JP4789925B2 - Iodine polarizing film, method for producing the same, and polarizing plate using the same - Google Patents

Description

  The present invention relates to an iodine polarizing film, a production method thereof, and an iodine polarizing plate using the iodine polarizing film.

  A polarizing plate is generally a protective film made of triacetyl cellulose or the like through an adhesive layer on one or both sides of a polarizing film by adsorbing and orienting a dichroic dye such as iodine or a dichroic dye onto a polyvinyl alcohol resin film. A film is bonded to form a polarizing plate, which is used for a liquid crystal display device or the like. A polarizing plate made of a polarizing film using iodine as a dichroic dye is called an iodine polarizing plate, while a polarizing plate made of a polarizing film using a dichroic dye as a dichroic dye is called a dye polarizing plate. be called. Iodine polarizing plates are widely used in general liquid crystal monitors, liquid crystal televisions, mobile phones, PDAs, and the like because they exhibit higher transmittance and higher degree of polarization, that is, higher contrast than dye-based polarizing plates. However, although iodine-based polarizing plates are superior to dye-based polarizing plates in terms of optical properties, they are inferior to dye-based polarizing plates in terms of optical durability, for example, if iodine-based polarizing plates are left under high temperature and high humidity. As a result, problems such as an increase in transmittance due to decolorization and a decrease in the degree of polarization have occurred. Furthermore, in terms of dry heat durability, the degree of polarization decreases when left at high temperatures. A polarizing plate having high transmittance and degree of polarization, high contrast, excellent heat resistance and moist heat resistance is required, and as an invention for this demand, as described in Patent Document 1 and Patent Document 2, a protective film is disclosed. It is described that the wet heat durability is improved by the improvement method by the method described above and the method of modifying the adhesive that adheres the protective film of triacetyl cellulose as in Patent Document 3 and Patent Document 4. In addition, there is an example in which durability is improved as an iodine-based polarizing plate by treating a polyvinyl alcohol-based resin film instead of improving the durability by a protective film or an adhesive. As one of them, Patent Documents 5, 6, 7 and 8 describe durability improvement by acid treatment and pH control. For example, in Patent Document 5, a polarizing film whose durability is improved by using a stretched polyvinyl alcohol resin stretched film obtained by immersing a polyvinyl alcohol resin film formed from a boron compound-containing polyvinyl alcohol resin film in an acidic aqueous solution. Is disclosed. Patent Document 6 discloses the production of a polarizing film excellent in moisture and heat resistance, in which a film made of a polyvinyl alcohol-based resin is oxidized in an oxidation bath containing an oxidizing agent such as hydrogen peroxide containing an alkali metal iodide. A method is disclosed. Patent Document 7 describes the production of an iodine-based polarizing film having improved wet heat resistance by treating a polyvinyl alcohol film that has been subjected to uniaxial stretching and iodine adsorption orientation treatment with an aqueous boric acid solution having a pH of 4.5 or less. A method is disclosed. Patent Document 8 discloses a patent for a polarizer (polarizing film) having a pH of 1.0 to 5.0 when dissolved in water.

JP-A-8-5836 JP 2001-272534 A JP2004-12578 JP 9-269413 A JP-A-6-254958 JP-A-7-104126 JP 2001-83329 A JP-A-2005-62458

  In the method of immersing and stretching a polyvinyl alcohol-based resin film formed from the boron compound-containing polyvinyl alcohol-based resin film described in Patent Document 5 in an acidic aqueous solution, boric acid, iodine, and potassium iodide immersed in the stretching are used. There was a problem that the acidic component was eluted from the polyvinyl alcohol-based resin film in an aqueous solution containing soda (so-called dyeing bath), and the durability improving effect of the obtained polarizing film could not be sufficiently obtained. Also in Patent Document 6, since the treatment is carried out in an oxidation bath adjusted in pH before stretching, the oxidizing agent is eluted from the polyvinyl alcohol-based resin film into the stretching bath at the time of stretching, and the heat and heat resistance improvement of the resulting polarizing film is improved. There was a problem that sufficient effects could not be obtained. Patent Document 7 describes that the treatment is carried out while maintaining an aqueous solution containing boric acid at pH ≦ 4.5 or less, but when the acid is treated together with boric acid, the treatment of the polyvinyl alcohol resin film and the acidic substance is performed. Inefficiency and processing variations occur in the film. For example, in the example of Patent Document 7, the change in polarization degree is 1.3 when treated with a boric acid-containing treatment solution at pH = 3.4, and the change in polarization degree is 2.0 when pH = 2.1. It is. From this, it is shown that stable characteristics cannot be obtained even if pH control is performed in this method, and just because the pH is controlled, it is not a division that can stably obtain the intended durability. Is shown. Furthermore, it is described in the literature that an acidic substance is vaporized when the processing temperature (processing solution temperature) in the process is high. Patent Document 8 discloses a patent relating to a polarizer, which is made of a film obtained by stretching a polyvinyl alcohol film, and the pH of a solution dissolved in water is 1.0 to 5.0. However, although the wet heat durability of the polarizing plate obtained by this method is improved, in the heat resistance test in a high temperature atmosphere of, for example, 90 ° C., the transmittance is drastically decreased. May darken. Because of these problems, a solution that does not contain boric acid in a polyvinyl alcohol-based resin film containing iodine so that the treatment can be efficiently performed and the treatment can be performed at a low temperature as well as a high temperature in order to stabilize the acid concentration. Thus, there has been a demand for an iodine-based polarizing plate that is improved in wet heat durability by applying an acidic substance treatment and excellent in dry heat durability.

  As a result of intensive studies to solve the above-mentioned problems, a polyvinyl alcohol-based resin film containing iodine, iodide, a crosslinking agent and / or a water resistance agent is treated with an inorganic acid or a salt thereof and / or an organic acid except boric acid after stretching treatment. Treated with a solution (hereinafter sometimes referred to as an acid treatment solution) containing 0.0001 to 5.0% by weight of acid (hereinafter abbreviated as wt%, and unless otherwise specified,% indicates weight%). The polarizing film obtained in this way has improved wet heat durability and little change in transmittance, and further, the acidic substance can volatilize because it can be processed at low temperatures as well as high temperatures. And stable treatment can be applied, and further, when the pH of the acid treatment solution is 2 to 5, more preferably 2.2 to 5, or in some cases 2.4 ≦ pH <6.0, dry heat durability Also rise In addition, rather than using an acidic substance with boric acid to bring the pH to ≦ 4.5, the acidic substance is contained with a halide without applying boric acid, and 2.4 ≦ pH <6.0. By applying the treatment with a solution and applying the drying treatment after the treatment with the acidic substance, it is newly found that a polarizing plate with little variation in optical properties, high wet heat durability and excellent dry heat durability can be obtained. It came to.

That is, the present invention
(1) An inorganic acid selected from sulfuric acid, hydrochloric acid and nitric acid, or an aluminum salt of the inorganic acid after stretching treatment of a polyvinyl alcohol-based resin film containing iodine, iodide, a crosslinking agent and / or a water resistance agent , or A method for producing a polarizing film comprising treating with an acid treatment solution of 2.4 ≦ pH <6.0 , comprising a C1-C6 saturated fatty acid which may have a hydroxy substitution ,
(2) A polyvinyl alcohol-based resin film containing iodine, iodide, and a crosslinking agent has an inorganic acid selected from sulfuric acid, hydrochloric acid and nitric acid, or an aluminum salt of the inorganic acid, or hydroxy substitution after the stretching treatment. A method for producing a polarizing film, characterized by treatment with a solution for acid treatment of 2.2 ≦ pH ≦ 5 containing a good C1-C6 saturated fatty acid,
(3) After stretching a polyvinyl alcohol resin film containing iodine, iodide, a crosslinking agent and / or a water resistance agent, an inorganic acid selected from sulfuric acid, hydrochloric acid and nitric acid, or an aluminum salt of the inorganic acid, or hydroxy the may C1-C6 saturated fatty acids which may have a substituent containing 0.0001~5.0wt%, wherein the pH is treated with 2 ≦ pH ≦ 5 is adjusted to Tei Ru acid treatment for soluble liquid polarization Film production method,
(4) Acid treatment solution, sulfuric acid, aluminum sulfate, aluminum chloride, aluminum nitrate, the aqueous solutions containing at least one acidic substance selected from either Ranaru group click enoate and acetic acid (1) - ( 3) The method for producing a polarizing film according to any one of
( 5 ) A method for producing a polarizing plate, wherein a polarizing film is produced by the production methods of (1) to (4 ) above, and then a protective layer is provided on one side or both sides of the obtained polarizing film,
About.
In the present specification, in relation to the above-described invention, for example,
( 6 ) After stretching a polyvinyl alcohol-based resin film containing iodine, iodide, a crosslinking agent and / or a water-resistant agent, an inorganic acid or a salt thereof and / or an organic acid excluding boric acid is added in an amount of 0.0001-5. A polarizing film obtained by treatment with a solution containing 0 wt% (hereinafter referred to as an acid treatment solution);
( 7 ) The polarizing film according to ( 6 ), wherein the pH of the acid treatment solution is 2 ≦ pH ≦ 5,
( 8 ) A polyvinyl alcohol-based resin film containing iodine, iodide, a crosslinking agent and / or a water-resistant agent is treated with an acid treatment solution having a pH of 2.4 ≦ pH <6.0 after the stretching treatment. ( 6 ) obtained polarizing film,
( 9 ) The polarizing film according to ( 6 ), wherein a halide is contained in a solution containing an inorganic acid other than boric acid or a salt thereof and / or an organic acid.
( 10 ) The polarizing film according to ( 6 ), wherein the inorganic acid excluding boric acid or a salt thereof is any one of aluminum sulfate, aluminum chloride, aluminum nitrate, or sulfuric acid, or two or more.
( 11 ) The polarizing film according to ( 6 ) or ( 7 ), wherein the inorganic acid other than boric acid or a salt thereof is aluminum sulfate.
( 12 ) The organic acid is one or more kinds of carboxylic acid and / or α-hydroxy acid, and obtained by treating with a solution containing the organic acid ( 6 ) to ( 11 ) Polarizing film,
( 13 ) The organic acid is any one or more of citric acid, oxalic acid, malic acid, tartaric acid or acetic acid, and is obtained by treating with a solution containing the organic acid ( 12 ) Polarizing film,
( 14 ) The polarizing film according to any one of ( 6 ) to ( 13 ), wherein the polyvinyl alcohol-based resin film after stretching is stretched at a stretching ratio of 3 to 8 times compared to before stretching. ,
( 15 ) The polarizing film as described in ( 6 ) or ( 14 ), wherein the cross-linking agent and / or water-resistant agent used in the stretching treatment is boric acid.
( 16 ) A polarizing plate provided with a protective layer on one side or both sides of the polarizing film according to any one of ( 6 ) to ( 15 ),
( 17 ) A liquid crystal display device comprising the polarizing plate according to (16 ) above ,
Etc. are also disclosed.

  Since the obtained polarizing film is treated with an acidic substance after stretching, no acidic substance is brought into the dyeing bath, and since no boric acid is used after stretching, problems due to precipitation of boric acid may also occur. Therefore, a polarizing film can be manufactured industrially stably. Further, when the product is manufactured under favorable conditions under a moist heat environment, for example, at a temperature of 65 ° C. and a relative humidity of 93%, the transmittance change is small, and when manufactured under favorable conditions, for example, at 90 ° C. Thus, an excellent polarizing film or polarizing plate with a small amount can be obtained. By using such a polarizing film or polarizing plate of the present invention, long-term display stability of a liquid crystal display can be ensured.

Hereinafter, the present invention will be described in detail.
The manufacturing method of the polyvinyl alcohol-type resin which comprises a polarizing film is not specifically limited, It can produce with a well-known method. As a production method, for example, it can be obtained by saponifying a polyvinyl acetate resin. Examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerized with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The saponification degree of the polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 95 mol% or more. This polyvinyl alcohol-based resin may be further modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. Moreover, the polymerization degree of polyvinyl alcohol-type resin is about 1,000-10,000 normally, Preferably it is about 1,500-5,000.

  A film formed from such a polyvinyl alcohol resin is used as a raw film. The method for forming a polyvinyl alcohol-based resin is not particularly limited, and can be formed by a known method. In this case, the polyvinyl alcohol-based resin film may contain glycerin, ethylene glycol, propylene glycol, low molecular weight polyethylene glycol or the like as a plasticizer. The amount of plasticizer is 5 to 20 wt%, preferably 8 to 15 wt%. Although the film thickness of the raw film which consists of polyvinyl alcohol-type resin is not specifically limited, 5-150 micrometers is preferable and 10-100 micrometers is especially preferable.

  The polyvinyl alcohol-based resin film (hereinafter also referred to as PVA film) is first subjected to a swelling treatment (also referred to as a swelling step). The swelling treatment is performed by immersing in a solution at 20 to 50 ° C. for 30 seconds to 10 minutes. The solution at that time is preferably water, but it may be a water-soluble organic solvent such as glycerin, ethanol, ethylene glycol, propylene glycol or low molecular weight polyethylene glycol, or a mixed solution of water and a water-soluble organic solvent. In the case of shortening the time for producing the polarizing film, the swelling process may be omitted because the film swells at the time of treatment with iodine and iodide.

  After the swelling process, the polyvinyl alcohol-based resin film is treated with a solution containing iodine and iodide (hereinafter also referred to as a dyeing process). The treatment method is preferably immersed in the solution, but the solution may be treated by coating or coating the polyvinyl alcohol resin film. As a solvent of the solution, for example, water is preferable, but it is not limited. As the iodide, for example, an alkali metal iodide compound such as potassium iodide, ammonium iodide, cobalt iodide or zinc iodide can be used, but is not limited, but usually an alkali metal iodide compound Is preferred, and potassium iodide is more preferred. The iodine concentration is preferably 0.0001 to 0.5 wt%, and more preferably 0.001 to 0.4 wt%. The iodide concentration is preferably 0.0001-8 wt%. The treatment temperature in this step is preferably 5 to 50 ° C, more preferably 5 to 40 ° C, and particularly preferably 10 to 30 ° C. Since the treatment time depends on the concentration at which iodine and iodide are adsorbed, it can be adjusted moderately, but it is preferably 30 seconds to 6 minutes, more preferably 1 to 5 minutes. After this treatment, cleaning may be performed before entering the next step. In general, water is used as a solvent for washing. By carrying out washing, it is possible to suppress migration of iodine and iodide into the liquid to be treated next.

In the treatment with iodine or iodide, a crosslinking agent and / or a water-resistant agent may be added to the solution. Usually, a crosslinking agent is used. Although it does not specifically limit as a crosslinking agent, Usually boric acid is preferable. The concentration of the crosslinking agent such as boric acid is preferably 0.1 to 5.0 wt%, more preferably 2 to 4 wt%. As the water-proofing agent, those described later can be used. The treatment temperature in this step is preferably 5 to 50 ° C, more preferably 5 to 40 ° C, and particularly preferably 10 to 30 ° C. Since the treatment time depends on the concentration at which iodine and iodide are adsorbed, it can be adjusted moderately, but it is preferably 30 seconds to 6 minutes, more preferably 1 to 5 minutes. After this treatment, cleaning may be performed before entering the next step. In general, water is used as a solvent for washing. By performing washing, it is possible to suppress the migration of iodine, iodide and boric acid into the liquid to be treated next.
In the present invention, in the case of a polyvinyl alcohol-based resin film containing iodine, iodide, a crosslinking agent and / or a water resistance agent, iodine, iodide, a crosslinking agent and / or a water resistance agent are not necessarily included in the PVA film as they are. It is not necessary that iodine, iodide, a crosslinking agent and / or a waterproofing agent are contained in the PVA film in a reacted form after the dyeing treatment and the crosslinking agent and / or waterproofing agent treatment. Is also included. As a PVA film containing iodine, iodide, a crosslinking agent and / or a water-resistant agent, a film containing iodine, iodide and a crosslinking agent (preferably boron) is preferable.

  Usually, after the dyeing step, a crosslinking agent treatment is performed (also referred to as a crosslinking agent treatment step). The crosslinking agent treatment can be performed by treating the polyvinyl alcohol resin film with a solution containing the crosslinking agent. As described above, the dyeing step can be performed in the presence of a crosslinking agent, but it is usually preferable to perform the step after the dyeing step. In this case, the crosslinking agent treatment is performed by treating the polyvinyl alcohol-based resin film obtained in the dyeing step (hereinafter also referred to as a dyed PVA film) with a crosslinking agent-containing solution. The treatment method with the crosslinking agent-containing solution is usually preferably a method of immersing a PVA film dyed in the solution, but may be a method of applying or coating the solution on a polyvinyl alcohol resin film. The immersion can be performed before or after the stretching process described later. When the stretching method is a dry stretching method, a crosslinking treatment is preferably performed before stretching, and when the stretching method is a wet stretching method, it is preferably performed together with the stretching treatment. Examples of the crosslinking agent include boron compounds such as boric acid or a salt thereof (for example, alkali metal salts such as borax or ammonium borate), polyvalent aldehydes such as glyoxal or glutaraldehyde, biuret type, isocyanurate type or block. A polyvalent isocyanate compound such as a mold, a titanium compound such as titanium oxysulfate, ethylene glycol glycidyl ether, or polyamide epichlorohydrin can be used. Boron compounds are usually preferred, and boric acid is more preferred. Moreover, you may make a water-resistant agent coexist in a crosslinking agent containing solution. Examples of waterproofing agents include succinic peroxide, ammonium persulfate, calcium perchlorate, benzoin ethyl ether, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, ammonium chloride or magnesium chloride, zinc chloride, and the like. Magnesium chloride or zinc chloride is preferred. For example, water, an alcohol solvent, a glycol solvent, glycerin or a mixed solvent thereof can be used as the solvent for the crosslinking agent treatment, and water is usually preferable. The concentration of the cross-linking agent in the solution containing the cross-linking agent varies depending on the type of the cross-linking agent, etc., and cannot be generally specified, but is usually about 0.1 to 10 wt / vol% with respect to the solvent. The concentration is preferably 0.1 to 6.0 wt / vol%, more preferably 2 to 4 wt / vol%. The treatment temperature is preferably 5 to 60 ° C, more preferably 5 to 40 ° C. The treatment time is preferably 30 seconds to 6 minutes, and more preferably 1 to 5 minutes.

  Next, the dyed PVA film or the dyed and crosslinked agent-treated PVA film is stretched (preferably uniaxially stretched) to impart polarization (hereinafter also referred to as a uniaxial stretch step). The stretching method may be either a wet stretching method or a dry stretching method. In the case of the dry stretching method, a crosslinker-treated PVA film is usually used. In the case of the wet stretching method, a PVA film treated with a cross-linking agent may be used, but it is preferable to perform a cross-linking agent treatment together with stretching, usually using a dyed PVA film not subjected to the cross-linking treatment.

  The dry stretching method is usually performed by heating and stretching the film in a gas medium. As the gas medium, air or an inert gas can be used, but air is usually used for economic reasons. In the case of an air medium, it is preferable to stretch the cross-linking agent-treated PVA film with the temperature of the medium being about room temperature to about 180 ° C. In the case of an inert gas or the like, it can be carried out in the same manner as in the case of air, or in some cases at a higher temperature. The stretching treatment is preferably performed in an atmosphere having a relative humidity of 20 to 95%. Examples of the heat stretching method for the film include an inter-roll zone stretching method, a roll heating stretching method, a pressure stretching method, an infrared heating stretching method, and the like, but the stretching method is not limited. The stretching process may be performed once (one stage), or a multi-stage process of two (two stages) or more may be applied. In that case, the draw ratio is preferably 3 to 8 times, more preferably 5 to 7 times.

  The wet stretching method is usually performed by immersing the film in an aqueous medium such as water, a water-soluble organic solvent, or a mixed solution of water and the organic solvent and stretching the film under normal heating. It is preferable to stretch the film while the film is immersed in a solution containing a crosslinking agent and / or a water resistance agent. The draw ratio is preferably 3 to 8 times, more preferably 5 to 7 times. The stretching is preferably performed in the aqueous medium heated to 40 to 60 ° C, more preferably 45 to 55 ° C. Examples of the crosslinking agent include those described above, for example, boron compounds such as boric acid, borax or ammonium borate, polyvalent aldehydes such as glyoxal or glutaraldehyde, biuret type, isocyanurate type or block type. And polyhydric isocyanate compounds, titanium compounds such as titanium oxysulfate, ethylene glycol glycidyl ether, and polyamide epichlorohydrin. As the crosslinking agent, a boron compound is preferable, and boric acid is more preferable. Water-proofing agents can also include those described above, for example, succinic peroxide, ammonium persulfate, calcium perchlorate, benzoin ethyl ether, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, ammonium chloride, magnesium chloride or chloride. Examples include zinc. For example, the concentration of the crosslinking agent and / or the waterproofing agent is preferably 0.5 to 8 wt%, and more preferably 2.0 to 4.0 wt%. The stretching time can be 30 seconds to 20 minutes, but 2 to 5 minutes is preferable. The stretching process may be performed once (one stage), or a multistage process of two (two stages) or more may be applied.

In the present invention, the above-described uniaxially stretched PVA film (hereinafter also simply referred to as a uniaxially stretched PVA film), an inorganic acid excluding boric acid or a salt thereof, and / or an organic acid (hereinafter also simply referred to as an acidic substance) is set to 0.0. The treatment is performed with a solution containing 0001 to 5.0% by weight (hereinafter also referred to as an acid treatment solution). By this treatment, the wet heat durability of the polarizing film can be improved, and in the preferred embodiment, the dry heat durability can also be improved. In some cases, this treatment is also simply referred to as “treatment with an acidic substance”. In the treatment with an acidic substance, it is preferable to immerse the stretched PVA film in a solution containing an acidic substance (preferably an aqueous solution, a water-soluble organic solvent solution or a mixed solution of the organic solvent and water).
After performing the stretching treatment, the film surface may be washed before the treatment with the acidic substance (hereinafter, also referred to as a washing step) because the cross-linking agent may be deposited on the film surface or foreign matter may adhere to the film surface. . In this cleaning process, cleaning with a solution containing boric acid may be performed, but in some cases, cleaning with a solution containing boric acid may cause foreign matters on the surface after the next step or after drying. In the case of washing, washing with a solution containing no boric acid, preferably water, is preferred. In addition, as a case where cleaning with a solution containing boric acid may be performed, after the cleaning, acid treatment is performed, and then drying is performed so that no foreign matter is generated on the film surface after cleaning with the boric acid-containing solution. This is a case including a processing step. The washing time can be 1 second to 5 minutes. The number of times of washing is not particularly limited, and may be once or may be two or more times as necessary.

  After the stretching treatment, it is preferable to treat the stretched PVA film with a solution containing a halide together with treatment with an acidic substance or separately. This treatment is aimed at adjusting the hue and improving the polarization properties (hereinafter also referred to as halide treatment). Examples of the treatment method include a method of immersing a stretched PVA film in the solution, a method of applying or coating the solution on the PVA film, and the like, and a method of immersing is more preferable. The halide treatment is preferably performed together with the treatment with an acidic substance. In this case, the PVA film may be treated by the method described above with a solution containing a halide together with an acidic substance. Examples of the halide include alkali metal iodide compounds such as potassium iodide and sodium iodide, iodides such as ammonium iodide, cobalt iodide and zinc iodide, alkali metal chloride compounds such as potassium chloride and sodium chloride, or Chlorides such as zinc chloride are preferred, and water-soluble is more preferred. Among chlorides and iodides, iodide is preferred, and among iodides, an alkali metal iodide compound, more preferably potassium iodide. The concentration of the halide is preferably 0.5 to 15 wt%, more preferably 3 to 8 wt%. The treatment temperature is preferably 5 to 50 ° C. or less, for example, but more preferably 20 to 40 ° C. For example, the treatment time is preferably 1 second to 5 minutes, but is preferably 5 to 30 seconds in consideration of the stability of the in-plane characteristics of the polarizing film. When the purpose is not to prepare the hue, the step of treating with the solution containing the halide can be omitted.

  After the treatment with the acidic substance and, if necessary, the halide treatment, the film is dried (hereinafter also referred to as a drying step). When drying, natural drying is good, but in order to further improve the drying efficiency, surface moisture may be removed by roll compression, an air knife or a water absorption roll, and / or blow drying. Also good. The treatment temperature is preferably 20 to 90 ° C, but preferably 40 to 80 ° C. The treatment time is preferably 30 seconds to 20 minutes, more preferably 2 to 10 minutes.

  Examples of the solvent of the treatment solution in the treatment steps so far include, but are not limited to, solvents such as water, alcohol solvents, and glycol solvents. Further, a mixed solvent of water and a water-soluble organic solvent, such as a mixed solution of water and alcohol, a mixed solvent of dimethyl sulfoxide and water, or the like may be used. Most preferred is water.

  The treatment with an acidic substance in the present invention may be carried out in any step as long as it is after stretching (preferably uniaxial stretching) a polyvinyl alcohol film containing iodine, iodide, a crosslinking agent and / or a water resistance agent. Good. For example, in the washing step after the stretching and / or the halide treatment step, treatment with an acidic substance is performed together, or after the film is stretched, or after the washing step performed as necessary, it is independently treated with an acidic substance. Any of processing may be performed. Usually, after stretching (preferably uniaxial stretching) for imparting polarization is completed, it is preferably washed as necessary, and then treated with an acidic substance (sometimes referred to as acid treatment). Moreover, you may carry out in a some process as needed. More preferably, the stretched PVA film is immersed in a solution containing an acidic substance and a halide, and the treatment with the acidic substance and the halide treatment are performed together. The treatment with an acidic substance may be carried out with a treatment solution containing a crosslinking agent and / or a water resistant agent excluding boric acid together with the acidic substance, if necessary. The concentration of the acidic substance in the treatment solution used for the treatment with the acidic substance is usually within a range of about 0.0001 to 5.0 wt%, preferably 0.0005 to 2 wt%, more preferably 0.001 to 1 wt%. In some cases, 0.01 to 2.0 wt% is more preferable. In addition, the pH of the treatment solution is preferably adjusted to 1.0 ≦ pH <6.0. A more preferable pH is a range of 2 or more and less than 6.0, and more preferably about 2.1 to 5. The temperature and time of the acid treatment are not particularly limited as long as the effects of the present invention are achieved. Usually, the treatment temperature is 5 to less than 60 ° C, preferably about 10 to 40 ° C, and the treatment time is 2 to 300 seconds, preferably It is 3 to 60 seconds, more preferably about 5 to 40 seconds.

  In some cases, in the washing step, the acid treatment can be performed simultaneously with the washing with a solution containing an acidic substance. The treatment temperature is preferably less than 5-60 ° C, more preferably 10-40 ° C. The treatment time is preferably 2 to 300 seconds, more preferably 2 to 60 seconds.

  The halide treatment may be performed after the stretching treatment or after the washing treatment, and may be performed alone or as described above, in the acid treatment step, together with the acid treatment. The halide treatment is a step of applying a halide-containing solution to the stretched PVA film (hereinafter also simply referred to as a stretched film) to treat the stretched film, and usually in the acid treatment step as described above. The acid treatment is preferably performed together. The method for treating the film with the halide-containing solution may be any method as long as the solution is applied to the surface of the stretched film. Usually, it is preferable to immerse the stretched film in the solution. When it is carried out together with the acid treatment step, the film may be treated with a solution containing the halide together with the acidic substance. Preferably, the stretched film is immersed in a solution containing both. The halide concentration of the halide-containing solution used for the halide treatment is preferably in the range of 0.5 to 15 wt%. When the halide treatment is performed together with the acid treatment, a solution containing a halide in the above concentration range and an acidic substance in a range of 0.0001 to 5.0 wt% may be used. The treatment temperature is preferably, for example, less than 5-60 ° C, more preferably 20-40 ° C. The treatment time can be 2 seconds to 5 minutes, preferably 5 seconds to 1 minute.

As the acidic substance, any of inorganic acids and organic acids can be used, and further, salts thereof whose aqueous solution shows acidity, preferably a salt solution whose aqueous solution shows a value smaller than pH 6, preferably pH 5 Smaller salts exhibiting a pH value of 1 or higher can also be used. Preferable inorganic acids include acids such as sulfuric acid, hydrochloric acid or nitric acid. Of these, sulfuric acid is more preferred. As the salt, a salt of an inorganic acid is usually used, and the preferred inorganic acid salt, particularly an aluminum salt, is preferred. Examples of such salts include aluminum sulfate, aluminum chloride, and aluminum nitrate. Aluminum sulfate is one of the particularly preferred ones. Zinc chloride used as a waterproofing agent or the like is not included in the acidic substance in the present invention because its aqueous solution does not fall within the above pH range. As organic acids there may be mentioned the usual carboxylic acids, hydroxy or C1-C 6 saturated fatty acids may have a halogeno substituent is preferably, alpha-soluble organic acid having a skeleton of the hydroxy acid is one of the preferred is there. Specific examples include formic acid, citric acid, chloroacetic acid, acetic acid, oxalic acid, malic acid or tartaric acid, citric acid or acetic acid being preferred, and acetic acid being most preferred. The acidic substances may be used one by one or in combination of two or more. Among these acidic substances, aluminum sulfate is one of particularly preferable ones because of its high effect of improving wet heat durability. Among organic acids, citric acid, acetic acid, oxalic acid and the like are generally used as food additives and can be said to be preferable acidic substances from the viewpoint of environment and safety.
Preferred as the acidic substance is at least one selected from the group consisting of sulfuric acid, aluminum salts of inorganic acids (preferably aluminum salts of inorganic acids selected from the group consisting of sulfuric acid, hydrochloric acid or nitric acid), citric acid and acetic acid. Examples include acidic substances, and aluminum sulfate and / or acetic acid are particularly preferable.

  The solution containing an acidic substance may contain a crosslinking agent (desirably, a crosslinking agent other than boric acid) and / or a water resistance-imparting agent at the same time. Examples of the crosslinking agent other than boric acid include polyvalent aldehydes such as glyoxal or glutaraldehyde, polyisocyanate compounds such as biuret type, isocyanurate type or block type, titanium compounds such as titanium oxysulfate, and the like. In addition, ethylene glycol glycidyl ether or polyamide epichlorohydrin can also be used. Examples of water-resistant agents include succinic peroxide, ammonium persulfate, calcium perchlorate, benzoin ethyl ether, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, ammonium chloride, magnesium chloride, and zinc chloride.

  When processing with a solution containing an acidic substance, the pH of the solution is also an important indicator. The lower the pH, the higher the wet heat durability of the polarizing film. However, if the pH is too low, the polyvinyl alcohol resin may be decomposed or polyeneized. As a result, the transmittance may change by 1% or more in a dry heat test, for example, a 90 ° C. heat resistance test. Therefore, when the pH of the solution containing an acidic substance (acid treatment solution) is adjusted to 1.0 ≦ pH <6.0, it is suitable for obtaining a product with high wet heat durability, and is more preferably in a range. Is 2 ≦ pH ≦ 5. In order to obtain a product having high dry heat durability, the pH is 2 or more, more preferably 2.2 or more, preferably in a range smaller than 6.0, and more preferably about 2.2 to 5. . Further, in some cases, 2.4 ≦ pH <6.0 is preferable, more preferably 2.4 ≦ pH ≦ 5.0, and still more preferably 2.4 ≦ pH ≦ 4.0.

A preferred polarizing film of the present invention has high wet heat durability and dry heat durability, and has little decrease in transmittance. In the excellent polarizing film of the present invention, the pH of the aqueous solution in which the polarizing film is dissolved is in the range of 5.0 <pH <6.0, which is one index of the excellent polarizing film of the present invention. It becomes. Moreover, it is more preferable when pH of this aqueous solution is the range of 5.1-5.6. In many cases, the aqueous solution is a more preferable polarizing film when the pH of the aqueous solution is 5.2 <pH <5.6. In the most preferable polarizing film, the pH of the solution is 5.2 <pH <5. 4. The pH of the aqueous solution in which the polarizing film of the present invention is dissolved can be measured as follows.
That is, 0.0380 g of the polarizing film of the present invention obtained after the drying step was cut out, placed in a screw mouth bottle (screw mouth bottle SV-30 manufactured by Takara Seisakusho Co., Ltd.) containing 10 cc of distilled water, and the lid was closed. It is obtained by immersing in a water bath for 2 hours to obtain an aqueous solution in which a polarizing film is dissolved, cooling the aqueous solution to 25 ° C., and measuring the pH of the aqueous solution using pH Controller PP-01 manufactured by ASONE Co., Ltd. The pH was the pH of the aqueous solution in which the polarizing film of the present invention was dissolved. In the aqueous solution, it is sufficient that the polarizing film is dissolved in the aqueous solution, and the polarizing film of the present invention used for the sample is not necessarily completely dissolved, and the polarizing film itself of the sample is semi-dissolved or sufficiently It may be in a swollen state. However, preferably, the insoluble portion of the sample polarizing film is less than 20 wt%.

Thus, the polyvinyl alcohol-based resin film obtained by treatment with a solution containing 0.0001 to 5.0 wt% of an acidic substance is treated with a solution having a high concentration of acidic substance (low pH), The pH of the solution in which the obtained polarizing film is dissolved shows a low value. This is because the concentration of the acidic substance correlates with the pH of the polarizing film, and by controlling the acidic substance of the treatment solution, the pH of the solution in which the polarizing film is dissolved, that is, the degree of treatment of the obtained polarizing film is controlled. It shows what you can do. The concentration of an acidic substance is an important factor for producing a polarizing film.

A preferable method for producing the polarizing film of the present invention is, for example, 3 to 8 times in an aqueous solution containing a crosslinking agent (preferably boron), in order to impart a polarizing property to a PVA film dyed with iodine and iodide. Preferably, the PVA film that has been stretched to about 4 to 7 times (preferably uniaxially stretched) or dyed with iodine and iodide and treated with a crosslinking agent (preferably boron treated) is 3 to 8 times by a dry stretching method. Preferably, the stretched film is stretched to about 4 to 7 times (preferably uniaxially stretched), and the resulting stretched film is treated with the acid treatment solution and the halide treatment with the acid treatment solution, preferably a solution containing the acidic substance and halide. The polarizing film of the present invention can be obtained by drying the treated film.
The iodine type polarizing film of this invention which extended | stretched the polyvinyl alcohol-type resin film by the above process is obtained.

  The obtained polarizing film is made into a polarizing plate by providing a transparent protective layer on at least one side or both sides. The transparent protective layer can be provided as a polymer-coated layer or as a film laminate layer. The transparent polymer or film forming the transparent protective layer is preferably a transparent polymer or film having high mechanical strength and good thermal stability. Furthermore, those having excellent moisture barrier properties are preferable. Examples of substances used as the transparent protective layer include cellulose acetate resins such as triacetyl cellulose and diacetyl cellulose or films thereof, acrylic resins or films thereof, polyvinyl chloride resins or films thereof, polyester resins or films thereof, polyarylate resins or Film, cyclic polyolefin resin containing cyclic olefin such as norbornene or film thereof, polyethylene, polypropylene, polyolefin having cyclo or norbornene skeleton or copolymer thereof, main chain / or side chain being imide and / or amide Or a resin or polymer thereof. Since polyvinyl alcohol functions as an alignment film for liquid crystal, rubbing treatment may be applied, or treatment may be performed with a photo-alignment film to provide a resin having liquid crystallinity or a film thereof. The thickness of the protective film is, for example, about 0.5 μm to 200 μm. A polarizing plate is produced by providing one or more of the same or different resins or films on one side or both sides.

  An adhesive layer such as a pressure-sensitive adhesive can be provided on one surface of the obtained polarizing plate, that is, on the surface of the protective layer or film that becomes a non-exposed surface after being bonded to the display device. By providing the adhesive layer, the polarizing plate can be attached to a display device such as a liquid crystal or organic electroluminescence.

  This polarizing plate has a known surface such as an antireflection layer, an antiglare layer, a hard coat layer, a liquid crystal coating layer for improving the viewing angle and / or contrast on the exposed surface of the protective layer or film. These functional layers may be included. The layer having various functionalities is preferably a coating method, but a film having the functions may be bonded via an adhesive or a pressure-sensitive adhesive. The various functional layers may be known retardation plates that are layers or films for controlling the retardation.

  When providing a transparent protective layer in a polarizing film, when the protective layer is a film, it is necessary to perform film lamination. In that case, an adhesive is required. A polyvinyl alcohol adhesive is used as the adhesive. Examples of the polyvinyl alcohol-based adhesive include, but are not limited to, Gohsenol NH-26 (manufactured by Nihon Gosei Co., Ltd.) or EXEVAL RS-2117 (manufactured by Kuraray Co., Ltd.). A cross-linking agent and / or a waterproofing agent may be added to the adhesive. Further, the adhesive may contain an acidic substance in a concentration of 0.0001 to 20 wt%, preferably 0.02 to 5 wt%. As the polyvinyl alcohol-based adhesive, an adhesive in which only a maleic anhydride-isobutylene copolymer / and a crosslinking agent are mixed can be used. As maleic anhydride-isobutylene copolymers, for example, isoban # 18 (manufactured by Kuraray), isoban # 04 (manufactured by Kuraray), ammonia-modified isoban # 104 (manufactured by Kuraray), ammonia-modified isoban # 110 (manufactured by Kuraray) ), Imidized isoban # 304 (manufactured by Kuraray), imidized isoban # 310 (manufactured by Kuraray), and the like. A water-soluble polyvalent epoxy compound can be used as the crosslinking agent at that time. Examples of the water-soluble polyvalent epoxy compound include Denacol EX-521 (manufactured by Nagase Chemtech) and Tetrat-C (manufactured by Mitsui Gas Chemical Co., Ltd.). As other adhesives, urethane-based, acrylic-based, and epoxy-based adhesives are frequently used, and known adhesives can be used, and the adhesive is not limited. Further, as an additive for the adhesive, a zinc compound or a halide can be simultaneously contained at a concentration of about 0.1 to 10 wt%. The additive is not limited. After laminating the transparent protective layer with an adhesive, the polarizing plate is obtained by drying or heat treatment at a suitable temperature.

  The polarizing plate of the present invention thus obtained has little change in transmittance and degree of polarization even when left in a high temperature and high humidity atmosphere for a long time. Further, for example, there is little decrease in transmittance in a high temperature environment at 90 ° C. and durability. Therefore, stable performance can be maintained for a long time. The image display device of the present invention can be obtained by using the polarizing plate of the present invention for a liquid crystal display, an electroluminescence display device, a CRT or the like. In particular, in the case of a liquid crystal display, the liquid crystal display of the present invention can be obtained by adhering the polarizing plate of the present invention to both sides of a liquid crystal cell constituting the liquid crystal display together with a retardation film as necessary. The image display device thus obtained, particularly a liquid crystal display, can suppress a decrease in the visibility of the display image due to deterioration of the polarizing plate, and can stably display an image for a long period of time.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these. In addition, the transmittance | permeability and polarization degree which are shown to an Example were performed as follows.

  When the two polarizing plates obtained by laminating protective films on both sides of the polarizing film are overlapped so that the absorption axis directions are the same, the transmittance is the parallel transmittance Tp, and the two polarizing plates are The transmittance when the absorption axes are stacked so as to be orthogonal to each other is defined as orthogonal transmittance Tc.

  The transmittance T was calculated by the following equation (1) by obtaining a spectral transmittance τλ at predetermined wavelength intervals dλ (here, 10 nm) in a wavelength region of 380 to 780 nm. In the equation, Pλ represents a spectral distribution of standard light (C light source), and yλ represents a 2 ° visual field color matching function.

Formula 1

  Spectral transmittance τλ was measured using a spectrophotometer (“U-4100” manufactured by Hitachi, Ltd.).

  The degree of polarization Py was obtained from the parallel transmission Tp and the orthogonal transmission Tc according to the equation (2).

      Py = {(Tp-Tc) / (Tp + Tc)} 1/2 * 100 Formula (2)

  The pH of the aqueous solution was measured using pH Controller “PP-01” manufactured by ASONE Co., Ltd.

  A polyvinyl alcohol film (Kuraray's product name: VF-XS) having a saponification degree of 99% or more and an average polymerization degree of 2400 is immersed in warm water at 40 ° C. for 2 minutes, and after swelling treatment, stretched to 1.30 times. did. The obtained film was made of boric acid (Societa Chimica Larderello spa) 28.6 g / l, iodine (made by Junsei Kagaku) 0.25 g / l, potassium iodide (made by Junsei Kagaku) 17.7 g / l and Ammonium iodide (manufactured by Junsei Chemical Co., Ltd.) was immersed in an aqueous solution containing 1.0 g / l at 30 ° C. for 2 minutes and dyed with iodine and iodide. The film obtained by the dyeing treatment was treated for 5 minutes in an aqueous solution at 50 ° C. containing 30.0 g / l boric acid while uniaxially stretching 5.0 times. In an aqueous solution adjusted to 50 g / l potassium iodide and aluminum sulfate 14-18 hydrate (manufactured by Wako Pure Chemical Industries, Ltd.) 0.02 g / l while maintaining the tension of the film obtained by boric acid treatment. The treatment was performed at 30 ° C. for 15 seconds. At that time, the pH of the aqueous solution was 4.8. The film obtained by treating with potassium iodide and acid was dried at 70 ° C. for 9 minutes. A film obtained by drying was laminated with a triacetylcellulose film (trade name: TD-80U, manufactured by Fuji Photo Film Co., Ltd.) obtained by alkali treatment using a polyvinyl alcohol adhesive to obtain a polarizing plate.

  The obtained polarizing plate was cut into 40 mm × 40 mm, and bonded to a glass plate having a thickness of 1 mm via an adhesive (trade name: PTR-3000 manufactured by Nippon Kayaku Co., Ltd.) to obtain a measurement sample. A dry heat test and a wet heat test were applied to the prepared samples.

The wet heat test was performed in an atmosphere of a temperature of 65 ° C. and a relative humidity of 93%, and the transmittance and the degree of polarization before and after leaving for 18 days (432 hours) were measured. A comparison was made between a case where the treatment was performed with a solution containing an acidic substance and a case where the treatment was not conducted, and this was used as an index for confirming the superior difference in the increase in transmittance (decoloration) and the decrease in the degree of polarization.

The dry heat test was performed in an atmosphere of 90 ° C., and the transmittance before and after leaving for 18 days (432 hours) was measured. The change in transmittance is preferably within 1.0% in absolute value, and is within 1.0% as an index. A change with a transmittance change of 1.0% or more is not preferable because of the influence that the color reproducibility of the display device cannot be obtained. When the change in the test result in the dry heat test as seen from the absolute value of the transmittance was 1.0% or less, it was regarded as “good” and 1.0% or more was regarded as “bad”.

  In Example 1, samples were prepared in the same manner except that the addition amount of aluminum sulfate 14-18 hydrate was 0.2 g / l and pH was 3.4, and durability in dry heat test and wet heat test was obtained. Compared. The pH when the polarizing film after the drying treatment was dissolved was 5.3.

  In Example 1, aluminum sulfate 14-18 hydrate was replaced with citric acid (anhydrous) (manufactured by Junsei Chemical Co., Ltd.), except that the addition amount was 0.05 g / l and pH was 4.8. Samples were prepared and the durability in the dry heat test and the wet heat test were compared.

  In Example 3, samples were prepared in the same manner except that the amount of citric acid added was 0.07 g / l and the pH was 4.3, and the durability in the dry heat test and the wet heat test was compared.

  In Example 3, samples were prepared in the same manner except that the amount of citric acid added was 0.1 g / l and pH was 3.8, and the durability in the dry heat test and the wet heat test was compared.

  In Example 3, samples were prepared in the same manner except that the amount of citric acid added was 0.3 g / l and the pH was 2.5, and the durability in the dry heat test and the wet heat test was compared. The pH when the polarizing film after the drying treatment was dissolved was 5.4.

  In Example 3, samples were prepared in the same manner except that the amount of citric acid added was 0.5 g / l and the pH was 2.3, and the durability in the dry heat test and the wet heat test was compared. The pH when the polarizing film after the drying treatment was dissolved was 5.3.

  In Example 1, except that the aluminum sulfate 14-18 hydrate was replaced with acetic acid (manufactured by Junsei Chemical Co., Ltd.), the addition amount was 0.04 g / l, and the pH of the solution was 5.1. It manufactured and compared the durability in a dry heat test and a wet heat test.

  In Example 8, samples were prepared in the same manner except that the amount of acetic acid added was 0.07 g / l and the pH was 4.0, and the durability in the dry heat test and the wet heat test was compared.

  In Example 8, samples were prepared in the same manner except that the amount of acetic acid added was 0.11 g / l and the pH was 3.8, and the durability in the dry heat test and the wet heat test was compared.

  In Example 8, samples were prepared in the same manner except that the amount of acetic acid added was 0.6 g / l and the pH was 3.4, and the durability in the dry heat test and the wet heat test was compared. The pH when the polarizing film after the drying treatment was dissolved was 5.7.

  In Example 8, samples were prepared in the same manner except that the amount of acetic acid added was 3.0 g / l and the pH was 2.6, and the durability in the dry heat test and the wet heat test was compared. The pH when the polarizing film after the drying treatment was dissolved was 5.4.

  In Example 8, samples were prepared in the same manner except that the amount of acetic acid added was 5.0 g / l and the pH was 2.4, and the durability in the dry heat test and the wet heat test was compared. The pH when the polarizing film after the drying treatment was dissolved was 5.1.

Comparative Example 1
In Example 1, samples were similarly prepared except that aluminum sulfate 14-18 hydrate was not added, and the durability in the dry heat test and the wet heat test was compared. The pH when the polarizing film after the drying treatment was dissolved was 6.0.

  Tables 1 and 2 show the measurement results of transmittance and polarization degree change in Examples 1 to 13 and Comparative Example 1.

Table 1 Change in transmittance and degree of polarization before and after wet heat durability test

Table 2 Change in transmittance and polarization degree before and after dry heat durability test

  As can be seen from the above Examples and Comparative Examples, the polyvinyl alcohol resin film containing iodine and iodide in the present invention contains a cross-linking agent, and in the film to which the stretching treatment is applied, an acidic substance other than boric acid is 0. A polarizing film obtained by treatment with a solution containing 0.0001 to 5.0 wt% and having a pH of 2.4 ≦ pH <6.0 is colored in a humid heat environment, for example, at a temperature of 65 ° C. and a relative humidity of 93%. It becomes a polarizing film or polarizing plate which does not take off and has little decrease in the degree of polarization. A polarizing plate having high transmittance, high contrast, and high wet heat durability in a polarizing film for liquid crystal displays can be obtained. Furthermore, it can be seen that the polarizing film obtained by the present invention has a dry heat durability, for example, a transmittance change within 1.0% in a dry heat test at 90 ° C. From the above results, it can be seen that the wet heat durability of the polarizing plate is improved by the pH of the treatment solution, and a polarizing plate having a small transmittance change in the dry heat durability is obtained. On the other hand, looking at the pH of the treatment solution and the pH when the polarizing film is dissolved, the pH when the polarizing film is dissolved is lower as the treatment is performed with a solution having a higher concentration of acidic substances. Therefore, it turns out that the density | concentration of an acidic substance and the density | concentration of a polarizing film have a correlation. As the acidic substance concentration is lower, the pH when the polarizing film is dissolved shows a value close to 6. In the dry heat test, for example, at 90 ° C., the transmittance does not decrease, but the wet heat durability gradually decreases. As the pH when the polarizing film is dissolved is closer to 5, the wet heat durability is higher. However, when the pH is 5 or less, the transmittance is significantly reduced in the 90 ° C. dry heat test. I can see that. Based on the above results, the polyvinyl alcohol-based resin film containing iodine is a solution containing 0.0001 to 5.0 wt% of an acidic substance other than boric acid and having a pH of 2.4 ≦ pH <6.0. It can be seen that the polarizing plate obtained by the treatment has improved wet heat durability, and a polarizing plate with little change in transmittance due to dry heat durability is obtained.

Example A-2
In Example 1, the preparation of the sample and the durability in the wet heat test were similarly compared except that the addition amount of aluminum sulfate 14-18 hydrate was 4.5 g / l and the pH was 2.73.

Example A-3
In Example 1, except that the aluminum sulfate 14-18 hydrate was replaced with sulfuric acid (manufactured by Junsei Chemical Co., Ltd.), the addition amount was 0.2 g / l, and the pH was 1.88. The durability in the wet heat test was compared.

Example A-4
In Example 1, except that the aluminum sulfate 14-18 hydrate was replaced with sulfuric acid (manufactured by Junsei Co., Ltd.), the addition amount was 0.03 g / l, and the pH was 3.4. The durability in the wet heat test was compared.

Example A-5
In Example 1, except that the aluminum sulfate 14-18 hydrate was replaced with aluminum nitrate (manufactured by Wako Pure Chemical Industries, Ltd.), the addition amount was 5 g / l, and the pH was 2.91. And the durability in the wet heat test was compared.

Example A-6
In Example 1, except that aluminum sulfate 14-18 hydrate was replaced with aluminum chloride hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.), the addition amount was 5 g / l, and the pH was 2.83. Similarly, the preparation of samples and the durability in wet heat tests were compared.

Example A-7
A polyvinyl alcohol film (trade name: VF-XS, manufactured by Kuraray Co., Ltd.) having an average polymerization degree of 2400 was immersed in warm water at 40 ° C. for 2 minutes, and a swelling treatment was applied to make the draw ratio 1.30 times. The swelled film is immersed in an aqueous solution containing iodine (made by Junsei Chemical Co.) 0.25 g / l and potassium iodide (made by Junsei Chemical Co., Ltd.) 17.7 g / l at 30 ° C. for 2 minutes, iodine and iodide. Processed. The dyed film was treated with boric acid (manufactured by Societa Chimica Larderello spa) at a concentration of 28 g / l, a treatment temperature of 30 ° C. for 5 minutes. The film to which the boric acid treatment was applied was treated for 5 minutes in a 50 ° C. aqueous solution containing 30.0 g / l boric acid while being stretched 5.0 times. While maintaining the tension of the film obtained by the boric acid treatment, it was treated for 15 seconds with an aqueous solution adjusted to 50 g / l potassium iodide and 3.5 g / l citric acid (made by Junsei Chemical Co., Ltd.) at 30 ° C. Went. The pH of the aqueous solution was 1.51. The film obtained by treating with potassium iodide containing citric acid was dried at 70 ° C. for 9 minutes. A triacetyl cellulose film (trade name: TD-80U, manufactured by Fuji Photo Film Co., Ltd.) obtained by subjecting the dried film to an alkali treatment was laminated using a polyvinyl alcohol adhesive to obtain a polarizing plate.
The obtained polarizing plate was cut into 40 mm × 40 mm, and bonded to a glass plate having a thickness of 1 mm via an adhesive (trade name: PTR-3000 manufactured by Nippon Kayaku Co., Ltd.) to obtain a measurement sample.

  A wet heat test was applied to the prepared sample. The wet heat test was performed in an atmosphere at a temperature of 65 ° C. and a relative humidity of 93%, and the single transmittance and the degree of polarization before and after being left for 18 days (432 hours) were measured.

Example A-8
In Example A-7, except that the amount of citric acid added was 0.05 g / l and the pH was 4.8, sample preparation and durability in a wet heat test were similarly compared.

Example A-9
In Example A-7, except that citric acid was replaced with acetic acid, the amount of acetic acid added was changed to 0.04 g / l, and the pH was changed to 5.1, and the preparation of the sample and the durability in the wet heat test were similarly compared. .

Example A-10
In Example A-7, except that citric acid was replaced with acetic acid, the amount of acetic acid added was changed to 3.0 g / l, and the pH was adjusted to 2.58. did.

Comparative Example 1
In Example 1, except that aluminum sulfate 14-18 hydrate was not added, the preparation of the sample and the durability in the wet heat test were similarly compared.

Comparative Example A-2
In Example A-7, except that citric acid was not added, the preparation of the sample and the durability in the wet heat test were similarly compared.

Comparative Example A-3
In Example A-4, the film obtained by dyeing was stretched 5.0 times in 5 minutes while maintaining the pH of a 50 ° C. aqueous solution containing 30.0 g / l boric acid at 3.4. In the same manner as in the preparation of the sample and the wet heat test, except that the film obtained by the boric acid treatment was kept in a tensioned state in an aqueous solution adjusted to 50 g / l of potassium iodide for 15 seconds at 30 ° C. The durability was compared.

  Table 1 shows the measurement results of the transmittance and polarization degree change in Example 1, A-2 to A-10, Comparative Example 1, A-2, and A-3.

Table A-1

As can be seen from the above Examples and Comparative Examples, the polyvinyl alcohol resin film containing iodine and iodide in the present invention contains a cross-linking agent, and in the film to which the stretching treatment is applied, an acidic substance other than boric acid is 0. A polarizing film obtained by treatment with a solution containing 0.0001 to 5.0 wt% and having a pH of 1.0 ≦ pH <6.0 is colored in a humid heat environment, for example, at a temperature of 65 ° C. and a relative humidity of 93%. It becomes a polarizing film or polarizing plate which does not take off and has little decrease in the degree of polarization. A polarizing plate having high transmittance, high contrast, and high wet heat durability in a polarizing film for liquid crystal displays can be obtained. Moreover, when Example 4 and Comparative Example 3 are compared, it can be seen that the treatment can be performed more effectively by setting the pH of the halide treatment tank to 1.0 ≦ pH <6.0.

Claims (5)

A polyvinyl alcohol-based resin film containing iodine, iodide, a crosslinking agent and / or a water-resistant agent is subjected to a stretching treatment , and then an inorganic acid selected from sulfuric acid, hydrochloric acid and nitric acid, an aluminum salt of the inorganic acid, or hydroxy substitution The manufacturing method of the polarizing film characterized by processing by the solution for acid treatment of 2.4 <= pH <6.0 containing the C1-C6 saturated fatty acid which may have . A polyvinyl alcohol-based resin film containing iodine, iodide, or a crosslinking agent may have an inorganic acid selected from sulfuric acid, hydrochloric acid, and nitric acid, or an aluminum salt of the inorganic acid, or a hydroxy substitution after stretching. A method for producing a polarizing film, which comprises treating with a solution for acid treatment of 2.2 ≦ pH ≦ 5 containing a —C6 saturated fatty acid. After stretching a polyvinyl alcohol-based resin film containing iodine, iodide, a crosslinking agent and / or a water resistance agent, an inorganic acid selected from sulfuric acid, hydrochloric acid and nitric acid, an aluminum salt of the inorganic acid, or hydroxy substitution production of a polarizing film and containing 0.0001～5.0Wt% to be C1-C6 saturated fatty acids also characterized in that the pH is treated with 2 ≦ pH ≦ 5 is adjusted to Tei Ru acid treatment for soluble liquid Method. Acid treatment solution is sulfuric acid, sulfuric acid, aluminum chloride, aluminum nitrate, any one of claims 1 to 3 which is an aqueous solution containing at least one acidic substance selected from the click-enoic acid and acetic or Ranaru group The manufacturing method of the polarizing film of description. A polarizing film is manufactured with the manufacturing method of Claims 1-4, Then, a protective layer is provided in the single side | surface or both surfaces of the obtained polarizing film, The manufacturing method of the polarizing plate characterized by the above-mentioned.