TW202031759A - Method for producing polarizer - Google Patents

Abstract

Provided is a method for producing a polarizer, the polarizer having excellent humidification durability even at high crystallinity and a high iodine concentration. A method for producing a polarizer according to the present invention is a method for producing a polarizer having an iodine content of 10-25 wt%. This method for producing a polarizer includes: dry-stretching a polyvinyl alcohol-based resin film; dyeing the dry-stretched polyvinyl alcohol-based resin film in a dye bath; and treating the dyed polyvinyl alcohol-based resin film with an ascorbic acid.

Description

Manufacturing method of polarizer

Invention field The present invention relates to a manufacturing method of a polarizer.

Background technique Polarizers are used in image display devices such as liquid crystal display devices. In recent years, the demand for thinner image display devices has increased. Therefore, the thinning of the polarizer has been further developed. The polarizer is typically manufactured by dyeing a polyvinyl alcohol (PVA)-based resin film with a dichroic substance such as iodine (for example, Patent Documents 1 and 2). When a polarizer with a thin thickness is manufactured, the thickness of the resin film also becomes thin, and therefore, it may not be sufficiently dyed. Therefore, a method to dye the resin film more efficiently is sought.

A method for dyeing the resin film efficiently includes a method using a high-concentration dyeing bath (for example, an iodine aqueous solution). However, when a high-concentration dyeing bath is used, iodine may be taken into other treatment baths and the treatment bath may be contaminated by iodine. If the resin film is dyed by the iodine taken into other treatment baths, iodine without complex formation and iodine complex with incomplete orientation may be formed. These iodine and iodine complexes are easily separated from the polarizer, and therefore, the characteristics (monomer transmittance, degree of polarization) of the polarizer may be reduced. Such problems may become more significant in humidified environments. It is difficult to form highly oriented iodine complexes in polarizers with high crystallinity and high iodine concentration. Therefore, the problems caused by iodine contamination of the treatment bath may become more significant.

Prior art literature Patent literature Patent Document 1: Japanese Patent No. 5048120 Patent Document 2: JP 2013-156391 A

Summary of the invention Problems to be solved by the invention The present invention is made to solve the above-mentioned conventional problems, and its main purpose is to provide a method that can produce a polarizer with excellent humidification durability even with high crystallinity and high iodine concentration.

Means to solve the problem The manufacturing method of the polarizer of the present invention is a method for manufacturing a polarizer with an iodine content of 10% by weight to 25% by weight. The manufacturing method of the polarizer includes: dry-stretching the polyvinyl alcohol-based resin film; dyeing the dry-stretched polyvinyl alcohol-based resin film in a dyeing bath; and the dyed polyvinyl alcohol-based resin The film is treated with ascorbic acid. In one embodiment, the crystallinity of the polyvinyl alcohol-based resin film after the above-mentioned dry process is 40% or more. In one embodiment, the dye bath is an iodine aqueous solution containing 0.3 parts by weight or more of iodine. In one embodiment, the dye bath contains iodide and an oxidant for iodide ions. In one embodiment, the above-mentioned oxidant is at least one selected from the group consisting of iron sulfate, iron chloride, and iron nitrate. In one embodiment, the aqueous solution containing the iodide and the oxidizing agent for iodide ions contains 0.5 to 10 parts by weight of the oxidizing agent and 1 to 40 parts by weight of the iodide with respect to 100 parts by weight of water, and the iodine The molar ratio of the compound to the above-mentioned oxidant (iodide/oxidant) is 2/1~50/1. In one embodiment, the ascorbic acid treatment is performed by an ascorbic acid bath. The ascorbic acid concentration in the ascorbic acid bath is 0.005% by weight to 1% by weight.

Invention effect According to the present invention, it is possible to provide a polarizer with excellent humidification durability even with high crystallinity and high iodine concentration. Specifically, the manufacturing method of the present invention applies ascorbic acid treatment to a polyvinyl alcohol (PVA)-based resin film that has been dry-stretched and dyed. In this way, it is possible to reduce the iodine being carried into other treatment baths. Therefore, even when a polarizer with high crystallinity and high iodine concentration is made, a polarizer with excellent humidification durability can be provided. Furthermore, even when a high-concentration dyeing bath is used, iodine contamination of other treatment baths can be prevented. Therefore, a dyeing bath with a high iodine concentration can also be used to dye the PVA resin film more efficiently.

The form used to implement the invention Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

A. Manufacturing method of polarizing element The manufacturing method of the polarizing element of the present invention is a method of manufacturing a polarizing element with an iodine content of 10% by weight to 25% by weight. The polarizer can be manufactured by, for example, subjecting the PVA-based resin film to a swelling step, a dyeing step, a crosslinking step, a stretching step, a washing step, and a drying step. The manufacturing method of the present invention includes: dry-stretching a polyvinyl alcohol-based resin film; dyeing the dry-stretched polyvinyl alcohol-based resin film in a dyeing bath; and the dyed polyvinyl alcohol-based resin film Carry out ascorbic acid treatment. In the manufacturing method of polarizing parts, when there is a large amount of iodide ions (I ₃ ¯) in the treatment bath after the dyeing step, I ₃ ¯ will be absorbed into the PVA-based resin in an incompletely oriented state to form polyvinyl alcohol-based resin -Iodine complexes. Therefore, the directionality of the obtained polarizer is reduced, and the characteristics of the polarizer may be reduced. In addition, iodide ions with incomplete orientation tend to leave the polarizer, and their influence becomes more pronounced in a humidified environment. The manufacturing method of the polarizer of the present invention is to apply ascorbic acid treatment to the PVA-based resin film that has been subjected to dry stretching and dyeing. Ascorbic acid can reduce iodine that may be taken into other treatment baths. Therefore, the iodide ions (I ₃ ¯) taken into other treatment baths may be reduced to I ¯ that does not show absorption in the visible region (380-780 nm). As a result, it is possible to prevent degradation of the characteristics of the obtained polarizer, and to obtain a polarizer having excellent humidification durability. The "iodine content" in this specification means the total amount of iodine contained in the polarizer (PVA-based resin film). More specifically, when iodine in the polarizer exists in the form of iodide ion (I¯), iodine molecule (I ₂ ), polyiodide ion (I ₃ ¯, I ₅ ¯), etc., the iodine content in this specification means to include The amount of iodine in all these forms. The iodine content can be calculated by, for example, the calibration curve method of fluorescent X-ray analysis. In addition, polyiodide ions exist in the polarizer in a state of forming a PVA-iodine complex. By forming such a complex, the absorption dichroism can be developed in the wavelength range of visible light. Specifically, the complex of PVA and triiodide ion (PVA·I ₃ ¯) has an absorption peak near 470 nm, and the complex of PVA and pentaiodide ion (PVA·I ₅ ¯) has absorption near 600 nm. peak. As a result, polyiodide ions can absorb light in a wide range of visible light according to its form. On the other hand, iodide ions (I¯) have an absorption peak near 230 nm, which is essentially not involved in the absorption of visible light. Therefore, polyiodide ions mainly present in the state of a complex with PVA can be involved in the absorption performance of the polarizer.

A-1. PVA series resin film Examples of PVA-based resins forming the PVA-based resin film include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol can be prepared by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be prepared by saponifying an ethylene-vinyl acetate copolymer. The degree of saponification of the PVA-based resin is usually 85 mol% or more and less than 100 mol%, preferably 95.0 mol%-99.99 mol%, more preferably 99.0 mol%-99.99 mol%. The degree of saponification can be determined according to JIS K 6726-1994. By using a PVA-based resin with such a degree of saponification, a polarizer with excellent durability can be obtained.

The average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose. The average degree of polymerization is usually 1000-10000, preferably 1200-4500, more preferably 1500-4300. In addition, the average degree of polymerization can be determined in accordance with JIS K 6726-1994.

The thickness of the PVA-based resin film is not particularly limited, and can be set according to the thickness of the desired polarizer. The thickness of the PVA-based resin film is, for example, 0.5 μm to 200 μm. The dyeing solution used in the present invention can dye the PVA-based resin film very efficiently. Therefore, for example, even if the PVA-based resin film is less than 10 μm, it can be sufficiently dyed in a short time, and it can be imparted with characteristics that can fully function as a polarizer.

In one embodiment, the PVA-based resin film may be a PVA-based resin layer formed on the substrate. The laminate of the base material and the resin layer can be produced by, for example, a method of applying a coating liquid containing the above-mentioned PVA-based resin to the base material, a method of laminating a PVA-based resin film on the base material, or the like. Any suitable resin substrate can be used as the substrate, for example, a thermoplastic resin substrate can be used.

As described above, the polarizer can be manufactured by, for example, subjecting the PVA-based resin film to the swelling step, the dyeing step, the crosslinking step, the stretching step, the washing step, and the drying step. Each step can be performed at any appropriate time. Moreover, if necessary, any steps other than the dyeing step may be omitted, plural steps may be performed at the same time, and each step may be performed several times. The steps are explained below.

A-2. Stretch In the stretching process, the PVA-based resin film is typically uniaxially stretched 3 to 7 times the original length. The above-mentioned PVA-based resin film is used for dry stretching. Dry stretching can be stretched in a wider temperature range, so it is ideal. The temperature during dry stretching is, for example, 50°C to 200°C, preferably 80°C to 180°C, and more preferably 90°C to 160°C. The stretching direction can be the length direction (MD direction) of the film or the width direction (TD direction) of the film. In addition, the stretching direction may correspond to the direction of the absorption axis of the polarized member.

In order to improve the crystallinity of the PVA resin film, dry stretching is suitable. The PVA-based resin film with high crystallinity is difficult to get iodine into the PVA space, and it is not easy to dye. As far as the manufacturing method of the present invention is concerned, even when a high-concentration dyeing solution is used, iodine contamination of other treatment baths can still be prevented. Therefore, a polarizer with high crystallinity can be easily manufactured. It is preferable to perform dry stretching so that the crystallinity of the PVA-based resin film after the stretching treatment and before the dyeing treatment becomes 40% or more, preferably 50% or more. In addition, the crystallinity is, for example, 80% or less. For example, by setting the stretching temperature and stretching ratio in any appropriate range, a PVA-based resin film with desired crystallinity can be made. Specifically, for example, the PVA-based resin film is uniaxially stretched at 90° C. to 160° C. so that the stretching ratio becomes 3 to 6 times, whereby a PVA-based resin film with a crystallinity of 50% or more can be produced. In addition, in this specification, the crystallinity of the PVA-based resin film means a value calculated by the following method.

(Evaluation method of crystallinity of PVA) A Fourier transform infrared spectrophotometer (FT-IR) (manufactured by Perkin Elmer, trade name: "SPECTRUM2000") was used as the measuring device, and polarized light was used as the measuring light. The surface of the PVA-based resin film was evaluated by the measurement of total reflection attenuated spectroscopy (ATR: attenuated total reflection). The calculation of crystallinity can be performed by the following procedure. The measurement was performed in a state where the measurement polarization was set to 0˚ and 90° with respect to the stretching direction, and the intensity of 1141 cm ^-1 and 1440 cm ^-1 of the obtained spectrum was used to calculate according to the following formula. It was confirmed in advance that the intensity of 1141 cm ^-1 was correlated with the amount of crystal parts, and 1440 cm ^{-1 was used} as the reference peak, and the crystal index (Equation 2) was calculated from the following formula. In addition, the crystallinity is based on using a known PVA sample, a calibration curve of the crystallinity index and the crystallinity is prepared in advance, and the crystallinity is calculated from the crystallinity index using the obtained calibration curve (Equation 1). Crystallinity = 63.8 × (crystallinity index) -44.8 (Formula 1) with crystallographic index ^{= (((1141cm -1) I} 0˚ + 2 × I (1141cm -1) 90˚) / 3) / ((I (1440cm - ¹ )0˚+2×I(1440cm ^-1 )90˚)/3) (Equation 2) However, I(1141cm ^-1 )0˚: when the polarized light is incident in a direction parallel to the stretching direction for measurement 1141cm ^-1 of the intensity I (1141cm ^-1) 90˚: that the polarization direction toward the stretching direction was perpendicular to the incident intensity I 1141cm ^-1 and the time of measurement (1440cm ^-1) 0˚: that the polarization toward the 1440cm ^-1 when the intensity of the polarized light so that the stretching direction toward a direction perpendicular to the incidence was measured: 1440cm ^-1 the intensity I (1440cm ^-1) at a direction parallel to the stretching direction was measured incidence 90˚

A-3. Dyeing The PVA-based resin film that has been subjected to the above dry stretching is then subjected to a dyeing process. The dyeing step is a step of dyeing the PVA-based resin film with a dichroic substance. Ideally, it is performed by adsorbing dichroic substances. Examples of the adsorption method include: a method of immersing a PVA-based resin film in a dyeing solution containing a dichroic substance; a method of applying the dyeing solution to a PVA-based resin film; spraying the dyeing solution on the PVA-based resin film The method and so on. It is more ideal to immerse the PVA-based resin film in the dyeing solution. This is because the dichroic substance can be adsorbed well.

Examples of the dichroic substance include iodine and dichroic dyes. Iodine is more ideal. When iodine is used as a dichroic substance, an aqueous iodine solution is suitable for the dyeing solution. The iodine content of the iodine aqueous solution is preferably 0.04 parts by weight to 5.0 parts by weight. In one embodiment, the iodine content in the iodine aqueous solution is preferably 0.3 parts by weight or more. In order to improve the solubility of iodine in water, it is advisable to blend iodide in the iodine aqueous solution. Potassium iodide should be used as iodide. The content of iodide is preferably 0.3 to 15 parts by weight relative to 100 parts by weight of water. As mentioned above, with regard to the manufacturing method of the present invention, even when a high-concentration iodine aqueous solution is used as a dyeing bath, iodine contamination of other treatment baths can still be prevented. Therefore, a higher-concentration dyeing solution can be used to produce a polarizer with a high iodine content (specifically, 10% to 25% by weight).

The temperature of the dyeing solution during dyeing can be set to any appropriate value, such as 20°C to 50°C. When the PVA-based resin film is immersed in the dyeing solution, the immersion time is, for example, 1 second to 1 minute.

In an embodiment of the present invention, the dye bath is a solution containing iodide and an oxidizing agent for iodide ions. The oxidant is an ionic compound composed of cations and anions. In this dyeing solution, polyiodide ions can be formed by oxidizing iodide ions. As a result, the content of polyiodide ions contained in the dyeing solution is increased, and the PVA-based resin film can be dyed efficiently. Furthermore, compared to the case where iodine is added to water or an aqueous solution containing iodide to prepare a dyeing solution, the content of polyiodide ions in the dyeing solution can be increased by using a smaller amount of iodine. Furthermore, in this embodiment, by adding an oxidizing agent for iodide ions to the dyeing solution, the iodine content in the dyeing solution can be adjusted. Therefore, the content of polyiodide ions in the dyeing solution can be adjusted more simply.

The content of the iodide contained in the dyeing solution is preferably 1 part by weight to 40 parts by weight, more preferably 3 parts by weight to 30 parts by weight relative to 100 parts by weight of the solvent. If the content of iodide is within the above range, sufficient polyiodide ions can be formed in the dyeing solution. Examples of the iodide include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. The more ideal one is potassium iodide.

In one embodiment, the oxidizing agent for iodide ions uses an ionic compound composed of cations and anions. Examples of the above-mentioned anions or cations include cations such as Fe ³⁺ , Ag ⁺ , Ag ²⁺ , Au ⁺ , Au ³⁺ , Co ³⁺ , Cu ²⁺ , Mn ³⁺ , Pt ²⁺ , Br ^3- , ClO _{3 ^{-, ClO 2 -, ClO -}} , Cr 2 O 7 2-, NO 3 -, MnO 4 - anions. More ideal is trivalent iron ion (Fe ³⁺ ). The trivalent iron ions are present in the dyeing solution in the form of divalent iron ions after oxidizing iodide ions. The trivalent iron ions and the divalent iron ions can be taken into the PVA-based resin film in the dyeing step. These iron ions have the effect of dehydrating PVA. Therefore, the effect of polyiodide ions from the PVA-based resin film in the subsequent steps can be suppressed. As a result, the dyeability of the PVA-based resin film can be further improved, which is preferable.

The above-mentioned oxidizing agent may be an ionic compound that causes a desired electrode reaction in the dyeing solution, and any appropriate compound can be used. For example, include: iron sulfate, iron chloride, iron nitrate and other compounds containing Fe ³⁺ as a cation; potassium permanganate and other compounds containing MnO ₄ ^- as an anion; copper chloride, copper sulfate and the like containing Cu ²⁺ as a cation compound, etc. From the viewpoint of Fe ³⁺ content, it is suitable to use at least one compound selected from the group consisting of iron sulfate, iron chloride, and iron nitrate. The oxidizing agent may be used alone or in combination of two or more kinds.

The content of the oxidant in the dyeing solution is preferably 0.1 parts by weight to 10 parts by weight relative to 100 parts by weight of the solvent, preferably 0.5 parts by weight to 10 parts by weight, more preferably 0.5 parts by weight to 4 parts by weight. The content of oxidant in the dyeing solution can be determined according to the iodide content in the dyeing solution.

The molar ratio of iodide to oxidant can be set to any appropriate value, for example, 2/1 to 50/1, preferably 10/1 to 50/1. If the molar ratio of the iodide to the oxidant is within the above range, the oxidant can fully function as an oxidant for iodide ions.

Any appropriate combination of iodide and oxidant can be used. For example, from the viewpoint of obtaining a polarizer having excellent characteristics such as durability, a combination of potassium iodide as the iodide and iron sulfate as the oxidizing agent is preferable.

Any suitable solvent can be used as the solvent of the dyeing solution, and water is usually used.

In addition to iodide and oxidant, the above-mentioned dyeing solution may also contain any other suitable compounds. For example, the dyeing solution may contain iodine. When the dyeing solution further contains iodine, the iodine content in the dyeing solution is, for example, 1 part by weight or less with respect to 100 parts by weight of the solvent.

A-4. Ascorbic acid treatment The PVA-based resin film that has been subjected to the above dry stretching and dyeing treatment is then subjected to ascorbic acid treatment. In one embodiment, the ascorbic acid treatment is performed using an aqueous solution containing ascorbic acid (vitamin C) and/or ascorbate (hereinafter also referred to as an ascorbic acid aqueous solution). Examples of the salt include alkali metal salts such as sodium salt and potassium salt. The PVA-based resin film contains iodine because it is used for the dyeing process. The iodine may contaminate other treatment baths (treatment baths other than the dyeing bath) in the steps after the dyeing step. After being used for dyeing treatment, it is advisable to perform ascorbic acid treatment before being used for treatment in other treatment baths. By applying ascorbic acid treatment, iodine excessively adsorbed on PVA molecules can be selectively removed. As a result, iodine contamination of other treatment baths can be prevented. In addition, due to the reducing effect of ascorbic acid, iodine excessively adsorbed on the PVA molecule will be reduced to iodide ions (I¯), and iodide ions that form I ₃ ¯ complexes and I ₅ ¯ complexes are increased. As a result, I ₃ ¯ complexes and I ₅ ¯ complexes increase, and humidification durability can be improved.

The ascorbic acid treatment can be carried out by any appropriate method. For example, a method of coating or spraying an aqueous solution containing ascorbic acid and/or ascorbate on a PVA-based resin film; and a method of immersing the PVA-based resin film in an aqueous solution containing ascorbic acid and/or ascorbate Wait.

The ascorbic acid treatment can be performed by preparing a treatment solution containing only ascorbic acid and/or ascorbate and contacting the PVA-based resin film with the treatment solution, or by adding ascorbic acid and/or ascorbate after the dry stretching and dyeing treatment In the treatment bath used in the treatment step (for example, a crosslinking bath), and the treatment bath is brought into contact with the PVA-based resin film, it is also possible to contact the two.

The concentration of ascorbic acid and/or ascorbate in the ascorbic acid aqueous solution can be set in any appropriate range according to the amount of iodine that may be brought into other treatment solutions. The ascorbic acid concentration of the ascorbic acid aqueous solution is preferably 0.005% to 1% by weight, preferably 0.005% to 0.5% by weight, more preferably 0.05% to 0.5% by weight. When the ascorbic acid concentration is less than 0.005% by weight, the effect of the treatment with ascorbic acid may not be sufficiently obtained. In addition, when the ascorbic acid concentration exceeds 1% by weight, the dyed PVA-based resin film may be discolored.

A-5. Swelling The swelling step is usually performed before the dyeing step. In one embodiment, the swelling step can also be performed together with the dyeing step in the same dipping bath. The swelling step is performed, for example, by immersing the PVA-based resin film in a swelling bath. Any appropriate liquid can be used for the swelling bath, for example, water such as distilled water and pure water can be used. The swelling bath can also contain any appropriate ingredients other than water. Examples of other components include solvents such as alcohols, additives such as surfactants, and iodides. The iodide can be exemplified above. It is more desirable to use potassium iodide. The temperature of the swelling bath is, for example, 20°C to 45°C. In addition, the immersion time is, for example, 10 seconds to 300 seconds.

A-6. Crosslinking In the crosslinking step, a boron compound is usually used as a crosslinking agent. Examples of boron compounds include boric acid and borax. More ideal is boric acid. In the cross-linking step, the boron compound is usually used in the form of an aqueous solution.

When a boric acid aqueous solution is used, the boric acid concentration of the boric acid aqueous solution is, for example, 2% by weight to 15% by weight, preferably 3% by weight to 13% by weight. The boric acid aqueous solution may further contain iodides such as potassium iodide, and zinc compounds such as zinc sulfate and zinc chloride.

The crosslinking step can be performed by any appropriate method. For example, a method of immersing a PVA-based resin film in an aqueous solution containing a boron compound; a method of coating a PVA-based resin film with an aqueous solution containing a boron compound; or spraying an aqueous solution containing a boron compound on the PVA The method of resin film. It is more desirable to be immersed in an aqueous solution containing a boron compound.

The temperature of the solution used for crosslinking is, for example, 25°C or higher, preferably 30°C to 85°C, more preferably 40°C to 70°C. The immersion time is, for example, 5 seconds to 800 seconds, preferably 8 seconds to 500 seconds.

A-7. Wash The washing step is performed with water or an aqueous solution containing the above-mentioned iodide. It is typically performed by immersing a PVA-based resin film in an aqueous potassium iodide solution. The temperature of the aqueous solution in the washing step is, for example, 5°C to 50°C. The immersion time is, for example, 1 second to 300 seconds.

A-8. Dry The drying step can be carried out by any appropriate method. For example, natural drying, air blowing drying, reduced-pressure drying, heat drying, etc. can be cited, and heat drying is preferable. When heating and drying are performed, the heating temperature is, for example, 30°C to 100°C. In addition, the drying time is, for example, 10 seconds to 10 minutes.

B. Polarizing parts The iodine content of the polarizer prepared by the manufacturing method of the present invention is 10% to 25% by weight, preferably 15% to 25% by weight. According to the manufacturing method of the present invention, a polarizer with high crystallinity and high iodine content but excellent humidification durability can be manufactured.

The thickness of the polarizer manufactured by the manufacturing method of the present invention is, for example, 0.5 μm to 80 μm, preferably 0.6 μm to 20 μm. In one embodiment, the thickness of the polarizer is preferably 0.8 μm to 10 μm. In another embodiment, the thickness of the polarizer is preferably 3 μm or less. As described above, the dyeing solution used in the present invention can efficiently dye the PVA-based resin film. Therefore, even with a thin polarizer, it is possible to sufficiently impart the desired single-cell transmittance.

The monomer transmittance of the polarizer manufactured by the manufacturing method of the present invention is, for example, 30% or more. In addition, the theoretical upper limit of the transmittance of the monomer is 50%, and the practical upper limit is 46%. In addition, the single transmittance (Ts) is the Y value measured using the 2 degree field of view (C light source) of JIS Z8701 and corrected for visual sensitivity. For example, a spectrophotometer with integrating sphere (manufactured by JASCO Corporation) can be used. , Product name: V7100) for measurement. In addition, the degree of polarization of the polarizer is, for example, 99.0% or more.

Example Hereinafter, embodiments are used to specifically illustrate the present invention, but the present invention is not limited to these embodiments.

[Example 1] An amorphous isophthalic acid copolymerized polyethylene terephthalate (IPA copolymerized PET) film (thickness: 100 μm) with a water absorption rate of 0.75% and a Tg of 75°C was used as the thermoplastic resin substrate. A corona treatment was applied to one side of the substrate, and the corona treated surface was coated with a ratio of 9:1 at 25°C containing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and ethyl acetate. Aqueous solution of modified PVA (polymerization degree of 1200, degree of acetylation modification 4.6%, degree of saponification of 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "GOHSEFIMER Z200"). It was dried to form a PVA-based resin layer with a thickness of 10 μm to produce a laminate. Using a tenter stretcher, the obtained laminate was stretched 4.5 times in the air in a direction orthogonal to the longitudinal direction of the laminate at 140°C (stretching treatment). Next, the layered body was immersed in a dyeing bath (aqueous solution with an iodine concentration of 1.4% by weight and a potassium iodide concentration of 9.8% by weight) at a liquid temperature of 25°C for 12 seconds, and was dyed (dyeing treatment). Next, the layered body was immersed in an ascorbic acid bath (an aqueous solution with an ascorbic acid concentration of 0.067% by weight, an iodine concentration of 0.1% by weight, and a potassium iodide concentration of 0.7% by weight) for 25 seconds (ascorbic acid treatment). Next, the layered body was immersed in a washing bath (pure water) with a liquid temperature of 25°C for 6 seconds (first washing treatment). Furthermore, it was immersed in a crosslinking bath (a boron concentration of 1% by weight and a potassium iodide concentration of 1% by weight) in a crosslinking bath (aqueous solution with a boron concentration of 1% by weight and a potassium iodide concentration of 1% by weight) at a liquid temperature of 60°C for 16 seconds (crosslinking treatment). Next, the layered body was immersed in a washing bath (a potassium iodide concentration of 1% by weight aqueous solution) with a liquid temperature of 25°C for 3 seconds (second washing treatment). Next, the laminate was dried in an oven at 60°C for 21 seconds to obtain a laminate having a PVA-based resin layer (polarizer) with a thickness of 2.5 μm.

(Comparative example 1) Except that an aqueous solution with an iodine concentration of 0.3% by weight and a potassium iodide concentration of 2.1% by weight was used as the dye bath and no ascorbic acid was added to the ascorbic acid bath, a PVA-based resin layer (polarized light) with a thickness of 2.5 μm was prepared in the same manner as in Example 1. Pieces) of the laminate.

[Example 2] In addition to forming a PVA-based resin layer with a thickness of 5μm and preparing a laminate, and immersing the laminate in a dyeing solution at 30°C (an aqueous solution containing 24.0 parts by weight of potassium iodide and 2.8 parts by weight of iron sulfate n-hydrate added to 100 parts by weight of water, The molar ratio of iodide to oxidizing agent: 21.0/1) was used for dyeing for 6 seconds, and a laminate having a PVA-based resin layer (polarizer) with a thickness of 1.2 μm was produced in the same manner as in Example 1.

(Comparative example 2) Except that an aqueous solution with an iodine concentration of 0.5% by weight and a potassium iodide concentration of 3.5% by weight was used as the dye bath, and no ascorbic acid was added to the ascorbic acid bath, a PVA-based resin layer with a thickness of 1.2 μm (polarized light) was prepared in the same manner as in Example 2. Pieces) of the laminate.

Using the laminates prepared in Examples 1 to 2 and Comparative Examples 1 to 2, the following methods were used to evaluate the monomer transmittance of the PVA-based resin layer (polarizer), the crystallinity of the PVA-based resin film before the dyeing step, and Transmittance changes. The results are shown in Table 1. 1. Monomer transmittance A spectrophotometer with integrating sphere (manufactured by JASCO Corporation, product name: V7100) was used to measure the monomer transmittance of the laminate. 2. Iodine content For the polarizers of the polarizers prepared in the examples and comparative examples, use a fluorescent X-ray analyzer (manufactured by Rigaku, trade name "ZSX-PRIMUS II", measuring diameter: φ20mm), Measure the fluorescence X-ray intensity (kcps). On the other hand, using a spectrophotometer (manufactured by Otsuka Electronics Co., Ltd., trade name "MCPD-3000"), the thickness (μm) of the polarizer was measured. The iodine content (% by weight) was calculated from the obtained fluorescent X-ray intensity and thickness using the following formula. (Iodine content)=20.5×(Fluorescence X-ray intensity)/(Film thickness) In addition, the coefficient when calculating the iodine content differs depending on the measuring device, and the coefficient can be obtained using an appropriate calibration curve. 3. Change in transmittance The laminates prepared in the examples and comparative examples were placed in a humidified environment (60° C., 90% RH) for 24 hours. Next, the monomer transmittance of the laminate was measured in the same manner as the above-mentioned method of measuring the monomer transmittance, and the transmittance change was calculated from the following formula. (Transmittance change) = (Monomer transmittance after humidification test)-(Monomer transmittance before humidification test) 4. The crystallinity measurement device of PVA uses Fourier transform infrared spectrophotometer (FT-IR) ( Perkin Elmer (Perkin Elmer) company, trade name: "SPECTRUM2000"), using polarized light as the measurement light, by total reflection attenuated spectroscopy (ATR: attenuated total reflection) measurement, to evaluate the surface of the PVA resin layer. The calculation of crystallinity can be performed by the following procedure. The measurement was performed in a state where the measurement polarization was set to 0° and 90° with respect to the stretching direction. Use the intensity of 1141 cm ^-1 and 1440 cm ^-1 of the obtained spectrum to calculate according to the following formula. It was confirmed in advance that the intensity of 1141 cm ^-1 was correlated with the amount of crystal parts, and 1440 cm ^{-1 was used} as the reference peak, and the crystal index (Equation 2) was calculated from the following formula. In addition, the crystallinity is based on using a known PVA sample, a calibration curve of the crystallinity index and the crystallinity is prepared in advance, and the crystallinity is calculated from the crystallinity index using the obtained calibration curve (Equation 1). Crystallinity = 63.8 × (crystallinity index) -44.8 (Formula 1) with crystallographic index ^{= (((1141cm -1) I} 0˚ + 2 × I (1141cm -1) 90˚) / 3) / ((I (1440cm - ¹ )0˚+2×I(1440cm ^-1 )90˚)/3) (Equation 2) However, I(1141cm ^-1 )0˚: when the polarized light is incident in a direction parallel to the stretching direction for measurement 1141cm ^-1 of the intensity I (1141cm ^-1) 90˚: that the polarization direction toward the stretching direction was perpendicular to the incident intensity I 1141cm ^-1 and the time of measurement (1440cm ^-1) 0˚: that the polarization toward the 1440cm ^-1 when the intensity of the polarized light so that the stretching direction toward a direction perpendicular to the incidence was measured: 1440cm ^-1 the intensity I (1440cm ^-1) at a direction parallel to the stretching direction was measured incidence 90˚

[Table 1] PVA thickness (μm) Monomer transmittance (%) Crystallinity (%) Iodine content (wt%) Transmittance change (60℃90%RH 24h) Example 1 2.5 39.8 67 13.5 0.9 Comparative example 1 2.5 40.0 67 14.5 1.2 Example 2 1.2 40.1 58 22.8 0.8 Comparative example 2 1.2 39.9 58 22.1 1.5

The polarizers obtained in Examples 1 and 2 have high iodine content and high crystallinity, but are excellent in humidification durability.

Industrial availability The manufacturing method of the present invention can provide a polarizer with high iodine content and high crystallinity but with excellent humidification durability. The polarizer made by the manufacturing method of the present invention can be widely used in LCD TVs, LCD monitors, mobile phones, digital cameras, video cameras, portable game machines, car navigation, photocopiers, printers, fax machines, clocks, LCD panels for microwave ovens, etc.

(no)

Claims (8)

A manufacturing method of a polarizing element is a manufacturing method of a polarizing element with an iodine content of 10% by weight to 25% by weight. The manufacturing method includes: Dry stretch the polyvinyl alcohol resin film; Dye the dry stretched polyvinyl alcohol resin film in a dye bath; and The dyed polyvinyl alcohol-based resin film was treated with ascorbic acid. The method for manufacturing a polarizing member of claim 1, wherein the polyvinyl alcohol-based resin film after the aforementioned dry step has a crystallinity of 40% or more. According to claim 1 or 2, the method of manufacturing a polarizing member, wherein the dyeing bath is an iodine aqueous solution containing 0.3 parts by weight or more of iodine. According to claim 1 or 2, the method for manufacturing a polarizer, wherein the dye bath is an aqueous solution containing iodide and an oxidizing agent for iodide ions. The method for manufacturing a polarizing element according to claim 4, wherein the aforementioned oxidizing agent is at least one selected from the group consisting of iron sulfate, iron chloride, and iron nitrate. According to claim 4 or 5, the method for manufacturing a polarizer, wherein the aqueous solution containing iodide and an oxidizing agent for iodide ions contains 0.5 to 10 parts by weight of the oxidizing agent and 1 part by weight of the iodide relative to 100 parts by weight of water ~40 parts by weight, and the molar ratio of the aforementioned iodide to the aforementioned oxidant (iodide/oxidant) is 2/1 to 50/1. According to the method for manufacturing a polarizer according to any one of claims 1 to 6, wherein the ascorbic acid treatment is performed using an ascorbic acid bath, and the ascorbic acid concentration in the ascorbic acid bath is 0.005% by weight to 1% by weight. The method for manufacturing a polarizer according to any one of claims 1 to 7, wherein the thickness of the polarizer is 3 μm or less.