Patent Application
20250115447
The invention relates to a method for transporting sheets of print media between electrodes of a plasma treatment unit of a printer and to such a printer.
Plasma treatment, as known from e.g. EP2802455 B1, EP3344458 B1, and/or EP2988945 B1, may be used to adjust the surface properties of a sheet, so that the application of a liquid, such as primer or printing ink, thereon is improved. Specifically, the interaction between a primer and subsequently applied printing ink can be improved, e.g. to improve coalescence behavior of the printing ink on a layer of primer. The plasma treatment is performed prior to applying said liquid on the sheet. Such a printer comprises a plasma treatment unit, which comprises a pair of spaced apart electrodes for generating a plasma between them and a transport mechanism. The transport mechanism comprises a support structure spaced apart from one of the electrodes by a gap and a drive for transporting the sheet in a transport direction over the support structure, over the gap, and over the one of the electrodes. The gap is provided to electrically isolate the high voltage electrodes from the support structure, but also forms a free space wherein in the sheet can become temporarily trapped. The sheet may bend into the gap under the influence of gravity and/or a negative pressure applied for holding the sheet flat on the support structure, which could result in folds or wrinkles in the sheet, or even paper jams in the printer.
It is an object of the invention to provide an improved method of passing sheets of print media through a plasma treatment unit of a printer, preferably a more reliable method.
In accordance with the present invention, a method for transporting sheets of print media between electrodes of a plasma treatment unit of a printer according to claim 1 and a printer according to claim 11 are provided. The printer comprises comprising a support structure spaced apart from one of the electrodes by a gap.
The method comprises the step of:
The gap extends parallel to the upstream edge of the respective electrode. As the sheet's edge is at an angle with said upstream edge, it is at an angle with the gap. The sheet then moves over the gap, initially with only a relatively small or narrow portion, for example a corner of the sheet. Due to the relatively small or narrow width of the said portion in the lateral direction as compared to its length in the transport direction, the portion is relatively stiff or rigid, which reduces or prevents it from curving downwards into the gap due to e.g. gravity and/or suction applied to the portion at and/or around the gap. The angle is a non-zero angle, which preferably also positions the center of mass of the portion over the gap relatively close to the upstream edge of the gap. Relatively is herein with reference to the situation wherein the sheet would pass over the electrode and the gap with its leading edge parallel to the edge of the electrode. As the gap is relatively narrow, only a small portion of the sheet needs to pass reliably over the gap before the leading portion of the sheet becomes also supported on an electrode. Thus, the reliability of sheets passing through the plasma treatment unit is improved. Thereby the object of the present invention has been achieved.
More specific optional features of the invention are indicated in the dependent claims.
In an embodiment, the method further comprises the step of applying a negative pressure to a surface of the sheet facing the gap for drawing the sheet against a support structure which together with the edge of the one of the electrodes forms the gap. To pass the sheet flatly between the electrodes, a negative pressure is applied to one side of the sheet. This draws the sheet flat against the support structure and optionally also against one of the electrodes. The negative pressure may be applied in the form of suction, which also causes the sheet to be drawn into the gap. This would increase the risk of the leading edge of the sheet from becoming trapped in the gap, which risk is eliminated and/or reduced herein by the sheet being at a non-zero angle with respect to the edge of the electrode.
In an embodiment, the method comprises the step of transporting the sheet between the electrodes in a transport direction, so that a width in a lateral direction of a portion of the sheet over the upstream edge of the at least one of the electrodes increases from at least when the sheet initially moves over said upstream edge. Initially the width of the portion of the sheet over the gap increases as the sheet begins to cross over the gap. Preferably the increase is gradual. In consequence, the first portion of the sheet to extend over the gap is narrow, giving it a relatively high stiffness. Preferably, the center of mass of the portion is initially also upstream of a central point in the gap in the transport direction. As the sheet moves forward across the gap, the width of the portion over the gap increases. The gap is preferably sufficiently narrow, so that its leading portion is supported on the bottom electrode before a maximum width of the sheet is over the gap.
In an embodiment, the method further comprises the step of applying a liquid on the treated sheet. The plasma treatment adjusts the surface free energy of the sheet, at least on one side of it, so that a surface of the sheet is prepared for reliable adherence of the liquid. In another embodiment, a coating liquid is applied directly on the treated sheet, followed by the application of color inks on the coating liquid, preferably wherein the coating liquid is a primer liquid. The liquid is preferably a colorless or transparent primer, which is to cover the to be printed area of the sheet substantially fully. The primer ensures a reliable adherence to and/or improved coalescence of the color inks on the primer layer, which are to be printed on the layer of primer. It will be appreciated that the plasma treatment may alternatively be applied to prepare the sheet surface for direct adhesion of the color inks, without a layer of primer in between. Color inks may be any commercially available inkjet ink.
In an embodiment, the method further comprises the step of re-orienting the treated sheet, so that one of its edges is substantially parallel to a lateral direction perpendicular to a transport direction of the sheet. At certain positions in the printer, the sheet is preferably oriented with its leading edge perpendicular to the transport direction. Examples are e.g. at an output location when forming a sheet stack, at the print assembly so that the leading edge is parallel to the printhead array, at a turn station for flipping the sheet, etc. Thereto, the sheet is in one or more places is re-aligned so that its leading edge is substantially parallel to the lateral direction.
In an embodiment, the step of arranging comprises rotating the sheet upstream of the treatment unit, so that one of its edges is at a non-zero angle with the lateral direction.
The sheet moves through certain sections of the printer with its leading edge substantially perpendicular to the transport direction. Upstream of the treatment unit, the sheet is rotated out of this latter orientation, so that its previously leading edge is at a non-zero angle with the gap and the upstream edge of the bottom electrode.
In an embodiment, a substantially empty gap is positioned at the upstream edge of the at least one of the electrodes, and the method further comprises a portion of the sheet first passing over the gap before reaching said electrode. The gap forms an empty space directly upstream of the bottom electrode. The sheet has to traverse the gap to enter in between the electrodes. The gap is preferably narrow, equidistant, and/or parallel to said edge of the bottom electrode. Since the sheet is thus skewed with respect to the gap, only a relatively narrow portion of the sheet moves first over the gap, thereby allowing it to pass safely over the gap.
A further aspect of the invention relates to a printer comprising a plasma treatment unit with:
In an embodiment, the printer further comprises at least one registration drive of a registration unit for adjusting an orientation of the sheet with respect to the transport direction, wherein the at least one registration drive is configured for:
The printer comprises one or more registration drives which can change the angle between a forward facing edge of the sheet and the lateral direction from substantially zero to non-zero and/or vice versa. A registration drive can be applied to rotate the sheet so that its leading edge is perpendicular to the transport direction, for example when the sheet passes the printhead assembly or arrives at the output location. The same or a different registration drive can be applied to rotate the sheet, so that its edges are all at a skewed angle with the gap. In another embodiment, orienting the sheet, so that its leading edge is substantially perpendicular to the transport direction, is performed:
In another embodiment, the upstream edge of the one of the electrodes is substantially perpendicular to the transport direction, and at least one registration drive of a registration unit is configured to re-orient the sheet, so that its forward facing edge is at the non-zero angle with respect to the upstream edge of the one of the electrodes when passing between the electrodes.
In an embodiment, the upstream edge of the one of the electrodes is positioned substantially at a non-zero angle with respect to a lateral direction perpendicular to the transport direction, so that a forward facing edge of the sheet when parallel to the lateral direction passes over said upstream edge substantially at an angle therewith. The sheet may also pass the gap with its leading edge substantially perpendicular to the transport direction if the gap and the edge of the electrode are inclined with respect to the lateral direction. The electrode's edge may be positioned skewed with respect to the transport direction. The electrode's edge may also be curved, smoothly or irregular, so that portions of the edge are inclined with respect to the lateral direction. The gap therein preferably follows the curvature of the edge. Preferably, the registration unit is configured to orient the leading edge of the sheet, so that it is substantially parallel to the lateral direction as it passes over the electrode. Thereby, the sheet is at the non-zero angle with respect to the edge. This orientation of the sheet corresponds to the orientation wherein the sheet passes the printhead assembly.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the present invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
The present invention will now be described with reference to the accompanying drawings, wherein the same reference numerals have been used to identify the same or similar elements throughout the several views.
The sheet then passes through a treatment unit 20, which treats the surface of the sheet to alter its surface properties, such as its surface free energy. The surface of the sheet is adjusted to achieve a desired wetting behavior of the liquids to be jetted on its surface. The treatment unit 20 is preferably a plasma treatment unit, specifically a corona treatment unit. In FIG. the treatment unit 20 comprises a first and second electrode 21, 22 positioned on opposite sides of the print path in the vertical direction Z. A high voltage is applied between the electrodes 21, 22 to generate a plasma, specifically a corona, between them. As the sheet passes in between the electrodes 21, 22, its free or top surface is exposed to the plasma, thereby altering its surface free energy. Such a plasma treatment device is known from e.g. EP2802455 B1, EP3344458 B1, and/or EP2988945 B1, the contents of which are herein incorporated by reference.
The print path comprises a second registration unit 6 downstream of the treatment unit 20. The second registration unit 6 comprises a second sheet detector 5 for detecting a position and orientation of each sheet. The orientation of the sheet is e.g. the angle of its forward facing or leading edge with respect to the transport direction X. Dependent on the measured position and orientation, the second registration unit 6 controls its registration drive 7 to position the sheet to a predefined position and/or align the sheet to a predefined orientation, for example with its leading edge perpendicular to the transport direction X, so that it will be parallel to the printhead assembly 10.
The registered sheet subsequently passes by a coater 9, which applies a liquid coating on at least a portion of the treated surface. The coater 9 may for example comprise an array of printheads configured to jet droplets of coating liquid or comprise a roller for transferring coating liquid as the roller rolls over the sheet. Any suitable coating liquid may be applied, such as for example Canon ColorGrip. The coating liquid preferably forms a continuous coat on the sheet, which enables or improves the bonding of color inks to the sheet.
The coated sheets travels to the printhead assembly 10, which jets one or more layers of color inks onto the coated sheet. The printhead assembly 10 is preferably a page wide array of inkjet printheads to allow productive printing.
The jetted color inks are then fixed onto the sheet by means of a fixation unit 11. The fixation unit 11 applies or removes energy from the sheet, so that the jetted color inks undergo a phase change. The fixation unit 11 may comprise coolers and/or heaters, such radiation heaters with e.g. UV or IR light, hot air blowers, such as impingement blowers, contact heaters, such a heated transport belt or drum, etc. Alternatively or additionally, the fixation unit 11 may comprise curing station, which emits light with a wavelength which induces a chemical reaction in the color inks and/or coating liquid, causing these to solidify.
At the downstream side of the print path, a third registration unit 12 is provided to adjust the position and/or orientation of the sheets. This third registration unit 12 may be configured similar to the second registration unit 6. The third registration unit 12 can be applied to position and/or orientation a sheet with respect to a specific output location, for example a stacking location or a finisher, such as a cutter or book binder. The third registration unit 12 comprises its own registration drive 27 and may comprise a sheet detector 13, or the sheet position can be derived by tracking the sheet's movement after detection by the second sheet detector 7.
At the end of the print path, a further switch 26 is provided to selectively direct sheets into the duplex path or to the output location. The duplex path preferably comprises a turn station, which inverts the sheet, so that it leaves the duplex path with its unprinted side eventually facing the printhead assembly 10. The output location in
The detected orientation of the sheet is compared to a predetermined orientation, and based on that, the first registration drive 28 is controlled to adjust the orientation of the sheet S. The first registration drive 28 comprises two independently drivable rollers, so that by applying different speeds, the sheet S can be re-oriented and/or shifted. Different registration drives, such as sliders or shifters may be applied as well.
As shown in
The sheet S arrives in its rotated state at the treatment unit 20 in
The sheet S passes over the support structure 23 under the non-zero angle A, such that the forward corner of the sheet S first passes over the gap 24. As the sheet S moves further in the transport direction, the width of its portion over the gap 24 increases, at least until a second corner of the sheet S passes the gap 24. Due to the relatively large angle A, the sheet at the forward corner is relatively narrow as it passes over the gap 24. The portion of the sheet S overhanging the gap 24 is then relatively stiff or rigid, preventing it from bending into the gap due to the applied negative pressure and/or gravity. Since the rotated sheet S tapers in the transport direction X, it is able to pass over the gap 24 without folding or bending. The sheet S thus passes reliably over the gap 24 in between the electrodes 21, 22.
The skewed sheet S then passes over the bottom electrode 21, so that is top surface is exposed to the plasma between the electrodes 21, 22. Thereby, the surface energy of the sheet S is adjusted to a desired range corresponding to a coating liquid that is applied by the coater 9. The changed surface energy of the sheet S ensures a reliable adhesion of the coating liquid on the sheet S.
Before reaching the coater 9, the treated sheet 9 passes over the second registration unit 6 in a skewed state, as shown in
The registered and coated sheet S then is transported past the printhead assembly 1, which prints an image on the sheet S. Both the coater 9 and the printhead assembly 10 preferably comprise printheads configured to jet liquid droplets of respectively color ink or coating liquid onto the sheet S. The color ink(s) or coating liquid are then fixed on the sheet S by the fixation unit 11, which for example heats the sheet S by blowing heated air onto it. Thus, a robustly printed sheet S is achieved, as shown in
At the end of the print path, the sheet S passes over the third registration unit 12. Dependent on the subsequent destination, the sheet S may be re-oriented and/or positioned. In case, the print job for a sheet S has been entirely completed, the sheet S is passed to the output location via the further switch 26. The third registration unit 12 may then move the sheet S corresponding to an output position, for example a stacker or finisher. In case, the sheet S requires further printing, for example in the case of duplex printing, the sheet S is directed into the duplex path. The sheet S may then again be re-oriented into a skewed state wherein one of its edges is at an angle A with the lateral direction Y using the third registration drive 27. Thus, the sheet S is then in an orientation so that it will safely pass over the gap 24, when it returns for printing on its unprinted side. It will be appreciated that the number and/or positions of the registration units may be varied in any manner, as long as the sheet arrives at the treatment unit with a skewed angle with respect to the upstream edge of the electrode.
Although specific embodiments of the invention are illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations exist. It should be appreciated that the exemplary embodiment or exemplary embodiments are examples only and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.
It will also be appreciated that in this document the terms “comprise”, “comprising”, “include”, “including”, “contain”, “containing”, “have”, “having”, and any variations thereof, are intended to be understood in an inclusive (i.e. non-exclusive) sense, such that the process, method, device, apparatus or system described herein is not limited to those features or parts or elements or steps recited but may include other elements, features, parts or steps not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, the terms “a” and “an” used herein are intended to be understood as meaning one or more unless explicitly stated otherwise. Moreover, the terms “first”, “second”, “third”, etc. are used merely as labels, and are not intended to impose numerical requirements on or to establish a certain ranking of importance of their objects.
The present invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23202493.5 | Oct 2023 | EP | regional |
