JPS5840328B2 - Koubunshi Electret Noseizouhou - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for producing a polymer electret.

As is well known, a polymer electret is a polymer made of a dielectric material, and a charge remains permanently inside the polymer through a special polarization treatment.

The advantage of using a polymer material is that it is generally highly flexible and easy to form into a film, so it can be effectively used as a mechanical-electric conversion element in terms of shape.

In fact, polymer electrets have already been put into practical use as electret microphones and electret headphones.

The polymer materials used for the electret are polymers such as fluorinated ethylene-propylene copolymer, polypropylene, polyethylene terephthalate, and polyvinylidene fluoride.

The performance of electrets is evaluated by surface charge density and its stability.

The higher the surface charge density, the better, and moreover, it is desirable that the surface charge is kept stable for a long period of time.

The surface charge density is determined by polarization conditions, and the polarization conditions differ depending on the type of polymer material used.

Methods for converting polymers into electrets include thermal electret method, radioelectret method, etc.
Thermal electret method is commonly used.

The method for producing polymer thermal electrets involves sandwiching the polymer film to be used between two flat electrodes and applying a DC voltage (■P
: Polarization voltage) is applied at a certain temperature (Tp:
A common method is to raise the temperature to a temperature (referred to as polarization temperature), maintain that temperature for a certain period of time (referred to as tP: polarization time), then lower the temperature and remove the voltage.

Through this operation, charges are permanently retained in the polymer film and an electret is obtained.

Therefore, in the thermal electret method, the surface charge density of the electret is influenced by three conditions: VP, TP, and t.

The present invention uses poly(3,3-
This applies only to materials whose main component is bis(chloromethyl)oxacyclobutane] and relates to the polarization temperature among the electretization conditions.

The present inventor found that when a film of poly[3,3bis(chloromethyl)oxacyclobutane] is electretized at the same polarization voltage and the same polarization time, the polarization temperature is 70'
In the range of C to 145°C and above 145°C,
It was found that the retained surface charge densities are different.

That is, the surface charge density is large between 70°C and 145°C, and the surface charge density decreases as the temperature increases above 145°C.

Incidentally, the drawing shows the relationship between surface potential and polarization temperature.

The polarization conditions were as follows: vP was 500 volts, ip was 2 hours, and the film thickness of PoIJ (3,3-bis(chloromethyl)oxacyclobutane) used was ioum.

The cause of this phenomenon is unknown, but poly(3,3-bis(chloromethyl)oxacyclobutane)
This seems to be related to the transition of the crystal from the β type to the γ type.

As described above, it is possible to obtain an electret with a high surface charge density under the conditions for converting poly[3,3-bis(chloromethyl)oxacyclobutane] into an electret with a polarization temperature in the range of 70°C to 145°C. .

This effect does not depend on the Okazaki interval of polarization voltage and polarization time.

Furthermore, there are no limitations on the thickness of the film or the shape of the material used.

Note that if the temperature is 70° C. or lower, a long time is required for polarization, which is not practical.

Next, examples of the present invention will be described.

100 μm thick poly[3,3-bis(chloromethyl)
A film of oxacyclobutane] (bentone; trade name of Vercules Powder Co., Ltd.) was sandwiched between flat plate electrodes with a diameter of 7 cr/L, a DC voltage of 500 volts was applied, the temperature was rapidly raised to 115°C, and the temperature was maintained for 2 hours. After that, leave it at room temperature (about 2
Cool slowly to 5°C.

The surface potential of this electret was 610 volts.

Further, when polarized at 158° C. under similar conditions, the surface potential was 440 volts.

As described above, according to the production method of the present invention, an electret with high surface charge density and good stability can be obtained.

[Brief explanation of drawings]

The figure is a characteristic diagram of surface potential versus polarization temperature of electret.

Claims (1)

[Claims] 1. A method for producing a polymer electret, characterized in that the polarization temperature is within the range of 70°C to 145°C under the electretization conditions of a thermal electret of 1 PoIJ (3,3-bis(chloromethyl)oxacyclobutane). .