The present invention relates to a device for capping of a inkjet printhead during storage and transport.
More specifically the invention is related to the design of such a capping device.
Nowadays inkjet printing systems are used in a wide array of apparatuses and in a wide array of applications such as fax, colour photo printing, industrial applications etc. In these printing systems inks, possibly of various colours, are ejected out of at least one array of nozzles located in a printhead to the receiving material.
A long known problem in inkjet printers is that the nozzles through which the ink is projected to the receiving material are blocked by clogging of ink inside the nozzles and on the printhead. This renders certain nozzles inoperable and results in a defective print or deteriorated print quality.
To improve the clarity and contrast of the printed image, recent research has been focused to improvement of the used inks. To provide quicker, more waterfast printing with darker blacks and more vivid colours, pigment based inks have been developed. These pigment-based inks have a higher solid content than the earlier dye-based inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to forms high quality images.
In some industrial applications, such as making of printing plates using ink-jet processes, inks having special characteristics causing specific problems. E.g. UV curable inks exist to allow rapid hardening of inks by UV radiation after printing.
Different types of ink exist, having different chemical components. The combination of small nozzles and quick drying ink leaves the printheads susceptible to clogging, not only from dried ink and minute dust particles or paper fibres, but also from the solids within the new ink themselves.
Problems can be avoided by periodically cleaning the printhead by :
To prevent drying an external contamination the inkjet printhead is capped during non-operational periods. The printhead is thereby be sealed off from contaminants by a sealing enclosure. This also prevents the drying of the ink. The capping unit usually consists of a rubber seal placed around the nozzle array.
Another aspect of high end inkjet printing applications is that an industrial inkjet printing apparatus usually has plural inkjet printheads. These inkjet printheads are tested on the manufacturing site and are shipped to the client with the ink or a special transport fluid in them.
The openings in the printhead for supplying ink and for enabling reflow of the ink to e.g. a header tank are closed off by plugs, but also the nozzles should be sealed of by a capping device in order to safely transport the printheads without risk of ink leakage and drying out of the ink, possibly rendering the printhead defective.
A similar problem exists when inkjet printheads are temporarily removed from a printer, e.g. having exchangeable printheads, and are to be stored for possibly a long time.
It is clear that there is a need for a good capping device for use in a printer as well as for use in storage or transport of ink-laden inkjet printheads. Especially when there is a need for applying a vacuum to the nozzle plate capping has to be very efficient.
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Instead of anenclosing capping, a capping pressing directly upon the nozzle array is used. In order to avoid damage to the nozzle arrays a very soft rubber is used optionally covered with a flexible film to seal the rubber from the ink.
The proposed capping arrangement however poses several problems :
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Elasticity is obtained by use of a soft rubber. Cappings comprising soft rubber however tend to be more susceptible to loss of vacuum. Soft rubbers exhibit due to the pressing force against the nozzle plate a creep deformation leading to change in pressing force. Application of vacuum causes horizontal movement of the seal lip contacting the printhead over the printhead, possible causing damage. When soft rubbers are exposed to forces over a long period they tend to further deform.
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It is clear from the above description that there is a need for an improved design for a capping used for transport and for prolonged storage and which is compatible with different kinds on inks which can be used in an inkjet printhead.
The above-mentioned advantageous effects are realized by a device having the specific features set out in claim 1. Specific features for preferred embodiments of the invention are set out in the dependent claims.
Further advantages and embodiments of the present invention will become apparent from the following description and drawings.
While the present invention will hereinafter be described in connection with preferred embodiments thereof, it will be understood that it is not intended to limit the invention to those embodiments.
The greatest drawbacks situate can be avoided by using a harder rubber contacting the printhead which is substantially chemical inert and exhibits no creep phenomenon.
The problem to be solved is however to maintain the elasticity of the capping while using a harder rubber. Desired properties are :
The objects of the present invention are met by a capping device comprising a deformable base structure determining the sealing pressure of the sealing lip provided on the deformable base structure.
This can be obtained by different methods.
Fig. 1 shows a general view of a capping 1 for a printhead according to the present invention. A sealing lip 2 is provided for contacting the printhead. The sealing lip is supported by a deformable base structure 3.
Fig 2. shows a section of a capping 1 along the line X in Fig.1 wherein the deformable base structure 3 is made from a soft rubber, while the sealing lip 2 is relatively rigid. This means that the sealing lip 2 on top of the base structure 3 exhibits no significant deformation when it is pressed on the printhead.
The soft rubber of the base structure 3 ensures that the pressure on the head is relatively low and remains constant over a long distance.
Pressure force remains relatively constant over the compression distance due to the composition of the base structure 3.
A more preferable possibility is that the sealing pressure is determined by the geometry of the base structure 3.
Due to the geometrical characteristics of the base structure 3, it is easily deformable.
Preferably this is caused by bending of the structures of the base layer 3.
Fig. 3 shows a detail of the section of a preferred embodiment a capping 1 wherein the deformation of the base structure 3 is enabled by the use of a cavity 4 underneath the sealing lip 2.
The rubber of the base structure 3 under the sealing lip 2 is relatively thin and can bend over a considerable distance when the sealing lip 2 is pressed to a printhead. This ensures a relative constant force of the sealing lip 2 on the printhead, independent from the compression distance of the capping 1 on the head.
In the embodiment of Fig. 4 the deformation of the base structure 3 and thus the pressure of the capping seal 2 on the printhead is regulated by a transversal bridge structure 5 in the capping base structure 3. When the capping 1 is pressed on the printhead, the bridges 5 bend and compression and tension forces are generated within the bridges 5.
Fig. 5 shows a possible convex structure 6 of the base structure 3 to ensure flexibility.
In. Fig. 6 an embodiment is shown wherein two oblique supporting walls 7 support the sealing lip 2. The walls have preferably an angle of 15-90 degrees with the nozzle plate surface.
As illustrated in Fig. 7, another important aspect of the geometry of the base structure 3 is that deformation of the base structure 3 does not lead to lateral displacement of the sealing lip 2 over the printhead. The aim of the base structure 3 is to allow only displacement in a direction D transversal to the nozzle plate. Sideways movement is to be counteracted in order to avoid damage of the nozzle plate and to ensure long time good capping of the printhead.
This can be ensured by making a capping 1 wherein the geometry of the base structure 3 under the sealing lip exhibits symmetrical behavior, relative to the plane through the sealing lip 2 and perpendicular to the nozzle plate, and the direction of movement of sealing lip 2 during capping is thereby restricted substantially normal to the nozzle plate surface.
As illustrated in Fig. 7 this can be provided by having a perfect symmetrical geometry relative to the contact line of the sealing lip 2 indicated by the mirror plane P. Depending upon the conditions wherein the capping 1 will be used, it may be necessary to take into account the extra forces acting upon the sealing lip 2 caused by the vacuum which is placed inside the sealing ring formed by the sealing lip 2. The aim is to ensure symmetrical behavior.
In order to ensure bending of the base structure 3 it is also possible to provide locally extreme thinning of the supporting structures forming rubber hinges. This enables the use of even rubber having a higher hardness.
The advantage of a capping 1 according to the present invention are:
The hardness of the used rubbers preferably is about 40 shore A but may be even 100 shore A. Above this hardness the rubber connections and walls tend to be to thin giving rise to problems of breaking of the hinges and non reproducibility of the design properties. The rubber also exhibits not enough flexibility to be able to seal all surface irregularities of the printhead.
In Fig 1 a capping 1 used during transport for a printhead is shown having the section as illustrated in Fig 3. The capping 1 was fabricated using a rubber having a hardness of 60 shore A.
Due to the geometrical design the pressure upon the printhead does not remarkably vary when the capping 1 is pressed upon the printhead.
Although the capping 1 is not intended to be used in overpressure or vacuum conditions, test were made to check if sealing was sufficient.
A capping was mounted upon a printhead whereby it was compressed about 0.5mm. and pressure or vacuum conditions were applied.
No problems were encountered storing at relative pressures of +0.05 and -0.05 bar relative. It was further shown that a pressure of -0.5 was kept without leakage during 60 minutes. This indicates that sealing is sufficient.
After the tests no damage to the capping 1 or printhead could be detected.
Having described in detail preferred embodiments of the current invention, it will now be apparent to those skilled in the art that numerous modifications can be made therein without departing from the scope of the invention as defined in the appending claims.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.