JPH1120166A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet head capable of performing high quality printing irrespective of a size of a dot and of raising a printing speed. SOLUTION: An ellipsoidal pressure chamber 27 is formed between a substrate 25 and a nozzle plate 24 and an ink passage 28 is communicated to one end of the pressure chamber 27. A nozzle hole 23 is formed on the nozzle plate 24 at an upper section of the center of the pressure chamber 27. A pair of electrodes 29a are disposed on a bottom face of the pressure chamber 27 at a side of the ink passage 28 away from the nozzle hole 23. An ink jet head 21 is constituted such that a distance (a) between the electrodes 29a and the nozzle hole 23 and a distance (b) between the electrodes 29a and a side end 36 of the ink passage 28 are satisfied with a relationship of a/b>1/2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head for performing printing by applying ink droplets ejected from nozzles to recording paper.

[0002]

2. Description of the Related Art In recent years, an image recording apparatus such as a printer, a copying machine, a facsimile, etc., connected to a computer, a word processor, etc., is capable of forming images and characters on recording paper, such as paper or a plastic thin plate, based on image information. It is configured. One of the image recording apparatuses is an ink jet printer.

An ink jet printer is a non-impact type printer, capable of extremely low noise, high speed printing, and using inexpensive plain paper. Furthermore, it does not require processing such as development and fixing, and has excellent features such as flexibility in recording kanji and graphics and expansion of functions.

[0004] Ink jet printers are broadly classified into charge control systems and on-demand systems depending on the method of generating ink particles and the method of controlling the same. In addition, as one of the on-demand methods, bubbles are generated by heat,
There is a bubble jet method in which ink droplets are ejected by the volume change.

Here, a conventional bubble jet type ink jet head used in an ink jet printer will be described below.

FIG. 5 is a sectional view of a main part showing an ink jetting section of a conventional ink jet head, and FIG.
It is a B sectional view. 5 and 6, the ink jet head 1 has a pressure chamber 7 surrounded by a nozzle plate 4, a substrate 5, and an insulating member 6, and the inside thereof is filled with a conductive ink 2. The conductive ink 2 is supplied from the ink flow path 8 into the pressure chamber 7. The conductive ink 2 boils when an electric current is applied to generate bubbles. Inside the pressure chamber 7, a pair of electrodes 9a and 9b are formed in a predetermined pattern. A pair of electrodes 9a, 9b
Is connected to the signal generating unit 10, and a pair of electrodes 9a,
A predetermined voltage is applied during 9b. The nozzle plate 3 has a nozzle hole 3 for ejecting the conductive ink 2.

The principle of ejecting the conductive ink 2 in the ink jet head 1 configured as described above will be described.

In FIGS. 5 and 6, a voltage is applied from a signal generator 10 between a pair of electrodes 9a and 9b during printing. The lines of electric force 11 are generated between the electrodes 9 a and 9 b via the conductive ink 2, and current flows along the lines of electric force 11. The flowing current is concentrated on the current concentrating portion 12, which is a specific portion of the gap between the pair of electrodes 9a and 9b.
Then, the conductive ink 2 near the current concentrating portion 12 self-heats due to Joule loss, and the temperature rises, and finally, boiling starts and bubbles are generated. Volume change (expansion) of this bubble
Thereby, the pressure of the conductive ink 2 in the pressure chamber 7 is rapidly increased. As a result, a part of the conductive ink 2 whose pressure has increased is ejected from the nozzle hole 3 as an ink droplet 13.
The ejected ink droplets 13 adhere to the recording paper 14 arranged on the opposite surface of the nozzle plate 4 to form print dots.

When the voltage applied between the pair of electrodes 9a and 9b is increased, the volume of bubbles generated in the conductive ink 2 becomes smaller, and the ink droplet 13 becomes smaller. For this reason, print dots formed on the recording paper 14 are reduced. Conversely, when the voltage applied to the electrodes 9a and 9b is reduced,
The volume of the bubble increases, and a large print dot can be formed on the recording paper 14.

The signal generator 10 stops applying voltage to the electrodes 9a and 9b when the conductive ink 2 starts boiling. The conductive ink 2 consumed in the pressure chamber 7 by the ejection is supplied from an ink storage unit (not shown) through the ink flow path 8 before the signal generator 10 applies the next voltage.

By repeating the above-described jetting operation of the conductive ink 2, the ink jet head 1 forms the ink droplet 13 according to the signal from the signal generating unit 10 on the recording paper 14.
To form an image on the recording paper 14.

[0012]

However, in the above-described conventional ink jet head, the size of the pressure chamber 7 and the ink flow path 8 is set to such a size that a small amount of ink droplets 13 can be ejected in order to form small dots. Stipulated.
Therefore, when a large dot is formed, if a large bubble is generated to eject a large ink droplet 13, the bubble may overflow from the pressure chamber 7 and a part of the bubble may blow out from the nozzle hole 3. In this case, the ink droplets 13 scatter on the recording paper 14 and the shape of the dots is disturbed. As a result, there is a problem that the printing quality is reduced.

When a large ink droplet 13 is ejected to form a large dot, it takes a long time to replenish the consumed conductive ink 2 into the pressure chamber 7. For this reason, there is a problem that it becomes a hindrance factor for speeding up the printing operation of the inkjet head.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ink jet head which can perform high quality printing regardless of the size of a dot and can increase the printing speed.

[0015]

In an ink jet head according to the present invention, a bubble generating portion is disposed inside a pressure chamber having an ink discharge hole, and one end communicates with the pressure chamber and the other end stores ink. In the ink jet head which pressurizes the ink supplied into the pressure chamber through the ink flow path communicating with the ink jet head by the air bubbles generated by the air bubble generation unit and discharges the ink from the ink discharge holes, the distance between the air bubble generation unit and the ink discharge holes is a , The distance between the bubble generating section and the other end of the ink flow path is b, and the bubble generating section, the ink discharge holes and the ink flow path are arranged so as to satisfy the relationship of a / b> 1/2. .

In the ink jet head according to the present invention, bubbles are generated by the bubble generating portion, and the ink in the pressure chamber is pressurized by volume expansion of the bubbles to discharge the ink from the ink discharge holes. When the bubble expands in volume, one end of the bubble extends toward the ink ejection hole, and the other end extends toward the ink flow path. Therefore, by forming the distance from the bubble generating portion to the other end of the ink flow path longer than the distance from the bubble generating portion to the ink discharge hole so as to satisfy a predetermined relationship, a part of the bubble is formed in the ink discharge hole. To rupture the ink droplets by ejecting the ink droplets to the outside. Further, when the bubble portion extending toward the ink flow path contracts, the ink can be drawn into the pressure chamber from the ink storage section at a high speed. This makes it possible to replenish the ink after ejecting the ink droplets in a short time, and to speed up the printing operation.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In an ink jet head according to a first aspect of the present invention, a bubble generator is disposed inside a pressure chamber having an ink discharge hole, and one end communicates with the pressure chamber and the other end stores ink. In the ink jet head which pressurizes the ink supplied into the pressure chamber through the ink flow path communicating with the ink jetting section by the bubbles generated in the bubble generating section and discharges the ink from the ink discharging holes, the distance between the bubble generating section and the ink discharging holes is a , The distance between the bubble generating section and the other end of the ink flow path is b, and the bubble generating section, the ink discharge holes and the ink flow path are arranged so as to satisfy the relationship of a / b> 1/2. .

In this way, during printing operation with a large dot size, bubbles are prevented from being ejected from the ink ejection holes to rupture ink droplets, thereby enabling high quality and high gradation printing. Further, by growing and shrinking the bubbles on the ink flow path side, it is possible to replenish the ink into the pressure chamber in a short time, thereby speeding up the printing operation.

The ink jet head according to a second aspect of the present invention is the ink jet head according to the first aspect of the present invention, wherein the bubble generating section is disposed near one end of the ink flow path, and the ink discharge holes are formed in the bubble generating section. On the other hand, it is arranged on the side opposite to one end of the ink flow path.

Thus, the bubbles in the bubble generating section are prevented from extending toward the ink flow path and being ejected from the ink ejection holes, and high quality and high speed printing operation can be performed.

According to a third aspect of the present invention, in the ink jet head according to the first or second aspect of the present invention, the interval between the side walls of the pressure chambers is from the bubble generating portion side to one end portion of the ink flow path. The side wall surface is formed so as to narrow.

Thus, when the bubbles are contracted, the ink supplied from the ink flow path into the pressure chamber can be smoothly drawn into the pressure chamber.

An ink jet head according to a fourth aspect of the present invention is the ink jet head according to any one of the first to third aspects, wherein the bubble generating portion has a pair of electrodes arranged at a predetermined distance. It is.

In this case, the generation and shrinkage of bubbles can be easily controlled by controlling the energization between the pair of electrodes.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a partially cutaway perspective view of an ink jet head according to the present invention, FIG. 2 is a plan sectional view of an ink ejecting unit, and FIG. 3 is a sectional view taken along line AA in FIG. In FIG. 1 to FIG.
Has a substrate 25 made of an insulating glass substrate or the like, and a nozzle plate 24 is laminated on the surface of the substrate 25 via an insulating member 26. The insulating member 26 is cut out in a predetermined shape, and the cut-out portion is sandwiched between the substrate 25 and the nozzle plate 24 to form a pressure chamber 27 and an ink flow path 28.

As shown in FIG. 2, the pressure chamber 27 is formed in an elliptical planar shape, and one end thereof communicates with the ink flow path 28 through a communication portion 28a. The pressure chamber 27
It is formed so that the width between the side wall surfaces is gradually narrowed from the center side toward the communication portion 28a. Further, the width of the ink flow path 28 is formed larger than the width of the communication portion 28a. Further, the other end of the ink flow path 28 opposite to the communication part 28a communicates with a common ink chamber 37 that supplies conductive ink to the plurality of nozzle ejection parts.

On the surface of the substrate 25 in the pressure chamber 27, a pair of electrodes 29a and 29b are arranged at a predetermined interval. Opposite end faces of the pair of electrodes 29a and 29b are formed in an elliptical shape. The pair of electrodes 29a and 29b are connected to a print signal generator 30 for applying a voltage between the electrodes 29a and 29b. A circular nozzle hole 23 is formed in the nozzle plate 24 above the center of the pressure chamber 27. The center of the pair of electrodes 29a and 29b is set to be shifted toward the ink flow path 28 with respect to the center of the nozzle hole 23.

Here, the nozzle holes 23 correspond to the ink discharge holes of the present invention, the ink chambers 37 correspond to the ink storing portions,
The pair of electrodes 29a and 29b correspond to a bubble generator.

Inkjet head 2 having the above configuration
The first ink ejection operation will be described.

1 to 3, the pressure chamber 27 is filled with the conductive ink 22 in the initial state. In this state, a pair of electrodes 29a, 29b
When a voltage is applied therebetween, a line of electric force 31 is generated between the electrodes 29 a and 29 b via the conductive ink 22. Then, a current flows along the lines of electric force 31, and I ² × R
Due to the Joule loss of the current represented by (I is the current value, R is the resistance value of the conductive ink 22), the conductive ink 22 self-heats at the current concentration portion 32 of the electric flux line 31, and finally boils. As a result, bubbles are generated in the conductive ink 22.

When the generated bubble expands in the pressure chamber 27, the pressure of the conductive ink 22 in the pressure chamber 27 is rapidly increased, and a part of the conductive ink 22 is caused to drop from the nozzle hole 23 by the pressure. It is injected outside. The ejected ink droplets 33 adhere to the surface of the recording paper 34 and form print dots.

The print signal generator 30 is provided with the conductive ink 22
When the start of boiling, the application of voltage to the pair of electrodes 29a and 29b is stopped. Thus, the bubbles expand to a certain amount, then contract and disappear.

Ink droplets 33 ejected from the nozzle holes 23
Conductive ink 22 in the pressure chamber 27 consumed by the
Is supplied into the pressure chamber 27 through the ink flow path 28.
Thereafter, the print signal generator 30 starts applying a voltage for the next print.

Next, the configuration and operation of the above-described ink jet head 1 for printing large dots will be described. In order to form a large print dot by discharging a large ink droplet 33 from the nozzle hole 23, it is necessary to grow a large bubble. On the other hand, when the bubble grows large toward the nozzle hole 23, a part of the bubble is discharged from the nozzle hole 23, causing the ink droplet 33 to burst. For this reason, it is not preferable that the bubbles grow large toward the nozzle hole 23 side.

In order to satisfy such a condition, in FIG. 1 or FIG. 4 (a), the distance between the center of the electrodes 29a and 29b and the end of the nozzle hole 23 is a, and 29b and the ink flow path 2
The distance between the side end portion 8 (the boundary position between the ink flow path 28 and the ink chamber 37) 36 is b, and a / b> 1/2.
The relational expression (1) is established.

FIGS. 4A to 4D are explanatory diagrams of the operation at the time of printing a large dot. In FIG. 4A,
A region indicates the pressure chamber 27 and B region indicates the ink flow path 28. The positions of the A and B regions are the same in FIGS. 4B to 4D.

First, in FIG. 4A, a pair of electrodes 2
When a voltage is applied between the electrodes 9a and 29b from the print signal generator 30, bubbles 38 are generated from the vicinity of the current concentrator 32 between the electrodes 29a and 29b. When printing large dots, use electrode 2
The voltage applied between 9a and 29b is set low, whereby the bubble 38 grows large as shown in FIG. 4 (b).

The bubble 38 grows larger around the pair of electrodes 29a and 29b on the ink flow path 28 side than on the pressure chamber 27 side. This is because the electrodes 29a and 29b are arranged shifted toward the ink flow path 28 from the center of the pressure chamber 27,
This is because bubbles 38 easily grow on the side of the ink flow path 28 having a large volume.

When the bubble 38 grows, the pressure of the conductive ink 22 in the pressure chamber 27 is rapidly increased, and the pressure in the nozzle hole 23 is increased.
Injected from outside.

At this time, the application of voltage from the print signal generator 30 to the pair of electrodes 29a and 29b is stopped.

In FIG. 4C, the bubble 38 that has grown largely toward the ink flow path 28 contracts rapidly toward the pressure chamber 27 side. This is because the bubble 38 has a property of contracting toward a higher temperature. That is, the temperature in the pressure chamber 27 is higher than the temperature of the ink flow path 28. Therefore, the bubbles 38 grown on the ink flow path 28 side
This time, on the contrary, it contracts toward the pressure chamber 27 side and generates the ink flow 39 from the ink chamber 37 toward the pressure chamber 27 side. Thus, the conductive ink 22 can be quickly supplied from the ink chamber 37 into the pressure chamber 27. As a result, as shown in FIG. 4D, the inside of the pressure chamber 27 after the ink droplet 33 is discharged becomes the conductive ink 2.
2 is filled in a short time.

As described above, by disposing the pair of electrodes 29a and 29b at positions shifted from immediately below the nozzle hole 23 toward the ink flow path 28 and generating bubbles at this position, the bubbles 38 are formed. Even when the growth is large, a part of the bubble 38 can be prevented from blowing out from the nozzle hole 23.

Further, when the bubble 38 which has grown largely on the ink flow path 28 side contracts, the ink flow 39 of the conductive ink 22 from the ink chamber 37 side to the pressure chamber 27 side can be generated vigorously. As a result, the time for supplying the conductive ink 22 to the pressure chamber 27 can be reduced.

A prototype of the ink jet head having the above-described configuration was manufactured, and a printing test was performed. As the conductive ink 22, an ink obtained by dispersing a dye or a pigment in a mixed solvent liquid of highly volatile water, alcohol, or the like and glycerin or the like having a low volatility was used. The resistivity of the conductive ink 22 is 10 to 5
It was 0 Ω · cm.

The electrode 2 shown in FIG. 1 and FIG.
9a, 29b and the distance a between the nozzle hole 23 and the electrode 29
Samples 1 to 24 were prepared by changing the distance b between the a and 29b and the side end 36 of the ink flow path 28, and the formed dot diameter, droplet discharge stability and droplet discharge frequency characteristics were measured. . The measurement results are shown in (Table 1) and (Table 2).

[0046]

[Table 1]

[0047]

[Table 2]

As is clear from Tables 1 and 2, in the ink jet head satisfying the above-mentioned relational expression (1), the blowing of bubbles from the nozzle holes 23 is prevented, and the resolution is high and stable. It has been found that dot formation takes place. In particular, the ratio of the distance a to the distance b (a /
It has been found that the larger the value of b) is, the more stable printing is performed even when the formed dot diameter is large.

In the above embodiment, the conductive ink 22
Although the ink jet head of the method of performing printing by generating a bubble by applying a voltage between the pair of electrodes 29a and 29b immersed in the ink jet head has been described, the configuration of the present invention is to perform printing by generating a bubble. And the same effect can be obtained.

[0050]

As described above, in the ink-jet head according to the present invention, even when the bubbles grow large, some of the bubbles are prevented from being ejected from the ink discharge holes, thereby preventing the rupture of the ink droplets. Thus, high-quality printing with high resolution and good gradation can be performed.

Further, at the time of bubble contraction, the ink can be quickly and smoothly introduced from the ink flow path into the pressure chamber, so that a high-speed printing operation can be realized.

Further, by controlling the generation of bubbles with a pair of electrodes, a printing operation with excellent controllability can be performed.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view of an ink jet head according to the present invention.

FIG. 2 is a cross-sectional plan view of an ink ejecting unit.

FIG. 3 is a sectional view taken along line AA in FIG. 2;

FIG. 4 is an explanatory diagram of an operation at the time of printing a large dot.

FIG. 5 is a cross-sectional view illustrating a main part of an ink jet unit of a conventional inkjet head.

FIG. 6 is a sectional view taken along line BB in FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Ink jet head 22 Conductive ink 23 Nozzle hole 24 Nozzle plate 25 Substrate 26 Insulating member 27 Pressure chamber 28 Ink flow path 29a, 29b Electrode 30 Print signal generation part 33 Ink droplet

Claims (4)

[Claims] An air bubble generating section is disposed inside a pressure chamber having an ink discharge hole, and one end of the pressure chamber communicates with the pressure chamber and the other end communicates with the ink reservoir through an ink flow path. In the ink jet head which pressurizes the ink supplied to the nozzle by the bubbles generated by the bubble generation unit and discharges the ink from the ink discharge holes, a distance between the bubble generation unit and the ink discharge holes is a, Let b be the distance between the other end of the ink flow path and a /
An ink jet head, wherein the bubble generating section, the ink ejection holes, and the ink flow paths are arranged so as to satisfy a relationship of b> 1/2. 2. The method according to claim 1, wherein the bubble generating section is disposed near the one end of the ink flow path, and the ink ejection hole is disposed on the opposite side of the ink flow path from the bubble generating section to the one end of the ink flow path. 2. The ink jet head according to claim 1, wherein: 3. The side wall surface of the pressure chamber is formed so that an interval between side wall surfaces of the pressure chamber becomes narrower from the bubble generating portion side to the one end portion side of the ink flow path. 2. The inkjet head according to 2. 4. The air bubble generating unit has a pair of electrodes arranged at a predetermined distance.
3. The inkjet head according to any one of 3.