Optical switching layer for use in an optical switching element
The present invention presents a switching layer S for use in a switching element which has forwards-scattering properties in at least one switching state. Furthermore, a switching element which comprises the switching layer S and a window element which includes the switching element are presented.
1. A switching layer S for a switching element, where the switching layer S has switching states and comprises
an upper switching layer plane USLP and a lower switching layer plane LSLP, and, arranged between USLP and LSLP,
a liquid-crystalline medium, which comprises a chiral dopant,
where, in one of the switching states, parallel light rays which hit the upper switching layer plane USLP in the directions of incidence D(=) are deflected out of D(=) on passing through the switching layer S, so that, after leaving the lower switching layer plane LSLP, the originally parallel light rays are scattered in the forwards-scattering directions D(<) away from the lower switching layer plane LSLP and are thus scattered forwards, resulting in forwards scattering, which is measured as diffusive transmission T d , where T d is >20%, and where T d is defined in accordance with formula (1)
T d =( I ≥2.5° /I tot )·100[%] (1)
in which
I ≥2.5° denotes the intensity of the large-angle scattering with scattering angles≥2.5° and
I tot denotes the intensity of the total transmission.
2. The switching layer S according to claim 1 , wherein the diffusive transmission T d in another switching state is <5%.
3. The switching layer S according to claim 1 , wherein the liquid-crystalline medium comprises nematically arranged molecules and a polymer component.
4. The switching layer S according to claim 3 , wherein the polymer component comprises a polymeric network which is obtained by polymerisation of reactive mesogens.
5. The switching layer S according to claim 4 , wherein the nematically arranged molecules and the polymeric network are homogeneously distributed in one another.
6. The switching layer S according to claim 5 , wherein the nematically arranged molecules have a proportion by weight w LC and the polymeric network has a proportion by weight w PN , and w PN , based on a weight w LC +w PN , is in the region<60% by weight.
7. The switching layer S according to claim 1 , wherein the molecules of the liquid-crystalline medium in the switching state where T d >20% are in a chirally nematic phase.
8. The switching layer S according to claim 7 , wherein the chirally nematic phase is a phase aligned in polydomains.
9. The switching layer S according to claim 1 , wherein the switching layer S has an average refractive index n, and the molecules of the liquid-crystalline medium have a pitch p, where the product n·p is >0.8 μm.
10. The switching layer S according to claim 1 , wherein the chiral dopant has a proportion by weight w D in the liquid-crystalline medium of 0.1% by weight to 30.0% by weight.
11. The switching layer S according to claim claim 1 , the chiral dopant has a helical twisting power β=(p·c) −1 μm −1 , where p is the pitch of the molecules of the liquid-crystalline medium in μm and c is the concentration of the chiral dopant in % by weight, based on the entire liquid-crystalline medium, and β is greater than 5 μm −1 .
12. The switching layer S according to claim 1 , wherein the liquid-crystalline medium has a clearing point of >90° C.
13. The switching layer S according to claim 1 , which comprises at least one dichroic dye in a dye concentration in the range from 0.01% by weight to 25% by weight, based on the weight of the liquid-crystalline medium.
14. The switching layer S according to claim 1 , wherein the switching layer S has a thickness of 3 μm to 200 μm, and, in one switching state, the total transmission T total is between 60% and 100% and the diffusive transmission T d is between 25% and 100% at a wavelength of the light rays of 550 nm.
15. The switching layer S according to claim 1 , wherein, in all its switching states, the switching layer S scatters less than 45% of the parallel light rays in the backwards-scattering directions D(>) away from the upper switching layer plane USLP.
16. A switching element comprising the switching layer S according to claim 1 , where the switching layer S is arranged in a first layer sequence, and where the first layer sequence comprises, from the outside inwards,
an outer substrate layer,
an outer electrically conductive layer,
the switching layer S,
an inner electrically conductive layer and
an inner substrate layer.
17. The switching element according to claim 16 , which comprises one or more layers which block UV light.
18. The switching element according to claim 16 , which further comprises a second layer sequence on the outer substrate layer of the first layer sequence and/or on the inner substrate layer of the first layer sequence, where the second layer sequence comprises, from the outside inwards,
a substrate layer,
an electrically conductive layer,
a switching layer comprising a liquid-crystalline medium,
an electrically conductive layer and
a substrate layer.
19. The switching element according to claim 16 , which further comprises a third layer sequence on the outer substrate layer of the first layer sequence and/or on the inner substrate layer of the first layer sequence, where the third layer sequence comprises, from the outside inwards,
a substrate layer,
an electrically conductive layer,
a switching layer comprising a liquid-crystalline medium,
an electrically conductive layer,
a substrate layer,
an electrically conductive layer,
a switching layer comprising a liquid-crystalline medium,
an electrically conductive layer and
a substrate layer.
20. The switching element according to claim 18 , wherein the liquid-crystalline medium of the switching layer of the second layer sequence comprises at least one dichroic dye in a dye concentration in the range from 0.01% by weight to 25% by weight, based on the weight of the respective liquid-crystalline medium.
21. A window element which includes the switching element according to claim 16 .
22. The switching element according to claim 19 , wherein the liquid-crystalline medium of one or both switching layers of the third layer sequence comprises at least one dichroic dye in a dye concentration in the range from 0.01% by weight to 25% by weight, based on the weight of the respective liquid-crystalline medium.