EP2578408B1

EP2578408B1 - Inkjet head and method for producing inkjet head

Info

Publication number: EP2578408B1
Application number: EP11789892.4A
Authority: EP
Inventors: Hikaru Takamatsu
Original assignee: Konica Minolta IJ Technologies Inc
Current assignee: Konica Minolta IJ Technologies Inc
Priority date: 2010-06-03
Filing date: 2011-06-02
Publication date: 2016-05-18
Anticipated expiration: 2031-06-02
Also published as: EP2578408A1; EP2578408A4; WO2011152490A1; JP5720682B2; JPWO2011152490A1

Description

TECHNICAL FIELD

The present invention relates to an inkjet printhead and a method for making the same, and, in particular, to an inkjet printhead and a method for making the same that can prevent crosstalk in a simple way when drive signals are applied to channels of multiple channel rows.

BACKGROUND ART

So-called harmonica-type head chips are conventionally known as inkjet printheads that deform drive walls by applying predetermined drive signals (drive voltage) to drive electrodes provided on drive walls defining channels, and that discharge ink in the channels through nozzles using the pressure produced by the deformation. The harmonica-type head chips have openings of the channels on the front and rear faces thereof.
Such harmonica-type head chips have the problem of how to electrically connect the drive electrodes and a drive circuit with each other because the drive electrodes are provided inside the channels and are not exposed to the outside. Specifically, while a channel row disposed at the outer part of the head chip can easily be electrically connected to a flexible printed circuit (FPC) at the end of the head chip, it is not the case with a channel row disposed at the inner part of the head chip of the multiple channel rows arranged in parallel. More specifically, in the case of the outer channel row, connection electrodes which are electrically connected to the drive electrodes extend from the respective channels to the end of the head chip so as to electrically connect the channels to the FPC. However, when drive signals are applied at the end of the head chip to the drive electrodes of the inner channel row, the connection electrodes, which electrically connect with the respective drive electrodes, have to cross the outer channel row to the end of the head chip.
The technique disclosed in Patent Literature 1 has conventionally been known as a technique to provide electrodes that are electrically connected to drive electrodes of an inner channel row and that extend to the end of the head chip. Such a technique is illustrated in FIGS. 12A and 12B. FIG. 12A is a rear view of a head chip; and FIG. 12B is a cross-sectional view along the line xi-xi of FIG. 12A. In these drawings, only two channel rows on one side of the line O-O among four channel rows are shown.
The rear face 100a of the head chip 100 has the connection electrodes 102B thereon. The connection electrodes 102B are electrically connected to the drive electrodes 104 provided inside the respective channels 101 that are disposed in an inner channel row 101B out of the channel rows 101A and 101B. The connection electrodes 102B run on the drive walls 103 between the channels 101 of the outer channel row 101A and extend to the end 100b of the head chip 100. Accordingly, at the end 100b of the head chip 100, the connection electrodes 102A, which are pulled out from the respective channels 101 of the outer channel row 101A, and the connection electrodes 102B, which are pulled out from the respective channels 101 of the inner channel row 101B, are alternately arranged. This facilitates electric connection with the FPC at the end 100b of the head chip 100.
Similarly, the technique disclosed in Patent Literature 2 has conventionally been known as a technique to make electrodes that are electrically connected to the drive electrodes of an inner channel row and that extend to the end of the head chip. Such a technique is illustrated in FIGS. 13A and 13B. FIG. 13A is a rear view of a head chip; and FIG. 13B is a cross-sectional view along the line xii-xii of FIG. 13A. In these drawings, only two channel rows on one side of the line O-O among four channel rows are shown.
In the head chip 200, a connection electrodes, which is electrically connected to a drive electrode 204 provided inside a corresponding channel 201 of the inner channel row 201B out of the channel rows 201A and 201B, is provided as two separate parts. More specifically, one of the two separate parts is a first connection electrode 202B that is pulled out from the corresponding channel 201 in row B; and the other of the two parts is a second connection electrode 203B provided at the end portion 200b of the head chip 200. A laminated member 205 is stretched between the first connection electrode 202B and the second connection electrode 203B.
The laminated member 205 is composed of an insulating layer 205a and a metal layer 205b, and is disposed such that the insulating layer 205a is closer to the rear face 200a of the head chip 200 than the metal layer 205b. The laminated member 205 has overlapping portions where the laminated member 205 overlap the first connection electrode 202B, and where the laminated member 205 overlap the second connection electrode 203B. At each of the overlapping portions, a penetration portion 205c is provided where the metal layer 205b penetrates the insulating layer 205a. Thus, the overlapping portions of the laminated member 205 are connected with the first connection electrode 202B and the second connection electrode 203B, respectively. At the end 200b of the head chip 200, the connection electrodes 202A, which are pulled out from the respective channels 201 of the outer channel row 201A, and the second connection electrodes 203B, which are electrically connected to the respective drive electrodes 204 of the inner channel row 201B through the laminated members 205, are alternately arranged. This facilitates electric connection with the FPC at the end 200b of the head chip 200.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

Patent Literature 1: Japanese Patent Publication Laid-Open No. 2002-283560
Patent Literature 2: Japanese Patent Publication Laid-Open No. 2009-274328

EP 2 119 567 A1 teaches that on the back surface of a head chip having a plurality of rows of channels (row A, row B), the connection electrodes for row A that are electrically connected to the drive electrodes of the channels of row A are arranged, a first connection electrodes for row B that are electrically connected to the drive electrodes of the channels of row B are arranged between the rows of channels of row A and the rows of channels of row B, and also, between neighboring connection electrodes for row A, a second connection electrodes for row B are separately placed from the first connection electrodes for row B, the first connection electrodes and the second connection electrodes are connected electrically by drawing out interconnections, and the drawing out interconnections are in contact only with the first connection electrodes, the second connection electrodes, and not with the back surface of the head chip.

DISCLOSURE OF INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

With the technique disclosed in Patent Literature 1 as shown in FIGS. 12A and 12B, the connection electrodes directly adhere to the rear face 100a of the head chip 100. This makes it relatively easy for the connection electrodes 102B, which are electrically connected to the respective drive electrodes of the inner channel row 101B, to cross the outer channel row and to extend to the end 100b of the head chip 100. However, as the density of channels increases, the interval between channels (i.e., the thickness of a drive wall), between which each of the connection electrodes 102B is to pass, becomes smaller. Further, as the L length (i.e., the drive length of a channel) becomes shorter, the problem of crosstalk with the channels 101 having the drive walls 103 to which the connection electrodes 102B adhere becomes more serious.
That is, as shown in FIG. 12B, when drive signals are applied to the connection electrodes 102B adhering to the respective drive walls 103 of the outer channel row 101A on the rear face 100a of the head chip 100 in order to drive the channels 101 of the inner channel row 101B, difference in voltage might be produced between the connection electrodes 102B and the drive electrodes 104 provided on the drive walls 103 of the outer channel row. As a result, a portion of one of the drive walls 103, which is enclosed by a broken line in FIG. 12B, might be deformed at an unexpected timing. In the worst-case scenario, ink drops are discharged from the channels 101 of the outer channel row 101A, which is not a desired channel row.
With the technique disclosed in Patent Literature 2 as shown in FIGS. 13A and 13B, the electrodes do not adhere directly to the respective drive walls of the outer channel row 201A. Therefore, the problem of crosstalk does not arise.
In order to connect the first connection electrode 202B to the second connection electrode 203B, however, it is necessary to additionally provide the laminated member 205 over the rear face 200a of the head chip 200. That means the technique disclosed in Patent Literature 2 has a problem of low productivity. In addition, it is necessary to provide through-holes and lands in the insulating layer 205a in order that the metal layer 205b penetrates the insulating layer 205a at the positions of the first connection electrodes 202B and the second connection electrodes 203B for the laminated member 205. Since the diameters of through-holes and lands are difficult to reduce, providing through-holes and lands on the rear face of the head chip becomes more difficult as the density of channels increases. That is because the width between channels and the connection-electrode pitch become smaller as the density of channels increases.
In view of the above, an object of the present invention is to provide an inkjet printhead that does not let crosstalk occur when each of the connection electrodes, which is electrically connected to the drive electrode of a corresponding channel, runs over a drive wall between channels of another channel row and extends to the end of the head chip; and to provide an inkjet printhead that can easily include increased density of channels.
Another object of the present invention is to provide the method for making an inkjet printhead with ease that does not let crosstalk occur when each of the connection electrodes, which is electrically connected to the drive electrode of a corresponding channel, runs over a drive wall between channels of another channel row and extends to the end of the head chip; and to provide an inkjet printhead that can easily include increased density of channels.
Another object of the present invention will become apparent from the descriptions given below.

MEANS FOR SOLVING PROBLEMS

In order to solve the above-mentioned objects, there is provided an inkjet printhead, as set out in independent claim 1, and a method for making an inkjet printhead, as set out in independent claim 7. Advantageous developments are defined in the dependent claims. electrode provided on the rear face of the head chip, wherein the connection electrode extends from the channel of a first channel row of the channel rows, running over the drive wall between the channel and another channel of a second channel row of the channel rows, to an end of the head chip; and the connection electrode has a shape of a continuous single line; a nozzle from which ink in the channel is discharged by deforming the drive wall when a drive signal is applied to the drive electrode through the connection electrode; and an insulating film provided between a surface of the drive wall of the second channel row and the connection electrode running over the drive wall of the second channel row on the rear face of the head chip.
The present invention of claim 2 provides the inkjet printhead according to claim 1, wherein the insulating film is made of inorganic insulating material.
The present invention of claim 3 provides the inkjet printhead according to claim 2, wherein the inorganic insulating material is one of SiO₂ and Al₂O₃.
The present invention of claim 4 provides the inkjet printhead according to claim 1, wherein the insulating film is made of organic insulating material.
The present invention of claim 5 provides the inkjet printhead according to claim 4, wherein the organic insulating material is photopolymer material.
The present invention of claim 6 provides the inkjet printhead according to claim 4 or 5, wherein the organic insulating material is polyimide.
The present invention of claim 7 provides a method for making an inkjet printhead including a head chip that includes : multiple channel rows, each of the channel rows including a channel and a drive wall alternately arranged, wherein the drive wall is composed of a piezoelectric element, and the channel has an opening disposed in each of a front face and a rear face of the head chip; a drive electrode provided on the drive wall facing inside of the channel; a connection electrode provided on the rear face of the head chip, wherein the connection electrode extends from the channel of a first channel row of the channel rows, running over the drive wall between the channel and another channel of a second channel row of the channel rows, to an end of the head chip; and the connection electrode has a shape of a continuous single line; and a nozzle from which ink in the channel is discharged by deforming the drive wall when a drive signal is applied to the drive electrode through the connection electrode, the method comprising: forming an insulating film at least on a surface of the drive wall over which the connection electrode is to be provided on the rear face of the head chip; and forming the connection electrode on the rear face of the head chip on which the insulating film has been formed.
The present invention of claim 8 provides the method for making the inkjet printhead according to claim 7, wherein the insulating film is formed by sputtering using inorganic insulating material such that the insulating film is patterned.
The present invention of claim 9 provides the method for making the inkjet printhead according to claim 8, wherein the insulating film is made of one of SiO₂ and Al₂O₃.
The present invention of claim 10 provides the method for making the inkjet printhead according to claim 7, wherein the insulating film is formed by an inkjet method using organic insulating material such that the insulating film is patterned.
The present invention of claim 11 provides the method for making the inkjet printhead according to claim 7, wherein the insulating film is formed using photopolymer material and patterned by performing exposure and development.
The present invention of claim 12 provides the method for making the inkjet printhead according to claim 10 or 11,

EFFECTS OF THE INVENTION

According to the present invention, there is provided an inkjet printhead that does not let crosstalk occur when each of the connection electrodes, which is electrically connected to the drive electrode of a corresponding channel, runs over a drive wall between channels of another channel row and extends to the end of the head chip. Further, the inkjet printhead can easily include increased density of channels.
Further, according to the present invention there is provided the method for making an inkjet printhead with ease that does not let crosstalk occur when each of the connection electrodes, which is electrically connected to the drive electrode of a corresponding channel, runs over a drive wall between channels of another channel row and extends to the end of the head chip; and that can easily include increased density of channels.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a rear view of a head chip;
FIG. 2 is a cross-sectional view along the line ii-ii of FIG. 1;
FIG. 3 is a cross-sectional view along the line iii-iii of FIG. 1;
FIG. 4 is an exploded perspective view of an inkjet printhead according to the present invention;
FIG. 5A illustrates a method of forming insulating films on the head chip;
FIG. 5B illustrates a method of forming insulating films on the head chip;
FIG. 6A illustrates another method of forming insulating films on the head chip;
FIG. 6B illustrates another method of forming insulating films on the head chip;
FIG. 7A illustrates still another method of forming insulating films on the head chip;
FIG. 7B illustrates still another method of forming insulating films on the head chip;
FIG. 8 is a rear view of a head chip having another type of an insulating film;
FIG. 9 is a rear view of a head chip having still another type of an insulating film;
FIG. 10 is a cross-sectional view along the line x-x of FIG. 9;
FIG. 11 is a rear view of a head chip having six channel rows;
FIG. 12A is a rear view of a conventional head chip;
FIG. 12B is a cross-sectional view along the line xi-xi of FIG. 12A;
FIG. 13A is a rear view of a conventional head chip; and
FIG. 13B is a cross-sectional view along the line xii-xii of FIG. 13A.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

In the head chip according to the present invention, multiple channel rows are arranged in parallel. In each of the channel rows, drive walls, which are composed a piezoelectric element, and channels are alternately disposed. In the head chip, the openings of the respective channels are provided on the front and rear faces. On the surfaces of the drive walls facing inside the respective channels, drive electrodes are respectively provided.
The head chip is a so-called harmonica-type head chip which has a shape of hexahedron. Connection electrodes are provided on the rear face of the head chip so that predetermined drive signals will be applied to the drive electrodes provided on both surfaces of the drive walls. Each of the connection electrodes has a shape of a continuous single line. Each of the connection electrodes extends from a corresponding channel of a channel row, running over the drive wall between channels of another channel row, to the end of the head chip. When drive signals are applied to the drive electrodes through the connection electrodes, the drive walls are each deformed into a dog-leg shape. This causes change in pressure on ink in channels for the ink to be discharged. Thus, ink drops are discharged from nozzles arranged on the front face of the head chip.
In the present invention, the side of the harmonica-type head chip having nozzles to discharge ink is referred to as "front face", and the other side is referred to as "rear face".
The connection electrodes are disposed at the end portion, parallel to the channel rows, of the rear face of the head chip. Drive signals are applied to the connection electrodes at the end of the rear face of the head chip. In a case where one or more additional channel rows are disposed between the channels which are electrically connected with the connection electrodes and the end of the head chip, each of the connection electrodes is formed as a continuous single line and runs over a drive wall between channels of the additional channel rows to extend to the end of the head chip.
A connection electrode formed as a continuous single line means that a connection electrode provided on the rear face of the head chip extends from a corresponding channel to the end of the head chip as a single line with no break. That is, "a connection electrode formed as a continuous single line" does not include separate electrodes that are connected with another wiring member interposed therebetween, even if such separate electrodes are electrically connected with each other.
Though any number of channel rows may be arranged on the head chip as long as the number is more than two, the number is preferably eight or less. That is because the number of connection electrodes to be arranged within a limited width of a drive wall between channels increases as the number of channel rows increases.
In the rear face of the head chip, an insulating film is provided between a connection electrode running over each drive wall of the channel row and the surface of each drive wall. Therefore, each of the connection electrodes, which runs over a drive wall between channels of another channel row and which extends to the end of the head chip, never fails to run on the surface of an insulating film.
Therefore, each of the connection electrodes running over a corresponding drive wall between channels of another channel row does not directly come in contact with the drive wall at least at the position of the drive wall. As a result, there is no danger that the voltage will leak to the drive walls when drive signals of a predetermined voltage are applied to the connection electrodes. That is, there is no danger of causing crosstalk. In addition, since each of the connection electrodes is formed as a continuous single line, there is no need to provide through-holes and lands which would be necessary in a conventional case where a laminated member composed of an insulating layer and metal layer is formed. This allows a width between channels or an electrode pitch to be extremely small in the case of a high channel density.
The insulating film may be provided only on the surface of each drive wall on which a connection electrode is to be provided between channels on the rear face of the head chip, or may be provided on another region including the surface of each drive wall between the channels, e.g., may be provided on the whole rear face of the head chip (except for the positions of openings of channels).
Any one of inorganic insulating material and organic insulating material may be used to form an insulating film. The thickness of the insulating film is preferably 0.1 to 20 µm.
As inorganic insulating material, SiO₂, Al₂O₃, TiO₂, Si₃N₄, or glass may be used, and above all, SiO₂ or Al₂O₃ is preferable. An insulating film in a desired pattern can easily be formed by sputtering using suitable mask material such as a dry film on the rear face of the head chip.
As organic insulating material, photopolymer material may be preferably used. An insulating film in a desired pattern can easily be formed by performing exposure and development on photopolymer material which has been applied to the rear face of the head chip.
An insulating film may be formed in such a way that liquid organic insulating material is applied to form a layer on the rear face of the head chip by an inkjet method. In this case, an insulating film in a desired pattern can easily be formed as well. As the organic insulating material, polyimide may be used.
In the method for making an inkjet printhead according to the present invention, an insulating film is provided at least on the surface of each drive wall on which a connection electrode is to be provided on the rear face of the head chip. After that, the connection electrodes, each of which has a shape of a continuous single line, are provided on the insulating film on the rear face of the head chip.
According to the method, the only required step is to provide connection electrodes after the insulating film is provided on the rear face of the head chip. Therefore, a head chip can be made easily that avoids occurrence of crosstalk and eliminates problems that would arise in high density of channels.
An embodiment of the present invention is described below with reference to the drawings.
FIG. 1 is a rear view of a head chip; FIG. 2 is a cross-sectional view along the line ii-ii of FIG. 1; FIG. 3 is a cross-sectional view along the line iii-iii of FIG. 1; and FIG. 4 is an exploded perspective view of an inkjet printhead according to the present invention.
The head chip 1 has multiple channel rows that are arranged in parallel in the vertical direction in FIG. 1. In one of the rows, drive walls 11A and channels 12A are arranged alternately; and in another row, drive walls 11B and channels 12B are arranged alternately. Each of the drive walls 11A and 11B is composed of a piezoelectric element. In the head chip 1, the outermost channel row, i.e., the lower channel row in FIG. 1, is referred to as row A; and the inner channel row adjacent to the channel row A, i.e., the upper channel row in FIG. 1, is referred to as row B.
The head chip 1 in the present embodiment has four channel rows that are arranged in parallel in the vertical direction in FIG. 1. Since the head chip 1 having the four channel rows is symmetrical about the line O-O, only the lower two channel rows are shown in FIG. 1. Of the four channel rows, the two outermost channel rows can be taken as rows A, and the two inner channel rows adjacent to the respective two rows A can be taken as rows B. In the case of a head chip having only two channel rows, the line O-O corresponds to the upper end of the head chip. In the case of a head chip having three channel rows, another channel row is added on the side of the line O-O such that the added channel row is symmetrical to the channel row A shown in FIG. 1.
The openings of the channels 12A and 12B are provided in the front face 1a and the rear face 1b of the head chip 1, with the corresponding openings facing each other. The channels 12A of row A are displaced by half a pitch relative to the channels 12B of row B.
Drive electrodes 13 each composed of a metal film, such as Ni, Au, Cu, or Al, adhere to the inner walls of channels 12A and 12B (including the surfaces of the respective drive walls 11A and 11B facing inside the channels 12A and 12B, respectively).
Connection electrodes 14A for row A that are electrically connected to the respective drive electrodes 13 in all the channels 12A of row A are provided on the rear face 1b of the head chip 1. Each of the connection electrodes 14A separately extends from a corresponding channel 12A to the lower end 1c of the rear face 1b of the head chip 1, as shown in FIG. 1, in the direction perpendicular to the channel row (i.e., vertical direction in FIG. 1). The connection electrodes 14A are arranged at the lower end 1c at the same pitch as the channels 12A of row A. The connection electrodes 14A for row A are each formed of a single-line continuous metal film with no break extending from a corresponding channel 12A to the lower end 1c.
In a similar manner, connection electrodes 14B for row B that are electrically connected to the respective drive electrodes 13 in all the channels 12B of row B are provided on the rear face 1b of the head chip 1. Each of the connection electrodes 14B separately extends from a corresponding channel 12B to the lower end 1c, where the connection electrodes 14A for row A are also provided. That is, the connection electrodes 14A and 14B are arranged alternately at the lower end 1c. The connection electrodes 14B for row B are each formed of a single-line continuous metal film with no break extending from a corresponding channel 12B to the lower end 1c, in the same manner as the connection electrodes 14A. Each of the connection electrodes 14B extends from a corresponding channel 12B, running over a drive wall 11A between channels 12A of row A, to the lower end 1c.
An insulating film 15 adheres to the surface of each drive wall 11A between channels 12A of row A on the rear face of the head chip 1. Accordingly, each of the connection electrodes 14B for row B is provided on the surface of the insulating film 15 as shown in FIGS. 2 and 3, and is not in direct contact with the rear face 1b of the head chip 1 at the position between channels 12A of row A. This structure prevents drive signals of a predetermined voltage, which are applied to the connection electrodes 14B for row B, from leaking to the drive walls 11A each composed of a piezoelectric element. Therefore, the drive walls 11A are prevented from being driven at unexpected timings, i.e., a problem of crosstalk is avoided.
In providing the separate insulating films 15 on the respective drive walls 11A, any method may be employed as long as the insulating films 15 are provided on the surfaces of the respective drive walls 11A such that the connection electrodes 14B for row B do not directly come in contact with the surfaces of the drive walls 11A. However, from the viewpoint of avoiding occurrence of crosstalk without fail, it is preferable that the inequality of L1<L2 be satisfied as shown in FIG. 2, wherein L1 is the height of each channel 12A of row A (the length of each channel 12A in the direction perpendicular to the channel-row direction) ; and L2 is the length of each insulating film 15 (the length of each insulating film 15 in the direction perpendicular to the channel-row direction).
A nozzle plate 2 is bonded to the front face 1a of the head chip 1. In the nozzle plate 2, nozzles 21 are provided at the positions corresponding to the channels 12A and 12B of rows A and B, respectively.
A circuit board 3 is bonded to the rear face 1b of the head chip 1. The circuit board 3 is a plate which has an area at least larger than the rear face 1b of the head chip 1, which circuit board 3 is composed of, for example, glass or ceramic. The circuit board 3 has an opening 31 in the central region thereof. The opening 31 has an area which is smaller than the rear face 1b of the head chip 1 but is large enough to include all the openings of the channels 12A and 12B in the rear face 1b.
On the surface of the circuit board 3 to be bonded to the head chip 1, wiring electrodes 32 are provided which individually extend from the edges, which face each other, of the opening 31 to the outer edges of the circuit board 3. The wiring electrodes 32 correspond to the respective connection electrodes 14A for row A and connection electrodes 14B for row B which are arranged at both outermost portions of the rear face 1b of the head chip 1. The circuit board 3 is bonded to the rear face 1b of the head chip 1 with, for example, anisotropic conductive adhesive, and thus the connection electrodes 14A for row A and the connection electrodes 14B for row B are electrically connected to the wiring electrodes 32, respectively. In this way, the drive electrodes 13 in the channels 12A and channels 12B are pulled out to the both-end portions 3a of the circuit board 3 through the connection electrodes 14A for row A, the connection electrodes 14B for row B, and the wiring electrodes 32.
The both-end portions 3a of the circuit board 3 are to be bonded to electrical wiring members 4, such as flexible printed circuit boards (FPC). Drive signals from a drive circuit (not shown in the drawings) are applied to the drive electrodes 13 through the electrical wiring members 4.
On the rear side of the circuit board 3, an ink manifold (not shown in the drawings) is provided to supply ink to the channels 12A and 12B in common through the opening 31.
Next, the method of forming the insulating films 15 on the rear face 1b of the head chip 1 is described with reference to FIGS. 5 to 7.
FIG. 5 shows an example where photopolymer material (dry film) made of polyimide, organic insulating material, is used to form the insulating films 15.
First, a dry film 5 which is large enough to cover the channel row A in the rear face 1b of the head chip 1 is prepared and is put on the channel row A such that the dry film 5 completely covers all the channels 12A and drive walls 11A of row A as shown in FIG. 5A. Then, by using a publicly-known method, patterning of the dry film 5 is performed by exposure and development so that the dry film 5 separately remains only on the surfaces of the respective drive walls 11A in row A. This process provides insulating films 15, made of the dry film 5, only on the surfaces of the respective drive walls 11A on the rear face 1b of the head chip 1, as shown in FIG. 5B.
After that, by appropriately using the publicly-known method, patterned metal films are formed on the rear face 1b of the head chip 1 where the insulating films 15 have been formed. Thus, the connection electrodes 14A for row A and connection electrodes 14B for row B, each of which has a shape of a continuous single line, are formed as shown in FIG. 1. Accordingly, each of the connection electrodes 14B for row B is provided on the surface of the insulating film 15, and is not in direct contact with the rear face 1b of the head chip 1 at the position of each drive wall 11A in row A.
In the case where the insulating films 15 are patterned by an inkjet method using organic insulating material, any pattern can be formed easily without using mask material such as a resist. In such a case, the insulating films 15 can be patterned using a coating film made of organic insulating material. More specifically, organic insulating material is directly discharged from the inkjet printhead to the rear face 1b so that the insulating films 15 will be formed only at the surfaces of the respective drive walls 11A on the rear face 1b of the head chip 1, as shown in FIG. 5B.
FIGS. 6 and 7 show an example where SiO₂ or Al₂O₃, which is inorganic insulating material applicable to sputtering, is used to form the insulating films 15.
First, a resist 6 is formed on the whole rear face 1b of the head chip 1 as mask material, as shown in FIG. 6A. Then, patterning of the resist 6 is performed using a publicly-known method so that openings 61 are provided only at the positions at which insulating films 15 are to be formed later, i.e., only at the positions of the surfaces of the respective drive walls 11A of row A, as shown in FIG. 6B.
Then, inorganic insulating material is applied by sputtering to the surface of the resist 6 having the openings 61. Thus, a film 7 made of the inorganic insulating material is formed on the whole rear face 1b, as shown in FIG. 7A. At the positions of the openings 61, the inorganic insulating material adheres directly to the rear face 1b of the head chip 1.
After that, the resist 6 is removed, and thus the insulating films 15 made of the inorganic insulating material are formed only at the positions at which the film 7 directly adheres to the rear face 1b of the head chip 1 through the openings 61, i.e. , only on the surfaces of the respective drive walls 11A of row A, as shown in FIG. 7B.
Then, by appropriately using a publicly-known method, such as vapor deposition, patterned metal films are formed on the rear face 1b of the head chip 1, on which the insulating films 15 have been provided. Thus, the connection electrodes 14A for row A and connection electrodes 14B for row B are provided. As shown in FIG. 1, each of the connection electrodes 14A and 14B has a shape of a continuous single line. Since each of the connection electrodes 14B for row B is provided on the surface of the insulating film 15 at the position of a drive wall 11A of row A, each of the connection electrodes 14B does not directly come in contact with the rear face 1b of the head chip 1.
FIG. 8 illustrates another mode of an insulating film. The components identical to those in FIG. 1 are indicated by the same reference number/letter as those in FIG. 1, and repetitive explanations are omitted.
The insulating film 16 is different from the insulating films 15 in that the insulating film 16 surrounds all the channels 12A in row A. Specifically, the insulating film 16 is formed as a single film having openings at the positions corresponding to the channels 12A, and surrounds all the channels 12A in row A. That is, the insulating film 16 covers the surfaces of the respective drive walls 11A where the connection electrodes 14B for row B cross row A.
Such an insulating film 16, which is formed as a single continuous film and extends along row A, has the advantage that the insulating film 16 is less likely to peel off compared to the insulating films 15 which are separately provided only on the surfaces of the respective drive walls 11A.
FIGS. 9 and 10 illustrate another mode of an insulating film. FIG. 10 is a cross-sectional view along the line x-x of FIG. 9. The components identical to those in FIGS. 1 and 2 are indicated by the same reference number/letter as those in FIGS. 1 and 2, and repetitive explanations are omitted.
The insulating film 17 is different from the insulating films 15 and 16 in that the insulating film 17 covers almost the whole surface of the rear face 1b of the head chip 1. Specifically, the insulating film 17 is formed as a single film having openings at the positions corresponding to the channels 12A and 12B, and covers almost the whole surface of the rear face 1b of the head chip 1. That is, the insulating film 17 covers the surfaces of the respective drive walls 11A where the connection electrodes 14B for row B cross row A.
Openings 171 are separately provided at the positions where the openings of the channels 12A and the respective connection electrodes 14A for row A are connected with each other, and where the openings of the channels 12B and the respective connection electrodes 14B for row B are connected with each other. Accordingly, the connection electrodes 14A for row A and the connection electrodes 14B for row B directly adhere to the rear face 1b of the head chip 1 at the openings 171.
Similarly to the insulating film 16, the insulating film 17 has an advantage of being less likely to peel off compared to the insulating films 15 which are separately provided only on the surfaces of the respective drive walls 11A. Since the connection electrodes 14A for row A and the connection electrodes 14B for row B directly adhere to the rear face 1b of the head chip 1 at the openings 171 in the insulating film 17, the insulating film 17 does not exist at and near the positions where the connection electrodes 14A for row A and the respective electrodes 13 are connected with each other and where the connection electrodes 14B for row B and the respective electrodes 13 are connected with each other. That results in stable conduction state.
The lower-end side of the insulating film 17 does not reach the lower end 1c of the rear face 1b of the head chip 1. That is, between the lower edge of the insulating film 17 and the lower end 1c, there is an exposed part 172 where the rear face 1b of the head chip 1 is exposed. The exposed part 172 has a predetermined width with no insulating film 17 and extends along the direction of the channel row. The connection electrodes 14A for row A and the connection electrodes 14B for row B are provided on the exposed part 172 near the lower end 1c, i.e. , directly adhere to the rear face 1b of the head chip 1 at this portion.
In the exposed part 172, which is to bond to the circuit board 3, the connection electrodes 14A for row A and the connection electrodes 14B for row B directly adhere to the rear face 1b of the head chip 1 with no insulating film 17 provided therebetween. That results in stable bonding state among the head chip 1, the connection electrodes 14A and 14 B for rows A and B, and the circuit board 3 in spite of various peeling-off stresses that would be applied when the exposed part 172 and the circuit board 3 are bonded to each other to form an inkjet printhead.
FIG. 11 is a rear view of a head chip 1 having six channel rows.
Since the head chip 1 having the six channel rows is symmetrical about the line O-O, only the lower three channel rows are shown in FIG. 1. Of the six channel rows, the outermost channel rows can be taken as rows A, the inner channel rows adjacent to the respective rows A can be taken as rows B, and the inner channel rows adjacent to the respective rows B can be taken as rows C.
In the case of six channel rows, each of the connection electrodes 14B for row B which extends from a corresponding channel 12B to the lower end 1c of the head chip 1 runs on a insulating film 15 on the surface of the a drive wall 11A of row A, as in the above-mentioned embodiment. Further, in a similar manner, an insulating film 15 is also provided on each of the drive walls 11B of row B, and connection electrodes 14C for row C are provided which extend from respective channels 12C of row C to the lower end 1c of the head chip 1. Each of the connection electrodes 14C runs on the insulating film 15 on the surface of a corresponding drive wall 11B of row B; and further runs on the insulating film 15 on the surface of a corresponding drive wall 11A of row A to reach the lower end 1c of the head chip 1.
According to this structure, when drive signals are applied to the channels 12C through the connection electrodes 14C for row C, the applied drive signals do not affect the channels 12A and 12B of rows A and B.
In the case of a head chip having five channel rows, two channel rows, connection electrodes 14A and 14B for rows A and B, and an insulating films 15 as shown in FIG. 1 are additionally provided on the other side of the line O-O. In the case of a head chip having seven or eight channel rows, another channel row (row D) is added between row C and the line O-O such that each of the connection electrodes for row D has a shape of a continuous single line and runs over a corresponding drive wall 11C for row C, drive wall 11B for row B, and drive wall 11A for row A to extend to the lower end 1c of the head chip 1.
In the case of a head chip having five or more channel rows, insulating film 16 or 17 may also be employed as shown in FIG. 8 or FIG. 9.

[EXAMPLE]

The effects of suppressing crosstalk brought about by the present invention are illustrated below.
A harmonica-type head chip in conformity with the following specifications was used as a head chip.

channel: 256 channels x 4 rows
L length: 1.0 mm
channel height (L1: see FIG. 2): 200 µm
channel width: 82 µm
channel pitch: 141 µm
drive wall width: 59 µm
nozzle diameter: 23 µm

Separate insulating films made of insulating material were formed only on the surfaces of the respective drive walls of the channel row A, which was the outermost row, on the rear face of the head chip in the same pattern as FIG. 1. Methods of forming insulating films and film thicknesses are shown in TABLE 1.
Then, connection electrodes for row A and connection electrodes for row B were formed, using Al as an electrode metal, in the same pattern as FIG. 1 by vapor deposition on the rear face of the head chip where the insulating films had been formed.
Nozzles α for the outermost channel row A and nozzles β for the inner channel row B were simultaneously driven, while the connection electrodes for row B were disposed on the drive walls for driving the nozzles α. The drive voltage was a voltage that allowed ink to be discharged from the nozzles α at 6 m/sec when only the nozzles α of the outermost channel row A were driven. The ratio of the speed at which ink was discharged from the nozzles α to the speed of 6 m/sec was obtained, and the assessment of crosstalk was made.
For comparison, the same experiment was performed using a head chip with no insulating films. This head chip, otherwise, conformed to the same specifications as the above-mentioned head chip. Similarly to the above, drive voltage was applied simultaneously to rows A and B. In this case, the drive voltage applied to the nozzles of row B through the connection electrodes for row B leaked to the drive walls of row A and caused crosstalk. As a result, the speed at which ink drops were discharged from the nozzles of row A was reduced by an average of 0.12 m/sec (2%) relative to the speed of 6 m/sec. Therefore, if there was little difference between the speed of 6 m/sec and the speed at which ink drops were discharged from the nozzles of row A when drive voltage was applied simultaneously to rows A and B, it was judged that crosstalk was improved.

Here, it was judged that crosstalk was improved when the average speed difference was 0.06 m/sec (1%) or less. The results are shown in TABLE 1 below.

[TABLE 1]

TYPE OF INSULATING FILM	METHOD OF FORMING INSULATING FILM	FILM THICKNESS (µm)	ASSESSMENT
POLYIMIDE	PHOTOPOLYMER MATERIAL	20	IMPROVED
POLYIMIDE	PHOTOPOLYMER MATERIAL	10	IMPROVED
SiO₂	SPUTTERING	5	IMPROVED
SiO₂	SPUTTERING	1	IMPROVED
SiO₂	SPUTTERING	0.1	IMPROVED
Al₂O₃	SPUTTERING	5	IMPROVED
Al₂O₃	SPUTTERING	1	IMPROVED
Al₂O₃	SPUTTERING	0.1	IMPROVED
POLYIMIDE	INKJET METHOD		5	IMPROVED
POLYIMIDE	INKJET METHOD		1	IMPROVED
POLYIMIDE	INKJET METHOD	0.5	IMPROVED

REFERENCE NUMERALS

1:: head chip
1a:: front face
1b:: rear face
1c:: lower end
11A, 11B, and 11C:: drive wall
12A, 12B, and 12C:: channel
13:: drive electrode
14A:: connection electrode for row A
14B:: connection electrode for row B
14C:: connection electrode for row C
15, 16, and 17:: insulating film
171:: opening
172:: exposed part
2:: nozzle plate
21:: nozzle
3:: circuit board
31:: opening
32:: wiring electrode
4:: electrical wiring member
5:: dry film
6:: resist
61:: opening
7:: film composed of inorganic insulating material

Claims

An inkjet printhead comprising a head chip (1) including:
a first channel row (B) and a second channel row (A) arranged in parallel and in such a way that the first channel row, the second channel row, and an end of the head chip are disposed in this order on a rear face of the head chip, each of the first and second channel rows including a channel (12A, 12B) and a drive wall (11A, 11B) alternately arranged, wherein the drive wall is composed of a piezoelectric element, and the channel has an opening disposed in each of a front face and the rear face of the head chip;

a drive electrode (13) provided on the drive wall facing inside of the channel;

a first connection electrode (14B) corresponding to the channel of the first channel row and provided on the rear face of the head chip, wherein the first connection electrode extends from the channel of the first channel row, running over the drive wall between the channel and another channel of the second channel row, to the end of the head chip, and the first connection electrode has a shape of a continuous single line;

a second connection electrode (14A) corresponding to the channel of the second channel row and provided on the rear face of the head chip, wherein the second connection electrode extends from the channel of the second channel row to the end of the head chip;

a nozzle (21) from which ink in the channel is discharged by deforming the drive wall when a drive signal is applied to the drive electrode through the first and second connection electrodes (14B, 14A); and

an insulating film (15) directly adhering to the rear face of the head chip to be provided between a surface of the drive wall of the second channel row (A) and the first connection electrode (14B) running over the drive wall of the second channel row on the rear face of the head chip.
The inkjet printhead according to claim 1, wherein the insulating film (15) is made of inorganic insulating material.
The inkjet printhead according to claim 2, wherein the inorganic insulating material is one of SiO₂ and Al₂O₃.
The inkjet printhead according to claim 1, wherein the insulating film (15) is made of organic insulating material.
The inkjet printhead according to claim 4, wherein the organic insulating material is photopolymer material.
The inkjet printhead according to claim 4 or 5, wherein the organic insulating material is polyimide.
A method for making an inkjet printhead including a head chip (1) that includes:
a first channel row (B) and a second channel row (A) arranged in parallel and in such a way that the first channel row, the second channel row, and an end of the head chip are disposed in this order on a rear face of the head chip, each of the first and second channel rows including a channel (12A, 12B) and a drive wall (11A, 11B) alternately arranged, wherein the drive wall is composed of a piezoelectric element, and the channel has an opening disposed in each of a front face and the rear face of the head chip;

a drive electrode (13) provided on the drive wall facing inside of the channel;

a first connection electrode (14B) corresponding to the channel of the first channel row and provided on the rear face of the head chip, wherein the first connection electrode extends from the channel of the first channel row, running over the drive wall between the channel and another channel of the second channel row, to the end of the head chip, and the first connection electrode has a shape of a continuous single line;

a second connection electrode (14A) corresponding to the channel of the second channel row and provided on the rear face of the head chip, wherein the second connection electrode extends from the channel of the second channel row to the end of the head chip; and

a nozzle (21) from which ink in the channel is discharged by deforming the drive wall when a drive signal is applied to the drive electrode through the first and second connection electrodes (14B, 14A), the method comprising:
forming an insulating film (15) in such a way that the insulating film directly adheres to the rear face of the head chip and is provided at least on a surface of the drive wall over which the first connection electrode (14B) is to be provided on the rear face of the head chip; and

forming the first connection electrode (14B) on the rear face of the head chip on which the insulating film (15) has been formed.
The method for making the inkjet printhead according to claim 7, wherein the insulating film (15) is formed by sputtering using inorganic insulating material such that the insulating film is patterned.
The method for making the inkjet printhead according to claim 8, wherein the insulating film (15) is made of one of SiO₂ and Al₂O₃.
The method for making the inkjet printhead according to claim 7, wherein the insulating film (15) is formed by an inkjet method using organic insulating material such that the insulating film is patterned.
The method for making the inkjet printhead according to claim 7, wherein the insulating film (15) is formed using photopolymer material and patterned by performing exposure and development.
The method for making the inkjet printhead according to claim 10 or 11, wherein the insulating film (15) is made of polyimide.