A flexible wet distance sensing film based on vacuum filtration and its preparation method

Abstract

The present invention discloses a flexible wet distance sensing film based on vacuum filtration and a preparation method thereof. The flexible wet distance sensing film comprises a spiral humidity sensitive layer, an insulating layer, a center lead, a microporous filter membrane, a nanocellulose layer, and a flexible support layer. The preparation method comprises the following steps: first filtering the nanocellulose layer on the microporous filter membrane, then covering the spiral humidity sensitive layer with a mask and filtering to obtain the spiral humidity sensitive layer; attaching the microporous filter membrane to a flat polymer, and obtaining a flexible support layer after polymerization; covering the microporous filter membrane with an insulating layer mask, and spin-coating the polymer thereon as an insulating layer; after polymerization, screen-printing the center lead on the insulating layer using a conductive silver paste to obtain the flexible wet distance sensing film. The present invention combines the mask with vacuum filtration and uses the nanocellulose layer as an intermediate bonding agent to achieve the spiralization of the nano-conductive humidity sensitive material on the microporous filter membrane. The preparation is simple, the process consistency is high, and the resulting sensing film is flexible, light, and has both humidity and distance sensing capabilities.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible sensing films, and in particular to a flexible wet distance sensing film based on vacuum filtration and a preparation method thereof. Background Art

[0002] With the advancement of technology, facilities and equipment in industrial applications are becoming increasingly miniaturized and integrated, resulting in the emergence of numerous narrow curved structures, such as the ball joint hinges in industrial robots, and the pipes, bearings, and turbine blades in aerospace facilities. Excessive humidity can accelerate equipment aging and affect operational stability, while the gaps between narrow curved surfaces in equipment are closely related to operational safety and efficiency. Therefore, to ensure engineering quality and industrial safety, it is necessary not only to monitor the humidity of the industrial environment but also the gaps within these curved structures. Traditional humidity and distance sensors mostly measure only a single parameter, making it difficult to install multiple sensors in narrow curved environments. Furthermore, sensor elements with low flexibility struggle to operate in a bent state for extended periods. To overcome these drawbacks, a flexible, lightweight, and wet-distance sensing film is needed that can operate in narrow curved environments for humidity detection and distance detection between narrow curved surfaces. Summary of the Invention

[0003] (1) Technical issues

[0004] Provided are a flexible moisture-distance sensing film based on vacuum filtration and a preparation method thereof. By combining a mask method with vacuum filtration, the spiralization of nano-conductive moisture-sensitive materials on a microporous filter membrane is achieved. The prepared flexible sensing film has both humidity sensing and distance sensing capabilities, and its preparation efficiency and process consistency are improved.

[0005] (2) Technical solution

[0006] The present invention provides a technical solution to solve the above problems: a flexible wet distance sensing film based on vacuum filtration, comprising

[0007] Spiral humidity sensitive layer, insulating layer, center lead, microporous filter membrane, middle bonding layer, flexible support layer;

[0008] The microporous filter membrane is a hydrophilic microporous filter membrane used for vacuum filtration;

[0009] The nanocellulose layer is a nanocellulose film tightly bonded to the microporous filter membrane, and is formed by vacuum filtration of a nanocellulose aqueous solution on the microporous filter membrane;

[0010] The spiral humidity-sensitive layer is a humidity-sensitive conductive film with a planar spiral structure. It is formed by vacuum filtering an aqueous dispersion of a nano-conductive material with humidity-sensitive properties onto a nano-cellulose layer covering a mask of the spiral humidity-sensitive layer. The nano-cellulose layer is tightly bonded to the spiral. The center of the spiral is connected to a central lead, and the other end is connected to a test circuit. The nano-conductive material with humidity-sensitive properties can be titanium carbide, carbon nanotubes, graphene, etc.

[0011] The insulating layer is a thin, rectangular insulating film that covers and extends from the innermost circle to the outermost circle of the spiral humidity sensitive layer;

[0012] The center lead is a conductive silver paste with one end connected to the center of the spiral humidity sensitive layer and led out along the insulating layer, and the other end is connected to the test circuit;

[0013] The flexible support layer is an insulating film supported on the bottom of the microporous filter membrane;

[0014] The insulating layer and the flexible supporting layer are made of flexible high molecular polymer by paving or spin coating. The flexible high molecular polymer can be polydimethylsiloxane, polyurethane, silicone rubber and the like.

[0015] The method for preparing a flexible wet distance sensing film based on vacuum filtration comprises the following steps:

[0016] 1) Design the dimensional parameters of the spiral humidity sensitive layer, insulation layer, and center lead;

[0017] 2) manufacturing a spiral moisture-sensitive layer mask and an insulating layer mask according to the size parameters of the spiral moisture-sensitive layer and the insulating layer, respectively, and manufacturing a center lead screen for screen printing according to the size parameters of the center lead;

[0018] 3) preparing a nano-conductive moisture-sensitive material aqueous dispersion and a nano-cellulose aqueous dispersion;

[0019] 4) Cover the microporous filter membrane on the sand core of the filtration device, then place the filtration cup on top and tightly connect it to the microporous filter membrane and the sand core through a clamp, spread 1 ml of the nanocellulose aqueous dispersion onto the microporous filter membrane, turn on the vacuum pump for vacuum filtration, remove the microporous filter membrane after the filtration is completed, and dry it at room temperature for 1 hour to obtain a microporous filter membrane tightly bonded to the nanocellulose layer;

[0020] 5) The spiral moisture-sensitive layer mask is covered with the nanocellulose layer on the microporous filter membrane and placed together on the sand core. A filtration cup is then placed on top and tightly connected to the spiral moisture-sensitive layer mask, the microporous filter membrane with the nanocellulose layer, and the sand core via a clamp. A vacuum pump is turned on to ensure that the spiral moisture-sensitive layer mask is in close contact with the microporous filter membrane and is adsorbed onto the sand core. An appropriate amount of an aqueous dispersion of a nano-conductive moisture-sensitive material is then spread on the mask and vacuum filtered. The nano-conductive moisture-sensitive material is deposited only in the spiral area of ​​the microporous filter membrane not covered by the mask. The nanocellulose layer tightly bonds the spiral moisture-sensitive layer to the microporous filter membrane.

[0021] 6) After the filtration is completed, the spiral humidity-sensitive layer mask is separated from the microporous filter membrane and dried at room temperature for 1 hour to obtain a microporous filter membrane tightly bonded to the spiral humidity-sensitive layer;

[0022] 7) Spreading or spin-coating a flexible polymer on a smooth flat surface and prepolymerizing it for 2 hours, attaching a microporous filter membrane having a spiral humidity-sensitive layer to the incompletely polymerized flexible polymer. After the flexible polymer is fully polymerized, it tightly bonds to the microporous filter membrane and serves as a flexible support layer for the flexible wet-distance film.

[0023] 8) Covering the insulating layer mask on the microporous filter membrane tightly bonded to the spiral humidity sensitive layer, flattening or spin-coating a flexible polymer on the insulating layer mask, separating the insulating layer mask from the microporous filter membrane, and after the flexible polymer is completely polymerized, screen-printing a conductive silver paste as a center lead on the insulating layer using a center lead screen, drying at room temperature for 12 hours, peeling off the microporous filter membrane, and trimming the flexible support layer along the edge of the microporous filter membrane to obtain a flexible wet distance sensing film.

[0024] The device used for vacuum filtration includes a vacuum pump and a filtration cup-sand core-filtration bottle connected filtration device. A microporous filter membrane or a microporous filter membrane covered with a spiral humidity-sensitive layer mask is placed between the filtration cup and the sand core. The three are tightly connected by a clamp. The lower part of the sand core is connected to the filtration bottle, and the filtration bottle is connected to the vacuum pump through an exhaust pipe.

[0025] (3) Beneficial effects

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] 1. By first depositing a nanocellulose layer on the microporous filter membrane, then covering the microporous filter membrane with a spiral humidity sensitive layer mask and filtering the nano-conductive humidity sensitive material, the nanocellulose layer is used as an intermediate bonding layer to tightly bond the spiral humidity sensitive layer to the microporous filter membrane, thereby enhancing the flexibility of the flexible wet distance sensing film, making it both light and flexible.

[0028] 2. The negative pressure provided by the vacuum pump is used to make the spiral humidity-sensitive layer mask close to the microporous filter membrane and adsorbed on the sand core together. Then, the aqueous dispersion of the nano-conductive humidity-sensitive material is spread on it and vacuum filtered to make the nano-conductive humidity-sensitive material deposited in a spiral shape to obtain a spiral humidity-sensitive layer. This preparation method is simple and easy, and improves preparation efficiency and process consistency.

[0029] 3. The spiral humidity sensitive layer enables the flexible wet distance sensing film to have the ability to measure both humidity and distance. It can detect humidity through resistance under DC excitation and detect distance through equivalent reactance under AC excitation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic diagram of the flexible wet distance sensing film;

[0031] Figure 2 is a schematic diagram of a spiral-shaped humidity-sensitive layer mask;

[0032] Figure 3 is a schematic diagram of an insulating layer mask;

[0033] Figure 4 It is a schematic diagram of the center lead screen;

[0034] Figure 5 is a schematic diagram of the apparatus used for vacuum filtration;

[0035] Figure 6 This is a schematic diagram of connecting the filter cup, microporous filter membrane, sand core and filter bottle through a clamp;

[0036] Figure 7 Schematic diagram of connecting the filtration cup, the spiral humidity sensitive layer mask, the microporous filter membrane, the sand core and the filtration bottle through a clamp;

[0037] Figure 8 is a flow chart for preparing the flexible wet distance sensing film in Example 1;

[0038] The accompanying drawings include:

[0039] Spiral humidity sensitive layer L1, insulating layer L2, central lead L3, microporous filter membrane L4, nanocellulose layer L5, flexible support layer L6;

[0040] Spiral humidity sensitive layer mask M1, insulating layer mask M2, center lead screen B1;

[0041] Vacuum pump 1, filter cup 2, sand core 3, filter bottle 4, clamp 5, exhaust pipe 6. DETAILED DESCRIPTION

[0042] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0043] See also Figure 1 As shown, a flexible wet distance sensing film based on vacuum filtration is characterized by comprising a spiral humidity sensitive layer L1, an insulating layer L2, a central lead L3, a microporous filter membrane L4, a nanocellulose layer L5, and a flexible support layer L6;

[0044] The microporous filter membrane L4 is a hydrophilic microporous filter membrane used for vacuum filtration;

[0045] The nanocellulose layer L5 is a nanocellulose film tightly bonded to the microporous filter membrane L4, and is formed by vacuum filtration of a nanocellulose aqueous solution on the microporous filter membrane L4;

[0046] The spiral humidity-sensitive layer L1 is a humidity-sensitive conductive film with a planar spiral structure. It is formed by vacuum filtration of an aqueous dispersion of a nano-conductive material with humidity-sensitive properties onto a nano-cellulose layer L5 covering a spiral humidity-sensitive layer mask M1. The layer is tightly bonded to the nano-cellulose layer L5. The center of the spiral is connected to the center lead L3, and the other end is connected to a test circuit. The humidity-sensitive nano-conductive material can be titanium carbide, carbon nanotubes, graphene, etc.

[0047] The insulating layer L2 is a thin and long rectangular insulating film, which covers the innermost circle above the spiral humidity sensitive layer L1 and extends to the outermost circle;

[0048] The center lead L3 is a conductive silver paste with one end connected to the center of the spiral humidity sensitive layer L1 and led out along the insulating layer L2, and the other end is connected to the test circuit;

[0049] The flexible support layer L6 is an insulating film supported on the bottom of the microporous filter membrane L4;

[0050] The insulating layer L2 and the flexible supporting layer L6 are made of flexible high molecular polymer by paving or spin coating, and the flexible high molecular polymer can be polydimethylsiloxane, polyurethane, silicone rubber, etc.;

[0051] The method for preparing a flexible wet distance sensing film based on vacuum filtration comprises the following steps:

[0052] 1) Design the dimensional parameters of the spiral humidity-sensitive layer L1, the insulating layer L2, and the center lead L3: the spiral humidity-sensitive layer L1 is a spiral with a line width of 0.5 mm, a line pitch of 0.5 mm, and 10 turns; the insulating layer L2 is a rectangle with a length of 20 mm and a width of 1 mm; and the center lead L3 is a rectangle with a length of 40 mm and a width of 0.5 mm.

[0053] 2) The spiral moisture-sensitive layer mask M1 and the insulating layer mask M2 made of stainless steel and the center lead screen B1 for screen printing are respectively made according to the corresponding size parameters. Figure 2 、 Figure 3 and Figure 4 As shown;

[0054] 3) preparing a nano-conductive moisture-sensitive material aqueous dispersion and a nano-cellulose aqueous dispersion;

[0055] 4) See Figure 5 and Figure 6 As shown, the microporous filter membrane L4 is covered on the sand core 3 of the filtration device, and then the filtration cup 2 is placed on the top and tightly connected to the microporous filter membrane L4 and the sand core 3 through the clamp 5. 1 ml of the nanocellulose aqueous dispersion is spread on the microporous filter membrane L4, and the vacuum pump 1 is turned on for vacuum filtration. After the filtration is completed, the microporous filter membrane L4 is removed and dried at room temperature for 1 hour to obtain the microporous filter membrane L4 tightly combined with the nanocellulose layer L5;

[0056] 5) See Figure 5 and Figure 7 As shown, the spiral humidity-sensitive layer mask M1 is covered with the nanocellulose layer L5 on the microporous filter membrane L4 and placed together on the sand core 3. Then, the suction cup 2 is placed on top and tightly connected to the spiral humidity-sensitive layer mask M1, the microporous filter membrane L4 with the nanocellulose layer L5, and the sand core 3 via a clamp 5. The vacuum pump 1 is turned on to make the spiral humidity-sensitive layer mask M1 close to the microporous filter membrane L4 and adsorbed on the sand core 3. Then, an appropriate amount of nano-conductive humidity-sensitive material aqueous dispersion is spread on it and vacuum filtered. The nano-conductive humidity-sensitive material will only be deposited on the spiral area of ​​the microporous filter membrane L4 not covered by the spiral humidity-sensitive layer mask M1, wherein the nanocellulose layer L5 tightly bonds the spiral humidity-sensitive layer L1 to the microporous filter membrane L4.

[0057] 6) After the filtration is completed, the spiral humidity-sensitive layer mask M1 is separated from the microporous filter membrane L4 and dried at room temperature for 1 hour;

[0058] 7) Spread or spin-coat a flexible polymer on a smooth flat surface and prepolymerize for 2 hours. Attach the microporous filter membrane L4, which is tightly bonded to the spiral humidity-sensitive layer L1, to the incompletely polymerized flexible polymer. After the flexible polymer is fully polymerized, it tightly bonds to the microporous filter membrane L4, serving as the flexible support layer L6 of the flexible wet-distance film.

[0059] 8) Cover the insulating layer mask M2 on the microporous filter membrane L4 tightly bonded to the spiral humidity sensitive layer L1, spread or spin-coat a flexible polymer on the insulating layer mask M2, separate the insulating layer mask M2 from the microporous filter membrane L4, and after the flexible polymer is completely polymerized, use the center lead screen B1 to screen-print a conductive silver paste on the insulating layer L2 as the center lead L3. Dry at room temperature for 12 hours, peel off the microporous filter membrane L4, and trim the flexible support layer L6 along the edge of the microporous filter membrane L4 to obtain a flexible wet distance sensing film.

[0060] See also Figure 5 As shown, the device used for vacuum filtration includes a vacuum pump 1 and a filter cup 2-sand core 3-filter bottle 4 connection type filtration device, see Figure 6 and Figure 7 As shown, the microporous filter membrane L4 or the microporous filter membrane L4 covered with a spiral moisture-sensitive layer mask M1 is placed between the filtration cup 4 and the sand core 3, and the three are tightly connected by a clamp 5. The lower part of the sand core 3 is connected to the filtration bottle 4, and the filtration bottle 4 is connected to the vacuum pump 1 through the exhaust pipe 6.

[0061] Example 1

[0062] See also Figure 1 As shown, a flexible wet distance sensing film based on vacuum filtration includes

[0063] Spiral humidity sensitive layer, insulating layer, central lead, microporous filter membrane, nanocellulose layer, flexible support layer;

[0064] The microporous filter membrane is a mixed cellulose ester (MCE) filter membrane with a diameter of 50 mm and a pore size of 0.22 μm, which has good hydrophilicity, electrical insulation and flexibility;

[0065] The nanocellulose layer is a nanocellulose (CNF) film with a diameter of 48 mm, which is formed by vacuum filtration of a CNF aqueous solution on an MCE filter membrane and is tightly bonded to the MCE filter membrane;

[0066] The spiral humidity sensitive layer is a titanium carbide (Ti3C2T x ) Conductive humidity sensitive film, the spiral center is connected to the center lead, and the other end is connected to the test circuit, which is composed of a single layer of Ti3C2T x The aqueous dispersion is covered with Figure 2 The spiral moisture-sensitive layer mask is formed by vacuum filtration on the nanocellulose layer and is tightly connected to the nanocellulose layer;

[0067] The insulating layer is a slender rectangular polyurethane (PU) film, covering and extending from the innermost circle to the outermost circle of the spiral humidity sensitive layer;

[0068] The center lead is a conductive silver paste with one end connected to the center of the spiral humidity sensitive layer and led out along the insulating layer, and the other end is connected to the test circuit;

[0069] The flexible support layer is a PU insulating film with a diameter of 52 mm, which is supported on the bottom of the microporous filter membrane;

[0070] The insulating layer and the flexible support layer are made of a single-component water-based PU emulsion by spin coating, and have good electrical insulation and flexibility;

[0071] Figure 8 A method for preparing a flexible wet distance sensing film based on vacuum filtration is schematically described, comprising:

[0072] 1) Design the dimensional parameters of the spiral humidity-sensitive layer, insulating layer, and center lead: the spiral humidity-sensitive layer has a line width of 0.5 mm, a line spacing of 0.5 mm, and 10 turns; the insulating layer is a rectangle with a length of 20 mm and a width of 1 mm; and the center lead is a rectangle with a length of 40 mm and a width of 0.5 mm.

[0073] 2) The spiral moisture-sensitive layer mask and the insulating layer mask made of stainless steel and the center lead screen for screen printing are respectively as follows: Figure 2 、 Figure 3 and Figure 4 As shown;

[0074] 3) 40 mg of clay-like multilayer Ti3C2T x The powder was dispersed in 20 ml of deionized water and stirred for 2 hours. Ultrasonic dispersion was performed for 30 minutes in an ice bath with an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. After the ultrasonic dispersion was completed, the mixture was centrifuged at a speed of 3000 r / min for 15 minutes, and the supernatant was collected to obtain a uniformly dispersed monolayer Ti3C2T x Aqueous dispersion;

[0075] 4) Disperse 10 mg of nanocellulose (CNF) in 10 ml of deionized water and stir for 2 hours. Ultrasonic dispersion was performed for 30 minutes at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. Stirring was continued for 1 hour to obtain a uniformly dispersed CNF aqueous solution.

[0076] 5) See Figure 5 and Figure 6 As shown, the MCE filter membrane is covered on the sand core of the filtration device, and then the filtration cup is placed on the top and tightly connected to the microporous filter membrane and the sand core through a clamp. 1 ml of CNF aqueous dispersion is spread on the microporous filter membrane, and the vacuum pump is turned on for vacuum filtration. After the filtration is completed, the MCE filter membrane is removed and dried at room temperature for 1 hour;

[0077] 6) See Figure 5and Figure 7 As shown, the spiral humidity sensitive layer mask is covered with the CNF layer on the MCE filter membrane and placed together on the sand core. Then, the suction cup is placed on the top and tightly connected to the spiral humidity sensitive layer mask, the MCE filter membrane with the CNF layer and the sand core through a clamp. The vacuum pump is turned on to make the spiral humidity sensitive layer mask close to the MCE filter membrane and adsorbed on the sand core together. Then, 4 ml of a single layer of Ti3C2T x The aqueous dispersion was spread on it and vacuum filtered. The single layer Ti3C2T x The CNF layer will only be deposited on the spiral area of ​​the MCE filter membrane that is not covered by the mask, where the planar spiral structure of Ti3C2T x The layer is tightly bonded to the MCE filter membrane;

[0078] 7) After filtration, separate the spiral humidity-sensitive layer mask from the MCE filter membrane and dry it at room temperature for 1 hour;

[0079] 8) Spin-coat a single-component aqueous PU emulsion on a smooth polyethylene terephthalate (PET) plate at a spin-coating speed of 1500 r / min for 60 seconds and prepolymerize for 2 hours to form a spiral Ti3C2T x The MCE filter membrane of the first layer is attached to the unpolymerized PU. After the PU film is fully polymerized, it is tightly combined with the MCE filter membrane to serve as a flexible support layer.

[0080] 9) Cover the insulating layer mask with the spiral Ti3C2T x The MCE filter membrane is tightly bonded to the insulating layer, and the PU emulsion is spin-coated on the insulating layer mask at a spin coating speed of 2500r / min for 60 seconds. The insulating layer mask and the MCE filter membrane are separated. After the PU is completely polymerized, a conductive silver paste is screen-printed on the insulating layer using a center lead screen as a center lead. The membrane is dried at room temperature for 12 hours, and the MCE filter membrane is peeled off from the smooth PET plate. The PU film is trimmed along the edge of the MCE filter membrane to obtain the following: Figure 1 Flexible wet distance sensing film shown.

[0081] Among them, the device used for vacuum filtration is as follows Figure 5 As shown, it includes a vacuum pump, a filter cup-sand core-filter bottle connection type filter device and a clamp, see Figure 6 and Figure 7 As shown, the MCE filter membrane or the MCE filter membrane covered with a spiral moisture-sensitive layer mask is placed between the filtration cup and the sand core, and the three are tightly connected by a clamp. The lower part of the sand core is connected to the filtration bottle, and the filtration bottle is connected to the vacuum pump through the exhaust pipe.

[0082] The humidity sensing process and distance sensing process of the flexible wet distance sensing film are as follows:

[0083] In the humidity sensing process, due to the Ti3C2T x The surface has many hydrophilic groups such as -OH and -F, which are conducive to the adsorption of water molecules. Therefore, when the humidity increases, the flexible wet distance sensing film will adsorb a large amount of water molecules, making Ti3C2T x The gap between the sheets becomes larger, and the overall resistance of the flexible wet distance sensing film increases; on the contrary, when the humidity decreases, the water molecules adsorbed in the flexible wet distance sensing film decrease, making the Ti3C2T x After being tightly stacked again, the overall resistance of the flexible wet distance sensing film is reduced.

[0084] In the distance sensing process, the spiral Ti3C2T flexible wet distance sensing film x The layer generates an alternating magnetic field under AC excitation, which stimulates eddy currents in the conductive target to resist the alternating magnetic field. When the distance between the sensing film and the target decreases, the resisting magnetic field generated by the eddy currents in the target increases, which reduces the equivalent reactance of the sensing film. Conversely, when the distance increases, the equivalent reactance of the sensing film increases. By detecting the change of the equivalent reactance of the sensing film with distance, the distance between the sensing element and the target can be sensed.

[0085] Example 2

[0086] See also Figure 1 As shown, a flexible wet distance sensing film based on vacuum filtration includes

[0087] Spiral humidity sensitive layer, insulating layer, central lead, microporous filter membrane, nanocellulose layer, flexible support layer;

[0088] The microporous filter membrane is a hydrophilic polytetrafluoroethylene (PTFE) filter membrane with a diameter of 50 mm and a pore size of 0.22 μm, which has good electrical insulation, hydrophilicity and flexibility;

[0089] The nanocellulose layer is a nanocellulose (CNF) film with a diameter of 48 mm, which is formed by vacuum filtration of a CNF aqueous solution on a hydrophilic PTFE filter membrane and is tightly bonded to the hydrophilic PTFE filter membrane;

[0090] The spiral humidity sensitive layer is a multi-walled carbon nanotube (MWCNTs) humidity sensitive conductive film with a planar spiral structure. The center of the spiral is connected to the center lead, and the other end is connected to the test circuit. Figure 2 The spiral moisture-sensitive layer mask is formed by vacuum filtration on the nanocellulose layer and is tightly connected to the nanofiber layer;

[0091] The insulating layer is a slender rectangular polyurethane (PU) insulating film, covering and extending from the innermost circle to the outermost circle of the spiral humidity sensitive layer;

[0092] The center lead is a conductive silver paste with one end connected to the center of the spiral humidity sensitive layer and led out along the insulating layer, and the other end is connected to the test circuit;

[0093] The flexible support layer is a PU insulating film with a diameter of 52 mm, which is supported on the bottom of the microporous filter membrane;

[0094] The insulating layer and the flexible support layer are made of a single-component water-based PU emulsion by spin coating, and have good electrical insulation and flexibility;

[0095] A method for preparing a flexible wet distance sensing film based on vacuum filtration, comprising:

[0096] 1) Design the dimensional parameters of the spiral humidity-sensitive layer, insulating layer, and center lead: the spiral humidity-sensitive layer has a line width of 0.5 mm, a line spacing of 0.5 mm, and 10 turns; the insulating layer is a rectangle with a length of 20 mm and a width of 1 mm; and the center lead is a rectangle with a length of 40 mm and a width of 0.5 mm.

[0097] 2) The spiral moisture-sensitive layer mask and the insulating layer mask made of stainless steel and the center lead screen for screen printing are respectively as follows: Figure 2 、 Figure 3 and Figure 4 As shown;

[0098] 3) 40 mg of MWCNTs and 20 mg of sodium dodecylbenzenesulfonate (SDBS) were added to 20 ml of deionized water and stirred for 4 hours. The mixture was ultrasonicated at room temperature for 30 minutes at a power of 200 W and a frequency of 40 kHz. After the ultrasonication, a uniformly dispersed MWCNTs aqueous dispersion was obtained.

[0099] 4) Disperse 10 mg of nanocellulose (CNF) in 10 ml of deionized water and stir for 2 hours. Ultrasonic dispersion was performed for 30 minutes at an ultrasonic power of 200 W and an ultrasonic frequency of 40 kHz. Stirring was continued for 1 hour to obtain a uniformly dispersed CNF aqueous solution.

[0100] 5) Place a hydrophilic PFTE filter membrane over the sand core of the filtration apparatus, then place a filtration cup on top and securely connect it to the hydrophilic PFTE filter membrane and sand core using a clamp. Spread 1 ml of CNF aqueous dispersion onto the hydrophilic PFTE filter membrane and start vacuum filtration. After filtration, remove the hydrophilic PFTE filter membrane and dry at room temperature for 1 hour.

[0101] 6) The spiral moisture-sensitive layer mask is placed over the CNF layer of the hydrophilic PFTE filter membrane and placed together on a sand core. A filtration cup is then placed on top and tightly connected to the spiral moisture-sensitive layer mask, the hydrophilic PFTE filter membrane with the CNF layer, and the sand core using a clamp. The vacuum pump is turned on to allow the spiral moisture-sensitive layer mask to adhere closely to the hydrophilic PFTE filter membrane and be adsorbed to the sand core. 4 ml of the MWCNT aqueous dispersion is then spread over the mask and vacuum filtered. The MWCNTs will only be deposited in the spiral areas of the hydrophilic PFTE filter membrane not covered by the mask. The CNF layer tightly bonds the spiral MWCNT layer to the hydrophilic PFTE filter membrane.

[0102] 7) After filtration, separate the spiral humidity-sensitive layer mask from the hydrophilic PFTE filter membrane and dry at room temperature for 1 hour;

[0103] 8) Spreading a one-component waterborne polyurethane (PU) emulsion on a smooth acrylic plate and prepolymerizing it for 2 hours, a hydrophilic PFTE filter membrane with a spiral MWCNT layer was attached to the incompletely polymerized PU. After the PU film was fully polymerized, it was tightly bonded to the hydrophilic PFTE filter membrane, serving as flexible support layer 6;

[0104] 9) Covering the insulating layer mask with the hydrophilic PFTE filter membrane tightly bonded to the spiral MWCNTs layer, spin-coating the PU emulsion on the insulating layer mask at a spin coating speed of 2500 r / min for 60 seconds, separating the insulating layer mask from the hydrophilic PFTE filter membrane, and after the PU is completely polymerized, screen-printing a conductive silver paste as a center lead on the insulating layer using a center lead screen, drying at room temperature for 12 hours, peeling off the hydrophilic PFTE filter membrane from the smooth acrylic plate, and trimming the PU film along the edge of the hydrophilic PFTE filter membrane to obtain the following: Figure 1 Flexible wet distance sensing film shown.

[0105] Among them, the device used for vacuum filtration is as follows Figure 5 As shown, it includes a vacuum pump, a filter cup-sand core-filter bottle connection type filter device and a clamp, see Figure 6 and Figure 7 As shown, a hydrophilic PFTE filter membrane or a hydrophilic PFTE filter membrane covered with a spiral humidity sensitive layer mask is placed between the filtration cup and the sand core, and the three are tightly connected by a clamp. The lower part of the sand core is connected to the filtration bottle, and the filtration bottle is connected to the vacuum pump through an exhaust pipe.

[0106] The humidity sensing process and distance sensing process of the flexible wet distance sensing film are as follows:

[0107] During the humidity sensing process, since the MWCNTs surface has many defects and is a p-type conductive material, when the humidity increases, the MWCNTs will adsorb electrons from water molecules, neutralize the holes that are majority carriers, and increase the spacing between the MWCNTs, resulting in an increase in the overall resistance of the flexible wet distance sensing film; conversely, when the humidity decreases, the water molecules adsorbed in the flexible wet distance sensing film decrease, the holes increase, and the MWCNTs are tightly stacked again, resulting in a decrease in the overall resistance of the flexible wet distance sensing film.

[0108] During the distance sensing process, the spiral MWCNTs layer of the flexible wet distance sensing film generates an alternating magnetic field under AC excitation, which stimulates eddy currents in the conductive target to resist the alternating magnetic field. When the distance between the sensing film and the target decreases, the resisting magnetic field generated by the eddy currents in the target increases, causing the equivalent reactance of the sensing film to decrease. Conversely, when the distance increases, the equivalent reactance of the sensing film increases. By detecting the change in the equivalent reactance of the sensing film with distance, the distance between the sensing element and the target can be sensed.

[0109] This proposal aims to provide a flexible wet distance sensing film based on vacuum filtration and its preparation method. By first depositing a nanocellulose layer on a microporous filter membrane, then covering the microporous filter membrane with a spiral humidity-sensitive layer mask and filtering the nanoconductive humidity-sensitive material, the nanocellulose layer acts as an intermediate bonding layer, tightly bonding the spiral humidity-sensitive layer to the microporous filter membrane. This enhances the flexibility of the flexible wet distance sensing film, making it both lightweight and flexible. Using negative pressure provided by a vacuum pump, the spiral humidity-sensitive layer mask is pressed against the microporous filter membrane and adsorbed onto a sand core. An aqueous dispersion of the nanoconductive humidity-sensitive material is then spread flat on the core and vacuum filtered, allowing the nanoconductive humidity-sensitive material to deposit in a spiral shape, resulting in a spiral humidity-sensitive layer. The preparation method is simple and easy, and improves preparation efficiency and process consistency. The spiral humidity-sensitive layer enables the flexible wet distance sensing film to measure both humidity and distance, enabling it to detect humidity through resistance under DC excitation and distance through equivalent reactance under AC excitation.

[0110] Finally, the method of the present invention is only a preferred embodiment and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A flexible wet distance sensing film based on vacuum filtration, characterized by: It includes a spiral humidity sensitive layer (L1), an insulating layer (L2), a central lead (L3), a microporous filter membrane (L4), a nanocellulose layer (L5), and a flexible support layer (L6); The microporous filter membrane (L4) is a hydrophilic microporous filter membrane used for vacuum filtration; The nanocellulose layer (L5) is a nanocellulose film tightly bonded to the microporous filter membrane (L4), and is formed by vacuum filtration of a nanocellulose aqueous solution on the microporous filter membrane (L4); The spiral humidity sensitive layer (L1) is a humidity sensitive conductive film with a planar spiral structure, formed by vacuum filtration of an aqueous dispersion of a nano-conductive material having humidity sensitive properties on a nano-cellulose layer (L5) covering a spiral humidity sensitive layer mask (M1). The layer is tightly bonded to the nano-cellulose layer (L5), with the center of the spiral connected to a center lead (L3), and the other end connected to a test circuit. The nano-conductive material having humidity sensitive properties can be titanium carbide, carbon nanotubes, graphene, etc. The insulating layer (L2) is a thin and long rectangular insulating film, covering the innermost circle above the spiral humidity sensitive layer (L1) and extending to the outermost circle; The central lead (L3) is a conductive silver paste having one end connected to the center of the spiral humidity sensitive layer (L1) and extending along the insulating layer (L2), and the other end connected to the test circuit; The flexible support layer (L6) is an insulating film supported on the bottom of the microporous filter membrane (L4); The insulating layer (L2) and the flexible supporting layer (L6) are made of flexible high molecular polymer by paving or spin coating. The flexible high molecular polymer can be polydimethylsiloxane, polyurethane, silicone rubber, etc.

2. The method for preparing a flexible wet distance sensing film based on vacuum filtration according to claim 1, wherein: The following steps are involved: 1) Design the dimensional parameters of the spiral humidity-sensitive layer (L1), the insulating layer (L2), and the center lead (L3); 2) manufacturing a spiral moisture-sensitive layer mask (M1) and an insulating layer mask (M2) according to the size parameters of the spiral moisture-sensitive layer (L1) and the insulating layer (L2), respectively, and manufacturing a center lead screen (B1) for screen printing according to the size parameters of the center lead (L3); 3) preparing a nano-conductive moisture-sensitive material aqueous dispersion and a nano-cellulose aqueous dispersion; 4) Covering the microporous filter membrane (L4) above the sand core (3) of the filtration device, then placing the filtration cup (2) on the top and tightly connecting it to the microporous filter membrane (L4) and the sand core (3) through a clamp (5), spreading 1 ml of the nanocellulose aqueous dispersion onto the microporous filter membrane (L4), turning on the vacuum pump (1) for vacuum filtration, removing the microporous filter membrane (L4) after the filtration is completed, and drying at room temperature for 1 hour to obtain a microporous filter membrane (L4) tightly combined with the nanocellulose layer (L5); 5) The spiral moisture-sensitive layer mask (M1) is covered on the nanocellulose layer (L5) on the microporous filter membrane (L4) and placed together on the sand core (3), and then the suction cup (2) is placed on the top and tightly connected to the spiral moisture-sensitive layer mask (M1), the microporous filter membrane (L4) with the nanocellulose layer (L5) and the sand core (3) through the clamp (5), and the vacuum pump (1) is turned on to make the spiral moisture-sensitive layer mask (M1) close to the microporous filter membrane (L4) and adsorbed on the sand core (3), and then an appropriate amount of nano-conductive moisture-sensitive material aqueous dispersion is spread on it and vacuum filtered. The nano-conductive moisture-sensitive material will only be deposited on the spiral area of ​​the microporous filter membrane (L4) not covered by the spiral moisture-sensitive layer mask (M1), wherein the nanocellulose layer (L5) tightly bonds the spiral moisture-sensitive layer (L1) and the microporous filter membrane (L4); 6) After the filtration is completed, the spiral humidity sensitive layer mask (M1) is separated from the microporous filter membrane (L4) and dried at room temperature for 1 hour; 7) Spreading or spin-coating a flexible polymer on a smooth flat plate and prepolymerizing it for 2 hours, attaching a microporous filter membrane (L4) tightly bonded to the spiral humidity sensitive layer (L1) to the incompletely polymerized flexible polymer, and after the flexible polymer is completely polymerized and tightly bonded to the microporous filter membrane (L4), serving as a flexible support layer (L6) of the flexible wet distance film; 8) Covering the insulating layer mask (M2) on the microporous filter membrane (L4) tightly bonded to the spiral humidity sensitive layer (L1), spreading or spin-coating a flexible polymer on the insulating layer mask (M2), separating the insulating layer mask (M2) from the microporous filter membrane (L4), and after the flexible polymer is completely polymerized, using a center lead screen (B1) to screen-print a conductive silver paste on the insulating layer (L2) as a center lead (L3), drying at room temperature for 12 hours, peeling off the microporous filter membrane (L4), and trimming the flexible support layer (L6) along the edge of the microporous filter membrane (L4) to obtain a flexible wet distance sensing film.

3. The preparation method according to claim 2, wherein: The device used for vacuum filtration comprises a vacuum pump (1) and a filtration cup (2)-sand core (3)-filtration bottle (4) connection filtration device, wherein a microporous filter membrane (L4) or a microporous filter membrane (L4) covered with a spiral-shaped humidity-sensitive layer mask (M1) is placed between the filtration cup (2) and the sand core (3), and the three are tightly connected by a clamp (5), the lower part of the sand core (3) is connected to the filtration bottle (4), and the filtration bottle (4) is connected to the vacuum pump (1) via an exhaust pipe (6).

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