JPH02126798A - Piezoelectric diaphragm and its manufacture - Google Patents

Abstract

PURPOSE:To reduce the dispersion of resonant frequencies by providing second grooves having the same depth as a first groove at mutually different positions of the both surfaces of a supporting plate. CONSTITUTION:Electrodes 11 are formed on the both disk surfaces of a piezoelectric member 14, and bonded to a supporting plate 15. A first groove 16 having the even depth to partially bond the piezoelectric member 14 to the surface to be bonded is formed. Between the external peripheral part of the piezoelectric member 14 and the support fixing body 17 to support the external periphery of the supporting plate 15, second grooves 18, which are at mutually different positions and have the same depth as that of the groove 16, are prepared. A thermoplastic substrate 24 is used for the supporting plate 15, the substrate 24 is pinched by upper and lower molds 21 and 22 projecting at a part corresponding to the groove, heated and left for a prescribed time, then pressure is applied, and the groove is shaped on the substrate 24. That is, since the depth of the first and second grooves 16 and 18 can be controlled to a constant value by the height of a projecting pattern formed on the upper and lower molds 21 and 22 and the width of the frame 25 placed between the molds, the dispersion of the resonant frequencies can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a piezoelectric diaphragm and a method for manufacturing the same, and particularly relates to a piezoelectric diaphragm and a method for manufacturing the same.
This invention relates to a piezoelectric diaphragm that can be used in piezoelectric sounding bodies that achieve high sound pressure levels at low frequencies, and a method for manufacturing the same.

[Conventional technology]

A piezoelectric sounding body is produced by gluing a plate-shaped piezoelectric material with electrodes on both sides to a support plate, and applying an alternating voltage between the electrodes, resulting in the relationship between the expansion and contraction of the piezoelectric material in the plane direction and the fixation by the support plate. It utilizes flexural vibration, and there are two types: a unimorph structure in which a piezoelectric material is bonded to one side of the support plate, and a bimorph structure in which piezoelectric materials are bonded to both sides of the support plate.

This piezoelectric sounding body can be made smaller and thinner, and because it does not generate particularly important magnetism, it can be used for the I/O of information equipment.
It has become indispensable for pagers and mobile communication devices that may be carried along with the D card.

Conventionally, the piezoelectric diaphragm of this piezoelectric sounding body has been obtained simply by forming electrodes on a disc-shaped piezoelectric material and gluing it to a thin metal support plate. In order to reduce the thickness of the piezoelectric material and the support plate to 50 μm or less, the outer periphery of the support plate is used as a near-free support using an elastic adhesive. However, as the thickness of the support plate becomes thinner, the influence of the elastic adhesive becomes stronger, and the elastic adhesive cannot be applied uniformly, resulting in more variations in the performance obtained.

In order to solve such problems, a patent application filed in 1888
In No. 194, by providing grooves at different positions alternately on both sides between the outer peripheral fixing part of the support plate and the outer peripheral part of the piezoelectric material,
The resonant frequency is lower than that of elastic adhesives, achieving a smaller size and lower frequency.

Furthermore, Japanese Patent Application No. 62-188195 proposes a structure that prevents a decrease in the sound pressure level caused by a decrease in displacement due to adhesion of the piezoelectric material when the thickness of the piezoelectric material becomes thinner due to lower frequencies. The plates are partially bonded, and by integrating the former invention and the latter invention, it has become possible to obtain a piezoelectric sounding body that is small and has good low frequency characteristics.

[Problem to be solved by the invention]

In the above-mentioned conventional piezoelectric diaphragm and its manufacturing method, the peripheral support part has grooves arranged alternately on both sides as dormitory positions, or the adhesive surface has grooves for partial adhesion. Good low frequency characteristics were obtained. but,
In applications such as pagers, it is desired to include many functions in a small space, so the space for batteries and sounding elements becomes smaller.

For this reason, there is a need for a sounding body that can produce a sound pressure level that is sufficient for practical use even with a small shape with a 13IIIIII mouth using a single battery, and that can also produce sounds with a low frequency of 2 to 3k)Iz. In order to meet the requirements without variation, the depth of the grooves alternately placed at different positions on both sides of the peripheral support and the grooves for partial adhesion must be uniform.

The above-mentioned Japanese Patent Application No. 62-188194 discloses that a thin metal plate is patterned and etched to form a support plate, and a piezoelectric material is bonded to this support plate. In a diaphragm having such a structure, the resonant frequency changes depending on the depth of the grooves.

For example, FIG. 4 shows the relationship between the groove depth and the resonant frequency when a stainless steel plate with a thickness of 50 μm is used as the support plate material.

As shown in Figure 4, curve A is the case without grooves, and curve B
~D is the depth of the groove relative to the thickness of the support plate 215.315
．． This is the relationship between the support diameter and the resonant frequency when the diameter is 415. As can be understood from FIG. 4, it can be seen that as the depth of the groove changes, the resonant frequency changes greatly. Therefore, accurately controlling the depth of the grooves will reduce variations in the diaphragm. However, since this groove is formed by etching, conditions such as the concentration and temperature of the etching solution and the etching time must be carefully controlled.Furthermore, the etching time must also be controlled for a support plate thickness of several tens of micrometers. Therefore, it takes a short time and it is difficult to set the groove depth accurately. As a result, the resonant frequency changes, so when using the maximum amplitude at the resonant point, for example, in a separately excited type piezoelectric buzzer, the sound pressure level changes due to the shift in the resonant frequency, and in the worst case, The disadvantage is that it does not meet the standards.

In addition, metal plates such as stainless steel or brass are used for the support plate formed by etching because of the ease of etching, but this material itself is conductive, and the piezoelectric material is bonded using an insulating adhesive. Even if the adhesive is applied, the thickness of the adhesive is thin and it is difficult to maintain insulation from the piezoelectric electrode. For this reason, since the electric field applied to the piezoelectric material is also applied to the support plate itself, there is a drawback that sufficient insulation treatment is required when used as an actuator for a micropump for fluid transfer or a piezoelectric relay.

[Means to solve the problem]

The piezoelectric diaphragm of the present invention includes a plate-shaped piezoelectric material, a first groove having a uniform depth for dividing and adhering the piezoelectric material at at least two points, and a first groove on the outside of the outer periphery of the piezoelectric material. A support plate made of a thermoplastic base material and comprising at least one continuous second groove having the same depth as the first groove formed on each surface at different positions alternately on both sides; and a support and fixing body that supports the outside of the second groove on the outer periphery.

Furthermore, in the method for manufacturing a piezoelectric diaphragm of the present invention, a support plate to which a plate-shaped piezoelectric material is divided and bonded at at least two points is formed of a thermoplastic substrate, and an upper metal plate is provided to press the support plate from the upper surface of the support plate. a first protrusion forming a first groove for the split adhesion on a surface of the mold in contact with the support plate; and a second protrusion forming a second groove on the support plate outside the outer periphery of the piezoelectric material. and third protrusions are formed at alternately different positions from the second protrusions on a surface of a lower mold that supports the support plate from the lower surface of the support plate and are in contact with the support plate; The support plate is sandwiched between the upper mold and the lower mold to perform press molding.

[Effect]

A thermoplastic substrate is used as a support plate, and this substrate is sandwiched from above and below between molds having a convex shape at the portion corresponding to the groove position, and after being left at a temperature of 80 to 200° C. for a predetermined time, pressure is applied. Thereafter, by cooling the mold to room temperature, grooves can be formed in the substrate sandwiched within the mold. Therefore, if the convex patterns corresponding to these grooves are formed in the upper and lower molds at alternate positions, the substrate obtained by this manufacturing method will have different positions alternately on both sides. A support plate with grooves is obtained.

The depth of the groove to be formed can be freely controlled by placing a support frame spacer in the support plate thus obtained, which is determined by the relationship between the thickness of the substrate and the depth of the groove to be formed. Also, the position of the grooves and the pitch of the grooves may vary depending on the mold pattern.
This can be determined freely, and in addition to the grooves alternating on both sides of the support part, grooves for partial gluing of the adhesive part can also be obtained at the same time.

A piezoelectric diaphragm of the present invention can be obtained by bonding a piezoelectric material on which electrodes have been formed to the support plate obtained as described above. At this time, the depth of the grooves at different positions alternately on both sides of the support plate is accurately formed, and the variation is much smaller than in the conventional etching method.At the same time, the grooves on the support plate facilitate flexural vibration, and this displacement growing. Therefore, by fixing the peripheral portion of this support plate, a sounding body with a low resonance frequency and a high sound pressure level with little variation can be obtained.

〔Example〕 Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a partially cutaway perspective view of a piezoelectric diaphragm according to a first embodiment of the present invention.

As shown in FIG. 1, the first embodiment is a piezoelectric diaphragm used for a piezoelectric sounding body, and the piezoelectric material 14 has electrodes 11 formed on both sides of a disk shape, and the electrodes on the adhesive side are drawn out. A through hole 12 and a lead terminal 13 are formed. Piezoelectric material 1
4 is adhered to the support plate 15.

The support plate 15 has a first groove 16 of uniform depth for partial adhesion on the surface to which the piezoelectric material 14 is pasted, and also supports the outer periphery of the piezoelectric material 14 and the outer periphery of the support plate 15. Between the support fixtures 17 there are second grooves 18 of the same depth as the grooves 16 alternately located on both sides and at different positions.

Next, a method for manufacturing a piezoelectric diaphragm according to the present invention will be explained.

FIG. 2 is a cross-sectional view of a supporting plate groove forming jig used in a method of manufacturing a piezoelectric diaphragm according to a second embodiment of the present invention.

As shown in FIG. 2, an upper mold 21 for forming grooves.
and the lower mold 22 has a first projection 23. which forms the first groove 16 of the first embodiment described above with a convex pattern in a portion corresponding to the groove forming position. and a second groove 18 forming the second groove 18.
protrusion 23b and third protrusion 23. are formed on the surfaces of the upper mold 21 and the lower mold 22 by etching.

The support plate 15 shown in FIG. 1 is placed between the upper mold 21 and the lower mold 22.
A thermoplastic substrate 24 is placed, and a frame 25 serving as a spacer to obtain the desired groove depth is connected to the positioning pins 26 and holes 27.
placed between.

The thermoplastic substrate 24 is made of polyarylate, glass fiber reinforced polyester resin, etc.
It can be thermally deformed at a temperature of C.

The grooves are formed by sandwiching the thermoplastic substrate 24 between the upper mold 21 and the lower mold 22, but the temperature of the mold increases,
Until the thermoplastic substrate 24 is sufficiently heated, a dummy spacer is placed in addition to the frame 25 on the outer periphery between the upper mold 21 and the lower mold 22 to lift the upper mold 21, and then, After removing this dummy spacer, molding is performed by applying pressure.Next, after taking out this mold from the press machine, the support plate shown in FIG. 1 mentioned above is formed with grooves by cooling the mold. 15 is obtained.

In the support plate obtained by such a method, the depth of the grooves is determined by the thickness of the frame 25 and the thickness of the sandwiched thermoplastic substrate 24, and the depth of the grooves can always be constant under the same conditions. Therefore, unstable factors such as delicate control of processing time and concentration control of etching solution, which are required in conventional etching to form grooves, can be eliminated, and variations in the diaphragm can be extremely reduced.

The upper mold 21 and lower mold 22 shown in Fig. 2 have a thickness of 3 m.
Protrusions for forming grooves are formed on a 1 m stainless steel plate by etching, and the depth of this etching is set to 0.1.
Let it be mm. Further, the thickness of the frame 25 as a spacer placed between the upper mold 21 and the lower mold 22 is 0.15 mm.

Furthermore, as the thermoplastic substrate 24, a polyarylate with a thickness of 0.1 mm is used, and as described above, this is used as the upper mold 2.
1 and the lower mold 22, and set it in a press capable of heating to about 80 to 200°C.

On the other hand, the piezoelectric material bonded to the support plate with grooves formed is made of magnesium lead niobate Pb (Mgl/3/Nb2/3).
Powder of an electrostrictive material containing 03 as a main component is dispersed in a solvent together with an organic binder to form a slurry. This is made into a piezoelectric green sheet with a uniform thickness of about 40 to 100 μm by slip casting using a doctor blade. Next, this piezoelectric green sheet is punched out to a predetermined size, and the adhesive side is A through-hole connection hole for pulling the electrode to the front side is formed using a punch and die.Next, an electrode paste is printed on both sides of the piezoelectric material green sheet with the holes made using a screen printer. At this time, the side that will be the adhesive surface is a solid electrode over the entire surface, and the opposite surface, which is the front side, is an electrode pattern that partially has a terminal pattern connected to the through-hole portion. Furthermore, the piezoelectric green sheet with this electrode pattern printed on it was set in a press mold and heated at 100°C.
The piezoelectric green sheet is heated at a temperature of around 200 lbs. and then a pressure of about 250 kg/cm is applied to create a piezoelectric green sheet with high density.Next, the pressed piezoelectric green sheet is cut into predetermined dimensions, and then placed in a ceramic green sheet. In the debinding process, the organic substances present in the organic substances are gradually heated in an oxidizing atmosphere to decompose and disappear.
It will completely decompose and oxidize by ~600°C, but if the temperature is suddenly raised to the decomposition temperature, the piezoelectric material will be damaged.
The temperature is raised at a rate of 25° C. per hour or at a slower heating rate and maintained at 500 to 600° C. for a sufficiently long time to completely eliminate organic substances. Thereafter, by firing at a temperature of 900 to 1200[deg.] C., a piezoelectric material flat plate to be attached to the support plate described in the second embodiment described above is obtained.

As is clear from the above explanation, the thickness of the support plate and the depth of the groove can always be created in a constant state, and there is little variation in the resonance frequency, so even a separately excited type piezoelectric buzzer can always maintain a constant sound pressure level. can get.

In the first embodiment described above, one piezoelectric type sounding body is shown, but the shape of the support plate can be freely configured by the convex pattern of the mold formed by etching, so it can be formed by one press molding. A large number of support plates can be obtained. In addition, the shape of the diaphragm is not limited to a circle, and any support plate shape such as a square or an ellipse is possible, and if the piezoelectric material itself is cut to match the shape of the support plate after the electrode printing press. good.

The piezoelectric diaphragm of the first embodiment can be used not only as a sounding body but also as an actuator or a diaphragm in devices that require insulation, such as micro pumps for fluid transfer and piezoelectric relays.

FIG. 3 is a perspective view of a piezoelectric diaphragm according to a third embodiment of the present invention.

As shown in FIG. 3, the third embodiment is an actuator having a cantilevered unimorph structure and is used as a diaphragm for a piezoelectric pump. In this case as well, the support plate 32 fixed by the support fixing body 31 is provided with a mold having a convex pattern corresponding to the groove forming position as in the second embodiment described above using a thermoplastic base material. A double-sided electrode is formed on the support plate 32, and an extraction electrode is drawn out as a terminal on the front side by through-hole connection. A piezoelectric material 36 having a diameter of 35 is bonded.

Even with the piezoelectric diaphragm as an actuator configured in this way, the peripheral support part has 33 mm and the 34 mm has been partially bonded.
The depth of the groove can be controlled by the thickness of the frame used as a spacer when molding with a mold, and if molded under certain conditions, the depth of the groove is always constant, and the resonant frequency and An actuator with little variation in the amount of displacement can be obtained.

In the above explanation, the piezoelectric diaphragm of the present invention has been shown to be used as a piezoelectric sounding body or an actuator, but it can also be used as a sensor that uses electric charges generated by external force instead of applying an electric field to a piezoelectric material. Also, when used as a pressure sensor or a microphone, it is possible to obtain a device with little variation in the amount of charge generated in response to external input.

On the other hand, the thermoplastic resin molded with these molds is
Polyarylate and glass fiber reinforced polyester resins are available, but other materials are not limited as long as they soften within the range of 80 to 200'C.

〔Effect of the invention〕

As described above, the present invention provides a piezoelectric diaphragm in which the depth of the groove of the peripheral support part formed in the support plate to which the piezoelectric material is bonded and the groove for partial bonding are the same as the convex shape formed in the upper and lower molds. Since it can be controlled to a constant level by controlling the height of the pattern and the thickness of the frame as a spacer placed between the molds, there is less variation in the resonance frequency of the piezoelectric diaphragm. As a result, even in the configuration as a separately excited piezoelectric buzzer, a constant sound pressure level can be obtained. In addition, since the support plate itself is made of thermoplastic resin, the support plate obtained is an insulator, and therefore the electric field applied to the piezoelectric material is insulated by the support plate, making it suitable for use as micro pumps for fluid transfer, piezoelectric relays, etc. This has the effect of making it possible to use it as a diaphragm in devices that require insulation.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of a piezoelectric diaphragm according to a first embodiment of the present invention, and FIG. 2 is a support plate groove forming treatment used in a method of manufacturing a piezoelectric diaphragm according to a second embodiment of the present invention. FIG. 3 is a perspective view of a piezoelectric diaphragm according to the third embodiment of the present invention, and FIG. 4 shows the correlation between resonance frequency and support diameter when the depth of the groove in the support plate is changed. FIG. 11... Electrode, 12... Through hole, 13...
Output terminal, 14... Piezoelectric material, 15... Support plate, 1
6...Groove for partial adhesion, 17...Supporting and fixing body,
18...Groove, 21...Upper mold, 22...Lower mold, 23. . 23b, 23°...protrusion, 24...thermoplastic substrate, 25...frame, 26...alignment bin, 27...
- Hole, 31... Supporting fixing body, 32... Supporting plate, 33
...Groove of peripheral support portion, 34...Groove for partial adhesion, 35...Leader electrode, 36...Piezoelectric material.

Claims (2)

[Claims] (1) A plate-shaped piezoelectric material, a first groove having a uniform depth for dividing and adhering the piezoelectric material at at least two points, and alternately different positions on both sides of the piezoelectric material outside the outer periphery. a thermoplastic substrate support plate comprising at least one continuous second groove having the same depth as the first groove formed on each surface of the support plate; 1. A piezoelectric diaphragm comprising: a support fixing body supporting the outside of the groove of No. 2; (2) A support plate to which a plate-shaped piezoelectric material is divided and bonded at at least two points is formed of a thermoplastic substrate, and a surface of an upper mold that presses the support plate from the upper surface of the support plate is in contact with the support plate. a first protrusion forming a first groove for the split adhesion and a second protrusion forming a second groove on the support plate outside the outer periphery of the piezoelectric material; Third protrusions are formed at alternately different positions from the second protrusions on the surface of the lower mold that supports the support plate from the lower surface of the lower mold, and the third protrusions are arranged at different positions alternately from the second protrusions. A method for manufacturing a piezoelectric diaphragm, characterized in that press molding is performed by sandwiching the support plate.