Piezoelectric film device

Abstract

To provide a piezoelectric film device capable of inhibiting a hydrolytic cleavage while preventing deterioration in piezoelectric characteristic.SOLUTION: A piezoelectric film device comprises: a piezoelectric film that has a first main surface and a second main surface; and a first film that is arranged on at least one of the first main surface or the second main surface, is in contact with the piezoelectric film, and contains a hydrolytic cleavage inhibitor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a piezoelectric film device including a piezoelectric film. [Background technology]

[0002] Patent Document 1 discloses a polyester resin composition containing 100 parts by weight of a polyester resin (A), 0.01 to 15 parts by weight of at least one hydrolysis inhibitor (B) selected from a carbodiimide compound, an isocyanate compound, and an oxazoline compound, and 0.01 to 1 part by weight of a phosphorus-based stabilizer (C). Patent Document 1 discloses polylactic acid as an example of the polyester resin composition. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-291336 A Summary of the Invention [Problem to be solved by the invention]

[0004] Polylactic acid can be used as a piezoelectric material, but there is no description regarding the piezoelectricity of polylactic acid in Patent Document 1. The polylactic acid in Patent Document 1 contains a hydrolysis inhibitor, which disrupts the crystal structure that expresses the piezoelectric properties of polylactic acid, thereby deteriorating the piezoelectric properties.

[0005] An object of the present invention is to provide a piezoelectric film device that inhibits hydrolysis while preventing deterioration of the piezoelectric characteristics. [Means for solving the problem]

[0006] The piezoelectric film device comprises a piezoelectric film having a first principal surface and a second principal surface, and a first film disposed on at least one of the first principal surface or the second principal surface, in contact with the piezoelectric film, and including a hydrolysis inhibitor. Effect of the Invention

[0007] The electronic device of the present invention can inhibit hydrolysis while preventing deterioration of the piezoelectric characteristics. [Brief description of the drawings]

[0008] [Figure 1] 1 is a plan view of a piezoelectric film device 1 according to an embodiment of the present invention; [Diagram 2] 2 is a cross-sectional view taken along the line AA shown in FIG. 1. [Diagram 3] 1 is a cross-sectional view of a piezoelectric film device 1 according to a first modified example. [Figure 4] 11 is a cross-sectional view of a piezoelectric film device 1 according to a second modified example. FIG. [Diagram 5] 11 is a cross-sectional view of a piezoelectric film device 1 according to a fourth modified example. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a piezoelectric film device 1 according to an embodiment of the present invention will be described. Fig. 1 is a plan view of the piezoelectric film device 1 according to an embodiment of the present invention. Fig. 2 is a cross-sectional view taken along line AA shown in Fig. 1.

[0010] The piezoelectric film device 1 has a rectangular shape having a long side direction (Y direction) and a short side direction (X direction) in a plan view.

[0011] The piezoelectric film device 1 includes a first electrode 11, a piezoelectric film 12, a second electrode 13, and a hydrolysis inhibiting film 14. The first electrode 11, the piezoelectric film 12, the second electrode 13, and the hydrolysis inhibiting film 14 are each rectangular in shape having a long side direction (Y direction) and a short side direction (X direction) in a plan view. The length of the piezoelectric film 12 in the thickness direction (Z direction) is longer than the length of the hydrolysis inhibiting film 14 in the thickness direction (Z direction). The length of the hydrolysis inhibiting film 14 in the Z direction is preferably 10 times or less than the length of the piezoelectric film 12 in the Z direction. However, the length of the piezoelectric film 12 in the Z direction may be shorter than the length of the hydrolysis inhibiting film 14 in the Z direction. Alternatively, the length of the piezoelectric film 12 in the Z direction may be the same as the length of the hydrolysis inhibiting film 14 in the Z direction.

[0012] The piezoelectric film device 1 is attached to the housing of an electronic device with, for example, an adhesive, etc. In this way, the piezoelectric film device 1 is used to detect, for example, the deflection of the housing.

[0013] The piezoelectric film 12 has a first main surface S1 and a second main surface S2 that face each other in the thickness direction. The first electrode 11 is formed on the first main surface S1 of the piezoelectric film 12. The first electrode 11 is, for example, a thin metal film such as copper foil, or a polymer conductive material such as PEDOT (polyethylenedioxythiophene). The first electrode 11 is formed directly on the first main surface S1 by a process such as printing or vapor deposition. The first electrode 11 may be attached to the first main surface S1 via an adhesive. Alternatively, the first electrode 11 may be, for example, a conductive adhesive.

[0014] The hydrolysis inhibitor film 14 is an example of the first film of the present invention. The hydrolysis inhibitor film 14 is formed so that the fourth main surface S4 is in contact with the second main surface S2 of the piezoelectric film 12. The hydrolysis inhibitor film 14 is a resin sheet. The hydrolysis inhibitor film 14 forms a three-dimensional network structure by polymerizing a hardly hydrolyzable polymer and an easily hydrolyzable polymer. The easily hydrolyzable polymer is a resin having an ester bond or a carbonate ester bond in the molecular chain, and is, for example, at least one of polyester, polybutylene terephthalate, polycarbonate, polyamide, polythioester, and polyurethane. The hardly hydrolyzable polymer is, for example, at least one of fluororesin, PPE (polyphenylene ether), polysulfone, polyethersulfone, PPS (polyphenylene sulfide), PEEK (polyethyl ether ketone), and hard urethane. In addition, a hydrolysis inhibitor having a molecular size smaller than the mesh size of the three-dimensional network structure is added to the hydrolysis inhibitor film 14. The hydrolysis inhibitor material is a compound having at least one functional group selected from the group consisting of a carbodiimide group, an oxazoline group, and an epoxy group, and is characterized in that many hydrolysis inhibitors are occupied at the mesh positions of the three-dimensional mesh structure of the hydrolysis inhibitor film 14.

[0015] The second electrode 13 is formed on the third main surface S3 of the hydrolysis-inhibiting film 14. The second electrode 13 is, for example, a thin metal film such as copper foil, or a polymer conductive material such as PEDOT (polyethylenedioxythiophene). The second electrode 13 is formed directly on the third main surface S3 by a process such as printing or vapor deposition. The second electrode 13 may be attached to the third main surface S3 via an adhesive. Alternatively, the second electrode 13 may be, for example, a conductive adhesive.

[0016] One of the first electrode 11 and the second electrode 13 is a reference electrode (ground electrode), and the other is a detection electrode. For example, the first electrode 11 is a detection electrode.

[0017] The piezoelectric film 12 is a film whose main material is a chiral polymer such as polylactic acid. The polylactic acid may be either poly-L-lactic acid (PLLA) or poly-D-lactic acid (PDLA).

[0018] Polylactic acid is a chiral polymer with a helical main chain, and has the property of exhibiting piezoelectricity when oriented in a specific axial direction. This piezoelectricity is expressed by the piezoelectric tensor component d14, with the thickness direction of the film as the first axis and the direction in which the polylactic acid molecules are oriented as the third axis.

[0019] If the piezoelectric film 12 is oriented in a direction (stretching direction) in which the molecules of polylactic acid are oriented in a direction intersecting the long and short sides of the piezoelectric film device 1, polarization occurs due to expansion and contraction in the long or short side direction of the piezoelectric film device 1. For example, by stretching the piezoelectric film 12 in a direction at an angle of about 45° to the long and short sides of the piezoelectric film device 1, polarization occurs due to expansion and contraction in the long or short side direction of the piezoelectric film device 1, and an output as a piezoelectric sensor appears.

[0020] The angle of the stretching direction of the piezoelectric film 12 is not limited to exactly 45° with respect to the long and short sides of the piezoelectric film device 1, but may be any angle close to 45°. However, the closer the angle of the stretching direction is to 45° or 0° with respect to the long and short sides, the more efficiently the deflection of the long and short sides of the piezoelectric film device 1 can be detected.

[0021] Therefore, in this embodiment, approximately 45° refers to an angle in a predetermined range with 45° as the center, for example, about 45°±10°. These specific angles may be appropriately determined according to the overall design based on the application of the displacement sensor and the characteristics of each part.

[0022] As described above, when the piezoelectric film device 1 is used as a sensor, it detects the deflection of the housing to which it is attached with high sensitivity.

[0023] On the other hand, the polylactic acid of the piezoelectric film 12 is a hydrolyzable polymer. When the piezoelectric film 12 is exposed to high humidity for a long period of time, the piezoelectric properties of the film 12 are degraded by hydrolysis. In JP 2007-291336 A, a hydrolysis inhibitor is added to suppress the hydrolysis of the polylactic acid. However, when the hydrolysis inhibitor is added to the piezoelectric film 12, the crystal structure that expresses the piezoelectric properties of the polylactic acid is disturbed, and the piezoelectric properties are degraded. Therefore, only a small amount of the hydrolysis inhibitor can be added to the polylactic acid. If the amount of the hydrolysis inhibitor added is small, the effect of suppressing hydrolysis is reduced.

[0024] In contrast, in the piezoelectric film device 1 of the present embodiment, no hydrolysis inhibitor is added or only a small amount is added to the piezoelectric film 12. Meanwhile, a hydrolysis inhibitor film 14 is disposed on at least one of the first main surface S1 or the second main surface S2 of the piezoelectric film 12.

[0025] The hydrolysis inhibitor film 14 contains a large amount of a hydrolysis inhibitor. As hydrolysis progresses, the easily hydrolyzable polymers in the above-mentioned three-dimensional network structure are decomposed, and part of the network structure is destroyed. As a result, the hydrolysis inhibitor contained in large quantities in the hydrolysis inhibitor film 14 is released. The released hydrolysis inhibitor reaches the piezoelectric film 12. The hydrolysis inhibitor diffuses into the piezoelectric film 12 and exerts its ability (repairing and rebonding molecular chains cut by hydrolysis) in the piezoelectric film 12. As a result, the polymer structure of the piezoelectric film 12 is maintained.

[0026] In the piezoelectric film device 1 of this embodiment, no hydrolysis inhibitor or only a small amount of hydrolysis inhibitor is added to the piezoelectric film 12, so there is no degradation of the piezoelectric properties due to the hydrolysis inhibitor. On the other hand, the hydrolysis inhibitor film 14 contains a large amount of a hydrolysis inhibitor, so the hydrolysis inhibition lasts for an extremely long time.

[0027] (Variation 1) Fig. 3 is a cross-sectional view of the piezoelectric film device 1 according to Modification 1. Components common to those in Fig. 2 are given the same reference numerals and description thereof will be omitted.

[0028] In the piezoelectric film device 1 according to the first modification, the length of the hydrolysis inhibiting film 14 in the thickness direction (Z direction) is longer than the length of the piezoelectric film 12 in the thickness direction (Z direction).

[0029] Therefore, the amount of the hydrolysis inhibitor in the piezoelectric film device 1 according to the first modification is greater than the amount of the hydrolysis inhibitor contained in the piezoelectric film device 1 of the above-mentioned embodiment, and therefore the hydrolysis inhibition lasts longer.

[0030] On the other hand, the piezoelectric film device 1 of the above-described embodiment is less affected by the parasitic capacitance due to the hydrolysis inhibiting film 14 than the piezoelectric film device 1 according to Modification 1. Therefore, the piezoelectric film device 1 of the above-described embodiment has a higher sensitivity as a sensor than the piezoelectric film device 1 according to Modification 1.

[0031] The thickness of hydrolysis inhibiting film 14 may be appropriately set taking into consideration the desired sensitivity of the sensor and the duration of hydrolysis inhibition.

[0032] (Variation 2) Fig. 4 is a cross-sectional view of the piezoelectric film device 1 according to the modified example 2. The same components as those in Fig. 2 are denoted by the same reference numerals, and the description thereof will be omitted.

[0033] The piezoelectric film device 1 according to the first modification includes a hydrolysis inhibiting film 14, which is an example of a first film, and further includes a second hydrolysis inhibiting film 15 disposed on the second main surface S2.

[0034] This allows the hydrolysis inhibitor to diffuse from both sides of the piezoelectric film 12, further enhancing the effect of inhibiting hydrolysis.

[0035] (Variation 3) The structure of the hydrolysis inhibiting film 14 is not limited to the above-mentioned three-dimensional mesh structure. For example, the structure of the hydrolysis inhibiting film 14 may be a capsule shape. In this case, the wall of the capsule shape is made of a polymer that is difficult to hydrolyze and a polymer that is easily hydrolyzable. A hydrolysis inhibitor is contained in the capsule shape. As hydrolysis progresses, the easily hydrolyzable polymer in the wall of the capsule shape is decomposed, and part of the wall is destroyed. As a result, the hydrolysis inhibitor contained in a large amount in the hydrolysis inhibiting film 14 is released.

[0036] (Variation 4) Fig. 5 is a cross-sectional view of the piezoelectric film device 1 according to Modification 4. The same components as those in Fig. 2 are denoted by the same reference numerals, and the description thereof will be omitted.

[0037] The piezoelectric film device 1 according to the fourth modification has a porous conductive polymer film 16 instead of the second electrode 13 and the hydrolysis inhibitor film 14. The porous conductive polymer film 16 has a resistant conductive polymer, an easily hydrolyzable polymer, and a hydrolysis inhibitor. The resistant conductive polymer has a porous film such as conductive polypyrrole. The porous conductive polymer film 16 forms a three-dimensional network structure by polymerization of a resistant conductive polymer and an easily hydrolyzable polymer. As hydrolysis progresses, the easily hydrolyzable polymer in the three-dimensional network structure is decomposed, and a part of the network structure is broken. Therefore, the hydrolysis inhibitor contained in the porous conductive polymer film 16 is released. The released hydrolysis inhibitor reaches the piezoelectric film 12. The hydrolysis inhibitor diffuses into the piezoelectric film 12 and exerts its ability (repairing and recombining molecular chains cut by hydrolysis) in the piezoelectric film 12. As a result, the polymer structure of the piezoelectric film 12 is maintained.

[0038] In this way, the piezoelectric film device 1 according to the fourth modification has a single layer of porous conductive polymer film 16. This improves the manufacturing efficiency of the piezoelectric film device 1. Finally, the above-described embodiments should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not the above-described embodiments. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the claims.

[0039] The technical concept of this embodiment is as follows. (1) a piezoelectric film including a first principal surface and a second principal surface; a first film disposed on at least one of the first principal surface or the second principal surface, in contact with the piezoelectric film, and including a hydrolysis inhibitor; A piezoelectric film device comprising:

[0040] (2) The hydrolysis inhibitor material is a compound having at least one functional group selected from the group consisting of a carbodiimide group, an oxazoline group, and an epoxy group. A piezoelectric film device according to (1) above.

[0041] (3) The thickness of the first film is greater than the thickness of the piezoelectric film. A piezoelectric film device according to (1) or (2) above.

[0042] (4) The thickness of the first film is smaller than the thickness of the piezoelectric film. A piezoelectric film device according to (1) or (2) above.

[0043] (5) further comprising a second film containing a hydrolysis inhibitor; the first film is disposed on the first major surface; The second film is disposed on the second major surface. A piezoelectric film device according to any one of (1) to (3) above.

[0044] (6) the first film includes a third major surface and a fourth major surface; the first film is in contact with the piezoelectric film such that the fourth principal surface is in contact with the first principal surface, The piezoelectric film device includes: A first electrode disposed on the second major surface; A second electrode disposed on the third major surface; Further comprising: A piezoelectric film device according to any one of (1) to (5) above. [Explanation of symbols]

[0045] 1: Piezoelectric film device 11: 1st electrode 12: Piezoelectric film 13:Second electrode 14: Hydrolysis-inhibiting film 15: Second hydrolysis inhibition film S1: First main surface S2: 2nd principal surface S3: Third main surface S4: Fourth main surface

Claims

1. a piezoelectric film including a first major surface and a second major surface; a first film disposed on at least one of the first principal surface or the second principal surface, in contact with the piezoelectric film, and including a hydrolysis inhibitor; A piezoelectric film device comprising:

2. 2. The piezoelectric film device according to claim 1, wherein the hydrolysis inhibitor material is a compound having at least one functional group selected from the group consisting of a carbodiimide group, an oxazoline group, and an epoxy group.

3. The thickness of the first film is greater than the thickness of the piezoelectric film. The piezoelectric film device according to claim 1 or 2.

4. The thickness of the first film is smaller than the thickness of the piezoelectric film. The piezoelectric film device according to claim 1 or 2.

5. a second film comprising a hydrolysis inhibitor; the first film is disposed on the first major surface; The second film is disposed on the second major surface. The piezoelectric film device according to claim 1 or 2.

6. the first film includes a third major surface and a fourth major surface; the first film is in contact with the piezoelectric film such that the fourth principal surface is in contact with the first principal surface; The piezoelectric film device includes: A first electrode disposed on the second major surface; A second electrode disposed on the third major surface; Further comprising: The piezoelectric film device according to claim 1 or 2.

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