An aqueous polyurethane / silver microsphere self-adhesive composite film and its preparation method

Abstract

An embodiment of the present invention discloses a preparation method of an aqueous polyurethane / silver microsphere self-adhesive composite film, which comprises preparing a first dispersion liquid using silver microspheres; preparing a second dispersion liquid using D-sorbitol particles and an aqueous polyurethane emulsion, wherein the mass concentration of D-sorbitol in the second dispersion liquid is 10 wt% to 20 wt%; spraying the first dispersion liquid and the second dispersion liquid onto a polytetrafluoroethylene substrate to prepare a sample, and the areal density of the silver microspheres on the polytetrafluoroethylene substrate is in the range of 2 to 4 mg / cm<supgt;2< / supgt>; and post-treating the sample to obtain the aqueous polyurethane / silver microsphere self-adhesive composite film. The aqueous polyurethane / silver microsphere self-adhesive composite film has good strain sensing sensitivity, stable signal output for both large strains and small deformations, low production cost, simple operation, excellent performance, and good controllability.

Description

Technical Field

[0001] The present invention relates to the technical field of functional materials, and particularly to an aqueous polyurethane / silver microsphere self-adhesive composite film and a preparation method thereof. Background Art

[0002] With the development of medical technology and the demand for health monitoring, people have paid more and more attention to the application value and research prospect of sensing devices. In recent years, a large number of flexible strain sensors based on conductive composites have emerged. Conductive materials such as metal fillers, carbon nanotubes, graphene sheets, etc. form various conductive structures inside the polymer matrix material, and reflect external deformation by outputting the change of their own electrical behavior signals. However, most of the reported products have defects such as low sensitivity, slow response, and high hysteresis, and the actual application effect is not ideal.

[0003] Many of the reported strain sensors are usually not adhered to the skin, but are fixed on the skin by auxiliary means such as medical tapes. Such a structure has some disadvantages. Although the sensor can deform with the movement of the skin, the synergy of the whole process is poor. Moreover, skin deformation is usually not one-dimensional, but irregular, and the strain generated by the whole sensor may deviate from the actual deformation, especially when the strain direction is inconsistent with the actual detection direction of the sensor, resulting in an error in the output signal. The long-term use of medical tapes will also affect the comfort of human skin. And during the use of the strain sensor, it is easy to appear convex or even fall off, and it cannot accurately feedback on human behavior actions. Summary of the Invention

[0004] An embodiment of the present invention provides an aqueous polyurethane / silver microsphere self-adhesive composite film and a preparation method thereof, which are used to alleviate the technical problem of low strain sensing sensitivity of the current strain sensor.

[0005] To solve the above technical problems, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of an aqueous polyurethane / silver microsphere self-adhesive composite film,

[0007] Prepare a first dispersion liquid using silver microspheres;

[0008] Prepare a second dispersion liquid using D-sorbitol particles and an aqueous polyurethane emulsion, and the mass concentration of D-sorbitol in the second dispersion liquid is 10 wt% to 20 wt%;

[0009] Spray the first dispersion liquid and the second dispersion liquid onto a polytetrafluoroethylene substrate to prepare a sample, and the areal density of the silver microspheres on the polytetrafluoroethylene substrate is in the range of 2-4 mg / cm 2 range;

[0010] The sample is post-treated to obtain a waterborne polyurethane / silver microsphere self-adhesive composite film.

[0011] In one embodiment, the areal density of the silver microspheres on the polytetrafluoroethylene substrate is 3 mg / cm 2 , and the mass concentration of the D-sorbitol is 18.2 wt%.

[0012] In one embodiment, before the step of spraying the first dispersion liquid and the second dispersion liquid onto the polytetrafluoroethylene substrate to prepare a sample, the following steps are further included:

[0013] The waterborne polyurethane emulsion is sprayed onto the polytetrafluoroethylene substrate to form a first coating.

[0014] In one embodiment, the step of spraying the first dispersion liquid and the second dispersion liquid onto the polytetrafluoroethylene substrate to prepare a sample includes:

[0015] The first dispersion liquid is sprayed onto the surface of the first coating to form a second coating, and then the second dispersion liquid is sprayed onto the surface of the second coating to form a third coating.

[0016] In one embodiment, the step of spraying the first dispersion liquid onto the surface of the first coating to form a second coating includes:

[0017] The first dispersion liquid is transferred into a spray gun, the spray gun is 15 cm away from the polytetrafluoroethylene substrate, and the first dispersion liquid is slowly and evenly sprayed onto the surface of the first coating through the spray gun.

[0018] In one embodiment, the step of spraying the second dispersion liquid onto the surface of the second coating to form a third coating includes:

[0019] The second dispersion liquid is transferred into a spray gun, the spray gun is 15 cm away from the polytetrafluoroethylene substrate, and the second dispersion liquid is slowly and evenly sprayed onto the surface of the second coating through the spray gun.

[0020] In one embodiment, the size of the polytetrafluoroethylene substrate is 5×5 cm 2 , and a hot stage at 80 °C is provided under the polytetrafluoroethylene substrate.

[0021] In one embodiment, the step of preparing the first dispersion liquid using silver microspheres includes:

[0022] The silver microspheres are ultrasonically dispersed in an organic solvent for 30 - 60 min to obtain the first dispersion liquid.

[0023] In one embodiment, the organic solvent is a solution with an equal volume ratio of alcohol and water.

[0024] In one embodiment, the second dispersion further includes glycerol.

[0025] In one embodiment, the steps of preparing the second dispersion include:

[0026] Dissolve the D-sorbitol particles in deionized water and stir magnetically for 10 - 20 min at a stirring rate of 2000 - 4000 r / min;

[0027] Then sequentially add the aqueous polyurethane emulsion and the glycerol, and stir magnetically for 30 - 60 min at a stirring rate of 2000 - 4000 r / min to obtain the second dispersion.

[0028] In one embodiment, the mass concentration of the aqueous polyurethane is 30 wt%; the mass concentration of the glycerol is 5 wt%.

[0029] In one embodiment, the steps of post-treating the sample to obtain the self-adhesive composite film of aqueous polyurethane / silver microspheres include:

[0030] Cure the sample in a forced-air drying oven and dry it at 50 - 70 °C for 20 - 40 min, and then peel it off to obtain the self-adhesive composite film of aqueous polyurethane / silver microspheres.

[0031] The present application provides a self-adhesive composite film of aqueous polyurethane / silver microspheres, and the self-adhesive composite film of aqueous polyurethane / silver microspheres is prepared by any of the above preparation methods.

[0032] The preparation method of the self-adhesive composite film of aqueous polyurethane / silver microspheres in the present application uses silver microspheres to prepare a first dispersion; uses D-sorbitol particles and an aqueous polyurethane emulsion to prepare a second dispersion, and the mass concentration of D-sorbitol in the second dispersion is 10 wt% - 20 wt%; spray the first dispersion and the second dispersion onto a polytetrafluoroethylene substrate to prepare a sample, and the areal density of the silver microspheres on the polytetrafluoroethylene substrate is in the range of 2 - 4 mg / cm 2 range; post-treat the sample to obtain the self-adhesive composite film of aqueous polyurethane / silver microspheres. The self-adhesive composite film of aqueous polyurethane / silver microspheres has good strain sensing sensitivity, stable signal output for both large strains and small deformations, low production cost, simple operation, excellent performance, and good controllability. Description of the Drawings

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0034] Figure 1 It is a simplified preparation diagram of the composite film provided in Embodiment 1 of the present invention;

[0035] Figure 2a It is a microscopic morphology diagram of the composite film provided in Embodiment 1 of the present invention;

[0036] Figure 2b It is the microscopic morphology diagram after 5% strain of the composite film provided in Embodiment 1 of the present invention

[0037] Figure 3 It is a stress-strain curve diagram provided by Embodiment 1 of the present invention and Comparative Example 1;

[0038] Figure 4 It is an adhesion force diagram provided by Embodiment 1 of the present invention and Comparative Example 1;

[0039] Figure 5a It is the composite film strain sensor provided in Embodiment 1 of the present invention monitoring the change of finger bending behavior;

[0040] Figure 5b It is the composite film strain sensor provided in Embodiment 1 of the present invention monitoring the change of wrist bending behavior;

[0041] Figure 6a It is the composite film strain sensor provided in Embodiment 1 of the present invention monitoring the change of abdominal breathing behavior;

[0042] Figure 6b It is the composite film strain sensor provided in Embodiment 1 of the present invention monitoring the change of neck pulse behavior. Detailed implementation manners

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0044] The present application provides an aqueous polyurethane / silver microsphere self-adhesive composite film and a preparation method thereof. A first dispersion liquid is prepared using silver microspheres, and a second dispersion liquid is prepared using D-sorbitol particles and an aqueous polyurethane emulsion. The mass concentration of D-sorbitol in the second dispersion liquid is 10 wt% to 20 wt%. The first dispersion liquid and the second dispersion liquid are sprayed onto a polytetrafluoroethylene substrate to prepare a sample, and the areal density of the silver microspheres on the polytetrafluoroethylene substrate is in the range of 2 to 4 mg / cm 2 Within this range, the mass concentration of D-sorbitol in the second dispersion liquid is 10 wt% to 20 wt%. The sample is post-treated to obtain the aqueous polyurethane / silver microsphere self-adhesive composite film.

[0045] In one embodiment, alcohol and water are mixed in an equal volume ratio to obtain an organic solvent, and the silver microspheres are ultrasonically dispersed in the organic solvent for 30 to 60 min to obtain the first dispersion liquid.

[0046] The sprayed silver microspheres are in physical contact with each other through physical lapping to form a conductive network. The stability of this network is poor and there are many gaps between the particles, and slight aggregation will cause initial microcracks on the surface of the conductive layer, which means that a very small strain can break the original conductive network structure, endowing the strain sensor with the potential of high sensitivity. When the areal density of the silver microspheres on the polytetrafluoroethylene substrate is in the range of 2 to 4 mg / cm 2 Within this range, the prepared aqueous polyurethane / silver microsphere self-adhesive composite film has good sensing sensitivity. When the areal density of the silver microspheres on the polytetrafluoroethylene substrate is 3 mg / cm 2 , the prepared aqueous polyurethane / silver microsphere self-adhesive composite film has excellent sensing sensitivity.

[0047] In one embodiment, D-sorbitol particles are dissolved in deionized water and magnetically stirred for 10 to 20 minutes at a stirring rate of 2,000 to 4,000 r / min. Then, an aqueous polyurethane emulsion and glycerol are added sequentially, and magnetically stirred for 30 to 60 minutes at a stirring rate of 2,000 to 4,000 r / min to obtain a second dispersion. When the mass concentration of D-sorbitol in the second dispersion is 10 wt% to 20 wt%, the self-adhesion of the prepared aqueous polyurethane / silver microsphere self-adhesive composite film is better. Among them, when the mass concentration of D-sorbitol is 18.2 wt%, the self-adhesion of the prepared aqueous polyurethane / silver microsphere self-adhesive composite film is excellent. The addition of the aqueous polyurethane emulsion makes the prepared aqueous polyurethane / silver microsphere self-adhesive composite film elastic, making the strain sensing effect of the aqueous polyurethane / silver microsphere self-adhesive composite film more sensitive. Among them, when the mass concentration of the aqueous polyurethane in the second dispersion is 30 wt%, the elastic effect of the aqueous polyurethane / silver microsphere self-adhesive composite film makes the sensitivity of its strain sensing better. Glycerol makes the aqueous polyurethane / silver microsphere self-adhesive composite film have a moisturizing effect, making the self-adhesive effect of the aqueous polyurethane / silver microsphere self-adhesive composite film better. Among them, when the mass concentration of glycerol in the second dispersion is 5 wt%, the moisturizing effect of the aqueous polyurethane / silver microsphere self-adhesive composite film makes its self-adhesive effect better.

[0048] It can be understood that the preparation order of the first dispersion and the second dispersion can be changed. For example, the second dispersion can be prepared first, and then the first dispersion is prepared. This method is also within the protection scope of this application; in another embodiment, the preparation of the second dispersion and the spraying step of the first dispersion can also be changed. This method is also within the protection scope of this application, that is, after the first dispersion is prepared, the first dispersion can be sprayed onto the polytetrafluoroethylene substrate, and then the second dispersion is prepared.

[0049] In one embodiment, before the step of spraying the first dispersion and the second dispersion onto the polytetrafluoroethylene substrate to prepare a sample, the following steps are further included: spraying the aqueous polyurethane emulsion onto the polytetrafluoroethylene substrate to form a first coating. If the first dispersion is directly sprayed onto the polytetrafluoroethylene substrate, the silver microspheres are likely to splash. After spraying the aqueous polyurethane emulsion to form a first coating, spraying the first dispersion on the first coating can better encapsulate the silver microspheres.

[0050] In one embodiment, the first dispersion is transferred to a spray gun, and the spray gun is 15 cm away from the polytetrafluoroethylene substrate. The first dispersion is slowly and evenly sprayed onto the surface of the first coating through the spray gun to form a second coating. The size of the polytetrafluoroethylene substrate is 5×5 cm 2 , and there is a hot stage at 80 °C under the polytetrafluoroethylene substrate. The hot stage at 80 °C can be used to accelerate the evaporation of droplets and prevent the deposition of Ag microflakes during the curing process.

[0051] Transfer the second dispersion liquid into a spray gun. The spray gun is 15 cm away from the polytetrafluoroethylene substrate. Slowly and evenly spray the second dispersion liquid onto the surface of the second coating through the spray gun to form a third coating. The size of the polytetrafluoroethylene substrate is 5×5 cm. 2 There is a hot plate at 80 °C under the polytetrafluoroethylene substrate. The hot plate at 80 °C can be used to accelerate the evaporation of droplets and prevent the deposition of Ag microflakes during the curing process.

[0052] In one embodiment, the sample is cured in a forced-air drying oven and dried at 50-70 °C for 20-40 min. After peeling, a waterborne polyurethane / silver microsphere self-adhesive composite film is obtained.

[0053] In one embodiment, the waterborne polyurethane / silver microsphere self-adhesive composite film prepared in this application has good strain sensing sensitivity and self-adhesion.

[0054] Example 1

[0055] For the waterborne polyurethane / silver microsphere self-adhesive composite film and its preparation method in this example, the specific operation steps are as follows:

[0056] 1) Prepare the first dispersion liquid using silver microspheres: Disperse 75 mg of silver microspheres into an equal-volume ratio solution of alcohol and water, and perform ultrasonic dispersion for 30 min.

[0057] 2) Prepare the second dispersion liquid using D-sorbitol particles and waterborne polyurethane emulsion: Weigh a certain amount of D-sorbitol particles, dissolve them in deionized water, and stir magnetically for 10 min. Then, sequentially add the waterborne polyurethane emulsion and glycerol, and stir magnetically for 30 min to obtain a uniformly mixed solution. Among them, the mass concentration of D-sorbitol is 18.2 wt%, the mass concentration of waterborne polyurethane is 30 wt%, the mass concentration of glycerol is 5 wt%, and the magnetic stirring rate is 3000 r / min.

[0058] 3) Spray the first dispersion liquid and the second dispersion liquid onto the polytetrafluoroethylene substrate to prepare a sample (as Figure 1 shown): Spray the waterborne polyurethane emulsion with a mass concentration of 30 wt% onto the polytetrafluoroethylene substrate to form a first coating. Spray the first dispersion liquid onto the surface of the first coating to form a second coating. Among them, the areal density of silver microspheres on the polytetrafluoroethylene substrate is 3 mg / cm 2 . Spray the second dispersion liquid onto the surface of the second coating to form a third coating. Among them, the spray gun is 15 cm away from the polytetrafluoroethylene substrate, and the size of the polytetrafluoroethylene substrate is 5×5 cm 2 . There is a hot plate at 80 °C under the polytetrafluoroethylene substrate.

[0059] 4) Post-treat the sample to obtain a waterborne polyurethane / silver microsphere self-adhesive composite film: Place the sprayed sample in a forced-air drying oven and dry it at 60 °C for 20 min, then slowly peel it off to obtain the composite film.

[0060] Performance testing of the composite film prepared in this example:

[0061] 1. Observe the structure of the waterborne polyurethane / silver microsphere self-adhesive composite film prepared in this example using a scanning electron microscope. As shown in Figure 2, before applying strain ( Figure 2a ), the sprayed silver microspheres are in physical contact with each other through lap joints, forming a conductive network. The stability of this network is poor and there are many gaps between the particles. Moreover, slight aggregation will cause initial microcracks to appear on the surface of the conductive layer, which means that a very small strain can break the original conductive network structure, endowing the strain sensor with the potential of high sensitivity. In addition, it can be clearly found that after applying a 5% strain ( Figure 2b ), the surface of the film is stretched and multiple cracks appear in the vertical direction, indicating that the generation of microcracks is the main reason for the destruction of the conductive network and the increase in resistance.

[0062] 2. Use a universal tensile testing machine to test the mechanical properties and adhesion properties of the waterborne polyurethane / silver microsphere self-adhesive composite film prepared in this example: The elongation at break of the film reaches 800% (as Figure 3 shown), and the adhesion force reaches 2.2 N / m (as Figure 4 shown);

[0063] 4. Use a universal tensile testing machine, a digital multimeter, and a mobile power supply to test the change in the resistance of the waterborne polyurethane / silver microsphere self-adhesive composite film prepared in this example with strain: For large strains such as finger bending (as Figure 5a shown) and wrist bending (as Figure 5b shown), the relative current of the waterborne polyurethane / silver microsphere self-adhesive film sensor can change regularly with movement. And for small strains, such as the small deformations of the abdomen during human breathing (as Figure 6a shown) and the neck pulse (as Figure 6b shown), it also has sensitive sensing performance.

[0064] Example 2

[0065] The waterborne polyurethane / silver microsphere self-adhesive composite film and its preparation method in this example, the specific operation steps are as follows:

[0066] 1) Prepare the first dispersion liquid using silver microspheres: Disperse 75 mg of silver microspheres into an equal-volume ratio solution of alcohol and water, and perform ultrasonic dispersion for 30 min;

[0067] 2) Prepare the second dispersion using D-sorbitol particles and aqueous polyurethane emulsion: Weigh a certain amount of D-sorbitol particles, dissolve them in deionized water, and stir magnetically for 10 min. Then, add the aqueous polyurethane emulsion and glycerol in sequence, and stir magnetically for 30 min to obtain a uniformly mixed solution. Among them, the mass concentration of D-sorbitol is 18.2 wt%, the mass concentration of aqueous polyurethane is 30 wt%, the mass concentration of glycerol is 5 wt%, and the magnetic stirring rate is 4000 r / min;

[0068] 3) Spray the first dispersion and the second dispersion onto a polytetrafluoroethylene substrate to prepare a sample: Spray the aqueous polyurethane emulsion with a mass concentration of 30 wt% onto the polytetrafluoroethylene substrate to form a first coating. Spray the first dispersion onto the surface of the first coating to form a second coating. Among them, the areal density of silver microspheres on the polytetrafluoroethylene substrate is 3 mg / cm 2 Spray the second dispersion onto the surface of the second coating to form a third coating. Among them, the spray gun is 15 cm away from the polytetrafluoroethylene substrate, and the size of the polytetrafluoroethylene substrate is 5×5 cm 2 There is a hot stage at 80 °C under the polytetrafluoroethylene substrate;

[0069] 4) Post-treat the sample to obtain an aqueous polyurethane / silver microsphere self-adhesive composite film: Place the sprayed sample in a blast drying oven and dry it at 60 °C for 20 min, and then slowly peel it off to obtain the composite film.

[0070] The properties of the aqueous polyurethane / silver microsphere self-adhesive composite film prepared in this example are basically equivalent to those of Example 1.

[0071] In other examples, in step 1), the ultrasonic dispersion time can also be 30 - 60 min.

[0072] In step 2), when dissolving the D-sorbitol particles in deionized water and stirring magnetically, the stirring time can also be 10 - 20 min, and the stirring rate can also be 2000 - 4000 r / min; then add the aqueous polyurethane emulsion and the glycerol in sequence, and the magnetic stirring time can also be 30 - 60 min, and the stirring rate can also be 2000 - 4000 r / min.

[0073] In step 4), the post-treatment conditions can also be drying at 50 - 70 °C for 20 - 40 min.

[0074] Comparative Example 1

[0075] The difference between the aqueous polyurethane / silver microsphere self-adhesive composite film of this comparative example and Example 1 is that the mass concentration of D-sorbitol when preparing the second dispersion is 26.1%, and the others are the same as in Example 1.

[0076] The mechanical properties and adhesion were tested using a universal tensile testing machine. The elongation at break of the waterborne polyurethane / silver microsphere self-adhesive composite film prepared by the method was 560% (as shown in FIG. 2 ). The network structure inside the waterborne polyurethane was affected and could not withstand greater tensile deformation. The average adhesion of the waterborne polyurethane / silver microsphere self-adhesive composite film prepared by the method was 0.75 N / m (as shown in FIG. Figure 3 As shown in the figure, only a small force is needed to destroy the integrity of the film and peel it off from the substrate, which cannot meet the adhesion requirements.

[0077] Comparative Example 2

[0078] The waterborne polyurethane / silver microsphere self-adhesive composite film of this comparative example is different from that of Example 1 in that when spraying the second coating, the surface density of the silver microspheres on the polytetrafluoroethylene substrate is controlled to be 1 mg / cm 2 , the rest is the same as Example 1.

[0079] The conductivity and were tested using a digital multimeter and a mobile power supply. The waterborne polyurethane / silver microsphere self-adhesive composite film prepared by this method was not conductive and could not meet the requirements of the sensor.

[0080] Comparative Example 3

[0081] The waterborne polyurethane / silver microsphere self-adhesive composite film of this comparative example is different from that of Example 1 in that when spraying the second coating, the surface density of the silver microspheres on the polytetrafluoroethylene substrate is controlled to be 5 mg / cm 2 , the rest is the same as Example 1.

[0082] A universal tensile testing machine, a digital multimeter and a mobile power supply were used to test the change in resistance of the waterborne polyurethane / silver microsphere self-adhesive composite film with strain. The waterborne polyurethane / silver microsphere self-adhesive composite film prepared by this method has low sensitivity to tiny deformations such as the abdomen and neck pulse during human breathing, because the conductive network is relatively complete at this time, and tiny deformations are not enough to destroy the conductive network. Therefore, tiny deformations cannot be detected and the high sensitivity requirements of the sensor cannot be met.

[0083] Comparative Example 4

[0084] The waterborne polyurethane / silver microsphere self-adhesive composite film of this comparative example is different from that of Example 1 in that no 80° C. heating stage is provided under the polytetrafluoroethylene substrate, and the rest is the same as that of Example 1.

[0085] It was observed that the droplets evaporated slowly and the silver microspheres were deposited during the solidification process, which could not meet the effect of uniform distribution of the silver microspheres.

[0086] Comparative Example 5

[0087] The difference between this comparative example's waterborne polyurethane / silver microsphere self-adhesive composite film and that of Example 1 is that the silver microspheres are evenly dispersed in deionized water, and the others are the same as in Example 1.

[0088] It was observed that the droplet evaporation was slow, and the silver microspheres were deposited during the curing process, failing to achieve the effect of uniform distribution of silver microspheres.

[0089] The preparation method of a waterborne polyurethane / silver microsphere self-adhesive composite film provided by the embodiments of the present invention has been introduced in detail above. Specific examples are used herein to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those skilled in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A preparation method of an aqueous polyurethane / silver microsphere self-adhesive composite film, characterized in that: Ultrasonically disperse silver microspheres in an organic solvent to prepare a first dispersion; Prepare a second dispersion using D-sorbitol particles and an aqueous polyurethane emulsion, and the mass concentration of D-sorbitol in the second dispersion is 10 wt% to 20 wt%; Spray the aqueous polyurethane emulsion onto a polytetrafluoroethylene substrate to form a first coating, and there is a hot stage at 80 °C under the polytetrafluoroethylene substrate; Spray the first dispersion onto the surface of the first coating to form a second coating, and then spray the second dispersion onto the surface of the second coating to form a third coating, thereby obtaining an aqueous polyurethane / silver microsphere self-adhesive composite film with a specific three-layer structure; The areal density of the silver microspheres on the polytetrafluoroethylene substrate is in the range of 2 to 4 mg / cm 2 ; Post-treat the sample to obtain an aqueous polyurethane / silver microsphere self-adhesive composite film.

2. The preparation method of the aqueous polyurethane / silver microsphere self-adhesive composite film according to claim 1, characterized in that, The areal density of the silver microspheres on the polytetrafluoroethylene substrate is 3 mg / cm 2 , and the mass concentration of the D-sorbitol is 18.2 wt%.

3. The preparation method of the aqueous polyurethane / silver microsphere self-adhesive composite film according to claim 1, wherein, The step of spraying the first dispersion onto the surface of the first coating to form a second coating includes: Transfer the first dispersion into a spray gun, the spray gun is 15 cm away from the polytetrafluoroethylene substrate, and slowly and evenly spray the first dispersion onto the surface of the first coating through the spray gun.

4. The preparation method of the aqueous polyurethane / silver microsphere self-adhesive composite film according to claim 1, characterized in that, The step of spraying the second dispersion onto the surface of the second coating to form a third coating includes: Transfer the second dispersion into a spray gun, the spray gun is 15 cm away from the polytetrafluoroethylene substrate, and slowly and evenly spray the second dispersion onto the surface of the second coating through the spray gun.

5. The preparation method of the aqueous polyurethane / silver microsphere self-adhesive composite film according to claim 3 or 4, characterized in that, The size of the polytetrafluoroethylene substrate is 5×5 cm 2 .

6. The preparation method of the aqueous polyurethane / silver microsphere self-adhesive composite film according to claim 1, characterized in that The step of preparing the first dispersion using silver microspheres includes: Ultrasonically disperse the silver microspheres in an organic solvent for 30 to 60 min to obtain the first dispersion.

7. The preparation method of the waterborne polyurethane / silver microsphere self-adhesive composite film according to claim 6, characterized in that, The organic solvent is a solution with an equal volume ratio of alcohol and water.

8. The preparation method of the aqueous polyurethane / silver microsphere self-adhesive composite film according to claim 1, characterized in that, The second dispersion also includes glycerol.

9. The preparation method of the waterborne polyurethane / silver microsphere self-adhesive composite film according to claim 8, wherein, The step of preparing the second dispersion includes: Dissolve the D-sorbitol particles in deionized water and magnetically stir for 10 to 20 min, and the stirring rate is 2000 to 4000 r / min; Then sequentially add the aqueous polyurethane emulsion and the glycerol, and magnetically stir for 30 to 60 min, and the stirring rate is 2000 to 4000 r / min to obtain the second dispersion.

10. The preparation method of the waterborne polyurethane / silver microsphere self-adhesive composite film according to claim 9, characterized in that, The mass concentration of the aqueous polyurethane is 30 wt%; the mass concentration of the glycerol is 5 wt%.

11. The preparation method of the waterborne polyurethane / silver microsphere self-adhesive composite film according to claim 1, wherein, The step of post-treating the sample to obtain an aqueous polyurethane / silver microsphere self-adhesive composite film includes: Cure the sample in a forced-air drying oven, dry it at 50 to 70 °C for 20 to 40 min, and obtain the aqueous polyurethane / silver microsphere self-adhesive composite film after peeling.

12. An aqueous polyurethane / silver microsphere self-adhesive composite film, characterized in that, The aqueous polyurethane / silver microsphere self-adhesive composite film is prepared by any of the preparation methods of claims 1-11.

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