JP2001121701A - Ink jet head and method for heat generation of heating resistor used therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet head wherein a volume of an ink drop to be ejected can be controlled by a roof-shooter method. SOLUTION: A plurality of heating resistors 1 are coaxially provided in an ink chamber 2 so that it is possible to provide the plurality of heating resistors 1 without varying an area of the bottom of the ink chamber 2. Since a center of an ejection nozzle 6 is provided opposite to the center of the heating resistors provided coaxially, it is possible to raise the accuracy of ejection of the ink drop 7 in the ejecting direction. The heating resistors 1 are heated by delaying the timing from each other so that it is possible to vary a volume of the ink drop 7 in a wide range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type ink jet head for recording an image by ejecting ink droplets from nozzles by pressure when bubbles generated in ink heated via a heating resistor expand. About.

[0002]

2. Description of the Related Art As a structure of a thermal type ink jet head for ejecting ink droplets from nozzles by the pressure of bubbles generated in ink heated via a heating resistor as a heating means, as shown in FIG. There is a roof shooter system in which the heat generating surface of the heat generating resistor 61 is arranged in a direction orthogonal to the direction in which the ink droplet 67 is ejected. The roof shooter type ink jet head includes a substrate 65 having a rectangular flat heating resistor 61 and an electrode 68 for energizing the heating resistor 61 together with a driving circuit (not shown) and the like.
A partition member 64 for forming an ink chamber 62 on the upper surface of the
A nozzle plate 63 formed with a discharge nozzle 66 communicating with the ink chamber 62 and discharging ink to the outside. The substrate 65, the partition member 64, and the nozzle plate 63 are stacked in this order, and are adhered to each other on the contact surface with an adhesive or the like.

[0003] An ink jet head used in an ink jet printer has a configuration shown in FIG.
The opening holes of the plurality of discharge nozzles 66 are arranged linearly at predetermined intervals, or are arranged in a predetermined arrangement pattern repeatedly. Further, each ink chamber 62 is provided with each ink supply path 6.
Through 9, it is connected to an ink container (usually one) which is an ink storage unit (not shown).

The discharge nozzle 66 is provided at a position facing the heating resistor 61 in the nozzle plate 63, and is provided in the ink chamber 62 and the discharge nozzle 66 from an ink container (not shown) via an ink supply path 69. Ink is supplied. When current flows from the electrode 68 to the heating resistor 61 in accordance with an image signal, the heating resistor 61 generates heat. As a result, the ink in contact with the heating resistor 61 is heated in the ink chamber 62 to generate air bubbles, and the ink in the ejection nozzle 66 moves outward due to the pressure when the air bubbles expand, forming ink droplets 67. Is discharged. This ink drop 6
Numeral 7 flies to a position facing the discharge nozzle 66 on a recording medium such as a sheet positioned outside the nozzle plate 63, and forms an image as a recording pattern.

As a structure of a conventional ink jet head, there is an edge shooter system in which a heating surface of a heating resistor 71 is arranged in parallel with a discharge direction of an ink droplet 77 as shown in FIG. The edge shooter type ink jet head includes a substrate 75 provided with a rectangular flat heating resistor 71 and an electrode 78 for energizing the heating resistor 71 together with a driving circuit (not shown) and an ink on the upper surface of the substrate 75. It is composed of a partition wall member 74 and a top plate 74 ′ for forming the chamber 72, and a nozzle plate 73 in which a discharge nozzle 76 communicating with the ink chamber 72 is formed. The nozzle plate 73 is provided on the substrate 7 stacked vertically.
5, among the end faces of the partition wall 74 and the top plate 74 ', the ink chamber 7
2 is arranged on one open end face in a direction orthogonal to the laminating direction of the substrate 75, the partition wall 74 and the top plate 74 ', and the discharge nozzle 76 penetrates the nozzle plate 73 in parallel with the heat generating surface of the heat generating resistor 71. I do.

[0006] An ink jet head used in an ink jet printer has a configuration shown in FIG.
The opening holes of the plurality of discharge nozzles 76 are linearly arranged at predetermined intervals, or are repeatedly arranged in a predetermined arrangement pattern. Further, each ink chamber 72 is provided with each ink supply path 7.
Through 9, it communicates with an ink container (usually one) not shown.

In the ink chamber 72 and the discharge nozzle 76,
Ink is supplied from an ink container (not shown) via an ink supply path 79. When current flows from the electrode 78 to the heating resistor 71 in accordance with an image signal, the heating resistor 71 generates heat. As a result, the ink in contact with the heating resistor 71 is heated in the ink chamber 72 to generate air bubbles, and the ink in the ejection nozzles 76 moves outward by the pressure when the air bubbles expand, forming ink droplets 77. Is discharged. The ink droplet 77 flies to a position facing the discharge nozzle 76 on a recording medium such as a sheet of paper located outside the nozzle plate 73, and forms an image as a recording pattern.

In an ink jet printer using an ink jet head configured as described above, an image is formed by a set of dots formed when ink droplets discharged from a discharge nozzle adhere to the surface of a recording medium. Therefore, in order to form an image with less graininess, it is necessary to reduce the diameter of each dot and increase the spatial frequency (density of the dots). For this purpose, the volume of the ink droplets ejected from the ejection nozzles is required. Must be reduced. That is, in order to form a high-quality image, it is desirable to minimize the volume of the ink droplet.

In this respect, the roof shooter method has a smaller ink chamber volume than the edge shooter method, and the amount of ink bubbles generated in the ink by heating from the heating resistor must be moved by pressure. Therefore, when ejecting ink droplets of the same volume, the roof shooter method can reduce the pressure of bubbles compared to the edge shooter method. In the roof shooter method, since the heating resistor is located immediately below the discharge nozzle, the expansion direction of the bubble matches the discharge direction of the ink droplet, and the discharge efficiency of the ink droplet is essentially high. From these, the roof shooter system is
It can be said that the method is more suitable than the edge shooter method in discharging minute ink droplets.

On the other hand, if the volume of the ink droplets ejected from the ejection nozzles is reduced and the diameter of the dots formed on the recording medium is reduced, the graininess is reduced, but it takes time to form a solid image or a character pattern. . For this reason, an ink jet head has been proposed that can control the ejection amount to form ink droplets of different sizes in order to realize an image quality with less graininess and to shorten the formation time of a solid image or a character pattern. The volume of the ink droplet ejected from the ejection nozzle can be controlled by changing the opening diameter of the ejection nozzle. However, the method of mechanically changing the opening diameter requires a complicated mechanism, and has problems in terms of manufacturing cost and reliability.

Therefore, a method has been proposed in which the flow of ink is controlled by the size of bubbles generated by heating the heating resistor and the pressure when the bubbles expand. For example, Japanese Patent Application Laid-Open No. 1-156075 discloses a technique relating to a thermal ink jet print head that changes the volume of ink droplets ejected by a roof shooter method. In this print head, an ink injection chamber and a drop ejection chamber are formed in series between an ink supply source and an ink ejection orifice formed immediately above the drop ejection chamber. The ink injection chamber has at least one ink injection heater resistor, and the drop ejection chamber has at least one drop ejection heater resistor.

[0012] The ink injection heater resistor has a function of moving the ink in the ink injection chamber to the drop ejection chamber. Further, the drop ejection heater resistor has a function of ejecting ink in the drop ejection chamber.

The ejection of ink droplets having different volumes is performed by adjusting the phase of a heating pulse applied to the resistance of the ink injection heater and the resistance of the drop ejection heater. That is, by heating the ink injection heater resistance prior to the drop ejection heater resistance, the flow of the ink moving toward the ejection nozzle is formed in the ink chamber in advance. And
Thereafter, a larger ink droplet is ejected by heating the resistance of the drop ejection heater. By adjusting the phase of the heating pulse applied to the resistance of the ink injection heater and the resistance of the drop ejection heater, the direction and size of the ink flowing in the ink chamber can be controlled, so that the ejection amount can be arbitrarily controlled.

Japanese Patent Application Laid-Open No. 9-207337 proposes a technique relating to a recording head and an image forming apparatus for changing the size of ink droplets ejected by an edge shooter method. In this recording head, low-power heaters and high-power heaters are alternately arranged in a flow path between an ink supply source and an orifice. By heating each of the low-power heater and the high-power heater independently or simultaneously, it is possible to eject ink droplets having different volumes.

[0015]

However, in a conventional ink jet head in which the discharge amount is controlled by providing a plurality of heaters, a plurality of heaters are arranged in parallel. For this reason, the area of the ink jet head becomes large, and it is impossible to form the nozzles with high density. Further, since the bottom area of the ink chamber becomes large, there is a problem that the time required for ink supply becomes long. In particular, in the roof shooter method, in the case of an inkjet head that prints at 300 dpi, the nozzle pitch is 84.7 μm, and in consideration of the crosstalk between adjacent nozzles due to heat, the width of the ink chamber in the nozzle row direction is about 60 μm. . If a plurality of drop ejection heater resistors are provided in parallel in an ink chamber of this width, the area of each heater becomes very small, and it is not possible to generate bubbles sufficient to eject ink droplets.

Further, when a plurality of conventional substantially rectangular heaters are provided in parallel, bubbles generated by heating by the heaters are eccentric from the center of the opening of the discharge nozzle. The ink that moves toward the ejection nozzle due to the pressure when the bubble expands receives a pressure eccentric from the center of the ejection nozzle opening. For this reason, there has been a problem that the ejection accuracy is deteriorated, the ejection direction varies, and the number of satellites increases.

In the thermal ink jet print head of the roof shooter type disclosed in Japanese Patent Application Laid-Open No. 1-156075, the functions of ink injection and drop injection are shared, the drop injection heater resistance is reduced to one, and the ink injection heater resistance is reduced. Is provided separately. Then, the timing and the amount of heating of these two heaters are controlled to make the drop diameter variable. Therefore, in order to accurately control the drop diameter, it is necessary to precisely control the heating timing and the heating amount, and the control program becomes complicated. In addition, in order to variably control the drop diameter, the drop ejection heater resistance needs a certain area, and if the nozzles are provided at a high density as described above, it is difficult to secure the area of the drop ejection heater resistance. is there.

The recording head and the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 9-207337 are edge shooter type ink jet heads, and small power heaters and high power heaters are alternately arranged. Therefore, since the amount of ink existing from the heater to the discharge nozzle is larger than that of the roof shooter system, a heater having a larger area than the roof shooter system is essentially required. Further, since two types of heaters having a large area are used, power consumption is increased, and the temperature of the heater substrate is also increased. Therefore, there is a problem that ink droplets cannot be stably ejected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide an ink jet head capable of controlling the volume of ink droplets ejected by a roof shooter method.

[0020]

The present invention has the following arrangement as means for solving the above-mentioned problems.

(1) At least one set of an ink discharge nozzle, an ink chamber communicating with the ink discharge nozzle and provided with a heating means, and an ink supply path for supplying ink to the ink chamber is provided. A heating unit for heating the ink to generate bubbles, and the ink contact surface of the heating resistor is formed by the pressure when the bubbles expand. In an ink jet head for ejecting ink from the ink ejection nozzle in a direction perpendicular to the ink jet head, the heating means is a plurality of heating resistors arranged concentrically.

In this configuration, ink is supplied from the ink storage unit to the ink chamber via the ink supply path, and the ink is supplied by a plurality of concentric heating resistors which are heating means provided in the ink chamber. Is heated to generate bubbles, and ink is ejected from the ink ejection nozzles by the pressure when the bubbles expand. Therefore, since the plurality of heating elements are arranged concentrically, the ink ejection nozzles can be formed at a high density without increasing the bottom area of the ink chamber, so that a high quality image can be formed. . In addition, a solid image can be formed in a short time by causing a plurality of heating resistors to generate heat and ejecting large-volume ink droplets.

(2) The center of the plurality of heating resistors arranged concentrically is substantially the same as the center of the opening of the ink discharge nozzle.

In this configuration, the centers of the plurality of concentric heating resistors provided in the ink chamber are substantially the same as the centers of the openings of the ink discharge nozzles communicating with the ink chamber. Therefore, the bubbles generated by being heated by any one of the plurality of heating resistors arranged concentrically do not become eccentric from the center of the hole of the ink discharge nozzle, so that the ink discharge direction is fixed in a certain direction. Can be stabilized.

(3) The plurality of heating resistors arranged concentrically are provided with electrodes capable of selectively conducting current.

In this configuration, selectively energizable electrodes are provided on a plurality of heating resistors arranged concentrically. Therefore, since the number of heating resistors to be energized can be selected, the amount of ink ejected from the ink ejection nozzle can be changed according to the number of heating resistors to be energized.

(4) The plurality of heating resistors have different surface areas.

In this configuration, the plurality of heat generating resistors arranged concentrically in the ink chamber have different surface areas. Therefore, when the surface area of the heating resistor is different, the size of bubbles generated by heating the heating resistor is different. Therefore, by selecting the heating resistor to be heated, it is possible to change the amount of ink ejected from the ink ejection nozzle. it can.

(5) The ink chamber is lower than the height at which the bubble is most expanded, and at least one of the plurality of concentrically arranged heating resistors is provided with at least one of the ink discharge nozzles of the ink chamber. It is characterized by being disposed at a position facing the periphery of the ink discharge nozzle on the communicating surface.

In this configuration, the height of the ink chamber in which the plurality of heating resistors, which are heating means, is disposed, is lower than the height when bubbles generated by heating by the heating resistors are expanded most, and is concentric. Since at least one of the plurality of heating resistors disposed in the nozzle is disposed at a position facing the periphery of the ink discharge nozzle, when the bubbles are heated by the heating resistor,
The ink expands so as to close an ink supply path for supplying ink to the ink chamber, and contacts the upper surface of the ink chamber. Therefore, the ink is ejected from the ink ejection nozzle without flowing back to the ink storage section via the ink supply path, so that the ink ejection amount can be reliably controlled.

(6) Ink is supplied from the ink storage unit to the ink chamber via the ink supply path, and at least one of a plurality of heating resistors arranged concentrically in the ink chamber is heated to generate bubbles. A method of heating a heating resistor of an ink jet head for causing ink to be ejected from an ink ejection nozzle by a pressure generated when bubbles are expanded, wherein the plurality of heating resistors are selectively heated. .

In this configuration, a plurality of heating resistors arranged concentrically in the ink chamber are selectively heated to generate bubbles, and the pressure at the time of expansion of the bubbles causes ink to be ejected from the ink discharge nozzle. Is discharged. Therefore, since the plurality of heating resistors are arranged concentrically, the amount of ink ejected from the ink ejection nozzle can be changed without increasing the bottom area of the ink chamber.

(7) Ink is supplied from the ink storage unit to the ink chamber via the ink supply path, and at least one of the plurality of heating resistors arranged concentrically in the ink chamber is heated to generate bubbles. A method of heating a heating resistor of an ink jet head that causes ink to be ejected from an ink ejection nozzle by pressure when bubbles are expanded, wherein one of the heating resistors is heated. Before the generated air bubbles disappear, another heating resistor is heated to generate air bubbles.

In this configuration, one of a plurality of heating resistors concentrically arranged in the ink chamber is heated to generate bubbles, and another heating resistor is generated before the bubbles disappear. Is heated to generate air bubbles. Therefore, the air bubbles act like a wall, so that ink flowing back to the ink storage unit via the ink supply path can be suppressed, and a larger volume ink droplet can be ejected.

[0035]

FIG. 1 is a perspective view showing the structure of an ink jet head according to a first embodiment of the present invention in the vicinity of a discharge nozzle, and FIG. 2 is an enlarged view of a heating resistor.

The ink jet head according to the embodiment of the present invention employs a roof shooter system in which the heat generating surface of the heat generating resistor 1 as a heating means is arranged in a direction orthogonal to the direction in which the ink droplets 7 are ejected. The roof shooter type ink jet head includes heating resistors 1a and 1a concentrically arranged.
b, a substrate 5 provided with an electrode 8 for energizing the heating resistor 1 together with a driving circuit (not shown), a partition member 4 for forming the ink chamber 2 on the upper surface of the substrate 5, and a And a nozzle plate 3 on which ejection nozzles 6, which are ink ejection nozzles communicating with each other, are formed. The substrate 5, the partition member 4, and the nozzle plate 3 are laminated in this order, and are adhered to each other at the contact surface. Further, the partition wall member 4 and the nozzle plate 3 may be integrally formed by molding with resin or the like.

An ink-jet head used in an ink-jet printer is a set of the structure shown in FIG.
The opening holes of the plurality of discharge nozzles 6 are linearly arranged at predetermined intervals, or are repeatedly arranged in a predetermined arrangement pattern. In addition, each ink chamber 2 is connected via an ink supply path 9 to an ink container (not shown) serving as an ink storage unit.
).

The discharge nozzle 6 is provided at a position facing the heating resistor 1 in the nozzle plate 3, and is provided in the ink chamber 2 and the discharge nozzle 6 from an ink container (not shown) via an ink supply path 9. Ink is supplied. When current flows from the electrode 8 to the heating resistor 1 according to an image signal, the heating resistor 1 generates heat. As a result, the ink in contact with the heating resistor 1 is heated in the ink chamber 2 to generate bubbles, and the pressure when the bubbles expand expands the discharge nozzle 6.
The ink inside moves to the outside and is ejected as ink droplets 7. The ink droplet 7 flies to a position facing the discharge nozzle 6 on a recording medium such as a sheet of paper located outside the nozzle plate 3 and forms an image as a recording pattern.

A feature of the present invention is that a plurality of heating resistors formed in a rectangular plate shape are conventionally arranged concentrically as described above. By disposing the heating resistors in this way, a plurality of heating resistors can be provided without increasing the bottom area of the ink chamber.

Another feature is that the center of the hole of the discharge nozzle 6 provided through the nozzle plate 3 is substantially the same as the center of the plurality of heating resistors 1a and 1b arranged concentrically. It is the point provided in. With such a positional relationship, bubbles generated by being heated by each of the plurality of heating resistors become bubbles that are not eccentric with respect to the opening of the discharge nozzle 6, so that the accuracy of the ink droplet discharge direction can be improved. Can be higher.

FIG. 3 is a view schematically showing the appearance of bubbles in the cross section A of the ink jet head shown in FIG. 1. FIG. 3 (A) shows a case where the inner heating resistor 1a is heated. FIG. 3B shows a case where the outer heating resistor 1b is heated, and FIG. 3C shows a case where the inner heating resistor 1a and the outer heating resistor 1b are simultaneously heated.

As an example, the inner heat generating resistor 1a has an inner diameter of 16 μm and an outer diameter of 30 μm, and the outer heat generating resistor 1b has an inner diameter of 40 μm and an outer diameter of 55 μm. Also, the heat generating resistor 1b on the outer peripheral side has a larger surface area and a larger volume of generated bubbles. The volume of the ink droplet 7 ejected from the ejection nozzle 6 due to bubbles generated by heating the ink by energizing the heating resistor increases as the bubbles increase. Therefore, when it is desired to discharge the ink droplet 7 having a larger volume than the ink droplet ejected by heating the ink by energizing the heating resistor 1a on the inner peripheral side, energizing the heating resistor 1b on the outer peripheral side is preferable. Heat it up. When it is desired to discharge ink droplets larger than the ink droplets which are heated and discharged by energizing the heating resistor 1b on the outer peripheral side, the heating resistors 1a and 1b on the inner peripheral side and the outer peripheral side are simultaneously energized. It is also possible to heat the ink.

That is, as shown in FIG. 3A, when the heating resistor 1a on the inner peripheral side is energized, the ink in contact with the heating resistor 1a is heated, the liquid ink becomes gas, and bubbles 10a are generated. .

As shown in FIG. 3B, when the heating resistor 1b on the outer peripheral side is energized, the ink in contact with the heating resistor 1a is heated to generate bubbles 10b. Since the surface area of the heating resistor 1b on the outer peripheral side is larger than the surface area of the heating resistor 1a on the inner peripheral side, when the height of the bubble 10a and the generated bubble 10b are the same, the volume of the bubble 10b is smaller than the volume of the bubble 10a. growing.

Further, as shown in FIG. 3 (C), when the inner heating resistor 1a and the outer heating resistor 1b are energized simultaneously, the ink contacting the heating resistor 1a and the heating resistor 1b is formed. Are heated and two bubbles are generated during expansion.
And become bubbles 10c. Bubble 10b and bubble 10c
Are the same, the volume of the bubble 10c is
Larger than the volume of

As described above, the size of the bubble generated can be changed by appropriately selecting the heating resistor to be heated, and the volume of the ink droplet ejected from the ejection nozzle 6 becomes
3A, 3B, and 3C.

In the present embodiment, two heat generating resistors are used as an example. However, the present invention is not limited to this. It is also possible to use three or more concentric heat generating resistors. Thus, it is possible to discharge a larger volume of different ink droplets.

FIG. 4 is a sectional view of an ink jet head according to a second embodiment of the present invention. In this embodiment,
An ink-jet head capable of further increasing the change range of the volume of the ejected ink droplet and a method of heating the heating resistor will be described. Since the configuration of the inkjet head shown in FIG. 4 is substantially the same as the configuration of the inkjet head shown in FIG. 1, the description of the same parts will be omitted.
In the present embodiment, similarly to the first embodiment, the centers of the plurality of heating resistors arranged concentrically are aligned with the centers of the openings of the discharge nozzles 6 provided through the nozzle plate 3. They are almost the same. Therefore, a plurality of heating resistors can be provided without increasing the bottom area of the ink chamber. In addition, since the bubbles generated by the respective heating resistors are not eccentric with respect to the center of the opening of the discharge nozzle 6, the discharge direction accuracy of the ink droplet can be improved.

A feature of the ink jet head shown in FIG. 4 is that the height h at a position communicating with the ink supply passage 9 of the ink chamber 2 is generated by heating the ink by supplying electricity to the heat generating resistor 1b on the outer peripheral side. The heating resistor 1b is located at a position where the ink supply path 9 can be closed by bubbles 10 generated by heating the heating resistor 1b on the outer peripheral side, which is smaller than the height of the bubble when it is most expanded. Is to be. That is, the heating resistor 1 b is disposed on the substrate 5 so as to face the surface around the discharge nozzle 6 formed on the nozzle plate 3. Therefore, the term B of the bubble 10 d is located to face a part of the periphery of the opening C of the nozzle plate 3,
When the bubble 10d expands to the maximum, the height of the bubble 10d becomes higher than the height of the ink chamber 2, so that the vertex B of the bubble 10d comes into contact with the nozzle plate 3.

As described above, the bubble 10 d is formed in the ink supply path 9.
And the ink chamber 2, the size of the bubbles can be changed by delaying the heating timing of the heating resistor 1 a on the inner peripheral side and the heating resistor 1 b on the outer peripheral side. The volume of the ink droplet can be controlled in a wider range. Details will be described later.

Since the average volume of bubbles for forming ink droplets is about 30 pl (picoliter), the height h at a position communicating with the ink supply path is 30 μm.
It is sufficient if it is less than about. In FIG. 4, the magnitude relationship between the area of the heating resistor 1a and the area of the heating resistor 1b is not particularly limited.

When the ink is heated by energizing the heat generating resistor 1a on the inner peripheral side, ink droplets can be ejected in the same manner as in FIG. When the heating resistor 1b on the outer peripheral side is heated, the bubbles 10d expand so as to close the ink supply path 9, so that the ink in the ink chamber 2 flows back to the ink storage unit (not shown) through the ink supply path 9. And is effectively used for ejection. As a result, a larger volume ink droplet can be ejected.

In order to eject ink droplets having a larger volume, there is a method of simultaneously heating the inner heating resistor 1a and the outer heating resistor 1b. However, the heating resistor 1b on the inner circumference side is delayed with respect to the heating resistor 1b on the outer circumference side.
If the heating element a is heated, the bubble generated by the heating resistor 1b on the outer peripheral side before the ink droplet is ejected due to the pressure of the bubble generated by heating the heating resistor 1a on the inner peripheral side as described above is generated as described above. It functions as a wall that blocks the ink supply path 9 and the ink chamber 2. Therefore, it is possible to reliably prevent the ink flowing backward to the ink storage unit via the ink supply path 9,
It is possible to eject ink droplets having a larger volume. At the same time, the ink droplets are ejected into the ink chamber 2 via an ink supply path 9 from an ink storage unit (not shown).
The ink can be quickly replenished.

Further, of the plurality of heating resistors, the heating resistor 1a on the inner periphery may be heated with a delay before bubbles generated by heating the heating resistor 1b on the outer periphery disappear. The bubbles generated by heating the heating resistor 1b act as walls. Then, after blocking the ink supply path 9 and the ink chamber 2, the heating resistor 1 a is energized to heat the ink, and the ink is ejected from the ejection nozzle 6 by the pressure when the bubble generated expands. Therefore, the heating resistors 1a and 1
b, the ink flowing back to the ink storage unit through the ink supply path 9 can be suppressed, and a larger volume ink droplet can be suppressed as compared with a case where the ink is heated simultaneously to generate ink bubbles. It can be ejected.

FIG. 5 is a sectional view showing another shape of the ink jet head shown in FIG. In FIG. 4, the height of the ink chamber 2 is constant irrespective of the location. However, as shown in FIG. 5, only the height of the portion facing the nodal point portion of the bubble generated by the heat generating resistor 1b on the outer periphery side May be set to h, the height of the other part of the ink chamber 2 may be set to h or more, and a structure may be provided in which an aperture is provided. With this structure, the volume of the ink chamber 2 can be increased, so that a larger volume ink droplet can be ejected.

As described above, in the present invention, by changing the surface area of the heating resistor, not only the size of the generated bubble can be changed, but also the bubble acts as a wall that blocks the ink supply path and the ink chamber. I do. Therefore, by delaying the heating timing of the heating resistor 1a on the inner circumference side and the heating resistor 1b on the outer circumference side, the size of the bubble can be changed, so that the ink droplet size can be controlled in a wider range. Can be.

[0057]

According to the present invention, the following effects can be obtained.

(1) Ink is supplied from the ink storage section to the ink chamber via an ink supply path, and the ink is heated by a plurality of concentric heating elements which are heating means provided in the ink chamber. Since bubbles are generated and ink is ejected from the ink ejection nozzle by the pressure when the bubbles expand, the plurality of heating elements are arranged concentrically, so that the bottom area of the ink chamber is increased. In addition, since the ink discharge nozzles can be formed at a high density, a high quality image can be formed. In addition, a solid image can be formed in a short time by causing a plurality of heating resistors to generate heat and ejecting large-volume ink droplets.

(2) Since the centers of the plurality of concentric heating resistors provided in the ink chamber are substantially the same as the centers of the openings of the ink discharge nozzles communicating with the ink chamber, they are arranged concentrically. Bubbles generated by being heated by any one of the plurality of heating resistors do not become eccentric from the center of the hole of the ink discharge nozzle, and can stabilize the ink discharge direction in a certain direction.

(3) Since the number of heating resistors to be energized can be selected by providing a plurality of heating resistors arranged concentrically with electrodes that can be selectively energized, the heating resistor to be energized can be selected. The amount of ink ejected from the ink ejection nozzles can be changed according to the number of bodies.

(4) Since the plurality of heating resistors arranged concentrically in the ink chamber have different surface areas, if the surface areas of the heating resistors are different, the size of bubbles generated by heating by the heating resistors is different. Therefore, by selecting the heating resistor to be heated, the amount of ink ejected from the ink ejection nozzle can be changed.

(5) The height of the ink chamber in which a plurality of heating resistors, which are heating means, is disposed, is lower than the height at which bubbles generated by heating the heating resistors are most expanded, and are arranged concentrically. Since at least one of the plurality of heating resistors provided is disposed at a position facing the periphery of the ink discharge nozzle, when the bubbles are heated by the heating resistor, the ink supply that supplies ink to the ink chamber is provided. The ink expands so as to close the path and contacts the upper surface of the ink chamber, so that the ink is discharged from the ink discharge nozzle without flowing back to the ink storage section via the ink supply path, so that the ink discharge amount can be reliably reduced. Can control.

(6) A plurality of heating resistors arranged concentrically in the ink chamber are selectively heated to generate bubbles, and ink is discharged from the ink discharge nozzle by the pressure when the bubbles expand. By doing so, the plurality of heating resistors are arranged concentrically, so that the amount of ink ejected from the ink ejection nozzle can be changed without increasing the bottom area of the ink chamber.

(7) One of a plurality of heating resistors arranged concentrically in the ink chamber is heated to generate bubbles,
Before the bubble disappears, another heating resistor is heated to generate a bubble, so that the bubble acts like a wall and suppresses ink flowing back to the ink storage unit through the ink supply path. Therefore, a larger volume ink droplet can be ejected.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a first embodiment of an ink jet head of the present invention.

FIG. 2 is a view showing the shape of a heating resistor.

FIG. 3 is a diagram schematically showing a state of generation of bubbles.

FIG. 4 is a sectional view showing a second embodiment of the ink jet head of the present invention.

FIG. 5 is a sectional view showing another example of the second embodiment of the ink jet head of the present invention.

FIG. 6 is a perspective view showing a structure of a roof shooter system in a conventional inkjet head.

FIG. 7 is a perspective view showing a structure of an edge shooter system in a conventional inkjet head.

[Explanation of symbols]

 1-Heating resistor (heater) 2-Ink chamber 6-Discharge nozzle 7-Ink droplet

Claims (7)

[Claims] An ink discharge nozzle, an ink chamber communicating with the ink discharge nozzle and provided with a heating means, and an ink supply path for supplying ink to the ink chamber are provided as one.
A plurality of pairs of ink supply passages, each of which has one ink storage unit communicating with each of the ink supply paths, wherein the heating means heats the ink to generate bubbles, and the pressure of the bubbles when the ink expands causes the ink of the heating resistor to be heated. An ink jet head for discharging ink from the ink discharge nozzle in a direction perpendicular to a contact surface, wherein the heating means is a plurality of heating resistors arranged concentrically. 2. The ink jet head according to claim 1, wherein a center of the plurality of heating resistors arranged concentrically is substantially the same as a center of an opening of the ink discharge nozzle. . 3. The ink-jet head according to claim 1, wherein the plurality of heating resistors arranged concentrically are provided with electrodes capable of selectively conducting electricity. 4. The ink jet head according to claim 1, wherein the plurality of heating resistors arranged concentrically have different surface areas. 5. The ink chamber is lower than a height at which the bubble is expanded most, and at least one of the plurality of concentrically arranged heating resistors communicates with the ink discharge nozzle of the ink chamber. The inkjet head according to any one of claims 1 to 4, wherein the inkjet head is arranged at a position facing the periphery of the ink discharge nozzle on the surface of the ink jet nozzle. 6. An ink supply section supplies ink to an ink chamber via an ink supply path, and heats at least one of a plurality of heating resistors arranged concentrically in the ink chamber to generate bubbles. A method of heating a heating resistor of an ink jet head for ejecting ink from an ink ejection nozzle by a pressure when an air bubble expands, wherein the plurality of heating resistors are selectively heated. Heating method of the heating resistor used for the head. 7. An ink supply section supplies ink to an ink chamber via an ink supply path, and heats at least one of a plurality of heating resistors arranged concentrically in the ink chamber to generate bubbles. A method for heating a heating resistor of an ink jet head for ejecting ink from an ink ejection nozzle by a pressure when an air bubble expands, comprising: heating one heating resistor of the plurality of heating resistors. A heating method for a heating resistor used in an ink-jet head, wherein another heating resistor is heated to generate bubbles before the generated bubbles disappear.