KR20150103349A - Polarizer having high durability and method for preparing the same - Google Patents

Abstract

The polarizer of the present invention includes boric acid and potassium iodide. The ratio (W_BA/W_KI) of the content of the boric acid (W_BA) to the content of the potassium iodide (W_KI) is 5 to 10.

Description

TECHNICAL FIELD [0001] The present invention relates to a high-durability polarizer, and a method of manufacturing the same. BACKGROUND ART [0002]

The present invention relates to a high-durability polarizer and a manufacturing method thereof. More specifically, the present invention relates to a high-durability polarizer excellent in optical durability and low in color change in a high-temperature environment by adjusting the content of boric acid and potassium iodide to a specific range, and a method for producing the same.

BACKGROUND ART [0002] Liquid crystal displays (LCDs) are one of the most widely used flat panel displays. A liquid crystal display device includes a liquid crystal display panel including a liquid crystal layer sandwiched between two display plates on which an electric field generating electrode is formed and a voltage is applied to the electric field generating electrode to generate an electric field in the liquid crystal layer, The image is displayed by determining the orientation of the molecules and controlling the polarization of the incident light.

On the other hand, a polarizing plate is provided outside the liquid crystal display panel. The polarizing plate can control the polarization by selectively transmitting light in a specific direction among light incident from the backlight and light passing through the liquid crystal layer.

The polarizer includes a polarizer capable of polarizing light in a specific direction and a protective layer for supporting and protecting the polarizer. Such a polarizer is produced by dyeing a polyvinyl alcohol-based film with iodine with dichroism, and then crosslinking it with boric acid or the like.

In recent years, a high optical durability is required for a polarizer. Accordingly, US 4,591,512 proposes a method of improving red leakage at high temperatures by impregnating a polarizer with zinc ions. However, the above method has a problem of increasing the transmittance in the short wavelength region in the orthogonal state of the polarizing plate, thereby lowering the degree of polarization or making the polarizing plate bluish

In addition, a method of controlling the optical durability and color change under heating by controlling the content of iodine (I) / potassium (K) in the inside of the polarizer has been developed. However, this method is merely a method of controlling the KI content If the KI content is excessively reduced to improve the durability of the polarizer, the chromaticity control is not easy. If the KI content is excessively large, the KI remaining on the surface may cause adverse effects in terms of durability.

An object of the present invention is to provide a polarizer having excellent light durability in a high temperature environment and having little color change, and a method for producing the same.

Another object of the present invention is to provide a polarizer excellent in polarization degree, transmittance and appearance, and a method for producing the same.

It is still another object of the present invention to provide a polarizing plate comprising the polarizer.

One aspect of the present invention relates to a polarizer. Wherein the polarizer comprises boric acid and potassium iodide, and the ratio (W _BA / W _KI ) of the content (W _BA ) of the boric acid to the content (W _KI ) of the potassium iodide is 5 to 10.

In an embodiment, the polarizer may have a ratio of the boric acid content to the potassium iodide content (W _BA / W _KI ) of from 6.5 to 8.5.

In an embodiment, the polarizer may have a boric acid content of 18-22 wt% and a potassium iodide content of 2-4 wt%.

In an embodiment, the polarizer may have a color coordinate change amount? Ab in an orthogonal state according to the following formula 1: 1 to 4:

[Formula 1]

In the above, ac ₃ and bc ₃ are the chromaticity of the orthogonal state measured after standing at 105 ° C for 3 hours, and ac ₀ and bc ₀ are orthogonal chromaticity _values in the initial state.

Another aspect of the present invention relates to a method for producing the polarizer. The method comprises stretching a polyvinyl alcohol-based film while dyeing it in a dyeing bath containing iodine and potassium iodide; Stretching the dyed polyvinyl alcohol-based film in a stretching bath containing boric acid and potassium iodide; And stretching the stretched polyvinyl alcohol-based film in a sub-color bath comprising boric acid and potassium iodide.

In an embodiment, the stretching bath comprises 2.5 to 3.5% by weight of boric acid, 2.5 to 3.5% by weight of potassium iodide, and the balance water, and the temperature may be 45 to 65 ° C.

The boil-off hue may contain 0.8 to 1.2% by weight of boric acid, 3.0 to 4.0% by weight of potassium iodide, and the balance water, and the temperature may be 35 to 45 ° C.

The stretching ratio in the dyeing bath is 1.5 to 2.2 times, the stretching ratio in the stretching bath is 2.0 to 3.2 times, and the total dyeing ratio in the dyeing bath is 5 to 6.5 times.

Another aspect of the present invention relates to a polarizing plate. The polarizer has a structure in which a protective film is laminated on at least one surface of the polarizer.

The present invention has the effects of providing a polarizer excellent in light durability in a high temperature environment, less change in color, excellent in polarization degree, transmittance and appearance, a method for producing the same, and a polarizing plate comprising the polarizer.

The polarizer of the present invention comprises boric acid and potassium iodide and the ratio (W _BA / W _KI ) of the content (W _BA ) of the boric acid to the content (W _KI ) of the potassium iodide is 5 to 10, 8.5. If the content ratio of boric acid to potassium iodide (W _BA / W _KI ) is less than 5, the color change in the orthogonal state increases and the optical durability decreases. Also, when the content ratio of boric acid and potassium iodide (W _BA / W _KI ) exceeds 10, the color change in the orthogonal state increases and the light durability and appearance and transmittance are lowered.

In an embodiment, the polarizer has a boric acid content of 18-22 wt%, preferably 18.5-21.5 wt%. Can exhibit excellent light durability within the above range, can minimize color change, can prevent breakage (breakage of the film) in the stretching process, and has excellent characteristics such as polarization degree.

In addition, the polarizer may have a potassium iodide content of 2 to 4% by weight, preferably 3 to 3.8% by weight. It is possible to minimize the color change while having excellent light durability in the above range, and also to prevent the color of the polarizing plate from becoming bluish or the polarization degree from being lowered.

The polarizer may have a color coordinate change amount? Ab in an orthogonal state according to the following formula 1: 1 to 4, preferably 1 to 3, more preferably 1 to 2:

[Formula 1]

In the above, ac ₃ and bc _{3 are} the chromaticity of the orthogonal state measured after standing at 105 ° C for 3 hours, and ac ₀ and bc ₀ are orthogonal chromaticity _values in the initial state.

The method for producing a polarizer of the present invention comprises stretching a polyvinyl alcohol-based film while dyeing it in a dyeing bath containing iodine and potassium iodide; Stretching the dyed polyvinyl alcohol-based film in a stretching bath containing boric acid and potassium iodide; And stretching the stretched polyvinyl alcohol-based film in a sub-color bath comprising boric acid and potassium iodide.

The polyvinyl alcohol-based film that can be used in the present invention is not particularly limited as long as it can be used for producing polarizers. For example, a polymer having a degree of polymerization of 1,000 to 3,500 and a degree of saponification of 99.8 mol% or more may be used and is not necessarily limited thereto.

In a specific example, a swelling process may be performed before dyeing the polyvinyl alcohol-based resin film with iodine. The swelling process is performed at a temperature of about 22-35 DEG C in a swelling bath, and is a process for removing foreign matters on the surface of the film or for dyeing well. The swelling bath may comprise water or a chloride, boric acid, mineral acid, organic solvent, and the like. The manufacture and selection of a swelling bath can be readily carried out by one of ordinary skill in the art to which this invention belongs. In a specific example, stretching can be performed in the swelling bath. In the specific example, the cumulative stretching ratio in the swelling tank is 1.1 to 1.6 times.

The swollen polyvinyl alcohol-based film may be stained in a staining bath. The dyeing bath comprises iodine and potassium iodide. In an embodiment, the iodine dyeing bath may comprise about 0.05 to 0.2 parts by weight of iodine and about 0.5 to 2.5 parts by weight of potassium iodide, based on 100 parts by weight of water. The iodine dyeing can be performed at a temperature of about 20 to 40 캜. The stretching can be performed in the dyeing bath, and the cumulative stretching ratio may be 1.5 to 2.2 times.

The dyed polyvinyl alcohol-based film is stretched in a stretching bath containing boric acid and potassium iodide. The stretching can be carried out by a conventional method. In the embodiment of the present invention, stretching can be performed so that the stretching ratio in the stretching bath is about 2.0 to 3.2 times. In an embodiment, the stretching bath comprises 2.5 to 3.5% by weight of boric acid, 2.5 to 3.5% by weight of potassium iodide, and the balance water, and the temperature may be 45 to 65 ° C.

The polyvinyl alcohol-based film stretched in the stretching bath may be crosslinked and stretched in a borosilicate bath containing boric acid and potassium iodide. The boil-off hue may contain 0.8 to 1.2% by weight of boric acid, 3.0 to 4.0% by weight of potassium iodide, and the balance water, and the temperature may be 35 to 45 ° C. And may be stretched to have a total m / e ratio of 5 to 6.5 in the beam shade. Preferably, the total mnemonic ratio is adjusted to 5.8 to 6.2 times, more preferably the total mnemonic ratio is 5.9 to 6.1 times.

The polarizer of the present invention produced as described above has a thickness of about 0.5 to 400 탆, preferably about 5 to 200 탆.

Another aspect of the present invention relates to a polarizing plate comprising the polarizer. In a specific example, the polarizing plate is characterized in that a protective film is formed on at least one surface of the polarizer. The protective film may have functions of a retardation film, a brightness enhancement film, a reflective film, a transflective film, a diffusion film, an optical compensation film, and the like, and the film may be further laminated on the protective film. In embodiments, the thickness of the protective film ranges from 50 to 400 microns, preferably from about 70 to 200 microns. The protective film may be laminated to the polarizer through an adhesive.

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense. The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

Example

Example  One

The PVA film (VF-PS # 7500, thickness: 75 μm, KURARAY Co., Ltd., having a degree of polymerization of 2,400, a width of 3,000 mm and a degree of saponification of 99.9 mol% or more) is kept in tension so as not to loosen the film in a deionized water filled with deionized water at 30 ° C. And the stretching ratio of the swelling bath was 1.40 times. Iodine / potassium iodide in a weight ratio of 1/23 with a salt water solution at 30 DEG C, so as to obtain a cumulative stretching ratio of 1.70. Next, 3.0% by weight of boric acid and 3.0% by weight of potassium iodide were drawn 2.5 times in an aqueous solution of a drawing tank at 54 DEG C, and then the total mnemonic ratio was 6.0-fold in an aqueous solution of 40 DEG C in a continuous bath consisting of 1.0% by weight of boric acid and 3.0% by weight of potassium iodide So as to be uniaxially stretched. And then dried at 50 DEG C for 4 minutes to prepare an iodine polarizer having a thickness of 28 mu m. An adhesive was applied to both surfaces of the prepared polarizer, and a saponified triacetylcellulose film (Fujita TAC T80UNL, Fuji Photo Film Co., Ltd.) was bonded to the surface with a thickness of 80 탆 and dried at 60 캜 for 5 minutes to prepare a polarizing plate .

Example  2

The PVA film (VF-PS # 7500, thickness: 75 μm, KURARAY Co., Ltd., having a degree of polymerization of 2,400, a width of 3,000 mm and a degree of saponification of 99.9 mol% or more) is kept in tension so as not to loosen the film in a deionized water filled with deionized water at 30 ° C. And the stretching ratio of the swelling bath was 1.40 times. Iodine / potassium iodide in a weight ratio of 1/23 with a salt water solution at 30 DEG C, so as to obtain a cumulative stretching ratio of 1.70. Then, 3.2% by weight of boric acid and 3.0% by weight of potassium iodide were drawn 2.5 times in an aqueous solution of the drawing at 53 ° C, and then the total mnemonic ratio was 6.0 times in an aqueous solution of 40 ° C in a borosilicate bath composed of 1.0% by weight of boric acid and 3.0% And then uniaxially stretched. And then dried at 50 DEG C for 4 minutes to prepare an iodine polarizer having a thickness of 28 mu m. An adhesive was applied to both surfaces of the prepared polarizer, and a saponified triacetylcellulose film (Fujita TAC T80UNL, Fuji Photo Film Co., Ltd.) was bonded to the surface with a thickness of 80 탆 and dried at 60 캜 for 5 minutes to prepare a polarizing plate .

Comparative Example 1

The PVA film (VF-PS # 7500, thickness: 75 μm, KURARAY Co., Ltd., having a degree of polymerization of 2,400, a width of 3,000 mm and a degree of saponification of 99.9 mol% or more) is kept in tension so as not to loosen the film in a deionized water filled with deionized water at 30 ° C. And the stretching ratio of the swelling bath was 1.40 times. Iodine / potassium iodide in a weight ratio of 1/23 with a salt water solution at 30 DEG C, so as to obtain a cumulative stretching ratio of 1.70. 2.0% by weight of boric acid and 3.0% by weight of potassium iodide were drawn 2.5 times in an aqueous solution of the drawing at 60 ° C, and then the total mnemonic ratio was set to 6.0 times in an aqueous solution of 40 ° C bauxite continuously composed of 1.0% by weight of boric acid and 4.0% And then uniaxially stretched. And then dried at 50 DEG C for 4 minutes to prepare an iodine polarizer having a thickness of 28 mu m. An adhesive was applied to both surfaces of the prepared polarizer, and a saponified triacetylcellulose film (Fujita TAC T80UNL, Fuji Photo Film Co., Ltd.) was bonded to the surface with a thickness of 80 탆 and dried at 60 캜 for 5 minutes to prepare a polarizing plate .

Comparative Example 2

The PVA film (VF-PS # 7500, thickness: 75 μm, KURARAY Co., Ltd., having a degree of polymerization of 2,400, a width of 3,000 mm and a degree of saponification of 99.9 mol% or more) is kept in tension so as not to loosen the film in a deionized water filled with deionized water at 30 ° C. And the stretching ratio of the swelling bath was 1.40 times. Iodine / potassium iodide in a weight ratio of 1/23 with a salt water solution at 30 DEG C, so as to obtain a cumulative stretching ratio of 1.70. 3.5% by weight of boric acid and 3.0% by weight of potassium iodide were drawn 2.5 times in an aqueous solution at 50 ° C, and then the total mnemonic ratio was 6.0-fold in an aqueous solution of a 40 ° C continuous solution composed of boric acid 1.0% by weight and potassium iodide 4.0% So as to be uniaxially stretched. And then dried at 50 DEG C for 4 minutes to prepare an iodine polarizer having a thickness of 28 mu m. An adhesive was applied to both surfaces of the prepared polarizer, and a saponified triacetylcellulose film (Fujita TAC T80UNL, Fuji Photo Film Co., Ltd.) was bonded to the surface with a thickness of 80 탆 and dried at 60 캜 for 5 minutes to prepare a polarizing plate .

Comparative Example 3

The PVA film (VF-PS # 7500, thickness: 75 μm, KURARAY Co., Ltd., having a degree of polymerization of 2,400, a width of 3,000 mm and a degree of saponification of 99.9 mol% or more) is kept in tension so as not to loosen the film in a deionized water filled with deionized water at 30 ° C. And the cumulative stretching ratio of the swelling bath was 2.3 times. Was drawn so as to have a cumulative stretching ratio of 2.8 times in a salt bath filled with an aqueous salt solution at 30 캜 comprising iodine / potassium iodide in a weight ratio of 1/23. Then, a total mordenite ratio of 6.0% by weight was obtained in an aqueous solution of a boron-containing dye solution at a temperature of 40 ° C, which consisted of 3.0% by weight of boric acid, 3.0% by weight of potassium iodide, 2.0 times of a draw bath aqueous solution at 54 ° C and 1.0% by weight of boric acid and 3.0% And then uniaxially stretched. And then dried at 50 DEG C for 4 minutes to prepare an iodine polarizer having a thickness of 28 mu m. An adhesive was applied to both surfaces of the prepared polarizer, and a saponified triacetylcellulose film (Fujita TAC T80UNL, Fuji Photo Film Co., Ltd.) was bonded to the surface with a thickness of 80 탆 and dried at 60 캜 for 5 minutes to prepare a polarizing plate .

Table 1 shows the temperature and boric acid contents of the stretching baths of Examples 1 and 2 and Comparative Examples 1 to 3 and the conditions of potassium iodide content in the sub-color bath.

division Stretching tank Bose Hue Temperature Boric acid content (% by weight) Stretching cost Potassium iodide content (% by weight) Example 1 54 ℃ 3.0 2.5 3.0 Example 2 53 ℃ 3.2 2.5 3.0 Comparative Example 1 60 ° C 2.0 2.5 4.0 Comparative Example 2 50 ℃ 3.5 2.5 4.0 Comparative Example 3 54 ℃ 3.0 2.0 3.0

≪ Property evaluation method &

(1) Contents of boric acid and potassium iodide (KI): 1 g of a polarizer and 50 g of deionized water were placed in a beaker, heated and completely dissolved, and 10 g of a solution of Manitol solution (Manitol: distilled water = 1: 7 weight ratio) NaOH aqueous solution to determine the boric acid content (W _BA ). 1 g of the polarizer and 50 g of deionized water were placed in a beaker, heated and completely dissolved, and titrated with a 0.1N aqueous solution of AgNO ₃ to measure the potassium iodide (KI) content (W _KI ). The content ratio (W _BA / W _KI ) of the obtained boric acid content (W _BA ) and potassium iodide (KI) content (W _KI ) was determined and shown in Table 2.

(2) Orthogonal State Color Change (Δab): After each sample prepared in the above Examples and Comparative Examples was lapped on an alkali-free glass, the characteristics of the polarizing plate were measured using a spectrophotometer V-7100 manufactured by JASCO ( Japan) Respectively. Each sample was then placed in an oven at 105 ° C, heated for 3 hours, and then characterized using a spectrophotometer. Through the Hunter color coordinate, the orthogonal chromaticity at the initial stage of the polarizing plate (ac ₀ bc ₀ ), the orthogonal chromaticity after leaving at 105 ° C for 3 hours (ac _{3 ,} bc ₃ ) were measured and found by the following formula (1).

[Formula 1]

In the above, ac ₃ and bc ₃ are the chromaticity of the orthogonal state measured after standing at 105 ° C for 3 hours, and ac ₀ and bc ₀ are orthogonal chromaticity _values in the initial state.

(3) Polarization degree: One polarizing plate was measured for the parallel transmittance and the orthogonal transmittance at 0 degree and 90 degree using the above spectrophotometer, and the degree of polarization was calculated from the following equation 2, and is shown in Table 3.

[Formula 2]

In the above, Tp is the parallel transmittance, Tc is the orthogonal transmittance (the visibility correction Y value by the 2-degree field of view (C light source)

(4) Transmittance: The transmittance of one polarizing plate was measured using a spectrophotometer V-7100 manufactured by JASCO Co., Ltd., and is shown in Table 3. The transmittance of the polarizing plate is a Y value obtained by performing visibility correction by a 2-degree field of view (C light source) of JIS Z8701.

(5) Appearance and visual evaluation: Evaluation was conducted after heating in an oven at 85 ° C for 500 hours. The degree of redness of color is classified into 0 level ~ 4 level, and the number is set higher as the degree of redness is greater.

division Boric acid content (% by weight) KI content (% by weight) Boric acid content / KI content ratio (W _BA / W _KI ) Example 1 21.5 2.6 8.3 Example 2 22.0 3.0 7.3 Comparative Example 1 17.5 4.5 3.9 Comparative Example 2 22.5 2.0 11.3 Comparative Example 3 24.0 1.8 13.3

division Orthogonal state
Color change (? Ab) Polarization degree (%) Exterior Mock assessment Early 105 degrees 3 hours Example 1 1.4 99.98 99.96 Good 0 Example 2 1.6 99.97 99.97 Good One Comparative Example 1 4.8 99.97 99.93 Good 4 Comparative Example 2 4.5 99.98 99.92 Good 4 Comparative Example 3 5.0 99.95 99.90 Good 4

As shown in Table 3, the content of boric acid ratio (W _BA / W _KI) is in the range of 7.3 to 8.5, the practice of the (W _BA) and the amount of potassium iodide (W _KI) Example 1-2 is in a high-temperature environment The optical durability is excellent and the amount of color change is small. In contrast, Comparative Examples 1 to 3, in which the W _BA / W _KI was less than 7.3 or more than 8.5, showed high color change.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the embodiments described above are in all respects illustrative and not restrictive.

Claims (8)

Boric acid and potassium iodide,
_Wherein the ratio (W _BA / W _KI ) of the content of boric acid (W _BA ) to the content of potassium iodide (W _KI ) is 7.3 to 8.5.
The polarizer according to claim 1, wherein the polarizer has a boric acid content of 18 to 22 wt% and a potassium iodide content of 2 to 4 wt%.
The polarizer according to claim 1, wherein the polarizer is a polarizer having a color coordinate change amount? Ab in an orthogonal state according to the following formula (1) is 1 to 4:

[Formula 1]

In the above, ac ₃ and bc ₃ are the chromaticity of the orthogonal state measured after standing at 105 ° C for 3 hours, and ac ₀ and bc ₀ are orthogonal chromaticity _values in the initial state.
Stretching the polyvinyl alcohol-based film while dyeing it in a dyeing bath containing iodine and potassium iodide;
Stretching the dyed polyvinyl alcohol-based film in a stretching bath containing boric acid and potassium iodide; And
Stretching the stretched polyvinyl alcohol-based film in a boron color tone bath containing boric acid and potassium iodide;
≪ / RTI >
_Wherein the ratio (W _BA / W _KI ) of the content of boric acid (W _BA ) to the content of potassium iodide (W _KI ) is 7.3 to 8.5.
5. The method of claim 4, wherein the stretching bath comprises 2.5 to 3.5% by weight of boric acid, 2.5 to 3.5% by weight of potassium iodide, and the balance water and the temperature is 45 to 65 占 폚.
5. The method according to claim 4, wherein the boron color tone comprises 0.8 to 1.2% by weight of boric acid, 3.0 to 4.0% by weight of potassium iodide and the balance water and the temperature is 35 to 45 占 폚.
The method according to claim 4, wherein the cumulative stretching ratio in the dyeing bath is 1.5 to 2.2 times, the cumulative stretching ratio in the stretching bath is 2.0 to 3.2 times, and the total draw ratio is 5 to 6.5 times in the boat color bath.
A polarizing plate in which a protective film is laminated on at least one surface of the polarizer of any one of claims 1 to 3.