Liquid crystal aligning agent composition, method for producing liquid crystal alignment film using same, and liquid crystal alignment film using same

Abstract

The present invention provides a liquid crystal aligning agent composition that has excellent storage stability, can secure a high imidization rate, and can produce a liquid crystal alignment film having improved film strength together with liquid crystal alignment properties, a method for producing a liquid crystal alignment film using the same, and a liquid crystal alignment film and a liquid crystal display device using the same.

Claims

1. A liquid crystal aligning agent composition comprising: i) a first polymer for a liquid crystal aligning agent including two or more repeating units selected from the group consisting of a repeating unit represented by Chemical Formula 1, a repeating unit represented by Chemical Formula 2, and a repeating unit represented by Chemical Formula 3, wherein the first polymer includes the repeating unit represented by Chemical Formula 1 in an amount of 36.4 mol % to 74 mol % with respect to all repeating units represented by the Chemical Formulae 1 to 3, ii) a second polymer for a liquid crystal aligning agent including a repeating unit represented by Chemical Formula 4, iii) a compound having two or more epoxy groups in a molecule, and iv) a primary or secondary amine compound in which at least one hydrogen atom bonded to a nitrogen atom is substituted with at least one functional group selected from the group consisting of a tert-butoxycarbonyl group, a 9-fluorenylmethoxycarbonyl group, and a carboxybenzyl group, wherein a weight ratio between the first polymer for a liquid crystal aligning agent and the second polymer for a liquid crystal aligning agent is 15:85 to 85:15: ##STR00009## wherein, in Chemical Formulae 1 to 4, at least one of R.sup.1 and R.sup.2 is a C.sub.1-10 alkyl, and the rest is hydrogen, R.sup.3 and R.sup.4 are each independently hydrogen or C.sub.1-10 alkyl, and X.sup.1 is a tetravalent organic group represented by Chemical Formula 5, X.sup.2, X.sup.3, and X.sup.4 are each independently a tetravalent organic group derived from a hydrocarbon having 4 to 20 carbon atoms, or a tetravalent organic group in which at least one H in the tetravalent organic group is substituted with a halogen, or at least one —CH.sub.2— is replaced by —O—, —CO—, —S—, —SO—, —SO.sub.2—, or —CONH— such that oxygen or sulfur atoms are not directly linked, and ##STR00010## wherein, in Chemical Formula 5, R.sup.5 to R.sup.8 are each independently hydrogen or a C.sub.1-6 alkyl, Y.sup.1, Y.sup.2, Y.sup.3, and Y.sup.4 are each independently a divalent organic group represented by Chemical Formula 6, ##STR00011## wherein, in Chemical Formula 6, R.sup.9 and R.sup.10 are each independently a halogen, a cyano, a C.sub.1-10 alkyl, a C.sub.2-10 alkenyl, a C.sub.1-10 alkoxy, a C.sub.1-10 fluoroalkyl, or a C.sub.1-10 fluoroalkoxy, p and q are each independently an integer between 0 and 4, and L.sup.1 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.z—, —O(CH.sub.2).sub.zO—, —O(CH.sub.2).sub.z—, —OCH.sub.2—C(CH.sub.3).sub.2—CH.sub.2O—, —COO—(CH.sub.2).sub.z—OCO—, or —OCO—(CH.sub.2).sub.z—COO—, wherein z is an integer between 1 and 10, and m is an integer between 0 and 3.

2. The liquid crystal aligning agent composition of claim 1, wherein the functional group substituted in the primary or secondary amine is capable of being substituted with a hydrogen atom at a temperature of 90° C. or higher.

3. The liquid crystal aligning agent composition of claim 1, wherein the primary or secondary amine compound is included in an amount of 0.03 parts by weight to 30 parts by weight, based on a total of 100 parts by weight of the first polymer for the liquid crystal aligning agent and the second polymer for the liquid crystal aligning agent.

4. The liquid crystal aligning agent composition of claim 1, wherein the primary amine or the secondary amine in the primary or secondary amine compound each independently has a linear or cyclic structure.

5. The liquid crystal aligning agent composition of claim 1, wherein the X.sup.2, X.sup.3, and X.sup.4 are each independently a tetravalent organic group represented by Chemical Formula 7: ##STR00012## wherein, in Chemical Formula 7, R.sup.11 to R.sup.14 are each independently hydrogen, or a C.sub.1-6 alkyl, and L.sup.2 is a single bond, —O—, —CO—, —S—, —C(CH.sub.3).sub.2—, —C(CF.sub.3).sub.2—, —CONH—, —COO—, —(CH.sub.2).sub.Z—, —O(CH.sub.2).sub.ZO—, or —COO—(CH.sub.2).sub.Z—OCO—, wherein z is an integer between 1 and 10.

6. The liquid crystal aligning agent composition of claim 1, wherein the molecular weight of the compound having two or more epoxy groups in a molecule is 100 g/mol to 10,000 g/mol.

7. The liquid crystal aligning agent composition of claim 1, wherein the compound having two or more epoxy groups in a molecule is a cycloaliphatic-based epoxy, a bisphenol-based epoxy, or a novolac-based epoxy.

8. The liquid crystal aligning agent composition of claim 1, wherein the compound having two or more epoxy groups in a molecule is included in an amount of 0.1 parts by weight to 30 parts by weight based on a total of 100 parts by weight of the first polymer for a liquid crystal aligning agent and the second polymer for a liquid crystal aligning agent.

9. A method for producing a liquid crystal alignment film comprising the steps of: 1) coating the liquid crystal aligning agent composition of claim 1 onto a substrate to form a coating film; 2) drying the coating film; 3) subjecting the coating film to alignment treatment immediately after the drying step; and 4) heat-treating and curing the alignment-treated coating film.

10. The method for producing a liquid crystal alignment film of claim 9, wherein the liquid crystal aligning agent composition is dissolved or dispersed in an organic solvent.

11. The method for producing a liquid crystal alignment film of claim 9, wherein the drying of Step 2 is performed at a temperature of 50° C. to 130° C.

12. The method for producing a liquid crystal alignment film of claim 9, wherein the alignment treatment of Step 3 is performed by irradiating polarized ultraviolet rays having a wavelength of 150 nm to 450 nm.

13. The method for producing a liquid crystal alignment film of claim 9, wherein Step 4 comprises the steps of: 4-1) subjecting the alignment-treated coating film to a low-temperature heat treatment at 200° C. or less; and 4-2) heat-treating and curing the heat-treated coating film at a temperature of higher than that of the low-temperature heat treatment.

14. The method for producing a liquid crystal alignment film of claim 13, wherein the low-temperature heat treatment of Step 4-1 is performed at a temperature of 110° C. to 200° C.

15. The method for producing a liquid crystal alignment film of claim 13, wherein the heat treatment of Step 4-2 is performed at a temperature of 200° C. to 250° C.

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

17. A liquid crystal display device comprising the liquid crystal alignment film of claim 16.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) The prevention 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.

Production Example 1: Synthesis of Diamine

Production Example 1-1) Synthesis of Diamine DA-1

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

(3) ##STR00007##

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

Production Example 1-2) Synthesis of Diamine DA-2

(5) ##STR00008##

(6) DA-2 having the above structure was produced in the same manner as in Production Example 1-1, except that cyclobuthane-1,2,3,4-tetracarboxylic dianhydride (CBDA) was used instead of 1,3-dimethylcyclobuthane-1,2,3,4-tetracarboxylic dianhydride.

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

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

(7) (Step 1)

(8) 5.0 g (13.3 mmol) of DA-2 produced in Production Example 1-2 was completely dissolved in 71.27 g of anhydrous N-methyl pyrrolidone (NMP). Then, 2.92 g (13.03 mmol) of 1,3-dimethyl-cyclobuthane-1,2,3,4-tetracarboxylic dianhydride (DMCBDA) was 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 poured into an excess amount of distilled water to form a precipitate. Then, the formed precipitate was filtered and washed twice with distilled water and again three times with methanol. The thus-obtained solid product 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 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 was determined by the equivalent ratio of the monomers used, and the ratio of imine structure in the molecule was 50.5%, while the ratio of amic acid structure was 49.5%.

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

(12) 5.0 g of DA-1 produced in Production Example 1-1 and 1.07 g of p-phenylenediamine (PDA) were completely dissolved in 103.8 g of NMP. Then, 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 at room temperature for 16 hours. The polymer P-2 was then produced in the same manner as in Step 2 of Production Example 2-1.

(13) As a result of confirming the molecular weight of 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, as for the polymer P-2, the ratio of the imine structure in the molecule was 36.4%, and the ratio of the amic acid structure was 63.6%.

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

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

(15) As a result of confirming the molecular weight of 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, as for the polymer P-3, the ratio of the imide structure in the molecule was 41.9%, and the ratio of the amic acid structure was 58.1%.

Production Example 2-4) Production 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. Then, 14.55 g of 4,4′-biphthalic anhydride was added to the solution under an ice bath and stirred at room temperature for 16 hours. The polymer Q-1 was then produced in the same manner as in Step 2 of Production Example 2-1.

(17) As a result of confirming the molecular weight of 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.

Example: Production of Liquid Crystal Aligning Agent Composition

Example 1

(18) 5 parts by weight of P-1 produced in Production Example 2-1, 5 parts by weight of Q-1 produced in Production Example 2-4, 0.5 parts by weight of (3′,4′-epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate (Celloxide 2021P manufactured by Daicel), and 1 part by weight of tert-butoxycarbonyl imidazole were completely dissolved in a mixed solvent of NMP and n-butoxyethanol at a weight ratio of 8:2. Then, the resultant was subjected to pressure filtration with a filter made of poly(tetrafluoroethylene) having a pore size of 0.2 μm to produce a liquid crystal aligning agent composition.

Example 2

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

Example 3

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

Comparative Example: Production of Liquid Crystal Aligning Agent Composition

Comparative Example 1

(21) A liquid crystal aligning agent composition was produced in the same manner as in Example 1, except that tert-butoxycarbonyl imidazole was not used.

Comparative Example 2

(22) A liquid crystal aligning agent composition was produced in the same manner as in Example 1, except that Celloxide 2021P was not used.

Comparative Example 3

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

Comparative Example 4

(24) A liquid crystal aligning agent composition was produced in the same manner as in Example 1, except that imidazole was used instead of tert-butoxycarbonyl imidazole.

Experimental Example 1

(25) 1) Production of Liquid Crystal Cell

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

(27) Specifically, the liquid crystal aligning agent composition produced in the examples and comparative examples was coated onto a substrate (lower plate) in which comb-shaped IPS (in-plane switching) mode ITO electrode patterns having a thickness of 60 nm, an electrode width of 3 μm, and a spacing between electrodes of 6 μm were formed on a rectangular glass substrate having a size of 2.5 cm×2.7 cm and onto a glass substrate (upper plate) having no electrode pattern each using a spin coating method.

(28) Then, the substrates onto which the liquid crystal aligning agent composition was coated were placed on a hot plate at about 70° C. for 3 minutes to evaporate the solvent. In order to subject the thus-obtained coating film to alignment treatment, ultraviolet rays of 254 nm were irradiated with an intensity of 1 J/cm.sup.2 using an exposure apparatus in which a linear polarizer was adhered to the coating film of each of the upper and lower plates.

(29) Thereafter, the coating film was calcinated (cured) in an oven at about 230° C. for 30 minutes to obtain a coating film having a thickness of 0.1 μm. Then, a sealing agent impregnated with a ball spacer having a size of 3 μm was applied to the edge of the upper plate excluding the liquid crystal injection hole. Subsequently, the alignment films formed on the upper plate and the lower plate were aligned such that they faced each other and the alignment directions were aligned with each other, and then the upper and lower plates were bonded together and the sealing agent was cured to prepare an empty space. Then, a liquid crystal was injected into the empty cells to produce an IPS mode liquid crystal cell.

(30) 2) Imidization Conversion Rate (%)

(31) The FT-IR spectra of the liquid crystal alignment films obtained from the liquid crystal aligning agent compositions of the examples and comparative examples were measured by an ATR method, and the ratio of imide structure in the polymer molecules contained in the alignment film was measured.

(32) 3) Evaluation of Liquid Crystal Alignment Properties

(33) Polarizers were attached to the upper and lower substrates of the liquid crystal cell produced by the above method so that they were perpendicular to each other. The polarizer-attached liquid crystal cell 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 attached vertically to each other, and it is observed as dark without defects. In this case, the alignment properties were evaluated as ‘good’, and when light leakage such as liquid crystal flow mark or bright spot is observed, it was evaluated as ‘poor’. The results are shown in Table 1 below.

(34) 4) Evaluation of Alignment Film Strength

(35) The alignment films obtained from the liquid crystal aligning agent compositions produced in the examples and comparative examples were subjected to rubbing treatment while rotating the surface of the alignment film at 850 rpm using a rubbing machine (SHINDO Engineering), and then the haze value was measured using a haze meter. The difference between the haze value after rubbing treatment and the haze value before rubbing treatment was calculated as shown in the following Equation 1 to evaluate the film strength. If the change in haze values is less than 1, it was evaluated that the film strength is excellent.
Film strength (%)=Haze of the liquid crystal alignment film after rubbing treatment (%)−Haze of the liquid crystal alignment film before rubbing treatment (%)  [Equation 1]

(36) 5) Storage Stability

(37) For the liquid crystal aligning agent compositions of Example 1 and Comparative Example 4, the initial viscosity and the viscosity after storage at room temperature for 30 days were respectively measured, and the viscosity change rate was measured according to the following Equation 2. When the change in viscosity over 30 days is 10% or less, it was evaluated that the storage stability is excellent.

(38) The viscosity of the liquid crystal aligning agent composition may be determined by measuring the amount of torque using a Brookfield viscometer with an RV-7 spindle at a temperature of 25° C. and a rotational speed of 0.5 rpm.
Viscosity change rate (%)=(Viscosity of the liquid crystal aligning agent composition after storage at room temperature for 30 days−Initial viscosity of the liquid crystal aligning agent composition)/Initial viscosity of the liquid crystal aligning agent composition*100  [Equation 2]

Experimental Example 2

(39) 1) Production of Liquid Crystal Cell

(40) A liquid crystal cell was produced in the same manner as in Experimental Example 1, except that a step of placing the coating film on a hot plate at 130° C. for 500 seconds to perform a low-temperature heat treatment is further included, before calcinating (curing) the coating film in an oven at about 230° C. for 30 minutes.

(41) TABLE-US-00001 TABLE 1 Results of measurement of examples and comparative examples Comparative Comparative Comparative Comparative Class Example 1 Example 2 Example 3 Example 1 Example 2 Example 3 Example 4 Polymer Production Production Production Production Production Production Production Example Example Example Example Example Example Example 2-1 2-2 2-3 2-1 2-1 2-4 2-1 Production Production Production Production Production Production Example Example Example Example Example Example 2-4 2-4 2-4 2-4 2-4 2-4 Epoxy Celloxide Celloxide Celloxide Celloxide — Celloxide Celloxide additive 2021P 2021P 2021P 2021P 2021P 2021P Catalyst tert- tert- tert- — tert- tert- Imidazole butoxycarbonyl butoxycarbonyl butoxycarbonyl butoxycarbonyl butoxycarbonyl imidazole imidazole imidazole imidazole imidazole Imidization 93.1 92.7 92 80.5 91.4 92.5 92.9 conversion rate (%) Alignment Good Good Good Good Good Poor Good properties Film 0.87 0.9 0.7 1.47 5 1.9 0.85 strength (%) Viscosity 8.3 — — — — — 20.8 change (%)

(42) As shown in Table 1, the liquid crystal aligning agent compositions of the examples containing the polymer synthesized in Production Example 2-1 to 2-3, an epoxy additive, and a catalyst exhibited an imidization rate of 93.1%, 92.7%, and 92% even at a curing temperature of 230° C., respectively, which was a very high value of 90% or more. Thus, in the liquid crystal cell produced from the liquid crystal aligning agent composition of the examples, excellent alignment properties were exhibited and simultaneously a change in haze values before and after the rubbing treatment was very low, i.e., less than 1, indicating that the film strength performance was improved.

(43) In particular, in the case of the liquid crystal aligning agent composition of Example 1, by attaching a protecting functional group such as tert-butoxycarbonyl group to the reactive functional group of the catalyst compound, the storage stability of the liquid crystal aligning agent composition was shown to be 8.3%, and therefore the stability was greatly improved, and also the final liquid crystal alignment film after the heat treatment step could secure excellent alignment properties and rubbing resistance. On the contrary, in the case of the liquid crystal aligning agent composition of Comparative Example 4, it was confirmed that by using a catalyst to which no protecting functional group was bonded, the storage stability of the liquid crystal aligning agent composition was 20.8%, which was greatly increased as compared with that of the examples, and so the stability was decreased.

(44) On the other hand, in the case of the alignment film obtained from the liquid crystal aligning agent composition of Comparative Example 1 containing no catalyst, it was confirmed that the imidization rate at a curing temperature of 230° C. appeared to be 80.5%, which was reduced as compared with that of the examples.

(45) In addition, in the case of the alignment film obtained from the liquid crystal aligning agent composition of Comparative Example 2 containing no epoxy additive, it was confirmed that the change in haze values before and after the rubbing treatment was greatly increased to 5, and so the film strength was remarkably poor as compared with the examples.

(46) 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 Production Example 2-1 was significantly poor in alignment properties as compared with the examples.