CN1845353A - A kind of preparation method of porous polymer piezoelectric electret film - Google Patents

Abstract

The invention belongs to the technical field of functional materials, and particularly relates to a preparation method of a porous polymer piezoelectric electret film. The method comprises two parts of preparation and charging of the porous polymer film, wherein the preparation process of the porous polymer film comprises the following steps: laminating polymer films with different melting points to form a composite film system, arranging a grid on one surface or two surfaces of the film, and then applying pressure at a certain temperature, wherein the pressure is 1 MPa-10 MPa, and the time is 2-120 minutes. And then charging the composite film system, wherein the charging mode can adopt corona charging, contact charging or electron beam charging. The method has simple process, and can obtain the porous polymer piezoelectric electret film with high thermal stability and high voltage activity.

Description

A kind of preparation method of porous polymer piezoelectric electret film

technical field

The invention belongs to the technical field of functional materials, and in particular relates to a preparation method of a porous polymer piezoelectric electret film.

technical background

The polymer film with a porous structure exhibits outstanding piezoelectric properties after proper electric polarization treatment. It has the characteristics of piezoelectric materials and electrets at the same time, and is named porous polymer piezoelectric electret film, piezoelectric electret Body or ferroelectret, it is a new type of electromechanical sensor material developed around 1990. The piezoelectric d ₃₃ coefficient of the porous polymer electret piezoelectric film is an order of magnitude higher than the piezoelectric activity of the ferroelectric polymer PVDF and its copolymer P(VDF/TrFE); compared with piezoelectric ceramic materials, the porous In addition to the high piezoelectric d ₃₃ coefficient, the polymer electret piezoelectric film also has the flexibility of polymers, large-area film formation, low cost, low permittivity, and low sound matching air and water. Prominent characteristics such as impedance. At present, the only commercialized porous polymer electret piezoelectric film is based on polypropylene (PP) resin, which is formed into a porous structure through chemical or physical foaming process. This porous PP electret piezoelectric film material has been applied in pressure sensors, electroacoustics, acoustic electricity, ultrasonic sensors, alarms, clinical medicine, etc., and is expected to be used in communications, security, control, life sciences and It has broad application prospects in military and other fields.

The piezoelectric activity of the porous polymer piezoelectric electret film material originates from the space charge with opposite polarity deposited on the upper and lower walls of the inner hole and the hole structure of the material. The piezoelectric sensitivity of the material is directly related to the electret properties of the hole medium wall, the mechanical properties of the hole film system, the shape and size of the hole, and the volume ratio of the medium and the air gap, while the thermal stability of the piezoelectric activity mainly depends on the medium Electret thermal stability. Commodity porous PP electret piezoelectric film is limited by the thermal stability of the electret itself of the PP material, and its working temperature generally cannot exceed 60°C. Above this temperature, its piezoelectric activity will decrease or even disappear due to the aggravation of charge attenuation. , limiting the application of such functional materials. However, some other electret materials with high thermal stability (such as PTFE, FEP, COC, PET, PI, etc.) cannot form an ideal porous structure due to the limitations of traditional membrane-making processes. Report of porous polymer piezoelectric electret films with high-voltage electroactivity.

Contents of the invention

The purpose of the present invention is to propose a preparation method for a porous polymer electret piezoelectric film with high thermal stability and high voltage electrical activity.

The preparation method of the porous polymer electret piezoelectric thin film proposed by the invention includes two parts: preparation of the porous polymer thin film and charging the thin film. Wherein, the preparation process of the porous polymer film is: one, or two, or two or more polymers (such as PTFE, FEP, COC, PET, PI, PE, PEN or PP) films with different melting points (this paper Among them, if two or more polymer films are used, the polymer film with the lowest melting point is called film 1, and the polymer film with the highest melting point is called film 2; if only one polymer film is used, the film 1 and The melting point of film 2 is equal to the melting point.) Laminated into a composite film system, and a grid is placed on one or both sides of the film, and then a certain value in the temperature range higher than or equal to the melting point of film 1 and lower than or equal to the melting point of film 2 Apply pressure (P) to the composite membrane system under (T), and form a porous membrane after time (t). The range of P is 1kPa-10MPa, and the range of t is 2min-120min. The preferred range of P is 1MPa-8MPa; The preferred range of t is 10-50 minutes,

In the present invention, the piezoelectric electret film is made by charging the porous polymer film, and its charging method can adopt conventional methods, mainly including:

(1) Corona charging, the steps are: place the porous film on the metal electrode to flatten (the electrode can be plated on one side, or not plated on both sides), and a corona electrode is placed on the porous film. Connect a DC high-voltage power supply, and perform corona charging under the condition of no grid voltage or grid voltage regulation to obtain a porous polymer electret piezoelectric film; the corona charging condition is: the voltage is +2kV～+100kV or -2kV～- 100kV, the maximum temperature is not higher than the melting point of the thin film 2, the electrification time is 1 second to 1 hour, and the distance between the electrode and the porous membrane is 2 cm to 50 cm.

(2) contact method charging, its step is: the two sides of porous film are plated with electrodes, then the upper and lower electrodes are respectively connected to the two poles of a DC high-voltage power supply, charged to obtain porous polymer electret piezoelectric film; contact method charging conditions Yes: the voltage is +2kV～+100kV or -2kV～-100kV, the highest temperature is not higher than the melting point of the film 2, and the power-on time is 1 second-1 hour.

(3) Electron beam charging, the electron beam charging conditions are: the energy of the electron beam is 5keV-100keV, the maximum temperature is not higher than the melting point of the film 2, and the electrification time is 1 second to 1 hour.

In the present invention, the material of the grid can be metal or non-metal material.

In the present invention, the mesh number of the grid is 2-2000 mesh, the wire diameter is 0.001-2mm, and the hole diameter is 0.005-35mm.

In the present invention, the grid can be independent or composited on the pressure wheel or the pressure plate.

In the present invention, the meshes of the grid can be horizontally connected or closed.

In the present invention, the number of layers of various types of films is 1 or more.

In the present invention, various types of membranes may be dense membranes or porous membranes.

In the present invention, negative corona charging or positive corona charging can be used for corona charging.

In the present invention, the corona charging electrode is needle-shaped, or wire-shaped, or knife-edge-shaped.

In the present invention, during corona charging, a grid can be used between the corona electrode and the porous film, and the surface potential of the porous film can be controlled by grid bias, or no grid can be used.

The working principle of the corona charging of the present invention is as follows: under a certain air pressure, under constant voltage or constant current charging conditions, the non-uniform electric field existing between the electrodes is used to cause partial discharge of the gas between the electrodes, that is, corona discharge, and corona discharge produces The ions are deposited on the surface of the porous membrane or exchanged with the surface of the porous membrane, so that a certain potential difference is generated on the upper and lower surfaces of the porous membrane. When this potential difference reaches or exceeds the discharge voltage of the internal air gap of the porous membrane, the internal air gap discharge will be caused. The ions of opposite polarity generated by discharge are deposited on the surface of the medium in the pores of the porous membrane or exchanged with the surface of the medium, so that the upper and lower walls of the internal pores have opposite charges to achieve the purpose of charging.

The working principle of the contact method charging in the present invention is as follows: under a certain air pressure, under a reasonable (controlled) DC voltage, when the potential difference between the upper and lower surfaces of the porous membrane coated with electrodes on both sides reaches a certain value, air gaps in the pores inside the membrane are caused. The air gap discharge, the ions of opposite polarity generated by the discharge are deposited on the surface of the medium in the pores of the porous membrane or exchange charges with the surface of the medium, so that the upper and lower walls of the internal pores have opposite charges to achieve the purpose of charging.

In the present invention, the thermal stability of the porous polymer electret piezoelectric film can be improved by adjusting the charging temperature.

The invention has simple technological process and novel concept, and can obtain the porous polymer piezoelectric electret thin film with high thermal stability and high voltage electric activity.

Description of drawings

Fig. 1 is the schematic diagram of the preparation process of porous polymer film (film 1 is two layers, film 2 is three layers).

Fig. 2 is a scanning electron microscope image of a cross-section of a porous polymer film.

Fig. 3 is a pressure characteristic graph of a porous polymer electret piezoelectric film.

Fig. 4 is a frequency characteristic diagram of a porous polymer electret piezoelectric film.

Fig. 5 is the isothermal decay diagram of the porous polymer electret piezoelectric film at 90°C.

Fig. 6 is an isothermal decay diagram of the pre-aged porous polymer electret piezoelectric film at 90°C.

Numbers in the figure: 1 is a low melting point polymer film, 2 is a high melting point polymer film, 3 is rolling pressure, and 4 is a grid.

Detailed ways

The present invention is further described below by way of examples.

Embodiment 1, a metal grid is used, and the mesh is a 1mm×1mm square hole. Film 1 is made of FEP film (two layers) with a film thickness of 12.7 μm; film 2 is made of PTFE film (three layers) with a film thickness of 3 μm. The pressing temperature is 280°C; the pressing time is 15 minutes; and the pressing pressure is 4kPa. The corona electrode is needle-shaped; the corona voltage is 32kV; there is no grid control voltage; the charging temperature is 20°C; the charging time is 60s; the distance between the corona electrode and the sample is 7cm. Aluminum electrodes of 100 nm were vacuum-deposited on both sides of the porous membrane.

In embodiment 2, a metal grid is used, and the mesh is a square hole of 0.125mm×0.125mm. Film 1 is made of FEP film (one layer) with a film thickness of 12.7 μm; film 2 is made of PTFE film (two layers) with a film thickness of 3 μm. The pressing temperature is 280°C; the pressing time is 5 minutes; and the pressing pressure is 4kPa. The corona electrode is needle-shaped; the corona voltage is 64kV; there is no grid control voltage; the charging temperature is 25°C; the charging time is 40s; the distance between the corona electrode and the sample is 4cm. Aluminum electrodes of 100 nm were vacuum-evaporated on both sides of the porous membrane.

Embodiment 3, a metal grid is used, and the mesh is a square hole of 0.125mm×0.125mm. Film 1 is made of FEP film (one layer) with a film thickness of 12.7 μm; film 2 is made of PTFE film (two layers) with a film thickness of 3 μm. The pressing temperature is 280°C; the pressing time is 10 minutes; and the pressing pressure is 4kPa. The corona electrode is needle-shaped; the corona voltage is 5kV; there is no grid control voltage; the charging temperature is 20°C; the charging time is 10 minutes; the distance between the corona electrode and the sample is 10cm. Aluminum electrodes of 100 nm were vacuum-deposited on both sides of the porous membrane.

Embodiment 4, a metal grid is used, and the mesh is a square hole of 0.125mm×0.125mm. The film adopts PP film (three layers) with a film thickness of 6 μm. The pressing temperature is 190°C; the pressing time is 2min; and the pressing pressure is 10kPa. The corona electrode is needle-shaped; the corona voltage is 20kV; there is no grid control voltage; the charging temperature is 20°C; the charging time is 30s; the distance between the corona electrode and the sample is 4cm. Aluminum electrodes of 100 nm were vacuum-deposited on both sides of the porous membrane.

In embodiment 5, a metal grid is used, and the mesh is a square hole of 0.125mm×0.125mm. FEP film (one layer, film thickness 6 μm); PP film (one layer, film thickness 6 μm); and PTFE film (one layer, film thickness 3 μm) were used. The pressing temperature is 230°C; the pressing time is 35 minutes; and the pressing pressure is 1kPa. The corona electrode is needle-shaped; the corona voltage is 32kV; there is no grid control voltage; the charging temperature is 20°C; the charging time is 60s; the distance between the corona electrode and the sample is 7cm. Aluminum electrodes of 100 nm were vacuum-evaporated on both sides of the porous membrane.

The test results of the above-mentioned porous FEP/PTFE composite electret piezoelectric film are:

1. Scanning electron microscope image of the cross-section of the porous polymer film (as shown in Figure 2).

2. The pressure characteristic test results of the piezoelectric d ₃₃ coefficient of the porous polymer electret film (as shown in Figure 3)

3. The frequency characteristic test results of the piezoelectric d ₃₃ coefficient of the porous polymer electret film (as shown in Figure 4)

4. Isothermal decay test results of porous polymer electret film piezoelectric d ₃₃ coefficient (as shown in Figure 5)

5. The isothermal decay test results (as shown in Figure 6) of the porous polymer electret film piezoelectric d ₃₃ coefficient of pre-aging treatment

Claims (6)

1, a kind of preparation method of porous polymer piezo-electric electret thin film, comprise the preparation of porous polymer film and to this film two parts of charging, the preparation process that it is characterized in that porous polymer film is as follows: with a kind of, or two kinds, or the thin polymer film of two or more different melting points is laminated into and is compound film system, and place aperture plate at the one or both sides of film, be greater than or equal to film 1 fusing point then, be less than or equal under the certain value T in the warm area of film 2 fusing points to the compound film system P that exerts pressure, elapsed time t forms perforated membrane, the scope of P is 1kPa-10MPa, and the scope of t is 2min-120min; Here, film 1 is the film of minimum fusing point in the thin polymer film, and film 2 is the film of peak melting point in the thin polymer film; Described polymer is PTFE, FEP, COC, PET, PI, PE, PEN or PP.

2, the preparation method of porous polymer piezo-electric electret thin film according to claim 1, it is characterized in that charging employing corona charging, the steps include: perforated membrane placed on the metal electrode and flatten, above perforated membrane, settle a corona electrode, corona electrode connects DC high-voltage power supply, under the condition of no grid voltage or grid voltage regulation and control, carry out corona charging, obtain porous polymer electret piezoelectric membrane; The corona charging condition is: voltage for+2kV～+ 100kV or-2kV～-100kV, maximum temperature is not higher than the fusing point of film 2, be 1 second-1 hour conduction time, the distance of electrode and perforated membrane is 2cm～50cm.

3, the preparation method of porous polymer piezo-electric electret thin film according to claim 1, it is characterized in that the charging of charging employing contact method, the steps include: the two sides of perforated membrane is plated electrode, upper/lower electrode respectively is connected respectively to the two poles of the earth of a DC high-voltage power supply then, and charging obtains porous polymer electret piezoelectric membrane; Charge condition is: voltage for+2kV～+ 100kV or-2kV～-100kV, maximum temperature is not higher than the fusing point of film 2, be 1 second-1 hour conduction time.

4, the preparation method of porous polymer piezo-electric electret thin film according to claim 1, it is characterized in that the charging of charging employing electron beam, condition is: electron beam can be 5keV～100keV, and maximum temperature is not higher than the fusing point of film 2, and be 1 second-1 hour conduction time.

5, the preparation method of porous polymer piezo-electric electret thin film according to claim 1, the order number that it is characterized in that described aperture plate is the 2-2000 order, and the silk footpath is 0.001-2mm, and the aperture is 0.005-35mm.

6, the preparation method of porous polymer piezo-electric electret thin film according to claim 1 is characterized in that using aperture plate between corona electrode and the porous polymer film.

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