DE102020003265B3 - Optical element with variable transmission and screen with such an optical element - Google Patents

Abstract

The invention relates to an optical element, comprising an essentially plate-shaped substrate (S) with a first large area formed as a light entry surface and a second large area formed as a light exit surface, a liquid or a framework matrix (F) which is arranged between the first and second large area and contains up to 60 percent by volume electrophoretically or magnetophoretically movable particles of a first type (PA), with a large number of particles of the first type (PA) being present, which absorb light of one or more wavelengths or wavelength ranges, planar on one or both large areas and / or electromagnetic switching means formed between the large areas in the substrate (S) which, when switched on, generate an electromagnetic field effective between the large areas, whereby the particles of the first type (PA) are moved in the liquid or the framework matrix (F) so that yourself a Angle-dependent transmission of the optical element for light of the wavelengths or wavelength ranges that are absorbed by the particles of the first type (PA), which enters the substrate (S) via the light entry surface, changes.

Description

Field of invention

In recent years, great advances have been made in widening the viewing angle in LCDs. However, there are often situations in which this very large viewing area of a screen can be a disadvantage. Information is also increasingly available on mobile devices such as notebooks and tablet PCs, such as bank details or other personal details and sensitive data. Accordingly, people need control over who can see this sensitive data; You have to be able to choose between a wide viewing angle in order to share information on your display with others, e.g. when looking at vacation photos or for advertising purposes. On the other hand, you need a small viewing angle if you want to treat the image information confidentially. A similar problem arises in vehicle construction: With the engine switched on, the driver must not be distracted by image content, such as digital entertainment programs, while the front passenger wants to consume it while driving. A screen is therefore required that can switch between the corresponding display modes.

State of the art

Additional films based on micro-slats have already been used for mobile displays in order to achieve their visual data protection. However, these foils were not switchable, they always had to be put on by hand and then removed again. You also have to transport them separately to the display when you don't need them. A major disadvantage of using such lamellar foils is also associated with the associated loss of light.

the US 6,765,550 B2 describes such a privacy screen through micro-slats. The greatest disadvantage here is the mechanical removal or mechanical attachment of the filter as well as the loss of light in protected mode.

In the U.S. 5,993,940 A describes the use of a film with evenly arranged, small prism strips on its surface in order to achieve a privacy mode. Development and production are quite complex.

In the WO 2012/033583 A1 the switch between free and restricted view is generated by controlling liquid crystals between so-called "chromonic" layers. This results in a loss of light and the effort involved is quite high.

the US 2012/0235891 A1 describes a very complex backlight in a screen. There come according to 1 and 15th Not only several light guides are used, but also other complex optical elements such as microlens elements 40 and prismatic structures 50, which transform the light from the rear lighting on the way to the front lighting. This is expensive and time-consuming to implement and also associated with loss of light. According to the variant after 17th in the US 2012/0235891 Both light sources 4R and 18 produce light with a narrow angle of illumination, the light from the rear light source 18 first being converted into light with a large angle of illumination in a complex manner. This complex transformation is - as already noted above - strongly reducing the brightness.

According to the JP 2007-155783 A special optical surfaces 19, which are complex to calculate and manufacture, are used, which then deflect light into various narrow or wide areas depending on the angle of incidence of light. These structures are similar to Fresnel lenses. There are also interference edges that deflect light in undesired directions. It therefore remains unclear whether really sensible light distributions can be achieved.

In the US 2013/0308185 A1 describes a special, stepped light guide that emits light over a large area in different directions, depending on the direction from which it is illuminated from a narrow side. In interaction with a transmissive image display device, for example an LC display, a screen that can be switched between free and restricted viewing mode can thus be generated. The disadvantage here is, among other things, that the restricted visual effect can be generated either only for left / right or for up / down, but not for left / right / up / down at the same time, as is necessary for certain payment transactions, for example. In addition, residual light is still visible from blocked viewing angles in restricted viewing mode.

the WO 2015/121398 A1 the applicant describes a screen with two operating modes, in which scatter particles are essentially present in the volume of the corresponding light guide for switching the operating modes. The scattering particles selected there from a polymer, however, usually have the disadvantage that light is coupled out from both large surfaces, so that about half of the useful light is emitted in the wrong direction, namely towards the background lighting, and is not there to a sufficient extent due to the structure can be recycled. In addition, the polymer scattering particles distributed in the volume of the light guide can, under certain circumstances, especially at a higher concentration, lead to scattering effects that cause the Reduce the privacy effect in the protected operating mode.

the DE 10 2019 006 022 B3 describes an optical element comprising a plate-shaped substrate with a plurality of lamellar fluid chambers embedded therein, these chambers being filled with a liquid. The liquid contains electrophoretically or magnetophoretically movable particles which absorb light. Due to variable electromagnetic fields that can be applied via switching means, these particles are selectively moved so that an angle-dependent transmission of the optical element for light which enters the substrate at angles such that it hits the fluid chambers changes. Here, however, the said fluid chambers are absolutely necessary, which entails a certain mastering and manufacturing effort.

the US 2015/0346578 A1 discloses a method to drive an electrophoretic display. A dielectrophoretic movement of particles is used here. A function for the defined variation of the angle-dependent transmission of this device is not provided here and cannot be implemented with the means disclosed in this document.

In the WO 2018/232 099 A1 describes an electro-optical medium with encapsulated pigments in a gelatin binder. A function for the defined variation of the angle-dependent transmission of this device is not provided here either and cannot be implemented with the means disclosed in this document either.

Finally describes the U.S. 6,323,989 , B1 an electrophoretic display with nanoparticles. However, the teaching on which it is based does not allow a function for the defined variation of the angle-dependent transmission and cannot be implemented with the means available there either.

The aforementioned methods and arrangements generally have the disadvantage that they significantly reduce the brightness of the basic screen and / or require a complex and expensive optical element for mode switching and / or reduce the resolution in the freely viewable mode.

Description of the invention

It is therefore the object of the invention to describe an optical element which can influence the transmission as a function of the angle (optionally perpendicular) and which can switch between at least two operating states. The optical element should be able to be implemented inexpensively and, in particular, be universally usable with different types of screen in order to enable switching between a privacy screen and a free viewing mode, the resolution of such a screen being essentially not to be reduced. Optionally, the optical element should do without lamellar chambers.

• - ein im Wesentlichen plattenförmiges Substrat mit einer als Lichteintrittsfläche ausgebildeten ersten Großfläche und einer als Lichtaustrittsfläche zweiten ausgebildeten Großfläche,
• - eine Flüssigkeit oder eine Gerüstmatrix, die zwischen der ersten und der zweiten Großfläche angeordnet ist und bis zu 60 Volumenprozent elektrophoretisch oder magnetophoretisch bewegbare Partikel einer ersten Art P_A enthält, wobei eine Vielzahl an Partikeln der ersten Art P_A vorhanden ist, welche Licht einer oder mehrerer Wellenlängen oder Wellenlängenbereiche absorbieren,
• - flächenförmig an einer oder beiden Großflächen und/oder zwischen den Großflächen im Substrat ausgebildete elektromagnetische Schaltmittel, welche in einem eingeschalteten Zustand ein zwischen den Großflächen wirksames elektromagnetisches Feld erzeugen, wodurch die Partikel der ersten Art P_A in der Flüssigkeit oder der Gerüstmatrix bewegt werden, so dass sich eine winkelabhängige Transmission des optischen Elements für Licht der Wellenlängen oder Wellenlängenbereiche, die von den Partikeln der ersten Art P_A absorbiert werden, welches über die Lichteintrittsfläche in das Substrat eintritt, ändert, so dass mittels der elektromagnetischen Schaltmittel und einer Ansteuerschaltung mindestens zwei Betriebszustände definiert sind, wobei in einem ersten Betriebszustand B1 die winkelabhängige Transmission bei mehr als 50% liegt und in einem zweiten Betriebszustand B2 bei weniger als 50% in einem Winkelbereich von mehr als 30° um eine Flächennormale der zweiten Großfläche des Substrats,

According to the invention, this object is achieved by an optical element comprising

• - an essentially plate-shaped substrate with a first large area designed as a light entry area and a second large area designed as a light exit area,
• - a liquid or a framework matrix, which is arranged between the first and the second large area and up to 60 percent by volume electrophoretically or magnetophoretically movable particles of a first type P _A contains, wherein a plurality of particles of the first type P _A is present which absorb light of one or more wavelengths or wavelength ranges,
• - Electromagnetic switching means which are designed flat on one or both large areas and / or between the large areas in the substrate, which, when switched on, generate an electromagnetic field effective between the large areas, whereby the particles of the first type P _A are moved in the liquid or the framework matrix, so that an angle-dependent transmission of the optical element for light of the wavelengths or wavelength ranges, which is caused by the particles of the first type P _A which enters the substrate via the light entry surface changes, so that at least two operating states are defined by means of the electromagnetic switching means and a control circuit, with the angle-dependent transmission being more than 50% in a first operating state B1 and in a second operating state B2 with less than 50% in an angular range of more than 30 ° around a surface normal of the second large surface of the substrate,

The invention is designed in such a way that all electromagnetic switching means are designed as flat electrodes EPN with polarity reversible between positive and negative on the first and second large area, and that in the first operating state B1 the electrodes EPN on the first large area have a positive and the electrodes EPN on the second large area have a negative polarity or vice versa, so that more than 70% of the particles of the first type P _A in each case not more than a quarter of the thickness of the liquid or the matrix F away from the electrodes EPN and / or diffusely distributed in the liquid or the framework matrix F are localized, and in the second operating state B2 seen along a surface normal of the first or second large area negatively polarized electrodes EPN on the first large area negatively polarized electrodes EPN on the second large area and positively polarized electrodes EPN on the first large area positively polarized electrodes EPN on the second Large areas are opposite, with a negative electrode EPN arranged between two positively polarized electrodes EPN on each of the large areas and a positive electrode EPN between two negatively polarized electrodes EPN, so that more than 70% of the particles of the first type ( P _A ) are each located between electrodes EPN with the same polarity, as a result of which the angle-dependent transmission in the first operating state B1 is more than 60% and in the second operating state B2 is less than 5%. This applies in an angle range of preferably +/- 30 ° to +/- 90 ° (i.e. in each case from -90 ° to -30 ° and at the same time from + 30 ° to + 90 °, but not between -30 ° and + 30 ° ) based on a surface normal of the second large area of the substrate and measured in a direction perpendicular to a longitudinal extension of the electrodes EPN. The angular range can also be varied and instead of +/- 30 ° also the range from +/- 10 ° to +/- 90 °, +/- 20 ° to +/- 90 °, +/- 45 ° to + / -90 ° or +/- 25 ° to +/- 90 °. Said preferred direction can be oriented here, for example, parallel to the second large area of the substrate and in a horizontal position for a viewer arranged in front of the optical element.

The framework matrix is designed, for example, as a polymer matrix, preferably as a gel matrix. The liquid can be polar or non-polar. It can also consist, for example, of water, oil, toluene or formaldehyde, also mixed with a 10% by volume ferrofluid and / or electrolyte.

The one or more wavelengths or wavelength ranges in which the electrophoretically or magnetophoretically movable particles P _A Absorb light, are preferably in the visible spectrum and particularly preferably completely cover it. For special purposes, however, they can also be outside the visible spectrum, for example if UV or IR light is to be influenced, for example for purposes of measurement technology.

The first and second large areas of the plate-shaped substrate are preferably arranged parallel to one another. However, in special configurations, for example if special angle-dependent transmissions of the optical element are to be achieved, they can also be arranged non-parallel, e.g. in a wedge shape at a defined angle of up to 20 degrees to one another.

The first large area of the plate-shaped substrate, designed as a light entry area, is usually located on the rear side of the substrate from the observer's point of view and, depending on the application of the optical element, is adjacent to an image display device, a light source or an air volume, for example. From the last-mentioned objects, light then enters the substrate through the said light-entry surface.

With the particles of the first kind P _A it can be nanoparticles, quantum dots and / or dyes which have a spatial extension of a maximum of 200 nm, preferably a maximum of 50 nm, particularly preferably a maximum of 20 nm. However, other configurations are explicitly possible. Spatial expansion here means the maximum expansion in three-dimensional space or the hydrodynamic radius, whichever is larger. In the case of spherical particles, this is the diameter. In the case of chain-shaped particles, this is the greatest possible distance that two points on the surface of the particle can have from one another.

Furthermore, the particles of the first type P _A as BPQDs (Black Phosphorus Quantum Dots), lead sulfide (PbS), CdTeSeS quantum dots, azo dyes and / or as metal oxide particles, preferably made of chromium (IV) oxide or Fe ₂ O ₃ , and a size between 2 nm and 50 nm each inclusive.

Alternatively, it is possible that the particles of the first type P _A as paramagnetic bodies, preferably as spheres with a diameter of at least 100 nm, made of a paramagnetic or diamagnetic carrier material with a relative magnetic permeability between 0 and 2, preferably melanic resin or polystyrene, are formed, the bodies either with paramagnetic or superparamagnetic nanoparticles with a relative magnetic permeability greater than 10, preferably Fe ₂ O ₃ nanoparticles, are coated, or the carrier material is interspersed with these nanoparticles. Other implementation variants are also possible.

The particles should preferably P _A still have a surface functionalization with a high zeta potential, on the one hand as stabilization in the liquid and on the other hand for an improvement of the electrophoretic properties. This can be implemented, for example, with PVP (polyvinylpyrrolidone) or PEG (polyethylene glycol) for aqueous systems.

In general, within the scope of the invention, the particles of the first type P _A either electrically charged and the electromagnetic Switching means are designed as electrodes for generating a static or dynamic electrical field or the particles of the first type P _A are magnetic, in particular paramagnetic or superparamagnetic, and the electromagnetic switching means are designed as electrically conductive layers for generating a static or dynamic magnetic field, so that the electromagnetic or magnetophoretic particles of the first type P _A move in an electric or magnetic field in the liquid or framework matrix.

As already described above, at least two operating states are defined by means of the electromagnetic switching means and a control circuit, with the angle-dependent transmission being more than 50% in a first operating state B1 and less than 50% in an angular range in a second operating state B2 of more than 30 ° (this angle can also be varied, for example 10 °, 20 ° or 25 °) about a surface normal of the second large surface of the substrate. Said angular range around a surface normal can be measured, for example, within a plane which contains the center perpendicular as surface normal, ie perpendicular to the second large surface of the substrate S. and is horizontal from the point of view of a beholder. This definition also applies to further considerations.

In other words: the different operating states B1, B2, ... differ in particular in that the respective local concentration and localization of the particles within the substrate is changed in order to change the transmission properties due to the absorption by the particles.

It is also within the scope of the invention that more than two operating states B1, B2, B3 etc. can be set. For this purpose, for example, compared to the variants described above for the operating states B1 and B2 in a third (fourth, fifth, ...) operating state, a different type of electromagnetic field would be applied, which means that the concentrations or the positions of the particles or particle types are different is strong between the operating states, so that a total of three or more different angle-dependent degrees of transmission can be achieved. This can be of interest, for example, for angle-dependent dimming applications.

The leading physical effects for the movement of the particles when an electromagnetic field is applied, in particular a static field, are accordingly (di-) electrophoresis or magnetophoresis. In the event that no electrical or no magnetic field is applied, the particles move in the chambers, in particular due to diffusion, and thus spread homogeneously over time. For particles that are no larger than 50 nm, gravity does not play a role; they do not sediment, i.e. the particles remain suspended in the liquid or gel matrix.

For all configurations of the optical element described above, the electromagnetic switching means for perpendicularly across the light entry surface into the substrate S. incident light in the visible wavelength range is at least 50% transparent.

Furthermore, it is conceivable that the electromagnetic switching means are divided into several, separately switchable segments, so that local switchability between the first operating state B1 and the second operating state B2 is made possible. Local switchability means that the operating state between B1 and B2 is not changed simultaneously in all areas of the optical element, but rather that areas with both operating states B1 and B2 are present on the optical element at the same time. This is advantageous, for example, when, when using the optical element in front of a screen, parts of the displayed image content are to be visible and others are not to be visible from a viewing angle of more than 30 degrees to the side.

In a further advantageous variation, several types of particles (Px, Py, ...) are present in the liquid at the same time, which differ in their optical or absorption properties and / or their transport properties in the electromagnetic field. “Transport properties” particularly mean the behavior of the particles during the respective phoresis (transport in the field). This variant is particularly important in the case of nanoparticles: the difference between the types of particles is, for example, the particle size and / or the surface functionalization, i.e. the zeta potential. If quantum dots or dyes are used as particles and if these are fluorescent, a so-called “quencher” material is preferably used to suppress the fluorescence.

• - ein erfindungsgemäßes optisches Element, und
• - eine dem optischen Element von einem Betrachter aus gesehen nach- oder vorgeordnete Bildwiedergabeeinheit.

In addition, the invention also includes a screen which can be operated in a first operating state B1 for a free viewing mode and in a second operating state B2 for a restricted viewing mode

• - An optical element according to the invention, and
• - An image reproduction unit arranged downstream or upstream of the optical element as seen by a viewer.

The image display unit is, for example, an OLED, an LCD display, an SED display, a FED display, in a microLED display or a VFD display. Since the optical element is effective regardless of the type of image display unit, any other types of screen are also possible.

It is also possible, for example, to use the optical element according to the invention in an image display unit which has a background lighting, such as, for example, in an LCD screen. The optical element would then advantageously be arranged between the image display panel (i.e. the LCD panel) and the backlight in order to switch between a first operating state B1 for a free viewing mode and a second operating state B2 for a restricted viewing mode, because the light of the Backlight is focused once (B2) and once not focused (B1) due to the optical element. “Focusing” does not mean focusing in the manner of lenses, but rather a narrowing of the radiation area.

In principle, the performance of the invention is retained if the parameters described above are varied within certain limits.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the specified combinations, but also in other combinations or on their own, without departing from the scope of the present invention.

• 1 die Prinzipskizze eines optischen Elements im Betriebszustand B2,
• 2 die Prinzipskizze eines optischen Elements im Betriebszustand B1 in einer ersten Variante,
• 3 die Prinzipskizze eines optischen Elements im Betriebszustand B1 in einer zweiten Variante, sowie
• 4 die Prinzipskizze zur beispielhaften Wirkung eines optischen Elements in beiden Betriebszuständen B1 und B2 hinsichtlich der Transmission über verschiedene Winkel.

The invention is explained in more detail below with reference to drawings, which also show features essential to the invention. It shows

• 1 the schematic diagram of an optical element in operating state B2,
• 2 the schematic diagram of an optical element in operating state B1 in a first variant,
• 3 the schematic diagram of an optical element in the operating state B1 in a second variant, as well as
• 4th the schematic diagram for the exemplary effect of an optical element in both operating states B1 and B2 with regard to the transmission over different angles.

The drawings are not true to scale and only represent basic representations. In addition, for the sake of better clarity, only a small selection of electrodes, light beams, particles or the like are shown in each case, although in reality there can or is a veritable large number of these.

In 1 the schematic diagram of an optical element in the operating state B2 is thus shown. 2 shows the schematic diagram of an optical element in the operating state B1 in a first variant and 3 in a second variant.

• - ein im Wesentlichen plattenförmiges Substrat S mit einer als Lichteintrittsfläche ausgebildeten ersten Großfläche und einer als Lichtaustrittsfläche zweiten ausgebildeten Großfläche,
• - eine Flüssigkeit oder eine Gerüstmatrix F, die zwischen der ersten und der zweiten Großfläche angeordnet ist und bis zu 60 Volumenprozent elektrophoretisch oder magnetophoretisch bewegbare Partikel einer ersten Art P_A enthält, wobei eine Vielzahl an Partikeln der ersten Art P_A vorhanden ist, welche Licht einer oder mehrerer Wellenlängen oder Wellenlängenbereiche absorbieren,
• - flächenförmig an einer oder beiden Großflächen und/oder zwischen den Großflächen im Substrat S ausgebildete elektromagnetische Schaltmittel, welche in einem eingeschalteten Zustand ein zwischen den Großflächen wirksames elektromagnetisches Feld erzeugen, wodurch die Partikel der ersten Art P_A in der Flüssigkeit oder der Gerüstmatrix F bewegt werden, so dass sich eine winkelabhängige Transmission des optischen Elements für Licht der Wellenlängen oder Wellenlängenbereiche, die von den Partikeln der ersten Art P_A absorbiert werden, welches über die Lichteintrittsfläche in das Substrat S eintritt, ändert, so dass mittels der elektromagnetischen Schaltmittel und einer Ansteuerschaltung mindestens zwei Betriebszustände definiert sind, wobei in einem ersten Betriebszustand B1 die winkelabhängige Transmission bei mehr als 50% liegt und in einem zweiten Betriebszustand B2 bei weniger als 50% in einem Winkelbereich von mehr als 30° um eine Flächennormale der zweiten Großfläche des Substrats.

The optical element comprises

• - a substantially plate-shaped substrate S. with a first large area designed as a light entry area and a second large area designed as a light exit area,
• - a liquid or a framework matrix F. , which is arranged between the first and the second large area and up to 60 percent by volume electrophoretically or magnetophoretically movable particles of a first type P _A contains, wherein a plurality of particles of the first type P _A is present which absorb light of one or more wavelengths or wavelength ranges,
• - flat on one or both large areas and / or between the large areas in the substrate S. trained electromagnetic switching means which, when switched on, generate an electromagnetic field effective between the large areas, whereby the particles of the first type P _A in the liquid or the framework matrix F. are moved, so that an angle-dependent transmission of the optical element for light of the wavelengths or wavelength ranges, which by the particles of the first type P _A are absorbed, which through the light entry surface in the substrate S. occurs, changes, so that at least two operating states are defined by means of the electromagnetic switching means and a control circuit, the angle-dependent transmission being more than 50% in a first operating state B1 and less than 50% in an angular range of more in a second operating state B2 than 30 ° around a surface normal of the second large area of the substrate.

The optical element is designed in such a way that all electromagnetic switching means are designed as flat electrodes EPN with polarity reversible between positive and negative on the first and second large area, and that in the first operating state B1 the electrodes EPN on the first large area have a positive and a Electrodes EPN on the second large area have a negative polarity or vice versa, so that more than 70% of the particles of the first type P _A in each case not more than a quarter of the thickness of the liquid or the matrix F. from the electrodes concerned EPN removed (as in 3 shown) and / or diffusely distributed in the liquid or the framework matrix F. are localized (as in 2 shown). The arrows indicate selected light rays that show that the light can penetrate the substrate over a large angular range. Thus, the angle-dependent transmission in the first operating state B1 is more than 60% in an angle range of more than 30 ° (this angle can also be varied, for example 10 °, 20 ° or 25 °) around a surface normal of the second large surface of the substrate S. .

Furthermore, the 1 the schematic diagram of an optical element in operating state B2. Here, seen along a surface normal of the first or second large area, negatively polarized electrodes EPN on the first large area, negatively polarized electrodes EPN on the second large area and positively polarized electrodes EPN on the first large area opposite positively polarized electrodes EPN on the second large area, with along a preferred direction between two positively polarized electrodes EPN on each of the large areas a negatively polarized electrode EPN and between two negatively polarized electrodes EPN a positive electrode EPN is arranged, so that more than 70% of the particles of the first type ( P _A ) are each located between electrodes with the same polarity EPN, whereby the angle-dependent transmission is less than 5%, in an angular range of more than 30 ° (this angle can also be varied, e.g. 10 °, 20 ° or 25 °) around a surface normal second large area of the substrate S. . Said preferred direction can here, for example, be parallel to the second large area of the substrate S. and be aligned in a horizontal position for a viewer arranged in front of the optical element.

The scaffolding matrix F. is designed, for example, as a polymer matrix, preferably as a gel matrix. The liquid F. can be polar or non-polar. It can also consist, for example, of water, oil, toluene or formaldehyde, also mixed with electrolytes.

The first large area of the plate-shaped substrate, designed as a light entry area S. is usually located on the back of the substrate from the observer's point of view S. and, depending on the application of the optical element, is adjacent, for example, to an image display device, a light source or to a volume of air. From the last-mentioned objects, light then enters the substrate through the said light-entry surface.

The one or more wavelengths or wavelength ranges in which the electrophoretically or magnetophoretically movable particles P _A Absorb light, are preferably in the visible spectrum and particularly preferably completely cover it.

The first and the second large area of the plate-shaped substrate S. are preferably arranged parallel to one another. However, in special configurations, for example when special angle-dependent transmissions of the optical element are to be achieved, they can also be arranged non-parallel, for example in a wedge shape at a defined angle of up to 20 degrees to one another.

With the particles of the first kind P _A it can be nanoparticles, quantum dots and / or dyes which have a spatial extension of a maximum of 200 nm, preferably a maximum of 50 nm, particularly preferably a maximum of 20 nm. However, other configurations are explicitly possible. Spatial expansion here means the maximum expansion in three-dimensional space or the hydrodynamic radius, whichever is larger. In the case of spherical particles, this is the diameter. In the case of chain-shaped particles, this is the greatest possible distance that two points on the surface of the particle can have from one another. Furthermore, the particles of the first type P _A as BPQDs (Black Phosphorus Quantum Dots), lead sulfide (PbS), CdTeSeS quantum dots, azo dyes and / or as metal oxide particles, preferably made of chromium (IV) oxide or Fe ₂ O ₃ , and a size between 2 nm and 50 nm each inclusive.

Alternatively, it is possible that the particles of the first type .P _A as paramagnetic bodies, preferably as spheres with a diameter of at least 100 nm, made of a paramagnetic or diamagnetic carrier material with a relative magnetic permeability between 0 and 2, preferably melanin resin or polystyrene, are formed, wherein the bodies are coated either with paramagnetic or superparamagnetic nanoparticles with a relative magnetic permeability greater than 10, preferably Fe ₂ O ₃ nanoparticles, or the carrier material is interspersed with these nanoparticles. Other implementation variants are also possible. The particles should preferably P _A additionally have a surface functionalization with a high zeta potential, on the one hand as a stabilization in the liquid F. and on the other hand for an improvement of the electrophoretic properties. This can be implemented, for example, with PVP (polyvinylpyrrolidone) or PEG (polyethylene glycol) for aqueous systems.

In general, within the scope of the invention, the particles of the first type P _A are either electrically charged and the electromagnetic switching means are designed as electrodes for generating a static or dynamic electric field or the particles of the first type P _A are para- or superpararmagnetic and the electromagnetic switching means are designed as electrically conductive layers for generating a static or dynamic magnetic field, so that the electro- or magnetophoretic particles of the first type P _A in the electric or magnetic field in the liquid or framework matrix F. move.

As already described, at least two operating states are defined by means of the electromagnetic switching means and a control circuit, with the angle-dependent transmission being more than 50% in a first operating state B1 and less than 50% in an angular range of more than 30% in a second operating state B2 ° (this angle can also be varied, for example 10 °, 20 ° or 25 °) about a surface normal of the second large surface of the substrate. Said angular range around a surface normal can be measured, for example, within a plane which contains the center perpendicular as surface normal, ie perpendicular to the second large surface of the substrate S. and is horizontal from the point of view of a beholder. This definition also applies to further considerations.

For all configurations it should apply that the electromagnetic switching means for perpendicularly over the light entry surface in the substrate S. incident light in the visible wavelength range is at least 50%, preferably over 80%, transparent.

Furthermore, it is conceivable for all design variants of the optical element that the electromagnetic switching means EPN, E1 or E2 are divided into several separately switchable segments, so that local switchability between the first operating state B1 and the second operating state B2 is made possible. Local switchability here means that the operating state between B1 and B2 is not changed simultaneously in all areas of the optical element, but rather that areas with both operating states B1 and B2 are realized on the optical element at the same time. This is advantageous, for example, when, when using the optical element in front of a screen, parts of the displayed image content are to be visible and others are not to be visible from a viewing angle of more than 30 degrees to the side. It is also conceivable here that at least one electrode of the electrodes EPN (e.g. the one in the middle) can advantageously be configured to reflect downwards in order to improve the performance and the efficiency of the optical structure.

For all of the aforementioned configurations of the optical element, FIG 4th the schematic diagram for the exemplary effect in each of the two operating states B1 and B2 with regard to the transmission over different angles. For the sake of simplicity, these are standardized values. The dashed line corresponds to the operating state B2, the solid line to the operating state B1.

The above-described optical element solves the problem: An optical element was described which can influence the transmission as a function of the angle (and optionally perpendicular) and which can switch between at least two operating states. The optical element can be implemented inexpensively and, in particular, can be used universally with different types of screen in order to enable switching between a privacy screen and a free viewing mode, the resolution of such a screen being essentially not reduced.

The invention described above can be used in conjunction with an image display device wherever confidential data is displayed and / or entered, such as when entering a PIN or for displaying data at ATMs or payment terminals or for entering passwords or when reading emails on mobile phones Devices. As described above, the invention can also be used in cars.

Claims (9)

An optical element, comprising - a substantially plate-shaped substrate (S) with a first large area designed as a light entry surface and a second large area designed as a light exit area, - a liquid or a framework matrix (F) which is arranged between the first and the second large area and Contains up to 60 percent by volume electrophoretically or magnetophoretically movable particles of a first type (P _A ), with a large number of particles of the first type (P _A ) being present, which absorb light of one or more wavelengths or wavelength ranges, flat on one or both large surfaces and / or electromagnetic switching means formed between the large areas in the substrate (S) which, when switched on, generate an electromagnetic field effective between the large areas, whereby the particles of the first type (P _A ) are moved in the liquid or the framework matrix (F) so that an angle-dependent ge transmission of the optical element for light of the wavelengths or wavelength ranges that are _{absorbed by the particles of the first type (P A} ), which enters the substrate (S) via the light entry surface, changes, so that by means of the electromagnetic switching means and a control circuit at least two operating states are defined, whereby in a first operating state B1 the angle-dependent transmission is more than 50% and in a second operating state B2 less than 50% in an angular range of more than 30 ° around a surface normal of the second large surface of the substrate, wherein all electromagnetic switching means are designed as planar electrodes (EPN) with polarity reversible between positive and negative on the first and second large area and in the first operating state B1 the electrodes (EPN) on the first large area have a positive and the electrodes (EPN) on the second large area have a negative polarity or vice versa, so that more than 70% of the particles of the first type (P _A ) are no more than a quarter of the thickness of the liquid or the matrix (F) away from the electrodes (EPN) and / or are located diffusely distributed in the liquid or the framework matrix (F), and in the second operating state B2 Negatively polarized electrodes (EPN) on the first large surface, negatively polarized electrodes (EPN) on the second large surface and positively polarized electrodes (EPN) on the first large surface, positively polarized electrodes (EPN) on the second large surface, seen along a surface normal of the first or second large surface opposite, wherein a negative electrode (EPN) and between two negatively polarized electrodes (EPN) a positive electrode EPN is arranged along a preferred direction between two positively polarized electrodes (EPN) on each of the large areas, so that more than 70% of the particles of first type (P _A ) are each located between electrodes with the same polarity (EPN), whereby the angle-dependent transmission in the first operating state B1 is more than 60% and in the second operating state B2 less than 5%, in an angular range of more than 30 ° around a Area normals of the second large area of the substrate. Optical element according to Claim 1 , characterized in that the framework matrix (F) is designed as a polymer matrix, preferably as a gel matrix. Optical element according to one of the preceding claims, characterized in that the particles of the first type (P _A ) are designed as nanoparticles, quantum dots and / or dyes and have a spatial extension of a maximum of 200 nm, preferably a maximum of 50 nm, particularly preferably a maximum 20 nm. Optical element according to Claim 3 , characterized in that the particles of the first type (P _A ) as BPQDs (Black Phosphorus Quantum Dots), lead sulfide (PbS), CdTeSeS quantum dots, azo dyes and / or as metal oxide particles, preferably made of chromium (IV) oxide or Fe ₂ O _{3 are} formed and have a size between 2 nm and 50 nm inclusive. Optical element according to Claim 3 , characterized in that the particles of the first type (P _A ) as paramagnetic bodies, preferably as spheres with a diameter of at least 100 nm, made of a paramagnetic or diamagnetic carrier material with a relative magnetic permeability between 0 and 2, preferably melanin resin or polystyrene, are formed, wherein the bodies are coated either with paramagnetic or superparamagnetic nanoparticles with a relative magnetic permeability greater than 10, preferably Fe ₂ O ₃ nanoparticles, or the carrier material is interspersed with these nanoparticles. Optical element according to Claim 1 , characterized in that the particles of the first type (P _A ) are either electrically charged and the electromagnetic switching means are designed as electrodes for generating a static or dynamic electric field or the particles of the first type (P _A ) are magnetic and the electromagnetic switching means are designed as electrically conductive layers for generating a static or dynamic magnetic field, so that the electro- or magnetophoretic particles of the first type (P _A ) move in the electric or magnetic field in the liquid or framework matrix (F). Optical element according to one of the preceding claims, characterized in that the electromagnetic switching means are divided into several, separately switchable segments, so that local switchability between the first operating state B1 and the second operating state B2 is made possible. Optical element according to one of the preceding claims, characterized in that several types of particles (Px, Py, ...) which differ in their transport properties in the electromagnetic field are present in the liquid or in the framework matrix (F). Screen that can be operated in a first operating state B1 for a free viewing mode and in a second operating state B2 for a restricted viewing mode, comprising - an optical element according to one of the Claims 1 until 8th , and an image display unit arranged downstream or upstream of the optical element as seen by a viewer.

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