Preparation method and application of piezoelectric film with adjustable microporous structure

Abstract

The invention provides a preparation method and application of a piezoelectric film with an adjustable microporous structure. The preparation method of the piezoelectric film comprises the following steps: placing a polymer raw material between functional films, carrying out hot pressing treatment, placing the obtained polymer film and a film fixing device in a pressure device together for foaming, removing the film fixing device, and carrying out corona charging treatment on the obtained film with a microporous structure to obtain the piezoelectric film. The obtained piezoelectric film is subjected to surface metallization, an electrode is led out, and a piezoelectric film transducer can be prepared. The piezoelectric film transducer prepared by the invention has the characteristics of high piezoelectric sensitivity, large working temperature interval, soft texture and convenience in large-area film forming application.

Description

Technical Field

[0001] The present invention belongs to the fields of electronic information technology and instrument technology, and particularly relates to a preparation method of a piezoelectric film with an adjustable microporous structure and application thereof. Background Art

[0002] In recent years, with the development of the Internet of Things (IoT) and the rapid evolution of automation and informatization, sensors have become indispensable to industrial development. Sensing technology, one of the three major components of next-generation information technology, is crucial to the development of the IoT and its applications, and a key foundational component for the growth of China's equipment manufacturing industry. Its role is increasingly recognized and valued by industry, the scientific community, the defense and military industries, and government decision-making bodies.

[0003] The transducer is the core of the sensor input part. It can be divided into ten categories based on the sensing function, including thermal sensors, light sensors, force sensors, and sound sensors. Among them, pressure sensors composed of force sensors account for the largest share in the sensor market.

[0004] Films with microporous structures based on certain polymers can exhibit piezoelectric activity after appropriate processing. Their piezoelectric properties stem from the ability of the film's internal microporous structure to capture and store positive and negative charges on the upper and lower surfaces of the pore walls, as well as the difference in Young's modulus across the thickness. For example, porous polypropylene (PP) piezoelectric films, a typical piezoelectric film, are porous structures formed through chemical or physical foaming processes. These films possess the high-voltage electrical activity of piezoelectric ceramic transducers, while also possessing the flexibility, low dielectric constant, and low acoustic impedance that piezoelectric ceramic transducers lack. These films can be easily formed over large areas, and their low cost and environmental friendliness make them promising for broad application in sensors. However, due to the inherent thermal stability of porous polypropylene (such as IXPP) piezoelectric films, their piezoelectric activity decreases as their charge storage performance decays when the operating temperature exceeds 60°C, limiting their application. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the aforementioned prior art by providing a method for preparing a piezoelectric film with an adjustable microporous structure and its application. The preparation of the piezoelectric film with an adjustable microporous structure in the present invention comprises the preparation of a polymer film, the preparation and adjustment of the film's microporous structure, and corona charging of the film. The resulting film is then subjected to surface metallization to produce a piezoelectric film transducer.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The present invention provides a method for preparing a piezoelectric film with an adjustable microporous structure, the preparation method comprising the following steps:

[0008] S1, placing the polymer raw material between the functional films and performing heat pressing to obtain a polymer film;

[0009] S2, placing the polymer film together with the film fixing device in a pressure device, filling it with gas and then allowing it to stand for a while, then performing foaming by reducing the pressure or increasing the temperature, and removing the film fixing device to obtain a film with a microporous structure;

[0010] S3. Performing corona charging treatment on the film containing the microporous structure to obtain a piezoelectric film.

[0011] As an embodiment of the present invention, in step S1, the polymer raw material is polymer particles or mixed particles comprising a polymer and a filler.

[0012] The polymer includes one or more of a cycloolefin polymer and a cycloolefin copolymer.

[0013] The cycloolefin polymers and copolymers used in this invention possess only electrical storage properties, not piezoelectric properties. The microporous structure formed during the foaming process imparts piezoelectric properties after corona charging treatment. Furthermore, they exhibit excellent electrothermal stability, effectively ensuring the performance of the resulting piezoelectric film. While other materials, such as polypropylene film, experience a sharp drop in charge thermal stability above 60°C, the electrothermal stability of the cycloolefin polymers / copolymers of this invention can be controlled to maintain between 90°C and 120°C.

[0014] The filler includes silicon dioxide. The present invention can improve the mechanical properties and processing properties of the film through such modification of the filler, but other fillers need to be selected without affecting its electrical storage properties.

[0015] As one embodiment of the present invention, in step S1, the pressure of the hot pressing treatment is 1 to 50 MPa, the temperature of the hot pressing treatment is 0 to 350° C., preferably 100° C. to 240° C., and the time of the hot pressing treatment is 1 second to 60 minutes, preferably 2 to 10 minutes. Hot pressing treatment can produce a dense film.

[0016] As an embodiment of the present invention, in step S1 , the thickness of the polymer film is 10 to 300 μm, preferably 30 to 200 μm.

[0017] As an embodiment of the present invention, in step S2, the film fixing device includes a functional film and / or a clamp. The film fixing device limits the foaming in the thickness direction of the film (perpendicular to the functional film or the clamp) to obtain flat micropores.

[0018] Method for using the functional film: During the hot pressing treatment in step S1, the polymer film and the functional films on both sides form a composite film, and the composite film is placed in a pressure device for foaming treatment.

[0019] Method for using the fixture: During the hot pressing treatment in step S1, the polymer film or composite film (polymer film and functional films on both sides) is placed in the fixture, and then placed in the pressure device for foaming treatment.

[0020] During the hot pressing process, a polymer film can also be prepared with the aid of a mold, with the functional film being placed on the upper and lower surfaces of the mold.

[0021] In conventional foaming film preparation, the function of the functional film is to prevent the film from sticking to the equipment (mold release). The functional film or fixture of the present invention plays a shaping role in the pressure device, ensuring the flatness of the film surface, and can also serve as a gas barrier film during the foaming process. During conventional foaming (without a film fixing device), the micropore foaming process is unconstrained, and the micropores formed are circular. However, during foaming of the present invention, the thickness direction of the micropores (perpendicular to the direction of the functional film or fixture) is constrained, so the micropores formed are not circular, and most are flat, such as elliptical.

[0022] As an embodiment of the present invention, in step S2, the pressure device is a reactor.

[0023] As an embodiment of the present invention, in step S2, the gas includes one or more of carbon dioxide and nitrogen.

[0024] As an embodiment of the present invention, in step S2, the parameters of the pressure reduction and foaming step are: the pressure after filling with gas is 1 to 50 MPa, preferably 10 to 30 MPa; the temperature during static soaking is 50 to 350°C, preferably 80 to 220°C, and the static soaking time is 1s to 1440min, preferably 20min to 1440min; after static soaking, the pressure is reduced and exhausted to atmospheric pressure, and the exhaust time is 0.1 to 10min.

[0025] As one embodiment of the present invention, the pressure-reduced foaming process in step S2 can be repeated 1-3 times. This repeated process involves placing the foamed polymer film containing the film-fixing device back into the pressure device, filling it with gas, and allowing it to rest. After this rest, the pressure-reduced foaming process is repeated again. Multiple pressure-reduced foaming cycles produce better results. The resting time for foaming is generally determined by the thickness of the substrate, but the introduction of the functional film and / or fixture can result in a longer pressure-reduced foaming time.

[0026] As an embodiment of the present invention, in step S2, the parameters of the temperature-raising foaming step are: the pressure after filling with gas is 3-10 MPa, preferably 4-6 MPa, the temperature during static soaking is 30-50°C, preferably 30-50°C, and the static soaking time is 1s-1440min, preferably 20min-1440min; after static soaking, the pressure is reduced and exhausted to atmospheric pressure for 0.1-10min; after depressurization and exhaust, oil bath treatment is performed, the temperature of the oil bath treatment is 50-350°C, preferably 100-240°C, and the time of the oil bath treatment is 1s-10min, preferably 5s-120s.

[0027] Supercritical foaming is a physical foaming method for creating microporous structures. Compared to chemical foaming, it avoids the degradation of the electret's electrical storage properties caused by residual chemical foaming. During the foaming process, supercritical CO2 is first dissolved into the film. The formation of the cellular structure is induced by changes in external conditions (temperature / pressure). Adjusting the parameters of the foaming process can adjust the number and morphology of the pores to a certain extent.

[0028] As an embodiment of the present invention, in step S2, the thickness of the polymer film containing a microporous structure is 10-1000 μm, preferably 100-500 μm.

[0029] In one embodiment of the present invention, in step S2, the microporous structure of the polymer film containing a microporous structure is flat (circular or elliptical) micropores. The flat micropores have a thickness of 5-100 μm, preferably 10-40 μm, and an aspect ratio of 1:2 to 1:10. The film of the present invention can exhibit enhanced piezoelectric properties after corona charging treatment and surface metallization.

[0030] As one embodiment of the present invention, in step S3, the corona charging process is as follows: the prepared film containing a microporous structure is placed on a metal electrode, and an electroacupuncture is placed above the film, the electroacupuncture being connected to a DC high voltage source to perform a corona treatment. The corona treatment can be performed under the condition of heating the metal electrode. During the treatment process, a metal grid can be used between the corona electrode and the film having the microporous structure, and the bias applied to the metal grid makes the charging more uniform, or the metal grid can be omitted for control.

[0031] Corona charging conditions: charging voltage ±1~100kV, preferably ±20~40kV, more preferably negative charge, charging temperature 50~350℃, preferably 100℃-240℃, charging time 1~300s, preferably 60s~120s, repeatedly rechargeable, electric needle-film distance 1~20cm, preferably 8cm~12cm, metal grid-film distance 1~50cm, preferably 1-2cm, metal grid voltage (DC low voltage source) is -100~+100kV, preferably ±0~10kV]. Corona charging treatment is performed under the condition of heating the metal electrode, so that the upper and lower surfaces of the microporous structure inside the polymer film respectively store positive and negative charges, the charge distribution is uniform, and the charge thermal stability is better.

[0032] The present invention also provides an application of the piezoelectric film in preparing a transducer.

[0033] The present invention also provides a method for preparing the transducer, comprising the steps of metallizing the surface of the piezoelectric film and extending electrodes to obtain a piezoelectric film transducer. The resulting piezoelectric film can be connected to a circuit through surface metallization (electrode plating) to facilitate processing of electrical signals converted by the piezoelectric effect, thereby obtaining meaningful information for use as a sensor transducer.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] 1) The piezoelectric thin film transducer substrate of the present invention has good electrothermal stability, which can significantly broaden the application range of pressure sensors prepared based on this material in application scenarios;

[0036] 2) The piezoelectric thin film transducer of the present invention has high piezoelectric activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0038] Figure 1 It is a schematic diagram of the process and structure when using a mold for hot pressing treatment;

[0039] Figure 2 This is a schematic diagram of the process and structure when hot pressing is performed without using a mold;

[0040] Figure 3 Schematic diagram of a polymer film with functional films on both sides;

[0041] Figure 4 Schematic diagram of a polymer film without a functional membrane;

[0042] Figure 5A schematic diagram of a fixture used in the present invention;

[0043] Figure 6 Schematic diagram of the microporous structure of the polymer film of Example 1 of the present invention and Comparative Example 2;

[0044] Figure 7 Schematic diagram of the structure of the piezoelectric thin film transducer of the present invention;

[0045] Figure 8 Schematic diagram of the quasi-static sensitivity testing device of the present invention;

[0046] Figure 9 The figure shows the quasi-static sensitivity comparison of the embodiment of the present invention, the comparative example and the commonly used piezoelectric polymer film (PVDF, IXPP).

[0047] The numbers in the figure show:

[0048] 1. Functional film (mold release), 2. Mold, 3. Polymer particles A, 4. Polymer film, 5. Cross-section of polymer film, 6. Functional film (gas barrier), 7. Polymer particles B, 8. Composite film, 9. Cross-section of composite film, 10. Fixture, 11. Polymer film containing circular microporous structure, 12. Cross-section of polymer film containing circular microporous structure, 13. Composite film containing flat microporous structure, 14. Cross-section of composite film containing flat microporous structure, 15. Film after surface metallization treatment, 16. Cross-section of film after surface metallization treatment, 17. Upper electrode (positive electrode), 18. Lower electrode (negative electrode), 19. DuPont wire (positive electrode), 20. DuPont wire (negative electrode). DETAILED DESCRIPTION

[0049] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments described are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0050] The preparation of a piezoelectric thin film transducer with a controllable microporous structure in the present invention includes four steps: preparing a polymer film, preparing and controlling the film's microporous structure, corona charging the film, and metallizing the film's surface. The polymer film is prepared by hot-pressing polymer particles (cycloolefin polymer / cycloolefin copolymer) or polymer particles mixed with a filler (silicon dioxide) to obtain the polymer film. The hot-pressing parameters used are pressure (1-50 MPa) and processing time (0.1-60 minutes).

[0051] The preparation and control process of the film microporous structure in the present invention is as follows: the prepared polymer film / composite film and / or fixture is placed in a reactor, filled with one or more types of gases such as carbon dioxide and nitrogen, and the reactor is heated. After a period of static soaking, the sample is exhausted and taken out to obtain a polymer film containing a microporous structure. The treatment conditions are (gas pressure 1~50MPa, reactor temperature 50~350℃, static soaking time 1~1440min, exhaust time 0.1~10min); the prepared polymer film / composite film is placed in a reactor, filled with one or more types of gases such as carbon dioxide and nitrogen, and the reactor is heated. After a period of static soaking, the sample is exhausted and taken out, and the sample is subjected to oil bath treatment to obtain a polymer film containing a microporous structure. The treatment conditions are (gas pressure 3~10MPa, reactor temperature 50~350℃, static soaking time 1~1440min, exhaust time 0.1~10min, oil bath treatment temperature 50~350℃, oil bath treatment time 0.1~10min).

[0052] The corona charging process of the polymer film containing a microporous structure in the present invention is as follows: placing the prepared microporous polymer film on a metal electrode, placing an electric needle above the film, connecting the electric needle to a DC high-voltage source, placing a metal grid with a DC low-voltage source below the electric needle, and performing corona charging under the condition of heating the metal electrode. The corona charging conditions are as follows: charging voltage of ±1 to 100 kV, charging temperature of 50 to 350° C., charging time of 1 to 300 s, electric needle-film distance of 1 to 20 cm, metal grid-film distance of 1 to 50 cm, and metal grid voltage (DC low-voltage source) of -100 to +100 kV.

[0053] The working principle of the present invention is:

[0054] Through corona polarization, the gas in the microporous structure inside the film is broken down. Under the action of the electric field, positive and negative charges can be captured and stored on the upper and lower surfaces of the pore walls of the microporous structure inside the film respectively. Due to the difference in Young's modulus in the thickness direction, the amount of induced charge on the electrode changes during the deformation of the film, and then an electrical signal is generated in the external circuit, realizing the conversion of mechanical signals into electrical signals or electrical energy, which is the piezoelectric effect. It can be used in micro-vibration sensors, acoustic sensors, micro-energy harvesters, etc. Conversely, the deformation of the film can be caused by external current, which is the inverse piezoelectric effect. It can be used as a transducer device in electroacoustic sensors such as speakers.

[0055] Comparative Examples 1 and 2 of the present invention are compared with Example 1 to illustrate the role of flat pores in the piezoelectric film. Examples 1 and 2 compare single and multiple foaming methods using a clamp, Examples 1 and 3 compare two foaming methods, Examples 1, 4, and 5 compare mold clamps and functional membranes (gas barrier), and Examples 4 and 6 compare different materials. Specific conditions are shown in Table 1:

[0056] Table 1

[0057] polymer Using a mold Film fixing device Foaming method Example 1 Cyclic olefin polymers yes fixture Blood pressure reduction / 1 time Example 2 Cyclic olefin polymers yes fixture Blood pressure reduction / 2 times Example 3 Cyclic olefin polymers yes fixture Warming up Example 4 Cyclic olefin polymers no Functional Film Blood pressure reduction / 1 time Example 5 Cyclic olefin polymers yes Functional Film Blood pressure reduction / 1 time Example 6 Cyclic olefin copolymer no Functional Film Blood pressure reduction / 1 time Comparative Example 1 Cyclic olefin polymers yes none Unfoamed Comparative Example 2 Cyclic olefin polymers yes none Blood pressure reduction / 1 time

[0058] Example 1 (Mold + fixture + one-time pressure reduction foaming)

[0059] The specific preparation process is:

[0060] (1) Figure 1 As shown, cycloolefin polymer particles A3, mold 2 and functional film (release) 1 (500 μm, to prevent the prepared film from sticking to the equipment) are used. The polymer particles A3 are placed in a sandwich structure of functional film (release) 1-mold 2-functional film (release) 1, and are placed in a hot pressing device for preheating for 30 minutes. The polymer particles are then processed using a hot pressing device (hot pressing parameters: 160°C, pressure: 5 MPa, hot pressing time: 2 min). After demolding, the polymer film is separated from the functional film (release) 1, and the polymer film 4 is taken out, as shown. Figure 4 As shown (polymer film cross section Figure 5 , non-functional film (mold release) 1, area 6cm*6cm, thickness 50μm).

[0061] (2) Place the polymer film 4 prepared in (1) on a Figure 5 The fixture 10 shown is placed in a reactor as a whole and preheated for 30 minutes. Carbon dioxide gas is injected into the reactor (control parameters, temperature 140°C, gas pressure 20 MPa). After static treatment for 30 minutes, the gas is discharged (gas discharge time 10 seconds). After the gas pressure drops to atmospheric pressure, the sample is taken out to obtain a polymer film with a flat microporous structure (thickness 125 μm).

[0062] (3) The polymer film with a flat microporous structure prepared in (2) was charged by corona poling (charging parameters: corona voltage: -40 kV, charging time: 120 s, charging temperature 120 ° C, and needle-film distance 10 cm) to obtain a uniformly polarized piezoelectric film with a flat microporous structure, such as Figure 6 As shown in the figure below.

[0063] (4) The upper and lower surfaces of the piezoelectric film with a flat microporous structure prepared in (3) are subjected to surface metallization treatment (aluminum layer, thickness 150 nm) by vacuum evaporation equipment to obtain an upper electrode (positive electrode) 17 and a lower electrode (negative electrode) 18, and a film 15 after surface metallization treatment is prepared, as shown in FIG. Figure 7 As shown (film section 16 after surface metallization treatment).

[0064] (5) Figure 7As shown, using DuPont wire (positive electrode) 19 and DuPont wire (negative electrode) 20, electrodes are drawn out from the upper and lower surfaces of the film 15 after surface metallization treatment in (4), thereby obtaining a transducer that can be used in a pressure sensor.

[0065] In this example, the thickness of the microporous structure of the film (average / maximum number of pores) is about 25 μm, and the circular pores have an aspect ratio of 1:4. The transducer has a piezoelectric effect after corona poling and surface metallization treatment.

[0066] Example 2 (mold + fixture + two pressure reduction foaming)

[0067] The specific preparation process is:

[0068] (1) Figure 1 As shown, cycloolefin polymer particles A3, mold 2 and functional film (release) 1 (500 μm, to prevent the prepared film from sticking to the equipment) are used. The polymer particles A3 are placed in a sandwich structure of functional film (release) 1-mold 2-functional film (release) 1, and are placed in a hot pressing device for preheating for 30 minutes. The polymer particles are then processed using a hot pressing device (hot pressing parameters: 160°C, pressure: 5 MPa, hot pressing time: 2 min). After demolding, the polymer film is separated from the functional film (release) 1, and the polymer film 4 is taken out, as shown. Figure 4 As shown (polymer film cross section Figure 5 Non-functional film (mold release) 1, area 6cm*6cm, thickness 50μm).

[0069] (2) Place the polymer film 4 prepared in (1) on a Figure 5 In the fixture 10 shown, the tightness of the fixture is adjusted, and then the whole is placed in a reactor for preheating for 30 minutes, and carbon dioxide gas is injected into the reactor (control parameters, temperature 140°C, gas pressure 20MPa). After static treatment for 30 minutes, the gas is discharged (gas discharge time 10s), and the sample is taken out after the gas pressure drops to atmospheric pressure to obtain a polymer film with a microporous structure.

[0070] (3) Adjust the clamp 10 in (2) to make it tighter, and repeat process (2) once to obtain a polymer film with a flat microporous structure.

[0071] (4) The polymer film with a flat microporous structure prepared in (3) was charged by corona poling (charging parameters: corona voltage: -40 kV, charging time: 120 s, charging temperature 120°C, and electric needle-film distance 10 cm) to obtain a uniformly polarized film with a flat microporous structure.

[0072] (5) The upper and lower surfaces of the thin film with a flat microporous structure prepared in (4) are subjected to surface metallization treatment respectively by vacuum evaporation equipment to obtain an upper electrode (positive electrode) 17 and a lower electrode (negative electrode) 18, thereby preparing a thin film 15 after surface metallization treatment.

[0073] (6) Using DuPont wire (positive electrode) 19 and DuPont wire (negative electrode) 20, electrodes are drawn from the upper and lower surfaces of the film 15 after the surface metallization treatment in (5), thereby obtaining a transducer that can be used in a pressure sensor. The other structures and operating principles of this embodiment are the same as those of Example 1.

[0074] In this example, the thickness of the microporous structure of the film is about 25 μm, and the circular holes have an aspect ratio of 1:5. The transducer has a piezoelectric effect after corona poling and surface metallization treatment.

[0075] Example 3 (Mold + fixture + heating foaming)

[0076] The specific preparation process is:

[0077] (1) Figure 1 As shown, cycloolefin polymer particles A3, mold 2 and functional film (release) 1 (500 μm, to prevent the prepared film from sticking to the equipment) are used. The polymer particles A3 are placed in a sandwich structure of functional film (release) 1-mold 2-functional film (release) 1, and are placed in a hot pressing device for preheating for 30 minutes. The polymer particles are then processed using a hot pressing device (hot pressing parameters 160° C., pressure 5 MPa, hot pressing time 2 min). After demolding, the polymer film is separated from the functional film (release) 1, and the polymer film 4 is taken out, as shown. Figure 4 As shown (polymer film cross section Figure 5 Non-functional film (mold release) 1, area 6cm*6cm, thickness 50μm).

[0078] (2) Place the polymer film 4 prepared in (1) on a Figure 5 The fixture 10 shown is placed in a reactor as a whole and preheated for 30 minutes. Carbon dioxide gas is injected into the reactor (control parameters, temperature 40°C, gas pressure 5MPa), and the gas is discharged after static treatment for 30 minutes (gas discharge time 10s). After the gas pressure drops to atmospheric pressure, the sample is taken out and the sample is treated with an oil bath (control parameters, oil bath temperature 140°C, oil bath time 20s) to obtain a film with a flat microporous structure.

[0079] (3) The polymer film with a flat microporous structure prepared in (2) is charged by corona poling (charging parameters: corona voltage: -40 kV, charging time: 120 s, charging temperature 120°C, electric needle-film distance 10 cm) to obtain a uniformly polarized piezoelectric film with a flat microporous structure.

[0080] (4) The upper and lower surfaces of the piezoelectric film with a flat microporous structure prepared in (3) are subjected to surface metallization treatment by vacuum evaporation equipment to obtain an upper electrode (positive electrode) 17 and a lower electrode (negative electrode) 18, and a film 15 after surface metallization treatment is prepared, as shown in FIG. Figure 7 As shown (film section 16 after surface metallization treatment).

[0081] (5) Figure 7 As shown, using DuPont wire (positive electrode) 19 and DuPont wire (negative electrode) 20, electrodes are drawn out from the upper and lower surfaces of the film 15 after surface metallization treatment in (4), thereby obtaining a transducer that can be used in a pressure sensor.

[0082] The thickness of the microporous structure of the film in this example is about 25 μm, and the circular holes have an aspect ratio of 1:4. The transducer has a piezoelectric effect after corona poling and surface metallization treatment.

[0083] Example 4 (no mold + functional film + 1 pressure reduction foaming)

[0084] The specific preparation process is:

[0085] (1) Figure 2 As shown, cycloolefin polymer particles B7 and functional film (gas barrier) 6 (40 μm, used as a gas barrier film and to prevent the prepared film from sticking to the equipment) are used. The polymer particles B7 are placed between the functional film (gas barrier) 6 and the functional film (gas barrier) 6, and after being preheated in a hot pressing device for 30 minutes, the polymer particles are processed using the hot pressing device (hot pressing parameters 160°C, pressure 5 MPa, hot pressing time 2 min), and a composite film 8 comprising the functional film (gas barrier) 6-polymer film-functional film (gas barrier) 6 is taken out, as shown Figure 3 As shown (composite membrane section Figure 9 , area 6cm*6cm, thickness 120μm).

[0086] (2) The composite membrane 8 prepared in (1) was placed in a reactor and preheated for 30 minutes. Nitrogen was injected into the reactor (control parameters: temperature 140°C, gas pressure 20 MPa). After static treatment for 360 minutes, the gas was exhausted (gas exhaust time 10 s). After the gas pressure dropped to atmospheric pressure, the sample was taken out to obtain a composite membrane 13 with a flat microporous structure. The polymer film in the composite membrane 13 containing the flat microporous structure was separated from the functional membrane (gas barrier) 6 to obtain a film with a flat microporous structure, such as Figure 6 As shown in the figure below (cross section 14 of the composite membrane containing a flat microporous structure).

[0087] (3) The thin film with a flat microporous structure prepared in (2) was charged by corona poling (charging parameters: corona voltage: -40 kV, charging time: 120 s, charging temperature 120°C, and electric needle-film distance 10 cm) to obtain a uniformly polarized thin film with a microporous structure.

[0088] (4) The upper and lower surfaces of the thin film with a flat microporous structure prepared in (3) are subjected to surface metallization treatment respectively by vacuum evaporation equipment to obtain an upper electrode 17 and a lower electrode 18, thereby obtaining a thin film 15 after surface metallization treatment.

[0089] (5) Using DuPont wires 19 and 20, electrodes are drawn from the upper and lower surfaces of the metallized film 15 in (4), thereby obtaining a transducer that can be used in a pressure sensor. The rest of the structure and operating principle of this embodiment are the same as those of embodiment 1.

[0090] The thickness of the microporous structure of the film in this example is about 15 μm, and the flat pores have an aspect ratio of 1:3. The transducer has a piezoelectric effect after corona poling and surface metallization treatment.

[0091] Example 5 (mold + functional film + 1 pressure reduction foaming)

[0092] The specific preparation process is:

[0093] (1) Figure 1 As shown, cycloolefin polymer particles A3, mold 2 and functional film (release) 1 (40 μm, to prevent the prepared film from sticking to the equipment) are used, and the polymer particles A3 are placed in a sandwich structure of functional film (release) 1-mold 3-functional film (release) 1. After being preheated in a hot pressing device for 30 minutes, the polymer particles are processed using a hot pressing device (hot pressing parameters 120°C, pressure 5 MPa), and the polymer film 4 (area 6 cm*6 cm, thickness 130 μm) is taken out after demolding.

[0094] (2) The polymer film 4 prepared in (1) was placed in a reactor and preheated for 30 minutes. Carbon dioxide gas was injected into the reactor (control parameters: temperature 140°C, gas pressure 20 MPa). After static treatment for 360 minutes, the gas was discharged (gas discharge time 10 seconds). After the gas pressure dropped to atmospheric pressure, the sample was taken out to obtain a film 11 with a microporous structure.

[0095] (3) The film 11 with a microporous structure prepared in (2) was charged by corona poling (charging parameters: corona voltage: +60 kV, charging time: 120 s, metal grid voltage: +10 kV, charging temperature 180° C., electric needle-film distance 10 cm, metal grid-film distance 1 cm) to obtain a uniformly polarized film with a microporous structure. The film 13 with a microporous structure was obtained, as shown in FIG. Figure 6 As shown in the figure below (cross section 14 of the composite membrane containing microporous structure).

[0096] (4) The upper and lower surfaces of the thin film with a microporous structure prepared in (3) are subjected to surface metallization treatment by vacuum evaporation equipment to obtain an upper electrode 17 and a lower electrode 18, and a surface metallized thin film 15 is prepared.

[0097] (5) Using DuPont wires 19 and 20, electrodes are drawn from the upper and lower surfaces of the microporous structure film 15 with surface metallization treatment in (4), thereby obtaining a transducer that can be used in a pressure sensor. The other structures and operating principles of this embodiment are the same as those of Example 1.

[0098] The thickness of the microporous structure of the film in this example is about 15 μm, and the flat pores have an aspect ratio of 1:3. The transducer has a piezoelectric effect after corona poling and surface metallization treatment.

[0099] Example 6 (no mold + functional film + 1 pressure reduction foaming)

[0100] The specific preparation process is:

[0101] (1) Using cycloolefin copolymer particles B7 and functional film 6 (40 μm, used as a gas barrier film and to prevent the prepared film from sticking to the equipment), the polymer particles B7 were placed between functional film 6 and functional film 6, and placed in a hot pressing device for preheating for 30 minutes. The polymer particles were then processed using a hot pressing device (hot pressing parameters 160°C, pressure 5 MPa, hot pressing time 2 min), and a composite film 8 (area 6 cm*6 cm, thickness 120 μm) comprising functional film 6-polymer film-functional film 6 was taken out.

[0102] (2) The composite membrane 8 prepared in (1) was placed in a reactor and preheated for 30 minutes, and nitrogen was injected into the reactor (control parameters, temperature 140°C, gas pressure 20 MPa). The gas was discharged after static treatment for 360 minutes (gas discharge time 10 s). After the gas pressure dropped to atmospheric pressure, the sample was taken out to obtain a composite membrane with a flat microporous structure, and the polymer film and the functional membrane in the composite membrane containing the flat microporous structure were separated to obtain a film with a flat microporous structure.

[0103] (3) The thin film with a flat microporous structure prepared in (2) was charged by corona poling (charging parameters: corona voltage: -40 kV, charging time: 120 s, charging temperature 120°C, and electric needle-film distance 10 cm) to obtain a uniformly polarized thin film with a microporous structure.

[0104] (4) The upper and lower surfaces of the thin film with a flat microporous structure prepared in (3) are subjected to surface metallization treatment respectively by vacuum evaporation equipment to obtain an upper electrode and a lower electrode, thereby obtaining a thin film after surface metallization treatment.

[0105] (5) Using DuPont wire and DuPont wire, electrodes are drawn from the upper and lower surfaces of the film after surface metallization treatment in (4) to obtain a transducer that can be used in a pressure sensor. The other structures and working principles of this embodiment are the same as those of embodiment 1.

[0106] Comparative Example 1 (Mold + Non-functional Film + No Foaming)

[0107] The specific preparation process is:

[0108] (1) Figure 1 As shown, cycloolefin polymer particles A3, mold 2 and functional film (demolding) 1 (to prevent the prepared film from sticking to the equipment) are used, and the polymer particles A3 are placed in a sandwich structure of functional film (demolding) 1-mold 2-functional film (demolding) 1. After being preheated in a hot pressing device for 30 minutes, the polymer particles are processed using a hot pressing device (hot pressing parameters 160°C, pressure 5MPa, hot pressing time 2min). After demolding, the polymer film is separated from the functional film (demolding) 1, and the polymer film 4 (without functional film (demolding) 1, area 6cm*6cm, thickness 50μm) is taken out.

[0109] (2) The polymer film 4 prepared in (1) was charged by corona poling (charging parameters: corona voltage: -40 kV, charging time: 120 s, charging temperature 120° C., and electric needle-film distance 10 cm) to obtain a piezoelectric film.

[0110] (3) The upper and lower surfaces of the polymer film 4 prepared in (3) are subjected to surface metallization treatment respectively by vacuum evaporation equipment to obtain an upper electrode and a lower electrode, thereby preparing a surface metallized film.

[0111] (4) Using DuPont wire and DuPont wire, electrodes are drawn out from the upper and lower surfaces of the film with surface metallization treatment in (4), thereby obtaining a transducer that can be used in a pressure sensor.

[0112] In this example, the film is not foamed, and the transducer does not have a strong piezoelectric effect after corona poling and surface metallization treatment.

[0113] Comparative Example 2 (Mold + Non-functional Film + 1 Pressure Reduction Foaming)

[0114] The specific preparation process is:

[0115] (1) Figure 1As shown, cycloolefin polymer particles A3, mold 2 and functional film (demolding) 1 (to prevent the prepared film from sticking to the equipment) are used, and the polymer particles 1 are placed in a sandwich structure of functional film (demolding) 1-mold 2-functional film (demolding) 1. After being preheated in a hot pressing device for 30 minutes, the polymer particles are processed using a hot pressing device (hot pressing parameters 160°C, pressure 5 MPa, hot pressing time 2 min). After demolding, the polymer film is separated from the functional film (demolding) 1, and the polymer film 4 (without functional film (demolding) 1, area 6 cm*6 cm, thickness 50 μm) is taken out.

[0116] (2) The polymer film 4 prepared in (1) was fixed on all sides and placed in a reactor for preheating for 30 minutes. Carbon dioxide gas was injected into the reactor (control parameters, reactor temperature 140°C, gas pressure 20 MPa). After static treatment for 30 minutes, the gas was discharged (gas discharge time 10 seconds). After the gas pressure dropped to atmospheric pressure, the sample was taken out to obtain a film with a circular microporous structure.

[0117] (3) The film 11 with a microporous structure prepared in (2) is charged by corona poling (charging parameters: corona voltage: -40 kV, charging time: 120 s, charging temperature 120° C., and electric needle-film distance 10 cm) to obtain a uniformly polarized film with a microporous structure.

[0118] (4) The upper and lower surfaces of the thin film with a microporous structure prepared in (3) are subjected to surface metallization treatment respectively by vacuum evaporation equipment to obtain an upper electrode and a lower electrode, thereby preparing a surface metallized thin film.

[0119] (5) Using DuPont wire and DuPont wire, electrodes are drawn out from the upper and lower surfaces of the microporous structure film with surface metallization treatment in (4), thereby obtaining a transducer that can be used in a pressure sensor.

[0120] The thickness of the microporous structure of the film in this example is about 20 μm, and the circular holes with an aspect ratio of 1:1 (the cross-sectional structure is as follows Figure 6 As shown in the figure above, the transducer has a certain piezoelectric effect after corona poling and surface metallization treatment.

[0121] Performance test: The test method is quasi-static sensitivity test.

[0122] The piezoelectric effect reflects the conversion relationship between the mechanical and electrical quantities of piezoelectric functional materials. The piezoelectric coefficient d in the thickness direction of the Z axis of the rectangular coordinate system is 33 It is an important parameter to characterize the mechanical and electrical quantities of piezoelectric functional materials, and its dimension is C / N. We use a quasi-static method to measure, such as Figure 8As shown in the figure, the measurement steps are to place the sample on the lower electrode of the sample holder (the entire measuring device is placed in the atmospheric environment), and then add the upper electrode and a certain weight to the sample in sequence. The electrometer (Keithley 6514B electrometer, USA) directly detects the charge Q generated between the upper and lower electrodes during the process of unloading the weight.

[0123] According to the formula:

[0124]

[0125] The quasi-static charge sensitivity d can be calculated 33 In formula (3.11), Q is the charge induced on the sample electrode, and F is the mechanical force applied to the sample.

[0126] Comparative Example 1, Comparative Example 2, Example 1, and common piezoelectric materials PVDF and IXPP were tested. Figure 9 As shown, the sample of comparative example 1 has no piezoelectric activity, the sample with a circular microporous structure in comparative example 2 has a certain piezoelectric activity, and the sample with a flat microporous structure in embodiment 1 has a higher piezoelectric activity.

[0127] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions are intended to be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A method for preparing a piezoelectric film with an adjustable microporous structure, characterized in that: The preparation method comprises the following steps: S1, placing the polymer raw material between the functional films and performing heat pressing to obtain a polymer film; S2, placing the polymer film together with the film fixing device in a pressure device, filling it with gas and then allowing it to stand for a while, then performing foaming by reducing the pressure or increasing the temperature, and removing the film fixing device to obtain a film with a microporous structure; S3. Performing corona charging treatment on the film containing the microporous structure to obtain a piezoelectric film.

2. The method for preparing a piezoelectric film according to claim 1, wherein: In step S1, the polymer raw material is polymer particles or mixed particles containing polymer and filler; the polymer includes one or more of cycloolefin polymer and cycloolefin copolymer.

3. The method for preparing a piezoelectric film according to claim 1, wherein: In step S2, the film fixing device includes a functional film and / or a clamp; Method for using the functional film: During the hot pressing treatment in step S1, the polymer film and the functional films on both sides form a composite film, and the composite film is placed in a pressure device for foaming treatment; Method for using the clamp: During the hot pressing treatment in step S1, the polymer film or composite film is placed in the clamp, and then placed in the pressure device for foaming treatment.

4. The method for preparing a piezoelectric film according to claim 1, wherein: In step S2, the gas includes one or more of carbon dioxide and nitrogen.

5. The method for preparing a piezoelectric film according to claim 1, wherein: In step S2, the parameters for the decompression foaming step are as follows: the pressure after filling with gas is 1 to 50 MPa; the temperature during the static soaking is 50 to 350°C, and the static soaking time is 1 second to 1440 minutes; after the static soaking, the pressure is reduced and exhausted to atmospheric pressure for 0.1 to 10 minutes; And / or, the parameters of the temperature-raising foaming step are: the pressure after filling with gas is 3-10 MPa, the temperature during static soaking is 30-50°C, and the static soaking time is 1s-1440min; after static soaking, the pressure is reduced and exhausted to atmospheric pressure for 0.1-10min; after depressurization and exhaust, oil bath treatment is performed, the oil bath treatment temperature is 50-350°C, and the oil bath treatment time is 1s-10min.

6. The method for preparing a piezoelectric film according to claim 1, wherein: In step S2, the thickness of the polymer film containing the microporous structure is 10-1000 μm.

7. The method for preparing a piezoelectric film according to claim 1, wherein: In step S2, the microporous structure of the polymer film containing the microporous structure is flat micropores.

8. The method for preparing a piezoelectric film according to claim 1, wherein: In step S3, the corona charging process is as follows: placing the prepared film containing a microporous structure on a metal electrode, inserting an electric needle above the film, and connecting the electric needle to a DC high voltage source for corona charging treatment.

9. Use of the piezoelectric film obtained by the preparation method according to claim 1 in preparing a transducer.

10. A method for preparing a transducer, characterized in that: The method comprises the following steps: metallizing the surface of the piezoelectric film obtained by the preparation method according to claim 1, and leading out electrodes to obtain a piezoelectric film transducer.

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