Light modulation element

Patent metadata

Field	Value
Publication number	US-10416518-B2
Application number	US-201415106656-A
Country	US
Kind code	B2
Filing date	Nov 28, 2014
Priority date	Dec 19, 2013
Publication date	Sep 17, 2019
Grant date	Sep 17, 2019

Abstract

The invention provides a light modulation element comprising a flexoelectric polarisable liquid-crystalline medium, characterized in that the switching from a boundary state A to a boundary state B comprises a combination of a distinct flexoelectric switching regime and a distinct dielectric switching regime upon application of an electric field. Furthermore, the present invention relates to the use of such a light modulation element in an electro-optical device, i.e. an LCD display device, and electrooptical devices comprising the light modulation element according to the present invention. Moreover, the invention relates to a method of production of the light modulation element according to the present invention.

First claim

The invention claimed is:

1. Light modulation element comprising at least two substrates and a flexoelectric polarisable liquid-crystalline medium sandwiched between at least two substrates, wherein the liquid-crystalline medium is homeotropically aligned to both substrate surfaces it is sandwiched between in a boundary state A when no electric field is applied, and wherein the element effects switching from the boundary state A to a boundary state B through a combination of a flexoelectric switching regime and a dielectric switching regime upon application of an electric field, and
wherein the liquid crystal medium comprises at least one bent core compound selected from the compounds of formula I,
R 1 -M 1 -Y 1 —B—Y 2 -M 2 -R 2   I

wherein
Y 1 and Y 2 are in each case independently —O—, —S—, —CO—, —COO—, —OCO—, —OCO—O—, —CO—NR0-, —NR 0 —CO—, —OCH 2 —, —CH 2 O—, —SCH 2 —, —CH 2 S—, —CH═CH—COO—, —OOC—CH═CH— or a single bond,
R 0 is H or alkyl with 1 to 4 C atoms,
M 1 and M 2 are independently of each other a mesogenic group,
B is selected from the following groups:

where L 1 , L 2 and L 3 are selected from F, CN, NO 2 , CH 3 , C 2 H 5 , OCH 3 , OC 2 H 5 , COCH 3 , COC 2 H 5 , COOCH 3 , COOC 2 H 5 , CF 3 , OCF 3 , OCHF 2 , and OC 2 F 5 , and
R 1 and R 2 denote, each and independently from another, H, F, Cl, CN, OCN, SCN, SF 5 , NO 2 or a straight-chain or branched alkyl radical with up to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH 2 groups to be replaced, in each case independently from one another, by —O—, —S—, —NH—, —N(CH 3 )—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CH═CH— or —C≡C— in such a manner that oxygen atoms are not linked directly to one another.

2. The light modulation element according to claim 1 , wherein the liquid-crystalline medium comprises a bent core liquid-crystalline compound having an absolute value of the bend flexoelectric coefficient |e 3 | in the range from 1 pCm −1 to 60 pCm −1 .

3. The light modulation element according to claim 1 , wherein the amount of compounds of formula I in the liquid-crystalline medium as a whole is in the range from 3 to 70%.

4. The light modulation element according to claim 1 , wherein the liquid-crystalline medium comprises one or more compounds of formulae II and III,

in which
R 21 denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms,

on each appearance, independently of one another, denote

L 21 and L 22 denote H or F,
X 21 denotes halogen, halogenated alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxy having 2 or 3 C atoms,
m denotes 0, 1, 2 or 3,
R 31 denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms,

on each appearance, independently of one another, are

L 31 and L 32 independently of one another, denote H or F,
X 31 denotes halogen, halogenated alkyl or alkoxy having 1 to 3 C atoms or halogenated alkenyl or alkenyloxy having 2 or 3 C atoms,
Z 31 denotes —CH 2 CH 2 —, —CF 2 CF 2 —, —COO—, trans-CH═CH—, trans-CF═CF—, —CH 2 O— or a single bond, and
n denotes 0, 1, 2 or 3.

5. The light modulation element according to claim 1 , wherein the liquid-crystalline medium comprises one or more compounds of formula IV

in which
R 41 and R 42 independently of one another, denote alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms,
L 21 and L 22 denote H or F,

independently of one another and, if

occurs twice, also these independently of one another, denote

Z 41 and Z 42 independently of one another and, if Z 41 occurs twice, also these independently of one another, denote —CH 2 CH 2 —, —COO—, trans-CH═CH—, trans-CF═CF—, —CH 2 O—, —CF 2 O—, —C≡C— or a single bond, and
p denotes 0, 1 or 2.

6. The light modulation element according to claim 1 , wherein the liquid-crystalline medium comprises one or more compounds of the formula V,

in which
R 51 and R 52 independently of one another, denote alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy having 1 to 7 C atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl having 2 to 7 C atoms,
L 21 and L 22 denote H or F,

on each appearance, independently of one another, denotes

Z 51 and Z 52 independently of one another and, if Z 51 occurs twice, also these independently of one another, denote —CH 2 CH 2 —, —COO—, trans-CH═CH—, trans-CF═CF—, —CH 2 O—, —CF 2 O— or a single bond, and
r denotes 0, 1 or 2.

7. The light modulation element according to claim 4 , wherein the amount of compounds of the formulae II and/or III in the liquid-crystalline medium as a whole is in the range from 2 to 90%.

8. The light modulation element according to claim 5 , wherein the amount of compounds of the formulae IV in the liquid-crystalline medium as a whole is in the range from 2 to 70%.

9. The light modulation element according to claim 1 , wherein the liquid-crystalline medium exhibits a dielectric positive anisotropy of ≥3.

10. The light modulation element according to claim 1 , wherein the liquid-crystalline medium exhibits a birefringence in the range from 0.10 or more to 0.35 or more.

11. The light modulation element according to claim 1 , wherein the element exhibits light modulation induced by an applied in-plane electric field.

12. The light modulation element according to claim 1 , wherein the element exhibits flexoelectric switching at an applied electric field strength lower than 0.5 V/μm−1.

13. The light modulation element according to claim 1 , wherein the boundary state B has a transmission T B when an electrical field is applied, which is termed in the “on” state, and the element exhibits an induced retardation in the “on”-state in the range from 1 nm to 300 nm.

14. Method for production

Assignees

• Merck Patent Gmbh

Inventors

• Tuffin Rachel
• Proctor Rebecca
• Siemianowski Simon
• Skjonnemand Karl
• Parri Owain Llyr
• Luckhurst Geoffrey

Classifications

• C09K19/04 Primary

  characterised by the chemical structure of the liquid crystal components {, e.g. by a specific unit} · CPC title

• C09K19/2007

  the chain containing -COO- or -OCO- groups · CPC title

• G02F1/1341

  Filling or closing of cells · CPC title

• C09K2019/0481

  Phenylene substituted in meta position · CPC title

• C09K2019/3004

  Cy-Cy · CPC title