WO2004004615A1

WO2004004615A1 - Diaper with moisture sensor

Info

Publication number: WO2004004615A1
Application number: PCT/NL2003/000490
Authority: WO
Inventors: Gerardus Titus Van Heck; Peter Hillebrand De Haan
Original assignee: Nederlandse Organisatie Voor Toegepast- Natuurwetenschappelijk Onderzoek Tno
Priority date: 2002-07-04
Filing date: 2003-07-03
Publication date: 2004-01-15
Also published as: NL1021002C2

Abstract

A moisture sensor for detecting moisture, with the moisture sensor being provided with two electrodes and a moisture-absorbing dielectric included between the electrodes, wherein, upon moistening of the dielectric, an electrical voltage difference between the electrodes is detectable, with salt crystals of a first type and/or salt components of the first type being provided against and/or near at least a part of only one of the electrodes, so that the electrodes, at least upon detecting moisture, have a mutually different chemical potential.

Description

Title: DIAPER WITH MOISTURE SENSOR

The invention relates to a moisture sensor for detecting moisture, with the moisture sensor being provided with two electrodes and a moisture-absorbing dielectric included between the electrodes, with an electrical voltage difference between the electrodes being detectable upon moistening of the dielectric.

The Dutch patent publication 101 59 40 describes such a moisture sensor. In this known moisture sensor, at least one of the electrodes is formed by a ribbon-shaped carrier on which an Inherently Conductive Polymer (ICP) is provided. Further, the electrodes are mutually different in such a manner that the electrodes have mutually different chemical potentials. The electrode designed as a ribbon-shaped carrier provided with an ICP is relatively expensive. Such a moisture sensor is particularly suitable for detecting moisture in, for instance, diapers. However, such moisture sensors are preferably for single use and should therefore be inexpensive.

It is an object of the invention to provide a solution to this problem. The moisture sensor according to the invention is accordingly characterized in that against and/or near at least a part of only one of the electrodes, salt crystals of a first type and/or salt components of the first type are provided so that the electrodes, at least upon detecting moisture, have a mutually different chemical potential. In the absence of the salt crystals and/or the salt components, the electrodes can have the same or virtually the same chemical potential and can optionally even be the same. This means that, in manufacturing, there only need to be two identical electrodes which, at least upon detecting moisture, have a different chemical potential by providing salt crystals and/or salt components against and/or near at least a part of only one of the electrodes. The salt crystals and/or salt components are inexpensive per se and their provision can also be carried out in an inexpensive manner.

Surprisingly, it has been found that, when salt crystals are provided against one of the electrodes, the chemical potential of this electrode in relation to the chemical potential of the other electrode changes such that, upon moistening the dielectric located between the electrodes, a voltage difference is detectable. Such salt crystals and/or salt components can also be provided near the electrode instead of against the electrode. In this case, the salt crystals can be provided against the electrodes by the moisture during moistening. Changing the chemical potential of one of the two electrodes in such a simple manner yields, as stated, a very inexpensive manner for manufacturing such a moisture sensor.

In particular, the electrodes have the same chemical potential in the absence of salt crystals and/or salt components.

Preferably, the electrodes are designed in the same manner, except for the salt crystals and/or salt components. This makes the manufacture of the moisture sensor extremely simple.

The electrodes can each have a wire-shaped design. This results in the electrodes being flexible and being able to assume virtually any desired pattern. This makes it possible for any shape of an area where moisture is expected to be absorbed by the dielectric to be provided with the electrodes. It is, for instance, possible to limit one side of that area with one electrode and to limit another side of that area with the other electrode. Preferably, the electrodes are each provided with a plastic core provided with a conductive coating. Such a plastic can, for instance, comprise acryl, polyester or polyamide. The conductive coating can comprise an inorganic compound, such as for instance copper sulphide. Such electrodes are commercially available at very low cost. Preferably, the salt crystals and/or the salt components are provided against the electrodes by bringing one electrode into contact with a salt solution. Such a salt solution can also comprise a colloidal graphite dispersion. Any water-soluble salt is suitable for obtaining the salt solution. For instance, magnesium salts and alkali salts such as sodium carbonate, sodium chloride and potassium silicate are available at low cost and can be used in a simple manner. It is self-evident that a treatment of one of the electrodes with such a salt solution can be carried out in a very simple and very inexpensive manner.

The electrodes can be provided with a cotton wrap. This can, for instance, serve as camouflage of the electrodes or, in use, to prevent, for instance, a contact between a skin part and an electrode from causing irritations of the skin. The electrodes are preferably included in a fibrous material. This can, for instance, be a diaper. However, what is not excluded is that the electrodes are included in a package for moisture -sensitive products. Such a package can also be manufactured from a fibrous material. The electrodes can be interwoven with the fibrous material. However, it is also conceivable that the electrodes are held in a certain position in or on the fibrous material by using an adhesive, such as for instance a hot -melt. Such an adhesive can also have a wire -shaped design and can, in addition, be electrically insulating. In that case, it is possible to use the hot-melt as a weft when manufacturing a moisture sensor designed as a tape which is

"glued" on the moisture -absorbing dielectric. For detection of the electrical voltage difference, the electrodes can each be connected to a light -emitting diode (LED). Here, it may be necessary to connect the LED to a separate power source as well. However, it is also possible that the electrodes are each connected to a resonance circuit which, upon detecting an electrical voltage difference, and thus upon moistening of the dielectric, transmits a signal which can be received by a receiving device. In this case as well, it may be necessary to separately connect the active electronics to a supply source for supplying sufficient electric energy. In this case, the transmitted signal can even comprise an identification code so that a receiving device located at a distance obtains information about the detection of moisture by a specific moisture sensor. In use, this can be advantageous in situations in which a plurality of moisture sensors are present in the neighborhood of the receiving device. By means of a predetermined relation between an identification code and a moisture sensor, a user of the receiving device can determine which moisture sensor is detecting moisture.

The invention also relates to a diaper provided with such moisture sensor.

In addition, the invention relates to a moisture sensor for detecting moisture, with the moisture sensor being provided with two electrodes between which an electrical voltage difference is detectable upon a contact formed by means of moisture between the electrodes.

The invention further relates to a package for a moisture -sensitive product. The invention will now be explained with reference to a drawing, in which:

Fig. 1 diagrammatically shows a first embodiment of a moisture sensor according to the invention;

Fig. 2 diagrammatically shows a second embodiment of a moisture sensor according to the invention;

Fig. 3 diagrammatically shows a third embodiment of a moisture sensor according to the invention;

Fig. 4 diagrammatically shows a cross -section along the line A-A of the third embodiment of a moisture sensor according to the invention shown in Fig. 3;

Fig. 5 diagrammatically shows a moisture sensor provided on a diaper according to a fourth embodiment of the invention; and

Fig. 6 diagrammatically shows a moisture sensor without a dielectric between the electrodes. Fig. 1 shows a moisture sensor 1 for detecting moisture. The moisture sensor is provided with two electrodes 2, 3 which each have a chemical potential. The electrodes 2, 3 are included in a moisture -absorbing dielectric 4 which is therefore also located between the electrodes 2, 3. The electrodes 2, 3 preferably have a wire -shaped design. Both electrodes 2, 3 comprise, for instance, a plastic core provided with an electrically conductive coating 6. The plastic core is preferably manufactured from acryl, polyester or polyamide. The conductive coating comprises, for instance, an inorganic compound such as, for instance, copper sulphide. Against one of the electrodes, salt crystals and/or salt components are provided. For this purpose, the relevant electrode can have been in contact with a salt solution. Any water-soluble salt is suitable for obtaining the salt solution. Possible salts are magnesium salts and alkali salts such as, for instance, sodium carbonate, sodium chloride or potassium silicate. In this context, the salt solution can also comprise a colloidal graphite dispersion in water. An electrode against which or near which salt crystals and/or salt components are provided is called a treated electrode (B) in this context. An electrode against which or near which no salt crystals and/or salt components are provided is called an untreated electrode (O) in this context. The moisture sensor works as follows. When the dielectric 4 located between the electrodes 2, 3 absorbs moisture, an electrolyte is formed. Its contact with the electrode against which salt crystals and/or salt components are provided, in this example electrode B, causes an electrochemical potential between the electrode B and the electrolyte. The contact between the electrode against which no salt crystals and/or salt components are provided, in this example electrode O, and the electrolyte also causes an electrochemical potential between the electrode O and the electrolyte. Because the two electrodes 2, 3 have a different chemical potential, the electrochemical potentials in relation to the electrolyte will differ. When the resistance of the electrolyte is sufficiently low, the said electrical voltage difference between the two electrodes 2, 3 arises. A battery is formed. This voltage difference can comprise any measurable voltage difference. The voltage difference is preferably between 0-500 mV and, in many cases, will be between 150 and 200 millivolt. Such a voltage difference is very well detectable. Such a voltage difference is sufficiently high to drive a detection device 7. The detection device 7 can optionally be equipped with a separate supply source for amplified signaling of a voltage difference measured between the electrodes. For instance, the detection device 7 can comprise a resonance circuit, which is not shown but is known per se, which, upon detecting moisture, can generate a radio-frequency signal by means of the electrical voltage difference thus generated. A relatively nearby receiving device can receive such a radio -frequency signal. This enables the detection of moisture in the moisture -absorbing dielectric 4 to be registered even at a distance. Fig. 2 shows an embodiment in which the electrodes 2, 3 are each provided on an inside 11 of a moisture-absorbing layer 8. The layers 8 have an identical design. Between the layers 8, a moisture -absorbing dielectric 10 is provided. In this case, near one of the electrodes 2, 3, salt in powder form is provided between the moisture -absorbing layer 10 and, for instance, the superjacent layer 12. When a tissue built up from such layers becomes moist, the salt crystals provided between layer 12 and layer 10 will dissolve in the moisture and will, among other things, join against the electrode 2. This makes the chemical potential of this electrode 2 different from the chemical potential of the other electrode 3. Then, the moisture can be detected in a manner analogous to the manner as described in the discussion of Fig. 1. The electrode 2 is the treated electrode (B) in this context and electrode 3 is the untreated electrode (O) in this context.

Fig. 3 shows an embodiment in which the electrodes 2, 3 are interwoven with each other. In this case, one of the electrodes is in a treated condition while the other electrode is in the untreated condition. The electrodes 2, 3 are interwoven with a moisture -absorbing dielectric 4.

Fig. 4 diagrammatically shows a cross -section along the line A- A of the embodiment of Fig.3. This shows that the electrodes 2, 3 are included in the dielectric separately from each other.

Fig. 5 shows a moisture sensor 5 provided on a diaper 6. This moisture sensor 5 is provided with two electrodes which each have a chemical potential and which are connected to each other by means of electrically insulating connections 15, 16. The electrically insulating connections 15, 16 are, for instance, hot-melt wires. The electrodes 2, 3 are each connected to a signaling device 7. In this case, the electrodes 2, 3 are fixed against the diaper by heating the hot-melt wires 15, 16. The hot-melt wires 16 are, as it were, interwoven with the electrodes 2, 3. The hot-melt wires 15, on the other hand, are either provided between the electrodes 2, 3 and the diaper 6, or provided such that the electrodes 2, 3 are located between the hot-melt wires 15 and the diaper 6. Such a moisture sensor 5 can be manufactured such that the moisture sensor can be fixed against the diaper 6, for instance, by means of a warm iron. One of the electrodes 2, 3 is in the treated condition, which, in this example, means that salt crystals are provided against that electrode, for instance by means of contacting a salt solution with this electrode. This results in this electrode having a chemical potential which differs from the chemical potential of the other electrode.

It will be clear that this moisture sensor 5 can be manufactured without involving the diaper 6 in this. Such a moisture sensor can be provided with each of the above aspects which are not related to the moisture-absorbing dielectric. Fig. 6 shows an example of such a moisture sensor which can also be provided on other moisture -absorbing materials. The treated electrode (B) and the untreated electrode (O) are connected by non-conductive wires 18, 19. These non-conductive wires 18, 19 can each comprise one long wire, as drawn. One or each non-conductive wire can optionally be a hot-melt wire. It is possible for the non-conductive wires to comprise a plurality of wires which are not of continuous design at the ends of the tissue formed with the wires and the electrodes O, B. Such a moisture sensor can be designed as a ribbon which can be provided against a moisture-absorbing dielectric in a simple manner. The hot-melt wefts 18, 19 and/or other non-conductive wires can be so close together that they are more like a closed tape in which the electrodes are included. Such a ribbon or tape can be provided without a signaling device on, for instance, a diaper or a garment or packaging material at a position where moisture detection is important. In that case, a user can decide for himself what type of signaling device is to be connected to the electrode at the ends of electrodes 20, 21. The user can also decide in what manner the ribbon or tape is to be provided against or on the diaper, the garment or the packaging material. In such a manner, also a ribbon-shaped whole can be formed which is composed of a dielectric 4 and electrodes 2, 3. This embodiment also provides a very inexpensive moisture sensor. The signaling device 7 can comprise a very simple and inexpensive light emitting diode (LED). Here, it may be necessary to use a separate supply source and to feed the voltage difference measurable upon moisture detection as a driving signal. This makes it possible to register by means of a light signal that the moisture sensor detects moisture. As already indicated, the signaling device 7 can also comprise a resonance circuit (not shown) by means of which a radio or frequency signal can be transmitted which can be received by a nearby receiving device. In this case as well, it may be necessary to include a separate supply source in the moisture sensor. Such an application is particularly suitable for incontinence diapers which are used, for instance, in hospitals and nursing homes. The resonance circuit can be arranged to transmit a radio-frequency signal with an identification code. In this manner, it cannot only be registered that a moisture sensor detects moisture, but it can also be registered which moisture sensor detects moisture. It is, for instance, possible to determine at a distance that an incontinence diaper worn by a predetermined person has started to absorb moisture. Instead of directly visually or audibly signaling near the diaper that the diaper has detected moisture, in this manner, it can be registered elsewhere which diaper has absorbed moisture. In such an application, moistening of the diaper by the person wearing the diaper is not directly made known to all surrounding persons. Only a person who can receive and interpret the radio-frequency signal with the identification code is informed of the detection of moisture in the relevant diaper. However, application of such a moisture sensor is not limited to the use of diapers. It is also possible to include such a moisture sensor in materials used to store goods which are preferably to be kept dry. This concerns a package of a moisture -sensitive product. The package can be provided with a moisture sensor. For instance, rice can be contained in a fibrous bag, which is provided with such a moisture sensor. In this case, the signaling device can be a fuse, which breaks down at a specific breakdown voltage. In this manner, it can be observed whether the package of the dry rice has remained dry. Such a fuse can have a very inexpensive design, in which a color difference simply arises due to the resistance being blown. Such packaging material provided with a moisture sensor according to the invention can, for instance, also be used for packaging dry and sterile gauzes, or for packaging cookies. Other possibilities are, for instance, cigar packages, and packages for film material, powders and fireworks. In all these applications, the moisture sensor can have a very simple and inexpensive design and be provided on a moisture -absorbing dielectric.

Providing such a moisture sensor can be done in many ways, in particular by means of gluing and/or connecting mechanically. The mutual connection of the electrodes can also be done in various manners.

Providing the salt crystals and/or salt components against and/or near one of the electrodes can also be done in various manners. It is possible for the electrode to be led through a salt solution in a very simple manner. Any person skilled in the art will be able to determine in a simple manner what quantity of salt per volume unit of solvent is suitable for an optimal change of the chemical potential of one of the electrodes 2, 3. What is not excluded, of course, is that against or near only one electrode, salt crystals and/or salt components of a first type are provided and against or near only the other electrode, salt crystals and/or salt components of a second type are provided. In this case, of course, the salt crystals of the first type differ from the salt crystals of the second type such that, in use, the chemical potentials of the electrodes differ sufficiently to detect a moisture connection between the electrodes.

The above embodiments and combinations of selected aspects thereof are all considered to be within the scope of the invention.

Claims

1. A moisture sensor for detecting moisture, wherein the moisture sensor is provided with two electrodes and a moisture-absorbing dielectric which is included between the electrodes, wherein upon moistening of the dielectric, an electrical voltage difference between the electrodes is detectable, characterized in that against and/or near at least a part of only one of the electrodes, salt crystals of a first type and/or salt components of the first type are provided so that the electrodes, at least upon detection of moisture, have a mutually different chemical potential.

2. A moisture sensor according to claim 1, characterized in that the electrodes have the same chemical potential in the absence of salt crystals and/or salt components.

3. A moisture sensor according to claim 1, characterized in that the electrodes each have a wire-shaped design.

4. A moisture sensor according to claim 1, characterized in that the electrodes are each provided with a plastic core provided with an electrically conductive coating.

5. A moisture sensor according to claim 1, characterized in that the salts comprise magnesium salts and/or alkali salts.

6. A moisture sensor according to claim 1, characterized in that the electrodes are each connectable to a signaling device for signaling the electrical voltage difference, a Light Emitting Diode (LED) or a resonance circuit for transmitting an RF signal upon detection of moisture.

7. A moisture sensor according to claim 1, characterized in that salt crystals of a second type and/or salt components of a second type are provided against and/or near the electrode which differs from the electrode against and/or near which salt crystals of the first type and/or salt components of the first type are provided, wherein the salt crystals of the first type and the salt crystals of the second type are mutually different.

8. A moisture sensor for detecting moisture, wherein the moisture sensor is provided with two electrodes between which, at a contact formed by means of moisture between the electrodes, an electrical voltage difference is detectable, wherein against at least a part of only one of the electrodes, salt crystals of a first type and/or salt components of the first type are provided.

9. A diaper provided with a moisture sensor according to any one of the p re ce ding claims .

10. A package for a moisture-sensitive product wherein the package is provided with a moisture sensor according to any one of claims 1-8.