JP6779013B2 - Polarizing elements and polarizing plates with uniform transmittance at each wavelength - Google Patents

Description

The present invention relates to a polarizing element and a polarizing plate having uniform transmittance at each wavelength.

The polarizing element is generally manufactured by adsorbing and orienting iodine or a dichroic dye, which is a dichroic dye, on a polyvinyl alcohol resin film. A protective film made of triacetyl cellulose or the like is attached to at least one surface of the polarizing element via an adhesive layer to form a polarizing plate, which is used in liquid crystal display devices and the like. A polarizing plate using iodine as a dichroic dye is called an iodine-based polarizing plate, while a polarizing plate using a dichroic dye as a dichroic dye is called a dye-based polarizing plate. Of these, dye-based polarizing plates have high heat resistance, high humidity heat durability, and high stability, and are characterized by high color selectivity depending on the composition, while iodine-based polarized light having the same degree of polarization. There is a problem that the transmittance is low as compared with the plate, that is, the contrast is low. When the conventional polarizing elements are installed parallel to the absorption axis to show white color, the transmittance at 380 nm to 480 nm is lower than the transmittance at 500 nmm to 600 nm, and the emission uniformity at each wavelength cannot be maintained. It was. Therefore, for example, when the absorption axes of the polarizing elements are installed in parallel, an attempt has been made to improve each wavelength transmittance so as to have a constant transmittance. However, even in this case, when installed on an axis orthogonal to the absorption axis, there is a problem that the wavelength of 380 nm to 480 nm, particularly the wavelength of 460 nm, becomes higher than the transmittance near 550 nm, which has high visibility, and the contrast is lowered. there were. Therefore, as a polarizing element or a polarizing plate, a polarizing element or a polarizing plate capable of keeping each wavelength transmittance in the visible region constant while having high polarization performance, that is, high contrast has been required.

JP 2005-49698 JP-A-2005-202367

Application of functional dyes 1st printing edition, CMC Publishing Co., Ltd., supervised by Masahiro Irie, P98-100

A method for making the transmittance of the polarizing plate constant at each wavelength is disclosed in, for example, Patent Document 1 or Patent Document 2. Patent Document 1 discloses a technique for a polarizing element having a thickness of 8 to 18 μm and having a transmittance of 0.001% to 0.1% when cross-nicoled at 410 nm. However, this technique only improves color loss and hue at orthogonal positions, and does not improve each wavelength transmittance at parallel positions. Patent Document 2 discloses a technique of a polarizing element made of a film having a structure in which minute regions are dispersed in a matrix formed of a water-soluble resin containing a divalent metal. However, even with this technique, a polarizing element or a polarizing plate having a constant transmittance at each wavelength of the parallel position and the orthogonal position has not been obtained.

The present inventor has completed the present invention as a result of diligent studies to solve the above problems.

That is, the present invention
"(1) A polarizing element made of a hydrophilic polymer adsorbed and stretched with boric acid and containing a base material containing iodine and having a polarizing function.
The luminosity factor correction single transmittance Ys when the base material is measured by itself is 40.0% to 42.5%.
The difference between the luminosity factor correction single transmittance Ys and the single transmittance Ts _{460 at 460} nm is within 1%.
The difference between the luminosity factor correction single transmittance Ys and the single transmittance Ts _{550 at 550} nm is within 1%.
The difference between the luminosity factor correction single transmittance Ys and the single transmittance Ts _{610 at 610} nm is within 1%.
A polarizing element characterized in that the luminosity factor correction orthogonal transmittance Yc is 0.01% or less when the two substrates are measured orthogonally to the absorption axis direction;
(2) The luminosity factor correction parallel transmittance Yp when the two substrates are measured parallel to the absorption axis direction is in the range of 33% to 37%.
The difference between the parallel transmittance Yp and the parallel transmittance Tp _{460 at 460} nm when the two substrates are measured parallel to the absorption axis direction is within 3%. 1) The polarizing element;
(3) The luminosity factor correction parallel transmittance Yp when the two base materials are measured parallel to the absorption axis direction is in the range of 33% to 37%.
The parallel transmittance Yp and the transmittance Tp _{295 of 295} nm when the two substrates are measured parallel to the absorption axis direction satisfy the following formula (1) and
The above-mentioned (1), wherein the parallel transmittance Yp and the transmittance Tp _{360 of 360} nm when the two substrates are measured parallel to the absorption axis direction satisfy the following formula (2). The polarizing element according to 1) or (2);
1.05 × Yp-26 ≦ Tp ₂₉₅ ≦ 1.05 × Yp-13 ・ ・ ・ Equation (1)
1.25 × Yp-26.25 ≦ Tp ₃₆₀ ≦ 1.25 × Yp-16.25 ・ ・ ・ Equation (2)
(4) The transmittance Tc _{295 at 295} nm when the two substrates are measured orthogonally to the absorption axis direction satisfies the following formula (3) and
Any of the above (1) to (3), wherein the transmittance Tc _{360 at 360} nm when the two substrates are measured parallel to the absorption axis direction satisfies the following formula (4). The polarizing element according to item 1;
2.0 × 10 ^-30 × Yp ^18.6 ≦ Tc ₂₉₅ ≦ 2.0 × 10 ^-30 × Yp ^19.4・ ・ ・ Equation (3)
4.0 × 10 ⁻³⁷ × Yp ^22.12 ≦ Tc ₃₆₀ ≦ 4.0 × 10 ⁻³⁷ × Yp ^22.67・ ・ ・ Equation (4)
(5) The transmittance Tc _{460 at 460} nm when the two substrates are measured orthogonally to the absorption axis direction is 0.035% or less, and
Any of the above (1) to (4), characterized in that the transmittance Tc _{610 at 610} nm is 0.01% or less when the two substrates are measured orthogonally to the absorption axis direction. The polarizing element according to item 1;
(6) The base material is made of a polyvinyl alcohol-based resin film.
The polarizing element according to any one of (1) to (5) above, wherein the polyvinyl alcohol-based resin film has a degree of polymerization of 3000 to 7000.
(7) A polarizing plate having a support film provided on at least one side of the polarizing element according to any one of (1) to (6) above;
(8) A liquid crystal display device including the polarizing element according to any one of (1) to (6) above or the polarizing plate according to (7) above;
(9) A method for producing a polarizing element, which is made of a hydrophilic polymer adsorbed and stretched with boric acid and contains a base material containing iodine and having a polarizing function.
(I) A step of adding a dichroic dye to a polyvinyl alcohol-based resin film to obtain a film containing the dichroic dye.
(Ii) A step of stretching a film containing the dichroic dye to obtain a stretched film.
(Iii) A step of subjecting the stretched film to a post-treatment using a chloride-containing solution or an iodide-containing solution.
(Iv) The step of drying the film after the post-treatment to obtain the base material is included.
A production method, wherein the concentration of the chloride-containing solution or the iodide-containing solution is 0.1 to 15% by weight. "
Regarding.

The present invention relates to a polarizing element and a polarizing plate having a constant transmittance at each wavelength, and the polarizing element and the polarizing plate have a high transmittance, a high contrast ratio, and a very high color reproducibility. It can be used as a polarizing plate for a display, particularly a polarizing plate for a liquid crystal display.

<Polarizing element>
As a method for producing the polarizing element of the present invention, for example, a step of swelling a hydrophilic polymer film, then a dyeing step of containing a dichroic dye, then a water-resistant treatment step if necessary, and then a stretching step are performed. Then, a method of producing through a post-treatment step and finally a drying step can be mentioned.

Examples of the hydrophilic polymer film used for the polarizing element include a film made of a polyvinyl alcohol-based resin, an amylose-based resin, a starch-based resin, a cellulose-based resin, a polyacrylate-based resin, and the like, and cast these resins and the like. Use a film formed in the form of a film. Among these, a polyvinyl alcohol-based resin (hereinafter, may be abbreviated as “PVA”) film is preferable. In the present invention, a polarizing element composed of a polyvinyl alcohol-based resin film and a dichroic substance such as iodine is most preferable. The thickness of these polarizing elements is not particularly limited, but is generally about 5 to 80 μm.

The method for producing the polyvinyl alcohol-based resin is not particularly limited, and can be produced by a known method. For example, a polyvinyl alcohol-based resin can be obtained by saponifying a polyvinyl acetate-based resin. Here, examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and a copolymer of vinyl acetate and another monomer copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers and unsaturated sulfonic acids. This polyvinyl alcohol-based resin may be further modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes can also be used. A film made of a polyvinyl alcohol-based resin is used as a polyvinyl alcohol-based resin film.

In order to improve the optical properties of the present invention, the degree of polymerization of PVA needs to be 3000 to 10000, and if the degree of polymerization of PVA is less than 3000, it is difficult to exhibit high polarization performance. Become. When the degree of polymerization exceeds 7,000, PVA becomes hard, film forming property and stretchability decrease, and productivity decreases. Therefore, from an industrial point of view, it is preferably 10,000 or less.

The degree of polymerization of PVA means the degree of polymerization (viscosity average degree of polymerization) measured as follows.
0.28 g of PVA is dissolved in 70 g of distilled water at 95 ° C. to prepare a 0.4% PVA aqueous solution and cooled to 30 ° C. It is cooled in a constant temperature water bath at 30 ° C. to prepare a sample for measuring the degree of polymerization. Next, 10 mL of the sample for measuring the degree of polymerization is dried in an evaporating dish in a dryer at 105 ° C. for 20 hours, and the weight [α (g)] of the sample for measuring the degree of polymerization after drying is measured. The concentration C (g / L) of the sample for measuring the degree of polymerization is calculated by the following formula (i).

Further, a sample for measuring the degree of polymerization or distilled water is put into an Ostwald viscometer with a 10 mL volumetric pipette and stabilized in a constant temperature water bath at 30 ° C. for 15 minutes. Measure the number of seconds of dropping t ₁ (seconds) of the input sample for measuring the degree of polymerization and the number of seconds of dropping t ₀ (seconds) of distilled water, and calculate the viscosity average degree of polymerization E by the following formulas (ii) to (iv). To do.

The degree of saponification of PVA is preferably 99 mol% or more, more preferably 99.5 mol% or more. If the degree of saponification is less than 99 mol%, PVA is likely to elute, inducing in-plane unevenness in optical characteristics, deterioration of dyeability in the dyeing process, and cutting in the stretching process, which significantly reduces productivity. There is a risk and it is not preferable.

The PVA used in the present invention can be produced by saponifying a polyvinyl ester-based polymer obtained by polymerizing a vinyl ester. Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatic acid, vinyl laurate, vinyl stearate, vinyl benzoate, and the like. Select one or more. Of these, vinyl acetate is preferably used. The polymerization temperature is not particularly limited, but when methanol is used as the polymerization solvent, the boiling point of methanol is around 60 ° C., so it is preferably around 60 ° C. PVA is not limited to the saponified product of the homopolymer of vinyl ester as long as the effect of the present invention is not impaired. For example, modified PVA vinyl ester obtained by graft-copolymerizing PVA with unsaturated carboxylic acid or its derivative, unsaturated sulfonic acid or its derivative, α-olefin having 2 to 30 carbon atoms, etc. at a ratio of less than 5 mol%, and unsaturated. Carboxylic acid or a derivative thereof, unsaturated sulfonic acid or a derivative thereof, α-olefin having 2 to 30 carbon atoms, etc., copolymerized in a proportion of less than 15 mol%, a saponified polyvinyl ester, 1 formalin, butyl aldehyde, benzaldehyde, etc. It may be a polyvinyl acetal-based polymer in which a part of the hydroxyl group of PVA is crosslinked with the aldehydes of the above.

By forming a film of PVA obtained as described above, a film raw fabric can be obtained. As a PVA film forming method, in addition to a method of melt-extruding hydrous PVA, a casting film forming method, a wet film forming method (discharge into a poor solvent), and a gel film forming method (the PVA aqueous solution is once cooled and gelled). After that, the solvent is extracted and removed), a cast film forming method (a PVA aqueous solution is poured on a substrate and dried), and a method using a combination thereof, but are not limited to these methods.

Examples of the solvent used for film formation include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. Examples include, but are not limited to, ethylenediamine, diethylenetriamine, water and the like. The solvent may be one kind, or two or more kinds may be mixed and used. The amount of the solvent used in the film formation is, for example, 50 to 95% by mass, preferably 70 to 95% by mass, but is not limited to these ranges. However, if the amount of the solvent is less than 50% by mass, the viscosity of the film-forming stock solution becomes high, filtration and defoaming during preparation become difficult, and it is difficult to obtain a film raw fabric containing no foreign matter and having no defects. It becomes. In addition, if the volatile fraction exceeds 95% by mass, the viscosity of the film-forming stock solution becomes too low, making it difficult to control the desired thickness, and the effect of surface fluctuations due to the wind during drying and the drying time become long, resulting in production. The sex is reduced.

A plasticizer may be used in producing the raw film. Examples of the plasticizer include, but are not limited to, glycerin, diglycerin, ethylene glycol and the like. The amount of the plasticizer used is not particularly limited, but it is usually preferably in the range of 5 to 15 parts by mass with respect to 100 parts by mass of PVA.

Examples of the method for drying the raw film after film formation include, but are not limited to, drying with hot air, contact drying with a hot roll, and drying with an infrared heater. One of these methods may be adopted alone, or two or more of these methods may be combined and dried. The drying temperature is also not particularly limited, but is preferably in the range of 50 to 70 ° C.

After drying, the raw film is preferably heat-treated in order to control the degree of swelling within a predetermined range described later. Examples of the heat treatment method for the film raw material after film formation include a method using hot air and a method in which the film raw material is brought into contact with a hot roll, and the method is not particularly limited as long as it can be treated by heat. One of these methods may be adopted alone, or two or more of these methods may be combined. The heat treatment temperature and time are not particularly limited, but are preferably in the range of 110 to 140 ° C., and are preferably treated for about 1 to 10 minutes, but are not particularly limited.

The thickness of the film raw material thus obtained is preferably 20 to 100 μm, more preferably 20 to 80 μm, and even more preferably 20 to 60 μm. If the thickness is less than 20 μm, the film is likely to break. If the thickness exceeds 100 μm, the stress applied to the film during stretching increases, the mechanical load in the stretching process increases, and a large-scale device capable of withstanding the load is required.

The swelling degree F of the original film is preferably 180 to 250%, more preferably 205 to 235%, and even more preferably 210 to 230%. If the swelling degree F is less than 180%, the elongation at the time of stretching is small, the possibility of breaking at a low magnification increases, and it becomes difficult to perform sufficient stretching. Further, when the degree of swelling F exceeds 240%, the swelling becomes excessive, wrinkles and slacks occur, and it causes cutting at the time of stretching. In order to control the swelling degree F, for example, the swelling degree F suitable for the temperature and time when heat-treating the film raw fabric after film formation can be obtained.

The method for measuring the swelling degree F of the original film is as follows.
The raw film is cut into 5 cm × 5 cm and immersed in 1 liter of distilled water at 30 ° C. for 4 hours. The soaked film is taken out from the distilled water, sandwiched between two filter papers to absorb water droplets on the surface, and then the weight [β (g)] of the film soaked in water is measured. Further, the film that was immersed and absorbed water droplets was dried in a dryer at 105 ° C. for 20 hours, cooled in a desiccator for 30 minutes, and then the weight [γ (g)] of the dried film was measured and the formula ( The degree of swelling F of the original film is calculated by v).

Using the raw film produced as described above, the polarizing element of the present invention is manufactured by a method including the steps described below.
(Swelling process)
The above-mentioned raw film is first subjected to a swelling step of swelling the film.
In this step, swelling is achieved by immersing the polyvinyl alcohol-based resin film in a solution at 20 to 50 ° C. for 15 seconds to 10 minutes. The solution at that time is preferably water, but a water-soluble organic solvent such as glycerin, ethanol, ethylene glycol, propylene glycol, or low molecular weight polyethylene glycol, or a mixed solution of water and a water-soluble organic solvent may be used. In order to prevent the occurrence of wrinkles and folds even in the swelling step, it is preferably stretched appropriately, and the stretching ratio is preferably 1.00 to 1.50 times, more preferably 1.10 to 1.35 times. Is. When the time for producing the polarizing element is shortened, the swelling effect can be obtained even in the dyeing step of the dye during the treatment with iodine and iodide, so this step may be omitted.

(Dyeing process)
Next, the swollen polyvinyl alcohol-based resin film is subjected to a dyeing step of dyeing with a solution containing a dichroic dye.
Water is preferable as the solvent of the solution, but the solvent is not particularly limited. Examples of the dichroic dye include polyiodine ions obtained from a mixed solution of iodine and iodide, a dichroic dye of an organic compound, and the like. As the iodide, for example, potassium iodide, ammonium iodide, cobalt iodide, zinc iodide and the like can be used, but the iodide is not limited to the iodide shown here. The iodine concentration in the mixed solution of iodine and iodide is 0.0001 to 0.5 wt%, preferably 0.001 to 0.4 wt%. The concentration of iodide used is preferably 0.0001 to 8 wt%. In some cases, as the dichroic dye of the organic compound, for example, the dichroic dye described in Non-Patent Document 1 may be used to perform color correction within a range that does not impair the performance required by the present application. The dye is not limited, and a known dichroic dye can be used. The dye concentration is not particularly limited, but is preferably about 0.006 wt% to 0.3 wt%, for example. When the dyeability is insufficient, it is preferable to add a coloring aid such as sodium tripolyphosphate and / or Glauber's salt (Natrilium sulfate) for dyeing. The dyeing temperature is 5 ° C to 50 ° C, preferably 5 to 40 ° C, and more preferably 10 ° C to 30 ° C. The dyeing time can be appropriately adjusted according to the transmittance of the obtained polarizing element and the like, but is about 30 seconds to 6 minutes, more preferably 1 minute to 5 minutes. Also in this step, it is preferable to stretch appropriately in order to prevent the occurrence of wrinkles and folds. The draw ratio is preferably 0.99 to 2.00 times, more preferably 1.00 to 1.30 times.

In the dyeing step, a cross-linking agent and / or a water resistant agent may be added to the solution containing the dichroic dye. Examples of the cross-linking agent include boron compounds such as boric acid, borax and ammonium borate, polyhydric aldehydes such as glioxal and glutaaldehyde, biuret-type, isocyanurate-type and block-type polyvalent isocyanate compounds, and titanium oxy. Titanium-based compounds such as sulfate can be used, but ethylene glycol glycidyl ether, polyamide epichlorohydrin and the like can also be used. Examples of the water resistant agent include succinic peroxide, amonmonium persulfate, calcium perchlorate, benzoin ethyl ether, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, ammonium chloride, magnesium chloride and the like. Acid is good. The concentration to be added is, for example, 0.1 to 5.0 wt%, preferably 2 to 4 wt% with respect to the solution containing the dichroic dye when boric acid is added. Further, if necessary, the polyvinyl alcohol-based resin film containing the dichroic dye may be washed after the dyeing step and before entering the next stretching step. Water is generally used as the solvent for cleaning, but alcohol-based solvent, glycol-based solvent, glycerin, a mixed solvent thereof and the like can be used, and the solvent is not particularly limited. Further, the temperature and time for cleaning may be appropriately adjusted according to the transmittance of the target polarizing element and the type of dichroic dye to be used.

(Water resistant treatment process)
Subsequently, after the dyeing step, the dyed film is subjected to a water resistance treatment step of subjecting the dyed film to a water resistance treatment as needed.
In this step, the film is treated with a solution containing a cross-linking agent and / and a water resistant agent. Examples of the cross-linking agent and / and the water resistant agent include boric acid, boric acid, boron compounds such as ammonium borate, polyvalent aldehydes such as glioxal and glutaaldehyde, and polyvalent isocyanates such as biuret type, isocyanurate type and block type. System compounds, titanium compounds such as titanium oxysulfate, ethylene glycol glycidyl ether, polyamide epichlorohydrin, succinic peroxide, amonmonium persulfate, calcium perchlorate, benzoine ethyl ether, ethylene glycol diglycidyl ether, glycerin Examples thereof include diglycidyl ether, ammonium chloride and magnesium chloride, but boric acid is preferable. As the solvent at that time, for example, water, an alcohol solvent, a glycol solvent, glycerin or a mixed solvent thereof and the like can be used. In the case of an aqueous boric acid solution, for example, the concentration of the cross-linking agent and / and the water resistant agent is preferably about 0.1 wt% to 6.0 wt%, more preferably 2 wt% to 4 wt% in the solution. The treatment temperature in this step is about 5 ° C. to 60 ° C., preferably about 5 to 45 ° C. The treatment time is preferably about 1 minute to 5 minutes. Also in this step, in order to prevent the occurrence of wrinkles and folds, it is preferable to stretch appropriately, and the stretching ratio is about 0.95 to 1.5 times.

(Stretching process)
Further, the polyvinyl alcohol-based resin film is subjected to a stretching step of stretching.
In this step, the film is uniaxially stretched. As the stretching method, either a wet stretching method or a dry stretching method may be used.

Specific methods of the dry stretching method include, for example, an inter-roll zone stretching method, a roll heating stretching method, a pressure stretching method, an infrared heating stretching method, and the like, but are not particularly limited. The temperature at the time of stretching is preferably room temperature to 180 ° C., and the humidity is preferably about 20 to 95% RH. The stretching may be carried out in one step, or may be multi-step stretching in two steps or more.

The wet stretching method is a method of stretching in water, a water-soluble organic solvent, or a mixed aqueous solution thereof, but preferably boric acid and boric acid are contained in the water, a water-soluble organic solvent, or a mixed aqueous solution thereof. , Boron compounds such as ammonium borate, polyvalent aldehydes such as glioxal and glutaaldehyde, polyvalent isocyanate compounds such as biuret type, isocyanurate type and block type, titanium compounds such as titanium oxysulfate, ethylene glycol glycidyl ether , Polyamide epichlorohydrin, succinic acid peroxide, amonmonium persulfate, calcium perchlorate, benzoin ethyl ether, ethylene glycol diglycidyl ether, glycerin diglycidyl ether, ammonium chloride, magnesium chloride and other cross-linking agents such as boric acid or / and water resistant It is preferable to perform stretching treatment while immersing in a solution containing an agent, and more preferably to stretching in an aqueous boric acid solution. The concentration of the cross-linking agent and / and the water resistant agent is preferably 0.5 to 8 wt%, preferably 2.0 to 4.0 wt%. The draw ratio is preferably 3 to 8 times, more preferably about 5 to 7 times. The stretching temperature is preferably 40 to 60 ° C, more preferably 45 to 55 ° C. The stretching time is preferably 30 seconds to 20 minutes, more preferably 2 minutes to 5 minutes. The stretching treatment may be one-step stretching or multi-step stretching of two or more steps.

Foreign matter may precipitate or adhere to the surface of the polyvinyl alcohol-based resin film containing the stretched dichroic dye, so that the film may be washed. Water, an alcohol solvent, or the like can be used as the solvent for cleaning, but the solvent is not limited thereto. The cleaning solvent may contain a cross-linking agent such as boric acid and / or a water resistant agent for the purpose of improving the durability of the film. The concentration of the cross-linking agent and / or the water resistant agent is not limited, but is, for example, 0.1 to 10 wt%.

(Post-treatment process)
Next, in order to adjust the hue, improve the polarization characteristics, and improve the durability, a post-treatment step of post-treating the film is performed.
In this step, specifically, a polyvinyl alcohol-based resin film containing a dichroic dye and stretched uniaxially is treated with a solution containing chloride or iodide. Examples of the chloride or iodide include iodides such as potassium iodide, sodium iodide, ammonium iodide, cobalt iodide and zinc iodide, and chlorides such as zinc chloride, potassium chloride and sodium chloride. Treatment is performed by mixing one or more of the contents with the solution. The concentration of chloride or iodide in the solution is preferably 0.1 to 15 wt%, more preferably 0.15 to 10 wt%. Also in this step, in order to prevent the occurrence of wrinkles and folds, it is preferable to stretch appropriately, and the stretching ratio at that time is preferably 0.99 to 1.10 times. The treatment temperature is, for example, preferably 5 to 50 ° C. or lower, more preferably 20 to 40 ° C. The processing time is, for example, about 1 second to 5 minutes, preferably 5 seconds to 30 seconds. In this step, the cross-linking agent and / or water resistant agent may be added. The concentration to be added is, for example, 0.5% to 10 wt%.

Examples of the solvent used in the treatment steps up to this point include water, dimethylsulfoxide, N-methylpyrrolidone, methanol, ethanol, propanol, isopropyl alcohol, glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol or. Examples thereof include alcohols such as trimethylolpropane and solvents such as amines such as ethylenediamine or diethylenetriamine, but the present invention is not limited thereto. It is also possible to use a mixture of one or more of these solvents. The most preferred solvent is water.

(Drying process)
The substrate for the polarizing element of the present invention can be obtained by going through a drying step after the post-treatment step.
Examples of the drying method include natural drying, compression by a roll, a method of removing moisture on the surface by an air knife, a water absorbing roll, and the like, and drying by heating. In the case of heat drying, the drying temperature is preferably 20 to 90 ° C, more preferably 40 to 70 ° C. The drying time is preferably about 30 seconds to 20 minutes, more preferably about 2 minutes to 10 minutes. Also in this drying step, in order to prevent the generation of wrinkles and streaks due to the shrinkage of the polyvinyl alcohol-based resin film due to drying, it is preferable to stretch the film appropriately, and the stretching ratio at that time is preferably 0.95 to 1.10 times. ..

The base material of the polarizing element is obtained by going through the swelling step, the dyeing step, an arbitrary water resistance treatment step, a stretching step, a post-treatment step, and a drying step. The base material thus obtained has a luminosity factor-corrected single transmittance Ys of 40.0% to 42.5% when measured by itself, and has a luminosity factor-corrected single-transmittance Ys of 460 nm. The difference from the transmittance Ts ₄₆₀ is within 1%, the difference between the luminous factor correction single transmittance Ys and the transmittance Ts _{550 at 550} nm is within 1%, and the visible sensitivity correction single transmittance Ys and the transmittance at 610 nm. The difference from Ts ₆₁₀ is within 1%, and the visible sensitivity-corrected transmittance Yc obtained by measuring the two substrates at right angles to the absorption axis direction is adjusted to 0.01% or less.

In order to obtain a polarizing element having a substrate having the above characteristics, it is important to treat the film with a solution containing chloride or iodide having an appropriate concentration in the post-treatment step. In this step, it is necessary to adjust the concentration of chloride or iodide in the solution and the treatment time thereof according to the stretching conditions. It is very important that the concentration and treatment time are adjusted according to the impregnation of iodine in the polarizing element, iodide such as potassium iodide, and chloride such as potassium chloride in the polarizing element. Is. In particular, the concentration is affected by the stretching state of the stretching step, the temperature and humidity of the place where the polarizing element is manufactured, and the like, so very delicate fine adjustment is required. Generally, the concentration of the chloride-containing solution or iodide-containing solution used in the post-treatment step is 1.0 part by weight to 150 parts by weight, preferably 1.5 parts by weight or more, based on 1000 parts by weight of water. It was prepared by adding 100 parts by weight.
Further, it is preferable to perform the treatment while maintaining the stretch ratio and / or the stretch tension stretched so that the film does not shrink or expand as much as possible. Further, it is preferable to perform the treatment in a state where there is no difference in the relative speed between the speed at which the film is conveyed and the water flow speed in the post-treatment step. It is more preferable to sufficiently treat the inside of the film. The polarizing element of the present application can be obtained by performing the post-treatment step by the above method.

As an index for adjusting better production as a polarizing element, the visible sensitivity correction parallel transmittance Yp obtained by measuring two substrates parallel to the absorption axis direction is in the range of 33% to 37%. The difference between the transmittance Yp and the transmittance Tp _{460 at 460} nm when the two substrates are measured parallel to the absorption axis direction is within 3%. In order to keep the difference between Yp and Tp ₄₆₀ within 3%, it is necessary to adjust the transmittance at 295 nm and the transmittance at 360 nm obtained by measuring the two substrates parallel to the absorption axis direction. is there. It is said that the transmittance at 295 nm and the transmittance at 360 nm fluctuate due to the content of polyiodine such as I ₃ ⁻ and I ₅ ⁻ in the polarizing element. _I ³ in the polarizing element -, _{I 5} ^- by adjusting the content of polyiodine such, can adjust the 295nm and 360nm transmittance, is possible to adjust the difference between the Yp and _{Tp 460} to within 3% it can.

In order to manufacture a better polarizing element, the visible sensitivity-corrected transmittance Yp obtained by measuring the two substrates in parallel with the absorption axis direction is in the range of 33% to 37%. The transmittance Yp and the transmittance Tp _{295 of 295} nm when the two substrates are measured parallel to the absorption axis direction satisfy the following formula (1), and the Yp and the substrate 2 are satisfied. It is necessary to adjust the transmittance Tp _{360 at 360} nm when the sheet is measured parallel to the absorption axis direction so as to satisfy the following equation (2).

1.05 × Yp-26 ≦ Tp ₂₉₅ ≦ 1.05 × Yp-13 ・ ・ ・ Equation (1)
1.25 × Yp-26.25 ≦ Tp ₃₆₀ ≦ 1.25 × Yp-16.25 ・ ・ ・ Equation (2)

To further improve the performance of the polarizing element, in particular, to improve the 380nm to 480nm performance in the visible region of the polarizing element 295 nm, 360 nm of _I ³ - improving the orientation of polyiodine such ^-, _{I 5} The transmittance Tc _{295 at 295} nm when the above formulas (1) and (2) are satisfied and the two substrates are measured orthogonally to the absorption axis direction is as follows. It is more preferable that the transmittance Tc _{360 at 360} nm when the formula (3) is satisfied and the two substrates are measured parallel to the absorption axis direction satisfies the following formula (4). In the following formula, each of Yp ^18.6 , Yp ^19.4 , Yp ^22.12 and Yp ^22.67 represents a multiplier of the parallel transmittance Yp.

2.0 × 10 ^-30 × Yp ^18.6 ≦ Tc ₂₉₅ ≦ 2.0 × 10 ^-30 × Yp ^19.4・ ・ ・ Equation (3)
4.0 × 10 ⁻³⁷ × Yp ^22.12 ≦ Tc ₃₆₀ ≦ 4.0 × 10 ⁻³⁷ × Yp ^22.67・ ・ ・ Equation (4)

Further, in recent LED backlight light sources, blue light of 460 nm is emitted in white by using a phosphor, so that the transmittance centered on 460 nm is important for improving the contrast of the polarizing element. .. In particular, if the transmittance of the polarizing element is high when two substrates are measured orthogonally to the absorption axis direction at 460 nm, blue light leaks and true black cannot be expressed as a display. Further, at that time, if the transmittance at 610 nm does not have a certain transmittance or less as compared with 460 nm, true black cannot be expressed in the same manner, and the contrast between white and black cannot be realized. Therefore, the transmittance of the polarizing element is 0.035% or less when the two substrates are orthogonal to the absorption axis direction and the transmittance at 460 nm is 0.035% or less, and the two substrates are oriented in the absorption axis direction. On the other hand, it is preferable to prepare so that the transmittance at 610 nm when measured orthogonally is 0.01% or less.

Further, for that purpose, the present application can be easily achieved by using a film raw fabric made of a polyvinyl alcohol-based resin film having a degree of polymerization of the polyvinyl alcohol-based resin of 3000 to 10000 as the base material of the polarizing element. More preferably, the degree of polymerization of the polyvinyl alcohol-based film is 3500 to 6000, and even more preferably, the degree of polymerization is 4500 to 6000.

<Polarizer>
The polarizing plate of the present invention can be obtained by providing a transparent protective layer on at least one side or both sides of the polarizing element of the present invention obtained through the above steps. Specifically, the transparent protective layer can be provided by applying or laminating a polymer or film forming the protective layer to the polarizing element of the present invention. 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. Further, those having excellent water blocking property are more preferable. As a substance used as a transparent protective layer, for example, a cellulose acetate resin or a film thereof such as triacetyl cellulose or diacetyl cellulose, an acrylic resin or a film thereof, a polyester resin or a film thereof, a polyarylate resin or a film thereof, or a ring such as norbornene. Cyclic polyolefin resin or film having olefin as monomer, polyethylene, polypropylene, polyethylene terephthalate, polyolefin having cyclo- or norbornene skeleton or copolymer thereof, resin or polymer having imide or / and amide main chain or side chain or amide thereof Examples include films. Further, since it is generally known that a polyvinyl alcohol-based resin functions as an alignment film, for example, a rubbing treatment, an alignment film coating, or an alignment treatment is applied to the surface of the obtained polarizing element to make it liquid crystal. A resin or a film thereof may be provided. The thickness of the protective film is, for example, about 0.5 to 200 μm. When these films are provided on both sides of the polarizing element, the same film may be used, or different films may be used.

When the film which is the transparent protective layer is laminated with the polarizing element of the present invention, it is preferable to use an adhesive. Examples of the adhesive include polyvinyl alcohol-based, urethane-based, acrylic-based, and epoxy-based adhesives. Examples of the polyvinyl alcohol-based adhesive include, but are not limited to, Gosenol NH-26 (manufactured by Nippon Synthetic Chemistry Co., Ltd.) and Exevar RS-2117 (manufactured by Kuraray Co., Ltd.). A cross-linking agent and / or a water resistant agent may be added to the adhesive. Further, the adhesive may contain an inorganic acid or a salt thereof and / or an organic acid at a concentration of 0.0001 wt% to 20 wt%, preferably 0.02 to 5 wt%. As the polyvinyl alcohol-based adhesive, an adhesive in which a maleic anhydride-isobutylene copolymer is mixed alone or in combination with a cross-linking agent can be used. Examples of maleic anhydride-isobutylene copolymers include Isovan # 18 (manufactured by Kuraray), Isoban # 04 (manufactured by Kuraray), Ammonia-modified Isovan # 104 (manufactured by Kuraray), and Ammonia-modified Isovan # 110 (manufactured by Kuraray). ), Imidized Isovan # 304 (manufactured by Kuraray), Imidized Isovan # 310 (manufactured by Kuraray), and the like. A water-soluble polyvalent epoxy compound can be used as the cross-linking agent at that time. Examples of the water-soluble polyvalent epoxy compound include Denacol EX-521 (manufactured by Nagase Chemtech Co., Ltd.) and Tetrat-C (manufactured by Mitsui Gas Chemicals Co., Ltd.). Further, as the additive of the adhesive, the above-mentioned buffer agent or inorganic acid or salt thereof and / or organic acid, zinc compound, chloride or iodide, etc., more preferably the above-mentioned buffer agent or inorganic acid or salt thereof and / Alternatively, the durability can be similarly improved by containing an organic acid at a concentration of about 0.01 to 10 wt% with respect to the adhesive component. The film, which is a transparent protective layer, and the polarizing element of the present invention are bonded to each other with the adhesive, dried by heating, and further heat-treated to bond them.

When the obtained polarizing plate is attached to a display device such as a liquid crystal display or used in a polarizing filter or a polarizing lens, the viewing angle is improved and / or on the surface of a protective layer or film which will be a non-exposed surface later. Various functional layers for improving contrast, layers or films having brightness improving properties can also be provided. It is preferable to use an adhesive to attach the polarizing plate to these films and display devices.

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, the protective layer or the exposed surface of the film. In order to produce the layers having various functionalities, it is preferable to provide them on the other surface by a coating method, but a film having the functions can also be attached via an adhesive or an adhesive. Further, the various functional layers can be a layer or a film for controlling the phase difference.

By the method described above, a polarizing element or a polarizing plate having a constant transmittance at each wavelength can be obtained. The polarizing element or polarizing plate of the present invention thus obtained is stable for a long period of time because it has high polarization performance, that is, high contrast, can keep each wavelength transmittance in the visible region constant, and has excellent durability. Performance can be maintained.
<Liquid crystal display device>
Further, by using the polarizing plate of the present invention in a liquid crystal display, an electroluminescence display device, a CRT, or the like, the image display device of the present invention can be obtained. In particular, a liquid crystal display device can be obtained by attaching the polarizing plate of the present invention to both sides of a liquid crystal cell constituting a liquid crystal display with an adhesive together with a retardation film, if necessary.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

The transmittance shown in each example was evaluated as follows.
The transmittance of each wavelength when one polarizing element or polarizing plate is measured is defined as the single transmittance Ts, and each wavelength when two polarizing elements or polarizing plates are stacked so that their absorption axis directions are the same. The transmittance of each wavelength was defined as the parallel transmittance Tp, and the transmittance of each wavelength when two polarizing plates were stacked so that their absorption axes were orthogonal to each other was defined as the orthogonal transmittance Tc.

Each of the spectral transmittances Ts, Tp and Tc was measured using a spectrophotometer [“U-4100” manufactured by Hitachi, Ltd.].

The luminosity factor correction single transmittance Ys was calculated by the following formula (5) from the single transmittance Ts measured at predetermined wavelength intervals dλ (here, 5 nm) in the wavelength region of 400 to 700 nm. In the equation, Pλ represents the spectral distribution of standard light (C light source), and yλ represents the color matching function based on JIS Z 8729 (C light source 2 ° field of view).

The luminosity factor correction parallel transmittance Yp was calculated by the following formula (6) from the parallel transmittance Tp measured at predetermined wavelength intervals dλ (here, 5 nm) in the wavelength region of 400 to 700 nm. In the equation, Pλ represents the spectral distribution of standard light (C light source), and yλ represents the color matching function based on JIS Z 8729 (C light source 2 ° field of view).

The luminosity factor correction orthogonal transmittance Yc was calculated by the following formula (7) from the orthogonal transmittance Tc measured at predetermined wavelength intervals dλ (here, 5 nm) in the wavelength region of 400 to 700 nm. In the equation, Pλ represents the spectral distribution of standard light (C light source), and yλ represents the color matching function based on JIS Z 8729 (C light source 2 ° field of view).

The degree of polarization Py was obtained from the luminosity factor corrected parallel transmittance Yp and the luminosity factor corrected orthogonal transmittance Yc by the following equation (8).

Example 1
A polyvinyl alcohol-based film (VF-PM manufactured by Kuraray Co., Ltd.) having a thickness of 60 μm, a degree of polymerization of 5500, and a degree of polymerization of 99% or more is swollen with warm water at 40 ° C. .P.a.) 28.6 parts by weight, boric acid (manufactured by Genuine Chemical Co., Ltd.) 0.25 parts by weight, potassium iodide (manufactured by Genuine Chemical Co., Ltd.) 17.7 parts by weight, 2 at 30 ° C. It was soaked for a minute and dyed. The dyed film was stretched 5 times at 58 ° C. in a solution containing 3% by weight of boric acid, and after stretching, 3.5 parts by weight of potassium iodide was added to 1000 parts by weight of water to prepare the dyed film. In the iodide-containing aqueous solution, the stretching ratio is maintained while maintaining the tension after stretching, and the relative speed difference between the transport speed at which the film is treated and the water flow speed in the treatment step is almost constant, and is 20 to 40 kHz. The solution was immersed while applying the ultrasonic waves of the above, and the post-treatment step was performed for 20 seconds. The film in which the potassium iodide aqueous solution was immersed for 20 seconds was then dried in a dryer at 70 ° C. for 10 minutes to obtain a polarizing element.

Example 2
A polyvinyl alcohol-based film having a thickness of 60 μm, a degree of polymerization of 4000, and a saponification degree of 99% or more (VF-PM manufactured by Kuraray), and a polyvinyl alcohol-based film having a thickness of 40 μm, a degree of polymerization of 4000, and a saponification degree of 99% or more (manufactured by Kuraray). A polarizing element was obtained in the same manner as in Example 1 except that VF-PH) was used.

Example 3
A polarizing element was obtained in the same manner as in Example 2 except that the dyeing treatment time was 1 minute and 30 seconds.

Example 4
A polarizing element was obtained in the same manner as in Example 1 except that the dyeing treatment time was 1 minute and 30 seconds.

Comparative Example 1
After stretching, the post-treatment step was carried out for 20 seconds while maintaining the post-stretching magnification while stirring the aqueous solution prepared by adding 35 parts by weight of potassium iodide to 1000 parts by weight of water at a speed of 60 rpm. Obtained a polarizing element in the same manner as in Example 1.

Comparative Example 2
After stretching, the post-treatment step was carried out for 20 seconds while maintaining the post-stretching magnification while stirring the aqueous solution prepared by adding 35 parts by weight of potassium iodide to 1000 parts by weight of water at a speed of 60 rpm. Obtained a polarizing element in the same manner as in Example 2.

Comparative Example 3
After stretching, the post-treatment step was performed for 20 seconds while maintaining the post-stretching magnification while stirring the aqueous solution prepared by adding 50 parts by weight of potassium iodide to 1000 parts by weight of water at a speed of 60 rpm. Obtained a polarizing element in the same manner as in Example 3.

Comparative Example 4
After stretching, the post-treatment step was performed for 20 seconds while maintaining the post-stretching magnification while stirring the aqueous solution prepared by adding 50 parts by weight of potassium iodide to 1000 parts by weight of water at a speed of 60 rpm. Obtained a polarizing element in the same manner as in Example 4.

Comparative Example 5
The iodine-based polarizing plate SKN-18242P manufactured by Polatechno Co., Ltd. was immersed in dichloromethane to extract a polarizing element, which was used as a comparative example sample.

Comparative Example 6
After stretching, a polarizing element was obtained in the same manner as in Example 1 except that the film was immersed in water and treated for 20 seconds, and used as a comparative example sample.

Table 1 shows the parameters of the polarizing elements obtained in Examples 1 to 4 and Comparative Examples 1 to 6. The parameters shown in Table 1 are as follows.
Luminosity factor correction single transmittance Ys,
Luminosity factor correction parallel transmittance Yp,
Luminosity factor correction orthogonal transmittance Yc,
Elementary transmittance of 460 nm Ts ₄₆₀ ,
Parallel transmittance Tp ₄₆₀ of 460 nm when two base materials are measured parallel to the absorption axis direction,
Orthogonal transmittance Tc ₄₆₀ of 460 nm when two base materials are measured orthogonally to the absorption axis direction,
Elementary transmittance Ts _{550 at 550} nm,
Elementary transmittance of ₆₁₀ nm Ts ₆₁₀ ,
Orthogonal transmittance Tc ₆₁₀ of 610 nm when two base materials are measured orthogonally to the absorption axis direction,
Parallel transmittance Tp _{295 of 295} nm when two base materials are measured parallel to the absorption axis direction,
Orthogonal transmittance Tc _{295 of 295} nm when two base materials are measured orthogonally to the absorption axis direction,
Parallel transmittance Tp ₃₆₀ of 360 nm when two base materials are measured parallel to the absorption axis direction,
Orthogonal transmittance Tc ₃₆₀ of 360 nm when two base materials are measured orthogonally to the absorption axis direction.

As can be seen from the above results, the polarizing elements of Examples 1 to 4 are polarizing elements having a substantially constant transmittance at each wavelength, and the visible sensitivity correction single transmittance Ys when measured alone is 40.0%. It is 42.5%, the difference between the transmittance correction single transmittance Ys and the transmittance Ts _{460 at 460} nm is within 1%, and the difference between the visibility correction single transmittance Ys and the transmittance Ts _{550 at 550} nm. It is within 1%, and the difference between the transmittance correction Ys and the transmittance Ts _{610 at 610} nm is within 1%, and it is obtained by measuring the two substrates orthogonal to the absorption axis direction. It can be seen that the transmittance correction Yc of the visual sensitivity correction unit is 0.01% or less.
Further, a polarizing plate can be obtained by laminating the polarizing element with a protective layer, but when the polarizing elements of Examples 1 to 4 are installed parallel to the absorption axis, the transmittance at 380 nm to 480 nm is 500 nmm to 650 nm. It has almost constant optical characteristics compared to the transmittance of, and it was possible to maintain the uniformity of light emission at each wavelength. Furthermore, since the luminosity factor correction orthogonal transmittance Yc is 0.01% or less, these polarizing elements have high contrast and can be a polarizing element or a polarizing plate capable of making each wavelength transmittance in the visible region constant. It turned out that there was.
Therefore, the polarizing elements of Examples 1 to 4 obtained by the above method or the polarizing plate produced by using these polarizing elements are for displays having high transmittance, high contrast ratio, and very high color reproducibility. It can be used as a polarizing plate, particularly as a polarizing plate for a liquid crystal display. Further, a display using this is expected to be a display having high reliability, being able to maintain high contrast for a long period of time, and having high color reproducibility.

Claims (6)

A polarizing element composed of a hydrophilic polymer adsorbed and stretched with boric acid and containing a base material containing iodine and having a polarizing function.
The luminosity factor correction single transmittance Ys when the base material is measured by itself is 40.0% to 42.5%.
The difference between the luminosity factor correction single transmittance Ys and the single transmittance Ts _{460 at 460} nm is within 1%.
The difference between the luminosity factor correction single transmittance Ys and the single transmittance Ts _{550 at 550} nm is within 1%.
The difference between the luminosity factor correction single transmittance Ys and the single transmittance Ts _{610 at 610} nm is within 1%.
The luminosity factor correction orthogonal transmittance Yc when the two substrates are measured orthogonally to the absorption axis direction is 0.01% or less;
The luminosity factor correction parallel transmittance Yp when the two substrates are measured parallel to the absorption axis direction is in the range of 33% to 37%.
The difference between the parallel transmittance Yp and the parallel transmittance Tp _{460 at 460} nm when the two substrates are measured parallel to the absorption axis direction is within 3%;
The parallel transmittance Yp and the transmittance Tp _{295 of 295} nm when the two substrates are measured parallel to the absorption axis direction satisfy the following formula (1) and
And the parallel transmittance Yp, and 360nm transmittance Tp ₃₆₀ as measured in the parallel two base material with respect to the absorption axis direction, meets the following formula (2),
Further, the transmittance Tc _{295 at 295} nm when the two substrates are measured orthogonally to the absorption axis direction satisfies the following formula (3) and
360nm transmittance Tc ₃₆₀ as measured by the base material 2 sheets orthogonal to the absorption axis direction, and wherein Succoth satisfy the following expression (4), the polarizing element.
1.05 × Yp-26 ≦ Tp ₂₉₅ ≦ 1.05 × Yp-13 ・ ・ ・ Equation (1)
1.25 × Yp-26.25 ≦ Tp ₃₆₀ ≦ 1.25 × Yp-16.25 ・ ・ ・ Equation (2)
2.0 × 10 ^-30 × Yp ^18.6 ≦ Tc ₂₉₅ ≦ 2.0 × 10 ^-30 × Yp ^19.4 ・ ・ ・ Equation (3)
4.0 × 10 ⁻³⁷ × Yp ^22.12 ≦ Tc ₃₆₀ ≦ 4.0 × 10 ⁻³⁷ × Yp ^22.67 ・ ・ ・ Equation (4) When the two substrates are measured orthogonally to the absorption axis direction, the transmittance Tc _{460 at 460} nm is 0.035% or less, and
The polarizing element according to claim 1 , wherein the transmittance Tc _{610 at 610} nm is 0.01% or less when the two substrates are measured orthogonally to the absorption axis direction. The polarizing element according to claim 1 or 2 , wherein the base material is made of a polyvinyl alcohol-based resin film, and the degree of polymerization of the polyvinyl alcohol-based resin film is 3000 to 7000. A polarizing plate having a support film provided on at least one side of the polarizing element according to any one of claims 1 to 3 . A liquid crystal display device including the polarizing element according to any one of claims 1 to 3 or the polarizing plate according to claim 4 . The method for manufacturing a polarizing element according to any one of claims 1 to 3 .
(I) A step of adding a dichroic dye to a polyvinyl alcohol-based resin film having a degree of polymerization of 3000 to 10000 to obtain a film containing the dichroic dye.
(Ii) A step of stretching a film containing the dichroic dye to obtain a stretched film.
(Iii) A step of subjecting the stretched film to a post-treatment using a chloride-containing solution or an iodide-containing solution.
(Iv) The step of drying the film after the post-treatment to obtain the base material is included.
The concentration of the chloride-containing solution or the iodide-containing solution is 0.1 to 15% by weight, and the stretched film is post-treated by using ultrasonic waves in the step (iii). Production method.