WO2008153287A1

WO2008153287A1 - Low temperature processable substituted alicyclic polyimide photo-alignment layers and method for preparing liquid crystal cells

Info

Publication number: WO2008153287A1
Application number: PCT/KR2008/003155
Authority: WO
Inventors: Mi Hye Yi; Taek Ahn; Yoon Chul Yang
Original assignee: Korea Research Institute Of Chemical Technology
Priority date: 2007-06-13
Filing date: 2008-06-05
Publication date: 2008-12-18
Also published as: KR100902159B1; KR20080109387A

Abstract

The present invention relates to a method for the preparation of alicyclic polyimide photo -alignment layers with high hardness that can be used for a low temperature process. More specifically, the present invention provides novel soluble polyimide photo-alignment layers that are prepared from the solution polymerization of acid dianhydrides comprising alicyclic acid dianhydrides at certain ratio or more and aromatic diamines comprising an aromatic diamine at certain ratio or more, and a method of producing them. Said compositions provide characteristics including low temperature processability, excellent heat resistance, surface hardness and transparency, and an alignment property of a liquid crystal under polarized UV light, etc.

Description

[DESCRIPTION]

[Invention Title]

LOW TEMPERATURE PROCESSABLE SUBSTITUTED ALICYCLIC POLYIMIDE PHOTO-ALIGNMENT LAYERS AND METHOD FOR PREPARING LIQUID CRYSTAL CELLS

[Technical Field]

The present invention relates to a method for the preparation of alicyclic polyimide photo-alignment layers with high hardness that can be used for a low temperature process. More specifically, the present invention provides a novel soluble polyimide that is prepared from the solution polymerization of acid dianhydrides comprising alicyclic acid dianhydrides at certain ratio or more and aromatic diamines comprising an aromatic diamine at certain ratio or more, photo-alignment layers prepared thereof, a liquid crystal cell prepared from said photo-alignment layers, and a method of producing said photo-alignment layers. The novel soluble polyimide of the present invention provides characteristics including low temperature processability, excellent heat resistance, surface hardness and transparency, and an alignment property of a liquid crystal under polarized UV light, etc.

In addition, the thin film made from said novel soluble polyimide for liquid crystal alignment layers is characterized in that it has low surface roughness, excellent printability on a conductive glass (ITO glass) , and excellent heat resistance and transparency, and the liquid crystal cell made therefrom has low pretilt angles in the range of 0.1 ~ 1.0°and excellent voltage holding ratio (VHR) of 98% or more at room temperature .

[Background Art]

Generally, polyimide resin represents a highly heat- resistant resin which is prepared by polycondensation of aromatic tetracarboxylic acid or derivatives thereof and an aromatic diamine or an aromatic diisocyanate followed by imidation.

Polyimide resin may have various molecular structures depending on the kind of monomers used. In general, pyromellitic acid dianhydride (PMDA) or biphthalic anhydride

(BDPA) as an aromatic tetracarboxylic acid and para-phenylene diamine (p-PDA) , meta-phenylene diamine (m-PDA) , 4,4- oxydianiline (ODA), 4 , 4-methylene dianiline (MDA), 2,2- bisaminophenyl hexafluoropropane (HFDA) , metabisaminophenoxydiphenyl sulfone (m-BAPS) , parabisaminophenoxydiphenyl sulfone (p-BAPS) , 1,4- bisaminophenoxybenzene (TPE-Q), 1 , 3-bisaminophenoxybenzene (TPE-R), 2, 2-bisaminophenoxyphenylpropane (BAPP), 2,2- bisaminophenoxyphenylhexafluoropropane (HFBAPP) and the like as an aromatic diamine are used for the polylcondensation. Most of the polyimide resin is an insoluble, infusible and highly heat-resistant resin and has characteristics of (1) an excellent heat and oxidation resistance, (2) superior heat- resistance based on the utilization at high temperature, i.e., 260 ^°C for short-term use and 480 ^°C for long term use, (3) radiation resistance, (4) an excellent property at low temperature, and (5) an excellent chemical resistance, etc.

However, in spite of having the above-mentioned characteristics, the polyimide resin has a problem that, since it has low light transmittance in visible light region due to the formation of a charge transfer complex, it is hardly applied for a field which requires transparency.

In addition, for the polyimide resin which has been developed until now and used for liquid crystal-alignment layers and comprises an alicyclic group introduced in the main skeleton, diamines having an aromatic cycle have been mainly used. However, in most of cases, it remains as a problem that an electric characteristic such as VHR, etc. is impaired due to the high polarizability of the aromatic diamines included therein.

In addition, there is another problem that the polyimide resin which has been developed until now and used for liquid crystal-alignment layers requires a high process temperature so that it is difficult to be applied for a plastic substrate that is used for preparing a flexible liquid crystal display device .

[Disclosure of Invention] [Technical Subject]

Therefore, the present invention is to provide soluble polyimide having high hardness and a low temperature processability which can be used to solve the above-described problems and a method of preparing the same. Further, the present invention provides photo-alignment layers that are made from said soluble polyimide and a method for producing the same.

Further, the present invention provides a novel polyimide resin which has low temperature processability, excellent heat resistance, surface hardness and transparency, and a liquid crystal alignment property under polarized UV light and photo- alignment layers that are produced therefrom.

Still further, the present invention provides a liquid crystal cell that is produced from the liquid crystal alignment layers that are based on the above-described soluble polyimide .

More specifically, the present invention provides soluble polyimide liquid crystal alignment layers, characterized in that the thin film made from the soluble polyimide for liquid crystal alignment layers has low surface roughness, excellent printability on a conductive glass (ITO glass) , excellent heat resistance and transparency, and the liquid crystal cell made therefrom has low pretilt angles in the range of 0.1 ~ 1.0°and excellent VHR of 98% or more at room temperature. Still further, the present invention provides novel photolytic-type liquid crystal alignment layers that are prepared by illuminating polarized UV light to a soluble polyimide thin film having heat resistance and high transparency in visible light region. In addition, a liquid crystal cell which is produced from said liquid crystal alignment layers and has low process temperature, excellent VHR and low pretilt angles is provided according to the present invention.

[Technical Solution]

In order to solve the problems described above, intensive studies had been carried out by the inventors of the present invention. As a result, by reacting an acid dianhydride having alicyclic structure with a substituent and an aromatic diamine, soluble polyimide was prepared and by using the same a soluble polyimide thin film was produced. Further, by illuminating polarized UV light to thus-obtained thin film, novel photo- alignment layers having excellent liquid crystal alignment property, excellent voltage holding ratio (VHR) , and low pretilt angles in the range of 0.1 ~ 1.0° were developed, and therefore the present invention was completed.

Specifically, in the present invention one or more of acid anhydride that is selected from acid dianhydrides having alicyclic structure with a substituent such as 1, 3 -dimethyl- 1, 2, 3 , 4-cyclobutane tetracarboxylic acid dianhydride (DM-CBDA), 1 , 3 -diethyl-1 , 2 , 3 , 4-cyclobutane tetracarboxylic acid dianhydride (DE-CBDA), 1, 3-dipropy1-1, 2 , 3 , 4-cyclobutane tetracarboxylic acid dianhydride (DP-CBDA), 1, 3-diphenyl- 1 , 2 , 3 , 4 -cyclobutane tetracarboxylic acid dianhydride (DPh- CBDA) and the like are polymerized with aromatic diamines that is selected from 1 , 4 -diaminobenzene, 1 , 3-diaminobenzene, 4,4'- diamino-3 , 3 ' -dimethyl-diphenylmethane, 4,4' -oxydianiline, 4,4' -methylenedianiline, 4,4'- (perfluloropropan-2, 2' - diyl) dianiline, 4 , 4 ' - (1 , 3-phenylenebis (oxy) ) dianiline, 4,4'- (1, 4 -phenylenebis (oxy) ) dianiline, 4-amino-N- (4- aminophenyDbenzamide, 4,4 ' - (4, 4 ' -sulfonylbis (4, 1- phenylene)bis (oxy) ) dianiline, 4, 4 ' - (4, 4 ' - (perfluoropropan-2 , 2- diyl) bis (4 , 1-phneylene) ) bis (oxy) dianiline, 4 , 4 ' - (4 , 4 ' - (propan- 2, 2-diyl) bis (4 , 1-phenylene) ) bis (oxy) dianiline and the like or mixture thereof to obtain the soluble polyimide, and therefore the present invention was completed.

When the soluble polyimide that is prepared from the acid dianhydride having alicyclic structure with the substituent and the aromatic diamine is formed into a thin film by a publicly known method and then illuminated with polarized UV light, novel liquid crystal photo-alignment layers which have low temperature processability enabling an easy application to a low temperature process, excellent heat resistance and transparency, high surface hardness and VHR, and low pretilt angles are developed, and therefore the present invention was unexpectedly completed.

Hereinafter, the present invention is described in more detail .

The present invention provides a soluble alicyclic polyimide resin for low temperature process, which is represented by the following chemical formula 1. [chemical formula l]

In the above chemical formula 1, m is a natural number in the range of from 1 to 500;

Ri to R₄ are independently to each other a hydrogen, a linear or branched, saturated or unsaturated alkyl group of Ci - C₃₀, an aryl group of C₆ - Ci₂, an aryl group of C₆ - C₃₀ or a heteroaryl group of C₆ - C₃₀ which is substituted with an alkoxy group of C_x - C₃₀, wherein said aryl group may substituted with a linear or branched, saturated or unsaturated alkyl group of C] - C₃₀, an ester group, a carbonyl group, a halogen or an amino group;

comprises one or more of aromatic divalent groups which is selected from the following,-

The above described group is a divalent group which is derived from an aromatic diamine having the chemical formulae 1-1 to 1-12 as follows.

Preparation based on the polymerization between an acid dianhydride mixture comprising the acid dianhydrides with an alicyclic structure with one or more substituent that is selected from R₁ to R₄ of the following chemical formula 2 and an aromatic diamine mixture comprising one or more of the aromatic diamines that are selected from the above-described chemical formulae 1-1 to 1-12 also falls within the scope of the present invention. In this case, the compound represented by the following chemical formula 2 is used in an amount of 1-100 tnol% in total acid dianhydrides and one or more of the aromatic diamines that are selected from the above-described chemical formulae 1-1 to 1-12 can be also used in an amount that is suitably selected from the range of 1-100 mol%. [ Chemical formula 2 ]

(wherein, R₁ to R₄ are the same as those described for the above-described chemical formula 1) . The soluble polyimide resin that is represented by the above-described formula 1 or copolymer thereof in the present invention is a novel material and a soluble polyimide that is prepared from the acid dianhydrides with a substituted alicyclic structure and the aromatic diamines. It has low temperature processability, heat resistance, mechanical characteristics, and transparency, and a liquid crystal cell that is produced from said soluble polyimide has a favorable effect showing a significant improvement in pretilt angles and electro-optical properties. The soluble polyimide resin according to the present invention has characteristics as follows; weight average molecular weight (Mw) of 10,000 to 500,000 g/mol, intrinsic viscosity in the range of 0.3 to 2.0 dL/g, a glass transition temperature in the range of 200 to 400 ^°Q and the process temperature of less than 130 ^°C preferably 40 to 130 ^°C

In addition, the soluble polyimide resin according to the present invention is freely soluble in aprotic polar solvent such as dimethylacetamine (DMAc) , dimethylformamide (DMF) , N- methyl-2 -pyrollidone (NMP) and in an organic solvent at room temperature. In particular, even in low water-absorptive solvent such as garama-butyrolactone it has high solubility of at least 10 weight % at room temperature, and also has high solubility in a solvent mixture comprising the solvents described above.

Even for a mixture in which various soluble polyimide resins having different physical properties are mixed, it was found that the physical properties desired in the present invention can be obtained.

Because the soluble polyimide resin according to the present invention has low temperature processability, favorable heat resistance and mechanical characteristics , anύ excellent liquid crystal alignment characteristics, etc. while still maintaining the favorable properties of conventional polyimide resin of polyamic acid type, it can be used as a core heat-resistant material for a high-tech industry including various electric, electronic, space and aeronautical field. In addition, the polyimide thin film prepared from the above-described soluble polyimide resin can be formed into a photo-alignment layer by illuminating the film with polarized UV light having wavelength of 220 ~ 460 nm with intensity of 100 ~ 2,000 mJ/cm². Further, the electro-optical property of a liquid crystal cell which is produced from such photo- alignment layer was found to have pretilt angles in the range of 0.1~l°and VHR of 98.0-99.5% at 25 ^°Cand 3V voltage. In this case, the liquid crystal used was E- 7 that has been obtained from Merck. 5

[Advantageous Effect]

As explained in the above, a new type of liquid crystal alignment layers has been developed according to the present invention and it has lower temperature processability than

10 prior art processes, i.e., the process temperature of 130^°Cor less, high surface hardness, excellent light transmittance, heat resistance and mechanical characteristics as well as excellent photo-alignment property, low pretilt angles and excellent VHR. In addition, it was confirmed that the liquid

15 crystal alignment layers of the present invention are useful as liquid crystal alignment layers for IPS(In plane switching) -type TFT-TN and STN LCD and as a heat resistant material for various high-tech, heat-resisting structures.

20 [Brief Description of Drawings]

Figure 1 is a ¹H NMR spectrum of DM-SPI-I that is prepared according to Example 5 of the present invention.

Figure 2 is a DSC spectrum of DM-SPI-I that is prepared according to Example 5 of the present invention. ά^o Figure 3 is a ¹H NMR spectrum of DM-CBDA that is prepared according to Preparation example 1 of the present invention.

Figure 4 is a ¹H NMR spectrum of DM-CBDA that is prepared according to Preparation example 4 of the present invention.

5 [Best Mode]

Hereinafter, the present invention is described in more detail based on the preparation example and the example. But, these examples are not intended to limit the scope of the present invention. 10

Preparation of acid dianhydrides having alicyclic structure substituted with chemical formula 2

Preparation example 1. Preparation of 1, 3 -dimethyl- 1, 2, 3 , 4- IT) cyclobutane tetracarboxylic acid dianhydride (DM-CBDA)

To a 2L quartz glass photoreactor equipped with sixteen UV lamps (300nm) , a stirrer and a cooler were installed and 250ml of ethyl acetate and lOOg of citraconic anhydride were added thereto followed by stirring for complete mixing. To 0 avoid an excessive temperature increase by UV lamps, an air- cooling type cooler was first run and then UV lamps were turned on for a photoreaction for 150 hours with stirring so as not to have the reactants adhered to the reactor walls. As a result, 40 g of white solid was obtained. 5 After the filtration, the white solid was dried for 24 hours in a vacuum dryer at 60 ^°C Thus-obtained solid was then added to acetic anhydride, dissolved therein and slowly heated to 150 ^"C followed by the reaction for 24 hours. Hot reaction solution was filtered through a filter paper to remove 5 impurities and kept in a freezer at the temperature of 0 ^°C or less for recrystallization for 24 hours to obtain a yellow solid. Thus-obtained solid was filtered and washed three times with 1,4-dioxane to remove acetic anhydride, and then dried in a vacuum oven at 60^°Cfor 48 hours to obtain 35 g of slightly 10 yellow-colored 1, 3-dimethyl-l , 2 , 3 , 4-cyclobutane tetracarboxylic acid dianhydride (DM-CBDA) . Figure 3 is a ¹H NMR spectrum of said DM-CBDA compound.

Preparation example 2. Preparation of 1, 3-diethyl-l, 2, 3, 4- 15 cyclobutane tetracarboxylic acid dianhydride (DE-CBDA)

The reaction was carried out with the same method described for above Preparation example 1 except that 3 -ethyl- 2 , 5-furandione was used instead of citraconic anhydride for the photoreaction for 200 hours under UV lamp illumination. As 20 a result, 27 g of 1, 3-diethyl-l , 2 , 3 , 4-cyclobutane tetracarboxylic acid dianhydride (DE-CBDA) was obtained. The product was confirmed by ¹H-NMR, similar to the above Preparation example 1.

?.h Preparation example 3. Preparation of 1, 3 -dipropyl-1, 2 , 3 , 4- cyclobutane tetracarboxylic acid dianhydride (DPR-CBDA)

The reaction was carried out with the same method described for above Preparation example 1 except that 3- propyl-2 , 5-furandione was used instead of citraconic anhydride T for the photoreaction for 180 hours under UV lamp illumination. As a result, 24 g of 1 , 3-dipropyl-l, 2 , 3 , 4-cyclobutane tetracarboxylic acid dianhydride (DPR-CBDA) was obtained. The product was confirmed by ¹H-NMR.

10 Preparation example 4. Preparation of 1, 4-diphenyl-l, 2 , 3 , 4- cyclobutane tetracarboxylic acid dianhydride (DP-CBDA)

To a 2L quartz glass photoreactor equipped with sixteen UV lamps (300nm) , a stirrer and a cooler were installed and 500ml of dichloromethane and lOOg of phenylmaleic anhydride

IS were added thereto followed by stirring for complete mixing. To avoid an excessive temperature increase by UV lamps, an air- cooling type cooler was first run and then UV lamps were turned on for a photoreaction for 200 hours with stirring so as not to have the reactants adhered to the reactor walls. As

20 a result, 55 g of white solid was obtained. After the filtration, the white solid was dried for 24 hours in a vacuum dryer at 60^°C Thus -obtained solid was then added to acetic anhydride, dissolved therein and slowly heated to 150 ^°C followed by the reaction for 24 hours. Hot reaction solution

?">^■ was filtered through a filter paper to remove impurities and kept in a freezer at the temperature of 0°C or less for recrystallization for 24 hours to obtain a white solid. Thus- obtained solid was filtered and washed three times with toluene to remove acetic anhydride, and then dried in a vacuum oven at 60^°Cfor 48 hours to obtain 35 g of white-colored 1,4- diphenyl-1 , 2 , 3 , 4 -cyclobutane tetracarboxylic dianhydride (DP- CBDA) . From ¹H NMR spectrum, said DP-CBDA product was confirmed (Figure 4) .

[Table 1] Chemical structure of acid dianhydrides of chemical formula 2 for different preparation examples

Production of soluble polyimide photo-alignment layers

Examples 1 to 48 are related to the production of the soluble polyimide, that is used for preparing photo-alignment layers of the present invention, as described in the following Table 2. Specifically, polyimide was produced from the reaction between the aromatic diamine monomer which is selected from chemical formulae 1-1 to 1-12 and the substituted alicyclic acid dianhydride which is produced from Preparation examples 1 to 4 described above, present in a molar ratio of 50:50.

Herein below, the preparation and the physical properties of the soluble polyimide of Examples 1 to 48, the preparation of photo-alignment layers using the same and their physical properties observed therefrom are explained in greater detail in view of specific examples.

[Table 2] Compositional ratio of the soluble polyimide produced in Examples 1 to 48

Example 1. Preparation of soluble polyimide photo-alignment layers (DM-SPI-I)

In a 100ml reactor equipped with a stirrer, a nitrogen gas injector, a temperature controller, and a condenser, 0.01 mole of aromatic diamine of chemical formula 1-1 was dissolved in meta-cresol under slow nitrogen flushing. Then, 2.24 g (O.Olmol) of DM-CBDA, which had been prepared in Preparation example 1, was slowly added thereto under nitrogen flushing.

In this case, the solid content was fixed at 20 weight %, and while gradually increasing the reaction temperature the reaction was carried out at 70 ^°C for 2 hours, at 160 ^°C for 2 hours, and at 200 "C under reflux for 2 hours to obtain soluble polyimide in liquid state.

Thus-obtained reactant was precipitated in methanol, washed with methanol to remove meta-cresol, and dried in the oven at 60 °Cto obtain 3.33 g of soluble polyimide (SPI) resin in solid state. The soluble polyimide powder was diluted in a solution of gamma-butyrolactone and 2-butoxyethanol (4:1) until the viscosity of the solution becomes 30 cp at room temperature, which was then spin-coated on a ITO glass plate to 0.08 μm thickness. The plate was dried at the temperatures of 90 ^°C for 10 min and 160 ^°C for 30 min, followed by an irradiation of polarized UV light having wavelengths of 220- 460nm (intensity 600mJ/cm²) to obtain a photo-aligned polyimide thin film (DM-SPI-I) . Physical properties of the resulting soluble polyimide thin film are summarized in Table 3 described below.

Example 2. Preparation of soluble polyimide photo-alignment ^ layers (DM-SPI-2)

In a 100ml reactor equipped with a stirrer, a nitrogen gas injector, a temperature controller, and a condenser, 0.01 mole of aromatic diamine of chemical formula 1-2 was dissolved m meta-cresol under slow nitrogen flushing. Then, 2.24 g

10 (O.Olmol) of DM-CBDA, which had been prepared m Preparation example 1, was slowly added thereto under nitrogen flushing.

In this case, the solid content was fixed at 20 weight %, and while gradually increasing the reaction temperature the reaction was carried out at 70 "C for 2 hours, at 160 ^°C for 2

15 hours, and at 200 ^°C under reflux for 2 hours to obtain soluble polyimide m liquid state.

Thus-obtained reactant was precipitated m methanol, washed with methanol to remove meta-cresol, and dried in the oven at 60 ^°C to obtain 3.29 g of soluble polyimide (SPI) resin

/0 m solid state. The soluble polyimide powder was diluted in a solution of gamma-butyrolactone and 2-butoxyethanol (4:1) until the viscosity of the solution becomes 30 cp at room temperature, which was then spm-coated on a ITO glass plate to 0.08 μm thickness. The plate was dried at the temperatures

2" of 90 C for 10 mm and 160 ^°C for 30 min, followed by an irradiation of polarized UV light having wavelengths of 220- 460nm (intensity 600mJ/cm²) to obtain a photo-aligned polyimide thin film (DM-SPI-2) . Physical properties of the resulting soluble polyimide thin film are summarized in Table 3 described below.

Example 3. Perparation of soluble polyimide photo-alignment layers (DM-SPI-3)

In a 100ml reactor equipped with a stirrer, a nitrogen gas injector, a temperature controller, and a condenser, 0.01 mole of aromatic diamine of chemical formula 1-3 was dissolved in meta-cresol under slow nitrogen flushing. Then, 2.24 g

(O.Olmol) of DM-CBDA, which had been prepared in Preparation example 1, was slowly added thereto under nitrogen flushing. In this case, the solid content was fixed at 20 weight %, and while gradually increasing the reaction temperature the reaction was carried out at 70 ^°C for 2 hours, at 160 ^°C for 2 hours, and at 200 ^°C under reflux for 2 hours to obtain soluble polyimide in liquid state. Thus -obtained reactant was precipitated in methanol, washed with methanol to remove meta-cresol, and dried in the oven at 60 "C to obtain 4.25 g of soluble polyimide (SPI) resin in solid state. The soluble polyimide powder was diluted in a solution of gamma-butyrolactone and 2-butoxyethanol (4:1) until the viscosity of the solution becomes 30 cp at room temperature, which was then spin-coated on a ITO glass plate to 0.08 μm thickness. The plate was dried at the temperatures of 90 ^"C for 10 rain and 160 ^°C for 30 min, followed by an irradiation of polarized UV light having wavelengths of 220- F) 460nm (intensity 600mJ/cm²) to obtain a photo-aligned polyimide thin film (DM-SPI-3) . Physical properties of the resulting soluble polyimide thin film are summarized in Table 3 described below.

10 Examp1e 4. Preparation of soluble polyimide photo-alignment layers (DM-SPI-4)

In a 100ml reactor equipped with a stirrer, a nitrogen gas injector, a temperature controller, and a condenser, 0.01 mole (1.98 g) of aromatic diamine of chemical formula 1-4 was

If) dissolved in meta-cresol under slow nitrogen flushing. Then, 2.24 g (O.Olmol) of DM-CBDA, which had been prepared in Preparation example 1, was slowly added thereto under nitrogen flushing .

In this case, the solid content was fixed at 20 weight %, 0 and while gradually increasing the reaction temperature the reaction was carried out at 70 "C for 2 hours, at 160 ^°Cfor 2 hours, and at 200 ^"C under reflux for 2 hours to obtain soluble polyimide in liquid state.

Thus-obtained reactant was precipitated in methanol, 5 washed with methanol to remove meta-cresol, and dried in the oven at 60 ^"C to obtain 4.22 g of soluble polyimide (SPI) resin m solid state. The soluble polyimide powder was diluted in a solution of gamma-butyrolactone and 2-butoxyethanol (4:1) until the viscosity of the solution becomes 30 cp at room temperature, which was then spin-coated on a ITO glass plate to 0.08 μm thickness. The plate was dried at the temperatures of 90 ^°C for 10 min and 160 ^°C for 30 min, followed by an xrradiation of polarized UV light having wavelengths of 220- 460nm (intensity δOOmJ/cm'') to obtain a photo-aligned polyimide thin film (DM-SPI-4) . Physical properties of the resulting soluble polyimide thin film are summarized in Table 3 described below.

Example 5. Preparation of soluble polyimide photo-alignment layers (DM-SPI- 5)

In a 100ml reactor equipped with a stirrer, a nitrogen gas injector, a temperature controller, and a condenser, 0.01 mole (2.26 g) of aromatic diamine of chemical formula 1-5 was dissolved in meta-cresol under slow nitrogen flushing. Then, 2.24 g (O.Olmol) of DM-CBDA, which had been prepared in

Preparation example 1, was slowly added thereto under nitrogen flushing .

In this case, the solid content was fixed at 20 weight %, and while gradually increasing the reaction temperature the reaction was carried out at 70 °C for 2 hours, at 160 ^°C for 2 hours, and at 200 ^°C under reflux for 2 hours to obtain soluble polyimide in liquid state.

Thus -obtained reactant was precipitated in methanol, washed with methanol to remove meta-cresol, and dried in the oven at 60 ^°C to obtain 4.14 g of soluble polyimide (SPI) resin in solid state. From the NMR spectrum of Figure 1 and DSC spectrum of Figure 2 measured for the resulting soluble polyimide, the production of the polymer was confirmed. The soluble polyimide powder was diluted in a solution of gamma- butyrolactone and 2-butoxyethanol (4:1) until the viscosity of the solution becomes 30 cp at room temperature, which was then spin-coated on a ITO glass plate to 0.08 μm thickness. The plate was dried at the temperatures of 90 ^°C for 2 min and 160 ^°C for 10 min, followed by an irradiation of polarized UV light having wavelengths of 220~460nm (intensity 600mJ/cm²) to obtain a photo-aligned polyimide thin film (DM-SPI-5) . Physical properties of the resulting soluble polyimide thin film are summarized in Table 3 described below.

Example 6. Preparation of soluble polyimide photo-alignment layers (DM-SPI-6)

In a 100ml reactor equipped with a stirrer, a nitrogen gas injector, a temperature controller, and a condenser, 0.01 mole (3.34 g) of aromatic diamine of chemical formula 1-6 was dissolved in meta-cresol under slow nitrogen flushing. Then, 2.24 g (O.Olmol) of DM-CBDA, which had been prepared in Preparation example 1, was slowly added thereto under nitrogen flushing .

In this case, the solid content was fixed at 20 weight %,

5 and while gradually increasing the reaction temperature the reaction was carried out at 70 ^°C for 2 hours, at 160 ^°C for 2 hours, and at 200 ^°C under reflux for 2 hours to obtain soluble polyimide in liquid state.

Thus -obtained reactant was precipitated in methanol,

10 washed with methanol to remove meta-cresol, and dried in the oven at 60 ^°C to obtain 5.58 g of soluble polyimide (SPI) resin in solid state. The soluble polyimide powder was diluted in a solution of gamma-butyrolactone and 2-butoxyethanol (4:1) until the viscosity of the solution becomes 30 cp at room

If) temperature, which was then spin-coated on a ITO glass plate to 0.08 thickness. The plate was dried at the temperatures of 90 °C for 10 min and 160 ^°C for 30 min, followed by an irradiation of polarized UV light having wavelengths of 220~460nm (intensity 600mJ/cm²) to obtain a photo-aligned 0 polyimide thin film (DM-SPI-6) . Physical properties of the resulting soluble polyimide thin film are summarized in Table 3 described below.

Example 7. Preparation of soluble polyimide photo-alignment 5 layers (DM-SPI-7) In a 100ml reactor equipped with a stirrer, a nitrogen gas injector, a temperature controller, and a condenser, 0.01 mole (2.27 g) of aromatic diamine of chemical formula 1-7 was dissolved in meta-cresol under slow nitrogen flushing. Then, T) 2.24 g (O.Olmol) of DM-CBDA, which had been prepared in Preparation example 1, was slowly added thereto under nitrogen flushing .

In this case, the solid content was fixed at 20 weight %, and while gradually increasing the reaction temperature the0 reaction was carried out at 70 ^°C for 2 hours, at 160 ^°C for 2 hours, and at 200 ^°C under reflux for 2 hours to obtain soluble polyimide in liquid state.

Thus -obtained reactant was precipitated in methanol, washed with methanol to remove meta-cresol, and dried in the ") oven at 60 °C to obtain 4.51 g of soluble polyimide (SPI) resin in solid state. The soluble polyimide powder was diluted in a solution of gamma-butyrolactone and 2-butoxyethanol (4:1) until the viscosity of the solution becomes 30 cp at room temperature, which was then spin-coated on a ITO glass plate0 to 0.08 μm thickness. The plate was dried at the temperatures of 90 °C for 10 min and 160 ^°C for 30 min, followed by an irradiation of polarized UV light having wavelengths of 220~460nm (intensity 600mJ/cm²) to obtain a photo-aligned polyimide thin film (DM-SPI- 7) . Physical properties of the5 resulting soluble polyimide thin film are summarized in Table 3 described below.

Example 8. Preparation of soluble polyimide photo-alignment layers (DM-SPI-8)

5 In a 100ml reactor equipped with a stirrer, a nitrogen gas injector, a temperature controller, and a condenser, 0.01 mole (2.92 g) of aromatic diamine of chemical formula 1-8 was dissolved in meta-cresol under slow nitrogen flushing. Then, 2.24 g (O.Olmol) of DM-CBDA, which had been prepared in

10 Preparation example 1, was slowly added thereto under nitrogen flushing .

If) hours, and at 200 ^°C under reflux for 2 hours to obtain soluble polyimide in liquid state.

Thus-obtained reactant was precipitated in methanol, washed with methanol to remove meta-cresol, and dried in the oven at 60 °C to obtain 5.16 g of soluble polyimide (SPI) resin 0 in solid state. The soluble polyimide powder was diluted in a solution of gamma-butyrolactone and 2-butoxyethanol (4:1) until the viscosity of the solution becomes 30 cp at room temperature, which was then spin-coated on a ITO glass plate to 0.08 thickness. The plate was dried at the temperatures 5 of 90 ^°C for 10 min and 160 ^"C for 30 min, followed by an irradiation of polarized UV light having wavelengths of 220~460nm (intensity 600mJ/cm²) to obtain a photo-aligned polyimide thin film (DM-SPI-8) . Physical properties of the resulting soluble polyimide thin film are summarized in Table 3 described below.

Example 9. Preparation of soluble polyimide photo-alignment layers (DM-SPI-9)

In a 100ml reactor equipped with a stirrer, a nitrogen gas injector, a temperature controller, and a condenser, 0.01 mole (2.92 g) of aromatic diamine of chemical formula 1-9 was dissolved in meta-cresol under slow nitrogen flushing. Then, 2.24 g (O.Olmol) of DM-CBDA, which had been prepared in Preparation example 1, was slowly added thereto under nitrogen flushing.

In this case, the solid content was fixed at 20 weight %, and while gradually increasing the reaction temperature the reaction was carried out at 70 ^°C for 2 hours, at 160 ^°C for 2 hours, and at 200 ^°C under reflux for 2 hours to obtain soluble polyimide in liquid state.

Thus-obtained reactant was precipitated in methanol, washed with methanol to remove meta-cresol, and dried in the oven at 60 ^°C to obtain 5.16 g of soluble polyimide (SPI) resin in solid state. The soluble polyimide powder was diluted in a solution of gamma-butyrolactone and 2-butoxyethanol (4:1) until the viscosity of the solution becomes 30 cp at room temperature, which was then spin-coated on a ITO glass plate to 0.08 μm thickness. The plate was dried at the temperatures of 90 "C for 10 min and 160 ^°C for 30 min, followed by an irradiation of polarized UV light having wavelengths of 220~460nm (intensity 600mJ/cm²) to obtain a photo-aligned polyimide thin film (DM-SPI-9) . Physical properties of the resulting soluble polyimide thin film are summarized in Table 3 described below.

Example 10. Preparation of soluble polyimide photo-alignment layers (DM-SPI-10)

In a 100ml reactor equipped with a stirrer, a nitrogen gas injector, a temperature controller, and a condenser, 0.01 mole (4.32 g) of aromatic diamine of chemical formula 1-10 was dissolved in meta-cresol under slow nitrogen flushing. Then, 2.24 g (O.Olmol) of DM-CBDA, which had been prepared in Preparation example 1, was slowly added thereto under nitrogen flushing . In this case, the solid content was fixed at 20 weight %, and while gradually increasing the reaction temperature the reaction was carried out at 70 ^°C for 2 hours, at 160 ^°C for 2 hours, and at 200 ^°C under reflux for 2 hours to obtain soluble polyimide in liquid state. Thus-obtained reactant was precipitated in methanol, washed with methanol to remove meta-cresol, and dried in the oven at 60 ^°C to obtain 6.56 g of soluble polyimide (SPI) resin in solid state. The soluble polyimide powder was diluted in a solution of gamma-butyrolactone and 2-butoxyethanol (4:1) until the viscosity of the solution becomes 30 cp at room temperature, which was then spin-coated on a ITO glass plate to 0.08 μm thickness. The plate was dried at the temperatures of 90 "C for 10 min and 160 ^°C for 30 min, followed by an irradiation of polarized UV light having wavelengths of 220~460nm (intensity 600mJ/cm²) to obtain a photo-aligned polyimide thin film (DM-SPI-10) . Physical properties of the resulting soluble polyimide thin film are summarized in Table 3 described below.

Example 11. Preparation of soluble polyimide photo-alignment layers (DM-SPI-Il)

In a 100ml reactor equipped with a stirrer, a nitrogen gas injector, a temperature controller, and a condenser, 0.01 mole (5.18 g) of aromatic diamine of chemical formula 1-11 was dissolved in meta-cresol under slow nitrogen flushing. Then, 2.24 g (O.Olmol) of DM-CBDA, which had been prepared in Preparation example 1, was slowly added thereto under nitrogen flushing .

In this case, the solid content was fixed at 20 weight %, and while gradually increasing the reaction temperature the reaction was carried out at 70 ^°C for 2 hours, at 160 ^°C for 2 hours, and at 200 ^°C under reflux for 2 hours to obtain soluble polyimxde m liquid state.

Thus -obtained reactant was precipitated in methanol, washed with methanol to remove meta-cresol, and dried in the oven at 60 ^°Cto obtain 7.42 g of soluble polyimide (SPI) resin m solid state. The soluble polyimide powder was diluted in a solution of gamma-butyrolactone and 2-butoxyethanol (4:1) until the viscosity of the solution becomes 30 cp at room temperature, which was then spin-coated on a ITO glass plate to 0.08 urn thickness. The plate was dried at the temperatures of 90 ^"C for 10 min and 160 ^°C for 30 min, followed by an irradiation of polarized UV light having wavelengths of 220~460nm (intensity 600mJ/cm²) to obtain a photo-aligned polyimide thin film (DM-SPI-Il) . Physical properties of the resulting soluble polyimide thin film are summarized in Table 3 described below.

Example 12. Preparation of soluble polyimide photo-alignment layers (DM-SPI-12)

In a 100ml reactor equipped with a stirrer, a nitrogen gas injector, a temperature controller, and a condenser, 0.01 mole (4.11 g) of aromatic diamine of chemical formula 1-12 was dissolved in meta-cresol under slow nitrogen flushing. Then, 2.24 g (O.Olmol) of DM-CBDA, which had been prepared in Preparation example 1, was slowly added thereto under nitrogen flushing .

In this case, the solid content was fixed at 20 weight %, and while gradually increasing the reaction temperature the reaction was carried out at 70 ^°C for 2 hours, at 160 °C for 2 hours, and at 200 ^°C under reflux for 2 hours to obtain soluble polyimide in liquid state.

Thus-obtained reactant was precipitated in methanol, washed with methanol to remove meta-cresol, and dried in the oven at 60 ^"C to obtain 6.35 g of soluble polyimide (SPI) resin m solid state. The soluble polyimide powder was diluted in a solution of gamma-butyrolactone and 2-butoxyethanol (4:1) until the viscosity of the solution becomes 30 cp at room temperature, which was then spin-coated on a ITO glass plate to 0.08 μm thickness. The plate was dried at the temperatures of 90 ^"C for 10 min and 160 ^°C for 30 min, followed by an irradiation of polarized UV light having wavelengths of 220~460nm (intensity 600mJ/cm²) to obtain a photo-aligned polyimide thin film (DM-SPI-12) . Physical properties of the resulting soluble polyimide thin film are summarized in Table 3 described below.

Example 13 - Example 24

As an example corresponding to the above Examples 1 to 12, the reaction was carried out similarly except that the same number of moles of DE-CBMA of Preparation example 2 was used instead of DM-CBMA of Preparation example 1. As a result, photo-aligned soluble polyimide type DE-SPI-I to DE-SPI-12 polyimide thin films were obtained. Their physical properties are summarized in Table 3 described below.

Example 25 - Example 36

As an example corresponding to the above Examples 1 to 12 , the reaction was carried out similarly except that the same number of moles of DPR-CBMA of Preparation example 3 was used instead of DM-CBMA of Preparation example 1. As a result, photo-aligned soluble polyimide type DPR-SPI-I to DPR-SPI-12 polyimide thin films were obtained. Their physical properties are summarized in Table 3 described below.

Example 37 - Example 48

As an example corresponding to the above Examples 1 to 12, the reaction was carried out similarly except that the same number of moles of DP-CBMA of Preparation example 4 was used instead of DM-CBMA of Preparation example 1. As a result, photo-aligned soluble polyimide type DP-SPI-I to DP-SPI-12 polyimide thin films were obtained. Their physical properties are summarized in Table 3 described below.

Comparative example 1. Production of photo-alignment layers made of pσlyamic acid (CPAA-I)

In a 100ml reactor equipped with a stirrer and a nitrogen gas injector, 0.01 mole (1.98 g) of methylene dianiline was dissolved in JV-methyl-2-pyrrolidone under slow nitrogen flushing. Then, 1.96 g (O.Olmol) of solid 1, 2 , 3 , 4 , -cyclobutane tetracarboxylic anhydride was slowly added thereto under nitrogen flushing. In this case, the solid content was fixed at 20 weight %, and while maintaining the reaction temperature at 0 ^"C or less the mixture was stirred for 24 hours to obtain a solution of polyamic acid (CPAA) . After adjusting the viscosity of the polyamic acid solution to 30 cp at room temperature, the resulting polyamic acid solution was spin- coated on a ITO glass plate to 0.08 μm thickness. The plate was heated at the temperatures of 90 ^°C for 10 min and 230 ^°C for 30 min for thermosetting, followed by illuminating with polarized UV light having wavelengths of 220~460nm (intensity l,000mJ/cm²) to obtain photo-aligned polyamic acid (CPAA-I). Physical properties of the resulting soluble polyimide thin film are summarized in Table 3 described below.

Comparative example 2. Production of photo-alignment layers made of polyamic acid (CPAA-2)

In a 100ml reactor equipped with a stirrer and a nitrogen gas injector, 0.01 mole (2.00 g) of 4 , 4 ' -oxydianiline was dissolved in iV-methyl-2-pyrrolidone as a reaction solvent under slow nitrogen flushing. Then, 1.96 g (O.Olmol) of solid 1, 2, 3 , 4 , -cyclobutane tetracarboxylic anhydride was slowly added thereto under nitrogen flushing. In this case, the solid content was fixed at 20 weight %, and while maintaining the reaction temperature at 0 ^°C or less the mixture was stirred for 24 hours to obtain a solution of polyamic acid (CPAA) . After adjusting the viscosity of the polyamic acid solution to 30 cp at room temperature, the resulting polyamic acid solution was spin-coated on a ITO glass plate to 0.08 μm thickness. The plate was heated at the temperatures of 90 ^°C for 10 min and 230 ^"C for 30 min for thermosetting, followed by illuminating with polarized UV light having wavelengths of 220~460nm (intensity 1 , OOOmJ/cm²) to obtain photo-aligned polyamic acid (CPAA-I) . Physical properties of the resulting soluble polyimide thin film are summarized in Table 3 described below. In Table 3, MDT (Maximum Decomposition Temperature) indicates the temperature at which thermal decomposition occurs, while RW represents a residual amount after the thermal decomposition.

[Table 3] Physical properties of the polyimide prepared from Examples and Comparative examples

As it is shown in Table 3 above, it was confirmed that the polyamic acid resins according to the present invention have intrinsic viscosity of 0.30 dL/g or more. In addition, it was found that the resins of the present invention have excellent mechanical properties and film formability under solvent casting.

As it is shown in the above Table 3, pencil hardness of the polyimide thin films comprising an alkyl group in the soluble polyimide that had been prepared according to Examples 1 to 48 was 4H or more, indicating a significant improvement over the thin film produced from the polyamic acids of Comparative examples 1 and 2, which contain no such alkyl group. In particular, for Example 5 and Example 12 that are related to the resin in which a methyl group is introduced both to the acid dianhydride and the diamine, remarkably excellent surface hardness of 6H or so was observed.

Preparation of photo-alignment layers and characteristics measurement test for the liquid crystal cell made of the layers

The soluble polyimide resin of the present invention that had been obtained from the above-described Examples 1 to 48 was dissolved in a solution of gamma-butyrolactone and 2- butoxyethanol (4:1), and then spin-coated on a ITO glass plate to 0.08 (M\ thickness while maintaining the viscosity of the solution at 30 cp at room temperature. The plate was subjected to thermosetting at 160 ^°C for 30 min to obtain a thin film, which was then irradiated with polarized UV light to give a liquid crystal cell. Each of the characteristics of the resulting liquid crystal cell are summarized in Table 4 described below. For the illumination, the wavelength was controlled to be in the range of 220~460nm and in accordance with the exposure dose of 600-1,000 mJ/cm², homogeneous alignment of the liquid crystals was observed. In the following table, VFR stands for Voltage Holding Ratio.

The liquid crystal used for the test was E-7 by Merck. By inserting a polarization plate between the thin film and the UV lamp, polarized UV light was generated. The polarization plate used was Gran-taylor prism polarization plate which has a degree of polarization of 99.999% or more and UV transparency of 30% or more.

The alignment state of the liquid crystal was visually measured by using a polarization microscope, and pretilt angles of each liquid crystal cell were determined based on a crystal rotation method.

[Table 4] Characteristic of the liquid crystal cells that are produced under the illumination with polarized UV light

As it is shown in Table 4 above, the liquid crystal cells that had been prepared by using the soluble polyimide of the present invention according to Examples 1 to 48 all show an excellent alignment property and have an excellent VHR and pretilt angles that are relatively lower than those of Comparative examples 1 and 2 relating to the polyamic acid. Specifically, the pretilt angles were 0.10~1.0°or so, that are reduced compared to Comparative examples 1 and 2 relating to the polyamic acid. In addition, VHR at a room temperature of 98% or more is an increased value compared to that of Comparative examples 1 and 2. Moreover, Example 5 and Example 12, which relate to the resin in which a methyl group is introduced both to the acid dianhydride and the diamine, show better VHR than Examples 1 to 4 and Examples 6 to 11 that are related to the resin in which a methyl group is introduced only to the acid dianhydride.

In other words, it was confirmed that the liquid crystal cells that had been prepared by using the soluble polyimide of the present invention according to Examples 1 to 48 can be suitably used as liquid crystal alignment layers for IPS (in plane switching) -type TFT-TN and STN LCD, which require low pretilt angles and high VHR.

Although the present invention was explained in detail in view of the above-described examples, it would be evident to a skilled person in the art that a various modification and a change can be made within the technical spirit of the present invention, and such modification and change absolutely fall within the scope of the claims attached herewith.

[industrial Applicability]

It is expected that the soluble alicyclic polyimide photo-alignment layers that are produced according to the present invention can be used in a broad range of application m various types such as a functional coating agent, etc., as an essential element for miniaturization, lightweighting, and reliability enhancement of various electric-electronic industrial products, in particular electronic products.

Claims

[CLAIMS]

[Claim l]

A soluble alicyclic polyimide resin for low temperature process comprising the unit of the following chemical formula 1. [Chemical formula 1]

[In the above chemical formula 1, m is a natural number in the range of from 1 to 500;

R₁ to R/, are independently to each other a hydrogen, a linear or branched, saturated or unsaturated alkyl group of Ci - C₃₀, an aryl group of C₆ - C₁₂, an aryl group of C₅ - C₃₀ or a heteroaryl group of C₆ - C₃₀ which is substituted with an alkoxy group of C₁ - C₃₀, wherein said aryl group may substituted with a linear or branched, saturated or unsaturated alkyl group of C₁ - Cj₀, an ester group, a carbonyl group, a halogen or an amino group;

comprises one or more of aromatic divalent groups which is selected from the following;

[ Claim 2 ]

The soluble alicyclic polyimide resin for low temperature process of claim 1, wherein R₁ to R₄ are independently to each other selected from a hydrogen, a alkyl group of Ci - C₃, and a phenyl group . [Claim 3]

The soluble alicyclic polyimide resin for low temperature process of claim 1, wherein said soluble alicyclic polyimide resin for low temperature process has intrinsic viscosity of 0.

3 ~ 2.0 dL/g and weight average molecular weight (Mw) of 10,000 ~ 500,000 g/mol.

[Claim 4]

The soluble alicyclic polyimide resin for low temperature process of claim 1, wherein the polyimide film can be prepared at 40 ~ 130 ^"C

[Claim 5]

The soluble alicyclic polyimide resin for low temperature T) process of claim 1, wherein said soluble alicyclic polyimide resin for low temperature process is soluble in an organic solvent selected from dimethylacetamide (DMAc) , dimethylformamide (DMF) , AT-methyl-2-pyrrolidone (NMP) and gamma- butyrolactone or their mixture. 10

[Claim 6]

Photo-alignment layers produced by coating the soluble alicyclic polyimide resin for low temperature process of any one selected of claims 1 to 5.

[Claim 7]

IT) The photo-alignment layers of claim 6, wherein said photo-alignment layers are produced by an irradiation of the polarized UV light of 220 ~ 460 nm. [Claim 8]

The photo-alignment layers of claim 7, wherein said 0 photo-alignment layers are produced by an irradiation of the polarized UV light of 100 ~ 2,000 mJ/cm². [Claim 9]

The photo-alignment layers of claim 6, wherein said photo-alignment layers have a pencil hardness of 4 ~ 6H. o [ Claim l θ ]

The liquid crystal cell comprising the photo-alignment layers of claim 6.

[Claim ll] The liquid crystal cell of claim 10, wherein said liquid crystal cell has a pretilt angle of 0.01 ~ 1°. [Claim 12]

The liquid crystal cell of claim 10, wherein said liquid crystal cell has VHR (voltage holding ratio) of 98 ~ 99.5% at the voltage of 3V at 25 ^°C .