Electrochromic glass component

[0002] The invention relates to an elecerochromic glass component, particularly for motor vehicle mirrors, which contains a doped ion-conducting basic polymer as the ion-conducting layer.

[0003] Electrochromic mirrors, particularly for motor vehicles, are known in the state of the art. The essential element of these electrochromic mirrors is a layer of electrochromic material. A material is termed electrochromic when it changes its optical constants (n, k) and hence its optical properties on application of an electric field. Typical examples of such electrochromic materials are WO₃and MoO₃, which are virtually colourless when applied to a substrate in thin layers. An electrochromic layer may change its optical properties by oxidation or reduction processes. If protons move in such a layer, in the case of tungsten oxide there is a reduction to blue tungsten bronze. The intensity of colouration is determined by the quantity of charge which has flowed in the layer.

[0004] Numerous electrochromic mirrors, particularly for motor vehicles, are now know from the state of the art and have electrochromic layers of this type in different layered structures. German 3 008 768 describes an electrochromic mirror which essentially consists of a layer system built on a glass substrate at least one electrochromic layer, at least two electrodes, at least one proton-conducting layer and at least one proton-delivering and one proton-storing layerbeing present.

[0005] The optical change properties of a mirror of this type are determined, inter alia, by the proton conductivity of the proton-conducting layer. The higher the proton conductivity, the higher also the rate of change of reflection. In the mirrors of the state of the art, proton-conducting glass plates, which were soaked with sulphuric acid, have been used hitherto as proton-conducting layers (for example in German Offenlegungaschrift 2 504 905) or as in German 3 008 768 so-called solid ion-conducting layers.

[0006] It has been shown all these ion-conducting layers from the state of the art used hitherto for the electrochromic glass components still do not have satisfactory results with regard to ion conductivity. Furthermore, it is disadvantageous for the mirrors of the state of the art, that the ion-conducting layers described there are either too thick or are too complex and expensive as regards their mode of manufacture.

[0007] The object of the present invention is therefore, starting from the electrochromic mirror as described in german 3 008 766, to indicate a significantly improved embodiment which is characterised particularly by an ion-conducting layer which is favourable to apply as regard to manufacture and processing and furthermore has a high ion conductivity, with which it is possible to change the electrochromic layer quickly.

[0008] The invention is achieved by the characterizing features of patent claim 1. The sub-claims show advantageous further developments.

[0009] According to the invention it is thus proposed to use a doped ion-conducting basic polymer as the ion-conducting layer. It has been shown that these doped ion-conduction basic polymers are particularly well suited. The doped ion-conducting basic polymer is preferably selected from polybenzimidazoles (PBI), polypyridines, polyimidazoles, polybenzthiazolea, polybenzoxazoles, polyquinolines, polythiazoles, polyoxadiazoles and polytetrapyrenes. The ion-conducting layer is thus a layer which preferably conducts protons. However, in principle the layer is also suitable for other ions, such as for example lithium.

[0010] The invention is illustrated in more detail below using FIG. 1 and FIG. 2.

[0011] FIG. 1 snows an electrochromic glass component of the invention, here as a motor vehicle mirror.

[0012] FIG. 2 shows the concrete structure of a mirror.

[0013] The electrochromic glass component, which is used as a motor vehicle mirror, consists of a glass substrate 1 having a thickness of 2 mm. A layer system which has the following successive layers is applied to this substrate 1.

[0014] An electrochromic layer 2 of tungsten oxide having a thickness of ˜700 nm, a mirror layer 3 of palladium having a thickness of ˜70 nm, a polymer membrane 4 of polybenzimidazols polymer having a thickness of 30 μm, a proton store 5 of tungsten trioxide having a thickness of 700 nm, a rear electrode 6 of gold having a thickness of 100 nm, a polyester film 7 having a thickness of about 175 μm as well as a sealing layer 8 of traditional plastics, which wraps around the entire coating system including the glass substrate 1 and thus seals the coating system comprising layers 2 to 7. Seal 8 is only interrupted by copper wires 5, which contact the mirror layer 3 on the one side and the rear electrode 6 on the other side to apply a voltage to the latter.

[0015] FIGS. 2aand 2bshow the electrochromic glass component according to FIG. 1, but the function of a glass component of this type becomes visible here. In the exemplary embodiment according to FIG. 2, a primer 10 for better adhesion promotion is also applied between the electrochromic layer 2 and the mirror layer 3. FIG. 2athus shows the light position and FIG. 2bthe dark position.

[0016] It is particularly preferable for the electrochromic glass component of the invention if the doped ion-conducting polymer is present in the form of a polymer membrane, A proton-conduction polymer membrane particulate preferred. It should be emphasized in particular for the ion-conducting layer according to the invention that it may be applied easily using all conventional techniques. Examples of these are screen printing, immersion, spraying, blade coating or also application of a gel.

[0017] According to the present invention it is particularly preferable if the polymer membrane is a polybenzimidazole.

[0018] It should be emphasized in particular for the electrocromic glass component of the invention that the doped ion-conducting layer has particularly good properties with regard to its ion conductivity if the ion-conducting layer is doped with an acid, in particlarly with a strong acid. It is preferable if the pKa value of the doping acid ≦4.5, preferably ≦3.5 for the first dissociation stage at 25° C. For acid it has proved to be particularly advantageous if the acid is a phosphoric acid, in particular a polyphosphoric acid. Acid treatment of polybenzimidazoles is described in U.S. Pat. No. 5,599,639, to which reference is made expressly here.

[0019] It is particularly preferable for the electrochromic glass conponent of the invention if it contains a proton-conducting polymer membrane of polybenzimidazole.

[0020] Polymer membranes of this type, which are composed of polybenzimidazoles and are proton-conducting, are known from the state of the art, for example from U.S. Pat. No. 5,017,681. All named polybenzimidazoles in the above-mentioned United States patent specification may be used in principle for the proton-conducting layer of the invention. It is particularly preferable if the polymer consists of a polybenzimidazole having a molecular weight between 1,000 and 500,000 which consists of repeating units of the following structural formula:

[0021] It has proved to be particularly favourable for the electrohromic glass component if the ion-conducting layer described in more detail above is used at a layer thickness of 1 μm to 1 mm, preferably 5 μm to 100 μm. Application of the layer, in particular the polymer membrane, may thus be affected by screen printing, immersion, spraying, blade coating or even as a gel. Provision is thus made according to the invention in that the layer is applied either as a finished film or is even produced directly on the substrate or a layer lying underneath. These application procedures may also be used in combination.

[0022] The electrochromic layer, which preferably has a layer thickness of 300 nm to 8,000 nm, preferably 300 nm to 8,000 nm, preferably consists of WO₃, MoO₃, IrO₂or mixed oxides thereof. The electrochromic layer is applied by sputtering, sol-gel or by vapour deposition.

[0023] The electrodes, which are necessary for constructing the layer system of the invention, are preferably metallic layers having a layer thickness of 50 nm to 10 μm. Examples of layers of this type are those which contain rhodium, palladium. platinum or alloys thereof.

[0024] According to a preferred embodiment, provision is made in that a metallic electrode layer at the same time forms a reflector which may accept protons This reflector preferably consists of a layer having a layer thickness of 30 nm to 500 nm, which contains rhodium, palladium, platinum or alloys thereof.

[0025] As already described in German 3 008 768, it is also preferable for the electrochromic glass component of the invention if the ion-delivering layer and the ion-storing layer at the same time form a layer or a composite. According to a preferred embodiment of the invention, provision is thus made in that the proton-storing layer is the electrochromic layer at the same time. In this case, for example a WO₃layer, thus functions at the same time as a hydrogen ion-storing layer and as an electrochromic layer. According to a preferred embodiment, the composite consists of the proton-storing and at the same time proton-delivering layer on a film, preferably a polyester film with metallisation which is the counter-electrode. Instead of the film of polyester, glass, metal or other plastics are suitable as substrate materials for the composite.

[0026] With regard to the possible layered structure variants of the electrochromic glass component of the invention, reference is made to German 3 008 768 and the layered structure described therein.

[0027] However, it is preferable for the glass component of the invention if the glass component has been constructed from two layered composites. Hence, in the manufacture of the electrochromic glass component according to a preferred embodiment, a first layer system is constructed on a glass substrate, an electrochromic layer applied thereto and metallisation as a reflector. These layers are produced by means of sputtering processes.

[0028] The second part of the layer system is then a composite which consists of a proton-storing layer, metallisation and a film arranged thereabove, in particular a polyester film. This composite is manufactured in a separate process step and then joined to the above-mentionad first layered composite of the layer system. This procedure facilitates cost-effective and simple manufacture of the electrochromic glass component.

[0029] A further favourable embodiment of the invention makes provision, if it is necessary, in that adhesion-promoting layers for better bonding are applied between the individual layers. Examples of this are chromium, titanium or even silicon oxides SiO_x. For application as motor vehicle mirrors, provision is also made in that the layer system is tightly sealed externally. Hence the layer system may be sealed at the and-faces and a final layer, that is a layer opposite the glass substrate seen in the viewing direction, may be provided with a protective layer, for example a diffusion barrier. Diffusion barriers of this type have a water permeability >1,000, preferably >100 cm³. For motor vehicle mirrors it has proved to be particularly favourable if the glass substrate is a reflection-reducing thin glass having a layer thickness of 0,1 to 3 mm. For motor vehicle mirrors it is also advisable if a transparent conductive layer for heating the mirror is applied in front of the substrate, seen in the viewing direction.