CN106842403B - The manufacture method of polarizer - Google Patents

Abstract

The present invention provides a method for producing a polarizing plate capable of further improving productivity by removing PVA dissolved in a dyeing solution. The production method includes a dyeing step in which the polyvinyl alcohol (PVA) resin film is dipped in a dye solution containing a dichroic dye (iodine), thereby dyeing the PVA resin film. The dye solution contains Cross-linking agent (boric acid), utilize filter material to filter above-mentioned dyeing solution.

Description

Manufacturing method of polarizer

technical field

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

Background technique

Conventionally, polarizing plates have been widely used as polarized light supply elements and polarized light detection elements in display devices such as liquid crystal display devices. A polarizing plate is generally an element in which a protective film is bonded to one or both sides of a polarizing film (polarizing plate) with an adhesive.

A polarizing plate is produced by subjecting an unstretched polyvinyl alcohol (PVA)-based resin film (raw film) to swelling treatment, dyeing treatment, stretching treatment, crosslinking treatment, washing treatment, etc., and then drying.

In recent years, along with improvements in performance and thickness of liquid crystal display devices, reduction in thickness has also been demanded for polarizing plates. For example, a polarizing plate with a thickness of 10 μm or less is formed by coating a PVA-based resin solution on a thermoplastic resin substrate and drying it to form a laminate having a PVA-based resin layer, and then using the laminate as a raw film to perform the above-mentioned reasons. This is made.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2008-292935

Contents of the invention

The problem to be solved by the invention

However, in the above-mentioned dyeing process of dyeing the PVA-based resin film (PVA-based resin layer), the raw film is immersed in a dyeing solution containing iodine (dichroic dye) in a dyeing bath. At this time, a part of PVA may dissolve in the dyeing solution from the PVA-based resin film. In particular, a polarizing plate (PVA-based resin film) thinned to a thickness of 10 μm or less has high solubility.

In this case, if the continuous production of the polarizer is carried out, the dissolved PVA is accumulated in the dyeing bath, and the PVA concentration in the dyeing solution increases, so that the precipitated PVA adheres to the PVA-based resin film, resulting in poor dyeing of the polarizer. equal. In addition, when the raw film is taken out from the dyeing bath, dehydration (dehydration) of the dyeing solution is deteriorated. As a result, there arises a problem that the yield of polarizing plates decreases. In addition to the above-mentioned problems, the increase in the concentration of PVA in the dyeing solution also reduces the rate of adsorption of iodine on the PVA-based resin film (dyeing rate) and impairs productivity.

As a countermeasure against this, there is disclosed a method of adsorbing and removing foreign matter including PVA generated in a crosslinking bath by contacting it with activated carbon (refer to the above-mentioned Patent Document 1). However, activated carbon also adsorbs iodine, so it is not preferable for dyeing baths that need to keep the iodine concentration constant.

Therefore, the PVA dissolved in the dyeing solution cannot be removed, and therefore, as a countermeasure against the increase in the PVA concentration in the dyeing bath, the treatment solution is generally renewed (replaced) periodically before the above-mentioned problem occurs. However, in the conventional dyeing process, iodine, potassium iodide, etc. are often used as the dyeing solution. Therefore, frequent renewal (replacement) of the dyeing solution is also not preferable from the viewpoint of environmental problems caused by the discharge of halogens, high cost, and the like.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for producing a polarizing plate capable of further improving productivity by removing PVA dissolved in a dyeing solution.

means of solving problems

As means for solving the above-mentioned problems, according to an aspect of the present invention, there is provided a method of manufacturing a polarizing plate, which includes a dyeing step in which a polyvinyl alcohol (PVA)-based resin film is dipped in a layer containing dichroic The above-mentioned PVA-based resin film is thus dyed in a dyeing solution of a pigment, the above-mentioned dyeing solution contains a crosslinking agent, and the above-mentioned dyeing solution is filtered through a filter material.

Moreover, the manufacturing method of the polarizing plate of the said aspect may be the manufacturing method which circulates the said dyeing liquid through the said filter material.

Moreover, the manufacturing method of the polarizing plate of the said aspect may be a manufacturing method which stirs the said dyeing liquid.

Moreover, in the manufacturing method of the polarizing plate of the said aspect, the manufacturing method in which the said crosslinking agent is a boron compound may be sufficient.

Moreover, in the manufacturing method of the polarizing plate of the said aspect, the manufacturing method in which the said boron compound is boric acid may be sufficient.

Moreover, in the manufacturing method of the polarizing plate of the said aspect, the manufacturing method in which the said PVA-type resin film is 10 micrometers or less in thickness, and is formed on a thermoplastic resin base material may be used.

Moreover, in the manufacturing method of the polarizing plate of the said aspect, the manufacturing method in which the density|concentration of the said crosslinking agent is 0.01-0.1 weight part may be used.

Moreover, in the manufacturing method of the polarizing plate of the said aspect, the manufacturing method in which the said dichroic dye is iodine may be sufficient.

Moreover, in the manufacturing method of the polarizing plate of the said aspect, the manufacturing method in which the density|concentration of the said dichroic dye is 0.01-10 weight part may be used.

Moreover, in the manufacturing method of the polarizing plate of the said aspect, the manufacturing method which contains potassium iodide in the said dyeing liquid may be sufficient.

Invention effect

As mentioned above, according to the aspect of this invention, the manufacturing method of the polarizing plate which can further improve productivity by removing the PVA dissolved in the dyeing liquid can be provided.

Detailed ways

In this embodiment, as a method of manufacturing a polarizing plate to which the present invention is applied, the following case is described as an example: a PVA-based resin solution is coated on a thermoplastic resin substrate and dried to form a polarizer with a PVA-based resin. A laminate of layers (films) is then subjected to various treatments as a raw film to manufacture a polarizing plate with a thickness of 10 μm or less.

<Thermoplastic resin substrate>

First, the thermoplastic resin base material used for the manufacturing method of the polarizing plate to which this invention is applied is demonstrated. As a thermoplastic resin base material, the thermoplastic resin base material conventionally used as the transparent protective film of a polarizing plate can be used.

As a material constituting the thermoplastic resin substrate, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy, stretchability, etc. can be used. Specific examples of such thermoplastic resins include: cellulose resins such as triacetyl cellulose; polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polyethersulfone resins; Polysulfone resin; polycarbonate resin; polyamide resin such as nylon and aromatic polyamide; polyimide resin; polyolefin resin such as polyethylene, polypropylene, ethylene-propylene copolymer; with ring structure or norbornene Cyclic polyolefin resins (norbornene-based resins); (meth)acrylic resins; polyarylate resins; polystyrene resins; polyvinyl alcohol resins;

In addition, in order to improve the adhesiveness with the PVA-based resin layer, the thermoplastic resin substrate may be subjected to surface treatment (for example, corona treatment, etc.), or may be formed with a thin layer such as an undercoat layer (primer layer).

Thermoplastic resins can be broadly classified into: thermoplastic resins in which macromolecules are in an ordered crystalline state, and thermoplastic resins in which macromolecules are in an amorphous or non-crystalline state with no or only a small portion of ordered arrangements. The former is called a crystalline state, and the latter is called an amorphous or non-crystalline state. Correspondingly, a thermoplastic resin that has the property of forming a crystalline state is called a crystalline resin, and a thermoplastic resin that does not have such a property is called an amorphous resin.

On the other hand, regardless of whether it is a crystalline resin or an amorphous resin, a resin that is not in a crystalline state or a resin that has not reached a crystalline state is called an amorphous (amorphous) or amorphous (amorphous) resin. Here, an amorphous or non-crystalline resin is used in distinction from an amorphous resin that does not form a crystalline state.

As the crystalline resin, there are, for example: olefin-based resins including polyethylene (PE) and polypropylene (PP); including polyethylene terephthalate (PET), polybutylene terephthalate ( PBT) ester resin. One of the characteristics of crystalline resins is that they generally have the property of crystallizing by aligning polymers by heating and stretching. The physical properties of the resin vary in various ways depending on the degree of crystallization.

On the other hand, for example, crystalline resins such as polypropylene (PP) and polyethylene terephthalate (PET) also hinder the alignment of polymers caused by heat treatment and stretching orientation. Crystallization can be suppressed. Such polypropylene (PP) and polyethylene terephthalate (PET) whose crystallization is suppressed are called amorphous polypropylene and amorphous polyethylene terephthalate, and they are respectively Collectively referred to as amorphous olefin resins and amorphous ester resins.

For example, in the case of polypropylene (PP), an amorphous polypropylene (PP) in which crystallization is suppressed can be produced by forming an atactic structure without stereoregularity. In addition, for example, in the case of polyethylene terephthalate (PET), by copolymerizing modified groups such as isophthalic acid and 1,4-cyclohexanedimethanol as polymerized monomers, that is, by copolymerizing Molecules that inhibit the crystallization of polyethylene terephthalate (PET) can produce amorphous polyethylene terephthalate (PET) in which crystallization is suppressed.

The thickness of the thermoplastic resin substrate (before stretching) can be appropriately determined, but is generally 10 to 500 μm from the viewpoint of workability such as strength and handleability, and thin layer properties. In particular, it is preferably 20 to 300 μm, more preferably 30 to 200 μm. It is especially preferable when the thickness of a thermoplastic resin base material is 50-150 micrometers.

<Polyvinyl alcohol (PVA)-based resin layer (film)>

In the manufacturing method of the polarizing plate to which this invention is applied, the laminated body containing a PVA-type resin layer (film) is formed on the said thermoplastic resin base material. As the PVA-based resin, a PVA-based resin in which dichroic substances such as iodine and a dichroic dye are dispersed and adsorbed, which has translucency in the visible light region, can be used without particular limitation.

As the PVA-based resin, it is preferable to use a PVA-based resin conventionally used as a polarizing plate. As PVA-type resin, PVA or its derivative(s) are mentioned. Examples of derivatives of PVA include polyvinyl formal, polyvinyl acetal, and the like. Other examples include olefins such as ethylene and propylene; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, and their alkyl esters; and those modified with acrylamide or the like.

The degree of polymerization of PVA is preferably 100-10000, more preferably 1000-10000. Regarding the degree of saponification, PVA having a degree of saponification of 80 to 100 mol % is generally used.

Additives such as plasticizers and surfactants may also be contained in the PVA-based resin. Examples of the plasticizer include polyhydric alcohols and condensates thereof. Specifically, glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, polyethylene glycol etc. are mentioned, for example. The usage-amount of a plasticizer etc. is not specifically limited, It is preferable that it is 20 weight part or less per 100 weight part of PVA-type resins.

<Laminate (raw film)>

The laminated body which becomes a raw film can be obtained by coating the aqueous solution containing a PVA-type resin on a thermoplastic resin base material, and drying it, and forming a PVA-type resin layer. In addition, the laminated body may have a structure in which a thermoplastic resin base material and a PVA-based resin layer are laminated with an undercoat layer interposed therebetween. In addition, the laminate may have a structure in which a thermoplastic resin substrate and a PVA-based resin layer are directly laminated, or a laminate in which a substrate layer and a hydrophilic polymer layer are integrated.

The aqueous solution can be prepared, for example, by dissolving powder, pulverized, chopped, and the like of a PVA-based resin in water (hot water) heated appropriately. The concentration of the aqueous solution is preferably 2 to 20 parts by weight, more preferably 4 to 10 parts by weight, relative to 100 parts by weight of water.

For coating the aqueous solution on the thermoplastic resin substrate, for example, roll coating methods such as wire bar coating, reverse coating, and gravure coating, spin coating, screen coating, and spray coating can be appropriately selected. , dip coating method, spray coating method, die coating method, comma coating method, lip coating method, spin coating method, etc.

When the thermoplastic resin substrate has an undercoat layer, the aqueous solution is directly coated on the undercoat layer. On the other hand, in the case where the thermoplastic resin substrate does not have an undercoat layer, the aqueous solution is directly coated on the substrate layer. In addition, it is preferable to set drying temperature to 50-200 degreeC, and it is more preferable to set it as 60-150 degreeC. The drying time is preferably set to 5 to 30 minutes.

The PVA-based resin layer is formed so that the thickness of the obtained polarizing plate is 10 μm or less in consideration of the stretch ratio in the stretching treatment performed on the laminate. The thickness of the unstretched PVA-based resin layer is preferably set to 3 to 20 μm, more preferably 5 to 15 μm.

<Procedure>

In the manufacturing method of the polarizing plate to which this invention was applied, at least dyeing process and stretching process are given to a laminated body (raw film). Moreover, in the manufacturing method of the polarizing plate to which this invention is applied, crosslinking process can be performed. Each of the dyeing bath, crosslinking bath, and stretching bath is used in the dyeing treatment, the crosslinking treatment, and the stretching treatment, respectively. When using a treatment bath, a treatment liquid (aqueous solution, etc.) corresponding to each treatment can be used.

<Dyeing process>

In the dyeing process, dyeing treatment is performed by adsorbing iodine or a dichroic dye to the PVA-based resin layer in the laminate and aligning them. In the dyeing process, dyeing treatment may be performed together with stretching treatment.

The dyeing process is carried out by immersing the laminate in a dyeing solution in a dyeing bath (dyeing bath). As a staining solution, iodine solution is generally used. As the iodine aqueous solution used as the iodine solution, an aqueous solution containing iodide ions using iodine and iodide as a dissolution aid may be used.

As the iodide, for example, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. can be used . As iodide, potassium iodide is preferable. In addition, when the iodide used in this embodiment is used in another process, it is the same as the said iodide.

The iodine concentration in the iodine solution is preferably 0.01 to 10 parts by weight, more preferably 0.02 to 5 parts by weight, and still more preferably 0.1 to 1.0 parts by weight, based on 100 parts by weight of the solvent. The iodide concentration is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 8 parts by weight, based on 100 parts by weight of the solvent. When dyeing with iodine, the temperature of the iodine solution is preferably set at 20 to 50°C, more preferably at 25 to 40°C. The immersion time is preferably set to 10 to 300 seconds, more preferably 20 to 240 seconds. It should be noted that the dyeing time can be dipped in an optional time in such a way that a specified degree of polarization or transmittance can be achieved.

<Stretching process>

In the stretching process, both dry stretching treatment and wet stretching treatment can be used. In the stretching step, stretching treatment is performed by uniaxially stretching the laminate. The uniaxial stretching may be any of longitudinal stretching in the longitudinal direction of the laminate and transverse stretching in the width direction of the laminate.

In lateral stretching, it may shrink in the longitudinal direction while stretching in the width direction. Examples of the transverse stretching method include a fixed-end uniaxial stretching method in which one end is fixed via a tenter, a free-end uniaxial stretching method in which one end is not fixed, and the like.

On the other hand, in longitudinal stretching, for example, an inter-roll stretching method, a compression stretching method, a stretching method using a tenter, or the like can be used. In addition, the stretching treatment may be performed in multiple stages. In addition, stretching treatment can be performed by using biaxial stretching, diagonal stretching, or the like.

The dry stretching treatment is preferable in that the temperature range for stretching the laminate can be widely set. In the dry stretching treatment, it is preferable to perform the stretching treatment while heating the laminate at 50 to 200°C, more preferably at 80 to 180°C, and even more preferably at 100 to 160°C. When a dry stretching process is included in the stretching process, it is preferable to perform the dry stretching process before the dyeing process.

Iodide may be contained in the treatment liquid used in the wet stretching treatment. When the treatment liquid contains iodide, the concentration of iodide is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight, based on 100 parts by weight of the solvent. The treatment temperature in the wet stretching method is preferably set to 25°C or higher, more preferably 30 to 85°C, further preferably 50 to 70°C. The immersion time is preferably set to 10 to 800 seconds, more preferably 30 to 500 seconds. In addition, stretching treatment may be performed together with dyeing treatment and crosslinking treatment.

In the stretching step, stretching treatment is performed so that the total stretch ratio is 4 to 8 times the original length of the laminate. The total draw ratio is preferably 5 to 7 times. In addition, the total stretching ratio means the cumulative stretching ratio including stretching in other steps when stretching is accompanied by stretching in steps other than the stretching step. The total draw ratio is appropriately determined in consideration of draw ratios in other steps and the like.

When the total draw ratio is low, the orientation is insufficient, and it is difficult to obtain a polarizing plate with high optical characteristics (degree of polarization). On the other hand, when the total stretching ratio is too high, tensile fracture is likely to occur. Moreover, the polarizing plate becomes too thin, and there exists a possibility that the processability in a subsequent process may fall.

In the stretching step, as described in "Japanese Patent No. 4751481", wet stretching may be performed after auxiliary stretching in an air atmosphere. The stretching temperature in the auxiliary stretching treatment in the gas atmosphere is preferably set in advance at a temperature as high as 60 to 180°C, more preferably 95 to 150°C. In addition, the stretching ratio in the auxiliary stretching treatment in the gas atmosphere is preferably set to 1.3 to 4 times, and more preferably set to 1.5 to 3 times. In addition, the treatment temperature in the wet stretching treatment performed after the auxiliary stretching treatment in an air atmosphere is preferably set to 50 to 80°C, more preferably 60 to 70°C. The immersion time is preferably set to 5 to 120 seconds, more preferably 10 to 60 seconds. In addition, the stretching ratio in the wet stretching treatment is preferably set to 4 to 7 times the total stretching ratio, more preferably 5 to 6 times.

When the stretching step includes auxiliary stretching in air and wet stretching, it is preferable to perform auxiliary stretching in air before dyeing and wet stretch after dyeing. In this case, the treatment bath used for the wet stretching treatment is also used as a crosslinking bath, and it is preferable to perform the crosslinking treatment together with the wet stretching treatment.

<Crosslinking process>

In the crosslinking step, a boron compound is used as a crosslinking agent to perform a crosslinking treatment. Crosslinking treatment can be performed together with dyeing treatment and stretching treatment. In addition, the crosslinking treatment may be divided into multiple times. As a boron compound, boric acid, borax, etc. can be used, for example. A boron compound is generally used in the form of an aqueous solution or a water-organic solvent mixed solution.

When using an aqueous boric acid solution, since heat resistance is imparted by the degree of crosslinking, the concentration of boric acid in the aqueous boric acid solution is preferably 1 to 10 parts by weight, more preferably 2 to 7 parts by weight, based on 100 parts by weight of the solvent. Iodides such as potassium iodide may be contained in boric acid aqueous solution or the like. When iodide is contained in the boric acid aqueous solution, the concentration of iodide is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, relative to 100 parts by weight of water.

The crosslinking treatment can be performed by immersing the laminate in an aqueous solution of boric acid or the like. The treatment temperature in the crosslinking treatment is preferably set to 25°C or higher, more preferably 30 to 85°C, and furthermore 30 to 60°C. The treatment time is preferably set to 5 to 800 seconds, more preferably 8 to 500 seconds.

<Insolubilization process>

In the method of manufacturing a polarizing plate to which the present invention is applied, insolubilization treatment may be performed before dyeing treatment or crosslinking treatment is performed on the laminate. The purpose of the insolubilization process is to perform an insolubilization treatment for insolubilizing the PVA-based resin layer.

In the insolubilization step, the insolubilization treatment can be performed by immersing the PVA-based resin layer in the laminate in, for example, boric acid or a solution containing a boron compound such as borax. The solution is generally used in the form of an aqueous solution or a water-organic solvent mixed solution.

When using a boric-acid aqueous solution, it is preferable to set the boric-acid density|concentration of boric-acid aqueous solution to 1-4 weight part with respect to 100 weight part of solvents. The treatment temperature in the insolubilization step is preferably set to 25°C or higher, more preferably 30 to 85°C, further preferably 30 to 60°C. The treatment time is preferably set to 5 to 800 seconds, more preferably 8 to 500 seconds.

<Washing process>

In the method for producing a polarizing plate to which the present invention is applied, the laminate may be subjected to dyeing treatment, stretching treatment, and further crosslinking treatment, but washing treatment may be performed after performing these treatments.

In the washing step, washing treatment may be performed using a potassium iodide solution. The concentration of potassium iodide in the potassium iodide solution is preferably 0.5 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, and still more preferably 1 to 6 parts by weight, based on 100 parts by weight of the solvent.

In the washing treatment with a potassium iodide solution, the treatment temperature is preferably set to 5 to 60°C, more preferably 10 to 40°C. The immersion time is preferably set to 1 to 120 seconds, more preferably 3 to 90 seconds. The stage of the washing treatment with the potassium iodide solution is not particularly limited as long as it is before the drying treatment.

In addition, as washing treatment, water washing treatment may be performed. The water washing treatment is performed by immersing the PVA-based resin in pure water such as ion-exchanged water or distilled water. The water washing temperature is preferably set at 5 to 50°C, more preferably at 10 to 45°C, and even more preferably at 15 to 40°C. The immersion time is preferably set to 5 to 300 seconds, more preferably 10 to 240 seconds.

In the washing step, washing treatment with a potassium iodide solution and washing treatment with water may be combined, and for example, a solution in which a liquid alcohol such as methanol, ethanol, isopropanol, butanol, or propanol is appropriately blended may be used.

<Drying process>

Moreover, in the manufacturing method of the polarizing plate to which this invention was applied, after carrying out each process mentioned above, drying processing is finally performed, and a polarizing plate is manufactured. In the drying process, the optimum drying time and drying temperature are set according to the moisture content required for the obtained polarizing plate (film). Specifically, the drying temperature is preferably set to 20 to 150°C, more preferably 40 to 100°C. When the drying temperature is too low, the drying time becomes long and efficient production cannot be performed, which is not preferable. On the other hand, when the drying temperature is too high, the obtained polarizing plate is deteriorated, and the optical characteristics and color tone are deteriorated. The heat drying time is preferably set to 1 to 10 minutes.

<Water-soluble antioxidant>

In the method of manufacturing a polarizing plate to which the present invention is applied, treatment with a treatment liquid containing at least one water-soluble antioxidant may be performed in at least one step after the above-mentioned dyeing step.

In the treatment with the treatment solution containing the water-soluble antioxidant, at least one of the respective baths used in each treatment of the laminate after the dyeing treatment contains the water-soluble antioxidant. Alternatively, treatment with a treatment liquid containing a water-soluble antioxidant is separately performed. The treatment with a treatment liquid containing a water-soluble antioxidant is preferably performed together with crosslinking treatment and/or stretching treatment.

It should be noted that the cross-linking treatment and the stretching treatment can be performed by a unified treatment in which a plurality of treatments are performed at the same time. In the unified treatment in which a plurality of treatments are performed simultaneously, a water-soluble antioxidant is contained in the bath used in the unified treatment. In addition, in the multistage treatment in which the crosslinking treatment and the stretching treatment are separately performed, a water-soluble antioxidant is contained in at least one of the crosslinking treatment and the stretching treatment.

Examples of water-soluble antioxidants include ascorbic acid (vitamin C), erythorbic acid, thiosulfuric acid, sulfurous acid, chlorogenic acid, citric acid, rosmarinic acid, and salts thereof.

Examples of the salt include alkali metal salts such as sodium salts and potassium salts.

Among them, ascorbic acid, erythorbate, thiosulfate, and sulfite are preferably used. These water-soluble antioxidants can be used individually by 1 type or in combination of 2 or more types.

The addition amount of the water-soluble antioxidant is determined according to the contamination concentration of the dichroic substance (iodine or dichroic dye) contained in each treatment liquid after the dyeing step. The higher the concentration of contamination caused by dichroic substances in the contaminated treatment liquid, the greater the amount of water-soluble antioxidant to be added.

In each treatment liquid, the concentration of the water-soluble antioxidant is preferably 0.005 to 1 part by weight, more preferably 0.005 to 0.5 part by weight, based on 100 parts by weight of the solvent. When the concentration of the water-soluble antioxidant is less than 0.005 parts by weight, the proportion of the water-soluble antioxidant in the contaminated treatment liquid decreases, and the characteristics (single transmittance, polarization degree) of the obtained polarizer cannot be sufficiently suppressed. reduce. On the other hand, when the concentration of the water-soluble antioxidant exceeds 1 part by weight, the ratio of the water-soluble antioxidant in the bath increases, so that the resulting polarizing plate is discolored and the transmittance increases. Along with this, it may be necessary to increase the iodine concentration in the dyeing bath, but there is no problem such as a decrease in optical properties.

<Polarizer>

The polarizing plate manufactured by applying the method for producing a polarizing plate of the present invention is formed on a thermoplastic resin substrate, but the above-described implementation may be performed using an unstretched PVA-based resin layer film as a raw film without using the above-mentioned thermoplastic resin substrate. Each treatment is manufactured. In this case, the thickness of the polarizing plate may be 10 μm or more, preferably 5 to 50 μm.

The thermoplastic resin substrate can be used as it is as a transparent protective film for a polarizing plate described later. In addition, a transparent protective film may be bonded to the surface of the polarizer opposite to the thermoplastic resin substrate. On the other hand, when not using a thermoplastic resin base material, you may bond a transparent protective film to both sides of a polarizing plate. Moreover, after peeling a thermoplastic resin base material from a polarizer, you may bond a transparent protective film to both sides of this polarizer.

As a material constituting the transparent protective film, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy, and the like can be used. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, etc. , (meth)acrylic resins, cyclic polyolefin resins (norbornene-based resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof.

<Staining solution containing cross-linking agent>

The PVA-based resin used in the dyeing step is preferably undyed. Moreover, in the manufacturing method of the polarizing plate to which this invention was applied, the dyeing liquid used in the said dyeing process contains a crosslinking agent. As the crosslinking agent, for example, boron compounds such as boric acid and borax, glyoxal, glutaraldehyde, and the like can be used at least one or in combination of two or more. Among them, boron compounds are preferably used, and boric acid is more preferably used.

In the above dyeing step, the boric acid crosslinks (complexes) the PVA dissolved in the dyeing liquid from the PVA-based resin layer by making the dyeing liquid contain a trace amount of boric acid (crosslinking agent). As a result, a gel-like iodine/PVA/boric acid complex (hereinafter referred to as a complex compound) in which PVA dissolved in the staining liquid is bonded to iodine and boric acid in the staining liquid is produced.

In order to crosslink (complex) the PVA dissolved in the dyeing solution, the concentration of boric acid (crosslinking agent) in the dyeing solution is preferably set at 0.01 to 0.1 parts by weight, more preferably 0.02 to 100 parts by weight of the solvent. 0.1 parts by weight. When the concentration of boric acid is 0.01 parts by weight or more, PVA dissolved in the dyeing solution can be crosslinked (complexed). On the other hand, when the concentration of boric acid exceeds 0.2 parts by weight, boric acid may precipitate on the surface of the laminate (raw film) or the surface of the roller for transporting the laminate (raw film), causing defects in the polarizer.

As a method of adjusting the concentration of boric acid in the staining liquid, there may be a method of adding a predetermined amount of boric acid to the staining liquid. In addition, when there is a treatment bath containing boric acid before the dyeing treatment, boric acid brought in together with the laminate from the treatment bath can be used.

In the method of manufacturing a polarizing plate to which the present invention is applied, the above-mentioned dyeing solution contains a trace amount of boric acid (crosslinking agent), and this boric acid crosslinks (complexes) the PVA dissolved in the dyeing solution, thereby avoiding the conventional There are problems such as adhesion of such PVA and reduction in dyeing speed. That is, the PVA dissolved in the dyeing solution is cross-linked (complexed), and thus is less likely to adhere to the PVA-based resin layer (raw film). In addition, the dehydration (dehydration) property of the dyeing solution when the raw film is taken out from the dyeing bath is improved. Thereby, a polarizing plate free from coloring unevenness can be obtained.

<Filtration of staining solution>

Moreover, in the manufacturing method of the polarizing plate to which this invention was applied, a dyeing liquid is filtered with a filter medium.

Thereby, the complex compound produced by crosslinking (complexing) the PVA dissolved in the dyeing solution can be isolated from the dyeing solution. For example, organic substances such as PVA can be separated from different components of the dyeing solution by adjusting the film-forming conditions of the flat membrane constituting the membrane or performing surface treatment for separation into the membrane. As a filter material, a polypropylene filter material, a polyester filter material, a nylon filter material, etc. can be used, for example. The module is not particularly limited, but is preferably a cartridge type having a structure in which a filter material is accommodated in a sealable container and detachably installed in the device.

More specifically, by adjusting the internal pore diameter of the flat membrane inside the membrane (for example, adjusting to prevent the passage of substances with a molecular weight of 300 or more), or forming a barrier to determine whether the substance can pass through the membrane according to the difference in ion charge repulsion force Functional coating film or surface treatment film, which can separate organic substances such as PVA from other components in the dyeing liquid.

As the filtration membrane, for example, an ultrafiltration (UF) membrane, a fine filtration (MF) membrane, a nanofiltration (NF) membrane, a reverse osmosis (RO) membrane, etc. can be used, among which UF membrane and MF membrane are preferably used. In addition, among the filter membranes, it is preferable to use a filter membrane capable of setting multiple separation criteria (for example, molecular weight and ion charge repulsion) capable of separating organic substances such as PVA from different components of the dyeing solution.

In addition, the dyeing solution in the dyeing bath is preferably circulated through a filter medium. Thereby, the complex compound in a dyeing bath can be efficiently removed (collected) by a filter medium. In addition, the staining solution can be reused.

In addition, it is preferable to stir the dyeing solution in the dyeing bath. Thereby, the crosslinking (complexation) of PVA dissolved in the dyeing solution can be promoted, and the complex compound can be efficiently removed from the dyeing solution.

As a method of stirring the dyeing solution, a method of agitating the dyeing solution in the dyeing bath by providing stirring means such as stirring blades in the dyeing bath can be used. In addition, the dyeing liquid in the dyeing bath can also be stirred by the circulation of the above-mentioned dyeing liquid. Moreover, the dyeing liquid in a dyeing bath can also be stirred by the raw film conveyed (in and out) in a dyeing bath.

As mentioned above, in the manufacturing method of the polarizing plate to which this invention was applied, the PVA dissolved in the dyeing liquid can be removed. Thereby, while avoiding the influence of the PVA dissolved in the dyeing solution, it is possible to prolong the renewal (replacement) period of the dyeing solution, and therefore, the productivity of the polarizing plate can be further improved.

Example

Below, the effects of the present invention will be clarified through examples. In addition, this invention is not limited to the following Example, It can change suitably and implement in the range which does not change the summary.

(Example 1)

In Example 1, a polarizing laminated film in which a polarizing plate was formed on a thermoplastic resin substrate was produced using the method for producing a polarizing plate to which the present invention was applied.

Specifically, first, as a thermoplastic resin substrate, an amorphous polyethylene terephthalate (A-PET) film (manufactured by Mitsubishi Chemical Corporation, trade name "Novacrya (registered trademark)" was prepared, and the thickness was: 200μm).

Next, corona treatment was performed on one side of the thermoplastic resin substrate (treatment condition: 90 W·min/m ² ), and a coating with a degree of polymerization of 4000 and a degree of saponification of 99.0 moles was applied on the corona-treated surface at 65°C. % above PVA in water and then allowed to dry. Thus, a laminate in which a PVA-based resin layer having a thickness of 8.3 μm was formed on one surface of a thermoplastic resin substrate was obtained as a raw film.

Next, the obtained raw film was uniaxially stretched by 1.8 times in the oven of 90 degreeC (stretching process).

Next, the stretched raw film was immersed in an insolubilization bath (a boric acid aqueous solution in which 3 parts by weight of boric acid was dissolved in 100 parts by weight of water) at a liquid temperature of 30° C. for 30 seconds (insolubilization treatment).

Next, the raw film was immersed in a dyeing bath while adjusting the iodine concentration and the immersion time so that the transmittance of the polarizing plate was about 42.0% (dyeing treatment).

In Example 1, a staining solution in which 0.18 parts by weight of iodine, 1.26 parts by weight of potassium iodide, and 0.02 parts by weight of boric acid were dissolved with respect to 100 parts by weight of water was prepared. Then, the liquid temperature of this dyeing liquid was set to 30 degreeC, and the raw film was immersed for 13 seconds.

In addition, 0.05 parts by weight of PVA was added to this dyeing liquid, and the dyeing liquid filtered through a polypropylene filter was circulated while stirring for 15 minutes with a magnetic stirrer.

Next, the raw film was immersed in a crosslinking bath (a boric acid aqueous solution in which 3 parts by weight of potassium iodide and 3 parts by weight of boric acid were dissolved in 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (crosslinking treatment).

Next, the raw film was uniaxially stretched in the longitudinal direction (longitudinal direction) while immersing the raw film in a boric acid aqueous solution (an aqueous solution in which 4 parts by weight of boric acid and 5 parts by weight of potassium iodide were dissolved in 100 parts by weight of water) at a liquid temperature of 70°C. (longitudinal stretching in liquid). At this time, the maximum draw ratio of the laminate was 5.94 times.

Next, the raw film was immersed in a washing bath (an aqueous solution in which 4 parts by weight of potassium iodide was dissolved in 100 parts by weight of water) at a liquid temperature of 30° C. for 5 seconds, and then dried with warm air at 60° C. (washing and drying deal with).

Through the above steps, a polarizing laminated film in which a 4.5-μm-thick polarizing plate was formed on a thermoplastic resin substrate was produced.

(Example 2)

In Example 2, the dyeing liquid similar to Example 1 was prepared except having made boric acid into 0.05 weight part. Then, using this dyeing solution, a polarizing plate was produced by the same method as in Example 1.

(Example 3)

In Example 3, the dyeing solution similar to Example 1 was prepared except having made boric acid into 0.1 weight part. Then, using this dyeing solution, a polarizing plate was produced by the same method as in Example 1.

(Example 4)

In Example 4, the dyeing liquid similar to Example 1 was prepared except having made boric acid into 0.2 weight part. Then, using this dyeing solution, a polarizing plate was produced by the same method as in Example 1.

(Example 5)

In Example 5, the same dyeing solution as in Example 1 was prepared except that boric acid was used as 0.01 parts by weight. Then, using this dyeing solution, the same method as in Example 1 was carried out up to the dyeing process.

(comparative example 1)

In Comparative Example 1, the same staining solution as in Example 1 was prepared except that boric acid was not contained.

Then, using this dyeing solution, a polarizing plate was produced by the same method as in Example 1.

Then, about each polarizing plate produced in these Examples 1-5 and the comparative example 1, the presence or absence of occurrence of "dyeing unevenness" was visually observed. In addition, the residual amount of the complex compound captured by the filter medium was measured, and the "filterability" of the dyeing solution was evaluated. Among them, the very good ones were made "⊚", the good ones were made "◯", and the bad ones were made "×". Furthermore, the presence or absence of "contamination by boric acid" adhering to the apparatus and the like during the dyeing process was visually observed. These are collectively shown in Table 1 below.

[Table 1]

As shown in Table 1, compared with Examples 1 to 5 in which boric acid was contained in the dyeing liquid, in Comparative Example 1 which did not contain boric acid in the dyeing liquid, it was found that the filterability was inferior and dyeing unevenness occurred.

On the other hand, compared with Examples 1-3, 5, in Example 4, the quantity of the boric acid contained in the staining solution was excessive, and contamination by the precipitation of boric acid was observed.

On the other hand, in Examples 1 to 3 and 5, the filterability was good, there was no uneven dyeing, and contamination by boric acid was not observed.

Claims (9)

1. A method for producing a polarizing plate, comprising a dyeing step of immersing an undyed polyvinyl alcohol-based resin film in a dyeing solution containing a dichroic dye, whereby the polyvinyl alcohol The resin film is dyed, The staining solution contains a cross-linking agent, The concentration of the crosslinking agent is 0.01 to 0.1 parts by weight relative to 100 parts by weight of the solvent contained in the dyeing liquid, In the dyeing solution, the polyvinyl alcohol dissolved in the polyvinyl alcohol-based resin film, the dichroic dye, and the crosslinking agent are bonded to form a complex compound, The dyeing liquid containing the complex compound is filtered through a filter material, and the complex compound is separated from the dyeing liquid. 2. The method of manufacturing a polarizing plate according to claim 1, wherein the dyeing solution is circulated through the filter material. 3. The method of manufacturing a polarizing plate according to claim 1 or 2, wherein the dyeing solution is stirred. 4. The method of manufacturing a polarizing plate according to claim 1 or 2, wherein the crosslinking agent is a boron compound. 5. The method of manufacturing a polarizing plate according to claim 4, wherein the boron compound is boric acid. 6. The method for producing a polarizing plate according to claim 1 or 2, wherein the polyvinyl alcohol-based resin film has a thickness of 10 μm or less and is formed on a thermoplastic resin substrate. 7. The method for producing a polarizing plate according to claim 1 or 2, wherein the dichroic dye is iodine. 8. The method for producing a polarizing plate according to claim 1 or 2, wherein the concentration of the dichroic dye is 0.01 to 10 parts by weight relative to 100 parts by weight of the solvent. 9. The method of manufacturing a polarizing plate according to claim 1 or 2, wherein the dyeing solution contains potassium iodide.