Abstract:
An ink jet print head has nozzles and ink passages each communicating with one of the nozzles. The head includes piezoelectric actuators each for changing one of the passages in volume to eject ink from the associated nozzle. The actuators include leading electrodes extending through the thickness of the body of the head. Because the electrodes are exposed in a surface of the body, an actuator drive IC can be connected directly to the head, and therefore the electrical connections of the head can be simple. A process for making the head body includes the step of laminating green sheets together in which predetermined areas are replaced with materials for forming the leading electrodes of actuators, and the step of sintering the laminate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink-jet recording head and a process for making same. In particular, the invention relates to an ink-jet recording head having a body which is a laminate of green sheets made of piezoelectric material. Each of the sheets has films formed in it. At the same time that the sheets are laminated, the films are laminated to form leading electrodes integrally in the head body. The electrodes will be connected to piezoelectric actuators. 
     2. Description of Related Art 
     A conventional ink jet printer has ink jet nozzles communicating with ink passages, which can be supplied with ink from an ink supply source. Droplets of ink can be ejected from the nozzles. Printers of such a type have been popular which can be small, which can make high speed recording, and which use on-demand systems, and particularly pressure control systems or bubble control systems by means of heat. 
     Ink jet printers which use pressure control systems have been made practicable and proposed which use piezoelectric systems with piezoelectric ceramics or other elements. 
     FIGS. 14-16 of the accompanying drawings show the ink jet head  100  of a conventional ink jet printer using such piezoelectric system. The head  100  includes a body  101 , which has ink passages  111  each defined between partition walls  114  made of piezoelectric material. The passages  111  can be supplied with ink from an ink supply source through a manifold. As shown in FIG. 16, an electrode  112  is formed on each side surface of each partition  114 . As shown in FIG. 14, a drive IC  107  is formed on a printed board  119 . While a drive signal is supplied for a predetermined slight time from the drive IC  107  to the electrodes  112  on the adjoining partitions  114  associated with the passage  111  through which ink should be ejected, these partitions  114  are deformed by shearing strain in such a manner that the passage  111  enlarges in volume to be replenished with ink. When the deformed partitions  114  return to their original shape, ink is ejected from the passage  111  out through the nozzle  110  at the front end of the passage. 
     The head body  101  also has leading electrodes  105  formed on its top to feed the electrodes  112  of the actuators each formed for one of the passages  111 . The leading electrodes  105  are connected electrically through a flexible print circuit (FPC)  115  to terminals of the wiring pattern  116  of the drive IC  107 . 
     The leading electrodes  105  are exposed, and each has a width of tens of microns and a thickness of several or some microns. Therefore, when the recording head  100  is assembled, or when it is mounted on a carriage for moving it, the electrodes  105  are liable to come off the head body  101  and break. 
     The FPC  115  includes a number of signal conductors, which corresponds to the number of leading electrodes  105 . Therefore, the electrical connections between the FPC  115  and the electrodes  105  and between it and the terminals of the wiring pattern  116  are complicated. In order to prevent the ink ejected from the nozzles  110  from sticking to the pattern  116  and the drive IC  107 , it is preferable that the printed board  119  be protected with resin or the like. If the board  119  is thus protected, however, the heat generated in the IC  107  cannot radiate well. 
     Japanese Patent application Laid-Open No. 8-112895 discloses an ink jet head, which includes an actuator plate. The plate has first channels formed in it in parallel for ejecting ink. The plate also has second channels, which extend perpendicularly to the first channels and in parallel to their side walls. Each of the second channels communicates with one of the first channels. Formed on the side walls of each first channel are first electrodes, to which actuator drive voltage can be applied. Formed on the side walls of each second channel are second electrodes (ejection channel lead wires), which are connected electrically to the first electrodes. 
     U.S. patent application Ser. No. 08/635,655 filed Apr. 22, 1996 discloses an ink jet print head, which includes an actuator plate. A leading pattern for a driver circuit is formed on a board, which is bonded to the actuator plate. The body consisting of the board and the plate has a number of channels formed in it, some of which serve as ink chambers. The partitions between the channels function as actuators. For use as a drive electrode, a conductive film is formed on part of each side surface of each partition by oblique vapor deposition and electroplating in such a manner that it is connected electrically to the leading pattern. The film extends on both the board and the plate. Therefore, voltage can be applied directly from the driver circuit to the drive electrodes. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to form integrally in the body of an ink jet print head a plurality of leading electrodes each for connection to the electrode of a piezoelectric actuator, and thereby protect the leading electrodes. 
     It is another object to simplify electrical connections in an ink jet print head and the mounting of a drive IC on the head body. 
     It is a further object to make efficient the heat radiation from the drive IC of an ink jet print head. 
     In accordance with a first aspect of the invention, an ink jet print head is provided, which includes a body having nozzles. The body also has ink passages formed in it to be filled with ink. The passages each communicate with one of the nozzles. The head also includes piezoelectric actuators each for changing the volume of one of the passages to eject ink from the associated nozzle. The actuators have leading electrodes extending through the thickness of the body. 
     As stated above, the leading electrodes of the actuators extend through the thickness of the head body perpendicularly to the ink passages. This prevents the electrodes from being damaged or broken when the print (recording) head is assembled or mounted on a carriage. One end of each leading electrode is exposed to the outside of the head body. Therefore, a drive circuit for the actuators can be connected directly to the exposed ends of the electrodes. Consequently, the IC chip including the circuit can be mounted directly on the body. This simplifies the structure of the head, and particularly its electrical connections, and accelerates the radiation of heat from the chip through the body. 
     The print head may further include second leading electrodes embedded in the head body for connecting the drive circuit to an electric system outside the head. The ends of the second electrodes may be exposed to the outside of the body. In this case, one end of each second leading electrode can be connected to the actuator drive circuit, and the other can be connected to wiring for supplying the circuit with data signals, a drive voltage, etc. It is therefore possible to simplify the electrical connections between the head and an external circuit, and between the drive circuit and the external circuit. 
     In accordance with a second aspect of the invention, an ink jet printer is provided, which comprises a print head and a device for supplying the head with ink. The head includes a body having nozzles. The body also has ink passages formed in it to be filled with ink. The passages each communicate with one of the nozzles. The head also includes piezoelectric actuators each for changing the volume of one of the passages to eject ink from the associated nozzle. The actuators have leading electrodes extending through the thickness of the body. 
     As stated above, the leading electrodes of the actuators extend through the thickness of the head body. This prevents the electrodes from being damaged or broken when the print (recording) head is assembled or mounted on a carriage. It is possible to make the head compact, thereby making the printer small. It is also possible to reduce the printer trouble or failure due to wiring breakage or the like. 
     In accordance with a third aspect of the invention, a process is provided for producing a print head for ejecting ink through nozzles by means of piezoelectric actuators. The process comprises the steps of: 
     laminating green sheets together in which predetermined areas are replaced with materials for forming leading electrodes for the actuators; 
     sintering the laminated sheets to form a sintered body; 
     polarizing the sintered body; and 
     forming ink passages in the sintered body, the passages each communicating with one of the nozzles. 
     This process includes laminating the green sheets to form the piezoelectric sintered body. Those areas of the sheets, where the leading electrodes are programmed to be formed, are replaced in advance with the materials for forming these electrodes. Therefore, the laminating and sintering of the sheets connect the materials across the thickness of the sheets, forming the electrodes extending across the sheet thickness. The process makes it possible to produce, with high accuracy and ease, a print head having a body through which the leading electrodes of piezoelectric actuators extend. 
     The process may also comprise the step of mounting on the print head a circuit for driving the head in such a manner that the circuit is connected to those ends of the leading electrodes which are exposed to the outside of the sintered body. Because of the electrode ends exposed in a surface of the sintered (head) body, it is easy to mount directly on the body the IC chip including the circuit for driving the head. 
     The process may further comprise the step of forming electrodes for driving the piezoelectric actuators on the side walls of the ink passages in such a manner that the driving electrodes are each connected to one of the leading electrodes. 
     The ink passages may each take the form of a channel. The process may further comprise the step of fitting a cover plate on the sintered body in such a manner that the plate covers the passages. The plate may be another sintered body. The two sintered bodies may be polarized in the opposite directions. The plate may have channels formed in it and each facing one of the channels in the head body (see FIG.  13 ). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are shown in the accompanying drawings, in which: 
     FIG. 1 is a flow chart of a process for making an ink-jet recording head according to the invention; 
     FIG. 2 is an exploded perspective view of a laminate of green sheets for an ink-jet recording head according to the invention; 
     FIG. 3 is an exploded vertical cross section of the laminate; 
     FIG. 4 is a vertical cross section of the laminate; 
     FIG. 5 is a vertical cross section of the body of the head; 
     FIG. 6 is a vertical cross section of the head body in which channels are formed; 
     FIG. 7 is a cross section taken along line VII—VII of FIG. 6; 
     FIG. 8 is an enlarged view of part of FIG. 7, but showing the head body on which actuator electrodes are formed; 
     FIG. 9 is a view similar to FIG. 8, but showing the head body of which partition walls have shear-deformed; 
     FIG. 10 is an exploded perspective view of the head; 
     FIG. 11 is a perspective view of the head; 
     FIG. 12 is a perspective view of the head fitted to a printed board; 
     FIG. 13 is a partial vertical cross section of the body of a modified ink-jet recording head according to the invention; 
     FIG. 14 is a perspective view of a conventional ink jet head; 
     FIG. 15 is an exploded view of the conventional head; 
     FIG. 16 is a cross section of the conventional head. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Ink-jet recording heads according to the illustrated embodiments each have sets of ink jet nozzles, ink passages and piezoelectric actuators incorporated therein. The nozzles are positioned at the front ends of the heads. FIG. 1 shows a process according to the invention for making such a head. 
     First step K 1  of the process includes adding small amounts of organic binder, plasticizer, dispersant, etc. to pre-burnt piezoelectric ceramic powder to form slurry, forming the slurry into a thick film which has a thickness of tens of microns by means of a film forming apparatus, and cutting the film into green sheets  10 - 13  which have a predetermined size, as shown in FIGS. 2 and 3. 
     Second step K 2  includes forming a number of openings  11   a  through a rear end portion of each lower green sheet  11  at regular intervals in a line across the sheet width. Step K 2  also includes forming openings  12   a  likewise through a rear end portion of each upper green sheet  12 . The openings  11   a  and  12   a  extend longitudinally of the sheets, and have a predetermined length and a width of tens of microns. Step K 2  further includes forming a number of openings  12   b  through each sheet  12  at regular intervals in a line across the sheet width. The openings  12   b  extend longitudinally of the sheets, and have a predetermined length and a width of tens of microns. Step K 2  yet further includes forming openings  13   a,    13   b  and  13   c  through each top green sheet  13  at regular intervals in line across the sheet width. The openings  13   a,    13   b  and  13   c  extend longitudinally of the sheets. The openings  13   a  have a predetermined length and a width of tens of microns. The openings  13   b  have a predetermined length and a width of tens of microns. The openings  13   c  have a predetermined length and a width of tens of microns. The openings Ha are each aligned with one of the openings  12   a  and one of the openings  13   a.  The openings  12   b  are each aligned with one of the openings  13   b  and one of the openings  13   c.    
     Third step K 3  includes forming an electrically conductive film  15  in each of the openings  11   a  of the lower green sheets  11  and the openings  12   a  of the upper sheets  12 , by rubbing a metal paste on the sheet with a spatula or knife through a mesh sheet (not shown) blinded except its portions corresponding to the openings. The paste contains a fine powder of platinum or other metal dispersed in a resinous liquid. Step K 3  also includes forming an electrically conductive film  16  likewise in each opening  12   b  of the upper green sheets  12 . Step K 3  further includes likewise forming an electrically conductive film  17  in each opening  13   a  of the top green sheets  13 , an electrically conductive film  18  in each opening  13   b  of these sheets  13 , and an electrically conductive film  19  in each opening  13   c  of the sheets  13 . The conductive films  15 - 19  are equal substantially in thickness to the green sheets  10 - 13 . 
     As shown in FIG. 4, fourth step K 4  includes laminating the green sheets  10 - 13  together in that order, with the adjacent conductive films  15  and  17  laminated together, and with the adjacent conductive films  16 ,  18  and  19  laminated together. Step K 4  also includes heat-sealing the sheets  10 - 13  together to form a green laminate. 
     Fifth step K 5  includes removing the binder from the green laminate by heating the laminate to a temperature of about 400 centigrade to thermally crack all the organic components contained in the laminate. Step K 5  also includes sintering the heated laminate by reheating it at a temperature of about 1,000 or more centigrade. 
     This, as shown in FIG. 5, forms a head body  1  made of piezoelectric ceramic which is a sintered body. At the same time, this forms in the body  1  first leading electrodes  25  each by joining associated conductive films  15  of the green sheets  11  and  12  together, and first terminals  27  each by joining associated conductive films  17  of the top green sheets  13  together. The electrodes  25  are each joined to the associated terminal  27 . This also forms in the body  1  second leading electrodes  26  each by joining associated conductive films  16  of the upper sheets  12  together, second terminal s  28  each by joining associated conductive films  18  of the top sheets  13  together, and third terminals  29  each by joining associated conductive films  19  of the sheets  13  together. The electrodes  26  are each joined to the associated terminals  28  and  29 . The terminals  27   29  are exposed outside the body  1 . 
     In sixth step K 6 , for polarization in the upward direction  38  (FIG.  8 ), a high DC voltage is applied between the top and bottom surfaces of the head body  1 . 
     In seventh step K 7 , as shown in FIGS. 6 and 7, a channel cutter (not shown) is used to form narrow longitudinal channels  30  at regular lateral intervals in a bottom portion of the head body  1 . The channels  30  each extend between the front end of the body  1  and adjacent two of the first leading electrodes  25 . Each of the channels  30  is wider than the space between the adjacent electrodes  25 , and formed with the opposite surfaces of these electrodes cut partially. As shown in FIG. 7, the formation of each channel  30  exposes bottom portions of the associated electrodes  25  in its side walls. The channels  30  are partitione d by partition walls  31 . Every other channel  30  except both end channels serves as an ink passage  32 . 
     As shown in FIG. 8, eighth step K 8  includes masking the lower halves of both side surfaces of each partition  31  with masking seals as shown by the two-dot chain lines. Step K 8  also includes depositing platinum or another metal on the upper halves of the half masked wall surfaces to form an electrodes  35  or  36  on the upper half of each partition  31 . Each of the electrodes  35  and  36  is connected by itself to the bottom portion of the adjacent first leading electrode  25 , which is exposed to the associated channel  30 . Step K 8  further includes removing the masking seals thereafter. 
     The electrodes  35  on the side walls of the ink passages  32  are each grounded through the associated leading electrode  25 . A drive voltage V can be applied to the other electrodes  36  on side walls of the other channels  30  each through the associated leading electrode  25 . The partitions  31 , the electrodes  35  and  36  on them, etc. constitute piezoelectric actuators. 
     As shown in FIGS. 9 and 10, ninth step K 9  includes bonding a cover plate  40  to the bottom of the head body  1  to cover the channels  30 . Step K 9  also includes bonding a nozzle plate  41  to the front end of the body  1 . The plate  41  has ink jet nozzles  42  formed through it and each aligned with one of the ink passages  32 . This can make a recording head  45  which has sets of ink jet nozzles  42 , ink passages  32  and piezoelectric actuators incorporated in it. As shown in FIG. 11, the cover plate  40  has a lateral slot or opening  40 a formed through its rear portion to supply ink to the passages  32 . A manifold or ink supply member (not shown) can be fitted to the slot  40   a  to connect the head to an ink cartridge (not shown). 
     As shown in FIG. 10, tenth step K 10  includes mounting a drive IC  46  on the top of the head body  1  with an adhesive or the like, and at the same time brazing the output and input terminal areas of the IC  46  to the first and second terminals  27  and  28 , respectively. The IC  46  can supply the drive electrodes  36  with drive signals. As shown in FIG. 12, step K 10  also includes brazing the third terminals  29  to one end of an FPC (flexible print circuit)  47 . It is then possible to mount the recording head  45  as a unit on a carriage (not shown) by fitting the rear end of the head  45  to a printed board  48  with an adhesive or the like, and connecting the other end of the FPC  47  to the wiring pattern (not shown) formed on the board  48 . 
     The FPC  47  includes a clock signal conductor, a data signal conductor, a voltage conductor and a ground return. In synchronism with the train of clock pulses supplied through the clock signal conductor, the IC  46  judges which nozzles  42  ink should be ejected through, from the data appearing on the data signal conductor, and applies to the associated drive electrodes  36  the voltage on the voltage conductor. 
     When, as shown in FIG. 9, the drive voltage V is applied from the drive IC  46  to the electrodes  36  on the two partitions  31  on both sides of one of the ink passages  32 , the upper halves of these partitions  31  shear-deform away from each other perpendicularly to the direction  38  of polarization (which is shown in FIG.  8 ). As a result, the middle of each of the two partitions  31  shifts away from the other, expanding the passage  32 . This replenishes or refills the passage  32  with ink from an ink supply source (not shown). When the voltage application to the electrodes  36  is stopped, the two partitions  31  are released from the shear deformation and return to their original positions. This ejects ink from the passage  32  out through the associated nozzle  42 . 
     FIG. 13 shows a modified ink-jet recording head according to the invention, which includes a head body  1 A having narrow bottom channels  30 A formed in it. Fixed to the bottom of the body  1 A is a cover plate  40 A, which is formed out of green sheets laminated together and sintered. The plate  40 A has narrow top channels  50  formed in it and each aligned with one of the body channels  30 A. The body  1 A and the plate  40 A are polarized in the opposite directions  38  and  51 , respectively. Electrodes  52  and  53  extend over the channels  30 A and  50 . The electrodes  52  are grounded, and a drive voltage V can be applied to the other electrodes  53 . Such structure can double the efficiency of ink ejection and reduce the electric power consumption. 
     As stated above, the green sheets  10 - 13  of piezoelectric material are laminated together to form the head body  1 . The films  15  are formed in the sheets  11  and  12 , and each equal in thickness to each of the sheets. When the sheets  10 - 13  are laminated, associated films  15  are laminated together to form the first leading electrodes  25 . Each of these electrodes  25  except both end ones is connected to one of the piezoelectric actuator electrodes  35  and  36 . It is therefore possible to form the leading electrodes  25  in the body  1  integrally with it, thereby protecting them securely from damage and breakage or disconnection. 
     The films  16  for the second leading electrodes  26  are formed in the upper green sheets  12 . The drive IC  46  for driving the piezoelectric actuators is connected to the leading electrodes  25  and  26 . Therefore, when the IC  46  is mounted on the head body  1 , the IC  46  can be connected to the electrodes  25  and  26  at the same time. Because the IC  46  is mounted on the body  1 , the heat generated in the IC  46  by the ink ejection operation is transferred efficiently to the body  1 . Therefore, the heat of the IC  46  can be radiated effectively. In the meantime, the radiated heat heats the ink in the passages  32 , thereby lowering the ink viscosity. This improves the ink ejection performance of the recording head  45 . 
     Formed in the head body  1  are the second leading electrodes  26  for connecting the drive IC  46  to the wiring pattern on the printed board  48  positioned outside the recording head. The third terminals  29 , which are each connected to one of these electrodes  26 , are exposed in the top surface of the body  1 . The signal conductors of the FPC  47 , which are connected through the second leading electrodes  26  to the input terminal area of the IC  46 , are several for the data and control signals etc. It is therefore possible to simplify the electrical connection between each third terminal  29  and the wiring pattern on the board  48 . 
     The recording head  45  might be modified in such a manner that the third terminals  29  might be formed in the rear end of the head body  1 . In this case, when the rear end of the head  45  is fitted to the printed board  48 , these terminals  29  are connected to the wiring pattern on the board  48  at the same time by brazing, wire bonding or the like. This omits the FPC  47 . 
     The invention can be applied to ink-jet recording heads, which includes a head for ejecting ink by producing bubbles thermally, and to various processes for making such heads. 
     A recording head according to the invention may be applied to an ink jet printer as disclosed in U.S. Pat. No. 5,639,220, the disclosure of which is incorporated herein by reference.