JPH0148151B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a print head for an ink-on-demand type inkjet printer.

In the print head of an inkjet printer, which uses a piezoelectric element to generate pressure in a pressure chamber and uses this pressure to eject ink droplets from an ejection port onto recording paper, electrodes must be provided to apply an applied voltage to the piezoelectric element. Among these electrodes, the electrode that must be obtained from between the diaphragm and the piezoelectric element (hereinafter referred to as the lower electrode for convenience) has conventionally been obtained by several methods. In other words, if the diaphragm is made of non-conductive material such as plastic, ceramic, or glass, it is common to use lead wires from the piezoelectric element by soldering. For conductive devices such as those with a Nesa film attached to the surface, a method is used in which the piezoelectric element is directly bonded to the diaphragm and conduction is established from the surface of the diaphragm. A conventional example of the method for drawing out the lower electrode will be described in more detail with reference to the drawings, and its problems will also be described.

FIG. 1 shows a specific example of a method for drawing out the lower electrode when the diaphragm is not conductive, such as plastic, ceramics, glass, etc. In FIG. 1, 1 is a piezoelectric element, 2 is a vapor deposited film applied to the piezoelectric element 1, 3 is a diaphragm, 4 is an epoxy adhesive, and 5
is solder, and 6 is a lead wire. The method for leading out the lower electrode in this configuration is to connect the lead wire once for each piezoelectric element having the vapor deposited film 2 on its surface and then bond it to the diaphragm 3. In a multi-type print head using piezoelectric elements, the wiring is labor intensive and the cost is very high. Furthermore, it takes time and effort to process the lead wires 6 drawn out from each piezoelectric element, and the above method cannot be said to be suitable for mass production.

Next, FIG. 2 is a cross-sectional view showing the method for taking out the electrodes when the surface of the diaphragm is conductive.
3' is a glass diaphragm, 5' is a conductive adhesive, and 7 is a Nesa membrane. In the electrode extraction method with this configuration, since the Nesa film 7 on the surface of the diaphragm 3' is electrically conductive, conduction can be achieved by closely contacting the piezoelectric element 1 to the diaphragm 3', that is, by reducing the thickness of the adhesive 4. A lead wire 6 is connected from the Nesa film 7 via a conductive adhesive 5'.
It can be obtained by extracting the . If the diaphragm 3' is made of metal, the diaphragm 3' itself has conductivity, so the Nesa film 7 is not necessary and the metal vapor deposited film 2
It is sufficient to directly use the piezoelectric element 1 having a surface as the diaphragm 3', and it is also possible to draw out the lead wires 6 and the like by soldering. As mentioned above, the disadvantage of the method of taking out the lower electrode as shown in FIG. 2 is that when the diaphragm 3' is made of glass, the process of attaching the Nesa membrane 7 to the diaphragm 3' is complicated and costly. ,
If the diaphragm 3' is metal, the difference in thermal expansion coefficient between the piezoelectric element 1 and the diaphragm 3' (in the case of metal, linear expansion coefficient α = 1.0 to 2.0 × 10 ^-6 , in the case of piezoelectric element α = 1.5 ×
10 ^-5 , where α=1/l ₀ ·dl/dt, where l ₀ is the length at 0°C. ), when there is a temperature change, the piezoelectric element 1 having the metal vapor deposited film 2 on its surface is caused by the stress strain applied to the thinly stretched adhesive 4.
An accident may occur in which the diaphragm comes off from the diaphragm 3'. In this method, the adhesive 4, which is a nonconductor,
In order to establish conduction between the piezoelectric element 1 having the vapor deposited film 2 on its surface and the diaphragm 3' by making the layer thinner,
Another drawback is that the stability of the contact portion between the two cannot be ensured, that is, the continuity is unreliable. Furthermore, Japanese Patent Laid-Open No. 55-86765 discloses a structure in which a common electrode is laminated between a diaphragm and a piezoelectric element. However, there is no mention of the material of the common electrode or the diaphragm, and if the diaphragm were made of plastic, it would not have enough rigidity to increase the natural frequency, and as a result, the response would not improve. However, problems arise in that the printing speed does not improve and that it is difficult to reduce the size of the dots.

The present invention solves these problems of the prior art, and its purpose is to ensure that the adhesive strength between the diaphragm and the piezoelectric element does not decrease even with environmental changes such as temperature changes, and to ensure that voltage is applied to the piezoelectric element. It is an object of the present invention to provide a highly reliable printing head that can be used to apply voltage and is free from malfunctions.

Another object of the present invention is to provide a print head which can effectively pressurize ink in a pressure chamber with a low voltage even in a print head made of a low-rigidity plastic material, and which is capable of high-speed, high-resolution printing.

The present invention will be described below using specific examples shown in FIGS. 3 to 9.

8 in FIG. 3 is a perspective view of a metal plate having a thickness of about 30 to 80 μm obtained by etching or pressing.
This metal plate 8 is bonded in a laminated state between the diaphragm 3 and the piezoelectric element 1 having the vapor deposited film 2 on its surface.
By applying a voltage through this metal plate 8, the purpose is to obtain conduction to the piezoelectric element 1 having the vapor deposited film 2 on its surface. In our experiments, good results were obtained when stainless steel was selected as the material, since the metal plate 8 was not corroded or oxidized by the adhesive 4. A description of the hatched portion in FIG. 3 will be given later. Next, FIG. 4 is a sectional view showing a manufacturing process in which the piezoelectric element 1 having the vapor deposited film 2 on its surface and the diaphragm 3 are bonded together using the metal plate 8 shown in FIG. 3, and a lower electrode is obtained. It is. In FIG. 4A, the diaphragm 3 is coated in advance with an adhesive 4 such as epoxy, and a metal plate 8 and a piezoelectric element 1 having a vapor deposited film 2 on the surface are laminated in the direction of the arrow. By pressurizing and adhering, a lower electrode as shown in FIG. 4B is obtained. Figures 3 and 4 a, b
As is clear from the figure, the metal plate 8 has a contact portion that contacts the piezoelectric element 1 and an opening for bonding the piezoelectric element 1 and the diaphragm, and the adhesive 4 is filled into the opening by pressure. Then, the piezoelectric element 1 and the diaphragm 3 are directly bonded. Therefore, the contact portion of the metal plate 8 contacts the piezoelectric element 1 without using the adhesive 4, so that good conduction is achieved, and the piezoelectric element and the diaphragm 3 are connected to each other through the opening of the metal plate 8. Because it is directly bonded, the thickness of the adhesive layer is greater than the thickness of the metal plate, and the diaphragm 3 is bonded to the piezoelectric element 1 like plastic.
Bonding between a piezoelectric element 1 and a diaphragm 3 having a vapor-deposited film 2 on its surface that can withstand environmental changes such as temperature changes without peeling off due to stress and strain applied to the adhesive layer even when the material has a significantly different coefficient of thermal expansion. is obtained.

In addition, the diaphragm 3 has a low rigidity like plastic.
Since a metal plate 8 with higher rigidity is laminated on top of the plastic diaphragm, the problem that the plastic diaphragm alone contracts and cannot effectively convert the contraction of the piezoelectric element into a pressurizing effect on the ink due to flexure is solved. Deflection generated by the laminated structure of the piezoelectric element 1 and the metal plate 8 can be effectively transmitted to the pressure chamber via the plastic diaphragm. Next, Figure 5-A and B are
In order to further ensure conduction between the piezoelectric element 1 having the vapor deposited film 2 on its surface and the metal plate 8, the hatched portion shown in Fig. 3 is pressed and bent to provide a springy metal plate 8'. FIG.
In our experiments, even in the manufacturing method shown in Figure 4-A and B, sufficient conduction between the piezoelectric element 1 having the vapor deposited film 2 on its surface and the metal plate 8 was obtained, and environmental resistance was also obtained. As shown in FIG. 5-A, a metal plate 8' having a spring property and a piezoelectric element 1 having a vapor deposited film 2 on the surface are laminated on a diaphragm 3 coated with an adhesive 4.
Figure 5-B obtained by pressurizing and adhering
Such a configuration can more reliably establish electrical conduction between the piezoelectric element 1 having the vapor deposited film 2 on its surface and the metal plate 8'. Next, Figure 6-A, B, C is Figure 4-A,
B or FIG. 5 - A cross section showing a manufacturing method using a method of dropping adhesive 4 onto the diaphragm 3 instead of coating the diaphragm 3 with the adhesive 4 of the manufacturing method shown in A and B. It is a diagram. In FIG. 6-A, the metal plate 8' has been set on the diaphragm 3 from the beginning, and the adhesive 4 has been dripped onto the central part of the metal plate 8'. Next, as shown in FIG. 6-B, the piezoelectric element 1 having the vapor-deposited film 2 on its surface is placed on top of the adhesive 4 that has been dropped, and is bonded by applying pressure, thereby creating the state shown in FIG. 6-C. It has gained. This method not only facilitates production using an automatic machine or the like and provides a mass production effect, but also has the effect of simplifying the manufacturing method shown in FIGS. 7 and 8 below. FIGS. 7 and 8 are examples of methods for further ensuring conduction between the piezoelectric element 1 having the vapor deposited film 2 on its surface and the metal plate 8 or 8' in FIGS. 4, 5, and 6 described above. It is something. 3'' in FIG. 7 is a perspective view of a diaphragm with a bank as shown in the figure. This is to prevent the adhesive 4 from intervening in the contact portion between the metal plate 8' and the metal plate 8'.
The manufacturing method using this diaphragm 3″ is shown in Figure 8-A.
This is shown using a cross-sectional view of B. In Figure 8-A,
A metal plate 8' is set on top of the diaphragm 3'' with a bank, and adhesive 4 is dripped onto the central part of the plate as shown in FIG. Figure 8-B shows a product manufactured by laminating the piezoelectric elements 1 in the direction of the arrow and bonding them under pressure. Since there is a bank, the adhesive 4 does not flow in, and more reliable conduction is obtained without the intervention of the non-conducting adhesive 4.

Above, we have listed several ways to attach the lower electrode and ways to bond the piezoelectric element 1 and the diaphragm 3 or 3', 3'', but the common effect is that all methods ensure reliable conduction. Furthermore, since the thickness of the adhesive 4 can be made uniform and sufficient, the material of the diaphragm 3 or 3', 3'' can be made of plastic, metal, etc., and has a coefficient of thermal expansion similar to that of the piezoelectric element 1. Even if they differ greatly, they have sufficient adhesive strength and can withstand environmental changes such as temperature changes. Furthermore, in the case of a multi-nozzle in which a number of piezoelectric elements 1 are used in one print head, this manufacturing method is much simpler and cheaper than the case where electrodes are taken out from each piezoelectric element 1 one by one. Become. Reference numeral 9 in FIG. 9 is a metal plate for the printing head of such a multi-nozzle, and by using this metal plate, it can be shared by seven piezoelectric elements 1.

As described above in detail, by using the metal plate 8 or 8', 9 of the present invention as the lower electrode, the first
The disadvantages of the conventional lower electrode extraction method shown in Fig. 2 are mass production, cost, safety of conduction, and environmental resistance of bonding the piezoelectric element 1 with the vapor deposited film 2 on the surface and the diaphragm 3. It is possible to provide the market with a reliable, highly mass-producible, and low-cost printing head that solves problems such as performance and other problems. As described above, according to the present invention, the metal plate for applying voltage to the piezoelectric element is laminated between the plastic diaphragm and the piezoelectric element, which makes it possible to use the plastic diaphragm. A plastic inkjet head can be realized. That is, in order to generate pressure within the pressure chamber, a laminated structure consisting of a piezoelectric element that contracts and a diaphragm that does not contract is used to create a bending action to pressurize the ink within the pressure chamber. Since the diaphragm is weak and contracts, the amount of bending (deflection) decreases and is not effectively converted into a pressurizing action. However, in a structure in which a metal plate is laminated between a plastic diaphragm and a piezoelectric element as in the present invention, a bending action occurs due to the laminated structure of a contracting piezoelectric element and a metal plate that does not easily contract, and the bending is absorbed by the plastic vibration plate. It can be effectively transmitted to the pressure chamber via the plate. In addition, in the case of a laminated structure of a plastic diaphragm and a piezoelectric element, the amount of deflection is small as described above, so the voltage applied to the piezoelectric element is also high. A structure in which metal plates are laminated enables lower voltage driving than a laminated structure in which a plastic diaphragm and a piezoelectric element are laminated. Also,
By laminating the metal plate on top of the plastic diaphragm, the rigidity is improved and the natural frequency can be increased, which improves the response frequency and, as a result, enables high-speed printing. In addition, the improvement of natural frequency,
That is, by shortening the period, it becomes easier to reduce the dot size, and high resolution printing becomes possible without reducing the size of the nozzle, which causes problems such as precision control, difficulty in processing, and clogging.

Further, according to the present invention, the metal plate bonded on the plastic diaphragm between the plastic diaphragm and the piezoelectric element has a contact portion where the metal plate comes into contact with the piezoelectric element, and an opening where the piezoelectric element and the diaphragm are bonded. By filling the opening with adhesive and directly bonding the piezoelectric element and the diaphragm, the contact part of the metal plate comes into contact with the piezoelectric element without using adhesive, resulting in good conduction. On the other hand, since the piezoelectric element and the diaphragm are directly bonded to each other through the opening in the metal plate, the thickness of the adhesive layer is greater than the thickness of the metal plate, so even when subjected to environmental changes such as temperature changes, No reduction in adhesive strength or peeling occurs between a plastic diaphragm and a piezoelectric element having different coefficients of thermal expansion. Therefore, it is possible to provide a highly reliable printing head with reliable conduction and stable ink jetting characteristics.

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional views showing a conventional method of forming a lower electrode. 1... Piezoelectric element, 2... Vapor deposited film, 3, 3'...
diaphragm, 4...adhesive, 6...lead wire, FIG. 3 is a perspective view showing the electrode plate of the present invention. 8... Electrode plate. Figure 4 A, B, Figure 5 A, B, Figure 6 A, B,
C is a sectional view showing a manufacturing method using the electrode plate of the present invention. 8'... Electrode plate with spring properties. FIG. 7 is a perspective view showing the diaphragm of the present invention, and FIGS. 8A and 8B are sectional views showing a manufacturing method using this diaphragm. 3''...A diaphragm with a bank. FIG. 9 is a perspective view showing an electrode plate for a multi-nozzle head.

Claims (1)

[Claims] 1. A diaphragm made of plastic that constitutes a part of the pressure chamber, and an electrode film laminated on the diaphragm and formed on a surface on the diaphragm side and a surface opposite to the surface. a piezoelectric element, the print head generates pressure in the pressure chamber via the diaphragm by driving the piezoelectric element, and ejects ink droplets from an ejection port communicating with the pressure chamber; A metal plate for applying voltage to the piezoelectric element is mounted on the plastic vibration plate between the plate and the piezoelectric element, and the metal plate has a contact portion that contacts the piezoelectric element;
A print head comprising an opening for bonding the piezoelectric element and the diaphragm, the opening being filled with an adhesive to directly bond the piezoelectric element and the diaphragm.