Polarizing plate and manufacturing method thereof

Abstract

To provide a polarizing plate with good heat resistance.SOLUTION: A polarizing plate 1 provided comprises a polarizer 10, a first adhesive layer 101, and a first resin film 102 which are arranged in this order. The polarizer 10 is in direct contact with the first adhesive layer 101. The polarizing plate 1 has a luminosity-corrected single transmittance of 45.5% or greater. Zinc element content of the polarizer 10 and the adhesive layer 101 in direct contact with the polarizer is 0.15 mass% or greater. The polarizer has a thickness of 10 μm or greater.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polarizing plate and a method for producing the same. [Background technology]

[0002] As a polarizer, a polyvinyl alcohol-based resin film in which a dichroic pigment such as iodine or a dichroic dye is adsorbed and oriented is known. Patent Documents 1 to 3 propose such polyvinyl alcohol-based resin films containing zinc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-29042 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-61565 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-102353 Summary of the Invention [Problem to be solved by the invention]

[0004] Polarizers are used as polarizing plates in image display devices. When image display devices are used at high temperatures for long periods of time, the optical properties of polarizing plates can change. In particular, polarizing plates with high transmittance, such as those used in organic electroluminescence (EL) displays, contain a small amount of circular dichroic dye in the polarizer, making it difficult to pass durability tests such as heat resistance. Therefore, there is a demand for improved heat resistance in polarizing plates.

[0005] An object of the present invention is to provide a polarizing plate having good heat resistance. [Means for solving the problem]

[0006] The present invention provides the following polarizing plate and method for producing a polarizing plate. [1] A polarizing plate including a polarizer, a first adhesive layer, and a first resin film in this order, the polarizer and the first adhesive layer are in direct contact with each other, The luminosity correction single transmittance is 45.5% or more, the content of zinc element contained in the polarizer and the adhesive layer that is in direct contact with the polarizer is 0.15% by mass or more, The polarizer has a thickness of 10 μm or more. [2] The polarizing plate according to [1], which has a luminosity-corrected polarization degree of 94.0% or more. [3] The polarizing plate according to [1] or [2], wherein the content of zinc element contained in the polarizer and the adhesive layer in direct contact with the polarizer is 0.22 mass % or less. [4] The first resin film has a moisture permeability of 100 g / m at a temperature of 40°C and a relative humidity of 90% RH. 2 The polarizing plate according to any one of [1] to [3], wherein the polarizing plate has a temperature of 120°C / 24 hours or more. [5] The polarizing plate according to any one of [1] to [4], wherein the first adhesive layer contains elemental zinc. [6] The polarizing plate according to any one of [1] to [5], further comprising a second adhesive layer and a second resin film, in this order, on the side of the polarizer opposite to the first resin film, from the side closer to the polarizer. [7] The second resin film has a moisture permeability of 100 g / m at a temperature of 40°C and a relative humidity of 90% RH. 2 / 24h or more. [8] The polarizing plate according to [6] or [7], wherein the second adhesive layer contains a zinc element. [9] A method for producing the polarizing plate according to any one of [1] to [8], A manufacturing method comprising a step of treating a polyvinyl alcohol-based resin film with a treatment liquid containing a zinc salt to produce a polarizer. [Effects of the Invention]

[0007] According to the present invention, a polarizing plate having good high-temperature durability can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a polarizing plate according to one embodiment of the present invention. [Figure 2] 1 is a flowchart illustrating a method for manufacturing a polarizer according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Polarizing plate] FIG. 1 is a cross-sectional view schematically showing a polarizing plate according to one embodiment of the present invention. Polarizing plate 1 includes a polarizer 10, a first adhesive layer 101, and a first resin film 102, in this order. Polarizer 10 and first adhesive layer 101 are in direct contact with each other. The polarizing plate has a luminous-corrected single transmittance (Ty) of 45.5% or more and a zinc content of 0.15% by mass or more. The polarizer has a thickness of 10 μm or more. When the luminous-corrected single transmittance (Ty) of a polarizing plate is 45.5% or more, changes in optical properties are more easily visible compared to polarizing plates having a luminous-corrected single transmittance (Ty) of less than 45.5%. According to the present invention, by setting the content of zinc element contained in the polarizing plate and the thickness of the polarizer within the above-mentioned ranges, it is possible to provide a polarizing plate having a luminous efficacy-corrected single transmittance (Ty) of 45.5% or more, excellent heat resistance, and suppressing changes in optical properties before and after a heat resistance test, even when subjected to a heat resistance test.

[0010] The polarizing plate preferably has a luminous efficiency-corrected single transmittance (Ty) of 46.0% or more, more preferably 47.0% or more. The luminous efficiency-corrected single transmittance (Ty) of the polarizing plate is usually 50% or less.

[0011] In this specification, the heat resistance test refers to a durability test of heat resistance conducted according to the method described in the Examples section below. When a polarizing plate is subjected to a heat resistance test, the luminous efficacy-corrected degree of polarization (Py) can be cited as an optical property whose change before and after the durability test is suppressed. The rate of change (ΔPy) of the luminous efficacy-corrected degree of polarization (Py) of the polarizing plate before and after the heat resistance test is, for example, 4.0% or less, preferably 3.5% or less, and more preferably 3.0% or less. According to the present invention, a polarizing plate exhibiting excellent heat resistance with a rate of change (ΔPy) in this range can be obtained.

[0012] The polarizing plate has a luminous efficiency-corrected polarization degree (Py) of preferably 92.0% or more, more preferably 93.0% or more, and even more preferably 94.0% or more. The luminous efficiency-corrected polarization degree (Py) of the polarizing plate may be 99.9% or less, or in another embodiment, 99% or less, or 98% or less.

[0013] In the polarizing plate, the zinc content between the polarizer and the adhesive layer in direct contact with the polarizer is 0.15% by mass or more. By having the zinc content between the polarizer and the adhesive layer in direct contact with the polarizer be 0.15% by mass or more, a polarizing plate with good high-temperature durability can be provided. The zinc content is preferably 0.16% by mass or more, and more preferably 0.17% by mass or more. From the viewpoint of obtaining a polarizing plate with a desired color, the zinc content is preferably 0.22% by mass or less, and more preferably 0.20% by mass or less.

[0014] The total zinc content in the polarizer and the adhesive layer in direct contact with the polarizer can be adjusted by adjusting the zinc content in the polarizer, the zinc content in the first adhesive layer and / or the second adhesive layer in direct contact with the polarizer, etc. The zinc content in the polarizer and the adhesive layer in direct contact with the polarizer is measured by the method described in the examples below.

[0015] The b value of the single hue of the polarizing plate is, for example, from −1.0 to 4.0, preferably from −0.5 to 3.0, and more preferably from 0 to 2.0. The absorbance A700 of the polarizing plate at a wavelength of 700 nm is, for example, 0.5 or more and 3.0 or less, preferably 0.7 or more and 2.0 or less, and more preferably 0.9 or more and 1.5 or less.

[0016] In this specification, the luminous efficiency-corrected single transmittance (Ty), luminous efficiency-corrected polarization degree (Py), the rate of change (ΔPy) of luminous efficiency-corrected polarization degree (Py), the single hue b value, the absorbance A700 at a wavelength of 700 nm, and the zinc element content between the polarizer and the adhesive layer directly in contact with the polarizer are values measured according to the measurement method described in the Examples section below.

[0017] The first resin film is bonded to the surface of the polarizer via, for example, a first adhesive layer. The polarizing plate may further include, on the opposite side of the first resin film, a second adhesive layer and a second resin film, in this order, from the side closer to the polarizer. The second resin film is bonded to the surface of the polarizer via, for example, a second adhesive layer. In determining the "total zinc elemental content contained in the polarizer and the adhesive layer directly in contact with the polarizer" in a polarizing plate, the adhesive layer directly in contact with the polarizer refers to the first adhesive layer, and if the second adhesive layer is provided directly in contact with the polarizer, the second adhesive layer also refers to the second adhesive layer. Hereinafter, the first resin film and the second resin film are collectively referred to as resin films, and the first adhesive layer and the second adhesive layer are collectively referred to as adhesive layers.

[0018] <Polarizer> The polarizer is an absorption-type polarizer that has the property of absorbing linearly polarized light having a vibration plane parallel to its absorption axis and transmitting linearly polarized light having a vibration plane perpendicular to the absorption axis (parallel to its transmission axis). The polarizer may be, for example, a polarizer in which a dichroic dye is adsorbed and oriented in a uniaxially stretched polyvinyl alcohol-based resin film, and such a polarizer can be produced according to the polarizer production method described below.

[0019] The thickness of the polarizer is 10 μm or more. By having a polarizer thickness of 10 μm or more, a polarizing plate with excellent durability can be provided. The thickness of the polarizer is preferably 12 μm or more, more preferably more than 15 μm. The thickness of the polarizer is preferably 50 μm or less, more preferably 30 μm or less.

[0020] The thickness of the polarizer can be adjusted to fall within the above range by, for example, selecting a polyvinyl alcohol-based resin film, adjusting the stretching ratio, and the like.

[0021] The zinc content in the polarizing plate is preferably adjusted by adjusting the zinc content in the polarizer. The polarizer in the polarizing plate of the present invention usually contains zinc. The content of zinc element contained in the polarizer can be set to the above-mentioned range by adjusting, for example, the concentration of zinc salt in the treatment liquid used to treat the polyvinyl alcohol-based resin film, the immersion time of the polyvinyl alcohol-based resin film in the treatment liquid containing the zinc salt, the temperature of the treatment liquid, etc.

[0022] <Polarizer manufacturing method> A method for producing a polarizer according to another embodiment of the present invention will be described with reference to the drawings. The manufacturing method shown in FIG. 2 is a manufacturing method of a polarizer containing a polyvinyl alcohol-based resin, and includes the following steps: a dyeing step S20 in which the polyvinyl alcohol-based resin film is dyed by immersing it in a dyeing tank containing a treatment liquid containing a dichroic dye; a crosslinking step S30 in which the film after the dyeing step is immersed in a crosslinking bath containing a treatment liquid containing a crosslinking agent to perform a crosslinking treatment; may include:

[0023] The production method may further include other steps in addition to those described above, specific examples of which include a swelling step S10 in which the polyvinyl alcohol-based resin film before the dyeing step S20 is immersed in a swelling tank containing a treatment liquid containing water, a cleaning step S40 in which the film after the crosslinking step S30 is immersed in a cleaning tank, and a drying step S50 after the cleaning step S40, as shown in Fig. 2. The polyvinyl alcohol-based resin film is uniaxially stretched (stretching step) in one or more stages of the polarizer production process, more specifically, in one or more stages from before the swelling step S10 to the crosslinking step S30.

[0024] In the manufacturing method, at least one of the treatment solutions used to treat the polyvinyl alcohol-based resin film contains a zinc salt. Examples of treatment tanks containing the treatment solution include a swelling tank, a dyeing tank, a crosslinking tank, a cleaning tank, and a color-complementing tank (described later). The treatment tank containing the zinc salt-containing treatment solution is preferably a treatment tank located after the dyeing tank and before the cleaning tank, more preferably at least one selected from a crosslinking tank and a color-complementing tank, and even more preferably at least one selected from the final crosslinking tank and color-complementing tank when there are two or more crosslinking tanks. By immersing the polyvinyl alcohol-based resin film in a treatment solution containing a zinc salt, zinc can be incorporated into the resulting polarizer. The zinc content in the polarizer can be adjusted to the above-mentioned range by adjusting the concentration of the zinc salt in the treatment solution, the immersion time of the polyvinyl alcohol-based resin film in the treatment solution containing the zinc salt, the temperature of the treatment solution, and the like.

[0025] Examples of zinc salts contained in the processing solution include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, and zinc nitrate. Among these, zinc nitrate is preferred because it is inexpensive. The zinc salt can be added to the processing solution as a zinc salt solution.

[0026] The concentration of the zinc salt in the treatment solution may differ for each treatment tank, but is preferably 2 to 10 parts by mass, more preferably 3 to 6 parts by mass, per 100 parts by mass of treatment solution contained in the treatment tank.

[0027] The immersion time of the polyvinyl alcohol-based resin film in the treatment solution and the temperature of the treatment solution may vary for each treatment bath. The specific immersion time and temperature of the treatment solution will be described for each step in the following paragraphs.

[0028] The various treatment steps included in the manufacturing method of the present invention can be continuously carried out by continuously transporting the raw polyvinyl alcohol-based resin film along a film transport path of a polarizer manufacturing apparatus. The film transport path is equipped with equipment (treatment tanks, furnaces, etc.) for carrying out the various treatment steps described above in the order in which they are carried out.

[0029] The film transport path can be constructed by arranging guide rolls, nip rolls, etc. in appropriate positions in addition to the above-mentioned equipment. For example, guide rolls can be placed before, after, or inside each processing tank, allowing the film to be introduced into, immersed in, and withdrawn from the processing tank. More specifically, two or more guide rolls can be provided in each processing tank, and the film can be immersed in each processing tank by transporting the film along these guide rolls.

[0030] The polyvinyl alcohol resin constituting the polyvinyl alcohol resin film, which is the raw film, can be a saponified polyvinyl acetate resin. Examples of polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other monomers copolymerizable therewith. 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. The saponification degree of the polyvinyl alcohol resin is typically about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. In this specification, "(meth)acrylic" refers to at least one selected from acrylic and methacrylic. The same applies to "(meth)acryloyl."

[0031] The polyvinyl alcohol resin may be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes may also be used.

[0032] The average degree of polymerization of the polyvinyl alcohol resin is preferably from 100 to 10,000, more preferably from 1,500 to 8,000, and even more preferably from 2,000 to 5,000. The average degree of polymerization of the polyvinyl alcohol resin can be determined in accordance with JIS K 6726 (1994). If the average degree of polymerization is less than 100, it is difficult to obtain favorable polarizing performance, and if it exceeds 10,000, film processability may be poor.

[0033] The thickness of the polyvinyl alcohol resin film is preferably 20 μm or more and 100 μm or less, more preferably 30 μm or more and 80 μm or less, and even more preferably 40 μm or more and 65 μm or less, from the viewpoint of making the thickness of the polarizer 10 μm or more.

[0034] The polyvinyl alcohol-based resin film, which is the raw film, can be prepared, for example, as a roll (wound product) of a long unstretched or stretched polyvinyl alcohol-based resin film. In this case, the polarizer is also obtained as a long product. Each step will be described in detail below.

[0035] (1) Swelling step S10 The swelling treatment in this step is a treatment carried out as needed for the purposes of removing foreign matter from the raw polyvinyl alcohol-based resin film, removing plasticizers, imparting dyeability, plasticizing the film, etc. Specifically, it can be a treatment in which the polyvinyl alcohol-based resin film is immersed in a swelling tank containing a treatment solution containing water. The film may be immersed in one swelling tank or sequentially in two or more swelling tanks. The film may be subjected to a uniaxial stretching treatment before, during, or both the swelling treatment.

[0036] The treatment liquid contained in the swelling tank may be water (e.g., pure water), or may be an aqueous solution containing a water-soluble organic solvent such as an alcohol. As described above, the treatment liquid contained in the swelling tank may contain a zinc salt.

[0037] The temperature of the treatment solution contained in the swelling tank when the film is immersed is usually about 10 to 70°C, preferably about 15 to 50°C, and the immersion time of the film is usually about 10 to 600 seconds, preferably about 20 to 300 seconds.

[0038] (2) Dyeing process S20 The dyeing treatment in this step is a treatment performed for the purpose of adsorbing and orienting a dichroic dye in the polyvinyl alcohol-based resin film. Specifically, it can be a treatment in which the polyvinyl alcohol-based resin film is immersed in a dyeing tank containing a treatment solution containing a dichroic dye. The film may be immersed in one dyeing tank, or may be immersed sequentially in two or more dyeing tanks. In order to improve the dyeability of the dichroic dye, the film subjected to the dyeing step may be subjected to at least some degree of uniaxial stretching. Instead of or in addition to the uniaxial stretching treatment before the dyeing treatment, uniaxial stretching treatment may be performed during the dyeing treatment.

[0039] The dichroic dye may be iodine or a dichroic organic dye. Specific examples of the dichroic organic dye include Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Supra Blue G, Supra Blue GL, Supra Orange GL, Direct Sky Blue, Direct Fast Orange S, and Fast Black. The dichroic dye may be used alone or in combination of two or more.

[0040] When iodine is used as the dichroic dye, the treatment solution contained in the dyeing tank can be an aqueous solution containing iodine and potassium iodide. Other iodides, such as zinc iodide, may be used instead of potassium iodide, or potassium iodide may be used in combination with other iodides. Compounds other than iodides, such as boric acid, zinc chloride, or cobalt chloride, may also be present. Adding boric acid is distinguished from the crosslinking treatment described below in that it contains iodine. The iodine content in the aqueous solution is typically 0.01 to 1 part by weight per 100 parts by weight of water. The content of iodides, such as potassium iodide, is typically 0.5 to 20 parts by weight per 100 parts by weight of water. As mentioned above, the treatment solution contained in the dyeing tank can contain a zinc salt.

[0041] The temperature of the treatment solution contained in the dyeing tank when the film is immersed is usually 10°C or more and 45°C or less, preferably 10°C or more and 40°C or less, and more preferably 20°C or more and 35°C or less, and the immersion time of the film is usually 30 seconds or more and 600 seconds or less, and preferably 60 seconds or more and 300 seconds or less.

[0042] When a dichroic organic dye is used as the dichroic pigment, an aqueous solution containing the dichroic organic dye can be used as the treatment liquid contained in the dyeing tank. The content of the dichroic organic dye in the aqueous solution is usually 1 × 10 per 100 parts by mass of water. -4 parts by mass or more and 10 parts by mass or less, preferably 1×10 -3 The amount is from 1 part by mass to 1 part by mass. The dyeing tank may contain dyeing auxiliaries, such as inorganic salts such as sodium sulfate, surfactants, etc. The dichroic organic dye may be used alone or in combination of two or more types. The temperature of the treatment solution contained in the dyeing tank when the film is immersed is, for example, from 20°C to 80°C, preferably from 30°C to 70°C, and the immersion time of the film is usually from 30 to 600 seconds, preferably from 60 to 300 seconds.

[0043] (3) Crosslinking step S30 The crosslinking treatment of the polyvinyl alcohol-based resin film after the dyeing process with a crosslinking agent is a treatment carried out for the purpose of imparting water resistance or adjusting the hue by crosslinking, and specifically, it can be a treatment in which the film after the dyeing process is immersed in a treatment solution contained in a crosslinking tank containing a crosslinking agent. The film may be immersed in one crosslinking tank or may be immersed sequentially in two or more crosslinking tanks. A uniaxial stretching treatment may be carried out during the crosslinking treatment.

[0044] Examples of crosslinking agents include boric acid, glyoxal, and glutaraldehyde, with boric acid being preferred. Two or more crosslinking agents can also be used in combination. The content of boric acid in the treatment solution contained in the crosslinking tank is typically 0.1 to 15 parts by mass, preferably 1 to 10 parts by mass, per 100 parts by mass of water. When the dichroic dye is iodine, the treatment solution contained in the crosslinking tank preferably contains an iodide in addition to boric acid. The content of iodide in the treatment solution contained in the crosslinking tank is typically 0.1 to 15 parts by mass, preferably 5 to 12 parts by mass, per 100 parts by mass of water. Examples of iodides include potassium iodide and zinc iodide. Compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and sodium sulfate, may also be present in the crosslinking tank. As mentioned above, the treatment solution contained in the crosslinking bath may contain a zinc salt. When there are two or more crosslinking baths, it is preferred that the treatment solution contained in the last crosslinking bath contains a zinc salt.

[0045] The temperature of the processing solution contained in the crosslinking tank when the film is immersed is usually 50°C or more and 85°C or less, preferably 50°C or more and 70°C or less, and the immersion time of the film is usually 10 seconds or more and 600 seconds or less, preferably 20 seconds or more and 300 seconds or less.

[0046] The crosslinking step S30 may include two or more crosslinking tanks. In this case, the composition and temperature of the treatment liquid contained in each crosslinking tank may be the same or different. The treatment liquid contained in the crosslinking tank may have a concentration of a crosslinking agent, an iodide, etc., and a temperature according to the purpose of immersing the polyvinyl alcohol-based resin film. The crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for hue adjustment (complementary color) may each be performed in multiple steps (e.g., multiple tanks). Generally, when both a crosslinking treatment for water resistance through crosslinking and a crosslinking treatment for hue adjustment (complementary color) are performed, the tank (complementary color tank) in which the crosslinking treatment for hue adjustment (complementary color) is performed is disposed in the latter stage. The temperature of the processing solution contained in the complementary color tank is, for example, 10°C or higher and 55°C or lower, and preferably 20°C or higher and 50°C or lower. The content of the crosslinking agent in the processing solution contained in the complementary color tank is, for example, 1 part by mass or higher and 5 parts by mass or lower per 100 parts by mass of water. The content of iodide in the processing solution contained in the complementary color tank is, for example, 3 parts by mass or higher and 30 parts by mass or lower per 100 parts by mass of water. As mentioned above, the processing solution contained in the complementary color tank may contain a zinc salt.

[0047] As described above, in producing a polarizer, a polyvinyl alcohol-based resin film is uniaxially stretched at one or more stages from before the swelling step S10 to the crosslinking step S30 (stretching step, FIG. 2). From the viewpoint of improving the dyeability of the dichroic dye, the film to be subjected to the dyeing step is preferably a film that has been subjected to at least some degree of uniaxial stretching, or it is preferable to perform uniaxial stretching during the dyeing step instead of or in addition to the uniaxial stretching before the dyeing step.

[0048] The uniaxial stretching process may be dry stretching in air, wet stretching in a tank, or both. The uniaxial stretching process may be inter-roll stretching, in which longitudinal uniaxial stretching is performed by applying a peripheral speed difference between two nip rolls, hot roll stretching, tenter stretching, or the like, but preferably includes inter-roll stretching. The stretching ratio based on the raw film (the cumulative stretching ratio when stretching is performed in two or more stages) is 3 to 8 times. To impart good polarization properties, the stretching ratio is preferably 4 times or more, more preferably 5 times or more.

[0049] (4) Cleaning process S40 The cleaning treatment in this step is a treatment carried out as necessary for the purpose of removing excess crosslinking agent, dichroic dye, and other chemicals adhering to the polyvinyl alcohol-based resin film, and is a treatment of cleaning the polyvinyl alcohol-based resin film after the crosslinking step using a cleaning liquid containing water. Specifically, it can be a treatment of immersing the polyvinyl alcohol-based resin film after the crosslinking step in a treatment liquid (cleaning liquid) contained in a cleaning tank. The film may be immersed in one cleaning tank, or may be immersed sequentially in two or more cleaning tanks. Alternatively, the cleaning treatment may be a treatment of spraying the cleaning liquid as a shower onto the polyvinyl alcohol-based resin film after the crosslinking step, or a combination of the above-mentioned immersion and spraying.

[0050] The cleaning liquid may be water (e.g., pure water) or an aqueous solution containing a water-soluble organic solvent such as alcohol. The temperature of the cleaning liquid may be, for example, 5°C or higher and 40°C or lower.

[0051] The cleaning step S40 is an optional step and may be omitted, or, as will be described later, the cleaning treatment may be performed during the drying step S50. Preferably, the film after the cleaning step S40 is subjected to the drying step S50.

[0052] (5) Drying process S50 The drying step S50 is a zone for drying the polyvinyl alcohol-based resin film after the cleaning step S40. The polyvinyl alcohol-based resin film after the cleaning step S40 can be subjected to a drying treatment by introducing the film into the drying step S50 while continuing to be transported, thereby obtaining a polarizer.

[0053] The drying treatment is carried out using a film drying means (heating means). A suitable example of the drying means is a drying oven. The drying oven is preferably one that can control the temperature inside the oven. The drying oven is, for example, a hot air oven that can increase the temperature inside the oven by supplying hot air, etc. The drying treatment by the drying means may also be a process in which the polyvinyl alcohol-based resin film after the cleaning step S40 is brought into close contact with one or more heating bodies having a convex curved surface, or a process in which the film is heated using a heater.

[0054] The heating body may be a roll (e.g., a guide roll that also functions as a heating roll) that has a heat source (e.g., a heat medium such as hot water or an infrared heater) inside and can increase the surface temperature. Examples of the heater include an infrared heater, a halogen heater, and a panel heater.

[0055] The temperature of the drying treatment (for example, the temperature inside the drying oven, the surface temperature of the heated roll, etc.) is usually 30° C. or higher and 100° C. or lower, and preferably 50° C. or higher and 90° C. or lower. The drying time is not particularly limited, but is, for example, 30 seconds or higher and 600 seconds or lower.

[0056] Through the above steps, a polarizer can be obtained in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film.

[0057] The obtained polarizer can be transported as it is to the next polarizing plate production step (a step of laminating a thermoplastic resin film on one or both sides of the polarizer).

[0058] <Resin film> The resin film may be a transparent resin film made of a thermoplastic resin, for example, a polyolefin resin such as a linear polyolefin resin (such as a polypropylene resin) or a cyclic polyolefin resin (such as a norbornene resin); a cellulose ester resin such as triacetyl cellulose or diacetyl cellulose; a polyester resin such as polyethylene terephthalate, polyethylene naphthalate, or polybutylene terephthalate; a polycarbonate resin; a (meth)acrylic resin such as a polymethyl methacrylate resin; or a mixture, copolymer, or the like of these.

[0059] Either the first resin film or the second resin film, or preferably both, have a moisture permeability of 100 (g / m 2) at a temperature of 40°C and a relative humidity of 90% RH. 2 / 24h) or more, especially 300 (g / m 2 This is particularly effective when the moisture permeability is 100 (g / m 2 / 24h) or more. Films with such high moisture permeability tend to have low high-temperature durability due to the ingress and egress of moisture, but by satisfying the invention requirements of this patent, high high-temperature durability can be achieved. Triacetyl cellulose and the like are examples of resin films that satisfy this moisture permeability. In addition, resin films with a moisture permeability of 100 (g / m 2 / 24h) or more at a temperature of 40°C and a relative humidity of 90% RH are also suitable. 2 / 24h) or more, the surface of the resin film may have a surface treatment layer such as a hard coat layer or an antireflection layer. When a resin film with such moisture permeability is used, the heat resistance of the polarizing plate tends to deteriorate, but the polarizing plate of the present invention has good durability.

[0060] Either or both of the first resin film and the second resin film may be a protective film having optical functions such as a retardation film, a brightness enhancement film, etc. For example, a retardation film having an arbitrary retardation value can be obtained by stretching (uniaxially or biaxially stretching, etc.) a transparent resin film made of the above-mentioned material or by forming a liquid crystal layer or the like on the film.

[0061] A surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer or an antifouling layer may be formed on the surface of the resin film opposite to the polarizer.

[0062] The thickness of the resin film is preferably thin from the viewpoint of thinning the polarizing plate, but if it is too thin, the strength tends to decrease and the processability tends to be poor, so the thickness is preferably 5 to 150 μm, more preferably 5 to 100 μm, and even more preferably 10 to 60 μm.

[0063] (adhesive layer) A polarizing plate can be obtained by laminating a resin film to one or both surfaces of a polarizer via an adhesive layer. Examples of adhesives used to bond the polarizer and the resin film include active energy ray-curable adhesives such as ultraviolet-curable adhesives, aqueous solutions of polyvinyl alcohol-based resins or aqueous solutions containing crosslinkers, and water-based adhesives such as urethane-based emulsion adhesives. An adhesive containing zinc may also be used. By applying an adhesive containing zinc to the surface of the polarizer, migration of zinc from the polarizer to other layers can be suppressed, thereby preventing a decrease in high-temperature durability. An example of a method for incorporating zinc into the adhesive is adding a zinc salt during adhesive preparation. Examples of zinc salts that can be used include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, and zinc nitrate. The zinc content of the adhesive, calculated as solid content, can be, for example, 0.1 to 5 parts by mass, based on 100 parts by mass of the total amount of the adhesive.

[0064] When resin films are laminated to both sides of a polarizer, the adhesives forming the two adhesive layers may be the same or different. For example, when resin films are laminated to both sides, one side may be laminated using a water-based adhesive and the other side may be laminated using an active energy ray-curable adhesive. The ultraviolet-curable adhesive may be a mixture of a radically polymerizable (meth)acrylic compound and a photoradical polymerization initiator, or a mixture of a cationically polymerizable epoxy compound and a photocationic polymerization initiator. Alternatively, a cationically polymerizable epoxy compound and a radically polymerizable (meth)acrylic compound may be used in combination, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used in combination as initiators.

[0065] When an active energy ray-curable adhesive is used, the adhesive is cured by irradiating it with active energy rays after lamination. The light source of the active energy rays is not particularly limited, but active energy rays (ultraviolet rays) having an emission distribution of wavelengths of 400 nm or less are preferred, and specifically, low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, chemical lamps, black light lamps, microwave-excited mercury lamps, metal halide lamps, etc. are preferably used.

[0066] In order to improve the adhesion between the polarizer and the resin film, prior to bonding the polarizer and the resin film, the bonding surfaces of the polarizer and / or the resin film may be subjected to surface treatment such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation treatment, primer coating treatment, or saponification treatment.

[0067] As described above, the polarizing plate of the present invention can be produced by laminating a resin film to a polarizer that is a single-layer film via an adhesive layer, but the method is not limited to this. For example, the polarizing plate can also be produced by a method that uses a substrate film, as described in JP-A-2009-98653. The latter method is advantageous for obtaining a polarizing plate having a thin-film polarizer (polarizer layer), and can include, for example, the following steps:

[0068] a resin layer forming step of applying a coating liquid containing a polyvinyl alcohol-based resin to at least one surface of a substrate film and then drying the coating liquid to form a polyvinyl alcohol-based resin layer, thereby obtaining a laminated film; a stretching step of stretching the laminated film to obtain a stretched film; a dyeing step of dyeing the polyvinyl alcohol-based resin layer of the stretched film with a dichroic dye to form a polarizer layer (corresponding to a polarizer) to obtain a polarizing laminate film; a first lamination step of laminating a resin film (first resin film) onto a polarizer layer of the polarizing laminate film using an adhesive (first adhesive layer) to obtain a laminated film; A peeling step in which the substrate film is peeled off from the laminating film to obtain a polarizing plate with a resin film on one side. It is sufficient that zinc is contained in at least one of the dyeing step and the first laminating step. When zinc is contained in the dyeing step, zinc can be contained in the polarizing plate by adding a zinc salt to the treatment liquid containing the dichroic dye. When zinc is contained in the first laminating step, zinc can be contained in the polarizing plate by adding zinc to the adhesive.

[0069] When resin films are laminated on both sides of the polarizer layer (polarizer), a second lamination step is further included in which a second resin film is laminated to the polarizer surface of the single-sided polarizing plate with the first resin film using an adhesive (second adhesive layer). The adhesive for laminating the second resin film may contain zinc element.

[0070] In the above method using a substrate film, a drying step can be included in the dyeing step for obtaining a polarizing laminate film (for example, after a crosslinking step or a washing step during the dyeing step for obtaining a polarizing laminate film). The polarizers contained in the above polarizing laminate film, the polarizing plate with a thermoplastic resin film on one side, and the polarizing plate with thermoplastic resin films on both sides obtained through the second lamination step, or polarizers isolated from these, also belong to the polarizer of the present invention.

[0071] The polarizing plate can be used in a display device. The display device may be any type, such as a liquid crystal display device or an organic EL display device, but is preferably an organic EL display device. When incorporated into a liquid crystal display device, it is preferably used on the viewing side of a liquid crystal light-emitting element. When incorporated into an organic EL display device, a circular polarizing plate in which a retardation film and the polarizing plate of the present invention are combined may be used as an antireflection film.

[0072] The polarizing plate is suitable for an in-vehicle display device that includes, in this order, a polarizing plate, a light-transmitting member attached to the surface of the polarizing plate facing the first resin film, and a display device attached to the surface of the polarizing plate facing the second resin film. The light-transmitting member may be a glass plate, a light-transmitting resin film, or the like.

[0073] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to these examples. [Example]

[0074] [Luminous sensitivity corrected single transmittance (Ty), luminous sensitivity corrected polarization (Py) and single hue b value] The MD transmittance and TD transmittance of the polarizing plate were measured in the wavelength range of 380 to 780 nm using a spectrophotometer with an integrating sphere ("V7100" manufactured by JASCO Corporation). The following formula: Single transmittance (%) = (MD + TD) / 2 Degree of polarization (%)={(MD-TD) / (MD+TD)}×100 The single transmittance and polarization degree at each wavelength were calculated based on the above. "MD transmittance" is the transmittance when the direction of polarized light exiting the Glan-Thompson prism is parallel to the transmission axis of the polarizing plate, and is represented as "MD" in the above formula. "TD transmittance" is the transmittance when the direction of polarized light exiting the Glan-Thompson prism is perpendicular to the transmission axis of the polarizing plate, and is represented as "TD" in the above formula. The obtained single transmittance and degree of polarization were subjected to luminosity correction using a 2-degree visual field (C light source) in accordance with JIS Z 8701:1999 "Methods of representing color - XYZ color system and X10Y10Z10 color system," to determine the luminosity-corrected single transmittance (Ty) and luminosity-corrected degree of polarization (Py). Furthermore, based on the method described in WO 2016 / 117659, the spectral transmittance τ(λ) of the polarizing plates produced in the examples and comparative examples was measured using a spectrophotometer (V7100, JASCO Corporation), and the orthogonal spectral transmittance spectrum was obtained, from which the simplex hue b value and the A700 value defined by the following formula were calculated. A700=-Log 10 {(T MD,700 ×T TD,700 ) / 10000} In the above formula, T MD,700 is the transmittance at a wavelength of 700 nm obtained when the polarizing plate is placed so that the absorption axis of the polarizer is perpendicular to the linearly polarized light of the measurement light, and T TD,700 is the transmittance at a wavelength of 700 nm obtained when the polarizing plate is placed in a state where the absorption axis of the polarizer is in equilibrium with the linearly polarized light of the measurement light, and the units of these are all %.

[0075] [Heat resistance test] A 40mm x 40mm test piece was cut from the manufactured polarizing plate, and 40mm x 40mm alkali-free glass sheets were attached to both sides of the cut polarizing plate using a 25μm thick acrylic adhesive to prepare samples. For each sample, the luminous efficiency-corrected single transmittance (Ty), luminous efficiency-corrected polarization degree (Py), single hue b value, and A700 were calculated based on the measured values according to the above-mentioned method before subjecting it to the heat resistance test.

[0076] Each sample was subjected to a heat resistance test in which it was left in an oven at 80°C for 500 hours. After the heat resistance test, the luminous efficacy-corrected degree of polarization (Py) of each sample was measured according to the method described above, and the rate of change ΔPy [%] of the luminous efficacy-corrected degree of polarization was calculated according to the following method.

[0077] The rate of change ΔPy [%] is the rate of change in the luminous efficacy-corrected polarization degree (Py) before and after the heat resistance test, and is a value calculated using the following formula (1) when the luminous efficacy-corrected polarization degree (Py) before the durability test is P1 and the luminous efficacy-corrected polarization degree (Py) after the heat resistance test is P2. ΔPy={(P1-P2) / P1}×100 (1)

[0078] [Measurement of zinc element content] The polarizing plate was immersed in methylene chloride for 30 minutes and ultrasonically treated, dissolving the resin film (triacetyl cellulose film) on both sides of the polarizing plate in methylene chloride, and a sample consisting of the polarizer and the adhesive layer in contact with the polarizer was extracted. 1 g of the extracted sample and 50 ml of mannitol solution were placed in a 100 ml container, and an electrode was inserted and titrated with 0.1 N NaOH. The primary and secondary endpoints of the analytical instrument were recorded, and the concentration was calculated using the following formula. Zinc content (mass%) in the polarizer and the adhesive layer in contact with the polarizer = (amount of 0.1N NaOH used at the secondary endpoint [mL] - amount of 0.1N NaOH used at the primary endpoint [mL]) x 0.29749 x 0.1 x 0.5 / sample weight [g]

[0079] Analytical equipment: Metrohom 736GP Titrino Electrode: Combined pH electrode (Metrohm cat.#6.0258.000) Titration solution: 0.1N NaOH Composition of mannitol solution: 500g mannitol, 3500g purified water

[0080] <Preparation of adhesive> Polyvinyl alcohol resin adhesive A was prepared by dissolving 3.5 parts of Gohsefimer Z-200 (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 0.12 parts of zinc chloride, and 0.89 parts of glyoxal in 100 parts of water.

[0081] Example 1 (Polarizer manufacturing) A transparent, 45 μm-thick, unstretched polyvinyl alcohol film (TS4500, manufactured by Kuraray Co., Ltd.) with a saponification degree of 99.9% or higher was immersed in deionized water at 30°C for 2 minutes to swell, and then dyed by immersion in a dyeing solution containing 0.45 mmol / L iodine, 2 parts by weight of potassium iodide, and 0.35 parts by weight of boric acid at 30°C for 2 minutes. The film was stretched at stretch ratios of 1.72 and 1.54 during the swelling and dyeing stages, respectively, resulting in a cumulative stretch ratio of 2.64 up to the dyeing tank. The film was then immersed in a crosslinking solution containing 7.9 parts by weight of potassium iodide and 4.3 parts by weight of boric acid at 56°C for 30 seconds (crosslinking stage) to crosslink the film while stretching at a stretch ratio of 2.2. The film was then immersed in a 40°C crosslinking solution containing 10.6 parts by weight of potassium iodide, 5.0 parts by weight of zinc nitrate, and 3.9 parts by weight of boric acid for 5 seconds (complementary color step) to crosslink and stretch. The total cumulative stretch ratio for the swelling, dyeing, crosslinking, and complementary color steps was adjusted to 5.9 times. After crosslinking was complete, the polyvinyl alcohol film was dried in an oven at 100°C to produce a polarizer. The polarizer had a thickness of 18 μm.

[0082] (Polarizing plate manufacturing) Using the polyvinyl alcohol-based adhesive A prepared above, protective films were attached to both sides of the polarizer. As the protective film, a triacetyl cellulose film (KC4UAW, manufactured by Konica Minolta, Inc., thickness 40 μm, moisture permeability 800 g / m at a temperature of 40°C and a relative humidity of 90% RH) was attached to one side of the polarizer. 2 On one side, an anti-reflection (LR) surface-treated triacetyl cellulose film (thickness: 60 μm, reflectance: 1%) was used, and on the other side, an anti-reflection (LR) surface-treated triacetyl cellulose film (thickness: 60 μm, reflectance: 1%) was used. For lamination, polyvinyl alcohol-based adhesive A was applied to both sides of the polarizer, and then the polarizers were bonded together using nip rolls, followed by drying at 80° C. for 5 minutes, thereby producing the polarizing plate of Example 1.

[0083] <Example 2> (Polarizer manufacturing) A polarizer was produced in the same manner as in Example 1, except that the temperature of the crosslinking liquid in the crosslinking step was changed from 56°C to 60°C, and the boric acid concentration of the crosslinking liquid in the complementary color step was changed to 3.0 parts by mass. The polarizer had a thickness of 18 μm.

[0084] (Polarizing plate manufacturing) A polarizing plate of Example 2 was produced in the same manner as in Example 1 using the polarizer produced above.

[0085] Example 3 (Polarizer manufacturing) A polarizer was produced in the same manner as in Example 1, except that the drying temperature of the polyvinyl alcohol film after crosslinking was changed from 100°C to 90°C, and the boric acid concentration of the crosslinking liquid in the complementary color stage was changed to 3.0 parts by mass. The polarizer had a thickness of 18 μm.

[0086] (Polarizing plate manufacturing) A polarizing plate of Example 3 was produced in the same manner as in Example 1 using the polarizer produced above.

[0087] Example 4 (Polarizer manufacturing) A polarizer was produced in the same manner as in Example 1, except that a transparent, 45 μm-thick, unstretched polyvinyl alcohol film (TS4500, manufactured by Kuraray Co., Ltd.) having a saponification degree of 99.9% or more was replaced with a transparent, 60 μm-thick, unstretched polyvinyl alcohol film (PE-6000, manufactured by Kuraray Co., Ltd.) having a saponification degree of 99.9% or more, and the boric acid concentration in the crosslinking liquid at the complementary color stage was changed to 3.0 parts by mass. The thickness of the polarizer was 23 μm.

[0088] (Polarizing plate manufacturing) A polarizing plate of Example 4 was produced in the same manner as in Example 1 using the polarizer produced above.

[0089] <Comparative Example 1> (Polarizer manufacturing) A polarizer was produced in the same manner as in Example 1, except that the content of zinc nitrate in the crosslinking liquid in the complementary color step was changed from 5.0 parts to 3.0 parts. The thickness of the polarizer was 18 μm.

[0090] (Polarizing plate manufacturing) A polarizing plate of Comparative Example 1 was produced in the same manner as in Example 1 using the polarizer produced above.

[0091] <Comparative Example 2> (Polarizer manufacturing) A polarizer was produced in the same manner as in Example 1, except that the content of zinc nitrate in the crosslinking liquid in the complementary color step was changed from 5.0 parts to 0 parts. The thickness of the polarizer was 18 μm.

[0092] (Polarizing plate manufacturing) A polarizing plate of Comparative Example 1 was produced in the same manner as in Example 1 using the polarizer produced above.

[0093] <Test> The polarizing plates of Examples 1 to 4 and Comparative Examples 1 to 3 were measured for luminous efficiency-corrected single transmittance (Ty), luminous efficiency-corrected degree of polarization (Py), single hue b value, and A700 as described above. The resulting polarizing plates were also measured for the zinc element content of the polarizer as described above. Furthermore, the resulting polarizing plates were subjected to a heat resistance test to calculate the rate of change ΔPy of luminous efficiency-corrected degree of polarization. The results are shown in Table 1.

[0094] [Table 1] [Explanation of symbols]

[0095] 1 polarizing plate, 10 polarizer, 101 first adhesive layer, 102 first resin film.

Claims

1. A polarizing plate including a polarizer, a first adhesive layer, and a first resin film in this order, the polarizer and the first adhesive layer are in direct contact with each other, The visibility corrected single transmittance is 47.0% or more, a total zinc content in the polarizer and the adhesive layer in direct contact with the polarizer is 0.15% by mass or more and 0.22% by mass or less, The polarizer has a thickness of 10 μm or more, the polarizer contains zinc; the first adhesive layer is made of an adhesive containing elemental zinc, The adhesive contains, in terms of solid content, 1.28 parts by mass or more and 5 parts by mass or less of zinc element when the total amount of the adhesive is taken as 100 parts by mass.

2. 2. The polarizing plate according to claim 1, which has a luminosity-corrected polarization degree of 94.0% or more.

3. The first resin film has a moisture permeability of 100 g / m at a temperature of 40° C. and a relative humidity of 90% RH. ２ The polarizing plate according to claim 1 or 2, wherein the polarizing plate has a temperature of 24 hours or more.

4. The polarizing plate according to any one of claims 1 to 3, further comprising a second adhesive layer and a second resin film, in this order from the side closer to the polarizer, on the opposite side of the polarizer from the first resin film.

5. The second resin film has a moisture permeability of 100 g / m at a temperature of 40° C. and a relative humidity of 90% RH. ２ The polarizing plate according to claim 4 , wherein the polarizing plate has a temperature of 24 hours or more.

6. The polarizing plate according to claim 4 , wherein the second adhesive layer contains elemental zinc.

7. A method for producing the polarizing plate according to any one of claims 1 to 6, comprising the steps of: A manufacturing method comprising a step of treating a polyvinyl alcohol-based resin film with a treatment liquid containing a zinc salt to produce a polarizer.

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