JP2004346295A - Highly efficient method of purification for liquid crystal having high specific resistance and device for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly efficient method for purifying much soiled liquid crystal in a short time to obtain the liquid crystal having a high specific resistance and purity, and a highly efficient device for the same. <P>SOLUTION: This highly efficient method of purification for the liquid crystal having the high specific resistance (HSR) is characterized by combining both of an inorganic salt absorption method and an electrophoresis purification method, and especially the highly efficient method of purification for the HSR liquid crystal products required in a TFT, LCD and/or other field is also provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and an apparatus for purifying a liquid crystal having a high specific resistance, particularly to a method and an apparatus for purifying a liquid crystal having a high specific resistance using a salt absorption method and an electrophoresis method, and to efficiently purify a large amount of TFT liquid crystals in a short time. It relates to an electrophoresis apparatus.

  Liquid crystal displays (LCDs) have the features of thinness, light weight, power conservation, and low radiation. Thin film transistor (TFT) technology brings LCDs to the color world, which has the momentum to replace traditional CRT monitors and has great market potential. TFT-LCD requires a liquid crystal with high specific resistance, that is, high purity. As a result, many liquid crystals must be scrapped during the manufacturing process due to trace contamination. With current LCD panel technology, yields are slightly greater than 50%, while 30% to 50% of contaminated liquid crystals must be discarded. Since liquid crystals are expensive chemicals, recycling, refining and reusing waste liquid crystals are considered important technologies.

  Some techniques relating to the recycling of liquid crystals are disclosed in patents such as JP-A-8-277391 which describes a method for purifying liquid crystals by adding an inorganic salt and an organic solvent, and then heating and stirring. . However, the method can only purify liquid crystals with low purity requirements and containing impurities that are significantly higher than those required by TFT liquid crystals, and therefore liquid crystals such as TFT liquid crystals that require high resistivity values. Cannot be used for purification and recycling. There are also several techniques for purifying liquid crystals by using an electrophoresis method, and these are described in JP-A-50-108186, JP-A-51-011079, JP-A-4-171419, JP-A-4-288520, No. 8-297290 and claims in JP-A-2002-60752. However, such techniques use pure electrophoretic methods for purification without combining any other mechanisms.

  The claims of JP-A-50-108186 describe a method of purifying liquid crystals by removing certain gases by a pump (to create a vacuum) and applying an external electric field. . As the liquid crystal moves from one storage tank to another, it passes through a tube containing electrodes provided on the outer wall. The electrode will absorb impurity ions for purification purposes. However, liquid crystals can only be purified to a limited extent because strong electric fields cannot be established due to electrode clearances greater than 1 cm and the liquid crystals undergo electrophoresis for only a limited time. The claims of the above-mentioned Japanese Patent Application Laid-Open No. 4-171419 clarify a method of purifying a liquid crystal when the liquid crystal is filled in an LCD panel in a vacuum environment. An electric field is applied externally to the liquid crystal container to absorb impurity ions and reduce the likelihood of such ions being absorbed by the panel. However, a voltage of 1 V is used for electrodes having a clearance greater than 1 cm. As a result, the TFT liquid crystal cannot be substantially purified. The claims of the above-mentioned Japanese Patent Application Laid-Open No. 4-288520 disclose a method of filling an LCD panel in an external electric field. The metal container used to contain the liquid crystal also acts as the cathode, which delivers an increased electrode area. In addition, the voltage is increased to 20V. However, the method cannot be used directly to purify TFT liquid crystals because the electrodes still have a clearance of more than 1 cm.

Claims of the Japanese Patent Laid-Open No. 8-297290 is an electrode clearance was reduced to 0.01cm using SiO ₂ sputtering coating, also increasing the voltage up to 500V. Unfortunately, the SiO ₂ contained in the coat also carries the risk of releasing impurity ions. Therefore, the method still cannot provide SR values that fall within the requirements of TFT liquid crystals. None of the purification techniques disclosed in the above four claims are sufficient to effectively purify the TFT liquid crystal described in the present invention or any other liquid crystal having higher purity or SR value. However, they can be used to purify liquid crystals with low purity requirements, for example STN liquid crystals.
The claims of the above-mentioned JP-A-2002-60752 describe the purification of a liquid crystal having a high specific resistance (HSR) in a vacuum environment when a 300 V electrode is applied to an electrode having a clearance of 1 cm for electrophoretic purification. A method is described. With repeated electrode washing, the HSR liquid crystal can be purified in 2-17 hours. However, the electrode area is 10 cm ² and only about 30 ml of liquid crystal is processed per cycle. Therefore, the method is not directly applicable to mass plant production, which requires refining to be performed on a large scale.

In order to eliminate the disadvantages of the above technology when recycling HSR and high purity liquid crystal, the present invention provides a purification method suitable for large-scale plant purification of TFT liquid crystal and other liquid crystal having higher purity and SR value. Establish a series of technologies, including the following devices. Such liquid crystals are indicated for TFT liquid crystals that require metal impurity ions below 5 ppb and an SR higher than 10 ¹³ Ωcm.
An object of the present invention is to provide a method for purifying an HSR liquid crystal. It combines inorganic salt absorption and electrophoresis methods to purify contaminated liquid crystals. Recycled liquid crystals can be manufactured with a resistivity greater than 10 ¹³ Ωcm.

The method comprises the following steps: a step of bringing the contaminated liquid crystal into contact with an inorganic salt to absorb impurities; a step of filtering the liquid crystal having absorbed the impurity by the inorganic salt to obtain a low-purified liquid crystal; A step of treating the low-purified liquid crystal by electrophoresis to remove residual impurities. The inorganic salt absorption method may be performed at room temperature without adding a solvent.
The inorganic salt may be selected from the group consisting of alumina, silica gel, activated alumina, zeolite, titanium oxide and analogs thereof.
It is recommended that the method treat contaminated liquid crystals having an SR in the range of 10 ¹¹ Ωcm to 10 ¹³ Ωcm.
The electrophoresis method is performed in an argon environment from which both water and particles have been removed.
Another object of the present invention is to provide an electrophoresis device for purifying liquid crystals. The apparatus includes an inert gas supply unit, a dehydration unit, a departicle unit, an electrophoresis tank, and a power supply. Preferably, the inert gas supply unit supplies argon.
The electrophoresis tank includes an electrophoresis container assembly (including a composite electrophoresis container), a container base, and a quick coupler for connecting the electrode plate to a power source. The composite electrophoresis container includes two or more electrode plates, an electrode base on which the electrode plate is placed, and a container body on which the electrode plate and the electrode base are placed.

Preferably, the electrode plates are placed in parallel for both the anode and the cathode. The number of electrode bases may be increased or decreased whenever needed according to the amount of liquid crystal to be refined to add more electrode plates or to remove some electrode plates. The electrode plates are not limited in area for each. The electrode base may be of a removable type or a fixed type.
The electrode plate may be made of platinum, nickel, silver, zinc, or other materials, with platinum being preferred. The electrode plates are preferably placed at a distance of 0.2-1.0 cm. It is preferable that both the electrode base and the container body are made of Teflon (registered trademark).
The purification method disclosed in the present invention has the ability to substantially remove impurities from liquid crystals and produce liquid crystal products that meet the required specifications for the application. Compared with the above technique disclosed in JP-A-8-277391 (which uses a purification method requiring 1-3 hours by adding a salt and an organic solvent, then heating and stirring), the present invention Uses a salt absorption method that takes only 30 minutes. For the electrophoresis method, the present invention uses an electrophoresis apparatus that takes only three hours, and uses the claimed technology disclosed in Japanese Patent Application Laid-Open No. 2002-60752 (which will spend 17 hours for electrophoresis). Can be compared. In addition, the device can process significantly more liquid crystals in one cycle than such techniques.
As indicated by the above description, the method and apparatus for refining a liquid crystal having a high specific resistance disclosed in the present invention greatly reduces the time required for refining, and addresses the requirement for cleanliness in the refining stage. Provide safe and easy driving. More importantly, the present invention reveals an electrophoresis apparatus that is suitable for mass plant production and offers considerable market potential.

  The features of the electrophoretic device as well as the electrophoretic device disclosed in the present invention will be described in detail below. FIG. 1 shows one embodiment of the electrophoresis apparatus disclosed in the present invention. The apparatus includes a steel argon cylinder 1, a dehydration unit 2, a departicle unit 3, a flow target tube 4, a needle valve 5, an electrophoresis tank 6, a DC power supply 7, and a ball valve 8. During the electrophoresis method disclosed in the present invention, argon gas flows out of the steel argon cylinder 1 at a flow rate of more than 50 ml / min as recommended, and the dehydration unit 2, departicle unit 3, and flow rate After passing through the target tube 4 and reaching the electrophoresis tank 6, the electrophoresis operation is kept in a steady argon atmosphere.

As shown in FIG. 2, the detailed structure of the electrophoresis tank 6 includes an electrophoresis container assembly 9, an acrylic box 10, a feedthrough 11, and a rubber sealing 12. The electrophoresis tank 6 is designed with the following advantages. The electrophoresis environment finely tunes the introduction flow rate of the argon gas with the needle valve 5 and positions both the argon outlet and the inlet, as well as hermeticity by using the rubber sealing 12 and the ball valve on the top. Sampling by opening 8 improves its cleanness. The feedthrough 11 (which may be located directly on the enlarged metal box) is used to pass an external power supply to the electrophoresis tank 6 to ensure safe operation at high voltage and prevent short circuits.
FIG. 3 shows a partial cross-sectional view of the electrophoresis assembly 9, which is a composite electrophoresis container 13 (preferably made of Teflon®), an acrylic container base 14, and the composite electric device. It includes a quick coupler 15 for connecting the electrode plate 16 in the electrophoresis container 13 to an external power supply.

  FIG. 4 shows the structure of the composite electrophoresis container 13. FIG. 4A shows a diagram of a composite electrophoresis container 13, which includes a container body 17, an electrode base 18, and more than one electrode plate 16 placed parallel within said electrode base 18. FIG. 4B shows that the electrode base 18 is of a removable type. Such a type of base has negligible clearance so that the electrode plate 16 (if its use is completed) can be removed from the electrode base 18 for cleaning to address the difficulty of cleaning the electrode plate. However, the electrode base 18 may be fixed and fixed to the container body 17. FIG. 4C shows a plan view of the composite electrophoresis container 13. As can be seen, the electrode plates 16 lie parallel in corresponding grooves 19 in the two electrode bases 18. The number of plates 16 may be increased or decreased as needed, as the electrode plates 16 may be inserted into grooves 19 and removed therefrom. In addition, each of the electrode plates 16 can be designed with any desired area.

FIG. 5 is a plan view of the quick coupler 15 for connecting the electrode plate 16 to a power source. By using the quick coupler 15 designed in the present invention, the electrode plate 16 can be quickly and easily connected to an external power supply in a standard manner. In addition, the coupler also ensures ideal conductor contact to reduce concerns regarding tripping and shorting.
In particular, based on the implementation of the electrophoresis vessel 13 disclosed in the present invention, the platinum electrode plates 16 each having an area of up to 620 cm ² are placed in an argon environment (where high voltages up to 700 V are applied). When used for electrophoresis with a clearance of 0.2 cm between each two adjacent plates, the amount of liquid crystal that can be processed up to 130 ml for each cycle takes only three hours to reach the TFT liquid crystal purity requirement. No need. In addition, it is not necessary to repeatedly remove the electrode plate for washing during the electrophoresis method. Therefore, such processing can be substantially deployed in mass production.
The present invention includes special techniques for substantially purifying TFT liquid crystals and other liquid crystals having higher SR by using both salt absorption and electrophoresis methods. The operation is as follows.

Inorganic salt absorption method In the inorganic salt absorption method, the liquid crystal is mixed with 10% by weight of AC61, which contains more than 99.3% alumina, and then the mixture is stirred for 20 minutes. When the stirring is completed, the mixture is left for 10 minutes and then filtered through a 0.2 μm PTFE filter disc to obtain a purified liquid crystal.
Electrophoretic purification method The electrophoretic purification method for liquid crystal is that the liquid crystal is put between the electrode plates (these are applied with high voltage (500-1100V)) and the ions are separated as a result of the electrophoretic effect of the ions in the electric field. Absorption and separation from the liquid crystal to the surface of the electrode. The operation of electrophoretic purification is as follows.

1. Place the platinum electrode plate in the electrophoresis container so that the anode and cathode alternate.
2. Fill the electrophoresis container with the contaminated liquid crystal until the electrode plate is submerged.
3. Move the electrode container to the electrophoresis tank. The cabinet is filled with argon gas at a flow rate of 500 cc / min for at least 20 minutes.
4. Adjust the argon flow up to 300cc / min. Turn on the power and adjust the voltage to 700V. Start electrophoresis.
5. During the electrophoresis method, a certain amount of the purified liquid crystal is sampled by using a suction pipette to measure the SR value.
6. Test the SR value and, if appropriate, leave the power supply on and drain the liquid crystal into a storage bottle to facilitate subsequent physical analysis.
The above inorganic salt absorption method and the electrophoretic purification method may be used separately. However, if both methods are used in combination, the best results can be expected to give purified liquid crystals with SR values greater than 10 ¹³ Ωcm.
Some examples are set forth below to demonstrate the benefits of the present invention, but these examples are not intended to limit the scope of the invention.

Example 1
An amount of liquid crystal having an SR value of 2.0 × 10 ¹¹ Ωcm is purified directly by electrophoresis. The SR value is only improved to about 6.0 × 10 ¹¹ Ωcm. Because too many impurities remain, the purification has no apparent effect and the liquid crystal finished from the electrophoretic purification can still not meet the required specifications as shown in FIG.

Example 2
A certain amount of liquid crystal having an SR value of 2.0 × 10 ¹¹ Ωcm is purified by AC61 purification method to increase the SR value to 7.0 × 10 ¹² Ωcm. After the further electrophoresis purification method, the value was increased to 3.8 × 10 ¹³ Ωcm as shown in FIG. 7, in which the left curve portion of “0” indicates the AC61 purification method, and Part indicates electrophoretic purification.

Example 3
A certain amount of liquid crystals already having an SR value of up to 3.0 × 10 ¹² Ωcm is directly purified by electrophoretic methods. As shown by the curve “A” in FIG. 8, the SR value increased to 3.3 × 10 ¹³ Ωcm at the end of 3 hours, which indicates that the waste liquid crystal having high purity is substantially equal to the purified liquid crystal in the present invention. It means that it can be purified directly on the disclosed electrophoresis apparatus. If a liquid crystal of this type already having an SR value of up to 3.0 × 10 ¹² Ωcm is purified by the AC61 purification method, its value will increase to 1.2 × 10 ¹³ Ωcm. If the electrophoresis method is used for further purification, the value will increase to 3.7 × 10 ¹³ Ωcm. See curve “B” in FIG. 8 (the left curve portion for “0” indicates the AC61 purification method, and the right portion indicates electrophoretic purification). The SR value of the finished liquid crystal is higher than the SR value of the liquid crystal directly purified by electrophoretic purification without using the AC61 treatment, and the electrophoresis apparatus disclosed in the present invention is capable of increasing the SR value of the purified liquid crystal. It shows that it has the ability to increase even near the SR value of the TFT liquid crystal.

1 illustrates an electrophoresis apparatus disclosed in the present invention. 1 illustrates the structure of an electrophoresis tank disclosed in the present invention. FIG. 2 illustrates a partial cross-sectional view of an electrophoresis container assembly as disclosed in the present invention. 4A, 4B and 4C illustrate the structure of the composite electrophoresis container disclosed in the present invention. Figure 2 illustrates a rapid coupler as revealed in the present design connected to an electrode plate. 1 shows the results of Example 1 of the present invention in which a liquid crystal is directly purified by an electrophoresis method. The result of Example 2 of the present invention in which a liquid crystal is purified by combining both the inorganic salt absorption method and the electrophoretic purification method is shown. The results of Example 3 of the present invention in which a liquid crystal is purified by directly using an electrophoresis method and by sequentially using an inorganic salt absorption method and an electrophoresis purification method are shown in comparison.

Explanation of reference numerals

1-Steel argon cylinder 2-Dehydration unit 3-Draining unit 4-Flow rate target tube 5-Needle valve 6-Electrophoresis tank 7-DC power supply 8-Ball valve 9-Electrophoresis container assembly 10-Acrylic box 11-Field Through 12-Rubber sealing 13-Composite electrophoresis container 14-Acrylic container base 15-Rapid coupler 16-Electrode plate 17-Container body 18-Electrode base 19-Groove

Claims (24)

A method for purifying a liquid crystal having a high specific resistance, comprising both a salt absorption method and an electrophoretic purification method, comprising the following steps:
Contacting the contaminated liquid crystal with an inorganic salt,
Filtering the liquid crystal absorbed by the inorganic salt to obtain a low-purity liquid crystal; and purifying the low-purity liquid crystal by an electrophoretic purification method to remove residual impurities from the liquid crystal.   The method according to claim 1, wherein the salt absorption method is carried out at room temperature without solvent.   The method of claim 1, wherein said inorganic salt is selected from the group consisting of alumina, silica gel, activated alumina, zeolite, titanium oxide, and analogs thereof.   The method according to claim 1, wherein the inorganic salt is alumina. 2. The method according to claim 1, wherein the specific resistance of the purified liquid crystal increases to 10 ¹³ Ωcm or more. An inert gas supply unit for supplying an inert gas to the electrophoresis environment,
A dehydration unit for removing water from said gas,
A departicle unit for removing particles from the gas,
An electrophoresis tank for electrophoresis, and a power supply for applying a voltage to the electrophoresis tank for performing electrophoresis, the liquid crystal electrophoresis purification apparatus.   7. The apparatus according to claim 6, wherein said inert gas is argon.   7. The apparatus of claim 6, wherein said electrophoresis tank includes an electrophoresis vessel assembly, said assembly including a composite electrophoresis vessel, an electrophoresis base, and a quick coupler for connecting an electrode plate to a power source.   9. The apparatus according to claim 8, wherein the composite electrophoresis container includes at least two electrode plates, an electrode base for placing the electrode plate, and a container body for placing the electrode plate and the electrode base.   The device according to claim 9, wherein the electrode plates are arranged in parallel.   An electrophoresis container assembly comprising a composite electrophoresis container, an electrophoresis base and a quick coupler for connecting the electrodes to a power source.   12. The electrophoresis container assembly according to claim 11, wherein the composite electrophoresis container includes at least two electrode plates, an electrode base for placing the electrode plate, and a container body for placing the electrode plate and the electrode base.   A composite electrophoresis container comprising at least two electrode plates, an electrode base on which the electrode plate is placed, and a container body on which the electrode plate and the electrode base are placed.   14. The composite electrophoresis container according to claim 13, wherein the electrode plate is made of platinum.   The composite electrophoresis container according to claim 13, wherein the electrode plate is fixed in a groove of the electrode base.   14. The composite electrophoresis container according to claim 13, wherein a clearance between the electrode plates is 0.2 to 1.0 cm.   14. The composite electrophoresis container according to claim 13, wherein a clearance between the electrode plates is 0.2 cm.   14. The composite electrophoresis container according to claim 13, wherein the electrode plates are arranged in parallel.   14. The composite electrophoresis container according to claim 13, wherein the electrode base is a removable type or a fixed type.   14. The composite electrophoresis container according to claim 13, wherein the electrode base is of a removable type.   An electrophoresis method for purifying a liquid crystal, the method being completed by the apparatus according to claim 6.   An electrophoresis method for purifying a liquid crystal, which is performed using the apparatus according to claim 11.   An electrophoresis method for purifying a liquid crystal, which is performed using the apparatus according to any one of claims 13 to 20.   24. The method according to any one of claims 21 to 23, wherein said method is capable of purifying liquid crystals in combination with a salt absorption method.

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