Polarizing plate and method for producing same

Abstract

To provide a polarizing plate having good heat resistance.SOLUTION: A polarizing plate includes 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 corrected unit 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 mass% or more, and the polarizer has a thickness of 10 μm or more.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] A polarizer is used as a polarizing plate in an image display device. When the image display device is used at a high temperature for a long time, the optical characteristics of the polarizing plate may change. In particular, in a polarizing plate with high transmittance such as for organic EL applications, the amount of the circular dichroic dye in the polarizer is small, and it is difficult to satisfy durability tests such as heat resistance. Therefore, improvement of the heat resistance of the polarizing plate is required.

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

Means for Solving the Problems

[0006] The present invention provides the following polarizing plate and a method for manufacturing the polarizing plate. [1] A polarizing plate including a polarizer, a first adhesive layer, and a first resin film in this order, wherein the polarizer and the first adhesive layer are in direct contact, the single transmittance for visual sensitivity correction is 45.5% or more, the content of zinc element contained in the polarizer and the adhesive layer in direct contact with the polarizer is 0.15% by mass or more, and the polarizer has a thickness of 10 μm or more. [2] The polarizing plate according to [1], wherein the polarization degree for visual sensitivity correction is 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% by mass or less. [4] The polarizing plate according to any one of [1] to [3], wherein the water vapor transmission rate of the first resin film at a temperature of 40 ° C and a relative humidity of 90% RH is 100 g / m 2 / 24 h or more. [5] The polarizing plate according to any one of [1] to [4], wherein the first adhesive layer contains a zinc element. [6] The polarizing plate according to any one of [1] to [5], further including 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 polarizing plate according to [6], wherein the water vapor transmission rate of the second resin film at a temperature of 40 ° C and a relative humidity of 90% RH is 100 g / m 2 / 24 h or more. [8] The polarizing plate according to [6] or [7], wherein the second adhesive layer contains a zinc element. [9] A method for manufacturing the polarizing plate according to any one of [1] to [8], comprising a step of manufacturing a polarizer by treating a polyvinyl alcohol-based resin film with a treatment liquid containing a zinc salt. [Effects of the Invention]

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

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Embodiments for Carrying Out 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. The polarizing plate 1 includes a polarizer 10, a first adhesive layer 101, and a first resin film 102 in this order. The polarizer 10 and the first adhesive layer 101 are in direct contact. The polarizing plate has a visual sensitivity corrected single transmittance (Ty) of 45.5% or more and a zinc element content of 0.15% by mass or more. The polarizer has a thickness of 10 μm or more. When the visual sensitivity corrected single transmittance (Ty) of the polarizing plate is 45.5% or more, a change in optical characteristics is more easily visually recognized as compared with a polarizing plate having a visual sensitivity corrected single transmittance (Ty) of less than 45.5%. According to the present invention, by setting the content of the zinc element contained in the polarizing plate and the thickness of the polarizer within the above ranges, a polarizing plate having a visual sensitivity corrected single transmittance (Ty) of 45.5% or more, excellent in heat resistance, and even when subjected to a heat resistance test, a polarizing plate in which a change in optical characteristics before and after the heat resistance test is suppressed can be provided.

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

[0011] In this specification, the heat resistance test means the durability test of the heat resistance test conducted according to the method described in the column of the examples below. In the polarizing plate, when subjected to the heat resistance test, the visually corrected polarization degree (Py) can be cited as an optical property whose change is suppressed before and after the durability test. The change rate (ΔPy) of the visually corrected polarization degree (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 the change rate (ΔPy) within such a range can be obtained.

[0012] The visually corrected polarization degree (Py) of the polarizing plate is preferably 92.0% or more, more preferably 93.0% or more, and even more preferably 94.0% or more. The visually corrected polarization degree (Py) of the polarizing plate may be 99.9% or less, or in another form may be 99% or less, or may be 98% or less.

[0013] The content of zinc element in the polarizer and the adhesive layer in direct contact with the polarizer is 0.15% by mass or more. By having the content of zinc element in the polarizer and the adhesive layer in direct contact with the polarizer be 0.15% by mass or more, a polarizing plate having good high-temperature durability can be provided. The content of such zinc element 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 tone, the content of such zinc element is preferably 0.22% by mass or less, and more preferably 0.20% by mass or less.

[0014] The total content of zinc element contained in the polarizer and the adhesive layer in direct contact with the polarizer can be adjusted by adjusting the content of zinc element in the polarizer, the content of zinc element in the first adhesive layer and / or the second adhesive layer in contact with the polarizer, etc. Also, the method for measuring the content of zinc element in the adhesive layer in direct contact with the polarizer shall be based on the method described in the examples below.

[0015] The b value of the single - body color phase of the polarizing plate is, for example, not less than - 1.0 and not more than 4.0, preferably not less than - 0.5 and not more than 3.0, and more preferably not less than 0 and not more than 2.0. The absorbance A700 of the polarizing plate at a wavelength of 700 nm is, for example, not less than 0.5 and not more than 3.0, preferably not less than 0.7 and not more than 2.0, and more preferably not less than 0.9 and not more than 1.5.

[0016] In this specification, the single - body transmittance (Ty) after visual - sensitivity correction, the degree of polarization (Py) after visual - sensitivity correction, the change rate (ΔPy) of the degree of polarization (Py) after visual - sensitivity correction, the b value of the single - body color phase, the absorbance A700 at a wavelength of 700 nm, and the content of zinc element in the polarizer and the adhesive layer in direct contact with the polarizer shall be the values measured according to the measurement methods described in the column of Examples below.

[0017] The first resin film is, for example, bonded to the surface of the polarizer through the first adhesive layer. The polarizing plate may further include, in this order from the side close to the polarizer on the side opposite to the first resin film, the second adhesive layer and the second resin film. The second resin film is, for example, bonded to the surface of the polarizer through the second adhesive layer. In the polarizing plate, when obtaining the "total content of zinc element contained in the polarizer and the adhesive layer in direct contact with the polarizer", the first adhesive layer corresponds to the adhesive layer in direct contact with the polarizer, and when the second adhesive layer is provided in direct contact with the polarizer, the second adhesive layer also corresponds. Hereinafter, the first resin film and the second resin film are collectively referred to as the resin film, and the first adhesive layer and the second adhesive layer are collectively referred to as the adhesive layer.

[0018] <Polarizer> The polarizer is an absorption - type polarizer having 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 the transmission axis). The polarizer may be, for example, a polarizer in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol - based resin film, and such a polarizer can be manufactured according to the manufacturing method of the polarizer described below.

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

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

[0021] The adjustment of the content of the zinc element contained in the polarizing plate is preferably carried out by adjusting the content of the zinc element contained in the polarizer. The polarizer contained in the polarizing plate of the present invention usually contains zinc. The content of the zinc element contained in the polarizer can be made to be within the above-described range of the content of the zinc element, for example, by adjusting the concentration of the zinc salt in the treatment liquid for treating 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, and the like.

[0022] <Method for manufacturing a polarizer> A method for manufacturing a polarizer according to another aspect of the present invention will be described with reference to the drawings. The manufacturing method shown in FIG. 2 is a method for manufacturing a polarizer containing a polyvinyl alcohol-based resin, and includes the following steps: A dyeing step S20 of immersing a polyvinyl alcohol-based resin film in a dyeing tank containing a treatment liquid containing a dichroic dye for dyeing; A crosslinking step S30 of immersing the film after the dyeing step in a crosslinking tank containing a treatment liquid containing a crosslinking agent for crosslinking treatment; can be included.

[0023] The manufacturing method can further include other steps other than the above. Specific examples thereof are, as shown in FIG. 2, a swelling step S10 of immersing a polyvinyl alcohol-based resin film before the dyeing step S20 in a swelling tank containing a treatment liquid containing water, a cleaning step S40 of immersing the film after the crosslinking step S30 in a cleaning tank, and a drying step S50 after the cleaning step S40. Further, the polyvinyl alcohol-based resin film is uniaxially stretched (stretching step) at any one or more stages of the polarizer manufacturing process, more specifically, at any 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 liquids for treating the polyvinyl alcohol-based resin film contains a zinc salt. Examples of the treatment tank for containing the treatment liquid include a swelling tank, a dyeing tank, a crosslinking tank, a cleaning tank, a complementary color tank described later, and the like. The treatment tank for containing the treatment liquid containing the zinc salt is preferably a treatment tank after the dyeing tank and before the cleaning tank, more preferably at least one selected from the crosslinking tank and the complementary color tank, and still more preferably at least one selected from the last crosslinking tank and the complementary color tank when there are two or more crosslinking tanks. By immersing the polyvinyl alcohol-based resin film in the treatment liquid containing the zinc salt, the obtained polarizer can contain zinc elements. The content of zinc elements in the polarizer can be made to be within the above-mentioned range by adjusting the concentration of the zinc salt in the treatment liquid, the immersion time of the polyvinyl alcohol-based resin film in the treatment liquid containing the zinc salt, the temperature of the treatment liquid, and the like.

[0025] Examples of the zinc salt contained in the treatment liquid include zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, zinc nitrate, and the like. Among them, zinc nitrate is preferred because of its low cost. The zinc salt can be added to the treatment liquid as a zinc salt solution.

[0026] The concentration of the zinc salt in the treatment liquid may vary for each treatment tank, but is preferably 2 parts by mass or more and 10 parts by mass or less, more preferably 3 parts by mass or more and 6 parts by mass or less, based on 100 parts by mass of the treatment liquid 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 be different 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 according to the present invention can be continuously carried out by continuously transporting the polyvinyl alcohol-based resin film, which is the raw film, along the film transport path of the polarizer manufacturing device. 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 arranged before and after each processing tank or inside the processing tank, which allows the film to be introduced into and immersed in the processing tank and drawn out from the processing tank. More specifically, two or more guide rolls are provided in each processing tank, and the film can be immersed in each processing tank by transporting the film along these guide rolls.

[0030] Polyvinyl alcohol that constitutes the polyvinyl alcohol-based resin film, which is the base film As the alcohol-based resin, a saponified polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and 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-based resin is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. In this specification, "(meth)acrylic" means at least one selected from acrylic and methacrylic. The same applies to "(meth)acryloyl".

[0031] The polyvinyl alcohol-based resin may be modified. For example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes can also be used.

[0032] The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 or more and 10,000 or less, more preferably 1,500 or more and 8,000 or less, and still more preferably 2,000 or more and 5,000 or less. The average degree of polymerization of the polyvinyl alcohol-based 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 polarization performance, and if it exceeds 10,000, the film processability may be inferior.

[0033] From the viewpoint of making the thickness of the polarizer 10 μm or more, the thickness of the polyvinyl alcohol-based 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 still more preferably 40 μm or more and 65 μm or less.

[0034] The polyvinyl alcohol-based resin film as 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 can also be obtained as a long product. Hereinafter, each step will be described in detail.

[0035] (1) Swelling step S10 The swelling treatment in this step is a treatment that is carried out as necessary for the purposes of removing foreign substances, removing plasticizers, imparting easy dyeability, plasticizing the film, etc. of the polyvinyl alcohol-based resin film as the raw film. Specifically, it can be a treatment of immersing the polyvinyl alcohol-based resin film in a swelling tank containing a treatment liquid containing water. The film may be immersed in one swelling tank or may be sequentially immersed in two or more swelling tanks. Before the swelling treatment, during the swelling treatment, or before and during the swelling treatment, a uniaxial stretching treatment may be performed on the film.

[0036] The treatment liquid contained in the swelling tank can be water (e.g., pure water), or it can be an aqueous solution added with a water-soluble organic solvent such as alcohols. As described above, the treatment liquid contained in the swelling tank can contain zinc salts.

[0037] The temperature of the treatment liquid 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 step S20 The dyeing treatment in this step is a treatment performed for the purpose of adsorbing and orienting dichroic dyes on the polyvinyl alcohol-based resin film. Specifically, it can be a treatment of immersing the polyvinyl alcohol-based resin film in a dyeing tank containing a treatment liquid containing dichroic dyes. The film may be immersed in one dyeing tank or sequentially immersed in two or more dyeing tanks. In order to enhance the dyeability of the dichroic dye, the film subjected to the dyeing step may be subjected to at least a certain degree of uniaxial stretching treatment. Instead of the uniaxial stretching treatment before the dyeing treatment, or in addition to the uniaxial stretching treatment before the dyeing treatment, a uniaxial stretching treatment may be performed during the dyeing treatment.

[0039] The dichroic dye can be iodine or a dichroic organic dye. Specific examples of the dichroic organic dye include Red BR, Red LR, Red R, Pink LB, Rubine 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, Spra Blue G, Spra Blue GL, Spra Orange GL, Direct Sky Blue, Direct Fast Orange S, Fast Black. The dichroic dye may be used alone or in combination of two or more.

[0040] When iodine is used as the dichroic pigment, an aqueous solution containing iodine and potassium iodide can be used as the treatment liquid accommodated in the dyeing bath. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. Further, compounds other than iodides, for example, boric acid, zinc chloride, cobalt chloride, etc. may coexist. When adding boric acid, it is distinguished from the crosslinking treatment described later in that it contains iodine. The iodine content in the above aqueous solution is usually 0.01 parts by mass or more and 1 part by mass or less per 100 parts by mass of water. Further, the content of iodides such as potassium iodide is usually 0.5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of water. As described above, the treatment liquid accommodated in the dyeing bath can contain a zinc salt.

[0041] The temperature of the treatment liquid accommodated in the dyeing bath when dipping the film is usually 10°C or more and 45°C or less, preferably 10°C or more and 40°C or less, more preferably 20°C or more and 35°C or less, and the dipping time of the film is usually 30 seconds or more and 600 seconds or less, 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 accommodated in the dyeing bath. The content of the dichroic organic dye in the aqueous solution is usually 1×10 -4 parts by mass or more and 10 parts by mass or less per 100 parts by mass of water, preferably 1×10 -3 parts by mass or more and 1 part by mass or less. A dyeing assistant or the like may coexist in the dyeing bath, for example, an inorganic salt such as sodium sulfate or a surfactant may be contained. Only one kind of dichroic organic dye may be used alone, or two or more kinds may be used in combination. The temperature of the treatment liquid accommodated in the dyeing bath when dipping the film is, for example, 20°C or more and 80°C, preferably 30°C or more and 70°C or less, and the dipping time of the film is usually 30 seconds or more and 600 seconds or less, preferably 60 seconds or more and 300 seconds or less.

[0043] (3) Crosslinking step S30 The crosslinking treatment of treating the polyvinyl alcohol-based resin film after the dyeing process with a crosslinking agent is a treatment performed for purposes such as water resistance improvement and hue adjustment by crosslinking. Specifically, it can be a treatment of immersing the film after the dyeing process in a treatment liquid contained in a crosslinking tank containing a crosslinking agent. The film may be immersed in one crosslinking tank or sequentially immersed in two or more crosslinking tanks. A uniaxial stretching treatment may be performed during the crosslinking treatment.

[0044] Examples of the crosslinking agent include boric acid, glyoxal, glutaraldehyde, etc., and boric acid is preferably used. Two or more crosslinking agents can also be used in combination. The content of boric acid in the treatment liquid contained in the crosslinking tank is usually 0.1 part by mass or more and 15 parts by mass or less, preferably 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of water. When the dichroic dye is iodine, the treatment liquid contained in the crosslinking tank preferably contains an iodide in addition to boric acid. The content of the iodide in the treatment liquid contained in the crosslinking tank is usually 0.1 part by mass or more and 15 parts by mass or less, preferably 5 parts by mass or more and 12 parts by mass or less per 100 parts by mass of water. Examples of the iodide include potassium iodide, zinc iodide, etc. Also, compounds other than iodides, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. may coexist in the crosslinking tank. As described above, the treatment liquid contained in the crosslinking tank can contain a zinc salt. When there are two or more crosslinking tanks, it is preferable that the treatment liquid contained in the last crosslinking tank contains a zinc salt.

[0045] The temperature of the treatment liquid contained in the crosslinking tank when immersing the film is usually 50°C or higher and 85°C or lower, preferably 50°C or higher and 70°C or lower, 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] In the crosslinking step S30, there may be 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 and temperature of a crosslinking agent and iodide, etc., 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 color tone adjustment (complementary color) may be performed in a plurality of steps (for example, a plurality of tanks), respectively. Generally, when performing both the crosslinking treatment for water resistance by crosslinking and the crosslinking treatment for color tone adjustment (complementary color), the tank (complementary color tank) for performing the crosslinking treatment for color tone adjustment (complementary color) is arranged at the rear stage. The temperature of the treatment liquid contained in the complementary color tank is, for example, 10°C or higher and 55°C or lower, preferably 20°C or higher and 50°C or lower. The content of the crosslinking agent in the treatment liquid contained in the complementary color tank is, for example, 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of water. The content of iodide in the treatment liquid contained in the complementary color tank is, for example, 3 parts by mass or more and 30 parts by mass or less per 100 parts by mass of water. As described above, the treatment liquid contained in the complementary color tank can contain a zinc salt.

[0047] As described above, in the production of a polarizer, the polyvinyl alcohol-based resin film is uniaxially stretched at any one or two or more stages from before the swelling step S10 to the crosslinking step S30 (stretching step, Figure 2). From the viewpoint of enhancing 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 a certain degree of uniaxial stretching treatment, or instead of the uniaxial stretching treatment before the dyeing treatment, or in addition to the uniaxial stretching treatment before the dyeing treatment, it is preferable to perform the uniaxial stretching treatment during the dyeing treatment.

[0048] The uniaxial stretching treatment may be either a dry stretching method that performs stretching in the air or a wet stretching method that performs stretching in a bath, or both may be performed. The uniaxial stretching treatment can be, for example, inter-roll stretching, hot roll stretching, tenter stretching, etc., in which a circumferential speed difference is created between two nip rolls to perform longitudinal uniaxial stretching. Preferably, it includes inter-roll stretching. The stretching ratio based on the original film (the cumulative stretching ratio when stretching treatments are performed in multiple stages with a stretching ratio of 2 or more) is 3 times or more and 8 times or less. In order to impart good polarization characteristics, the stretching ratio is preferably 4 times or more, more preferably 5 times or more.

[0049] (4) Cleaning step S40 The cleaning treatment in this step is a treatment that is carried out as necessary for the purpose of removing excess cross-linking agents, dichroic dyes, and other chemicals adhering to the polyvinyl alcohol-based resin film. It is a treatment for cleaning the polyvinyl alcohol-based resin film after the cross-linking step using a cleaning liquid containing water. Specifically, it can be a treatment of immersing the polyvinyl alcohol-based resin film after the cross-linking step in a treatment liquid (cleaning liquid) housed in a cleaning tank. The film may be immersed in one cleaning tank or sequentially immersed 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 cross-linking step, or a combination of the above immersion and spraying may be used. The cleaning liquid can be water (e.g., pure water), or an aqueous solution added with a water-soluble organic solvent such as alcohols. The temperature of the cleaning liquid can be, for example, 5°C or more and 40°C or less.

[0050] The cleaning step S40 is an optional step and may be omitted. As described later, the cleaning treatment may also be performed during the drying step S50. Preferably, the drying step S50 is performed on the film after the cleaning step S40.

[0051]

[0052] (5) Drying step S50 ​The drying step S50 is a zone for drying the polyvinyl alcohol-based resin film after the washing step S40. While continuously conveying the polyvinyl alcohol-based resin film after the washing step S40, the film can be introduced into the drying step S50 to perform a drying treatment, whereby a polarizer can be obtained.

[0053] The drying treatment is performed using a drying means (heating means) for the film. A preferred example of the drying means is a drying furnace. The drying furnace is preferably one capable of controlling the temperature inside the furnace. The drying furnace is, for example, a hot air oven capable of increasing the temperature inside the furnace by supplying hot air or the like. Further, the drying treatment by the drying means may be a treatment of bringing the polyvinyl alcohol-based resin film after the washing step S40 into close contact with one or more heating bodies having a convex curved surface, or a treatment of heating the film using a heater.

[0054] Examples of the above heating body include a roll (for example, a guide roll also serving as a hot roll) having a heat source (for example, a heat medium such as warm water or an infrared heater) inside and capable of increasing the surface temperature. Examples of the above heater include an infrared heater, a halogen heater, a panel heater, and the like.

[0055] The temperature of the drying treatment (for example, the temperature inside the drying furnace, the surface temperature of the hot 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 more and 600 seconds or less.

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

[0057] The obtained polarizer can be conveyed, for example, directly to the next polarizing plate manufacturing step (a step of laminating a thermoplastic resin film on one or both sides of the polarizer).

[0058] <Resin Film> As the resin film, it can be a transparent resin film made of a thermoplastic resin, for example, a polyolefin resin such as a chain 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, etc. thereof.

[0059] Either one or preferably both of the first resin film and the second resin film have a moisture permeability of 100 (g / m 2 / 24h) or more, particularly 300 (g / m 2 / 24h) or more at a temperature of 40°C and a relative humidity of 90%RH, and particularly effective in this case. In such a film with a high moisture permeability, since there is an inflow and outflow of moisture, the high-temperature durability tends to be low. However, by satisfying the invention requirements of this patent, high high-temperature durability can be provided. Examples of the resin film satisfying such a moisture permeability include triacetyl cellulose and the like. Further, if the resin film has a moisture permeability of 100 (g / m 2 / 24h) or more at a temperature of 40°C and a relative humidity of 90%RH, it may have a surface treatment layer such as a hard coat layer or an antireflection layer on the surface of the resin film. When using such a resin film with a moisture permeability, the heat resistance of the polarizing plate tends to deteriorate, but the polarizing plate of the present invention has good durability.

[0060] Either one or both of the first resin film and the second resin film can also be a protective film having an optical function such as a retardation film or a brightness enhancement film. For example, by stretching (uniaxial stretching, biaxial stretching, etc.) a transparent resin film made of the above materials or forming a liquid crystal layer or the like on the film, a retardation film with an arbitrary retardation value can be obtained.

[0061] On the surface of the resin film opposite to the polarizer, surface treatment layers (coating layers) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer can also be formed.

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

[0063] (Adhesive layer) The polarizing plate can be obtained by laminating (bonding) a resin film via an adhesive layer on one or both sides of the polarizer. Examples of the adhesive used for bonding 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 a crosslinking agent added thereto, and aqueous adhesives such as urethane-based emulsion adhesives. As the adhesive, an adhesive containing a zinc element may be used. By applying an adhesive containing a zinc element to the surface of the polarizer, the migration of the zinc element in the polarizer to other layers can be suppressed, and the reduction of high-temperature durability can be suppressed. Examples of the method of incorporating a zinc element into the adhesive include adding a zinc salt during the preparation of the adhesive. As the zinc salt, zinc halides such as zinc chloride and zinc iodide, zinc sulfate, zinc acetate, zinc nitrate, etc. can be used. The content of the zinc element in the adhesive can be, for example, 0.1 part by mass or more and 5 parts by mass or less in terms of solid content when the total amount of the adhesive is 100 parts by mass.

[0064] When bonding resin films to both sides of a polarizer, the adhesives forming the two adhesive layers may be of the same type or different types. For example, when bonding resin films to both sides, one side may be bonded using an aqueous adhesive, and the other side may be bonded using an active energy ray curable adhesive. The ultraviolet curable adhesive can be a mixture of a radical polymerizable (meth)acrylic compound and a photo radical polymerization initiator, a mixture of a cationic polymerizable epoxy compound and a photo cationic polymerization initiator, or the like. Further, a cationic polymerizable epoxy compound and a radical polymerizable (meth)acrylic compound can be used in combination, and a photo cationic polymerization initiator and a photo radical polymerization initiator can be used in combination as initiators.

[0065] When using an active energy ray curable adhesive, after bonding, the adhesive is cured by irradiating with active energy rays. The light source of the active energy rays is not particularly limited, but active energy rays (ultraviolet rays) having an emission distribution at a wavelength of 4 00 nm or less are preferred. Specifically, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a chemical lamp, a black light lamp, a microwave-excited mercury lamp, a metal halide lamp, etc. are preferably used.

[0066] In order to improve the adhesiveness between the polarizer and the resin film, before bonding the polarizer and the resin film, surface treatments such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation treatment, primer coating treatment, saponification treatment, etc. may be performed on the bonding surfaces of the polarizer and / or the resin film.

[0067] As described above, the polarizing plate of the present invention can be produced by bonding a resin film to a polarizer which is a single-layer film via an adhesive layer, but is not limited to this method. For example, it can also be produced by a method using a base 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 obtaining a laminated film by applying a coating liquid containing a polyvinyl alcohol-based resin to at least one surface of a base film and then drying to form a polyvinyl alcohol-based resin layer. A stretching step of stretching the laminated film to obtain a stretched film. A dyeing step of obtaining a polarizing laminated film by dyeing the polyvinyl alcohol-based resin layer of the stretched film with a dichroic dye to form a polarizer layer (corresponding to a polarizer). A first laminating step of obtaining a laminated film by laminating a resin film (first resin film) on the polarizer layer of the polarizing laminated film using an adhesive (first adhesive layer). A peeling step of peeling and removing the base film from the laminated film to obtain a polarizing plate with a single-sided resin film. It may contain zinc in at least one of the above dyeing step and the first laminating step. When containing zinc element in the above dyeing step, zinc can be contained in the polarizing plate by containing a zinc salt in the treatment liquid containing the dichroic dye. Also, when containing zinc element in the first laminating step, zinc element can be contained in the polarizing plate by containing zinc element in the adhesive.

[0069] When laminating resin films on both sides of the polarizer layer (polarizer), it further includes a second laminating step of laminating a second resin film on the polarizer surface of the single-sided polarizing plate with a first resin film using an adhesive (second adhesive layer). Also, the adhesive for laminating the second resin film may contain zinc element.

[0070] In the above method using a base film, a drying step can be included in the dyeing step of obtaining a polarizing laminated film (for example, after the cross-linking step or the washing step during the dyeing step of obtaining a polarizing laminated film). The polarizer contained in the above polarizing laminated film, the polarizing plate with a single-sided thermoplastic resin film, and the polarizing plate with a double-sided thermoplastic resin film obtained through the second laminating step, or the polarizer 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 the liquid crystal light-emitting element. Further, when incorporated into an organic EL display device, a circular polarizing plate formed by combining a retardation film and the polarizing plate of the present invention may be used as an antireflection film.

[0072] The in-vehicle display polarizing plate includes, in this order, a polarizing plate, a light-transmissive member bonded to the surface of the polarizing plate on the first resin film side, and a display device bonded to the surface of the polarizing plate on the second resin film side. The light-transmissive member may be a glass plate, a resin film having light-transmittance, or the like.

[0073] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited by these examples.

Examples

[0074] [Visual sensitivity correction single transmittance (Ty), visual sensitivity correction degree of polarization (Py), and single hue b value] Regarding the polarizing plate, the MD transmittance and TD transmittance in the wavelength range of 380 to 780 nm were measured 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 Based on this, the single transmittance and degree of polarization at each wavelength were calculated. The “MD transmittance” is the transmittance when the direction of polarization emerging from the Glan-Thompson prism is parallel to the transmission axis of the polarizing plate, and is represented as “MD” in the above formula. The “TD transmittance” is the transmittance when the direction of polarization emerging from the Glan-Thompson prism is perpendicular to the transmission axis of the polarizing plate, and is represented as “TD” in the above formula. Regarding the obtained single transmittance and degree of polarization, visual sensitivity correction was performed according to the 2-degree field of view (C light source) of JIS Z 8701:1999 "Color Display Method - XYZ Color System and X10Y10Z10 Color System" to obtain the visually sensitivity-corrected single transmittance (Ty) and the visually sensitivity-corrected degree of polarization (Py). Furthermore, based on the method described in International Publication No. 2016 / 117659, the spectral transmittance τ(λ) of the polarizing plates produced in the examples and comparative examples was measured with a spectrophotometer (V7100, manufactured by JASCO Corporation), and from this, the orthogonal spectral transmittance spectrum was obtained, and the single-color phase b value and the value of A700 defined by the following formula were obtained. 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 arranged such that the absorption axis of the polarizer is orthogonal 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 arranged such that the absorption axis of the polarizer is parallel to the linearly polarized light of the measurement light, and the units of both are %.

[0075] [Heat Resistance Test] A test piece of 40 mm × 40 mm was cut out from the manufactured polarizing plate, and 40 mm × 40 mm of non-alkali glass was bonded to both sides of the cut-out polarizing plate using an acrylic adhesive with a thickness of 25 μm to prepare a sample. For each sample, before subjecting it to the heat resistance test, in accordance with the above-described method, based on the measured values, the visually sensitivity-corrected single transmittance (Ty), the visually sensitivity-corrected degree of polarization (Py), the single-color phase b value, and A700 were calculated.

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

[0077] The rate of change ΔPy [%] is the rate of change of the visually corrected polarization degree (Py) before and after being subjected to the heat resistance test. When the visually corrected polarization degree (Py) before being subjected to the durability test is P1 and the visually corrected polarization degree (Py) after being subjected to the heat resistance test is P2, it is the value calculated by the following formula (1). ΔPy={(P1 - P2) / P1}×100 (1)

[0078] [Measurement of the content of zinc element] The polarizing plate was immersed in methylene chloride for 30 minutes and subjected to ultrasonic treatment to dissolve the resin films (triacetyl cellulose films) on both sides of the polarizing plate with methylene chloride, and a sample composed of a polarizer and the adhesive layer in contact with the polarizer was taken out. 1 g of the sample taken out and 50 ml of mannitol solution were put into a 100 ml container, electrodes were put in, and titration was carried out with 0.1 N NaOH. The first end point and the second end point of the analytical instrument were recorded, and the concentration was calculated from the following calculation formula. The content (% by mass) of zinc contained in the polarizer and the adhesive layer in contact with the polarizer =(Amount of 0.1 N NaOH used at the second end point [mL] - Amount of 0.1 N NaOH used at the first end point [mL])×0.29749×0.1×0.5 / Sample amount [g]

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

[0080] [Preparation of adhesive] To 100 parts of water, 3. 5 parts of Gosefimer Z - 200 (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 0.12 part of zinc chloride, and 0.89 part of glyoxal were dissolved to prepare a polyvinyl alcohol - based resin adhesive A.

[0081] [Example 1] (Manufacture of polarizer) A transparent unstretched polyvinyl alcohol film (TS4500, manufactured by Kuraray Co., Ltd.) with a saponification degree of 99.9% or more and a thickness of 45 μm was immersed in water (deionized water) at 30°C for 2 minutes to swell it, and then dyed by immersing it in a dyeing solution at 30°C containing 0.45 mmol / L of iodine, 2 parts by mass of potassium iodide, and 0.35 parts by mass of boric acid for 2 minutes. At this time, stretching was performed at stretching ratios of 1.72 times and 1.54 times during the swelling and dyeing steps, respectively, so that the cumulative stretching ratio up to the dyeing tank was 2.64 times. Subsequently, while immersing in a crosslinking solution at 56°C containing 7.9 parts by mass of potassium iodide and 4.3 parts by mass of boric acid for 30 seconds (crosslinking step) to crosslink, stretching was performed at a stretching ratio of 2.2 times. Further, while immersing in a crosslinking solution at 40°C containing 10.6 parts by mass of potassium iodide, 5.0 parts by mass of zinc nitrate, and 3.9 parts by mass of boric acid for 5 seconds (complementary color step) to crosslink, stretching treatment was performed. At this time, the total cumulative stretching ratio in the swelling, dyeing, crosslinking, and complementary color steps was set to 5.9 times. After the crosslinking was completed, the polyvinyl alcohol film was dried in an oven at 100°C to produce a polarizer. The thickness of the polarizer was 18 μm.

[0082] (Manufacture of polarizer) Using the polyvinyl alcohol-based adhesive A prepared above, protective films were laminated on both sides of the polarizer. As the protective films, a triacetyl cellulose film (KC4UAW, manufactured by Konica Minolta, Inc., thickness 40 μm, moisture permeability at a temperature of 40°C and a relative humidity of 90% RH of 800 g / m 2 / 24 h) was used on one side of the polarizer, and an antireflection (LR) surface-treated triacetyl cellulose film (thickness 60 μm, reflectance 1%) was used on the other side. The lamination was carried out by applying the polyvinyl alcohol-based adhesive A to both sides of the polarizer, then joining them using a nip roll, and drying at 80°C for 5 minutes to produce the polarizer of Example 1.

[0083] <Example 2> (Manufacture of polarizer) In Example 1, a polarizer was produced in the same manner as in Example 1, except that the temperature of the crosslinking solution in the crosslinking step was changed to 60°C instead of 56°C, and the concentration of boric acid in the crosslinking solution in the complementary color step was set to 3.0 parts by mass. It was. The thickness of the polarizer was 18 μm.

[0084] (Manufacture of polarizing plate) Using the polarizer manufactured above, a polarizing plate of Example 2 was manufactured in the same manner as in Example 1.

[0085] <Example 3> (Manufacture of polarizer) In Example 1, a polarizer was manufactured in the same manner as in Example 1, except that the drying temperature of the polyvinyl alcohol film after the crosslinking was completed was changed from 100 °C to 90 °C, and the boric acid concentration of the crosslinking solution in the complementary color stage was 3.0 parts by mass. The thickness of the polarizer was 18 μm.

[0086] (Manufacture of polarizing plate) Using the polarizer manufactured above, a polarizing plate of Example 3 was manufactured in the same manner as in Example 1.

[0087] <Example 4> (Manufacture of polarizer) In Example 1, instead of the transparent unstretched polyvinyl alcohol film (TS4500, manufactured by Kuraray Co., Ltd.) with a saponification degree of 99.9% or more and a thickness of 45 μm, a transparent unstretched polyvinyl alcohol film (PE-6000, manufactured by Kuraray Co., Ltd.) with a saponification degree of 99.9% or more and a thickness of 60 μm was used, and a polarizer was manufactured in the same manner as in Example 1, except that the boric acid concentration of the crosslinking solution in the complementary color stage was 3.0 parts by mass. The thickness of the polarizer was 23 μm.

[0088] (Manufacture of polarizing plate) Using the polarizer manufactured above, a polarizing plate of Example 4 was manufactured in the same manner as in Example 1.

[0089] <Comparative Example 1> (Manufacture of polarizer) In Example 1, a polarizer was manufactured in the same manner as in Example 1, except that the content of zinc nitrate in the crosslinking solution in the complementary color stage was changed from 5.0 parts to 3.0 parts. The thickness of the polarizer was 18 μm.

[0090] (Manufacture of polarizing plate) Using the polarizer manufactured above, a polarizing plate of Comparative Example 1 was manufactured in the same manner as in Example 1.

[0091] <Comparative Example 2> (Manufacture of Polarizer) In Example 1, a polarizer was manufactured in the same manner as in Example 1, except that the content of zinc nitrate in the crosslinking solution at the complementary color stage was changed to 0 parts instead of 5.0 parts. The thickness of the polarizer was 18 μm.

[0092] (Manufacture of Polarizing Plate) Using the polarizer manufactured above, a polarizing plate of Comparative Example 1 was manufactured in the same manner as in Example 1.

[0093] <Test> For the polarizing plates of Examples 1 to 4 and Comparative Examples 1 to 3, the visually corrected single transmittance (Ty), visually corrected polarization degree (Py), single hue b value, and A700 were measured as described above. Also, for the obtained polarizing plates, the content of zinc element in the polarizer was measured as described above. Further, the obtained polarizing plates were subjected to a heat resistance test to calculate the change rate ΔPy of the visually corrected polarization degree. 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 45.5% or more, a total zinc content in the polarizer and the adhesive layer in direct contact with the polarizer is 0.15 mass% or more, The polarizer has a thickness of 10 μm or more.

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

3. 3. The polarizing plate according to claim 1, wherein a total content of zinc element contained in the polarizer and the adhesive layer that is 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 claims 1 to 3, wherein the polarizing plate has a thermal conductivity of 100 / 24h or more.

5. 5. The polarizing plate according to claim 1, wherein the first adhesive layer contains elemental zinc.

6. The polarizing plate according to any one of claims 1 to 5, further comprising, on the opposite side of the polarizer to the first resin film, a second adhesive layer and a second resin film, in this order, 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 The polarizing plate according to claim 6, wherein the polarizing plate has a thermal conductivity of 100 / 24h or more.

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

9. A method for producing the polarizing plate according to any one of claims 1 to 8, comprising the steps of: The method includes 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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