JP2004330564A - Electrostatic ink jet head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic ink jet head capable of recording an image or a character surely in safety on a recording medium at a low cost. <P>SOLUTION: The electrostatic ink jet head for recording an image on a recording medium P by ejecting ink containing fine charged particles utilizing electrostatic force comprises an ink guide 14 having forward end part directing the recording medium P side, an ink channel 30 for supplying ink Q to the ink guide 14, and an ejection electrode 18 arranged to surround the ink guide 14 while spaced apart therefrom and ejecting the ink Q guided from the ink channel 30 to the forward end part of the ink guide 14 by an electrostatic force. The ink guide 14 has a means for supplying charges to the ink Q guided to the forward end. Since charges are supplied to the ink Q guided to the forward end of the ink guide 14, field strength of the ink Q is enhanced and an ink liquid drop R is ejected under a low electric field. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention uses a liquid ink containing fine particles charged by an electrostatic force, and discharges the liquid ink onto a recording medium to record an image, characters, and the like in an inkjet recording apparatus for controlling the discharge of the ink. The present invention relates to an electric inkjet head.
[0002]
[Prior art]
The ink jet recording apparatus uses ink containing charged fine particle components, and applies a predetermined voltage to the discharge electrode of the ink jet head in accordance with image data, print data, etc., thereby discharging ink using electrostatic force. For example, an image corresponding to image data is recorded on a recording medium, which is disclosed in Patent Document 1 and Patent Document 2, for example.
[0003]
FIG. 3 is a conceptual diagram schematically illustrating an example of a schematic configuration of an electrostatic inkjet head in the inkjet recording apparatus disclosed in Patent Document 1. The inkjet head 1 shown in the figure conceptually represents only individual electrodes that are one ejection means constituting the inkjet head disclosed in Patent Document 1, and includes a head substrate 2, an ink guide 3, An insulating substrate 4, a discharge electrode 5, a counter electrode 6 that supports the recording medium P, a bias voltage source 7, and a signal voltage source 8 are provided.
[0004]
The ink guide 3 has a tip formed in a protruding shape, and a conductive film such as copper is deposited on a plastic resin or the like by a method such as vapor deposition or sputtering, and is disposed on the head substrate 2. . Further, a through hole 4 a is opened in the insulating substrate 4 at a position corresponding to the arrangement of the ink guide 3. The ink guide 3 passes through the through-hole 4 a opened in the insulating substrate 4, and the tip portion protrudes above the upper surface of the insulating substrate 4. Further, the head substrate 2 and the insulating substrate 4 are arranged with a predetermined distance therebetween, and a flow path 9 for the ink Q is formed between them.
[0005]
In addition, the discharge electrode 5 is provided in a ring shape for each individual electrode on the upper surface of the insulating substrate 4 so as to surround the periphery of the through hole 4a opened in the insulating substrate 4. The ejection electrode 5 is connected to a signal voltage source 8 that generates a pulse signal corresponding to ejection data (ejection signal) such as image data and print data. The signal voltage source 8 is connected via a bias voltage source 7. Grounded.
The counter electrode 6 is disposed at a position facing the tip of the ink guide 3 and is grounded. Further, the recording medium P is disposed so as to face the lower surface of the counter electrode 6, and the counter electrode 6 functions as a platen for guiding the recording medium P.
[0006]
In the inkjet head 1 configured as described above, at the time of recording, an ink containing a fine particle component charged with the same polarity as the voltage applied to the ejection electrode 5 is transferred in a predetermined direction, in the illustrated example, by an ink circulation mechanism (not shown). The ink Q is circulated in the ink channel 9 from the right side to the left side, and a part of the ink Q in the ink channel 9 passes through the through hole 4a of the insulating substrate 4 due to a capillary phenomenon or the like and passes through the ink guide 3. Supplied to the tip.
[0007]
Here, a predetermined high voltage, for example, a voltage of 1.5 kV, is always applied to the ejection electrode 5 by the bias voltage source 7. In this state, the electric field strength in the vicinity of the tip portion of the ink guide 3 is low, and the ink Q does not jump out from the tip portion of the ink guide 3, but a part of the ink Q in the ink flow path 9, particularly a charged fine particle component. Further passes through the through-hole 4 a of the insulating substrate 4 and rises above the upper surface of the insulating substrate 4 and aggregates at the tip of the ink guide 3.
[0008]
On the other hand, when a pulse voltage, for example, 500 V is applied from the signal voltage source 8 to the ejection electrode 5 biased to, for example, 1.5 kV by the bias voltage source 7, both high voltages are superimposed on the ejection electrode 5. For example, 2 kV is applied. As a result, the ink Q, particularly the charged fine particle component in the ink Q, further rises along the ink guide 3 and aggregates at the tip thereof.
In this way, the ink Q containing the charged fine particle component aggregated at the front end portion of the ink guide 3 is ejected as an ink droplet R from the front end portion by the electrostatic force, and is pulled by the grounded counter electrode 6 to be recorded on the recording medium P. It adheres to the top and a dod is formed by the charged fine particle component.
[0009]
Thus, by recording with the dots of the charged fine particle component while relatively moving the inkjet head 1 and the recording medium P supported on the counter electrode 6, an image corresponding to the image data is recorded on the recording medium P. To be recorded.
[0010]
Further, in Patent Document 2, when a flying electrode connected to a power source for ejection control is in contact with ink and an ink droplet is ejected to a recording medium, a charge is injected into the ink by the flying electrode. Accordingly, an ink jet recording apparatus that efficiently ejects ink droplets is disclosed.
[0011]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-230608 [Patent Document 2]
Japanese Patent Laid-Open No. 08-142331
[Problems to be solved by the invention]
However, in Patent Document 1, in the case of a recording apparatus that requires high definition and high speed, a line head capable of simultaneously recording an image for one line is inevitably required. A line head capable of recording an image on the recording medium P requires an enormous number of individual electrodes corresponding to the number of pixels for one line and the same number of signal voltage sources 8 that drive the individual electrodes.
[0013]
In this case, it is necessary for the line head to mount the individual electrodes and the signal voltage source 8 physically at a very high density in the line direction. Since the signal voltage source 8 uses a high voltage of about 500 V, for example, if the individual electrodes and the signal voltage source 8 are arranged at high density, the risk of discharge increases. It is extremely difficult to achieve both high-density mounting and high voltage. The signal voltage source 8 needs to generate a pulse voltage in order to apply the pulse voltage to the ejection electrode 5. Here, since the discharge electrode 5 is a small electrode, the current consumed by the discharge itself is small. However, when the pulse voltage generated by the signal voltage source 8 is high, the consumed current increases. Furthermore, since the current is also consumed in order to generate the pulse voltage with the signal voltage source 8, there is a situation that the consumed current becomes large when the pulse voltage is high.
[0014]
Further, in the ink jet recording apparatus disclosed in Patent Document 2, the flying electrode is connected to a power supply for ejection control, and when ink having high conductivity is used, there is a situation in which a short circuit occurs and the operation becomes impossible.
[0015]
The technical problem of the present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an electrostatic inkjet head capable of reliably recording images and characters on a recording medium safely and at low cost. Is to provide.
The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an electrostatic inkjet head that records an image on a recording medium by discharging an ink containing charged fine particles using an electrostatic force, the tip portion of the recording medium side. An ink guide that faces the ink guide, an ink channel that supplies ink to the ink guide, and a space that surrounds the outer periphery of the ink guide, and is guided from the ink channel to the tip of the ink guide. An electrostatic ink jet head comprising: an ejection electrode for ejecting the ink with electrostatic force; and the ink guide includes means for supplying electric charge to the ink guided to a tip portion of the ink guide. To do.
As a result, charge is supplied to the ink guided to the tip of the ink guide, so that the charge of the ink is increased and ink droplets are ejected with a low electric field.
[0017]
In addition, it is preferable that a charge releasing material is deposited on at least the tip of the ink guide.
The charge emitting material is preferably a carbon nanotube, a ferroelectric, or aluminum nitride.
In addition, it is preferable that at least a tip portion of the ink guide has a charge emission material that emits charges with an electric field of 1 MV / m or less.
The charge releasing material is preferably PZT.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a structural conceptual diagram schematically showing an embodiment of an electrostatic ink jet head according to the present invention, and FIG. 2 is a perspective view of a main part of FIG.
An ink jet head 10 shown in FIGS. 1 and 2 ejects ink Q by electrostatic force, and records an image on a recording medium P according to image data. The head substrate 12 and the ink guide 14 are insulated from each other. A conductive substrate 16, a discharge electrode 18, a counter electrode 20 that supports the recording medium P, a signal voltage source 24, and a floating conductive plate 26 are provided.
[0019]
In the ink Q, a fine particle component such as a pigment (for example, toner) is dispersed in an insulating solvent, and the fine particle component is charged to a negative charge by a charge adjusting agent. As a pigment used as a colorant, regardless of an inorganic pigment or an organic pigment, those generally used in the technical field of printing can be used. For example, carbon black, cadmium red, molybdenum red, chrome yellow, cadmium yellow, titanium yellow, chromium oxide, viridian, cobalt green, ultramarine blue, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, Conventionally known pigments such as isoindolinone pigments, dioxazine pigments, selenium pigments, perylene pigments, perinone pigments, thioindigo pigments, quinophthalone pigments, metal complex pigments, and the like can be used without any particular limitation. it can.
[0020]
The ink guide 14 is made of an insulating resin flat plate having a projecting tip and having a predetermined thickness, and is arranged on the head substrate 12 for each individual electrode. Further, a through hole 16 a is opened in the insulating substrate 16 at a position corresponding to the arrangement of the ink guide 14. The ink guide 14 passes through the through-hole 16 a opened in the insulating substrate 16, and the tip portion protrudes above the upper surface of the insulating substrate 16. Note that a cutout serving as an ink guide groove for collecting the ink Q at the tip end portion by capillary action may be formed in the central portion of the ink guide 14 in the vertical direction in the drawing.
[0021]
The tip portion of the ink guide 14 is formed into a substantially triangular shape (or trapezoid) that gradually becomes thinner toward the counter electrode 20, and an epoxy resin film 14a in which a charge-emitting substance, for example, carbon nanotube is dispersed is 1 μm or less on the surface of the tip portion. It is applied to the thickness of The shape of the ink guide 14 is not particularly limited as long as the charged fine particle component in the ink Q can be concentrated to the tip portion through the through hole 16a of the insulating substrate 16, and the tip portion is, for example, It is not limited to a projecting shape and may be changed as appropriate. The tip of the ink guide 14 may be grounded by providing a switch in the middle, and the switch is turned off during operation.
[0022]
The head substrate 12 and the insulating substrate 16 are spaced apart from each other by a predetermined distance, and an ink flow functioning as an ink reservoir (ink chamber) for supplying the ink Q to the ink guide 14 is interposed therebetween. A path 30 is formed. The ink Q in the ink flow path 30 is printed at a predetermined speed (for example, 200 mm / second) from the right side to the left side in the ink flow path 30 in the illustrated example by an ink circulation mechanism (not shown) during recording. s ink flow).
[0023]
The discharge electrode 18 is arranged in a ring shape for each individual electrode on the upper surface of the insulating substrate 16 so as to surround the periphery of the through hole 16a opened in the insulating substrate 16. The ejection electrode 18 is connected to a signal voltage source 24 that generates a pulse signal corresponding to ejection data (ejection signal) such as image data and print data. Further, for example, a voltage of −1.5 kV is applied to the ejection electrode 18 as a constant bias.
[0024]
The counter electrode 20 is disposed so as to oppose a position 500 μm away from the tip of the ink guide 14, and includes an electrode substrate 20a and an insulating sheet 20b disposed on the lower surface of the electrode substrate 20a. The electrode substrate 20a is grounded, and the counter electrode 20 is set to a ground potential of 0V. The counter electrode 20 has a recording medium P disposed on the lower surface of the insulating sheet 20b and functions as a platen of the recording medium P.
[0025]
The floating conductive plate 26 is disposed below the ink flow path 30 and is electrically insulated (high impedance state). In the illustrated example, it is arranged inside the head substrate 12. In the present invention, the floating conductive plate 26 may be disposed anywhere as long as it is below the ink flow path 30. For example, it may be below the head substrate 12 or more than the position of the individual electrode. It may be arranged upstream of the ink flow path 30 and inside the head substrate 12.
[0026]
The floating conductive plate 26 generates an induced voltage in accordance with the voltage value applied to the individual electrode during recording of images and characters, and insulates the fine particle component in the ink Q in the ink flow path 30. For migration to the conductive substrate 16 side and concentration.
Therefore, the floating conductive plate 26 needs to be disposed closer to the head substrate 12 than the ink flow path 30. Further, the floating conductive plate 26 is preferably arranged on the upstream side of the ink flow path 30 from the position of the individual electrode.
Since the floating conductive plate 26 increases the concentration of the charged fine particle component in the upper layer in the ink flow path 30, the concentration of the charged fine particle component in the ink Q passing through the through hole 16 a of the insulating substrate 16 is increased to a predetermined concentration. It is possible to stabilize the concentration of the charged fine particle component in the ink Q that is condensed at the tip of the ink guide 14 and ejected as the ink droplet R to a predetermined concentration.
[0027]
In addition, by arranging the floating conductive plate 26, the induced voltage changes according to the number of operating channels, so that charged particles necessary for ejection can be supplied without controlling the voltage to the floating conductive plate 26. Clogging can be prevented. A power source may be connected to the floating conductive plate 26 and a predetermined voltage may be applied.
[0028]
Since the electrostatic ink jet head is configured as described above, at the time of recording, the ink is charged to the same polarity as the voltage applied to the ejection electrode 18, for example, a negative charge, by an ink circulation mechanism including a pump (not shown). Ink Q containing particulate components is circulated in the ink flow path 30 in the direction of arrow a in FIG. 1, that is, from the right side to the left side. At this time, the floating conductive plate 26 is in an insulated state (high impedance state).
[0029]
Here, when the pulse voltage is not applied to the ejection electrode 18 or when the applied pulse voltage is at a low voltage level (0 V), the gap between the ejection electrode 18 and the counter electrode 20 (recording medium P). The voltage (potential difference) is, for example, −1.5 kV corresponding to the bias voltage, and the electric field strength in the vicinity of the front end portion of the ink guide 14 is low. The ink Q does not jump out from the front end portion of the ink guide 14 and ink droplets It is not discharged as R.
However, a part of the ink Q in the ink flow path 30, particularly the charged fine particle component contained in the ink Q, passes through the through hole 16 a of the insulating substrate 16 due to the migration phenomenon and the capillary phenomenon, etc. It rises in the direction b, that is, from the lower side to the upper side of the insulating substrate 16, and is supplied to the tip portion of the ink guide 14, that is, the epoxy resin film 14a in which carbon nanotubes are dispersed. Here, the ink Q receives electrons emitted from the epoxy resin film 14a, and its electric field strength is increased.
[0030]
On the other hand, when a pulse voltage of, for example, -200 V (conventionally -500 V) obtained by subtracting the amount of increase in the electric field strength of the ink Q is applied to the ejection electrode 18, this becomes -1.5 kV corresponding to the bias voltage. Since the voltage (potential difference) between the discharge electrode 18 and the counter electrode 20 (recording medium P) is superposed and becomes −2 kV, the electric field strength near the tip of the ink guide 14 is increased. At this time, the ink Q that has risen at the tip of the ink guide 14, in particular, the charged fine particle component concentrated in the ink Q, is transferred from the tip of the ink guide 14 by an electrostatic force as an ink droplet R containing the charged fine particle component. It jumps out against the tension, is pulled by the counter electrode 20 (recording medium P), and adheres to the recording medium P.
[0031]
As described above, while the inkjet head 10 and the recording medium P supported on the counter electrode 20 are relatively moved, recording is performed by forming dots on the recording medium P by ink ejection according to the image and print data. By performing the above, it is possible to record an image or an image corresponding to print data on the recording medium P.
[0032]
As described above, in the electrostatic ink jet head according to the present embodiment, the electric field strength of the ink Q increases due to the supply of electric charge from the epoxy resin film 14a applied to the tip portion of the ink guide 14, and the electric field strength increases. Therefore, even when the pulse voltage applied to the ejection electrode 18 is low, the ink droplet R can be ejected. Therefore, even in the case of an ink jet recording apparatus that requires high definition and high speed, there is a risk of discharge. In addition, the current consumption can be reduced and the discharge electrode 18 is not connected to the power supply for discharge control as in the prior art, so there is no short circuit and no inability to operate. .
[0033]
The electrostatic ink jet head according to the embodiment of the present invention has been described in detail above. However, the present invention is not limited to the electrostatic ink jet head described in the above embodiment, and the claims of the present invention are provided. Various changes can be made in the design without departing from the spirit of the invention described in.
For example, in the above-described embodiment, the epoxy resin film 14a in which carbon nanotubes are dispersed is applied to the tip portion of the ink guide 14, but the epoxy resin film 14a may be applied to the entire surface of the ink guide 14. Further, in place of the carbon nanotube, a ferroelectric or aluminum nitride may be applied to at least the tip portion of the ink guide 14.
[0034]
Further, instead of applying the epoxy resin film 14a to the tip portion of the ink guide 14, the ink guide 14 is formed by PZT that discharges charges with an electric field of 1 MV / m or less, and the fine particle component of the ink Q is formed by a charge adjusting agent. A positive charge may be charged, and a voltage of, for example, 1.5 kV may be applied to the ejection electrode 18 as a constant bias.
When recording, first, an initialization voltage of −200 V is applied, the spontaneous polarization of the ink guide 14 is made downward in FIG. 1, and then a discharge voltage of +200 V is applied to the discharge electrode 18 so that the spontaneous discharge of the ink guide 14 occurs. Polarization may be reversed to discharge positive charges to the ink Q on the upper side of the ink guide 14, that is, at the tip, thereby increasing the electric field strength of the ink Q and ejecting the ink droplet R. In this case, the counter electrode 20 is kept 500 μm away from the ink guide 14 and charged at 0V.
Even in such an electrostatic ink jet head, the electric field strength of the ink Q at the tip of the ink guide 14 can be increased, so that the ink droplet R can be ejected at a low ejection voltage.
[0035]
【The invention's effect】
As can be understood from the above description, according to the electrostatic ink jet head of the present invention, the leading end portion of the ink guide has the charge releasing material that supplies charges to the ink, so that it is guided to the leading end portion of the ink guide. Electric charges are supplied to the ink, the electric field strength of the ink is increased, and ink droplets can be ejected with a low electric field.
Therefore, the risk of discharge is mitigated, current consumption is reduced, and a short-circuit state can be avoided, so that images and characters can be recorded safely and reliably at low cost.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a configuration of an embodiment of an electrostatic ink jet head according to the present invention.
FIG. 2 is a perspective view of a main part of FIG.
FIG. 3 is a conceptual diagram illustrating an example of a conventional electrostatic ink jet head.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Electrostatic inkjet head 12 Head substrate 14 Ink guide 14a Epoxy resin film 16 Insulating substrate 16a Through-hole 18 Discharge electrode 20 Counter electrode 20a Electrode substrate 20b Insulating sheet 24 Signal voltage source 26 Floating conductive plate 30 Ink flow path P Recording medium Q ink R ink droplet

Claims (5)

An electrostatic inkjet head that records an image on a recording medium by discharging electrostatically charged ink containing fine particles,
An ink guide whose leading end faces the recording medium,
An ink flow path for supplying ink to the ink guide;
A discharge electrode that is disposed so as to surround the outer periphery of the ink guide, and discharges the ink guided from the ink flow path to the tip of the ink guide with an electrostatic force;
The electrostatic ink jet head according to claim 1, wherein the ink guide has means for supplying electric charges to the ink guided to a tip portion thereof. The electrostatic ink jet head according to claim 1, wherein a charge emission material is attached to at least a tip portion of the ink guide. The electrostatic ink jet head according to claim 2, wherein the charge emission material is a carbon nanotube, a ferroelectric, or aluminum nitride. 2. The electrostatic ink jet head according to claim 1, wherein the ink guide has a charge emitting material that emits a charge with an electric field of 1 MV / m or less at least at a front end portion of the ink guide. The electrostatic ink jet head according to claim 4, wherein the charge emission material is PZT.

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