JP4660993B2 - Inkjet head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet head having a plurality of ink nozzles, and more particularly to an ink jet head capable of suppressing the occurrence of print unevenness due to pressure interference between the ink nozzles.
[0002]
[Prior art]
In general, an inkjet head includes a plurality of ink nozzles, an ink pressure chamber formed corresponding to each ink nozzle to generate pressure fluctuations for discharging ink droplets from each ink nozzle, and each ink pressure. And a common ink chamber for supplying ink to the chamber. As a method for generating a pressure fluctuation in each ink pressure chamber, a heater is heated to boil the ink, and a bubble pressure generated thereby is applied, or a piezoelectric element attached to the ink pressure chamber is applied. In some cases, the volume of the ink pressure chamber is changed, and in other cases, the volume of the ink pressure chamber is changed using electrostatic force.
[0003]
Here, when a pressure fluctuation is generated in the ink pressure chamber in order to discharge ink droplets, the discharge pressure is transmitted to the common ink chamber. When pressure fluctuations occur in the common ink chamber, pressure interference occurs between the ink nozzles via this common ink chamber, and the ink droplet ejection amount changes or other than the drive ink nozzle that wants to eject ink droplets. This causes a problem that unnecessary ink droplets leak from the non-driven ink nozzles. In order to avoid such an adverse effect, it is not preferable to wait for the pressure fluctuation to attenuate before performing the next ink droplet ejection operation because the ink nozzle cannot be driven at high speed.
[0004]
Therefore, conventionally, a method has been proposed in which a diaphragm for pressure interference that can be elastically deformed is provided on the wall of the common ink chamber, or a pressure buffer chamber containing a compressible fluid is provided in the common ink chamber. For example, the latter method is disclosed in Japanese Patent Application Laid-Open No. 8-281943.
[0005]
These methods attempt to absorb and attenuate the pressure by vibrating an elastically deformable member formed in a part of the common ink chamber with a pressure generated when ink droplets are ejected. is there.
[0006]
[Problems to be solved by the invention]
However, even in an ink jet head provided with such an elastically deformable member for preventing pressure interference, pressure interference between ink nozzles cannot be sufficiently prevented, resulting in variations in ink ejection characteristics between ink nozzles. Printing unevenness may occur between nozzles.
[0007]
That is, the elastically deformable member generally has a natural frequency due to a plurality of vibration modes, and such a natural frequency is due to variations due to the specifications of the member, variations in the constraint conditions of the member, etc. It fluctuates slightly. For this reason, a frequency component that resonates with the pressure fluctuation of the ink nozzle is generated in the pressure fluctuation frequency component in the common ink chamber having the elastically deformable member, and the pressure fluctuation due to the frequency component is not attenuated. In some cases, the ejection characteristics between the ink nozzles may be adversely affected.
[0008]
As described above, the vibration characteristics of the elastically deformable member are slightly different due to the difference in each ink head, so that only the elastically deformable member for pressure interference is used. However, there is a limit in preventing or suppressing pressure interference between ink nozzles.
[0009]
In view of this point, an object of the present invention is to propose an ink jet head capable of reliably preventing or suppressing pressure interference between ink nozzles.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, the inkjet head of the present invention is arranged corresponding to each ink nozzle in order to generate a plurality of ink nozzles and pressure fluctuations for ejecting ink droplets from each ink nozzle. An ink pressure chamber, a common ink chamber that supplies ink to each ink pressure chamber, and a pressure interference prevention unit that is formed in the common ink chamber to prevent pressure interference between the ink nozzles. The pressure interference prevention unit includes at least an elastically deformable elastic plate portion forming a part of the common ink chamber, and a vibration attached to the elastic plate portion to attenuate the vibration of the elastic plate portion. It is characterized by having an attenuation substance.
[0011]
The ink jet head of the present invention includes an elastic plate portion that can be elastically deformed and a vibration damping material attached thereto in order to prevent or suppress pressure interference between the ink nozzles. Since a plurality of members having different vibration characteristics are used as described above, pressure interference between the ink nozzles can be reliably prevented or suppressed.
[0012]
Here, in order to suppress a decrease in compliance required for pressure interference by the elastic plate portion, the vibration damping material is preferably flexible, and its Young's modulus is 1/10 of the Young's modulus of the elastic plate portion. The following is desirable. In particular, 1/10 ⁵ or less is desirable.
[0013]
Further, the ink is not brought into contact with the vibration damping material and the vibration damping material is peeled off from the elastic plate portion, or the ink is contacted with the vibration and eluted to cause clogging of the ink nozzle. It is desirable that the vibration damping material has ink resistance. It is desirable to use a silicone adhesive as such a substance.
[0014]
Next, the present invention can be applied to an electrostatic drive type ink jet head configured to generate a pressure fluctuation in each ink pressure chamber by electrostatic force.
[0015]
In this case, the inkjet head can have a configuration in which the first and second semiconductor substrates are stacked, and at least the common ink chamber is partitioned between them. In this case, the elastic plate portion can be formed by thinning a part of the substrate portion of the first or second semiconductor substrate that defines the common ink chamber.
[0016]
Furthermore, the elastic plate portion can be formed at the bottom portion of the recess formed by etching a part of the substrate portion, and the recess can be used as the filling portion of the vibration damping material.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an inkjet head to which the present invention is applied will be described with reference to the drawings.
[0018]
(overall structure)
FIG. 1 is a perspective view showing the external shape of an inkjet head to which the present invention is applied. 2 is an exploded perspective view of a part of the inkjet head, and FIG. 3 is a partial cross-sectional view thereof.
[0019]
As shown in these drawings, the inkjet head 1 is a face inkjet type that ejects ink droplets from an ink nozzle provided on the upper surface of a substrate, and is of an electrostatic drive type. The inkjet head 1 has a laminated structure in which a nozzle plate (first substrate) 2, a cavity plate (second substrate) 3, and a glass substrate 4 are joined together in this order.
[0020]
The cavity plate 3 is, for example, a silicon substrate, and a recess 7 that forms an ink pressure chamber 6 whose bottom wall functions as the diaphragm 5 on the surface of the plate, and an ink supply port provided at the rear of the recess 7. 8 are formed by etching and a recess 11 that forms a common ink chamber 10 for supplying ink to each ink pressure chamber 6 is formed. The lower surface of the cavity plate 3 is smoothed by mirror polishing and serves as a mounting portion for the glass substrate 4.
[0021]
In the nozzle plate 2 joined to the upper surface of the cavity plate 3 (the substrate surface on the groove forming side), a plurality of ink nozzles 21 communicating with the ink pressure chambers 6 are formed on the wall portion defining the upper surface of the ink pressure chamber 6. Is formed. The ink nozzle 21 has a stepped cross section, and a circular small section nozzle portion 21a is formed on the front side in the ink droplet ejection direction, and a circular large section nozzle portion 21b is formed on the rear side.
[0022]
When the nozzle plate 2 and the cavity plate 3 are overlapped with each other, the ink pressure chamber 6, the ink supply port 8, and the common ink chamber 10 are arranged in the plane direction H between the plates 2 and 3. It is divided into sections.
[0023]
In the glass substrate 4 bonded to the lower surface of the cavity plate 3, an ink supply hole 19 is formed in a wall portion corresponding to the bottom surface of the common ink chamber 10. The ink supply hole 19 extends to the common ink chamber 10. An external ink supply source such as an ink tank is connected to the ink supply hole 19 via a connection pipe. The ink can be supplied from the ink supply source to the common ink chamber 10 through the ink supply hole 19.
[0024]
In the glass substrate 4, concave portions 13 that constitute the vibration chambers 12 are formed in portions facing the respective vibration plates 5. An individual electrode 14 that faces the diaphragm 5 is disposed on the bottom surface of the recess 13. The individual electrode 14 is connected to the terminal portion 16 via the lead portion 15. The individual electrodes 14 and the lead portions 15 except for the terminal portions 16 are covered with an insulating film 17. A lead wire 18 is bonded to each terminal portion 16.
[0025]
The diaphragm 5 that defines the bottom surface of each ink pressure chamber 6 formed in the cavity plate 2 functions as a common electrode, and a driver 20 is connected between the common electrode and the terminal portion 16 of each individual electrode 14. Has been. When applied to the individual electrode 14 by the driver 20, the diaphragm 5 facing the individual electrode 14 to which voltage is applied vibrates due to electrostatic force, and the pressure in the ink pressure chamber 6 fluctuates accordingly, and the ink nozzle 21. Ink droplets 23 are ejected from.
[0026]
For example, when a positive voltage pulse is applied to charge the surface of the individual electrode 14 to a positive potential, the corresponding lower surface of the diaphragm 5 is charged to a negative potential. Therefore, the diaphragm 5 is attracted by the electrostatic force and bent downward. Next, when the voltage pulse applied to the individual electrode 14 is turned off, the diaphragm 5 returns to the original position. By this returning operation, the internal pressure of the ink pressure chamber 6 is rapidly increased, and the ink droplets 23 are ejected from the ink nozzles 21. Then, when the vibration plate 5 is bent downward, ink is supplied from the common ink chamber 10 to the ink pressure chamber 6 through the ink supply port 8.
[0027]
The ink used in the inkjet head 1 is prepared by dissolving or dispersing a surfactant such as ethylene glycol and a dye or pigment in a main solvent such as water, alcohol or toluene. Furthermore, if a heater is provided in the ink jet head, hot melt ink can also be used.
[0028]
Here, the common ink chamber 10 is formed with a pressure interference prevention unit 22 for buffering pressure fluctuations in the common ink chamber 10 and preventing pressure interference between the ink nozzles. The pressure interference prevention unit 22 of this example includes a diaphragm 22A that is an elastically deformable elastic plate part that forms a part of the common ink chamber 10, and the surface of the diaphragm 22A in order to attenuate vibrations of the diaphragm 22A. And a vibration damping material 22B applied to the substrate.
[0029]
In this example, a portion of one nozzle plate 2 that defines the common ink chamber 10 is etched by a predetermined depth from the surface to form a total of six rectangular recesses 22a. A thin portion formed on the bottom surface portion by forming is a diaphragm 22A that can be elastically deformed in the out-of-plane direction. Each recess 22a is filled with a predetermined amount of vibration damping material 22B. The vibration damping material 22B of this example is a gel type silicone adhesive.
[0030]
Here, FIG. 4 shows a correlation between the compliance Cr of the common ink chamber 10 in which the pressure interference preventing unit 22 is formed and the weight change rate of the ink discharge amount. As can be seen from this figure, when the compliance Cr of the common ink chamber 10 is 1 × 10 ⁻¹⁷ (N / m ⁵ ), the weight conversion rate of the ink ejection amount can be maintained at about 75%, and the ink ejection characteristics. Can fully satisfy the demands. Further, it is preferable that the compliance Cr is 3 × 10 ⁻¹⁷ (N / m ⁵ ) or more because there is almost no change in the weight of the ink discharge amount.
[0031]
In this example, the common Cr chamber 10 has a compliance Cr of 1 × 10 ⁻¹⁷ (N / m ⁵ ) or more, preferably 3 × 10 ⁻¹⁷ (N / m ⁵ ) or more. The thickness and area of the diaphragm 22A constituting the pressure interference prevention unit 22 are adjusted, and the elastic characteristics and application amount of the vibration damping material 22B are adjusted.
[0032]
From this point of view, it is desirable that the vibration damping material 22B be flexible so that its Young's modulus is 1/10 or less of the Young's modulus of the diaphragm 22A. × 10 ^-17 (N / m ⁵ ) or more. Further, since the vibration damping material 22B may come into contact with ink droplets ejected from the ink nozzle 21, an ink resistant material is desirable. That is, it is desirable that the ink nozzle 21 is not peeled off from the surface of the diaphragm 22A in contact with the ink, or is eluted by contact with the ink so that the ink nozzle 21 is not clogged.
[0033]
In this example, in view of such points, a silicone adhesive that is flexible and has high ink resistance is used as the vibration damping material 22B.
[0034]
As described above, in the inkjet head 1 of this example, the pressure interference prevention unit 22 including the diaphragm 22A and the vibration damping material 22B is provided in the portion of the nozzle plate 2 that defines the common ink chamber 10. The pressure interference prevention unit 22 having two portions having different vibration characteristics can reliably suppress the pressure fluctuation of the common ink chamber 10 due to the pressure fluctuation generated in the ink pressure chamber 6 by driving the ink nozzle. Accordingly, pressure interference between the ink nozzles can be reliably prevented or suppressed, so that it is possible to prevent deterioration in print quality such as print unevenness due to variations in ink discharge characteristics between the ink nozzles.
[0035]
(Other embodiments)
In order to protect the pressure interference preventing unit 22 from the outside, it is desirable to cover each recess 22a with a protective cover 25 as shown in FIG. In this case, if the concave portion 22a is completely sealed, the protective cover 25 is provided with a vent hole 25a because the airtight state may occur and the vibration of each part of the pressure interference preventing portion 22 may be adversely affected. It is desirable.
[0036]
From this point of view, it is desirable that the vibration damping material 22B be flexible so that its Young's modulus is 1/10 ⁵ or less of the Young's modulus of the diaphragm 22A, thereby preventing pressure interference. The vibration of each part of the part 22 is not adversely affected, and good print quality can be ensured.
[0037]
Next, the above embodiment is a face eject type that ejects ink droplets from the upper surface of the nozzle plate, but it is also applicable to an edge eject type inkjet head that ejects ink droplets from the end surface of the nozzle plate. Of course, the present invention can be similarly applied.
[0038]
In the above-described embodiment, the pressure interference prevention unit 22 is composed of two parts, the diaphragm 22A and the vibration damping material 22B. However, three or more parts including another vibration damping material added thereto. It is also possible to configure from
[0039]
Further, the above embodiment relates to an electrostatic drive type ink jet head, but the present invention can be similarly applied to other drive type ink jet heads.
[0040]
【The invention's effect】
As described above, in the ink jet head according to the present invention, the common ink chamber is formed with the elastic plate portion that can be elastically deformed and the pressure interference preventing portion provided with the vibration damping material attached to the elastic plate portion. The pressure variation between the ink nozzles is prevented by buffering the pressure fluctuation in the common ink chamber.
[0041]
Since the pressure interference prevention unit of the present invention has portions with different vibration characteristics, even if the vibration plate portion resonates with the driving frequency of the inkjet head, the resonance amplitude of the resonance vibration can be attenuated by the vibration damping material. it can. Therefore, the pressure fluctuation in the common ink chamber can be reliably buffered, and the pressure interference between the ink nozzles can be reliably prevented or suppressed. Therefore, it is possible to prevent uneven printing due to variations in ink ejection characteristics between ink nozzles due to pressure interference between the ink nozzles.
[0042]
In the present invention, a flexible material having a Young's modulus of 1/10 or less, preferably 1/10 ⁵ or less of the Young's modulus of the elastic plate portion, such as a gel type silicone adhesive, is used as the vibration damping material. Therefore, it is possible to suppress a decrease in compliance necessary for pressure buffering by the elastic plate portion.
[0043]
Furthermore, in the present invention, as the vibration damping material, a material having high ink resistance, for example, a gel type silicone adhesive is used, so that the ink touches the pressure interference prevention part, and the vibration damping material peels off, Alternatively, it is possible to prevent adverse effects such as elution and clogging of the ink nozzles.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an external shape of an inkjet head to which the present invention is applied.
2 is an exploded perspective view showing a part of the ink jet head of FIG. 1. FIG.
3 is a partial cross-sectional view showing a part of the ink jet head of FIG. 1;
FIG. 4 is a graph showing a correlation between a compliance of a common ink chamber and a weight change rate of an ink discharge amount.
5 is a partial cross-sectional view showing a modified example of the ink jet head of FIG. 1, in which a protective cover is attached to the pressure interference prevention unit.
[Explanation of symbols]
1 Inkjet head 2 Nozzle plate (first semiconductor substrate)
3 Cavity plate (second semiconductor substrate)
4 Glass substrate 5 Vibration chamber 6 Ink pressure chamber 10 Common ink chamber 12 Individual electrode 21 Ink nozzle 22 Pressure interference prevention unit 22A Diaphragm (elastic plate portion)
22B Vibration damping material 22a Recess 25 Protective cover 25a Vent

Claims (4)

A plurality of ink nozzles, an ink pressure chamber disposed corresponding to each ink nozzle to generate pressure fluctuations for ejecting ink droplets from each ink nozzle, and ink is supplied to each ink pressure chamber A common ink chamber, and a pressure interference prevention unit formed in the common ink chamber in order to prevent pressure interference generated between the ink nozzles via the common ink chamber,
The pressure interference prevention unit includes at least an elastically deformable elastic plate portion that forms a part of the common ink chamber, and an anti-resistance disposed on the elastic plate portion in order to attenuate vibration of the elastic plate portion. An ink-jet head comprising: a vibration damping material having ink properties. The inkjet head according to claim 1, wherein
The inkjet head according to claim 1, wherein a Young's modulus of the vibration damping material is 1/10 or less of a Young's modulus of the elastic plate portion. The inkjet head according to claim 1, wherein
The inkjet head according to claim 1, wherein a Young's modulus of the vibration damping material is 1/10 ⁵ or less of a Young's modulus of the elastic plate portion. In the liquid jet head according to any one of claims 1 to 3,
The inkjet head according to claim 1, wherein the vibration damping material is a silicone adhesive.

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