JPS6048119B2 - Manufacturing method of polymer piezoelectric film - Google Patents

Description

Detailed Description of the Invention The present invention relates to a method for producing a polymeric piezoelectric film exhibiting high piezoelectricity, such as polyvinylidene fluoride (PVF2) film, which can polarize a large amount of polymeric piezoelectric film having no defects and having a high piezoelectric constant. A manufacturing method is provided.

Polymer piezoelectric films are used in audio microphones, ultrasonic transmitting and receiving elements, pyroelectric elements, and the like.

The size of the polymer piezoelectric film used for these is at most a few α angles, and films of this size can be manufactured without defects using the conventional polarization method. Like the polymer piezoelectric film used for piezoelectric keyboard switches, etc., 20C77Z x 3
The size of 0cm etc., n=! Yofu inside-', 7rr
-7 When polarizing a single stone, it was difficult to polarize the entire surface without a single defect. Many methods have been proposed for polarizing polymer piezoelectric films. For example, there is a method in which electrodes are formed on both sides of a uniaxially stretched PVF2 film by vapor deposition and a high voltage is applied between the two electrodes, or a method in which a polymer piezoelectric film is sandwiched between two metal plates instead of vapor-deposited electrodes. Other methods have been proposed, including applying a high voltage using an electron beam, and polarizing using an electron beam or corona discharge. Methods using vapor-deposited electrodes are capable of self-healing and are suitable for applications in which a relatively large area is covered with electrodes, but they have the disadvantages of having to form the electrodes before polarization, complicated electrode configurations, and the inability to perform continuous processing. There are drawbacks such as the inability to obtain voltage-electricity without defects such as pinholes.

In the sandwich method using the second metal plate, if there is even one defect in the film, the defect will be torn by discharge and the entire area will not be polarized, and the metal plate will not be kept completely parallel and the electric field strength will be uneven. However, it is difficult to obtain a piezoelectric constant with a uniform piezoelectric constant, and continuous polarization is also difficult. Methods using electron beams are currently used for electret production, but continuous polarization over a large area is difficult in practice because it requires a vacuum system.

Methods using corona discharge are also currently used in the production of electrets.

In this method, a corona discharge is generated between a corona house consisting of a thin tungsten wire to which a high voltage is applied and a grounded metal cover, and the generated charge is repelled by the high voltage to a position opposite to the opening of the corona house. The electric charge is caused to fall like rain on a grounded metal flat plate, and the above-mentioned charges are placed on a film closely attached to the grounded metal flat plate, causing it to be polarized. In this method, polarization is insufficient with only generated charges, resulting in low piezoelectricity, and continuous polarization is also difficult. The present invention eliminates the above-mentioned conventional drawbacks, and one embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1, 2, and 3 are polymer films, at least one of these three is a polymer piezoelectric film such as PVF2 film, and the others are insulating,
It has properties such as no pinholes. Tetrafluoroethylene,
These films are polymer films such as polyethylene terephthalate and polyimide, and these films 1, 2, and 3 are stacked and fed. Film feeding mechanisms 8 and 9 are high voltage generators, each generating voltages of opposite signs.

10 to 17 are protective resistors, 18 to 25 are high voltage application devices,
26 to 29 are insulating heat insulating materials for preventing leakage of heated air from the constant temperature bath 34.

30 is a thermocouple, 31 is a heater, 32 is a motor for rotating an air stirring fan, and 33 is a temperature controller.

35 to 41 are film winding mechanisms.

The high voltage application devices 18 to 25 are as shown in FIG.
Provided inside and outside of the constant temperature bath 34 to ensure uniform polarization. conduct.

In order to keep the polarization time constant, the film feed speed
By changing the size of the constant temperature bath 34, the number of high voltage application devices can also be increased or decreased. As the films 1, 2, and 3 are fed, the polymer piezoelectric films are polarized from the time they are at room temperature, and are polarized throughout the entire time in the high-temperature thermostat 34 and into the cooling section. This method provides stable, uniform, and high piezoelectric polarization.
For example, when a positive voltage is applied to the high voltage application device 8 on the upper side of the film in FIG. 1, a negative high voltage is applied to the high voltage application device 9 on the lower side of the film. . Note that the above polymer piezoelectric film (PVF2
A uniaxially stretched film is used. At this time, the film feeding speed and winding speed are almost the same. PV
When an unstretched F2 film is used, polarization can be performed simultaneously with stretching by setting the winding speed to 2 to 5 times the feed speed. Figure 2 shows the above high voltage application device 1.
8 to 25 are detailed views.

In FIG. 2, 42 and 43 are insulators, and these insulators 42 and 43 support tungsten wires 44 and 45 and a metal plate 46 having a U-shaped cross section. This metal plate 4
6 is not directly connected to the high voltage generators 8 and 9 and is electrically insulated, but the tungsten wire 44
, 45, electric charges are generated, a portion of which is trapped in the metal plate 46, and the potential of the metal plate 46 rises to about the same level as the voltage applied to the tungsten wires 44, 45. Conversely, new charges are repelled by this potential,
It is concentrated at the opening of the metal plate 46, which has a U-shaped cross section. In this direction, there is a polymeric piezoelectric film and, furthermore, facing a high voltage application device to which a high voltage of the opposite sign is applied.
Since the charges emitted from these pair of high voltage application devices have opposite signs, they are attracted to each other and fixed on the polymer film.This charge and the electric field between the pair of high voltage application devices There are devices that can move and polarize dipoles in the film. Reference numerals 47 and 48 are parts for attaching tungsten wires 44 and 45, and 49 and 50 are springs that apply tension to the tungsten wires.

FIG. 3 is a sectional view of the center part of FIG. 2. A continuous polarization device such as the one described above can polarize a single piece of polymer piezoelectric film, but pinholes, foreign objects, etc.
If there are thin parts, the withstand voltage will drop and polarization will not be sufficient. In the present invention, two or three polymer films are stacked, and the probability that defects in the films overlap at the same position is extremely low. Furthermore, by simultaneously using a highly insulating film such as a polymer film used in film capacitors in addition to a piezoelectric polymer film such as PVF2, it is difficult to generate electrical discharge that penetrates the film, and the piezoelectric polymer film is substantially The voltage that can be applied to the molecular piezoelectric film is high, and as a result, the polarization efficiency is high and a high piezoelectric constant can be achieved. The same kind of polymeric piezoelectric film, e.g. PV
When polarizing multiple F2 films by stacking them, if the maximum applied voltage that does not cause discharge breakdown when polarizing with one film is ■1, and if the applied voltage in the case of two films is polarized is ■2 = 2V1, then this If one of them is defective, the voltage applied to the other one at that location will be 2V1. In the case of three-sheet polarization, V3=3V1, and if one sheet is defective, the voltage applied to each of the other two sheets will be 312V1.

Similarly, when n sheets are polarized and one sheet has a defect, the voltage applied to each of the other (n-1) sheets is n.
/(n-1)V1. By stacking the number of sheets in this way, the applied voltage per sheet approaches V1, where V
In No. 1, the applied voltage was set so as not to cause discharge breakdown in the film, but the actual breakdown voltage can withstand even higher voltages if the film does not have the above-mentioned defects. In addition, defects in the film are rarely completely perforated and can withstand a certain amount of voltage, so by stacking two or three films, a sufficiently high voltage can be applied to each film, resulting in high piezoelectricity and uniformity. can be realized. In the polarization apparatus shown in FIG. 1, one uniaxially stretched PVF2 film was polarized.

The PVF2 film has a thickness of approximately 30PT1. , the temperature of the constant temperature bath is 80℃, and the distance between each pair of high voltage application devices is 1cm1.
The voltage to be applied to this is 6.5KV each, plus and minus.
When passed through the polarization device about 3 times, the piezoelectric constant of the polarized polymer piezoelectric film is about 25×10-12C1
It was N1. When the voltage applied to the high voltage application device was increased to 7 KV, discharge breakdown occurred at 10° in the film feeding direction.
It occurred at a rate of about 1 piece per cm. Next, embodiments of the present invention will be described in detail.

In the polarization device shown in Figure 1, two sheets of uniaxially stretched PVF
1 polyethylene terephthalate film between 2 films
Continuous polarization was performed by sandwiching the sheets. Two PVF2 films are
Both were obtained from the same original fabric and had a diameter of about 30 μm. The polyethylene terephthalate film is used for film capacitors, has very few defects such as pinholes, and has a thickness of about 20 μm. Constant temperature bath 3
4, the temperature is 80°C1 each, and the distance between the pair of high voltage application devices is 1c! When n, these high voltage application devices were able to apply 13 KV to each of the positive and negative voltages. It passed through the polarizer for about 30 minutes. Two PVF2s that have been polarized
The film had a piezoelectric constant of about 30 x 10-12 C1N. The present invention has the above-described structure, and the manufacturing method of the present invention has the advantage that a high voltage can be applied to each sheet, a piezoelectric constant is high, and a piezoelectric film with small deviation depending on location can be obtained. It is possible to continuously polarize a polymer piezoelectric film having the following characteristics, and the productivity is improved by the number of layers stacked in the same polarization time compared to the conventional method.

Therefore, the method of the present invention is effective when a large area and defect-free high piezoelectricity are required, such as piezoelectric films used in piezoelectric keyboard switches and the like.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus for carrying out the manufacturing method of the present invention, FIG. 2 is a bottom view of the high voltage application device of the same apparatus, and FIG.
1, 2, 3... polymer film, 8, 9...
... High voltage generator, 18-25 ... High voltage application device, 34 ... Constant temperature bath.

Claims (1)

[Claims] 1 Between at least one pair of high voltage application devices to which positive and negative high voltages are applied, there is at least one polymer piezoelectric film, and at least four polymer films made of a different material from the polymer piezoelectric film. A method for producing a polymer piezoelectric film, which comprises feeding and polarizing a plurality of stacked polymer films including a polymer film made of one of fluorinated ethylene, polyethylene terephthalate, and polyimide.