JP6877285B2 - Piezoelectric resin membranes and piezoelectric devices - Google Patents

Description

The present invention relates to piezoelectric resin membranes and piezoelectric devices.

Conventionally, resin-based piezoelectric elements having a piezoelectric effect are known. For example, in Patent Document 1, a piezoelectric film having a prefabricated α-type crystal structure is subjected to a stretching treatment to stretch a molecular chain to convert a TGTG'structure into a TT structure. The manufacturing method of is disclosed.

Japanese Unexamined Patent Publication No. 55-157801

However, although various methods for producing a piezoelectric resin film have been proposed, sufficient research and studies have not yet been made on structural improvements focusing on the crystalline state.

An object of the present invention is to provide a novel piezoelectric resin film having excellent piezoelectric properties.

In order to solve such a problem, the first invention provides a novel structure of a piezoelectric resin film. This piezoelectric resin film contains at least a piezoelectric resin and a silane compound, and has a crystal structure in which granular crystals are isotropically dispersed. The crystallinity of this crystal structure is greater than 50% and less than 80%.

Here, in the first invention, the size of the crystal of the granular, have preferably be smaller than larger 10μm than 0.1 [mu] m.

The second invention provides a piezoelectric device having a pair of electrodes and a piezoelectric resin film. This piezoelectric resin film is sandwiched between a pair of electrodes and is the piezoelectric resin film according to the first invention.

According to the present invention, the crystal structure of crystals of the particulate is isotropically dispersed chromatic piezoelectric resin film, and, since the crystallinity of the crystal structure is less than 80% greater than 50% , A piezoelectric resin film having excellent piezoelectric characteristics can be realized.

Schematic of the piezoelectric device Cross-sectional photograph of the piezoelectric resin film according to this embodiment Cross-sectional photograph of the piezoelectric resin film according to the first comparative example Cross-sectional photograph of the piezoelectric resin film according to the second comparative example Comparison graph of piezoelectric characteristics

FIG. 1 is a schematic view of a piezoelectric device. The piezoelectric device 1 is mainly composed of a lower electrode 2, an upper electrode 3, and a piezoelectric resin film 4 sandwiched between these electrodes 2 and 3. The piezoelectric device 1 can be widely used in applications such as sensors, power generation, actuators, and on-off valves.

FIG. 2 is a cross-sectional photograph of the piezoelectric resin film according to the present embodiment. FIG. 6A is a grayscale photograph taken with an electron microscope (SEM), and FIG. 9B is a binarized version of this photograph (the same applies to the drawings described later). The piezoelectric element has a configuration in which a pair of electrodes are arranged above and below a piezoelectric resin film containing at least a piezoelectric resin and a silane compound. In the same photograph, the upper electrode (silver paste) is peeled off. Indicates the state. The relatively large grains scattered in the upper part of the photograph are the remnants of the peeled silver paste.

In FIG. 3B, the granular white spots (high brightness region) existing in the piezoelectric resin film are crystals of the piezoelectric resin film, and the other black regions (low brightness region) are crystallized. It is an amorphous part that is not. As can be seen from this photograph, the granular crystals are dispersed almost uniformly over the entire piezoelectric resin film without being unevenly distributed in a specific direction. That is, a structural feature of the piezoelectric resin film is that it has a crystal structure in which granular crystals are isotropically dispersed.

The second feature is that the crystal is finely granular. Specifically, the size of the granular crystal is larger than 0.1 μm and smaller than 10 μm. The size of the granular crystal can be calculated using an SEM, a digital microscope (microscope), or the like.

Furthermore, a third feature is that the crystallinity of the crystal structure is greater than 50% and less than 80%. The crystallinity is the ratio of the crystalline region to the entire piezoelectric resin film, and can be calculated by using an X-ray diffraction method, DSC (differential scanning calorimetry), or the like.

The piezoelectric resin film having the above-mentioned characteristic structure can be produced by using a spray coating method. The outline of the spray coating method is as follows.

First, the piezoelectric resin powder is dissolved in a solvent, and a silane coupling agent is added to the solution to prepare a coating solution. Specifically, an amino group or an epoxy group, a mercapto group, a ureido group, a vinyl group, a methacryl group or an amino group, an epoxy group, a mercapto group, a ureido group, a vinyl group and a methacryl group, which are reactive groups with a piezoelectric resin. A silane-based coupling agent that is a composite of any two types and has a hydrolyzable group that is reactive with the object to be coated is added to the solution of the piezoelectric resin in an amount of about 0.001 to 1% by mass. After stirring and mixing at room temperature, a silane coupling agent is further added.

Next, the coating solution is sprayed to form a piezoelectric resin film on the surface of the object to be coated (including the electrodes described above). The solvent component in the coating solution is volatilized by applying hot air, a far-infrared heater, a halogen lamp, or the like to the coating solution sprayed on the object to be coated. In this process, a cross-linking reaction occurs between the piezoelectric resin and the silane coupling agent. In this cross-linking reaction, the dipole of the molecular chain of the piezoelectric resin is any of an amino group or an epoxy group, a mercapto group or an amino group, an epoxy group and a mercapto group, which are reactive groups of the silane coupling agent with the piezoelectric resin. Or a combination of the two types is combined and arranged with regularity. In addition, a hydrolyzing group that is reactive with the object to be coated binds to the object to be coated and is arranged in the same direction as the sequence. As a result, the entire dipole of the molecular chain of the piezoelectric resin is oriented perpendicularly to the object to be coated between the piezoelectric resin film and the object to be coated. Along with the orientation, a β-type crystal structure exhibiting piezoelectricity is formed, and the proportion of the β-type crystal structure in the entire film increases as compared with the case where nothing is added. Therefore, it is a silane type. The addition of the coupling agent significantly improves the piezoelectricity.

Then, after the piezoelectric resin film is dried, a high voltage is applied to the piezoelectric resin film to perform a polarization treatment. Among the β-type crystal structures in the piezoelectric resin film, those that are not completely oriented are aligned in one direction by the force of the electric field due to the application of a high voltage. This increases the piezoelectricity of the piezoelectric resin film.

By using the spray coating method as described above, a piezoelectric resin film containing a piezoelectric resin and a silane compound as main components can be obtained (the solvent volatilizes and disappears). However, even if the spray coating method is used, the above-mentioned crystal structure cannot be obtained unless the conditions are optimized. As a result of repeated experiments and diligent studies by the present inventors, the atomization when the piezoelectric paint is sprayed changes depending on the air condition of the spray. Therefore, the most important condition for obtaining the above-mentioned crystal structure is the air of the spray. It turned out to be pressure. Since the degree of atomization is effective as a factor for forming fine crystals in the cross section of the film, the higher the atomization, the easier it is to form fine crystals. From this point of view, the air pressure of the spray should be set relatively high, and specifically, it is preferably in the range of more than 0.05 MPa and less than 0.5 MPa. The cross-sectional photograph shown in FIG. 2 was generated by setting the air pressure to 0.3 MPa. The viscosity of the piezoelectric paint to be sprayed may be appropriately adjusted in consideration of the usage environment and the like.

The piezoelectric resin film produced by the spray coating method on the premise of optimizing the conditions is structurally clearly different from that produced by other production methods. FIG. 3 is a cross-sectional photograph of a piezoelectric resin film produced by the print coating method as a first comparative example. In this piezoelectric resin film, white spots (crystals) are locally present in the intermediate layer, but most of the upper and lower layers are amorphous. Further, the crystallinity of the piezoelectric resin film is larger than 45% and smaller than 50%. That is, in this piezoelectric resin film, the crystals are not dispersed as a whole, nor are they isotropic. From the above, the piezoelectric resin film produced by the spray coating method is structurally significantly different from the piezoelectric resin film according to the present embodiment.

FIG. 4 is a cross-sectional photograph of a piezoelectric resin film produced by the stretched film method as a second comparative example. In this piezoelectric resin film, there are almost no granular crystals), and because of the stretching treatment, the amorphous portion extends in the lateral direction (the stretching direction of the film), which is different. It has a directional wavy pattern (horizontal stripe pattern). Further, the crystallinity of the piezoelectric resin film is larger than 40% and smaller than 45%. That is, neither the crystals in this piezoelectric resin film are dispersed as a whole, nor are they isotropic. From the above, the piezoelectric resin film produced by the stretched film method is also structurally significantly different from the piezoelectric resin film according to the present embodiment.

FIG. 5 is a comparison graph of piezoelectric characteristics. The generated voltage with respect to the film thickness of the piezoelectric resin film is plotted for the present embodiment (spray coating method), the first comparative example (print coating method), and the second comparative example (stretched film method). .. It can be seen that the generated voltage is larger in this embodiment than in the first and second comparative examples, that is, the piezoelectric characteristics are superior, regardless of the size of the film thickness.

As described above, according to the present embodiment, the piezoelectric resin film having excellent piezoelectric characteristics can be realized by forming the entire piezoelectric resin film into an isotropic and granular crystal structure.

1 Piezoelectric device 2 Lower electrode 3 Upper electrode 4 Piezoelectric resin film

Claims (3)

In the piezoelectric resin membrane
Contains at least a piezoelectric resin and a silane compound
The piezoelectric resin film, a crystal structure crystal granular isotropically dispersed chromatic, crystallinity of the crystal structure, the piezoelectric, characterized in that less than 80% greater than 50% Resin film. The piezoelectric resin film according to claim 1, wherein the size of the granular crystal is larger than 0.1 μm and smaller than 10 μm. A pair of electrodes and
It has a piezoelectric resin film sandwiched between the pair of electrodes.
The piezoelectric device according to claim 1 or 2 , wherein the piezoelectric resin film is the piezoelectric resin film.

Images