阅读说明：本技术 柔性压力传感器及其制备方法 (Flexible pressure sensor and preparation method thereof ) 是由 周龙涛 黄佳 陈绍江 于 2020-04-03 设计创作，主要内容包括：本发明涉及一种柔性压力传感器及其制备方法。所述柔性压力传感器包括a)基底；b)经由铬或钛涂层附着在所述基底上的叉指电极；和c)在所述叉指电极上的发泡的热塑性聚氨酯-碳复合片材,其包含热塑性聚氨酯树脂与导电碳材料。本发明的柔性压力传感器具有良好的柔性、高弹性和压敏特性,并且其稳定性好。同时制备本发明的柔性压力传感器的工艺简单,成本低。(The invention relates to a flexible pressure sensor and a preparation method thereof. The flexible pressure sensor includes a) a substrate; b) interdigitated electrodes attached to the substrate via a chromium or titanium coating; and c) a foamed thermoplastic polyurethane-carbon composite sheet on the interdigital electrodes, which comprises a thermoplastic polyurethane resin and an electrically conductive carbon material. The flexible pressure sensor has good flexibility, high elasticity and pressure-sensitive characteristics, and has good stability. Meanwhile, the flexible pressure sensor is simple in process and low in cost.)

1. A flexible pressure sensor, comprising:

a) a substrate;

b) interdigitated electrodes attached to the substrate via a chromium or titanium coating; and

c) a foamed thermoplastic polyurethane-carbon composite sheet on the interdigital electrode, comprising a thermoplastic polyurethane resin and an electrically conductive carbon material.

2. The flexible pressure sensor of claim 1, wherein the substrate is selected from a glass substrate, a polylactic acid substrate, and a silicon substrate.

3. A flexible pressure sensor according to claim 1 or 2, characterized in that the thickness of the chromium or titanium coating is in the range of 2-10 nm.

4. The flexible pressure sensor according to any of claims 1-3, wherein the electrode material of the interdigitated electrodes is selected from gold, copper and silver.

5. The flexible pressure sensor according to any of claims 1-4, wherein the interdigitated electrodes have a thickness in the range of 20-100 nm.

6. The flexible pressure sensor of any of claims 1-5, wherein the foamed thermoplastic polyurethane-carbon composite sheet is comprised of a thermoplastic polyurethane resin and a conductive carbon material.

7. The flexible pressure sensor of any of claims 1-6, wherein the foamed thermoplastic polyurethane-carbon composite sheet has a foaming ratio of 3.5 to 5.

8. The flexible pressure sensor according to any of claims 1-7, wherein the foamed thermoplastic polyurethane-carbon composite sheet has a hardness of 30A or less, preferably in the range of 10-30A, determined according to ISO 868.

9. The flexible pressure sensor of any of claims 1-8, wherein the thermoplastic polyurethane resin is polyether based.

10. The flexible pressure sensor according to any of claims 1-9, wherein the conductive carbon material is selected from the group consisting of conductive carbon black, carbon nanotubes, graphene powder and graphene nanoplatelets, preferably from the group consisting of conductive carbon black and carbon nanotubes, more preferably carbon nanotubes.

11. A flexible pressure sensor according to any of claims 1-10, characterized in that the conductive carbon material is conductive carbon black in an amount of 0.5-5 parts by weight based on 100 parts by weight of thermoplastic polyurethane resin, preferably the particle size of the conductive carbon black is in the range of 10-50nm, such as 30-45 nm.

12. A flexible pressure sensor according to any of claims 1-10, characterized in that the electrically conductive carbon material is carbon nanotubes in an amount of 0.5-1 parts by weight based on 100 parts by weight of thermoplastic polyurethane resin, preferably the length of the carbon nanotubes is in the range of 0.5-30 μ ι η, such as 3-15 μ ι η.

13. Method for manufacturing a flexible pressure sensor according to any of claims 1-12, characterized in that it comprises the following steps:

I) applying a chromium or titanium coating on the substrate;

II) disposing the interdigitated electrodes on the chromium coating; and

III) affixing the foamed thermoplastic polyurethane-carbon composite sheet to the interdigitated electrodes to form the flexible pressure sensor.

14. The method of claim 13, wherein the preparing of the foamed thermoplastic polyurethane-carbon composite sheet comprises the steps of:

1) mixing a conductive carbon material and a thermoplastic polyurethane resin to obtain a mixture;

2) processing the mixture into thermoplastic polyurethane-carbon composite chips; and

3) the thermoplastic polyurethane-carbon composite chips are foamed to obtain foamed thermoplastic polyurethane-carbon composite sheets.

15. The method according to claim 14, wherein the thermoplastic polyurethane-carbon composite chip is foamed at a foaming ratio of 3.5 to 5 in step 3.

16. A method of production according to any one of claims 13 to 15, characterised in that the chromium or titanium coating is applied to the substrate by evaporation or sputtering.

17. A method of manufacturing as claimed in any one of claims 13 to 16, characterized in that the interdigitated electrodes are provided on the chromium coating by evaporation or sputtering.

Technical Field

The invention relates to the technical field of sensor manufacturing. In particular, the present invention relates to flexible pressure sensors and methods of making the same.

Background

The pressure sensor is a device which converts force signals into electric signals to be output by capturing the electrical property change of a sensitive material when the sensitive material is stressed. The application of the pressure sensor is deeply applied to many aspects of people's life, such as aerospace, national defense, military, water conservancy and hydropower, resource development, railway and marine transportation, medical diagnosis, electronic touch screens, electronic scales and the like.

At present, most pressure sensors are made of rigid sensitive materials such as metal and semiconductor strain gauges, and have the defects of high brittleness, small strain, lack of flexibility and poor comfort. However, the fields of human health, rehabilitation, physical exercise, and motion biology all have requirements for flexibility of sensors, for example, when the distribution of contact pressure between a diabetic foot of a diabetic patient and the ground is studied, the rigid sensor is difficult to be in complete contact with the sole of the foot of the diabetic patient, which makes it difficult to obtain the complete pathological change condition of the diabetic foot.

Therefore, it is necessary to make the pressure sensor flexible so as to be able to measure contact stress variations on a surface of a complex shape.

CN106370327A discloses a flexible pressure sensor, which includes two electrode structures oppositely disposed, each electrode structure includes a flexible substrate and a conductive layer disposed on the flexible substrate, the conductive layers of the two electrode structures are connected in contact toward each other; the flexible substrate comprises a substrate body and a plurality of convex structures arranged on the substrate body, and the conductive layer is arranged on the surface of the flexible substrate with the convex structures in a covering mode. The material of the flexible substrate is selected from any one of polydimethylsiloxane, ethylene-vinyl acetate copolymer, polyvinyl alcohol, styrene-butadiene-styrene block copolymer, aromatic random copolymer, styrene-butadiene rubber, polyurethane elastomer, polyolefin elastomer and polyamide elastomer.

However, many flexible materials have very little change in electrical properties under stress, resulting in a flexible pressure sensor made therefrom that is insensitive to pressure changes.

Accordingly, there remains a need in the art for a flexible pressure sensor that is sensitive to pressure changes.

Disclosure of Invention

It is an object of the present invention to provide a flexible pressure sensor which is sensitive to pressure variations.

Thus, according to a first aspect of the present invention, there is provided a flexible pressure sensor, characterized in that it comprises:

a) a substrate;

b) interdigitated electrodes attached to the substrate via a chromium or titanium coating; and

c) a foamed thermoplastic polyurethane-carbon composite sheet on the interdigital electrode, comprising a thermoplastic polyurethane resin and an electrically conductive carbon material.

According to a second aspect of the present invention, there is provided a method for manufacturing the above flexible pressure sensor, comprising the steps of:

I) applying a chromium or titanium coating on the substrate;

II) disposing the interdigitated electrodes on the chromium or titanium coating; and

III) affixing the foamed thermoplastic polyurethane-carbon composite sheet to the interdigitated electrodes to form the flexible pressure sensor.

The flexible pressure sensor has good flexibility, high elasticity and pressure-sensitive characteristics, and has good stability. Meanwhile, the flexible pressure sensor is simple in process and low in cost.

Drawings

The invention will be illustrated hereinafter with reference to the accompanying drawings, in which:

fig. 1 is a schematic structural view of a flexible pressure sensor according to an embodiment of the present invention, a: front view, b: a top view, wherein (r) represents a substrate; ② an interdigital electrode; and thirdly, showing the foamed thermoplastic polyurethane-carbon composite sheet.

Fig. 2 shows pressure-capacitance response curves of the flexible pressure sensors prepared in examples 1 to 5 and comparative example 1, where the ordinate Δ C is Cp-Co, Cp is capacitance at different compression ratios, and Co is capacitance when uncompressed.

Figure 3 shows the time-capacitance response curve of a flexible pressure sensor made in example 3 (with 5 wt% conductive carbon black added, relative to the weight of the thermoplastic polyurethane).

Figure 4 shows the time-capacitance response curve of the flexible pressure sensor prepared in example 5 (with 1 wt% carbon nanotubes added, relative to the weight of the thermoplastic polyurethane).

Detailed description of the preferred embodiments

Various aspects of the invention and still further objects, features and advantages will be more fully apparent hereinafter.

According to a first aspect of the present invention, there is provided a flexible pressure sensor, characterized in that it comprises:

a) a substrate;

b) interdigitated electrodes attached to the substrate via a chromium or titanium coating; and

c) a foamed thermoplastic polyurethane-carbon composite sheet on the interdigital electrode, comprising a thermoplastic polyurethane resin and an electrically conductive carbon material.

Fig. 1 is a schematic structural view of a flexible pressure sensor according to the present invention. As shown in fig. 1, r denotes a substrate; ② an interdigital electrode; and thirdly, showing the foamed thermoplastic polyurethane-carbon composite sheet. It should be understood that fig. 1 is merely illustrative and not intended to limit the present invention.

The substrate may be any substrate suitable for use in a sensor, and may be, for example, a glass substrate, a polylactic acid substrate, or a silicon substrate.

The interdigital electrodes are attached to the same surface of the substrate.

In order to allow the interdigital electrodes to be effectively attached to the substrate, the thickness of the chromium or titanium coating is preferably in the range of 2 to 10 nm.

Preferably, the electrode material of the interdigital electrode is selected from gold, copper, and silver.

Preferably, the thickness of the interdigital electrode is in the range of 20-100 nm.

Preferably, the width of each finger of the interdigital electrode is in the range of 10-100 μm, and the finger spacing is in the range of 10-100 μm.

In some embodiments, the interdigitated electrodes have a width of 100 μm per finger and a finger pitch of 50 μm.

In some embodiments, the thermoplastic polyurethane-carbon composite sheet is comprised of a thermoplastic polyurethane resin and a conductive carbon material.

Preferably, the thermoplastic polyurethane-carbon composite sheet has a foaming ratio of 3.5 to 5.

Preferably, the foamed thermoplastic polyurethane-carbon composite sheet has a hardness of 30A or less, preferably in the range of 10-30A, as determined according to ISO 868.

The thermoplastic polyurethane resin is not particularly limited and may be a thermoplastic polyurethane resin commonly used in the polyurethane field.

Preferably, the thermoplastic polyurethane resin is a Thermoplastic Polyurethane (TPU) resin suitable for supercritical foaming.

Preferably, the thermoplastic polyurethane resin has a hardness of 80A or less, preferably in the range of 60-80A, as determined according to ISO 868.

Preferably, the thermoplastic polyurethane is polyether-based.

Preferably, the conductive carbon material is selected from conductive carbon black, carbon nanotubes, graphene powder and graphene nanoplatelets, more preferably from conductive carbon black and carbon nanotubes, most preferably carbon nanotubes.

Preferably, the conductive carbon black has a particle size in the range of 10-50nm, such as 30-45 nm.

Preferably, the length of the carbon nanotubes is in the range of 0.5-30 μm, such as 3-15 μm.

Preferably, the graphene powder has a single layer rate of more than 80% and a thickness in the range of 0.1-2 nm.

Preferably, the conductivity of the graphene nano-sheet is within the range of 500-1000S/cm, and the thickness is within the range of 1-10 nm.

In some embodiments, the conductive carbon material is conductive carbon black in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of the thermoplastic polyurethane.

In some embodiments, the conductive carbon material is carbon nanotubes in an amount of 0.5 to 1 parts by weight based on 100 parts by weight of the thermoplastic polyurethane.

In the foamed thermoplastic polyurethane-carbon composite sheet, the thermoplastic polyurethane is physically bonded to the conductive carbon material.

The foamed thermoplastic polyurethane-carbon composite sheet may have any thickness or shape.

Preferably, the thickness of the foamed thermoplastic polyurethane-carbon composite sheet is in the range of 6 to 12 mm.

Preferably, the foamed thermoplastic polyurethane-carbon composite sheet has a density of 210-410kg/m³Within the range.

According to a second aspect of the present invention, there is provided a method for manufacturing the above flexible pressure sensor, comprising the steps of:

I) applying a chromium or titanium coating on the substrate;

II) disposing the interdigitated electrodes on the chromium or titanium coating; and

III) affixing the foamed thermoplastic polyurethane-carbon composite sheet to the interdigitated electrodes to form the flexible pressure sensor.

The chromium or titanium coating may be applied to the substrate by methods such as evaporation, sputtering (including dc sputtering and magnetron sputtering), and the like.

The interdigitated electrodes may also be disposed on the chromium coating by methods such as evaporation, sputtering (including dc sputtering and magnetron sputtering), and the like.

The foamed thermoplastic polyurethane-carbon composite sheet may be fixed on the interdigitated electrodes by a method known in the art of electronic devices (with a glue, such as a polypropylene glue).

In some embodiments, the method of making further comprises the step of providing the foamed thermoplastic polyurethane-carbon composite sheet described above.

Providing the foamed thermoplastic polyurethane-carbon composite sheet described above can be carried out by:

1) mixing a conductive carbon material with a thermoplastic polyurethane resin to obtain a mixture;

2) processing the mixture into thermoplastic polyurethane-carbon composite chips; and

3) foaming the thermoplastic polyurethane-carbon composite chips to obtain a foamed thermoplastic polyurethane-carbon composite sheet.

Those skilled in the art can readily mix and process the conductive carbon material with the thermoplastic polyurethane by blending processes known in the art (e.g., by single screw extrusion) into thermoplastic polyurethane-carbon composite chips, e.g., in the form of particles, short sheets, or other useful forms.

Also, those skilled in the art can easily prepare a foamed thermoplastic polyurethane-carbon composite sheet by a foaming process known in the art (e.g., a supercritical foaming process).

Preferably, the thermoplastic polyurethane-carbon composite chips are foamed at a foaming ratio of 3.5 to 5 in the above step 3.

The resulting foamed thermoplastic polyurethane-carbon composite sheet has a hardness of 30A or less, preferably in the range of 10-30A, as determined according to ISO 868.

The terms "comprising" and "including" as used herein encompass the case where other elements not explicitly mentioned are also included or included and the case where they consist of the mentioned elements.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the event that a definition of a term in this specification conflicts with a meaning commonly understood by those skilled in the art to which the invention pertains, the definition set forth herein shall govern.

Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that can vary depending upon the desired properties to be obtained.

Examples

The concept and technical effects of the present invention will be further described with reference to the following examples so that those skilled in the art can fully understand the objects, features and effects of the present invention. It should be understood that the examples are illustrative only and are not intended to limit the scope of the present invention.

The materials used

Thermoplastic polyurethane: from COVESTRO Inc9380AU DPS650；

Conductive carbon black: XF115 from XFNANO, 30-45 nm;

carbon nanotube: XFQ039 from XFNANO corporation, 3-15 μm in length.

Pressure-capacitance response curve test

The pressure-capacitance response curve under applied pressure was tested by connecting the two electrodes of a flexible piezoelectric transducer to a co-existing LCR TH2827C digital bridge via wires. The application of pressure was performed by a mechanical testing machine, and the change in capacitance with pressure was measured.

Time-capacitance response curve

Both electrodes of the flexible piezoelectric transducer were wired to a co-existing LCR TH2827C digital bridge, and the pressure application and removal processes were cycled to test the time-capacitance response curves.

Example 1

Preparation of foamed thermoplastic polyurethane-carbon composite sheet

100 parts by weight of thermoplastic polyurethane and 0.5 part by weight of conductive carbon black are premixed and extruded by a single screw extruder to obtain the thermoplastic polyurethane-carbon composite slice, wherein the barrel temperature of the single screw extruder is 170-200 ℃, and the rotating speed is 50-90 RPM.

Foaming the obtained thermoplastic polyurethane-carbon composite slice for 60 minutes at the temperature of 120 ℃ and under the pressure of 12mpa by adopting supercritical foaming equipment to obtain a foamed thermoplastic polyurethane-carbon composite sheet, wherein the foaming ratio is 5, and the thickness is 5 mm.

Preparation of flexible pressure sensor

And (2) placing the glass substrate in an acetone and isopropanol solution for ultrasonic cleaning, then washing with deionized water and ethanol, then drying with nitrogen, and placing in an oven for drying.

The glass substrate was covered with a mask and placed in a vacuum evaporator to evaporate a chromium coating having a thickness of about 5nm on the glass substrate.

The glass substrate with the chromium coating was covered with a mask and placed in a vacuum evaporator to evaporate gold interdigitated electrodes with a thickness of about 50nm on the chromium coating, wherein the width of each finger was 100 μm and the finger spacing was 50 μm.

The foamed thermoplastic polyurethane-carbon composite sheet was fixed on the interdigitated electrodes with polypropylene glue, resulting in a flexible pressure sensor 1 within the scope of the present invention.

Example 2

Example 2 was conducted with reference to example 1, except that 1 part by weight of conductive carbon black was used, to obtain a flexible pressure sensor 2 within the scope of the present invention.

Example 3

Example 3 was conducted with reference to example 1, except that 5 parts by weight of conductive carbon black was used, to obtain a flexible pressure sensor 3 within the scope of the present invention.

Example 4

Example 4 was conducted with reference to example 1, except that 0.5 parts by weight of carbon nanotubes was used, to obtain a flexible pressure sensor 4 within the scope of the present invention.

Example 5

Example 5 was conducted with reference to example 1, except that 1 part by weight of carbon nanotubes was used, to obtain a flexible pressure sensor 5 within the scope of the present invention.

Comparative example 1

Comparative example 1 was conducted with reference to example 1, except that a foamed thermoplastic polyurethane sheet was prepared using pure thermoplastic polyurethane instead of the foamed thermoplastic polyurethane-carbon composite sheet without using a conductive carbon material, to obtain a comparative flexible pressure sensor 1 which was out of the scope of the present invention.

Example 6

The flexible pressure sensors prepared in examples 1 to 5 and comparative example 1 were subjected to a pressure-capacitance response curve test.

Fig. 2 shows pressure-capacitance response curves of the flexible pressure sensors prepared in examples 1 to 5 and comparative example 1, in which the ordinate represents the difference between the capacitance under applied pressure and the initial capacitance, and the abscissa represents the pressure value.

As can be seen from the pressure-capacitance response curve of fig. 2, the flexible pressure sensor prepared in comparative example 1 showed almost no change in capacitance when compressed.

It can also be seen from the pressure-capacitance response curves of fig. 2 that the flexible pressure sensors prepared in examples 1 to 5 have high sensitivity response characteristics compared to the flexible pressure sensor prepared in comparative example 1. The larger the doping ratio of the conductive carbon material, the larger the change in capacitance with pressure. When pressure is applied to create elastic deformation, the capacitance will gradually increase, and when the pressure is removed, the capacitance will return to its original value.

It can also be seen from the pressure-capacitance response curve of fig. 2 that even though the proportion of carbon nanotubes is lower than the proportion of conductive carbon black, the flexible pressure sensor with carbon nanotubes has a stronger piezoelectric response than the flexible pressure sensor with conductive carbon black.

Example 7

The flexible pressure sensors prepared in examples 3 and 5 were subjected to a time-capacitance response curve test.

The time-capacitance response curve of the foamed TPU carbon composite was tested by cycling the applied and removed pressure through an LCR precision digital bridge as the sample was compressed from 10mm to 4mm or 6 mm.

Figure 3 shows the time-capacitance response curve of a flexible pressure sensor made in example 3 (with 5 wt% conductive carbon black added, relative to the weight of the thermoplastic polyurethane).

Figure 4 shows the time-capacitance response curve of the flexible pressure sensor prepared in example 5 (with 1 wt% carbon nanotubes added, relative to the weight of the thermoplastic polyurethane).

As can be seen from fig. 3 and 4, the capacitance increases with increasing pressure, returns to the original value with decreasing pressure, and maintains good stability after a certain number of cycles.

It can also be seen from fig. 3 and 4 that the flexible pressure sensor with carbon nanotubes has a more stable piezoelectric response than the flexible pressure sensor with conductive carbon black.

Although a few aspects of the present invention have been shown and discussed, it would be appreciated by those skilled in the art that changes may be made in this aspect without departing from the principles and spirit of the invention, the scope of which is therefore defined in the claims and their equivalents.