JP2001341309A - Thermal ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal ink jet head in which a larger kinetic energy per unit volume can be generated for a micro liquid drop by eliminating uneven heating of a heater. SOLUTION: A heater 16 facing a nozzle 13 has a recessed shape and an upper electrode 17 is connected electrically with the opening of the heater 16 while a lower electrode 18 is connected electrically with the bottom part of the heater 16. The heater 16 is heated by supplying the pair of electrodes with pulsating power and ink, stored in an ink heating chamber 15 through an ink channel 14, is heated by means of the heater 16 and bubbled before being ejected selectively from the nozzle 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal ink jet head which discharges ink by heating and foaming the ink.

[0002]

2. Description of the Related Art A thermal ink jet head is a recording head that generates a pressure wave in ink by heating and bubbling the ink with a heating resistor to discharge ink droplets to the outside through nozzles. However, the rate at which the heat energy generated by the heating resistor is converted into the kinetic energy of the ejected ink droplets is extremely small, and most of the heat energy is consumed due to a rise in the temperature of the ink jet head or ink and a pressure loss to the ink passage. Is done. This not only hinders the reduction in power consumption, but also makes it impossible to shorten the heat cycle time of heating and cooling, which is an obstacle to high-speed printing.

On the other hand, the quality of recording has been rapidly improved, and as a result, the size of ink droplets ejected from one nozzle at a time has become smaller. However, when the ink droplet size is smaller than 3 picoliters, the ink droplets tend to be decelerated during flight due to the viscous resistance of the air and are likely to bend, and the landing positions on the recording paper are likely to shift. Thus, a greater initial velocity must be given to the ink droplets.

[0004] For these reasons, in thermal ink jet heads, it is required to improve the thermal efficiency and generate a larger kinetic energy per unit volume for fine droplets.

For example, Japanese Patent Application Laid-Open No. 6-183001 proposes improving the discharge efficiency by making the shape of the heater concave so that the discharge pressure is concentrated at the center of the discharge port.

[0006]

However, particularly in the case where the heating resistor and the discharge port are provided facing each other as in the fifth embodiment of JP-A-6-183001, a nozzle having a pair of electrodes at both ends is provided. As shown in FIG. 6, in the heater having the concave surface facing the portion, the current flows intensively at the end of the concave surface having a small electric resistance. Heat generation over the entire surface cannot be performed uniformly. This cannot always be said to contribute to the improvement of the thermal efficiency described above. In addition, since the current is concentrated at the heater end, an excessive load is applied to heaters and electrodes in the vicinity thereof, which may cause a reduction in the life of the heater and the electrodes.

An object of the present invention is to provide a thermal ink jet head which can eliminate the above-mentioned uneven heat generation of the heater and can generate a larger kinetic energy per unit volume for minute droplets.

[0008]

According to a first aspect of the present invention, there is provided a thermal ink jet head in which a heater has an opening and a bottom and has a concave shape, and the opening faces a nozzle. The opening side of the concave heater is connected to the first electrode, and the bottom of the concave heater is connected to the second electrode.
Are connected to the electrodes. Then, by supplying power in a pulsed manner between the first electrode and the second electrode by the power supply means, the concave heater generates heat, and the ink accumulated in the ink heating chamber formed inside the concave heater. Are heated and foamed, and ink is selectively ejected from the nozzles.

According to a second aspect of the present invention, there is provided a thermal ink jet head, wherein an opening and a bottom of a heater and a side portion sandwiched between the opening and the bottom are rotationally symmetric with respect to a center line of the nozzle, and the first electrode is a concave heater. The surface in contact with the opening has a rotationally symmetric shape with respect to the center of the nozzle, and the second electrode has a surface in contact with the bottom of the concave heater with a rotationally symmetric shape with respect to the center line of the nozzle. Have.

[0010] In the thermal ink jet head according to the third aspect, a part of the bottom of the concave heater is connected to the second electrode.

According to a fourth aspect of the present invention, a side surface of the ink heating chamber sandwiched between the opening and the bottom of the concave heater and a side portion of the concave heater sandwiched between the opening and the bottom with respect to the ink ejection direction. It has an inclined surface or a concave surface having a curvature.

According to a fifth aspect of the present invention, there is provided a thermal ink jet head having a cavitation resistant film for protecting the concave type heater inside the concave type heater, wherein a conductive member is used for the cavitation resistant film. The cavitation-resistant film is used as the first electrode by connecting to the concave heater via a via hole formed in the adjacent insulating layer between the concave heater.

According to a sixth aspect of the present invention, the first electrode is fixed to the GND electrode, and a pulse potential is supplied to the second electrode.

[0014]

Embodiments of the present invention will be described below.

The ink jet head according to the present embodiment (hereinafter referred to as the present head) is a thermal ink jet type recording head used in a general ink jet printer.

First, the outline of the head will be described.

FIG. 1 is a perspective view showing the structure of the head. In this head, a nozzle plate 12 is provided on a substrate 11 via a spacer (not shown) so as to maintain a constant distance from the substrate 11. The nozzle plate 12 is provided with a nozzle (hole) 13 serving as an ink discharge port, and a heater 16 is provided on the substrate 11 so as to face the nozzle (hole) 13. The shape of the heater 16 is concave, and the opening faces the nozzle 13. Spacers (not shown) are removed where the heater 16 and the ink flow path 14 are provided. Further, the heater 16 is sandwiched between the insulating layers 19.
A pair of electrodes are provided on the opening side and the bottom side of the.
(Here, the opening side of the heater 16 is referred to as an upper electrode 17, the bottom side is referred to as a lower electrode 18, the opening side is referred to as an upper side, and the bottom side is referred to as a lower side.) Also, the ink ejected inside the heater 16 is heated. An ink heating chamber 15 is formed. The head has one or a plurality of nozzle channels composed of 11 to 19.

Next, the structure of the heater portion, which is a characteristic configuration of the present head, will be described.

FIG. 2A shows a cross-sectional structure near the nozzle and the heater. The heater 16 facing the nozzle 13 has a concave shape, and the upper electrode 17 is electrically connected on the opening side of the heater 16. The lower electrode 18 is electrically connected to the bottom of the heater 16. One of these electrodes is connected to a voltage level (G
ND), and by supplying a pulse potential to the other electrode, the heater 16 generates heat. The ink stored in the ink heating chamber 15 via the ink flow path 14 is heated by the heater 16 and foams. To selectively discharge.

Here, the upper electrode 17 and the lower electrode 1
There is no problem if the potential of the head 8 is not specified but is unified to either one in the head.

As shown in the figure, the heater bottom does not generate heat because it is in contact with the electrodes. However, when the depth of the concave portion is sufficient, the side area (heat generating portion) of the heater 16 is increased and the amount of generated heat is reduced. Since the contact area with the ink increases, the heat loss to the ink flow path 14 can be suppressed, and only the ink in the ink heating chamber 15 can be efficiently heated.

On the other hand, when the bottom area is large, FIG.
As shown in (b), by connecting a part of the center of the bottom of the heater 16 to the lower electrode 18, the other bottom can also generate heat, and the amount of heat generated by the heater can be increased. In this structure, the second insulating layer is formed of two materials (the second insulating layer a (21a),
This can be easily realized by depositing and etching the second insulating layer b (21b)).

Here, a specific manufacturing method will be described.

First, after forming the lower electrode 18, a second insulating layer a (21 a) (for example, a silicon oxide film) is deposited, and patterning is performed by photolithography to make contact with the lower electrode 18. A contact hole is formed using a system etchant. Next, after removing the photoresist, a second insulating layer b (21b) (for example, silicon nitride) is deposited, patterning of the hole of the heater is performed by photolithography, and hole processing of the concave portion is performed by plasma etching. I do. In the plasma etching, the etching rate of the second insulating layer b (21b) is increased by the second insulating layer a (21b).
By selecting a condition sufficiently larger than that of a), a hole can be formed without damaging the shape of the already formed second insulating layer a (21a).

FIG. 3 is a diagram schematically showing the flow of current when this head is used.

Here, the upper electrode 17 is on the high potential side and the lower electrode 18 is on the low potential side. By arranging the electrodes with respect to the concave heater in this manner, the current density of the heater heating portion becomes uniform, and the current flows from the upper electrode 17 to the heater 16.
And the ink flows evenly to the lower electrode connection surface 27 at the bottom of the heater 16, so that the ink is uniformly heated from the side surface of the ink heating chamber 15 toward the nozzle and the center 26 of the heater, and the thermal efficiency with respect to the ink is improved.

Further, by forming the upper electrode 17 and the lower electrode 18 in a three-dimensional wiring, it is advantageous in terms of space saving around the heater 16.

Further, the fact that the bottom of the heater 16 does not generate heat as described above means that even when ink is ejected, the ink adjacent to this portion remains without being ejected. In order to absorb the impact of pressure generated when the heater 16 disappears, damage to the heater 16 is reduced, and the life can be improved.

In FIG. 3, the center line of the nozzle coincides with the center of the heater, and the electrodes (upper electrode 17 and lower electrode 18) in contact with the heater and the heater with respect to the center are the nozzle and heater. Are symmetrical with respect to the center 26 of FIG. In this case, the planar shape of the heater (the upper electrode 17 and the lower electrode 18) in contact with the heater is preferably circular. This has an effect of evenly concentrating the ejection pressure on the center of the nozzle 13 so as to minimize the pressure loss and an effect of preventing the ejection ink droplet from flying and bending.

Next, a method for improving the discharge capacity will be described. FIG. 4 (a) shows the heater 16 sandwiched between the opening and the bottom.
4B and the side surface of the ink heating chamber 15 are inclined with respect to the ink ejection direction. FIG. 4B shows that the side portion and the side surface of the ink heating chamber 15 have a curvature with respect to the ink ejection direction. It shows that it is a face. The curvature preferably has a constant curvature at a distance from the center of the nozzle. Such a shape can be easily realized by isotropic etching using a normal chemical solution or semi-anisotropic etching in which bias plasma etching is slightly isotropic.

This structure has two advantages, one of which is:
With such a shape, bubbles generated on the heater are generated toward the center of the nozzle, so that the discharge pressure can be directed to the center of the nozzle 13 and efficient discharge can be performed. Another advantage is that variations in the amount of ejected ink can be reduced. Since the shape of the heater 16 is a funnel shape, the cross-sectional area of the heater 16 becomes smaller and the resistance value becomes larger toward the bottom, and a certain amount of current flows through the heater 16. The amount increases. Further, since the amount of ink decreases as approaching the bottom, the ink is sequentially heated from below the ink heating chamber 15 by the influence of both. As a result, the foaming of the ink always grows from the bottom of the heater 16, so that the foaming position becomes constant, and the variation in the amount of ejected ink can be reduced.

Next, an embodiment in which simplification of the manufacturing process of the present head is considered will be described.

FIG. 5 shows a structure around a heater and an electric connection method for simplifying a manufacturing process. In the thermal ink jet, a cavitation-resistant film is deposited on the heater in order to protect the heater from an impact pressure generated when bubbles disappear. In this embodiment,
A conductive member is used for the anti-cavitation film, and is also used as an electrode. As a material having conductivity and used for the cavitation-resistant film, Ta (tantalum) is exemplified. As shown in FIG. 5, the upper electrode has a structure that also serves as a cavitation-resistant film. (Here, this is referred to as an upper electrode / cavitation-resistant film 24.) The heater 16 and the upper electrode / cavitation-resistant film 24 are connected by a conductive member 29 via a via hole 28 formed in the third insulating layer 22 on the heater 16. By doing so, the anti-cavitation film can be used as the upper electrode, and furthermore, with such a structure, the process of forming the upper electrode can be simplified.

In this case, since the upper electrode and anti-cavitation film 24 comes into direct contact with the ink, the upper electrode and the anti-cavitation film 24 are always connected to the reference potential (GND) so as not to have an adverse effect such as electrolysis on the ink, and a pulse is applied to the lower electrode 18 side. It has become.

[0035]

According to the first aspect of the present invention, the thermal ink jet head uses a concave heater, and the concave heater has a larger contact area with ink than a flat heater, so that more heat is supplied to the ink in the ink heating chamber. At the same time, there is an effect that the pressure generated by the heating of the ink is prevented from escaping to the ink flow path (loss). In addition, by forming the first electrode and the second electrode three-dimensionally at the opening and the bottom of the concave heater, respectively, the space around the heater can be saved. Further, heat generation of the concave heater, which cannot be realized by electrode wiring on one plane, can be uniformly performed. Furthermore, since the heater portion in contact with the second electrode does not generate heat, even in the event of ink ejection, ink adjacent to the portion remains without being ejected, and absorbs the impact of pressure generated when bubbles disappear. In addition, cavitation resistance can be improved.

In the thermal ink jet head according to the second aspect, the concave heater, the first electrode and the second electrode are rotationally symmetric with respect to the center line of the nozzle, so that the heat generated by the concave heater is equalized and the discharge is performed. The pressure can be concentrated on the nozzles to prevent the ejection ink from flying and bending.

In the thermal ink jet head according to the third aspect, by connecting a part of the bottom of the concave heater to the second electrode, it is possible to generate heat at a part of the bottom of the concave heater which is not in contact with the second electrode. Thus, the total heat generation can be further increased. Thereby, the ink can be heated more quickly and more efficiently.

According to a fourth aspect of the present invention, the side surface of the ink heating chamber and the side portion of the concave heater have a surface inclined with respect to the ink ejection direction or a concave surface having a curvature. Since the bubbles generated on the heater are more likely to be generated toward the center of the nozzle than when the side surface of the ink heating chamber is parallel to the ejection direction, the ejection pressure can be concentrated on the nozzle. Also, since the electrical resistance increases toward the bottom of the heater, the ink is sequentially heated from the bottom of the ink heating chamber.
The bubbling position is constant, and variations in the amount of ejected ink can be reduced.

The thermal ink jet head according to the fifth aspect can be used as the first electrode by using a conductive material for the anti-cavitation film for protecting the concave heater. Thereby, the electrode forming process can be simplified.

According to a sixth aspect of the present invention, in the fifth aspect, since the first electrode directly contacts the ink, the first electrode is used as a reference electrode (GND).
By supplying a pulse potential to the second electrode, adverse effects such as electrolysis are not exerted on the ink.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of an embodiment of the present invention.

FIG. 2A is a cross-sectional view of the vicinity of a nozzle and a heater, showing one embodiment of the present invention. (B) is a sectional view of the vicinity of the nozzle and the heater, showing another embodiment.

3A and 3B are a cross-sectional view and a top view of the vicinity of a nozzle and a heater, respectively, showing an embodiment of the present invention, and a diagram schematically showing a current flow.

FIG. 4 is a sectional view showing a shape of a heater according to another embodiment of the present invention.

FIG. 5 is a sectional view showing a configuration around a heater according to another embodiment of the present invention.

6A and 6B are a cross-sectional view and a top transparent view in the vicinity of a nozzle and a heater of a thermal ink-jet head according to a conventional example, and are diagrams schematically showing the flow of current.

[Explanation of symbols]

 Reference Signs List 11 substrate 12 nozzle plate 13 nozzle 14 ink flow path 15 ink heating chamber 16 heater 17 upper electrode 18 lower electrode 19 insulating layer 20 first insulating layer 21 second insulating layer 21a second insulating layer a 21b second insulating layer b 22nd 3 Insulating layer 23 Protective film 24 Upper electrode and cavitation resistant film 25 Center line of nozzle and heater 26 Center of nozzle and heater 27 Lower electrode connection surface 28 Via hole 29 Conductive electrode material 30a Electrode material (high potential side) 30b Electrode material (low Potential side)

Claims (6)

[Claims] 1. An ink jet head comprising: a nozzle for discharging ink; and an ink heating chamber, wherein the ink in the ink heating chamber is supplied with electric power, heated and foamed to discharge from the nozzle. A concave heater having an opening facing the nozzle, an ink heating chamber formed inside the concave heater, and an opening connected to the opening of the concave heater. A first electrode, a second electrode connected to the bottom side of the concave heater, and power supply means for supplying pulsed power between the first electrode and the second electrode. A thermal inkjet head, comprising: 2. The concave heater, wherein the opening, the bottom, and a side portion sandwiched between the both have a rotationally symmetrical shape with respect to a center line of the nozzle, and the first electrode has a concave shape. The surface of the heater that is in contact with the opening has a rotationally symmetric shape with respect to the center line of the nozzle, and the second electrode is such that the surface that is in contact with the bottom of the concave heater rotates with respect to the center line of the nozzle. The thermal inkjet head according to claim 1, wherein the thermal inkjet head has a symmetric shape. 3. The thermal ink jet head according to claim 1, wherein the second electrode is connected to a part of the bottom of the concave heater. 4. A side portion of the ink heating chamber sandwiched between the opening and the bottom, and a side portion of the heater sandwiched between the opening and the bottom have an inclination with respect to an ink ejection direction. surface,
Or a concave surface having a curvature.
The thermal inkjet head according to 1. 5. An anti-cavitation film for protecting the concave heater, wherein the anti-cavitation film is formed of a conductive material inside the concave heater, and is formed between the concave heater and the anti-cavitation film. Forming an insulating layer therebetween, and connecting the concave heater and the anti-cavitation film through a via hole formed in the insulating layer, thereby using the anti-cavitation film as the first electrode. The thermal inkjet head according to claim 1. 6. The first electrode is a GND electrode, and the second electrode is
6. The thermal inkjet head according to claim 5, wherein a pulse potential is supplied to the electrodes.