JP4055883B2 - Droplet discharge head - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a droplet discharge head.
[0002]
[Prior art]
In general, an inkjet head, which is a droplet ejection head in an inkjet recording apparatus used in an image recording apparatus (including an image forming apparatus) such as a printer, a facsimile machine, a copying apparatus, or a plotter, is a nozzle plate having nozzles that eject ink drops. A flow path substrate having a discharge chamber (also referred to as an ink flow path, an ink chamber, a pressure chamber, a pressurizing chamber, a pressurized liquid chamber, etc.) that communicates with the nozzle, and a pressure for pressurizing the ink in the discharge chamber Generating means, and driving the pressure generating means to pressurize the ink in the discharge chamber to discharge droplets from the nozzles.
[0003]
As a conventional inkjet head, a piezoelectric type that discharges ink droplets by deforming and displacing a diaphragm that forms the wall surface of the discharge chamber using a piezoelectric element, and a heating resistor disposed in the discharge chamber are used. A bubble type that generates bubbles by boiling the ink film and ejects ink droplets, and a diaphragm that forms the wall surface of the ejection chamber (or an electrode integrated with it) and electrodes are used to deform the diaphragm with electrostatic force There is an electrostatic type that discharges ink droplets by being displaced.
[0004]
In such an ink jet head, materials such as plastic, ceramic, and glass have been used as members for forming the discharge chamber. However, these materials sufficiently meet the demand for high definition and high accuracy. Therefore, various techniques for etching a silicon wafer to form a flow path member have been disclosed.
[0005]
For example, in Japanese Patent Application Laid-Open No. 11-993, as shown in FIG. 8, a silicon substrate having a crystal plane orientation (110) is used for the flow path substrate 101, and the discharge chamber 102 and the discharge chamber 102 are connected to the flow path substrate 101. In this case, a common liquid chamber 104 for supplying ink via the ink supply path 103 is disclosed. In this case, the (111) plane is perpendicular to the (110) plane of the surface. The wall surface to be the spacing wall can be formed by a vertical wall.
[0006]
[Problems to be solved by the invention]
However, even if a silicon substrate having a (110) plane is used as in the conventional inkjet head described above, the (111) planes in the silicon crystal are not orthogonal to each other and have a certain angle with each other. A portion 105 having an acute angle is generated in the discharge chamber as shown in FIG.
[0007]
Here, in an inkjet head that uses pressure generated by deforming and displacing the diaphragm forming the wall surface of the discharge chamber, the generated pressure strongly depends on the compliance of the discharge chamber. For this reason, if bubbles remain in the discharge chamber when ink is filled, the generated pressure will decrease rapidly and the ejection characteristics will become abnormal. Therefore, bubble ejection is extremely important for ensuring stable ink droplet ejection characteristics. It is.
[0008]
However, since the portion 105 on the ink supply path 103 side has an acute angle in the direction opposite to the ink flow as in the conventional ink jet head described above, there is a problem that bubbles accumulate in this portion 105.
[0009]
The present invention has been made in view of the above points, and an object of the present invention is to provide a droplet discharge head capable of improving bubble discharge performance and obtaining stable ink droplet ejection characteristics.
[0010]
[Means for Solving the Problems]
To solve the above problems, the liquid drop discharge head of the present invention, the discharge chamber of a nozzle for discharging droplets are communicated to form a recess closed on the main plane of the substrate, the ink for supplying ink to the discharge chamber In the droplet discharge head in which the member forming the supply path is bonded to the main plane of the substrate and the ink flow path is formed, the discharge chambers are parallel to each other in a direction substantially perpendicular to the nozzle row direction and to the main plane. a first face and a second face perpendicular Te, located in Lee ink supply path side of the discharge chamber, a third surface perpendicular to and the main plane in contact with the first surface, and a and a main plane contact with the second surface and a sharp fourth surface to the discharge chamber side against, is formed in addition third and fourth surfaces and first vertex primary and plane contact deviates from the first surface and the second surface position, the One apex is configured to be positioned in the ink supply path in a planar perspective state.
[0011]
Here, it is preferable that the center position of the ink supply path is offset from the center position between the first surface and the second surface toward the second surface. In this case, it is preferable that the second surface and the ink supply path are not in contact with each other and are separated by 1 μm or more. Furthermore, it is preferable that the member in which the ink supply path is formed is a nozzle plate or a lid member in which nozzles are formed. Furthermore, a common liquid chamber for supplying ink to the discharge chamber via the ink supply path is formed on the silicon substrate, and a surface of the wall surface of the common liquid chamber that is in contact with the ink supply path is a surface perpendicular to the main plane. It is preferable. The substrate may be a silicon substrate having a ( 110 ) plane as the main plane, and the first surface and the fourth surface may each be composed of (111) planes.
[0012]
Each of these droplet discharge heads includes a diaphragm that forms the wall surface of the discharge chamber and an electrode that faces the diaphragm, and is a static discharge device that deforms and displaces the diaphragm with an electrostatic force to discharge droplets. It can be an electric head.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an exploded perspective view of an ink jet head that is a droplet discharge head according to the present invention, FIG. 2 is a cross-sectional view of the head in the longitudinal direction of the diaphragm, and FIG. It is an expanded sectional view.
[0014]
The inkjet head includes a flow path substrate 1 that is a first substrate using a single crystal silicon substrate having a main plane having a (110) plane orientation, and a silicon substrate or pyrex glass provided below the flow path substrate 1. A plurality of nozzles 4 each including an electrode substrate 2 that is a second substrate using a substrate or a ceramic substrate, and a nozzle plate 3 that is a third substrate provided on the upper side of the flow path substrate 1, each ejecting ink droplets, A discharge chamber 6 that is an ink flow path communicating with the nozzle 4, a common liquid chamber 8 that communicates with each discharge chamber 6 via a fluid resistance portion 7 that also serves as an ink supply path, and the like are formed.
[0015]
The flow path substrate 1 is formed with a plurality of discharge chambers 6 with which the nozzles 4 communicate with each other and concave portions that form a vibration plate 10 (also serving as an electrode) that forms the bottom of the wall of the discharge chamber 6. Forms a hole for forming the nozzle 4 and a groove for forming the fluid resistance portion 7, and a through-hole for forming the common liquid chamber 8 is formed in the flow path substrate 1 and the electrode substrate 2.
[0016]
Here, the flow path substrate 1 forms a high-concentration boron layer serving as an etching stop layer by previously injecting a high-concentration P-type impurity, for example, high-concentration boron, into the vibration plate thickness into a silicon substrate having a (110) plane. After bonding to the electrode substrate 2, the concave portion that becomes the discharge chamber 6 is anisotropically etched using an etching solution such as a KOH aqueous solution, so that the high-concentration boron layer at this time becomes an etching stop layer. The diaphragm 10 is formed with high accuracy.
[0017]
In addition, an electrode film serving as a first electrode may be separately formed on the vibration plate 10, but as described above, the vibration plate also serves as an electrode by diffusion of impurities or the like. An insulating film can also be formed on the surface of the vibration plate 10 on the electrode substrate 2 side. As this insulating film, an oxide film insulating film such as SiO ₂ , a nitride film insulating film such as Si ₃ N _4, or the like can be used. The insulating film can be formed by thermally oxidizing the vibration plate surface to form an oxide film or using a film forming method.
[0018]
Further, a p-type or n-type single crystal silicon substrate is used as the electrode substrate 2, an oxide layer 2 a is formed by a thermal oxidation method or the like, a recess 14 is formed in the oxide layer 2 a, and the bottom of the recess 14 is formed. An electrode 15 facing the diaphragm 10 is provided, a gap 16 is formed between the diaphragm 10 and the electrode 15, and the diaphragm 10 and the electrode 15 constitute an actuator portion (pressure generating means). At this time, the depth of the recess 14 defines the length of the gap 16. Further, pyrex glass (borosilicate glass) can be used for the electrode substrate 2, and in this case, since it has insulating properties, the recess 14 is formed as it is. Similarly, a ceramic substrate can be used as the electrode substrate 2.
[0019]
A dielectric insulating film 17 made of an oxide film insulating film such as a SiO ₂ film and a nitride film insulating film such as a Si ₃ N ₄ film is formed on the surface of the electrode 15. As described above, the insulating film 17 can be formed on the vibration plate 10 side without forming the insulating film 17 on the surface of the electrode 15. In addition, as the electrode 15 of the electrode substrate 2, gold, a metal material such as Al, Cr, or Ni generally used in a process of forming a semiconductor element, a refractory metal such as Ti, TiN, or W, or A polycrystalline silicon material whose resistance is reduced by an impurity can be used.
[0020]
The flow path substrate 1 and the electrode substrate 2 can be joined by direct joining when the flow path substrate 1 and the electrode substrate 2 are both formed of a silicon substrate. This direct bonding is performed at a high temperature of about 1000 ° C. Alternatively, the electrode substrate 2 can be formed of silicon and anodic bonding can be performed. In this case, Pyrex glass is formed between the electrode substrate 2 and the flow path substrate 1, and the anode is interposed through this film. Bonding can also be performed. Furthermore, the flow path substrate 1 and the electrode substrate 2 can be bonded by eutectic bonding using a silicon substrate and a binder such as gold interposed on the bonding surface.
[0021]
The flow path substrate 1 and the electrode substrate 2 can be joined by anodic bonding when the flow path substrate 1 is formed of a silicon substrate and the electrode substrate 2 is formed of Pyrex glass. In anodic bonding, precise bonding can be performed at a relatively low temperature (300 ° C. to 400 ° C.) by applying a voltage (about −300 V to −500 V) between the substrates.
[0022]
In order to reliably perform such anodic bonding, either the flow path substrate (first substrate) 1 or the electrode substrate (second substrate) 2 so that the substrates are covalently bonded at the bonding interface of the substrates. Must be a substrate containing a large amount of alkali ions, and when bonding, a material whose thermal expansion coefficients of the substrates are relatively the same is selected so that distortion between the substrates due to thermal stress is reduced. It is preferable. Therefore, a single crystal silicon substrate is used for the flow path substrate 1 and a Pyrex glass (borosilicate glass) substrate containing a large amount of alkali ions such as Na for the electrode substrate 2 and having a relatively high thermal expansion coefficient with the silicon substrate. By using, reliable joining with less thermal distortion between the substrates can be obtained.
[0023]
In the nozzle plate 3, a large number of nozzles 4 are formed, and a groove portion for forming a fluid resistance portion 7 for communicating the common liquid chamber 8 and the discharge chamber 6 is formed. Here, a water-repellent film is formed on the ink ejection surface (the nozzle 4 surface side). This nozzle plate 3 uses a stainless steel substrate (SUS). In addition to this, a nickel plated film by electroforming (electroforming) method, excimer laser processing on a resin such as polyimide, or metal plate by press working It can also use what carried out the hole processing.
[0024]
The water-repellent film can be formed by a plating film by electrolytic or electroless nickel eutectoid plating (PTFE-Ni eutectoid plating) in which polytetrafluoroethylene fine particles, which are fluororesin fine particles, are dispersed.
[0025]
In this inkjet head, two rows of nozzles 4 are arranged, and two rows of discharge chambers 6, diaphragms 10, electrodes 15, etc. are arranged corresponding to each nozzle 4, and are arranged at the center of each nozzle row (head central portion). A configuration is adopted in which the common liquid chamber 8 is arranged and ink is distributed and supplied from the common liquid chamber 8 to the left and right ejection chambers 6. Accordingly, the ink supply to each discharge chamber 6 can be evenly distributed, and even when the discharge state of each discharge chamber is hardly received, uniform ink droplet discharge characteristics can be ensured. A multi-nozzle head having a number of nozzles 4 in the head configuration can be configured. The ejection density of the head defined by the arrangement density of the nozzles 4 is 300 dpi.
[0026]
The electrode 15 is extended to the outside to form a connection portion (electrode pad portion) 15a, and an FPC cable on which a driver IC as a head drive circuit is mounted by wire bonding is connected via an anisotropic conductive film or the like. ing.
[0027]
In the ink jet head configured as described above, the diaphragm 10 is used as a common electrode, the electrode 15 is used as an individual electrode, and a drive waveform is applied between the diaphragm 10 and the electrode 15, whereby the diaphragm 10 and the electrode 15 are separated. An electrostatic force (electrostatic attractive force) is generated in the meantime, and the diaphragm 10 is deformed and displaced toward the electrode 15. As a result, the internal volume of the discharge chamber 6 is expanded and the internal pressure is lowered, so that the discharge chamber 6 is filled with ink from the common liquid chamber 8 via the fluid resistance portion 7.
[0028]
Next, when the voltage application to the electrode 15 is cut off, the electrostatic force stops working, and the diaphragm 10 is restored by its own elasticity. With this operation, the internal pressure of the discharge chamber 6 increases, and ink droplets are discharged from the nozzles 4. When a voltage is applied to the electrode again, the diaphragm is again pulled toward the electrode by electrostatic attraction.
[0029]
Next, the configuration of the liquid chamber of the flow path substrate 1 in this inkjet head will be described with reference to FIG. In addition, the same figure is plane explanatory drawing of the state which saw through the nozzle plate.
As described above, the flow path substrate 1 is wet-etched with an alkaline etchant having a high etching selectivity with respect to the (111) plane, using a silicon substrate having a main plane having a (110) plane orientation as described above. A recess for forming the discharge chamber 6 is formed, and among the wall surfaces of the discharge chamber 6 (actually a recess), a surface other than the surface of the diaphragm 10 and the surface joined to the nozzle plate 3 is defined as the (111) surface. It is formed with.
[0030]
That is, the first surface 31, the second surface 32, the third surface 33, and the fourth surface 34 that are the wall surfaces of the discharge chamber 6 are all (111) surfaces, and the first surface 31 and the second surface 32 are The third surfaces 33 are parallel to each other in a direction substantially perpendicular to the nozzle row direction and perpendicular to the main plane 30, and the third surface 33 is located on the ink supply path 7 side and is on the first surface 31. The fourth surface 34 is in contact with and perpendicular to the main plane 30. The fourth surface 34 is in contact with the second surface 32 and is an acute angle surface inside the discharge chamber 6 with respect to the main plane 30. The first vertex 35 where the surface 33, the fourth surface 34 and the main plane 30 are in contact with each other is formed at a position deviated from the first surface 31 and the second surface 32, and the first vertex 35 is in a plane see-through state (state shown). In the ink supply path 7.
[0031]
With such a configuration, there is no sharp corner at the portion deviating from the ink flow line from the ink supply path 7 toward the nozzle 4, the bubble discharge performance is improved, and the stability of the ejection characteristics is improved.
[0032]
Here, the ejection is performed such that the center line S1 along the longitudinal direction of the diaphragm of the ink supply path 7 is offset toward the second surface 32 side with respect to the center line S2 along the longitudinal direction of the diaphragm of the ejection chamber 6. A chamber 6 and an ink supply path 7 are formed.
[0033]
Therefore, the ink supply path 7 comes into contact with the fourth surface 34 having a forward taper angle more than the third surface 33 perpendicular to the ink flow. Thereby, the flow of ink becomes smooth, and the bubble discharge property is further improved.
[0034]
The distance D between the ink supply path 7 and the second surface 55 is 1 μm or more. As a result, variations in ink droplet volume can be reduced and stable ink droplet ejection characteristics can be obtained.
[0035]
That is, in order to perform the most accurate alignment for joining the nozzle plate 3 and the flow path substrate 1 made of a silicon substrate, the positions of the nozzle plate 3 and the flow path substrate 1 are optically read. Based on the result, the nozzle plate 3 and the flow path substrate 1 are positioned and joined. In this case, in principle, the reading position accuracy is about a wavelength, and the wavelength of visible light that is normally used is about 0.5 μm, and this variation in positioning between the ink supply path 7 and the discharge chamber 6 is allowed. There must be.
[0036]
Further, positional displacement between the ink supply path 7 and the discharge chamber 6 also occurs due to curing shrinkage of the adhesive used when the nozzle plate 3 and the flow path substrate 1 are joined. FIG. 5 shows an example of the measurement result of the relationship between the distance D between the ink supply path 7 and the second surface 32 and the variation in the drop volume of the head. From this figure, the distance between the ink supply path 7 and the second surface 32 is shown. It can be seen that when D is less than 1 μm, the variation in droplet volume increases rapidly. This is because the ink supply path 7 runs on the second surface 32 due to the pattern shift, and the fluid resistance value of this portion changes accordingly.
[0037]
Therefore, by ensuring that the distance D between the ink supply path 7 and the second surface 55 is 1 μm or more, even if the above-described variation due to positioning or due to the curing shrinkage of the adhesive occurs, the ink supply path 7 and the second surface 55 are separated from each other. It is possible to prevent the fluid resistance value from fluctuating due to overlapping with the surface 32.
[0038]
Next, the common liquid chamber 8 side will be described with reference to FIGS. 7 and 8 are cross-sectional explanatory views taken along line AA in FIG.
The surface 36 on the common liquid chamber 8 side that is in contact with the ink supply path 7 is formed only by a surface perpendicular to the main plane 30.
[0039]
Therefore, as shown in FIG. 7, the ink flow 41 when ink is supplied from the common liquid chamber 8 to the discharge chamber 6 via the ink supply path 7 is such that the fourth surface 34 of the discharge chamber 6 has a forward tapered shape. Therefore, the separation flow is suppressed in the ink flow at the portion 42 of the discharge chamber 6. For this reason, a negative pressure is generated in the portion 42 of the discharge chamber 6, a force for drawing ink is generated, and the flow of ink is promoted.
[0040]
On the other hand, as shown in FIG. 8, the ink flow 43 when the pressure is generated in the discharge chamber 6 and the ink flows back into the common liquid chamber 8 through the ink supply path 7 is the wall surface 36 of the common liquid chamber 8. Is perpendicular to the ink flow, a vortex is generated in the ink flow due to the separation flow in the portion 44, and the generation of negative pressure is eliminated.
[0041]
Thus, the fluid resistance when supplying ink to the discharge chamber 6 is low on the supply side, the ink supply efficiency is improved, the high frequency characteristics are improved, and the resistance on the discharge side is high. Pressure loss is reduced and injection efficiency is improved.
[0042]
In each of the above embodiments, the present invention is applied to a side shooter type inkjet head in which the vibration plate displacement direction and the ink droplet ejection direction are the same. However, the edge shooter orthogonal to the vibration plate displacement direction and the ink droplet ejection direction is used. The same can be applied to the inkjet head of the type. Furthermore, the present invention can be applied not only to an ink jet head but also to a droplet discharge head that discharges a liquid resist or the like. Further, although the diaphragm and the liquid chamber substrate are formed from the same substrate, the diaphragm and the liquid chamber substrate can be joined separately. Furthermore, the pressure generating means can be applied to one using an electromechanical transducer such as a piezoelectric element, or one using a heating resistor.
[0043]
【The invention's effect】
As described above, according to the droplet discharge head according to the present invention, the discharge chamber has the first surface and the second surface that are parallel to each other in a direction substantially orthogonal to the nozzle row direction and perpendicular to the main plane. and the surface, located in Lee ink supply path side of the discharge chamber, the sharp corners on the discharge chamber side relative to the third surface, and a second surface in contact and the major plane perpendicular to and the main plane contact with the first surface and a fourth surface, is formed on the further position where the third and fourth surfaces and first vertex primary and plane contact deviates from the first and second surfaces, the first vertex ink supply in a perspective plan state Since the configuration is located in the path, the bubble discharge performance is improved and the ink droplet ejection characteristics are stabilized.
[0044]
Here, by adopting a configuration in which the center position of the ink supply path is offset from the center position between the first surface and the second surface toward the second surface side, the bubble discharge property is further improved. improves. In this case, by adopting a configuration in which the second surface and the ink supply path are not in contact with each other and are separated by 1 μm or more, it is possible to reduce variations in the fluid resistance value and prevent variations in the ink droplet ejection characteristics.
[0045]
Furthermore, since the member that forms the ink supply path is a nozzle plate or a lid member on which nozzles are formed, it is easy to form the liquid chamber pattern of the flow path substrate. Furthermore, the ink to form a common liquid chamber for supplying the discharge chamber through the ink supply path to the board, the plane perpendicular to the plane is the main plane tangent to the ink supply path of the wall surface of the common liquid chamber As a result, the injection efficiency is improved.
[0046]
Each of these droplet discharge heads includes a diaphragm that forms the wall surface of the discharge chamber and an electrode that faces the diaphragm, and is a static discharge device that deforms and displaces the diaphragm with an electrostatic force to discharge droplets. By using an electric head, a head capable of high density and high image quality recording can be obtained.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of an ink jet head according to the present invention. FIG. 2 is a cross sectional view of the head in the longitudinal direction of the diaphragm. FIG. 4 is an enlarged plan view of the flow path portion of the head. FIG. 5 is an explanatory view for explaining the relationship between variation in the positional relationship between the ink supply path and the discharge chamber and variation in droplet volume. FIG. 7 is an enlarged explanatory view of an ink supply path portion of the head. FIG. 8 is an enlarged plan explanatory view of a conventional flow path portion.
DESCRIPTION OF SYMBOLS 1 ... Flow path board | substrate, 2 ... Electrode board | substrate, 3 ... Nozzle plate, 4 ... Nozzle, 6 ... Discharge chamber, 7 ... Fluid resistance part (ink supply path), 8 ... Common liquid chamber, 10 ... Vibration plate, 14 ... Recessed part , 30 ... main plane, 31 ... first surface, 32 ... second surface, 33 ... third surface, 34 ... fourth surface.

Claims (7)

A discharge chamber communicating with a nozzle for discharging droplets is formed as a concave portion closed on the main plane of the substrate, and a member formed with an ink supply path for supplying ink to the discharge chamber is joined to the main plane of the substrate. In the droplet discharge head that formed the flow path,
The ejection chambers are located on a first surface and a second surface that are parallel to each other in a direction substantially orthogonal to the nozzle row direction and perpendicular to the main plane, and on the ink supply path side of the ejection chamber. A third surface that is in contact with the surface and perpendicular to the main plane, and a fourth surface that is in contact with the second surface and is acute on the discharge chamber side with respect to the main plane, and further includes the third surface and the fourth surface. The liquid is characterized in that a first vertex where the surface and the main plane contact each other is formed at a position deviated from the first surface and the second surface, and the first vertex is located in the ink supply path in a planar perspective state. Drop ejection head.   2. The liquid droplet ejection head according to claim 1, wherein a center position of the ink supply path is offset from the center position between the first surface and the second surface toward the second surface. A droplet discharge head characterized by that.   3. The liquid droplet ejection head according to claim 2, wherein the second surface and the ink supply path are not in contact with each other and are separated by 1 [mu] m or more.   4. The liquid droplet ejection head according to claim 1, wherein the member that forms the ink supply path is a nozzle plate or a lid member that forms the nozzle.   5. The liquid droplet ejection head according to claim 1, wherein a common liquid chamber is formed on the substrate to supply ink to the ejection chamber via an ink supply path, and the common liquid chamber of the wall surface of the common liquid chamber is formed. A droplet discharge head, wherein a surface in contact with an ink supply path is a surface perpendicular to the main plane. 6. The droplet discharge head according to claim 1, wherein the substrate is a silicon substrate having a ( 110 ) plane as a main plane, and both the first surface and the fourth surface are formed from a (111) plane. A droplet discharge head characterized by that.   7. The droplet discharge head according to claim 1, further comprising: a diaphragm that forms a wall surface of the discharge chamber; and an electrode facing the diaphragm, wherein the diaphragm is deformed and displaced by an electrostatic force. And a droplet discharge head characterized by discharging the droplet.

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