KR19980057659A - An alignment layer formed from the composition, and a liquid crystal display element having the alignment layer - Google Patents

Abstract

The present invention discloses a photo-orientable composition and an alignment film having excellent thermal stability by being formed therefrom, and a liquid crystal display device having the same. INDUSTRIAL APPLICABILITY According to the present invention, it is possible to obtain an alignment film having improved thermal stability and pretilt angle characteristics. When the liquid crystal is aligned using such an alignment layer, problems such as damage to the thin film transistor, occurrence of static electricity or dust due to rubbing occurring in the case of using the conventional rubbing method can be solved, and a liquid crystal display element having excellent performance can be manufactured can do.

Description

An alignment layer formed from the composition, and a liquid crystal display element having the alignment layer

[0001] The present invention relates to a photo-orientable composition, an alignment film formed therefrom, and a liquid crystal display element comprising the alignment film. More specifically, the present invention relates to an alignment film formed by using a photo-orientable composition comprising polyimide, And a liquid crystal display element provided with an alignment film.

A typical liquid crystal display device comprises a pair of upper and lower substrates 2 and 2 'spaced apart from each other by a predetermined distance as shown in FIG. 1, a transparent electrode layer 3 and a transparent electrode layer 3' 3 '), insulating layers 4 and 4', and alignment films 5 and 5 'for alignment of the liquid crystal are sequentially formed on the upper and lower substrates 2 and 2' And a liquid crystal layer 7 in which liquid crystal is injected into the space. The spacers 6 serve to maintain the gap between the upper and lower substrates 2 and 2 'at a predetermined thickness and polarizations of incident light and projected light are formed on the outer surfaces of the substrates 2 and 2' Polarizing plates 1 and 1 'are provided, respectively.

The basic driving principle of a liquid crystal display element is that the arrangement of liquid crystal influenced by an electric field is changed according to whether an external voltage is applied or not and the property of blocking and transmitting external light flowing into the liquid crystal display element will be. That is, when a voltage is applied to the transparent electrode layer, an electric field is formed in the liquid crystal layer. As a result, the liquid crystal is driven in a predetermined direction, and the light that flows into the liquid crystal of the display element is blocked or transmitted depending on whether the liquid crystal is driven or not.

In such a liquid crystal display element, the function as a display element such as light transmittance, response speed, viewing angle, and contrast is determined depending on the arrangement characteristics of the liquid crystal molecules. Therefore, a technology for uniformly controlling the orientation of liquid crystal molecules is very important.

The uniform alignment state of the liquid crystal is difficult to obtain simply by interposing the liquid crystal between the upper and lower substrates. Therefore, as can be seen from the liquid crystal display device of Fig. 1, the alignment film is formed on the transparent electrode layer.

Examples of the alignment layer include a rubbing method in which a thin film made of an organic polymer material such as polyimide or polyamide is formed on a substrate and cured, and then the resultant is rubbed with a special type of cloth to control the alignment direction of the liquid crystal molecules Is mainly used. However, the above method is easy to carry out, the process is simple, and a large area liquid crystal can be aligned at one time. However, since fine particles or fibrils are separated from a special type of cloth used for rubbing, the orientation film may be contaminated, the orientation may not be properly aligned depending on the orientation film material, and the problem that the thin film transistor is damaged by static electricity generated during rubbing have.

In order to solve the above problem, a photo-alignment technique which does not generate dust or static electricity has been developed. This method is a non-destructive alignment method. When polarized light is irradiated on a photo-alignment alignment film, anisotropic photo- And is uniformly oriented.

Polyvinyl cinnamate (PVCN) and polyvinyl methoxycinnamate (PVMC) are mainly used as the material of the alignment layer. However, such a polymer compound is excellent in orientation performance by light, but has a problem that the thermal stability of the orientation is lowered and the pretilt angle is reduced to almost 0 degree. In other words, the thermal stability of the orientation film depends on the thermal stability of the polymer. PVCN or PVCM has a relatively low glass transition temperature of less than about 100 ° C, which results in poor thermal stability and the formation of a pretilt angle due to a symmetric structure It is difficult.

A first object of the present invention is to provide a photo-orientable composition having improved thermal stability and a pretilt angle.

A second object of the present invention is to provide an alignment layer formed from the photo-orientable composition.

A third aspect of the present invention is to provide a liquid crystal display device having the alignment layer.

1 is a cross-sectional view of a general liquid crystal display device.

DESCRIPTION OF THE REFERENCE NUMERALS

1,1 '... polarizer 2, 2' ... substrate

3,3 '... Electrodes 4,4' ... Insulating layer

5,5 '... Orientation layer 6 ... Spacer

7 ... liquid crystal layer

A first aspect of the present invention is to provide a photo-orientable composition comprising a polymer selected from a cinnamate-based polymer and a coumarin-based polymer and a polyimide having an alkyl group (R) at both terminals, wherein R is C ₃ to provide a C ₂₀ alkyl group).

A second object of the present invention is to provide an alignment film comprising a polymer selected from a cinnamate-based polymer and a coumarin-based polymer and a polyimide having an alkyl group (R) at both terminals, wherein R is C ₃ to C ₂₀ Alkyl group).

A third object of the present invention is to provide an alignment film comprising a polymer selected from a cinnamate-based polymer and a coumarin-based polymer and a polyimide having an alkyl group (R) at both terminals, wherein R is C ₃ to C ₂₀ An alkyl group).

The polyimide in which the alkyl group is introduced at both ends is selected from the compounds represented by the formula (1).

Wherein,

R ₁ is a C ₃ -C ₁₀ cycloalkyl or a cycloalkyl having at least one substituent (G), a C ₃ -C ₁₀ cycloalkenyl or a cycloalkenyl having at least one substituent and a compound of the formula AYB Lt; / RTI >

Wherein A and B are each independently selected from the group consisting of an unsubstituted aromatic or aromatic ring having at least one substituent (G) wherein the aromatic ring is a monocyclic ring of 6 carbon atoms, A ring or a tricyclic substituent having 14 carbon atoms)

Y represents -O-, carbonyl (C = O) or -C (R ₃ ) (R ₄ ) -, wherein R ₃ and R ₄ are each independently selected from hydrogen, C ₁ -C ₁₀ selected from the group consisting of alkyl of C ₁ ~C ₁₀ alkyl and having at least one substituent (G))];

R ₂ represents an unsubstituted aromatic ring, an aromatic ring having at least one substituent (G) (wherein the aromatic ring is a monocyclic ring having 6 carbon atoms, a bicyclic ring having 10 carbon atoms, or a tricyclic ring having 14 carbon atoms) , C ₃ ~C C ₃ ~ ₁₀ cycloalkyl, or having at least one substituent (G) substituent (G) of the C ₃ ~C ₁₀ cycloalkyl, C ₃ ~C ₁₀ cycloalkyl or alkenyl having at least one C ₁₀ cycloalkenyl, and compounds of formula AYB, wherein A, B and Y are as defined above.

Wherein the substituent (G) is selected from the group consisting of C ₁ -C ₁₀ alkyl, aromatic, amino, substituted amino, halide, hydroxy (OH), nitro group (NO ₂ ), cyano (SCN), thiol (SH), and carboxyl (COOH).

Wherein R < _{1 >} is

≪ / RTI >

R ₂ is

And n is a number of from 2 to 19. [

The present invention relates to a photo-orientable composition comprising polyimide known as a heat-resistant polymer as a main chain, a polymer prepared by introducing an alkyl group at both ends of the polymer, and a common cinnamate-based polymer or a coumarin-based polymer, (C ₃ to C ₂₀ alkyl group), especially the long chain alkyl group of C ₈ to C ₁₂ , and the liquid crystal, so as to improve the tilt angle of the liquid crystal .

In the present invention, the mixing weight ratio of the polyimide to the polymer selected from the group consisting of a cinnamate-based polymer and a coumarin-based polymer is preferably from 1:99 to 20:80, since the photoinduced property and the thermal stability are excellent in this range.

The weight average molecular weight of the polyimide having an alkyl group at both terminals is preferably 5 × 10 ³ to 1 × 10 ⁵ . The cinnamate-based polymer is selected from polyvinyl cinnamate, polyvinylmethoxy cinnamate, and polyimide having a cinnamate group introduced into its side chain, and the weight average molecular weight of the compound is preferably 5 × 10 ³ to 2 × 10 ⁵ Do.

The coumarin-based polymer is selected from the group consisting of a polymer represented by the general formulas (2) to (4) and a polymer having a coumarin component in the side chain, and the weight average molecular weight of the compound is preferably 5 × 10 ³ to 2 × 10 ⁵ .

Hereinafter, a photo-orientable composition of the present invention, an alignment layer using the same, and a method of manufacturing a liquid crystal display device will be described.

A method for synthesizing a soluble polyimide having an alkyl group at both ends of the polymer will be described below.

First, an acid anhydride (1), a diamine compound (2) and a solvent are mixed and an alkylamine (CH ₃ (CH ₂ ) _n NH ₂ ) of 1 to 10 mol% based on the acid anhydride is added thereto Polyamic acid (3) is synthesized at a temperature of 0 to 25 ° C. Thereafter, the polyamic acid (3) is imidized to synthesize soluble polyimide (4).

The polyimide synthesized according to the above method is mixed with a polymer selected from a cinnamate-based polymer and a coumarin-based polymer at a weight ratio of 1:99 to 20:80, followed by mixing with a suitable solvent to prepare a photo-orientable composition. N-methylpyrrolidone (NMP), dimethylformamide (DMA), methylcellosolve and the like are used as the large solvent.

The composition is coated on two glass substrates, and then the solvent is dried to form an alignment film. Subsequently, linearly polarized light (wavelength: 300 to 400 nm) is irradiated to perform photoreaction, and then the two substrates are bonded together with a spacer maintained at a constant gap to complete the cell. Thereafter, liquid crystal is injected into the cell, and liquid crystal is injected to complete the liquid crystal display element.

Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited thereto.

Example 1

3.22 g of 3,3 ', 4,4'-benzophenonetracarboxylic acid dianhydride and 1.80 g of 4,4'-diaminodiphenyl ether were mixed in NMP and then CH ₃ (CH ₂ ) ₁₀ NH ₂ 0.28 g was slowly added thereto to synthesize polyamic acid through a series of reaction steps. Then, the polyamic acid was dehydrated to obtain polyimide.

A composition containing 0.02 g of the polyimide obtained according to the above method, 0.18 g of polyvinyl cinnamate (Aldrich) and 10 g of NMP was adjusted to an appropriate viscosity and then spin-coated on each of two glass substrates coated with ITO electrode layers . Subsequently, the resultant was dried at about 100 ° C for 1 hour to form an alignment film.

The alignment film was irradiated with linearly polarized light having a wavelength of about 300 to 400 nm and subjected to photoreaction for about 5 minutes. Two glass substrates obtained while keeping spacing between two glass substrates at a predetermined thickness by using a spacer were bonded to each other to prepare a vacant cell. Liquid crystal was injected into the open cell to complete a liquid crystal display device.

Example 2

0.04 g of the polyimide prepared in Example 1 and 0.16 g of polyvinyl cinnamate were used.

Comparative Example

Except that 0.2 g of polyvinyl cinnamate (Aldrich) and 10 g of a solvent were used as the photo-aligning composition.

In the liquid crystal display device manufactured according to Example 1-2 and Comparative Example, the pretilt angle and thermal stability of the alignment film were measured. Here, the pretilt angle was measured using a crystal rotation method. The thermal stability was raised to 180 DEG C, then allowed to stand for a predetermined time, lowered to room temperature, and then, And the state of the alignment film according to the change was examined and measured.

As a result of the measurement, it was found that the alignment stability of the alignment layer was not changed even when the temperature was increased up to 180 ° C in the liquid crystal display device manufactured according to Example 1-2. And the pretilt angle of liquid crystal alignment could be improved to 15 degrees. However, in the case of the liquid crystal display device manufactured according to the comparative example, the orientation was excellent, but the thermal stability was greatly reduced, and the orientation film was denatured from about 70 ° C, and the pretilt angle was about 0 °.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to obtain an alignment film having improved thermal stability and pretilt angle characteristics. By orienting the liquid crystal using such an alignment layer, it is possible to improve problems such as damage to the thin film transistor, static electricity and dust generation due to the rubbing which occurs in the case of using the conventional rubbing method, thereby manufacturing a liquid crystal display element having excellent performance can do.

Claims (24)

(Wherein R is a C ₃ to C ₂₀ alkyl group), which comprises a polymer selected from a cinnamate-based polymer and a coumarin-based polymer, and a polyimide having an alkyl group (R) Lt; / RTI > The photo-orientable composition according to claim 1, wherein the polyimide is selected from compounds represented by the formula (1). [Chemical Formula 1] Wherein, R ₁ is a C ₃ -C ₁₀ cycloalkyl or a cycloalkyl having at least one substituent (G), a C ₃ -C ₁₀ cycloalkenyl or a cycloalkenyl having at least one substituent and a compound of the formula AYB Lt; / RTI > Wherein A and B are each independently selected from the group consisting of an unsubstituted aromatic or aromatic ring having at least one substituent (G) wherein the aromatic ring is a monocyclic ring of 6 carbon atoms, A ring or a tricyclic substituent having 14 carbon atoms) Y represents -O-, carbonyl (C = O) or -C (R ₃ ) (R ₄ ) -, wherein R ₃ and R ₄ are each independently selected from hydrogen, C ₁ -C ₁₀ selected from the group consisting of alkyl of C ₁ ~C ₁₀ alkyl and having at least one substituent (G))]; R ₂ represents an unsubstituted aromatic ring, an aromatic ring having at least one substituent (G) (wherein the aromatic ring is a monocyclic ring having 6 carbon atoms, a bicyclic ring having 10 carbon atoms, or a tricyclic ring having 14 carbon atoms) , C ₃ ~C C ₃ ~ ₁₀ cycloalkyl, or having at least one substituent (G) substituent (G) of the C ₃ ~C ₁₀ cycloalkyl, C ₃ ~C ₁₀ cycloalkyl or alkenyl having at least one C ₁₀ cycloalkenyl, and compounds of formula AYB, wherein A, B and Y are as defined above. Wherein the substituent (G) is selected from the group consisting of C ₁ -C ₁₀ alkyl, aromatic, amino, substituted amino, halide, hydroxy (OH), nitro group (NO ₂ ), cyano (SCN), thiol (SH), and carboxyl (COOH). The method of claim 2, wherein in Formula 1, R ₁ ≪ / RTI > R ₂ is And n is a number of from 2 to 19, The photo-orientable composition according to claim 1, wherein the weight ratio of the polyimide to the cinnamate-based polymer is from 1:99 to 20:80. The photo-orientable composition according to claim 1, wherein the cinnamate-based polymer is selected from the group consisting of polyvinylcinnamate, polyvinylmethoxy cinnamate, and polyimide having a cinnamate group introduced into its side chain. The photo-orientable composition according to claim 1, wherein the coumarin-based polymer is selected from the group consisting of a polymer represented by Chemical Formula 2 to Chemical Formula 4 and a polymer having a coumarin component in a side chain. (2) (3) [Chemical Formula 4] The photo-orientable composition according to claim 1, wherein the weight average molecular weight of the polyimide having an alkyl group at both terminals is 5 x 10 ³ to 1 x 10 ⁵ . The photo-orientable composition according to claim 1, wherein the cinnamate-based polymer or the coumarin-based polymer has a weight average molecular weight of 5 × 10 ³ to 2 × 10 ⁵ . (R is a C ₃ to C ₂₀ alkyl group) comprising a polymer selected from a cinnamate-based polymer and a coumarin-based polymer and a polyimide having an alkyl group (R) at both terminals. The alignment film according to claim 9, wherein the polyimide having an alkyl group at both terminals is selected from compounds represented by the general formula (1). [Chemical Formula 1] Wherein, R ₁ is a C ₃ -C ₁₀ cycloalkyl or a cycloalkyl having at least one substituent (G), a C ₃ -C ₁₀ cycloalkenyl or a cycloalkenyl having at least one substituent and a compound of the formula AYB Lt; / RTI > Wherein A and B are each independently selected from the group consisting of an unsubstituted aromatic or aromatic ring having at least one substituent (G) wherein the aromatic ring is a monocyclic ring of 6 carbon atoms, A ring or a tricyclic substituent having 14 carbon atoms) Y represents -O-, carbonyl (C = O) or -C (R ₃ ) (R ₄ ) -, wherein R ₃ and R ₄ are each independently selected from hydrogen, C ₁ -C ₁₀ selected from the group consisting of alkyl of C ₁ ~C ₁₀ alkyl and having at least one substituent (G))]; R ₂ represents an unsubstituted aromatic ring, an aromatic ring having at least one substituent (G) (wherein the aromatic ring is a monocyclic ring having 6 carbon atoms, a bicyclic ring having 10 carbon atoms, or a tricyclic ring having 14 carbon atoms) , C ₃ ~C C ₃ ~ ₁₀ cycloalkyl, or having at least one substituent (G) substituent (G) of the C ₃ ~C ₁₀ cycloalkyl, C ₃ ~C ₁₀ cycloalkyl or alkenyl having at least one C ₁₀ cycloalkenyl, and compounds of formula AYB, wherein A, B and Y are as defined above. Wherein the substituent (G) is selected from the group consisting of C ₁ -C ₁₀ alkyl, aromatic, amino, substituted amino, halide, hydroxy (OH), nitro group (NO ₂ ), cyano (SCN), thiol (SH), and carboxyl (COOH). 11. The method of claim 10 wherein, R ₁ is in the formula (1) ≪ / RTI > R ₂ is And n is a number of from 2 to 19, The alignment film according to claim 9, wherein the weight ratio of the polyimide to the cinnamate-based polymer is from 1:99 to 20:80. The alignment film according to claim 9, wherein the cinnamate-based polymer is selected from the group consisting of polyvinyl cinnamate, polyvinylmethoxy cinnamate, and polyimide having a cinnamate group introduced into its side chain. The alignment film according to claim 9, wherein the coumarin-based polymer is selected from the group consisting of polymers represented by formulas (2) to (4) and polymers having a coumarin component in the side chain. (2) (3) [Chemical Formula 4] The alignment film according to claim 9, wherein the polyimide having alkyl groups at both terminals has a weight average molecular weight of from 5 × 10 ³ to 1 × 10 ⁵ . The alignment film according to claim 9, wherein the cinnamate-based polymer or the coumarin-based polymer has a weight average molecular weight of from 5 × 10 ³ to 2 × 10 ⁵ . A liquid crystal display element comprising an alignment film comprising a polymer selected from a cinnamate-based polymer and a coumarin-based polymer and a polyimide having an alkyl group (R) at both terminals, wherein R is C ₃ to C ₂₀ alkyl group). The liquid crystal display element according to claim 17, wherein the polyimide having an alkyl group at both terminals is selected from compounds represented by formula (1). [Chemical Formula 1] Wherein, R ₁ is a C ₃ -C ₁₀ cycloalkyl or a cycloalkyl having at least one substituent (G), a C ₃ -C ₁₀ cycloalkenyl or a cycloalkenyl having at least one substituent and a compound of the formula AYB Lt; / RTI > Wherein A and B are each independently selected from the group consisting of an unsubstituted aromatic or aromatic ring having at least one substituent (G) wherein the aromatic ring is a monocyclic ring of 6 carbon atoms, A ring or a tricyclic substituent having 14 carbon atoms) Y represents -O-, carbonyl (C = O) or -C (R ₃ ) (R ₄ ) -, wherein R ₃ and R ₄ are each independently selected from hydrogen, C ₁ -C ₁₀ selected from the group consisting of alkyl of C ₁ ~C ₁₀ alkyl and having at least one substituent (G))]; R ₂ represents an unsubstituted aromatic ring, an aromatic ring having at least one substituent (G) (wherein the aromatic ring is a monocyclic ring having 6 carbon atoms, a bicyclic ring having 10 carbon atoms, or a tricyclic ring having 14 carbon atoms) , C ₃ ~C C ₃ ~ ₁₀ cycloalkyl, or having at least one substituent (G) substituent (G) of the C ₃ ~C ₁₀ cycloalkyl, C ₃ ~C ₁₀ cycloalkyl or alkenyl having at least one C ₁₀ cycloalkenyl, and compounds of formula AYB, wherein A, B and Y are as defined above. Wherein the substituent (G) is selected from the group consisting of C ₁ -C ₁₀ alkyl, aromatic, amino, substituted amino, halide, hydroxy (OH), nitro group (NO ₂ ), cyano (SCN), thiol (SH), and carboxyl (COOH). 19. The method of claim 18 wherein, R ₁ is in the formula (1) ≪ / RTI > R ₂ is And n is a number of from 2 to 19. 15. The liquid crystal display element according to claim 1, 18. The liquid crystal display according to claim 17, wherein the weight ratio of the polyimide to the cinnamate-based polymer is from 1:99 to 20:80. 18. The liquid crystal display device according to claim 17, wherein the cinnamate-based polymer is selected from the group consisting of polyvinyl cinnamate, polyvinylmethoxy cinnamate, and polyimide having a cinnamate group introduced into its side chain. 18. The liquid crystal display device according to claim 17, wherein the coumarin-based polymer is selected from the group consisting of polymers represented by formulas (2) to (4) and polymers having a coumarin component in the side chain. (2) (3) [Chemical Formula 4] The method of claim 17, wherein the liquid crystal display element, characterized in that the weight average molecular weight of a polyimide having an alkyl group on the both ends of 5 × 10 ³ to 1 × 10 ^5. The liquid crystal display element according to claim 17, wherein the cinnamate-based polymer has a weight average molecular weight of 5 x 10 ³ to 2 x 10 ⁵ .