JP2002086713A - On-demand ink jet printing head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an on-demand ink jet printing head of a piezoelectric element system which can protect piezoelectric elements and electric circuits connected to the elements and can flexibly meet temperature and pressure changes with the superior reliability and long life. SOLUTION: The on-demand ink jet printing head has part of the piezoelectric elements and a wiring line connected to the elements sealed, with a pressure control mechanism set to part of the sealed chamber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a print head of an ink jet printer that forms an ink image on a recording medium by causing ink droplets to fly by pressure generated by a piezoelectric actuator.

[0002]

2. Description of the Related Art In a conventional print head of an on-demand type ink jet printer, a method of ejecting ink includes a thermal method in which bubbles are generated in ink by an electric heater to eject ink, and a pressure method using a piezoelectric element. There is a piezoelectric element type in which a part of a wall surface of a chamber is deformed to eject ink.

The thermal method has the advantage that fine processing can be performed by photolithography technology and the nozzle pitch can be reduced to 100 μm or less. However, the frequency at the time of continuous injection is limited to about 10 kHz and the life is several hundred million times. There is a disadvantage that stays in the injection of.

On the other hand, in the piezoelectric element method, since the displacement of the piezoelectric element is small, it is necessary to increase the surface area of the diaphragm of the pressurizing chamber for ink ejection.
It can only be reduced to about 0 μm. However, since the driving frequency depends on the shape of the piezoelectric element, the driving frequency can be set to 20 kHz or more, which can be said to be a method suitable for increasing the printing speed. Another advantage is that, unlike the thermal method, the type of ink is not selected.

However, as shown in FIG. 9, in the piezoelectric element method, the piezoelectric element, the conductive adhesive and the electrodes connected thereto are exposed, and when the ink used is conductive, it adheres to the nozzle member. When the ink 26 flows or the ink mist 27 adheres to them, the current which should originally flow to the piezoelectric element leaks or flows into another piezoelectric element, so that not only a normal ink discharge amount cannot be obtained, but also the drive is performed. Discharge from the missing nozzles causes disturbance of the output image, and in the worst case, damage to the printer control circuit.

In order to prevent the above-mentioned piezoelectric elements, conductive adhesives, electrodes connected thereto and the like from coming into contact with the ink, it is conceivable to seal them with a sealing member to prevent short circuits. However, when the piezoelectric element, the conductive adhesive, and the electrodes connected to the element are sealed, the piezoelectric element generates heat by continuously discharging ink for a long time, the internal pressure increases, and a pressure difference occurs between the external pressure and the external pressure. There has been a problem that the diaphragm is deformed and adversely affects ink ejection characteristics. In addition, as a cause of the difference between the internal pressure and the atmospheric pressure, the atmospheric pressure also varies depending on the region or the climate in which the internal pressure is used, and a large pressure difference is generated even when the print head is transported by air. at the worst case,
The adhesion between the piezoelectric element and the vibration plate may be peeled off, and the head may be damaged.

[0007]

SUMMARY OF THE INVENTION The present invention solves such a conventional problem, and its object is to solve the following problems.
Provided is a long-life, on-demand ink-jet printhead which prevents a piezoelectric element and a wiring connected thereto from being short-circuited by ink, and has high reliability without changing characteristics due to an external environment or use conditions. It is.

[0008]

According to the present invention, there is provided a pressure chamber for storing ink, pressure generating means for generating pressure fluctuation in the pressure chamber by applying an electric signal, and A diaphragm that forms at least a part of a wall surface and is connected to the pressure generating unit, a restrictor that is a flow path that supplies ink to the pressure chamber,
In a housing having a common ink passage for supplying ink to the restrictor and an ink jet print head having a nozzle for discharging ink droplets from the pressure chamber, the vibration plate, the pressure generating means, and wiring for applying an electric signal thereto Is closed so as not to communicate with the atmosphere, and a pressure adjusting mechanism for adjusting the pressure of the sealed space to the same pressure as the atmospheric pressure is provided.

In the above-described pressure adjusting mechanism, a part of a member constituting a closed portion is made of an elastic material made of a thin film. Alternatively, it has a structure in which a hole provided in a part of a member constituting the sealing portion and communicating with the atmosphere, and a non-volatile high-viscosity liquid is injected into the hole. Alternatively, a hole formed in a part of the member constituting the sealed portion to communicate with the atmosphere, and a part thereof is formed of an elastic material following the inner wall shape of the hole, and is freely movable in the length direction of the hole. And members that can be used.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is an exploded perspective view illustrating the structure of a main part of an ink jet print head according to the present invention.

In FIG. 1, reference numeral 2 denotes an orifice plate on which a plurality of nozzles 1 are formed. The processing accuracy of the opening shape of the nozzle 1 has a great influence on the ink ejection characteristics of the ink jet print head. In order to suppress these nozzle accuracy variations among the plurality of nozzles 1 to a low level, the method of manufacturing the orifice plate 2 requires high processing accuracy. For this purpose, the orifice plate 2 is formed by precision pressing of stainless steel, laser processing, electroforming of nickel, or the like.

The orifice plate 2 has a chamber plate 4 in which a pressure chamber 3 is formed, and a restrictor 5 which connects the ink supply passage 10 to the pressure chamber 3 and controls the flow of ink into the pressure chamber 3. The restricted restrictor plate 6 is positioned and joined.

Further, a diaphragm plate formed with a vibration plate 7 for efficiently transmitting the pressure of the piezoelectric actuator 13 to the pressure chamber and a filter portion 8 for removing dust and the like in the ink flowing into the restrictor 5 from the common ink passage 10. 9 and a housing 11 having a common ink passage 10 formed therein
And are similarly positioned and joined.

The above-described chamber plate 4, restrictor plate 6, and diaphragm plate 9 are formed by a stainless steel etching method or a nickel material electroforming method. The housing 11 is formed by cutting stainless steel or the like, and is joined to an ink introduction pipe 20 for leading ink from an external ink tank to the common ink passage 10.

Finally, a plurality of laminated piezoelectric elements 14 and a piezoelectric actuator 13 comprising a support substrate 16 for fixing the same are positioned and joined. The order of manufacturing the piezoelectric actuator 13 of the present invention is as follows. First, a plurality of laminated piezoelectric element bars are arranged and adhered and fixed on the support substrate 16, and then the laminated piezoelectric element rods are divided by cutting using a dicing saw, a wire saw or the like. I do. At this time, each of the divided laminated piezoelectric elements 14 corresponds to one of the pressure chambers.

Further, on the support substrate 16, an individual electrode 17 and a common electrode 18 for transmitting an electric signal independent of an external drive circuit to each of the laminated piezoelectric elements 14 are formed. Selective electric signal from the external drive circuit is applied to the piezoelectric element 1
4, the piezoelectric element 14 is distorted. Since the piezoelectric element 14 is joined to the high-rigidity support substrate 16, the diaphragm 7 is preferentially displaced to increase the pressure in the pressure chamber 3.

As described above, the ink jet print head described in this embodiment is used in an apparatus that forms an ink image on a recording medium by discharging ink from the nozzles 1 based on such a principle.

In this example, the arrangement pitch was set to 1/3 inch inch and about 677 μm, but the number of nozzles, the number of rows,
The unit configuration is not limited to any combination.

FIG. 2 is a partial sectional view of a print head according to the present invention.

The piezoelectric actuator 13 includes a support substrate 16 and a laminated piezoelectric element 14. Multilayer piezoelectric element 1
Reference numeral 4 is connected to the diaphragm 7 via an elastic material 12.
The diaphragm 7 and the chamber plate 4 constitute the pressure chamber 3. The pressure in the pressure chamber 3 fluctuates rapidly due to the deformation of the diaphragm 7. An individual electrode 17 and a common electrode 18 are formed on the support substrate 16, and are electrically connected to the laminated piezoelectric element 14 by a conductive bonding member 15. When a selective electric signal is applied to the laminated piezoelectric element 14 from an external drive circuit, the laminated piezoelectric element 14 generates a displacement in a direction toward the nozzle 1. Due to this displacement, the diaphragm 7 is deformed via the elastic member 12, and the ink filled in the pressure chamber 3 is pressurized and ejected from the nozzle 1 as ink droplets.

In the print head described above, according to the present invention, the diaphragm 7, the housing 11, and the sealing member 21 are provided.
A sealed chamber 21a is formed by the elastic member 12 and the laminated piezoelectric element 14, which is joined to the vibration plate 7 in the sealed chamber 21a by the elastic member 12, and a conductive element for connecting the laminated piezoelectric element 14, the individual electrode 17, and the common electrode 18. The structure is such that the adhesive 15 is shielded from the outside air. Further, in order to eliminate the difference between the internal pressure of the closed chamber 21a and the atmospheric pressure outside the closed chamber 21a, a hole is formed in the housing 11 and a pressure adjusting member 22 partially formed of a thin film is mounted to adjust the pressure. I was able to do it. In this case, the pressure adjusting member 22 is made of an elastic body having sufficient elasticity, and is freely deformed as shown by a broken line 22a according to a pressure difference between the inside and the outside. Further, a gas such as dry nitrogen may be sealed in the closed chamber 21a in order to prevent oxidation and dew condensation of the members constituting the closed chamber 21a.

Incidentally, as shown in FIG.
By using a bellows or corrugated structure, the pressure adjusting member 22 can be greatly deformed at the time of adjustment, so that it is possible to cope with a greater pressure fluctuation.

As an example, the pressure at the time of sealing is 1 atm.
When the temperature is 25 ° C., when the atmospheric pressure is reduced by 20% and the internal temperature is changed to 75 ° C., the volume becomes about 146% when the volume is closed according to Boyle-Charles law. When the atmospheric pressure increases by 20% and the internal temperature changes to −50 ° C., the volume becomes about 62% of the volume when sealed. Therefore about ±
It can be seen that a volume change of 38-46% occurs. Although this is an extreme example, even when such a volume change occurs, the pressure can be adjusted by increasing the surface area of the pressure adjusting member 22 sufficiently and using a material having excellent elasticity.

FIG. 4 shows a closed chamber 21a composed of the diaphragm 7, the housing 11, the sealing member 21 and the sealing member 23, and the elastic member 12
And the conductive adhesive 15 for connecting the laminated piezoelectric element 14 with the individual electrodes 17 and the common electrode 18 blocks communication with the outside air. In this configuration, in order to eliminate the difference between the internal pressure of the closed chamber 21a and the atmospheric pressure outside the closed chamber 21a, the sealing member 23 having a bellows structure is fixed with an adhesive 23a so that the pressure can be adjusted. The sealing member 23 is made of an elastic body having sufficient elasticity, and is freely deformed according to a pressure difference between the inside and the outside. Further, a gas such as dry nitrogen may be sealed in the closed chamber 21a in order to prevent oxidation and dew condensation of the members constituting the closed chamber 21a.

FIG. 5 shows a sealed chamber 21a constituted by the vibration plate 7, the housing 11, and the sealing member 21, in which a laminated piezoelectric element 14 joined to the vibration plate 7 by an elastic member 12; Multilayer piezoelectric element 14 and individual electrode 1
The conductive adhesive 15 connecting the electrode 7 and the common electrode 18 has a structure in which communication with the outside air is cut off. In order to eliminate the difference between the internal pressure of the closed chamber 21a and the atmospheric pressure outside the closed chamber 21a, a thin portion 11a is provided in the housing 11 so that the pressure can be adjusted. The thin portion 11a has a structure with a sufficiently large surface area and a large elasticity compared to the diaphragm 7 so that the pressure difference can be eliminated by the thin portion 11a without deformation of the diaphragm 7 due to a change in the outside air pressure. did.
Further, a gas such as dry nitrogen may be sealed in the closed chamber 21a in order to prevent oxidation and dew condensation of the members constituting the closed chamber 21a.

FIG. 6 shows a sealed chamber 21a constituted by the vibration plate 7, the housing 11, and the sealing member 21, in which the laminated piezoelectric element 14 joined to the vibration plate 7 by the elastic member 12; Multilayer piezoelectric element 14 and individual electrode 1
The conductive adhesive 15 connecting the common electrode 7 and the common electrode 18 is in a state of blocking communication with the outside air. Here, in order to eliminate the difference between the internal pressure of the closed chamber 21a and the atmospheric pressure outside the closed chamber 21a, a hole is made in the housing 11, and a flowable high-viscosity liquid (eg, grease) member 24 is injected therein. The pressure can be adjusted. The high-viscosity liquid 24 is non-volatile and highly viscous, and can eliminate internal and external pressure differences by moving left and right on the drawing.

Instead of the structure shown in FIG. 6, a pipe member 24a having a helical structure is provided in a hole of the housing 11 as shown in FIG. 7, and a high-viscosity liquid 24 is injected into the pipe member 24a. In addition, the moving distance of the high-viscosity liquid 24 is greatly increased, and it is possible to cope with a greater pressure fluctuation. Further, a gas such as dry nitrogen may be sealed in the closed chamber 21a in order to prevent oxidation and dew condensation of the members constituting the closed chamber 21a.

FIG. 8 shows a sealed chamber 21a constituted by the vibration plate 7, the housing 11, and the sealing member 21, in which the laminated piezoelectric element 14 joined to the vibration plate 7 by the elastic member 12; Multilayer piezoelectric element 14 and individual electrode 1
The conductive adhesive 15 connecting the common electrode 7 and the common electrode 18 is in a state of blocking communication with the outside air. Then, in order to eliminate the difference between the internal pressure of the closed chamber 21a and the atmospheric pressure outside thereof, a hole is formed in the housing 11 and the piston member 25 is opened.
Embedded to allow pressure adjustment. The piston member 25 has an elastic member 25a serving as a gasket, and the contact point with the piston case 25b is very smooth.
In the figure, it can be freely moved in the left-right direction. A lubricant or the like may be applied to the contact surface between the piston case 25b and the elastic member 25a for the purpose of assisting the smooth movement and further improving the airtightness. Thereby, it is possible to cope with a slight pressure fluctuation and the piston member 2
5 can sufficiently cope with a large pressure fluctuation by a sufficient stroke. Further, a gas such as dry nitrogen may be sealed in the closed chamber 21a in order to prevent oxidation and dew condensation of the members constituting the closed chamber 21a.

[0030]

As described above, the piezoelectric element and the wiring connected thereto are hermetically sealed and a pressure adjusting mechanism is provided to prevent the piezoelectric element and the wiring connected thereto from being short-circuited by ink, and to further reduce the pressure. Since it is possible to prevent the diaphragm from being deformed due to the fluctuation, it is possible to provide an on-demand type ink jet print head having high reliability and long life.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating the structure of a main part of an inkjet print head as an example of the present invention.

FIG. 2 is a partial cross-sectional view of an inkjet printhead as an example of the present invention.

FIG. 3 is a partial cross-sectional view of an ink jet print head as an example of the present invention.

FIG. 4 is a partial cross-sectional view of an inkjet printhead as an example of the present invention.

FIG. 5 is a partial cross-sectional view of an inkjet print head as an example of the present invention.

FIG. 6 is a partial cross-sectional view of an inkjet print head as an example of the present invention.

FIG. 7 is a partial cross-sectional view of an ink jet print head as an example of the present invention.

FIG. 8 is a partial cross-sectional view of an inkjet print head as an example of the present invention.

FIG. 9 is a partial cross-sectional view of an ink jet print head illustrating a conventional technique.

[Explanation of symbols]

1 is a nozzle, 2 is an orifice plate, 3 is a pressure chamber, 4
Is a chamber plate, 5 is a restrictor, 6 is a restrictor plate, 7 is a vibration plate, 8 is a filter section, 9 is a diaphragm plate, 10 is a common ink passage, 11 is a housing, 12 is an elastic material, 13 is a piezoelectric actuator,
14 is a laminated piezoelectric element, 15 is a conductive bonding member, 16 is a support substrate, 17 is an individual electrode, 18 is a common electrode, 19 is a connection cable, 20 is an ink introduction pipe, 21 is a sealing member, and 22 is a pressure adjusting member. , 23 are a sealing member, 24 is a grease member, 25 is a piston member, 26 is ink, and 27 is an ink mist.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Osamu Machida 1060 Takeda, Hitachinaka-shi, Ibaraki F-term in Hitachi Koki Co., Ltd. (reference) 2C057 AF65 AG47 AG99 BA03 BA14

Claims (4)

[Claims] 1. A pressure chamber for storing ink, pressure generating means for generating pressure fluctuation in the pressure chamber by application of an electric signal, and at least a part of a wall surface of the pressure chamber being formed and connected to the pressure generating means. A diaphragm, a restrictor as a flow path for supplying ink to the pressure chamber, a housing having a common ink passage for supplying ink to the restrictor, and a nozzle for discharging ink droplets from the pressure chamber. In the ink jet print head, the diaphragm, the pressure generating means and a part of the wiring for applying an electric signal thereto are sealed so as not to communicate with the atmosphere, and the pressure of the sealed space is set to the same pressure as the atmospheric pressure. An ink jet print head comprising a pressure adjusting mechanism for adjusting. 2. An ink jet print head according to claim 1, wherein said pressure adjusting mechanism has a part of a member forming a closed portion made of an elastic material made of a thin film. 3. The pressure adjusting mechanism is characterized in that it has a hole provided in a part of a member constituting a closed portion and communicating with the atmosphere, and a structure in which a non-volatile high-viscosity liquid is injected into the hole. The on-demand type ink jet print head according to claim 1. 4. The pressure mechanism comprises a hole formed in a part of a member constituting a closed part for communicating with the atmosphere, and a part of the hole formed of an elastic material conforming to the inner wall shape of the hole. 2. An ink jet print head according to claim 1, wherein said ink jet print head comprises a member which can move freely in the length direction.