GB2280149A

GB2280149A - Preventing nozzle clogging in ink-jet printers.

Info

Publication number: GB2280149A
Application number: GB9312993A
Authority: GB
Inventors: Christopher Michael Bates; Robert Lionel Walton
Original assignee: Willett International Ltd
Current assignee: Willett International Ltd
Priority date: 1993-06-23
Filing date: 1993-06-23
Publication date: 1995-01-25
Also published as: GB9312993D0

Abstract

A method for reducing the drying out of ink in or around the nozzles of an ink jet print head comprises causing solvent vapour to flow across the ink jet nozzle apertures while printing takes place. The invention extends to apparatus for carrying out the method. In one form a stream of vapour is blown across the surface of an exposed nozzle plate. In another form the printhead is contained in an enclosure within which vapour is circulated. Printing is via a slot in the enclosure walls, which slot may be closed by a shutter when not printing. <IMAGE>

Description

METHOD AND DEVICE This invention relates to a method and device for reducing the drying out of ink in or around an ink jet printer nozzle.

A first type of ink jet printer prints by producing a stream of ink from a nozzle, breaking the stream up into droplets, and directing or diverting those droplets onto variable positions on a target medium to build up an image ("continuous" ink jet). A second type of ink jet printer prints by discontinuously producing individual ink droplets from one or more nozzles in an array, when required, to build up a dot matrix print ("drop on demand" or "DOD" ink jet).

The term "print head" is used herein to denote a member carrying one or more nozzles; a print head may comprise an array of nozzles which consists of individual nozzles which are clamped together or multiple nozzles of unitary construction, optionally with a common nozzle end plate and/or associated drive means and actuating electronics.

Ink employed in ink jet printing commonly uses a solvent or carrier medium comprised of one or more volatile organic solvents. This type of ink has the advantage of quick drying. During printing, ink drops are propelled from one or more nozzles onto a receptive print medium where they dry by solvent evaporation.

A problem with solvent ink jet systems may be that during printing ink may collect and dry in or around the nozzle, and this may cause the nozzle to become wholly or partially blocked, causing a deterioration in print quality.

print accuracy. The presence of the solvent vapour does help reduce drying out of the ink, thereby reducing the tendency of the nozzles to block and improving the print quality.

The invention will, for convenience, be described hereinafter in terms of the use of solvent which is a volatile organic liquid and an ink the colouring agent of which is soluble therein. The invention is not, however, limited to this embodiment. For example the solvent may act as a dispersant for the colouring agent of the ink or the solvent may be a liquid not generally renowned for its volatility.

Preferably, the solvent used is the same as the solvent or carrier medium used to make up the ink. A particularly preferred solvent is butanone.

The present invention also provides an apparatus for use in the method described above, the apparatus comprising fluid distribution means and fluid collection means, the fluid distribution means being adapted to be connected to a solvent reservoir, and the distribution and collection means -being adapted to be attached to an ink jet print head so that solvent emerging from the fluid distribution means vaporizes and flows over the print head nozzle apertures and is received by the collecting means so as to maintain a stream of solvent vapour over the print head nozzle apertures.

The solvent which is collected by the fluid collection means is preferably substantially returned to the fluid distribution means. This reduces wastage of solvent and the need for solvent disposal.

solvent resistant plastics material, or a strip of foraminous material such as an open cell plastics foam material, felt, woven fabric, or a porous glass frit; alternatively, the fluid distribution means may be in the form of one or more slots or nozzles.

The fluid collection means may include means for producing a partial vacuum to enhance the tendency of the fluid to flow in the direction of the collection means. In a preferred embodiment the fluid collection means is provided by the walls of a housing which contains the fluid distribution and collection means and the ink jet print head. Solvent vapour may collect on these walls and be returned to the fluid distribution means by gravity or pump means, or the vapour may be blown towards the fluid distribution means by a fan. In a particularly preferred embodiment the same fan that is used to evaporate solvent from the fluid distribution means is also used to direct solvent vapour back towards the fluid distribution means after the vapour has passed over the print head nozzles.

This arrangement allows easy recirculation of the solvent vapour around the housing via the print head nozzles.

A flame trap may additionally be incorporated to isolate the vapour in the region of the nozzles from the vapour in the solvent reservoir, in case accidental ignition of the vapours in the nozzle region should occur, for example by static discharge. The flame trap may, for example, be formed from a wire gauze.

The optimal arrangement for a given pair of fluid distribution and collection means will depend upon the shape of the print head and the arrangement of any array of ink jet nozzle apertures in a specific print head.

apertures 4 through which a jet or droplets of ink may be fired. Affixed to the upper part of the face of the head 2, above the uppermost nozzle aperture, is a strip of felt 10, which acts as a fluid distribution means. The felt 10 is connected to a reservoir 6 which contains a solvent 8.

A slot 12 is affixed to the lower end of the face of the print head 2, below the lowest nozzle aperture. The slot 12 is connected to a vacuum pump (not shown).

In operation, solvent 8, for example butanone or ethanol, saturates the felt strip 10 and evaporates. Solvent vapour passes over the face of the nozzle plate 3 in the direction of the arrow 16; the tendency to flow in the direction of the arrow 16, which is parallel to the plane of the nozzle apertures 4, is enhanced by the action of the vacuum pump connected to the slot 12 which pulls fluid in the direction of the arrow 14. As solvent 8 evaporates from the felt strip 10 it is continually replenished by solvent 8 from the reservoir 6, so as to build up and maintain a continuous stream of solvent vapour over the face of the print head 2.

Increasing the rate of flow of the solvent 8 causes liquid solvent 8 to flow down the face of the nozzle plate 3, and this may wash residues from the nozzle plate when the print head is not printing.

When the print head 2 is operated, ink issues from the nozzle apertures 4 as droplets. Any residuum of ink which remains in or around the nozzle apertures 4 is surrounded by solvent vapour and therefore has a reduced tendency to dry out.

Figure 2 shows an alternative embodiment of the device viewed from the face of the nozzle plate 3, which carries an Passage of liquid solvent onto the print head face could also be achieved by increasing the solvent pressure against a porous glass frit, felt, or woven fabric so as to cause evaporation and cooling as described above.

To spread out the solvent from a narrow bore inlet pipe, a "fish tail" distributor may be used, wherein the single inlet stream is diverted into a plurality of smaller streams by diverging passages connected to the inlet.

Figures 4 and 5 show a particularly preferred embodiment of the invention. The print head 2 is contained within a housing 24 through which external connections 42 are provided for controlling the printing process. The housing 24 is sealed except for an aperture 44 in the front wall which is spaced apart from and in registration with nozzle apertures in the nozzle plate 3, and which is parallel with the nozzle plate 3. The housing 24 is provided with a fan 28, drivable by a motor 26, and a heater 30 underneath and towards the rear end of the housing 24. In use, the housing is tilted a few degrees from the horizontal so that liquid solvent 8 collects in a pool at the rear of the housing 24, above the heater. Operation of the fan 28 tends to blow solvent vapour in the direction of the arrows 32, causing the solvent vapour to pass over the nozzle plate 3. By operating the heater 30, the rate of evaporation of solvent 8 may be increased to produce a substantially saturated vapour within the housing 24. Solvent vapour passing along the upper and rear side walls of the housing 24 will partially condense and be returned to the pool of solvent 8 above the heater to be re-vaporised and recycled.

The print head 2 is provided with a shutter 34 which is adapted to be interposed between the wall aperture 44 and the nozzle plate 3 so as substantially to seal off the shutter operated by pneumatic or hydraulic means, for example, could also be used. The invention could also be operated without the use of a shutter, although the solvent losses would increase.

Although it is preferred to bias the shutter with spring means to aid in its return to the closed position the invention may also be operated by allowing the shutter to return to the closed position under gravity, or by the use of motorised or electomagnetic impulsion.

By using a fan it is possible to keep a stream of solvent vapour moving over the nozzle apertures of the print head in a relatively controlled manner. The use of a fan is not however essential to the working of the invention; it is possible to maintain a stream of vapour over the nozzle apertures by, for example, heating a pool of liquid solvent and allowing convection currents within the housing to maintain a vapour stream.

Claims

also houses the ink jet print head.

8. Apparatus as claimed in any one of claims 5 to 7, wherein a shutter is provided between the ink jet print head and a medium for receiving the ink, the shutter being provided with means for opening the shutter when the print head is firing ink droplets, and for closing the shutter when the print head is not printing.

9. Apparatus as claimed in any one of claims 5 to 8, wherein the solvent is distributed by metering it onto the external surface of a wall which carries the nozzle aperture or apertures, and by evaporation from that wall.

10. Apparatus as claimed in any one of claims 5 to 9, wherein a fan is provided for blowing solvent vapour from the surface of the solvent liquid towards the nozzle apertures of the print head.

11. Apparatus as claimed in claim 10, wherein means for heating the solvent are provided.

12. Apparatus as claimed in any one of claims 5 to 11, wherein the fluid collection means are provided with means for producing a partial vacuum.

13. Apparatus substantially as hereinbefore described with reference to and as shown in any one of the drawings.