Device for covering jet nozzle of printing head

(24) Race day (62) National application number (86) International filing day (86) Filing date for European patent application (30) Priority information (11) Publication86-02-10 ^number 442 371

82-05-04

81-10-29. , ___ Application received as

- 10-29 [3 Swedish patent application □ Completed international patent application with number

Π converted European patent application with number

80-11-03 DE 3041187 (71) Applicant NV Philips' Gloeilampenfabrieken, Eindhoven NL (72) Inventor A. Glättli, Hamburg DE (74) Representative Holmgren H (54) Designation Device for coating nozzles in an ink jet print head (56) Published publications: - (57) Summary: Device for coating nozzles (6) in an ink jet printing head including a container print head (1) which is filled with a wetting agent and whose side facing the jet nozzles (6) is covered by a semi-permeable membrane (4). The membrane (4) may be tightly closed or loosely stretched over the container (1). The membrane is permeable to the wetting agent (2) and preferably consists of a cullulose hydrate having an approximate thickness of 22 µm.

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The present invention relates to an apparatus for covering the jet nozzles in an ink jet printing head using a deformable material.

A device of this kind is known from DE Auslegeschrift 27 02 663. The printing head with its jet nozzles is movable along guide rails along a recording carrier for the printing function. The length of the guide rails is greater than the print width, whereby the print head is in the rest position at the beginning or end of the printing area during intervals between the printing occasions. In order to prevent dehydration of the jet nozzles in the rest position, the jet nozzle plates of the printing head are covered by a pillow consisting of a material exhibiting viscous elastic properties. Since the print head is normally linearly moved, the cover device is rotatably mounted on the ink jet printer housing outside the printing area. As soon as the print head assumes the rest position, the covering device is moved towards the jet nozzles so that the nozzles are covered.

This known overcoating device has the advantage that the quick-drying ink penetrates from the nozzles into the cavity of the viscous material and thereby provides a tight closure of the jet nozzles. Although the surface deformation of such a material is normally recurrent, permanent deformation occurs to a greater or lesser extent when used for a longer period. For this reason, such a coating of the jet nozzles is not suitable for long-term use, and this is especially so because after removal of the coating device from the jet nozzles, the ink remaining on the viscously elastic pillow also dries very quickly and creates a load on the surface of the pillow which counteracts the return formation. This effect can be reduced by pressing the cover device against the jet nozzles with comparatively large force, in which case it is necessary to increase the compressive forces as the cover device is used for an extended period of time. On the other hand, the viscous elastic pillow must be replaced regularly.

It is an object of the invention to provide a coating nozzle for the jet nozzles in an ink jet printing head in which contamination of the jet nozzles and coating material by drying ink or wetting agents and penetration of the wetting agent into the jet nozzle channel is prevented. In addition, the device must be of a comparatively simple mechanical design.

For this purpose, the device according to the invention is characterized in that a container is provided with a wetting agent content and whose side facing the jet nozzles and in any case at the area of ​​the jet nozzles is covered by a semi-permeable membrane, which can be applied to the jet nozzle.

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the mouths of the pieces. The wetting agent may be miscible with the ink in the jet nozzles, or be soluble therein, or may also be insoluble therein. Preferably, as a wetting agent, a liquid which is not easily vaporizable is used, for example polyethylene glycol, ethylene glycol, diethylene glycol or glycerine.

The container with the wetting agent can be refilled at regular intervals or also continuously from a storage container. The diaphragm is preferably loosely extended over the side of the container facing the jet nozzles, the wetting agent present in the container being pressed against the diaphragm under pressure so that the diaphragm takes a position against the surface of the jet nozzles of the printing head. Preferably, for the membrane, a cellulose hydrate material is used.

The invention is described in greater detail below with reference to two embodiments shown in the drawings, in which Fig. 1 shows a device according to the invention in which the diaphragm is loosely stretched over the side of the container facing the jet head jet nozzles, and Fig. 2 shows a further development of the device of Fig. 1 in which the diaphragm is stretched over the relevant side of the container.

Most important is that inks that emit from the jet nozzles in the ink jet printer dry as soon as the ink reaches the record carrier. This prevents ink from entering the recording carrier material. Penetration into the record carrier would result in low print quality. The short drying time is in contrast to a desirable longer drying time in the jet nozzles. The longer drying time is desirable to prevent tapping of the jet nozzles in the event that printing does not take longer. Since high print quality is of crucial importance, devices which cover the nozzles during periods of printing are not used to thereby protect the nozzles from dehydration.

The device for covering the jet nozzles of an ink jet printing head according to the invention comprises a container 1, which in the illustrated examples is cylindrical. On the side facing the printing head 5, the container 1 is provided with a cone-shaped end portion 13 which is open at least in the area of ​​the jet nozzles 6. The opposite side of the container 1 is closed by a removable bottom part 16.

The open side of the container 1 is closed by a semi-permeable membrane 4 which is stretched between the cone-shaped end part 13 and the inside of a coupling nut 11. This is achieved by screwing the nut 11 onto the container 1 with an intermediate sealing ring 12 after the membrane is first applied over the cone 13 The membrane is made of a material that is giving

8106378-6 permeable to the wetting agent. However, with respect to the ink, the membrane may either be or not permeable according to desires.

In the embodiment of Fig. 1, the diaphragm 4 is loosely arranged over the cone 13. In addition, in the container 1 is arranged a piston 8 which is pressed in the direction of the open side of the container 1 through a spring 7. The wetting means 2 in the container are thus pressed against the diaphragm 4, which is thus pressed outwards to a position against the nozzles of the jet nozzles. The wetting agent 2 is introduced by removing the bottom 16 in accordance with the piston 8 and by reattaching said parts after the introduction of the wetting agent. As an alternative to this embodiment, instead of the spring 7, a device can be used through which the piston 8 can be moved forward and backward as desired. This gives the advantage that in the position of the piston 8, the diaphragm 4 is no longer pressed outwardly, thereby exposing the nozzles 6. A device of this kind can be used when using a stationary container 1 instead of a rotatable container. If it is necessary to turn the print head 5 during printing, then the piston 8 can be returned. At the moment when the printhead 5 re-enters the rest position, the piston 8 is again moved forward, whereby the diaphragm 4 again takes a position against the jet nozzles 6.

A further advantage of the loosely stretched diaphragm is that printheads with ends which are not flat can also be covered, for example printheads including curved jet nozzle plates, annular nozzles, tapered nozzles etc.

In the embodiment of Figure 2, the membrane 4 is tightly extended over the cone

13th In this case, it is necessary to pivot the container 1 against the jet nozzles 6 to cover the nozzles of the nozzles 6. To eliminate the requirement for regular replacement of the wetting agent 2, there is a tube 15 connecting the container 1 with a storage container (not shown) for the wetting agent 2. It will be appreciated that a tube 15 of this kind is also useful in the embodiment of Figure 1. - t

when the container 1 contains wetting agent 2 under pressure, it is then necessary to introduce a valve which prevents the return of the wetting agent to the storage container.

The container 1 is enclosed by an additional container 10 containing an absorbent material 9. The additional container 10 has an outlet opening.

14th The additional container is designed to capture the ink and contaminants deposited on the membrane 4 and to remove these substances via the outlet opening 14. Ink which is ejected to clean the jet nozzles and reaches the membrane as well as wetting agent 2 passing through the membrane 4 flows to the container 10.

The wetting agent 2 may be soluble in the ink 3, be miscible therewith or

8106378-6 also insoluble in the ink. The wetting agent may be volatile or non-volatile. However, a non-volatile wetting agent which is miscible with the ink is preferably used. When using a wetting agent 2 under pressure, the permeability of the membrane and the force exerted by the piston 8 must be so adapted that only minor amounts of the wetting agent pass through the membrane, as otherwise the supply of wetting agent would quickly deplete. For this reason, it is appropriate to use a device where the wetting agent is supplied from a storage container.

Alternatively, it is possible to design the entire Covering Device as a cartridge, which is replaced with a new, full cartridge when the wetting agent is consumed. The fastening device for the covering device must then be constructed accordingly. For example, the fastener may consist of a fastener for the cartridge.

The described device for covering the jet nozzles in an ink jet printing head has the advantage that the wetting agent is not contaminated by the ink and that it allows any position of the jet nozzles within the coating area.

Experiments with the described covering device have produced excellent results. The jet nozzles 6 are used on an ink 3 consisting of dye, wetting agent and about 90% water. The container was filled with diethylene glycol as a wetting agent and the membrane consisted of a cell of 1 µl of osahydrate of thickness 22 µm. Immediately after the printing was completed, the membrane was contacted with the jet nozzles. After eighteen days, the container 1 was removed. The jet nozzles 6 worked immediately, producing the correct jet write after about 300 pulses. After writing for about 30 minutes. the nozzles were turned off and left uncovered. After 15 minutes, the jet nozzles were completely dry and no longer usable. Thus, it can be found that the membrane 4, which is always slightly moist on the outside, prevents dehydration of the jet nozzles for many days.

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