ES2264900B1 - PRESSURE SENSORS DISTRIBUTED FROM LARGE SURFACE BASED ON POLYTIOPHENES. - Google Patents

Abstract

Large surface distributed pressure sensors based on polythiophenes. The present invention relates to large surface distributed pressure sensors comprising at least two flexible substrates, at least one of them being completely or partially covered by a layer of a polythiophene containing repetitive structural units of formula (I), in the that R1 and R2 are independently a C1-C12 alkyl group or form a 1, n-C1-C12 alkylene group, where n = 1-12, optionally substituted by a C1-C12 alkyl group, C2-C12 alkene, vinyl, benzyl , phenyl, halogen, or by an ester, amino, amido or ether functional group optionally substituted by a C1-C12 alkyl group; and one or more insulating spacers. These sensors are flexible and easy to manufacture and can have different symmetrical configurations, simple or multilayer, as desired.

Description

Large distributed pressure sensors surface based on polythiophenes.

Field of the Invention

This invention relates to pressure sensors distributed based on polythiophenes. More specifically, it refers to flexible plastic sheets coated with type compounds polythiophene and assembled in different configurations using appropriate insulating spacers. These settings include symmetric configuration, simple configuration and multilayer configuration, among others. The devices of the Present invention are flexible, easy to manufacture and employ as intrinsic conductive polymer sensor elements of the type polythiophenes.

Background of the invention

Distributed pressure sensors are useful to determine force or pressure on soft objects, by example, to measure the interfacial pressures of a person sitting on a chair. For this application it is necessary that the sensor be flexible to fit the shape of the curvature of the chair and properly measure the forces exerted. In addition, the sensor must be thin enough not to enter reading errors This type of sensors usually has thicknesses between 0.1 and a few millimeters. To measure the pressure at different points on a surface, it is necessary that the sensor area of each element in the distributed sensor be the most Small possible. In general, depending on the number of elements sensors used these are classified into: unique sensors and series (arrays) of sensors of n x n elements. In turn, they can be classified according to the output signals as two sensors (on-off) or more outputs (analog sensors or digital).

The benefits demanded for sensors Flexible pressures are usually lower than those required at conventional rigid sensors, admitting inaccuracies in the measure between 5 and 10%. Flexible pressure sensors they are usually made up of series of rows and columns in a matrix type arrangement Flexible pressure sensors of n x n sensor elements provide pressure distribution data over n2 sensor zones. This data is collected in the form of electronic signal through conversion to voltage or intensity of resistance change measurement provided by the sensor element The data thus obtained are linearized to optimize resolution and simplify the interpretation of same. To increase the accuracy of the measurement, a calibration of the different sensor elements through the adjustment of the corresponding gains and offsets or through of the establishment of calibration curves. The data like this treaties allow the generation of bi-pressure maps Tri-dimensional in real time.

Among the different existing technologies to develop distributed pressure sensors, we can mention: the technology that uses piezoelectric elements, pneumatic, hydraulic, resistive and capacitive. Piezo-electric technology is not used for static measurements due to the loss of current in these sensors, which causes the response signal to zero over time. Sensors based on pneumatic and hydraulic technologies require very complicated assemblies and very large thicknesses, which limits their application in flexible sensors. Today, resistive and capacitive technology are the most used in pressure sensors
flexible

The principle of operation of the sensors resistive is based on the change in electrical resistance that occurs in piezo-resistive materials when a force or pressure is applied to them. In the case of capacitive sensors, these are based on the change of capacitance that occurs between two parallel plates, between that there is a non-conductive elastomeric material, when applying a force or pressure on them. This last type of sensors has the inconvenience that you need very precise electronics, highly sensitive and stable, since capacitance changes measured are usually lower than picofarads. Conversely, flexible pressure sensors of resistive type use a very simple electronics, since the resistance changes are of several orders of magnitude, fast, which is important for series (arrays) of many sensing elements, and not very sensitive to electromagnetic fields (another drawback of capacitive) Among its disadvantages, the non-linearity, the dependence of your response on number of cycles and the history of the sensor. In addition, the response of these sensors usually depend on the temperature and the degree of relative humidity, being able to manifest a signal stability low and a life time not long enough.

In general, flexible pressure sensors existing in the market have a three-way configuration with the outer layers made of a flexible material (fabric or polymer, US 6,155,120 and US 6,501,465) which is coated with conductive lines, usually metallic wires (requests for US Patent 200310173195 and WO 99/39168) or charged conductive paste with metal particles (US 6,646,540 and US 6,291,568) or carbon black (US Patent 6,597,276 and WO patent application 00125325), and the intermediate layer formed by a material sensitive to pressure, of the conductive ink type (US 5,652,395 and US patents 5,838,244) or a non-conductive dielectric elastomer (US Pat. 5,010,774 and patent application WO 2004/061401).

The state of the art has not been described use of polythiophenes, a family of conductive polymers intrinsic high stability and processable from aqueous dispersions, as active materials for the manufacture of distributed pressure sensors. US Patents 4,959,430 and US 4,987,042 describe different procedures for preparing dispersions based on poly (ethylene) dioxy-thiophene) and US patents 5,766,515 and US 5,370,981 its use as a transparent electrode in devices electroluminescent and to prepare antistatic plastics, respectively.

Thus, it continues to exist in the state of technique the need for large distributed pressure sensors alternative surfaces that overcome the inconveniences of the state of technique

Object of the invention

The invention aims at sensors of distributed pressure of large area comprising at least two flexible substrates, being coated at least one of them total or partially by a layer of a polythiophene, and one or more insulating spacers.

Likewise, the invention aims at a procedure for the preparation of said sensors of Pressure.

Brief description of the figures

Figure 1 shows a microscopy photo of Atomic force (AFM) of the surface of a conductive polymer type polythiophene and a statistical graph of micro-roughness

Figure 2 is a schematic diagram of the symmetric configuration of a pressure sensor according to the invention in which white lines represent spacers non-conductive insulators that separate conductive tracks from polythiophene

Figure 3 is the response graph in form of current of the pressure sensor with configuration symmetric of the invention described in example 1 against weight applied.

Figure 4 represents different matrices of epoxy resin points useful for sensor construction pressure with simple configuration of the invention described in the example 2.

Figure 5 represents the variation of pressure sensor resistance with simple configuration of the invention described in example 2 as a function of the applied weight.

Detailed description of the invention

The present invention provides a sensor of distributed pressure of large area comprising at least two flexible substrates, being coated at least one of them total or partially by a layer of a polythiophene containing units repetitive structural formula (I),

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one

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wherein R 1 and R 2 are independently a C 1 -C 12 alkyl group or form a 1, n-C 1 -C 12 alkylene group, where
n = 1-12, optionally substituted by a C 1 -C 12 alkyl group, C 2 -C 12 alkene, vinyl, benzyl, phenyl, halogen, or by an ester, amino, functional group, amido or ether optionally substituted by a C1-C12 alkyl group;

and one or more insulating spacers.

In the context of the invention, the term "large surface distributed pressure sensor" refers to a sensor that is capable of giving pressure measurements in a large surface (larger than 1 cm x 1 cm) which in turn can be curved and flexible, unlike point pressure sensors.

A completely novel aspect of the present invention is the use of polythiophenes described above (in hereinafter "polythiophenes of the invention") as elements sensory Thus, in a particular embodiment of the sensor of the invention, the R 1 and R 2 groups of the polythiophene form a alkylene group selected from methylene, 1,2-ethylene and 1,3-propylene. In a preferred embodiment said groups R1 and R2 form a 1,2-ethylene group, that is, polythiophene preferred for the realization of the sensor of the invention is the poly (ethylene-dioxy-thiophene).

In another particular embodiment of the sensor of the invention, the flexible substrate is a flexible plastic sheet. In a preferred embodiment, the flexible plastic sheet is constituted by polymers of high melting point or high temperature glass transition, preferably poly (ethylene terephthalate) or poly (carbonate). In another embodiment preferred, the flexible plastic sheet is made of PVC plasticized, thermoplastic rubbers, fibers or fabrics polymeric

Surprisingly, it has been found that when two flexible plastic sheets coated with the polythiophenes of the invention so that both films conductors approach each other (using spacers appropriate insulators) and a potential difference is established between the two, the electric current that passes is directly proportional to the pressure exerted on the sheets, in a given range of pressures until, at very high pressures, the Electric current is saturated at a constant value.

This effect, which is used herein invention for the manufacture of distributed pressure sensors based on the polythiophenes described, could be attributed to the rugged nature (and at the same time visco-elastic), at the nanometer level, of the conductive films used, as shown in Figure 1 performed by atomic force microscopy (AFM). Said morphology would include conductive particles (electronic conductivity) of polythiophene together with relatively insulating areas of a polyanion used as a dopant, as described below. This shape, you can think that by increasing the pressure on the sheets polythiophene coated the number of contact points conductors, on a nanometer scale, will increase to a pressure determined in which the maximum possible number of points is reached of contact, and therefore, the value of the current is saturated electric When removing the pressure, due to nature visco-elastic material would return, approximately, to the original state in the absence of pressure.

To avoid short circuits (in the absence of pressure) when assembling the distributed pressure sensors of the present invention as well as to adjust the pressure range in which the sensors respond within the linearity, it is convenient to use insulating spacers. Said spacers will preferably be materials of an appropriate elastic modulus to cover a given pressure range so that the pressure range that the sensor is able to detect is controlled based on its thickness and its viscous properties.
elastic.

Thus, in a preferred embodiment the spacer Insulator is a silicone, a polymer foam or a resin epoxy

As mentioned, these polythiophenes in their oxidized state can additionally incorporate anionic groups stabilizing positive type charge carriers relocated in polymer chains. Thus, in one embodiment Particular of the sensor of the invention, polythiophene incorporates a anionic dopant In a preferred embodiment, said dopant anionic is an inorganic anion, preferably a sulfate anion, chloride or bromide In another preferred embodiment, said dopant Anionic is an organic anion with sulfonate or phosphate groups, preferably an acid p-toluene sulphonic or p-toluene-phosphonic. In other preferred embodiment, said anionic dopant is a polyanion organic selected from polymeric carboxylic acids, preferably poly (acrylic acid), poly (methacrylic acid) or poly (maleic acid); polymeric sulfonic acids, preferably poly (styrene sulfonic acid) or poly (vinyl acid sulfonic); or copolymers of vinylcarboxylic acids and vinylsulfonic with other polymerizable monomers, preferably styrene and acrylic or methacrylic monomers. In one embodiment even more preferred, the molecular weight of said polyanions will be preferably, between 15,000 and 300,000 Daltons.

Regarding the possible configurations in which the present invention can be realized, the simplest is symmetric configuration consisting of two flexible sheets identical on which conductive tracks of polythiophene periodically separated by insulating spacers, and that are placed perpendicular to each other. In this case, the height of these spacers must be greater than that of the tracks polythiophene conductors. As previously noted, non-conductive insulating spacers have the function prevent the conductive tracks of both sheets once assembled these in sandwich form, and optionally encapsulated, give electrical contact between them, in the absence of pressure, when applying a current intensity between the sheets upper and lower, as shown in Figure 2.

The pressure sensor thus constructed provides an electrical signal proportional to the applied pressure and its matrix arrangement (n rows x n columns) allows data to be obtained pressure distribution over n2 sensor zones. Further, the pressure range that it is able to detect can be modified depending on the visco-elastic properties of employee spacer.

A variant of the previous configuration is the replacement of one of the sheets containing conductive tracks of polythiophenes by conductive tracks made from the deposition of any other conductive material. So, in another particular embodiment of the sensor of the invention, it has a simple configuration consisting of a flexible sheet on the that separate polythiophene conductive tracks have been deposited, periodically, by insulating spacers, and a flexible sheet not conductor on which tracks of a material have been deposited conductor which, in another preferred embodiment, forms two electrodes

In the context of the invention the term "conductive material" refers to a metallic material (silver, copper, nickel, etc.) of the silver conductive paste type, graphite, copper, or an intrinsic conductive polymer of type polypyrrole, polyaniline or polythiophene deposited from a dissolution or dispersion

Other configurations contained herein invention are those that use sheets with a homogeneous deposition of polythiophenes (a film or film, for example) on them.

Thus, in a particular embodiment of the invention, the sensor has a three-layer configuration formed by a flexible sheet on which a layer has been deposited homogeneous conductive polythiophene, a flexible sheet not conductor on which tracks of a material have been deposited conductor and a deposition of an insulating spacer on the conductive sheet of polythiophene.

In another particular embodiment, the sensor presents a three-layer configuration formed by a flexible sheet on which a homogeneous conductive layer of polythiophene, a flexible non-conductive sheet on which they have deposited tracks of a conductive material and a deposition of a insulating spacer on the non-conductive sheet with tracks Conductive material.

These configurations have a structure multilayer formed by a sheet with a homogeneous deposition of polythiophenes, a non-homogeneous electrical insulating layer or spacer insulator and a sheet with conductive tracks made from the deposition of any conductive material that, in particular, They can form two electrodes. The electrical insulating layer can be done through the deposition of any material not conductor or high electrical resistance on any of the other layers and present different configurations, thicknesses and visco-elastic coefficients that allow adaptation and optimization of the measuring range of the sensor, as previously described.

In another aspect of the invention, it is provided a procedure for the preparation of a pressure sensor large area distributed as previously described, in the that polythiophene is deposited on the total flexible substrate or partially, in the form of a film or in the form of tracks, for example, as previously mentioned.

The polythiophenes used in the present invention have film-forming capacity if they are applied from true solutions, colloidal dispersions or stable dispersions of finely divided particles, either aqueous or solvent based, by oxidative polymerization of the corresponding monomer or by in situ polymerization methods on the substrate as described in reference ADVANCED FUNCTIONAL MATERIALS 14, 615-622, 2004. Among the preferred solvents are alcohols, methanol, ethanol and isopropanol, as well as mixtures of water with these alcohols or other water-miscible organic solvents such as Acetone Among the preferred oxidants are ammonium persulfate, iron trichloride and ferric tosylate. Additionally, polymeric binders of the type polyvinyl alcohol, polyvinyl acetate, etc. can be used. and adhesion promoters, of the silane type, tackifying resins, etc. to facilitate the formation of highly adherent films on the substrate.

Thus, in a particular embodiment of said procedure, polythiophene is deposited in the form of a film to from true solutions, colloidal dispersions or stable dispersions of finely divided particles, well aqueous well based solvent, by oxidative polymerization of corresponding polythiophene monomer. In a preferred embodiment a polymeric binder of the type is used poly (vinyl alcohol) or poly (vinyl acetate) and a adhesion promoter such as silanes or tackifying resins for facilitate the formation of a highly adherent film on the flexible substrate.

In another particular embodiment of said process, the polythiophene is deposited on the flexible substrate in the form of a film from true solutions, colloidal dispersions or stable dispersions of finely divided particles, either aqueous or solvent based, by in situ polymerization methods on said substrate.

The forms of application on the substrates flexible can be by direct evaporation of the solvent once extended the dispersion or dissolution on it (painted), immersion, spray, rotation coating techniques or "spiin-coating", etc.

Thus, in another particular embodiment of said procedure, the solution or dispersion of polythiophene is applied on the flexible substrate by painting, dipping, spraying or rotation coating techniques or "spin-coating", and subsequent evaporation Direct solvent.

In another particular embodiment of said procedure, polythiophene is deposited on the substrate flexible in the form of tracks using conventional methods of lithography, selective deposition of the conductive polymer in the form of tracks by inkjet printing or "ink-jet printing" or by starting the material flexible sheet conductor by mechanical methods, preferably by milling.

In a preferred embodiment, the tracks conductors form 2n electrodes corresponding to n sensors.

The present invention is illustrated below. with two examples, which in no case should be considered as limiting the scope of it.

Example 1 Preparation of a pressure sensor based on a configuration symmetrical 5 cm x 5 cm active area

A pressure sensor was prepared from two 5 cm flexible poly (ethylene terephthalate) (PET) sheets x 5 cm of active area and 175 microns thick each coated with a thin layer (1-2 microns) of poly (ethylene-dioxy-thiophene) containing as polyanion a poly (styrene sulfonic acid) (PEDOT-PSS) deposited by oxidative polymerization of the ethylene-dioxy-thiophene monomer in water, resulting in a dispersion with solids content of the 2.5% The sheets were assembled using an insulating spacer (EA) 0.125mm thick double-sided adhesive on a symmetric sandwich configuration (PET / PEDOT-PSS / EA / PEDOT-PSS / PET), placing the spacer in the form of a flat ribbon 0.5 cm wide at along the edges of the coated sheets of PEDOT-PSS. The device thus mounted gave no signal current flow in the absence of pressure when applying a potential between both sheets. The sensor response, in the form of measured current intensity when applying different weights on the sensor surface, applying a potential difference of 1 V between both sheets, is illustrated in Figure 2.

Example 2 Preparation of a pressure sensor based on a configuration single 1 cm x 1 cm active area

A pressure sensor was prepared from a 1 cm x flexible poly (ethylene terephthalate) (PET) sheet 1 cm of active area and 175 microns thick each coated with a thin layer (1-2 microns) of poly (ethylene-dioxy-thiophene) containing as polyanion a poly (styrene sulfonic acid) (PEDOT-PSS) deposited by oxidative polymerization of the ethylene-dioxy-thiophene monomer in water, resulting in a dispersion with solids content of the 2.5% On this sheet a matrix of resin dots was deposited epoxy with one of the configurations shown in Figure 3 (thickness of 15 microns). The sample thus obtained was adhered to another flexible sheet (polyester) on which they had been deposited two electrodes of conductive material (silver). The device assembled presented an electrical resistance between the two electrodes very high (M \ Omegas). The variation of resistance of the sensor to apply different weights on the surface thereof illustrated in Figure 4.

Claims (22)

1. Large distributed pressure sensor surface comprising at least two flexible substrates, being at least one of them completely or partially covered by a layer of a polythiophene containing repetitive structural units of  formula (I),

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2

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wherein R 1 and R 2 are independently a C 1 -C 12 alkyl group or form a 1, n-C 1 -C 12 alkylene group, where
n = 1-12, optionally substituted by a C 1 -C 12 alkyl group, C 2 -C 12 alkene, vinyl, benzyl, phenyl, halogen, or by an ester, amino, functional group, amido or ether optionally substituted by a C1-C12 alkyl group; and one or more insulating spacers. 2. Large distributed pressure sensor surface according to claim 1, wherein the R1 groups and R2 of the polythiophene form a selected alkylene group between methylene, 1,2-ethylene and 1,3-propylene. 3. Large distributed pressure sensor surface according to claim 2, in the groups R1 and R2 of polythiophene form a group 1,2-ethylene. 4. Large distributed pressure sensor surface according to claim 1, wherein the substrate flexible is a flexible plastic sheet. 5. Large distributed pressure sensor surface according to claim 4, wherein the plastic sheet flexible consists of high melting point polymers or high glass transition temperature, preferably poly (ethylene terephthalate) or poly (carbonate). 6. Large distributed pressure sensor surface according to claim 4, wherein the plastic sheet flexible consists of plasticized PVC, rubbers thermoplastics, fibers or polymeric fabrics. 7. Large distributed pressure sensor surface according to claim 1, wherein the spacer Insulator is a silicone, a polymer foam or a resin epoxy 8. Large distributed pressure sensor surface according to claim 1, wherein the polythiophene incorporates an anionic dopant. 9. Large distributed pressure sensor surface according to claim 8, wherein the anionic dopant it is an inorganic anion, preferably a sulfate, chloride or anion bromide. 10. Large distributed pressure sensor surface according to claim 8, wherein the anionic dopant it is an organic anion with sulfonate or phosphate groups, preferably an acid p-toluene sulphonic or p-toluene-phosphonic. 11. Large distributed pressure sensor surface according to claim 8, wherein the anionic dopant it is an organic polyanion selected from carboxylic acids Polymers, preferably poly (acrylic acid), poly (acid methacrylic) or poly (maleic acid); polymeric sulfonic acids, preferably poly (styrene sulfonic acid) or acid poly (vinyl sulfonic); or acid copolymers vinylcarboxylic and vinyl sulfonic with other monomers polymerizable, preferably styrene and acrylic monomers or methacrylic 12. Large distributed pressure sensor surface according to claim 11, wherein the polyanion employee has a molecular weight between 15,000 and 300,000 Daltons 13. Large distributed pressure sensor surface according to claim 1, with symmetrical configuration consisting of two identical flexible sheets on which they have been deposited separate polythiophene conductive tracks, periodically, by insulating spacers, and placed perpendicular to each other. 14. Large distributed pressure sensor surface according to claim 1, with simple configuration constituted by a flexible sheet on which they have been deposited conductive tracks of polythiophene separated, periodically, by insulating spacers, and a flexible non-conductive sheet on the that tracks of a conductive material have been deposited. 15. Large distributed pressure sensor surface according to claim 1, with three-layer configuration formed by a flexible sheet on which a homogeneous conductive layer of polythiophene, a flexible sheet not conductor on which tracks of a material have been deposited conductor and a deposition of an insulating spacer on the conductive sheet of polythiophene. 16. Large distributed pressure sensor surface according to claim 1, with three-layer configuration formed by a flexible sheet on which a homogeneous conductive layer of polythiophene, a flexible sheet not conductor on which tracks of a material have been deposited conductor and a deposition of an insulating spacer on the non-conductive sheet with conductive material tracks. 17. Procedure for the preparation of a large area distributed pressure sensor according to claims 1 to 16, wherein the polythiophene is deposited on the flexible substrate in the form of a film from solutions true, colloidal dispersions or stable dispersions of finely divided particles, either aqueous or solvent based, by oxidative polymerization of the polythiophene monomer correspondent. 18. Method according to claim 17, in which uses a polymeric binder of the poly (vinyl) type alcohol) or poly (vinyl acetate) and an adhesion promoter of the type silanes or tackifying resins to facilitate the formation of a highly adherent film on the flexible substrate. 19. Method for preparing a large surface distributed pressure sensor according to claims 1 to 16, wherein the polythiophene is deposited on the flexible substrate in the form of a film from true solutions, colloidal dispersions or stable dispersions of finely divided particles, either aqueous or solvent based, by in situ polymerization methods on said substrate. 20. Method according to the claims 17-19, in which the dissolution or dispersion of Polythiophene is applied to the flexible substrate by painting, immersion, spray or rotation coating techniques or "spin-coating", and subsequent evaporation Direct solvent. 21. Procedure for the preparation of a large area distributed pressure sensor according to claims 1 to 16, wherein the polythiophene is deposited on the flexible substrate in the form of tracks using methods Conventional lithography, selective polymer deposition driver in the form of tracks by inkjet printing or "ink-jet printing" or by starting the material flexible sheet conductor by mechanical methods, preferably by milling. 22. Method according to claim 21, in which conductive tracks form 2n corresponding electrodes to n sensors.