JP2001310466A - Ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet head capable of allowing an ink drop to accurately arrive at a predetermined position on a recording paper. SOLUTION: There is disclosed the ink jet head wherein a top plate 5 having a plurality of ink ejection nozzles 6 is placed on a substrate 1 having a plurality of main heating elements 2 arranged in a main scanning direction with a gap in such a manner that each of the ink ejection nozzles 6 is positioned on each of the corresponding main heating elements 2, the gap between the substrate 1 and the top plate 5 and the ink ejection nozzles 6 are filled with ink 7 and a bubble A is created in the ink 7 on the main heating element 2 and then a part of the ink 7 is ejected from the ink ejection nozzle 6 by virtue of the pressure of the created bubble A, thereby forming an image. Auxiliary heating elements 8 are provided to both sides of each of the main heating elements 2, respectively in the vicinity of each main heating element in the main scanning direction on the substrate 1.

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 forming an image by depositing ink droplets on a recording paper in a predetermined pattern.

[0002]

2. Description of the Related Art Conventionally, an ink jet head has been used as a recording device for forming an image on recording paper.

[0003] The recording method of the ink-jet head includes a method using thermal energy generated by a heating resistor, a method using deformation of a piezoelectric element, and a method using electromagnetic waves to eject and fly ink droplets toward recording paper. Some of them use heat generated by irradiation. Among them, the thermal jet type, which uses the heat energy of the heat generating resistor, is not only easy to form the pattern of the heat generating resistor, but also Since it can generate a relatively large amount of heat energy even if the area is small, it is attracting attention as being suitable for high-density recording.

As such a thermal jet type ink jet head, for example, as shown in FIG.
A top plate 15 having a plurality of ink ejection holes 16 is placed on a substrate 11 on which a plurality of heating resistors 12 are arranged in the main scanning direction. In addition, there is known a structure in which the ink 17 is filled in the gap between the substrate 11 and the top plate 15 and the ink ejection holes 16 while being arranged at a predetermined interval so as to be positioned above the recording medium. While the paper is being conveyed along the top surface of the top plate 15, the heating resistors 12 are selectively and individually heated based on image data from the outside, and the generated thermal energy causes the ink 17 to rapidly boil to generate heat. A bubble A is generated on the resistor 12, and the ink 1 on the heating resistor 12 is generated by pressure generated by the bubble A.
7 is pushed upward, a part of the ink 17 is ejected from the ink ejection hole 16 to the outside, and this is attached to recording paper to form an image.

In such a conventional ink jet head, since no partition is provided for separating the ink 17 between the substrate 11 and the top plate 15 into regions corresponding to the individual heating resistors 12, the ink jet heads are adjacent to each other. Compared with an ink jet head in which a partition is provided between heat generating resistors, the structure and manufacturing process are significantly simplified, and an ink jet head with high productivity can be obtained.

[0006]

However, according to the above-described conventional ink jet head, a partition for partitioning the ink 17 into regions corresponding to the individual heating resistors 12 is provided between the substrate 11 and the top plate 15. Since the ink 1 is not provided, the ink 1
When the bubble A is generated in 7, the dispersion of the pressure due to the bubble A in the main scanning direction cannot be effectively suppressed.
For this reason, the pressure of the bubble A generated on the heating resistor 12 is not efficiently transmitted to the ink 17 in the ink ejection hole 16,
There is a disadvantage that the ejection speed of the ink droplet i is significantly reduced, and the landing position of the ink droplet i on the recording paper is shifted.

In the above-described conventional ink-jet head, after the ink droplet i is ejected by the heat energy of the heating resistor 12, a large bubble A generated between the substrate 11 and the top plate 15 is removed from the ink tank (not shown). )), Most of which disappears when the ink 17 is supplied.
Some small bubbles may remain. Such a residual bubble remains in the same place until the start of the recording operation of the next line. Therefore, when the heating resistor 12 is heated again to generate a new bubble A, the ink 1
7 is ejected to the outside while containing fine residual air bubbles, or an excessively large air bubble is formed by combining newly generated air bubbles A and residual air bubbles, etc. Was uneven, and there was a drawback that image density unevenness was formed.

Further, the ink 17 filled between the substrate 11 and the top plate 15 of the above-mentioned conventional ink-jet head.
Hardly flows except when bubbles are generated or when the ink 17 is replenished. Therefore, a large amount of water or oil in the ink 17 flows through the ink ejection holes 16 due to heat or the like generated by the heating resistor 12. When the ink 17 evaporates and the viscosity of the ink 17 rises, the ink 17 solidifies in the vicinity of the ink ejection hole 16 where the viscosity rises remarkably, causing clogging, and it is impossible to form an accurate image corresponding to the image data on the recording paper. It also had the disadvantage that

Further, in the above-mentioned conventional ink jet head, since the ink 17 between the substrate 11 and the top plate 15 hardly flows as described above, heat is easily stored in the ink 17 and the inside of the substrate 11, and the ink If the head is used for a long time, the temperature of the substrate 11 becomes excessively high, causing a variation in the discharge amount of the ink 17 or a problem that unnecessary ink 17 is discharged to the outside. If a sufficient cooling time is provided between the recording operations of the respective lines in order to avoid troubles, a disadvantage that the time required for the recording becomes long and the high-speed recording cannot be performed is induced.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks.
On a substrate having a plurality of main heating elements arranged in the main scanning direction, a top plate having a plurality of ink ejection holes is placed in a predetermined position such that each ink ejection hole is located above the corresponding main heating element. The ink is filled in the gap formed between the substrate and the top plate and in the ink ejection holes, and the main heating element is selectively heated to generate the ink on the main heating element. In an ink jet head that forms an image by generating a bubble and discharging a part of the ink from an ink discharge hole by the pressure of the generated bubble, on the both sides in the main scanning direction of the individual main heating elements on the substrate. An auxiliary heating element is provided close to the main heating element.

In the ink jet head according to the present invention, when the main heating element generates heat, the auxiliary heating elements disposed on both sides thereof are simultaneously heated to generate air bubbles on the auxiliary heating element. It is assumed that.

Further, in the ink jet head according to the present invention, the width W2 of the auxiliary heating element in the main scanning direction is set to 25% to 80% of the width W1 of the main heating element in the main scanning direction. Is what you do.

Still further, the ink jet head according to the present invention is characterized in that the auxiliary heating element is arranged in a region between adjacent ink ejection holes so as to face the lower surface of the top plate.

Further, in the ink jet head according to the present invention, the voltage applied to each of the auxiliary heating elements is controlled so that the amount of heat generated by the two auxiliary heating elements disposed on both sides of the main heating element can be individually controlled. It is characterized by adjusting the power.

Further, the ink jet head according to the present invention is characterized in that the ink is circulated so that the ink between the substrate and the top plate flows in a direction orthogonal to the arrangement of the ink ejection holes.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is an exploded perspective view of an inkjet head according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of the inkjet head of FIG. 1 in the main scanning direction, where 1 is a substrate, 2 is a main heating element, and 5 is a top plate. , 6 are ink ejection holes, 7 is ink, and 8 is an auxiliary heating element.

The substrate 1 is made of an electrically insulating material such as alumina ceramics, and functions as a supporting base material for supporting a plurality of main heating elements 2 and the like on its upper surface.

When the substrate 1 is made of, for example, alumina ceramics, an appropriate organic solvent and a suitable solvent are added to and mixed with a ceramic raw material powder such as alumina, silica, magnesia, etc. to form a slurry, and a conventionally known doctor blade is used. A ceramic green sheet is obtained by employing a method, a calendar roll method, or the like. Thereafter, the ceramic green sheet is punched into a predetermined shape, and then fired at a high temperature.

A plurality of main heating elements 2 are provided on the substrate 1.
Are linearly attached and arranged along the main scanning direction.

The plurality of main heating elements 2 are, for example, 600
They are arranged linearly at a dot density of dpi, each of which is TaN-based, TaSiO-based, TaSiNO-based, TiSiO-based.
System, TiSiCO system, NbSiO system or the like, so that when power is applied via the electrode layers 3 and 3 electrically connected to both ends of each main heating element 2, Joule heat is generated. This causes the ink 7 to rapidly boil to generate a predetermined heat energy required to form the bubble A.

The main heating element 2 has an electric resistance of, for example, 100Ω to 2500Ω, and the width W2 of each main heating element 2 in the main scanning direction is set to 20 μm to 200 μm. Is used, for example, from 83 mJ / mm ^{2 to} 215 mJ /
mm ² .

Auxiliary heating elements 8 are arranged on both sides of the individual main heating elements 2 in the main scanning direction on the substrate 1 so as to be close to the main heating elements 2.

The auxiliary heating element 8 includes the main heating element 2 described above.
Between the main heating element 2 and the main heating element 2 located at both ends in the main scanning direction.
μm, and an electric resistance material of the same quality as the main heating element 2 described above, for example, TaN or TaS.
The electric resistance value of the main heating element 2 is made of an iO-based electric resistance material.
Is formed so that the width W2 in the main scanning direction is 50 μm to 160 μm corresponding to 25% to 80% of the main heating element 2.

During the recording operation, the auxiliary heating element 8 is given the same image data as that of the main heating element 2 disposed adjacent to the auxiliary heating element 8. The two auxiliary heating elements 2 also generate heat at the same time, and generate bubbles A ′ even in the ink 7 on the auxiliary heating element 8.

At this time, the power energy applied to the auxiliary heating element 8 is 83 m
J / mm ^{2 to} 215 mJ / mm ² , for example, 38 mJ
/ Mm ^{2 to} 83 mJ / mm ² .

The main heating element 2 and the auxiliary heating element 8 are
It is formed by applying the above-mentioned electric resistance material to the upper surface of the substrate 1 in a predetermined thickness and a predetermined pattern by a conventionally known thin-film method, specifically, sputtering, photolithography, etching or the like.

The main heating element 2 and the auxiliary heating element 8 are covered with a protective film 4 made of silicon nitride or the like and having a thickness of about 1.0 μm to 15.0 μm. The heating element 8 is effectively prevented from being corroded by the contact of the ink 7 described later.

On the substrate 1, a top plate 5 having a plurality of ink ejection holes 6 is provided, for example, in a range of 30 μm to 600 μm.
They are arranged in parallel with the upper surface of the substrate 1 with an interval of m.

The top plate 5 is positioned so that the ink ejection holes 6 corresponding to the position directly above the main heating element 2 and the area 6-6 between the ink ejection holes to the position directly above the auxiliary heating element 8 are positioned. Then, it is mounted on the substrate 1 via a spacer (not shown).

The ink discharge holes 6 of the top plate 5 are for discharging ink droplets i toward the recording paper during the recording operation of the ink jet head, and include a plurality of main heating elements 2 and 1.
They are arranged linearly in the main scanning direction at the same density as the main heating elements 2 in a one-to-one correspondence.

The top plate 5 is made of a metal material such as Mo (molybdenum) or a ceramic material such as alumina ceramic. For example, when the top plate 5 is made of Mo, an ingot of Mo is formed to a predetermined thickness by a conventionally known metal working method. It is manufactured by forming a plurality of ink ejection holes 6 having a diameter of 50 μm to 110 μm in the obtained plate by laser processing or etching.

Further, the gap between the substrate 1 and the top plate 5 is filled with ink 7, and the ink 7 is circulated (not shown) so as to flow in a direction (sub-scanning direction) orthogonal to the arrangement of the ink ejection holes 6. Circulated between the ink tank by a pump or the like.

The ink 7 flows in a region immediately below all the ink discharge holes 6, and its flow rate is controlled, for example, to 50 μm / sec to 2000 μm / sec. Regardless, the main heating element 2 is always kept substantially constant both when it is generating heat and when it is not generating heat.

The ink 7 is, for example, a pigment type oil-based ink or a water-based dye ink. When heat energy from the main heating element 2 or the auxiliary heating element 8 is applied to the ink 7, the heat generated by the ink 7 is reduced. The ink 7 is rapidly boiled in the vicinity of the bodies 2 and 8, and bubbles A and A 'are generated.

Thus, in the above-described ink jet head, while the recording paper is transported along the upper surface of the top plate 5 in the direction orthogonal to the arrangement direction of the ink ejection holes 6, the plurality of main heating elements 2 and auxiliary heating elements 8 Is selectively heated based on image data from the outside, and the thermal energy generates bubbles A, A ′ in the ink 7 on the main heating element 2 and the auxiliary heating element 8, and generates the generated bubbles A, A ′. A predetermined image is formed by ejecting the ink droplet i to the outside from the ink ejection hole 6 by the pressure of A ′ and attaching the ink droplet i to the recording paper.

In the ink jet head of this embodiment as described above, the auxiliary heating elements 8 are arranged on both sides of each of the main heating elements 2 in the main scanning direction in the vicinity of the main heating elements 2. When the main heating element 2 generates heat, the auxiliary heating elements 8 arranged on both sides of the main heating element 2 are simultaneously heated to generate bubbles A ′ and A ′ on the auxiliary heating element 8, so that these air bubbles A ′ and A ′ are generated. By giving A ′ a function similar to that of the partition, it is possible to effectively suppress the bubble A generated on the main heating element 2 from spreading in the main scanning direction. Therefore, the pressure of the bubble A is efficiently transmitted to the ink 7 near the ink ejection hole 6, and the ejection speed of the ink droplet i is maintained at a high speed so that the ink droplet i can land on a predetermined position of the recording paper accurately. It becomes possible.

In the ink jet head of this embodiment, the width W2 of the auxiliary heating element 8 in the main scanning direction is set to 25% to 80% of the width W1 of the main heating element 2 in the main scanning direction. The board space required for disposing the heating elements 8 is made as small as possible, and the main heating elements 2 can be arranged at a high density in the main scanning direction, so that the resolution of an image can be maintained high.

Further, in the ink jet head of this embodiment, since the auxiliary heating element 8 is disposed so as to face the lower surface of the top plate 5 in the region between the adjacent ink ejection holes 6, 6, The pressure of the bubble A ′ generated by the thermal energy of the main heating element 2 does not greatly disperse in the vertical direction. By maintaining the pressure on the bubble A generated on the main heating element 2 high, the bubble A is moved in the main scanning direction. Spreading can be suppressed more effectively.

Further, in the ink jet head of the present embodiment, if the amounts of heat generated by the two auxiliary heating elements 8, 8 disposed on both sides of the ink ejection hole 6 can be individually controlled, the recording can be performed. In operation, the power applied to the auxiliary heating elements 8, 8 arranged on both sides of the main heating element 2 is individually adjusted to vary the size of the bubbles A ', A', thereby discharging the ink droplet i. By finely adjusting the direction, the ink droplet i can be landed at a more accurate position.

Further, in the ink jet head of this embodiment, the ink 7 filled between the substrate 1 and the top plate 5
Is circulated so as to flow in a direction perpendicular to the arrangement of the ink ejection holes 6, so that the ink droplets i are ejected by the bubbles A generated by the thermal energy of the main heating element 2, and then the substrate 1 is ejected. Even if some fine bubbles remain between the top plate 5, these remaining bubbles move in the direction orthogonal to the arrangement of the ink ejection holes 6 together with the ink 7 flowing between the substrate 1 and the top plate 5, By the time the printing operation of the next line is started, it is quickly removed from the area between the main heating element 2 and the ink ejection holes 6. Therefore, the main heating element 2 is heated again by the recording operation of the next line, and a new bubble A
Is generated, fine residual bubbles are included in the ink droplet i ejected from the ink ejection hole 6, or a large bubble is formed by combining the newly generated bubble A and the residual bubble. There is very little
It is possible to form a good image with less density unevenness while keeping the discharge amount of the ink jet image constant.

When the direction of flow of the ink 7 is set to a direction other than the sub-scanning direction, for example, the main scanning direction parallel to the arrangement of the ink ejection holes 6, the direction in which the residual bubbles move with the flow of the ink 7 is set. Since a large number of other ink ejection holes 6 are arranged, the recording operation of the next line is started in order to eliminate all the residual bubbles from the area between the main heating element 2 and the ink ejection holes 6. In the meantime, it is necessary to flow the ink 7 in the main scanning direction. In this case, it takes an extremely long time to start the printing operation of the next line, and the printing is not performed at high speed. Therefore, it is important that the flow direction of the ink 7 coincides with the sub-scanning direction in order to quickly remove the residual air bubbles from immediately below the ink ejection holes 6.

Further, in the ink jet head of this embodiment, the ink 7 between the substrate 1 and the top plate 5 flows in a region immediately below all the ink ejection holes 6. For this reason, even if the water or oil in the ink 7 evaporates in a large amount from the ink ejection hole 6 due to the heat or the like generated by the main heating element 2, and the viscosity of the ink 7 in the ink ejection hole 6 tries to increase, The ink 7 does not solidify due to the replenishment of water or oil from the ink 7 flowing immediately below the ink ejection holes 6, and clogging of the ink ejection holes 6 can be effectively prevented. Therefore, an accurate image corresponding to the image data can be formed, and the reliability of the inkjet head can be improved.

Further, in this case, the ink 7 flowing in the area immediately below the ink discharge holes 6 is always in contact with the main heating element 2, the substrate 1, or the protective film 4 covering them, so that the ink jet head can be extended. When used over time, the heat accumulated in the main heating element 2 and the substrate 1 is well absorbed by the ink 7 flowing thereon, so that the temperature of the substrate 1 is maintained at a temperature suitable for a printing operation. Become. Accordingly, the discharge amount of the ink 7 from each of the ink discharge holes 6 can always be made substantially constant without providing a sufficient cooling time between the recording operations of the respective lines, and a clear image with less density unevenness can be produced at a high speed. It becomes possible to record with.

After passing through the space between the substrate 1 and the top plate 5, the ink 7 returns to the above-described ink tank and is again supplied between the substrate 1 and the top plate 5. Accordingly, the ink 7 repeatedly circulates between the region between the substrate 1 and the top plate 5 and the ink tank. In this case, the heat absorbed by the ink 7 flowing between the substrate 1 and the top plate 5 is radiated to the outside in the process of flowing through the circulation path as described above, and until the ink is supplied again between the substrate 1 and the top plate 5. In the meantime, it is cooled to a sufficiently low temperature.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications and improvements can be made without departing from the spirit of the present invention.

For example, in the above embodiment, two auxiliary heating elements 8 are arranged between the main heating elements, but instead, one auxiliary heating element is arranged between the main heating elements. No problem. In this case, the auxiliary heating element 8 is in charge of two main heating elements 2 adjacent to both sides thereof, so that the adjacent main heating elements 2 cannot be driven simultaneously, and every other main heating element 2 is provided. Are driven alternately.

In the embodiment described above, a polyimide resin film may be further adhered to the upper surface of the top plate 5 made of a metal material or a ceramic material. In this case, the film is provided with ink discharge holes that are slightly smaller than the discharge holes 6 at the positions where the ink discharge holes 6 are formed,
The ink droplet i is ejected to the outside from an ink ejection hole provided in the film.

[0048]

According to the ink jet head of the present invention, the auxiliary heating elements are disposed on both sides of the individual main heating elements in the main scanning direction. By causing the provided auxiliary heating elements to generate heat at the same time and generating bubbles on the auxiliary heating elements, these bubbles have the same function as the partition walls, and the bubbles generated on the main heating element are moved in the main scanning direction. It is possible to effectively suppress an attempt to spread to the area. Therefore, the pressure of the bubble is efficiently transmitted to the ink in the vicinity of the ink ejection hole, and the ejection speed of the ink droplet can be maintained at a high speed so that the ink droplet can be accurately landed at a predetermined position on the recording paper.

Further, in the ink jet head of the present invention, the width W2 of the auxiliary heating element in the main scanning direction is set to 25% to 80% of the width W1 of the main heating element in the main scanning direction. The board space required for the arrangement can be made as small as possible, and the main heating elements can be arranged at a high density in the main scanning direction, so that the resolution of an image can be maintained high.

Further, in the ink jet head of the present invention, the auxiliary heating element is disposed so as to face the lower surface of the top plate in a region between the adjacent ink ejection holes, so that the auxiliary heating element is generated by the heat energy of the auxiliary heating element. The pressure of the generated bubbles does not largely disperse in the vertical direction, and it is possible to more effectively suppress the bubbles generated on the main heating element from spreading in the main scanning direction.

Further, in the ink-jet head of the present invention, the amount of heat generated by the two auxiliary heating elements disposed on both sides of the ink ejection holes can be individually controlled, so that the recording operation can be performed during the recording operation. By individually adjusting the electric power applied to the auxiliary heating elements arranged on both sides of the main heating element to vary the size of bubbles generated on the auxiliary heating element, finely adjusting the ejection direction of ink droplets, The ink droplet can be landed at a more accurate position.

Further, in the ink jet head of the present invention, the ink filled between the substrate and the top plate is circulated so as to flow in a direction perpendicular to the arrangement of the ink ejection holes. After the ink droplets are ejected by the bubbles generated by the thermal energy of the main heating element, even if some small bubbles remain between the substrate and the top plate, these bubbles are still present in the ink flowing between the substrate and the top plate. Together with the ink ejection holes in the direction perpendicular to the array,
By the time the printing operation of the next line is started, it is quickly removed from the area between the main heating element and the ink ejection holes.
Therefore, when the main heating element is reheated to generate new air bubbles in accordance with the recording operation of the next line, fine air bubbles are included in the ink droplets ejected from the ink ejection holes, or newly generated air bubbles are generated. There is almost no formation of large bubbles due to the coalescence of the residual bubbles with the residual bubbles. This makes it possible to form a good image with less density unevenness while keeping the ink ejection amount constant.

Further, in the ink jet head of the present invention, the ink between the substrate and the top plate is made to flow in a region immediately below all the ink discharge holes, so that the ink is generated by the heat generated by the main heating element. Even if a large amount of water or oil in the ink evaporates from the ink ejection hole and the viscosity of the ink in the ink ejection hole is going to increase, water or oil is sequentially replenished to this portion from the ink flowing immediately below the ink ejection hole. As a result, the ink does not solidify, and clogging of the ink ejection holes can be effectively prevented. Therefore, an accurate image corresponding to the image data can be formed, and the reliability of the inkjet head can be improved.

Further, in this case, since the ink flowing in the area immediately below the ink discharge holes is always in contact with the main heating element, the substrate, or the protective film covering these, the ink jet head may be used for a long time. The heat accumulated in the main heating element and the substrate is well absorbed by the ink flowing thereon, and the substrate temperature is maintained at a temperature suitable for the printing operation. Therefore, the amount of ink ejected from each ink ejection hole can always be made substantially constant without providing a sufficient cooling time between the recording operations of each line, and a clear image with less density unevenness can be recorded at high speed. It is possible to do.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of an inkjet head according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view of the inkjet head of FIG. 1 in the main scanning direction.

FIG. 3 is a cross-sectional view of a conventional inkjet head in a main scanning direction.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Main heating element, 5 ... Top plate, 6
..Ink ejection holes, 7 ... ink, 8 ... auxiliary heating elements

Claims (6)

[Claims] 1. A top plate having a plurality of ink ejection holes is provided on a substrate having a plurality of main heating elements arranged in the main scanning direction, and each ink ejection hole is positioned above a corresponding main heating element. In such a way that they are arranged at a predetermined interval,
The gap formed between the substrate and the top plate and the ink discharge holes are filled with ink, and the main heating element is selectively heated to generate air bubbles in the ink on the main heating element and generate the ink. An ink jet head that forms an image by discharging a part of the ink from the ink discharge holes by the pressure of the generated air bubbles, wherein the main heat generating elements are disposed on both sides of the individual main heat generating elements on the substrate in the main scanning direction. An ink-jet head comprising an auxiliary heating element. 2. The method according to claim 1, wherein when the main heating element generates heat, auxiliary heating elements disposed on both sides thereof are simultaneously heated to generate air bubbles on the auxiliary heating element. The inkjet head according to the above. 3. The width W2 of the auxiliary heating element in the main scanning direction is:
2. The ink jet head according to claim 1, wherein the width of the main heating element in the main scanning direction is set to 25% to 80%. 4. The ink jet head according to claim 1, wherein the auxiliary heating element is arranged in a region between adjacent ink ejection holes so as to face a lower surface of the top plate. 5. The electric power applied to each of the auxiliary heating elements is adjusted so that the amounts of heat generated by the two auxiliary heating elements disposed on both sides of the main heating element can be individually controlled. The inkjet head according to claim 1, wherein 6. The ink jet head according to claim 1, wherein the ink is circulated so that the ink between the substrate and the top plate flows in a direction orthogonal to the arrangement of the ink ejection holes.