CA2218984C

CA2218984C - Cleaning fluid apparatus and method for continuous printing ink-jet nozzle

Info

Publication number: CA2218984C
Application number: CA002218984A
Authority: CA
Inventors: Henk Haan; Roger J. Rowland; Anthony V. Moscato; Kenneth C. Chapin; Michael A. Graziano; Paul J. Paroff
Original assignee: Moore Wallace North America Inc
Current assignee: Moore Wallace North America Inc
Priority date: 1995-05-09
Filing date: 1996-04-09
Publication date: 2006-09-12
Anticipated expiration: 2016-04-09
Also published as: CA2218984A1

Abstract

A fluid (liquid or water) wash (46) is used to clean the front surface of an ink jet printer cartridge (17). In addition, a nozzle plate (24) that overlies the nozzle shields the nozzle array (23) from the splatter of ink (32). In ink jet printers, ink droplets are propelled from an array of orifices in a nozzle plate in the printer head.
During the ink droplet ejection, ink is sprayed or deposited around the orifices. The ink droplets are deposited on a paper web (14) adjacent the nozzle and mist from the droplets drifts back to coat the face of the nozzle plate.
Some ink seeps behind the nozzle plate (24) onto the array of nozzle orifices (23).
The ink coating attracts particles that tend to clog the nozzle orifices. The ink coating is washed away by fluid streams (46) that flow over the nozzle surface and in some embodiments flow over the nozzle orifices themselves. The fluid (46) may be water, ink or other liquid that is channelled across the nozzle surface, or the fluid may be an air stream that blows across the nozzle surface.

Description

CLEANING FLUID APPARATUS AND METHOD FOR
CONTINUOUS PRINTING INK-JET NOZZLE
FIELD OF THE INVENTION
The invention relates to the fields of print nozzles and, in particular, drop-on-demand printer nozzles, such as ink jet and bubble jet printer nozzles. The invention f-~as particuler application to the problems associated with dust, other particles and ink that disrupt and clog tf-~ese printing nozzles during continuous operation.
BACKGROUND AND SUMMARY OF THE 1NVENTtON
Drop-on-demand ink-jet and bubble-jet printers [collectively referred to as ink jet printers] propel fine ink droplets from nozzles onto a paper substrate adjacent the nozzle. Examples of these types of printers are the Cannon nozzles known as BCO'1 and BC02. By precisely controlling the trajectory and tf-~e=_ time of ejection of the ink droplets, the ink jet nozzles print clear dots on paper. To achieve precise positioning of droplets of ink, ink jet nozzles must ' provide clear and clean orifices for the droplets to pass through as they fly from tf~e nozzle to the surface of the paper. In a conventional drop-on-demand ink jest nozzle, there is an array of several orinces on the face WO 96/3558.1 PCT/US96/04943 d of the nozzle from which the ink droplets are propelled.
During printing, ink is ejected out of selected orifices in the array to form the desired images on the paper.
The flight of the ink droplets and especially their impact on the paper surface creates a fine mist of ink that coats the surface of the nozzle. Also. durinr, rr,o ejection of the droplets, extraneous ink is sprayed and deposited on the nozzle face adjacent the orinces.
This moist ink coating attracts paper fiber, dust, grit and other types of particles that can obstruct the nozzle orifices and block the ink droplets being sprayed from the nozzle. Also, the extraneous ink can build up such that it blocks the orifices. Accordingly, there is a need to regularly clean the nozzle plate of ink jet printers so that the array of orifices remains clear of ink and particles that would otherwise interfere with the printing of ink on the paper.
In the past, ink jet printers I-gave been cleaned by wiper mechanisms that clean the nozzle plates and orifices. Between print jobs, the printer head moves away from the paper web to a cleaning station where is slides against a cleaning wiper. These wipers squeegee across the face of the nozzle plate and the 2~ openings of the orifices to remove particles that may be obstructing ink in the nozzles. Because the wipers themselves temporarily obstruct the nozzles, the wipers are used only when the ink jet printer is not printing. For example, a wiper may be positioned at the far edges of a carriage path, beyond the edges of the paper held adjacent the carriage path. Examples of wiping systems are disclosed in U.S. Patent No.
5 S,'1 2!=,765, entitled "Ink Jet Recording Apparatus Having Cleaning Means For Cleaning A Recording Head" and in German Patent Document No. DE
~, 8'I 7,~S4A.
10 Wipers have proven generally acceptable for desk top printing applications where each individual print job is relatively short and the times between when the print nozzles are wiped clean are relatively brief. In a typical desk-top ink-jet printer the carriage 15 with the ink jet printing head can be shifted to a cleaning station after each print operation. Thus, in the usual desktop application, the printing nozzles are cleaned frequently by conventional wipers and tend not to clog with particles.

With continuous web-feed printing, the print nozzle is required to constantly print for many hours.
This is unlike typical desk-top printing applications in which each printing operation is conducted in a 25 relatively short period of time. shifting the print head to a cleaning station away from the paper to be printed necessarily interrupts the printing operation of a continuous printer. While these interruptions do not substantially interfere with typical desktop print 30 jobs, AMIENDED SHEE?

WO 96/3558=t PCT/US96104943 they do interfere with commercial printing of continuous webs. In this regard, conventional ink jet print heads have been found to require cleaning for every ~D to ~D minutes of continuous printing.
Remote cleaning stations for ink jet printers are undesirable for commercial continuous printers because the print operation must be interrupted every one-foaff hour to one hour to clean the nozzles.
Accordingly, there is a long-felt need for an apparatus and method for cleaning an ink jet nozzle without interrupting a print job.
Other prior art techniques for cleaning the nozzle face of an ink printer are to blow air at or around the l~ ink nozzles to blow particles ofF the nozzle face or prevent particles from adhering to the nozzle face.
Some of these techniques have included using ionized air to neutralize the static charges on dust particles that attract the dust to the nozzles. These techniques have achieved only partial success as is reported in U.S. Patent No. 4,4'I '1 ,7Oo, entitled "Method And Apparatus For ~(iminating Dust From Ink Jet Printers."
While blowing air at the nozzles can_be accomplished as the nozzles are spraying ink, the turbulent air flow caused by the prior art blowers disrupts the trajectory of the ink droplets to the paper. Given that the prior systems for cleaning ink jet nozzles have been lass than satisfactory, there f-gas been a Long felt-need for a S
technique for effectively cleaning the nozzles. That ' need was not fully satisfied until the current invention.
Tf-~e current invention relates to a tecf-inique for ~ cleaning an ink jet nozzle with a fluid, such as water or air, that flows across the face of the printing nozzle and entrains the dust and paper particles that adhere=_ to the face of the nozzle. Once caught in the fluid, them particles are removed from the nozzles by the flow of the fluid.
fn one embodiment of the invention, a fluid stream flows across the face of the nozzle of an ink jet printer, to clean the printer. This stream is located proximate=
l~ to the nozzle array from which the ink droplets are propelled. Dust and paper particles that would otherwise clog the nozzle array are entrained in the fluid stream before they obstruct the orifices of the nozzle. A fluid source, drain supply fluid and network of fluid channels on the nozzle create a fluid stream patf adapted to remove the particles and dust in the vicinity of the nozzle array. By continuously flowing fluid across the nozzle face, ink, grit and paper particles are continuously captured and removed from the nozzle array. In some embodiments, the fluid stream does not disrupt the projection of ink droplets from the nozzle array and, thus, does not interfere with printing.

f~
In a first embodiment of the invention, the cleaning fluid is confined to channels adjacent the nozzle orifices. The orifices are not flushed with fluid.
Accordingly, the ink jet nozzle can print while the cleaning fluid is flowing because the fluid flow does not obstruct or interfere with the ink droplets ejected from the nozzles to the paper. Accordingly, the first embodiment of the current invention provides a . technique and apparatus for continually removing particles from an ink jet printer face while printing continues.
In a second embodiment of the invention, cleaning fluid flows directly over the print nozzle orifices to wash 1~ the orifices and nozzle in general. Printing is interrupted while the orifices are washed using the second embodiment. This orince wash embodiment of the invention flushes out any ink residue, dust or paper fibers clogging the orinces. Ti-ius, the second embodiment provides a more thorough cleaning of the print nozzle than does the first embodiment. The second embodiment of the invention may be used in conjunction with the first embodiment.
In a third embodiment of the invention, the array of nozzle orifices is shielded from ink spray and splatter by a nozzle plate. The nozzle plate is positioned in front of the orifices and includes a narrow slit through which ink droplets fly. The nozzle plate is separated by a small gap from the array of nozzle orifices and excess ink drains through this gap away from the nozzle orifices. This third embodiment may be used in conjunction with the first and second embodiments of the invention.
Thus, in a broad aspect, the invention provides an ink jet printer head comprising: a. an array of nozzle orifices through which ink droplets are projected in a path towards a substrate for printing and a front surface of said array of nozzle orifices having channels passing between the orifices; b. a nozzle plate disposed between said array of nozzle orifices and the substrate and separated by a gap from the array, said nozzle plate having a slit aligned with respect to the path to allow the ink droplets to fly through the slit; and c. a liquid cleaning fluid stream flowing in the channels of the front surface, and through the gap between the nozzle plate and array of nozzle orifices, wherein said liquid fluid stream flows while ink droplets are being projected from the nozzle orifices during printing.
In another aspect, the invention provides an ink jet printer comprising: a. an ink jet printer head having a front surface and an array of nozzle orifices arranged on the front surface, wherein ink droplets are projected through the orifices along a path towards a substrate; b. a bracket having a recess adapted to receive the ink jet printer head; c. a mounting plate removably attached to said bracket and securing said ink jet printer head in the recess, said mounting plate having an opening into which projects the front surface of the ink jet printer heads;
d. a nozzle plate attached to said mounting plate and covering the opening in the mounting plate and separated by a gap from the front surface the ink jet printer head, , CA 02218984 2005-07-13 7a wherein said nozzle plate having a slit aligned with the array of nozzle orifices and through which pass ink jet droplets on their path, and e. liquid cleaning fluid stream flowing in the gap between the nozzle plate and front surface of the printer head, wherein said liquid fluid stream flows adjacent to the nozzle orifices while ink droplets are projected from the nozzle orifices to the substrate.
In another aspect, the invention provides a method for cleaning an ink jet printing head having a front surface with a nozzle array of orifices, and a nozzle plate separated by a gap from the front surface of the printing head, the method comprising the following steps:
a. propelling ink from the nozzle array through a slit in the nozzle plate and towards a web for printing on the web;
b. shielding the orifices from ink splatter and airborne fibers and particles with the nozzle plate; c. washing the front surface of the printing head with a liquid fluid stream while propelling ink during step (a), and d. draining the liquid fluid stream and excess ink on the nozzle array down through the gap between the front surface of the printing head and nozzle plate.

7b An object of the current invention is to clean the nozzle array of an ink jet printer and prevent ink, dirt and paper particles from obstructing the orinces of the nozzle array. It is a further object of the invention to continually capture and remove ink and particles from the nozzle array while the nozzles are printing and to wash the nozzles completely at other times. A
further object of the invention is to extend the period of maintenance Free printing for ink jet printers and to reduce the frequency of ofr print cleaning occurrences required for ink jet printers. Moreover, another objective of the invention is to enhance the print quality of ink jet printers by overcoming many of the problems caused by extraneous, girt and paper particles that I ~ have clogged prior ink jet printers. These and other objectives are achieved by the invention that is shown and described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained in greater detail with reference to the drawings identified as follows:
FIGURE 'I is a cross-sectional view of an ink jet printer head with an associated fluid cleaning mechanisms, forming a nrst embodiment of the invention;
FIGURE 2 is a front view of the face of the ink jet printer head shown in Figure 'I , and F=LURES ~ and 4 show cross-sectional and front 1~ views, respectfully, of another embodiment of the invention;
F=ICURI= ~ shows a front view of a further embodiment of the invention, and FIGURES ~ and 7 show a front view of yet another embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure '1 shows an ink jet printer head '1 O
mounted as a carriage on a shaft 'I 2 in a printing mechanism. In particular, the printing mechanism may WU 96!35584 PCTIUS96I04943 ' be an otherwise conventional continuous web-feed printer, for high volume computer printing. It is common for the web speed in such printers to be OOO
feet per minute and have an operating speed range of ~ 200 to SOO web-feet per minute. In addition, these printers operate continuously and will typically print for' periods as long as twelve hours without interruption, provided that the ink jet printer does not require cleaning in that period.
The paper or other web substrate moves as a web '1 4 in the direction of arrow 'I S. The web moves across the surface of a platen 'I B adjacent the printer head. The platen positions the web for printing directly l~ in front of and generally parallel to tf-~e ink jet printer head. The printing mechanism may include conventional web handling devices [not shown], e.g., tractor feeders, to move the web at a predetermined speed, in a precisely controlled fashion and along a predetermined path. The ink jet printer head is attached to the shaft by a bracket 'I 7 such that the printer head may be fixed in position on the shaft and arranged in an array with other printer heads uniformly spaced across the width of the web. Alternatively, the printer head may be slidably mounted on the shaft, and moved back and forth across the shaft in a controlled fashion during printing, to position the printer head with respect to the moving web. The bracket may also WO 96!35584 PCT/US96/04943 'I O
includes fins 'I 8 that dissipate heat away from the ink jet printer head. A thermocouple may be attached to the root of a heat fin to sense the temperature of the printer head. The bracket may be formed of aluminum or any other material that is suitable for securely holding the ink jet nozzle assembly.
The ink jet nozzle assembly includes a mounting plate 'I J on the front face of the print head bracket '1 7. The mounting plate holds the print head in a recess 2O of the bracket. The plate overlaps the bracket recess and is removably attached to the bracket by screws or other fastening devices. The mounting plate includes a rectangular slot 2'I through 1~ which protrudes the front nose 2~ of the printer head.
The array of nozzle orinces 2~ are located on the front surface of the nose of the print head. The mounting plate may be made of machined copper and coated with a hydrophilic coating, e.g. Teflon, at and near the area of the orifices 2~ to reduce the tendency of excess ink to clog the orifices.
A nozzle plate 24 overlaps the.mounting plate and the nose of the print head. The nozzle plate is attached to the mounting plate or bracket by screws or other fastening device. A seal 2S may be located between the nozzle plate and mounting plate prevents cleaning fluid from leaking out from the gap between the two plates. In addition, the nozzle plate includes a narrow slit 28 aligned with the array of orifice nozzles 23 in the print head to allow ink droplets to fly from the orifices, through the slit 28 and towards the paper web 'I 4. The slit is in alignment with the array of orifice nozzles. In addition, the slit has an opening area that is just slightly larger than the area of the nozzle array.
The nozzle plate partially shields the nozzle array from the splash of ink hitting the paper web. The nozzle plate may be formed of a pores material so that ink splattered onto the nozzle plate can be drawn through the plate and into the gap between the back of tf-re nozzle plate and the mounting plate.
The nozzle plate shields the printer head from the=_ splatter of ink droplets as they impact on the paper web. lnk spray collects on the outer face of the nozzle plate instead of splashing back onto the nozzle array.
In addition, ink that does seep into the gap 40 between ?0 the mounting and nozzle plate is shielded from paper and web fibers and other particles that tend to be attracted to surfaces wetted with ink. The ink that does collect on the nozzle surface 48 of the printer head does not collect web fibers and other particles ?5 because of tine nozzle plate. It is believed that the presence of the nozzle plate alone can extend to several hours [opposed to O.S to 'I .S hours] the period of time during which a print head nozzle can reliably and continuously print between cleanings. , Ink droplets 27 are propelled from the nozzle orifices ~~ in a direction towards the paper web 'I 4 for printing. As the ink droplets impact on the web, most of the ink remains on the web as dots ~O, or other indicia. Some of the ink will splatter as it hits the paper and form a mist of ink particles ~2. In addition, there will be some residue of ink mist resulting from the ejection of the ink droplets from the nozzle orifices.
This ink mist floats in the vicinity of the nozzle plate, print head nose 22 and paper web, and tends to settle on these surfaces, as an ink coating 34 that builds in I~ thickness a' ink printing continues. Since the paper web is moving, there is no noticeable build-up on any one section of the web. The print head does not move.
Accordingly, the ink build up on the print head surfaces can pose problems, that are solved by the current invention.
The impact of the ink droplets, movement of the paper web and other factors cause paper fibers and other nne particles ~~ to dislodge from the web and 2~ other surfaces and float in the ink mist. In addition to the build-up of ink around the nozzle caused by the misting of the ink, some of these particles contribute to tl-~e build-up ~4 of ink and particles in tF-~e vicinity of WO 96/35554 PCTlUS96104943 ~8 the ink-jet nozzles. If this build-up is permitted to continue without being removed by cleaning, the build-up will clog the nozzle orifices 28 and disrupt printing of the ink. While the nozzle plate shields the print head from much of the ink spray and stray particles, the nozzle plate does not entirety avoid the need to wipe clean the array of nozzle orifices. The current invention also includes a technique for removing ink and particle build-up surrounding the nozzle orifices while printing continues.
It has been found that by filushing a fluid, such as water or air, across the face of the nose 2~ of the print head, that the ink and particles coating the nozzles 1~ array can be washed away. In one embodiment, water is supplied to the gap 40 between the mounting plate 'I J and nozzle plate 24 from a water source via conduirt;
42 that passes through the bracket '1 7 and mounting plate and discharges from an relatively wide opening[s]
44 on the front surface of the mounting plate. Fluid discharged from these openings enters the gap 40 between the mounting and nozzle plates and flows downwardly, as indicated by arrow 48, between those plates and towards the nose 22 of the print head. As " ?5 the fluid reaches the print head nose 22, it wets and flows over the front surface 48 of that nose. In doing so, ink, web fibers and particles coating the front surface of the nose are washed away with the fluid.

WO 96/3558=1 PCT/US96/04943 'I 4 The fluid with the ink, fibers and other particles flows downward through the gap between the mounting and nozzle plates until reaching a suction opening SO in the mounting plate. Due to a slight suction applied at that opening, the fluid is drawn into the opening and away through conduits S2 to a discharge [not shown). The fluid, if water or other liquid, may be disposed of or filtered and recycled through the printer. Alternatively, the fluid drawn by suction into the suction opening SO may be just the excess ink in the gap 40 between the mounting and nozzle plates. The suction of fluid will create capillary farces in the gap that draw the ink downward through the gap to the suction opening and away from the 1~ nozzle array. In this alternative embodiment, a separate source of fluid, supply conduits 42 and fluid discharge openings 44 above the printer head are unnecessary, because the excess ink is itself used as the cleaning fluid.
If a washing fluid, such as distilled water, is supplied, then printing may have to be interrupted or may continue while the fluid washes the front surface 48 of the nozzle, depending on the flow path of fluid across the face of the nozzle array. If the flow of fluid is heavy across the entire nozzle array, then the fluid will wash across the orifices 28. While such a heavy flow is particularly effective at cleaning clogged print orifices, WO 96/35584 PCTIUS96lOd9d3 S
the fluid would interfere with the projection of ink '' droplets and, thus, printing may be interrupted or even stopped for heavy flows of cleaning fluid.
Alternatively, a fighter flow of fluid confined to channels S4 on the mounting plate and/or front surface 4i~ of the nozzle may be used while printing continues because the channels do not cut across any of the print orifices thereby interfering with the ink flow.
>=xcess ink, fibers and other particles can be attracted to these channels by coating the channels and surfaces near the channels with hydrophilic coatings.
Ti-~e fluid in tf-~e channels carries the ink, fibers and other particles away from the front surface of the nozzle array and to the suction opening SO.
1~
In another alternative embodiment, such as shown in FIGURES ~ and 4, [the same numerals from figures 'I and 2 have been used in these figures to refer to features that era common to all figures], the single filuid path of the first embodiment has been changed to a dual-path fluid system for cleaning away excess ink, paper fibers and other particles. This dual-path fluid wash is intended for use while the print head is not printing, as the wash might interfere with the 2~ printing operation. A pair of fluid conduits 60, E2 extend through a top portion of the .print head bracke=t 'I 7 from a pair of outlets E=4 to a fluid source [not shown] to first and second fluid discharge ports, ~~, 6B, respectively. In this embodiment, the nozzle plate is attached directly to the mounting plate by means of screws 74 or other attachment means.
T he first discharge part E6 opens from the brack=_t'1 7 out to a gap 70 between the nozzle plate 24 and a front surface section 72 of the bracket and print head, which section includes the front surface of the nozzle 46. Fluid flows downwardly through this gap until it passes over the orinces '3 of the nozzle array. Below the nozzle array, the front surface of the print head drops back along an inclined section 74 until it meets with another vertical section 76 that ends at the suction opening Sp for the bracket. The inclined 1~ surface widens the gap 70 into a relatively-large reservoir 78 which collects the fluid, excess ink, web fibers and other accumulated particles. Fluid flows downwardly into the reservoir and is drawn by capillary forces into the suction opening EO of the bracket.
Similarly, the second fluid conduit 60 carries fluid to ti-~e second discharge port 66, that may constitute a row of openings as shown in Figure 4, through which the quid exits to the surface 80 of the nozzle plate 1 J.
The fluid wets and washes the front surface of the nozzl=_ plate as the fluid flows down.and across the surface of the plate. At the slit 2fl in nozzle plate 24, portions of the fluid may flow around, over and into the slit. The fluid that flows around and over the slit, washes away ink and particles that have collected on the plate. This outer path fluid, ink and particle mixture continues its downward flow over the nozzle plate ~ [surface tension holds the fluid stream onto the plate surface] until the fluid is drawn into an opening 82 in the nozzle plate in communication with the suction opening SO of the bracket. Fluid that is drawn into the slit 28, washes the slit and is drawn into the cavity ~8 between the nozzle plate and printer head, from where the fluid, ink and particle mixture is drawn in by the suction opening 80 of the bracket.
FI~U(~E S shows another embodiment of the invention in which a pair of fluid streams 88, 88 flow across the nozzle front surface 48 on either side of the nozzle array 23 to clean ink from the surface 48 while printing is ongoing. This embodiment may be employed with or without [as shown] a nozzle plate. A
pair of horizontal fluid conduits JO, 82 mounted on or within the mounting plate '1 3 are connected to a fluid source [represented by arrows J4] and discharge from openings H8 adjacent the front surface 48 of the' print head nozzle. Fluid from the discharge openings 2~ enter a pair of horizontal channels JB, 'I OD that are parallel and on opposite sides of tf-Ze, nozzle array 28.
The channels and surfaces proximate the channels and nozzle orifices may be coated with a hydrophobic 'I 8 material so that ink will not be allowed to accumulate in these areas and is drawn into the channels and washed away by the channel flow. As the fluid in the channel reaches the opposite end of the channel, the fluid is drawn by suction into openings '1 02, '1 O4 on the mounting plate. These openings are connected to conduits '1 08, 'f 08 that are also connected to a drain 'I '1 O that imparts suction to the conduits and openings '1 02, 'I 04 to draw the fluid through the channels.
FIGURES 8 and 7 show another embodiment of the invention especially adapted to using air [or other gas] as a cleaning fluid. An air bellows manifold 'I 'I 2, such as a oval shaped funnel, provides a low-pressure l~ air flow directed horizontally [Fig. 8) or vertically [Fig. 7) across the front surface 48 of the nozzle array 28.
The bellows manifold is connected to a source of compressed air [not shown]. The air flow pressure blows on the ink wetted to the front surface of the nozzle array and causes the ink [including entrained fibers and other particles] to flow away from the bellows 'I 'f 2 and towards a vacuum manifold 'I 'I 4, that may have a shape similar to that of the bellows. The vacuum manifold collects the ink flow and directs [sea ''S arrow 'I 1 8] towards a drain [not shown]. In addition, the vacuum manifold may be connected to a vacuum pump to draw air across the nozzle array and into the manifold. Depending on whether the pressure of the WO 96/35584 PCTlUS96104943 air flow across the nozzle array disrupts tf~e trajectory of tf,e ink jet nozzles, the bellows and vacuum manifolds may or may not be operated wf,ile printing is ongoing.
The invention has been described in what is considered to be the most practical and preferred embodiments. The invention is not limited to the disclosed embodiments, but covers various modifications and equivalent arrangements included within tt~e spirit and scope of the appended claims.

Claims

CLAIMS:

1. An ink jet printer head (10) comprising:
a. an array of nozzle orifices (23) through which ink droplets (27) are projected in a path towards a substrate for printing and a front surface of said array of nozzle orifices having channels passing between the orifices;
b. a nozzle plate (24) disposed between said array of nozzle orifices and the substrate and separated by a gap from the array, said nozzle plate having a slit aligned with respect to the path to allow the ink droplets to fly through the slit (26); and c. a liquid cleaning fluid stream flowing in the channels of the front surface, and through the gap between the nozzle plate and array of nozzle orifices, wherein said liquid fluid stream flows while ink droplets are being projected from the nozzle orifices during printing.

2. An ink jet printer head as in claim 1 wherein the slit (26) in the nozzle plate (24) has an area that is slightly larger than an area of said array of nozzle orifices (23).

3. An ink jet printer head (10) as in claim 1 wherein said nozzle plate (26) is formed of an ink adsorbent, porous material.

4. An ink jet printer comprising:
a. an ink jet printer head (10) having a front surface and an array of nozzle orifices (23) arranged on the front surface, wherein ink droplets (27) are projected through the orifices along a path towards a substrate (14);

b. a bracket (17) having a recess adapted to receive the ink jet printer head;
c. a mounting plate (19) removably attached to said bracket and securing said ink jet printer head in the recess, said mounting plate having an opening into which projects the front surface of the ink jet printer heads;
d. a nozzle plate (24) attached to said mounting plate and covering the opening in the mounting plate and separated by a gap (40) from the front surface the ink jet printer head, wherein said nozzle plate having a slit (26) aligned with the array of nozzle orifices and through which pass ink jet droplets on their path, and e. liquid cleaning fluid stream flowing in the gap between the nozzle plate and front surface of the printer head, wherein said liquid fluid stream flows adjacent to the nozzle orifices while ink droplets are projected from the nozzle orifices to the substrate.

5. An ink jet printer head as in claim 4 further comprising a cleaning fluid stream flowing across the front surface of the ink jet printer head.

6. An ink jet printer head as in claim 4 wherein said nozzle plate (24) has a front surface (80) facing the substrate and a rear surface facing the printer head, and said nozzle plate is porous such that ink splattered on the front surface is drawn through the nozzle plate and washed away by the liquid cleaning fluid stream.

7. An ink jet printer as in claim 4 further comprising a second liquid fluid stream on a front surface (80) of the nozzle plate facing the substrate and wherein at least a portion of the second liquid fluid stream is drawn through the slit (26) in the nozzle plate to merge with the liquid cleaning fluid stream.

8. An ink jet printer as in claim 4 wherein said front surfaces of said printer head is furrowed with channels (98, 100) for the liquid cleaning fluid stream(s).

9. An ink jet printer as in claim 8 wherein said channels are coated with a hydrophilic material.

10. An ink jet printer as in claim 4 wherein the gap between the front surface of the ink jet printer head and the nozzle plate widens to form a reservoir (78) below the array of nozzle orifices.

11. An ink jet printer as in claim 4 further comprising a suction opening (82, 50) in said bracket and located below the array of nozzle orifices and said suction opening having a slight vacuum for drawing excess ink from the gap between the ink jet printer head and the nozzle plate.

12. An ink jet printer as in claim 4 further comprising a suction opening (50, 82) in said bracket and located below the array of nozzle orifices and said suction opening having a slight vacuum for drawing in the liquid fluid stream after the stream washes across the front surface of the printer head.

13. An ink jet printer as in claim 12 wherein said nozzle plate includes an opening aligned with the suction opening (50, 82) in the bracket and liquid fluid flowing over the nozzle plate is drawn into the opening in the plate and further into the suction opening.

14. A method for cleaning an ink jet printing head (10) having a front surface with a nozzle array of orifices (23), and a nozzle plate (24) separated by a gap (40) from the front surface of the printing head, the method comprising the following steps:
a. propelling ink from the nozzle array through a slit (26) in the nozzle plate and towards a web (14) for printing on the web;
b. shielding the orifices from ink splatter and airborne fibers and particles with the nozzle plate;
c. washing the front surface of the printing head with a liquid fluid stream while propelling ink during step (a), and d. draining the liquid fluid stream and excess ink on the nozzle array down through the gap between the front surface of the printing head and nozzle plate.

15. A method for cleaning an ink jet printing head as in claim 14 wherein the nozzle plate includes a channel (98, 100) adjacent the orifices and step (c) is further practiced by flowing the liquid fluid stream through the channel in the nozzle plate.

16. A method for cleaning an ink jet printing head as in claim 14 wherein step (c) further includes washing a front surface of the nozzle plate with a liquid fluid stream and drawing a portion of the liquid fluid stream across the nozzle plate through the slit (26) in the nozzle plate.