JP2000015810A - Ink-jet recording head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high image quality prints by setting a shape characteristic or electric characteristic of an ink-heating means so that a center position of a boiling air bubble when growing to a maximum diameter is moved to the side of a nozzle with respect to a center position of the air bubble at a moment when generated. SOLUTION: In accordance with a growth of boiling air bubbles, a boiling air bubble over a heater 20 grows towards a nozzle 4 and finally becomes a boiling air bubble 23 of a maximum diameter. A center 25 of the maximum boiling air bubble 23 at this time is moved to the nozzle 4 as shown by an arrow in comparison with a center 24 of an initial boiling air bubble 22. Since the heater is designed in shape so that the growing boiling air bubble is moved towards the nozzle 4, extra air bubbles other than the boiling air bubbles present in the ink can be efficiently eliminated when the ink is discharged. A stability of the discharged ink is improved, whereby high-quality images can be obtained without disturbances of dots formed on recording papers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an ink jet recording head for ejecting ink droplets to print or print on printing paper.

[0002]

2. Description of the Related Art In recent years, ink jet printers have been widely used as output printers for home and office computers because of their quietness during printing, high-speed printing, and easy colorization. Such ink-jet printers perform recording by making ink droplets fly and attaching them to recording paper, and are broadly classified into a continuous system and an on-demand system according to a method of generating droplets and a method of controlling a flying direction. At present, the on-demand system is the mainstream.

[0003] As one of the on-demand systems, there is a bubble jet system in which ink is heated to generate bubbles in the ink, and the ink flies by a change in volume. The principle of ink ejection by this method will be described with reference to FIG.

FIG. 5 (a) is a cross-sectional view of a main part of a heater type ink jet recording head. In the figure, 1 is a substrate, 2 is a heater, 3 is an ink flow path, 4 is a nozzle, and 5 is a boiling bubble. , 6 are flying droplets, and 7 is a recording paper. When a voltage is applied to the heater 2, the ink in the ink flow path 3 is heated, and boiling bubbles 5 are generated. The droplets 6 flying from the nozzle 4 due to the volume change due to the boiling bubbles 5 form recording paper 7.
Form dots on top.

FIG. 5B is a cross-sectional view of a main portion of a conventional ink jet recording head of the energization type.
9 is a substrate, 10 is an outer electrode, 11 is an inner electrode, 12 is an insulating film that defines the exposed area of the outer and inner electrodes 10 and 11, and 13 is a current flowing between the outer and inner electrodes 10 and 11. The lines of electric force are shown. Reference numeral 8 denotes a nozzle plate which forms the nozzles 14 with the ink flow path 15 and the pressure chamber 16 interposed therebetween, 6 denotes a flying ink droplet, 7 denotes a recording paper, and 17 denotes a recording paper.
Is a signal generator. When a voltage is applied to the outer and inner electrodes 10, 11, a current flows through the conductive ink filled in the pressure chamber 16, and the Joule heat causes the outer and inner electrodes 10, 11 to flow.
A part of the conductive ink between the tips of 11 is vaporized. Further, the vaporized conductive ink vapor expands until it generates pressure sufficient to discharge from the nozzle 14,
The droplets 6 flying from above form dots on the recording paper 7.

[0006]

In the conventional ink jet recording head using the heater heating method, the basic shape of the heater is a square so that the heater surface is uniformly heated. The growth of bubbles in the ink is circular, whereas the shape of the heater is square, so that unnecessary areas will be heated, and the boiling bubbles will grow in the form of being divided without being united, The bubbles may stay.
If the bubbles stay near the flow path, they cause dot missing or the like.

[0007] In addition, the ink jet recording head of the ink energizing and heating method has a problem that a defect such as dot missing occurs due to electrolytic bubbles generated on the electrode surface in addition to bubbles contained in the ink. . In addition, due to the area where the electrode is exposed from the insulating film, the size of the area where the ink is heated, or the amount of ink droplets ejected due to the deposits on the electrode surface or the corrosion of the electrode, the frequency characteristics may vary. Holding, or having the thermal history of previous ejections, may affect the size of the dots formed.

The problem to be solved by the present invention is to efficiently discharge bubbles existing in ink to form stable dots, and realize high-quality images by realizing ink discharge conditions without frequency characteristics and heat history. To get a print of

[0009]

SUMMARY OF THE INVENTION According to the present invention, there is provided an ink jet recording head which heats ink to generate boiling bubbles and discharges ink from nozzles by a change in volume thereof.
The condition is such that the center position of the bubble when the boiling bubble grows and grows to the maximum bubble diameter moves to the nozzle side with respect to the center position of the bubble at the moment when the boiling bubble is generated. By making the shape characteristics or electric characteristics of the ink heating means that match this condition, in the process of growing from the moment when the boiling bubble is generated and reaching the maximum bubble diameter, the center position of the bubble moves in the nozzle direction, This has the effect of pushing air bubbles, which are considered to adversely affect the boiling of dissolved oxygen, electrolytic bubbles, and the like, present in the ink in the nozzle direction.

[0010]

According to the first aspect of the present invention, there is provided an ink jet recording head which heats ink to generate boiling bubbles and discharges ink from a nozzle by a change in volume of the ink. Alternatively, the electrical characteristics are such that the center position of the bubble when the boiling bubble grows and grows to the maximum bubble diameter moves to the nozzle side with respect to the center position of the bubble at the moment when the boiling bubble is generated. . By setting the shape characteristics or electric characteristics of the ink heating means that meets this condition,
In the process of growing to the maximum bubble diameter from the moment when the boiling bubble is generated, the center position of the bubble moves toward the nozzle, which seems to adversely affect the boiling of dissolved oxygen, electrolytic bubbles, etc. existing in the ink. This has the effect of pushing the bubbles that are generated toward the nozzle.

According to a second aspect of the present invention, in the ink jet recording head, wherein the ink heating means is a heater, the surface shape of the heater has a shape whose area increases toward a nozzle for discharging ink. is there. By setting the surface shape of the heater to such a shape, the center of the boiling bubble moves toward the nozzle side as the boiling bubble generated on the ink flow path grows, and thus, exists in the ink. This has the effect of pushing air bubbles, which are considered to have an adverse effect on boiling such as dissolved oxygen and electrolytic air bubbles, in the nozzle direction.

In an ink jet recording head according to a third aspect of the present invention, in the ink jet recording head in which the ink heating means is a heater, the electric resistance value of the heater is increased toward a nozzle for discharging ink.
By making the electric resistance of the heater different in this way, the center of the boiling bubble moves toward the nozzle side as the boiling bubble generated on the ink flow path grows, thereby causing the presence of the bubble in the ink. This has the effect of pushing air bubbles, which are considered to adversely affect the boiling of dissolved oxygen, electrolytic bubbles, etc., in the nozzle direction.

According to a fourth aspect of the present invention, there is provided an ink jet recording head wherein the ink heating means is an ink energization using a pair of electrodes, wherein one of the electrodes has a shape enclosing the other electrode. ,
It is arranged so that the electrode on the side to be wrapped is on the nozzle side. By making the shape and arrangement of the electrodes in this way, boiling bubbles are generated from a place where both electrodes are closest to each other, and as the boiling bubbles grow, the center of the boiling bubbles is oriented in the direction of the other electrode on the wrapped side. Move to. This has the effect of controlling the moving direction of the bubbles, which is considered to have a bad influence on the boiling of the dissolved oxygen, electrolytic bubbles and the like.

According to a fifth aspect of the present invention, in the ink-jet recording head according to the fourth aspect, a portion of the pair of electrodes closest to each other is located at a position opposite to the nozzle with respect to the center of the wrapped electrode. It is a position. Here, the shape of both electrodes can be a shape combining circular, elliptical, parabolic, hyperbolic, and the like. By making the shape and arrangement of the electrodes in this manner, boiling bubbles are generated from a point where both electrodes are closest to each other, and as the boiling bubbles grow, the center of the boiling bubbles is oriented in the direction of the other electrode on the wrapped side. Move to. This has the effect of controlling the moving direction of the bubbles, which is considered to have a bad influence on the boiling of the dissolved oxygen, electrolytic bubbles and the like.

In the ink jet recording head according to a sixth aspect of the present invention, in the pair of electrodes according to the fourth and fifth aspects, the distance between the two electrodes facing each other is 30 μm or less. By arranging the electrodes in this manner, the region where the ink is heated between the two electrodes is limited, thereby having the effect of reducing the heat history and frequency characteristics due to the heating of the ink.

According to a seventh aspect of the present invention, in the ink jet recording head according to the fourth to sixth aspects, a ratio of an exposed area of the wrapping electrode to an exposed area of the wrapping electrode is 0.5 to 1.5. It was done. By defining the ratio of the exposed area of both electrodes in this way, the region where the ink is heated can be prevented from being biased to one electrode,
It has the effect of reducing heat history and frequency characteristics due to heating of the ink. In particular, when the radius of the inner electrode is 10 μm or more, the area ratio is desirably 1.0 or less so that the center of boiling does not deviate from the gap between the outer and inner sides.

According to an eighth aspect of the present invention, in the ink jet recording head, an area where the ink is heated to 200 ° C. or more by energization by the pair of electrodes according to the fourth aspect is provided.
0 μm ² or less. 1500μ heating area
m ² or less can be achieved by reducing the radius of the inner electrode to 10 μm or less, or reducing the fogging angle (see θ in FIG. 3C) to 120 degrees or less. By defining the region in which the ink is heated in this manner, it has an effect of reducing the heat history and frequency characteristics due to the heating of the ink.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) FIG. 1A is a cross-sectional view of a main part showing a first embodiment in which the present invention is applied to a heater heating type ink jet recording head, and FIG. FIG. 2C is a plan view of a main part showing a first embodiment applied to the ink jet recording head of FIG. 1, and FIG. 3C is a side view of a main part showing the first embodiment of the present invention applied to a heater heating type ink jet recording head. FIG. 4D is a diagram for explaining the operation of the first embodiment in which the present invention is applied to a heater heating type ink jet recording head. In the figure, 1
Denotes a substrate, 20 denotes a heater, 3 denotes an ink flow path, 4 denotes a nozzle, 5 denotes a boiling bubble, 6 denotes a droplet, and 7 denotes a recording paper.

In this embodiment, as shown in FIG. 1B, the plane shape of the heater 20 for heating the ink to generate the boiling bubbles 5 is directed from the ink flow path 3 to the nozzle 4 side. It is designed to be trapezoidal so that its area can be expanded.

With such a trapezoidal shape, when the lead 21 is connected to the heater 20, the portion having a small area has a smaller electric resistance value from the lead 21 and is heated faster than the portion having a large area. Since the heating points of the heater 20 are concentrated in the flow path direction, the center 24 of the initial boiling bubble 22 is located on the flow path side of the heater 20 as shown in FIG.

Thereafter, as the boiling bubble grows, the boiling bubble on the heater 20 grows toward the nozzle 4 and finally reaches the boiling bubble 23 at the maximum diameter. At this time, the center 25 of the maximum boiling bubble 23 has moved toward the nozzle 4 as shown by an arrow in the figure, compared to the center 24 of the initial boiling bubble 22.

As described above, the growing boiling bubbles are generated by the nozzle 4
By designing the shape of the heater 20 so as to move in the direction, extra bubbles other than boiling bubbles existing in the ink can be efficiently removed at the time of discharging the ink.
As a result, the stability of the ejected ink is improved, and a high-quality image without disturbance of dots formed on the recording paper can be obtained.

(Embodiment 2) FIG. 2A is a sectional view of a main part showing a second embodiment in which the present invention is applied to an ink jet recording head of an ink energization heating type, and FIG. Is a plan view of a main part showing a second embodiment in which is applied to an ink jet recording head of an ink energization heating system,
FIG. 4C is a diagram for explaining the operation of the second embodiment in which the present invention is applied to an ink-jet recording head of an ink energization heating system.

In the ink jet recording head according to the present embodiment, a pair of electrodes each having a shape in which the outer electrode 31 wraps around the inner electrode 30 is arranged such that the inner electrode 30 is on the nozzle 14 side. The current is concentrated most where the inner electrode 30 and the outer electrode 31 are closest, and the temperature of the ink rises quickly. The position is the initial boiling bubble 40
Is the center 41. After a few microseconds, the boiling bubble grows further by supplying current from the electrode, and the maximum boiling bubble 4
Reach 2. In this process, since the outer electrode 31 is configured to surround the inner electrode 30,
The current is concentrated from the outer electrode 31 to the inner electrode 30. For this structural reason, the center 43 of the maximum boiling bubble 42 moves toward the nozzle 14 with respect to the center 41 of the initial boiling bubble 40. Due to the movement of the boiling bubbles, extra bubbles other than the boiling bubbles existing in the ink are efficiently discharged together with the ejection of the ink, whereby the stability of the ejected ink is improved and formed on the recording paper. It is possible to obtain a high-quality image without disturbing dots.

(Embodiment 3) FIG. 3 (a) shows the relationship between the exposed area ratio of a pair of electrodes and the variation in ink boiling time, and FIG. 3 (b) shows the relationship between the electrode gap length and the variation in ink boiling time. FIG. 3C is a top view of a main part of the electrode. Each point in the figure is an inner electrode 30 and an outer electrode 31.
Are the measurement data when the shape of is varied, and φ30 and φ60 shown in the figure are the nozzle for the dot diameter of 30 μm and the nozzle for the dot diameter of 60 μm.

Here, the gap length is the length 32 of the outer peripheral portion of the inner electrode 30 wrapped by the outer electrode 31 in the top view of the main part of the electrode shown in FIG. In other words, it can be said that it is the distance of the portion where the inner electrode 30 faces. The gap length g is as follows: g = 2π × (inner electrode radius r) × (fog angle θ)
/ 360.

FIG. 3A shows that the variation in the ink boiling time tends to increase as the exposed area ratio between the outer electrode 31 and the inner electrode 30 increases. It can be seen that the minimum value is between 0.5 and 1.5. It is considered that this is because when the balance between the exposed area ratios of the two electrodes is lost, the current density becomes unbalanced.

FIG. 3B shows that the longer the gap length g, the greater the degree of variation in the ink boiling time. This is because the longer the gap length g, the larger the area where the ink is heated, and as a result, the ink that has been heated even after the ink is ejected remains in the pressure chamber 16, resulting in a difference in the ink boiling time. It is because it can be done.

FIG. 4 shows the projected area from above the area where the ink is heated to 150 ° C. and the projected area from above the area where the ink is heated to 200 ° C. FIG. 6 is a diagram showing a relationship between the variation of the ink boiling time and the variation of the ink boiling time. From FIG.
By setting the area where the ink is heated to 1500 μm ² or less as described above, the amount of the heated ink remaining in the pressure chamber 16 even when the ink is ejected is reduced, and the variation in the boiling time due to the heat history and frequency characteristics is reduced by 20 μs. It can be seen that it can be suppressed below.

As described above, in the case where one electrode takes a shape enclosing the other electrode, the exposed area ratio between the outer electrode and the inner electrode is set to 0.5 to 1.5, and the gap length is set to 3
By setting it to 0 μm or less, the area of the heating area of the ink can be limited. In particular, by setting the area where the heating temperature of the ink is 200 ° C. or more to 1500 μm ² or less, variation in boiling time due to heat history and frequency characteristics is small. That is, it can be seen that an ink jet head with little dot system variation can be realized, and high quality image quality can be obtained.

[0031]

(1) The shape characteristics or electric characteristics of the ink heating means are set such that the boiling bubble grows to the maximum bubble diameter with respect to the center position of the bubble at the moment when the boiling bubble is generated. By setting the condition that the center position moves to the nozzle side, extra bubbles other than boiling bubbles existing in the ink can be efficiently removed at the time of discharging the ink.
As a result, the stability of the ejected ink is improved, and a high-quality image with no disturbance of dots formed on the recording paper can be obtained.

(2) When the ink heating means is a heater, the surface shape of the heater may be such that the area increases toward the nozzle for discharging the ink, or the electric resistance value of the heater may be set to By increasing the size toward the nozzle to be ejected, the center of the boiling bubble moves toward the nozzle as the boiling bubble generated on the ink flow path grows. Excess air bubbles other than the existing boiling air bubbles are efficiently discharged together with the discharge of the ink, and the stability of the discharged ink is improved.

(3) In the case where the ink heating means is energization of ink using a pair of electrodes, one electrode has a shape enclosing the other electrode, and the enclosing electrode is on the nozzle side. By arranging such an arrangement, or by setting the point where the two electrodes are closest to each other to a position opposite to the nozzle from the center of the wrapped side electrode, boiling bubbles generated on the ink flow path side As the bubble grows, the center of the boiling bubble moves toward the nozzle side, and due to the movement of the boiling bubble, extra bubbles other than the boiling bubble present in the ink are efficiently discharged together with the ejection of the ink, The stability of the ejected ink is improved.

(4) In the case where the ink heating means uses a pair of electrodes to conduct ink, the distance between the two electrodes facing each other, the ratio of the exposed area of the wrapping electrode to the exposed area of the wrapping electrode, and By defining a region where the ink is heated to 200 ° C. or more by energization in a specific range, the heat history and frequency characteristics due to the heating of the ink are reduced, and a high-quality image can be obtained.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view of a main part showing a first embodiment in which the present invention is applied to a heater heating type inkjet recording head. FIG. 1B is a second embodiment in which the present invention is applied to a heater heating type inkjet recording head. (C) Side view of main part showing the first embodiment in which the present invention is applied to a heater heating type ink jet recording head. (D) The present invention is applied to a heater heating type. For explaining the operation of the first embodiment applied to the ink jet recording head of FIG.

FIG. 2 (a) is a sectional view of a main part showing a second embodiment in which the present invention is applied to an ink jet recording head of an ink energizing and heating type; and (b) the present invention is applied to an ink jet recording head of an ink energizing and heating type. (C) A view for explaining the operation of the second embodiment in which the present invention is applied to an ink jet recording head of an ink energization heating type.

3A is a diagram showing a relationship between an exposed area ratio of a pair of electrodes and variation in ink boiling time. FIG. 3B is a diagram showing a relationship between electrode gap length and variation in ink boiling time. Top view of part

FIG. 4 is a diagram showing a relationship between a heating area and a variation in ink boiling time.

FIG. 5A is a cross-sectional view of a main part of a heater type ink jet recording head. FIG. 5B is a cross-sectional view of a main part of a conventional energizing type ink jet recording head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Heater 3 Ink flow path 4 Nozzle 5 Boiling bubble 6 Droplet 7 Recording paper 8 Nozzle plate 9 Substrate 10 Outer electrode 11 Inner electrode 12 Insulation film 13 Line of electric force 14 Nozzle 15 Ink flow path 16 Pressure chamber 17 Signal generator Reference Signs List 20 heater 21 lead 22 initial boiling bubble 23 boiling bubble at maximum diameter 24 center of initial boiling bubble 25 center of maximum boiling bubble 30 inner electrode 31 outer electrode 32 gap length 40 initial boiling bubble 41 center of initial boiling bubble 42 maximum diameter Boiling bubble at the time of 43 43 Center of maximum boiling bubble θ Fogging angle r Inner electrode radius

Claims (8)

[Claims] 1. An ink is heated to generate boiling bubbles,
In an ink jet recording head that discharges ink from a nozzle by its volume change, the shape characteristics or electric characteristics of the ink heating means are set such that the boiling bubble grows to the maximum bubble diameter with respect to the center position of the bubble at the moment when the boiling bubble is generated. An ink jet recording head, characterized in that the condition is such that the center position of the bubble when it has grown into the nozzle moves to the nozzle side. 2. The apparatus according to claim 1, wherein said ink heating means is a heater, and the surface of the heater has a shape having an area increasing toward a nozzle for discharging ink.
The inkjet recording head according to the above. 3. An ink jet recording head according to claim 1, wherein said ink heating means is a heater, and an electric resistance value of said heater is increased toward a nozzle for discharging ink. 4. The method according to claim 1, wherein the ink heating means is an ink supply using a pair of electrodes, and one of the electrodes has a shape surrounding the other electrode. 2. The arrangement according to claim 1, wherein
The inkjet recording head according to the above. 5. The ink jet recording head according to claim 4, wherein a position where said pair of electrodes is closest to each other is a position opposite to a nozzle with respect to a center of the wrapped electrode. 6. The ink jet recording head according to claim 4, wherein the distance between the portions where the pair of electrodes face each other is 30 μm or less. 7. The method according to claim 4, wherein the ratio of the exposed area of the wrapping electrode to the wrapping electrode of the pair of electrodes is 0.5 to 1.5. The inkjet recording head according to the above. 8. An ink jet recording head according to claim 1, wherein a region where the ink is heated to 200 ° C. or more by energization by said pair of electrodes is set to 1500 μm ² or less.