JP6105796B1 - Method for producing polarizer and method for detecting polyvinyl alcohol - Google Patents

Abstract

Disclosed is a method of manufacturing a polarizer that can stably manufacture a polarizer by optimizing the renewal (exchange) time of the staining liquid by quantitatively analyzing the PVA dissolved in the staining liquid. provide. A dyeing process for dyeing a PVA resin film by immersing a polyvinyl alcohol (PVA) resin film in a dye solution containing dichroic dye (iodine), and a part of the dye bath solution as a sample. And an analysis step of quantitatively analyzing the PVA dissolved in the staining solution by measuring the absorbance of the sample, and the staining solution contains a crosslinking agent (boric acid). [Selection] Figure 1

Description

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

  Conventionally, polarizing plates have been widely used as polarized light supplying elements and polarized light detecting elements in display devices such as liquid crystal display devices. The polarizing plate generally has a configuration in which a protective film is bonded to one side or both sides of a polarizing film (polarizer) using an adhesive.

  The polarizer is produced by subjecting an unstretched polyvinyl alcohol (PVA) resin film (raw film) to swelling treatment, dyeing treatment, stretching treatment, crosslinking treatment, washing treatment, and the like, and then drying. .

  In recent years, with the improvement in performance and thickness of liquid crystal display devices, the polarizer is also required to be thin. For example, for a polarizer having a thickness of 10 μm or less, a PVA resin solution is applied on a thermoplastic resin substrate and dried to form a laminate having a PVA resin layer. As mentioned above, it manufactures by performing each process mentioned above.

JP 2008-292935 A

  By the way, in the dyeing | staining process which dye | stains the PVA-type resin film (PVA-type resin layer) mentioned above, immersing a raw film in the dyeing | staining liquid containing the iodine (dichroic dye) in a dyeing bath is performed. At this time, a part of PVA may dissolve from the PVA resin film into the dyeing solution. In particular, a polarizer (PVA resin film) thinned to a thickness of 10 μm or less has high solubility.

  In this case, when the polarizer is continuously produced, the dissolved PVA accumulates in the dyeing bath, and the PVA concentration in the dyeing solution increases, so that the deposited PVA adheres to the PVA resin film, and the polarizer This may cause uneven dyeing. Moreover, when taking out a raw film from the inside of a dyeing bath, the dyeing liquid runs out (drains). As a result, there arises a problem that the yield of the polarizer is lowered. Furthermore, in addition to the above-described problems, an increase in the concentration of PVA in the dyeing solution causes a problem that the adsorption rate (dyeing rate) of iodine to the PVA-based resin film is lowered and the productivity is impaired. .

  As a countermeasure against this, a method of adsorbing and removing foreign substances made of PVA generated in a crosslinking bath by bringing it into contact with activated carbon has been disclosed (see Patent Document 1 above). However, activated carbon also adsorbs iodine, which is not preferable in a dyeing bath that needs to keep the iodine concentration constant.

  Therefore, since the PVA dissolved in the staining solution cannot be removed, as a countermeasure against the increase in the PVA concentration in the staining bath, the processing solution is regularly updated (replaced) before the above-described problem occurs. It is common. However, in the conventional staining process, there is no method for quantitatively analyzing the PVA dissolved in the staining solution, and it is difficult to accurately grasp the renewal (exchange) time of the staining solution. For this reason, it is often the case that the processing solution is updated after the above-described problems such as adhesion of PVA and a decrease in the dyeing speed occur.

  The present invention has been proposed in view of such a conventional situation, and by optimizing the renewal (exchange) time of the staining liquid by quantitatively analyzing the PVA dissolved in the staining liquid, the polarizer It is an object of the present invention to provide a method for producing a polarizer that makes it possible to stably produce a polymer, and a method for detecting polyvinyl alcohol that makes it possible to detect PVA dissolved in a staining solution.

  As means for solving the above-mentioned problems, according to the embodiment of the present invention, dyeing of the PVA resin film by immersing the polyvinyl alcohol (PVA) resin film in a dye solution containing a dichroic dye. And a step of extracting a part of the staining solution as a sample and measuring the absorbance of the sample to quantitatively analyze the PVA dissolved in the staining solution. The staining solution is crosslinked. A method for producing a polarizer containing an agent is provided.

  In the method for producing a polarizer according to the aspect, in the analysis step, the sample is periodically extracted from the staining solution, and the absorbance of each sample is measured. The production method may quantitatively analyze the PVA dissolved in the staining solution based on the change in absorbance with time.

  Moreover, the manufacturing method of the polarizer of the said aspect may be a manufacturing method which selects at least 1 wavelength from wavelength 500-700nm as said specific wavelength.

  Moreover, the manufacturing method of the polarizer of the said aspect WHEREIN: The manufacturing method which is a boron compound may be sufficient as the said crosslinking agent.

  Moreover, the manufacturing method of the polarizer of the said aspect WHEREIN: The manufacturing method which is a boric acid may be sufficient as the said boron compound.

  Moreover, the manufacturing method of the polarizer of the said aspect WHEREIN: The thickness may be 10 micrometers or less, and the manufacturing method currently formed on the thermoplastic resin base material may be sufficient as the said PVA-type resin film.

  Moreover, the manufacturing method of the manufacturing method of the polarizer of the said aspect WHEREIN: The density | concentration of the said crosslinking agent may be 0.01-0.1 weight part.

  Moreover, the manufacturing method of the polarizer of the said aspect WHEREIN: The manufacturing method which is an iodine may be sufficient as the said dichroic dye.

  In the method for manufacturing a polarizer according to the aspect described above, the concentration of the dichroic dye may be 0.01 to 10 parts by weight.

  Moreover, the manufacturing method of the polarizer of the said aspect WHEREIN: The manufacturing method containing potassium iodide may be sufficient as the said dyeing | staining liquid.

  Moreover, according to the aspect of this invention, it melt | dissolved in the said dyeing liquid when dyeing the said PVA-type resin film by immersing a polyvinyl alcohol (PVA) type-resin film in the dyeing liquid containing a dichroic dye. A method of detecting polyvinyl alcohol for detecting PVA, comprising: measuring the absorbance of the staining solution before dyeing the PVA resin film; and adding a cross-linking agent to the staining solution. A step of cross-linking PVA dissolved in the staining solution from a resin film; a step of measuring the absorbance of the staining solution after staining the PVA-based resin film; and the absorbance of the staining solution measured before the staining Quantifying the PVA dissolved in the staining solution based on a change in absorbance of the staining solution measured after staining Detection method of polyvinyl alcohol is provided.

  As described above, according to the aspect of the present invention, the PVA dissolved in the staining solution is quantitatively analyzed to optimize the renewal (exchange) time of the staining solution and stably manufacture the polarizer. It is possible to provide a method for producing a polarizer that makes it possible, and a method for detecting polyvinyl alcohol that makes it possible to detect PVA dissolved in a staining solution.

In 2nd Example, it is the graph which measured the change of the light absorbency of the dyeing | staining liquid when PVA was dissolved with respect to the dyeing | staining liquid containing a fixed boric acid.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In this 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 substrate and dried to form a laminate having a PVA resin layer (film). Then, the case where a polarizer having a thickness of 10 μm or less is manufactured by performing each treatment using the laminate as a raw fabric film will be described as an example.

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

  As a material constituting the thermoplastic resin base material, for example, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropic property, stretchability and the like is used. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyethersulfone resins, polysulfone resins, polycarbonate resins, and polyamides such as nylon and aromatic polyamide. Resin, polyimide resin, polyethylene resin, polyolefin resin such as polypropylene, ethylene / propylene copolymer, cyclic polyolefin resin having a cyclo or norbornene structure (norbornene resin), (meth) acrylic resin, polyarylate resin, polystyrene resin, polyvinyl Mention may be made of alcohol resins and mixtures thereof. In addition, the thermoplastic resin base material may be subjected to surface treatment (for example, corona treatment) in order to improve adhesion with the PVA resin layer, and a thin layer such as a primer layer (undercoat layer) may be provided. It may be formed.

  Thermoplastic resins can be broadly classified into those in which the polymer is in a crystalline state in which the polymer is regularly arranged and those in which the polymer has no regular arrangement, or in an amorphous or amorphous state with only a small part. The former is called a crystalline state, and the latter is called an amorphous or amorphous state. Correspondingly, a thermoplastic resin having a property of producing 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, regardless of whether the resin is a crystalline resin or an amorphous resin, 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. Here, an amorphous or amorphous resin is used in distinction from an amorphous resin having a property of not producing 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 it generally has a property that crystallization proceeds by arranging polymers by heating or stretching orientation. The physical properties of the resin vary depending on the degree of crystallization.

  On the other hand, for example, even with a crystalline resin such as polypropylene (PP) or polyethylene terephthalate (PET), crystallization can be suppressed by inhibiting the polymer arrangement caused by heat treatment or stretching orientation. These polypropylene (PP) and polyethylene terephthalate (PET) whose crystallization is suppressed are called amorphous polypropylene and amorphous polyethylene terephthalate. These are collectively called amorphous olefin resin and amorphous ester type. It is called resin.

  For example, in the case of polypropylene (PP), amorphous polypropylene (PP) in which crystallization is suppressed can be produced by using an atactic structure without stereoregularity. Further, for example, in the case of polyethylene terephthalate (PET), copolymerization of a modifying group such as isophthalic acid or 1,4-cyclohexanedimethanol as a polymerization monomer, that is, crystallization of polyethylene terephthalate (PET) is inhibited. By copolymerizing the molecules, amorphous polyethylene terephthalate (PET) with suppressed crystallization can be produced.

  The thickness of the thermoplastic resin substrate (before stretching) can be determined as appropriate, but is generally 10 to 500 μm from the viewpoints of workability such as strength and handleability, and thin layer properties. In particular, 20-300 micrometers is preferable and 30-200 micrometers is more preferable. The thickness of the thermoplastic resin substrate is particularly suitable when the thickness is 50 to 150 μm.

<Polyvinyl alcohol (PVA) resin layer (film)>
In the method for producing a polarizer to which the present invention is applied, a laminate including a PVA-based resin layer (film) is formed on the thermoplastic resin substrate. As the PVA-based resin, those having translucency in the visible light region and capable of dispersing and adsorbing dichroic substances such as iodine and dichroic dyes can be used without particular limitation.

  As the PVA resin, a PVA resin conventionally used as a polarizer is preferably used. As PVA-type resin, PVA or its derivative (s) can be mentioned. Examples of PVA derivatives include polyvinyl formal and polyvinyl acetal. In addition, olefins such as ethylene and propylene, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, and alkyl esters thereof, acrylamide, and the like can be used.

  The polymerization degree of PVA is preferably 100 to 10,000, and more preferably 1000 to 10,000. A saponification degree of 80 to 100 mol% is generally used.

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

<Laminated body (raw film)>
The laminate that becomes the raw film can be obtained by applying an aqueous solution containing a PVA resin to a thermoplastic resin substrate and then drying to form a PVA resin layer. Moreover, the structure by which the thermoplastic resin base material and the PVA-type resin layer were laminated | stacked through the primer layer may be sufficient as a laminated body. The laminate may be a structure in which a thermoplastic resin substrate and a PVA resin layer are directly laminated, or a laminate in which a substrate layer and a hydrophilic polymer layer are integrated.

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

  Application of aqueous solution on thermoplastic resin substrate is, for example, wire bar coating method, reverse coating, roll coating method such as gravure coating, spin coating method, screen coating method, fountain coating method, dipping method, spray method, die coating Method, comma coat method, lip coat method and the like can be appropriately selected and used.

  When the thermoplastic resin substrate has a primer layer, an aqueous solution is applied directly to the primer layer. On the other hand, when the thermoplastic resin substrate does not have a primer layer, an aqueous solution is applied directly to the substrate layer. In addition, it is preferable that a drying temperature shall be 50-200 degreeC, More preferably, it is 60-150 degreeC. The drying time is preferably 5 to 30 minutes.

  The PVA resin layer is formed in such a thickness that the thickness of the obtained polarizer is 10 μm or less in consideration of the draw ratio in the drawing treatment applied to the laminate. The thickness of the unstretched PVA resin layer is preferably 3 to 20 μm, and more preferably 5 to 15 μm.

<Processing process>
In the method for producing a polarizer to which the present invention is applied, at least a dyeing process and a stretching process are performed on the laminate (raw film). Moreover, in the manufacturing method of the polarizer to which this invention is applied, a crosslinking process can be performed. For the dyeing treatment, the crosslinking treatment and the stretching treatment, treatment baths of a dyeing bath, a crosslinking bath and a stretching bath can be used, respectively. When a treatment bath is used, a treatment liquid (aqueous solution or the like) corresponding to each treatment is used.

<Dyeing process>
In the dyeing process, the dyeing process is performed by adsorbing and orienting iodine or a dichroic dye to the PVA resin layer in the laminate. In the dyeing process, the dyeing process can be performed together with the stretching process.

  The dyeing process is performed by immersing the laminate in a dyeing solution in a dyeing bath (dyeing bath). As the staining solution, an iodine solution is generally used. As the iodine aqueous solution used as the iodine solution, an aqueous solution containing iodine ions with iodine and an iodide compound which is a dissolution aid is used.

  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 iodide. Titanium or the like can be used. As the iodide compound, potassium iodide is preferred. Further, the iodide compound used in the present embodiment is the same as the iodide compound when used in other steps.

  The iodine concentration in the iodine solution is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the solvent, more preferably 0.02 to 5 parts by weight, and still more preferably 0.1 to 1.0 parts by weight. Part. The iodide compound concentration is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 8 parts by weight with respect to 100 parts by weight of the solvent. In iodine staining, the temperature of the iodine solution is preferably 20 to 50 ° C, more preferably 25 to 40 ° C. The immersion time is preferably 10 to 300 seconds, more preferably 20 to 240 seconds. In addition, the dyeing | staining time can be immersed in arbitrary time so that the designated polarization degree or transmittance | permeability can be achieved.

<Extension process>
In the stretching step, either a dry stretching process or a wet stretching process can be used. In the stretching step, stretching is performed by uniaxially stretching the laminate. Uniaxial stretching may be either longitudinal stretching performed in the longitudinal direction of the laminate or transverse stretching performed in the width direction of the laminate.

  In transverse stretching, the film can be contracted in the longitudinal direction while stretching in the width direction. Examples of the transverse stretching method include a fixed end uniaxial stretching method in which one end is fixed via a tenter, and a free end uniaxial stretching method in which one end is not fixed.

  On the other hand, in the longitudinal stretching, for example, an inter-roll stretching method, a compression stretching method, a stretching method using a tenter, or the like can be used. Further, the stretching treatment can be performed in multiple stages. Furthermore, the stretching treatment can be performed by performing biaxial stretching, oblique stretching, or the like.

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

  The treatment liquid used in the wet stretching process can contain an iodide compound. When an iodide compound is contained in the treatment liquid, the iodide compound concentration is preferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight with respect to 100 parts by weight of the solvent. The treatment temperature in the wet stretching method is preferably 25 ° C. or higher, more preferably 30 to 85 ° C., and even more preferably 50 to 70 ° C. The immersion time is preferably 10 to 800 seconds, and more preferably 30 to 500 seconds. In addition, a stretching process can be performed together with the dyeing process and the crosslinking process.

  In the stretching step, the stretching process is performed so that the total stretching ratio is 4 to 8 times the original length of the laminate. The total draw ratio is preferably 5 to 7 times. The total draw ratio refers to the cumulative draw ratio including stretching in those steps when stretching is involved in steps other than the stretching step. The total draw ratio is appropriately determined in consideration of the draw ratio in other steps. When the total draw ratio is low, the orientation is insufficient and it is difficult to obtain a polarizer having high optical properties (polarization degree). On the other hand, when the total draw ratio is too high, stretch breakage tends to occur. Further, the polarizer becomes too thin, and the processability in the subsequent process may be reduced.

  In the stretching step, as described in “Patent No. 4751481”, a wet stretching process can be performed after the air auxiliary stretching process. The stretching temperature in the air auxiliary stretching treatment is preferably set to a high temperature of 60 to 180 ° C, and more preferably 95 to 150 ° C. Moreover, it is preferable to set it as 1.3-4 times, and, more preferably, the draw ratio in an air auxiliary extending | stretching process is set to 1.5-3 times. Moreover, it is preferable that the process temperature in the wet-type extending | stretching process given after an air auxiliary | assistant extending | stretching process shall be 50-80 degreeC, More preferably, it is 60-70 degreeC. The immersion time is preferably 5 to 120 seconds, more preferably 10 to 60 seconds. Moreover, it is preferable that the draw ratio in a wet-type extending | stretching process sets a total draw ratio to 4-7 times, More preferably, it is 5-6 times.

  In the stretching step, when the air auxiliary stretching process and the wet stretching process are included, it is preferable to perform the air auxiliary stretching process before the dyeing process and the wet stretching process after the dyeing process. In this case, the treatment bath used for the wet stretching treatment also serves as a crosslinking bath, and it is preferable to perform the crosslinking treatment together with the wet stretching treatment.

<Crosslinking process>
In the crosslinking step, a crosslinking treatment is performed using a boron compound as a crosslinking agent. The crosslinking treatment can be performed together with the dyeing treatment and the stretching treatment. Moreover, the crosslinking treatment can be performed in a plurality of times. As the boron compound, for example, boric acid, borax or the like can be used. The boron compound is generally used in the form of an aqueous solution or a water-organic solvent mixed solution.

  When using a boric acid aqueous solution, the boric acid concentration in the boric acid aqueous solution is preferably 1 to 10 parts by weight, more preferably 2 to 7 parts per 100 parts by weight of the solvent in order to impart heat resistance depending on the degree of crosslinking. Parts by weight. The boric acid aqueous solution or the like can contain an iodide compound such as potassium iodide. When the iodide compound is contained in the boric acid aqueous solution, the iodide compound concentration is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight with respect to 100 parts by weight of the solvent. .

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

<Insolubilization process>
In the method for producing a polarizer to which the present invention is applied, an insolubilization treatment can be performed before the laminate is subjected to a dyeing treatment or a crosslinking treatment. An insolubilization process aims at giving the insolubilization process for not dissolving a PVA-type resin layer.

  In the insolubilization step, 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 mixed solution.

  When using the boric acid aqueous solution, the boric acid concentration of the boric acid aqueous solution is preferably 1 to 4 parts by weight with respect to 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., and further preferably 30 to 60 ° C. The treatment time is preferably 5 to 800 seconds, more preferably 8 to 500 seconds.

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

  In the cleaning step, a cleaning process can be performed using a potassium iodide solution. The potassium iodide concentration 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 with respect to 100 parts by weight of the solvent. It is.

  In the washing treatment with a potassium iodide solution, the treatment temperature is preferably 5 to 60 ° C, more preferably 10 to 40 ° C. The immersion time is preferably 1 to 120 seconds, more preferably 3 to 90 seconds. There is no particular limitation on the stage of the washing treatment with the potassium iodide solution as long as it is before the drying treatment.

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

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

<Drying process>
Moreover, in the manufacturing method of the polarizer to which this invention is applied, after performing each process mentioned above, finally a drying process is performed and a polarizer is manufactured. In the drying process, an optimal drying time and drying temperature are set according to the moisture content required for the obtained polarizer (film). Specifically, the drying temperature is preferably 20 to 150 ° C, more preferably 40 to 100 ° C. If the drying temperature is too low, the drying time becomes longer, which is not preferable because efficient production cannot be performed. On the other hand, when the drying temperature is too high, the obtained polarizer is deteriorated and deteriorated in terms of optical characteristics and hue. The heat drying time is preferably 1 to 10 minutes.

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

  In the treatment with the treatment liquid containing a water-soluble antioxidant, at least one of the baths used for each treatment performed after the dyeing treatment on the laminate is made to contain a water-soluble antioxidant. Alternatively, a treatment with a treatment liquid containing a water-soluble antioxidant is separately performed. The treatment with the treatment liquid containing the water-soluble antioxidant is preferably performed together with the crosslinking treatment and / or the stretching treatment.

  In addition, a crosslinking process and an extending | stretching process can be performed by the batch process which performs a some process simultaneously. In a batch process in which a plurality of processes are performed simultaneously, a water-soluble antioxidant is contained in the bath used for the batch process. In a multistage process in which the crosslinking process and the stretching process are separately performed, a water-soluble antioxidant is contained in at least one of the crosslinking process and the stretching process.

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

  Examples of the salt include alkali metal salts such as sodium salt and potassium salt. Among these, ascorbic acid, erythorbate, thiosulfate, and sulfite are preferably used. These water-soluble antioxidants can be used alone or in combination of two or more.

  The addition amount of the water-soluble antioxidant is determined by the contamination concentration of the dichroic substance (iodine or dichroic dye) contained in each treatment liquid after the dyeing process. If the contamination concentration by the dichroic substance in the contaminated processing liquid is high, the amount of the water-soluble antioxidant to be added increases.

  It is preferable to add a water-soluble antioxidant to each treatment solution so that the concentration of the water-soluble antioxidant is 0.005 to 1 part by weight with respect to 100 parts by weight of the solvent. 005 to 0.5 parts 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 processing liquid decreases, and the characteristics of the obtained polarizer (single transmittance, polarization) Deterioration of the degree) cannot be sufficiently suppressed. On the other hand, when the concentration of the water-soluble antioxidant exceeds 1 part by weight, since the proportion of the water-soluble antioxidant in the bath increases, the resulting polarizer is decolored and the transmittance is increased. Along with this, there is a concern that the iodine concentration in the dye bath should be increased, but there is no problem such as a decrease in optical characteristics.

<Polarizer>
The polarizer produced by the method for producing a polarizer to which the present invention is applied is formed on a thermoplastic resin substrate, but an unstretched PVA resin layer film is used without using the thermoplastic resin substrate. It can also manufacture by giving each process mentioned above as an original fabric film. In this case, the thickness of the polarizer may be 10 μm or more, preferably 5 to 50 μm.

  The thermoplastic resin substrate can be used as it is as a transparent protective film for the polarizing plate described later. Moreover, a transparent protective film can be bonded to the surface of the polarizer opposite to the thermoplastic resin substrate. 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. Moreover, after peeling a thermoplastic resin base material from a polarizer, a transparent protective film can be bonded together on the both sides of the said polarizer.

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

<Analysis process>
By the way, in the manufacturing method of the polarizer to which this invention is applied, the dyeing liquid used at the said dyeing | staining process contains a crosslinking agent. As the crosslinking agent, for example, at least one kind may be used from boron compounds such as boric acid and borax, glyoxal, glutaraldehyde, or two or more kinds may be used in combination. Among them, it is preferable to use a boron compound, and it is more preferable to use boric acid.

  In the said dyeing | staining process, when a dyeing liquid contains a trace amount boric acid (crosslinking agent), this boric acid bridge | crosslinks (complexes) PVA which melt | dissolved in the dyeing liquid from the PVA-type resin layer. As a result, a gel-like iodine / PVA / boric acid complex (hereinafter referred to as a complex compound) in which PVA dissolved in the staining liquid is combined with iodine and boric acid in the staining liquid is generated.

  In order to crosslink (complex) the PVA dissolved in the staining solution, the concentration of boric acid (crosslinking agent) in the staining solution may be 0.01 to 0.1 parts by weight with respect to 100 parts by weight of the solvent. Preferably, it is 0.02 to 0.1 part by weight. If the concentration of boric acid is 0.01 parts by weight or more, PVA dissolved in the dyeing solution can be crosslinked (complexed). On the other hand, when the concentration of boric acid exceeds 0.2 parts by weight, boric acid is deposited on the surface of the laminate (raw film), the surface of the roll that transports the laminate (raw film), etc. May cause defects.

  As a method for adjusting the concentration of boric acid in the staining solution, a method of adding a predetermined amount of boric acid to the staining solution may be used. Moreover, when the processing bath containing a boric acid exists just before a dyeing process, the boric acid brought in with a laminated body from the processing 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 an analysis step, a part of the staining solution is extracted as a sample, and the absorbance of this sample is measured. Specifically, the sample is periodically extracted from the staining solution, and the absorbance of each sample is measured, and among the measured absorbance of each sample, the staining solution is determined based on the change over time in the absorbance at a specific wavelength. It is preferable to quantitatively analyze the PVA dissolved therein. The absorbance can be measured by, for example, a commercially available spectrophotometer. At this time, the sample may be diluted with an appropriate solvent.

  As the specific wavelength, it is preferable to select at least one wavelength from a wavelength of 500 to 700 nm. That is, it is preferable that this specific wavelength is a wavelength which shows the maximum value among the absorbance of each sample. In this 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 staining solution contains a small amount of boric acid (crosslinking agent), and this boric acid crosslinks (complexes) the PVA dissolved in the staining solution, so that this staining solution contains The amount of dissolved PVA can be easily monitored (quantified). Thereby, it is possible to accurately determine the renewal (replacement) timing of the staining liquid while avoiding problems such as conventional PVA adhesion and a decrease in the staining 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 part or all of the staining solution with the amount of the complex compound as a standard, preferably with the absorbance of the complex compound as a standard.

<Polyvinyl alcohol (PVA) detection method>
The detection method of polyvinyl alcohol (PVA) to which the present invention is applied is preferably used in the analysis step described above. That is, in this PVA detection method, before dyeing the PVA-based resin layer (PVA-based resin film), a step of performing a reference and measuring the absorbance of the staining solution, and adding the boric acid (crosslinking agent) to the staining solution The step of crosslinking the PVA dissolved in the staining solution from the PVA-based resin layer, the step of measuring the absorbance of the staining solution after staining the PVA-based resin layer, and the absorbance of the staining solution measured before staining Quantifying the PVA dissolved in the staining solution based on the change in the absorbance of the staining solution measured after the staining. When the polarizer is continuously produced, the staining solution during the staining process may be used as a reference sample or a target sample for PVA quantification, not only before and after the (temporal) staining process.

  In the detection method of PVA to which the present invention is applied, not only when the sample is periodically extracted from the staining solution and the absorbance of each sample is measured as in the analysis step described above, the staining solution measured before staining is used. Based on the change (difference) between the absorbance and the absorbance of the staining solution measured after staining, it is possible to quantify the PVA dissolved in the staining solution.

  Hereinafter, the effects of the present invention will be made clearer by examples. In addition, this invention is not limited to a following example, In the range which does not change the summary, it can change suitably and can implement.

[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 solution, and the boric acid contained in the dyeing solution is dissolved. Each sample of Examples 1-11 and the comparative example 1 which changed the quantity was produced. And about each sample, while measuring the light absorbency in wavelength 620nm, the presence or absence of the stain | pollution | contamination by a boric acid was observed visually. A summary of these is shown in Table 1 below.

Example 1
In Example 1, as a sample, dyeing was performed by dissolving 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 with respect to 100 parts by weight of water. A liquid was prepared.

  And the ultraviolet visible absorption spectrum of this dyeing | staining liquid was measured, and the light absorbency of wavelength 620nm derived from an iodine / PVA / boric acid complex was measured. The ultraviolet-visible absorption spectrum was measured using a spectrophotometer (UV-2450 manufactured by Shimadzu Corporation). In addition, the glass cell (optical path length: 1 mm) was used for the measurement. Moreover, after preparing this dyeing | staining liquid, the presence or absence of the boric acid deposited on the glass cell was observed visually.

(Example 2)
In Example 2, a staining solution similar to that in Example 1 was prepared except that 0.02 part by weight of boric acid was used as a sample. And about this dyeing | staining liquid, the same measurement and observation as Example 1 were performed.

(Example 3)
In Example 3, a dyeing solution similar to that in Example 1 was prepared except that 0.03 part by weight of PVA and 0.02 part by weight of boric acid were used as samples. And about this dyeing | staining liquid, the same measurement and observation as Example 1 were performed.

Example 4
In Example 4, a staining solution similar to Example 1 was prepared except that 0.05 part by weight of PVA and 0.02 part by weight of boric acid were used as samples. And about this dyeing | staining liquid, the same measurement and observation as Example 1 were performed.

(Example 5)
In Example 5, a staining solution similar to that in Example 1 was prepared except that 0.07 part by weight of boric acid was used as a sample. And about this dyeing | staining liquid, the same measurement and observation as Example 1 were performed.

(Example 6)
In Example 6, a staining solution similar to that in Example 1 was prepared except that boric acid was changed to 0.10 parts by weight as a sample. And about this dyeing | staining liquid, the same measurement and observation as Example 1 were performed.

(Example 7)
In Example 7, a staining solution similar to Example 1 was prepared except that boric acid was 0.2 parts by weight as a sample. And about this dyeing | staining liquid, the same measurement and observation as Example 1 were performed.

(Example 8)
In Example 8, a staining solution similar to that in Example 3 was prepared except that boric acid was changed to 0.07 parts by weight as a sample. And about this dyeing | staining liquid, the same measurement and observation as Example 1 were performed.

Example 9
In Example 9, a staining solution similar to that in Example 4 was prepared except that 0.07 part by weight of boric acid was used as a sample. And about this dyeing | staining liquid, the same measurement and observation as Example 1 were performed.

(Example 10)
In Example 10, a staining solution similar to that in Example 3 was prepared except that boric acid was changed to 0.10 parts by weight as a sample. And about this dyeing | staining liquid, the same measurement and observation as Example 1 were performed.

(Example 11)
In Example 11, as a sample, a staining solution similar to that in Example 4 was prepared except that boric acid was changed to 0.10 parts by weight. And about this dyeing | staining liquid, the same measurement and observation as Example 1 were performed.

(Comparative Example 1)
In Comparative Example 1, a staining solution similar to Example 1 was prepared as a sample except that boric acid was not contained. And about this dyeing | staining liquid, the same measurement and observation as Example 1 were performed.

  As shown in Table 1, in the samples of Examples 1 to 11 in which boric acid was contained in the staining solution, the absorbance at a wavelength of 620 nm was almost linear as the amount of PVA increased in each boric acid content sample. It can be seen that it increases. On the other hand, in the sample of Comparative Example 1 that did not contain boric acid in the staining solution, since complex formation was not performed, the wavelength compared to the samples of Examples 1 to 6 and Comparative Example 2 that contained boric acid in the staining solution. It can be seen that 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 staining 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 no contamination due to precipitation of boric acid was observed.

(Second embodiment)
Next, in the second example, a staining solution was prepared by dissolving 0.18 parts by weight of iodine, 1.26 parts by weight of potassium iodide, and 0.02 parts by weight of boric acid with respect to 100 parts by weight of water. . And the light absorbency of this dyeing | staining liquid was measured by the method similar to a 1st Example. Thereafter, the absorbance when 0.013 parts by weight, 0.029 parts by weight and 0.051 parts by weight of PVA were dissolved in this staining solution was measured by the same method as in the first example, and PVA was dissolved. The difference from the absorbance before the measurement was obtained. A summary of these is shown in FIG.

  As shown in FIG. 1, it can be seen that the absorbance increases as the amount of PVA dissolved in the staining solution increases. In particular, it can be seen that the maximum value of absorbance is shown at a wavelength of 620 nm. Therefore, by measuring the change in absorbance at the wavelength of 620 nm, it is possible to quantify the PVA dissolved in the staining solution. That is, according to the present invention, it is possible to grasp the replacement time of the liquid by quantifying the amount of PVA, and thus it is possible to stably manufacture a polarizer without color unevenness.

Claims (10)

A staining solution containing a dichroic dye, by immersing the polyvinyl alcohol (PVA) resin film undyed, a dyeing process for dyeing the PVA-based resin film,
An analytical step of extracting a part of the staining solution as a sample and quantitatively analyzing the PVA dissolved in the staining solution by measuring the absorbance of the sample,
The dyeing liquid contains a crosslinking agent ,
The concentration of the cross-linking agent is 0.01 to 0.1 part by weight with respect to 100 parts by weight of the solvent contained in the dyeing solution .   In the analysis step, the sample is periodically extracted from the staining solution, and the absorbance of each sample is measured, and among the measured absorbance of each sample, based on the change over time in absorbance at a specific wavelength, The method for producing a polarizer according to claim 1, wherein the PVA dissolved in the staining solution is quantitatively analyzed.   The method for manufacturing a polarizer according to claim 2, wherein at least one wavelength is selected from wavelengths of 500 to 700 nm as the specific wavelength.   The method for producing a polarizer according to claim 1, 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 thickness of the said PVA-type resin film is 10 micrometers or less, The manufacturing method of the polarizer as described in any one of Claims 1-5 currently formed on the thermoplastic resin base material. The method for producing a polarizer according to any one of claims 1 to 6 , wherein the dichroic dye is iodine. The concentration of the dichroic dye, the production method of a polarizer according to any one of the solvents 100 wt claim 1 from 0.01 to 10 parts by weight per part 7. The said dyeing | staining liquid is a manufacturing method of the polarizer as described in any one of Claims 1-8 containing potassium iodide. A staining solution containing a dichroic dye, by immersing the polyvinyl alcohol (PVA) resin film undyed polyvinyl alcohol for detecting the PVA dissolved in the dyeing liquid during the time of staining the PVA-based resin film Detection method,
Measuring the absorbance of the dye solution before dyeing the PVA resin film;
PVA dissolved in the dyeing liquid from the PVA-based resin film by adding 0.01 to 0.1 part by weight of a crosslinking agent to 100 parts by weight of the solvent contained in the dyeing liquid. Cross-linking the step;
After dyeing the PVA resin film , measuring the absorbance of the dyeing solution used for dyeing the PVA resin film ;
A method for detecting polyvinyl alcohol, comprising: quantifying PVA dissolved in the staining solution based on a change between the absorbance of the staining solution measured before the staining and the absorbance of the staining solution measured after the staining.

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