LIQUID CRYSTAL ALIGNMENT FILM, METHOD FOR PREPARING THE SAME AND LIQUID CRYSTAL DISPLAY DEVICE USING THE SAME

Abstract

The present invention provides a liquid crystal alignment film not only having an excellent alignment property and stability, but also having high film strength, and thus exhibiting excellent durability and a high residual image property, a method for preparing the same, and a liquid crystal display device using the same.

Claims

1-8. (canceled)

9. A method for preparing a liquid crystal alignment film including the steps of: 1) coating a liquid crystal aligning agent composition onto a substrate to form a coating film; 2) drying the coating film; 3) irradiating the coating film with light immediately after the drying step to perform alignment treatment; 4) subjecting the alignment-treated coating film to a low-temperature heat treatment at 200 C. or lower; and 5) subjecting the heat-treated coating film to heat treatment at a higher temperature than that of the low-temperature heat treatment to cure it, wherein the liquid crystal aligning agent composition includes: i) a first polymer for a liquid crystal aligning agent including at least two repeating units selected from the group consisting of a repeating unit represented by Chemical Formula 21 below, a repeating unit represented by Chemical Formula 22 below, and a repeating unit represented by Chemical Formula 23 below, wherein the repeating unit represented by Chemical Formula 21 below is contained in an amount of 5 mol % to 74 mol % relative to the entire repeating units represented by Chemical Formulae 21 to 23 below; ii) a second polymer for a liquid crystal aligning agent including a repeating unit represented by Chemical Formula 24 below; and iii) a reactive mesogenic epoxy: ##STR00024## wherein, in Chemical Formulae 21 to 24, R.sup.22 and R.sup.23 are each independently hydrogen or a C.sub.1-10 alkyl, with the proviso that R.sup.22 and R.sup.23 are not all hydrogen, R.sup.24 and R.sup.25 are each independently hydrogen or a C.sub.1-10 alkyl, and X.sup.11 is a tetravalent organic group represented by Chemical Formula 25 below: ##STR00025## wherein, in Chemical Formula 25, R.sup.26 to R.sup.29 are each independently hydrogen or a C.sub.1-6 alkyl, X.sup.12, X.sup.13, and X.sup.14 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 hydrogen in the tetravalent organic groups is substituted with a halogen or in which at least one CH.sub.2 is substituted with O, CO, S, SO, SO.sub.2, or CONH, so that it is not directly bonded to oxygen or sulfur atoms, and Y.sup.11, Y.sup.12, Y.sup.13, and Y.sup.14 are each independently a divalent organic group represented by Chemical Formula 26 below: ##STR00026## wherein, in Chemical Formula 26, R.sup.30 and R.sup.31 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, h and i are each independently an integer of 0 to 4, L.sup.3 is a single bond, O, CO, S, SO.sub.2, C(CH.sub.3).sub.2.sup., 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.2C(CH.sub.3).sub.2CH.sub.2O, COO(CH.sub.2).sub.zOCO, or OCO(CH.sub.2).sub.zCOO, z is an integer of 1 to 10, and j is an integer of 0 to 3.

10. The method for preparing a liquid crystal alignment film of claim 9, wherein the X.sup.12, X.sup.13, and X.sup.14 are each independently a tetravalent organic group represented by Chemical Formula 27 below: ##STR00027## wherein, in Chemical Formula 27, R.sup.32 to R.sup.35 are each independently hydrogen or a C.sub.1-6 alkyl, L.sup.4 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.zOCO, and z is an integer of 1 to 10.

11. The method for preparing a liquid crystal alignment film of claim 9, wherein the reactive mesogenic epoxy is represented by Chemical Formula 28 below:
R.sup.36-MG-R.sup.36[Chemical Formula 28] wherein, in Chemical Formula 28, R.sup.36 is glycidyloxy or N(glycidyloxy).sub.2, and MG is a divalent mesogenic group.

12. The method for preparing a liquid crystal alignment film of claim 11, wherein the MG is represented by Chemical Formula 29 below: ##STR00028## wherein, in Chemical Formula 29, Ar.sub.3 and Ar.sub.4 are each independently phenylene or naphthylene, each L.sup.5 is independently a single bond, an alkylene having 1 to 3 carbon atoms, COO, C(CH.sub.3)CH, or C(CH.sub.3)NNC(CH.sub.3), n is 0, 1, or 2, and m is an integer of 1.

13. The method for preparing a liquid crystal alignment film of claim 11, wherein the MG is any one selected from the groups listed below: ##STR00029##

14. The method for preparing a liquid crystal alignment film of claim 9, wherein the mesogenic epoxy is included in an amount of 0.1% by weight to 30% by weight relative to the weight of the polymers for the liquid crystal aligning agent.

15. The method for preparing a liquid crystal alignment film of claim 9, wherein the first polymer for the liquid crystal aligning agent and the second polymer for the liquid crystal aligning agent may be mixed in a weight ratio of 15:85 to 85:15.

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

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

18. The method for preparing a liquid crystal alignment film of claim 9, wherein the low-temperature heat treatment of Step 4 is performed at 110 C. to 200 C.

19. The method for preparing a liquid crystal alignment film of claim 9, wherein the heat treatment of Step 5 is performed at 200 C. to 250 C.

20. (canceled)

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0164] Hereinafter, 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: Synthesis of Diamine

[0165] ##STR00019##

[0166] Cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA) 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 mixture was reduced at 45 C. under hydrogen pressure of 6 bar for 20 minutes to prepare a diamine

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

[0167] (Step 1)

[0168] 5.0 g (13.3 mmol) of the diamine prepared in Preparation Example 1 was completely dissolved in 71.27 g of anhydrous N-methyl pyrrolidone (NMP).

Then, 2.92 g (13.03 mmol) of 1,3-dimethyl-cyclobutane-1,2,3,4-tetracarboxylic dianhydride was added to the solution under an ice bath and stirred at room temperature for 16 hours.

[0169] (Step 2)

[0170] 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 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.

[0171] 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 the imine structure in the molecule was 50.5%, while the ratio of the amic acid structure was 49.5%.

Preparation Example 3: Preparation of Polymer for Liquid Crystal Aligning Agent Q-1

[0172] 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. Subsequently, the polymer Q-1 was prepared in the same manner as in Step 2 of Preparation Example 2.

Example 1

[0173] (1) Preparation of Liquid Crystal Aligning Agent Composition

[0174] 5 parts by weight of P-1 prepared in Preparation Example 2, 5 parts by weight of Q-1 prepared in Preparation Example 3, and 0.8 parts by weight of 4-(oxiran-2-ylmethoxy)phenyl 4-(oxiran-2-ylmethoxy)benzoate (8% by weight relative to the polymer for the liquid crystal aligning agent) were completely dissolved in a mixed solvent of NMP and n-butoxyethanol in 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 m to prepare a liquid crystal aligning agent composition.

[0175] (2) Preparation of Liquid Crystal Alignment Film

[0176] The liquid crystal aligning agent composition prepared in Example 1 was coated onto a substrate (lower plate) in which comb-shaped IPS mode-type ITO electrode patterns having a thickness of 60 nm, an electrode width of 3 m, and spacing between the electrodes of 6 m are formed on a rectangular glass substrate having a size of 2.5 cm2.7 cm and onto a glass substrate (upper plate) having no electrode pattern each using a spin coating method.

[0177] Then, the substrates onto which the liquid crystal aligning agent composition was coated were placed on a hot plate at about 80 C. for one minute to evaporate the solvent. In order to align the thus-obtained coating film, ultraviolet light of 254 nm was irradiated with an intensity of 0.3 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.

[0178] Subsequently, the coating film was placed on a hot plate at 130 C. for 500 seconds, thereby subjecting it to a low-temperature heat treatment. Then, the coating film was calcinated (cured) in an oven at about 230 C. for 20 minutes to obtain a liquid crystal alignment film having a film thickness of 0.1 m.

Example 2

[0179] A liquid crystal aligning agent composition and liquid crystal alignment film were prepared in the same manner as in Example 1, except that 4-(oxiran-2-ylmethoxy)phenyl 4-(oxiran-2-ylmethoxy)benzoate was used in an amount of 1.0 part by weight (10% by weight relative to the polymer for the liquid crystal aligning agent).

Example 3

[0180] A liquid crystal aligning agent composition and liquid crystal alignment film were prepared in the same manner as in Example 1, except that 1,4-phenylene bis(4-(oxiran-2-ylmethoxy)benzoate) was used instead of 4-(oxiran-2-ylmethoxy)phenyl 4-(oxiran-2-ylmethoxy)benzoate.

Comparative Example 1

[0181] A liquid crystal aligning agent composition and liquid crystal alignment film were prepared in the same manner as in Example 1, except that the following compound (BATG) was used instead of 4-(oxiran-2-ylmethoxy)phenyl 4-(oxiran-2-ylmethoxy)benzoate.

##STR00020##

Comparative Example 2

[0182] A liquid crystal aligning agent composition and liquid crystal alignment film were prepared in the same manner as in Example 1, except that the following compound (CDMDG) was used instead of 4-(oxiran-2-ylmethoxy)phenyl 4-(oxiran-2-ylmethoxy)benzoate.

##STR00021##

Comparative Example 3

[0183] A liquid crystal aligning agent composition and liquid crystal alignment film were prepared in the same manner as in Example 1, except that the low-temperature heat treatment was omitted and the calcination (curing) temperature was adjusted to 240 C.

Comparative Example 4

[0184] A liquid crystal aligning agent composition and liquid crystal alignment film were prepared in the same manner as in Example 2, except that the low-temperature heat treatment was omitted and the calcination (curing) temperature was adjusted to 240 C.

Comparative Example 5

[0185] A liquid crystal aligning agent composition and liquid crystal alignment film were prepared in the same manner as in Example 1, except that 4-(oxiran-2-ylmethoxy)phenyl 4-(oxiran-2-ylmethoxy)benzoate was not used.

Experimental Example

[0186] A sealing agent impregnated with a ball spacer having a size of 3 m was applied to the edge of the upper plate except the liquid crystal injection hole. Further, the alignment films of the examples and comparative examples 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. Subsequently, a liquid crystal was injected into the empty cells to produce a parallel-alignment mode liquid crystal cell.

[0187] (1) Retardation (R)

[0188] The retardation (R) of the liquid crystal alignment films obtained in the examples and comparative examples was measured. Specifically, each retardation was measured by irradiating polarized light having a wavelength of 550 nm using AxoStep equipment, manufactured by Axometrics, and the average value of the measured values for 5 repeated measurements is shown in Table 1 below.

[0189] (2) Film Strength

[0190] The film strength for the alignment films obtained in the examples and comparative examples was measured, and the results are shown in Table 1 below. Specifically, the film strength of the alignment films was measured via a pencil hardness tester according to the ASTM D3363 test standard by loading a weight of 50 g and using pencils of various hardnesses.

[0191] (3) Brightness Fluctuation Rate

[0192] The brightness fluctuation rate of the prepared liquid crystal cells was measured using the liquid crystal alignment films obtained in the examples and comparative examples. Specifically, polarizing plates were adhered to the upper plate and the lower plate of the liquid crystal cells such that they were perpendicular to each other. Then, the liquid crystal cells, to which the polarizing plates were adhered, were adhered onto a backlight of 7000 cd/m.sup.2, and the brightness in a black mode was measured using PR-880 equipment, which is a device for measuring brightness. Then, the liquid crystal cells were driven at room temperature for 24 hours with an AC voltage of 5 V. Subsequently, the brightness in a black mode was measured in the same manner as described above in a state in which the voltage of the liquid crystal cells was turned off, and the results are shown in Table 1 below.

[0193] The difference between the initial luminance (L0) measured before driving the liquid crystal cell and the luminance (L1) measured after driving was divided by the initial luminance (L0) and multiplied by 100 to calculate the brightness fluctuation rate. As the thus-calculated brightness fluctuation rate is closer to 0%, it means that the alignment stability is excellent.

TABLE-US-00001 TABLE 1 Retar- Brightness Epoxy dation Film fluctuation Category additives (nm) strength rate Example 1 A-1 8.3 3H 2.7% (8% by weight relative to the polymer for the liquid crystal aligning agent) Example 2 A-1 7.9 4H 2.9% (10% by weight relative to the polymer for the liquid crystal aligning agent) Example 3 A-2 8.7 3H 2.5% (8% by weight relative to the polymer for the liquid crystal aligning agent) Comparative B-1 2.6 3H 8.4% Example 1 (8% by weight relative to the polymer for the liquid crystal aligning agent) Comparative B-2 2.4 3H 7% Example 2 (8% by weight relative to the polymer for the liquid crystal aligning agent) Comparative A-1 2.3 3H 4% Example 3 (8% by weight relative to the polymer for the liquid crystal aligning agent) Comparative A-1 2.8 4H 6% Example 4 (10% by weight relative to the polymer for the liquid crystal aligning agent) Comparative 3.9 0H 2.1% Example 5 *A-1: 4-(oxiran-2-ylmethoxy)phenyl 4-(oxiran-2-ylmethoxy)benzoate *A-2: 1,4-phenylene bis(4-(oxiran-2-ylmethoxy)benzoate) *B-1: BATG [00022]*B-2: CDMDG [00023]

[0194] As shown in Table 1 above, when the epoxy additives with different structures compared to those of the examples were used similarly to Comparative Examples 1 and 2, it was confirmed that the retardation value was significantly lower than those of the examples, and the brightness fluctuation rate was increased. From this, it was confirmed that, in the case of the liquid crystal alignment films obtained by using the phenyl benzoate-based RM (reactive mesogen) epoxy additive, the retardation is increased, thereby implementing excellent AC residual image properties, and also the brightness fluctuation rate is reduced, thereby implementing excellent aligning stability.

[0195] In addition, in Table 1, similarly to Comparative Examples 3 and 4, although the same amount of the phenyl benzoate-based epoxy additive was used, when the low-temperature heat treatment was omitted and the calcination (curing) temperature was adjusted to 240 C., it was confirmed that the retardation value was significantly lower than those of the examples, and the brightness fluctuation rate was increased. From this, it was confirmed that, similarly to the examples, as curing was carried out after heat treatment, the retardation of the finally prepared alignment film is increased, thereby implementing excellent AC residual properties, and also the brightness fluctuation rate is reduced, thereby implementing excellent aligning stability.

[0196] Meanwhile, similarly to Comparative Example 5, when no phenyl benzoate-based epoxy additives were added, it was confirmed that the film strength was significantly reduced compared to those of the examples, and thus the strength of the liquid crystal alignment films can be enhanced by using the specific epoxy additives in the examples.