JPS6325516B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a bimorph element,
The present invention aims to provide a method for manufacturing a bimorph device with good electrical and mechanical properties. Generally, bimorph elements are used in vibrating bodies such as microphones, pickups, buzzers, and speakers. Using this element enables power saving and thinning. The conversion element handled here has electrodes attached to both sides, and two piezoelectric elements are arranged facing each other, and a conductive member is sandwiched between the electrodes to form a bimorph vibrator. Bimorph oscillators are made by pasting together two pieces of piezoelectric ceramics that expand and contract in the length direction, and when one expands, the other contracts, resulting in a bending motion as a whole.It lowers mechanical impedance and can generate a large output voltage. This is how it was done. Usually, a piezoelectric element used in a bimorph element has a thin disk shape, and the following description will also be made using a thin disk-shaped element as an example. The fundamental resonant frequency of a bimorph element is approximately determined by its size and shape. Piezoelectric constants require high dielectric constants and high electro-mechanical coupling coefficients. In order to set the fundamental resonance frequency to an audible frequency band, a thin piezoelectric element is required. However, thin ceramic elements have low mechanical strength, and various problems arise when they are used as electronic components. Therefore, a conductive reinforcing plate is used. An adhesive is used to integrate the reinforcing plate and the ceramic plate. Significant acoustic reflections occur at the interface between the ceramic plate and the reinforcing plate, resulting in a substantial loss of acoustic energy. These reflections further significantly alter the frequency response of the piezoelectric element. Furthermore, since the adhesive, which is an organic material, and the piezoelectric element have different thermal expansion coefficients, the thermal shock resistance is poor, and cracks or cracks occur inside the piezoelectric element, which can be a fatal defect. An object of the present invention is to provide a method for mass-producing bimorph elements that has high conversion efficiency, low energy loss in the adhesive, and is reliable against thermal changes. Regarding an example of the bimorph element according to the present invention,
This will be explained using drawings. In the figure, 1 and 1' are piezoelectric ceramic sheets, and electrodes 2 and 3 and 2' and 3' are provided on both surfaces of each sheet. Reference numeral 4 denotes a conductive member (hereinafter referred to as an intermediate electrode plate), and piezoelectric ceramic sheets 1 and 1' are bonded to both surfaces of the conductive member, with the electrodes 3 and 3' serving as adhesive surfaces. 5 and 5' are solvent-free two-component mixed modified acrylic adhesive layers containing a plasticizer. Lead wires 6, 7, and 8 are connected to the electrodes 2, 2', and the intermediate electrode plate 4, respectively. This bent bimorph vibrator is divided into a series bimorph element and a parallel bimorph element, depending on how the electrical terminals are taken out. In either case, it is necessary that the intermediate electrode plate 4 and the electrodes 3, 3' bonded thereto be electrically conductive. However, since the piezoelectric element is driven by voltage, it does not need to have low resistance, and it is sufficient that the surface of the electrode 3 of the piezoelectric element and the surface of the intermediate electrode plate 4 are in point contact at a portion. For this purpose, when assembling the element, it is sufficient to make the adhesive layer a thin film and adhere them together over the entire surface. The curing of the adhesive resin is achieved through relatively opposite rotations, such as by lightly tightening the two parts to be joined, or by applying a load while fixing one and rotating the other, or by rotating the other in opposite directions. This is done by letting people know. It is desirable that the resin used be one that does not require heating or the addition of a solvent during curing. Heat causes thermal deterioration because the piezoelectric element has a Curie point, and mechanical strain occurs when the piezoelectric element is cooled to room temperature after curing. Adhesives using solvents are not preferred because evaporation is difficult to occur and air bubbles remain on the adhesive surface. The optimum adhesive should cure without substantial volume change and the thickness of the joint should be controlled by the viscosity of the applied adhesive and the applied pressure. The modified acrylic resin used in this example is an acrylic resin that partially contains rubber and has methyl methacrylate as its main component. This is commercially available, for example, under the trade name "Hardlock." The desired adhesive strength is achieved after a curing time of 2 to 3 minutes, and maximum strength is reached within 24 hours. Since it is a solvent-free type and 100% solidified, and the two liquids do not mix, it can be applied separately to adherends.
This is important in order to obtain a device that is easy to manufacture and of high quality. Its physical property is viscosity
10000~100cps, specific gravity 1.01 (20℃), flash point 12℃,
The ignition point is 421℃. In general, epoxy resins and cyanoacrylate resins are often used as adhesives for electronic components, but when they are used to bond thin ceramic devices such as bimorph devices, they are difficult to maintain due to mechanical strength and temperature changes. Must be kept in mind. This is because the expansion coefficient of the resin is different from that of the ceramic element or the intermediate electrode plate. There is no problem when the ceramic element has sufficient strength, but when thin plate ceramics such as bimorph elements are bonded together, cracks or cracks occur in the ceramic body. In order to prevent this, it is possible to match the expansion coefficients, but it is difficult to match them completely, so it is desirable that the resin remains flexible even after curing. On the other hand, with elastic rubber adhesives,
The disadvantage is that internal loss is large and a sufficiently large output cannot be obtained. Moreover, the change over time is large, and there is a problem in the stability of electrical characteristics.
The object of the present invention is to solve these problems and provide a method for manufacturing a bimorph element that has excellent electrical characteristics and reliability. Hereinafter, a method for assembling a bimorph element using an adhesive having such characteristics will be described using FIG. 2. The above-mentioned modified acrylic resin has many excellent properties, but because the curing reaction proceeds quickly when the two parts come into contact, it is not possible to use a method of kneading the two parts and applying with a brush or screen printing. Difficult to mass produce. It is necessary to mix the two liquids and laminate them together. Therefore, as shown in FIG. 2A, two liquids 11,
Adhesive is dripped with a dispenser in a state where 12 is not in contact with the adhesive. When bonding, use two liquid adhesives 11,
It is desirable that 12 be mixed uniformly, so drop them alternately. The more places this drop is applied, the more uniform adhesion can be achieved. In other words, this is to prevent the adhesive from shifting to one side during bonding if there are many dripping locations, and to ensure complete bonding at the periphery. When bonding a bimorph element, if there is even a part of the piezoelectric sheet and the intermediate electrode plate that are not bonded, the higher-order (secondary, third-order) resonance waveforms will be disturbed, making it difficult to obtain sufficient acoustic characteristics. This is so that you will not be affected. When the two liquids 11 and 12 are not in contact with each other, they hardly harden even if left at room temperature for several hours, which eases the time constraints on the next step in manufacturing. In the bonding process, two liquids 11,
The piezoelectric sheet 2 is placed on top of the 12 dropped intermediate electrode plates 4, with the center axis of the piezoelectric sheet 2 aligned. And Figure 2B
As shown in the figure, while applying a load 13 to the piezoelectric sheet 2, the two are relatively rotated concentrically. As a result, the two resin liquids 11 and 12 are mixed and spread, and cured in that state. At this time, it will be more effective if the intermediate electrode plate 4 is fixed or rotated in the opposite direction to the rotation direction of the piezoelectric sheet 2. When bonding is performed using this method, since the resin is cured at the same time as the bonding, the adhesive layer can be made uniformly thin over the entire surface, and a bimorph element with little variation can be obtained. The same procedure is repeated for the other piezoelectric sheet 2'. Examples will be described below. Example 1 Piezoelectric ceramic sheet with a thickness of 100 μm and a diameter of 23 mm (dielectric constant ε ^T ₃₃ /ε ₀ ≧3000, coupling coefficient K _p ≧60%)
Electrodes were attached to both sides of the electrode, and the electrodes were polarized at 4KV/mm for 30 minutes. 100μm thick as intermediate electrode plate,
Use a brass plate with a diameter of 25 mm, align the polarization direction of piezoelectric ceramic sheets on both sides, and apply the adhesive shown in Table 1 (epoxy resin, cyanoacrylate resin, rubber adhesive, solvent-free two-component mixed modified acrylate). (resin) was dropped as shown in FIG. 2, and they were rotated and bonded while being brought into contact with pressure to form a bimorph element. We measured the initial properties of bimorph devices using each adhesive, and also measured the thermal shock properties (from 85℃ to -40℃
The presence or absence of cracks was confirmed using a magnifying glass. As is clear from the results in Table 1, when an acrylate adhesive is used, the mechanical coupling coefficient is large and the thermal shock resistance is also good.

[Table] Example 2 Using phosphor bronze with a diameter of 25 mm and a thickness of 100 μm as an intermediate electrode plate, a solvent-free modified acrylate resin with a viscosity of 1000 cps was dropped from a dispenser using the dropping method shown in Table 2. Thickness
A piezoelectric sheet having electrodes of 100 μm with silver baked on both sides was aligned with the center axis of the intermediate electrode plate, and then a load was applied and the sheet was adhered while being rotated. The nozzle of the dispenser was adjusted so that the total amount of resin dropped was the same regardless of the number of drops. Other conditions were the same as those in Example 1.

[Table] Example 3 On a brass plate having a diameter of 25 mm and a thickness of 100 μm as an intermediate electrode plate, two points of each solvent-free modified cyanoacrylate resin having various viscosities were dropped at equal intervals using a dispenser. A piezoelectric ceramic sheet having electrodes on both sides was aligned with its center axis on the intermediate electrode plate, and then rotated and adhered while applying pressure to assemble a bimorph element. Other conditions are example 1
It is the same as that of . Table 3 shows the results of investigating the initial characteristics of bimorph devices using adhesives of various viscosities and the presence or absence of cracks in thermostrophic tests. As is clear from this, if the viscosity is too high, it becomes difficult to obtain a product with sufficiently satisfactory properties. Its preferred range is 5000 cps or less.

【table】 [Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of a bimorph element,
FIGS. 2A and 2B are process diagrams for explaining the method of the present invention. 1...Piezoelectric ceramic sheet, 2, 3, 2',
3'... Electrode, 4... Intermediate electrode plate, 5, 5'... Adhesive layer, 11, 12... Adhesive, 13... Pressing direction.

Claims (1)

[Scope of Claims] 1. On a disc-shaped intermediate electrode plate made of a conductive member, two parts of a solvent-free two-part mixed modified acrylic resin are dropped alternately and dotted without contacting each other, and then A disk-shaped piezoelectric element having electrodes on both sides is placed on the intermediate electrode plate, and by applying a load and relatively rotating in a concentric manner in reverse, the piezoelectric element and the intermediate electrode plate are electrically connected. A method for manufacturing a bimorph device, which is characterized by bonding and bonding the device in such a manner. 2. The method for producing a bimorph device according to claim 1, wherein the viscosity of the solvent-free two-component mixed modified acrylic resin does not exceed 5000 cps at a temperature of 25°C.