JP4508370B2 - Inkjet head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet head that forms an image by adhering ink droplets to a recording paper in a predetermined pattern.
[0002]
[Prior art]
Conventionally, an ink jet head has been used as a recording device for forming an image on recording paper.
[0003]
The inkjet head recording system uses thermal energy generated by the heating resistor to eject and fly ink droplets toward the recording paper, uses the deformation of the piezoelectric element, and is accompanied by irradiation with electromagnetic waves. Among these, the thermal jet type using the heat energy of the heating resistor is easy to form the heating resistor pattern, and the area of the heating resistor Since a relatively large thermal energy can be generated even when the size is small, it is attracting attention as being suitable for high-density recording.
[0004]
As such a thermal jet type ink jet head, for example, a large number of heating resistors and a substrate provided with a protective film covering these heating resistors, and a large number of ink discharges corresponding to the heating resistors one to one. There is a known structure in which a top plate in which holes are perforated is arranged with a predetermined space between them, and a gap between the substrate and the top plate is filled with ink. While conveying along the top surface of the top plate, a large number of heating resistors are selectively heated individually based on the image data, and bubbles are generated in the ink by this thermal energy, and the pressure by the generated bubbles Accordingly, a predetermined image is recorded by ejecting a part of the ink to the outside from the ink ejection hole of the top plate and attaching it to the recording paper.
[0005]
In addition, after the ink is ejected to the outside through the ink ejection holes, the same amount of ink as the ejected ink flows between the substrate and the top plate and is replenished. The operation can be repeated continuously.
[0006]
[Problems to be solved by the invention]
By the way, in the conventional ink jet head described above, after ink droplets are ejected by the heat energy of the heating resistor, most of the bubbles between the substrate and the top plate disappear by replenishment of the ink described above, but they are fine. Bubbles may remain. Since the ink between the substrate and the top plate containing residual bubbles is in the same place until the recording operation of the next line is started, the heating resistor is reheated to generate new bubbles. If this happens, the ink will be ejected outside with small residual bubbles, or the newly generated bubbles and residual bubbles will merge to form large bubbles, resulting in variations in the amount of ink discharged. And uneven density of the image is formed.
[0007]
In addition, the ink filled between the substrate and the top plate of the conventional ink jet head described above hardly flows except when bubbles are generated or when ink is replenished, and heat tends to be trapped in the ink and the substrate. It has become. Therefore, if the ink jet head is used for a long time, the temperature of the substrate or the like becomes excessively high, which also causes variations in the ink discharge amount, resulting in uneven density, or unnecessary ink is discharged to the outside. It had the fault which produces malfunctions, such as being.
[0008]
Therefore, in order to eliminate the above disadvantages, the ink filled between the substrate and the top plate is made to flow to remove residual bubbles from between the ink discharge holes and the heating resistor, and at the same time, the ink that flows between the substrate and the top plate. It has been studied to cool the substrate by absorbing the heat in the substrate.
[0009]
However, in the ink jet head described above, since the ink is filled in a narrow gap between the substrate and the top plate, when the ink is flowed at a high speed, a spiral shape is formed in the ink near the heating resistor and the ink discharge hole. There is a disadvantage that the flow of the ink is stopped and the flow of the ink is stopped by the generation of the spiral. In this case, it takes a long time to remove the residual bubbles, and the ink flow rate necessary for cooling the substrate in a short time cannot be obtained, which causes a disadvantage that it cannot be used for high-speed recording. Is done.
[0010]
In the conventional inkjet head described above, the substrate temperature tends to be higher in the central region than the both end regions in the main scanning direction with the recording operation, and the recording operation is performed with such a temperature distribution. Continuing, in the region where the substrate temperature is high, that is, in the central region in the main scanning direction, the size of bubbles generated in the ink increases, and the amount of ink ejected from the ink ejection holes increases. For this reason, there is a drawback that the density of the image formed on the recording paper is increased in the central area in the main scanning direction.
[0011]
[Means for Solving the Problems]
The present invention has been devised in view of the above drawbacks, and the inkjet head of the present invention includes a plurality of heating resistors arranged linearly in the main scanning direction and a substrate having a protective film covering these heating resistors, A predetermined interval is provided between the heating resistor and a top plate having a large number of one-to-one corresponding ink discharge holes so that the ink discharge holes are positioned above the heating resistor. The gap is formed between the substrate and the top plate and filled with ink, and the ink is caused to flow by the heat energy generated by the heating resistor while flowing the ink in a direction orthogonal to the arrangement of the heating resistors. An ink jet head for forming an image by ejecting ink droplets from the ink ejection holes, wherein a plurality of grooves along the ink flow direction are formed on a surface of a protective film in contact with the ink. Ri, and is characterized in that the depth and / or the formation density of the groove is are no large in the central region than in both end regions of the main scanning direction.
[0012]
The ink jet head of the present invention is characterized in that the flow rate of the ink is controlled to 50 μm / sec to 2000 μm / sec at least in a region between the heating resistor and the ink discharge hole.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
1 is an exploded perspective view of an ink jet head according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the ink jet head of FIG. 1 in the sub-scanning direction, and FIG. 3 is a main part of the ink jet head of FIG. 1 is a substrate, 3 is a heating resistor, 5 is a protective film, 6 is a groove on the surface of the protective film, 7 is a top plate, 8 is an ink ejection hole, and 9 is ink.
[0014]
The substrate 1 is formed in a rectangular shape by an electrically insulating material such as alumina ceramics, and functions as a support base material for supporting the glaze layer 2 and a large number of heating resistors 3 on the upper surface thereof.
[0015]
When the substrate 1 is made of, for example, alumina ceramics, an appropriate organic solvent and solvent are added to and mixed with ceramic raw material powders such as alumina, silica, and magnesia to form a slurry, and this is formed into a conventionally known doctor blade. A ceramic green sheet is obtained by adopting a method, a calender roll method or the like, and thereafter, the ceramic green sheet is punched into a predetermined shape and then fired at a high temperature so as to form a rectangular shape.
[0016]
Further, on the upper surface of the substrate 1, a glaze layer 2 having a mountain-like cross section is formed in a strip shape along one long side, and a number of heating resistors 3 are linearly deposited and arranged on the top. .
[0017]
The glaze layer 2 is formed of glass or the like so as to have a mountain-shaped cross section, and since the surface thereof is extremely smooth, a large number of heating resistors 3 are formed on the glaze layer 2 by a conventionally known photolithography or the like. When the pattern is formed, fine processing of the heating resistor 3 can be performed relatively easily.
[0018]
When the glaze layer 2 is made of glass, a predetermined glass paste obtained by adding and mixing an appropriate organic solvent, organic binder, etc. to the glass powder is applied to the upper surface of the substrate 1 by a conventionally known screen printing. It is formed so as to have a cross-sectional mountain shape by printing and applying in a strip shape by, for example, and baking at high temperature.
[0019]
A number of heating resistors 3 deposited on the glaze layer 2 are linearly arranged in the main scanning direction with a dot density of, for example, 600 dpi, and are TaN, TaSiO, TaSiNO, TiSiO, Since it consists of electric resistance materials, such as a TiSiCO type | system | group and a NbSiO type | system | group, power supply electric power is supplied to the heating resistor 3 via the electrode layers 4 and 4 electrically connected to the both ends of each heating resistor 3 Joule heat is generated, and the heat energy necessary to form the bubbles A in the ink 9 is generated.
[0020]
The heating resistor 3 employs a conventionally well-known thin film technique, specifically, sputtering, photolithography technique, etching technique, etc., and the above-described electric resistance material is applied to the upper surface of the glaze layer 2 in a predetermined thickness and pattern. It is formed by depositing.
[0021]
Further, a protective film 5 made of silicon nitride or the like is deposited on the upper surface of the heat generating resistor 3 or the like with a substantially constant thickness, and the heat generating resistor 3 and the electrodes 4 and 4 are covered with the protective film 5.
[0022]
The protective film 5 is for protecting the heat generating resistor 3 and the electrode layers 4 and 4 from corrosion due to contact with the ink 10 and is, for example, 2.0 μm on the upper surface of the heat generating resistor 3 or the like by well-known sputtering or the like. Deposited to a thickness of ˜20.0 μm.
[0023]
A number of grooves 6 are formed on the surface of the protective film 5 in a direction (sub-scanning direction) orthogonal to the arrangement of the heating resistors 3, and the depth of these grooves 6 is shown in FIG. As shown in (b), the central area (for example, 15% to 20% area on both sides from the center of the substrate 1) as compared to the both end areas in the main scanning direction (for example, areas of 30% to 35% from both ends of the substrate 1). It ’s big.
[0024]
The number of grooves 6 is set such that the formation density in the main scanning direction is, for example, 6 lines / mm to 300 lines / mm, and the width of each groove 6 in the main scanning direction is, for example, 3 μm to 160 μm. Since the region on the body 3 is provided in a direction orthogonal to the arrangement of the heating resistors 3 (sub-scanning direction), the action of causing the ink 9 to be described later to flow well and stably along the groove 6 formation direction. Do it.
[0025]
Further, as described above, the depth of each of the plurality of grooves 6 is larger in the central region than both end regions in the main scanning direction, and the surface area of the protective film 5 in contact with the ink 9 is the central region in the main scanning direction. It has become wide. Accordingly, during the recording operation, the heat accumulated in the substrate 1 and the glaze layer 2 is absorbed more efficiently by the ink 9 side in the central area in the main scanning direction than in the both end areas.
[0026]
The numerous grooves 6 are formed by employing a conventionally known photolithography technique and dry etching technique. At this time, in order to make the depth of the groove 6 deeper than the both end areas in the central region in the main scanning direction, the etching time for forming the groove 6 in the both end regions of the protective film is longer than that in forming the groove 6 in the central region. Can be set longer. As a result, the depth of the groove 6 in both end regions in the main scanning direction is, for example, 0.1 μm to 4.0 μm, and the depth of the groove 6 in the central region is, for example, 5.0 μm to 10.0 μm.
[0027]
A top plate 7 having a large number of ink discharge holes 8 corresponding to the heating resistors 3 on a one-to-one basis is disposed on the substrate 1 described above in a substantially parallel manner to the upper surface of the substrate with a predetermined interval therebetween. Is done.
[0028]
The top plate 7 is aligned so that the ink discharge holes 8 are located above the corresponding heat generating resistors 3, and the lower surface of the top plate 7 is used to keep the distance between the substrate 1 and the top plate 7 substantially constant. A spacer (not shown) is arranged along the outer periphery of the top plate 7, and a predetermined gap is formed between the substrate 1 and the top plate 7 by the spacer.
[0029]
The ink ejection holes 8 formed in the top plate 7 are for ejecting ink droplets i toward the recording paper during the recording operation of the ink-jet head. Correspondingly, they are arranged in a straight line in the main scanning direction at a density substantially equal to that of the heating resistors 3, for example, a dot density of 600 dpi.
[0030]
The top plate 7 is made of a metal such as molybdenum or an electrically insulating material such as alumina ceramics. For example, when the top plate 7 is made of molybdenum, the molybdenum ingot is formed into a plate having a predetermined thickness by a conventionally known metal processing method. The obtained plate is manufactured by punching a plurality of ink ejection holes 8 having a diameter of 50 μm to 110 μm by a conventionally known laser processing or the like.
[0031]
A gap formed between the top plate 7 and the substrate 1 is filled with ink 9.
As the ink 9, for example, pigment type oil-based ink or water-based dye ink is used. The ink 9 is supplied from an ink tank (not shown) between the substrate 1 and the top plate 7, and the heat energy of the heating resistor 3 described above. As a result, when bubbles A are generated in the ink 9, a part of the ink 9 becomes ink droplets i by the pressure of the bubbles A and is ejected to the outside from the ink ejection holes 9.
[0032]
Further, such ink 9 is circulated between the ink tanks by a circulation pump (not shown) that flows in a direction (sub-scanning direction) orthogonal to the arrangement of the ink discharge holes 8.
[0033]
The ink 9 is controlled so as to flow at a flow rate of, for example, 50 μm / sec to 2000 μm / sec in the region between the heating resistor 3 and the ink discharge hole 8. Regardless of the driving state of the body 3, the heating resistor 3 is always kept at substantially the same flow rate when the heating resistor 3 is generating heat and when it is not generating heat.
[0034]
For this reason, even if some fine bubbles a remain between the substrate 1 and the top plate 7 after the ink droplets are ejected by the thermal energy from the heating resistor 3, these residual bubbles a are not formed on the substrate 1-1. It moves in the direction orthogonal to the arrangement of the ink discharge holes 8 together with the ink 9 flowing between the top plates 8 and before the recording operation of the next line is started, the heating resistor 3 and the ink discharge holes 8 Quickly eliminated from the area in between. Accordingly, when the heating resistor 3 is reheated in association with the recording operation of the next line to generate new bubbles, fine residual bubbles a are included in the ink droplets i ejected from the ink ejection holes 8. The newly generated bubbles A and the residual bubbles a are rarely combined to form a large bubble, thereby forming a good image with little variation in density with the discharge amount of the ink 9 being substantially constant. It becomes possible.
[0035]
When the flow direction of the ink 9 is set to a direction other than the sub-scanning direction, for example, a main scanning direction parallel to the arrangement of the ink discharge holes 8, there are other directions in which the residual bubble a moves along with the flow of the ink 9. In order to eliminate all residual bubbles a from the region between the heating resistor 3 and the ink discharge holes 8, the recording operation of the next line is started. During this time, it is necessary to cause the ink 9 to flow in the main scanning direction. In this case, it takes a very long time to start the recording operation for the next line, and the high-speed recording is not performed. Therefore, in order to quickly remove the residual bubbles a immediately below the ink discharge holes 8, it is important to match the flow direction of the ink 9 with the sub-scanning direction.
[0036]
Further, since the ink 9 flows while being in contact with the heating resistor 3 and the protective film 5 covering the substrate 1, the heating resistor is used even when the ink jet head is used for a long time. The heat accumulated in the body 3, the substrate 1, the glaze layer 2, etc. is absorbed well by the ink 9 side through the protective film 5, and the temperature of the substrate 1, the glaze layer 2, etc. becomes excessively high. Absent. Accordingly, even if a sufficient cooling time is not provided between the recording operations of the respective lines, the temperature of the heating resistor 3 can be maintained at a temperature suitable for the recording operation and the discharge amount of the ink 9 can be made substantially constant at all times. It is possible to cope with high-speed recording.
[0037]
Moreover, in this embodiment, a large number of grooves 6 are formed on the surface of the protective film 5 along the flow direction of the ink 9, and the ink 9 is good along the direction in which the grooves 6 are formed, that is, in the sub-scanning direction. It is designed to flow stably. For this reason, even if the ink 9 is made to flow at a relatively high flow rate (50 μm / sec to 2000 μm / sec), a spiral flow hardly occurs in the ink 9 and the flow of the ink 9 stops locally. Such inconveniences can be effectively prevented. Accordingly, the residual bubbles a in the ink 9 are removed well in a shorter time than between the heating resistor 3 and the ink discharge holes 8, and a predetermined flow velocity required to quickly cool the substrate 1 with the flowing ink 9 is obtained. be able to.
[0038]
In this embodiment, as described above, the groove 6 on the surface of the protective film is formed deeper in the central region than both end regions in the main scanning direction, and heat is radiated from the substrate 1, the glaze layer 2 and the like into the ink 9. Since the heat radiation characteristic in the central region is improved in the central region in the main scanning direction, the temperature of the substrate 1 and the like is kept substantially constant in the main scanning direction even when the recording operation takes a relatively long time. This also makes it possible to make the discharge amount of the ink 9 uniform.
[0039]
The ink 9 passes between the substrate 1 and the top plate 7 and then returns to the ink tank and is supplied between the substrate 1 and the top plate 7 again. Thus, the ink 9 is repeatedly circulated between the region between the substrate 1 and the top plate 7 and the ink tank.
[0040]
Further, the heat absorbed from the substrate 1 or the like by the ink 9 flowing between the substrate 1 and the top plate 7 is dissipated outside in the process of flowing through the circulation path as described above, and is supplied again between the substrate 1 and the top plate 7. Until the temperature is sufficiently low.
[0041]
Thus, the ink jet head described above individually transfers a number of heating resistors 3 on the basis of image data from the outside while transporting the recording paper along the top surface of the top plate 7 in a direction orthogonal to the arrangement direction of the ink discharge holes 8. Heat is selectively generated, and bubbles A are generated on the heating resistor 3 by the generated thermal energy, and a part of the ink 9 is discharged to the outside from the ink discharge holes 8 of the top plate 7 by the pressure of the bubbles A. A predetermined image is recorded by adhering the ejected ink droplets i to the recording paper.
[0042]
In addition, this invention is not limited to the above-mentioned form, A various change, improvement, etc. are possible in the range which does not deviate from the summary of this invention.
[0043]
For example, in the above-described embodiment, the photolithography technique and the etching technique are adopted to form the groove 6 on the surface of the protective film 5, but instead of this, aluminum oxide or silicon carbide, The groove 6 may be formed by rubbing the surface of the protective film 5 in the sub-scanning direction with a wrapping film to which hard inorganic fine particles made of diamond or the like are bonded. At this time, in order to make the depth of the groove 6 formed in the central region in the main scanning direction different from the depth of the groove 6 formed in both end regions, two types of wrapping films bonded with inorganic fine particles having different particle sizes are used. Use.
[0044]
In the above-described embodiment, the depth of the groove 6 formed on the surface of the protective film is changed between the central area in the main scanning direction and the both end areas to improve the heat dissipation characteristics in the central area. Thus, the formation density of the grooves 6 on the surface of the protective film (formation density in the main scanning direction) is larger than the both end areas in the central area in the main scanning direction, or the formation density of the grooves 6 and the depth of the grooves 6 Even if both are made larger in the central region in the main scanning direction than the both end regions, the heat radiation characteristic in the central region in the main scanning direction is improved, and the same effect as in the above embodiment can be obtained.
[0045]
Furthermore, in the above-described embodiment, a polyimide resin film may be further adhered to the upper surface of the top plate 8 made of a metal material or a ceramic material. In this case, an ink discharge hole that is slightly smaller than the discharge hole 9 is formed in the film at a position where the ink discharge hole 9 is formed, and the ink droplet i is directed toward the recording paper from the ink discharge hole provided in the film. It will be discharged.
[0046]
Further, in the above-described embodiment, if the ink 9 between the substrate 1 and the top plate 7 is always allowed to flow in the region immediately below all the ink discharge holes 8, the ink is generated by the heat generated by the heating resistor 3 or the like. Even if water or oil in the ink 9 evaporates in a large amount from the ink discharge hole 8 and the viscosity of the ink 9 in the ink discharge hole 8 is about to increase, By sequentially replenishing the oil component, the ink 9 does not harden in the vicinity of the ink ejection holes 8 and the clogging of the ink ejection holes 8 can be effectively prevented. In this case, an accurate image corresponding to the image data can be formed, and there is an advantage that the reliability of the inkjet head is improved.
[0047]
【The invention's effect】
According to the ink jet head of the present invention, since ink between the substrate and the top plate is made to flow in a direction orthogonal to the arrangement of the ink discharge holes, ink droplets are discharged by the heat energy of the heating resistor. After that, even if some fine bubbles remain between the substrate and the top plate, these bubbles move with the ink flowing between the substrate and the top plate in the direction perpendicular to the arrangement of the ink ejection holes, and the next line. Until the recording operation is started, it is promptly removed from the region between the heating resistor and the ink ejection holes. Therefore, when the heating resistor is reheated during the next line recording operation to generate new bubbles, fine residual bubbles may be included in the ink droplets discharged from the ink discharge holes or newly generated. The combined bubbles and residual bubbles rarely form a large bubble, and this makes it possible to form a good image with little unevenness in density while keeping the ink ejection amount substantially constant.
[0048]
Further, according to the ink jet head of the present invention, since the ink flows in a state of being in contact with the protective film covering the heat generating resistor, the heat is generated even when the ink jet head is used for a long time. The heat accumulated inside the resistor, the substrate, etc. is well absorbed by the ink through the protective film, and the temperature of the substrate does not become excessively high. Therefore, the ink discharge amount can be made substantially constant by maintaining the temperature of the heating resistor at a temperature suitable for the recording operation without providing a sufficient cooling time between the recording operations of each line. Makes it possible to support high-speed recording.
[0049]
Furthermore, in the ink jet head of the present invention, a large number of grooves extending along the direction of ink flow are formed on the surface of the protective film in contact with the ink. Thus, it becomes possible to flow in a predetermined direction well and stably, and it is possible to effectively prevent the occurrence of a spiral flow in the ink. Accordingly, it is possible to remove the residual bubbles in the ink satisfactorily in a shorter time than between the heating resistor and the ink ejection holes, and to obtain a predetermined flow rate necessary for quickly cooling the substrate.
[0050]
Furthermore, in the ink jet head of the present invention, the depth and / or density of the groove is made larger in the central region than in the both end regions in the main scanning direction. The surface area becomes wider in the central area in the main scanning direction, and the heat dissipation characteristics in the central area are improved. Therefore, even if the recording operation takes a relatively long time, the temperature of the substrate or the like can be kept substantially constant in the main scanning direction, and the ink discharge amount can also be made uniform.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of an ink jet head according to an embodiment of the present invention.
2 is a cross-sectional view of the inkjet head of FIG. 1 in the sub-scanning direction.
3 is a partial cross-sectional view of the inkjet head of FIG. 1 in the main scanning direction, where (a) is an enlarged cross-sectional view in the central area in the main scanning direction, and (b) is an enlarged cross-section in both end areas in the main scanning direction. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Substrate, 3 ... Heat generating resistor, 5 ... Protective film, 6 ... Groove, 7 ... Top plate, 8 ... Ink ejection hole, 9 ... Ink

Claims (2)

A substrate having a large number of heating resistors arranged in the main scanning direction and a protective film covering these heating resistors, and a top plate in which a large number of ink discharge holes corresponding to the heating resistors are provided. Are arranged with a predetermined gap therebetween so that the ink discharge hole is positioned above the heating resistor, and the gap formed between the substrate and the top plate is filled with ink. An ink jet head that forms an image by ejecting ink droplets from the ink ejection holes by thermal energy generated by the heating resistors while flowing the ink in a direction perpendicular to the arrangement of the heating resistors,
A number of grooves along the direction of ink flow are formed on the surface of the protective film in contact with the ink, and the depth and / or density of the grooves is greater in the central region than in the two end regions in the main scanning direction. An ink jet head characterized by being enlarged. 2. The ink jet head according to claim 1, wherein the flow rate of the ink is controlled to 50 μm / sec to 2000 μm / sec at least in a region between the heating resistor and the ink ejection hole.

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