JPS6053475B2 - Polymer piezoelectric material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly sensitive piezoelectric polymer material.

Conventionally, many polymers exhibiting piezoelectricity are crystalline polymers with a large dielectric constant, and their piezoelectricity is often based on the spontaneous polarization of the polymer itself.

Polymer materials that specifically exhibit piezoelectricity include natural polymers such as cellulose and polypeptides, as well as polyvinylidene fluoride, polyvinylidene chloride, polycyanovinylidene,
Examples include polyvinyl fluoride, polyvinyl chloride, polyamide, and polyethylene terephthalate, and many of them are polar crystalline polymers that are easily polarized. Among them, vinylidene-type polymers have high dielectric properties and are suitable for piezoelectric materials as described above. Among these vinylidene-type polymers, polyvinylidene fluoride has added fluorine, which is a halogen element with the highest electronegativity, and is generally considered to be the best piezoelectric polymer. In addition to this spontaneous polarization, these piezoelectric polymers must also have high insulation resistance, and must not be a material that contains a large amount of ionic impurities.

In addition, this piezoelectric polymer is processed into functional elements through processes that impart orientational polarization, such as stretching and electrical poling, so it is required to be a material with excellent formability (mechanical properties). Ru. The present invention provides piezoelectric polymers that change orientation polarization sensitively to mechanical deformation.
By adding and dispersing an organic compound exhibiting piezochromism as described below, a piezoelectric material with a high frequency range can be provided.

Organic compounds exhibiting piezochromism are organic compounds that reversibly change color due to variable changes in chemical structure caused by changes in pressure, and there are not many research examples of such organic compounds.

In the present invention, the following compounds are used. 1) Anyls, such as p-oxybenzylidene-p-toluidine {2) Bianthrones (3) Imidazolyls, such as hexaphenyl rubimidazolyl These generally have complex molecular structures and exhibit rigidity and steric hindrance. It has a chemical structure and often exhibits photochromism or thermochromism.

Piezochromism causes a color change due to chemical or geometric changes in the molecular structure of an organic compound. The composition exhibits highly sensitive piezoelectric properties due to reversible chemical and geometrical changes in the molecular structure of the compound due to pressure. It is desirable that the organic compound exhibiting piezochromism has compatibility with the piezoelectric polymer matrix and is dispersed in a state close to molecular dispersion.

Piezoelectric polymers are crystalline polymers that are composed of crystalline regions and amorphous regions. The organic compound exhibiting piezochromism is mainly dispersed in the amorphous region in the piezoelectric polymer matrix, increasing the piezoelectricity of that region, and may also act as a nucleating agent for the crystalline region. . Organic compounds exhibiting piezochromism undergo changes in their chemical structure and molecular geometry due to pressure stimulation, as shown in photochromism and thermochromism, although the detailed mechanism for each substance is not clear. It is clear that these changes cause a large change in the charge density in the polymer composition in which it is dispersed, resulting in an induced electrode. In addition, piezoelectric materials have a piezoelectric constant that changes greatly depending on their orientational polarization, and are made into functional elements through a process of orientational polarization such as by stretching, so they are required to have excellent moldability. ,
In the present invention, since the organic compound exhibiting piezochromism has good compatibility and is dispersed in a form close to molecular dispersion, an excellent piezoelectric material can be provided without impairing the excellent processability of the matrix piezoelectric polymer.

Therefore, the present invention does not have poor formability like a composite piezoelectric composition in which ferroelectric inorganic crystal particles are dispersed in a piezoelectric polymer, but a matrix. It has moldability similar to that of piezoelectric polymers. Next, an example will be shown. Example 1 2, 7, 4, 4", 5, 5" on aromatic polyamide 85f
A film in which -hexaphenyl-1●1''-biimidazolyl 15f was dispersed was stretched four times and then subjected to orientation polarization under an electric field of 400 KVI0.

The thickness of this film is 40PWL, and both sides of this film are deposited with silver. When the piezoelectric constant was determined, the piezoelectric constant of the film made of aromatic polyamide alone was 1.7 × 10-℃G
The value was 8 times that of Sesu. Example 2 A polymer film containing diphenylmethylene atron 2f dispersed in polyvinylidene fluoride 18y was orientated and polarized in the same manner as in Example 1 to produce a piezoelectric film.

The piezoelectric constant of this material was 5.4 times the piezoelectric constant of polyvinylidene fluoride alone (2.5 0-7 CGSesuf). Example 3 Polyacrylonitrile 18y was dissolved in dimethylformamide, diphenylmethylene-N-methylacridine 2f was added thereto, and after being well dispersed, a film was formed by casting to obtain a film of 120 pTn.

This was subjected to orientation polarization in the same manner as in Example 1 to form a piezoelectric film. The piezoelectric constant of this film was 6.1 times the piezoelectric constant of the polyacrylonitrile film, 2×10 -8 CGSesu. As described above, the present invention provides a high-sensitivity polymeric piezoelectric material, and can be applied to keyboard switches, microphones, speakers, headphones, etc. as pressure-sensitive elements and pressure-sensitive switches.

Claims (1)

[Claims] 1 P-oxybenzylidene-P-toluidine, bianthrone, bis(triphenylimidazolyl), hexaphenyl-biimidazolyl and diphenylmethylene-N-
A polymeric piezoelectric material comprising a composition in which a compound exhibiting piezochromism selected from the group consisting of acridine is contained in a polymer exhibiting piezoelectricity.