KR20170077100A - Method for producing polarizer and method for detecting polyvinyl alcohol - Google Patents

Abstract

Provided is a method for producing a polarizer capable of stably producing a polarizer by quantitatively analyzing PVA dissolved in a dyeing solution to optimize the update (exchange) timing of the dyeing solution.
A dyeing step of dyeing a PVA resin film by dipping a polyvinyl alcohol (PVA) based resin film in a dyeing solution containing a dichroic dye (iodine), and a dyeing step of extracting a part of the dyeing solution as a sample and measuring the absorbance And an analysis step of quantitatively analyzing the PVA dissolved in the dyeing solution by measurement, wherein the dyeing solution contains a crosslinking agent (boric acid).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing a polarizer and a method for detecting polyvinyl alcohol,

The present invention relates to a method for producing a polarizer and a method for detecting polyvinyl alcohol.

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

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

In recent years, according to the performance and thinness of a liquid crystal display device, a thinner polarizer is also required. For example, a polarizer having a thickness of 10 占 퐉 or less can be produced by applying a PVA resin solution onto a thermoplastic resin base material and drying it to form a laminate having a PVA resin layer, . ≪ / RTI >

Japanese Patent Application Laid-Open No. 2008-292935

Incidentally, in the dyeing step of dyeing the aforementioned PVA resin film (PVA resin layer), the original film is immersed in a dyeing solution containing iodine (dichroism dye) in the dyeing bath. At this time, a part of the PVA may dissolve in the dyeing solution from the PVA 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 concentration of PVA 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 taking out the original film from the dye bath, dripping of the dye solution becomes difficult. As a result, problems such as lowering the yield of the polarizer occur. Further, in addition to the above-mentioned problems, the increase of the PVA concentration in the dyeing solution lowers the adsorption rate (dyeing speed) of the iodine to the PVA resin film, resulting in problems such as impaired productivity.

As a countermeasure thereto, there is disclosed a method of adsorbing and removing by contacting a foreign material composed of PVA generated in a crosslinking bath with activated carbon (see Patent Document 1). However, since activated carbon 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, it is general that the treatment solution is periodically renewed (exchanged) before the above-mentioned problem occurs. However, in the conventional dyeing process, there is no method of quantitatively analyzing the PVA dissolved in the dyeing solution, and it is difficult to accurately grasp the update (exchange) timing of the dyeing solution. For this reason, in many cases, the treatment liquid is updated after the problems such as the attachment of the PVA and the decrease in dyeing speed actually occur.

The present invention has been proposed in view of such conventional circumstances, and it is an object of the present invention to provide a polarizer capable of stably producing a polarizer by optimizing the update (exchange) timing of a staining solution by quantitatively analyzing PVA dissolved in a dyeing solution And a method for detecting polyvinyl alcohol which makes it possible to detect PVA dissolved in a dyeing solution.

As a means for solving the above problems, according to an aspect of the present invention, there is provided a dyeing method comprising dyeing a PVA resin film by dipping a polyvinyl alcohol (PVA) based resin film in a dyeing solution containing a dichroic dye, A method of quantitatively analyzing PVA dissolved in the dyeing solution by extracting a part of the dyeing solution as a sample and measuring the absorbance of the sample, wherein the dyeing solution contains a crosslinking agent .

Further, in the method for producing a polarizer of the above aspect, in the analysis step, the sample is periodically extracted from the dyeing solution, the absorbance of each sample is measured, and the absorbance of each sample measured The PVA dissolved in the dyeing solution may be quantitatively analyzed on the basis of the change in the amount of the PVA dissolved in the dyeing solution.

Further, in the method for producing a polarizer of the above aspect, at least one wavelength may be selected from the wavelengths of 500 to 700 nm as the specific wavelength.

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

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

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

In the method for producing a polarizer of the above embodiment, the concentration of the dichroic dye may be 0.01-10 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.

According to an embodiment of the present invention, a PVA-based resin film is immersed in a dyeing solution containing a dichroic dye to detect PVA dissolved in the dyeing solution when the PVA-based resin film is dyed The method comprising the steps of: measuring the absorbance of the dyeing solution before dyeing the PVA-based resin film; and dissolving the dyeing solution in the dyeing solution from the PVA-based resin film by adding a crosslinking agent to the dyeing solution Crosslinking the PVA based resin film, measuring the absorbance of the dyeing solution after staining the PVA resin film, and measuring the absorbance of the dyeing solution measured before the dyeing and the absorbance of the dyeing solution measured after the dyeing , A method for detecting polyvinyl alcohol comprising quantifying PVA dissolved in the dyeing solution is provided.

INDUSTRIAL APPLICABILITY As described above, according to the embodiment of the present invention, it is possible to stably produce a polarizer by optimizing the update (exchange) timing of the dye solution by quantitatively analyzing the PVA dissolved in the dyeing solution, and , It is possible to provide a method of detecting polyvinyl alcohol which makes it possible to detect PVA dissolved in a dyeing solution.

1 is a graph showing changes in absorbance of a staining solution when PVA is dissolved in a staining solution containing a certain amount of boric acid in the second embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In the present embodiment, as a method for producing a polarizer to which the present invention is applied, a PVA resin solution is applied on a thermoplastic resin base material and dried to form a laminate having a PVA resin layer (film) A case where a polarizer having a thickness of 10 탆 or less is produced by performing various treatments as a film will be described as an example.

≪ Thermoplastic resin substrate &

First, the thermoplastic resin base material 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 the 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, nylon and aromatic polyamides Polyamide resins, polyimide resins, polyolefin resins such as polyethylene, polypropylene and ethylene / propylene copolymer, cyclic polyolefin resins having cyclo or norbornene structures (norbornene resins), (meth) acrylic resins, 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) to improve the adhesion with the PVA resin layer, or may be formed with a thin layer such as a primer layer (undercoat layer).

The thermoplastic resin can be roughly distinguished from the fact that the polymer is in a crystalline state in which the polymers are regularly arranged and the polymer is in an amorphous or amorphous state in which the polymer does not have a regular arrangement or only a part thereof. The former is called the crystalline state, and the latter is called the amorphous or amorphous state. Corresponding to this, 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 referred to as 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, crystallization can also be inhibited by inhibiting the arrangement of the polymer caused by heat treatment or stretching orientation even in a crystalline resin such as polypropylene (PP) or polyethylene terephthalate (PET). These polypropylene (PP) and polyethylene terephthalate (PET) in which 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), an amorphous polypropylene (PP) in which crystallization is suppressed can be produced by making it an atactic structure having no stereoregularity. Further, in the case of polyethylene terephthalate (PET), for example, a copolymer obtained by copolymerizing a polymerizable monomer such as isophthalic acid or 1,4-cyclohexanedimethanol as a polymerization initiator, that is, a polymer which inhibits crystallization of polyethylene terephthalate (PET) By copolymerization, amorphous polyethylene terephthalate (PET) in which crystallization is suppressed can be produced.

The thickness of the thermoplastic resin base material (before stretching) can be suitably determined, but generally 10 to 500 占 퐉 from the viewpoints of workability such as strength and handling properties and thin layer properties. Particularly preferably 20 to 300 mu m, and more preferably 30 to 200 mu m. The thickness of the thermoplastic resin base material is particularly suitable in the case of 50 to 150 占 퐉.

≪ 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 substrate. The PVA resin has transparency in the visible light region and can be used without particular limitation to disperse and adsorb dichroic substances such as iodine and dichroic dyes.

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 degree of saponification is generally 80 to 100 mol%.

The PVA resin may contain an additive such as a plasticizer and a surfactant. Examples of the plasticizer include a polyol and a condensate thereof. Specific examples thereof include glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, and polyethylene glycol. The amount of the plasticizer or 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 (original film) >

The laminate to be the original film can be obtained by applying an aqueous solution containing a PVA resin to the thermoplastic resin substrate and then drying the resultant to form a PVA resin layer. Further, 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. 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 a powder, a pulverized product, a cut product, etc. of a PVA resin in appropriately heated water (hot water). The concentration of the aqueous solution is preferably 2 to 20 parts by weight, more preferably 4 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 by a roll coating method such as a wire bar coating method, a reverse coating method or a gravure coating method, a spin coating method, a screen coating method, a fountain coating method, a dipping method, A comma coating method, a lip 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, and more preferably 60 to 150 캜. The drying time is preferably 5 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 to 20 占 퐉, more preferably 5 to 15 占 퐉.

<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 carried out on the laminate (original 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, the dyeing treatment is carried out by adsorbing and orienting iodine or a dichroic dye on the PVA-based resin layer in the laminate. In the dyeing step, the dyeing treatment can be performed together with 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 this embodiment is 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 to 10 parts by weight, more preferably 0.02 to 5 parts by weight, and still more preferably 0.1 to 1.0 part by weight, based on 100 parts by weight of the solvent. The concentration of the iodide compound 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. 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 to 300 seconds, more preferably 20 to 240 seconds. The dyeing time can be dipped for an arbitrary time so as to achieve the specified degree of polarization or transmittance.

<Stretching Step>

In the drawing step, both the dry drawing process and the wet drawing process 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 may be performed. Examples of the transverse drawing method include a fixed single-axis uniaxial drawing method in which one end is fixed through a tenter, and a free-end uniaxial drawing method in which one end is not fixed.

On the other hand, in 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 steps. 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 layered product is preferably heated to 50 to 200 占 폚, more preferably 80 to 180 占 폚, and still more preferably 100 to 160 占 폚. 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 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 25 占 폚 or higher, more preferably 30 to 85 占 폚, further preferably 50 to 70 占 폚. The immersion time is preferably 10 to 800 seconds, more preferably 30 to 500 seconds. Further, 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 draw ratio refers to the cumulative draw ratio including the draw in these steps when the draw is accompanied by a process other than the draw process. The total drawing magnification is appropriately determined in consideration of the drawing magnification in another process or the like.

If the total draw ratio is low, the alignment is insufficient and a polarizer with high optical properties (polarization degree) is difficult to obtain. On the other hand, if the total draw ratio is excessively high, stretch cutting tends to occur. Further, the polarizer becomes too thin, and the workability in the subsequent process may be deteriorated.

In the stretching step, as described in Japanese Patent No. 4751481, the wet stretching treatment can be performed after the air-assisted stretching treatment. The stretching temperature in the air-assisted stretching treatment is preferably set to a high temperature of 60 to 180 캜, further 95 to 150 캜. 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 stretching treatment performed after the air-assisted stretching treatment is preferably 50 to 80 占 폚, and more preferably 60 to 70 占 폚. The immersion time is preferably 5 to 120 seconds, more preferably 10 to 60 seconds. The draw 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. Further, the crosslinking treatment can be carried out in plural circuits. 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.

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 10 parts by weight, more preferably 2 to 7 parts by weight, based on 100 parts by weight of the solvent, because heat resistance is imparted depending on the degree of crosslinking. 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 boric acid solution, the concentration of the iodide compound is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the solvent.

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 占 폚 or higher, more preferably 30 to 85 占 폚, further preferably 30 to 60 占 폚. The treatment time is preferably 5 to 800 seconds, more preferably 8 to 500 seconds.

&Lt; Insolubilization step &

In the method for producing a polarizer to which the present invention is applied, the laminate may be subjected to the insolubilization treatment before 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 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 to 85 ° C, further preferably 30 to 60 ° C. The treatment time is preferably 5 to 800 seconds, more preferably 8 to 500 seconds.

<Cleaning step>

In the method for producing a polarizer to which the present invention is applied, the layered product can be subjected to a dyeing treatment or a stretching treatment and to a crosslinking treatment, but a cleaning treatment can be carried out after these treatments.

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 still more preferably 1 to 6 parts by weight, based on 100 parts by weight of the solvent.

In the cleaning treatment with the potassium iodide solution, the treatment temperature is preferably 5 to 60 캜, more preferably 10 to 40 캜. The immersion time is preferably from 1 to 120 seconds, and more preferably from 3 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.

Further, the cleaning process can be performed with a water cleaning process. 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 to 50 캜, more preferably 10 to 45 캜, and still more preferably 15 to 40 캜. The immersion time is preferably 5 to 300 seconds, more preferably 10 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 manufactured by carrying out the above-mentioned respective treatments and finally performing a drying treatment. In the drying treatment, 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 占 폚, more preferably 40 to 100 占 폚. 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 obtained polarizer is deteriorated and deteriorates in terms of optical characteristics and color. The heating and drying time is preferably 1 to 10 minutes.

&Lt; Water-soluble antioxidant >

In the method for producing a polarizer to which the present invention is applied, the treatment with the 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 the treatment liquid containing the 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. Alternatively, treatment with a treatment liquid containing a water-soluble antioxidant is separately carried out. 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. In a batch process 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), erosorbic 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.

Of these, ascorbic acid, erythorbate, thiosulfate and sulfite are preferably used. 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 dichroic substance (iodine or dichroic dye) contained in each treatment liquid after the dyeing step. If the contamination concentration due to the dichroic substance in the contaminated treatment liquid is high, the addition amount of the water-soluble antioxidant 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 to 1 part by weight based on 100 parts by weight of the solvent, more preferably 0.005 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 by the method for producing a polarizer to which the present invention is applied is formed on the thermoplastic resin base material. However, the above-mentioned respective processes are carried out by using the unvulcanized PVA resin layer film as the original film without using the thermoplastic resin base material . In this case, the thickness of the polarizer may be 10 탆 or more, preferably 5 to 50 탆.

The thermoplastic resin base material can be used as it is as a transparent protective film of a later-described polarizing plate. 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 a 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 can be bonded to both sides of the polarizer.

As a material for 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) acrylic resins , Cyclic polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof.

<Analytical Process>

The PVA-based resin used in the dyeing step is preferably unstained. 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 crosslinking agent. As the crosslinking agent, for example, a boron compound such as boric acid or borax, or at least one of glyoxal, glutaraldehyde and the like, or a combination of two or more of them may be used. 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.

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 0.01 to 0.1 parts by weight, more preferably 0.02 to 0.1 parts by weight, 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 precipitates on the surface of the laminate (original film) or on the surface of the roll that carries the laminate (original film), which may cause defects of the polarizer .

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 this case, the concentration of boric acid may be monitored.

The complex compound produced in the staining solution changes the absorbance of the staining solution. Therefore, in the method for producing a polarizer to which the present invention is applied, as the analysis step, a part of the dyeing solution is extracted as a sample and the absorbance of the sample is measured. Specifically, the sample is periodically extracted from the staining solution, the absorbance of each sample is measured, and the PVA dissolved in the staining solution is quantitatively determined based on the change in absorbance of each sample measured at a specific wavelength over time Analysis is desirable. The absorbance can be measured by, for example, a commercially available spectrophotometer. At this time, the sample may be diluted with an appropriate solvent.

It is preferable to select at least one wavelength of the specific wavelength from 500 to 700 nm. That is, it is preferable that the specific wavelength is a wavelength indicating the maximum value of the absorbance of each sample. In the present embodiment, the maximum absorption wavelength of the complex compound exists in the vicinity of about 620 nm which is different from the maximum absorption wavelength of the iodine complex.

As described above, in the present invention, the amount of PVA dissolved in the dyeing solution is easily monitored by cross-linking (condensing) the PVA in which the dyeing solution contains a small amount of boric acid (crosslinking agent) and the boric acid dissolved in the dyeing solution (Quantification). Thus, it is possible to accurately determine the update (replacement) timing of the staining solution while avoiding problems such as adhesion of PVA and lowering of dyeing speed in the continuous production of the polarizer.

That is, in the method for producing a polarizer to which the present invention is applied, it is preferable to provide a step of exchanging a part or all of the dyeing solution based on the amount of the complexing compound, preferably based on the absorbance of the complexing compound.

&Lt; Detection method of polyvinyl alcohol (PVA)

The detection method of polyvinyl alcohol (PVA) to which the present invention is applied is suitably used in the above-described analysis step. That is, this PVA detection method is characterized in that before the PVA resin layer (PVA resin film) is dyed, the absorbance of the dyeing solution as a reference is measured, and the amount of the PVA- Crosslinking the PVA dissolved in the staining solution from the stratum; measuring the absorbance of the staining solution after staining the PVA resin layer; and measuring the absorbance of the staining solution measured before staining and the absorbance of the staining solution measured after staining Based on the change, quantifying the PVA dissolved in the dyeing solution.

In the case of continuously producing polarizers, the dyeing solution during the dyeing process may be used as a reference sample or a target sample for PVA quantitation, not only before and after the dyeing process (temporally).

The PVA detection method of the present invention is not limited to the case where the sample is periodically extracted from the staining solution and the absorbance of each sample is measured as in the above-described analysis step, and the absorbance of the staining solution measured before staining and the staining It is possible to quantify the PVA dissolved in the dyeing solution based on the change (difference) of the absorbance of the dyeing solution thus measured.

Example

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

[First Embodiment]

First, in Examples 1 to 11, a predetermined amount of PVA (0.02 parts by weight, 0.03 parts by weight or 0.05 part by weight) was dissolved in the dyeing solution and the amount of boric acid contained in the dyeing solution was changed. Each sample of Example 1 was produced. With respect to each sample, the absorbance at a wavelength of 620 nm was measured, and the presence or absence of contamination with boric acid was visually observed. These are summarized in Table 1 below.

(Example 1)

In Example 1, as a sample, a dyeing solution was prepared by dissolving 0.18 parts by weight of iodine, 1.26 parts by weight of iodide, 0.02 parts by weight of PVA and 0.01 part by weight of boric acid, based on 100 parts by weight of water.

Then, the ultraviolet visible absorption spectrum of the dye solution was measured, and the absorbance at a wavelength of 620 nm derived from iodine / PVA / boric acid complex was measured. The ultraviolet visible absorption spectrum was measured using a spectrophotometer (UV-2450, manufactured by Shimadzu Corporation). Glass cells (optical path length: 1 mm) were used for measurement. After the dyeing solution was prepared, the presence or absence of boric acid precipitated in the glass cell was visually observed.

(Example 2)

In Example 2, the same dyeing solution as in Example 1 was prepared, except that 0.02 part by weight of boric acid was used as a sample. The dyeing solution was subjected to the same measurement and observation as in Example 1.

(Example 3)

In Example 3, the same dyeing solution as in Example 1 was prepared except that 0.03 parts by weight of PVA and 0.02 part by weight of boric acid were used as samples. The dyeing solution was subjected to the same measurement and observation as in Example 1.

(Example 4)

In Example 4, the same dyeing solution as in Example 1 was prepared except that 0.05 parts by weight of PVA and 0.02 part by weight of boric acid were used as samples. The dyeing solution was subjected to the same measurement and observation as in Example 1.

(Example 5)

In Example 5, the same dyeing solution as in Example 1 was prepared except that 0.07 part by weight of boric acid was used as a sample. The dyeing solution was subjected to the same measurement and observation as in Example 1.

(Example 6)

In Example 6, the same dyeing solution as in Example 1 was prepared except that 0.10 part by weight of boric acid was used as a sample. The dyeing solution was subjected to the same measurement and observation as in Example 1.

(Example 7)

In Example 7, the same dyeing solution as in Example 1 was prepared except that boric acid was used as a sample in an amount of 0.2 part by weight. The dyeing solution was subjected to the same measurement and observation as in Example 1.

(Example 8)

In Example 8, the same dyeing solution as in Example 3 was prepared except that 0.07 part by weight of boric acid was used as a sample. The dyeing solution was subjected to the same measurement and observation as in Example 1.

(Example 9)

In Example 9, the same dyeing solution as in Example 4 was prepared except that 0.07 part by weight of boric acid was used as a sample. The dyeing solution was subjected to the same measurement and observation as in Example 1.

(Example 10)

In Example 10, the same dyeing solution as in Example 3 was prepared, except that 0.10 parts by weight of boric acid was used as a sample. The dyeing solution was subjected to the same measurement and observation as in Example 1.

(Example 11)

In Example 11, the same dyeing solution as in Example 4 was prepared except that 0.10 part by weight of boric acid was used as a sample. The dyeing solution was subjected to the same measurement and observation as in Example 1.

(Comparative Example 1)

In Comparative Example 1, the same dyeing solution as in Example 1 was prepared, except that boric acid was not contained as a sample. The dyeing solution was subjected to the same measurement and observation as in Example 1.

As shown in Table 1, in the samples of Examples 1 to 11 containing boric acid in the dyeing solution, the absorbance at a wavelength of 620 nm almost linearly increased as the amount of PVA was increased in each sample of the content of boric acid . On the other hand, as compared with the samples of Examples 1 to 6 and Comparative Example 2 containing boric acid in the dyeing solution, in the sample of Comparative Example 1 containing no boric acid in the dyeing solution, Is extremely low.

On the other hand, in the sample of Example 7, the amount of boric acid contained in the dyeing solution was excessive as compared with the samples of Examples 1 to 6 and 8 to 11, and contamination due to precipitation of boric acid was observed.

On the other hand, in the samples of Examples 1 to 6 and 8 to 11, the absorbance at a wavelength of 620 nm was high and contamination due to precipitation of boric acid was not observed.

(Second Embodiment)

Next, in Example 2, 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 absorbance of this staining solution was measured in the same manner as in the first example. Thereafter, 0.013 part by weight, 0.029 part by weight, and 0.051 part by weight of PVA were dissolved in this dyeing solution, and the respective absorbances were measured in the same manner as in Example 1 to obtain the difference from the absorbance before the PVA was dissolved . These are summarized in Fig.

As shown in Fig. 1, it can be seen that as the amount of PVA dissolved in the dyeing solution increases, the absorbance increases. In particular, it can be seen that the maximum value of the absorbance is shown at a wavelength of 620 nm. Therefore, it is possible to quantify the PVA dissolved in the dyeing solution by measuring the change of the absorbance at this wavelength of 620 nm. In other words, according to the present invention, since the amount of PVA can be quantified, it is possible to grasp the exchange time of the liquid, thereby making it possible to stably produce a polarizer free from color unevenness.

Claims (11)

A dyeing step of dyeing the PVA resin film by dipping a polyvinyl alcohol (PVA) based resin film in a dyeing solution containing a dichroic dye,
And an analysis step of quantitatively analyzing the PVA dissolved in the dyeing solution by extracting a part of the dyeing solution as a sample and measuring the absorbance of the sample,
Wherein the dyeing solution contains a crosslinking agent. The method according to claim 1, wherein in the analysis step, the sample is periodically extracted from the dyeing solution, and the absorbance of each sample is measured. Based on the absorbance of each sample measured over time, And quantitatively analyzing the PVA dissolved in the dyeing solution. 3. The method according to claim 2, wherein as the specific wavelength, at least one wavelength is selected from a wavelength of 500 to 700 nm. 4. The method of producing a polarizer according to any one of claims 1 to 3, wherein the cross-linking 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 3, wherein the PVA resin film has a thickness of 10 占 퐉 or less and is formed on a thermoplastic resin base material. 4. The method of producing a polarizer according to any one of claims 1 to 3, wherein the concentration of the crosslinking agent is 0.01 to 0.1 parts by weight. 4. The method of producing a polarizer according to any one of claims 1 to 3, wherein the dichroic dye is iodine. 4. The method of producing a polarizer according to any one of claims 1 to 3, wherein the concentration of the dichroic dye is 0.01 to 10 parts by weight. The method of any one of claims 1 to 3, wherein the dyeing solution contains potassium iodide. A polyvinyl alcohol detection method for detecting PVA dissolved in a dyeing solution obtained by dying a polyvinyl alcohol (PVA) based resin film in a dyeing solution containing a dichroic dye, wherein the PVA based resin film is dyed,
Measuring the absorbance of the dye solution before dyeing the PVA resin film;
Crosslinking the PVA dissolved in the dyeing solution from the PVA resin film by adding a crosslinking agent to the dyeing solution;
Measuring the absorbance of the dye solution after dyeing the PVA resin film;
Quantifying the PVA dissolved in the dyeing solution based on the absorbance of the dyeing solution measured before the dyeing and the change in absorbance of the dyeing solution measured after the dyeing step
Wherein the polyvinyl alcohol is a polyvinyl alcohol.

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