TWI891861B - Polarizing plate, polarizing plate with phase difference layer, and image display device including the polarizing plate or the polarizing plate with phase difference layer - Google Patents

Abstract

The present invention provides a polarizing plate that is extremely thin but suppresses cracks in irregularly shaped processed parts. The polarizing plate of the present invention has a polarizer and a protective layer arranged on at least one side of the polarizer, and has an irregular shape other than a rectangle. The protective layer is composed of a resin film having a thickness of less than 10µm. The polarizer is composed of a PVA resin film containing a dichroic substance. In one embodiment, the polarizer satisfies the following formula (1) when the single body transmittance is x% and the birefringence of the PVA resin is y. In another embodiment, the polarizer satisfies the following formula (2) when the single body transmittance is x% and the in-plane phase difference of the PVA resin film is znm. In yet another embodiment, the polarizer satisfies the following formula (3) when the monomer transmittance is x% and the orientation function of the PVA resin film is f. In yet another embodiment, the puncture strength of the polarizer is 30 gf/µm or more. y＜-0.011x+0.525　　　　　(1) z＜-60x+2875　　　　　  　(2) f＜-0.018x+1.11　　　　   　(3)

Description

Polarizing plate, polarizing plate with phase difference layer, and image display device including the polarizing plate or the polarizing plate with phase difference layer

The present invention relates to a polarizing plate, a polarizing plate with a phase difference layer, and an image display device including the polarizing plate or the polarizing plate with a phase difference layer.

Background of the Invention In recent years, image display devices, typified by liquid crystal displays and electroluminescent (EL) displays (e.g., organic EL displays and inorganic EL displays), have rapidly gained popularity. Due to the image formation method of image display devices, a polarizing plate is disposed on at least one side of the image display device. In recent years, with the increasing demand for thinner image display devices, the demand for thinner polarizing plates has also increased. However, in recent years, there has been a desire to process polarizing plates into shapes other than rectangular (special-shaped processing: for example, forming notches and/or through-holes). However, there is a problem that cracks are easily generated in the special-shaped processed portions of thin polarizing plates. Prior Art Patent

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

Problems to be Solved by the Invention This invention was developed to address the aforementioned conventional problems. Its primary purpose is to provide an extremely thin polarizing plate that suppresses cracking in irregularly shaped processed areas.

Means for solving the problem A polarizing plate in one embodiment of the present invention has a polarizer and a protective layer disposed on at least one side of the polarizer, and has an irregular shape other than a rectangle. The protective layer is composed of a resin film having a thickness of 10µm or less. The polarizer is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and when the single body transmittance is x% and the birefringence of the polyvinyl alcohol-based resin is y, the following formula (1) is satisfied: y＜-0.011x+0.525　　　　　　　　(1). A polarizing plate in another embodiment of the present invention has a polarizer and a protective layer disposed on at least one side of the polarizer, and has an irregular shape other than a rectangle. The protective layer is composed of a resin film having a thickness of 10µm or less. The polarizer is composed of a polyvinyl alcohol resin film containing a dichroic substance, and when the monomer transmittance is x% and the in-plane phase difference of the polyvinyl alcohol resin film is znm, the following formula (2) is satisfied: z＜-60x+2875　　　　　　　　(2). In another embodiment of the present invention, a polarizing plate has a polarizer and a protective layer arranged on at least one side of the polarizer, and has an irregular shape other than a rectangle. The protective layer is composed of a resin film having a thickness of less than 10µm. The polarizer is composed of a polyvinyl alcohol resin film containing a dichroic substance, and when the monomer transmittance is x% and the orientation function of the polyvinyl alcohol resin is f, the following formula (3) is satisfied: f＜-0.018x+1.11　　　　(3). Yet another embodiment of the present invention provides a polarizing plate having a shape other than rectangular and a protective layer disposed on at least one side of the polarizer. The protective layer is formed from a resin film having a thickness of 10 µm or less. The polarizer is formed from a polyvinyl alcohol-based resin film containing a dichroic substance, and the polarizer has a puncture strength of 30 gf/µm or greater. 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 irregular shape is selected from the group consisting of a through hole, a V-shaped notch, a U-shaped notch, a recess having a shape similar to a boat when viewed from above, a rectangular notch when viewed from above, an R-shaped notch having a shape similar to a bathtub when viewed from above, and combinations thereof. In one embodiment, the radius of curvature of the U-shaped notch is 5 mm or less. In one embodiment, the resin film comprises at least one resin selected from epoxy resins and (meth)acrylic resins. In one embodiment, the resin film is formed from a photo-cured epoxy resin, and the softening temperature of the resin film is above 100°C. In one embodiment, the resin film is formed from a cured product of a coating film of an epoxy resin in an organic solvent solution, and the softening temperature of the resin film is above 100°C. In another embodiment, the resin film is formed from a cured product of a coating film of a thermoplastic (meth)acrylic resin in an organic solvent solution, and the softening temperature of the resin film is above 100°C. In one embodiment, the thermoplastic (meth)acrylic resin comprises at least one member 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. According to another aspect of the present invention, a polarizing plate with a retardation layer is provided. The polarizing plate with a phase difference layer comprises the aforementioned polarizing plate and a phase difference layer; the phase difference layer is disposed on the side of the polarizer opposite to the side on which the protective layer is disposed. In one embodiment, the Re(550) of the phase difference layer is 100 nm to 190 nm, the Re(450)/Re(550) is greater than 0.8 and less than 1, and the angle formed between the slow axis of the phase difference layer and the absorption axis of the polarizer is 40° to 50°. In one embodiment, the phase difference layer is laminated on the polarizing plate via an adhesive layer. According to another aspect of the present invention, an image display device is provided. The image display device comprises the aforementioned polarizing plate or the polarizing plate with a phase difference layer.

Effects of the Invention According to embodiments of the present invention, by controlling the orientation of the polyvinyl alcohol (PVA)-based resin in the polarizer of a polarizing plate having an irregular shape (an irregularly shaped portion), a polarizing plate can be realized that is extremely thin while suppressing cracking in the irregularly shaped portion. Furthermore, the polarizer (and, consequently, the polarizing plate) exhibits optical properties acceptable for practical use.

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

A. Polarizing Plate A-1. Overall Structure of the Polarizing Plate Figure 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The illustrated polarizing plate 100 comprises a polarizer 10 and a protective layer 20 disposed on one side of the polarizer 10. Depending on the intended purpose, a further protective layer (not shown) may be provided on the side of the polarizer 10 opposite the protective layer 20. The protective layer 20 is formed of a resin film having a thickness of less than 10µm. The polarizing plate can be used as either a viewing-side polarizing plate or a back-side polarizing plate for an image display device. Typically, the polarizing plate is used as a viewing-side polarizing plate. In this case, the protective layer 20 is disposed on the viewing side (the side opposite the image display unit).

The polarizing plate of the embodiment of the present invention has an irregular shape other than a rectangle. In this specification, "having an irregular shape other than a rectangle" means that the top view shape of the polarizing plate has a shape other than a rectangle. The irregular shape represents an irregularly processed portion. Therefore, "a polarizing plate having an irregular shape other than a rectangle" (hereinafter sometimes referred to as "irregularly processed polarizing plate") not only includes the case where the entire irregularly shaped polarizing plate (i.e., the outer edge used to define the top view shape of the polarizing plate) is other than a rectangle, but also includes the case where an irregularly shaped processed portion is formed on the portion that is retreated inward from the outer edge of the rectangular polarizing plate. In the case of a polarizing plate, cracks are easily generated in the irregularly shaped processed portion, but according to the embodiment of the present invention, the cracks can be significantly suppressed. More details are as follows. In a typical (i.e., non-irregular) polarizing plate (essentially, a polarizer), cracks typically occur along the polarizer's absorption axis (extending direction). However, irregularly processed portions can develop L-shaped cracks (cracks that are diagonal to the absorption axis). According to embodiments of the present invention, as described below, by aligning the molecular chains of the polarizer's PVA resin more gently along the absorption axis than in conventional polarizers, not only typical cracks but also L-shaped cracks can be significantly suppressed.

Examples of irregular shapes (irregularly shaped processed parts) include those with chamfered corners into R-shapes, through holes, and cut parts that are concave when viewed from above, as shown in Figures 2 and 3. Representative examples of concave parts include shapes similar to a boat shape, a rectangle, an R-shape similar to a bathtub shape, a V-shaped notch, and a U-shaped notch. Another example of an irregular shape (irregularly shaped processed part) is a shape corresponding to a car instrument panel, as shown in Figures 4 and 5. This shape has an outer edge that forms an arc along the direction of rotation of the instrument needle, and includes a portion where the outer edge forms a V-shape (including an R-shape) that bulges inward in the surface direction. Of course, the shape of the irregular shape (irregularly shaped processed part) is not limited to the examples shown in the figures. For example, in addition to the roughly circular shape shown in the diagram, the through hole can also be any appropriate shape (e.g., elliptical, triangular, quadrilateral, pentagonal, hexagonal, or octagonal) depending on the purpose. Furthermore, the through hole can be located at any appropriate position depending on the purpose. As shown in FIG3 , the through hole can be located approximately in the center of the end portion in the long direction of the rectangular polarizing plate, or can be located at a predetermined position in the long direction of the end portion, or can be located at a corner of the polarizing plate. Although not shown, it can be located at the end portion in the short direction of the rectangular polarizing plate. It can also be located in the center of an irregularly shaped polarizing plate as shown in FIG4 or FIG5 . As shown in FIG3 , multiple through holes can also be provided. Furthermore, the shapes shown in the diagram can be appropriately combined depending on the purpose. For example, a through hole can be formed at any position of the irregular polarizing plate in FIG. 2 ; a V-shaped notch and/or a U-shaped notch can also be formed at any appropriate position on the outer edge of the irregular polarizing plate in FIG. 4 or FIG. 5 . The irregular polarizing plate can be suitably used in image display devices such as automobile dashboards, smart phones, tablet PCs, or smart watches. In addition, for example, when the irregular shape includes an R shape, its curvature radius is, for example, greater than 0.2 mm, and for example, greater than 1 mm, and for example, greater than 2 mm. On the other hand, the curvature radius is, for example, less than 10 mm, and for example, less than 5 mm. For another example, when the irregular shape is a U-shaped notch, its curvature radius (the curvature radius of the U-shaped portion) is, for example, less than 5 mm, and for example, 1 mm to 4 mm, and for example, 2 mm to 3 mm.

The irregular shape (irregularly shaped processed portion) can be formed by any appropriate method. Specific examples of the forming method include cutting with an end mill, punching with a punch such as a Thompson cutter, and cutting with laser irradiation. These methods may also be combined.

A-2. Polarizer The polarizer is formed of a PVA resin film containing a dichroic substance. In one embodiment, the polarizer satisfies the following equation (1) when the single-element transmittance is x% and the birefringence of the polyvinyl alcohol resin constituting the polarizer is y. In one embodiment, the polarizer satisfies the following equation (2) when the single-element transmittance is x% and the in-plane phase difference of the polyvinyl alcohol resin film constituting the polarizer is znm. In one embodiment, the polarizer satisfies the following equation (3) when the single-element transmittance is x% and the orientation function of the polyvinyl alcohol resin film constituting the polarizer is f. In one embodiment, the puncture strength of the polarizer is 30 gf/µm or greater. 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), the in-plane retardation of the PVA resin film (hereinafter referred to as "PVA in-plane retardation"), the orientation function of the PVA resin (hereinafter referred to as "PVA orientation function"), and the puncture strength of the polarizer are all values related to the degree of orientation of the molecular chains of the PVA resin constituting the polarizer. Specifically, the birefringence, in-plane retardation, and orientation function of PVA increase with increasing orientation, while the puncture strength decreases with increasing orientation. In the polarizer of the embodiment of the present invention (i.e., a polarizer satisfying the above formulas (1) to (3) or the puncture strength), the molecular chain of the PVA-based resin is more gently oriented in the absorption axis direction than in conventional polarizers, thereby suppressing thermal shrinkage in the absorption axis direction. As a result, although the polarizer (or, in other words, a polarizing plate) is extremely thin, cracks can be suppressed in the irregularly processed portion. In addition, because the polarizer (or, in other words, a polarizing plate) has excellent flexibility and bending durability, it is suitable for application in a curved image display device, more preferably in a bendable image display device, and even more preferably in a foldable image display device. In the past, polarizers with low orientation levels struggled to achieve acceptable optical properties (typically, single-element transmittance and polarization). However, the polarizers used in the embodiments of the present invention can achieve both a lower orientation level of PVA-based resin and acceptable optical properties.

The polarizer preferably satisfies the following formula (1a) and/or formula (2a), and more 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, thus enabling retardation measurement. 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 850 nm. The measured retardation values, R(λ), are plotted against the wavelength, λ, and then fitted to the following Sellmeier equation using the least squares method. Here, 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 as follows into the in-plane retardation of PVA (Rpva), which has no wavelength dependence, and the in-plane retardation value of iodine (Ri), which has a strong wavelength dependence. Rpva = A Ri = B / (λ ² - 600 ² ) Based on this separation formula, the in-plane retardation of PVA at a wavelength of λ = 1000 nm (i.e., Rpva) can be calculated. Furthermore, the evaluation method for the in-plane phase difference of PVA is also described in Japanese Patent No. 5932760, which can be referred to as needed. Furthermore, the birefringence (Δn) of the PVA can be calculated by dividing the phase difference by the thickness.

Commercially available devices for measuring the in-plane retardation of the above-mentioned PVA at a wavelength of 1000 nm include the KOBRA-WR/IR series and KOBRA-31X/IR series manufactured by Oji Instruments.

The orientation function (f) of the polarizer should preferably satisfy the following formula (3a), and more preferably satisfy the following formula (3b). If the orientation function is too small, it may be impossible to obtain an acceptable single-element 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 orientation function (f) is determined, for example, by attenuated total reflection (ATR) spectroscopy using a Fourier transform infrared spectrophotometer (FT-IR) with polarized light as the measurement light. Specifically, the microcrystals used to bond the polarizer are germanium, the measurement light is incident at an angle of 45°, and the incident polarized infrared light (measurement light) is polarized parallel to the surface of the germanium crystal sample to be bonded (s-polarized light). Measurements are performed with the polarizer extending in both parallel and perpendicular directions to the polarization direction of the measurement light. The intensity at 2941 cm ^-1 in the resulting absorbance spectrum is then used to calculate the orientation function according to the following formula. Here, intensity I is referenced to the peak at 3330 cm ^-1 and is calculated as 2941 cm ^-1 /3330 cm ^-1 . Furthermore, f = 1 indicates perfect alignment, while f = 0 indicates random alignment. Furthermore, we believe the peak at 2941 cm ^-1 is due to absorption from the ( _-CH2- ) vibration of the PVA main chain in the polarizer. f = (3 < ^cos2θ > -1)/2 = (1-D)/[c(2D+1)] = -2 × (1-D)/(2D+1). However, when c = ( ^3cos2β -1)/2 and the vibration at 2941 cm ^-1 is β = 90°. θ: The angle of the molecular chain relative to the extension direction β: The angle of the transition dipole moment relative to the molecular chain axis D = (I _⊥ ) / (I _// ) (At this time, the more oriented the PVA molecules are, the larger D is) 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 10µm or less, more preferably 8µm or less. The lower limit of the polarizer thickness can be, for example, 1µm. In one embodiment, the thickness of the polarizer can be 2µm to 10µm, and in another embodiment, it can be 2µm to 8µm. By making the polarizer very thin as described, thermal shrinkage can be minimized. This configuration is also believed to help prevent cracking in irregularly shaped areas of the polarizer.

The polarizer preferably exhibits absorption dichroism at any wavelength between 380 nm and 780 nm. The single-element transmittance of the polarizer is preferably 40.0% or greater, more preferably 41.0% or greater. The upper limit of the single-element transmittance may be, for example, 49.0%. In one embodiment, the single-element transmittance of the polarizer is 40.0% to 45.0%. The polarization degree of the polarizer is preferably 99.0% or greater, more preferably 99.4% or greater. 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 99.9%. One of the characteristics of the polarizer of the embodiment of the present invention is that even if the orientation degree of the PVA-based resin constituting the polarizer is lower than before and has the in-plane phase difference, birefringence and/or orientation function as described above, the monomer transmittance and polarization degree that are allowable in practical use can still be achieved. We speculate that this is due to the manufacturing method described later. In addition, the monomer transmittance is represented by the Y value obtained by measuring and correcting the visual sensitivity using an ultraviolet-visible spectrophotometer. The polarization degree can be obtained by the following formula based on the parallel transmittance Tp and the orthogonal transmittance Tc obtained by measuring and correcting the visual sensitivity using an ultraviolet-visible spectrophotometer. 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, more preferably 45 gf/µm or more, and particularly preferably 50 gf/µm or more. The upper limit of the puncture strength can be, for example, 80 gf/µm. By setting the puncture strength of the polarizer to the above range, the occurrence of cracks in the irregularly processed portion and the splitting of the polarizer along the absorption axis can be significantly suppressed. As a result, a polarizer (in other words, a polarizing plate) with very excellent flexibility can be obtained. The puncture strength indicates the polarizer's resistance to cracking when the polarizer is punctured with a predetermined strength. Puncture strength can be expressed, for example, as the strength required to break a polarizer when a predetermined needle is inserted into the polarizer at a predetermined speed in a compression tester (breaking strength). Furthermore, as is apparent from the unit, puncture strength refers to the puncture strength per unit thickness (1µm) of the polarizer.

As described above, the polarizer is formed from a PVA-based resin film containing a dichroic substance. The PVA-based resin forming the PVA-based resin film (essentially the polarizer) preferably includes a PVA-based resin modified with an acetyl group. With this configuration, a polarizer having the desired puncture strength can be obtained. When the total weight of the PVA-based resin is 100%, the blending amount of the acetyl-based resin modified with an acetyl group is preferably 5% to 20% by weight, more preferably 8% to 12% by weight. When the blending amount is within this range, the puncture strength can be set to a more suitable range.

Polarizers are typically manufactured using a laminate of two or more layers. A specific example of a polarizer using a laminate is a laminate comprising a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer formed using a laminate comprising a resin substrate and a PVA-based resin layer coated on the resin substrate can be produced, for example, by the following steps: applying a PVA-based resin solution to the resin substrate and drying it to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; and stretching and dyeing the laminate to form the polarizer. In this embodiment, a polyvinyl alcohol-based resin layer containing a halogenated compound and a polyvinyl alcohol-based resin is preferably formed on one side of the resin substrate. Stretching typically includes immersing the laminate in an aqueous boric acid solution. Furthermore, the stretching preferably further includes the following step: stretching the laminate in the air at a high temperature (e.g., 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 to 4.5 times, which is significantly smaller than the general ratio. Even with the total stretching ratio, a polarizer with acceptable optical properties can be obtained by combining the addition of halides and dry shrinkage treatment. Furthermore, in the embodiment of the present invention, the stretching ratio of the air-assisted stretching is preferably greater than the stretching ratio of the stretching in boric acid water. By making the above-mentioned structure, a polarizer with acceptable optical properties can be obtained even if the total stretching ratio is small. Furthermore, the laminate is preferably subjected to a drying and shrinking treatment in which the laminate is heated while being transported along its longitudinal direction, thereby shrinking the laminate by more than 2% in its width direction. In one embodiment, the method for manufacturing a polarizer comprises 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, the crystallinity of the PVA resin can be improved even when the PVA resin is coated on a thermoplastic resin, thereby achieving high optical properties. Furthermore, by simultaneously improving the orientation of the PVA resin in advance, problems such as a reduction in orientation or dissolution of the PVA resin when immersed in water during the subsequent dyeing or stretching steps can be prevented, thereby achieving high optical properties. Furthermore, immersing the PVA resin layer in a liquid can further suppress the orientational disorder of the polyvinyl alcohol molecules and the reduction of their orientation compared to a PVA resin layer without halides. This can improve the optical properties of polarizers produced through treatments such as dyeing and underwater stretching, where the laminate is immersed in a liquid. Furthermore, shrinking the laminate in the width direction during drying and shrinking can further enhance optical properties. The resulting resin substrate/polarizer laminate can be used directly (i.e., the resin substrate can also be used as a protective layer for the polarizer), or the resin substrate can be peeled off from the resin substrate/polarizer laminate and then used after applying any appropriate protective layer to the peeled-off area. Details of the polarizer manufacturing method are described in Section A-3.

A-3. Polarizer Manufacturing Method The polarizer manufacturing method preferably includes the following steps: forming a polyvinyl alcohol resin layer (PVA resin layer) containing 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 the laminate while conveying it longitudinally, thereby shrinking it by at least 2% in the width direction. 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 heated rollers at a temperature of 60°C to 120°C. The shrinkage rate of the laminate in the width direction during the drying and shrinking treatment is preferably no less than 2%. Furthermore, the stretching ratio during the air-assisted stretching is preferably greater than the stretching ratio during the underwater stretching. The polarizer described in Section A-2 above can be obtained using the aforementioned manufacturing method. In particular, a polarizer with excellent optical properties (represented by single-unit transmittance and polarization degree) can be obtained by the following method: after producing a laminate including a PVA-based resin layer containing a halogenated compound, the laminate is stretched through a multi-stage stretching process including air-assisted stretching and underwater stretching, and the stretched laminate is then heated with a heating roller to shrink it by more than 2% in the width direction.

A-3-1. Laminated Product Preparation Any appropriate method can be used to prepare a laminate of a thermoplastic resin substrate and a PVA-based resin layer. A coating solution containing a halogenated compound and a PVA-based resin is preferably applied to the surface of the thermoplastic resin substrate and dried to form the PVA-based resin layer on the thermoplastic resin substrate. 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 by any appropriate method. Examples include roll coating, spin coating, wire rod coating, dip coating, die coating, curtain coating, spray coating, and doctor blade coating (e.g., notched wheel coating). 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 as described above and reducing the total stretching ratio as described below, a polarizer with acceptable monomer transmittance and polarization degree can be obtained even though the PVA resin has a lower degree of orientation than conventional polarizers.

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

A-3-1-1. Thermoplastic Resin Substrate The thermoplastic resin substrate can be any suitable thermoplastic resin film. Details regarding thermoplastic resin film substrates are described, for example, in Japanese Patent Publication No. 2012-73580. This publication is incorporated herein by reference in its entirety.

A-3-1-2. Coating Liquid The coating liquid comprises the halogenated compound and the PVA-based resin as described above. 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, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyols such as trihydroxymethylpropane, and amines such as ethylenediamine and diethylenetriamine. These solvents may 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. At this resin concentration, a uniform coating film can be formed that adheres closely to the thermoplastic resin substrate. The halogen content in the coating solution is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin.

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

The above-mentioned PVA resin can adopt any appropriate resin. For example, polyvinyl alcohol and ethylene-vinyl alcohol copolymer can be mentioned. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer can be obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of PVA resin is generally 85 mol%~100 mol%, preferably 95.0 mol%~99.95 mol%, and more preferably 99.0 mol%~99.93 mol%. The saponification degree can be obtained in accordance with JIS K 6726-1994. By using a PVA resin with the above-mentioned saponification degree, a polarizer with excellent durability can be obtained. When the saponification degree is too high, there is a risk of gelling. As mentioned above, the PVA resin preferably includes a PVA resin modified with an acetyl group.

The average degree of polymerization of PVA-based resins can be appropriately selected depending on the intended purpose. It is generally between 1,000 and 10,000, preferably between 1,200 and 4,500, and more preferably between 1,500 and 4,300. The average degree of polymerization can be determined in accordance with JIS K 6726-1994.

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

The amount of halogenated compound in the coating solution should be 5 to 20 parts by weight, more preferably 10 to 15 parts by weight, relative to 100 parts by weight of the PVA resin. If the amount of halogenated compound exceeds 20 parts by weight, the halogenated compound may overflow, resulting in a cloudy white appearance in the resulting polarizer.

Generally speaking, after stretching a PVA resin layer, the orientation of the polyvinyl alcohol molecules within the PVA resin layer increases. However, if the stretched PVA resin layer is immersed in an aqueous solution, the orientation of the polyvinyl alcohol molecules may become disrupted, and this orientation may decrease. This tendency to decrease orientation is particularly pronounced when stretching a laminate of a thermoplastic resin substrate and a PVA resin layer in boric acid water at relatively high temperatures to stabilize the stretching of the thermoplastic resin substrate. For example, stretching of a PVA film monomer in boric acid water is typically performed at 60°C. In contrast, stretching of a laminate composed of an A-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a higher temperature, around 70°C. At this temperature, the orientation of the PVA at the beginning of stretching decreases before it is elevated by stretching in water. To address this issue, by preparing a laminate composed of a halogenated PVA-based resin layer and a thermoplastic resin substrate and stretching the laminate at a high temperature in air (assisted stretching) before stretching in boric acid water, crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after assisted stretching can be promoted. As a result, when the PVA resin layer is immersed in a liquid, the orientation disorder and reduction of the polyvinyl alcohol molecules are suppressed compared to the case where the PVA resin layer does not contain halides. This can improve the optical properties of polarizers produced through treatment steps such as dyeing and underwater stretching, where the laminate is immersed in a liquid.

A-3-2. Air-Assisted Stretching In particular, to achieve high optical properties, a two-stage stretching method combining dry stretching (assisted stretching) and stretching in boric acid water is often used. In this two-stage stretching method, the introduction of the auxiliary stretching allows stretching to be performed while suppressing crystallization of the thermoplastic resin substrate. Furthermore, when coating PVA resin on a thermoplastic resin substrate, the coating temperature must be lower than when coating PVA resin on a conventional metal roller to minimize the effect 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. By introducing assisted stretching, the crystallinity of the PVA resin can be enhanced even when it is coated on a thermoplastic resin, achieving high optical properties. Furthermore, by pre-enhancing the orientation of the PVA resin, problems such as loss of orientation or dissolution during subsequent dyeing or stretching steps can be avoided, thus achieving high optical properties.

The stretching method for in-flight assisted stretching can be fixed-end stretching (e.g., stretching using a tenter stretching machine) or free-end stretching (e.g., uniaxial stretching by passing the laminate between rollers with different circumferential speeds). However, to achieve high optical properties, free-end stretching is preferred. In one embodiment, the in-flight stretching process includes a heated roller stretching step, in which the laminate is stretched while being transported along its longitudinal direction using the circumferential speed difference between the heated rollers. The in-flight stretching process typically includes a zone stretching step and a heated roller stretching step. Furthermore, the order of the zone stretching step and the heated roller stretching step is not limited; the zone stretching step may be performed first, or the heated roller stretching step may be performed first. The regional stretching step can also be omitted. In one embodiment, the regional stretching step and the heated roller stretching step are performed sequentially. In another embodiment, the film ends are gripped in a tenter stretching machine, and the distance between the tenters is expanded in the direction of travel to stretch (the increase in the distance between the tenters is the stretching ratio). At this time, the distance between the tenters in the width direction (perpendicular to the direction of travel) is set so that they can be arbitrarily approached. It is preferable to set the stretching ratio relative to the direction of travel to use free-end stretching for approach. In the case of free-end stretching, the shrinkage ratio in the width direction is calculated as (1/stretching ratio) ^1/2 .

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 in each stage. The stretching direction in air-assisted stretching should be substantially the same as the stretching direction in underwater stretching.

The stretching ratio of 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 within the range, the total stretching ratio can be set to the desired range when combined with the underwater stretching, and the desired birefringence, in-plane phase difference and/or orientation function can be achieved. As a result, a polarizer (in other words, a polarizing plate) can be obtained in which cracks in the irregularly processed portion are suppressed. Moreover, as mentioned above, the stretching ratio of the air-assisted stretching is preferably greater than the stretching ratio of the underwater stretching. By making the above-mentioned structure, a polarizer with acceptable optical characteristics can be obtained even if the total stretching ratio is small. 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's material, stretching method, and other factors. The stretching temperature is preferably above the thermoplastic resin substrate's glass transition temperature (Tg), more preferably above the thermoplastic resin substrate's glass transition temperature (Tg) + 10°C, and most preferably above Tg + 15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. Stretching at this temperature suppresses the rapid crystallization of the PVA resin, thereby minimizing adverse effects caused by this crystallization (e.g., interference with orientation of the PVA resin layer due to stretching).

A-3-3. Insolubilization, Dyeing, and Crosslinking Treatments 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 can typically be performed by immersing the PVA resin layer in an aqueous boric acid solution. Details of the insolubilization treatment, dyeing treatment, and crosslinking treatment are described, for example, in Japanese Patent Publication No. 2012-73580.

A-3-4. 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. This results in a polarizer with excellent optical properties.

The laminate can be stretched using any appropriate method. Specifically, it can be fixed-end stretching or free-end stretching (for example, a method in which the laminate passes between rollers with different circumferential speeds for uniaxial stretching). Free-end stretching is preferred. Stretching of the laminate can be performed in a single stage or in multiple stages. When stretching in multiple stages, the total stretching ratio is the product of the stretching ratios in 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 required to withstand the tension applied during stretching, as well as water-insoluble resistance. Specifically, boric acid in aqueous solution forms tetrahydroxyboric acid anions, which crosslink with the PVA resin via hydrogen bonds. This imparts rigidity and water resistance to the PVA resin layer, allowing for excellent stretching and resulting in polarizers with superior optical properties.

The boric acid aqueous solution is 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, more preferably 2.5 to 6 parts by weight, and particularly 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, resulting in the production of polarizers with higher performance. 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.

An iodide is preferably added to the stretching bath (boric acid aqueous solution). This addition can suppress the dissolution of iodine adsorbed in the PVA-based resin layer. Specific examples of the iodide are described above. The concentration of the iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, per 100 parts by weight of water.

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At this temperature, the dissolution of the PVA-based resin layer can be suppressed, while at the same time, stretching at a high rate can be achieved. Specifically, as mentioned above, in relation to the formation of the PVA-based 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 if the thermoplastic resin substrate is plasticized with water, it may not be stretched well. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and 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 for underwater stretching is preferably 1.0 to 2.2 times, more preferably 1.1 to 2.0 times, more preferably 1.1 to 1.8 times, and even more preferably 1.2 to 1.6 times. If the stretching ratio for underwater stretching is within the aforementioned range, the total stretching ratio can be set to the desired range, thereby achieving the desired birefringence, in-plane phase difference, and/or orientation function. As a result, a polarizer (or, in other words, a polarizing plate) can be obtained in which cracks in the irregularly processed portion are suppressed. As described above, the total stretching ratio (the sum of the stretching ratios for the combined air-assisted stretching and underwater stretching) is preferably 3.0 to 4.5 times, more preferably 3.0 to 4.3 times, and even more preferably 3.0 to 4.0 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 the air-assisted stretching and underwater stretching, and performing a drying and shrinking treatment, a polarizer with acceptable optical properties can be obtained even at the aforementioned total stretching ratio.

A-3-5. Drying and Shrinking Treatment The drying and shrinking treatment can be performed by heating the entire area (zone heating) or by heating the transport rollers (so-called heating roller drying). Using both methods is preferred. Using heating rollers for drying effectively suppresses heat warping of the laminate, resulting in a polarizer with excellent appearance. Specifically, drying while the laminate passes over heating rollers effectively promotes crystallization of the thermoplastic resin matrix, increasing its crystallinity. Even at relatively low drying temperatures, this can significantly improve the crystallinity of the thermoplastic resin matrix. As a result, the rigidity of the thermoplastic resin substrate increases, allowing it to withstand the shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. Furthermore, by using heated rollers, the laminate can be dried while maintaining a flat state, thereby suppressing not only curling but also wrinkling. In this case, the laminate shrinks in the width direction through the drying and shrinking treatment, improving optical properties. This is because it effectively improves the orientation of the PVA and PVA/iodine complex. The widthwise shrinkage rate of the laminate during the drying and shrinking treatment is preferably 1% to 10%, more preferably 2% to 8%, and most preferably 2% to 6%.

Figure 6 schematically illustrates an example of a drying and shrinking process. During the drying and shrinking process, conveyor rollers R1-R6 and guide rollers G1-G4, heated to predetermined temperatures, are used to convey the laminate 200 while drying it. In the illustrated example, the conveyor rollers R1-R6 are positioned to alternately and continuously heat the PVA resin layer and the thermoplastic resin substrate. However, the conveyor rollers R1-R6 can also be positioned to continuously heat only one side of the laminate 200 (e.g., the thermoplastic resin substrate).

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 particularly preferably 70°C to 80°C. This can effectively increase the crystallinity of the thermoplastic resin and effectively suppress curling, while producing an optical laminate with excellent durability. In addition, the temperature of the heating rollers can be measured with a contact thermometer. In the example shown in the figure, six conveyor rollers are provided, but there is no particular limitation if multiple conveyor rollers are provided. The number of conveyor rollers is generally 2 to 40, with 4 to 30 being preferred. The contact time (total contact time) between the laminate and the heating roller should preferably be 1 second to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

The heating rollers can be installed in a heating furnace (such as an oven) or in a general manufacturing line (at room temperature). They are preferably installed in 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 rollers can be suppressed, making it easier to control shrinkage in the width direction. The hot air drying temperature should preferably be between 30°C and 100°C. Furthermore, the hot air drying time should preferably be between 1 second and 300 seconds. The hot air velocity should preferably be between 10m/s and 30m/s. Furthermore, this velocity is the velocity within the heating furnace and can be measured with a mini fan-type digital anemometer.

A-3-6. Other Treatments After the water stretching treatment and before the drying and shrinking treatment, a cleaning treatment is preferably performed. This cleaning treatment can typically be performed by immersing the PVA resin layer in an aqueous potassium iodide solution.

A-4. Protective Layer The protective layer has a thickness of 10µm or less. A protective layer thickness of 10µm or less contributes to thinning the polarizer. Conventionally, to protect the polarizer by tracking its shrinkage during heating, a protective layer with a thickness of 20µm or greater has been used. However, the polarizer used in the present embodiment, as described above, has a lower degree of orientation of the PVA resin than conventional polarizers. Consequently, shrinkage due to heating is minimized. Therefore, even with a protective layer thickness of 10µm or less, cracking during heating can be suppressed. Furthermore, this polarizer helps suppress cracking in irregularly shaped areas.

The thickness of the protective layer is preferably 7µm or less, more preferably 5µm or less, and even more preferably 3µm or less. The thickness of the protective layer is, for example, 1µm or more.

The protective layer is composed of a resin film. Any appropriate resin can be used as the resin forming the resin film, depending on the intended purpose. Specific examples include cellulose resins such as (meth)acrylic acid and cellulose triacetate (TAC); thermoplastic resins such as polyesters, polyurethanes, polyvinyl alcohols, polycarbonates, polyamides, polyimides, polyether sulfones, polysulfones, polystyrenes, polynorbornenes, polyolefins, and acetates; thermosetting resins or active energy ray-curing resins such as (meth)acrylic acid, urethanes, (meth)acrylic urethanes, epoxies, and silicones; and glassy polymers such as silicone polymers. In one embodiment, the resin forming the resin film can be epoxy resin or (meth) acrylic resin. These resins can be used alone or in combination.

The resin film constituting the protective layer may be, for example, a molded product of a molten resin, a solidified product of a coating film of a resin solution obtained by dissolving or dispersing the resin in an aqueous solvent or an organic solvent, or a cured product of a curable resin (e.g., a photoion-cured product).

In one embodiment, the protective layer can be a cured product of a coating film of a thermoplastic (meth)acrylic resin (hereinafter, (meth)acrylic resin may be simply referred to as "acrylic resin") in an organic solvent solution, a photo-cured epoxy resin, or a cured product of an epoxy resin in an organic solvent solution. Details are described below.

A-4-1. 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. From the perspective of wet durability, the softening temperature of the protective layer in this embodiment is preferably 100°C or higher, preferably 115°C or higher, more preferably 120°C or higher, and particularly preferably 125°C or higher. Furthermore, from the perspective of formability, the softening temperature is preferably 300°C or lower, preferably 250°C or lower, more preferably 200°C or lower, and particularly preferably 160°C or lower.

The glass transition temperature (Tg) of acrylic resin is preferably above 100°C. As a result, the softening temperature of the protective layer is also almost above 100°C. If the Tg of acrylic resin is above 100°C, the polarizing plate including the protective layer obtained from the resin will not only have excellent crack resistance but also excellent durability under humidity. The Tg of acrylic resin is preferably above 110°C, more preferably above 115°C, even more preferably above 120°C, and particularly preferably above 125°C. On the other hand, the Tg of acrylic resin is preferably below 300°C, more preferably below 250°C, more preferably below 200°C, and particularly preferably below 160°C. If the Tg of acrylic resin is within the above range, the moldability is excellent.

Any suitable acrylic resin can be used as long as it has the Tg described above. Typically, the acrylic resin contains an alkyl (meth)acrylate as the main component as a monomer unit (repeating unit). In this specification, "(meth)acrylic acid" means acrylic acid and/or methacrylic acid. Examples of the alkyl (meth)acrylate constituting the main skeleton of the acrylic resin include linear or branched alkyl groups having 1 to 18 carbon atoms. These can be used alone or in combination. Furthermore, any suitable comonomer can be introduced into the acrylic resin by copolymerization. By appropriately setting the type, amount, combination, and blending ratio of the alkyl (meth)acrylate, the type, amount, combination, and blending ratio of the comonomer, and polymerization conditions, an acrylic resin capable of forming a desired protective layer can be obtained.

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. Acrylic resins containing lactone ring units are described, for example, in Japanese Patent Publication No. 2008-181078. Acrylic resins having glutarimido units are described, for example, in Japanese Patent Application Publication Nos. 2006-309033, 2006-317560, 2006-328334, 2006-337491, 2006-337492, 2006-337493, and 2006-337569. The disclosures of these publications are incorporated herein by reference.

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 lower 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.

In embodiments of the present invention, acrylic resins may be used in combination with other resins. Specifically, the monomer components of the acrylic resin may be copolymerized with the monomer components of the other resins, and the copolymer may be used to form the protective layer described below. Alternatively, a blend of the acrylic resin and the other resin may be used to form the protective layer.

The protective layer of this embodiment can be formed by, for example, applying an organic solvent solution of acrylic resin on the surface of the polarizer to form a coating film, and curing the coating film.

Any suitable organic solvent that can dissolve or uniformly disperse the acrylic resin can be used as the organic solvent. Specific examples of the organic solvent include ethyl acetate, toluene, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, and cyclohexanone.

The acrylic resin concentration in the solution is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. This concentration allows for a uniform coating film that adheres closely to the polarizer.

The solution can be applied to any appropriate substrate or to a polarizer. When applied to a substrate, the cured product of the coating film formed on the substrate is transferred to the polarizer. When applied to a polarizer, a protective layer is formed directly on the polarizer by drying (curing) the coating film. It is preferred that the solution be applied to the polarizer to form a protective layer directly on the polarizer. With the above-mentioned structure, the adhesive layer or the pressure-sensitive adhesive layer required for transfer can be omitted, so the polarizer can be made thinner. Any appropriate method can be used for applying the solution. Specific examples include roller coating, spin coating, wire rod coating, dip coating, die coating, curtain coating, spray coating, and scraper coating (such as the notched wheel coating method).

The protective layer is formed by drying (curing) the applied solution. The drying temperature is preferably below 100°C, more preferably between 50°C and 70°C. A drying temperature within this range prevents adverse effects on the polarizer. The drying time varies depending on the drying temperature. For example, the drying time can be between 1 and 10 minutes.

A-4-2. Photocurable Epoxy Resin In one embodiment, the protective layer is formed from a photocurable epoxy resin. This protective layer suppresses cracking and achieves excellent moisture durability. As mentioned above, the protective layer is a photocurable epoxy resin, so the protective layer-forming composition includes a photocatalytic polymerization initiator. A photocatalytic polymerization initiator is a photosensitive agent that functions as a photoacid generator, typically an ionic onium salt composed of a cationic portion and a cationic portion. In the onium salt, the cationic portion absorbs light, while the anionic portion becomes an acid generator. The acid generated from the photocationic polymerization initiator causes ring-opening polymerization of the epoxy groups. The resulting photocationic cured product has a high softening temperature on the protective layer, which reduces iodine adsorption. This provides a polarizing plate with suppressed cracking and excellent durability under humidification.

From the perspective of humidification durability, the softening temperature of the protective layer of this embodiment is preferably 100°C or higher, more preferably 110°C or higher, more preferably 120°C or higher, and particularly preferably 125°C or higher. From the perspective of formability, it is preferably 300°C or lower, more preferably 250°C or lower, more preferably 200°C or lower, and particularly preferably 160°C or lower.

A-4-2-1. Epoxy Resin Any suitable epoxy resin can be used, and epoxy resins having aromatic or aliphatic rings are particularly preferred. In this embodiment, 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, naphthalene, and fluorene. The epoxy resin may be used singly or in combination of two or more. An epoxy resin having a biphenyl or bisphenol skeleton as the aromatic skeleton, or a hydrogenated epoxy resin thereof, is particularly preferred. The use of such epoxy resins provides a polarizing plate having superior durability and flexibility.

In one embodiment, the epoxy resin having a biphenyl skeleton includes an epoxy resin having the following structure. The epoxy resin having a biphenyl skeleton may be used alone or in combination of two or more. [Chemical Formula 1] (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).

In one embodiment, the epoxy resin having a biphenyl skeleton is an epoxy resin represented by the following formula: [Chemical Formula 2] (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 another 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 case, the ratio (molar ratio) of chemical structures other than the biphenyl skeleton is preferably less than that of the biphenyl skeleton.

The above-mentioned epoxy resin (epoxy resin after photoion curing) preferably has a glass transition temperature (Tg) of 100°C or higher. As a result, the softening temperature of the protective layer is also almost above 100°C. If the Tg of the epoxy resin is above 100°C, the polarizing plate including the obtained protective layer tends to have excellent durability. The Tg of the epoxy resin is preferably above 110°C, more preferably above 120°C, and particularly preferably above 125°C. On the other hand, the Tg of the epoxy resin is preferably below 300°C, more preferably below 250°C, more preferably below 200°C, and particularly preferably below 160°C. If the Tg of the epoxy resin is within the above range, the formability can be excellent.

The epoxy equivalent weight of the epoxy resin is preferably 100 g/equivalent or greater, more preferably 150 g/equivalent or greater, and even more preferably 200 g/equivalent or greater. Furthermore, the epoxy equivalent weight of the epoxy resin is preferably 3000 g/equivalent or less, more preferably 2500 g/equivalent or less, and even more preferably 2000 g/equivalent or less. An epoxy equivalent weight within this range provides a more stable protective layer (one that contains minimal residual monomers and is fully cured). In this specification, "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 K 7236.

In this embodiment, the epoxy resin described above can be used in combination with other resins. Specifically, a blend of the epoxy resin described above (e.g., an epoxy resin having at least one selected from the group consisting of an aromatic skeleton and a hydrogenated aromatic skeleton) and other resins can be used to form the protective layer. Examples of other resins include acrylic resins and cyclohexane resins.

Any suitable (meth)acrylic compound can be used as the acrylic resin. Examples of the (meth)acrylic compound include a (meth)acrylic compound having one (meth)acrylic group in the molecule (hereinafter referred to as a "monofunctional (meth)acrylic compound") and a (meth)acrylic compound having two or more (meth)acrylic groups in the molecule (hereinafter referred to as a "polyfunctional (meth)acrylic compound"). 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 Publication No. 2019-168500. The entire disclosure of this publication is incorporated herein by reference.

Any suitable compound having one or more cyclohexyl groups in the molecule can be used as the cyclohexyloxybutane resin. Examples thereof include 3-ethyl-3-hydroxymethylcyclohexyloxybutane, 3-ethyl-3-(2-ethylhexyloxymethyl)cyclohexyloxybutane, 3-ethyl-3-(phenoxymethyl)cyclohexyloxybutane, 3-ethyl-3-(cyclohexyloxymethyl)cyclohexyloxybutane, 3-ethyl-3-(oxiranylmethoxy)cyclohexyloxybutane, and (meth)acrylate (3-ethylcyclohexyl-3-yl)methyl ester. Oxycyclobutane compounds containing one oxocyclobutane group; oxocyclobutane compounds containing two or more oxocyclobutane groups in the molecule, such as 3-ethyl-3{[(3-ethyloxocyclobutane-3-yl)methoxy]methyl}oxocyclobutane, 1,4-bis[(3-ethyl-3-oxocyclobutane)methoxymethyl]benzene, and 4,4'-bis[(3-ethyl-3-oxocyclobutane)methoxymethyl]biphenyl. These oxocyclobutane resins may be used alone or in combination of two or more. Preferred cyclohexane resins include 3-ethyl-3-hydroxymethylcyclohexane, 1,4-bis[(3-ethyl-3-cyclohexane)methoxymethyl]benzene, 3-ethyl-3-(2-ethylhexyloxymethyl)cyclohexane, 3-ethyl-3-(oxiranylmethoxy)cyclohexane, (3-ethylcyclohexane-3-yl)methyl (meth)acrylate, and 3-ethyl-3{[(3-ethylcyclohexane-3-yl)methoxy]methyl}cyclohexane. These cyclohexane resins are readily available and have excellent diluting properties (low viscosity) and compatibility.

In one embodiment, from the perspective of compatibility and adhesion, an oxycyclobutane resin having a molecular weight of 500 or less and being liquid at room temperature (25°C) is preferably used. In one embodiment, an oxycyclobutane compound containing two or more oxycyclobutane groups in the molecule, or an oxycyclobutane compound containing one oxycyclobutane group and one (meth)acryloyl group or one epoxy group in the molecule is preferably used. 3-Ethyl-3-{[(3-ethyloxycyclobutane-3-yl)methoxy]methyl}oxycyclobutane, 3-Ethyl-3-(oxiranylmethoxy)oxycyclobutane, and (3-ethyloxycyclobutane-3-yl)methyl (meth)acrylate are more preferably used. By using these cyclohexane oxychloride resins, the hardening and durability of the protective layer can be improved.

A-4-2-2. Photocationic Polymerization Initiators Photocationic polymerization initiators are photosensitive agents that function as photoacid generators. Representative examples include ionic onium salts composed of a cationic portion and an anionic portion. In these onium salts, the cationic portion absorbs light, while the anionic portion serves as a source of acid. The acid generated by the photocationic polymerization initiator causes ring-opening polymerization of epoxy groups. Any suitable compound that can cure epoxy resins having at least one selected from the group consisting of aromatic skeletons and hydrogenated aromatic skeletons 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 the photocatalytic polymerization initiator include triphenylcorbium hexafluoroantimonylate, triphenylcorbium hexafluorophosphate, p-(phenylthio)phenyldiphenylcorbium hexafluoroantimonylate, p-(phenylthio)phenyldiphenylcorbium hexafluoroantimonylate, 4-chlorophenyldiphenylcorbium hexafluorophosphate, 4-chlorophenyldiphenylcorbium hexafluoroantimonylate, bis[4-(diphenylcorbyl)phenyl]sulfide bishexafluorophosphate, bis[4-(diphenylcorbyl)phenyl]sulfide bishexafluoroantimonylate, (2,4-cyclopentadien-1-yl)[(1-methylethyl)benzene]-Fe-hexafluorophosphate, and diphenyliodonium hexafluoroantimonylate. Preferred photocatalytic polymerization initiators are triphenylsulfonium hexafluoroantimonate salts and diphenyliodonium hexafluoroantimonate salts.

The protective layer of this embodiment can be formed, for example, by applying a composition comprising the above-mentioned epoxy resin and a photocatalytic polymerization initiator to form a coating film, and then irradiating the coating film with light (e.g., ultraviolet rays).

The epoxy resin concentration in the above composition is preferably 10 to 30 parts by weight relative to 100 parts by weight of the solvent. This resin concentration allows for a uniform coating film that adheres closely to the polarizer.

The above-mentioned composition can be applied to any appropriate substrate or to a polarizer. When applied to a substrate, the cured coating formed on the substrate is transferred to the polarizer. When applied to a polarizer, the coating is cured, for example, by irradiation with light, thereby forming a protective layer directly on the polarizer. It is preferable to apply the above-mentioned composition to the polarizer and form a protective layer directly on the polarizer. If the above-mentioned structure is adopted, the adhesive layer or the adhesive layer required for transfer can be omitted, so the polarizer can be made thinner. The method of applying the composition is as described above.

The coating film can be cured by irradiating it with light (typically ultraviolet light) using any suitable light source to achieve any suitable irradiation dose. After irradiation, a heat treatment may be applied to complete the curing process by the photoreaction. The heat treatment may be performed at any suitable temperature and for any suitable time.

A-4-3. 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. From the perspective of wet durability, the softening temperature of the protective layer in this embodiment is preferably 100°C or higher, preferably 110°C or higher, more preferably 120°C or higher, and particularly preferably 125°C or higher. Furthermore, from the perspective of formability, the softening temperature is preferably 300°C or lower, preferably 250°C or lower, more preferably 200°C or lower, and particularly preferably 160°C or lower.

A-4-3-1. Epoxy Resin In this embodiment, the epoxy resin preferably has a glass transition temperature (Tg) of 100°C or higher. As a result, the softening temperature of the protective layer is also approximately 100°C or higher. When the Tg of the epoxy resin is 100°C or higher, the polarizing plate including the protective layer obtained from the resin tends to have excellent durability. The Tg of the epoxy resin is preferably 110°C or higher, more preferably 120°C or higher, and particularly preferably 125°C or higher. On the other hand, the Tg of the epoxy resin is preferably 300°C or lower, more preferably 250°C or lower, more preferably 200°C or lower, and particularly preferably 160°C or lower. If the Tg of epoxy resin is within the above range, the moldability can be excellent.

Any appropriate epoxy resin may be used as long as it has the Tg described above. Epoxy resins typically refer to resins having an epoxy group in their molecular structure. Preferred epoxy resins include those having an aromatic ring in their molecular structure. 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 a benzene ring, a naphthalene ring, and a fluorene ring. Epoxy resins may be used alone or in combination of two or more. When using two or more epoxy resins, you can also use a combination of epoxy resins containing aromatic epoxy and epoxy resins that do not contain aromatic epoxy.

Epoxy resins with aromatic rings in their molecular structure can be specifically listed as: bisphenol A diglycidyl ether type epoxy resin, bisphenol F diglycidyl ether type epoxy resin, bisphenol S diglycidyl ether type epoxy resin, resorcinol diglycidyl ether type epoxy resin, Hydroquinone diglycidyl ether type epoxy resin, terephthalate diglycidyl ester type epoxy resin, diphenoxyethanol 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 interrupted diamine type). Furthermore, hexahydrophthalic anhydride type epoxy resin, tetrahydrophthalic anhydride type epoxy resin, dialcic acid type epoxy resin, p-oxybenzoic acid type epoxy resin, or other glycidyl ester type epoxy resin can also be used.

The epoxy equivalent weight of the epoxy resin is preferably 1000 g/equivalent or greater, more preferably 3000 g/equivalent or greater, and even 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 even more preferably 20,000 g/equivalent or less. By keeping the epoxy equivalent weight within this range, a more stable protective layer can be obtained. In this specification, "epoxy equivalent weight" means "the mass of the epoxy resin containing one equivalent of epoxy groups" and can be measured in accordance with JIS K 7236.

In this embodiment, epoxy resin and other resins may be used in combination. That is, a blend of epoxy resin and other resins may be used to form the protective layer. The other resin may be appropriately selected according to the intended purpose.

The protective layer of this embodiment can be formed, for example, by applying an organic solvent solution containing the aforementioned epoxy resin to form a coating film, and then curing the coating film. The epoxy resin concentration in the organic solvent solution is preferably 3 to 20 parts by weight per 100 parts by weight of the solvent. This resin concentration allows for a uniform coating film that adheres closely to the polarizer.

The organic solvent may be any suitable solvent that can dissolve or uniformly disperse the epoxy resin. Specific examples of the solvent include ethyl acetate, toluene, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), cyclopentanone, and cyclohexanone.

The solution can be applied to any suitable substrate or to a polarizer. When applied to a substrate, the cured product of the coating film formed on the substrate is transferred to the polarizer. When applied to a polarizer, a protective layer is formed directly on the polarizer by drying (curing) the coating film. It is preferred that the solution be applied to the polarizer to form a protective layer directly on the polarizer. If the structure is as described above, the adhesive layer or the adhesive layer required for transfer can be omitted, so the polarizer can be made thinner. The method of applying the solution is as described above.

By drying (curing) the solution coating, a protective layer is formed as a cured product of the coating. The drying temperature is preferably below 100°C, more preferably between 50°C and 70°C. Within this range, adverse effects on the polarizer can be prevented. The drying time can vary depending on the drying temperature. For example, the drying time can be between 1 and 10 minutes.

B. Polarizing Plate with Phase Difference Layer B-1. Overall Structure of Polarizing Plate with Phase Difference Layer Figure 7 is a schematic cross-sectional view of a polarizing plate with phase difference layer according to one embodiment of the present invention. The polarizing plate with phase difference layer 200 shown in the illustrated example comprises the polarizing plate 100 described in Section A above and a phase difference layer 120. Therefore, the polarizing plate with phase difference layer 200 has the same shape as the polarizing plate 100. In the polarizing plate with phase difference layer 200, the phase difference layer 120 also functions as a protective layer for the polarizer 10. The phase difference layer 120 is typically laminated onto the polarizing plate 100 (in the illustrated example, the polarizer 10) via a bonding layer (not shown). The bonding layer is a bonding agent layer or an adhesive layer, and from the perspective of workability, an adhesive layer (e.g., an acrylic adhesive layer) is preferably used. Although not shown in the figure, the polarizing plate with a phase difference layer may also have another protective layer (not shown) on the phase difference layer 120 side of the polarizer 10 as needed. Furthermore, the polarizing plate with a phase difference layer may also have another phase difference layer (not shown) on the side of the phase difference layer 120 opposite the polarizing plate 100 as needed. The other phase difference layer is typically a so-called positive C plate, whose refractive index characteristics exhibit the relationship nz>nx=ny.

The Re(550) of the phase difference layer 120 is preferably 100 nm to 190 nm, and the Re(450)/Re(550) is preferably greater than 0.8 and less than 1. In addition, the angle formed by the slow axis of the phase difference layer 120 and the absorption axis of the polarizer 10 is preferably 40° to 50°.

B-2. Phase Difference Layer The phase difference layer 120 can have any appropriate optical and/or mechanical properties depending on the intended purpose. The phase difference layer typically has a slow axis. In one embodiment, the angle θ formed between the slow axis of the phase difference layer and the absorption axis of the polarizer 10 is preferably 40° to 50°, more preferably 42° to 48°, and even more preferably approximately 45°, as described above. If the angle θ is within this range, by forming the phase difference layer into a λ/4 plate, as described later, a polarizing plate with a phase difference layer having excellent circular polarization properties (and consequently, excellent anti-reflection properties) can be obtained.

The phase difference layer preferably exhibits a refractive index characteristic exhibiting the relationship nx>ny≧nz. The phase difference layer is typically provided to impart antireflection properties to the polarizing plate, and in one embodiment, it can function as a λ/4 plate. In this case, the in-plane phase difference Re(550) of the phase difference layer is preferably 100nm-190nm, more preferably 110nm-170nm, and even more preferably 130nm-160nm. Furthermore, "ny=nz" here encompasses not only the case where ny and nz are exactly the same, but also the case where they are substantially the same. Therefore, a situation where ny<nz is possible without compromising the effects of the present invention.

The Nz coefficient of the retardation layer is preferably 0.9-3, more preferably 0.9-2.5, even more preferably 0.9-1.5, and most preferably 0.9-1.3. By satisfying this relationship, the resulting polarizing plate with a retardation layer can achieve excellent reflected hue when used in an image display device.

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

The retardation layer preferably comprises a resin having an absolute photoelastic coefficient of 2× ^{10-11 m2} /N or less, more preferably 2.0× ^10-13 m2/ ^N to 1.5 ^{×10-11 m2} /N, and even more preferably 1.0× ^{10-12 m2} /N to 1.2× ^{10-11 m2} /N. When the absolute photoelastic coefficient falls within this range, retardation changes due to shrinkage stress during heating are less likely to occur. As a result, thermal nonuniformity in the resulting image display device can be effectively prevented.

The phase difference layer is typically formed of a stretched film of a resin film. In one embodiment, the thickness of the phase difference layer is preferably 70µm or less, more preferably 45µm to 60µm. If the thickness of the phase difference layer is within the aforementioned range, curling during heating can be effectively suppressed, and curling during bonding can be effectively adjusted. Furthermore, as described later, in an embodiment in which the phase difference layer is formed of a polycarbonate resin film, the thickness of the phase difference layer is preferably 40µm or less, more preferably 10µm to 40µm, and more preferably 20µm to 30µm. By forming the phase difference layer with a polycarbonate resin film having the aforementioned thickness, curling can be suppressed and the anti-bending durability and reflective hue can be improved.

The phase difference layer can be formed from any suitable resin film that satisfies the above-mentioned properties. Representative examples of such resins include polycarbonate resins, polyester carbonate resins, polyester resins, polyvinyl acetal resins, polyarylate resins, cycloolefin resins, cellulose resins, polyvinyl alcohol resins, polyamide resins, polyimide resins, polyether resins, polystyrene resins, and acrylic resins. These resins can be used alone or in combination (e.g., by blending or copolymerization). When the phase difference layer is formed of a resin film exhibiting reverse dispersion wavelength characteristics, a polycarbonate resin or a polyester carbonate resin (hereinafter sometimes simply referred to as a polycarbonate resin) can be suitably used.

Any appropriate polycarbonate resin can be used as the polycarbonate resin as long as the effects of the present invention are achieved. For example, the polycarbonate resin comprises structural units derived from a fluorene-based dihydroxy compound, structural units derived from an isosorbide-based dihydroxy compound, and structural units derived from at least one dihydroxy compound selected from the group consisting of alicyclic diols, alicyclic dimethanols, di-, tri- or polyethylene glycols, and alkylene glycols or spiroglycerol. The polycarbonate resin preferably includes structural units derived from fluorene-based dihydroxy compounds, structural units derived from isosorbide-based dihydroxy compounds, structural units derived from alicyclic dimethanols, and/or structural units derived from di-, tri-, or polyethylene glycol. More preferably, the polycarbonate resin includes structural units derived from fluorene-based dihydroxy compounds, structural units derived from isosorbide-based dihydroxy compounds, and structural units derived from di-, tri-, or polyethylene glycol. The polycarbonate resin may also include structural units derived from other dihydroxy compounds as needed. In addition, the details of the polycarbonate resin that can be suitably used in the present invention are described in, for example, Japanese Patent Publication No. 2014-10291, Japanese Patent Publication No. 2014-26266, Japanese Patent Publication No. 2015-212816, Japanese Patent Publication No. 2015-212817, and Japanese Patent Publication No. 2015-212818, and these descriptions are incorporated herein by reference.

The glass transition temperature of the polycarbonate resin is preferably 110°C to 150°C, more preferably 120°C to 140°C. If the glass transition temperature is too low, heat resistance tends to deteriorate, potentially causing dimensional changes after film formation, or reducing the image quality of the resulting organic EL panel. If the glass transition temperature is too high, film forming stability may deteriorate or the transparency of the film may be compromised. The glass transition temperature can be determined in accordance with JIS K 7121 (1987).

The molecular weight of the aforementioned polycarbonate resin can be expressed as its concentrated viscosity. This viscosity is measured using an Oodel viscometer at 20.0°C ± 0.1°C using methylene chloride as a solvent, after precisely adjusting the polycarbonate concentration to 0.6 g/dL. The lower limit of the concentrated viscosity is generally preferably 0.30 dL/g, preferably 0.35 dL/g or higher. The upper limit of the concentrated viscosity is generally preferably 1.20 dL/g, preferably 1.00 dL/g, and more preferably 0.80 dL/g. If the concentrated viscosity is below the lower limit, the mechanical strength of the molded product may decrease. On the other hand, if the specific viscosity exceeds the upper limit, the fluidity during molding may decrease, which may lead to problems with productivity or moldability.

Commercially available polycarbonate resin films may also be used. Specific examples of commercially available products include "PURE-ACE WR-S," "PURE-ACE WR-W," and "PURE-ACE WR-M" manufactured by Teijin Co., Ltd., and "NRF" manufactured by Nitto Denko Co., Ltd.

The phase difference layer can be obtained, for example, by stretching a film formed from the above-mentioned polycarbonate resin. The method of forming a film from a polycarbonate resin can adopt any appropriate molding method. Specific examples include: compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, casting and coating (such as casting), calendering molding, hot pressing, etc. Extrusion molding or casting and coating is preferred. This is because the smoothness of the obtained film can be improved, thereby obtaining good optical uniformity. The molding conditions can be appropriately set according to the composition or type of the resin used, the desired properties of the phase difference layer, etc. Furthermore, as mentioned above, many polycarbonate resin films are commercially available, so these commercially available films can be directly subjected to the stretching process.

The thickness of the resin film (unstretched film) can be set to any appropriate value depending on the desired thickness of the phase difference layer, the desired optical properties, the stretching conditions described below, etc. It is preferably 50µm to 300µm.

The above-mentioned stretching can adopt any appropriate stretching method and stretching conditions (such as stretching temperature, stretching ratio, stretching direction). Specifically, various stretching methods such as free end stretching, fixed end stretching, free end shrinking, fixed end shrinking, etc. can be used separately, or they can be used simultaneously or successively. Regarding the stretching direction, it can also be carried out along various directions or dimensions such as the length direction, width direction, thickness direction, and oblique direction. The stretching temperature is preferably Tg-30℃~Tg+60℃ relative to the glass transition temperature (Tg) of the resin film, and more preferably Tg-10℃~Tg+50℃.

By appropriately selecting the stretching method and stretching conditions, a retardation film having the desired optical properties (such as refractive index properties, in-plane retardation, and Nz coefficient) can be obtained.

In one embodiment, the retardation film can be produced by uniaxially stretching a resin film or by fixed-end uniaxial stretching. A specific example of fixed-end uniaxial stretching is stretching the resin film in its widthwise (lateral) direction while moving it in its longitudinal direction. The stretching ratio is preferably 1.1x to 3.5x.

In another embodiment, the phase difference film can be produced by continuously stretching a long strip of resin film obliquely in the direction of the aforementioned angle θ relative to the long side direction. By adopting the oblique stretching, a long strip of stretched film having an orientation angle of angle θ relative to the long side direction of the film (having a slow axis in the direction of angle θ) can be obtained. For example, when laminating with a polarizer, a roll-to-roll process can be performed, thereby simplifying the manufacturing steps. In addition, the angle θ can be the angle formed by the absorption axis of the polarizer in the polarizing plate with a phase difference layer and the slow axis of the phase difference layer. As mentioned above, the angle θ is preferably 40°~50°, more preferably 42°~48°, and more preferably about 45°.

The stretching machine used for diagonal stretching can be a tenter-type stretching machine, which, for example, applies conveying forces, stretching forces, or pulling forces at different speeds in the transverse and/or longitudinal directions. Tenter-type stretching machines include transverse single-axis stretching machines and synchronous dual-axis stretching machines. Any suitable stretching machine can be used as long as it can continuously diagonally stretch a long strip of resin film.

By appropriately controlling the left and right speeds in the stretching machine, a phase difference layer (essentially a long strip of phase difference film) having the desired in-plane phase difference and a slow axis in the desired direction can be obtained.

The stretching temperature of the film can vary depending on the desired in-plane retardation value and thickness of the retardation layer, the type of resin used, the film thickness, the stretching ratio, and other factors. Specifically, the stretching temperature is preferably between Tg-30°C and Tg+30°C, more preferably between Tg-15°C and Tg+15°C, and most preferably between Tg-10°C and Tg+10°C. By stretching at these temperatures, a retardation layer with suitable properties can be obtained in the present invention. Tg is the glass transition temperature of the film's constituent material.

C. Image Display Device The aforementioned polarizing plate or polarizing plate with a phase difference layer can be applied to an image display device. Therefore, embodiments of the present invention include an image display device including the aforementioned polarizing plate or polarizing plate with a phase difference layer. 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). The image display device of an embodiment of the present invention includes the polarizing plate described in item A or the polarizing plate with a phase difference layer described in item B on its viewing side. The polarizing plate with a phase difference layer is laminated such that the phase difference layer is on the side of an image display unit (e.g., a liquid crystal unit, an organic EL unit, an inorganic EL unit) (such that the polarizer is on the viewing side). The image display device preferably has a shape other than rectangular. In the aforementioned image display device, the effects brought about by the embodiment of the present invention are very significant. Specific examples of image display devices with different shapes include car dashboards, smart phones, tablet PCs, and smart watches.

EXAMPLES The present invention is described below in detail using examples, but the present invention is not limited to these examples. The measurement methods for various properties are described below. In addition, unless otherwise noted, "parts" and "%" in the examples and comparative examples are by weight.

(1) The thickness was measured using an interferometer film thickness meter (manufactured by Otsuka Electronics Co., Ltd., product name "MCPD-3000"). The wavelength range used for thickness calculation was 400nm~500nm, and the refractive index was set to 1.53. (2) In-plane phase difference (Re) of PVA The in-plane phase difference (Rpva) of PVA at a wavelength of 1000nm was evaluated using a phase difference measuring device (manufactured by Oji Scientific Instruments, Ltd., product name "KOBRA-31X100/IR") for the polarizer (polarizer single body) obtained by peeling off the resin substrate from the polarizer/thermoplastic resin substrate laminate obtained in the embodiment and the comparative example (according to the principle described, the value is the value obtained by subtracting the in-plane phase difference (Ri) of iodine from the total in-plane phase difference at a wavelength of 1000nm). The absorption end wavelength is set to 600 nm. (3) Birefringence (Δn) of PVA The birefringence (Δn) of PVA is calculated by dividing the in-plane phase difference of PVA measured in (2) above by the thickness of the polarizer. (4) Single body transmittance and polarization degree The single body transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc of the polarizer (polarizer single body) obtained from the polarizer/thermoplastic resin substrate laminate obtained in the embodiment and the comparative example after the resin substrate is removed are measured using an ultraviolet-visible spectrophotometer ("V-7100" manufactured by JASCO Corporation). These Ts, Tp, and Tc are the Y values obtained by measuring the 2-degree field of view (light source C) of JIS Z 8701 and performing visual sensitivity correction. 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. Equivalent measurements can be performed using a spectrophotometer such as the "LPF-200" manufactured by Otsuka Electronics Co., Ltd. Equivalent results can be obtained regardless of the spectrophotometer used. (5) Puncture strength (fracture strength per unit thickness) The polarizer was peeled off from the polarizer/thermoplastic resin substrate laminate obtained in the Examples and Comparative Examples and placed on a compression tester equipped with a needle (manufactured by KATO TECH CO., LTD., product name "NDG5" needle penetration test specification). At room temperature (23°C ± 3°C), the polarizer was punctured at a puncture speed of 0.33 cm/s. The strength at which the polarizer broke was taken as the fracture strength. The evaluation value was the fracture strength of 10 test pieces and the average value was adopted. In addition, the needle used had a tip diameter of 1 mmφ and a radius of 0.5. The polarizer to be measured was fixed from both sides of the polarizer using a jig with a circular opening of 11 mm in diameter, and then the needle was pierced into the center of the opening to conduct the test. (6) Orientation function of PVA The polarizer (polarizer unit) obtained from the polarizer/thermoplastic resin substrate laminate obtained in the Examples and Comparative Examples was stripped of the resin substrate. The surface of the polarizer was measured by attenuated total reflection (ATR) using a Fourier transform infrared spectrophotometer (FT-IR) (manufactured by Perkin Elmer, trade name: "Frontier") with polarized infrared light as the measurement light. The microcrystals used to bond the polarizer are made of germanium, and the incident angle of the measurement light is set at 45°. The orientation function is calculated according to the following procedure. The incident polarized infrared light (measurement light) is set to vibrate parallel to the surface of the germanium crystal sample to bond it (s-polarization). The absorbance spectra are measured with the polarizer extended perpendicular (⊥) and parallel (//) to the polarization direction of the measurement light. From the resulting absorbance spectra, the intensity (2941 cm ^-1 ) is calculated, with the intensity (3330 cm ^- 1) serving as a reference. I _⊥ represents the (2941 cm ^-1 intensity) / (3330 cm ^-1 intensity) obtained from the absorbance spectrum when the polarizer is positioned perpendicular (⊥) to the polarization direction of the measurement light. Furthermore, I _// represents the (2941 cm ^- 1 intensity) / (3330 cm ^-1 intensity) obtained from the absorbance spectrum when the polarizer is positioned parallel (//) to the polarization direction of the measurement light. Here, (2941 cm ^-1 intensity) represents the absorbance at 2941 cm-1 at the bottom of the absorbance spectrum, using 2770 cm ^-1 and 2990 cm ^-1 as baselines, and (3330 cm ^-1 intensity) represents the absorbance at 3330 cm- ¹ , using 2990 cm ^-1 and 3650 cm ^{- 1} as baselines. Using the obtained I _⊥ and I _// , the orientation function f is calculated according to Equation 1. Note that f = 1 indicates complete orientation, and f = 0 indicates random orientation. Furthermore, the peak at 2941 cm ^-1 can be considered to be due to the absorption of the (-CH ₂ -) vibration of the PVA main chain in the polarizer. Furthermore, the peak at 3330 cm ^-1 can be considered to be due to the absorption of the hydroxyl vibration of PVA. (Equation 1) f = (3 < cos ² θ > -1)/2 = (1 - D)/[c(2D + 1)] However, when c = (3 cos ² β - 1)/2 and 2941 cm ^-1 is used as described above, β = 90° ⇒ y = -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 (7) Crack Occurrence Rate A surface protection film was temporarily adhered to the protective layer surface of the polarizing plate (or polarizing plate with a phase difference layer) obtained in the embodiment and the comparative example. Then, a separator was temporarily adhered to the adhesive layer of the polarizing plate (or polarizing plate with a phase difference layer). The laminate was cut into approximately 130 mm × approximately 70 mm. At this time, the polarizer is cut so that the absorption axis becomes the short side direction. A U-shaped notch with a width of 5mm, a depth (recess length) of 6.85mm, and a curvature radius of 2.5mm is formed in the center of the short side of the cut laminate. The U-shaped notch is formed by end milling. The outer diameter of the end mill is 4mm, the feed speed is 500mm/minute, the number of rotations is 35000rpm, the cutting amount and the number of cutting times are 0.2mm/time for rough cutting and 0.1mm/time for fine cutting, totaling 2 times. The separation piece is peeled off from the laminate with the U-shaped notch formed and attached to a glass plate (thickness 1.1mm) through an acrylic adhesive layer. Finally, the surface protective film is peeled off to obtain a test sample consisting of a protective layer/polarizer/adhesive layer/glass plate (or protective layer/polarizer/adhesive layer/retardation layer/adhesive layer/glass plate). This sample is subjected to a thermal shock test, which involves 300 cycles of maintaining the sample at -40°C for 30 minutes followed by maintaining the sample at 85°C for 30 minutes. The sample is then visually inspected for the presence of L-shaped cracks after the test. This evaluation is performed using three polarizing plates (or polarizing plates with retardation layers), and the number of polarizing plates (or polarizing plates with retardation layers) that exhibit cracks (substantially L-shaped cracks) is evaluated.

[Example 1] 1. Preparation of Polarizers: A long, amorphous polyethylene terephthalate (PET) film (thickness: 100µm) with a water absorption of 0.75% and a Tg of approximately 75°C was used as the thermoplastic resin substrate. One side of the resin substrate was subjected to a corona treatment (treatment conditions: 55W min/ ^m² ). 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 resin composed of a 9:1 mixture of polyvinyl alcohol (DP4200, saponification degree 99.2 mol%) and acetyl-modified PVA (manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., trade name "GOHSEFIMER Z410"). The PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60°C to form a 13µm-thick PVA resin layer, creating a laminate. The resulting laminate was then subjected to free-end uniaxial stretching to 2.4 times its original length in the longitudinal direction (longitudinal direction) between rollers of varying circumferential speeds in an oven at 130°C (in-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 polarizer was immersed in a dye bath (an aqueous iodine 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, with the concentration adjusted to achieve a single-unit transmittance (Ts) of 40.5% (dyeing treatment). The polarizer was then immersed 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 treatment). 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 (longitudinal direction) between rolls of varying circumferential speeds to a total stretching ratio of 3.0x (in-water stretching: the stretching ratio for the in-water stretching treatment was 1.25x). The laminate was then immersed in a cleaning bath (an aqueous solution of 4 parts by weight of potassium iodide per 100 parts by weight of 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 heating roll 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 during the drying and shrinking process was 2%. Through the above process, a polarizer with a thickness of 7.4µm was formed on the resin substrate.

2. Polarizing Plate Preparation: 15 parts of a biphenyl-skeletal epoxy resin (Mitsubishi Chemical Co., trade name: jER (registered trademark) YX4000) and 10 parts by weight of an oxycyclobutane resin (Toagosei Co., trade name: ARON OXETANE (registered trademark) OXT-221) were dissolved in 73 parts of methyl ethyl ketone to obtain an epoxy resin solution. Two parts of a photocatalytic polymerization initiator (San-Apro Ltd., trade name: CPI (registered trademark)-100P) were added to the resulting epoxy resin solution to obtain a protective layer-forming composition. The resulting protective layer-forming composition is applied directly (i.e., without forming an easy-adhesion layer) to the polarizer surface of the resin substrate/polarizer laminate obtained in step 1 above using a wire rod, and the coated film is dried at 60°C for 3 minutes. Next, a high-pressure mercury lamp is used to irradiate the film with ultraviolet light at a cumulative light intensity of 600mJ/ ^cm2 to form a protective layer. The thickness of the protective layer is 3µm. Next, the resin substrate is peeled off, and an acrylic adhesive layer (15µm thick) is provided on the peeled surface. In this manner, a polarizing plate having a structure of protective layer (photoion-cured layer of epoxy resin)/polarizer/adhesive layer is obtained.

[Examples 2-4] A polarizer (thickness: 7.4µm) was formed on a resin substrate in the same manner as in Example 1, except that dye baths with varying iodine concentrations (weight ratio of iodine to potassium iodide = 1:7) were used. The following procedures were similar to those in Example 1 to produce a polarizing plate consisting of a protective layer (photoion-curable epoxy resin layer), a polarizer, and an adhesive layer.

[Example 5] A polarizer (thickness: 6.7µm) was formed on a resin substrate in the same manner as in Example 1, except that the underwater stretching magnification was set to 1.46x (resulting in a total stretching magnification of 3.5x). The following procedures were repeated in the same manner as in Example 1 to obtain a polarizing plate having a protective layer (photoion-cured epoxy resin layer), polarizer, and adhesive layer.

[Example 6-1] A polarizer (thickness: 6.7µm) was formed on a resin substrate in the same manner as in Example 5, except that a dye bath with different iodine concentrations (weight ratio of iodine to potassium iodide = 1:7) was used. The following procedures were similar to those in Example 1, resulting in a polarizing plate comprising a protective layer (photoion-curable epoxy resin layer), a polarizer, and an adhesive layer.

[Example 6-2] A resin substrate/polarizer laminate (thickness: 6.7µm) was obtained in the same manner as in Example 6-1. Separately, 20 parts of an epoxy resin (manufactured by Mitsubishi Chemical Co., trade name: jER (registered trademark) YX6954BH30, weight-average molecular weight: 36,000, epoxy equivalent: 13,000) was dissolved in 80 parts of methyl ethyl ketone to obtain an epoxy resin solution (20%). This epoxy resin solution was applied to the polarizer surface of the laminate using a wire bar. The coated film was dried at 60°C for 3 minutes to form a protective layer consisting of a cured product of the coated film. The protective layer had a thickness of 3µm. Next, the resin substrate is peeled off, and an acrylic adhesive layer similar to that in Example 1 is applied to the peeled surface. In this manner, a polarizing plate having a structure of protective layer (cured layer of epoxy resin coating film)/polarizer/adhesive layer is obtained.

[Example 6-3] A resin substrate/polarizer (thickness: 6.7µm) laminate was obtained in the same manner as in Example 6-1. A polyurethane aqueous dispersion resin (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: SUPERFLEX SF210) was applied to a thickness of 0.1µm on the polarizer surface of the laminate to form an easy-adhesion layer. Separately, an acrylic resin solution (20%) was prepared by dissolving 20 parts by weight of a 100% polymethyl methacrylate acrylic resin (manufactured by Kusumoto Chemicals Co., Ltd., product name: B-728) in 80 parts by weight of methyl ethyl ketone. The acrylic resin solution was applied to the adhesive layer using a wire bar. The coating was dried at 60°C for 5 minutes to form a protective layer consisting of a cured product of the coating. The protective layer had a thickness of 2µm. A hard coat layer (3µm thick) was further formed on the side of the protective layer opposite the adhesive layer. The hard coat (HC) was formed by mixing 70 parts by weight of dihydroxymethyl-tricyclodecane diacrylate (produced by Kyoei Chemicals, trade name: LIGHT ACRYLATE DCP-A), 20 parts by weight of isoborneol acrylate (produced by Kyoei Chemicals, trade name: LIGHT ACRYLATE IB-XA), 10 parts by weight of 1,9-nonanediol diacrylate (produced by Kyoei Chemicals, trade name: LIGHT ACRYLATE 1.9NA-A), and a photopolymerization initiator (produced by BASF, trade name: IRGACURE 907) by weight, mixed with an appropriate solvent, and the resulting coating liquid was applied to the protective layer surface to a thickness of 3µm after curing. The solvent was then dried and irradiated with UV light using a high-pressure mercury lamp in a nitrogen atmosphere at a cumulative radiation dose of 300mJ/ ^cm² . Finally, the resin substrate was peeled off, and an acrylic adhesive layer similar to that in Example 1 was applied to the peeled surface. Following this procedure, a polarizing plate having a structure consisting of an HC layer/protective layer (cured layer of acrylic resin coating film)/easy-adhesion layer/polarizer/adhesive layer was obtained.

[Examples 7-8] A polarizer (thickness: 6.7µm) was formed on a resin substrate in the same manner as in Example 5, except that dye baths with varying iodine concentrations (weight ratio of iodine to potassium iodide = 1:7) were used. The following procedures were similar to those in Example 1, resulting in a polarizing plate comprising a protective layer (photoion-curable epoxy resin layer), a polarizer, and an adhesive layer.

[Examples 9-12] A polarizer (thickness: 6.2µm) was formed on a resin substrate in the same manner 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). The following procedures were followed in the same manner as in Example 1 to produce a polarizing plate having a protective layer (photoion-curable epoxy resin layer), polarizer, and adhesive layer.

[Examples 13-16] A polarizer (thickness: 6.0µm) was formed on a resin substrate in the same manner as in Example 1, except that the underwater stretching ratio was set to 1.88 (resulting in a total stretching ratio of 4.5), and dye baths with varying iodine concentrations (weight ratio of iodine to potassium iodide = 1:7). The following procedures were similar to those in Example 1 to produce a polarizing plate having a protective layer (photoion-curable epoxy resin layer), polarizer, and adhesive layer.

[Comparative Example 1] A polarizer (5.5µm thick) was formed on a resin substrate in the same manner as in Example 1, except that the underwater stretching magnification was set to 2.29x (resulting in a total stretching magnification of 5.5x). The following procedures were repeated in the same manner as in Example 1 to obtain a polarizing plate having a protective layer (photoion-curable epoxy resin layer), polarizer, and adhesive layer.

[Comparative Example 2-1] A polarizer (thickness: 5.5µm) was formed on a resin substrate in the same manner as in Comparative Example 1, except that a dye bath with a different iodine concentration (weight ratio of iodine to potassium iodide = 1:7) was used. The following procedures were similar to those in Example 1, resulting in a polarizing plate consisting of a protective layer (photoion-curable epoxy resin layer), a polarizer, and an adhesive layer.

Comparative Example 2-2 A polarizing plate having a protective layer (cured epoxy resin coating layer)/polarizer/adhesive layer structure was obtained in the same manner as in Comparative Example 2-1, except that the protective layer was formed using the same epoxy resin solution as in Example 6-2.

Comparative Example 2-3 A polarizing plate having a protective layer (cured layer of acrylic resin coating)/polarizer/adhesive layer structure was obtained in the same manner as in Comparative Example 2-1, except that the protective layer was formed using the same acrylic resin solution as in Example 6-3.

[Comparative Examples 3-4] A polarizer (thickness: 5.5µm) was formed on a resin substrate in the same manner as in Comparative Example 1, except that dye baths with different iodine concentrations (weight ratio of iodine to potassium iodide = 1:7) were used. The following procedures were similar to those in Example 1, resulting in a polarizing plate consisting of a protective layer (photoion-curable epoxy resin layer), a polarizer, and an adhesive layer.

[Example 17] 1. Preparation of a Retardation Film Constituting a Retardation Layer: Polymerization was carried out using a batch polymerization apparatus consisting of two vertical reactors equipped with stirring blades and a reflux cooler controlled at 100°C. The reaction mixture consisted of 29.60 parts by mass (0.046 mol) of bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane, 29.21 parts by mass (0.200 mol) of isosorbide (ISB), 42.28 parts by mass (0.139 mol) of spiroglycerol (SPG), 63.77 parts by mass (0.298 mol) of diphenyl carbonate (DPC), and 1.19× ^10⁻² parts by mass (6.78× ^10⁻⁵ mol) of calcium acetate monohydrate as a catalyst. After the reactor was depressurized and purged with nitrogen, it was heated with a heating medium and stirred when the internal temperature reached 100°C. 40 minutes after the start of the temperature increase, the internal temperature was brought to 220°C. While maintaining this temperature, the pressure was reduced to 13.3 kPa over 90 minutes after reaching 220°C. Phenol vapor, a by-product of the polymerization reaction, was introduced into a 100°C reflux cooler to return a small amount of monomeric components contained in the phenol vapor to the reactor. Uncondensed phenol vapor was then recovered in a 45°C condenser. Nitrogen was introduced into the first reactor to temporarily return it to atmospheric pressure. The oligomerized reaction solution in the first reactor was then transferred to the second reactor. Next, the temperature and pressure in the second reactor were raised and reduced, reaching an internal temperature of 240°C and a pressure of 0.2 kPa over 50 minutes. Polymerization was then continued until the predetermined stirring power was reached. At this point, nitrogen was introduced into the reactor to restore the pressure, and the resulting polyester carbonate resin was extruded into water. The resulting strands were then cut into pellets.

The resulting polyester carbonate resin pellets were vacuum-dried at 80°C for 5 hours. Then, a 130µm thick strip of resin film was produced using a film-forming apparatus equipped with a uniaxial extruder (Toshiba Machine Co., Ltd., cylinder set temperature: 250°C), a T-die (200mm width, set temperature: 250°C), a cooling roll (set temperature: 120-130°C), and a winder. The resulting strip of resin film was then stretched while adjusting to achieve a predetermined retardation, resulting in a 48µm thick retardation film. Stretching conditions were: a widthwise stretching temperature of 143°C and a stretching ratio of 2.8x. The obtained retardation film had a Re(550) of 141 nm, a Re(450)/Re(550) of 0.86, and an Nz coefficient of 1.12.

2. Preparation of a Polarizing Plate with a Retardation Layer A resin substrate/polarizer (thickness: 6.7µm) laminate was obtained in the same manner as in Example 6-1. A protective layer (photoion-cured epoxy resin layer) was formed on the polarizer surface of the laminate in the same manner as in Example 1. Next, the resin substrate was peeled off, and the resulting retardation film (retardation layer) was bonded to the peeled surface via a 5µm-thick acrylic adhesive layer. The slow axis of the retardation layer was bonded at a 45° angle to the absorption axis of the polarizer. Finally, an acrylic adhesive layer similar to that in Example 1 was applied to the surface of the retardation layer. According to the above method, a polarizing plate with a phase difference layer is obtained, which has a structure of protective layer (photoion curing layer of epoxy resin)/polarizer/adhesive layer/phase difference layer/adhesive layer.

[Comparative Example 5] A resin substrate/polarizer (thickness: 5.5µm) laminate was obtained in the same manner as in Comparative Example 2-1. A polarizing plate with a retardation layer was obtained in the same manner as in Example 17, except that this laminate was used, and the structure of the polarizing plate was: protective layer (photoion-cured epoxy resin layer), polarizer, adhesive layer, retardation layer, and adhesive layer.

The polarizing plates or polarizing plates with phase difference layers obtained in the Examples and Comparative Examples were subjected to the evaluations (2) to (7) above. The results are listed in Table 1.

[Table 1]

As is apparent from Table 1, the polarizing plate and the polarizing plate with a phase difference layer of the embodiment have suppressed the occurrence of cracks in the irregularly shaped processed portion (U-shaped notch portion).

In addition, Figures 8 to 10 show the relationship between the monomer transmittance of the polarizer obtained in the embodiment and the comparative example and the Δn of PVA, the in-plane phase difference or the orientation function. As shown in Figures 8 and 10, it can be seen that even if the birefringence, in-plane phase difference or orientation function are of the same degree (in terms of the same degree of orientation), when the monomer transmittance is high, cracks are still likely to occur in the irregularly processed part. For example, when Δn is around 35 (× ^10-3 ) in Figure 8, if the monomer transmittance is greater than about 44.2%, it will become unsatisfactory to equation (1), and as a result, cracks will occur as shown in Comparative Example 4. Therefore, it can be seen that in order to effectively suppress the occurrence of cracks in the irregularly processed part, it is important to adjust not only the orientation degree of the PVA resin but also the monomer transmittance (in terms of the adsorption amount of the dichroic substance). Furthermore, it can be seen that the polarizer that satisfies formula (1), formula (2) and/or formula (3) has been properly adjusted and can appropriately suppress the occurrence of cracks in the irregularly processed part.

Industrial Applicability The polarizing plate of this invention can be used in image display devices, particularly those with irregular shapes, such as automotive dashboards, smartphones, tablet PCs, and smart watches.

10: Polarizer 20: Protective layer 100: Polarizer 120: Retardation layer 200: Polarizer with retardation layer (laminated structure) G1-G4: Guide rollers R1-R6: Transport rollers

Figure 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. Figure 2 is a schematic top view illustrating an example of a non-uniform shape or a non-uniformly processed portion of a polarizing plate according to an embodiment of the present invention. Figure 3 is a schematic top view illustrating a modified example of a non-uniform shape or a non-uniformly processed portion of a polarizing plate according to an embodiment of the present invention. Figure 4 is a schematic top view illustrating another modified example of a non-uniform shape or a non-uniformly processed portion of a polarizing plate according to an embodiment of the present invention. Figure 5 is a schematic top view illustrating another modified example of a non-uniform shape or a non-uniformly processed portion of a polarizing plate according to an embodiment of the present invention. Figure 6 is a schematic diagram illustrating an example of a drying and shrinking process using heated rollers in a method for manufacturing a polarizing element that can be used in a polarizing plate according to an embodiment of the present invention. Figure 7 is a schematic cross-sectional view of a polarizing plate with a retardation layer according to an embodiment of the present invention. Figure 8 is a graph showing the relationship between the single-unit transmittance of polarizers produced in the Examples and Comparative Examples and the birefringence of the PVA-based resin. Figure 9 is a graph showing the relationship between the single-unit transmittance of polarizers produced in the Examples and Comparative Examples and the in-plane retardation of the PVA-based resin film. Figure 10 is a graph showing the relationship between the single-unit transmittance of polarizers produced in the Examples and Comparative Examples and the orientation function of the PVA-based resin.

Claims (15)

A polarizing plate having a polarizer and a protective layer disposed on at least one side of the polarizer; the polarizer has an irregular shape other than a rectangle; the protective layer is formed of a resin film having a thickness of 10µm or less; the polarizer has a single-element transmittance of 40.0% or more and a polarization degree of 99.0% or more; the polarizer has a puncture strength of 30gf/µm or more; the polarizer is formed of a polyvinyl alcohol-based resin film containing a dichroic substance, and when the single-element transmittance is x% and the birefringence of the polyvinyl alcohol-based resin film is y, the following formula (1) is satisfied: y＜-0.011x+0.525　　　　　(1). As claimed in claim 1, the polarizing plate, wherein the polarizer is composed of a polyvinyl alcohol resin film containing a dichroic substance, and when the monomer transmittance is x% and the in-plane phase difference of the polyvinyl alcohol resin film is znm, satisfies the following formula (2): z＜-60x+2875　　　　　　　　(2). As claimed in claim 1, the polarizing plate is composed of a polyvinyl alcohol resin film containing a dichroic substance, and when the monomer transmittance is x% and the orientation function of the polyvinyl alcohol resin film is f, the following formula (3) is satisfied: f＜-0.018x+1.11　　　　(3). A polarizing plate as claimed in any one of claims 1 to 3, wherein the thickness of the polarizer is less than 10µm. A polarizing plate as claimed in any one of claims 1 to 3, wherein the aforementioned irregular shape is selected from the group consisting of: a through hole, a V-notch, a U-notch, a recess having a shape approximately boat-shaped when viewed from above, a rectangular recess having a shape approximately bathtub-shaped when viewed from above, an R-shaped recess having a shape approximately bathtub-shaped when viewed from above, and a combination thereof. The polarizing plate of claim 5, wherein the radius of curvature of the U-shaped notch is less than 5 mm. The polarizing plate according to any one of claims 1 to 3, wherein the resin film comprises at least one resin selected from epoxy resins and (meth)acrylic resins. In the polarizing plate of any one of claims 1 to 3, the resin film is composed of a photo-cured epoxy resin, and the softening temperature of the resin film is above 100°C. In the polarizing plate of any one of claims 1 to 3, the resin film is formed by curing a coating film of an organic solvent solution of an epoxy resin, and the softening temperature of the resin film is above 100°C. In the polarizing plate of any one of claims 1 to 3, the resin film is formed by curing a coating film of an organic solvent solution of a thermoplastic (meth)acrylic resin, and the softening temperature of the resin film is above 100°C. The polarizing plate of claim 10, wherein the thermoplastic (meth) acrylic resin comprises at least one 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. A polarizing plate with a phase difference layer, comprising the polarizing plate of any one of claims 1 to 11 and a phase difference layer; wherein the phase difference layer is disposed on the side of the polarizer opposite to the side on which the protective layer is disposed. The polarizing plate with a phase difference layer as claimed in claim 12, wherein the Re(550) of the phase difference layer is 100 nm to 190 nm, and the Re(450)/Re(550) is greater than 0.8 and less than 1; and the angle formed by the slow axis of the phase difference layer and the absorption axis of the polarizer is 40° to 50°. The polarizing plate with a phase difference layer according to claim 12 or 13, wherein the phase difference layer is laminated on the polarizing plate via an adhesive layer. An image display device comprises the polarizing plate of any one of claims 1 to 11 or the polarizing plate with a phase difference layer of any one of claims 12 to 14.