Alignment film material comprising polyimide and a vinyl-type monomer, alignment film comprising polyimide and polyvinyl compound, method of forming the alignment film, and liquid crystal display having the same

1. An alignment film material comprising:

a precursor of a first polyimide;

at least one of a second polyimide and a precursor thereof, the second polyimide being different from the first polyimide; and

a vinyl-type monomer having a vinyl group, wherein the vinyl-type monomer is represented by general formula (1) P1-A1-(Z1-A2)n-P2 (in general formula (1), P1 and P2 are, independently, acrylate, methacrylate, acrylamide or methacrylamide; A1 and A2 represent, independently, 1,4-phenylene, 1,4-cyclohexane or 2,5-thiophene, or naphthalene-2,6-diyl or anthracene-2,7-diyl; at least one of A1 and A2 is substituted by at least one fluorine group; and Z1 is a —COO— group, a —OCO— group, a —O— group, a —CONH— group or a single bond, where n is 0 or 1).

2. The alignment film material of claim 1 , wherein the vinyl-type monomer is a bifunctional monomer having a symmetric structure.

3. The alignment film material of claim 1 , wherein the vinyl-type monomer is a dimethacrylate monomer.

4. The alignment film material of claim 1 , wherein the vinyl-type monomer is represented by structural formula (1a)

5. The alignment film material of claim 1 , wherein the precursor of the first polyimide is represented by general formula (2)

6. The alignment film material of claim 1 , wherein a side chain of the precursor of the first polyimide does not have any vertical alignment groups.

7. The alignment film material of claim 1 , wherein,

the precursor of the second polyimide is represented by general formula (3); and

the second polyimide is represented by general formula (3′)

8. The alignment film material of claim 1 , wherein the second polyimide has a side chain including a fluorine group.

9. The alignment film material of claim 1 , wherein the second polyimide has a photoreactive functional group.

10. The alignment film material of claim 9 , wherein the photoreactive functional group is at least one selected from the group consisting of a cinnamate group, a chalcone group, a tolan group, a coumarin group, and an azobenzene group.

11. The alignment film material of claim 9 , wherein at least one of the second polyimide and the precursor thereof has a side chain represented by general formula (4)

12. The alignment film material of claim 1 , wherein at least one of the second polyimide and the precursor thereof has a side chain including a vertical alignment group.

13. The alignment film material of claim 1 , wherein a concentration of the vinyl-type monomer on the basis of the alignment film material is no less than 2 wt % and no more than 20 wt %.

14. An alignment film comprising:

a first polyimide;

a second polyimide different from the first polyimide; and

a polyvinyl compound resulting from polymerization of a vinyl-type monomer, wherein

the vinyl-type monomer is represented by general formula (1) P1-A1-(Z1-A2)n-P2 (in general formula (1), P1 and P2 are, independently, acrylate, methacrylate, acrylamide or methacrylamide; A1 and A2 represent, independently, 1,4-phenylene, 1,4-cyclohexane or 2,5-thiophene, or naphthalene-2,6-diyl or anthracene-2,7-diyl; at least one of A1 and A2 is substituted by at least one fluorine group; and Z1 is a —COO— group, a —OCO— group, a —O— group, a —CONH— group or a single bond, where n is 0 or 1).

15. The alignment film of claim 14 , wherein the alignment film has a first alignment layer containing the first polyimide and a second alignment layer containing the second polyimide.

16. The alignment film of claim 15 , wherein the polyvinyl compound is present within the second alignment layer and on a surface of the second alignment layer.

17. A liquid crystal display device comprising:

an active matrix substrate having a pixel electrode;

a counter substrate having a counter electrode; and

a vertical-alignment type liquid crystal layer provided between the active matrix substrate and the counter substrate, wherein,

at least one of the active matrix substrate and the counter substrate further includes an alignment film provided on the liquid crystal layer side;

the alignment film includes

a first polyimide,

a second polyimide different from the first polyimide, and

a polyvinyl compound resulting from polymerization of a vinyl-type monomer; and

the vinyl-type monomer is represented by general formula (1) P1-A1-(Z1-A2)n-P2 (in general formula (1), P1 and P2 are, independently, acrylate, methacrylate, acrylamide or methacrylamide; A1 and A2 represent, independently, 1,4-phenylene, 1,4-cyclohexane or 2,5-thiophene, or naphthalene-2,6-diyl or anthracene-2,7-diyl; at least one of A1 and A2 is substituted by at least one fluorine group; and Z1 is a —COO— group, a —OCO— group, a —O— group, a —CONH— group or a single bond, where n is 0 or 1).

18. The liquid crystal display device of claim 17 , wherein the alignment film has a first alignment layer containing the first polyimide and a second alignment layer containing the second polyimide.

19. The liquid crystal display device of claim 18 , wherein,

the second alignment layer is provided so as to be closer to the liquid crystal layer than is the first alignment layer; and

the polyvinyl compound is present within the second alignment layer and on a surface of the second alignment layer.

20. The liquid crystal display device of claim 17 , wherein the alignment film regulates liquid crystal molecules in the liquid crystal layer so that the liquid crystal molecules are inclined with respect to a normal direction of a principal face of the alignment film in the absence of an applied voltage.

21. The liquid crystal display device of claim 17 , wherein

the liquid crystal display device has a plurality of pixels; and

in each of the plurality of pixels, the liquid crystal layer has a plurality of liquid crystal domains having respectively different reference alignment azimuths.

22. The liquid crystal display device of claim 21 , wherein the plurality of liquid crystal domains are four liquid crystal domains.

23. A method of forming an alignment film, comprising the steps of:

providing an alignment film material containing a precursor of a first polyimide, at least one of a second polyimide and a precursor thereof, and a vinyl-type monomer, the second polyimide being different from the first polyimide;

applying the alignment film material; and

heating the alignment film material so that at least a portion of the precursor of the first polyimide is imidized into the first polyimide and that the vinyl-type monomer is polymerized to form a polyvinyl compound,

wherein, in the step of providing the alignment film material the vinyl-type monomer is represented by general formula (1) P1-A1-(Z1-A2)n-P2 (in general formula (1), P1 and P2 are, independently, acrylate, methacrylate, acrylamide or methacrylamide; A1 and A2 represent, independently, 1,4-phenylene 1,4-cyclohexane or 25-thiophene, or napthalene-2,6-diyl or anthracene-2,7-diyl; at least one of A1 and A2 is substituted by at least one fluorine group; and Z1 is a —COO— group, a —OCO— group, a —O— group, a —CONH— group or a single bond, where n is 0 or 1).

24. The method of forming an alignment film of claim 23 , wherein, after the step of heating, a fraction of imide units of the second polyimide is greater than a fraction of imide units of the first polyimide.

25. The method of forming an alignment film of claim 23 , wherein the step of applying the alignment film material comprises a step of performing the application of the alignment film material by a printing technique, an ink jet technique, or a spin coating technique.