KR20170062400A - Method for producing polarizer - Google Patents

Abstract

The present invention provides a method for producing a polarizer capable of further improving productivity by removing PVA dissolved in a dyeing solution.
The manufacturing method includes a dyeing step of dying a PVA resin film by dipping a polyvinyl alcohol (PVA) based resin film into a dyeing solution containing a dichroic dye (iodine), wherein the dyeing solution is a crosslinking agent ), And the dyeing solution is filtered with a filter.

Description

[0001] METHOD FOR PRODUCING POLARIZER [0002]

The present invention relates to a method for producing a polarizer.

2. Description of the Related Art Conventionally, a polarizing plate has been widely used as a polarizing element for a polarizing element in a display device such as a liquid crystal display or as a polarizing element. The polarizing plate generally has a structure in which a protective film is bonded to one or both sides of a polarizing film (polarizer) using an adhesive.

The polarizer is produced by subjecting an unstretched polyvinyl alcohol (PVA) based resin film (fabric film) to a swelling treatment, a dyeing treatment, a stretching treatment, a crosslinking treatment, a cleaning treatment, and the like.

In recent years, as the performance and thickness of a liquid crystal display device have been improved, thinner polarizers are also required. For example, a polarizer having a thickness of 10 占 퐉 or less can be obtained by applying a PVA resin solution onto a thermoplastic resin substrate and drying the PVA resin solution to form a laminate having a PVA resin layer, And then subjected to a single angle treatment.

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

In the dyeing step of dyeing the PVA resin film (PVA resin layer), the fabric film is immersed in a dyeing solution containing iodine (dichromatic dye) in the dyeing bath. At this time, a part of the PVA may dissolve in the dyeing solution from the PVA-based resin film. Particularly, a polarizer (PVA resin film) thinned to a thickness of 10 占 퐉 or less has high solubility.

In this case, when the polarizer is continuously produced, the dissolved PVA is accumulated in the dyeing bath, and the PVA concentration in the dyeing solution is increased, so that the precipitated PVA adheres to the PVA-based resin film and causes uneven dyeing of the polarizer . Further, when the fabric film is taken out from the dye bath, the dyed solution (dehydration) deteriorates. As a result, there arises a problem that the yield of the polarizer is lowered. Further, in addition to the above-mentioned problems, there is also a problem that the adsorption rate (dyeing speed) of iodine to the PVA resin film is lowered due to an increase in the PVA concentration in the dyeing solution, thereby impairing productivity.

As a countermeasure thereto, there is disclosed a method of adsorbing and removing PVA produced in a crosslinking bath by contacting a foreign matter with activated carbon (see Patent Document 1). However, since activated carbon also adsorbs iodine, it is not preferable in a dyeing bath in which the iodine concentration needs to be kept constant.

Therefore, since the PVA dissolved in the dyeing solution can not be removed, as a countermeasure against the increase of the PVA concentration in the dyeing bath, the treatment solution is generally periodically renewed (exchanged) before the above-mentioned problem occurs. However, in the conventional dyeing step, iodine, potassium iodide and the like are widely used as a dyeing solution. For this reason, it is not preferable to frequently perform the update (exchange) of the staining solution even from problems such as environmental problems caused by discharge of halogen and high cost.

The present invention has been made in view of such conventional circumstances, and an object of the present invention is to provide a method of manufacturing a polarizer capable of further improving productivity by removing PVA dissolved in a dyeing solution.

As means for solving the above problems, according to an aspect of the present invention, there is provided a dyeing process for dyeing a PVA resin film by dipping a polyvinyl alcohol (PVA) based resin film into a dyeing solution containing a dichroic dye And the dyeing solution contains a crosslinking agent, and the dyeing solution is filtered with a filter.

Further, the method for producing the polarizer of the above-mentioned aspect may be a manufacturing method for circulating the dyeing solution through the filter.

Further, the method for producing the polarizer of the above embodiment may be a manufacturing method for stirring the dyeing solution.

In the method for producing a polarizer of the above embodiment, the crosslinking agent may be a boron compound.

Further, in the method for producing the polarizer of the above embodiment, the boron compound may be a process for producing phosphorus borate.

Further, in the method of producing the polarizer of the above aspect, the PVA resin film may be a manufacturing method in which the thickness thereof is 10 占 퐉 or less and formed on the thermoplastic resin base.

In the method for producing a polarizer of the above embodiment, the concentration of the cross-linking agent may be 0.01 part by weight to 0.1 part by weight.

In the method for producing a polarizer of the above embodiment, the dichroic dye may be iodine.

In the method for producing a polarizer of the embodiment, the concentration of the dichroic dye may be 0.01 to 10 parts by weight.

Further, in the method for producing a polarizer of the above embodiment, the dyeing solution may be a production method containing potassium iodide.

As described above, according to the embodiment of the present invention, it is possible to provide a method of manufacturing a polarizer capable of further improving the productivity by removing the PVA dissolved in the dyeing solution.

In the present embodiment, as a method for producing a polarizer to which the present invention is applied, a PVA resin solution is coated on a thermoplastic resin substrate and dried to form a laminate having a PVA resin layer (film) A polarizing plate having a thickness of 10 mu m or less is produced by using a sieve as a raw film and performing various treatments.

≪ Thermoplastic resin substrate &

First, the thermoplastic resin substrate used in the method for producing a polarizer to which the present invention is applied will be described. As the thermoplastic resin base material, those conventionally used as a transparent protective film of a polarizer can be used.

As a material constituting the thermoplastic resin base material, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy, stretchability and the like is used. Specific examples of such a thermoplastic resin include cellulose resins such as triacetylcellulose, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyether sulfone resins, polysulfone resins, polycarbonate resins, polyamides such as nylon and aromatic polyamides (Norbornene resin) having a cyclic system or a norbornene structure, (meth) acrylic resin, polyarylate resin, polyamide resin, polyimide resin, polyolefin resin such as polyethylene, polypropylene or ethylene- Polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. The thermoplastic resin base material may be subjected to a surface treatment (e.g., corona treatment or the like) or a thin layer such as a primer layer (primer layer) in order to improve the adhesion with the PVA resin layer.

The thermoplastic resin can roughly be classified into a crystalline state in which polymers are regularly arranged and an amorphous or amorphous state in which the polymer does not have regular arrangement or only a part thereof. The former is called the crystalline state, and the latter is called the amorphous or amorphous state. Correspondingly, a thermoplastic resin having a property of making a crystalline state is called a crystalline resin, and a thermoplastic resin having no such property is called an amorphous resin.

On the other hand, a resin that is not in a crystalline state or a resin that does not reach a crystalline state is called an amorphous or amorphous resin, regardless of whether it is a crystalline resin or an amorphous resin. Here, the amorphous or amorphous resin is used separately from the amorphous resin which does not form a crystalline state.

Examples of the crystalline resin include olefin resins including polyethylene (PE) and polypropylene (PP), and ester resins including polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). One of the characteristics of the crystalline resin is that the polymer is arranged by heating or stretching orientation and crystallization progresses. The physical properties of the resin vary in various ways depending on the degree of crystallization.

On the other hand, even if a crystalline resin such as polypropylene (PP) or polyethylene terephthalate (PET) is used, it is possible to suppress crystallization by inhibiting the arrangement of the polymer generated by heat treatment or stretching orientation. These polypropylene (PP) and polyethylene terephthalate (PET) whose crystallization is inhibited are referred to as amorphous polypropylene and amorphous polyethylene terephthalate, and these are collectively referred to as amorphous olefin resin and amorphous ester resin.

For example, in the case of polypropylene (PP), noncrystalline polypropylene (PP) in which crystallization is suppressed can be produced by making it an atactic structure having no stereoregularity. In addition, in the case of polyethylene terephthalate (PET), for example, a copolymerized monomer such as isophthalic acid or 1,4-cyclohexanedimethanol is copolymerized, that is, a polymer which inhibits crystallization of polyethylene terephthalate (PET) Amorphous polyethylene terephthalate (PET) in which crystallization is suppressed can be produced.

The thickness of the thermoplastic resin base material (before stretching) can be appropriately determined, but generally it is from 10 탆 to 500 탆 in terms of workability such as strength and handling properties and thin layer properties. In particular, it is preferably from 20 탆 to 300 탆, more preferably from 30 탆 to 200 탆. The thickness of the thermoplastic resin base material is particularly suitably from 50 m to 150 m.

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

In the method for producing a polarizer to which the present invention is applied, a laminate including a PVA resin layer (film) is formed on the thermoplastic resin base. The PVA-based resin has transparency in the visible light region and can be used without particular limitation in dispersing and adsorbing a dichroic substance such as iodine or a tricolor dye.

As the PVA-based resin, a PVA-based resin conventionally used as a polarizer is suitably used. As the PVA resin, PVA or a derivative thereof may be mentioned. As the derivatives of PVA, polyvinylformal, polyvinyl acetal and the like can be mentioned. In addition, examples thereof include those modified with unsaturated carboxylic acids such as olefins such as ethylene and propylene, acrylic acid, methacrylic acid and crotonic acid, and alkyl esters and acryl amides thereof.

The polymerization degree of PVA is preferably 100 to 10,000, more preferably 1,000 to 10,000. The saponification degree is generally 80 mol% to 100 mol%.

The PVA resin may contain an additive such as a plasticizer and a surfactant. Examples of the plasticizer include polyols and condensates thereof. Specific examples thereof include glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. The amount of plasticizer and the like to be used is not particularly limited, but is preferably 20 parts by weight or less per 100 parts by weight of the PVA-based resin.

≪ Laminate (Fabric Film) >

The laminate to be a raw film can be obtained by applying an aqueous solution containing a PVA resin to a thermoplastic resin substrate and then drying to form a PVA resin layer. The laminate may have a structure in which a thermoplastic resin base material and a PVA-based resin layer are laminated through a primer layer. Further, the laminate may be a laminate in which a thermoplastic resin base material and a PVA-based resin layer are directly laminated or a base layer and a hydrophilic polymer layer are integrated.

The aqueous solution can be prepared, for example, by dissolving powders, pulverized products, cut products, etc. of PVA resin in appropriately heated water (hot water). The concentration of the aqueous solution is preferably 2 parts by weight to 20 parts by weight, more preferably 4 parts by weight to 10 parts by weight, based on 100 parts by weight of water.

The application of the aqueous solution onto the thermoplastic resin substrate can be carried out, for example, by a roll coating method such as wire bar coating method, reverse coating or gravure coating, a spin coating method, a screen coating method, a fountain coating method, a dipping method, , A comma coating method, a lip coating method, a spin coating method, and the like can be appropriately selected and used.

When the thermoplastic resin base material has a primer layer, an aqueous solution is directly applied to the primer layer. On the other hand, when the thermoplastic resin base material does not have a primer layer, an aqueous solution is directly applied to the base material layer. The drying temperature is preferably 50 to 200 캜, more preferably 60 to 150 캜. The drying time is preferably 5 minutes to 30 minutes.

The PVA resin layer is formed so as to have a thickness such that the thickness of the resulting polarizer is 10 占 퐉 or less in consideration of the draw ratio in the stretching treatment applied to the laminate. The thickness of the unstretched PVA resin layer is preferably 3 m to 20 m, and more preferably 5 m to 15 m.

<Processing Step>

In the method for producing a polarizer to which the present invention is applied, at least a dyeing treatment and a stretching treatment are performed on the laminate (raw film). Further, in the method for producing a polarizer to which the present invention is applied, a cross-linking treatment can be carried out. For each of the dyeing treatment, crosslinking treatment and stretching treatment, each treating bath of a dyeing bath, a crosslinking bath and a stretching bath can be used. When a treatment bath is used, a treatment solution (aqueous solution or the like) according to each treatment is used.

<Dyeing Process>

In the dyeing step, dyeing treatment is carried out by adsorbing and orienting iodine or dichromatic dye on the PVA-based resin layer in the laminate. In the dyeing step, the dyeing treatment can be performed as in the case of the stretching treatment.

The dyeing treatment is carried out by immersing the laminate in a dyeing solution in a dyeing bath (dyeing bath). As the dyeing solution, an iodine solution is generally used. An iodine aqueous solution used as an iodine solution is an aqueous solution containing iodine by iodine and a iodide compound as a dissolution aid.

Examples of the iodide compound include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide and titanium iodide. As the iodide compound, potassium iodide is suitable. The iodide compound used in the present embodiment is also the same as the iodide compound in the case of being used in another step.

The iodine concentration in the iodine solution is preferably 0.01 part by weight to 10 parts by weight, more preferably 0.02 parts by weight to 5 parts by weight, and even more preferably 0.1 part by weight to 1.0 part by weight with respect to 100 parts by weight of the solvent. The concentration of the iodide compound is preferably 0.1 part by weight to 10 parts by weight, more preferably 0.2 part by weight to 8 parts by weight, based on 100 parts by weight of the solvent. In iodine dyeing, the temperature of the iodine solution is preferably 20 to 50 캜, more preferably 25 to 40 캜. The immersion time is preferably 10 seconds to 300 seconds, more preferably 20 seconds to 240 seconds. Further, the dyeing time can be immersed in an arbitrary time so as to achieve the specified degree of polarization or transmittance.

<Stretching Step>

In the stretching step, either dry stretching treatment or wet stretching treatment can be used. In the stretching step, uniaxial stretching is performed on the laminate to conduct stretching treatment. The uniaxial stretching may be either longitudinal stretching performed in the longitudinal direction of the laminate and transverse stretching performed in the width direction of the laminate.

In transverse stretching, stretching in the width direction and shrinking in the longitudinal direction can be performed. Examples of the transverse stretching method include a fixed single-axis uniaxial stretching method in which one end is fixed through a tenter, and a free-end uniaxial stretching method in which one end is not fixed.

On the other hand, in the longitudinal stretching, for example, a roll-to-roll stretching method, a compression stretching method, a stretching method using a tenter, or the like can be used. The stretching process may be performed in multiple stages. The stretching treatment can be performed by biaxial stretching, warp stretching, or the like.

The dry stretching treatment is preferable in that the temperature range when the laminate is stretched can be set to a wide range. In the dry stretching treatment, the laminate is preferably heated to 50 to 200 캜, more preferably 80 to 180 캜, and still more preferably 100 to 160 캜. In the stretching process, when the dry stretching process is included, the dry stretching process is preferably performed before the dyeing process.

The iodinated compound may be contained in the treatment liquid used in the wet drawing process. When the iodide compound is contained in the treatment liquid, the concentration of the iodide compound is preferably 0.1 part by weight to 10 parts by weight, more preferably 0.2 part by weight to 5 parts by weight, based on 100 parts by weight of the solvent. The treatment temperature in the wet stretching method is preferably 25 占 폚 or higher, more preferably 30 占 폚 to 85 占 폚, and still more preferably 50 占 폚 to 70 占 폚. The immersion time is preferably 10 seconds to 800 seconds, more preferably 30 seconds to 500 seconds. The stretching treatment can be carried out together with the dyeing treatment or the crosslinking treatment.

In the stretching step, the stretching process is performed so that the original length of the laminate is 4 to 8 times the total stretching ratio. The total draw ratio is preferably 5 to 7 times. The total stretching ratio refers to the stretching ratio of the cumulative stretching including the stretching in these steps when the stretching accompanies the steps other than the stretching step. The total drawing magnification is appropriately determined in consideration of the drawing magnification in other processes and the like.

When the total draw ratio is low, the alignment is insufficient, and it is difficult to obtain a polarizer having high optical characteristics (polarization degree). On the other hand, if the total draw ratio is too high, stretching breakage tends to occur. In addition, the polarizer becomes too thin, which may lower the workability in subsequent steps.

In the stretching step, as described in Japanese Patent No. 4751481, wet stretching treatment can be performed after the air-assisted stretching treatment. The stretching temperature in the air-assisted stretching treatment is preferably set at a high temperature of 60 to 180 占 폚, further 95 to 150 占 폚. The stretching magnification in the air-assisted stretching treatment is preferably 1.3 to 4 times, more preferably 1.5 to 3 times. In addition, the treatment temperature in the wet drawing process performed after the air-assisted stretching process is preferably from 50 to 80 캜, and more preferably from 60 to 70 캜. The immersion time is preferably 5 seconds to 120 seconds, more preferably 10 seconds to 60 seconds. The drawing ratio in the wet drawing process is preferably 4 to 7 times, more preferably 5 to 6 times.

In the stretching step, when the air-assisted stretching treatment and the wet-type stretching treatment are included, it is preferable that the air-assisted stretching treatment is performed before the dyeing treatment and the wet-type stretching treatment is performed after the dyeing treatment. In this case, the treatment bath used for the wet-type stretching treatment also serves as a cross-linking bath, and it is preferable to carry out the cross-linking treatment together with the wet-type stretching treatment.

&Lt; Crosslinking step &

In the crosslinking step, a crosslinking treatment is carried out using a boron compound as a crosslinking agent. The crosslinking treatment can be carried out together with the dyeing treatment and the stretching treatment. The crosslinking treatment can be carried out in a plurality of steps. As the boron compound, for example, boric acid, borax and the like can be used. The boron compound is generally used in the form of an aqueous solution or a water-organic solvent mixture solution.

When boric acid aqueous solution is used, the boric acid concentration of the aqueous solution of boric acid is preferably 1 part by weight to 10 parts by weight, more preferably 2 parts by weight to 7 parts by weight Wealth. A boric acid aqueous solution or the like may contain an iodide compound such as potassium iodide. When the iodide compound is contained in the aqueous solution of boric acid, the concentration of the iodide compound is preferably 0.1 part by weight to 10 parts by weight, more preferably 0.5 part by weight to 8 parts by weight, based on 100 parts by weight of water.

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

&Lt; Insolubilization step &

In the method for producing a polarizer to which the present invention is applied, the insolubilization treatment can be carried out before the laminate is subjected to the dyeing treatment or the crosslinking treatment. The insolubilization step is intended to carry out the insolubilization treatment so as not to dissolve 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 a solution containing a boron compound such as boric acid or borax. The solution is generally used in the form of an aqueous solution or a water-organic solvent mixture solution.

In the case of using an aqueous solution of boric acid, the boric acid concentration of the aqueous solution of boric acid is preferably 1 to 4 parts by weight based on 100 parts by weight of the solvent. The treatment temperature in the insolubilization step is preferably 25 ° C or higher, more preferably 30 ° C to 85 ° C, further preferably 30 ° C to 60 ° C. The treatment time is preferably 5 seconds to 800 seconds, more preferably 8 seconds to 500 seconds.

<Cleaning step>

In the method for producing a polarizer to which the present invention is applied, the laminate can be subjected to a dyeing treatment or a stretching treatment to further perform a crosslinking treatment. After these treatments, a washing treatment can be carried out.

In the cleaning step, a cleaning treatment can 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 even more preferably 1 to 6 parts by weight, relative to 100 parts by weight of the solvent Parts by weight.

In the cleaning treatment with the potassium iodide solution, the treatment temperature is preferably 5 ° C to 60 ° C, and more preferably 10 ° C to 40 ° C. The immersion time is preferably from 1 second to 120 seconds, more preferably from 3 seconds to 90 seconds. In the step of the cleaning treatment with the potassium iodide solution, there is no particular limitation as long as it is before the drying treatment.

As the cleaning treatment, a water cleaning treatment can be performed. The water washing treatment is carried out by immersing the PVA resin in pure water such as ion-exchanged water or distilled water. The water washing temperature is preferably 5 ° C to 50 ° C, more preferably 10 ° C to 45 ° C, and still more preferably 15 ° C to 40 ° C. The immersion time is preferably 5 seconds to 300 seconds, more preferably 10 seconds to 240 seconds.

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

<Drying step>

Further, in the method for producing a polarizer to which the present invention is applied, the polarizer is finally produced by carrying out the above-mentioned each treatment and finally drying treatment. In the drying process, the optimum drying time and drying temperature are set according to the moisture content required for the resulting polarizer (film). Specifically, the drying temperature is preferably 20 to 150 캜, more preferably 40 to 100 캜. If the drying temperature is too low, the drying time becomes long and efficient production can not be performed, which is not preferable. On the other hand, if the drying temperature is too high, the resultant polarizer deteriorates and deteriorates in terms of optical characteristics and color. The heating and drying time is preferably from 1 minute to 10 minutes.

&Lt; Water-soluble antioxidant >

In the method for producing a polarizer to which the present invention is applied, the treatment with a treatment liquid containing at least one water-soluble antioxidant may be performed in at least one step after the dyeing step described above.

In the treatment with a treatment liquid containing a water-soluble antioxidant, a water-soluble antioxidant is contained in at least one of the baths used for each treatment performed after the dyeing treatment. Further, treatment with a treatment liquid containing a water-soluble antioxidant is separately performed. The treatment with the treatment liquid containing the water-soluble antioxidant is preferably carried out together with the crosslinking treatment and / or the stretching treatment.

The crosslinking treatment and the stretching treatment can be performed by a batch treatment in which a plurality of treatments are simultaneously performed. As a batch treatment in which a plurality of treatments are simultaneously performed, a water-soluble antioxidant is contained in the bath used for the batch treatment. 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 the water-soluble antioxidant include ascorbic acid (vitamin C), erysorbic acid, thiosulfuric acid, sulfurous acid, chlorogenic acid, citric acid, rosmarinic acid and salts thereof.

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

Among them, it is preferable to use ascorbic acid, erythorbate, thiosulfate and sulfite. These water-soluble antioxidants may be used singly or in combination of two or more kinds.

The addition amount of the water-soluble antioxidant is determined according to the contamination concentration of the dichromatic substance (iodine or dichromatic dye) contained in each treatment liquid after the dyeing step. When the contamination concentration due to the dichroic substance in the contaminated treatment liquid is high, the addition amount of the water-soluble antioxidant to be added is also increased.

It is preferable to add a water-soluble antioxidant to each treatment liquid so that the concentration of the water-soluble antioxidant is 0.005 part by weight to 1 part by weight with respect to 100 parts by weight of the solvent, more preferably 0.005 part by weight to 0.5 part by weight. When the concentration of the water-soluble antioxidant is less than 0.005 part by weight, the proportion of the water-soluble antioxidant in the contaminated treatment liquid becomes small, and the deterioration of the characteristics (single transmittance, polarization degree) of the resulting polarizer can not be suppressed sufficiently. On the other hand, when the concentration of the water-soluble antioxidant exceeds 1 part by weight, the proportion of the water-soluble antioxidant in the bath becomes large, so that the obtained polarizer is discolored and the transmittance is increased. Accordingly, there is a concern that it is necessary to increase the iodine concentration of the dye bath, but there is no problem such as deterioration in optical characteristics.

<Polarizer>

The polarizer produced according to the method for producing a polarizer to which the present invention is applied is formed on a thermoplastic resin base material but the PVA resin layer film of an unstretched PVA resin film is used as the raw film without using the thermoplastic resin base material, And the like. In this case, the thickness of the polarizer may be 10 占 퐉 or more, and preferably 5 占 퐉 to 50 占 퐉.

The thermoplastic resin base material can be used as a transparent protective film of a polarizing plate described later as it is. Further, a transparent protective film can be bonded to the surface of the polarizer opposite to the thermoplastic resin base. On the other hand, when the thermoplastic resin base material is not used, a transparent protective film can be bonded to both sides of the polarizer. Further, after the thermoplastic resin base material is peeled from the polarizer, a transparent protective film may be bonded to both sides of the 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 is used. Specific examples of such a thermoplastic resin include cellulose resins such as triacetyl cellulose, polyester resins, polyether sulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) Polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof.

&Lt; Dyeing solution containing crosslinking agent >

The PVA-based resin used in the dyeing step is preferably undyed. Further, in the method for producing a polarizer to which the present invention is applied, the dyeing solution used in the dyeing step contains a cross-linking agent. As the crosslinking agent, for example, boron compounds such as boric acid and borax, and at least one of glyoxal, glutaraldehyde and the like, or two or more kinds thereof may be used in combination. Among them, a boron compound is preferably used, and boric acid is more preferably used.

In the dyeing step, the boric acid contains a small amount of boric acid (crosslinking agent) so that the PVA resin layer crosslinks (complexes) the PVA dissolved in the dyeing solution. Thereby, a gel type iodine / PVA / boric acid complex (hereinafter referred to as a complex compound) in which PVA dissolved in the dyeing solution and iodine and boric acid in the dyeing solution are combined is produced.

The concentration of the boric acid (crosslinking agent) in the dyeing solution is preferably 0.01 part by weight to 0.1 part by weight with respect to 100 parts by weight of the solvent for crosslinking (complexing) the PVA dissolved in the dyeing solution, 0.02 parts by weight to 0.1 parts by weight. If the concentration of boric acid is 0.01 part by weight or more, the PVA dissolved in the dyeing solution can be crosslinked (complexed). On the other hand, when the boric acid concentration exceeds 0.2 parts by weight, boric acid is precipitated on the surface of the laminate (raw film) or on the surface of the roll for conveying the laminate (raw film) have.

As a method of adjusting the concentration of boric acid in the dyeing solution, a predetermined amount of boric acid may be added to the dyeing solution. When a treatment bath containing boric acid is present immediately before the dyeing treatment, boric acid introduced together with the layered product from the treatment bath can be used.

In the method for producing a polarizer to which the present invention is applied, the above-mentioned dyeing solution contains a small amount of boric acid (crosslinking agent), and the PVA dissolved in the dyeing solution is crosslinked (complexized) It is possible to avoid problems such as a decrease in speed. That is, the PVA dissolved in the dyeing solution becomes difficult to adhere to the PVA resin layer (raw film) due to crosslinking (complexation). Further, the dyed liquid (dewatering) property of the dyed film when the dyed film is taken out in the dyeing bath is improved. Thereby, it is possible to obtain a polarizer having no staining unevenness.

<Filtration of dye solution>

Further, in the method for producing a polarizer to which the present invention is applied, the dyeing solution is filtered by a filter.

Thereby, the complex compound produced by cross-linking (complexing) the PVA dissolved in the dyeing solution can be separated from the dyeing solution. For example, an organic material such as PVA can be separated from a different component of the dyeing solution by adjusting the film production conditions of the flat film constituting the film or performing surface treatment for separating the film. As the filter, for example, a polypropylene filter, a polyester filter, a nylon filter, or the like can be used. The module is not particularly limited, but is preferably a cartridge type having a structure in which a filter is housed in a sealable container and can be detachably installed in the device.

More specifically, it is possible to determine the permeability of the substance depending on the difference in the repulsive force of the ionic charge on the film, by adjusting the inner pore diameter of the flat membrane inside the membrane (for example, by controlling the passage of a substance having a molecular weight of 300 or more) An organic substance such as PVA can be separated from other components in the dyeing liquid by forming a functional coating film or a surface treatment film having a functional group on the surface thereof.

As the filtration membrane, for example, an ultrafiltration (UF) membrane, a microfiltration (MF) membrane, a nanofiltration (NF) membrane, a reverse osmosis (RO) membrane and the like can be used. Among them, UF membrane and MF membrane are preferably used. It is preferable to use a filter film capable of setting a plurality of separation standards (for example, molecular weight and ionic charge repelling force) capable of separating an organic matter such as PVA from a different component of the dyeing solution.

The dyeing solution in the dyeing bath is preferably circulated through a filter. Thereby, the complex compound in the dye bath can be efficiently removed (trapped) by the filter. It is also possible to reuse the dyeing solution.

The dyeing solution in the dyeing bath is preferably stirred. This facilitates the crosslinking (complexation) of the PVA dissolved in the dyeing solution, so that the complex compound can be efficiently removed from the dyeing solution.

As a method of stirring the dyeing solution, a method of providing stirring means such as a stirring blade in the dyeing bath and stirring the dyeing solution in the dyeing bath can be used. It is also possible to stir the dyeing solution in the dyeing bath by circulation of the dyeing solution described above. In addition, it is also possible to stir the dyeing solution in the dyeing bath by the raw film which is transported (in and out) in the dyeing bath.

As described above, in the method for producing a polarizer to which the present invention is applied, the PVA dissolved in the dyeing solution can be removed. Thereby, it is possible to extend the updating (replacement) timing of the dye solution while avoiding the influence of the PVA dissolved in the dyeing solution, so that the productivity of the polarizer can be further improved.

[Example]

Hereinafter, the effects of the present invention will be more apparent from the examples. The present invention is not limited to the following examples, and can be appropriately changed without departing from the gist of the present invention.

(Example 1)

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

Specifically, amorphous polyethylene terephthalate (A-PET) film (NovaClear (registered trademark) manufactured by Mitsubishi Chemical Corporation, thickness: 200 μm) was first prepared as a thermoplastic resin base material.

Next, a corona treatment (treatment condition: 90 W · min / m 2) was applied to one side of the thermoplastic resin substrate, and an aqueous solution of PVA having a degree of polymerization of 4000 and a saponification degree of 99.0 mol% After coating at 65 캜, it was dried. As a result, a laminate having a PVA resin layer having a thickness of 8.3 占 퐉 was formed on one surface of the thermoplastic resin base material as the raw film.

Next, the obtained raw material film was uniaxially stretched 1.8 times in an oven at 90 캜 (stretching treatment).

Next, the stretched raw film was immersed (insolubilization treatment) for 30 seconds in an insolubilizing bath (aqueous solution of boric acid in which 3 parts by weight of boric acid was dissolved per 100 parts by weight of water) at 30 占 폚.

Then, the fabric film was immersed in the dyeing bath (dyeing treatment) while adjusting the iodine concentration and immersion time so that the transmittance of the polarizer was about 42.0%.

In Example 1, a dyeing solution was prepared by dissolving 0.18 part by weight of iodine, 1.26 parts by weight of potassium iodide and 0.02 part by weight of boric acid based on 100 parts by weight of water. Then, the solution temperature of the dyeing solution was adjusted to 30 占 폚, and the fabric film was immersed for 13 seconds.

Further, 0.05 part by weight of PVA was added to this dyeing solution, and the dyeing solution filtered with a polypropylene filter was circulated while stirring with a magnetic stirrer for 15 minutes.

Next, the fabric film was immersed (cross-linking treatment) for 30 seconds in a crosslinking bath (aqueous solution of boric acid 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 占 폚.

Next, the raw material film was uniaxially stretched in the longitudinal direction (longitudinal direction) while immersing the raw material film in an aqueous boric acid solution having a liquid temperature of 70 占 폚 (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) (Vertical stretching in liquid). At this time, the maximum draw ratio of the laminate was 5.94 times.

Next, the fabric film was immersed in a cleansing bath (an aqueous solution in which 4 parts by weight of potassium iodide was dissolved in water of 30 parts of water) for 5 seconds, followed by drying with warm air at 60 占 폚 (cleaning treatment and drying treatment) .

By carrying out the above steps, a polarizing laminated film having a polarizer having a thickness of 4.5 탆 was formed on a thermoplastic resin substrate.

(Example 2)

In Example 2, the same dyeing solution as in Example 1 was prepared except that the boric acid was changed to 0.05 part by weight. Using this dyeing solution, a polarizer was produced in the same manner as in Example 1.

(Example 3)

In Example 3, the same dyeing solution as in Example 1 was prepared, except that 0.1 part by weight of boric acid was used. Using this dyeing solution, a polarizer was produced in the same manner as in Example 1.

(Example 4)

In Example 4, the same dyeing solution as in Example 1 was prepared, except that the boric acid was changed to 0.2 part by weight. Using this dyeing solution, a polarizer was produced in the same manner as in Example 1.

(Example 5)

In Example 5, the same dyeing solution as in Example 1 was prepared except that the boric acid was changed to 0.01 part by weight. Then, dyeing treatment was carried out in the same manner as in Example 1 using this staining solution.

(Comparative Example 1)

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

Using this dyeing solution, a polarizer was produced in the same manner as in Example 1.

For each of the polarizers fabricated according to Examples 1 to 5 and Comparative Example 1, the presence or absence of occurrence of &quot; uneven dyeing &quot; was visually observed. Further, the amount of the residual complex compound captured by the filter was measured to evaluate the "filtering property" of the dyeing solution. Among them, the very good was rated as &quot; &quot;, the good was rated as &quot; &quot;, and the worse was rated as &quot; x &quot;. In addition, the presence or absence of &quot; contamination with boric acid &quot; attached to the apparatus or the like during the dyeing treatment was visually observed. These are summarized in Table 1 below.

Boric acid content
(Parts by weight) Filterability Remaining amount Uneven dyeing Pollution by boric acid Example 1 0.02 ○ 0.15 radish radish Example 2 0.05 ○ 0.44 radish radish Example 3 0.10 ◎ 1.03 radish radish Example 4 0.20 ◎ 2.12 radish U Example 5 0.01 ○ 0.08 radish radish Comparative Example 1 0.00 × 0.00 U radish

As shown in Table 1, in Comparative Example 1 containing no boric acid in the dyeing solution, filtration properties were poor and uneven dyeing occurred as compared with Examples 1 to 5 containing boric acid in the dyeing solution.

On the other hand, in Example 4, as compared with Examples 1 to 3 and 5, the amount of boric acid contained in the dyeing solution was excessive, and contamination due to precipitation of boric acid was observed.

On the other hand, in Examples 1 to 3 and 5, the filterability was good, there was no staining unevenness, and no contamination with boric acid was observed.

Claims (10)

And a dyeing step of dying the PVA resin film by dipping a polyvinyl alcohol (PVA) based resin film in a dyeing solution containing a dichroic dye,
The dyeing solution contains a crosslinking agent,
And filtering the dyeing solution with a filter. The method of claim 1, wherein the dye is circulated through the filter. The method of producing a polarizer according to claim 1 or 2, wherein the dyeing solution is stirred. The method for producing a polarizer according to claim 1 or 2, wherein the crosslinking agent is a boron compound. 5. The method of claim 4, wherein the boron compound is boric acid. The method of producing a polarizer according to any one of claims 1 to 5, wherein the PVA resin film has a thickness of 10 탆 or less and is formed on a thermoplastic resin substrate. The method of producing a polarizer according to claim 1 or 2, wherein the concentration of the crosslinking agent is 0.01 to 0.1 parts by weight. The method according to claim 1 or 2, wherein the dichroic dye is iodine. The method of producing a polarizer according to claim 1 or 2, wherein the concentration of the dichroic dye is 0.01 to 10 parts by weight. 3. The method of claim 1 or 2, wherein the dyeing solution contains potassium iodide.