KR20130116200A - Method for preparing polarizer and polarizing plate using the same - Google Patents

Abstract

PURPOSE: A manufacturing method of a polarizer and a polarizing plate using the same are provided to improve the color durability. CONSTITUTION: A manufacturing method of a polarizer includes a swelling step, a dyeing step, and a cross-linking step of a polyvinyl alcohol film in order. A stretching step is performed for each step. The cross-linking step includes a first cross-linking step for extension of 1.4 to 3.0 times and cross-linking and a second cross-linking step for extension of 1.01 to 2.0 times and cross-linking. The accumulated draw ratio of the first and the second steps is 1.5 to 5.0 times. The first cross-linking step or the second cross-linking step uses a cross-link aqueous solution containing metal nitrates and boron compounds.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a polarizer,

The present invention relates to a method for producing a polarizer having excellent optical properties and preventing deterioration even after being left under dry heat and having excellent color durability, and a polarizing plate using the same.

The polarizing plate has a structure in which a transparent protective film is laminated on both sides or one side of a polarizer made of a polyvinyl alcohol-based resin in which dichroic dye is adsorbed and oriented.

A polarizer using iodine as a dichroism pigment is an iodine polarizer, and a polarizer using a dichroic dye is a dye-based polarizer. The dual iodine polarizer is widely used because it has high transmittance and high polarization (high contrast) as compared with the dye type polarizer.

However, the iodine polarizer has better optical characteristics than the dye-based polarizer, but has a lower optical durability. For example, when the iodine polarizer or the polarizing plate including the polarizer is left under dry heat, the transmittance is lowered or discolored.

Furthermore, in recent years, the field of use of liquid crystal display devices has been expanding and peripheral technologies have been advanced, and the demand for the performance of polarizing plates has become more severe. Specifically, a polarizing plate having high contrast (high transmittance and high polarization degree) and excellent optical durability such as heat resistance is required.

Korean Patent Laid-Open Publication No. 2010-89793 discloses a method of adding a zinc salt to a crosslinking tank. However, this method is disadvantageous in that the stretching is not performed in the swelling and dyeing process for producing the polarizer, wrinkles are generated due to excessive swelling, the dyeing is uneven, and the appearance of the polarizer is poor.

The present invention is intended to provide a method for producing a polarizer that is prevented from deteriorating after being left under dry heat and is excellent in color durability.

The present invention also provides a method for producing a polarizer that is prevented from leaking an iodine complex and has excellent optical properties such as transmittance and polarization degree.

The present invention also provides a polarizing plate comprising the polarizer.

In order to accomplish the above object, the present invention provides a method for producing a polarizer by performing a swelling, dyeing and crosslinking step of a polyvinyl alcohol-based film in the order of: 1.4 And a second crosslinking step of stretching at 1.01 to 2.0 times and a crosslinking step, wherein the cumulative stretching ratio of the first and second steps is 1.5 to 5.0 times, and the first crosslinking step and Wherein at least one of the crosslinking steps in the second crosslinking step uses a crosslinked aqueous solution containing a metal nitrate and a boron compound.

The swelling step may be a step of stretching to 1.1 to 3.5 times of swelling.

The dyeing step may be stretched to 1.01 to 2.0 times, and the cumulative stretching ratio to the dyeing step may be 1.2 to 4.0 times.

The metal nitrate may be contained in an amount of 0.1 to 10% by weight based on 100% by weight of the aqueous crosslinked solution.

The metal nitrate may be contained in an amount of 0.1 to 10% by weight based on 100% by weight of the aqueous crosslinking solution in the first crosslinking step, and may be included in an amount of 0.1 to 10% by weight based on 100% by weight of the crosslinking aqueous solution in the second crosslinking step.

The metal nitrate is selected from the group consisting of Li, Na, K, Rb, Cs, Ag, Mg, Ca, Sr, Ba, Cu, Zn, Fe, Co, Ni, Ru, Rh, Pd, Zr, Pt, A nitrate of a metal selected from the group consisting of Ti, La, Ce, Eu, Gd, Y, Nd, Smp, Tm, Er, Sn, Zr, V, Cr, Mo and Mn.

Preferably, the metal nitrate is a nitrate of a metal selected from the group consisting of Zn, Cu, Al, Mg and Zr.

And may further include 0.05 to 15% by weight of iodide relative to 100% by weight of the aqueous crosslinking solution.

The first crosslinking step and the second crosslinking step may be repeated two or more times, respectively.

In addition, the present invention provides a polarizing plate in which a protective film is laminated on at least one surface of a polarizer produced by the above production method.

The polarizer according to the present invention is useful for a liquid crystal display device which is prevented from deteriorating after being left under dry heat and is excellent in color durability and is likely to be exposed to a high temperature such as a cellular phone or a vehicle.

In addition, the polarizer according to the present invention is excellent in optical characteristics such as transmittance and polarization degree by preventing leakage of iodine complex.

The present invention relates to a method for producing a polarizer having excellent optical properties and preventing deterioration even after being left under dry heat and having excellent color durability, and a polarizing plate using the same.

Hereinafter, the present invention will be described in detail.

The method for producing a polarizer of the present invention is a method for producing a polarizer by performing a swelling, dyeing and crosslinking step of a polyvinyl alcohol-based film in the order of performing the stretching step during each of the above steps.

The crosslinking step includes a first crosslinking step of stretching at a ratio of 1.4 to 3.0 times and a second crosslinking step of crosslinking at a stretching ratio of 1.01 to 2.0 times, and the cumulative stretching ratio of the first and second steps is 1.5 to 5.0 times.

In this case, the cumulative stretching ratios of the first and second steps refer to the cumulative stretching ratios of only the crosslinking steps except for the swelling and dyeing steps in the polarizer manufacturing step.

The crosslinking step of at least one of the first crosslinking step and the second crosslinking step uses a crosslinked aqueous solution containing a metal nitrate salt and a boron compound.

In the present invention, the polarizer means a conventional iodine-based polarizer in which iodine is adsorbed and oriented on a polymer film.

The type of the polymer film for producing the polarizer is not particularly limited as long as it is a dichroic material, that is, a film which can be dyed with iodine. Specifically, the type of the polymer film is a polyvinyl alcohol film, a partially saponified polyvinyl alcohol film; A hydrophilic polymer film such as a polyethylene terephthalate film, an ethylene-vinyl acetate copolymer film, an ethylene-vinyl alcohol copolymer film, a cellulose film, a partially saponified film thereof and the like; Or a dehydrated polyvinyl alcohol film, a dehydrochloric acid-treated polyvinyl alcohol film, and the like. Of these, a polyvinyl alcohol-based film is preferable because it has an excellent effect of enhancing the uniformity of the degree of polarization in the plane and is excellent in dye affinity for iodine.

Generally, a method for producing a polarizer includes a swelling step, a dyeing step, a crosslinking step, a stretching step, a washing step and a drying step, and is mainly classified by a stretching method. For example, a dry stretching method, a wet stretching method, or a hybrid stretching method in which the two kinds of stretching methods are mixed can be used. Hereinafter, a method of producing the polarizer of the present invention will be described with reference to a wet drawing method, but the present invention is not limited thereto.

The remaining steps except the drying step are performed in a state in which the polyvinyl alcohol film is immersed in a constant temperature bath filled with one or more kinds of solutions selected from various kinds of solutions.

The swelling step is carried out by immersing the unstretched polyvinyl alcohol film in a swelling tank filled with a swelling aqueous solution before dyeing to remove impurities such as dust and anti-blocking agent deposited on the surface of the polyvinyl alcohol film, Is a step for improving the physical properties of the polarizer by improving the stretching efficiency and preventing uneven dyeing by swelling the film.

Water (pure water, deionized water) can usually be used as a swelling aqueous solution, and when a small amount of glycerin or potassium iodide is added thereto, the swelling of the polymer film and the processability can be improved. The content of glycerin is preferably 5% by weight or less based on 100% by weight of the aqueous swelling solution, and the content of potassium iodide is preferably 10% by weight or less.

The swelling bath temperature is preferably 20 to 45 캜, more preferably 25 to 40 캜.

The execution time (swelling tank immersion time) of the swelling step is preferably 180 seconds or less, more preferably 90 seconds or less. When the immersion time is within the above range, it is possible to prevent the swelling from becoming excessive and saturation, to prevent breakage due to softening of the polyvinyl alcohol film and to improve the polarization degree by uniformly adsorbing iodine in the dyeing step have.

The stretching step is carried out together with the swelling step, wherein the stretching ratio is about 1.1 to 3.5 times, preferably 1.5 to 3.0 times. If the stretching ratio is less than 1.1 times, wrinkles may occur. If the stretching ratio is more than 3.5 times, initial optical characteristics may become weak.

The dyeing step is a step of dipping the polyvinyl alcohol-based film in a dyeing bath filled with an aqueous solution for dyeing containing a dichroic substance, for example, iodine to adsorb iodine on the polyvinyl alcohol-based film.

The dyeing aqueous solution may comprise water, a water-soluble organic solvent or a mixed solvent thereof and iodine. The content of iodine is preferably 0.4 to 400 mmol / L, more preferably 0.8 to 275 mmol / L, and most preferably 1 to 200 mmol / L with respect to 100 wt% of the aqueous solution for dyeing. To further improve the dyeing efficiency, iodide may be further included as a dissolution aid. As the iodide, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide and titanium iodide may be used alone or in combination of two or more. Of these, potassium iodide is preferable in view of high solubility in water. The content of iodide is preferably 0.01 to 10% by weight, more preferably 0.1 to 5% by weight based on 100% by weight of the dyeing aqueous solution.

The temperature of the dye bath is preferably 5 to 42 ° C, more preferably 10 to 35 ° C. The immersion time of the polyvinyl alcohol film in the dyeing bath is not particularly limited, and is preferably 1 to 20 minutes, and more preferably 2 to 10 minutes.

And the stretching step is carried out together with the dyeing step. In this case, the stretching ratio is preferably 1.01 to 2.0 times, and more preferably 1.1 to 1.8 times.

The cumulative stretching ratio up to the dyeing step including the swelling and dyeing steps is preferably 1.2 to 4.0 times. If the cumulative stretching ratio is less than 1.2 times, wrinkles of the film may occur to cause appearance defects. If the cumulative stretching ratio exceeds 4.0 times, the initial optical characteristics may be poor.

The crosslinking step is a step of immobilizing the adsorbed iodine molecules by immersing the dyed polyvinyl alcohol film in a crosslinking aqueous solution so that the dyeability due to physically adsorbed iodine molecules is not lowered by the external environment. Although dichroic dyes are not often eluted in a humidity environment, iodine molecules often dissolve or sublimate depending on the environment when the crosslinking reaction is unstable, and sufficient crosslinking reaction is required. In addition, the crosslinking step is important because, in order to orient the iodine molecules positioned between all the polyvinyl alcohol molecules and the molecules and to improve the optical properties, the crosslinking step generally needs to be elongated to the largest stretching ratio.

The present invention carries out the crosslinking step composed of the first and second crosslinking steps, wherein at least one of the first and second crosslinking steps is characterized by using a crosslinked aqueous solution containing a metal nitrate and a boron compound. As a result, the optical characteristics of the polarizer and the color durability can be improved at the same time.

Specifically, when a polyvinyl alcohol film subjected to the dyeing step is immersed in an aqueous solution containing the metal nitrate salt, a chelate structure is formed between the metal salt and the polyvinyl alcohol to improve the degree of crosslinking. When the degree of crosslinking is improved, it is possible to manufacture a polarizer and a polarizer excellent in durability by preventing deterioration (redness phenomenon) even after being left under dry heat, preventing poor appearance and preventing leakage of iodine complex (bonding of polyvinyl alcohol and polyvalent iodide ion) have.

Further, the first and second crosslinking steps of the present invention can be repeatedly carried out at least twice.

A crosslinked aqueous solution containing the metal nitrate salt and the boron compound may be used in the first crosslinking step, the second crosslinking step, or both the first and second crosslinking steps.

The metal nitrate is selected from the group consisting of Li, Na, K, Rb, Cs, Ag, Mg, Ca, Sr, Ba, Cu, Zn, Fe, Co, Ni, Ru, Rh, Pd, Zr, Pt, A nitrate of a metal selected from the group consisting of Ti, La, Ce, Eu, Gd, Y, Nd, Smp, Tm, Er, Sn, Zr, V, Cr, Mo and Mn.

Considering optical characteristics and economical efficiency, nitrate of a metal selected from the group consisting of Zn, Cu, Al, Mg and Zr is preferable.

The metal nitrate may contain 0.1 to 10% by weight, preferably 0.5 to 7.0% by weight, based on 100% by weight of the aqueous crosslinked solution. If the content is less than 0.1% by weight, the effect of the metal nitrate salt may be insufficient. If the content is more than 10% by weight, excessive chemical bonding between the metal salt and the polyvinyl alcohol may cause a problem of breakage, .

When the metal nitrate is included in both the first and second crosslinking steps, the amount of the metal nitrate is 0.1 to 10% by weight based on 100% by weight of the crosslinking aqueous solution of the first crosslinking step, 10% by weight.

The crosslinked aqueous solution may further comprise water as a solvent, a boron compound such as boric acid, sodium borate, and the metal nitrate salt, and an organic solvent and an iodide mutually soluble together with water.

The boron compound imparts short crosslinking and rigidity to suppress wrinkling during processing, thereby improving handling properties and forming iodine alignment.

The content of the boron compound is preferably 1 to 10% by weight, more preferably 2 to 6% by weight based on 100% by weight of the aqueous crosslinked solution. When the content is less than 1% by weight, the crosslinking effect of the boron compound is reduced and it is difficult to impart rigidity. When the content is more than 10% by weight, the crosslinking reaction of the inorganic crosslinking agent is excessively activated and the crosslinking reaction of the organic crosslinking agent is difficult to proceed effectively.

Iodide is used to prevent the uniformity of the degree of polarization in the plane of polarizers and the desorption of dyed iodine. The iodide may be the same as that used in the dyeing step, and the content thereof may be 0.05 to 15% by weight, preferably 0.5 to 11% by weight, based on 100% by weight of the aqueous crosslinked solution. If the content is less than 0.05% by weight, the iodide ions in the film may escape to increase the transmittance. If the content exceeds 15% by weight, the iodide ions in the aqueous solution may penetrate into the film, thereby decreasing the transmittance.

The temperature of the crosslinking bath is 20 to 70 캜, and the immersion time of the polyvinyl alcohol film in the crosslinking bath may be 1 second to 15 minutes, preferably 5 seconds to 10 minutes.

The stretching step is carried out together with the crosslinking step, wherein the stretching ratio of the first crosslinking step is 1.4 to 3.0 times, preferably 1.5 to 2.5 times. If the stretching ratio of the first crosslinking step is less than 1.4 times, the optical characteristics may be deteriorated. If the stretching ratio is more than 3.0 times, residual stress may increase and contraction may occur.

The stretching ratio of the second crosslinking step is preferably 1.01 to 2.0 times, more preferably 1.2 to 1.8 times. If the stretching ratio of the second crosslinking step is less than 1.01 times, the optical characteristics may be deteriorated. If the stretching ratio is more than 1.8 times, the residual stress may increase and shrinkage may occur.

The cumulative stretching ratio of the first and second crosslinking steps is preferably 1.5 to 5.0 times, and more preferably 1.7 to 4.5 times. If the cumulative stretching ratio is less than 1.5 times, the effect of the nitrate metal salt may be insufficient. If the cumulative stretching ratio is more than 5.0 times, the film may be broken due to excessive stretching and the production efficiency may be lowered.

It is preferable that the present invention is stretched so that the total cumulative stretching ratio is 4.0 to 7.0 times. In the present specification, "cumulative stretching ratio" represents the value of the product of the stretching ratio at each step.

The crosslinked and stretched polyvinyl alcohol film is dipped in a water bath filled with aqueous solution for washing to remove unnecessary residues such as boric acid attached to the polyvinyl alcohol film in the previous steps.

The aqueous solution for washing may be water, and iodide may be further added thereto.

The temperature of the water bath is preferably 10 to 60 ° C, more preferably 15 to 40 ° C.

The wash step may be omitted and may be performed each time previous steps such as a dyeing step or a bridging step are completed. It may also be repeated one or more times, and the number of repetition is not particularly limited.

The drying step is a step of drying the washed polyvinyl alcohol-based film and further improving the orientation of the iodine molecules dyed by the necking by drying, thereby obtaining a polarizer excellent in optical characteristics.

As the drying method, natural drying, air drying, heating and drying, far infrared ray drying, microwave drying, hot air drying and the like can be used. Recently, microwave drying in which only water in the film is activated and dried is newly used, Drying is mainly used. For example, it may be hot air dried at 20 to 90 DEG C for 1 to 10 minutes. The drying temperature is preferably low in order to prevent deterioration of the polarizer, more preferably 80 ° C or lower, and most preferably 60 ° C or lower.

In addition, the present invention provides a polarizing plate in which a protective film is laminated on at least one surface of a polarizer produced by the above production method.

The protective film is not particularly limited as long as it is a film excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy, and the like. Specifically, polyester resins such as polyethylene terephthalate, polyethylene isophthalate and polybutylene terephthalate; Cellulose-based resins such as diacetylcellulose and triacetylcellulose; Polycarbonate resin; Acrylic resins such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; Styrene resins such as polystyrene and acrylonitrile-styrene copolymer; Polyolefin resins such as polyethylene, polypropylene, cyclo- or norbornene-structured polyolefins, and ethylene propylene copolymers; Vinyl chloride resin; Polyamide resins such as nylon and aromatic polyamide; Imide resin; Polyether sulfone type resin; Sulfone based resin; Polyether ketone resin: a polyphenylene sulfide resin; Vinyl alcohol-based resin; Vinylidene chloride resins; Vinyl butyral resin; Allylate series resin; Polyoxymethylene type resin; Epoxy resin, and the like, and a film composed of the blend of the thermoplastic resin may also be used. Further, a film made of a thermosetting resin such as (meth) acrylic, urethane, epoxy, or silicone or a film made of an ultraviolet curable resin may be used. Among them, a cellulose-based film having a surface saponified (saponified) by alkali or the like is preferable in consideration of polarization characteristics or durability. Further, the protective film may have the function of the optical layer described below.

In the present invention, the structure of the polarizing plate is not particularly limited, and various kinds of optical layers capable of satisfying the required optical characteristics may be laminated on the polarizer. For example, a structure in which a protective film for protecting a polarizer is laminated on at least one side of a polarizer; A structure in which a surface treatment layer such as a hard coating layer, an antireflection layer, an anti-adhesion layer, a diffusion prevention layer, and an anti-glare layer is laminated on at least one surface of a polarizer or on a protective film; Or a structure in which an alignment liquid crystal layer or another functional film is laminated on at least one surface of the polarizer or on the protective film to compensate for the viewing angle. Further, it is also possible to use an optical film such as a polarization conversion device used for forming various image display devices, a retardation film including a reflector, a half-transparent plate, a half-wave plate or a quarter- A plate, a viewing angle compensating film, and a luminance improving film may be laminated with an optical layer. More specifically, a polarizing plate having a structure in which a protective film is laminated on one side of a polarizer, includes: a reflective polarizing plate or a transflective polarizing plate in which a reflector or a transflective reflector is laminated on a laminated protective film; An elliptic or circular polarizer in which a retarder is stacked; A wide viewing angle polarizer in which a viewing angle compensation layer or a viewing angle compensation film is laminated; Or a polarizing plate in which a brightness enhancement film is laminated.

Such a polarizing plate is applicable not only to a general liquid crystal display but also to various image display devices such as an electroluminescent display device, a plasma display device, and a field emission display device.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention. Such variations and modifications are intended to be within the scope of the appended claims.

Example  One

(VF-PS, KURARAY Co.) having a degree of saponification of 99.9% or more was immersed in water (deionized water) at 30 DEG C for 2 minutes to swell, and then 3.5 mmol / L of iodine and 2 wt% of potassium iodide Was dipped in an aqueous solution for dyeing at 30 DEG C for 4 minutes. At this time, stretching was performed at a stretching ratio of 1.3 times and 1.4 times at the swelling and dyeing stages, respectively, and the stretching ratio was increased to 1.82 times at the dyeing bath. Subsequently, the resultant was stretched at a draw ratio of 2 times while being crosslinked (first cross-linking step) in an aqueous solution for crosslinking at 50 ° C containing 10 wt% of potassium iodide, 3.7 wt% of boric acid and 3 wt% of zinc nitrate for 30 seconds. Thereafter, the resultant was stretched at a drawing ratio of 1.5 times while being immersed (crosslinked in a second crosslinking step) for 20 seconds in an aqueous solution for crosslinking at 50 DEG C containing 10 wt% of potassium iodide and 3.7 wt% of boric acid (first and second crosslinking The cumulative stretching ratio of the step is 3 times).

At this time, the total cumulative stretching ratio of the swelling, dyeing and crosslinking steps was made to be 5.46 times. After the crosslinking was completed, the polyvinyl alcohol film was dried in an oven at 70 DEG C for 4 minutes to prepare a polarizer.

A triacetylcellulose (TAC) film was laminated on both sides of the prepared polarizer to prepare a polarizing plate.

Example  2

A polarizer and a polarizing plate were prepared in the same manner as in Example 1 except that the stretching ratios of the respective steps were varied as shown in Table 1 below.

Example  3

(First crosslinking step) for 30 seconds in an aqueous solution for crosslinking at 50 ° C containing 10% by weight of potassium iodide and 3.7% by weight of boric acid, followed by stretching at a draw ratio of 2 times Respectively. Thereafter, the resultant was immersed in a crosslinking aqueous solution at 50 DEG C containing 10 wt% of potassium iodide, 3.7 wt% of boric acid and 3 wt% of zinc nitrate for 20 seconds (second crosslinking step) Was 5.46 times (the cumulative stretching ratio up to the dyeing step was 1.82 times, the cumulative stretching ratio of the crosslinking step was three times).

Example  4

The procedure of Example 1 was repeated, (First crosslinking step) for 30 seconds in an aqueous solution for crosslinking at 50 占 폚 containing 10% by weight of potassium iodide, 3.7% by weight of boric acid and 3% by weight of zinc nitrate, followed by stretching at a draw ratio of 2. Thereafter, it was immersed in a crosslinking aqueous solution at 50 캜 containing 10% by weight of potassium iodide, 3.7% by weight of boric acid and 3% by weight of zinc nitrate for 20 seconds (second crosslinking step) and stretched at a draw ratio of 1.5 times while crosslinking.

Example  5

The same procedure as in Example 1 was carried out except that 1 weight% of zinc nitrate was used.

Example  6

The same procedure as in Example 1 was carried out except that 5 wt% of zinc nitrate was used.

Example  7

The same procedure as in Example 1 was carried out except that 7 weight% of zinc nitrate was used.

Example  8

In the same manner as in Example 1, magnesium nitrate was used instead of zinc nitrate.

Example  9

The procedure of Example 1 was repeated except that cobalt nitrate was used instead of zinc nitrate.

Example  10

The procedure of Example 1 was repeated, except that copper nitrate was used instead of zinc nitrate.

Table 1 summarizes the stretching ratios applied at each step of Examples 1 to 4.

division swelling
step dyeing
step Accumulation up to dyeing stage Bridging step 1st Second accumulate Example 1 1.3 1.4 1.82 2 1.5 3 Example 2-1 2.5 1.1 2.75 1.8 1.3 2.34 Example 2-2 1.2 1.7 2.04 1.5 1.5 2.25 Example 2-3 1.2 1.01 1.212 2.7 1.8 4.86 Examples 2-4 3.2 1.01 3.232 1.4 1.2 1.68 Example 2-5 3.6 1.01 3.636 1.4 1.2 1.68 Examples 2-6 1.3 3.4 4.42 1.4 1.2 1.68 Example 3 1.3 1.4 1.82 2 1.5 3 Example 4 1.3 1.4 1.82 2 1.5 3

Comparative Example  One

(First crosslinking step) for 30 seconds in an aqueous solution for crosslinking at 50 ° C containing 10% by weight of potassium iodide and 3.7% by weight of boric acid, followed by stretching at a draw ratio of 2 times Respectively. Thereafter, it was immersed in a crosslinking aqueous solution at 50 캜 containing 10% by weight of potassium iodide and 3.7% by weight of boric acid for 20 seconds (second crosslinking step) and stretched at a drawing ratio of 1.5 times while crosslinking.

Comparative Example  2

The stretching was carried out in the same manner as in Example 1 except that the stretching was not performed in the swelling and dyeing steps but the stretching was 3 and 1.5 times in the first and second crosslinking steps to maintain the total stretching ratio at 4.5

Comparative Example  3

Polarizers and polarizing plates were prepared in the same manner as in Example 1 except that the stretching ratios of the respective steps were varied as shown in Table 2 below.

division swelling
step dyeing
step Accumulation up to dyeing stage Bridging step 1st Second accumulate Comparative Example 3-1 1.3 1.4 1.82 1.3 1.1 1.43 Comparative Example 3-2 1.3 1.4 1.82 3.5 1.6 5.6 Comparative Example 3-3 1.0 4.1 4.1 1.3 1.3 1.69 Comparative Example 3-4 1.0 1.0 1.0 2.0 2.5 5.0

Comparative Example  4

The same procedure as in Example 1 was carried out except that the steel sheet was immersed in an aqueous crosslinking solution at 50 ° C. containing 10 wt% of potassium iodide, 3.5 wt% of boric acid and 3 wt% of zinc nitrate for 35 seconds, Was carried out.

Test Example

The physical properties of the polarizers prepared in the above Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 3 below.

1. Optical characteristics (polarization degree, transmittance)

The prepared polarizer was cut into a size of 4 cm x 4 cm and the transmittance was measured using an ultraviolet-visible light spectrometer (V-7100, manufactured by JASCO). At this time, the polarization degree is defined by the following equation (1).

(Wherein T ₁ is the parallel transmittance obtained when the pair of polarizers are arranged in parallel with the absorption axis, and T ₂ is the orthogonal transmittance obtained when the pair of polarizers are arranged so that the absorption axes are perpendicular to each other) .

Thereafter, the polarizer was allowed to stand in a dry atmosphere at 105 캜 for 30 minutes (durability test), and optical characteristics were again measured to confirm the amount of change.

2. Durability evaluation (ΔA700, Δ orthogonal b, ΔE )

The spectral transmittance? (?) Of the polarizer was measured using a spectrophotometer (V7100, manufactured by Nippon Bunko KK). An orthogonal spectral transmittance spectrum was obtained from the measured spectral transmittance? (?), And an A700 was determined from the spectral transmittance spectrum using an orthogonal color b and the following formula (2).

Thereafter, the polarizer was allowed to stand in a dry atmosphere at 105 캜 for 30 minutes (durability test), and the spectral transmittance τ (λ) was measured again. The orthogonal spectral transmittance spectrum was obtained from the measured spectral transmittance τ A700 was obtained from the spectrum using the orthogonal color b and the following equation 2 to determine the difference between the orthogonal color b before and after the durability test as? Orthogonal b, and the difference between before and after the durability test of A700 as? A700. At this time, it is judged that the larger the Δ orthogonal b and the ΔA 700 value, the greater the discoloration degree under dry heat.

(Wherein T _{MD , 700} is a parallel transmittance at a wavelength of 700 nm obtained when a pair of polarizing plates are arranged in parallel with the absorption axes, and T _{TD , 700} indicates a state in which the pair of polarizers is orthogonal to the absorption axis Lt; RTI ID = 0.0 > 700nm < / RTI > wavelength)

Further, the difference between before and after the durability test was defined as DELTA E by using the orthogonal L, orthogonal a and orthogonal b values obtained from the spectral transmittance spectrum and the following equation (3).

(In the formula, L ₀ is the duration before the orthogonal value L, L ₁ is an orthogonal L value after the durability test, a ₀ is the duration before orthogonal a value, a ₁ is the orthogonal a value after the durability test, b ₀ is the duration before the orthogonal b value, and b ₁ is an orthogonal b value after the durability)

It is considered that the ΔA700 is less than 1.3, the Δ orthogonal b is less than 0.3, and the smaller the ΔE is, the smaller the discoloration degree is.

After standing for 30 minutes in the dry atmosphere at 105 캜, it was confirmed by visual observation whether or not the polarizer was generated.

division Transmittance
(%) Polarization degree
(%) A700 △ Orthogonal b Rash occurrence
The presence or absence Other Example 1 43.0 99.992 0.37 0.27 radish - Example 2-1 43.0 99.994 0.35 0.22 radish - Example 2-2 43.1 99.991 0.52 0.26 radish - Example 2-3 42.9 99.993 0.41 0.22 radish - Examples 2-4 43.1 99.990 0.79 0.41 radish - Example 2-5 43.0 99.989 0.92 0.51 radish - Examples 2-6 42.8 99.990 0.88 0.59 radish - Example 3 43.0 99.985 0.57 0.22 radish - Example 4 42.9 99.993 0.21 0.09 radish - Example 5 42.8 99.993 0.52 0.29 radish - Example 6 43.0 99.992 0.55 0.22 radish - Example 7 43.0 99.991 0.45 0.19 radish - Example 8 43.0 99.989 0.78 0.47 radish - Example 9 43.2 99.990 0.88 0.52 radish - Example 10 43.1 99.989 0.92 0.34 radish - Comparative Example 1 42.9 99.992 1.48 0.53 U - Comparative Example 2 44.0 99.61 2.2 0.98 U Wrinkle Comparative Example 3-1 42.6 99.96 1.80 0.65 U Wrinkle Comparative Example 3-2 Not measurable Fracture occurrence Comparative Example 3-3 42.5 99.60 2.0 0.82 U Wrinkle Comparative Example 3-4 43.0 99.55 2.1 0.77 U Wrinkle Comparative Example 4 42.9 99.988 1.3 0.48 U -

As shown in Table 1 above, the polarizers of Examples 1 to 10 prepared according to the present invention had deterioration and color durability after being left under dry heat as compared with Comparative Examples 1 to 4, and leakage of iodine complex was prevented, And optical characteristics such as polarization degree were excellent.

Claims (10)

A method for producing a polarizer by performing a swelling, dyeing and crosslinking step of a polyvinyl alcohol-based film in this order,
Performing an elongating step during each of the steps,
Wherein the crosslinking step comprises a first crosslinking step of stretching at a ratio of 1.4 to 3.0 times and a second crosslinking step of crosslinking at a stretching ratio of 1.01 to 2.0 times, and wherein the cumulative stretching ratio of the first and second steps is 1.5 to 5.0 times,
Wherein at least one of the first crosslinking step and the second crosslinking step uses a crosslinked aqueous solution containing a metal nitrate salt and a boron compound.
The method of manufacturing a polarizer according to claim 1, wherein the swelling step is performed by stretching to 1.1 to 3.5 times.
[2] The method of manufacturing a polarizer according to claim 1, wherein the dyeing step is stretched to 1.01 to 2.0 times and the cumulative stretching ratio to the dyeing step is 1.2 to 4.0.
[2] The method of claim 1, wherein the metal nitrate is 0.1 to 10% by weight based on 100% by weight of the aqueous crosslinked solution.
[Claim 4] The method according to claim 4, wherein the metal nitrate is contained in an amount of 0.1 to 10% by weight based on 100% by weight of the aqueous crosslinking solution in the first crosslinking step, and 0.1 to 10% A method for producing a polarizer.
The method of claim 1, wherein the metal nitrate is selected from the group consisting of Li, Na, K, Rb, Cs, Ag, Mg, Ca, Sr, Ba, Cu, Zn, Fe, Co, Ni, Ru, Rh, Pd, A method for producing a polarizer which is a nitrate of a metal selected from the group consisting of Ga, In, Ti, La, Ce, Eu, Gd, Y, Nd, Smp, Tm, Er, Sn, Zr, V, Cr, .
7. The method of claim 6, wherein the metal nitrate is a nitrate of a metal selected from the group consisting of Zn, Cu, Al, Mg, and Zr.
The method of manufacturing a polarizer according to claim 1, further comprising 0.05 to 15% by weight of iodide based on 100% by weight of the aqueous crosslinking solution.
The method of claim 1, wherein the first crosslinking step and the second crosslinking step are repeated two or more times, respectively.
A polarizing plate in which a protective film is laminated on at least one surface of a polarizer produced by the manufacturing method according to any one of claims 1 to 9.