WO2024105140A1

WO2024105140A1 - Method for thermally treating a pdlc-functional element

Info

Publication number: WO2024105140A1
Application number: PCT/EP2023/081991
Authority: WO
Inventors: Achim ZEICHNER; Jefferson DO ROSARIO; Huixing Zhang; Tobias Peter ASCHENBRENNER
Original assignee: Saint-Gobain Glass France
Priority date: 2022-11-18
Filing date: 2023-11-16
Publication date: 2024-05-23

Abstract

The invention relates to a method for thermally treating a PDLC-functional element (4), wherein A) i. a voltage-free switch state (off) is applied to the switch region by means of a PDLC-control unit (10) and ii. the PDLC-functional element (4) is heated to a temperature TA which is greater than or equal to the phase transition temperature (PT) by means of a heating device (20) and is kept at a temperature which is greater than or equal to the phase transition temperature (PT), and B) after a duration t of more than 1 min, the PDLC-functional element (4) is cooled to a temperature TB which is lower than or equal to the phase transition temperature (PT), wherein the voltage-free switch state (off) is maintained at the switch region.

Description

Process for heat treatment of a PDLC functional element

The invention relates to a method for heat treatment and in particular for restoring the optical properties of a PDLC functional element, preferably a PDLC functional element with several independently switchable switching regions, a device for carrying out the method and the use thereof.

Glazing with electrically controllable optical properties is known as such. They usually comprise composite panes which are equipped with functional elements whose optical properties can be changed by an applied electrical voltage. The electrical voltage is applied via a PDLC control unit which is connected to two surface electrodes of the functional element, between which the active layer of the functional element is located. An example of such functional elements are SPD functional elements (suspended particle device), which are known, for example, from EP 0876608 B1 and WO 2011033313 A1. The transmission of visible light through SPD functional elements can be controlled by the applied voltage. Another example is standard PDLC functional elements (polymer dispersed liquid crystal), which are known, for example, from DE 102008026339 A1. The active layer contains liquid crystals which are embedded in a polymer matrix. In the "off" switching state, no voltage is applied, so the liquid crystals are aligned in a disordered manner, which leads to a strong scattering of the light passing through the active layer. In the "on" switching state, a voltage is applied to the surface electrodes, so that liquid crystals align in a common direction and the scattering of light through the active layer is reduced. The PDLC functional element therefore works less by reducing the overall transmission than by increasing the scattering, which can prevent clear visibility or ensure glare protection. Electrochromic functional elements are also known, for example from US 20120026573 A1, WO 2010147494 A1 and EP 1862849 A1 and WO 2012007334 A1, in which a change in transmission occurs through electrochemical processes induced by the applied electrical voltage.

Such glazing can be used, for example, as vehicle windows, the optical properties of which can then be controlled electrically. They can be used, for example, as roof windows to reduce solar radiation or to reduce annoying reflections. Such roof windows are known, for example, from DE 10043141 A1 and EP 3456913 A1. Windshields have also been proposed in which an electrically controllable sun visor is implemented by means of a switchable functional element in order to replace the conventional mechanically folding sun visor in motor vehicles. Windshields with electrically controllable sun visors are known, for example, from DE 102013001334 A1, DE 102005049081 B3, DE 102005007427 A1 and DE 102007027296 A1.

It is also known to provide such glazings, or the switchable functional elements in the glazings, with several switching areas whose optical properties can be switched independently of one another. In this way, an area of the functional element can be selectively darkened or provided with a high level of light scattering, while other areas remain light or transparent. Glazings with independent switching areas and a method for producing them are known, for example, from WO 2014072137 A1 or WO 2017157626 A1.

The independent switching areas are typically formed by dividing one of the surface electrodes by insulation lines into separate switching areas ((electrode) segments), which are each independently connected to the PDLC control unit and can therefore be controlled independently, while the other surface electrode, for example, has no insulation lines. The insulation lines are typically introduced into the surface electrode by laser processing. The surface electrodes cannot be selected with regard to optimal electrical conductivity, since they must be transparent to ensure visibility through the composite pane. ITO layers are typically used as surface electrodes, which have low conductivity or high electrical resistance.

The present invention is based on the object of providing a method for heat treatment and in particular for restoring the optical properties of a PDLC functional element, preferably with at least two adjacent, independently switchable switching regions.

The invention further comprises a device for carrying out the method according to the invention. The method according to the invention and the device according to the invention are presented together below, with explanations and preferred Embodiments relate equally to the method and the device. If preferred features are described in connection with the method, this means that the device is preferably designed and suitable accordingly. Conversely, if preferred features are described in connection with the device, this means that the method is preferably carried out accordingly.

The object is achieved according to the invention by a method for heat treatment of a PDLC functional element, preferably with at least two adjacent, independently switchable switching areas, wherein in a first method step A) i. a control unit applies a voltage-free switching state (off) to the switching area(s) and ii. the PDLC functional element is heated by a heating device to a temperature TA greater than or equal to a phase transition temperature and is kept at a temperature greater than or equal to the phase transition temperature, and

B) after a time period t of more than 1 min., the PDLC functional element is cooled to a temperature TB less than or equal to the phase transition temperature, whereby the voltage-free switching state (off) is maintained at the switching area(s).

Process step A i) can advantageously be carried out before, after or during process step A ii).

The functional element according to the invention is a PDLC functional element (polymer dispersed liquid crystal). The active layer of a PDLC functional element contains liquid crystals which are embedded in a polymer matrix.

Since PDLC functional elements are generally not used individually or free-standing, but are usually built into glazing (so-called PDLC glazing), the methods and embodiments mentioned here also apply to PDLC glazing.

The present invention is based on the following finding of the inventors: PDLC functional elements and glazings in which they are installed can, due to their Switching and temperature history can result in different and inhomogeneous optical properties, such as diffusivity (turbidity or scattering behavior) or transparency.

Thanks to the human eye's high sensitivity to optical differences, this effect occurs particularly in segmented PDLC functional elements, where different switching areas are arranged directly next to each other and a user can directly compare differently degraded areas. In unfavorable lighting conditions, this can impair road safety and lead to unaesthetic visibility.

The above-mentioned deterioration of the optical properties occurs when a PDLC functional element is activated at high temperatures (e.g. in a parking lot situation) to temperatures in or above the phase transition range, e.g. above 70-80°C, i.e. switched on and cooled down while still activated (e.g. by driving and/or the effects of an air conditioning system). This leads to a permanent degraded state of the liquid crystals in the respective switching area of the PDLC functional element and is also referred to below as the phase transition in electrical field (PTF) effect.

The PTF effect does not disappear by simply switching the PDLC functional element again and is therefore also referred to as the “permanent memory effect”.

The present invention is based on the idea of providing a solution with which the undesirable changed optical properties of such impaired areas can be restored and the entire (vehicle) glazing can finally be reset to the "factory setting" - i.e. the state of homogeneous scattering and complete opacity.

The solution comprises a method for heat treatment and a device for locally heating a PDLC functional element of a glazing to a temperature above the phase transition temperature at a suitable switching voltage and subsequent targeted cooling. This leads to a homogenization of the optical properties and in particular to a homogenization of adjacent switching areas and thus to the restoration of traffic safety and customer satisfaction.

In an advantageous embodiment of the method according to the invention, in step A ii) the PDLC functional element according to the invention is heated to a temperature TA of at least 80°C and preferably of at least 90°C and in particular of 90°C to 130°C. The liquid crystals of the PDLC functional element are then in the so-called isotropic phase and return to their original configuration after cooling below the phase transition temperature. The temperature required to reach the isotropic phase depends on the material of the PDLC functional element and can be determined from data sheets or through simple experiments.

In a further advantageous embodiment of the method according to the invention, in step B) after a time period t of greater than or equal to 5 minutes, the PDLC functional element is cooled to a temperature TB less than or equal to the phase transition temperature. In an alternative advantageous embodiment of the method according to the invention, in step B) after a time period t of 1 minute to 60 minutes, the PDLC functional element is cooled to a temperature TB less than or equal to the phase transition temperature. The specified time periods ensure that a sufficient number of liquid crystals or all of the liquid crystals have returned to their original configuration.

In a further advantageous embodiment of the method according to the invention, in step B) the PDLC functional element is cooled to a temperature TB of less than 70°C and in particular to room temperature. The necessary cooling temperature depends on the respective material of the PDLC functional element and can be determined in simple experiments.

In a further advantageous embodiment of the method according to the invention, the heating device is controlled as a function of the temperature of the PDLC functional element (or the PDLC glazing in which the PDLC functional element is installed).

A further aspect of the invention comprises a device for heat treating a PDLC functional element and preferably a PDLC functional element with at least two adjacent, independently switchable switching regions.

The device according to the invention is preferably used to carry out the method according to the invention.

The device according to the invention comprises at least one heating device which is designed to be arranged on a PDLC functional element and to heat the PDLC functional element, preferably by convection, heat conduction, radiant heating, for example by infrared (IR) radiation or microwave radiation, and/or induction. In an advantageous embodiment of a device according to the invention, the PDLC functional element is arranged within a PDLC glazing.

In a further advantageous embodiment of a device according to the invention, the PDLC glazing is arranged in a vehicle, preferably as a roof window, windshield or rear window.

The device is advantageously only temporarily placed on the PDLC functional element (or the PDLC glazing) or arranged above it to carry out the method according to the invention and is removed again after completion of the method, for example in a workshop.

In a further advantageous embodiment of a device according to the invention, the heating device contains or consists of at least one heating element, a heating blanket, a heating hood or a radiant heater.

In an alternative advantageous embodiment of the invention, the heating device, preferably heating wires or an electrically heatable layer (in particular a transparent electrically heatable layer), is arranged within the PDLC glazing or is firmly connected to it.

In a further advantageous embodiment of the invention, the device according to the invention comprises a control unit with which the heating duration and/or the heating power of the heating device (and thus the temperature of the PDLC functional element) can be controlled.

In a further advantageous embodiment of a device according to the invention, the control unit is designed to read a temperature sensor on the heating device, on the PDLC functional element and/or on or in the PDLC glazing (i.e. to measure the temperature) and to control the heating power of the heating device depending on the measured temperature.

It is assumed that the PDLC glazing as a whole has a homogeneous temperature, i.e. the temperature of the PDLC functional element corresponds to the temperature of other areas of the PDLC glazing, which is typically at least approximately the case. Determining the temperature of the PDLC glazing therefore corresponds at least approximately to determining the temperature of the PDLC functional element. In a further advantageous embodiment, the control unit is suitable for being coupled to the PDLC functional element and for determining the electrical impedance of the active layer and from this the temperature of the PDLC glazing, or more precisely of the PDLC functional element. This is possible because the impedance (the equivalent of the classic ohmic resistance for alternating voltages) is temperature-dependent. In particular, there is an injective relationship between the real part of the electrical impedance and the temperature of the functional element. In this way, a temperature can be assigned to each impedance. In particular, the real part of the impedance is strictly monotonically decreasing as a function of temperature. The embodiment has the advantage that a temperature sensor can be dispensed with, which has to be integrated as an additional component and therefore complicates the structure and increases the manufacturing costs. Advantageously, the control unit of the device according to the invention can read a PDLC control unit of the PDLC glazing (e.g. in a vehicle).

The method and the device according to the invention are in principle suitable for the heat treatment of all PDLC functional elements.

The functional element according to the invention is preferably a standard PDLC functional element which, in the "on" switching state with applied voltage, has maximum transmission and minimal turbidity (clear, transparent state) and in the "off" switching state with switched off voltage, has minimal transmission with maximum turbidity (cloudy, non-transparent (diffuse) state). This means that if no voltage is applied to the surface electrodes, the liquid crystals are aligned in a disordered manner, which leads to a strong scattering of the light passing through the active layer. If a voltage is applied to the surface electrodes, the liquid crystals align in a common direction and the transmission of light through the active layer is increased. However, other functional elements can also be used whose variability of the optical properties is based on liquid crystals, for example PNLC functional elements (polymer networked liquid crystal).

Alternatively, the functional element according to the invention is preferably a reverse PDLC functional element (also called reverse mode PDLC), which in the “off” switching state with the voltage switched off has a maximum transmission and minimum turbidity (clear, transparent state) and in the “on” switching state with the voltage applied has a minimum Transmission with maximum turbidity (cloudy, non-transparent (diffuse) state). The teaching of the invention applies here accordingly.

The controllable PDLC functional elements mentioned and their mode of operation are known to the person skilled in the art, so that a detailed description can be dispensed with at this point.

In an advantageous embodiment, the PDLC functional element comprises two carrier films in addition to the active layer and the surface electrodes, the active layer and the surface electrodes preferably being arranged between the carrier films. The carrier films are preferably made of thermoplastic material, for example based on polyethylene terephthalate (PET), polypropylene, polyvinyl chloride, fluorinated ethylene propylene, polyvinyl fluoride or ethylene tetrafluoroethylene, particularly preferably based on PET. The thickness of the carrier films is preferably from 10 pm to 200 pm. Such functional elements can advantageously be provided as multilayer films, in particular purchased, cut to the desired size and shape and then laminated into the composite pane, preferably via a thermoplastic connecting layer with the outer pane and the inner pane. It is possible to segment the first surface electrode using laser radiation, even if it is embedded in such a multilayer film. Laser processing can produce a thin, visually inconspicuous insulation line without damaging the carrier film typically lying over it.

The side edge of the functional element can be sealed, for example by fusing the carrier layers or by means of a (preferably polymeric) tape. This can protect the active layer, in particular against components of the intermediate layer (particularly plasticizers) diffusing into the active layer, which can lead to degradation of the functional element.

For electrical contacting of the surface electrodes or electrode segments, these are preferably connected to so-called flat or foil conductors, which extend from the intermediate layer beyond the side edge of the composite pane. Flat conductors have a band-like metallic layer as a conductive core, which is typically surrounded by a polymeric insulation sheath with the exception of the contact surfaces. Optionally, so-called bus bars, for example strips of an electrically conductive foil (e.g. copper foil) or electrically conductive prints can be arranged on the surface electrodes, with the flat or foil conductors being connected to these bus conductors. The flat or foil conductors are connected to a PDLC control unit directly or via additional conductors.

The composite pane can be provided with an opaque cover print, in particular in a peripheral edge area, as is common in the vehicle sector, in particular for windshields, rear windows and roof windows. The cover print is typically made of an enamel containing glass frits and a pigment, in particular black pigment. The printing ink is typically applied using a screen printing process and baked in. Such a cover print is applied to at least one of the pane surfaces, preferably the interior surface of the outer pane and/or the inner pane. The cover print preferably surrounds a central see-through area in a frame-like manner and serves in particular to protect the adhesive by which the composite pane is connected to the vehicle body from UV radiation. If the PDLC control unit is attached to the interior surface of the inner pane, then preferably in the opaque area of the cover print.

The thermoplastic intermediate layer serves to connect the two panes, as is usual with composite panes. Typically, thermoplastic films are used and the intermediate layer is formed from these. In a preferred embodiment, the intermediate layer is formed from at least a first thermoplastic layer and a second thermoplastic layer, between which the functional element is arranged. The functional element is then connected to the outer pane via an area of the first thermoplastic layer and to the inner pane via an area of the second thermoplastic layer. The thermoplastic layers preferably protrude all the way around the functional element. Where the thermoplastic layers are in direct contact with one another and are not separated from one another by the functional element, they can fuse during lamination in such a way that the original layers may no longer be recognizable and a homogeneous intermediate layer is present instead.

A thermoplastic layer can be formed, for example, by a single thermoplastic film. A thermoplastic layer can also be formed from sections different thermoplastic films whose side edges are joined together.

In a preferred embodiment, the functional element, or more precisely the side edges of the functional element, is surrounded all the way around by a third thermoplastic layer. The third thermoplastic layer is designed like a frame with a recess into which the functional element is inserted. The third thermoplastic layer can be formed by a thermoplastic film into which the recess has been cut out. Alternatively, the third thermoplastic layer can also be composed of several film sections around the functional element. The intermediate layer is then formed from a total of at least three thermoplastic layers arranged flat on top of one another, with the middle layer having a recess in which the functional element is arranged. During production, the third thermoplastic layer is arranged between the first and second thermoplastic layers, with the side edges of all thermoplastic layers preferably being in line. The third thermoplastic layer preferably has approximately the same thickness as the functional element. This compensates for the local difference in thickness introduced by the locally limited functional element, so that glass breakage during lamination can be avoided and an improved optical appearance is created.

The layers of the intermediate layer are preferably made of the same material, but in principle they can also be made of different materials. The layers or films of the intermediate layer are preferably based on polyvinyl butyral (PVB), ethylene vinyl acetate (EVA), or polyurethane (PU). This means that the layer or film mainly contains the said material (a proportion of more than 50% by weight) and can optionally contain other components, for example plasticizers, stabilizers, UV or IR absorbers. The thickness of each thermoplastic layer is preferably from 0.2 mm to 2 mm, particularly preferably from 0.3 mm to 1 mm. For example, films with standard thicknesses of 0.38 mm or 0.76 mm can be used.

The outer pane and the inner pane are preferably made of glass, particularly preferably soda-lime glass, as is usual for window panes. However, the panes can also be made of other types of glass, for example quartz glass, borosilicate glass or aluminosilicate glass, or made of rigid clear plastics, such as polycarbonate or polymethyl methacrylate. The panes can be clear or tinted or colored. Depending on the application, the degree of tinting or coloring may be limited: for example, a prescribed light transmission must be guaranteed, for example a light transmission of at least 70% in the main viewing area A in accordance with Regulation No. 43 of the Economic Commission for Europe of the United Nations (UN/ECE) (ECE-R43, "Uniform provisions concerning the approval of safety glazing materials and their installation in vehicles").

The outer pane, the inner pane and/or the intermediate layer can have suitable coatings known per se, for example anti-reflective coatings, non-stick coatings, anti-scratch coatings, photocatalytic coatings, UV-absorbing or reflective coatings or IR-absorbing or reflective coatings such as sun protection coatings or low-E coatings.

The thickness of the outer pane and the inner pane can vary widely and can thus be adapted to the requirements of the individual case. The outer pane and the inner pane preferably have thicknesses of 0.5 mm to 5 mm, particularly preferably 1 mm to 3 mm.

PDLC functional elements according to the invention are advantageously arranged in PDLC glazings. The PDLC functional element particularly advantageously has at least two adjacent, independently switchable switching areas.

In an advantageous embodiment, the PDLC glazing according to the invention comprises a composite pane, wherein the composite pane comprises an outer pane and an inner pane, which are connected to one another via a thermoplastic intermediate layer, and an electrically controllable functional element, which is arranged between the outer pane and the inner pane. The functional element has an active layer with electrically controllable optical properties between a first surface electrode and a second surface electrode.

In a further advantageous embodiment, the PDLC functional element comprises an active layer with electrically controllable optical properties and is arranged between a first surface electrode and a second surface electrode. Advantageously, the first surface electrode is divided into at least two separate electrode segments by at least one insulation line, each electrode segment forming an independently switchable switching area.

In a further advantageous embodiment, each electrode segment of the first surface electrode and the second surface electrode are electrically connected to the PDLC control unit, so that an electrical voltage can be applied independently between each electrode segment of the first surface electrode and the second surface electrode in order to control the optical properties of the section of the active layer located therebetween.

In a further advantageous embodiment, the second surface electrode has no insulation lines or a smaller number of insulation lines and consequently a smaller number of electrode segments than the first surface electrode, so that at least one electrode segment of the second surface electrode is assigned to several electrode segments of the first surface electrode.

The PDLC glazing according to the invention is preferably intended to separate the interior from the external environment in a window opening (in particular a window or roof opening of a vehicle, but alternatively also a window opening of a building or a room). In the sense of the invention, the inner pane refers to the pane facing the interior. The outer pane refers to the pane facing the external environment. The outer pane and the inner pane each have an outside surface and an inside surface and a circumferential side edge surface running between them. In the sense of the invention, the outside surface refers to the main surface which is intended to face the outside environment in the installed position. In the sense of the invention, the inside surface refers to the main surface which is intended to face the interior in the installed position. The inside surface of the outside pane and the outside surface of the inner pane face each other and are connected to one another by the thermoplastic intermediate layer.

The PDLC glazing according to the invention as a composite pane contains a PDLC functional element with electrically controllable optical properties, which is located between the Outer pane and inner pane, i.e. embedded in the intermediate layer. The functional element is preferably arranged between at least two layers of thermoplastic material of the intermediate layer, whereby it is connected to the outer pane by the first layer and to the inner pane by the second layer. Alternatively, the functional element can also be arranged directly on the surface of the outer pane or the inner pane facing the intermediate layer. Preferably, the side edge of the functional element is completely surrounded by the intermediate layer, so that the functional element does not extend to the side edge of the composite pane and thus has no contact with the surrounding atmosphere.

The PDLC functional element comprises at least one active layer and two surface electrodes, which are arranged on both sides of the active layer, so that the active layer is arranged between the surface electrodes. The surface electrodes and the active layer are typically arranged essentially parallel to the surfaces of the outer pane and the inner pane. The active layer has the variable optical properties that can be controlled by an electrical voltage applied to the active layer via the surface electrodes. In the sense of the invention, electrically controllable optical properties are understood to mean in particular those properties that can be controlled continuously. In the sense of the invention, the switching state of the functional element refers to the extent to which the optical properties are changed compared to the voltage-free state. A switching state of 0% corresponds to the voltage-free state, a switching state of 100% to the maximum change in the optical properties. By selecting the voltage appropriately, all switching states in between can be realized continuously. For example, a switching state of 20% corresponds to a change in the optical properties by 20% of the maximum change. The said optical properties particularly concern the light transmission and/or the scattering behavior.

In principle, however, it is also conceivable that the electrically controllable optical properties can only be switched between two discrete states. Then there are only two switching states, for example 0% (off) and 100% (on). It is also conceivable that the electrically controllable optical properties can be switched between more than two discrete states. The surface electrodes are preferably transparent, which in the sense of the invention means that they have a light transmission in the visible spectral range of at least 50%, preferably at least 70%, particularly preferably at least 80%. The surface electrodes preferably contain at least one metal, a metal alloy or a transparent conductive oxide (transparent conducting oxide, TCO). The surface electrodes can be based, for example, on silver, gold, copper, nickel, chromium, tungsten, indium tin oxide (ITO), gallium-doped or aluminum-doped zinc oxide and/or fluorine-doped or antimony-doped tin oxide, preferably based on silver or ITO. The surface electrodes preferably have a thickness of 10 nm to 2 pm, particularly preferably 20 nm to 1 pm, most preferably 30 nm to 500 nm.

According to the invention, the first surface electrode has at least two segments (electrode segments) which are separated from one another by an insulation line. The insulation line is understood to be a line-like region in which the material of the surface electrode is not present, so that the adjacent segments are materially separated from one another and are therefore electrically insulated from one another. This means that there is no direct electrical connection between the electrode segments, although the electrode segments can be indirectly electrically connected to one another to a certain extent via the active layer in contact with them. The first surface electrode can be divided into several segments by several insulation lines. Each electrode segment forms a switching area of the glazing arrangement. The number of electrode segments can be freely selected by the person skilled in the art according to the requirements in the individual case. In a preferred embodiment, the insulation lines run essentially parallel to one another and extend from one side edge of the surface electrode to the opposite side edge. However, any other geometric shapes are also conceivable.

Two electrode segments separated only by an insulation line form an adjacent switching region within the meaning of the invention, which can also be referred to as an immediately adjacent switching region.

The insulation lines have a width of 5 pm to 500 pm, for example, in particular 20 pm to 200 pm. They are preferably introduced into the surface electrode using laser radiation. The width of the segments, i.e. the distance between adjacent insulation lines, can be selected by the expert according to the requirements in the individual case. The second surface electrode and the active layer preferably each form a continuous, complete layer which is not divided into segments by insulation lines. In principle, however, it is also conceivable that the second surface electrode is segmented to a lesser extent than the first surface electrode, i.e. has fewer insulation lines and electrode segments, so that at least one electrode segment of the second surface electrode is assigned to several electrode segments of the first surface electrode. In this case, too, the problem of "cross talk" occurs, which can be reduced by the approach according to the invention. Each insulation line of the second surface electrode is arranged in alignment with an insulation line of the first surface electrode in the direction of viewing through the composite pane.

The electrode segments of the first surface electrode are electrically connected to the PDLC control unit independently of one another, so that a first (in the case of an alternating voltage, time-varying) electrical potential can be applied to each electrode segment (independently of the other electrode segments), which is referred to as the switching potential in the sense of the invention. The second surface electrode is also electrically connected to the PDLC control unit, so that a second electrical potential can be applied to the second surface electrode as a whole, which is referred to as the reference potential (“ground”) in the sense of the invention. If the first and second potentials are identical, there is no voltage between the electrodes in the respective switching range (switching state off, 0%). If the first and second potentials are different, there is a voltage between the electrodes in the respective switching range, which creates a finite switching state.

In a variant of the invention, the second surface electrode is also segmented, but to a lesser extent than the first surface electrode, so that at least one electrode segment of the second surface electrode is assigned several electrode segments of the first surface electrode. In this case, the electrode segments of the second surface electrode are also electrically connected to the PDLC control unit independently of one another, so that a second electrical potential (reference potential, "ground") can be applied to each electrode segment (independently of the other electrode segments). However, there is at least one electrode segment of the second surface electrode which provides the reference potential for several switching areas. The switching areas concerned can be controlled independently of one another by Switching potential can be applied independently to the electrode segments of the first surface electrode, while a single reference potential is applied to the associated electrode segment of the second surface electrode.

PDLC functional elements according to the invention are usually connected to electrical PDLC control units during operation. The PDLC control unit is intended and suitable for controlling the optical properties of the PDLC functional element. The PDLC control unit is electrically connected on the one hand to the surface electrodes of the functional element and on the other hand to a voltage source. The PDLC control unit contains the necessary electrical and/or electronic components in order to apply the required voltage to the surface electrodes depending on a switching state. The switching state can be specified by the user (for example by operating a switch, a button or a rotary or slide control), determined by sensors and/or transmitted via a digital interface from the central control unit of the vehicle (if the composite pane is a vehicle pane, usually LIN bus or CAN bus). The switches, buttons, rotary or slide controls can, for example, be integrated into the vehicle's instruments if the composite pane is a vehicle pane. However, touch buttons can also be integrated directly into the composite pane, for example capacitive or resistive buttons. Alternatively, the functional element can also be controlled by contactless methods, for example by recognizing gestures, or depending on the state of the pupil or eyelid determined by a camera and suitable evaluation electronics. The PDLC control unit can, for example, comprise electronic processors, voltage converters, transistors and other components.

The voltage that is applied to the surface electrodes is preferably an alternating voltage. In a preferred embodiment, the voltage source is a direct voltage source that provides a direct voltage and supplies the PDLC control unit with it. This situation occurs, for example, in a vehicle when the composite pane is a vehicle pane and is connected to the on-board voltage. The PDLC control unit is preferably connected to the on-board electrical system, from which it in turn obtains the electrical voltage and optionally the information about the switching state. The PDLC control unit is then equipped with at least one inverter to convert the direct voltage into the alternating voltage. In a first embodiment, the PDLC control unit has a single inverter. For separate To control the electrode segments of the first surface electrode, an output pole of the inverter has several independent outputs, with each electrode segment being connected to one of the outputs. Each switching area is therefore assigned an output of the inverter and connected to the associated electrode segment of the first surface electrode. The individual outputs are typically implemented by switches, with the inverter generating a voltage which is then switched. These switches can be integrated directly in the inverter. Alternatively, it is also possible for the inverter itself to strictly speaking only have a single output, to which external switches are then connected in order to distribute the voltage to the switching areas. In the sense of the invention, such externally connected switches are also considered outputs of the inverter. The second surface electrode is also connected to the inverter. In a second embodiment, the PDLC control unit has several inverters, with each electrode segment being connected to its own inverter for the separate control of the electrode segments of the first surface electrode. Each switching area is therefore assigned an inverter and connected to the associated electrode segment of the first surface electrode. The first design has the advantage that it is more cost-effective and saves space. However, it has the disadvantage that the switching ranges can only be switched digitally between a switching state of 0% and a finite switching state that corresponds to the current output voltage of the inverter. The switching ranges cannot be provided with different finite switching states (i.e. be independently "dimmable"), which is easily possible with the second design.

The inverter(s) can be operated in such a way that a real alternating voltage is generated, including its negative components. This is possible both in the case where there is only a single inverter with independent outputs, and in the case where each switching area is assigned its own inverter. However, since in the case of a direct voltage source, such as in the case of a vehicle, no negative potentials are available, this solution is technically complex. Alternatively, it is possible and often preferred to simulate the alternating voltage. The PDLC control unit is equipped with several inverters, with each electrode segment of the first surface electrode connected to a separate inverter and the second surface electrode to another inverter. Each electrode segment of the first surface electrode and the second Each surface electrode is therefore assigned its own inverter. The potentials of the inverters are modulated with a variable function, for example a sine function, whereby the potentials of the inverters of the electrode segments of the first surface electrode are in phase and the potential of the inverter of the second surface electrode is phase-shifted, in particular with a phase shift of 180°. The signal for the second surface electrode is then inverted compared to that of the first surface electrode. This generates a time-varying, periodic potential difference with alternating relatively positive and relatively negative contributions, which corresponds to an alternating voltage.

Since the on-board voltage of vehicles (for example 12 to 14 V) is typically not sufficient to completely switch the functional element, the PDLC control unit is also preferably equipped with a DC-DC converter that is suitable for increasing the supply voltage provided (primary voltage), i.e. converting it into a higher secondary voltage (for example 65 V). The use of a DC-DC converter is not limited to the situation in vehicles, but can also be necessary or advantageous in other cases. The PDLC control unit is connected to the DC voltage source and is supplied with a primary voltage by it. The primary voltage is converted into the higher secondary voltage by the DC-DC converter. The secondary voltage is converted into an AC voltage (for example 48 V) by the inverter, which is what it is suitable for. The AC voltage is then applied on the one hand to the electrode segments of the first surface electrode and on the other hand to the second surface electrode.

In an advantageous embodiment, the secondary voltage is from 5 V to 70 V, the alternating voltage from 5 V to 50 V.

The invention also includes the use of a device according to the invention for heat treating a PDLC functional element or a PDLC glazing, preferably with a PDLC functional element with at least two adjacent, independently switchable switching areas, in buildings or in means of transport for traffic on land, in the air or on water, preferably as a window pane of a vehicle, in particular a motor vehicle, for example as a windshield, roof pane, rear window pane or side window. The invention further comprises the use of the method according to the invention or a device according to the invention for restoring the optical properties of a PDLC functional element.

The invention is explained in more detail using a drawing and exemplary embodiments. The drawing is a schematic representation and not to scale. The drawing does not limit the invention in any way. It shows:

Fig. 1 is a plan view of an embodiment of the PDLC glazing according to the invention, Fig. 2 is a cross-section through the glazing from Figure 1, Fig. 3 is an enlarged view of the area Z from Figure 2,

Fig. 4 the PDLC functional element of the glazing from Figure 1 in an equivalent circuit diagram,

Fig. 5a) a cross-sectional view of a vehicle according to the invention with PDLC functional element,

Fig. 5b) a top view of the vehicle from Fig. 5a),

Fig. 6a), b) a schematic representation of temperature and voltage curves, and Fig. 6c), d), e) a schematic view through a PDLC functional element according to the invention.

Figure (Fig.) 1, Figure 2, Figure 3 and Figure 4 each show a detail of a PDLC glazing 100 according to the invention with a PDLC functional element 4, which has electrically controllable optical properties. The PDLC glazing 100 comprises a composite pane, which is provided, for example, as the roof pane of a passenger car, the optical properties of which, such as light transmission or light scattering, can be electrically controlled in certain areas, for example. The composite pane comprises an outer pane 1 and an inner pane 2, which are connected to one another via an intermediate layer 3. The outer pane 1 and the inner pane 2 consist, for example, of soda-lime glass, which can optionally be tinted. The outer pane 1 has, for example, a thickness of 2.1 mm, the inner pane 2 a thickness of 1.6 mm.

The intermediate layer 3 comprises, for example, a total of three thermoplastic layers 3a, 3b, 3c, each of which is formed by a thermoplastic film with a thickness of 0.38 mm made of PVB. The first thermoplastic layer 3a is connected to the outer pane 1, the second thermoplastic layer 3b to the inner pane 2. The third thermoplastic layer 3c lying between them has a cutout in which a PDLC functional element 4 is inserted in a substantially precise manner, i.e. approximately flush on all sides. The third thermoplastic layer 3c thus forms a kind of passepartout or frame for the approximately 0.4 mm thick functional element 4, which is thus encapsulated all around in thermoplastic material and thus protected. The PDLC functional element 4 is, for example, a PDLC multilayer film that can be switched from a clear, transparent state to a cloudy, non-transparent (diffuse) state.

The PDLC multilayer film here, for example, is a standard PDLC multilayer film which, in the “on” switching state with applied voltage, has maximum transmission and minimal turbidity (clear, transparent state) and, in the “off” switching state with switched off voltage, has minimal transmission with maximum turbidity (cloudy, non-transparent (diffuse) state).

The PDLC functional element 4 is a multilayer film consisting of an active layer 5 between two surface electrodes 8, 9 and two carrier films 6, 7. The active layer 5 contains a polymer matrix with liquid crystals dispersed therein, which align themselves depending on the electrical voltage applied to the surface electrodes 8, 9, whereby the optical properties can be regulated. The carrier films 6, 7 consist of PET and have a thickness of, for example, 0.125 mm. The carrier films 6, 7 are provided with a coating of ITO facing the active layer 5 with a thickness of approximately 100 nm, which forms the surface electrodes 8, 9. The surface electrodes 8, 9 are connected via bus bars (not shown) (for example formed from strips of copper foil) to electrical cables 14, which establish the electrical connection to a PDLC control unit 10.

This PDLC control unit 10 is, for example, attached to the interior side surface of the inner pane 2 facing away from the intermediate layer 3. For this purpose, for example, a fastening element (not shown) is glued to the inner pane 2, into which the PDLC control unit 10 is inserted. However, the PDLC control unit 10 does not necessarily have to be attached directly to the composite pane. Alternatively, it can be attached to the dashboard or the vehicle body, for example, or integrated into the vehicle's on-board electrical system. The composite pane has a peripheral edge area which is provided with an opaque cover print 13. This cover print 13 is typically made of black enamel. It is printed as a printing ink with a black pigment and glass frits using a screen printing process and burned into the pane surface. The cover print 13 is applied, for example, to the interior surface of the outer pane 1 and also to the interior surface of the inner pane 2. The side edges of the functional element 4 are covered by this cover print 13. The PDLC control unit 10 is arranged in this opaque edge area, i.e. glued to the cover print 13 of the inner pane 2. There, the PDLC control unit 10 does not interfere with the view through the composite pane and is visually unobtrusive. In addition, it is a short distance from the side edge of the composite pane, so that only advantageously short cables 14 are required for the electrical connection of the functional element 14.

The PDLC control unit 10 is also connected to the vehicle's on-board electrical system, which is not shown in Figures 1 and 2 for the sake of simplicity. The PDLC control unit 10 is suitable for applying the voltage to the surface electrodes 8, 9 of the PDLC functional element 4, which is required for the desired optical state of the PDLC functional element 4 (switching state "on'7"off"), depending on a switching signal which the driver specifies, for example, by pressing a button.

The composite pane has, for example, four independent switching areas S1, S2, S3, S4, in which the switching state of the PDLC functional element 4 can be set independently of one another by the PDLC control unit 10. The switching areas S1, S2, S3, S4 are arranged one behind the other in the direction from the front edge to the rear edge of the roof pane, whereby the terms front edge and rear edge relate to the direction of travel of the vehicle. Using the switching areas S1, S2, S3, S4, the driver of the vehicle can choose (for example depending on the position of the sun) to provide only one area of the composite pane with the diffuse state instead of the entire composite pane, while the other areas remain transparent.

In order to form the switching areas S1, S2, S3, S4, the first surface electrode 8 is interrupted by three insulation lines 8', which are arranged essentially parallel to one another and extend from one side edge to the opposite side edge of the functional element 4. The insulation lines 8' are typically introduced into the first surface electrode 8 by laser processing and divide it into four material separate electrode segments 8.1, 8.2, 8.3 and 8.4. Each electrode segment 8.1, 8.2, 8.3 and 8.4 is connected to the PDLC control unit 10 independently of the others. The PDLC control unit 10 is suitable for independently applying an electrical voltage between each electrode segment 8.1, 8.2, 8.3 and 8.4 of the first surface electrode 8 on the one hand and the second surface electrode 9 on the other hand, so that the section of the active layer 5 located therebetween is subjected to the required voltage in order to achieve a desired switching state.

As illustrated in the equivalent circuit diagram in Figure 4, the PDLC control unit 10 is connected to a voltage source 15 via the vehicle's on-board electrical system. In the vehicle area, the voltage source 15 typically provides a direct voltage in the range of 12 V to 14 V (vehicle on-board voltage). The PDLC control unit 10 is equipped, for example, with a direct voltage converter 11, which converts the on-board voltage (primary voltage) into a direct voltage with a higher value, for example 65 V (secondary voltage). The secondary voltage must be sufficiently high to realize a switching state of the PDLC functional element 4 of 100%. The PDLC control unit 10 is also equipped with an inverter 12, which converts the secondary voltage into an alternating voltage. One pole of the inverter 12 is connected to the second surface electrode 9. For the other pole, the inverter 12 has several independent outputs, each of which is connected to an electrode segment 8.1, 8.2, 8.3 and 8.4 with one of the independent outputs, so that the switching state of the associated switching range S1, S2, S3, S4 can be set independently of the others.

In a switching state of 0% (“off”), the electrode segments 8.1, 8.2, 8.3, 8.4 and the second surface electrode 9 always have the same electrical potential, so that no voltage is present. In a switching state greater than 0% (“on”) of a switching area S1, S2, S3, S4, a voltage is present between the associated electrode segment 8.1, 8.2, 8.3, 8.4 and the second surface electrode 9. As a result of the voltage, a current flows through the associated section of the active layer 5.

Figures 5a) and 5b) each show different views of a vehicle 101 according to the invention with a PDLC glazing 100 which contains a PDLC functional element 4. Figure 5a) shows a cross-sectional view of the vehicle 101, and Figure 5b) shows a plan view of the top side (with the roof) of the vehicle 101 from Figure 5a).

The PDLC glazing 100 with the PDLC functional element 4 is designed here, for example, as a roof pane and arranged in a roof cutout of the vehicle body.

To carry out the method according to the invention, a heating element 20 is arranged on the PDLC glazing 100, for example placed on top.

The heating element 20 is designed here, for example, as an electrically heatable hood or box, the dimensions of which are essentially congruent with the PDLC glazing 100 and completely covers the PDLC glazing 100 in plan view.

In another advantageous embodiment, the heating element 20 is designed, for example, as an electrically heatable hood or box, the dimensions of which are essentially congruent with the PDLC functional element 4 and completely covers the PDLC functional element 4 in plan view.

In a further example, the PDLC functional element 4, the PDLC glazing 100 or the heating element 20 has a temperature sensor (not shown here) which allows the temperature T to be measured during the heat treatment. The temperature sensor is advantageously integrated in the PDLC glazing 100 or is firmly or detachably connected to the PDLC glazing 100.

Figures 6 a) and b) show a schematic representation of the temperature and voltage curves, respectively during the occurrence of the unfavorable PTF effect (a) and during the method according to the invention (b) for heat treatment and thus for restoring the optical properties of the PDLC functional element 4.

Figures 6 c), d) and e) show a schematic view through a PDLC functional element 4 according to the invention before the occurrence of the PTF effect (Fig. 6 c)), after the occurrence of the PTF effect (Fig. 6 d)) and after restoration of the optical properties of the PDLC functional element 4 (Fig. 6 e)) by the method according to the invention. In this embodiment, the PDLC functional element 4 shown in Figures 6 c), d) and e) has six adjacent and independently switchable switching areas (S1-S6) which are connected to a PDLC control unit 10 not shown here (for example following the principle according to Figures 1-4).

The unfavorable PTF effect occurs as soon as one or more of the switching areas S1 -S6 have a temperature T greater than the nematic range (NP, nematic phase) when a voltage II is applied, for example with a voltage "on". The temperature T can be in the phase transition range (PT, phase transition) or in the isotropic range above it (IP, isotropic phase). For example, the PDLC functional element 4 is heated to a temperature of 80°C.

Fig. 6 d) shows an example of the view through a PDLC glazing 100, in which the switching areas S1, S3 and S5 were heated to a temperature in the phase transition range by applying a voltage U of the amount "on" and cooled to the nematic range NP by applying the voltage U of the amount "on". The switching areas S1, S3 and S5 show different optical properties, such as less scattering or clouding or transparency, than the switching areas S2, S4 and S6. A normal switching process from "off" to "on" or vice versa does not change the unfavorable different optical properties of the switching areas.

A heat treatment according to the invention is then carried out. For this purpose, in a method step A), at a voltage U of 0V, which corresponds to the "off" operating state, the entire PDLC glazing 100 including the PDLC functional element 4 is brought to a temperature TA of greater than or equal to the phase transition temperature (PT). This means that the PDLC functional element 4 is heated to the temperature range of the isotropic phase (IP).

In a method step B), after a time period t of 5 min., the heating is switched off, whereby the voltage U of 0V is maintained until the temperature TB of the PDLC functional element 4 is below a temperature of the phase transition region and, for example, at room temperature, see Fig. 6 b). Fig. 6 e) shows the view through a PDLC glazing 100 heat-treated in this way. All switching areas S1-S6 show a homogeneous optical behavior, which corresponds to the original state of the PDLC functional element 4 without an unfavorable PTF effect.

List of reference symbols:

1 outer pane

2 inner pane

3 thermoplastic intermediate layer

3a first layer of intermediate layer 3

3b second layer of the intermediate layer 3

3c third layer of intermediate layer 3

4 PDLC functional element, functional element with electrically controllable optical properties

5 active layer of the functional element 4

6 first carrier film of the functional element 4

7 second carrier film of the functional element 4

8 first surface electrode of the functional element 4

8.1 , 8.2, 8.3, 8.4 Electrode segments of the first surface electrode 8

8' Insulation line between two electrode segments 8.1, 8.2, 8.3, 8.4

9 second surface electrode of the functional element 4

10 PDLC control unit

11 DC-DC converter

12 inverters

13 Cover printing

14 electrical cables

15 Voltage source / DC voltage source

20 Heating device

100 PDLC glazing

101 Vehicle

IP isotropic phase

PT phase transition temperature

PTF Phase Transition in Electrical Field

NP nematic phase

RT Room temperature

S1, S2, S3, S4, S5, S6, Sn, Sn+1 Switching range n natural number t Duration

T, TA, TB Temperature

X-X‘ cutting line

Z enlarged area on, off switching state

Claims

Claims Method for heat treatment of a PDLC functional element (4), preferably with at least two adjacent, independently switchable switching areas (Sn,Sn+1 with n = 1 ...8), wherein

A) i. a voltage-free switching state (off) is applied to the switching area(s) (Sn, Sn+1) by a PDLC control unit (10) and ii. the PDLC functional element (4) is heated by a heating device (20) to a temperature TA greater than or equal to a phase transition temperature (PT) and is maintained at a temperature greater than or equal to the phase transition temperature (PT), and

B) after a time period t of more than 1 min., the PDLC functional element (4) is cooled to a temperature TB less than or equal to the phase transition temperature (PT), the voltage-free switching state (off) being maintained at the switching region(s) (Sn, Sn+1). Method according to claim 1, wherein step A i) is carried out before, after or during step A ii). Method according to one of claims 1 or 2, wherein in step A ii) the PDLC functional element (4) is heated to a temperature TA of at least 80°C and preferably of at least 90°C and in particular of 90°C to 130°C. Method according to one of claims 1 to 3, wherein in step B) after a time period t of greater than or equal to 5 min., particularly preferably from 1 min. to 60 min., the PDLC functional element (4) is cooled to a temperature TB less than or equal to the phase transition temperature (PT). Method according to one of claims 1 to 3, wherein in step B) after a time period t of from 1 min. to 60 min., preferably from 5 min. to 60 min., the PDLC functional element (4) is cooled to a temperature TB below the phase transition temperature (PT). 6. Method according to one of claims 1 to 5, wherein in step B) the PDLC functional element (4) is cooled to a temperature TB of less than 70°C and in particular to room temperature.

7. Method according to one of claims 1 to 6, wherein the heating device (20) is controlled as a function of the temperature of the PDLC functional element (4).

8. Device for heat treatment of a PDLC functional element (4), preferably a PDLC functional element (4) with at least two adjacent, independently switchable switching areas (Sn, Sn+1 with n = 1...8), according to one of claims 1 to 7, comprising at least one heating device (20) which is suitable for being arranged on a PDLC functional element (4) and for heating the PDLC functional element (4), preferably by convection, heat conduction, radiant heating, for example by IR radiation or microwave radiation, and/or induction.

9. Device according to claim 8, wherein the PDLC functional element (4) is arranged within a PDLC glazing (100).

10. Device according to claim 9, wherein the PDLC glazing element (100) is arranged in a vehicle (101), preferably as a roof window, windshield or rear window.

11. Device according to one of claims 8 to 10, wherein the heating device (20) contains or consists of at least one heating element, a heating blanket, a heating hood or a radiant heater.

12. Device according to one of claims 8 to 11, further comprising a control unit with which the heating time and/or the temperature of the heating device (20) can be controlled.

13. Device according to claim 12, wherein the control unit is designed to read a temperature sensor on the heating device (20), on the PDLC functional element (4) and/or on or in the PDLC glazing (100) and to control the heating power of the heating device (20) depending on the measured temperature.

14. Use of a device according to one of claims 8 to 12 for restoring the optical properties of a PDLC functional element (4).