Flexible wet distance sensing film based on vacuum filtration and preparation method thereof

Abstract

The invention discloses a flexible wet distance sensing film based on vacuum filtration and a preparation method of the flexible wet distance sensing film. The flexible wet distance sensing film comprises a spiral humidity sensitive layer, an insulating layer, a central lead, a microfiltration membrane, a nano cellulose layer and a flexible supporting layer, the preparation method comprises the following steps: firstly, carrying out suction filtration on the nanocellulose layer on the microporous filter membrane, and then covering with the spiral humidity sensitive layer mask for suction filtration to obtain the spiral humidity sensitive layer; a microfiltration membrane is attached to the tiled high-molecular polymer, and a flexible supporting layer is obtained after polymerization; the insulating layer mask covers the microfiltration membrane, the high-molecular polymer is spin-coated on the microfiltration membrane to serve as an insulating layer, and after polymerization, a central lead is subjected to silk-screen printing on the insulating layer by using conductive silver paste to obtain the flexible wet distance sensing film. Masking is combined with vacuum suction filtration, the nano cellulose layer is used as middle bonding to realize the spiral of the nano conductive humidity-sensitive material on the microporous filter membrane, the preparation is simple, the process consistency is high, and the obtained sensing film is flexible, light and thin, and has humidity and distance sensing capabilities.

Description

Technical Field

[0001] The 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 development of science and technology, facilities and devices in industrial applications tend to be miniaturized and integrated, and many narrow curved structures have emerged, such as the ball joint hinge structure in industrial robots, pipes, bearings and turbine blades in aerospace facilities, etc. Excessive humidity will accelerate the aging of equipment and affect the stability of equipment operation. The narrow curved gap in the equipment is closely related to the safety and efficiency of equipment operation. Therefore, in order to ensure the quality of engineering and industrial safety, it is necessary not only to monitor the humidity of the industrial environment, but also to monitor the gaps in the above curved structures. Most traditional humidity sensors and distance sensors only measure a single parameter. It is difficult to install multiple sensors in a narrow curved environment, and the sensor elements with low flexibility are difficult to work in a bent state for a long time. In order to overcome the above defects, it is necessary to develop a flexible and thin wet distance sensing film so that it can work in a narrow curved environment to perform humidity detection and distance detection tasks between narrow curved surfaces. Summary of the invention

[0003] 1. Technical issues

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

[0005] (II) 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, central 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 combined with a microporous filter membrane, and is formed by vacuum filtering 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, which is formed by vacuum filtration of a water dispersion of a nano-conductive material with humidity sensitive properties on a nano-cellulose layer covering a mask of the spiral humidity sensitive layer, and is tightly combined with the nano-cellulose layer. The center of the spiral is connected to the center 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 an elongated rectangular insulating film, covering and extending from the innermost circle to the outermost circle of the spiral humidity sensitive layer;

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

[0013] The flexible support layer is an insulating film supported at 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 the 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 on 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 combined with the nanocellulose layer;

[0020] 5) The spiral moisture-sensitive layer mask is covered on the nanocellulose layer on the microporous filter membrane and placed together on the sand core, and then a suction filter cup is placed on the top and is tightly connected to the spiral moisture-sensitive layer mask, the microporous filter membrane with the nanocellulose layer and the sand core through a clamp, and the vacuum pump is turned on to make the spiral moisture-sensitive layer mask close to the microporous filter membrane and adsorbed on the sand core together, and then an appropriate amount of nano-conductive moisture-sensitive material aqueous dispersion is spread on it for vacuum filtration, and the nano-conductive moisture-sensitive material is only deposited on the spiral area of ​​the microporous filter membrane that is not covered by the mask, and the nano-cellulose 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 combined with the spiral humidity sensitive layer;

[0022] 7) Spread or spin-coat a flexible high molecular polymer on a smooth flat plate, prepolymerize for 2 hours, attach a microporous filter membrane with a spiral humidity sensitive layer to the incompletely polymerized flexible high molecular polymer, and after the flexible high molecular polymer is completely polymerized, tightly combine with the microporous filter membrane to serve as a flexible support layer of the flexible wet distance film;

[0023] 8) Cover the insulating layer mask on the microporous filter membrane that is tightly combined with the spiral humidity sensitive layer, spread or spin-coat a flexible polymer on the insulating layer mask, separate the insulating layer mask from the microporous filter membrane, and after the flexible polymer is completely polymerized, use a center lead screen to screen-print a conductive silver paste on the insulating layer as a center lead, dry it at room temperature for 12 hours, peel off the microporous filter membrane, and trim 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, 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.

[0025] (III) 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 for vacuum filtration, so that the nano-conductive humidity-sensitive material can be deposited into a spiral shape to obtain a spiral humidity-sensitive layer. This preparation method is simple and easy, and improves the 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 a flexible wet distance sensing film;

[0031] Figure 2 is a schematic diagram of a spiral moisture-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 It is a schematic diagram of connecting the suction filter cup, microporous filter membrane, sand core and suction filter bottle through a clamp;

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

[0037] Figure 8 is a flow chart of the preparation of 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 moisture 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 specific implementation of the present invention is further described in detail below in conjunction with 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 combined with 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, which is formed by vacuum filtration of a water dispersion of a nano-conductive material with humidity sensitive properties on a nano-cellulose layer L5 covering a spiral humidity sensitive layer mask M1, and is tightly combined with 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 nano-conductive material with humidity sensitive properties 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 central lead L3 is a conductive silver paste having 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 connected to the test circuit;

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

[0050] The insulating layer L2 and the flexible support 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 size 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 spacing of 0.5 mm, and a number of turns of 10; the insulating layer L2 is a rectangle with a length of 20 mm and a width of 1 mm; 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 covers the nanocellulose layer L5 on the microporous filter membrane L4 and is placed together on the sand core 3, and then the suction cup 2 is placed on the top and is tightly connected with the spiral humidity 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 humidity sensitive layer mask M1 close to the microporous filter membrane L4 and adsorbed on the sand core 3 together, and then a proper amount of nano-conductive humidity sensitive material aqueous dispersion is spread on it for vacuum filtration, and the nano-conductive humidity sensitive material will only be deposited on the spiral area of ​​the microporous filter membrane L4 that is not covered by the spiral humidity sensitive layer mask M1, wherein the nano-cellulose 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 high molecular polymer on a smooth flat plate, prepolymerize for 2 hours, attach a microporous filter membrane L4 tightly bonded to the spiral humidity sensitive layer L1 to the incompletely polymerized flexible high molecular polymer, and after the flexible high molecular polymer is completely polymerized, tightly bonded to the microporous filter membrane L4 to serve as a 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 combined with the spiral humidity sensitive layer L1, spread or spin-coat the 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 conductive silver paste on the insulating layer L2 as the center lead L3, dry it at room temperature for 12 hours, peel off the microporous filter membrane L4, trim the flexible support layer L6 along the edge of the microporous filter membrane L4, and 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 filtration cup 2-sand core 3-filtration bottle 4 connection 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 humidity 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, and 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 center of the spiral is connected to the center lead, and the other end is connected to the test circuit. 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 of the spiral humidity sensitive layer to the outermost circle;

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

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

[0070] The insulating layer and the flexible support layer are made of a single-component aqueous 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 size parameters of the spiral humidity sensitive layer, the insulating layer and the center lead: the spiral humidity sensitive layer is a spiral with 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; 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 powder was centrifuged at a speed of 3000 r / min for 15 minutes, and the supernatant was taken 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, perform ultrasonic dispersion for 30 minutes, the ultrasonic power is 200 W, the ultrasonic frequency is 40 kHz, and continue stirring 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 in the figure, the spiral humidity sensitive layer mask is covered with the CNF layer on the MCE filter membrane and placed together on the sand core, and then the suction cup is placed on the top and is tightly connected with 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, and then 4 ml of a single layer of Ti3C2T x The aqueous dispersion was spread on it for vacuum filtration, and 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 the filtration is completed, the spiral humidity sensitive layer mask is separated from the MCE filter membrane and dried at room temperature for 1 hour;

[0079] 8) Spin coating 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 prepolymerization for 2 hours to form a spiral Ti3C2T x The MCE filter membrane of the first layer is attached to the incompletely polymerized PU. After the PU film is completely 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 with tight bonding is spin-coated with PU emulsion on the insulating layer mask at a spin-coating speed of 2500r / min for 60 seconds. The insulating layer mask is separated from the MCE filter membrane. 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 film is dried at room temperature for 12 hours, the MCE filter membrane is peeled off from the smooth PET plate, and 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 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 a suction pipe.

[0082] The humidity sensing process and distance sensing process of the above-mentioned 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 number of water molecules, making Ti3C2T x As the gap between the sheets increases, 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 Once again tightly stacked, the overall resistance of the flexible wet distance sensing film decreases.

[0084] In the distance sensing process, the spiral Ti3C2T 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 the 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, and 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 combined with 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, which is tightly connected to the nanofiber layer;

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

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

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

[0094] The insulating layer and the flexible support layer are made of a single-component aqueous 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 size parameters of the spiral humidity sensitive layer, the insulating layer and the center lead: the spiral humidity sensitive layer is a spiral with 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; 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 MWCNTs and 20 mg sodium dodecylbenzene sulfonate (SDBS) were added to 20 ml deionized water and stirred for 4 hours, and ultrasonicated for 30 minutes at room temperature with an ultrasonic power of 200 W and an ultrasonic 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, perform ultrasonic dispersion for 30 minutes, the ultrasonic power is 200 W, the ultrasonic frequency is 40 kHz, and continue stirring for 1 hour to obtain a uniformly dispersed CNF aqueous solution;

[0100] 5) Cover the hydrophilic PFTE filter membrane on the sand core of the filtration device, then place the filtration cup on the top and tightly connect it to the hydrophilic PFTE filter membrane and the sand core through a clamp, spread 1 ml of CNF aqueous dispersion on the hydrophilic PFTE filter membrane, turn on the vacuum pump for vacuum filtration, remove the hydrophilic PFTE filter membrane after filtration is completed, and dry it at room temperature for 1 hour;

[0101] 6) Cover the CNF layer of the hydrophilic PFTE filter membrane with the spiral humidity sensitive layer mask and place them together on the sand core, then place the filtration cup on the top and tightly connect it with the spiral humidity sensitive layer mask, the hydrophilic PFTE filter membrane with the CNF layer and the sand core through a clamp, turn on the vacuum pump to make the spiral humidity sensitive layer mask close to the hydrophilic PFTE filter membrane and adsorbed on the sand core together, then spread 4 ml of MWCNTs aqueous dispersion on it for vacuum filtration, and MWCNTs will only be deposited on the spiral area of ​​the hydrophilic PFTE filter membrane that is not covered by the mask, wherein the CNF layer tightly bonds the spiral MWCNTs layer to the hydrophilic PFTE filter membrane;

[0102] 7) After the filtration is completed, the spiral humidity sensitive layer mask is separated from the hydrophilic PFTE filter membrane and dried at room temperature for 1 hour;

[0103] 8) Spreading a single-component waterborne polyurethane (PU) emulsion on a smooth acrylic plate, prepolymerizing for 2 hours, attaching a hydrophilic PFTE filter membrane with a spiral MWCNTs layer to the incompletely polymerized PU, and after the PU film is completely polymerized, it is tightly combined with the hydrophilic PFTE filter membrane to serve as a flexible support layer 6;

[0104] 9) Cover the insulating layer mask on the hydrophilic PFTE filter membrane tightly combined with the spiral MWCNTs layer, spin-coat the PU emulsion on the insulating layer mask at a spin coating speed of 2500 r / min for 60 seconds, separate the insulating layer mask from the hydrophilic PFTE filter membrane, and after the PU is completely polymerized, use a center lead screen to screen-print a conductive silver paste on the insulating layer as a center lead, dry it at room temperature for 12 hours, peel off the hydrophilic PFTE filter membrane from the smooth acrylic plate, and trim 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, the hydrophilic PFTE filter membrane or the 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 a suction pipe.

[0106] The humidity sensing process and distance sensing process of the above-mentioned 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 absorb electrons from the water molecules, neutralize the holes as the 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] The purpose of this scheme is to provide a flexible wet distance sensing film based on vacuum filtration and a preparation method thereof. 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 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 and making it both light and flexible. 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, and then the nano-conductive humidity sensitive material aqueous dispersion is spread on it for vacuum filtration, so that the nano-conductive humidity sensitive material can be deposited into a spiral shape to obtain a spiral humidity sensitive layer. The preparation method is simple and easy, and the preparation efficiency and process consistency are improved. The spiral humidity sensitive layer enables the flexible wet distance sensing film to have the ability to measure both humidity and distance, and can detect humidity through resistance under DC excitation, and can detect 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 protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A flexible wet distance sensing film based on vacuum filtration, characterized in that: 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 combined with the microporous filter membrane (L4), and is formed by vacuum filtering 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, which is formed by vacuum filtration of a water dispersion of a nano-conductive material with humidity sensitive properties on a nano-cellulose layer (L5) covering a spiral humidity sensitive layer mask (M1), and is tightly combined with 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 nano-conductive material with 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 led out 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, and the flexible high molecular polymer can be polydimethylsiloxane, polyurethane, silicone rubber and the like.

2. The method for preparing a flexible wet distance sensing film based on vacuum filtration according to claim 1, characterized in that: The following steps are involved: 1) Design the size 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, 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 with the nanocellulose layer (L5) on the microporous filter membrane (L4) and placed together on the sand core (3), and then the suction filter cup (2) is placed on the top and tightly connected with 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 for vacuum filtration, and 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 high molecular polymer on a smooth flat plate, prepolymerizing for 2 hours, attaching a microporous filter membrane (L4) tightly bonded to the spiral humidity sensitive layer (L1) to the incompletely polymerized flexible high molecular polymer, and after the flexible high molecular polymer is completely polymerized, tightly bonded to the microporous filter membrane (L4) to serve as a flexible support layer (L6) of the flexible wet distance film; 8) Cover the insulating layer mask (M2) on the microporous filter membrane (L4) tightly combined with 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 a center lead screen (B1) to screen-print a conductive silver paste on the insulating layer (L2) as a 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.

3. The preparation method according to claim 2, characterized in that: 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, a microporous filter membrane (L4) or a 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 an exhaust pipe (6).

Images