WO2019234304A9

WO2019234304A9 - An electrochemical indicator and a method for manufacturing an electrochemical indicator

Info

Publication number: WO2019234304A9
Application number: PCT/FI2019/050437
Authority: WO
Inventors: Timo Tarvainen; Timo Peltoniemi
Original assignee: Elcoflex Oy
Priority date: 2018-06-07
Filing date: 2019-06-06
Publication date: 2020-07-02
Also published as: FI20185523A1; EP3803361A1; WO2019234304A1; FI130414B

Abstract

The present invention discloses an electrochemical indicator with a component sensitive to temperature, UV radiation, moisture, or pressure, such as a thermistor (21), and a switch (31, 110, 113, 140) and a desired number of electrochemical cells (22, 22a to 22e) in parallel or in series, equipped with suitable resistors (21, 23, 25, 32a to 32e, 41a to 41d, 91), and a transistor (24). One cell consists of an anode (62, 25b, 133), a cathode (51 to 54, 61, 125a, 132, 132a to 132e) and an electrolyte (17, 127) on a suitable substrate, and the array can be manufactured by printing, and the cells (22, 22a to 22e) can be charged at the stage of manufacture. Either one of the electrodes is arranged to be visually exposed to the outside. When the indicator is subjected to e.g. a high temperature or a UV radiation dose for a sufficiently long time, a chemical reaction will transform the substance of the visible electrode to another, and this can be detected visually from the change in the colour of the substance. Discharged in series or in parallel, the cells may form a digitally readable optical code. The change in the dielectric constant of the electrode can be indicated by means of a capacitor and a UHF antenna manufactured to accompany the electrode, whereby a change in the antenna impedance, caused by the change in the electrode, is detected upon reading the UHF tag.

Description

An electrochemical indicator and a method for manufacturing an electrochemical indicator

Field of the invention

The invention relates to batteries made by printing, and their novel use in, for exam ple, the food industry.

Background of the invention

In the food industry, there is a need to indicate freshness or spoilage of different food products. At present, this is done by product-specific expiration dates or "best before" dates which are calculated directly from the date of manufacture or packing of the product. Consequently, the expiration date is typically selected to be earlier than required at an average rate of spoilage of the product. This, in turn, results in unnecessary wastage which is already a great problem in the handling of expired products in stores, and an enormous economical expense. Therefore, it would be advantageous to have more accurate tools for monitoring, for example, the cold chain of food products, which tools should also be easily attached to packages or manufactured directly as a part of the packaging. Furthermore, it would be advan tageous that said "indicator product" were inexpensive to manufacture.

Chemical indicators have existed for a long time. A chemical indicator may be based on e.g. a reaction between a liquid substance and a substance in an indicator strip, changing the colour of the indicator strip. On the other hand, the chemical indicator could be used in such a way that when exposed to contact with air instead of a vacuum, it changes its colour and thereby reveals e.g. the time of opening or break ing of the package.

Time Temperature Indicator (TTI) technology is a business area growing at present and in the foreseeable future. A major factor is the need to reduce wastage, which is a significant cost factor in perishable goods and some drugs. At present, the best known functioning system is the "best before" date which was developed in the 1970's, and its shortcomings are generally recognized. Current TTI's are usually based on a mechanical, chemical, electrochemical, enzymatic, or microbiological principle. The principle may be, for example, the transport of a substance in a microfluidic channel (UWI technology / UWI label) after opening a product package, or a method based on corrosion of a material (Freshpoint indicator developed by Freshpoint Quality Assurance, Israel). Freshpoint uses the principle of chemical cor rosion of an aluminium layer.

Thus, it can be stated that the TTI indicator is a device or a so-called smart label which indicates the cumulated time-temperature history of the product. TTI indica tors are commonly used in food and medical applications, such as drugs, to indicate exposure to too high temperatures or also the time of exposure to too high temper atures.

Document "Pavel kova: Time temperature indicators as devices intelligent packag ing, Mendel University, Brno (CZ), 5 October 2012” provides a good summary of TTI technology as well as enterprises using the technology, and their products, in 2012.

Document“Taoukis: Modelling the use of time-temperature indicators in distribution and stock rotation, National Technical University of Athens (GR), December 2001” describes the use of TTI technology in distribution chains and in optimization of stock rotation.

Currently used methods involve the problem of inaccuracy in the manufacturing pro cess. In the electrochemical method, simulation can be scaled precisely by electron ics designing methods, and the resolution can be improved by using several cells in succession. In printed electronics, too, the manufacturing tolerances of resistors are relatively high, but they can be calibrated in a so-called on-line R2R (roll-to-roll) pro cess, for example by laser.

Flowever, electro-technical solutions relating to indicator-like activity and being implementable by a smart and cost-efficient printing technique, are at a minimum in the prior art.

Document EP 2256670 ("Furuya") describes an integrated circuit (IC) card, and its object is to provide a secondary power supply for a thin IC card to avoid relying solely on energy supplied by electromagnetic induction via an antenna; furthermore, the document wants to avoid using a liquid electrolyte for safety reasons, as well as to keep the circuit board thin. The product of the document relates to energy sup plied either by electromagnetic induction or via a solar cell, and to be charged in a thin-film battery which also contains solid electrolyte material. On the basis of para graph [0079] and Fig. 10, Furuya involves a scale "62", with which a user can com pare the colour of an area "61 ": According to paragraph [0081 ], the colour is changed as a function of a charging and discharging reaction, and lithium ions are mentioned as an example. Furuya uses a transparent layer (as a collector) whose material "oxide of indium and tin" is mentioned in this context, linked with an indica tor application. The subject matter relating to the indicator is mentioned in claim 4 of Furuya, with reference to any of the preceding claims 1 to 3. In the EP patent granted for the Furuya application, the indicator element is included in the scope of protection, namely in claim 1 .

Daily consumer goods chain Lidl has introduced a so-called Tempix smart label (Swedish technology) on its fish products, to be fixed partly on top of the bar code of a fish product package. The Tempix idea is to trace the cold chain integrity of the product from the completion of the package up to the moment of purchase at the checkout of a supermarket. In the meantime, if the product is subjected to to too high a temperature, indicator fluid in the Tempix smart label will expand and destroy the end of the bar code on the package. This will be sufficient to make the product unreadable at the checkout of the supermarket and thereby to prevent the sale of the product.

In general, a battery can be set up in two different forms of a printed structure, which are a coplanar structure and a stacked structure. Figure 1 A shows a coplanar struc ture in a vertical cross-sectional view. The structure comprises a layered protective film or release liner 1 1 as a base which is covered by a layer of an adhesive sub stance 12, such as a glue. The actual substrate 13 is applied on top of the adhesive substance, and a positive electrode 14 and a negative electrode 15 are printed on the substrate 13. A resistor or resistors 16 (R), in turn, are exposed on the substrate 13, on the left-hand side of the positive electrode 14. An electrolyte 17, in turn, is applied onto and around the electrodes 14, 15 to connect them; the electrolyte may be e.g. a solid or paste/gel-like electrolyte (to stay in place). In relation to the inven tion, the electrolyte 17 may advantageously be a transparent substance. Finally, a graphic layer 18 is printed on the electrolyte 17, the resistor area 16 and other parts of the substrate 13. The graphic layer may be simply a coat protecting the structure. With respect to the description of the invention hereinbelow, and particularly in view of the indicator application, a small part of the protective coat at one of the two elec trodes is left exposed, to enable visualization of a change in the colour of the elec trode through the transparent electrolyte.

As to the technique of manufacturing the lowermost layers (1 1 to 15) of Fig. 1A, the electrodes 14 to 15 are, in practice, printed on the substrate 13 before the adhesive 12 is applied. After applying the adhesive layer 12 on one side of the substrate, the release liner 12 is applied on the adhesive layer 12.

Figure 1 B, in turn, shows a so-called stack structure for a printed battery, in a cor responding cross-sectional view. The layers 1 1 to 14, i.e. the protective film or release liner 1 1 , the adhesive substance 12, the substrate 13, and the resis tor/resistors 16 are equal to those in Fig. 1A. The electrodes now have a novel struc ture. In this example, the positive electrode 14 is first printed on the substrate 13 (also as a wider structure in this figure), followed by printing of a solid or paste/gel like electrolyte 17 to completely surround the positive electrode 14. In the examples, the areas of the electrolyte 17 and the resistor 16 are adjacent to each other in cross-section. The negative electrode 15, which in this example is equal in size with the positive electrode 14, is printed on the electrolyte 17, directly on top of the pos itive electrode 14. The whole structure is covered by a graphic layer 18 which is typically a coat protecting the structure in this example, too. For the sake of clarity, anode and cathode current collectors are omitted in Fig. 1 B. A disadvantage in the stack structure is that the electrolysis reactions on the electrodes take place on the lower surface of the negative electrode 15 and on the upper surface of the positive electrode 15, which are not easily visualized from the outside, even if the electrolyte were solid and transparent, and even if an aperture were made in a suitable location in the protective coat. One way to solve this problem is to arrange the stack structure to comprise a colour-changing electrode at the bottom, a transparent electrolyte on top of it, and the other electrode on top, with an aperture. A change in the colour of the opposite electrode is visible through the aperture. Flowever, a coplanar structure is a more effective solution than this.

In the prior art, the main problem has thus been the lack of an existing solution based on an inexpensive printed battery for indicator use, for example, for monitor ing the cold chain in the food industry.

Summary of the invention

The present invention provides an electrochemical indicator and a corresponding method for manufacturing an electrochemical indicator.

According to a first aspect of the invention, an electrochemical indicator is intro duced, which comprises one or more electrochemical cells connected to each other, each cell comprising an anode and a cathode, as electrodes, and an electrolyte. The invention is characterized in that physical changes in at least one of the elec trodes are used to indicate the state of charge of each cell.

In an embodiment of the invention, the indicator is made in the form of a printed coplanar structure of thick film type.

In an embodiment of the invention, the electrochemical cell is discharged via a resistor or resistor network changing as a function of a change in temperature, pres sure, a radiation dose, or a chemical change.

In an embodiment of the invention, the electrochemical cell is discharged via an active circuit coupling comprising at least one transistor, changing as a function of a change in temperature or a radiation dose.

In an embodiment of the invention, the state of charge of the cell or cells is detected optically on the basis of the colour of the electrode.

In an embodiment of the invention, the state of charge of the cell or cells is detected capacitively on the basis of a change in the dielectric constant of the electrode.

In an embodiment of the invention, the change in the dielectric constant of the elec trode is detected by a capacitor manufactured to accompany the electrode and cou pled to a UHF antenna so that the change in the electrode changes the impedance of the antenna, and said change can be detected when reading the UHF tag.

In an embodiment of the invention, the change in the dielectric constant of the elec trode is detected by means of a passive resonant circuit formed by a capacitor and a coil manufactured to accompany the electrode.

In an embodiment of the invention, the state of charge of the cell or cells indicates a heat dose, a radiation dose, a moisture dose, a pressure dose, or a change in the content of a chemical substance to which the cell or cells have been exposed since the time of switching on the indicator.

In an embodiment of the invention, the indicator comprises either several cells con nected in parallel so that each cell has a discharge resistor of a different size and a different discharge current, or several cells connected in series so that only one cell in the series will be discharged at a time, and after the discharging, the electric circuit section comprising the cell in question will be electrically disconnected. In an embodiment of the invention, the indicator comprises several cells connected in such a way that the discharging cells make up a digitally readable optical code. The code may be, for example, a QR code or a conventional bar code.

In an embodiment of the invention, the cells are charged by separate resistors of equal size, whereby all the cells are charged to a substantially equal charge level at the stage of manufacture of the indicator.

In an embodiment of the invention, the materials selected are Zn for one electrode and Ag₂<3 for the other electrode, whereby after the electrode reactions, the surface materials of the electrodes will be ZnO and Ag, respectively.

In an embodiment of the invention, the cells are discharged or charged by means of a separate power source.

In an embodiment of the invention, each cell is coupled to an outlet of an electronic circuit, whereby the cell can be used for indicating the state of the electronic circuit.

In an embodiment of the invention, either the anodes or the cathodes of the electro chemical cells are coupled to form a 7-segment digital display.

In an embodiment of the invention, the indicator comprises a switch for starting the discharging or charging of the cell or cells.

In an embodiment of the invention, anisotropic conductive material is printed or applied between two adjacent or superimposed conductors, to make the coupling conductive by compressing the material.

In an embodiment of the invention, the anisotropic conductive material is a paste comprising an adhesive, wherein the adhesive is cured by UV radiation.

In an embodiment of the invention, the terminals of the switch are connected by means of a solder which is melted by thermocompression, ultrasound, laser, or an inductive loop belonging to the circuit.

In an embodiment of the invention, the terminals of the switch are connected by crimping, either by a separate piece of metal or by printed or added paste that con tains metal particles.

In an embodiment of the invention, the terminals of the switch are connected by using printed metal oxide which is photosintered to be conductive by strong radia- tion, or by using plasma discharge for reducing the oxide, or by including chemical catalysts in the printing ink to accelerate the reduction of the oxide by means of external energy.

In an embodiment of the invention, the switch is a printed transistor which is in the OFF state and is turned to the ON state by disconnecting the electric circuit to the grid at the moment of taking the switch into use.

In an embodiment of the invention, the indicator circuit is equipped with a switch area, onto which a strip can be folded, conductive adhesive being printed on the strip, which conductive adhesive will short-circuit the switch area and keep the switch area connected after the strip has been folded onto the switch area.

In an embodiment of the invention, the indicator circuit comprises a switch area which is adjacent to a conductive area, and conductive adhesive on a foldable strip being adjacent to this conductive area, wherein two parallel cuts are provided on respective sides of the conductive area, extending to the surface of the conductive adhesive, placed symmetrically and transversely to the fold, wherein the central strip separated by the cuts is provided with an upward crease and downward creases on both sides of it, wherein the conductive area will short-circuit the switch area, and the conductive adhesive will keep the switch area connected when the strip with its central strip remains folded onto the switch area.

In an embodiment of the invention, the indicator comprises a switch part and a con tact part, wherein the switch part comprises two nearly triangular openings placed symmetrically, and two switch contact ends, and the contact part comprises two tongues and a conductive area in which the contact part is slidable up and down in relation to the switch part so that after sliding, the conductive area connects the switch contact ends, and simultaneously the tongues are placed at the narrower end of the triangular openings, locking the contact in position.

According to a second aspect of the invention, a method for manufacturing an elec trochemical indicator is presented. The method is characterized in comprising the following steps:

- printing or etching a conductive layer onto the substrate;

- printing, as the electrodes, an anode and a cathode for one cell onto the conduc tive layer, and an electrolyte onto the electrodes, and in this way printing a sufficient number of electrochemical cells connected to each other; - protecting the structure by a layer which filters at least visible light so that at least one of the electrodes is visible from the outside of the indicator; and wherein, upon using the manufactured indicator:

- physical changes in at least one of said two electrodes are used to indicate the state of charge of each cell.

Brief description of the drawings

Figure 1 a shows a coplanar design for a battery according to prior art;

Fig. 1 b shows a stack design for a battery according to prior art; Figs. 2a and 2b show a basic solution of implementing a discontinuity in a temper ature change curve by means of one cell and a transistor;

Fig. 3 shows an example of a circuit relating to the invention and applying parallel connection;

Fig. 4 shows an example of a circuit relating to the invention, comprising five cells and applying connection in series;

Fig. 5 shows an example of an X-shaped indicator structure;

Fig. 6 shows an indicator of one cathode area and a switch for manual connection;

Fig. 7a shows an anisotropic connection between two opposite conductors;

Fig. 7b shows an anisotropic connection in which the particle size is > 0.5 ^* the distance between the conductors;

Fig. 8a shows a 7-segment display structure in which electrochemical cells may be used;

Fig. 8b shows a bar graph display structure with LEDs which may be replaced by electrochemical cells; Fig. 9 shows a principle connection in a UV dosimeter application which in this example comprises five cells;

Fig. 10 shows an implementation of a switch used in the invention Fig. 1 1 shows an example implementation of a switch structure formed by two superimposed films;

Fig. 12 shows a possible diagrammatic view of the invention, made on a paper label;

Fig. 13 shows the principle structure of a UV dosimeter circuit without resistor lay ers in an embodiment of the invention;

Fig. 14a shows yet another example of a switch that can be turned on for single use only; and

Fig. 14b shows a so-called "cold prototype" for applying the switch of Fig. 14a in a UV dosimeter.

Detailed description of the invention

The basic idea of the invention is that printable batteries may be used not only as energy sources but for other purposes as well.

When the structure of a printed battery is made coplanar, as shown in Fig. 1A already, and the electrolyte is a transparent substance, chemical changes in the electrode may be visualized through the electrolyte. When the materials are selected so that the electrochemical changes fall in the range of visible light, a good contrast is obtained between a charged electrode and a discharged electrode.

Electrochemical changes fall in the range of visible light in the case of e.g. silver oxide. Silver oxide is very black, whereas silver is light grey or clear. This phenom enon may be used for indicating the state of a measuring circuit outside the battery, or it may also be used for indicating the state of an electronic circuit, i.e. as a digital display, when the rate of change in the electrochemical process is sufficient for indicating said state.

By suitable selection of the materials for the external measuring circuit, it is possible to simulate a moisture, UV or CO2 dose to which the element of interest has been exposed or which it has received, as a function of time. Changes in other physical variables may be simulated as well. By providing an external measuring circuit with a resistor changing with temperature, it is possible to simulate the process of deg radation of a perishable product or a drug as a function of the temperature (Time Temperature Indicator, TTI). In its simplest form, a circuit indicating the degradation of a perishable product com prises a battery and a thermistor, i.e. an NTC resistor (NTC = Negative Temperature Coefficient). The temperature behaviour of the circuit thus follows the resistor-tem perature curve of the thermistor. By adding active components, it is possible to sim ulate temperature changes more precisely. By designing the circuit in such a way that the resistor will abruptly change at for example, +3 degrees Celsius, it is possi ble to implement a TTI circuit which meets the requirements of US Food and Drug Administration (FDA) for controlling fish products in order to prevent botulism.

Figures 2a and 2b show a basic solution of implementing a discontinuity in a tem perature change curve by means of one cell and a transistor. It should be noted that the resistance values in Fig. 2B are only indicative. Figure 2a shows a thermistor

21 , i.e. an NTC resistor, connected directly to the terminals of a battery 22 of 1 .5 V (which is also just an exemplary value). When the temperature rises, the resistance of the thermistor 21 will decrease in this case. The magnitude of the resistance will determine the rate at which the battery cell will be discharged; the higher the resistance, the lower the current through the thermistor 21 , discharging the battery

22. In the examples of Figs. 2a and 2b, the temperature tc = 25°C.

Figure 2b shows not only the NTC resistor 21 and the battery 22 but also a transistor 24 which, by means of resistors 23, 25 in the circuitry shown in the figure, will provide a discontinuity in the temperature change curve.

Connecting separate batteries in parallel or in series will result in a better resolution for the simulation. Because the number of components will not affect the price in printing technique, more pixels can be included within the scope of resolution of the printing technique and the capacity requirements of the cell. The structure of Fig. 3 comprises five cells, each of the equal batteries 22 connected in parallel being pro vided with a respective discharging resistor 32a to 32e. The circuit also comprises a switch 31 (S1 ). Such a parallel connection, in which each cell is provided with a respective discharging resistor of unique size (in the example, the resistance is always doubled from one resistor on the left to the next one on the right), is simple but involves the problem of simultaneous discharging of the cells. A better resolution is achieved by connecting every second cell opposite each other, whereby the cells will be discharged one by one according to the circuitry shown in Fig. 4. Thus, Fig. 4 represents an advantageous embodiment of the invention. On the left-hand side, the structure comprises a circuit similar to that shown in Fig. 2B, equipped with an NTC thermistor 21 and a transistor 24, and also including resistors 23, 25. In the example, the adjustment range is between 0.1 and 2 MW, and the resistance of the resistors 23, 25 is 1 MW. In principle, the structure operates so that after closing the switch 31 (S1 ), the first battery 22a will start to discharge, whereby, in terms of the current flow, the situation corresponds to the circuit of Fig. 2b. The second battery 22b will not be discharged, because its poles are opposite to those of the battery 22a. As a result, no current will pass through the circuit components 41 a, 22b, 41 b and the wires and components on their right-hand side; in other words, I = 0 in each wire on the right-hand side of the circuit corresponding to the structure of Fig. 2b.

After the battery 22a has been completely discharged, i.e. after the first cell has been discharged, its internal resistance will increase and the current flowing through it will stop, and the electric circuit of said cell will effectively open. Discharging of the next cell will take place, whereby the current will flow in the part on the right-hand side of the switch 31 , through the resistor 41 a and the second battery 22b to the emitter of the transistor circuitry. In this situation, either, no current will flow through the circuit components 41 b to 41 d, 22c to 22e, nor the battery 22a that was dis charged earlier.

The process will continue in the same way until all the cells have been discharged. When the third battery 22c is discharged, the components of the electric circuit on the right-hand side of the switch 31 will be the resistors 41 a and 41 b. When the fourth battery 22d is discharged, the electric circuit will include the resistors 41 a, 41 c and 41 b, correspondingly. Correspondingly, when the fifth battery 22e is discharged, the resistors on the right-hand side of the vertical line at the switch will include the resistors 41 a to 41 d, that is, all the resistors shown in the figure. The operation of the circuit will stop after the last cell, i.e. the battery 22e, has been discharged. This gives the set of cells a longer time of operation and also a possibility of serial type activation which directly provides good additional potential for the indicator applica tion (to be described in more detail further below). The circuitry also has the advantage of better resolution and better contrast compared with cells connected in parallel. Moreover, the circuitry has the advantage of a smaller capacity requirement per cell, because only one cell is discharged at a time.

Since the number of cells does not affect the manufacturing costs in practice, it is possible to make a number of different graphic configurations. The cells may be configured according to a linear, polar or random principle.

A significant potentiality of the present invention is to present analog information in a sequence of areas which may be comprised as pixels of digital information. Consequently, e.g. optical information of five electrochemical cells in a sequence may be inserted in a digital code which may be read by digital detecting methods, for example as a QR code or a conventional bar code. This allows quick interpreta tion of the information at a desired resolution. Because the accuracy of the printing technique is the only limiting factor in practice, e.g. a 10-tier scale may be easily embedded in the code. A new application is automated pricing of e.g. milk cartons, whereby cells changing in a sequence constitute a machine readable digital code, by which a cash register will automatically determine the price of the product according to its freshness, on the basis of a set of criteria entered in the cash register system. Naturally, this may be applied for any food product or any other product which is perishable, such as fish products. When a QR or bar code is used, it may also include product identification data. In the described digital code reading embodiment, the electrochemical cells may be discharged in series, one after another, but on the other hand, discharging of cells in parallel and digital reading of the code formed in this way are possible in this embodiment as well.

In the following, examples on the graphic design of the indicator will be presented. An example of a graphic design is shown in Fig. 5. This structure presents an indi cator in the shape of the letter X, having four cells, i.e. cathode areas, namely ele ments 51 to 54. The other elements may be connected to each other by wires and thereby to the ground 55. The final result of the operation of the X structure of Fig. 5, as a function of time, is that in the first step, the cathode area 51 will change its colour (such as from black to light/silver, or vice versa). Next, the second battery will begin to discharge, and this is shown as a change in the colour of the cathode area 52. After this, the third cathode area 53 will change its colour correspondingly, fol lowed by the fourth cathode area 54. The change in colour from light to dark as a function of time is illustrated by the set of bars at the bottom of Fig. 5. This type of an indicator structure of the invention is an illustrative and user-friendly way to indi cate e.g. the level or risk of spoilage of a product.

Figure 6 shows an indicator with one cathode area and a switch for manual connec tion. The circular area in the center is a cathode 61 , surrounded by an anode 62 having a rectangular shape and an opening. A gap is provided between the cathode 61 and the anode 62. In this embodiment, the anode 62 is covered by a colour mask, and in practice, this graphic may be printed so that the gap between the cathode and the anode is not visible from the outside. An integrated circuit 63 made of e.g. graphite is shown above the anode area in the figure. Above this, a folding area 64 is provided, having conductive adhesive applied on its surface and acting as a man- ual switch for determining the moment of starting the operation of the indicator. When a user folds the folding area with the conductive adhesive onto the integrated circuit 63 so that the conductive adhesive comes to electrical contact with the inte grated circuit, the indicator circuit will start to function; that is, the anode and cathode reactions will start as the battery is discharged. Because the adhesive is obviously sticky, the electrical contact between the left and right parts of the integrated circuit will be maintained as well. The illustration 65 of the indicator at the bottom left shows the initial situation; that is, it shows the colour of the surface of the cathode 61 of the indicator when no significant cathode reactions have taken place, namely when the temperature conditions (as an example) of the product are in order. Consequently, in an "OK" situation according to the illustration, the material of the surface of the cathode 61 remains black, as in the case of, for example, silver oxide. On the other hand, when the cold chain is broken at some point, the battery will start to discharge, and thereby silver oxide will turn to silver in the cathode reaction (in the example situation). The change takes place very quickly, and the illustration 66 of the indica tor at bottom right will thus show the end result, that is, the light colour of the cathode area (such as silver colour). In this case, it will be concluded that "the product is not OK" (="NOK"). Because the product is typically for single use only, any subsequent reactions between the cathode 61 and the anode 62 can be normally omitted. After the use, the product can be recycled in a respective bin.

A significant advantage of a silver oxide/zinc cell, used as an example of the inven tion, is constant voltage until the end of the life cycle, which means that the dis charging is also constant and predictable as long as leakage currents of the cell are insignificant compared with the discharging resistance. However, this may become a problem in simulations of a very long term. Assuming a simulation period of a week, a voltage of 1 .5 V, a capacity of 10 uAh per cell, and 5 cells in a sequence, wherein the total capacity is 50 uAh, the discharging resistance R will have a value of:

R = 168 h x 1 .5 V / 50 uAh = 5.0 MW (1 ) which is still relatively low compared with leakage resistances. Moisture may accel erate the simulation in the case of high resistance values.

For simulations taking several months, increasing the capacity of each cell and sim ultaneously higher manufacturing costs will be required. In the following, an embodiment of the invention will be presented, in which an elec trode change in a TTI type indicator can be measured by means of an ultra-high frequency (UHF) antenna upon reading a so-called UHF tag (RFID tag). Normally, the TTI is intended to be read by the end user, but in logistics chains there is a need for automated reading of things. Modern camera technology enables quick optical reading, but it requires a short distance and exact positioning. When a change in the state of charge of an electrochemical cell can be transmitted quickly in the form of wireless information, the invention finds new uses in locations where manual reading by a user is too slow. By combining a circuit according to the invention and a radio readable tag, particularly a UFIF tag, it is possible to make indicators which can be read quickly from even several meters.

RF Micron (now Axzon) has developed a UFIF chip which measures the impedance of an antenna circuit and converts it to digital format, for example to a 5-bit word, and this data is attached to identification data. Smartrac (NL) applies this principle to their DogBone sensor for measuring humidity.

In relation to the present invention, in turn, Elcoflex has developed a method based on a UFIF chip for measuring a physical variable, wherein a scanning device scans UFIF tags at different frequencies and uses the results to conclude changes in the antenna impedance. Both of the methods may be used in a TTI type indicator when the change in the electrode is indicated by a change in the capacitance, and a capacitor provided on the electrode is connected as part of the resonance circuit of the antenna. In the former method, scanning devices of standard type may be used, whereas the latter requires a customized reader for concluding the impedance by scanning a number of different frequencies. Because the latter method uses mass- produced standard chips, it is more suitable for automatic control of perishable goods, thanks to its low price, too.

In RFID applications, an antenna in the high frequency (FHF) range has a resonance frequency of 13.56 MFIz, which makes it more difficult to apply a corresponding prin ciple in the NFC technology at low capacitance values. In the NFC technology, the measurement may be converted to readable data by means of e.g. an analog input of an NFC circuit, for example by connecting the electrode to be measured as part of an RC circuit connected to the NFC circuit. Austrian Micro Systems (AMS AG) has developed an NFC chip, AS39513, which has an analog input and a digital out put as well. With these, it is possible to implement the measurement of a change in an electrode in a desired frequency range. A more advantageous solution is probably to construct a separate UHF antenna and a UHF chip in connection with the NFC.

In an embodiment of the invention, the above described RFID solutions may be supplemented by connecting the above described TTI indicator capacitance as part of a passive resonance circuit whose frequency is read by a dedicated reader device. The coil of the resonance circuit may be made in the same process with the other conductors. The lack of an active component means that reading can only be performed at close range.

In the following, a so-called switch application of the invention will be discussed. Because there may be a considerably long period of time between the time of man ufacture and the time of taking the indicator into use, it is sensible to equip the circuit with a current switch. If the circuit contains active semiconductors, the switch may be implemented by e.g. a channel transistor, whereby the current may be switched on by cutting off the circuit of the grid of the transistor. However, the manufacture of a sufficiently good transistor operating at a voltage of 1 .5 V requires a very precise technique of printing the grid insulation, which increases the cost. The aim is to make the product by screen printing by applying thick film technology, to achieve low manufacturing costs. In the manufacture, it is possible to use other techniques as well, such as sputtering, chemical vapor deposition (CVD), atomic layer deposi tion (ALD), dispensing, lamination, chemical coating, and any other printing tech niques, comprising gravure and flexo printing techniques. In this context, the word "printing" refers to any of said techniques. The point is that the manufacture takes place from reel to reel ("R2R"), to achieve the required cost level.

An easily operable ON-OFF switch is needed in any printed battery, not only in the electrochemical indicator according to the present invention. For example, in an RFID tag which contains a printed battery integrated in the structure, there is the same need to turn on the battery first at the time of taking it into use. In TTI and RFID applications, the switching can be performed by an automated device, and the switching method may thus be more complex. In a product intended for the end user, the situation is more challenging. It must be possible to turn on the switch manually without an external light or other source of energy.

The switch of the invention may be implemented by a variety of methods. The required resistance for the ON state of the switch may be as high as 1 kQ, which would be only 0.2 per mille of the resistance of the preceding example. If the nominal value of the resistance is exact, it may be part of the total resistance of the discharg ing circuit.

One option is to apply the anisotropic adhesive technique of prior art, as shown in Figs. 7a to 7b. Figure 7a shows an anisotropic joint between two opposite conduc tors. In this method, conductive particles in an adhesive of low electrical conductivity are pressed to be conductive in the direction of the Z axis. In a case where the diameter of the particles is approximately one fifth of the distance between the con ductors, as shown in Fig. 7a, no conductivity will be induced in the horizontal plane. By making the particles larger in relation to the distance between the conductors, conductivity can be induced in the horizontal plane as well, whereby two vertical conductive surfaces will not be necessary, but a contact will be formed between the adjacent conductors. This is shown in Fig. 7b, where the particle size (diameter) in the anisotropic joint is at least one half of the distance between the conductors. In Fig. 7b, two conductors 72 are placed on a substrate 71 . This structure is covered by adhesive 73 which contains conductive particles 74. In a case where the size of the conductive particles in relation to the distance between the conductors is suffi ciently large, an electrical contact is formed via the conductive particles 74 from one conductor 72 to the other by physically pressing or compressing the area containing the adhesive 73.

Normally, the adhesive agent in anisotropic paste is a thermosetting type substance (e.g. a polymer) which is cured by heating. In a reel-to-reel process, a more advan tageous way is to use an adhesive curable by ultraviolet (UV) radiation, which mul tiplies the speed of the process. There is no restraint against using UV radiation, because the conductors run in parallel and thereby do not prevent light from pene trating into the adhesive substance. If long-term stability of the joint is not required, it is possible to use pressing alone as well. This method is close to crimping, wherein metal particles are pressed onto a conductor, that is, joined to it by pressing.

Solder has the best conductivity but involves technical problems relating to the pro duction. The solder has to be maintained in a non-conductive state before melting. The melting itself may be implemented either by laser, a soldering iron, an induction heating coil, or ultrasound.

A novel technology for making conductive circuits is so-called photonic sintering: applying a high luminous intensity to reduce a metal oxide to conductive metal. Because the transfer resistance may be high, this method has a lot of potential if only because it is commercially available in reel-to-reel form. Novacentrix provides copper oxide for silkscreen printing, and exposure devices. Other methods for reducing a variety of metal oxides are also found in prior art.

In the following, an embodiment of the use of the invention will be discussed, namely the use of the indicator arrangement as a display component. This is shown in Figs. 8a and 8b, where Fig. 8a shows a so-called 7-segment display structure in which electrochemical cells can be applied. Figure 8b, in turn, shows a so-called bar graph display structure with LEDs which may be replaced by electrochemical cells.

If an electrochemical cell is discharged by an external voltage source with a suffi ciently high current, an optical change in the electrode can be achieved in a few seconds. By connecting a cell e.g. to the output of a processor, the cell can be used as a display pixel. The method may be used to construct e.g. 7-segment, bar-graph or dot-matrix displays whose state cannot be restored without a bipolar voltage. This (i.e. the one-way/non-recurrent change in the appearance of the element) is, how ever, a sufficient function in cheap disposable products for indicating, for example, the state of the device, a single-use code, or a measurement value.

A typical application in RFID products might be, for example, to indicate the charge of a battery with e.g. ten pixels at intervals of 10%, or a so-called "tamper evident" type indicator.

In Fig. 8a, the "Arduino Uno" element on the left-hand side is a processor whose outputs D2 to D9 are connected via respective resistors to each of seven display elements, and D5 is further connected by a respective connector to a DP point indi cating the activation state. The ground connector is "cc". In the invention, each of the areas a to g may be a cathode or an anode of an electrochemical cell subjected to a change in colour, as described above.

In Fig. 8b, in turn, the "Arduino" element on the left-hand side represents a processor of a Bar Graph display application. The outputs D2 to D11 are connected to components marked as LEDs, and in the invention, it is precisely these LEDs that may be replaced with electrochemical cells according to the invention. Included in the coupling of the figure are, in this example, serial resistors of 220 W and an adjustable resistor, i.e. potentiometer, connected to A0. The operating voltage is 5 V in this example.

As a second embodiment example, the invention may be used as a UV dosimeter. In the method according to the invention, an NTC resistor may be replaced with any resistor changing according to a physical phenomenon. Semiconductors are typi cally materials whose conductivity is changed by external energy, such as electro magnetic radiation. For example, zinc oxide (ZnO), which has a so-called band gap of 3.37 eV, reacts to UVA and UVB wavelengths from 280 to 400 nm. Zinc oxide is therefore used in UV protection lotions. By making a resistor paste of zinc oxide and integrating a resistor printed with it in an indicator according to the invention, a dosimeter is obtained which reacts to UV radiation. ZnO is only an example, and a photoresistor may be implemented with a number of other materials as well.

Figure 9 shows an example of a principle coupling with five cells in a UV dosimeter application. On the left, a UV sensitive resistor 91 is shown, which is connected to the circuit via a switch 31 (S1 ). In other respects, the structure is similar to the battery and resistor network shown in Fig. 4. In this example, too, the batteries 22a to 22e are electrochemical cells of 1 .5 V, and the resistors 41 a to 41 d are resistors of 1 kQ.

In a case where the UV dosimeter is a product for an end user, it has to be switched on manually, for example by means of conductive adhesive. The switching can be done, for example, by folding a conductive adhesive area, printed at the edge of a tag, onto two adjacent conductors placed outside the measuring area. Sufficient conductivity can be obtained, for example, by admixing conductive carbon, gra phene or metal particles into pressure sensitive adhesive (PSA). In this case, the adhesive is anisotropic, requiring no specific pressure to achieve conductivity. Another option is to make a molded membrane switch which remains connected when pressed down. Flowever, it is a more expensive option than printed adhesive, and requires a suitable plastic membrane.

Figure 10 shows one way of implementing a switch for use in an embodiment of the invention. At the lower right, the indicator membrane comprises a UV measuring area whose other, narrower end is equipped with wirings forming the switch ele ments. These wires can be designed in the form of parallel conductor wires extend ing in a fork-like manner between each other, not providing a connection to each other in the basic state. Above the switch element (on the side opposite to the UV measuring area), a fold is provided, separating a fold element whose surface com prises an area covered with conductive adhesive, such as PSA material. A separate perforation may also be provided at the fold. When a user folds the fold element with the PSA adhesive onto the switch elements, and presses it onto the counterpart, the conductive PSA adhesive will act as an electrical connector between the branches of the switch elements, and the circuit will be closed in this respect. The adhesive will keep the switch closed, and because the switch only needs to be closed and opening is typically not needed afterwards, the adhesive is a useful material for forming the connection here.

The switch may also comprise two conductive surfaces sliding with respect to each other which can form a connection when the tag is removed from its delivery pack age. This requires a second membrane layer, and it is therefore a more expensive option than that described above.

Figure 1 1 shows a different type of a switch structure, comprising a switch element 1 10 and a contact element 1 13 in two separate membranes. The switch element 1 10 on the left comprises two almost triangular apertures 1 1 1 arranged symmetri cally, and two switch contact ends 1 12. The switch element 1 10 is used as the lower membrane here. The contact element 1 13 on the right acts as the upper membrane with stamped tongues 1 14 (two tongues also placed symmetrically). Furthermore, a conductive area 1 15 is printed on the contact element 1 13. When the membrane 1 13 on the right is folded onto the membrane 1 10 on the left and then slid down wards, the conductive area 1 15 will slide downwards and come into contact with the switch contact ends 1 12. Thus, the switch contact ends 1 12 will be electrically con nected. At the same time, the tongues 1 14 will be placed in the narrower end of the apertures 1 1 1 , locking the contact. Deviating from the paper illustration shown in Fig. 1 1 , the switch element 1 10 and the contact element 1 13 may thus be separate parts freely movable with respect to each other, or at least they are arranged to be movable with respect to each other in the vertical direction.

Figure 12 shows one possible structural image of a product according to the inven tion, the product being made on a paper label. The lowermost layer is a protective film or a release liner 121 . This is covered by a second layer made of PSA adhesive 122 which is thus a pressure-sensitive sticky substance. This, in turn, is covered by a paper layer 123. On top of this, a conductive layer is provided, i.e. an electrode layer 124 which made be made of, for example, silver. In practice, the electrodes are conductive wirings on top of the paper layer 123, and the conductive layer 124 is designed by, for example, the inter-digitated electrode (IDE) principle. Next, a cathode and an anode are printed on the conductive layer 124, marked as elec trodes with positive 125a and negative 125b signs. In the example figure, the posi tive electrode, i.e. the cathode 125a, may consist of silver oxide (Ag₂0), and the negative electrode, i.e. the anode 125b, may consist of zinc (Zn). A zinc oxide (ZnO) layer 126 composed of an ink-type substance is printed onto the conductive layer 124, outside the cathode 125a and the anode 125b. After this, a layer of electrolyte 127 is printed or dispensed onto the cathode 125a and the anode 125b. The elec trolyte may be a solid or pasty substance. In this embodiment, the electrolyte is a transparent substance. Finally, a visible-light filtering layer is printed as the topmost layer which may comprise graphic elements, i.e. markings and/or colours, made on top of it or as part of it. This layer acts as the outer coat of the indicator. Because the filter layer has an opening at the cathode 125a (the cathode only serving as an example here), any material changes and thereby colour changes induced by elec trical reactions in it will be detectible via the opening in the graphic coat. Surely, thin transparent plastic may be advantageously provided on top of the electrolyte layer 127, to protect the structure.

Naturally, the opening may be optionally provided at the anode 125b, or even at both of the electrodes 125a and 125b, if this should be needed for illustration.

The PSA adhesive 122 may also be selected as a medical grade substance.

Figure 13, in turn, shows the principle structure of a UV dosimeter circuit without resistor layers. In this structural option of the UV example embodiment, the layered structure may consist of the same elements in the same order as the layered struc ture of Fig. 12. In this context, the circuit layer 130 as well as the filter and graphics layer 131 will be discussed separately in the UV dosage application. Flere, the circuit layer 130 comprises anodes 133, cathodes 132, digitated silver conductor wires 134, and a zinc oxide (ZnO) layer 135. In this example, five cells are provided; that is, there are five pairs of anodes 133 and cathodes 132 next to each other. In an advantageous embodiment, a digitated pattern is used for arraying the conductor wires 134. This is because the zinc oxide layer 135 has a very high resistivity, and the effective resistance value of the circuit can be reduced by the digitated conductor array.

The partial drawing on the right in Fig. 13 shows the filter and graphics layer 131 in the same structure, placed on top of the structure on the left in the finished product. It shows the light filter 136 with a rectangular window or opening 137. The filter layer thus prevents the entry of visible light at e.g. the conductor wires 134, but the open ing 137 is placed at the cathodes 132. Graphics can be printed directly on the filter layer. In this example, the graphics comprises the information texts "UV Guard", "DOSE", i.e. UV dose, as well as the corresponding information texts from zero to 100 per cent, at intervals of 20%. When using the UV dosimeter, each cathode 132 of the indicator is initially black (i.e. the colour of silver oxide in an example using silver/silver oxide). After the indicator has absorbed a sufficient amount of UV radi ation, the cathode 132a of the first cell turns from black to silver (i.e. clear). The clear area will thus extend up to the 20% limit in the dose window or opening 137. As the UV dose increases, the cells (including the cathodes 132a to 132e), one by one from the bottom, will change their colour from black to clear. The uppermost cathode 132e will be the last one to change its colour. Thus, the UV dose will have reached the maximum threshold value set, indicated by the figure 100% in this scale. This dose (100%) may represent, for example, a UV dose to which a user with average pigmentation has been exposed having just burned the skin. In this way, the dosi meter indicates the safe time in the sun, and particularly exposure to the UV dose in real time. This is advantageous, because otherwise the burning of the skin will be visible with a slight delay, typically after moving indoors, when damage may already have been caused to the skin.

The substances used, and their colours in the reactions of the substances, may naturally be different from clear (colour of silver) and black (colour of silver oxide) in the UV dosimeter, as long as the visibility of progress of the UV column, to the user of the device, is not compromised.

The UV dosimeter will find a number of uses; for example, there is a need to meas ure UV powers of production equipment in the industry; and on the beach it is useful to know the dose of UVA and UVB radiation to which one has been exposed, to avoid a possible risk of melanoma.

Now returning to the switch options of Figs. 7a and 7b as well as Figs. 10 and 1 1 , Figs. 14a and 14b show yet another option for implementing a single-use switch. This option, too, can be made on an automated reel-to-reel type production line. The structure of the indicator 140 in Fig. 14a comprises an adhesive surface 141 which may consist of said PSA type adhesive, at one end of the strip. On the opposite side of the fold 144, a conductive area 145 is printed, consisting of graphite or another conductive material. Vertical cuts are made on both sides of the conductive area 145, extending from the lower edge to the area of the adhesive surface on the other side of the fold 144 so that the cuts extend symmetrically to an equal length to either side from the fold. For the cuts, creases may be advantageously made to facilitate the turning of the tongue in the correct direction, i.e. upwards upon folding. Right below the conductive area 145, a switch area 142 is provided, with separate switch contacts 143. The switch is turned on by folding the indicator part with the adhesive surface 141 down around the fold 144 so that the central tongue separated by the cuts, assisted by the creases, is turned in the direction of the interior angle, as illustrated by the drawing on the right hand side of Fig. 14a. When the fold part with the adhesive surface is completely folded against the rest of the surface of the indicator area, and pressed together by fingers, the adhesive surface 141 will adhere to the opposite part so that the conductive area 145 and the switch area 142 are contacted with each other. In other words, the contacts 143 of the switch, with the switch area 142, are connected via graphite (or, more generally, the conductive area 145). Because an area with a thickness of four substrate layers is formed at the tongue part folded off, but an area with a thickness of only two substrate layers is formed around it, the adhesive substance generates a pressure in the switch area 142, keeping the con tact closed. Because the switch is for single use only in the indicator application, there is no need to remove the adhesive surface from the opposite surface later on. Because, in the product of the invention, conductive paste is printed in any case, the auxiliary cost for the materials of the embodiment of Fig. 14a only concerns the adhesive and the film applied to protect it. With respect to the manufacturing tech niques, a difference naturally lies in the provision of the cuts and the creases, but this solution can also be well implemented by printing techniques based on the reel- to-reel principle.

Figure 14b shows a switch solution of Fig. 14a applied in a UV dosimeter. The figure shows a cold prototype made of paper, with the components and the views of the opening drawn with a pen for illustration. In the same way as in Fig. 14a, Fig. 14b shows the tongue area folded in the direction of the inner angle, with the conductive area approaching the switch area. The five-cell UV dosimeter shows the magnitude of UV exposure graphically as a change of colour of five zones in the opening so that the zone "1 " is the first one and the zone "5" the last one to change its colour. Receiving a UV dose will start at the moment when the fold containing the switch is adhered to the opposite surface by pressing with fingers. In this way, the "measur ing" of UV radiation can be started precisely and manually from the moment of turn ing on the switch, and, in practice, product storage time does not affect the operation of the indicator product. This is one significant advantage provided by the switch. Similarly, the use of adhesive and the above-described 4-layer structure in the switch area make the electrical operation of the switch reliable.

Consequently, in the invention, a UV sensitive resistor, i.e. a so-called photoresistor as represented by the element 91 in Fig. 9, can be used for measuring the UV dose. The chemical change, in turn, can be measured by applying e.g. a moisture-sensi tive resistor in place of the NTC resistor 21 (see Figs. 2a and 2b, and 4), i.e. the thermistor 21 . Another application of the invention is to use a pressure-sensitive resistor in place of the thermistor 21 .

In an embodiment of the invention, the state of charge of the cell or cells is detected capacitively on the basis of a change in the permittivity of the electrode. This can be measured by pressing a capacitor disc onto the changing electrode and also the electrolyte, to detect the state of charge by means of the change in the capacitance without interfering with the cell, i.e. the electrochemical cell, galvanically.

In an example of the invention, the state of charge of the cell or cells indicates the thermal dose, radiation dose, moisture dose, pressure dose, or a change in the con tent of a chemical compound in the cell or cells, from the time of switching on the indicator. In an example, said chemical compound may be CO2, i.e. carbon dioxide.

In an embodiment of the invention, the indicator comprises either several cells con nected in parallel so that each cell has a discharge resistor of a different size and a different discharge current, or several cells connected in series so that only one cell in the series will be discharged at a time, and after the discharging, the electric circuit section comprising the cell in question will be electrically disconnected. A circuit structure with a parallel connection enables a display application and, for example, a bar graph display as shown in Fig. 8b, because each cell (electrochemical cell) has a different time of discharge.

In an application of the invention, the cells are charged via separate resistors of equal size, by which all the cells are charged to a substantially equal charge at the stage of manufacture of the indicator.

In an embodiment of the invention, the materials of the electrodes are selected to be Zn (zinc, for the anode) and Ag₂<3 (silver oxide, for the cathode), whereby after the electrode reactions, the surface materials of the electrodes will be ZnO (zinc oxide) and Ag (silver), respectively. If silver is used as the cathode, the silver has to be oxidized in a separate manufacturing process providing each cell with an equal charge. Therefore, the charging resistors should be advantageously equal, to pro vide good precision for the measurement. In this way, the embodiment with equal charging resistors (in the previous paragraph) and the selections of Zn and Ag₂<3 as the anode and the cathode (this paragraph) are linked together. Indeed, in relation to any material selected for the anode and the cathode, all the cells can be charged to equal charge levels.

When a battery (that is, a cell) is charged in advance, a situation is achieved in which the charge level is precisely known. Consequently, the discharging will take place precisely as well, if the resistance values of the resistors are precise. Another option is to use silver oxide as the cathode, that is, a ready-made charged cell. A problem here is the inaccuracy in the amount of silver oxide, caused by the printing process.

In an embodiment, the cells are made in the form of pre-charged electrodes. An example is a battery formed of zinc oxide (ZnO) and silver (Ag) electrodes, charged before use. Thus, in the electrode reactions induced by the charging, zinc (Zn) and silver oxide (Ag₂0) are formed as the materials of the electrodes. After this, the indicator is ready for use. In another embodiment of the invention, cells are dis charged or charged by means of a separate power source. In practice, this means a situation in which a battery of zinc and silver oxide electrodes is provided which does not require separate charging but is directly ready for use. In a third embodi ment, a galvanic cell is used, in which another battery (power source) is used for charging the measuring cell, i.e. for changing the colour in a galvanic process. In practice, this means using a separate battery for the change, i.e. for charging the cell(s), because the discharging will not require an external power source. This third alternative is a more complex and expensive solution than the first two alternatives.

It should be noted that the use of silver and silver oxide in the indicator is only an advantageous example, because the mutual change in the colour is visually so obvious and easy to detect with this pair of materials. Any other substance may be used as well, if only its colour is changed by the electrode reaction in a visually detectable way.

In the switch application of the invention, anisotropic conductive material is printed or applied between two adjacent conductors, for example in the form of a paste or a film (such as anisotropic conductive paste, ACP; or anisotropic conductive film, ACF), with which the connection is made by pressing the material to be conductive (see Fig. 7b above). The pressing can be done manually, i.e. by the user pressing manually at the desired time of switching on the indicator.

With respect to the display application of the invention, various display combinations may be constructed, which may also be different from a conventional 7-segment display. The cells may be connected so that they constitute e.g. a bar graph analog display. Because the number of cells has hardly any effect on the price, e.g. 10 cells can be easily set up at intervals of 10% to provide a scale from 0 to 100%.

On the other hand, electrochemical cells according to the invention may be con nected to e.g. processor outputs to provide a slowly changing digital display. With auxiliary circuits, it can be made reversible. An application for such structures is temperature measuring tags which may have a display of, for example, three pix els. It does not have to be reversible. Another application of a "slow" display is dis plays showing the price in, for example, stores, supermarkets and filling stations, and in any other place where the display information does not have to change all the time.

The switch application of the invention involves the following. Because the times of manufacturing and taking into use of the indicator are different, a switch has to be provided to start discharging when the product is packed. The switch has to be suf ficiently conductive so that its resistor does not substantially change the discharging time but simultaneously so isolating that discharging will not take place between the times of manufacturing and packing of the indicator. This will be a common problem in any products with printed batteries.

In the switch application, solder is used for connecting the terminals of the switch, to be melted either by thermocompression, ultrasound, laser, or an inductive loop in the circuit.

As to anisotropic conductive substances, so-called ACP (conductive paste) and ACF (conductive film) are prior art. A rule of thumb in applying the invention is that the particle size has to be 5 times smaller than the interval between the conductors, to prevent conductivity in the lateral direction. If the particle size is larger than that, conductivity in the lateral direction is induced. In the switch embodiment, Fig. 7b shows a situation of lateral conductivity with anisotropic conductive materials. This is an advantageous alternative in the invention, because ACP is easy to print on the structure. If the paste is partly cured by UV radiation, it will remain stable between the times of manufacturing and packing, after which it can be exposed to UV radia tion again, to be fully cured.

In a switch application of the invention, the terminals of the switch are connected by using a solder which is melted either by thermocompression, ultrasound, laser, or an inductive loop in the circuit. In this application relating to the use of solder, it should be noted that the solder gives the best conductivity, but it has to be printed in the form of a paste, and a problem may be caused by the stability of the paste before melting.

In a switch application of the invention, the terminals of the switch are connected by crimping, by means of either a separate piece of metal, or printed or applied paste that contains metal particles. With respect to this application, crimping is a straight forward and inexpensive operation, but it normally requires two conductors on top of each other, or a metal plate connecting adjacent conductors. All in all, the use of ACP in the invention is thus a more advantageous alternative than crimping.

In a switch application of the invention, the terminals of the switch are connected by printed metal oxide which is subjected to photonic sintering by strong radiation, to become conductive. Photonic sintering is an advantageous option for connecting the terminals of the switch, and a useful and easy method in printed products. For example, copper oxide (CuO) paste is available, as are lighting devices, so that photonic sintering is a useful way of making the switch embodiment of the invention. In addition to luminous radiation, it is possible to apply plasma discharge for reduc ing the oxide, or to add chemical catalysts in the printing ink, to accelerate the reduction of the oxide by means of external energy.

In a switch embodiment of the invention, a printed transistor in OFF state is used as the switch and is switched to ON state by cutting off the circuit to the grid at the moment of taking the switch into use. The transistor can be used if the conductivity of the channels is weak in the OFF state. The conductivity of the transistor in the ON state does not need to be good if it is well known, because it can be included in the discharge resistor of the cell. In other words, the transistor might also be used in the production, particularly if it is also used for modifying the tempera ture/resistance (T/R) curve.

In a switch embodiment of the invention (corresponding to Fig. 10), the indicator circuit is also provided with a switch area, onto which a strip with conductive adhe sive can be folded, whereby the conductive adhesive will short-circuit the switch area and keep the switch area connected after the strip has been folded onto the switch area. This is particularly suitable for manual connecting (by hand/fingers), but it can be easily automated as well.

In a switch embodiment of the invention (corresponding to Figs. 14a and 14b), the indicator circuit comprises a switch area with a conductive area adjacent to it, and conductive adhesive on a foldable tongue adjacent to this, wherein two parallel cuts are provided on both sides of the conductive area, extending to the conductive area, placed symmetrically and transversely to the fold, wherein the central tongue sepa rated by the cuts is provided with an upward crease and downward creases on both sides of this, wherein the conductive area short-circuits the switch area, and the conductive adhesive keeps the switch area connected together when the strip with its central tongue remains folded onto the switch area.

In a switch embodiment of the invention (corresponding to Fig. 1 1 ), the indicator comprises a switch element and a contact element, wherein the switch element comprises two nearly triangular openings placed symmetrically, and two switch con tact ends, and the contact element comprises two tongues and a conductive area in which the contact element is slidable up and down in relation to the switch element so that after sliding, the conductive area connects the switch contact ends, and sim ultaneously the tongues are placed at the narrower end of the triangular openings, locking the contact in position.

The inventive idea of the present invention also comprises a method for manu facturing an electrochemical indicator. The manufacturing method comprises all the alternative ways of manufacturing the different embodiments of the device itself which have been described above and in the appended claims. Similarly, the method for manufacturing the switch is comprised in the inventive idea of the pre sent invention.

In the method for manufacturing an electrochemical indicator, the method in its gen eral form (see Fig. 12) comprises the following steps:

- printing or etching a conductive layer onto a substrate;

- printing, as electrodes, an anode and a cathode for one cell onto the conductive layer, and an electrolyte onto the electrodes, and in this way printing a sufficient number of electrochemical cells connected to each other;

- protecting the structure by a layer which filters at least visible light so that at least one of the electrodes is visible from the outside of the indicator; and wherein, upon using the manufactured indicator:

Consequently, the manufacturing process does not necessarily start from printing of a conductive pattern, but the conductors may also be made by etching a metal layer in a film. The metal layer may consist of, for example, copper or aluminium. Applications of the present invention comprise monitoring cold chains in the food industry by means of indicators placed in product packages, monitoring other tem perature-sensitive products and rooms, display applications, UV dose metering e.g. in the form a personal UV radiometer, meters for moisture or pressure in a variety of applications, and, for example, measuring carbon dioxide content in air.

The present invention is not limited to applying merely to the embodiment examples presented above, but the invention may vary within the scope of protection defined in the appended claims.

Claims

1. An electrochemical indicator comprising one or more electrochemical cells (22, 22a to 22e) connected to each other, wherein each cell comprises, as electrodes, an anode (62, 125b, 133) and a cathode (51 to 54, 61 , 125a, 132, 132a to 132e), as well as an electrolyte (17, 127), characterized in that physical changes in at least one of the electrodes are used to indicate the state of charge of each cell (22, 22a to 22e) as a change in the colour of the respective electrode through the transparent electrolyte, and that the indicator is made in the form of a printed coplanar structure of thick film type.

2. The indicator according to claim 1 , characterized in that the electrochemical cell (22, 22a to 22e) is discharged via a resistor or resistor network (21 , 23, 25, 32a to 32e, 41 a to 41 d, 91 ) changing as a function of a change in the temperature, the pressure, a radiation dose, or a chemical change.

3. The indicator according to claim 2, characterized in that the electrochemical cell (22, 22a to 22e) is discharged via an active circuitry comprising at least one transistor (24), changing as a function of a change in temperature or a radiation dose.

4. The indicator according to claim 1 , characterized in that the state of charge of the cell or cells (22, 22a to 22e) is detected optically on the basis of the colour of the electrode.

5. The indicator according to claim 1 , characterized in that the state of charge of the cell or cells (22, 22a to 22e) is detected capacitively on the basis of a change in the dielectric constant of the electrode.

6. The indicator according to claim 5, characterized in that the change in the dielectric constant of the electrode is detected by a capacitor manufactured to accompany the electrode and coupled to a UHF antenna so that the change in the electrode changes the impedance of the antenna, and said change can be detected upon reading the UHF tag.

7. The indicator according to claim 5, characterized in that the change in the dielectric constant of the electrode is detected by means of a passive resonant cir cuit formed by a capacitor and a coil manufactured to accompany the electrode.

8. The indicator according to claim 2, characterized in that the state of charge of the cell or cells (22, 22a to 22e) indicates a heat dose, a radiation dose, a moisture dose, a pressure dose, or a change in the content of a chemical substance to which the cell or cells have been exposed since the time of switching on the indicator.

9. The indicator according to claim 1 , characterized in that the indicator com prises either several cells (22) connected in parallel so that each cell (22) has a different discharge resistor and a different discharge current, or several cells (22a to 22e) connected in series so that only one cell (22a to 22e) in the series is dis charged at a time, and after the discharging, the electric circuit section comprising the cell (22a to 22e) in question will be electrically disconnected.

10. The indicator according to claim 1 , characterized in that the indicator com prises several cells (22) connected so that the discharging cells make up a digitally readable optical code.

1 1 . The indicator according to claim 1 , characterized in that the cells (22, 22a to 22e) are charged by separate resistors of equal size, whereby all the cells (22, 22a to 22e) are charged to a substantially equal charge level at the stage of manufacture of the indicator.

12. The indicator according to claim 1 or 1 1 , characterized in that the materials selected are Zn for one electrode and Ag₂<3 for the other electrode, whereby after the electrode reactions, the surface materials of the electrodes will be ZnO and Ag, respectively.

13. The indicator according to claim 1 , characterized in that the cells (22, 22a to 22e) are discharged or charged by means of a separate power source.

14. The indicator according to claim 13, characterized in that each cell (22, 22a to 22e) is coupled to the outlet of an electronic circuit, whereby the cell (22, 22a to 22e) can be used for indicating the state of the electronic circuit.

15. The indicator according to claim 13, characterized in that either the anodes (62, 125b, 133) or the cathodes (51 to 54, 61 , 125a, 132, 132a to 132e) of the elec trochemical cells (22, 22a to 22e) are coupled to form a 7-segment digital display.

16. The indicator according to claim 1 , characterized in that the indicator com prises a switch (31 , 1 10, 1 13, 140) for starting the discharging or charging of the cell or cells (22, 22a to 22e).

17. The indicator according to claim 16, characterized in that anisotropic conduc tive material (73, 74) is printed or applied between two adjacent or superimposed conductors (72), to make the coupling conductive by compressing the material.

18. The indicator according to claim 17, characterized in that the anisotropic con ductive material (73, 74) is a paste comprising an adhesive, wherein the adhesive is cured by UV radiation.

19. The indicator according to claim 16, characterized in that the terminals of the switch (31 ) are connected by means of a solder which is melted by thermocompres sion, ultrasound, laser, or an inductive loop belonging to the circuit.

20. The indicator according to claim 16, characterized in that the terminals of the switch (31 ) are connected by crimping, either by a separate piece of metal or by printed or added paste that contains metal particles.

21 . The indicator according to claim 16, characterized in that the terminals of the switch (31 ) are connected by means of printed metal oxide which is photosintered to be conductive by strong radiation, or by plasma discharge for reducing the oxide, or by including chemical catalysts in the printing ink to accelerate the reduction of the oxide by means of external energy.

22. The indicator according to claim 16, characterized in that the switch (31 ) is a printed transistor which is in the OFF state and is turned to the ON state by discon necting the electric circuit to the grid at the moment of taking the switch into use.

23. The indicator according to claim 16, characterized in that the indicator circuit is equipped with a switch area, onto which a strip can be folded, conductive adhe sive being printed on the strip, which conductive adhesive will short-circuit the switch area and keep the switch area connected after the strip has been folded onto the switch area.

24. The indicator according to claim 16, characterized in that the indicator circuit comprises a switch area (142) with a conductive area (145) adjacent to it, and con ductive adhesive (141 ) on a foldable strip adjacent to this, two parallel cuts being provided on respective sides of the conductive area, extending to the surface of the conductive adhesive, placed symmetrically and transversely to the fold, wherein the central tongue separated by the cuts is provided with an upward crease and down ward creases on both sides of it, wherein the conductive area will short-circuit the switch area, and the conductive adhesive will keep the switch area connected when the strip with its central tongue remains folded onto the switch area.

25. The indicator according to claim 16, characterized in that the indicator com prises a switch element (1 10) and a contact element (1 13), wherein the switch ele ment (1 10) comprises two nearly triangular openings (1 1 1 ) placed symmetrically, and two switch contact ends (1 12), and the contact element (1 13) comprises two tongues (1 14) and a conductive area (1 15) in which the contact element (1 13) is slidable up and down in relation to the switch element (1 10) so that after the sliding, the conductive area (115) connects the switch contact ends (1 12), and simultane ously the tongues (114) are placed at the narrower end of the triangular openings (1 1 1 ), locking the contact in position.

26. A method for manufacturing an electrochemical indicator, characterized in that the method comprises the following steps:

- printing or etching a conductive layer (124) onto a substrate,

- printing, as electrodes, an anode (125b) and a cathode (125a) for one cell onto the conductive layer (124), and an electrolyte (127) onto the electrodes, and in this way printing a sufficient number of electrochemical cells (22, 22a to 22e) connected to each other;

- protecting the structure by a layer (128) which filters at least visible light so that at least one of the electrodes is visible from the outside of the indicator; and wherein, upon using the manufactured indicator:

- physical changes in at least one of said two electrodes are used to indicate the state of charge of each cell (22, 22a to 22e) as a change in the colour of the respective electrode through the transparent electrolyte, and that the indicator is made in the form of a printed coplanar structure of thick film type.