Piezoelectric element

Abstract

To provide a piezoelectric element with excellent output characteristics. [Solution] A piezoelectric element 1 comprises a wound laminate 2 formed by winding a film 3 which is laminated in the order of a first conductive layer 31, a piezoelectric layer 32, and a second conductive layer 33, the end of the first conductive layer 31 protruding from the first laminated surface 21A of the wound laminate 2, and the end of the second conductive layer 33 protruding from the second laminated surface 21B opposite to the first laminated surface 21A of the wound laminate 2, and a first external electrode 4A electrically connected to the first conductive layer 31, and the second conductive layer 3 The piezoelectric element 1 further comprises a second external electrode 4B electrically connected to 3, wherein the first external electrode 4A extends from a first portion 21A1 on the outer periphery of the first laminated surface 21A to a second portion 21A2 different from the first portion 21A1, passing through the center of the first laminated surface 21A, and the second external electrode 4B extends from a first portion 21B1 on the outer periphery of the second laminated surface 21B to a second portion 21B2 different from the first portion, passing through the center of the second laminated surface 21B.

Description

Technical Field

[0001] The present invention relates to a piezoelectric element including a wound laminate formed by winding a film.

Background Art

[0002] Patent Document 1 discloses that in a wound laminate formed by winding a piezoelectric polymer film that exhibits piezoelectricity in the plane direction of the film, a substantially constant voltage continues to be output even after the load becomes constant. By using a piezoelectric element including such a wound laminate, a static load can be detected.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, as shown in Example 2 of Patent Document 1, in the case of a conventional wound laminate disclosed in Patent Document 1, when the number of layers is 100, the maintainability of the output voltage with respect to a static load is low, and in order to obtain good maintainability of the output voltage, it is necessary to set the number of layers to 500 or more.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a piezoelectric element having excellent output characteristics.

Means for Solving the Problems

[0006] The inventors of the present invention have found that the above problem is caused by the fact that external electrodes for extracting an output voltage are formed over the entire both laminated surfaces of the wound laminate, and have found that the above object can be achieved by devising the shape of the electrodes and the like, and have completed the present invention.

[0007] In other words, the present invention encompasses the subject matter described in the following sections, for example. Section 1. A piezoelectric element comprising a wound laminate formed by winding a film in which a first conductive layer, a piezoelectric layer, and a second conductive layer are laminated in that order, wherein the end of the first conductive layer protrudes from the first laminated surface of the wound laminate, and the end of the second conductive layer protrudes from the second laminated surface of the wound laminate opposite to the first laminated surface, A first external electrode electrically connected to the first conductive layer, The present invention further comprises a second external electrode electrically connected to the second conductive layer, The first external electrode extends from a first portion of the outer periphery of the first laminated surface to a second portion different from the first portion, passing through the center of the first laminated surface. The second external electrode is a piezoelectric element that extends from a first portion on the outer periphery of the second laminated surface through the center of the second laminated surface to a second portion different from the first portion. Section 2. The piezoelectric element according to item 1, wherein the film is a piezoelectric polymer film that exhibits piezoelectricity in the planar direction. Section 3. The piezoelectric element according to item 1, wherein the first external electrode and the second external electrode are metallicon electrodes. Section 4. The area of ​​the first external electrode is 15% to 80% of the first laminated surface. The piezoelectric element according to item 1, wherein the area of ​​the second external electrode is 15% to 80% of the second laminated surface. Section 5. The piezoelectric element according to item 1, wherein the first external electrode and the second external electrode are strip-shaped. Section 6. A piezoelectric element as described in item 1, wherein the measured hardness using an Asker rubber hardness tester type C is 60 to 80. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a piezoelectric element with excellent output characteristics. [Brief explanation of the drawing]

[0009] [Figure 1] It is a perspective view showing the configuration of a piezoelectric element according to an embodiment of the present invention. [Figure 2] It is a partial cross-sectional view of the wound laminate of the piezoelectric element. [Figure 3] (a) is a plan view of the first laminated surface of the piezoelectric element, and (b) is a plan view of the second laminated surface of the piezoelectric element. [Figure 4] It is a plan view showing the laminated surfaces in Examples 1 to 5. [Figure 5] It is a plan view showing the laminated surface in Example 6. [Figure 6] It is a plan view showing the laminated surface in Example 7. [Figure 7] It is a plan view showing the laminated surface in Comparative Example 1. [Figure 8] It is a plan view showing the laminated surface in Comparative Example 2. [Figure 9] It is a plan view showing the laminated surface in Comparative Example 3. [Figure 10] It is a perspective view showing the piezoelectric element in Comparative Example 4.

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In this specification, the expressions "containing" and "including" include the concepts of "containing", "including", "substantially consisting of", and "consisting only of".

[0011] (Structure of Piezoelectric Element) FIG. 1 is a perspective view showing the configuration of a piezoelectric element 1 according to an embodiment of the present invention, and FIG. 2 is a partial cross-sectional view of a wound laminate 2 of the piezoelectric element 1. The piezoelectric element 1 includes a wound laminate 2 formed by winding a film 3 in which a first conductive layer 31, a piezoelectric body layer 32, a second conductive layer 33, and an insulator layer 34 are laminated in this order. The end of the first conductive layer 31 protrudes from the first laminated surface 21A of the wound laminate 2, and the end of the second conductive layer 33 protrudes from the second laminated surface 21B on the opposite side of the first laminated surface 21A of the wound laminate 2.

[0012] Note that the wound laminate 2 is further press-processed after the film 3 is wound into a cylindrical shape, and the laminated surface (side surface) is a rounded rectangle, but the above press process may not be performed.

[0013] The piezoelectric element 1 further includes a first external electrode 4A electrically connected to the first conductive layer 31 and a second external electrode 4B electrically connected to the second conductive layer 33. That is, the first external electrode 4A is formed on the first laminated surface 21A where the end of the first conductive layer 31 protrudes, and the second external electrode 4B is formed on the second laminated surface 21B where the end of the second conductive layer 33 protrudes. The first external electrode 4A and the second external electrode 4B can be formed by performing metallikon spraying on the first laminated surface 21A and the second laminated surface 21B, and function as extraction electrodes for extracting the output voltage of the wound laminate 2 to the outside.

[0014] Note that an insulating margin M is formed between the first conductive layer 31 and the second external electrode 4B and between the second conductive layer 33 and the first external electrode 4A so that the first conductive layer 31 and the second conductive layer 33 do not short-circuit.

[0015] Here, in the conventional wound laminate, the external electrodes for extracting the output voltage are formed on the entire both laminated surfaces of the wound laminate. However, in the wound laminate 2 according to the present embodiment, the first external electrode 4A and the second external electrode 4B are respectively formed on a part of the first laminated surface 21A and the second laminated surface 21B. Specifically, as shown in FIG. 3(a), the first external electrode 4A extends from the first part 21A1 on the outer periphery of the first laminated surface 21A to the second part 21A2 different from the first part 21A1 through the central part of the first laminated surface 21A. As shown in FIG. 3(b), the second external electrode 4B extends from the first part 21B1 on the outer periphery of the second laminated surface 21B to the second part 21B2 different from the first part 21B1 through the central part of the second laminated surface 21B.

[0016] The centers of the first laminated surface 21A and the second external electrode 4B do not necessarily have to coincide with the centers (centroids) of the first laminated surface 21A and the second external electrode 4B, but only need to include the winding start point of the film 3. Also, in the first laminated surface 21A, the first portion 21A1 and the second portion 21A2 face each other, but the first portion 21A1 and the second portion 21A2 do not need to face each other. Similarly, in the second laminated surface 21B, the first portion 21B1 and the second portion 21B2 face each other, but the first portion 21B1 and the second portion 21B2 do not need to face each other. In other words, the first external electrode 4A and the second external electrode 4B are each formed so as to connect two spaced-apart portions of the outer circumference passing through the centers of the first laminated surface 21A and the second laminated surface 21B. Furthermore, although the first external electrode 4A and the second external electrode 4B are strip-shaped, they may also be, for example, arc-shaped, V-shaped, L-shaped, rectangular, or the like.

[0017] Film 3 is a piezoelectric polymer film that exhibits piezoelectricity in the planar direction. When a load is applied to the piezoelectric element 1, stress is generated in the thickness direction and planar direction of film 3, and the voltage generated in the piezoelectric layer 32 is extracted from the first external electrode 4A and the second external electrode 4B via the first conductive layer 31 and the second conductive layer 33. Furthermore, even after the load becomes constant, the piezoelectric element 1 continues to output voltage.

[0018] Furthermore, as described above, in the wound laminate 2 according to this embodiment, the first external electrode 4A extends from the first portion 21A1 on the outer circumference of the first laminate surface 21A to the second portion 21A2, passing through the center of the first laminate surface 21A, and the second external electrode 4B extends from the first portion 21B1 on the outer circumference of the second laminate surface 21B to the second portion 21B2, passing through the center of the second laminate surface 21B. As a result, as shown in the embodiments described later, the piezoelectric element 1 according to this embodiment can improve the output characteristics of at least one of the maximum output voltage for dynamic loads and the voltage maintenance time for static loads compared to conventional piezoelectric elements.

[0019] Preferably, the area of ​​the first external electrode 4A is 15% to 80% of the first laminated surface 21A, and the area of ​​the second external electrode 4B is 15% to 80% of the second laminated surface 21B. This further improves the output characteristics of the piezoelectric element 1.

[0020] Furthermore, the piezoelectric element 1 after the formation of the first external electrode 4A and the second external electrode 4B has a measured hardness of preferably 60 to 80, more preferably 60 to 70, and particularly preferably 65 to 69, using an Asker rubber hardness tester type C. Therefore, when the first external electrode 4A and the second external electrode 4B are strip-shaped, they preferably have a width of 15% to 80% of the width of the first laminated surface 21A and the second laminated surface 21B, and a width of 3 mm or more, and a thickness of preferably 0.3 to 0.7 mm.

[0021] (material) The following describes the materials of the first conductive layer 31, piezoelectric layer 32, second conductive layer 33, and insulating layer 34 that constitute the film 3, as well as the first external electrode 4A and the second external electrode 4B.

[0022] The materials of the first conductive layer 31 and the second conductive layer 33 are not particularly limited as long as they are conductive, and include, for example, aluminum, zinc, tin, lead, nickel, iron, copper, and alloys thereof.

[0023] The piezoelectric layer 32 is formed by a piezoelectric polymer film. The piezoelectric polymer film contains polylactic acid as its main component. The type of polylactic acid is not particularly limited, and known polylactic acids can be widely used, for example, polylactic acid obtained by condensation polymerization of lactic acid components as raw material monomers. The polylactic acid may contain only one optical isomer of L-lactic acid (L-form, PLLA) and D-lactic acid (D-form, PDLA), or both. When the polylactic acid mainly consists of L-lactic acid (L-form), the content of the D-form is preferably 5.0 mol% or less, more preferably 3.0 mol% or less, even more preferably 1.0 mol% or less, and particularly preferably 0.01 mol% or less. When the polylactic acid mainly consists of D-lactic acid (D-form), the content of the L-form is preferably 5.0 mol% or less, more preferably 3.0 mol% or less, even more preferably 1.0 mol% or less, and particularly preferably 0.01 mol% or less. The glass transition temperature, crystallization temperature, molecular weight, etc., of polylactic acid are not particularly limited.

[0024] The method for producing polylactic acid is not particularly limited; for example, it can be obtained by known manufacturing methods. Polylactic acid can also be obtained from commercially available products. Representative commercially available polylactic acid products include NatureWorks' "4032D" and TotalCorbion's Luminy series, specifically "L175," "LX175," and "LX575."

[0025] As the insulating layer 34, various insulating resins such as polypropylene (PP), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyethylene naphthalate (PEN), and polyvinylidene difluoride (PVDF) can be used.

[0026] The materials for the first external electrode 4A and the second external electrode 4B can be any conductive material, such as individual metals like zinc, lead, silver, chromium, aluminum, copper, and nickel, mixtures of multiple metals, or alloys thereof.

[0027] (Summary) As described above, in this embodiment, as shown in Figure 3(a), the first external electrode 4A extends from the first portion 21A1 on the outer circumference of the first laminated surface 21A to the second portion 21A2, passing through the center of the first laminated surface 21A, and as shown in Figure 3(b), the second external electrode 4B extends from the first portion 21B1 on the outer circumference of the second laminated surface 21B to the second portion 21B2, passing through the center of the second laminated surface 21B. By forming the first external electrode 4A and the second external electrode 4B in a part of the first laminated surface 21A and the second laminated surface 21B, respectively, the hardness of the piezoelectric element 1 can be reduced compared to the case where the first external electrode 4A and the second external electrode 4B are formed on the entire surface of the first laminated surface 21A and the second laminated surface 21B, respectively. As a result, deformation of the wound laminate 2 becomes easier, and the output voltage can be increased, as shown in the embodiments described later. Furthermore, since the first external electrode 4A and the second external electrode 4B are formed to connect two spaced-apart portions of the outer periphery, passing through the centers of the first laminated surface 21A and the second laminated surface 21B, respectively, the electrical connection between the first conductive layer 31 and the second conductive layer 33 and the first external electrode 4A and the second external electrode 4B can be maintained in the same manner as when the first external electrode 4A and the second external electrode 4B are formed over the entire surface of the first laminated surface 21A and the second laminated surface 21B, respectively. Therefore, a piezoelectric element 1 with excellent output characteristics can be provided.

[0028] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. [Examples]

[0029] The following describes examples of the present invention, but the present invention is not limited to the following examples.

[0030] (Examples 1-7) As the piezoelectric layer 32, a poly-L-lactic acid (PLLA) film having piezoelectric properties in the planar direction of the film was subjected to oil deposition to provide an insulating margin M, and then aluminum deposition was performed with a deposition resistance of 5Ω / □ (also written as Ω / square) to form the first conductive layer 31, thereby creating a first metallized film.

[0031] Next, as an insulating layer 34, an oil deposition was performed on a polypropylene film to provide an insulating margin, and then an aluminum deposition was performed with a deposition resistance of 5Ω / □ (also written as Ω / square) to form a second conductive layer 33, thereby creating a second metallized film.

[0032] After slitting the obtained first and second metallized films into narrow strips, the first and second metallized films were joined together and wound 395 times at a winding tension of 100g using a 3KAW-N2 automatic winding machine manufactured by Kaito Seisakusho Co., Ltd. to produce a cylindrical wound laminate 2. Furthermore, this wound laminate 2 was subjected to a winding tension of 5.2kgf / cm². 2 By pressing at room temperature under a load to flatten the material, a wound laminate 2 with a rounded rectangular laminate surface was fabricated.

[0033] Next, while maintaining the load, the first and second external electrodes 4A and 4B, each 0.6 mm thick, were formed by thermal spraying of metallicon onto the first and second laminated surfaces 21A and 21B of the wound laminate 2. Subsequently, without performing heat setting (thermal aging), the press load was released to fabricate the piezoelectric element 1.

[0034] In each embodiment, the first external electrode 4A and the second external electrode 4B have the same shape and size; therefore, hereafter, when the first external electrode 4A and the second external electrode 4B are not distinguished, they will simply be referred to as "electrode 4". Similarly, when the first laminated surface 21A and the second laminated surface 21B are not distinguished, they will simply be referred to as "laminated surface 21".

[0035] As shown in Figure 4, in the piezoelectric element 1 of Examples 1 to 7, the width L of the laminated surface 21 was 30 mm and the length H was 20 mm. On the other hand, the shape and size of the electrode 4 differed from one another in Examples 1 to 7.

[0036] In Examples 1 to 5, as shown in Figure 4, the shape of the electrode 4 is a single strip extending in the L direction of the laminated surface 21 (extending from one end on the outer circumference through the center to the other end), and the width of the electrode 4 was varied in each example.

[0037] In Example 6, as shown in Figure 5, the electrode 4 was formed in a rectangular shape over the entire area of ​​the laminated surface 21, excluding the two semicircular portions.

[0038] In Example 7, as shown in Figure 6, the electrode 4 was formed by continuously thermal spraying four strip-shaped metal layers, alternating by 1.5 mm in the width direction of the laminated surface 21.

[0039] In Examples 1 to 7, the ratio of the width and area of ​​electrode 4 to the laminated surface 21 was as shown in Tables 1 and 2.

[0040] [Table 1]

[0041] [Table 2]

[0042] (Comparative Examples 1-4) In Comparative Examples 1 to 4, the piezoelectric element 1 was fabricated in the same manner as in Examples 1 to 7, except for the electrode 4.

[0043] In Comparative Example 1, as shown in Figure 7, the electrode 4 was formed over the entire laminated surface 21. That is, Comparative Example 1 corresponds to the prior art described in Patent Document 1.

[0044] In Comparative Example 2, as shown in Figure 8, the electrode 4 was formed in a strip shape only in the central part of the laminated surface 21. That is, in Comparative Example 2, the electrode 4 does not extend to the outer periphery of the laminated surface 21.

[0045] In Comparative Example 3, as shown in Figure 9, the electrode 4 was formed in a strip shape only on the bottom edge of the laminated surface 21. That is, in Comparative Example 3, the electrode 4 does not pass through the center of the laminated surface 21.

[0046] In Comparative Example 4, the first external electrode 4A and the second external electrode 4B were formed so as to be point-symmetric. Specifically, as shown in Figure 10, the first external electrode 4A was formed in the lower left quadrant portion facing the surface of the first laminated surface 21A, and the second external electrode 4B was formed in the upper right quadrant portion facing the surface of the second laminated surface 21B.

[0047] In Comparative Examples 1 to 4, the ratio of the width and area of ​​electrode 4 to the laminated surface 21 was as shown in Table 3.

[0048] [Table 3]

[0049] (Evaluation results) The performance of the piezoelectric elements in Examples 1-7 and Comparative Examples 1-4 was evaluated. Specifically, pressurization was started at a speed of 100 mm / min from a state where a 20 mm x 40 mm indenter was in contact with the piezoelectric element (pressure 0 N), and the maximum pressure was maintained from the moment the maximum load (600 N) was reached. During this time, the voltage output from piezoelectric element 1 was measured, and the time until the output voltage decreased to a predetermined percentage (30% and 20%) of the maximum voltage was measured as the voltage maintenance time.

[0050] Furthermore, the hardness of the piezoelectric element and the strength of the electrodes were measured. The hardness of the piezoelectric element was measured using an Asker rubber hardness tester type C. The strength of the electrodes was observed when the piezoelectric element was pressurized with 600N or 1000N using the indenter described above.

[0051] The evaluation results for Examples 1-7 and Comparative Examples 1-4 are shown in Tables 4 and 5.

[0052] [Table 4]

[0053] [Table 5]

[0054] In Tables 4 and 5, "◎" indicates that no cracking, delamination from the laminated surface, or distortion has occurred due to the load, while "○" indicates that distortion has occurred, but no cracking or delamination from the laminated surface has occurred.

[0055] From the measurement results above, the maximum output voltage in Examples 1 to 7 was significantly increased compared to Comparative Examples 1 to 4, and the voltage maintenance time was also equivalent or better. Furthermore, the dielectric loss tangent in Examples 1 to 7 was equivalent to that of Comparative Example 1, but significantly lower than that of Comparative Examples 2 to 4. Therefore, it was shown that by forming the electrode 4 so as to connect two spaced-out portions of the outer circumference passing through at least the center of the laminated surface 21, the electrical connection does not deteriorate compared to when the electrode 4 is formed over the entire surface of the laminated surface 21. Thus, it was found that the present invention can provide a piezoelectric element with excellent output characteristics. [Industrial applicability]

[0056] This invention can be applied to vibrating bodies such as sensors that utilize piezoelectric properties, and electrical components such as piezoelectric actuators. [Explanation of symbols]

[0057] 1. Piezoelectric element 2-turn laminate 3 Films 4 electrodes 4A 1st external electrode 4B 2nd external electrode 21 Laminated surface 21A 1st laminated surface 21A1 Part 1 21A2 2nd part 21B 2nd laminated surface 21B1 Part 1 21B2 2nd part 31 First conductive layer 32 Piezoelectric layer 33 Second conductive layer 34 Insulator layer M Insulation margin

Claims

1. A piezoelectric element comprising a wound laminate formed by winding a film in which a first conductive layer, a piezoelectric layer, and a second conductive layer are laminated in that order, wherein the end of the first conductive layer protrudes from the first laminated surface of the wound laminate, and the end of the second conductive layer protrudes from the second laminated surface of the wound laminate opposite to the first laminated surface, A first external electrode electrically connected to the first conductive layer, The present invention further comprises a second external electrode electrically connected to the second conductive layer, The first external electrode extends from a first portion of the outer periphery of the first laminated surface to a second portion different from the first portion, passing through the center of the first laminated surface. The second external electrode is a piezoelectric element that extends from a first portion on the outer periphery of the second laminated surface through the center of the second laminated surface to a second portion different from the first portion.

2. The piezoelectric element according to claim 1, wherein the film is a piezoelectric polymer film that exhibits piezoelectricity in the planar direction.

3. The piezoelectric element according to claim 1, wherein the first external electrode and the second external electrode are metallicon electrodes.

4. The area of ​​the first external electrode is 15% to 80% of the first laminated surface. The piezoelectric element according to claim 1, wherein the area of ​​the second external electrode is 15% to 80% of the second laminated surface.

5. The piezoelectric element according to claim 1, wherein the first external electrode and the second external electrode are strip-shaped.

6. The piezoelectric element according to claim 1, wherein the measured hardness using an Asker rubber hardness tester type C is 60 to 80.

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