JP2783965B2 - Thermal inkjet head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-impact method in which bubbles are instantaneously generated in ink in a flow path, and the ink is ejected from fine discharge ports as a driving force to perform recording. The present invention relates to a thermal inkjet head which is one of recording heads.

[0002]

2. Description of the Related Art The non-impact recording method is considered to be a recording method of great interest in that the generation of noise during recording is extremely small to a negligible level. Above all, the so-called ink jet recording method, which enables high-speed recording and can perform recording on so-called plain paper without requiring a special fixing process, is an extremely effective recording method. In view of the above, various types of ink jet recording methods have been proposed in the past, and various improvements have been made. Some types are currently commercialized and some are in the development stage for practical use.

In such an ink jet recording method, recording is performed by causing droplets of a recording liquid called so-called ink to fly and adhere to a recording medium such as plain paper. An example is disclosed in Japanese Patent Publication No. 56-9429 proposed by the present applicant. In summary, the ink in the flow path is heated to generate air bubbles to generate a pressure rise in the ink, and the ink is ejected from a fine capillary nozzle for recording.

After that, many proposals have been made utilizing such an ink flying principle. One of these proposals is, for example, Japanese Patent Application Laid-Open No. 56-139970. This is because, in this type of head, when the bubbles generated in the flow path reach the ceiling surface of the flow path, the supply of ink is interrupted, and the replenishment of the next ink is not sufficiently performed. Drop ejection mistake or drop in ejection speed, or
This takes into account the problem that the ejection direction is disturbed.

[0005]

However, Japanese Unexamined Patent Publication No.
In the case of -13-97070, there is only a statement such as "do not block by air bubbles", but it is not clearly specified how to do it, and it is unclear how to realize it. It is.

In this type of thermal head, when the ink meniscus of the discharge nozzle portion retreats after the ink is ejected, air is sucked into the discharge nozzle portion to the flow path, and the air is sucked into the bubble generation portion (that is, the air bubble generation portion). (The vicinity of the heating element), so that the next ink ejection cannot be performed.

[0007]

According to the first aspect of the present invention, there is provided a discharge port for ejecting a recording liquid, a flow path communicating with the discharge port, and the recording path in communication with the flow path. A liquid chamber for supplying a liquid, a heating element disposed in a part of the flow path for generating air bubbles in the flow path, and an electrode for energizing the heating element. In the thermal ink jet head, the heating element and the electrode are formed as a planar pattern on a substrate by photofabrication, and a resin layer having a constant thickness is formed on the substrate to cover the heating element and the electrode. A heating element exposed portion having a shape substantially similar to the heating element was formed in the opening corresponding to the heating element by photolithography.

According to a second aspect of the invention, the same as the first aspect of the invention, except that a heating element exposed portion having a larger area than the heating element area is formed.

[0009] In these inventions, in the invention according to the third aspect, the fixed thickness of the resin layer is at least half the maximum height of the bubbles generated by the heating element. The constant thickness of the layer was less than the maximum height of bubbles generated by the heating element.

On the other hand, with respect to the resin layer, in the invention according to claim 5, it is formed of a liquid photoresist.
In the invention described in the above, the photoresist is formed by a dry film photoresist, and in the invention described in claim 7, these photoresists are negative photoresists.

[0011]

According to the first aspect of the present invention, since the resin layer covering the heating element and the like is formed on the substrate, and the heating element exposed portion is formed in the heating element corresponding area of the resin layer, the opening is formed.
The bubble generation area substantially corresponding to the heating element is located one channel away from the flow path.
This is a stepped area, and the inconvenience of shutting off the flow path and stopping the liquid injection due to the suction of air from the discharge port and the arrival of air bubbles at the flow path ceiling surface is eliminated. At this time, since the heating element exposed portion is formed in a substantially similar shape to the heating element, the stability of bubble generation is enhanced, and the efficiency of the driving force is also increased.

[0012] In the second aspect of the invention, the first aspect is also provided.
In the same manner as in the described invention, blockage of the flow path is prevented. At this time, since the heating element exposed portion is formed to be larger than the heating element area, the resin layer does not come into contact with the heating element, and thus deterioration due to heat is reduced.

According to the third aspect of the present invention, the height of the resin layer is set to at least half of the maximum height of the generated bubbles.
The driving force for bubble growth can be effectively contributed to the liquid injection, and high-speed jet speed and injection stability are ensured.

According to the fourth aspect of the present invention, since the height of the resin layer is set to be equal to or less than the maximum height of the generated bubbles, the opening pattern of the heating element exposed portion can be easily formed by the photolithography method.

In the present invention, since the resin layer is formed of a liquid photoresist, it is easy to form the resin layer to a desired thickness.

In the sixth aspect of the present invention, since the resin layer is formed of a dry film photoresist,
Even if the resin layer is thicker than 0 μm, it can be easily formed.

In the present invention, since a negative type photoresist is used for these photoresists,
The head is excellent in corrosion resistance to an alkaline recording liquid, and is a highly reliable head for a long period of time.

[0018]

An embodiment of the present invention will be described with reference to the drawings. The basic configuration and operation principle of the thermal inkjet head according to the present embodiment will be described with reference to FIGS.
As shown in FIG. 5, the head chip 1 has a liquid path substrate 3 stacked on a heating element substrate 2. Here, an inflow port 5 for ink (recording liquid) is formed in the flow path substrate 3, and a plurality of flow paths 7 for forming orifices 6 are formed in a rectangular groove shape as shown in FIG. I have. The inflow port 5 has a flow path 7
The liquid chamber 8 communicates with the liquid chamber 8. Heating element substrate 2
A plurality of heaters (heating elements) 9 (see FIGS. 6 and 8) corresponding to each orifice 6 (flow path 7) are formed on the upper part,
Each of them is individually connected to the control electrode 10 and commonly connected to the common electrode 11 (see FIGS. 6 and 8).

In such a head chip 1 configuration,
The ink ejection by the bubble jet is performed by a process as shown in FIG. First, in the steady state, the state is as shown in FIG. 7A, and the surface tension of the ink 12 and the external pressure are in an equilibrium state on the orifice surface. Next, when the heater 9 is heated and heated until its surface temperature rises rapidly and a boiling phenomenon occurs in the adjacent ink layer, as shown in FIG.
Fine bubbles 13 are scattered. Further, the adjacent ink layer rapidly heated on the entire surface of the heater 9 is instantaneously vaporized to form a boiling film, and the bubble 13 grows as shown in FIG. At this time, the pressure in the nozzle rises by an amount corresponding to the growth of the bubble 13, the balance with the external pressure on the orifice surface is lost, and the ink column 14 starts to grow from the orifice 6.
FIG. 4D shows a state in which the bubble 13 has grown to the maximum, and the ink 12 corresponding to the volume of the bubble 13 from the orifice surface.
Is extruded. At this time, no current is flowing through the heater 9 already, and the surface temperature of the heater 9 is decreasing. The maximum value of the volume of the bubble 13 is slightly delayed from the timing of applying the electric pulse. Eventually, the bubble 13 is cooled by the ink 12 or the like and starts to contract as shown in FIG. At the front end of the ink column 14, the ink 12 moves forward while maintaining the extruded speed, and at the rear end, the ink 12 flows backward from the orifice surface into the nozzle due to the decrease in the nozzle internal pressure due to the contraction of the bubble 13, and constricts to the base of the ink column 14. Occurs. Thereafter, as shown in FIG. 3F, the bubbles 13 further contract, the ink 12 comes into contact with the surface of the heater 9, and the surface of the heater 9 is further cooled. At the orifice surface, the external pressure is higher than the internal pressure of the nozzle, so that a large meniscus enters the nozzle. The leading end of the ink column 14 becomes a droplet 15 and flies in the direction of a recording paper (not shown) at a speed of 5 to 10 m / sec. Thereafter, as shown in FIG. 9G, the ink 12 is again supplied (refilled) to the orifice 6 by capillary action and returns to the steady state of FIG.
Disappears completely.

FIG. 7 and FIG. 8 are typical examples showing more specifically the main components of a thermal ink jet head based on such a principle. FIG. 7 is a detailed front view of the head chip 1 as viewed from the orifice 6, and FIG.
It is a B sectional view. This head chip 1 is covered with a flow path substrate 3 provided with a predetermined number of flow paths 7 having a predetermined linear density and a predetermined width on a heating element substrate 2 having an electrothermal transducer 20 provided on a surface thereof. In this way, a liquid discharge portion (discharge port) 21 including the orifice 6 for causing the liquid to fly is formed. The liquid discharge part 21 has an orifice 6 at its end and a heat energy generated from the electrothermal transducer 20 acting on the liquid to generate bubbles 13, causing a sudden state change due to expansion and contraction of the volume. And a heat acting portion 22. The heat acting portion 22 is located above the heater 9 of the electrothermal converter 20 and has a heat acting surface 22a as a surface of the heater 9 that comes into contact with the ink 12 as its bottom surface. The heater 9 includes a lower layer 23, a heating resistor layer 24, and an upper layer (protective layer) 25 sequentially provided on the substrate 2.
It consists of. In order to generate heat, the heating resistor layer 24 has an electrode 1 for supplying electricity to the heating resistor layer 24.
0 and 11 are provided. The electrode 10 is a control electrode for selecting each heater 9 to generate heat, and
The electrode 10 is provided along one liquid flow path,
This is a common electrode common to one heater 9.

The protective layer 24 fills the heat generating resistance layer 24 and the flow path 7 of the liquid discharge section 21 in order to protect the heat generating resistance layer 24 chemically and physically from the ink 12 to be used in the area of the heater 9. While isolating the ink 12
It has the role of preventing the electrodes 10 and 11 from being short-circuited through the ink 12 and of preventing electrical leakage between adjacent electrodes.

The flow paths 7 provided in the respective liquid discharge sections 21 are respectively connected to the liquid chambers 8 on the upstream side of the respective liquid discharge sections 21. Further, the electrodes 10 and 11 connected to the electrothermal transducers 20 provided for each liquid discharge unit 21
Is formed so as to be protected by the protective layer 25 and pass under the liquid chamber 8 on the upstream side of the heat acting portion 22 due to the design.

By the way, useful materials for forming the heating resistance layer 24 include, for example, tantalum-SiO.
_2, a mixture of tantalum nitride, nichrome, silver-palladium alloy, silicon semiconductor, or hafnium, lanthanum,
Examples include boride of a metal such as zirconium, titanium, tantalum, tungsten, molybdenum, niobium, chromium, and vanadium. Among the materials constituting the heat generating resistance layer 24, metal borides are particularly preferable. Among them, hafnium boride, zirconium boride, lanthanum boride, tantalum boride, and boride are listed in the order of particularly excellent characteristics. Vanadium, then niobium boride. The heating resistance layer 24 can be formed using such a material by using a method such as an electron beam evaporation method or a sputtering method. Heating resistance layer 2
The film thickness of No. 4 is determined according to its area, material and shape and size of the heat acting portion, and furthermore, according to actual power consumption and the like, so that the calorific value per unit time is as desired. In a normal case, the thickness is 0.001 to 5 μm, preferably 0.01 to 1 μm.

The materials constituting the electrodes 10 and 11 include:
Many commonly used electrode materials are effectively used, and specifically, for example, Al, Ag, Au, Pt, C
u, etc., and are provided at a predetermined position in a predetermined size, shape, and thickness by a technique such as a vapor deposition method.

The characteristics required for the protective layer 25 do not prevent the heat generated in the heat generating resistive layer 24 from being effectively transmitted to the ink 12. Is to protect. Examples of useful materials for forming such a protective layer 25 include silicon oxide, magnesium oxide, aluminum oxide, tantalum oxide, and zirconium oxide. These can be formed using a technique such as an electron beam evaporation method or a sputtering method. The film thickness of the protective layer 25 is usually 0.1.
The thickness is from 0.1 to 10 μm, preferably from 0.1 to 5 μm (optimally, from 0.1 to 3 μm).

In the head chip 1 having such a basic structure, in the present embodiment, as shown in FIGS. 1 to 3, a resist layer 31 is formed as a resin layer on the entire surface of a heating element substrate 2 and a heater is formed. In the 9 corresponding area, a heater exposure part (heating element exposure part) 32 is formed in an opening. To explain in more detail, first, the method as described above, that is,
Heater 9 and electrode 1 by photofabrication
A heating element substrate 2 in which 0 and 11 are formed as a planar pattern is prepared, and a resist layer 31 is formed over the entire surface of the heating element substrate 2 with a constant thickness (shaded lines in FIG. 2). Shown). In the region corresponding to the heater 9 with respect to such a resist layer 31, a heater exposure portion 32 having a substantially similar shape to the heater 9 by photolithography, here a rectangular shape, and having a larger area than the heater 9 area is formed. Is done. The head chip 1 (which is a feature of the present embodiment) is laminated and bonded to the heating element substrate 2 on which the resist layer 31 having the heater exposed portion 32 is formed by using the flow path substrate 3 as a lid as described above. FIG. 1A is manufactured.

The manner in which bubbles 13 are formed near the heater 9 in such a head chip 1 will be described with reference to FIG. In FIG. 1, the structure of the heater 9 is simplified for easy understanding mainly of the air bubbles 13 and the like. In this embodiment, the resist layer 31 is used.
The thickness is also important, and the degree of the thickness will be described later. However, the thickness is at least about 1 μm, which is the thickness used in so-called photolithography to etching in the semiconductor industry, and is about the extent that affects the bubble generation. Thickness.

FIG. 1B shows a bubble 13 generated by the heating of the heater 9.
This shows a state in which is occurring. 4D, it can be seen that the bubble generation region corresponding to the heater 9 is substantially a recessed region that is one step lower than the flow path 7 due to the heater exposure portion 32. Therefore, the bubbles 13 generated by the heat generated by the heater 9 do not reach the ceiling surface of the flow path 7 even when the height h is maximized. Therefore, the bubbles 13 do not block the flow of the ink 12 in the flow path 7.
In addition, by setting the thickness of the resist layer 31 appropriately, there is no possibility that air is sucked from the liquid discharge unit 21 and the ink jetting is stopped due to this. Needless to say, the presence of the opening concave portion serving as the heater exposed portion 32 does not hinder the ink ejection operation accompanying the generation of the bubble 13.

Table 1 shows the results of an ink jetting experiment in which the thickness t of the resist layer 31 was varied. The head structure and the driving conditions used in the experiment are as follows. Head; size of heater 9: 32 μm × 160 μm (1
15 Ω) rectangular shape Distance between liquid discharger 21 to heater 9: 180 μm Total length of flow path 7: 640 μm Flow path 7 is formed by forming a rectangular groove in Pyrex glass with a dicing saw, and has a cross-sectional dimension of 36 μm.
m × 36 μm Resist layer 31: A liquid resist (a negative resist BMRS1000 manufactured by Tokyo Ohka Co., Ltd.) is used up to a thickness of 30 μm (the thickness is changed by changing the number of rotations during spin coating). For the above thickness, dry film resist (Audil SX manufactured by Tokyo Ohkasha)
The size of the heater exposed part 32: 36 μm × 180 μm Driving condition: Driving voltage V _O = 28 V Driving pulse width P _W = 6 μs Continuous driving frequency F _O = 7.2 kHz Liquid used: 75% water, 18% glycerin, A transparent liquid vehicle having a composition of 7% ethyl alcohol The maximum height of the air bubbles 13 to be formed; (measured by immersing only the heater 9 in the above vehicle) 52 μm × 240 μm (an elliptical or elliptical shape having a minor axis × major axis) ) × 50μm (height)

[0030]

[Table 1]

According to the results shown in Table 1, the resist layer 31
It can be seen that when the thickness t is smaller than 20 μm, the bubble 13 grows to the ceiling surface of the flow path 7 and sometimes shuts off the flow path 7 and stops the injection. If the thickness t of the resist layer 31 is smaller than 25 μm, the air is easily sucked from the liquid discharge unit 21 and the sucked air is
In some cases, the fuel may not be ejected by staying in the vicinity of the heater 9 inside the heater. On the other hand, when the thickness of the resist layer 31 is 25 μm or more, no air suction or flow path interruption occurs, and a good jetting condition is obtained. In addition, it has been found that the jet speed at this time is high, and very stable liquid ejection is performed. Further, when the thickness t is increased, when the resist layer 31 is formed by a spin coating method of a liquid resist, the upper limit of the thickness is 30 μm (the rotation speed of the spinner at this time is 500 rpm). Thus, when the resist layer 31 was formed from a dry film resist, the heater exposed portion 32 having the above-mentioned predetermined size could be formed with an opening up to a thickness t of 50 μm. However, when the thickness t is 50 μm, the pattern accuracy is slightly inferior to that when the thickness t is thinner. On the other hand, with respect to a thickness of 60 μm or more, the pattern of the heater exposed portion 32 itself could not be formed.

Incidentally, in forming the resist layer 31, a liquid resist and a dry film resist are selectively used for the following reason. That is, in the case of a liquid resist, although it depends on its viscosity, generally only a resist having a thickness of about 30 μm can be produced. However, the thickness can be freely changed only by changing the rotation speed of the spinner at the time of spin coating, so that it is very convenient to obtain a pattern having a desired thickness of 30 μm or less. By the way, the liquid resist used in this experiment: BMRS100
0 (viscosity: 1000 cp) indicates that the thickness of the resist layer 31 could be continuously changed from 30 to 5 μm by changing the rotation speed during spin coating from 500 to 4000 rpm.

Judging from the above results, the thickness t of the resist layer 31 is set to be equal to or more than half (here, 25 μm) of the maximum height of the generated bubbles 13 (here, 50 μm).
m or more and not more than the maximum height (here, 5
0 μm or less) is necessary for stable injection.

Further, according to the results shown in Table 1, it can be seen that when the resist layer 31 having such a heater exposed portion 32 is formed, the jet speed can be increased and the jet can be stabilized. This corresponds to the heater exposure portion 32 corresponding to the heater 9.
It is considered that this is because the propulsive force of the generated bubble 13 is efficiently reflected. Therefore, it is considered that it is desirable that such a heater exposed portion 32 be formed in a region as close to the heater 9 as possible. On the other hand, the surface temperature when the heater 9 is driven reaches 350 to 400 ° C. And the durability of the resist layer 31 becomes a problem.

Therefore, as the next experiment, the heater exposed portion 3
What size should we make 2?
In other words, how far the heater exposed portion 32 should be formed with respect to the heater 9 was examined, and the results are shown in Table 2. The head structure, head driving conditions, liquid used, and the like used in this experiment were the same as those in the experiment. However, the thickness t of the resist layer 31 is 30 μm,
The size of the heater exposed portion 32 is variously changed as shown in Table 2 as the opening size.

[0036]

[Table 2]

According to the results shown in Table 2, the heater exposed portion 3
As for the size of 2, if it is formed so as to be separated from the heater 9 by 2 μm or more, there is no problem in practical use, but if it is formed with an opening size smaller than this, it can be seen that it will be destroyed immediately. . On the other hand, if the opening size is too large, it can be seen that the jet velocity is reduced and the role of reflecting the propulsive force of the bubbles 13 at the heater exposed portion 32 is lost. Therefore, it can be said that the opening size is at least larger than the heater 9, but is preferably smaller than the size of the bubble 13 to be generated.

Incidentally, as the resist layer 31 of the present embodiment, it is preferable to use a negative type photoresist. That is, a photoresist is generally classified into a negative type and a positive type. As a developing solution, a solvent is used for a negative type, and an alkali solution is used for a positive type. Therefore, in general, the negative type has sufficient durability against an alkaline solution, while the positive type has a property that it is weak against an alkaline solution. Here, in the ink jet, in consideration of the corrosion resistance of various members in contact with the ink, the solubility of the dye, and the like, the ink is generally formulated to be more alkaline. Therefore, also in the present embodiment, it is preferable to form the resist layer 31 by using a negative type photoresist because it is excellent in corrosion resistance and the like.

[0039]

According to the first and second aspects of the present invention, a resin layer covering a heating element and the like is formed on a substrate, and a heating element exposed portion is formed in a region corresponding to the heating element in the resin layer. So
The bubble generation area substantially corresponding to the heating element is located one channel away from the flow path.
It is a stepped area, and it is possible to eliminate the inconvenience of sucking air from the discharge port and stopping the liquid injection by stopping the liquid injection by the air bubbles reaching the flow path ceiling surface. According to the invention described above, since the heating element exposed portion is formed in a shape substantially similar to the heating element, the stability of bubble generation can be enhanced, and the efficiency of the propulsion can be increased. In the present invention, since the heating element exposed portion is formed to be larger than the heating element area, the resin layer does not come into contact with the heating element, so that deterioration due to heat can be reduced.

According to the third aspect of the present invention, since the height of the resin layer is set to at least half of the maximum height of the generated bubbles, the driving force of the bubble growth can be effectively contributed to the liquid injection. As a result, it is possible to ensure a high jet speed and a stable jet.

According to the fourth aspect of the invention, since the height of the resin layer is equal to or less than the maximum height of the generated bubble, the opening pattern of the heating element exposed portion can be easily formed by the photolithography method.

According to the fifth aspect of the present invention, since the resin layer is formed of a liquid photoresist, it can be easily formed to a desired thickness.

According to the sixth aspect of the present invention, since the resin layer is formed of a dry film photoresist,
Even a resin layer thicker than μm can be easily formed.

According to the seventh aspect of the present invention, since a negative type photoresist is used as the photoresist, the photoresist has excellent corrosion resistance to an alkaline recording liquid.
A highly reliable head can be provided for a long period.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of the present invention.

FIG. 2 is a schematic perspective view showing the appearance of a heating element substrate.

FIG. 3 is an enlarged sectional view taken along line AA.

FIG. 4 is a schematic sectional view showing the principle of ink ejection in the order of processes.

FIG. 5 is an external perspective view of a head structure.

FIG. 6 is an exploded perspective view thereof.

FIG. 7 is a front view showing a head structure.

FIG. 8 is a sectional view taken along the line BB.

[Explanation of symbols]

 2 Substrate 7 Flow path 8 Liquid chamber 9 Heating element 10, 11 Electrode 12 Recording liquid 13 Bubbles 21 Discharge port 31 Resin layer 32 Heating element exposed portion

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/05 B41J 2/16

Claims (7)

(57) [Claims] A discharge port for ejecting a recording liquid; a flow path communicating with the discharge port; a liquid chamber communicating with the flow path and supplying the recording liquid to the flow path; In a thermal ink jet head including a heating element disposed in a part of a passage and configured to generate air bubbles in the passage, and an electrode for energizing the heating element, the heating element and the electrode are disposed on a substrate. It is formed as a planar pattern by photofabrication on it, and a resin layer of a constant thickness is formed on the substrate to cover these heating elements and electrodes. A thermal ink jet head characterized in that a heating element exposed portion having a shape substantially similar to the body is formed in an opening. A discharge port for ejecting the recording liquid, a flow path communicating with the discharge port, a liquid chamber communicating with the flow path and supplying the recording liquid to the flow path, In a thermal ink jet head including a heating element disposed in a part of a passage and configured to generate air bubbles in the passage, and an electrode for energizing the heating element, the heating element and the electrode are disposed on a substrate. It is formed as a planar pattern by photofabrication on it, and a resin layer of a constant thickness is formed on the substrate to cover these heating elements and electrodes. A thermal ink jet head, wherein a heating element exposed portion larger than a body area is formed in an opening. 3. The thermal ink jet head according to claim 1, wherein the fixed thickness of the resin layer is at least half of the maximum height of bubbles generated by the heating element. 4. A thermal ink jet head according to claim 1, wherein the fixed thickness of the resin layer is equal to or less than the maximum height of bubbles generated by the heating element. 5. The thermal ink jet head according to claim 1, wherein the resin layer is formed of a liquid photoresist. 6. The thermal ink jet head according to claim 1, wherein the resin layer is formed of a dry film photoresist. 7. The thermal ink jet head according to claim 5, wherein the photoresist is a negative photoresist.