HK1192778B - Dye-based polarizing element and polarizing plate - Google Patents

Abstract

To develop a polarizing element having favorable polarizing characteristics and that is a pigment having an excellent blue dye without using a starting material belonging to specific chemical substances such as dianisidine. [Solution] The polarizing element, which contains dichroic pigments and comprises a film of a polyvinyl alcohol resin that has been stretched by a factor of at least three or a derivative thereof, is characterized by at least one of the dichroic pigments being the azo compound represented by formula (1) or a salt thereof, and the amount of the azo compound represented by formula (2) or a salt thereof contained being within 10% of the total amount of dichroic pigments.

Description

Dye-based polarizing element and polarizing plate

Technical Field

The present invention relates to a dye-based polarizing element and a polarizing plate using the same.

Background

The polarizing element is generally produced by adsorbing iodine or a dichroic dye, which is a dichroic dye, on a polyvinyl alcohol resin film and aligning the adsorbed iodine or dichroic dye. A protective film made of triacetyl cellulose or the like is bonded to at least one surface of the polarizer via an adhesive layer to form a polarizing plate, which is used in a liquid crystal display device or the like. A polarizing plate using iodine as a dichroic dye is called an iodine-based polarizing plate, and a polarizing plate using a dichroic dye as a dichroic dye is called a dye-based polarizing plate. Among them, the dye-based polarizing plate has a problem that, when compared with a polarizing plate having the same polarization degree, the dye-based polarizing plate has a lower transmittance than an iodine-based polarizing plate, that is, has a low contrast ratio, but has the following characteristics: pigments having high heat resistance, high humidity and heat resistance, high stability and various colors have been developed and blended to provide high color selectivity.

Conventionally, c.i. direct blue 15, 200, 202, 203 and the like have been known as dyes for dyeing papermaking materials and cellulosic fibers into a fast blue color, and are used in large amounts in the papermaking industry and the dyeing industry. However, the common disadvantages of these dyes are as follows: as a common problem when these dyes are used as raw materials, dianisidine used as a main raw material is a toxic chemical substance corresponding to the first class of specific chemical substances, and the pigment itself is a dianisidine-based pigment, so that when dianisidine is used, the labor safety and health law must be strictly followed, and it is necessary to perform work under very strict protective equipment, and the restriction factor is large in terms of safety and health control and improvement of production efficiency.

On the other hand, blue dyes other than dianisidine include c.i. direct blue 67, 78, 106, and 108, for example, and all have a disadvantage of significantly poor dyeing property (staining property) as compared with dianisidine-based blue dyes. That is, when dianisidine is not used, a blue dye having fastness and good dyeability is not easily obtained; therefore, although dianisidine is a toxic chemical corresponding to the first class of specific chemicals, and a lot of expenses are spent in the protection equipment for preventing its exposure to the workers, it is the present situation that blue dyes using dianisidine are widely manufactured and used. Accordingly, in the dye industry, the paper industry, and also in the development of polarizing plates, there has been a long-standing strong demand for obtaining a blue dye having high fastness and good dyeability without using a raw material corresponding to a specific chemical substance such as dianisidine. In particular, in the development of polarizing elements, it is difficult to achieve both a polarizing function and color and durability on the premise of having high polarizing characteristics.

In addition, in recent years, the intensity of a light source for optical use has increased, and this intense light and the heat generated therewith have caused a problem of discoloration of a polarizing plate, and there is an increasing demand for improvement thereof.

Documents of the prior art

Patent document

Patent document 1: japanese examined patent publication No. 64-5623

Patent document 2: japanese patent No. 2985408

Patent document 3: japanese laid-open patent publication No. 2004-075719

Non-patent document

Non-patent document 1: dye chemistry; thin field with high quality

Disclosure of Invention

Problems to be solved by the invention

Patent document 1 discloses an excellent blue dye which does not use a raw material belonging to a specific chemical substance such as dianisidine. Patent document 2 discloses a polarizing plate obtained by stretching a polyvinyl alcohol film containing the patent disclosed in patent document 1.

However, the dyes used in patent documents 1 and 2 have problems that the purity of the dye is low, a large amount of impurities are contained, and the polarization characteristics are low when the dyes are used as they are in order to use the dyes in a polarizing element.

Means for solving the problems

The present inventors have conducted detailed studies on impurities contained in a dye, and as a result, have found that a compound represented by formula (2) generated as an impurity causes a decrease in the degree of polarization of a film when producing a dye represented by formula (1), thereby completing the present invention.

[ solution 1]

[ solution 2]

Namely, the present invention relates to:

(1) a polarizing element comprising a film of a polyvinyl alcohol resin or a derivative thereof, which contains a dichroic dye and is stretched at a magnification of 3 times or more; the polarizing element is characterized in that at least one of the dichroic dyes is an azo compound represented by formula (1) or a salt thereof, and the content of the azo compound represented by formula (2) or the salt thereof is 10% or less relative to the total amount of the dichroic dyes;

[ solution 3]

[ solution 4]

(2) A polarizing plate, wherein a protective layer is provided on one side or both sides of the polarizing element described in (1);

(3) a method for manufacturing a polarizing element comprising a film of a polyvinyl alcohol resin or a derivative thereof, which contains a dichroic dye and is stretched at a magnification of 3 times or more; the method is characterized in that the content ratio of the azo compound represented by the formula (1) or the salt thereof as at least one of the dichroic dyes to the azo compound represented by the formula (2) or the salt thereof as at least one of the dichroic dyes is 9:1 to 10: 0.

ADVANTAGEOUS EFFECTS OF INVENTION

The polarizing element or polarizing plate of the present invention, which contains a dichroic dye in a polyvinyl alcohol resin or a derivative thereof, has good polarizing properties using a blue dye having good fastness and dyeing properties without using a raw material corresponding to a specific chemical substance such as dianisidine.

Detailed Description

The present invention is described in detail below. Hereinafter, the compound of formula (1) or a salt thereof is referred to as "pigment of formula (1)" and the compound of formula (2) or a salt thereof is referred to as "pigment of formula (2)".

The polarizing element of the present invention is a film which contains a polyvinyl alcohol resin or a derivative thereof and is stretched at a magnification of 3 times or more, wherein at least one of the dichroic dyes is a dye represented by the above formula (1). The dye represented by formula (1) has good polarization characteristics, but if the dye represented by formula (2) is contained as an impurity in the film, the polarization characteristics are greatly reduced. Therefore, the dye represented by formula (2) is preferably within 10%, preferably within 5%, more preferably within 3%, and even more preferably within 1% of the total amount of the compound of formula (1) and the compound of formula (2).

The "content" of the dye is a ratio measured by an area ratio based on high performance liquid chromatography (hereinafter, abbreviated as HPLC), which is a ratio relative to the total amount of the compound of formula (1) and the compound of formula (2), and is a ratio represented by a peak area ratio when 0.5g of a polyvinyl alcohol resin containing a dichroic dye is immersed in 50 wt% of pyridine water for 24 hours to extract the dye and then measured by HPLC.

When the dye represented by the formula (1) is dissolved in water and the solution is measured by HPLC, the concentration of the dye represented by the formula (2) in the dye is preferably 10% or less by area ratio. The dye represented by formula (2) is an impurity generated in the production process of formula (1) or the production process of a polarizing element, and is mainly generated when copper contained in the dye of formula (1) is dissociated. Therefore, the content of the pigment of formula (2) is preferably small. In the production of the polarizing element or the polarizing plate, the purity of the dye of formula (1) is preferably 90% or more, more preferably 95% or more, and still more preferably 98% or more. Therefore, the ratio of the dye of formula (1) to the dye of formula (2) is preferably 9:1 to 10: 0.

The dye of formula (1) is easily produced by: according to the general method for producing an azo dye described in non-patent document 1, it can be easily produced by performing known diazotization and coupling. As a specific production method, 2-aminonaphthalene-4, 8-disulfonic acid (common name: C acid) is diazotized by a known method, followed by coupling of 2-methoxy-4-methylaniline (パラクレシジン, para cresidine) at 10 ℃ to 20 ℃ and hydrolysis as necessary to obtain an aminoazo compound represented by the formula (3).

[ solution 5]

Next, the amino azo compound represented by the formula (3) is diazotized by a known method and base-coupled to 6-phenylamino 1-naphthol-3-sulfonic acid (common name: J acid) at 10 to 20 ℃ to obtain the disazo compound represented by the formula (4).

[ solution 6]

Next, for example, copper sulfate, ammonia water, aminoalcohol, and hexamethylenetetramine are added to carry out a cuprinization reaction at 85 to 95 ℃ to obtain a solution containing the pigment represented by the formula (1).

Then, the solution is evaporated to dryness or dried by salting out filtration, and pulverized to obtain a pigment represented by formula (1) of the present application in a powder form. The thus obtained tetra-compound represented by formula (1) (テトラキス compound) is usually used in the form of a sodium salt, but may be used in the form of a lithium salt, a potassium salt, an ammonium salt, an alkylamine salt, or the like.

Factors for producing the dye of formula (2) include the temperature at the time of evaporation to dryness, the solution at the time of salting out, the concentration of the solution, and the time until the dye is produced. The dye of formula (2) is generated also in the production of the polarizing element, depending on the steps such as the dyeing temperature, dyeing time, drying temperature after stretching, and drying time, which will be described later. The dye represented by formula (2) has low polarization characteristics, and the wavelength at which the transmittance is lowest differs between the transmittance when 2 polarizing plates including the polarizing element of formula (1) are stacked so that the absorption axes are orthogonal to each other and the transmittance when 2 polarizing plates including the polarizing elements of formula (1) and formula (2) are stacked so that the absorption axes are orthogonal to each other; in the case of containing the formula (2), the color is not blue but red, and thus purple or a color close thereto is obtained. In order to obtain a polarizing element having good polarizing properties, and in the case where a blue polarizing plate is required, the content of formula (2) in the polarizing element needs to be 10% or less with respect to formula (1). When the formula (2) is contained in an amount of 10% or more, good polarization characteristics and a preferable blue color cannot be obtained. Therefore, the content of the pigment represented by the formula (2) is preferably small.

The coloring matter represented by the formula (1) can correct the color tone and improve the polarizing performance by being used in combination with other organic coloring matters. The organic dye used in this case is a dye having absorption characteristics in a wavelength region different from the absorption wavelength region of the dye used in the present invention, and may have high polarization characteristics; the dichroic dye is not particularly limited as long as it can dye a hydrophilic polymer, and examples thereof include azo-based, anthraquinone-based, quinophthalone-based, and the like dichroic dyes, and further, pigments described by a color index can be exemplified. Examples thereof include: c.i. direct yellow 12, c.i. direct yellow 28, c.i. direct yellow 44, c.i. direct orange 26, c.i. direct orange 39, c.i. direct orange 107, c.i. direct red 2, c.i. direct red 31, c.i. direct red 79, c.i. direct red 81, c.i. direct red 247, c.i. direct green 80, c.i. direct green 59; and organic dyes described in Japanese patent laid-open Nos. 2001-33627, 2002-296417, 2003-215338, WO2004/092282, 2001-0564112, 2001-027708, 11-218611, 11-218610, and 60-156759. These organic dyes may be used in the form of an alkali metal salt (e.g., Na salt, K salt, Li salt), ammonium salt, or salt of an amine, in addition to the free acid. The dichroic dye is not limited to this, and a known dichroic compound may be used, but an azo dye is preferable. In addition to the dichroic dyes exemplified, other organic dyes may be used in combination as necessary.

The target polarizing element is different in the kind of organic dye to be blended depending on whether it is a neutral color polarizing element, a color polarizing element for a liquid crystal projector, or other color polarizing elements. The mixing ratio is not particularly limited, and the mixing amount can be arbitrarily set according to the requirements of the light source, durability, required color tone, and the like.

The dye represented by the formula (1) is a feature of the present invention in that it penetrates into the polyvinyl alcohol resin film. The method for producing the polyvinyl alcohol resin constituting the polarizing element is not particularly limited, and the polyvinyl alcohol resin can be produced by a known method. The polyvinyl alcohol resin can be produced, for example, by saponifying a polyvinyl acetate resin. Examples of the polyvinyl acetate resin include polyvinyl acetate as a vinyl acetate homopolymer, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of the other monomer copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The saponification degree of the polyvinyl alcohol resin is preferably 85 mol% to 100 mol%, and more preferably 95 mol% or more. The polyvinyl alcohol resin may be further modified, and for example, polyvinyl formal, polyvinyl acetal, or the like modified with aldehydes may be used. The polymerization degree of the polyvinyl alcohol resin is preferably 1,000 to 10,000, and more preferably 1,500 to 6,000.

A film obtained by forming the polyvinyl alcohol resin into a film was used as a base film (proto- フィルム). The method for forming the film of the polyvinyl alcohol resin is not particularly limited, and the film can be formed by a known method. In this case, the polyvinyl alcohol resin film may contain glycerin, ethylene glycol, propylene glycol, low molecular weight polyethylene glycol, or the like as a plasticizer. The amount of the plasticizer is preferably 5 to 20% by weight, more preferably 8 to 15% by weight. The thickness of the raw material film made of the polyvinyl alcohol resin is not particularly limited, but is, for example, preferably 5 to 150 μm, more preferably 10 to 100 μm.

First, the polyvinyl alcohol resin film is subjected to a swelling step. The swelling step is performed by immersing the polyvinyl alcohol resin film in a solution at 20 to 50 ℃ for 30 seconds to 10 minutes. The solution is preferably water. When the time required for producing the polarizing element is shortened, the dye swells even during the dyeing process of the dye, and thus the swelling step can be omitted.

The dyeing step is performed after the swelling step. The dyeing step is performed by immersing the polyvinyl alcohol resin film in a solution containing a dichroic dye to perform impregnation. The solution temperature in this step is preferably 5 to 60 ℃, more preferably 20 to 50 ℃, and particularly preferably 35 to 50 ℃. The time for immersing in the solution can be appropriately adjusted, and is preferably adjusted within a range of 30 seconds to 20 minutes, and more preferably 1 minute to 10 minutes. The dyeing method is preferably carried out by dipping in the solution, but may be carried out by applying the solution to a polyvinyl alcohol resin film.

The solution containing the dichroic dye may contain sodium chloride, sodium sulfate, anhydrous sodium sulfate, sodium tripolyphosphate, or the like as a dyeing assistant. The content of these compounds can be adjusted to any concentration depending on the time and temperature of dyeing property of the dye, and is preferably 0 to 5% by weight, more preferably 0.1 to 2% by weight, based on the content of each compound.

The method of incorporating the coloring matter may be carried out by immersing the film in a solution containing the dichroic coloring matter, or may be a method of incorporating the coloring matter in a stage of molding a raw film (original film) of the polyvinyl alcohol resin film.

After the dyeing step, a washing step (hereinafter referred to as washing step 1) may be performed before proceeding to the next step. The cleaning step 1 is a step of cleaning the dye solvent adhering to the surface of the polyvinyl alcohol resin film in the dyeing step. By performing the washing step 1, the dye can be prevented from transferring to the liquid to be treated next. Water is generally used for the cleaning step 1. The cleaning method is preferably immersion in the solution, and the solution may be applied to a polyvinyl alcohol resin film to clean the film. The time for cleaning is not particularly limited, but is preferably 1 to 300 seconds, more preferably 1 to 60 seconds. The temperature of the solvent in the cleaning step 1 needs to be a temperature at which the hydrophilic polymer is not dissolved. The washing treatment is usually carried out at 5 to 40 ℃.

After the dyeing step or the washing step 1, a step of adding a crosslinking agent and/or a water-resistant agent may be performed. As the crosslinking agent, for example, there can be used: boron compounds such as boric acid, borax, or ammonium borate; polyaldehydes such as glyoxal and glutaraldehyde; a polyisocyanate compound such as a biuret type, an isocyanurate type or a blocked type; titanium compounds such as titanyl sulfate, etc., and ethylene glycol glycidyl ether, polyamide epichlorohydrin, etc. can also be used. Examples of the water-resistant agent include succinic peroxide, ammonium persulfate, calcium perchlorate, benzoin ethyl ether, ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ammonium chloride, and magnesium chloride, and boric acid is preferably used. The step of containing the crosslinking agent and/or the water-resistant agent is performed using at least one of the crosslinking agent and/or the water-resistant agent described above. The solvent in this case is preferably water, but is not limited to water. In the step of containing the crosslinking agent and/or the water-resistant additive, the concentration of the crosslinking agent and/or the water-resistant additive in the solvent is preferably 0.1 to 6.0% by weight, more preferably 1.0 to 4.0% by weight, based on the solvent, in boric acid, for example. The temperature of the solvent in this step is preferably 5 to 70 ℃ and more preferably 5 to 50 ℃. In the method of incorporating the crosslinking agent and/or the water resistance agent into the polyvinyl alcohol resin film, it is preferable to dip the polyvinyl alcohol resin film in the solution, and the solution may be coated (painted) or coated (painted) onto the polyvinyl alcohol resin film. The treatment time in this step is preferably 30 seconds to 6 minutes, more preferably 1 minute to 5 minutes. However, it is not essential to contain a crosslinking agent and/or a water-resistant agent, and the treatment step may be omitted when the time is to be shortened or when the crosslinking treatment or the water-resistant treatment is not necessary.

After the dyeing step, the washing step 1, or the step of adding a crosslinking agent and/or a water-resistant agent, the stretching step is performed. The stretching step is a step of uniaxially stretching the polyvinyl alcohol film. The stretching method may be either a wet stretching method or a dry stretching method, and the stretching ratio may be 3 times or more from the initial length, thereby achieving the present invention. The stretching ratio may be 3 times or more, preferably 5 to 7 times, from the initial length.

In the case of the dry stretching method, when the stretching heating medium is an air medium, the stretching is preferably performed at a temperature of the air medium of from room temperature to 180 ℃. The treatment is preferably performed in an atmosphere of 20% RH to 95% RH with respect to humidity. Examples of the heating method include, but are not limited to, a roll zone-drawing method (ゾーン rolling zone-drawing) in a cell of ロール, a roll heating stretching method, a pressure stretching (press stretching) method, an infrared heating stretching method, and the like. The stretching step may be 1-stage stretching or may be performed by 2-stage or more multistage stretching.

In the case of the wet stretching method, stretching is performed in water, a water-soluble organic solvent, or a mixed solution thereof. It is preferable to dip the film in a solution containing a crosslinking agent and/or a water-resistant agent while performing the stretching treatment. As the crosslinking agent, for example: boron compounds such as boric acid, borax, or ammonium borate; polyaldehydes such as glyoxal and glutaraldehyde; a polyisocyanate compound such as a biuret type, an isocyanurate type or a blocked type; titanium compounds such as titanyl sulfate, etc., and ethylene glycol glycidyl ether, polyamide epichlorohydrin, etc. can also be used. Examples of the water-resistant agent include succinic peroxide, ammonium persulfate, calcium perchlorate, benzoin ethyl ether, ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ammonium chloride, and magnesium chloride. Stretching may be performed in a solution containing at least one or more of the crosslinking agents and/or the water resistance agents shown above. The crosslinking agent is preferably boric acid. The concentration of the crosslinking agent and/or the water resistance improver in the stretching step is, for example, preferably 0.5 to 15 wt%, more preferably 2.0 to 8.0 wt%. The stretching ratio is preferably 2 to 8 times, and more preferably 5 to 7 times. The stretching temperature is preferably 40 to 60 ℃ and more preferably 45 to 58 ℃. The stretching time is usually 30 seconds to 20 minutes, and more preferably 2 minutes to 5 minutes. The wet stretching step may be performed by 1-stage stretching or 2-stage or more stretching.

After the stretching step, a cleaning step (hereinafter referred to as a cleaning step 2) of cleaning the film surface can be performed because the crosslinking agent and/or the water resistant agent are precipitated on the film surface or foreign matter is attached to the film surface. The washing time is preferably 1 second to 5 minutes. The cleaning method is preferably immersion in a cleaning solution, and cleaning may also be performed by coating (painting) or coating (painting) the solution to the polyvinyl alcohol resin film. The cleaning treatment may be performed in 1 stage, or may be performed in 2 or more stages. The temperature of the solution in the washing step is not particularly limited, but is usually 5 to 50 ℃ and preferably 10 to 40 ℃.

Examples of the solvent used in the treatment steps include: water; dimethyl sulfoxide; n-methyl pyrrolidone; alcohols such as methanol, ethanol, propanol, isopropanol, glycerol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane; and amines such as ethylenediamine and diethylenetriamine, but not limited thereto. Furthermore, mixtures of 1 or more of these solvents can also be used. The most preferred solvent is water.

The film drying step is performed after the stretching step or the cleaning step 2. The drying treatment may be performed by natural drying, and in order to further improve the drying efficiency, the surface water may be removed by compression with a roller, by an air knife, a water suction roller, or the like, and/or may be air-dried. The drying temperature is preferably 20 to 100 ℃ and more preferably 60 to 100 ℃. The drying treatment time may be applied for 30 seconds to 20 minutes, preferably 5 minutes to 10 minutes.

The polyvinyl alcohol resin film polarizing element having improved durability according to the present invention can be obtained by the above method. The film adsorbing the dichroic dye in the polarizing element is not a polyvinyl alcohol resin, but a film obtained from an amylose resin, a starch resin, a cellulose resin, a polyacrylate resin, or the like, and the same polarizing element can be produced by orienting a hydrophilic resin by stretching, shear orientation, or the like, by containing the dichroic dye, but a polarizing element film formed of a polyvinyl alcohol resin film is most preferable.

The polarizing plate was produced by providing a transparent protective layer on one side or both sides of the obtained polarizing element. The transparent protective layer can be provided as a coating layer produced from a polymer, or as a laminate of films. As the transparent polymer or film forming the transparent protective layer, a transparent polymer or film having high mechanical strength and good thermal stability is preferable. Examples of the transparent protective layer include: cellulose acetate resins such as triacetyl cellulose and diacetyl cellulose, and films thereof; an acrylic resin or a film thereof; a polyvinyl chloride resin or a film thereof; nylon resin or a film thereof; polyester resins or films thereof; a polyarylate resin or a film thereof; cyclic polyolefin resins based on cyclic olefins such as norbornene or films thereof; polyethylene, polypropylene; a polyolefin having a cyclic system or a norbornene skeleton or a copolymer thereof; a resin or polymer having an imide and/or amide as a main chain or a side chain, a film thereof, or the like. Further, as the transparent protective layer, a resin having liquid crystallinity or a film thereof may be provided. The thickness of the protective film is, for example, about 0.5 μm to 200 μm. The polarizing plate is produced by providing 1 or more layers of the same or different resins or films on one or both surfaces.

In the above, an adhesive is required to bond the transparent protective layer to the polarizer. The binder is not particularly limited, and a polyvinyl alcohol-based binder is preferable. Examples of the polyvinyl alcohol-based adhesive include, but are not limited to, Gohsenol NH-26 (manufactured by Nippon synthetic Co., Ltd.), Exceval RS-2117 (manufactured by KURARAAY Co., Ltd.). A crosslinking agent and/or a water resistant agent may be added to the cement. The polyvinyl alcohol-based adhesive is a mixture of a maleic anhydride-isobutylene copolymer and, if necessary, a crosslinking agent. Examples of the maleic anhydride-isobutylene copolymer include Isobam # 18 (manufactured by KURAAY corporation), Isobam # 04 (manufactured by KURAAY corporation), ammonia-modified Isobam # 104 (manufactured by KURAAY corporation), ammonia-modified Isobam # 110 (manufactured by KURAAY corporation), imidized Isobam # 304 (manufactured by KURAAY corporation), and imidized Isobam # 310 (manufactured by KURAAY corporation). In this case, a water-soluble polyepoxy compound may be used as the crosslinking agent. Examples of the water-soluble polyvalent epoxy compound include Denacol EX-521 (manufactured by Nagase ChemteX Co., Ltd.), and tetra-C (テトラット -C, manufactured by Mitsui gas chemical Co., Ltd.). As the adhesive other than the polyvinyl alcohol resin, known adhesives such as urethane, acrylic, and epoxy adhesives may be used. In addition, additives such as zinc compounds, chlorides, and iodides may be added to the adhesive at a concentration of about 0.1 to 10 wt% for the purpose of improving the adhesion of the adhesive or improving water resistance. The additive is not limited. After the transparent protective layer is bonded with an adhesive, the resultant is dried or heat-treated at an appropriate temperature to obtain a polarizing plate.

The obtained polarizing plate may be provided with various functional layers for improving the visibility and/or the contrast, or a layer or film having a luminance improving property on the surface of a protective layer or film which is a non-exposed surface, depending on the case, for example, when the polarizing plate is bonded to a display device such as a liquid crystal display or an organic electroluminescence display. In order to bond these polarizing plates to a film or a display device, an adhesive is preferably used.

The polarizing plate may have various known functional layers such as an antireflection layer, an antiglare layer, and a hard coat layer on the other surface, that is, on the exposed surface of the protective layer or the film. In order to produce the layers having various functionalities, a coating method is preferred, and the functional film may be bonded by an adhesive or a sticking agent. Further, the various functional layers may be layers or films for controlling phase difference.

The above method can provide a polarizing element and a polarizing plate of the present invention having excellent blue dye without using a raw material corresponding to a specific chemical substance such as dianisidine, and having good polarization characteristics and high durability. A display panel using the polarizing element or the polarizing plate of the present invention has high reliability, high contrast for a long period of time, and high color reproducibility.

The polarizing element or polarizing plate of the present invention thus obtained is used as a polarizing plate with a protective film, a protective layer, a functional layer, a support, and the like as needed, in a liquid crystal projector, a desktop computer, a watch, a notebook computer, a word processor, a liquid crystal television, a polarizing lens, polarizing glasses, a satellite navigation device, an indoor/outdoor instrument, a display, and the like.

Examples

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. The transmittance and the degree of polarization shown in the examples were evaluated as follows.

Protective films were bonded to both surfaces of the original polarizing film (base film), and the transmittance when the obtained 2 polarizing plates were stacked with their absorption axes in the same direction was represented by parallel transmittance Tp, and the transmittance when the 2 polarizing plates were stacked with their absorption axes orthogonal to each other was represented by orthogonal transmittance Tc.

The polarization degree Py is obtained from the parallel transmittance Tp and the orthogonal transmittance Tc by the following equation.

Py＝{(Tp－Tc)/(Tp+Tc)}1/2×100

The transmittances were measured by using a spectrophotometer ("U-4100" manufactured by Hitachi Ltd.).

Synthesis example 1

< preparation of dye solution >

32.5 parts of 2-aminonaphthalene-4, 8-disulfonic acid (conventional name: C acid) was dissolved in 145 parts of water, and the solution was added to 140 parts of water containing 26 parts of 35% hydrochloric acid, and 6.9 parts of sodium nitrite was added thereto at 15 ℃ to 20 ℃ to conduct diazotization for 1 hour. Then, an aqueous solution containing 13.7 parts of 2-methoxy-4-methylaniline and 17.5 parts of 35% hydrochloric acid was added thereto, and the mixture was coupled at 20 ℃ for 4 hours while maintaining pH3.0 to 3.5 with sodium acetate until the 2-methoxy-4-methylaniline was not confirmed by a spot test. Then, 21.4 parts of 35% hydrochloric acid, 6.9 parts of sodium nitrite at 10 ℃ and 2-3 hours at 15 to 20 ℃ are added to the amino azo compound to conduct diazotization 2 times. Subsequently, the mixture was added to an aqueous solution containing 31.5 parts of phenyl J acid, 125 parts of water and 11 parts of sodium carbonate (ソーダ ash), and a sodium carbonate solution was further added thereto, and while maintaining pH at 8.5 to 9.5, coupling was performed for 2 times at 20 ℃ for 3 hours until no diazotization matter was confirmed in the spot test, to obtain a disazo compound. Next, a copper complex salt obtained by adding 30.5 parts of monoethanolamine to 25 parts of copper sulfate aqueous solution was added, and a cuprinization reaction was performed at 95 ℃ for 10 hours until no unreacted substance was detected by thin layer chromatography, thereby preparing a solution containing 20% by weight of the dye represented by formula (1).

Example 1

< preparation of polarizing element >

A polyvinyl alcohol resin film (VF series, manufactured by KURARAAY corporation) having a saponification degree of 99% or more and a film thickness of 75 μm was immersed in warm water at 40 ℃ for 2 minutes to carry out a swelling treatment. The membrane after swelling treatment was immersed in a 20 wt% aqueous solution of a dye represented by formula (1) using 25 wt% disproportionation salt (サヌキ salt (Sanuki salt)), dried at 60 ℃ and then in a 45 ℃ aqueous solution containing 0.05 wt% of dried dye powder (HPLC purity 98.2%) and 0.1 wt% of sodium tripolyphosphate to adsorb the dye. The dye-adsorbed film was washed with water, and after washing, boric acid treatment was performed for 1 minute with a 40 ℃ aqueous solution containing 2 wt% boric acid. The film obtained by the boric acid treatment was stretched 5.0 times and treated in an aqueous solution containing 3.0 wt% boric acid at 55 ℃ for 5 minutes. The film obtained by the boric acid treatment was washed with water at 30 ℃ for 15 seconds while maintaining the tension state. The film obtained by the treatment was immediately dried at 70 ℃ for 9 minutes to obtain a polarizer having a film thickness of 28 μm.

The obtained polarizing element was dissolved and subjected to HPLC measurement, and the purity of the dye represented by formula (1) in the film was 99.2%.

The obtained polarizing element and an alkali-treated triacetyl cellulose film (TD-80U manufactured by Fuji film Co., Ltd., hereinafter abbreviated as "TAC") having a film thickness of 80 μm were laminated using a polyvinyl alcohol-based adhesive in the composition of polarizing element/adhesive layer/TAC to obtain a polarizing plate. The polarizing plate thus obtained was cut into 40mm × 40mm pieces, and bonded to a 1mm transparent glass plate with a polarizing element/adhesive layer/TAC/adhesive layer/transparent glass plate configuration by an adhesive PTR-3000 (manufactured by Nippon chemical Co., Ltd.) to prepare an evaluation sample.

Comparative example 1

Salting out a 20 wt% solution containing the dye represented by the formula (1) used in example 1 with 25 wt% of common salt; the temperature during drying was adjusted to 90 ℃ and the dried pigment powder (HPLC purity 87.9%) was used; other than this, a polarizing element was produced in the same manner. The pigment powder after drying contained 7.5% of the pigment represented by the formula (2). The obtained polarizing element was dissolved and subjected to HPLC measurement, and the purity of the dye represented by formula (1) in the film was 88.7%.

Table 1 shows the wavelength at which the evaluation samples obtained in examples and comparative examples have the maximum polarization degree, and the contrast indicating the brightness calculated by dividing the parallel transmittance, the orthogonal transmittance, the polarization characteristics, and the parallel transmittance by the orthogonal transmittance at that wavelength.

[ Table 1]

As shown in table 1, the polarizing plate of the present invention exhibited high polarization degree and high contrast, while the polarization degree in the comparative example was low, reduced by about 2%, and the contrast was low, about 1 in 4. Accordingly, the polarizing plate of example 1 of the present invention has a high polarization ratio, and when used in a liquid crystal projector, a desktop computer, a watch, a notebook computer, a word processor, a liquid crystal television, a polarizing lens, polarizing glasses, a satellite navigation system, an indoor/outdoor instrument, a display, or the like, a liquid crystal display instrument, a lens, or the like having a high contrast and high stability can be obtained without using a dye belonging to a specific chemical substance such as dianisidine.

Claims (2)

1. A polarizing element comprising a film of a polyvinyl alcohol resin or a derivative thereof, which contains a dichroic dye and is stretched at a magnification of 3 times or more,

the polarizing element is characterized in that at least one of the dichroic dyes is an azo compound represented by formula (1) or a salt thereof, the content of the azo compound represented by formula (2) or the salt thereof is within 10% of the total amount of the dichroic dyes,

2. a polarizing plate provided with a protective layer on one side or both sides of the polarizing element according to claim 1.