WO2015018619A1

WO2015018619A1 - Device for irreversibly detecting an exceedance of a predetermined temperature and method for producing the device

Info

Publication number: WO2015018619A1
Application number: PCT/EP2014/065356
Authority: WO
Inventors: Mathias Maier; Oleksandr Marchuk; Friedemann Tonner
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2013-08-08
Filing date: 2014-07-17
Publication date: 2015-02-12
Also published as: DE102013108557B3

Abstract

The invention relates to a device for irreversibly detecting an exceedance of a predetermined temperature, and to a method for producing the device, comprising a substrate layer (12), to which a meltable material layer (17) is applied, which upon exceeding a melting point of the material layer (17), transitions from a solid state of aggregation to a liquid state of aggregation. The device further comprises particles (19) introduced into the material layer (17), wherein the substrate layer (14) is made of a porous material, which after exceeding the melting point, accommodates the material layer (17), at least partially, and the particles (19) contained in the material layer (17) are filtered out on the surface (18) of the substrate layer (12), at least partially.

Description

Einrichtung zur irreversiblen Erfassung einer Überschreitung Device for the irreversible detection of an excess
einer vorbestimmten Temperatur sowie Verfahren zur a predetermined temperature and method for
Herstellung der EinrichtungProduction of the device

The invention relates to a device for irreversible detection of exceeding a temperature and a method for producing such a device.

DE 10 2005 041 495 A1 discloses a device for monitoring an impermissible exceeding of a temperature acting on an object, which comprises a substrate consisting of glass, ceramic, plastic, a plastic film or another flexible material. On this substrate two spaced apart electrodes are provided and at least one layer of material. This material layer extends between the two electrodes, whereby the material layer changes in dependence on the temperature acting on the material layer. In the material layer, metallic particles or an electrically conductive metal powder are mixed in, wherein in the functional state of the temperature sensor without heat, ie in the initial state, the particles are provided locally and limited in the surface in the material layer. The material layer consists of wax, so that when a heat supply, a change in the state of matter takes place and the metallic particles can be evenly distributed within the then liquid material layer between the electrodes. It uses the law of entropy, which remains minimal in a closed system. Due to this uniform distribution of the metallic particles, it is possible that a changed electrically conductive behavior can be measured. If the heat supply is completed, the physical state of the material layer is changed from "liquid" to "solid", so that it is also possible to prove an inadmissible supply of heat or heat due to the change in the electrically conductive behavior at a later time.

This device has the disadvantage that the change in the electrically conductive behavior of the material layer is often low, so that a clear statement regarding an inappropriate heat supply can not be detected by a significant change in the electrical resistance. In addition, there is an uncontrolled flow of the material layer in the physical state change from "solid" to "liquid" on the substrate.

From DE 699 11 395 T2 a time-temperature integrating display device with barrier material is known. This serves to provide a visually perceptible indication of cumulative heat on an object. For this purpose, a substrate with a diffuse light-reflecting porous matrix and a carrier with a viscoelastic indicator material on its surface for contacting the material and a barrier material is provided. The viscoelastic indicator material, in an activated state, migrates through the temperature into the porous matrix at a rate which increases with increasing temperature, thereby producing the visually perceptible indication.

From DE 34 90 397 T1 further an indicator unit for a temperature control is known. For this purpose, microcapsules are applied to a substrate, which includes a hydrophobic organic compound having an arbitrarily selected melting point, as well as an amethine dye and an oxidizing material.

From JP 2006-029945 a temperature-sensitive device is known, which is formed from a wax layer, which is applied to a substrate and covered by a transparent film. The wax layer comprises a powdered wax layer as well as a certain amount of a viscous agent on a colored layer of a color paper.

These devices have the disadvantage that an often insufficient visual change to detect a temperature exceeded is indicated.

The invention has for its object to provide a means for irreversible detection of exceeding a temperature, which allows for an adjustable triggering temperature or melting temperature, a significant change in a Perkolationszustandes a material layer with particles contained therein. Furthermore, the invention has for its object to propose a simple method for producing such a device.

The object underlying the invention is achieved by a device in which the substrate layer consists of a porous material which at least partially absorbs or absorbs the material layer applied thereto after exceeding the melting point of the material layer or a triggering temperature and absorbs the particles contained in the material layer the surface of the substrate layer at least partially filtered off. The particles remain at least partially, in particular substantially or completely, on or on the surface of the substrate layer. As a result, the material layer, which undergoes the state of aggregation due to the melting temperature being exceeded and passes from the solid to the liquid state, is drawn into the substrate layer, in particular into the pores of the substrate layer, due to capillary forces or the like, the particles on or on the surface the porous substrate layer remain behind or be filtered off. As a result, the volume concentration of the particles contained in the material layer increases significantly, so that a significant change in the percolation state can be detected. Such an impermissible effect of a temperature or exceeding of a predetermined or monitored temperature on the device causes an irreversible state change of the device, so that this device does not need to be continuously monitored and / or buffered to obtain the information. Rather, the impermissible heat input above a melting point can also be verifiable at a later time.

Preferably, the substrate layer is formed of an open-pored material. As a result, a rapid absorption of the liquid material layer can be made possible. By acting capillary forces the absorption of the liquid material layer is supported in the substrate layer.

Preferably, the porous substrate layer consists of a natural filter material. Here, for example, a single-layer or multi-layer paper filter can be provided. Alternatively, an artificial filter material may be used, which consists for example of thermoplastic materials. Further, a ceramic filter material such as a porous alumina or the like may also be used. Depending on the application and the amount of material to be absorbed, the pore size can also be determined.

The material layer is preferably made of wax, in particular carnauba wax. Alternatively, thermoplastic polymers or other substances having a melting temperature, such as fatty acids and their esters, in particular pentanoic, propanoic, butanoic, heptanoic, hexanoic, methanoic, nonanoic, ethanoic, octanoic, undecanoic, decanoic, dodecanoic, pentadecanoic, tetradecanoic, heptadecanoic , Hexadecanoic acid, nonadecanoic acid, octadecanoic acid or eicosane / icosanoic acid or, for example, polyethylene glycol, Polyethylene, polyamide, polypropylene, polybutene, polylactide are used, which have a narrow melting point.

The particles introduced into the material layer are preferably designed as electrically conductive or optically reflective particles. In the case of the electrically conductive particles, the proof of an impermissible excess can be guided by a simple resistance measurement. In the case of optically reflective particles, the amount of reflected rays can be detected by means of a laser measuring device or other light sensors, thereby guiding the impermissible overshoot.

A preferred embodiment of the porous substrate layer provides that the pores are smaller than the size of the particles. As a result, on the one hand, suction of the softened material layer and, on the other hand, filtering off of the particles on the surface of the substrate layer can take place. Alternatively, the pores can be configured to be the same size or even slightly larger than the particles, so that in the event of agglomeration of the particles, filtering is likewise provided on the surface of the substrate layer. This may be sufficient to provide evidence of an inadmissible temperature effect. In particular, a pore size of less than 10 microns is provided.

The material layer is advantageously provided in an initial state with a particle concentration of the particles which is below a percolation threshold. In the initial state of the device, the material layer has a particle concentration with electrically conductive particles in such a way that no or almost non-measurable conductive material layer is formed. When the melting point of the material layer is exceeded, the material layer is absorbed by the substrate layer, the percolation threshold being exceeded when the material layer is only slightly absorbed by the substrate layer. The particle concentration above the percolation threshold increases in proportion strongly, whereby a substantial change in the electrical resistance is given, so that this change in state is very simple and easy to detect. Alternatively, the particle concentration of the particles in the material layer may be equal to or slightly above the percolation threshold. In particular, in the latter case, an initial state of the device can be checked, since at least a low electrical conductivity can be detected. It is essential in all the aforementioned alternatives that a small change in the initial state of the material layer greatly increases the electrical conductivity of the particles-that is to say a curve with a steep gradient.

After the material layer has been filtered off through the substrate layer when a triggering temperature of the material layer is exceeded, an electrically conductive layer is preferably formed by the particles. Thus, there is a change in the electrical resistance at least over a decade in the measurement of the electrical resistance, so that a simple and secure detection of temperature exceeding is made possible on an object.

Advantageously, electrical contacts are provided on the substrate layer, which are adjacent to the material layer in the initial state or partially covered by it. As a result, measuring points can be formed in order to check the initial state of the device and to carry out a control measurement in a simple manner after the temperature has been exceeded. Advantageously, the contact elements can be connected to a wirelessly operating storage medium, in particular an RFID, so that optionally further information can be detected in addition to exceeding the triggering temperature and read out at a later time. It can be provided that the substrate layer is formed without electrical contacts. In such a case, a measuring device with two layered contact elements can be placed directly on the material layer in order to measure the electrical resistance of the material layer or the filtered particle layer on the substrate layer both in the initial state and after an impermissible heat input.

The particles introduced into the material layer are preferably carbon nanotubes (CNT). Alternatively, electrically conductive soot particles (carbon black), silver nanowires, graphitic nanoplates or even glitter or the like may be provided. In addition, a combination of the aforementioned particles or a modification can be introduced.

The device for detecting an irreversible excess of a predetermined temperature, according to the invention is prepared by a method in which a substrate layer is provided consisting of a porous material, wherein the material layer of polymers or wax as a material matrix and particles introduced therein and prepared this material matrix on the Substrate layer is applied and then cured. This allows a simple production in which the material layer is separately adjustable to the desired ratio with respect to the particles in the material matrix of polymers or in viscous wax, so that it is subsequently applied to the substrate layer.

A preferred embodiment of the method provides that the material layer is produced as a dispersion matrix from a polymer dispersion or a viscous wax and a particle dispersion, and this dispersion matrix is applied to the substrate layer and cured as a solid material layer. Such a dispersion matrix enables a simple and rapid preparation and specific tuning of the particles in the polymer dispersion or the percentage by weight required in the viscous wax.

The application of the dispersion matrix to form the material layer is preferably carried out by spraying, printing, knife coating, dipcoating, curtain or spin coating or the like. This allows a cost-effective way to produce such facilities.

Before applying the dispersion matrix of the material layer to the substrate layer, at least one electrical contact is preferably applied. This electrical contact can be applied by application, spraying, sticking, vapor deposition, sputtering or the like.

Furthermore, the dispersion matrix is adjusted to form the matrix with a viscosity, so that a penetration-free application to the substrate layer is made possible. In this case, the dispersion matrix is preferably adjusted to be gel-like, so that, in any case, penetration of the material layer into the substrate layer does not occur during the application of the material layer. In this case, the aqueous dispersion can preferably be made gel-like or viscous with a thickener.

Furthermore, it is preferably provided that the dispersion matrix of the material layer is applied with a layer thickness of less than 500 μm, preferably less than 100 μm. As a result, in particular a fast filtering of the particles on the substrate surface can take place.

The invention and further advantageous embodiments and developments thereof are described in more detail below with reference to the examples shown in the drawings and explained. The features to be taken from the description and the drawings can be applied individually according to the invention individually or in combination in any combination. Show it:

FIG. 1 a shows a schematic top view of the device according to the invention in the initial state,

FIG. 1b a schematic top view of the device according to the invention according to FIG. 1a after exposure to an impermissible temperature,

FIG. 2a shows a schematic sectional view along the line II-II in FIG. 1a,

FIG. 2b shows a schematic sectional view along the line III-III in FIG. 1b,

FIG. 3 a shows a schematic top view of a material layer of the device of a specific embodiment in the starting state,

FIG. 3b shows a schematic top view of a material layer of the device of a specific embodiment according to FIG. 1b,

Figure 4a is a schematic top view of an alternative device to Figure 1a in the initial state and

Figure 4b is a schematic top view of the device according to Figure 4a after the action of an impermissible exceeding a temperature.

Figure 1 shows a schematic view from above of a device 11 according to the invention for detecting an impermissible exceeding an acting on a not-shown item temperature. FIG. 2a shows a schematic sectional view along the line II-II in FIG. 1a.

This device 11 comprises a substrate layer 12, which can be fastened to an underside 14 on a non-illustrated object to be monitored. Similarly, the device may detect a room temperature or other irradiation temperature or other radiation temperature, wherein the device 11 hang freely in space or rest on a substrate or object, or may be fixed. For example, the bottom 14 may be provided with an adhesive surface or adhesive film or coated with adhesive. Also, other alternatives may be provided to secure the substrate layer 12 to the surface of the article to be monitored for external heat input. On the underside 14 opposite upper side 16 of the substrate layer 12, a material layer 17 is applied. This has, for example, a limited areal extent, which is smaller than the areal extent of the substrate layer 12. This can also be the same size.

The material layer 17 comprises particles 19, which are provided randomly distributed in the material layer 17. In this embodiment according to FIGS. 1a and 2a, electrical contacts 21 are applied to the substrate layer 12, for example. If these electrical contacts 21 are applied, the material layer 12 extends at least as far as the electrical contacts 21 or advantageously covers them in part so that the electrical contacts 21 are in contact with the material layer 17.

The substrate layer 12 is open-pored. The open pores 20 are formed to receive the material layer 17 in a liquid or flowable state. The substrate layer 12 consists for example of a filter medium, such as filter paper, porous plastic or porous alumina. The pore size is preferably smaller than the particle size of the particles 19 in the material layer 17. The material layer 17 applied thereon consists for example of wax or else of a thermoplastic polymer. The materials can be adjusted to a defined melting temperature, so that the melting temperature of the material for the material layer 17 determines a triggering temperature for an aggregate state change.

In the material layer 17, for example, particles 19 are introduced. These may be electrically conductive particles. In particular, carbon nanotubes, graphitic nanoplates, electrically conductive soot particles, silver nanowires or glitter or glitter flakes are used. These particles 19 are preferably introduced with a substantially different aspect ratio.

With a measuring device 23, shown only schematically, which has two measuring contacts 24, a resistance measurement can be carried out by positioning on the electrical contacts 21 in order to check the device 11 in the initial state. In this case, it is advantageously provided in the case of the electrically conductive particles 19 that an electrical resistance of, for example, greater than 1 GΩ exists before the action of temperature. The material layer 17 is virtually not electrically conductive.

FIG. 1b shows a schematic top view of the device 11 after an impermissible temperature effect, which was above the triggering temperature of the material layer, as a result of which an aggregate state change from "solid" to "liquid" took place. It is therefore indicated an inadmissible exceeding a heat or temperature. FIG. 2b shows a schematic sectional view along the line III-III in FIG. 1b.

The material begins to melt and liquefy, wherein the material layer 17 is absorbed by the porous substrate layer 12 and / or a wetting of the large surface of the substrate layer 12 is given. At the same time, a filtering process or a filtering of the particles 19 takes place on the surface of the substrate layer 12, so that in the remaining dispersion matrix of the material layer 12 there is a considerable increase in the concentration of the particles 19. Preferably, the wax or thermoplastic elastomer of the material layer 17 is completely absorbed by the substrate layer 12. This results in an irreversible state change of the device 11, in which the volume concentration of the electrically conductive particles 19 increases significantly. A subsequent measurement with the measuring device 23 of the layer of particles 19 or with still small portions of the material of the material layer 17 shows a large signal change. For example, an electrical resistance of less than 1 MOhm can be measured.

Shown in FIGS. 3a and 3b are light micrographs of a surface of a material layer 17 according to FIGS. 1a and 1b. In this embodiment, a material layer 17 of a matrix material was used, which consisted of wax in which less than 3 wt.% Of electrically conductive carbon nanotube particles 19 were dispersed. In this case, it was possible to achieve a change in the electrical resistance from an initial state according to FIG. 3 a to a final state according to FIG. 3 b of more than three decades, so that reliable evaluation and detection of the impermissible temperature overshoot is provided. The layer thickness of the material layer 17 in this exemplary embodiment was preferably less than 500 μm, in particular less than 100 μm. As the substrate layer 12, a filter paper was used.

FIGS. 4a and 4b show an alternative embodiment to FIGS. 1a and 1b of the device 11. Instead of electrically conductive particles 19, optically conductive particles are introduced into the material layer 17. The operation of this device 11 is analogous to that in Figures 1a and 1b. The evaluation takes place instead of detecting the electrical resistance by detecting the proportion of reflected radiation through the particles 19, so that an analogous evaluation is given.

Claims

Device for the irreversible detection of an exceeding of a predetermined temperature, comprising a substrate layer (12) on which a meltable material layer (17) is applied, which on exceeding a melting point of the material layer (17) of the solid state state merges into the liquid state and state in the Material layer (17) introduced particles (19), characterized

- That the substrate layer (14) consists of a porous material which at least partially receives the material layer (17) after exceeding the melting point and

- That the particles (19) contained in the material layer (17) on the surface (18) of the substrate layer (12) are at least partially filtered off.
Device according to claim 1, characterized in that the substrate layer (12) is open-pored.
Device according to claim 1, characterized in that the porous substrate layer (12) is made of a natural filter material, in particular filter paper, or an artificial filter material, in particular a plastic filter or a ceramic filter material, in particular a porous aluminum trioxide.
Device according to Claim 1, characterized in that the material layer (17) consists of a wax, in particular carnauba wax or thermoplastic polymers, or other substances having a melting temperature, such as, for example, the fatty acids and their esters, in particular pentanoic acid, propionic acid, butanoic acid, heptanoic acid, Hexanoic, methanoic, nonanoic, ethanoic, octanoic, undecanoic, decanoic, dodecanoic, pentadecanoic, tetradecanoic, heptadecanoic, hexadecanoic, nonadecanoic, octadecanoic, eicosane / icosanoic or polyethyleneglycol, Polyethylene, polyamide, polypropylene, polybutene, polylactide ,.
Device according to one of the preceding claims, characterized in that the particles (19) are formed as electrically conductive or optically reflective particles (19).
Device according to one of the preceding claims, characterized in that the porous substrate layer (12) has pores (20) which are smaller than the size of the particles (19) or equal or slightly larger pores (20), so that by agglomerations the particle (19) on the surface of the substrate layer (12) is given a filtering of the particles (19) thereto.
Device according to one of the preceding claims, characterized in that in a starting state of the material layer (17), a particle concentration of the particles (19) is provided below a percolation threshold or slightly above the percolation threshold.
Device according to one of the preceding claims, characterized in that the particles (19) form an electrically conductive layer after the filtering of the material layer (17) on the surface of the substrate layer (12).
Device according to one of the preceding claims, characterized in that on the substrate layer (12) electrical contacts (21) are provided, which are adjacent to the material layer (17) in the initial state or partially covered by it or rest on the material layer (17).
Device according to claim 1, characterized in that the particles (19) are formed as carbon nanotubes, graphitic nanoplates, electrically conductive soot particles, silver nanowires or glitter.
Method for producing a device (11) for irreversibly detecting an exceeding of a predetermined temperature, in particular according to one of the preceding claims, characterized

that a substrate layer (12) consisting of a porous material is provided,

- That the material layer (17) of polymers or wax as a matrix material and introduced therein particles (19) is produced.
Method according to claim 11, characterized in that

- That the material layer (17) is prepared as a dispersion matrix of a polymer dispersion or a viscous wax and a particle dispersion, and

- That the dispersion matrix is applied to the substrate layer (12) and cured thereon as a solid material layer (17).
A method according to claim 11 or 12, characterized in that the dispersion matrix of the material layer (17) by spraying, printing, knife coating, dipcoating, curtain coating or spin coating is applied.
A method according to claim 11 to 13, characterized in that applied prior to the application of the material layer (17) at least one electrical contact (21) on the substrate layer (12), in particular applied, sprayed, vapor-deposited, sputtered or printed, is.
A method according to claim 11 to 14, characterized in that the dispersion matrix of the material layer (17) is adjusted with a viscosity for penetration-free application to the substrate layer (12).
Method according to one of claims 11 to 15, characterized in that the dispersion matrix of the material layer (17) having a layer thickness of less than 500 microns, preferably less than 100 microns, is applied.