OPTICAL SWITCHING DEVICE

Abstract

An optical switching device comprising a polarisation layer and a switching layer which comprises a liquid-crystalline material and a dye compound. Use of the optical switching device for the regulation of the passage of light through an area element. A window element which has the optical switching device therein.

Claims

1. Optical switching device comprising a polarisation layer, and arranged parallel to the polarisation layer, a switching layer comprising a liquid-crystalline material comprising at least one dichroic dye, where the switching layer has a dark switching state having low light transmission through the switching layer and a bright switching state having high light transmission through the switching layer, where the light transmittance τv, in accordance with the EN410 standard, of the switching layer in the dark switching state of the device for light which is polarised parallel to the principal axis of absorption of the at least one dichroic dye is less than 5%.

2. Optical switching device according to claim 1, which has the layer sequence: polarisation layer; substrate layer; electrically conductive transparent layer; alignment layer; switching layer comprising a liquid-crystalline material comprising at least one dichroic dye; alignment layer; electrically conductive transparent layer; and substrate layer.

3. Optical switching device according to claim 1, which comprises precisely one polarisation layer.

4. Optical switching device according to claim 1, wherein the polarisation layer is formed from a material which comprises one or more different organic dye compounds which have a common fixed spatial alignment.

5. Optical switching device according to claim 1, wherein the polarisation layer linearly polarises light.

6. Optical switching device according to claim 5, wherein the absorption axis of the polarisation layer which linearly polarises light is arranged, in the dark switching state of the switching layer, at an angle of 70°-110° to the principal axis of absorption of the at least one dichroic dye.

7. Optical switching device according to claim 2, wherein the alignment directions of the two alignment layers which surround the switching layer enclose an angle of 0° to 270°.

8. Optical switching device according to claim 1, wherein the switching layer has a thickness between 2 and 15 μm.

9. Optical switching device according to claim 1, wherein the molecules of the liquid-crystalline material of the switching layer are twisted in a planar manner in at least one switching state of the device, where the twist has a value between 30° and 360° over the thickness of the switching layer.

10. Optical switching device according to claim 1, wherein at least one of the dichroic dyes of the switching layer is fluorescent.

11. Optical switching device according to claim 1, wherein at least one of the dichroic dyes of the switching layer is selected from azo compounds, anthraquinones, benzothiadiazoles, diketopyrrolopyrroles and rylenes.

12. Optical switching device according to claim 1, wherein the liquid-crystalline material comprises a compound of a formula (I) ##STR00085## where R.sup.1 is selected from alkyl groups having 1 to 10 C atoms.

13. Optical switching device according to claim 2, wherein the substrate layer which is adjacent to the polarisation layer consists of a polymer.

14. Optical switching device according to claim 2, wherein both substrate layers consist of a polymer.

15. Optical switching device according to claim 1, wherein the device is curved in space.

16. Optical switching device according to claim 1, which comprises one or more substrate layers including a substrate layer on the side of the polarisation layer toward the switching layer, and which comprises a layer selected from adhesive layers and adhesive films between the polarisation layer and the that substrate layer.

17. Window for buildings, containers or motor vehicles, which comprises an optical switching device according to claim 1.

18. Window for buildings, containers or motor vehicles, which comprises an optical switching device according to claim 2.

19. A method for regulating the passage of sunlight from a sunlight-providing environment into a space substantially sealed off from the environment, which comprises providing an optical switching device according to claim 1 between the environment and the space.

Description

WORKING EXAMPLES

1) Materials Used for the Switching Layer

[0086] Structures of liquid-crystalline compounds are reproduced by means of abbreviations (acronyms). For the abbreviations used, reference is made to the explanations in WO 2012/052100, pp. 63-89.

[0087] All physical properties are determined in accordance with “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Status November 1997, Merck KGaA, Germany, and apply for a temperature of 20° C.

[0088] The following host mixture is prepared:

TABLE-US-00003 Composition of host mixture H1 Clearing point 114.5° C. Delta-n 0.1342 n.sub.e 1.6293 n.sub.o 1.4951 Compound Composition CPG-3-F 5 CPG-5-F 5 CPU-3-F 15 CPU-5-F 15 CP-3-N 16 CP-5-N 16 CCGU-3-F 7 CGPC-3-3 4 CGPC-5-3 4 CGPC-5-5 4 CCZPC-3-3 3 CCZPC-3-4 3 CCZPC-3-5 3

[0089] The following dye compounds are used:

##STR00083## ##STR00084##

[0090] These are used to prepare mixtures M1 and M2, having the following composition:

M1: H1 host mixture further comprising 0.47% by weight of D1, 1.03% by weight of D2 and 0.892% by weight of D3.
M2: H1 host mixture further comprising 0.6% by weight of D4; 0.3% by weight of D5; 1.0% by weight of D6; 1.5% by weight of D7 and 1.5% by weight of D8.

2) Production of the Switching Devices

[0091] The devices according to the invention have the following general layer sequence:

a0) ITOS XP40HT polariser film
a) polymer layer comprising 125 μm of polycarbonate with retardation less than 10 nm
b) indium zinc oxide (ITO) layer, 200 çngström
c) polyimide AL-1054 alignment layer from JSR, 300 çngström
d) switching layer, thickness 10 μm
e) as c)
f) as b)
g) as a).

[0092] The alignment layers are rubbed in order to achieve a preferential direction of the molecules of the liquid-crystalline material. If a twist of 90° is to be achieved, the two alignment layers are arranged crossed to one another in the device, i.e., in such a way that the rubbing directions enclose an angle of 90° to one another. In addition, 0.05% by weight of the chiral dopant S-811 is, in this case of the layer having a twist, present in the liquid-crystalline material. The ITO layers (other electrically conductive transparent layers known to the person skilled in the art can alternatively be used) are provided with corresponding contacts in order to be electrically switchable. The state without voltage is the dark state in the case of the switching devices produced. By application of a voltage which sets the molecules of the liquid-crystalline material in the upright position relative to the plane of the alignment layers, the devices are switched into the bright switching state.

[0093] The following switching devices are produced:

E1: switching layer comprising mixture M1, 90° twist
E2: switching layer comprising mixture M1, 0° twist
E3: switching layer comprising mixture M2, 0° twist

3) Performance Data of the Switching Devices

[0094] a) Determination of the Light Transmittance τ.sub.v dark of the Switching Layer

[0095] The light transmittance τ.sub.v dark is determined in accordance with European standard EN410, equation (1) (Determination of luminous and solar characteristics of glazing) from the measured spectral transmittances taking into account the relative spectral distribution of the standard illuminant and the spectral brightness sensitivity of the standard observer. The transmittance τ.sub.v of the switching layer of the devices for light which is polarised parallel to the principal axis of absorption of the dichroic dye in the dark switching state of the device is measured.

[0096] For measurement of the properties of the switching layer, the spectrometer is fitted with two Glan Thompson quartz polarisers in the reference and measurement beams. The device to be measured is mounted with its surface precisely perpendicular to the light beam. The alignment direction of the first device substrate facing the light beam is selected, for example, so that it points from down to up, i.e., vertically to the laboratory space. Since positively dichroic dyes align precisely along this direction, the principal axis of the most intense absorption for the untwisted examples E2 and E3 is precisely parallel to this direction. (For the twisted example E1, the first layer is likewise precisely parallel to this direction and the final layer is precisely perpendicular to this direction).

[0097] The two Glan Thompson polarisers are aligned in such a way that the transmission correspondingly reaches the lowest possible value precisely at this angular position.

[0098] The measurement of the spectral transmittance is compared with an otherwise identical device without dye in the switching layer as reference, i.e., the τ.sub.v dark in % value in the table below corresponds to the quotient of the light intensities through the switching layer with dye(s) (numerator) and the light intensities through the switching layer without dye(s) (denominator).

TABLE-US-00004 Light transmittance Temperature T.sub.v dark in % Device in ° C. switching layer E1 20 1.8 60 2.6 80 2.8 120 13.8 E2 20 1.3 60 1.8 80 2.0 100 2.6 120 11.3 E3 20 1.8 40 2.0 60 2.3 80 2.6 100 3.6 120 17.6
b) Determination of the Light Transmittance τ.sub.v dark of the Complete Device with Polariser

[0099] To this end, the procedure as under a) is followed, with the difference that, in order to calculate the light transmittance, the intensities after passage of light through the complete device with polariser are determined (numerator), and these are compared with the intensities through a device which is complete with switching layer but without polariser and without dyes, i.e., the τ.sub.v dark in % value in the table below corresponds to the quotient of the light intensities through the switching layer with polariser and dye(s) (numerator) and the light intensities through the switching layer without polariser and dye(s) (denominator). The τ.sub.v bright in % values are also measured through the whole device and they are determined in the bright switching state, where the liquid-crystalline material comprising the dye(s) has a homeotropic alignment.

TABLE-US-00005 Temperature Light transmittance Light transmittance Device in ° C. T.sub.v dark in % T.sub.v bright in % E1 20 0.7 23.9 60 1.0 23.9 80 1.1 22.2 120 5.4 9.1 E2 20 0.5 25.5 60 0.7 23.4 80 0.8 21.8 100 1.0 19.0 120 4.4 10.1 E3 20 0.7 24.5 40 0.8 23.4 60 0.9 21.8 80 1.0 19.6 100 1.4 16.2 120 6.9 6.9

[0100] The results show that excellent darkening is achieved with the devices according to the invention in the dark switching state of the device (τ.sub.v dark=0.5%-0.7%). In addition, the very dark switching state is achieved over a broad temperature range. Even at a temperature above the clearing point of the host mixture, low values for τ.sub.v dark in the single-figure percentage range are still obtained.

c) Determination of the Angle Dependence of the Transmission

[0101] The transmission as a function of wavelength is determined for devices E1 to E3 in each case for various value pairs of polar angle θ and azimuth angle φ. It is found here that the spectral transmission is substantially independent of the angle at which light passes through the device. This relates to a broad wavelength range. The devices therefore do not have an undesired colour for the observer if they are observed from different viewing angles. A further advantage is that the devices block light effectively for a broad range of passage angles if they are switched into the dark switching state.

[0102] The maximum transmission changes for devices E1, E2 and E3 are indicated in the following tables:

TABLE-US-00006 Device E1 Value of the maximum change in transmission (Δ T %) for an angle θ = 60° from the perpendicular and the angles φ = 0, 45, 90, 135, 180, 225, 270, 315° within the plane relative to the value of the angle θ = 0°, φ = 0° Wavelength (= perpendicular) smaller than 450 nm 0.8% 500 nm 1.6% 550 nm 1.4% 600 nm 1.2% 650 nm 1.2% 700 nm 1.1%

TABLE-US-00007 Device E2 Value of the maximum change in transmission (Δ T %) for an angle θ = 60° from the perpendicular and the angles φ = 0, 45, 90, 135, 180, 225, 270, 315° within the plane relative to the value of the angle θ = 0°, φ = 0° Wavelength (= perpendicular) smaller than 450 nm 1.5% 500 nm 1.2% 550 nm 1.0% 600 nm 1.2% 650 nm 1.4% 700 nm 2.2%

TABLE-US-00008 Device E3 Value of the maximum change in transmission (Δ T %) for an angle θ = 60° from the perpendicular and the angles φ = 0, 45, 90, 135, 180, 225, 270, 315° within the plane relative to the value of the angle θ = 0°, φ = 0° Wavelength (= perpendicular) smaller than 450 nm 2.1% 500 nm 1.0% 550 nm 1.0% 600 nm 1.1% 650 nm 1.6% 700 nm 1.3%

d) Production of Three-Dimensionally Curved Devices

[0103] The devices obtained under 2) are converted into a curved shape by fixing them between two watch glasses having a large radius and pressing them against the latter so that they are in contact with the watch glasses and take on their curvature.

[0104] The devices are subsequently switched, and their transmission is measured. Uniform transmission over the area of the device is observed here, both in the dark switching state and also in the bright switching state. Furthermore, no colour changes which are visible to the eye are observed. This shows that curved devices which have uniform transmission and colour can be obtained with the devices comprising substrate layers comprising polymer.

4) Switching Devices Comprising Glass Substrate Layers

[0105] Devices are produced as indicated above under 2), which differ merely in that, instead of layers a) and b), they have the layers a′) and b′) indicated below:

a′) glass layer comprising 1.1 mm of soda-lime glass from Corning
b′) ITO layer, 200 çngström

[0106] The same values for the light transmittance τ.sub.v as given above for the devices having a polymer substrate layer are obtained with these devices. The same values for the maximum transmission changes indicated above are also obtained.

[0107] However, devices having significantly less good curvature can be produced, since these unexpectedly break easily. Furthermore, curved devices of this type having glass substrate layers exhibit colour effects when viewed from angles which differ from the perpendicular.

[0108] 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.

[0109] In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.

[0110] The entire disclosures of all applications, patents and publications, cited herein and of corresponding European patent application No. EP 16175747.1, filed Jun. 22, 2016, are incorporated by reference herein.

[0111] 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.

[0112] From the foregoing 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.