Device for temperature-dependent regulation of the passage of energy through a light-permeable surface

0001The present invention relates to a device for regulating the passage of energy through a translucent surface, 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, the two polarization layers being characterized by suitable selection of their transmission in the transmission direction and their degree of polarization. The invention further relates to a method for producing the device according to the invention and the use of the device for temperature-dependent influencing of the light transmission and / or the passage of energy into an interior.

0002The energy efficiency of buildings becomes more important with increasing energy costs. Windows and glass facades represent critical parts of the building, through which the majority of a building's thermal energy is lost at low outside temperatures, or through which the majority of the energy input into a building takes place in intense sunlight.

0003There is therefore a need for devices which control the passage of light and thus the flow of energy through windows or glass surfaces. In particular, there is a need for devices which can adapt the energy flow through glass surfaces to the prevailing conditions (heat, cold, high solar radiation, low solar radiation).

0004In the context of the present invention, the term light is understood to mean electromagnetic radiation in the UV-A, VIS and NIR range. In particular, this is understood to mean radiation which is not absorbed by the materials usually used in windows (for example glass) or is absorbed only to a negligible extent. According to the definitions usually used in the field of radiation physics, UV-A light is understood to mean radiation of a wavelength of 320 to 380 nm, VIS light is understood to be radiation of a wavelength of 380 nm to 780 nm and NIR light is a radiation of wavelength 780 nm to 3000 nm understood. In the context of the present invention, the term light is therefore understood to mean radiation with a wavelength of 320 to 3000 nm.

0005In the cold season, it is desirable that a maximum of light and thus transported energy enter a building through glass surfaces. This can save heating and lighting costs.

0006On the other hand, in the warm season it is desirable that the lowest possible energy input through glass surfaces into a building. This makes it possible to achieve a more comfortable indoor climate or to save costs for air conditioning. In these cases, it may also be desirable to reduce the incident light intensity, for example in order to reduce glare from direct sunlight.

0007There is therefore a need for switching elements which regulate the energy input in the form of light in interiors, for example through windows or other glass surfaces. In particular, there is a need for switching elements which automatically adapt the regulation of light passage to the prevailing conditions, as shown above (smart windows). There is also a need for switching elements which work in an energy-efficient manner, can be installed with as little technical effort as possible, are technically reliable and satisfy aesthetic requirements. Other aspects include easy processing of the switching element, robustness in operation and retrofitting to existing glass surfaces in buildings.

0008In <patcit id="pcit0001" dnum="US20090015902A"><text>US 2009/0015902</text></patcit> and <patcit id="pcit0002" dnum="US20090167971A"><text>US 2009/0167971</text></patcit> discloses temperature-reactive devices which contain a liquid-crystalline medium in a layer between two highly efficient polarizers. The switching between a state with higher light transmission and a state with lower light transmission is achieved by a phase transition of the liquid-crystalline medium from a nematic state to an isotropic state without the need to apply a voltage.

0009<patcit id="pcit0003" dnum="US20090167971A"><text>US 2009/0167971</text></patcit> discloses the features of the characterizing part of claim 1.

0010However, such devices have the disadvantage that they have a light transmission in the state with a higher light transmission of theoretically at most 50%, in practice from at most 30 to 40%. Furthermore, the transmission in the state with low light transmission is almost zero, so the device darkens completely.

0011However, for use of the devices in practice, for example in buildings or in vehicles, it would be desirable for them to have a transmission in the state with higher light transmission (= open state) of 50 to 70%. Otherwise there would be an impression of a clear darkening of the window when the device is open.

0012Furthermore, in practice it is desirable that the device in the state with lower transmission (= closed state) is not completely dark, but has a residual transmission. A minimum transmission of 7% is considered subjectively pleasant for windows.

0013In <patcit id="pcit0004" dnum="US20110102878A"><text>US 2011/0102878</text></patcit> it is disclosed that in the devices according to <patcit id="pcit0005" dnum="US20090015902A"><text>US 2009/0015902</text></patcit> and <patcit id="pcit0006" dnum="US20090167971A"><text>US 2009/0167971</text></patcit> thinner polarizers with increased transmissivity can be used instead of highly efficient polarizers. As a result of the disclosure of the abovementioned application, this has the effect that the transmission is increased when the device is open. However, the switching stroke of the device, that is to say the difference in light transmission between the open and the closed state, is reduced by such an embodiment.

0014In devices for regulating the passage of energy, it is desirable to be able to predetermine both the transmission in the bright state and the switching stroke of the device as required. For example, it can be advantageous for certain applications that the device has a very high switching stroke. For other applications it can be advantageous to combine a relatively high switching stroke with a relatively high light transmission.

0015According to the invention, it was found that this can be achieved by suitable selection of the parameters P (degree of polarization) and T1 (transmission in the transmission direction) of the polarizers.

0016In <patcit id="pcit0007" dnum="US2009167971A1"><text>US 2009/167971 A1</text></patcit> discloses a device for regulating the passage of energy through a transparent surface which contains two polarization layers and an interposed switching layer which changes the polarization properties of polarized light as a function of temperature.

0017The invention thus relates to a device for regulating the passage of energy through a translucent surface, the device containing the following layers:<ul id="ul0001" list-style="dash" compact="compact"><li>a first polarization layer,</li><li>a second polarization layer, and</li><li>a switching layer arranged between the two polarization layers, which changes the polarization properties of polarized light as a function of temperature,</li></ul>wherein the two polarization layers have the same or different degree of polarization P in the range of 20-85% and a transmission in the transmission direction T1 in the range of 70-100%, determined at a wavelength of 550 nm, and wherein one or both of the polarization layers consist of one Layer containing a liquid-crystalline medium and one or more dichroic dyes are formed.

0018The use of polarization layers which have both the degrees of polarization P mentioned and the transmissions mentioned in the transmission direction T1 results in devices which have a satisfactory dark transmission of at least 7.5%. There is also a satisfactory light transmission of at least 30%, preferably of at least 40%. There is also a switching stroke of at least 5%, preferably of at least 7.5%.

0019Furthermore, by suitable selection of both parameters P and T1, devices can be produced from the named areas, in which the values ​​for the light transmission and the switching stroke can be set independently of one another.

0020The parameters P and T1 are, as is well known to those skilled in the art in the field of devices containing polarization layers, as follows:<ul id="ul0002" list-style="none" compact="compact"><li>P is through the equation <maths id="math0001" num=""><math display="block"><mrow><mi mathvariant="normal">P</mi><mo>=</mo><mfenced separators=""><mi mathvariant="normal">T</mi><mn mathvariant="normal">1</mn><mo>−</mo><mi mathvariant="normal">T</mi><mn mathvariant="normal">2</mn></mfenced><mo>/</mo><mfenced separators=""><mi mathvariant="normal">T</mi><mn mathvariant="normal">1</mn><mo>+</mo><mi mathvariant="normal">T</mi><mn mathvariant="normal">2</mn></mfenced></mrow></math><img file="EP2798397B1_D0001.tif" /></maths></li></ul>available from the values ​​for T1 and T2. T1 represents the transmission of the polarizer in the transmission direction at a wavelength of 550 nm. The transmission direction is understood to mean the orientation of irradiated polarized light at which the highest transmission through the polarizer occurs. T2 represents the transmission of the polarizer in the reverse direction at a wavelength of 550 nm. The blocking direction is understood to mean the orientation of incident polarized light at which the least transmission through the polarizer occurs.

0021The light transmission of the device, as stated above, means the transmission through the device which occurs in the switching state with higher light transmission. Correspondingly, the dark transmission of the device is understood to mean that transmission through the device which occurs in the switching state with less light transmission. The transmissions are again defined for the 550 nm wavelength of light.

0022Finally, the switching stroke of the device is understood to mean the difference between the values ​​for light transmission and dark transmission.

0023It is noted that in the present application the optical values ​​T1, T2, P and the light transmission, the dark transmission and the switching stroke were basically determined for a wavelength of 550 nm, unless explicitly stated otherwise.

0024In the context of the present invention, the term energy is understood to mean energy from electromagnetic radiation (light energy) in the UV-A, VIS and NIR range. In particular, this is understood to mean light energy which is not absorbed by the materials usually used in windows (for example glass) or is absorbed only to a negligible extent.

0025According to the invention, the two switching states of the device are a switching state with higher light transmission through the device (light state) and a switching state with lower light transmission through the device (dark state).

0026Due to generally known physical laws, high light transmission through the device leads to a high energy input into the interior, which the device has applied to a translucent surface. Low light transmission through the device accordingly leads to a low energy input into the interior. By switching its light transmittance, the device therefore regulates the energy input into the interior.

0027The device switches depending on the temperature from a switching state with higher light transmission to a switching state with lower light transmission. The switching states of the device are consequently connected to different temperature ranges of the device. The device is preferably switched gradually in a temperature range between 0 ° C. and 80 ° C., preferably between 10 ° C. and 70 ° C. and very particularly preferably between 20 ° C. and 60 ° C.

0028According to a preferred embodiment of the invention, the switching state with higher light transmission is present at relatively lower temperatures of the device, and the switching state with lower light transmission is present at relatively higher temperatures of the device. Accordingly, the bright state of the device occurs preferably at temperatures below 0 ° C., particularly preferably below 10 ° C. and very particularly preferably below 20 ° C. The dark state of the device occurs preferably at temperatures above 80 ° C., particularly preferably above 70 ° C. and very particularly preferably above 60 ° C.

0029The functioning of the device is based on the fact that incident light is polarized by the first polarization layer. This means that predominantly light with certain polarization properties is let through. The switching layer is arranged behind the first polarization layer. In a first state, this does not affect the polarization properties of the light that passes through it. The light then strikes the second polarization layer, which is arranged behind the switching layer. According to the arrangement of the transmission directions of the polarization layers to one another, a certain proportion of the light can now also pass through the second polarization layer. In the other of the two switching states, the polarization-influencing switching layer changes the polarization properties of the light that passes through it. As a result, a higher or a lower proportion of the polarized light can now pass through the second polarizer, depending on the manner in which the polarization properties of the light have been changed by the switching layer. In any case, the change in the polarization properties of the light through the switching layer in its second state results in a change in the light transmission of the device compared to the first state of the switching layer, in which it does not influence the polarization properties of the light.

0030According to a preferred embodiment of the invention, the two polarization layers are linear polarizers, the preferred directions of polarization of which are rotated relative to one another by an angle of 60-120 °, preferably 75-105 ° and particularly preferably 80 to 100 °. The switching layer does not or only slightly rotates the plane of polarization of the light in one of the two states. In the other of the two states, it rotates the plane of polarization of the light by an angle which corresponds to the angle at which the preferred directions of polarization of the polarizers are rotated relative to one another, or deviates only slightly from this angle, for example by 1-10 °. In this configuration, the light which passes through the first polarizer also passes through the second polarizer when the switching layer is in the state in which it rotates the plane of polarization of the light. The active state of the switching layer thus corresponds to the light state of the device. If, however, the switching layer is in its inactive state, ie the state in which it does not rotate the plane of polarization of light, the light which strikes the second polarizer cannot pass through it, since the preferred directions of polarization of the two polarizers are rotated relative to one another. In this embodiment, the inactive state of the switching layer therefore corresponds to the dark state of the device.

0031The active state of the switching layer is connected to an optically anisotropic state, preferably a liquid-crystalline state of the switching layer, and the inactive state of the switching layer is connected to a largely isotropic state of the switching layer.

0032In the optically anisotropic state, the switching layer preferably rotates the polarization plane of linearly polarized light by an angle of 10 ° or more, while in the isotropic state it does not rotate the polarization plane of linearly polarized light or only rotates it to a negligible extent. It particularly preferably rotates the plane of polarization of linearly polarized light by an angle of more than 40 °, very particularly preferably by an angle of more than 70 °. The most preferred are angles of rotation of 70 to 110 °, even more angles of 80 to 100 °. However, angles of rotation are also possible which are multiples of 180 ° larger than the preferred angles of rotation indicated.

0033According to the invention, the switching process between the two switching states does not proceed abruptly at a certain temperature, but gradually in a transition area which lies within a temperature range. This temperature range of the transition region preferably has a width of 5 to 100 degrees Celsius, that is to say for example between 15 and 110 ° C. The temperature range particularly preferably has a width of 10 to 50 degrees Celsius. Within the temperature range of the transition range, the transmission of the device changes gradually via intermediate values ​​of the transmission from the value for the light transmission to the value for the dark transmission of the device.

0034The device preferably switches only temperature-controlled. It therefore preferably does not contain any devices for electrically actuating the switching process. It particularly preferably contains no wires, cables, electrical connections or circuits. Furthermore, it is preferably not electrically controlled or supplied with power from the outside, so it represents an autonomous system.

0035The passage of energy preferably takes place through a translucent surface into an interior. The interior is preferably the interior of a building, for example a residential building, an office building, or a commercial building. Alternatively, the interior can also be the interior of a vehicle, for example a car, or the interior of a transport container, for example a container. According to the invention, the device can be used for any interior, provided that it has only limited air exchange with the surroundings and has translucent boundary surfaces through which energy can be introduced from outside in the form of light energy. The invention is particularly relevant for interiors which are exposed to strong solar radiation through translucent surfaces, for example through window surfaces.

0036Translucent surfaces such as windows or ceilings with a size of more than 0.5 m are preferred², particularly preferably more than 1 m², very particularly preferably more than 3 m². This is due to the fact that such surfaces, when they are irradiated by the sun, can absorb a large amount of energy into the interior. Also preferred are translucent surfaces that are exposed to high levels of solar radiation due to their spatial orientation and / or the geographic and climatic location of the building.

0037The device is preferably arranged area-wide on a translucent surface, so that the light transmission through the surface can be regulated as completely as possible. In one possible embodiment, the cover is provided by a single device. In an alternative embodiment, however, the cover can also be provided by a plurality of devices which either adjoin one another directly or are arranged such that gaps remain.

0038In a preferred embodiment, the translucent surface is a glass pane or a plexiglass pane. In the case of window panes, multi-pane insulating glass is preferred. According to a preferred embodiment, the device according to the invention is applied directly to this pane.

0039Such an application can be done by retrofitting an existing arrangement or by completely new installation.

0040According to a preferred embodiment, the device is attached to the inside of multi-pane insulating glass or attached to the outside of such glass. It is generally preferred to use on a side of a pane facing the interior or in the space between two glass panes in the case of multi-pane insulating glass. However, other arrangements are also conceivable and preferable in certain cases. The person skilled in the art can weigh up the advantages and disadvantages of certain arrangements with regard to the durability of the device, optical and aesthetic points of view, practical points of view with regard to the cleaning of the panes and with regard to the reactivity of the device with respect to temperature changes, and select an embodiment which is optimal for the present case.

0041According to a preferred embodiment, the device is characterized in that it has a surface area of ​​at least 0.05 m², preferably from 0.1 m² up to 20 m² and particularly preferably of 0.2 m² up to 5 m² having.

0042It is preferred according to the invention that the polarization layers of the device, the same or different, have a degree of polarization P in the range of 30-85% and a transmission in the transmission direction T1 in the range of 75 to 100%, the values ​​being determined at a wavelength of 550 nm. A degree of polarization P in the range from 35 to 80% and a transmission T1 in the range from 75 to 100% is particularly preferred for the polarization layers.

0043Within the ranges for P and T1 according to the invention, certain combinations of value ranges for P and T1 were found for which certain properties of the characteristic parameters of the light transmission device and switching stroke occur. The dark transmission remains above the minimum value of 7%.

0044A device with the highest possible switching stroke is obtained if P for the polarizers is selected identically or differently from the range from 45-85% and T1 from the range from 75-100%. P is preferably selected from the range of 55-85% and T1 from the range of 80-100%. P is very particularly preferably selected from the range from 65-85% and T1 from the range from 85-100%.

0045The above-mentioned minimum values ​​for light transmission and dark transmission are observed.

0046A device with a moderately high switching stroke combined with moderately high light transmission is obtained if P for the polarizers is selected identically or differently from the range from 30 to 85% and T1 from the range from 80 to 100%. P is preferably selected from the range from 40 to 75% and T1 from the range from 90 to 100%. The above-mentioned minimum values ​​for dark transmission are observed.

0047A device with the highest possible light transmission is obtained if P for the polarizers is selected identically or differently from the range from 25 to 60% and T1 from the range from 90 to 100%. P is preferably selected from the range from 30 to 40% and T1 from the range from 95 to 100%. The above-mentioned minimum values ​​for dark transmission and the switching stroke are observed.

0048The values ​​for P and T1 can be set independently of one another for the polarization layers. Methods for this are known to the person skilled in the art. These include, for example, the change in the layer thickness of the polarization layer, the change in the degree of orientation of the polarization layer and the change in the concentration of the light-absorbing species in the polarization layer.

0049In the case of polarizers containing a liquid-crystalline medium and a dichroic dye, the parameters P and T1 can be varied independently of one another, for example by changing the liquid-crystalline medium and changing the concentration of the dichroic dye. For this purpose, explicit exemplary embodiments are given in a following section.

0050In many cases it will be necessary to manufacture a larger number of different polarizers by varying the manufacturing parameters given above and to measure their values ​​P and T1. From this, an empirical relationship between manufacturing parameters (e.g. degree of stretching and concentration of dye) and value pairs T1 and P can be recognized, on the basis of which the person skilled in the art can produce polarizers with any values ​​T1 and P in a targeted manner.

0051The invention thus furthermore relates to a method for producing a device for regulating the passage of energy through a translucent surface, the device comprising the following layers:<ul id="ul0003" list-style="dash" compact="compact"><li>a first polarization layer,</li><li>a second polarization layer,</li><li>a switching layer arranged between the two polarization layers, which changes the polarization properties of polarized light as a function of temperature,</li></ul>characterized in that the two parameters polarization degree P and transmission in the transmission direction T1 for the polarization layers are selected independently of one another by varying one or more production parameters selected from the layer thickness, degree of orientation of the polarization layer, concentration of embedded substance, degree of orientation of the embedded substance, absorption properties of the embedded substance, Structure of the stored substance, Dichroism of the stored substance and aggregation properties of the stored substance.

0052The structure of the embedded substance is understood to mean its molecular structure, in particular its length-to-width ratio. In general, the greater the length-to-width ratio of a substance, the greater the degree of orientation.

0053The aggregation properties of the stored substance mean in particular the ability to form chains from single molecules or single atoms of the substance.

0054In the method, the degree of polarization P is preferably selected from the range of 20-85% and the transmission in the transmission direction is selected from the range of 70-100%. P is particularly preferably selected from the range from 30-85% and T1 is selected from the range from 75 to 100%.

0055The preferred embodiments of the polarization layers and the switching layer which are specified for the device according to the invention are also preferred for the method.

0056Another object of the invention is the use of the device according to the invention for temperature-dependent influencing of the passage of energy through a translucent surface. It is preferably used for temperature-dependent influencing of the energy input through a translucent surface in an interior.

0057When using the device according to the invention, the passage of energy is influenced by the fact that the device changes its light transmission between a switching state with higher light transmission (bright state) and a switching state with lower light transmission (dark state). The switching process is temperature-controlled and takes place in the preferred ranges for the switching process specified above.

0058The use according to the invention takes place without the application of electrical voltage. The use consequently requires no energy, in particular no electrical energy.

0059According to the invention, the device has two or more polarization layers, one of which is arranged on one side of the switching layer and another on the opposite side of the switching layer. The switching layer and the two polarization layers are preferably arranged parallel to one another. The polarization layers have the values ​​for parameters P and T1 given above as according to the invention and preferably have the values ​​for parameters P and T1 given as preferred above.

0060The polarization layers can represent linear polarizers or circular polarizers. Exactly two polarization layers are preferably present in the device. In this case, it is further preferred that the polarization layers represent either both linear polarizers or both circular polarizers.

0061The two polarization layers are particularly preferably each the same or different absorptive or reflective linear polarizers. The two polarization layers are very particularly preferably absorptive linear polarizers.

0062A reflective polarizer in the sense of the present application reflects light of one polarization direction or a type of circularly polarized light, while it is transparent to light of the other polarization direction or the other type of circularly polarized light. Accordingly, an absorptive polarizer absorbs light of one polarization direction or a type of circularly polarized light, while for light of the other polarization direction or the other type of circularly polarized light is transparent.

0063If two linear polarizers are present in the device, it is preferred according to the invention that the polarization planes of the two polarizers are rotated relative to one another by an angle of 70 ° to 110 °, particularly preferably 80 ° to 100 ° and very particularly preferably 85 ° to 95 °.

0064According to the invention, one or both of the polarization layers is formed from a layer containing a liquid-crystalline medium and one or more dichroic dyes. The liquid-crystalline medium preferably contains two or more, particularly preferably 5 or more, very particularly preferably 7 or more different liquid-crystalline compounds.

0065In the context of the present application, the term liquid-crystalline compound is understood to mean a compound which shows liquid-crystalline properties under certain conditions, and in particular a compound which forms a nematic liquid-crystalline phase under certain conditions.

0066The liquid-crystalline compounds can be chosen arbitrarily from liquid-crystalline compounds known to the person skilled in the art. Liquid-crystalline compounds with limited size and molecular weight (small molecules) are preferred. It is particularly preferred if the liquid-crystalline compound has a molecular weight of not more than 1000 Da, very particularly preferably of not more than 800 Da and most preferably of not more than 600 Da.

0067Suitable liquid-crystalline media for use in the polarization layers are those media which have high temperature stability and are light-stable. They preferably have a clearing point of more than 50 ° C., particularly preferably more than 70 ° C. and very particularly preferably more than 90 ° C.

0068According to a preferred embodiment of the invention, the liquid-crystalline medium contains one or more polymeric compounds. According to a preferred embodiment, the polymer is present as a continuous phase in a polymer network (polymer network systems). The polymer network is preferably penetrated by the liquid-crystalline medium and / or dissolved in the liquid-crystalline medium, so that there is an optically uniform appearance. It is preferably formed by polymerizing mono- or diacrylate monomers, which are added to the liquid-crystalline medium. The liquid-crystalline medium is preferably present in a proportion of more than 60% in the mixture with the polymeric compound, particularly preferably 70 to 95%. Such systems are for example in<patcit id="pcit0008" dnum="EP452460A"><text>EP 452460</text></patcit>, <patcit id="pcit0009" dnum="EP313053A"><text>EP 313053</text></patcit> and <patcit id="pcit0010" dnum="EP359146A"><text>EP 359146</text></patcit> described in detail.

0069As dichroic dyes, the in<nplcit id="ncit0001" npl-type="b"><text> Liquid Crystals, Applications and Uses, 1992, World Scientific Publishing, Editor B. Bahadur, pages 73-81</text></nplcit> disclosed compounds are used. Anthraquinone, naphthoquinone, benzoquinone, perylene and tetrazine dyes and compounds containing one or more azo groups or one or more Schiff bases are preferred.

0070The dichroic dyes are preferably selected from the following compounds:<tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="1" colsep="0"><colspec colnum="1" colname="col1" colwidth="161mm" colsep="1" /><tbody><row><entry align="center"><chemistry id="chem0001" num="0001"><img file="EP2798397B1_D0002.tif" /></chemistry></entry></row><row><entry align="center">1</entry></row><row><entry align="center"><chemistry id="chem0002" num="0002"><img file="EP2798397B1_D0003.tif" /></chemistry></entry></row><row><entry align="center">2</entry></row><row><entry align="center"><chemistry id="chem0003" num="0003"><img file="EP2798397B1_D0004.tif" /></chemistry></entry></row><row><entry align="center">3</entry></row><row><entry align="center"><chemistry id="chem0004" num="0004"><img file="EP2798397B1_D0005.tif" /></chemistry></entry></row><row><entry align="center">4</entry></row></tbody></tgroup></table></tables>

0071The dyes are preferably present in the mixture in a concentration of 0.01% by weight to 5% by weight, particularly preferably 0.05% by weight to 1% by weight. They are preferably dissolved in the liquid-crystalline medium.

0072It is further preferred that two or more dyes are used together. Exactly two or three dyes are particularly preferably used. The dyes used are preferably selected so that their absorption spectra complement one another to give the human eye a neutral, that is to say non-colored, impression. For certain embodiments, however, it may also be preferred to use one or more dyes which together give a colored impression.

0073The switching layer of the device according to the invention preferably contains a liquid-crystalline medium which contains at least one liquid-crystalline compound. A mixture of different liquid-crystalline compounds is preferably present in the switching layer. At least 5 and at most 15 different liquid-crystalline compounds are particularly preferably present in the switching layer.

0074The liquid-crystalline compounds can be chosen arbitrarily from liquid-crystalline compounds known to the person skilled in the art. Liquid-crystalline compounds with limited size and molecular weight (small molecules) are preferred. It is particularly preferred if the liquid-crystalline compound has a molecular weight of not more than 1000 Da, completely compound has a molecular weight of not more than 1000 Da, very particularly preferably not more than 800 Da and most preferably not more than 600 Da.

0075The mixture of the liquid-crystalline compounds (or in the case that only one liquid-crystalline compound is used, the individual liquid-crystalline compound) preferably has a clearing point between -20 ° C. and 200 ° C., particularly preferably a clearing point between 10 ° C. and 180 ° C.

0076Particularly preferred for use as liquid-crystalline media are those in <patcit id="pcit0011" dnum="WO2011134582A"><text>WO 2011/134582</text></patcit>, <patcit id="pcit0012" dnum="WO2011144299A"><text>WO 2011/144299</text></patcit>, <patcit id="pcit0013" dnum="WO2011154077A"><text>WO 2011/154077</text></patcit> and those in the not yet published applications <patcit id="pcit0014" dnum="EP10008779A"><text>EP 10008779.0</text></patcit> and <patcit id="pcit0015" dnum="EP10013797A"><text>EP 10013797.5</text></patcit> disclosed mixtures of liquid crystalline compounds.

0077The liquid-crystalline medium of the switching layer preferably changes from a nematic to an isotropic state during the switching process with increasing temperature. The nematic state is preferably associated with the state of the device with higher light transmission, and the isotropic state is connected with the state of the device with lower light transmission.

0078The liquid-crystalline medium can also contain one or more polymeric compounds. The medium is particularly preferably one of the liquid-crystalline media comprising polymeric compounds which are described in the not yet disclosed application<patcit id="pcit0016" dnum="EP11008518A"><text>EP 11008518.0</text></patcit> to be discribed. For even more information on polymer network systems, reference is made to the disclosure of the applications<patcit id="pcit0017" dnum="EP452460A"><text>EP 452460</text></patcit>, <patcit id="pcit0018" dnum="EP313053A"><text>EP 313053</text></patcit> and <patcit id="pcit0019" dnum="EP359146A"><text>EP 359146</text></patcit> referred.

0079According to a preferred embodiment of the invention, the switching layer comprises a twisted nematic layer. The preferred direction of rotation of the liquid-crystalline compounds is preferably effected by two or more orientation layers, at least one of which is located on one side of the switching layer and at least one on the opposite side of the switching layer.

0080The device according to the invention preferably comprises at least one substrate layer, which is preferably formed from glass, a polymer or ITO. The substrate layer is preferably rigid.

0081Furthermore, in addition to the polarization layers and the switching layer, it can have one or more further functional layers. Some of the types of functional layers given below can be present in the device or all types. The layers are preferably passive, ie their effect cannot be changed.

0082The other functional layers are preferably selected from protective layers against weather influences, damage caused by the action of hard objects, aging and UV light. Such protective layers, their effects and methods for their application and use are known to the person skilled in the art.

0083Further preferred layers are selected from layers which block light of a certain wavelength or reduce its transmission, for example NIR light or light of a certain wavelength (color) in the visible range. NIR transmission-preventing layers, for example made of cholesteric liquid-crystalline material, ceramic material, metal or metal oxide, are preferred.

0084Further preferred functional layers are selected from orientation layers for liquid-crystalline compounds known to the person skilled in the art. At least two orientation layers are preferably present, at least one orientation layer being arranged on one side of the switching layer and at least one orientation layer on the opposite side of the switching layer. The orientation layers can also serve as substrate layers, so that no substrate layers are required in the device. In a preferred embodiment of the invention, the orientation layers consist of rubbed polyimide or rubbed polyacrylate.

0085The device preferably has the in <figref idref="f0001">Fig. 1</figref> shown structure. Here, (1) denotes the device, (2) denotes the switching layer, and (3a) and (3b) denote the polarization layers.<figref idref="f0001">Fig. 1</figref> describes the basic arrangement of the layers and is not intended to rule out, for example, that further functional layers, for example one or more orientation layers and / or one or more protective layers which block external influences or light of a certain wavelength, are located between the layers shown or outside the layer arrangement.

0086In <figref idref="f0001">Fig. 2</figref> A further preferred structure of the layer arrangement is shown, in which the arrangement containing the switching layer and the two polarization layers are located on a substrate layer (4).

0087The following exemplary embodiments describe preferred embodiments of the device according to the invention. Based on the examples, the person skilled in the art can recognize the functional principle of the invention and apply it to further, not explicitly described embodiments. No limitation of the invention to what is directly described can be derived from the examples.

Embodiments

1. Production of the polarization layers

0088The following components are used to produce the polarization layers:<tables id="tabl0002" num="0002"><table frame="all"><title>LC mixture A:</title><tgroup cols="2"><colspec colnum="1" colname="col1" colwidth="27mm" /><colspec colnum="2" colname="col2" colwidth="15mm" /><thead><row><entry valign="top">LC connection</entry><entry valign="top">%</entry></row></thead><tbody><row><entry>CP-3-N</entry><entry>20</entry></row><row><entry>PZG-5-N</entry><entry>10</entry></row><row><entry>PZP-1O-1</entry><entry>11</entry></row><row><entry>PZP-1O-5</entry><entry>16</entry></row><row><entry>PGU-3-F</entry><entry>9</entry></row><row><entry>CPZG-3-N</entry><entry>5</entry></row><row><entry>CPZG-4-N</entry><entry>5</entry></row><row><entry>CPZG-5-N</entry><entry>5</entry></row><row><entry>CCCZPC-3-3</entry><entry>3</entry></row><row><entry>CCZPC-3-4</entry><entry>3</entry></row><row><entry>CGPC-3-3</entry><entry>5</entry></row><row><entry>CGPC-5-3</entry><entry>4</entry></row><row><entry>CGPC-5-5</entry><entry>4</entry></row></tbody></tgroup></table></tables><tables id="tabl0003" num="0003"><table frame="all"><title>LC mixture B:</title><tgroup cols="2"><colspec colnum="1" colname="col1" colwidth="27mm" /><colspec colnum="2" colname="col2" colwidth="15mm" /><thead><row><entry valign="top">LC connection</entry><entry valign="top">%</entry></row></thead><tbody><row><entry>PZG-3-N</entry><entry>2</entry></row><row><entry>PZG-4-N</entry><entry>9</entry></row><row><entry>PZG-5-N</entry><entry>9</entry></row><row><entry>PZP-1-5</entry><entry>10</entry></row><row><entry>PZP-1O-1</entry><entry>17</entry></row><row><entry>PZP-1O-5</entry><entry>16</entry></row><row><entry>CP-3-N</entry><entry>12</entry></row><row><entry>PP-2-N</entry><entry>10</entry></row><row><entry>PGU-3-F</entry><entry>9</entry></row><row><entry>CPZG-3-N</entry><entry>3</entry></row><row><entry>CPZG-4-N</entry><entry>3</entry></row></tbody></tgroup></table></tables><tables id="tabl0004" num="0004"><table frame="all"><title>Dye mixture:</title><tgroup cols="2"><colspec colnum="1" colname="col1" colwidth="147mm" /><colspec colnum="2" colname="col2" colwidth="19mm" /><thead><row><entry valign="top">dye</entry><entry valign="top">Parts</entry></row></thead><tbody><row><entry><chemistry id="chem0005" num="0005"><img file="EP2798397B1_D0006.tif" /></chemistry></entry><entry>37</entry></row><row><entry><chemistry id="chem0006" num="0006"><img file="EP2798397B1_D0007.tif" /></chemistry></entry><entry>76</entry></row><row><entry><chemistry id="chem0007" num="0007"><img file="EP2798397B1_D0008.tif" /></chemistry></entry><entry>90</entry></row></tbody></tgroup></table></tables>

0089The following polarization layers EP-1 to EP-4 are produced from the specified components:<tables id="tabl0005" num="0005"><table frame="all"><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="13mm" /><colspec colnum="2" colname="col2" colwidth="24mm" /><colspec colnum="3" colname="col3" colwidth="41mm" /><thead><row><entry valign="top" /><entry valign="top">LC mixture</entry><entry valign="top">Proportion of dye mixture</entry></row></thead><tbody><row><entry>EP-1</entry><entry>A</entry><entry>0.1 %</entry></row><row><entry>EP-2</entry><entry>A</entry><entry>0.3 %</entry></row><row><entry>EP-3</entry><entry>A</entry><entry>0.5 %</entry></row><row><entry>EP-4</entry><entry>B</entry><entry>0.3 %</entry></row></tbody></tgroup></table></tables>

0090Furthermore, the following polarization layers VP-1 to VP-3 are produced or purchased commercially (VP-3) for comparison:<tables id="tabl0006" num="0006"><table frame="all"><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="13mm" /><colspec colnum="2" colname="col2" colwidth="24mm" /><colspec colnum="3" colname="col3" colwidth="41mm" /><thead><row><entry valign="top" /><entry valign="top">LC mixture</entry><entry valign="top">Proportion of dye mixture</entry></row></thead><tbody><row><entry>VP-1</entry><entry>A</entry><entry>1 %</entry></row><row><entry>VP-2</entry><entry>B</entry><entry>1 %</entry></row><row><entry namest="col1" nameend="col3" align="left" /></row><row><entry>VP-3</entry><entry namest="col2" nameend="col3" align="left">absorptive polarizer ITOS XP38</entry></row></tbody></tgroup></table></tables>

0091The following values ​​T1, T2 and P are obtained for the polarization layers (determined at 550 nm): T1: Transmission of the polarizer layer in the forward direction T2: Transmission of the polarizer layer in the blocking direction P: degree of polarization, can be determined from the equation: <maths id="math0002" num=""><math display="block"><mrow><mi mathvariant="normal">P</mi><mo>=</mo><mfenced separators=""><mi mathvariant="normal">T</mi><mn mathvariant="normal">1</mn><mo>−</mo><mi mathvariant="normal">T</mi><mn mathvariant="normal">2</mn></mfenced><mo>/</mo><mfenced separators=""><mi mathvariant="normal">T</mi><mn mathvariant="normal">1</mn><mo>+</mo><mi mathvariant="normal">T</mi><mn mathvariant="normal">2</mn></mfenced></mrow></math><img file="EP2798397B1_D0009.tif" /></maths><tables id="tabl0007" num="0007"><table frame="all"><tgroup cols="4"><colspec colnum="1" colname="col1" colwidth="13mm" /><colspec colnum="2" colname="col2" colwidth="14mm" /><colspec colnum="3" colname="col3" colwidth="14mm" /><colspec colnum="4" colname="col4" colwidth="12mm" /><thead><row><entry valign="top" /><entry valign="top">T1 /%</entry><entry valign="top">T2 /%</entry><entry valign="top">P /%</entry></row></thead><tbody><row><entry>EP-1</entry><entry>94.1</entry><entry>60.9</entry><entry>21.5</entry></row><row><entry>EP-2</entry><entry>86.1</entry><entry>22.2</entry><entry>58.9</entry></row><row><entry>EP-3</entry><entry>79.7</entry><entry>9.1</entry><entry>79.5</entry></row><row><entry>EP-4</entry><entry>79.1</entry><entry>26.3</entry><entry>50.2</entry></row><row><entry>VP-1</entry><entry>63.3</entry><entry>0.7</entry><entry>97.8</entry></row><row><entry>VP-2</entry><entry>48.0</entry><entry>1.2</entry><entry>95.0</entry></row><row><entry>VP-3</entry><entry>71.5</entry><entry>0.1</entry><entry>98.6</entry></row></tbody></tgroup></table></tables>

0092After producing and measuring a large number of differently produced polarization layers, an empirical relationship between the production parameters and the obtained value pairs T1 and P can be determined. In the present example it can be seen that as the dye concentration increases with the same LC mixture, there is an increase in P and a decrease in T1. When changing from mixture A to mixture B (cf. EP-3 and EP-4), with T1 remaining the same, a significantly reduced value for P can be achieved.

0093In the manner described, corresponding polarization layers can be produced for any desired value pairs T1 and P by using different concentrations of dye mixture and using different LC mixtures.

2nd Manufacture of devices

0094The devices E-1 to E-4 and the comparison devices V-1 to V-3 are produced by applying the polarization layers described above in each case on the top and on the bottom of a nematic rotary cell. The nematic rotary cell contains orientation layers and a layer made of a liquid-crystalline medium and is produced in accordance with methods which are generally known to the person skilled in the art.

0095For the devices obtained, the transmission in the state with higher light transmission (light transmission) and the transmission in the state with low light transmission (dark transmission) are determined. The switching stroke results from the difference between the two values. All values ​​were again determined at 550 nm.<tables id="tabl0008" num="0008"><table frame="all"><tgroup cols="4"><colspec colnum="1" colname="col1" colwidth="11mm" /><colspec colnum="2" colname="col2" colwidth="33mm" /><colspec colnum="3" colname="col3" colwidth="37mm" /><colspec colnum="4" colname="col4" colwidth="24mm" /><thead><row><entry valign="top" /><entry valign="top">Light transmission /%</entry><entry valign="top">Dark transmission /%</entry><entry valign="top">Switching stroke /%</entry></row></thead><tbody><row><entry>E-1</entry><entry>62.8%</entry><entry>57.3%</entry><entry>5.5%</entry></row><row><entry>E-2</entry><entry>39.5%</entry><entry>19.2%</entry><entry>20.3%</entry></row><row><entry>E-3</entry><entry>32.2%</entry><entry>7.3%</entry><entry>24.9%</entry></row><row><entry>E-4</entry><entry>34.8%</entry><entry>20.8%</entry><entry>14%</entry></row><row><entry>V-1</entry><entry>20.0%</entry><entry>0.5%</entry><entry>19.5%</entry></row><row><entry>V-2</entry><entry>11.5%</entry><entry>0.6%</entry><entry>10.3%</entry></row><row><entry>V-3</entry><entry>37.2</entry><entry>~0%</entry><entry>37.2%</entry></row></tbody></tgroup></table></tables>

0096The table shows that the devices according to the invention all have an acceptable dark transmission (approx. 7% and more). The values ​​for the light transmission and the switching stroke can be set independently of one another (see e.g. E-3 and E-4). This is highly desirable for the intended use, since the advantages of a high switching stroke and the advantages of high light transmission can be weighed against one another and the desired combination of the two values ​​can be set.

0097In the range of the parameters P (20-85%) and T1 (70-100%), which is selected for the devices E-1 to E-4, advantageous values ​​are obtained for both the light transmission and the switching stroke (see Table above).

0098The comparison devices according to the prior art (V-1 to V-3), which show values ​​for the parameters P and T1 outside these ranges, have a dark transmission which is disadvantageously low for the use of the devices in windows.

0099In the <figref idref="f0002 f0003 f0004">3 to 8</figref> the transmission spectra obtained for the devices E-1 to E-4 and V-1 and V-2 in the range from 400 to 900 nm are shown in the light state (curve 1) and in the dark state (curve 2).<ul id="ul0004" list-style="none"><li><figref idref="f0002">Fig. 3</figref> shows the transmission spectrum for the device E-1 according to the invention.</li><li><figref idref="f0002">Fig. 4</figref> shows the transmission spectrum for the device E-2 according to the invention.</li><li><figref idref="f0003">Fig. 5</figref> shows the transmission spectrum for the device E-3 according to the invention.</li><li><figref idref="f0003">Fig. 6</figref> shows the transmission spectrum for the device E-4 according to the invention.</li><li><figref idref="f0004">Fig. 7</figref> shows the transmission spectrum for the comparison device V-1.</li><li><figref idref="f0004">Fig. 8</figref> shows the transmission spectrum for the comparison device V-2.</li></ul>

3rd Alternative manufacturing processes for the polarization layers

0100According to a further example, the polarization layers are produced by additionally adding polymerizable monomers to the LC mixture and the dye mixture. For example, these are acrylates such as monoacrylates, diacrylates and multifunctional acrylates or epoxies or vinyl ethers. Mixtures of monomers can be used, for example mixtures of mono- and diacrylates or mixtures of epoxides and vinyl ethers. The monomers can have mesogenic groups. The mixture containing the liquid-crystalline medium, the dye and the monomers is then polymerized as a layer in the present case. The polymerization can take place, for example, by induction with UV light.

0101Particularly robust and temperature-stable polarization layers for devices according to the present invention can be produced by the method described above.

0102According to a further example (not according to the invention), the polarization layers are produced by stretching a polymer film made of polyvinyl alcohol (PVO). Iodine is then stored in the foils.

0103Polarization layers with different degrees of stretching of the PVA film, different iodine concentrations and different thicknesses are produced. The values ​​for the transmission in the forward direction (T1) and the degree of polarization are determined for the polarization layers obtained. After the production and measurement of a large number of differently produced polarization layers, an empirical relationship between the production parameters and the pairs of values ​​T1 and P obtained can be established. In this way, corresponding polarization layers can be produced for any desired value pairs T1 and P.