Ferroelectric liquid crystal with positive dielectric anisotropy, chevron structure and grey scale

• US 5,353,136 A
• Filed: 12/13/1991
• Issued: 10/04/1994
• Est. Priority Date: 06/17/1989
• Status: Expired due to Fees

• Current Assignee: Hoechst Aktiengesellschaft (Sanofi )
• Original Assignee: Hoechst Aktiengesellschaft (Sanofi )
• Inventors: Illian, Gerhard, Harada, Takamasa, Murakami, Mikio, Dubal, Hans-Rolf, Escher, Claus, Ohlendorf, Dieter
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Parker, Kenneth
• Application Number:
  US07/778,175
• Time in Patent Office: 1,026 Days
• Field of Search: 359/100, 359/104, 359/56, 359/55, 340/784, 345/89, 345/97
• US Class Current: 349/173
• CPC Class Codes: C09K 19/0225 Ferroelectric
• CPC Class Codes: C09K 19/3463 Pyrimidine with a carbon chain containing at least one asymmetric carbon atom, i.e. optically active pyrimidines
• CPC Class Codes: G02F 1/141 using ferroelectric liquid crystals
• CPC Class Codes: G02F 1/1416 Details of the smectic layer structure, e.g. bookshelf, chevron, C1 and C2

Abstract

A method of driving a ferroelectric liquid crystal element which enlarges the effective cone angle. A ferroelectric liquid crystal is held between two substrates such that the helix is suppressed and a chevron layer structure is present. The ferroelectric material has a positive dielectric anisotropy. A first pulse is applied which causes switching from one state to the other, and a subsequent smaller AC pulse is applied which does not cause switching. The second pulse voltage control the effective cone angle, enabling grey scale.

Claims

1. A process for enlarging the effective cone angle in a liquid crystal element comprising a housing, which contains an interstice bordered by a sealing material between two transparent sheets, and additionally at least one polarization film, at least one rubbed orientation layer, furthermore two electrodes on both inner surfaces of the transparent sheets and a liquid-crystalline, ferroelectric smectic material present in the interstice, wherein the liquid-crystalline material firstly forms a chevron structure, and formation of a helix is suppressed, and secondly has spontaneous polarization and a positive dielectric anisotropy, said process comprising firstly applying a pulse of a high voltage (V_s) and a length τ

_s which has the effect that the molecules can be switched from one state to the other, and secondly applying subsequent smaller alternating current pulses (V_ac), which have a length τ

_ac, which is the same or shorter than the length of the first pulse, and which do not allow further switching.

2. The process as claimed in claim 1, wherein the liquid-crystalline material forms an S_c^*, S_F^*, S_G^*, S_I^* or S_J^* phase.

3. The process as claimed in claim 1, wherein the liquid-crystalline material has an N^* phase in a temperature range above the ferroelectric phase.

4. The process as claimed in claim 1, wherein grey steps can be controlled with the aid of the effective value of the voltage.