EP4656389A1

EP4656389A1 - Printing device, printing method and method for capping a print unit

Info

Publication number: EP4656389A1
Application number: EP24208459.8A
Authority: EP
Inventors: Laurentius P.E.G. KUIJPERS; Age Bakker; Yagiz ALTUNAY; Richard VAN ENCKEVORT; Tobias R. BREINTNER; Walter Brenner; Kai-Yannic SCHÖNEWOLF; Franz J. BITZER; Lucian Petrut
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2024-05-27
Filing date: 2024-10-23
Publication date: 2025-12-03

Abstract

The invention relates to a printing device. The invention further relates to a printing method. In addition, the present invention relates to a method for capping a print unit.

Description

Background of the invention

Inkjet printers are known in the art. In an inkjet printer, an image is formed by ejecting small droplets of ink and applying these droplets in a predetermined pattern to form an image onto a recording medium. The small droplets of ink are generally ejected through the nozzles of an inkjet print head. Nozzles are tiny apertures in the print head. These nozzles may get clogged in case ink dries out. This may happen if a print head is in non-printing state for a certain period of time. Clogging of nozzles is unwanted. Clogged nozzle may require maintenance operations, such as spitting and wiping. However, if a maintenance operation on clogged nozzles is unsuccessful, the print head may need to be replaced. It is therefore desired to prevent clogging of nozzles. It is known to use capping units for capping print heads. Capping a print head creates a closed environment around the print heads and the nozzles of the print head. However, known capping systems often require a lot of space. This is unwanted, as space within printing systems is scarce. Further, it is desired that clogging of nozzles can be preventing keeping into account the requirements and circumstances of an individual print head or print head assembly.
It is therefore an object of the invention to provide an inkjet printer comprising a capping unit that requires less floor space. It is a further object of the invention to provide a method for capping a print unit.
It is a further object of the invention to provide an inkjet printer, wherein a print unit not printing can be capped, whereas another print unit can continue printing. It is a further object of the invention to provide a print method, wherein at least one print unit is in a capped state.

Summary of the Invention

The object of the invention is achieved in a printing device, the printing device comprising:

a. A recording medium support for supporting the recording medium during printing;
b. A recording medium transport unit for transporting and/or advancing the recording medium;
c. A plurality of print units, the print units being configured to, in printing operation, apply a predetermined pattern of ink onto the recording medium; and
d. A plurality of capping units, for capping the plurality of print units,

The printing device comprises a recording medium support for supporting the recording medium during printing. A printing apparatus may also be referred to as printer or printing device. The recording medium may be any suitable type of media, including media in the form of a sheet or web. The recording medium support may comprise a table or a belt for supporting the recording medium during printing.
The printing device comprises a recording medium transport unit for transporting and/or advancing the recording medium. The transporting means may comprise a belt, such as an endless belt, for transporting the recording medium. Optionally, the endless belt may be guided by one or more rollers, for guiding and driving the endless belt. The printing device may further be provided with a recording medium input module for inputting the recording medium into the printer. Optionally, the printing device may further be provided with a recording medium output module for outputting the recording medium from the printer.
The printing device comprises a plurality of print units, the print units being configured to, in printing operation, apply a predetermined pattern of ink onto the recording medium. The print units may be a single ink applicator or an assembly of ink applicators. An example of a single ink applicator is a single print head. An example of an assembly of ink applicators is a print bar comprising a number of ink jet print heads. Inkjet print heads typically comprise a plurality of nozzles. Fluids, such as ink, primer or overcoat may be expelled in response to a stimulus provided to the ink in proximity of the nozzle. The stimulus may be for example applying an amount of heat to locally heat the ink (bubble yet) or applying a pressure using e.g. a piezoelectric element to ink in proximity of the nozzle (piezo inkjet). The plurality of nozzles of the print head may be provided in a nozzle surface. In printing operation, droplets of ink may be expelled from the print head via the plurality of nozzles. If the print unit is not in printing operation, no ink may be expelled from the print head via the plurality of nozzles. In case no ink is expelled via the plurality of nozzles, some of the fluid in the print unit may evaporate, which may result in a change in viscosity of the liquid within the print unit, or may even result in the formation of solid precipitation, such as precipitation formed by solid components of the fluids (e.g. resins and/or pigments). In the printing apparatus, the mode of operation of the plurality of print units may differ; all print units of the plurality of print units may be in printing operation, none of the plurality of print units may be in printing operation or one or more of the plurality of print units may be in printing operation and a remainder of the plurality of print units may not be in printing operation. For example, if the printing device is printing a black-and-white print job, then the print unit for printing black ink may be in printing operation, whereas the print units configured to print coloured ink (such as, cyan, magenta and yellow ink, optionally light magenta, light cyan, red, green, orange, purple and brown ink) may not be in printing operation.
The printing device may further comprise a plurality of capping units, for capping the plurality of print units. The capping units may be configured to cap the print units. Preferably, one capping unit is provided per print unit. Alternatively, one additional capping unit may be provided as a spare. When capping a print unit, a closed environment may be created around the nozzles of the print unit. The closed environment may prevent, or at least decrease, evaporation of fluids from the nozzles to prevent drying of the nozzles. Optionally, the cap may comprise an amount of fluid. The presence of fluid in the cap may even further suppress evaporation of the fluid from the nozzles.
The cap may be shaped such that is has an opening configured to accommodate at least a part of the print unit.
The cap unit may be provided with a ring, such as a polymeric ring or a rubber ring for creating an airtight closure between the print unit and the cap unit.
In an embodiment, at least one of the print unit and the capping unit is provided with a first connecting member.
The first connecting member may be provided on the print unit. Alternatively, the first connecting may be provided on the print unit. In a further alternative, both the print unit and the capping unit may be provided with a first connecting member.
The other one of the print unit and the capping unit may be provided with a second connecting member.
The first connecting member may be configured to engage and/or disengage with the second connecting member, depending on the mode of operation.
In capping operation, the first connecting member may engage with the second connecting member. When going from capping operation to another mode of operation, such as printing operation or cleaning operation, the first connecting member may disengage with the second connecting member.
The first and second connecting member may be configured to engage and/or disengage mechanically, electronically and/or magnetically.
In a further embodiment, the first connecting member is a grappling hook. The grappling hook may be configured to connect with the second connecting member. The second connecting member may be, for example, a ring or a bar.
In an alternative embodiment, the first connecting member is a first part of a snap-fit mechanism. A second one of the print unit and the capping unit may be provided with a second part of a snap-fit mechanism. In this way, the print unit and the capping unit may be connected using a snap-fit.
In capping operation, the print unit may be capped. In printing operation, the print unit may print. In printing operation, the print unit may not be capped. In cleaning operation, the print unit may be subject to a maintenance operation, such as wiping. In cleaning operation, the print unit may not be capped.
The grappling member may be movable relative to at least one of the print unit and the capping unit. Preferably, the grappling member is moveable relative to both the print unit and the cap unit.
When the grappling member is engaged with the second connecting member, the grappling member capping unit and the print unit can be moved towards one another and/or away from one another.
In an embodiment, the printing device further comprises a capping tray, the capping tray being configured to support the capping units when the print units are in printing operation.
The capping tray may carry one or more capping units. In an embodiment, the printing device may comprise a plurality of capping trays, wherein each capping tray may carry one or more capping units. The number of capping units carried by a single capping tray may be the same or different from a number of capping units carried by another capping tray in the printing device.
The capping tray may be in a location remote from the print zone when the print unit is printing, for example in a capping tray home position. When the print unit goes from printing operation to capping operation, the one or more capping trays may be moved towards the print zone, thereby positioned the one or more capping units in the print zone.
When the capping units are in the print zone, the print units may be capped. This may be done by moving the print unit and the cap unit towards one another until the print unit is capped. This may be done by lowering the print unit and/or lifting the capping tray. In an embodiment, the grappling member and the second connecting member may engage to cap the print unit.
In an embodiment, the capping tray is movable from a capping tray home position to the print zone.
The capping tray may be in a home position home position during printing operation and during cleaning operation. The home position is a position away from the print zone. For example, the home position may be a position adjacent to the print belt.
When capping one or more print units, the capping tray may move towards the print zone. When the one or more print heads are capped, the capping tray may move from the print zone to the home position. When the print units are capped, the capping tray may stay in the print zone or in the home position. Preferably, the capping tray is placed in the home position when the print units are capped.
In an embodiment, each print unit is individually cappable by one of the capping units from the plurality of capping units.
The capping units may be configured to in capping operation cap a single print unit. The print units may be individually capable; one or more print units may be capped, whereas one or more of the other print units may not be capped. The one or more of the other print heads may be e.g. in printing operation or may undergo maintenance.
In case all capping units are placed on a capping tray, the position of a specific capping unit in the capping tray may ensure that the capping unit is matched to the corresponding print unit.
In an embodiment, at least one of the plurality of print units is in printing operation and at least one of the plurality of print units is non-printing operation, wherein the at least one print unit that is in non-printing operation is capped by one of the plurality of capping units.
A printing device may comprise a plurality of print units. The print units may be configured to in printing operation eject a specific type of fluid. The types of fluid may be for example one or more primers, one or more overcoat liquids, one or more ink compositions and one or more specialty ink compositions. Examples of ink compositions are black inks, cyan inks, magenta inks, yellow inks, grey inks, light magenta inks, light cyan inks, red inks, green inks, brown inks, orange inks and purple inks. Examples of specialty ink compositions include metallic inks and MICR inks.
In a print job, not all types of fluids available in the printer may be needed. For example, when printing a black-and -white print job on a white recording medium, only a print unit configured to eject black ink may be in printing operation; the print units configured to eject other types of fluid may not be in printing operation. To keep the print units not in printing operation in good condition, these print units may be kept, while the print unit configured to eject black ink is in printing operation and is not capped.
Depending on the characteristics of a print job, such as the duration of the print job, the fluids required for performing a certain print job and the characteristics of the printing device, such as the amount of time the print units are allowed to stay uncapped, it may be determined whether one or more print units are capped while at least one other print unit is in printing operation.
In an embodiment, the capping unit may be (partially) filled with fluid, at least when the print unit is capped. The presence of fluid may reduce the rate of evaporation of fluid from the nozzles. The fluid in the capping unit may be the same as the ink in the print unit. Alternatively, a capping fluid may be used. The capping fluid may have a vapor pressure higher than the vapor pressure of the fluid in the print unit. The capping unit may be provided with a capping fluid supply. The capping fluid may comprise a capping fluid reservoir and a connector to transfer the capping fluid from the reservoir to the capping unit.
In an aspect of the invention, a method for capping a print unit is provided, the method comprising the steps of:

a. Moving the capping unit and the print unit relatively towards one another;
b. Connecting the first connecting member provided on one of the print unit and the capping unit to the other of the print unit and the capping unit;
c. Relatively moving the print unit and the cap unit towards one another to a capping position.

In step a), the capping unit and the print unit may be moved relative to one another. The capping unit may move towards the print unit. Alternatively, the print unit may move towards the capping unit. In a further alternative, both the capping unit and the print unit may move. The capping unit and/or the print unit may be moved using suitable means. In step b), the first connecting member provided on one of the print unit and the capping unit may be connected to the other of the print unit and the capping unit. The other one of the print unit and the capping unit may be provided with an second connecting member. The second connecting member may be for example, a ring or a bar.
The first connecting member may be configured to engage and/or disengage with the second connecting member, depending on the mode of operation.
In capping operation, the first connecting member may engage with the second connecting member. When going from capping operation another mode of operation, such as printing operation or cleaning operation, the first connecting member may disengage with the second connecting member.
In capping operation, the print unit may be capped. In printing operation, the print unit may print. In printing operation, the print unit may not be capped. In cleaning operation, the print unit may be subject to a maintenance operation, such as wiping. In cleaning operation, the print unit may not be capped.
The first connecting member may be movable relative to at least one of the print unit and the capping unit. Preferably, the first connecting member is moveable relative to both the print unit and the cap unit.
When the first connecting member is engaged with the second connecting member, the first connecting member capping unit and the print unit can be moved towards one another.
In step c, the print unit and the cap unit may be moved relative towards one another to a capping position. The print unit and the capping unit may be moved towards one another until the print unit is in the capped state. In the capped state, at least one surface of the print unit is covered by the capping unit. Capping the print unit provides a confined space around the at least one surface of the print head. The at least one surface preferably comprises the nozzle surface of the print unit. By forming a confined space around the nozzle surface of the print unit, the nozzles in the nozzle surface may be preventing from drying.
In an embodiment, step a) includes moving the capping tray towards the print zone. The at least one capping unit may be positioned on a capping tray. The capping tray may move towards the print zone, thereby moving the capping unit relative to the print unit. When the capping tray arrives in the print zone, at least one of the print units may engage with one of the capping unit to bring the at least one of the print units in the capped state.
The capping tray may be moved along one or more guide rails. The capping tray may be driven by suitable driving means. An example of suitable driving means is a drive unit, such as a gear box and a motor, in co-operation with one or more rack and pinion units.

Brief Description of the Drawings

The present invention will become more fully understood from the detailed description given herein below and accompanying schematical drawings which are given by way of illustration only and are not limitative of the invention, and wherein:

Fig. 1 shows a schematic representations of an inkjet printing system.
Fig. 2 shows a schematic representation of an inkjet marking device: A) and B) assembly of inkjet heads; C) detailed view of a part of the assembly of inkjet heads.
Fig. 3A-3F show a first example of a method for capping a print unit according to the present invention.
Fig. 4A shows a first example of a grappling member according to the present invention;
Fig. 4B shows a first example of a capping unit according to the present invention.

Printing process

A printing process in which the inks according to the present invention may be suitably used is described with reference to the appended drawings shown in Fig. 1 and Fig. 2. Figs. 1 and 2 show schematic representations of an inkjet printing system and inkjet marking device, respectively.
Fig. 1 shows that a sheet of a receiving medium, in particular a machine coated or offset coated medium, P, is transported in a direction for conveyance as indicated by arrows 50 and 51 and with the aid of transportation mechanism 12. Transportation mechanism 12 may be a driven belt system comprising one (as shown in Fig. 1) or more belts. Alternatively, one or more of these belts may be exchanged for one or more drums. A transportation mechanism may be suitably configured depending on the requirements (e.g. sheet registration accuracy) of the sheet transportation in each step of the printing process and may hence comprise one or more driven belts and/or one or more drums. For a proper conveyance of the sheets of receiving medium, the sheets need to be fixed to the transportation mechanism. The way of fixation is not particularly limited and may be selected from electrostatic fixation, mechanical fixation (e.g. clamping) and vacuum fixation. Of these vacuum fixation is preferred.
The printing process as described below comprises of the following steps: media pre-treatment, image formation, drying and fixing and optionally post treatment.

Media pre-treatment

To improve the spreading and pinning (i.e. fixation of pigments and water-dispersed polymer particles) of the ink on the receiving medium, in particular on slow absorbing media, such as machine coated or offset coated media, the receiving medium may be pretreated, i.e. treated prior to printing an image on the medium. The pre-treatment step may comprise one or more of the following:

preheating of the receiving medium to enhance spreading of the used ink on the receiving medium and/or to enhance absorption of the used ink into the receiving medium;
primer pre-treatment for increasing the surface tension of receiving medium in order to improve the wettability of the receiving medium by the used ink and to control the stability of the dispersed solid fraction of the ink composition (i.e. pigments and dispersed polymer particles). Primer pre-treatment may be performed in the gas phase, e.g. with gaseous acids such as hydrochloric acid, sulfuric acid, acetic acid, phosphoric acid and lactic acid, or in the liquid phase by coating the receiving medium with a pre-treatment liquid. The pre-treatment liquid may comprise water as a solvent, one or more cosolvents, additives such as surfactants and at least one compound selected from a polyvalent metal salt, an acid and a cationic resin (discussed in detail above);
corona or plasma treatment.

Primer pre-treatment

As an application way of the pre-treatment liquid, any conventionally known methods can be used. Specific examples of an application way include: a roller coating, an ink-jet application, a curtain coating and a spray coating. There is no specific restriction in the number of times with which the pre-treatment liquid is applied. It may be applied at one time, or it may be applied in two times or more. Application in two times or more may be preferable, since cockling of the coated printing paper can be prevented and the film formed by the surface pre-treatment liquid will produce a uniform dry surface having no wrinkle by applying in 2 steps or more.
Especially a roller coating (see 14 in Fig. 1) method is preferable because this coating method does not need to take into consideration of ejection properties and it can apply the aqueous pre-treatment liquid homogeneously to a recording medium. In addition, the amount of the applied pre-treatment liquid with a roller or with other means to a recording medium can be suitably adjusted by controlling: the physical properties of the pre-treatment liquid; and the contact pressure of a roller in a roller coater to the recording medium and the rotational speed of a roller in a roller coater which is used for a coater of the pre-treatment liquid. As an application area of the pre-treatment liquid, it may be possible to apply only to the printed portion, or to the entire surface of both the printed portion and the non-printed portion. However, when the pre-treatment liquid is applied only to the printed portion, unevenness may occur between the application area and a non-application area caused by swelling of cellulose contained in the coated printing paper with the water in the pre-treatment liquid followed by drying. Then, from the viewpoint of drying uniformly, it is preferable to apply a pre-treatment liquid to the entire surface of a coated printing paper, and roller coating can be preferably used as a coating method to the whole surface.

Corona or plasma treatment

Corona or plasma treatment may be used as a pre-treatment step by exposing a sheet of a receiving medium to corona discharge or plasma treatment. In particular when used on media like polyethylene (PE) films, polypropylene (PP) films, polyethyleneterephtalate (PET) films and machine coated or offset coated media, the adhesion and spreading of the ink can be improved by increasing the surface energy of the media. With machine coated or offset coated media, the absorption of water can be promoted which may induce faster fixation of the image and less puddling on the receiving medium. Surface properties of the receiving medium may be tuned by using different gases or gas mixtures as medium in the corona or plasma treatment. Examples are air, oxygen, nitrogen, carbon dioxide, methane, fluorine gas, argon, neon and mixtures thereof. Corona treatment in air is most preferred.
Fig. 1 shows that the sheet of receiving medium P may be conveyed to and passed through a first pre-treatment module 13, which module may comprise a preheater, for example a radiation heater, a corona/plasma treatment unit, a gaseous acid treatment unit or a combination of any of the above. Optionally and subsequently, a predetermined quantity of the aqueous pre-treatment liquid is applied on the surface of the receiving medium P at aqueous pre-treatment liquid applying member 14. Specifically, the aqueous pre-treatment liquid is provided from storage tank 15 of the aqueous pre-treatment liquid to the aqueous pre-treatment liquid applying member 14 composed of double rolls 16 and 17. Each surface of the double rolls may be covered with a porous resin material such as a sponge. After providing the aqueous pre-treatment liquid to auxiliary roll 16 first, the aqueous pre-treatment liquid is transferred to main roll 17, and a predetermined quantity is applied on the surface of the receiving medium P. Subsequently, the coated printing paper P on which the aqueous pre-treatment liquid was supplied may optionally be heated and dried by drying member 18 which is composed of a drying heater installed at the downstream position of the aqueous pre-treatment liquid applying member 14 in order to decrease the quantity of the water content in the aqueous pre-treatment liquid to a predetermined range. It is preferable to decrease the water content in an amount of 1.0 weight% to 30 weight% based on the total water content in the provided pre-treatment liquid provided on the receiving medium P.
To prevent the transportation mechanism 12 being contaminated with pre-treatment liquid, a cleaning unit (not shown) may be installed and/or the transportation mechanism may be comprised multiple belts or drums as described above. The latter measure prevents contamination of the upstream parts of the transportation mechanism, in particular of the transportation mechanism in the printing region.

Image formation

Image formation is performed in such a manner that, employing an inkjet printer loaded with inkjet inks, ink droplets are ejected from the inkjet heads based on the digital signals onto a print medium.
Although both single pass inkjet printing and multi pass (i.e. scanning) inkjet printing may be used for image formation, single pass inkjet printing is preferably used since it is effective to perform high-speed printing. Single pass inkjet printing is an inkjet recording method with which ink droplets are deposited onto the receiving medium to form all pixels of the image by a single passage of a receiving medium underneath an inkjet marking module.
In Fig. 1, 11 represents an inkjet marking module comprising four inkjet marking devices, indicated with 111, 112, 113 and 114, each arranged to eject an ink of a different color (e.g. Cyan, Magenta, Yellow and blacK). The nozzle pitch of each head is e.g. about 360 dpi. In the present invention, "dpi" indicates a dot number per 2.54 cm.
An inkjet marking device for use in single pass inkjet printing, 111, 112, 113, 114, has a length, L, of at least the width of the desired printing range, indicated with double arrow 52, the printing range being perpendicular to the media transport direction, indicated with arrows 50 and 51. The inkjet marking device may comprise a single printhead having a length of at least the width of said desired printing range. The inkjet marking device may also be constructed by combining two or more inkjet heads, such that the combined lengths of the individual inkjet heads cover the entire width of the printing range. Such a constructed inkjet marking device is also termed a page wide array (PWA) of printheads. Fig. 2A shows an inkjet marking device111 (112, 113, 114 may be identical) comprising 7 individual inkjet heads (201, 202, 203, 204, 205, 206, 207) which are arranged in two parallel rows, a first row comprising four inkjet heads (201 - 204) and a second row comprising three inkjet heads (205 - 207) which are arranged in a staggered configuration with respect to the inkjet heads of the first row. The staggered arrangement provides a page wide array of nozzles which are substantially equidistant in the length direction of the inkjet marking device. The staggered configuration may also provide a redundancy of nozzles in the area where the inkjet heads of the first row and the second row overlap, see 70 in Fig. 2B. Staggering may further be used to decrease the nozzle pitch (hence increasing the print resolution) in the length direction of the inkjet marking device, e.g. by arranging the second row of inkjet heads such that the positions of the nozzles of the inkjet heads of the second row are shifted in the length direction of the inkjet marking device by half the nozzle pitch, the nozzle pitch being the distance between adjacent nozzles in an inkjet head, d_nozzle (see Fig. 2C, which represents a detailed view of 80 in Fig. 2B). The resolution may be further increased by using more rows of inkjet heads, each of which are arranged such that the positions of the nozzles of each row are shifted in the length direction with respect to the positions of the nozzles of all other rows.
In image formation by ejecting an ink, an inkjet head (i.e. printhead) employed may be either an on-demand type or a continuous type inkjet head. As an ink ejection system, there may be usable either the electric-mechanical conversion system (e.g., a single-cavity type, a double-cavity type, a bender type, a piston type, a shear mode type, or a shared wall type), or an electric-thermal conversion system (e.g., a thermal inkjet type, or a Bubble Jet type (registered trade name)). Among them, it is preferable to use a piezo type inkjet recording head which has nozzles of a diameter of 30 µm or less in the current image forming method.
Fig. 1 shows that after pre-treatment, the receiving medium P is conveyed to upstream part of the inkjet marking module 11. Then, image formation is carried out by each color ink ejecting from each inkjet marking device 111, 112, 113 and 114 arranged so that the whole width of the receiving medium P is covered.
Optionally, the image formation may be carried out while the receiving medium is temperature controlled. For this purpose a temperature control device 19 may be arranged to control the temperature of the surface of the transportation mechanism (e.g. belt or drum) underneath the inkjet marking module 11. The temperature control device 19 may be used to control the surface temperature of the receiving medium P, for example in the range of 30°C to 60°C. The temperature control device 19 may comprise heaters, such as radiation heaters, and a cooling means, for example a cold blast, in order to control the surface temperature of the receiving medium within said range. Subsequently and while printing, the receiving medium P is conveyed to the down stream part of the inkjet marking module 11.

Drying and fixing

After an image has been formed on the receiving medium, the prints have to be dried and the image has to be fixed onto the receiving medium. Drying comprises the evaporation of solvents, in particular those solvents that have poor absorption characteristics with respect to the selected receiving medium.
Fig. 1 schematically shows a drying and fixing unit 20, which may comprise a heater, for example a radiation heater. After an image has been formed, the print is conveyed to and passed through the drying and fixing unit 20. The print is heated such that solvents present in the printed image, to a large extent water, evaporate. The speed of evaporation and hence drying may be enhanced by increasing the air refresh rate in the drying and fixing unit 20. Simultaneously, film formation of the ink occurs, because the prints are heated to a temperature above the minimum film formation temperature (MFFT). The residence time of the print in the drying and fixing unit 20 and the temperature at which the drying and fixing unit 20 operates are optimized, such that when the print leaves the drying and fixing unit 20 a dry and robust print has been obtained. As described above, the transportation mechanism 12 in the fixing and drying unit 20 may be separated from the transportation mechanism of the pre-treatment and printing section of the printing apparatus and may comprise a belt or a drum.

Post treatment

To increase the print robustness or other properties of a print, such as gloss level, the print may be post treated, which is an optional step in the printing process.
In an embodiment, the prints may be post treated by laminating the prints.
In an embodiment, the post-treatment step comprises a step of applying (e.g. by jetting) a post-treatment liquid onto the surface of the coating layer, onto which the inkjet ink has been applied, so as to form a transparent protective layer on the printed recording medium. In the post-treatment step, the post-treatment liquid may be applied over the entire surface of an image on the recording medium or may be applied only to specific portions of the surface of an image. The method of applying the post-treatment liquid is not particularly limited, and is selected from various methods depending on the type of the post-treatment liquid. However, the same method as used in the coating method of the pre-treatment liquid or an inkjet printing method is preferably used. Of these methods, inkjet printing method is particularly preferable in view of, avoiding contact between the printed image and the used post-treatment liquid applicator; the construction of an inkjet recording apparatus used; and the storage stability of the post-treatment liquid. In the post-treatment step, a post-treatment liquid containing a transparent resin is applied on the surface of a formed image so that a dry adhesion amount of the post-treatment liquid is 0.5 g/m² to 10 g/m², preferably 2 g/m² to 8 g/m², thereby forming a protective layer on the recording medium. When the dry adhesion amount is less than 0.5 g/m², almost no improvement in image quality (image density, color saturation, glossiness and fixability) is obtained. When the dry adhesion amount is more than 10 g/m², it is disadvantageous in cost efficiency, because the dryness of the protective layer degrades and the effect of improving the image quality is saturated.
As a post-treatment liquid, an aqueous solution comprising components capable of forming a transparent protective layer over a recording medium (e.g. a water-dispersible resin, a surfactant, water, and additives as required) is preferably used. The water-dispersible resin comprised in the post-treatment liquid, preferably has a glass transition temperature (T_g) of -30°C or higher, and more preferably in the range of -20°C to 100°C. The minimum film forming temperature (MFFT) of the water-dispersible resin is preferably 50°C or lower, and more preferably 35°C or lower. The water-dispersible resin may be radiation curable to improve the glossiness and fixability of the image.
As the water-dispersible resin, for example, an acrylic resin, a styrene-acrylic resin, a urethane resin, an acryl-silicone resin, a fluorine resin and the like are preferably used. The water-dispersible resin can be suitably selected from the same materials as those used for the inkjet ink. The amount of the water-dispersible resin contained, as a solid content, in the protective layer is preferably 1% by mass to 50% by mass.
The surfactant comprised in the post-treatment liquid is not particularly limited and may be suitably selected from those used in the inkjet ink. Examples of the other components of the post-treatment liquid include antifungal agents, antifoaming agents, and pH adjustors.
Hitherto, the printing process was described such that the image formation step was performed in-line with the pre-treatment step (e.g. application of an (aqueous) pre-treatment liquid) and a drying and fixing step, all performed by the same apparatus (see Fig. 1). However, the printing process is not restricted to the above-mentioned embodiment. A method in which two or more machines are connected through a belt conveyor, drum conveyor or a roller, and the step of applying an aqueous pre-treatment liquid, the (optional) step of drying a coating solution, the step of ejecting an inkjet ink to form an image and the step or drying an fixing the printed image are performed. It is, however, preferable to carry out image formation with the above defined in-line image forming method.
Fig. 3A-3F show a first example of a method for capping a print unit according to the present invention.
Fig 3A-3F show a print unit 111 and a capping unit 60. The capping tray is provided with an second connecting member 140. The print unit 111 is provided with a grappling member 130 The grappling member 130 is an example of a first connecting member. The capping unit 60 is positioned on a capping tray 120.
In Fig. 3A, the capping tray 120 carrying the cap unit 60 is moved in the direction indicated by arrow A. By moving the capping tray 120 in the direction indicated by arrow A, the capping unit 60 is brought into a pre-capping position, from which the print unit 111 can connect with the capping unit 60 to cap the print unit 111.
In Fig 3B, the print unit 111 is moving in the direction B. By moving in direction B, the distance between the print unit 111 and the capping unit 60 decreases. Further, grappling member 130 is moved relative to the print unit 111 in direction B, thereby bringing the grappling member 130 closer to the capping unit 60.
In Fig. 3C, the capping tray 120 carrying the cap unit 60 is moved in the direction indicated by arrow A. In the situation shown in Fig. 3C, the grappling member 130 is in contact with the second connecting member 140.
Fig 3D shows a next step in the capping process. The grappling member 130 moves relative to the print unit 111 in direction B', which is opposite to direction B. By moving the grappling member 130 relatively to the print unit 111 in direction B', the capping unit 60 is brought closer to the print unit 111.
In Fig 3E, the capping unit 60 covers a surface of the print unit 111. The capping unit 60 and the print unit 111 are connected via the grappling member 130 and the second connecting member 140. The print unit is moved in direction B', which is opposite to direction B, thereby moving away from the capping tray 120. By moving away the print unit 111, also the capping unit 60 is moved away from the capping tray 120.
In Fig 3F, the print unit 111 and the capping unit 60 connected to the print unit 111 are in an upper position. The print unit 111 is capped by the capping unit 60. The capping tray 120 moves in direction A', which is opposite to direction A, thereby moving away from the print unit 111.
Fig. 4A shows a first example of a grappling member 130 according to the present invention. The grappling member 130 comprises a hook member 131. The hook member 131 is capable of engaging a connecting member of the capping unit (not shown in Fig. 4A). The grappling member 130 further comprises a holding member 132 for holding the hook member 131. The grappling member 130 also comprises an spindle 133. The spindle 133 is provided with a screw thread (not shown). The holding member 132 holding the hook member 131 can be moved in the z-direction via the spindle 133. The grappling member 130 is further provided with a motor 134. The motor 134 is configured to in operation drive the spindle 133 to move the holding member 132 holding the hook member 131. The grappling member 130 is further provided with a gear box 135 to enable the motor 134 to drive the spindle 133.
Fig. 4B shows a first example of a capping unit 60 according to the present invention. The capping unit 60 has a plurality of inner surfaces 61a, 61b, 61c as well as additional inner surface not shown in Fig. 4B. These inner surfaces together form the inner surface 61. The inner surface 61, together with a print unit, forms a confined space in capping operation. The capping unit further has outer surfaces 62a, 62b as well as additional outer surface not shown in Fig. 4B. These outer surfaces together form the outer surface 62. The caping unit is further provided with connecting member 140. In the example shown in Fig. 4B, the connecting member is positioned on outer surface 62a.
The hook member 313 of the grappling member 130 is configured to engage with the connecting member 140 of the capping unit 60.
Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually and appropriately detailed structure. In particular, features presented and described in separate dependent claims may be applied in combination and any combination of such claims are herewith disclosed. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. The terms "a" or "an", as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language).

Claims

Printing device, the printing device comprising:
a. a recording medium support for supporting the recording medium during printing;

b. a recording medium transport unit for transporting and/or advancing the recording medium;

c. a plurality of print units, the print units being configured to, in printing operation, apply a predetermined pattern of ink onto the recording medium; and

d. a plurality of capping units, for capping the plurality of print units,
wherein each individual print unit can be capped by a capping unit.
Printing device according to claim 1, wherein at least one of the print unit and the capping units is provided with a first connecting member.
Printing device according to claim 2, wherein the first connecting member is a grappling member.
Printing device according to any of the preceding claims, wherein the printing device further comprises a capping tray, the capping tray being configured to support the capping units when the print units are in printing operation.
Printing device according to claim 4, wherein the capping tray is movable from a capping tray home position to the print zone.
Printing device according to any of the preceding claims, wherein each print unit is individually cappable by one of the capping units from the plurality of capping units.
Printing method using a printing device according to any of the claims 1 - 6, wherein at least one of the plurality of print units is in printing operation and at least one of the plurality of print units is non-printing operation, wherein the at least one print unit that is in non-printing operation is capped by one of the plurality of capping units.
Method for capping a print unit, the method comprising the steps of:
a. moving the capping unit and the print unit relatively towards one another;

b. connecting the first connecting member provided on one of the print unit and the capping unit to the other of the print unit and the capping unit;

c. relatively moving the print unit and the cap unit towards one another to a capping position.
Method according to claim 8, wherein step a) includes moving the capping tray towards the print zone.