Polyimides for anchoring liquid crystals, display devices including same and method for the preparation of said devices

• US 7,022,809 B2
• Filed: 05/30/2002
• Issued: 04/04/2006
• Est. Priority Date: 05/31/2001
• Status: Active Grant

• Current Assignee: Nemoptic SA
• Original Assignee: Nemoptic SA
• Inventors: Gallaire, Didier, Dubois, Jean-Claude, Lamarque, Sandrine
• Primary Examiner(s): HAMPTON HIGHTOWER, PATRICIA
• Application Number:
  US10/479,274
• Publication Number:
  US 20040161541A1
• Time in Patent Office: 1,405 Days
• Field of Search: 528/353, 528/125, 528/126, 528/128, 528/172, 528/174, 528/26, 528/176, 528/183, 528/188, 528/220, 528/229, 528/350, 528/351, 428/1.26, 428/1.1, 428/1.3, 428/1.6, 428/473.5, 428/1.2, 427/385.5
• US Class Current: 528/353
• CPC Class Codes: C08G 73/1039 comprising halogen-containing substituents
• CPC Class Codes: C09B 57/08 Naphthalimide dyes; Phthalimide dyes
• CPC Class Codes: C09K 2323/00 Functional layers of liquid crystal optical display excluding electroactive liquid crystal layer characterised by chemical composition
• CPC Class Codes: C09K 2323/02 Alignment layer characterised by chemical composition
• CPC Class Codes: C09K 2323/027 Polyimide
• CPC Class Codes: G02F 1/133723 Polyimide, polyamide-imide
• CPC Class Codes: Y10T 428/31721 Of polyimide

Abstract

The present invention relates to novel polyimides derived from 6FDA and from 3,3-dihydroxy-4,4′-diaminobiphenyl and novel polyimides derived from PMDA and from Bis-AP-AF, having alkyl, arylalkyl, heteroarylalkyl, (cycloalkyl)alkyl, fluoroalkyl or siloxane side groups.

The present invention also relates to a method of producing nematic liquid-crystal devices, which comprises the steps consisting in:

• • depositing one of the polyimides according to the invention on a substrate;
  • annealing the polyimide in one or more steps; and
  • defining an azimuthal orientation of the polyimide coating.

Claims

1. Polyimides for producing low-energy anchoring layers in nematic liquid-crystal cells, according to the following types:

polyimide derived from 2,2′

-bis (3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and from 3,3′

-dihydroxy-4, 4′

diaminobiphenyl of formula I;

in which the radicals R₁ and R₂, which are identical or different, represent an alkyl, arylalkyl, heteroarylalkyl, (cycloalkyl)alkyl, fluoroalkyl or siloxane radical and n is between 1 and 20;

polyimide derived from pyromellitic anhydride (PMDA) and from 2,2-bis (3-amino-4-hydroxyphenyl)hexafluoropropane (Bis-AP-AF) of formula II.

in which the radicals R₃ and R₄, which are identical or different, have the same meaning as R₁ and R₂ and n is between 1 and 20; and

copolymers of polyimide (I) and of polyimide (II).

2. The polyimides as claimed in claim 1, wherein the radicals R₁ and R₂ are identical and the radicals R₃ and R₄ are identical and represent independently of one another:

a C₈ and C₁₈ alkyl;

or

2-(1-adamantyl)ethyl or 2-(cyclohexyl)ethyl;

or

a phenyl alkyl, especially 8-phenyl octyl or 2-phenyl ethyl;

or 2-(9-carbazolyl) ethyl.

3. The polyimides of formula (II) as claimed in claim 2, wherein the radicals R₃ and R₄ and the radicals R₁ and R₂ are identical and represent n-dodecyl or 2-(cyclohexyl) ethyl.

4. A method for producing nematic liquid-crystal cells with confining plates, which comprises the steps of:

depositing a polyimide as claimed in claim 1 on a substrate;

annealing the polyimide in one or more steps at a temperature of between 100°

C. and 230°

C. for a time of between a few minutes and 2 hours; and

defining an azimuthal orientation of the polyimide coating, inducing control of azimuthal anchoring of the liquid crystal in order to obtain a low zenithal anchoring energy of the liquid crystal on at least one of its confining plates.

5. The method as claimed in claim 4, wherein one or more annealing operations are carried out during the various steps before or after the step consisting in defining the controlled azimuthal anchoring of the liquid crystal.

6. The method as claimed in claim 4, wherein the annealing is carried out at a temperature of around 200°

C. for one hour.

7. The method as claimed in claim 4, wherein the step of azimuthally orienting the liquid crystal is provided by rubbing the polyimide with a fabric roller.

8. The method as claimed in claim 4, wherein the step of defining the controlled azimuthal anchoring of the liquid crystal is provided by depositing the polyimide on a substrate already made anisotropic by a particular treatment, such as another drawn polymer, SiO or another evaporated oxide, or a grating which is etched in the substrate, printed or photoinduced.

9. The method as claimed in claim 4, wherein the polyimide is deposited on a substrate by spin coating.

10. The method as claimed in claim 4, characterized in that the polyimide is deposited in solution in a solvent based on dioxane, tetrahydrofurane, N-methylpyrrolidone, dimethyl sulfoxide or dimethylfonnamide.

11. The method as claimed in claim 4, wherein the thickness of the polyimide coating is between a few nanometers and 100 nm.

12. A bistable nematic liquid-crystal device using at least one low-energy anchoring layer produced according to the method as claimed in claim 4.

13. The device as claimed in claim 12, wherein the anchoring layer is deposited on a transparent or reflecting electrode.

14. The bistable nematic liquid-crystal device comprising at least one confining plate on which a substrate comprising a polyimide as claimed in claim 1 is deposited.

15. A method of preparing polyimides as claimed in claim 1, which employs a Mitsunobu reaction.

16. The polyimides as claimed in claim 2, wherein the C₈ and C₁₈ alkyl are selected from the group consisting of n-octyl, n-dodecyl, n-octadecyl and 2-(ethyl)hexyl.