Polarizing plate

Abstract

[Problem] To provide a novel polarizing plate that inhibits a poor external appearance of a polarizing film due to thermal contraction, and that excels in durability. [Solution] This polarizing plate comprises a polarizing film composed of a polyvinyl alcohol–based resin, and a supporting base material layered on at least one of the surfaces of the polarizing film with a bonding layer therebetween, said supporting base material being light-transmitting, and is characterized in that the bonding layer is composed of a molecular bonding agent that binds the polarizing film and the supporting base material together via a chemical bond.

Description

[Technical Field]

[0001] The present invention relates to a polarizing plate, and more particularly to a polarizing plate formed by laminating a polarizing film made of a polyvinyl alcohol resin and a light-transmitting supporting substrate via a molecular bonding agent. [Background technology]

[0002] Conventionally, a polarizing plate has been known as an optical component that transmits light polarized or wave-polarized in a specific direction. The polarizing plate has a structure in which a polarizing film made of a polyvinyl alcohol resin (PVA polarizing film) is laminated on a translucent support substrate such as glass or quartz via an adhesive. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO13 / 154139 Summary of the Invention [Problem to be solved by the invention]

[0004] The PVA polarizing film used in polarizing plates is a uniaxially stretched polyvinyl alcohol resin film to which iodine or a dichroic dye has been adsorbed and aligned. However, due to its characteristics, PVA polarizing film absorbs light parallel to its absorption axis. This causes a temperature rise in the PVA polarizing film due to the absorbed light energy, which generates shrinkage stress in the stretching direction, resulting in thermal shrinkage. Thermal shrinkage of PVA polarizing film causes appearance deformation (or appearance defects) such as unevenness and wrinkles. In image display devices such as liquid crystal displays, PVA polarizing film with such appearance defects can cause poor image quality and reduced contrast.

[0005] On the other hand, image display devices and the like are required to have high brightness and high resolution, and in recent years, light sources with large or high values ​​of luminous flux, luminous intensity, brightness, light density, etc. When such light sources are used, the light energy absorbed by the PVA polarizing film increases, and the appearance defects due to thermal shrinkage of the PVA polarizing film become more pronounced.

[0006] The present invention has been made in view of the above problems, and an object of the present invention is to provide a new polarizing plate that is excellent in durability and that suppresses the poor appearance caused by the thermal shrinkage of PVA polarizing films. [Means for solving the problem]

[0007] The present inventors conducted extensive research to find a way to prevent poor appearance caused by thermal shrinkage of the polarizing film in a polarizing plate. As a result, they discovered that by using a molecular bonding technique to chemically bond the PVA polarizing film to the supporting substrate, the PVA polarizing film and the supporting substrate can be more firmly adhered to each other, and heat generated in the PVA polarizing film can be efficiently dissipated to the supporting substrate, thereby reducing the thermal load on the PVA polarizing film, thereby completing the present invention.

[0008] According to the present invention, there is provided a polarizing plate comprising a polarizing film made of a polyvinyl alcohol-based resin and a light-transmitting supporting substrate laminated on at least one side of the polarizing film via an adhesive layer, wherein the adhesive layer is made of a molecular adhesive that chemically bonds the polarizing film and the supporting substrate.

[0009] The present invention also provides a method for producing a polarizing plate, comprising the steps of: applying a molecular bonding agent to the surface of a polarizing film made of a polyvinyl alcohol-based resin and / or a light-transmitting supporting substrate; laminating the polarizing film and / or the supporting substrate via the molecular bonding agent present on the surface thereof; and thermocompression bonding the polarizing film and the supporting substrate to chemically bond the polarizing film and the supporting substrate together. [Effects of the Invention]

[0010] In the polarizing plate of the present invention, the PVA polarizing film and the supporting substrate are bonded together by chemical bonding, which reduces the thermal load on the PVA polarizing film and prevents poor appearance due to thermal shrinkage of the PVA polarizing film. Furthermore, in the polarizing plate of the present invention, the PVA polarizing film and the supporting substrate are bonded together by chemical bonding, which firmly adheres the supporting substrate and the polarizing film and prevents thermal shrinkage of the PVA polarizing film, thereby preventing poor appearance due to thermal shrinkage of the PVA polarizing film. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of a polarizing plate of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below. However, the present invention is not limited to the following embodiments, and various embodiments can be made within the scope of the effects of the present invention.

[0013] [Polarizing plate] FIG. 1 shows an example of a polarizing plate of the present invention. The polarizing plate 1 shown in FIG. 1 includes a polarizing film 2 made of a polyvinyl alcohol-based resin and a support substrate 4 laminated on at least one side of the polarizing film 2 via a bonding layer 3. More specifically, the polarizing film 2 and the support substrate 4 are laminated via a bonding layer 3 made of a molecular bonding agent using molecular bonding technology to chemically bond them together. Molecular bonding technology is a technique for chemically bonding components using one or several molecular layers. Polarizing plates bonded using molecular bonding technology have higher thermal conductivity than conventional bonding using intermolecular forces, which can reduce the thermal load on the polarizing film and thereby suppress poor appearance due to thermal shrinkage of the polarizing film. Furthermore, polarizing plates bonded using molecular bonding technology are directly bonded by chemical bonds, which provides stronger adhesion than conventional bonding using intermolecular forces, thereby enabling strong adhesion between the polarizing film and the support substrate, thereby suppressing thermal shrinkage of the polarizing film and suppressing poor appearance. Therefore, polarizing plates bonded using molecular bonding technology have high durability, maintaining the performance of the polarizing film for a long period of time. Although not shown, the other surface of the polarizing film may also be provided with another supporting substrate via a bonding layer made of a molecular bonding agent.

[0014] [Polarizing film] The polarizing film has absorptive dichroism at any wavelength from 380 to 780 nm and is made of a polyvinyl alcohol-based resin film. Examples of polarizing films having absorptive dichroism at any wavelength from 380 to 780 nm include polyvinyl alcohol-based resin films in which iodine and / or a dichroic dye is adsorbed and oriented (H-type polarizing films) and polyvinyl alcohol-based resin films in which light-absorbing vinylene block segments are formed in the polymer by dehydrating a polyvinyl alcohol resin (K-type polarizing films).

[0015] An H-type polarizing film made of a polyvinyl alcohol-based resin having iodine and / or a dichroic dye adsorbed and oriented thereon can be produced, for example, by a method including the steps of uniaxially stretching a polyvinyl alcohol-based resin film, dyeing the polyvinyl alcohol-based resin film with iodine and / or a dichroic dye to adsorb it, crosslinking the polyvinyl alcohol-based resin film having iodine and / or a dichroic dye adsorbed thereon with a crosslinking liquid such as an aqueous boric acid solution, and washing the polyvinyl alcohol-based resin film with water.

[0016] The polyvinyl alcohol resin may be a saponified polyvinyl acetate resin. Examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other monomers copolymerizable with vinyl acetate. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.

[0017] The saponification degree of the polyvinyl alcohol resin is usually 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes can be used. The average polymerization degree of the polyvinyl alcohol resin is usually 1,000 to 10,000, preferably 1,500 to 5,000. The average polymerization degree of the polyvinyl alcohol resin can be determined in accordance with JIS K 6726.

[0018] Such a polyvinyl alcohol-based resin is formed into a film and used as a raw film for a polarizing film. The method for forming the polyvinyl alcohol-based resin into a film is not particularly limited, and known methods are used. The thickness of the polyvinyl alcohol-based raw film is not particularly limited, but it is preferable to use one having a thickness of, for example, 10 to 200 μm.

[0019] The uniaxial stretching of the polyvinyl alcohol-based resin film can be carried out before, simultaneously with, or after dyeing with iodine and / or a dichroic dye. When uniaxial stretching is carried out after dyeing, this uniaxial stretching may be carried out before or during a crosslinking treatment. Moreover, uniaxial stretching may be carried out in these multiple stages. In uniaxial stretching, the film may be uniaxially stretched between rolls with different peripheral speeds, or may be uniaxially stretched using a heated roll. Moreover, the uniaxial stretching may be dry stretching in which stretching is carried out in the air, or wet stretching in which the polyvinyl alcohol-based resin film is stretched in a swollen state using a solvent or water. The stretching ratio is usually 3 to 8 times.

[0020] A method for dyeing a polyvinyl alcohol-based resin film with iodine and / or a dichroic dye may be, for example, a method of immersing the film in an aqueous solution containing iodine and / or a dichroic dye. It is preferable that the polyvinyl alcohol-based resin film be immersed in water before the dyeing treatment.

[0021] As a crosslinking treatment after dyeing, for example, a method of immersing the dyed polyvinyl alcohol-based resin film in an aqueous solution containing boric acid can be mentioned. The crosslinking treatment may be carried out in one step or in multiple steps.

[0022] The water-washing treatment after crosslinking can be carried out, for example, by immersing the dyed and crosslinked polyvinyl alcohol-based resin film in water, spraying it with water as a shower, or using both water and spraying. After the water-washing treatment, the polyvinyl alcohol-based resin film may be dried by a known method.

[0023] A K-type polarizing film made of a polyvinyl alcohol-based resin in which light-absorbing vinylene block segments are formed in the polymer by dehydrating the polyvinyl alcohol-based resin can be produced, for example, by a method including the steps of uniaxially stretching the polyvinyl alcohol-based resin film, dehydrating the polyvinyl alcohol-based resin film, crosslinking the dehydrated polyvinyl alcohol-based resin film with a crosslinking liquid such as an aqueous boric acid solution, and washing the polyvinyl alcohol-based resin film. The raw film is as described above.

[0024] The uniaxial stretching of the polyvinyl alcohol-based resin film can be carried out in various stages. For example, the uniaxial stretching may be carried out before the dehydration treatment, simultaneously with the dehydration treatment, simultaneously with the boric acid crosslinking after the dehydration treatment, or before or after the boric acid crosslinking. The uniaxial stretching may also be carried out in a plurality of these stages. The method of uniaxial stretching is as described above.

[0025] For example, a method for dehydrating a polyvinyl alcohol-based resin film involves exposing the polyvinyl alcohol-based resin film to an acid having a pH of 3 or higher and then heating the exposed film. Specifically, the polyvinyl alcohol-based resin film can be immersed in deionized water for about 1 second to about 5 minutes, and then immersed in an acid having a pH of 3 or higher for a desired time. The polyvinyl alcohol-based resin film can also be exposed to the dehydration catalyst in a different manner. For example, the film can be dipped or immersed in an aqueous dehydration catalyst for a sufficient residence time to allow the catalyst to diffuse into the film.

[0026] The acid used for the dehydration treatment can be any acid that has a pH of 3 or higher and that, under heat or other suitable treatment conditions, can remove hydrogen and oxygen atoms from the hydroxylated portions of the linear polymer to leave conjugated vinylene units. Specific examples include hydrochloric acid, hydrobromic acid, hydroiodic acid, phosphoric acid, and sulfuric acid. These acids may also be diluted with water or alcohols such as methanol.

[0027] After exposing the polyvinyl alcohol-based resin film to the dehydration catalyst, the polyvinyl alcohol-based resin film and the adsorbent catalyst can be heated, thereby converting a portion of the oriented film to the desired dehydration product, polyvinylene. The film can be heated by conductive heating, convection heating, radiation heating, or a combination thereof. For example, the film and catalyst can be passed through a heating oven at a temperature ranging from about 88°C to about 205°C for about a few seconds to about 10 minutes. Alternatively, the film and catalyst can be exposed to microwave radiation heating, laser heating, or radiant infrared heating.

[0028] During the dehydration process, some of the vinyl alcohol polymer in the polyvinyl alcohol resin film is converted into polarizing molecules of poly(vinylene-co-vinyl alcohol) block copolymers. The effect of the dehydration process is to form conjugated polyvinylene blocks from the polyvinyl alcohol blocks. By orienting the PVA matrix in one direction, the transition moment of the conjugated polyvinylene blocks is also oriented, making the material visibly dichroic.

[0029] As a crosslinking treatment after dehydration, for example, a method of immersing the dehydrated polyvinyl alcohol resin film in an aqueous solution containing boric acid can be mentioned. Specifically, the dehydrated polyvinyl alcohol resin film can be brought into contact with an aqueous solution of boric acid with a concentration of 10 to 20% at a temperature of 85 to 95°C.

[0030] The water washing treatment after crosslinking can be carried out, for example, by immersing the crosslinked polyvinyl alcohol-based resin film after dehydration treatment in water, spraying it with water as a shower, or using both water and spraying. After the water washing treatment, the polyvinyl alcohol-based resin film may be dried by a known method.

[0031] The thickness of the polarizing film is not particularly limited, but is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less. The thickness of the polarizing film is usually 1 μm or more, and preferably 3 μm or more.

[0032] [Joining layer] The bonding layer is made of a molecular bonding agent that uses molecular bonding technology to chemically bond the polarizing film and supporting substrate. Molecular bonding technology is a technique for chemically bonding components using one or several molecular layers. For example, the surface of the adherend is converted to a surface with one type of functional group, and bonding is achieved through the bonding of these functional groups.

[0033] The molecular bonding agent preferably contains a triazine derivative having a functional group that chemically bonds the polarizing film and the supporting substrate. The bonding layer made of the molecular bonding agent containing a triazine derivative preferably contains the triazine derivative as a main component. Here, "main component" means that the constituent ratio of the components that make up the bonding layer is 50% by weight or more, preferably 60% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

[0034] The triazine derivative is preferably a compound containing two or more OH groups and / or OH-yielding groups and one triazine ring. The triazine derivative containing two or more OH groups and / or OH-yielding groups and one triazine ring forms a bonding layer in which the OH groups on the surface of the support substrate and / or the OH groups on the surface of the polarizing film are chemically bonded to the OH groups or OH-yielding groups of the triazine derivative by dehydration condensation. Conventionally known compounds can be used as the triazine derivative. The OH groups or OH-yielding groups are preferably alkoxysilyl groups.

[0035] The molecular binder may contain components other than the triazine derivative, such as a crosslinking agent, fine particles, an ultraviolet absorber, an antifoaming agent, a thickener, a dispersant, a surfactant, a catalyst, a lubricant, and an antistatic agent, as long as the effects of the present invention are not impaired.

[0036] The thickness of the bonding layer is not particularly limited, but is, for example, preferably 5 μm to 0.001 μm, more preferably 1 μm to 0.001 μm, even more preferably 0.1 μm to 0.005 μm, and particularly preferably 0.05 μm to 0.01 μm. The thickness of the bonding layer is preferably thin from the viewpoint of efficiently dissipating heat generated in the polarizing film to the outside and suppressing a rise in temperature of the polarizing film. However, if the surface properties of the adherend are poor, OH groups of the triazine derivative present on the surface of the polarizing film and / or supporting substrate or OH groups generated from OH-yielding groups are less likely to come into contact with the other surface, and therefore the thickness may be appropriately designed taking these factors into consideration.

[0037] Although dehydration condensation can also occur between the OH groups on the surface of the support substrate and the OH groups on the surface of the polarizing film, the contact area between the two surfaces is small due to the surface roughness of both materials, resulting in extremely low adhesion. If the thickness of the bonding layer is 0.01 μm or more and 0.05 μm or less, it can fill in the surface roughness of the support substrate and polarizing film, increasing the contact area and improving bonding strength.

[0038] [Supporting base material] The supporting substrate supports the polarizing film, which is fragile and difficult to handle by itself, facilitates its handling, and protects the polarizing film, and is made of a material that is translucent to visible light. Translucency here means a total light transmittance of 80% or more, preferably 85% or more, and more preferably 90% or more. The light transmittance can be measured in accordance with JIS K0115 using a spectrophotometer (V-570 ultraviolet-visible-near-infrared spectrophotometer manufactured by JASCO Corporation).

[0039] Examples of materials that are translucent to visible light include organic materials, inorganic materials, and organic-inorganic hybrid materials. Examples of organic materials include triacetyl cellulose, diacetyl cellulose, polyester resin, polyimide resin, polyamide, polyolefin resins such as polyethylene and polypropylene, cycloolefin resins such as cycloolefin polymers and cycloolefin copolymers, polyethersulfone, polysulfone, polyvinyl chloride, acrylic resin, polycarbonate resin, and urethane resin. Examples of inorganic materials include silicate glass, borosilicate glass, titanium silicate glass, fluoride glass such as zirconium fluoride, fused silica, quartz, sapphire, YAG crystal, fluorite, magnesia, and spinel (MgO·Al2O3). Examples of organic-inorganic hybrid materials include resins made of silsesquioxane derivatives with organic functional groups such as (meth)acryloyl groups.

[0040] From the viewpoint of efficiently dissipating heat generated in the polarizing film to the outside and suppressing thermal shrinkage of the polarizing film, it is preferable that the support substrate laminated on at least one side of the polarizing film has a higher thermal conductivity than the polarizing film. The thermal conductivity is, for example, preferably 0.7 W / mK or higher, more preferably 1 W / mK or higher, and even more preferably 5 W / mK or higher. Examples of such materials include sapphire (thermal conductivity: 40 W / mK) and quartz (thermal conductivity: 8 W / mK).

[0041] The thickness of the support substrate is not particularly limited, and may be appropriately designed so as to facilitate handling of the polarizing film and protect the polarizing film, and is, for example, 10 to 3000 μm, preferably 20 to 1500 μm, and more preferably 30 to 1000 μm.

[0042] Various functional layers may be formed on the surface of the support substrate as needed, such as a conductive layer, an antistatic layer, an antiglare layer, an antifouling layer such as a photocatalyst layer, an antireflection layer, a hard coat layer, an ultraviolet shielding layer, a heat ray shielding layer, an electromagnetic wave shielding layer, and a gas barrier layer.

[0043] [Polarizing plate manufacturing method] Next, a method for manufacturing a polarizing plate will be described. The method for manufacturing a polarizing plate includes the steps of providing a molecular bonding agent on the surface of a polarizing film made of a polyvinyl alcohol-based resin and / or a light-transmitting supporting substrate, laminating the polarizing film and / or the supporting substrate with the molecular bonding agent present on the surface thereof, and thermocompression bonding the polarizing film and the supporting substrate to chemically bond them together.

[0044] <Step 1: Preparation> First, the polarizing film and supporting substrate described above are prepared. The polarizing film and supporting substrate may be either continuous or sheet-like. The surfaces of the polarizing film and supporting substrate may be cleaned as needed, for example, by cleaning with a cleaning agent such as ethanol or acetone. The surfaces of the polarizing film and supporting substrate may be activated as needed, for example, by ultraviolet irradiation, corona discharge treatment, plasma treatment, etc.

[0045] A solution or dispersion of the molecular bonding agent is prepared. The molecular bonding agent may be diluted with a solvent, such as water, alcohol (e.g., methanol, ethanol, isopropanol, ethylene glycol, propylene glycol, cellosolve, or carbitol), ketone (e.g., acetone, methyl ethyl ketone, or cyclohexanone), aromatic hydrocarbons (e.g., benzene, toluene, or xylene), aliphatic hydrocarbons (e.g., hexane, octane, decane, dodecane, or octadecane), esters (e.g., ethyl acetate, methyl propionate, or methyl phthalate), or ethers (e.g., tetrahydrofuran, ethyl butyl ether, or anisole). The triazine derivative content may be appropriately determined taking into account the coating process, and is, for example, 0.0001 to 10 wt%, preferably 0.001 to 3 wt%, and more preferably 0.01 to 2 wt%.

[0046] <Step 2: Application> A molecular bonding agent is provided on the surface of the polarizing film and / or supporting substrate. Specifically, this is achieved by applying a solution containing the molecular bonding agent to the surface of the polarizing film and / or supporting substrate. Thereafter, drying is performed as necessary, and the solvent volatilizes, leaving the molecular bonding agent on the surface of the polarizing film and / or supporting substrate. The application method is not particularly limited, and known methods can be used, such as wire bar coating, dipping, spraying, spin coating, roll coating, gravure coating, air knife coating, curtain coating, slide coating, extrusion coating, and die coating. The drying method is not particularly limited, and known methods can be used.

[0047] <Process 3: Lamination> After providing a molecular adhesive on the surface of the polarizing film and / or the supporting substrate, these are laminated via the molecular adhesive present on the surface of the polarizing film and / or the supporting substrate. Specifically, this is achieved by laminating the polarizing film and / or the supporting substrate so that the surfaces coated with the solution containing the molecular adhesive face each other.

[0048] <Process 4: Heat compression bonding> The polarizing film and the supporting substrate are then thermocompression bonded to each other to integrally bond them together through chemical bonding, specifically by heating the polarizing film while applying a pressing force toward the supporting substrate, heating the supporting substrate while applying a pressing force toward the polarizing film, or heating the polarizing film and the supporting substrate while applying a pressing force to each of them.

[0049] The pressing force is a pressing force that allows OH groups of the triazine derivative present on the surface of the polarizing film and / or the supporting substrate, or OH groups generated from OH-yielding groups, to contact the other surface. The pressing force is, for example, preferably 0.01 to 50 MPa, more preferably 0.1 to 20 MPa, even more preferably 0.5 to 10 MPa, and particularly preferably 0.5 to 5 MPa. The application time is, for example, 0.1 to 200 minutes. As a result, even if the polarizing film or the supporting substrate has minute irregularities on its surface, the polarizing film or the supporting substrate deforms accordingly, and the OH groups of the triazine derivative present on these surfaces reach and bond to the other surface. In other words, the polarizing film and the supporting substrate are firmly bonded together through chemical bonding (reaction) by the triazine derivative. The heating temperature is a temperature that promotes the chemical reaction of the triazine derivative. The heating temperature is, for example, 30 to 300°C, preferably 50 to 250°C, more preferably 70 to 200°C, and even more preferably 80 to 150°C. [Example]

[0050] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0051] Example 1 First, a 25 μm-thick iodine-based polarizing film laminated with a surface protection film was prepared. The surface opposite the surface protection film was washed with ethanol and dried, and then the surface was subjected to a corona discharge treatment. A 0.7 mm-thick quartz substrate was also prepared. The quartz substrate was ultrasonically cleaned in acetone (10 minutes), dried, and then the surface was subjected to a corona discharge treatment. Next, an ethanol solution containing 0.1 wt% of a triazine derivative (product name: MB1015 aqueous solution, manufactured by Io Chemical Research Institute Co., Ltd.) was applied to the corona discharge-treated surface of the polarizing film by spin coating (application amount: 2 ml, spin rotation speed: 3000 rpm), and then dried at room temperature, thereby providing the triazine derivative on the surface of the polarizing film. Similarly, an ethanol solution containing 0.1 wt% of a triazine derivative (product name: MB1015 Aqueous Solution, manufactured by Io Chemical Laboratory Co., Ltd.) was spin-coated (2 ml, 3000 rpm) onto the corona-discharge-treated surface of a quartz substrate, which was then placed in a hot-air drying oven and dried at 80°C for 10 minutes to form a triazine derivative on the surface of the quartz substrate. The triazine-derivative-coated surfaces of the polarizing film and the quartz substrate were then overlapped and thermocompressed using a heat press (pressure: 5 MPa, temperature: 120°C, time: 20 minutes) to form a polarizing plate (surface protection film / iodine-based polarizing film / bonding layer / quartz substrate).

[0052] Example 2 First, a 25 μm-thick iodine-based polarizing film laminated with a surface protective film was prepared. The surface opposite the surface protective film was washed with ethanol and dried, and then the surface was subjected to a corona discharge treatment. A 0.7 mm-thick sapphire substrate was also prepared. The sapphire substrate was ultrasonically cleaned in acetone (10 minutes), dried, and then the surface was subjected to a corona discharge treatment. Next, an ethanol solution containing 0.1 wt% of a triazine derivative (product name: MB1015 aqueous solution, manufactured by Io Chemical Research Institute Co., Ltd.) was applied to the corona discharge-treated surface of the polarizing film by spin coating (application amount: 2 ml, spin rotation speed: 3000 rpm), and then dried at room temperature, thereby providing the triazine derivative on the surface of the polarizing film. Similarly, an ethanol solution containing 0.1 wt% of a triazine derivative (product name: MB1015 aqueous solution, manufactured by Io Chemical Laboratory Co., Ltd.) was spin-coated onto the corona-discharge-treated surface of a sapphire substrate (coating amount: 2 ml, spin speed: 3000 rpm), and then placed in a hot-air drying oven and dried at 80°C for 10 minutes to provide the triazine derivative on the surface of the sapphire substrate.The triazine-derivative-provided surfaces of the polarizing film and the sapphire substrate were then overlapped and thermocompressed using a heat press (pressure: 5 MPa, temperature: 120°C, time: 20 minutes) to produce a polarizing plate (surface protection film / iodine-based polarizing film / bonding layer / sapphire substrate).

[0053] (Comparative Example 1) First, a 25 μm-thick iodine-based polarizing film laminated with a surface protective film was prepared. The surface of the polarizing film opposite the surface protective film was washed with ethanol and dried, and then the surface was subjected to a corona discharge treatment. A 0.7 mm-thick quartz substrate was also prepared. The quartz substrate was ultrasonically cleaned in acetone (10 minutes), dried, and then the surface was subjected to a corona discharge treatment. Next, a pressure-sensitive adhesive layer (15 μm thick, NCF-211S, manufactured by Lintec Corporation) was laminated to the corona-discharge-treated surface of the polarizing film. A quartz substrate was then laminated to the pressure-sensitive adhesive layer on the side opposite the polarizing film and pressed with a hand roller to produce a polarizing plate (surface protective film / iodine-based polarizing film / pressure-sensitive adhesive layer / quartz substrate).

[0054] (Comparative Example 2) First, a 25 μm-thick iodine-based polarizing film laminated with a surface protection film was prepared. The surface of the polarizing film opposite the surface protection film was washed with ethanol and dried, and then the surface was subjected to a corona discharge treatment. A 0.7 mm-thick quartz substrate was also prepared. The quartz substrate was ultrasonically cleaned in acetone (10 minutes), dried, and then the surface was subjected to a corona discharge treatment. Next, an acrylate-based ultraviolet-curing adhesive (product name: LOCTITE AA 3105, solid content: 100%, manufactured by Henkel Japan Co., Ltd.) was applied to the corona-discharge-treated surface of the polarizing film by spin coating (application amount: 2 ml, spin speed: 3000 rpm) to form a coating layer. The polarizing film and the quartz substrate were then superimposed with the coating layer interposed between them and pressed with a hand roller. Then, an ultraviolet irradiation device was used to apply an integrated light dose of 1000 mJ / cm2 to the surface. 2 The ultraviolet-curable adhesive was cured by irradiating it with ultraviolet light from the quartz substrate side so that the polarizing plate (surface protection film / iodine-based polarizing film / ultraviolet-curable adhesive layer / quartz substrate) was fabricated.

[0055] The polarizing plates obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated as follows. The evaluation results are shown in Table 1. Note that the polarizing plates from which the surface protective film had been peeled off were used in the following evaluations. (Durability evaluation) Air was blown toward the polarizing plates (23 mm x 20 mm) obtained in the Examples and Comparative Examples, and while the air was blown at a constant speed against the polarizing plate, laser light (wavelength: 455 nm) was irradiated from the polarizing film side of the polarizing plate using a laser irradiator for 2 minutes, and the temperature of the hottest point on the polarizing film surface was measured from the polarizing film side using a thermograph as the surface temperature of the polarizing film. After laser irradiation, the appearance of the polarizing film on the polarizing plate and the projected image of the polarizing plate when using a backlight were visually evaluated according to the following criteria. The polarizing plate was positioned so that the polarizing film absorbed the polarized light of the laser (the polarization of the laser and the absorption axis of the polarizing film were parallel). ○: No change in appearance or projected image △: Slight changes in appearance (unevenness, wrinkles, etc.) and slight changes in the projected image (distortion, unevenness) ×: Changes in appearance (unevenness, wrinkles, etc.) are observed, and changes in the projected image (distortion, unevenness) are observed ××: Significant changes in appearance (unevenness, wrinkles, etc.) and changes in the projected image (distortion, unevenness)

[0056] [Table 1]

[0057] As shown in Table 1, the polarizing plate of Example 1, which was formed by bonding a polarizing film and a quartz substrate together with a molecular bonding agent using a molecular bonding technique that chemically bonds them, showed a lower surface temperature of the polarizing film after laser irradiation and exhibited excellent results in the appearance and projected image of the polarizing film after laser irradiation compared to the polarizing plates of Comparative Examples 1 and 2. Also, as shown in Table 1, the polarizing plate of Example 2, which was formed by bonding a polarizing film and a sapphire substrate together with a molecular bonding agent that chemically bonds them, showed an even lower surface temperature of the polarizing film and exhibited excellent results in the appearance and projected image of the polarizing film after laser irradiation.

[0058] As described above, a polarizing plate bonded by molecular bonding technology can reduce the thermal load on the PVA polarizing film and firmly bond the support substrate and the polarizing film, thereby suppressing poor appearance due to thermal shrinkage of the PVA polarizing film and maintaining the performance of the PVA polarizing film for a long period of time, resulting in high durability. Therefore, polarizing plates bonded by molecular bonding technology are particularly useful in applications using light sources with large or high values ​​for luminous flux, luminous intensity, brightness, light density, etc. [Explanation of symbols]

[0059] 1: Polarizing plate 2: Polarizing film 3: Bonding layer 4: Support base material

Claims

1. a polarizing plate comprising a polarizing film made of a polyvinyl alcohol-based resin and a light-transmitting supporting substrate laminated on at least one surface of the polarizing film via an adhesive layer, wherein the adhesive layer is made of a molecular adhesive that chemically bonds the polarizing film and the supporting substrate, the molecular adhesive containing a triazine derivative having two or more OH groups and / or OH yielding groups and one triazine ring, the triazine derivative chemically bonding to both the polarizing film and the supporting substrate by dehydration condensation of the OH groups and / or OH yielding groups with OH groups on the surface of the polarizing film and OH groups on the surface of the supporting substrate, and the supporting substrate has a higher thermal conductivity than the polarizing film.

2. The polarizing plate according to claim 1, characterized in that the OH groups and / or OH-yielding groups are alkoxysilyl groups, and the OH groups on the surface of the pre-polarizing film and the OH groups on the surface of the supporting substrate are chemically bonded to the alkoxysilyl groups of the triazine derivative by dehydration condensation.

3. 3. The polarizing plate according to claim 1, wherein the thickness of the bonding layer is in the range of 0.05 [mu]m to 0.001 [mu]m.

4. 4. The polarizing plate according to claim 1, wherein the supporting substrate is made of at least one material selected from the group consisting of organic materials, inorganic materials, and organic-inorganic hybrid materials.

5. 5. The polarizing plate according to claim 1, wherein the supporting substrate has a thermal conductivity of 1 W / mK or more.

6. 6. The method for manufacturing a polarizing plate according to claim 1, further comprising the steps of: providing the molecular bonding agent on a surface of the polarizing film and / or the supporting substrate; laminating the polarizing film and / or the supporting substrate via the molecular bonding agent present on the surface of the polarizing film and / or the supporting substrate; and thermocompression bonding the polarizing film and the supporting substrate to chemically bond the polarizing film and the supporting substrate.

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