first alignment cured layer/adhesive layer/second alignment cured layer) was obtained using the same method as in Example 1, except that the resulting laminate having a polarizer/resin substrate structure was used. The total thickness of the obtained polarizing plate with a phase difference layer is 18 μm.

[Example 9] A polarizing plate with a retardation layer was obtained using the same method as in Example 7, except that the acrylic resin containing methyl methacrylate units (manufactured by Kusumoto Chemicals Co., Ltd., trade name: B728) was replaced with an acrylic resin containing polymethyl methacrylate containing lactone ring units (lactone ring unit content: 30 mol%). The total thickness of the obtained polarizing plate with a retardation layer was 18 μm.

[Example 10] A polarizing plate with a retardation layer was obtained using the same method as in Example 9, except that the acrylic resin containing methyl methacrylate units (manufactured by Kusumoto Chemicals, trade name: B728) was replaced with an acrylic resin containing polymethyl methacrylate containing glutarimido ring units (glutarimido ring unit content: 4 mol%). The total thickness of the obtained polarizing plate with a retardation layer was 18 μm.

[Example 11] In Example 9, instead of the acrylic resin solution, a 20% epoxy resin solution (20 parts epoxy resin (manufactured by Mitsubishi Chemical Co., Ltd., trade name: jER (registered trademark) YX6954BH30, weight-average molecular weight: 36,000, epoxy equivalent: 13,000) dissolved in 80 parts methyl ethyl ketone was used to form a protective layer, which formed a cured product of the coating film. Specifically, the epoxy resin solution was applied to the adhesive layer using a wire bar, and the coated film was dried at 60°C for 3 minutes to form the protective layer. The protective layer had a thickness of 3 μm and a Tg of 130°C. In this way, a polarizing plate with a phase difference layer was obtained in the same manner as in Example 9, except that a protective layer was formed and no easy-adhesion layer and hard coating layer were formed on the polarizer. The total thickness of the obtained polarizing plate with a phase difference layer was 16 μm.

[Example 12] A polarizing plate with a phase difference layer was obtained in the same manner as in Example 7, except that a protective layer was formed as described below, and no easy-adhesion layer and hard coating layer were formed on the polarizer. The total thickness of the polarizing plate with a phase difference layer obtained was 16 μm. 15 parts of an epoxy resin having a biphenyl skeleton (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) YX4000) were dissolved in 83.8 parts of methyl ethyl ketone to obtain an epoxy resin solution. 1.2 parts of a photocatalytic polymerization initiator (manufactured by SANAPRO, trade name: CPI (registered trademark)-100P) were added to the obtained epoxy resin solution to obtain a protective layer forming composition. The resulting protective layer-forming composition was applied to the adhesive layer using a wire bar. The coated film was dried at 60°C for 3 minutes. Next, the film was irradiated with ultraviolet light using a high-pressure mercury lamp at a cumulative dose of 600 mJ/ ^cm² to form a protective layer. The thickness of the protective layer was 3 μm.

[Example 13] A polarizing plate with a retardation layer was obtained using the same method as in Example 12, 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. The total thickness of the obtained polarizing plate with a retardation layer was 16 μm.

[Example 14] A polarizing plate with a retardation layer was obtained using the same method as in Example 12, except that a hydrogenated bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) YX8000) was used instead of the biphenyl-based epoxy resin. The total thickness of the obtained polarizing plate with a retardation layer was 16 μm.

[Example 15] 15 parts of a hydrogenated bisphenol-type epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) YX8000) and 10 parts of an oxetane resin (manufactured by Toagosei Co., Ltd., trade name: ARONE OXETANE (registered trademark) OXT-221) were dissolved in 73 parts of methyl ethyl ketone to obtain an epoxy resin solution. To the obtained epoxy resin solution, 2 parts of a photocatalytic polymerization initiator (manufactured by SANAPRO, trade name: CPI (registered trademark)-100P) were added to obtain a protective layer-forming composition. A polarizing plate with a retardation layer was obtained by the same method as in Example 12, except that the obtained protective layer-forming composition was used. The total thickness of the obtained polarizing plate with a phase difference layer is 16 μm.

[Example 16] A polarizing plate with a retardation layer was obtained using the same method as in Example 15, except that the thickness of the protective layer was set to 8 μm.

[Example 17] A polarizing plate with a retardation layer was obtained using the same method as in Example 15, except that the thickness of the protective layer was set to 10 μm.

[Example 18] A protective layer (cured product) was formed using the same method as in Example 12, except that a UV-curable epoxy resin (manufactured by DAICEL, product name "CELLOXIDE 2021P") was used. Specifically, a composition comprising 95% by weight of the epoxy resin and 5% by weight of a photopolymerization initiator (CPI-100P, manufactured by SANAPRO) was applied to the adhesive layer. The cured layer (protective layer) was then irradiated with UV light using a high-pressure mercury lamp at a cumulative dose of 500 mJ/ ^cm² in an air atmosphere. A polarizing plate with a retardation layer was produced using the same method as in Example 7, except that this protective layer was used. The thickness of the polarizing plate was 16 μm.

[Examples 19-22] A 6.2μm-thick polarizer was formed on a resin substrate using the same method as in Example 1, except that the underwater stretching ratio was set to 1.67x (resulting in a total stretching ratio of 4.0x) and dye baths with varying iodine concentrations (weight ratio of iodine to potassium iodide = 1:7). A polarizing plate with a retardation layer structured as in Example 1 was obtained, having a protective layer (hard coat layer/acrylic resin layer (cured coating film))/easy adhesive layer/polarizer/adhesive layer/retardation layer (first alignment cured layer/adhesive layer/second alignment cured layer) structure. The total thickness of the obtained polarizing plate with a phase difference layer is 18 μm.

[Examples 23-26] A 6.0 μm thick polarizer was formed on a resin substrate using the same method as in Example 1, except that the underwater stretching ratio was set to 1.88, the total stretching ratio was set to 4.5, and dye baths with varying iodine concentrations (weight ratio of iodine to potassium iodide = 1:7) were used. A polarizing plate with a retardation layer having a structure of protective layer (hard coat layer/acrylic resin layer (cured coating film))/easy adhesive layer/polarizer/adhesive layer/retardation layer (first alignment cured layer/adhesive layer/second alignment cured layer) was obtained using the same method as in Example 1, except that the resulting laminate having a polarizer/resin substrate structure was used. The total thickness of the obtained polarizing plate with a phase difference layer was 17.0 μm.

(Comparative Examples 1-4) A 5.5μm-thick polarizer was formed on a resin substrate using the same method as in Example 1, except that the underwater stretching ratio was set to 2.29x, the total stretching ratio was set to 5.5x, and dye baths with varying iodine concentrations (weight ratio of iodine to potassium iodide = 1:7) were used. A polarizing plate with a retardation layer having a structure of protective layer (hard coat layer/acrylic resin layer (cured coating film))/easy adhesive layer/polarizer/adhesive layer/retardation layer (first alignment cured layer/adhesive layer/second alignment cured layer) was obtained using the same method as in Example 1, except that the resulting laminate having a polarizer/resin substrate structure was used. The total thickness of the obtained polarizing plate with a phase difference layer is 16 μm.

(Comparative Example 5) A polarizer with a thickness of 5.5 μm was obtained using the same method as in Example 1, except that the underwater stretching ratio was set to 2.29x, the total stretching ratio was set to 5.5x, and the stretching bath temperature was set to 70°C. A polarizer with a retardation layer was obtained using the same method as in Example 1, except that a 40 μm thick acrylic film was deposited on the surface of the obtained polarizer via a UV-curable adhesive as a protective layer. The total thickness of the obtained polarizer with a retardation layer was 53 μm.

(Comparative Example 6) A polarizing plate with a retardation layer was obtained using the same method as in Comparative Example 2, except that a 20 μm thick acrylic film was used as the protective layer. The total thickness of the resulting polarizing plate with a retardation layer was 33 μm.

(Comparative Example 7) A polarizing plate with a retardation layer was obtained using the same method as in Comparative Example 2, except that the protective layer was formed in the same manner as in Example 11. The total thickness of the obtained polarizing plate with a retardation layer was 15 μm.

(Comparative Example 8) A polarizing plate with a retardation layer was obtained using the same method as in Comparative Example 2, except that the protective layer was formed in the same manner as in Example 12. The total thickness of the obtained polarizing plate with a retardation layer was 15 μm.

(Comparative Example 9) A polarizing plate with a retardation layer was obtained using the same method as in Comparative Example 2, except that the protective layer was formed in the same manner as in Example 15. The total thickness of the obtained polarizing plate with a retardation layer was 15 μm.

[Evaluation] The polarizing plates with phase difference layers obtained in the embodiments and comparative examples were evaluated as follows. The results are shown in Table 1. (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 wavelength range used to calculate the thickness was 400nm~500nm, and the refractive index was 1.53. In addition, the thickness of the protective layer was measured using an interference film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"), and the calculation wavelength range and refractive index were appropriately selected. The thickness of the easy-to-bond layer was determined by observation using a scanning electron microscope (SEM). Thicknesses exceeding 110 μm were measured using a digital micrometer (manufactured by ANRITSU, product name "KC-351C"). (2) In-plane retardation (Re) of PVA The in-plane retardation (Rpva) of the PVA at a wavelength of 1000 nm was evaluated using a retardation measuring device (manufactured by Oji Scientific Instruments, product name "KOBRA-31X100/IR") for the polarizer/thermoplastic resin substrate laminates obtained in the Examples and Comparative Examples after the resin substrate was removed. (Based on the principle described, the in-plane retardation (Ri) of iodine was subtracted from the total in-plane retardation at a wavelength of 1000 nm.) The absorption edge wavelength was 600 nm. (3) Birefringence (Δn) of PVA The birefringence (Δn) of PVA was calculated by dividing the in-plane phase difference of PVA measured in (2) above by the thickness of the polarizer. (4) Orientation function The polarizers used in the embodiments and comparative examples were measured using a Fourier transform infrared spectrometer (FT-IR) (manufactured by Perkin Elmer, trade name: "Frontier"), with polarized infrared light as the measurement light, to perform attenuated total reflection (ATR) measurement on the surface of the polarizer. Germanium was used for the microcrystals to which the polarizer was attached, and the incident angle of the measurement light was 45°. The orientation function was calculated according to the following method. The incident polarized infrared light (measurement light) is polarized light (s-polarized light) oscillating parallel to the surface of the germanium crystal sample in close contact. The absorption spectra are measured with the polarizer extending perpendicular (⊥) or parallel (//) to the polarization direction of the measurement light. From the obtained absorption spectra, the intensity (2941 cm ^-1 ) is calculated, using the intensity (3330 cm ^-1 ) as a reference. _I⊥ is the ratio (2941 cm-1)/(3330 cm ^{- 1} ) obtained from the absorption spectrum when the polarizer extending perpendicular (⊥) to the polarization direction of the measurement light. Furthermore, I _// is the (2941 cm ^-1 intensity) / (3330 cm ^-1 intensity) obtained from the absorption spectrum obtained when the polarizer's extension direction is arranged parallel to the polarization direction of the measurement light (//). (2941 cm ^{-1 intensity) is the absorbance at 2941 cm -1} at the bottom of the absorption spectrum, using 2770 cm ^-1 and 2990 cm ^-1 as reference lines, and (3330 cm ^-1 intensity) is the absorbance at 3330 cm ^-1 using 2990 cm ^-1 and 3650 ^{cm -1 as} reference lines. Using the obtained I _⊥ and I _// , the alignment function f is calculated according to Equation 1. f = 1 indicates perfect alignment, and f = 0 indicates random alignment. The peak at 2941 cm ^-1 is likely due to absorption caused by the vibration of the main chain ( _-CH2- ) of PVA in the polarizer. Furthermore, the peak at 3330 cm ^-1 is likely due to absorption caused by the vibration of the hydroxyl group of PVA. (Equation 1) f = (3 < ^cos2 θ > -1)/2 = (1-D)/[c(2D+1)] where c = ( ^3cos2 β-1)/2. As mentioned above, when using 2941 cm ^-1 , β = 90° ⇒ f = -2 × (1-D)/(2D+1). θ: Angle of the molecular chain relative to the extension direction β: Angle of the transition dipole moment relative to the molecular chain axis D = (I _⊥ ) / (I _// ) I⊥: Absorption intensity when the polarization direction of the measured light is perpendicular to the extension direction of the polarizer I//: Absorption intensity when the polarization direction of the measured light is parallel to the extension direction of the polarizer (5) Crack Occurrence Rate The polarizing plates with phase difference layers obtained in the Examples and Comparative Examples were cut into 10 mm × 10 mm sizes. The cut polarizing plates with phase difference layers were bonded to a glass plate (1.1 mm thick) via a 20 μm thick acrylic adhesive layer. After placing the sample bonded to the glass plate in an oven at 100 degrees for 120 hours, visually check whether cracks are generated in the absorption axis direction (MD direction) of the polarizer. This evaluation is performed using three polarizers with phase difference layers, and the number of polarizers with phase difference layers that have cracks is evaluated. (6) Bending resistance The polarizers with phase difference layers obtained in the examples and comparative examples are cut into 50 mm × 100 mm sizes. At this time, the polarizer is cut so that the absorption axis direction becomes the long side direction. The cut polarizers with phase difference layers are subjected to a bending test at room temperature using a bending tester (manufactured by Yuasa-system, product name: DLDM111LH). Specifically, a polarizing plate with a retardation layer was folded 50,000 times along the absorption axis at 60 rpm, with the retardation layer facing inward and the protective layer or hard coating formed on the protective layer facing outward. The bending diameter was set to 1 mmφ (R = 0.5 mm). The plates were then visually inspected for cracks. Those with no cracks were considered good, while those with cracks were considered defective. The bending direction was along the transmission axis of the polarizer. (7) Single-body transmittance and polarization degree For the polarizers used in the Examples and Comparative Examples, the single-body transmittance Ts, parallel transmittance Tp, and perpendicular transmittance Tc measured using an ultraviolet-visible spectrometer (manufactured by JASCO Corporation, product name "V-7100") are set as the polarizer's Ts, Tp, and Tc, respectively. These Ts, Tp, and Tc are measured using a 2-degree field of view (illuminant C) in accordance with JIS Z8701, and the Y value is corrected for visual sensitivity. The polarization degree P is calculated from the obtained Tp and Tc using the following formula. Polarization degree P (%) = {(Tp-Tc)/(Tp+Tc)} ^1/2 × 100 (8) Puncture strength The polarizer was peeled off from the polarizer/thermoplastic resin substrate laminate used in the embodiment and the comparative example, and placed on a compression tester equipped with a needle (manufactured by Katotech, product name "NDG5" needle penetration force measurement specification). Puncture was performed at room temperature (23℃±3℃) at a puncture speed of 0.33cm/s. The strength when the polarizer broke was used as the fracture strength (puncture strength). The evaluation value was obtained by measuring the fracture strength of 10 sample pieces and using the average value. In addition, the needle used had a tip diameter of 1mmφ and 0.5R. For the polarizer to be tested, a fixture with a circular opening of approximately 11mm in diameter is clamped from both sides of the polarizer. The polarizer is fixed and a needle is inserted into the center of the opening for testing.

[Table 1]

As shown in Table 1, the polarizing plates with retardation layers of Examples 1-26 suppress cracking even when subjected to heat treatment. Furthermore, they exhibit excellent durability when flexed. Industrial Applicability

The polarizing plate with a phase difference layer of the present invention is suitable for use in image display devices.

10: Polarizing plate 11: Polarizer 12: First protective layer 13: Second protective layer 20: Retardation layer (first retardation layer) 21: First alignment cured layer 22: Second alignment cured layer 50: Another retardation layer (second retardation layer) 60: Conductive layer or isotropic substrate with conductive layer 100: Polarizing plate with retardation layer 101: Polarizing plate with retardation layer 102: Polarizing plate with retardation layer 200: Laminated body G1-G4: Guide rollers R1-R6: Transport rollers

Figure 1 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to one embodiment of the present invention. Figure 2 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to another embodiment of the present invention. Figure 3 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to yet another embodiment of the present invention. Figure 4 is a schematic diagram illustrating an example of a drying and shrinking process using heated rollers in a method for manufacturing a polarizer used in the polarizing plate with a retardation layer according to the present invention.

10:Polarizing plate

11:Polarizer

12: First protective layer

13: Second protective layer

20: Phase difference layer

100: Polarizing plate with phase difference layer

Claims (9)

A polarizing plate with a phase difference layer comprises a polarizing plate and a phase difference layer, wherein the polarizing plate comprises a polarizer and a protective layer, wherein the polarizer is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and the protective layer is disposed on one side of the polarizer; the phase difference layer is an alignment cured layer of a liquid crystal compound; the thickness of the protective layer is less than 10 μm; the protective layer is selected from a thermoplastic (formaldehyde) At least one of the group consisting of a cured product of a coating film of an organic solvent solution of an acrylic resin, a photo-cured product of an epoxy resin, and a cured product of a coating film of an organic solvent solution of an epoxy resin; when the monomer transmittance of the polarizer is set to x% and the birefringence of the polyvinyl alcohol resin is set to y, the following formula (1) is satisfied: y<-0.011x+0.525 (1). A polarizing plate with a phase difference layer comprises a polarizing plate and a phase difference layer, wherein the polarizing plate comprises a polarizer and a protective layer, wherein the polarizer is composed of a polyvinyl alcohol resin film containing a dichroic substance, and the protective layer is disposed on one side of the polarizer; the phase difference layer is an alignment cured layer of a liquid crystal compound; the thickness of the protective layer is less than 10 μm; the protective layer is selected from thermoplastic (methyl) At least one of the group consisting of a cured product of an organic solvent solution of an acrylic resin coating film, a photo-cured product of an epoxy resin, and a cured product of an organic solvent solution of an epoxy resin coating film; when the monomer transmittance of the polarizer is set to x%, and the in-plane phase difference of the polyvinyl alcohol resin film is set to znm, the following formula (2) is satisfied: z<-60x+2875 (2). A polarizing plate with a phase difference layer comprises a polarizing plate and a phase difference layer. The polarizing plate includes a polarizer and a protective layer. The polarizer is composed of a polyvinyl alcohol-based resin film containing a dichroic substance. The protective layer is disposed on one side of the polarizer. The phase difference layer is an alignment cured layer of a liquid crystal compound. The protective layer has a thickness of 10 μm or less. The protective layer is selected from a thermoplastic (aluminum) At least one of the group consisting of a cured product of a coating film of an organic solvent solution of an acrylic resin, a photo-cured product of an epoxy resin, and a cured product of a coating film of an organic solvent solution of an epoxy resin; when the monomer transmittance of the polarizer is set to x%, and the orientation function of the polyvinyl alcohol resin is set to f, the following formula (3) is satisfied: f<-0.018x+1.11 (3). The polarizing plate with a phase difference layer as described in any one of claims 1 to 3 has a total thickness of 30 μm or less. The polarizing plate with a phase difference layer according to any one of claims 1 to 3, wherein the thickness of the polarizer is 10 μm or less. The polarizing plate with a phase difference layer according to any one of claims 1 to 3, wherein the single polarizer has a transmittance of 40.0% or more and a degree of polarization of 99.0% or more. The polarizing plate with a phase difference layer according to any one of claims 1 to 3, wherein the thermoplastic (meth)acrylic resin comprises at least one repeating unit selected from the group consisting of a lactone ring unit, a glutaric anhydride unit, a glutarimide unit, a maleic anhydride unit, and a maleimide unit. The polarizing plate with a phase difference layer according to any one of claims 1 to 3, wherein the protective layer is a photo-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 includes a polarizing plate with a phase difference layer as described in any one of claims 1 to 8.