KR20110073931A - Method for preparing a polarizer - Google Patents

Abstract

PURPOSE: A method for manufacturing a polarizer is provided to effectively eliminate iodine which does not contribute to a polarization feature, thereby obtaining a polarizer which has a superior polarization value and a superior group transmission rate. CONSTITUTION: A method for manufacturing a polarizer includes a swelling step, a dyeing step, a bridging step, an extending step, and washing and drying steps. A dyed polymer film is dipped in a boric acid aqueous solution to fix suctioned iodine particles wherein the dye feature of the dyed polymer film is weakened because Iodine particles are physically bonded. The dipping time of the polymer film is between five seconds and ten minutes.

Description

Manufacturing method of polarizer {METHOD FOR PREPARING A POLARIZER}

The present invention relates to a method of manufacturing a polarizer capable of improving the single transmittance without lowering the degree of polarization.

In order to provide images with high brightness and excellent color reproducibility to various image display devices such as liquid crystal display (LCD), electroluminescence (EL) display, plasma display (PDP) and field emission display (FED), Constant research has been conducted, and as a result, the optical properties of the polarizer are found to be an important factor.

To date, most polarizers clean and swell polymer films such as polyvinyl alcohol (PVA) films, dye the swollen polymer films to adsorb substances such as dichroic iodine or dichroic dye, and then crosslink the reaction. It was prepared by fixing the dye adsorbed through and orienting the fixed dye through stretching.

However, as the liquid crystal display device is gradually enlarged in recent years, in a situation where the demand for a liquid crystal display device having improved luminance without a decrease in the contrast ratio is rapidly increasing, it is possible to manufacture a polarizer capable of improving the unitary transmittance without decreasing the polarization degree. There is a study on how to do that.

In Korean Patent No. 916955, a dyed polyvinyl alcohol-based film is stretched in an aqueous solution of boric acid containing 4 wt% or more of iodide and washed with 0.8-2.5 wt% of an iodide solution to give a unit transmittance of 43% or more and a degree of polarization. Disclosed is a method for producing a polarizer of 99.9% or more. This technique was able to provide a polarizer with a single transmittance and a polarization degree up to a certain level by adjusting the concentration of potassium iodide in aqueous boric acid solution and an iodide solution, but when the polarization degree is improved, the single transmittance is increased. When lowered and the group transmittance was improved, the polarization degree was not overcome.

An object of the present invention is to provide a method for producing a polarizer capable of improving the unity transmittance without lowering the degree of polarization by lowering the iodide concentration and the boric acid solution temperature of the last crosslinking tank of two or more crosslinking tanks.

1. The dyeing process includes immersing the polymer film in two or more crosslinking tanks, wherein the last crosslinking tank of the two or more crosslinking tanks has an iodide concentration of 0.6 to 0.9 times as compared to the previous crosslinking tank, and the boric acid aqueous solution has a temperature of 10 ° C. or lower. Method of manufacturing a polarizer to be set.

2. The method according to the above 1, wherein the iodide concentration of the last crosslinking bath is 3-6 times the iodide concentration of the dye bath.

3. In the above 1, the boric acid aqueous solution is a method of manufacturing a polarizer in which the weight ratio of the boron compound and iodide is 1: 0.1-3.5.

4. In the above 1, wherein the polymer film is a polyalcohol-based film, polyethylene terephthalate film, ethylene-vinyl acetate copolymer film, a cellulose film and the manufacturing method of the polarizer is selected from the group consisting of these saponified film.

5. The method according to the above 1, wherein the immediately before the crosslinking tank comprises 0.05 to 15% by weight of iodide and 1 to 7% by weight of boron compound with respect to 100% by weight of boric acid aqueous solution.

6. In the above 1, the cross-linking tank is a manufacturing method of three polarizers.

The present invention has the effect of being able to manufacture a polarizer excellent in both polarization and group transmittance at the same time by removing the iodine not involved in the polarization characteristic expression in an effective manner.

In particular, the present invention is distinguished from the prior art in that a polarizer exhibiting excellent single transmittance can be produced without lowering the polarization degree, unlike the conventional case in which the single transmittance is lowered in the degree of polarization.

The liquid crystal display including the polarizer manufactured according to the present invention may exhibit high brightness without deterioration of the front contrast ratio.

The present invention is eco-friendly and energy-saving because it does not incur additional equipment costs.

It includes immersing the polymer film subjected to the dyeing process of the present invention in two or more crosslinking tanks, the last crosslinking tank of the two or more crosslinking tanks has an iodide concentration of 0.6 to 0.9 times compared to the previous crosslinking tank, the temperature of the boric acid aqueous solution is 10 ℃ or more By setting it low, the present invention relates to a method for manufacturing a polarizer having improved single transmittance without deterioration in polarization degree.

Hereinafter, the present invention will be described in more detail.

In the present invention, the polymer film used for preparing the polarizer is not limited to that of a specific material, for example, polyvinyl alcohol-based film, partially saponified polyvinyl alcohol-based film; Hydrophilic polymer films such as polyethylene terephthalate films, ethylene-vinyl acetate copolymer films, cellulose films, partially gumified films thereof, polyene orientations such as dehydrated polyvinyl alcohol-based films, dehydrochlorinated polyvinyl chloride, and the like Film and the like. However, among these, the polyvinyl alcohol-based film is preferable in that not only the effect of maintaining the uniformity of the degree of polarization in the plane is excellent, but also the dye affinity for a dichroic substance, for example, iodine, is excellent as a polarizer.

The degree of polymerization of the polyvinyl alcohol-based film is usually 500 to 10,000, preferably 1,000 to 6,000, and more preferably 1,400 to 4,000. In the polyvinyl alcohol-based saponification film, the saponification degree is preferably 95.0 mol% or more, more preferably 99.0 mol% or more, and most preferably 99.9 mol% or more from the viewpoint of solubility.

Usually, the method of manufacturing a polarizer includes a swelling step, a dyeing step, a crosslinking step, an stretching step, and a washing and drying step, and are mainly classified according to the stretching method. For example, a dry stretching method for stretching and dyeing a polymer film as a raw material by stretching in a hot roll, a wet stretching method for simultaneously stretching and crosslinking in the state of impregnation with hot water, or a combination of the two stretching methods. Hybrid stretching method is mentioned. Hereinafter, the manufacturing method of the polarizer of this invention is demonstrated based on a wet drawing method as an example.

The remaining steps except the drying step are performed in a state where the polymer film is immersed in a constant temperature bath filled with at least one solution selected from several kinds of solutions.

In addition, the order of the steps and the number of repetitions are not particularly limited, and the steps may be performed simultaneously or sequentially, and some steps may be omitted. For example, the stretching step may be performed before or after the dyeing step, and may be performed simultaneously with the swelling step or the dyeing step.

The swelling step is a step of immersing the unstretched polymer film in a swelling tank filled with an aqueous solution for swelling (deionized water). Through this step, impurities such as dust or blocking agents deposited on the surface of the polymer film may be cleaned, and the polymer film may swell to improve the stretching efficiency and prevent dyeing nonuniformity.

The swelling aqueous solution is the same as the aqueous solution at the time of measuring the water expansion rate, and water (deionized water) can be used alone, and when a small amount of glycerin, iodine or potassium iodide is added thereto, the processability is improved along with the swelling of the polymer film. Can be. 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 iodine or potassium iodide is 10% by weight or less.

In addition, the aqueous solution for swelling may be an aqueous solution to which an organic solvent of an alcohol such as ethanol is added, which is preferable in view of controlling the swelling degree of the unstretched polymer film in the swelling step. The content of alcohol may be 0.1 to 30% by weight in 100% by weight of the aqueous solution for swelling, preferably 1 to 20% by weight. If the content of alcohol exceeds 30% by weight, the specific heat of the swelling aqueous solution is lowered and the volatility becomes high, which is a danger when applied to the process.

The temperature of the swelling tank is the same as the temperature at the time of water expansion rate measurement, and it is preferable that it is 20-35 degreeC. If the temperature is less than 20 ℃, difficulty occurs in the stretch processability and causes a decrease in the dyeability in the subsequent dyeing step, if it exceeds 35 ℃, the molecular motion of the swelling solution is active and sudden expansion of the film Will cause.

The execution time (swelling tank immersion time) of the swelling step is preferably 180 seconds or less, more preferably 10 to 120 seconds, most preferably 20 to 60 seconds.

The stretching step may be performed together with the swelling step, wherein the stretching ratio is preferably about 1.1 to 3.5 times.

In addition, the first cleaning step for cleaning the impurities of the polymer film may be further included before the swelling step.

The dyeing step is a step of adsorbing iodine on the polymer film by immersing the swollen polymer film in a dye bath filled with a dichroic dye or a dye solution containing a dichroic material, for example, iodine.

The aqueous solution for dyeing may include water (deionized water) or a water-soluble organic solvent and iodine. The content of iodine is 0.01 to 2% by weight based on 100% by weight of the aqueous solution for dyeing. Iodide may be further included together with iodine to further improve dyeing efficiency. As iodide, potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, etc. may be used alone or in combination of two or more thereof. Of these, potassium iodide is preferred. The content of iodide is 0.5 to 20% by weight with respect to 100% by weight of the aqueous solution for dyeing.

The weight ratio of iodine and iodide (potassium iodide) is not particularly limited, for example, 1: 5 to 1: 100, preferably 1: 6 to 1:80, more preferably 1: 7 to 1 It is good to be: 70.

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

The stretching step may be performed together with the dyeing step, in which case the draw ratio is preferably 1.1 to 4.0 times.

In addition to the dyeing method as described above, a method of applying or spraying a dyeing solution containing iodine on the polymer film may be used, or may be dyed by mixing iodine with the polymer resin before casting the polymer film.

The crosslinking step is a step of fixing the adsorbed iodine molecules by immersing the dyed polymer film, which can be dyed, because the iodine molecules are physically bonded (adsorption) in an aqueous solution of boric acid (aqueous solution for crosslinking). Iodine molecules may be dissolved or sublimed according to the environment, and only iodine molecules positioned and oriented between molecules of the polymer resin affect polarization degree, but not all iodine molecules affect polarization degree.

The aqueous boric acid solution may include at least one crosslinking agent selected from boron compounds such as water (deionized water), boric acid, sodium borate, and the like, and glyoxal and glutalaldehyde. In addition, the organic solvent may be further dissolved together with water (deionized water).

The content of the boron compound is not particularly limited, and is preferably 1 to 7% by weight, more preferably 2 to 6% by weight based on 100% by weight of aqueous boric acid solution. In addition, the content of the crosslinking agent is not particularly limited, preferably 1 to 10% by weight, more preferably 2 to 6% by weight based on 100% by weight of boric acid aqueous solution.

In addition, the boric acid aqueous solution 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 with respect to 100% by weight of boric acid aqueous solution, preferably 0.5 to 11% by weight. The weight ratio of the boron compound to the iodide such as boric acid and potassium iodide is preferably 1: 0.1-3.5, more preferably 1: 0.5-2.5. The boric acid aqueous solution is most preferably used in combination with boric acid and potassium iodide.

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

The crosslinking bath of the present invention is preferably provided with two or more for sufficient crosslinking, since the draw ratio and residence time for the polarizer are short in the manufacturing process of the continuous polarizer.

Conventionally, when the polarization degree of the polarizer is improved, the single transmittance is lowered, and when the single transmittance is improved, the polarization degree is lowered.

In order to improve this, the present invention is set so that the boric acid solution contained in the last crosslinking tank of two or more crosslinking tanks has a lower temperature and concentration of iodide than the boric acid solution of the immediately preceding crosslinking tank, and is set to be higher than the concentration of the dye bath iodide and polarized. By removing the iodine molecules that are simply adsorbed on the surface of the polarizer without being involved in the, it is possible to improve the single transmittance without decreasing the degree of polarization.

At this time, the boric acid solution contained in the last crosslinking tank has a concentration of iodide of 0.6 to 0.9 times, preferably 0.7 to 0.8 times as compared to the boric acid solution of the immediately preceding crosslinking tank. If the concentration is less than 0.6 times, the iodine molecules adsorbed in the polyvinyl alcohol film may also be eluted into the aqueous solution through a reversible reaction, and the polarization degree may be lowered. If the concentration is more than 0.9 times, simply remove the adsorbed iodine molecules. May be insufficient.

In addition, the boric acid aqueous solution contained in the last crosslinking tank is preferably lowered in temperature by at least 10 ° C, preferably at least 15 ° C, as compared to the boric acid solution in the immediately preceding crosslinking tank. When the temperature is lowered by 10 ° C. or more, the mobility of the polyvinyl alcohol polymers is reduced and contracted to prevent the elution of the internally adsorbed iodine molecules caused by the low concentration of potassium iodide in the aqueous solution of boric acid, but the effect is less than 10 ° C. Since it is insignificant, the polarization degree may be lowered.

In addition, the boric acid aqueous solution contained in the last crosslinking tank is preferably 3-6 times the iodide concentration of the dye bath, preferably 3-5 times. If the concentration is less than 3 times, the iodine molecules adsorbed in the polyvinyl alcohol film may also be eluted into the aqueous solution through a reversible reaction, and the polarization degree may be lowered. If the concentration is more than 6 times, the adsorbed iodine molecules are simply removed. May be insufficient.

Specifically, for example, in the case of three crosslinking tanks, the iodide of the dyeing bath is 2.5% by weight, the boric acid aqueous solution temperature of the first and intermediate crosslinking baths is 56 ° C, and the iodide concentration is 12% by weight. The boric acid solution temperature of the last crosslinking tank can be designed to 45 ℃, iodide concentration of 8.4% by weight.

In the case of four crosslinking baths, the iodide of the dyeing bath is 1.5% by weight, the boric acid solution temperature of the first and second crosslinking baths is 56 ° C, the iodide concentration is 13% by weight, and the boric acid solution temperature of the third crosslinking bath is 55 ° C and iodide. The concentration is 11% by weight, the boric acid aqueous solution temperature of the last crosslinking bath can be designed to 45 ℃, iodide concentration of 8.8% by weight.

The stretching step may be performed together with the crosslinking step.

In addition to the crosslinking method as described above, other methods such as in the dyeing step may be used.

The stretching step may be performed together with the swelling step, the dyeing step, and the crosslinking step, or may be performed as an independent stretching step using a separate drawing tank filled with an aqueous solution for drawing after the crosslinking step.

The kind of stretching aqueous solution is not particularly limited, and may be a solution including at least one selected from a solvent such as water, ethanol or an organic solvent and a metal salt, iodine, boron and zinc compounds. In particular, a solution containing 2 to 18% by weight boric acid, 2 to 10% by weight potassium iodide or mixtures thereof is preferred. In addition, when boric acid and potassium iodide are used together, their weight ratio is preferably 1: 0.1 to 1: 4, more preferably 1: 0.5 to 1: 3.

It is preferable that the temperature of a drawing tank is 40-67 degreeC, More preferably, it is 50-62 degreeC.

The stretching method is not particularly limited, and for example, in the case of roll stretching, a stretching method is used based on the difference in circulation speed between rolls.

The stretching direction may be a longitudinal direction (MD, progress direction of the process) or a width direction of the polymer film, and the stretching is preferably performed such that the final cumulative stretching ratio is 3.0 to 7.0 times. At this time, the cumulative stretching ratio means a value of the product of the stretching ratios in each step.

The washing step is a step of removing the unnecessary residue such as boric acid deposited on the polymer film in the previous step by immersing the cross-linked polymer film in the cleaning tank filled with the aqueous solution for cleaning.

The aqueous cleaning solution may be water (deionized water), and an iodine compound may be further added thereto. As the iodide, the same ones as used in the dyeing step can be used, and among them, it is preferable to use sodium iodide or potassium iodide. The content of potassium iodide may be 0.1 to 10 parts by weight with respect to 100 parts by weight of the aqueous solution for washing, preferably 3 to 8 parts by weight.

It is preferable that the temperature of a washing tank is 10-60 degreeC, More preferably, it is 15-40 degreeC.

The washing step may be repeated one or more times, and the number of repetitions is not particularly limited. In addition, the type and content of the components of the aqueous solution for cleaning may be changed according to the number of times repeated.

The cleaning step may be performed whenever previous steps such as swelling step, dyeing step, crosslinking step or stretching step are completed.

In the steps as described above, when the polymer film is raised from the reaction tank into the air, in order to prevent the liquid, such as a solution attached to the polymer film, from falling off, a conventional liquid liquid such as a pinch roll is used. cutting rolls may be used, or excess solution may be removed by a liquid cutting method using an air knife.

The drying step is a step of drying the washed polymer film to obtain a polarizer with iodine adsorption orientation.

As a drying method, methods, such as natural drying, air drying, heat drying, etc. can be used, and heat drying is generally used preferably. For example, it may be heat dried at 20 to 80 ° 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.

According to the above drying method, in the present invention is prepared so that the moisture content of the polarizer is less than 8% by weight. If the moisture content is more than 8% by weight, it is difficult to suppress curl when a protective film having different moisture permeability is bonded to both sides of the polarizer.

The final draw ratio of the polarizer produced by such steps is preferably 3.0 to 7.0 times, more preferably 5.5 to 6.2 times. When the draw ratio of the polarizer is less than 3.0 times, it is difficult to obtain a polarizer having high polarization efficiency, and when the draw ratio exceeds 7.0 times, the polarizer is easily broken.

In the manufacturing method of the present invention, the prepared polarizer may have a transmission efficiency of 12 to 20 according to Equation 1 below.

Transmission Efficiency = (Py-99.9) / (50-Ty) × 1000

(Py: polarization degree, Ty: group transmittance)

Although the thickness in particular of a polarizer is not restrict | limited, Usually, it is 5-40 micrometers, Preferably it is 10-37 micrometers, More preferably, it is 15-35 micrometers.

The polarizer manufactured by the manufacturing method of the present invention can be used in a conventional liquid crystal display device.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is obvious that the examples are not intended to limit the scope of the present invention but only to show an example belonging to the present invention. It is natural that modifications and variations of the embodiments fall within the scope of the present invention without departing from the basic technical spirit of the present invention.

[Example]

Example 1

A transparent unstretched polyvinyl alcohol-based film (VF-PS 70 μm, KURARAY Co., Ltd.) having a degree of saponification of 99.9% or more was swelled by immersion for 2 minutes in an aqueous solution for swelling at 30 ° C. in which 1.5 mmol / L of iodine was dissolved in deionized water. 1.3 times uniaxial stretching was carried out to the longitudinal direction (MD) of a film. Thereafter, the mixture was immersed for 4 minutes in a dyeing solution at 30 ° C. containing 3.5 mmol / L of iodine and 2% by weight of potassium iodide, and 1.4 times uniaxially stretched in the longitudinal direction (MD) of the film. The dyed polyvinyl alcohol-based film was crosslinked by immersion in three crosslinking baths for a total of 3 minutes. At this time, the first and intermediate crosslinking tanks of the three crosslinking tanks were maintained at 53 ° C. in an aqueous boric acid solution containing 10% by weight of potassium iodide and 3.5% by weight of boric acid, and the last crosslinking tank contained 8% by weight of potassium iodide and 3.5% by weight of boric acid. The boric acid aqueous solution was used at 40 degreeC was used. In the cross-linking step, the draw ratio was stretched to 1.8 times, 1.8 times, and 1.0 times, respectively, so that the cumulative draw ratio was 5.9. Then, the polyvinyl alcohol-based film was dried in an oven at 60 ℃ for 4 minutes to prepare a polarizer.

Example 2

A polarizer was prepared in the same manner as in Example 1, with 11 wt% of potassium iodide in the first and intermediate crosslinking baths and 9 wt% of potassium iodide in the last crosslinking bath.

Comparative Example 1

The polarizer was prepared in the same manner as in Example 1 except that the concentration of boric acid solution of the last crosslinking bath was the same as the concentration of boric acid solution of the first and intermediate crosslinking baths.

Comparative Example 2

A polarizer was prepared in the same manner as in Example 1 except that 5 wt% of potassium iodide in the last crosslinking bath was used.

Comparative Example 3

A polarizer was prepared in the same manner as in Example 1 except that the temperature of the last crosslinking bath was 53 ° C.

Test Example

1. Measurement of Polarization Degree (%)

After the prepared polarizer was cut into 4 × 4 cm size, the degree of polarization was measured using an ultraviolet visible light spectrometer (V-7100, manufactured by JASCO). The degree of polarization is defined by Equation 2 below.

Polarization degree (P) = [(T ₁ -T ₂ ) / (T ₁ + T ₂ )] ^1/2

T ₁ : Parallel transmittance obtained when a pair of polarizers are arranged in parallel with absorption axes

T ₂ : Orthogonal transmittance obtained when a pair of polarizers are arranged in a state where the absorption axis is orthogonal to each other

2. Measurement of group transmittance (%)

The single transmittance of one polarizer was measured using an ultraviolet visible light spectrometer (V-7100, manufactured by JASCO).

3. Evaluation of luminance and front contrast ratio (C / R)

The manufactured polarizer was installed in the liquid crystal display device, and the luminance (cd / m ² ) and contrast ratio (C) in the white display state and the black display state were obtained using the luminance measuring device SR3A (manufactured by Topcon Co., Ltd.) in the dark room. / R) was measured.

division Optical properties Luminance evaluation Group transmittance (%) % Polarization Lw Ld C / R Example 1 42.2 99.995 208.5 0.221 943.4 Example 2 42.0 99.996 204.1 0.217 940.6 Comparative Example 1 41.0 99.995 200.3 0.220 910.5 Comparative Example 2 42.3 99.965 204.6 0.238 859.7 Comparative Example 3 40.7 99.995 201.8 0.221 913.1

As shown in the above table, the polarizers of Examples 1 to 2 prepared by lowering the concentration and temperature of the final crosslinking bath according to the present invention were improved in single transmittance without decreasing polarization degree, but the polarizers of Comparative Examples 1 to 3 were improved in single transmittance. It confirmed that polarization degree fell. In addition, it was confirmed that the liquid crystal display device in which the polarizers of Examples 1 and 2 were provided exhibited high luminance without decreasing the contrast ratio.

As described above, the polarizer of the present invention is a polarizer having excellent optical characteristics and uniform in-plane polarization characteristics, and is used for various image display apparatuses such as a liquid crystal display device, an electroluminescence display device, a plasma display device or an field emission display device. Applicable to

Claims (6)

It includes immersing the polymer film subjected to the dyeing process in two or more crosslinking tank, the last crosslinking tank of the two or more crosslinking tank is set to 0.6 to 0.9 times the concentration of iodide compared to the previous crosslinking tank, the temperature of the aqueous solution of boric acid is set to 10 ℃ or lower Method of manufacturing a polarizer. The method of claim 1, wherein the iodide concentration of the last crosslinking bath is 3 to 6 times the iodide concentration of the dye bath. The method of claim 1, wherein the aqueous solution of boric acid has a weight ratio of boron compound and iodide of 1: 0.1 to 3.5. The method of claim 1, wherein the polymer film is selected from the group consisting of a polyalcohol-based film, a polyethylene terephthalate film, an ethylene-vinyl acetate copolymer film, a cellulose film, and a film in which they are saponified. The method of claim 1, wherein the immediately before-crosslinking bath comprises 0.05 to 15% by weight of iodide and 1 to 7% by weight of boron compound based on 100% by weight of aqueous boric acid solution. The method of manufacturing a polarizer according to claim 1, wherein the crosslinking tank is three.