KR20140086018A - Polarizing plate having superior durability - Google Patents

Abstract

The present invention relates to a polarizing plate with enhanced durability. More specifically, the polarizing plate includes a polarizer and a protection film attached on at least one surface of the polarizer. The polarizing plate also satisfies the mathematical equation 1 to increase the durability in a high-temperature and high-humidity environment, thereby maintaining the original color even when the polarizing plate is exposed to such an environment for an extended period of time.

Description

[0001] The present invention relates to a polarizing plate having superior durability,

The present invention relates to a polarizer excellent in durability.

Research has been conducted to provide a polarizing plate having a high degree of polarization and transmittance in order to provide an image excellent in color reproducibility at a high luminance with the development of various image display devices such as a liquid crystal display (LCD) device and a plasma display device (PDP) Has come. In general, a polarizing plate has a basic structure in which a polyvinyl alcohol (PVA) polarizer dyed with a dichroic dye or iodine and a protective film of cellulose (TAC) based protective film for protecting both sides of the polarizer are laminated And a phase difference plate, a viewing angle compensating film, a luminance improving film, and the like may be additionally stacked on the protective film according to a display device.

Since the polyvinyl alcohol polarizer of the polarizing plate thus constructed is thermodynamically unstable and vulnerable to moisture and the TAC protective film has a large moisture absorption rate and moisture permeability, if the polarizer is exposed to a high temperature and high humidity environment for a long time, the polarizer shrinks, There is a problem that the absorption axis of the polarizer is distorted and color discoloration occurs.

Korean Patent Laid-Open Publication No. 2009-82197 discloses a polarizer protective film, a polarizing plate, and an image display device, but fails to provide an alternative to the above problem.

Korea Patent Publication No. 2009-82197

An object of the present invention is to provide a polarizing plate excellent in durability in a high temperature and high humidity environment.

1. A polarizer comprising a polarizer and a protective film bonded to at least one surface of the polarizer,

A polarizing plate satisfying the following formula (1): < EMI ID =

[Equation 1]

(B x I) / W > 2.9 wt%

Wherein B is the boron content (% by weight) in the polarizer, I is the iodine content (% by weight) in the polarizer and W is the moisture content (% by weight) in the polarizing plate.

2. The polarizer of claim 1, wherein the boron content in the polarizer is 3.5 to 7 wt% of the total weight of the polarizer.

3. The polarizer of claim 1, wherein the iodine content in the polarizer is 2 to 5 wt% of the total weight of the polarizer.

4. The polarizer according to 1 above, wherein the water content in the polarizer is 0.05 to 5 wt% of the total weight of the polarizer.

5. The polarizing plate according to item 1 above, wherein the polarizer has a transmittance of 40 to 50% in the visible light region.

The polarizer of the present invention is excellent in durability against high temperature and high humidity environment.

The polarizing plate of the present invention does not cause a color drop phenomenon even if it is exposed to a high temperature and high humidity environment for a long time.

The polarizing plate of the present invention can suppress the occurrence of a color separation phenomenon that may occur in a polarizing plate having a high transmittance.

The present invention relates to a polarizer and a polarizer, which comprises a protective film adhered to at least one surface of a polarizer, satisfies the following formula (1), and is excellent in durability against high temperature and high humidity environment, .

Hereinafter, the present invention will be described in detail.

The polarizing plate of the present invention comprises a polarizer and a protective film adhered to at least one surface of the polarizer, and satisfies the following formula (1): " (1) "

[Equation 1]

(B x I) / W > 2.9 wt%

Wherein B is the boron content (% by weight) in the polarizer, I is the iodine content (% by weight) in the polarizer and W is the moisture content (% by weight) in the polarizing plate.

In the present invention, when the relationship between the boron and iodine content in the polarizer and the water content in the polarizing plate satisfies the above-mentioned formula (1), the durability of the polarizing plate is improved, and color dropout does not occur even after long exposure to a high temperature and high humidity environment .

The polarizing plate having a high transmittance may have a poor polarizing function and a high brightness due to such high transmittance, resulting in color dropout. However, when the above formula (1) is satisfied, the occurrence of color dropout in a polarizer having a high transmittance is suppressed can do.

Boron is typically contained in the polarizer during the process of boronizing and crosslinking the film during the production of the polarizer, and its content can be controlled by the process conditions in addition to the boric acid concentration of the boric acid-containing aqueous solution, It does not.

The boron content in the polarizer is not particularly limited, and may be, for example, 3.5 to 7 wt%, and preferably 4 to 6 wt% of the total weight of the polarizer. When the content of boron in the polarizer is within the above range, it is possible to maintain the proper durability and to prevent the polarizer from being broken, and the iodine complex in the polarizer can be effectively fixed in the polyvinyl alcohol chain, thereby preventing the depolarization of the polarizer at high temperature and high humidity.

The iodine may be typically contained in the polarizer during the film dyeing process during the production of the polarizer, and its content can be controlled by the process conditions other than the boric acid concentration in the dyeing aqueous solution, but the controlling method is not particularly limited.

The content of iodine in the polarizer is not particularly limited, and may be, for example, 2 to 5% by weight, and preferably 2.5 to 3% by weight. When the iodine content in the polarizer is within the above range, a polarizer having a high transmittance can be produced.

The moisture content can be controlled by a drying process during the production process of the polarizer, a conventional drying process after bonding the protective film to the polarizer, and the like.

The water content of the polarizing plate is not particularly limited and may be, for example, 0.05 to 5% by weight, and preferably 0.1 to 3% by weight, based on the total weight of the polarizing plate. When the moisture content of the polarizing plate is within the above range, it is possible to prevent warpage or breakage in the subsequent joining process, and to prevent deformation and discoloration due to moisture in the polarizer in a high temperature and high humidity environment.

The polarizing plate of the present invention comprises a polarizer and a protective film adhered to at least one side of the polarizer.

The polarizer according to the present invention is usually produced by a process of uniaxially stretching a polyvinyl alcohol film, dyeing with a dichroic dye and adsorbing it, processing with an aqueous solution of boric acid and crosslinking, and washing and drying. The order of each step and the number of iterations are not limited. Hereinafter, one embodiment of a method of manufacturing a polarizer will be described in detail.

The step of uniaxially stretching the polyvinyl alcohol film may be performed before dyeing, concurrently with dyeing, or after dyeing. If uniaxial stretching is carried out after dyeing, it may be carried out before the boric acid treatment or during the boric acid treatment. Of course, it is also possible to perform uniaxial stretching by a plurality of steps each of which is combined. The uniaxial stretching may use other rolls or hot rolls with a main circumference, may be dry stretching in air, or may be wet stretching in the state of being swollen with a solvent. The stretching ratio is usually 3 to 8 times.

As a step of dyeing a polyvinyl alcohol film with a dichroic dye, for example, a method of immersing a polyvinyl alcohol film in an aqueous solution containing a dichroic dye may be used. A specific example of the dichroic dye is iodine or a dichroic organic dye. It is preferable that the polyvinyl alcohol film is pre-immersed in water before dyeing to swell.

When iodine is used as the dichroic dye, a method in which a polyvinyl alcohol-based film is dipped in an aqueous solution for dyeing usually containing iodine and potassium iodide may be used. Usually, the content of iodine in an aqueous solution for dyeing is 0.01 to 1 part by weight with respect to 100 parts by weight of water (distilled water), and the content of potassium iodide is 0.5 to 20 parts by weight with respect to 100 parts by weight of water. The temperature of the aqueous solution for dyeing is usually 20 to 40 占 폚, and the immersion time, for example, the dyeing time is usually 20 to 1800 seconds.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method in which a polyvinyl alcohol film is dipped in an aqueous solution for dyeing usually containing a water-soluble dichroic organic dye is used. The content of the dichroic organic dye in the dyeing aqueous solution is usually 1 × 10 ^-4 to 10 parts by weight, preferably 1 × 10 ^-2 to 1 part by weight, based on 100 parts by weight of water. The aqueous solution for dyeing may further contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the aqueous solution for dyeing is usually 20 to 80 캜, and the immersion time, for example, the dyeing time is usually 10 to 1,800 seconds.

The step of subjecting the dyed polyvinyl alcohol film to a boric acid treatment and crosslinking can be carried out by immersing in a boric acid-containing aqueous solution. In general, the content of boric acid in an aqueous solution containing boric acid is preferably 3.5 to 15 parts by weight, and preferably 5 to 12 parts by weight based on 100 parts by weight of water. The aqueous solution containing boric acid when iodine is used as the dichroic dye is preferably contained in an amount of 0.1 to 15 parts by weight, preferably 5 to 12 parts by weight, based on 100 parts by weight of water. The temperature of the boric acid-containing aqueous solution is preferably 50 占 폚 or higher, preferably 50 to 85 占 폚, more preferably 50 to 80 占 폚. The immersion time is preferably 60 to 1,200 seconds, preferably 150 to 600 seconds, more preferably 200 to 400 seconds.

After the boric acid treatment, the polyvinyl alcohol film is washed with water and dried. The water treatment can be carried out by immersing the boric acid-treated polyvinyl alcohol-based film in water. The water temperature during the water treatment is 5 to 40 ° C, and the immersion time is 1 to 120 seconds. After washing with water, the polarizer can be obtained by drying. The drying treatment is usually carried out using a hot air dryer or a far infrared ray heater. The drying treatment temperature is usually 30 to 100 ° C, preferably 50 to 80 ° C, and the drying time is usually 60 to 600 seconds, 600 seconds is good. The thickness of the polarizer may be from 5 to 40 mu m.

A protective film is adhered to at least one surface of the polarizer manufactured by the above process.

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 films such as polyethylene terephthalate, polyethylene isophthalate and polybutylene terephthalate; Cellulose-based films such as diacetylcellulose and triacetylcellulose; Polycarbonate-based films; Acrylic films such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; Styrene-based films such as polystyrene and acrylonitrile-styrene copolymer; Polyolefin films; Vinyl chloride film; Polyamide-based films such as nylon and aromatic polyamide; Imidazole film; Sulfone based films; Polyether ketone-based films; A sulfided polyphenylene-based film; Vinyl alcohol film; Vinylidene chloride films; Vinyl butyral film; Allylate-based films; Polyoxymethylene-based films; Urethane-based films; Epoxy-based films; Silicone-based films, and the like. 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.

The adhesion between the polarizer and the protective film may be made of an adhesive commonly used in the art.

The protective film may be adhered to the polarizer by any method known in the art. For example, a polarizer, a protective film, or a protective film may be formed by a flexible method, a wire bar coating method, a gravure coating method, a die coating method, A method in which an adhesive is applied to the joint surfaces of all of them, and these are adhered. Here, the "softening" is a method in which a polarizer or a protective film as an object to be coated is moved in a substantially vertical direction, a substantially horizontal direction, or an inclined direction between them, and an adhesive is applied to the surface of the object to be coated. After the adhesive is applied, the polarizer and the protective film are adhered to each other through a bonding roll or the like.

After the polarizer and protective film are adhered, a drying step is performed.

The drying can be carried out by a drying apparatus commonly used in the art.

The drying temperature is not particularly limited and may be, for example, 20 to 80 캜, preferably 40 to 60 캜.

The drying time is not particularly limited, and may be, for example, 10 seconds to 30 hours, preferably 5 minutes to 20 minutes.

In the drying step, the moisture of the adhesive may be evaporated toward the protective film or absorbed toward the polarizer, which may have a major influence on the moisture content of the polarizer. If the drying is performed within the above range, the moisture content can be easily adjusted.

The transmittance of the polarizing plate of the present invention is not particularly limited, and can be, for example, 40 to 50%, and preferably 44 to 50% in the visible ray region band. When the transmittance of the polarizing plate is within the above range, proper polarizing function and visibility can be maintained, and power consumption of the liquid crystal display device and the organic light emitting device can be reduced due to high brightness.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to be illustrative of the present invention and are not intended to limit the scope of the appended claims. It will be apparent to those skilled in the art that such variations and modifications are within the scope of the appended claims.

Example  One

A polyvinyl alcohol film (VF-PS, KURARAY Co.) having an average degree of polymerization of 2,400 and a degree of saponification of 99.9 mol% or more was dry-stretched by 6 times in a monoaxial direction, and water of 60 DEG C (deionized water ) For 1 minute, and then immersed in an aqueous solution of 28 ° C at a weight ratio of iodine / potassium iodide / water of 0.013 / 5/100 for 60 seconds. Thereafter, it was immersed in an aqueous solution at 55 캜 for a period of 300 seconds in which the weight ratio of potassium iodide / boric acid / water was 11/10/100. Subsequently, the film was washed with water at 10 DEG C for 20 seconds and then dried at 45 DEG C for 4 minutes to produce a polarizer in which iodine adsorbed and oriented in a polyvinyl alcohol resin.

A protective film (40CHC, TOPPAN) was bonded to one side of the prepared polarizer using a laminator with an adhesive and dried in an oven at 50 ° C for 3 minutes to prepare a polarizing plate.

The whole process was repeated one more time.

Example  2

A polarizing plate was prepared in the same manner as in Example 1, except that the protective film was bonded to one surface of the polarizer and then dried at 60 캜 for 24 hours.

The whole process was repeated one more time.

Comparative Example  One

A polarizing plate was prepared in the same manner as in Example 1, except that the content of boric acid in the crosslinking step was 3 parts by weight based on 100 parts by weight of water.

The whole process was repeated one more time.

Comparative Example  2

A polarizing plate was prepared in the same manner as in Example 1, except that the protective film was bonded to one surface of the polarizer, dried, and then humidified at 60 DEG C and 90% RH for 1 hour.

The whole process was repeated one more time.

Comparative Example  3

A polarizing plate was prepared in the same manner as in Example 1 except that the content of iodine in the dyeing step was 0.005 part by weight based on 100 parts by weight of water.

The whole process was repeated one more time.

Experimental Example  One. Polarizer  Determination of boron content, iodine content

The surface of the polarizer produced in the examples and the production examples was etched step by step using an electro-optic spectrometer (ESCA, model name ESCA LAB 250 system (VG)) according to ESCA (Electron Spectroscopy of Chemical Analysis) , Atomic% (at%) of boron and iodine were measured, and the weight of each element component was calculated therefrom. The ESCA analysis conditions were as follows.

<ESCA analysis conditions>

(1) All ESCA system conditions

Base chamber pressure: 2.5 x 10 ^-10 mbar

X-ray source: monochromatic Al K? (1486.6 eV)

X-ray spot size: 400 탆

Lens mode: LargeAreaXL

Operation mode: Constant Analyzer Energy (CAE) mode

Ar ion etching: etching rate exceeding 0 nm 0.1 nm / sec or less (Mag 10) SiO ₂ criterion

Charge Compensation: Low energy flood gun, no ion flood gun.

The measurement results are shown in Table 1 below.

Experimental Example  2. Measurement of moisture content of polarizer

Three samples of 10 cm x 10 cm were cut out from three different points of the polarizing plate prepared in Examples and Production Examples, and the weight (W0) of each sample was measured.

Thereafter, each of the samples was heated in an oven at 105 DEG C for 2 hours, and the weight (W1) of each sample was measured again.

Then, the moisture content (% by weight) of each sample was calculated according to the following formula (2), and the average value of the moisture contents of the three samples was taken as the moisture content of the polarizing plate.

&Quot; (2) &quot;

Water content (% by weight) = {(W0 - W1) / W0} x100

(W0: moisture content (% by weight) of initial sample, W1: moisture content (% by weight) of sample after heating)

The measurement results are shown in Table 1 below.

division Boron content in the polarizer (B)
(weight%) Within the polarizer
Iodine content (I)
(weight%) Water content (W) of polarizer
(weight%) (B x I) / W
(weight%) Example 1 4.56 2.79 2.79 4.56 Example 2 4.12 2.76 0.78 14.58 Comparative Example 1 2.97 2.72 3.12 2.59 Comparative Example 2 3.24 2.71 4.44 1.98 Comparative Example 3 3.31 1.72 2.77 2.06

Experimental Example  3. Color separation  Assessing the occurrence of the phenomenon

The polarizing plates prepared in Examples and Comparative Examples were allowed to stand at 85 ° C and 85% RH for 24 hours, and then placed in a cross-nicol state on the backlight to visually evaluate the occurrence of color separation phenomenon. Observation results are shown in Table 2 below.

<Evaluation Criteria>

○: Many color drop phenomenon occurs

△: Color dropout occurred slightly

Ⅹ: No color drop phenomenon occurred

division Whether a color dropout occurs Example 1 X Example 2 X Comparative Example 1 O Comparative Example 2 O Comparative Example 3 O

Referring to Table 1, it can be confirmed that the polarizing plates of Examples 1 and 2 do not cause color dropout, and thus have excellent durability against high temperature and high humidity environment.

However, it was confirmed that the polarizing plates of Comparative Examples 1 to 3 suffered from color discontinuity and durability against high temperature and humidity environment.

Claims (5)

A polarizer, and a protective film adhered to at least one side of the polarizer,
A polarizing plate satisfying the following formula (1): &lt; EMI ID =
[Equation 1]
(B x I) / W &gt; 2.9 wt%
(Wherein B is the boron content (% by weight) in the polarizer,
I is the iodine content (% by weight) in the polarizer,
And W is the water content (% by weight) in the polarizing plate).
The polarizer of claim 1, wherein the boron content in the polarizer is 3.5 to 7 wt% of the total weight of the polarizer.
The polarizer of claim 1, wherein the iodine content in the polarizer is 2 to 5 wt% of the total weight of the polarizer.
The polarizing plate according to claim 1, wherein the water content in the polarizing plate is 0.05 to 5 wt% of the total weight of the polarizing plate.
The polarizer according to claim 1, having a transmittance of 40 to 50% in the visible light region.