Polyvinylidene fluoride film as well as preparation method and application thereof

Abstract

The invention belongs to the field of polymer films, and discloses a polyvinylidene fluoride film and a preparation method and application thereof, and the preparation method comprises the following steps: mixing dimethyl sulfoxide and polyvinylidene fluoride to obtain a polyvinylidene fluoride solution; the polyvinylidene fluoride solution is subjected to solvent curing, cleaning and drying, and the polyvinylidene fluoride film is obtained. According to the preparation method of the polyvinylidene fluoride film, the polyvinylidene fluoride film rich in polar phases is prepared in a solvent curing mode, and it is found through detection and comparison that compared with a polyvinylidene fluoride film obtained through solvent volatilization, the content of the polar phases in the polyvinylidene fluoride film obtained through the solvent curing mode is obviously increased. In addition, the thin film is formed by mutually connecting microspheres with uniform diameters. Meanwhile, the preparation method is simple in process and convenient to operate, the stable polyvinylidene fluoride film containing a large number of beta and gamma phase crystals can be prepared in a short time, and the method has the advantages of being low in reaction temperature, short in time and easy to industrialize.

Description

Technical Field

[0001] The invention belongs to the field of polymer films and relates to a polyvinylidene fluoride film and a preparation method and application thereof. Background Art

[0002] The functionalization of polymer film materials has always received widespread attention, and polymer materials with special properties have become the research focus. Among them, polyvinylidene fluoride (PVDF) has become a research hotspot due to its special properties. Polyvinylidene fluoride is a semi-crystalline polymer with polymorphs. The three most common crystal forms are α, β and γ. The β-PVDF crystal exists in an all-trans conformation (TTT conformation), and the unit cell contains polar zigzag chains, and the dipoles are arranged in parallel; while the molecular chains in the γ-PVDF crystal present a unique conformation of TTTGTTTG′. Both of these crystal forms of polyvinylidene fluoride exhibit excellent piezoelectric and ferroelectric effects, and therefore have been widely used in pressure-sensitive devices, humidity-sensitive devices, storage devices, and smart appliances.

[0003] In view of the excellent performance of β-crystalline and γ-crystalline polyvinylidene fluoride, how to efficiently prepare these two polar crystal forms has become the focus of current research. In order to obtain a high proportion of β-crystalline and γ-crystalline forms, researchers have tried a variety of methods, including stretching, blending and nano-composite. Among them, the stretching method changes the crystal structure of polyvinylidene fluoride through external force, causing it to transform into a polar crystal form; the blending method is to mix polyvinylidene fluoride with other polymers to promote the formation of polar crystal forms through interaction; the nano-composite method is to compound polyvinylidene fluoride with nanomaterials, and use the special properties of nanomaterials to induce polyvinylidene fluoride to form a polar crystal form.

[0004] These methods have improved the content of β-crystalline and γ-crystalline to a certain extent, but there are still some problems. On the one hand, the preparation steps of these preparation methods are relatively complicated and require precise control of various conditions such as temperature, pressure and time, which increases the difficulty and cost of preparation. On the other hand, the preparation process of these preparation methods is time-consuming and difficult to meet the needs of large-scale production. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art and provide a polyvinylidene fluoride film and a preparation method and application thereof.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a polyvinylidene fluoride film, comprising: mixing dimethyl sulfoxide and polyvinylidene fluoride to obtain a polyvinylidene fluoride solution; and solidifying the polyvinylidene fluoride solution with a solvent, washing and drying to obtain a polyvinylidene fluoride film.

[0008] Optionally, the mixing of dimethyl sulfoxide and polyvinylidene fluoride to obtain a polyvinylidene fluoride solution comprises: adding polyvinylidene fluoride to dimethyl sulfoxide and stirring the mixture uniformly at a rotation speed of 1000 to 5000 r / min to obtain a polyvinylidene fluoride solution.

[0009] Optionally, the stirring at a rotation speed of 1000-5000 r / min includes: stirring at a rotation speed of 1000-5000 r / min at 40-50° C.

[0010] Optionally, in the polyvinylidene fluoride solution, the mass fraction of polyvinylidene fluoride is 5% to 30%.

[0011] Optionally, the temperature during the solidification of the solvent is -100 to -20°C.

[0012] Optionally, solidifying the polyvinylidene fluoride solution comprises: placing the polyvinylidene fluoride solution on a glass sheet and solidifying the solvent in a vacuum oven.

[0013] Optionally, the cleaning includes: cleaning with deionized water for several times.

[0014] Optionally, placing the polyvinylidene fluoride solution on a glass sheet includes: casting the polyvinylidene fluoride solution on a glass sheet.

[0015] In a second aspect, the present invention provides a polyvinylidene fluoride film, which is prepared by the above-mentioned polyvinylidene fluoride film preparation method.

[0016] According to a third aspect of the present invention, there is provided a use of the polyvinylidene fluoride film in preparing a pressure-sensitive sensor, a humidity-sensitive sensor or a capacitor insulating film.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention discloses a method for preparing a polyvinylidene fluoride film, firstly, by mixing dimethyl sulfoxide and polyvinylidene fluoride to obtain a polyvinylidene fluoride solution; then, the polyvinylidene fluoride solution is subjected to solvent solidification, cleaning and drying to obtain a polyvinylidene fluoride film. The present invention prepares a polyvinylidene fluoride film rich in polar phase by solidifying the solvent. After detection and comparison, it is found that compared with the polyvinylidene fluoride film obtained by volatile solvent, the content of polar phase in the polyvinylidene fluoride film obtained by solidifying the solvent is significantly increased. At the same time, the preparation method is simple in process and easy to operate. A stable polyvinylidene fluoride film containing a large amount of β and γ phase crystals can be prepared in a relatively short time, and has the characteristics of low reaction temperature, short time and easy industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1Fourier transform infrared spectra of polyvinylidene fluoride films prepared by solvent curing and solvent volatilization according to the embodiments of the present invention.

[0020] Figure 2 Fourier transform infrared spectra of polyvinylidene fluoride films prepared from polyvinylidene fluoride solutions with different mass fractions according to an embodiment of the present invention.

[0021] Figure 3 X-ray diffraction spectra of polyvinylidene fluoride films prepared from polyvinylidene fluoride solutions with different mass fractions in the embodiments of the present invention.

[0022] Figure 4 This is an enlarged view of the Fourier transform infrared spectrum of the polyvinylidene fluoride film prepared from the polyvinylidene fluoride solution with different mass fractions in the embodiment of the present invention.

[0023] Figure 5 This is a graph showing the contents of different crystal forms in polyvinylidene fluoride films prepared from polyvinylidene fluoride solutions with different mass fractions according to an embodiment of the present invention.

[0024] Figure 6 This is a crystallinity diagram of polyvinylidene fluoride films prepared from polyvinylidene fluoride solutions with different mass fractions in an embodiment of the present invention.

[0025] Figure 7 This is a cross-sectional scan of a polyvinylidene fluoride film prepared in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0027] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0028] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0029] In one embodiment of the present invention, a method for preparing a polyvinylidene fluoride film is provided, specifically a method for preparing a polyvinylidene fluoride film rich in polar phase by solidifying a solvent. The method has the characteristics of low reaction temperature, short reaction time and easy industrialization, and can greatly reduce the difficulty of preparing a polyvinylidene fluoride film rich in polar phase.

[0030] Specifically, the method for preparing the polyvinylidene fluoride film of the present invention comprises the following steps:

[0031] Dimethyl sulfoxide and polyvinylidene fluoride are mixed to obtain a polyvinylidene fluoride solution; the polyvinylidene fluoride solution is subjected to solvent solidification, washing and drying to obtain a polyvinylidene fluoride film.

[0032] Explanatory, first, by mixing dimethyl sulfoxide and polyvinylidene fluoride powder, a uniform and stable polyvinylidene fluoride solution is obtained. This step is crucial, because dimethyl sulfoxide, as a polar solvent, can fully penetrate and dissolve polyvinylidene fluoride, ensuring that the polyvinylidene fluoride molecular chains in the solution are fully stretched, laying a solid foundation for the subsequent preparation of polyvinylidene fluoride film. Subsequently, this polyvinylidene fluoride solution is treated with a special curing solvent, which is the core of the present invention. By gradually curing the dimethyl sulfoxide in the polyvinylidene fluoride solution, rather than simply volatilizing it. This curing process helps the rearrangement and crystallization of the polyvinylidene fluoride molecular chains, forming a film structure rich in polar phases, and after subsequent cleaning and drying steps, a high-quality polyvinylidene fluoride film is finally obtained.

[0033] Compared with the traditional method of preparing polyvinylidene fluoride film by volatile solvents, the polar phase content in the polyvinylidene fluoride film obtained by curing the solvent is significantly increased. This is because during the curing process, the polyvinylidene fluoride molecular chain is driven by the gradual curing of the solvent and tends to form a polar phase (such as β and γ phase) crystal structure. These polar phase crystals have excellent piezoelectric, thermoelectric and ferroelectric properties, which makes the prepared polyvinylidene fluoride film have a wider application prospect.

[0034] In addition, the preparation method of the present invention has simple process and convenient operation, and does not require complex equipment or harsh experimental conditions. The entire preparation process can be completed in a relatively short time, greatly improving production efficiency. At the same time, due to the low reaction temperature and short time, not only energy is saved, but also energy consumption and carbon emissions in the production process are reduced, which conforms to the green and environmentally friendly production concept. More importantly, the polyvinylidene fluoride film preparation method of the present invention is easy to industrialize. The raw materials dimethyl sulfoxide and polyvinylidene fluoride used are common chemicals on the market, easy to obtain and relatively low in cost. Each step in the preparation process can be mass-produced by existing industrial equipment without the need for additional equipment investment or technical transformation. Therefore, the present invention has extremely high industrial application value and is expected to provide a more efficient way for the industrial production of polyvinylidene fluoride film.

[0035] In summary, the method for preparing a polyvinylidene fluoride film of the present invention prepares a polyvinylidene fluoride film rich in polar phase by means of a solidifying solvent. After detection and comparison, it is found that compared with the polyvinylidene fluoride film obtained by a volatile solvent, the polar phase content in the polyvinylidene fluoride film obtained by the solidifying solvent is significantly increased. At the same time, the preparation method is simple in process and easy to operate. It can prepare a stable polyvinylidene fluoride film containing a large amount of β and γ phase crystals in a relatively short time, and has the characteristics of low reaction temperature, short time and easy industrialization.

[0036] In a possible implementation, the mixing of dimethyl sulfoxide and polyvinylidene fluoride to obtain a polyvinylidene fluoride solution includes: adding polyvinylidene fluoride to dimethyl sulfoxide and stirring at a rotation speed of 1000 to 5000 r / min to obtain a polyvinylidene fluoride solution.

[0037] In a possible implementation manner, the stirring at a rotation speed of 1000 to 5000 r / min includes: stirring at a rotation speed of 1000 to 5000 r / min at 40 to 50° C.

[0038] In a possible implementation manner, in the polyvinylidene fluoride solution, the mass fraction of polyvinylidene fluoride is 5% to 30%.

[0039] In a possible implementation, the temperature during the solidification of the solvent is -100 to -20°C.

[0040] In a possible implementation, the solidifying the polyvinylidene fluoride solution comprises: placing the polyvinylidene fluoride solution on a glass sheet and solidifying the solvent in a vacuum oven.

[0041] In a possible implementation, the cleaning includes: cleaning with deionized water for several times.

[0042] In a possible implementation manner, placing the polyvinylidene fluoride solution on a glass sheet includes: casting the polyvinylidene fluoride solution on a glass sheet.

[0043] In another embodiment of the present invention, a polar polyvinylidene fluoride film is provided. Specifically, the polar polyvinylidene fluoride film is prepared by the above-mentioned polyvinylidene fluoride film preparation method.

[0044] In another embodiment of the present invention, there is provided an application of the polyvinylidene fluoride film in preparing a pressure-sensitive sensor, a humidity-sensitive sensor or a capacitor insulating film.

[0045] PVDF film is a piezoelectric material that has the ability to convert mechanical pressure into electrical signals. When an external force is applied to the surface of the PVDF film, the PVDF film will deform, and an internal force will interact between its internal parts, resulting in internal polarization and generating an internal electric field, which causes positive and negative charges to move to the two sides of the PVDF film, thereby realizing the conversion between mechanical energy and electrical energy. It can be used to make pressure-sensitive sensors, such as pressure sensors, acceleration sensors, and vibration sensors.

[0046] PVDF film has strong hydrophobicity and its static contact angle is much larger than 90°, which gives it a unique advantage in the field of humidity sensors. PVDF film can achieve sensitive response to humidity. When the humidity in the environment changes, the electrical properties of PVDF film (such as resistance, capacitance, etc.) will change accordingly, thereby achieving humidity measurement.

[0047] Polyvinylidene fluoride film has excellent insulation properties, can remain stable under high voltage, and is not prone to breakdown and leakage. It can be used as an insulating film for capacitors to improve the insulation performance and reliability of capacitors.

[0048] The following is a specific example to illustrate the method for preparing the polyvinylidene fluoride film of the present invention.

[0049] Example 1

[0050] Step 1: Using dimethyl sulfoxide as the solvent and polyvinylidene fluoride as the solute, according to the requirement that the mass fraction of polyvinylidene fluoride is 5%, 0.58g of polyvinylidene fluoride is added to 10mL of dimethyl sulfoxide, and magnetically stirred at 45°C and at a speed of 4000r / min to obtain a polyvinylidene fluoride solution with a mass fraction of 5% of polyvinylidene fluoride.

[0051] Step 2: Cast the polyvinylidene fluoride solution in step 1 on a glass sheet, ensuring that the solution evenly covers the surface of the glass sheet. Place the glass sheet cast with the polyvinylidene fluoride solution in a vacuum oven and set the temperature to -20°C. Solidify the solvent at -20°C, so that the solvent in the polyvinylidene fluoride solution gradually solidifies to form a stable film structure. Take out the solidified glass sheet and wash it with deionized water several times to completely remove the residual solvent. Place the washed glass sheet in a drying oven to dry and remove moisture to obtain a dry polyvinylidene fluoride film.

[0052] Example 2

[0053] Step 1: Using dimethyl sulfoxide as the solvent and polyvinylidene fluoride as the solute, according to the requirement that the mass fraction of polyvinylidene fluoride is 7%, 0.82g of polyvinylidene fluoride is added to 10mL of dimethyl sulfoxide, and magnetically stirred at 50°C and at a speed of 1000r / min to obtain a polyvinylidene fluoride solution with a mass fraction of 7% of polyvinylidene fluoride.

[0054] Step 2: Cast the polyvinylidene fluoride solution in step 1 on a glass sheet, ensuring that the solution evenly covers the surface of the glass sheet. Place the glass sheet cast with the polyvinylidene fluoride solution in a vacuum oven and set the temperature to -40°C. Solidify the solvent at -40°C, so that the solvent in the polyvinylidene fluoride solution gradually solidifies to form a stable film structure. Take out the solidified glass sheet and wash it with deionized water several times to completely remove the residual solvent. Place the washed glass sheet in a drying oven to dry and remove moisture to obtain a dry polyvinylidene fluoride film.

[0055] Example 3

[0056] Step 1: Using dimethyl sulfoxide as the solvent and polyvinylidene fluoride as the solute, according to the requirement that the mass fraction of polyvinylidene fluoride is 10%, 1.22g of polyvinylidene fluoride is added to 10mL of dimethyl sulfoxide, and magnetically stirred at 40°C and at a speed of 5000r / min to obtain a polyvinylidene fluoride solution with a mass fraction of 10% of polyvinylidene fluoride.

[0057] Step 2: Cast the polyvinylidene fluoride solution in step 1 on a glass sheet, ensuring that the solution evenly covers the surface of the glass sheet. Place the glass sheet cast with the polyvinylidene fluoride solution in a vacuum oven and set the temperature to -60°C. Solidify the solvent at -60°C, so that the solvent in the polyvinylidene fluoride solution gradually solidifies to form a stable film structure. Take out the solidified glass sheet and wash it with deionized water several times to completely remove the residual solvent. Place the washed glass sheet in a drying oven to dry and remove moisture to obtain a dry polyvinylidene fluoride film.

[0058] Example 4

[0059] Step 1: Using dimethyl sulfoxide as the solvent and polyvinylidene fluoride as the solute, according to the requirement that the mass fraction of polyvinylidene fluoride is 20%, 2.75g of polyvinylidene fluoride is added to 10mL of dimethyl sulfoxide, and magnetically stirred at 45°C and at a speed of 3000r / min to obtain a polyvinylidene fluoride solution with a mass fraction of 20% of polyvinylidene fluoride.

[0060] Step 2: Cast the polyvinylidene fluoride solution in step 1 on a glass sheet, ensuring that the solution evenly covers the surface of the glass sheet. Place the glass sheet cast with the polyvinylidene fluoride solution in a vacuum oven and set the temperature to -80°C. Solidify the solvent at -80°C, so that the solvent in the polyvinylidene fluoride solution gradually solidifies to form a stable film structure. Take out the solidified glass sheet and wash it with deionized water several times to completely remove the residual solvent. Place the washed glass sheet in a drying oven to dry and remove moisture to obtain a dry polyvinylidene fluoride film.

[0061] Example 5

[0062] Step 1: Using dimethyl sulfoxide as the solvent and polyvinylidene fluoride as the solute, according to the requirement that the mass fraction of polyvinylidene fluoride is 30%, 4.71g of polyvinylidene fluoride is added to 10mL of dimethyl sulfoxide, and magnetically stirred at 45°C and at a speed of 2000r / min to obtain a polyvinylidene fluoride solution with a mass fraction of polyvinylidene fluoride of 30%.

[0063] Step 2: Cast the polyvinylidene fluoride solution in step 1 on a glass sheet, ensuring that the solution evenly covers the surface of the glass sheet. Place the glass sheet cast with the polyvinylidene fluoride solution in a vacuum oven and set the temperature to -100°C. Solidify the solvent at -100°C, so that the solvent in the polyvinylidene fluoride solution gradually solidifies to form a stable film structure. Take out the solidified glass sheet and wash it with deionized water several times to completely remove the residual solvent. Place the washed glass sheet in a drying oven to dry and remove moisture to obtain a dry polyvinylidene fluoride film.

[0064] See also Figure 1 , shows the Fourier infrared spectra of polyvinylidene fluoride films prepared by solvent curing and solvent evaporation. Among them, the mass fraction of polyvinylidene fluoride in the polyvinylidene fluoride solution corresponding to the polyvinylidene fluoride film prepared by solvent curing is 5%. It can be seen from the figure that the polyvinylidene fluoride film prepared by solvent curing has a mass fraction of 5% at 1234 cm -1 The absorbance at 760 cm -1 and 796cm -1 The absorbance at the point is significantly reduced, indicating that compared with the polyvinylidene fluoride film prepared by solvent evaporation, the polar phase in the polyvinylidene fluoride film prepared by solvent curing has been significantly improved.

[0065] See also Figure 2 , shows the Fourier transform infrared spectra of the polyvinylidene fluoride films prepared in Examples 1 to 5. Figure 3 , shows the X-ray diffraction spectra of the polyvinylidene fluoride films prepared in Examples 1 to 5. Among them, 5%-P means that the mass fraction of polyvinylidene fluoride in the polyvinylidene fluoride solution is 5%; 7%-P means that the mass fraction of polyvinylidene fluoride in the polyvinylidene fluoride solution is 7%; 10%-P means that the mass fraction of polyvinylidene fluoride in the polyvinylidene fluoride solution is 10%; 20%-P means that the mass fraction of polyvinylidene fluoride in the polyvinylidene fluoride solution is 20%; 30%-P means that the mass fraction of polyvinylidene fluoride in the polyvinylidene fluoride solution is 30%. It can be seen that two polar crystal forms, β and γ, are generated in the polyvinylidene fluoride film prepared by solvent curing.

[0066] See Figure 4, which shows the enlarged Fourier transform infrared spectra of the polyvinylidene fluoride films prepared in Examples 1 to 5. It can be seen that as the mass fraction of polyvinylidene fluoride in the polyvinylidene fluoride solution increases, the CF bond gradually shifts to a lower wavenumber, which is caused by the weakening interaction between the solvent and the polyvinylidene fluoride. In addition, due to the strong interaction between the solvent and the polyvinylidene fluoride in the low mass fraction polyvinylidene fluoride solution, more β-crystals are formed in the polyvinylidene fluoride film. As the mass fraction increases, the β-crystal at 840 cm-1 is formed. -1 The infrared absorption peak at shifts to a lower wave number, indicating that a large amount of γ crystals are formed in the polyvinylidene fluoride film at this time.

[0067] See also Figure 5 , showing the contents of different crystal forms in the polyvinylidene fluoride films prepared in Examples 1 to 5. It can be clearly seen that with the increase of the mass fraction of polyvinylidene fluoride in the polyvinylidene fluoride solution, the content of β crystal form in the polyvinylidene fluoride film is gradually decreasing, while the content of γ crystal form is gradually increasing.

[0068] See also Figure 6 , showing the crystallinity of the polyvinylidene fluoride films prepared in Examples 1 to 5. It can be seen that the crystallinity of all polyvinylidene fluoride films is below 30%, which is due to the incomplete crystallization of polyvinylidene fluoride during the rapid solidification of the solvent. However, as the mass fraction of polyvinylidene fluoride in the polyvinylidene fluoride solution increases, the crystallinity of the prepared polyvinylidene fluoride film increases slightly.

[0069] See also Figure 7 , shows a cross-sectional scan of a polyvinylidene fluoride film prepared from a polyvinylidene fluoride solution in the embodiment. It can be seen that the polyvinylidene fluoride film is composed of round microspheres, and the diameters of the round microspheres are relatively uniform and connected to each other to form a complete film.

[0070] After testing and comparison, it was found that the content of polar phase in the polyvinylidene fluoride film prepared by solidifying solvent was significantly increased compared with the polyvinylidene fluoride film prepared by volatile solvent. The present invention prepares a polyvinylidene fluoride film rich in polar phase by solidifying solvent. In addition, the film is composed of microspheres with uniform diameters connected to each other. The preparation method is simple and easy to operate, and can prepare a stable polyvinylidene fluoride film containing a large amount of β and γ phase crystals in a relatively short time.

[0071] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a polyvinylidene fluoride film, characterized in that: include: mixing dimethyl sulfoxide and polyvinylidene fluoride to obtain a polyvinylidene fluoride solution; The polyvinylidene fluoride solution is subjected to solvent solidification, cleaning and drying to obtain a polyvinylidene fluoride film.

2. The method for preparing a polyvinylidene fluoride film according to claim 1, characterized in that: The mixing of dimethyl sulfoxide and polyvinylidene fluoride to obtain a polyvinylidene fluoride solution comprises: Add polyvinylidene fluoride into dimethyl sulfoxide and stir evenly at a rotation speed of 1000-5000 r / min to obtain a polyvinylidene fluoride solution.

3. The method for preparing a polyvinylidene fluoride film according to claim 2, characterized in that: The stirring at a speed of 1000 to 5000 r / min comprises: At 40-50°C, stir evenly at a speed of 1000-5000r / min.

4. The method for preparing a polyvinylidene fluoride film according to claim 1, characterized in that: In the polyvinylidene fluoride solution, the mass fraction of polyvinylidene fluoride is 5% to 30%.

5. The method for preparing a polyvinylidene fluoride film according to claim 1, characterized in that: The temperature of the solidifying solvent is -100 to -20°C.

6. The method for preparing a polyvinylidene fluoride film according to claim 1, characterized in that: The solvent for solidifying the polyvinylidene fluoride solution comprises: The polyvinylidene fluoride solution was placed on a glass slide and the solvent was cured in a vacuum oven.

7. The method for preparing a polyvinylidene fluoride film according to claim 1, characterized in that: The cleaning comprises: cleaning with deionized water for several times.

8. The method for preparing a polyvinylidene fluoride film according to claim 1, characterized in that: Placing the polyvinylidene fluoride solution on the glass sheet includes: casting the polyvinylidene fluoride solution on the glass sheet.

9. A polyvinylidene fluoride film, characterized in that: The polyvinylidene fluoride film is prepared by the method for preparing the polyvinylidene fluoride film described in any one of items 1 to 8 above.

10. Use of the polyvinylidene fluoride film according to claim 9 in preparing a pressure-sensitive sensor, a humidity-sensitive sensor or a capacitor insulating film.

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