Device for the regulation of light transmission

Abstract

Devices for the regulation of light transmission and in particular switchable windows, including window elements containing a switchable optical cell having a homeotropically aligned liquid crystal layer with a pretilt angle in the range of 77° to 88°.

Claims

1. A window element comprising a switchable optical cell having a layer structure comprising in this order a first substrate, a first electrode layer, a first alignment layer, a switchable layer, a second alignment layer, a second electrode layer, and a second substrate, wherein the switchable layer is a homeotropically aligned liquid crystal layer comprising a liquid crystalline medium comprising one or more dichroic dyes, wherein, in the optical cell, the first and second alignment layers are in direct contact with the liquid crystalline medium, wherein the switchable optical cell is operable in and electrically switchable between a bright state and a dark state, wherein the window element has a degree of visible light transmission, determined in accordance with DIN EN410, of more than 45% in the bright state and of less than 30% in the dark state, wherein the one or more dichroic dyes preferentially absorb light in one orientation so that light transmission may be modulated by changing the orientation of the one or more dichroic dyes, and wherein a pretilt angle in the range of 84° to 86° is set by at least one of the first alignment layer and the second alignment layer.

2. The window element according to claim 1, wherein the switchable layer has a thickness of at least 5 μm.

3. The window element according to claim 1, wherein, in the absence of an electric field, the switchable layer is homeotropically aligned.

4. The window element according to claim 1, wherein the liquid crystalline medium has a negative dielectric anisotropy Δε, an optical anisotropy Δn in the range of 0.03 to 0.30, and a clearing point of at least 70° C.

5. The window element according to claim 1, wherein a pretilt angle of 84° is set.

6. The window element according to claim 1, wherein the switchable optical cell further comprises one or more polarizer layers and optionally one or more optical retarder layers.

7. The window element according to claim 1, wherein the switchable layer is polymer stabilized.

8. The window element according to claim 1, wherein a pretilt angle of 85° is set by the first alignment layer and the second alignment layer.

9. The window element according to claim 1, wherein the first alignment layer and the second alignment layer comprise a rubbed or phototreated organic material.

10. The window element according to claim 1, wherein the first alignment layer and the second alignment layer are polyimide-based layers.

11. The window element according to claim 1, wherein a pretilt angle of 86° is set.

12. The window element according to claim 1, wherein, in addition to the switchable optical cell, the window element comprises a further switchable optical cell.

13. The window element according to claim 1, wherein the window element has an area of at least 100 cm.sup.2, and wherein the switchable layer is unsegmented or is segmented into compartments each having an area of at least 1 cm.sup.2.

14. The window element according to claim 1, wherein, in the presence of an electric field, the switchable layer has a twisted or supertwisted configuration.

15. The window element according to claim 1, wherein the liquid crystalline medium comprises one or more compounds of formulae CY, PY and/or AC ##STR00306## wherein a denotes 1 or 2, b denotes 0 or 1, c denotes 0, 1 or 2, d denotes 0 or 1, ##STR00307## denotes ##STR00308## ##STR00309## denote ##STR00310## denotes ##STR00311## R.sup.1, R.sup.2, R.sup.AC1 and R.sup.AC2 each, independently of one another, denote alkyl having 1 to 12 C atoms, in which one or two non-adjacent CH.sub.2 groups are optionally replaced by ##STR00312##  —O—, —CH═CH—, —CO—, —COO— or —COO— in such a way that O atoms are not linked directly to one another, Z.sup.x, Z.sup.y and Z.sup.AC each, independently of one another, denote —CH.sub.2CH.sub.2—, —CH═CH—, —CF.sub.2O—, —OCF.sub.2—, —CH.sub.2O—, —OCH.sub.2—, —CO—O—, —O—CO—, —C.sub.2F.sub.4—, —CF═CF—, —CH═CH—CH.sub.2O— or a single bond, and L.sup.1-4 each, independently of one another, denote F, Cl, CN, OCF.sub.3, CF.sub.3, CH.sub.3, CH.sub.2F or CHF.sub.2.

16. The window element according to claim 15, wherein R.sup.1, R.sup.2, R.sup.AC1 and R.sup.AC2 each, independently of one another, denote alkyl or alkoxy having 1 to 6 C atoms, Z.sup.x, Z.sup.y and Z.sup.AC each denote a single bond, and/or L.sup.1-4 each denote F.

17. The window element according to claim 15, wherein L.sup.1 and L.sup.2 denote F or one of L.sup.1 and L.sup.2 denotes F and the other denotes Cl, and both L.sup.3 and L.sup.4 denote F or one of L.sup.3 and L.sup.4 denotes F and the other denotes Cl.

18. A window of a building or a vehicle comprising the window element according to claim 1.

19. The window element according to claim 1, which comprises two switchable optical cells, each comprising in this order a first substrate, a first electrode layer, a first alignment layer, a switchable layer, a second alignment layer, a second electrode layer, and a second substrate, wherein the switchable layer in each optical switchable cell is a homeotropically aligned liquid crystal layer comprising a liquid crystalline medium, and wherein a pretilt angle of 84° to 86° is set by at least one of the first alignment layer and the second alignment layer in each optical switchable cell.

20. The window element according to claim 1, wherein the switchable layer has a thickness of at least 10 μm.

21. The window element according to claim 1, wherein the liquid crystalline medium contains polymerizabe compounds, and wherein all polymerizabe compounds in the liquid crystalline medium are reactive mesogens.

22. The window element according to claim 1, wherein the liquid crystalline medium does not contain a polymerizabe compound.

Description

EXAMPLES

(1) In the Examples,

(2) TABLE-US-00008 V.sub.o denotes threshold voltage, capacitive [V] at 20° C., n.sub.e denotes extraordinary refractive index at 20° C. and 589 nm, n.sub.o denotes ordinary refractive index at 20° C. and 589 nm, Δn denotes optical anisotropy at 20° C. and 589 nm, ϵ∥ denotes dielectric permittivity parallel to the director at 20° C. and 1 kHz, ϵ⊥ denotes dielectric permittivity perpendicular to the director at 20° C. and 1 kHz, Δϵ denotes dielectric anisotropy at 20° C. and 1 kHz, cl.p., denotes clearing point [° C.], T(N, I) γ.sub.1 denotes rotational viscosity measured at 20° C. [mPa .Math. s], determined by the rotation method in a magnetic field, K.sub.1 denotes elastic constant, “splay” deformation at 20° C. [pN], K.sub.2 denotes elastic constant, “twist” deformation at 20° C. [pN], K.sub.3 denotes elastic constant, “bend” deformation at 20° C. [pN].

(3) The term “threshold voltage” for the present invention relates to the capacitive threshold (V.sub.0), unless explicitly indicated otherwise. In the Examples, as is generally usual, the optical threshold can also be indicated for 10% relative contrast (V.sub.10).

Reference Example 1

(4) A liquid crystal host mixture H-1 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

(5) TABLE-US-00009 CY-3-O2  9.00% clearing point [° C.]: 110.5 CY-3-O4  9.00% Δn [589 nm, 20° C.]: 0.132 CY-5-O2 12.00% n.sub.e [589 nm, 20° C.]: 1.62 CY-5-O4  8.00% Δϵ [1 kHz, 20° C.]: −4.9 CCY-3-O2  5.00% ϵ⊥ [1 kHz, 20° C.]: 8.8 CCY-3-O3  5.00% K.sub.1 [pN, 20° C.]: 16.8 CCY-4-O2  5.00% K.sub.3 [pN, 20° C.]: 20.4 CPY-2-O2  7.00% V.sub.0 [V, 20° C.]: 2.14 CPY-3-O2  6.00% PYP-2-3 12.00% CCP—V-1  6.00% CCZPC-3-3  3.00% CCZPC-3-4  3.00% CGPC-3-3  5.00% CGPC-5-3  5.00% Σ 100.00%

(6) A mixture M-1 is prepared by mixing 99.01% of mixture H-1, 0.05% of compound

(7) ##STR00301##
0.16% of compound

(8) ##STR00302##
0.35% of compound

(9) ##STR00303##
and 0.43% of compound

(10) ##STR00304##

Reference Example 2

(11) A liquid crystal base mixture B-2 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

(12) TABLE-US-00010 CC(CN)-4-7 14.00% clearing point [° C.]: 114.6 CC(CN)-5-5 14.00% Δn [589 nm, 20° C.]: 0.045 CC(CN)-3-3  6.00% n.sub.e [589 nm, 20° C.]: 1.52 CCZC-3-3  3.00% Δϵ [1 kHz, 20° C.]: −5.2 CCZC-3-5  3.00% ϵ⊥ [1 kHz, 20° C.]: 8.5 CCZC-4-3  3.00% CCZC-4-5  3.00% CC-3-O1 11.00% CC-5-O1  4.00% CC-5-O2  4.00% CC(CN)C-3-5 10.00% CC(CN)C-5-5 12.00% CC(CN)C-5-3 10.00% CCZPC-3-3  3.00% Σ 100.00%

(13) A mixture M-2 is prepared analogous to mixture M-1 described in Reference Example 1 above, wherein instead of mixture H-1 the mixture B-2 is used.

Reference Example 3

(14) A liquid crystal base mixture B-3 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

(15) TABLE-US-00011 CCZPC-3-3  4.00% clearing point [° C.]: 77.1 CCOC-3-3  4.00% Δn [589 nm, 20° C.]: 0.064 CCOC-4-3  4.00% n.sub.e [589 nm, 20° C.]: 1.54 CCY-3-O1  5.50% Δϵ [1 kHz, 20° C.]: −2.7 CCY-3-O2  5.00% ϵ⊥ [1 kHz, 20° C.]: 6.3 CCY-3-O3  7.50% CCY-4-O2  8.00% CCY-5-O2  7.50% CC-2-3 18.00% CC-3-O1 14.50% CC-3-O3 10.00% CC-5-O1  2.00% Y—4O—O4 10.00% Σ 100.00%

(16) A mixture M-3 is prepared by mixing 99.638% of mixture B-3, 0.332% of the compound of formula S-811 as described in Table F above and 0.030% of the compound of formula

(17) ##STR00305##

Reference Example 4

(18) A liquid crystal base mixture B-4 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

(19) TABLE-US-00012 CY-3-O2 24.50% clearing point [° C.]: 80.5 CCY-3-O2 12.00% Δn [589 nm, 20° C.]: 0.092 CCY-4-O2 10.00% n.sub.e [589 nm, 20° C.]: 1.57 CPY-3-O2  6.50% Δϵ [1 kHz, 20° C.]: −3.3 CC-2-5 11.00% ϵ⊥ [1 kHz, 20° C.]: 6.8 CC-3-4  7.00% CC-3-O1  8.00% CC-3-O3  5.50% CCP-3-1  9.00% PGP-2-4  6.50% Σ 100.00%

(20) A mixture M-4 is prepared by mixing 99.51% of mixture B-4 and 0.49% of the compound of formula S-811 as described in Table F above.

Reference Example 5

(21) A liquid crystal mixture B-5 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

(22) TABLE-US-00013 CC(CN)-4-7 20.00% clearing point [° C.]: 101 CC(CN)-5-5 21.00% Δn [589 nm, 20° C.]: 0.044 CCZC-3-3  4.00% n.sub.e [589 nm, 20° C.]: 1.52 CCZC-3-5  4.00% Δϵ [1 kHz, 20° C.]: −4.8 CCZC-4-3  4.00% ϵ⊥ [1 kHz, 20° C.]: 8.1 CCZC-4-5  4.00% CC-3-O1 11.00% CC-5-O1  5.00% CC-5-O2  5.00% CC(CN)C-5-5 22.00% Σ 100.00%

Reference Example 6

(23) A liquid crystal mixture M-6 is prepared and characterized with respect to its general physical properties, wherein the compound CY-a-1 is defined as specified in the description above.

(24) TABLE-US-00014 compound CY-a-1 24.50% CCY-3-O2 12.00% CCY-4-O2 10.00% CPY-3-O2 6.50% CC-2-5 11.00% CC-3-4 7.00% CC-3-O1 8.00% CC-3-O3 5.50% CCP-3-1 9.00% PGP-2-4 6.50% Σ 100.00%

Comparative Example 1

(25) Two optical cells are assembled each using 2 glass plates (20 mm×26 mm, thickness of 1.1 mm), where each glass plate is coated with an indium tin oxide (ITO) layer (thickness of 50 nm, resistance is 100Ω/□).

(26) For each glass plate, on top of the ITO layer a layer of polyimide (50 nm, JSR, JALS-2096-R1) is applied by spincoating. The polyimide layers are rubbed antiparallel with a velvet cloth (Yoshikawa YA-20R) on a metal roller.

(27) The rubbing induces a pretilt angle of 88.5°, where the pretilt angle is determined using the Mueller Matrix Polarimeter “AxoScan” from Axometrics.

(28) Including plastic spacers having a diameter of 25 μm, two glass plates each with the polyimide layers facing inwards and each other are assembled to form a cell, where a 3 mm offset on the short edge is used to provide cabling access. Apart from filling ports, the cell edges are sealed.

(29) The dye-doped liquid crystalline mixture M-1 as described in Reference Example 1 above is filled in the cells by capillary forces, and the filling ports are sealed. Electric cables are soldered to the offset contact areas of the cells.

(30) The two cells are stacked using double-sided adhesive tape near the edges to form a double cell, where one cell is turned by 90° with respect to the other.

(31) Using a square wave voltage of 30 Vrms the double cell is switched into a dark state having a grainy and irregular appearance, where small bright spots and irregular narrow bright lines are visible. These defects disappear gradually over time. Only after 120 seconds following the switching a dark state is obtained having a uniformly dark appearance.

Comparative Example 2

(32) A switchable cell is assembled analogous to Comparative Example 1 above, wherein however instead a cell thickness of 15 μm and a pretilt angle of 89° are set.

(33) Using a square wave voltage of 20 Vrms for switching, the grainy defects in the initial dark state disappear after 60 seconds to obtain a uniformly dark appearance.

Example 1

(34) Two optical cells are assembled each using 2 glass plates (20 mm×26 mm, thickness of 1.1 mm), where each glass plate is coated with an indium tin oxide (ITO) layer (thickness of 50 nm, resistance is 100 Ω/□).

(35) For each glass plate, on top of the ITO layer a layer of polyimide (50 nm) is applied by spincoating. The polyimide layers are rubbed with a velvet cloth (Yoshikawa YA-20R) on a metal roller using a rotation speed 200 rpm, a moving speed of 25 mm/s and a rubbing depth of 0.3 mm.

(36) The rubbing induces a pretilt angle of 86°, where the pretilt angle is determined using the Mueller Matrix Polarimeter “AxoScan” from Axometrics.

(37) Including plastic spacers having a diameter of 25 μm, two glass plates each with the polyimide layers facing inwards and each other are assembled to form a cell, where a 3 mm offset on the short edge is used to provide cabling access. Apart from filling ports, the cell edges are sealed.

(38) The dye-doped liquid crystalline mixture M-1 as described in Reference Example 1 above is filled in the cells by capillary forces, and the filling ports are sealed. Electric cables are soldered to the offset contact areas of the cells.

(39) The two cells are stacked using double-sided adhesive tape near the edges to form a double cell, where one cell is turned by 90° with respect to the other.

(40) Using a square wave voltage of 30 Vrms the double cell is switched into a dark state having a grainy and irregular appearance, where small bright spots and irregular narrow bright lines are visible. These defects disappear quickly and after 10 seconds after the switching a dark state having a uniformly dark appearance is obtained.

Example 2

(41) A switchable cell is assembled analogous to Example 1 above, wherein however instead a cell thickness of 15 μm and a pretilt angle of 85° are set.

(42) Using a square wave voltage of 20 Vrms for switching, the grainy defects in the initial dark state disappear after 10 seconds to obtain a uniformly dark appearance.

Example 3

(43) A switchable double cell is assembled analogous to Example 1 above, wherein however in each of the cells having a thickness of 25 μm at one polyimide layer a pretilt angle of 86° is set and at the other polyimide layer a pretilt angle of 89° is set.

(44) Using a square wave voltage of 20 Vrms for switching, the grainy defects in the initial dark state disappear after 15 seconds to obtain a uniformly dark appearance.

Example 4

(45) A switchable cell is assembled analogous to Example 1 above using a cell thickness of 25 μm and setting a pretilt angle of 85°, wherein at an applied voltage of 20 V a twisted TN configuration with a twist angle of 90° is provided.

(46) Using a square wave voltage of 20 Vrms for switching, the grainy defects in the initial dark state disappear after less than 10 seconds to obtain a uniformly dark appearance.

(47) The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

(48) Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. From the description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

(49) The entire disclosures of all applications, patents and publications, cited herein and of corresponding EP Patent Application No. 19216581.9, filed Dec. 16, 2019, are incorporated by reference herein.