Ink-jet printer

Abstract: An ink-jet printer comprises, an ink tank (1) for receiving an ink, a printing head (9) including a nozzle (5) for injecting an array of ink-particles, electrode means (21) for charging the ink-particles with electricity, electrically controllably energized deflecting means (22) for deflecting the electrically charged ink-particles so that each of the ink-particles injected from the ink-jet printer reaches a desirable position on a work piece to be printed, and a gutter (6) for receiving a part of the array of ink-particles which is not used to print the work piece, and pump means (7) for taking the part of the array of ink-particles through the gutter (6) into the ink tank (1), wherein an air in the printing head (9) is taken into the pump means (7) through the gutter (6), and the ink-jet printer further comprises a feed back path (25) which opens to an inside of the printing head (9) at an outside of the gutter (6) to return the air taken from the printing head (9) by the pump means (7) through the gutter (6) to the inside of the printing head (9) at the outside of the gutter (6).

Description: BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT The present invention relates to an ink-jet printer according to the preamble of claim 1. A basic structure of the ink-jet printer as above mentioned is disclosed by, for example, U.S.P. 4,083,053. As shown in Fig. 4, a conventional ink-jet printer has a suction pump 7 so that a part of the array of ink-particles which is not used to print the work piece and an air in a gutter 6 for receiving the part of the array of ink particles are taken into an ink-tank 1 from a printing head 9. The part of the array of ink-particles which is not used to print the work piece is contained again in the ink-tank 1, but, the air taken from the gutter into the ink-tank 1 is discharged from the ink-tank 1 to the atmosphere through a filter 16 in which an organic solvent contained by and generated from the ink absorbed by an activated charcoal or the like. The ink is supplied to a nozzle tube 5 from the ink-tank 1 by an ink-pump 2 through an ink-pressure regulator 4. An air compressor 15 supplies a pressurized air into the printing head 9 from the atmosphere to prevent a penetration of undesirable substance into the printing head 9. EP-A-0 123 523 relates to an ink-jet printer comprising an ink tank which is connected to a nozzle through which the ink is ejected as a jet broken up into single droplets. The droplets are given an electrical charge and are passed through an electric field, whereby they are deflected to a desired extent onto a substrate to be printed or, alternatively, into a catching gutter within the printing head. Collected ink in the catching gutter is recycled for re-use back into the ink tank through a recycle line. In order to prevent the loss of solvent from the recycled ink, there is provided a return air line returning the solvent-laiden air from the ink tank into the intake of the recycle line adjacent to the gutter. OBJECT AND SUMMARY OF THE INVENTION An object of the present invention is to provide an ink-jet printer in which the penetration of undesirable substance into the printing head is securely prevented, an ink-mist generated from the ink-particles in the printing head is effectively taken from the inside of the printing head into the ink-tank, and the loss of solvent from the recycled ink is prevented. This object of the present invention is solved according to the features of the characterizing part of claim 1. Since the ink-jet printer comprises the feed back path which opens to the inside of the printing head at a location outside of the gutter to return the air taken from the printing head by the pump means through the gutter to the inside of the printing head at the outside of the gutter, the air circulates from the outside of the gutter in the inside of the printing head through an inside of the gutter, the pump means and the feed back path to the inside of the printing head at a location outside of the gutter. Therefore, the atmosphere is prevented from flowing from an outside of the printing head to the inside of the printing head so that the penetration of undesirable substance into the printing head is securely prevented, and the ink-mist generated from the ink-particles at the outside of the gutter in the printing head is effectively taken from the inside of the printing head including the outside of the gutter into the ink-tank by the air flow from the outside of the gutter to the inside of the gutter. A decrease in flow rate of the vaporized ink-solvent from the ink-jet printer to the outside thereof causes a decrease in running cost of the ink-jet printer. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a first embodiment of the present invention. Fig. 2 is a schematic partially cross-sectional view showing an ink-solvent absorbing device. Fig. 3 is a schematic view showing another embodiment of the ink-solvent absorbing device. Fig. 4 is a schematic view showing a conventional ink-jet printer. Fig. 5 is a schematic view showing a second embodiment of the present invention. Fig. 6 is a schematic view showing a third embodiment of the present invention. Fig. 7 is a schematic view showing a fourth embodiment of the present invention. Fig. 8 is a schematic view showing a fifth embodiment of the present invention. Fig. 9 is an oblique projection view showing in detail a structure in a printer head according to the present invention. Fig. 10 is a schematic view showing a further embodiment of the present invention. Fig. 11 is a partially cross-sectional view showing the inside of the printer head. Fig. 12 is a partially cross-sectional view showing a structure of a gutter according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In an ink-jet printer as shown in Fig. 1, an ink tank 1, an ink feed pump 2, an ink filter 3, an ink pressure regulator 4, and a longitudinally vibrating nozzle tube 5 are connected in series to generate an array of ink-particles from the longitudinally vibrating nozzle tube 5. A gutter 6 receives a part of the array of ink-particles which is not deflected by a deflecting plate pair 22 and is not used to print a work piece (not-shown). A part of the array of ink-particles are charged with electricity by a voltage-variable electrode pair 21 to control a moving direction of the ink-particles, and subsequently, the electrically charged ink-particles are deflected by the deflecting plate pair 22 whose one plate is electrically energized to deflect a direction of the part of the array of ink-particles toward the work piece by an electrical field strength in the deflecting plate pair 22. Another part of the array of ink-particles which is not charged with electricity by the electrode pair 21 moves towards the gutter. An ink suction pump 7 feeds the part of the array of ink-particles which is not deflected by the deflecting plate pair 22 and is not used to print the work piece from the gutter 6 to the ink tank 1. The ink tank 1, the ink feed pump 2, the ink filter 3, the ink pressure regulator 4, and the ink suction pump 7 forms an ink circulation device 8. A printing head 9 includes the longitudinally vibrating nozzle tube 5, the electrode pair 21, the deflecting plate pair 22, the gutter 6 and an opening 92 through which a part of the array of ink-particles which is deflected by the deflecting plate pair 22 and is used to print the work piece passes toward the work piece. An forward end of the longitudinally vibrating nozzle tube 5, the electrode pair 21, the deflecting plate pair 22, the gutter 6 are covered by a head cover 91, as shown in detail in Fig. 9. A feed back path 25 extends from an upper air portion in the ink tank 1 through an ink-solvent absorbing tank 11 to the outside of the gutter 6 in the printing head 9. The feed back path 25 may extend directly from the ink suction pump 7 or from the ink tank 1 to the outside of the gutter 6 in the printing head 9 without passing the ink-solvent absorbing tank 11, in all of the embodiments of the present invention. As shown in Figs. 2, the ink-solvent absorbing tank 11 includes a cooling pipe 12 into which a refrigerant expanded adiabatically through an orifice (not shown) after being compressed by a cooling pump 14 and being cooled by a heat exchange between the refrigerant and the atmosphere is supplied to cool the cooling pipe 12. An ink solvent, particularly, an organic solvent, which was vaporized from the ink and is included by the air supplied from the gutter 6 is cooled and liquified by the cooling pipe 12 in the ink-solvent absorbing tank 11 at about 5°C so that the ink-solvent is separated from the air supplied from the gutter 6. The air after the separation of the ink-solvent thereform is supplied to the outside of the gutter 6 in the printing head 9, and the separated ink-solvent flows into an ink-solvent container 13. The absorbed ink-solvent in the ink-solvent container 13 may be supplied into the ink tank 1 as shown in Fig. 3. The ink-solvent absorbing tank 11, the cooling pipe 12, the ink-solvent container 13 and the cooling pump 14 forms an ink-solvent absorbing device 10. Since the air circulates among the inside of the gutter 6 in the printing head 9, the ink suction pump 7, the ink-solvent absorbing device 10 and the outside of the gutter 6 in the printing head 9, the ink-solvent is prevented from flowing out from the ink-jet printer. If the absorbed ink-solvent in the ink-solvent container 13 is supplied into the ink tank 1 as shown in Fig. 3, a viscosity of the ink is not changed by a vaporization or separation of the ink-solvent from the ink and the ink-solvent does not need to be supplied into the ink tank 1 from the outside of the ink-jet printer to adjust the viscosity of the ink. As shown in Fig. 5, the ink suction pump 7 may be mounted on the feed back path 25 between the upper air portion in the ink tank 1 and the ink-solvent absorbing tank 11. As shown in Fig. 6, the ink suction pump 7 may be mounted on the feed back path 25 between the outside of the gutter 6 in the printing head 9 and the ink-solvent absorbing tank 11. As shown in Fig. 7, the feed back path 25 may be extend from a liquid-air separating device 101 to the outside of the gutter 6 in the printing head 9 without passing the ink tank 1. In the liquid air separating device 101, the ink from the gutter 6 is stored at a bottom portion of the liquid-air separating device 101 and flows through an orifice for limiting a flow rate of the ink into the ink tank 1 so that the inside of the liquid-air separating device 101 and that of the ink tank 1 are partitioned from each other by the ink stored at the bottom portion of the liquid-air separating device 101. The feed back path 25 extends from an upper air portion in the liquid-air separating device 101 through the ink-solvent absorbing tank 11 to the outside of the gutter 6 in the printing head 9. As shown in Fig. 10, the feed back path 25 may be extend from the liquid-air separating device 101 to the outside of the gutter 6 in the printing head 9 without passing the ink tank 1 and the ink-solvent absorbing device 10 so that a forward end of the feed back path 25 is arranged adjacently to a path of the array of the ink-particles. As shown in Fig. 8, the ink-solvent may be absorbed by one of a pair of activated charcoal type ink-solvent absorbing devices 103 mounted on the feed back path 25. When the one of the pair of activated charcoal type ink-solvent absorbing devices 103 is absorbing the ink-solvent, the ink-solvent is taken out from another one of the pair of activated charcoal type ink-solvent absorbing devices 103 by a steam from a steam generator 104, and is cooled and liquified in a condensor 102, so that each of the activated charcoal type ink-solvent absorbing devices 103 is used alternatively to absorb the ink-solvent. Valves closed when the one of the pair of activated charcoal type ink-solvent absorbing devices 103 is absorbing the ink-solvent are opened when ink-solvent is taken out therefrom. The other valves opened when the one of the pair of activated charcoal type ink-solvent absorbing devices 103 is absorbing the ink-solvent are closed when ink-solvent is taken out therefrom.

Claims: An ink-jet printer comprising, an ink tank (1) for receiving an ink, a printing head (9) including a nozzle (5) for generating an array of ink-particles, electrode means (21) for charging the ink-particles with electricity, electrically energized deflecting means (22) for deflecting the electrically charged ink-particles so that a part of the ink-particles ejected from the ink-jet printer reaches a desirable position on a work piece to be printed, and a gutter (6) for catching another part of the array of ink-particles which is not used to print the work piece, and pump means (7) for taking the another part of the array of ink-particles through the gutter (6) into the ink tank, wherein an air in the printing head (9) is taken into the pump means (7) through the gutter (6) characterized in that the ink-jet printer further comprises a feed back path (25) which opens to an inside of the printing head (9) at a location outside of the gutter (6) to return the air taken from the printing head (9) through the gutter (6) by the pump means (7) to the inside of the printing head (9) at the location outside of the gutter (6). An ink-jet printer according to claim 1, wherein the ink-jet printer further comprises an ink-solvent absorbing means (10) mounted on the feed back path (25) to absorb an ink-solvent from the air taken from the inside of the printing head (9) through the gutter (6) into the feed back path (25) by the pump means (7). An ink-jet printer according to claim 1, wherein the ink-jet printer further comprises a liquid-air separating means (101) for separating the ink from the air taken from the inside of the printing head (9) through the gutter (6) by the pump means (7) to supply the separated ink into the ink tank (1) and to supply the separated air into the feed back path (25). An ink-jet printer according to claim 1, wherein the air flows into the feed back path (25) through the ink tank (1). An ink-jet printer according to claim 1, wherein the ink-jet printer further comprises a liquid-air separating means (101) for separating the ink from the air taken from the inside of the printing head (9) through the gutter (6) by the pump means (7) to supply the separated ink into the ink tank (1) and to supply the separated air into the feed back path (25), and the air separated from the ink flows into the feed back path (25) with bypassing the ink tank (1). An ink-jet printer according to claim 1, wherein the pump means (7) is mounted on the feed back path (25). An ink-jet printer according to claim 2, wherein the pump means (7) is mounted on the feed back path (25) between the ink tank (1) and the ink-solvent absorbing means (10). An ink-jet printer according to claim 2, wherein the pump means (7) is mounted on the feed back path (25) between the outside of the gutter (6) in the printing head (9) and the ink-solvent absorbing means (10). An ink-jet printer according to claim 3, wherein the liquid-air separating means (101) stores the ink from the gutter (6) at a bottom portion of the liquid-air separating means (101) so that an inside of the liquid-air separating means (101) and that of the ink tank (1) are partitioned from each other by the ink stored at the bottom portion of the liquid-air separating means (101). An ink-jet printer according to claim 2, wherein the ink-solvent absorbing means (10) absorb the ink-solvent from the air by cooling and liquefying the ink-solvent in the air. An ink-jet printer according to claim 2, wherein the ink-solvent absorbing means (10) includes an activated charcoal for absorbing the ink-solvent from the air. An ink-jet printer according to claim 1, wherein the feed back path (25) extends to the inside of the printing head (9) so that the array of ink-particles passes adjacently to a forward end of the feed back path (25) is arranged. An ink-jet printer according to claim 1, wherein the feed back path (25) opens to the inside of the printing head at an upstream side of the gutter (6) in a moving direction of the another part of the array of ink-particles.

Inventors: TAKAHASHI NAOSHI, TAKAHASHI, NAOSHI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1993
Main classification: B41J2
IPC codes: B41J2