Polarizing plate and polarizing plate with retardation layer

Abstract

Provided is a polarizing plate that is very thin but has excellent adhesion and curve followability. The polarizing plate of the present application includes a polarizing member and protective layers disposed on both surfaces of the polarizing member, the protective layers including an epoxy resin having an aromatic skeleton and a glycol skeleton, the epoxy resin having a glass transition temperature of 40°C or lower, and the polarizing plate having an elongation of 1.40 mm or more in a puncture test.

Description

Technical Field

[0001] This invention relates to polarizing plates and polarizing plates with phase retardation layers. Background Technology

[0002] In image display devices (e.g., liquid crystal displays, organic EL displays), due to their image formation methods, a polarizing plate is usually disposed on at least one side of the display unit. In recent years, image display devices have been progressing towards thinner and more flexible designs, and consequently, there is a strong desire for thinner polarizing plates. However, if conventional thin polarizing plates are applied to flexible image display devices, problems arise such as reduced polarizing plate adhesion and decreased polarizing plate conformity to curved surfaces.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2015-210474 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] The present invention was made to solve the above-mentioned problems, and its main objective is to provide a polarizing plate that is very thin but has excellent adhesion and excellent surface following properties.

[0008] Solution for solving the problem

[0009] The polarizing plate of the present invention includes a polarizing element and a protective layer disposed on both sides of the polarizing element. The protective layer includes an epoxy resin having an aromatic backbone and a glycol backbone. The glass transition temperature of the epoxy resin is below 40°C, and the elongation of the polarizing plate during a puncture test is above 1.40 mm.

[0010] In one embodiment, the polarizing element is made of a polyvinyl alcohol-based resin film containing a dichroic substance, wherein the orientation function of the polyvinyl alcohol-based resin is 0.30 or less.

[0011] In one embodiment, the protective layer is composed of a photocationically cured epoxy resin or a solidified coating of an organic solvent solution of the epoxy resin.

[0012] In one embodiment, the total thickness of the polarizing plate is 20 μm or less.

[0013] In one embodiment, the puncture strength of the polarizing plate is 300g or more.

[0014] In one embodiment, the glass transition temperature of the above-mentioned protective layer is above 0°C.

[0015] In another aspect of the present invention, a polarizing plate with a phase retardation layer is provided. The polarizing plate with a phase retardation layer includes the phase retardation layer, the aforementioned polarizing element, and the aforementioned protective layer.

[0016] The effects of the invention

[0017] According to the present invention, the protective layer disposed on both sides of the polarizer comprises an epoxy resin having an aromatic backbone and a glycol backbone, wherein the glass transition temperature of the epoxy resin is below 40°C, thereby obtaining a polarizer plate that is very thin but has excellent adhesion and excellent surface following properties. Attached Figure Description

[0018] Figure 1 This is a cross-sectional schematic diagram of a polarizing plate according to one embodiment of the present invention. Detailed Implementation

[0019] A. Overview of polarizing plates

[0020] Figure 1 This is a cross-sectional schematic diagram of a polarizing plate according to one embodiment of the present invention. The polarizing plate 100 shown in the figure includes a polarizing element 10 and protective layers 20 and 30 disposed on both sides of the polarizing element 10. When the polarizing plate 100 is applied to an image display device, it can be disposed on the visual recognition side of the display unit, or on the side opposite to the visual recognition side (back side). The polarizing plate can be in the form of a strip or a sheet. If the polarizing plate is in the form of a strip, it is preferable that it be wound into a roll.

[0021] Typically, the polarizing plate has an adhesive layer as the outermost layer on one side, which can be attached to the display unit. If necessary, a surface protective film and / or a carrier film can be temporarily adhered to the polarizing plate in a peelable manner to reinforce and / or support it. When the polarizing plate includes an adhesive layer, spacers are temporarily adhered to the surface of the adhesive layer in a peelable manner to protect the adhesive layer until actual use and to allow the polarizing plate to be rolled up.

[0022] In embodiments of the present invention, the protective layer comprises an epoxy resin having an aromatic backbone and a glycol backbone, wherein the glass transition temperature of the epoxy resin is below 40°C. With this configuration, a polarizing plate with excellent adhesion and surface following properties can be achieved.

[0023] The protective layer is preferably composed of a photocationically cured epoxy resin having an aromatic backbone and a glycol backbone, or a solidified coating film of an organic solvent solution of the epoxy resin. With this configuration, the protective layer can be made very thin (e.g., 10 μm or less). Furthermore, the protective layer can be formed directly on the polarizing element (i.e., without the aid of an adhesive layer or bonding agent). According to embodiments of the present invention, as described above, the protective layer is very thin, and the adhesive layer or bonding agent can be omitted, thus enabling an extremely thin total thickness of the polarizing plate. In addition, the adhesion between the polarizing element 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 even more preferably 12 μm or less. The total thickness of the polarizing plate can, for example, be 4 μm or more.

[0024] The elongation of the polarizing plate during the puncture test is 1.40 mm or more, preferably 1.60 mm or more. By making the elongation of the polarizing plate within such a range during the puncture test, a polarizing plate with excellent sealing performance and excellent surface following performance can be obtained.

[0025] In embodiments of the present invention, the puncture strength of the polarizing plate is preferably 300g or more, more preferably 340g or more. When the puncture strength of the polarizing plate is within such a range, a polarizing plate with excellent sealing performance and surface following properties can be obtained.

[0026] In embodiments of the present invention, the polarizing plate can be extremely thin, as described above. Therefore, it can be suitably applied to flexible image display devices. More preferably, the image display device has a curved shape (essentially a curved display screen) and / or is flexible or bendable. Specific 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). Of course, the above description does not preclude the application of the polarizing plate of the present invention to conventional image display devices.

[0027] The polarizing element and protective layer will be explained in detail below.

[0028] B. Polarizing components

[0029] As a polarizing element, any suitable polarizing element can be used. A typical polarizing element is composed of a PVA-based resin film containing dichroic substances. The resin film forming the polarizing element can be, for example, a single-layer resin film or a laminate of two or more layers.

[0030] Specific examples of polarizing elements composed of a single-layer resin film include those formed by applying dyeing and stretching treatments based on dichroic substances such as iodine and dichroic dyes to hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films; dehydrated PVA products; and dehydrochlorinated polyvinyl chloride products, as well as polyene-oriented films. Preferably, from the perspective of superior optical properties, polarizing elements obtained by dyeing PVA films with iodine and then uniaxially stretching them are used.

[0031] The aforementioned iodine-based dyeing is performed, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. Stretching can be performed after dyeing or during dyeing. Alternatively, dyeing can be performed after stretching. Depending on the needs, the PVA-based film may undergo swelling treatment, crosslinking treatment, cleaning treatment, drying treatment, etc. For example, by immersing the PVA-based film in water for washing before dyeing, not only can stains and anti-blocking agents on the surface of the PVA-based film be removed, but the PVA-based film can also swell, thereby preventing uneven dyeing.

[0032] The aforementioned polarizing element is representative of those that can be manufactured using a laminate of two or more layers. As a specific example of a polarizing element obtained using a laminate, a polarizing element obtained using a resin substrate and a PVA-based resin layer coated on the resin substrate can be cited. A polarizing element obtained using a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate is manufactured, for example, by coating a PVA-based resin solution onto a resin substrate, allowing it to dry, forming a PVA-based resin layer on the resin substrate, thus obtaining a laminate of the resin substrate and the PVA-based resin layer; stretching and dyeing the laminate to form a polarizing element from the PVA-based resin layer. In this embodiment, it is preferable to form a polyvinyl alcohol-based resin layer comprising a halide and a polyvinyl alcohol-based resin on one side of the resin substrate. Stretching is representative of immersing the laminate in an aqueous boric acid solution for stretching. Furthermore, stretching preferably also includes air stretching the laminate at a high temperature (e.g., 95°C or higher) before stretching in the aqueous boric acid solution. The total stretch ratio of the above-mentioned laminate is preferably 5.0 times or more, and more preferably 5.5 times or more, relative to the original length of the laminate. Hereinafter, the embodiment of the present invention in which the polarizing element is obtained by such operation will be referred to as Embodiment A. Details of the manufacturing method of such a polarizing element are described, for example, in Japanese Patent Application Publication No. 2012-73580 (Japanese Patent No. 5414738) and Japanese Patent No. 6470455. The entire contents of these publications are incorporated herein by reference.

[0033] In one embodiment of the present invention, the total stretching ratio of the above-mentioned laminate is preferably 3.0 to 4.5 times the original length of the laminate, which is significantly smaller than usual. Even with such a total stretching ratio, a polarizer with acceptable optical properties can be obtained by combining the addition of halides and drying shrinkage treatment. Furthermore, in embodiments of the present invention, it is preferable that the stretching ratio of air-assisted stretching is greater than that of stretching in boric acid water. More specifically, the ratio of the stretching ratio of air-assisted stretching to the stretching ratio of water stretching (water stretching / air-assisted stretching) is preferably 0.4 to 0.9, more preferably 0.5 to 0.8. By making such a configuration, a polarizer with acceptable optical properties can be obtained even with a small total stretching ratio. Moreover, the laminate is preferably subjected to a drying shrinkage treatment, which is performed by heating while conveying the laminate along the length direction, thereby shrinking it by more than 2% in the width direction. In one embodiment, the method for manufacturing a polarizer includes sequentially performing an air-assisted stretching treatment, a dyeing treatment, a water stretching treatment, and a drying shrinkage treatment on the laminate. By introducing assisted stretching, the crystallinity of PVA-based resin can be improved even when coating a thermoplastic resin with PVA-based resin, resulting in high optical properties. Furthermore, by simultaneously improving the orientation of the PVA-based resin beforehand, problems such as decreased orientation and dissolution during subsequent dyeing and stretching processes when immersed in water can be prevented, further achieving high optical properties. Moreover, when the PVA-based resin layer is immersed in liquid, compared to when the PVA-based resin layer does not contain halogens, the disorder of polyvinyl alcohol molecule orientation and the reduction of orientation can be suppressed. This improves the optical properties of polarizers obtained through processes such as dyeing and underwater stretching where the laminate is immersed in liquid. Furthermore, by shrinking the laminate in the width direction through a drying shrinkage treatment, optical properties can be further improved. The resulting resin substrate / polarizer laminate can be used directly (i.e., the resin substrate can be used as a protective layer for the polarizer), or the resin substrate can be peeled off from the resin substrate / polarizer laminate, and any suitable protective layer for the desired purpose can be laminated on the peeled surface for use. Hereinafter, the embodiment of the present invention in which the polarizer is obtained by such operation will be referred to as Embodiment B.

[0034] The thickness of the aforementioned polarizing element 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 polarizing element very thin as described above, it is possible to achieve a thinner polarizing plate. Furthermore, thermal shrinkage can be minimized.

[0035] The aforementioned polarizing element preferably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The polarizing element obtained in Embodiment A preferably has a single-cell transmittance of 42.0% to 46.0%, more preferably 44.5% to 46.0%. The polarization degree of the polarizing element is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more. The polarizing element obtained in Embodiment B preferably has a single-cell transmittance of 40.0% or more, more preferably 41.0% or more. The upper limit of the single-cell transmittance can be, for example, 49.0%. The single-cell transmittance of the polarizing element in Embodiment B is, for example, 40.0% to 45.0%. The polarization degree of the polarizing element obtained in Embodiment B preferably is 99.0% or more, more preferably 99.4% or more. The upper limit of the polarization degree can be, for example, 99.999%. The polarization degree of the polarizing element in Embodiment B is, for example, 99.0% to 99.9%.

[0036] The orientation function (f) of the PVA-based resin constituting the polarizing element obtained in Embodiment B above 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, acceptable monomer transmittance and / or polarization may not be obtained.

[0037] For the orientation function (f), for example, using a Fourier transform infrared spectrometer (FT-IR), polarized light is used as the measurement light, and the value is determined by attenuated total reflection (ATR). Specifically, germanium is used to seal the microcrystals of the polarizer, the incident angle of the measurement light is set to 45°, and the incident polarized infrared light (measurement light) is s-polarized light that vibrates parallel to the plane of the sample sealing the germanium crystal. The measurement is performed with the stretching direction of the polarizer parallel and perpendicular to the polarization direction of the measurement light, and the absorbance spectrum at 2941 cm⁻¹ is used. -1 The strength is calculated using the following formula. Here, the strength I is the value of 3330 cm³. -1 2941 cm, used as a reference peak -1 / 3330cm -1 The value of f. It should be noted that f=1 indicates complete orientation, and f=0 indicates random orientation. Additionally, 2941cm is considered... -1 The peak is due to the absorption caused by the vibration of the PVA main chain (-CH2-) in the polarizer.

[0038] f = (3 <cos 2 θ>-1) / 2

[0039] = (1-D) / [c(2D+1)]

[0040] = -2×(1-D) / (2D+1)

[0041] in,

[0042] c=(3cos 2 β-1) / 2, 2941cm -1 Under the condition of vibration, β=90°.

[0043] θ: Angle of the molecular chain relative to the stretching direction

[0044] β: The angle of the transition dipole moment relative to the molecular chain axis

[0045] D = (I ⊥ ) / (I / / (In this case, the more oriented the PVA molecule, the larger D becomes.)

[0046] I ⊥ : Measure the absorption intensity when the polarization direction of the light is perpendicular to the stretching direction of the polarizer.

[0047] I / / : Determine the absorption intensity when the polarization direction of the light is parallel to the stretching direction of the polarizer.

[0048] In the polarizing element obtained in Embodiment B described above, the PVA-based resin constituting the PVA-based resin film (essentially a polarizing element) preferably comprises an acetyl-modified PVA-based resin. With this configuration, a polarizing element having the desired puncture strength can be obtained. When the total PVA-based resin is set to 100% by weight, the amount of the acetyl-modified PVA-based resin is preferably 5% to 20% by weight, more preferably 8% to 12% by weight.

[0049] C. Protective layer

[0050] The protective layer comprises an epoxy resin having an aromatic backbone and a diol backbone.

[0051] C-1. Epoxy resin

[0052] The protective layer is preferably composed of a photocationically cured epoxy resin having an aromatic backbone and a glycol backbone, or a solidified coating film of an organic solvent solution of the epoxy resin. By including the epoxy resin having an aromatic backbone and a glycol backbone in the protective layer, a polarizing plate with excellent adhesion and excellent surface following properties, despite being very thin, can be obtained. Furthermore, the protective layer is more preferably a photocationically cured epoxy resin having an aromatic backbone and a glycol backbone. Hereinafter, the composition of the protective layer will be specifically described, followed by an explanation of the characteristics of the protective layer.

[0053] Examples of aromatic skeletons in the aforementioned epoxy resins include bisphenol A type skeletons, bisphenol F type skeletons, and biphenyl skeletons. More specifically, examples include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, biphenyl type epoxy resins, epoxy resins containing naphthalene rings, epoxy resins having a diene-based skeleton, phenolic varnish type resins, cresol varnish type epoxy resins, triphenylmethane type epoxy resins, aliphatic epoxy resins, and copolymer epoxy resins of aliphatic and aromatic epoxy resins. Among these, bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, biphenyl type epoxy resins, and epoxy resins containing naphthalene rings are preferred, and bisphenol A type epoxy resins, bisphenol F type epoxy resins, epoxy resins containing naphthalene rings, and biphenyl type epoxy resins are even more preferred.

[0054] The aforementioned diol skeleton preferably comprises an aliphatic skeleton having 2 to 6 carbon atoms. More specifically, examples include 1,4-butanediol, 1,6-hexanediol, 1,4-naphthodiol, and 1,6-naphthodiol, among which 1,4-butanediol and 1,6-hexanediol are preferred.

[0055] The glass transition temperature (Tg) of the aforementioned 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. When the glass transition temperature (Tg) of the epoxy resin is within such a range, a polarizing plate with excellent adhesion and excellent surface following properties can be obtained. On the other hand, if the glass transition temperature (Tg) of the epoxy resin is lower than 0°C, there is a concern that the epoxy resin may become sticky.

[0056] In embodiments of the present invention, epoxy resin can be used in combination with other resins. That is, mixtures or copolymers of epoxy resin and other resins can be used for molding the protective layer. Examples of other resins include styrene-based resins, polyethylene, polypropylene, polyamide, polyphenylene sulfide, polyetheretherketone, polyester, polysulfone, polyphenylene ether, polyacetal, polyimide, polyetherimide, and other thermoplastic resins. The types and amounts of resins used in combination can be appropriately determined according to the purpose and desired properties of the resulting film.

[0057] When epoxy resin and other resins are used in combination, the epoxy resin content is preferably 50% to 100% by weight, more preferably 60% to 100% by weight, further preferably 70% to 100% by weight, and particularly preferably 80% to 100% by weight, relative to the total amount of epoxy resin and other resins. If the content is less than 50% by weight, there is a concern that the heat resistance of the protective layer and sufficient adhesion to the polarizing element may not be achieved.

[0058] C-2. Curing agent

[0059] Epoxy resin can be cured by using it in conjunction with any suitable curing agent. As the curing agent, any suitable curing agent capable of curing epoxy resin can be used. In one embodiment, the curing agent comprises a photocationic polymerization initiator. By comprising a photocationic polymerization initiator, a protective layer can be formed as a cationic polymer cured product. As the photocationic polymerization initiator, any suitable compound that can be used to cure epoxy resin having an aromatic backbone and a glycol backbone by irradiation with light such as ultraviolet light can be used. Only one photocationic polymerization initiator can be used, or two or more can be used in combination.

[0060] Examples of photocationic polymerization initiators 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-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]sulfide bis[4-(diphenylsulfonyl)phenyl]-Fe-hexafluorophosphate, and diphenyliodonium hexafluoroantimonate. Photocationic polymerization initiators of the triphenylsulfonium salt hexafluoroantimonate type and the diphenyliodonium salt hexafluoroantimonate type are preferred.

[0061] Commercially available products can be used as photocationic polymerization initiators. Examples of commercially available products include SP-170 (manufactured by ADEKA), CPI-101A (manufactured by SAN-APRO), WPAG-1056 (manufactured by Wako Pure Chemical Industries, Ltd.), and WPI-116 (manufactured by Wako Pure Chemical Industries, Ltd.), which are triphenylsulfonium salt-based hexafluoroantimonate types.

[0062] The content of the photocationic polymerization initiator is preferably 0.1 to 3 parts by weight, more preferably 0.25 to 2 parts by weight, relative to 100 parts by weight of epoxy resin. When the content of the photocationic polymerization initiator is less than 0.1 parts by weight, sometimes even when irradiated with light (ultraviolet light), it will not cure sufficiently.

[0063] C-3. Composition and characteristics of the protective layer

[0064] The protective layer, as described above, comprises an epoxy resin having an aromatic backbone and a glycol backbone. Furthermore, the protective layer is preferably composed of a photocationically cured epoxy resin having an aromatic backbone and a glycol backbone, or a solidified coating film of an organic solvent solution of the epoxy resin. With such a cured or solidified material, the thickness can be exceptionally thin compared to an extruded film. The thickness of the protective layer is preferably 10 μm or less, more preferably 7 μm or less, further preferably 5 μm or less, and particularly preferably 3 μm or less. The thickness of the protective layer can, for example, be 1 μm or more. The protective layer, being a cured epoxy resin having an aromatic backbone and a glycol backbone, exhibits excellent adhesion to the polarizing element. Therefore, even with the thickness described above, the polarizing element can be protected to the same extent as with a protective layer using a conventional film.

[0065] The protective layer (a cured epoxy resin with an aromatic and glycol backbone) may contain any suitable additives depending on the purpose. Specific examples of additives include: ultraviolet absorbers; leveling agents; hindered phenolic, phosphorus, and sulfur-based antioxidants; light stabilizers, weather stabilizers, and heat stabilizers; reinforcing materials such as glass fiber and carbon fiber; near-infrared absorbers; flame retardants such as tris(dibromopropyl) phosphate, triallyl phosphate, and antimony oxide; antistatic agents such as anionic, cationic, and nonionic surfactants; colorants such as inorganic pigments, organic pigments, and dyes; organic or inorganic fillers; resin modifiers; organic and inorganic fillers; plasticizers; lubricants; antistatic agents; flame retardants; etc. Additives are usually added to the solution during the formation of the protective layer. The type, quantity, combination, and amount of additives can be appropriately determined according to the purpose.

[0066] D. Polarizing plate with phase retardation layer

[0067] The polarizing plate described in item C above can be provided as a laminate with other optical thin films and / or optical components. In one embodiment, the polarizing plate can be provided as a laminate with a phase retardation film (a polarizing plate with a phase retardation layer). Therefore, the present invention includes a polarizing plate with a phase retardation layer having the above-described polarizing plate. The polarizing plate with a phase retardation layer according to the embodiments of the present invention includes the above-described polarizing plate and a phase retardation layer. The optical characteristics (e.g., refractive index characteristics, in-plane phase retardation (Re), thickness-direction phase retardation (Rth), wavelength dispersion characteristics), quantity, combination, and arrangement order of the phase retardation layer can be appropriately set according to the purpose.

[0068] Example

[0069] The present invention will now be described in detail through examples, but the present invention is not limited to these examples. The methods for measuring each characteristic are as follows. It should be noted that, unless otherwise specified, "parts" and "%" in the examples are based on weight.

[0070] (1) Puncture test

[0071] The polarizing plates or polarizing elements obtained in the examples or comparative examples were placed in a compression testing machine (manufactured by KATO TECH CO.,LTD., product name "NDG5", needle penetration force testing specification) equipped with needles, and punctured with a load of 5 kg at room temperature (23℃±3℃). The elongation (mm) and strength (g) at the time of fracture of the polarizing plate or polarizing element were calculated.

[0072] (2) Thickness

[0073] The thickness of the polarizing plate or polarizing element obtained in the examples or comparative examples was measured using a micro gauge (manufactured by PEACOCK, product name "DG-205", micro gauge holder (product name "pds-2")).

[0074] (3) Glass transition temperature (Tg)

[0075] After the protective layer obtained in the examples or comparative examples was cut into strips, the results were measured using a viscoelastic spectrometer (manufactured by SIINano Technology Inc., product name "DMS6100") under the conditions of a temperature range of -80℃ to 150℃, a heating / cooling rate of 2℃ / min, and a frequency of 1Hz.

[0076] (4) Fit

[0077] Test pieces (50mm × 50mm) were cut from the polarizing plates obtained in the examples and comparative examples. These test pieces were formed with two sides facing both the direction perpendicular to the absorption axis of the polarizer and the direction of the absorption axis. Adhesive was applied to the polarizer-side surface of the test piece, which was then attached to a glass plate. Next, slits were cut into the protective layer (solidified coating) side surface using a cutting tool in a 10 × 10 checkerboard pattern, and adhesive tape (manufactured by Sekisui Chemicals Co., Ltd.) was attached to the surface. The adhesive tape was then peeled off, and the number of peeled checkerboard patterns out of 100 was evaluated.

[0078] Good: The number of chessboard squares is 50 or more.

[0079] Defect: The number of chessboard squares is less than 50

[0080] (5) Surface following property

[0081] A jig, assuming to be the corner of a smartphone, is made using acrylic resin. The polarizing plate obtained in the examples and comparative examples is stretched by hand following the bending portion, and the polarizing element is visually evaluated to determine whether wrinkles or cracks occur.

[0082] Good: No wrinkles, cracks, or fissures detected.

[0083] Defects: Wrinkles, cracks, and fissures are confirmed.

[0084] <Example 1>

[0085] 1. Fabrication of a laminate of polarizing element / resin substrate

[0086] As the resin substrate, a strip-shaped amorphous polyethylene terephthalate (PET) copolymer film (thickness: 100 μm) with a water absorption rate of 0.75% and a Tg of approximately 75 °C was used. One side of the resin substrate was subjected to corona treatment.

[0087] A PVA aqueous solution (coating solution) was prepared by adding 13 parts by weight of potassium iodide to 100 parts by weight of a PVA-based resin composed of polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Mitsubishi Chemical Corporation, trade name "GOHSEFIMER Z410") at a ratio of 9:1.

[0088] The above-mentioned PVA aqueous solution is coated on 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.

[0089] The resulting laminate was subjected to unidirectional stretching at the free end to 2.4 times its original length between rollers with different circumferential speeds in an oven at 130°C (air-assisted stretching treatment).

[0090] Next, the laminate is immersed in an insoluble bath (an aqueous solution of boric acid prepared by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insoluble treatment).

[0091] Next, the concentration was adjusted in a dyeing bath at a liquid temperature of 30°C (an iodine aqueous solution prepared by mixing iodine and potassium iodide in a weight ratio of 1:7 relative to 100 parts by weight of water) to make the monomer transmittance (Ts) of the final polarizer 41.5% ± 0.1% and then immersed for 60 seconds (dyeing treatment).

[0092] Next, immerse the sample in a crosslinking bath at 40°C (a boric acid aqueous solution prepared by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid relative to 100 parts by weight of water) for 30 seconds (crosslinking treatment).

[0093] Subsequently, the laminate was immersed in a boric acid aqueous solution (boric acid concentration 4.0 wt%, potassium iodide 5 wt%) at a liquid temperature of 70°C and subjected to unidirectional stretching (water stretching treatment) in the longitudinal direction (length direction) between rollers with different circumferential speeds at a total stretch ratio of 5.5 times.

[0094] Subsequently, the laminate was immersed in a cleaning bath at a liquid temperature of 20°C (an aqueous solution of 4 parts by weight of potassium iodide mixed with 100 parts by weight of water) (cleaning treatment).

[0095] Subsequently, it was dried in an oven maintained at 90°C and then contacted with SUS heated rollers with a surface temperature maintained at 75°C for approximately 2 seconds (drying shrinkage treatment). The width-direction shrinkage rate of the laminate based on the drying shrinkage treatment was 5.2%.

[0096] This process forms a 5μm thick polarizing element on a resin substrate, creating a laminate of the polarizing element and the resin substrate. Hereinafter, this polarizing element will be referred to as polarizing element A.

[0097] 2. Preparation of the protective layer forming composition

[0098] 30 parts of an epoxy resin (manufactured by Mitsubishi Chemical Corporation, "YX7105") having an aromatic backbone and a glycol backbone were dissolved in 67.6 parts of methyl ethyl ketone to obtain an epoxy resin solution. 2.4 parts of a photocationic polymerization initiator (manufactured by SAN-APRO Corporation, trade name: CPI (registered trademark)-100P) were added to the obtained epoxy resin solution to obtain a protective layer forming composition.

[0099] 3. Fabrication of polarizing plates

[0100] The protective layer composition obtained in step 2 is applied to the surface of the polarizer of the polarizing plate obtained above using a wire rod, and the coating film is dried at 60°C for 3 minutes. Then, a high-pressure mercury lamp is used to accumulate light at a concentration of 600 mJ / cm². 2 The protective layer is formed by irradiating the material with ultraviolet light. The thickness of the protective layer is 2μm to 3μm, and the glass transition temperature (Tg) is 31℃. Hereinafter, this protective layer will be referred to as protective layer A.

[0101] This process yields a laminate consisting of a protective layer A, a polarizing element A, and a resin substrate. The resin substrate of this laminate is then peeled off, and a protective layer A is formed on the side of the polarizing element opposite to the protective layer using the same method. This process yields a polarizing plate consisting of a protective layer A, a polarizing element A, and a protective layer A. The polarizing plate has an elongation of 1.44 mm, a strength of 344 g, and a thickness of 11 μm. The obtained polarizing plate was evaluated according to (4) and (5) above. The results are shown in Table 1.

[0102] <Example 2>

[0103] 1. Fabrication of a laminate of polarizing element / resin substrate

[0104] As the thermoplastic resin substrate, a long strip of amorphous polyethylene terephthalate (PET) copolymer (thickness: 100 μm) with a water absorption rate of 0.75% and a Tg of approximately 75 °C was used. One side of the resin substrate was subjected to corona treatment (treatment conditions: 55 W·min / m). 2 ).

[0105] A PVA aqueous solution (coating solution) was prepared by adding 13 parts by weight of potassium iodide to 100 parts by weight of a PVA-based resin composed of polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z410") in a ratio of 9:1.

[0106] The above-mentioned PVA aqueous solution is coated on 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.

[0107] The resulting laminate was subjected to unidirectional stretching at the free end to 2.4 times its original length between rollers with different circumferential speeds in an oven at 130°C (air-assisted stretching treatment).

[0108] Next, the laminate is immersed in an insoluble bath (an aqueous solution of boric acid prepared by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insoluble treatment).

[0109] Next, the concentration was adjusted in a dyeing bath at a liquid temperature of 30°C (an iodine aqueous solution prepared by mixing iodine and potassium iodide in a weight ratio of 1:7 relative to 100 parts by weight of water) so that the monomer transmittance (Ts) of the final polarizer was 41.6%, and the sample was immersed for 60 seconds (dyeing treatment).

[0110] Next, immerse the sample in a crosslinking bath at 40°C (a boric acid aqueous solution prepared by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid relative to 100 parts by weight of water) for 30 seconds (crosslinking treatment).

[0111] Subsequently, the laminate was immersed in a boric acid aqueous solution (boric acid concentration 4.0 wt%, potassium iodide 5.0 wt%) at a liquid temperature of 62°C and unidirectionally stretched along the longitudinal direction (length direction) between rollers with different circumferential speeds, with a total stretch ratio of 3.0 times (water stretching treatment: the stretch ratio in the water stretching treatment is 1.25 times).

[0112] Subsequently, the laminate was immersed in a cleaning bath at a liquid temperature of 20°C (an aqueous solution of 4 parts by weight of potassium iodide mixed with 100 parts by weight of water) (cleaning treatment).

[0113] Subsequently, it is dried in an oven maintained at 90°C and contacted with a SUS heated roller maintained at 75°C for approximately 2 seconds (drying shrinkage treatment). The shrinkage rate in the width direction of the laminate based on the drying shrinkage treatment is 2%. This process forms a polarizing element with a thickness of 6.0 μm on a resin substrate. Hereinafter, this polarizing element will be referred to as polarizing element B. The orientation function of the resulting polarizing element is 0.15.

[0114] The polarizing element was prepared by the method described above. Except for this, the operation was the same as in Example 1 to obtain a polarizing plate having a protective layer A / polarizing element B / protective layer A. The polarizing plate had an elongation of 1.66 mm, a strength of 415 g, and a thickness of 12 μm. The obtained polarizing plate was used for evaluation in (4) and (5) above. The results are shown in Table 1.

[0115] (Comparative Example 1)

[0116] 1. Preparation of the protective layer forming composition

[0117] 15 parts of an epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: jER (registered trademark) YX4000) with a biphenyl backbone were dissolved in 83.8 parts of methyl ethyl ketone to obtain an epoxy resin solution. 1.2 parts of a photocationic polymerization initiator (manufactured by SAN-APRO Corporation, trade name: CPI (registered trademark)-100P) were added to the obtained epoxy resin solution to obtain a protective layer forming composition. Hereinafter, the protective layer formed by this protective layer forming composition will be referred to as protective layer B. The glass transition temperature (Tg) of protective layer B is 106°C. The protective layer forming composition was prepared by the above method, except that the procedure was the same as in Example 1, to obtain a polarizing plate having a structure of protective layer B / polarizer A / protective layer B. The polarizing plate had an elongation of 1.17 mm, a strength of 256 g, and a thickness of 11 μm. The obtained polarizing plate was evaluated in (4) and (5) above. The results are shown in Table 1.

[0118] (Comparative Example 2)

[0119] Polarizing element B was obtained using the same method as in Example 2. Otherwise, a polarizing plate with a structure of protective layer B / polarizing element B / protective layer B was obtained using the same method as in Comparative Example 1. The polarizing plate had an elongation of 1.26 mm, a strength of 337 g, and a thickness of 12 μm. The obtained polarizing plate was subjected to the evaluation described in (4) and (5) above. The results are shown in Table 1.

[0120] (Comparative Example 3)

[0121] A protective layer A was provided only on one side of the polarizer A. Otherwise, the process was the same as in Example 1 to obtain a polarizing plate having a protective layer A and a polarizer A. The elongation of the polarizing plate was 1.35 mm when punctured from the protective layer side and less than 1.00 mm when punctured from the polarizer side. The strength of the polarizing plate was 285 g when punctured from the protective layer side and less than 100 g when punctured from the polarizer side. Furthermore, the thickness of the polarizing plate was 8 μm. The obtained polarizing plate was subjected to the evaluations described in (4) and (5) above. The results are shown in Table 1.

[0122] (Comparative Example 4)

[0123] Polarizing element A was fabricated using the same method as in Example 1, without a protective layer. The polarizing element had an elongation of 1.00 mm or less, a strength of 100 g or less, and a thickness of 5 μm. The resulting polarizing element was evaluated in (4) and (5) above. The results are shown in Table 1.

[0124] (Comparative Example 5)

[0125] Polarizing element B was fabricated using the same method as in Example 2, without a protective layer. The polarizing element had an elongation of 1.38 mm, a strength of 267 g, and a thickness of 6 μm. The resulting polarizing element was evaluated in (4) and (5) above. The results are shown in Table 1.

[0126] (Comparative Example 6)

[0127] An acrylic film (20 μm thick, glass transition temperature (Tg) 123 °C, hereinafter referred to as protective layer C) was used as the protective layer. Otherwise, the procedure was the same as in Example 1 to obtain a polarizing plate having the structure of protective layer C / polarizer A / protective layer C. The polarizing plate had an elongation of 1.00 mm or less, a strength of 500 g or more, and a thickness of 45 μm. The obtained polarizing plate was subjected to the evaluation described in (4) and (5) above. The results are shown in Table 1.

[0128] (Comparative Example 7)

[0129] A protective layer C was formed only on one side of polarizer A. Otherwise, the procedure was the same as in Comparative Example 6 to obtain a polarizing plate with a protective layer C on polarizer A. The polarizing plate had an elongation of 1.00 mm or less, a strength of 500 g or more, and a thickness of 25 μm. The obtained polarizing plate was evaluated in (4) and (5) above. The results are shown in Table 1.

[0130] [Table 1]

[0131]

[0132] Comparative Example 3(1) shows the results of the puncture test performed from the protective layer side, and (2) shows the results of the puncture test performed from the polarizer side.

[0133] <Evaluation>

[0134] As can be clearly seen from Table 1, the polarizing plates with the configurations of Examples 1 and 2 have excellent adhesion and excellent surface following properties.

[0135] Industrial availability

[0136] The polarizing plate of the present invention can be appropriately used in image display devices. Examples of image display devices include portable devices such as portable information terminals (PDAs), smartphones, mobile phones, watches, digital cameras, and portable game consoles; office automation (OA) equipment such as computer monitors, laptops, and copiers; household electrical appliances such as cameras, televisions, and microwave ovens; in-vehicle equipment such as rearview monitors, monitors for in-vehicle navigation systems, and car audio systems; display equipment such as digital signage and information displays for commercial shops; security equipment such as surveillance displays; and nursing and medical equipment such as nursing monitors and medical monitors.

[0137] Explanation of reference numerals in the attached figures

[0138] 10 polarizers

[0139] 20 protective layers

[0140] 30 protective layers

[0141] 100 polarizing plate

Claims

1. A polarizing plate comprising a polarizing element and protective layers disposed on both sides of the polarizing element. The protective layer comprises an epoxy resin having an aromatic backbone and a glycol backbone, wherein the glass transition temperature of the epoxy resin is below 40°C. The polarizing plate elongates at least 1.40 mm during the puncture test. The protective layer is composed of a photocationically cured epoxy resin or a solidified coating of an organic solvent solution of the epoxy resin.

2. The polarizing plate according to claim 1, wherein, The polarizing element is made of a polyvinyl alcohol-based resin film containing dichroic substances, wherein the orientation function of the polyvinyl alcohol-based resin is 0.30 or less.

3. The polarizing plate according to claim 1 or 2, wherein the total thickness is less than 20 μm.

4. The polarizing plate according to claim 1 or 2, wherein its puncture strength is 300g or more.

5. The polarizing plate according to claim 1 or 2, wherein, The glass transition temperature of the protective layer is above 0°C.

6. A polarizing plate with a phase difference layer, comprising: a phase difference layer, a polarizing element according to any one of claims 1 to 5, and a protective layer.

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