KR101202721B1 - New polyimide, liquid crystal aligning film comprising the same and liquid crystal display comprising the same - Google Patents

Abstract

The present invention relates to a polyimide for producing a liquid crystal alignment film of a liquid crystal display, and more particularly, to a polyimide having a cinnamate group and a liquid crystal alignment film including the same, a method for manufacturing the same, and a liquid crystal display including the liquid crystal alignment film. will be.

The liquid crystal alignment film according to the present invention not only exhibits an excellent alignment state but also maintains an excellent alignment state of the liquid crystal even after a long time thermal stability test, and there is an effect that an afterimage does not appear in an afterimage, which is an electrical characteristic.

Polyimide, cinnamate, liquid crystal alignment film, liquid crystal display

Description

Novel polyimide, liquid crystal aligning film including the same and liquid crystal display comprising the same {NEW POLYIMIDE, LIQUID CRYSTAL ALIGNING FILM COMPRISING THE SAME AND LIQUID CRYSTAL DISPLAY COMPRISING THE SAME}

The present invention relates to a polyimide for producing a liquid crystal alignment film of a liquid crystal display, and more particularly, to a polyimide introduced with cinnamate, a liquid crystal alignment film including the same, a method for manufacturing the same, and a liquid crystal display including the liquid crystal alignment film. will be.

With the development of the display industry, liquid crystal displays provide a low driving voltage, high resolution, reduced monitor volume, and flat panel monitors. One of the key technologies in such a liquid crystal display technology is a technology for aligning liquid crystals in a desired direction.

Conventionally, the contact rubbing method which apply | coated a polymer film like polyimide to the board | substrates, such as glass, and rubbed the surface in a fixed direction with the fibers, such as nylon and polyester, was used as a conventional method of orienting a liquid crystal. However, the contact rubbing method may generate fine dust or electrostatic discharge (ESD) when the fiber and the polymer film are rubbed, and may cause serious problems in manufacturing the liquid crystal panel due to process difficulties.

Therefore, in order to solve the problem of the contact rubbing method, the research on the manufacture of a non-contact alignment film in recent years has been actively conducted.

As a method for producing a non-contact alignment film, there is a photo-alignment method, an energy beam alignment method, a vapor deposition orientation method, or an etching method using lithography. The most realistic of these methods is the photo-alignment method which causes anisotropic chemical reaction by irradiating linearly polarized light onto the photosensitive polymer thin film and induces liquid crystal alignment as a result.

The photo-alignment method can be divided into photoisomerization method, photopolymerization method or photolysis method depending on the reaction mechanism. Among them, the photolysis method using a polyimide thin film widely commercially available as an alignment film has attracted much attention. The polyimide used in the photolysis method is a straight polymer. The photolysis method induces liquid crystal alignment by selectively photodegrading a polymer backbone coinciding with linearly polarized light. When polyimide is decomposed by light, small units of decomposition by-products are inevitably generated. These degradation byproducts can cause serious problems in terms of orientation stability, long-term reliability, especially afterimages, in the manufacture of actual liquid crystal displays. Problems appearing in the orientation stability, long-term reliability and afterimage side surface has emerged as the biggest problem that prevents the commercialization of the optical alignment method.

Accordingly, there is a demand for the development of a liquid crystal alignment film having excellent orientation stability and improved long-term reliability and afterimage, and a new liquid crystal material that can be used therein.

An object of the present invention is to provide a polyimide having a cinnamate group introduced therein.

Another object of the present invention is to provide a liquid crystal alignment film including a polyimide having the cinnamate group introduced therein and improved thermal stability, liquid crystal alignment, and afterimage property, a method of manufacturing the same, and a liquid crystal display including the liquid crystal alignment film. .

The present invention provides a polyimide having a cinnamate group introduced therein.

In addition, the present invention provides a liquid crystal alignment film containing the polyimide in which the cinnamate group is introduced.

In addition,

1) dissolving the polyimide in which the cinnamate group is introduced into a solvent and then applying it on a substrate surface to form a coating film,

2) drying the solvent contained in the coating film, and

3) irradiating polarized ultraviolet rays to the dried coating surface to perform alignment treatment

It provides a method for producing a liquid crystal alignment film comprising a.

In addition, the present invention provides a liquid crystal display comprising the liquid crystal alignment film.

The liquid crystal aligning film using the novel polyimide according to the present invention not only shows an excellent alignment state, but also maintains an excellent alignment state of the liquid crystal even after a long time thermal stability test, and there is an effect that no afterimage appears in the afterimage, which is an electrical property. .

The present invention provides a polyimide in which a cinnamate group including a repeating unit represented by the following Chemical Formula 1 is introduced.

In Formula 1,

A is selected from the group consisting of the following structural formulas as a tetravalent organic group,

D is hydrogen, a halogen group, an alkyl group having 1 to 21 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms, preferably an alkyl group having 1 to 7 carbon atoms,

p is an integer from 1 to 5,

B is selected from the group consisting of the following structural formulas as a trivalent organic group,

및

And

here,

E is hydrogen, a halogen group, an alkyl group having 1 to 21 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms,

r is 1 to 3,

F is a divalent organic group consisting of -CH ₂ -,-(CH ₂ ) _m -O- (where m is 1 to 15) and-(CH ₂ ) _k -OCO- (where k is 1 to 20) Selected from the group,

The number average molecular weight of the polyimide is 30,000 to 100,000.

The polyimide having the cinnamate group represented by Formula 1 according to the present invention introduced therein may be prepared from a dianhydride compound represented by Formula 2 below, or a diamine compound represented by Formula 3 below. Other reaction conditions may use methods known in the art.

In Formula 2, X ₁ is selected from the group consisting of the following structural formulas.

In Chemical Formula 3, X ₂ is selected from the group consisting of the following structural formulas.

및

And

Here, E, F, D, r and p are as defined in the formula (1).

Specifically, the method for preparing the polyimide is prepared by dissolving at least one of the diamine compounds represented by Formula 3 in a solvent, and adding and reacting at least one of the dianhydrides represented by Formula 2 to this solution. can do. The reaction of the diamine and dianhydride is preferably carried out at 0 to 5 ℃ for 24 hours. At this time, it is advantageous to mix dianhydride and diamine in a molar ratio of 1: 0.9 to 1: 1.1 to achieve desirable molecular weight, mechanical properties and viscosity.

Examples of the dianhydride compound represented by Chemical Formula 2 include PMDA (pyromellitic dianhydride) and CBDA (cyclobutane-1,2,3,4-tetracarboxylic dianhydride) (cyclobutane-1 , 2,3,4-tetracarboxylic dianhydride), BPDA (3,3 ', 4,4'-biphenyltetra-carboxylic dianhydride) (3,3', 4,4'-biphenyltetra-carboxylic dianhydride), ODPA (4,4'-oxydiphthalic anhydride) (4,4'-oxydiphthalic anhidride) and the like, but are not limited thereto.

The polyimide in which the cinnamate group is introduced according to the present invention induces an anisotropic [2 + 2] Cycloaddition reaction when irradiated with polarized ultraviolet rays. Due to the anisotropic [2 + 2] cycloedition reaction, the liquid crystal is oriented in its major axis in a direction perpendicular to the direction of the irradiated polarized ultraviolet light. In particular, the alkyl group introduced into the cinnamate group can improve the coating properties, improve the dissolution properties in the solvent when preparing the polymer solution, control the pretilt angle of the liquid crystal when used as a liquid crystal alignment layer, liquid crystal alignment properties due to improved interaction between the liquid crystal molecules and the alignment layer molecules By increasing the degree of freedom of molecular movement of the cinnamate group, which is an increase and a photosensitive functional group, it can play a role of exhibiting effects such as improvement in photosensitive characteristics. The liquid crystal alignment layer of the present invention reflecting the above characteristics has a property of inducing liquid crystal alignment perpendicular to the polarized ultraviolet direction, that is, parallel to the polyimide polymer backbone, and furthermore, more stable alignment can be obtained.

In addition, the present invention provides a liquid crystal alignment film comprising a polyimide having a cinnamate group represented by the formula (1).

Method for producing a liquid crystal alignment film according to the present invention,

1) dissolving the polyimide in which the cinnamate group is introduced into a solvent and then applying it on a substrate surface to form a coating film,

2) drying the solvent contained in the coating film, and

3) irradiating polarized ultraviolet rays to the dried coating surface to perform alignment treatment

It includes.

In the step 1), it is possible to determine the concentration of the solution, the type of solvent and the application method according to the type and use of the polyimide.

The solvent in step 1) includes cyclopentanone, cyclohexanone, N-methylpyrrolidone, DMF (Dimethylformamide), THF (Tetrahydrofuran), CCl ₄ or a mixture thereof, and the like, but is not limited thereto.

In addition, solvents such as ethylene glycol monoethyl ether acetate, ethylene glycol monoisopropyl ether, and ethylene glycol monomethyl ether may be used in combination with the solvents exemplified above in order to prevent film thickness uniformity and printing defects after coating. Can be.

The solution of step 1) may be applied onto the surface of the substrate formed by patterning a transparent conductive film or a metal electrode using a method such as a roll coater method, a spinner method, a printing method, an inkjet spraying method, or a slit nozzle method.

In the application of the solution, the functional silane-containing compound, the functional fluoro-containing compound, and the functional titanium-containing compound are previously applied to the substrate in order to further improve the adhesion of the substrate surface, the transparent conductive film, the metal electrode and the coating film. In some cases.

The temperature at which the polyimide of step 1) is dissolved in the solution is 0 to 100 ° C, more preferably 15 to 70 ° C.

The solid content concentration of the polyimide in which the cinnamate group is introduced is selected in consideration of the molecular weight, viscosity, volatility, and the like of the polyimide represented by Chemical Formula 1, and has an appropriate viscosity to achieve a desired liquid crystal alignment effect and to have desirable coating properties. For this purpose, the polyimide in which the cinnamate group is introduced is preferably selected within the range of 0.5 to 20% by weight based on the total weight of the solution dissolved in the solvent.

In step 2), the solvent may be dried by heating the coating or vacuum evaporation.

When drying the solvent of step 2) it may be dried within 35 hours at 35 to 80 ℃, preferably 50 to 75 ℃.

In step 3), the dried coating film obtained in step 2) may be subjected to an alignment treatment by irradiating ultraviolet rays in a region of 150 to 450 nm. At this time, the intensity of exposure varies depending on the type of polyimide, and energy of 50 mJ / cm 2 to 10 J / cm 2, preferably 500 mJ / cm 2 to 5 J / cm 2, can be irradiated.

As the ultraviolet rays, ① a polarizing device using a substrate coated with a dielectric anisotropic substance on the surface of a transparent substrate such as quartz glass, soda lime glass, soda lime free glass, ② a polarizing plate finely deposited aluminum or metal wire, or ③ An alignment treatment is performed by irradiating polarized ultraviolet rays selected from polarized ultraviolet rays by a method of passing or reflecting through a Brewster polarizer or the like by reflection of quartz glass. At this time, the polarized ultraviolet ray may be irradiated perpendicularly to the substrate surface, or may be irradiated at an angle of incidence at a specific angle. In this way, the alignment ability of the liquid crystal molecules is imparted to the coating film.

The substrate temperature when irradiating the ultraviolet rays of step 3) is preferably room temperature. However, in some cases, ultraviolet rays may be irradiated in a heated state within a temperature range of 80 ° C or lower.

It is preferable that the film thickness of the final coating film formed by such a series of processes is 0.002-2 micrometers, and in order to play a role in a display apparatus, the range of 0.004-0.6 micrometers is more preferable.

After the above-described process, it is possible to obtain a liquid crystal alignment layer having a liquid crystal alignment ability stable to external thermal, physical, and chemical impact.

The liquid crystal alignment film according to the present invention may include conventional solvents or additives known in the art, in addition to the polyimide into which the cinnamate group is introduced.

In the liquid crystal alignment layer according to the present invention, the polyimide into which the cinnamate group is introduced is induced perpendicular to the polarizing ultraviolet ray irradiation direction when the polarized ultraviolet ray is irradiated, that is, parallel to the polymer main chain, and is introduced by the alkyl group introduced into the cinnamate group. Further stabilized liquid crystal alignment can be obtained.

In addition, the present invention provides a liquid crystal display comprising the liquid crystal alignment film.

Liquid crystal displays can be manufactured according to conventional methods known in the art. For one embodiment thereof, one of the two glass substrates with the photoreaction with the liquid crystal alignment film according to the present invention is applied to the end of the glass substrate with a photoreactive adhesive containing a ball spacer at the end of the glass substrate The glass substrates are bonded together, and only the portion to which the adhesive is applied is irradiated with ultraviolet rays to bond the cells. After injecting the liquid crystal into the completed cell and heat treatment, to complete the liquid crystal cell.

In fact, the liquid crystal display of the present invention having the liquid crystal alignment film not only exhibits an excellent alignment state, but also maintains an excellent alignment state of the liquid crystal even after a long time thermal stability test, and does not have an afterimage appearance in terms of an afterimage as an electrical property. have.

Hereinafter, preferred embodiments of the present invention will be described in order to facilitate understanding of the present invention. However, the following examples are merely provided to more easily understand the present invention, and the scope of the present invention is not limited thereto.

Example  One

(One) 3,5- Dinitrophenyl Cinnamate  synthesis

Under nitrogen atmosphere, cinnamoyl chloride (9 g, 0.054 mol) in anhydrous THF (40 mL) was added to 3,5-dinitrophenol (10 g and 0.054 mol) and triethylamine in THF (600 mL) at 0 ° C. TEA) (5.5 g, 0.055 mol) was added dropwise. The resulting mixture was then warmed to room temperature and stirred for 12 hours. After THF was removed under reduced pressure, the residue was dissolved in methylene chloride (MC) and washed once with an aqueous solution of 0.1 N NaOH and three times with distilled water. The methylene chloride layer was dried over anhydrous sodium sulfate and filtered. The methylene chloride was removed under reduced pressure to give a yellow solid which was washed with methanol and dried to give 15.5 g. (91% yield)

(2) 3,5- Diaminophenyl Cinnamate  synthesis

2 g (0.006 mol) of 3,5-dinitrophenyl cinnamate, 12 mL of water and 150 mL of isopropanol were mixed in a three neck round bottom flask. The mixture was mechanically stirred and heated to 60 ° C. 1 mL of concentrated hydrochloric acid and 20 g of iron powder were added to the flask and heated to 70 ° C. After the reaction was completed (confirmed by thin layer chromatography (TLC)), the solution was filtered. The filtrate was condensed under reduced pressure and diluted with water. The resulting solution was neutralized with aqueous sodium hydroxide solution and extracted with ethyl acetate (EA). The ethyl acetate layer was chromatographed to give 1.1 g of a yellow solid. (Yield: 68%)

(3) Synthesis of Polyimide

2.593 g (0.0102 mol) of 3,5-diaminophenyl cinnamate and 43 mL of NMP were fed to a reactor equipped with a stirrer. After completely dissolving the solid diamine in NMP, 2.224 g (0.0102 mol) of pyromellitic dianhydride (PMDA) was added at a time as a solid mixture at room temperature and stirred for 20 hours to give a viscous polyamic acid solution. The polyamic acid (PAA) solution exhibited an inherent viscosity of 0.98 dL / g at a concentration of 0.5 g / dL in NMP at 30 ° C. The resulting polyamic acid was filtered through a poly (tetrafluoroethylene) filter (pore size = 1 μm) and used for liquid crystal photoalignment measurement. For thermal imidization, the resulting polyamic acid (PAA) solution was diluted to about 4% solids concentration using NMP, cast on a clean silicon wafer, dried at 80 ° C. for 1 hour and at 150 ° C. for 1 hour. Bake at 230 ° C. for 30 minutes.

IR (Film, Silicon Wafer): 1778, 1717, 1727, 1629, 1374, 721 cm ^-1

Example  2

(1) 3,5- Dinitrobenzyl Cinnamate  synthesis

Under nitrogen atmosphere, cinnamoyl chloride (20 g, 0.12 mol) in dry THF (60 mL) was added to 3,5-dinitrobenzol (23.78 g, 0.12 mol) and triethylamine (TEA) in THF (600 mL) ( 55 g, 0.12 mol) was added dropwise at 0 ° C over 1 hour. The mixture was then warmed to room temperature and stirred for 8 hours. After the THF was removed under reduced pressure, the residue was dissolved in methylene chloride (MC) and washed once in an aqueous solution of 0.1 N NaOH and three times in distilled water. The methylene chloride layer was dried over anhydrous sodium sulfate and filtered. The methylene chloride was removed under reduced pressure to give a solid, which was dried to give 33.8 g. (Yield 86%)

(2) 3,5- Diaminobenzyl Cinnamate  synthesis

10 g (0.03 mol) of 3,5-dinitrobenzyl cinnamate, 40 mL of water and 120 mL of isopropanol were mixed in a three neck round bottom flask. The mixture was mechanically stirred and heated to 60 ° C. 1.5 mL of concentrated hydrochloric acid and 18 g of iron powder were added to the flask and heated to 70 ° C. After the reaction was complete (confirmed by TLC), the solution was filtered to remove unreacted iron. The filtrate was concentrated under reduced pressure and diluted with water. The resulting solution was neutralized with aqueous sodium hydroxide solution and extracted with ethyl acetate (EA). The ethyl acetate layer was chromatographed to give 4.7 g of a yellow solid. (Yield 58%)

(3) Synthesis of Polyimide

2.2578 g (0.0084 mol) of 3,5-diaminobenzyl cinnamate and 35 mL of NMP were fed to a reactor equipped with a stirrer. After completely dissolving the solid diamine in NMP, 1.6503 g (0.0084 mol) of cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA) was added at a time as a solid mixture at room temperature, 20 hours Stirring to obtain a viscous polyamic acid solution. The polyamic acid (PAA) solution exhibited an inherent viscosity of 0.75 dL / g at a concentration of 0.5 g / dL in NMP at 30 ° C. The resulting polyamic acid solution was filtered through a polytetrafluoroethylene filter (pore size = 1 μm) and used for liquid crystal photoalignment measurement. For thermal imidization, the resulting polyamic acid (PAA) solution was diluted to about 4% solids content using NMP, cast on a clean silicon wafer and then dried at 80 ° C. for 1 hour, and at 150 ° C. 1 Bake at 230 ° C. for 30 hours.

IR (Film, Silicon Wafer): 1784, 1722, 1638, 1387, 720 cm ^-1

Example  3

(1) 2- Bromoethyl  3,5- Of dinitrobenzoate  synthesis

Under nitrogen atmosphere, 3,5-dinitrobenzoyl chloride (10 g, 0.0434 mol) in MC (40 mL) was added 2-bromoethanol (5.42 g, 0.0434 mol) and TEA (4.44 g, 0.044 mol) was added dropwise at 0 ° C. over 1 hour. After stirring addition, the mixture was warmed to room temperature and stirred for 5 hours. The reaction mixture was washed once with an aqueous solution of 0.1 N NaOH and three times with distilled water. The methylene chloride layer was dried over anhydrous sodium sulfate and filtered. The methylene chloride was removed under reduced pressure to give a yellow solid which was washed with methanol and dried in vacuo to give 12.3 g. (89% yield)

(2) 2- ( Cinnamoyloxy Ethyl 3,5- Of dinitrobenzoate  synthesis

Cinnamic acid (3.10 g, 0.021 mol) and 2-bromoethyl 3,5-dinitrobenzoate (6 g, 0.019 mol) were added to K ₂ CO ₃ (5.20 g, 0.038 mol) and KI (0.62). g, 0.0038 mol) was added to a mixture of 50 mL of DMSO and 120 mL of DMF. The reaction was carried out at 70 ° C. until TLC indicated the end of the reaction. The solution was concentrated to about 30 mL under reduced pressure and poured into 500 mL of water while stirring to obtain a solid. The solid was filtered, washed with water and dried in vacuo to give 5.9 g of a white solid. (Yield 82%)

(3) 2- ( Cinnamoyloxy Ethyl 3,5- Of diaminobenzoate  synthesis

5 g (0.013 mol) of 2- (cinnamoyloxy) ethyl 3,5-dinitrobenzoate, 25 mL of water and 140 mL of isopropanol were mixed in a three neck round bottom flask. The mixture was mechanically stirred and heated to 60 ° C. 1.8 mL of concentrated hydrochloric acid and 25 g of iron powder were added to the flask and heated to 70 ° C. After the reaction was complete (confirmed by TLC), the solution was filtered. The filtrate was concentrated under reduced pressure and diluted with water. The resulting solution was neutralized with aqueous sodium hydroxide solution and extracted with ethyl acetate (EA). The ethyl acetate layer was chromatographed to give 3.1 g of a yellow solid. (Yield 74%) mp: 121 ~ ( DSC at a scan rate of 10 ℃ / min under N ₂ condition) 122 ℃

(4) Synthesis of Polyimide

6.45 g (0.019 mol) 2- (cinnamoyloxy) ethyl 3,5-diaminobenzoate and 98 mL of NMP were fed to a reactor equipped with a stirrer. After the solid diamine was completely dissolved in NMP, 8.78 g (0.019 mol) of 4,4'-hexafluoroisopropylidenediphthalic anhydride (6FDA) was added to the mixture at once. The reaction mixture was stirred at room temperature for 20 hours. The resulting polyamic acid (PAA) solution exhibited an inherent viscosity of 0.58 dL / g at a concentration of 0.5 g / dL in NMP at 30 ° C. The polyamic acid solution was filtered through a poly (tetrafluoroethylene) filter (pore size = 1 μm) and used for liquid crystal photoalignment measurement. For thermal imidization, the resulting polyamic acid solution was diluted to about 5% solids content using NMP, cast on a clean silicon wafer and then dried at 80 ° C. for 1 hour, at 150 ° C. for 1 hour, 230 Thermoset at 30 ° C. for 30 minutes.

IR (film, silicon wafer): 1789, 1728, 1636, 1395, 719 cm ^-1

Example  4

(1) 6- Bromohexyl  3,5- Of dinitrobenzoate  synthesis

Under nitrogen atmosphere, 3,5-dinitrobenzoyl chloride (10 g, 0.0434 mol) in MC (50 mL) was mixed with 6-bromo-1-hexanol (7.85 g, 0.0434 mol) and TEA in MC (600 mL). (4.44 g, 0.044 mol) was added dropwise at 0 ° C. over 1 hour. After stirring addition, the mixture was warmed to room temperature and stirred for 12 hours. The reaction mixture was washed once with an aqueous solution of 0.1 N NaOH and three times with distilled water. The methylene chloride layer was dried over anhydrous sodium sulfate and filtered. The methylene chloride was removed under reduced pressure to give a yellow solid, which was washed with methanol and dried in vacuo to give 13.8 g. (Yield 85%)

(2) 6- ( Cinnamoyloxy ) Hexyl  3,5- Of dinitrobenzoate  synthesis

Cinnamic acid (1.26 g, 0.0085 mol) and 6-bromohexyl 3,5-dinitrobenzoate (3 g, 0.008 mol) were added to K ₂ CO ₃ (2.21 g, 0.016 mol) and KI (1.33). g, 0.008 mol) was added to a mixture of 15 mL of DMSO and 110 mL of DMF. The reaction was carried out at 70 ° C. until TLC indicated the end of the reaction. The solution was concentrated to about 30 mL under reduced pressure and poured into 500 mL of water while stirring to obtain a solid. The solid was filtered, washed with water and dried in vacuo to yield 2.7 g of a white solid. (Yield 75%)

(3) 6- ( Cinnamoyloxy ) Hexyl  3,5- Of diaminobenzoate  synthesis

7 g (0.016 mol) of 6- (cinnamoyloxy) hexyl 3,5-dinitrobenzoate, 50 mL of water and 250 mL of isopropanol were mixed in a three neck round bottom flask. The mixture was mechanically stirred and heated to 58 ° C. 2 mL of concentrated hydrochloric acid and 34 g of iron powder were added to the flask and heated to 70 ° C. After the reaction was complete (confirmed by TLC), the solution was filtered. The filtrate was concentrated under reduced pressure and diluted with water. The resulting solution was neutralized with aqueous sodium hydroxide solution and extracted with ethyl acetate (EA). The ethyl acetate layer was chromatographed to give 4.1 g. (66% yield)

(4) Synthesis of Polyimide

3.6 g (0.009 mol) of 6- (cinnamoyloxy) hexyl 3,5-diaminobenzoate and 56 mL of NMP were fed to a reactor equipped with a stirrer. After the solid diamine was completely dissolved in NMP, 2.052 g (0.009 mol) of PDMA was added to the mixture at once. The reaction mixture was stirred at room temperature overnight. The resulting polyamic acid (PAA) solution showed an inherent viscosity of 0.38 dL / g at a concentration of 0.5 g / dL in NMP at 30 ° C. The polyamic acid solution was filtered through a poly (tetrafluoroethylene) filter (pore size = 1 μm) and used for liquid crystal photoalignment measurement. For thermal imidization, the resulting polyamic acid (PAA) solution was diluted to about 6% solids content using NMP, cast on a clean silicon wafer, dried at 80 ° C. for 1 hour, and at 150 ° C. Bake at 230 ° C. for 1 hour for 30 minutes.

IR (film, silicon wafer): 1779, 1718, 1634, 1375, 719 cm ^-1

Experimental Example

The thermal stability of the polyimide prepared in Example 3 and the liquid crystal orientation of the liquid crystal alignment film including the polyimide were measured and shown in FIGS. 1 and 2, respectively.

Thermal stability

The thermal stability was measured using TGA (Thermogravimetric Analysis), which is shown in FIG. As can be seen in Figure 1 it can be seen that the polyimide of Example 3 has a thermal stability up to about 330 ℃.

Liquid crystal Orientation

The liquid crystal alignment property was irradiated with a linearly polarized light of 254 nm at an irradiation dose of 1 J / cm 2 to the liquid crystal alignment film containing the polyimide of Example 3, followed by alignment treatment, and then the liquid crystal was injected to measure the absorbance of the liquid crystal. . If the alignment of the liquid crystal is not good, the measured absorbance pattern is formed in a spherical shape, and as the alignment of the liquid crystal is better, a dumbbell-shaped pattern is formed. As shown in FIG. 2, the alignment property of the liquid crystal alignment layer including the polyimide of Example 3 may be understood that the absorbance pattern is formed in the form of a dumbbell so that the liquid crystal alignment is excellent. Arrows in FIG. 2 indicate the electric field direction of linearly polarized light.

1 is a thermogravimetric analysis (TGA) pyrolysis curve of the polyimide of Example 3,

FIG. 2 is a polar diagram of absorbance of the liquid crystal alignment layer including the polyimide of Example 3. FIG.

Claims (11)

A polyimide having a cinnamate group introduced therein including a repeating unit represented by Formula 1 below: [Formula 1]

In Formula 1, A is selected from the group consisting of the following structural formulas as a tetravalent organic group,

D is hydrogen, a halogen group, a C1-C21 alkyl group, or a C1-C6 alkoxy group, p is an integer from 1 to 5, B is a trivalent organic group selected from the group consisting of the following structural formulas,

here, E is hydrogen, a halogen group, an alkyl group having 1 to 21 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms, r is 1 to 3, F is a divalent organic group consisting of -CH ₂ -,-(CH ₂ ) _m -O- (where m is 1 to 15) and-(CH ₂ ) _k -OCO- (where k is 1 to 20) Selected from the group, The number average molecular weight of the polyimide is 30,000 to 100,000. The polyimide of claim 1, wherein the polyimide is prepared from a dianhydride compound represented by Formula 2 and a diamine compound represented by Formula 3 below: [Formula 2]

In Formula 2, X ₁ is selected from the group consisting of the following structural formulas,

(3)

In Chemical Formula 3, X ₂ is selected from the group consisting of the following structural formulas,

Here, E, F, D, r and p are as defined in the formula (1). The method of claim 2, wherein the dianhydride compound of Formula 2 is PMDA (pyromellitic dianhydride), CBDA (cyclobutane-1,2,3,4-tetracarboxylic dianhydride), BPDA (3,3 ', 4,4'-biphenyltetra-carboxylic dianhydride) and ODPA (4,4'-oxydiphthalic anhydride). 1) dissolving the polyimide in which the cinnamate group according to any one of claims 1 to 3 is introduced into a solvent and then coated on the substrate surface to form a coating film, 2) drying the solvent contained in the coating film, and 3) irradiating polarized ultraviolet rays to the dried coating surface to perform alignment treatment; Solid content concentration of the polyimide in which the cinnamate group is introduced is a method for producing a liquid crystal alignment film of 0.5 to 20% by weight. The method of claim 4, wherein the solvent of step 1) is selected from cyclopentanone, cyclohexanone, N-methylpyrrolidone, DMF (Dimethylformamide), THF (Tetrahydrofuran), CCl ₄ and mixtures thereof. Method for producing a liquid crystal alignment film. The method of claim 5, wherein ethylene glycol monoethyl ether acetate, ethylene glycol monoisopropyl ether or ethylene glycol monomethyl ether is added to the solvent. delete The method of claim 4, wherein the drying in step 2) is performed at 35 to 80 ° C. within 1 hour. Liquid crystal aligning film containing the polyimide in any one of Claims 1-3. The liquid crystal alignment film according to claim 9, wherein the film thickness of the liquid crystal alignment film is 0.002 to 2 µm. A liquid crystal display comprising the liquid crystal alignment film of claim 9.

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