JPH0832140A - Device and mold for press molding sheet-like piezoelectric element and their using methods - Google Patents

Abstract

PURPOSE:To provide a device and mold for press molding a sheet-like piezoelectric element by which the element can be molded by filling up a cavity in a pressure-reduced vacuum tank with a highly viscous resin even when the depth of the cavity is shallow at the time of using a casting method and molded products having smooth surfaces and a uniform thickness can be obtained, and then, electrode surfaces can be stably joined simultaneously with the molding. CONSTITUTION:A cylinder 8 is mounted on a vacuum tank 1 and a top force 9 is fitted to the front end of a piston rod hang in the tank 1 from the top through a joint 25 which can be bent in all direction. Then a bottom force 15 incorporating an electric heater 16 which can be controlled in temperature through a transformer 20 and a thermocouple 12 connected to a thermometer 21 is installed below the top force 9 and a sheet-like intermediate force 13 which has a uniform thickness and a cavity formed by cutting out the central part of the force 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure molding apparatus and a pressure molding die for a sheet-like piezoelectric element made of a liquid thermosetting resin such as a lead zirconate titanate (PZT) powder mixed epoxy resin. Furthermore, it relates to the usage of both.

[0002]

2. Description of the Related Art Conventionally, a PZT powder mixed epoxy resin piezoelectric element is manufactured by using an aluminum foil (thickness: 15 μm, conductivity: 10 S).
/ Cm), PZT powder mixed piezoelectric epoxy resin is printed by screen printing, and heat-cured (160 ° C, 1 hour)
Thus, a film is formed, and printing is repeated on the film to repeatedly increase the thickness of the device to form a film having a desired thickness.

[0003]

However, this method has the following problems.

1) In terms of dimensional accuracy, since the printing screen of the squeegee of the printing tool for applying the resin on the rubber surface is pressed relatively strongly at the central portion, the thickness of printing becomes thinner at the central portion than at the periphery.

2) Since it is only possible to increase the thickness of about 30 μm in one printing, the number of manufacturing steps increases the thickness by performing multiple printing. Therefore, it took a lot of work.

3) Regarding the electrodes for applying a voltage to both end faces of the element and for extracting the voltage generated from the element to the outside, the material, conductivity and thickness are uniform and stable as good electrode conditions. In addition, it is flexible and has a high conductivity, and it is necessary to prevent an insulating layer from being formed in the bonding between the element surface and the electrode surface. However, conventionally, aluminum foil is used as it is on one side, and epoxy / PZT powder composite piezoelectric resin is cured on the other side to form a film, which has adhesiveness and flexibility after curing. A certain conductive paint (for example, carbon paste manufactured by Asahi Chemical Laboratory Co., Ltd .; FTU-20, conductivity 5 × 10S
/ Cm) was screen-printed and cured to form an electrode film having a thickness of about 10 μm, resulting in uneven thickness of the electrode film and low conductivity. For this reason, the quality is inferior, and an element for application to a highly accurate sensor or the like cannot be manufactured.

As a method for molding a liquid thermosetting resin such as a PZT powder mixed epoxy resin, there is a casting method in which the resin is poured into a mold and cured by heat. However, in this method, unlike the method of filling a mold with high-viscosity resin by applying high pressure like injection molding, in a vacuum chamber depressurized to remove the air contained therein, it is allowed to flow by its own weight. As the mold is filled, it is difficult to fill the resin as the cavity thickness becomes thinner, as can be seen from the fact that it is targeted for molding with a resin having a relatively low viscosity. It is not suitable for molding sheet-like elements with viscous resin.

That is, in the production of a sheet-like PZT powder high-viscosity epoxy resin piezoelectric element made of a high-viscosity liquid thermosetting resin such as a PZT powder-mixed epoxy resin, the resin has poor fluidity. Because it is a thin sheet-shaped molding,
It did not fill the cavity well and was not suitable for casting.

In addition, regarding the mold to be used, since the epoxy resin has adhesiveness, when a metal mold is used, the surface of the cavity is coated with Teflon or the like for release (adhesion of coating film). The surface of the mold is roughened and treated to improve the property), so that the surface becomes rough and the rough surface is transferred to the surface of the shaped article, resulting in poor element quality. Further, when the material of the mold is changed to Teflon resin or silicone rubber, there is a problem that heat conduction becomes poor and it takes a very long time to cure. In addition, there is a disadvantage that the electrode surface must be joined in a later process.

According to the present invention, in the casting method, even if the thickness of the cavity is thin in the depressurized vacuum chamber, the resin can be sufficiently filled with the high-viscosity resin for molding, and the surface is smooth and the thickness is uniform. Another object of the present invention is to provide a pressure molding apparatus and a pressure molding die for a sheet-shaped piezoelectric element capable of bonding a stable electrode surface simultaneously with molding, and a method of using both of them.

[0011]

In order to achieve the above object, a sheet-shaped piezoelectric element pressure molding apparatus according to the present invention has a cylinder mounted on the upper portion of a vacuum chamber, and the cylinder is mounted inside the vacuum chamber from above. An upper mold is attached to the tip of the hanging piston rod through a joint that bends freely, and an electric heater whose temperature can be adjusted with a transformer and a thermocouple connected to a thermometer are built into this upper mold. The lower mold is characterized by being installed in the lower part.

The pressure mold used in the above-mentioned apparatus has an upper mold having a flat molding surface attached to the lower end of a vertically driven piston rod through a joint that bends freely, and the temperature can be adjusted by a transformer. A lower mold with a uniform molding surface that contains a thermocouple connected to an electric heater and thermometer,
It is characterized in that it has a sheet-like shape with a uniform thickness and comprises an intermediate mold in which a central portion is cut out in the shape of an element to form a cavity.

Further, the above-mentioned molding apparatus and method of using the molding die are as follows: in a vacuum chamber under reduced pressure, with the electrode sheet inserted between the upper die and the intermediate die and between the lower die and the intermediate die,
It is characterized in that the liquid thermosetting resin injected into the cavity is made to flow by the pressure of the mold clamping and is heated and cured in the state of being filled into the cavity shape, and at the same time, the electrode sheet is joined to form the electrode.

[0014]

[Operation] Since the upper die is attached to the tip of the piston rod through a joint that bends freely, when the upper die and the lower die are engaged by the downward drive of the piston rod, the cavity is uniformly pressurized and filled with resin. You can Moreover, since the molding die uses a sheet-shaped intermediate die with a uniform thickness between the upper die and the lower die, the cavity surface becomes a smooth flat surface, and when the intermediate die is disposable once, The electrode can be inserted between the intermediate mold and the electrode between the upper mold and the intermediate mold so that the resin and the upper mold and the lower mold can be adhered when there is a sheet electrode between them during molding. Therefore, the electrodes of the element can be integrally joined to the element simultaneously with molding.

[0015]

EXAMPLE In the example of FIG. 1, the vacuum chamber 1 has a diameter of 300.
Inverted container type vacuum chamber body 1b made of mm polycarbonate
And the bottom plate 2 which is a flat plate made of iron, the O-ring 3 is interposed between them to form a dome shape. In any case, the molding die M is housed therein, and the sheet-shaped piezoelectric element is pressure-molded by the force of the air cylinder 8. The vacuum chamber body 1b
The material may be acrylic resin, iron, or the like.
Further, the shape may be a cylinder, a box shape, a spherical shape, or the like. By the way, in its structural form, various modes of the vacuum chamber 1 such as a door-integrated type and a vertically separated type can be adopted. In the embodiment shown in FIG. 2, the vacuum chamber 1 is almost entirely formed integrally. Hereinafter, the embodiment of FIG. 1 will be mainly described.

To attach the air cylinder 8, a hole is formed in the center of the upper portion of the vacuum chamber body 1b for fitting the piston rod projecting base, and the chamber wall is sandwiched with rubber packing 51 inside and outside with a diameter of 40 mm. A piston rod 19 having a driving distance of 100 mm was inserted, and the piston rod projecting base was fixed to the vacuum chamber main body 1b with a screw 50 from the inside. A hydraulic linder can be used instead of the air cylinder 8.

The upper die 9 has an aluminum plate (5
0mm x 50mm x 35mm), make a screw hole in the upper part, and attach the joint 25 that bends in the free direction to the bolt 18
The aluminum foil (5
(0 mm × 60 mm × 15 μm) was adhered and fixed to both side surfaces with Teflon adhesive tape 45, and the joint 25 and the tip of the piston rod 19 were joined with screws. An iron plate may be used instead of the aluminum plate.

An aluminum plate (100 mm × 10
(0 mm × 20 mm) was used, but an iron plate may also be used, and two holes parallel to the lower mold 15 are opened from the side surface, a heater 16 is inserted in each, and a hole is also formed in the upper part of the temperature sensor. 12 built-in.

As the intermediate mold 13, a polyester film (a material having a uniform thickness of 0.1 mm and a heat resistance of 160 ° C. or more) having a 4 cm diameter circle cut out was used. This hollow hole serves as a cavity, and its shape varies depending on the element shape to be manufactured.

The lower mold 15 is placed at the center of the iron flat plate 2 of the vacuum chamber 1. As a molding procedure, first, an aluminum foil (100 mm × 100 mm ×) as the lower electrode sheet 14 is formed thereon.
100 × 15 μm) and the intermediate mold 13 are sequentially stacked. next,
Air in the resin is obtained by injecting the material into the cavity of the intermediate mold 13 and evacuating from the exhaust port 5 with a vacuum pump while reducing the temperature of the hot plate to around 70 ° C. and reducing the pressure (about 10 ^-1 ). Then, the upper mold 9 is lowered by the operation of the air cylinder 8 to apply pressure. After pressing, the temperature of the hot plate is raised to 160 ° C., which is the curing temperature of the piezoelectric resin, and left for 1 hour to manufacture a piezoelectric element. The manufactured piezoelectric element is a vacuum chamber 1
Then, the air cylinder 8 is pulled up, the vacuum state is released and the air cylinder 8 is taken out.

As the material to be injected into the cavity, about 0.2 g of PZT powder mixed epoxy resin, which is about 1.5 times the weight obtained by multiplying the cavity volume by the specific gravity (3.0 to 3.3) of the piezoelectric resin, is used. Weighed as a batch.

Regarding the pressure applied to the mold and the resin during molding, the air pressure of 7 kgf / cm ² was applied to the air cylinder 8 having a cylinder diameter of 4 cm, and the total pressure of the air cylinder 8 was about 88 kgf. Then, since the projected area of the fitting portion of the mold was 25 cm ^2, it was about 3.5 kgf / cm ² .

[0023]

As described above, according to the present invention, there are the following excellent effects.

Since the piezoelectric resin can be pressed into the shape of the mold by pressing the piezoelectric resin with the upper mold and the lower mold in the decompressed vacuum chamber, the electrodes of the aluminum foil can be attached to both surfaces at the same time. The piezoelectric resin and the electrode sheet are in close contact with each other without air and the like, and the adhesive force of the liquid thermosetting resin allows the electrodes to be formed on both surfaces simultaneously with curing.

By using the metal foil for the electrode sheet, a high-quality electrode having a uniform thickness and high electrical conductivity can be formed.

Since the thickness of the piezoelectric element is the same as that of the intermediate die, it is possible to manufacture a piezoelectric element having a uniform thickness by using an intermediate die having a uniform thickness such as a polyester film. Further, an element having a desired thickness can be manufactured by simply changing the thickness of the intermediate die. Moreover, since the piezoelectric element can be manufactured by one-time heat curing, the manufacturing process is shortened as compared with the case of using the printing method, which is very efficient.

The upper die is attached to the tip of the piston rod of the cylinder that expands and contracts by pressure through a joint that bends in the free direction, and the intermediate die and the lower die have a simple structure that only needs to be set, so the die switching is easy. It is easy to manufacture small lots and many kinds. Further, since the production proceeds in a vacuum chamber in which air, moisture, dust, etc. are exhausted and removed, defects due to contamination are drastically reduced as in the case of production in a clean room.

[Brief description of drawings]

FIG. 1 is an explanatory cross-sectional view showing a pressure molding device for a sheet-shaped piezoelectric element.

FIG. 2 is a cross-sectional explanatory view showing another embodiment.

[Explanation of symbols]

 M Pressing mold 1 Vacuum tank 4 Liquid thermosetting resin 8 Cylinder 9 Upper mold 10,14 Electrode sheet 12 Thermocouple 13 Middle mold 15 Lower mold 16 Electric heater 20 Transformer 21 Thermometer 25 Joint that bends freely

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Claims (3)

[Claims] 1. A cylinder is mounted on an upper part of a vacuum chamber, and an upper mold is attached to the tip of a piston rod hanging from the inside of the vacuum chamber via a joint that bends in a free direction. A sheet-shaped piezoelectric element pressure-molding apparatus is characterized in that a lower die having an electric heater whose temperature can be adjusted by a transformer and a thermocouple connected to a thermometer is installed in the lower portion. 2. An upper mold having a flat molding surface attached to the lower end of a vertically driven piston rod through a joint that bends freely, and a thermocouple connected to an electric heater and a thermometer whose temperature can be adjusted by a transformer. 2. The sheet according to claim 1, characterized in that it comprises a lower die having a uniform molding surface in which is embedded, and an intermediate die having a uniform thickness and having a central portion cut out in the shape of an element to form a cavity. Molding die for use in pressure molding equipment for piezoelectric elements. 3. A liquid thermosetting resin injected into a cavity is clamped with an electrode sheet inserted between an upper mold and an intermediate mold and between a lower mold and an intermediate mold in a depressurized vacuum chamber. 2. The pressure-forming apparatus for a sheet-shaped piezoelectric element according to claim 1, wherein the sheet-shaped piezoelectric element is formed by bonding the electrode sheets at the same time as being heated and cured in a state of being filled with a cavity shape by being flowed by the pressure of 1. The method of using the molding die according to claim 2.