Display cell with compartmentalized liquid-crystal layer, method for its production and a liquid-crystal material-containing mixture suitable therefor

• US 8,330,902 B2
• Filed: 07/08/2008
• Issued: 12/11/2012
• Est. Priority Date: 07/10/2007
• Status: Expired due to Fees

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Bauer, Monika, Kuschel, Frank, Mueller, Joachim
• Primary Examiner(s): Doan, Jennifer
• Application Number:
  US12/668,416
• Publication Number:
  US 20100195025A1
• Time in Patent Office: 1,617 Days
• Field of Search: 349/56, 349/84, 349/86, 349/88, 349/89, 349/92
• US Class Current: 349/89
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals

Abstract

The invention relates to a display cell, comprising two transparent, equidistant plates, wherein the gap between the plates is filled with a liquid-crystal material-containing layer, characterized in that the liquid-crystal material-containing layer is inhomogeneous and anisotropic, wherein it has a first region made up of compartments, which comprise entirely, substantially or mainly liquid-crystal material, and a second, coherent region which comprises entirely, substantially or mainly an organic polymer material and surrounds the compartments made of liquid-crystal material. In addition, the invention relates to a liquid-crystal material-containing mixture which can be used to produce the layer between the plates, and to a method for producing the display cell.

Claims

1. A display cell comprising:

a first plate and a second plate that are equidistantly spaced from one another, wherein at least the first plate is light-transparent and wherein an intermediate space is formed between the first and second plates;

an inhomogeneous and anisotropic layer disposed in the intermediate space, the layer comprising a liquid crystal material and an organic polymer material, wherein the layer has first regions that are entirely, substantially or mainly comprised of the liquid crystal material and second regions that are entirely, substantially or mainly comprised of the organic polymer material;

wherein the first regions are divided into separate compartments and the second regions surround the compartments;

wherein the organic polymer material is comprised of a first polymer substance and a second polymer substance, wherein the second regions have first areas containing the first polymer substance and second areas containing the second polymer substance;

wherein the second polymer substance has a glass transition temperature that is lower than a glass transition temperature of the first polymer substance;

wherein a lateral expansion of the compartments is greater than a thickness of the layer and/or is in a range of 20 μ

m to 100 μ

m, wherein, when the compartments are surrounded by the second polymer substance, the lateral expansion is in a range of 10 μ

m to 100 μ

m.

2. The display cell according to claim 1, wherein the layer has a thickness of 2 μ

m to 10 μ

m.

3. The display cell according to claim 1, wherein the plates have sides that are facing the intermediate space and the sides are provided with an electrically conducting material.

4. The display cell according to claim 1, wherein the first polymer substance comprises an organic polymer with a glass transition temperature of at least 60°

C., preferably of at least 80°

C., and particularly preferred of at least 100°

C., or comprises a mixture of such organic polymers.

5. The display cell according to claim 1, wherein the first polymer substance is comprised of one or several poly(meth)acrylates or contains the one or several poly(meth)acrylates as a main component.

6. The display cell according to claim 5, wherein the one or several poly(meth)acrylates are selected from homopolymers and copolymers or mixtures thereof.

7. The display cell according to claim 5, wherein at least some of the poly(meth)acrylates are selected from polyalkyl methacrylates or polycycloalkyl methacrylates or mixtures thereof.

8. The display cell according to claim 6, wherein the polyalkyl methacrylates and/or polycycloalkyl methacrylates contain condensed and/or bridged cyclic carbon structures and/or branched alkyl groups.

9. The display cell according to claim 1, wherein the second polymer substance has a glass transition temperature that is near or below a clearing point of the liquid crystal material.

10. The display cell according to claim 9, wherein the second polymer substance is selected from polymethacrylates with at least two carbon atoms in the alcohol portion of the ester, cellulose esters, and polyvinyl acetals.

11. The display cell according to claim 9, wherein some of the compartments are surrounded by the first areas of the first polymer substance and some of the compartments are surrounded by the second areas of the second polymer substance.

12. The display cell according to claim 11, wherein the compartments that are surrounded by the second areas of the second polymer substance have a lateral expansion of less than 20 μ

m.

13. The display cell according to claim 12, wherein the compartments having a diameter of less than 20 μ

m constitute not more than 70%, preferably not more than 50%, and particularly preferred not more than 30% of all of the compartments of the layer.

14. A mixture comprising:

a liquid crystal material;

an organic polymer material that comprises a first polymer substance with a glass transition temperature of at least 60°

C. and a second polymer substance with a glass transition temperature that is below the glass transition temperature of the first polymer substance;

wherein the mixture becomes homogeneous and isotropic upon heating above a clearing point of the liquid crystal material and, upon cooling below the clearing point of the liquid crystal material, separates into first and second regions;

wherein the first regions are comprised entirely, substantially or mainly of the liquid crystal material that is anisotropic,

wherein the second regions entirely, substantially or mainly are comprised of the organic polymer material, wherein the organic polymer material is present in a proportion of 5% by weight to 30% by weight, relative to a sum of the liquid crystal material and the organic polymer material.

15. The mixture according to claim 14, wherein the first polymer substance contains a polyacrylate or polymethacrylate, selected from polyalkyl (meth)acrylates as well as polycycloalkyl(meth)acrylates that comprise at least one substituted or unsubstituted cyclic hydrocarbon and/or a branched alkyl group in the alcohol portion of the esters.

16. The mixture according to claim 15, wherein the substituted or unsubstituted cyclic hydrocarbon is a cycloalkane and/or component of a condensed or bridged cyclic system.

17. The mixture according to claim 15, wherein the first polymer substance is selected from homopolymers and copolymers of the polyacrylates and polymethacrylates or from mixtures thereof.

18. The mixture according to claim 14. wherein the clearing point of the liquid crystal material is near or below the glass transition temperature of the organic polymer material.

19. The mixture according to claim 14, wherein the glass transition temperature of the first polymer substance is at least 80°

C., preferably at least 100°

C.

20. The mixture according to claim 14, wherein the second polymer substance has a glass transition temperature that is near or below the clearing point of the liquid crystal material.

21. The mixture according to claim 20, wherein the second polymer substance is selected from polymethacrylates with at least two carbon atoms in the alcohol portion of the ester, cellulose esters, and polyvinyl acetals.

22. A method for producing a compartmentalized liquid crystal layer in a display cell, comprising:

(a) providing a mixture according to clam 14;

(b) heating the mixture to a temperature above the clearing point of the liquid crystal material;

(c) filling the mixture into a display cell; and

(d) cooling the mixture with a temperature regime that enables separation of the liquid crystal material and the organic polymer material, wherein cooling is carried out so slowly that the first regions of the liquid crystal Material obtain a lateral expansion of 10 μ

m-100 μ

m.

23. The method according to claim 22, wherein the glass transition temperature of the second polymer substance of the organic polymer material is near or below the clearing point of the liquid crystal material.

24. The method according to claim 22, wherein cooling is carried out so slowly that the at least 30% of the first regions of the liquid crystal material obtain a lateral expansion of at least 20 μ

m.

25. The method according to claim 24, wherein cooling is carried out so slowly that at least 50% of the first regions of the liquid crystal material obtain a lateral expansion of at least 20 μ

m.