EP0899105B1

EP0899105B1 - Electrostatic ink jet recording head

Info

Publication number: EP0899105B1
Application number: EP19980113591
Authority: EP
Inventors: Shima Kazuo; Suetsugu Junichi; Mizoguchi Tadashi; Minemoto Hitoshi; Takemoto Hitoshi; Saeki Tomoya; Hagiwara Yoshihiro; Yakushiji Toru
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 1997-07-22
Filing date: 1998-07-21
Publication date: 2003-05-28
Anticipated expiration: 2018-07-21
Also published as: EP0899105A3; DE69815000T2; EP0899105A2; JPH1134338A; JP2937955B2; DE69815000D1

Description

The present invention relates to an electrostatic ink jet recording head whereby printing is performed by using the electrostatic force created by an electric field to discharge ink containing charged toner particles.
Conventionally, printer recording technology based on non-impact systems has the advantage that the generation of noise during recording etc. is so small as to be negligible. Ink-jet recording systems, in particular, allow printing and recording at high speed directly onto a recording medium, using a simple construction.
Furthermore, they also allow recording onto normal paper, and therefore represent extremely advantageous recording systems.
For example, Figs. 6 - 9 illustrate a conventional example of a recording head proposed as an ink-jet recording system. This conventional example uses an ink containing toner particles dispersed in a carrier liquid for printing onto recording paper 8. In addition to needle-shaped recording electrodes 3 provided on the recording head side, an opposing electrode 7 is also provided at the rear side of the recording paper in a position opposing the recording electrodes 3. In this system, an electric field is generated by applying a voltage to the recording electrodes 3 and the opposing electrode 7, and the toner particles in the ink are ejected towards the recording paper 8 by means of the electrostatic force created by the electric field.
As shown in Fig. 6, the ink-jet recording head comprises a substrate 1 made from an insulating material of plastic, or the like, and a base film 2 covering this substrate 1. The base film 2 is made from an insulating material, such as polyimide, and has a thickness of approximately 50 µm. A plurality of recording electrodes 3 are patterned on the surface of this base film 2.
The recording electrodes 3 are formed by plating a conductive material of copper (Cu), or the like, onto the surface of the base film 2 to a thickness of 20 - 30 µm, and then patterning such that the interval between adjacent electrodes is 300 dpi pitch, namely, about 85 µm.
The end portion of each recording electrode 3 projects externally (towards the opposing electrode) from one edge of the base film 2 by about 80 - 500 µm. The surface of the recording electrodes 3 is covered uniformly by a film of insulating coating material 4 to a thickness of 10 µm or less, as shown in Fig. 7 and Fig. 8, which are enlargements of the portion indicated by arrow A in Fig. 6.
Furthermore, in the ink-jet recording head, a portion of the upper surface of the base film 2 is covered by a cover 5. The cover 5 is formed from an insulating material and is shaped such that it does not interfere with the projecting end portions of the recording electrodes 3. An ink supply inlet 5a and an ink drain outlet (not illustrated) are provided, respectively.
The space enclosed by the base film 2 and the cover 5 forms an ink chamber, and ink is introduced via the ink supply inlet 5a such that the ink 6 is always in a full state inside the chamber.
A slit-shaped ink spray outlet 5b is formed at the edge of the cover 5, between the cover 5 and the base film 2. The aforementioned end portions of the recording electrodes 3 project through this ink spray outlet 5b. Thereby, an ink meniscus indicated by symbol 6a is formed at this slit-shaped ink spray outlet 5b.
A constant back-pressure is applied to the ink 6 in the ink chamber.
Therefore, due to the surface tension and capillary action of the ink itself, the ink 6 forms an ink meniscus 6a having a concave shape at the ink spray outlet 5b. Since the end portions of the recording electrodes 3 project from the base film 2 and the cover 5, when viewed from above as in Fig. 7, the ink meniscus 6a forms a U-shape between adjacent recording electrodes 3. Furthermore, as shown in Fig. 8, when viewed from the side, the ink meniscus 6a has a downward concave shape.
Therefore, when a high-voltage pulse is supplied to one of the recording electrodes, the electric field concentrates on the end region of the ink meniscus 6a at the projecting end portion of that electrode. Induced by this electric field, the charged toner in the ink is expelled from the end region of the ink meniscus 6a. This forms an ink drop 6b, as shown in Fig. 7, which is ejected towards the recording paper 8 on the side of the opposing electrode 7 positioned opposite the recording head, and is thereby printed onto the recording paper 8.
Fig. 9 shows an approximate diagram of equipotential lines showing the potential generated between the recording electrodes 3 and the opposing electrode 7 during recording in a conventional ink-jet recording head.
When a voltage is supplied to a recording electrode 3, the equipotential lines in the vicinity of the projecting point 3a at the end of that recording electrode 3 assume a semi-elliptical shape surrounding the recording electrode 3, whose end portion is projecting from the ink spray outlet 5b. Furthermore, in PCT international publication (International Publication Number WO 93/11866), an invention is disclosed wherein conductive members projects towards an opposing electrode, and prescribed particles are caused to fly out from the ends of the conductive members by an electric field generated between these conductive members and the opposing electrode.
However, the conventional ink-jet recording heads described above, have the following kinds of problems. A first problem is that it is difficult to form the ink into a desired dot size when recording onto recording paper. This is because a high-voltage pulse is supplied to the recording electrode 3 as a recording voltage, and the end portion of the recording electrode 3 itself forms a discharge point 3a for the ink 6. In this process, there is insufficient electrostatic force acting on the toner particles near the discharge point 3a in the direction of the discharge point 3a.
In other words, as shown in Fig. 9, in the region surrounding the recording electrode 3, the equipotential lines 9 are virtually parallel to the direction of ink discharge, with the exception of the region in front of the discharge point 3a (opposing electrode side). Therefore, insufficient electrostatic force is generated in the direction of the discharge point 3a with respect to toner particles in the vicinity of the discharge point 3a. Since the electrostatic force acting on the toner particles is weak, the amount of toner particles supplied to the discharge point 3a is insufficient for forming the desired dot size.
A second problem is that the discharge of ink droplets becomes unstable. This is because the ink meniscus 6a connects continuously across the recording electrodes 3, having vertices at the discharge points 3a, and therefore, the liquid surface in the vicinity of a discharge point 3a which has discharged ink will vibrate and affect the ink meniscus 6a, thus making it impossible to obtain an ink meniscus 6a that is stable at all times.
A third problem is the occurrence of ink droplet discharge faults due to excessive concentration of toner particles in the ink spray outlet 5b. The reason for this is that the ink spray outlet 5b in the cover which supplies ink 6 to the discharge points 3a for discharge, is formed in a portion of the ink chamber in the shape of a slit of a size which prevents overflowing of ink. Consequently, no flow of ink 6 is produced at the ink spray outlet 5b, and there is an excessive concentration of toner particles in this region, causing the ink viscosity to rise above the required level.
Further, a fourth problem is that, in a conventional electrostatic ink jet recording head as described above, in order to feed recording paper 8 between recording electrode 3 and counter electrode 7, it is necessary to ensure a gap between recording electrode 3 and counter electrode 7 of at least about 0.5 ∼ 1 mm. However, a problem with such an electrostatic ink jet recording head is that, in order to effect discharge of ink drops by means of an electrical field between recording electrode 3 and counter electrode 7, the recording voltage needed for discharge of the ink drops must be made high.
In JP 05 208499A an ink jet head is provided with a first head member comprising delivery ports which are formed as cylindrical openings on a front plate. Further a second head member is provided having a recessed part detachably receiving the first head member and an ink delivery opening on a front plate which is disposed opposite to said ink delivery ports. A control electrode is provided around the ink delivery ports and a common electrode is provided around the ink delivery opening.
An object of the present invention is to reduce a recording voltage.
This object of the present invention is achieved by means of an electrostatic ink jet recording head comprising: a jet member equipped with at least one ink jet terminal projecting towards the recording paper that is fed thereto, an ink supply path for feeding ink containing toner to each ink jet terminal, at least one recording electrode whereby ink from each discharge terminal is made to fly individually towards the recording paper, and a control electrode that attracts the toner arranged between the recording paper and the ink jet terminal.
With such an electrostatic ink jet recording head, when a pulse voltage is applied to the recording electrodes, ink drops are discharged from the ink jet terminals. An electric field is then produced in the direction from the ink jet terminals towards the control electrode, causing the ink drops to fly towards the recording paper.
Since the control electrode is arranged in front of the recording paper, it can be arranged closer to the ink jet terminal than the conventional counter electrode. The voltage applied to the recording electrodes can therefore be lower.
A further object of the present invention is to prevent deterioration of printing at high drive frequencies.
In this case, the recording electrodes are arranged in positions in the vicinity of the ink jet terminals described above. The terminals of the recording electrodes that are closest to the recording paper are then installed in positions further from the recording paper than the respective ink jet terminals. By this means, all of the ink supplied to the ink jet terminals and that is still adhering further forward than the recording electrode flies out due to the effect of the electrical field formed by the recording electrode. Consequently, printing deterioration is prevented since ink insufficiency cannot occur even if voltage of high drive frequency is applied to the recording electrode.
A further object of the present invention is to stabilise discharge of ink drops.
In this case, two planar surfaces are formed adjacent the jet member described above, and a plurality of parallel grooves are provided from the edge of one planar surface through the boundary line as far as the edge of the other planar surface. These grooves constitute ink supply paths. Recording electrodes are then provided in alternate ones of the plurality of rail-shaped sections defined between the grooves. The portions of the rail-shaped sections where the recording electrodes are provided that project due to the boundary line then constitute ink jet terminals.
In this way, each ink jet terminal has, arranged on both sides thereof, a rail-shaped section provided with a recording electrode. Consequently, the ink meniscus that is formed at the periphery of each ink jet terminal is partitioned by a rail-shaped section¹ from the ink meniscus of the adjacent ink jet terminal. Effects from the surroundings when the ink flies out can thus be suppressed.
A further object of the present invention is to avoid discharge of ink drops being adversely affected by excessive concentrations of toner particles.
In this case, one terminal of each groove formed in the projecting member is connected with an ink chamber for supply purposes, while the other terminal is connected with an ink chamber for discharge purposes. The ink therefore flows within each groove from one terminal to the other terminal. Poor ink discharge can thereby be prevented since the recording electrode assists part of this flowing ink to fly out, with the result that excess ink cannot accumulate around the ink jet terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a cross-sectional view of an electrostatic ink jet recording head according to the present invention;
Fig. 2 is a detail view of Fig. 1;
Fig. 3 is a perspective view shown partially a cross-section of an electrostatic ink jet recording head;
Fig. 4 is a detail view of Fig. 3;
Fig. 5 is a view seen from above of the ink jet terminals;
Fig. 6 is a perspective view of a prior art electrostatic ink jet recording head;
Fig. 7 is a top view of the ink jet terminals of a prior art electrostatic ink jet recording head;
Fig. 8 is a cross-sectional view seen from the side of the ink jet terminals of a prior art electrostatic ink jet recording head; and
Fig. 9 is a diagram of equipotential lines generated on recording by a prior art electrostatic ink jet recording head.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, an electrostatic ink jet recording head 10 according to the present invention as set out in the appended claims will be described with reference to the drawings.
Fig. 1 is a cross-sectional view of an electrostatic ink jet recording head 10 according to the present invention; Fig. 2 is a detail view of Fig. 1; Fig. 3 is a perspective view shown partially in cross-section of electrostatic ink jet recording head 10; Fig. 4 is a detail view of Fig. 3; and Fig. 5 is a view showing a discharging portion from above.
This electrostatic ink jet recording head 10 comprises the following:
(a) a jet member 20 comprising at least one ink jet terminal 22 that projects towards recording paper 41 that is fed thereto;
(b) a holding block 25 that holds jet member 20 from the side nearest the recording paper 41;
(c) grooves 61 constituting ink supply paths for surpplying ink containing toner to each ink jet terminal 22;
(d) at least one recording electrode 31 whereby ink drops from each ink jet terminal 22 are made to fly individually towards recording paper 41;
(e) a control electrode 64 that attracts toner and that is arranged between ink jet terminals 22 and recording paper 41, and
(f) a coupling block 70 that sandwiches jet member 20 by co-operating with holding block 25.
Further a counter electrode 40 that attracts toner is provided opposite the recording head 10 is arranged in a position behind recording paper 41.
Thus, jet member 20 has two adjacent planar faces 23, 24 and the ink jet terminals 22 are arranged in a row along a boundary line 62 formed at the boundary of these.
Also, holding block 25 has a flat face 25a facing recording paper 41; and a recessed face 25b in contact with the two planar faces 23, 24 of the jet member 20.
Furthermore, holding block 25 is provided with a discharge port 25c as through hole communicating from recessed face 25b facing the ink jet terminals 22 as far as the flat face 25a.
The various sections are described in detail below.
Jet member 20 is a rectangular prismatic block made of insulating material of dielectric coefficient less than 10. As specific examples, ceramics or polymer materials etc. may be employed.
This jet member 20 is formed with a plurality of concave/convex shapes that are continuous over the mutually contacting two planar faces 23, 24.
These concave/convex shapes are formed by a plurality of parallel grooves 61 on planar faces 23, 24 provided from the top edge of planar face 23 and extending to the bottom edge of planar face 24. The boundary of the two planar faces 23, 24 constitutes the boundary line 62, which projects in the direction in which the ink 50 flies. Grooves 61 are formed along the perpendicular direction with respect to the boundary line 62 of planar faces 23, 24, and all the grooves 61 pass through boundary line 62.
These grooves 61 constitute ink supply paths of a plurality of ink jet terminals 22.
A plurality of rail-shaped sections 63 are formed defined between these grooves 61. Recording electrodes 31 are installed on alternate ones of these rail-shaped sections 63 on the face corresponding to planar face 23.
Ink jet terminals 22 are constituted by the tips of portions of rail-shaped sections 63 that are bent along the boundary line 62 where the recording electrodes 31 are installed. Jet member 20 is held by holding block 25 and coupling block 70 in a condition with the ink jet terminals 22 facing counter electrode 40.
Recording electrodes 31 are held within recording electrode substrate 3. This recording electrode substrate 3 comprises a thin plate-shaped insulating substrate or film consisting of polymeric material, respectively independent recording electrodes 31 being formed thereon.
Furthermore, the surfaces of recording electrodes 31 are covered by an insulating coating material 32. The thickness of substrate 3 is set less than 10 µm. Also, this recording electrode substrate 3 is installed at the upper surface of rail-shaped sections 63 in a position retracted by a few tens of µm from the discharge terminal 22. It thus covers the open portions of grooves 61 that belong to planar face 23 so that ink can flow within grooves 61.
Furthermore, the tips (i.e. the portions nearest the recording paper that is fed thereto) of recording electrodes 31 are arranged at the same interval as the desired dot pitch at one end of recording electrode substrate 3. At the rear end of recording electrodes 31, there are provided electrode pads for connection to an external driver power source, not shown.
The rail-shaped sections 63 of jet member 20 are formed at intervals of 1/2 of the desired dot pitch. Recording electrodes 31 are arranged on the top face of rail-shaped sections 63 along alternate rail sections 63 in a condition with their respective central axes aligned. The width of rail-shaped sections 63 is desirably a width of less than 20 µm but, in contrast, the width of recording electrodes 31 is set to a width that is greater than this.
The rail-shaped sections 63 where recording electrodes 31 are not installed function as partitions. Specifically, these partitions prevent transmission of vibrations of meniscus 52 after discharge of an ink drop 21 from ink jet terminal 22 to a meniscus 52 of another ink jet terminal 22.
Holding block 25 is formed of an insulating material (ceramics or polymeric material etc.) of dielectric coefficient less than 10. Its recessed face 25b is provided with a contact face 252b that directly contacts planar face 24 and contact face 251b where the planar face 23 of jet member 20 is in contact through recording electrode substrate 3. This contact face 252b covers the open section of the portion of grooves 61 belonging to planar face 24.
Ink can thereby flow within grooves 61.
At the boundary portion of the two planar faces 251b, 252b, there is provided discharge port 25c in the form of minute slits communicating from recessed face 25b to side face 25a. These discharge ports 25c open more widely as they approach side face 25a. Consequently, even if the ink in grooves 61 overflows to discharge port 25c, return to grooves 61 can be rapidly effected.
Furthermore, a control electrode 64 is installed on holding block 25 above its side face 25a. This control electrode 64 is of flat plate shape along side face 25a and is provided at the periphery of discharge ports 25c. Also, this control electrode 64 is formed with holes 64a for passage of ink corresponding to discharge ports 25c.
The side face 25a of holding block 25 is arranged nearer to printing paper 41 than the ink jet terminals 22. Control electrode 64 is therefore also positioned nearer to recording paper 41 than ink jet terminals 22. This control electrode 64 consists of conductive material such as metal and is earthed. The toner in ink 50 is positively charged. Consequently, when a positive pulse voltage is applied to recording electrodes 30, ink 50 is attracted towards the side of control electrodes 64, and is easily made to fly towards recording paper 41. Control electrode 64 may be connected to the negative electrode of an external voltage source, not shown.
Counter electrode 40 is arranged opposite the side face 25a of holding block 25. This counter electrode 40 is arranged such as to maintain a desired separation from side face 25a. Counter electrode 40 also functions as a platen for transporting recording paper 41. The recording paper 41 that is fed by a feed mechanism not shown, is therefore conveyed along a planar surface of counter electrode 40 facing ink jet terminals 22.
Also, this counter electrode 40 is made of conductive material such as metal and is earthed. Consequently, when a positive pulse voltage is applied to the recording electrodes, ink drops 51 fly towards counter electrode 40. Counter electrode 40 may be connected with the negative electrode of an external voltage source, not shown.
Coupling block 70 holds jet member 20 from the opposite side to block 25. Jet member 20 is therefore enclosed in a tightly sealed condition by means of the holding block 25 and coupling block 70.
This coupling block 70 is provided with an ink chamber 71 for ink supply purposes facing the bottom edge of planar face 24 of jet member 20. This ink chamber 71 is likewise connected to the lower end of each groove 61. An ink supply conduit 71a for supplying ink 50 from outside is connected to this ink chamber 71.
Furthermore, this coupling block 70 is provided with an ink chamber 72 for ink discharge purposes facing the upper edge of planar face 23 of jet member 20. This ink chamber 72 is also connected with the upper end of each groove 61. An ink discharge conduit 72a for discharging ink 50 to the outside is connected to this ink chamber 72.
Furthermore, an ink tank having a circulatory mechanism, not shown, is connected to ink supply conduit 71a and ink discharge conduit 72a. In this way, circulation of ink is constantly effected between electrostatic ink jet recording head 10 and the ink tank.
Consequently, ink 50 that is supplied to ink chamber 71 is discharged to ink chamber 72 through grooves 61. Circulation of ink 50 within grooves 61 is therefore performed continuously. It is desirable that the ink chamber 72 for discharge purposes should be arranged above ink chamber 71 for supply purposes in order to prevent any bubbles of air from ink jet terminals 22 that are entrained being left behind in the electrostatic ink jet recording head 10.
A migration electrode 13 that effects liquid contact with ink 50 in each groove is installed within ink chamber 71 for supply purposes. This migration electrode 13 is made of a conductive material such as metal, is connected to an external voltage source, not shown, and has a positive voltage applied to it.
The operation of electrostatic ink jet recording head 10 will now be described.
Circulation of ink 50 is effected with a pressure within a range not exceeding the capillary force of the ink jet terminals 22 that are formed in jet member 20. As a result, as shown in Fig. 5, meniscuses 52 whose apices are the ink discharging terminals 22 are formed on both sides of the ink discharging terminals 22.
A fixed bias voltage of the same polarity as the charged toner particles is applied to migration electrode 13. Also, a fixed bias voltage of different polarity from the charged toner particles or of ground level is applied to control electrode 64.
Furthermore, a bias voltage of potential lower than that of the control electrode 64 or of the same potential as control electrode 64 is constantly applied to the counter electrode 40.
Ink 50 in which toner particles are dispersed is pulled up to a potential such that discharge does not occur, by means of migration electrode 13, and is supplied to each ink jet terminal 22.
On printing, a drive pulse voltage of the same polarity as the toner is applied from a driver, not shown, to the desired recording electrode 31. By this means, an electric field is generated between recording electrode 31 and control electrode 64. An electrostatic force acts on the toner particles in the ink 50 that is supplied to ink jet terminal 22 and, since this exceeds the surface tension of meniscus 52, ink drops 51 containing toner particles are discharged towards counter electrode 40 from the ink jet terminals 22. After passing through discharge port 25c, ink drops 51, maintaining the inertial force produced by their discharge, attach themselves to recording paper 41 on counter electrode 40, thereby effecting printing.
As shown in Fig. 4, the equipotential lines 60 in front of ink jet terminals 22 when recording voltage is applied are formed such as to intersect practically at right angles the discharge direction. Also, an electrostatic force in the forwards direction is generated on toner particles at the side face of ink jet terminal 22. Consequently, toner particles are supplied to the tip of ink jet terminal 22 even whilst recording voltage is being applied. Furthermore, since meniscus 52 is formed in front of recording electrode 31, an ample supply of toner particles can be supplied to the tip of ink jet terminal 22 when recording voltage is applied. Consequently, since the supply of toner particles to ink jet terminals 22 can be altered by changing the time for which recording voltage is applied, dots of any desired diameter can be formed.
Also, since the electric field for effecting discharge is generated between the recording electrode 31 and control electrode 64, a sufficient electric field density for effecting discharge can be concentrated in the vicinity of ink jet terminal 22. Furthermore, even when the separation between the recording electrode 31 and counter electrode 40 is varied, the effect of this on discharge of ink drops 51 can be reduced.
It is possible to provide recording electrodes 31 on all of the rail-shaped sections 63 described above. In this way, the dot pitch can be halved, albeit there is some effect on adjacent meniscuses when ink flies from a particular ink jet terminal 22.
The invention may be embodied in other specific forms without departing from the disclosure of claim 1 and its depending claims.
The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

An Electrostatic ink jet recording head (10) comprising:

(a) a jet member (20) having at least one ink jet terminal (22) that projects towards recording paper (41) that is fed thereto;

(b) an ink supply path (61) for feeding ink (50) containing toner to said ink jet terminal (22);

(c) at least one recording electrode (31) that causes the ink drop containing toner (51) from said ink jet terminal (22) to fly towards said recording paper (41);

(d) a control electrode (64) that attracts said ink drop containing toner and is arranged between said ink jet terminal (22) and said recording paper (41) and ;

(e) a holding block (25) that holds said jet member (20) from the side nearest said recording paper (41); wherein

said holding block (25) has one flat face (25a) facing said recording paper (41) and a recessed face (25b) having two faces (251b,252b) in contact with two planar faces (23, 24) of said jet member (20); and

said holding block (25) comprises a discharge port (25c) as through hole that effects communication from recessed face (25b) facing the ink jet terminal (22), to the flat face (25a) of said holding block (25), wherein said discharge port (25c) has a shape that diverges from a boundary portion of the two planar faces (251b,252b) of the recessed face (25b) towards said flat face (25a).
The electrostatic ink jet recording head (10) according to claim 1, said head further comprising, a counter electrode (40) arranged in a position behind said recording paper for attracting said toner, wherein the recording paper is between the ink jet recording head (10) and the counter electrode (40)
The electrostatic ink jet recording head according to claim 1 or 2, wherein recording electrodes (31) are arranged individually in positions in the vicinity of said ink jet terminals (22), and the recording electrode terminals that are closest to the recording paper are installed in positions further from said recording paper (41) than said ink jet terminals (22).
The electrostatic ink jet recording head according to any of claims 1 to 3, wherein said control electrode (64) is a flat plate-shaped electrode arranged between said ink jet terminals (22) and said recording paper (41), and having a hole (64a) for passage of ink drops (51) that fly from said ink jet terminals (22).
The electrostatic ink jet recording head (10) according to any of claims 1 to 4, comprising

said two planar faces (23, 24), whose boundary defines a boundary line (62) on which said ink jet terminals (22) are arranged in a row; and wherein

said holding block (25) having one flat face (25a) facing said recording paper (41) has said control electrode (64) installed thereon.
The electrostatic ink jet recording head according to any of claims 1 to 5, wherein said control electrode (64) is a plate-shaped electrode installed at the periphery of said discharge port (25c) of said one flat face (25a) of said holding block (25), and having a hole (64a) for the passage of ink in positions corresponding to said discharge port (25c).
The electrostatic ink jet recording head according to any of claims 1 to 6, wherein said ink supply path is formed as mutually parallel grooves (61) that extend continuously over said-planar face (23) and said planar face (24); and a plurality of rail-shaped sections (63) defined by said grooves (61) constitute respectively said ink jet terminals (22) along said boundary line (62).
The electrostatic ink jet recording head according to any of claims 1 to 7, wherein said at least one recording electrode (31) is installed on said rail-shaped sections (63) belonging to one or other of said planar faces (23,24).
The electrostatic ink jet recording head according to any of claims 1 to 6, wherein said ink supply path is formed as mutually parallel grooves (61) extending continuously over said planar face (23) and said planar face (24); and a plurality of rail-shaped sections (63) defined by said grooves (61) constitute, alternately, said ink jet terminals (22) along said boundary line (62).
The electrostatic ink jet recording head according to claim 9, wherein said recording electrodes (31) are installed on said rail-shaped sections (63) having said ink jet terminals (22), belonging to one or other of said planar faces (23,24).
The electrostatic ink jet recording head according to claim 10, wherein the width of said recording electrodes (31) is set to be wider than the width of said rail-shaped sections (63).
The electrostatic ink jet recording head (10) according to any of claims 1 to 11, further comprising a coupling block (70) for sandwiching said jet member (20) by co-operating with said holding block (25); wherein said coupling block (70) includes a first ink chamber (71) which is supplied with said ink (50) from outside and communicates with the grooves (61) that are provided on one of said planar faces (24) of said jet member (20); and said coupling block further includes a second ink chamber (72) which communicates with the grooves (61) that are provided on said other planar face (23) of said jet member (20), so as to discharge said ink.
The electrostatic ink jet recording head according to claim 12, said head further comprising a migration electrode (13) which is installed within said ink chamber (71) and is directly in contact with ink (50) and to which voltage of the same polarity as the toner in said ink (50) is applied.
The electrostatic ink jet recording head according to any of claims 1 to 13, wherein said recording electrodes (31) are covered by a film of insulating coating material.
The electrostatic ink jet recording head according to any of claims 1 to 14, wherein said jet member (20) and said holding block (25) are made from an insulating material of dielectric coefficient less than 10.