JP2009090608A - Electrostatic suction type ink jet head and ink jet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce inflow of electric current into a driving electrode during discharge in an electrostatic suction type ink jet head. <P>SOLUTION: The electrostatic suction type ink jet head includes: a pressure generating body in which a cavity 14 and a driving wall 15 made of a piezoelectric material with the driving electrode 16 formed thereon, are alternately arranged; and a nozzle plate 11 made of an insulating material jointed to the open face of the cavity 14 of the pressure generating body, the nozzle plate 11 being provided with a nozzle 12. The electrostatic suction type ink jet head generates an electric field between a counter electrode opposite to the nozzle plate 11 and it, thereby accelerating suction of ink emitted from the nozzle 12. In the electrostatic suction type ink jet head, the ink is conductive, at least a wall in the cavity 14 that emits ink is provided with a ground electrode 17 grounded separately from the driving electrode 16. If the shortest distance between the nozzle 12 and the leading end, on the nozzle plate 11 side, of the driving electrode 16 in the cavity 14 provided with the ground electrode 17 is defined as A and the shortest distance between the nozzle 12 and the leading end, on the nozzle plate 11 side, of the ground electrode 17 is B, the condition A>B is satisfied. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrostatic suction ink jet head and an ink jet recording apparatus, and more specifically, a counter electrode is disposed so as to face a nozzle plate of the ink jet head, and an electric field is formed between the ink jet head and the counter electrode. The present invention relates to an electrostatic suction ink jet head and an ink jet recording apparatus which are applied to, for example, a printer and a facsimile.

  There are various ink jet heads used in the ink jet recording apparatus, and one of them is an on-demand type ink jet head using a piezoelectric material.

  As such an ink jet head, for example, Patent Document 1 discloses an ink jet head shown in FIG. This ink jet head 100 has discharge cavities 104 filled with ink communicating with nozzles 102 provided on a nozzle plate 101 and dummy cavities 105 not filled with ink alternately arranged in parallel via a drive wall 106 made of a piezoelectric material. The pressure generator 103 is provided with drive electrodes 107 on the wall surfaces of the drive walls 106 on both sides of the discharge cavity 104 and the dummy cavity 105.

  The ink jet head 100 deforms the driving wall 106 by applying a driving voltage to the driving electrode 107 from a driving power source (not shown), applies ejection energy to the ink in the ejection cavity 104, and ejects ink droplets from the nozzles 102. The ink is ejected and landed on the recording medium 200 facing the nozzle plate 101.

  However, for example, when trying to reduce the size of the ink droplets ejected in order to achieve high definition of recording, there are the following problems.

  In general, it is known that when the scale of an object is reduced, the surface force such as a viscous force is relatively larger than the bulk force such as an inertial force or gravity. An inkjet recording apparatus having such an inkjet head is known. However, since there is no response to the viscous force of air, which increases the influence of small droplets, the smaller the ink droplets, the faster the speed decreases, and it is impossible to reach or reach the recording medium at a predetermined distance. However, the landing position accuracy will deteriorate.

  In order to solve such a problem, it is necessary to increase the ejection energy when ejecting ink droplets from the nozzle. However, the reduction of the droplet size of the ink droplet and the increase of the ejection energy are contradictory issues, In reality, it is extremely difficult.

On the other hand, as one of countermeasures for reducing droplets, for example, Patent Document 2 discloses an electrostatic suction type inkjet recording apparatus that accelerates charged droplets toward a recording medium by an electric field.
JP 2004-314312 A JP 2005-136151 A

  In an inkjet head using conductive ink, it is necessary to apply a protective film of an insulator to the electrode surface in contact with the ink in order to prevent conduction due to a voltage applied to the driving electrode.

  However, in the electrostatic suction type inkjet head, when a discharge occurs between the conductive ink and the counter electrode, current flows into the cavity through the ink meniscus formed in the nozzle, and the protective film breaks down. As a result, there is a problem that there is a high possibility of conduction with the driving electrode.

  On the other hand, for example, if the electrode in the dummy cavity is an individual electrode to which a voltage is applied individually, the electrode in the discharge cavity is a common electrode, and the common electrode is grounded, the ink will be in contact with the common electrode. Even when the ink is used, the risk of conduction can be avoided.

  However, even in this case, it has been found that when a discharge occurs between the nozzle plate and the counter electrode, the nozzle plate breaks down and there is a risk that current flows into the individual electrodes.

  Further, in order to ground the common electrode, it is necessary to drop the ground between the common electrode and the drive substrate in order to prevent current from flowing into the drive substrate through the common electrode. Furthermore, in order to ensure safety, it is necessary to prevent a current exceeding a certain level from flowing to the drive substrate side. Therefore, there is a problem that a protective circuit must be interposed between the common electrode and the driving substrate.

  Accordingly, the present invention provides an electrostatic suction ink jet head that can reduce the risk of current flowing into the drive electrode formed on the wall surface of the drive wall when a discharge occurs, and an ink jet recording apparatus including the same. Is an issue.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

  According to the first aspect of the present invention, a pressure generator in which drive walls and cavities made of a piezoelectric material having drive electrodes formed on both sides are alternately arranged, and a surface of the pressure generator that is open to the cavity are bonded. A nozzle plate made of an insulating material, and a nozzle is provided in the nozzle plate so as to communicate with the cavity, and an electric field is formed between the nozzle plate and a counter electrode disposed facing the nozzle plate. In the electrostatic suction ink jet head that accelerates and sucks the ink ejected from the nozzle, the ink is a conductive ink, and is separated from the driving electrode at least on the wall surface in the cavity from which the ink is ejected. A grounded earth electrode, and the nozzle plate of the driving electrode in the cavity in which the earth electrode is provided When the shortest distance between the tip of the nozzle and the nozzle is A and the shortest distance between the tip of the ground electrode on the nozzle plate side and the nozzle is B, the condition of A> B is satisfied. This is an electrosuction inkjet head.

  According to a second aspect of the present invention, the cavities are all discharge cavities for discharging the ink, and the nozzle plate is provided with the nozzles so as to communicate with all the discharge cavities, and the ground electrode The electrostatic suction ink jet head according to claim 1, wherein the electrostatic suction ink jet head is provided on a wall surface in all of the discharge cavities.

  According to a third aspect of the present invention, in the cavity, a discharge cavity that discharges the ink and a dummy cavity that does not discharge the ink are alternately arranged via the drive wall, and the nozzle includes the discharge cavity. The electrostatic attraction type ink jet head according to claim 1, wherein the electrostatic attraction type ink jet head is provided so as to communicate only with the discharge cavity, and the ground electrode is provided only on a wall surface in the discharge cavity.

  According to a fourth aspect of the present invention, there is provided a pressure generator in which drive walls and cavities made of a piezoelectric material having drive electrodes formed on both surfaces are alternately arranged, and a surface of the pressure generator that is bonded to a surface of the cavity where the cavity opens. A nozzle plate made of an insulating material, and a nozzle is provided in the nozzle plate so as to communicate with the cavity, and an electric field is formed between the nozzle plate and a counter electrode disposed facing the nozzle plate. Thus, in the electrostatic suction ink jet head that accelerates and sucks the ink ejected from the nozzle, the ink is a non-conductive ink, and is grounded on a wall surface in all the cavities separately from the driving electrode. A ground electrode is provided, and the tip of each of the drive electrode and the ground electrode on the nozzle plate side in the cavity is the drive electrode. A straight line extending from an arbitrary point on the tip of the pole on the nozzle plate side to the tip of the ground electrode on the nozzle plate side includes a plane including the straight line and extending in a direction perpendicular to the nozzle plate and the ground The electrostatic attraction type ink jet head is characterized by being arranged so as to form an angle of 60 ° or less with respect to a line of intersection with the surface of the electrode.

  According to a fifth aspect of the present invention, in the electrostatic attraction type according to any one of the first to fourth aspects, the ground electrode extends to a surface of the pressure generating body where the cavity opens. It is an inkjet head.

  The invention according to claim 6 is characterized in that the ground electrode is formed in a single band extending over all the cavities on a substrate provided so as to close the upper and / or lower sides of the cavities. Item 6. The electrostatic attraction type inkjet head according to Item 1, 2, 4 or 5.

  According to a seventh aspect of the invention, a recording medium is sandwiched between the electrostatic suction ink jet head according to any one of the first to sixth aspects and the nozzle plate of the electrostatic suction ink jet head. An ink jet recording apparatus comprising: a counter electrode arranged in such a manner; and a power source that forms an electric field by applying a voltage between the electrostatic suction ink jet head and the counter electrode. .

  According to the present invention, there is provided an electrostatic suction ink jet head capable of reducing the risk of current flowing into a drive electrode formed on the wall surface of a drive wall when a discharge occurs, and an ink jet recording apparatus including the same. Can do.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic view showing an example of an ink jet recording apparatus according to the present invention, and shows a cross section of an ink jet head.

  The ink jet recording apparatus includes an electrostatic suction ink jet head 10 </ b> A having a nozzle plate 11 provided with a plurality of nozzles 12 for ejecting ink droplets, and a counter electrode 20. The counter electrode 20 is disposed so as to face the nozzle plate 11 with a distance of about 1 mm to 3 mm with the recording medium 30 between the nozzle plate 11 of the inkjet head 10A.

  A power source 21 is connected to the counter electrode 20 so that a negative voltage can be applied.

  The ink jet head 10A has a pressure generator 13 in which a cavity 14 filled with ink and ejecting ink droplets from a nozzle 12 toward a recording medium 30 is arranged in parallel via a drive wall 15 made of a piezoelectric material. is doing.

  In the inkjet head 10A, conductive ink is used as ink. Examples of the conductive ink include water-based ink.

  The nozzle plate 11 is joined to the surface of the pressure generator 13 where the cavities 14 are opened, and each of the plurality of nozzles 12 formed on the nozzle plate 11 corresponds to the cavity 14 of the pressure generator 13. The inside of each cavity 14 is communicated with the outside.

  The nozzle plate 11 is made of an insulating material. As an insulating material, glass etc. other than synthetic resins, such as a polyimide, are mentioned, for example. The thickness of the nozzle plate 11 is preferably 50 to 200 μm.

  As a piezoelectric material for constituting the drive wall 15 of the pressure generator 13, a known piezoelectric material that deforms when a voltage is applied can be used, and lead zirconate titanate (PZT) is particularly preferable.

  FIG. 2 is a cross-sectional view taken along the line A-A ′ of FIG. 1. As shown in the figure, each drive wall 15 is formed by stacking two polarized piezoelectric materials 15a and 15b so that the polarization directions are opposite to each other and bonding with an adhesive. ing. In the figure, reference numeral 13 a denotes an upper substrate that covers the upper side of each cavity 14, and 13 b denotes a lower substrate that closes the lower side of each cavity 14.

  Driving electrodes 16 and 16 for forming an electric field across the driving wall 15 by a driving voltage supplied from a driving substrate (not shown) are formed in close contact with both wall surfaces facing the cavity 14 in each driving wall 15. .

  In addition, the drive electrode formed in close contact with the drive wall 15 includes an individual electrode to which a voltage is individually applied and a common electrode to which a voltage is commonly applied, and both surfaces of the drive wall 15 are used as individual electrodes. In some cases, one of the surfaces may be a common electrode, but the present invention may be any of them, and the drive electrode in the present invention includes an individual electrode and a common electrode.

  In the ink jet head 10A, when a driving voltage is applied to the driving electrode 16 in each cavity 14 from a driving substrate (not shown) and an electric field is formed between the driving electrodes 16 and 16 on both surfaces of the driving wall 15, a piezoelectric material is obtained. The drive wall 15 is deformed into a dogleg shape by a shear deformation action. Due to the deformation of the drive wall 15, the volume of the cavity 14 is changed, and ejection energy is given to the ink filled therein, so that the ink droplets are ejected from the nozzle 12. The ejected ink droplets land on the recording medium 30 disposed on the counter electrode 20 under the action of an electric field formed between the inkjet head 10 and the counter electrode 20.

  At this time, it is preferable that the ink jet head 10 </ b> A is at a ground potential. The electric field formed between the inkjet head 10 </ b> A and the counter electrode 20 may be formed perpendicular to the recording medium 30, and forms an electric field sufficient for accelerating droplets by electrostatic attraction. I can do it.

  Each cavity 14 is provided with a grounded earth electrode 17 that is different from the driving electrode 16. Here, each ground electrode 17 is formed in close contact with the wall surface of the upper substrate 13 a in parallel with the length direction of the cavity 14. The width is a narrow width of about 40 to 60% of the width of the wall surface of the upper substrate 13 a in the cavity 14. For this reason, the ground electrode 17 is not in contact with the wall surfaces of the drive walls 15 adjacent to the upper substrate 13a, and is therefore electrically separated from the drive electrodes 16.

  The ground electrode 17 may be on at least one wall surface in contact with the wall surface of the drive wall 15 in each cavity 14, and therefore may be the wall surface of the lower substrate 13b, or both wall surfaces of the upper substrate 13a and the lower substrate 13b. It is also possible to form in the following manner.

  Ni, Co, Cu, Al, or the like can be used as the metal for forming the driving electrode 16 and the ground electrode 17, but it is preferable to use Al or Cu from the viewpoint of electrical resistance. From the viewpoint of strength and cost, Ni is preferably used. Further, for example, a laminated structure in which Au is laminated on Al can be used.

  Examples of the method for forming the driving electrode 16 and the ground electrode 17 include a vapor deposition method, a sputtering method, a plating method, a method using a CVD method vacuum device, and the like. It is preferable to form by. By electroless plating, a uniform and pinhole-free metal coating can be formed. The thickness of the plating film is preferably in the range of 0.5 μm to 5 μm.

  In order to form the ground electrode 17, a known patterning technique such as exposure / development using a photosensitive resist, for example, may be used to pattern the surface of the upper substrate 13a in a narrow width at a pitch corresponding to each cavity 14 in advance. Good. An insulating protective film is not formed on the surface of the earth electrode 17.

  FIG. 3 shows the inside of one cavity 14. Here, the shortest distance between the tip 16a of the driving electrode 16 in the cavity 14 on the nozzle plate 11 side and the nozzle 12 (the center of the opening of the nozzle 12 on the cavity 14 side) is A, and the tip of the ground electrode 17 on the nozzle plate 11 side. When the shortest distance between 17a and the nozzle 12 (the opening center of the nozzle 12 on the cavity 14 side) is B, the condition of A> B is satisfied. That is, the tip 16 a of the drive electrode 16 is farther from the nozzle 12 than the tip 17 a of the ground electrode 17. For this reason, a region 15c where the driving material 16 is not formed and the piezoelectric material is exposed exists on the side of the end surface 13c joined to the nozzle plate 11 of both wall surfaces of the driving wall 15 facing each cavity 14. Yes.

  As a result, even if a discharge occurs between the inkjet head 10A and the counter electrode 20 and a current enters the cavity 14 from the nozzle 12 through the conductive ink, the current due to the discharge is grounded more than the driving electrode 16. It becomes easy to flow into the electrode 17 side, and the risk of current flowing into the driving electrode 16 side can be reduced. Further, since the driving electrode 16 is separated from the nozzle plate 11, it is possible to reduce the interference of the accelerating electric field of the ink droplet by the counter electrode 20 due to the electric field formed when a driving voltage is applied to the driving electrode 16. It is possible to improve the stability when ejecting ink droplets.

  In order to form each drive electrode 16 so as to be separated from the end face 13c joined to the nozzle plate 11, a dry film is previously applied to the wall surface of the drive wall 15 corresponding to the region 15c when the metal coating is formed. It is possible to adopt a method in which the driving electrode 16 is partially formed on the wall surface of the driving wall 15 by wearing or removing a resist after forming a metal film.

  Further, the ground electrode 17 in each cavity 14 may be provided so as to protrude from the drive electrode 16 toward the nozzle plate 11 so as to satisfy the above relationship, but current flows into the drive electrode 16 side. In order to further reduce the risk, it is particularly preferable that the pressure generator 13 extends to the surface where the cavity 14 opens.

  Further, the ground electrode 17 is not limited to be formed to have the same width toward the nozzle plate 11 side, and as long as it is electrically separated from the driving electrode 16, as shown in FIG. It is good also as a shape which has the expansion part 17b by enlarging an area. Since the drive wall 15 where the drive electrode 16 is formed has a region 15c where the drive electrode 16 is not formed on the nozzle plate 11 side, the widened portion 17b has the drive walls 15 adjacent to each other as illustrated. The width of the cavity 14 may be in contact with the nozzle plate 11, and the cavity 14 may be extended to the surface where the cavity 14 is open.

  Further, the ground electrode 17 is not limited to being provided independently in each cavity 14 as described above, and a substrate provided so as to close the upper and / or lower sides of the cavity 14 as in the inkjet head 10B shown in FIG. (Upper substrate 13 a and lower substrate 13 b) may be formed in a single band extending over all the cavities 14 along a direction perpendicular to the length direction of the cavities 14. In FIG. 5, the ground electrode 17 is formed on the upper substrate 13a. In FIG. 5, the same reference numerals as those in FIG. 1 indicate the same components. Here, the counter electrode 20 and the recording medium 30 are not shown.

  The one strip-shaped ground electrode 17 is located close to the nozzle plate 11 side of the upper substrate 13a and adjacent to the region 15c in each cavity 14 where the drive electrode 16 is not formed. Are electrically separated from each other. Therefore, the condition of A> B is satisfied as described above. It is also preferable to form the earth electrode 17 in such a width as to contact the nozzle plate 11 and to extend to the surface where the cavity 14 opens.

  According to such a ground electrode 17, for example, it is sufficient to form only one on the upper substrate 13 a, so that the formation of the ground electrode 17 becomes easier, and the ground connection is also performed, for example, on the side of the head. Since connection with 17 is sufficient at one place, there is an advantage that the connection structure can be simplified.

  The shape of the tip 16a of each driving electrode 16 on the nozzle plate 11 side is parallel to the nozzle plate 11 as shown in FIG. 6A so that the sharpened portion on the nozzle plate 11 side is not formed. It is preferable to bend so that it may become convex at the nozzle plate 11 side like 6 (B).

  In the above embodiment, the ink jet head 10 </ b> A has been exemplified in which all the cavities 14 formed in the pressure generator 13 are filled with ink and ink droplets are ejected from the nozzles 12 communicating with the cavities 14. The cavity may be divided into a discharge cavity that discharges ink and a dummy cavity that does not discharge ink.

  FIG. 7 shows an inkjet head 10C in which a cavity 14 formed in the pressure generator 13 is divided into a discharge cavity 14A that discharges ink (conductive ink) and a dummy cavity 14B that does not discharge ink. In FIG. 7, the same reference numerals as those in FIG. 1 denote the same components. Again, the counter electrode 20 and the recording medium 30 are not shown.

  In the ink jet head 10 </ b> C, the discharge cavities 14 </ b> A and the dummy cavities 14 </ b> B are alternately arranged via the drive wall 15. Nozzle communicating with the dummy cavity 14B is not provided in the nozzle plate 11, and the ground electrode 17 is provided in parallel to the length direction of the discharge cavity 14 only in each discharge cavity 14A. It is not provided in 14B. The ground electrode 17 is also formed on the upper substrate 13a so as to satisfy the above-described conditions with respect to the drive electrode 16 provided on the drive wall 15.

  For this reason, when a discharge occurs between the counter electrode 20 and the discharge electrode, the current due to the discharge normally enters the discharge cavity 14A through the nozzle 12 provided to communicate with the discharge cavity 14A. The current thus flows more easily into the ground electrode 17 side than the drive electrode 16, and the risk of current flowing into the drive electrode 16 side can be reduced.

  Since the inkjet head 10C is not provided with the nozzles 12 corresponding to the dummy cavities 14B, each driving electrode 16 facing the dummy cavities 14B discharges the position of the tip on the nozzle plate 11 side as shown in the drawing. It is not necessary to match with each driving electrode 16 facing the cavity 14A.

  If there is a risk of the dielectric breakdown of the nozzle plate 11 due to the discharge generated between the counter electrode 20 and the discharge cavity 14A, as shown in FIG. The inkjet head 10D in which the driving electrode 16 and the ground electrode 17 are formed under the same conditions is preferable. Of course, it is also possible to form the ground electrode 17 in a single band shape as in the inkjet head 10B shown in FIG.

  In the ink jet head 10C shown in FIG. 7 and the ink jet head 10D shown in FIG. 8, each of the driving electrodes 16 has one of the discharge cavities 14A or the dummy cavity 14B facing as an individual electrode and the other as a common electrode. However, according to the present invention, it is possible to prevent the current from flowing into the drive electrode formed on the drive wall 15 by the ground electrode 17, so that even if the common electrode is used as the ground electrode, the drive substrate It is not necessary to drop to the ground, and it is not necessary to provide a protective circuit or the like between the common electrode and the drive substrate.

  In each of the above embodiments, the conductive ink is used as the ink, but an example of an ink jet head that is preferable when a non-conductive ink is used as the ink is shown in FIGS. 9 is a partial perspective view showing the inside of one cavity 14 of the inkjet head 10E, and FIG. 10 is a cross-sectional view of the inside of the cavity 14 in FIG. 9 as viewed from the direction facing the nozzle plate 11. As shown in FIG. Parts having the same reference numerals as those in FIG. 1 indicate the same configurations.

  In the inkjet head 10E, nozzles 12 are provided so as to communicate with all the cavities 14 as in FIG. 1, and ink is ejected from the nozzles. A ground electrode 17 is provided in parallel along the length direction.

  Examples of the non-conductive ink include oil-based ink.

  When such a non-conductive ink is used, the current due to discharge does not necessarily flow into the cavity 14 through the ink meniscus formed in the nozzle 12 as in the case of using the conductive ink. The plate 11 may break into the cavity 14 due to dielectric breakdown. Therefore, the tip 16a, 17a on the nozzle plate 11 side of each of the driving electrode 16 and the ground electrode 17 in each cavity 14 of the inkjet head 10E is an arbitrary one of the tip 16a on the nozzle plate 11 side of the driving electrode 16 A straight line that extends from the point to the tip 17a of the ground electrode 17 on the nozzle plate 17 side at the shortest distance with respect to the intersection line between the plane including the straight line and perpendicular to the nozzle plate 11 and the surface of the ground electrode 17 , So as to form an angle of 60 ° or less.

  That is, in the example shown in FIGS. 9 and 10, when the tip 16a1 on the upper substrate 13a side of one drive electrode 16 in the cavity 14 is viewed, the tip 17a on the nozzle plate 17 side of the ground electrode 17 from the tip 16a1. The angle a1 formed with respect to the intersection line Pa between the plane P1 that includes the straight line L1 and is perpendicular to the nozzle plate 11 and the surface of the earth electrode 17 is 60 ° or less. When the tip 16a2 on the lower substrate 13b side of the driving electrode 16 is viewed at an angle, a straight line L2 that extends from the tip 16a2 to the tip 17a on the nozzle plate 17 side of the ground electrode 17 at the shortest distance is The angle a2 formed with respect to the intersecting line Pa between the plane P2 including the straight line L2 and extending perpendicularly to the nozzle plate 11 and the surface of the ground electrode 17 is an angle of 60 ° or less. There is no.

  9 and 10, the shapes of the tip 16 a of the driving electrode 16 and the tip 17 a of the ground electrode 17 are formed so as to be parallel to the surface of the nozzle plate 11. If the positions of the tip 16a of the drive electrode 16 and the tip 17a of the ground electrode 17 are arranged so that the straight line L2 of the L2 forms an angle of 60 ° or less with respect to the intersection line Pa, the tip of the drive electrode 16 Similarly, any other point of 16a has an angle of 60 ° or less.

  If both of these angles are 60 ° or less, even if a discharge occurs with the counter electrode 20 and the current flows into the cavity 14 due to the dielectric breakdown of the nozzle plate 11, the ground electrode 17 side Each drive electrode 16 is protected from current by air or a piezoelectric material, and the risk of current flowing into the drive electrode 16 can be reduced.

  Even when non-conductive ink is used in this way, the cavity 14 may be divided into a discharge cavity 14A that discharges ink (non-conductive ink) and a dummy cavity 14B that does not discharge ink. Even in this case, the drive electrode 16 and the ground electrode 17 are provided in both the ejection cavity 14A and the dummy cavity 14B under the same conditions as the ink jet head 10E. In this case, the driving electrode 16 formed on each driving wall 15 can be either an individual electrode facing the discharge cavity 14A or the dummy cavity 14B, and the other electrode being a common electrode.

  Further, even in an inkjet head using non-conductive ink, the ground electrode 17 may be formed in a single belt shape as in the inkjet head 10B shown in FIG.

  FIG. 11 is a partial perspective view showing the inside of one cavity 14 in an aspect in which the ground electrode 17 is formed in one strip shape in the inkjet head 10F using non-conductive ink.

  Similarly to FIG. 9, when the tip 16a1 on the upper substrate 13a side of one of the drive electrodes 16 in the cavity 14 is viewed, the tip 16a1 extends from the tip 16a1 to the tip 17a on the nozzle plate 17 side of one belt-like earth electrode 17. A straight line L1 that travels at the shortest distance is an intersection line Pa (driving with the upper substrate 13a) between the plane P1 (the wall surface of the upper substrate 13a) that includes the straight line L1 and is perpendicular to the nozzle plate 11 and the surface of the ground electrode 17. The angle a1 made with respect to the boundary line with the wall 15 is 60 ° or less (here, 0 ° because the drive electrode 16 is formed to the full height of the drive wall 15), and When the tip 16a2 on the lower substrate 13b side of the driving electrode 16 is viewed, a straight line L2 that extends from the tip 16a2 to the tip 17a on the nozzle plate 17 side of the ground electrode 17 at the shortest distance includes the straight line L2. The angle a2 formed with respect to the intersecting line Pa between the plane P2 (wall surface of the drive wall 15) and the surface of the earth electrode 17 along the vertical direction with respect to the nozzle plate 11 is also grounded so as to form an angle of 60 ° or less. An electrode 17 and a driving electrode 16 are formed.

  Hereinafter, the effect of the present invention will be illustrated by examples.

(1) In the case of conductive ink <Configuration of inkjet recording apparatus>
Inkjet head configuration An electrostatic suction type inkjet head No. 1 that uses PZT as a piezoelectric material and has the following configuration. 1-22 were created.

  Each cavity was an ejection cavity for ejecting ink, and conductive ink (water-based dummy ink) was used as the ink. The dimension of each part is a part shown in FIG.

Cavity width (Lb): 80 μm
Depth (La): 200 μm
Number: 256 Drive wall width: 80μm
Nozzle plate Material: Polyimide Thickness: 80μm
Number of nozzles: 256 nozzles Driving electrode Metal used: Al
Thickness: 0.5μm
Width (Le): 200 μm
Earth electrode Metal used: Al
Thickness: 0.5μm
Width (Lf): 40 μm

  In addition, the earth electrode was formed for every cavity in the narrow width parallel along the length direction of the cavity. In addition, the tip shapes of the drive electrodes and the ground electrodes were formed so as to be parallel to the surface of the nozzle plate.

  In each inkjet head, the distance (Ld) from the tip of the driving electrode to the nozzle plate, the distance (Lc) from the tip of the ground electrode to the nozzle plate, and the shortest distance between the tip of the driving electrode on the nozzle plate side and the nozzle Table 1 shows the distance (A) and the shortest distance (B) between the tip of the earth electrode on the nozzle plate side and the nozzle.

  The above inkjet head No. 1 to 22, an ink jet recording apparatus is configured by setting the distance between the nozzle plate and the counter electrode to be 2.3 mm, and a voltage of 2 kV is applied between the ink jet head and the counter electrode. I did it.

<Discharge evaluation method>
As shown in FIG. 13, an ammeter was interposed between the driving electrode of the inkjet head and the driving substrate. When a current flows into the driving electrode, it is detected by an ammeter. Therefore, the current flowing into the driving electrode at the time of discharge was confirmed based on whether or not the current was detected by the ammeter.

  The evaluation was performed according to the following criteria by observing the ratio of the current flowing into the driving electrode with respect to the frequency of the generated discharge.

○: Always discharged to the ground electrode Δ: 80% or more discharged to the ground electrode ×: 80% or more discharged to the drive electrode

  From the results of Table 1, it can be seen that when the condition of A> B is satisfied, no current flows into the drive electrode due to discharge.

(2) In the case of non-conductive ink Inkjet heads Nos. 1 to 22 having the same configuration. 23 to 44, non-conductive ink (oil-based dummy ink) was used as the ink, and the discharge was evaluated in the same manner as described above.

  Similarly to FIGS. 9 and 10, a straight line L2 that extends from one point 16a2 of the tip 16a of the driving electrode 16 on the nozzle plate 11 side to the tip 17a of the ground electrode 17 on the nozzle plate 11 side is the shortest distance. The angle a2 formed with respect to the intersecting line Pa between the plane P2 including the straight line L2 and extending in the direction perpendicular to the nozzle plate 11 and the surface of the ground electrode 17 is as shown in Table 2.

  Since the tip shapes of the drive electrodes and the ground electrodes are both parallel to the surface of the nozzle plate, if this a2 is 60 ° or less, the angle a1 shown in FIG. 9 is also 60 ° or less. Will be satisfied.

  From the results in Table 2, it can be seen that when the angle a2 is 60 ° or less, no current flows into the drive electrode due to discharge.

Schematic showing an example of an inkjet recording apparatus according to the present invention Sectional drawing which follows the A-A 'line of FIG. Partial perspective view showing the inside of the cavity Sectional drawing which shows the other aspect of the shape of the front end side of an earth electrode Schematic showing an inkjet head having a ground electrode according to another embodiment (A) (B) is sectional drawing which follows the B-B 'line | wire of FIG. 1 which shows the front-end | tip shape of the electrode for a drive. Schematic which shows the other aspect of the inkjet head which concerns on this invention. Schematic which shows the further another aspect of the inkjet head which concerns on this invention. The fragmentary perspective view which shows the inside of the cavity of the further another aspect of the inkjet head which concerns on this invention. 9 is a cross-sectional view of the inside of the cavity in FIG. 9 as viewed from the direction facing the nozzle plate. The fragmentary perspective view which shows the inside of the cavity of the further another aspect of the inkjet head which concerns on this invention. The perspective view which shows the dimension of each part in an Example Schematic showing the experimental method of the ink jet recording apparatus Schematic showing an example of a conventional inkjet head

Explanation of symbols

10A to 10F: Inkjet head 11: Nozzle plate 12: Nozzle 13: Pressure generator 13a: Upper substrate 13b: Lower substrate 13c: End face 14: Cavity 14A: Discharge cavity 14B: Dummy cavity 15: Drive walls 15a, 15b: Piezoelectric material 15c: area 16: driving electrodes 16a, 16a1, 16a2: tip 17: ground electrode 17a: tip 20: counter electrode 21: power source 30: recording medium P1, P2: plane Pa: cross line

Claims (7)

Pressure generators in which drive walls and cavities made of piezoelectric material with drive electrodes formed on both sides are alternately arranged, and nozzle plates made of an insulating material joined to the surfaces of the pressure generators where the cavities open The nozzle plate is provided so that the nozzle communicates with the cavity, and is discharged from the nozzle by forming an electric field between the nozzle plate and a counter electrode disposed facing the nozzle plate. In an electrostatic suction inkjet head that accelerates and sucks ink,
The ink is a conductive ink;
At least a grounded ground electrode different from the driving electrode is provided on the wall surface in the cavity for discharging the ink,
The shortest distance between the nozzle on the nozzle plate side of the drive electrode and the nozzle in the cavity provided with the ground electrode is A, and the shortest distance between the nozzle on the nozzle plate side of the ground electrode and the nozzle. An electrostatic suction ink jet head characterized by satisfying the condition of A> B when B is satisfied. The cavities are all discharge cavities that discharge the ink,
The nozzle plate is provided with the nozzle so as to communicate with all the discharge cavities,
The electrostatic suction ink jet head according to claim 1, wherein the ground electrode is provided on a wall surface in all of the discharge cavities. In the cavity, a discharge cavity that discharges the ink and a dummy cavity that does not discharge the ink are alternately arranged via the drive wall,
The nozzle is provided to communicate only with the discharge cavity,
The electrostatic suction ink jet head according to claim 1, wherein the ground electrode is provided only on a wall surface in the discharge cavity. Pressure generators in which drive walls and cavities made of piezoelectric material with drive electrodes formed on both sides are alternately arranged, and nozzle plates made of an insulating material joined to the surfaces of the pressure generators where the cavities open The nozzle plate is provided so that the nozzle communicates with the cavity, and is discharged from the nozzle by forming an electric field between the nozzle plate and a counter electrode disposed facing the nozzle plate. In an electrostatic suction inkjet head that accelerates and sucks ink,
The ink is a non-conductive ink;
A grounded earth electrode different from the driving electrode is provided on the wall surface in all the cavities,
The tip of each of the driving electrode and the earth electrode in the cavity on the nozzle plate side is from an arbitrary point on the nozzle plate side of the driving electrode to the tip of the earth electrode on the nozzle plate side. The straight line that is the shortest distance is arranged so as to form an angle of 60 ° or less with respect to the intersecting line between the plane that includes the straight line and that is perpendicular to the nozzle plate and the surface of the ground electrode. An electrostatic suction type inkjet head characterized by the above.   5. The electrostatic suction ink jet head according to claim 1, wherein the ground electrode extends to a surface of the pressure generating body where the cavity opens.   6. The ground electrode is formed in a single strip extending over all the cavities on a substrate provided so as to block the upper and / or lower sides of the cavities. The electrostatic attraction type inkjet head described. The electrostatic attraction type inkjet head according to any one of claims 1 to 6,
A counter electrode disposed so as to oppose a recording medium between the nozzle plate of the electrostatic suction ink jet head; and
An ink jet recording apparatus comprising: a power source that forms an electric field by applying a voltage between the electrostatic suction ink jet head and the counter electrode.

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