WO2020212189A1

WO2020212189A1 - Electric polymer pressure sensor

Info

Publication number: WO2020212189A1
Application number: PCT/EP2020/059803
Authority: WO
Inventors: Martin BARTUSCH; Markus Burghart
Original assignee: Uvex Safety Gloves Gmbh & Co. Kg
Priority date: 2019-04-18
Filing date: 2020-04-06
Publication date: 2020-10-22
Also published as: DE102019110264A1

Abstract

The invention relates to a pressure sensor having a component, the electric resistance of which is variable by deformation. The component is an at least ternary system and comprises at least one binder, an electrically conductive additive embedded into the binder and gas inclusions. The binder is an electrically insulting polymer which has been foamed.

Description

Electrical polymer pressure sensor

The present invention relates to an electrical pressure sensor with a polymer component, and to protective clothing in which a corresponding pressure sensor is integrated.

In the field of intelligent personal protective equipment, items of clothing with integrated sensors are known. (Safety) gloves are products with a generally limited useful life, so that the sensors used and their embedding in the glove material should be designed to be as economical and ecologically compatible as possible.

In the textile sector, sensors are incorporated, for example, using conductive threads made from silver or copper wires. Sensors printed from conductive ink can first be printed on transfer labels and then transferred to the textile using heat and pressure. Alternatively, the sensors can be printed directly onto the textile. The disadvantage of these known methods is that they are either time-consuming and uneconomical, as in the case of conductive games, or are not compatible with the desired polymeric coatings, as is the case with printed sensors.

Binary pressure sensors with a component consisting of a binder and an electrically conductive additive embedded in the binder are known. The conductive particles are homogeneously and randomly distributed within the binder; the binder is, for example, a non-conductive matrix material. Due to the elasticity of the matrix material, it can be compressed under the action of force, with the volume remaining constant. This has the consequence that the distribution of the conductive particles becomes inhomogeneous with a greater concentration of particles parallel to the acting force. If the force is sufficiently high, the concentration of the particles is high enough that they come into contact with one another and form electrically conductive paths. The more paths that are formed, the greater the conductivity. The pressure exerted can thus be determined by means of the change in conductivity ds. However, the measuring range is limited to the range between the conductivity in the unloaded state and the maximum conductivity G _max in the loaded state. Binary systems have the disadvantage that the change in conductivity ds, due to the insulating effect of the binder between the conductive paths, is relatively small. It is desirable to maximize the difference in conductivity ds between so and G _max , an upper limit for G _{max being given} by the conductivity of the embedded particles and the lower limit for so being determined by the conductivity of the binder.

From DE 1 465 966 an elastically deformable material with a cell-like structure is known, in which at least partially open cells are provided. Conductive material is absorbed by this material. If the cells break down, neighboring particles come into contact and increase conductivity.

From US 2008/0067477 A1 a polymer body is known in which electrical particles with a spherical shape and a diameter of 0.05 to 100 μm are introduced, these having a volume fraction of more than 30% by volume.

From US 2014/0260653 A1, an elastic polymer has become known which is equipped with electrically conductive nanoparticles and electrically conductive stabilizers, the stabilizers approximately 1 to 7% by weight and the conductive ones Nanoparticles have about 5 to 30 wt .-%.

From DE 600 11 078 T2 structures with a variable conductance have become known, in which an elastic polymer material is mixed with a conductive filler, for example made of metal or metal oxide, the conductive filler particles being arranged in the cavities of the polymer material.

The object of the invention is to provide a pressure sensor that can be integrated into protective clothing, has a sufficiently accurate measuring range, can be easily implemented using existing processes and is compatible with common material compositions. Furthermore, the invention is based on the object of providing protective clothing with a sensor according to the invention.

According to the invention, the object is achieved by a pressure sensor according to claim 1 and protective clothing according to claim 10. Advantageous configurations are the subject of the subclaims.

The pressure sensor according to the invention has a component whose electrical resistance can be changed by deformation. The component is an at least ternary system and comprises at least one binder, an electrically conductive additive embedded in the binder and gas inclusions.

The at least ternary system according to the invention increases the difference in conductivity ds in comparison to known binary systems and thus extends the accessible measuring range. According to the invention, the binder has a foam-like or sponge-like structure. A foam-like structure has individual closed gas inclusions, such as, for example, bubbles. A sponge-like structure, on the other hand, is defined by the fact that it only has a single surface and thus all gas inclusions are connected to one another. A combination of the two structures is also possible.

According to the invention, the electrically conductive additives are distributed inhomogeneously within the binder. The conductive additives collect at the interfaces between the binder and gas inclusions, so that the concentration of additives is highest at these interfaces. Naturally, additives are not present within the gas inclusions, so that the pressure sensor according to the invention can be implemented with both open-pore and closed-pore structures. The gas inclusions interrupt electrically conductive paths that result when a plurality of additive particles are arranged adjacent to one another within the binder. Accordingly, the component has a very low conductivity in the unloaded state. Electrically conductive paths, which are created by percolation in the binary system even in the unloaded state, are broken up in the ternary system by the gas inclusions. As soon as the ternary system is compressed, however, the interrupted conductive paths touch one another at the inner interfaces of the gas inclusions and a large number of conductive paths arise, which leads to a higher conductivity G _max than in the binary system.

In a preferred embodiment of the pressure sensor, the usable measuring range is determined by the range in which the conductivity is preferably linear to the pressure exerted. When approaching the limit values so and G _max , the conductivity s (R) shows a non-linear behavior as a function of the exerted pressure P. In a further preferred embodiment of the pressure sensor, the conductivity in the unloaded state is thus dependent on the concentration of the electrically conductive additives. The higher the concentration of the electrically conductive additives, the greater. The concentration should preferably be selected so that it is as low as possible, but sufficient conductive paths can still form under load.

A measuring range is preferably provided for the pressure sensor. In the measuring range, the conductivity changes greatly with the pressure exerted. The change can be abrupt or also continuous; the change in conductivity is preferably proportional to the pressure exerted. Outside the measuring range, i.e. when the pressure exerted is smaller or larger than the measuring range, the conductivity asymptotically approaches the minimum or maximum conductivity.

In a further preferred embodiment of the pressure sensor, the measuring range of the pressure sensor can be set by the thickness and / or density of the component. For applications in which low forces are to be recorded, a component with a lower density and higher compressibility is suitable. The density can be adjusted using the total volume of the gas inclusions.

In a further preferred embodiment of the pressure sensor, the electrically conductive additives approach one another when the component is compressed and electrically conductive paths are increasingly formed. With compression, the gas inclusions are compressed and the additives located on the inside of the gas inclusions come into electrically conductive contact. Paths which are interrupted by the gas inclusions in the unloaded state are under Compression linked. The electrically conductive additives inside the component also approach under pressure due to the elasticity of the binder. All of this leads to an increase in conductivity.

In a further preferred embodiment of the pressure sensor, the binder consists of an electrically insulating polymer, preferably of silicone or polyurethane, particularly preferably of nitrile rubber. Compared to conventional sensors made of conductive yarns or conductive ink, it is advantageous that the polymers mentioned are compatible with coatings in common work clothing.

In a further preferred embodiment of the pressure sensor, the gas inclusions consist of air and are mechanically introduced into the binder and fixed in the binder during curing. Alternatively, other gases can be used to achieve additional properties (thermal insulation, thermal expansion, etc.). It is also possible to introduce gases via chemical substances, e.g. Carbon dioxide from the thermal decomposition of carbonates during the curing of the binder. In addition, the electrical properties, but also the shape of the pores created (size, distribution, open or closed pores, etc.) can be influenced. In the uncured state, the binders preferably contain between 5 and 50% by volume of the gas, preferably 15% by volume to 40% by volume, in order to achieve an adequate sensor effect with simultaneous mechanical stability.

In a further preferred embodiment of the pressure sensor, the embedded, electrically conductive additives consist of metal or metallized particles, conductive oxides, carbon black, graphite, graphene, conductive polymers, Carbon fibers, carbon nanotubes, or a combination of these. The dimension of the additives is preferably between 0.5 mm and 0.5 mmhi in the largest direction of expansion, on the one hand to achieve enrichment at the interface and on the other hand to obtain sufficient processability. Compared to metallic additives, carbon-based additives have the advantage of lower density and thus reduced settling behavior in the non-hardened binder. A suitable chemical and / or physical surface modification of the additives adapted to the binder used is obvious to the person skilled in the art.

The protective clothing according to the invention has an integrated sensor, the integrated sensor having a pressure sensor according to the invention. A pressure sensor integrated into the protective clothing makes it possible to determine forces that act on the wearer. Necessary control units or further means for evaluating the pressure signals can also be connected in or on the protective clothing.

The protective clothing is preferably an industrial safety glove. The safety glove comprises a component which has an at least ternary system, consisting of at least one binder, an electrically conductive additive embedded in the binder and gas inclusions. Particularly preferably, the safety glove comprises a one-piece textile glove blank which is coated with a polymer substrate in the manufacturing process.

In a preferred embodiment of the protective gloves, several pressure sensors are embedded in order to measure the forces acting on the wearer's hand. to be able to analyze differentiated. A combination of individual pressure sensors on the fingertips, the palm and the back of the hand is possible. The measuring ranges of the pressure sensors are preferably adapted to the placement of the protective gloves. The pressure sensors on the fingertips could be designed for measuring lower pressures and the pressure sensors on the palm of the hand or the back of the hand could have a measuring range for higher pressures.

In a preferred embodiment of the protective clothing, it has a polymeric coating in which the pressure sensor is embedded. The pressure sensor can be applied to the protective clothing as an inner or outer layer, depending on the area of application.

In a further preferred embodiment of the protective clothing, the coating of the protective clothing consists of the same polymer substrate as the binder of the component of the pressure sensor. This enables the pressure sensor to be integrated into the protective clothing coating in a completely compatible manner. In this embodiment, the protective clothing can be treated like protective clothing without a sensor during disposal. With regard to pollutants and disposal, no differences to protective clothing without a sensor can be determined.

In a particularly preferred embodiment, the protective clothing is coated with nitrile rubber. The component of the embedded sensor is made of a nitrile rubber foam and is accordingly completely compatible with the nitrile rubber of the protective clothing coating. The protective clothing can be treated like protective clothing without a sensor during disposal. Figures 1 to 3 show schematically the functional principle of the polymer pressure sensor. It shows:

Fig. La a binary system in the unloaded state and

Fig. 1 b the binary system in the loaded state,

2 a shows a ternary system in the unloaded state and FIG. 2 b shows the ternary system in the loaded state, and FIG

3 shows a sketch of the relationship between conductivity and pressure exerted.

Figures la) and lb) show a polymeric component 1 of a pressure sensor as it is known from the prior art (SdT). In Figure la) the component 1 can be seen in the unloaded state. The electrically conductive additives 3 are distributed homogeneously in the binder 2. Figure lb) shows the same system under load P. The component 1 is compressed and the concentration of the additives 3 has increased parallel to the pressure P exerted. Conductive paths are formed within the compressed component 1, as a result of which the conductivity increases.

Figures 2a) and 2b) show a ternary system according to the invention. Fig. 2a) shows the component 1 in the unloaded state. The additives 3 are preferably located at the interfaces of the gas inclusions 4. This applies to both a foam-like and a sponge-like structure of component 1. In Fig. 2b) the component 1 is loaded with a pressure P. The gas inclusions 4 are compressed and the additives 3 come into contact with one another. Electrically conductive paths are formed in the loaded state.

3 shows schematically the dependence of the conductivity s of component 1 on the pressure P exerted. The conductivity has a lower limit so, which characterizes the conductivity of the unloaded component 1. The maximum conductivity of component 1 is given by G _max . With increasing pressure P, the conductivity s (R) increases. The range P, in which the conductivity is linear to the pressure, is the accessible measuring range.

example 1

A conductive foam was produced from a polymer dispersion based on nitrile rubber. To this end, 7% by weight of a metal powder (copper-plated iron particles, <5 μm) were added to the dispersion and the dispersion was then foamed with air to a foam liter weight of approx. 800 g / l. The foam was spread out as a layer and vulcanized.

Example 2

A conductive foam was produced from the same polymer dispersion as in Example 1 by adding 12% by weight of a pigment powder (metallized mica; <15 μm) to the dispersion and mixing the dispersion with air

Foam liter weight of approx. 800g / l was foamed. As in Example 1, the foam was spread out as a layer and vulcanized. Example 3

A conductive foam was produced from the same polymer dispersion as in Example 1 by adding 1.5% by weight of carbon fibers (length <10 μm) to the dispersion and foaming the dispersion with air to a foam liter weight of approx. 800 g / l. As in Example 1, the foam was spread out as a layer and vulcanized.

The polymer dispersion from the examples without the addition of an additive, foamed to 800 g / l and vulcanized as a layer, served as reference.

The volume resistance was determined after conditioning the samples at 23 ° C ± 1 and 25 + 5% relative humidity.

Claims

Expectations

1. Pressure sensor comprising a component whose electrical resistance is variable by deformation, the component being an at least ternary system and at least one binder having a foam-like and / or sponge-like structure, an electrically conductive additive embedded in the binder and gas inclusions thereby characterized in that the concentration of the electrically conductive additives in the component is inhomogeneous and increased at the interfaces between the binder and gas inclusions.

2. Pressure sensor according to claim 1, characterized in that the component has a conductivity in the unloaded state and a maximum conductivity of G _max in the loaded state and the measuring range is the range in which the conductivity increases with the pressure exerted.

3. Pressure sensor according to claim 1 or 2, characterized in that the conductivity is dependent on the concentration of the electrically conductive additives in the unloaded state.

4. Pressure sensor according to one of the preceding claims, characterized in that the conductivity changes in a measuring range when pressure is exerted on the pressure sensor and outside the measuring range it approaches the maximum G _max or minimum conductivity asymptotically.

5. Pressure sensor according to one of the preceding claims, characterized in that the measuring range of the pressure sensor extends through the Can adjust the thickness and / or density of the component.

6. Pressure sensor according to one of the preceding claims, characterized in that the electrically conductive additives approach each other when the component is compressed and form electrically conductive paths.

7. Pressure sensor according to one of the preceding claims, characterized in that the volume of the component decreases upon compression.

8. Pressure sensor according to one of the preceding claims, characterized in that the binder consists of an electrically insulating polymer, preferably of silicone or polyurethane, particularly preferably of nitrile rubber.

9. Pressure sensor according to one of the preceding claims, characterized in that the embedded electrically conductive additive made of metal, metallized particles, conductive oxides, carbon black, graphite, graphene, conductive polymers, carbon fibers,

Carbon nanotubes or a combination of these.

10. Protective clothing with an integrated sensor, characterized in that the sensor is a pressure sensor according to one of the preceding claims.

11. Protective clothing according to claim 10, characterized in that the protective clothing has a polymeric coating in which the pressure sensor is embedded.

12. Protective clothing according to claim 10 or 11, characterized in that the coating of the protective clothing consists of the same polymer substrate as the binder of the component of the pressure sensor.

13. Protective clothing according to one of claims 10 to 12, characterized in that the coating of the protective clothing consists of nitrile rubber and the binder consists of nitrile rubber foam.

14. Protective clothing according to one of claims 10 to 13, characterized in that a protective work gloves are provided as protective clothing.