Device for regulating the passage of energy

Abstract

The present invention relates to a device for regulating the passage of energy through a light-transmitting area, comprising a first polarization layer, a second polarization layer and a switching layer which is arranged between the two polarization layers and changes the polarization properties of polarized light as a function of temperature, where the two polarization layers are characterized by a suitable choice of their transmission in the transmission direction and their degree of polarization. The invention furthermore relates to a process for the production of the device according to the invention and to the use of the device for influencing light transmission and/or the passage of energy into an interior as a function of temperature.

Claims

1. Device for regulating the passage of energy through a light-transmitting area, where the device comprises the following layers: a first polarisation layer, a second polarisation layer, and a switching layer, arranged between the two polarisation layers, which changes the polarisation properties of polarised light as a function of temperature, where the two polarisation layers have, identically or differently, a degree of polarisation P in the range 20-85% and a transmission in the transmission direction T1 in the range 70-100%, determined at a wavelength of 550 nm, and where one or both of the polarisation layers are formed from a layer comprising a liquid-crystalline medium and one or more dichroic dyes, with the one or more dichroic dyes present in an amount of 0.01 to 5% by weight of said liquid crystalline medium.

2. Device according to claim 1, wherein the passage of energy takes place into an interior which is selected from interiors of a building, a vehicle or a transport container.

3. Device according to claim 1, which switches from a switching state having relatively high light transmission to a switching state having relatively low light transmission as a function of temperature.

4. Device according to claim 3 wherein the switching from the switching state having relatively high light transmission to the switching state having relatively low light transmission takes place gradually in a temperature range from 0 C. to 80 C.

5. Device according to claim 1, wherein the two polarisation layers have, identically or differently, a degree of polarisation P in the range 30%-85% and a transmission in the transmission direction T1 in the range 75%-100%, determined at a wavelength of 550 nm.

6. Device according to claim 1, wherein the two polarisation layers are linear polarisers whose planes of polarisation are rotated by an angle of 70 to 110 with respect to one another.

7. Device according to claim 1, wherein both of the polarisation layers are formed from a layer comprising a liquid-crystalline medium and one or more dichroic dyes.

8. Device according to claim 1, wherein one or both of the polarisation layers are formed from a layer comprising an aligned polymer.

9. Device according to claim 1, wherein the switching layer comprises a liquid-crystalline medium which changes from a nematic state to an isotropic state during the switching operation with increasing temperature.

10. Device according to claim 1, wherein the switching layer in the optically anisotropic state rotates the plane of polarisation of linear-polarised light by an angle of 10 or more, and in the isotropic state does not rotate the plane of polarisation of linear-polarised light or only does so to a negligible extent.

11. Device according to claim 1, which additionally comprises a substrate layer, which is formed from glass, a polymer or ITO.

12. A method which comprises operating a device according to claim 1 for influencing the passage of energy through a light-transmitting area as a function of temperature.

13. A method according to claim 12, wherein the device switches from a state having relatively high light transmission to a state having relatively low light transmission without application of electrical voltage.

Description

(1) The device preferably has the structure depicted in FIG. 1. (1) here denotes the device, (2) denotes the switching layer, and (3a) and (3b) denote the polarisation layers. FIG. 1 describes the basic arrangement of the layers and is not intended, for example, to exclude further functional layers, for example one or more alignment layers and/or one or more protective layers which block external influences or light of a certain wavelength, from being located between the layers shown or outside the layer arrangement.

(2) FIG. 2 depicts a further preferred structure of the layer arrangement, in which the arrangement comprising the switching layer and the two polarisation layers is located on a substrate layer (4).

(3) The following working examples describe preferred embodiments of the device according to the invention. The person skilled in the art will be able to recognise the function principle of the invention with reference to the examples and apply it to further embodiments which are not described explicitly. The examples do not imply any restriction of the invention to that directly described.

WORKING EXAMPLES

1. Production of the Polarisation Layers

(4) The following components are used for the production of the polarisation layers:

(5) LC Mixture A:

(6) TABLE-US-00001 LC compound % CP-3-N 20 PZG-5-N 10 PZP-1O-1 11 PZP-1O-5 16 PGU-3-F 9 CPZG-3-N 5 CPZG-4-N 5 CPZG-5-N 5 CCZPC-3-3 3 CCZPC-3-4 3 CGPC-3-3 5 CGPC-5-3 4 CGPC-5-5 4

(7) LC Mixture B:

(8) TABLE-US-00002 LC compound % PZG-3-N 2 PZG-4-N 9 PZG-5-N 9 PZP-1-5 10 PZP-1O-1 17 PZP-1O-5 16 CP-3-N 12 PP-2-N 10 PGU-3-F 9 CPZG-3-N 3 CPZG-4-N 3

(9) Dye Mixture:

(10) TABLE-US-00003 Dye Parts 37 76 90

(11) The following polarisation layers EP-1 to EP-4 are produced from the components indicated:

(12) TABLE-US-00004 LC mixture Proportion of dye mixture EP-1 A 0.1% EP-2 A 0.3% EP-3 A 0.5% EP-4 B 0.3%

(13) Furthermore, the following polarisation layers VP-1 to VP-3 are produced or purchased commercially (VP-3) for comparison:

(14) TABLE-US-00005 LC mixture Proportion of dye mixture VP-1 A 1% VP-2 B 1% VP-3 absorptive polariser ITOS XP38

(15) The following values T1, T2 and P are obtained for the polarisation layers (determined at 550 nm):

(16) T1: transmission of the polariser layer in the transmission direction

(17) T2: transmission of the polariser layer in the blocking direction

(18) P: degree of polarisation, can be determined from the equation:
P=(T1T2)/(T1+T2)

(19) TABLE-US-00006 T1/% T2/% P/% EP-1 94.1 60.9 21.5 EP-2 86.1 22.2 58.9 EP-3 79.7 9.1 79.5 EP-4 79.1 26.3 50.2 VP-1 63.3 0.7 97.8 VP-2 48.0 1.2 95.0 VP-3 71.5 0.1 98.6

(20) After production and measurement of a relatively large number of polarisation layers produced in different ways, an empirical correlation can be observed between the production parameters and the value pairs T1 and P obtained. In the present example, it can be seen that an increase in P and a reduction in T1 occur with an increase in the dye concentration for the same LC mixture. On changing from mixture A to mixture B (cf. EP-3 and EP-4), a significantly reduced value for P can be achieved with constant T1.

(21) Corresponding polarisation layers can be produced in the manner described for any desired value pairs T1 and P through the use of different concentrations of dye mixture and the use of different LC mixtures.

2. Production of the Devices

(22) Devices E-1 to E-4 and comparative devices V-1 to V-3 are produced by applying the polarisation layers described above in each case to the top side and underside of a nematic twisted cell.

(23) The nematic twisted cell contains alignment layers and a layer of a liquid-crystalline medium and is produced by processes which are generally known to the person skilled in the art.

(24) For the devices obtained, the transmission in the state having relatively high light transmission (bright transmission) and the transmission in the state having relatively low light transmission (dark transmission) are determined in each case. The switching range arises from the difference between the two values. All values were again determined at 550 nm.

(25) TABLE-US-00007 Bright Dark Switching transmission/% transmission/% range/% E-1 62.8% 57.3% 5.5% E-2 39.5% 19.2% 20.3% E-3 32.2% 7.3% 24.9% E-4 34.8% 20.8% .sup.14% V-1 20.0% 0.5% 19.5% V-2 11.5% 0.6% 10.3% V-3 37.2% ~0% 37.2%

(26) It can be seen from the table that the devices according to the invention all have an acceptable dark transmission (about 7% or more). The values for the bright transmission and the switching range can be set independently of one another (cf., for example, E-3 and E-4). This is highly desired for the intended use, since the advantages of a large switching range and the advantages of a high bright transmission can thus be weighed up against one another and the desired combination of the two values can be set.

(27) In the range of the parameters P (20-85%) and T1 (70-100%) which is selected for devices E-1 to E-4, advantageous values are obtained both for the bright transmission and also for the switching range (see table above).

(28) The comparative devices in accordance with the prior art (V-1 to V-3), which exhibit values for the parameters P and T1 outside these ranges, have an unfavourably low dark transmission for use of the devices in windows.

(29) FIGS. 3 to 8 show the transmission spectra obtained for devices E-1 to E-4 and V-1 and V-2 in the range from 400 to 900 nm, in each case in the bright state (curve 1) and in the dark state (curve 2).

BRIEF DESCRIPTION OF FIGURES

(30) FIG. 1 denotes a device of this invention

(31) FIG. 2 denotes a structure of the layer arrangement

(32) FIG. 3 shows the transmission spectrum for device E-1 according to the invention.

(33) FIG. 4 shows the transmission spectrum for device E-2 according to the invention.

(34) FIG. 5 shows the transmission spectrum for device E-3 according to the invention.

(35) FIG. 6 shows the transmission spectrum for device E-4 according to the invention.

(36) FIG. 7 shows the transmission spectrum for comparative device V-1.

(37) FIG. 8 shows the transmission spectrum for comparative device V-2.

3. Alternative Production Processes for the Polarisation Layers

(38) In accordance with a further example, the polarisation layers are produced by admixing polymerisable monomers in addition to the LC mixture and the dye mixture. These are, for example, acrylates, such as monoacrylates, diacrylates and multifunctional acrylates, or epoxides or vinyl ethers. It is possible to use mixtures of monomers, for example mixtures of mono- and diacrylates or mixtures of epoxides and vinyl ethers. The monomers may contain mesogenic groups. The mixture comprising the liquid-crystalline medium, the dye and the monomers is subsequently polymerised in the form of a layer. The polymerisation can be carried out, for example, by induction with UV light.

(39) The process described above enables particularly robust and temperature-stable polarisation layers to be produced for devices in accordance with the present invention.

(40) According to a further example, the polarisation layers are produced by stretching a polymer film comprising polyvinyl alcohol (PVA). Iodine is subsequently incorporated into the films.

(41) Polarisation layers having a different degree of stretching of the PVA film, a different iodine concentration and different thickness are produced. The values for the transmission in the transmission direction (T1) and the degree of polarisation are determined for the polarisation layers obtained. After production and measurement of a relatively large number of polarisation layers produced in different ways, an empirical correlation can be observed between the production parameters and the value pairs T1 and P obtained. In this way, corresponding polarisation layers can be produced for any desired value pairs T1 and P.