KR101350360B1 - Method and device for recycling liquid crystal alignment solution - Google Patents

Abstract

The invention is an alignment waste solution of an LCD comprising at least one of (a) a polyimide or a precursor thereof, (b) a first solvent, (c) an additive and (d) metal ions and moisture. It provides a method for recycling the liquid crystal aligning solution comprising the step of providing. A second solvent is added to the alignment liquid to remove water by azeotropic distillation. The alignment waste solution is then filtered with a filter material, the adsorbent comprising a high purity adsorbent, a high purity aluminum oxide or a high purity alumina silicate. Moreover, the recycling apparatus of a liquid crystal aligning liquid is provided.

Description

Recycling method and apparatus for liquid crystal aligning liquid TECHNICAL FIELD

The present invention relates to a method and apparatus for recycling a liquid crystal alignment solution for a liquid crystal display, and more particularly, to a method and apparatus for recycling a liquid crystal alignment liquid with high efficiency.

This application claims the benefit of priority of Taiwan Patent Application No. 099143452, filed December 13, 2010, which is hereby incorporated by reference in its entirety.

Alignment films are the main material for controlling the display quality of liquid crystal displays (LCDs). Typically, an alignment film with jagged grooves is disposed on the inner surfaces of the upper electrode substrate and the lower electrode substrate so that the liquid crystal molecules are aligned neatly along the direction of the grooves. Therefore, the rotation angle of the liquid crystal molecules is controlled in the electric field and the liquid crystal molecules can be used as switches of the LCD. The alignment film is mainly formed of polyimide. Polyimide can be formed from diamines and dianhydrides. In a typical method, an alignment solution comprising an imide monomer is coated on a glass substrate. After the imide monomers are gathered at a specific angle, photopolymerize or thermal polymerize to form polyimide in which the imide monomers are uniformly aligned along a specific direction. The polyimide forms an alignment film that can control the rotation angle of the liquid crystal molecules.

In addition to the polyimide and its precursors, the alignment solution also includes an alignment solvent and additives. The additive may be various materials depending on its use. However, when the alignment solution is in contact with air or stored for a long time, the moisture and metal ions in the air will dissolve in the alignment solution, which means that a large amount of water and metal ions are in the alignment solution. The alignment film present and produced has defects such as non-uniform thickness, low voltage holding ratio (VHR), high residual direct current (RDC) or high ion density. Therefore, the generated LCD will have a problem of image sticking or mura. In addition, in the present LCD industry, about 70% of the excess alignment solution in the production line cannot be recycled and is mostly disposed of as waste solution.

Recently, some approaches have been developed for recycling long-placed or excess alignment solutions (collectively referred to as alignment waste solutions from now on). For example, US Pat. No. 6,420,440 discloses a method for recycling alignment materials, wherein polyimide or its precursor is solidified by diethyl ether and filtered from an organic solvent. The filtered polyimide or its precursor is then dissolved with a mixed solvent of the same composition as that used as the original solvent of the alignment solution. In this way, recycled alignment materials are obtained. In another approach, a method similar to US Pat. No. 6,420,440 is disclosed in Korean Patent No. 66749, except that the filtered organic solvent is recyclable. When water is removed from the alignment waste solution according to the method, the additives may also be removed and the metal ion content may increase. Therefore, the quality and properties of the recycled alignment solution differ significantly from that of the original solution. Although the recycled alignment solution is again applied to the production line, the resulting alignment film does not have the original quality.

Therefore, the present invention provides a method and apparatus for recycling an alignment solution of an LCD, which removes moisture and metal ions from the alignment solution without changing any components in the alignment solution.

Therefore, the present invention provides one embodiment of the following method for recycling the alignment solution: at least (a) a polyimide or precursor thereof, of a liquid crystal alignment material, (b) agent Providing an alignment solution comprising one solvent, (c) an additive and (d) at least one metal ion and moisture; Adding a second solvent to the alignment solution; Removing water and the second solvent by azeotropic distillation; And purifying with a filter material to obtain a purified alignment solution, wherein the filter material includes an adsorbent and a filtering membrane, and the adsorbent has a high purity. Aluminum oxide or high purity alumina silicate.

The present invention also provides another embodiment of a recycling apparatus for the following alignment solution: a reactor comprising an alignment waste solution; A water removal system comprising a temperature control unit for controlling the temperature of the vessel and a vacuum unit for reducing the pressure in the reactor and removing water from the alignment waste solution; And a metal ion removal system for receiving an alignment solution in the water removal system, wherein the metal ion removal system includes a filtering membrane disposed on the bottom of the reactor and an adsorbent disposed on the filtering membrane. adsorbent).

It will be described in detail in the following embodiments with reference to the accompanying drawings.

The present invention may be fully understood by reading the detailed description and examples which follow with reference to the accompanying drawings in which:
1 shows a flowchart illustrating a method of recycling an alignment solution of an LCD according to one embodiment of the present invention;
2 illustrates a cross-sectional view of an alignment solution recycling apparatus of an LCD according to another embodiment of the present invention;
3 and 4 show the comparison between the original solution and the alignment solution purified in Examples 1 and 2 by Fourier transform infrared spectroscopy (FTIR).
5 and 6 show the comparison between the original solution and the alignment solution purified in Examples 1 and 2 by gel permeation chromatography (GPC).
FIG. 7 shows a comparison between the original solution and the alignment solution purified in the Comparative Example by analyzing GPC (gel permeation chromatography).

According to an embodiment of the present invention, a liquid crystal alignment material in which water is removed from an alignment solution by azeotropic distillation and metal ions are removed from the alignment solution by a filtering material ( Disclosed is a method of recycling an alignment solution of an alignment material. In addition, components of the original solution (ie, unused new alignment solution) (e.g., polyimide or its precursors, additives or other components) may not be degraded and their content may be preserved. have. Thus, the recycled alignment solution and the components of the original solution are substantially identical to each other, and the recycled alignment solution and the alignment film produced from the original solution may have substantially the same quality. have. In addition, embodiments according to the present invention disclose an apparatus for recycling an alignment solution of liquid crystal alignment material provided with a reactor, a water removal system and a metal ion removal system. In one embodiment, the recycling apparatus may be used to implement a method of recycling the alignment solution as described above.

1 is a flowchart illustrating a recycling method of an alignment solution of a liquid crystal alignment material according to an embodiment of the present invention. 2 is a cross-sectional view of an apparatus for recycling an alignment solution of a liquid crystal alignment material according to another embodiment of the present invention. In FIG. 1, in step S10, an alignment waste solution is first provided. For example, as shown in FIG. 2, alignment waste solution may be added to the container 204 of the recycling apparatus 200 via the inlet 202. In one embodiment, the alignment waste solution comprises at least (a) a polyimide or precursor thereof, (b) a first solvent, (c) an additive (d) at least one metal ion and moisture You may. (D) metal ions or moisture that need to be removed from the alignment waste solution are impurities, and (a) polyimide or its precursors, (b) the first solvent and (c) the additives inherently It is the original component of the solution. In one embodiment, the polyimide or precursor thereof may be produced by reacting in diamines and dianhydrides. The polyimide or precursor thereof may be polyimide or polyamic acid based on the type of liquid crystal molecules, such as twisted nematic (TN) type or vertical alignment (VA) type. The first solvent may be an alignment solvent, and may include N-methylpyrrolidone (NMP), Butyl Cellosolve (BCS), γ-butyrolactone (γ-BL), or a mixture thereof. In one embodiment, the additives may include suitable additives as needed. For example, the additive may be a silane coupling agent or a titanium coupling agent or an alignment film to increase the adsorption on an anti-static agent or substrate to prevent static electricity. It may be a surfactant to improve the coating performance of the.

Next, in step S12, a second solvent is added to the alignment waste solution for azeotropic distillation so that water and the second solvent can be simultaneously removed from the alignment waste solution. . For example, as shown in FIG. 2, a second solvent is added to the reactor 204 through the inlet 202 and mixed thoroughly with the alignment waste solution. The moisture removal system 206 may include a vacuum unit 208 and a temperature control unit 212. Vacuum unit 208 and temperature control unit 212 may control the pressure and temperature of vessel 204, respectively. Thus, in the vessel 204, the azeotropic point of the water and the second solvent of the alignment waste solution can be reached, and the water together with the second solvent can be removed by azeotropic distillation. . In one embodiment, the second solvent is methanol, ethanol, n-propanol, isopropanol, n-butanol, isopentanol, isopentanol, di It may also include dioxane, tetrahydrofuran, acetone, acetonitrile, methyl isobutyl ketone or mixtures thereof. The second solvent may be about 5 wt% to 50 wt%, or preferably about 10 wt% to 20 wt% of the alignment waste solution. In this embodiment, the removal of the water and the second solvent by azeotropic distillation to prevent degradation of other components of the alignment waste solution due to the high temperature is carried out at a pressure of less than about 30 torr and about At a temperature of 20 ° C. to 50 ° C. or preferably 30 ° C. to 40 ° C. The boiling point of the first solvent is much higher than the boiling point of moisture, making it difficult for the first solvent to form an azeotrope with water.

In one embodiment, the vacuum unit 208 couples to the condensation unit 210. In order to prevent the vaporized water and the second solvent from condensing back into the alignment waste solution, the vaporized water and the second solvent may be condensed in the condensation unit 210 while the vacuum unit 208 is operating. have. In other embodiments, the condensation unit 210 may be disposed directly in the vacuum unit 208. In one embodiment, the temperature of the condensation unit 210 is less than about -10 ° C. After the azeotropic distillation step, the alignment waste solution is less than about 0.5 wt%, or preferably less than about 0.4 wt%, based on the total weight of the alignment waste solution. It may have a content.

Next, in step S14, metal ions and other impurities are removed by a filter material. For example, as shown in FIG. 2, an alignment waste solution having a low moisture content (eg, less than about 0.4 wt%) of the water removal system 206 may be a metal ion removal system 214. Is accommodated in. In metal ion removal system 214, metal ions and other impurities are removed by a filtering material. The filtering material may include an adsorbent 216 and a filtration membrane 218. In one embodiment, the adsorbent 216 may be high purity aluminum oxide or high purity alumina silicate, which means greater than 99% purity. In a preferred embodiment, the purity of aluminum oxide or alumina silicate is higher than 99.5%. The aluminum oxide may be formed into a β phase or a γ phase, but a γ phase is preferred. In other embodiments, the adsorbent 216 may comprise titanium oxide, magnesium oxide, or disperse silicon, with each purity at least 99%. In one embodiment, the adsorbent 216 has particles having a large surface area of 60 to 250 μm and is uniformly dispersed in an alignment waste solution. The adsorbent 216 may be about 1 wt% to 20 wt% of the alignment waste solution. In particular, when about 5 wt% of the adsorbent 216 is added to the alignment waste solution, unit adsorption efficiency for better metal ions may be obtained.

The filtration membrane 218 is placed at the bottom of the reactor 204 to block all suspension particles (including adsorbent 216) and other solid impurities. The filtration membrane 218 may be formed of a plurality of membranes made of different materials and having different pore sizes. For example, the filtration membrane 218 may be comprised of a stainless steel plate 218a and a plurality of micropore membranes 218b having a pore size of about 0.1 to 0.5 mm. To prevent the micropore membrane 218b under the stainless steel plate 218a from peeling off due to the pressure difference due to the pressure unit 208 which blocks and reduces the adsorbent 216 dispersed in the alignment waste solution. The stainless steel plate 218a is disposed on the filtration membrane 218. The micropore film 218b may be formed of polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, stainless steel, or a combination thereof. have. The pore size of the micropore membrane 218b is about 0.2-0.8 μm, or about 0.1-0.5 μm, or 0.05-0.3 μm, to filter and adsorb small sized adsorbents and other solid impurities. In one embodiment, after purification in the metal ion removal system 218, the alignment waste solution may have a metal ion content of less than 500 ppb, or less than 300 ppb, or preferably less than 70 ppb.

Next, in step S16, the purified alignment solution is collected. For example, as shown in FIG. 2, the purified alignment solution moves through the outlet 220 to the collection vessel 222. In one embodiment, the purified alignment solution may have a moisture content of less than about 0.4 wt% and a metal ion content of less than 500 ppb. In addition, the components of the original solution (eg additives) and their content were preserved in the purified alignment solution. Thus, the purified alignment solution may be recycled back for application in the production line. The resulting alignment film will have properties similar to those of quality substantially equivalent to the alignment film produced in the original solution.

In addition, in one embodiment, step S18 is optionally performed. In step S18, an additional first solvent is added to the recycled alignment solution. Therefore, it is possible to compensate for the loss of the first solvent in the water removal system 206. In one embodiment, only less than 10 wt%, or preferably 1 wt% of an additional first solvent is added (based on the total weight of the purified alignment solution) to the purified alignment solution. Thus, even if some first solvent is lost in the water removal system, the recycled alignment solution can still maintain the same concentration of each component as the original solution. In addition, the alignment solution may have a recycling efficiency of at least about 90% and preferably at least about 95%.

In summary, according to an embodiment of the present invention, it was possible to remove water and / or metal ions of the alignment waste solution with high efficiency. The components of the original solution (eg polyimide or its precursors, additives or other components) and their content are preserved in the recycled alignment solution. In addition, the method is very economical and time-saving over conventional methods requiring complex processes such as solidification, separation or vacuum drying. Therefore, the alignment solution stored for a long time or in contact with air can be purified and recycled. On the other hand, the quality of the alignment film produced from the recycled alignment solution is almost the same as that of the alignment film originally produced from the solution, so that the manufacturing cost of the alignment film of the LCD is remarkably high. Can be reduced.

Example 1

At the bottom of the reactor of the recycling apparatus, as shown in FIG. To provide an alignment waste solution (applied to the VA type liquid crystal). The alignment waste solution is formed of 6 wt% polyimide, 93 wt% alignment solution and 1 wt% silane coupling agent, 6.8 wt% solids content, 22.3 viscosity, 3.9 moisture content of wt% and metal ion content of 515 ppb. Next, 20 wt% of isopropanol (based on the total weight of the alignment waste solution) was added to the reactor. The reactor was heated to 36 ° C. to remove isopropanol and water in the alignment solution of the reactor with a vacuum condenser. Next, 5 wt% aluminum oxide having 99% purity (based on the total weight of the alignment waste solution) was added. Finally, the alignment waste solution was filtered with a stainless steel plate and a number of polyvinylidene fluoride membranes and moved through the outlet to the collection vessel. Purified alignment solution was obtained and the analysis results are summarized in Table 1.

Example 2

An alignment waste solution (applied to TN type liquid crystals) is formed of 6 wt% polyamic acid, 93 wt% alignment liquid and 1 wt% silane coupling agent, 6.0 wt% solids content, The same procedure as in Example 1 was repeated except that it had a viscosity of 20, a water content of 3.84 wt% and a metal ion content of 93.1 ppb. In addition, only 10 wt% of isopropanol was added to the reactor. Purified alignment solution was obtained and the analysis results are summarized in Table 2.

Example 3

The same process as in Example 2 was repeated in Example 3 except that 10 wt% acetone was added to the reactor instead of isopropanol. Purified alignment solution with a water content of about 0.29 wt% was obtained.

Comparative Example

The recycling method disclosed in US Pat. No. 6,420,440 was performed. An alignment waste solution as in Example 2 was provided. Ethyl ether was added to the alignment waste solution to solidify the polyimide. The solid polyimide was then filtered and dried. Finally, the dried solid polyimide was dissolved in the same organic solvent as the original solution to obtain a purified alignment solution.

Table 1 shows the unused alignment solution (the original solution applied to the VA type liquid crystal), the (unpurified) alignment waste solution, the purified alignment solution (Example 1) and the alignment. Comparisons are made between commercial standards of alignment solutions. Table 2 shows the unused alignment solution (original solution applied to TN type liquid crystal), (unpurified) alignment waste solution, purified alignment solution (Example 2) and orientation Comparisons are made between commercial standards of alignment solutions. As shown in Tables 1 and 2, the water content and metal ion content of the recycled alignment solution of Examples 1 and 2 were significantly lower than the alignment waste solution and were substantially different from the original solution. Equivalent. In addition, other properties of the purified alignment solution, such as solids content and viscosity, were also substantially the same as the original solution and met the commercial criteria for alignment solution.

Original solution Waste liquid Refined alignment liquid Commercial standard Solid content (wt%) 6.5 6.8 6.6 6.3 ± 0.3 Viscosity (Cps) 20.7 22.3 20.5 19 ± 4 Moisture content (wt%) 0.62 3.9 0.7 <1 Total content of metal ions (ppb) 255 515 231 <500

Original solution Waste liquid Refined alignment liquid Commercial standard Solids content (wt%) 5.9 6.0 6.1 60 ± 0.3 Viscosity (Cps) 22.2 20 22 25 ± 5 Water content (wt%) 0.34 3.84 0.36 <0.40 Total content of metal ions (ppb) 49.9 93.1 53.0 <500

3 and 4 show the comparison between the original solution and the purified alignment solution of Examples 1 and 2 by Fourier transform infrared spectroscopy (FTIR). In Figures 3 and 4, the wave numbers and the relative intensities of all the peaks of Examples 1 and 2 are substantially the same as the original solution. In addition, the absence of a peak located at 1728 cm ⁻¹ means that no imidization was formed in Examples 1 and 2. Thus, it may be suggested that the polymer components of the original solution did not degrade in the purified alignment solution. In addition, the content of polymer components in the purified alignment solution also remained the same as the original solution.

5 and 6 show the comparison between the original solution and the purified alignment solution of Examples 1 and 2 by gel permeation chromatography (GPC), respectively. FIG. 7 shows a comparison between the original solution and the purified alignment solution of the Comparative Example by analyzing GPC (gel permeation chromatography). 5 and 6, the retention times of the original alignment solution and the purified alignment solution of Examples 1 and 2 are substantially the same, which means that the polymer components of the original solution are Examples 1 and 2 Proved to be preserved in the purified alignment solution. In FIG. 5, two peaks at retention times of 14 minutes and 16 minutes represent polyimide and silane coupling agent. It can be seen that the ratio of the peak intensities of the polyimide and silane coupling agent of the purified alignment solution of Example 1 is substantially the same as the original solution. In FIG. 6, two distinguishable peaks at 5 minutes and 7 minutes represent polyimide and silane coupling agents. The ratio of peak intensity was also substantially the same as the original solution. In contrast, in FIG. 7, the content of the silane coupling agent (appearing at about 17 minutes) of the purified alignment solution of the comparative example was significantly reduced. In the comparative example, it can be suggested that when separating the polyimide, most of the silane coupling agent is removed.

Table 3 also shows the recycling efficiency of the alignment solutions of Examples 1 and 2. The results show that in both Example 1 and Example 2 the recycling efficiency is at least 90%.

Amount of waste liquid (g) Amount of recycled alignment liquid (g) Recycling Efficiency (%) Example 1 432 395 91.4% Example 2 2105 2009 95.1%

As mentioned above, the recycled alignment solution according to the method or apparatus of the embodiment of the present invention has substantially the same components and properties as the original solution, and impurities such as moisture and / or metal ions can be removed with high efficiency. It is known that it can. Therefore, recycled alignment solutions can be repeatedly used in production lines, which can significantly reduce the manufacturing cost of LCDs.

Although the present invention has been described by way of example and in terms of preferred embodiments, the invention is not limited to the disclosed embodiments. On the contrary, it is intended to include various modifications and similar arrangements (obvious to those skilled in the art). Therefore, the scope of the appended claims should be construed broadly to encompass all such modifications and similar arrangements.

Claims (14)

As a method of recycling the alignment solution,
Providing an alignment solution of liquid crystal alignment material, wherein the alignment solution comprises at least (a) a polyimide or a precursor thereof, (b) a first solvent, (c) an additive and (d) at least one metal ion and moisture,
Adding a second solvent to the alignment solution;
Removing the water and the second solvent by azeotropic distillation; And
And filtering the alignment solution with a filter material to obtain a purified alignment solution.
The first solvent includes N-methylpyrrolidone (NMP), Butyl Cellosolve (BCS), γ-BL (γ-butyrolactone), or a mixture thereof.
The additive includes an anti-static agent, a silane coupling agent, a titanium coupling agent, a surfactant, or a mixture thereof,
The second solvent is methanol, ethanol, n-propanol, isopropanol, isopropanol, n-butanol, isopentanol, dioxane Tetrahydrofuran, acetone, acetonitrile, methyl isobutyl ketone or mixtures thereof;
The filter material includes an adsorbent and a filtering membrane, and the adsorbent is aluminum oxide having a purity of 99% or more or alumina-silicate having a purity of 99% or more. It includes, the recycling method of the alignment liquid. delete delete delete delete The method of claim 1,
The filtering membrane is a pore size of 0.1 μm to 0.5 mm in polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, stainless steel steel) or a combination thereof. The method of claim 1,
Wherein the purified alignment liquid has a water content of less than 0.4 wt% and a metal ion content of less than 500 ppb. The method of claim 1,
Removing the water and the second solvent by azeotropic distillation (azeotropic distillation) is carried out at a pressure of 30 torr and a temperature of 20 ℃ to 50 ℃, recycling method of the alignment liquid. The method of claim 1,
The alignment solution and the purified alignment solution comprises a polyimide or precursors and additives of the same content, recycling method of the alignment solution. The method of claim 1,
Further comprising adding less than 10 wt% of a first solvent to the purified alignment solution based on the total weight of the purified alignment solution. The method of claim 1,
The recycling efficiency of the alignment liquid, which is the ratio of the purified alignment liquid to the alignment liquid, is 90% or more. As a recycling apparatus of the alignment liquid,
A reactor comprising the alignment liquid;
Moisture removal system; And
A metal ion removal system receiving the alignment liquid from the water removal system;
The alignment liquid comprises (a) a polyimide or a precursor thereof, (b) a solvent, (c) an additive and (d) at least one metal ion and water, wherein the additive is an anti-static agent ), A silane coupling agent, a titanium coupling agent, a surfactant, or a mixture thereof, and the solvent includes N-methylpyrrolidone (NMP), Butyl Cellosolve (BCS), γ- Γ-butyrolactone (BL) or a mixture thereof,
The moisture removal system comprises a temperature control unit for controlling the temperature of the vessel; And a vacuum unit which lowers the pressure of the reactor and removes moisture of the alignment solution.
And said metal ion removal system comprises a filtering membrane disposed at the bottom of said reactor and an adsorbent disposed above said filtration membrane. The method of claim 12,
Wherein said adsorbent is aluminum oxide having a purity of at least 99% or alumina-silicate having a purity of at least 99%. The method of claim 12,
The reactor has a pressure of 30 torr and a temperature of 20 ℃ to 50 ℃, apparatus for recycling the alignment liquid.

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