Liquid crystal aligning agent composition, method for preparing liquid crystal alignment film using same, alignment film, and liquid crystal display device using same

Abstract

A liquid crystal aligning agent composition for forming a liquid crystal alignment film having improved electrical characteristics and high reliability while exhibiting excellent alignment properties and durability, a method for preparing a liquid crystal alignment film using the same, and a liquid crystal alignment film and a liquid crystal display device using the liquid crystal alignment film.

Claims

1. A liquid crystal aligning agent composition comprising: a polymer containing a polyimide or a precursor thereof; and a polyoxazoline crosslinking agent containing a repeating unit represented by Chemical Formula 1: ##STR00022## wherein, in the Chemical Formula 1, R.sub.1 is an alkyl group having 1 to 20 carbon atoms, or a heteroatom-substituted alkyl group having 1 to 20 carbon atoms, and a is an integer of 1 to 10,000.

2. The liquid crystal aligning agent composition of claim 1, wherein the polyoxazoline crosslinking agent has, at one end thereof, at least one selected from the group of an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, a thiol group, an alkynyl group, an amine group, an azide group, and a silyl group.

3. The liquid crystal aligning agent composition of claim 2, wherein the polyoxazoline crosslinking agent has, at the opposite end at least one selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a heteroatom-substituted an alkyl group having 1 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, and an arylalkyl group having 6 to 30 carbon atoms.

4. The liquid crystal aligning agent composition of claim 1, wherein the polyoxazoline crosslinking agent includes a homopolymer represented by Chemical Formula 1-1: ##STR00023## wherein, in the Chemical Formula 1-1, R.sub.1 is an alkyl group having 1 to 20 carbon atoms, or a heteroatom-substituted alkyl group having 1 to 20 carbon atoms, R.sub.2 is an alkyl group having 1 to 20 carbon atoms, a heteroatom-substituted alkyl group having 1 to 20 carbon atoms, an alkynyl group having 2 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, or an arylalkyl group having 6 to 30 carbon atoms, X is an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, a thiol group, an alkynyl group, an amine group, an azide group, or a silyl group, and a is an integer of 1 to 10,000.

5. The liquid crystal aligning agent composition of claim 1, wherein the polyoxazoline crosslinking agent includes a copolymer containing two or more different repeating units represented by Chemical Formula 1.

6. The liquid crystal aligning agent composition of claim 1, wherein the polyoxazoline crosslinking agent has a weight average molecular weight of 5000 g/mol to 1,000,000 g/mol as measured by a GPC method.

7. The liquid crystal aligning agent composition of claim 1, wherein the polyoxazoline crosslinking agent is contained in an amount of 0.1 to 20% by weight based on the total weight of the liquid crystal aligning agent composition.

8. The liquid crystal aligning agent composition of claim 1, wherein the polymer includes: a first polymer for a liquid crystal aligning agent including one or more repeating units selected from the group consisting of a repeating unit represented by Chemical Formula 2, a repeating unit represented by Chemical Formula 3, and a repeating unit, represented by Chemical Formula 4; and a second polymer for a liquid crystal aligning agent including one or more repeating units selected from the group consisting of a repeating unit represented by Chemical Formula 5, a repeating unit represented by Chemical Formula 6, and a repeating unit represented by Chemical Formula 7: ##STR00024## wherein, in the Chemical Formulas 2 to 7, at least one of R.sub.3 and R.sub.4 is an alkyl group having 1 to 10 carbon atoms and the other is hydrogen, at least one of R.sub.5 and R.sub.6 is an alkyl group having 1 to 10 carbon atoms and the other is hydrogen, X.sub.1 to X.sub.6 are each independently a first tetravalent organic group represented by Chemical Formula 8, ##STR00025## wherein, in the Chemical Formula 8, R.sub.9 to R.sub.14 are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and L.sub.1 is any one selected from the group consisting of a single bond, —O—, —CO—, —COO—, —S—, —SO—, —SO.sub.2—, —CR.sub.15R.sub.16—, —(CH.sub.2).sub.Z—, —O(CH.sub.2).sub.ZO—, —COO(CH.sub.2).sub.ZOCO—, —CONH—, phenylene, and a combination thereof, wherein R.sub.15 and R.sub.16 are each independently hydrogen, an alkyl group, or a fluoroalkyl group having 1 to 10 carbon atoms, z is an integer of 1 to 10, and Y.sub.1 to Y.sub.3 are each independently a divalent organic group represented by Chemical Formula 9, ##STR00026## wherein, in Chemical Formula 9, T is a second tetravalent organic group represented by Chemical Formula 8, D.sub.1 and D.sub.2 are each independently an alkylene group having 1 to 20 carbon atoms, a heteroalkylene group having 1 to 10 carbon atoms, a cycloalkylene group having 3 to 20 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a heteroarylene group having 2 to 20 carbon atoms, and Y.sub.4 to Y.sub.6 are each independently a divalent organic group represented by Chemical Formula 10, ##STR00027## wherein, in the Chemical Formula 10, R.sub.17 and R.sub.18 are each independently hydrogen, a halogen, a cyano, a nitrile, an alkyl having 1 to 10 carbon atoms, an alkenyl having 1 to 10 carbon atoms, an alkoxy having 1 to 10 carbon atoms, a fluoroalkyl having 1 to 10 carbon atoms, or a fluoroalkoxy having 1 to 10 carbon atoms, p and q are each independently an integer of 0 to 4, L.sub.2 is a single bond, —O—, —CO—, —S—, —SO.sub.2—, —C(CH.sub.3).sub.2—, —C(CF.sub.3).sub.2—, —CONH—, —COO—, —(CH.sub.2).sub.y—, —O(CH.sub.2).sub.yO—, —O(CH.sub.2).sub.y—, —NH—, —NH(CH.sub.2).sub.y—NH—, —NH(CH.sub.2).sub.yO—, —OCH.sub.2—C(CH.sub.3).sub.2—CH.sub.2O—, —COO—(CH.sub.2).sub.y—OCO—, or —OCO—(CH.sub.2).sub.y—COO—, y is an integer of 1 to 10, k and m are each independently an integer of 0 to 3, and n is an integer of 0 to 3.

9. The liquid crystal aligning agent composition of claim 8, wherein a weight ratio of the first polymer and the second polymer is 1:9 to 9:1.

10. The liquid crystal aligning agent composition of claim 1, further comprising a compound having two or more epoxy groups in a molecule.

11. The liquid crystal aligning agent composition of claim 10, wherein the compound having two or more epoxy groups in a molecule includes a compound represented by Chemical Formula 11: ##STR00028## wherein, in the Chemical Formula 11, R.sub.24 is an alkylene group having 1 to 10 carbon atoms, Ar.sub.1 and Ar.sub.2 are each independently an arylene group having 6 to 10 carbon atoms, and Q.sub.1 to Q.sub.4 are each independently hydrogen or a glycidyl group.

12. The liquid crystal aligning agent composition of claim 10, wherein the compound having two or more epoxy groups in a molecule is contained in an amount of 0.1 to 30 parts by weight based on 100 parts by weight of the total weight of the first polymer and the second polymer.

13. A method for preparing a liquid crystal alignment film comprising the steps of: coating the liquid crystal aligning agent composition of claim 1 on a substrate to form a coating film; drying the coating film; alignment treatment by irradiating the coating film immediately after the drying step with light or rubbing the coating film; and heat-treating and curing the alignment-treated coating film.

14. The method for preparing a liquid crystal alignment film of claim 13, wherein the liquid crystal aligning agent composition is dissolved or dispersed in an organic solvent.

15. The method for preparing a liquid crystal alignment film of claim 13, wherein the step of drying the coating film is performed at 50° C. to 150° C.

16. The method for preparing a liquid crystal alignment film of claim 13, wherein the light in the alignment treatment step is polarized ultraviolet rays having a wavelength of 150 nm to 450 nm.

17. The method for preparing a liquid crystal alignment film of claim 13, wherein in the step of heat-treating and curing, the temperature of the heat treatment, is 150° C. to 300° C.

18. A liquid crystal alignment film comprising an aligned and cured product of the liquid crystal aligning agent composition of claim 1.

19. A liquid crystal display device comprising the liquid crystal alignment film of claim 18.

20. A liquid crystal alignment film produced by the method of claim 13.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) The present invention will be described in more detail by way of examples. However, these examples are given for illustrative purposes only, and the scope of the invention is not intended to be limited by these examples.

Preparation Example 1-1: Synthesis of Diamine

Preparation Example 1-1): Synthesis of Diamine DA-1

(2) Diamine DA-1 was synthesized according to the following reaction scheme.

(3) ##STR00016##

(4) Specifically, 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride (DMCBDA) and 4-nitroaniline were dissolved in DMF (dimethylformamide) to prepare a mixture. Then, the mixture was reacted at about 80° C. for about 12 hours to prepare an auric acid. Subsequently, the auric acid was dissolved in DMF, and acetic anhydride and sodium acetate were added thereto to prepare a mixture. Then, the auric acid contained in the mixture was imidized at about 90° C. for about 4 hours. The imide thus obtained was dissolved in DMAc (dimethylacetamide), and then Pd/C was added thereto to prepare a mixture. The resulting mixture was reduced at about 45° C. under hydrogen pressure of about 6 bar for 20 minutes to prepare diamine DA-1.

Preparation Example 1-2): Synthesis of Diamine DA-2

(5) ##STR00017##

(6) DA-2 having the above structure was prepared in the same manner as in Preparation Example 1, except that cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA) was used instead of 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride.

Preparation Example 2: Preparation of Polymer for Liquid Crystal Aligning Agent

Preparation Example 2-1): Preparation of Polymer for Liquid Crystal Aligning Agent P-1

(7) (Step 1)

(8) 5.0 g (13.3 mmol) of DA-2 prepared in Preparation Example 1-1 was completely dissolved in 71.27 g of anhydrous N-methyl pyrrolidone (NMP). 2.92 g (13.03 mmol) of 1,3-dimethyl-cyclobutane-1,2,3,4-tetracarboxylic dianhydride (DMCBDA) was then added to the solution under an ice bath and stirred at room temperature for 16 hours.

(9) (Step 2)

(10) The solution obtained in step 1 was added to an excess amount of distilled water to produce a precipitate. The resulting precipitate was then filtered, washed twice with distilled water, and then washed again with methanol three times. The solid product thus obtained was dried in a vacuum oven at 40° C. for 24 hours to obtain 6.9 g of a polymer for a liquid crystal aligning agent P-1.

(11) As a result of confirming the molecular weight of the polymer P-1 through GPC, the number average molecular weight (Mn) was 15,500 g/mol, and the weight average molecular weight (Mw) was 31,000 g/mol. Further, the monomer structure of the polymer P-1 is determined by the equivalent ratio of the monomers used, and the ratio of an imide structure in the molecule was 50.5%, while the ratio of an amic acid structure was 49.5%.

Preparation Example 2-2): Preparation of Polymer for Liquid Crystal Aligning Agent P-2

(12) 5.0 g of DA-1 prepared in Preparation Example 1-1 and 1.07 g of p-phenylenediamine (PDA) were completely dissolved in 103.8 g of NMP. 2.12 g of cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA) and 3.35 g of 4,4′-oxydiphthalic dianhydride (OPDA) were added to the solution under an ice bath and stirred for 16 hours at room temperature. Then, the polymer P-2 was prepared in the same manner as in step 2 of Preparation Example 2-1.

(13) As a result of confirming the molecular weight of the polymer P-2 through GPC, the number average molecular weight (Mn) was 18,000 g/mol, and the weight average molecular weight (Mw) was 35,000 g/mol. Further, the polymer P-2 showed that the ratio of an imide structure in the molecule was 36.4%, and the ratio of an amic acid structure was 63.6%.

Preparation Example 2-3): Preparation of Polymer for Liquid Crystal Aligning Agent P-3

(14) 6.0 g of DA-2 prepared in Preparation Example 1-2 and 1.37 g of 4,4′-oxydianiline (ODA) were completely dissolved in 110.5 g of NMP. 3.47 g of DMCBDA and 1.44 g of pyromellitic dianhydride (PMDA) were added to the solution under an ice bath and stirred for 16 hours at room temperature. Then, the polymer P-3 was prepared in the same manner as in step 2 of Preparation Example 2-1.

(15) As a result of confirming the molecular weight of the polymer P-3 through GPC, the number average molecular weight (Mn) was 14,500 g/mol, and the weight average molecular weight (Mw) was 29,000 g/mol. Further, the polymer P-3 showed that the ratio of an imide structure in the molecule was 41.9%, and the ratio of an amic acid structure was 58.1%.

Preparation Example 2-4): Preparation of Polymer for Liquid Crystal Aligning Agent Q-1

(16) 5.00 g of 4,4′-methylenedianiline and 5.05 g of 4,4′-oxydianiline were completely dissolved in 221.4 g of NMP. 14.55 g of 4,4′-bisphthalic anhydride was added to the solution under an ice bath and stirred for 6 hours at room temperature. Then, the polymer Q-1 was prepared in the same manner as in step 2 of Preparation Example 2-1.

(17) As a result of confirming the molecular weight of the polymer Q-1 through GPC, the number average molecular weight (Mn) was 25,000 g/mol, and the weight average molecular weight (Mw) was 40,000 g/mol.

Examples: Preparation of Liquid Crystal Aligning Agent Composition

Example 1

(18) 5 parts by weight of P-1 prepared in Preparation Example 2-1, 5 parts by weight of Q-1 prepared in Preparation Example 2-4, 0.5 parts by weight of N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGMDA), and 1 part by weight of a polymer of the following Chemical Formula A [PEOX, weight average molecular weight: about 50,000 g/mol] were completely dissolved in a mixed solvent of NMP and N-butoxyethanol in a weight ratio of 8 to 2. Then, the obtained solution was subjected to pressure filtration through a filter having a pore size of 0.2 μm made of poly(tetrafluoroethylene) to prepare a liquid crystal aligning agent composition.

(19) ##STR00018##

(20) in Chemical Formula A, x is 500 to 510 (about 505).

Example 2

(21) A liquid crystal aligning agent composition was prepared in the same manner as in Example 1, except that P-2 prepared in Preparation Example 2-2 was used instead of P-1 prepared in Preparation Example 2-1.

Example 3

(22) A liquid crystal aligning agent composition was prepared in the same manner as in Example 1, except that P-3 prepared in Preparation Example 2-3 was used instead of P-1 prepared in Preparation Example 2-1.

Example 4

(23) A liquid crystal aligning agent composition was prepared in the same manner as in Example 1, except that a polymer of the following Chemical Formula B (number average molecular weight: about 10,000 g/mol) was used instead of a polymer of Chemical Formula A.

(24) ##STR00019##

(25) In Chemical Formula B, x is 110 to 120 (about 117).

Example 5

(26) A liquid crystal aligning agent composition was prepared in the same manner as in Example 1, except that a polymer of the following Chemical Formula C (number average molecular weight: about 10,000 g/mol) was used instead of a polymer of Chemical Formula A.

(27) ##STR00020##

(28) In Chemical Formula C, x is 80 to 90 (about 88).

Comparative Example: Preparation of Liquid Crystal Aligning Agent Composition

Comparative Example 1

(29) A liquid crystal aligning agent composition was prepared in the same manner as in Example 1, except that a polymer of Chemical Formula A was not used.

Comparative Example 2

(30) A liquid crystal aligning agent composition was prepared in the same manner as in Example 1, except that N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane was not used.

Comparative Example 3

(31) A liquid crystal aligning agent composition was prepared in the same manner as in Example 1, except that Q-1 prepared in Preparation Example 2-4 was used instead of P-1 prepared in Preparation Example 2-1.

Comparative Example 4

(32) A liquid crystal aligning agent composition was prepared in the same manner as in Example 1, except that poly(styrene-co-2-isopropenyl-oxazoline) (EPOCROS RPS-1005, manufactured by Nippon Shokubai Co., Ltd.) having a structure of the following Chemical Formula D was used instead of a polymer of Chemical Formula A.

(33) ##STR00021##

Experimental Example 1

(34) 1) Preparation of Liquid Crystal Alignment Cell

(35) A liquid crystal alignment cell was prepared by using the liquid crystal aligning agent compositions prepared in the examples and comparative examples.

(36) Specifically, the liquid crystal alignment agent compositions prepared in the examples and comparative examples were coated onto a substrate (lower plate) in which comb-shaped IPS (in-plane switching) mode type of ITO electrode patterns having a thickness of 60 nm, an electrode width of 3 μm, and an interval between electrodes of 6 μm were formed on a rectangular glass substrate having a size of 2.5 cm×2.7 cm and a glass substrate (upper plate) in which the electrode patterns were not formed, respectively, by using a spin coating method.

(37) Subsequently, the substrates coated with the liquid crystal alignment agent were placed and dried on a hot plate at about 70° C. for 3 minutes to evaporate the solvent. In order to align the coating films thus obtained, the respective coating films of the upper and lower plates were irradiated with 254 nm ultraviolet rays in an exposure amount of 1 J/cm.sup.2 using an exposure machine to which a linear polarizer was attached.

(38) Then, the aligned upper and lower plates were fired (cured) in an oven at about 230° C. for 30 minutes to obtain a coating film having a film thickness of 0.1 μm. Then, a sealing agent impregnated with ball spacers having a size of 3 μm was coated to the edge of the upper plate except at a liquid crystal injection hole. Further, the alignment films formed on the upper plate and the lower plate were arranged so that they were opposite each other and alignment directions thereof were parallel to each other, and then the upper and lower plates were bonded together and the sealing agent was cured, thereby manufacturing an empty cell. In addition, the liquid crystal was injected into the empty cell, thereby manufacturing an IPS mode liquid crystal cell.

(39) 2) Measurement of Voltage Holding Ratio (VHR)

(40) The voltage holding ratio (VHR), which is an electrical characteristic of the prepared liquid crystal alignment cell, was measured using 6254C equipment available from TOYO Corporation. The voltage holding ratio (VHR) was measured under the conditions of 1 Hz and 60° C. (VHR 60° C. and 1 Hz n-LE conditions). The measurement results of the voltage holding ratio (VHR) of the liquid crystal alignment cell are shown in Table 1 below.

(41) 3) Evaluation of Liquid Crystal Alignment Properties

(42) Polarizing plates were adhered to the upper and lower plates of the liquid crystal cell prepared as above with their polarizing axes perpendicular to each other. The liquid crystal cell to which the polarizing plates were adhered was then placed on a backlight with brightness of 7000 cd/m.sup.2, and light leakage was observed with the naked eye. At this time, if the alignment properties of the liquid crystal alignment film are excellent and the liquid crystal is arranged well, light is not passed through the upper and lower polarizing plates adhered with their polarizing axes perpendicular to each other, and it is observed dark without defects. In this case, the alignment properties are evaluated as ‘good’, and when light leakage such as a liquid crystal flow, mark or bright spot is observed, it is evaluated as ‘poor’. The results are shown in Table 1 below.

(43) 4) Evaluation of Alignment Film Strength

(44) For the alignment films obtained from the liquid crystal aligning agent composition prepared in the examples and comparative examples, the surface of the alignment film was rubbed while rotating the surface of the alignment film at 850 rpm using a rubbing machine (manufactured by Sindo Engineering), and then the haze value was measured using a hazemeter. The film strength was evaluated by calculating the difference between the haze value before rubbing treatment and the haze value after rubbing treatment. If the haze change value is less than 1, the film strength is excellent.
Film strength (%)=haze (%) of liquid crystal alignment film after rubbing treatment−haze (%) of liquid crystal alignment film before rubbing treatment.  [Mathematical Equation 1]

Experimental Example 2

(45) 1) Preparation of Liquid Crystal Alignment Cell

(46) A liquid crystal alignment cell was prepared in the same manner as in Experimental Example 1, except that before firing (curing) the coating film in a hot plate at 230° C. for 30 minutes, a step of leaving the coated film on a hot plate at 130° C. for 500 seconds and subjecting it to a low-temperature heat treatment is further included.

(47) TABLE-US-00001 TABLE 1 Measurement Results of Examples and Comparative Examples Compar- Compar- Compar- Compar- ative ative ative ative Cate- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- gory ple 1 ple 2 ple 3 ple 4 ple 5 ple 1 ple 2 ple 3 ple 4 Polymer Prepa- Prepa- Prepa- Prepa- Prepa- Prepa- Prepa- Prepa- Prepa- ration ration ration ration ration ration ration ration ration Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 2-1 ple 2-2 ple 2-3 ple 2-1 ple 2-1 ple 2-1 ple 2-1 ple 2-4 ple 2-1 Prepa- Prepa- Prepa- Prepa- Prepa- Prepa- Prepa- Prepa- ration ration ration ration ration ration ration ration Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 2-4 ple 2-4 ple 2-4 ple 2-4 ple 2-4 ple 2-4 ple 2-4 ple 2-4 Epoxy TGMD TGMD TGMD TGMD TGMD TGMD — TGMD TGMD additive A A A A A A A A Polyoxa- Chem- Chem- Chem- Chem- Chem- — Chem- Chem- Chem- zoline ical ical ical ical ical ical ical ical cross- Formula Formula Formula Formula Formula Formula Formula Formula linking A A A B C A A D agent VHR 90 or 90 or 90 or 90 or 90 or 80 90 or 90 or 82 (%) more more more more more more more Align- Good Good Good Good Good Good Good Poor Poor ment proper- ties Film 0.87 0.9 0.7 0.6 0.8  0.8 5 0.93  3 strength (%)

(48) As shown in Table 1, the liquid crystal aligning agent composition of the examples containing the polymer synthesized in Preparation Example 2-1, an epoxy additive, and a polyoxazoline crosslinking agent exhibited a high voltage holding ratio value of 90% or more. Thus, the alignment cell produced from the liquid crystal aligning agent composition of the above examples realized excellent electrical characteristics, and simultaneously the haze value change before and after the rubbing treatment was very low, i.e., less than 1, while the film strength performance was improved.

(49) Meanwhile, it was confirmed that the alignment film obtained from the liquid crystal aligning agent composition of Comparative Example 1 containing no polyoxazoline crosslinking agent had a voltage holding ratio of 80%, which was decreased as compared with the examples.

(50) In addition, the alignment film obtained from the liquid crystal aligning agent composition of Comparative Example 2 containing no epoxy additive had a significantly increased haze change value before and after the rubbing treatment, indicating that the film strength was remarkably poor as compared with the examples.

(51) Further, it was confirmed that the alignment film obtained from the liquid crystal aligning agent composition of Comparative Example 3 containing no polymer synthesized in Preparation Example 2-1 had remarkably poor alignment properties as compared with the examples.

(52) Further, the alignment film obtained from the liquid crystal aligning agent composition of Comparative Example 4 containing a polyoxazoline crosslinking agent represented by Chemical Formula D having a different structure from the polyoxazoline crosslinking agent of the present invention represented by Chemical Formula A was not only poor in alignment properties as compared with the examples, but also exhibited a voltage holding ratio of 82%, confirming that the electrical characteristics were decreased as compared with the examples. Further, the haze change value before and after rubbing treatment was greatly increased to 3%, confirming that the film strength was remarkably poor as compared with the examples.