Patent Publication Number: US-7896474-B2

Title: Liquid ejection head and recording apparatus

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to a liquid Ejection head provided with wiring lines for Electrically connecting heat generating elements and a Recording apparatus including the liquid ejection head. 
     A recording apparatus is constituted so that Information is recorded on a recording material such as a recording sheet, by ejecting recording ink from a Plurality of minute ejection outlets of a liquid Ejection head depending on a recording signal. Such a Recording apparatus has advantages such as non-contact Recording on the recording material, easy colorization, less-noisiness, etc. 
     As an example of a liquid ejection method, an ink jet method for ejecting ink by utilizing thermal energy will be described. A liquid ejection head used in the ink jet method is provided with recording Elements (e.g., heat generating elements or heaters) corresponding to ejection outlets for ejecting liquid such as ink. The liquid ejection head ejects ink droplets by generating heat under application of a current to the heater to cause bubble generation of the ink, thus effecting recording. 
     The liquid ejection head is required to dispose heaters on a liquid ejection substrate of silicon or the like (hereinafter referred to as a “device substrate”) with a high density in order to obtain a high-definition recording image. In such a liquid ejection head using the liquid ejection method, a constitution in which a plurality of square or rectangular heat generating elements (hereinafter referred to as “heaters”) is arranged in a line on the device substrate and thereafter wiring lines are connected and flow paths are formed has been known. A recording head having such a constitution, compared with those of other types, has advantages such that ink ejection outlets are arranged with a high density and that a high-speed and high-definition image can be obtained. 
     Such a liquid ejection head is disclosed in U.S. Pat. No. 6,139,761 and schematic views thereof are shown in  FIGS. 6A and 6B . As shown in  FIGS. 6A and 6B , the liquid ejection head includes an ink supply port  601  formed in a silicon substrate through anisotropic etching. Further, partition walls  603  for ink flow paths  604  and ink ejection outlets  602  are formed by a known production method such as an exposure technology or etching. Heaters  607  are provided correspondingly to the ink ejection outlets  602  one by one. The ink ejection outlets  602  and the heaters  607  which oppose those through the ink supply port  601  are arranged with a pitch shifted by ½ of The pitch from the opposite ink ejection outlets  602  and heaters  607  with respect to an arrangement direction (a long side direction of the ink supply port  601 ). The ink ejection outlets  602  and the heaters  607  for each ink supply port  601  are arranged with a high density along the long side direction of the ink supply port  601 . 
     In order to carry out recording with higher definition and higher speed by the above-described production process and constitution, the density of the ink ejection outlets is increased by various methods or means. However, various problems arise with the increase in density of the ink ejection outlets. 
     First, there is a problem with respect to a heater size.  FIG. 7  shows a layout of a conventional heater and a periphery of the heater. As shown in  FIG. 7 , at a position opposite from an ink ejection outlet  704 , a heater  703  is provided. An ink flow path  705  for connecting the ink ejection outlet  704  and an ink supply port  707  is formed by a partition wall  708 . A plurality of heaters  703  is arranged with a certain interval of a density of 600 dpi, i.e., with a pitch of about 42 μm. To each of the heaters  703 , an individual power wiring line (individual electrode)  701  to be electrically connected to a VH power source for supplying electric power to the heater  703  and an individual driver wiring line (individual electrode)  702  to be electrically connected to a driver for controlling a heating time of the heater  703  is provided. 
     In the case where an ink droplet with an ejection amount 5 pl is ejected by the heater  703 , assuming that a sheet resistance of the heater  703  is 350 Ω/□, it is necessary to use a heater having a size of about 20 μm×20 μm. In the case of this constitution, a pitch of the heaters  703  with respect to an arrangement direction is about 42 μm, so that a space between adjacent heaters  703  with respect to the arrangement direction has a margin of about 20 μm. For this reason, in the case of the constitution, it is possible to comfortably form the partition wall  708  constituting the ink flow path  705  and the individual power source wiring line (Al wiring line)  701  as an individual VH electrode. 
     However, in the case where the heaters  703  having the above-described size are arranged with an interval of a density of 1200 dpi (a pitch of about 21 μm) which is two times that in the above-described constitution, a spacing between adjacent heaters  703  is substantially “0 (zero)”, so that it is difficult to form the partition wall between the adjacent heaters  703 . Further, also with respect to the individual power source wiring line  701 , similarly, the space for arrangement thereof between the adjacent heaters  703  cannot be ensured, so that it is difficult to realize the arrangement with the density of 1200 dpi by using the heaters having the size in this case. 
     For that reason, in order to realize the arrangement with the heater density of 1200 dpi, it is necessary to decrease a heater size. In the case where the heater size is decreased, thermal energy for heating the ink is also decreased, so that it is necessary to decrease the size of the ink droplet. 
     For example, in the case where an ejection amount of the ink droplet is decreased down to 0.5 p1, it is possible to decrease the heater size down to about 15 μm×15 μm (when the same material as that of the above-described heater is used). In this case, the spacing between adjacent heaters is about 6 μm, so that it is possible to form the partition wall. However, a thickness of such a partition wall fails to ensure a mechanical strength resistant to bubble generation of the ink. 
     Further, in the spacing of about 6 μm, only the individual power source wiring line having a very small width can be formed, so that a wiring resistance is high, thus resulting in liability to heat generation and power loss. 
     It is also possible to employ a method in which the shape of the heater is made rectangular thereby to decrease a width of the heater to increase a space between adjacent heaters. However, the rectangular heater is liable to be subjected to constraints of dimension design and design of a driving circuit or a heater resistance. In addition, the rectangular heater, compared with a square heater, involves a problem that it is largely affected by a change in ejection direction by ink ejection outlets, so that it is desirable that the shape of the heater is square. 
     As another constitution for realizing the arrangement with the heater density of 1200 dpi, a constitution in which wiring lines are disposed immediately under heaters is disclosed in U.S. Pat. No. 4,458,256.  FIG. 8  shows a layout of the wiring lines. As shown in  FIG. 8 , at a position opposite from an ink ejection outlet  804 , a heater  803  is provided. An ink flow path  805  for communicating the ink ejection outlet  804  and an ink supply port  807  with each other is formed by a partition wall  808 . Further, each wiring line as an electrode connected to each heater  803  is formed in two layers consisting of an individual power source wiring line  801  as an upper layer and an individual driver wiring line  802  as a lower layer. These upper and lower layers, i.e., the individual power source wiring line  801  and the individual driver wiring line  802  establish electrical conduction through a through hole  806 . 
     However, in the case of such a layout of the wiring lines, the individual driver wiring line  802  as the lower layer is formed below the heater  803 , so that heat generated by the heater  803  adversely affects an Al wiring line constituting the individual driver wiring line  802 . In this case, e.g., a minute projection called a hillock is liable to occur at the surface of a wiring line film of the individual driver wiring line  802 , so that short circuit failure can occur between the individual power source wiring line  801  and the individual driver wiring line  802  which constitute the upper and lower (two) layers. Further, in the case where the Al wiring line constituting the individual driver wiring line  802  as the lower layer causes thermal deformation, flatness of the heater  803  is deteriorated by the thermal deformation of the lower layer, so that an ink ejection characteristic can also be adversely affected by the thermal deformation. 
     SUMMARY OF THE INVENTION 
     A principal object of the present invention is to provide a liquid ejection head capable of sufficiently ensuring a thickness of a partition wall between adjacent heat generating elements arranged in a staggered fashion and realizing a wiring structure with relatively low power loss and temperature rise to result in arrangement of ejection outlets with a high density. 
     Another object of the present invention is to provide a recording apparatus including the liquid ejection head. 
     According to an aspect of the present invention, there is provided a liquid ejection head comprising: 
     a plurality of ejection outlets for ejecting a liquid droplet; 
     a plurality of flow paths communicating with the ejection outlets; 
     an ink supply port for supplying liquid to the flow paths; and 
     a plurality of heat generating elements provided correspondingly to the ejection outlets, for generating thermal energy for ejecting liquid present inside the flow paths, 
     wherein the plurality of heat generating elements is arranged in a staggered fashion with predetermined intervals with respect to a direction of a long side of the ink supply port, and 
     wherein adjacent staggered ones of the heat generating elements are connected to a common wiring line and are connected to individual wiring lines. 
     According to the present invention, the common wiring line is provided, so that a thickness of the partition wall between the adjacent staggered ones of the heat generating elements is sufficiently ensured and a wiring structure with relatively low power loss and temperature rise. As a result, it is possible to increase in density of arrangement of the ejection outlets. 
     These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a plan view showing a liquid ejection head of First Embodiment and  FIG. 1B  is a sectional view taken along A-A line shown in  FIG. 1A . 
         FIGS. 2A and 2B  are plan views each showing an example of a wiring pattern for heaters in the liquid ejection head of First Embodiment. 
         FIG. 3  is a diagram showing a driving circuit of the heaters in the liquid ejection head of First Embodiment. 
         FIGS. 4A and 4B  are plan views each showing an example of a heater wiring pattern of a liquid ejection head of Second Embodiment. 
         FIG. 5  is a schematic perspective view showing a principal portion of a recording apparatus applicable to an embodiment of the present invention. 
         FIG. 6A  is a plan view showing a conventional liquid ejection head and  FIG. 6B  is a sectional view taken along B-B line shown in  FIG. 6A . 
         FIG. 7  is a plan view showing a heater wiring pattern of the conventional liquid ejection head. 
         FIG. 8  is a plan view showing a heater wiring pattern increased in arrangement density. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinbelow, embodiments of the present invention will be described with reference to the drawings. 
     &lt;Recording Apparatus&gt; 
     First, a recording apparatus to which a liquid ejection head of this embodiment is applicable will be described.  FIG. 5  is a schematic perspective view showing a recording apparatus according to a representative embodiment of the present invention. As shown in  FIG. 5 , a carriage HC on which an ink jet cartridge IJC is mounted is reciprocated in directions indicated by arrows a and b by a carriage motor  5013 . The ink jet cartridge IJC includes a liquid ejection head IJH (hereinafter simply referred to as a “head”) and a container IT for storing ink as liquid to be ejected from this head. Recording paper P is conveyed by a platen  5000 . Further, the recording apparatus includes a suction unit  5015  for carrying out suction inside a capping member  5022  for covering an ink ejection outlet side of the head. The suction unit  5015  refreshes an ejection characteristic of the head by sucking ink from the head through an inner cap opening  5023  formed in the capping member  5022 . Further, the suction unit  5015  includes a cleaning blade  5017  for wiping ink adhered to the ink ejection outlet of the head. 
     First Embodiment 
     &lt;Circuit Layout an Device Substrate&gt; 
       FIG. 1A  is a plan view showing a liquid ejection head of this embodiment and  FIG. 1B  is a sectional view of the liquid ejection head taken along A-A line shown in  FIG. 1A . 
     As shown in  FIGS. 1A and 1B , the liquid ejection head of this embodiment includes a plurality of ink ejection outlets  102  for ejecting ink droplets toward a silicon substrate  108  and a plurality of ink flow paths  104  communicating with the ink ejection outlets  102 . The liquid ejection head further includes an ink supply port  101  as a supply port for supplying liquid (ink) to the ink flow paths  104  and a plurality of heaters  107  as a heat generating element for generating thermal energy for ejecting the liquid from the inside of the ink flow paths  104 . 
     The heaters  107  are provided correspondingly to the ink ejection outlets  102 . The ink ejection outlets  102  and the heaters  107  are disposed along a direction of a long side of an elongated ink supply port  101  with a predetermined (certain) interval (of about 21 μm corresponding to a density of 1200 dpi in this embodiment). Further, with respect to a direction of a short side of the ink supply port  101 , the ink ejection outlets  102  and the heaters  107  are disposed in a staggered fashion so that adjacent ink ejection outlets (and heaters) are shifted from each other with respect to the short side direction. When respect to one heater, one ink flow path  104  and one ink ejection outlet  102  are provided. Further, the plurality of ink ejection outlets  102  is formed in the same size. Similarly, the plurality of heaters is formed in the same size. 
     Oppositely disposed two ink ejection outlets  102  (and heaters  107 ) with respect to the ink supply port  101  are shifted from each other by about 10.5 μm with respect to the long side direction of the ink supply port  101 . That is, the ink ejection outlets  102  and the heaters  107 , each of which is provided for one ink supply port  101 , are arranged along a longitudinal direction of the ink supply port  101  with a density of 2400 dpi. Further, the ink flow paths  104  have different shapes depending on the difference in distance of the heaters  107  from the ink supply port  101 . 
     The ink is supplied from the ink supply port  101  through the ink flow paths  104  to be filled in the ink flow paths  104  up to the ink ejection outlets  102 . In this state, the heaters  107  are supplied with a current to generate heat, so that the ink is heated to cause bubble generation. The ink is ejected from the ink ejection outlets  102  by resultant pressure. At this time, an ejection amount of ink droplets to be ejected is set to about 0.5 ml and a size of each of the heaters  107  is about 15 μm×15 μm. 
     In the case where the heaters  107  are arranged in a line as in the above-described conventional manner, the distance between ends of adjacent heaters is about 6 μm as described above. As a result, it is very difficult to form a partition wall between the adjacent heaters. However, in this embodiment, the heaters  107  are arranged in the staggered fashion, so that the width the ink flow paths  104  can be increased from 7 μm to 10 μm and the width of the partition walls  103  can be increased from 7 μm to 8 μm. 
       FIG. 2A  shows a layout of heater arrangement and wiring lines during arrangement of ink ejection outlets  102 . As shown in  FIG. 2A , adjacent two heaters  107   a  and  107   b  arranged in the staggered fashion form a pair. To the pair of heaters  107   a  and  107   b , a common wiring line  203  as a common electrode and individual wiring lines  204  as an individual electrode are electrically connected, respectively. That is, the liquid ejection head includes the common wiring line  203  which is connected to each of the pair of heaters  107   a  and  107   b  and is led out together as a single line and individual wiring lines  204   a  and  204   b  which are connected to the heaters  107   a  and  107   b , respectively, and are independently led out. Further, the common wiring line  203  and the individual wiring lines  204   a  and  204   b  are formed in the same layer. 
       FIG. 3  is a schematic diagram showing a driving circuit of the pair of heaters  107   a  and  107   b . The individual wiring lines  204   a  and  204   b  individually connected to the associated one of the heaters  107   a  and  107   b  are connected to drivers  303  and  304  for each segment, respectively. The common wiring line  203  connected to each of the heaters  107   a  and  107   b  is connected to a heater power source VH. By a driver driving signal, the drivers  303  and  304  for each segment are controlled, respectively, to actuate the heaters  107   a  and  107   b , respectively. 
     The common wiring line  203  and the individual wiring lines  204   a  and  204   b  are formed of a metal material such as aluminum. These wiring lines shown in  FIG. 2  are laid out by such a rule that a width thereof is generally 6 μm or more in view of a density of current passing through the wiring lines and a distance between the wiring lines is 4 μm or more in view of parasitic capacity. 
     As shown in  FIG. 7 , in the case of the constitution in which the wiring lines are individually connected to the pair of heaters, as described above, the space of 6 μm between the adjacent heaters can only be ensured at the high heater density (1200 dpi) with values not more than those of the above-described wiring rule. For this reason, in the case of this constitution, a wiring resistance is increased. 
     However, in this embodiment, the common wiring line  203  which is connected to the adjacent heaters  107   a  and  107   b  at branched two ends, respectively, and is led out as a single line at the remaining end opposite from the branched two ends is provided. By this constitution, the number of wiring line at a periphery of the heaters  107   a  and  107   b  is decreased, so that a latitude of the wiring line layout can be improved. Further, by the above-described constitution, the wiring resistance is reduced, so that so-called energy saving can also be realized. Particularly, in the constitution in which the ink ejection outlets  102  are arranged with the high density as in this embodiment, since the heaters  107  and the wiring lines therefore are disposed with high densities, it is necessary to sufficiently consider the temperature rise of the heaters. However, in this embodiment, the common wiring line  203  is provided, thus being very effective to save energy. 
     As described above, in this embodiment, the common wiring line  203  which is branched and connected to the pair of heaters  107   a  and  107   b  arranged in the staggered fashion and is led out as the single line is provided. By this constitution, the thickness of the partition wall  103  between the adjacent heaters  107   a  and  107   b  can be sufficiently ensured and it is possible to realize a wiring structure with relative low power loss and temperature rise. 
     Further, according to the liquid ejection head of this embodiment, it is possible to dispose the ink ejection outlets  102  and the heaters  107  with a further high density. As a result, the heaters  107  can be disposed so as to meet a droplet size from a large droplet to a small droplet with the pitch of 1200 dpi (the density of 2400 dpi per ink supply port  101 ). 
     Modified Embodiment of First Embodiment 
       FIG. 2B  is a plan view showing a modified embodiment of a heater arrangement and a wiring line layout, wherein the arrangement of the ink ejection outlets is the same as that in First Embodiment. In this embodiment, as shown in  FIG. 2B , a common wiring line  208  and individual wiring lines  209   a  and  209   b  connected to the pair of heaters  107   a  and  107   b  are formed in the same layer. Further, the common wiring line  208  is led out from a side opposite from a side where the electrically connected individual wiring lines  209   a  and  209   b  oppose each other. In other words, the common wiring line  208  is led out so as to be adjacent to only one of the electrically connected individual wiring lines  209   a  and  209   b.    
     In this embodiment, the common wiring line  208  is disposed close to an electrode pad, thus approaching the power source, so that it is possible to reduce the power loss of the heaters  107  due to the wiring lines for the heaters  107  compared with the case of First Embodiment. However, in the case where the common wiring line  208  is disposed at a position opposite from the position of the electrode pad, compared with the constitution of this embodiment, it is possible to suppress the power loss when the constitution of First Embodiment is employed. 
     Second Embodiment 
       FIG. 4A  is a plan view showing a heater arrangement and a wiring line layout in this embodiment, wherein the arrangement of the ink ejection outlets is the same as that in the above-described embodiments. As shown in  FIG. 4A , a common wiring line  403  and individually wiring lines  404   a  and  404   b  are electrically connected to the pair of heaters  107   a  and  107   b  arranged in the staggered fashion. 
     Further, in this embodiment, the common wiring line  403  is formed in a two-layer structure consisting of a lower layer of a common wiring line  403   a  and an upper layer of a common wiring line  403   b  which establish electrical conduction through a through hole  406 . The upper common wiring line  403   b  and the lower common wiring line  403   a  are formed at a position in which these wiring lines do not overlap with the pair of heaters  107   a  and  107   b . As a result, it is possible to avoid adverse affect of heat generated by the heaters  107   a  and  107   b  on an Al wiring line constituting the common wiring lines  403   a  and  403   b.    
     These wiring lines  403   a ,  403   b ,  404   a  and  404   b  are formed of a metal material such as aluminum. 
     In this embodiment, a driving circuit of the heaters  107   a  and  107   b  is constituted similarly as in First Embodiment as shown in  FIG. 3 . 
     According to this embodiment, the common wiring line  403  is formed in the two-layer structure, so that a total number of the upper common wiring lines  403   b  is decreased. Therefore, compared with the wiring pattern in First Embodiment, a wiring layout further improved in latitude can be realized. Further, a width of each lower common wiring line can also be increased, so that when compared with the case of First Embodiment, the wiring resistance at the periphery of the heaters  107  can be decreased as a whole, with the result that further energy saving can be achieved to suppress temperature rise and increase in electric power of the liquid ejection head. 
     In addition, by forming the common wiring line  403  in the two layers, the number of wiring lines disposed at the periphery of the heaters  107  can be reduced. As a result, a free space can be ensured at the periphery of the heaters  107  and a size of each heater can be increased, so that it is possible to dispose the heaters with a high density even when the ink ejection amount is 5 p1 and each heater has the size of 20 μm×20 μm. 
     Further, by the two-layer structure of the common wiring line  403 , the number of the wiring lines formed in the same layer as the heaters  107   a  and  107   b  is decreased. For this reason, it is possible to further decrease a distance between the heaters  107   a  and  107   b  arranged in the staggered fashion with respect to a short side direction of the ink supply port  101  (a direction perpendicular to the arrangement direction of the ink ejection outlets  102 ). As a result, a position of the ink ejection outlet  102  on a side where a longer ink flow path  104  extending from the ink supply port  101  is located can be brought close to the ink supply port  101 . It is possible to quickly refill the ink from the ink supply port  101  into the ink ejection outlet  102  on the side where the longer ink flow path  104  is located when compared with the case of First Embodiment. 
     In this embodiment, the common wiring line  403  is formed in the two-layer structure but may also be formed in a layer structure having three or more layers. 
     Modified Embodiment of Second Embodiment 
       FIG. 4B  shows a modified embodiment of Second Embodiment, wherein the heat arrangement and the wiring line layout when the ink ejection outlets are arranged as shown in  FIG. 1  are modified. The same constitution as that in Second Embodiment will be omitted from redundant description. In this constitution, a common wiring line (Al wiring line as a lower layer)  413  is led out to the outside of the pair of heaters  107   a  and  107   b.    
     This modified embodiment will be described with reference to  FIG. 4B . An unshown electrode pad for supplying electric power to the heaters  107  is disposed at an end portion of the ink supply port  101  with respect to the long side direction of the ink supply port  101 . 
     As shown in  FIG. 4B , the common wiring line  413  and individual wiring lines  414   a  and  414   b  are electrically connected to the pair of adjacent heaters  107   a  and  107   b  arranged in the staggered fashion. The common wiring line  413  is formed in a two-layer structure consisting of a common wiring line  413   a  as a lower layer and a common wiring line  413   b  as an upper layer. The lower and upper wiring lines  413   a  and  413   b  establish electrical conduction through a through hole  406 . 
     The lower common wiring line  413   a  connected to the pair of adjacent heaters  107   a  and  107   b  is led out to a position where the lower wiring line  413   a  overlaps with an individual wiring line  414   a  for another pair of adjacent heaters  107   a  and  107   b  and is disposed closer to the electrode pad. 
     According to this modified embodiment, the lower common wiring line  413   a  of the common wiring line  413  is led out toward the electrode pad, so that the common wiring line  413  is disposed closer to the power source. As a result, compared with the constitution shown in  FIG. 4A , it is possible to decrease power loss due to the wiring lines. However, in the case where the electrode pad is disposed on a side opposite from the side where the lower common wiring line  413   a  is led out, the constitution shown in  FIG. 4A  can suppress the power loss rather than the case of the constitution in this modified embodiment. 
     While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims. 
     This application claims priority from Japanese Patent Application No. 221219/2007 filed Aug. 28, 2007, which is hereby incorporated by reference herein.