Method for manufacturing polarizer

Abstract

To improve heat resistance of a polarizer composed of a polyvinyl alcohol-based resin film.SOLUTION: A method for manufacturing a polarizer which manufactures a polarizer 11 from a raw fabric film 21 that is a polyvinyl alcohol-based resin film includes a swelling step of immersing the film in a swelling liquid 14 and thereby swelling the film. The manufacturing method includes a dyeing step of immersing the film after the swelling step in a dyeing liquid 15, and thereby dyeing the film. The manufacturing method includes a crosslinking step of immersing the film after the dyeing step in crosslinking liquids 16a and 16b, and thereby crosslinking the film. The manufacturing method performs a drawing step of drawing the film, in at least one step of the swelling step, the dyeing step, and the crosslinking step. At least one of the swelling liquid 14, the dyeing liquid 15, and the crosslinking liquids 16a and 16b contains aldonic acid salt and nitrate.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing a polarizer by producing a polarizer from a polyvinyl alcohol-based resin film.

Background Art

[0002] Patent Document 1 describes that gluconic acid or zinc gluconate is contained in a polarizer made of a polyvinyl alcohol-based resin film in which iodine is adsorbed and oriented.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the case of using the polarizer described in Patent Document 1 in a more severe environment (for example, a high-temperature environment) such as an in-vehicle image display device such as a car navigation device or a back monitor, it may not always have sufficient durability.

Means for Solving the Problems

[0005] The present invention includes the following inventions. [Invention 1] A method for producing a polarizer by producing a polarizer from a polyvinyl alcohol-based resin film, a swelling step of swelling the polyvinyl alcohol-based resin film by immersing it in a swelling liquid, a dyeing step of dyeing the polyvinyl alcohol-based resin film after the swelling step by immersing it in a dyeing liquid, and a crosslinking step of crosslinking the polyvinyl alcohol-based resin film after the dyeing step by immersing it in a crosslinking liquid. At least one of the swelling step, the dyeing step, and the crosslinking step is performed in combination with a stretching step of stretching the polyvinyl alcohol-based resin film. A method for producing a polarizer, wherein at least one of the swelling liquid, the dyeing liquid, and the crosslinking liquid contains an aldonic acid salt and a nitrate salt.

[0006] [Invention 2] The method for producing a polarizer according to [Invention 1], wherein the aldonic acid salt is a metal gluconate.

[0007] [Invention 3] The method for producing a polarizer according to [Invention 1] or [Invention 2], wherein the nitrate salt is an alkali metal nitrate salt.

[0008] [Invention 4] The method for producing a polarizer according to any one of [Invention 1] to [Invention 3], wherein the content of the nitrate salt is 20 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the aldonic acid salt.

[0009] [Invention 5] The method for producing a polarizer according to any one of [Invention 1] to [Invention 4], wherein the crosslinking liquid contains the aldonic acid salt and the nitrate salt. [Advantages of the Invention]

[0010] According to the production method of the present invention, a polarizer having good durability can be produced even in a high-temperature environment such as in-vehicle use. [Brief Description of the Drawings]

[0011]

Figure 1

[0012] Hereinafter, the method for producing a polarizer of the present invention will be described. The method for manufacturing a polarizer according to this embodiment includes a swelling step, a dyeing step, and a crosslinking step. In the method for manufacturing a polarizer, at least one of the swelling step, the dyeing step, and the crosslinking step is performed in combination with a stretching step.

[0013] Hereinafter, the method for manufacturing a polarizer may sometimes be simply referred to as the manufacturing method. As used herein, the expression "at least one" means "one or more" of the desired options. For example, as used herein, the expression "at least one" means "only one option" or "any combination of two or more options" if the number of options is three or more.

[0014] <Polarizer> A polarizer is one in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film. As the polyvinyl alcohol-based resin, for example, one obtained by saponifying a polyvinyl acetate-based resin can be used. The saponification degree of the polyvinyl acetate-based resin is preferably 85 mol% or more, more preferably 90 mol% or more, and still more preferably 99 mol% or more.

[0015] As the polyvinyl acetate-based resin, for example, polyvinyl acetate which is a homopolymer of vinyl acetate, a copolymer of vinyl acetate and other monomers copolymerizable therewith, etc. can be used. Examples of other monomers copolymerizable therewith include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and the like.

[0016] The degree of polymerization of the polyvinyl alcohol-based resin is preferably 1000 or more and 10000 or less, and more preferably 1500 or more and 5000 or less. The polyvinyl alcohol-based resin may be modified. Examples of the modified polyvinyl alcohol-based resin include polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes.

[0017] Examples of the dichroic pigment include iodine, water-soluble dichroic dyes, and the like. The thickness of the polarizer is not particularly limited, but is, for example, 1 μm or more, preferably 5 μm or more, more preferably 8 μm or more. It is also 50 μm or less, preferably 30 μm or less.

[0018] <Method for manufacturing a polarizer> As described above, the method for manufacturing a polarizer of the present invention includes a swelling step, a dyeing step, and a crosslinking step, and at least one of the swelling step, the dyeing step, and the crosslinking step is performed in combination with a stretching step. The swelling step is a step of swelling an unstretched polyvinyl alcohol-based resin film (raw film) by immersing it in a swelling liquid, the dyeing step is a step of dyeing the polyvinyl alcohol-based resin film after the swelling step by immersing it in a dyeing liquid, the crosslinking step is a step of crosslinking the polyvinyl alcohol-based resin film after the dyeing step by immersing it in a crosslinking liquid, and the stretching step is a step of subjecting the polyvinyl alcohol-based resin film to a uniaxial stretching treatment.

[0019] The method for manufacturing a polarizer of the present invention may further include other treatment steps other than the swelling step, the dyeing step, the crosslinking step, and the stretching step, if necessary. Examples of other treatment steps include a cleaning step of cleaning the polyvinyl alcohol-based resin film, a drying step of drying the polyvinyl alcohol-based resin film, and the like.

[0020] Also, the swelling step, the dyeing step, and the crosslinking step may each be a process of immersing the polyvinyl alcohol-based resin film in one liquid, or a process of sequentially immersing the polyvinyl alcohol-based resin film in two or more liquids. Among these, the crosslinking step is preferably a process of sequentially immersing the polyvinyl alcohol-based resin film in two or more liquids.

[0021] Hereinafter, with reference to FIG. 1, the method for manufacturing a polarizer according to the present invention will be described in more detail. As shown in FIG. 1, the manufacturing of the polarizer 11 is performed using a polarizer manufacturing apparatus 20. The polarizer manufacturing apparatus 20 shown in FIG. 1 includes a swelling liquid 14, a dyeing liquid 15, a first crosslinking liquid 16a, a second crosslinking liquid 16b, and a cleaning liquid 17, and the crosslinking process is a process of sequentially immersing in two or more liquids. Further, the polarizer manufacturing apparatus 20 includes a drying furnace 18, guide rolls 30 to 48, 60, 61, and nip rolls 70 to 76. By appropriately arranging the guide rolls and nip rolls, a conveyance path for the polyvinyl alcohol-based resin film can be constructed.

[0022] When manufacturing the polarizer 11, a raw film 21, which is an unstretched polyvinyl alcohol-based resin film, is used. The raw film 21 is wound around a roll 22. First, while unwinding the raw film 21 from the roll 22, it is conveyed along the film conveyance path of the polarizer manufacturing apparatus 20. Next, a processing step of immersing the raw film 21 in a processing liquid and then pulling it out is performed. Further, by performing a drying step, a long polarizer 11 can be continuously manufactured. Note that the arrows in FIG. 1 indicate the conveyance direction of the film.

[0023] The polarizer manufacturing apparatus 20 conveys the film using guide rolls 30 to 48, 60, 61 and nip rolls 70 to 76. Then, the swelling liquid 14, the dyeing liquid 15, the first crosslinking liquid 16a, the second crosslinking liquid 16b, and the cleaning liquid 17 provided on the film conveyance path are sequentially passed through. Finally, it is passed through the drying furnace 18.

[0024] The guide rolls 30 to 48, 60, 61 and the nip rolls 70 to 76 can be arranged before and after each processing liquid or in the processing liquid. Thereby, the introduction / immersion of the film into the processing liquid and the pulling out from the processing liquid can be efficiently performed. For example, by providing one or more guide rolls in each processing liquid and conveying the film along these guide rolls, the film can be efficiently immersed in each processing liquid.

[0025] As shown in FIG. 1, in the method for manufacturing a polarizer, a swelling step, a dyeing step, a crosslinking step, a washing step, and a drying step are performed in this order. Hereinafter, the details of the swelling step, the dyeing step, the crosslinking step, the washing step, the drying step, and the stretching step will be described.

[0026] 〔Stretching Step〕 The stretching step in the method for manufacturing a polarizer will be described. The guide rolls 30 to 48, 60, 61 of the polarizer manufacturing apparatus 20 are used to support the film being conveyed or to change the conveyance direction of the film. The nip rolls 70 to 76 are used to press and sandwich the film being conveyed and apply the driving force due to their rotation to the film. Further, by disposing the nip rolls 70 to 76 before and after each treatment liquid, a peripheral speed difference can be created between the nip rolls 70 to 76 disposed before and after in any one or more of the treatment liquids. By creating a peripheral speed difference between the nip rolls 70 to 76, it becomes possible to perform inter-roll stretching. That is, during a series of treatment steps from the swelling step to the washing step, that is, before, after, or during any one or more of the treatment steps, a uniaxial stretching treatment can be performed as the stretching step. The stretching step can be performed in combination with at least one of the swelling step, the dyeing step, and the crosslinking step.

[0027] The final cumulative stretching ratio of the polarizer 11 with respect to the raw film 21 is, for example, 4 times or more and 8 times or less, preferably 4.5 times or more and 7 times or less, and more preferably 5 times or more and 6.5 times or less.

[0028] 〔Swelling Step〕 In the swelling step, it is also possible to remove foreign substances on the surface of the raw film 21, remove plasticizers in the raw film 21, impart easy dyeability, plasticize the raw film 21, and the like.

[0029] The treatment conditions are determined within a range where extreme changes such as dissolution or devitrification of the raw film 21 do not occur. As shown in Fig. 1, in the swelling process, the raw film 21 is continuously unwound from the roll 22 and conveyed along the film conveyance path. Further, the raw film 21 is immersed in the swelling liquid 14 for a predetermined time and then pulled out to carry out the process.

[0030] As the swelling liquid 14, pure water can be used. Also, as the swelling liquid, an aqueous solution such as boric acid (Japanese Patent Laid-Open No. 10-153709), chloride (Japanese Patent Laid-Open No. 06-281816), inorganic acid, inorganic salt, water-soluble organic solvent, alcohols, etc. can be used. The concentration in the aqueous solution can be in the range of 0.01 mass% or more and 10 wt% or less.

[0031] The temperature of the swelling liquid 14 is, for example, 10°C or more, preferably 20°C or more. Also, it is 50°C or less, preferably 40°C or less. The immersion time of the raw film 21 is 10 seconds or more, preferably 20 seconds or more. Also, it is 300 seconds or less, preferably 200 seconds or less.

[0032] In the swelling process, the raw film may be swollen and a stretching treatment may be performed on the raw film. When performing the stretching treatment in the swelling process, the stretching ratio is preferably 1.2 to 2.5 times.

[0033] 〔Dyeing process〕 The dyeing process is a process of performing a dyeing treatment by immersing the polyvinyl alcohol-based resin film after the swelling process in a dyeing solution. Specifically, in the dyeing process, a dichroic dye is adsorbed and oriented on the polyvinyl alcohol-based resin film after the swelling treatment.

[0034] As shown in Fig. 1, in the dyeing process, the film after the swelling treatment is conveyed along the film conveyance path constructed by the nip rolls 71, guide rolls 33 to 36, and nip roll 72. Then, it is immersed in the dyeing liquid 15 for a predetermined time and then pulled out to carry out the process.

[0035] In order to enhance the dyeability of the dichroic pigment, the film to be subjected to the dyeing process is preferably a film that has been subjected to at least a certain degree of uniaxial stretching treatment. Alternatively, 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. In the dyeing process, when performing the stretching treatment, the stretching ratio is preferably 1.2 to 2 times.

[0036] As the dichroic pigment, for example, iodine or the like can be used. When iodine is used as the dichroic pigment, for the dyeing solution 15, for example, an aqueous solution with a concentration of iodine / potassium iodide / water = 0.003 to 3 / 0.1 to 20 / 100 by mass ratio can be used.

[0037] Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. Also, compounds other than iodides, for example, boric acid, zinc chloride, cobalt chloride, etc. may coexist.

[0038] When adding boric acid to the dyeing solution 15, it is distinguished from the crosslinking solution described later in that it contains iodine. As long as the aqueous solution contains 0.003 parts by mass or more of iodine with respect to 100 parts by mass of water, it can be regarded as the dyeing solution 15. When the dyeing solution contains boric acid, for the dyeing solution, for example, an aqueous solution with a mass ratio of iodine / potassium iodide / boric acid / water = 0.003 to 3 / 0.003 to 20 / 0.5 to 2.0 / 100 can be used.

[0039] The temperature of the dyeing solution 15 when immersing the film is 10°C or higher, preferably 20°C or higher. Also, it is 50°C or lower, preferably 40°C or lower. The immersion time of the film is 10 seconds or longer, preferably 30 seconds or longer. Also, it is 600 seconds or shorter, preferably 300 seconds or shorter.

[0040] 〔Crosslinking process〕 The cross-linking process is a process of performing a cross-linking treatment by bringing a cross-linking solution into contact with a polyvinyl alcohol-based resin film after a dyeing treatment. The cross-linking process is a treatment process performed for the purpose of water resistance improvement and hue adjustment (complementary color) by cross-linking. The cross-linking treatment may be performed multiple times. When the cross-linking treatment is performed multiple times, the cross-linking treatment for the purpose of water resistance improvement by cross-linking may be performed multiple times, or the cross-linking treatment for the purpose of hue adjustment may be performed multiple times. However, it is preferable to perform the cross-linking treatment for the purpose of water resistance improvement by cross-linking at least once and the cross-linking treatment for the purpose of hue adjustment at least once. More preferably, the cross-linking process for the purpose of hue adjustment is performed after the cross-linking process for the purpose of water resistance improvement by cross-linking.

[0041] As the cross-linking solution, a solution in which a cross-linking agent is dissolved in a solvent can be used, and it is preferable to use an aqueous solution in which a cross-linking agent is dissolved in water. As the cross-linking agent, a boron compound is used. Specific examples of the boron compound include boric acid.

[0042] In addition, as the boron compound, borax may be contained in addition to boric acid. Also, in addition to boric acid, a compound other than the boron compound may be contained. Examples of the compound other than the boron compound include glyoxal and glutaraldehyde. These may be used alone or in combination of two or more.

[0043] As shown in FIG. 1, when the cross-linking process is performed multiple times, in the first cross-linking process, the film after the dyeing treatment is conveyed along the film conveyance path constructed by the nip roll 72, the guide rolls 37 to 40, and the nip roll 73. Then, it is immersed in the first cross-linking solution 16a for a predetermined time and then pulled out to be carried out.

[0044] When the first cross-linking process is a cross-linking treatment for the purpose of water resistance improvement by cross-linking, the first cross-linking solution 16a contains 5 parts by mass or less of boric acid, preferably 4 parts by mass or less, with respect to 100 parts by mass of water. The first cross-linking solution 16a contains 1 part by mass or more of boric acid, preferably 1.5 parts by mass or more, with respect to 100 parts by mass of water.

[0045] When the dichroic dye used in the dyeing treatment is iodine, the first crosslinking liquid 16a preferably contains iodide in addition to boric acid. The amount of iodide can be, for example, 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of water.

[0046] Examples of iodides include potassium iodide and zinc iodide. Further, compounds other than iodides, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and sodium sulfate, may coexist.

[0047] In the first crosslinking step, the concentrations of boric acid and iodide in the first crosslinking liquid 16a and the temperature of the first crosslinking liquid 16a can be appropriately selected. When the first crosslinking step is a crosslinking treatment for the purpose of water resistance by crosslinking, the first crosslinking liquid 16a is preferably an aqueous solution of boric acid / potassium iodide / water = 1 to 5 / 1 to 20 / 100 by mass ratio.

[0048] The temperature of the first crosslinking liquid 16a when immersing the film is 40°C or higher, preferably 50°C or higher. Also, it is 80°C or lower, preferably 70°C or lower. The immersion time of the film is 10 seconds or longer, preferably 20 seconds or longer, more preferably 30 seconds or longer. Also, it is 600 seconds or shorter, preferably 300 seconds or shorter, more preferably 150 seconds or shorter.

[0049] (Second crosslinking step) As shown in FIG. 1, in the second crosslinking step, the film after the first crosslinking step is conveyed along a film conveyance path constructed by nip rolls 73, guide rolls 41 to 44, and nip roll 74. Then, it is immersed in the second crosslinking liquid 16b for a predetermined time and then pulled out to be carried out.

[0050] The temperature of the second crosslinking liquid 16b when immersing the film is 20°C or higher, preferably 30°C or higher. Also, it is 60°C or lower, preferably 50°C or lower. When dipping the film, the temperature of the second crosslinking liquid 16b is preferably lower than the temperature of the first crosslinking liquid 16a from the viewpoint of enhancing the neck-in of the film and consequently improving the degree of polarization.

[0051] The dipping time of the film is 1 second or more. Also, from the viewpoint of adjusting the crosslinking degree of the polarizer 11 within the above range, it is 30 seconds or less, preferably 20 seconds or less. The second crosslinking liquid 16b contains 10 parts by mass or less of boric acid, preferably 8 parts by mass or less, based on 100 parts by mass of water. The second crosslinking liquid 16b contains 1 part by mass or more of boric acid, preferably 1.5 parts by mass or more, based on 100 parts by mass of water.

[0052] In the second crosslinking step, the concentrations of boric acid and iodide in the second crosslinking liquid 16b and the temperature of the second crosslinking liquid 16b can be appropriately selected. When the second crosslinking step is a crosslinking treatment step for the purpose of hue adjustment, the content of boric acid in the second crosslinking liquid 16b is, for example, 1 part by mass or more and 20 parts by mass or less, preferably 1 part by mass or more and 10 parts by mass or less, more preferably 1 part by mass or more and 5 parts by mass or less, per 100 parts by mass of water. It is preferable that the boric acid content contained in the second crosslinking liquid 16b is more than the boric acid content contained in the first crosslinking liquid 16a, as the durability of the resulting polarizer will be good.

[0053] When the second crosslinking step is a crosslinking treatment step for the purpose of hue adjustment, the content of potassium iodide in the second crosslinking liquid 16b is, for example, 1 part by mass or more and 20 parts by mass or less, preferably 1 part by mass or more and 10 parts by mass or less, more preferably 1 part by mass or more and 5 parts by mass or less, per 100 parts by mass of water.

[0054] In the crosslinking step, when performing a stretching treatment, the stretching ratio throughout the crosslinking step is preferably 1.2 to 3 times. In the present invention, at least one of the swelling liquid in the swelling step, the dyeing liquid in the dyeing step, and the crosslinking liquid in the crosslinking step can contain one or more of various aldonic acid salts described below and one or more of various nitrates described below, in appropriate combination. Hereinafter, the aldonic acid salts and nitrates will be described.

[0055] [Aldonic acid salt] Aldonic acid is a polyhydroxycarboxylic acid obtained by oxidizing the aldehyde group of aldose, and is represented by the general formula HOCH2(CHOH) n COOH (where n is an integer of 1 or more). Examples of typical aldonic acids include gluconic acid, galactonic acid, mannonic acid, talonic acid, gulonic acid, idonic acid, allonic acid, altroonic acid, etc. The aldonic acid used in the present invention is not necessarily limited to those specifically exemplified herein. Aldonic acids may be used alone or in combination of a plurality thereof. Among aldonic acids, gluconic acid is preferable because it is easily available industrially. Examples of the salts of aldonic acid include alkali metal salts of aldonic acid such as sodium salt and potassium salt, alkaline earth metal salts of aldonic acid such as calcium salt, and metal salts of aldonic acid such as zinc salt. Among them, the metal salt of aldonic acid (preferably the zinc salt of aldonic acid) is preferable because it has a high effect of suppressing problems such as discoloration of a polarizer or a polarizing plate provided with a polarizer under dry heat. Therefore, as the aldonic acid salt, an alkali metal salt of aldonic acid or a metal salt of aldonic acid is preferable, an alkali metal salt of gluconic acid or a metal salt of gluconic acid is more preferable, and zinc gluconate is even more preferable.

[0056] Aldonic acids are generally in an equilibrium relationship with aldono lactones in an aqueous solution, and the abundance ratio of aldonic acids and aldono lactones changes depending on the pH in the aqueous solution. The stronger the alkalinity of the aqueous solution, the higher the proportion of aldonic acids, and conversely, the stronger the acidity of the aqueous solution, the higher the proportion of aldono lactones. Also, when attempting to obtain a solid by concentrating an aldonic acid aqueous solution, aldono lactones are obtained. Therefore, the aldonic acids in the present invention shall include, in addition to aldonic acids themselves, mixtures containing aldono lactones which are the lactones of aldonic acids. Examples of aldono lactones in an equilibrium relationship with aldonic acids are glucono lactone for gluconic acid and galactono lactone for galactonic acid, and similarly, corresponding aldono lactones exist for other aldonic acids.

[0057] Aldonic acids and aldonate salts are usually produced by fermenting glucose and sold in that form. The aldonate salt used in this embodiment may be any as long as it has an effect of suppressing problems such as discoloration under dry heat when incorporated into the polarizer. Also, additives such as a small amount of stabilizer or preservative may be contained as long as the effects of such aldonate salts are not inhibited.

[0058] The content of the aldonate salt is not particularly limited in each treatment liquid. For example, it is 0.01 parts by mass or more and 60 parts by mass or less, preferably 0.5 parts by mass or more and 30 parts by mass or less, more preferably 0.5 parts by mass or more and 15 parts by mass or less, still more preferably 0.5 parts by mass or more and 10 parts by mass or less, and even more preferably 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of water. If the amount of the aldonate salt is less than 0.01 parts by mass per 100 parts by mass of water, the effect of suppressing problems such as discoloration under dry heat of the obtained polarizer is not sufficiently exhibited.

[0059] The content of the aldonic acid salt in the polarizer 11 is, for example, 0.001% by mass or more and 30% by mass or less, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and preferably 25% by mass or less. If the amount is too small, the effect of suppressing problems such as discoloration of the obtained polarizer under dry heat is not sufficiently exerted.

[0060] The amount of aldonic acid and its salts contained in the polarizer made of a polyvinyl alcohol-based resin can be quantified, for example, by dissolving the polarizer in a solvent and analyzing the sample by an enzymatic method. As reagents for the enzymatic method, for example, "F-Kit D-Gluconic acid / D-Glucono-γ-lactone" sold by J.K. International Co., Ltd. can be used.

[0061] [Nitrate] The nitrate is not particularly limited, and examples thereof include alkali metal nitrates, alkaline earth metal nitrates, metal nitrates, etc.

[0062] Specific examples of the alkali metal nitrate include lithium nitrate, sodium nitrate, potassium nitrate, rubidium nitrate, cesium nitrate, and francium nitrate. Specific examples of the alkaline earth metal nitrate include magnesium nitrate, calcium nitrate, etc.

[0063] Examples of the metal nitrate include zinc nitrate. The nitrate is preferably a metal nitrate or an alkali metal nitrate, and more preferably potassium nitrate.

[0064] The content of the nitrate is not particularly limited in each treatment solution. For example, it is usually 10 parts by mass or more, preferably 20 parts by mass or more, based on 100 parts by mass of the aldonic acid salt. Also, it is usually 80 parts by mass or less, preferably 70 parts by mass or less, and more preferably 55 parts by mass or less.

[0065] The content of nitrate is not particularly limited in each treatment liquid. For example, it is 0.01 part by mass or more and 20 parts by mass or less, preferably 0.1 part by mass or more and 10 parts by mass or less, more preferably 0.2 part by mass or more and 5 parts by mass or less, and even more preferably 0.5 part by mass or more and 3 parts by mass or less, per 100 parts by mass of water.

[0066] The content of nitrate in the polarizer 11 is, for example, 0.001% by mass or more and 10% by mass or less, preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and also preferably 5% by mass or less.

[0067] Aldonate and nitrate may be contained in at least one of the swelling liquid, the dyeing liquid, and the crosslinking liquid, and it is preferably contained in the crosslinking liquid. When performing the crosslinking step multiple times, it is preferably performed in the crosslinking step on the more downstream side. When performing the crosslinking step twice as shown in FIG. 1, it is preferably contained in the second crosslinking step (the second crosslinking liquid). When the crosslinking liquid contains an aldonate and a nitrate, the combination of the aldonate and the nitrate is preferably a combination of a metal gluconate and an alkali metal nitrate or a combination of an alkali metal gluconate and a metal nitrate, more preferably a combination of a metal gluconate and an alkali metal nitrate, and even more preferably a combination of zinc gluconate and potassium nitrate.

[0068] 〔Washing step〕 The washing step is a step of performing a washing treatment by bringing a washing liquid into contact with the polyvinyl alcohol-based resin film after the crosslinking step. The washing step is performed for the purpose of removing excess chemicals such as boric acid and iodine adhering to the polyvinyl alcohol-based resin film.

[0069] As shown in FIG. 1, in the washing step, the polyvinyl alcohol-based resin film after the crosslinking step is conveyed along a film conveyance path constructed by the nip roll 74, the guide rolls 45 to 48, and the nip roll 75. Then, it is immersed in the washing liquid 17 for a predetermined time and then pulled out to carry out the washing.

[0070] Examples of the cleaning liquid 17 used in the cleaning step include water such as pure water. Instead of immersing the film in the cleaning liquid 17, the cleaning step can also be carried out by spraying the cleaning liquid onto the film as a shower, or by using a combination of immersion in the cleaning liquid 17 and spraying of the cleaning liquid.

[0071] The temperature of the cleaning liquid 17 in the cleaning treatment is preferably 2°C or higher and 40°C or lower, and the immersion time of the film is preferably 1 second or longer and 120 seconds or shorter. In the example shown in FIG. 1, the film drawn out from the cleaning liquid 17 passes through the guide roll 48 and the nip roll 75 in sequence and is introduced into the drying furnace 18.

[0072] 〔Drying step〕 After the crosslinking step or the cleaning step, it is preferable to perform a treatment for drying the polyvinyl alcohol-based resin film.

[0073] The method for drying the film is not particularly limited, but as shown in FIG. 1, it is preferably carried out using the drying furnace 18. The drying furnace 18 can use, for example, one equipped with a hot air dryer.

[0074] The drying temperature is, for example, 30°C or higher, preferably 50°C or higher, more preferably 60°C or higher, and still more preferably 70°C or higher. Also, it is 100°C or lower, preferably 90°C or lower, and more preferably 80°C or lower.

[0075] The drying time is, for example, 30 seconds or longer, preferably 50 seconds or longer, and more preferably 80 seconds or longer. Also, it is 600 seconds or shorter, preferably 300 seconds or shorter, and more preferably 200 seconds or shorter. The treatment for drying the polyvinyl alcohol-based resin film can also be carried out using a far-infrared heater.

[0076] The obtained polarizer 11 may be sequentially wound around a winding roll to form a roll shape. Alternatively, without winding, it can be directly subjected to the polarizing plate manufacturing process, that is, the process of laminating a protective film or the like on one or both sides of the polarizer 11. A known method can be adopted for the method of manufacturing the polarizing plate.

Example

[0077] The method for manufacturing the polarizer of the present invention will be described in more detail based on the following examples. Note that the present invention is not limited to the configurations described in the example section. <Various measurement methods> (1) Measurement of the thickness of the polarizing element: It was measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

[0078] (2) Measurement of the single transmittance with visual sensitivity correction of the polarizing plate: It was measured using a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Corporation, 2-degree field of view; C light source].

[0079] <Comparative Example 1> (Production of polarizer 1) A long polyvinyl alcohol (PVA) raw film with a thickness of 30 μm [product name "VF-TS#3000" manufactured by Kuraray Co., Ltd., saponification degree of 99.9 mol% or more] was continuously conveyed while being unwound from a roll, immersed in a swelling liquid composed of pure water at 23°C for 110 seconds, and uniaxially stretched 2.1 times (swelling process). Then, the film pulled out from the swelling liquid was immersed in a staining liquid containing iodine (23°C) with a mass ratio of iodine / potassium iodide / boric acid / water = 0.057 / 0.057 / 2.0 / 100 for 163 seconds, and uniaxially stretched 1.22 times (staining process). Next, the film pulled out from the staining liquid was immersed in a first crosslinking liquid (59°C) with a mass ratio of potassium iodide / boric acid / water of 2.3 / 3.7 / 100 for 92 seconds, and uniaxially stretched 2.24 times (first crosslinking process).

[0080] Subsequently, the film drawn from the first crosslinking solution was immersed in a second crosslinking solution (45 °C) with zinc gluconate / potassium iodide / boric acid / water at 5.0 / 2.1 / 5.0 / 100 (mass ratio) for 14 seconds, and uniaxially stretched to 1.02 times (second crosslinking step). Subsequently, the drawn film was retained in a drying oven at 55 °C for 90 seconds to be dried (drying step). The thickness of the obtained polarizer 1 was 13 μm.

[0081] <Example 1> (Production of polarizer 2) A polarizer 2 was obtained in the same manner as in Comparative Example 1, except that the film drawn from the first crosslinking solution was immersed in a second crosslinking solution (45 °C) with potassium nitrate / zinc gluconate / potassium iodide / boric acid / water at 1.28 / 5.0 / 2.1 / 5.0 / 100 (mass ratio) for 14 seconds, and uniaxially stretched to 1.02 times (second crosslinking step). The thickness of the obtained polarizer 2 was 13 μm.

[0082] <Example 2> (Production of polarizer 3) A polarizer 3 was obtained in the same manner as in Comparative Example 1, except that the film drawn from the first crosslinking solution was immersed in a second crosslinking solution (45 °C) with potassium nitrate / zinc gluconate / potassium iodide / boric acid / water at 2.56 / 5.0 / 2.1 / 5.0 / 100 (mass ratio) for 14 seconds, and uniaxially stretched to 1.02 times (second crosslinking step). The thickness of the obtained polarizer 3 was 13 μm.

[0083] <Example 3> (Production of polarizer 4) A polarizer 4 was obtained in the same manner as in Comparative Example 1, except that the film drawn from the first crosslinking solution was immersed in a second crosslinking solution (45 °C) with potassium nitrate / zinc gluconate / potassium iodide / boric acid / water at 3.84 / 5.0 / 2.1 / 5.0 / 100 (mass ratio) for 14 seconds, and uniaxially stretched to 1.02 times (second crosslinking step). The thickness of the obtained polarizer 4 was 13 μm.

[0084] <Test Example> (Preparation of PVA solution A for adhesive) 50 g of a modified PVA-based resin containing an acetoacetyl group (“Gohsenex Z-410” manufactured by Mitsubishi Chemical Corporation) was dissolved in 950 g of pure water, heated at 90 °C for 2 hours, and then cooled to room temperature to obtain a PVA solution for an adhesive (hereinafter referred to as “PVA solution A”).

[0085] (Preparation of Adhesive) The above-prepared PVA solution A, pure water, a 40% by mass glyoxal solution, and methanol were blended so as to have the following contents per 100 parts by mass of the adhesive to prepare an adhesive (hereinafter referred to as “adhesive 1”). PVA content: 3 parts by mass Methanol content: 36 parts by mass Glyoxal content: 0.3 parts by mass Pure water: 60.7 parts by mass (Preparation of Polarizing Plate) A saponified cellulose acetate film (manufactured by Fuji Film Co., Ltd., film thickness: 40 μm) was laminated on both sides of each polarizing element (polarizer 1, polarizer 2, polarizer 3, polarizer 4) via adhesive 1 using a roll laminator, and then heat-treated at 90 °C for 150 seconds to dry the adhesive, thereby obtaining polarizing plates 1, 2, 3, and 4. The single transmittance of each polarizing plate was 41.2 ± 0.2%.

[0086] (High-Temperature Optical Durability Evaluation) The high-temperature optical durability was evaluated as a heat resistance test. An acrylic adhesive (manufactured by Lintec Corporation) was formed on one side of Polarizer 1, Polarizer 2, Polarizer 3, and Polarizer 4. Further, the polarizers were cut to a size of 40 mm × 35 mm so that the absorption axis of the polarizer was parallel to the long side, and non-alkali glass (Corning's "EAGLE XG", size 50 mm × 40 mm) was bonded to the adhesive surface of each to prepare evaluation samples. The evaluation samples thus obtained were subjected to autoclave treatment for 15 minutes under the conditions of 50 °C and 5 atmospheres, and then spectroscopic measurement was performed using a spectrophotometer V-7100 manufactured by JASCO Corporation. Spectroscopic measurement was also performed after exposing the same samples to an environment of 110 °C for 1000 hours. The change amount (ΔTy) of the transmittance at 480 nm after 1000 hours was calculated. The ΔTy of Polarizer 1 was 3.47. The ΔTy of Polarizer 2 was 0.44, the ΔTy of Polarizer 3 was 0.49, and the ΔTy of Polarizer 4 was 0.98. Compared with the ΔTy of Polarizer 1 using Polarizer 1 of Comparative Example 1, the ΔTy of Polarizers 2 to 4 using Polarizers 2 to 4 of Examples 1 to 3 were all smaller. Compared with Polarizer 1 using Polarizer 1 of Comparative Example 1, in Polarizers 2 to 4 using Polarizers 2 to 4 of Examples 1 to 3, the polarizers mixed with potassium nitrate rather than zinc gluconate alone had an effect of suppressing the change amount after the heat resistance test.

[0087]

Table 1

Explanation of Symbols

[0088] 11…Polarizer 14…Swelling liquid 15…Staining liquid 16a…First crosslinking liquid 16b…Second crosslinking liquid 17…Washing liquid 18…Drying furnace 20…Polarizer manufacturing apparatus 21…Original film (polyvinyl alcohol-based resin film)

Claims

1. A method for producing a polarizer by producing a polarizer from a polyvinyl alcohol-based resin film, a swelling step of swelling the polyvinyl alcohol-based resin film by immersing it in a swelling liquid; a dyeing step of dyeing the polyvinyl alcohol-based resin film after the swelling step by immersing it in a dyeing liquid; a crosslinking step of crosslinking the polyvinyl alcohol-based resin film after the dyeing step by immersing it in a crosslinking liquid, and at least one of the swelling step, the dyeing step, and the crosslinking step is performed in combination with a stretching step of stretching the polyvinyl alcohol-based resin film, A method for producing a polarizer, wherein at least one of the swelling liquid, the dyeing liquid, and the crosslinking liquid contains an aldonic acid salt and a nitrate salt.

2. The method for producing a polarizer according to claim 1, wherein the aldonic acid salt is a metal gluconate.

3. The method for producing a polarizer according to claim 1 or 2, wherein the nitrate salt is an alkali metal nitrate salt.

4. The method for producing a polarizer according to claim 1, wherein the content of the nitrate salt is 20 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the aldonic acid salt.

5. The method for producing a polarizer according to claim 1, wherein the crosslinking liquid contains the aldonic acid salt and the nitrate salt.

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