Liquid crystal display device and method of manufacturing the same
Provided is a method of manufacturing new liquid crystal display device according to an embodiment of the present invention. Firstly, an alignment film is formed on a substrate. The alignment film is divided into a first alignment film formed using, as a precursor, liquid-state polyimide that contains a photodecomposition substance and a second alignment film formed using, as a precursor, a polyamic acid that does not contain a photodecomposition substance. UV light is irradiated to the alignment film, and decomposed substances formed by irradiation of the UV light is removed by an at least two-step removing process. By the method of manufacturing a liquid crystal display device according to the exemplary embodiment of the present disclosure, bright spots are minimized in pixels and a brightness of black is lowered, so that a liquid crystal display device with a high contrast ratio can be realized.
1. A method of manufacturing a liquid crystal display device, the method comprising:
forming an alignment film on at least one of a pair of substrates, the alignment film having an upper section that is substantially comprised of polyimide with a photo-decomposable material and a lower section that is substantially comprised of polyimide without the photo-decomposable material;
irradiating the alignment film with ultra-violet (UV) light;
performing a chemical impurity molecule removal (C-IMR) process on the alignment film;
performing a thermal impurity molecule removal (T-IMR) process on the alignment film; and
sealing a liquid crystal layer between the pair of substrates,
wherein forming the alignment film includes:
settling a solution of a precursor mixture dispersed in an organic solvent on at least one of the substrates, the precursor mixture including soluble pre-imidized polyimide with the photo-decomposable material, polyamic acid with the photo-decomposable material and polyamic acid without the photo-decomposable material; and
heating the settled solution of precursor mixture and the organic solvent on the substrate to cause imidization of polyamic acid with the photo-decomposable material and polyamic acid without the photo-decomposable material included therein such that the pre-imidized polyimide with the photo-decomposable material and the polyamic acid with the photo-decomposable material form the upper section and the polyamic acid without the photo-decomposable material forms the lower section of the alignment film.
2. The method according to claim 1 , wherein the alignment film has a weight average molecular weight of 10,000 Da to 15,000 Da.
3. The method according to claim 2 , wherein the alignment film including a polyimide chain with a molecular weight of 100,000 Da or more.
4. The method according to claim 1 , wherein the C-IMR process includes applying a lactate-based organic solvent on the alignment film to swell the surface of the alignment film.
5. The method according to claim 4 , wherein the lactate-based organic substance includes at least one of methyl lactate, ethyl lactate, n-propyl lactate, n-butyl lactate and a combination thereof.
6. The method according to claim 5 , wherein the lactate-based organic solvent is ethyl lactate.
7. The method according to claim 6 , wherein the application of ethyl lactate on the alignment film is performed by one of a spray method, a dipping method or a puddle method.
8. The method according to claim 1 , wherein the T-IMR process includes baking the alignment film to restructure the surface of the alignment film.
9. The method according to claim 1 , wherein the C-IMR process is performed for a predetermined duration sufficient to remove high-molecular weight impurities from the alignment film.
10. The method according to claim 9 , wherein the C-IMR process is carried out for a range of 10 to 60 seconds.
11. The method according to claim 9 , wherein the high-molecular weight impurities have at least two or more maleimides.
12. The method according to claim 1 , wherein the T-IMR process is carried out for 1,000 seconds or less.
13. The method according to claim 1 , further comprising:
rinsing the alignment film with deionized (DI) water.
14. The method according to claim 1 , wherein the polyimide with the photo-decomposable material in the precursor mixture is a compound represented by Chemical Formula 1:
wherein, X represents cyclobutane, Y represents an aromatic hydrocarbon group having 2 or more rings, and n represents a natural number.
15. The method according to claim 14 , wherein the polyamic acid without the photo-decomposable material is a compound represented by Chemical Formula 2:
wherein X represents an aromatic hydrocarbon group having 2 or more rings, Y represents an aromatic hydrocarbon group having 1 or more rings, and n represents a natural number.
16. The method according to claim 1 , wherein a volume resistance of the upper section is higher than a volume resistance of the lower section.
17. The method according to claim 16 , wherein the volume resistance of the lower section is 1.0·10 13 Ω·cm or less.
18. The method according to claim 1 , wherein a weight average molecular weight of the lower section is higher than a weight average molecular weight of the upper section.
19. The method according to claim 1 , wherein the photo-decomposable material includes a cyclobutane.
20. The method according to claim 1 , wherein the liquid crystal layer includes negative dielectric anisotropy liquid crystal molecules.