KR20040110833A - Method of forming alignment film and liquid crystal display device comprising alignment film prepared by the same - Google Patents

Abstract

PURPOSE: A method for forming an alignment layer and an LCD(Liquid Crystal Display) comprising the alignment layer manufactured using the same are provided to prevent damage of an alignment layer due to infiltration of liquid crystals, thereby enhancing the reliability of the alignment layer and the productivity of manufacturing process by raising the degree of imidization in the alignment layer. CONSTITUTION: A composite solution for alignment layer is coated on a substrate(S10). The composite solution is pre-dried to be transformed into a compound containing polyamide acid(S20). And then, the compound containing polyamide acid is hardened to be transformed into the first compound containing polyimide(S30). And then, the first compound is hardened to be transformed into the second compound containing polyimide. The second compound is larger than the first compound in a degree of imidization.

Description

A method of forming an alignment layer and a liquid crystal display including the alignment layer manufactured thereby TECHNICAL FIELD

The present invention relates to a method of forming an alignment film and a liquid crystal display device used in a liquid crystal display device, and more particularly, to a method of forming an alignment film having a significantly improved physical and chemical resistance, and a liquid crystal display device having an alignment film formed thereby. will be.

Liquid crystal is a material having both the fluid characteristics of the liquid and the optical characteristics of the solid at the same time has the advantage that can easily control the molecular arrangement and optical properties. LIQUID CRYSTAL DISPLAY DEVICE (LCD) is a display device made by using the characteristics of the liquid crystal and displays information on the screen by adjusting the transmittance of light. In such a liquid crystal display device, the control of the molecular arrangement of the liquid crystal has a great influence on stabilization of the display quality of the liquid crystal display device. The alignment layer serves to orient the liquid crystal molecules on the surface of the alignment layer in a predetermined direction. However, when the liquid crystal has an unwanted pattern due to the physical and chemical influences generated in the process, the pattern is transferred to the liquid crystal alignment to show screen defects.

This will be described in detail as follows. Scheme 1 below shows a general imidization step in forming a polyimide organic alignment film.

First, an alignment film solution including a dianhydride represented by Chemical Formula 1 and a diamine represented by Chemical Formulas 2 to 3 is applied onto a substrate of a liquid crystal display, and then the solvent is evaporated through preliminary drying. The polyamic acid represented by 4 is synthesize | combined. Subsequently, the polyamic acid is converted into the polyimide represented by Chemical Formula 5 through the present curing process. At this time, the main curing is performed for about 30 minutes at about 200 to 300 ℃.

However, even after this main hardening, sufficient imidation does not advance and a considerable part of an alignment film remains in a polyamic acid state. The polyamic acid remaining in the alignment film is physically damaged by the liquid crystal, particularly when the liquid crystal layer is formed through the dropping method. Specifically, in the case of applying a dropping method in which a liquid crystal cell is dropped by compressing a liquid crystal in a drop shape using a syringe or the like on a substrate on which an alignment layer is applied, and leveling is applied over the entire panel at the point where the liquid crystal is dropped. ) Requires more than a certain amount of time and pressure. However, in the state where the liquid crystal is not sufficiently leveled, damage is caused to the alignment film by a chemical reaction between the liquid crystal compound and the alignment film compound.

That is, the liquid crystal includes functional groups such as ester groups, halogen groups, cyano groups, and alkyl groups depending on the type thereof, and the amide groups and carboxyl groups of the polyamic acid in which the functional groups contained in the liquid crystal in a sufficiently leveled state remain in the alignment layer. Electrostatic bonding with an acid group or partial dissolution of the alignment film that is not sufficiently imidated causes the state change of the alignment film according to the distribution of the liquid crystal in a subsequent process.

As described above, an irreversible change is caused in the alignment layer according to the drop pattern of the liquid crystal droplets, resulting in a permanent pattern of liquid crystal alignment, which is observed as a stain when the liquid crystal display device is driven.

1 is a photograph showing dripping spots observed upon liquid crystal dropping in an alignment film formed by the prior art. Referring to FIG. 1, it can be seen that luminance varies depending on the dropping point of the liquid crystal when the liquid crystal display device manufactured by the dropping method is driven.

There is known a technique for preventing unevenness of such an alignment film. For example, Korean Patent Laid-Open Publication No. 10-2003-0037820 discloses a liquid crystal display device which can improve a bright point defect of an alignment layer by differently setting positions of vacuum holes provided in a plurality of hot plates when a glass substrate for pre-drying is moved. An alignment film forming apparatus and method are disclosed. According to the above-described invention, the uniformity of the thermal conductivity can be improved by preventing the drying at a specific point from being different from other points. By overcoming the difference in thermal conductivity, it is possible to prevent defect defects of the alignment layer and to improve a problem of bright point caused when the alignment layer is dried.

According to this method, it is possible to prevent unevenness of the alignment film by achieving the same dryness throughout the preliminary alignment film, but there is a limit in improving the degree of imidization. Therefore, when the liquid crystal layer is formed using a dropping method, a liquid crystal display device having a method of manufacturing an alignment film capable of sufficiently proceeding imidization of the alignment film and preventing damage to the alignment film by liquid crystal, and an alignment film manufactured by such a method. Development of technology is required.

Accordingly, a first object of the present invention is to provide a method of forming an alignment film having physical and chemical resistance by improving the degree of imidization of the alignment film solution.

A second object of the present invention is to provide a liquid crystal display device comprising an alignment film formed by the above method.

1 is a photograph showing dripping spots observed upon liquid crystal dropping in an alignment film formed by the prior art.

2 is a flowchart illustrating a method of forming an alignment layer according to an embodiment of the present invention.

3 is a flowchart illustrating a method of forming an alignment layer according to another embodiment of the present invention.

4 is a schematic cross-sectional view illustrating a liquid crystal display device including an alignment layer manufactured by the method of FIG. 2 or 3.

Brief description of the main parts of the drawing

10, 11 substrate 20, 21 thin film electrode

30, 31 alignment film 40 liquid crystal

In order to achieve the first object of the present invention, in the method for forming an alignment film according to an embodiment of the present invention, first, the alignment film solution is applied to a substrate, and the alignment film solution is pre-dried to be converted into a compound containing polyamic acid. do. Subsequently, the compound containing the polyamic acid is first cured to convert the first compound containing the polyimide, and the first compound is second cured to convert the second compound containing the polyimide to form an alignment film. The secondary cure here is a post cure process which is added after the primary cure, which is the usual main cure process, and is performed at about 250 to 350 ° C. for about 30 minutes to 2 hours.

In order to achieve the first object of the present invention described above, a method of forming an alignment film according to another embodiment of the present invention is applied to the substrate, the alignment film solution is preliminarily dried to convert the compound containing a polyamic acid and , First curing under 1 to 100 mmTorr to form a first compound containing a polyimide to form an alignment film.

In order to achieve the above-described second object of the present invention, an embodiment of the present invention is a pre-drying of a pair of substrates facing each other, a thin film electrode formed on the substrate, the alignment film solution to convert to a compound containing a polyamic acid And a second compound comprising a polyimide prepared by first curing the compound containing polyamic acid and converting it into a first compound containing polyimide, followed by secondary curing of the first compound. Provided is a liquid crystal display device including a liquid crystal filled between an alignment film and an alignment film formed on the formed substrate.

In order to achieve the above-described second object of the present invention, another embodiment of the present invention is a pre-drying of a pair of substrates facing each other, a thin film electrode formed on the substrate, the alignment film solution to convert to a compound containing a polyamic acid And a compound including a polyimide prepared by curing the compound including the polyamic acid under 1 to 100 mmTorr, and including a liquid crystal filled between an alignment layer and an alignment layer formed on a substrate on which the thin film electrode is formed. Provide a display device.

By using the method for forming the alignment film according to the present invention, the degree of imidization of the alignment film can be quickly increased, and the physical and chemical resistance of the alignment film can be improved. Therefore, even when the liquid crystal layer is formed by the dropping step, local damage of the alignment film due to the liquid crystal can be prevented. As a result, the present invention can improve the reliability of the alignment film and the economics of the manufacturing process thereof, thereby making it possible to economically manufacture high quality liquid crystal display devices.

Hereinafter, with reference to the accompanying drawings will be described in detail an example of a method of forming an alignment film according to the present invention and a liquid crystal display device comprising the alignment film manufactured thereby.

2 is a flowchart illustrating a method of forming an alignment layer according to an embodiment of the present invention. Referring to FIG. 2, the alignment film solution is first applied to a substrate (S10), preliminarily dried (S20), and then subjected to primary curing (S30) and secondary curing (S40) to have an imidation degree of 80% or more. An alignment film can be formed.

In this embodiment, the alignment film solution is first applied to the substrate (S10). Specifically, the contamination and dirt remaining on the patterned substrate is removed using a cleaning liquid, and then the alignment layer solution is applied onto the substrate. The coating is carried out using a spin method, a dipping method, a roller coating method, or the like.

In the present embodiment, in order to form a polyimide organic alignment layer, an dianhydride including a phenylene group represented by the following formula (1) and a diamine (diamine) represented by the following formulas (2) to (3) are used in an alignment layer solution in which a solvent is dissolved. . However, in the following Chemical Formula 3, R is, for example, O (CH 2) 15 CH 3 or COO (CH 2) 15 CH 3.

In addition, as the solvent, butyrolactone, N-methylpyrrolidone (N-methyl-2-pyroridone: NMP), or butyl cellosolve may be used in order to improve coatability.

Subsequently, the alignment layer solution is pre-dried to form a polyamic acid (S20). The dianhydride including the phenylene group represented by Chemical Formula 1 and the diamine represented by Chemical Formulas 2 to 3 are reacted in the solvent to form a polyamic acid represented by Chemical Formula 4 through a preliminary drying process. R at 4 is for example O (CH 2) 15 CH 3 or COO (CH 2) 15 CH 3). In addition, the solvent is evaporated prior to the curing process by the predrying, the predrying process is carried out at about 80 ℃.

Subsequently, the compound containing the polyamic acid is first cured and converted to the first compound containing the polyimide (S30).

The primary curing is a process corresponding to a conventional alignment film solution curing process, it is carried out by firing the alignment film for about 20 to 40 minutes at a temperature of about 200 to 300 ℃. Part of the polyamic acid is converted to the polyimide represented by the following Chemical Formula 5 by the dehydration polycondensation reaction by the primary curing. However, even if it performs the said 1st hardening, sufficient imidation cannot be expected.

When liquid crystal is dripped at the oriented film in the state in which sufficient imidation is not achieved, the amide group and carboxylic acid group of the polyamic acid of an oriented film react with the ester group, halogen group, cyano group, alkyl group, etc. which are contained in a liquid crystal. Specifically, the functional groups included in the liquid crystal in a level that is not sufficiently leveled form an electrostatic bond with an amide group or a carboxylic acid of polyamic acid or partially dissolve and swell an alignment film that is not sufficiently imidized, thereby aligning the alignment film according to the distribution of the liquid crystal in a subsequent process. It causes a change of state.

Therefore, in order to prevent such a problem and to achieve sufficient imidization and to prevent damage of the alignment film, it is necessary to proceed with post curing.

In the present embodiment, the first compound obtained by the first curing is secondary cured to convert to a second compound containing polyimide to form an alignment layer (S40).

The secondary curing is carried out at about 250 to 350 ℃ for about 30 minutes to 2 hours, as a result of the imidization progressed more than 80%. If the secondary curing temperature is less than about 250 ° C., sufficient curing may not be achieved. If the secondary curing temperature is higher than about 350 ° C., there is a fear that heat damage occurs. In addition, when the curing time is less than about 30 minutes, imidation of 80% or more may not be achieved, and dropping may occur due to liquid crystals. If curing is performed for more than about 2 hours, there is a problem of inferior economic efficiency in manufacturing a liquid crystal display device. .

By secondary hardening of the said 1st compound, imidation advances more and the physical chemical resistance of an alignment film improves, and local damage of the alignment film by the liquid crystal which arises at the dropping point of a liquid crystal can be prevented. For example, when the degree of imidization of the alignment film is about 80% or more, dropping stains are not observed visually.

3 is a flowchart illustrating a method of forming an alignment layer according to another embodiment of the present invention. Referring to FIG. 3, first, an alignment layer solution is applied to a substrate (S100), and the alignment layer solution is preliminarily dried (S200), and then first cured under 1 to 100 mmTorr to form an alignment layer (S300). The degree of imidation of the alignment film can be further improved by selectively adding a secondary curing step.

According to this embodiment, first, the alignment film solution is applied to the substrate (S100). Contaminants and dust remaining on the patterned substrate are removed using a cleaning liquid, and then the alignment layer solution is applied onto the substrate. Coating is performed using the spin method, impregnation method, roller nose method, or the like.

In this embodiment, in order to form a polyimide organic alignment layer, an dianhydride including a phenylene group represented by Formula 1 and an alignment layer solution in which diamine represented by Formulas 2 to 3 are dissolved in a solvent are used. . However, in Chemical Formulas 1 to 3, R is, for example, O (CH 2) 15 CH 3 or COO (CH 2) 15 CH 3. In addition, butyrolactone, NMP, or butyl cellosolve may be used as the solvent.

Subsequently, the alignment layer solution is preliminarily converted into a compound containing polyamic acid (S200).

The dianhydride including the phenylene group represented by Formula 1 in the alignment layer solution and the diamine represented by Formulas 2 to 3 react in the solvent to form a polyamic acid represented by Formula 4. In addition, the solvent is evaporated prior to the curing process by the predrying, it is carried out at about 80 ℃.

Subsequently, the compound containing the polyamic acid is first cured under 1 to 100 mmTorr to form a first compound including the polyimide to form an alignment layer (S300).

The primary curing is carried out at 150 to 250 ° C. for 15 to 20 minutes under a low pressure of 1 to 100 mm Torr. This is because the process of forming the polyimide from the polyamic acid is due to the dehydration polycondensation reaction, thereby maintaining a sufficient pressure of imidization at a low temperature than the above-described embodiment by maintaining the reaction pressure at a low pressure of 1 to 100 mmTorr. You can do it.

A low pressure of less than 1 mmTorr is unnecessary to achieve imidation of about 80%, and it is economically undesirable to form such a low pressure atmosphere. In addition, when the reaction pressure exceeds 100 mmTorr, the time required for imidation of 80% or more takes a long time, which is not economically desirable. The degree of imidization through this primary curing is 80% or more, and no dripping spots are observed.

In addition, by selectively curing the first compound after the first curing and converting the first compound to the second compound (S400), the degree of imidation may be further improved as necessary.

According to the above-described method, since curing proceeds at low temperature, damage to the alignment film due to heat can be reduced, and sufficient degree of imidation can be achieved quickly.

The present invention provides a liquid crystal display device having an alignment film formed by the above-described alignment film forming method. FIG. 4 is a schematic cross-sectional view illustrating a liquid crystal display manufactured by the method of FIG. 2 or 3.

Referring to FIG. 4, the liquid crystal display of the present invention includes an alignment layer formed according to the method of forming the alignment layer described above on the pair of substrates 10 and 11, the thin film electrodes 20 and 21, and the substrate on which the thin film electrodes are formed. 30, 31, and a liquid crystal 40 filled between the alignment layers.

According to one embodiment of the above-described liquid crystal display device, the liquid crystal display device has a pair of opposing substrates 10 and 11. The pair of substrates 10 and 11 may be substrates commonly used in liquid crystal display devices. For example, one of the pair of substrates is a color filter substrate 10 on which a common electrode 20 and an RGB pixel (not shown) are formed, and the other is a pixel electrode 21 and a thin film transistor. Transistor: TFT substrate 11 on which TFTs are formed.

The liquid crystal display according to the present exemplary embodiment includes thin film electrodes 20 and 21 formed on the substrates 10 and 11. The thin film electrodes 20 and 21 are formed to face each other on the pair of substrates 10 and 11 facing each other, and the common electrode 20 is formed on the color filter substrate 10 of the pair of substrates. The pixel electrode 21 is formed on the TFT substrate 20.

The liquid crystal display according to the present exemplary embodiment includes alignment layers 30 and 31 formed on the substrates 10 and 11 having the thin film electrodes 20 and 21. Formation of the alignment layers 30 and 31 is performed by the embodiment of the method of forming the alignment layer described above. Specifically, an alignment layer solution including a compound selected from the compounds represented by Chemical Formulas 1 to 3 or a mixture thereof is coated on the substrates 10 and 11 having the thin film electrodes 20 and 21. The coating is carried out using a spin method, an impregnation method, a roller coating method, or the like. Subsequently, the alignment film solution is preliminarily converted to a compound containing polyamic acid. The predrying process is carried out at about 80 ℃.

Subsequently, the compound containing the polyamic acid is first cured to be converted into the first compound containing the polyimide, and then the first compound is second cured to be converted to the second compound containing the polyimide to form an alignment layer ( 30, 31). The primary curing is a process corresponding to a conventional alignment film solution curing process, is carried out by firing the alignment film for about 20 to 40 minutes at a temperature of about 200 to 300 ℃, the secondary curing at about 250 to 350 ℃ It is carried out for about 30 minutes to 2 hours, with the result that imidation proceeds more than 80%.

The liquid crystal display according to the present embodiment has a liquid crystal filled between the alignment layers.

The liquid crystal can be filled by a vacuum injection method or the like, but in this embodiment, since the degree of imidization progresses by 80% or more and uses an orientation in which physical and chemical resistance is improved, no dropping stain occurs even when a dropping method is applied.

As another embodiment of the liquid crystal display device according to the present invention, the alignment layer of the liquid crystal display device is pre-drying the alignment film solution to convert to a compound containing a polyamic acid, the compound containing the polyamic acid under 1 to 100mmTorr It includes a polyimide compound containing a polyimide prepared by primary curing. The liquid crystal display device described above is excellent in terms of reliability and productivity because it prevents dropping of liquid crystals and does not require a separate post-curing process.

By using the method for forming the alignment film according to the present invention, the degree of imidization of the alignment film can be increased to improve the physical and chemical resistance of the alignment film. Therefore, even when the liquid crystal layer is formed by the dropping step, local intrusion of the alignment film by the liquid crystal can be prevented. As a result, the present invention can improve the reliability of the alignment film and the economics of the manufacturing process thereof, thereby making it possible to economically manufacture high quality liquid crystal display devices.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below You can understand that you can.

Claims (11)

Applying the alignment film solution to the substrate; Pre-drying the alignment layer solution to convert the compound into a polyamic acid-containing compound; Converting the compound including the polyamic acid into a first compound including a polyimide by first curing; And And curing the first compound to convert the second compound into a second compound including polyimide. The method of claim 1, wherein the alignment layer solution comprises at least one compound selected from the group consisting of compounds represented by Formulas 1 to 3 below. [Formula 1] [Formula 2] [Formula 3] However, in Chemical Formula 3, R is O (CH 2) 15 CH 3 or COO (CH 2) 15 CH 3. The method of claim 1, wherein the polyamic acid comprises a compound represented by Formula 4 below. [Formula 4] However, in Chemical Formula 4, R is O (CH 2) 15 CH 3 or COO (CH 2) 15 CH 3. The method of claim 1, wherein the degree of imidization of the second compound is 80% or more. The method of claim 1, wherein the first curing is performed at 200 to 300 ° C. for 20 to 40 minutes. The method of claim 1, wherein the secondary curing is performed at 250 to 350 ° C. for 30 minutes to 2 hours. Applying the alignment film solution to the substrate; Pre-drying the alignment layer solution to convert the compound into a polyamic acid-containing compound; And Forming a first compound comprising a polyimide by first curing the compound including the polyamic acid under 1 to 100 mmTorr. The method of claim 7, wherein the primary curing is carried out at 150 to 250 ℃ for 15 to 20 minutes. 8. The method of claim 7, further comprising the step of secondary curing the first compound to produce a second compound comprising polyimide. A pair of substrates facing each other; A thin film electrode formed on the substrate; After preliminarily drying the alignment film solution, the compound is converted into a compound containing polyamic acid, the compound including the polyamic acid is first cured and converted into a first compound containing polyimide, and then the first compound is second cured. An alignment layer including a second compound including a manufactured polyimide, and formed on a substrate on which the thin film electrode is formed; And And a liquid crystal filled between the alignment layers. A pair of substrates facing each other; A thin film electrode formed on the substrate; A substrate on which the thin film electrode is formed, wherein the alignment layer solution is pre-dried to be converted into a compound containing polyamic acid, and the compound including polyimide prepared by curing the compound containing polyamic acid under 1 to 100 mmTorr. An alignment film formed on the substrate; And And a liquid crystal filled between the alignment layers.