JPH081937A - Ink jet head - Google Patents

Abstract

PURPOSE:To provide an ink jet head capable of reducing stagnation of ink in a pressure chamber and removing electrolytic bubbles remaining in a current passing part. CONSTITUTION:An ink jet head prints by applying a voltage to electrodes 24a, 24b arranged in a pressure chamber 27 and energizing a conductive ink so as to generate bubbles. Ink passages 29a and 29b are formed in an opposed arrangement with center at a current passing part 28 in the pressure chamber 27. Thus, an ink jet head with which stagnation of the ink is largely reduced, the ink in the current passing part is dispersed, local temperature rise and remaining of electrolytic bubbles are prevented, boiling at high speed driving is stabilized, and discharging direction and speed and size of drops of the conductive ink are stable can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet head used in an inkjet printer.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for higher speed, quieter, and color printers, and ink jet printers have received a great deal of attention. Inkjet printers are roughly classified into continuous type and on-demand type,
Among the on-demand systems, there are a Kaiser system that is driven by a piezo element, and a bubble jet system that causes bubbles to be generated by heat and causes the ink to fly by volume change.

Among the bubble jet methods, there are a heater heating method as a method for generating bubbles, and an energization method in which a current is applied to conductive ink to generate heat. The present invention relates to an ink jet head of this energization method.
An energization type inkjet head is disclosed in US Pat. No. 3,17.
The concept is shown in No. 9,042, but there is room for improvement in frequency response, flight stability, and the like.

A conventional energizing ink jet printer will be described below. 8 is a vertical sectional view of a nozzle of a conventional inkjet head, and FIGS. 9 and 10 are sectional views taken along line AA of FIG. In FIG. 8, 1 is a substrate, 2 is a heat insulating layer laminated on the substrate 1, and the self-heating of the conductive ink is generated by the substrate 1.
This is for efficiently generating bubbles without letting them escape. 3 is a nozzle serving as an ink ejection port, 4a and 4b are rectangular electrodes patterned on the heat insulating layer 2 corresponding to the nozzle 3, 5 is a nozzle plate having the nozzle 3, and 6 is interference between the nozzles. The pressure chamber 7 is composed of a heat insulating layer 2, a nozzle plate 5, and a partition member 6 which are laminated on the substrate 1 by a partition member made of an insulating material.

In FIG. 9, an arrow B indicates a line of electric force passing through the conductive ink between the electrodes 4a and 4b facing each other, and 9
Indicates a current passing portion of the conductive ink, and 10 indicates a bubble immediately after generation. Reference numeral 8 is an ink flow path for supplying ink to the pressure chamber 7.

In FIG. 8, 20 is a conductive ink drop,
The conductive ink in the pressure chamber 7 self-heats due to the electric current flowing along the line of electric force B and is ejected from the nozzle 3 in accordance with the pressure change in the pressure chamber 7 caused by the generation of vapor bubbles. 40 is a recording paper to which the conductive ink droplets 20 adhere,
Reference numeral 41 is a signal generator for applying an AC voltage between the electrodes 4a and 4b.

The operation of the ink jet head having the above structure will be described below. First, the signal generator 41 applies a voltage to the electrodes 4a and 4b. The voltage is an AC voltage in order to prevent wear of the electrodes 4a and 4b. At this time, minute electrolysis bubbles (not shown) are generated on the surfaces of the electrodes 4a and 4b. Due to this voltage, a line of electric force B is generated in the conductive ink having a predetermined volume resistivity, a current flows along the line of electric force B, and the conductive ink in the current passing portion 9 self-heats. In particular, the current density near the center of the opposing electrodes 4a and 4b is higher than that of the other portions, and the conductive ink self-heats due to I (current) ² × R (resistance of conductive ink), so the temperature is higher than the surroundings. Then, the boiling that becomes the nucleus occurs around this, the bubble 10 is generated, and it grows by the heat of the surroundings. As a result, the pressure of the conductive ink in the pressure chamber 7 is rapidly increased, and the conductive ink droplet 20 is ejected from the nozzle 3 and is ejected to adhere to the recording paper 40 to form dots.

The bubble 10 in the pressure chamber 7 is deprived of heat by the surroundings and rapidly contracts and disappears. As the bubble 10 contracts, the surrounding electrolysis bubbles are attracted toward the bubble 10 and become a group of electrolysis bubbles that take time to dissolve in the ink and are scattered around the center. The conductive ink consumed by the dot formation is stored in an ink tank (not shown).
To be supplied through the ink flow path 8 to form any continuous dot formation.

FIG. 10 shows the instant when the bubble of the conventional energizing ink jet disappears, and (a) shows the flow of ink flowing from the flow path. In this flow path arrangement, the portion B does not change during the dot formation process and becomes a stagnation portion. The ink in this part that is not replaced changes its quality due to the fact that it has boiled once and has reached a high temperature, and the volume resistivity etc. has changed.
It causes abnormal boiling. Further, when ejecting continuously at a high frequency, the heat of the ink in this portion is not diffused to the surroundings, and only a part of the ink becomes considerably high temperature. Therefore, the temperature inside the pressure chamber 7 is constant for each ejection. However, it will hinder the stable growth of the bubble.

FIG. 11 is a cross-sectional view of the nozzle of another conventional ink jet head, wherein a shows the flow of ink when the bubble disappears. In this arrangement, stagnation occurs in the area of (b). However, this portion is the portion where the current density is the highest at the time of energization and is the starting point of nucleate boiling and the center of bubble growth, so the boiling will be very variable. Further, during continuous discharge, a very high temperature portion exists between the electrodes, and nucleate boiling starts abnormally quickly. However, since the surrounding atmosphere does not have enough heat, the bubbles shrink without sufficiently growing. In addition, c is a group of bubbles in which minute electrolysis bubbles are gathered near the center of the electrode due to rapid contraction of the bubbles. If the bubbles are dispersed into small bubbles, they quickly dissolve in the ink, but as they are Very difficult to dissolve.

In the structure of FIG. 11, since the inflowing ink cannot diffuse the bubble group (c), the bubble group (c) does not dissolve and remains between the electrodes. When this bubble group (c) serves as a nucleus, boiling starts before the surrounding temperature becomes high, and the bubble cannot grow sufficiently as described above. Further, the frequency and size of occurrence of the bubble group C vary, which hinders stable boiling.

[0012]

However, in the above-mentioned conventional structure, as shown in FIG. 10, a portion where ink stagnates occurs in a portion of the pressure chamber 7 facing the ink flow path 8.
The ink in this portion has once changed its quality by boiling and becoming high temperature, which causes abnormal boiling. Further, when ejecting continuously at a high frequency, the heat of the ink in this portion is not diffused to the surroundings and locally rises in temperature, so that variations in bubble growth and the velocity and ejection direction of the conductive ink droplet 20 are caused. However, there is a problem in that it causes variations in

In addition, in FIG. 11, since the ink is rotated as indicated by the arrow a, in the ink jet head in which the inflow direction of the ink is not toward the center of the electrodes 4a and 4b facing each other, the starting point of nucleate boiling and Ink stagnation occurs in the central portion between the electrodes 4a and 4b, which is the center of bubble growth, and during continuous ejection, only this portion has a high temperature,
Since the surrounding atmosphere does not have enough heat, the bubbles shrink without growing sufficiently. Furthermore, since the micro electrolysis bubbles cannot diffuse the bubbles c gathered near the center, the bubbles c become the nucleus of boiling, and boiling starts before the surrounding temperature becomes high, and the bubbles cannot grow sufficiently. . In addition, the frequency and the size of the bubble group (c) vary, which hinders stable boiling. Therefore, the flight of the conductive ink droplet 20 becomes unstable, and the frequency response is low.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an ink jet head having a stable ejection direction, size and speed of ink droplets and high frequency response.

[0015]

In order to achieve this object, an ink jet head of the present invention is provided with a pressure chamber filled with conductive ink, an ink flow path for supplying ink to the pressure chamber, and a pressure chamber. An inkjet head that includes a nozzle and an electrode that is provided in the pressure chamber and that opposes each other. A voltage is applied to the electrode to evaporate the ink between the electrodes to generate bubbles, thereby ejecting the ink from the nozzle. The ink flow path is formed so as to face each other with the current passage portion of the electrode as the center.

[0016]

With this structure, the stagnation of the ink in the pressure chamber can be reduced, and the residual ink between the electrodes and the electrolysis bubbles can be removed, so that abnormal boiling due to heat or electrolysis bubbles does not occur, and the conductive ink droplets are not generated. The discharge direction, speed, and size of are stable, and the frequency response is high.

[0017]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical cross-sectional view of an ink jet head in one embodiment of the present invention, and FIG. 2 is AA of FIG.
It is sectional drawing. 3 is an exploded perspective view of the inkjet head, FIG. 4 is a perspective view of the inkjet head incorporated in an ink cartridge, FIG. 5 is a partially cutaway perspective view of an ink cartridge incorporating the inkjet head, and FIG. 6 is a perspective view of the inkjet head. FIG. 3 is an exploded perspective view of an inkjet printer to which the incorporated ink cartridge is attached.

In FIG. 1, 21 is a substrate and 22 is a substrate 2.
1 is a heat insulating layer laminated on 1; 23 is a nozzle serving as an ink ejection port; 25 is a nozzle plate having nozzles 23; 26 is a partition member made of an insulating material that prevents interference between the nozzles, and is laminated on the substrate 21. The heat insulating layer 22, the nozzle plate 25, and the partition member 26 form a pressure chamber 27. In FIG. 2, reference numerals 24 a and 24 b are rectangular electrodes, which correspond to the nozzles 23 and are formed on the substrate 21 so as to face each other. In this embodiment, the distance between the electrodes 24a and 24b is 10
μm or less. An arrow B indicates a line of electric force passing through the conductive ink between the electrodes 24a and 24b, and a reference numeral 28 indicates a current passing portion of the conductive ink. 29a and 29b are current passing portions 28
Is a plurality of ink flow paths arranged so as to face each other. 40 is a recording paper to which the conductive ink droplets 20 are attached.
Reference numeral 1 is a signal generator for applying a voltage between the electrodes 24a and 24b.

In FIG. 3, reference numerals 30a and 30b denote pressure chambers 2.
It is a common ink chamber for supplying the conductive ink to 7, and is formed of a heat insulating layer 22, a partition member 26, and a nozzle plate 25 laminated on the substrate 21. 31a and 31b are common ink chambers 30a,
The ink supply holes are provided in the substrate 21 to supply the conductive ink to 30b. In FIG. 4, reference numeral 100 denotes an ink jet head of this embodiment, which includes a substrate 21, a partition member 26, and a nozzle plate 25, and is attached to the fixed groove 101 of the ink cartridge 32.

In FIG. 5, 33 is an ink tank provided in the ink cartridge 32, 34 is an ink filter for removing dust and dirt contained in the conductive ink in the ink tank 33, and 35 is common conductive ink. It is an ink introduction groove that leads to the ink chambers 30a and 30b.

In FIG. 6, reference numeral 36 is a cartridge insertion port for inserting the ink cartridge 32 into the printer, 37 is a carriage for fixing the inserted ink cartridge 32, 38 is a guide shaft for guiding the serially reciprocating carriage 37, 39 is a recording paper. It is a platen roller that sends 40.

Next, the operation of the ink jet head configured as described above will be described. First, FIG.
A voltage is generated by the signal generator 41 shown in FIG.
Add to b. The voltage is an AC voltage to prevent the electrodes 24a and 24b from being worn. By applying this voltage, the electrode 24a
When a potential difference occurs between the electrode 24b and the electrode 24b, a line of electric force B is generated in the conductive ink having a predetermined volume resistivity, and a current flows along the line of electric force B. The lines of electric force B are dense in the current passing portion 28 between the electrodes 24a and 24b and the current is concentrated, so that there is a point where the current density is highest in the current passing portion 28 between the electrodes 24a and 24b.

Since the conductive ink self-heats with I (current) ² × R (resistance of the conductive ink), the conductive ink becomes higher in temperature than the surroundings at the point where the current density is high, and finally, in the conductive ink. The minute bubbles of the above become foam nuclei to generate bubbles (not shown), which rapidly expand due to evaporation from the overheated conductive ink in the periphery. As a result, the pressure chamber 2
The pressure of the conductive ink in 7 rapidly increases, and the nozzle 23
A conductive ink drop 20 is ejected from the recording paper 4 to fly.
0 to form dots. Since the expanded bubble hinders the current in the current passing portion 28, self-heating of the conductive ink is hindered, while the conductive ink rapidly evaporates due to evaporation latent heat to the bubble and heat loss to the pressure chamber wall surface. To lower its temperature. Therefore, the bubble shrinks rapidly and disappears.

When the bubbles disappear, the electrodes 24a, 24b
The current again starts to flow during the period, but before the bubble is generated again, the signal generator 41 stops the voltage application between the electrodes 24a and 24b to prevent unnecessary ejection of the conductive ink droplets. The amount of the conductive ink consumed by the ejection of the conductive ink droplet 20 is supplied from the ink tank 33 to the pressure chamber 27 through the ink flow paths 29a and 29b, and returns to the initial state.

By repeating the above operation, the ink cartridge 32, which is inserted from the cartridge insertion port 36 and mounted on the carriage 37, reciprocates along the guide shaft 38 in response to a print signal sent from a computer or the like. , The signal generator 41 applies a driving voltage between the arbitrary electrodes 24a and 24b in accordance with the position of the carriage 37, the conductive ink droplets 20 are continuously generated, and adhere to the recording paper 40 sent by the platen roller 39. Then
The dots can be printed on the recording paper 40.

With the printing operation, the conductive ink enters the common ink chambers 30a and 30b from the ink tank 33 through the ink filter 34, the ink introduction groove 35 and the ink supply holes 31a and 31b, and the common ink chamber 30a and 30a.
The pressure chamber 2 from 30b through the ink flow paths 29a and 29b.
7 is supplied.

FIG. 7 is a sectional view taken along the line AA in FIG.
B indicates the flow of ink flowing from the respective ink flow paths 29a and 29b. B is a part that is not replaced during the dot formation process. Ink flow paths 29a, 29
Since b is disposed so as to face toward the centers of the electrodes 24a and 24b, the portion where the ink is not replaced in the pressure chamber 27 is limited to the peripheral portion that has little effect on boiling, and the area occupied by it is also small. It is much smaller than before. In addition, the ink flow paths 29a, 2 are provided between the electrodes 24a, 24b.
Since the ink directly flows from 9b, the ink is completely replaced, and the temperature rise of the ink between the electrodes is suppressed even when electricity is continuously supplied at a high speed, and the electrolysis bubble group is also dispersed in the surroundings to facilitate the ink. It becomes minute electrolysis bubbles that dissolve in. Therefore, abnormal boiling does not occur even when electricity is continuously applied at high speed, and an inkjet head having a stable frequency response and a stable ejection direction, speed and size of the conductive ink droplet 20 can be realized.

As described above, according to this embodiment, the ink channels 29a and 29b are opposed to each other with the current passing portions 28 of the electrodes 24a and 24b facing each other, so that the pressure chamber 27 is formed.
Abnormal boiling is prevented by limiting the stagnation point of the ink inside to the part that does not contribute to boiling and by greatly reducing the volume occupied by it. In addition, the ink in the current passing portion 28 is diffused, the local temperature rise in the current passing portion 28 and the residual of the electrolysis bubbles are prevented, and the boiling during high speed driving is stabilized,
The ejection direction, ejection speed, and size of the conductive ink droplet 20 can be stabilized.

[0029]

As described above, according to the present invention, since the ink flow paths are formed so as to face each other with the current passage portion of the electrode as the center, the stagnation of the ink is greatly reduced, and the ink of the current passage portion is removed. It is possible to realize an ink jet head having a stable ejection direction, ejection speed, and size of conductive ink droplets by diffusing, preventing local temperature rise and electrolysis bubbles from remaining, stabilizing the boiling during high-speed driving.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an inkjet head according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1 of the inkjet head according to the embodiment of the present invention.

FIG. 3 is an exploded perspective view of an inkjet head according to an embodiment of the present invention.

FIG. 4 is a diagram showing how an inkjet head is assembled into an ink cartridge according to an embodiment of the present invention.

FIG. 5 is a partially cutaway perspective view of an ink cartridge incorporating an inkjet head according to an embodiment of the present invention.

FIG. 6 is an exploded perspective view of an inkjet printer to which an ink cartridge incorporating an inkjet head according to an embodiment of the present invention is attached.

FIG. 7 is a cross-sectional view taken along the line AA of FIG. 1 of the inkjet head according to the embodiment of the present invention.

FIG. 8 is a vertical cross-sectional view of a nozzle of a conventional inkjet head.

9 is a cross-sectional view of the nozzle of the conventional inkjet head taken along the line AA in FIG.

FIG. 10 is a diagram of a nozzle of a conventional inkjet head.
A-A sectional view

FIG. 11 is a cross-sectional view of a nozzle of another conventional inkjet head.

[Explanation of symbols]

 23 Nozzle 24a, 24b Electrode 27 Pressure chamber 28 Current passing part 29a, 29b Ink flow path

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Matsuzaki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A pressure chamber filled with conductive ink, a plurality of ink channels for supplying ink to the pressure chamber, a nozzle provided in the pressure chamber, and a nozzle provided in the pressure chamber facing each other. An ink jet head comprising an electrode, wherein a voltage is applied to the electrode to evaporate the ink between the electrodes to generate bubbles to eject the ink from the nozzle, wherein the plurality of ink flow paths are connected to the electrode. An ink jet head characterized in that they are formed so as to face each other with a current passing portion according to 1.