KR100288271B1 - Polymaleimide and Polyimide Based Photoinduced Liquid Crystal Alignment Film - Google Patents

Abstract

The photoalignment material having a polymaleimide and a copolymer thereof as a main chain thereof is represented by the following Chemical Formulas 1, 2, and 3, wherein R represents a structure including a cinnamate group as a side chain for photoreaction.

Another embodiment of the present invention is a photo-alignment material having a polyimide as a main chain is represented by the following formula (4), in which T is an alicyclic or aliphatic group from dianhydride, Q is diamine (diamine).

Description

Polymaleimide and Polyimide Based Photoinduced Liquid Crystal Alignment Film for Liquid Crystal Display

Field of invention

The present invention uses a polymaleimide as a main backbone, or a cinnamate photopolymerizable alignment material and a polyimide having a main chain formed of a single chain or a copolymer formed with styrene, hydroxystyrene, acrylonitrile, or the like. It relates to a cinnamate photopolymerizable homopolymer and a copolymer alignment material.

Background of the Invention and Prior Art

In the liquid crystal display, a method of aligning liquid crystals to date has been applied by printing a heat-resistant polymer such as polyimide on the transparent conductive glass 2 to a thickness of about 500-1000 kPa as shown in FIG. A method of forming a polymer alignment layer 4 and rubbing the alignment layer 3 while rotating the rotating roller 5 wrapped with a rubbing cloth 6 such as nylon or rayon at high speed is referred to as a rubbing process. Call.

As shown in FIG. 1, during the rubbing process, the liquid crystal molecules are aligned with a constant pretilt angle θ at the surface of the alignment material. The liquid crystal alignment method by the rubbing process is currently applied to most mass production processes because the alignment material can be applied quickly and easily, which has the advantage of simplifying the production process.

However, the rubbing process causes mechanical scratches on the surface of the liquid crystal aligning material during rubbing, or generates high static electricity, thus destroying the thin film transistors and causing defects due to minute fibers generated in the rubbing cloth. It is an obstacle to improvement. Therefore, recently, studies to orient the liquid crystal without rubbing have been actively conducted. This is called a non-rubbing process.

In addition, as the liquid crystal display has been enlarged in recent years, as the use has been gradually expanded from personal use such as laptops to home use such as wall-mounted TVs, high quality, high quality and wide viewing angles are required for the liquid crystal display.

As one of methods for achieving a wide viewing angle of a liquid crystal display, there is a multi-domain technology that widens a viewing angle by dividing one pixel into small pixels so that the liquid crystal alignment state of each divided pixel is changed. In order to make multi-domain display using the alignment material for rubbing process, complicated lithographic process such as alignment film coating, rubbing, coating of photoresist, exposure and development, rubbing and removal of photoresist ), Which is undesirable in terms of productivity.

In order to solve this problem, an alignment method by a non-rubbing process using a photopolymerizable alignment material has been developed as described in FIG. Representative examples of such non-rubbing processes include M. Schadt et al. (Jpn. J. Appl. Phys., Vol. 31, 1992, 2155), Dae S. Kang et al. (US Pat. No. 5,464,669). , Photoalignment by photopolymerization, published by Yuriy Reznikov (Jpn. J. Appl. Phys., Vol. 34, 1995, L1000). Photo-alignment means that the photosensitive group bonded to the polymer by ultraviolet light linearly polarized by the polarizer 7 causes a photoreaction, and in this process, the alignment materials are arranged in a constant direction, thereby forming a photopolymerizable liquid crystal alignment layer 9 in which liquid crystals are aligned. Refers to the forming mechanism.

As described above, the photo-alignment material used in the existing patents and papers is an alignment material in which cinnamate is bonded to polyvinyl alcohol, and a double bond of cinnamate is cycloaddition by irradiated UV light. The principle of causing a reaction was used. Only cinnamate groups coincident with the polarization direction cause a cycloaddition reaction so that the polymers are arranged in a constant direction to induce the alignment of the liquid crystal. By using such an optical alignment, a multi-domain pixel can be obtained using only a mask, so that a liquid crystal display having a wide viewing angle can be obtained by a simple method.

However, the conventional optical alignment material using the polyvinyl alcohol hydrocarbon polymer of the prior art as a main chain not only has low thermal stability but also lowers the orientation force, which is a physical bonding force between the alignment film and the liquid crystal, than the conventional polyimide alignment material by the rubbing process. Has disadvantages.

Accordingly, the present inventors have overcome the problems of the conventional optical alignment material and have developed a polymaleimide or polyimide optical alignment material excellent in heat resistance and optical properties.

An object of the present invention is to provide a cinnamate photopolymerizable liquid crystal alignment material having an imide-based polymer having excellent heat resistance and optical characteristics and a copolymer of various general-purpose polymers as a main chain thereof.

1 is a schematic diagram illustrating a liquid crystal alignment method according to a conventional rubbing process.

2 is a schematic view illustrating a liquid crystal alignment method by optical alignment.

Explanation of symbols on the main parts of the drawings

1: glass substrate 2: transparent conductive glass

3: liquid crystal molecule 4: polymer alignment film

5: rotary roller 6: rubbing cloth

7 polarizer 8 mask

9: photopolymerization type liquid crystal aligning film

The photoalignment material of the present invention having a polymaleimide as a main chain is a maleimide homopolymer or a maleimide copolymer. In the present invention, represented by the following Chemical Formula 1, Chemical Formula 2 and Chemical Formula 3:

Formula 1

Formula 2

Formula 3

In Formula 1, R is the following Formula (1a), and in Formula 2 and Formula 3, R is H or the following Formula (1a), provided that R is not all H,

(1a)

In formula (1a) R ₁ is one selected from the following groups,

(Where p = 0 to 6)

R ₂ in formula (1a) is one selected from the following groups:

(Wherein X is F, H, CN, CF ₃ or — (— CH ₂ —) _r −, Y is F or H, and r = 0 to 6).

Another embodiment of the present invention is a photo-alignment material having a polyimide as a main chain is represented by the following formula (4):

Formula 4

In the above formula, T is an alicyclic or aliphatic acid dianhydride, Q is represented by the following formula (4a),

R 'in the formula (4a) is represented by the formula (1a).

Acid dianhydride portion (T) in the photo-alignment material of Formula 4 is formed from alicyclic or aliphatic acid dianhydride. Acid dianhydride in the above formula (4) is not particularly limited, but the following examples are preferred.

In synthesizing the optical alignment material of Formula 4, when using alicyclic or aliphatic acid dianhydride, light transmittance, solubility, coating property of solution, etc. are more than that of aromatic acid dianhydride which is generally used. There is a feature that the necessary characteristics as the alignment film are greatly improved. Of course, among the monomers used for synthesizing the photo-alignment material of Formula 4 according to the present invention, dianhydride is a single use of alicyclic or aliphatic acid dianhydride, as well as mixed use of these, aromatic ( aromatic) includes mixed use with acid dianhydrides. The photo-alignment material of Chemical Formula 4 is generally synthesized using acid dianhydride and diamine. However, instead of acid dianhydride, a compound having an acid structure may be used, or an isocyanate may be used instead of diamine.

In order to align the liquid crystal when the liquid crystal display cell is manufactured using the photopolymerizable liquid crystal aligning material of the present invention, the synthesized photo aligning material may be used as chlorobenzene, N-methylpyrrolidone (NMP) or dimethyl sulfoxide ( DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), gamma butyrolactone, butyl cellulsolve, tetrahydrofuran (THF), etc. in a concentration of 1wt% to 10wt% and a viscosity of 5cps to 50cps. After dissolving in an ITO glass substrate by spin coating or printing to form a alignment film with a thickness of 500 Å to 1,000 Å, the alignment film was inclined for about 3 to 10 minutes by irradiating linearly polarized ultraviolet rays to the alignment film surface using a polarizer. To prepare.

The liquid crystal display (LCD) manufactured using the photopolymerizable liquid crystal alignment material of the present invention is capable of adjusting the pretilt angle according to the irradiation angle of ultraviolet rays, and has recently been studied by a novel method as well as the existing TFT-LCD and STN-LCD. It is in progress and can be applied to various types of LCDs from IPS (In Plane Switching) mode with a pretilt angle of nearly 0 ° to Vertically Aligned Twisted Nematic (VATN) with a pretilt angle of close to 90 °. Higher quality and higher quality displays are achieved by exhibiting properties equivalent to or higher than the polyimide used in the process.

Hereinafter, the present invention will be described in detail with reference to Examples, but the following Examples are merely illustrative of specific embodiments of the present invention and should not be construed as limiting or limiting the protection scope of the present invention.

Example

Example 1 Photo-alignment Material with Maleimide as Main Chain

(1) Synthesis of Polyhydroxyphenylmaleimide

In a nitrogen-filled three-necked round flask, 5 g of maleic anhydride polymer (Polyscience co., USA) and 3 g of aminophenol were added to 100 ml of xylene and stirred at room temperature for 30 minutes, followed by 2.9 g of isoquinoline. After adding the temperature and gradually raising the temperature to 150 ℃ and continued the reaction for about 3 hours while continuing to remove the water produced while the reaction. After stopping the reaction and lowering the temperature to room temperature, the precipitate was poured into 500 ml of methanol, and the precipitate was filtered and vacuum-dried at 100 ° C. to obtain polyhydroxyphenylmaleimide.

(2) synthesis of side chains

16.42 g (0.1 mol) of p-hydroxycinnamic acid is dissolved in 100 ml of water dissolved in 8 g of sodium hydroxide and 100 ml of dimethyl sulfoxide (DMSO), and 15.86 g (0.1 mol) of parafluorobenzoyl chloride at 0 ° C. ) Was stirred vigorously while slowly dropping. The mixture was further reacted at room temperature for about 2 hours and neutralized with dilute hydrochloric acid to pH = 6-7. The obtained solid intermediate was filtered and washed thoroughly with water. After drying thoroughly in vacuo, it was recrystallized in ethanol to give parafluorobenzoyloxycinnamic acid in a yield of 90%. 1.2 equivalents of thionyl chloride were added, and about 50 ml of methylene chloride was added, followed by reaction until a clear solution was obtained at room temperature. After the reaction, the solvent and thionyl chloride (SOCl ₂ ) were removed in vacuo and thoroughly dried to obtain parafluorobenzoylcinnamoylchloride.

(3) Synthesis of Photoalignment Material Based on Maleimide

After 1.7 g of polyhydroxyphenylmaleimide obtained in (1) was dissolved in 50 mL of N-methylpyrrolidone (NMP), 1.0 g of triethylamine was added thereto, followed by stirring for 30 minutes. The reaction temperature was lowered to 5 ° C. and vigorously stirred while slowly dropping 2.13 g of parafluorobenzoyl cinnamoyl chloride obtained in the above (2). When parafluorobenzoyl cinnamoyl chloride ran out, stirring was continued for about 1 hour and the reaction was terminated. This was poured into a beaker mixed with 200 ml of water and methanol, and the precipitate was filtered and subsequently washed thoroughly with excess water and methanol, followed by vacuum drying to synthesize a photoimide having a main chain of maleimide.

(4) Fabrication of Liquid Crystal Display Cells

The obtained photo-alignment material was dissolved in a mixed solvent of NMP and gamma butyrolactone at a concentration of 5 wt%. This was printed on a glass substrate coated with a transparent electrode, and the coated glass substrate was dried at 100 to 200 ° C. for about 1 hour to remove the solvent. Irradiation was performed once for 1 minute to photoreact the cinnamate group to prepare a polymer liquid crystal alignment film. The photoreacted glass substrates were bonded to the cell gap (4 to 5㎛) between the top and bottom using an epoxy adhesive, and the cells were prepared by a hot press process for 1 hour at 160 ° C or more. . After injecting the liquid crystal into the finished cell and the heat treatment for 1 hour at 100 ~ 130 ℃ and dropped to room temperature, the electro-optical properties of the liquid crystal display cell was measured and evaluated and the results are shown in Table 1 below.

Example 2 Photo-alignment Material Based on Styrene / Maleimide Copolymer

Instead of the maleimide homopolymer used in Example 1 (1), styrene / hydroxyphenylmaleimide copolymer was used in the same equivalence ratio, and other materials and synthetic methods were used in the same manner as in Example 1 using styrene / maleimide. A fluorescent alignment material was obtained, and the liquid crystal cell manufactured by using the same was also manufactured in the same manner as in Example 1 to measure and evaluate the electro-optical characteristics of the liquid crystal display cell, and the results are shown in Table 1 below.

Comparative Example 1: Conventional polyimide alignment material by rubbing process

The existing rubbing process polyimide was spin-coated at 3000 rpm on a glass plate coated with a transparent electrode and coated with a thickness of about 800 mm 3. After coating, the plate was dried at 200 ° C. for 1 hour using a heating plate. Rayon was wound around a 10 cm diameter roller to rub the polyimide surface once at a speed of 1000 rpm. The contact strength of the rayon cloth and the polyimide alignment layer was fixed at the moment when the rayon cloth was in contact with the surface of the alignment layer. The rubbed upper and lower glass substrates were bonded in the same manner as in Example 1 to prepare a liquid crystal cell having a cell thickness of 4 to 5 μm. The temperature was lowered to room temperature to measure and evaluate the electro-optical characteristics of the liquid crystal display cell, and the results are shown in Table 1.

Note ¹⁾ Voltage / light transmittance (%): Measured using LCD-5000.

²⁾ Pretilt angle was measured using the Crystal Rotation Method.

³⁾ Ton: The time when the liquid crystal rises under the electric field

⁴⁾ Toff: The time when the liquid crystal is restored to the initial orientation when the electric field is removed.

As confirmed through Table 1, the polymaleimide photopolymerizable liquid crystal alignment material of the present invention has thermal stability, optical transparency, and excellent coating properties, which are basic characteristics of polyimide, and also liquid crystal display cells manufactured using the same. It is possible to obtain a multi-domain pixel by a simple process while maintaining the pretilt angle even after high temperature process over 160 ℃, and the light transmittance and response speed are remarkably improved, so it is applied to the liquid crystal display device requiring high quality and wide viewing angle. Can be.

Example 3 Synthesis of Polyimide Photoalignment I

(1) 2,2-bis (3-amino-4-hydroxyphenyl) propane (2,2-bis (3-amino-4-hydroxyphenyl)

propane synthesis

In a 250 ml three-necked round flask filled with nitrogen, 20 g of (2,2-bis (4-hydroxyphenyl) propane) (2,2-bis (4-hydroxyphenyl) propane) and 150 ml of acetic acid were added. Then, 20 ml of nitric acid was slowly dropped while stirring vigorously. The reaction progresses gradually to reddish brown, and after nitric acid is dropped, the reaction is terminated after 30 minutes. The reaction mixture is poured into 1000 ml of ethanol, and the solid is filtered and recrystallized from ethanol. 23 g of (3-nitro-4-hydroxyphenyl) propane (2,2-bis (3-nitro-4-hydroxy phenyl) propane) was obtained.

A 250 ml three-necked round flask equipped with a nitrogen line and a condenser was prepared using 12 g of 2,2-bis (3-nitro-4-hydroxyphenyl) propane. Pour 100ml of ethanol, add 15ml of hydrazine monohydrate and 0.5g of palladium catalyst (Pd / C), raise the temperature to 80 ℃, and react for 3 hours. 2,2-bis (3-nitro-4 -Hydroxyphenyl) propane (2,2-bis (3-amino-4-hydroxyphenyl) propane gradually dissolved in ethanol by reduction of 2,2-bis (3-nitro-4-hydroxyphenyl) propane) Is converted to (2,2-bis (3-amino-4-hydroxyphenyl) propane). After the solid particles are completely dissolved in ethanol, the reaction is terminated and the palladium catalyst is filtered off to obtain a pale yellow transparent solution. When left at room temperature, yellow transparent crystal grains are formed, which are filtered and dried in 2,2-bis. 9 g of (3-amino-4-hydroxyphenyl) propane (2,2-bis (3-amino-4-hydroxyphenyl) propane) was obtained.

(2) Synthesis of polyimide backbone using alicyclic acid dianhydride

4- (2,5-dioxotetrahydrofuran-3-yl) -tetralin-1,2-dicarboxylic unhydride (4- (2,5-dioxotetrahydrofuran-3-yl) -tetralin- 1,2-dicarboxylic anhydride) (hereinafter referred to as DOTDA) 3 g (0.01 mol) and 2,2-bis (3-amino-4-hydroxyphenyl) propane (2,2-bis (3-amino-4-hydroxyphenyl) propane 2.58 g (0.01 mol) of BAHP (hereinafter referred to as BAHP) were placed in a 100 ml three-necked round flask, and 50 ml of N-methylpyrrolidone (hereinafter referred to as NMP) was poured and stirred vigorously. After all the monomers were dissolved, 3-4 drops of isoquinoline were administered, and the temperature was gradually heated to 200 ° C., followed by continuous draining of water. After 3 hours, the reaction was terminated, poured into 500 ml of methanol, and the precipitate was collected. The precipitate was filtered under reduced pressure and dried under vacuum to synthesize polyimide having DOTDA and BAHP as monomers.

(3) synthesis of side chains

16.42 g (0.1 mol) of p-Hydroxycinnamic acid is dissolved in 100 ml of water dissolved in 8 g of sodium hydroxide and 100 ml of dimethyl sulfoxide (DMSO), and 15.86 g (0.1 mol) of parafluorobenzoyl chloride at 0 ° C. ) Was stirred vigorously while slowly dropping. The mixture was further reacted at room temperature for about 2 hours and neutralized with dilute hydrochloric acid to pH 6-7. The obtained solid intermediate was filtered and washed thoroughly with water. After thoroughly drying in vacuo, it was recrystallized in ethanol to give parafluorobenzoyloxycinnamic acid in a yield of 90%. 1.2 equivalents of thionyl chloride were added, and about 50 ml of methylene chloride was added, followed by reaction until a clear solution was obtained at room temperature. After the reaction, the solvent and thionyl chloride (SOCl ₂ ) were removed under vacuum and thoroughly dried to obtain parafluorobenzoylcinnamoyl chloride.

(4) Synthesis of Polyimide Photoalignment Material I

3.8 g of the polyimide obtained in (2) was dissolved in 100 ml of tetrahydrofuran (THF), and 2.5 g of triethylamine was added thereto, followed by stirring for 30 minutes. The reaction temperature was lowered to 5 ° C., and 5.3 g of parafluorobenzoyl cinnamoyl chloride obtained in (3) was slowly dropped while being vigorously stirred. When parafluorobenzoyl cinnamoyl chloride ran out, stirring was continued for about 1 hour and the reaction was terminated. The precipitate was poured into 1000 ml of water, and the precipitate was filtered and then washed thoroughly with excess water and methanol, followed by vacuum drying to finally synthesize polyimide photoalignment material I.

(5) Fabrication of Liquid Crystal Display Cells

The photoalignment material I obtained was dissolved in a mixed solvent of NMP and gamma butyrolactone at a concentration of 5 wt%. This was printed on a glass substrate coated with a transparent electrode, and the coated glass substrate was dried at 100 to 200 ° C. for about 1 hour to remove the solvent, and the ultraviolet light of the 1KW mercury lamp lamp was 3 at an angle of 45 ° to the glass substrate. Irradiation was performed once for 1 minute to photoreact the cinnamate group to prepare a polymer liquid crystal alignment film. The photoreacted two glass substrates were bonded with an epoxy adhesive to a cell thickness of 4 to 5 μm between the upper and lower sides, and a cell was prepared through a hot press process at 160 ° C. or higher for 1 hour. After injecting the liquid crystal into the finished cell and the heat treatment for 1 hour at 100 ~ 130 ℃ and dropped to room temperature, the electro-optical characteristics of the liquid crystal display cell was measured and evaluated and the results are shown in Table 2 below.

Example 4 Synthesis of Polyimide Photoalignment Agent II

Meso-butane-1,2,3,4-tetracarboxylic dianhydride instead of DOTDA, an acid dianhydride used in (2) of Example 3 (meso-butane-1,2,3,4-tetracarboxylic dianhydride) ) (Hereinafter referred to as MBDA) was used in the same equivalent ratio, and other materials and synthesis methods were used in the same manner as in Example 3 to obtain polyimide photoalignment material II. A liquid crystal cell prepared using this was also manufactured in the same manner as in Example 3 to measure and evaluate the electro-optical characteristics of the liquid crystal display cell, and the results are shown in Table 2 below.

The results for Examples 3 and 4 are shown in Table 2 below in comparison with Comparative Example 1.

Note) ¹⁾ Voltage / light transmittance (%): Measured using LCD-5000.

²⁾ Pretilt angle was measured using the Crystal Rotation Method.

³⁾ Ton: The time when the liquid crystal rises under the electric field

⁴⁾ Toff: the time for the liquid crystal to return to the initial orientation upon removal of the electric field

As confirmed through Table 2, the polyimide photopolymerizable liquid crystal alignment material of the present invention has thermal stability, optical transparency, and excellent coating properties, which are basic characteristics of polyimide, and also liquid crystal display cells manufactured using the same. Since multi-domain pixels can be obtained by a simple process, the pretilt angle is maintained even after a high temperature process of 160 ° C. or higher, and the light transmittance and response speed are remarkably improved. Can be applied.

The present invention synthesizes a photopolymerizable liquid crystal aligning agent having a polyimide polymer as a main chain and a cinnamate photosensitive group as a side chain, and uses it as an alignment layer. It is possible to overcome the problem that the thermal stability is low and the alignment force, which is the physical bonding force between the alignment layer and the liquid crystal, can be overcome, so that the liquid crystal display tools manufactured by the liquid crystal aligning agent of the present invention have high display quality and high quality display.

Simple modifications or changes of the present invention can be easily made by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

Claims (4)

A photo-alignment compound consisting of a polyimide polymer of formula 4 having a polyimide as a main chain: Formula 4 In Formula (4), T is an alicyclic or aliphatic acid dianhydride, Q is represented by the following formula (4a), R 'in the formula (4a) is represented by the following formula (1a). The photoalignment compound according to claim 1, wherein the acid dianhydride portion (T) is one selected from the following groups: Dissolving the photoalignment material of claim 1 in an organic solvent at a concentration of 1 wt% to 10 wt% and a viscosity of 5 cps to 50 cps; Applying the solution to the ITO glass substrate by a thickness of 500 kPa to 1,000 kPa by spin coating or printing to form an alignment film; And Obliquely irradiating ultraviolet light linearly polarized using a polarizer on the surface of the alignment layer for about 3 to 10 minutes; The manufacturing method of the alignment film for liquid crystal displays characterized by consisting of the steps. The method of claim 3, wherein the organic solvent is chlorobenzene, N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), gamma butyro A process for producing an alignment film for a liquid crystal display, characterized in that it is selected from the group consisting of lactones, butyl cellulsolve and tetrahydrofuran (THF).