WO2013037492A1

WO2013037492A1 - Process for determining a code by means of capacities

Info

Publication number: WO2013037492A1
Application number: PCT/EP2012/003836
Authority: WO
Inventors: Udo Merker; Frank Puttkammer; Udo Guntermann; Andreas Elschner; Armin Sautter
Original assignee: Heraeus Precious Metals Gmbh & Co. Kg
Priority date: 2011-09-14
Filing date: 2012-09-13
Publication date: 2013-03-21
Also published as: TW201316259A

Abstract

The invention relates to a method for recognising an item of information (20), comprising the steps a. provision of a layer structure (10) comprising i. a dielectric (50), ii. at least a first electrically conductive layer (30) and at least one further electrically conductive layer (60) separated by the dielectric (50), wherein the first conductive layer (30) comprises an electrically conductive polymer, wherein the first layer (30) comprises a cell (35, 35') with a surface resistance Z, wherein this cell (35, 35') is adjacent to a region (45, 45') with a surface resistance B, wherein the surface resistance Z is lower than the surface resistance B; b. electrical contacting of the first layer (30) over a period of time of less than 60 seconds, an electrical capacitance being determined; c. comparison of the electrical capacitance with a target value corresponding to the item of information (20).

Description

Process for determining a code by means of capacities

The invention relates to the field of recognition of information, in particular codes, on objects, in particular recognition of information on the basis of electrical capacitances. These methods can serve, for example, for security purposes or data acquisition of objects of which counterfeiting is to be avoided or the batch data of which can otherwise be accessed only with difficulty.

Methods for recognition of security codes or for data transmission are known from the prior art. Thus, for example, the application of radio frequency (RF) codes to goods or packaging of goods in order to store and to make available batch data, shelf life data or other important data is known. This is described, for example, in EP 2 006 794 Al for RFID systems.

The contactless reading of codes as information carriers on packaging of objects of value, such as pharmaceuticals, foodstuffs and luxury articles, is adequately known. WO 02/071345 A2 thus describes the introduction of electronic codes which can be read by contactless methods into the packaging of such objects of value. However, the method proposed therein requires a quite high difference in the surface resistances to establish the code. Due to the high differences in the surface resistances, conterfeitability of the code is facilitated.

In general, these contactless security methods are easy to handle and can also be read on sensitive devices without the risk of destruction. However, due to the low resolution only comparatively highly textured surface codes can be read with the methods known from the prior art. High frequency sources of interference can moreover falsify the reading results. The measurement result of contactless capacitive measurement methods depends very greatly on the distance between the sensor and the test object, which can lead to falsification of measurement results. An object of the present invention is therefore to at least partly overcome at least one of the disadvantages emerging from the prior art. In particular, an improved resolution of the structure of the code is to be achieved. Furthermore, the precision of the measurement is to be increased. An object of the present invention is furthermore to provide a good value for money and secure coding system on which as much information as possible which cannot be read by known methods, e.g. contactless, can easily be stored on a small space. It should moreover be possible to store the information as securely as possible from counterfeiting.

In addition, an object of the present invention is to provide a coding system which essentially is not recognisable by inspection in visible light and equally meets high security standards. Recognition of the code by conventional methods should thus be made difficult and security against counterfeiting therefore increased.

An object of the present invention is furthermore to provide a coding system which is flexible in thin layers, is good value for money and has a high density of information. A contribution towards achieving at least one of the above objects is made by the invention with the features of the independent claims. Advantageous further developments of the invention, which can be realized individually or in any desired combination, are described in the dependent claims.

In a first aspect, the invention relates to a method for recognition of an item of information, comprising the steps a. provision of a layer structure comprising i. a dielectric, ii. at least a first electrically conductive layer and at least one further electrically conductive layer separated by the dielectric, - wherein the first layer comprises an electrically conductive polymer, preferably to the extent of at least 10 wt.%, particularly preferably to the extent of at least 20 wt.%, extremely preferably to the extent of at least 30 wt.%, in each case based on this layer,

- wherein the first layer comprises a cell with a surface resistance Z,

• wherein this cell is adjacent to a region with a surface resistance B, · wherein the surface resistance Z is lower than the surface resistance B; b. electrical contacting of the first layer over a period of time of less than 60 seconds, an electrical capacitance being determined; c. comparison of the electrical capacitance with a target value corresponding to the item of information. The method for recognition of an item of information in the context of the invention can be configured for any embodiment of the item of information. In one embodiment the item of information can be a code, preferably a security code, such as security markings on bank notes, medicaments, tickets or goods, or in another embodiment an item of quality-information, such as compliance with product or process requirements, or a combination thereof. The information can result from any type of configuration of the layer structure. Thus, as a first configuration, the two- or also three-dimensional construction of the cell can result in a spatial form characteristic of certain item of information. A second configuration can represent the position of at least two cells relative to one another. This can be effected by a smaller or larger separation of the cells, it being possible for the larger separation to be assigned to a first item and the smaller separation to another item of information as the configuration. A third configuration can be effected by varying the thickness of the dielectric. Thus, a first item of information can be assigned one thickness and a further item of information a thickness which differs from the first thickness. Information can also result from a combination of two and more configurations. A combination of at least two of the first, second and third configuration to obtain an item of information is preferred.

The layer structure which embodies the item of information can be incorporated into an object or applied to this. In the case of incorporation or application, it is preferable for contacting always to be able to take place with adequate security and reliability. The object can also be part of the layer structure.

The joining of the layer structure or parts of the layer structure to the object is preferably effected such that detachment of the layer structure or parts of the layer structure can lead to destruction of the item of information.

The mechanical stability, in particular tensile and flexural strength, of the layer structure can be achieved in various ways. Thus, each of the two layers as such or also the dielectric can contribute to the mechanical stability. Furthermore, the dielectric or the further layer or both can contribute to the mechanical stability. In the production of the layer structure according to the invention, it is therefore preferable to provide the layer chiefly contributing towards the mechanical stability or the dielectric and to provide it with the further layers.

Layer structure is furthermore to be understood as meaning a unit which is built up from at least one layer, preferably from several layers, and has a length and width which is at least 2 times greater than the thickness of the unit. The unit can have, for example, a width or length in a range of between 0.1 mm and 5 m, preferably in a range of between 1 mm and 1 m, particularly preferably in a range of between 1.5 mm and 50 cm. The thickness of the unit can be, for example, in a range of between 0.001 mm and 1 cm, preferably in a range of between 0.005 mm and 0.5 cm, particularly preferably in a range of between 0.01 mm and 0.1 cm. The layer structure can be realized, for example, in the form of a hard or preferably flexible and therefore bendable or also rollable film of one or more layers. The preferably flexible material moreover preferably has transparency to electromagnetic waves, in particular in the range of visible light (usually in a range of from 400 to 700 ran) in a range of from 20 to 100 %, preferably in a range of between 50 and 99 %, particularly preferably in a range of from 80 to 95 %. The layer structure comprises a dielectric. The dielectric can be any material which has an electrical surface resistance which is higher than that of the first and of the further electrically conductive layer. For example, the dielectric can be an oxide, preferably a metal oxide, such as a ceramic or a glass, or a polymer, preferably a polymer. The dielectric can also be, however, a paper or a card. Preferably, the dielectric is a polymer. Possible polymers are, for example, polyvinyl alcohols, polyvinylpyrrolidones, polyvinyl chlorides, polyvinyl acetates, polyvinyl butyrates, polyacrylic acid esters, polyacrylic acid amides, polymethacrylic acid esters, polymethacrylic acid amides, polyacrylonitriles, styrene/acrylic acid esters, vinyl acetate/acrylic acid esters and ethylene/vinyl acetate copolymers, polybutadienes, polyisoprenes, polystyrenes, polyethers, polyesters, polycarbonates, polyurethanes, polyamides, polyimides, polysulphones, melamine-formaldehyde resins, epoxy resins, silicone resins or celluloses or mixtures of at least two of these. Possible polymers are furthermore also those which are produced by addition of crosslinking agents, such as, for example, melamine compounds, masked isocyanates or functional silanes, such as e.g. 3- glycidoxypropyltrialkoxysilane, tetraethoxysilane and tetraethoxysilane hydrolysate, or crosslinkable polymers, such as e.g. polyurethanes, polyacrylates or polyolefins, and subsequent crosslinking. The polymer can preferably be chosen from the group consisting of polyester, polyvinyl chloride (PVC), polyvinyl acetate (PVAc), polyethylene (PE), ABS, polystyrene (PS), polycarbonate (PC), polymethyl methacrylate (PMMA), polyethylene glycol (PEG) or at least two of these. It is preferable for the dielectric also to be transparent. Generally, the dielectric preferably constructed as a layer can have a thickness which leads to an electrical separation of the first and the further conductive layer. Preferably, the thickness of the dielectric is in a range of from 1 nm to 1 mm, preferably in a range of from 50 nm to 500 μιη and particularly preferably in a range of from 100 nm to 200 μηι and furthermore preferably in a range of from 200 nm to 100 μιη. Furthermore, the dielectric acts as an insulator between the first and the further electrically conductive layer. The surface resistances of the dielectrics employed according to the invention are preferably in a range of greater than 10¹⁰ ohm/square, preferably in a range of greater than 10¹¹ ohm/square and particularly preferably in a range of greater than 10¹² ohm/square. Furthermore, in one embodiment according to the invention it is preferable for the dielectric of the layer structure to carry this. For this, it is preferable for the dielectric to have a high strength or mechanical stability or both. This is achieved, for example, by a dielectric of a polymer film. Between the first and the further electrically conductive layer there can also be, in addition to the dielectric, one or more further functional layers, such as, for example, separating layers or optical filters. These functional layers can be present on one or both sides of the dielectric. Such functional layers can be in any plane of the layer structure.

The layer structure furthermore has at least a first electrically conductive layer and at least one further electrically conductive layer separated electrically by the dielectric. The first electrically conductive layer comprises at least one electrically conductive polymer. The first electrically conductive layer can moreover comprise a binder. Preferably, the first electrically conductive layer contains a polymeric, organic binder. Possible particularly preferred polymeric, organic binders are, for example, polyvinyl alcohols, polyvinylpyrrolidones, polyvinyl chlorides, polyvinyl acetates, polyvinyl butyrates, polyacrylic acid esters, polyacrylic acid amides, polymethacrylic acid esters, polymefhacrylic acid amides, polyacrylonitriles, styrene/acrylic acid esters, vinyl acetate/acrylic acid esters and ethylene/vinyl acetate copolymers, polybutadienes, polyisoprenes, polystyrenes, polyethers, polyesters, polycarbonates, polyurethanes, polyamides, polyimides, polysulphones, melamine- formaldehyde resins, epoxy resins, silicone resins or celluloses. Preferred possible polymeric organic binders are furthermore also those which are produced by addition of crosslinking agents, such as, for example, melamine compounds, masked isocyanates or functional silanes, such as e.g. 3-glycidoxypropyltrialkoxysilane, tetraethoxysilane and tetraethoxysilane hydrolysate, or crosslinkable polymers, such as e.g. polyurethanes, polyacrylates or polyolefins, and subsequent crosslinking. Such crosslinking products which are suitable as polymeric binders can also be formed, for example, by reaction of the added crosslinking agents with polymeric anions optionally contained in the first conductive layer.

Generally, the length and width of the first and the further conductive layer are guided by or correspond to the dimensions of the layer structure or are smaller than these dimensions. The first and at least one of the at least one further electrically conductive layer can have, for example, a width or length in a range of between 0.1 mm to 5 m, preferably in a range of between 1 mm and 1 m, particularly preferably in a range of between 1.5 mm and 50 cm. The thickness of the first layer and the at least one further electrically conductive layer can be, for example, in a range of from 1 ran to 100 μπι, preferably in a range of from 5 nm to 10 μιτι, particularly preferably 10 nm to 5 μιτι, very particularly preferably in a range of from 15 nm to 1 μηι. The first electrically conductive layer comprises a cell with a surface resistance Z, wherein this cell is adjacent to a region with a surface resistance B, wherein the surface resistance Z is lower than the surface resistance B. It is preferable according to the invention

7 6 for Z to be in a range of from 1 to 10 ohm/square, preferably in a range of from 10 to 10 ohm/square and particularly preferably in a range of from 100 to 10⁵ ohm/square.

The cell with a surface resistance Z is furthermore preferably in the same plane as the region with a surface resistance B. The cell and the region are preferably both a constituent of the first electrically conductive layer.

It is thus furthermore preferable according to the invention for the conductive layer to result from one and the same application step. It is preferable here for the conductive layer to be applied in a first step and for the surface resistance of the layer applied in this way to be increased in a part of the layer, to form the regions, in a further step.

The first electrically conductive layer can have several cells or regions. In this context, the cell can be adjacent to more than one region. The extension of the cell and of the region in one dimension preferably forms at least a part of the first electrically conductive layer. Thus, the cell or the region can have an extension in this dimension in a range of from 1 μπι to 50 cm, preferably in a range of from 10 μηι to 5 cm and particularly preferably in a range of from 10 μΓη to 1 cm.

If there are more than one cell and one region in the first conductive layer, these can be arranged in the most diverse manner. Generally, the cells and regions can have any shape. The cells and regions can have, for example, the following shapes in the plane of the layer structure: angular or polygonal, for example tri-, terra-, penta- or hexagonal, circular or elliptical. These can be arranged either regularly or irregularly relative to one another. A uniform two- or multidimensional pattern can thus result, for example a chequered arrangement or a diamond-shaped pattern. Alternatively or in addition, an irregular arrangement of the cells and regions can be effected in the layer structure. The difference in the surface resistances Z and B of the cell and the region can be achieved by various methods. For example, the cell and the region can be made of the same material, such as an electrically conductive polymer. In the at least one region, a part of the surface resistance can be reduced by measures which modify the chemical or structural form of the layer, for example by irradiation, chemical treatment, such as etching, mechanical treatment, such as scratching, or heating or a combination of at least two of these, as will be explained further below. Alternatively, the cell and the region can also be made of different materials which have surface resistances Z and B which differ from one another and in each case have a lower surface resistance than the dielectric. The at least one further electrically conductive layer can likewise comprise an electrically conductive polymer. Furthermore or alternatively, the at least one further electrically conductive layer can comprise a further electrically conductive material, for example a metal, preferably chosen from the group consisting of copper, gold, silver, aluminium, chromium or platinum. At least one of the at least one further electrically conductive layer can also alternatively or additionally contain further electrically conductive materials, such as, for example, carbon or graphite. Preferably, the at least one further layer comprises aluminium or a conductive polymer or a combination of both. The first electrically conductive layer is preferably separated spatially from the at least one further electrically conductive layer such that no electrical contact exists between the layers. Preferably, the at least one further electrically conductive layer has a surface resistance of less than 10⁶ ohm/square, particularly preferably of less than 10⁵ ohm/square and extremely preferably of less than 10⁴ ohm/square. The surface resistance of the at least one further electrically conductive layer is preferably lower than the surface resistance of the cell of the first electrically conductive layer.

The arrangement of the at least one cell with respect to the at least one region can be effected in various ways. It is thus preferable for the first electrically conductive layer to be applied by coating processes. Possible coating processes are, in particular, printing, impregnation, whirler coating, spraying, pouring or lamination or a combination of at least two of these. Preferred printing processes are, for example, gravure, relief, ink jet or screen printing or a combination of at least two of these. These include printing processes which are often employed in the electrical industry and are often employed as offset or flexographic printing.

Preferably, a resolution of less than 5 mm, preferably of less than 1 mm, particularly preferably of less than 100 μπι can be allowed with the coating. Thus, for example, a cell in which at least one region of conductive polymer which is adjacent to a region without a conductive polymer is applied to the surface of the dielectric can be obtained by the printing. In other coating processes, such as impregnation, whirler coating, spraying or pouring, a layer of conductive polymer is first produced. In a subsequent step, which is often called structuring, the surface resistance is increased locally by the measures already described above, in order to obtain a cell and a region by this means. The structuring is preferably carried out by the use of masks.

On the basis of the spatial form, such as height, width, length, and arrangement of the at least one cell and the at least one region, the thickness of the dielectric or the position of at least two cells or regions relative to one another or a combination of at least two of these, a code can be conceived. The dimensions or arrangement of each cell or each region or both is suitable for embodying in the layer structure information which corresponds to a code. Depending on the extension of the cells and regions within the first electrically conductive layer, a different number of information units can be stored within the first electrically conductive layer and determined by the method according to the invention. The area of the cells in the plane of the layer structure can be in a range of from 0.01 mm² to 10 cm², preferably in a range of from 0.1 mm² to 0.5 cm², and particularly preferably in a range of from 0.5 mm² to 0.1 cm². A further step of the method according to the invention comprises an electrical contacting of the first layer over a period of time of less than 60 seconds, preferably less than 10 seconds, particularly preferably less than 1 second, an electrical capacitance being determined. The contacting is preferably carried out by making contact with at least the first electrically conductive layer. This making of contact is preferably detachable, for example by passing a contact element over a part of the first electrically conductive layer. In this context it is preferable for the contact element to have dimensions such that it can distinguish between a cell according to the invention and a region according to the invention. This is preferably achieved by the contact element having a contact area which is smaller in its area than the area of the smallest cell or smallest region, whichever is the smaller.

The contacting can be effected directly or indirectly. Direct contacting can be effected if, for example, the cell or the region is directly accessible for a contact. Indirect contacting means that the contact takes place indirectly. Contacting can be effected indirectly via at least one intermediate layer provided between the contact area and the first conductive layer. When choosing the intermediate layer, it is preferable for this to have at least such a low surface resistance that contact arises between the first conductive layer and the contact area. Preferably, layers as mechanical protective layers of the first electrically conductive layer are employed as the intermediate layer. In another embodiment, the intermediate layer is electrically insulating to the extent that a weakening, preferably a piercing of the intermediate layer is necessary for a contacting.

The contacting of the first layer takes place, for example, via a device, for example a measuring device, which, for example, can have at least one contact element which can be supplied with current via a voltage generator. The contact element can have, for example, a wire, a pin, a ball or a carbon brush, preferably a ball. The contact element can have any shape in order to be able to effect adequate contact with the layer structure for determination of the capacitance of the layer structure. The contact element can thus be punctiform, circular or flat in configuration, for example in the form of a pin, a needle tip or a crown contact, a ball or a plate. The contact element can be produced from any material which is suitable for adequately conducting electric current in order to be able to determine the capacitance of the layer structure. The material of the contact element can preferably be made of a metal or carbon or a combination thereof. The metal can be chosen from the group of copper, gold, silver, aluminium, chromium or platinum and at least two of these. The dimensions of the contact should be matched to the dimensions of the cell and the region of the first electrically conductive layer. The contact should thus have a spatial resolution which is lower than the smallest extension of an individual cell or an individual region. Preferably, the extension of the

2 2 2 contact is in a range of between 1 μιη to 10 cm , preferably in the range of from 1 μπι to

2 2 2

1 cm , preferably in a range of from 1 μιη to 0.5 cm , particularly preferably in a range of from 1.5 μη ² to 0.1 cm². In one embodiment of the invention, a first and a further contact element which have extensions which differ from one another are employed. According to the invention, the further contact element can also be of a large-area configuration, for example in the form of a further conductive layer which can be separated off. It is thus preferable for the first contact element to have the abovementioned extensions. The further contact element preferably has a larger extension than the first contact element, preferably in a range of from the area of a cell to the area of the layer structure.

The capacitances of the cells and regions can be measured, for example, with commercially available LCR measuring apparatus or multimeters. A further step of the method according to the invention comprises a comparison of the electrical capacitance with a target value corresponding to the code. This comparison can either be manual, that is to say by reading off a measurement result and comparing it with known values, for example in a table, or can be carried out electronically by comparison of the measurement results with a stored content, a reference or a data bank. The data bank in this context can be a constituent, for example, of the layer structure for contacting or a separate data bank which can be electronically connectable, such as, for example, via contactless contact to the internet or a contact to the internet effected by means of a cable.

In a preferred embodiment of the method, the surface resistances of the first conductive layer and of the further electrically conductive layer differ by a maximum of 50,000 ohm/square. In a further preferred embodiment of the method, the first conductive layer has a higher surface resistance than the further conductive layer. In a preferred embodiment, the cell and the region comprise the electrically conductive polymer. The cell and the region can contain different electrically conductive polymers or at least in part the same electrically conductive polymer. The different surface resistances in the cells and the regions can be achieved by different concentrations of electrically conductive polymer or different compositions of the conductive polymer. A further possibility for providing cells and regions of different surface resistances in the first electrically conductive layer is the use of a uniform electrically conductive polymer, the surface resistance of which is modified, preferably increased, in at least one region, e.g. by irradiation, preferably in the UV or IR range, chemical treatment, such as etching, mechanical treatment, such as scratching, or heating, preferably to a temperature in a range of from 150 to 350 °C, or a combination of at least two of these, as a surface resistance treatment. Areas which comprise at least one cell and at least one region can be provided in the layer structure in this manner, the cells or regions or both of one area differing in their surface resistance from cells or regions or both of another area. The capacitance differences of different areas of the layer structure can serve to store a particular item of information in the layer structure in the form of a code. The dimensions of the dielectric also have a considerable influence on the capacitance differences of the various layers. It is furthermore preferable for the surface resistance B to be greater than the surface resistance of the dielectric. Preferably, the surface resistance of the region B of the electrically conductive layer is in a range of from 10⁵ to 10¹⁰ ohm/square, preferably in a range of from 10⁶ to 10⁹ ohm/square, particularly preferably in a range of from 10⁵ to 10⁸ ohm/square. In a further preferred embodiment of the method, the at least one further electrical layer has an electrically conductive polymer. The same electrically conductive polymer as in the first conductive layer or another electrically conductive polymer can be used. Any polymer which has a lower surface resistance than the dielectric can be used as the electrically conductive polymer. The electrically conductive polymer of the first or the at least one further electrically conductive layer can comprise an electrically conductive polymer chosen from the group consisting of polypyrroles, polyanilines, polythiophenes, polyacetylenes, polyisothionaphthalenes and poly-p-phenylen and derivatives and mixtures of at least two of these.

It is furthermore preferable for the electrically conductive polymer to be poly(3,4- ethylenedioxythiophene), also called PEDOT, particularly preferably poly(3,4- ethylenedioxythiophene) poly(styrenesulphonate), also called PEDOT/PSS, for example obtainable under the trade name Clevios^®P. The electrically conductive polymer can be either the only material of the first or at least one further electrically conducting layer, or, together with another material, can build up one of the electrically conducting layers. As already mentioned, possible further materials are binders or other polymers or other electrically conducting materials, such as metals, for example aluminium, copper, gold, silver or platinum. In a preferred embodiment, at least one of the conductive layers is transparent. A high transparency is desirable, above all, if the layer structure containing the code is to be attached to an object or incorporated into an object which is not to be covered visually by the layer structure. A high optical transparency can furthermore be advantageous if an optical coding is to be effected in addition to the electronic code. The transparency of the layer structure can also serve to effect inconspicuous coding of an object. A layer structure transparent to the human eye is therefore preferred. In particular, optical transparency is referred to according to the invention if the layer structure has a transparency for incident light for at least a wavelength in the range of from 400 to 700 nm of at least 30 %. Preferably, the layer structure is transparent at least at a wavelength in a wavelength range of between 500 and 600 nm, particularly preferably in a wavelength range of between 520 and 580 nm, very particularly preferably in a wavelength range of between 540 and 560 nm. Preferably, the transparency in these ranges is greater than 30 %, preferably greater than 50 %, particularly preferably greater than 80 %. The transparency is often determined at 550 nm. It is furthermore preferable for the first conductive layer and the dielectric to be made of a flexible material. It is regarded as particularly preferable for at least one of the at least one further electrically conductive layer furthermore to be made of a flexible material. Suitable materials for the dielectric for this are, for example, polymers, preferably in the form of layers or films, thin glass or cellulose. In a preferred embodiment of the method, Z/B is < 10. This ratio can be achieved, for example, by the cell being produced exclusively from an electrically conductive polymer, while the region contains no electrically conductive polymer at all or contains it only in a part. This ratio can furthermore be established by the surface resistance treatment described above on a conductive polymer layer. It is furthermore preferable for the cell and the region to be visually essentially indistinguishable. Essentially indistinguishable at this point means that the differences in transparency between the cell and the region for in each case a wavelength in the range of from 300 to 800 nm is not greater than 20 %, preferably not greater than 15 %, particularly preferably not greater than 10 %. As a result of this, the item of information cannot be recognised by the naked eye.

In one embodiment according to the invention, the colour separation AE_cen_, region is at most 4.5, particularly preferably at most 3.0 and most preferably at most 1.5. The colour separation ΔΕ₀εΐι, region is calculated as follows:

AE _1Ί . = ( * ,, ---* . )² +<a* , -, -a * · . )² +(b* -,-, -b* . )² cell, region cell region cell region cell region

In this context, L*cell, a*cell and b*cell are the L, a and, respectively, b values of the L*a*b* colour space of the cell and L*region, a*region and b*region are the L, a and, respectively, b values of the L*a*b* colour space of the region.

In a preferred embodiment, the capacitance between the first and the further electrically conductive layer is determined. For this, the further electrically conductive layer can be contacted directly. The contacting can also be effected by a contact through the dielectric to at least one cell of the first conductive layer, which is often also called a through- contacting.

Alternatively, the capacitance between the cell and the region can be determined. For determination of the capacitance between two points of the layer structure, at least two points of the layer structure are contacted with in each case an electrode in the form of a contact element.

In a further preferred embodiment, the capacitance between the cell and the region is determined. In one embodiment according to the invention, it is preferable for the capacitance to be measured not only between the cell and the region directly adjacent to this cell. Rather, determination of the capacitance between a cell and at least one region adjacent to other cells is equally included in this embodiment.

Preferably, the layer structure can comprise a first and at least one further cell, the capacitance between the first cell and the at least one further cell being determined. As already mentioned, a pattern of electrical capacitances which can be used for coding can be produced by targeted arrangement of various cells separated by different regions. Thus, various cells in the first electrically conductive layer can have different electrical capacitances.

In one embodiment according to the invention, it is preferable for the capacitance between an individual cell on the one side and a group of cells on the other side to be determined. In another embodiment according to the invention, it is preferable for the capacitance between at least two groups of cells to be determined. The cell groups are preferably formed by connecting two and more cells in parallel. Several cells can be contacted simultaneously by in each case one contact element.

In a preferred embodiment the capacitance a. between the first cell and the region; or b. the at least one further cell and the region is determined. The capacitances of several cells and regions can also be determined successively or simultaneously. Preferably, the determination of the capacitance between the first cell and the region is carried out in time before the determination of the capacitance of the at least one further cell and the region.

In one method embodiment according to the invention, it is furthermore preferable for the cells to be provided in the outer region, often in the surface, and thus accessible from the outside, of the layer structure. In order to be able to achieve the highest possible reading speed by a good contact, it is advantageous if the cells are in a row in the outer region of the layer structure. They are thus easily accessible by the measuring device. To protect the first electrically conductive layer, a further layer can be applied over this layer. This is preferably likewise electrically conducting, so that the capacitance can be measured through this additional layer. This additional layer can be, for example, an antistatic layer, which prevents the layer structure from becoming charged during the measurement. The additional layer, which often acts as a protective layer, can furthermore be a preferably insulating layer which is weakened or even broken through for contacting the first conductive layer. The additional layer preferably comprises a polymer. Preferred polymers for the additional layer are the polymers mentioned in connection with the binders and the dielectric. As already stated in the above paragraph, in a further method embodiment according to the invention, a protective layer is applied over the first electrically conducting layer. This protective layer can be one of the layers also called further layers. The protective layer can be applied directly over the first conducting layer or indirectly. It is preferred for the protective layer to be applied directly over the first electrically conductive layer. The protective layer is preferred to comprise an electrically conductive polymer. The electrically conductive polymer of the protective layer preferably comprises an electrically conductive polymer, in particular selected from the group consisting of polypyrroles, polyanilines, polythiophenes, polyacetylenes, polyisothionaphthalenes and poly-p-phenylen and derivatives and mixtures of at least two of these. It is furthermore preferable for the electrically conductive polymer to be poly(3,4-ethylenedioxythiophene), also called PEDOT. It can be furthermore preferred that the conductive polymer comprises a polymeric anion, which is preferably poly(styrenesulphonate), also called PSS. Particularly preferred is therefore poly(3,4-ethylenedioxythiophene) poly(styrenesulphonate), also called PEDOT/PSS, for example obtainable under the trade name Clevios^®P.

The protective layer is preferred to comprise a non-conductive polymer, which is preferably cross-linked. Possible polymers are, for example, polyvinyl alcohols, polyvinylpyrrolidones, polyvinyl chlorides, polyvinyl acetates, polyvinyl butyrates, polyacrylic acid esters, polyacrylic acid amides, polymethacrylic acid esters, polymethacrylic acid amides, polyacrylonitriles, styrene/acrylic acid esters, vinyl acetate/acrylic acid esters and ethylene/vinyl acetate copolymers, polybutadienes, polyisoprenes, polystyrenes, polyethers, polyesters, polycarbonates, polyurethanes, polyamides, polyimides, polysulphones, melamine- formaldehyde resins, epoxy resins, silicone resins or celluloses or mixtures of at least two of these. Possible polymers are furthermore also those which are produced by addition of crosslinking agents, such as, for example, melamine compounds, masked isocyanates or functional silanes, such as e.g. 3-glycidoxypropyltrialkoxysilane, tetraethoxysilane and tetraethoxysilane hydrolysate. Preferred crosslinkable polymers are polyurethanes, polyacrylates or polyolefins. The polymer can preferably be chosen from the group consisting of polyester, polyvinyl chloride (PVC), polyvinyl acetate (PVAc), polyethylene (PE), ABS, polystyrene (PS), polycarbonate (PC), polymethyl methacrylate (PMMA), polyethylene glycol (PEG) or at least two of these. The non-conductive polymer is preferably radiation cured, such as a lacquer.

It is preferred that the protective layer comprises the electrically conductive polymer and the non conductive polymer in a ratio of 1 : 1.5 to 1 : 10, particularly preferred in a ratio of form 1 : 1.5 to 1 : 5.

In a preferred method embodiment the surface resistance of the protective layer is in a range of from 10⁵ to 10¹⁰ ohm/square, particularly preferred in a range of from 10⁶ to 10⁹ ohm/square, furthermore preferred in a range of from 10 to 10 ohm/square.

In a preferred method embodiment the surface resistance of the protective layer is higher than the surface resistance of the first and further electrically conductive layer and lower than the surface resistance of the dielectric. By choosing the surface resistance in the region between the surface resistance of the conducting layer and the dielectric it can be achieved that on the one hand side no crosstalk between the different cells appears however on the other hand side the layer structure will not become electrically overloaded. In one method embodiment according to the invention, it is furthermore preferable for the width of the cells to be in a range of from 0.01 mm to 1 cm, particularly preferably in a range of from 0.1 mm to 0.5 cm and very particularly preferably in a range of from 0.1 mm to 0.1 cm. It is equally preferable for the regions to be in these width ranges.

In one method embodiment according to the invention, it is preferable for the first electrically conductive layer to comprise at least two cells which differ in length. The difference in length provokes a proportional difference in capacitance values if the height and width stays the same. A difference in capacitance can also be reached by changing the width while fixing the values of length and height of the cells. Furthermore it is preferred that the cells are oriented parallel to each other. It is preferred that at least two cells differ in length by a factor in a range of from 1.1 to 100, particular preferably in a range of from 1.1 to 50 and very particularly preferably in a range of from 1.1 to 10 referred to the length of the smallest cell. In one method embodiment according to the invention, it is in turn preferable for the dielectric and the first electrically conductive layer to be joined to one another. The joining can be effected in any manner which avoids detachment of the two layers by the pure force of gravity. The dielectric can thus be joined to the first electrically conductive layer by an adhesion promoter, for example an adhesive. The dielectric can equally be melted on to the first electrically conductive layer, or vice versa.

It is furthermore preferable for the further electrically conductive layer to be separable from the layer structure. The separation can preferably be effected by lifting manually. Preferably, the further electrically conductive layer is not joined to another layer of the layer structure by gluing or comparable joining.

Further details and features of the invention emerge from the following description of preferred embodiment examples, in particular in combination with the sub-claims. The particular features can be realized here by themselves or several in combination with one another. The invention is not limited to the embodiment examples. The embodiment examples are shown in diagram form in the figures. In this context, the same reference symbols in the individual figures designate elements which are the same or the same in function or correspond to one another with respect to their functions.

TEST METHODS Determination of the surface resistance

For determination of the surface resistance, Ag electrodes of 2.5 cm length are vapour- deposited via a shadow mask such that a resistance measurement is possible in each of the areas A and B. The surface resistance is determined by contacting the Ag electrodes with a electrometer (Keithly 614). The determination was carried out by means of the so-called "four point probe" measurement as is described, for example, in US 6,943,571 Bl . As a rule ohm/square is used as the unit for the surface resistance. Determination of the colour values L, a and b and the transmission

The procedure for measurement of the transmission spectra of coated PET films is in accordance with ASTM 308-94a. For this, a 2-channel photospectrometer from Perkin Elmer, type Lambda 900 is used. The apparatus is equipped with a 15 cm photometer sphere. Proper functioning of the photospectrometer is ensured by regular checking of the wavelength calibration and the linearity of the detector in accordance with the manufacturer's recommendations and is documented. For the transmission measurement, the film to be measured is fixed in front of the entry opening of the photometer sphere with the aid of a press-on holder, so that the measuring beam penetrates through the film without shadowing. The film is visually homogeneous in the region of the penetrating measuring beam. The film is orientated with the coated side towards the sphere. The transmission spectrum is recorded in the wavelength range of 320 - 780 nm in wavelength increments of 5 nm. In this context, there is no sample in the reference beam path, so that measurement is against air.

For evaluation of the colour of the transmission spectrum the "WinCol - version 1.2" software provided by the manufacturer of the apparatus is used. In this context, the CIE tristimulus values (standard colour values) X, Y and Z of the transmission spectrum in the wavelength range of 380-780 nm are calculated in accordance with ASTM 308-94a and DIN 5033. From the standard colour values, the standard colour value components x and y and CIELAB coordinates L*, a* and b* are calculated in accordance with ASTM 308-94a and DIN 5033.

In detail: Figure 1 : Schematic representation of a production process for a layer structure,

Figure 2a: Schematic representation of a layer structure with a metal plate as a further electrically conductive layer, Figure 2b: Schematic representation of a layer structure with an electrically conducting polymer as a further electrically conductive layer,

Figure 3: Schematic representation of a layer structure in which the capacitance from at least one cell to a region is measured,

Figure 4a: Schematic representation of a layer structure in which the capacitance from at least one cell to a region and also from at least one cell or one region to the further electrically conductive layer is measured,

Figure 4b: Schematic representation of a layer structure with an additional protective layer in which the capacitance from at least one cell or one region to the further electrically conductive layer is measured,

Figure 5: Schematic representation of the calculated capacitance with respect to the capacitance measured for an item of information in plan view,

Figure 6a - d: Schematic representation of a provision of an:

6a) unstructured information pattern,

6b) information pattern structured with a UV laser,

6c) information pattern covered by a protective layer,

6d) diagram of measurement results established for the pattern shown in fig. 6c with a measurement arrangement shown in fig. 4b,

Figure 7a: Schematic representation of an information pattern in the form of a layer structure on an object,

Figure 7b: Schematic representation of an information pattern in the form of a layer structure on an object,

Figure 8: Schematic representation of an information pattern in the form of a layer structure integrated into an object. Figure 1 shows schematically the production of a layer structure 10 into which an item of information 20 is introduced with the aid of step 110. To produce the layer structure 10, a further electrically conductive layer 60 is first provided. For this, an electrically conductive polymer in the form of an aqueous PEDOT/PSS dispersion (Clevios FET, Heraeus) is knife- coated on to a substrate 40 with a 12 μηι wet film doctor blade (Erichsen) and dried at 130 °C for 5 min. In the example shown here, this layer 60 is applied to a substrate 40 consisting of a PET film. The production comprises as the first step 80 the application of a thin layer of a dielectric 50 to the further electrically conductive layer 60. This application can be carried out, for example, by simple coating, spraying on or printing. In this case, the polymer was applied by means of an 18 μηι wet film doctor blade (Erichsen). A photoresist (mr-UVL 6000, Micro Resist Technology) was used here as the polymer. The photoresist was cured by means of UV radiation (Hg vapour lamp, wavelength 365 nm, 500 mJ/cm²). In the second step 90, the first electrically conductive layer 30 in the form of a PEDOT/PSS dispersion (Clevios F 010, Heraeus) is applied with a 6 μηι wet film doctor blade (Erichsen) and dried at 130 °C for 5 min. In the third step 100, an additional layer 70 in the form of an antistatic PEDT/PSS protective layer 70 (Clevios F 14 ID) was knife-coated on to the first electrically conductive layer 30 with a 4 μηι wet film doctor blade (Erichsen) and dried at 130 °C for 5 min. In a fourth step 110 a structure in the form of a code 20 is incorporated into the layer structure 10 on the side of the protective layer 70 by means of UV radiation (Hg vapour lamp, wavelength 253.6 nm, UV-C output 15 mW/cm², exposure time 1,000 s) and a mask. This structure has at least one cell 35, 35' and at least one region 45, 45' which have different surface resistances Z and B due to the irradiation 120 of the first electrically conductive layer 30 in the 4th step 110.

Figure 2a shows by way of example a layer structure (10) consisting of the first conductive layer 30, the dielectric 50 and a further electrically conductive layer 60. In this case the dielectric 50 is formed by a PET film. The first conductive layer 30 comprises an electrically conductive polymer. The dielectric 50 is laid on the further electrically conductive layer 60, in this case in the form of a metal plate. The dimensions of the dielectric 50 are chosen here such that they do not project beyond the further electrically conductive layer 60. In this case the further electrically conductive layer 60 chosen is longer and wider than the dielectric 50. This layer structure 10 can of course comprise further layers. The first electrically conductive layer 30 comprises several cells 35, 35' and several regions 45, 45'. Both the cells 35, 35' and the regions 45, 45' can have different surface resistances. The cells 35, 35' all have a lower surface resistance than the regions 45, 45'. For measurement of the various capacitances at different points of the layer structure 10, in this example the second electrically conductive layer 60 serves as a counter-pole to the particular point to be measured on the first electrically conductive layer 30. This is carried out with the aid of a capacitance measuring apparatus 130, which is led piece by piece over the surface of the first electrically conductive layer 30. The capacitance meter 130 thereby contacts the various positions of the electrically conductive layer 30 in succession. This is indicated schematically once with the continuous arrow starting from the measuring apparatus 130, symbolizing a first measurement 131, which is connected to a cell 35, 35'. The measuring head of the measuring apparatus 130 then migrates to the next position, indicated by the broken line starting from the capacitance meter 130, and performs a second measurement 132. The capacitance of a part of or the complete surface of the layer structure 10 can be measured in this manner. The localized capacitance values determined in this way can then be compared with known capacitance threshold values and thus provide an item of information, for example an authentication.

Figure 2b shows in turn a layer structure 10 as from Figure 2a, but with the difference that the further electrically conductive layer 60 is provided not by a metal plate, but by a further electrically conductive polymer 60'. As already mentioned, this can be the same polymer as that of the first electrically conductive layer 30, or a different polymer to this. In this case it is the same polymer. This arrangement has the advantage that the second electrically conductive layer 60 is firmly joined to the remaining part of the layer structure 10, so that no measurement inaccuracies due to air gaps between the dielectric 50 and the further electrically conductive layer 60 can occur. The measurements are carried out in succession initially in the first measurement 131, then in the second measurement 132, in the third measurement 133, in the fourth measurement 134 and finally in the fifth measurement 135. These data were further processed with the aid of an arrangement as shown in Figure 6.

Figure 3 shows a measurement structure with the same layer structure 10 as that from Figure 2a or 2b, but the measuring apparatus 130 is not attached between the further electrically conductive layer 60, 60' and the first electrically conductive layer 30, but the capacitances between various cells 35, 35' and various regions 45, 45' are determined.

For the measurements as shown in Figures 2a, 2b and 3, one measuring apparatus is sufficient. In the abovementioned measurements, an LCR meter (Agilent 4284A) is employed as the capacitance measuring apparatus and gold-plated contact pins are employed for the contacting. A combination of the measurements from Figures 2a or 2b and the measurement from Figure 3 is shown in Figure 4a. Both measurements between different cells 35, 35' and regions 45, 45', and between the first electrically conductive layer 30 and the further electrically conductive layer 60 were thus carried out here. In order to be able to perform such measurements in parallel, in this case two measuring apparatuses are required, otherwise the measurements must be performed in succession. The advantage of the double determination of capacitances is a higher accuracy of the reading of the code information. Furthermore, it is easier to establish whether the layer structure has been damaged, destroyed or modified.

A further measurement structure similar to that of Figure 2a is shown in Figure 4b for a layer structure 10, wherein the layer structure 10 comprises a protective layer 70. A view onto the pattern of this structure 10 from the top is shown in Figure 6c. To achieve the layer structure 10 of Figure 4b a foil of polyethylene terephthalate (PET) (Melinex 505) was used as dielectric 50. Onto this dielectric 50 the cells 35, 35 'were built in the form of a parallel bar pattern by screen printing with a ESC Atma AT 80 P of ESC GmbH & Co. G. As conductive material for the cells 35, 35 ' a dispersion of Clevios™ S V3, commercial available from Heraeus Precious Metals GmbH & Co. KG was used as screen printing material. The foil with the printed pattern was then heated in a hot-air oven of Heraeus for 15 minutes at 130° C. The bar pattern of this layer structure 10 consists of eight bars, namely eight cells 35, 35^' which each have a distance to the neighbouring bar of 2 mm. On the top of the layer structure 10 a protective layer 70 is applied. To achieve this protective layer 70 an aqueous dispersion of Clevios™ CPP 103D was wire-bar-coated on to the patterned PET foil with a 6 μηι wet film wire-bar (commercial available from R K Print-Coat Instruments Ltd., UK) and dried at 130 °C for 5 min. This protective layer 70 covers the whole surface of the cells 35, 35 ^' and the dielectric 50 on this one side of the layer structure 10. To make a measurement with the capacitance measurement apparatus 130 the PET foil as dielectric 50 is positioned on the opposite side of the printed pattern on a Al plate 60. The metal plate 60 is brought into direct or indirect contact via the apparatus 130 with the different cells 35, 35 ' and regions 45, 45 ^' underneath the protective layer 70. In this way the fifteen measurements from the first measurement 131 to the fifteenth measurement 145 are established successively.

A measurement structure with a similar layer structure 10 to that from Figures 2 to 4a is shown in Figure 5, but only the structuring of the first electrically conductive layer 30 is shown in plan view (from the top). The cells 35, 35' were printed by means of ink jet (Dimatix 2831 inkjet printer) on to a 300 nm thick Si0₂ dielectric 50, which was on a doped Si wafer as a further electrically conductive layer 60, from a PEDT:PSS dispersion (Clevios P JET 700, Heraeus) and then dried at 120 °C. The capacitances were measured in succession in each case between cell 35 and one of the cells 35' from positions 1 to 5, designated in the drawing with the reference symbols 150, 160, 170, 180 and 190, by means of an LCR meter (Agilent 4284A). Gold-plated contact pins were employed for the contacting. The cell 35 is kept at a distance from the further cells 35' and the regions 45 and 45' by a spacer area 220. This has the effect of electrical insulation of the cell 35 from the remaining cells 35' and regions 45, 45'. The capacitances calculated and determined for the various positions are shown in Table 1. A PEDOT/PSS polymer was employed as the first electrically conducting layer 30. Storage of data in a code with the dimensions 100 μιη * 1 cm of 50 bits is possible in this manner. Table 1

Capacitances in pF (picofarad) calculated and determined for a code produced by the method according to Figure 5

As can be seen from the table and figure, the capacitances determined are slightly higher than those determined by calculation. This applies to all positions 1 to 5, with reference symbols 150, 160, 170, 180, 190. This lies in the idealized assumptions of the calculation and the non- optimized production process of the various layers. Since the capacitances can be determined after the production, this has virtually no influence on the use of the code.

Figure 6a shows a possibility for providing a universal information pattern 15 in a first electrically conductive layer 30. It has the same elements as cell 35 and cells 35', separated by the spacer area 220. The cells 35' are in turn separated from one another by regions 45 and 45'. The universal information pattern 15 from Fig. 6a can be modified by treatment with UV light to give a specific information pattern 15, shown in Figure 6b. This is particularly preferred if the end user wants first to produce the item of information 20 in a relatively simple manner. The not yet specific information pattern 15 is thus shown in Figure 6a, while Figure 6b shows the treatment of the universal information pattern 15 by punctiform UV irradiation by means of a UV laser. Such information 20 can be used in various ways as a constituent of the layer structure 10. It can thus be applied as an information carrier to packaging of pharmaceuticals or as a security feature to bank notes or other objects of value.

A further way to arrange an item of information 20, as shown in Figure 6c, is in the form of a parallel bar pattern (like a bar code). In this pattern eight cells 35, 35 ' in the form of eight bars with differing lengths are positioned at a distance of 2 mm to each other, wherein the length of the bars successively increases from the first bar to the last bar, oriented as shown in figure 6c, from left to right. The smallest cell 35 has a length of 5 mm followed by a cell 35 'of 9 mm, then a cell 35 'of 12 mm, then a cell 35 ' of 16 mm, then a cell 35^' of 21 mm, then a cell 35' of 26 mm, then a cell 35 ' of 32 mm and finally a cell 35 ' of 39 mm. The cells 35, 35 ' are symmetrically positioned with respect to a hypothetical horizontal line 250 running through the middle of the layer structure 10. The spaces between the cells 35, 35' are also regions 45, 45 '. The results of the measurements 131 to 145 of the structure shown in Figure 6c by a capacitance measuring apparatus 130 as arranged in Figure 4b are shown in Figure 6d. Here the first capacitance measurement 131 to the fifteenth measurement 145 are shown on the y- axis 240 as relative values, and the x-axis 230 reflects the position of the capacitance measuring apparatus 130 while scanning the layer structure 10 of Figure 6c from left to right. The measurement 131 shown in Figure 4b of the smallest cell 35 of Figure 6c has a relative value of capacitance of about 1. The largest cell 35' which is the one on the right hand side of the layer structure 10 of Figure 4b is measured by the measurement 145 and has the relative value of capacitance of about 8 in the diagram of Figure 6d. Thus the value of the measurement 145 is 8 times the capacitance value of measurement 131. This is directly related to the ratio of the lengths of the smallest bar, 5 mm, and the largest bar, 39 mm, the largest bar having a length almost 8 times that of the smallest bar.

It is thus conceivable to apply the item information 20 in the form of a layer structure 10, as shown in Figure 1, directly to the object 200 to be marked. This type of application to an object 200 is shown in Figure 7a. A further form of marking of a product can also be effected with the aid of a label 210 which comprises the layer structure 10 as shown in Figure 1, 2, 3, 4a or 4b. This label 210 can be stuck on, for example, to the object 200 to be marked, as shown in Figure 7b.

The layer structure 10 can alternatively be integrated into the object 200 as a constituent of it, as shown in Figure 8. It is thus conceivable, for example, that a bank note overall has a layer structure as from Figure 1, 2, 3 4a or 4b and the item of information 20 is introduced on to the bank note 200 at a particular point of this layer structure 10.

List of Reference Symbols

Layer structure 150 Position 1

Information pattern 160 Position 2

Item of information 170 Position 3

First electrically conductive layer 180 Position 4, 35 ' Cell 190 Position 5

Substrate 200 Object, bank note, 45' Region 210 Label

Dielectric 220 Spacer area, 60' Further electrically conductive layer 230 x-axis

Protective layer, additional layer 240 y-axis

1 st step

2nd step

0 3rd step

0 4th step

0 Radiation

0 Capacitance measuring apparatus

1 First measurement

2 Second measurement

3 Third measurement

4 Fourth measurement

5 Fifth measurement

6 Sixth measurement

7 Seventh measurement

8 Eighth measurement

9 Ninth measurement

0 Tenth measurement

1 Eleventh measurement

2 Twelfth measurement

3 Thirteenth measurement

4 Fourteenth measurement

5 Fifteenth measurement

Claims

Method for recognising an item of information (20), comprising the steps

a. provision of a layer structure (10) comprising

i. a dielectric (50),

ii. at least a first electrically conductive layer (30) and at least one further electrically conductive layer (60) separated by the dielectric (50),

wherein the first layer (30) comprises an electrically conductive polymer,

wherein the first layer (30) comprises a cell (35, 35') with a surface resistance Z,

• wherein this cell (35, 35') is adjacent to a region (45, 45') with a surface resistance B,

• wherein the surface resistance Z is lower than the surface resistance B;

b. electrical contacting of the first layer (30) over a period of time of less than 60 seconds, an electrical capacitance being determined;

c. comparison of the electrical capacitance with a target value corresponding to the item of information (20).

The method according to claim 1, wherein the surface resistances of the first conductive layer (30) and of the further electrically conductive layer (60) differ by a maximum of 50,000 ohm/square.

The method according to claim 1 or 2, wherein the first conductive layer (30) has a higher surface resistance than the further conductive layer (60).

The method according to one of the preceding claims, wherein a protective layer (70) is applied over the first electrically conductive layer (30).

5. The method according to claim 4, wherein the surface resistance of the protective layer (70) is in the range of from 10⁵ to 10¹⁰ ohm/square.

6. The method according to claim 4 or 5, wherein the surface resistance of the protective layer (70) is higher than the surface resistance of the electrically conducting layer (30) and lower than the surface resistance of the dielectric (50).

7. The method according to one of the preceding claims, wherein the cell (35, 35') and the region (45, 45') comprise the electrically conductive polymer.

8. The method according to one of the preceding claims, wherein the surface resistance B is lower than the surface resistance of the dielectric (50).

9. The method according to one of the preceding claims, wherein the at least one further electrical layer (60) contains an electrically conductive polymer.

10. The method according to one of the preceding claims, wherein the electrically conductive polymer is PEDOT/PSS.

11. The method according to one of the preceding claims, wherein at least one of the conductive layers (30, 60) is transparent.

12. The method according to one of the preceding claims, wherein the first conductive layer (30) and the dielectric (50) are made of a flexible material.

13. The method according to one of the preceding claims, wherein Z/B < 10.

14. The method according to one of the preceding claims, wherein the colour separation ΔΕοεΐι, region between the cell (35, 35') and the region (45, 45') is at most 4.5.

15. The method according to one of the preceding claims, wherein the capacitance between the first (30) and the further (60) electrically conductive layer is determined.

16. The method according to one of the preceding claims, wherein the capacitance between the cell (35, 35') and the region (45, 45') is determined.

17. The method according to one of the preceding claims, wherein the layer structure (10) comprises a first (35) and at least one further (35') cell, the capacitance between the first cell (35) and the at least one further (35') cell being determined.

18. The method according to claim 17, wherein the capacitance between a. the first cell (35) and the region (45, 45'), or

b. the at least one further cell (35') and the region (45, 45') is determined.

19. The method according to one of the preceding claims, wherein the cells (35, 35') are provided in the outer region of the layer structure (10).

20. The method according to one of the preceding claims, wherein the width of the cells (35, 35') is in a range of from 0.01 mm to 1 cm.

21. The method according to one of the preceding claims, wherein the first electrically conductive layer (30) comprises at least two cells (35, 35') which differ in length.

22. The method according to one of the preceding claims, wherein the dielectric (50) and the first electrically conductive layer (30) are joined to one another.

23. The method according to one of the preceding claims, wherein the further electrically conductive layer (60) can be separated from the layer structure (10).