Inkjet print method on objects

Technical Field

[0001] The present invention relates to direct (to) object printing with digital print technology.

Background Art

[0002] To mark images on objects; labels were in the past conventionally printed and the printed labels were glued on said objects. But nowadays, inkjet technology makes it possible to print directly on the object. This technical field is called direct (to) object printing.

[0003] Direct (to) object printing makes it possible for realizing a variable data printing solution and for eliminating the need for traditional labels. Rapid label change capabilities allow for consumer engagement opportunities, promotions, and customization without stopping the printing process, thereby eliminating downtime and costly plate changes. Consumer trends communications and regional-specific messages are facilitated easily with the adaptable printing technology.

[0004] Several solutions in the technical field can be found such as printing on mugs, bottles, containers, hides, leather articles or pharmaceutical tablets. The objects can be a three dimensional object or a flat object and the printing device can be

- a flatbed inkjet printing device having a support table whereon the object is applied; or

- a drum inkjet printing device wherein the object is rotated while an image is marking the object; or

- a robot arm for printing on curved surfaces.

[0005] Said objects have most of the time an irregular shape and/or may have several sizes or different shapes which makes it difficult to print on without spoiling ink and dirtying the support device whereon said objects are applied for printing. So in most cases if multiple objects have to be marked, the shape of the object and support zone of the object on the support device is not changing whereby the (variable data) image is marked always on the same position on the object such as a logo on a mug or product information on full front, back panel, or shoulder of a liquid container.

[0006] But if the shapes of the objects are unknown (e.g. changeable each time) or the support zone wherein said object is supported is unknown or even unknown number of objects are applied on the support device, possibly on unknown support zones; the print area (200) of the object or each object on said support has to be determined to avoid dirtying said support device with ink. The determination of a print area (200) for one or more objects on a support before printing can be found in the technical fields of spray booths; glass and leather decorating; apparel printing and printing on pharmaceutical tablets. Examples are disclosed in US2016107468A (OCE TECHNOLOGIES BV; publication date: 2016-04-21) and US2014168309A (KYOTO SEISAKUSHO CO LTD; publication date: 2014-06-19)

[0007] The print area (200) of an object is herein determined by exploring the support device by a detection device such as a camera system and the contour of the object or specific part of the object is recognized to obtain the print area (200) of the object. Tracking an object; contour analysis of an object; recognition of an object are well-known techniques in the technical field of machine vision technology such as implemented in LabVIEW™ from National Instruments™. In a very related technical field of the present invention said vison technology techniques are also well- known in digital cutters which are able to create said objects to be printed on. Examples are disclosed in US2015138262A (GIUSEPPE GALLUCCI; publication date: 2015-05-21) and EP2527103A1 (MATTHIAS FELBER; publication date: 2012-11-28). Some of said digital cutters are in 2008 and later converted to digital flatbed inkjet printers wherein the cutting means is replaced by one or more inkjet heads.

[0008] The detection device can be mounted movable in one or more directions above the support device for scanning said support device or can be firmly established above said support device such that the field of detection is large enough to detection all objects on said support device. Such a detection device is mostly of the time a camera system but a radiation sensing device; a DNA sensing device; a height sensing device for detecting the relief / thickness / topography of the object; whether or not combined with a camera system or other type of detection device is possible.

[0009] It is well-known that when the size of the image is bigger than the print area (200) that to avoid spoiling the support device with ink: a) a part of the image has to be clipped ; and/or b) a mask is applied around the applied object; and/or c) the object is applied first on a temporary carrier and applied together on the support.

Said clipping, also called digital masking or masking, is a process wherein the image is adapted with non-image areas according the determined print area (200). An example of said clipping is disclosed in US2016107468A (OCE TECHNOLOGIES BV; publication date: 2016-04-21).

[0010] One of the problems is that important content which is part of the image may be totally or partly clipped, especially when said object has an irregular shape.

Summary of invention

[0011] In order to overcome the problem described above, an embodiment of the present invention is defined in claim 1 as a method of inkjet printing an image on an object. The object may be a three dimensional object but it is preferably a flat object.

[0012] The object is preferably selected from the group consisting of mugs, bottles, containers, assembled or unassembled packaging boxes, hides, leather articles; leather panels for manufacturing leather articles and pharmaceutical tablets.

Brief description of drawings

[0013] Fig. 1 illustrates a flow of a preferred embodiment of the present embodiment wherein a print area (200), which has the contour of an object, is filled with an image (100) having a first image element (120), namely a triangle with a certain pattern and a second image element (130), namely a square with a certain other pattern. Several positions of the image (100) are determined (I, II, III, IV) and position III is selected because the first image element (120) is having a bigger importance to be marked on said object than the characteristic of the second image element (130). Position IV is hereby not selected because the image (100) is not fully filling the print area (200). In Fig. 3 the flow is further illustrated with said selected position III wherein the image parts outside the print area (200) are clipped before printed on the object.

[0014] Fig. 2 illustrates a flow of a preferred embodiment of the present embodiment wherein a print area (200), which has the contour of the object, is filled with a periodic tessellation (105) of an image (100) having a first image element (120), namely a triangle with a certain pattern and a second image element (130), namely a square with a certain other pattern. Several positions of the periodic tessellation (105) are determined (I, II, III, IV) and position III is selected because the first image element (120) is having a bigger importance to be marked on said object than the characteristic of the second image element (130). Position IV is hereby not selected because the periodic tessellation (105) is not fully filling the print area (200). In Fig. 4 the flow is further illustrated with said selected position III wherein the image parts outside the print area (200) are clipped before printed on the object.

Description of embodiments

[0015] The present embodiment is a method of inkjet printing an image (100) on an object; wherein said image (100) comprises

- a first image element (120) with a first characteristic; and a second image element (130) with a second characteristic wherein said both characteristics define for each corresponding image element the importance to be marked on said object; and said importance of said first image element (120) is larger than of said second image element (130); the method comprises the following steps: a) determining or selecting a print area (200) on said object b) determining, according said first characteristic and said second characteristic, a position (I, II, III, IV) of said image (100) on said print area (200) wherein the first image element (120) occurs more than the second image element (130) within said print area (200); c) inkjet printing said image (100) on said object according said determined position (I, II, III, IV). Said image elements of the image (100) may overlap each other but preferably are positioned separately in the image (100). The print area (200) has preferably an irregular shape. An irregular shape doesn't have equal sides or equal angles, “occurring more” means here that the first image element (120) is more present than the second image element (130) within said print area (200). The area of all printed first image elements (120) is hereby larger than the area of all printed second image elements (130) as illustrated in the figures.

[0016] By said different characteristics of minimum two image elements in the image (100); the marking of the object can be controlled to be sure that more important image elements shall be fully or partly printed on said object within the determined print area (200); which is preferably having an irregular shape. The most important image element in an image (100) shall hereby overlaying more part of the print area (200) when the image (100) is printed on the object than a lesser important image element in said image (100).

[0017] In the determination of the position an additional condition could be that the whole print area (200) have to be totally filled with a part of the image. (See position IV in Fig. 1 and Fig. 3 where this is not fulfilled).

[0018] Said first and second characteristic can be expressed for example in percentages. 100% means that the whole image element have to be printed on the print area (200), 0% means that the image element may be clipped or removed from the image (100). 50% may mean that 50% of the area of the image element have to be printed on the print area (200).

[0019] If the size of the image (100) is smaller than the print area (200) than all image elements shall be printed in said print area (200) but if said image (100) is larger in size than the print area (200) said different characteristics in the embodiment shall make it possible to control what part of an image (100) shall be printed on the object, especially an irregular shaped object. The size of image (100) is hereby preferably larger than the determined print area (200).

[0020] The first image element (120) determines a first image area and the second image element (130) determines a second image area. In a preferred embodiment the step b) comprises: b1) selecting a first position (I, II, III, IV) of said image (100) on said print area (200) and calculating the sum of

- the overlap area of said first image area and the print area (200) multiplied by a value that represents the first characteristic; and

- the overlap area of said second image area and the print area (200) multiplied by a value that represents the second characteristic; and b2) selecting a second position (I, II, III, IV) of said image (100) on said print area (200) and calculating the sum of

- the overlap area of said first image area at said second position (I, II, III, IV); and the print area (200) multiplied by said value that represents the first characteristic; and

- the overlap area of said second image area at said second position (I, II, III, IV); and the print area (200) multiplied by said value that represents the second characteristic; b3) comparing said both calculated sums to determine the position (I, II, III, IV) from said first position (I, II, III, IV) and said second position (I, II, III, IV). Herein the first and second image area may overlap each other but preferably there is no overlap.

[0021] Each image element may have an additional characteristic which here defines the minimum area of said image element have to be marked on the object. For example, a logo as image element may have the characteristic wherein is specified that it have to be marked totally (100%) on the object. Said characteristic for said first and second image element (130) may be additional compared within the previous mentioned overlap areas at the first and the second position (I, II, III, IV). An embodiment of the present invention is hereby also a method of inkjet printing an image (100) on an object; wherein said image (100) comprises

- a first image element (120) with a first characteristic; and a second image element (130) with a second characteristic wherein said both characteristics define for each corresponding image element the minimum area that have to be printed on said object; and said minimum area of said first image element (120) is larger than of said second characteristic; the method comprises the following steps: a) determining a print area (200) on said object b) determining , according said first characteristic and said second characteristic, a position (I, II, III, IV) of said image (100) on said print area (200) wherein the first image element (120) is more present, thus occurs more, than the second image element (130) within said print area (200); c) inkjet printing said image (100) on said object according said determined position (I, II, III, IV). Said image elements of the image (100) may overlap each other but preferably are positioned separately in the image (100). A position (I, II, III, IV) is preferably a Cartesian coordinate, three-dimensional or two-dimensional. The position (I, II, III, IV) may also be defined as a coordinate in a polar coordinate system or spherical coordinate system. [0022] It is possible that there is no solution to arrange the image (100) in the print area (200), the performer of the method may be notified if this happens for example by displaying a notification on a screen from a computer whereon the method is performed.

[0023] The characteristics may also be determined automatically (not by a operator) which selects the image elements and selects a certain value for said characteristics. If the image (100) is specified in a vector graphics format; the type of graphic element may be used to determine a value for the characteristic of said type of graphic element. If the image (100) is specified in a raster graphics format then an image analysis may be used to detect one or more image elements in an image (100). Depending on the type of image elements a value for the characteristic of said type of image element may be determined. Image recognition tools may be used to detect an image element in an image. Said tools may be performed by a neural network that processes all the pixels that make up an image (100).

[0024] The present invention provides also a solution if more than one image (100) have to be marked on the object. Said marking of more than one image (100) may be part of image-nesting or image-lay-outing said plurality of images to mark said images on the object. So in a preferred embodiment additionally an other image is marked on said object wherein said other image comprises - a third image element with a third characteristic; and a fourth image element with a fourth characteristic wherein said both characteristics define for each corresponding image element the importance to be marked on said object; and said importance of the third image element is larger than of said fourth image element; wherein step b) additional determines, according said third characteristic and said fourth characteristic, a position (I, II, III, IV) for said other image on said print area (200) wherein the third image element is more present, thus occurs more, than the fourth image element within the print area (200) and wherein said determined position (I, II, III, IV) of said other image is different than the determined position (I, II, III, IV) of the image; and wherein the step c) additional marks the other image according said determined position (I, II, III, IV) of said other image.

[0025] Said method is preferably for image nesting, also called nesting, the image and the other image on the object wherein the calculation of the position of the image and the position of the other copy additionally takes into account a parameter of said nesting. Image nesting is a method wherein a plurality of images are arranged to fill in an optimal way a certain area. Said image nesting may be:

(*) rectangular shape nesting which uses a rectangle with largest height and width around the shape of the content area or content extension area, such as bleed area, of an image. The shape of the content area or content extension area, such as bleed area, of the image is than treated as the geometry of the rectangle and not the real shape of the content area and/or content extension area, such as bleed area, of the image when placing the image on a substrate while or after nesting. This method is a fast nesting method and reduces the waste of a substrate; or

(*) true shape nesting which identifies a portion of the actual shape of the content area or content extension area, such as bleed area, of an image. For example, the left side and bottom of the actual shape of the content area or content extension area, such as bleed area, of an image is examined to determine how well it fits with adjacent shape of content area's or bleed area's of other images. The top and the right side of the actual shape of the content area or content extension area, such as bleed area, of an image are ignored until another image is placed next to it. The present embodiment may thus be part of a method for decorating an object with nested images.

[0026] Further, the present invention provides also a solution if more than one copy of the image has to be marked on the object. Said marking of more than one copy of the image may be part of image-tiling, tessellation (105; FIG 2; FIG 4), pattern repeating or image-lay-outing said plurality of copies to mark them on the object. So in a preferred embodiment additionally a second copy of the image is marked on said object and wherein the step b) additional determining, according said first characteristic and said second characteristic, a position for said second copy of the image on said print area (200), wherein the first image element (120) is more present, thus occurs more, than the second image element (130) within the print area (200) and wherein said determined position of said second copy of the image is different than the determined position of the image; and wherein the step c) additional marks said second copy of the image according said determined position of said second copy of the image.

[0027] In a preferred embodiment it is for decorating the object with a periodic tessellation (105; FIG 2; FIG 4) or pattern repeat of the image wherein the calculation of the position of the image and the position of the second copy of the image additional takes into account a parameter of said periodic tessellation (105; FIG 2; FIG 4) or said pattern repeat such as a certain amount of copies images per m ² ; periodicity of the periodic tessellation (105; FIG 2; FIG 4) or the pattern repeat. Said pattern repeat is preferably a lattice pattern which is more preferable selected from the group consisting of rectangular lattice, parallelogrammic lattice, equilateral triangular lattice, rhombic lattice, square lattice and hexagonal lattice.

[0028] The present embodiment may thus be part of a method for decorating an object with a periodic tessellation (105; FIG 2; FIG 4) of the image. This means that the image with its characteristics of image elements is repeated according the tessellation (105; FIG 2; FIG 4).

[0029] The inkjet printing method is preferably executed by an inkjet printing device and wherein the image is stored in a memory of a data processing system which is connected to said inkjet printing device for transferring images to said inkjet printing device and the determined print area (200) is stored in said memory or another memory of said data processing system.

[0030] The print area (200) may be determined by several methods but preferably step a) comprises: a1) supplying the object on a support device; a2) obtaining contour and/or dimensions of the supplied object for calculating the print area (200). Preferably the area inside said contour becomes the print area (200). The print area (200) may be made smaller by scaling for having an unmarked border around the determined print area (200). Said scaling is preferably uniform scaling more preferably between 70.000% and 100% while centre of the determined print area (200) and the scaled determined print area (200) remain the same.

[0031] Said support device may be part of the inkjet printing device which executes the inkjet printing method.

[0032] Preferably the present embodiment has an addition step between step b) and c) wherein the image is first masked (FIG. 2, FIG. 4) at the areas outside the print area (200) for not inkjet printing outside the print area (200).

[0033] The present embodiment is preferably executed by an inkjet printing device, wherein the image (100) is stored in a memory of a data processing system which is connected to said inkjet printing device for transferring images to said inkjet printing device and the determined print area (200) is stored in said memory or another memory of said data processing system. The inkjet printing device may comprise the support device and the inkjet printing of the image (100) is while the object is on said support device.

[0034] Said inkjet printing device is preferably a single pass inkjet printing device.

[0035] Further, it is an object of the presented embodiments and their preferred embodiments to provide a method for inkjet printing on a pharmaceutical tablet, wherein the object is a pharmaceutical tablet. It is clear that in said technical field that the most important content of the image (100) has to be printed on said tablets.

[0036] Further, it is an object of the presented embodiments and their preferred embodiments to provide a method for decorating natural leather with inkjet technology; especially with a repetitive pattern as image (100), wherein the object is natural leather.

[0037] Further, it is an object of the presented embodiments and their preferred embodiments to provide a method for inkjet printing on packaging boxes such as unassembled packaging boxes or assembled packaging boxes whether or not with one or more open panels for closing said packaging box.

[0038] The presented embodiments and their preferred embodiments relate to an inkjet printing method but said embodiment with all its preferred embodiment may also apply to general digital printing method of the image (100) on the object such as laser marking or xerography.

Object

[0039] The object of the embodiments in the present invention may be a three dimensional object but it is preferably a flat object, more preferably an irregular shaped flat object, most preferably selected from the group a hide; a panel for a leather article or a panel for an apparel. Irregular shaped flat object is a flat object which has one or more sides with changes in curvature of an arc or curve from concave to convex or conversely and/or has free spaces inside the surface of the flat object. Further the flat object may be also an unassembled packaging box or a pharmaceutical tablet.

[0040] The one or more objects may be supplied on a support device first where after the print area (200) on said one or more objects is determined. Said support device may be part of an inkjet printing device which uses the same support device for marking the image (100) on the object; more specifically marking the image (100) within the determined print area (200) of said one or more objects. The determination of a print area (200) of an object is preferably performed by a detection device which is preferably mounted movable in one or more directions above the support device for scanning said support device or preferably be firmly established above said support device such that the field of detection is large enough to detection the one or more objects on said support device. The support device may then also be moving, e.g. for transporting the object, while detecting the object when it moves underneath the detection device.

[0041] Said detection preferably comprises the following steps:

- object tracing; and/or

- contour scanning; and/or

- dimensions measurement. Image (100)

[0042] The content of the image (100) of the embodiments in the present invention may be defined in raster graphics format such as Portable Network Graphics (PNG), Tagged Image File Format (TIFF), Adobe Photoshop Document (PSD) or Joint Photographic Experts Group (JPEG) or bitmap (BMP) but more preferably in vector graphics format, such as Scale Vector Graphics (SVG) and AutoCad Drawing Exchange Format (DXF) and most preferably, in a page description language (PDL) format such as Adobe Postscript (PS) or Adobe Portable Document Format (PDF).

[0043] By using an image editor as software program on a data processing system, such as Adobe Photoshop™ or Adobe Illustrator™ or Adobe Indesign™ an image (100) may be created; adapted and/or converted to one of the previous mentioned formats. Such software program is sometimes called prepress software wherein a print job is created and/or prepared for printing.

[0044] An image (100) may contain one or more image elements such as a logo, text, a pattern, line work, photo....

[0045] The first and second characteristics of the present embodiment are preferably stored in the image file together with the content of the image or embedded as meta-data in the image file together with the content. It can also be stored in the job ticket file; such as the JDF-format (Job Description Format) managed by CIP4 www.cip4.org .

[0046] Said characteristics are preferably determined at the creation of the image for example in a prepress studio but it may also be determined by the operator of the inkjet printing device.

Detection device

[0047] To detect the object which is lay down on a support device or applied on a support device, a camera system may be used; which image captures the one or more objects on the support device. From said one or more captured images the position of the one or more supplied objects can be determined; contour of the one or more supplied objects; shape of the one or more supplied objects can be determined; and/or dimensions of the one or more supplied objects can be determined; wherefrom then the one or more print areas on the supplied objects can be determined.

[0048] If the support device is a flatbed surface, then the camera system may have a reach of at least the entire flatbed surface for detecting the one or more supplied objects on the flatbed surface with the camera system.

Unassembled packaging box

[0049] An unassembled packaging box is cut from packaging materials such as corrugated cardboard in a certain folding scheme. The pre-mentioned panels are used for forming the sides of the packaging box and/or for fixing and/or folding said sides to a three-dimensional packaging box. Said panels are also called flaps. Preferably said panel comprises one or more die-lines for easy folding the box. An unassembled packaging box may comprise also one or moving box handles for easy moving an assembled packaging box. Such unassembled packaging box is an irregular shaped flat object which comprises a plurality of inflections (= change in curvature of an arc or curve from concave to convex or conversely) at one more sides and/or internal has free spaces for making the assembly easy and/or for creating a strong boxes and/or for making the assembled box easy for carrying.

Assembled packaging box

[0050] The present embodiment may be part of a method of preparing packaging boxes such as in an e-commerce environment.

[0051] The role of e-commerce is becoming more and more significant in retail. Customers are increasingly placing orders online from the comfort of their homes via a website. The ordered merchandise is then put into a packaging box, referred to herein as an e-box, and delivered to the customer's residence or another desired address. In this manner a customer can conveniently make a purchase without having to devote time and effort to physically travel to a store to look for the desired merchandise, if available.

[0052] In e-commerce, the process of picking the ordered products and packing these products in a suitable packaging box (e-box) is typically referred to as fulfilment.

[0053] The present embodiment may be part of a method of preparing a packaging box wherein late stage customization is provided on the inside of the packaging box by said present embodiment. Said preferred embodiment may includes the steps of:

- selecting an unfolded packaging box;

- providing late stage customization on those parts of the unfolded packaging box that will form the inside of a packaging box;- folding the unfolded packaging box provided with the late stage customization to obtain the packaging box;- filling the packaging box (250) with one or more purchased articles; and- closing the filled packaging box. It was found that providing late stage customization on the inside of the packaging box just before, during or after filling the packaging box with one or more purchased articles results in an efficient process while enhancing customer experience and customer engagement.

[0054] There are several advantages when providing late stage customization on the inside of a packaging box, such as for example:

• During transport of a packaging box to a customer the exterior of the packaging box is typically provided with several adhesive labels, such as for example a shipment label. When such labels are provided on top of customized or personalized messaging provided on the outside of the packaging box, such messaging may lose its attractiveness and/or meaning for the customer.

• During transport of a packaging box the exterior of the packaging box may become damaged, again negatively influencing the appearance of customized or personalized messaging on the outside of the box.

• Providing information on the outside of the box increases the chances of theft because the content may be revealed from the outside print. Thus, providing information on the inside of a packaging box may reduce the chances of theft because people may be less likely to steal a package, which does not reveal its content.

• A customer may prefer that there are no indications on the content of the packaging box or other personal information on the outside of a packaging box for privacy purposes.

Late stage customization is preferably provided on the inside of a top flap of the packaging box. A packaging typically contains one or more top flaps that are used to close the packaging box after filling it with the purchased articles. When the customer receives the packaging box at home, opening the box will reveal the late stage customization and realize the unboxing experience.

[0055] Late stage customization as used herein is provided as late as possible in the packaging process. The latest stage for customization of the packaging box is just before, during or after filling the e-box with the purchased products.

[0056] The time between providing late stage customization and filling the packaging box with the one or more purchased articles is preferably less than 1 day, more preferably less than 12 hour, most preferably less than 1 hour. However, to speed up the packaging process, the time may be less than 15 minutes, more preferably less than 5 minutes, most preferably less than 1 minute.

[0057] The time wherein late stage customization is provided on the packaging box is preferably less than 120 seconds, more preferably less than 60 seconds, most preferably less than 10 seconds.

[0058] Preferably, each packaging box manufactured according to the method of the present invention is unique because the late stage customization, dependent on the order, the customer, the timing, etc. is different for each packaging box.

[0059] A packaging box may also be referred to as a shipment container.

[0060] The method of preparing a packaging box may include the steps Deselecting an unfolded packaging box;- folding the selected unfolded packaging box to obtain an assembled packaging box; - providing late stage customized information on the inside of the packaging box before, during or after filling the packaging box with one or more purchased articles; and- closing the filled packaging box.

[0061] in a time between providing late stage customization and filling the packaging box with one or more purchased articles is preferably less than 12 hours.

[0062] The packaging box may include one or more top flaps and wherein late stage customization is provided on the inside of at least one top flap.

[0063] The unfolded packaging box (200, 430) is preferably selected according to a minimal packaging box dimension, the minimal packaging box dimension determined based on outer dimension of one or more purchased articles and wherein preferably late stage customization is provided taking into account the minimal packaging box dimension.

Inkjet printing

[0064] Method of inkjet printing is performed by an inkjet printing device which comprises one or more inkjet print heads for forming small droplets of a liquid in a controlled manner through nozzles on print media. Said liquid is all so called ink. The one or more inkjet print head move(s) relative to said print media for marking said print media. More information on inkjet printing and inkjet printing devices can be found in Pond, S.F., "Inkjet Technology and Product Development Strategies", Carlsbad: Torrey Pines Research (2000).

[0065] A preferred print head for an inkjet printing system in the present invention is a piezoelectric head. Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied thereto. The application of a voltage changes the shape of the piezoelectric ceramic transducer in the print head creating a void, which is then filled with ink. When the voltage is again removed, the ceramic expands to its original shape, creating a pressure wave which leads to the formation of a drop ejected from the nozzle of a print head.

[0066] However, the inkjet printing method in the present invention is not restricted to piezoelectric inkjet printing. Other inkjet print heads can be used and include various types, such as a continuous type and a thermal or electrostatic drop on demand type. [0067] The print head is preferably a piezo electric through-flow print head, more preferably greyscale piezo electric through-flow print head. In a through- flow print head, often also called a recirculating print head, the ink flows continuously via an ink inlet through the ink chamber and exits the nozzle only when required, otherwise the ink continuously exits the ink channel via an ink outlet of the print head. The other type of print head is a so- called end shooter print head or single ended print head, wherein the ink flows via an ink inlet of the print head into the ink chamber and can only exit through a nozzle. An advantage of a piezo electric through-flow print head is that sedimentation of colour pigments in the nozzles is reduced, thus improving reliability and productivity of the inkjet printing system. Suitable piezoelectric through-flow print heads include the print heads Samba G3L and G5L from FUJI DIMATIX and the through-flow print heads from XAAR.

[0068] For obtaining good image quality, greyscale print heads are preferred as they can generate different sized droplets by selectively activating different pulses of a wave form. A wave form is a set of timed actuator movements used to propagate and control acoustic pressure waves within an ink chamber of a greyscale print head to eject an ink droplet through a nozzle.

[0069] The greyscale print heads preferably have nozzles with an outer nozzle surface area NS smaller than 500 pm ² , more preferably between 100 and 350 pm ² and most preferably between 200 and 250 pm ² . In these ranges, the greyscale print heads can produce images of excellent image quality.

[0070] In multi-pass printing, the inkjet print head scans back and forth in a transversal direction across the moving print media surface. However, inkjet printing is preferably performed by a single pass printing process for increasing productivity. This can be performed by using page wide inkjet print heads or multiple staggered inkjet print heads which cover the entire width of the print media surface. In a single pass printing process, the inkjet print heads preferably remain stationary while the print media surface is transported under the inkjet print heads.

[0071] An example of an inkjet printing device in a multi-pass inkjet printing method is Jeti Tauro™ manufactured by AGFA™ NV with a maximum printable width of 254 cm and which can accommodate for example rigid media up to 400 cm in length. An example of another inkjet printing device with a single-pass inkjet printing method is KBA™ RotaJet™ L-series with a maximum print width of 1.3 meter.

[0072] The one or more inkjet inks that are used in inkjet printing method of the embodiments of the present invention may be pigmented inks preferably selected from aqueous pigmented inkjet inks, solvent based pigmented inkjet inks and radiation curable pigmented inkjet inks. However, the one or more pigmented inkjet inks are preferably one or more radiation curable inkjet ink, most preferably one or more UV curable inkjet inks.

[0073] The one or more pigmented inkjet inks preferably contain organic colour pigments as they allow for obtaining a high colour gamut on the print media. Carbon black and titanium dioxide are inorganic pigments, which can be advantageously used in the present invention for composing black respectively white pigmented inkjet inks.

[0074] In a preferred embodiment, the one or more pigmented inkjet inks form a CMYK(W) or CRYK(W) inkjet ink set.

[0075] The inkjet inks of the embodiments in present invention preferably are cured by exposing them to ultraviolet radiation. The UV curing means may be arranged in combination with the print head of the inkjet printing device, travelling therewith so that the curable composition is exposed to curing radiation very shortly after been jetted.

[0076] The source of UV radiation may be arranged to move with the print head, but may also be an elongated radiation source extending transversely across the print media surface to be cured.

[0077] Any ultraviolet light source may be employed as long as part of the emitted light can be absorbed by the photo-initiator or photo-initiator system. Suitable UV radiation sources include a high or low pressure mercury lamp, a cold cathode tube, a black light, an ultraviolet LED, an ultraviolet laser, and a flash light. Of these, the preferred source is one exhibiting a relatively long wavelength UV-contribution having a dominant wavelength of 300-400 nm. Specifically, a UV-A light source is preferred due to the reduced light scattering therewith resulting in more efficient interior curing. [0078] It is possible to cure the image using, consecutively or simultaneously, two light sources of differing wavelength or illuminance. For example, the first UV-source can be selected to be rich in IIV-C, in particular in the range of 260 nm-200 nm. The second UV-source can then be rich in UV-A, e.g. a gallium-doped lamp, or a different lamp high in both UV-A and UV-B. The use of two UV-sources has been found to have advantages e.g. a fast curing speed and a high curing degree.

[0079] In a preferred embodiment, the inkjet printing device contains UV LEDs with a wavelength larger than 360 nm, preferably UV LEDs with a wavelength between 370 nm and 405 nm. The use of UV LEDs is beneficial for productivity as they consume less energy than other UV light sources, such as a mercury bulb.

[0080] For facilitating curing, the inkjet printing device may include one or more oxygen depletion units. The oxygen depletion units place a blanket of nitrogen or other relatively inert gas (e.g. CO2), with adjustable position and adjustable inert gas concentration, in order to reduce the oxygen concentration in the curing environment. Residual oxygen levels are usually maintained as low as 200 ppm, but are generally in the range of 200 ppm to 1200 ppm. The productivity of inkjet printing is improved as this allows for faster curing and/or reducing the energy consumption of the UV radiation sources.

Prepress workflow system

[0081] A prepress workflow system is a tool for managing digital documents, preferably defined in a page description languages (PDL) such as Postscript™, wherein said documents are prepared for printing on a printing device, such as an offset press. Said tool is typically a data processing system adapted to manage and preparing said documents for printing or a computer program comprising instructions to manage and to prepare said documents for printing. Said computer program is preferably stored on a computer-readable storage medium. An example of such prepress workflow system is Apogee™ from AGFA NV.

[0082] In a preferred embodiment a prepress workflow system comprises a raster image processor which is capable of performing the method of digital halftoning from the present invention and its preferred embodiments. The prepress workflow system or raster image processor preferably further comprises means for transmitting the halftone raster image to an inkjet printing device, digital printing press or a plate setter for obtaining a printing plate.

Data processing system

[0083] A data processing system operates one or more computer programs for example a raster image processor and/or prepress workflow system. Part or whole of the data processing system and/or the functional units or blocks thereof may be implemented in one or more circuits or circuitry, such as an integrated circuit(s) or as an LSI (large scale integration). Each functional unit or block of the data processing system may be individually made into an integrated circuit chip. Alternatively, part or whole of the functional units or blocks may be integrated and made into an integrated circuit chip.

[0084] A software program, also called a computer program, which is operated in the data processing system is a program controlling a processor in order to realize functions of the various preferred embodiments according to the present invention. Therefore, information which is handled by the data processing system is temporarily accumulated in a RAM, as memory, at the time of the processing. Thereafter, the information, such as images or a determined print area (200), may be stored in various types of circuitry in the form of ROMs and HDDs, as memory, and read out by circuitry within, or included in combination with, the data processing system as necessary, and modification or write-in is performed thereto. As a recording medium storing the program, any one of a semiconductor medium (for example, the ROM, a non-volatile memory card or the like), an optical recording medium (for example, a DVD, an MO, an MD, a CD, a BD or the like), and a magnetic recording medium (for example, a magnetic tape, a flexible disc or the like) may be used. Moreover, by executing the loaded software program, the functions of the various preferred embodiments of the present invention are not only realized, but the functions of preferred embodiments of the present invention may be realized by processing the loaded software program in combination with an operating system or other application programs, based on an instruction of the program.

[0085] Moreover, in a case of being distributed prepress workflow system or even a distributed raster image processor, the program can be distributed by being stored in the portable recording medium, or the program can be transmitted to a server computer which is connected through a network such as the Internet. In addition, a portion of a terminal device, a wireless base station, a host system, or other devices, or the whole thereof may be realized as an LSI which is typically an integrated circuit. Each functional unit or block of the data processing system may be individually chipped, or a portion thereof, or the whole thereof may be chipped by being integrated. In a case of making each functional block or unit as an integrated circuit, an integrated circuit controller that controls the integrated circuits, is added.

[0086] Finally, it should be noted that the description referring to “circuit” or “ circuitry” is in no way limited to an implementation that is hardware only, and as persons of ordinary skill in the relevant art would know and understand, such descriptions and recitations of “circuit” or “circuitry” include combined hardware and software implementations in which the circuit or circuitry is operative to perform functions and operations based on machine readable programs, software or other instructions in any form that are usable to operate the circuit or circuitry.

[0087] There is no limitation on the location of the data processing system, it may be located at a prepress bureau, at the printing device or even at a third party location.

[0088] Digital connections with the data processing system may be made in any form. It can be a connection using an optical fiber or a wireless connection, such as a Wi-Fi connection according to the IEEE 802.11 standard.

Other embodiments

[0089] The present embodiment and its preferred embodiments may also be performed by other digital printing technique then only inkjet printing. The digital printing technique is preferably selected from the group consisting of laser marking, laser engraving, thermal printing, inkjet printing and electrophotography, more preferably selected from the group consisting of laser marking, laser engraving, thermal printing and inkjet printing, most preferably selected from the group consisting of laser marking and inkjet printing.