Liquid crystal display material comprising a liquid crystal dispersion in a thermoplastic resin

• US 4,685,771 A
• Filed: 05/22/1986
• Issued: 08/11/1987
• Est. Priority Date: 09/17/1985
• Status: Expired due to Term

• Current Assignee: Kent State University A Nonprofit Organization
• Original Assignee: Kent State University A Nonprofit Organization
• Inventors: West, John L., Zumer, Slobodan, Doane, Joseph W.
• Primary Examiner(s): Arnold, Bruce Y.
• Assistant Examiner(s): Gallivan, Richard F.
• Application Number:
  US06/866,216
• Time in Patent Office: 446 Days
• Field of Search: 350/320, 350/347 R, 350/347 V, 350/350 R, 350/351
• US Class Current: 349/94
• CPC Class Codes: C09K 19/544 as dispersing or encapsulating medium around the liquid crystal
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: Y10S 359/90 Methods

Abstract

The invention provides a new liquid crystal display material prepared by the phase separation of a homogeneous solution of liquid crystal and thermoplastic resin to create in situ microdroplets of liquid crystal within a set transparent resin matrix. The new display material is characterized by ease of fabrication and the ability to be reworked by simple heating and cooling of the thermoplastic resin containing microdroplets of liquid crystal. It has been discovered that such a material fabricated from a thermoplastic resin and a liquid crystal having a liquid crystalline phase to isotropic phase transition temperature above the softening temperature of the resin exhibits a reversible field-independent memory.

Claims

1. A light modulating, liquid crystal-plastic material capable of transmitting and scattering light comprising:

microdroplets of liquid crystal dispersed in a thermoplastic resin, said microdroplets being of a size effective to scatter incident light when the optical axes of said microdroplets are randomly aligned, and said microdroplets being formed by phase separation from a homogeneous solution of said liquid crystal and thermoplastic resin.

2. A liquid crystal-plastic material as claimed in claim 1 wherein said liquid crystal has a liquid crystalline to isotropic phase transition temperature above the softening temperature of the thermoplastic resin.

3. A liquid crystal-plastic material as claimed in claim 1 wherein said liquid crystal comprises a liquid crystal selected from the group consisting of nematic and smectic liquid crystals.

4. A light modulating, liquid crystal-plastic material capable of transmitting and scattering light and having an erasable image memory comprising:

microdroplets of liquid crystal dispersed in a thermoplastic resin, said microdroplets being of a size effective to scatter incident light when the optical axes of said microdroplets are randomly aligned, said microdroplets being formed by phase separation from a homogeneous solution of said liquid crystal and said resin, and said liquid crystal having the characteristic of remaining in the liquid crystalline phase when the resin is softened so that the microdroplets are oriented by the application of an electric or magnetic field and maintain the orientation when the resin is hardened and the field is removed.

5. A method of making a light modulating, liquid crystal-plastic material capable of transmitting and scattering light comprising the steps of:

forming a homogeneous solution of liquid crystal and a thermoplastic resin;

phase separating and spontaneously forming microdroplets of liquid crystal in the resin; and

hardening the resin to form a matrix in which said microdroplets are dispersed.

6. A liquid crystal-plastic material as claimed in claim 5 wherein said liquid crystal has a liquid crystalline to isotropic phase transition temperature above the softening temperature of the thermoplastic resin.

7. A liquid crystal-plastic material as claimed in claim 5 wherein said liquid crystal comprises a liquid crystal selected from the group consisting of nematic and smectic liquid crystals.

8. A method of making a liquid crystal-plastic material as claimed in claim 5 wherein the step of forming the homogeneous solution is carried out by dissolving the liquid crystal in the thermoplastic resin heated to a temperature effective to cause dissolution of the liquid crystal and wherein the step of phase separating and spontaneously forming microdroplets of liquid crystal is effected by cooling said solution.

9. A method of making a liquid crystal-plastic material as claimed in claim 5 wherein the step of forming the homogeneous solution is carried out by dissolving the liquid crystal and the resin in a solvent and the step of phase separating and spontaneously forming microdroplets of liquid crystal is effected by evaporating said solvent.

10. A method of making a liquid crystal-plastic material as claimed in claim 5 wherein the step of phase separating and spontaneously forming the microdroplets is effected by polymerizing said resin.

11. A method of making a liquid crystal-plastic material as claimed in claim 10 wherein resin comprises an uncured resin and a curing agent.

12. A method of making a light modulating, liquid crystal-plastic material comprising the steps of:

forming a homogeneous solution of thermoplastic resin and liquid crystal; and

polymerizing said resin while phase separating said liquid crystal to spontaneously form microdroplets of liquid crystal dispersed in a polymerized resin matrix.

13. A method of making a light modulating, liquid crystal-plastic material as claimed in claim 12 wherein the thermoplastic resin comprises an uncured resin and a curing agent.

14. A method of making a light modulating, liquid crystal-plastic material capable of transmitting and scattering light comprising the steps of forming a homogeneous solution by dissolving a liquid in a thermoplastic resin heated to a temperature effective to cause dissolution of the liquid crystal and cooling said solution while phase separating said liquid crystal to spontaneously form microdroplets of liquid crystal dispersed in a hardened resin matrix.

15. A method of making a light modulating, liquid crystal-plastic material capable of transmitting and scattering light comprising the steps of:

forming a homogeneous solution by dissolving a thermoplastic resin and liquid crystal in a solvent; and

evaporating said solvent while phase separating said liquid crystal to spontaneously form microdroplets of liquid crystal dispersed in a hardened resin matrix.

16. A method of making a light modulating, liquid crystal material having optical memory comprising the steps of:

forming a homogeneous solution of liquid crystal and a thermoplastic resin, said liquid crystal having a liquid crystalline to isotropic phase transition temperature above the softening temperature of the resin;

phase separating and spontaneously forming microdroplets of liquid crystal in the resin; and

hardening the resin to from a matrix in which said microdroplets are dispersed.

17. The method as claimed in claim 16 wherein the liquid crystal comprises a liquid crystal selected from the group consisting of nematic and smectic liquid crystals.

18. A method of making a material having optical memory comprising the steps of:

heating a thermoplastic resin containing dispersed microdroplets of liquid crystal, said liquid crystal having a liquid crystalline phase to isotropic phase transition temperature above the softening temperature of the resin;

applying an electric or magnetic field sufficient to align the optical axes of the liquid crystal; and

cooling the resin in the presence of said field to form microdroplets of liquid crystal which are optically aligned in the resin.

19. A method of preparing a material having optical memory comprising the steps of:

softening a resin containing dispersed microdroplets of liquid crystal;

orienting the liquid crystal microdroplets in a selected area of the resin; and

rehardening the resin while maintaining the liquid crystal microdroplets in the oriented position.

20. A method of preparing a material capable of polarizing incident light comprising the steps of:

softening a resin containing dispersed microdroplets of liquid crystal;

stretching the resin to orient the microdroplets in the direction of stretch; and

rehardening the resin while maintaining the stretch.

21. A method of plasticizing a thermoplastic resin useful for liquid crystal display devices comprising the step of lowering the softening temperature of the thermoplastic resin by forming a homogeneous solution of thermoplastic resin and liquid crystal, and phase separating microdroplets of liquid crystal from the solution so that a part of the liquid crystal is in the form of phase separated microdroplets and part of the liquid crystal remains in homogeneous solution.

22. The method as claimed in claim 21 including the further step of hardening the resin to form a matrix containing dissolved liquid crystals and dispersed microdroplets of liquid crystal.