Ink jet recording apparatus and ink cartridge

Abstract: An ink jet recording apparatus with which air bubbles in the ink supply path connecting a recording head to an ink holding member can be easily expelled even when there is a boundary plane (151) inside the ink supply path (66) at which air bubbles tend to stop. Even when the air bubbles are not completely expelled, occlusion of the ink supply path by an air bubble is prevented. Within the ink supply path a plurality of capillary paths (67a) is provided on the upstream side of boundary plane (151). The capillary paths (67a) are disposed at a specific distance to boundary plane (151).

Description: The invention relates to an ink jet recording apparatus for recording on a recording medium by ejecting ink droplets from nozzles of a recording head. An ink jet recording apparatus in accordance with the prior art portion of claim 1 is disclosed in e.g. EP-A-0 661 160. It comprises a recording head mounted on a slidable carriage, an ink container for storing the ink, and supply tubes connecting the ink container to the recording head. The ink container (ink holding member) is commonly a plastic case containing a rubber sack or a porous member soaked with ink. When such an ink jet recording apparatus is used over an extended period of time, the passage of air through the container results in a build-up of air bubbles inside the container, and some air bubbles flow into the ink supply tubes. Bubbles can also be introduced to the supply tubes when the ink jet recording apparatus is subjected to sharp, sudden impacts, such as when the ink jet recording apparatus is accidentally dropped. In ink jet recording apparatuses in which the ink container can be changed, air bubbles can also be introduced to the supply tubes in the course of replacing the ink container. Bubbles can also occur when nitrogen contained in the ink vaporizes due to a rise in temperature. When such air bubbles occur it is preferable to purge the bubbles from the recording head since they tend to seriously affect the proper operation of the recording head. This purging can be accomplished by means of a recovery device such as those disclosed in EP-A-0 661 160 and US-A-4,967,209, respectively. The recovery devices disclosed in these documents employ a method in which pressure is applied to the ink in the container thereby to expel high viscosity ink near the nozzles and air bubbles inside the recording head in what is called a "priming" or "recovery" operation. According to another known method the nozzles of the recording head are covered with a cap and, a pump connected to the cap is used to suck the air bubbles and surrounding ink out of the recording head. The term "priming" as used hereinafter is intended to cover both of these and other similar methods. With each of the above-noted methods, however, there are cases in which the air bubbles inside the ink supply path from the container to the nozzles cannot be removed. Among others a stagnation point existing in the ink supply path is often the reason for air bubbles remaining in the ink supply path, i.e., a point at which the ink flow is essentially zero even when pressure is applied to the ink inside the ink supply path). Air bubbles gather at this stagnation point, and may not be completely removed even by the priming process unless a much greater volume of ink is also removed with the air bubbles. An example of an ink supply path in which air bubbles tend to collect is described below with reference to FIG. 14. Shown in FIG. 14 is the connection between a recording head 155 and an ink supply tube 153. Recording head 155 comprises ink intake opening 158 to which ink supply tube 153 supplies the ink stored in an ink container not shown. The end portion of recording head 155 is inserted into ink supply opening 152 formed in the end portion of ink supply tube 153. The outside perimeter of the connection is sealed with an adhesive 159, thereby forming an ink supply path for supplying ink to the nozzles. As shown in FIG. 14 the ink supply path thus formed has at the boundary plane 151 defined by the end face of ink intake opening 158, a shoulder at which the cross sectional area of the ink supply path changes abruptly. Relatively large air bubbles 168 tend to stop at this boundary plane 151. The contact area between the relatively large air bubble 168 and the side walls of the ink supply path is also large. The large contact area increases the flow drag when the relatively large air bubble 168 moves, and air bubbles stopped at this boundary plane cannot be sufficiently removed even by the above priming operation. While the air bubbles are sometimes completely removed, much ink is usually consumed at the same time, and ink waste thus increases. When a relatively small air bubble 169 comes flowing from the upstream side, the smaller air bubble is absorbed by relatively large air bubble 168, and the relatively large air bubble 168 thus grows even larger. In the worst case the air bubble may grow to cover the entire boundary plane and thus obstruct ink intake opening 158. When this happens ink can no longer be supplied to recording head 155, and recording is thereby disabled. In addition to ink supply paths having such an abrupt internal shoulder, another type of ink supply path comprising a boundary plane at which air bubbles tend to collect are ink supply paths in which a filter is disposed to prevent the inflow of foreign matter to the recording head. Relatively large air bubbles tend to gather in front of the filter, creating the same problems as described above. US-A-4,537,680 discloses a comb filter including a first capillary path means in the form of a first plurality of generally parallel grooves, second capillary path means in the form of a single groove and third capillary path means in the form of a second plurality of generally parallel grooves. The three capillary path means are arranged in this order between the upstream end and the downstream end of the filter. Even though the cross-sectional area of the single groove is larger than that of each of those parallel grooves, the cross-sectional area of the filter naturally becomes smaller between the downstream end of the first capillary path means and the upstream end of the second capillary path means as it becomes larger between the downstream end of the second capillary path means and the upstream end of the third capillary path means. An object of the present invention is to solve the aforementioned problem of the prior art and to provide an ink jet recording apparatus which allows air bubbles to be expelled with relative ease and, even if an air bubble cannot be completely expelled, prevents the supply of ink to the recording head from being blocked by an air bubble. This object is achieved with an ink jet recording apparatus as claimed in claim 1 and an ink jet cartridge as claimed in claim 11. Preferred embodiments of the invention are subject- matter of the dependent claims. According to the invention, capillary paths formed by plural wall surfaces are disposed substantially parallel to the direction of ink flow inside the ink supply path on the upstream side of the boundary plane at which air bubbles tend to stop. As a result, air bubbles inside the ink supply path are fractionated as they pass through the capillary paths when the ink inside the ink supply path is sucked out or pressurized by recovery (priming) means. The fractionated air bubbles can thus flow more easily to the downstream side of the boundary plane. Air bubbles can thus be more reliably purged, and stoppage of a large air bubble inside the ink supply path can be prevented. It is preferable for the cross section of the capillary paths to have a triangular, rectangular, or other non-circular shape. By providing a shape having at least one angle or corner, air bubbles that may grow inside a capillary path are prevented from completely occupying the path. In addition, because the downstream ends of the wall members forming the capillary paths are disposed at a particular distance from the boundary plane, it is difficult for air bubbles to occupy the space between these ends and the boundary plane. As a result, despite the presence of air bubbles ink can be supplied through the angle or corner portion of the capillary path and flow to the downstream ends of the wall surfaces forming the capillary path to then easily pass to the downstream side of the boundary plane. Thus, problems such as air bubbles preventing the supply of ink to the recording head can be prevented. It is further preferable that the distance from the downstream end of the wall members to the boundary plane be in the range of 0.05 mm - 0.5 mm. When the distance is in this range, the supply of ink to the recording head can be more reliably assured even if air bubbles are stopped in the ink supply path. The preferred shapes for the capillary paths are achieved by disposing wall members in a comb-like or grid-like configuration upstream of the boundary plane, and forming the capillary paths from the wall surfaces of these wall members, or disposing a porous plate having plural through-holes upstream of the boundary plane. In each case, however, the cross section of the capillary paths thus formed is non- circular. Preferred embodiments of the invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic view of one example of a known ink jet printer to which the present invention may be applied. FIG. 2 is a partially exploded view of the ink jet cartridge shown in FIG. 1. FIG. 3 is a partially exploded view of an alternative embodiment of the ink jet cartridge shown in FIG. 1. FIG. 4 is a scematic view of the ink flow path of the ink jet cartridges shown in FIG. 2 and FIG. 3. FIG. 5 shows capillary path means according to a preferred embodiment of the invention. FIG. 6 is a plan view of the capillary paths as seen in the direction of arrow D in FIG. 5, i.e., from the ink intake opening of the head chip. FIG. 7 is a plan view of the capillary paths as seen in the direction of arrow C in FIG. 5, i.e., the connection between the head chip and the capillary paths. FIG. 8 is a cross section used to describe air bubble expulsion in FIG. 5. FIG. 9 is a plan view showing the shape of the capillary paths in a second embodiment of the invention from the ink intake opening side of the head chip. FIG. 10 is a top view (from the direction of arrow E in FIG. 9) of the connection between the head chip and capillary paths in the embodiment shown in FIG. 9. FIG. 11 is a plan view showing the shape of the capillary paths in a third embodiment of the invention from the ink intake opening side of the head chip. FIG. 12 is a top view (from the direction of arrow F in FIG. 11) of the connection between the head chip and capillary paths in the embodiment shown in FIG. 11. FIG. 13 is a cross section of the capillary paths in a fourth embodiment of the invention. FIG. 14 is a cross section of air bubbles collecting at the boundary plane of the ink supply path in the prior art. As an example of an ink jet recording apparatus to which the present invention may be applied FIG. 1 shows the ink jet printer described in EP-A-0 661 160. In this ink jet printer, ink jet cartridge 1 is mounted on carriage 2 and driven in the recording direction of the recording medium 6 by motor 3 via belt 5 with carriage 2 guided on guide rail 4. FIG. 2 is a partially exploded view of ink jet cartridge 1. Except for the particular feature of the present invention described later, this ink jet cartridge 1 may be the same as that shown and described in EP-A-0 661 160 and will, therefore, be explained hereinafter only to the extent necessary for understanding the present invention. Ink jet cartridge 1 mainly comprises head case 10, head chip 55, ink sack 30, and ink supply case 50. Nozzle plate 11 having an opening 11a in which nozzles 57 of head chip 55 appear when the latter is mounted is provided at the right front shoulder of head case 10. An ink injection opening 13 is disposed at the bottom front of head case 10, and is plugged by plug 14 except when ink sack 30 is being filled with ink. As is further described below an ink supply tube is integrally formed on the back of head case 10. A filter 15 is heat-fused to the intake part of this ink supply tube. The ink supply tube formed on the back of head case 10 and an ink supply tube integrally formed with ink supply case 50 are connected using an 0-ring 16. 0-ring 16 is disposed between head case 10 and ink supply case 50, and thus forms part of the ink supply tube. Plural pins 17 are also disposed on the back of head case 10 for coupling with ink supply case 50. Ink sack 30 is manufactured from a butyl rubber material. The open end 31 of ink sack 30 is circular as shown in FIG. 2, and comprises packing 32 around the perimeter. Packing 32 is held between head case 10 and ink supply case 50, thereby forming a seal. Opening 51 is provided at the end of ink supply case 50 facing head case 10, and ink sack 30 is accommodated in opening 51. Engaging holes 52 are also formed for coupling ink supply case 50 and head case 10 by press-fitting pins 17 of head case 10 into engaging holes 52. An ink supply opening 53 shaped identically to opening 11a in nozzle plate 11 is formed at the side of ink supply case 50 facing head case 10. Plural nozzles 57 are arrayed at equal intervals on one end of head chip 55. Ink intake opening 58 is disposed at the other end of head chip 55. Ink intake opening 58 has a roughly rectangular, long, narrow cross section oriented substantially parallel to the nozzle array. Head chip 55 is disposed in space 18 formed on the back of head case 10. Nozzles 57 are inserted into opening 11 a of nozzle plate 11, and are fixed in place with adhesive applied around the perimeter of the nozzle block. Ink intake opening 58 is inserted into ink supply opening 53, i.e., the ink supply opening in ink supply case 50, and the perimeter is sealed and fixed with an adhesive. FIG. 3 is a partially exploded view of an alternative embodiment of ink jet cartridge 1. The ink jet cartridge shown in FIG. 3 is identical to that shown in FIG. 2 except for the ink holding member 70 which is made from a porous material and used instead of ink sack 30. Ink holding member 70 may be made, for example, from a urethane foam material having many fine pores and is used as an absorber soaked with ink. Ink holding member 70 is housed inside opening 51 of ink supply case 50. FIG. 4 is a simplified perspective view of the ink supply tube arrangement of the ink jet cartridges shown in FIG. 2 and FIG. 3. Ink supply tube 66 is integrally formed with head case 10 and ink supply case 50 accommodating ink sack 30 or ink holding member 70. As will be explained in detail below, the capillary paths that is a feature of the present invention is disposed in the ink supply opening 53 of ink supply case 50 where ink supply tube 66 is connected to ink intake opening 58 of head chip 55. A preferred embodiment of the capillary paths of the invention is described next with reference to FIG. 5 to 8. As shown by the broken lines in FIG. 6, the shape of ink intake opening 58 of head chip 55 is rectangular with width L greater than height h2. Height h1 of the ink supply opening 53 is significantly greater than height h2 of ink intake opening 58, thus creating a boundary plane 151 at which large air bubbles tend to collect. As best seen in Fig. 5, inside ink supply opening 53 plural long, narrow wall members 69 are disposed in a row in a direction roughly perpendicular to the long side of the rectangular ink intake opening 58 when ink supply case 50 is inserted into ink supply opening 53. As shown in Fig. 7, the ends 69a of these wall members 69 are positioned at a specific distance d to the end face (boundary plane 151) of ink intake opening 58. As a result, a series of very narrow flow channels (capillary paths) 67a (width c, height h3) forming a comb-like pattern are formed upstream from this boundary plane. These wall members 69 may be formed integrally with ink supply case 50 which is preferably made from poylacrylate (PAR), polysulfone (PSF), polycarbonate (PC) or other transparent material. FIG. 8 is a cross section used to describe air bubble expulsion in this embodiment of the invention. Air bubbles 68 inside ink supply tube 66 are moved towards head chip 55 by the priming process, and are fractionated by capillary paths (flow channels) 67a. The inflow resistance to ink intake opening 58 is thereby reduced, the ink therefore flows in easily, and air bubbles can be reliably purged. In tests conducted with a recording head having an ink intake opening with width L of 4.5 mm and height h2 of 0.087 mm, and six capillary paths each with a height h3 of 0.84 mm and a width c of 0.3 mm disposed at a distance d of 0.15 mm from the boundary plane, good results were achieved. Specifically, with an ink supply tube not comprising these capillary paths, large air bubbles stopped at the boundary plane and could not be sufficiently expelled even with the priming process. Using the capillary paths described above, however, air bubbles could be expelled with relative ease. With an ink supply tube not comprising these capillary paths it is possible that an air bubble becomes large enough to completely block the ink intake opening, thus preventing ink from being supplied to the recording head and preventing recording from proceeding. With the ink supply tube comprising capillary paths according to the invention, however, ink supply to the recording head is not stopped even if an air bubble grows. Tests have shown that prevention of blockage of the ink supply to the recording head is particularly reliable when the distance from the boundary plane to the capillary paths is anywhere in the range from 0.05 mm to 0.5 mm. Figs. 9 and 10 are views, similar to those of Figs. 6 and 7, of a second embodiment of the invention. In this embodiment a grid-like member 82 is arranged within ink supply opening 53. Member 82 has numerous, extremely narrow holes or channels forming capillary paths 67b. Note that in the embodiment shown capillary paths 67b are also formed by grooves in the peripheral surface of member 82 and adjacent surface portions of the inner surface defining ink supply opening 53. Member 82 is preferably made from polysulfone (PSF) or other plastic material resistant to ink but may also be made from stainless steel or other metal. another metallic material. It will be understood that whatever material is employed it should be resistant to the ink. It is sufficient if the grid grid-like member divides the inside of ink supply opening 53 into a grid pattern dividing the ink flow path from ink supply tube 66 to ink intake opening 58 into a plurality of separate parallel channels. Preferably, the channels have a non-circular, particularly a polygonal cross-section. Air bubbles inside ink supply tube 66 are thus moved toward head chip 55 by the priming process or suction operation and are fractionated by member 82. This reduces the flow resistance into ink intake opening 58, enables reliable purging of air bubbles, and thus enables reliable priming and recovery. Figs. 11 and 12 are views, similar to those of Figs. 6 and 7, of a third embodiment of the invention. In this embodiment a porous plate 83 is housed within ink supply opening 53. The preferred materials for porous plate 83 are the same as those for member 82. Capillary paths 67c are formed from plural through-holes in porous plate 83. Ink is supplied to the cavity formed by ink supply opening 53 by ink supply tube 66. Capillary paths 67c have a triangular cross section. As a result, air bubbles that pass through a capillary path 67c are prevented from completely occluding the capillary path. Note that the cross section of these capillary paths 67c is not limited to triangular shapes and can be any shape capable of preventing spherical air bubbles to contact all of the wall surfaces of the capillary paths. FIG. 13 is a cross section of the capillary paths in a fourth embodiment of the invention. Note that both capillary paths 67d and filter 115 for preventing foreign matter from flowing downstream are disposed inside ink supply tube 166. Filter 115 is an extremely fine mesh filter provided to retain foreign matter capable of clogging the nozzles, which have the smallest cross sectional area of any part of the ink supply path. As a result, even relatively small air bubbles flowing from upstream are stopped at the filter face, grow into relatively large air bubbles as more bubbles continue to flow, and can be difficult to purge even with the priming operation. It is also possible for the air bubbles to completely occlude the ink supply path, thereby making it difficult to supply ink downstream. More specifically, a boundary plane 151 at which air bubbles tend to collect is also formed in front of filter 115 disposed inside the ink supply tube. By providing capillary paths 67d at a specified distance d upstream from boundary plane 151, the above-described effect of improving air bubble expulsion is achieved, and occlusion of the ink supply path by air bubbles collecting and growing can be prevented. It should be noted that the capillary paths 67d in this embodiment can be formed in accordance with any of the preceding embodiments, namely by wall members 69, grid-like member 82 or porous plate 83. Other means for providing the capillary paths and/or shapes of the capillary paths can also be used as long as the shape of the capillary paths is appropriately determined according to the cross sectional shape of the ink supply tube. The above embodiments have been described with reference to an ink cartridge including a recording head (the head chip 55) and an ink supply unit. As will be appreciated by those skilled in the art, the invention can be applied to cases where a recording head and an ink supply unit are separate units. In such case the capillary paths of the invention are disposed in the ink supply tube connecting the recording head and ink supply unit. By forming capillary paths at the ink intake opening of the recording head, the present invention can efficiently expel air bubbles inside the ink supply tube, and can thereby reliably refresh the nozzles and recover printing. The invention also minimizes the amount of ink that is also expelled when expelling air bubbles. Furthermore, even when air bubbles are not completely expelled, occlusion of the ink supply tubes by growing air bubbles is prevented, and interruption of the ink supply to the recording head by such air bubbles can be reliably prevented.

Claims: An ink jet recording apparatus having an ink holding member (30, 50; 50, 70) for storing ink, a recording head (55) comprising nozzles (57) for ejecting ink, and an ink supply path (66) connecting the nozzles to the ink holding member, the ink supply path having a boundary plane (151) at which the cross sectional area of the ink supply path decreases abruptly from the upstream side to the downstream side, wherein capillary path means (67d; 69; 82; 83) dividing the cross sectional area of the ink supply path into a plurality of separate channels (67a; 67b; 67c) extending substantially in parallel to the ink flow direction is disposed on the upstream side of the boundary plane, the downstream end of the channels being spaced apart from the boundary plane by predetermined distance (d). The apparatus according to claim 1 wherein said predetermined distance (d) is in the range of 0.05 to 0.5 mm. The apparatus according to claim 1 or 2, wherein said capillary path means comprises a plurality of wall members (69) arranged in parallel to each other in a comb-like configuration. The apparatus according to claim 3 wherein the cross section of said ink supply path in the vicinity of said boundary plane (151) has a rectangular shape and said wall members (69) are arranged approximately perpendicularly to the long side of said rectangular shape. The apparatus according to claim 1 or 2 wherein said capillary path means comprises a grid-like wall member (82). The apparatus according to claim 1 or 2 wherein said capillary path means comprises a porous plate (83) having plural through-holes (67c) forming said channels, wherein the cross sectional shape of said through-holes is non-circular. The apparatus according to any one of claims 1 to 6 wherein the recording head (55) comprises an ink intake opening (58), the ink supply path (66) comprises an ink supply opening (53) adapted to be connected to said ink intake opening, the cross sectional area of the ink supply opening is greater than the cross sectional area of the ink intake opening, and the capillary path means (67d; 69; 82; 83) is disposed at said predetermined distance (d) to the boundary plane (151) defined by the end face of the ink intake opening. The apparatus according to any one of claims 1 to 6 comprising a filter (115) in said ink supply path for preventing foreign matter from flowing to said nozzles (57), wherein the capillary path means (67d; 69; 82; 83) is disposed at said predetermined distance (d) to the boundary plane (151) defined by the filter surface facing said ink holding member (30, 50; 50, 70). The apparatus according to any one of claims 1 to 8 further comprising suction means for sucking ink out of the recording head (55) through the nozzles (57). The apparatus according to any of claims 1 to 8 further comprising pressurizing means adapted to rise the pressure inside said ink supply path (66) upstream of said capillary path means for expelling ink from inside the recording head through the nozzles. An ink cartridge comprising the ink holding member (30, 50; 50, 70), recording head (55), ink supply path (66), and capillary path means (67d; 69; 82; 83) described in any one of claims 1 to 8, and a housing for holding these components.

Inventors: HANAOKA YUKIHIRO, NISHIOKA ATUSHI, SATO KAZUHIKO, YAMAZAKI TSUTOMU, HANAOKA, YUKIHIRO, NISHIOKA, ATUSHI, SATO, KAZUHIKO, YAMAZAKI, TSUTOMU
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1997
Main classification: B41J2
IPC codes: B41J2