TWI597485B - Method for producing polarizer and method for detecting polyvinyl alcohol - Google Patents

Description

Method for producing polarizer and method for detecting polyvinyl alcohol

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

Conventionally, a polarizing plate has been widely used as a supply element for polarized light in a display device such as a liquid crystal display device, or a detecting element for polarized light. The polarizing plate is generally formed by laminating a protective film on one side or both sides of a polarizing film (polarizing sheet).

The polarizer is produced by performing a swelling treatment, a dyeing treatment, a stretching treatment, a crosslinking treatment, a washing treatment, and the like on an unstretched polyvinyl alcohol (PVA)-based resin film (embryonic film), followed by drying.

In recent years, with the increase in performance and thickness of a liquid crystal display device, it is required to be thinner even for a polarizer. For example, the polarizer having a thickness of 10 μm or less can be formed by applying a PVA-based resin solution to a thermoplastic resin substrate and drying it to form a laminate having a PVA-based resin layer, and then using the laminate as a precursor film. It is manufactured by various processes.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2008-292935

However, in the dyeing step of dyeing the PVA-based resin film (PVA-based resin layer) described above, the dyeing liquid containing iodine (dichroic dye) is immersed in the dyeing bath. At this time, one part of the PVA may be dissolved from the PVA-based resin film into the dyeing liquid. The polarizer (PVA-based resin film) which has been thinned to a thickness of 10 μm or less is particularly highly soluble.

In this case, if the continuous production of the polarizer is performed, the dissolved PVA is accumulated in the dye bath, and the PVA concentration in the dye solution increases, and the precipitated PVA adheres to the PVA resin film, and the polarizer is not dyed. The reason for equality. Further, when the embryo film is taken out from the dyeing bath, the liquid removal (water removal) of the dyeing liquid is deteriorated. As a result, there is a problem that the yield of the polarizer is lowered. Further, in addition to the above problems, the PVA concentration in the dyeing liquid is increased, and the adsorption speed (dyeing speed) of iodine to the PVA resin film is lowered to impair the productivity.

In this regard, a method of adsorbing and removing foreign matter composed of PVA generated by a crosslinking bath in contact with activated carbon has been disclosed (see Patent Document 1 above). However, since activated carbon also contains iodine, it is not preferable in a dye bath which must maintain a certain iodine concentration.

Therefore, since the PVA dissolved in the dyeing liquid cannot be removed, as a measure for increasing the PVA concentration in the dyeing bath, the treatment liquid is generally periodically (exchanged) before the above problem occurs. However, the past In the dyeing step, the method of quantitatively analyzing the PVA dissolved in the dyeing liquid is difficult to accurately grasp the period of renewal (exchange) of the staining solution. Therefore, in many cases, the renewal of the treatment liquid is performed after the problems such as the adhesion of the PVA described above or the decrease in the dyeing speed actually occur.

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a polarizer for a polarizer that can be stably produced by quantitatively analyzing PVA dissolved in a dyeing liquid to optimize the renewal (exchange) period of the dyeing liquid. The manufacturing method and the method for detecting the polyvinyl alcohol of PVA dissolved in the dyeing liquid.

As a means for solving the above problems, according to an aspect of the present invention, a method for producing a polarizer can be provided, which comprises: immersing a polyvinyl alcohol (PVA) resin film in a dye containing a dichroic dye a dyeing step of dyeing the PVA-based resin film in the liquid; and extracting a portion of the dyeing liquid as a sample, and measuring an absorbance of the sample to quantitatively analyze an analysis step of PVA dissolved in the dyeing liquid; The staining solution contains a crosslinking agent.

Further, in the method for producing a polarizer according to the above aspect, in the analyzing step, the sample may be periodically taken out from the dyeing liquid, and the absorbance of each sample may be measured, and among the measured absorbances of the respective samples, depending on the specificity. A method for producing PVA dissolved in the dyeing liquid by quantitatively analyzing the change in absorbance at a wavelength.

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

Further, in the method for producing a polarizer according to the above aspect, the crosslinking agent may be a method for producing a boron compound.

Further, in the method for producing a polarizer according to the above aspect, the boron compound may be a method for producing boric acid.

In the method of producing a polarizing plate of the above aspect, the PVA-based resin film may have a thickness of 10 μm or less and may be formed on a thermoplastic resin substrate.

Further, in the method for producing a polarizer according to the above aspect, the method may be a method in which the concentration of the crosslinking agent is 0.01 to 0.1 part by weight.

Further, in the method for producing a polarizer according to the above aspect, the method for producing the dichroic dye may be iodine.

Further, in the method for producing a polarizer according to the above aspect, the method of producing the dichroic dye may have a concentration of 0.01 to 10 parts by weight.

Further, in the method for producing a polarizer according to the above aspect, the method for producing potassium iodide may be used as the dyeing liquid.

Further, according to the aspect of the present invention, a method for detecting polyvinyl alcohol can be provided by immersing a polyvinyl alcohol (PVA) resin film in a dyeing liquid containing a dichroic dye to detect the PVA resin. PVA which is dissolved in the dyeing liquid after dyeing the film; and includes a step of measuring the absorbance of the dyeing liquid before dyeing the PVA-based resin film; and the PIV system is obtained from the PVA system by including the crosslinking agent a step of crosslinking the PVA of the resin film dissolved in the dyeing liquid; the aforementioned PVA a step of measuring the absorbance of the dyeing liquid after dyeing the resin film; and dissolving in the dyeing liquid according to the change in the absorbance of the dyeing liquid measured before the dyeing and the absorbance of the dyeing liquid measured after the dyeing The step of quantification of PVA.

As described above, according to the aspect of the present invention, it is possible to provide a polarizer for stably producing a polarizer by quantitatively analyzing the PVA dissolved in the dyeing liquid to optimize the renewal (exchange) period of the dyeing liquid. The method, and the method for detecting the polyvinyl alcohol of PVA dissolved in the dyeing solution.

Fig. 1 is a graph for measuring changes in absorbance of a dyeing solution when a PVA containing a certain amount of boric acid is dissolved in a dye solution in a second embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In the present embodiment, the PVA-based resin solution is applied onto a thermoplastic resin substrate and dried to form a laminate having a PVA-based resin layer (film). A case where the laminate is used as the embryonic film and various treatments are performed to produce a polarizer having a thickness of 10 μm or less will be described as an example.

<Thermoplastic resin substrate>

First, a 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 substrate, a transparent protective film which has been conventionally used as a polarizer can be used.

As the material constituting the thermoplastic resin substrate, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropic property, and elongation can be used. Specific examples of such a thermoplastic resin include cellulose resins such as triacetonitrile cellulose, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyether oxime resins, and polyfluorene resins. Polyamide resin such as polycarbonate resin, nylon or aromatic polyamide, polyimine resin, polyolefin resin such as polyethylene, polypropylene, ethylene/propylene copolymer, and ring-to-northene structure A cyclic polyolefin resin (northene-based resin), a (meth)acrylic resin, a polyarylate resin, a polystyrene resin, a polyvinyl alcohol resin, and a mixture thereof. Further, the thermoplastic resin substrate may be subjected to a surface treatment (for example, corona treatment or the like) to form a thin layer such as a primer layer (undercoat layer) in order to improve adhesion to the PVA-based resin layer.

The thermoplastic resin can be roughly classified into a crystallized state in which the polymer is regularly aligned, and the polymer does not have a regular alignment, or has only a part of an amorphous or amorphous state. The former is called a crystalline state, and the latter is called an amorphous or amorphous state. Corresponding to this, a thermoplastic resin having a property of being formed into a crystalline state is referred to as a crystalline resin, and a thermoplastic resin having such a property is referred to as an amorphous resin.

On the other hand, whether it is a crystalline resin or an amorphous resin, a resin which is not in a crystalline state or a resin which cannot reach a crystalline state is called an amorphous or amorphous resin. Here, amorphous or amorphous resin, It is used in distinction from an amorphous resin which does not have a crystalline state.

Examples of the crystalline resin include olefin-based resins containing polyethylene (PE) and polypropylene (PP), and polyethylene terephthalate (PET) and polybutylene terephthalate. (PBT) ester resin. One of the characteristics of the crystalline resin is a property in which the polymer is aligned and crystallized by general heating and elongation alignment. The physical properties of the resin vary depending on the degree of crystallization.

On the other hand, for example, even a crystalline resin such as polypropylene (PP) or polyethylene terephthalate (PET) can block the alignment of the polymer caused by heat treatment or elongation. Inhibition of crystallization. The polypropylene (PP) and polyethylene terephthalate (PET), which are inhibited by crystallization, are called amorphous polypropylene and amorphous polyethylene terephthalate, which are collectively referred to as non- A crystalline olefin resin or an amorphous ester resin.

For example, in the case of polypropylene (PP), amorphous polypropylene (PP) which suppresses crystallization can be produced by adopting an atactic structure having no stereoregularity. Further, for example, polyethylene terephthalate (in the case of PE, a modified group such as isophthalic acid or 1,4-cyclohexanedimethanol which is a polymerization monomer can be copolymerized, that is, Amorphous polyethylene terephthalate (PET) which inhibits crystallization is produced by copolymerization of molecules which hinder crystallization of polyethylene terephthalate (PET).

The thickness of the thermoplastic resin substrate (before stretching) can be appropriately determined, but it is generally from 10 to 500 μm from the viewpoints of workability, thinness, and the like of strength and workability. In particular, it is preferably 20 to 300 μm, more preferably 30 to 200 μm. The thickness of the thermoplastic resin substrate is particularly suitable in the case of 50 to 150 μm.

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

In the method for producing a polarizer according to the present invention, a layered body containing a PVA-based resin layer (film) is formed on the thermoplastic resin substrate. The PVA-based resin can be used in a light-transmitting region in the visible light region, and a dichroic material such as iodine or a dichroic dye can be dispersed and adsorbed without particular limitation.

The PVA-based resin is preferably a PVA-based resin that has been conventionally used as a polarizer. The PVA-based resin can be exemplified by PVA or a derivative thereof. Examples of the derivative of PVA include polyvinyl formaldehyde, polyvinyl acetal, and the like. Other examples include an olefin such as ethylene or propylene, an unsaturated carboxylic acid such as acryl acid, methacrylic acid or crotonic acid, and an alkyl ester or decylamine acrylate.

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

The PVA resin may also contain an additive such as a plasticizer or a surfactant. The plasticizer can be exemplified by a polyol, a condensate thereof and the like. 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.

<Laminated body (embryonic membrane)>

The laminated body of the embryonic film can be formed by applying an aqueous solution containing a PVA-based resin to a thermoplastic resin substrate, followed by drying to form a PVA-based resin layer. Got it. In addition, the laminated body may have a structure in which a thermoplastic resin substrate and a PVA-based resin layer are laminated via a primer layer. Further, the laminate may be a structure in which a thermoplastic resin substrate and a PVA-based resin layer are directly laminated, or a laminate in which a base layer and a hydrophilic polymer layer are integrated.

The aqueous solution can be prepared, for example, by dissolving a PVA-based resin powder, a pulverized product, a cut product, or the like in a suitably 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, per 100 parts by weight of the water.

The coating of the aqueous solution on the thermoplastic resin substrate can be suitably selected, for example, by a roll coating method such as a bar coating method, a reverse coating method, or a gravure coating method, a spin coating method, a screen printing method, or a spray coating method (Fountain). Coater), dipping method, spray coating method, die coating method, corner wheel coating method, nozzle coating method, and the like.

In the case where the thermoplastic resin substrate has a primer layer, an aqueous solution is directly applied to the primer layer. On the other hand, in the case where the thermoplastic resin substrate does not have a primer layer, an aqueous solution is directly applied to the substrate layer. Further, the drying temperature is preferably set to 50 to 200 ° C, more preferably 60 to 150 ° C. The drying time is preferably set to 5 to 30 minutes.

The PVA-based resin layer is formed so that the thickness of the obtained polarizer becomes 10 μm or less in consideration of the stretching ratio in the stretching process performed on the laminated body. The thickness of the unstretched PVA-based resin layer is preferably set to 3 to 20 μm, more preferably 5 to 15 μm.

<Processing steps>

In the method for producing a polarizer to which the present invention is applied, at least a solid dyeing treatment and an elongation treatment are applied to the laminate (primary membrane). Further, in the method for producing a polarizer to which the present invention is applied, a crosslinking treatment can be carried out. In the dyeing treatment, the crosslinking treatment, and the elongation treatment, each treatment bath of the dye bath, the crosslinking bath, and the extension bath may be used separately. When a treatment bath is used, a treatment liquid (aqueous solution or the like) for each treatment is used.

<staining step>

In the dyeing step, the dyeing treatment is carried out by adsorbing/aligning iodine or a dichroic dye to the PVA-based resin layer in the laminate. In the dyeing step, the dyeing treatment can be carried out together with the stretching treatment.

The dyeing treatment is carried out by immersing the layered body in a dyeing liquid (dyeing bath) in the dyeing bath. As the dyeing liquid, it is generally an iodine solution. An aqueous solution of iodine as an iodine solution is used, and an aqueous solution containing an iodide ion by an iodinated compound of iodine and a dissolution aid is used.

As the iodinated compound, for example, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, cesium iodide, calcium iodide, tin iodide, or titanium iodide can be used. The iodinated compound is suitably potassium iodide. Further, the iodinated compound used in the present embodiment is also the same as the above-described iodinated compound when it is 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, still more preferably 0.1 to 1.0 part by weight, based on 100 parts by weight of the solvent. The concentration of the iodinated compound is preferably set to 0.1 to 10 parts by weight, more preferably 0.2, based on 100 parts by weight of the solvent. Up to 8 parts by weight. When iodine is dyed, the temperature of the iodine solution is preferably set to 20 to 50 ° C, more preferably 25 to 40 ° C. The immersion time is preferably set to 10 to 300 seconds, more preferably 20 to 240 seconds. In addition, the dyeing time can be immersed at any time in such a manner that a specified degree of polarization or transparency can be achieved.

<Extension step>

Any of the dry stretching treatment and the wet stretching treatment may be used in the stretching step. In the extending step, the stretching process can be performed by performing a shaft extension on the laminated body. The one-axis extension may be either a longitudinal extension of the longitudinal direction of the laminate or a lateral extension of the width direction of the laminate.

The lateral extension can extend in the width direction while also shrinking in the length direction. As a method of laterally extending, for example, a fixed-end one-axis extending method in which one end is fixed by a tenter, and a free-end one-axis extending method in which one end is not fixed can be exemplified.

On the other hand, in the longitudinal extension, for example, an inter-roll stretching method, a compression stretching method, an extension method using a tenter, or the like can be used. In addition, the extension process can also be carried out in multiple stages. Further, the stretching process can be performed by performing biaxial stretching, oblique stretching, or the like.

The dry stretching treatment is preferable in that the temperature range at which the laminate is extended is set to be wide. The dry stretching treatment is preferably carried out by heating the laminate to 50 to 200 ° C, more preferably 80 to 180 ° C, and more preferably to a state of heating to 100 to 160 ° C for elongation treatment. When the stretching step includes a dry stretching treatment, it is preferred to carry out the dry stretching before the dyeing step. Reason.

The treatment liquid used in the wet stretching treatment may contain an iodinated compound. When the iodinated compound is contained in the treatment liquid, the concentration of the iodinated compound is preferably from 0.1 to 10 parts by weight, more preferably from 0.2 to 5 parts by weight, per 100 parts by weight of the solvent. The treatment temperature in the wet stretching method is preferably set to 25 ° C or higher, more preferably 30 to 85 ° C, further 50 to 70 ° C. The immersion time is preferably set to 10 to 800 seconds, more preferably 30 to 500 seconds. Further, the stretching treatment can be carried out together with the dyeing treatment and the crosslinking treatment.

In the extending step, the stretching treatment is performed in such a manner that the total stretching ratio is 4 to 8 times with respect to the original length of the laminated body. The total stretching ratio is preferably from 5 to 7 times. Further, when the total stretching ratio is accompanied by the stretching in steps other than the stretching step, it means the cumulative stretching ratio including the stretching in the steps. The total stretching ratio is appropriately determined in consideration of the stretching ratio in other steps and the like.

When the total stretching ratio is low, the alignment is insufficient, and it is difficult to obtain a polarizer having high optical characteristics (polarity). On the other hand, when the total stretching ratio is too high, elongation fracture tends to occur. Further, the polarizer becomes too thin, and there is a concern that the workability is lowered in the subsequent steps.

In the extension step, as described in Japanese Patent No. 4751481, the wetting extension treatment can be performed after the air-assisted extension treatment. The extension temperature in the air-subsidy extension treatment is 60 to 180 ° C, and more preferably, the temperature is preset to a high temperature of 95 to 150 ° C. Further, the stretching ratio in the air-subsidy extension processing is preferably set to 1.3 to 4 times, more preferably 1.5 to 3 times. In addition, after the air subsidy extension process In the wet stretching treatment to be carried out, the treatment temperature is preferably set to 50 to 80 ° C, more preferably 60 to 70 ° C. The immersion time is preferably set to 5 to 120 seconds, more preferably 10 to 60 seconds. Further, the stretching ratio in the wetting extension treatment is preferably such that the total stretching ratio is 4 to 7 times, more preferably 5 to 6 times.

In the extending step, when the air-assisted extension treatment and the wet extension treatment are included, it is preferred to carry out the air-assisted extension treatment before the dyeing treatment, and perform the wetting extension treatment after the dyeing treatment. At this time, the treatment bath used in the wet stretching treatment preferably has a crosslinking bath and is subjected to a crosslinking treatment simultaneously with the wet stretching treatment.

<Crosslinking step>

In the crosslinking step, a boron compound is used as a crosslinking agent for crosslinking treatment. The crosslinking treatment can be carried out together with the dyeing treatment or the elongation treatment. Further, the crosslinking treatment can be carried out in plural times. As the boron compound, for example, boric acid, borax or the like can be used. The boron compound is generally in the form of a mixed solution of an aqueous solution or a water-organic solvent.

When a boric acid aqueous solution is used, in order to impart heat resistance by the degree of crosslinking, the boric acid concentration of the boric acid aqueous solution is preferably from 1 to 10 parts by weight, more preferably from 2 to 7 parts by weight, per 100 parts by weight of the solvent. An iodinated compound such as potassium iodide may be contained in an aqueous solution of boric acid or the like. When the iodinated compound is contained in the aqueous boric acid solution, the concentration of the iodinated compound is preferably from 0.1 to 10 parts by weight, more preferably from 0.5 to 8 parts by weight, per 100 parts by weight of the solvent.

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

<insolubilization step>

In the method for producing a polarizer to which the present invention is applied, the insolubilization treatment may be performed before the layered body is subjected to a dyeing treatment or a crosslinking treatment. The purpose of the insolubilization step is to carry out an insolubilization treatment for insolubilizing the PVA-based resin layer.

In the insolubilization step, the insoluble treatment can be carried out 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 in the form of an aqueous solution or a water-organic solvent mixed solution.

When a boric acid aqueous solution is used, the boric acid concentration of the boric acid aqueous solution 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 set to 25 ° C or higher, more preferably 30 to 85 ° C, further preferably 30 to 60 ° C. The treatment time is preferably set to 5 to 800 seconds, more preferably 8 to 500 seconds.

<washing step>

In the method for producing a polarizer to which the present invention is applied, the layered body may be subjected to a dyeing treatment or an extension treatment to further perform a crosslinking treatment, but after performing the treatment, a cleaning treatment may be performed.

In the washing step, the potassium iodide solution can be used for the washing treatment. Potassium iodide in potassium iodide solution relative to 100 parts by weight of solvent The degree is preferably from 0.5 to 10 parts by weight, more preferably from 0.5 to 8 parts by weight, still more preferably from 1 to 6 parts by weight.

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

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

In the washing step, a washing treatment using a potassium iodide solution or a water washing treatment may be used in combination, and for example, a solution of a liquid alcohol such as methanol, ethanol, isopropanol, butanol or propanol may be appropriately formulated.

<drying step>

Further, in the method for producing a polarizer to which the present invention is applied, after performing each of the above-described processes, finally, a drying treatment is performed to produce a polarizer. In the drying treatment, the moisture content necessary for the obtained polarizer (film) is set, and the optimum drying time and drying temperature are set. Specifically, the drying temperature is preferably set to 20 to 150 ° C, more preferably 40 to 100 ° C. When the drying temperature is too low, the drying time becomes long and it cannot be efficiently produced, which is not preferable. On the other hand, when the drying temperature is too high, the resulting polarizer will deteriorate, in terms of optical characteristics and The point of hue will deteriorate. The heat drying time is preferably set to 1 to 10 minutes.

<Water-soluble antioxidant>

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

In the treatment with the water-soluble antioxidant treatment liquid, at least one of each of the baths used in the respective treatments after the dyeing treatment is carried out contains a water-soluble antioxidant. Alternatively, treatment with a treatment liquid containing a water-soluble antioxidant is additionally carried out. The treatment with a water-soluble antioxidant treatment liquid is preferably carried out together with the crosslinking treatment and/or the elongation treatment.

Further, the crosslinking treatment and the elongation processing can be carried out by performing the processing of the plural processing at the same time. In the simultaneous treatment of the plural treatment, the bath used in the primary treatment contains a water-soluble antioxidant. Further, the cross-linking treatment and the stretching treatment are performed in a plurality of stages, and the water-soluble antioxidant is contained in any at least one of the cross-linking treatment and the elongation treatment.

Examples of the water-soluble antioxidant include ascorbic acid (vitamin C), erythorbic acid, thiosulfuric acid, sulfurous acid, chlorogenic acid, and lemon. Acid, rosmarinic acid, and the like.

The salt may, for example, be an alkali metal salt such as a sodium salt or a potassium salt.

Among these, ascorbate, isoascorbate, thiosulfate, and sulfite are preferably used. These water soluble antioxidants can be used separately One type may be used, or two or more types may be used in combination.

The amount of the water-soluble antioxidant added is determined by the concentration of the dichroic substance (iodine or dichroic dye) contained in each treatment liquid after the dyeing step. If the concentration of the contamination caused by the dichroic substance in the contaminated treatment liquid is higher, the added amount of the added water-soluble antioxidant becomes larger.

In each of the treatment liquids, it is preferred to add a water-soluble antioxidant, more preferably 0.005 to 0.5 parts by weight, based on 100 parts by weight of the solvent, and the concentration of the water-soluble antioxidant is 0.005 to 1 part by weight. When the concentration of the water-soluble antioxidant is less than 0.005 parts by weight, the proportion of the water-soluble antioxidant in the contaminated treatment liquid is small, and the characteristics of the obtained polarizer (monomer penetration, polarization degree) cannot be sufficiently suppressed. ) is reduced. 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 increases, so that the obtained polarizer decolorizes and the transmittance becomes high. Accompanying this, there is a concern that the iodine concentration of the dyeing bath is increased, but there is no problem such as reduction in optical characteristics.

<Polarizer>

The polarizer produced by the method for producing a polarizer of the present invention is formed on a thermoplastic resin substrate, but the unextended PVA-based resin layer film may be used as the embryonic film without using the above-mentioned thermoplastic resin substrate. It is manufactured by performing each of the above processes. At this time, the thickness of the polarizer may be 10 μm or more, preferably 5 to 50 μm.

As the thermoplastic resin substrate, a transparent protective film which is a polarizing plate to be described later can be used as it is. In addition, the polarizing plate and the thermoplastic resin substrate are On the opposite side, the transparent protective film can be attached. On the other hand, when a thermoplastic resin substrate is not used, a transparent protective film can be bonded to both sides of the polarizer. Further, after the thermoplastic resin substrate is peeled off from the polarizer, a transparent protective film can be bonded to both sides of the polarizer.

As the material constituting the transparent protective film, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, and isotropic properties can be used. As a specific example of such a thermoplastic resin, for example, triterpenoid acesulfame, etc., ceramide resin, polyester resin, polyether oxime resin, polyfluorene resin, polycarbonate resin, polyamide resin, poly phthalate An amine resin, a polyolefin resin, a (meth)acrylic resin, a cyclic polyolefin resin (northene-based resin), a polyarylate resin, a polystyrene resin, a polyvinyl alcohol resin, and a mixture thereof.

<Analysis step>

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 liquid used in the dyeing step contains a crosslinking agent. The crosslinking agent can be used, for example, from at least one type of boron compound such as boric acid or borax, or glyoxal or glutaraldehyde, or two or more types thereof. Among them, a boron compound is preferably used, and boric acid is more preferably used.

In the dyeing step, since the dyeing liquid contains a trace amount of boric acid (crosslinking agent), the boric acid crosslinks (disforms) the PVA dissolved in the dyeing liquid from the PVA-based resin layer. Thereby, the PVA dissolved in the dyeing solution and the iodine/PVA/ combined with the iodine in the dyeing solution and the boric acid are formed. Boric acid conjugate (hereinafter referred to as a conjugate compound).

In order to crosslink (decode) the PVA dissolved in the dyeing liquid, the concentration of boric acid (crosslinking agent) in the dyeing liquid is preferably 0.01 to 0.1 parts by weight, based on 100 parts by weight of the solvent. It is preferably 0.02 to 0.1 parts by weight. When the concentration of the boric acid is 0.01 parts by weight or more, the PVA dissolved in the dyeing liquid can be crosslinked (disorganized). On the other hand, when the concentration of the boric acid is more than 0.2 parts by weight, boric acid may be precipitated on the surface of the laminate (primary film) or the surface of the roll on which the laminate (sheath film) is transferred, causing defects such as a polarizer.

The method of adjusting the concentration of boric acid in the dyeing liquid may be a method of adding a predetermined amount of boric acid to the dyeing liquid. Further, when a treatment bath containing boric acid is present before the dyeing treatment, boric acid which is carried together with the laminate from the treatment bath can be used. At this time, the concentration of boric acid can also be monitored.

The dysfunctional compound formed 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 an analysis step, one part of the dyeing liquid is taken out as a sample, and the absorbance of the sample is measured. Specifically, it is preferred to periodically take a sample from the dyeing liquid, measure the absorbance of each sample, and quantitatively analyze and dissolve in the dyeing solution according to the change in absorbance of the specific wavelength in the absorbance of each sample measured. PVA. The absorbance can be measured, for example, by a commercially available spectrophotometer. At this point, the sample can be diluted with a suitable solvent.

The specific wavelength is preferably selected from at least one of wavelengths of 500 to 700 nm. That is, the specific wavelength is preferably a wavelength indicating a maximum value in the absorbance of each sample. In this embodiment, in the extreme with iodine The maximum absorption wavelength of the complex compound exists in the vicinity of about 620 nm in which the absorption wavelength is large.

As described above, in the present invention, the dyeing liquid contains a trace amount of boric acid (crosslinking agent), whereby the PVA dissolved in the dyeing liquid is crosslinked (disorganized) by the boric acid, and the solution can be easily monitored (quantitatively). The amount of PVA in the staining solution. Thereby, it is possible to avoid problems such as adhesion of the PVA and reduction in the dyeing speed in the continuous production of the polarizer, and accurately determine the update (exchange) period of the dyeing liquid.

That is, in the method for producing a polarizer to which the present invention is applied, it is preferred to use the amount of the complex compound as an index, and it is preferable to use one or all of the dye liquid as the index of the absorbance of the compound. The steps of the exchange.

<Detection method of polyvinyl alcohol (PVA)>

The method for detecting polyvinyl alcohol (PVA) to which the present invention is applied is suitably used in the above-described analysis step. That is, the detection method of the PVA includes a step of measuring the absorbance of the dyeing liquid as a control group before dyeing the PVA-based resin layer (PVA-based resin film); and containing boric acid (crosslinking agent) in the dyeing liquid. a step of crosslinking the PVA dissolved in the dyeing liquid from the PVA-based resin layer; a step of measuring the absorbance of the dyeing solution after dyeing the PVA-based resin film; and, based on the absorbance of the dyeing liquid measured before dyeing and after dyeing The step of quantifying the PVA dissolved in the dyeing solution by measuring the change in the absorbance of the dyeing solution.

When the polarizer is continuously manufactured, (time) is not limited to dyeing treatment Before and after, the staining solution in the dyeing treatment can be used as a control sample or a PVA-quantized subject sample.

The detection method of the PVA to which the present invention is applied, such as the above-mentioned analysis step, is not limited to the periodic extraction of the sample from the dyeing liquid, and the absorbance of each sample is measured, and the absorbance of the dyeing liquid measured before dyeing and the dyeing after the dyeing can be determined. The change in absorbance of the liquid (difference) quantifies the PVA dissolved in the dyeing solution.

[Examples]

Hereinafter, the effects of the present invention will be more clarified by the examples. The present invention is not limited to the embodiments described below, and may be modified as appropriate without departing from the scope of the invention.

[First Embodiment]

First, in the first embodiment, a predetermined amount of PVA (0.02 parts by weight, 0.03 parts by weight, or 0.05 parts by weight) is dissolved in the dyeing liquid, and at the same time, Example 1 in which the amount of boric acid contained in the dyeing liquid is changed is prepared. Each of the samples of 11 and Comparative Example 1. Then, the absorbance at a wavelength of 620 nm was measured for each sample, and the presence or absence of contamination due to boric acid was visually observed. The consolidation thereof is shown in Table 1 below.

(Example 1)

In Example 1, as a sample, a dyeing liquid containing 0.18 parts by weight of iodine, 1.26 parts by weight of potassium iodide, 0.02 parts by weight of PVA, and 0.01 parts by weight of boric acid was dissolved in 100 parts by weight of water.

Then, the ultraviolet-visible absorption spectrum of the dyeing liquid was measured, and the absorbance at a wavelength of 620 nm from the iodine/PVA/boric acid complex was measured. The ultraviolet-visible absorption spectrum was measured using a spectrophotometer (UV-2450 manufactured by Shimadzu Corporation). Further, in the measurement, a glass tank (GALSS CELL, optical path length: 1 mm) was used. Further, after the dyeing liquid was prepared, the presence or absence of the boric acid precipitated in the glass tank was visually observed.

(Example 2)

In Example 2, the same dyeing liquid as in Example 1 was prepared as a sample except that boric acid was 0.02 parts by weight. Then, the same measurement and observation as in Example 1 were carried out for the staining solution.

(Example 3)

In the example 3, a dyeing liquid similar to that of Example 1 was prepared as a sample except that PVA was 0.03 part by weight and boric acid was 0.02 part by weight. Then, the same measurement and observation as in Example 1 were carried out for the staining solution.

(Example 4)

In the example 4, a dyeing liquid similar to that of Example 1 was prepared as a sample except that PVA was 0.05 parts by weight and boric acid was 0.02 parts by weight. Then, the same measurement and observation as in Example 1 were carried out for the staining solution.

(Example 5)

In Example 5, the same dyeing liquid as in Example 1 was prepared as a sample except that boric acid was 0.07 part by weight. Then, the same measurement and observation as in Example 1 were carried out for the staining solution.

(Example 6)

In Example 6, as a sample, except that boric acid was made 0.10 parts by weight. The same staining solution as in Example 1 was prepared. Then, the same measurement and observation as in Example 1 were carried out for the staining solution.

(Example 7)

In Example 7, the same dyeing liquid as in Example 1 was prepared as a sample except that boric acid was 0.2 parts by weight. Then, the same measurement and observation as in Example 1 were carried out for the staining solution.

(Example 8)

In Example 8, the same dyeing liquid as in Example 3 was prepared as a sample except that boric acid was 0.07 part by weight. Then, the same measurement and observation as in Example 1 were carried out for the staining solution.

(Example 9)

In Example 9, the same dyeing liquid as in Example 4 was prepared as a sample except that boric acid was 0.07 part by weight. Then, the same measurement and observation as in Example 1 were carried out for the staining solution.

(Embodiment 10)

In Example 10, a dyeing liquid similar to that of Example 3 was prepared as a sample except that boric acid was 0.10 part by weight. Then, the same measurement and observation as in Example 1 were carried out for the staining solution.

(Example 11)

In Example 11, a dyeing liquid similar to that of Example 4 was prepared as a sample except that boric acid was 0.10 part by weight. Then, the same measurement and observation as in Example 1 were carried out for the staining solution.

(Comparative Example 1)

In Comparative Example 1, the same dyeing liquid as in Example 1 was prepared as a sample except that boric acid was not contained. Then, the same measurement and observation as in Example 1 were carried out for the staining solution.

As shown in Table 1, it was found that in the samples of Examples 1 to 11 containing boric acid in the dyeing solution, the absorbance at a wavelength of 620 nm increased almost linearly with the increase in the amount of PVA in each of the samples having a boric acid content. On the other hand, it can be seen that in the sample of Comparative Example 1 which does not contain boric acid in the dyeing solution, since no deformed body is formed, compared with the samples of Examples 1 to 6 and Comparative Example 2 containing boric acid in the dyeing liquid, the wavelength is The absorbance at 620 nm is extremely low.

On the other hand, in the sample of Example 7, the amount of boric acid contained in the dyeing liquid was excessive as compared with the samples of Examples 1 to 6, 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, 8 to 11, the absorbance at a wavelength of 620 nm was high, and no contamination due to precipitation of boric acid was observed.

(Second embodiment)

Next, in the second embodiment, the preparation is 100 parts by weight with respect to water. A dyeing liquid containing 0.18 parts by weight of iodine, 1.26 parts by weight of potassium iodide, and 0.02 parts by weight of boric acid was dissolved. Then, the absorbance of the dyeing liquid was measured by the same method as in the first embodiment. Thereafter, the absorbances of 0.013 parts by weight, 0.029 parts by weight, and 0.051 parts by weight of PVA dissolved in the dyeing solution were measured by the same method as in the first example, and the difference between the absorbances before the dissolution of PVA was determined. The summary is shown in Fig. 1.

As shown in Fig. 1, it is understood that as the amount of PVA dissolved in the dyeing liquid increases, the absorbance increases. In particular, it is understood that the maximum value of the absorbance is displayed at a wavelength of 620 nm. Therefore, PVA dissolved in the dyeing solution can be quantified by measuring the change in absorbance at the wavelength of 620 nm. That is, according to the present invention, since the exchange period of the liquid can be grasped by quantifying the amount of the PVA, the polarizer having no color unevenness can be stably produced.

The drawing of this case is the experimental result, not the representative figure of the invention of the case, so there is no designated representative figure.

Claims (10)

A method for producing a polarizer comprising: a dyeing step of immersing an undyed polyvinyl alcohol (PVA) resin film in a dyeing liquid containing a dichroic dye to dye the PVA resin film; and Extracting a portion of the dyeing liquid as a sample, and measuring an absorbance of the sample to quantitatively analyze an analysis step of PVA dissolved in the dyeing liquid; wherein the dyeing liquid contains a crosslinking agent, which is contained in the dyeing liquid The solvent is used in an amount of from 0.01 to 0.1 parts by weight based on 100 parts by weight of the solvent. The method for producing a polarizer according to claim 1, wherein in the analyzing step, the sample is periodically taken out from the dyeing liquid, and the absorbance of each sample is measured, and among the measured absorbances of the respective samples, The PVA dissolved in the aforementioned staining solution was quantitatively analyzed based on the temporal change in absorbance at a specific wavelength. The method for producing a polarizer according to claim 2, wherein at least one of wavelengths from 500 to 700 nm is selected as the specific wavelength. The method for producing a polarizer according to any one of claims 1 to 3, wherein the crosslinking agent is a boron compound. The method for producing a polarizer according to claim 4, wherein the boron compound is boric acid. The polarizer according to any one of claims 1 to 3 In the manufacturing method, the PVA-based resin film has a thickness of 10 μm or less and is formed on a thermoplastic resin substrate. The method for producing a polarizer according to any one of claims 1 to 3, wherein the dichroic dye is iodine. The method for 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 based on 100 parts by weight of the solvent. The method for producing a polarizer according to any one of claims 1 to 3, wherein the dyeing liquid contains potassium iodide. A method for detecting polyvinyl alcohol by immersing an undyed polyvinyl alcohol (PVA) resin film in a dyeing liquid containing a dichroic dye, and detecting that the PVA resin film is dyed and dissolved in the dyeing liquid In the PVA, the detection method includes the step of measuring the absorbance of the dyeing liquid before dyeing the PVA-based resin film, and the dyeing liquid is contained in an amount of 0.01 by weight based on 100 parts by weight of the solvent contained in the dyeing liquid. a step of crosslinking PVA from the PVA-based resin film dissolved in the dyeing liquid to 0.1 part by weight of a crosslinking agent; and dyeing the PVA-based resin film, and measuring the dyeing of the PVA-based resin film a step of absorbance of the dyeing solution; and, according to the change in absorbance of the dyeing liquid measured before the dyeing and the absorbance of the dyeing liquid measured after the dyeing, is dissolved in the foregoing The step of quantifying the PVA in the staining solution.