Polarizing plate and polarizing plate with retardation layer

Abstract

To provide a polarizing plate which is excellent in adhesion and curved surface followability despite its very small thickness.SOLUTION: A polarizing plate includes a polarizer and protective layers provided on both surfaces of the polarizer. The protective layers contain an epoxy resin having an aromatic skeleton and a diol skeleton. The epoxy resin has a glass transition temperature of 40°C or less and the amount of elongation of 1.40 mm or more during a penetrating test.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polarizing plate and a polarizing plate with a retardation layer.

Background Art

[0002] In an image display device (for example, a liquid crystal display device, an organic EL display device), in many cases, a polarizing plate is disposed on at least one side of a display cell due to its image forming method. In recent years, the image display device has been becoming thinner and more flexible, and along with this, a strong demand for thinning of the polarizing plate has also arisen. However, when a conventional thin polarizing plate is applied to a flexible image display device, there is a problem that the adhesion of the polarizing plate decreases and the followability of the polarizing plate to a curved surface decreases.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention has been made to solve the above-described conventional problems, and its main object is to provide a polarizing plate that is excellent in adhesion and excellent in curvature followability despite being very thin.

Means for Solving the Problems

[0005] The polarizing plate of the present invention includes a polarizer and protective layers disposed on both surfaces of the polarizer, the protective layer includes an epoxy resin having an aromatic skeleton and a diol skeleton, its glass transition temperature is 40° C. or lower, and the elongation amount during a piercing test of the polarizing plate is 1.40 mm or more. In one embodiment, the polarizer is composed of a polyvinyl alcohol-based resin film containing a dichroic substance, and the orientation function is 0.30 or lower. In one embodiment, the protective layer is composed of a photocationic polymerization cured product of the epoxy resin or a solidified product of a coating film of an organic solvent solution of the epoxy resin. In one embodiment, the total thickness of the polarizing plate is 20 μm or less. In one embodiment, the piercing strength of the polarizing plate is 300 g or more. In one embodiment, the glass transition temperature of the protective layer is 0°C or higher. In another aspect of the present invention, a polarizing plate with a retardation layer is provided. This polarizing plate with a retardation layer includes a retardation layer, the polarizer, and the protective layer.

Advantages of the Invention

[0006] According to the present invention, the protective layers disposed on both sides of the polarizer contain an epoxy resin having an aromatic skeleton and a diol skeleton, and the glass transition temperature thereof is 40°C or lower. Thus, a polarizing plate that is very thin, has excellent adhesion, and has excellent curvature followability can be obtained.

Brief Description of the Drawings

[0007]

Figure 1

Embodiments for Carrying Out the Invention

[0008] A. Schematic of the Polarizing Plate FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 in the illustrated example has a polarizer 10 and protective layers 20 and 30 disposed on both sides of the polarizer 10. When the polarizing plate 100 is applied to an image display device, it may be disposed on the viewing side of the display cell or on the side opposite to the viewing side (back side). The polarizing plate may be in a long strip shape or in a sheet form. When the polarizing plate is in a long strip shape, preferably, it can be wound into a roll.

[0009] Typically, the polarizing plate has an adhesive layer as the outermost layer on one side and can be attached to the display cell. If necessary, a surface protection film and / or a carrier film are removably temporarily attached to the polarizing plate to reinforce and / or support the polarizing plate. When the polarizing plate includes an adhesive layer, a separator is removably temporarily attached to the surface of the adhesive layer to protect the adhesive layer until actual use and enable the rolling of the polarizing plate.

[0010] In an embodiment of the present invention, the protective layer includes an epoxy resin having an aromatic skeleton and a diol skeleton, and its glass transition temperature is 40 °C or lower. With such a configuration, a polarizing plate excellent in adhesion and curvature followability can be realized.

[0011] The protective layer is preferably composed of a photocation-cured product of an epoxy resin having an aromatic skeleton and a diol skeleton, or a solidified product of a coating film of an organic solvent solution of the epoxy resin. With such a configuration, the protective layer can be made very thin (for example, 10 μm or less). Further, the protective layer can be formed directly on the polarizer (that is, without passing through an adhesive layer or an adhesive layer). According to an embodiment of the present invention, since the protective layer is very thin as described above and the adhesive layer or the adhesive layer can be omitted, the total thickness of the polarizing plate can be made extremely thin. Also, the adhesion between the polarizer and the protective layer is excellent. The total thickness of the polarizing plate is preferably 20 μm or less, more preferably 15 μm or less, and still more preferably 12 μm or less. The total thickness of the polarizing plate can be, for example, 4 μm or more.

[0012] The elongation amount of the polarizing plate during the piercing test is 1.40 mm or more, preferably 1.60 mm or more. When the elongation amount of the polarizing plate during the piercing test is within such a range, a polarizing plate excellent in adhesion and curvature followability can be obtained.

[0013] In an embodiment of the present invention, the piercing strength of the polarizing plate is preferably 300 g or more, more preferably 340 g or more. If the piercing strength of the polarizing plate is within such a range, a polarizing plate excellent in adhesion and curvature followability can be obtained.

[0014] In an embodiment of the present invention, the thickness of the polarizing plate can be extremely thin as described above. Therefore, it can be suitably applied to a flexible image display device. More preferably, the image display device has a curved shape (substantially a curved display screen) and / or is bendable or foldable. Specific examples of the image display device include a liquid crystal display device and an electroluminescence (EL) display device (for example, an organic EL display device, an inorganic EL display device). Needless to say, the above description does not prevent the polarizing plate of the present invention from being applied to a normal image display device.

[0015] Hereinafter, the polarizer and the protective layer will be described in detail.

[0016] B. Polarizer As the polarizer, any suitable polarizer can be adopted. Typically, the polarizer is composed of a PVA-based resin film containing a dichroic substance. The resin film forming the polarizer may be, for example, a single-layer resin film or a laminate of two or more layers.

[0017] Specific examples of the polarizer composed of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA)-based films, partially formalized PVA-based films, and ethylene-vinyl acetate copolymer-based partially saponified films, which are subjected to dyeing treatment with a dichroic substance such as iodine or a dichroic dye and stretching treatment, and polyene-based alignment films such as dehydrated products of PVA and dehydrochlorinated products of polyvinyl chloride. Preferably, a polarizer obtained by dyeing a PVA-based film with iodine and uniaxially stretching it is used because of its excellent optical properties.

[0018] The above iodine staining is performed, for example, by immersing a PVA-based film in an aqueous iodine solution. The stretching ratio of the above uniaxial stretching is preferably 3 to 7 times. The stretching may be performed after the staining treatment, or may be performed while staining. Further, it may be stained after stretching. If necessary, the PVA-based film is subjected to a swelling treatment, a crosslinking treatment, a washing treatment, a drying treatment, etc. For example, by immersing the PVA-based film in water and washing it before staining, not only can the dirt on the surface of the PVA-based film and the blocking inhibitor be washed, but also the PVA-based film can be swollen to prevent uneven staining and the like.

[0019] The above polarizer can typically be produced using a laminate of two or more layers. Specific examples of the polarizer obtained using a laminate include a polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate. The polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer formed by coating on the resin substrate can be produced, for example, by 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; stretching and dyeing the laminate to make the PVA-based resin layer a polarizer; The embodiment of the present invention for obtaining a polarizer in this way is hereinafter referred to as Embodiment A. Details of such a method for manufacturing a polarizer are described, for example, in Japanese Patent Application Laid-Open No. 2012-73580 (Patent No. 5414738) and Patent No. 6470455. The entire description of the publication is incorporated herein by reference.

[0020] In one embodiment of the present invention, the total draw ratio of the laminate is preferably 3.0 to 4.5 times the original length of the laminate, which is significantly smaller than normal. Even with such a total draw ratio, a polarizer having acceptable optical properties can be obtained by combining the addition of a halide and a drying shrinkage treatment. Further, in the embodiment of the present invention, preferably, the draw ratio of the air-assisted drawing is larger than the draw ratio of the drawing in boric acid water. More specifically, the ratio of the draw ratio of the air-assisted drawing to the draw ratio of the drawing in water (drawing in water / air-assisted drawing) is preferably 0.4 to 0.9, more preferably 0.5 to 0.8. By adopting such a configuration, a polarizer having acceptable optical properties can be obtained even if the total draw ratio is small. In addition, the laminate is preferably subjected to a drying shrinkage treatment in which it is heated while being conveyed in the longitudinal direction to shrink by 2% or more in the width direction. In one embodiment, the method for manufacturing a polarizer includes subjecting the laminate to an air-assisted drawing treatment, a dyeing treatment, a drawing treatment in water, and a drying shrinkage treatment in this order. By introducing the assisted drawing, even when a PVA-based resin is applied onto a thermoplastic resin, it becomes possible to enhance the crystallinity of the PVA-based resin and achieve high optical properties. At the same time, by enhancing the orientation of the PVA-based resin in advance, problems such as a decrease in the orientation and dissolution of the PVA-based resin when immersed in water in the subsequent dyeing step and drawing step can be prevented, and high optical properties can be achieved. Further, when the PVA-based resin layer is immersed in a liquid, the disorder of the orientation and the decrease in the orientation of polyvinyl alcohol molecules can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. Thereby, the optical properties of the polarizer obtained through treatment steps such as a dyeing treatment and a drawing treatment in water, in which the laminate is immersed in a liquid, can be improved. Further, by shrinking the laminate in the width direction by a drying shrinkage treatment, the optical properties can be improved. The obtained resin substrate / polarizer laminate may be used as it is (that is, the resin substrate may be used as a protective layer of the polarizer), or the resin substrate may be peeled off from the resin substrate / polarizer laminate, and an arbitrary appropriate protective layer according to the purpose may be laminated on the peeled surface and used. Hereinafter, the embodiment of the present invention for obtaining a polarizer in this way is referred to as Embodiment B.

[0021] The thickness of the above polarizer is preferably 1 μm to 12 μm, more preferably 2 μm to 10 μm, and even more preferably 3 μm to 8 μm. By making the thickness of the polarizer extremely thin in this way, it is possible to contribute to the thinning of the polarizing plate. Furthermore, the thermal shrinkage can be made extremely small.

[0022] The above polarizer preferably exhibits absorption dichroism at any wavelength in the range of 380 nm to 780 nm. The single transmittance of the polarizer obtained in the above Embodiment A is preferably 42.0% to 46.0%, more preferably 44.5% to 46.0%. The degree of polarization of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more. The single transmittance of the polarizer obtained in the above Embodiment B is preferably 40.0% or more, more preferably 41.0% or more. The upper limit of the single transmittance can be, for example, 49.0%. The single transmittance of the polarizer is, for example, 40.0% to 45.0% in Embodiment B. The degree of polarization of the polarizer obtained in the above Embodiment B is preferably 99.0% or more, more preferably 99.4% or more. The upper limit of the degree of polarization can be, for example, 99.999%. The degree of polarization of the polarizer is, for example, 99.0% to 99.9% in Embodiment B.

[0023] The orientation function (f) of the PVA-based resin constituting the polarizer obtained in the above Embodiment B is preferably 0.30 or less, more preferably 0.25 or less, even more preferably 0.20 or less, and particularly preferably 0.15 or less. The lower limit of the orientation function can be, for example, 0.05. If the orientation function is too small, an acceptable single transmittance and / or degree of polarization may not be obtained.

[0024] The orientation function (f) is obtained, for example, by using a Fourier transform infrared spectrophotometer (FT-IR), measuring polarization as the measurement light, and performing attenuated total reflection (ATR) measurement. Specifically, germanium is used for the crystallites that are in close contact with the polarizer, the incident angle of the measurement light is set to 45° incidence, and the polarized infrared light (measurement light) to be incident is polarized light (s-polarized light) that vibrates parallel to the surface in contact with the germanium crystal sample. The measurement is carried out with the stretching direction of the polarizer arranged parallel and perpendicular to the polarization direction of the measurement light, and the intensity at 2941 cm -1 is used to calculate according to the following formula. Here, the intensity I uses 3330 cm -1 as the reference peak, and is the value of 2941 cm -1 / 3330 cm -1 . Note that when f = 1, it is completely oriented, and when f = 0, it is random. Also, the peak at 2941 cm -1 is considered to be an absorption caused by the vibration of the main chain (-CH2-) of PVA in the polarizer. f=(3<cos 2 θ>-1) / 2 =(1-D) / [c(2D+1)] =-2×(1-D) / (2D+1) However, c=(3cos 2 β-1) / 2, and in the case of the vibration at 2941 cm -1 , β = 90°. θ: Angle of the molecular chain with respect to the stretching direction β: Angle of the transition dipole moment with respect to the molecular chain axis D=(I ⊥ ) / (I / / ) (in this case, D increases as the PVA molecules are more oriented) I ⊥ : Absorption intensity when the polarization direction of the measurement light and the stretching direction of the polarizer are perpendicular I / / : Absorption intensity when the polarization direction of the measurement light and the stretching direction of the polarizer are parallel

[0025] The polarizer obtained in the above Embodiment B preferably contains a PVA-based resin having an acetoacetyl-modified PVA-based resin as the PVA-based resin constituting the PVA-based resin film (substantially a polarizer). With such a configuration, a polarizer having a desired piercing strength can be obtained. The blending amount of the acetoacetyl-modified PVA-based resin is preferably 5% by weight to 20% by weight, more preferably 8% by weight to 12% by weight, when the total amount of the PVA-based resin is 100% by weight.

[0026] C. Protective layer The protective layer contains an epoxy resin having an aromatic skeleton and a diol skeleton.

[0027] C-1. Epoxy resin The protective layer is preferably composed of a photocationic polymerization cured product of an epoxy resin having an aromatic skeleton and a diol skeleton, or a solidified product of a coating film of an organic solvent solution of the epoxy resin. By including an epoxy resin having an aromatic skeleton and a diol skeleton in the protective layer, a polarizing plate with excellent adhesion and excellent curvature followability can be obtained despite being very thin. Further, the protective layer is more preferably a photocationic polymerization cured product of an epoxy resin having an aromatic skeleton and a diol skeleton. Hereinafter, the constituent components of the protective layer will be specifically described, and then the characteristics of the protective layer will be described.

[0028] Examples of the aromatic skeleton in the above epoxy resin include bisphenol A type skeleton, bisphenol F type skeleton, biphenyl skeleton, etc. More specifically, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenyl type epoxy resin, naphthalene ring-containing epoxy resin, epoxy resin having a dicyclopentadiene skeleton, phenol novolak type resin, cresol novolak type epoxy resin, triphenylmethane type epoxy resin, aliphatic epoxy resin, copolymer epoxy resin of aliphatic epoxy resin and aromatic epoxy resin, etc. are exemplified. Among these, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenyl type epoxy resin, naphthalene ring-containing epoxy resin are preferred, and more preferably bisphenol A type epoxy resin, bisphenol F type epoxy resin, naphthalene ring-containing epoxy resin, biphenyl type epoxy resin are used.

[0029] The above diol skeleton preferably includes an aliphatic skeleton having 2 to 6 carbon atoms. More specifically, 1,4-butanediol, 1,6-hexanediol, 1,4-naphthalenediol, 1,6-naphthalenediol, etc. are exemplified. Among these, 1,4-butanediol and 1,6-hexanediol are preferably used.

[0030] The glass transition temperature (Tg) of the above epoxy resin is 40°C or lower, preferably 35°C or lower. As a result, the Tg of the protective layer is 40°C or lower, preferably 35°C or lower. The lower limit of the glass transition temperature (Tg) of the epoxy resin is preferably 0°C. If the glass transition temperature (Tg) of the epoxy resin is in such a range, a polarizing plate excellent in adhesion and excellent in curvature followability can be obtained. On the other hand, if the glass transition temperature (Tg) of the epoxy resin is less than 0°C, the epoxy resin may be sticky.

[0031] In an embodiment of the present invention, an epoxy resin and another resin may be used in combination. That is, a blend or copolymer of an epoxy resin and another resin may be used for forming a protective layer. Examples of the other resin include thermoplastic resins such as styrene resins, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyether ether ketone, polyester, polysulfone, polyphenylene oxide, polyacetal, polyimide, and polyetherimide. The type and blending amount of the resin used in combination can be appropriately set according to the purpose and properties desired for the obtained film.

[0032] When an epoxy resin and another resin are used in combination, the content of the epoxy resin relative to the total of the epoxy resin and the other resin is preferably 50% by weight to 100% by weight, more preferably 60% by weight to 100% by weight, still more preferably 70% by weight to 100% by weight, and particularly preferably 80% by weight to 100% by weight. If the content is less than 50% by weight, there is a possibility that the heat resistance of the protective layer and sufficient adhesion to the polarizer cannot be obtained.

[0033] C-2. Curing Agent The epoxy resin can be used together with any suitable curing agent to obtain a cured product. As the curing agent, any suitable curing agent capable of curing the epoxy resin can be used. In one embodiment, the curing agent includes a photo cationic polymerization initiator. By including a photo cationic polymerization initiator, a protective layer that is a cationic polymerization cured product can be formed. As the photo cationic polymerization initiator, any suitable compound capable of curing an epoxy resin having an aromatic skeleton and a diol skeleton by light irradiation such as ultraviolet rays can be used. Only one type of photo cationic polymerization initiator may be used, or two or more types may be used in combination.

[0034] Examples of the cationic photoinitiator include triphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluorophosphate, p-(phenylthio)phenyl diphenylsulfonium hexafluoroantimonate, p-(phenylthio)phenyl diphenylsulfonium hexafluorophosphate, 4-chlorophenyl diphenylsulfonium hexafluorophosphate, 4-chlorophenyl diphenylsulfonium hexafluoroantimonate, bis[4-(diphenylsulfonio)phenyl]sulfide bishexafluorophosphate, bis[4-(diphenylsulfonio)phenyl]sulfide bishexafluoroantimonate, (2,4-cyclopentadien-1-yl)[(1-methylethyl)benzene]-Fe-hexafluorophosphate, diphenyliodonium hexafluoroantimonate, and the like. Preferably, a triphenylsulfonium salt-based hexafluoroantimonate type cationic photoinitiator or a diphenyliodonium salt-based hexafluoroantimonate type cationic photoinitiator is used.

[0035] Commercially available products may be used as the cationic photoinitiator. Examples of the commercially available products include SP-170 (manufactured by ADEKA Corporation), CPI-101A (manufactured by San-Apro Ltd.), WPAG-1056 (manufactured by Wako Pure Chemical Industries, Ltd.), which are triphenylsulfonium salt-based hexafluoroantimonate type, and WPI-116 (manufactured by Wako Pure Chemical Industries, Ltd.), which is a diphenyliodonium salt-based hexafluoroantimonate type.

[0036] The content of the cationic photoinitiator is preferably 0.1 to 3 parts by weight, more preferably 0.25 to 2 parts by weight, based on 100 parts by weight of the epoxy resin. When the content of the cationic photoinitiator is less than 0.1 part by weight, it may not be sufficiently cured even when irradiated with light (ultraviolet light).

[0037] C-3. Configuration and Characteristics of the Protective Layer The protective layer contains, as described above, an epoxy resin having an aromatic skeleton and a diol skeleton. Further, the protective layer is preferably composed of a photocationic polymerization cured product of an epoxy resin having an aromatic skeleton and a diol skeleton, or a solidified product of a coating film of an organic solvent solution of the epoxy resin. With such a cured product or solidified product, the thickness can be significantly reduced compared to an extruded film. The thickness of the protective layer is preferably 10 μm or less, more preferably 7 μm or less, still more preferably 5 μm or less, and particularly preferably 3 μm or less. The thickness of the protective layer can be, for example, 1 μm or more. The protective layer, which is a cured product of an epoxy resin having an aromatic skeleton and a diol skeleton, has excellent adhesion to the polarizer. Therefore, even with the above thickness, the polarizer can be protected to the same extent as a conventional protective layer using a film.

[0038] The protective layer (cured product of an epoxy resin having an aromatic skeleton and a diol skeleton) may contain any appropriate additive according to the purpose. Specific examples of the additive include ultraviolet absorbers; leveling agents; antioxidants such as hindered phenol-based, phosphorus-based, and sulfur-based antioxidants; stabilizers such as light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fibers and carbon fibers; near-infrared absorbers; flame retardants such as tris(dibromopropyl) phosphate, triallyl phosphate, and antimony oxide; antistatic agents such as anionic, cationic, and nonionic surfactants; colorants such as inorganic pigments, organic pigments, and dyes; organic fillers or inorganic fillers; resin modifiers; organic fillers and inorganic fillers; plasticizers; lubricants; antistatic agents; flame retardants; and the like. The additive is usually added to the solution during the formation of the protective layer. The type, number, combination, addition amount, etc. of the additive can be appropriately set according to the purpose.

[0039] D. Polarizer with a retardation layer The polarizing plate described in Item C above can be provided as a laminate with other optical films and / or optical members. In one embodiment, the polarizing plate can be provided as a laminate with a retardation film (polarizing plate with a retardation layer). Therefore, the present invention includes a polarizing plate with a retardation layer having the above polarizing plate. The polarizing plate with a retardation layer according to an embodiment of the present invention includes the above polarizing plate and a retardation layer. The optical properties (e.g., refractive index properties, in-plane retardation (Re), retardation in the thickness direction (Rth), wavelength dispersion properties), number, combination, arrangement order, etc. of the retardation layer can be appropriately set according to the purpose.

Examples

[0040] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. The measurement methods for each property are as follows. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

[0041] (1) Puncture test For the polarizing plate or polarizer obtained in the example or comparative example, it was placed on a compression tester equipped with a needle (manufactured by Kato Tech Co., Ltd., product name "NDG5", needle penetration force measurement specification), and punctured at a load of 5 kg in an environment at room temperature (23°C ± 3°C). The elongation rate (mm) and strength (g) when the polarizing plate or polarizer broke were calculated. (2) Thickness For the polarizing plate or polarizer obtained in the example or comparative example, the thickness was measured using a dial gauge (manufactured by PEACOCK Co., Ltd., product name "DG-205", dial gauge stand (product name "pds-2")). (3) Glass transition temperature (Tg) After cutting out the protective layer obtained in the example or comparative example into strips, measurement was performed using a viscoelastic spectrometer (manufactured by SII NanoTechnology Inc., product name "DMS6100") under the conditions of a temperature range of -80°C to 150°C, a heating and cooling rate of 2°C / min, and a frequency of 1 Hz. (4) Adhesion Test pieces (50 mm × 50 mm) were cut out from the polarizing plates obtained in the examples and comparative examples, with two sides facing each other in the direction orthogonal to the absorption axis direction of the polarizer and in the absorption axis direction, respectively. An adhesive was applied to the surface of the test piece on the polarizer side and attached to a glass plate. Next, cuts were made with a cutter knife on the surface of the protective layer (solidified product of the coating film) to form a 10×10 grid, and an adhesive tape (manufactured by Sekisui Chemical Co., Ltd.) was attached to the surface. Then, the adhesive tape was peeled off, and the number of peeled squares out of 100 squares was evaluated. Good: The number of squares is 50 or more. Defective: The number of squares is less than 50. (5) Curvature followability A jig assuming the corner of a smartphone was made of acrylic resin, and the polarizing plates obtained in the examples and comparative examples were made to follow the curved portion and pulled by hand, and it was visually evaluated whether wrinkles, cracks, or crevices occurred in the polarizer. Good: No wrinkles, cracks, or crevices were confirmed. Defective: Wrinkles, cracks, or crevices were confirmed.

[0042] <Example 1> 1. Preparation of a laminate of a polarizer / resin substrate As the resin substrate, an amorphous isophthalic copolymer polyethylene terephthalate film (thickness: 100 μm) in a long strip shape with a water absorption rate of 0.75% and a Tg of about 75°C was used. One side of the resin substrate was subjected to corona treatment. 13 parts by weight of potassium iodide was added to 100 parts by weight of a PVA-based resin obtained by mixing polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Mitsubishi Chemical Corporation, trade name "Gosefimer Z410") in a ratio of 9:1 to prepare a PVA aqueous solution (coating solution). The above PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60°C to form a PVA-based resin layer with a thickness of 13 μm, thereby producing a laminate. The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (lengthwise direction) between rolls with different peripheral speeds in an oven at 130°C with free ends (air-assisted stretching treatment). Next, the laminate was immersed in an insolubilization bath at a liquid temperature of 40°C (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment). Next, the laminate was immersed in a dyeing bath at a liquid temperature of 30°C (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer was 41.5% ± 0.1% (dyeing treatment). Next, the laminate was immersed in a crosslinking bath at a liquid temperature of 40°C (an aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (crosslinking treatment). Thereafter, while immersing the laminate in an aqueous boric acid solution at a liquid temperature of 70°C (boric acid concentration 4.0% by weight, potassium iodide 5% by weight), uniaxial stretching was performed in the longitudinal direction (lengthwise direction) between rolls with different peripheral speeds so that the total draw ratio was 5.5 times (stretching treatment in water). Thereafter, the laminate was immersed in a washing bath at a liquid temperature of 20°C (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) (washing treatment). Thereafter, while drying in an oven maintained at 90°C, it was brought into contact with a SUS heating roll whose surface temperature was maintained at 75°C for about 2 seconds (dry shrinkage treatment). The shrinkage rate in the width direction of the laminate by the dry shrinkage treatment was 5.2%. In this way, a polarizer with a thickness of 5 μm was formed on the resin substrate, and a laminate of the polarizer / resin substrate was produced. Hereinafter, the polarizer is referred to as polarizer A.

[0043] 2. Preparation of the protective layer forming composition 30 parts of an epoxy resin having an aromatic skeleton and a diol skeleton (manufactured by Mitsubishi Chemical Corporation, "YX7105") was dissolved in 67.6 parts of methyl ethyl ketone to obtain an epoxy resin solution. To the obtained epoxy resin solution, 2.4 parts of a photo cationic polymerization initiator (manufactured by San-Apro Ltd., trade name: CPI (registered trademark)-100P) was added to obtain a protective layer forming composition.

[0044] 3. Production of the polarizing plate 2. The protective layer-forming composition obtained in the above was applied to the polarizer surface of the polarizing plate obtained above using a wire bar, and the coating film was dried at 60 °C for 3 minutes. Then, ultraviolet rays were irradiated using a high-pressure mercury lamp so that the integrated light quantity became 600 mJ / cm 2 , and a protective layer was formed. The thickness of the protective layer was 2 μm to 3 μm, and the glass transition temperature (Tg) was 31 °C. Hereinafter, the said protective layer is called protective layer A. In this way, a laminate having a structure of protective layer A / polarizer A / resin substrate was obtained. Further, the resin substrate of the laminate was peeled off, and a protective layer A was formed on the surface of the polarizer opposite to the protective layer in the same manner. In this way, a polarizing plate having a structure of protective layer A / polarizer A / protective layer A was obtained. The elongation rate of the polarizing plate was 1.44 mm, the strength was 344 g, and the thickness was 11 μm. The obtained polarizing plate was subjected to the evaluations in the above (4) and (5). The results are shown in Table 1.

[0045] <Example 2> 1. Preparation of a laminate of a polarizer / resin substrate As a thermoplastic resin substrate, an amorphous isophthalic copolymer polyethylene terephthalate film (thickness: 100 μm) which is long, has a water absorption rate of 0.75%, and a Tg of about 75 °C was used. Corona treatment (treatment conditions: 55 W·min / m 2 ) was performed on one side of the resin substrate. 13 parts by weight of potassium iodide was added to 100 parts by weight of a PVA-based resin in which polyvinyl alcohol (degree of polymerization 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer Z410") were mixed at 9:1 to prepare a PVA aqueous solution (coating solution). The PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60 °C to form a PVA-based resin layer with a thickness of 13 μm, thereby producing a laminate. The obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (lengthwise direction) between rolls with different peripheral speeds in an oven at 130 °C with free ends (air-assisted stretching treatment). Next, the laminate was immersed in an insolubilization bath at a liquid temperature of 40°C (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds (insolubilization treatment). Next, the laminate was immersed in a dyeing bath at a liquid temperature of 30°C (an aqueous iodine solution obtained by mixing iodine and potassium iodide at a weight ratio of 1:7 with respect to 100 parts by weight of water) for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizer was 41.6% (dyeing treatment). Next, the laminate was immersed in a crosslinking bath at a liquid temperature of 40°C (an aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds (crosslinking treatment). Thereafter, while immersing the laminate in an aqueous boric acid solution at a liquid temperature of 62°C (boric acid concentration 4.0% by weight, potassium iodide 5.0% by weight), uniaxial stretching was performed between rolls with different peripheral speeds so that the total stretching magnification in the longitudinal direction (lengthwise direction) was 3.0 times (stretching treatment in water: the stretching magnification in the stretching treatment in water was 1.25 times). Thereafter, the laminate was immersed in a washing bath at a liquid temperature of 20°C (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) (washing treatment). Thereafter, while drying in an oven maintained at 90°C, the laminate was brought into contact with a SUS heating roll maintained at a surface temperature of 75°C for about 2 seconds (dry shrinkage treatment). The shrinkage rate in the width direction of the laminate due to the dry shrinkage treatment was 2%. In this way, a polarizer with a thickness of 6.0 μm was formed on the resin substrate. Hereinafter, the polarizer is referred to as polarizer B. The orientation function of the obtained polarizer was 0.15. A polarizing plate having a structure of protective layer A / polarizer B / protective layer A was obtained in the same manner as in Example 1 except that the polarizer was prepared by the above method. The elongation rate of the polarizing plate was 1.66 mm, the strength was 415 g, and the thickness was 12 μm. The obtained polarizing plate was subjected to the evaluations in (4) and (5) above. The results are shown in Table 1.

[0046] (Comparative Example 1) 1. Preparation of the protective layer forming composition 15 parts of an epoxy resin having a biphenyl skeleton (manufactured by Mitsubishi Chemical Corporation, trade name: jER® YX4000) was dissolved in 83.8 parts of methyl ethyl ketone to obtain an epoxy resin solution. To the obtained epoxy resin solution, 1.2 parts of a photo cationic polymerization initiator (manufactured by San-Apro Ltd., trade name: CPI®-100P) was added to obtain a protective layer forming composition. Hereinafter, the protective layer formed from the protective layer forming composition is referred to as protective layer B. The glass transition temperature (Tg) of protective layer B was 106°C. A polarizing plate having a structure of protective layer B / polarizer A / protective layer B was obtained in the same manner as in Example 1 except that the protective layer forming composition was prepared by the above method. The elongation rate of the polarizing plate was 1.17 mm, the strength was 256 g, and the thickness was 11 μm. The obtained polarizing plate was subjected to the evaluations in (4) and (5) above. The results are shown in Table 1.

[0047] (Comparative Example 2) A polarizing plate having a structure of protective layer B / polarizer B / protective layer B was obtained in the same manner as in Comparative Example 1 except that a polarizer B was obtained in the same manner as in Example 2. The elongation rate of the polarizing plate was 1.26 mm, the strength was 337 g, and the thickness was 12 μm. The obtained polarizing plate was subjected to the evaluations in (4) and (5) above. The results are shown in Table 1.

[0048] (Comparative Example 3) A polarizing plate having a structure of protective layer A / polarizer A was obtained in the same manner as in Example 1 except that the protective layer A was provided only on one side of the polarizer A. The elongation rate of the polarizing plate was 1.35 mm when the piercing test was performed from the protective layer side, and 1.00 mm or less when the piercing test was performed from the polarizer side. The strength of the polarizing plate was 285 g when the piercing test was performed from the protective layer side, and 100 g or less when the piercing test was performed from the polarizer side. Further, the thickness of the polarizing plate was 8 μm. The obtained polarizing plate was subjected to the evaluations in (4) and (5) above. The results are shown in Table 1.

[0049] (Comparative Example 4) A polarizer A was produced in the same manner as in Example 1, and no protective layer was provided. The elongation rate of the polarizer was 1.00 mm or less, the strength was 100 g or less, and the thickness was 5 μm. The obtained polarizer was subjected to the evaluations (4) and (5) above. The results are shown in Table 1.

[0050] (Comparative Example 5) A polarizer B was produced in the same manner as in Example 2, and no protective layer was provided. The elongation rate of the polarizer was 1.38 mm, the strength was 267 g, and the thickness was 6 μm. The obtained polarizer was subjected to the evaluations (4) and (5) above. The results are shown in Table 1.

[0051] (Comparative Example 6) A polarizing plate having a structure of protective layer C / polarizer A / protective layer C was obtained in the same manner as in Example 1, except that an acrylic film (thickness 20 μm, glass transition temperature (Tg) 123 °C, hereinafter referred to as protective layer C) was used for the protective layer. The elongation rate of the polarizing plate was 1.00 mm or less, the strength was 500 g or more, and the thickness was 45 μm. The obtained polarizing plate was subjected to the evaluations (4) and (5) above. The results are shown in Table 1.

[0052] (Comparative Example 7) A polarizing plate having a structure of protective layer C / polarizer A was obtained in the same manner as in Comparative Example 6, except that the protective layer C was formed only on one side of the polarizer A. The elongation rate of the polarizing plate was 1.00 mm or less, the strength was 500 g or more, and the thickness was 25 μm. The obtained polarizing plate was subjected to the evaluations (4) and (5) above. The results are shown in Table 1.

[0053]

Table 1

[0054] <Evaluation> As is clear from Table 1, it can be seen that the polarizing plates having the configurations of Examples 1 and 2 are excellent in adhesion and excellent in curvature followability.

Industrial Applicability

[0055] The polarizing plate of the present invention is suitably used for an image display device. Examples of the image display device include portable devices such as portable information terminals (PDAs), smartphones, mobile phones, watches, digital cameras, and portable game machines; OA devices such as personal computer monitors, notebook personal computers, and copiers; household electrical appliances such as video cameras, televisions, and microwave ovens; in-vehicle devices such as rear monitors, monitors for car navigation systems, and car audio; display devices such as digital signage and monitors for commercial store information; security devices such as monitoring monitors; and care / medical devices such as care monitors and medical monitors.

Explanation of Reference Numerals

[0056] 10 Polarizer 20 Protective layer 30 Protective layer 100 Polarizing plate

Claims

**Claim 1** A polarizer and protective layers disposed on both sides of the polarizer, wherein the protective layer contains an epoxy resin having an aromatic skeleton and a diol skeleton, and the glass transition temperature thereof is 40° C. or lower, and the elongation amount during the piercing test is 1.40 mm or more, A polarizing plate.

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