JP5112758B2 - Piezoelectric and pyroelectric elements made of polymer materials - Google Patents

Description

  The present invention relates to a piezoelectric / pyroelectric element made of a high molecular weight material and excellent in heat resistance and environmental resistance among high molecular weight piezoelectric / pyroelectric elements.

  Conventionally, as a piezoelectric / pyroelectric element made of a polymer material, polyvinylidene fluoride (PVdF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), porous polypropylene (E-PP), etc. are used. There was something that was there. These piezoelectric / pyroelectric elements are widely used because they have flexibility, flexibility, and wear resistance that are not found in inorganic piezoelectric / pyroelectric elements.

  PVdF is produced as a piezoelectric / pyroelectric element by stretching and polarizing a molded nonporous sheet (Patent Document 1). FEP is a non-polar polymer, but it is known to become a piezoelectric / pyroelectric element by trapping charges on the polymer surface, and traps charges by corona discharge etc. on the non-porous sheet of FEP. By doing so, it is created as a piezoelectric / pyroelectric element. However, PVdF and FEP have a drawback that their piezoelectricity is lower than that of inorganic material piezoelectric / pyroelectric elements.

  On the other hand, E-PP stretches a polypropylene film, forms it into a film with many independent holes using a gas such as nitrogen, and traps charges on the upper and lower surfaces of the film holes. It was created as a piezoelectric / pyroelectric element. In E-PP, a large number of holes constitute a huge dipole, and when pressure is applied to the film surface, the holes are compressed, so that the charge induced in the electrodes on both sides of the film also changes. Due to the above mechanism, the piezoelectric / pyroelectric element of E-PP has high piezoelectricity.

JP 60-055034 A

E-PP mentioned above has a problem in terms of environmental resistance and heat resistance, and the usage environment is limited. And it is expensive because it takes time to create.
The present invention has been made in view of the various problems as described above, and an object of the present invention is to provide a piezoelectric / pyroelectric element of a polymer material having high piezoelectricity. Another object of the present invention is to provide an inexpensive polymer piezoelectric / pyroelectric element having excellent environmental resistance and heat resistance.

In order to achieve the above object, in the piezoelectric / pyroelectric device of the present invention , a foamed core material is mixed with tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and a piezoelectric polymer material containing a plurality of closed cells. A pyroelectric element that is polarized while being irradiated with ultraviolet rays. Thereby, the ultraviolet rays assist the discharge in the closed bubbles, and many charges generated by the discharge are charged on the inner walls of the closed bubbles, so that the piezoelectricity of the element can be improved. Since all the bubbles present inside the element are all independent, it is difficult to collapse even when compressive stress is applied, and the rigidity of the element can be increased.

In addition, the polymer substance is a tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and the foamed core material is mixed with the FEP to generate the closed cells. An excellent element can be obtained, and closed cells included in the element can be easily generated.

  Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below do not limit the invention according to the scope of claims, and all combinations of features described in the embodiments are not necessarily essential to the establishment of the present invention. Absent.

First, the piezoelectric / pyroelectric device of this embodiment will be described with reference to FIG.
FIG. 1A is a plan view of the piezoelectric / pyroelectric element of this embodiment, and FIG. 1B is a cross-sectional view taken along the line α-α in FIG.
In this piezoelectric / pyroelectric element 1, a foamed FEP (F-FEP) sheet formed by foaming a tetrafluoroethylene-hexafluoropropylene copolymer (FEP) is formed into a rectangular shape as shown in FIG. It is created by cutting and trapping (polarizing) charges by applying corona discharge while irradiating with ultraviolet rays (hereinafter referred to as UV light) which is a characteristic part of the present invention.

  Such a piezoelectric / pyroelectric element 1 has many needle-like closed cells 2 as shown in FIG. When corona discharge is applied while irradiating the piezoelectric / pyroelectric element 1 with UV light, charges are trapped on the element upper surface 11, the element lower surface 12, the bubble upper surface 21 of the needle-like closed cell 2, and the bubble lower surface 22, respectively. The In the present embodiment, positive charges are trapped on the element upper surface 11 and the bubble lower surface 22, and negative charges are trapped on the element lower surface 12 and the bubble upper surface 21. A large number of needle-like closed cells 2 trapping this electric charge are present inside the piezoelectric / pyroelectric element 1, so that a huge dipole is formed inside the piezoelectric / pyroelectric element 1. .

Next, a procedure for creating the piezoelectric / pyroelectric element 1 will be described.
The piezoelectric / pyroelectric element 1 creates FEP-based pellets as a first procedure. As a second procedure, the FEP-based pellet is formed as a sheet and cut into a rectangular shape to create a rectangular sheet. As a third procedure, a piezoelectric / pyroelectric element 1 is produced by applying corona discharge while irradiating the rectangular sheet with UV light to trap charges.

First, the production of FEP-based pellets, which is the first procedure, will be described.
FEP-based pellets are prepared by mixing FOB with aluminum borate as a foam core and extruding it with a twin-screw extruder. The weight ratio of FEP to aluminum borate is 5 for aluminum borate with respect to 100 for FEP. In this embodiment, aluminum borate is used as the foam core material, but the present invention is not limited to this. For example, boron nitride may be used.

Next, the creation of a F-FEP rectangular sheet obtained by foaming FEP, which is the second procedure, will be described.
A T-shaped die is attached to an extruder capable of introducing nitrogen gas from the middle of the cylinder, and the pellets produced in the first procedure are set in the extruder. Then, the pellet is extruded from the cylinder while adding nitrogen gas at a constant pressure, and cooled while being wound by a hot roll having a temperature lower than the die temperature, thereby forming a sheet having needle-like closed cells 2. Then, the sheet is cut into a rectangular shape to create a rectangular sheet. In this embodiment, the sheet having closed cells 2 obtained by foaming FEP is formed with a width of 150 mm, a thickness of 200 μm, and a foaming rate of 40%. Further, the rectangular sheet is cut into a 60 mm × 60 mm square.

Finally, the creation of the piezoelectric / pyroelectric element 1 by UV light irradiation polarization, which is the third procedure, will be described.
FIG. 2 is a schematic view showing a corona discharge device used for UV light irradiation polarization.
The corona discharge device 4 includes a base 41, a side plate 42, an electrode plate 43, a grid electrode 44, a plurality of wire electrodes 45, and a high-pressure mercury lamp 46. One side plate 42 is provided on each of the left and right ends of the base 41, and an electrode plate 43 is placed on the center upper surface. A grid electrode 44 and a plurality of wire electrodes 45 are spanned between the two side plates 42. The plurality of wire electrodes 45 are spanned in parallel with a predetermined interval between the side plates 42.

  The grid electrode 44 is disposed at a distance a (for example, 3 mm) upward from the surface of the rectangular sheet 3 in order to uniformly charge and polarize the surface of the rectangular sheet 3. The wire electrode 45 is disposed at a distance b (for example, 35 mm) upward from the surface of the rectangular sheet 3. A positive voltage is applied to the wire electrode 45, a negative voltage is applied to the grid electrode 44, and the electrode plate 43 is grounded. The high-pressure mercury lamp 46 is disposed at a distance c (for example, 300 mm) upward from the surface of the rectangular sheet 3.

  The corona discharge device 4 used this time is made of a base 41, the side plate 42 is made of polytetrafluoroethylene (PTFE), the electrode plate 43 is made of stainless steel, and the grid electrode 44 and the wire electrode 45 are made of tungsten. However, the material of the base 41 and the side plate 42 is not limited to PTFE, and any material may be used as long as it has heat resistance and does not affect the charge trapping.

  The rectangular sheet 3 is placed on the electrode plate 43 of the corona discharge device 4 as described above, and the wire electrode 45 is irradiated with UV light (wavelength: 250 nm to 440 nm) using a 250 W high-pressure mercury lamp 46. A piezoelectric / pyroelectric element 1 is formed by applying a positive voltage of 20 kV, applying a negative voltage of 1.5 kV to 3 kV to the grid electrode 44 for polarization, and trapping charges in the rectangular sheet 3. The attenuation of UV light by the grid electrode 44 is 30% or less.

Next, the test results of the quasi-static piezoelectric rate d ₃₃ value of the piezoelectric / pyroelectric element 1 when UV light is irradiated and when not irradiated will be described with reference to FIG.
FIG. 3 is a comparison diagram of the quasi-static piezoelectric constant d ₃₃ value (pC / N) of the piezoelectric / pyroelectric element 1 when UV light is irradiated and not irradiated, and FIG. voltage graph showing the quasi-static piezoelectric constant _{d 33} value of the piezoelectric-pyroelectric element 1 at the time of changing the (Grid voltage (kV)), FIG. 3 (B) was changed polarization time (min) it is a graph showing a quasi-static piezoelectric constant d ₃₃ value of the piezoelectric-pyroelectric element 1 when. This test is a measurement of the quasi-static piezoelectric rate d ₃₃ value generated when pressure is applied to the piezoelectric / pyroelectric element 1.

As shown in FIG. 3A, the voltage (Corona voltage (kV)) of the wire electrode 45 is constant at 20 kV and the polarization time is 4 minutes. If not irradiated with UV light, quasi-static piezoelectric when quasistatic piezoelectric constant _{d 33} value when the voltage of the grid electrode 44 is 1.5kV is 349pC / N ± 18pC / N, the voltage of the grid electrode 44 is 3kV rate _{d 33} value was 298pC / N ± 89pC / N.

On the other hand, when UV light is irradiated, the quasi-static piezoelectric constant d ₃₃ value when the voltage of the grid electrode 44 is 1.5 kV is 452 pC / N ± 18 pC / N, and the quasi-static voltage when the voltage of the grid electrode 44 is 3 kV. The target piezoelectric constant d ₃₃ value was 375 pC / N ± 45 pC / N. Thus, the quasi-static piezoelectric constant d ₃₃ value is increased by about 25% to about 30% in the case of irradiating UV light compared to the case of not irradiating UV light, and the effect of UV light is great. it is conceivable that.

As shown in FIG. 3B, the voltage of the wire electrode 45 (Corona voltage (kV)) is constant at 16 kV, and the voltage of the grid electrode 44 is constant at 1.5 kV. When UV light was not irradiated, the quasi-static piezoelectric constant d ₃₃ value when the polarization time was 8 minutes was 266 pC / N ± 40 pC / N.

On the other hand, when UV light is irradiated, the quasi-static piezoelectric constant d ₃₃ value when the polarization time is 2 minutes is 388 pC / N ± 50 pC / N, and the quasi-static piezoelectric constant d ₃₃ value when the polarization time is 8 minutes. Was 420 pC / N ± 37 pC / N. Thus, the quasi-static piezoelectric constant d ₃₃ value is increased by about 60% in the case of irradiating with UV light compared to the case of not irradiating with UV light, and the effect of UV light is considered to be great.

Here, the increase in the quasi-static piezoelectric constant d ₃₃ value due to the irradiation of UV light is estimated as follows. The energy of the UV light is about 2 eV to 6 eV, which is slightly smaller than the energy band of the piezoelectric / pyroelectric element 1. For this reason, the UV light reaches the inside of the closed cell 2 of the piezoelectric / pyroelectric element 1 without being absorbed by the surface of the piezoelectric / pyroelectric element 1. As a result, the following effects can be expected. That is, the carrier generated in the vicinity of the closed cell 2 assists the discharge. The UV light reaching the closed cell 2 excites the gas in the closed cell 2 and facilitates the generation of discharge. The resistivity of the piezoelectric / pyroelectric element 1 is decreased, and the voltage applied to the closed cell 2 is relatively increased. Due to these effects, it is presumed that the polarization treatment of the piezoelectric / pyroelectric element 1 has progressed and the piezoelectricity has been improved.

FIG. 4 is a diagram showing a difference in performance between the present embodiment and a conventional piezoelectric / pyroelectric element. In FIG. 4, a piezoelectric / pyroelectric element using F-FEP when irradiated with UV light, a piezoelectric / pyroelectric element using F-FEP when not irradiating UV light, and a piezoelectric / pyroelectric element using solid FEP. Pyroelectric elements, piezoelectric / pyroelectric elements using poly (vinylidene fluoride) (PVdF), piezoelectric / pyroelectric elements using porous polypropylene (E-PP), quasi-static piezoelectric constant d ₃₃ value, rigidity, resistance The environmental properties and heat resistance were described.

As shown in FIG. 4, the F-FEP piezoelectric / pyroelectric element 1 when irradiated with UV light according to the present embodiment is the second from the top in terms of the quasi-static piezoelectric constant d ₃₃ value. The highest value is E-PP piezoelectric / pyroelectric element. However, E-PP has difficulties in rigidity, environmental resistance, and heat resistance. Therefore, it can be seen that the F-FEP piezoelectric / pyroelectric element 1 of the present embodiment when irradiated with UV light has high piezoelectricity and rigidity, and is excellent in environmental resistance and heat resistance.

  As described above, according to the piezoelectric / pyroelectric element 1 of the present embodiment, it is made of a polymer material containing a plurality of closed cells 2 and is polarized while being irradiated with UV light. Assisting the discharge in 2 and a large amount of electric charge generated by the discharge is charged on the inner wall of the closed cell 2, so that the piezoelectricity of the element 1 can be enhanced. Since all the bubbles 2 existing inside the element 1 are all independent, it is difficult to collapse even when a compressive stress is applied, and the rigidity of the element 1 can be increased.

  The polymer substance is FEP, and the foamed core material such as aluminum borate or boron nitride is mixed with the FEP to form closed cells 2, which are excellent in environmental resistance and heat resistance. The element 1 can be formed, and the closed cell 2 included in the element 1 can be easily generated.

  Any device provided with a flexible piezoelectric / pyroelectric device is applicable. For example, the present invention can be applied to electronic devices such as a computer, a computer, and a mobile phone, and can also be applied to a control circuit of a machine that needs to be equipped with a control device such as an automobile or an airplane in a narrow portion.

It is a figure explaining the piezoelectric and pyroelectric element of this embodiment. It is a figure of the corona discharge apparatus which polarizes the piezoelectric / pyroelectric element of FIG. It is a comparison diagram of the quasi-static piezoelectric constant d ₃₃ value of the piezoelectric-pyroelectric element when not irradiated with when irradiated with UV light. It is a figure which shows the performance difference of this embodiment and the conventional piezoelectric / pyroelectric element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric / pyroelectric element 2 Independent bubble 3 Rectangular sheet 4 Corona discharge device 11 Element upper surface 12 Element lower surface 21 Bubble upper surface 22 Bubble lower surface 41 Base 42 Side plate 43 Electrode plate 44 Grid electrode 45 Wire electrode

Claims (1)

A polymeric piezoelectric / pyroelectric element comprising a foam core material mixed with tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and containing a plurality of closed cells, which is polarized while being irradiated with ultraviolet rays. Piezoelectric / pyroelectric element of polymer material characterized by

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