KR20120047499A - Method of preparing polarizer - Google Patents

Abstract

A method of manufacturing a polarizer capable of preventing dyeing phenomena and manufacturing a polarizer showing excellent display quality is proposed. In the polarizer manufacturing method of the present invention, the polyvinyl alcohol-based film is swelled, the swollen polyvinyl alcohol-based film is dyed with iodine, and the dyed polyvinyl alcohol-based film is crosslinked. Thereafter, the crosslinked polyvinyl alcohol-based film is washed with a deionized water and potassium iodide and washed in a washing solution having a pH of 7.0 to 11.0 and dried to prepare a polarizer.

Description

Polarizer manufacturing method {METHOD OF PREPARING POLARIZER}

The present invention relates to a polarizer manufacturing method, and more particularly, to a polarizer manufacturing method capable of manufacturing a polarizer showing excellent display quality by preventing the dyeing mura phenomenon.

In the liquid crystal display device, it is indispensable to arrange polarizers on both sides of the glass substrate forming the surface of the liquid crystal panel in terms of its image forming method. The polarizer is generally obtained by dyeing a polyvinyl alcohol (PVA) -based film with a dichroic material such as iodine, crosslinking with a crosslinking agent, uniaxially stretching the film, and forming the film. Since the polarizer is produced by stretching, it tends to shrink, and in particular, since the polyvinyl alcohol-based film uses a hydrophilic polymer, it is easy to deform under particularly humid humid conditions. In addition, since the mechanical strength of the film itself is weak, there is a problem that the film is torn. Therefore, the polarizing plate which supplemented the intensity | strength by adhering a protective film to the both sides or one side of a polarizer is used.

BACKGROUND ART Liquid crystal display devices have been widely used, and have been widely developed from portable terminals to large TVs for home use. Accordingly, technology development for ensuring excellent display quality in each liquid crystal display device has been progressed.

Recently, as part of the development of technology for reducing power consumption in the LCD, efforts have been made to ensure high transmittance of the polarizer. However, in the process of increasing the transmittance of the polarizing plate, for example, when the transmittance of the polarizing plate is 43.0% or more, in-plane dyeing unevenness is likely to occur. As a result, when the panel is mounted and evaluated, dyeing mura phenomenon often occurs in which white lines appear in the horizontal direction.

Therefore, there is a request for a technology that can obtain a desired display quality while ensuring a high transmittance.

The present invention is to solve the above-mentioned problems, an object of the present invention is to provide a polarizer manufacturing method that can produce a polarizer showing excellent display quality by preventing the dyeing mura phenomenon.

Polarizer manufacturing method according to an aspect of the present invention for achieving the above object is a swelling step of swelling a polyvinyl alcohol-based film; A dyeing step of dyeing the swollen polyvinyl alcohol-based film with iodine; A crosslinking step of crosslinking the dyed polyvinyl alcohol-based film; Washing the cross-linked polyvinyl alcohol-based film in a washing solution containing deionized water and potassium iodide and having a pH of 7.0 to 11.0; And a drying step of drying the washed polyvinyl alcohol-based film.

The content of potassium iodide is preferably 3.0 to 10.0 parts by weight based on 100 parts by weight of deionized water.

The washing step may be performed for 5 seconds to 20 seconds, the temperature of the washing solution is preferably 5 ℃ to 12 ℃.

The crosslinking step can be carried out using boric acid as the crosslinking agent.

The polarizer manufactured according to the polarizer manufacturing method according to the present invention is prepared by adding potassium iodide to the washing liquid for washing and performing a washing process with a pH in a predetermined range, thereby exhibiting high permeability for reducing power consumption of the liquid crystal display device. Dye-mura does not occur, and there is an effect of exhibiting excellent display quality with little variation in in-plane optical characteristics.

Hereinafter, embodiments of the present invention will be described. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

Polarizer manufacturing method according to an embodiment of the present invention swelling step of swelling a polyvinyl alcohol-based film; A dyeing step of dyeing the swollen polyvinyl alcohol-based film with iodine; A crosslinking step of crosslinking the dyed polyvinyl alcohol-based film; Washing the cross-linked polyvinyl alcohol-based film in a washing solution containing deionized water and potassium iodide and having a pH of 7.0 to 11.0; And a drying step of drying the washed polyvinyl alcohol-based film.

The polarizer manufactured according to an embodiment of the present invention is prepared by dyeing and orienting a hydrophilic polymer film with iodine and a dichroic material, and a film such as a PVA-based film, a partially saponified PVA-based film, etc. is used as the hydrophilic polymer film. do.

The polyvinyl alcohol-based film has a polymerization degree of usually 500 to 10,000, preferably 1,000 to 6,000, more preferably 1,400 to 4,000 can be used, in the case of polyvinyl alcohol-based safflower film, saponification degree is solubility aspect Is preferably at least 95.0 mol%, more preferably at least 99.0 mol%, and most preferably at least 99.9 mol% may be used.

The hydrophilic polymer film is not particularly limited as long as it is a film that can be dyed with iodine in addition to the polyvinyl alcohol-based film. For example, hydrophilic polymer films such as polyethylene terephthalate film, ethylene-vinyl acetate copolymer film, ethylene-vinyl alcohol copolymer film, cellulose film, and partially gumified films thereof, and polyvinyl alcohol based on dehydration treatment Films, and polyene oriented films such as dechlorinated polyvinyl chloride and the like can be used.

The thickness of the polarizer is not particularly limited, but is, for example, in the range of 5 to 40 µm, preferably 10 to 30 µm, and more preferably 15 to 25 µm.

In the polarizer manufacturing method according to the present invention to prepare a polarizer by washing and drying the polarizer prepared through the swelling step, the dyeing step, and the crosslinking step.

The swelling step is a step of immersing the unstretched PVA film in a swelling tank filled with an aqueous solution for swelling before dyeing with iodine. Through this process, impurities deposited on the surface of the PVA film can be cleaned, and impurities such as an antiblocking agent can be washed. Also, the PVA film is swelled to improve drawing efficiency, prevent dye nonuniformity, and improve dyeing properties. Can be improved.

Deionized water may be used alone as the aqueous solution for swelling, and when a small amount of glycerin, potassium iodide or boric acid is added thereto, the processability may be improved along with the swelling of the PVA-based film. The content of glycerin in 100% by weight of the aqueous solution for swelling is preferably 5% by weight or less, and the content of potassium iodide is 10% by weight or less.

It is preferable that the temperature of a swelling tank is 20-45 degreeC, More preferably, it is 25-40 degreeC. The execution time (immersion time) of the swelling step is preferably 180 seconds or less. When the immersion time is in the range, it is possible to prevent the swelling from being excessively saturated, thereby preventing breakage due to softening of the PVA-based film, and uniformly adsorbing iodine in the dyeing step, thereby improving polarization degree.

The stretching step may be performed together with the swelling step, wherein the stretching ratio is preferably 1.7 to 2.4 times.

The dyeing step is performed by immersing a non-plasticized polyvinyl alcohol-based film containing no plasticizer in a dye bath filled with a dyeing solution containing iodine in a dry state without swelling and swelling and adsorbing iodine on the polyvinyl alcohol-based film. can do.

The aqueous solution for dyeing may include deionized water or a water-soluble organic solvent and iodine. The content of iodine is preferably 0.1 to 5.0 mM, more preferably 0.5 to 3.0 mM, most preferably 0.8 to 2.0 mM.

In the high transmissive polarizer, it is important to reduce the absolute dyeing amount of iodine to increase the transmittance, but to perform in-plane dyeing without variation.

In particular, iodide may be further included as a dissolution aid for further improving the dyeing efficiency in the manufacture of the iodine-based polarizer. As the iodide, at least one of 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. Potassium iodide is most commonly used because of its high solubility in water. The iodide content is preferably 1.0 to 5.0 parts by weight based on 100 parts by weight of the mixed solvent with deionized water or a water-soluble organic solvent.

Moreover, it is preferable that the aqueous solution for dyeing further contains a small amount of crosslinking agents. As the crosslinking agent, one or more selected from boron compounds such as boric acid and sodium borate, dicarboxylic acid compounds and dialdehyde compounds may be used. Preferably, boric acid and sodium borate may be used in combination. In the case of further comprising a crosslinking agent, there is an effect of further strengthening the crosslinking of the iodine molecule. The content of the crosslinking agent is preferably 0.01 to 6% by weight, more preferably 0.10 to 3% by weight based on 100% by weight of the aqueous solution for dyeing.

It is preferable that the temperature of a dye bath is 5-42 degreeC, More preferably, it is 10-35 degreeC. The immersion time of the PVA-based film in the dye bath is not particularly limited, and is preferably 1 to 20 minutes, more preferably 2 to 10 minutes.

The stretching process may be performed together with the dyeing step, wherein the cumulative stretching ratio is preferably 1.10 to 2.50 times. More preferably, it is 1.30 times-2.20 times, Most preferably, it is 1.50 times-2.00 times.

The crosslinking step is to fix the adsorbed iodine molecules or dye molecules by immersing a polyvinyl alcohol-based film in which the iodine and the dichroic dye are adsorbed and physically bonded so that dyeability may be degraded by an external environment in an aqueous solution for crosslinking. to be. In the case of dyes, they are not eluted in a moisture resistant environment. In the case of iodine, iodine molecules are dissolved or sublimed depending on the environment. Therefore, crosslinking treatment between polyvinyl alcohol molecules by an aqueous solution for crosslinking is very important for iodine molecules to be adsorbed to the oriented polyvinyl alcohol molecules to exhibit optical properties stably.

The aqueous solution for crosslinking is a polyhydric carboxylic acid containing two or more carboxyl groups such as deionized water, a boric compound such as boric acid and sodium borate, dicarboxylic acid, and tricarboxylic acid, and derivatives thereof, dialdehyde, and aldehyde groups such as trialdehyde. It may include one or more organic crosslinking agents selected from more than one polyvalent aldehyde and derivatives thereof. In addition, the organic solvent may be further dissolved together with the deionized water.

The content of the crosslinking agent is not particularly limited, and is preferably 1 to 10% by weight, more preferably 2 to 7% by weight based on the total content of the aqueous solution for crosslinking (100% by weight).

In addition, the aqueous solution for crosslinking may further include a small amount of iodide in order to obtain uniformity of the degree of polarization in the polarizer plane. Iodide may be the same as the one used in the dyeing step, the content may be 0.05 to 15% by weight, preferably 0.5 to 11% by weight relative to the total content (100% by weight) of the aqueous solution for crosslinking. Most preferably, boric acid and potassium iodide are used in combination, and in this case, the weight ratio of boric acid and potassium iodide is preferably 1: 0.1 to 1: 3.5, more preferably 1: 0.5 to 1: 2.5. The temperature of the crosslinking bath is 20 to 70 ° C., and the immersion time of the polyvinyl alcohol-based film in the crosslinking bath may be 1 second to 15 minutes, and preferably 5 seconds to 10 minutes.

In the washing step, the polyvinyl alcohol-based film, which has been crosslinked, is immersed in a washing tank filled with a washing solution to remove foreign substances attached to the polyvinyl alcohol-based film remaining in the previous processes, that is, unnecessary residues such as boric acid. .

In the washing step, depending on the temperature of the washing solution and the washing time, the residue attached to the surface of the film may be removed, and the iodine destained inside the film, the iodine ion transition, and the like may be partially desorbed in the plane. Due to the different degrees, in-plane dyeing imbalance may occur through this, resulting in dyeing-mura in the liquid crystal panel.

When in-plane dyeing imbalance occurs, dye polarization is made by attaching two polarizers orthogonal to the inside and outside of the liquid crystal cell to make a liquid crystal panel, and then turn it on and observe the panel when it is black in the dark room. It is shaped like a white line, which means that the light transmittance in the backlight is different and appears in the form of Mura. It is usually found easily in the case of high single transmittance, which is one of the main problems to be solved in the manufacturing process in response to the demands of high transmittance polarizers.

As a result of many studies, potassium iodide (KI) was added to the washing solution of the washing process, and the pH of the washing solution was adjusted to 7.0 to 11.0 to prevent the desorption of iodine due to osmotic pressure. It was found that dyeing mura does not occur even in the case of maintaining and producing a high-permeability polarizer.

The aqueous solution for washing is mainly using deionized water, in the present invention, by adding potassium iodide to improve the dyeing mura, by adjusting the pH of the washing solution to have a neutral or basic to prevent the desorption of iodine due to osmotic pressure, boric acid It is possible to maintain the borate bond of. The amount of potassium iodide added to the flushing solution is 1.0 to 20.0 parts by weight, preferably 3.0 to 10.0 parts by weight based on 100 parts by weight of deionized water. More preferably, it is 4.5-8.0 weight part.

In addition, the pH of the flushing solution is 7.0 to 11.0, preferably 8.0 to 10.0. The pH of the flushing solution can be adjusted using sodium hydroxide. In the case of a polarizing plate including a polarizer manufactured by applying a washing process as in the present invention, dyeing mura does not occur and may exhibit excellent display quality.

It is preferable that the temperature of a washing tank is 5-12 degreeC by another washing process conditions. In addition, the time for performing the washing step is 1 second to 60 seconds, preferably 3 seconds to 30 seconds, more preferably 5 seconds to 20 seconds.

The washing process may be performed whenever previous processes such as dyeing, crosslinking or stretching are completed. In addition, it may be repeated one or more times, and the number of repetitions is not particularly limited.

The drying step is a step of obtaining an iodine-based polarizer having excellent optical properties by drying the polyvinyl alcohol-based film that has undergone dyeing, crosslinking and extension, and further improving the orientation of iodine molecules adsorbed by the neck-in by drying.

As a drying method, natural drying, air drying, far-infrared drying, microwave drying, heat drying, hot air drying, etc. may be used. Recently, a microwave drying method for activating and evaporating and drying only water in a film is newly introduced. The most commonly used drying method among the listed drying methods is hot air drying. For example, the polarizer may be hot air dried at 20 to 90 ° 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 less, and most preferably 60 ° C. or less.

Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited by these examples.

Example 1

As a polymer film for polarizers, a polyvinyl alcohol-based film having a saponification degree of 99.9% or more and a thickness of 75 microns was swelled in deionized water (swelling tank) at 30 ° C. for 2 minutes and simultaneously stretched by 1.40 times. Iodine (2.0 mM) and potassium iodide were dyed by immersion for 4 minutes while stretching 1.50 times in an aqueous solution for dyeing at 30 ° C. (dyeing tank) mixed at a weight ratio of 1:17. The dyed PVA-based film was immersed for 3 minutes in an aqueous solution for crosslinking (crosslinking) at 55 ° C. mixed at a weight ratio of boric acid and potassium iodide 1: 3, and immersed for 3 minutes to crosslink.

Finally, 8.0 parts by weight of potassium iodide was added to 100 parts by weight of deionized water to prepare a washing solution, and the pH of the washing solution was added to sodium hydroxide to give a basicity of pH 9.0. After washing for 15 seconds without stretching to a water solution of 10 ℃, and dried for 4 minutes in a drying oven of 60 ℃ to prepare a polarizer. At this time, the total cumulative stretching ratio was 6.3 times. A triacetyl cellulose (TAC) film was laminated on both surfaces of the prepared polarizer to prepare a polarizing plate. The collective transmittance was adjusted to be over 43.0%.

[Example 2]

A polarizer was prepared in the same manner as in Example 1 except that the content of KI was 3.0, and a polarizing plate was prepared using the same.

Example 3

A polarizer was manufactured in the same manner as in Example 1 except that the content of KI was 10.0, and a polarizing plate was prepared using the same.

Comparative Example 1

A polarizer was prepared in the same manner as in Example 1 except that pH was set to 6.1 without adding KI to the washing solution, and a polarizing plate was prepared using the same.

Comparative Example 2

A polarizer was prepared in the same manner as in Example 1 except that the content of KI was 1.0, and a polarizer was manufactured using the same.

Comparative Example 3

A polarizer was prepared in the same manner as in Example 1 except that the pH of the flushing solution was 4.5, and a polarizing plate was prepared using the same.

[Comparative Example 4]

A polarizer was prepared in the same manner as in Example 1 except that the pH of the flushing solution was 13.0, and a polarizing plate was prepared using the same.

[Comparative Example 5]

A polarizer was prepared in the same manner as in Example 1 except that the temperature of the washing solution was 3 ° C., and a polarizing plate was prepared using the same.

[Comparative Example 6]

A polarizer was prepared in the same manner as in Example 1 except that the temperature of the washing solution was 15 ° C., and a polarizing plate was prepared using the same.

[Comparative Example 7]

A polarizer was manufactured in the same manner as in Example 1 except that the execution time of the washing process was 2 seconds, and a polarizing plate was manufactured using the same.

Comparative Example 8

A polarizer was manufactured in the same manner as in Example 1 except that the execution time of the washing process was 30 seconds, and a polarizing plate was manufactured using the same.

Table 1 below shows the process conditions of Examples 1 to 3 and Comparative Examples 1 to 8.

Process conditions KI content (parts by weight) pH Washing time (sec) Water washing temperature (℃) Example 1 8.0 9.0 15 10 Example 2 3.0 9.0 15 10 Example 3 10.0 9.0 15 10 Comparative Example 1 0.0 6.1 15 10 Comparative Example 2 1.0 9.0 15 10 Comparative Example 3 8.0 4.5 15 10 Comparative Example 4 8.0 13.0 15 10 Comparative Example 5 8.0 9.0 15 3 Comparative Example 6 8.0 9.0 15 15 Comparative Example 7 8.0 9.0 2 10 Comparative Example 8 8.0 9.0 30 10

[Test Example]

The polarizing plates produced in Examples 1 to 3 and Comparative Examples 1 to 8 were tested as follows.

(1) Optical property evaluation (polarization degree, group transmittance, orthogonal b, A700)

After the prepared polarizer was cut to a size of 4 cm × 4 cm, polarization degree, single transmittance, orthogonal b, and A700 were measured using an ultraviolet visible light spectrometer (V-7100, manufactured by JASCO). Polarization degree P was computed by following formula (1), and A700 was computed by following formula (2).

 [Equation 1]

P = [(T ₁ -T ₂ ) / (T ₁ + T ₂ )] ^1/2

In the formula, T ₁ is a parallel transmittance is obtained when placing the polarizing plate of the pair in a state parallel to the absorption axis, T ₂ is a cross transmissivity is obtained when placing the polarizing plate of the pair to a state of the absorption axis orthogonal.

[Equation 2]

A700 =-Log ₁₀ {(T _{MD , 700} × T _{TD , 700} ) / 10000}

In the formula, T _{MD , 700} is a parallel transmittance at a wavelength of 700 nm obtained when the pair of polarizers are arranged in parallel with the absorption axis, and T _{TD , 700} is a pair of polarizers in the state where the absorption axis is orthogonal to each other. It is orthogonal transmittance | permeability in 700 nm wavelength obtained when.

(2) Dyeing Village Evaluation

 The polarizing plate was affixed orthogonally to both surfaces of the liquid crystal cell, and it was judged whether Mura in the black state in the dark room. Judgment criteria are as follows.

○: Excellent, no dyeing mura.

(Triangle | delta): Usually, a horizontal pattern is one or less, and Mura is weakly recognized

×: Bad, two or more horizontal stripes, Mura strongly admitted

result % Polarization Transmittance (%) Ortho b A700 Dye-mura Example 1 99.995 43.2 0.24 4.23 ○ Example 2 99.994 43.1 0.10 3.91 ○ Example 3 99.996 43.1 0.40 4.21 ○ Comparative Example 1 99.995 43.0 -0.11 4.04 × Comparative Example 2 99.994 43.0 -0.07 3.88 △ Comparative Example 3 99.995 42.9 -0.08 4.39 △ Comparative Example 4 99.990 43.3 -0.83 3.20 × Comparative Example 5 99.993 43.2 -0.10 4.55 △ Comparative Example 6 99.980 43.9 -1.33 3.64 × Comparative Example 7 99.997 42.1 -0.01 4.93 ○ (with foreign substance) Comparative Example 8 99.968 43.9 -1.50 2.69 ×

In Examples 1 to 3 and Comparative Examples 1 to 8, the transmittance was 42% or more, and the A700 value related to durability was also excellent overall. However, the orthogonal b values of Examples 1 to 3 and Comparative Examples 1 to 8 generally did not coincide, and the orthogonal b values were related to the dyeing mura evaluation. That is, the greater the orthogonal b value, the more excellent the result in the dyed radish ramen.

In Example 1, in which potassium iodide was added to the washing step and the pH was adjusted to 9.0, the orthogonal b value was increased, and the dyeing mura evaluation was also excellent. However, in Comparative Example 1, in which potassium iodide was not added and pH was not adjusted separately, the orthogonal b value was low, and the evaluation was poor in terms of dyeing mura evaluation. That is, it can be seen that dyeing mura occurs when the pH is not adjusted to a predetermined range without using potassium iodide in the washing step.

In Examples 1 to 3, when the content of potassium iodide was 3.0 to 10.0, the dyeing-mura evaluation was found to be excellent. That is, in Comparative Example 2, as the amount of potassium iodide was 1.0 parts by weight, it was found that dyeing-mura evaluation occurred at a normal level. Therefore, the content of potassium iodide should be included in a predetermined amount or more to prevent desorption of iodine due to osmotic pressure. And it turns out that it can play the role which maintains the borate bond of boric acid effectively.

In Comparative Example 3, the pH of the washing solution was set to 4.5, and in Comparative Example 4, the pH was set to 13.0. Accordingly, the dyeing mura was not excellent in evaluation. It can be seen that the pH should also be adjusted so as not to be too high or too low while adding potassium.

However, even when the potassium iodide was added to the washing solution and the pH was adjusted to a predetermined range, the dyeing mura evaluation was not excellent even in the case of the comparative examples 5 and the comparative example 6, which was too low at 3 ° C. and too high at 15 ° C. Did. In addition, in Comparative Example 7 in which the washing time was 2 seconds in terms of washing time, the dyeing-mura evaluation was excellent, but because it was too short, sufficient time to remove foreign substances such as iodine or boric acid remaining on the surface was not secured. In Comparative Example 8 in which the washing time was 30 seconds, the dyeing-mura evaluation was found to be poor.

Therefore, dyeing mura does not occur when a predetermined range of potassium iodide is added to the washing solution in the washing process in the manufacturing process of the polarizer as described in the present invention, and the pH is adjusted to a neutral or predetermined range of basicity for an appropriate temperature and time. It can be seen that a polarizer of good quality can be produced.

The invention is not to be limited by the foregoing embodiments and the accompanying drawings, but should be construed by the appended claims. In addition, it will be apparent to those skilled in the art that various forms of substitution, modification, and alteration are possible within the scope of the present invention without departing from the technical spirit of the present invention.

Claims (5)

A swelling step of swelling the polyvinyl alcohol-based film;
A dyeing step of dyeing the swollen polyvinyl alcohol-based film with iodine;
A crosslinking step of crosslinking the dyed polyvinyl alcohol-based film;
Washing the crosslinked polyvinyl alcohol-based film in a washing solution containing deionized water and potassium iodide and having a pH of 7.0 to 11.0; And
And a drying step of drying the washed polyvinyl alcohol-based film. The method according to claim 1,
The content of the potassium iodide is a polarizer manufacturing method, characterized in that 3.0 to 10.0 parts by weight based on 100 parts by weight of the deionized water. The method according to claim 1,
The washing step is a polarizer manufacturing method characterized in that performed for 5 seconds to 20 seconds. The method according to claim 1,
The temperature of the washing solution is a polarizer manufacturing method, characterized in that 5 ℃ to 12 ℃. The method according to claim 1,
The crosslinking step is a polarizer manufacturing method characterized in that it is carried out using boric acid as a crosslinking agent.