Patent Application
20060114295
1. Field of the Invention
The present invention relates to a liquid discharge head for discharging liquid droplets such as ink droplets to record an image on a recording material, and a method of manufacturing the head, more particularly to a liquid discharge head which records an image in an ink jet recording system.
2. Related Background Art
An ink jet recording system is one of so-called non-impact recording systems. In this ink jet recording system, noises generated during the recording are so small that they can be ignored, and high-speed recording is possible. In the ink jet recording system, the recording is possible with respect to various recording materials, ink is fixed to even so-called plain paper without requiring any special treatment, and a high-definition image can be obtained inexpensively. From such advantage, in recent years, the ink jet recording system has rapidly spread as not only a printer which is a peripheral of a computer but also recording means such as a copying machine, a facsimile machine, or a word processor.
As an ink discharge method of the ink jet recording system, there is a method in which an electrothermal transducing element such as a heater is used as a discharge energy generating element for use in discharging ink droplets. A principle is that a voltage is applied to the electrothermal transducing element to thereby bring the ink in the vicinity of the electrothermal transducing element to boil momentarily. Bubbles rapidly grow owing to a phase change of the ink during the boiling to thereby discharge the ink droplets at a high speed.
In Japanese Patent Application Laid-Open No. 4-10941, a discharge method is disclosed in which bubbles generated by driving the electrothermal transducing element in response to a recording signal are vented to outside air. Examples of a typical constitution for venting the bubbles to the outside air include a constitution in which the shortest distance between the electrothermal transducing element and a discharge port is largely shortened as compared with a conventional constitution.
There is a demand for a further increase of a recording speed in order to achieve a higher image quality output of a recorded image, a high quality level image, a high resolution output and the like with respect to a recording device provided with the above-described liquid discharge head.
In U.S. Pat. No. 6,158,843, there is disclosed a constitution in which a space where an ink channel is locally narrowed or a protrusion-like fluid resistant element is disposed in the vicinity of a supply port to thereby improve a flow of ink from the supply port to a supply path. According to such constitution, a discharge frequency can be enhanced, and the recording speed can be increased.
Additionally, in the above-described conventional liquid discharge head, when the ink droplets are discharged, a part of the ink with which a bubbling chamber is filled is pushed back into the supply path by means of the bubbles growing in the bubbling chamber. Therefore, the conventional liquid discharge head has a disadvantage that a discharge amount of ink droplets decreases with a decrease of a volume of the ink in the bubbling chamber.
Moreover, in the conventional liquid discharge head, in a case where a part of the ink with which the bubbling chamber is filled is pushed back into the supply path, a part of a pressure of the growing bubbles opposed to the side of the supply path escapes toward the supply path, or a pressure loss is generated by friction between an inner wall of the bubbling chamber and the bubbles. Therefore, the conventional liquid discharge head has a problem that a discharge speed of the ink droplets drops with a decrease of the pressure of the bubbles.
Furthermore, in the conventional liquid discharge head, a size of the discharge port is miniaturized in order to obtain the higher image quality output, higher quality level image, higher resolution output and the like. Therefore, there is a problem that the charged ink is easily secured to the discharge port. The conventional liquid discharge head also has a problem that the ink charged up to the discharge port is evaporated by an atmosphere in atmospheric air on the surface of the discharge port, viscosity of the ink fluctuates, and discharge defects are generated.
An object of the present invention is to provide a liquid discharge head which can increase a discharge speed of liquid droplets, stabilize a discharge amount of the liquid droplets, and enhance a discharge efficiency of the liquid droplets, and a method of manufacturing the head.
To achieve the above-described object, according to the present invention, there is provided a liquid discharge head comprising: a discharge energy generating element which generates energy for discharging liquid droplets; an element substrate on which the discharge energy generating element is disposed; and an orifice substrate having a nozzle for discharging the liquid droplets and a supply chamber for supplying a liquid to the nozzle and bonded to a main surface of the element substrate. The nozzle has a discharge port to discharge the liquid droplets, a bubbling chamber in which bubbles are generated by the discharge energy generating element, and a supply path for supplying the liquid to this bubbling chamber. The bubbling chamber has: a first bubbling chamber which is connected to the supply path while the main surface of the element substrate is a bottom surface and in which the bubbles are generated in the liquid by the discharge energy generating element; and a second bubbling chamber connected to the first bubbling chamber. Moreover, the nozzle has a discharge port portion including the discharge port connected to the second bubbling chamber. Assuming that an average sectional area of the first bubbling chamber is S1, an average sectional area of the second bubbling chamber is S2, and an average sectional area of the discharge port portion is S3 in a section parallel to the main surface of the element substrate, the nozzle satisfies a relation of S2>S1>S3.
As described above, according to the liquid discharge head of the present invention, since the average sectional area of the second bubbling chamber is set to be larger than that of the first bubbling chamber, the liquid is inhibited from being evaporated on the surface of the discharge port, and discharge impossibility due to thickening of the liquid can be avoided to enhance stability of a discharge operation. Furthermore, according to the present invention, it is possible to enhance a degree of freedom of a component or viscosity of a liquid for use, and printing with a more satisfactory quality level is possible. Consequently, it is possible to enhance liquid discharge characteristics and enhance reliability of the discharge operation.
There will be described hereinafter typical embodiments of a liquid discharge head which discharges droplets of a liquid such as ink according to the present invention in detail with reference to the drawings.
First, an outline of the liquid discharge head will be described according to the present embodiment. In the present embodiment, the liquid discharge head is an ink jet recording head which is provided with means for generating heat energy as energy for use in discharging liquid ink and in which a system is adopted to cause a state change of the ink by the heat energy. In the present embodiment, heat generating resistant element is used as the means for generating the heat energy, and the ink is discharged utilizing a pressure due to bubbles generated when the ink is heated by the heat generating resistant element to boil a film.
As described later in detail, the liquid discharge head has a constitution in which a partition wall for individually and independently forming nozzles as ink channels is extended from a discharge port to the vicinity of a supply port in each of a plurality of heaters as the heat generating resistant elements. Such liquid discharge head has ink discharge means to which an ink jet recording system is applied as disclosed in, for example, Japanese Patent Application Laid-Open Nos. H04-10940 and H04-10941, and the bubbles generated during the discharging of the ink are vented to outside air through the discharge port.
Moreover, as shown in
In each of the first and second nozzle rows 16 and 17, an interval between the adjacent nozzles is set to a pitch of 600 dpi. The second and first nozzle rows 17 and 16 are arranged in such a manner that the pitch between the adjacent nozzles of the second nozzle row dethroughtes by a ½ pitch from that between the adjacent nozzles of the first nozzle row.
Moreover, the first and second nozzle rows 16 and 17 are constituted in such a manner that discharge amounts of ink droplets discharged from the discharge ports differ from each other. The first nozzle row 16 is different from the second nozzle row 17 in an opening area of each discharge port and an area of the heater parallel to a main surface of the element substrate described later. Furthermore, the first and second nozzle rows 16 and 17 are formed so as to have an equal shortest distance between the heater and the discharge port.
Here, there will be briefly described a concept to optimize the liquid discharge head provided with the first and second nozzle rows 16 and 17 in which a plurality of heaters and nozzles are arranged with a high density.
In general, as physical amounts that influence discharge characteristics of the liquid discharge head, an inertance (inertia force) and a resistance (viscosity resistance) in the plurality of nozzles largely act. Dynamic equations of a non-compressive fluid which moves in a channel having an arbitrary shape are represented by the following two equations:
Δ·v=0 (equation of continuity Equation 1;
and
(∂v/∂t)+(v·Δ)v=−Δ(P/ρ)+(μ/ρ)Δ2v+f (Navier Stokes equation) Equation 2.
When Equations 1 and 2 are approximated assuming that a convection term and a viscosity term are sufficiently small and there is not any external force, the following equation results:
Δ2P=0 Equation 3, and
a pressure is represented using a harmonic function.
Moreover, the liquid discharge head is represented by a three-opening model shown in
The inertance is defined as “difficulty in moving” at a time when a static fluid rapidly starts moving. When the inertance is electrically represented, it has a function similar to that of inductance L which obstructs a change of a current. A mechanical spring mass model corresponds to a weight (mass).
When the inertance is represented by an equation, it is represented by a two-stage time differential of a fluid volume V at a time when a pressure difference is imparted to an opening, that is, a ratio of a flow rate F (=ΔV/Δt) to a time differential.
(Δ2V/Δt2)=(ΔF/Δt)=(1/A)×P Equation 4,
wherein A: inertance.
For example, assuming a pipe channel having a density ρ, a length L, and a sectional area S0 in a pseudo manner, an inertance A0 of this pseudo one-dimensional pipe channel is represented by:
A0=ρ×L/S0.
It is seen that the inertance is proportional to the length of the channel, and inversely proportional to the sectional area.
The discharge characteristics of the liquid discharge head can be predicted and analyzed as a model based on the equivalent circuit shown in
In the liquid discharge head of the present invention, a discharge phenomenon is regarded as a phenomenon in which an inertial flow shifts to a viscous flow. In an initial stage of bubbling in the bubbling chamber by the heater, the inertial current is principal. Conversely, in a later stage of the discharging (i.e., a time from a time when a meniscus generated in the discharge port starts moving toward the ink channel until the ink is charged up to an opening end surface of the discharge port and returned by a capillary phenomenon), the viscous flow is principal. In this case, from the above-described relational equation, there is a large contribution to the discharge characteristics, especially a discharge volume and a discharge speed owing to a relation between the inertance amounts in the initial stage of the bubbling. In the later stage of the discharging, a resistance (viscosity resistance) amount largely contributes to the discharge characteristics, especially a time required for refilling the ink (hereinafter referred to as the refill time).
Here, the resistance (viscosity resistance) is represented by Equation 1 and a constant Stokes flow represented by the following equation:
ΔP=ηΔ2μ Equation 5.
A viscosity resistance B can be obtained. In the later stage of the discharging, in a model shown in
That is, the resistance can be obtained by a poiseuille equation 6 in which a viscous fluid is described:
(ΔV/Δt)=(1/G)×(1/η){(ΔP/Δx)×S(x)} Equation 6,
wherein G: shape factor. Since the viscosity resistance B is attributable to the fluid flowing in accordance with an arbitrary pressure difference, the resistance is obtained by:
B=∫0L{(G×η)/S(x)}Δx Equation 7.
According to Equation 7, assuming the pipe channel having the density ρ, length L, and sectional area S0, the resistance (viscosity resistance) is represented by:
B=8η×L/(π×S02) Equation 8.
The resistance is approximately proportional to the length of the nozzle, and inversely proportional to a square of the sectional area of the nozzle.
To enhance all of the discharge characteristics of the liquid discharge head, especially the discharge speed, discharge volume of the ink droplets, and refill time, the followings are necessary and sufficient conditions from the inertance relation. The conditions are that the inertance amount from the heater toward the discharge port is set to be as large as possible as compared with the inertance amount from the heater toward the supply port, and the resistance in the nozzle is reduced. The liquid discharge head according to the present invention can satisfy both of the above-described viewpoint and a proposition to arrange the plurality of heaters and nozzles with the high density.
Next, there will be described a typical constitution of the liquid discharge head according to the present embodiment with reference to the drawings.
As shown in
The element substrate 11 is formed of, for example, glass, ceramic, resin, metal or the like, and is generally formed of Si.
On the main surface of the element substrate 11, there are arranged: the heater 20 disposed for each ink channel; an electrode (not shown) which applies a voltage to the heater 20; and a wiring line (not shown) constituting a predetermined wiring line pattern electrically connected to the electrode. It is to be noted that, for example, a piezoelectric element (not shown) may be used instead of the heater 20. When the voltage is applied to the piezoelectric element, the piezoelectric element is displaced, and the ink droplets are discharged by a pressure generated by this displacement.
Moreover, on the main surface of the element substrate 11, an insulating film (not shown) to enhance a diffusing property of accumulated heat is disposed to cover the heater 20. Further on the main surface of the element substrate 11, a protective film (not shown) for protecting the main surface from cavitation generated at a time when the bubbles disappear is disposed to cover the insulating film.
The orifice substrate 12 is formed of a resin material into a thickness of about 20 to 75 μm. As shown in
Moreover, the element substrate 11 is provided with a supply chamber 18 having a supply port 19 for supplying the ink to each nozzle 27 from a back-surface side of the main surface of the element substrate adjacent to the orifice substrate 12.
Each nozzle 27 has: a discharge port portion 25 including the discharge port 26; a first bubbling chamber 29 in which bubbles are generated in the ink by the heater 20; a second bubbling chamber 30 which connects the discharge port portion 25 to the first bubbling chamber 29; and a supply path 28 for supplying the ink to the first bubbling chamber 29.
Furthermore, as shown in
Each discharge port portion 25 is connected to an opening in an upper end surface of the second bubbling chamber 30, and a stepped portion is formed between a side wall surface of the discharge port portion 25 and that of the second bubbling chamber 30.
Each discharge port 26 of the discharge port portion 25 is formed in a position facing the heater 20 disposed on the element substrate 11. In the present embodiment, the discharge port 26 is formed into a round hole having a diameter of, for example, about 7 μm. It is to be noted that the discharge port 26 may be formed into a substantially radiating star shape if necessary for the discharge characteristics.
As shown in
In general, in a case where the bubbling chamber is formed by etching, when the tilt angle θ2 is in a range of 10° to 45°, the side wall surface can be inclined to form the chamber easily. Moreover, since the side wall surface is inclined in this range, the ink can satisfactorily flow toward the discharge port 26 in the nozzle 27, pressure losses of the bubbles are reduced, and a discharge speed can be enhanced.
In the above-described constitution of the nozzle 27, the side wall surface of the first bubbling chamber 29 and the wall surface of the discharge port portion 25 are formed in parallel with a direction crossing the main surface of the heater 20 at right angles, and the only side wall surface of the second bubbling chamber 30 is inclined at the tilt angle θ2. The side wall surface of the first bubbling chamber 29 and the wall surface of the discharge port portion 25 may be inclined at a desired tilt angle in the same manner as in the side wall surface of the second bubbling chamber 30.
As another constitution of the nozzle 27, there will be described hereinafter a constitution in which the side wall surface of the first bubbling chamber 29 and the wall surface of the discharge port portion 25 are inclined. It is to be noted that in the other constitution of the nozzle 27, even bubbling chambers and discharge port portions having different shapes are denoted with the same reference numerals as those of the above-described constitution for the sake of convenience.
In the other constitution of the nozzle 27, as shown in
Moreover, in at least a part of the supply path 28, the side wall surface of the supply path 28 is similarly in a range of a tilt angle of 10° to 45°, and a sectional area of a section parallel to the main surface of the element substrate 11 is reduced toward the surface of the orifice substrate 12 positioned on the side of the discharge port 26. In other words, in at least a part of the supply path 28, a width of the supply path 28 on the plane crossing an ink flow direction at right angles is changed along a thickness direction of the orifice substrate 12.
In still another constitution of the nozzle 27, as shown in
Moreover, an average sectional area of the section of the second bubbling chamber 30 parallel to the main surface of the element substrate 11 is set to be larger than that of the first bubbling chamber 29, and a stepped shape is formed in a portion which connects the first bubbling chamber 29 to the second bubbling chamber 30. Furthermore, an average sectional area of the section of the first bubbling chamber 29 parallel to the main surface of the element substrate 11 is set to be larger than that of the discharge port 26, and a stepped shape is formed in a portion which connects the discharge port 26 to the second bubbling chamber 30.
That is, in the section of the nozzle 27 parallel to the main surface of the element substrate 11, an average sectional area S1 of the first bubbling chamber 29, an average sectional area S2 of the second bubbling chamber 30, and an average sectional area S3 of the discharge port portion 25 are formed into such a structure as to satisfy a relation of S2>S1>S3.
Moreover, the first bubbling chamber 29 is connected to the second bubbling chamber 30 through the stepped portion. In the section parallel to the main surface of the element substrate 11, the sectional area of the second bubbling chamber 30 is set to be larger than that of the first bubbling chamber 29. The second bubbling chamber 30 is connected to the discharge port 26 through the stepped portion. In the section parallel to the main surface of the element substrate 11, the sectional area of the second bubbling chamber 30 is set to be larger than that of the discharge port 26.
Moreover, the first bubbling chamber 29 is disposed along an extension of the supply path 28, and a bottom surface of the first bubbling chamber facing the discharge port 26 is formed into a substantially rectangular shape.
Here, the nozzle 27 is formed in such a manner that the shortest distance OH between the discharge port 26 and the main surface of the heater 20 parallel to the main surface of the element substrate 11 is 75 μm or less.
In the nozzle 27, the upper end surface of the first bubbling chamber 29 parallel to the main surface of the heater 20 continues to that of the supply path 28 adjacent to the first bubbling chamber 29 and parallel to the main surface on the same plane up to the supply port 19.
One end of the supply path 28 is connected to the first bubbling chamber 29, and the other end thereof is connected to the supply chamber 18. A height of the supply path 28 from the main surface of the element substrate 11 is set to be equal to or less than that to the upper end surface of the second bubbling chamber 30.
Moreover, as shown in
Furthermore, in the supply chamber 18, a columnar nozzle filter (not shown) for filtering and removing dust in the ink stands ranging from the element substrate 11 to the orifice substrate 12 in a position adjacent to the supply port 19 for each nozzle 27. This nozzle filter is disposed in a position distant from the supply port 19 by, for example, about 20 μm. An interval between the nozzle filters in the supply chamber 18 is set to, for example, about 10 μm. This nozzle filter prevents the supply path 28 and the discharge port 26 from being clogged with the dust, and a satisfactory discharge operation is secured.
Next, there will be described an operation of the liquid discharge head to discharge the ink droplets from the discharge ports 26.
First, in the liquid discharge head, the ink supplied into the supply chamber 18 is supplied from the supply port 19 to the respective nozzles 27 of the first and second nozzle rows 16 and 17. The ink supplied from each nozzle 27 flows along the supply path 28 to fill the first bubbling chamber 29. The ink charged in the first bubbling chamber 29 is flied in a direction crossing the main surface of the element substrate 11 substantially at right angles by a bubble growth pressure generated by film boiling by the heater 20. The ink is discharged as the ink droplets from the discharge port 26 of the discharge port portion 25.
A method of manufacturing the liquid discharge head constituted as described above will be briefly described with reference to
As shown in
A second step is a step of pattern-forming the second bubbling chamber 30 and the first bubbling chamber 29 into the above-described characteristic shapes of the present invention. As shown in
Next, as shown in
A third step is a step of forming the discharge ports 26 in the orifice substrate 12. As shown in
A fourth step is a step of forming each nozzle 27 containing a channel from the supply port 19 to the discharge port 26. The whole surface of the orifice substrate 12 is coated with cyclized isoprene in order to protect the surface from an alkali solution. Subsequently, as shown in
Thereafter, the whole surface of the orifice substrate 12 is irradiated with an ionizing radiation having a wavelength which is not more than 330 nm by use of a low-pressure mercury lamp to cause a decomposing reaction between the first positive resist 13 containing PMIPK as the main component and the second positive resist 14 containing PMMA as the main component. Subsequently, the whole element substrate 11 is immerged into methyl lactate, and the respective resists 13 and 14 are collectively removed.
Finally, the epoxy resin 21 constituting the orifice substrate 12 is heated at about 200° C., and completely cured in the oven to thereby prepare the liquid discharge head as shown in
As described above, in the liquid discharge head of the present embodiment, the height, width, or sectional area of the channel changes in the nozzle 27. Moreover, a volume of the ink increases once in the second bubbling chamber 30 along a direction from the main surface of the element substrate 11 to the discharge port 26. Moreover, the vicinity of the discharge port 26 is constituted in such a manner that the discharged ink droplets are discharged in a direction perpendicular to the main surface of the element substrate 11 in a case where the ink droplets are discharged.
According to the liquid discharge head of the present embodiment, since the average sectional area S2 of the second bubbling chamber 30 is larger than that of the average sectional area S1 of the first bubbling chamber 29, the ink is inhibited from being evaporated on the surface of the discharge port 26, discharge impossibility by thickening of the ink is avoided, and stability of the discharge operation can be enhanced. Furthermore, according to the liquid discharge head, a degree of freedom of the component or the viscosity of the ink for use can be enhanced, and recording (printing) with a more satisfactory quality level can be performed. Consequently, the discharge characteristics, and reliability of the discharge operation can be enhanced.
It is to be noted that although not shown, a part of the upper surface of the supply path 28 parallel to the main surface of the element substrate 11 is set to be higher than the upper surface of the supply path 28 which continues to the upper end surface of the first bubbling chamber 29 in the same plane, and connected to the upper surface through the stepped portion. Here, a maximum height from the main surface of the element substrate 11 of the supply path 28 may be set to be lower than the height from the main surface of the element substrate 11 to the upper end surface of the second bubbling chamber 30.
Moreover, a sum of volumes of the first bubbling chamber 29, the second bubbling chamber 30, and the discharge port 26 may be smaller than the volume of the supply path 28.
Embodiments will be described hereinafter. Since a basic constitution of each example is similar to that of the above-described embodiment, a constitution different from that of the embodiment will be described.
The above-described liquid discharge head has a structure in which the bubbles generated by heating the heaters 20 communicate with the outside air through the discharge ports 26 as representatively shown in
Therefore, according to the liquid discharge head of the present example, an image having a high quality level can be recorded without any ink unevenness. It is to be noted that in the liquid discharge head of Example 1, the shortest distance OH between the main surface of the heater 20 and the discharge port 26 is set to 30 μm or less in order to vent the bubbles to the outside air. As described above, when the volume of the second bubbling chamber 30 is set to be comparatively large, the liquid discharge head can fly the ink droplets with a stable discharge amount.
In a liquid discharge head of the present example, as shown in a structure of
In a case where the discharge port portion 25 is formed into an elongated cylindrical shape, the ink is usually easily secured by evaporation. However, according to the liquid discharge head of the present example, it is possible to record an image without any discharge defect in the same manner as in Example 1. As described above, according to the liquid discharge head, when the average sectional area S2 of the second bubbling chamber 30 is set to be large, the ink droplets can be flied with a stable discharge amount.
In the liquid discharge head of the present example, as shown in representative structures of
This application claims priority from Japanese Patent Application No. 2004-348614 filed Dec. 1, 2004, which is hereby incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-348614 | Dec 2004 | JP | national |
