JPH03236290A - Piezoelectric device - Google Patents

Abstract

PURPOSE:To improve conductivity between a mounting surface of a base and a mounted surface of a piezoelectric body by composing an adhesive layer having conductivity interposed between a mounting surface of a base and a mounted surface of a piezoelectric body of an adhesive component and fibers, which are buried and oriented in the direction connecting the mounting surface of the base and the mounted surface of the piezoelectric body and having conductivity. CONSTITUTION:Each piezoelectric element 2 consists of a base 3 having a flat mounting surface 30 composing a conductive surface and a piezoelectric ceramic 4 as a piezoelectric body having a flat mounted surface 40 composing a conductive surface arranged opposing to the base 3 and an adhesive layer 5 interposed between the mounting surface 30 of the base 3 and the mounted surface 40 of the piezoelectric ceramic 4. The adhesive layer 5 consists of an adhesive component 50 composing a matrix and fibers 51 buried in the matrix and having conductivity. An electric field is made to act on the fibers 51 buried in the adhesive component 50 before hardening, and electrostatic orientation is performed so that fibers 51 may be oriented about in the vertical direction to the surfaces of the rings 34, 44 in order to harden the adhesive component 50.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to a piezoelectric device. This piezoelectric device is, for example, a piezoelectric buzzer, a piezoelectric speaker, a piezoelectric switch, a piezoelectric fan,
Applicable to ultrasonic motors, ultrasonic vibrators, piezoelectric sensors, etc.

[Prior Art] Piezoelectric devices convert electrical energy into mechanical energy, and convert mechanical energy into electrical energy.
In recent years, it has been widely used in the fields of actuators, sensors, etc.

By the way, as a piezoelectric device, as disclosed in JP-A-1-87679, there is a piezoelectric ceramic having a base having a mounting surface forming a conductive surface, a mounting surface forming a conductive surface, and a method for mounting the base. It consists of an adhesive layer interposed between the surface and the surface to which the piezoelectric ceramic is attached, and is made of nickel,
A device in which nearly spherical, highly conductive metal powder particles of copper, aluminum, etc. are embedded in an adhesive layer is known.

In this device, nearly spherical highly conductive metal powder particles embedded in the adhesive layer improve the conductivity between the mounting surface of the base and the mounting surface of the piezoelectric ceramic.

[Problems to be Solved by the Invention] Unlike the piezoelectric device described above in which nearly spherical highly conductive metal powder particles are embedded in an adhesive layer, the present invention embeds fibers in an adhesive layer, and the fibers are attached to the mounting surface of a base. It is an object of the present invention to provide a piezoelectric device which connects the mounting surface of the piezoelectric body and the mounting surface of the piezoelectric body and orients the piezoelectric body in the direction of the ball, thereby improving the electrical conductivity between the mounting surface of the base and the mounting surface of the piezoelectric body. purpose.

[Means for Solving the Problems] A piezoelectric device of the present invention includes: a base having a mounting surface constituting a conductive surface; a piezoelectric body having a mounting surface disposed facing the base and constituting a conductive surface; In a piezoelectric device consisting of a conductive adhesive layer interposed between the mounting surface of the base and the mounting surface of the piezoelectric body, the adhesive layer consists of an adhesive component constituting the matrix and an adhesive component embedded in the matrix and attached to the base. It is characterized by comprising conductive fibers oriented in the direction connecting the mounting surface and the mounting surface of the piezoelectric body.

The base is to which the piezoelectric body is attached, and has a mounting surface that constitutes a conductive surface. The shape and structure of the base can be appropriately selected depending on the type of piezoelectric device, and can be, for example, an electrode plate, a substrate with a conductive surface, or a housing with a conductive surface.

Piezoelectric materials convert electrical energy into mechanical energy,
It has piezoelectric properties that convert mechanical energy into electrical energy. Piezoelectric materials include piezoelectric ceramics, crystal,
In some cases it can be made of piezoelectric polymer. Piezoelectric ceramics such as PZT and barium titanate can be used. The piezoelectric polymer can be based on polyvinylidene fluoride. The piezoelectric body has an attached surface that constitutes a conductive surface.

The adhesive layer is interposed between the mounting surface of the base and the mounting surface of the piezoelectric body, and is used to adhere the piezoelectric body to the mounting surface of the base. This adhesive layer consists of an adhesive component constituting a matrix and conductive fibers embedded in the matrix. The adhesive component can be a known adhesive component, for example,
Epoxy resins, acrylic resins, urethane resins, phenol resins, cyanoacrylate resins, and the like can be used as appropriate, and may contain conductive carbon powder particles and metal powder particles. The thickness of the adhesive layer can be appropriately selected depending on the type of adhesive component, etc., and can be, for example, 5 to 20 μm.

Fibers are those whose length is larger than their thickness.
Including needle-like, whisker-like, thread-like, and rod-like. The fibers can be whiskers or short fibers. Whiskers generally refer to whisker-like single crystals without defects, but they also include those that are close to polycrystalline amorphous, and in some cases, those that have grown into tetrapod shapes.

The fibers have the required conductivity and are oriented in a direction connecting the mounting surface of the base and the mounting surface of the piezoelectric body.

The conductivity, material, diameter, and length of 4i1i1 can be appropriately selected depending on the type of piezoelectric device. The ratio of fiber to the adhesive component can be appropriately selected depending on the type of fiber, the type of adhesive component, etc. For example, when the adhesive component is 100 parts by weight, the ratio of fiber to the adhesive component is 1 to 100 parts by weight, especially 1 to 100 parts by weight. It can be 50 parts by weight.

The material of the fibers may be any material as long as it has the required conductivity, and may be metals such as iron, nickel, etc., potassium titanate, or barium titanate. Potassium titanate whiskers and barium titanate whiskers are usually dielectric materials, but those with a certain conductivity are also commercially available. 104Ω-cm, B
K-200 specific resistance 1~5Ω-Cm, BK-300 specific resistance 10-1Ω・cm The specific resistance is 100 kg/cm
ctA when pressurized).

For example, when the fibers have dielectric properties such as potassium titanate whiskers and barium titanate whiskers, the fibers can be oriented in the direction connecting the mounting surface of the base and the mounting surface of the piezoelectric body. An electrostatic orientation method using the Withrow effect that polarizes the ends of the fibers positively and negatively to orient the fibers in the direction of the electric field.When the fibers are magnetic, such as iron whiskers and nickel whiskers, the fibers are oriented in the direction of the magnetic field. It is possible to employ means for orienting the material. The above orientation treatment can be performed before or during curing of the adhesive component of the adhesive layer.

When orienting the fibers, it is desirable to connect the mounting surface of the base and the mounting surface of the piezoelectric body 75 and apply pressure to the adhesive component of the adhesive layer in one direction. The reason for this is that it is advantageous to bring the lengthwise ends of the oriented fibers into contact with the mounting surface of the base and the mounting surface of the piezoelectric body, thereby increasing electrical conductivity. The degree of pressurization can be selected as appropriate.

Examples of the cross-sectional structure of the adhesive layer include the forms schematically shown in FIGS. 1 to 3. In the embodiment shown in FIG. 1, the embodiment shown in FIG. 2, and the embodiment shown in FIG. It is oriented perpendicularly or substantially perpendicularly to the mounting surface 40. Here, in the form shown in FIG. 1, the longitudinal ends of the fibers 51 are in contact with the mounting surface 30 of the base 3 and the mounting surface 40 of the piezoelectric body 4. In the form shown in FIG. 2, the ends of the fibers 51 in the length direction are bent while contacting the mounting surface 30 of the base 3 and the mounting surface 40 of the piezoelectric body 4. In the form shown in FIG. 3, an appropriate number of fibers 51 are connected in the length direction, and the outer fibers 51 are in contact with the mounting surface 30 of the base 3 and the mounting surface 40 of the piezoelectric body 4. ] In the piezoelectric device of the present invention, the piezoelectric body converts electrical energy into mechanical energy or converts mechanical energy into electrical energy due to its piezoelectricity.

At this time, electricity is transmitted and received between the mounting surface of the base, which is a conductive surface, and the mounting surface of the piezoelectric body, which is a conductive surface. In this case, in the piezoelectric device of the present invention, the fibers are oriented in the direction connecting the mounting surface of the base and the mounting surface of the piezoelectric body, so that electricity between the mounting surface of the base and the mounting surface of the piezoelectric body is Sending and receiving is good.

[Example] A piezoelectric device of the present invention will be described with reference to a first example shown in FIGS. 4 to 6. The piezoelectric device of this embodiment is applied to an ultrasonic motor.

The piezoelectric device of this embodiment is formed by arranging a large number of piezoelectric elements 2 in a ring shape, as shown in FIG. As shown in FIG. 6, each piezoelectric element 2 includes a base 3 having a flat mounting surface 30 constituting a conductive surface, and a flat mounting surface 40 disposed opposite to the base 3 constituting a conductive surface. It consists of a piezoelectric ceramic 4 as a piezoelectric body having a shape, and an adhesive layer 5 interposed between the mounting surface 30 of the base 3 and the mounting surface 40 of the piezoelectric ceramic 4.

The base 3 is made of phosphor bronze and has a wall thickness of 7 mm. The piezoelectric ceramic 4 is made of PZT, and the wall thickness is Q, 5 mm.
It is. The adhesive layer 5 is composed of an adhesive component 50 constituting a matrix and conductive fibers 51 embedded in the matrix.

The thickness of the adhesive layer 5 is 10 μm. The adhesive component 50 of the adhesive layer 5 is a one-component heating and anaerobically curing acrylic resin (R306J manufactured by Nippon Loctite).

Fiber 51 is potassium titanate whisker (conductive whisker "Dentor BK series" manufactured by Jinu Kagaku Co., Ltd. BK-300)
> is. This potassium titanate whisker has a fiber diameter of 0.2 to 0.5 μm, a fiber length of 10 to 20 t1m, a dielectric constant of 2.5 to 3.5, and a specific resistance of 10 when pressurized at 100 kq/cIi. -1Ω·cm. In this example,
The blending ratio of the adhesive layer 5 is 1 part by weight of fiber to 100 parts by weight of acrylic resin.

This piezoelectric device was manufactured as follows. First, using a ring 44 made of piezoelectric ceramics having a predetermined wall thickness and a ring 34 made of thick phosphor bronze as shown in FIG. The required amount was uniformly applied to the surface of the ring 44. Thereafter, the rings 34 and 44 were pasted together to form an adhesive ring.

Further, a pair of copper electrode parts were used, a resin film was interposed between the copper electrode part and the adhesive ring, and the adhesive ring was sandwiched between the copper electrode parts from both sides in the thickness direction.

Then, while pressurizing the rings 34 and 44 with a pressure of 4 kg/CIi by the copper electrode part, a voltage of 100 volts is applied to the copper electrode part, and an electric field is applied to the fiber 51 embedded in the adhesive component 50 before curing. The adhesive component 50 was cured by holding at 120° C. for 1 hour while electrostatically aligning the Ili fibers 51 so that they were oriented substantially perpendicularly to the surface of the ring 34, 44. Then ring 4
Piezoelectric element 2 was obtained by dividing the piezoelectric element 4 and ring 34 into 16 parts in the circumferential direction. Note that the manufacturing conditions of the first example were
Shown in the table.

In the piezoelectric device 1 according to this embodiment, as schematically shown in FIG. 6, the fibers 51 are oriented in the direction connecting the mounting surface 30 of the base 3 and the mounting surface 40 of the piezoelectric ceramic 4. Electrical contact between the mounting surface 30 of the base 3 and the mounting surface 40 of the piezoelectric ceramic 4 is good. Therefore, while ensuring good conductivity between the mounting surface 30 of the base 3 and the mounting surface 40 of the piezoelectric ceramic 4, it is possible to reduce the amount of fibers 51 blended in the adhesive layer 5, and thus the adhesion due to excessive blending of fibers 51. This is advantageous in avoiding a decrease in the adhesion of layer 5.

Furthermore, in this embodiment, as described above, the fibers 51 are oriented in the direction connecting the mounting surface 30 of the base 3 and the mounting surface 40 of the piezoelectric ceramic 4 to ensure electrical contact. , the above ring 34 and ring 44
The force for pressurizing can be reduced accordingly. Therefore, it is advantageous to avoid damage to the ring 44 and piezoelectric ceramics 4 due to excessive pressure.

A second embodiment of the piezoelectric device of the present invention will be described. The basic configuration of the piezoelectric device of the second embodiment is basically the same as that of the first embodiment. However, the base 3 is made of an iron-nickel alloy, the adhesive component of the adhesive layer 5o is a one-component heat-curable epoxy resin (Three Bond R2065FJ), and the fibers 51 are barium titanate whiskers. This potassium titanate whisker has a fiber diameter of 0.1 to 0.3 μm,
Fiber length is 5 to 10 μm, dielectric constant is 5.2, specific resistance is 1
It is 0'Ω·cm. The blending ratio of the adhesive layer 5 is 40 parts by weight of fiber to 100 parts by weight of epoxy resin.

The piezoelectric device of the second example was also manufactured basically in the same manner as the first example. That is, using a thin ring 34 made of an iron-nickel alloy, a required amount of adhesive component 50 containing fibers 51 was applied to the surface of the ring 44 made of piezoelectric ceramics. Thereafter, using a pair of copper electrode parts as in the first embodiment, the ring 3 is applied with a pressure of 4 kQ/ctA by the copper electrode part.
4 and a piezoelectric ceramic ring 44, a voltage of 30 volts is applied to the copper electrode part, and the adhesive component 5 before curing is applied.
An electric field is applied to the fibers 51 embedded in the fiber 5.
1 was held at 120° C. for 1 hour while being electrostatically aligned, thereby curing the adhesive component 50@. Thereafter, the piezoelectric element 2 was obtained by dividing it in the same manner as in the first example. The manufacturing conditions of the second example are shown in Table 1.

Also in the piezoelectric device according to the second embodiment, the fibers 51 are connected to the mounting surface 30 of the base 3 and the mounting surface 4 of the piezoelectric ceramic 4.
0, the electrical contact is good.

(Evaluation) The conductivity of the adhesive layer 5 was tested for the piezoelectric device of the first example and the piezoelectric device of the second example described above.

In the test, the resistance of the adhesive layer 5 was measured with a resistance meter, and when the resistance was 1°Ω or less, it was determined that the conductivity was good. As for the test results, as shown in Table 1, all 16 piezoelectric elements 2 were determined to have good conductivity in both the piezoelectric device of the first example and the piezoelectric device of the second example.

Furthermore, the piezoelectric device of the first embodiment and the piezoelectric device of the second embodiment! ! The device was tested for vibration durability of the adhesive layer 5.

The test was carried out at 100 volts and 20 Kt on piezoelectric ceramics 4.
The piezoelectric ceramic 4 was vibrated continuously for 20 hours by applying a voltage of -iz, and the piezoelectric ceramic 4 in which no cracking occurred was judged to have good vibration durability. In addition, it was confirmed that cracks were also generated in the adhesive layer 5 in cases where the piezoelectric ceramic 4 was cracked. As for the test results, as shown in Table 1, all 16 piezoelectric elements 1o were judged to have good vibration durability in both the piezoelectric device of the first example and the piezoelectric device of the second example, and therefore the overall evaluation was also good. It was good.

Furthermore, as Comparative Example 1, the procedure was basically the same as in the case of the piezoelectric device of the first example described above, but as shown in Table 1, the voltage applied during curing of the adhesive component was set to O volts, and the fiber was A piezoelectric device was manufactured by performing electrostatic alignment treatment. In addition, as Comparative Example 2, basically the same procedure as in the case of the piezoelectric device of the second embodiment described above was carried out, and the voltage applied during curing of the adhesive component was set to O volts as shown in Table 1.
A piezoelectric device was manufactured by electrostatic orientation treatment of fibers.

Regarding Comparative Example 1 and Comparative Example 2, the conductivity and vibration durability of the adhesive layer were similarly tested. The test results showed that in Comparative Example 1, the resistance of the adhesive layer was 20Ω or more, and in Comparative Example 2, the resistance of the adhesive layer was 20Ω or more, and as shown in Table 1, the conductivity was not good in both cases. Ta. Regarding the vibration durability test, no cracks occurred in the piezoelectric ceramics of both the piezoelectric device of the first example and the piezoelectric device of the second example, and as shown in Table 1, the results were good in terms of the vibration durability test. Ta.

Further, as Comparative Example 3, a piezoelectric device was manufactured with basically the same configuration as the piezoelectric device of the second example described above, but using copper fiber as the fiber as shown in Table 1. This copper fiber has a fiber diameter of 1 to 3 μm and a fiber length of 10 to 20 μm.
μm, and the dielectric constant is ~O. The blending ratio of the adhesive layer is 100 parts by weight of epoxy resin to 5 parts by length of fiber. The voltage applied during curing of the adhesive component was set to 100 ports.

Furthermore, as Comparative Example 4, the structure was basically the same as that of the piezoelectric device of the above-described second embodiment, and as shown in Table 1, an iron-nickel ring was used at 10 kQ/cm without adding fiber to the adhesive layer. A piezoelectric device was manufactured by pressurizing a piezoelectric ceramic ring with a pressure of 7 tons of Cl.

Further, as Comparative Example 5, the piezoelectric device had basically the same configuration as the piezoelectric device of the second example described above, except that nickel powder particles were contained in the adhesive component instead of fibers, and they were used when the adhesive component was cured. A piezoelectric device was manufactured by setting the voltage to O port. This nickel powder has a maximum particle size of 10 μm. The mixing ratio of the adhesive layer is 0.5 parts by weight of nickel powder per 100 parts by weight of epoxy resin.

Regarding Comparative Example 3, Comparative Example 4, and Comparative Example 5, the conductivity and vibration durability of the adhesive layer were similarly tested.

The test results show that in the case of Comparative Example 3, the resistance of the adhesive layer was 200.
The above is the case, and in the case of Comparative Example 4, the resistance of the adhesive layer is 20Ω.
The above is the case, and in the case of Comparative Example 5, the resistance of the adhesive layer is 10Ω.
As shown in Table 1, both of Comparative Examples 3.4 and 3.4 could not be said to have good conductivity. In Comparative Example 3, although highly conductive copper fibers were embedded in the adhesive layer, the conductivity was not good, presumably because the copper was not electrostatically oriented. Regarding the vibration durability test, cracks occurred in the piezoelectric ceramics of both the piezoelectric devices of Comparative Example 4 and Comparative Example 5.

[Application Example] An application example in which the piezoelectric device of the present invention is applied to an automobile mirror device is shown in FIGS. 7 and 8. This automobile mirror device includes a support plate 80, eight transparent plates supported by the support plate 80 and having a reflective layer on the back surface, a heat generation layer 82 laminated on the back surface of the transparent plate 81, and a flexible film that supplies power to the heat generation layer 82. It is composed of a printed cable 83 and a piezoelectric device 84 that is installed on the support plate 80 and serves as an ultrasonic transducer. The piezoelectric device 84 is positioned by the regulating protrusion 80a of the support plate 80, and is electrically connected to a power supply lead wire (not shown). In this device, when the piezoelectric device 84 is powered and operated, its vibration is also transmitted to the transparent plate 81, thereby causing the transparent plate 80 to
water droplets on the surface are removed.

[Effects of the Invention] According to the piezoelectric device of the present invention, the conductive fibers in the adhesive layer are oriented in the direction connecting the mounting surface of the base and the mounting surface of the piezoelectric body, so that the mounting surface of the base The transmission and reception of electricity between the piezoelectric body and the mounting surface of the piezoelectric body is good. Therefore, the conductivity between the base and the piezoelectric body is good.

According to the piezoelectric device of the present invention, it is possible to ensure good electrical conductivity between the mounting surface of the base and the mounting surface of the piezoelectric body. You can do less. Therefore, it is advantageous to avoid a decrease in the adhesive strength of the adhesive layer due to excessive blending of fibers. Therefore, it is advantageous to maintain the adhesive property even if the piezoelectric body vibrates.

[Brief explanation of drawings]

1 to 3 are cross-sectional views schematically showing various forms of the structure of the adhesive layer of the piezoelectric device of the present invention. 4 to 6 show a first embodiment of the present invention, FIG. 4 is a perspective view of a piezoelectric device, FIG. 5 is a perspective view of the piezoelectric device in the middle of manufacturing, and FIG. 6 shows the vicinity of the adhesive layer. FIG. 2 is a schematic cross-sectional view. 7 and 8 show an example of application of the present invention, in which FIG. 7 is a plan view of the main part of the mirror device, and FIG. 8 is a sectional view taken along the line X--X in FIG. 7. In the figure, 3 is a base, 30 is a mounting surface, 4 is a piezoelectric ceramic, 40 is a mounting surface, 5 is an adhesive layer, 50 is an adhesive component,
51 indicates fibers.

Claims (1)

[Claims] (1) A base having a mounting surface forming a conductive surface, a piezoelectric body having a mounting surface disposed opposite to the base and forming a conductive surface, and a mounting surface of the base and a mounting surface of the piezoelectric body. In a piezoelectric device comprising a conductive adhesive layer interposed between a surface and a conductive adhesive layer, the adhesive layer includes an adhesive component constituting a matrix, and an adhesive component that is embedded in the matrix and connects the mounting surface of the base and the piezoelectric body. A piezoelectric device characterized by comprising conductive fibers oriented in a direction connecting the surface to which it is attached.